JPS62228701A - Control method for injection molding machine - Google Patents

Abstract

PURPOSE:To enable responsiveness by correcting an instruction signal which controlls the swash plate of a pump by a speed or a pressure feedback signal from a hydraulic actuator. CONSTITUTION:The discharging quantity of the pump 1 is varied by directly driving the swash plate of an electromagnetic proportional variable discharge type piston pump 1 which drives a hydraulic actuator 2, by means of an instruction signal So from a controller 3, and at the same time, the instruction signal So is corrected, by comparing a pressure feedback signal Sf with a set signal Ss. Thus, discharging quantity and pressure are positively determined and controlled by a set angle of the swash plate with is controlled by the instruction signal So so that high responsiveness on a control system can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention particularly relates to a method of controlling an injection molding machine equipped with an actuator driven by a variable displacement pump.

[Conventional technology]

Conventionally, injection molding machines use a fixed displacement pump to drive the mounted hydraulic actuator.
A flow regulating valve and a pressure regulating valve connected to the hydraulic circuit were used to control the speed and pressure of the hydraulic actuator.

However, although this control method is good when the load pressure or flow rate of pressure oil is constant, it is not suitable for cases where load pressure fluctuations or flow rate fluctuations are large, such as in the injection cylinder installed in an injection molding machine or the mold opening/closing cylinder. has the disadvantage that energy loss is large in the low pressure region and low speed region, and is not preferred from the viewpoint of energy saving.

To solve this problem, devices have recently been put into practical use that use variable discharge pumps to directly control the pressure and flow rate required by hydraulic actuators.

FIG. 2 shows an example of a control circuit using such a conventional variable displacement pump. Such a control circuit (70)
Then, the proportional flow valve (72) and the proportional pressure valve (73) are controlled by a command signal from the controller (71), thereby setting the flow rate and pressure. When the discharge volume and discharge pressure from the variable discharge volume pump (74) are large relative to the set flow rate and pressure, a discharge volume control valve (75);
The discharge amount of the pump (74) is reduced by the action of the discharge pressure control valve (76), and when the discharge pressure of the discharge m1 is small, the pump (74) is reduced by the action of the valves (75) and (76).
, thereby variably controlling the output of various hydraulic actuators (78) in the injection molding machine (77),
Efforts are being made to prevent unnecessary energy loss.

[Problem that the invention attempts to solve]

However, the conventional control method using the above-mentioned control circuit has the following problems.

First of all, with this type of control method, energy loss can be suppressed considerably, but since the differential pressure before and after the proportional flow valve (72) is controlled to be constant by the discharge amount control valve (75), the proportional flow valve (72) A loss occurs. In other words, the proportional flow valve (72) is essential in the circuit configuration, but since the proportional flow valve (72) has an inherent characteristic of increasing flow resistance in the circuit, the proportional flow valve (72) itself consumes energy.

The controller (71) also connects the proportional flow valve (72).
It outputs three signals: a valve opening command signal to control the proportional pressure valve (73), and a pressure setting command signal to control the proportional pressure valve (73).
The configuration of the entire system including the control method and control device becomes complicated.

Furthermore, when performing feedback control as shown in FIG. 2, first, the valve opening command signal and The pressure setting signal is corrected, and the swash plate angle of the pump (74) is varied in response to the corrected signal. That is, the command signal is given to each valve (72), (73), and after these set values are changed, the pump swash plate is changed passively to control the pump discharge amount and discharge pressure. As a result, the responsiveness of the control system deteriorates significantly, resulting in negative effects such as a direct adverse effect on molding quality.

[Means for solving problems]

The present invention provides a control method for an injection molding machine that solves the problems existing in the prior art, and can be achieved by the control method described below.

That is, the method for controlling an injection molding machine according to the present invention is as shown in FIG.
The swash plate of the electromagnetic proportional variable discharge piston pump (1) that drives ... is directly driven by the command signal (So) from the controller (3) to vary the discharge volume of the pump (1). urge In addition, a feedback signal (S) of speed and/or pressure obtained from the actuator (2)...
r) corrects the command signal (So) by comparing it with, for example, a setting signal (Ss).

[For production]

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

The control method according to the present invention utilizes an electromagnetic proportional variable displacement piston pump (1) and performs control without using any proportional flow valve or proportional pressure valve. Therefore, the command signal (SO) functions as a signal for directly varying the swash plate angle of the pump (1). Further, correction to the command signal (SO) based on the feedback signal (Sr) is also directly performed to the swash plate angle of the pump (1). That is, the discharge flow rate and discharge pressure of the pump (1) are actively determined and controlled by the set angle of the swash plate controlled by the command signal (So).

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a hydraulic circuit diagram including a partial cross section of an injection molding machine to which the method of the present invention is applied.

First, in order to clarify the present invention, the schematic configuration of the injection molding machine (M) will be described with a focus on the hydraulic system.

The mold opening/closing device (32) is installed on the left side of the top surface of the machine stand (31), and the injection device (inline screw set) is installed on the right side of the top surface.
33).

The mold opening/closing device (32) includes a mold clamping cylinder (34), which is composed of a high speed cylinder (35) and a powerful cylinder (36). A mold clamping ram (37) is provided within the mold clamping cylinder (34), and a movable platen (38) is provided at the tip of this ram (37). The movable plate (38) has a tie bar (
39)...A movable type (41) and a fixed type (42) that move forward and backward on the top and are attached to a movable platen (38) and a fixed platen (40).
The mold is opened and closed. In addition, the movable plate (38) includes a movable type (
41) is provided with a protruding cylinder (43) for releasing the molded product adhering to the molded product.

