Design and Biomechanical Analysis of Supernumerary Robotic Limbs

A new type of wearable robot that provides a third and fourth arm for performing manipulative tasks with the wearer’s own arms is presented. These Supernumerary Robotic Limbs (SRL) work so closely with the human that he/she can potentially perceive them to be his/her own. The SRL consist of two independently acting robotic limbs that can function as either arms or legs to help the user position objects, lift weights, and maintain balance. These wearable robots are aimed to augment not only the strength and the precision of the human users, but also their range of skills and interactions with the environment. The guiding principles of the robotic design are safety, transparency and user comfort. Series viscoelastic actuators provide suitable joint torques while ensuring compliance and robust torque sensing. A Bowden cable transmission actuates the elbow joint, minimizing the robotic arms’ weight. A tuned elastic human-robot coupling ensures wearability and comfort. To quantify the mechanical advantage the SRL offers to the operator during use, joint torques generated in the human while performing static manipulation tasks have been reconstructed experimentally.