Reachability Analysis for Robustness Evaluation of the Sit-To-Stand Movement for Powered Lower Limb Orthoses
Provides a method for robustness evaluation of control systems in assistive robotics, but is incremental as it applies existing techniques to a specific biomechanical model.
The paper uses sensitivity-based reachability analysis to over-approximate reachable sets for a powered lower limb orthosis under parameter uncertainties, evaluating worst-case performance of an LQR controller for sit-to-stand movement.
A sensitivity-based approach for computing over-approximations of reachable sets, in the presence of constant parameter uncertainties and a single initial state, is used to analyze a three-link planar robot modeling a Powered Lower Limb Orthosis and its user. Given the nature of the mappings relating the state and parameters of the system with the inputs, and outputs describing the trajectories of its Center of Mass, reachable sets for their respective spaces can be obtained relying on the sensitivities of the nonlinear closed-loop dynamics in the state space. These over-approximations are used to evaluate the worst-case performances of a finite time horizon linear-quadratic regulator (LQR) for controlling the ascending phase of the Sit-To-Stand movement.