A Bio-Inspired Condylar Hinge for Robotic Limbs

This paper presents a novel condylar hinge for robotic limbs which was inspired by the human knee joint. The ligaments in the human knee joint can be modeled as an inverted parallelogram four-bar mechanism. The knee joint also has a condylar cam mechanism between the femur and tibia bones. The bio-inspired joint mimics the four-bar mechanism and the cam mechanism of the human knee joint. The bio-inspired design has the same desirable features of a human knee joint including compactness, high mechanical advantage, high strength, high stiffness and locking in the upright position. These characteristics are important for robotic limbs where there are often tight space and mass limitations. A prototype hinge joint similar in size to the human knee joint has been designed and tested. Experimental tests have shown that the new condylar hinge joint has superior performance to a pin-jointed hinge in terms of mechanical advantage and stiffness. The prototype hinge has a mechanical advantage that is greater than a pin-jointed hinge by up to 35% which leads to a corresponding reduction in the peak force of the actuator of up to 35% for a squatting movement. The paper also presents a five-step design procedure to produce a combined inverted parallelogram mechanism with a cam mechanism.