Topology Optimization of General-Joint Planar Linkage Mechanisms with an Application to Finger Rehabilitation Device Design

Abstract

Although topology optimization methods can inspire designers, their use for the design of linkage mechanisms is not yet fully developed. However, there are a number of new mechanism design problems, as in robots or robotic rehabilitation devices. One of the critical limitations of earlier linkage mechanism synthesis methods by gradient-based topology optimization is that mechanisms only with one type of joint, a revolute joint, can be synthesized. The handling of revolute joints alone limits the capability of topology optimization considerably, and some mechanisms involving prismatic joints cannot therefore be synthesized. Here, we aim to develop a topology optimization method that can synthesize mechanisms with general joints including revolute and prismatic joints. The specific application in mind is the topology-optimization-based design of several robotic rehabilitation mechanisms. To this end, we propose a new ground model termed the joint element connected rigid-block model (JBM). The key idea of the proposed JBM is that the existence of prismatic joints and revolute joints are directly controlled by design variables. After testing the validity of the developed formulation with the JBM, we applied it to the design of a robotic finger rehabilitation device. An interesting design, not available in the existing literature, was synthesized, and the result may inspire designers in the field. It is expected that this method can be more useful as an inspirational design tool for the robotic industry in the future.