Classical Sliding and Generalized Variable Structure Controls for a Manipulator Robot Arm with Pneumatic Artificial Muscles

Abstract

Service robotics is a domain in full effervescence because it allows a human being to interact directly with a robot while guaranteeing both safety and comfort to the human. The pneumatic artificial muscle (PAM), as an actuator, has become a solution increasingly adopted in the applications of service robotics because it provides a robot with joint compliance comparable to that of the human body. Although possessing known qualities, the PAM's nonlinearities make it one of the actuators the most difficult to model. This inconvenience limits the use of classical control as it can result in an unexpected or unwanted behavior of the system. It is thus advisable to opt for robust control algorithms to deal with these problems. Amongst robust controllers, the Classical Variable Structure (CVS) control generating a sliding mode is implemented. This control law is known by its robustness versus modeling errors, parametric uncertainties and external matched disturbances. However, the main disadvantage of this control is the appearance of high frequency oscillations once the sliding surface is reached. This phenomenon known as chattering can cause precision loss and premature actuators' wear. Results in both simulation and experiment show that these oscillations are due to the discontinuous component of the control. Numerous solutions exist for its attenuation. One is presented in this paper, the Generalized Variable Structure (GVS). The objective of this work is the synthesis and implementation of Classical and Generalized Variable Structure Control for a manipulator robot arm actuated by PAMs.