Performance Maps for a Bio-Inspired Robotic Condylar Hinge Joint

This paper presents performance charts that map the design space of a bio-inspired robotic condylar hinge joint. The joint mimics the design of the human knee joint by copying the condylar surfaces of the femur and tibia and by copying the four-bar motion of the cruciate ligaments. Four aspects of performance are modeled: peak mechanical advantage, RMS (root mean square) mechanical advantage, RMS sliding ratio, and range of movement. The performance of the joint is dependent on the shape of the condylar surfaces and the geometry of the four-bar mechanism. The design space for the condylar hinge joint is large because the four-bar mechanism has a very large number of possible configurations. Also, it is not intuitive what values of design parameters give the best design. Performance graphs are presented that cover over 12,000 different geometries of the four-bar mechanism. The maps are presented on three-dimensional graphs that help designers visualize the limits of performance of the joint and visualize tradeoffs between individual aspects of performance. The maps show that each aspect of performance of the joint is very sensitive to the geometry of the four-bar mechanism. The trends in performance can be understood by analyzing the kinematics of the four-bar mechanism and the shape of the condylar surfaces.