Cascaded NMPC for the Precise Position Control of a Pneumatic Actuator

This paper presents the design and a comparison of two cascaded control schemes based on nonlinear model predictive controllers (NMPC) for the position control of a pneumatic actuator. Both control schemes consist of a NMPC for the pneumatic subsystem while the outer mechanical subsystem is in one case controlled by a NMPC as well, and in the other case by a state-feedback controller (LQR). To cope with the high impact of nonlinear friction, a feedforward friction compensation is employed, and the mechanical subsystem is extended by an integrator. The control approaches are implemented on a test rig consisting of a double-acting pneumatic cylinder actuated by a single 5/3-proportional valve using the GRAMPC-toolbox. Based on experimental results on the test rig it can be shown that both controllers achieve a precise position tracking for different desired trajectories.