CA2206911C - Improved method and apparatus for cooling extruded film tubes - Google Patents

Abstract

The present invention is directed to a blown film extrusion apparatus in which film is extruded as a tube from an annular die and then pulled along a predetermined path. The improved blown film extrusion apparatus includes a means for gauging and controlling the surface of the extruded film tube, which includes a number of components which cooperate together. At least one transducer means is provided and positioned adjacent the extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, the extruded film tube, and for producing a signal corresponding to a detected position of the extruded film tube. A control means is provided for substituting a filtered position signal derived from a dynamic filtering process in lieu of the detected position signal. A means is provided for varying a quantity of air within the extruded film tube in response to the control means for urging the extruded film tube to a desired position.

Description

BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates generally to blown film extrusion lines, and specifically to signal filtering for improved cooling systems for use with blown film systems.
Description of the Prior Art:
Blown film extrusion lines are used to manufacture plastic bags and plastic sheets. A molten tube of plastic is extruded from an annular die, and then stretched and expanded to a larger diameter and a reduced radial thickness by the action of overhead nip rollers and internal air pressure. Typically, air is entrained by one or more blowers to provide a cooling medium which absorbs heat from the molten material and speeds up the change in state from a molten material back to a solid material. Additionally, blowers are used to provide air pressure which is utilized to control the size and thickness of the film tube. One type of blown film extrusion line utilizes an air flow on the exterior surface of the film tube in order to 2 absorb heat. A different, and more modern, type of blown film extrusion line s utilizes both an external flow of cooling air and an internal flow of cooling air in a order to cool and size the film tube.
Whether the blown film tube is cooled from either the interior surface, s the exterior surface, or both, one common problem in blown film extrusion lines is that of obtaining precise control over the diameter of the extruded film tube.
Tight s control over the diameter insures uniform product dimensions, which includes the s size of the extruded product, as well as the thickness of the plastic material.
1o Acoustic sensors may be utilized to gauge the diameter of the product without 1 ~ deforming the product, in the manner of mechanical dimension sensors. One 12 drawback with utilization of ultrasonic sensors is that they are very sensitive to 13 ambient noise, as well as flutter or slight vibration of the extruded film tube.
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0291 MH-26521139815.1 It is one objective of the present invention to provide an improved 4 blown film extrusion system which includes a plurality of position signal filtering s options, each of which is suitable for a different mode of frequently encountered s extruded film tube conditions, such as relatively unstable modes of operation (such as, for example, bubble startup conditions, overblown bubble conditions, s underblown bubble conditions, and loss of position signal conditions), as well as s relatively stable operating conditions, wherein the extruded film tube is in a ~ o substantially fixed position.
11 It is another objective of the present condition to provide an improved 12 blown film extrusion system which provides a dynamic filtering process which 1s substitutes a filtered position signal derived from the dynamic filtering process in 14 lieu of a detected position signal, in order to provide more stable control of the 1s extruded film tube.
1s It is another objective of the present invention to provide the dynamic 1~ filtering process by utilizing a rolling average of position signals in lieu of a ~ s detected position signal during intervals of relatively stable operation, wherein the is rolling average is dynamically altered by modifying the number of samples utilized 2o to calculate the rolling average.
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0291 MH-26521 !39815.1 According to one aspect the present invention provides in a blown film extrusion apparatus in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus for gauging and controlling the circumference of said extruded film tube, comprising: at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing a signal corresponding to a detected position of said extruded film tube; control means for substituting a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal; and means for varying a quantity of air within said extruded film tube in response to said control means for urging said extruded film tube to a desired position.
According to another aspect the present invention provides in a blown film extrusion apparatus in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus for gauging and controlling the circumference of said extruded film tube, comprising: at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing a signal corresponding to a detected position of said extruded film tube; control means for substituting a filtered position signal developed from a particular one of a plurality of available filtering routines in lieu of said detected position signal; and means for varying a quantity of air within said extruded film tube in response to said control means for urging said extruded film tube to a desired position.
According to yet another aspect the present invention provides in a blown film extrusion apparatus in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus for gauging and controlling the circumference of said extruded film, comprising: at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing a signal corresponding to a detected position of said extruded film tube; control means including executable instructions defining a plurality of filters including: a. a first filter which receives said signal corresponding to a detected position of said extruded film tube and modifies it based upon information derived from at least one previous detected position, during intervals of relatively unstable operation; b. a second filter which receives said signal corresponding to a detected position of said extruded film tube and modifies it by dynamic filtering it, only during intervals of relatively stable operation; means for varying a quantity of air within said extruded film tube in response to said control means for urging said extruded film tube to a desired position.
According to still another aspect the present invention provides a method of gauging and controlling the circumference of an extruded film tube formed from film extruded from an annular die, comprising: providing a transducer; placing said transducer adjacent said extruded 5a film tube; transmitting an interrogating signal to, and receiving an interrogating signal from, said extruded film tube; producing a detected position signal based on information contained in said interrogating signal;
providing a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal;
and varying a quantity of air within said extruded film tube in response to said filtered position signal.
According to a further aspect the present invention provides a method of gauging and controlling the circumference of an extruded film tube formed from film extruded from an annular die, comprising: providing a transducer; placing said transducer adjacent said extruded film tube; transmitting an interrogating signal to, and receiving an interrogating signal from, said extruded film tube; producing a detected position signal based on information contained in said interrogating signal;
substituting a filtered position signal developed from a particular one of a plurality of available filtering routines in lieu of said detected position signal; and varying a quantity of air within said extruded film tube in response to said filtered position signal.
According to a final aspect the present invention provides a method of gauging and controlling the circumference of an extruded film tube formed from film extruded from an annular die, comprising the method steps of: providing at least one ultrasonic transducer; placing said at least one ultrasonic transducer adjacent said extruded film tube; transmitting and receiving sonic 5b interrogating pulses with said at least one ultrasonic transducer to said extruded film tube; producing a position signal based on information contained in said interrogating pulses; filtering said position signal with a plurality of filters, including: a. a first filter which receives said position signal and modifies it based upon information derived from at least one previous position signal during intervals of relatively unstable operation; and b. a second filter which receives said position signal and modifies it by dynamic filtering only during intervals of relatively stable operation; varying a quantity of air within said extruded film tube in response to said position signal after filtering has occurred.
The above as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.
5c BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are set 4 forth in the appended claims. The invention itself however, as well as a preferred s mode of use, further objects and advantages thereof, will best be understood by s reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
s Figure 1 is a view of a blown film extrusion line equipped with the s improved control system of the present invention;
Figure 2 is a view of the die, sizing cage, control subassembly and > > rotating frame of the blown film tower of Figure 1;
12 Figure 3 is a view of the acoustic transducer of the improved control 13 system of the present invention coupled to the sizing cage of the blown film ~ 4 extrusion line tower adjacent the extruded film tube of Figures 1 and 2;
Figure 4 is a view of the acoustic transducer of Figure 3 coupled to 1 s the sizing cage of the blown film tower, in two positions, one position being shown in phantom;
~a Figure 5 is a schematic and block diagram view of the preferred ~s control system of the present invention;
2o Figure 6 is a schematic and block diagram view of the preferred 2i control system of Figure 5, with special emphasis on the supervisory control unit;
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0291 MH-28521 /39815.1 Figure 7A is a schematic and block diagram view of the signals 2 generated by the ultrasonic sensor which pertain to the position of the blown film s layer;
Figure 7B is a view of the ultrasonic sensor of Figure 3 coupled to s the sizing cage of the blown film tower, with permissible extruded film tube s operating ranges indicated thereon;
Figure 8A is a flow chart of the preferred filtering process applied to s the current position signal generated by the acoustic transducer;
s Figure 8B is a graphic depiction of the operation of the filtering i o system;
> > Figure 9 is a schematic representation of the automatic sizing and i 2 recovery logic (ASRL) of Figure 6;
~s Figure 10 is a schematic representation of the health/state logic (HSL) of Figure 6;
Figure 11 is a schematic representation of the loop mode control ~s logic (LMCL) of Figure 6;
Figure 12 is a schematic representation of the volume setpoint ~a control logic (VSCL) of Figure 6;
1s Figure 13 is a flow chart representation of the output clamp of 2o Figure 6.
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0291 MH-28521139815.1 Figure 14 is a schematic and block diagram, and flowchart views of z the preferred alternative emergency condition control system of the present s invention, which provides enhanced control capabilities for detected overblown and 4 underblown conditions, as well as when the control system determines that the s extruded film tube has passed out of range of the sensing transducer;
s Figure 15 is a schematic and block diagram view of the signals generated by the ultrasonic sensor which pertain to the position of the blown film 8 layer;
s Figure 16 is a view of the ultrasonic sensor of Figure 3 coupled to ~o the sizing cage of the blown film tower, with permissible extruded film tube 11 operating ranges indicated thereon;
Figure 17 is a schematic representation of the automatic sizing and 1s recovery logic (ASRL) of Figure 14;
14 Figure 18 is a schematic representation of the health/state logic ~s (HSL) of Figure 14;
1s Figure 19 is a schematic representation of the loop mode control i ~ logic (LMCL) of Figure 14;
1s Figure 20 is a schematic representation of the volume setpoint ~s control logic (VSCL) of Figure 14;
2o Figure 21 is a flow chart representation of the output clamp of z1 Figure 14;
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0291 MH-28621139816.1 1 Figure 22 is a schematic and block diagram view of emergency 2 condition control logic block of Figure 14;
Figures 23A through 23G depict the preferred software routines 4 utilized in the present invention, including a first filter routine which is utilized during s relatively unstable intervals of operation, and a second dynamic filtering routine s which is utilized during relatively stable intervals of operation;
Figure 24 is a graphic depiction of the normal operation of the s filtering system;
s Figure 25A is a graph which depicts the emergency condition control 1o mode of operation response to the detection of an underblown condition, with the 11 X-axis representing time and the Y-axis representing position of the extruded film 12 tube;
13 Figure 25B is a graph of the binary condition of selected operating 14 blocks of the block diagram depiction of Figure 22, and can be read in 1s combination with Figure 25A, wherein the X-axis represents time, and the Y-axis 1s represents the binary condition of selected operational blocks;
17 Figure 26A is a graph which depicts the emergency condition control i8 mode of operation response to the detection of an underblown condition, with the 1s X-axis representing time and the Y-axis representing position of the extruded film 2o tube;
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0291 MH-28521139815.1 1 Figure 26B is a graph of the binary condition of selected operating 2 blocks of the block diagram depiction of Figure 22, and can be read in 3 combination with Figure 26A, wherein the X-axis represents time, and the Y-axis 4 represents the binary condition of selected operational blocks;
Figure 27A is a graph which depicts the emergency condition control s mode of operation response to the detection of an underblown condition, with the X-axis representing time and the Y-axis representing position of the extruded film tube;
s Figure 27B is a graph of the binary condition of selected operating to blocks of the block diagram depiction of Figure 22, and can be read in 1 ~ combination with Figure 27A, wherein the X-axis represents time, and the Y-axis ~ 2 represents the binary condition of selected operational blocks;
13 Figure 28 is a schematic and block diagram depiction of one 14 embodiment of the improved air flow control system of the present invention;
1 s Figure 29 is a simplified and partial fragmentary and longitudinal ~s section view of the preferred air flow control device used with the air flow control 1 ~ system of the present invention;
1s Figure 30 is a schematic depiction of a IBC blown film extrusion line 1s equipped with mass air flow sensors in communication with both a supply of 2o cooling air and an exhaust of cooling air, which may be utilized to obtain uniformity Page - 10 DOCKET NO. 291 H-24528-CN
0291 MH-26521 !39815.1 1 in the mass air flow of the cooling air stream supply to the interior of the blown film z tube;
s Figure 31 is a schematic depiction of an IBC blown film line equipped 4 with mass air flow sensors for controlling the supply and exhaust of air to the interior of the blown film tube, and additionally equipped with a mass air flow s sensor for monitoring and controlling the supply of external cooling air;
Figures 32, 33, 34, and 35 are schematic depictions of an external s cooling air system for a blown film extrusion line, with a mass air flow sensor s provided to allow control over an adjustable air flow attribute modifier;
and 1o Figure 36 is a flowchart representation of computer program 11 implemented operations for achieving a feedback control loop for a blown film 1 z system.
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0291 MH-26521139815.1 DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

