JPH0543495B2 - - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin pressure control method in an injection molding machine, and more particularly to a control pressure control method for feedback-controlling the pressure applied to the resin, such as holding pressure or back pressure.

[0002]

2. Description of the Related Art In injection molding, the injection pressure, that is, the holding pressure, is variably controlled in stages to hold the resin in the mold at a constant pressure. and,
In a hydraulically driven injection molding machine, the drive oil pressure applied to the screw corresponds well to the pressure applied to the resin, so there are no problems in detecting resin pressure and controlling holding pressure and back pressure.

[0003] However, in the case of motor-driven injection molding machines that control holding pressure and back pressure by the output torque of the drive motor, mechanical friction in the components of the transmission system interposed between the motor and the screw, such as various bearings. Control errors are likely to occur due to deflection of the transmission system, etc., and it has been difficult to control the holding pressure and back pressure appropriately.

[0004] In order to eliminate the above-mentioned problems, it has conventionally been known to detect the holding pressure with an in-mold resin pressure sensor and to perform feedback control of the holding pressure based on the detected pressure value. However, resin pressure sensors are expensive and have poor reliability when used under high temperature and high pressure conditions.

[0005] In pressure holding and back pressure control, holding pressure and back pressure are also controlled by switching them into several stages.

[0006]

[Problems to be Solved by the Invention] In a motor-driven injection molding machine that controls holding pressure and back pressure using a motor that drives the screw in the axial direction, the holding pressure and back pressure are feedback-controlled and the command pressure is controlled. When controlling by switching (command holding pressure, command back pressure) in multiple stages, when starting pressure holding pressure or back pressure control, or when switching the command pressure, the difference between the command pressure and the resin pressure detected by the sensor , that is, the pressure deviation becomes large. In feedback control, which controls the output torque of a motor that applies holding pressure or back pressure to the resin by changing the amount of operation based on this pressure deviation, there is no problem if the command pressure changes continuously, but it is not a problem if the command pressure is changed. As a result, if the pressure deviation changes greatly, the torque command for the motor also changes greatly, causing a problem that the control system is unstable in a transient state such as when changing the command pressure.

[0007] Therefore, the purpose of the present invention is to obtain a stable control system even when changing the command pressure, and to control the resin pressure so that the resin pressure can quickly and smoothly shift to the command pressure when changing the command pressure. The purpose is to provide a method.

[0008]

[Means for Solving the Problems] The present invention provides a method for controlling resin pressure in an injection molding machine in which a servo motor that drives a screw in the axial direction performs injection and controls holding pressure and back pressure. A strain detector that detects the applied pressure is installed in the drive mechanism that drives the screw in the axial direction, and the pressure detected by the strain detector is feedback-controlled so that it becomes the commanded resin pressure. The above problem was solved by lowering the gain of the transfer function of the feedback control in the switched transient state and increasing the gain after stabilization.

[0009]

[Function] When the command pressure is switched, the pressure deviation, which is the difference between the command pressure and the pressure detected by the strain detector, increases step by step, but at this time, the transfer function of the feedback control By lowering the gain, the response becomes worse. Therefore,
Even if the pressure deviation increases step by step, the output torque of the servo motor does not change suddenly, but is controlled so that it changes gradually and reaches the command pressure, preventing overshoot,
No undershoot occurs. In addition, if the above gain is low even after the transient state has passed, the response will be poor and there will be a delay in response to the command, making it difficult to maintain the resin pressure without delay to the command pressure. By increasing the pressure and improving responsiveness, the delay is reduced and the resin pressure is controlled to be maintained at the command pressure.

