The MantisBot: Design and impedance control of supernumerary robotic limbs for near-ground work

A novel wearable robotic device is developed to support the wearer when performing bi-manual tasks near the ground. The device is worn around the upper torso and has two Supernumerary Robotic Limbs (SRLs) that reach the ground when the wearer assumes a crawling-like position, such that neither of the wearer's natural arms are needed to support the body. Rather, both human hands can be engaged in executing a required task. Coordinating actuators at both robotic limbs, the wearer's body is supported stably with a desired impedance. As the wearer moves away from an equilibrium position, restoring forces designated by the impedance act on the wearer. First, the design concept of the SRLs for near-ground work is described, followed by a derivation of the control laws used to produce virtual impedance. A proof-of-concept prototype is then presented along with experimental verification of the derived control laws.