Calibration method and non-transitory computer-readable storage medium storing calibration program for contact tool sensor in machine tool, and machine tool

A machine tool having three or more translational axes, a main spindle to which a tool for processing a workpiece is mountable, a table, a numerical control unit that controls the translational axes and the main spindle, and a contact tool sensor having a reference surface, which is a flat planar surface, that measures the tool being mounted to the main spindle, the machine tool comprising:

• a tool sensor measurement unit that obtains measurement position coordinates as respective tool sensor measurement values while a reference tool is mounted on the main spindle and the contact tool sensor is installed to the table, the measurement position coordinates being of a distal end of the reference tool in at least two different measurement regions on the reference surface of the contact tool sensor;
• a difference value output unit that outputs difference values based on a difference between the respective tool sensor measurement values;
• an abnormality detector that determines an abnormality when the difference values are compared with preliminarily set acceptable values and at least one of the difference values are out of the acceptable values, otherwise an abnormality is not determined;
• and
• a tool sensor calibration unit that calibrates a positional relation between the main spindle and the contact tool sensor based on the respective tool sensor measurement values when the abnormality is not determined by the abnormality detector.