Hybrid Impedance and Nonlinear Adaptive Control for a 7-DoF Upper Limb Rehabilitation Robot: Formulation and Stability Analysis

Physical rehabilitation aims to improve the condition of people with any musculoskeletal disorder. Different assistive technologies have been developed to provide support to this process. In this context, human-machine interaction has progressively improved to avoid abrupt movements and vibrations, to obtain a more natural interaction, where control strategies play a key role. In this work, a control technique based on the combination of nonlinear adaptive theory with a hybrid impedance control applied to a 7-DoF upper limb assistance robotic device is proposed. Additionally, we include the stability analysis using Lyapunov functions. Then, we validate the strategies through simulations for one rehabilitation routine test. The articular and cartesian obtained results demonstrate the effectiveness of the control to follow trajectories. The control stabilizes the trajectories in 0.9 seconds even when the initial conditions start far from the desired trajectories, without producing vibrations or overshoots, which is the desired behavior in rehabilitation applications like the one we propose.