JPH0628253Y2 - Holding pressure control device for electric injection molding machine - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure control device for an electric injection molding machine which uses a servomotor as a drive source for an injection screw.

[0002]

2. Description of the Related Art In general injection molding machines, an injection screw is reciprocated by an actuator such as a hydraulic cylinder.
By moving the injection screw forward, the molten resin on the tip side of the injection screw is filled in the mold.

In such an injection molding machine, the injection screw is moved forward to fill the resin into the mold, and then the injection screw is further pushed toward the tip side to make the resin filled in the mold. A holding pressure is applied to apply pressure (holding pressure) so as to compensate for the shrinkage due to the solidification of the resin in the mold.

On the other hand, in comparison with the above-mentioned conventional injection molding machine,
An electric injection molding machine that drives an injection screw with an electric motor has also been developed.

In this type of electric injection molding machine, the rotary motion of the servomotor is converted into a linear motion through a motion conversion mechanism composed of, for example, a ball screw and a bolt nut screwed with the ball screw, and by this motion conversion mechanism. , The injection screw is moved back and forth.

In the electric injection molding machine, the control as shown in FIG. 1 is performed.

That is, the filling control in the injection process is
The position of the injection screw is detected by detecting the rotation angle of the servo motor 1 by the encoder 2 as the position detecting means, and the position control circuit M1 and the speed are detected based on this position information and the injection speed command signal A separately input. The speed of the injection screw is set stepwise by the two control circuits including the control circuit M2, and the torque according to each speed control step is set in the torque control circuit, and signals based on these set values are set in the servo amplifier. Output to 3,
This is done by outputting a drive signal from the servo amplifier 3 to the servo motor 1.

In the pressure holding control, the changeover switch SW1 is switched by a signal from the encoder 2 when the injection screw reaches a predetermined position, and the speed control is performed based on the pressure holding command signal B input separately. Circuit M2
And the speed and torque of the injection screw are set in the torque control circuit M3, signals based on these set values are output to the servo amplifier 3, and a drive signal is output from the servo amplifier 3 to the servo motor 1. Therefore, the command value to the speed control circuit M2 is corrected by the feedback signal from the pressure sensor 4 which detects the resin pressure.

[0009]

By the way, in the stage of the pressure holding control, the injection screw is moved forward and backward in the vicinity of the most forward position, but with the above pressure holding control method, the encoder 2 is operated during the pressure holding control. Since the position information of the injection screw is not input to the control circuits M1 and M2, the position of the injection screw cannot be confirmed. Therefore, the injection screw advances more than necessary and its tip comes into contact with or collides with the heating cylinder. There is a risk that there is a need for countermeasures.

[0010]

SUMMARY OF THE INVENTION The present invention provides a holding pressure control device for an electric injection molding machine which can effectively solve the above-mentioned problems. And by advancing the injection screw by this linear movement, the molten resin filled in front of the injection screw is injected into the mold,
An electric injection molding machine that applies pressure to the resin injected into the mold to hold the pressure is provided with a controller that controls the operation of the servo motor and a position detection unit that detects the position of the injection screw. The controller is a speed control circuit that controls the resin pressure by controlling the speed of the servo motor during pressure holding, and a position control that controls the position and speed of the servo motor based on information from the position detection means. Circuit, a speed control circuit that controls the speed command value based on the amount of deviation between the pressure command signal at the time of pressure holding and the actual pressure value output from the pressure sensor, and the position of the injection screw is the most forward end of the injection screw. When the position before this is reached, the servo motor control mode is automatically switched from the speed control mode to the position control mode, and the injection screw Wherein the switching circuit makes it possible to stop the front position of Susumutan position is provided.

[0011]

In the electric injection molding machine according to the present invention, when the pressure holding operation is started after the resin injection operation, the speed control circuit is selected by the controller and the pressure holding is controlled by the speed control of the servo motor. Be seen.

Even during the holding pressure control,
The position of the injection screw is always detected by the position detection means, and when the injection screw reaches the vicinity of the most forward position at the end of the pressure control, the control mode of the controller is the position control circuit based on the information from the position detection means. And the speed of the injection screw is controlled under this position control so that the injection screw is stopped moving toward the set stop position.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
Shows an electric injection molding machine according to the present embodiment.

