JPS62207618A - Mold protective device in injection molder - Google Patents

Abstract

PURPOSE:To surely and precisely protect a mold by accurately controlling a driving force given to a moving platen from a driving motor by a structure wherein a torque limiting means is provided so as to limit the driving current of a mold clamping servo motor in such a manner as to make the driving force equal to the set driving force. CONSTITUTION:When a moving platen 104 is driven through power transmission gears by a mold clamping servo motor M, a movable mold installed on the moving platen 104 gets close to and drifts away from a stationary mold so as to perform a mold closing and a mold opening actions. During mold closing, when the movable mold reaches the mold protection starting position, the set driving force is set to a value suitable for mold protection, while the driving force actually applied to the moving platen 104 is detected with a strain detector. The detected driving force and the set driving force are compared with each other by a comparing means and further a torque limiting means limits the driving current of a driving servo motor M in accordance with the result of said comparison so as to make the driving force applied to the moving platen 104 equal to the set driving force in order to protect the mold.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a mold protection device that is installed in a motor-driven injection molding machine and that protects the mold reliably and precisely.

Conventional technology In a motor-driven injection molding machine, a torque limit circuit for limiting the output torque of the mold clamping motor is provided in the NC control device that controls the mold opening and mold closing operations of the mold clamping device.
During the mold closing operation, the motor output torque is limited to a small value by the circuit to the dork limit 1 in the mold protection operation area in front of the mold touch position, so that the movable mold can be used as a moving platen, for example, as a transmission mechanism. There is a known technique for protecting the molds from foreign objects that may somehow get in between the molds by driving with a small force via a motorized device including a toggle mechanism. However, this type of torque limitation is only performed by open-loop control based on a torque limit command from an NC control device. On the other hand, the transmission mechanism that transmits the output torque of the toggle drive motor to the toggle mechanism has friction, etc., which acts as a disturbance in the control of the movable mold drive force, so when protecting the mold, the toggle mechanism and the moving platen In some cases, the driving force applied to the motor cannot be accurately controlled to a predetermined value set by the torque limit.

Problems to be Solved by the Invention The present invention provides a means for moving the moving platen from the drive motor via the power transmission device without being affected by disturbances in the control of the movable mold drive force, such as friction in the power transmission device. The purpose of the present invention is to provide a mold protection device for an injection molding machine that can accurately control the driving force applied to the mold and protect the mold with real precision.

Means for Solving the Problems In an injection molding machine in which a moving platen on which a mold is mounted is driven by a mold clamping servo motor via a power transmission device, an injection molding machine is provided on the moving platen side of the power transmission device, a strain detector for detecting the driving force applied to the moving platen from the mold clamping servo motor; a comparison means for comparing the detected driving force with a set driving force; Torque limiting means for limiting the drive current of the mold clamping servo motor so that the drive force becomes the set drive force.

The rim is connected to the 1-nervo motor for mold clamping via the working power transmission device δ.
When the pin platen is driven, the movable mold attached to the moving platen approaches and moves away from the fixed mold, thereby performing mold closing and mold opening operations. When the movable mold reaches the mold protection start position when the mold is closed, the set driving force is set to a value suitable for mold protection, while the actual driving force applied to the moving platen is detected by a strain detector. Detected. The detected driving force and the set driving force are compared by a comparing means, and the driving current of the drive servo motor is limited by the 1-lux limiting means according to the comparison result, and the driving force applied to the Moogong platen is set. It is controlled by the driving force and protects the mold.

