Method and apparatus for calculating correction value for thermal displacement in machine tool

A method for calculating a correction value for thermal displacement occurring along an axis of a main spindle in a machine tool, the method comprising the steps of:

• measuring a temperature in the vicinity of the main spindle;
• estimating an amount of the thermal displacement on the basis of the measured temperature and a predetermined thermal displacement amount calculation expression;
• and
• calculating the correction value on the basis of the estimated thermal displacement amount,
• wherein, when the rotation of the main spindle is interrupted, an actual amount of displacement occurring along the axis of the main spindle during the interruption is estimated on the basis of an amount of the thermal displacement estimated on the basis of a temperature measured immediately before the interruption and a predetermined delay amount to the estimated thermal displacement amount, and the correction value is calculated on the basis of the estimated displacement amount.

An apparatus for calculating a correction value for thermal displacement occurring along an axis of a main spindle in a machine tool, the apparatus comprising:

• temperature measuring means for measuring a temperature in the vicinity of the main spindle;
• thermal displacement amount estimating means for estimating an amount of the thermal displacement on the basis of the temperature measured by the temperature measuring means and a predetermined thermal displacement amount calculation expression;
• correction value calculating means for calculating the correction value on the basis of the thermal displacement amount estimated by the thermal displacement amount estimating means;
• and
• adjusting displacement amount calculating means for estimating an amount of displacement delay occurring due to the interruption which an actual displacement amount of the main spindle has to the estimated thermal displacement amount when rotation of the main spindle is restarted after interruption thereof, and calculating an adjusting displacement amount on the basis of the estimated displacement delay amount;
• wherein, when the main spindle is continuously rotated without interruption after start-up thereof, the correction value calculating means calculates the correction value on the basis of the thermal displacement amount estimated by the thermal displacement amount estimating means alone;
• wherein, when the rotation of the main spindle is restarted after the interruption thereof, the correction value calculating means calculates a displacement amount by adding or subtracting the adjusting displacement amount calculated by the adjusting displacement amount calculating mean to/from the thermal displacement amount estimated by the thermal displacement amount estimating means, and calculates the correction value on the basis of the displacement amount.