JP6762829B2 - Injection molding machine - Google Patents

Description

The present invention relates to an injection molding machine.

The electric injection device described in Patent Document 1 includes an injection screw and an electric servomotor that drives the injection screw forward and backward. This electric injection device includes an injection filling step of applying an injection pressure to the resin stored in front of the injection screw, and a pressure holding step of applying a predetermined holding pressure to the stored resin following the injection filling step. , And a control device for sequentially performing each step of the back pressure step of applying the back pressure according to the plasticization condition of the resin to the injection screw. In this control device, the torque limit value of the electric servomotor is continuously set to be equal to or higher than the torque limit value at the start of the back pressure process from the end of the back pressure process to the start of the back pressure process, and at the end of the back pressure process. From to the end of the back pressure process, the electric servomotor is set to the zero speed state.

Japanese Unexamined Patent Publication No. 6-285926

The injection molding machine has a three-phase AC motor that drives a movable part, and a control device that supplies a current to the three-phase AC motor based on the difference between the actual value and the set value of the physical quantity to be controlled. As the three-phase AC motor, for example, a three-phase synchronous motor is used.

The control device maintains the state of the three-phase AC motor at a low speed and a high output state in a pressure holding process or the like. In this case, the current may continue to concentrate in a specific one of the three phases.

In particular, since the injection molding machine repeats the same operation in order to repeatedly manufacture the same molded product, the movable part stops at the same position each time, and the current tends to concentrate in a specific phase.

Conventionally, a specific one-phase current circuit may be overloaded, resulting in thermal fatigue fracture.

The present invention has been made in view of the above problems, and a main object of the present invention is to provide an injection molding machine that suppresses thermal fatigue fracture of a current circuit.

In order to solve the above problems, according to one aspect of the present invention,
A three-phase AC motor that drives moving parts,
It has a control device that supplies a current to the three-phase AC motor based on the difference between the actual value and the set value of the physical quantity to be controlled.
The physical quantity is among the pressure of the molding material, the mold clamping force, the position of the movable part, the speed of the movable part, the nozzle touch force, the electric angle of the three-phase AC motor, and the mechanical angle of the three-phase AC motor. At least one
Said control device, the difference between the actual value and the set value of the physical quantity, and based on the magnitude of the current instantaneous value in each phase of the three-phase AC motor, and supplies a current to the three-phase AC motor, also, An injection molding machine is provided that supplies a current to the three-phase AC motor so that the magnitude of the instantaneous current value of any one phase of the three-phase AC motor is equal to or less than a threshold value .

According to one aspect of the present invention, there is provided an injection molding machine that suppresses thermal fatigue fracture of a current circuit.

It is a figure which shows the state at the time of completion of the mold opening of the injection molding machine by one Embodiment. It is a figure which shows the state at the time of mold clamping of the injection molding machine by one Embodiment. It is a figure which shows the control device by one Embodiment, and the three-phase AC motor controlled by the control device. It is a flowchart which shows an example of the process in the pressure holding process by a control device. It is a figure which shows an example of the time change of the speed and current of an injection motor, and the pressure of a molding material. It is a figure which shows another example of the time change of the speed and current of an injection motor, and the pressure of a molding material.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings, but in each drawing, the same or corresponding configurations are designated by the same or corresponding reference numerals and the description thereof will be omitted.

FIG. 1 is a diagram showing a state at the end of mold opening of the injection molding machine according to the embodiment. FIG. 2 is a diagram showing a state at the time of mold clamping of the injection molding machine according to one embodiment. As shown in FIGS. 1 and 2, the injection molding machine includes a frame Fr, a mold clamping device 10, an injection device 40, an ejector device 50, an injection device moving device 60, and a control device 90.

First, the mold clamping device 10 and the ejector device 50 will be described. In the description of the mold clamping device 10 and the ejector device 50, the moving direction of the movable platen 13 when the mold is closed (right direction in FIGS. 1 and 2) is set to the front, and the moving direction of the movable platen 13 when the mold is opened (FIGS. 1 and 2). The left direction in FIG. 2) will be described as the rear.

The mold clamping device 10 closes, clamps, and opens the mold of the mold apparatus 30. The mold clamping device 10 is, for example, a horizontal type, and the mold opening / closing direction is the horizontal direction. The mold clamping device 10 includes a fixed platen 12, a movable platen 13, a toggle support 15, a tie bar 16, a toggle mechanism 20, a mold clamping motor 25, and a motion conversion mechanism 26.

The fixed platen 12 is fixed to the frame Fr. The fixed mold 32 is attached to the surface of the fixed platen 12 facing the movable platen 13.

The movable platen 13 is movable along a guide (for example, a guide rail) 17 laid on the frame Fr, and is movable back and forth with respect to the fixed platen 12. The movable mold 33 is attached to the surface of the movable platen 13 facing the fixed platen 12.

By advancing and retreating the movable platen 13 with respect to the fixed platen 12, mold closing, mold clamping, and mold opening are performed. The mold device 30 is composed of the fixed mold 32 and the movable mold 33.

The toggle support 15 is connected to the fixed platen 12 at intervals, and is movably placed on the frame Fr in the mold opening / closing direction. The toggle support 15 may be movable along a guide laid on the frame Fr. The guide of the toggle support 15 may be the same as that of the guide 17 of the movable platen 13.

In the present embodiment, the fixed platen 12 is fixed to the frame Fr and the toggle support 15 is movable in the mold opening / closing direction with respect to the frame Fr, but the toggle support 15 is fixed to the frame Fr and the fixed platen. 12 may be movable in the mold opening / closing direction with respect to the frame Fr.

The tie bar 16 connects the fixed platen 12 and the toggle support 15 at intervals. A plurality of tie bars 16 may be used. Each tie bar 16 is parallel to the mold opening / closing direction and extends according to the mold clamping force. At least one tie bar 16 is provided with a mold clamping force detector 18. The mold clamping force detector 18 detects the mold clamping force by detecting the strain of the tie bar 16, and sends a signal indicating the detection result to the control device 90.

The mold clamping force detector 18 is not limited to the strain gauge type, but may be a piezoelectric type, a capacitive type, a hydraulic type, an electromagnetic type, or the like, and the mounting position thereof is not limited to the tie bar 16.

