Patent ID: 7175374

Claim:
A machine tool in which a tool holder attached with a tool is mounted on a main spindle and which performs rotational driving of the main spindle to machine a work, the machine tool comprising: a controller for controlling a machining center which automatically selects various tools according to machining steps to be performed and mounts the tools on the main spindle; a noncontact measuring device having an eddy current sensor which measures a displacement of a peripheral surface of a flange of the tool holder mounted on the main spindle in a radial direction; a judging device which judges an abnormality of the machine tool from measurement data obtained by the noncontact measuring device; an index value calculating device which calculates an index value indicating a statistical variation of a plurality of pieces of measurement data obtained by performing a measurement of the displacement of the peripheral surface of the flange of the tool holder by the noncontact measuring device a plurality of times and by deleting the measurement data of which a value is extremely different from those of the other measurement data; and a determining device which determines an abnormality in the machining center from the index value obtained by the index value calculating device and outputs the determination to said controller.