JP2020013013A - Image forming apparatus and fixing device - Google Patents

Abstract

To accurately control a surface temperature of a fixation member (heating rotary body), which has been difficult, due to individual variation of components, in a conventional temperature control system configured to control an inner temperature detection result of the fixation member to maintain at a prescribed temperature, causing a mass production quality liable to vary, and thus leading to a risk of decrease in fixation function or a risk of decrease in component lifetime in some individual bodies.SOLUTION: Heat characteristic information based on an inner-outer surface temperature difference of a fixation member 20 is stored in advance in storage means 29 provided for a part of a fixation apparatus or an image formation apparatus, and by utilizing the information to modify target temperature at a temperature adjustment control of the fixation member 20, variation among individual bodies is suppressed regarding a surface temperature of the fixation member. This enables, as a result, prevention of problems related to fixation such as image quality deterioration or transfer failure due to heat quantity applied to the sheet, reduction of a rise time of the fixation apparatus and improvement of a lifetime of the fixation member.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus capable of forming an image on a sheet, such as an electrophotographic copying machine, a printer, a facsimile, and a multifunction machine having a plurality of these functions, and a fixing device (image heating apparatus) mounted on the image forming apparatus. ).

  2. Description of the Related Art In recent years, in an image forming apparatus using an electrophotographic method or the like, it has been required to reduce a rising time from receiving a print signal to starting printing. In addition, the rise time is often dominated by the heating time of the fixing device, and it is generally known that the rise time of the image forming apparatus can be shortened by shortening the heating time. I have.

  Patent Documents 1 and 2 disclose fixing device technologies that can shorten the rise time. The basic configuration of the fixing device proposed here is to fix a toner image on a sheet by heating the fixing belt with a fixing heater installed so as to sandwich the fixing belt opposite to the pressure roller. is there. By heating the temperature of the fixing nip portion of the fixing belt with an amount of heat necessary and sufficient to fix the toner image on the sheet, this contributes to shortening the rise time of the fixing device.

  Further, in the fixing device described in Patent Literature 1, a thermistor is installed inside a fixing belt on the back side of a fixing heater arranged in a fixing nip portion. The target temperature of the fixing heater is changed in accordance with the response speed characteristic of the thermistor to stably control the temperature on the surface side (the fixing belt contact side) of the fixing heater.

  Further, in the fixing device described in Patent Literature 2, it is attempted to directly control the temperature of the fixing belt by bringing a sub thermistor into contact with not only the main thermistor on the back surface of the fixing heater but also the inner peripheral surface side of the fixing belt. Is what you do.

JP 2001-282040 A JP 2004-078181 A

  However, the temperature control methods of the fixing device described in Patent Documents 1 and 2 have the following problems.

  In the case of the temperature control method of Patent Document 1, since the temperature of the fixing belt is indirectly controlled, even if the temperature control is performed while detecting the back surface temperature of the heater, the temperature of the fixing belt can be accurately controlled. Can not. Depending on the paper passing conditions (sheet type, image information, speed, temperature / humidity conditions, etc.), the temperature of the fixing belt may overshoot or increase the ripple, resulting in unintentional image failure or transport failure. There is a possibility that it will be.

  Further, in the case of the temperature control method of Patent Document 2, the temperature of the inner surface of the fixing belt is directly controlled. Therefore, the temperature detected on the inner surface of the fixing belt should be able to be accurately controlled. However, the temperature on the front side, not the inner side, of the fixing belt is important in determining the amount of heat actually applied to the toner image on the sheet. For this reason, the surface temperature varies depending on the individual fixing devices, which may cause problems such as poor image quality and poor conveyance due to insufficient heat control, and a reduction in the life of the fixing member.

  More specifically, when the fixing device is mass-produced, the dimensions and thermal characteristics of the constituent parts have normal variations within a standard range. For example, in the case of a fixing belt, thickness variations (base layer, elastic layer, surface layer) of each layer, and in the case of a temperature detecting thermistor, appropriate variations in the resistance value, shape, dimensions of a backup member, etc. of a temperature detecting thermistor are avoided as mass-produced parts. Can not pass. For this reason, when the apparatus is installed and operated in the apparatus, it is directly connected to the surface temperature variation, and affects various functions (fixing property, image property, transportability, etc.).

  Accordingly, an object of the present invention is to control the surface temperature of the fixing belt (heating rotator) to an appropriate temperature even when individual parts and the mounting state vary among individuals, thereby improving the basic fixing performance and the member life. , An image forming apparatus, and a fixing device.

(1) A typical configuration of an image forming apparatus according to the present invention for achieving the above object is as follows:
An image forming unit that forms a toner image on a sheet;
An endless heating rotator that heats the sheet on which the toner image is formed by the image forming unit while nipping and conveying the sheet at the nip portion, a heating source of the heating rotator, and an inner surface temperature of the heating rotator are detected. A fixing unit including a temperature detection unit;
A temperature control controller that controls the amount of power supplied to the heating source so that the temperature detected by the temperature detector becomes a predetermined temperature;
A storage unit that stores temperature difference information between a temperature detected by the temperature detection unit of the heating rotator and a surface temperature of the heating rotator measured by an external measuring device, which is acquired in advance under predetermined conditions. And
The temperature control unit controls the temperature detected by the temperature detection unit of the heating rotator to be a temperature adjusted by the temperature difference information read from the storage unit with respect to a reference temperature. It is characterized by doing.

(2) A typical configuration of the fixing device according to the present invention for achieving the above object is as follows.
An endless heating rotator that heats the sheet on which the toner image is formed while nipping and conveying the sheet at the nip portion;
A heating source for the heating rotator;
A temperature detector for detecting the inner surface temperature of the heating rotator,
A temperature control controller that controls the amount of power supplied to the heating source so that the temperature detected by the temperature detector becomes a predetermined temperature;
A storage unit that stores temperature difference information between a temperature detected by the temperature detection unit of the heating rotator and a surface temperature of the heating rotator measured by an external measuring device, which is acquired in advance under predetermined conditions. And
The temperature adjustment control unit controls the temperature detected by the temperature detection unit of the heating rotator to be a temperature adjustment temperature corrected based on temperature difference information read from the storage unit with respect to a reference temperature adjustment temperature. It is characterized by doing.

