Sliding-mode control of a nonlinear-input system: Application to a magnetically levitated fast-tool servo

Magnetic servo levitation (MSL) is currently being investigated as an alter native to drive fast-tool servo systems that could overcome the range limit ations inherent to piezoelectric driven devices while operating over a wide bandwidth. To control such systems, a feedback-linearized controller coupl ed with a Kalman filter has been previously described. Performance limitati ons that degrade tracking accuracy suggest the use of a more robust control ler design approach, such as sliding-mode control. Current literature on sl iding mode deals almost exclusively with systems that are affine on the inp ut, while the magnetic fast-tool servo is nonlinear on it when the control action is current command. This paper discusses a sliding-mode-based contro ller that overcomes the aforementioned problem by defining a modified slidi ng condition to calculate control action. Experimental results demonstrate the feasibility of achieving long-range fast tracking with magnetically Lev itated devices by using sliding-mode control.