Adaptive Sliding Mode Fault-Tolerant Control of the Uncertain Stewart Platform Based on Offline Multibody Dynamics

In this paper, we propose a novel adaptive sliding mode fault-tolerant control scheme based on offline multibody dynamics for the uncertain Stewart platform under loss of actuator effectiveness. The asymptotic stability is analyzed by Lyapunov method in the presence of friction, unmodeled dynamics, environmental disturbances, and even the unpredictable actuator faults. To cope with the nonlinear coupling and various properties of freedom directions, the offline nominal multibody dynamics are employed to design the initial upper bound of uncertainties and to realize the dynamic compensation, which achieves high online computational efficiency and significantly improves the characteristics of the six degree-of-freedom (DOF) directions. We also introduce a novel adaptive updating law to adjust the control torque based on the real-time position tracking errors, which alleviates the chattering phenomenon of the sliding mode controller. Finally, the fault-free and faulty conditions are analyzed to corroborate the advantages of the proposed control scheme in comparison with the nominal sliding mode control scheme.