JPH08207096A - Injection pressure control of injection molding machine - Google Patents

Abstract

PURPOSE: To obtain satisfactory control characteristics such as reduced electric power consumption, the capability of a response at a rapid starting speed to a change in pressure setting to a high value, and a minimum deviation between a setting value and an execution value, when controlling the retained injection pressure of an injection molding machine. CONSTITUTION: An addition signal 29 obtained by calculating a pressure deviation signal 22 for injection pressure is added to an oil volume control signal 26 for controlling a pumping means 8 when a retained injection pressure is controlled, in a closed loop control mode using a solenoid relief valve 7, based on an oil retained by controlling the pumping means 8 in the open loop control mode. A calculator 28 for arithmetic process consists of an amplifier and a differentiator, which are independent of each other and function side by side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving pressure responsiveness and followability in program control of injection holding pressure of an injection molding machine.

[0002]

2. Description of the Related Art In program control of injection holding pressure, the amount of oil held from a pump means is preset to the minimum required amount. However, since the screw hardly moves during the injection holding pressure process, the required amount of oil is being injected and filled. It is generally 30% or less. Moreover, since the set value is often not directly reflected on the molded product, it is customary not to change it once it is set.

[0003]

However, when the amount of the retained oil is excessive with respect to the set value of the retained pressure, the excessive oil amount causes a hydraulic pressure loss and raises the temperature of the hydraulic oil. On the other hand, if the holding oil amount is insufficient with respect to the holding pressure setting value, the holding pressure execution value may not reach the holding pressure setting value. Also, if the holding pressure setpoint is programmed to change from low to high,
The rise of pressure to a high value is delayed.

[0004]

Therefore, there is provided pump means for varying the amount of oil, a direction switching valve for switching the direction of the oil amount, and an electromagnetic valve provided in a pipe line between the pump means and the direction switching valve. When driving the hydraulic device consisting of a relief valve, injection filling control performs speed control by the pump means,
In the injection holding pressure control, in which the pump means is switched to the holding oil amount and the pressure is controlled in a closed loop by the electromagnetic relief valve, the pressure deviation signal of the closed loop pressure control circuit of the electromagnetic relief valve is changed to the injection holding pressure. During the control, it is added to the oil amount control signal of the pump means as an addition signal as a result of arithmetic processing, and the addition signal is obtained by differentiating the pressure deviation signal of the closed loop pressure control circuit of the electromagnetic relief valve to increase the internal oil amount It is configured and controlled so as to include the signal of the direction.

[0005]

With this configuration, the amount of retained oil can be set to a sufficiently low value with less loss, and when the retained pressure execution value does not reach the retained pressure set value, the calculator Since the addition signal based on the amplification action is added to the oil amount control signal of the pump means, the holding oil amount increases and the holding pressure execution value reaches the holding pressure set value.
In addition, when the rising pressure to the high value is slow in the program control of the holding pressure, the addition signal based on the differential action of the computing unit indicates that the oil of the pump means is increased only when the pressure is rising to the high value in the holding pressure program control. The pressure rises faster because it is added to the quantity control signal.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, one embodiment of the present invention will be described in detail with reference to FIG. Reference numeral 1 denotes a screw, which is inserted into a heating cylinder (not shown) to plasticize the raw material resin and injection-fills the plasticized raw material resin into a mold (not shown). 2 is screw 1
Is a hydraulic cylinder for reciprocating in the heating cylinder,
When the hydraulic oil is guided to the room on the anti-screw side, the screw advances and ejects. Reference numeral 3 is a hydraulic motor that rotates a screw to plasticize the raw material resin. Reference numeral 4 is a speed detector that detects the injection advance speed of the screw, and is composed of a rotary encoder and a potentiometer that rotate by a pinion or the like that is engaged with a rack or the like that is attached to a member that moves with the screw. Reference numeral 5 denotes a pressure detector for detecting the injection pressure, which is provided in the injection side chamber of the injection cylinder or in its pipeline.