[0010]

[Embodiment] Fig. 1 shows an injection device of an injection molding machine equipped with a resin pressure control device according to an embodiment of the present invention. 4. The rear plate 5 is fixed. The front plate 4
A heating cylinder 1 is fixed to the heating cylinder 1 by a barrel nut 6, and a screw 2 is fitted into the heating cylinder 1. Note that 3 is a hopper for charging the molding material into the heating cylinder 1. The screw shaft 8 of the screw 2 is connected to the screw sleeve 1.
1. It is rotatably fixed to the pressure plate 14 by a screw retainer 12, a nut 13, etc. That is, the screw sleeve 11 has a thrust bearing 16 and a radial bearing 1.
7, the screw sleeve 11 has a flange 11a at one end and a screw 11b at the other end.
A nut 1 is cut out and is screwed into the screw 11b.
3 and the flange 11a, the thrust bearing 16 and the radial bearing 17 are sandwiched between the bearing retainer 19 fixed to the pressure plate 14, so that the pressure plate 14 is rotatable but immovable in the axial direction. It is fixed.

[0011] The screw shaft 8 is connected to the screw sleeve 1 by the screw retainer 12.
1, and a spline shaft 18 is fixed to the other end surface of the screw sleeve 11, so that the rotation of the spline shaft 18 is transmitted to the screw sleeve 11 and the screw shaft 8. The spline shaft 18 is engaged with a nut 20 having internal teeth that engage with the teeth of the spline shaft 18, and the nut 20 is fixed to a rotary drive tube 21 with a bolt, and the rotary drive tube 21 is attached to the rear plate 5. bearing 2
3 and 24 to be rotatably fixed. Furthermore, a pulley 25 is fixed to the other end with a key or the like. The pulley 25 is rotated by a metering/kneading motor.

[0012] The pressure plate 14 is provided between the front plate 4 and the rear plate 5.
Two ball screws 7a and 7b are rotatably provided between the front plate 4 and rear plate 5 symmetrically with respect to the axis of the screw 7 while being guided by a tie rod (not shown).
Ball nuts 15a and 15b that are screwed together are fixed. And two ball screws 7a, 7b
Pulleys 9a and 9b are fixed to one end of the pump, and the pulleys 9a and 9b are rotationally driven by a servo motor M for injection via a timing belt. Note that 10a and 10b are retainers.

[0013] Furthermore, since the adhesive strain gauge 26 as a strain detector is attached to the outer peripheral surface of the annular intermediate wall of the bearing retainer 19, the resin pressure is transmitted through the screw 2 and the thrust bearing 16 to prevent distortion without pressure drop. The signal is transmitted to the gauge 26. This strain gauge 26 is made of, for example, a conventionally known resistance wire strain gauge, and outputs an electric signal representing the holding pressure and the like as described later. The lead wire 26a is led out through the notch 14a of the pressure plate 14 and connected to a strain gauge amplifier 27, and the output of the strain gauge amplifier 27 is fed to the servo motor M that drives the injection device. It is input to the control circuit 40 (see FIGS. 2 and 3).

[0014] That is, the pressure plate 14 is configured to be driven in the axial direction of the screw 2 by an injection servo motor M via a timing belt, pulleys 9a, 9b, and ball screws 7a, 7b. The screw 2 is rotatably but immovably fixed to the pressure plate 14 via a thrust bearing 16 and a bearing retainer 19 by a screw retainer 12 and a screw sleeve 11, and drives the screw 2 to rotate. The engagement portion with the rotary drive tube 21 is formed as a spline shaft 18 on the screw shaft 8 rearward of the bearing retainer 19.

[0015] Next, the operation of this injection device will be outlined. First, during measuring and kneading, the screw 2 is held at a set back pressure by the servo motor M for injection, and the motor for measuring and kneading rotates the pulley 25 to rotate the rotary drive tube 21, and the nut 20, The screw sleeve 11 and the screw 2 are rotated through the spline shaft 18 in a metered manner. Screw 2
Due to the rotation of , the resin in the hopper 3 is introduced into the heating cylinder 1 and melted, and the molten resin is
Furthermore, as the screw 2 rotates, the molten resin is fed into the tip of the heating cylinder 1 and gradually accumulates, and the pressure of the molten resin accumulated at the tip of the heating cylinder 1 gradually increases. The pressure of the molten resin pushes the screw 2 to the right (backwards) in Fig. 1, and when the pressure of the molten resin reaches the set back pressure, the molten resin is The pressing force is overcome and the screw 2 is moved rearward, and the pressure plate 14 is moved backward.

