Observer-based robust adaptive force-position controller design for quadruped robots with actuator faults

This paper deals with the robust adaptive tracking control problem for an uncertain quadruped robot subject to the time-varying actuator faults. First, the desired interaction forces of the robot legs with the ground are calculated using a pseudo-inverse method. The proposed scheme includes a sliding-mode angular velocity observer, an adaptive fault estimator, and an adaptive sliding-mode force-position controller. The amplitude of the actuator faults and the upper bounds of the lumped uncertainties are adaptively estimated, and appropriate modifications are provided to the joint torque control signal. The tracking errors of the overall closed-loop system, as well as the fault estimation error, are guaranteed to converge to the neighborhood of the origin using the Lyapunov stability theorem. Finally, numerical simulations are exhibited to demonstrate the performance of the developed method.