Reference numeral 6 denotes an oil quantity directional switching valve, which selectively switches the oil quantity from the pump means 8 to either the injection cylinder 2 or the hydraulic motor 3 in response to a command signal from a sequence control device (not shown). An electromagnetic relief valve 7 controls the hydraulic pressure of the pump means 8 by the current from the hydraulic pressure control amplifier 27. Reference numeral 8 denotes pump means, which is composed of a variable discharge pump of various types or a combination of a fixed discharge pump and a flow rate adjusting valve, and is controlled by a current from the oil amount control amplifier 20. Reference numeral 9 is a hydraulic oil tank.

An injection speed setting signal 10 is generated by an injection speed setting device provided in a molding machine control device (not shown). The injection speed setting signal 10 is matched with the injection forward speed signal from the speed detector 4 in the adder 13 to output the speed deviation signal 14, which constitutes a closed loop speed control circuit.
The switch 15 is provided so that the speed deviation signal 14 is effective only during injection filling, and the switch 15 is opened when the injection holding process is started and the injection holding signal 11 is turned on from a sequence controller (not shown). During injection filling, the speed deviation signal 14 is closed and the PID is passed through the switch 15.
It is input to the calculator 16. The PID calculator 16 is a known closed-loop calculator and performs proportional, integral, and derivative calculations.

The output of the PID calculator 16 is added to the injection speed setting signal 10 by the adder 17 and becomes the oil amount control signal 18. After the injection filling, the switch 15 is opened when the injection holding process is switched by the set value such as the screw position.
Only the injection speed setting signal 10 is input to the adder 17 and becomes the oil amount control signal as it is, and the injection holding oil amount is controlled in an open loop. An adder 19 is added for the present invention. The adder 19 adds the oil amount control signal 18 and the addition signal 29 and inputs them to the oil amount control amplifier 20.

Reference numeral 12 is an injection pressure setting signal, which is generated by an injection pressure setting device provided in a molding machine control device (not shown). The injection pressure setting signal 12 is matched with the injection pressure signal from the pressure detector 5 in the adder 21 to output the pressure deviation signal 22, which constitutes a closed loop pressure control circuit. The switch 23 is provided so that the pressure deviation signal 22 is effective only in the injection holding process, and the injection holding process is performed.
The switch 23 is closed when 1 is turned on by a sequence control device (not shown). During the injection holding process, the pressure deviation signal 22 is input to the PID calculator 24 via the switch 23 which is closed. The PID calculator 24 is a known closed-loop calculator, and performs proportional, integral, and derivative calculations.

The output of the PID calculator 24 is added to the injection pressure setting signal 12 by the adder 25 and becomes a hydraulic pressure control signal 26. Since the switch 23 is open during the injection filling, only the injection pressure setting signal 12 is input to the adder 25 and becomes the hydraulic control signal as it is, and the injection filling speed is controlled in the open loop. The hydraulic control signal 26 is input to the hydraulic control amplifier 27 and converted into a current for driving the electromagnetic relief valve 7.

On the other hand, the pressure deviation signal 22 that has passed through the switch 23 that is closed by turning on the injection hold signal 11 is also input to the calculator 28. The calculator 28 comprises an amplifier having a predetermined amplification degree and a differentiator having a predetermined differential constant. The differentiator has a polarity that increases the oil amount in the pump means when the injection holding pressure setting signal changes to a high value. Generates only the signal. The amplifier and differentiator are arithmetic units 28
Function independently and in parallel within the machine, and whether to activate both at the same time or selectively depends on the molding conditions.Therefore, an operating unit (not shown) connected to the molding machine control device or sequence control device It can be set. The output of the calculator 28 is input to the adder 19.