[0016] Also, during injection, when the injection servo motor M is driven and the pulleys 9a and 9b are rotated to rotate the ball screws 7a and 7b, the nuts 15a and 15b screwed with the ball screws 7a and 7b cause the pressure The plate 14 moves forward and the screw 2
will move forward and eject. Then, when the injection is completed and the pressure is held, the screw 2 is pressed at the set holding pressure by driving the injection servo motor M.

[0017] In both cases of measuring, kneading, and holding pressure, the pressure from the resin applied to the screw 2 distorts the bearing retainer 19 via the thrust bearing 16, and the distortion is detected by the strain gauge 26. It is detected as the pressure applied to the resin. Only the screw 2 and the thrust bearing 16 are interposed between the molten resin and the bearing retainer 19, and the inertial mass that acts until the pressure of the resin is transmitted to the bearing retainer 19 is small, so pressure detection is difficult. It has excellent responsiveness, and the frictional force that acts until the pressure of the resin is transmitted to the bearing retainer 19 is only the sliding resistance between the heating cylinder 1 and the screw 2, and there is no wasted contact part. Therefore, the pressure of the resin can be accurately detected without causing an inadvertent pressure drop during the pressure transmission process.

[0018] Next, the holding pressure and back pressure control will be described. FIG. 2 is a block diagram of a main part of a drive control section of an injection device according to an embodiment of the present invention, and this embodiment shows an example in which a permanent magnet synchronous motor M is used as a servo motor for injection. 30 represents a control device such as a numerical control device for controlling the entire injection molding machine, and 40 represents a servo control circuit. Although the outline of this servo control circuit 40 is already publicly known, some improvements have been made for the purpose of the present invention. This is because the transistor shown in FIG.
The PWM control circuit 41 is provided with a pressure control feedback circuit 52. The configuration and operation of this servo control circuit will be explained below.

[0019] E is a three-phase power supply, 42 is a rectifier circuit, 43
is a transistor inverter, 41 is a transistor
PWM control circuit, M is permanent magnet synchronous motor, 29
is a rotor position detector such as a pulse encoder for detecting the position and speed of the rotor of the permanent magnet synchronous motor M. Transistor PWM control circuit 4
1 compares the current speed detected by the rotor position detector 29 with the speed command value V0 from the control device, and
~Permanent magnet synchronous motor M by turning TF on and off
The electric motor M
It controls the speed of the The configuration of this transistor PWM control circuit 41 is as shown in FIG.

[0020] That is, in FIG. 3, 45 is a signal processing circuit, and 46 and 47 are U to be output with a phase orthogonal to the field main magnetic flux with respect to the current position of the rotor.
48 is a differential amplifier that stores the values of the phase and W phase, and the voltage V0 indicating the speed command and the signal processing circuit 4.
5 and the voltage Vs indicating the current speed is amplified and output. 49 is a filter which has a frequency characteristic such that the gain is reduced when the frequency is high and the gain is increased when the frequency is low, and the peak voltage is clamped by the Zener diode ZD1.

[0021] 50 is a control device 30 such as a numerical control device.
A D/A converter that converts the holding pressure or back pressure pressure command PL from a digital signal into an analog signal, 5
2 clamps (+Vc, -Vc) the voltage Vr generated due to the error between the speed command V0 from the filter 49, which is the input of the amplifier 51, and the current speed Vs in response to the pressure command from the D/A converter 50. a pressure control feedback circuit that performs feedback control so that the pressure applied to the resin becomes PL at the pressure command value;
3 and 54 are multiplying digital-to-analog converters, and the voltage output from the amplifier 51 is
U phase and W output from VE and ROM46, 47
The phase current commands RTC and TTC for the U phase and W phase are created by multiplying the phase command values.