In this detailed description of the invention, Figures 1 through 29, and 4 accompanying text, provide a very detailed overview of an internal-bubble-cooling blown film extrusion system which is equipped with a preferred sizing control s system. Figures 30 through 36, and accompanying text, provide a description of the preferred method and apparatus for cooling extruded film tubes of the present s invention used either in combination with the preferred sizing control apparatus, s or alone.
1o Figure 1 is a view of blown film extrusion line 11, which includes a number i ~ of subassemblies which cooperate to produce plastic bags and the like from 12 plastic resin. The main components include blown film tower 13, which provides ~s a rigid structure for mounting and aligning the various subassemblies, extruder subassembly 15, die subassembly 17, blower subassembly 19, stack 21, sizing ~s cage 23, collapsible frame 25, nips 27, control subassembly 28 and rollers 29.
~s Plastic granules are fed into hopper 31 of extruder subassembly 15. The plastic granules are melted and fed by extruder 33 and pushed into die subassembly 17, and specifically to annular die 37. The molten plastic granules is emerge from annular die 37 as a molten plastic tube 39, which expands from the 2o die diameter to a desired final diameter, which may vary typically between two to three times the die diameter.
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0291 MH-26521139816.1 i Blower subassembly 19 includes a variety of components which cooperate 2 together to provide a flow of cooling air to the interior of molten plastic tube 39, s and also along the outer periphery of molten plastic tube 39. Blower subassembly 4 includes blower 41 which pulls air into the system at intake 43, and exhausts air s from the system at exhaust 45. The flow of air into molten plastic tube 39 is s controlled at valve 47. Air is also directed along the exterior of molten plastic tube 7 from external air ring 49, which is concentric to annular die 37. Air is supplied to s the interior of molten plastic tube 39 through internal air diffuser 51. Air is pulled s from the interior of molten plastic tube 39 by exhaust stack 53.
io The streams of external and internal cooling airs serve to harden molten > > plastic tube 39 a short distance from annular die 37. The line of demarcation i 2 between the molten plastic tube 39 and the hardened plastic tube 55 is identified is in the trade as the "frost line." Normally, the frost line is substantially at or about the location at which the molten plastic tube 39 is expanded to the desired final is diameter.
16 Adjustable sizing cage 23 is provided directly above annular die 38 and 17 serves to protect and guide the plastic tube 55 as it is drawn upward through is collapsible frame 25 by nips 27. Afterwards, plastic tube 55 is directed through a is series of rollers 57, 59, 61, and 63 which serve to guide the tube to packaging or 20 other processing equipment.
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0291 MH-26521139815.1 1 In some systems, rotating frame 65 is provided for rotating relative to blown 2 film tower 13. It is particularly useful in rotating mechanical feeler arms of the prior a art systems around plastic tube 55 to distribute the deformations. Umbilical cord 4 67 is provided to allow electrical conductors to be routed to rotating frame 65.
Rotating frame 65 rotates at bearings 71, 73 relative to stationary frame 69.
s Control subassembly 28 is provided to monitor and control the extrusion 7 process, and in particular the circumference of plastic tube 55. Control 8 subassembly 28 includes supervisory control unit, and operator control panel 77.
s Figure 2 is a more detailed view of annular die 37, sizing cage 23, control 1o subassembly 28, and rotating frame 65. As shown in Figure 2, supervisory control 11 unit 75 is electrically coupled to operator control panel 77, valve 47, and acoustic 12 transducer 79. These components cooperate to control the volume of air ~s contained within extruded film tube 81, and hence the thickness and diameter of i4 the extruded film tube 81. Valve 47 controls the amount of air directed by blower 1s 41 into extruded film tube 81 through internal air diffuser 51.
1s If more air is directed into extruded film tube 81 by internal air diffuser 1 ~ than is exhausted from extruded film tube 81 by exhaust stack 43, the 1s circumference of extruded film tube 81 will be increased. Conversely, if more air ~s is exhausted from the interior of extruded film tube 81 by exhaust stack 53 than is 2o inputted into extruded film tube 81 by internal air diffuser 51, the circumference of 21 extruded film tube 81 will decrease.
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0291 MH-28521 !39815.1 1 In the preferred embodiment, valve 41 is responsive to supervisory control 2 unit 75 for increasing or decreasing the flow of air into extruded film tube 81.
s Operator control panel 77 serves to allow the operator to select the diameter of 4 extruded film tube 81. Acoustic transducer 79 serves to generate a signal s corresponding to the circumference of extruded film tube 81, and direct this signal s to supervisory control unit 75 for comparison to the circumference setting selected by the operator at operator control panel 77.
s If the actual circumference of extruded film tube 81 exceeds the selected s circumference, supervisory control unit 75 operates valve 47 to restrict the passage of air from blower 41 into extruded film tube 81. This results in a decrease in 11 circumference of extruded film tube 81. Conversely, if the circumference of i 2 extruded film tube 81 is less than the selected circumference, supervisory control 1s unit 75 operates on valve 47 to increase the flow of air into extruded film tube 81 1a. and increase its circumference. Of course, extruded film tube 81 will fluctuate in 1 s circumference, requiring constant adjustment and readjustment of the inflow of air 1s by operation of supervisory control unit 75 and valve 47.
Figure 3 is a view of ultrasonic sensor 89 of the improve control system of 1a the present invention coupled to sizing cage 23 adjacent extruded film tube 81.
1s In the preferred embodiment, acoustic transducer 79 comprises an ultrasonic 2o measuring and control system manufactured by Massa Products Corporation of 2i Hingham, Massachusetts, Model Nos. M-4000, M410/215, and M450, including a Page - 15 DOCKET NO. 291H-24528-CN
0291 MH-26521 !39815.7 Massa Products ultrasonic sensor 89. It is an ultrasonic ranging and detection 2 device which utilizes high frequency sound waves which are deflected off objects a and detected. In the preferred embodiment, a pair of ultrasonic sensors 89 are 4 used, one to transmit sonic pulses, and another to receive sonic pulses. For purposes of simplifying the description only one ultrasonic sensor 89 is shown, and s in fact a single ultrasonic sensor can be used, first to transmit a sonic pulse and 7 then to receive the return in an alternating fashion. The elapsed time between an a ultrasonic pulse being transmitted and a significant echo being received s corresponds to the distance between ultrasonic sensor 89 and the object being ~o sensed. Of course, the distance between the ultrasonic sensor 89 and extruded 11 film tube 81 corresponds to the circumference of extruded film tube 81. In the 12 present situation, ultrasonic sensor 89 emits an interrogating ultrasonic beam 87 is substantially normal to extruded film tube 81 and which is deflected from the outer surface of extruded film tube 81 and sensed by ultrasonic sensor 89.
The Massa Products Corporation ultrasonic measurement and control is system includes system electronics which utilize the duration of time between 1 ~ transmission and reception to produce a useable electrical output such as a ~s voltage or current. In the preferred embodiment, ultrasonic sensor 89 is coupled is to sizing cage 23 at adjustable coupling 83. In the preferred embodiment, 2o ultrasonic sensor 89 is positioned within seven inches of extruded film tube 81 to 21 minimize the impact of ambient noise on a control system. Ultrasonic sensor Page - 16 DOCKET NO. 291 H-2452&CN
0291 MH-28521139815.1 1 is positioned so that interrogating ultrasonic beam 87 travels through a path which 2 is substantially normal to the outer surface of extruded film tube 81, to maximize s the return signal to ultrasonic sensor 89.
4 Figure 4 is a view of ultrasonic sensor 89 of Figure 3 coupled to sizing cage 23 of the blown film tower 13, in two positions, one position being shown in s phantom. In the first position, ultrasonic sensor 89 is shown adjacent extruded film 7 tube 81 of a selected circumference. When extruded film tube 81 is downsized to a a tube having a smaller circumference, ultrasonic sensor 89 will move inward and s outward relative to the central axis of the adjustable sizing cage, along with the 1o adjustable sizing cage 23. The second position is shown in phantom with 11 ultrasonic sensor 89' shown adjacent extruded film tube 81' of a smaller i2 circumference. For purposes of reference, internal air diffuser 51 and exhaust 1s stack 53 are shown in Figure 4. The sizing cage is also movable upward and 14 downward, so ultrasonic sensor 89 is also movable upward and downward relative 1s to the frostline of the extruded film tube 81.
1s Figure 5 is a schematic and block diagram view of the preferred control 1 ~ system of the present invention. The preferred acoustic transducer 79 of the 1 s present invention includes ultrasonic sensor 89 and temperature sensor 91 which ~ s cooperate to produce a current position signal which is independent of the ambient 2o temperature. Ultrasonic sensor 89 is electrically coupled to ultrasonic electronics 2i module 95, and temperature sensor 91 is electrically coupled to temperature Page - 17 DOCKET NO. 291 H-24528-CN
0291 MH-26521139816.1 1 electronics module 97. Together, ultrasonic electronics module 95 and z temperature electronics module 97 comprise transducer electronics 93. Four s signals are produced by acoustic transducer 79, including one analog signal, and 4 three digital signals.
s As shown in Figure 5, four conductors couple transducer electronics to s supervisory control unit 75. Specifically, conductor 99 routes a 0 to 10 volts DC
7 analog input to supervisory control unit 75. Conductors 101, 103, and 105 provide s digital signals to supervisory control unit 75 which correspond to a target present s signal, maximum override, and minimum override. These signals will be described ~o below in greater detail.
i 1 Supervisory control unit 75 is electrically coupled to setpoint display 12 through analog display output 107. An analog signal between 0 and 10 volts DC
13 IS provided to setpoint display 109 which displays the selected distance between ultrasonic sensor 89 and extruded film tube 81. A distance is selected by the ~s operator through distance selector 111. Target indicator 113, preferably a light, is is provided to indicate that the target (extruded film tube 81) is in range.
Distance i ~ selector 111 is electrically coupled to supervisory control unit 75 by distance i8 setting conductor 119. Target indicator 113 is electrically coupled to supervisory is control unit 75 through target present conductor 121.
2o Supervisory control unit 75 is also coupled via valve control conductor 123 21 to proportional valve 125. In the preferred embodiment, proportional valve Page - 18 DOCKET NO. 291 H-24528-CN
0291 MH-28521139815.1 corresponds to valve 47 of Figure 1, and is a pressure control component 2 manufactured by Proportionair of McCordsville, Indiana, Model No. BB1.
s Proportional valve 125 translates an analog DC voltage provided by supervisory 4 control unit 75 into a corresponding pressure between .5 and 1.2 bar.
Proportional valve 125 acts on rotary valve 129 through cylinder 127. Pressurized air is s provided to proportional valve 125 from pressurized air supply 131 through 7 micron filter 133.
8 Figure 6 is a schematic and block diagram view of the preferred control s system of Figure 5, with special emphasis on the supervisory control unit 75.
to Extruded film tube 81 is shown in cross-section with ultrasonic sensor 89 adjacent i i its outer wall. Ultrasonic sensor 89 emits interrogating pulses which are bounced 12 Off of extruded film tube and sensed by ultrasonic sensor 89. The time delay 13 between transmission and reception of the interrogating pulse is processed by 14 transducer electronics 93 to produce four outputs: CURRENT POSITION signal ~s which is provided to supervisory control unit 75 via analog output conductor 99, ~s digital TARGET PRESENT signal which is provided over digital output 105, a minimum override signal (MIO signal) indicative of a collapsing or undersized ~s bubble which is provided over digital output conductor 103, and maximum override is signal (MAO signal) indicative of an overblown extruded film tube 81 which is 2o provided over a digital output conductor 101.
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0291 MH-26521139815.1 As shown in Figure 6, the position of extruded film tube 81 relative to 2 ultrasonic sensor 89 is analyzed and controlled with reference to a number of s distance thresholds and setpoints, which are shown in greater detail in Figure 7A.
4 All set points and thresholds represent distances from reference R. The control s system of the present invention attempts to maintain extruded film tube 81 at a s circumference which places the wall of extruded film tube 81 at a tangent to the 7 line established by reference A. The distance between reference R and set point s A may be selected by the user through distance selector 111. This allows the user s to control the distance between ultrasonic sensor 89 and extruded film tube 81.
io The operating range of acoustic transducer 79 is configurable by the user > > with settings made in transducer electronics 93. In the preferred embodiment, 12 using the Massa Products transducer, the range of operation of acoustic 1s transducer 79 is between 3 to 24 inches. Therefore, the user may select a ~4 minimum circumference threshold C and a maximum circumference threshold B, ~s below and above which an error signal is generated. Minimum circumference ~s threshold C may be set by the user at a distance d3 from reference R.
Maximum i ~ circumference threshold B may be selected by the user to be a distance d2 from reference R. In the preferred embodiment, setpoint A is set a distance of 7 inches is from reference R. Minimum circumference threshold C is set a distance of 10.8125 2o inches from reference R. Maximum circumference threshold B is set a distance 2~ of 4.1 inches from reference R. Transducer electronics 93 allows the user to set Page - 20 DOCKET NO. 291H-24528-CN
0291 MH-28621139815.1 1 or adjust these distances at will provided they are established within the range of 2 operation of acoustic transducer 79, which is between 3 and 24 inches.
3 Besides providing an analog indication of the distance between ultrasonic 4 sensors 89 and extruded film tube 81, transducer electronics 93 also produces s three digital signals which provide information pertaining to the position of extruded s film tube 81. If extruded film tube 81 is substantially normal and within the operating range of ultrasonic sensor 89, a digital "1" is provided at digital output a 105. The signal is representative of a TARGET PRESENT signal. If extruded film s tube 81 is not within the operating range of ultrasonic sensor 89 or if a return pulse 1o is not received due to curvature of extruded film tube 81, TARGET PRESENT
signal 11 of digital output 105 is low. As discussed above, digital output 103 is a minimum 12 override signal MIO. If extruded film tube 81 is smaller in circumference than the 1s reference established by threshold C, minimum override signal MIO of digital 14 output 103 is high. Conversely, if circumference of extruded film tube 81 is greater 1s than the reference established by threshold C, the minimum override signal MIO
16 IS IOW.
1 ~ Digital output 101 is for a maximum override signal MAO. If extruded film 1s tube 81 is greater than the reference established by threshold B, the maximum 1s override signal MAO is high. Conversely, if the circumference of extruded film tube 20 81 is less than the reference established by threshold B, the output of maximum 21 override signal MAO is low.
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0291 MH-28621139815.1 1 The minimum override signal MIO will stay high as long as extruded film 2 tube 81 has a circumference less than that established by threshold C.
Likewise, s the maximum override signal MAO will remain high for as long as the 4 circumference of extruded film tube 81 remains larger than the reference s established by threshold B.
s Threshold D and threshold E are also depicted in Figure 7A. Threshold D
is established at a distance d4 from reference R. Threshold E is established at a s distance d5 from reference R. Thresholds D and E are established by supervisory s control unit 75, not by acoustic transducer 79. Threshold D represents a minimum ~o circumference threshold for extruded film tube 81 which differs from that > > established by transducer electronics 93. Likewise, threshold E
corresponds to a 12 maximum circumference threshold which differs from that established by acoustic ~s transducer 79. Thresholds D and E are established in the software of supervisory ~a control unit 75, and provide a redundancy of control, and also minimize the ~s possibility of user error, since these threshold are established in software, and ~s cannot be easily changed or accidentally changed. The coordination of all of these i~ thresholds will be discussed in greater detail below. In the preferred embodiment, ~a threshold C is established at 10.8125 inches from reference R. Threshold E
is is established at 3.6 inches from reference R.
2o Figure 7B is a side view of the ultrasonic sensor 89 coupled to sizing cage 2~ 23 of the blown film tower 13, with permissible extruded film tube 81 operating Page - 22 -DOCKET NO. 291 H-24528-CN
0291 MH-28621139815.1 1 ranges indicated thereon. Setpoint A is the desired distance between ultrasonic z sensor 89 and extruded film tube 81. Thresholds D and C are established at 3 selected distances inward from ultrasonic sensor 89, and represent minimum 4 circumference thresholds for extruded film tube 81. Thresholds B and E are s established at selected distances from setpoint A, and establish separate maximum s circumference thresholds for extruded film tube 81. As shown in Figure 7B, 7 extruded film tube 81 is not at setpoint A. Therefore, additional air must be s supplied to the interior of extruded film tube 81 to expand the extruded film tube s 81 to the desired circumference established by setpoint A.
io If extruded film tube 81 were to collapse, two separate alarm conditions 1 i would be registered. One alarm condition will be established when extruded film ~2 tube 81 falls below threshold C. A second and separate alarm condition will be is established when extruded film tube 81 falls below threshold D. Extruded film tube 81 may also become overblown. In an overblown condition, two separate alarm is conditions are possible. When extruded film tube 81 expands beyond threshold ~s B, an alarm condition is registered. When extruded film tube 81 expands further 17 to extend beyond threshold E, a separate alarm condition is registered.
is As discussed above, thresholds C and B are subject to user adjustment is through settings in transducer electronics 93. In contrast, thresholds D
and E are 2o set in computer code of supervisory control unit 75, and are not easily adjusted.
21 This redundancy in control guards against accidental or intentional missetting of Page - 23 DOCKET NO. 291 H-2452&CN
0291 MH-26521139815.1 the threshold conditions at transducer electronics 93. The system also guards 2 against the possibility of equipment failure in transducer 79, or gradual drift in the 3 threshold settings due to deterioration, or overheating of the electronic 4 components contained in transducer electronics 93.
Returning now to Figure 6, operator control panel 137 and supervisory s control unit 75 will be described in greater detail. Operator control panel includes setpoint display 109, which serves to display the distance d1 between s reference R and setpoint A. Setpoint display 109 includes a 7 segment display.
s Distance selector 111 is used to adjust setpoint A. Holding the switch to the "+"
io position increases the circumference of extruded film tube 81 by decreasing ~ i distance d1 between setpoint A and reference R. Holding the switch to the "-"
~2 position decreases the diameter of extruded film tube 81 by increasing the distance ~s between reference R and setpoint A.
is Target indicator 113 is a target light which displays information pertaining ~s to whether extruded film tube 81 is within range of ultrasonic transducer 89, is whether an echo is received at ultrasonic transducer 89, and whether any alarm 1 ~ condition has occurred. Blower switch 139 is also provided in operator control ~s panel 137 to allow the operator to selectively disconnect the blower from the ~s control unit. As shown in Figure 6, all these components of operator control panel 20 137 are electrically coupled to supervisory control unit 75.
Page - 24 -DOCKET NO. 291H-24528-CN
0291 MH-28621139815.1 1 Supervisory control unit 75 responds to the information provided by acoustic 2 transducer 79, and operator control panel 137 to actuate proportional valve 125.
s Proportional valve 125 in turn acts upon pneumatic cylinder 127 to rotate rotary 4 valve 129 to control the air flow to the interior of extruded film tube 81.
s With the exception of analog to digital converter 141, digital to analog s converter 143, and digital to analog converter 145 (which are hardware items), 7 supervisory control unit 75 is a graphic representation of computer software $ resident in memory of supervisory control unit 75. In the preferred embodiment, s supervisory control unit 75 comprises an industrial controller, preferably a Texas io Instrument brand industrial controller Model No. PM550. Therefore, supervisory 11 control unit 75 is essentially a relatively low-powered computer which is dedicated 12 to a particular piece of machinery for monitoring and controlling. In the preferred is embodiment, supervisory control unit 75 serves to monitor many other operations 14 of blown film extrusion line 11. The gauging and control of the circumference of ~s extruded film tube 81 through computer software is one additional function which is is "piggybacked" onto the industrial controller. Alternately, it is possible to provide 17 an industrial controller or microcomputer which is dedicated to the monitoring and i8 control of the extruded film tube 81. Of course, dedicating a microprocessor to is this task is a rather expensive alternative.
2o For purposes of clarity and simplification of description, the operation of the 21 computer program in supervisory control unit 75 have been segregated into Page - 25 DOCKET NO. 291 H-24528-CN
0291 MH-26521 !39816.1 1 operational blocks, and presented as an amalgamation of digital hardware blocks.
2 In the preferred embodiment, these software subcomponents include: software s filter 149, health state logic 151, automatic sizing and recovery logic 153, loop 4 mode control logic 155, volume setpoint control logic 157, and output clamp 159.
These software modules interface with one another, and to PI loop program 147 s of supervisory control unit 75. PI loop program is a software routine provided in the Texas Instruments' PM550 system. The proportional controller regulates a a process by manipulating a control element through the feedback of a controlled s output. The equation for the output of a PI controller is:
1 o m = K*e + K/T j a dt + ms > > In this equation:
12 m = controller output 1a K = controller gain 14 a = error 1s T = reset time 1s dt = differential time 17 ms = constant 1s j a dt = integration of all previous errors is When an error exists, it is summed (integrated) with all the previous 2o errors, thereby increasing or decreasing the output of the PI controller (depending Page - 26 DOCKET NO. 291 H-2452&CN
0291 MH-26621139816.1 - _ CA 02206911 1997-06-04 1 upon whether the error is positive or negative). Thus as the error term 2 accumulates in the integral term, the output changes so as to eliminate the error.
CURRENT POSITION signal is provided by acoustic transducer 79 via 4 analog output 99 to analog to digital converter 141, where the analog CURRENT
POSITION signal is digitized. The digitized CURRENT POSITION signal is routed s through software filter 149, and then to PI loop program 147. If the circumference 7 of extruded film tube 81 needs to be adjusted, PI loop program 147 acts through 8 output clamp 159 upon proportional valve 125 to adjust the quantity of air provided s to the interior of extruded film tube 81.
Figure 8A is a flowchart of the preferred filtering process applied to 11 CURRENT POSITION signal generated by the acoustic transducer. The digitized ~2 CURRENT POSITION signal is provided from analog to digital converter 141 to 13 software filter 149. The program reads the CURRENT POSITION signal in step 14 161. Then, the software filter 149 sets SAMPLE (N) to the position signal.
15 In step 165, the absolute value of the difference between CURRENT
POSITION (SAMPLE (N)) and the previous sample (SAMPLE (N - 1)) is compared 17 to a first threshold. If the absolute value of the difference between the current ~s sample and the previous sample is less than first threshold T1, the value of is SAMPLE (N) is set to CFS, the current filtered sample, in step 167. If the absolute 2o value of the difference between the current sample and the previous sample 21 exceeds first threshold T1, in step 169, the CURRENT POSITION signal is Page-27 DOCKET NO. 291 H-24528-CN
0291 MH-28521139815.1 1 disregarded, and the previous position signal SAMPLE (N - 1) is substituted in its z place.
a Then, in step 171, the suggested change SC is calculated, by determining 4 the difference between the current filtered sample CFS and the best position s estimate BPE. In step 173, the suggested change SC which was calculated in step s 171 is compared to positive T2, which is the maximum limit on the rate of change.
7 If the suggested change is within the maximum limit allowed, in step 177, allowed s change AC is set to the suggested change SC value. If, however, in step 173, the s suggested change exceeds the maximum limit allowed on the rate of change, in 1 o step 175, the allowed change is set to + LT2, a default value for allowed change.
11 In step 179, the suggested change SC is compared to the negative limit for 12 allowable rates of change, negative T2. If the suggested change SC is greater than the maximum limit on negative change, in step 181, allowed change AC is set to negative -LT2, a default value for negative change. However, if in step 179 it is is determined that suggested change SC is within the maximum limit allowed on is negative change, in step 183, the allowed change AC is added to the current best 17 position estimate BPE, in step 183. Finally, in step 185, the newly calculated best i$ position estimate BPE is written to the PI loop program.
is Software filter 149 is a two stage filter which first screens the CURRENT
2o POSITION signal by comparing the amount of change, either positive or negative, 21 to threshold T1. If the CURRENT POSITION signal, as compared to the preceding Page - 28 DOCKET NO. 291H-24528-CN
0291 MH-26521 !39815.1 1 position signal exceeds the threshold of T1, the current position signal is 2 discarded, and the previous position signal (SAMPLE (N - 1)) is used instead. At 3 the end of the first stage, in step 171, a suggested change SC value is derived by 4 subtracting the best position estimate BPE from the current filtered sample CFS.
In the second stage of filtering, the suggested change SC value is s compared to positive and negative change thresholds (in steps 173 and 179).
If the positive or negative change thresholds are violated, the allowable change is set s to a preselected value, either + LT2, or -LT2. Of course, if the suggested change s SC is within the limits set by positive T2 and negative T2, then the allowable 1 o change AC is set to the suggested change SC.