  According to the present invention, it is possible to provide an image forming apparatus and a fixing device in which the surface temperature of the heating rotator of the fixing unit is controlled to an appropriate temperature to improve the basic fixing performance and the service life of the member.

FIG. 4 is a schematic cross-sectional view of the fixing device according to the embodiment. Configuration schematic diagram of an image forming apparatus according to an embodiment Block diagram of the control system of the device (A) and (b) are schematic cross-sectional views of examples of ceramic heaters, respectively. Configuration schematic diagram of the fixing device thermal characteristic measuring jig (external measuring device) of the embodiment Temperature transition fluff at the time of measuring the thermal characteristics of the fixing device of the embodiment. Flow chart for explaining the operation of the embodiment Temperature transition fluff during image forming operation showing the effect of the embodiment Comparative example Temperature transition fluff during image forming operation of image forming apparatus Frequency distribution diagram showing mass productivity of belt surface temperature

"Example"
(Image forming unit)
FIG. 2 is a schematic diagram of a configuration of an image forming apparatus (a tandem type-intermediate transfer type four-color full-color laser beam printer employing an electrophotographic method) 130 in this embodiment, and FIG. 3 is a block diagram of a control system. The image forming apparatus 130 performs a print operation (image formation operation: print operation) corresponding to a print job (image formation job, print job) input from the host device 200 to a control circuit unit (control unit) 21 represented by a CPU or the like. Execute As a result, a full-color or mono-color image formed product (product) is printed out (printed out).

  The sheet P (sheet, medium, recording material) as a recording medium on which a toner image can be formed by the image forming apparatus 130 includes, for example, plain paper, cardboard, envelopes, postcards, stickers, resin sheets, and overhead projectors Sheet (OHT sheet) and the like. In the following description, a sheet is referred to as paper or paper. The description will be made using terms related to paper such as paper passing, paper feeding, and paper discharging, but the material is not limited to paper.

  The host device 200 is a personal computer, an image reader, a facsimile, a network, or the like. The print job is an image forming instruction to which print condition information such as image data, a specified type of paper, basis weight, size, number of sheets, number of copies, layout, and post-processing is added.

  Reference numeral 112 denotes an operation unit (user interface for communicating with a user or an external device and accessing the device: an operation panel unit) for inputting various kinds of information to the control circuit unit 21, and a display unit (notification unit) and an operation input unit Having a part.

  The control circuit unit 21 includes an image forming unit 130B, a sheet feeding unit (sheet conveying unit) 110 (A / B), and a fixing device (fixing unit: image heating device) 100 inside the image forming apparatus main body 130A. Monitors and controls the status of various parts of the device. Then, the operation of the entire image forming apparatus is organized by controlling the instruction system between the apparatuses.

  The image forming unit 130B is configured to form four subtractive primary colors of yellow (Y), magenta (M), cyan (C), and black (K), and form four color toner images. It has an image unit U (Y, M, C, K). Further, it has an endless intermediate transfer belt (hereinafter, referred to as a transfer belt) 105.

  Each image forming unit U includes an electrophotographic process device such as a photosensitive drum (photosensitive member) 101, a charging roller 102, a laser scanner 103, a developing device 104, a primary transfer roller 111, a drum cleaner 107, and the like. The laser scanner 103 is an exposure unit that can execute an exposure operation to form an electrostatic image on the photosensitive drum 101. The image forming unit 130B starts the exposure operation by the laser scanner 103 with the start of the image forming operation. In order to avoid complication in the figure, reference numerals for these devices in the image forming units UM, UC, and UK other than the image forming unit UY are omitted.

  In the case of the full-color print mode, each image forming unit U forms a Y, M, C, and K toner image on the photosensitive drum 101, respectively. The principle and process of electrophotography for forming a toner image are well-known, and a description thereof will be omitted. The toner images of the four colors are primary-transferred sequentially from the photosensitive drum 101 of each image forming unit U onto the transfer belt 105 in a predetermined superimposed manner. Thus, a color toner image of four colors of Y + M + C + K is formed on the transfer belt 105.

  The toner image formed on the transfer belt 105 is secondarily transferred to the sheet P at a secondary transfer unit 109 which is a pressure nip between the transfer belt 105 and the secondary transfer roller 106. The secondary transfer residual toner on the surface of the transfer belt 105 is cleaned by a belt cleaner 108. The paper P is separated and fed one by one from a first paper feed cassette 110A or a second paper feed cassette 110B, which is a paper feed unit, and is conveyed to a registration roller pair 114 through a conveyance path 113.

  The registration roller pair 114 once receives the leading end of the sheet P, and straightens the sheet P when the sheet P is skewed. The registration roller pair 114 is driven at a predetermined control timing in synchronization with the toner image on the transfer belt 105. By driving the registration roller pair 114, the sheet P is conveyed to the secondary transfer unit 109, and the toner image on the transfer belt 105 is secondarily transferred to the sheet P sequentially. The sheet P that has passed through the secondary transfer unit 109 is introduced into the fixing device 100 through the transport path 117 and receives the toner image under heat and pressure.

  In the single-sided print mode, the sheet P that has exited the fixing device 100 passes above the flapper 118 and is conveyed to the discharge tray 120 as a one-sided printed product by the discharge roller pair 119 to be discharged.

  In the case of the double-sided printing mode, the single-sided printed sheet P exiting the fixing device 100 is guided to the reversing conveyance path 121 by the flapper 118, switch-back conveyed, and introduced into the double-sided conveyance path 122. Then, the toner image passes through the conveyance path 113 again from the double-sided conveyance path 122 and is conveyed to the secondary transfer unit 109 by the registration roller pair 114 to receive the secondary transfer of the toner image on the second surface. Thereafter, as in the case of the single-sided print mode, the sheet is conveyed to the discharge tray 120 as a product of double-sided printing through the path of the conveyance path 117, the fixing device 100, the upper side of the flapper 118, and the path of the discharge roller pair 119. .

  In the case of the mono-color print mode, only the image forming unit required for forming the designated mono-color image out of the four image forming units U performs the image forming operation, and the other image forming units are exposed to light. The drum 101 is idled.

