JP2665815B2 - Injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an injection molding machine using a servo valve for controlling an injection speed and a back pressure during plasticization.

(Prior Art) When a servo valve is used for precision molding in an injection molding machine, control of an injection speed, an injection holding pressure, and a screw back pressure is continuously performed by one servo valve.

(Problems to be Solved by the Invention) However, in the control using the servo valve, a shock is likely to occur particularly when switching from the speed control of the injection speed to the pressure control of the injection holding pressure. The delay in the mechanical response speed of the servo valve itself and the generation of an uncontrollable region due to the lap allowance at the time of the neutral time between the two have become problems in precision molding.

(Means for Solving the Problems) In order to solve such problems, in the present invention,
An injection cylinder for inserting the screw into the heating cylinder and enabling the screw to reciprocate, and an oil motor for enabling the screw to rotate at an arbitrary rotation speed are provided. An electromagnetic flow control valve is provided, and an electromagnetic switching valve is provided for selectively selecting and supplying discharge oil passing through the electromagnetic flow control valve to the injection cylinder or the oil motor. A servo valve is provided between the hydraulic chamber and the forward side oil chamber of the cylinder, and an electromagnetic pressure control valve is provided by branching from the middle of an oil passage connecting the hydraulic pump and the electromagnetic flow control valve. While providing a hydraulic pressure detector for detecting the oil pressure of the side oil chamber and a speed detector for detecting the speed of the screw, the controller of the injection molding machine has an injection speed control signal generator and a fully open signal generator for injection. , Injection hydraulic control A signal generation unit, a back pressure control signal generation unit, and an open loop / closed loop switching signal generation unit, which are used to control the injection speed during the injection process control by controlling the opening degree for adjusting the flow rate of the servo valve. As means, an adder that adds the injection speed control signal output from the injection speed control signal generation unit and the output of the speed detector to output a deviation signal, and outputs the deviation signal from the injection speed control signal and the deviation signal. An adder that outputs an addition signal; a zero-point setting device for minimizing a delay in mechanical response speed of the servo valve itself during the injection process control; and an addition device that adds the addition signal and the output of the zero-point setting device. And an adder for outputting a signal for controlling the opening of the servo valve, and an output signal from the injection full-open signal generator for fully opening the opening of the electromagnetic flow control valve is used for the electromagnetic flow control. valve A circuit for inputting, and a circuit for inputting an output signal from an injection hydraulic pressure control signal generator for controlling the pressure of the electromagnetic pressure control valve to a pressure higher than the injection flow pressure to the electromagnetic pressure control valve. A back pressure output from the back pressure control signal generation unit as electrical means for performing back pressure control of the screw during plasticization measurement process control by opening control for pressure adjustment of the servo valve. An adder for adding a control signal and an output of the hydraulic pressure detector to output a back pressure deviation signal; and setting a zero point for minimizing a delay in a mechanical response speed of the servo valve itself during back pressure control. And an adder for adding the back pressure deviation signal and the output of the zero point setting device and outputting an opening control signal for adjusting the pressure of the servo valve. Is performed by the electromagnetic pressure control valve. A control signal for the injection hydraulic pressure control signal generation section, and the output pressure from the open loop / closed loop switching signal generation section to perform the injection holding pressure control in a closed loop, The injection speed control signal generation unit may output a control signal that sets the opening to an opening corresponding to the holding flow rate, or
A position detector for detecting the position of the screw is provided, and the injection speed, the injection holding pressure and the back pressure can be program-controlled in accordance with the preset screw position.

(Operation) When controlling the injection speed, a control signal obtained by adding the speed setting signal and the deviation signal is supplied to the servo valve so that the opening can be controlled to adjust the flow rate of the servo valve. When controlling the screw back pressure, only the deviation signal of the pressure is used as a control signal to control the opening of the servo valve. Since a zero point setting device is provided for minimizing the delay of the mechanical response speed based on the initial lap allowance of the spool and the body of the servo valve, switching from speed control of the injection speed to pressure control of the injection holding pressure is performed. It eliminates shocks at the time, delays in the mechanical response speed of the servo valve itself, and the occurrence of an uncontrollable region.

(Example) Hereinafter, in order to clarify the present invention more specifically, an example will be described with reference to the drawings. In FIG. 1, 1
Reference numeral denotes a heating cylinder of the injection molding machine, and reference numeral 2 denotes a screw that is rotatably and reciprocally inserted into the heating cylinder 1.

Reference numeral 3 denotes a hopper for storing the raw material to be supplied to the screw 2.

