JPS61248718A - Injection molding machine controlling maximum injection pressure - Google Patents

Abstract

PURPOSE:To prevent generation of fins in a product, reduce the remaining stress of the molded product and uniform the quality of the product by a method wherein a torque limit circuit, effecting torque limits, is provided in a servo circuit. CONSTITUTION:When the maximum injection pressure is set by MDi and CRT in the torque limit circuit 5, a control device CNC outputs a torque control command (g), corresponding to the maximum injection pressure, and inputs limit voltages +Vr, -Vr as the torque control values into a buffer amplifier 12 through diodes D1, D2. When the voltage of torque commanding value (e) from an error amplifier 13 is increased to the limit voltages +Vr, -Vr or more, the diodes D1, D2 are conducted and the input of the buffer amplifier 12 is held at the limit voltages +Vr, -Vr even when the output (e) of the error amplifier 13 becomes any value higher than said limit voltages +Vr, -Vr, therefore, the torque commanding value (e) may be held lower than the limit voltages +Vr, -Vr.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an injection molding machine. In particular, the present invention relates to an injection molding machine that uses a servo motor as a drive source for an injection mechanism and that controls the maximum injection pressure.

Conventional technology Conventional injection molding machines use hydraulic pressure to drive the injection mechanism to move the screw in the axial direction to perform injection.
Control of injection pressure could be adjusted by controlling oil pressure. On the other hand, the injection mechanism is driven by a servo motor,
Injection molding machines that perform injection have also been developed. In this case, the injection pressure is determined by the output torque of the servo motor, so depending on the molded product, more injection pressure than necessary may be applied.
In some cases, this caused cracks in the molded product or left a large amount of residual stress in the molded product.

Problems to be Solved by the Invention The object of the present invention is to eliminate the above-mentioned drawbacks and to provide a method in which the torque during injection is limited to the torque corresponding to the set maximum injection pressure in an injection molding machine driven by a servo motor. By controlling the maximum injection pressure, we have developed an injection molding machine with a controlled maximum injection pressure that can prevent the occurrence of cracks in the product, reduce residual stress in the molded product, and control the quality at a constant level. It is about providing.

Means for Solving the Problems The injection molding machine of the present invention that controls the maximum injection pressure is provided with a torque limit circuit in the servo circuit that applies a torque limit, and the torque command to the servo motor that drives the injection mechanism is It outputs through the torque limit circuit and applies a torque limit to control the injection pressure within the maximum injection pressure.

Function: A torque limit circuit is provided in the servo circuit of the servo motor that drives the injection mechanism, and the maximum injection pressure is controlled by setting the torque limit circuit to an arbitrary value, and the torque command value to the servo motor is set. is held below the value
The injection pressure does not exceed the maximum injection pressure to prevent product fringing, reduce residual stress in the molded product, and maintain constant quality control.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing the main parts of the present invention, in which 1 is a heating cylinder of an injection molding machine, which has a screw 2 inside, 3 is an injection drive mechanism, and M is a screw 2 of the injection molding machine. This is a servo motor that moves in the axial direction to perform injection, and is driven and controlled by the servo circuit 4. P is an incremental pulse encoder, 5 is a torque limit circuit, CNC is a control device such as a numerical control device with a built-in microcomputer, 6 is an input/output circuit, and the servo circuit 4. It is connected to the torque limit circuit 5, pulse encoder P, etc. 7 is the central processing unit (CPL)
I), 8 is an MDi & CRT (operation with display!) that inputs various commands and data and displays images.
I, 9 is a ROM that stores a program for controlling the entire injection molding machine, 10 is a nonvolatile memory that stores NO programs, molding conditions, etc., and 11 is a RAM that is used for temporary storage of data.

FIG. 2 shows the servo circuit 4. A specific circuit diagram of the torque limit circuit 5 is shown.

The servo circuit 4 is almost the same as a conventionally known servo circuit, except that the buffer amplifier 12 of the torque limit circuit 5 is provided between the error amplifiers 13 and 14.

That is, when a position command a consisting of a pulse train is input as a drive command for the servo motor M as a movement amount per unit time, the relationship between this position command a and the movement amount of the servo motor M detected by the pulse encoder P is The difference is converted into an analog voltage as a speed command value C by a digital-to-analog converter (hereinafter referred to as a D/A converter) 15. That is, if there is a large difference between the position command a and the movement ff1b of the servo motor M from the pulse encoder P, a large value of the speed command value C will be output, and if the difference is small and the position command a and the movement Jib approach each other, the speed will have a small value. It is output as command value C. Roughly speaking, this servo circuit performs speed feedback to improve responsiveness, and this converts the signal from the pulse encoder P into a voltage using the F/V converter 16.
The voltage V corresponding to the actual speed of the servo motor M is subtracted from the speed command value C, and the difference between the command speed C and the actual speed V is amplified by the error amplifier 13 to generate the command torque e.
Output as . That is, this command torque e is output as a voltage corresponding to the current value flowing through the armature of the servo motor M. This command torque e! In this example,
The command torque e is output via a buffer amplifier 12 (in a normal servo circuit, there is no buffer amplifier 12 and the command torque e is directly output). The voltage corresponding to the armature current from the current detector 17 that detects the armature current of M is fed back, and the command torque e is
The difference between the feedback signal f of the armature current and the feedback signal f of the armature current is amplified by an error amplifier 14 and amplified by a power amplifier 18 to drive the servo motor M.

