JPH0518685B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field This invention relates to a control method and device for an electric injection molding machine.

(b) Conventional technology As a conventional electric injection molding machine, for example,
There is one as shown in Publication No. 61-72512.
The electric injection molding machine shown in this figure has a first electric motor that can drive a screw in an injection molding machine cylinder in the axial direction via a ball screw mechanism, and a second electric motor that can rotationally drive the screw. By controlling the operations of both electric motors, operations such as a plasticizing process, a pressure holding process, and an injection process are performed.

Also, as shown in Japanese Patent Application Laid-Open No. 64-85727,
There is a method in which a weak vibration signal is superimposed on the back pressure setting signal and the holding pressure setting signal during the plasticizing process and the holding pressure process, respectively.

(c) Problems to be Solved by the Invention The electric injection molding machine disclosed in this conventional Japanese Patent Application Laid-Open No. 61-72512 has a so-called stay in the mechanical friction part during the plasticizing process and the pressure holding process. There were problems in that a slip phenomenon occurred, the screw moved back and forth intermittently, and the resin pressure actually generated varied intermittently. This is due to the rolling friction of the ball screw mechanism, the rolling friction of each bearing,
This is because the screw driven by a low-output, slow-rotating electric motor alternates between a static friction state and a dynamic friction state due to the accumulation of processing tolerances of each operating member.

Unexamined Japanese Patent Publication No. 64-85727 attempted to solve this problem.
In the electric injection molding machine shown in the publication, during the plasticizing process and the pressure holding process, the electric motor for driving the screw in the axial direction is supplied with a basic drive current of 10 to 30 Hz.
However, this alone is effective only under certain settings in the case of plasticizing multi-stage holding pressure, and has not yet solved the problem under all conditions. Therefore, there was a problem that it was not suitable for precision molding.

The present invention aims to solve these problems.

(d) Means for Solving the Problems The present invention provides a control method for an electric injection molding machine in which the screw 12 is driven in the front-rear direction by an injection/back pressure electric motor 38. In this case, a weak vibration signal with a frequency and amplitude that is changed depending on the magnitude of the back pressure setting signal and the holding force setting signal, respectively, is superimposed on the back pressure setting signal and the holding force setting signal. .

In addition, the drive of the screw 12 in the front and back direction is
A control device for an electric injection molding machine operated by a back pressure electric motor 38 includes a back pressure setting device 50 for setting the torque of the injection/back pressure electric motor 38 in the plasticizing process, and a back pressure setting device 50 for setting the torque of the injection/back pressure electric motor 38 in the pressure holding process. a holding force setting device 52 for setting the torque of the electric motor 38;
an oscillator 56 that generates a weak vibration signal; a converter 73 that changes the value of the oscillator 56 according to a signal from one of the setting devices 50, 52; Oscillator 5
The above problem is solved by having an amplifier 60 that outputs a current to the injection/back pressure motor 38 based on a signal on which a weak vibration signal from 6 is superimposed.

(E) Action For example, in the plasticizing process, the screw gradually retreats due to the pressure of the molten resin. At this time, a predetermined current is supplied to the motor so that a predetermined back pressure is generated. The amount of back pressure varies depending on the type of resin, the shape of the screw, etc., and the current is based on a superposition of weak vibration signals with predetermined amplitude and frequency according to the back pressure. controlled. Therefore, in addition to the reference torque, the electric motor generates a weak high-speed pulsating torque depending on the back pressure. Therefore, friction parts such as a ball screw mechanism move slightly and at high speed. Therefore, these friction parts can always maintain a dynamic friction state, so that the so-called stick slip phenomenon does not occur, and the predetermined torque set by the back pressure setting device is generated, ensuring that the resin pressure is accurately controlled. controlled.

The same applies to the pressure holding process.

The above-mentioned weak vibration signal is in a range that does not directly affect the resin pressure, the amplitude is 1 to 10% of the set back pressure and holding pressure, and the frequency is 10 to 30 Hz.

(f) Examples Embodiments of the present invention are shown in FIGS. 1 and 2.

