Method for controlling measurement in injection molding machine, and injection molding machine

Abstract

A method for controlling measurement in a motor-driven in-line screw type injection molding machine using servo-motors as a measurement driving source and an injection driving source. Control is made so that all of a measured value of back pressure controlled by the measurement servo-motor, a measured value of an astern speed of a screw controlled by the injection servo-motor, and a measured rotational speed of the screw turn zero concurrently at timing when the screw reaches a measurement completion position. Thus, suck-back can be made dispensable.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a technique for controlling measurement in a motor-driven in-line screw type injection molding machine using servo-motors as a measurement driving source and an injection driving source. BACKGROUND ART [0002] In a motor-driven in-line screw type injection molding machine in the background art, a measuring stroke is often controlled as follows. That is, a measurement servo-motor is controlled by rotational velocity feedback control so that the rotational velocity of a screw coincides with a set value, while an injection servo-motor is controlled by pressure feedback control so that the back pressure applied onto the screw (resistant pressure against astern movement of the screw) coincides with a set value. When such rotational velocity feedback control is performed on the measurement servo-motor while such pressure feedback control is performed on the injection servo-motor, the back pressure applied to the screw is improv...

AI Technical Summary

Benefits of technology

[0007] The present invention was developed in consideration of the foregoing problem. It is an object of the present invention to make all of a measured value of the astern speed of a screw, a measured value of the back pressure and a measured rotational velocity of the screw (measurement servo-motor) zero concurrently at timing when the screw reaches a position where measurement is completed, so that suck-back can be made dispensable.

[0013] According to the invention, control is made so that all the measured value of the astern speed of the screw, the measured value of the back pressure, and the measured rotational speed of the screw (measurement servo-motor) turn zero concurrently at timing when the screw reaches the measurement completion position. Accordingly, the residual pressure of molten resin staying in a heating cylinder till the next injection becomes zero. Thus, there is no fear that drooling or cobwebbing occurs when a mold is opened and a molded item is released from the mold. It is therefore unnecessary to perform suck-back after measurement is completed. In addition, since it is unnecessary to perform suck-back and any injection operation can be always started in a constant measurement completion position, the injection rate is stabilized, and the cushion thickness is also stabilized. Furthermore, the back pressure and the screw (measurement servo-motor) rotation turn zero as soon as the screw stops its astern movement. Thus, the variation in weight among molded items can be made as low as possible in cooperation with the stabilized density of the measured molten resin, the stabilized injection rate and the stabilized cushion thickness.

Problems solved by technology

Accordingly, in the beginning of measurement, shortage of raw resin leads to failure in expected increase of the back pressure.

As a result, the measuring operation may be unstable.

In addition, the measuring operation may be unstable in some operating condition of a raw resin supply system or in some dry condition of the resin.

In spite of such control, there is a problem that it cannot be guaranteed that all of a measured value of the astern speed of the screw controlled by the injection servo-motor, a measured value of the back pressure controlled by the measurement servo-motor and a measured rotational velocity of the screw turn zero concurrently at timing when the screw reaches a position where measurement is completed.

That is, in the background art, the deceleration setting pattern for the astern speed of the screw is not proper but is apt to be set to be steep.

Thus, the back pressure is adversely increased near the zero point of the astern speed of the screw.

Images