On the Kinematic Synthesis of a Hand Rehabilitation System: A Case Study to Implement Spasticity Effect on Low-Velocity Physical Therapy

Vollständiger Abstract

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Abstract This work presents a kinematic synthesis methodology that is developed to implement a simple linear stiffness element into an existing single degree of freedom hand rehabilitation system without altering its mobility in order to render the system mechanically capable of replicating spasticity behaviour during low-velocity rehabilitation treatments. Due to velocity dependent nature of the spasticity, replicating its effects during these treatments conducted below certain velocity thresholds, where sudden increases in patient muscle tone are avoided, becomes a critical design constraint of the study. This allows utilization of simple linear stiffness element on the system to replicate increasing force disturbance observed during hand opening motion in physical therapies. Throughout the study spasticity behaviour is replicated as a linearly increasing flexion promoting force perpendicular to the fingers as the hand extension angle increases. In order to achieve this mechanically via simple stiffness element, a new trajectory is created by considering desired force limits and the actual end effector trajectory of the rehabilitation system. In light of this a new mechanism that is actuated by the end effector of the system is synthesized to follow constructed trajectory with minimal error. Having two distinct tip trajectories on the system with linearly increasing distances during hand extension, desired force disturbances as spasticity behaviour was achieved via attached spring with suitable stiffness constant. Once the prototype of the system was constructed, results were verified by using motion capture cameras through the operation of the system.