The toggle mechanism 20 is arranged between the movable platen 13 and the toggle support 15. The toggle mechanism 20 is composed of a crosshead 21, a pair of links, and the like. Each link group has a first link 22 and a second link 23 that are flexibly connected by a pin or the like. The first link 22 is swingably attached to the movable platen 13 with a pin or the like, and the second link 23 is swingably attached to the toggle support 15 with a pin or the like. The second link 23 is attached to the crosshead 21 via the third link 24. When the crosshead 21 is moved forward and backward, the first link 22 and the second link 23 bend and stretch, and the movable platen 13 moves back and forth with respect to the toggle support 15.

The configuration of the toggle mechanism 20 is not limited to the configuration shown in FIGS. 1 and 2. For example, in FIGS. 1 and 2, the number of nodes in each link group is 5, but it may be 4, and one end of the third link 24 is connected to the nodes of the first link 22 and the second link 23. May be done.

The mold clamping motor 25 is attached to the toggle support 15 and operates the toggle mechanism 20. The mold clamping motor 25 bends and stretches the first link 22 and the second link 23 by moving the crosshead 21 forward and backward, and moves the movable platen 13 forward and backward. The mold clamping motor 25 is directly connected to the motion conversion mechanism 26, but may be connected to the motion conversion mechanism 26 via a belt, a pulley, or the like.

The motion conversion mechanism 26 converts the rotational motion of the mold clamping motor 25 into a linear motion of the crosshead 21. The motion conversion mechanism 26 includes a screw shaft and a screw nut screwed onto the screw shaft. A ball or roller may be interposed between the screw shaft and the screw nut.

The mold clamping device 10 performs a mold closing step, a mold clamping step, a mold opening step, and the like under the control of the control device 90.

In the mold closing step, the movable platen 13 is advanced and the movable mold 33 is brought into contact with the fixed mold 32 by driving the mold clamping motor 25 to advance the crosshead 21 to the mold closing completion position at a set speed. The position and speed of the crosshead 21 are detected by using, for example, the encoder 25a of the mold clamping motor 25. The encoder 25a detects the rotation of the mold clamping motor 25 and sends a signal indicating the detection result to the control device 90.

In the mold clamping step, the mold clamping force 25 is further driven to further advance the crosshead 21 from the mold closing completion position to the mold clamping position to generate a mold clamping force. At the time of mold clamping, a cavity space 34 is formed between the movable mold 33 and the fixed mold 32, and the injection device 40 fills the cavity space 34 with a liquid molding material. A molded product is obtained by solidifying the filled molding material. The number of cavity spaces 34 may be plural, in which case a plurality of molded articles can be obtained at the same time.

In the mold opening step, the movable platen 13 is retracted by driving the mold clamping motor 25 to retract the crosshead 21 to the mold opening completion position at a set speed, and the movable mold 33 is separated from the fixed mold 32. After that, the ejector device 50 projects the molded product from the movable mold 33.

The mold clamping device 10 of the present embodiment has a mold clamping motor 25 as a drive source, but may have a hydraulic cylinder instead of the mold clamping motor 25. Further, the mold clamping device 10 may have a linear motor for opening and closing the mold and an electromagnet for mold clamping.

The ejector device 50 projects a molded product from the mold device 30. The ejector device 50 includes an ejector motor 51, a motion conversion mechanism 52, and an ejector rod 53.

The ejector motor 51 is attached to the movable platen 13. The ejector motor 51 is directly connected to the motion conversion mechanism 52, but may be connected to the motion conversion mechanism 52 via a belt, a pulley, or the like.

The motion conversion mechanism 52 converts the rotational motion of the ejector motor 51 into a linear motion of the ejector rod 53. The motion conversion mechanism 52 includes a screw shaft and a screw nut screwed onto the screw shaft. A ball or roller may be interposed between the screw shaft and the screw nut.

The ejector rod 53 is free to advance and retreat in the through hole of the movable platen 13. The front end portion of the ejector rod 53 comes into contact with a movable member 35 that is movably arranged inside the movable mold 33. The front end portion of the ejector rod 53 may or may not be connected to the movable member 35.

The ejector device 50 performs the ejection process under the control of the control device 90.

In the ejection step, the ejector motor 51 is driven to advance the ejector rod 53 at a set speed, thereby advancing the movable member 35 and projecting the molded product. After that, the ejector motor 51 is driven to retract the ejector rod 53 at a set speed, and the movable member 35 is retracted to the original position. The position and speed of the ejector rod 53 are detected by using, for example, the encoder 51a of the ejector motor 51. The encoder 51a detects the rotation of the ejector motor 51 and sends a signal indicating the detection result to the control device 90.

Next, the injection device 40 and the injection device moving device 60 will be described. In the description of the injection device 40 and the injection device moving device 60, unlike the description of the mold clamping device 10 and the like, the moving direction of the screw 43 during filling (left direction in FIGS. 1 and 2) is set to the front, and the screw 43 during weighing is set forward. The moving direction of (the right direction in FIGS. 1 and 2) will be described as the rear.

The injection device 40 is installed on a slide base Sb that can move forward and backward with respect to the frame Fr, and is adjustable with respect to the mold device 30. The injection device 40 is touched by the mold device 30, and fills the cavity space 34 in the mold device 30 with a molding material. A molded product is obtained by cooling and solidifying the molding material filled in the cavity space 34. The injection device 40 includes, for example, a cylinder 41, a nozzle 42, a screw 43, a cooler 44, a measuring motor 45, an injection motor 46, a pressure detector 47, a heater 48, and a temperature detector 49.

The cylinder 41 heats the molding material supplied internally from the supply port 41a. The supply port 41a is formed at the rear of the cylinder 41. A cooler 44 such as a water-cooled cylinder is provided on the outer periphery of the rear portion of the cylinder 41. A heater 48 such as a band heater and a temperature detector 49 are provided on the outer periphery of the cylinder 41 in front of the cooler 44.

The cylinder 41 is divided into a plurality of zones in the axial direction of the cylinder 41 (left-right direction in FIGS. 1 and 2). A heater 48 and a temperature detector 49 are provided in each zone. For each zone, the control device 90 controls the heater 48 so that the detection temperature of the temperature detector 49 reaches the set temperature.

The nozzle 42 is provided at the front end of the cylinder 41 and is pressed against the mold device 30. A heater 48 and a temperature detector 49 are provided on the outer periphery of the nozzle 42. The control device 90 controls the heater 48 so that the detection temperature of the nozzle 42 reaches the set temperature.