11 The operation of software filter 149 may also be understood with reference 12 to Figure 8B. In the graph of Figure 8B, the y-axis represents the signal level, and 1s the x-axis represents time. The signal as sensed by acoustic transducer 79 is 14 designated as input, and shown in the solid line. The operation of the first stage 1s of the software filter 149 is depicted by the current filtered sample CFS, which is 1s shown in the graph by cross-marks. As shown, the current filtered sample CFS
operates to ignore large positive or negative changes in the position signal, and 1s will only change when the position signal seems to have stabilized for a short is interval. Therefore, when changes occur in the current filtered sample CFS, they 20 occur in a plateau-like manner.
Page-29-DOCKET NO. 291 H-24528-CN
0291 MH-2852113987 5.1 1 In stage two of the software filter 149, the current filtered sample CFS is z compared to the best position estimate BPE, to derive a suggested change SC
s value. The suggested SC is then compared to positive and negative thresholds 4 to calculate an allowable change AC which is then added to the best position s estimate BPE. Figure 8B shows that the best position estimate BPE signal only s gradually changes in response to an upward drift in the POSITION SIGNAL. The 7 software filtering system 149 of the present invention renders the control apparatus 8 relatively unaffected by random noise, but capable of tracking the more "gradual"
s changes in bubble position.
1o Experimentation has revealed that the software filtering system of the 11 present invention operates best when the position of extruded film tube 81 is 12 sampled between 20 to 30 times per second. At this sampling rate, one is less 13 likely to incorrectly identify noise as a change in circumference of extruded film 14 tube 81. The preferred sampling rate accounts for the common noise signals ~s encountered in blown film extrusion liner.
1s Optional thresholds have also been derived through experimentation. In the 1 ~ first stage of filtering, threshold T1 is established as roughly one percent of the 18 operating range of acoustic transducer 79, which in the preferred embodiment is is twenty-one meters (24 inches less 3 inches). In the second stage of filter, 2o thresholds + LT2 and -LT2 are established as roughly 0.30% of the operating range 21 of acoustic transducer 79.
Page - 30 -DOCKET NO. 291 H-2452&CN
0291 MH-28621139815.1 1 Figure 9 is a schematic representation of the automatic sizing and recovery 2 logic ASRL of supervisory control unit 75. As stated above, this figure is a 3 hardware representation of a software routine. ASRL 153 is provided to 4 accommodate the many momentary false indications of maximum and minimum s circumference violations which may be registered due to noise, such as the noise s created due to air flow between acoustic transducer 79 and extruded film tube 81.
The input from maximum alarm override MAO is "ored" with high alarm D, from the 8 PI loop program, at "or" operator 191. High alarm D is the signal generated by the s program in supervisory control unit 75 when the circumference of extruded film io tube 81 exceeds threshold D of Figure 7A. If a maximum override MAO signal 11 exists, or if a high alarm condition D exists, the output of "or" operator 191 goes 12 high, and actuates delay timer 193.
13 Likewise, minimum override MIO signal is "ored" at "or" operator 195 with 14 low alarm E. If a minimum override signal is present, or if a low alarm condition ~s E exists, the output of "or" operator 195 goes high, and is directed to delay timer is 197. Delay timers 193, 197 are provided to prevent an alarm condition unless the condition is held for 800 milliseconds continuously. Every time the input of delay ~ s timers 193, 197 goes low, the timer resets and starts from 0. This mechanism is eliminates many false alarms.
2o If an alarm condition is held for 800 milliseconds continuously, an 2~ OVERBLOWN or UNDERBLOWN signal is generated, and directed to the health Page - 31 DOCKET NO. 291 H-24528-CN
0291 MH-28521139815.1 1 state logic 151. Detected overblown or underblown conditions are "ored" at "or"
2 operator 199 to provide a REQUEST MANUAL MODE signal which is directed to a loop mode control logic 155.
4 Figure 10 is a schematic representation of the health-state logic 151 of s Figure 6. The purpose of this logic is to control the target indicator 113 of operator s control panel 137. When in non-error operation, the target indicator 113 is on if the blower is on, and the TARGET PRESENT signal from digital output 105 is high.
s When an error is sensed in the maximum override MAO or minimum override MIO
s lines, the target indicator 113 will flash on and off in one half second intervals.
io In health-state logic HSL 151, the maximum override signal MAO is inverted 11 at inverter 205. Likewise, the minimum override signal is inverted at inverter 207.
12 "And" operator 209 serves to "and" the inverted maximum override signal is MAO, with the OVERBLOWN signal, and high alarm signal D. A high output from 14 "and" operator 209 indicates that something is wrong with the calibration of is acoustic transducer 79.
is Likewise, "and" operator 213 serves to "and" the inverted minimum override 1~ signal MIO, with the OVERBLOWN signal, and low alarm signal E. If the output of is "and" operator 213 is high, something is wrong with the calibration of acoustic is transducer 79. The outputs from "and" operators 209, 213 are combined in "or"
20 operator 215 to indicate an error with either the maximum or minimum override 2~ detection systems. The output of "or" operator 215 is channeled through oscillator Page - 32 DOCKET NO. 291H-24528-CN
0291 MH-26521139816.1 219, and inverted at inverter 217. "And" operator 211 serves to "and" the TARGET
2 PRESENT signal, blower signal, and inverted error signal from "or" operator 215.
s The output of "and" operator of 211 is connected to target indicator 113.
4 If acoustic transducer 79 is properly calibrated, the target is within range and normal to the sonic pulses, and the blower is on, target indicator 113 will be s on. If the target is within range and normal to the sonic pulses, the blower is on, 7 but acoustic transducer 79 is out of calibration, target indicator 113 will be on, but s will be blinking. The blinking signal indicates that acoustic transducer 79, and in s particular transducer electronics 93, must be recalibrated.
io Figure 11 is a schematic representation of loop mode control logic LMCL
i i of Figure 6. The purpose of this software module is coordinate the transition in 12 modes of operation. Specifically, this software module coordinates automatic 1 s startup of the blown film extrusion process, as well as changes in mode between 14 an automated "cascade" mode and a manual mode, which is the required mode ~ s of the PI controller to enable under and overblown conditions of the extruded film is tube 81 circumference. The plurality of input signals are provided to loop mode i7 control logic 155, including: BLOWER ON, REQUEST MANUAL MODE, PI LOOP
is IN CASCADE MODE, UNDERBLOWN and OVERBLOWN. Loop mode control ~s logic LMCL 155 provides two output signals: MANUAL MODE, and CASCADE
2o MODE.
Page - 33 DOCKET NO. 291 H-24528-CN
0291 MH-26521139815.1 1 Figure 11 includes a plurality of digital logic blocks which are representative 2 of programming operations. "Or" operator 225 "ores" the inverted BLOWER ON
3 SIGNAL to the REQUEST MANUAL MODE SIGNAL. "And" operator 227 "ands" the 4 inverted REQUEST MANUAL MODE SIGNAL with an inverted MANUAL MODE
s SIGNAL, and the BLOWER ON SIGNAL. "And" operator 229 "ands" the REQUEST
s MANUAL MODE SIGNAL to the inverted CASCADE MODE SIGNAL. This prevents MANUAL MODE and CASCADE MODE from both being on at the same time.
8 "And" operator 231 "ands" the MANUAL MODE SIGNAL, the inverted 9 UNDERBLOWN SIGNAL, and the OVERBLOWN SIGNAL. "And" operator 233 "ands" the MANUAL MODE SIGNAL with the UNDERBLOWN SIGNAL. This causes 11 the overblown condition to prevail in the event a malfunction causes both 12 underblown and overblown conditions to be on. Inverters 235, 237, 239, 241, and 1s 243 are provided to invert the inputted output signals of loop mode control logic 14 155 were needed. Software one-shot 245 is provided for providing a momentary 1s response to a condition. Software one-shot 245 includes "and" operator 247, 1s off-delay 249, and inverter 251.
1 ~ The software of loop mode control logic 155 operates to ensure that 1a the system is never in MANUAL MODE, and CASCADE MODE at the same time.
19 When manual mode is requested by REQUEST MANUAL MODE, loop mode 2o control logic 155 causes MANUAL MODE to go high. When manual mode is not 21 requested, loop mode control logic 155 operates to cause CASCADE MODE to go Page - 34 DOCKET NO. 291 H-2452&CN
0291 MH-26521 /39815.1 1 high. MANUAL MODE and CASCADE MODE will never be high at the same time.
2 Loop mode control logic 155 also serves to ensure that the system provides a s "bumpless transfer" when mode changes occur. The term "cascade mode" is 4 understood in the automation industries as referring to an automatic mode which s will read an adjustable setpoint.
s Loop mode control logic 155 will also allow for automatic startup of 7 the blown film extrusion process. At startup, UNDERBLOWN SIGNAL is high, PI
s LOOP IN CASCADE MODE is low, BLOWER ON SIGNAL is high. These inputs s (and inverted inputs) are combined at "and" operators 231, 233. At startup, "and"
~o operator 233 actuates logic block 253 to move the maximum air flow value address 11 to the PI loop step 261. At startup, the MANUAL MODE SIGNAL is high. For the 12 PI loop controller of the preferred embodiment, when MANUAL MODE is high, the 13 value contained in PI loop output address is automatically applied to proportional 14 valve 125. This results in actuation of proportional valve 125 to allow maximum air 1s flow to start the extruded film tube 81.
1s When extruded film tube 81 extends in size beyond the minimum ~7 threshold (C and D of Figure 7A), the UNDERBLOWN SIGNAL goes low, and the 1s PI LOOP IN CASCADE MODE signal goes high. This causes software one-shot is 245 to trigger, causing logic blocks 265, 267 to push an initial bias value contained 2o in a program address onto the PI loop. Simultaneously, logic blocks 269, z1 operate to place the selected setpoint value A onto volume-setpoint control logic Page - 35 DOCKET NO. 291 H-24528-CN
0291 MH-28521 (39815.1 1 VSCL 157. Thereafter, volume-setpoint control logic VSCL 157 alone serves to z communicate changes in setpoint value A to PI loop program 147.
s If an overblown or underblown condition is detected for a sufficiently 4 long period of time, the controller will request a manual mode by causing REQUEST MANUAL MODE SIGNAL to go high. If REQUEST MANUAL MODE
s goes high, loop mode control logic LMCL 155 supervises the transfer through 7 operation of the logic blocks.
s Loop mode control logic LMCL 155 also serves to detected s overblown and underblown conditions. If an overblown or underblown condition 1o is detected by the control system, REQUEST MANUAL MODE goes high, and the i1 appropriate OVERBLOWN or UNDERBLOWN signal goes high. The logic 12 operators of loop mode control logic LMCL 155 operate to override the normal 13 operation of the control system, and cause maximum or minimum air flow by 14 putting the maximum air flow address 261 or minimum air flow address 263 to the PI output address. As stated above, when MANUAL MODE is high, these 1 s maximum or minimum air flow address values are outputted directly to proportional valve 125. Thus, when the extruded film tube 81 is overblown, loop mode control 1s logic LMCL 155 operates to immediately cause proportional valve 125 to minimize 1s air flow to extruded film tube 81. Conversely, if an underblown condition is 2o detected, loop mode control logic LMCL 155 causes proportional valve 125 to 21 immediately maximize air flow to extruded film tube 81.
Page - 36 -DOCKET NO. 291 H-24528-CN
0291 MH-28521139815.1 1 Figure 12 depicts the operation of volume-setpoint control logic VSCL
2 157.
s Volume setpoint control logic VSCL 157 operates to increase or 4 decrease setpoint A in response to changes made by the operator at distance s selector 111 of operator control panel 137, when the PI loop program 147 is in s cascade mode, i.e. when PI LOOP IN CASCADE MODE signal is high. The 7 INCREASE SETPOINT, DECREASE SETPOINT, and PI LOOP IN CASCADE MODE
8 signals are logically combined at "and" operators 283, and 287. These "and"
s operators act on logic blocks 285, 289 to increase or decrease the setpoint 1o contained in remote setpoint address 291. When the setpoint is either increased ~ 1 or decreased, logic block 293 operates to add the offset to the remote setpoint for ~2 display, and forwards the information to digital to analog converter 143, for display 13 at setpoint display 109 of operator control panel 137. The revised remote setpoint 14 address is then read by the PI loop program 147.
1s Figure 13 is a flowchart drawing of output clamp 159. The purpose 1s of this software routine is to make sure that the PI loop program 147 does not over 17 drive the rotary valve 129 past a usable limit. Rotary valve 129 operates by moving 1s a vane to selectively occlude stationary openings. If the moving vane is over 1s driven, the rotary valve will begin to open when the PI loop calls for complete 2o closure. In step 301, the output of the PI loop program 147 is read. In step 303, 21 the output of PI loop is compared to a maximum output. If it exceeds the Page - 37 -DOCKET NO. 291 H-2452&CN
0291 MH-26621139815.1 _ CA 02206911 1997-06-04 1 maximum output, the PI output is set to a predetermined maximum output in step 2 305. If the output of PI loop does not exceed the maximum output, in step 307, s the clamped PI output is written to the proportional valve 125 through digital to 4 analog converter 145.
Figures 14, through 27 will be used to describe an alternative s emergency condition control mode of operation which provides enhanced control capabilities, especially when an overblown or underblown condition is detected by s the control system, or when the system indicates that the extruded film tube is out s of range of the position-sensing transducer. In this alternative emergency 1o condition control mode of operation, the valve of the estimated position is > > advanced to a preselected valve and a more rapid change in the estimated ~2 position signal is allowed than during previously discussed operating conditions, ~s and is particularly useful when an overblown or underblown condition is detected.
14 In the event the control system indicates that the extruded film tube is out of range is of the sensing transducer, the improved control system supplies an estimated ~s position which, in most situations, is a realistic estimation of the position of the 17 extruded film tube relative to the sensing transducer, thus preventing false ~a indications of the extruded film tube being out of range of the sensing transducer is from adversely affecting the estimated position of the extruded film tube, greatly 2o enhancing operation of the control system. In the event an overblown condition 21 IS detected, the improved control system supplies an estimated position which Page - 38 DOCKET NO. 291 H-24528-CN
0291 MH-26521139815.1 1 corresponds to the distance boundary established for detecting an overflow 2 condition. In the event an underblown condition is detected, the improved control s system supplies an estimated position which corresponds to the distance 4 boundary established for detecting an underblown condition.
Figures 14, through 27 are a block diagram, schematic, and flowchart s representation of the preferred embodiment of a control system which is equipped with the alternative emergency condition control mode of operation. Figures 25, 8 26, and 27 provide graphic examples of the operation of this alternative emergency s condition control mode of operation.
1o Figure 14 is a schematic and block diagram view of the preferred 11 alternative control system 400 of the present invention of Figure 5, with special 12 emphasis on the supervisory control unit 75, and is identical in almost all respects 13 to the supervisory control unit 75 which is depicted in Figure 6;
therefore, identical 14 referenced numerals are used to identify the various components of alternative 1s control system 400 of Figure 14 as are used in the control system depicted in 1s Figure 6.
Extruded film tube 81 is shown in cross-section with ultrasonic sensor 1a 89 adjacent its outer wall. Ultrasonic sensor 89 emits interrogating pulses which is are bounced off of extruded film tube and sensed by ultrasonic sensor 89.
The 2o time delay between transmission and reception of the interrogating pulse is 2~ processed by transducer electronics 93 to produce four outputs: CURRENT
Page - 39 DOCKET NO. 291 H-2452&CN
0291 MH-26521139815.1 POSITION signal which is provided to supervisory control unit 75 via analog output 2 conductor 99, digital TARGET PRESENT signal which is provided over digital s output 105, a minimum override signal (MIO signal) indicative of a collapsing or 4 undersized bubble which is provided over digital output conductor 103, and s maximum override signal (MAO signal) indicative of an overblown extruded film s tube 81 which is provided over a digital output conductor 101.
As shown in Figure 14, the position of extruded film tube 81 relative s to ultrasonic sensor 89 is analyzed and controlled with reference to a number of s distance thresholds and setpoints, which are shown in greater detail in Figure 15.
io All set points and thresholds represent distances from reference R. The control i i system of the present invention attempts to maintain extruded film tube 81 at a circumference which places the wall of extruded film tube 81 at a tangent to the ~s line established by reference A. The distance between reference R and set point 14 A may be selected by the user through distance selector 111. This allows the user ~s to control the distance between ultrasonic sensor 89 and extruded film tube 81.
is The operating range of acoustic transducer 79 is configurable by the t7 user with settings made in transducer electronics 93. In the preferred embodiment, using the Massa Products transducer, the range of operation of acoustic ~s transducer 79 is between 3 to 24 inches. Therefore, the user may select a 2o minimum circumference threshold C and a maximum circumference threshold B, 2i below and above which an error signal is generated. Minimum circumference Page - 40 DOCKET NO. 291H-24528-CN
0291 MH-26521139815.1 1 threshold C may be set by the user at a distance d3 from reference R.
Maximum 2 circumference threshold B may be selected by the user to be a distance d2 from s reference R. In the preferred embodiment, setpoint A is set a distance of 7 inches 4 from reference R. Minimum circumference threshold C is set a distance of 10.8125 inches from reference R. Maximum circumference threshold B is set a distance s of 4.1 inches from reference R. Transducer electronics 93 allows the user to set or adjust these distances at will provided they are established within the range of s operation of acoustic transducer 79, which is between 3 and 24 inches.
s Besides providing an analog indication of the distance between 1o ultrasonic sensors 89 and extruded film tube 81, transducer electronics 93 also 11 produces three digital signals which provide information pertaining to the position 12 of extruded film tube 81. If extruded film tube 81 is substantially normal and within 1s the operating range of ultrasonic sensor 89, a digital "1" is provided at digital 14 output 105. The signal is representative of a TARGET PRESENT signal. If 1s extruded film tube 81 is not within the operating range of ultrasonic sensor 89 or 1s if a return pulse is not received due to curvature of extruded film tube 81, TARGET
17 PRESENT signal of digital output 105 is low. As discussed above, digital output 18 103 is a minimum override signal MIO. If extruded film tube 81 is smaller in 1s circumference than the reference established by threshold C, minimum override 2o signal MIO of digital output 103 is high. Conversely, if circumference of extruded Page - 41 DOCKET NO. 291 H-24528-CN
0291 MH-28521 /39815.1 1 film tube 81 is greater than the reference established by threshold C, the minimum 2 override signal MIO is low.
s Digital output 101 is for a maximum override signal MAO. If extruded 4 film tube 81 is greater than the reference established by threshold B, the maximum s override signal MAO is high. Conversely, if the circumference of extruded film tube s 81 is less than the reference established by threshold B, the output of maximum override signal MAO is low.
s The minimum override signal MIO will stay high as long as extruded s film tube 81 has a circumference less than that established by threshold C.
io Likewise, the maximum override signal MAO will remain high for as long as the 11 circumference of extruded film tube 81 remains larger than the reference 12 established by threshold B.
is Threshold D and threshold E are also depicted in Figure 15.
14 Threshold D is established at a distance d4 from reference R. Threshold E
is is established at a distance d5 from reference R. Thresholds D and E are is established by supervisory control unit 75, not by acoustic transducer 79.
1 ~ Threshold D represents a minimum circumference threshold for extruded film tube i$ 81 which differs from that established by transducer electronics 93.
Likewise, is threshold E corresponds to a maximum circumference threshold which differs from 2o that established by acoustic transducer 79. Thresholds D and E are established 21 in the software of supervisory control unit 75, and provide a redundancy of control, Page - 42 DOCKET NO. 291 H-2452&CN
0291 MH-26521139815.1 1 and also minimize the possibility of user error, since these threshold are 2 established in software, and cannot be easily changed or accidentally changed.
a The coordination of all of these thresholds will be discussed in greater detail below.
4 In the preferred embodiment, threshold C is established at 10.8125 inches from s reference R. Threshold E is established at 3.6 inches from reference R.
s Figure 16 is a side view of the ultrasonic sensor 89 coupled to sizing cage 23 of the blown film tower 13, with permissible extruded film tube 81 s operating ranges indicated thereon. Setpoint A is the desired distance between s ultrasonic sensor 89 and extruded film tube 81. Thresholds D and C are to established at selected distances inward from ultrasonic sensor 89, and represent 11 minimum circumference thresholds for extruded film tube 81. Thresholds B
and 12 E are established at selected distances from setpoint A, and establish separate 1s maximum circumference thresholds for extruded film tube 81. As shown in Figure 14 16, extruded film tube 81 is not at setpoint A. Therefore, additional air must be 1s supplied to the interior of extruded film tube 81 to expand the extruded film tube ~ s 81 to the desired circumference established by setpoint A.
1~ If extruded film tube 81 were to collapse, two separate alarm 1 s conditions would be registered. One alarm condition will be established when 1s extruded film tube 81 falls below threshold C. A second and separate alarm 2o condition will be established when extruded film tube 81 falls below threshold D.
21 Extruded film tube 81 may also become overblown. In an overblown condition, Page - 43 DOCKET NO. 291 H-24528-CN
0291 MH-26521 /39815.1 two separate alarm conditions are possible. When extruded film tube 81 expands 2 beyond threshold B, an alarm condition is registered. When extruded film tube 81 s expands further to extend beyond threshold E, a separate alarm condition is 4 registered.
As discussed above, thresholds C and B are subject to user s adjustment through settings in transducer electronics 93. In contrast, thresholds D and E are set in computer code of supervisory control unit 75, and are not easily s adjusted. This redundancy in control guards against accidental or intentional s missetting of the threshold conditions at transducer electronics 93. The system 1o also guards against the possibility of equipment failure in transducer 79, or gradual 11 drift in the threshold settings due to deterioration, or overheating of the electronic 12 components contained in transducer electronics 93.
13 Returning now to Figure 14, operator control panel 137 and i4 supervisory control unit 75 will be described in greater detail. Operator control 1s panel 137 includes setpoint display 109, which serves to display the distance d1 is between reference R and setpoint A. Setpoint display 109 includes a 7 segment display. Distance selector 111 is used to adjust setpoint A. Holding the switch to i8 the "+" position increases the circumference of extruded film tube 81 by is decreasing distance d1 between setpoint A and reference R. Holding the switch 2o to the "-" position decreases the diameter of extruded film tube 81 by increasing 21 the distance between reference R and setpoint A.
Page - 44 DOCKET NO. 291 H-24528-CN
0291 MH-26521 /39815.1 1 Target indicator 113 is a target light which displays information 2 pertaining to whether extruded film tube 81 is within range of ultrasonic transducer s 89, whether an echo is received at ultrasonic transducer 89, and whether any error 4 condition has occurred. Blower switch 139 is also provided in operator control s panel 137 to allow the operator to selectively disconnect the blower from the s control unit. As shown in Figure 14, all these components of operator control panel 137 are electrically coupled to supervisory control unit 75.
s Supervisory control unit 75 responds to the information provided by s acoustic transducer 79, and operator control panel 137 to actuate proportional io valve 125. Proportional valve 125 in turn acts upon pneumatic cylinder 127 to 11 rotate rotary valve 129 to control the air flow to the interior of extruded film tube 81.
i2 With the exception of analog to digital converter 141, digital to analog 13 converter 143, and digital to analog converter 145 (which are hardware items), 14 supervisory control unit 75 is a graphic representation of computer software 1s resident in memory of supervisory control unit 75. In one embodiment, supervisory 1s control unit 75 comprises an industrial controller, preferably a Texas Instrument 17 brand industrial controller Model No. PM550. Therefore, supervisory control unit 1s 75 is essentially a relatively low-powered computer which is dedicated to a is particular piece of machinery for monitoring and controlling. In the preferred 2o embodiment, supervisory control unit 75 serves to monitor many other operations 2~ of blown film extrusion line 11. The gauging and control of the circumference of Page-45 DOCKET NO. 291 H-24528-CN
0291 MH-26521139815.1 1 extruded film tube 81 through computer software is one additional function which 2 is "piggybacked" onto the industrial controller. Alternately, it is possible to provide 3 an industrial controller or microcomputer which is dedicated to the monitoring and a control of the extruded film tube 81. Of course, dedicating a microprocessor to s this task is a rather expensive alternative.
s For purposes of clarity and simplification of description, the operation of the computer program in supervisory control unit 75 have been segregated into s operational blocks, and presented as an amalgamation of digital hardware blocks.
s In the preferred embodiment, these software subcomponents include: software io filter 149, emergency condition control mode logic 150, health state logic 151, > > automatic sizing and recovery logic 153, loop mode control logic 155, volume 12 setpoint control logic 157, and output clamp 159. These software modules 13 interface with one another, and to PI loop program 147 of supervisory control unit ~4 75. PI loop program is a software routine provided in the Texas Instruments' i s PM550 system. The proportional controller regulates a process by manipulating ~s a control element through the feedback of a controlled output. The equation for 17 the output of a PI controller is:
1 s m = K*e + K/T j a dt + ms is In this equation:
2o m = controller output 21 K = controller gain Page-46 DOCKET NO. 291 H-24528-CN