Embodiment FIG. 1 shows a mold clamping device for an injection molding machine equipped with a mold protection device according to an embodiment of the present invention.
A moving platen 104 with a movable mold 103 mounted thereon is located between a stationary platen 102 disposed at one end of the stationary mold 101 and a rear platen 106 disposed at the other end of the tie bar 105. It is supported by tie bars 105. The moving platen 104 has a power transmission device, that is, two sets of toggle links 1
The mold clamping servo motor (hereinafter referred to as electric motor) ~1, which is fixedly installed on the back of the rear platen 106 and is made up of a permanent magnet synchronous motor, drives the mold clamping servo motor (hereinafter referred to as electric motor) through a toggle mechanism 107 consisting of 0ε3,108' and a transmission mechanism to be described later. It is adapted to slide on the tie bar 105. A pole nut 110 and a gear 113 fixed to the pole nut 110 so as to be able to rotate integrally with the pole nut 110 are arranged in a through hole 109 bored in the center of the rear platen 106.
A ball screw 112 is screwed into 110. The above @f1113 is gear 1 fixed to the output shaft of electric 11M
14 mesh with each other, and the ball screw 112 has a cross head 1 for bending and extending the toggle links 108, 108'.
11 are connected, and these members 110 to 114 constitute the above-mentioned transmission device.

In general, an adhesive strain gauge 120 is attached to the outer peripheral surface of the end of the ball screw 112 on the side of the crosshead 111 as a strain detector for detecting the driving force applied to the toggle mechanism 107 from the mold clamping electric motor M. . This strain gauge 120 is made of, for example, a conventionally known resistance wire strain gauge, and its resistance changes according to the strain of the ball screw 112, so that the driving force applied to the toggle mechanism 107 from the strain of the ball screw 112, that is, the electric g1M, is reduced. An electrical signal representing the reaction force is output to the distortion amplifier 121.

Note that the other members in Fig. 1 are related to the mold thickness adjustment mechanism.
Since it is not directly related to the present invention, the explanation will be omitted.

FIG. 2 shows a control circuit for the mold clamping motor M, which together with the strain gauge 120 shown in FIG. 1 constitutes a mold protection device.

In Fig. 2, E is a three-phase power supply, 3 is a rectifier circuit, 4 is a transistor inverter, 1 is a transistor PWM control circuit, and M is a permanent magnet synchronous electric motor f as the above-mentioned mold clamping motor.
! IJ machine 2 is a rotor position detector such as a pulse encoder for detecting the position (bending/extending state of the toggle mechanism 107) and speed of the rotor of the electric IM. Transistor P
The WM control circuit 1 compares the current speed detected by the rotor position detector 2 with the speed command value Vo from the control device, turns on and off each transistor T△ to TF of the transistor inverter 4, and controls U, U of the electric motor M, The speed of the motor M is controlled by controlling the currents in the V and W phase windings. Then, this 1- for controlling the output 1-1 of the electric IM
The configuration of the transistor PWM control circuit 1 is as shown in FIG.

That is, in FIG. 3, 8 is a differential amplifier that amplifies and outputs the difference between the voltage Vo indicating the speed command and the voltage Vs indicating the current speed from the signal processing circuit 5. 9 is a filter with frequency characteristics that reduces the gain when the frequency is large and increases the gain when the frequency is small.
The built-in Zener diode ZD1 clamps the peak voltage.

50 is a D/A converter that converts the i-lux limit command PL from a digital signal into an analog signal for setting the force to be applied to the load from a numerical control device, etc., and 53 is described later (FIG. 4).
51 is an amplifier.

5 is a signal processing circuit; 6 and 7 are U phases that should output a phase orthogonal to the field main magnetic flux with respect to the current position of the rotor;
The ROM that stores the value of the W phase, 10° 11 is a multiplying digital-to-analog converter, which multiplies the voltage V[ output from the amplifier 51 and the U-phase and W-phase command values output from the ROM 6.7. Together, phase current commands RTC and TTC for the U phase and W phase are created. Also, 12
13.14 is an adder that adds the phase current commands RTC and TTC of the U-phase and W-phase to create a 7δ flow command STC of the ■ phase that is 120 degrees out of phase from the U-phase and W-phase, and 13.14 is the adder for the synchronous motor M. U
Detector 15 detects the currents 1u and IW flowing in the armature windings of the W phase and W phase, and 15 is the U phase.

