Variable end-point viscoelasticity control for a musculoskeletal redundant arm

This paper presents a novel approach for controlling variable end-point viscoelasticity in musculoskeletal robots to reduce contact forces during contact tasks. This is achieved by adjusting the desired end-point viscoelasticity in response to environmental contact, and by controlling the end-point viscoelasticity in muscle space. The musculoskeletal system of living bodies can adapt to the mechanical impedance of joints via the nonlinear properties of muscles, which are a significant factor in enhancing flexibility and safety during contact tasks. To take advantage of the characteristics of the musculoskeletal structure, we introduce nonlinear viscous properties into muscles and control the end-point viscosity by modulating the internal force. Numerical simulations are conducted to evaluate the proposed method, which demonstrates that the method successfully reduces contact forces during the crank-turning task while maintaining tracking performance. Overall, the proposed approach promises to achieve safer and more flexible interactions between robots and their environment.