Radial motion measurement of a high-revolution spindle motor

In industrial fields, the non-repeatable run out (NRRO) of the high-revolution spindle of a high-density recording system is often estimated. In contrast, repeatable run out (RRO) is usually not estimated. A three-point method based on correction is useful when radial motion includes RRO. However, experiments conducted at high revolution (over 2000 rpm) have not yet been reported. In the present report, a three-point method based on inverse filtering to obtain the radial motion is discussed and the optimal sensor setting angle is calculated based on the transfer function. Furthermore, the proposed method is applied to the radial motion measurement of a spindle for hard disk inspection in the high-revolution range of 4000–10,000 rpm. As a result, the main reason for the radial motion was concluded to be related to the inner or outer ring of the bearing.