Die cushion mechanism, and apparatus and method for controlling the same

A control apparatus for controlling a die cushion mechanism including a servo-motor as a drive source and producing a force adapted to be applied outside, comprising:

• a force commanding section for commanding a force to be produced by said die cushion mechanism;
• a force detecting section for detecting a force produced by said die cushion mechanism;
• a force controlling section for executing a force control on said servo-motor, based on a force command value commanded by said force commanding section and a force detected value detected by said force detecting section;
• a position commanding section for commanding a desired position of said servo-motor;
• a position detecting section for detecting an existing position of said servo-motor;
• a position controlling section for executing a position control for said servo-motor based on a position command value commanded by said position commanding section and a position detected value detected by said position detecting section;
• a control changing section for selecting either one of said force controlling section and said position controlling section to make a selected section execute a control of said servo-motor;
• and
• an abnormality preventing section for preventing, in association with a control state of said servo-motor, said die cushion mechanism from producing an abnormal force;
• wherein said abnormality preventing section includes an abnormality judging section for judging whether an abnormality is present in said force detected value detected by said force detecting section, by comparing said force detected value with a predetermined threshold value of force, during a period when said position controlling section selected by said control changing section executes said position control;
• wherein said abnormality judging section judges a presence of said abnormality when said force detected value becomes larger than said threshold value.