[0022] In addition, 55 adds the phase current commands RTC and TTC of the U phase and W phase, and calculates 120 from the U phase and W phase.
56 and 57 are detectors for detecting currents Iu and Iw flowing in the U-phase and W-phase armature windings of the synchronous motor M;
58 is V by adding the phase currents IR and IT of the U phase and W phase detected by the above U phase and W phase current detectors 56 and 57.
Adder for calculating the phase current IS of the phase, 59, 60, 6
1 is a circuit for outputting the current command voltage to be passed to the U phase, V phase, and W phase, and the only difference is the input signal.
The configuration is the same. That is, the circuit 59 is
A differential amplifier 62 that amplifies the difference between the phase current command RTC to the U phase and the current detected current IR of the U phase, and a low pass filter that allows only the frequency component of the reference carrier wave of the output of the differential amplifier 62 to pass through. circuit 6
3, and the other circuits 60 and 61 differ only in that they input the current commands STC and TTC for the V phase and W phase, respectively, and the current current values IS and IT, respectively, and the configuration is similar to that of circuit 59. are the same. 64 is
A circuit consisting of a PWM signal processing circuit and a transistor-based drive amplifier, and the above circuits 59, 60, 6
1 and the reference carrier wave VA, each transistor TA~ of the transistor inverter 43 is compared.
It outputs PWM signals PA to PF that turn TF on and off.

[0023] PST is a switching signal output from the control device 30 to determine whether or not to perform pressure feedback control, and PH is a detected pressure feedback signal output from the strain gauge amplifier 27. The servo control circuit 40 described above is improved in the present invention in that a pressure control feedback circuit 52 is provided, and the other configurations are conventionally known. Therefore, the pressure control feedback circuit 52
The circuit shown in FIG. 4 is a detailed explanation of the circuit.

[0024] In FIG. 4, 65 is a comparator circuit, which is composed of an operational amplifier IC3, and which connects the pressure command voltage PV obtained by converting the pressure command PL from the control device 30 into voltage by the D/A converter 50, the strain gauge 26, and the strain gauge. It compares the pressure feedback signal PH from the amplifier 27 and outputs the difference. 66 is an amplification compensation circuit, and the output from the comparison circuit 65 is used as a volume RV that determines the pressure feedback gain.
Input via 1, operational amplifier IC4, Zener diode to clamp the output at a constant voltage.
ZD2, a capacitor C1 for stabilizing pressure feedback, resistors R1 to R3, etc.

[0025] ASW is an analog switch that is switched by a switching signal PST to determine whether or not to perform pressure feedback control, and has three switches SW1 to SW3, I is an inverter, and switch SW1 and switch SW3 are linked and identical Performs on/off operation,
Switch SW2 performs the opposite on/off operation. That is, when the switching command PST is at the L level at the TTL logic level, the switches SW1 and SW3 are turned on, and the switch SW2 is turned off. Conversely, when the signal reaches the H level, the switches SW1 and SW3 are turned off, and the switch SW2 is turned on. 67 is two operational amplifiers IC1, IC2, diodes D1, D
The operational amplifier IC1 constitutes an amplifier, and the operational amplifier IC2 constitutes a sign converter. (which is a negative voltage) is amplified by the operational amplifier IC1 and output as a positive voltage, which becomes a positive clamp voltage +Vc.

[0026] Also, an operational amplifier as a code converter
IC2 converts the voltage +Vc into a negative voltage -Vc, forming a negative clamp voltage -Vc. That is, when the output Vr (see FIG. 3) of the filter 49 exceeds the positive clamp voltage +Vc, the diode D1 becomes conductive.
The input of the amplifier 51 does not exceed the clamp voltage +Vc. Similarly, when the output Vr of the filter 49 becomes less than the negative clamp voltage -Vc, the diode D
2 conducts and the input of amplifier 51 does not go below the negative clamp voltage -Vc.

