Tool change rotary position determining device and tool change rotary position determining method

A tool change rotary position determining device for use with a machine tool, the machine tool comprising:

• a revolving turret including a plurality of grips arranged along a circumferential direction thereof, each of the plurality of grips capable of holding a tool to be attached to an attachment hole of a spindle via a tool holder;
• and a turning motor configured to turn the turret, the tool change rotary position determining device determining a tool change rotary position of the turret when the machine tool transfers the tool between a specific grip of the plurality of grips and the spindle so as to attach the tool to or remove the tool from the spindle, the tool change rotary position determining device comprising:
• a processor programmed to:
• acquire a load torque on the turning motor from a load torque detector coupled to the turning motor;
• acquire a rotary position of the turning motor from a rotary position detector coupled to the turning motor;
• control the turning motor so as to turn the turret clockwise and counterclockwise in a state where the tool holder of the tool gripped by the specific grip of the plurality of grips is inserted in the attachment hole of the spindle;
• and
• determine the tool change rotary position of the turret when the tool is transferred between the specific grip and the spindle based on the load torque acquired by the load torque detector and the rotary position acquired by the rotary position detector when the turret is turned clockwise and counterclockwise;
• wherein the load torque acquired is the load torque that is calculated by subtracting an offset load torque arising in the turning motor before the tool holder of the tool gripped by the specific grip is inserted into the attachment hole of the spindle.