Effects of fixture dynamics on back-stepping control of a VR spherical motor

This paper presents the effects of fixture dynamics on the control of a variable-reluctance spherical motor (VRSM). The cascaded VRSM dynamics has the appropriate structure for the so-called back-stepping controller, however, requires the computation of the exact motor dynamics at each sampling time. This computational burden has an effect on the performance of the control algorithm and imposes constraints on the hardware/ software architecture of the control system. By only computing the dominant parts of the motor dynamics, this computational burden can be reduced. We have developed a robust back-stepping controller to compensate for uncertainties account for imperfect modeling and intentional computational simplification. The performance of the robust back-stepping controller has been evaluated experimentally against a classical PD controller and a standard back-stepping controller, which serve as bases for comparison.