Long-Stroke Hydraulic Robot Motion Control With Incremental Nonlinear Dynamic Inversion

High precision motion control of hydraulic manipulators is challenging due to the highly nonlinear dynamics and model uncertainties typical for hydraulic actuators. This paper addresses the implementation of a novel sensor-based incremental nonlinear dynamic inversion control technique for a high-precision hydraulic force controller in existence of parameter uncertainties. Combined with a widely used force computation outer-loop controller, the proposed motion control structure is implemented on a 6-DOF hexapod hydraulic robot, the Simulation, Motion and Navigation (SIMONA) Research Simulator, TU Delft. The proposed control technique is inherently robust to hydraulic parameter uncertainties. As an important contribution, the robustness against parameter uncertainty is rigorously proven. Stability of the proposed controller is also analyzed. Techniques for solving characteristic implementation issues, such as higher-order valve dynamics and oil transmission effects, are discussed in detail. Motion tracking experiment results on the SIMONA simulator validate the effectiveness of the proposed method in terms of performance and the robustness against parameter uncertainties. Significant control accuracy improvement is demonstrated by comparing with the state-of-the-art motion control implementations.