0291 MH-26521139815.1 1 a = error 2 T = reset time s dt = differential time 4 ms = constant j a dt = integration of all previous errors s When an error exists, it is summed (integrated) with all the previous 7 errors, thereby increasing or decreasing the output of the PI controller (depending s upon whether the error is positive or negative). Thus as the error term s accumulates in the integral term, the output changes so as to eliminate the error.
1o CURRENT POSITION signal is provided by acoustic transducer 79 11 via analog output 99 to analog to digital converter 141, where the analog 12 CURRENT POSITION signal is digitized. The digitized CURRENT POSITION signal 1s is routed through software filter 149, and then to PI loop program 147. If the 14 circumference of extruded film tube 81 needs to be adjusted, PI loop program 147 15 acts through output clamp 159 upon proportional valve 125 to adjust the quantity 1s of air provided to the interior of extruded film tube 81.
17 Figure 17 is a schematic representation of the automatic sizing and 1s recovery logic ASRL of supervisory control unit 75. As stated above, this figure is 1s a hardware representation of a software routine. ASRL 153 is provided to 2o accommodate the many momentary false indications of maximum and minimum 21 circumference violations which may be registered due to noise, such as the noise Page-47 DOCKET NO. 291 H-24528-CN
0291 MH-28621 /39815.1 1 created due to air flow between acoustic transducer 79 and extruded film tube 81.
2 The input from maximum alarm override MAO is "ored" with high alarm D, from the 3 PI loop program, at "or" operator 191. High alarm D is the signal generated by the 4 program in supervisory control unit 75 when the circumference of extruded film s tube 81 exceeds threshold D of Figure 15. If a maximum override MAO signal s exists, or if a high alarm condition D exists, the output of "or" operator 191 goes high, and actuates delay timer 193.
s Likewise, minimum override MIO signal is "ored" at "or" operator 195 s with low alarm E. If a minimum override signal is present, or if a low alarm 1 o condition E exists, the output of "or" operator 195 goes high, and is directed to 11 delay timer 197. Delay timers 193, 197 are provided to prevent an alarm condition 12 unless the condition is held for 800 milliseconds continuously. Every time the input 1a of delay timers 193, 197 goes low, the timer resets and starts from 0. This 14 mechanism eliminates many false alarms.
15 If an alarm condition is held for 800 milliseconds continuously, an 1s OVERBLOWN or UNDERBLOWN signal is generated, and directed to the health 17 state logic 151. Detected overblown or underblown conditions are "ored" at "or"
1s operator 199 to provide a REQUEST MANUAL MODE signal which is directed to is loop mode control logic 155.
2o Figure 18 is a schematic representation of the health-state logic 151 z1 of Figure 14. The purpose of this logic is to control the target indicator 113 of Page-48 DOCKET NO. 291 H-24528-CN
0291 MH-28521139815.1 1 operator control panel 137. When in non-error operation, the target indicator 113 2 is on if the blower is on, and the TARGET PRESENT signal from digital output a is high. When an error is sensed in the maximum override MAO or minimum 4 override MIO lines, the target indicator 113 will flash on and off in one half second intervals.
s In health-state logic HSL 151, the maximum override signal MAO is 7 inverted at inverter 205. Likewise, the minimum override signal is inverted at s inverter 207.
9 "And" operator 209 serves to "and" the inverted maximum override 1o signal MAO, with the OVERBLOWN signal, and high alarm signal D. A high output 1 ~ from "and" operator 209 indicates that something is wrong with the calibration of 12 acoustic transducer 79.
is Likewise, "and" operator 213 serves to "and" the inverted minimum 14 override signal MIO, with the OVERBLOWN signal, and low alarm signal E. If the output of "and" operator 213 is high, something is wrong with the calibration of ~s acoustic transducer 79. The outputs from "and" operators 209, 213 are combined 1~ in "or" operator 215 to indicate an error with either the maximum or minimum i s override detection systems. The output of "or" operator 215 is channeled through is oscillator 219, and inverted at inverter 217. "And" operator 211 serves to "and" the 2o TARGET PRESENT signal, blower signal, and inverted error signal from "or"
Page-49 DOCKET NO. 291 H-24528-CN
0291 MH-28521139816.1 . CA 02206911 1997-06-04 1 operator 215. The output of "and" operator of 211 is connected to target indicator 2 113.
If acoustic transducer 79 is properly calibrated, the target is within 4 range and normal to the sonic pulses, and the blower is on, target indicator s will be on. If the target is within range and normal to the sonic pulses, the blower s is on, but acoustic transducer 79 is out of calibration, target indicator 113 will be on, but will be blinking. The blinking signal indicates that acoustic transducer 79, s and in particular transducer electronics 93, must be recalibrated.
s Figure 19 is a schematic representation of loop mode control logic 1o LMCL of Figure 14. The purpose of this software module is coordinate the 11 transition in modes of operation. Specifically, this software module coordinates 12 automatic startup of the blown film extrusion process, as well as changes in mode is between an automated "cascade" mode and a manual mode, which is the required 14 mode of the PI controller to enable under and overblown conditions of the 15 extruded film tube 81 circumference. The plurality of input signals are provided to ~s loop mode control logic 155, including: BLOWER ON, REQUEST MANUAL MODE, 1~ PI LOOP IN CASCADE MODE, UNDERBLOWN and OVERBLOWN. Loop mode 18 control logic LMCL 155 provides two output signals: MANUAL MODE, and is CASCADE MODE.
2o Figure 19 includes a plurality of digital logic blocks which are z1 representative of programming operations. "Or" operator 225 "ores" the inverted Page - 50 DOCKET NO. 291 H-24528-CN
0297 MH-28621 !3987 5.1 BLOWER ON SIGNAL to the REQUEST MANUAL MODE SIGNAL. "And" operator 2 227 "ands" the inverted REQUEST MANUAL MODE SIGNAL with an inverted s MANUAL MODE SIGNAL, and the BLOWER ON SIGNAL. "And" operator 229 a "ands" the REQUEST MANUAL MODE SIGNAL to the inverted CASCADE MODE
SIGNAL. This prevents MANUAL MODE and CASCADE MODE from both being s on at the same time. "And" operator 231 "ands" the MANUAL MODE SIGNAL, the inverted UNDERBLOWN SIGNAL, and the OVERBLOWN SIGNAL. "And" operator 8 233 "ands" the MANUAL MODE SIGNAL with the UNDERBLOWN SIGNAL. This s causes the overblown condition to prevail in the event a malfunction causes both 1o underblown and overblown conditions to be on. Inverters 235, 237, 239, 241, and ~ 1 243 are provided to invert the inputted output signals of loop mode control logic 155 were needed. Software one-shot 245 is provided for providing a momentary 1a response to a condition. Software one-shot 245 includes "and" operator 247, off-delay 249, and inverter 251.
The software of loop mode control logic 155 operates to ensure that 1s the system is never in MANUAL MODE, and CASCADE MODE at the same time.
~7 When manual mode is requested by REQUEST MANUAL MODE, loop mode is control logic 155 causes MANUAL MODE to go high. When manual mode is not is requested, loop mode control logic 155 operates to cause CASCADE MODE to go 2o high. MANUAL MODE and CASCADE MODE will never be high at the same time.
21 Loop mode control logic 155 also serves to ensure that the system provides a Page - 51 DOCKET NO. 291H-24528-CN
0291 MH-28521139815.1 1 "bumpless transfer" when mode changes occur. The term "cascade mode" is 2 understood in the automation industries as referring to an automatic mode which a will read an adjustable setpoint.
4 Loop mode control logic 155 will also allow for automatic startup of the blown film extrusion process. At startup, UNDERBLOWN SIGNAL is high, PI
s LOOP IN CASCADE MODE is low, BLOWER ON SIGNAL is high. These inputs (and inverted inputs) are combined at "and" operators 231, 233. At startup, "and"
s operator 233 actuates logic block 253 to move the maximum air flow value address s to the PI loop step 261. At startup, the MANUAL MODE SIGNAL is high. For the 1o PI loop controller of the preferred embodiment, when MANUAL MODE is high, the 11 value contained in PI loop output address is automatically applied to proportional ~2 valve 125. This results in actuation of proportional valve 125 to allow maximum air 13 flow to start the extruded film tube 81.
14 When extruded film tube 81 extends in size beyond the minimum threshold (C and D of Figure 15 ), the UNDERBLOWN SIGNAL goes low, and the 1s PI LOOP IN CASCADE MODE signal goes high. This causes software one-shot 17 245 to trigger, causing logic blocks 265, 267 to push an initial bias value contained 18 in a program address onto the PI loop. Simultaneously, logic blocks 269, is operate to place the selected setpoint value A onto volume-setpoint control logic 2o VSCL 157. Thereafter, volume-setpoint control logic VSCL 157 alone serves to 21 communicate changes in setpoint value A to PI loop program 147.
Page - 52 DOCKET NO. 291H-24528-CN
0291 MH-28521139815.1 1 If an overblown or underblown condition is detected for a sufficiently 2 long period of time, the controller will request a manual mode by causing a REQUEST MANUAL MODE SIGNAL to go high. If REQUEST MANUAL MODE
4 goes high, loop mode control logic LMCL 155 supervises the transfer through s operation of the logic blocks.
s Loop mode control logic LMCL 155 also serves to detected overblown and underblown conditions. If an overblown or underblown condition s is detected by the control system, REQUEST MANUAL MODE goes high, and the s appropriate OVERBLOWN or UNDERBLOWN signal goes high. The logic io operators of loop mode control logic LMCL 155 operate to override the normal 11 operation of the control system, and cause maximum or minimum air flow by i2 putting the maximum air flow address 261 or minimum air flow address 263 to the 1s PI output address. As stated above, when MANUAL MODE is high, these 14 maximum or minimum air flow address values are outputted directly to proportional 15 valve 125. Thus, when the extruded film tube 81 is overblown, loop mode control is logic LMCL 155 operates to immediately cause proportional valve 125 to minimize air flow to extruded film tube 81. Conversely, if an underblown condition is detected, loop mode control logic LMCL 155 causes proportional valve 125 to 1s immediately maximize air flow to extruded film tube 81.
2o Figure 20 depicts the operation of volume-setpoint control logic VSCL
21 157.
Page - 53 DOCKET NO. 291 H-24528-CN
0291 MH-26521139815.1 Volume setpoint control logic VSCL 157 operates to increase or 2 decrease setpoint A in response to changes made by the operator at distance s selector 111 of operator control panel 137, when the PI loop program 147 is in 4 cascade mode, i.e. when PI LOOP IN CASCADE MODE signal is high. The s INCREASE SETPOINT, DECREASE SETPOINT, and PI LOOP IN CASCADE MODE
s signals are logically combined at "and" operators 283, and 287. These "and"
7 operators act on logic blocks 285, 289 to increase or decrease the setpoint s contained in remote setpoint address 291. When the setpoint is either increased s or decreased, logic block 293 operates to add the offset to the remote setpoint for 1o display, and forwards the information to digital to analog converter 143, for display 11 at setpoint display 109 of operator control panel 137. The revised remote setpoint 12 address is then read by the PI loop program 147.
13 Figure 21 is a flowchart drawing of output clamp 159. The purpose 14 of this software routine is to make sure that the PI loop program 147 does not over 15 drive the rotary valve 129 past a usable limit. Rotary valve 129 operates by moving is a vane to selectively occlude stationary openings. If the moving vane is over 1 ~ driven, the rotary valve will begin to open when the PI loop calls for complete 1s closure. In step 301, the output of the PI loop program 147 is read. In step 303, is the output of PI loop is compared to a maximum output. If it exceeds the 2o maximum output, the PI output is set to a predetermined maximum output in step 21 305. If the output of PI loop does not exceed the maximum output, in step 307, Page - 54 DOCKET NO. 291 H-24528-CN
0291 MH-26521139815.1 the clamped PI output is written to the proportional valve 125 through digital to 2 analog converter 145.
As shown in Figure 14, emergency condition control mode logic 150 4 is provided in supervisory control unit 75, and is shown in detail in Figure 22. As s shown in Figure 22, emergency condition control mode logic 150 receives three s input signals: the OVER BLOWN signal; the UNDERBLOWN signal; and the 7 TARGET filter signal. The emergency condition control mode logic 150 provides s as an output two variables to software filter 149, including: "SPEED HOLD";
and s "ALIGN HOLD". The OVERBLOWN signal is directed to anticipation state "or"
gate 403 and to inverter 405. The UNDERBLOWN signal is directed to anticipation state i ~ "or" gate 403 and to inverter 407. The TARGET signal is directed through inverter i2 401 to anticipation state "or" gate 403, and to "and" gate 409. The output of ~s anticipation "or" gate 403 is the "or" combination of OVERBLOWN signal, and the is inverted TARGET signal. Anticipation state "or" gate 403 and "and" gate 419 is cooperate to provide a locking logic loop. The output of "or" gate 403 is provided is as an input to "and" gate 419. The other input to "and" gate 419 is the output of ~ 7 inverter 417. The output of inverter 417 can be considered as a "unlocking" signal.
1s If the OVERBLOWN signal or UNDERBLOWN signal is high, or the inverted ~s TARGET signal is high, the output of anticipation state "or" gate 403 will go high, 2o and will be fed as an input into "and" gate 419, as stated above. The output of anticipation state "or" gate 403 is also provided as an input to "and" gates 413, Page - 55 -DOCKET NO. 291 H-24528-CN
0291 MH-2H521139815.1 1 411, and 409. The other input to "and" gate 413 is the inverted OVERBLOWN
2 signal. The other input to "and" gate 411 is the inverted UNDERBLOWN signal.
s The other input to "and" gate 409 is the TARGET signal. The outputs of "and"
4 gates 409, 411, and 413 are provided to "or" gate 415. The output of "or"
gate 415 s is provided to inverter 417.
s In operation, the detection of an overblown or underblown condition, or an indication that the extruded film tube is out of range of the sensor will cause s the output of anticipation state "or" gate 403 to go high. This high output will be s fed back through "and" gate 419 as an input to anticipation state "or" gate 403. Of io course, the output of "and" gate 419 will be high for so long as neither input to 1 ~ "and" gate 419 is low. Of course, one input to "and" gate 419 is high because a 12 change in the state of the OVER BLOWN signal, the UNDER BLOWN signal, and is the TARGET signal has been detected. The other input to "and" gate 419 is 14 controlled by the output of inverter 417, which is controlled by the output of is next-state "or" gate 415. As stated above, the output of next-state "or"
gate 415 is is controlled by the output of "and" gates 409, 411, 413. In this configuration, 17 anticipation state "or" gate 403 and "and" gate 419 are locked in a logic loop until is a change is detected in a binary state of one of the following signals: the ~s OVERBLOWN signal, the UNDERBLOWN signal, and the TARGET signal. A
2o change in state of one of these signals causes next-state "or" gate 415 to go high, Page - 56 -DOCKET NO. 291 H-2452&CN
0281 MH-28621 !39815.1 1 which causes the output of inverter 417 to go low, which causes the output of 2 "and" gate 419 to go low.
s The output of next-state "or" gate 415 is also provided to timer starter 4 421, the reset pin for timer starter 421, and the input of block 423. When a high s signal is provided to the input of timer starter 421, a three second software clock s is initiated. At the beginning of the three second period, the output of timer starter 7 421 goes from a normally high condition to a temporary low condition; at the end s of the three second software timer, the output of timer starter 421 returns to its s normally high condition. If any additional changes in the state of the OVERBLOWN
to signal, the UNDERBLOWN signal, and the TARGET signal are detected, the ~ 1 software timer is reset to zero, and begins running again. The particular change ~2 in the input signal of the OVERBLOWN signal, the UNDERBLOWN signal, and the 13 TARGET signal, also causes the transmission of a high output from "and"
gates 14 409, 411, and 413 to blocks 429, 427, and 425 respectively.
In operation, when the input to block 423 goes high, the numeric 1s value associated with the variable identified as "quick filter align" will be pushed to 17 a memory variable identified as "speed hold". "Quick filter align" is a filter variable 1s which is used by software filter 149 (of Figure 23, which will be discussed below), 1 s which determines the maximum allowable rate of change in determining the 2o estimated position. "Speed hold" is a holding variable which holds the numeric 21 value for the maximum allowable rate of change in determining the estimated Page - 57 DOCKET NO. 291 H-24528-CN
0291 MH-28521139815.1 1 position of the blown film tube. "Speed hold" can hold either a value identified as 2 "quick filter align" or a value identified as "normal filter align". "Normal filter align"
3 is a variable that contains a numeric value which determines the normal maximum 4 amount of change allowed in determining the estimated position of the blown film tube relative to the transducer. Blocks 423 and 431 are both coupled to block s which is an operational block representative of a "push" operation.
Essentially, 7 block 433 represents the activity of continuously and asynchronously pushing the s value held in the variable "speed hold" to "LT2" in software filter 149 via data bus s 402. The value for "normal filter align" is the same as that discussed herebelow in 1o connection with Figure 8a, and comprises thirteen counts, wherein counts are 11 normalized units established in terms of voltage. The preferred value for "quick 12 filter align" is forty-eight counts. Therefore, when the software filter 149 is provided is with the quick filter align value, the control system is able to change at a rate of 14 approximately 3.7 times as fast as that during a "normal filter align" mode of 1 s operation.
1s Also, when a "locked" condition is obtained by anticipation state "or"
~ 7 gate 403 and "and" gate 419, any additional change in state of the values of any 1a of the OVERBLOWN signal, the UNDERBLOWN signal, and the TARGET signal will 1 s cause "and" gates 409, 411, and 413 to selectively activate blocks 429, 427, 425.
2o Blocks 429, 427, and 425 are coupled to block 433 which is linked by data bus 21 402 to software filter 149. When block 429 receives a high input, the variable held Page - 58 DOCKET NO. 291 H-24528-CN
0297 MH-28521 !39815.1 1 in the memory location "target restore count" is moved to a memory location 2 identified as "align hold". When block 427 receives a high input signal, the value 3 held in the memory location identified as "underblown count" is moved to a 4 memory value identified as "align hold". When block 425 receives a high input s signal, the numeric value held in a memory location identified as "overblown count"
s is moved to a memory location identified as "align hold". As stated above, block 7 433 performs a continuous asynchronous "push" operation, and will push any s value identified to the "align hold" memory location to the values of SAMPLE
(N), s SAMPLE (N-1), and BPE in the software filter of Figure 23. In the preferred io embodiment of the present invention, the value of "overblown count" is set to i 1 correspond to the distance between reference R and maximum circumference ~2 threshold B which is depicted in Figure 16, which is established distance at which 13 the control system will determine that an "overblown" condition exists.
Also, in the 14 preferred embodiment of the present invention, the value of the "underblown" count 1 s will be set to a minimum circumference threshold C, which is depicted in Figure 16, ~s and which corresponds to the detection of an underblown condition. Also, in the 1 ~ present invention, the value of "target restore count" is preferably established to 1s correspond to the value of set point A, which is depicted in Figure 16, and which 1s corresponds generally to the distance between reference R and the imaginary 2o cylinder established by the position of the sizing cage with respect to the blown 2~ film tube.
Page - 59 DOCKET NO. 291 H-24528-CN
0291 MH-28521139815.1 ' . CA 02206911 1997-06-04 1 Figure 23A is a flowchart of the preferred filtering process applied to 2 CURRENT POSITION signal generated by the acoustic transducer. Preferably, it 3 includes multiple stages of filtering, for different operating conditions.
The first 4 stage of filtering pertains to relatively unstable operating conditions. The second s stage of filtering pertains to relatively stable operating conditions. The digitized s CURRENT POSITION signal is provided from analog to digital converter 141 to z software filter 149. The program reads the CURRENT POSITION signal in step a 161. Then, the software filter 149 sets SAMPLE (N) to the position signal.
s In step 165, the absolute value of the difference between CURRENT
1o POSITION (SAMPLE (N)) and the previous sample (SAMPLE (N - 1)) is compared > > to a first threshold. If the absolute value of the difference between the current 12 sample and the previous sample is less than first threshold T1, the value of 13 SAMPLE (N) is set to CFS, the current filtered sample, in step 167. If the absolute 14 value of the difference between the current sample and the previous sample exceeds first threshold T1, in step 169, the CURRENT POSITION signal is is disregarded, and the previous position signal SAMPLE (N - 1) is substituted in its 1 ~ place.
1 s Then, in step 171, the suggested change SC is calculated, by 1s determining the difference between the current filtered sample CFS and the best 2o position estimate BPE. In step 173, the suggested change SC which was 21 calculated in step 171 is compared to positive T2, which is the maximum limit on Page - so -DOCKET NO. 291 H-24528-CN
0291 MH-28621139816.1 1 the rate of change. If the suggested change is within the maximum limit allowed, 2 in step 177, allowed change AC is set to the suggested change SC value. If, s however, in step 173, the suggested change exceeds the maximum limit allowed 4 on the rate of change, in step 175, the allowed change is set to + LT2, a default s value for allowed change.
s In step 179, the suggested change SC is compared to the negative limit for allowable rates of change, negative T2. If the suggested change SC
is s greater than the maximum limit on negative change, in step 181, allowed change s AC is set to negative -LT2, a default value for negative change. However, if in step io 179 it is determined that suggested change SC is within the maximum limit allowed 11 on negative change, in step 183, the allowed change AC is added to the current 12 best position estimate BPE, in step 183. Finally, in step 185, the newly calculated 13 best position estimate BPE is written to the PI loop program.
14 Software filter 149 is a two stage filter which first screens the is CURRENT POSITION signal by comparing the amount of change, either positive is or negative, to threshold T1. If the CURRENT POSITION signal, as compared to 1 ~ the preceding position signal exceeds the threshold of T1, the current position is signal is discarded, and the previous position signal (SAMPLE (N - 1)) is used is instead. At the end of the first stage, in step 171, a suggested change SC
value 2o is derived by subtracting the best position estimate BPE from the current filtered 21 sample CFS.
Page - 61 DOCKET NO. 291 H-24528-CN
0291 MH-28521139815.1 1 In the second stage of filtering, the suggested change SC value is z compared to positive and negative change thresholds (in steps 173 and 179).
If a the positive or negative change thresholds are violated, the allowable change is set 4 to a preselected value, either + LT2, or -LT2. Of course, if the suggested change s SC is within the limits set by positive T2 and negative T2, then the allowable s change AC is set to the suggested change SC.
7 As is shown in Figure 23A, data bus 201 couples the emergency s condition control logic block 150 to software filter 149. As stated above, s emergency condition control logic block 150 is designed to asynchronously push ~o a numeric value identified in the memory location of "speed hold" to LT2 in ~ 1 software filter 149. Furthermore, emergency condition control logic block 150 will 12 asynchronously push a numeric value in the memory location identified as "ALIGN
1s HOLD" to SAMPLE (N), SAMPLE (N - 1), and BPE. As stated above, SAMPLE N
14 corresponds to the current position signal as detected by the transducer.
SAMPLE
~ s (N - 1 ) corresponds to the previous position signal as determined by the ~s transducer. BPE corresponds to the best position estimate.
1 ~ Since the operation of emergency condition control mode logic block 18 150 is asynchronous, block 186 of Figure 23A should be read and understood as is corresponding to an asynchronous read function. Therefore, at all times, as set 2o forth in block 186, software filter 149 receives values of "speed hold" and "align 21 hold" from emergency condition control mode logic block 150, and immediate Page-62 DOCKET NO. 291 H-24528-CN
0291 MH-28521 !39816.1 1 substitutes them into the various logic blocks found in software filter 149.
For 2 example, SAMPLE (N) is found in logic blocks 163, 165, and 167. SAMPLE (N -s 1 ) is found in logic blocks 165, and 169. BPE is found at logic block 183.
The 4 program function represented by block 186 operates to asynchronously and s immediately push the values of "speed hold" and "align hold" to these various s functional blocks, since OVERBLOWN, UNDERBLOWN, and lost TARGET
7 conditions can occur at any time.
s The normal operation of software filter 149 may also be understood s with reference to Figure 24, and will be contrasted with examples of the emergency 1o condition mode of operation as depicted in Figures 25, 26, and 27. In the graph 11 of Figure 24, the y-axis represents the signal level, and the x-axis represents time.
12 The signal as sensed by acoustic transducer 79 is designated as input, and shown 1a in the solid line. The operation of the first stage of the software filter 149 is 14 depicted by the current filtered sample CFS, which is shown in the graph by ~ s cross-marks. As shown, the current filtered sample CFS operates to ignore large 1s positive or negative changes in the position signal, and will only change when the 1 ~ position signal seems to have stabilized for a short interval. Therefore, when 18 changes occur in the current filtered sample CFS, they occur in a plateau-like 1 s manner.
2o In stage two of the software filter 149, the current filtered sample CFS
21 is compared to the best position estimate BPE, to derive a suggested change SC
Page - 63 DOCKET NO. 291 H-2452&CN
0291 MH-28521 /39815.1 1 value. The suggested SC is then compared to positive and negative thresholds z to calculate an allowable change AC which is then added to the best position a estimate BPE. Figure 24 shows that the best position estimate BPE signal only 4 gradually changes in response to an upward drift in the POSITION SIGNAL. The s software filtering system 149 of the present invention renders the control apparatus s relatively unaffected by random noise, but capable of tracking the more "gradual"
changes in bubble position.
s Experimentation has revealed that the software filtering system of the s present invention operates best when the position of extruded film tube 81 is 1o sampled between 20 to 30 times per second. At this sampling rate, one is less 11 likely to incorrectly identify noise as a change in circumference of extruded film 12 tube 81. The preferred sampling rate accounts for the common noise signals ~a encountered in blown film extrusion liner.
14 Optional thresholds have also been derived through experimentation.
