JPH05200808A - Method for controlling resin pressure of injection molder - Google Patents

Abstract

PURPOSE:To prevent excessive pressure from applying to resin and molding failure from developing by a method wherein current command required for speed control is compared with current command required for pressure control at the changing over from speed control to dwell control so as to use the smaller one between the current command as the current command to a servo motor. CONSTITUTION:At the changing over from speed control to dwell control, when the current command required for speed control or output Vr from a filter 49 is small and does not exceed clamping voltage, the current command Vr required for speed control is adopted as it is as the current command to a motor. When the current command Vr required for speed control exceeds the clamping voltage, the output of an amplifier 51 turns to be the voltage determined by the pressure deviation of pressure control and adopted as the current command to the motor. Or, between the current commands required for speed control and for pressure control, the smaller one is outputted as the current command to the motor.

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 for an injection molding machine, and more particularly to a resin pressure control method for an electric injection molding machine in which a screw is driven by a servomotor.

[0002]

2. Description of the Related Art In injection molding, the injection speed is controlled from the start of injection until the pressure holding control. That is, it is common to start injection at a set injection speed, switch this injection speed in several stages to perform injection speed control, and then switch to pressure control to control the pressure applied to the resin to the set pressure. Is done in a regular manner. It is known that in controlling the holding pressure, a sensor for detecting the resin pressure in the mold is provided, the resin pressure in the mold is detected by the sensor, and feedback control is performed so that the detected pressure value becomes the set holding pressure. There is.

[0003]

A servomotor is used as a drive source for axially driving a screw, and the injection speed is feedback-controlled, and at the same time, the motor-driven injection is performed in which the resin pressure is detected and the holding pressure and the back pressure are feedback-controlled. In the molding machine, when the injection speed control for controlling the injection speed is switched to the resin pressure control (holding pressure), the control amount is switched, so that the output torque of the motor varies. That is, in both the injection speed control and the pressure holding control, the operation amount is the drive current of the motor, but the control amount changes from speed to pressure, and there is a discontinuity. During speed control, the injection speed is controlled by controlling the drive current of the motor and the rotation speed of the servomotor based on the speed deviation that is the difference between the command speed and the detected speed. Also, at the time of pressure holding, the drive current of the motor is controlled based on the pressure deviation which is the difference between the command pressure holding and the detected resin pressure, and the output torque of the servo motor is controlled so that the detected resin pressure becomes the set pressure holding. Feedback controlled.

As described above, when the injection speed control is switched to the pressure holding control, the control amount changes from the speed to the pressure, so that there is a discontinuity and the control becomes unstable. In particular, it is not preferable that the output torque of the servo motor is rapidly increased during the transitional period of switching from speed control to pressure control. At the time of switching from speed control to pressure control, when the resin pressure during speed control is low, the set pressure when switching during pressure control is high, and the pressure deviation is large, the drive current rapidly increases in the servo motor. However, the output torque of the servomotor increases rapidly, causing an overshoot and excessive pressure applied to the resin. Therefore, an object of the present invention is to provide a resin pressure control method that prevents excessive pressure from being applied to the resin when switching from speed control to pressure control.

[0005]

A servomotor is used as a drive source for axially driving a screw, and a strain detector for detecting a pressure applied to the resin from the screw is arranged in a drive mechanism for axially driving the screw. Set up, when injecting,
In addition to controlling the injection speed with a servo motor,
In the resin pressure control method of the injection molding machine that controls the resin pressure detected by the strain detector to the commanded holding pressure and back pressure at the time of holding pressure and measuring, the pressure from the area that controls the injection speed In the transition period when shifting to control, the current command to the servo motor obtained by speed control is compared with the current command to the servo motor obtained by pressure control, and the smaller command is used as the current command to the servo motor to determine the resin pressure. Control.

