Die cushion controller

A die cushion controller, comprising:

• a pressure command signal output unit that outputs a pressure command signal in accordance with a pressure target value based on a predetermined pressure pattern;
• a pressure control unit that outputs a speed command signal based on the pressure command signal output from the pressure command signal output unit;
• a speed control unit that outputs a motor current command signal based on the speed command signal output from the pressure control unit;
• and
• a servo amplifier that supplies an electric current to an electric servomotor which drives a die cushion, in accordance with the motor current command signal output from the speed control unit;
• wherein the pressure target value of the predetermined pressure pattern includes:
• a low pressure target value which is provided for a predetermined period of time after a die attached to a slide of a press machine touches a workpiece and during which pressure of the die cushion exceeds the low pressure target value;
• a high pressure target value corresponding to a cushion pressure required for retaining the workpiece in contact with the die, the cushion pressure converging to the high pressure target value;
• and
• a complementary target value that starts at the low pressure target value, ends at the high pressure target value, and extends at a substantially linear increase rate therebetween for a predetermined period of time during which the cushion pressure exceeds the low pressure target value and reaches the high pressure target value.