Error identification method of machine tool

An error identification method for identifying a geometric error of axes in a machine tool including a table configured to hold a workpiece, one or more main spindle head configured to mount a tool, three or more axes of translational axes, one or more axis of a table rotation axis configured to perform a rotational motion on the table, and one or more axis of a main spindle head rotation axis configured to perform a rotational motion on the main spindle head, the error identification method comprising;

• a mounting step of mounting one of a measured jig and a position measurement sensor to one of the main spindle head and the table, or mounting another of the measured jig and the position measurement sensor to another of the main spindle head and the table, an initial position measurement step of indexing the main spindle head rotation axis to an initial angle to measure an initial position of the measured jig using the position measurement sensor;
• a table reference angle calculation step of calculating a reference angle from an angle of the table rotation axis in the initial position measurement step;
• a reference position measurement step of indexing the table rotation axis to the reference angle and indexes the main spindle head rotation axis to the initial angle to measure a reference position of the measured jig by the position measurement sensor;
• a relative position measurement step of indexing the table rotation axis to a plurality of predetermined angles based on the reference angle of the table rotation axis and indexing the main spindle head rotation axis to a plurality of predetermined angles to measure each position of the measured jig by the position measurement sensor;
• an arc approximation step of approximating the plurality of measured position values measured at the relative position measurement step into an arc;
• and
• an error calculation step of calculating an error of a center position of the rotation axis, a tilt error of the rotation axis, or a tilt error of the translational axis from the arc approximated in the arc approximation step.