The screw 43 is rotatably and movably arranged in the cylinder 41. When the screw 43 is rotated, the molding material is fed forward along the spiral groove of the screw 43. The molding material is gradually melted by the heat from the cylinder 41 while being fed forward. As the liquid molding material is fed forward of the screw 43 and accumulated in the front of the cylinder 41, the screw 43 is retracted. After that, when the screw 43 is advanced, the molding material in front of the screw 43 is ejected from the nozzle 42 and filled in the mold device 30.

The weighing motor 45 rotates the screw 43.

The injection motor 46 advances and retreats the screw 43. The rotational motion of the injection motor 46 is converted into a linear motion of the screw 43 by a motion conversion mechanism such as a ball screw.

The pressure detector 47 is provided in the force transmission path between the injection motor 46 and the screw 43, and detects the load acting on the pressure detector 47. The pressure detector 47 sends a signal indicating the detection result to the control device 90. The detection result of the pressure detector 47 is used for controlling and monitoring the pressure received by the screw 43 from the molding material, the back pressure on the screw 43, the pressure acting on the molding material from the screw 43, and the like.

The injection device 40 performs a filling step, a pressure holding step, a weighing step, and the like under the control of the control device 90.

In the filling step, the injection motor 46 is driven to advance the screw 43 at a set speed, and the liquid molding material accumulated in front of the screw 43 is filled in the cavity space 34 in the mold apparatus 30. The position and speed of the screw 43 are detected by using, for example, the encoder 46a of the injection motor 46. The encoder 46a detects the rotation of the injection motor 46 and sends a signal indicating the detection result to the control device 90. When the position of the screw 43 reaches the set position, switching from the filling process to the pressure holding process (so-called V / P switching) is performed. The set speed of the screw 43 may be changed according to the position and time of the screw 43.

After the position of the screw 43 reaches the set position in the filling step, the screw 43 may be temporarily stopped at the set position, and then V / P switching may be performed. Immediately before the V / P switching, the screw 43 may be moved forward or backward at a slow speed instead of stopping the screw 43.

In the pressure holding step, the injection motor 46 is driven to push the screw 43 forward at a set pressure to apply pressure to the molding material in the mold apparatus 30. The shortage of molding material due to cooling shrinkage can be replenished. The pressure of the molding material is detected using, for example, a pressure detector 47. The pressure detector 47 sends a signal indicating the detection result to the control device 90.

In the pressure holding step, the molding material in the cavity space 34 is gradually cooled, and at the end of the pressure holding step, the inlet of the cavity space 34 is closed with the solidified molding material. This state is called a gate seal, and backflow of the molding material from the cavity space 34 is prevented. After the pressure holding step, the cooling step is started. In the cooling step, the molding material in the cavity space 34 is solidified. A weighing step may be performed during the cooling step to shorten the molding cycle.

In the weighing step, the weighing motor 45 is driven to rotate the screw 43 at a set rotation speed, and the molding material is fed forward along the spiral groove of the screw 43. Along with this, the molding material is gradually melted. As the liquid molding material is fed forward of the screw 43 and accumulated in the front of the cylinder 41, the screw 43 is retracted. The rotation speed of the screw 43 is detected by using, for example, the encoder 45a of the measuring motor 45. The encoder 45a sends a signal indicating the detection result to the control device 90.

In the weighing step, the injection motor 46 may be driven to apply a set back pressure to the screw 43 in order to limit the sudden retreat of the screw 43. The back pressure on the screw 43 is detected using, for example, a pressure detector 47. The pressure detector 47 sends a signal indicating the detection result to the control device 90. When the screw 43 retracts to the set position and a predetermined amount of molding material is accumulated in front of the screw 43, the weighing process ends.

The injection device 40 of the present embodiment is an in-line screw type, but may be a pre-plastic type. The pre-plastic injection device supplies the molded material melted in the plasticized cylinder to the injection cylinder, and injects the molding material from the injection cylinder into the mold device. A screw is rotatably or rotatably arranged in the plasticized cylinder and can be moved forward and backward, and a plunger is rotatably arranged in the injection cylinder.

The injection device moving device 60 has an injection device moving motor 61 that moves the injection device 40 with respect to the mold device 30 under the control of the control device 90. The rotary motion of the injection device moving motor 61 is converted into a linear motion of the injection device 40 by a motion conversion mechanism such as a ball screw.

The injection device moving device 60 of the present embodiment is an electric type, but may be a hydraulic type.

The injection device moving device 60 suppresses leakage of the molding material from between the mold device 30 and the nozzle 42 by pressing the nozzle 42 against the mold device 30 in the filling step and the pressure holding step. The process of pressing the nozzle 42 against the mold device 30 is called a nozzle touch process, and the force of pressing the nozzle 42 against the mold device 30 is called a nozzle touch force.

In order to protect the mold device 30 and the mold clamping device 10, the injection device moving device 60 reduces the nozzle touch force after the pressure holding step and before the next filling step, or reduces the nozzle touch force from the mold device 30 to the nozzle 42. May be released.

The injection device moving device 60 presses the nozzle 42 against the mold device 30 before the start of the cycle operation for repeatedly manufacturing the same molded product, and reduces the nozzle touch force after the cycle operation is completed, or from the mold device 30. The nozzle 42 may be released.

As shown in FIGS. 1 and 2, the control device 90 includes a CPU (Central Processing Unit) 91, a storage medium 92 such as a memory, an input interface 93, and an output interface 94. The control device 90 performs various controls by causing the CPU 91 to execute the program stored in the storage medium 92. Further, the control device 90 receives a signal from the outside at the input interface 93 and transmits the signal to the outside at the output interface 94.

FIG. 3 is a diagram showing a control device according to an embodiment and a three-phase AC motor controlled by the control device. Examples of the three-phase AC motor 110 include a mold clamping motor 25, an injection motor 46, an ejector motor 51, and an injection device moving motor 61.

The control device 90 includes, for example, a power supply unit 95 that supplies power from the power supply 100 to the three-phase AC motor 110. The power supply unit 95 uses, for example, a converter 96 that converts AC power supplied from the power supply 100 into DC power, a DC link 97 that supplies DC power from the converter 96, and DC power supplied from the DC link 97. It has an inverter 98 that converts electric power and supplies it to the three-phase AC motor 110.

