Convergent Conditions of Feedforward Control for Musculoskeletal Systems with Multi 1-DOF Joints Driven by Monoarticular and Biarticular Muscles

Abstract

Muscles in the musculoskeletal system can only transmit forces in the tensile direction, thereby resulting in redundant actuation. This redundancy creates an internal force among the muscles. The musculoskeletal potential method uses a potential field generated by the internal force among muscles and performs a step input of the muscle tension balanced at the desired posture to achieve the point-to-point (PTP) position. This method is extremely simple and does not require any sensory feedback or complex real-time calculations, as long as the target muscle tension is achieved. However, it is known that convergence to a desired posture is strongly influenced by muscular arrangement. In a previous study, we limited our analysis to a specific structure with two joints and six muscles and explained the conditions for convergence to a desired posture. However, when the structure of the target system, number of joints, and number of muscles are different, the convergence conditions cannot be clarified using the previous method. In this study, we extend the previous method to a musculoskeletal system with multiple one degrees-of-freedom (DOF) joints driven by monoarticular and biarticular muscles. In this study, we clarify the conditions that must be satisfied by the muscular arrangement to converge to a desired posture in the musculoskeletal potential method and verify the results through simulation.