Double blank detecting device for press machine and die protecting device for press machine

A die protecting device for a press machine comprising:

• the press machine having a braking device that brakes a slide driven by a press driving device of the press machine, and a hydraulic cylinder that is incorporated in the slide, and moves a die mounting surface of the slide relative to movement of the slide driven by the press driving device;
• a double blank detecting device comprising a position signal acquiring unit that acquires a die cushion position signal indicating a position of a cushion pad of a die cushion device attached to the press machine, a load signal acquiring unit that acquires a die cushion load signal indicating a die cushion load generated in the cushion pad of the die cushion device, and a double blank detecting unit that detects, as a double blank, a state where a plurality of blank materials supplied to the press machine are overlapped, based on the die cushion position signal acquired by the position signal acquiring unit and the die cushion load signal acquired by the load signal acquiring unit, wherein the double blank detecting unit holds a die cushion position signal at a time point when the die cushion load signal rises to a predetermined value, compares a holding value of the held die cushion position signal with an abnormality identification value, and detects the double blank;
• and
• a safety processing device that causes the braking device to start quick braking of the slide, and depressurizes the hydraulic cylinder to relatively move one portion including the die mounting surface of the slide in an elevating direction, when the double blank detecting unit detects the double blank.