This is an adder that calculates the phase current Is of the ■ phase by adding the phase currents IR and IT of the U phase and W phase detected by the W phase current detectors 13 and 14.

16, 17, and 18 are circuits for outputting current command voltages to be passed to the U phase, ■ phase, and W phase, and the configurations are the same except that the input signals are different. That is, the circuit 16 is
Phase current command RTC to U phase and current U phase detection current IR
one operational amplifier that amplifies the difference between
A low-pass filter circuit 20 is configured to pass only the frequency component of the reference carrier wave of two outputs, and the circuits 17 and 18 are also configured with current commands ST for the ■ phase and W phase, respectively.
The configuration is the same as that of circuit 16, except that C, TTC1 and current current values IS' and IT are respectively input. 21 is a circuit consisting of a PWM signal processing circuit and a transistor base drive amplifier, which is similar to the circuits 16, 17.
It compares the signal from 18 with the reference carrier wave VA, and outputs PWM signals PA-PF that turn on and off each of the transistors TA to TF of the transistor impark 4.

In FIG. 3 and FIG. 4 showing the pressure control feedback circuit 53, PST is a switching command signal for controlling the feedback control of the force directly applied to the load by the electric tffiM, which switches the analog switch ASW. It is. In addition, PV is the voltage of the driving force command (O to - voltage). Furthermore, PH is a feedback signal from the strain gauge 120 attached to the ball screw 112 via the strain amplifier 121,
J131 represents the driving force applied from 1 to the gluing mechanism 107 from M.

In Fig. 4, a3 indicates a comparator circuit 54, and a D/A converter 5.
Driving force command voltage PV from 0 (Figure 3) and strain gauge 12
It compares the feedback signal PH from 0 and outputs the difference. 55 is an amplification compensation circuit which inputs the output from the comparator circuit 54 via a volume RV1 that determines the gain of pressure feedback, amplifies it, and outputs it. The ASW is an analog switch that is switched by a switching command signal nPsT to determine whether or not to perform feedback i and II control of the force applied to the load, as described above.
Reference numeral 56 denotes a bipolar clamp circuit, which outputs a clamp voltage of +Vc or -Vc according to the voltage input to the clamp circuit 56, which is input to the amplifier 51 (see FIG. 1), and outputs Vr from the filter 9. This clamp electric j earth ten VC, -
It is clamped by VC. Note that V2 is a volume for correcting the detection signal from the pressure detector.

The mold closing control of the mold clamping device by this control circuit will be explained below.

When the mold clamping device is between the mold opening operating position and the mold protection starting operating position, torque limitation is not performed, and the driving force command PL from the control η11 device is output at its maximum value, and the D/A converter 50 is The maximum voltage (eg -10v) is output from the output PV. Since the cuff and f-d pack are not performed, the switching command signal PST is not output.
The analog switch ASW is in the state shown in FIG. 4, and the driving force command voltage P is directly applied to the clamp circuit 56.
and from the clamp circuit 56 the maximum voltage +VC
.

-VC is being output. As a result, the speed command voltage V
The difference between the voltage Vs indicating the current speed and the voltage Vs representing the current speed is determined by the differential amplifier 8.
This electric power Vr is outputted through the filter 9 and is inputted to the multiplication digital-to-analog converter 10.11 through the amplifier 51 without being restricted by the clamp circuit 56. That is, no torque limitation is performed, only speed control is performed, the electric motor 11M is driven, and closed control is performed.

