Design and control of Supernumerary Robotic Limbs for balance augmentation

This paper presents a novel approach to balance assistance and joint load reduction for human bipedal walking. We introduce a new type of wearable robot, called Supernumerary Robotic Limbs (SRL), that provides two additional legs for augmenting stability and reducing the loads on human leg joints. Unlike exoskeletons, the SRL is kinematically independent of the human skeletal structure, and can therefore take an arbitrary posture to provide optimal assistance in coordination with human motions. Furthermore, unlike crutches, canes, and other balance assistance equipment, the SRL can provide balancing support autonomously and thereby free the human arms from holding those tools. First, the new design concept and balance assistance strategy are described, followed by kinematic and static modeling. Two gate patterns of the combined human and SRL are discussed. Optimal gate synthesis that maximizes the area of support polygon is discussed. Finally, the gate control strategies are implemented on a prototype SRL, using body motion sensors to enable real-time, seamless coordination between the user and the robot.