(Fixing device)
FIG. 1 is a schematic cross-sectional view of a fixing device (fixing unit) 100. The fixing device 100 in this embodiment is an on-demand fixing device (ODF fixing device) of a belt (film) heating type-pressing member driving type. Since the basic configuration and the fixing operation of the fixing device 100 are known, the description thereof will be briefly omitted.

This fixing device 100 is roughly divided into
1) a fixing unit (belt unit) 10 including a fixing belt (endless belt: hereinafter, referred to as a belt) 20 which is an endless heating rotator (first rotator: heat transfer member);
2) an elastic pressure roller 22 that is a pressure rotating body (second rotating body);
3) a housing (device frame) 24 accommodating them;
It consists of.

  A nip that fixes the toner image t with heat and pressure by nipping and transporting the paper P carrying the unfixed toner image t introduced from the image forming unit 130 </ b> B into the fixing device 100 by the belt 20 and the pressure roller 22. A part 27 is formed. Reference numeral 23 denotes a paper guide disposed on the paper entrance side of the housing 24, and reference numerals 37 and 38 denote a paper separation member and a paper guide disposed vertically opposite to the paper exit side of the nip portion 27. Reference numeral 26 denotes a fixing discharge roller pair disposed on the paper exit side of the housing 24.

  In this embodiment, the fixing unit 10 includes a fixing heater (heating element, heating source: hereinafter, referred to as a heater) 16 as a heating unit for heating the belt 20 from the inside, and a heater holder (hereinafter, referred to as a heater). 17). The heater 16 and the holder 17 are members that are long in the width direction of the belt 20 (longitudinal direction, generatrix direction: the direction perpendicular to the drawing in FIG. 1).

  In this embodiment, the belt 20 is formed by forming a silicone rubber layer (elastic layer) having a thickness of about 300 μm on a cylindrical base material formed of a cylindrical stainless steel having a thickness of about 30 μm, and forming a PFA resin tube having a thickness of about 30 μm on the surface layer. (The outermost surface layer). The belt 20 is a heat transfer member having flexibility, and has a substantially cylindrical shape in its free state due to its own elasticity.

  In the present embodiment, the heater 16 is a long and thin plate-shaped ceramic heater that generates heat when supplied with electricity (input of a predetermined electric power) and rapidly rises in temperature. The holder 17 is formed of a liquid crystal polymer resin having high heat resistance. A gutter-shaped member having a substantially semicircular arc-shaped cross section. The heater 16 is adhesively fixed along the length at a substantially central portion of the lower surface (outer surface) of the holder 17. The belt 20 is loosely fitted to the holder 17 to which the heater 16 is fixed, so that the inner surface of the belt 20 and the outer surfaces of the heater 16 and the holder 17 can slide. The holder 17 serves to hold the heater 16 and guide the orbit of the belt 20.

  4A and 4B are schematic cross-sectional views of examples of the ceramic heater.

  (A) is a surface heating type heater. This is a method in which a conductive paste containing a silver-palladium alloy is screen-printed on a surface of a long and thin plate-like ceramic substrate 16a made of alumina or aluminum nitride to a uniform film thickness of about 10 μm by a screen printing method. Has a resistive heating element 16b applied thereto. Further, a glass coat 16c is provided on the heating element 16b in order to secure a pressure resistance. The heater 16 is disposed with the surface of the substrate on which the resistance heating element 16b and the glass coat 16c are formed facing outward with respect to the holder 17. The surface of the glass coat 16c serves as a belt sliding surface.

  (B) is a back (back) heating type heater. This has a resistance heating element 16b on the back side of the ceramic substrate 16a along the length of the substrate. Further, a glass coat 16c is provided on the heating element 16b to ensure insulation. The heater 16 is disposed with the substrate front side opposite to the substrate back side on which the resistance heating element 16b and the glass coat 16c are formed facing the holder 17 facing outward. The substrate surface becomes the belt sliding surface.

  The pressure roller 22 of the present embodiment has a core metal 22a made of Fe, a silicone rubber layer 22b having a thickness of about 2.5 mm formed in a roller shape on the outer peripheral surface, and a thickness of about 2.5 mm laminated on the outer peripheral surface. And a surface layer 22c of a 50 μm PFA resin tube.

  The pressure roller 22 has one end and the other end of the cored bar 22a between the end plate and the other end plate (not shown) in the longitudinal direction (the direction perpendicular to the drawing of FIG. 1) of the housing 24, respectively. It is disposed so as to be rotatable. The pressure roller 22 functions as a driving rotating body by transmitting a driving force of a motor (M: driving source) 36 controlled by a fixing driving control unit 32 in the control circuit unit 21 via a driving transmission mechanism (not shown). It is driven to rotate.

  The fixing unit 10 is arranged between the side plates on one end side and the other end side in the longitudinal direction of the housing 24 with the heater 16 facing the pressure roller 22 and arranged in parallel with the pressure roller 22. Then, one end and the other end in the longitudinal direction of the holder 17 in the fixing unit 10 are directed to the axis of the pressure roller 22 by a force of 157 N on one side and a total pressure of 314 N by a pressing mechanism (not shown). Has been energized.

  As a result, the heater 16 is brought into pressure contact with a predetermined pressing force against the elasticity of the elastic layer 22 b of the pressure roller 22 via the belt 20, so that the heater 16 is moved between the belt 20 and the pressure roller 22 in the paper transport direction. Regarding a, a nip portion 27 having a predetermined width required for fixing is formed.

  Reference numerals 19 and 18 denote a backside thermistor (temperature detection thermistor) and a backside thermistor (temperature detection thermistor) as temperature detection means (temperature detection unit), respectively. The heater back thermistor 19 is installed on a surface (referred to as a back surface) opposite to the belt sliding surface of the heater 16 and has a function of detecting a back surface temperature of the heater 16. The belt back thermistor 18 is installed above the holder 17 so as to elastically contact the inner peripheral surface of the belt 20, and has a function of detecting the inner surface temperature of the belt 20.

