Thermal displacement correcting apparatus for machine tool

A method of correcting thermal displacement of a machine tool provided with a mechanism for feeding a main spindle via a spindle feed mechanism by applying a spindle feed command to a spindle feed motor, which comprises the steps of:

• stopping the main spindle at a predetermined first spindle feed position for initialization;
• feeding the main spindle to a second spindle feed position;
• detecting the main spindle position magnetically with a predetermined sensitivity to obtain a second spindle feed position signal;
• storing the detected second spindle feed position signal;
• feeding the main spindle to a third spindle feed position;
• detecting the main spindle position magnetically with the predetermined sensitivity to obtain a third spindle feed position signal;
• storing the detected third spindle feed position signal;
• calculating a correction function on the basis of the detected and stored second and third spindle feed position signals and previously determined reference values at the second and third spindle feed positions;
• calculating thermal displacement correction values at the second and third spindle feed position in accordance with the calculated correction function;
• and
• correcting the spindle feed command applied to the spindle feed motor at the second and third spindle feed positions on the basis of the calculated thermal displacement correction values, respectively.

A thermal displacement correcting apparatus for a machine tool, provided with a mechanism for feeding a main spindle, via a spindle feed mechanism, by applying a spindle feed command to a spindle feed motor, the apparatus comprising:

• at least one magnetic flux generating body fixed to the spindle feed mechanism;
• a magnetic sensor, fixed to the machine tool, for detecting magnetic flux generated by said magnetic flux generating body whenever said magnetic flux generating body is fed to a predetermined spindle feed position;
• means for detecting a thermal displacement value of the spindle feed mechanism on the basis of an output of said magnetic sensor;
• means for moving said magnetic sensor to the vicinity of said magnetic flux generating body in a direction perpendicular to the main spindle, whenever said magnetic flux generating body is fed to the predetermined spindle feed position by the spindle feed mechanism in response to the spindle feed command, to input a detection signal of said magnetic sensor to said thermal displacement value detecting means;
• means for calculating a thermal displacement correction value by comparing the detected thermal displacement value with a previously determined reference value at the predetermined spindle feed position, wherein said thermal displacement correction value calculating means first calculates a correction function on the basis of the detected thermal displacement value and the previously determined reference value, and then calculates the thermal displacement correction value from said correction function;
• and
• means for correcting the spindle feed command applied to the spindle feed motor on the basis of the calculated thermal displacement correction value.