Thermal displacement correction apparatus for machine tool

A controller for a machine tool, the controller comprising:

• a thermal displacement correction unit that estimates a thermal displacement amount from an operation of a machine of the machine tool or a temperature of each portion of the machine and calculates a thermal displacement correction amount for correcting thermal displacement by adding, to a position command value of a feed axis of the machine tool, the thermal displacement correction amount for cancelling the thermal displacement amount thus estimated;
• a thermal displacement correction amount adjustment unit that acquires information of an actual position in the machine by a measurement unit and adjusts the thermal displacement correction amount with an adjustment value;
• a machine-dependent coefficient calculation unit that calculates a machine-dependent coefficient depending on specifications of the machine for calculating the adjustment value on the basis of
• the thermal displacement correction amount that has been calculated in driving the machine,
• the actual position in the machine that is measured by the measurement unit, and
• an approximate expression representing a relation between the thermal displacement correction amount and the adjustment value;
• a machining condition-dependent coefficient calculation unit that calculates a machining condition-dependent coefficient, which is a numerical value specified depending on a machining program, for calculating the adjustment value on the basis of
• the thermal displacement correction amount that has been calculated in machining a workpiece on the basis of the machining program,
• the actual position in the machine that is acquired by measurement by the measurement unit, and
• the approximate expression representing the relation between the thermal displacement correction amount and the adjustment value;
• and
• a calculation unit that calculates the adjustment value corresponding to the estimated thermal displacement amount, from the approximate expression that contains the calculated machine-dependent coefficient and the calculated machining condition-dependent coefficient, wherein
• the thermal displacement correction amount adjustment unit corrects the thermal displacement correction amount with the calculated adjustment value, and
• the controller is configured to
• add the corrected thermal displacement correction amount is added to the position command value so as to obtain a corrected position command value, and
• control the feed axis of the machine tool using the corrected position command value.