  Specifically, the belt back thermistor 18 has a temperature detection thermistor attached to the tip of a stainless steel backup member (arm) 25 whose base is fixedly supported by the holder 17. Even when the movement of the inner surface of the rotating belt 20 becomes unstable due to the elastic swing of the backup member 25, the thermistor is kept in contact with the inner surface of the belt 20 at all times.

(Fixing operation)
The control circuit unit 21 starts the image forming operation of the image forming apparatus 130 based on the input of the print job. In the fixing device 100, the fixing drive control unit 32 in the control circuit unit 21 drives the motor 36. Thus, the pressure roller 22 is rotationally driven at a predetermined peripheral speed (process speed) in a counterclockwise direction indicated by an arrow R22 in FIG. With the rotation of the pressure roller 22, the belt 20, which is in pressure contact with the pressure roller 22 at the nip portion 27, has a peripheral speed corresponding to the rotation peripheral speed of the pressure roller 22 in the clockwise direction of arrow R <b> 20 in FIG. 1. It follows and rotates.

  At this time, the inner surface of the belt 20 rotates around the holder 17 while sliding in close contact with the belt sliding surface of the heater 16 at the nip portion 27. Heat resistant grease is applied to the inner surface of the belt 20 to ensure the slidability between the outer surfaces of the heater 16 and the holder 17 and the inner peripheral surface of the belt 20.

  When the pressure roller 22 is driven to rotate and the belt 20 is driven to rotate accordingly, the heater drive control unit 33 in the control circuit unit 21 controls the power supply unit 37 to supply power to the heater 16 (power supply: predetermined power). Start). As a result, the heater 16 generates heat and the temperature rises sharply. Due to the heat generated by the heater 16, the belt 20, which rotates while the inner surface is in close contact with the sliding surface of the heater in the nip portion 27, is heated from the inside (the inner side of the belt), and the temperature of the belt 20 rises.

  The heater back thermistor 19 and the belt back thermistor 18, which are temperature detecting units, are connected to the control circuit unit 21 via A / D converters 65 and 64, respectively. The control circuit section 21 samples the output from each thermistor at a predetermined cycle, and reflects the temperature information thus obtained in the temperature control.

  That is, the heater drive control unit 33 supplies the heater 16 from the power supply unit 37 to the heater 16 so that the belt 20 is heated to a desired temperature and maintained (temperature controlled) based on the temperature information input from the heater back thermistor 19 and the belt back thermistor 18. To control the power supply (power supply amount) to the power supply. As described above, the heater drive control unit 33 controls the amount of power supplied to the heater 16 serving as a heating unit so that the temperatures detected by the heater back thermistor 19 and the belt back thermistor 18 become a predetermined temperature. It functions as a temperature control control unit.

  When the temperature of the belt 20 reaches a desired temperature, the paper P carrying the unfixed toner image t is guided from the image forming unit 130B side to the nip portion 27 of the fixing device 100 along the paper guide 23 on the entrance side and is introduced. You. Then, in the nip portion 27, the toner image bearing surface side of the paper P is in close contact with the outer peripheral surface of the belt 20, and the paper P moves together with the belt 20. The heat of the belt 20 is applied to the paper P in the process of nipping and transporting the paper P at the nip portion 27, and the unfixed toner image t is fused and fixed on the paper P.

  The sheet P that has passed through the nip portion 27 is separated from the belt 20 by a curvature, passes between the sheet separating member 37 and the sheet guide 38, is spliced by the fixing sheet discharging roller pair 26, and is discharged from the fixing device 100.

(Temperature control method)
In the temperature control method of the fixing device 100, the power supply value to the heater 16 is determined mainly so that the detected temperature value of the belt back thermistor 18 can be stably maintained at a desired temperature. As a specific method, the temperature reaches the target temperature early by calculating from the target temperature of the belt back thermistor 18, the detected temperature, the amount of temperature change per unit time, the heater input power value, and the PI control parameter. The power is changed so as to maintain stability.

  At this time, since the direct heating source (heating unit) is the heater 16, the detected temperature and the amount of temperature change of the heater back thermistor 19 are also supplementarily PI controlled so that the temperature of the belt 20 does not fluctuate too abruptly. Thus, the inner surface temperature of the fixing belt 20 is stabilized earlier. The PI control is a control based on the set temperatures of the thermistor and the heater, for example, performing feedback control on the supplied electric power continuously so that the heater reaches the target temperature based on the difference between the set temperatures.

(Storage unit)
Reference numeral 29 denotes a storage unit (storage unit: hereinafter, referred to as a memory) provided in the fixing device 100 for storing individual information relating to thermal responsiveness (information unique to each fixing device). In this embodiment, a non-volatile memory such as NVRAM is employed, but an IC tag such as RFID or a format such as QR code (registered trademark) may be used.

  In the image forming apparatus of the present embodiment, the fixing device 100 is unitized so as to be attachable / detachable and replaceable with a predetermined mounting portion of the image forming apparatus main body (apparatus main body) 130A according to a predetermined operation procedure. When the fixing device 100 is mounted in the mounting portion of the image forming apparatus main body 130A in a predetermined manner, the memory 29 of the present embodiment reads the stored information by the reading section of the image forming apparatus main body side, and the control circuit 21 Communicates with the storage means communication unit 34 in the above. Then, the read and stored information is used to determine the regulated temperature of the belt 100.

  Another use of the memory 29 is to store operation history information (counter information, print information, error / jam occurrence history information, etc.) of the fixing device 100 as appropriate, and to determine the cause when an abnormality occurs in the fixing device 100. It also serves to facilitate investigation.

  In the image forming apparatus 130 according to the present embodiment, the fixing device 100 is assumed to be replaced when the life of the fixing device 100 is exceeded or a failure occurs.

  However, the present invention is not limited to this. If the replacement unit is not the fixing device 100 but the fixing unit 10, it is preferable that the memory 29 be provided in the fixing unit 10. That is, the fixing unit 10 is unitized so as to be detachable and replaceable with respect to the apparatus main body (housing 24) of the fixing device 100, and the memory 29 is provided in the fixing unit 10. When the image forming apparatus is not intended to replace the fixing device or the fixing unit, the memory 29 may be provided in a part of the image forming apparatus 130.

