Design, development, and clinical validation of a two degrees of freedom compliant ankle-foot prosthesis based on a 4-4r parallel mechanism

Compared with active prostheses, passive compliant ankle prostheses offer the advantages of reduced energy consumption, a lighter weight, a simple structure, and lower costs. However, although various commercial products are available, these designs do not provide adequate degrees of freedom (DOFs) for movement. This paper presents a compliant passive ankle–foot prosthesis (CPAF) capable of 2-DOF rotation during locomotion. The CPAF uses a 2-DOF parallel mechanism to support the bodyweight and offer limited rotation during movement, and it incorporates a compliant component to facilitate and generate torque to conform to uneven terrains. The kinematics of the parallel mechanism, including the workspace and singularities, were investigated. Then, a prototype was developed, and the performance evaluations showed that sufficient torque could be generated with an appropriate range of motion for the ankle. Concequently, clinical validations were conducted: the dynamic analysis indicated that the CPAF provided good gait movement and generated sufficient ankle torque during level-ground walking, and the metabolic tests demonstrated that the configuration-4 of the compliant component could achieve the best efficiency during walking.