New design of cylindrical capacitive sensor for on-line precision control of AMB spindle

A new cylindrical capacitive sensor (CCS) design for the displacement measurement of precision active magnetic bearing (AMB) spindle is presented in this paper. This research is motivated by the problem that the existing 4-segment CCS is still sensitive to the third harmonic component of the geometric errors of a rotor. The procedure of designing a new CCS starts from the modeling and error analysis of CCS. The angular size of CCS is set up as a design parameter, and a new configuration, i.e., 8-segment CCS, is introduced to possess an arbitrary angular size. The optimum sensor geometry to minimize the effects of geometric errors is determined through the minimum norm approach. Experimental results with test rotors have confirmed the improvement in geometric error suppression.