A Hybrid Powering Mechanism for a Transtibial Robotic Prosthesis

This paper proposes a hybrid powering mechanism for a unilateral transtibial robotic prosthesis named TRoPHy. The device includes both active and passive actuation methods for plantar flexion/ dorsiflexion while inversion/eversion is achieved passively. The proposed mechanism uses separate spring systems to vary the ankle stiffness and capture the biomechanical energy for the purpose of controlling plantar flexion and dorsiflexion phases of gait cycle. Here, energy stored during the controlled dorsiflexion phase is released and used for propulsion in the powered plantar flexion phase. The testing of the prosthesis was carried out on an able-bodied person, by using a test-rig to affix the prosthesis in parallel to the shank for mimicking the kinematics of the leg. The resulting ankle kinematic data of the prosthesis provided a 97.3% correlation with the natural human ankle kinematics, implying the viability of applying this mechanism to reproduce the ankle behavior accurately. An analysis of the power balance of the system reveals that 38% of the total power required for the powered plantar flexion phase can be reduced effectively from the proposed energy harvesting mechanism.