Abnormality diagnostic method and abnormality diagnostic device for feed axis

An abnormality diagnostic device for diagnosing an abnormality of a feed axis in a machine having the feed axis, the feed axis moving a moving body via a ball screw that is rotated by a servomotor, the device comprising:

• a servo information obtaining unit that causes the feed axis to perform an axis operation in a predetermined diagnosis condition to obtain servo information according to a control of the servomotor;
• a frequency analyzing unit that performs a frequency analysis on the obtained servo information;
• a damage frequency obtaining unit that obtains a damage frequency generated while the feed axis whose bearing is damaged performs the axis operation, from a result of the frequency analysis;
• and
• a determining unit that compares the obtained damage frequency with a predetermined threshold to determine a presence/absence of an abnormality, wherein
• in the determining unit, before the damage frequency is compared with the threshold, a determination whether a vibration frequency of the bearing interferes with a vibration frequency generated while a rolling element passes through a nut of the ball screw or not is performed, and the comparison is performed by setting the respective thresholds that are different in a case of the interference and a case of no interference.