Machine tool, chuck gripping force detection method, and chuck fastening amount setting method

A chuck holding force detection method for detecting a holding force applied to a workpiece by a chuck in a spindle of a machine tool in a case where the chuck holds the workpiece, comprising:

• a first step in which an open/close mechanism causes the chuck to perform a closing operation, from an open state in which the chuck allows a workpiece to be removed to a closed state in which the chuck holds a workpiece;
• a second step in which a first time and a second time are acquired, the first time being a time from when a control unit issues a control signal to the open/close mechanism for the closing operation in the first step to when a first sensor detects that the chuck is no longer in the open state, and the second time being a time from when the control unit issues the control signal to the open/close mechanism to when a second sensor detects that the chuck has assumed the closed state;
• and
• a third step in which the holding force is obtained on the basis of a correlation between a difference between the first time and the second time, a tightening amount adjusted by an adjustment mechanism applied to the workpiece by the chuck in the closed state, and the holding force.

A method for setting a tightening amount applied to a workpiece by a chuck in a spindle of a machine tool in a case where the chuck holds the workpiece, comprising:

• a first step in which, with the chuck in a closed state in which the chuck holds a workpiece, and with a tightening amount applied to the workpiece by the chuck in the closed state being adjusted by an adjustment mechanism to a first tightening amount, an open/close mechanism causes the chuck to perform a closing operation, from an open state in which the chuck allows a workpiece to be removed to the closed state,
• a second step in which a first time and a second time are acquired, the first time being a time from when a control unit issues a control signal to the open/close mechanism for the closing operation in the first step to when a first sensor detects that the chuck is no longer in the open state, and the second time being a time from when the control unit issues the control signal to the open/close mechanism to when a second sensor detects that the chuck has assumed the closed state;
• a third step in which a second tightening amount that enables the holding force to be set to a desired value is obtained on the basis of a correlation between a difference between the first time and the second time, a tightening amount adjusted by the adjustment mechanism applied to the workpiece by the chuck in the closed state, and a holding force applied to the workpiece by the chuck in the closed state;
• and
• a fourth step in which the tightening amount is adjusted by the adjustment mechanism to the second tightening amount obtained in the third step.