Straightness error compensation method and straightness error compensation apparatus for machine tool

A straightness error compensation apparatus for a machine tool, the machine tool including a bed, a table on which a workpiece is fixable, a main spindle head capable of rotating a mounted tool, a table drive axis that allows for a linear motion of the table with respect to the bed, and two main spindle head drive axes that allow for rectilinear motions of the main spindle head in directions each perpendicular to the table drive axis with respect to the bed, the straightness error compensation apparatus comprising:

• a bed curve storage unit that stores a straightness curve of an upper surface of the bed;
• a fixed position information storage unit that stores fixed position information of the workpiece with respect to a reference position of the table;
• a table curve calculator that calculates a table upper surface straightness curve based on a straightness curve of an upper surface of the bed stored in the bed curve storage unit and a command position of the table drive axis;
• a workpiece inclination calculator that calculates an inclination estimation value of the workpiece based on the fixed position information stored in the fixed position information storage unit and the calculated table upper surface straightness curve;
• a straightness error calculator that calculates a straightness error estimation value of the table drive axis at a position of the main spindle head based on the command position of the table drive axis, the calculated table upper surface straightness curve, and the calculated inclination estimation value of the workpiece;
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• a compensation control unit that controls to compensate at least one of the main spindle head drive axes using the calculated straightness error estimation value as a compensation amount.