Patent ID: 7194329

Claim:
A numerical control apparatus including a position instruction generating unit that generates and outputs a plurality of position instruction values indicative of a position of a tool of a numerical control machine tool, a plurality of servo controllers each of which controls a corresponding one of a plurality of servomotors in the numerical control machine tool based on a corresponding one of the position instruction values, and a plurality of detectors each of which detects a rotational position of a corresponding one of the servomotors and feeds back a position detection value indicative of detected rotational position to a corresponding one of the servo controllers, each of the servomotors driving a corresponding one of a plurality of shafts, at least one of the shafts being a clamp shaft that can be mechanically clamped and non-clamped, the numerical control apparatus further comprising: a clamp determining unit that determines a state of the clamp shaft, the state including a clamping state in which the clamp shaft is clamped and a non-clamping state in which the clamp shaft is non-clamped, and outputs a clamp state signal indicative of the state of the clamp shaft; and a correcting unit that corrects at least one of a position instruction value and a position detection value corresponding to at least one shaft other than the clamp shaft based on the clamp state signal and a correction value so as to cancel an error in a position of the tool due to a movement of the tool performed by the clamp shaft.