The inverter 98 has, for example, three legs composed of two switching elements. The number of legs is not particularly limited. Specific examples of the switching element include MOSFETs (Metal Oxide Semiconductor Filed-Effect Transistors), IGBTs (Insulated Gate Bipolar Transistors), bipolar transistors, and the like. Diodes are connected in antiparallel to each switching element. The diode may be built in each switching element.

The control device 90 further includes, for example, a signal generation unit 99 that generates a signal for controlling the switching element of the inverter 98. The signal generation unit 99 performs an operation such as a PID (Proportional, Integration and Differential) operation based on the difference between the actual value and the set value of the physical quantity to be controlled (hereinafter, also referred to as “control amount”). A current command is obtained so that the above difference becomes zero, and a PWM (Pulse Width Modulation) signal is generated by comparing the current command with the carrier wave. The inverter 98 switches according to the PWM signal from the signal generation unit 99, and supplies an alternating current to the three-phase alternating current motor 110.

In FIG. 3, the number of the three-phase AC motor 110 is one, but the number may be plural. A plurality of inverters 98 are provided corresponding to the plurality of three-phase AC motors 110. The plurality of inverters 98 may be connected in parallel to one converter 96, or one converter 96 may supply DC power to the plurality of inverters 98. A plurality of converters 96 may be provided corresponding to the plurality of inverters 98.

The control device 90 controls, for example, the injection motor 46 to control the pressure holding process. In the pressure holding step, the controlled amount is the pressure of the molding material, the actual value Pa is detected by the pressure detector 47, and the set value Pref is stored in the storage medium 92 in advance. The control device 90 controls the injection motor 46 so that the difference between the actual value Pa and the set value Pref becomes zero.

The control device 90 keeps the state of the injection motor 46 in a low speed and high output state in the pressure holding step. In this state, the instantaneous current values Iu, Iv, and Iw of each phase supplied to the injection motor 46 become substantially constant, and a large current may continue to concentrate in any one of the phases. Here, Iu represents the instantaneous current value of the U phase, Iv represents the instantaneous current value of the V phase, and Iw represents the instantaneous current value of the W phase.

Therefore, in the pressure holding step, the control device 90 is based on the difference between the actual value Pa and the set value Pref and the balance of the magnitudes of the instantaneous current values of each phase | Iu |, | Iv |, | Iw |. A current is supplied to the injection motor 46. As a result, it is possible to prevent a large current from being continuously concentrated on one of the three phases.

FIG. 4 is a flowchart showing an example of processing in the pressure holding process by the control device. The process shown in FIG. 4 is started at the time of V / P switching. Immediately after the V / P switching, the control device 90 supplies a current to the injection motor 46 so that the difference between the actual value Pa and the set value Pref becomes zero.

In step S11 shown in FIG. 4, the control device 90 checks whether or not the magnitude | Pref-Pa | of the difference between the actual value Pa and the set value Pref is equal to or less than the threshold value Pth. The threshold value Pth is obtained in advance by a test or the like and is stored in the storage medium 92. The threshold value Pth is set based on, for example, the defective rate of the molded product.

When | Pref-Pa | exceeds Pth (step S11, No), the pressure of the molding material is out of the permissible range, so the control device 90 returns to step S11 and continues the processing after step S11.

On the other hand, when | Pref-Pa | is Pth or less (step S11, Yes), the pressure of the molding material is within the permissible range, and the injection motor 46 is in a low speed / high output state. Since it is presumed, the control device 90 proceeds to step S12. In the processing after step S12, the balance of | Iu |, | Iv |, | Iw | is checked, which will be described in detail later.

In step S11, the control device 90 may actually confirm whether or not the state of the injection motor 46 is a state of low speed and high output. The speed of the injection motor 46 can be detected by an encoder 46a or the like. The output of the injection motor 46 is represented by a torque detection value, a torque command, a current detection value, a current command, and the like. When the speed of the injection motor 46 is equal to or less than the threshold value Vth and the output of the injection motor 46 is equal to or greater than the threshold value Tth, it is determined that the state of the injection motor 46 is a low speed / high output state. These threshold values Vth and Tth are obtained by, for example, a thermal fatigue fracture test of a current circuit or a thermal stress analysis.

If it is confirmed that the injection motor 46 is not in a low-speed, high-output state, there is no risk that a large current will continue to concentrate in any one of the three phases, and thermal fatigue failure of the current circuit will occur. Absent. Therefore, in this case, the control device 90 does not have to perform the processing after step S12, and does not have to check the balance of | Iu |, | Iv |, | Iw |. In this case, the control device 90 may supply a current to the injection motor 46 based on the difference between the actual value Pa and the set value Pref until the end of the pressure holding process as usual. On the other hand, when it is confirmed that the state of the injection motor 46 is a low speed and high output state, the control device 90 proceeds to step S12.

In step S12, the control device 90 checks whether | Iu | is Is or less. If Is is a threshold value and | Iu | is Is or less, the remaining | Iv | and | Iw | are set to be substantially the same.

The electric angle of the U phase, the electric angle of the V phase, and the electric angle of the W phase are deviated by 120 °. Therefore, as the magnitude of the instantaneous current value of any one phase approaches zero, the magnitude of the instantaneous current value of the remaining two phases approaches the same value.

When | Iu | exceeds Is (step S12, No), the current is not dispersed in the V phase and the W phase, and a large current may continue to concentrate in one of the three phases. , The control device 90 proceeds to step S13. In step S13, the control device 90 checks whether | Iv | is Is or less. When | Iv | exceeds Is (step S13, No), the current is not dispersed in the W phase and the U phase, and a large current may continue to concentrate in one of the three phases. , The control device 90 proceeds to step S14. In step S14, the control device 90 checks whether | Iw | is Is or less. When | Iw | exceeds Is (step S14, No), the current is not dispersed in the U phase and the V phase, and a large current may continue to concentrate in one of the three phases. , The control device 90 proceeds to step S15.

In step S15, the control device 90 rotates the electric angle of each phase of the injection motor 46 so that any one of | Iu |, | Iv |, | Iw | is Is or less. As a result, the current can be distributed to the remaining two phases.

The electric angle of each phase of the injection motor 46 is obtained from a current command or the like. While the electric angle of each phase of the injection motor 46 is rotated by 60 °, any of | Iu |, | Iv |, and | Iw | becomes Is or less. The control device 90 may rotate the electric angle of each phase of the injection motor 46 by 60 ° or more.