Reference numeral 4 denotes an injection cylinder for moving the screw 2 forward and backward, and 4A denotes a piston of the injection cylinder 4.
4B is the injection cylinder 4 defined by the piston 4A.
4C is a retreat-side oil chamber.

Reference numeral 5 denotes an oil motor for rotating the screw 2.

 Reference numeral 10 denotes a pump as a hydraulic source.

Reference numeral 11 denotes an electromagnetic flow control valve, the primary side of which is connected to the pump 10 by a pipe.

Reference numeral 12 denotes an electromagnetic pressure control valve, which is provided in a so-called bleed-off state by branching from a midway of a pipe connecting the pump 10 and the electromagnetic flow control valve 11. Reference numeral 13 denotes an electromagnetic switching valve, which is connected to the secondary side of the electromagnetic flow control valve 11 by a pipe. 13a and 13b are solenoids of the electromagnetic switching valve 13, respectively.

Reference numeral 14 designates an electromagnetic switching valve 13, a P port communicating with the pump 10 via the electromagnetic flow control valve 11, a T port communicating with the tank, an A port communicating with the forward oil chamber 4B of the injection cylinder 4, and a blind port in this example. This servo valve has a total of four B ports, and displaces the flapper by operating a torque motor and moves the spool by hydraulic pressure.
All ports of the servo valve 14 are cut off at the time of neutral, but at the time of injection, the P port A port is connected, and at the time of plasticization measurement, the A port and the T port are connected when the screw 2 rotates. ing.

On the secondary side of the electromagnetic switching valve 13, one port is the P port of the servo valve 14 and the other port is the injection cylinder 4
And the solenoid-operated switching valve 13
When both solenoids 13a and 13b are not energized, the two ports join and communicate with the tank, and the port connected to the pump 10 is disconnected. When the solenoid 13a is excited, the pump 10 and the circuit of the servo valve 14 communicate with each other, and the retreat oil chamber 4C of the injection cylinder 4 communicates with the tank. On the other hand, when the solenoid 13b is excited, the pump 10 and the circuit of the retraction oil chamber 4C of the injection cylinder 4 communicate with each other, and the servo valve
The 14 P port communicates with the tank.

Numeral 15 is an electromagnetic switching valve provided by branching from the middle of a pipe connecting the electromagnetic flow control valve 11 and the electromagnetic switching valve 13, and 15a
Is a solenoid of the electromagnetic switching valve 15. The electromagnetic switching valve 15
When the solenoid 15a is not excited, the inlet oil passage of the oil motor 5 is connected to the tank, and when the solenoid 15a is excited, the pump 10 is connected to the inlet oil passage of the oil motor 5.

Reference numeral 20 denotes a screw rotation speed detector that detects the rotation speed of the screw 2 and outputs it as an electric signal.

Reference numeral 21 denotes a hydraulic pressure detector which converts the hydraulic pressure of the forward oil chamber 4B of the injection cylinder 4 into an electric signal and outputs the electric signal. 22 is screw 2
The speed detector 23 detects a position and outputs a speed signal and an electric position signal.

Reference numeral 30 denotes a controller for generating a control signal. 30A is an injection signal generation unit of the controller 30, 30B is an injection full open signal generation unit, 30C is an injection speed control signal generation unit, 30D is an injection hydraulic control signal generation unit, 30E is an open loop / closed loop switching signal generation unit, 30F is a plasticizing signal generator, 30G is a screw rotation control signal generator, 30H is a plasticizing maximum pressure signal generator, and 30I is a back pressure control signal generator.

Each of 31 to 38 is an adder.

Each of 39 to 44 is a switch.

Each of 45 to 48 is a PID compensator.

Each of 49 to 51 is an amplifier.

Here, the main parts of the injection speed control circuit based on the addition type of the setting signal and the deviation signal that obtained the best results of the various tests and the back pressure control circuit based on the deviation signal alone will be described.

The main part of the addition type injection control circuit is an adder 32 to which a positive polarity control signal from the injection speed control signal generation unit 30C of the controller 30 and a negative polarity output signal from the speed detector 22 are added. An adder 33 adds the control signal from the injection speed control signal generator 30C and the output of the adder 32.
A PID compensator 46 is provided between the adder 32 and the adder 33. The output of the adder 32 is a difference between the set signal and the feedback signal, that is, a deviation signal, and the adder 33 adds the deviation signal and the set signal bypassing the adder 32. On the other hand, the back pressure control circuit is provided with an adder 35 for adding a positive polarity control signal from the back pressure control signal generator 30I of the controller 30 and a negative polarity output signal from the oil pressure detector 21. A deviation signal, which is a difference between the setting signal and the feedback signal, is output. After the adder 35, a PID compensator 47 is provided.

