Magnetic Servo Levitation (MSL) is currently being investigated as an alternative to drive fast-tool servo systems that could overcome the range limitations inherent to piezoelectric driven devices while operating over a wide bandwidth. To control such systems, a feedback-linearized controller coupled with a Kalman filter has been described. Performance limitations that degrade tracking accuracy suggest the use of a more robust controller design approach, such as sliding mode design. Current literature on sliding mode deals almost exclusively with systems that are affine on the input, while the magnetic fast-tool servo is nonlinear on it when the control action is current command. This paper discusses two sliding mode-based controllers, one that overcomes the aforementioned problem by using a modified sliding condition to calculate control action, and a second one that uses affine control command by operating in voltage mode.

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