Patent ID: 7503691

Claim:
A machine tool having at least one motor to be driven for machining, comprising: a temperature detector for detecting temperature of the motor; current detecting means for detecting a current value of the motor; motor temperature estimating means for estimating the temperature of the motor based on the current value of the motor detected by said current detecting means; and abnormality detecting means for detecting an abnormality of an ambient temperature change or an abnormality of said temperature detector, based on a comparison between the detected temperature of the motor by said temperature detector and the estimated temperature of the motor by said motor temperature estimating means and determining whether a difference therebetween is equal to, or less than, a first threshold, wherein the machine tool has two motors to be driven for machining, each of the two motors is provided with a respective said temperature detector, said current detecting means and said motor temperature estimating means, and said abnormality detecting means obtains a difference between the detected temperature and the estimated temperature of each of the two motors, and determines an abnormality of the ambient temperature change when both of the obtained differences exceed the first threshold value, and an abnormality of the temperature detector when only one of the obtained differences exceeds the first threshold value.