Kinetostatic Design of Ankle Rehabilitation Mechanism Capable of Adapting to Changes in Joint Axis

This paper proposes a simple spatial rehabilitation mechanism that aims to exert the desired flexion motion with adjustable load and also to provide an objective measure of recovery status, in terms of mobilization, force, and torque, on the affected part. This is to verify the condition of therapeutic exercise to support physiotherapists, as well as to establish selfrehabilitation by patients themselves. In this work, the composition of the mechanism is first determined by extending Oldham’s coupling mechanism. Next, a kinetostatic analysis of the mechanism is performed for two purposes. One is to determine a reasonable link dimension that achieves a suitable range of motion for the practical rehabilitation treatment of human ankle joints. The other is to calculate the magnitude of the shearing load on the ankle joint, caused by gravity and the friction of the cylindrical joints. A validation experiment demonstrates the effectiveness of the proposed mechanism and of the kinetostatic analysis. Shearing load is also compensated for through the introduction of springs to certain joints. The optimum location, spring constant, and initial offset of each spring are determined through the proposed kinetostatic analysis scheme.