The amount of rotation of the electric angle of each phase of the injection motor 46 is set so that the difference between the actual value Pa and the set value Pref is within an allowable range. Since the number of pole pairs of the injection motor 46 is usually 2 or more, the rotation amount of the mechanical angle is less than half the rotation amount of the electric angle. Since the amount of rotation of the mechanical angle is small compared to the amount of rotation of the electric angle, the position fluctuation of the screw 43 due to the rotation of the electric angle is small. Therefore, the fluctuation of the actual value Pa is small, and the difference between the actual value Pa and the set value Pref can be kept within the permissible range.

FIG. 5 is a diagram showing an example of time-dependent changes in the speed and current of the injection motor and the pressure of the molding material. In FIG. 5, at time t1, the injection motor 46 is in a low-speed, high-output state, and | Iu |, | Iv |, and | Iw | are all larger than Is, and a large current is in the V phase. focusing.

Therefore, as shown in FIG. 5, the control device 90 rotates the electric angle of each phase from the time t1 to the time t2 to set | Iw | to Is or less. As a result, the current is dispersed into the V phase and the U phase, so that it is possible to prevent a large current from continuing to concentrate in the V phase.

In FIG. 5, from time t1 to time t2, the electric angles of each phase of the injection motor 46 are rotated in the direction of reducing the driving force of the injection motor 46, that is, in the direction of retracting the screw 43. The maximum value of | Iu |, | Iv |, | Iw | at time t2 is smaller than the maximum value of | Iu |, | Iv |, | Iw | at time t1.

FIG. 6 is a diagram showing another example of the time variation of the speed and current of the injection motor and the pressure of the molding material. In FIG. 6, at time t1, the injection motor 46 is in a low-speed, high-output state, and | Iu |, | Iv |, and | Iw | are all larger than Is, and a large current is in the V phase. focusing.

Therefore, as shown in FIG. 6, the control device 90 rotates the electric angle of each phase of the injection motor 46 from the time t1 to the time t2 to set | Iu | to Is or less. As a result, the current is dispersed into the V phase and the W phase, so that it is possible to prevent a large current from continuing to concentrate in the V phase.

In FIG. 6, from time t1 to time t2, the electric angles of each phase of the injection motor 46 are rotated in the direction of increasing the driving force of the injection motor 46, that is, in the direction of advancing the screw 43. The maximum value of | Iu |, | Iv |, | Iw | at time t2 is smaller than the maximum value of | Iu |, | Iv |, | Iw | at time t1.

After step S15, the control device 90 may fix the electrical angle of each phase of the injection motor 46 to keep the position of the screw 43 until the end of the pressure holding step, but in FIG. 4, step S11 Return to, and the process after step S11 is continued. By returning to step S11, after step S15, it can be confirmed whether or not the difference between the actual value Pa and the set value Pref is within the permissible range.

On the other hand, when | Iu | is Is or less (step S12, Yes), | Iv | is Is or less (step S13, Yes), or | Iw | is Is or less (step S14, Yes). , The current is distributed in either two phases. Therefore, since the thermal fatigue failure of the current circuit can be suppressed, the control device 90 proceeds to step S16.

In step S16, the control device 90 fixes the electrical angle of each phase of the injection motor 46 to hold the position of the screw 43. At this time, the control device 90 may use the position of the screw 43 as the control amount instead of the pressure of the molding material. That is, the control device 90 may perform position control instead of pressure control.

After step S16, the control device 90 may fix the electrical angle of each phase of the injection motor 46 until the end of the pressure holding step, but in FIG. 4, the process proceeds to step S17. The processing after step S17 is for coping with the fluctuation of the actual value Pa with the passage of time. The fluctuation of the actual value Pa occurs, for example, when the molding material in the mold apparatus 30 gradually solidifies. It is effective when the volume change of the molding material due to the temperature change is large, or when the quality of the molded product tends to depend on the actual value Pa.

In step S17, the control device 90 checks whether | Pref-Pa | is larger than Pth. The threshold value Pth used in step S17 and the threshold value Pth used in step S11 have the same value in FIG. 4, but may be different values.

When | Pref-Pa | is larger than Pth (step S17, Yes), the pressure fluctuation of the molding material is large, so the control device 90 proceeds to step S18. In step S18, the control device 90 may release the fixation of the electric angle of each phase of the injection motor 46, and may release the position control. The control device 90 performs pressure control instead of position control. Specifically, the control device 90 supplies a current to the injection motor 46 so that the difference between the actual value Pa and the set value Pref becomes zero. After that, the control device 90 returns to step S11 and continues the processing after step S11.

On the other hand, when | Pref-Pa | is Pth or less (steps S17, No), the pressure of the molding material is maintained within the permissible range, so that the control device 90 proceeds to step S19. In step S19, the control device 90 checks whether or not the end condition of the pressure holding process is satisfied. The end condition of the pressure holding process is, for example, that the elapsed time from V / P switching has reached a predetermined time.

When continuing the pressure holding step (step S19, No), the control device 90 returns to step S16 and continues the processing after step S16.

On the other hand, when the pressure holding step is completed (step S19, Yes), the control device 90 ends the current process.

In the present embodiment, the set value Pref is constant from the start to the end of the pressure holding process, but may be switched according to the elapsed time from the start of the pressure holding process. When the set value Pref is switched, the control device 90 returns to step S11 and performs the processes after step S11.

As described above, in the pressure holding process, the control device 90 has the difference between the actual value Pa and the set value Pref, and the magnitude of the instantaneous current value in each phase of the injection motor 46 | Iu |, | Iv |, | A current is supplied to the injection motor 46 based on the balance of Iw |. As a result, it is possible to prevent a large current from being continuously concentrated on one of the three phases.

The control device 90 supplies a current to the injection motor 46 so that the difference between the actual value Pa and the set value Pref is within the permissible range and the magnitude of the instantaneous current value of any one phase is equal to or less than the threshold value Is. May be supplied. As a result, the current can be distributed to the remaining two phases.

When the difference between the actual value Pa and the set value Pref is within the permissible range, the control device 90 determines whether or not the magnitude of the instantaneous current value of any one phase is equal to or less than the threshold value Is. If the magnitude of the instantaneous current value of any one phase is equal to or less than the threshold value Is, it can be determined that the current is dispersed in the remaining two phases.

