System for controlling nozzle touch force

Abstract

A system for controlling nozzle touch force, which is capable of maintaining the touch force relying upon a simple constitution. An electric motor moves the injection unit forward via a spring to bring a nozzle into contact with a metal mold. Further, the spring is compressed to impart a preset nozzle touch force. In the injection/pressure-maintaining step, the screw is driven, and a position/speed detector provided on a servo motor for injecting the resin detects the injection speed at regular intervals. A force produced by the force of inertia of the moving portions such as the injection screw and the pusher plate that move due to the injection operation, is found from the acceleration that is found from the injection speed. The amount of compression of the spring is controlled by varying the rotational position of the motor by an amount corresponding to the force that is found to maintain the nozzle touch force constant. Since the nozzle touch force is maintained constant, no resin leaks and an excess of nozzle touch force is not produced, either.

Dependencies are inferred from the claim text.