Method and program for calculating correction value for machine tool

A method of computing a correction value for a machine tool including two or more translational axes and one or more rotational axes for correcting errors in a position and an orientation of a tool in relation to a workpiece fixed to the machine tool caused by geometric errors, the method comprising:

• a rotational axis correction value computing step for computing a correction value for the rotational axis using a sum of geometric parameters in the same rotation direction as the rotational axis or a sum with an opposite sign as a correction value for the rotational axis;
• wherein the axes are assumed to be sequentially connected from the tool to the workpiece and the geometric parameter represents the geometric errors including a relative translational error and rotational error between the tool and the axis, between the axes adjacent each other, and between workpieces, respectively;
• an ideal tool position computing step for computing an ideal tool position without the geometric errors using a command value for each of the translational axes and a command value for each of the rotational axes;
• an actual tool position computing step for computing an actual tool position with the geometric errors using the command value for each of the rotational axes, the command value for each of the translational axes, the geometric parameter, and the correction value for the rotational axis which is calculated in the rotational axis correction value computing step;
• a tool positional error computing step for computing a differential between the ideal tool position and the actual tool position;
• a tool position coordinate transformation step for performing a coordinate transformation of the differential;
• and
• a translational axis correction value computing step for computing a correction value for the translational axis using a transformed value obtained in the tool position coordinate transformation step.