Adaptive Robust Cascade Force Control of 1-DOF Hydraulic Exoskeleton for Human Performance Augmentation

Hydraulic exoskeleton with human-robot interaction becomes an important solution for those heavy load carrying applications. Good human motion intent inference and accurate human trajectory tracking are two challenging issues for the control of these systems, especially for hydraulically actuated exoskeleton where the nonlinear dynamics is quite complicated and various uncertainties exist. However, robust performance to model uncertainties has been ignored in most of the existing research. To regulate these control problems, an adaptive robust cascade force control strategy is proposed for 1-DOF hydraulically actuated exoskeleton, which is namely grouped into two control levels. In the high level, the integral of human-machine interaction force is minimized to generate the desired position (which can also be seen as the human motion intent). And in the low level, the accurate motion tracking of the generated human motion intent is developed. The nonlinear high-order dynamics with unknown parameters and modeling uncertainties are built, and adaptive robust control algorithms are designed in both control levels to deal with the complicated nonlinear dynamics and the effect of parametric and modeling uncertainties. Comparative simulation and experimental results indicate that the proposed approach can achieve smaller human-machine interaction force and good robust performance to various uncertainties.