End-Point Stiffness and Joint Viscosity Control of Musculoskeletal Robotic Arm Using Muscle Redundancy

This study focuses on replicating the muscu-loskeletal system of human arms for mimicking its movement. Muscle redundancy is critical for regulating the mechanical impedance of arms and legs. However, when implementing muscle redundancy on robots, making an ill-posed problem that cannot determine the muscle forces uniquely. In this paper, first, a method for controlling end-point stiffness in the muscle space for the joint and muscle redundant system is described. Next, the muscle model imitating the nonlinear viscosity characteristic of human muscles is introduced. Then, a method to control the joint viscosity by adjusting the internal forces of muscles adequately without affecting the stiffness control directly is proposed. Finally, numerical simulations are performed to investigate the effectiveness of the proposed method.