The Haptic Cycling Trainer (HaCT): a robotic device for lower-limb rehabilitation

This article presents a robotic rehabilitation device comprising a cycle ergometer that can guide a user's feet through non-circular trajectories while dynamically assisting or resisting motion. The device possesses three degrees of freedom: a central motor governs crank rotation, while two additional motors independently control each crank's effective length; three rotational encoders provide position feedback. Each motor is regulated by nested position (outer), velocity, and current (inner) control loops. Controller gains for each cascade stage were optimized through simulations employing a model of the physical system. Inertial and dissipative parameters within this model were estimated via system identification, wherein a population-based search algorithm minimized the discrepancy between the model's predictions and the system's measured response. Validation of both the system model and its derived controller proceeded in two stages: first examining each degree of freedom in isolation, then considering them simultaneously. Evaluation entailed comparing the physical system's response to commanded trajectories and further assessing model fidelity by contrasting simulated predictions against experimentally observed response.