[0027] By the way, the torque limit means conventionally used to control the torque of a servo motor is composed of only this clamp circuit 67, and the output of the D/A converter 50 is input to the clamp circuit 67.
Torque control is performed by clamping the output Vr of the filter 49 and controlling the drive current of the servo motor.

[0028] Furthermore, resistors R4, R5, capacitor C
Reference numeral 2 constitutes an integrating circuit, which operates to smooth the change (step voltage) in the pressure command voltage PV. Further, the switch SW3 of the analog switch ASW is a switch for shooting the capacitor C1 and discharging the charge of the capacitor C1 when the switch SW3 is on.

[0029] The operation of this embodiment having the above configuration will be described next. During injection, the motor M for driving the injection device is driven to rotate the pulleys 9a, 9b and the ball screws 7a, 7b as described above to move the screw 2 forward (to the left in FIG. 1). At this time, pressure control is not performed, and the switching command PST from the control device 30 is at L level, the switches SW1 and SW3 are on, and the switch SW2 is off. The pressure command PL outputs a value corresponding to the command resin pressure as the maximum injection pressure, and therefore,
Since the maximum pressure command voltage PV is input to the clamp circuit 67 via switch SW1 of the analog switch ASW, the output from the filter 49
Vr is not clamped (clamp voltage +Vc, -Vc in this case is larger than the highest voltage determined by the Zener diode ZD1 output from the filter 49) via the amplifier 51 to the multiplying digital-to-analog converter. 53,5
4 is input. That is, in this case, control is performed only by the speed command voltage V0 output from the control device 30, and only the injection speed is controlled. In this state, the pressure command PL outputs the maximum value, so loss of driving force due to frictional resistance of each part is sufficiently guaranteed, and the screw 2 can maintain the set injection speed.

[0030] Next, when the injection is completed and pressure holding is performed, the control device 30 sends an H level switching command signal.
PST is output, analog switch ASW is switched, switches SW1 and SW3 are off, switch SW
2 is turned on. On the other hand, a pressure command PL corresponding to pressure holding in the first stage is output from the control device 30,
The corresponding voltage PV (0 to - voltage) is input from the D/A converter 50 to the comparison circuit 65. on the other hand,
After injection is completed, the pressure of the resin in the mold is increased by screw 2,
Screw sleeve 11, thrust bearing 1
6 to the thrust bearing retainer 19, the thrust bearing retainer 19 generates strain, this strain is detected by the strain gauge 26, and the voltage PH corresponding to the pressure applied to the resin is transmitted through the strain gauge amplifier 27. (0 to + voltage) is detected.

[0031] Then, the pressure command voltage PV (0 to -
The difference between the voltage) and the detected pressure voltage PH is determined by the comparison circuit 66.
is input. At the moment when the pressure feedback control operation starts, the detected pressure PH from the strain gauge 26 is unstable and unstable, and in a transient state when the pressure command voltage PV changes, the capacitor C1 of the amplification compensation circuit 66 is The state is shot for a short time, and the gain of operational amplifier IC4 is −R2/
It becomes an inverting amplifier with a low gain determined by R1. When charging of the capacitor C1 is completed, the gain of the operational amplifier IC4 becomes -(R2+R3)/R1, which is a high gain. In other words, op amp IC4
When the input voltage is fluctuating in a transient state, lower the gain, increase the gain as it stabilizes, and gradually change the clamp voltage +Vc, -Vc.
Improves stability of pressure feedback control.

[0032] The amplification compensation circuit 66 output in this way
The output is the switch SW of the analog switch ASW.
2 to the clamp circuit 67, and the clamp circuit 67 outputs clamp voltages +Vc and -Vc according to the difference between the pressure holding command voltage PV and the detected pressure voltage PH from the strain gauge 26. .

