Adaptive Sliding Mode Control for Parallel Manipulator Hexapod

This paper presents an Adaptive Sliding Mode Control (ASMC) scheme to control the non-compliant motion for the parallel manipulator Hexapod. The Hexapod is comprised of two rigid platforms and six rotary actuators driven by servo motors. The ASMC is composed of the conventional sliding mode controllers and the proportional-derivative (PD) controllers as the compensation gain to overcome the chattering phenomenon generated by sliding surface torques. The PD controllers are adjusted by an adaptation law which is driven by the position error and velocity tracking error. The derivation of the adaptation law is based on the concept of Model Reference Adaptive Control (MRAC) and Lyapunov criteria. Experiments and simulations are conducted to evaluate the performance of the control scheme implemented to control the Hexapod to track sinusoid paths under the changes in payload and disturbance. The results show that the proposed adaptive control scheme provides superior tracking capability as compared to conventional sliding mode control.