Detecting rolling element bearing defects with the optical incremental motion encoder

This paper described the experimental use of a new type of optical sensor to detect rolling element bearing defects for the purpose of condition monitoring. The incremental motion encoder (IME) is a patented development of the industrially proven technology of the optical shaft encoder. It combines the measurement of angular position with that of 2D shaft center position to submicron accuracy. The operational principle of the IME is explained. Its high resolution measurements allow shaft motion directly related to the condition of the supporting bearing to be sensed. This presents potential advantages over current bearing condition monitoring sensors which monitor transmitted vibration in the machine structure. A model explaining the effect of a bearing condition monitoring sensors which monitor transmitted vibration in the machine structure. A model explaining the effect of a bearing inner race defect on the IME signal is presented. Based on this model the statistical parameter kurtosis is proposed as a method of detecting such defects from the IME signal. The results of experiments comparing the IME signal from a new undamaged roller bearing with the signal from the same bearing with an induced defect are presented. These confirm the application of the model to defect detection.