First, a schematic structure of the electric injection molding machine 10 will be described. A heating cylinder 11 to which a resin is supplied while being melted, a hopper 12 mounted on the heating cylinder 11 to supply a raw material of a resin, and the above-mentioned. An injection screw 13 (a screw is shown in this embodiment) which is rotatably fitted in the heating cylinder 11 and is movable in the axial direction of the heating cylinder 11, and a driven pulley integrally attached to the injection screw 13. 14, a drive pulley 16 connected to the driven pulley 14 via a timing belt 15, a first servomotor 17 connected to the drive pulley 16 to rotate the injection screw 13 about an axis, and The slider 18 continuously provided at the rear end of the injection screw 13 and the slider 1
8, a screw shaft 19 screwed coaxially with the injection screw 13, and a second servo motor 23 connected to the screw shaft 19 via a driven pulley 20, a timing belt 21, and a drive pulley 22. And the slider 1
8, a load cell 24 to which the injection screw 13 is brought into contact, a pressure sensor 25 connected to the load cell 24 to detect the internal pressure thereof, and the first
A first encoder 26 that detects the rotation angle of the servo motor 17, a second encoder 27 that detects the rotation angle of the second servo motor 23, and the encoders 26.
A controller 28 that receives signals from 27 and outputs drive signals to the servomotors 17 and 23.

Then, the controller 28 controls the speed of the second servomotor 23 at the time of pressure holding to control the resin pressure, and the speed control circuit M2 at the end of the resin injection and the pressure holding. Based on information from the second encoder 27, the second servo motor 2
3, a position control circuit M1 for controlling the position and speed of the third servomotor, and a torque control circuit M3 for controlling the torque of the second servomotor 23 are provided, and the injection screw 13 advances to a predetermined position. Then, the control mode of the injection screw 13 is set to the speed control circuit M2.
A switch SW1 for switching from the speed control mode by the position control circuit M1 to the position control mode by the position control circuit M1, and a speed switching circuit for switching the switch SW1 by a command from the position control circuit M1 when the injection screw 13 advances to a predetermined position. 29, a switch SW2 for switching the control command value to the torque control circuit M3 and inputting it to the torque control circuit M3, and this switch SW2.
A torque switching circuit 30 that switches between 2 and a servo amplifier 31 that outputs a drive signal to the second servo motor 23 based on an output signal from the torque control circuit.
And are provided.

Further, the controller 28 is provided with a back pressure control circuit (not shown) for controlling the operation of the first servo motor 17 based on the information from the first encoder 26.

Next, the operation of the present embodiment thus constructed will be described as follows.

First, in the filling control in the injection process, the rotation angle of the second servo motor 23 is detected by the second encoder 27 as the position detecting means, and the position of the injection screw 13 is detected. Based on the injection speed command signal A separately input from the setting device, the speed of the injection screw 13 corresponding to the position of the injection screw 13 is stepwise by two control modes of the position control circuit M1 and the speed control circuit M2. In addition to being set, the torque corresponding to each speed control stage is set in the torque control circuit M3, and command signals based on these set values are output to the servo amplifier 31, and the servo amplifier 31 outputs the command signals to the command signals. A driving signal based on the driving signal is output to the second servo motor 23.

At this stage, the torque is set to allow up to 300% of the rated output of the second servo motor 23.

As a result, the speed of the injection screw 13 is controlled according to the forward movement position, and the molten resin is filled in the mold at a speed based on a predetermined program.

By continuing such an operation, the injection screw 13 reaches a predetermined position and the injection of the molten resin is completed, but here, the filling speed-pressure switching position separately set for the position control circuit M1 is reached. Then, due to the action of the speed switching circuit 29, the switch SW is
1 is switched to shift from the speed control mode to the position control mode, and the control of the electric injection molding machine 10 is switched from the filling control to the pressure holding control.

On the other hand, in the above pressure-holding control, the actual pressure of the resin filled in the mold is constantly detected by the load cell 24 via the injection screw 13, and is fed back via the pressure sensor 25. The speed command value and the torque command value corrected based on the deviation amount between the feedback signal and the pressure holding command signal B are output to the servo amplifier 31, and the injection screw 13 is controlled based on these command values. The holding pressure is controlled with high accuracy.

The holding pressure control is performed by continuing a plurality of set pressures for a predetermined time for each pressure from the time when the filling control is completed.

As described above, the holding pressure control is controlled by a plurality of set pressures and their respective durations from the time when the filling control is completed. Even during such control, the second encoder is operated. The position of the injection screw 13 is continuously detected by 27, and when the second encoder 27 detects that the injection screw 13 has been advanced to the vicinity of the most advanced position, the position control circuit A speed command value for forcibly decelerating and stopping the injection screw 13 is output from M1 to the speed switching circuit 29.

