Nonlinear Robust Control Design for a Gravity Compensation Mechanism Under Human Walking Pattern Scenarios

Abstract

Dynamics of a two degree of freedom suspension mechanism design is incorporated with a nonlinear robust controller to enable trajectory tracking under human walking pattern scenarios. To facilitate model-based control design, the system dynamic model is first extracted by applying Lagrange’s technique in non-conservative form. An inverse kinematic analysis is performed to transform a specific walking pattern trajectory in the workspace to the joint space to extract the target joint variables for control testing. An open-loop numerical simulation is also performed to demonstrate the sensitivity of the lifting force against the link inertia under dynamic conditions. Finally, the system dynamic model is incorporated with a feedback controller based on a nonlinear, sliding mode control strategy. The tracking performance of the proposed nonlinear controller is validated in closed-loop numerical simulations to demonstrate possible performance improvements under feedback control.