On the other hand, the injection device (33) has a moving cylinder (
44) to move forward or backward. The injection device (33) includes a screw (46) in the heating cylinder (45), and the screw (46) moves forward and backward by the injection cylinder (47). Note that (48) is an oil motor, the output shaft of which is spline-coupled to the injection ram (49) within the injection cylinder (47).

Next, the hydraulic circuit and control system will be explained.

Code (1) is an electromagnetic proportional variable displacement piston pump (
Hereinafter, it is abbreviated as a pump) and is driven by a motor (4) via a coupling (not shown).

The pump (1) includes a swash plate, and the angle of the swash plate can be electromagnetically varied by supplying a predetermined command signal (So).

The variable amount of this swash plate is proportional to the magnitude of the input command signal (So). On the other hand, the pump (1) has multiple setting devices (5
)... is connected to the controller (3). The setting device (5) controls the output of the hydraulic actuator to be controlled;
For example, information such as speed, pressure magnitude, and control position is input to the controller (3). Also, the controller (
3) supplies a commonly used command signal (So) from the setting device to the pump (1), and drives and controls the swash plate of the pump (1) so that the pump discharge amount matches the information. Also,
Each cylinder (35), (36), (43), (44),
(47) are 4-port directional control valves (5G), (
51), (52), (53), and (54) in parallel to the pump (1), and the oil motor (48) is connected to the pump (1) through a four-boat directional control valve (55). Connect to.

On the other hand, a pressure sensor (6) is connected to the discharge path (9) of the pump (1).
0) and each cylinder (3
5), (36), (43), (44), and (47) pressures are detected. Note that this detected value is fed back to the controller (3). On the other hand, the protruding cylinder (43)
is a position sensor (62) that detects the position of the protruding piston.
), the injection device (33) has a position sensor (63) that detects the position of the screw (46), and the movable cylinder (44) has a position sensor (65) that detects the position of the injection device (33).
), and a position sensor (66) for detecting the position of the movable platen (38), respectively, and the detection value of each sensor is fed back to the controller (3). Note that the position information is differentiated within the controller (3) and converted into velocity.

Next, an injection process will be described as an example of the operation.

Now, it is assumed that the mold clamping process has been completed and the injection device (33) is brought into contact with the mold (fixed mold (40)). In this state, when the directional switching valve (54) is switched to the right side in the figure, the pressure oil discharged from the pump (1) is supplied to the rear chamber of the injection cylinder (47) via the directional valve (54).

As a result, the injection ram (49) and further the integrated screw (46) move forward, and the molten resin accumulated in front of the screw is filled into the mold cavity. In addition, in this injection process, the moving speed of the injection ram (49) is controlled in multiple stages. Including other steps, the injection ram (49) is controlled over an injection speed control area and an injection pressure control area, and the pressure is also controlled in multiple stages.

On the other hand, the moving speed and pressure of the injection ram (49) are controlled by the pump (
It is controlled by the discharge amount from 1). That is, the controller (3) sends a command signal (So
), which sets the corresponding swashplate angle. Then, the pump (1) outputs the required discharge amount to each hydraulic actuator (2) according to the swash plate angle.

In addition, a feedback control system is configured, and detected values from sensors related to the injection process are used as feedback signals (Sf
) and input to the controller (3). Then, in the controller (3), the setting signal (Ss) set by the setting device (5)... and the corresponding feedback signal (S'') are compared and calculated, and a command signal ( Feedback control is performed to correct So).

Although the injection process is shown as an example, each cylinder (35), (36), (35), (36), (
43) and (44), the movement speed control and pressure control can be performed.

Although the embodiments have been described in detail above, the detailed structure, format, quantity, etc. can be arbitrarily changed without departing from the spirit of the present invention.

〔Effect of the invention〕

As described above, the method for controlling an injection molding machine according to the present invention utilizes an electromagnetic proportional variable displacement piston pump, and directly controls the swash plate angle of the pump using a command signal, and also controls the command signal by feedback control. Since the correction is made directly, the following effects are obtained.

(2) Since there is no need for a flow valve placed in the middle of the discharge path unlike in the past, there is no flow resistance in the discharge path and energy savings can be achieved.

■ Since the pump swash plate can be driven and controlled directly by command signals, the entire hydraulic circuit including the control device is dramatically simplified, reducing wiring and piping man-hours, and also significantly reducing costs. .

■ Since the command signal is information for setting the swash plate angle of the pump, the transmission path is direct and the pump is actively controlled. Therefore, high responsiveness of the control system can be achieved.

[Brief explanation of drawings]

FIG. 1 is a hydraulic circuit diagram including a partial cross section of an injection molding machine to which a control method according to the present invention is applied. FIG. 2 is a hydraulic circuit diagram of an injection molding machine to which a conventional control method is applied. In the drawing, (1): Electromagnetic proportional variable displacement piston pump (2)
:Actuator (3):Controller C5O
: Feedback signal (Ss) : Setting signal (So)
: Command signal

Claims (1)

[Claims] A swash plate of an electromagnetic proportional variable displacement piston pump that drives a hydraulic actuator of an injection molding machine is driven by a command signal from a controller to vary the pump discharge amount, and a feedback signal of speed or pressure is sent from the hydraulic actuator. A method for controlling an injection molding machine, characterized in that the command signal is corrected in accordance with the above.