[0006]

[Operation] During the transition period from speed control to pressure control, the current command (target value of the drive current of the servo motor) determined by the speed deviation of the difference between the command speed and the actual speed during injection speed control The current command determined by the pressure deviation, which is the difference between the target resin pressure and the detected resin pressure in, is compared, and the smaller one is used as the current command to the servo motor.
Therefore, in this transition period, when the current command in speed control is smaller, even if switching to pressure control,
Since the current command in the speed control becomes the current command to the servo motor as it is, the pressure is continuously controlled, and the pressure applied to the resin changes continuously and no sudden change occurs. And since the resin is filled in the mold,
Since the actual injection speed decreases, the speed deviation increases, the current command also increases, and eventually the pressure control is started.

Further, when the current command in the speed control is larger than the current command in the pressure control when switching from the speed control to the pressure control, the current command in the pressure control is output, so that the injection speed decreases and the command It is controlled so that the holding pressure is the resin pressure. As a result, overshoot of pressure does not occur, and excessive pressure is not applied to the resin.

[0008]

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, in which an injection unit slidably mounted on the base of the injection molding machine has a front plate. 4, the rear plate 5 is fixed. The heating cylinder 1 is fixed to the front plate 4 by a barrel nut 6, and the screw 2 is fitted in the heating cylinder 1. Reference numeral 3 is a hopper for charging the molding material into the heating cylinder 1. The screw shaft 8 of the screw 2 is rotatably fixed to the pressure plate 14 by a screw sleeve 11, a screw retainer 12, a nut 13, and the like. That is, the screw sleeve 11 is rotatably held on the pressure plate 14 by a thrust bearing 16 and a radial bearing 17, and the screw sleeve 11 has a flange 11a at one end and a screw 11b at the other end. The thrust bearing 16 and the radial bearing 17 are rotatably attached to the pressure plate 14 by the nut 13 screwed with the screw 11b and the flange 11a so that the thrust retainer 16 and the radial bearing 17 are held by the bearing retainer 19 fixed to the pressure plate 14. It is fixed so that it cannot move in any direction.

The screw shaft 8 is fixed to the screw sleeve 11 by a screw retainer 12, and a spline shaft 18 is fixed to the other end surface of the screw sleeve 11, so that the spline shaft 18 is rotated by the screw sleeve 11 and the screw. It is designed to transmit to the 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, the nut 20 is fixed to a rotary drive pipe 21 with a bolt, and the rotary drive pipe 21 is attached to the rear plate 5. Bearing 2
It is rotatably fixed by 3, 24. Further, 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.

The pressure plate 14 is guided by four tie rods (not shown) provided between the front plate 4 and the rear plate 5, and is symmetrical with respect to the axis of the screw 7. Ball nuts 15a, 1 screwed with two ball screws 7a, 7b rotatably provided between the rear plates 5.
5b is stuck. And two ball screws 7a
, 7b are fixed to one ends of pulleys 9a, 9b, and the pulleys 9a, 9b are rotationally driven by a servomotor M for injection through a timing belt. Note that 10a and 10b are retainers.

Further, an adhesive strain gauge 2 as a strain detector
6 is affixed to the outer peripheral surface of the annular intermediate wall of the bearing retainer 19, the resin pressure is strained through the screw 2 and the thrust bearing 16 without pressure drop.
6 is transmitted. The strain gauge 26 is, for example, a conventionally known resistance wire strain gauge, and outputs an electric signal representing a holding pressure or the like as described later. And the lead wire 26a
Is drawn out through the notch 14a of the pressure plate 14 and connected to the strain gauge amplifier 27, and the output of the strain gauge amplifier 27 is input to the servo control circuit 40 of the servomotor M that drives the injection device. (See FIGS. 2 and 3).

That is, the pressure plate 14 is configured to be driven in the axial direction of the screw 2 by a servomotor M for injection through a timing belt and pulleys 9a and 9b and ball screws 7a and 7b. Reference numeral 2 is fixed to the pressure plate 14 by a screw retainer 12 and a screw sleeve 11 via a thrust bearing 16 and a bearing retainer 19 so as to be rotatable and immovable in the axial direction, and a rotary drive tube 21 for rotationally driving the screw 2. The engagement portion is formed as a spline shaft 18 on the screw shaft 8 rearward of the bearing retainer 19.