A screw 12 is inserted into a cylinder 10 of an injection molding machine. The rear end side (upstream side in the resin flow direction) of the cylinder 10 is attached to a frame 14 . Spline portion 1 at the rear end of the screw 12
2a is connected to the drive shaft 16. Drive shaft 16
is rotatably supported by a moving member 22 by a thrust bearing 18 and a radial bearing 20. A spline shaft portion 16a is formed on the other end side of the drive shaft 16, and this spline shaft portion 16a is combined with a sleeve 23 having a spline hole. Therefore, the drive shaft 16 and the sleeve 23 can move relative to each other in the axial direction and can transmit rotational force. The sleeve 23 is rotatably supported by the frame 14 via radial bearings 24 and 26. The aforementioned moving member 2
A plurality of ball nuts 28 are fixed to 2. The ball screw 30, which is combined with the ball nut 28 to constitute a ball screw mechanism, is attached to the frame 1.
4, the front end side is supported by a radial bearing 31, and the rear end side is supported by a thrust bearing 32.
and is supported by a radial bearing 34. The plurality of ball screws 30 are connected to an injection/back pressure electric motor 38 on their retreating side via a rotational force transmission mechanism 36 composed of a pulley and a belt.
is connected to. Further, the aforementioned drive shaft 16 is also connected to the plasticizing electric motor 42 via the rotational force transmission mechanism 40.

FIG. 2 shows a control device that controls the current supplied to the injection/back pressure motor 38. This control device includes a back pressure setting device 50, a holding pressure setting device 52, an injection speed setting device 54, an oscillator 56, a converter 73 that changes the value of the oscillator according to signals from the setting devices 50 and 52, and a converter 73 for speed control correction. It has an amplifier 58, an amplifier 60 for motor current control and power amplification, a switch 62, a switch 64, a switch 66, a current detector 68, and a rotation speed detector 70, which are connected as shown in the figure. . Further, the operations of switch 62, switch 64, and switch 66 are controlled by a sequencer 72.

Next, the operation of this embodiment will be explained.

First, the plasticizing electric motor 42 is rotated with the screw 12 in the most advanced state, and the screw 12 is rotationally driven via the rotational force transmission mechanism 40 and the drive shaft 16. This melts and kneads the plastic material and stores it in front of the screw 12. At this time, the screw 12 is pushed rearward by the stored resin pressure. During this plasticizing process, the screw 1 is
A predetermined forward pushing force is applied to 2, thereby maintaining a predetermined resin pressure. That is, the switch 62 is switched to the A side by a signal from the sequencer 72, the switch 64 is also switched to the A side, and the switch 66 is turned on. In this connected state, a weak vibration signal from the oscillator 56 is applied to the converter 7 in advance according to the back pressure setting voltage set by the back pressure setting device 50.
3, and superimpose it on the back pressure setting voltage. In this way, the amplifier 60 supplies the injection/back pressure motor 38 with a current proportional to the voltage obtained by superimposing the signal from the oscillator 56 on the signal from the back pressure setting device 50. Injection/back pressure electric motor 38
generates a torque proportional to the applied current, converts this into a linear force by the action of the ball screw 30 and the ball nut 28, and transmits it to the moving member 22, and this force is further transmitted via the thrust bearing 18 and the drive shaft 16. and is transmitted to the screw 12. As a result, a force directed to the left in FIG. 1 is generated in the screw 12, which acts as a force opposing the resin pressure during plasticization, that is, back pressure. Injection/
The current given to the back pressure motor 38 is supplied to the oscillator 56.
The torque of the injection/back pressure motor 38 also vibrates slightly at a predetermined frequency. Therefore, the friction at the friction portion between the ball nut 28 and the ball screw 30 becomes a dynamic friction state, and since the frictional force hardly changes, the back pressure applied to the screw 12 is always as set by the back pressure setting device 50. Become. Note that if the amplitude of the signal from the oscillator 56 is set at a frequency of 10 to 10% and 10 to 30 Hz, pressure fluctuations will not occur in the final resin pressure.

