Adaptive discrete sliding mode control of a pneumatic artificial muscles robot

Abstract

Pneumatic artificial muscles are very powerful pneumatic actuators that work very similarly to the human muscle. They are broadly used in the development of robotic manipulators for industry or in the medical domain mainly for their low cost, intrinsic safety and high compliance. However, devices driven by these actuators are characterized by complex nonlinear dynamics and time varying properties which impose a very challenging control issue. This can be handled using sliding mode control. Well known for its robustness and invariance, this control technique is very suitable for this type of systems. The only drawback is chattering produced by high frequency commutation due to discontinuity and overestimation of the controller gains. In this paper, we present an adaptive discrete sliding mode controller based on reaching law. Gains of the proposed controller are dynamically adjusted to the sliding motion to reduce chattering and ensure convergence in finite time with good precision. A comparison with a fixed gain discrete sliding mode controller is presented for position regulation and trajectory tracking of a robotic manipulator driven by pneumatic artificial muscles.