Method for calculating probe mounting position in on-machine measuring device

A method for calculating a probe mounting position in an on-machine measuring device, comprising:

• obtaining a system including the on-machine measuring device and a single rotary axis of a machine tool, wherein the on-machine measuring device includes the probe, and wherein the probe is mounted on the single rotary axis of the machine tool, and wherein the machine tool has at least three linear axes and the rotary axis, wherein the three linear axes extend at right angles to one another, one of the linear axes is aligned with the direction of the rotary axis, a probe of the on-machine measuring device moves at right angles to the direction of the rotary axis, a displacement of the probe is detected by a probe position detecting device mounted on the on-machine measuring device, and the distance between a rotation center of the rotary axis and a tip end of a measuring head mounted on a tip end of the probe is calculated with the tip end of the measuring head held against a reference sphere attached to the machine tool;
• and
• calculating the probe mounting position by performing the following steps:
• a first step of setting linear axes which move in two directions perpendicular to the rotary axis, out of the linear axes, as first and second linear axes, and previously defining a position of the tip end of the measuring head relative to the center of the rotary axis as coordinates of the first and second linear axes;
• a second step of creating a measurement program for measurement performed at two different predetermined angles of the rotary axis by moving the first and second linear axes so that a central axis of the probe is perpendicular to the surface of the reference sphere;
• a third step of moving the probe by activating motors of the system, and obtaining, as a result of the movement of the probe, as respective measurement errors at the two angles of the rotary axis, errors between original displacement data of the probe and displacement data of the probe measured at the two angles according to the created measurement program;
• a fourth step of obtaining measurement signals representing displacements of the first and second linear axes with which the measurement errors become zero respectively, as respective first correction amounts at the two angles;
• a fifth step of obtaining, as reference coordinates, coordinates of the first and second linear axes at the two angles of the measurement program, corrected with the first correction amounts, and further obtaining, as corrected coordinates, coordinates of the first and second linear axes at the two angles, using the measurement program created in the second step, based on the position obtained by correcting the position of the tip end of the measuring head, defined in the first step, with second correction amounts which are increased or decreased in stages respectively by minimum units equivalent to position detection resolutions of the linear axes, within a predetermined range;
• and
• a sixth step of correcting, the coordinates of the first and second linear axes, defined in the first step, with the second correction amount with which the differences between the reference coordinates and the corrected coordinates, individually obtained in the fifth step, become minimum, and obtaining final coordinates of the first and second linear axes at the position of the tip end of the measuring head relative to the center of the rotary axis.