The atlas of 1-DoF finger prostheses and orthoses based on six-bar linkages

Robotic solutions can be adopted to develop prostheses, and substitute hands following amputation, or orthoses, and assist impaired hands. Even if the human finger can be easily considered a planar kinematic chain with a single Degree of Freedom (DoF), in both applications, different mechanisms are able to replicate its motion. This paper presents a list of 1-DoF planar mechanisms for implementing finger flexion/extension in hand prostheses and orthoses, based on 6 links and 7 revolute joints (six-bar linkages). Our proposed enumeration process starts from 495 initial combinations, which are systematically analyzed and filtered through three tests that assess their topology based on adjacency matrix representation. The tests exclude mechanisms with open loops, which are isomorphic with respect to others, and which are not compatible with the human finger kinematic structure. This filtering process led to the identification of 14 resulting mechanisms, represented in the paper in terms of graphs, kinematic sketches and implementation concepts. The overview of the enumerated mechanisms highlights several topological solutions and provides perspective designers with useful hints for addressing specific needs such as comfort and compactness.