Next, the operation of this injection device will be outlined. First, at the time of metering / kneading, the screw 2 is maintained at a set back pressure by the injection servomotor M, the pulley 25 is rotationally driven by the metering / kneading motor to rotate the rotary drive tube 21, and the nut 20 and the spline shaft are rotated. The screw sleeve 11 and the screw 2 are measured and rotated via 18. The resin in the hopper 3 is introduced into the heating cylinder 1 by the rotation of the screw 2 and melted, and the molten resin is further sent to the tip of the heating cylinder 1 by the rotation of the screw 2 to gradually accumulate and heat. The pressure of the molten resin accumulated at the tip of the cylinder 1 gradually increases. The pressure of the molten resin pushes the screw 2 to the right (backward) in FIG. 1,
When the pressure of the molten resin reaches the set back pressure, the pressing force of the molten resin overcomes the holding force of the servo motor M that holds the screw 2 at the set back pressure, moves the screw 2 backward, and the pressure plate 14 retracts. Will be done.

Further, at the time of injection, a servo motor M for injection is used.
Drive the ball screw 7a by rotating the pulleys 9a and 9b.
, 7b are rotated, the pressure plate 14 is advanced by the nuts 15a, 15b screwed with the ball screws 7a, 7b, and the screw 2 is advanced to perform injection. Then, when the injection is completed and the pressure is held, the screw 2 is pressed at the set holding pressure by the driving of the injection servo motor M.

In both cases of measuring and 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 strain is detected by the strain gauge 26. It is detected as the pressure applied to the resin. Since only the screw 2 and the thrust bearing 16 are interposed between the molten resin and the bearing retainer 19, the inertial mass acting until the pressure of the resin is transmitted to the bearing retainer 19 is small, so that the pressure can be detected. The responsiveness is excellent, and the frictional force acting until the resin pressure 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 useless contact portion. So
Without inadvertent pressure drop in the pressure transmission process,
The pressure of the resin can be accurately detected.

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 unit of an injection apparatus according to an embodiment of the present invention. In this embodiment, an example is shown in which a permanent magnet synchronous motor M is used as a servo motor for injection. Reference numeral 30 denotes a control device such as a numerical control device for controlling the entire injection molding machine, and 40 is a servo control circuit.
The outline of the servo control circuit 40 is already publicly known, but some improvements have been made for the present invention. This is that the pressure such as the holding pressure detected from the strain gauge 26 is feedback-controlled, and the transistor PWM control circuit 41 shown in FIG. 3 is provided with a pressure control feedback circuit 52. The configuration and operation of this servo control circuit will be described below.

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 a permanent magnet synchronous motor, and 29 is for detecting the position and speed of the rotor of the permanent magnet synchronous motor M. Is a rotor position detector such as a pulse encoder. The transistor PWM control circuit 41 compares the current speed detected by the rotor position detector 29 and the speed command value V0 from the control device, and each transistor TA of the transistor inverter 43.
~ Turn TF on and off to turn U of the permanent magnet synchronous motor M,
The current of the V and W phase windings is controlled to control the speed of the electric motor M. The configuration of the transistor PWM control circuit 41 is as shown in FIG.

That is, in FIG. 3, reference numeral 45 is a signal processing circuit, and 46 and 47 are ROMs for storing values of U phase and W phase to be output in a phase orthogonal to the main magnetic flux of the field with respect to the current position of the rotor. Reference numeral 48 is a differential amplifier, which is a voltage V indicating a speed command.
0 and the voltage Vs indicating the current speed from the signal processing circuit 45
The speed deviation that is the difference between Four
Reference numeral 9 denotes a filter, which has a frequency characteristic such that the gain is suppressed when the frequency is large and the gain is increased when the frequency is small, and the peak voltage is clamped by the Zener diode ZD1 to output the current command Vr in the speed control. ..

