A biomimetic similarity index for prosthetic hands

Extreme upper limb prosthesis is a well researched problem. There are a number of research prototypes and a few sophisticated commercially launched variants. For a wider acceptance among amputees, prosthetic hands need to be anthropomorphic i.e. replicate the human hand in form and function. However, it is often difficult to compare and rank prosthetic hands on the extent of their being anthropomorphic. The focus of this paper is to evolve a framework for quantification of anthropomorphism for prosthetic hands. Using Formal Concept analysis, a formal context of anthropomorphism is constructed. Within such a context, an index expressing similarity between the prosthetic and the human hand is derived. Following on the lines of the functional similarity metric for design-by-analogy put forward by McAdams and Wood, a formalism to compare different prosthetic hands to a human hand based on a function-vector for each prosthesis expressed in terms of a set of functional and geometric characteristics is presented. Function-vector is characterized within a formal context of anthropomorphism. The Biomimetic Similarity Index (BSI) so computed reflects extent of anthropomorphism and allows a quantitative comparison of different prosthetic hands. Biomimetic design leads to higher anthropomorphism and should result in a higher BSI. We explore the case of TU Bionic Hand and compare the BSI for five different prosthetic hands.