In order to directly confirm that the current is dispersed in any two phases, the control device 90 determines the magnitude of the instantaneous current value of any one phase and the instantaneous current value of any one of the remaining phases. It may be determined whether or not the size is equal to or less than the threshold value. For example, in step S12, instead of determining whether | Iu | is Is or less, it may be determined whether or not the difference between | Iv | and | Iw | is less than or equal to the threshold value. Further, in step S13, instead of determining whether or not | Iv | is Is or less, it may be determined whether or not the difference between | Iw | and | Iu | is equal to or less than the threshold value. Further, in step S14, instead of determining whether or not | Iw | is Is or less, it may be determined whether or not the difference between | Iu | and | Iv | is equal to or less than the threshold value. While the determination of this modification can directly confirm that the current is dispersed in any two phases, the determination shown in FIG. 4 can be easily performed.

In the control device 90, when the difference between the actual value Pa and the set value Pref is within the permissible range, the magnitudes of the instantaneous current values of each phase | Iu |, | Iv |, | Iw | all set the threshold value Is. If it is determined that the value is exceeded, the electric angle of each phase of the injection motor 46 is rotated. The amount of rotation of the electric angle of each phase of the injection motor 46 is set so that any one of | Iu |, | Iv |, and | Iw | is Is or less. As a result, the current can be distributed to the remaining two phases.

The electric angle of each phase of the injection motor 46 is obtained from a current command or the like. While the electric angle of each phase of the injection motor 46 is rotated by 60 °, any of | Iu |, | Iv |, and | Iw | becomes Is or less. The control device 90 may rotate the electric angle of each phase of the injection motor 46 by 60 ° or more.

The amount of rotation of the electric angle of each phase of the injection motor 46 may be set so that the difference between the actual value Pa and the set value Pref is within an allowable range. The amount of rotation of the electric angle of each phase of the injection motor 46 may be set so that the difference between the actual value Pa and the set value Pref is out of the permissible range. In this case, the control device 90 performs the following controls (1) to (3) so that the electric angles of each phase do not return to their original values after the rotation of the electric angles of each phase.

(1) The control device 90 uses the position of the screw 43 as the control amount instead of the pressure of the molding material. That is, the control device 90 performs position control instead of pressure control. Specifically, the control device 90 holds the position of the screw 43. Therefore, the electric angle of each phase of the injection motor 46 is fixed to the electric angle after rotation.

(2) The control device 90 may continue to use the pressure of the molding material as the control amount, and after the electric angle of each phase rotates, the current command created based on the difference between the actual value Pa and the set value Pref is given. It may be corrected so that it is fixed to the electric angle of.

(3) The control device 90 may continue to use the pressure of the molding material as the control amount, widely change the permissible range of the difference between the actual value Pa and the set value Pref, and make the difference within the permissible range after the change. By accommodating, the electric angle of each phase may be fixed to the electric angle after rotation. However, if the difference does not fall within the changed permissible range, the control device 90 may rotate the electrical angle of each phase again so that the difference falls within the changed permissible range.

The controls (1) to (3) above can also be applied when the electric angle is fixed after step S15 or when the electric angle is fixed in step S16. When the control of (3) is performed in step S16, the threshold value Pth in step S17 may be set larger than the threshold value Pth in step S11.

As used herein, the term "fixed electrical angle" includes not only the case where the electrical angle is completely fixed without any fluctuation, but also the case where the electrical angle fluctuates slightly within an error range. ..

The direction of rotating the electric angle of each phase of the injection motor 46 may be a direction of reducing the driving force of the injection motor 46, that is, a direction of retracting the screw 43, or a direction of increasing the driving force of the injection motor 46, that is, , The direction in which the screw 43 is advanced may be used. By rotating the electric angle of each phase of the injection motor 46, the maximum values of | Iu |, | Iv |, | Iw | may be reduced.

The direction of rotating the electric angle of each phase of the injection motor 46 may be the direction in which the amount of rotation of the electric angle until any one of | Iu |, | Iv |, | Iw | becomes Is or less is small. Since the amount of rotation of the electric angle can be minimized, the fluctuation of the actual value Pa can be minimized.

Examples of the control for rotating the electric angle of each phase of the injection motor 46 include the following controls (1) to (3).

(1) The control device 90 uses the position of the screw 43 as the control amount instead of the pressure of the molding material. That is, the control device 90 performs position control instead of pressure control. Specifically, the control device 90 corrects the position of the screw 43 and rotates the electric angle of each phase of the injection motor 46.

As the control amount of the position control, the electric angle or the mechanical angle of the injection motor 46 may be used instead of the position of the screw 43.

(2) The control device 90 uses the speed of the screw 43 as the control amount instead of the pressure of the molding material. That is, the control device 90 performs speed control instead of pressure control. Specifically, the control device 90 corrects the speed of the screw 43, corrects the position of the screw 43, and rotates the electric angle of each phase of the injection motor 46.

(3) The control device 90 may continue to use the pressure of the molding material as the control amount, and the electric angle of each phase rotates with the current command created based on the difference between the actual value Pa and the set value Pref. Correct as follows.

On the other hand, when the control device 90 determines that the magnitude of the instantaneous current value of any one phase of the injection motor 46 is equal to or less than the threshold value Is when the difference between the actual value Pa and the set value Pref is within the allowable range. , The electric angle of each phase of the injection motor 46 may be fixed. If the magnitude of the instantaneous current value of any one phase is Is or less, the current is already dispersed in the remaining two phases.

When the electric angle of each phase of the injection motor 46 is fixed, the control device 90 determines whether or not the difference between the actual value Pa and the set value Pref is within the permissible range. As a result, it is possible to deal with fluctuations in the actual value Pa with the passage of time. The fluctuation of the actual value Pa occurs, for example, when the molding material in the mold apparatus 30 gradually solidifies. It is effective when the volume change of the molding material due to the temperature change is large, or when the quality of the molded product tends to depend on the actual value Pa.

As shown in FIG. 4, when the difference between the actual value Pa and the set value Def is within the permissible range (step S11, Yes), the control device 90 has an instantaneous current value of any one phase of the injection motor 46. (Steps S12 to S14) are determined as to whether or not the magnitude of is equal to or less than the threshold value Is, but the present invention is not limited thereto.

Of the three-phase instantaneous current values Iu, Iv, and Iw, if the maximum value is expressed as Imax, the intermediate value is expressed as Imid, and the minimum value is expressed as Imin, the total sum of Imax, Imid, and Imin is generally zero. That is, the equation of Imax + Imid + Imin = 0 holds.

