Bearing wear model for optical disk drive stepper motor

Failure analysis of field failed stepper motors of optical disk drive (ODD) reveal that the failure mechanism and failure site of the stepper motor is wear of the plastic bearing cup that supports the stepper motor worm shaft. In an ODD this worm shaft moves the sled carrying the optical head, thus generating both axial and lateral loads as well as circumferential sliding friction forces on the bearing cup. The wear rate is dependent on the total load on the bearing. Archard´s wear model, a well known model for fretting wear, has been employed in this study to simultaneously predict the instantaneous wear rate, cumulative worn out volume and wear out depth throughout the life of bearing. An incremental format of Archard´s model has been developed because the contact area and contact forces are continuously varying in the bearing cup. Tests were designed and implemented to study the wear rate of the bearing cups. The test results are used to identify the wear model constant of the bearing. The wear model can be used to estimate the life of the stepper motor inside optical disk drives (ODDs) for reliable performance under a given life cycle history, and also to facilitate redesign for improved reliability.