Robotic Physical Exercise and System (ropes): a Cable-driven Robotic Rehabilitation System for Lower-extremity Motor Therapy

Assisted motor therapies play a critical role in enhancing the functional musculoskeletal recovery and neurological rehabilitation. Our focus here is to assist the performance of repetitive motor-therapy of the human lower limbs – in both the sagittal and frontal planes. Hence, in this paper, we develop a lightweight, reconfigurable hybrid (articulated-multibody and cable) based robotic rehabilitative device as a surrogate for a human physiotherapists and analyze feasibility and performance. A hybrid cable-actuated articulated multibody system is formed when multiple cables are attached from a ground-frame to various locations on the lower limbs. The combined system now features multiple holonomic cable-loop-closure constraints acting on a tree-structured multibody system. Hence the paper initially focuses on developing the Newton-Euler dynamic equilibrium equations of the cable-driven lower limbs to develop a symbolic analysis framework. The desired motion for the proposed rehabilitative exercise are prescribed based upon normative subjects motion patterns. Trajectory-tracking within this system is realized by a position-based impedance controller in task-space and a feedback-linearized PD controllers in joint-space. Careful coordination of the multiple cable-motors are now necessary in order to achieve the co-robotic control of the overall system, avoiding development of internal stresses and ensuring continued satisfaction of the unilateral cable-tension constraints throughout the workspace. This is now evaluated via a simulation case-study and development of a physical testbed is underway.