Therefore, instead of determining whether (A) | Iu |, | Iv |, | Iw | is equal to or less than the threshold value Is, (B) the magnitude of the intermediate value Imide | Imid | is equal to or less than the threshold value Is. You may only judge whether or not.

Further, since the equation | Imid | = | Imax + Imin | holds, it may be determined whether (C) | Imax + Imin | is equal to or less than the threshold value Is. Here, | Imax + Imin | represents the magnitude of the sum of Imax and Imin.

The judgments (A), (B), and (C) above are substantially the same judgment, and if any one judgment is made, the other three judgments are made.

When the formula of | Imid | = 0 holds, the formula of | Imax | = | Imin | holds. Therefore, it may be determined whether or not the magnitude of the difference between | Imax | and | Imin | is equal to or less than the threshold value. Here, | Imax | represents the magnitude of Imax, and | Imin | represents the magnitude of Imin.

The control device 90 determines the position of the screw 43 in which the difference between the actual value Pa and the set value Pref is within the permissible range and the magnitude of the instantaneous current value of any one phase of the injection motor 46 is equal to or less than the threshold value Is. You may ask. The position can be predicted based on past performance. Since the injection molding machine repeats the same operation in order to repeatedly manufacture the same molded product, it is possible to make a prediction based on past results. That is, the control device 90 may have a learning function. In this case, the control device 90 may move the screw 43 to a position determined in advance after the start of the pressure holding process, and may hold the screw 43 at that position.

Further, the control device 90 may make another determination instead of determining whether or not the magnitude of the instantaneous current value of any one phase of the injection motor 46 is equal to or less than the threshold value Is (steps S12 to S14). Good. For example, the control device 90 keeps the difference between the actual value Pa and the set value Pref within an allowable range, and reduces the maximum values of | Iu |, | Iv |, | Iw | so that the electricity of each phase is reduced. You may decide whether it is possible to rotate the corner. The determination is made based on, for example, past data stored in association with the amount of rotation and the direction of rotation of the electric angle and the amount of fluctuation of the actual value Pa. When the control device 90 determines that the difference between the actual value Pa and the set value Pref can be maintained within an allowable range and the maximum values of | Iu |, | Iv |, | Iw | can be reduced, the electricity thereof Perform a corner rotation. The rotation of the electric angle may be performed regardless of the determination result of whether or not the magnitude of the instantaneous current value of any one phase of the injection motor 46 is equal to or less than the threshold value Is.

Further, the control device 90 may determine the balance of | Iu |, | Iv |, | Iw | of the current shot based on the balance of | Iu |, | Iv |, | Iw | of the past shots. .. In one shot, a mold closing step, a mold clamping step, a filling step, a pressure holding step, a cooling step, a mold opening step and the like are performed. Here, the past shot may be the most recent single shot or the most recent plurality of shots. For example, the control device 90 maintains the difference between the actual value Pa and the set value Pref within an allowable range in the pressure holding process of each shot, and sets the phase in which the magnitude of the instantaneous current value is minimized in each shot. The U phase, the V phase, and the W phase may be changed in this order. Since the phase in which the magnitude of the instantaneous current value is maximized is not fixed, thermal fatigue fracture can be further suppressed. The order is not particularly limited, and may be, for example, the order of U phase, W phase, and V phase. Further, the phase change that minimizes the magnitude of the instantaneous current value may be changed for each shot or for each of a plurality of shots. The phase having the smallest instantaneous current value may be alternately selected between two of the three phases. Further, the phase in which the magnitude of the instantaneous current value is minimized may be randomly selected instead of the order.

Although the embodiments of the injection molding machine have been described above, the present invention is not limited to the above-described embodiments and the like, and various modifications are made within the scope of the gist of the present invention described in the claims. It can be improved.

When the control device 90 keeps the state of the three-phase AC motor 110 in the low-speed and high-output state, the difference between the actual value and the set value of the control amount and the instantaneous current value in each phase of the three-phase AC motor 110. The current may be supplied to the three-phase AC motor 110 based on the balance of the magnitudes of. The type of the three-phase AC motor 110 and the type of the movable portion driven by the three-phase AC motor 110 are not particularly limited.

The control device 90 keeps the state of the injection motor 46 in a low speed and high output state when the speed of the screw 43 is reduced, such as by temporarily stopping the screw 43 immediately before the V / P switching. Therefore, when the speed of the screw 43 is reduced immediately before the V / P switching, the control device 90 increases the difference between the actual value and the set value of the control amount and the instantaneous current value in each phase of the injection motor 46. The current may be supplied to the injection motor 46 based on the balance. In this case, the movable part is, for example, the screw 43, and the control amount is the position or speed of the screw 43. When the injection device is a pre-plastic type, the movable part is a plunger.

The control device 90 keeps the state of the mold clamping motor 25 in a low speed and high output state in the mold clamping step. Therefore, in the mold clamping process, the control device 90 applies a current to the mold clamping motor 25 based on the balance between the actual value of the controlled amount and the set value and the magnitude of the instantaneous current value in each phase of the mold clamping motor 25. May be supplied. In this case, the movable portion is, for example, the crosshead 21, and the control amount is the position of the crosshead 21. The movable portion may be the movable platen 13, and the control amount may be the position of the movable platen 13. Further, the control amount may be a mold clamping force.

By the way, the mold clamping device 10 is a horizontal type in which the mold opening / closing direction is horizontal in FIGS. 1 and 2, but it may be a vertical type in which the mold opening / closing direction is vertical. The vertical clamping device includes a lower platen, an upper platen, a toggle support, a toggle mechanism, a tie bar, and the like. One of the lower platen and the upper platen is used as a fixed platen, and the other one is used as a movable platen. A lower mold is attached to the lower platen, and an upper mold is attached to the upper platen. A mold device is composed of a lower mold and an upper mold. The lower mold may be attached to the lower platen via a rotary table. The toggle support is located below the lower platen. The toggle mechanism is disposed between the toggle support and the lower platen. The tie bar is parallel in the vertical direction, penetrates the lower platen, and connects the upper platen and the toggle support.

