JPH0479289B2 - - Google Patents

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, and also control the speed and pressure of the hydraulic actuator using a flow rate adjustment valve and a pressure adjustment valve connected to the hydraulic circuit. Ta.

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 (for example, see Japanese Patent Application Laid-Open No. 60-64820). .

FIG. 2 shows an example of a control circuit using a typical conventional variable displacement pump. In the control circuit 70, a proportional flow valve 72 and a proportional pressure valve 73 are controlled by a command signal from a controller 71, thereby setting the flow rate and pressure. When the discharge amount and discharge pressure from the variable displacement pump 74 are large relative to the set flow rate and pressure, the discharge amount of the pump 74 is controlled by the actions of the discharge amount control valve 75 and the discharge pressure control valve 76. On the other hand, when the discharge amount and discharge pressure are small, the discharge amount of the pump 74 is increased by the action of each valve 75 and 76, and the various hydraulic actuators 7 in the injection molding machine 77 are
The output of 8 is variably controlled to prevent unnecessary energy loss.

[Problem that the invention seeks to solve]

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

First, 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 energy loss is reduced by the proportional flow valve 72. arise. In other words, although the proportional flow valve 72 is essential in the circuit configuration, the valve 72 itself consumes energy because it has an inherent characteristic of increasing flow resistance in the circuit.

In addition, the controller 71 also connects the proportional flow valve 72.
Since two signals are output: a valve opening command signal for controlling the proportional pressure valve 73 and a pressure setting command signal for controlling 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. The pressure setting signal is corrected, and the swash plate angle of the pump 74 is varied with respect to the corrected signal. In other words, the command signal is
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 method for controlling an injection molding machine that solves the problems existing in the prior art.
This can be achieved by the control method shown below.

That is, as shown in FIG. 1, the injection molding machine control method according to the present invention directly varies the swash plate angle of the hydraulic actuator 2 of the injection molding machine M in proportion to the magnitude of the input command signal So. The speed of the hydraulic actuator 2 is driven by an electromagnetic proportional variable displacement piston pump 1 which directly corrects the command signal So using a speed or pressure feedback signal Sf obtained from the hydraulic actuator 2. Alternatively, the pressure can be controlled by feedback.

[Effect]

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

The control method according to the present invention utilizes the 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. In addition, the command signal So based on the feedback signal Sf
The correction for is also made directly to the swash plate angle of the pump 1. In other words, the discharge flow rate and discharge pressure of the pump 1 are actively determined and controlled by the set angle of the swash plate, which is 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.

A mold opening/closing device 32 is provided on the left side of the top surface of the machine stand 31, and an in-line screw type injection device 33 is provided on the right side of the top surface.

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 inside the mold clamping cylinder 34, and a movable platen 38 is provided at the tip of this ram 37. The movable platen 38 moves forward and backward on the tie bars 39 to open and close the movable mold 41 and fixed mold 42 attached to the movable platen 38 and the fixed platen 40. Further, the movable platen 38 is provided with a protruding cylinder 43 for releasing the molded product attached to the movable mold 41.

On the other hand, the injection device 33 is moved forward or backward by a moving cylinder 44 provided at the bottom. Injection device 33
A screw 46 is provided in a heating cylinder 45, and this screw 46 is moved forward and backward by an injection cylinder 47. Note that 48 is an oil motor whose output shaft is connected to an injection ram 49 in an injection cylinder 47 by a spline.

