Method and program for calculating correction value for machine tool

A method of calculating a correction value for a machine tool having two or more translational axes and one or more rotational axes to correct an error in one of a position and a position and posture of a tool with respect to an object to be machined, which results from a geometric error in the machine tool, comprising a step of:

• calculating a correction value for each of the translational axes using a command position of each of the rotational axes, a coordinate value of a correction reference point as one point designated in advance in a command position space of each of the translational axes, a command position of each of the translational axes to which the coordinate value of the correction reference point is assigned, and a geometric parameter representing the geometric error as a geometric relative error between the respective axes,
• wherein an error in a position of the tool in a work coordinate system of the object to be machined with the geometric parameter is calculated using:
• a position of the tool including the geometric parameter obtained by a homogeneous coordinate conversion from the tool coordinate system to the work coordinate system of the object to be machined, and
• an optimal position of the tool where the geometric parameter is not included obtained by a homogenous coordinate conversion from the tool coordinate system to the work coordinate system of the object to be machined, and
• wherein the calculated error in the position of the tool is converted to a command value coordinate system for the respective axes by a homogeneous coordinate conversion from the work coordinate system to the command value coordinate system to provide the calculated correction value for each of the translational axes.