Hybrid Offset Slider Crank Mechanism for Anthropomorphic Flexion in Prosthetic Hands

The underactuated fingers used in prosthetic hands account for a large part of design consideration in anthropomorphic prosthetic hand design. There are considerable numbers of designs available for underactuated prosthetic fingers in literature but, emulating the anthropomorphic flexion movement is still a challenge due to the complex nature of the motion. To address this challenge, a hybrid mechanism using both linkage-based mechanism and tendon-driven actuation has been proposed in this paper. The presented mechanism includes a novel offset slider-crank-based finger that has been designed using a combination of different lengths of cranks and connecting rods. The prototypes of both the new mechanism and the conventional tendon-driven mechanism are constructed and compared experimentally based on interphalangeal joint angle trajectory during flexion. The angles achieved through the new hybrid mechanism are compared with the conventional tendon-driven mechanism and the Root Mean Square Error (RMSE) values have been calculated by comparing to the anthropomorphic flexion angles of the published literature. The RMSE values calculated for three interphalangeal joints of the hybrid mechanism are found to be less than their counter-parts of the conventional tendon-driven mechanism. In addition to achieving resemblance to anthropomorphic flexion angles, the mechanism is designed within the anthropometric human finger dimensions.