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

Reference numeral 1 denotes an electromagnetic proportional variable displacement piston pump (hereinafter abbreviated as pump), which has a motor 4.
is driven via a coupling (not shown). The pump 1 is equipped with a swash plate and receives a predetermined command signal So.
By supplying , the swash plate angle can be electromagnetically varied. That is, in this case, the swash plate is required to have a high response speed to the command signal So. The cylinders are connected so as to be integrally displaceable, and a portion of the oil discharged from the pump 1 is supplied to the cylinder via a control valve. The pump 1 also includes a swash plate angle detector that detects the swash plate angle to obtain the discharge flow rate, a pressure detector that detects the discharge pressure, and a predetermined control circuit. The detection signal obtained from the control valve is compared with the flow rate command signal So, and a control signal that generates a discharge flow proportional to the command signal So is supplied to the control valve to perform minor feedback control of the flow rate. The detection signal obtained from the detector is compared with the pressure command signal So, and a control signal for generating a discharge pressure proportional to the command signal So is supplied to the control valve to perform minor pressure feedback control. Due to this function, this type of pump is called an electromagnetic proportional variable displacement piston pump, and unlike conventional piston pumps, it is independent of valves and pump characteristics.
A highly linear output proportional to the command signal So is always obtained, and the command signal So directly changes the swash plate angle via the control valve, resulting in a prompt response. On the other hand, the pump 1 has a plurality of setting devices 5...
Connect the controller 3 equipped with... Setting device 5
inputs information such as the output of the hydraulic actuator to be controlled, such as speed, magnitude of pressure, and control position, to the controller 3. In addition, the controller 3 sends command signals corresponding to information from the setting device.
So is supplied to the pump 1, and the swash plate of the pump 1 is driven and controlled so that the pump discharge amount matches the information. In addition, each cylinder 35, 36, 43, 44,
47 are four-port directional control valves 50 and 5, respectively.
1, 52, 53, and 54 in parallel to the pump 1, and the oil motor 48 is connected to the pump 1 via a four-port directional switching valve 55.

On the other hand, a pressure sensor 60 is installed in the discharge path 9 of the pump 1.
Each cylinder 3 is arranged and operates in sequence.
Detect pressures at 5, 36, 43, 44, and 47.
Note that this detected value is fed back to the controller 3. On the other hand, the ejecting cylinder 43 has a position sensor 62 that detects the position of the ejecting 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. , furthermore, a position sensor 66 for detecting the position of the movable platen 38 is provided, and the detection value of each sensor is detected by the controller 3.
Feedback will be provided to Note that the position information is differentiated within the controller 3 and converted into speed.

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

It is now 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 control valve 54 is switched to the right side in the figure, the pressure oil discharged from the pump 1 is transferred to the same valve 54.
It is supplied to the rear chamber of the injection cylinder 47 via.

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 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 discharge amount from the pump 1. That is, the controller 3 outputs a command signal So for controlling the swash plate angle of the pump 1 according to speed and pressure setting signals (set values), and thereby the corresponding swash plate angle is set. 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 the detected value from the sensor related to the injection process becomes the feedback signal Sf and is sent to the controller 3.
input. Then, the controller 3 compares and calculates the setting signal Ss set by the setting device 5 with the corresponding feedback signal Sf, and performs feedback control to correct the command signal So so as to make this deviation zero. .

Although the injection process is shown as an example, each cylinder 3 is also
5, 36, 43, and 44, 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, directly controls the swash plate angle of the pump using a command signal, and also uses the command signal as feedback. Since the correction is directly performed through control, the following significant effects are obtained.

Unlike the conventional method, there is no need for a flow valve disposed in the middle of the discharge path, so 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 significantly reducing costs. can.

Feedback control is performed by directly correcting the swash plate angle command signal with a feedback signal from the hydraulic actuator, so the pump is actively controlled and high responsiveness of the control system can be achieved.

[Brief explanation of drawings]

FIG. 1: 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: 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, Sf: Feedback signal, Ss: Setting signal,
So: Command signal.

Claims (1)

[Claims] 1 Hydraulic actuator 2 of the injection molding machine...
It is driven by an electromagnetic proportional variable displacement piston pump 1 whose swash plate angle is directly varied in proportion to the magnitude of the input command signal So, and by a speed or pressure feedback signal Sf obtained from the hydraulic actuator 2. A method for controlling an injection molding machine, characterized in that the speed or pressure of the hydraulic actuator 2 is feedback-controlled by directly correcting the command signal So.