JPH09174638A - Force feedback control method for injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method for a motorized injection molding machine in which the characteristics of the force feedback control can easily be changed by a motorized servo motor. SOLUTION: The feedback of signals from a pressure sensor 4 for sensing the pressure applied to a screw 1 of a movable section of an injection molding machine is carried out. An injection servo motor 2 is driven from the difference of the pressure commanded by a program and the sensed pressure by a servo processor 13 to control the output torque of the injection servo motor. As the force feedback control is carried out by the processor and a software, the characteristics of the feedback control can easily be changed, and the optimum feedback control characteristics can be provided in compliance with an object to be controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an electric injection molding machine using an electric servomotor as a drive source for mold clamping, injection and the like.

[0002]

2. Description of the Related Art In a conventional electric injection molding machine, in response to a movement command issued to each servo motor, a servo circuit composed of hardware of a position control unit and a speed control unit is used to control the position of the servo motor. , The speed and torque were controlled.

For example, FIG. 2 shows an example of a conventional control system. Numeral 100 denotes a numerical controller (hereinafter, referred to as an NC device) for controlling an injection molding machine. The NC device 100 includes a microprocessor (hereinafter, referred to as a CPU) 101 for an NC and a CPU 102 for a programmable machine controller (hereinafter, referred to as a PMC). CPU1 for PMC
02 is connected to a ROM 105 storing a sequence program for controlling a sequence operation of the injection molding machine, and the like.
Also, a RAM 112 used for temporary storage of data and the like is connected. A ROM 10 in which a management program for controlling the entire injection molding machine is stored in the NC CPU 101
4 and a servo circuit 107 for driving and controlling the servo motors for each axis of injection, clamping, screw rotation, ejector, etc. are connected via a servo interface 106. 2, only the servomotor 2 for injection and the servo circuit 107 of the servomotor 2 are shown.

Reference numeral 108 denotes a non-volatile shared RAM constituted by a bubble memory or a CMOS memory, and a memory section for storing an NC program for controlling each operation of the injection molding machine and various setting values and parameters by macro variables. It has a memory section for storing macro variables. Reference numeral 103 denotes a bus arbiter controller (hereinafter, referred to as BAC).
3 includes a CPU 101 for NC and a CPU 102 for PMC,
Each bus 115 of the shared RAM 108, the input circuit 109, and the output circuit 110 is connected, and the bus used is controlled by the BAC 103. Further, 114 is a BAC1 via the operator panel controller 113.
A manual data input device with a CRT display device (hereinafter, referred to as CRT / MDI) connected to 03. Note that 111
Is a RAM that is connected to the NC CPU 101 by a bus and is used for temporary storage of data.

In the example of FIG. 2, the injection shaft of the injection molding machine, that is, the injection servomotor 2 for driving and injecting the screw 1, is attached to the injection servomotor, and the rotation of the servomotor is controlled. The pulse coder 3 for detecting and detecting the screw position, and the rotation of the injection servomotor 2 are converted into linear motions, and are arranged in the thrust bearing portion of the screw shaft of the pusher plate for moving the screw 1 in the screw axial direction. The pressure sensor 4 for detecting the pressure applied to the screw 1 from the resin is shown, and other mold clamping shafts, screw rotation shafts, ejector shafts, etc. are omitted. Therefore, only the servo circuit 107 in the NC device 100 for the injection servomotor is shown, and the servo circuits for the other axes are omitted. The servo circuit 107 is connected to the injection servo motor 2, and the outputs of the pulse coder 3 and the pressure sensor 4 are also included in the servo circuit 10.
7 has been entered. Further, a torque limit value for controlling the output torque of the injection servomotor 2 is output from the output circuit 110 to the servo circuit 107.

In the above-mentioned configuration, the NC device 10
0 is a PMC CPU based on the NC program for controlling each operation of the injection molding machine stored in the shared RAM 108 and the sequence program stored in the ROM 105.
While the CPU 102 performs the sequence control, the NC CPU 1
In order to control each operation of the injection molding machine, a pulse is distributed to a servo circuit 107 of each axis of the injection molding machine via the servo interface 106 to control the injection molding machine.