[0033] On the other hand, when the pressure is maintained, the movement of the screw of the injection mechanism is almost stopped, and the electric motor M is also stopped. However, since the speed command V0 has been output, the voltage Vr output from the filter 49 is determined by the setting value of the Zener diode ZD, and the voltage Vr that drives the motor M with the maximum force is output. Therefore, the input of the amplifier 51 is clamped to the voltage +Vc, -Vc clamped by the clamp circuit 67, and a voltage VE corresponding to the clamp voltages +Vc, -Vc is output, and the multiplying digital-to-analog converters 53, 54 The driving current of each phase of the electric motor M is controlled. As a result, the output torque of the electric motor M is controlled by the clamp voltages +Vc and -Vc, which means that it is controlled by the value of the pressure command PL.

[0034] Therefore, if the difference between the voltage PV according to the pressure command PL and the detected pressure voltage PH from the strain gauge 26 is large, the output of the amplification compensation circuit 66 becomes large, and the voltage input to the clamp circuit 67 becomes large. The voltages +Vc and -Vc increase, and as a result, the phase current commands RTC, TTC, and STC of each phase output from the multiplying digital-to-analog converters 53 and 54 and the adder 55 increase, and the output torque of the motor M increases. increase On the other hand, when the detected pressure voltage PH of the detection signal from the strain gauge 26 increases and the difference from the command voltage PV decreases, the output of the amplification compensation circuit 66 decreases, and the outputs +Vc and -Vc of the clamp circuit 67 also decrease. , the output torque of the electric motor M decreases.

[0035] As a result, the difference between the command voltage PV and the detected pressure voltage PH from the strain gauge 26 is stabilized at a constant value. This means that the resin pressure in the mold, which is the load, becomes stable when it reaches the pressure command commanded from the control device 30, that is, the target holding pressure, and the torque from the electric motor M increases due to the friction of the transmission device. Even if it is absorbed by the deflection of the spring, ball screw, etc., the detected output from the strain gauge 26 installed closest to the screw 2, which is the final operation target, is compared with the commanded holding pressure. This means that feedback control, which is substantially equivalent to a full closed loop, is performed so that the pressure inside the mold becomes the set pressure, and errors due to loss torque as in the conventional method are less likely to occur. Furthermore, although the holding pressure is switched over several stages, the holding pressure can be automatically switched to the set holding pressure by switching the voltage PV by changing the value of the pressure command PL.

[0036] When the pressure holding stage is completed and the metering/kneading step is to be performed, the metering/kneading motor (not shown) is driven to rotate the screw 2 via the pulley 25, rotary drive tube 21, and spline shaft 18. When the controller 30 outputs the set back pressure as the pressure command PL, the pressure applied to the resin detected by the strain gauge 26 is fed back as described above, so that the pressure applied to the resin becomes the set back pressure. This will be subject to feedback control.

[0037] Furthermore, in the above embodiment, the detected pressure signal PH of the strain gauge 26 is fed back to the servo control circuit 30 for feedback control, but the detected pressure signal PH of the strain gauge 26 is A/D converted. The detected pressure signal may be fed back to a control device 30 such as a numerical control device, and the detected pressure signal fed back within the control device 30 may be compared with the command pressure to perform feedback control so that the detected pressure becomes the command pressure. The configuration of the transistor PWM control circuit 41 in this case is a conventional circuit configuration that applies a torque limit and performs torque control. That is, in FIG. 4, the comparison circuit 65, the amplification compensation circuit 66, and the analog switch ASW are not necessary, and the pressure command voltage PV, which is the output of the D/A converter 50, is directly input to the clamp circuit 67 (when the analog switch SW1 is turned on). ), the clamp voltages +Vc and -Vc of the clamp circuit 67 are directly controlled by commands from the control device 30, the torque of the electric motor M is limited, and the resin pressure for holding pressure and back pressure is controlled. will be controlled.

