Backstepping Control of a High-Speed Linear Axis Driven by Pneumatic Muscles

This paper presents a backstepping control scheme for a new linear axis. Its guided carriage is driven by a nonlinear mechanism consisting of a rocker with a pair of pneumatic muscle actuators arranged at both sides. This innovative drive concept allows for an increased workspace as well as higher carriage velocities as compared to a direct actuation. Modelling leads to a system of nonlinear differential equations including polynomial approximations of the volume characteristic as well as the force characteristic of the pneumatic muscles. The proposed control has a cascade structure: The internal pressure of each pneumatic muscle is controlled by a fast underlying control loop, whereas in an outer control loop the carriage position and the mean internal pressure of the muscles are controlled. Remaining model uncertainties as well as nonlinear friction can be counteracted either by an observer-based disturbance compensation or an adaptive control strategy. Experimental results from an implementation on a test rig show a high control performance. Copyright c ©2008 IFAC