Abnormality diagnosis device for machine tool, and abnormality diagnosis method

An abnormality diagnosis device for a machine tool in which a tool for machining a work piece is attached to a spindle, the spindle is supported by a bearing, and the bearing is supported by a ram, and the ram is supported by a saddle, comprising:

• a displacement sensor configured to detect an amount of displacement of the bearing;
• an acceleration sensor configured to detect an acceleration of the ram;
• a first data processor configured to determine whether the ram or the spindle collides with the work piece on the basis of at least the amount of displacement of the bearing detected by the displacement sensor or the acceleration of the ram detected by the acceleration sensor;
• and
• a second data processor configured to determine a degree of damage to the bearing on the basis of a base frequency, a high-harmonic frequency and peak values of the base frequency and the high-harmonic frequency of a vibration of the ram due to a rotation of the spindle obtained from the acceleration of the ram when the first data processor determines that the ram or the spindle collides with the work piece;
• and
• a third data processor configured to estimate an amount of displacement of a tip of the ram,
• wherein the second data processor determines that the ram and the saddle are damaged when the amount of displacement of the tip of the ram estimated by the third data processor exceeds an assumed maximum amount of displacement of the tip under the condition that the ram and the saddle are not damaged, and
• wherein the assumed maximum amount of displacement is predetermined such that it decreases as an protrusion amount of the ram from the saddle increases.