Reference numeral 50 is a D / A converter for changing the pressure command PL for holding pressure or back pressure from the control device 30 such as a numerical controller to a digital signal, and 52 is a pressure command from the D / A converter 50. The current command voltage Vr generated by the error between the speed command V0 from the filter 49, which is the input of the amplifier 51, and the current speed Vs is clamped (+ Vc
, -Vc) to perform feedback control so that the pressure applied to the resin becomes the pressure command value PL, and 53 and 54 are multiplying digital-analog converters, which are the voltage VE output from the amplifier 51.
(Current command) and the U phase output from the ROMs 46 and 47,
Multiplying the W-phase command values, the U-phase and W-phase phase current commands RTC and TTC are created.

Further, 55 is an adder for adding the U-phase and W-phase current commands RTC and TTC to form a V-phase current command STC which is 120 degrees out of phase with the U-phase and W-phase, and 56 and 5
7 is a detector for detecting the currents Iu and Iw flowing in the U-phase and W-phase armature windings of the synchronous motor M, and 58 is the U-phase and W-phase detected by the U-phase and W-phase current detectors 56 and 57. Phase current I
Adders for adding the R and IT to calculate the phase current IS of the V phase, 59, 60 and 61 are circuits for outputting the current command voltage to be passed to the U phase, V phase and W phase, and the input signals are different. Only the configuration is the same. That is, the circuit 59
Phase current command RTC to U phase and current detection current IR of U phase
And a differential amplifier 62 for amplifying the difference between
2 is composed of a low-pass filter circuit 63 for passing only the frequency component of the reference carrier wave of the second output, and the other circuits 60 and 61 are also V-phase and W-phase current commands ST, respectively.
The configuration is the same as that of the circuit 59, except that C, TTC, and current current values IS, IT are respectively input. Reference numeral 64 is a circuit composed of a PWM signal processing circuit and a transistor base drive amplifier, and the circuits 59, 60, 61 are provided.
Is compared with the reference carrier wave VA, and PWM signals PA to PF for turning on / off the transistors TA to TF of the transistor inverter 43 are output.

Note that PST is a switching signal output from the controller 30 for determining whether or not to perform pressure feedback control, P
H is a detected pressure feedback signal output from the strain gauge amplifier 27. The above-mentioned servo control circuit 40 is improved in the present invention in that a pressure control feedback circuit 52 is provided, and other configurations are conventionally known. Therefore, the pressure control feedback circuit 5
2 is explained in detail in the circuit shown in FIG.

In FIG. 4, reference numeral 65 is a comparison circuit, which is composed of an operational amplifier IC3 and has a pressure command P from the control device 30.
Pressure command voltage P obtained by converting L to voltage by the D / A converter 50
V is compared with the pressure feedback signal PH from the strain gauge 26 and the strain gauge amplifier 27, and the difference is output. Reference numeral 66 denotes an amplification compensation circuit, which inputs the output from the comparison circuit 65 via a volume RV1 which determines the gain of pressure feedback, and stabilizes the pressure feedback by stabilizing the operational amplifier IC4 and the Zener diode ZD2 for clamping the output at a constant voltage. Capacitor C1 for planning
And resistors R1 to R3 and the like.

ASW is an analog switch which is switched by a switching signal PST for determining whether or not to perform pressure feedback control, and has three switches SW1 to SW3, I is an inverter, and the switches SW1 and SW3 are interlocked with each other to turn on the same. The switch SW2 performs an off operation, and the switch SW2 performs an opposite on / off operation. That is, when the switching command PST is the TTL logic level and the L level, the switches SW1 and SW3 are
Is on and the switch SW2 is off. On the other hand, at the H level, the switches SW1 and SW3 are turned off,
The switch SW2 is turned on. 67 is composed of two operational amplifiers IC1, IC2, diodes D1, D2, etc.,
The operational amplifier IC1 constitutes an amplifier, and the operational amplifier IC2
And a negative voltage (pressure command voltage PV and amplification compensation circuit 6) input to the operational amplifier IC1.
The output voltage of 6 is a negative voltage respectively) is an operational amplifier IC
It is amplified by 1 and output as a positive voltage, which becomes the positive clamp voltage + Vc.