The servo circuit for each axis subtracts the pulse from the pulse coder 3 from the distributed pulse received via the servo interface 106 and outputs an error register for outputting the current error amount for the command position and an output of the error register. D / A converted to D / A and output as speed command
A position control unit including a converter and a speed command from the position control unit are received, and the current speed is detected based on the speed command and the current speed (the output of the pulse coder 3 is F / V converted. (A tachogenerator may be provided and the current speed may be detected by the output of this tachogenerator), and a current command to be sent to the servomotor, that is, a speed controller that outputs a torque command, and a current to the servomotor 2 With a hardware configuration such as a speed control unit composed of a current controller that compares the current and the current command output from the speed controller, controls the current flowing to the servo motor 2, and controls the output torque, and a power amplifier. It is configured.

Further, like the injection shaft, the injection pressure and the holding pressure,
In order to control the back pressure and the like, the current command output from the speed controller to control the output torque of the servomotor 2 is limited to a predetermined value or less in order to control the torque. Torque limit means is inserted between the speed controller and the current controller, and the output from the output circuit 110 controls the torque limit value. Further, in the example of FIG. 2, the pressure sensor 4 detects the pressure applied to the resin (the pressure applied to the resin is applied to the screw 1 as a reaction), and it is possible to select a case in which pressure feedback control is performed during injection and pressure holding. In this case, the pressure detected by the pressure sensor 4 is compared with the torque limit value output from the output circuit 110, and the output torque of the servomotor is controlled according to the difference. I have.

[0009]

As described above, in the conventional electric injection molding machine, the servo circuit for controlling the servo motor of each axis of the injection molding machine has the position control unit, the speed control unit, and the torque. Since the limit means and the pressure feedback control means are also configured by hardware, a servo circuit of this hardware is required for each servo motor for each axis. Further, when changing the characteristics of the servo control method or the pressure feedback control means, it is necessary to change the circuit constants (resistance value, etc.) and the circuit itself.

Since the torque limit value is also input to the servo circuit 107 via the output circuit 110, the resolution (minimum unit size) of this torque limit value is also the resolution of the output circuit 110 (output signal Number of bits)
The control unit for pressure control is naturally limited.

Therefore, an object of the present invention is to provide a control method for an electric injection molding machine in which the characteristics of force feedback control by an electric servomotor can be easily changed.

[0012]

SUMMARY OF THE INVENTION The present invention provides an electric injection molding machine in which a drive source for driving a movable part of an injection molding machine is an electric servomotor, and a force sensor for detecting a force applied to the movable part. The output torque of the electric servo motor is provided so that the detection signal from the force sensor is fed back to the microprocessor, and the force detected by the force sensor matches the set force by the software controlling the microprocessor. Feedback control.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an essential part of an embodiment of the present invention. As with FIG. 2, an injection shaft of an injection molding machine is shown, and a mold clamping shaft, a screw rotating shaft, etc. are shown. Absent. 1 is a screw, 2 is an injection servomotor for injecting resin by moving the screw in the axial direction, 3 is a pulse coder attached to the injection servomotor 2, 4 is a pressure sensor for detecting the pressure applied to the resin, 5 Are cylinders, which are similar to those in FIG.

Further, 10 is an N for controlling the injection molding machine.
C device, the NC device 10 is an NC CPU 11, a PMC
A ROM 17 storing a control program and a RAM 18 used for temporary storage of data are connected to the NC CPU 11 by a bus 25.
The MC CPU 12 has a ROM 19 storing a sequence program, and a RAM 2 used for temporarily storing data.
0 are connected by a bus 25. 14 is BAC, NC
The shared RAM 15 for storing programs and various set values, the NC CPU 11 and the PMC CPU 12 are connected by a bus 25, and control the bus used by the BAC 14. A CRT / MDI 22 is connected to the BAC 14 via an operator panel controller 21. The above configuration is the same as that of the conventional NC device for controlling an injection molding machine shown in FIG.
11 differs in the method and configuration for driving the servomotors of each axis.