(Storing information in memory)
FIG. 5 is a configuration diagram of a fixing device thermal characteristic measuring jig (external measuring device) 200 that is installed in a final process after the fixing device is completed in the manufacturing process of the fixing device 100. The measurement jig 200 measures the temperature difference information on the inner and outer surfaces of the belt 20 as the thermal response characteristic of the fixing device 100, and stores the information in the memory 29 of the fixing device 100.

  The measuring jig 200 can drive and control the inner surface temperature of the belt in a single state of the fixing device 100. That is, the measuring jig 200 includes a control circuit unit 211, a motor (M: drive source) 236 controlled by the fixing drive control unit 232, and a power supply unit 237 controlled by the heater drive control unit 233.

  The pressure roller 22 of the fixing device 100 mounted on the measuring jig 200 is driven by the driving force of the motor 236 controlled by the fixing drive control unit 232 via a drive transmission mechanism (not shown). Is driven to rotate as a driving rotator in the same state as the fixing operation. Further, the heater 16 can receive power from the power supply unit 237 controlled by the heater drive control unit 233 and heat the belt 20 from the inside in the same state as the above-described fixing operation.

Then, the measuring jig 200 outputs the detection value of the belt back thermistor 18 via the A / D converter 235 inside the jig. At the same time, the surface temperature of the belt 20 can be measured synchronously by the non-contact temperature sensor (surface temperature sensor) 230 provided on the measurement jig 200 side. The arithmetic processing unit 231 in the control circuit unit 211 calculates the difference between both the detected temperature Tin of the belt back thermistor 18 and the detected temperature Tout of the surface temperature sensor 230,
Temperature difference ΔT = detected temperature Tin-detected temperature Tout
To get as Then, the arithmetic processing unit 231 can calculate the average value of ΔT in a predetermined period in units of 0.1 ° C., and can write the average value of the ΔT in the memory 29 after the measurement as a value specific to the individual fixing device 100.

  FIG. 6 shows the temperature transition of the detected temperature Tin of the belt backside thermistor 18 and the detected temperature Tout of the surface temperature sensor 230, which are obtained by measuring a specific fixing device 100 using the measuring jig 200 described above.

As the measurement conditions in this example,
-Start measurement from room temperature stable state (25 ± 4 ° C) after completion of fixing device 100;
・ Heater 16 startup power 500W ± 3%,
・ The temperature control temperature of the belt back thermistor 18 is 200 ° C,
・ Measurement time is 65 seconds after reaching the temperature
And

  The calculation period of the temperature difference ΔT to be written into the memory 29 was set to 20 seconds from the lapse of 40 seconds to the lapse of 60 seconds after the temperature control was reached.

  The arithmetic processing unit 31 in the control circuit unit 221 stores the detected temperature of the belt backside thermistor Tin and the detected temperature of the surface temperature sensor Tout during this period at a sampling cycle of 100 ms, and performs an averaging process after the measurement is completed to calculate the temperature difference ΔT. . Then, the control circuit unit 221 performs an operation of writing the measured value into the memory 29 of the fixing device 100 as a value unique to the individual fixing device 100. In this example, since the average temperature difference ΔT = 7.2 ° C. after the calculation, the value (48 hex) is written into the memory 29 by multiplying it by 10 for data processing and converting it to a hexadecimal number.

  As a result of measuring 50 randomly selected fixing devices that were mass-produced under these conditions, ΔT was approximately 6.0 to 14.0 ° C., and thus the measured value of this example is an individual having a relatively small ΔT. It can be said that.

  The unique temperature difference information ΔT stored in the memory 29 is used as a temperature control correction value when the fixing device 100 is mounted on the image forming apparatus 130 and operated. The method will be described in detail in a later section.

  It has been found that ΔT, which is the temperature difference between the inner and outer surfaces of the belt 20 under predetermined conditions, varies mainly due to the following factors. The thickness of the elastic layer and the surface layer of the belt 20, the detection sensitivity of the belt back thermistor 18, the shape and contact pressure of the backup member 25, the uniformity of the heat-resistant grease initially applied to the inner peripheral surface of the belt 20, and the like. The factors relating to these members can be simply increased in accuracy to suppress variations, but they are not appropriate measures because they lead to an increase in cost and reduce mass productivity.

  In the present invention, by accepting the normal variation of these members and manufacturing factors, the characteristics are quantified and used for control, so that the basic fixing function (image quality, transportability), durability, start-up time and energy saving performance are achieved. The aim is to improve the level of mass production quality.

  In the thermal characteristic measuring jig 200 of the fixing device 100 described here, the temperature difference ΔT (temperature difference information) is calculated after the temperature of the belt 20 enters the stable temperature control region, but is not limited thereto. Absent. The temperature difference may be calculated from a certain instantaneous value in the temperature rising process (for example, when passing through 190 ° C.). If the temperature transition after reaching the temperature control temperature does not vary so much depending on the individual (individual fixing device), the measurement tact can be shortened.

  In this example, the surface temperature measurement point of the belt 20 is also a region immediately before the nip in the rotation direction, but may be an arbitrary circumferential position. Alternatively, measurement may be performed such that scanning is performed at a plurality of points or continuously in the longitudinal direction of the fixing device 100, and calculation may be performed so as to extract a point at which the temperature difference ΔT is maximum.

  As described above, the temperature difference information can be obtained under the following various predetermined conditions.

  1) The temperature difference information is temperature difference information obtained when a predetermined amount of power is supplied to the heater 16 in the fixing device 100 in the initial state and the temperature of the belt 20 is raised to reach a predetermined temperature.

  2) The temperature difference information is temperature difference information acquired when the temperature control of the fixing device 100 in the initial state is controlled for a certain time so that the belt 20 has a predetermined temperature.

  3) The surface temperature measurement site of the belt 20 at the time of acquiring the temperature difference information is a position corresponding to at least one of a circumferential position and a longitudinal position at which the belt back thermistor 18 measures the inner surface temperature of the belt 20.

  4) The longitudinal position of the surface temperature measurement site of the belt 20 is a plurality of points, and the point at which the temperature difference from the temperature detected by the belt backside thermistor 18 is the largest is extracted to obtain temperature difference information.