Further, an operational amplifier IC as a code converter
2 converts the voltage + Vc into a negative voltage -Vc, forming a negative clamp voltage -Vc. That is, when the current command Vr (see FIG. 3) output from the filter 49 exceeds the positive clamp voltage + Vc, the diode D1 conducts, and the input of the amplifier 51 does not exceed the clamp voltage + Vc. Similarly, when the current command Vr of the output of the filter 49 becomes less than the negative clamp voltage -Vc, the diode D2 becomes conductive and the input of the amplifier 51 does not become less than the negative clamp voltage -Vc.

By the way, the torque limit means conventionally used for controlling the torque of the servomotor is composed of only this clamp circuit 67, and the output of the D / A converter 50 is inputted to the clamp circuit 67 to make the filter 49. Output Vr
Is clamped and the drive current of the servo motor is controlled to perform torque control.

The resistors R4, R5 and the capacitor C2 form an integrator circuit and operate to dull the change (step voltage) of the pressure command voltage PV. Further, the switch SW3 of the analog switch ASW is the switch S
When W3 is on, it is a switch for short-circuiting the capacitor C1 and discharging the electric charge of the capacitor C1.

The operation of this embodiment having the above configuration will be described below. At the time of injection, the motor M for driving the injection device is driven to rotate the pulleys 9a and 9b and the ball screws 7a and 7b to move the screw 2 forward (left in FIG. 1) as described above. At this time, pressure control is not performed, and the switching command PST from the control device 30 is at the L level and the switch S
W1 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, so that the maximum pressure command voltage PV is input to the clamp circuit 67 via the switch SW1 of the analog switch ASW. Therefore, the current command Vr which is the output from the filter 49 is not clamped (clamp voltage + Vc,
-Vc is larger than the maximum voltage determined by the Zener diode ZD1 output from the filter 49) Amplifier 5
1 is input to the multiplying digital / analog converters 53 and 54. That is, in this case,
It is controlled only by the speed deviation which is the difference between the speed command voltage V0 output from the control device 30 and the actual speed Vs,
Only the injection speed will be controlled. Since the pressure command PL outputs the maximum value in this state, the loss of the driving force due to the frictional resistance of each part is sufficiently ensured, and the screw 2 can maintain the set injection speed.

Next, when the injection is completed and the pressure is maintained,
An H level switching command signal PST is output from the control device 30, the analog switch ASW is switched, and the switch SW
1, SW3 is turned off and switch SW2 is turned on. On the other hand, the control device 30 outputs the pressure command PL corresponding to the holding pressure in the first stage, and the corresponding voltage PV (0 to 0
-Voltage) is input from the D / A converter 50 to the comparison circuit 65. On the other hand, after injection, the pressure of the resin in the mold is screw 2, screw sleeve 11, thrust bearing 1
6 is transmitted to the thrust bearing retainer 19 and the strain is generated in the thrust bearing retainer 19. The strain gauge 26 detects this strain and the voltage PH corresponding to the pressure applied to the resin via the strain gauge amplifier 27. (0 to
+ Voltage) is detected.

