Fractional impedance control for reproducing the material properties of muscle and its application in a body weight support system

We here report a novel impedance control method based on a fractional calculation inspired by the viscoelastic properties of biomaterials such as muscle. This fractional impedance controller was found to realize superior impact absorption for the purpose of flexible contact for assistive and rehabilitation robots for people. This paper presents an evaluation of this concept using simulations and experiments. The numerical analysis results demonstrated that a fractional impedance controller has superior impact absorption performance than a conventional controller for contact with elastic objects, especially for high-stiffness objects and high-velocity movement. Moreover, experiments using a robotic system for body weight support demonstrate the effectiveness of the fractional controller for suppressing a large contact force between subject and robot.