15 In the first stage of filtering, threshold T1 is established as roughly one percent of 1s the operating range of acoustic transducer 79, which in the preferred embodiment 17 is twenty-one meters (24 inches less 3 inches). In the second stage of filter, 1 s thresholds + LT2 and -LT2 are established as roughly 0.30% of the operating range 1 s of acoustic transducer 79.
2o Figure 25A is a graphic depiction of the control system response to 21 the detection of an UNDERBLOWN condition. The X-axis of the graph of Figure Page - 64 -DOCKET NO. 291H-24528-CN
0291 MH-28621139816.1 1 25A is representative of time in seconds, and the Y-axis of the graph of Figure 25A
2 is representative of position in units of voltage counts. A graph of the best position 3 estimate BPE is identified by dashed line 503. A graph of the actual position of the 4 extruded film tube with respect to the reference position R is indicated by solid line s 501. On this graph, line 505 is indicative of the boundary established for s determining whether the blown film tube is in an "underblown" condition.
Line 507 7 is provided as an indication of the normal position of the blown film tube.
Line 509 s is provided to establish a boundary for determining when a blown film tube is s considered to be in an "overblown" condition.
~o The activities represented in the graph of Figure 25A may be ~ 1 coordinated with the graph of Figure 25B, which has an X-axis which is 12 representative of time in seconds, and a Y-axis which represents the binary ~s condition of the TARGET signal, and the UNDERBLOWN signal, as well as the 14 output of block 421 of Figure 22, which is representative of the output of the time 1s out filter realignment software clock. Now, with simultaneous reference to Figures 1s 25A and 25B, segment 511 of the best position estimate indicates that for some 17 reason the best position estimate generated by software filter 149 is lagging ~a substantially behind the actual position of the blown film tube. As shown in Figure 1s 25A, both the actual and estimated position of the blown film tube are in an 2o underblown condition, which is represented in the graph of Figure 25B.
Page - 65 DOCKET NO. 291 H-24528-CN
0291 MH-28521 /39815.1 1 As stated above, in connection with Figure 22 and the discussion of 2 the operation of the emergency condition control logic block 150, the locking a software loop which is established by anticipation state "or" gate 403 and "and"
4 gate 419 will lock the output of anticipation state "or" gate 403 to a high condition.
s Therefore, next-state "or" gate 415 is awaiting the change in condition of any of the s following signals: the OVERBLOWN signal, the UNDERBLOWN signal, and the TARGET signal. As shown in Figure 25A, at a time of 6.5 seconds, the actual s position of the blown film tube comes within the boundary 505 established for the s underblown condition, causing the output of next-state "or" gate 415 to go high, io which causes the output of inverter 417 to go low, which causes the output of 1 ~ "and" gate 419 to go low. This change in state also starts the software timer of 12 block 421, and causes block 427 to push the value of "underblown count" to the is "align hold" variable. Also, simultaneously, software block 423 pushes the value i4 of "quick filter align" to the "speed hold" variable. The values of "speed hold" and 15 "underblown count" are automatically pushed to block 433. Meanwhile, the is software timer of block 421 overrides the normal and continuous pushing of 17 "normal filter align" to the "speed hold" variable for a period three seconds. The is three second period expires at 9.5 seconds.
1 s Thus, for the three second time interval 513, software filter 149 is 2o allowed to respond more rapidly to change than during normal operating 21 conditions. As shown in Figure 22, block 433 operates to automatically and Page - 66 -DOCKET NO. 291 H-24528-CN
0291 MH-28521 !39815.1 asynchronously push the value of "speed hold" to "LT2" in software filter 149.
2 Simultaneously, block 433 operates to continuously, automatically, and s asynchronously push the value of "align hold" to SAMPLE (N), SAMPLE (N-1) and 4 BPE in software filter 149. This overriding of the normal operation of software filter s 149 for a three second interval allows the software best position estimate 503 to s catch up with the actual position 501 of the blown film tube. The jump represented 7 by segment 515 in the best position estimate 503 of the blown film tube is s representative of the setting of SAMPLE (N), SAMPLE (N-1) and BPE to the s "underblown count" which is held in the "align hold" variable. Segment 517 of the ~o best position estimate 503 represents the more rapid rate of change allowable i i during the three second interval, and depicts the best position estimate line 503 ~ 2 tracking the actual position line 501 for a brief interval. At the expiration of the ~s three second interval, software filter 149 of the control system returns to a normal mode of operation which does not allow such rapid change in the best position is estimate.
~s Figures 26A and 26b provide an alternative example of the operation ~ 7 of the emergency condition control mode of operation of the present invention.
~s In this example, the TARGET signal represented in segment 525 of Figure 26b is is erroneously indicating that the blown film tube is out of range of the transducer.
2o Therefore, segment 529 of dashed line 527 indicates that the best position estimate 2~ according to software filter 149 is set at a default constant value indicative of the Page-67 DOCKET NO. 291H-2452&CN
0291 MH-26521139815.1 blown film tube being out of range of the transducer, and is thus far from indicative 2 of the actual position which is indicated by line 531. This condition may occur s when the blown film tube is highly unstable so that the interrogating pulses from 4 the transducer are deflected, preventing sensing of the blown film tube by the s transducer. Segment 533 of Figure 26b is representative of stabilization of the s blown film tube and transition of the TARGET signal from an "off" state to an "on"
state. This transition triggers initiation of the three second software timer which s is depicted by segment 535. The time period begins at 12.5 seconds and ends s at 15.5 seconds. The transition of the TARGET signal from a low to a high ~o condition triggers the pushing of the "target restore count" value to the "align hold"
variable, as is graphically depicted by segment 537. During the three second ~2 interval, the best position estimate established by software filter 149 is allowed to ~s change at a rate which is established by the "quick filter align" value which is pushed to the "speed hold" variable and bused to software filter 149. At the 1s termination of the three second interval, the software filter 149 returns to normal ~ s operation.
Figure 27A provides yet another example of the operation of the t$ emergency condition control mode. Segment 541 of Figure 27B indicates that the 19 TARGET signal is in a low condition, indicating that the blown film tube is out of 2o range of the transducer. Segment 543 indicates that the blown film tube has come 21 into range of the transducer, and the TARGET signal goes from a low to a high Page - s8 -DOCKET NO. 291 H-24528-CN
0291 MH-28521139815.1 1 condition. Simultaneous with the movement of the blown film tube into range of 2 the transducer, the UNDERBLOWN signal goes from a low to a high condition 3 indicating that the blown film tube is in an underblown condition. Segment 545 of 4 Figure 27B indicates a transition from a high UNDERBLOWN signal to a low s UNDERBLOWN signal, which indicates that the blown film tube is no longer in an s underblown condition. This transition initiates the three second interval which allows for more rapid adjustment of the best position estimate.
s The foregoing description related to the first stage of filtering which is s especially useful during relatively unstable operating conditions, wherein overblown 1o and underblown extruded film tube conditions are possible. The second stage of 11 filtering, which will now be described, pertains to relatively stable operating 12 conditions, when the extruded film tube is in a substantially fixed position. This 1s type of filtering is preferably a dynamic filtering operation, in which the influence of 14 the dynamic filter is increased or decreased, depending upon at least one pre-1s established criterion. Preferably, the criterion comprises a comparison of the 1s output of the filtering operation with the current bubble position. If there is a great 17 difference between the detected extruded film tube position and the output of the 18 filter, the operating assumption is that the extruded film tube is perhaps becoming 1s unstable, and the influence of the dynamic filtering operation should be reduced.
2o Conversely, if the difference between the output of the dynamic filtering process z1 and the current position of the extruded film tube is small or decreasing, the Page - s9 DOCKET NO. 291H-24528-CN
0291 MH-28521139815.1 assumption is made that the extruded film tube is in a relatively stable operating condition, and the influence of the dynamic filtering operation should be increased. In the present invention, the dynamic filtering operation comprises a rolling average of detected position signals, with the number of samples utilized to calculate the rolling average increasing if stability is detected and decreasing if instability is detected. The foregoing will become clear with reference to Figures 23A, 23B, 23C, 23D, 23E, 23F, and 23G.
With reference to Figure 23A, the basic filtering operation is depicted in flowchart form. At the termination of software step 183, a best position estimate (BPE)is calculated. The process continues at software block 184(a) of Figure 23B, wherein the best position estimate is provided. Next, in accordance with software block 184(b), it is determined whether or not an alarm condition exists;
if an alarm condition exists, the process continues at software block 184(c), wherein the process continues by going to block 185 of Figure 23A; if, however, it is determined in software block 184(b) that there is no alarm condition, the process continues. In software block 184(d), the processor determines whether or not the extruded film tube is in a startup mode of operation; if so, the process continues at software block 184(e) by passing control to software block 185 in Figure 23A; however, if it is determined in software block 184(d) that the bubble is not a startup mode of operation, the process continues. In software block 184(f), the controller determines whether or not there is an ongoing change in 1 extruded film tube balance; if so, the process continues at software block 184(g) 2 by passing control to software block 185 in Figure 23A. However, if it is s determined in software block 184(f) that there is no ongoing change in extruded 4 film tube balance, the process continues. In accordance with software block s 184(h), the controller determines whether the extruded film tube (or "bubble") has s been stable for sixty continuous seconds; if not, the process continues at software 7 block 184(i), wherein control is passed to software block 185 in Figure 23A;
how-s ever, if it is determined in software block 184(h) that the bubble has been stable s for sixty continuous seconds, then control is passed to software block 184(j), 1o wherein the dynamic filter of Figure 23C is utilized to process the position signals 11 during this relatively stable interval of operation.
12 In broad overview, the basic filtering operation of Figure 23A alone is 13 performed if any one of a variety of indicators reveal that stable operation is not 1a ongoing or is unlikely. A variety of the rudimentary indicators are identified in 1s Figure 23B, and various other indicators can be devised which can be added to 1s the items in Figure 23B which provide further screening which prevents the 17 dynamic filtering operation from commencing.
i 8 Once relatively stable operations are ongoing, the dynamic filtering operation is may be applied. The preferred embodiment of the dynamic filtering operation is 2o depicted in block diagram form in Figure 23C. As is shown, the process continues at software block 184(k), wherein the best position estimate is provided as an input Page - 71 DOCKET NO. 291 H-2452&CN
0291 Mli-28521 /39815.1 to a rolling average generator 184(1) which computes a rolling average from a 2 number of previous samples of the best position estimate (BPE), preferably based 3 upon the following formula:
4 RA = RA + ((BPE - RAP~e") - (Sample Number)) s wherein s RA is the rolling average;
7 ~prev is previous rolling average;
s BPE is the best position estimate currently provided; and s Sample Number is a number which determines the number of samples io utilized to calculate the rolling average 11 The output of rolling average generator 184(1) is subtracted from the input 12 to the rolling average generator 184(1), which is the best position estimate (BPE).
is This defines an "ERROR". This is provided as an input to the number of samples 14 calculator 184(m), which calculates the number of samples based upon the is ERROR (which is input), a predetermined GAIN value, and a BIAS value in is accordance with the following formula:
SAMPLE NUMBER = (ERROR X GAIN) + BIAS
is The BIAS 184(n) is a manufacturer-configurable variable which helps to is determine the span (or range) of available sample numbers utilized in determining 2o the rolling average. The output of the number of samples calculator 184(m) is Page - 72 DOCKET NO. 291 H-2452&CN
0291 MH-28521 !39815.1 i provided as an input to software block 184(0), which pushes the Sample Number 2 to the rolling average generator 184(1) every second.
s In accordance with present invention, the values for ERROR, GAIN and BIAS
4 are selected to insure that, during very stable operations, the rolling average s generator 184(1) utilizes ten (10) previous samples of the best position estimate s (BPE) in order to calculate the rolling average. If the difference between the input 7 to the rolling average generator 184(1) and the output of the rolling average 8 generator 184(1) increases, the number of samples calculator 184(m) reduces the s number of samples utilized by the rolling average generator 184(1). When the io difference (ERROR) is at its greatest (and most unacceptable) level, the number ~ i of samples calculator 184(m) reduces the number of samples to unity (1 ), therefore causing the input of the rolling average generator 184(1) to be provided as the ~s output of rolling average generator 184(1) without any dynamic filtering whatsoever.
In other words, as the ERROR increases, the influence of the rolling average is generator 184(1) is incrementally decreased from its maximum influence to its is minimum influence, which essentially bypasses the dynamic filtering operation 17 altogether.
As is shown in Figure 23C, the output of the rolling average generator 184(1) ~s is supplied to software block 184(p), which sets the BPE to the output of the rolling 2o average generator 184(1). Then, in accordance with 184(q), controls return to 21 software block 185 of Figure 23A.
Page - 73 DOCKET NO. 291 H-24528-CN
0291 MH-26521139815.1 1 The beneficial influence of the dynamic filtering operation can best be 2 understood with reference to Figures 23D and 23E. Figure 23D is a graphically s depiction of the bubble position 184(r) and the valve position 184(s) with respect 4 to time, without dynamic filtering. As is shown, the valve position moves in direct s correspondence with the bubble position, quite dynamically. Figure 23E is a s graphical depiction of bubble position 184(t) and the output of the rolling average generator 184(u), as well as valve position 184(v), all with respect to time.
As is 8 shown, the rolling average generator is much more stable than the detected s bubble position (BPE). The extreme positive and negative peaks of the bubble 1o position (BPE) are eliminated through the dynamic filtering process, making the 11 control system altogether less susceptible to noise and meaningless bubble flutter 12 than without the dynamic filtering process. As is shown in Figure 23(E), the valve ~s (or other flow control device) is basically controlled by the output of the rolling 14 average generator, and is also much less susceptible to the noise or bubble flutter.
1s This type of noise is a common problem in particularly stiff materials, such as 1 s nylon.
~7 Figure 23F is a graphical depiction of a frequency distribution comparison is of the dynamically filtered position signal shown in single cross-hatching and the 1s unfiltered position signal (BPE) shown in double cross-hatching. This frequency 2o distribution reveals that there is about a 33% reduction in the standard deviation 21 between the dynamically filtered position signal and the filtered, but not dynamically Page - 74 DOCKET NO. 291H-24528-CN
0291 MH-28621139815.1 1 filtered, position signal. In the real world, this relates to about a 2 millimeter 2 reduction in lay flat variation, which reduces a 6 millimeter total variation to about s a 4 millimeter total variation. This greatly increases the control system's 4 performance during these relatively stable operating intervals.
s Figure 23G is a graphical depiction of startup operations with the dynamic s filter in place. The X-axis represents time and the Y-axis represents the valve 7 position 184(w), the bubble position 184(x), the output of the rolling average s generator 184(y). As is shown, the dynamic filtering operation is not active until s time 184(z), after which the prerequisite stability has been obtained. It is at that io point that the position of the valve 184(w) is directly controlled through the rolling 11 average generator. Note the greater stability of valve position once the rolling 12 average generator has been activated.
Figure 28 is a schematic and block diagram representation of an airflow 14 circuit for use in a blown film extrusion system. Input blower 613 is provided to is provide a supply of air which is routed into airflow circuit 611. The air is received is by conduit 615 and directed to airflow control device 617 of the present invention.
17 Airflow control device 617 operates as a substitute for a conventional rotary-type is airflow valve 631, which is depicted in simplified form also in Figure 28.
The is preferred airflow control device 617 of the present invention is employed to 2o increase and decrease the flow of air to supply distributor box 619 which provides an air supply to annular die 621 from which blown film tube 623 extends upward.
Page - 75 DOCKET NO. 291H-24528-CN
0291 MH-28521139816.1 1 Air is removed from the interior of blown film tube 623 by exhaust distributor box 2 625 which routes the air to conduit 627, and eventually to exhaust blower 629.
s The preferred airflow control device 617 is depicted in fragmentary 4 longitudinal section view in Figure 29. As is shown, airflow control device s includes housing 635 which defines inlet 637 and outlet 639 and airflow pathway s 641 through housing 635. A plurality of selectively expandable flow restriction members 671 are provided within housing 635 in airflow pathway 641. In the view a of Figure 29, selectively-expandable flow restriction members 673, 675, 677, 679, s and 681 are depicted. Other selectively-expandable flow restriction members are to obscured in the view of Figure 29. Manifold 685 is provided to route pressurized 11 air to the interior of selectively-expandable flow restriction members 671, and 12 includes conduit 683 which couples to a plurality of hoses, such as hoses 687, is 689, 691, 693, 695 which are depicted in Figure 29 (other hoses are obscured in 14 Figure 29).
15 Each of the plurality of selectively-expandable flow restriction is members includes an inner air-tight bladder constructed of an expandable material 17 such as an elastomeric material. The expandable bladder is surrounded by an is expandable and contractible metal assembly. Preferably, each of the plurality of ~s selective-expandable flow restriction members is substantially oval in cross-section 2o view (such as the view of Figure 29), and traverse airflow pathway 641 across the 21 entire width of airflow pathway 641. Air flows over and under each of the plurality Page - 76 DOCKET NO. 291 H-24528-CN
0291 MH-28521139816.1 i of selectively-expandable airflow restriction members, and each of them operates z as an choke to increase and decrease the flow of air through housing 635 as they 3 are expanded and contracted. However, the flow restriction is accomplished 4 without creating turbulence in the airflow, since the selectively-actuable flow s restriction members are foil shaped.
s Returning now to Figure 28, airflow control device 617 is coupled to 7 proportional valve 657 which receives either a current or voltage control signal and s selectively vents pressurized fluid to airflow control device 617. In the preferred s embodiment, proportional valve 657 is manufactured by Proportion Air of ~o McCordsville, Indiana. Supply 651 provides a source of pressurized air which is ~ 1 routed through pressure regulator 653 which maintains the pressurized air at a constant 30 pounds per square inch of pressure. The regulated air is directed is through filter 655 to remove dust and other particulate matter, and then through 14 proportional valve 657 to airflow control device 617.
i5 In the preferred embodiment of the present invention, airflow control is device 617 is manufactured by Tek-Air Systems, Inc. of Northvale, New Jersey, ~7 and is identified as a "Connor Model No. PRD Pneumavalve". This valve is the is subject matter of at least two U.S. patents, including U.S. Patent No.
3,011,518, ~s which issued in December of 1961 to Day et al., and U.S. Patent No.
3,593,645, 2o which issued on July 20, 1971, to Day et al., which was assigned to Connor 2i Engineering Corporation of Danbury, Connecticut, and which is entitled "Terminal Page - 77 DOCKET NO. 291H-24528-CN
0291 MH-26521139816.1 Outlet for Air Distribution".
Experiments have revealed that this type of airflow control device provides for greater control than can be provided by rotary type valve 631 (depicted in Figure 28 for comparison purposes only), and is especially good at providing control in mismatched load situations which would ordinarily be difficult to control economically with a rotary type valve.
A number of airflow control devices like airflow control device 617 can be easily coupled together in either series or parallel arrangement to control the total volume of air provided to a blown film line or to allow economical load matching. In Figure 28, a series and a parallel coupling of airflow control devices is depicted in phantom, with airflow control devices 681, 683, and 685 coupled together with airflow control device 617. As shown in the detail airflow control device 617 is in parallel with airflow control device 683 but is in series communication with airflow control device 685. Airflow control device 685 is in parallel communication with airflow control device 681. Airflow control devices 681 and 683 are in series communication.
The present invention is also directed to a method and apparatus for cooling extruded film tubes, which utilizes a mass air flow sensor to provide a measure of the flow of air in terms of both the air density and air flow rate. The mass air flow sensor provides a numerical value which is indicative of the mass air 1 flow in an air flow path within a blown film extrusion system. A controller is 2 provided for receiving the measure of mass air flow from the mass air flow sensor s and for providing a control signal to an adjustable air flow attribute modifier which 4 serves to selectively modify the mass air flow in terms of mass per unit time by s typically changing one or more of the cooling air temperature, the cooling air s humidity, or the cooling air velocity. The preferred method and apparatus for cooling extrude film tubes is depicted and described in detail in Figures 30 through a 36, and the accompanying text.
s The particular type of mass air flow sensor utilized in the present 1o invention makes practical the utilization of mass air flow values in blown film ~ 1 extrusion systems. Of course, "mass air flow" is simply the total density of the ~2 cooling air or gas multiplied times the flow rate of the cooling air or gas. Typically, 13 blown film extrusion lines utilize ambient air for cooling and/or sizing the molten 14 blown film tube as it emerges from the annular die. It may become economically 1s practical in the future to utilize gases other than ambient air; for purposes of clarity 1s and simplicity, in this detailed description and the claims, the term "air"
is intended 1 ~ to comprehend both ambient air as well as specially provided gases or gas 1s mixtures.
1 s While it is simple to state what the "mass air flow" represents, it is far 2o more difficult to calculate utilizing conventional techniques. This is true because 2~ of the difficulty associated with calculating the density of air. Air which contains Page - 79 DOCKET NO. 291 H-24528-CN
0291 MH-28521139816.1 i water vapor requires the following information for the accurate calculation of "mass 2 air flow": the relative humidity of the air, the absolute pressure of the air, the s temperature of the air, the saturation vapor pressure for the air at the given 4 temperature, the partial pressure of the water vapor at the given temperature, the s specific gravity of the air, and the flow rate of the air. Utilizing conventional s sensors, one could easily measure relative humidity, temperature of the air, absolute pressure, and the flow rate of the air. With established data tables s correlating the temperature of the gas and the relative humidity, the saturation s vapor pressure and the partial pressure of the water vapor can be calculated. For io ambient air applications, the specific gravity of the gas is unity so it drops out of ~ i consideration. A good overview of the complexity associated with the calculation i 2 of these factors which make up the "mass air flow" is provided in a book entitled 13 Fan Engineering: An Engineers Handbook On Fans.4nd Their Applications, edited ~a by Robert Jorgensen, 8th edition, which is published by Buffalo Forge Company is of Buffalo, New York. While such calculations are not particularly difficult given ~s modern technologies for both sensors and data processors, the utilization of a i ~ single sensor which provides a direct indication of the "mass air flow"
lessens the ~a costs associated with implementation of the method and apparatus for cooling ~s extruded film tubes of the present invention. Such use of a mass air flow sensor 2o also reduces the complexity associated with calculating mass air flow utilizing a 2~ more conventional technique. This can be seen by comparing the calculations Page - 80 -DOCKET NO. 291H-24528-CN
0291 MH-28521139815.1 1 required for a system which does not utilize a mass air flow sensor, with one which 2 does utilize a mass air flow sensor. The "mass flow rate" of air is determined by s equation 1.1 which is set forth here below:
4 Equation 1.1 Mass Flow Rate = Density*Flow Rate s Of course, the flow rate is easy to obtain from flow rate meters, but 8 the density of the cooling air must be determined in accordance with equation 1.2 s which is set forth here below:
1o Equation 1.2 Densi ty= < < P Pwscp ) + Pwscp c.~ ) .7543 (T+459.7) 12 wherein P is representative of the absolute pressure of the air, Pws is 13 representative of the saturation vapor pressure, ~p is representative of the relative 1a humidity, and c~ is representative of the ratio of the density of the water vapor to 1s the density of dry air, and T is representative of the temperature of the cooling air 1s in degrees F. Since we measure P, gyp, and T directly, we only have to derive Pws 1~ and c~. By using a saturation vapor pressures table of water, we can determine 1 s the saturation vapor pressure (Pws) from the temperature of the cooling air. The Page - 81 DOCKET NO. 291 H-24528-CN
0291 MH-28621139816.1 following equation 1.3 allows one to calculate ca, which is the ratio of the water vapor density to dry air density:
Equation 1.3 ~~~s~l/1.42 ~=1.6214 l l+

