Method of controlling positions for changeover of injection/filling speed in injection molding machine

Claim 1

A method of controlling the injection speed selecting points of an injection molder which injects plasticized synthetic resin from the cylinder into the cavity of a mold at speed varied in multiple steps in each injection process, comprising the steps of: (a) preliminarily obtaining a formula for relation among the resin pressure value, specific volume value and temperature of plasticized synthetic resin, as a characteristic equation for the plasticized synthetic resin; (b) detecting the resin pressure and screw positional values immediately before injection under a reference injecting condition, and the resin pressure value with the screw at each injection speed selecting point; (c) detecting the resin pressure and screw positional values immediately before injection under a changed injecting condition; (d) determining the injection speed selecting points for the changed injecting condition, through operations on the basis of the obtained formula for relation among the resin pressure value, specific volume value and temperature of the resin as well as the detected resin pressure and screw positional values immediately before injection under the reference injecting condition and the detected resin pressure and screw positional values immediately before injection under the changed injecting condition; and (e) changing the injection speed when the screw has been moved from the position immediately before injection to each determined injection speed selecting point for the changed injecting condition.

Claim 4

A method of controlling the injection speed selecting points of an injection molder as described in any one of the claims 1 through 3, in which said resin pressure value is obtained by detecting the pushing pressure value applied to the screw to effect the resin pressure value.