Comparison of Cascaded Backstepping Control Approaches with Hysteresis Compensation for a Linear Axis with Pneumatic Muscles

This paper presents two control approaches for a linear axis with pneumatic muscles. Its guided carriage is driven by a nonlinear drive system consisting of two pulley tackles with 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. Both proposed control schemes have a cascaded structure, where the control design is based on backstepping techniques. Hysteresis in the force characteristic of the pneumatic muscles is considered by an asymmetric shifted Prandtl-Ishlinskii model, while remaining uncertainties are compensated using an adaptive backstepping strategy. The main difference between both approaches is the usage of either the internal muscle pressures or the muscle forces as controlled variables of the inner control loops. Both control approaches have been implemented on a test-rig and show an excellent closed-loop performance.