When the screw 12 retreats to a predetermined position while receiving a predetermined back pressure in this manner, the operations of the plasticizing motor 42 and the injection/back pressure motor 38 are stopped. Next, the switch 64 is switched to the B side by a signal from the sequencer 72, and the switch 66 is turned off. As a result, the injection/back pressure motor 38 rotates at a speed corresponding to the voltage set in the injection speed setting device 54 in the opposite direction to that in the above case, and the screw 12 moves forward. As the screw 12 moves forward, molten resin is injected into a mold (not shown). When the screw 12 advances to a predetermined position, charging speed control is switched to torque control. That is, the signal from the sequencer 72 causes the switch 62 to go to the B side, the switch 64 to the A side, and the switch 66 to turn on.
In this state, the voltage from the holding pressure setting device 52 is
The weak vibration signal is changed to a predetermined amplitude and frequency by a converter 73 according to the voltage, and is superimposed on the holding pressure setting voltage. In this way, a current corresponding to the voltage obtained by superimposing the signal from the oscillator 56 on the voltage from the holding pressure setting device 52 is applied to the injection/back pressure motor 3.
8. As a result, the screw 12 rotates with a predetermined torque, and the resin pressure is maintained at a predetermined level. At this time, as described above, the torque of the injection/back pressure motor 38 changes slightly due to the signal from the oscillator 56, and the friction section enters a dynamic friction state, so the injection/backpressure motor 38 changes slightly.
The torque of the back pressure electric motor 38 is accurately transmitted to the molten resin, and a predetermined holding force can be obtained.

Figure 3 shows the change in resin pressure associated with the change in holding pressure in the invention disclosed in JP-A-64-85727.
A weak vibration signal with a constant frequency and amplitude is not effective in all ranges, and a drop in resin pressure can be seen in the second stage. FIG. 4 shows an example of the effect of the present invention, and it can be seen that the present invention is effective in all ranges.

(G) Effects of the Invention As explained above, according to the present invention, a voltage from a setting device is used to change a weak vibration signal to a predetermined amplitude and frequency by a converter according to the voltage. Since the back pressure and holding force are controlled by superimposing them on the set voltage, the friction part is always in a state of dynamic friction, which prevents the so-called stick slip phenomenon from occurring, and reduces the resin pressure. It can be controlled precisely according to the settings. Thereby, precise injection molding can be performed.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an electric injection molding machine, Fig. 2 is a diagram showing a control device of the present invention, Fig. 3 is a resin pressure waveform in the pressure holding process according to the present invention, and Fig. 4 is a diagram showing a holding process using a conventional method. This is the resin pressure waveform during the pressure process. 10... cylinder, 12... screw, 16...
... Drive shaft, 28 ... Ball nut, 30 ... Bow screw, 38 ... Injection/back pressure motor, 42 ... Plasticizing motor, 50 ... Back pressure setting device, 52 ...
Holding pressure setting device, 54...Injection speed setting device, 56...
...Oscillator, 58...Amplifier, 60...Amplifier, 7
2...Sequencer, 73...Converter.

Claims (1)

[Scope of Claims] 1. A control method for an electric injection molding machine in which the screw 12 is driven in the front-rear direction by an injection/back pressure electric motor 38, in which back pressure is applied during the plasticizing process and the pressure holding process, respectively. A method for controlling an electric injection molding machine, characterized in that a weak vibration signal with a frequency and amplitude that is changed according to the magnitude of a setting signal and a holding force setting signal is superimposed on a back pressure setting signal and a holding force setting signal. . 2. In a control device for an electric injection molding machine in which the screw 12 is driven in the front-rear direction by an injection/back pressure motor 38, a back pressure setting device sets the torque of the injection/back pressure motor 38 in the plasticizing process. 50, a holding force setting device 52 that sets the torque of the injection/back pressure motor 38 in the holding pressure process, an oscillator 56 that generates a weak vibration signal, and any of the setting devices 50, 52.
a converter 73 that changes the value of the oscillator 56 according to a signal from the setter 50, 52;
A control device for an electric injection molding machine, comprising: an amplifier 60 that outputs a current to the injection/back pressure motor 38 based on a signal obtained by superimposing a weak vibration signal from an oscillator 56 on a signal from the oscillator 56.