JPH02120019A - Control method of injection molding machine and device - Google Patents

Abstract

PURPOSE:To eliminate generation of overshooting at the time of a speed reduction and transformation, by a method wherein after a signal relating to a changeover of an action of an actuator is put out, open-loop control is performed and after the lapse of a fixed period of time, closed-loop control is performed. CONSTITUTION:In the case where a screw 12 starts injection from a suspended state by putting out a command signal Vs, a switch 44 in a speed property compensating part 34 maintains an ON state. An input side and output side of an amplifier circuit part 41 are short-circuited to each other, a flow control signal Vo put out from the same compensating part 34 becomes Vo = Vs and open-loop control is performed. The screw 12 is moved forward through output of the speed command signal Vs, the open-loop control is kept ON until the same arrives at a position S1 and overshoot does not occur. When a fixed period of time lapses after a speed command signal Vs is put out, the screw arrives at a changeover position S1 and the switch 44 is turned OFF. In this instance, closed-loop control based on high gain is performed. Since an effect due to delay in response is already canceled, a speed arrives at a predetermined speed without performing overshooting.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control method for an injection molding machine, and particularly to a control method including operation switching control of an actuator, and a control device used in the method.

[Conventional technology]

In an injection molding machine, a closed loop control system (feedback control system) controls the operating speed and operating pressure of various actuators such as a hydraulic cylinder and an oil motor. In such a control system, a preset command value is compared with an actual value obtained from actual operation to obtain the deviation, and a control signal that has undergone characteristic compensation and amplification processing for the deviation is used to control the hydraulic circuit. control so that the execution value matches the command value.

[Problem to be solved by the invention]

By the way, between the controller and actuator of the closed-loop control system in an injection molding machine, there are various hydraulic circuit parts including piping, rubber hoses, valves, and the actuator body such as a hydraulic cylinder that impair responsiveness, and command signals are output. Even if the actuator is activated, there will be a response delay before the actuator actually starts operating.

Therefore, as shown in FIG. 5, when the actuator is moved from the stopped state Vx to the predetermined speed Vl (first speed), a response delay Tr occurs after the command signal for operation switching is output. In this case, the deviation between the command signal and the feedback signal obtained from the actual speed detection becomes extremely large. As a result, the command value of the command signal intended to compensate for this also becomes significantly large, resulting in the problem of overshoot E as shown in the figure. The figure shows a case where the operating state BV1 is further shifted to the second operating state V2 (second speed), but in this case, there is no major problem.

Note that overshoot E can be suppressed by setting the gain and time constant of the characteristic compensation circuit low and making its control characteristics gentle. Therefore, contradictory problems arise in that the responsiveness during gear changes and pressure changes and the responsiveness to disturbances during settling are reduced. After all, the reality is that a compromise point is determined through trial and error when setting conditions for the characteristic compensation circuit.

It is an object of the present invention to provide a control method and apparatus for an injection molding machine that eliminates the problems existing in the conventional technology.

[Means to solve the problem]

In the injection molding machine control method according to the present invention, when switching the actuator 2 from a stopped state Vx to an operating state v1 of a predetermined speed, at least a command signal Vs related to the operation switching is provided.
The present invention is characterized in that open-loop control is performed for a predetermined time Ti after outputting, and closed-loop control is performed after the elapse of the predetermined time Ti. In addition,
The predetermined time Ti can be set or detected based on when the actuator 2 reaches a predetermined position, a predetermined amount of change in position, or the like. Further, this control method can be similarly applied to the case where the operating pressure is switched from the first pressure to a different second pressure.

On the other hand, when configuring a control system for controlling, for example, the operating speed of the actuator 2, the control device 1 for an injection molding machine according to the present invention includes a first control system 3 that performs open-loop control, and a second control system that performs closed-loop control. System 4 and the predetermined speed V! from the stopped state Vx! It is characterized by comprising a control switching means 5 that switches from the first control system 3 to the second control system 4 after a predetermined time Tf has elapsed after the output of the command signal Vs for switching. Further, the present control device 1 can be similarly applied to the case where the operating pressure is switched from a first pressure to a different second pressure.

