Abnormality determination method and abnormality determination device for feed shaft clamp mechanism of machine tool

An abnormality determination device for a feed shaft clamp mechanism of a machine tool comprising a feed shaft drive device for driving a feed axis, a displacement measurement device for the feed axis, and a feed shaft clamp mechanism for maintaining a stopped state of driving of the feed axis, the device comprising:

• a shaft displacement/drive force correlation derivation device for exerting a plurality of different test drive forces set in advance on the feed axis by means of the feed shaft drive device in a state in which a stopped state of movement of the feed axis is maintained by the feed shaft clamp mechanism, and deriving, from feed shaft displacements measured by the displacement measurement device and the corresponding test drive forces, a correlation between the feed shaft displacements and drive force,
• an expected displacement prediction device for setting a judgment drive force different from the test drive forces from the correlation derived by the shaft displacement/drive force correlation derivation device, and predicting an expected displacement of the feed axis when the judgment drive force is exerted based on the correlation,
• a displacement tolerance calculation device for calculating a displacement tolerance which provides a predetermined allowable fluctuation range for the expected displacement predicted by the expected displacement prediction device, and
• a judgment device for judging that the feed shaft clamp mechanism is abnormal when the actual feed shaft displacement measured by the displacement measurement device in a state in which the judgment drive force is actually exerted on the feed shaft deviates from the displacement tolerance calculated by the displacement tolerance calculation device.