THERMAL DISPLACEMENT CORRECTING APPARATUS FOR MACHINE TOOL

A thermal displacement correcting apparatus suitable for a machine tool (1) provided with a mechanism for feeding a main spindle (2) is disclosed. Three magnetic flux generating bodies 61 to 63 are fixed to the main spindle; a magnetic sensor (7) is fixed to the machine tool to detect the magnetic flux generated by the magnetic flux generating body at each predetermined spindle feed position; a thermal displacement value detecting section (14A) detects the thermal displacement values of the main spindle on the basis of outputs of the magnetic sensor at the respective spindle feed positions; a thermal displacement correction value calculating section (15) calculates a correction function on the basis of the detected thermal displacement values and previously determined reference values, and obtains the thermal displacement correction value in accordance with the calculated correction function at each spindle feed position; and a spindle feed command correcting section (16) corrects the spindle feed command applied to the spindle feed motor on the basis of the obtained thermal displacement correction value at each spindle feed position.