Controller

A controller for controlling a machine tool that moves a tool relatively to a workpiece placed on a table via axes including three linear axes and at least one rotation axis, the controller comprising:

• a reference-sphere position obtaining unit that obtains coordinate values, on the three linear axes, of a reference sphere placed on the table, the coordinate values being measured by controlling the three linear axes while a target rotation axis included in the at least one rotation axis is positioned at three or more locations;
• a rotation-axis commanded-angle obtaining unit that obtains commanded angles given to the target rotation axis at the respective locations at which the target rotation axis was positioned during the measurement;
• an approximate circle calculating unit that calculates an approximate circle passing near the coordinate values of the reference sphere on the three linear axes under a constraint of the commanded angles, based on the coordinate values of the reference sphere on the three linear axes obtained by the reference-sphere position obtaining unit and the commanded angles given to the target rotation axis obtained by the rotation-axis commanded-angle obtaining unit;
• and
• a rotation axis position storage unit that stores a center position of the approximate circle calculated by the approximate circle calculating unit as coordinates of a center position of the target rotation axis.