JPH03248829A - Closed loop control method of injection cylinder pressure of injection molding machine - Google Patents

Abstract

PURPOSE:To enable controlling for even a change of an oil temperature by a method wherein both of oil pressures at the inlet of an injection side chamber of an injection cylinder and hydraulic pressure at the outlet of an injection return side chamber are detected, a pressure difference between them and a value set up beforehand are compared with each other, feedback of a command signal based on this amount of a difference is performed and closed loop control of a pressure control device is performed. CONSTITUTION:Pressure sensors S1, S2 are provided in a flow path of pressure oil connected with chambers 42, 44 each. A control circuit 50 performs operation of a pressure difference P(=P1-P2) by making use of a hydraulic pressure detected value P1 of an injection actuation side oil chamber and a hydraulic pressure detected value P2 of a back pressure actuation side oil chamber detected by both the pressure sensor S1, S2, to begin with. Then the pressure difference P is compared with a set up value P0 set up beforehand and a command signal based on its amount of a difference is sent out to a control device 52. Based on this command signal, the control device 52 of a valve or a pump adjusts discharge pressure so that substantial injection force of an injection cylinder 26 is not lowered.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an injection cylinder pressure closed-loop control method for an injection molding machine, and particularly to an injection cylinder pressure control method for an injection molding machine that can realize repeatable and stable control. The present invention relates to a cylinder pressure closed loop control method.

[Conventional technology]

Generally, the injection cylinder of an injection molding machine is controlled as shown in FIG. In FIG. 2, reference numeral 10 is a barrel, and at the tip of the barrel 10 there is provided a nozzle 12 that comes into contact with a mold (not shown) and guides molten resin to the resin injection port of the mold, and inside the nozzle 12. A screw 14 is inserted and can be rotated and moved back and forth in the axial direction.

A raw material supply hopper 20 is provided at the rear of the barrel 10, and resin raw materials in the form of pellets or powder are supplied into the barrel 10 through this hopper 20.

The screw 14 is connected at its rear end to a rotating member 16, and this rotating member 16 is connected to a connecting member 18 with a bearing 22.
It is rotatably supported through. This rotating member 16
is rotationally driven by a hydraulic motor 24 provided behind it. Further, a pair of injection cylinders 26.26 are separately provided, and are connected to bearing units 1 to 28 composed of a rotating member 16 and a connecting member 18, and to injection pistons 30, 30 within the injection cylinders 26.26. rod 32
32 is fixed.

Therefore, the screw 14 has a pair of injection cylinders 26, 26
As a result, the bearing unit 28 moves forward and backward in the axial direction. In this case, the hydraulic motor 24 is connected to the two-position switching valve 3.
4 to a variable discharge pump 36, and the screw 14 is rotationally driven via the rotating member 16 by switching the two-position switching valve 34.

In addition, the injection return side chamber 44.4 of the injection cylinder 26.26
4 and the injection side chambers 42 and 42 are respectively connected to a position switching valve 40, and this three-position switching valve 40 and the variable discharge pump 3
A flow rate regulating valve 38 is connected between the valve 6 and the valve 6.

The injection device configured in this manner operates as follows.

First, during metering, the two-position switching valve 34 connected to the hydraulic motor 24 is switched by excitation, and the hydraulic motor 24 is rotationally driven by the pressure oil discharged from the variable discharge pump 36. The rotation of the hydraulic motor 24 causes the rotary member 16 to rotate the screw 14, and the raw material supplied into the barrel 10 from the raw material supply hopper 20 is transferred to the heat of the filter provided on the outer periphery of the barrel 10 and the screw 14. The resin melts due to shear heat generated by the rotation of the resin. Furthermore, while accumulating molten resin in front of the barrel 10, the rotating screw 14 retreats due to the pressure of the molten resin accumulated in the front of the barrel 10, and when this molten resin reaches a predetermined amount, the two-position switching valve 34 is opened. The rotation of the hydraulic motor 24 is stopped by blocking due to de-energization.

Next, when the solenoid of the three-position switching valve 40 is energized,
Pressure oil discharged from the variable discharge pump 36 via the flow rate regulating valve 38 flows into the injection side chamber 42 of the injection cylinder 26,26.

In this case, the oil in the injection return side chamber 44 is discharged into the tank 46.

In this way, the pistons 30 and 30 of the pair of injection cylinders 2626 move to the left, so the rod 3 of this piston
The screw 14 connected to 2 and 32 is the bearing unit l~
It can move to the left together with 28 and inject molten resin.

In this case, conventionally, a pressure sensor S1 is disposed in the discharge path of the variable discharge pump 36, and the pressure sensor S1 is fed back to a controller (not shown), and the difference with a set value is compared in the controller, and a signal corresponding to the difference is sent to the electromagnetic relief valve 48. A method of controlling the feeding pressure has been developed.

Furthermore, in Japanese Patent Application Laid-Open No. 6.2-228701, in order to improve the responsiveness of pressure control of the injection cylinder 26, 26, a flow valve in the discharge passage is completely unnecessary, and a feedback signal from the sensor S1 and a setting are used. A command signal is directly sent to the variable discharge pump 36 to make the deviation zero, and the pressure oil flowing into the injection cylinder 2626 is controlled by controlling the discharge amount. A method to control is shown.

