Application of a specialized capacitance probe in bearing diagnosis

• Published in: Wear 1999-04, Vol.225, p.1215-1221
• Main Authors: Yang, Y., Kurfess, T., Liang, S., Danyluk, S.
• Format: Article
• Language: English
• Subjects: Contact potential difference; Defects; Diagnosis; Rolling element bearings
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/S0043-1648(98)00399-8

This paper reports on the potential of a new, non-contact sensor for the detection of defects in rotating systems. Proof-of-concept experiments have been performed with measurement of two gross `defects': a missing roller of a taper roller bearing, and an electrical discharge machined (EDM) line on a single taper roller. The probe used is based on the Contact Potential Difference (CPD) method, which measures the work function of dissimilar metals without physical contact. The work function is strongly influenced by the physical and chemical conditions of the surface, so the probe can be used to detect the geometrical features of a surface if the chemical conditions are fixed. The probe was inserted into a tapered roller bearing assembly via a hole in the cup to detect the signals from bearing rollers, without contacting the rollers. Individual rollers passing by the probe produce a repeatable electrical signal, and this signal can be used to monitor the surface condition of the rollers via the signal strength and frequency. The peak-to-peak voltage (Δ V cpd) of the probe increases with increasing rotational speed of a shaft and a decrease in spacing between the probe head and roller surface. Normal, undamaged bearing rollers generate a stable, steady state CPD signal with two main spikes. The defects on the roller surface cause the magnitude of the spikes of the CPD signal to decrease.