Bearing diagnostic device for machine tool

A bearing diagnostic device for sensing a failure in a bearing of a rotation shaft device in a machine tool, the bearing pivotally supporting a rotation shaft to be rotatably driven in the rotation shaft device, the bearing diagnostic device comprising:

• a rotation counting unit configured to measure a count of rotations of the rotation shaft at a specific rotation speed;
• a temperature measuring unit configured to measure a temperature of the rotation shaft device;
• a frictional torque calculating unit configured to calculate a frictional torque of the rotation shaft device;
• a rolling speed calculating unit configured to calculate a rolling speed of the bearing from the count of rotations;
• a bearing characteristic calculating unit configured to calculate a bearing characteristic from the frictional torque and the rolling speed;
• a storage unit storing a reference bearing characteristic;
• and
• a determination unit configured to compare the bearing characteristic calculated by the bearing characteristic calculating unit with the reference bearing characteristic stored in the storage unit to determine a presence of a failure.