(Image formation flow)
As described above, the fixing device 100 stores temperature difference information between the temperature detected by the belt back thermistor 18 of the belt 20 and the surface temperature of the belt 20 measured by the measuring jig 200, which is acquired in advance under predetermined conditions. Having a memory 29. The above-described image forming apparatus 130 in FIG. 2 has the fixing device 100 mounted thereon. The image forming process of the image forming apparatus 130 will be described with reference to the flowchart of FIG. 7 and the temperature transition diagram of FIG.

  When the control circuit unit 21 receives an image forming signal (S1), it sets a print mode (S2). Here, target basic information for controlling the temperature of the belt 20 by the belt back thermistor 18 based on paper information (type, basis weight, size), image information (monochrome mode / color mode), and outside air temperature information used for image formation. The temperature Tb and the printing speed S are determined from an internal table.

  In the example of 64 g of plain paper, color mode, and 25 ° C. environment, Tb = 190 ° C. and S = 100%. Generally, as the basis weight is higher and the boundary temperature is lower, toner peeling is more likely to occur, so the temperature control temperature is set higher. Extremely heavy paper or special paper that is still severe even when the temperature is raised to the limit may be dealt with by suppressing the printing speed.

  Next, in step S3, the control circuit unit 21 reads out unique thermal characteristic information (temperature difference information) ΔT from the memory 29 of the fixing device 100. Here, the fixing device 100 with ΔT = 7.2 (48 hex) described in the previous section will be described as an example. In step S4, a print temperature adjustment temperature T at which printing is actually performed is determined according to the following equation based on the target basic temperature Tb, the readout ΔT value, and the coefficient K.

T = Tb + (ΔT-10.0) * K
In this example, which is the plain paper mode, the coefficient K = 1, and when the printing condition is different from the above-described measurement condition on the thermal characteristic measuring jig, such as when the printing speed is slow, K = 0.3 to It is better to set it in the range of about 1.5. As described in the previous section, the reason why the fixed value 10 (° C.) is subtracted from ΔT is that ΔT = 6.0 to 14.0 (10.0 ± 4. 0) is known by prior verification.

  Therefore, in the fixing device 100 having the mode value ΔT = 10.0, it is set so that T = Tb so that even if a reading error of the memory 29 occurs, the degeneration operation can be performed without stopping the device. That's why.

  Thus, in this example, T = 190 + (7.2-10.0) = 187.2 ° C. is determined.

  Then, the control circuit unit 21 starts driving the pressure roller 22 and starts energizing the heater 16 via the heater drive control unit 28 (S5).

  When the detected temperature Tnow of the belt backside thermistor 18 satisfies the conditional expression (Tnow> T-12 ° C.), the control circuit unit 21 permits the paper P to be fed, and transmits an image forming command on the photosensitive drum 101 ( S6). This conditional expression is determined by the transport path length of the image forming apparatus 130. When the heater 16 is started at the maximum set power, the condition to the photosensitive drum 101 is lower than the print temperature regulation temperature T by Δ12 ° C. The image forming operation is started. Then, the conditional expression is set because the paper P carrying the toner image enters the nip portion 27 just when the belt 20 reaches the temperature T.

  In this example, the fixed conditional expression is used. However, a plurality of fixed conditional expressions may be provided depending on printing conditions (paper type / basis weight, image information) (such as a case where first print speed is more important than fixed image quality).

  In this way, the control circuit 21 repeats the image forming operation while controlling the temperature of the inner surface of the belt 20 under control (S7). When the last sheet of print is detected (S8), the image forming operation end processing (stop of temperature control, fall of high voltage, stop of drive mechanism) ends, and a series of flows ends.

  The summary of the above control is as follows. The heater control unit (temperature control unit) 33 in the control circuit unit 21 controls the temperature control in which the temperature detected by the belt back thermistor 18 of the belt 20 is corrected based on the temperature difference information read from the memory 29 with respect to the reference temperature. Control so that it becomes temperature. As described above, the temperature difference information of the inner and outer surfaces of the belt 20 is stored in the memory 29 provided in the fixing device 100 in advance, and is used to correct the temperature at the time of the temperature control. The life of the member can be improved.

  FIG. 8 shows the transition of the output of the thermistor on the inner surface of the back of the belt and the transition of the belt surface temperature (estimated value) when plain paper printing is performed for 2 minutes in the fixing device 100 of this embodiment. As for the measurement of the surface temperature, a measurement sensor is not provided in the inside of the image forming apparatus. Therefore, in this example, the thermocouple is experimentally measured by lightly contacting the surface of the belt 20, and only the heat capacity of the thermocouple is measured. Output by calculating by offsetting the temperature deviation.

  In addition, various image evaluations and conveyance evaluations were actually performed by paper passing, and the results were shown by broken lines so that the occurrence phenomenon could be understood for each temperature region. As an evaluation result, when the belt surface temperature is lower than 177 ° C., toner peeling (defective fixing) may occur, and when the belt surface temperature exceeds 183 ° C., jam may occur due to defective fixing separation. If the temperature exceeds 181 ° C., gloss unevenness in the high-density portion becomes remarkable and image quality deteriorates. Therefore, the proper belt surface temperature range in this evaluation is defined as 178 to 181 ° C.

  In this way, according to the image forming process flow of FIG. 7, the paper passing evaluation was actually performed in the fixing device 100 in which the print temperature control T on the inner surface of the belt was determined to be 187.2 ° C. As a result, as shown in FIG. 8, it was confirmed that the expected surface temperature transition was in a proper range of 178.4 to 180.3 ° C.

  In addition, similarly, as a result of performing temperature transition measurement and paper passing performance evaluation of a plurality of fixing devices by the present evaluation method, all of the fixing devices have a surface temperature transition within an appropriate range, and there is no defect in image quality and transportability. It was confirmed.

  Further, as another effect, the stabilization of the belt surface temperature transition (optimization of the inner surface temperature control) can shorten the rise time of the fixing device 100. When the first print time indicating the time until the discharge of the first sheet in the first state in the morning was completed was measured, the control in the present embodiment was 5.28 seconds, and the control in the comparative example in which the control according to the present invention was not applied was 5.53. It was also demonstrated that there was an advantage in shortening the seconds and rise time.

