JPH01159218A - Driving device of injection cylinder of motor-driven injection molding machine - Google Patents

Abstract

PURPOSE:To improve quality of an injection-molded product by preventing pressure surging within resin which is ascribable to a response lag of an injection motor, by interposing a specific torque transmission element between a ball screw and the injection motor. CONSTITUTION:A torque transmission element 14 is interposed between a ball screw 9 for movement of a screw and an injection motor 10. The torque transmission element 14 comprises an output side stationary disk 18 and a piezoelectric actuator 21 whose one end is provided with a movable disk 19 contactable with and separable from the disk 18 and other end is fixed to an input side stationary disk 17 through a force detector 20. The movable disk 19 is brought into contact with the outer side disk 18 through an expansion and contraction action of the piezoelectric actuator 21, pressing force at this time is detected by the force detector 20 and the pressing force is controlled. With this construction, transmissibility of turning torque to a load to be applied to the output side disk 18 by an input side disk 17 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an injection drive device for an electric injection molding machine.

(Prior Art) Fig. 4 shows the general structure of a conventional electric injection molding machine. During the injection process, the screw rotation motor 6 is stopped and held, and the injection motor 10 is speed-controlled using a rotation-linear converter such as a ball screw 9 to rotate the screw 3.
advance. When the resin filling is completed, the load cell 7
is used as a pressure detector to control force and maintain pressure.

At this time, the completion of filling is detected by monitoring the output of the load cell 7, but in order to shift to pressure holding, the motor must be rapidly reduced to a speed close to stopping.

However, at this time, as shown in FIG. 5(a), since the response of the motor itself is slow at 10 to 20 m5, overshoot occurs as shown in FIG. 5(b). As a result, a surge pressure is generated within the resin as shown in FIG. 5(c), resulting in a problem of degrading the quality of the plastic product.

(Problems to be Solved by the Invention) In view of the problems of the prior art, it is an object of the present invention to reduce the surge pressure generated in the resin due to the delay in response of the motor when switching from the filling process to the pressure holding process during the injection process. The purpose is to

(Means for solving the problem) A piezoelectric device having a fixed disk on the output side and a movable disk that can move toward and away from the disk at one end, and the other end fixed to the fixed disk on the input side via a force detector. The movable disk is brought into contact with the output side disk by the expansion and contraction action of the piezoelectric actuator, the pressing force at this time is detected by a force detector, and the pressing force is controlled to cause the movable disk to contact the output side disk. A torque transmission element that can control the transmission rate of applied rotational torque to the load was interposed between the screw moving ball screw and the injection motor to improve responsiveness.

(Embodiments of the Invention) FIG. 1 shows an injection molding machine equipped with a drive device according to the present invention.

1 is a cylinder, 2 is a molten resin, 3 is a screw that can rotate and move back and forth within the cylinder 1, and 4 is a resin material supply hopper. 5 is a gear that transmits the rotation of the rotation motor 6 to the screw 3 during measurement. 7 is a load cell for detecting pressure within the cylinder 1; 8 is a nut screwed into a ball screw 9;

The ball screw 9 is connected to a torque transmission element 14 via a coupling 11 and a shaft 16 on the output side. The torque transmission element 14 is connected to the injection motor 1o attached to the fixed bracket 13 via an input shaft 15. 12 is a guide bar.

During the injection process, the screw rotation motor 6 is stopped and held;
By controlling the speed of the injection motor 10, the rotation-linear converter of the ball screw 9 moves the screw 3 forward.

When the filling of the resin 2 is completed, the pressure is detected by the load cell 7, and force control is performed to maintain the pressure. At this time, the completion of filling is detected by monitoring the output of the rotor self, and the pressure is maintained by the load cell 7. In order to make the transition, the injection motor 10 must be rapidly reduced to a near-stop speed, but this creates a surge problem.

Therefore, the surge of the holding pressure can be prevented by the torque transmission element 14. Figure 2 shows the torque transmission element 14.
FIG. 15 is an input shaft from the injection motor 10, and 16 is an output shaft. 17 is an input side fixed disk fixed to one end of the input side shaft, and 18 is an output side fixed disk fixed to one end of the output side shaft 16. 19 is a movable disc facing the output side fixed disc 18;
A piezoelectric actuator 21 is fixed to the input side fixed disk 17 via a force detector 20, such as a load cell, and is attached to the end thereof.