This formula is accurate to 0.1% in the range of temperatures from 32°F to 400°F.
Therefore, it is evident that, in addition to a velocity sensor, sensors must be provided for the measurement of pressure, relative humidity, and temperature.
Additionally, the saturation vapor pressure and the ratio of the density of water vapor to the density of dry air must be calculated utilizing a provided table, which in microprocessor implementations must be represented by a data array maintained in memory. All together, the complexity and opportunity for error presented by such an array of sensors and series of calculations and table look-up operations renders this technique difficult and expensive to implement.
In contrast, the present invention for cooling extruded tubes utilizes a single sensor which provides a direct measurement of the mass air flow. Such mass air flow sensors have found their principle application in internal combustion engines, and are described and claimed in the following issued United States Patents:

(1) U.S. Patent No. 4,366,704, to Sato et al., entitled Air Intake 2 Apparatus For Internal Combustion Engine, which issued on January s 4, 1983, and which is owned by Hitachi, LTD., of Tokyo, Japan;
4 (2) U.S. Patent No. 4,517,837, to Oyama et al., entitled Air Flow Rate Measuring Apparatus, which issued on May 21, 1985, and which is s owned by Hitachi, LTD., of Tokyo, Japan;
7 (3) U.S. Patent No. 5,048,327, to Atwood, entitled Mass Air Flow Meter, s which issued on September 17, 1991;
s (4) U.S. Patent No. 5,179,858, to Atwood, entitled Mass Air Flow Meter 1o which issued on January 19, 1993.
11 Mass air flow sensors operate generally as follows. One or more 12 (typically platinum) resistor elements are provided in an air flow path way. An energizing current is provided to the one or more resistor elements. Air passing over the resistor elements reduces the temperature of the resistor elements. A
1s control circuit is provided which maintains currents at a constant amount in is accordance with King's Principal.
17 For the particular mass air flow sensor utilized in the preferred 18 embodiment of the present invention, the mass air flow of the air flowing through is an air pathway within a blown film extrusion system is established in accordance 2o with equation 1.4 as follows:
21 Equation 1.4 Page - 83 DOCKET NO. 291 H-24528-CN
0291 MH-28521 !39815.1 1 Mass Flow Rate = a1.601 (sensor reading+offset)°
2 wherein the constants are attributable to the specific construction of the s sensor assembly.
4 In accordance with the present invention, a mass air flow sensor is utilized to control air flow to cool molten polymers when extruded in a thin film s tube. The air flow may be provided in contact with either an interior surface of the thin film tube, an exterior surface of the thin film tube, or both an interior surface a of the thin film tube and an exterior surface of the thin film tube. The air flow s amount must be consistent in order to maintain the desired cooling rate of the 1o polymer. Changes in the cooling rate modify the extent to which polymer chains ~ 1 are formed, linked, and cross-linked. Under the prior art, the cooling air is at best 12 controlled to a constant temperature. There is no consideration in prior art 13 systems to the changes in the heat removing capacity of the air as the air gets i 4 more or less humid, or as the absolute pressure changes. Changes in the barometric pressure of one inch of mercury can change the mass air flow rate by 1s 3.3%. Changes in the temperature in the air typically have the greatest effect on 17 the heat removing capacity of the cooling air, with a 10% change in relative humidity causing a tenth of 1 % change in mass air flow rate. It is estimated that 1s utilization of the present invention in blown film extrusion lines which have 2o temperature control will add an additional accuracy in cooling up to 3.5%.
For 21 blown film extrusion lines which do not have temperature control, the consistency Page - 84 DOCKET NO. 291 H-24528-CN
0291 MH-26521139815.1 in cooling can be improved by an amount estimated at 13% to 15% provided 2 physical limits of the attribute modifying equipment are not reached.
a Cooling efficiency of course influences the production rate which can 4 be obtained blown film extrusion lines. Generally speaking, it is desirable to have s the extruded molten material change in state from a molten state to a solid state s before the blown film tube travels a predetermined distance from the annular die.
In the industry, the location of the state change is identified as the "frost line' in a s blown film tube. In the prior art, when big changes occur in the temperature, s humidity, or barometric pressure, the frost line of the extruded film tube may move ~o upward or downward relative to a desired location. This may cause the operator ~ 1 of the blown film line to decrease production volumes in order to keep from i 2 jeopardizing product quality, since product quality is in part determined by the 13 position or location of the frost line. While utilization of the present invention improves the cooling of extruded film tubes, the present invention also can be ~ s utilized to compensate for changes in the mass air flow rate of the cooling gas 1s supplied to the interior of a blown film tube and the hot exhaust gas drawn from the blown film tube, to provide essentially a constant frost line height, or at least ~a a frost line height that does not move because of changes in the mass air flow is rate. Of course, the present invention can be utilized in combination with prior art 2o external cooling devices for blown film extrusion lines to provide the same benefit.
Page - 85 DOCKET NO. 291H-24528-CN
0291 MH-28521139816.1 1 So considered broadly, the present invention can be utilized to z accomplish a number of desirable results, including:
s (1) it can be used as a frost line leveler for blown film extrusion line with 4 external air cooling only;
s (2) it can be used in both the supply and exhaust systems of an s internal-bubble-cooling blown film extrusion system to manage and maintain a balanced air flow between the supply and exhaust, which could greatly stabilize the s position of the frost line insofar as changes in the ambient temperature, humidity, s and barometric pressure effect the position of the frost line; this could eliminate the ~ o need for prior art frost line location sensors;
> > (3) the mass air flow sensor can be utilized in combination with the i z controller or computer to determine the most effective and efficient operating range ~a of flow pump devices such as blowers, and fans, by allowing the computer to is determine the mass air flow rate with relation to blower speed (and valve position) ~s and then systematically eliminate undesirable ranges of operation, which are 1s generally found at the lowest and highest ends of the operating range, where the i 7 flow pump or valve may perform in a non-linear fashion which would introduce ~s unstable characteristics into the operation of the blown film line;
1 s (4) the mass air flow sensor can be utilized to provide a rather slow feed 2o back signal to a supply blower in the blown film line, to compensate for changes Page - 86 DOCKET NO. 291H-24528-CN
0291 MH-28621139815.1 1 in the ambient air, such as temperature, humidity, and barometric pressure, which 2 effect the mass air flow rate;
s (5) the mass air flow sensor can be used to provide a feed back loop 4 which enhances the operation of a flow control valve in the line, to ensure that the valve operation is providing a particular air flow characteristic in response to a s particular valve activation signal.
7 In the following detailed description, Figures 30 and 31 are directed s to a blown film extrusion system which includes an internal cooling air flow and an s external cooling air flow. In contrast, the detailed description relating to Figures 32 ~ o through 35 are directed to a more simple blown film extrusion system which 11 includes only an external cooling air flow.
12 With reference first to Figure 30, there is depicted an internal-bubble-1s cooling blown film extrusion line 701 in schematic form. As is shown, blown film 14 tube 703 is extruded from annular die 705. An ultrasonic transducer 707 is utilized 1s to gage the position of blown film tube 703, and provides a control signal to 1s position processor 709, all of which has been discussed in detail in this detailed 17 description. A sizing cage 711 is provided to size and stabilize the blown film tube i s 703. A flow of internal cooling air is supplied to the interior of blown film tube 703 is through supply stack 713. As is conventional, exhaust stack 717 is also provided 2o in an interior position within blown film tube 703 for removing the cooling air from 21 the interior of Page - 87 DOCKET NO. 291 H-24528-CN
0291 MH-28521 !39815.1 blown film tube 703. A cooling air is supplied to supply stack 713 through supply 2 distributer box 715, and the exhausted air is removed from blown film tube s through exhaust distributor box 719. Additionally, an external cooling air ring 721 4 is provided for directing a cooling stream of air to an exterior surface of blown film tube 703. Cooling air ring 721 collaborates with the internal cooling air stream to s change the state of the molten material from a molten state to a solid state.
7 Cooling air ring 721 is provided with entrained ambient air from air ring blower 723 a which may be set tot a flow rate either manually or automatically.
s Supply distributor box 715 is provided with an entrained stream of io cooling air in the following manner. Ambient air is entrained by the operation of supply blower 729. It is received at input filter 725, and passed through (optional) 12 manual damper 727. If supply blower 729 is a variable-speed-drive type of supply 13 blower, then manual damper 727 is not required. Preferably, however, supply 14 blower 729 is a variable speed drive controller which provides a selected amount Of air flow in response to a command received at a control input of variable-speed-~ s drive 731. Also, preferably, variable speed drive controller is optionally subject to 17 synchronous command signals from IBC controller 753 which controls the general 1$ operations of the blown film extrusion line. The entrained ambient air is routed is through air flow path 755, first through cooling system 733, which preferably 2o includes a plurality of heat exchange coils and heat transference medium in 21 communication with the air flow, which receives a circulating heat exchange Page - 88 DOCKET NO. 291 H-24528-CN
0291 MH-26521139815.1 1 medium (such as chilled water for transferring heat), past mass air flow sensor 2 737, through air flow control device 739 (such as that depicted and described in s connection with Figures 28 and 29 above), and through supply distributer box 715.
4 Mass air flow sensor 737 provides a voltage signal which is indicative of the mass s air flow of the air flowing through air flow path 755 in the region between cooling s system 733 and air flow control device 739. Air flow control device 739 operates 7 in response to proportional valve 741 and selectively receives compressed air from s compressed air supply 743. Air flow control device 739 includes a plurality of s members which may be expanded and contracted to enlarge or reduce the air flow 1o path way through he housing of air flow control device. This allows for the 11 matching of loads, as is discussed above in connection with Figures 28 and 29.
12 Proportional valve 741 is under the control of IBC controller 753.
13 Exhaust distributer box 719 removes cooling air from blown film tube 14 703 and routes it through damper 745, into air flow path 755. The air passes 1s through mass air flow sensor 747 which provides a voltage which is indicative of 1s the mass air flow of the exhaust from blown film tube 703. The air is pulled from ~ 7 air flow path 755 by the operation of exhaust blower 749 which is responsive to an operator command, preferably through a variable speed drive 751, which is also is preferably under the synchronous control command of IBC controller 753.
2o In broad overview, mass air flow sensor 737 provides an indication 21 of the mass air flow of the cooling air which is supplied through supply distributor Page - 89 -DOCKET NO. 291H-24528-CN
0291 MH-26521139815.1 1 box 715 to supply stack 713. This cooling air removes heat from blown film tube 2 703, helping it change from a molten state to a solid state. Mass air flow sensor s 747 is in communication with the exhaust air removed through exhaust stack 4 and exhaust distributor box 719. Mass air flow sensor 747 provides a voltage s which is indicative of the mass air flow of the exhaust cooling air. The s measurements provided by mass air flow sensors 737,747 are supplied to a controller which includes a microprocessor component for executing s preprogrammed instructions.
s In accordance with the present invention, IBC controller 753 1o compares the values from mass air flow sensors, 737, 747 and then provides 11 command controls to variable speed drives 731, 751 in order to effect the operation of supply blower 729 and/or exhaust blower 749. Preferably, IBC
1s controller 753 may be utilized in response to an operator command to maintain 14 supply blower 729 and/or exhaust blower 749 at a particular level or magnitude 1s of blower operation, or to provide a particular ratio of blower operation, so that 1s when the temperature, humidity, or barometric pressure of the ambient air changes i ~ significantly, the blowers adjust the flow rate of the input cooling air and exhaust 18 cooling air to blown film tube 703 to maintain uniformity of heat absorbing capacity is of the internal cooling air, notwithstanding the change in temperature, humidity, 2o and/or barometric pressure.
Page - 90 DOCKET NO. 291 H-2452&CN
0281 MH-26621139816.1 1 The operation of this rather simple feed back loop is set forth in 2 flowchart form in Figure 36. The process starts at software block 771, and s continues at software block 773, wherein IBC controller 753 receives an operator 4 command from either an operator interface 757 on IBC controller 753, or an s operator interface 759 on variable speed drive 731. Next, values provided by mass s air flow sensors 737 and 747 are recorded in memory, in accordance with software block 775. Then in accordance with step 777, operation set points are derived.
s For example, a particular ratio between the mass air flow detected at mass air flow s sensor 737 and mass air flow sensor 747 may be derived. Then, in accordance 1o with step 779, IBC controller 75 monitors signals from mass air flow sensors 737 11 and 747 for changes in mass air flow, which are principly due to changes in the ~2 ambient temperature, humidity, and barometric pressure. Once a change is 13 detected, in accordance with step 781 IBC controller 753 synchronously adjusts 14 the variable speed drives 759, 731, 751 in order to affect the value of the mass air ~s flow of ambient air which has been entrained and which is flowing through air flow 1s passage way 755 in a manner which returns operation to the set point values 17 derived in step 777. For example, variable speed drive 731, 751 may be utilized 1s to increase or decrease the volume of air entrained by supply blower 729 and/or is exhausted by exhaust blower 749. In accordance with step 783, this process is 2o repeated until an additional operator command is received. Such commands may 21 include an instruction to obtain a new operation set point, or to discontinue the Page - 91 DOCKET NO. 291 H-2452&CN
0291 MH-26521 !39815.1 1 feed back loop until instructed otherwise. A cooling coil 738 may also be provided z in communication with air flow path 745, and may be adjusted in response to IBC
a controller 753 to adjust the value of mass air flow.
4 Figure 31 depicts an alternative to the embodiment of Figure 30 s wherein mass air flow sensors are utilized to control both the internal cooling air s supply to the interior of blown film tube 703 and an external cooling air stream which is supplied to the exterior surface of blown film tube 703 from air ring 721.
a The figures differ in that, in addition of having a control system for internal cooling s air, a control system for external cooling air is also provided with a mass air flow io sensor 747 positioned in air flow path 741 between air ring blower 723 and cooling 11 air ring 721. Mass air flow sensor 747 provides a measurement of the mass air 12 flow of the air flowing within air flow path 745. This measurement is provided to is IBC controller 753 and compared to a set point value which has been either 14 manually entered by the operator at operator interface 757 or which has been 1 s automatically obtained in response to an operator command made at operator is interface 757. IBC controller 753 supplies a control signal to variable speed drive 1~ 744 which is utilized to adjust the operating condition of air ring blower either ~ s upward or downward in order to maintain the established set point. If the mass is air flow sensor 747 indicates to IBC controller 753 that the total mass air flow has 2o been diminished (perhaps due to changes in temperature, humidity, and 2~ barometric pressure), then IBC controller 753 may supply a command signal to Page - 92 DOCKET NO. 291 H-2452&CN
0291 MH-26521 !39815.1 variable speed drive 744 which increases the throughput of air ring blower 723 in 2 a manner which compensates for the diminishment in mass air flow as detected s by mass air flow sensor 747. If mass air flow sensor 747 detects an increase in 4 the mass air flow, IBC controller 753 may provide a command signal to variable s speed drive 744 which increases the throughput of air ring blower 723 in a manner s which compensates for the diminishment in mass air flow a detected by mass air flow sensor 747. If mass air flow sensor 747 detects an increase in the mass air s flow, IBC controller 753 may provide a command signal to variable speed drive 744 s which reduces the throughput of air ring blower 723, thus diminishing the amount of mass air flow in order to make it equal to the set point maintained in memory > > in response to an operator command. This simple feedback loop is also 12 characterized by the flowchart depiction in Figure 36. Since changes in ambient 13 temperature, ambient humidity, and barometric pressure are rather slow, it is not 14 necessary that this feedback loop be a very fast loop. It is sufficient that every few ~s minutes the value for the mass air flow sensor be monitored to determine the 1s numeric value of the mass air flow, that this value be compared to a set point 1 ~ recorded in memory, and that an appropriate command be provided to blower in ~ s order to adjust the mass air flow upward or downward to make it equivalent to the 1s set point value. This allows a program which implement the present invention to 2o be "piggy backed" onto the IBC controller 753. The calculations required to 21 compare mass air flow values to set points is trivial and these operations need only Page - 93 DOCKET NO. 291 H-2452&CN
0291 MH-28521139815.1 i be performed every few minutes, so the IBC controller can spend the vast majority 2 of its computational power of controlling the blown film line, with only a de minimis s portion expended to occasional checking and adjusting of the mass air flow.
4 Additionally, a cooling coil 74 may be provided in communication with air flow path s 745, and may be provided in communication with air flow path 745, and may be s adjusted in response to IBC controller 753 to adjust the value of mass air flow.
The present invention can also be utilized in far simpler blow film 8 extrusion systems which utilize only external cooling air to remove heat from a s molten blown film tube. Four particular embodiments are depicted in Figures 32, 33, 34, and 35. In each of these embodiments, a mass air flow sensor is ~ 1 positioned intermediate and external cooling air ring and a blower for entraining 12 and supplying air to the cooling ring. Additionally an adjustable air flow attribute 1s modifier is provided in the air flow path for selectively modifying the air mass per 14 unit time. This adjustable air flow attribute modifier may comprise any mechanism ~s for adjusting for modifying the mass air flow, but in particular will most probably ~s comprise a cooling coil system which chills the cooling air, or an air flow control 17 device which restricts or enlarges the quantity of air available for entrainment by ~s the supply blower, or a fluid injection system which modifies the humidity of the is cooling air. Each of these three principle alternative embodiments will be 2o discussed in detail herebelow in connection with Figures 32, 33, 34, and 35.
Page - 94 DOCKET NO. 291 H-2452&CN
0291 MH-28521 !39816.1 1 Turning first to Figure 32, an external cooling blown film extrusion line 2 is depicted in schematic form. Plastic pellets are loaded into resin hopper 791, s passed through heating apparatus 793, and driven by extruder 795 through die 4 797 to form a molten extruded film tube 789, with a portion of the extruded film tube 789 below frost line 801 being in a molten state, and that portion above frost s line 801 being in a solid state. Air ring 799 is positioned adjacent die 797 and adapted to route cooling air along the exterior surface of blown film tube 789. Air ring 799 is supplied with cooling air which is entrained by air ring blower 803, s routed through cooling coils 805 of cooling system 809, and through mass air flow ~o sensor 807. Preferably, mass air flow sensor 807 is positioned in air flow path 821 > > intermediate cooling coils 805 and external cooling air ring 799. Cooling coils 805 12 are adapted to receive chilled water 813 from chiller system 81 1.
Controller 815 13 IS provided for receiving a signal from mass air flow sensor 807 which is indicative 14 of the mass air flow of the cooling air flowing through air flow path 821, and for ~s providing a command signal to chiller system 811 which adjusts the temperature is of chilled water 813 which is routed through cooling coil 805. A feed back loop is established about a set point selected by the operator when a set point selection 1a command button 817 is depressed. Controller 815 will respond to the command is by recording in memory the mass air flow value provided by mass air flow sensor 20 807, and by adjusting the chiller system 811 upward or downward in temperature 2i in order to maintain the mass air flow value of cooling air flowing through air flow Page - 95 DOCKET NO. 291 H-24528-CN
0291 MH-26521139815.1 i path 821 at a value established by the set point. Of course, the operator has an 2 operator interface for chiller system 811 which allows for the operator setting of the a temperature of chiller system 811. This system works once the operator has 4 established that sufficient cooling has been obtained, and should provide an s equivalent level of cooling from the external cooling air provided by air ring 799 s even though the ambient air changes its density through relatively slow changes in temperature, humidity, and barometric pressure. The embodiment of Figure 32 s is especially suited for blown film extrusion lines which have a dedicated chiller s system. The embodiment of Figure 33 depicts a more common scenario, wherein 1o a single chiller system is shared by multiple blown film lines. In this event, the i ~ configuration differs insofar as chiller system 811 is utilized to provide chilled water i2 813 for delivery to multiple heat exchange cooling coils, with a flow valve, such as 13 flow valve 825, being provided of each set of heat exchange cooling coils to increase or decrease the flow o circulating heat exchange fluid in order to alter the 15 temperature of the cooling air in air flow path 821. In the embodiment depicted in ~s Figure 33, controller 815 provides an electrical command signal to an electrically-i ~ actuated flow valve 825 in order to increase or decrease the flow of chilled water ~s 813 from chiller system 811 to cooling coil 805. Similar to the embodiment of is Figure 32, the operator instructs controller 815 to record the mass air flow value 2o from mass air flow sensor 807, and to utilize that as a set point for operation.
Thereafter, changes in the mass air flow property of the cooling air passing Page - 96 DOCKET NO. 291 H-2452&CN
0291 MH-28621 !39816.1 1 through air flow path 821, such as changes caused by changes in temperature, 2 humidity, and barometric pressure, are accommodated by increasing or s diminishing the flow of chilled water from chiller system 811 to heat exchange 4 cooling coil 805. Increases in mass air flow will result in the controller s providing a command to electrically-actuated flow valve 825 to diminish the flow of s chilled water; in contrast, decreases in mass air flow as detected by mass air flow sensor 807 will result in controller 815 providing a command signal to electrically-s actuated flow valve 825 to increase the flow of chilled water from chiller system 811 s to heat exchange cooling coils 805.
~o Figure 34 is a schematic depiction of an external air blown film 11 extrusion line, with blown film tube 789 extending upward from die 797 and being 12 cooled by an air stream in contact with an exterior surface of blown film tube 789 13 which is provided by air flow path 821. Air flow path 821 includes mass air flow i4 sensor 807 which provides a numerical indication of the mass air flow of the air i5 passing through air flow path 821. It provides this numerical indication to controller 1s 815, which in turn supplies a command signal to either variable speed controller 17 831 or air flow control device 833 (such as that depicted in Figures 28 &