Specifically, the signal S from the rotor position detector 2 is
The error between the current speed VS outputted from the signal processing circuit 5 and the speed command Vo is amplified by a differential amplifier 8, and then passed through a filter 9.
If the voltage Vr outputted through the amplifier 51 does not exceed the clamp voltages +Vc and -Vc set by the clamp circuit 56, the voltage Vr is outputted as is from the amplifier 51,
Furthermore, if the clamp voltages +Vc, -Vc are exceeded, the clamp voltages +Vc, -Vc are output as the output voltage VE (=+VC or -Vc) of the amplifier 51, and the multiplying digital-to-analog converter 10.1
1 is input. On the other hand, from the U-phase and W-phase ROMs 6.7 (receiving address signals corresponding to the current rotor position from the M processing circuit 5,
Multiplying digital command values for phase and W phase
Output to analog converter 10.11. The multiplying digital-to-analog converter 10.11 believes the above error and multiplies @VE by the command value from ROM6.7,
Output phase current commands RTC and TTC for U phase and W phase, respectively,
Furthermore, the adder 12 adds () phase, W phase current command RTC
, T-C and outputs the V-phase phase current command STC. Then, the current (J, V, W phase current values IR) detected by the U-phase, W-phase current detectors 13.
, Is, IT and the current commands for each phase above R, TC, STC,
The difference with TTC is amplified by the differential amplifier 19 of circuits 16, 17, and 18, filtered by the filter circuit 20, and the voltage corresponding to the command current value of each phase is output to the PWM signal processing circuit. , compares the voltage with the reference carrier wave VA, outputs the PWM signal PA-PF to the transistor inverter 4 via the transistor base drive amplifier 21, turns on and off the transistor inverters 1 to transistors TA to TF, and converts the motor into mM. This is to control the speed.

Next, when the mold clamping device reaches the mold protection start operating position, the control device outputs a switching command signal PST, the analog switch ASW is switched, the switch SW1 is turned off, and the switch SW2 is turned on.

On the other hand, the driving force command corresponding to the mold protection pressure, that is, the mold protection command PL, is output from the limiting device, and the corresponding voltage P
V is input from the D/A converter 50 to the comparison circuit 54, this voltage PV and the load pressure voltage PH (0 to + voltage) which is the detection signal from the strain gauge 120 are compared, and the difference is outputted. The output of the amplification compensation circuit 55 is inputted to the amplification compensation circuit 55 via the volume Rv1, and the output of the amplification compensation circuit 55 is inputted to the clamp circuit 56 via the switch SW2 of the analog switch ASW.
Clamp voltages +Vc and -Vc are output according to the difference between V and the load pressure voltage PI-1 from the strain gauge 120. That is, if the difference between the voltage PV caused by the mold protection command PL and the load pressure voltage P11 from the strain gauge 120 is large, the output of the amplification compensation circuit 55 becomes large, and the voltage input to the clamp circuit 56 becomes large. The clamp voltage +VC1-Vc increases, and as a result, the current command RTC for each phase is output from the multiplying digital-to-analog converters 10 and 11 and the adder 12.

TTC and STC increase, and the output torque of electric motor M increases. On the other hand, the detection signal ftv from the strain gauge 120
When the J pressure Pit increases and the difference from the command voltage PV decreases, the output of the amplification compensation circuit 55 decreases, the outputs +Vc and -vc of the clamp circuit 56 also decrease, and the electric lff1
The output torque of M decreases. As a result, the difference between the command voltage and the load pressure voltage PH of the signal from the strain gauge 120 becomes stable at a constant value. This means that the mold closing operation is stably performed with the mold protection command issued from the control device, that is, the target mold protection pressure. Even if the torque from the electric UWM is absorbed by the friction of the transmission devices 110 to 114, the deflection of the ball screw 112, etc., the electric UWM is driven according to the comparison result between the toggle mechanism driving force of the electric IIM and the commanded mold protection pressure. Since the force is feedback-controlled so that it becomes the set driving force, there are no errors like in the conventional method.