Then, the pressure deviation, which is the difference between the pressure command voltage PV (0 to -voltage) and the detected pressure voltage PH, is input to the comparison circuit 66. At the moment when the pressure feedback control operation is performed, the detected pressure PH from the strain gauge 26 is not fixed and is unstable, and in a transient state when the pressure command voltage PV changes, the capacitor C1 of the amplification compensation circuit 66 is changed. Short-circuited for a short time, and the operational amplifier IC
The gain of 4 is an inverting amplifier with a low gain determined by -R2 / R1. Then, when the charging of the capacitor C1 is completed, the gain of the operational amplifier IC4 is − (R2 + R3).
/ R1, which is a high gain. That is, in a transient state in which the voltage input to the operational amplifier IC4 fluctuates, the gain is lowered, the gain is increased as it stabilizes, and the clamp voltages + Vc and -Vc are gradually changed to stabilize the pressure feedback control. Is increasing.

The output of the amplification compensation circuit 66 thus output is input to the clamp circuit 67 via the switch SW2 of the analog switch ASW. From the clamp circuit 67, the holding pressure command voltage PV and the detected pressure voltage from the strain gauge 26 are input. The clamp voltages + Vc and -Vc are output according to the difference in PH.

When the speed control is switched to the pressure-holding control, if the output Vr from the filter 49, which is a current command by the speed control, is small and does not exceed the clamp voltage + Vc, -Vc, the current by the speed control. The command Vr is used as the current command to the motor as it is, but when the current command Vr by the speed control exceeds the clamp voltage + Vc, -Vc, the output of the amplifier 51 depends on this clamp voltage, that is, the pressure deviation of the pressure control. It becomes a fixed voltage, and this voltage becomes a current command to the motor. That is,
Of the current commands obtained by speed control and pressure control,
The smaller one is output as a current command to the motor.

Then, the analog switch AS is issued by the pressure holding command.
When W is switched and time elapses, the mold is filled with resin, the movement of the screw of the injection mechanism is almost stopped, and the rotation of the electric motor M is almost stopped. However, since the speed command V0 is output, the voltage Vr output from the filter 49 is determined by the set value of the Zener diode ZD, and the voltage Vr driven by the maximum force of the electric motor M is output. Therefore, the input of the amplifier 51 is clamped to the voltages + Vc and -Vc clamped by the clamp circuit 67, the voltage VE corresponding to the clamp voltages + Vc and -Vc is output, and the multiplying digital-analog converters 53 and 54 are output. Is input to the motor M and the drive 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.

Therefore, when 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 is large and the voltage input to the clamp circuit 67 is large, so that the clamp is performed. Voltage + Vc
, -Vc increases, whereby the phase current commands RTC, TTC, STC of each phase output from the multiplying digital-analog converters 53, 54 and the adder 55.
Increases, and the output torque of the electric motor M increases. 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 output of the clamp circuit 67 + Vc,
-Vc also decreases, and the output torque of the electric motor M decreases.

As a result, the command voltage PV and the strain gauge 26
It stabilizes in a state where the difference in the detected pressure voltage PH from is a constant value. This means that when the resin pressure in the mold, which is a load, reaches the pressure command instructed from the control device 30, that is, the target holding pressure, the torque from the electric motor M is reduced by friction of the transmission device. Even if it is absorbed by the deflection of the spring, the ball screw, etc., the detection output from the strain gauge 26 mounted at the position closest to the screw 2 which is the final operation target is compared with the command holding pressure, This means that feedback control, which is substantially equivalent to that of a full-closed loop, is performed so that the pressure inside the mold becomes the set pressure, and it is unlikely that an error due to loss torque as in the conventional case will occur.
Further, the holding pressure is switched over several stages, but the holding pressure can be automatically switched to the set holding pressure by switching the voltage PV by switching the value of the pressure command PL.

At the time of metering / kneading after the pressure-holding step is completed, a metering / kneading motor (not shown) is driven to rotate the screw 2 via the pulley 25, the rotary drive pipe 21, and the spline shaft 18. When the control device 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, and the pressure applied to the resin is fed back to the set back pressure. Will be controlled.