The term "open-loop control" in the present invention includes closed-loop control in which the gain and time constant of characteristic compensation are reduced to approximate open-loop control.

[For production]

Next, the operation of the present invention will be explained.

According to the method and apparatus 1 for controlling an injection molding machine according to the present invention, control is performed based on the first control system 3 that first performs open-loop control. On the other hand, when the actuator 2 is switched from the stopped state Vx to the operating state Vl of a predetermined speed, after the command signal Vs related to this operation switching is output, a predetermined time Ti elapses, for example, the actuator 2 reaches a predetermined position. At that point, the control system switches to the second control system 4, thereby performing closed loop control.

Therefore, open-loop control is performed while the response delay of the control system occurs, and closed-loop control is performed after the actual response starts, thereby avoiding the occurrence of overshoot.

〔Example〕

Preferred embodiments of the present invention will be listed below and explained in detail based on the drawings.

First, in order to clarify the present invention, a schematic configuration of an injection molding machine will be described with reference to FIG. 1.

In the figure, reference numeral 11 denotes an injection device, which includes a heating cylinder 13 in which a screw 12 is disposed. Heating cylinder! The rear end of the screw 12 is integrally connected to an injection cylinder 14 constituting the actuator 2, and the rear end of the screw 12 is connected to an injection ram 15 disposed inside the cylinder. Further, the inside of the injection cylinder 14 behind the injection ram 15 becomes an oil chamber 14a, and this oil chamber 14a is connected via a switching valve 16 to a proportional pump (electric proportional discharge pump) 17 which is a hydraulic pressure source.

Therefore, by applying hydraulic pressure to the oil chamber 14a and controlling its magnitude, the screw 12 moves forward at a predetermined operating speed or operating pressure to perform an injection operation. Further, the rear end of the injection ram 15 is connected to a spline shaft 1 which becomes the output shaft of the oil motor 18.
The screw 12 is spline-coupled to the oil motor 9, and the screw 12 is rotated by the rotation of the oil motor 18, thereby performing a metering operation. In addition,
2o is a hopper that supplies the contained molding material into the heating cylinder cylinder 3.

By the way, as the proportional pump 17, various proportional pumps 60, 70, 80, 90 illustrated in FIGS. 6 to 9 can be used.

The proportional pump 6o in FIG. 6 has a built-in pump body 61, and the discharge pressure and discharge amount of the pump body 6I can be varied by changing the angle of the swash plate 62. The swash plate 62 stops at a position where the pressing force of one operating piston 63 is balanced, and when pressure oil is supplied to the operating piston 63, the swash plate 62 is displaced in a direction in which the discharge amount of the pump body 61 decreases. Further, a control valve 64 is connected to the discharge side of the pump main body 61 in a branched manner, and this control valve 64 is further connected to the operation piston 63 via a safety valve 65. In addition, a potentiometer 66 for detecting the discharge amount of the pump body 61, a motor 67 for driving the pump body 61, and a tank 68 connected to the suction side of the pump body 61 are provided.

Therefore, the proportional pump 60 receives the flow rate control signal V input to the controller 69 connected to the control valve 64.

Alternatively, the discharge flow rate and discharge pressure are generated according to the pressure control signal PO. Note that the proportional pump 70 shown in FIGS. 7 and 8
and 80 also have different hydraulic circuit configurations, but basically the 6th
It exhibits the same function as the proportional pump 60 shown in the figure. In FIGS. 7 and 8, the same functional parts as in FIG. 6 are given the same reference numerals. Further, the proportional pump 90 shown in FIG. 9 is separately provided with a sub-pump 91 for control, and is different from the previous three proportional pumps in that it operates a control cylinder 94 attached to the pump body 61 via a control valve 92. different from. This proportional pump 90 has the advantage of excellent responsiveness. In addition, the controller 6 built in any of the proportional pumps 60 to 90
9 includes a compensation circuit for the control system in the proportional pump.

