Nonlinear model predictive control of a high-speed linear axis driven by pneumatic muscles

This paper presents a nonlinear predictive 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. For the control of the carriage position and the mean pressure a nonlinear model predictive trajectory control is designed. The main idea of the used method consists in a minimization of the tracking error at the end of the prediction horizon. That way the computation load can be kept relatively small. Remaining model uncertainties as well as nonlinear friction can be counteracted by an observer-based disturbance compensation. Experimental results from an implementation on a test rig show a high control performance.