Reference numeral 13 is a CPU for controlling the output torque, speed and position of the servo motor of each axis of the injection molding machine, that is, a servo control CPU. The CPU 13 is provided with a RAM 23, which is used for temporary storage of data by a bus 25. Servo shared RAM 1 for storing the output circuit 24 and a control program for servo control, etc.
6 is connected, and the CP for NC is
It is bus-connected to U11.

The input / output circuit 24 includes a driver (D / A
A power amplifier 6 is connected via a converter (including a converter) 7, and the output of the power amplifier 6 drives the injection servomotor 2. The output of the power amplifier 6, that is, the drive current of the injection servomotor 2 is supplied to the input / output circuit 24 by A.
The drive current value data converted by the / D converter 9, the pressure data obtained by converting the output of the pressure sensor 4 into a digital signal by the A / D converter 8, and the output of the pulse coder 3 are input. Other shafts of the injection molding machine (mold clamping shaft,
A screw amplifier, ejector shaft, etc.) also uses a power amplifier for each servo motor, a driver, and an A / D that converts the drive current of the servo motor into a digital signal when a servo motor is used as the drive source. Each converter is provided, and a driver, an A / D converter, and a pulse coder attached to each servo motor are connected to the input / output circuit 24.

In the above-described structure, when the injection molding machine is operated, in the NC device 10, the PMC CPU 12 performs sequence control by the sequence program stored in the ROM 19, and the NC CPU 11 shares the shared RAM 15 as in the conventional case. By the NC program stored in
It controls each operation of the injection molding machine and outputs a movement command to the servo motor of each axis.
It is stored in AM16.

The servo CPU 13 performs position control, speed control, and torque control of the servo motor for each axis in response to the movement command for each axis. For example, the movement command for the injection axis is servo-shared. When input to the RAM 16, the servo CPU 13 subtracts the value of the counter provided in the input / output circuit 24 that counts the feedback pulses from the pulse coder 3 from the movement command value for every predetermined period to obtain the current position deviation amount. Then, the command current to the servo motor 2 is calculated from the difference between this position deviation amount and the current speed of the servo motor 2 calculated from the change value of the value of the counter that counts the feedback pulse, and this command current The difference between the current drive current value of the servo motor input via the A / D converter 9 and the input / output circuit 24 is calculated by the input / output circuit 24 and the driver 7. And outputs to the power amplifier 6, and thus driving the injection servomotor 2.

At this time, when the output torque of the injection servo motor is limited and torque control is performed, the drive current command output to the driver 7 is held below the value set by the program. Further, when the pressure feedback control is performed by the resin pressure detected by the pressure sensor 4,
The difference between the resin pressure signal, which is the digital signal output by the A / D converter 8, and the pressure value instructed by the program is the driver 7
Will be output to. In the above example, the injection axis has been described, but the same processing is performed for the other axes.

[0020]

According to the present invention, since force feedback control is realized by a microprocessor and a control program, it becomes easy to change the characteristics of force feedback control (change of gain, etc.), and control objects (resin pressure, spine pressure) are controlled. Pressure, mold clamping pressure, etc.) can be optimally controlled. Also, since the feedback control is performed by directly detecting the force applied to the movable part of the injection molding machine, the resolution of the torque limit value is affected compared to the case where the output torque of the servomotor is limited by the torque limit value to control the force. It is possible to perform optimal control. Further, since control is performed by the microprocessor, learning control can be performed according to the state of the previous injection molding cycle.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of an embodiment of the present invention.

FIG. 2 is a main block diagram of a conventional system.

[Explanation of symbols]

 1 screw 2 injection servo motor 3 pulse coder 4 pressure sensor 10 NC device 13 servo microprocessor (servo CPU) 16 servo shared RAM

Claims (1)

[Claims] 1. An electric injection molding machine in which a drive source for driving a movable part of an injection molding machine is an electric servomotor, and a force sensor for detecting a force applied to the movable part is provided.
The detection signal from the force sensor is fed back to the microprocessor, and the software controlling the microprocessor feeds back the output torque of the electric servomotor so that the force detected by the force sensor matches the set force. A force feedback control method in an injection molding machine characterized by controlling.