Next, the operation of the arithmetic unit 28, which is a feature of the present invention, will be described. The problems in the injection holding process are listed below. When performing program control of the injection holding pressure that changes to a high value of the injection holding pressure, the pressure rises slowly. 2. Because the amount of retained oil is insufficient, the execution value becomes lower than the injection retention pressure set value. 3. Since the amount of retained oil is excessive, the oil temperature rises due to hydraulic pressure loss, and the amount of electric power increases. 4. In the case of molding conditions where injection filling is performed by the holding pressure even after switching to the holding pressure, the amount of the holding oil becomes the filling speed, and therefore the filling is performed at an unexpected speed.

The above 1. With respect to the above problem, the differentiator of the computing unit 28 works effectively, and the amount of oil required for the rapid increase of the holding pressure can be temporarily increased, so that the holding pressure rises quickly, and the sink mark of the molded product is reduced. It has a remarkable effect in prevention. 2. With respect to the above problem, since a steady pressure deviation signal is added to the oil quantity control signal as an appropriate addition signal by the amplifier of the calculator 28, the pressure deviation due to the oil quantity shortage can be eliminated. The above 3. Regarding the problem of 1., And 2. Although the amount of retained oil has been set excessively as a means for solving the above problem, by implementing the present invention, it is possible to solve the problem by setting the amount of retained oil itself to be smaller than before. 4. The above problem can be solved by enabling only the differentiator of the calculator 28. That is, when the pressure deviation signal has a large value due to filling during the injection holding step, if the pressure deviation signal is constantly added to the oil amount control signal by the amplifier in the calculator 28, The amplifier is disabled because there is a risk that the filling speed will change and molding defects such as burrs and short shots will occur in the molded product. In that case, the addition signal is not stationary, so that no problem occurs.

[0015]

Since the injection holding pressure control can be executed with the minimum required amount of oil, it is possible to obtain good holding pressure control with less power loss, faster pressure rise, and less deviation from the set value.

[Brief description of drawings]

FIG. 1 is a schematic hydraulic and electric control circuit showing an embodiment of the present invention.

[Explanation of symbols]

 1 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Screw 2 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Injection cylinder 4 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Injection speed Detector 5 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Injection pressure detector 6 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Direction switching valve 7 ・ ・ ・ ・ ・··· Electromagnetic relief valve 8 ······ Pump unit 10 ······ Injection speed setting signal 11 ···・ ・ ・ ・ ・ ・ ・ ・ Injection hold signal 12 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Injection pressure setting signal 13, 17, 19, 21, 25 ... Adder 14 ...・ ・ ・ ・ ・ ・ ・ ・ Velocity deviation signal 15, 23 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Switch 16, 24 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ PID calculator 18 ・ ・ ・ ・ ・..... Oil quantity control signal 2 0 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Oil quantity control amplifier 22 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Pressure deviation signal 26 ・ ・ ・ ・ ・ ・・ ・ Hydraulic control signal 27 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Hydraulic control amplifier 28 ・ ・ ・ ・ ・ ・ ・ ・ ・ Calculator 29 ・ ・ ・ ・ ・ ・... Addition signal

Claims (2)

[Claims] 1. A hydraulic system comprising a pump means for varying the amount of oil, a direction switching valve for switching the direction of the oil amount, and an electromagnetic relief valve provided in a conduit between the pump means and the direction switching valve. In the injection control method, the injection filling control performs speed control by the pump means, and the injection holding pressure control switches the pump means to the holding oil amount and controls the pressure in a closed loop by the electromagnetic relief valve. A control of injection holding pressure, wherein a pressure deviation signal of a closed loop pressure control circuit of the electromagnetic relief valve is added to an oil amount control signal of the pump means as an addition signal of a result of arithmetic processing during injection holding pressure control. Method. 2. The injection holding pressure, wherein the addition signal in claim 1 includes a signal in the direction of increasing the oil amount, among signals obtained by differentiating the pressure deviation signal of the closed loop pressure control circuit of the electromagnetic relief valve. Control method.