Although not shown, a circuit for supplying an applied voltage to the piezoelectric actuator 21 is provided. 22 is the movable disk 1
A plurality of springs are installed between the clutch 9 and the input side fixed disk 17 to ensure reliable operation of the clutch. However, this spring is not necessarily required.

In the above example, the movable disk 19 is brought into contact with and separated from the output side fixed disk 18, but it is of course possible to make it come into contact with and separated from the input side fixed disk 17.

The torque transmission element 14 expands when voltage is applied to the piezoelectric actuator 21, and the movable disk 19 moves to the left in the figure.
It is pressed against the output side fixed disk 18. The pressing pressure at this time is detected by the force detector 20. Since the amount of sliding between the output side fixed disk 18 and the movable disk 19 changes depending on the pressing pressure, the amount of torque transmitted to the output side shaft 16 out of the motor torque applied to the input side shaft 15 is determined by the piezoelectric actuator. It can be controlled with 21 voltages. Furthermore, if the voltage applied to the piezoelectric actuator 21 is reduced, it will contract and the movable disk 19 will separate and no longer transmit torque.

(Operation) FIG. 3(a) shows the motor rotation speed, FIG. 3(b) shows the screw position, and FIG. 3(Q) shows the resin pressure. As can be seen from these figures, although there is a delay in the motor 1o, the overshoot of the screw 3 and the surge in resin pressure are no longer compared to those in FIG. 5.

FIG. 3(d) is a graph showing the voltage applied to the piezoelectric actuator 21, and FIG. 3(e) is a graph showing the slip amount of the torque transmission element 14. In FIG. 3(e), the slip amount is "1". and rOJ indicate a state in which the torque is completely transmitted.

Now, when the switching point to pressure holding is reached, the rotational speed of the motor 10 is reduced, but at the same time, the voltage applied to the piezoelectric actuator 21 is also reduced. Then, since the motor torque is not transmitted to the ball screw 9, the screw 3 does not overshoot. Therefore, no surge pressure is generated.

When the motor is almost stopped, the piezoelectric actuator 21
Voltage is applied to the cylinder, torque is transmitted, and pressure holding control becomes possible.

In the example shown in Figure 5, the motor speed once drops to a negative value, but
This is because an attempt is made to restore the screw position to its original position. In the case of FIG. 3, the screw does not go too far, so the motor speed does not take a negative value.

Furthermore, even if the motor is separated, a slight overshoot will occur due to the inertia of movable parts such as the screw, but this is ignored in Figure 1 because it is much smaller than the inertia of the motor.

(Effects) Since a torque transmission element is interposed between the ball screw and the injection motor, it is possible to prevent pressure surges within the resin due to delayed response of the injection motor, improving the quality of injection molded products. be able to.

[Brief explanation of the drawing]

FIG. 1 shows an electric injection molding machine according to the present invention. FIG. 2 is a front view of the torque transmission element. FIG. 3 is an explanatory diagram of the operation of the injection molding machine. Figure 4 shows a conventional electric injection molding machine. FIG. 5 is an explanatory diagram of changes in position, speed, and pressure during the injection pressure holding process. In the figure: 1 cylinder 2 molten resin 3 screw 4 hopper 5 gear 6 motor 7 load cell 8 nut 9 ball screw 10 injection motor 11
Coupling lz Guide bar 13 Fixed bracket 14 Torque transmission element 15 Input end shaft
16 Output side shaft 17 Input end fixing disk 18
Output side fixed disk 19 Movable disk 20
Force detector 21 Piezoelectric actuator 22 Spring Applicant Sumitomo Heavy Industries, Ltd. Sub-agent Patent attorney Isamu Ohashi Figure 2 Figure 3 Figure 5

Claims (1)

[Claims] It consists of a piezoelectric actuator, which has a fixed disk on the output side, a movable disk that can move toward and away from the disk at one end, and the other end is fixed to the fixed disk on the input side via a force detector, and the expansion and contraction action of the piezoelectric actuator The movable disk is brought into contact with the output side disk, the pressing force at this time is detected by a force detector, and the transmission rate of the rotational torque applied from the input side disk to the load is determined by controlling the pressing force. 1. An injection cylinder drive device for an electric injection molding machine, characterized in that a torque transmission element capable of controllable is interposed between a ball screw for screw movement and an injection motor.