  Further, as another effect, since the variation in the belt surface temperature can be suppressed and excessive heating can be prevented, the wear of the surface layer (PFA resin layer) of the belt 20 can also be suppressed. As described above, the quality can be improved from the viewpoint of the life of the member due to the abnormal wear of the surface layer.

  As described above, by appropriately controlling the belt temperature during printing, the quality (transportability, rise time, fixing image quality, belt life, etc.) relating to the surface temperature of the belt 20 as the heating rotator is stabilized and improved. Can be achieved.

(Comparative example)
FIG. 9 shows the temperature transition in the case of the control of the comparative example in which the control according to the present invention is not applied to the same fixing device 100 as described in the embodiment. In the control flow of FIG. 7 described above, the steps of reading the individual information in step S3 and setting the print temperature adjustment in step S4 are eliminated. Therefore, the temperature control temperature at the time of printing by the belt backside thermistor 18 is 194 ° C. regardless of which fixing device is used.

  This is because, when the control of the present invention is employed, the optimum temperature control temperature is determined by correcting the maximum of ± 4.0 ° C. in accordance with the individual characteristic information with the temperature control at the back of the belt at 190 ° C. (mode). In contrast to what had been. In other words, it can be said that the temperature of the fixing device is set such that no fixing failure occurs even if the fixing device has any characteristic (even if the individual has the lowest surface temperature).

  In other words, in a method in which the control unit 21 of the image forming apparatus 130 is not provided with a means for recognizing the thermal characteristic information of the individual fixing device, even if the individual has the lowest fixability level due to variation in the mass production of the fixing device, the quality is low. Need to be secured. For this reason, most of the individual fixing devices are forced to set the temperature to an excessively high level.

  As shown in FIG. 9, the transition of the assumed surface temperature of the control method of the comparative example to which the control according to the present invention is not applied indicates that the same individual unit as the fixing device that was in the appropriate range when the control of the present invention described in the preceding paragraph was applied was used. In the control method described above, the amount of heat becomes excessive. Therefore, it can be read that the possibility of image quality deterioration and conveyance failure has increased.

  The frequency distribution diagram of FIG. 10 shows the mass production frequency distribution (frequency distribution) when the horizontal axis represents the belt surface temperature in a steady state under the same paper passing conditions (64 g of plain paper and printing for 2 minutes) as in FIG. It is an expression.

  According to the distribution of the comparative example, there are unavoidable fixing device individuals having a risk of lowering image quality and a risk of conveyance failure in order to avoid fixing defects. On the other hand, in the embodiment, since the variation in the belt surface temperature can be kept small, the stable mass-production quality in which the problem due to the surface temperature of the belt 20 is less likely to occur regardless of the type of the fixing device is provided. be able to.

(Other control configurations)
(1) When a predetermined electric power is applied to the heater 16 of the fixing device 100 and the belt 20 is heated until the belt back thermistor 18 reaches the first temperature, the surface temperature of the belt 20 becomes equal to the second temperature. Is assumed to be mounted on the mounting section.

  In this case, the control unit 21 that controls the operation of the image forming unit 130 </ b> A receives the first image forming command in a standby state in which the image forming operation can be started and waits for the input of the image forming command. The image forming unit 130A starts the image forming operation in response to the detection of the first target temperature by the belt back thermistor 18.

  (2) The surface temperature of the belt 20 is higher than the second temperature when the predetermined power is applied to the heater 16 and the belt 20 is heated until the belt back thermistor 18 reaches the first temperature. Consider a case where the fixing device 100 having the third temperature is mounted on the mounting portion.

  In this case, the control unit 21 determines that when the first image forming command is input in the standby state, the belt back thermistor 18 detects a second target temperature lower than the first target temperature. Accordingly, the image forming operation by the image forming unit 130A is started.

  (3) The fixing device 100 corresponds to the surface temperature of the belt 20 when the predetermined power is supplied to the heater 16 and the belt 20 is heated until the belt back thermistor 18 reaches the first temperature. It has a memory 29 for storing information. The control unit 21 controls the operation of the image forming unit 130A based on the information stored in the memory 29 of the fixing device 100 mounted on the mounting unit.

<< other matters >>
(1) The fixing device according to the present invention also includes an image modifying device for modifying the glossiness or the like of an image (fixed image or semi-fixed image) once fixed or temporarily fixed on paper (in this case, Is also referred to as a fixing device).

  (2) The heating unit (heating source) for heating the belt (heating rotator) from the inside is not limited to the ceramic heater 16 of the embodiment. Other internal heating type heating units such as a halogen heater and an infrared lamp can also be used. Alternatively, a method may be used in which the belt or a member that is in contact with the belt while being stretched is used as a heating element, and the belt or a member that is in contact with the belt while being stretched is heated by an induction heating method. The excitation coil and the magnetic core functioning as a heating source of the induction heating system may be arranged inside the belt or outside.

  (3) The endless heating rotator that heats the paper on which the toner image is formed while nipping and transporting the paper at the nip portion 27 is not limited to the cylindrical belt of the embodiment. It may be a flexible endless belt member stretched between a plurality of suspension members and driven to rotate, or a rigid rotatable sleeve member. The pressure rotating body is not limited to the roller body, but may be a fixing device having an endless belt member. It is also possible to adopt a fixing device configuration in which the heating rotator is driven to rotate, and the pressure rotator is driven to rotate by the rotation of the heating rotator.

  (4) The paper introduction method of the fixing device can be based on a so-called central conveyance standard or a so-called one-sided conveyance standard.

  (5) In the embodiment, the fixing device may be implemented by an image forming apparatus other than the color electrophotographic printer of the embodiment, a monochrome copying machine, a facsimile, a monochromatic printer, a multifunctional machine thereof, or the like. That is, the fixing device and the color electrophotographic printer or the copying machine of the embodiment are not limited to the combination of the above-described constituent members, but can be realized in another embodiment by partially or entirely replacing each of the substitute members. You may.

  (6) The image forming method of the image forming unit of the image forming apparatus is not limited to the electrophotographic method. An image forming unit of another system such as an electrostatic recording system or a magnetic recording system may be used. Further, the present invention is not limited to the transfer method. An image forming unit that forms an unfixed image directly on paper may be used.