The speed command value from the position control circuit M1 is intended to stop the injection screw 13 and is therefore smaller than the speed command value during pressure holding control. , The switch SW1 is switched, and the position control circuit M
The speed command value from 1 is used as a control value in the speed control circuit M2, the speed of the injection plunger 13 is controlled based on this command value, the speed is reduced by a predetermined deceleration, and then the speed is stopped at a predetermined position. (This control is called stop control).

Further, such filling control, pressure holding control,
In addition, in the process of stop control, a torque command value that allows a torque up to 300% of the rated torque of the second servo motor 23 is normally input to the torque control circuit M3, and based on this torque command value, Servo amplifier 3
A drive signal is output from 1 to the second servo motor 23.

On the other hand, the torque command value from the speed control circuit M2 and the torque command value according to the pressure holding command signal B are input to the torque switching circuit 30 and are compared with each other. Since the switch SW2 is switched by the operation and the smaller torque command value is selectively input to the torque control circuit M3, excessive torque is prevented from being generated in the servo motor 23 in each control stage.

According to the holding pressure control device of the electric injection molding machine of this embodiment having the above-mentioned structure, the holding pressure is fed back by comparing the speed of the second servomotor 23 and the actual pressure from the pressure sensor 25. The injection screw 13 is stopped at a predetermined position with high accuracy by controlling the speed of the injection screw 13 based on the position information when the injection screw 13 approaches the most advanced position. .

As a result, damage to the injection screw 13 and the heating cylinder 11 due to the advance of the injection screw 13 more than necessary can be prevented.

[0030]

As described above, the pressure control device in the electric injection molding machine according to the present invention converts the rotational movement of the servomotor into a linear movement, and the linear movement causes the injection screw to move forward. The operation of the servo motor in an electric injection molding machine that injects the molten resin transferred in front of the injection screw into the mold and applies pressure to the resin injected into the mold to maintain the pressure. A controller for controlling the position of the injection screw, and a position detecting means for detecting the position of the injection screw, wherein the controller controls the resin pressure by controlling the speed of the servomotor at the time of pressure holding, and a speed control circuit.
Based on the information from the position detecting means, a position control circuit for controlling the position and speed of the servo motor, and a deviation amount between a pressure holding command signal at the time of pressure holding and an actual pressure holding value output from a pressure sensor. The speed control circuit that controls the speed command value and when the position of the injection screw reaches the front position of the most forward end of the injection screw, the control mode of the servo motor is automatically switched from the speed control mode to the position control mode. The present invention is characterized in that a switching circuit that allows the injection screw to stop at a position before the most advanced end position is provided, and has the following effects.

During the holding pressure control, when the injection screw approaches the most advanced position, the speed control of the injection screw is performed based on the position information of the injection screw, so that the injection screw is accurately stopped at a predetermined position. Can be made. As a result, the forward movement of the injection screw more than necessary can be prevented, and damage to the injection screw and the heating cylinder can be reliably prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a conventional control device in an electric injection molding machine.

FIG. 2 is a schematic configuration diagram of an electric injection molding machine to which an embodiment of the control device of the present invention is applied.

FIG. 3 is a block diagram showing an embodiment of the present invention.

[Explanation of symbols]

 10 Electric Injection Molding Machine 11 Heating Cylinder 13 Injection Screw 18 Slider 19 Screw Shaft 23 Second Servo Motor 27 Second Encoder (Position Detection Means) 28 Controller 29 Speed Switching Circuit SW1 Switch M1 Position Control Circuit M2 Speed Control Circuit

Claims (1)

[Scope of utility model registration request] 1. The rotary motion of the servomotor is converted into a linear motion, and the linear motion causes the injection screw to move forward, thereby injecting the molten resin filled in front of the injection screw into the mold, and In an electric injection molding machine that applies pressure to the resin injected into the mold to hold the pressure, a controller that controls the operation of the servo motor and a position detection unit that detects the position of the injection screw are provided, The controller is a speed control circuit that controls the resin pressure by controlling the speed of the servo motor during pressure holding, and a position control circuit that controls the position and speed of the servo motor based on information from the position detection means. And the speed that controls the speed command value based on the amount of deviation between the pressure holding command signal during pressure holding and the actual pressure holding value output from the pressure sensor. When the position of the control circuit and the injection screw reaches the position just before the most forward end of the injection screw, the control mode of the servo motor is automatically switched from the speed control mode to the position control mode. A holding pressure control device for an electric injection molding machine, which is provided with a switching circuit capable of stopping at a front position.