Method and apparatus for correcting thermal displacement of machine tool

An apparatus for correcting thermal displacement of a machine tool having a rotation spindle, the apparatus comprising:

• a spindle rotation speed detection section for detecting a rotation speed of the spindle;
• a spindle load detection section for detecting a load on the spindle;
• a thermal displacement estimation section for estimating a thermal displacement amount of the spindle in the current cycle of execution of a program by using an arithmetic expression that is based at least on the spindle rotation speed, the spindle load, and a thermal displacement amount that has been estimated in the preceding cycle of execution of the program;
• and
• a correction section for using the estimated thermal displacement amount in the current cycle as a correction amount for canceling the thermal displacement of the spindle.

A method for correcting thermal displacement of a machine tool having a rotation spindle, comprising:

• detecting a rotation speed of the spindle;
• estimating a thermal displacement amount of the spindle in a current cycle of execution of a program by using an arithmetic expression that at least includes the following terms a) to d):
• a) a term having a thermal displacement amount that has been estimated in a preceding cycle of execution of the program as a variable;
• b) a term having the rotation speed of the spindle, which is detected at a predetermined interval, as a variable;
• c) a term having the square of the spindle rotation speed as a variable;
• and
• d) a term having the cube of the spindle rotation speed as a variable;
• and
• using the estimated thermal displacement amount in the current cycle as a correction amount for canceling the thermal displacement of the spindle.