[Invention or problem to be solved]

However, according to the injection cylinder pressure closed loop control method described above, the pressure is controlled by a feedback signal based on the discharge pressure from the pressure sensor installed in the discharge path of the variable discharge pump. Back pressure due to pressure loss on the injection return side of the cylinder increases, and the injection force substantially decreases. Moreover, since the pressure on the injection return side of the injection cylinder is not controlled, it also changes with changes in oil temperature. This may have little effect if the screw is stopped, but it becomes a problem because the screw is moving forward at the time of primary pressure holding when switching to pressure closed loop control. That is, since this is a method in which only the discharge pressure of the discharge pump is controlled and the hydraulic pressure entering the injection cylinder is controlled, the above-mentioned problem arises and it is difficult to perform repeatable and stable control.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a closed-loop control method for injection cylinder pressure of an injection molding machine with repeatability stability.

[Means to solve the problem]

The injection cylinder pressure closed loop control method for an injection molding machine according to the present invention includes a first sensor (S1) that detects the oil pressure in the injection operation side oil chamber of the injection cylinder of the injection molding machine, and a hydraulic pressure in the back pressure operation side oil chamber. a second sensor (S2) that detects the pressure of the oil chamber on the injection operation side; and a pressure control means that controls the pressure of the injection operation side oil chamber; S2) and the detected value (P2) (ΔP=P, -P2
) is compared with the set value (P0), and the differential pressure (ΔP) and set value (
It is characterized in that the pressure control means is controlled based on the difference between the pressure control means and the pressure control means.

[For production]

According to the injection cylinder pressure closed loop control method according to the present invention, both the hydraulic pressure entering the injection side chamber of the injection cylinder and the hydraulic pressure exiting from the injection return side chamber are detected, and the difference between these pressures and a preset value are detected. Since the pressure control means is controlled in a closed loop by feeding back a command signal based on the difference, it is possible to control changes in oil temperature and the like. Therefore, it is possible to achieve injection force with excellent repeatability without being affected by changes in oil temperature.

〔Example〕

Next, an embodiment of the injection cylinder pressure closed loop control method according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block circuit diagram illustrating an injection cylinder pressure closed loop control method according to an embodiment of the present invention, which can be applied to injection control of a conventional injection molding machine shown in FIG. 2.

For convenience of explanation, the same parts as those shown in FIG. 2 will be described with the same reference numerals.

In FIG. 1, an injection side chamber 42 and an injection return side chamber 44 in the injection cylinder 26 are separated by an injection piston 30 connected to a rod 32, and each chamber 42,44 is separated by an injection piston 30 connected to a rod 32.
Pressure sensors Sl and S2 are provided in the pressure oil flow path connected to the pressure oil flow path. And injection cylinder 2 for valves, pumps, etc.
A control circuit 50 is provided that sends a command signal to a control means 52 that controls the pressure in the injection operation side oil chamber of No. 6. Next, a method for controlling the pressure of the injection cylinder in a closed loop using the circuit block configured as described above will be described.

The control circuit 50 first calculates the differential pressure ΔP (=P,
-P2), and then calculate this differential pressure ΔP and a preset set value P. The control means 52 operates to send a command signal based on the difference to the control means 52. Based on this command signal, the control means 52 such as a valve or a pump operates to adjust the discharge pressure so that the substantial injection force of the injection cylinder 26 does not decrease. Therefore, changes due to oil temperature can also be controlled, resulting in a control method with excellent repeatability.

〔Effect of the invention〕

As is clear from the embodiments described above, according to the injection cylinder pressure closed loop control method of the present invention, even if the injection speed of the injection molding machine becomes far, the re-detected pressure values on the injection side and back pressure side of the injection cylinder can be controlled. Since this method performs pressure control by closed-loop control using differential pressure, it is possible to repeatedly obtain stable injection force regardless of changes in oil temperature, etc.

This pressure amount Lou 1 control method is primary holding pressure.

0 This is an effective control method for binary injection pressure control.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram illustrating a closed-loop control method for injection cylinder pressure according to the present invention, and FIG. 2 is a configuration diagram of main parts of an injection molding machine illustrating a conventional injection cylinder control method for an injection molding machine. . 10... Barrel 14... Screw 18... Connecting member 22... Bearing 26... Injection cylinder 30... Injection piston 12... Nozzle 16... Rotating member 20... Hopper 24 ... Hydraulic motor 28 ... Bearing units 1 to 32 ... Rod 34 ... Two-position switching valve 38 ... Flow rate adjustment valve 42 ... Injection side chamber 46 ... Tank 50 ... Control circuit 36... Variable discharge pump 40... Three-position direct switching valve 44... Injection return side chamber 48... Electromagnetic relief valve 52... Control means

Claims (1)

[Claims] (1) A first sensor (S_1) that detects the oil pressure in the oil chamber on the injection operation side of the injection cylinder of an injection molding machine, a second sensor (S_2) that detects the oil pressure in the oil chamber on the back pressure operation side, and A pressure control means for controlling the pressure in the oil chamber on the injection operation side, and a pressure difference (ΔP) between the detection value (P_1) of the first sensor (S_1) and the detection value (P_2) of the second sensor (S_2). =P
_1-P_2) is compared with the set value (P_0), and the differential pressure (Δ
An injection cylinder pressure closed loop control method for an injection molding machine, characterized in that the pressure control means is controlled based on the difference between P) and a set value (P_0).