Reference numeral 52 designates an initial lap allowance of the spool land and the body at the P port of the servo valve 14, and 53 designates a predetermined output to the torque motor so as to minimize the initial lap allowance at the T port. This is a zero point setting device for minimizing the delay of the mechanical response speed. Servo valve
At the 14 neutral position, all ports (P, T, A, B) need to be cut off. However, no matter how good the machining accuracy of the servo valve is, it is generally necessary to cut between the spool land and the body. A wrap margin of several percent of the maximum stroke of the spool is provided. However, this lap allowance causes problems such as a delay in response speed and an uncontrollable region, for example, a delay in rising of the injection speed and a failure in precise control in a low back pressure region. For this purpose, a zero point setting device 52 for setting and outputting a zero point adjustment signal during injection control and a zero point setting device 53 for setting and outputting a zero point adjustment signal during back pressure control are provided.

By the way, during the injection control, the servo valve 14 used in this embodiment, for example,
The opening degree from the port to the A port increases, and the opening degree from the A port to the T port increases as it moves rightward during back pressure control. That is, in the injection control and the back pressure control, the moving direction of the spool with respect to the opening of the servo valve 14 has a left-right opposite relationship. For this reason, the zero point adjustment signals of the zero point setter 52 and the zero point setter 53 also have opposite polarities. In this example, the output signal of the zero point setter 53 has a negative polarity.

 Next, the operation will be described.

At the start of the injection process, predetermined signals are simultaneously and simultaneously output from the injection signal generation unit 30A, the injection fully open signal generation unit 30B, the injection speed control signal generation unit 30C, and the injection oil pressure control signal generation unit 30D of the controller 30. At this time, the solenoid 13a of the electromagnetic switching valve 13 is also excited.

The switch 39 is activated by the injection start signal from the injection signal generator 30A, and the output signal from the fully open signal generator 30B during injection is input to the amplifier 49 via the switch 39. When the injection fully open signal amplified and output by the amplifier 49 is input to the electromagnetic flow control valve 11, the electromagnetic flow control valve is fully opened.

From the injection speed control signal generator 30C, an injection speed control signal based on a set value set in a setting unit (not shown) in advance is output and input to the adders 32 and 33. The adder 32 adds the output signal from the speed detector 22 and the injection speed control signal. The output signal of the speed detector and the injection speed control signal have opposite polarities, and the output from the speed detector 22 having a negative polarity which is a feedback signal that captures the actual forward speed of the screw 2. The difference between the signal and the setting signal is output from the adder 32. The deviation is input to the adder 33 via the PID compensator 46, added to the injection speed control signal based on the set value, and the added signal is input to the adder 34.

The zero point adjustment signal from the zero point setting unit 52 is further input to the adder 34.

Since the switch 41 operates simultaneously with the switch 39 already described, the output signal from the adder 34 is output from the switch 41 and the amplifier 50.
Is input to the servo valve 14 and the servo valve 14 is controlled to a predetermined opening degree. The output signal from the injection hydraulic pressure control signal generator 30D is passed through an adder 38 and an amplifier 51 to the electromagnetic pressure control valve 12.
And the pressure of the electromagnetic pressure control valve 12 is always controlled at a pressure higher than the flow pressure in the forward oil chamber 4B of the injection cylinder 4. However, the pressure of the electromagnetic pressure control valve 12 at this time is controlled in an open loop state in which the output signal of the oil pressure detector 21 does not act because the switch 44 is not operated.

Since the solenoid 13a of the electromagnetic switching valve 13 is excited, the pressure oil discharged from the pump 10 is flow-controlled by the electromagnetic flow control valve 11 in the fully opened state, the servo valve 14 through the electromagnetic switching valve 13, and the injection cylinder 4 To the forward oil chamber 4B. The pressure oil guided to the forward oil chamber 4B acts on the piston 4A, and the backward oil chamber 4C communicates with the tank via the electromagnetic switching valve 13, so that the piston 4A and, consequently, the screw 2 are driven based on the set speed. Move forward.

The forward speed of the screw 2 is detected by the speed detector 22 and is input to the adder 32, and the position is detected by the position detector 23 and input to the controller 30. Thereafter, the injection speed control at the set position is continued by the control loop described above.