[0038] Furthermore, the same effect can be expected even if a load cell or the like is incorporated into the bearing retainer instead of using a strain cage as a strain detector.

[0039] In this embodiment, during speed-prioritized injection control, the switching signal PST is set to L level, and by switching each switch SW1 to SW3 of the analog switch ASW, the pressure command PL corresponding to the command resin pressure as the maximum injection pressure is set. It is input to a clamp circuit 67 which is a torque limiter, and is passed through a filter 49.
Although the injection speed is controlled without clamping the output Vr from the pump, it is not necessarily necessary to provide an analog switch ASW for input switching between injection speed control and pressure control during holding pressure and metering. That is,
Analog switch ASW switch SW1, SW3
Remove the analog switch ASW switch
By permanently connecting the part corresponding to SW2, the analog switch ASW can be omitted.

[0040] In this case, even in the case of injection control, the pressure feedback signal PH from the strain gauge 26
The value obtained by amplifying the deviation between the pressure command voltage PV corresponding to the maximum injection pressure and the pressure command voltage PV corresponding to the maximum injection pressure will be input to the clamp circuit 67 via the permanent contact section corresponding to switch SW2, but if injection is performed before the filling of molten resin is completed In the control stage, the reaction force exerted by the molten resin on the screw 2, that is, the value of the resin pressure detected by the strain detector 26, is small, so the difference between the commanded resin pressure PV and the resin pressure PH detected by the strain detector is It is almost equal to the value of the command resin pressure PV itself, which is the maximum injection pressure, and even if this pressure deviation is input to the clamp circuit 67 and the output restriction of the servo motor M is released, speed-first injection can be performed without any problem. can be controlled.

[0041]

[Effects of the Invention] In the present invention, during pressure holding and back pressure control, even if the command pressure (command holding pressure, command back pressure) is switched, the gain of feedback control is reduced in the transient period at the time of switching, and the responsiveness is reduced. Therefore, even if the pressure deviation increases due to switching, the output torque of the servo motor will not change suddenly, and as a result, the pressure related to the resin will overshoot or undershoot the command pressure. The command pressure before switching smoothly shifts to the command pressure after switching, and phenomena such as over-pressure or under-pressure do not occur. Furthermore, since the gain is increased once the excessive state has passed, responsiveness is improved, and when the detected resin pressure deviates from the command pressure, feedback control is performed to immediately correct the deviation. As a result, holding pressure and back pressure can be controlled very accurately.

[Brief explanation of the drawing]

FIG. 1 is a partial vertical cross-sectional view showing an injection device of an injection molding machine equipped with a resin pressure control device implementing an embodiment of the present invention.

FIG. 2 is a block diagram of the main parts of the drive control section of the injection device in the same embodiment.

[Figure 3] Transistor PWM in the same example
FIG. 3 is a block diagram of a control circuit.

FIG. 4 is a detailed diagram of the pressure feedback circuit in the same embodiment.

[Explanation of symbols]

7 Screw 14 Pressure plate 16 Thrust bearing 19 Bearing retainer 26 Strain gauge 27 Strain gauge amplifier 52 Pressure control feedback circuit 65 Comparison circuit 66 Amplification compensation circuit PV pressure command voltage PH Detection pressure.

Claims (1)

[Claims] Claim 1: A strain detector for detecting the pressure applied to the resin from the screw in a resin pressure control method in an injection molding machine in which injection is performed using a servo motor that drives the screw in the axial direction, and holding pressure and back pressure are controlled. is installed in the drive mechanism that drives the screw in the axial direction, and feedback control is performed so that the pressure detected by the strain detector becomes the commanded resin pressure, and in a transient state where the commanded resin pressure is switched, the A method for controlling resin pressure in an injection molding machine, in which the gain of a transfer function for feedback control is lowered, and after the gain is stabilized, the gain is increased.