On the other hand, a pressure detector 23 facing the oil chamber 14a is attached to the injection cylinder 14. As the pressure detector 23, a strain gauge, a piezoelectric strain sensor, etc. can be used. Furthermore, a detection lever 24 that follows the movement of the screw 12 is provided at the front end of the injection ram 15, and a position detector 25 that detects the screw position based on the position of this detection lever 24 is provided.

Note that the actual speed value is obtained by calculating the screw position. As the position detector 25, a potentiometer, a magnetic scale, a linear encoder, etc. can be used.

Further, 30 is a central controller to which various setting devices (not shown) such as injection speed, injection speed change position, injection pressure, and injection pressure transformation timing are connected. The position detector 2
5 is connected to a central controller 30 via an amplifier 31, and the central controller 30 generates a speed command signal Vs and a pressure command signal Ps corresponding to the operating speed and operating pressure based on the detection signal of the position detector 25 and timing by a built-in timer. Output.

Furthermore, a switching position setter 32 is provided for characteristic compensation for operating speed, and is connected to the output side of the amplifier 31 as well as the input side of the comparator 33. 34 is a speed characteristic compensator, which connects the output side of the differentiator 35 for differentiating the output of the amplifier 31 and the output side of the comparator 33, and connects the central controller 30 to input the speed command signal VS. Then, the speed characteristic compensator 34
The output side of is connected to the proportional pump 17 and supplies a flow rate control signal Vo.

An example of a specific circuit of the speed characteristic compensator 34 is shown in FIG. The circuit has an adder H for the feedback signal Vf, which is the output of the differentiator 35, and the speed command signal Vs. In addition, the addition section H
The amplifier circuit 41 includes an amplifier circuit section 41 with a gain of G times to amplify the signal Vm, and an amplifier circuit 42 with a gain of 1 times to invert the phase of the output of the amplifier circuit section 41. The output of the circuit 42 becomes the flow rate control signal Vo. Note that the amplifier circuit section 4
A gain of 1 (G times) is set to a high gain so that it can quickly respond to speed changes or disturbances. On the other hand, it includes an amplifier circuit section 43 with a gain of 1 for inverting the phase of the speed command signal Vs, and the output side of the circuit section 43 is connected to the input side of the amplifier circuit section 42 . Further, the input side and the output side of the amplifier circuit section 4I are connected through a normally closed (normally on) switch (analog switch) 44, and the switch 44 is turned off by the coincidence signal Vc output from the comparator 33. Note that R1 to R8 are resistors, and CI is a capacitor.

On the other hand, 36 is a switching pressure setting device for characteristic compensation for the operating pressure, and is connected to the input end of a comparator 37 as well as the output side of an amplifier 38 for amplifying the detection signal of the pressure detector 23. Further, 39 is a pressure characteristic compensator,
The output side of the comparator 37 and the output side of the amplifier 38 are connected, and the pressure command signal PS of the central comparator 30 is inputted. The output side of the pressure characteristic compensator 39 is connected to the proportional pump 17 and supplies the pressure control signal Po. An example of a specific circuit of the pressure characteristic compensator 39 is shown in FIG. 3, but its configuration is similar to that of the speed characteristic compensator 34 shown in FIG.
It is the same as the circuit of Therefore, in the circuit shown in FIG. 3, the same parts as in FIG. 2 are given the same reference numerals to clarify the structure. In FIG. 3, Pf indicates a pressure feedback signal supplied from the amplifier 38, Pc indicates a coincidence signal supplied from the comparator 37, Pm indicates a signal from the adder Hp, and 44p indicates a switch.

Next, the operation of the control device 1 including the injection molding machine control method according to the present invention will be explained.

First, the case of speed control will be explained. In the switching position setter 32, the timing for switching from the stopped state Vx to the operating state v1 of a predetermined speed is preset as a speed switching position Sl. For example, as shown in FIG. 4, this switching position S1 is a speed command signal V for switching to the operating state VI.
The position at which the screw 12 actually starts responding can be set based on s, and corresponds to the predetermined time Ti.