  130 image forming apparatus, 130A image forming unit, P recording material, t toner image, 100 fixing unit, 20 heating rotator, 16 heating source, 18 temperature detection Unit, 33 ... temperature control unit, 29 ... storage unit, 200 ... external measuring instrument

Claims (16)

An image forming unit that forms a toner image on a sheet;
An endless heating rotator that heats the sheet on which the toner image is formed by the image forming unit while nipping and conveying the sheet at the nip portion, a heating source of the heating rotator, and an inner surface temperature of the heating rotator are detected. A fixing unit including a temperature detection unit;
A temperature control controller that controls the amount of power supplied to the heating source so that the temperature detected by the temperature detector becomes a predetermined temperature;
A storage unit that stores temperature difference information between a temperature detected by the temperature detection unit of the heating rotator and a surface temperature of the heating rotator measured by an external measuring device, which is acquired in advance under predetermined conditions. And
The temperature control unit controls the temperature detected by the temperature detection unit of the heating rotator to be a temperature adjusted by the temperature difference information read from the storage unit with respect to a reference temperature. An image forming apparatus.   The temperature difference information is temperature difference information obtained when a predetermined amount of power is supplied to the heating source by the fixing unit in an initial state and the temperature of the heating rotator is increased to reach a predetermined temperature. The image forming apparatus according to claim 1, wherein:   2. The temperature difference information, wherein the temperature difference information is acquired when the temperature of the heating rotator is controlled at a predetermined temperature by the fixing unit in an initial state for a predetermined time. 3. An image forming apparatus according to claim 1.   The surface temperature measurement site of the heating rotator at the time of acquiring the temperature difference information is a position corresponding to at least one of a circumferential position and a longitudinal position at which the temperature detection unit measures the inner surface temperature of the heating rotator. The image forming apparatus according to claim 1, wherein:   The longitudinal position serving as a surface temperature measuring portion of the heating rotator is a plurality of points, and the temperature difference information is obtained by extracting a point at which a temperature difference from a temperature detected by the temperature detecting unit is maximum. The image forming apparatus according to claim 4, wherein:   The image forming apparatus according to claim 1, wherein the fixing unit includes the storage unit and is detachably replaceable with respect to an image forming apparatus main body.   6. The heating rotator, the heating source, the temperature detecting unit, and the storage unit are unitized so as to be collectively detachable and replaceable with respect to the fixing unit. Item 10. The image forming apparatus according to item 1. An endless heating rotator that heats the sheet on which the toner image is formed while nipping and conveying the sheet at the nip portion;
A heating source for the heating rotator;
A temperature detector for detecting the inner surface temperature of the heating rotator,
A temperature control controller that controls the amount of power supplied to the heating source so that the temperature detected by the temperature detector becomes a predetermined temperature;
A storage unit that stores temperature difference information between a temperature detected by the temperature detection unit of the heating rotator and a surface temperature of the heating rotator measured by an external measuring device, which is acquired in advance under predetermined conditions. And
The temperature control unit controls the temperature detected by the temperature detection unit of the heating rotator to be a temperature adjusted by the temperature difference information read from the storage unit with respect to a reference temperature. A fixing device.   The temperature difference information is temperature difference information acquired when a predetermined amount of power is reached when a predetermined amount of power is supplied to the heating source by the device in an initial state and the temperature of the heating rotator is increased. The fixing device according to claim 8, wherein   9. The temperature difference information according to claim 8, wherein the temperature difference information is obtained when the temperature of the heating rotator is controlled to a predetermined temperature by a device in an initial state for a predetermined time. 10. Fixing device.   The surface temperature measurement site of the heating rotator at the time of acquiring the temperature difference information is a position corresponding to at least one of a circumferential position and a longitudinal position at which the temperature detection unit measures the inner surface temperature of the heating rotator. The fixing device according to claim 8, wherein:   The longitudinal position serving as the surface temperature measurement site of the heating rotator is a plurality of points, and the temperature difference information is obtained by extracting a point at which the temperature difference from the temperature detected by the temperature detection unit is maximum. The fixing device according to claim 11, wherein:   13. The heating rotator, the heating source, the temperature detecting unit, and the storage unit are unitized so as to be collectively detachable and replaceable with respect to an apparatus main body. 3. The fixing device according to claim 1. An image forming unit that forms a toner image on a sheet,
Mounting part,
An endless heating rotator that is a fixing unit attached to the attachment unit and heats the sheet on which the toner image is formed while nipping and conveying the sheet at the nip; a heating source of the heating rotator; A fixing unit having a temperature detecting unit for detecting the inner surface temperature of the rotating body,
A control unit for controlling the operation of the image forming unit,
The control unit includes:
When a predetermined power is supplied to the heating source and the temperature of the heating rotator is raised until the temperature detecting section reaches the first temperature, the surface temperature of the heating rotator becomes the second temperature. When the first image forming command is input in a standby state in which the image forming operation can be started when the first image forming command is input in a state where the image forming operation can be started, Starting an image forming operation by the image forming unit in response to detecting the first target temperature;
When the predetermined power is supplied to the heating source and the temperature of the heating rotator is increased until the temperature detection unit reaches the first temperature, the surface temperature of the heating rotator is changed to the second temperature. In a case where the fixing unit having a higher third temperature is mounted on the mounting unit, when the first image forming command is input in the standby state, the temperature detection unit may be configured to perform the first target operation. An image forming apparatus, wherein an image forming operation by the image forming unit is started in response to detection of a second target temperature lower than a temperature. The fixing unit is configured to supply the predetermined power to the heating source and raise the temperature of the heating rotator until the temperature detecting unit reaches the first temperature. A storage unit for storing corresponding information,
15. The image forming apparatus according to claim 14, wherein the control unit controls an operation of the image forming unit based on the information stored in the storage unit of the fixing unit mounted on the mounting unit. Image forming device. The image forming unit has a photoconductor, and an exposure unit that can perform an exposure operation to form an electrostatic image on the photoconductor,
The image forming apparatus according to claim 14, wherein the image forming unit starts the exposure operation when the image forming operation starts.