Comparison of two control approaches for a linear axis with pneumatic muscles using one or two valves

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. Remaining uncertainties are compensated using a recursive least squares algorithm. The main difference between both approaches is the usage of either one or two proportional valves for control of the mass flow in or out of the pneumatic muscles. The control approaches have been implemented on a test-rig and show an excellent closed-loop performance.