When the injection speed control in the injection advance step is completed, the process proceeds to the pressure holding step, and a signal for operating the switch 44 is issued from the open loop / closed loop switching signal generation unit 30E of the controller 30. Therefore, the hydraulic pressure detector 21
Is added to the injection oil pressure control signal from the injection oil pressure control signal generator 30D in an adder 37, and the added output signal is input to an adder 38 via a PID compensator 48 and a switch 44 for injection. It is added to the injection hydraulic control signal from the hydraulic control signal generator 30D, amplified by the amplifier 51, and output to the electromagnetic pressure control valve 12. That is, in the pressure holding step, unlike the injection advance step, a predetermined pressure holding control is performed by feedback-controlling the pressure of the electromagnetic pressure control valve 12. Then, a control signal is output from the injection speed control signal generator 30C to the servo valve 14 so as to give a signal corresponding to the held flow rate.

By feeding back the detection signal of the position detector 23 to the controller 30, the holding pressure can be changed and controlled at an arbitrary set position.

As described above, the flow control by the servo valve 14 is basically performed in the forward process in the injection process, and the pressure control by the electromagnetic pressure control valve 12 is basically performed in the pressure holding process.

 When the injection step is completed, the process shifts to the plasticization measuring step.

In the plasticizing and measuring step, the screw 2 is rotated by the rotation of the oil motor 5, and the raw material stored in the hopper 3 is transferred from the heating cylinder 1 while being transferred forward by the action of the rotating screw. Heated and melted by heat and its own shearing heat. The heated and melted raw material is gradually stored in front of the screw 2 while receiving an appropriate screw back pressure, and when a predetermined amount is measured, the plasticization measuring step is completed.

 Hereinafter, the plasticizing and measuring step will be described in detail.

In the plasticization measuring process, predetermined signals are simultaneously and simultaneously sent from the plasticization signal generation unit 30F, the screw rotation control signal generation unit 30G, the plasticization maximum pressure signal generation unit 30H, and the back pressure control signal generation unit 30I of the controller 30. Is output. At this time, the electromagnetic switching valve
The 15 solenoids 15a are excited, and all the solenoids of the electromagnetic switching valve 13 are not excited.

The output signal of the plasticizing signal generation unit 30F is used for the switches 40, 42, 4
3 and the switches 40, 42 and 43 are operated.

The positive control signal from the screw rotation control signal generator 30G is input to the adder 31, and is added to the negative detection signal of the screw speed detector 20 by the adder 31. As a result of the calculation, the output deviation signal is a PID compensator 45, a switch 4
0, input to the electromagnetic flow control valve 11 via the amplifier 49, and the opening of the electromagnetic flow control valve 11 is controlled. As described above, since the solenoid 15a of the electromagnetic switching valve 15 is excited, the pressure oil discharged from the pump 10 is controlled by the electromagnetic flow control valve 11, the electromagnetic switching valve 15, and the oil motor. 5 is introduced. As a result, the oil motor 5 and thus the screw 2 rotate at a predetermined rotation speed.

At this time, the output from the plasticizing maximum pressure signal generator 30H is input to the electromagnetic pressure control valve 12 via the switch 42 and the amplifier 51, so that the electromagnetic pressure control valve 12 is maintained at the maximum pressure.

The back pressure control is performed by controlling the pressure in the forward oil chamber 4B of the injection cylinder 4 to a predetermined value by the servo valve 14.

The output signal from the back pressure control signal generator 30I is input to the adder 35, and the feedback signal from the hydraulic pressure detector 21 for detecting and outputting the oil pressure in the forward oil chamber 4B of the injection cylinder 4 and the adder. Added at 35. The calculation result of the adder 35 is output as a deviation signal, input to the adder 36 via the PID compensator 47, and added to the output signal of the zero setter 53.

In the injection control circuit, an adder 33 is provided between the PID compensator 46 and the zero-point adjusting adder 34, and is an addition-type circuit that adds the deviation signal and the setting signal. However, the back pressure control circuit corresponds to the adder 33. This is a circuit based only on the deviation signal without providing an adder.

The zero-point-adjusted deviation signal output from the adder 36 is input as a control signal to the servo valve 14 via a switch 43 and an amplifier 50. The servo 14 is input by the input control signal.
Controls the screw back pressure to a predetermined pressure by controlling the amount of oil released from the forward oil chamber 4B of the injection cylinder 4 to the tank.

By feeding back the detection signal of the position detector 23 to the controller 30, the back pressure can be changed and controlled at an arbitrary set position.

