Motor control method for injection molding machine and motor controller for carrying out the same

A motor controller for an injection molding machine, comprising:

• a storing means for storing duty cycle data table including diverse duty cycles and values of allowable current corresponding to a given duty cycle;
• a setting means for injection molding condition data and a duty cycle for an injection motor on the basis of ratio between a predetermined injection period for which the injection motor operates and a predetermined injection molding cycle;
• a calculating means for calculating a shaft torque of the injection motor on the basis of set injection forces of the injection molding condition, and determining a maximum current applied to the injection motor on the basis of the calculated motor shaft torque;
• a deciding means for comparing the allowable current for the set duty cycle with the maximum current, and
• deciding that the injection motor is overloaded when the allowable current is lower than the maximum current;
• a correcting means for retrieving another duty cycle corresponding the maximum current from the duty cycle data table, and correcting time sharing of the present duty cycle on the basis of the retrieved duty cycle so as to enables the injection molding cycle to repeat continuously.