An integral sliding mode controller for the ultra-precision direct drive motor

In recent years, there has been much research in the development of ultra-precision control technology for automated machine tools to meet the increasingly stringent tolerance requirements. Minor disturbances in input torque, such as torque ripple and static friction that can normally be neglected, become apparent at micron-level scale. We propose a novel form of sliding mode control (SMC) to compensate for static friction and torque ripple in direct drive motor (DDM). A conventional SMC uses a sign function to drive the error on to the sliding surface, while our improved SMC uses the integral of the sign function to achieve the same purpose. Coupled with an exponential reaching law, this new algorithm can better suppress disturbance torque and chatter. This paper presents the derivation of our modified SMC algorithm. Simulation results demonstrate its robustness against disturbances and fitness for use in ultra-precision DDM.