Thermal displacement correction method and thermal displacement correction apparatus of machine tool

A thermal displacement correction apparatus for a machine tool including a tool-mounted portion and a spindle, a tool or a position measurement sensor being removably attachable to the tool-mounted portion, the spindle being rotatable with the tool mounted, the thermal displacement correction apparatus comprising:

• an initial tool temperature setting unit configured to set an initial tool temperature of the tool or the position measurement sensor at a time point at which the tool or the position measurement sensor is mounted to the spindle using any information of a use history of the tool or the position measurement sensor, a temperature of the tool or the position measurement sensor before the tool or the position measurement sensor is mounted to the spindle, a body temperature of the machine tool, and an ambient temperature of the machine tool;
• a tool temperature estimating unit configured to estimate a temperature of the tool or the position measurement sensor based on the initial tool temperature and a temperature of the spindle;
• an amount-of-thermal-displacement estimating unit configured to estimate an amount of thermal displacement of the tool or the position measurement sensor with a preliminarily set tool thermal displacement estimation formula based on the temperature estimated by the tool temperature estimating unit;
• and
• a thermal displacement correcting unit configured to move a feed shaft of the machine tool based on the estimated amount of thermal displacement to perform a correction, wherein
• the tool temperature estimating unit is configured to measure the temperature of the spindle by a temperature sensor mounted to a fixing portion of the spindle, the tool temperature estimating unit being configured to estimate a tool-mounted portion temperature of the spindle from the measured temperature of the spindle and a tool-mounted portion temperature estimation formula, the tool-mounted portion temperature estimation formula being set differently depending on whether the spindle rotates or stops, and
• the temperature of the tool or the position measurement sensor is estimated with the tool-mounted portion temperature, the initial tool temperature of the tool or the position measurement sensor, and the preliminarily set tool temperature estimation formula.