~ s above), each of which can effect the volume of air which is entrained by air ring 1s blower 803. Controller 815 includes a manual control 817 which is utilized by the 20 operator to establish a set point of operation. Typically, the operator will get the 21 blown film line operating in an acceptable condition, and then will actuate the set Page - 97 DOCKET NO. 291 H-24528-CN
0291 MH-26621139816.1 1 point command 817, causing controller 815 to record in memory the value 2 provided by mass air flow sensor 807. Thereafter, changes in the mass air flow s due to changes in temperature, humidity, or barometric pressure will be 4 compensated for by variation in the amount of air entrained by air ring blower 803, in order to maintain mass air flow value at or about the set point value. For s example, if the mass air flow value decreases, as determined by the mass air flow sensor 807, variable speed controller 831 or air flow control device 833 are s provided with command signals from controller 815 to increase the volume of air s flowing through air flow path 821; however, if the mass air flow value increases, as 1 o determined by mass air flow sensor 807, controller 815 provides a command signal 11 to either variable speed controller 831 or air flow control device 833 in order to 12 decrease the volume of air entrained by air ring blower 803. In this manner, 1s controller 815 may intermittently check the value of the mass air flow, compare it 14 to a set point value recorded in memory, and adjust the volume of air entrained by 1s air ring blower 803 in order to maintain a mass air flow value at or about the set 1s point. In this manner, the cooling ability the air stream in contact with the exterior i ~ of extruded film tube 789 is maintained at a constant level notwithstanding gradual ~s or dramatic changes in temperature, humidity, and barometric pressure.
1s Figure 35 depicts yet another embodiment of the invention, wherein 2o an external cooling blown film extrusion line is depicted in the schematic form, with 21 extruded film tube 789 extending upward from annular die 797, which is cooled by Page - 98 DOCKET NO. 291 H-24528-CN
0291 MH-26521 !3987 5.1 an air stream provided by cooling air ring 799 Cooling air ring 799 receives its 2 cooling air from air flow path 821. Mass air flow sensor 807 is positioned in air s flow path 821, and is adapted to provide a signal indicative of the mass air flow of 4 air flowing through this passage way, to controller 815. Controller 815 provides a command signal to water injector 835 which is also in communication with the s air passing through air flow path 821. Water injector 835 is adapted to increase the humidity of the air entrained by blower 803 in response to a command from s controller 815. In accordance with this embodiment of this invention, the operator s depresses a set point control 817 on controller 815 in order to establish a set point 0 operation for controller 815. Controller 815 records in memory the value of mass > > air flow sensor 807, and thereafter continuously monitors the values provided by ~2 mass air flow sensor 807 in comparison to the set point. When an increase in mass air flow is required, controller 815 provides a command signal to water 14 injector 835 which provides a predetermined amount of moisture which is ~ s immediately absorbed by the air entrained by air ring blower 803. When no ~s additional humidity is required, controller 815 will no provide such a command. In this manner, the mass air flow value for air entrained in air flow path 821 may be is moderated by operation of controller 815. Since this system easily allows an is increase in the mass air flow value, without allowing a corresponding decrease in 2o the mass air flow value, it is particularly useful in very hot and dry climates.
Page - 99 DOCKET NO. 291H-2452&CN
0291 MH-26521139815.1 In all embodiments, it is advisable to provide a predetermined time 2 interval of time interval of monitoring before the set point is recorded and s established. This allows the operator to make changes in the operating condition 4 of the various blowers and other equipment in the blown film line prior to s requesting that a set point be established. It takes many minutes (5, 10, or s minutes) in order for the system to reach a quiescent condition of operation.
Having a predefined interval of time after request for a set point, during which the s mass air flow values are monitored but not recorded, allows the operator to s change the operating state of the blown film line, and request a set point value, at io the same time, without obtaining a set point value which is perhaps not stable or 1 ~ quiescent. In yet another more particular embodiment of the present invention, the ~2 controller may be programmed to monitor the rate of change of the mass air flow 1 s value for predetermined time interval in order to determine for itself that a quiescent ~ 4 condition has been obtained. For example, a 10 or 20 minute interval may be 15 provided after operator request of a set point, during which the controller ~s continuously polls the mass air flow sensor, calculates a rate of change for a finite time interval, and records it in memory. Only when the rate of change reaches an ~a acceptable level will the controller determine that a quiescent interval has been is obtained, and thereafter record the mass air flow value in memory for utilization as 2o a set point, or in the derivation of a set point, about which the feedback loop is established.
Page - 100 DOCKET NO. 291H-24528-CN
0291 MH-28521139815.1 1 Although the invention has been described with reference to a specific 2 embodiment, this description is not meant to be construed in a limiting sense.
s Various modifications of the disclosed embodiment as well as alternative 4 embodiments of the invention will become apparent to persons skilled in the art s upon reference to the description of the invention. It is therefore contemplated that s the appended claims will cover any such modifications or embodiments that fall within the true scope of the invention.
Page - 101 DOCKET NO. 291 H-24528-CN
0291 MH-26521 !39815.1