If a foreign object or the like is present between the molds 101 and 103 during this mold protection, the moving platen 104.
The movement of the toggle mechanism 107 almost stops, and the rotation of the electric motor M also stops. However, since the speed command Vo has been output, the voltage Vr output from the filter 9 is determined by the setting value of the Zener diode ZD1, 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 voltages +Vc and -Vc clamped by the clamp circuit 56, and a voltage VE corresponding to the clamped voltages +Vc and -Vc is output.
Multiplying digital to analog converter 10.
11. As a result, the output torque of the IJ machine M is controlled by the clamp voltages VC and -VC, which means that they are controlled by the value of the mold protection command PL. Therefore, the molds can be protected even in the event of an abnormal situation where a foreign object or the like is present between the molds 101 and 103.

In addition, in the above embodiment, an example of a toggle type mold clamping mechanism using a 1-glue mechanism was shown as a power transmission device, but 1-1 is an example of a toggle type mold clamping mechanism using a glue mechanism, but the tip of the ball screw 112 is connected to the moving platen 104 without using a glue mechanism. A direct pressure mold clamping mechanism fixed directly to the rotary automatic r1 may also be used, and in this case, the strain gauge 120
may be glued to the tip of the ball screw 112.

Further, in the above embodiment, an example of torque control of an AC servo motor using a synchronous motor has been described, but the present invention can also be implemented in a DC servo motor.

Effects of the Invention As described above, according to the present invention, in an injection molding machine in which a moving platen on which a mold is mounted is driven by a servo motor via a power transmission device, the injection molding machine is provided on the moving platen side of the power transmission device. The comparison means compares the detected driving force detected by the strain detector and the set driving force, and in response to the comparison result, the torque limiting means drives the servo motor so that the driving force reaches the set value. Since the current is limited, the driving force that is driven through the power transmission device and applied to the moving platen overnight can be controlled without being affected by disturbances in driving force control, such as friction in the power transmission device. It can be controlled accurately and the mold installed in the injection molding machine can be reliably and precisely protected.

[Brief explanation of drawings]

FIG. 1 shows a mold image i! according to an embodiment of the present invention. A partially sectional side view showing a mold clamping device of an injection molding machine equipped with the device,
FIG. 2 is a base circuit diagram of the control circuit of the servo motor in the same embodiment, FIG. 3 is a block diagram of the transistor PWM control circuit of FIG. 2, and FIG. 4 is the pressure control feedback circuit of FIG. 3. FIG. DESCRIPTION OF SYMBOLS 1... Transistor PWM control circuit, 2... Position detector, M... Permanent magnet synchronous motor, 53... Pressure control feedback circuit, 54... Comparison circuit, PH...
・Feedback signal, PL...Mold protection command, 10
1.103...Mold, 104...Moving platen, 107...1-glue mechanism, 110...Ball neck 1-. 111...Cross head, 112...Ball screw, 11:'! , 114... gear, 120...
...Strain gauge, 121...Distortion amplifier.

Claims (3)

[Claims] (1) In an injection molding machine in which a moving platen on which a mold is mounted is driven by a mold clamping servo motor via a power transmission device, an injection molding machine is provided on the moving platen side of the power transmission device, and the drive servo motor is connected to the a distortion detector for detecting the driving force applied to the moving platen; a comparison means for comparing the detected driving force and the set driving force; A mold protection device for an injection molding machine, comprising: torque limiting means for limiting the drive current of the mold clamping servo motor so that (2) The power transmission device includes a transmission mechanism having a ball screw that is driven forward and backward by a mold clamping servo motor, and a toggle mechanism that is driven to bend and extend by the transmission mechanism, and the strain detector is equipped with a toggle mechanism that is driven to bend and extend by the transmission mechanism. A mold protection device for an injection molding machine according to claim 1, which is disposed at an end portion of the toggle mechanism. (3) The power transmission device is composed of a ball screw that is driven forward and backward by a mold clamping servo motor, the tip of the ball screw is rotatably fixed to the moving platen, and the tip of the ball screw is attached to the A mold protection device for an injection molding machine according to claim 1, which is disposed in a detector.