Coordinate system correcting apparatus for machine tool

A coordinate system correcting apparatus for correcting a reference coordinate system set for a work space of a machine tool, the coordinate system of the machine tool having orthogonal axes X, Y, and Z, the coordinate system correcting apparatus comprising:

• jig means for defining a plurality of space lattice points that are three-dimensionally arranged to serve as references of a reference coordinate system, the space lattice points defined by the jig means coinciding with predetermined normal space lattice points when the machine tool is not distorted, wherein eight adjacent normal space lattice points are positioned at vertexes of a hexahedron respectively, any one of three pairs of opposing two faces of the hexahedron being in parallel with each other and the three pairs of opposing two faces of the hexahedron being in parallel with planes X-Y, X-Z, and Y-Z of the coordinate system of the machine tool respectively;
• storage means for storing the positions of the normal space lattice points;
• measuring means for measuring distorted space lattice points defined by the jig means, the distorted space lattice points deviating from the normal space lattice points when the machine tool is distorted;
• and
• correcting means for three-dimensionally correcting the reference coordinate system according to each normal hexahedron formed from eight adjacent normal space lattice points and each corresponding distorted hexahedron formed from eight adjacent distorted space lattice points.