When the above loop is continued and the plasticized and melted raw material is stored in front of the screw 2 in a predetermined amount, the screw 2 is retracted by that amount based on a signal from the position detector 23 which detects the position of the screw 2. The rotation of 2 is stopped, and the plasticizing and measuring step is completed. If the screw 2 is required to be retracted due to suckback or the like, detailed description is omitted, but the solenoid 13b of the electromagnetic switching valve 13 is excited, and the discharge oil of the pump 10 whose flow rate is controlled by the electromagnetic flow control valve 11 is controlled. To the retraction oil chamber 4C of the injection cylinder 4 and the servo valve
It can be easily performed by switching 14 to a function that allows the forward oil chamber 4B to communicate with the tank.

(Effect) Injection speed control is flow rate control by servo valve, injection holding pressure control is pressure control by electromagnetic pressure control valve, and back pressure control is pressure control by the servo valve, and mechanical response of the servo valve itself Since the zero point setting device for minimizing the speed delay is provided, the shock at the time of switching from the injection speed control to the injection holding pressure control, the delay of the response speed of the servo valve and the uncontrollable range are eliminated, for example. Ultra-precision molding of disks and lenses becomes possible.

[Brief description of the drawings]

FIG. 1 is a main part block diagram for explaining an embodiment of the present invention. 1: heating cylinder, 2: screw 4: injection cylinder, 4B: forward oil chamber 5: oil motor, 10: pump 11: electromagnetic flow control valve 12: electromagnetic pressure control valve 13: electromagnetic switching valve, 14: servo Valve 15: Electromagnetic switching valve, 21: Position detector 30: Controller 30A: Injection signal generator 30B: Fully open signal generator at injection 30C: Injection speed control signal generator 30D: Injection hydraulic control signal generator 30E: Open loop Closed loop switching signal generator 30I: Back pressure control signal generator 32,33,34,35,36,37,38: Adder 39,41,43,44: Switch 46,47,48: PID compensator 49 , 50,51: Amplifier 52, 53: Zero point setting device

Claims (4)

(57) [Claims] 1. An injection cylinder for inserting a screw into a heating cylinder and reciprocating the screw, an oil motor for enabling the screw to rotate, and discharging oil from a hydraulic pump to the injection cylinder. An electromagnetic switching valve that selectively supplies the oil motor to the oil motor; an electromagnetic pressure control valve that is provided in a branch of an oil passage between the electromagnetic switching valve and the hydraulic pump; A servo valve provided between the cylinder and a forward-side oil chamber of the injection cylinder; a hydraulic pressure detector for detecting a hydraulic pressure of a forward-side oil chamber of the injection cylinder; and a speed for detecting a reciprocating speed of the screw. In the injection molding machine provided with the detector, the controller is provided with an injection speed control signal generation unit, an injection hydraulic control signal generation unit, a back pressure control signal generation unit, and an open loop / closed loop switching signal generation unit, and controls an injection process. The injection speed control signal output from the injection speed control signal generator and the output of the speed detector as electrical means for performing the injection speed control at the time by opening degree control for adjusting the flow rate of the servo valve. , An adder that outputs a deviation signal, an adder that outputs an addition signal of the injection speed control signal and the deviation signal, and a delay in mechanical response speed of the servo valve itself during injection process control. And a zero setter for minimizing the above, and an adder for adding the addition signal and the output of the zero setter to output an opening control signal of the servo valve, and An injection molding machine, comprising: a circuit for inputting an output signal from an injection hydraulic control signal generator to the electromagnetic pressure control valve so as to control pressure in an open loop. 2. A back pressure control signal generator outputs electric means for controlling the back pressure of the screw at the time of plasticizing and measuring step control by controlling the opening degree for adjusting the pressure of the servo valve. An adder for adding a back pressure control signal and an output of the oil pressure detector to output a back pressure deviation signal;
A zero-point setting device for minimizing the delay of the mechanical response speed of the servo valve itself during the back pressure control, and adding the back pressure deviation signal and the output of the zero-point setting device to obtain the pressure of the servo valve. 2. The injection molding machine according to claim 1, further comprising an adder for outputting an opening control signal for adjustment. 3. An injection pressure control signal generating section outputs a control signal for performing an injection holding pressure control during the injection process control by the electromagnetic pressure control valve, and generates the open loop / closed loop switching signal. The injection pressure control is performed in a closed loop by an output signal from the section, and a control signal for setting the opening of the servo valve to an opening corresponding to the holding flow rate is output from the injection speed control signal generating section. Claim 1 or Claim 2
3. The injection molding machine according to claim 1. 4. A control system according to claim 1, further comprising a position detector for detecting a position of the screw, wherein program control of the injection speed, the injection holding pressure and the back pressure is enabled in accordance with a preset screw position. Item 4. An injection molding machine according to any one of Items 3 to 5.