JPH0639116B2 - High-speed injection mechanism of electric injection molding machine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-speed injection mechanism of an electric injection molding machine.

(Prior Art) In a plastic injection molding machine, in order to obtain a product with a predetermined accuracy, the injection speed of the molten resin at the start of injection is extremely important. In recent injection molding, resin that cures in a shorter time is used, and because the molded products are becoming more precise and finer, the resin melted at high temperature at high speed can be started at the start of injection. I'm trying to shoot at.

In order to obtain such a high injection speed, in the conventional injection molding machine, a method of driving the injection screw by hydraulic pressure is generally used. On the other hand, in the case of an injection molding machine in which the driving force of an electric motor is transmitted to an injection screw with a ball screw or the like, the rising speed of the electric motor is slow, so
There was a problem that a high injection speed could not be obtained.

The problem that it is difficult to obtain a sufficient injection speed at the start of injection, which is the most important in injection molding, is a basic problem of an injection molding machine using an electric motor as a drive source. As a method of solving this problem, for example, an electric motor of high power is used, or a normal driving motor and a dedicated motor for high-speed injection are separately provided.

(Problems to be Solved by the Invention) As described above, the problem of the electric injection molding machine that a high injection speed cannot be obtained at the start of injection is solved by a method such as increasing the power of the motor. But
Even if a large power motor is used, it is difficult to obtain an injection speed equivalent to hydraulic pressure, and since a large motor is used, the device must be large.

Therefore, the present invention has been made to solve the above problems, and an object thereof is to obtain a sufficiently high injection speed at the start of injection in an injection molding machine using an electric motor as a drive source. It is to provide a high-speed injection mechanism that can.

(Means for Solving the Problems) The present invention has the following configuration in order to achieve the above object.

That is, in an injection mechanism of an electric injection molding machine that pushes an injection screw by the driving force of an electric motor to perform injection molding, a ball that is connected to the electric motor and moves back and forth in the axial direction of the injection screw at the rear side of the injection screw. A screw is provided, and a spring that elastically rebounds in the axial direction is provided between the front portion of the ball screw and the rear portion of the injection screw, and a locking device that locks the forward movement of the injection screw at an arbitrary retracted position of the injection screw is provided. It is characterized by

(Operation) After injecting the molten resin, the injection screw is retracted from the injection position in order to measure the molding material, and after the measurement, the injection screw is locked by the locking device so as not to move forward. Elastic energy is stored in the spring as the ball screw advances to a predetermined position. When a predetermined amount of energy is accumulated in the spring, the lock device is released to release the accumulated energy in the spring, and at the same time, the electric motor is activated to push the injection screw to inject the molten resin.

(Examples) Hereinafter, preferred examples of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory view showing an embodiment of a high-speed injection mechanism according to the present invention, showing an in-line screw type injection molding machine.

In the figure, 10 is an injection cylinder and 12 is an injection screw.
The outer peripheral surface of the injection screw 12 is formed in a screw shape, and is supported so as to be movable in the axial direction and rotatable about the axis. The injection screw 12 is connected to a rotation drive unit (not shown) that rotates the injection screw 12 at its base position.

14 is a hopper provided on the injection cylinder 10 for accommodating the molding material. The lower part of the hopper 14 is the injection cylinder 1.
Open within 0.

Reference numeral 16 is a spring having one end connected to a flange 18 provided at the rear end of the injection screw 12, and 20 is an injection ball screw connected to the other end of the spring 16. These injection screw 12, spring 16, and injection ball screw 20 are connected in series as shown in the drawing.

The spring 16 is used for accumulating elastic energy, and the end face of the injection screw 12 and the ball screw 2 are used.
It is urged to blast between 0 end faces.

The connecting portion between the injection screw 12 and the spring 16 is rotatable about the axis, and the spring 16 and the ball screw 20 are fixed.

The ball screw 20 is provided on the outer periphery on the rear end side of the ball screw 20.
A drive gear 22 for advancing and retracting in the axial direction is screwed, and the drive gear 22 is connected to a servomotor 26 for injection through a timing belt 24 and is rotated.

Reference numeral 28 denotes a stopper that contacts the inner wall surface of the flange 18 of the injection screw 12 and locks the injection screw 12 so as not to move forward. Reference numeral 30 is a position sensor for detecting the axial position of the injection screw 12, and 32 is a position sensor for detecting the axial position of the ball screw 20.

Reference numeral 34 is a computer for controlling the injection servomotor 26, the injection screw 12 and the like, and 36 is an injection condition setting device for externally inputting injection conditions according to a molded product, a molding material and the like. In the computer 34, the injection condition setting device 3
The injection conditions set in 6 and the position sensors 30, 3
Based on the sensor signal from 2 and the signal from the injection resin pressure sensor 38 that detects the injection resin pressure in the injection cylinder 10, each drive unit such as the injection servo motor 26 is controlled under optimum conditions.

Next, the operation of the high speed injection mechanism of the above embodiment will be described.

FIG. 1 (a) shows a state in which the injection screw 12 advances in the injection cylinder 10 and the injection molding is completed. From this state, the next injection molding operation is performed.

First, the injection screw 12 rotates, and the molding material is dropped from the hopper 12 onto the injection screw 12. The molding material is gradually injected into the injection cylinder 1 by the rotation of the injection screw 12.
It is sent to the front end side of 0. Since the injection cylinder 10 is heated by the heater, the molding material is melted and transferred, and at the same time, the injection screw 12 is rotated to be kneaded and sent forward. Thus, the molten resin gradually accumulates on the front end side of the injection cylinder 10 and the injection cylinder 10
The injection screw 12 itself rotates and retracts due to the resin pressure accumulated at the front end of the injection screw 12. The retraction of the injection screw 12 is stopped when a predetermined amount of molding material is supplied to the injection cylinder 10.

