Nonlinear adaptive backstepping control of two coupled hydraulic servo cylinders

This paper presents two nonlinear model-based control designs for a hydraulic system that consists of two mechanically coupled hydraulic cylinders actuated each by a separate servo-valve. Based on a physically-oriented nonlinear mathematical model of the test rig, a further model simplification results in a completely controllable MIMO system. Two different control structures are discussed in this paper: First, a cascaded backstepping control is designed, where fast inner control loops determine the difference pressure in each hydraulic cylinder, while the position as well as the generated force is controlled in the outer loop. In the second approach, the design of the outer control loop is based on adaptive backstepping. The efficiency of the proposed control structures is demonstrated by experimental results from a dedicated test rig.