Method and device for preparing error map and numerically controlled machine tool having error map preparation function

A method for preparing an error map of a numerically controlled machine tool which at least one linear feed axis and a plurality of rotational feed axes and in which a main spindle and a table are movable relative to each other, said method comprising steps of:

• defining a plurality of measurement points in a movable range of said at least one linear feed axis and said plurality of rotational feed axes;
• positioning each of said plurality of rotational feed axes to a respective one of a plurality of rotation angles corresponding to each of said measurement points and processing three mutually orthogonal surfaces of a test piece or work piece in a shape of a rectangular parallelepiped that is attached to said table at each of said plurality of measurement points with each of said plurality of rotational feed axes thus positioned,
• measuring inclinations of one or more processed reference surfaces of said test piece or work piece, said one or more processed reference surfaces being obtained when said test piece or work piece is processed with each of said plurality of rotational feed axes positioned to a respective one of a plurality of rotation angles corresponding to one of said plurality of measurement points, at each of said plurality of measurement points other than said one of said plurality of measurement points relative to inclinations of said one or more processed reference surfaces measured with each of said plurality of rotational feed axes positioned at a respective one of a plurality of rotation angles corresponding to said one of said plurality of measurement points to determine an attitude error at each plurality of rotation angles corresponding to each of said plurality of measurement points,
• measuring three mutually orthogonal processed surfaces of said test piece or work piece, processed with each of said plurality of rotational axes positioned to a respective one of said plurality of rotation angles corresponding to a respective one of said plurality of measurement points, at each of said plurality of measurement points to determine, for each plurality of rotation angles corresponding to each of said plurality of measurement points, a position of an intersection point of three planes containing said three mutually orthogonal processed surfaces,
• determining a position error at each of said plurality of measurement points from a difference of position between an intersection point of three planes containing three mutually orthogonal processed surfaces processed with each of said plurality of rotational feed axes positioned to said respective one of said plurality of rotation angles corresponding to said one of said plurality of measurement points and an intersection point of three planes containing three mutually orthogonal processed surfaces processed with each of said plurality of rotational feed axes positioned to a respective one of a plurality of rotation angles corresponding to another of said plurality of measurement points, and said attitude error, and
• storing said position error and said attitude error in correspondence to a respective plurality of rotation angles corresponding to each of said plurality of measurement points, in which said position error and said attitude error compose a multidimensional error map.

A method for preparing an error map of a numerically controlled machine tool which has at least one linear feed axis and a plurality of rotational feed axes and in which a main spindle and a table are movable relative to each other, said method comprising:

• defining a plurality of measurement points in a movable range of said plurality of rotational feed axes;
• positioning each of said plurality of rotational feed axes to a respective one of a plurality of rotation angles corresponding to each of said plurality of measurement points and processing three mutually orthogonal surfaces of a test piece or work piece in a shape of a rectangular parallelepiped attached to said table with each of said plurality of rotational feed axes thus positioned,
• measuring processed surfaces of said test piece or work piece to determine, for each of said plurality of measurement points, an inclination of three mutually orthogonal processed surfaces processed at a corresponding one of said plurality of measurement points and a position of intersection point of three planes containing said three mutually orthogonal processed surfaces that were processed at said corresponding one of said plurality of measurement points,
• determining an attitude error at each of said plurality of measurement points from a difference between inclinations of three mutually orthogonal processed surfaces obtained by processing said test piece or work piece with each of said plurality of rotational feed axes positioned to a respective one of a plurality of rotation angles corresponding to a reference measurement point selected from said plurality of measurement points and inclinations of three mutually orthogonal processed surfaces obtained by processing said test piece or work piece with each of said plurality of rotational feed axes positioned to a respective one of a plurality of rotation angles corresponding to each of said plurality of measurement points,
• determining a position error at each of said plurality of measurement points from a difference of position between an intersection point of three planes containing said three mutually orthogonal processed surfaces obtained by processing said test piece or work piece with each of said plurality of rotational feed axes positioned to a respective one of a plurality of rotation angles corresponding to said reference measurement point and an intersection point of three planes containing three mutually orthogonal processed surfaces obtained by processing said test piece or work piece with each of said plurality of rotational feed axes positioned to a respective one of a plurality of rotation angles corresponding to each of said plurality of measurement points, and said determined attitude error, and
• storing said position error and said attitude error in correspondence to a respective plurality of rotation angles corresponding to each of said plurality of measurement points, in which said position error and said attitude error compose a multidimensional error map.

A numerically controlled machine tool which has at least one linear feed axis and a plurality of rotational feed axes and in which a main spindle and a table are movable relative to each other, said numerically controlled machine tool having an error map preparation function comprising:

• a test piece or work piece attached to said table,
• a measurement device having a sensor provided on said main spindle for measuring processed surfaces of said test piece or work piece with said sensor at a desired measurement point,
• a computation section that computes a position error and an attitude error produced when said plurality of rotational feed axes are rotated at said measurement point, based on measurement data measured with said measurement device and coordinate values of said measurement point,
• a storage section for storing said position error and said attitude error computed by said computation section in correspondence to rotation angles of said plurality of rotational feed axes at said measurement point, in which said position error and said attitude error compose a multidimensional error map.