Now, assume that the screw 12 starts injection by outputting a command signal Vs for changing from a stopped state Vx to an operating state Vl at a predetermined speed. If the screw 12 is stopped, the coincidence signal Vc is not outputted because the position S1 is reached. Therefore, the switch 44 in the speed characteristic compensator 34 remains on. As a result, the input side and the output side of the amplifier circuit section 41 are short-circuited, and the flow rate control signal Vo output from the compensator 34 becomes V o =V s. That is, in this case, the first control system 3 is configured and substantially open loop control is performed. Therefore, the speed command signal Vs
The screw 12 moves forward by the output, and open loop control continues until it reaches position S1, and no overshoot occurs.

Further, after a predetermined time Ti has elapsed after the speed command signal Vs is output, the screw 12 reaches the switching position Sl. As a result, the switch 44 is turned off by the control switching means 5. That is, the switching position Sl is detected by the position detector 25, and the detection signal is sent to the comparator 3 via the amplifier 31.
3. Then, a match signal VC is output from the comparator 33, and the switch 44 is turned off. Therefore, in the adder H, the speed command signal Vs and the feedback signal V
f is added to become the signal Vm, and the flow rate control signal Vo output from the speed characteristic compensator 34 is Vo=Vs+(VmXG
). In this case, the second control system 4 is configured and can perform closed-loop control (feedback control) with a high gain, and since the influence of response delay has already been canceled, the overload control system 4 is configured as shown in FIG. Reach the set speed quickly without shooting.

Furthermore, it responds promptly to subsequent disturbances or gear changes. The figure shows a second operating state v2 in which the speed is further changed.
shows. In this case, closed-loop control is maintained as it is before and after switching the operation, but the occurrence of overshoot can be almost ignored. In this way, the speed characteristic compensator 34 adjusts the injection ram 15 from the start of outputting the speed command signal Vs.
The compensation value up to the start of the response and the compensation value thereafter can be switched and set.

On the other hand, the pressure command signal Ps output from the central controller 30 is similarly controlled using the pressure characteristic compensator 39. First, the oil pressure of the injection cylinder 14 is detected by the pressure detector 25 and inputted to the comparator 37 via the amplifier 38. A switching pressure S2 is set in the switching pressure setting device 36, and this switching pressure S2 can be set to, for example, the magnitude immediately after the pressure command signal Ps is output and the response actually starts.

Therefore, when the detected pressure in the feedback signal Pf is the first pressure lower than the switching pressure S2 set in the switching pressure setting device 36, the switch 44p is turned on, and as a result, the output from the pressure characteristic compensator 39 is increased. The pressure control signal PO is Po=P
It becomes s. Even if a pressure command signal Ps for shifting to the second pressure is output, open loop control is continued until pressure increase starts. On the other hand, if the detected pressure becomes larger than the switching pressure S2 by actually increasing the pressure in response to the pressure command signal Ps, the switch 44p is turned off, and the pressure control signal Po output from the speed characteristic compensator 39 becomes Po= Ps+ (PmXG), and closed loop control is performed. In this way, the pressure characteristic compensator 39 can also switch and set the compensation value from the start of outputting the pressure command signal Ps to the time when the pressure increase in the oil chamber 14a is confirmed, that is, the response is made, and the compensation value after that. can be controlled.

Although the embodiments have been described in detail above, the present invention is not limited to these embodiments.

For example, in the embodiment, control of the screw operation is shown, but it can be similarly applied to mold opening/closing operations, etc. Furthermore, various methods can be used for switching the characteristic compensation. In addition, the detailed structure, method, etc. may be arbitrarily changed without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, the method and apparatus for controlling an injection molding machine according to the present invention performs open-loop control for at least a predetermined period of time after a signal related to the operation switching is output when switching the operation of the actuator, and Since closed-loop control is then performed, it is possible to eliminate the occurrence of overshoot during gear changes and pressure changes, and it is possible to easily perform optimal characteristic compensation in the control process. In addition, it achieves high responsiveness, enables high-speed and accurate control, and achieves high quality molded products.