Claims (39)

1. In a blown film extrusion apparatus in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus for gauging and controlling the circumference of said extruded film tube, comprising:
at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing a signal corresponding to a detected position of said extruded film tube;
control means for substituting a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal; and means for varying a quantity of air within said extruded film tube in response to said control means for urging said extruded film tube to a desired position.

Page -102-

2. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 1:
wherein said blown film extrusion apparatus includes a processor;
wherein said control means includes instructions which are executed by said processor; and wherein said dynamic filtering process is defined by said instructions.

3. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 1:
wherein, during relatively stable operations, said control means produces said filtered position signal from a rolling average of position signals.

4. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 3:

Page -103-wherein a particular number of position signals utilized to develop said rolling average of position signals is dynamically determined.

5. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 1:
wherein said control means performs a continuous substitution of said filtered position signal only for so long as a relatively stable extruded film tube position is maintained.

Page -104-

6. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 1:
wherein said control means continuously adjusts said dynamic filtering process to decrease or increase its influence based upon a comparison of said signal corresponding to a detected position of said extruded film tube and said filtered position signal.

7. A method of gauging and controlling the circumference of an extruded film tube formed from film extruded from an annular die, comprising:
providing a transducer;
placing said transducer adjacent said extruded film tube;
transmitting an interrogating signal to, and receiving an interrogating signal from, said extruded film tube;
producing a detected position signal based on information contained in said interrogating signal;

Page -105-providing a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal; and varying a quantity of air within said extruded film tube in response to said filtered position signal.

Page -106-

8. A method according to Claim 7, further comprising:
providing a controller;
providing instructions which define said dynamic filtering process.

9. A method according to Claim 7, wherein said step of providing a filtered position signal comprises:
providing a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal only for so long as said extruded film tube is maintained in a relatively stable position.

10. A method according to Claim 7, wherein said step of providing a filtered position signal comprises:
providing a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal and automatically adjusting the influence of said dynamic filtering process.

Page -107-

11. A method according to Claim 7, wherein said step of providing a filtered position signal comprises:
providing a filtered position signal derived from a dynamic filtering process which generates a rolling average of position signals in lieu of said detected position signal.

Page -108-

12. In a blown film extrusion apparatus in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus for gauging and controlling the circumference of said extruded film tube, comprising:
at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing a signal corresponding to a detected position of said extruded film tube;
control means for substituting a filtered position signal developed from a particular one of a plurality of available filtering routines in lieu of said detected position signal; and means for varying a quantity of air within said extruded film tube in response to said control means for urging said extruded film tube to a desired position.

Page -109-

13. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 12:
wherein said blown film extrusion apparatus includes a processor;
wherein said control means includes instructions which are executed by said processor; and wherein said dynamic filtering process is defined by said instructions.

14. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 12:
wherein, during relatively stable operations, said control means produces said filtered position signal from a rolling average of position signals.

15. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 14:

Page -110-wherein a number of position signals utilized to develop said rolling average is dynamically determined.

Page -111-

16. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 12:
wherein said control means performs a continuous substitution of said filtered position signal only for so long as a relatively stable extruded film tube position is maintained.

17. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 12:
wherein said control means continuously adjusts said dynamic filtering process to decrease or increase its influence based upon a comparison of said signal corresponding to a detected position of said extruded film tube and said filtered position signal.

Page -112-

18. A method of gauging and controlling the circumference of an extruded film tube formed from film extruded from an annular die, comprising:
providing a transducer;
placing said transducer adjacent said extruded film tube;
transmitting an interrogating signal to, and receiving an interrogating signal from, said extruded film tube;
producing a detected position signal based on information contained in said interrogating signal;
substituting a filtered position signal developed from a particular one of a plurality of available filtering routines in lieu of said detected position signal;
and varying a quantity of air within said extruded film tube in response to said filtered position signal.

Page -113-

19. A method according to Claim 12, further comprising:
providing a controller;
providing instructions which define said dynamic filtering process when executed by said controller.

20. A method according to Claim 12, wherein said step of providing a filtered position signal comprises:
providing a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal only for so long as said extruded film tube is maintained in a relatively stable position.

21. A method according to Claim 12, wherein said step of providing a filtered position signal comprises:

Page -114-providing a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal and automatically adjusting the influence of said dynamic filtering process.

22. A method according to Claim 12, wherein said step of providing a filtered position signal comprises:
providing a filtered position signal derived from a dynamic filtering process which generates a rolling average of position signals in lieu of said detected position signal.

Page -115-

23. In a blown film extrusion apparatus in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus for gauging and controlling the circumference of said extruded film, comprising:
at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing a signal corresponding to a detected position of said extruded film tube;
control means including executable instructions defining a plurality of filters including:
a. a first filter which receives said signal corresponding to a detected position of said extruded film tube and modifies it based upon information derived from at least one previous detected position, during intervals of relatively unstable operation;
b. a second filter which receives said signal corresponding to a detected position of said extruded film tube and modifies it by Page -116-dynamic filtering it, only during intervals of relatively stable operation;
means for varying a quantity of air within said extruded film tube in response to said control means for urging said extruded film tube to a desired position.

24. An apparatus according to Claim 23 wherein said second filter modifies said signal corresponding to a detected position of said extruded film tube by generating a rolling average of signals corresponding to a plurality of previous detected positions.

25. An apparatus according to Claim 24 wherein said rolling average is determined from a pre-selected number of samples which is dynamically varied based upon at least one sampling criterion.

26. An apparatus according to Claim 25 wherein said sample criterion comprises a comparison of an input to a rolling average generator to an output of said rolling average generator.

27. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 23:

wherein said blown film extrusion apparatus includes a processor;
wherein said control means includes instructions which are executed by said processor; and wherein said dynamic filtering process is defined by said instructions.

28. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 23:
wherein, during relatively stable operations, said control means produces said filtered position signal from a rolling average of position signals.

29. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 28:

wherein a number of position signals utilized to develop said rolling average is dynamically determined.

30. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 23:
wherein said control means continues substitution of said filtered position signal only for so long as relatively a stable tube position is maintained.

31. An apparatus for gauging and controlling the circumference of an extruded film tube, according to Claim 23:
wherein said control means continuously adjusts said dynamic filtering process to decrease or increase its influence based upon a comparison of said signal corresponding to a detected position of said extruded film tube and said filtered position signal.

32. A method of gauging and controlling the circumference of an extruded film tube formed from film extruded from an annular die, comprising the method steps of:
providing at least one ultrasonic transducer;
placing said at least one ultrasonic transducer adjacent said extruded film tube;
transmitting and receiving sonic interrogating pulses with said at least one ultrasonic transducer to said extruded film tube;
producing a position signal based on information contained in said interrogating pulses;
filtering said position signal with a plurality of filters, including:
a. a first filter which receives said position signal and modifies it based upon information derived from at least one previous position signal during intervals of relatively unstable operation;
and b. a second filter which receives said position signal and modifies it by dynamic filtering only during intervals of relatively stable operation;
varying a quantity of air within said extruded film tube in response to said position signal after filtering has occurred.

33. A method according to Claim 32 wherein said second filter modifies said position signal by performing a rolling average operation.

34. A method according to Claim 33 wherein said rolling average operation is performed by utilizing a pre-selected but dynamically variable number of samples.

35. A method according to Claim 34 wherein said pre-selected but variable number of samples is dynamically adjusted based upon a comparison of a current position signal and an output of a rolling average generator.

36. A method according to Claim 32, further comprising:
providing a controller;
providing instructions which define said dynamic filtering process.

37. A method according to Claim 32, wherein said step of providing a filtered position signal comprises:
providing a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal only for so long as said extruded film tube is maintained in a relatively stable position.

38. A method according to Claim 32, wherein said step of providing a filtered position signal comprises:
providing a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal and automatically adjusting the influence of said dynamic filtering process.

39. A method according to Claim 32, wherein said step of providing a filtered position signal comprises:

providing a filtered position signal derived from a dynamic filtering process which generates a rolling average of position signals in lieu of said detected position signal.