Fig. 1 (b) shows the injection screw 1 after the above measuring process is completed.
2 is in a retracted state. At this time, ball screw 2
0 has also returned to the retracted position.

Here, the stopper 2 is attached to the flange 18 of the injection screw 12.
8 abuts and the forward movement of the injection screw 12 is locked.
Next, the injection servomotor 26 is driven and the drive gear 22 rotates to advance the ball screw 20 to a predetermined position. The spring 16 is compressed by the forward movement of the ball screw 20, and elastic energy is accumulated in the spring 16.
In the figure, the position A is the spring 16 when the ball screw 20 is retracted.
At the rear end position and the B position, the ball screw 20 advances and the spring 1
6 is the position when compressed.

The computer 34 calculates the optimum condition of the energy accumulated in the spring 16 according to the condition set by the condition setter 36, and drives the injection servomotor 26 based on the calculation result to determine the movement amount of the ball screw 20. Control. The moving position of the ball screw 20 is detected by the position sensor 32, and when the ball screw 20 moves forward to a predetermined position, the driving of the injection servomotor 26 is stopped. It should be noted that the energy stored in the spring 16 is made larger by the computer 34 so as to be larger than the rising speed of the injection servo motor 26.
Set in.

When the elastic energy thus set can be accumulated in the spring 16, the stopper 28 is removed and at the same time the injection servomotor 26 is activated to inject the molten resin. The elastic energy accumulated in the spring 12 is used for the injection servomotor 2
Before 6 reaches a predetermined set speed, it momentarily acts on the injection screw 12 to inject the molten resin at a high speed.

Since the elastic energy accumulated in the spring 16 and the drive amount by the injection servomotor 26 both act on the injection screw 12, the position sensors 30, 3 are used in the injection process.
The injection servomotor 26 is controlled based on the signals of the pressure sensor 2 and the injection finger pressure sensor 38 so that the optimum molding conditions are satisfied.

FIG. 2 shows a graph of injection speed when injection molding is performed by the high speed injection mechanism. The horizontal axis is the injection time.

In the figure, a graph a is a contribution part of the spring 16 to the injection speed, a graph b is a contribution part of the injection servomotor 26, and a graph c is an injection speed obtained by combining both. As shown in the figure, the contribution of the spring 16 is large at the start of injection but is momentary, and the contribution of the injection servomotor 26 is small at the start of injection because of the rise time of the motor, but reaches the set speed. After that, there is a feature that the injection speed is almost controlled.

As can be seen from this graph, the high-speed injection mechanism of this embodiment instantaneously changes the high-speed injection speed by releasing the stored energy of the spring within a short time at the start of injection until the motor reaches the set speed. Therefore, the maximum problem of the electric injection molding machine, that is, the problem that a sufficient injection speed cannot be obtained at the start of injection is solved. Since the problem at the start of injection is within a very short time, that is, the rise time of the motor, the injection speed at the start of injection can be sufficiently compensated by the energy accumulated in the spring.

Further, when elastic energy is stored in the spring 16, it is sufficient to gradually push the ball screw 20 to compress the spring 16, so that it is necessary to use a special high power motor as the injection servo motor 26. Therefore, the device can be easily miniaturized.

In the above high-speed injection mechanism, there is a contribution from the spring and a contribution to the injection speed from the motor, so when actually performing injection molding, it is best to use a computer while monitoring the injection resin pressure etc. with the sensor as described above. Control the conditions to eliminate the influence of the spring during injection.

Further, the energy accumulated in the spring also varies depending on the product actually manufactured, the weight of each part such as the injection screw, the ball screw, etc. Therefore, the injection condition setting device 36 sets an appropriate condition and the computer 34 sets the optimum condition. Try to control.

Although the above-mentioned embodiment describes the in-line screw type injection molding machine, other plunger type injection molding machines and the like can be configured to utilize the energy stored in the spring in the same manner.

Although the present invention has been variously described above with reference to the preferred embodiments, the present invention is not limited to these embodiments.
Of course, many modifications can be made without departing from the spirit of the invention.

(Effects of the Invention) As described above, the high-speed injection mechanism of the electric injection molding machine according to the present invention causes the spring to accumulate the energy for pushing the injection screw, and causes the elastic force as well as the driving force by the electric motor to act on the injection. Since the molding is performed, it is possible to easily obtain a high injection speed at the start of injection, and it is possible to solve the problem at the start of injection of the conventional electric injection molding machine. Also, the electric motor to be used can be made smaller, and the device can be made more compact and the function of the injection molding machine can be improved, which makes it possible to widely use it. Play.

[Brief description of drawings]

1 (a) and 1 (b) are explanatory views showing the operation of an embodiment of the high-speed injection mechanism according to the present invention, and FIG. 2 is a graph showing the injection speed of the embodiment. 10 ... Injection cylinder, 12 ... Injection screw, 16 ... Spring, 20 ... Ball screw, 22 ... Drive gear, 24 ... Timing belt, 26 ...
... Servo motor for injection, 28 ... Stopper, 30, 32 ... Position sensor, 34 ... Computer, 36 ... Injection condition setting device, 38 ... Injection resin pressure sensor.

Claims (1)

[Claims] 1. An injection mechanism of an electric injection molding machine, wherein an injection screw is pushed by the driving force of an electric motor to perform injection molding. In an injection mechanism of the electric injection molding machine, the injection screw is advanced and retracted in the axial direction of the injection screw, which is connected to the electric motor. A locking device that provides a moving ball screw and an elastic spring in the axial direction between the front part of the ball screw and the rear part of the injection screw, and locks the forward movement of the injection screw at an arbitrary retracted position of the injection screw. A high-speed injection mechanism of an electric injection molding machine, which is provided with.