A position measurement system of an object in a machine tool that measures a position of the object fixed on a table by a position measurement sensor in the machine tool, the machine tool including translational axes of three or more axes, a main spindle rotatable with a tool mounted thereon, the table, the position measurement sensor mountable to the main spindle, and a control device that controls the translational axes and the main spindle, the position measurement system comprising:
- a reference tool serving as a reference for a length of the tool;
- a tool sensor configured to detect a distal end position of the reference tool mounted to the main spindle;
- a reference block installed on a side of the tool sensor;
- a machining block installed on a side of the table;
- a tool sensor position acquisition unit configured to move the reference tool mounted to the main spindle with the translational axes, acquire a sensing position of a distal end of the reference tool using the tool sensor, and store the sensing position;
- a tool length correction value acquisition unit configured to move the tool mounted to the main spindle with the translational axes and acquire a length direction correction value of the tool by the tool sensor;
- a machined surface position acquisition unit configured to rotate the tool at a given position of the machining block such that the tool cuts into the machining block to machine a surface, the machined surface position acquisition unit being configured to move the position measurement sensor mounted to the main spindle with the translational axes, bring the position measurement sensor into contact with a machined surface to measure and acquire a position of the machined surface;
- a position measurement sensor length calculation unit configured to calculate a length of the position measurement sensor from the length direction correction value of the tool acquired in the tool length correction value acquisition unit and the position of the machined surface acquired in the machined surface position acquisition unit;
- a relative position calculation unit configured to measure a position of the reference block using the position measurement sensor mounted to the main spindle and store the position of the reference block, the relative position calculation unit being configured to calculate a relative position of the reference block to the sensing position from the sensing position acquired in the tool sensor position acquisition unit, the position of the reference block, the length of the position measurement sensor acquired in the position measurement sensor length calculation unit, and the length of the reference tool and store the relative position;
- a reference tool position acquisition unit configured to move the reference tool mounted to the main spindle with the translational axes, acquire a reference tool position as the distal end position of the reference tool using the tool sensor, and store the reference tool position;
- a reference block position measurement unit configured to measure a position of the reference block by the position measurement sensor mounted to the main spindle and store the position of the reference block;
- a length correction value calculation unit configured to calculate a length direction correction value of the position measurement sensor from the reference tool position acquired in the reference tool position acquisition unit, the position of the reference block acquired in the reference block position measurement unit, the relative position calculated in the relative position calculation unit, and the length of the reference tool and store the length direction correction value;
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- a position measurement unit configured to measure the object by the position measurement sensor mounted to the main spindle and correct a measurement position of the object using the length direction correction value of the position measurement sensor calculated in the length correction value calculation unit.