On the other hand, the torque limit circuit 5 converts the torque limit command value g, which is a digital signal from the illumination device CNC, into a current output using a D/A converter (not shown), and converts it into a torque limit command value Q using a current/voltage converter 19. Convert to the corresponding voltage,
The voltage -V corresponding to the torque limit command value g is inputted to the buffer amplifier 12 via the diode D2, and the sign converter 20 converts the sign of the current-voltage converter 19 to correspond to the torque limit command value 9. It is input to the buffer amplifier 12 via diodes 01.D2 as voltage elements Vr- and -Vr.

Next, the operation of this embodiment will be explained.

First, when the maximum injection pressure is set using MDi & CRT8, the control device CNC outputs the torque limit command 9 corresponding to the maximum injection pressure, and sets the limit voltage +Vr as the torque limit value via the diode D1°02.

-Vr is input to the buffer amplifier 12. Then, when the position command a for injection is input to the servo circuit 4, the D/A converter 15 converts the speed command value C into a voltage as described above.
is output, and the difference between the voltage V and the voltage V corresponding to the actual speed of the servo motor M is amplified by the error amplifier 13 and output as a torque command value e. This i ~ torque command value e is output as a voltage corresponding to the current value to be passed through the armature of the servo motor M. This voltage e is output via the buffer amplifier 12, and this voltage e and the servo motor M The detection output from the current detector 17 that detects the armature current of
(Voltage) difference is amplified by the error amplifier 14 and the power amplifier 18, and the servo motor M is driven to move the screw forward and perform injection. On the other hand, the voltage of the torque command value e from the error amplifier 13 increases, and in response to the torque limit command g commanded by the control device CNC, the current-voltage converter 19° sign converter 20 and the diode D1. When the limit voltages +Vr and -Vr inputted through D2 are exceeded, the diode D1. D2 is conductive, and the input of the buffer amplifier 12 is at the limit voltage +vr, no matter what value the output e from the error amplifier 13 is above the limit voltage +vr, -vr.
Since Vr is held at -Vr, the torque command 1iie
will be held below the limit voltages +Vr and -Vr. As a result, the armature current r of the servo motor M is equal to the above-mentioned limit voltage +Vr.

-Vr and saturates at a constant value.

That is, the output of the servo motor M is limited by the torque limit values +vr, -vr corresponding to the maximum injection pressure, and the injection pressure is limited to below the set maximum injection pressure, thereby preventing the occurrence of cracks in the molded product. This reduces the residual stress in the molded product, prevents deformation, etc., and eliminates variations in quality, making it possible to control quality at a constant level.

In the above embodiment, a DC motor is shown as the servo motor M, but the same applies to an AC motor, and
Although a pulse encoder P is used as a detector, other detectors such as a resolver, a speed generator, etc. may be used.

Effects of the Invention As described above, the present invention is capable of producing a molded product without applying excessive injection pressure, such as the force that limits the injection pressure to below the maximum injection pressure set during injection. Or,
A molded product of good quality can be obtained without producing a large amount of residual stress.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of an embodiment of the present invention, and FIG.
The figure is a specific circuit diagram of the servo circuit and torque 1 limit circuit same as above. 1...Heating cylinder, 2...Screw, 3...
Injection drive mechanism, 4... Servo circuit, 5... Torque limit circuit, 6... Input/output circuit, 7... Central processing unit, 8... MDi & CRT, 9... ROM110-.
・Non-volatile memory IJ, 11...RAM, 12...
・Buffer amplifier, 13.14...Error amplifier, 15
...Digital-analog converter, 16...F/V converter, 17...Current detector, 18...Power amplifier,
19... Current voltage converter, 12... Code converter, M
...Servo motor, P...Pulse encoder, CN
C...control device.

Claims (1)

[Claims] In an injection molding machine whose injection mechanism is driven by a servo motor to perform injection, a torque limit circuit is provided in the servo circuit of the servo motor, and the maximum injection pressure is controlled by setting the torque limit circuit to an arbitrary value. An injection molding machine that controls maximum injection pressure.