Further, in the above embodiment, the strain gauge 26
The detected pressure signal PH of the strain gauge 26 is fed back to the servo control circuit 40 for feedback control. However, the detected pressure signal PH of the strain gauge 26 is A / D converted and fed back to the control device 30 such as a numerical control device for control. Device 30
The detected pressure signal fed back inside may be compared with the command pressure, and feedback control may be performed so that the detected pressure becomes the command pressure. The configuration of the transistor PWM control circuit 41 in this case is a circuit configuration for performing torque control by applying a conventional torque limit. That is, FIG.
, 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 same state as above), the clamp voltage + Vc, -Vc of the clamp circuit 67 is directly controlled by a command from the control device 30, the torque of the electric motor M is limited, and the resin pressure such as the holding pressure and the back pressure is controlled. Become.

Even if a load cell or the like is incorporated in the bearing retainer instead of using a strain gauge as the strain detector, the same effect can be expected.

In this embodiment, the switching signal PST is set to the L level in the speed-first injection control, and the analog switch AS is set.
By switching the switches SW1 to SW3 of W,
The pressure command PL corresponding to the command resin pressure as the maximum injection pressure is input to the clamp circuit 67 which is the torque limit means to control the injection speed without clamping the output Vr from the filter 49. Control and holding pressure
It is not always necessary to provide the analog switch ASW for switching the input to the pressure control during measurement. That is, the switches SW1 and SW3 of the analog switch ASW are removed,
The analog switch ASW can be omitted by making the portion of the analog switch ASW corresponding to the switch SW2 a permanent contact.

In this case, even in the case of injection control, a value obtained by amplifying the deviation between the pressure feedback signal PH from the strain gauge 26 and the pressure command voltage PV corresponding to the maximum injection pressure is passed through the permanent contact portion corresponding to the switch SW2. However, the reaction force applied to the screw 2 by the molten resin, that is, the value of the resin pressure detected by the strain detector 26 is small in the injection control stage before the completion of the filling of the molten resin. Therefore, the difference between the command resin pressure PV and the resin pressure PH detected by the strain detector is almost equal to the value of the command resin pressure PV itself, which is the maximum injection pressure, and this pressure deviation is input to the clamp circuit 67 to perform servo control. By canceling the output restriction of the motor M, speed-first injection control can be performed without any trouble.

[0040]

According to the present invention, when the speed control is switched to the pressure holding control, the current command by speed control and the current command by pressure control are compared, and the smaller current command is used as the current command for the servo motor. Therefore, a suddenly large current command is not input to the servo motor at the time of switching, so that the output torque of the servo motor does not overshoot the output torque corresponding to the set holding pressure. for that reason,
Since excessive pressure is not applied to the resin, molding defects can be reduced.

[Brief description of drawings]

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 for carrying out an embodiment of the present invention.

FIG. 2 is a block diagram of a main part of a drive control unit of the injection device in the embodiment.

FIG. 3 is a block diagram of a transistor PWM control circuit in the embodiment.

FIG. 4 is a detailed view of a 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 Gage Amplifier 52 Pressure Control Feedback Circuit 65 Comparison Circuit 66 Amplification Compensation Circuit PV Pressure Command Voltage PH Detected Pressure

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuo Kodai, 3-5 Asahigaoka, Hino-shi, Tokyo 1-5 FANUC Co., Ltd. Product Development Laboratory (72) Toshio Kobayashi 3-5-1 Asahigaoka, Hino, Tokyo Nak Co., Ltd. Product Development Laboratory

Claims (1)

[Claims] 1. A servo motor for axially driving a screw, and a strain detector arranged in a drive mechanism for axially driving the screw to detect a pressure applied to the resin from the screw. In the resin pressure control method of the injection molding machine, which controls the resin pressure detected by the strain detector to be the commanded holding pressure and back pressure, while controlling the speed of During the transition period to shift to pressure control, the current command to the servo motor obtained by speed control is compared with the current command to the servo motor obtained by pressure control, and the smaller command is used as the current command to the servo motor to control the resin pressure. A resin pressure control method for an injection molding machine, comprising: