New Design of Cylindrical Capacitive Sensor for On-line Precision Control of AMB Spindles

A new design of cylindrical capacitive sensor (CCS) for the displacement measurement of precision active magnetic bearing (AMB) spindle is presented in this paper. This research is motivated by the problem that existing 4-segment CCS is still sensitive to the 3rd harmonic component of the geometric errors of a rotor. The procedure of designing new CCS starts from modeling and the error analysis of CCS. The angular size of CCS is set up as a design parameter, and new 8- segment CCS is introduced to possess an arbitrary angular size. The optimum geometry of CCS to minimize the effect of geometric errors is determined through minimum norm approach. Experimental results with test rotors have confirmed the improvement in geometric error suppression. Keywords : Cylindrical capacitive sensor, Geometric error, Active magnetic bearing.