When the upper platen is a movable platen and the lower platen is a fixed platen, the mold opening process is performed by raising the upper platen. Since the toggle mechanism is in the folded state after the mold opening process is completed, the toggle magnification is small, and the control device 90 keeps the mold clamping motor in a low speed and high output state until the mold closing process is started. Therefore, the control device 90 balances the difference between the actual value and the set value of the controlled amount and the magnitude of the instantaneous current value in each phase of the mold clamping motor after the mold opening process is completed and before the mold closing process is started. The current may be supplied to the mold clamping motor based on the above. In this case, the movable portion is, for example, the crosshead 21, and the control amount is the position of the crosshead 21. The movable portion may be a movable platen, and the control amount may be the position of the movable platen.

The control device 90 keeps the state of the injection device moving motor 61 in a low speed and high output state when the nozzle is touched. Therefore, the control device 90 determines the injection device moving motor 61 based on the balance between the actual value of the controlled amount and the set value and the magnitude of the instantaneous current value in each phase of the injection device moving motor 61 when the nozzle is touched. You may supply current to. In this case, the movable part is, for example, the injection device 40, and the control amount is the position of the injection device 40 or the nozzle touch force.

The control device 90 may maintain the state of the ejector motor 51 in a low speed and high output state in the ejection process. As such a case, for example, there is a case where the molded product is in close contact with the mold apparatus 30, and the close contact force hinders the advance of the ejector rod 53. Therefore, in the ejection process, the control device 90 supplies a current to the ejector motor 51 based on the balance between the actual value of the controlled amount and the set value and the magnitude of the instantaneous current value in each phase of the ejector motor 51. You may. In this case, the movable part is, for example, the ejector rod 53, and the control amount is the position or speed of the ejector rod 53.

The ejector device 50 may also serve as a compression device that compresses the molding material in the cavity space in the mold device 30. In this case, the ejector motor 51 also serves as the compression motor of the compression device. The compression device may be provided separately from the ejector device 50.

The compression device includes a compression motor that moves a compression core arranged in the mold device 30. A motion conversion unit that converts the rotational motion of the compression motor into the linear motion of the compression core may be provided between the compression motor and the compression core.

The control device 90 keeps the state of the compression motor in a low speed and high output state in the compression step of compressing the molding material in the cavity space in the mold device 30. Therefore, in the compression process, the control device 90 supplies a current to the compression motor based on the balance between the actual value of the controlled amount and the set value and the magnitude of the instantaneous current value in each phase of the compression motor. May be good. In this case, the moving part is, for example, a compression core, and the control amount is the position or speed of the compression core.

10 Mold clamping device 20 Toggle mechanism 21 Cross head 25 Mold clamping motor 40 Injection device 43 Screw 46 Injection motor 50 Ejector device 51 Ejector motor 53 Ejector rod 60 Injection device moving device 61 Injection device moving motor 90 Control device 95 Power supply unit 99 Signal Generator

Claims (10)

A three-phase AC motor that drives moving parts,
It has a control device that supplies a current to the three-phase AC motor based on the difference between the actual value and the set value of the physical quantity to be controlled.
The physical quantity is among the pressure of the molding material, the mold clamping force, the position of the movable part, the speed of the movable part, the nozzle touch force, the electric angle of the three-phase AC motor, and the mechanical angle of the three-phase AC motor. At least one
Said control device, the difference between the actual value and the set value of the physical quantity, and based on the magnitude of the current instantaneous value in each phase of the three-phase AC motor, and supplies a current to the three-phase AC motor, also, An injection molding machine that supplies a current to the three-phase AC motor so that the magnitude of the instantaneous current value of any one phase of the three-phase AC motor is equal to or less than a threshold value . In the control device, the difference between the actual value of the physical quantity and the set value is within the allowable range, and the magnitude of the instantaneous current value of any one phase of the three-phase AC motor is equal to or less than the threshold value. The injection molding machine according to claim 1, wherein an electric current is supplied to the three-phase AC motor. Whether or not the magnitude of the instantaneous current value of any one phase of the three-phase AC motor is equal to or less than the threshold value when the difference between the actual value of the physical quantity and the set value is within the allowable range. The injection molding machine according to claim 1 or 2, wherein the determination is made. When the control device determines that the magnitude of the instantaneous current value of each phase of the three-phase AC motor exceeds the threshold value when the difference between the actual value of the physical quantity and the set value is within the allowable range, When the electric angle of each phase of the three-phase AC motor is rotated , or when the difference between the actual value and the set value of the physical quantity is within the allowable range, the current instantaneous current of any one phase of the three-phase AC motor The injection molding machine according to any one of claims 1 to 3 , wherein when it is determined that the magnitude of the value is equal to or less than the threshold value, the electric angle of each phase of the three-phase AC motor is fixed . Claimed that the control device determines whether or not the difference between the actual value of the physical quantity and the set value is within an allowable range when the electric angle of each phase of the three-phase AC motor is fixed. The injection molding machine according to any one of 1 to 4 . The control device is a movable unit in which the difference between the actual value of the physical quantity and the set value is within an allowable range, and the magnitude of the instantaneous current value of any one phase of the three-phase AC motor is equal to or less than a threshold value. The injection molding machine according to any one of claims 1 to 5 , wherein the position of the injection molding machine is obtained. The control device maintains the difference between the actual value of the physical quantity and the set value within an allowable range, and reduces the maximum value of the instantaneous current value of each phase of the three-phase AC motor. The injection molding machine according to any one of claims 1 to 6 , which determines whether or not it is possible to rotate the electric angle of each phase of the three-phase AC motor. Wherein the control device, based on the magnitude of the current instantaneous value in each phase of the three-phase AC motor of past shots, determining the magnitude of the current instantaneous value in each phase of the three-phase AC motor of this shot, The injection molding machine according to any one of claims 1 to 7 . In the control device, the difference between the actual value of the physical quantity and the set value is within the permissible range, and the magnitude of the instantaneous current value of any one phase of the three-phase AC motor and the magnitude of the current instantaneous value of the three-phase AC motor. The injection molding machine according to any one of claims 1 to 8 , which supplies a current to the three-phase AC motor so that the difference from the magnitude of the instantaneous current value of any one of the remaining phases is equal to or less than a threshold value. .. In the control device, when the maximum value of the instantaneous current values in each phase of the three-phase AC motor is Imax, the intermediate value is Imid, and the minimum value is Imin, | Imid | is equal to or less than the threshold value, and | Imax | and | The injection molding machine according to any one of claims 1 to 9, wherein a current is supplied to the three-phase AC motor so that the magnitude of the difference from Imin | is equal to or less than a threshold value.

Images