[Brief explanation of the drawing]

Fig. 1.2 A block system diagram showing the control device for an injection molding machine according to the present invention. Fig. 2: A specific circuit diagram of the speed characteristic compensator in the control device. Fig. 3: Pressure characteristic compensator in the control device. 4: A timing chart showing the operating state of the control device; FIG. 5: A timing chart showing the operating state of the conventional control device; FIGS. 6 to 9 2 according to the present invention FIG. 3 is a hydraulic circuit diagram showing different proportional pumps in the control device. In the drawings, l2 control device 3: first control system 5: control switching means X: stopped state 2: actuator 4: second control system Ti22 fixed time l: operating state Fig. 2 Fig. 1 Figure 6

Claims (1)

[Scope of Claims] [1] When switching the operation of the actuator, open-loop control is performed at least for a predetermined time after a command signal related to the operation switching is output, and closed-loop control is performed after the predetermined time has elapsed. A method for controlling an injection molding machine, the method comprising a control process. [2] When switching the actuator from a stopped state to an operating state at a predetermined speed, open-loop control is performed at least for a predetermined time after the command signal related to operation switching is output, and closed-loop control is performed after the predetermined time elapses. A method for controlling an injection molding machine, characterized by performing the following steps. [3] A claim characterized in that the predetermined time is set or detected based on the actuator reaching one or more of a predetermined position, a predetermined amount of change in position, a predetermined operating speed, and a predetermined operating speed change rate. Item 2. A method for controlling an injection molding machine according to item 2. [4] In a control method for an injection molding machine that includes a control process in which the operating pressure of an actuator is controlled by switching from a first pressure to a different second pressure, at least a predetermined period of time after a command signal related to pressure switching is output. A method for controlling an injection molding machine, characterized in that open-loop control is performed during the predetermined time period, and closed-loop control is performed after the predetermined time period has elapsed. [5] The method for controlling an injection molding machine according to claim 4, wherein the predetermined time is set or detected based on when the actuator reaches a predetermined operating pressure, a predetermined operating pressure change rate, or both. [6] In a control device that controls the operation of an actuator, a first control system that performs open-loop control, a second control system that performs closed-loop control, and a predetermined period of time after a command signal related to actuator operation switching is output. 1. A control device for an injection molding machine, comprising control switching means for switching from a first control system to a second control system after the period of time. [7] A first control system that outputs a first control signal proportional to the command signal, and a calculated signal obtained by amplifying the deviation between the command signal and the detected feedback signal, and the first control signal obtained by adding the first control signal. 7. The control device for an injection molding machine according to claim 6, further comprising a second control system that outputs a second control signal. [8] In a control device for an injection molding machine that controls the operating speed of an actuator, there is a first control system that performs open-loop control, a second control system that performs closed-loop control, and a control system that controls the actuator from a stopped state to an operating state of a predetermined speed. 1. A control device for an injection molding machine, comprising control switching means for switching from a first control system to a second control system after a predetermined period of time has elapsed after a command signal for switching to the first control system is output. [9] Claim 8, wherein the predetermined time is set or detected based on the actuator reaching one or more of a predetermined position, a predetermined amount of change in position, a predetermined speed, and a predetermined speed change rate. A control device for the injection molding machine described above. [10] In a control device for an injection molding machine that controls the operating pressure of an actuator, a first control system that performs open-loop control, a second control system that performs closed-loop control,
The control system is characterized by comprising control switching means for switching from the first control system to the second control system after a predetermined period of time has elapsed after the output of a command signal for switching the operating pressure from the first pressure to a different second pressure. The control device for an injection molding machine according to claim 6. [11] The actuator maintains a predetermined operating pressure for a predetermined time;
Claim 1 characterized in that the setting or detection is based on reaching one or both of the predetermined operating pressure change rates.
A control device for an injection molding machine according to 0.