Nonlinear control of a pneumatic muscle actuator: backstepping vs. sliding-mode

This paper weighs up the pros and cons of three different tracking controllers for a pneumatic muscle actuator: robust backstepping, adaptive backstepping and sliding-mode. Robustness is assured for three controllers in the presence of model uncertainties and external perturbations. Ultimate boundedness is proved for the robust and adaptive backstepping tracking controller. Exponential stability is proved for the sliding-mode tracking controller. The tracking is well achieved by the sliding-mode and the adaptive controller. On the contrary, the robust backstepping shows a noticeable tracking error. The sliding-mode leads to a high-frequency switching control law.