Reflex-based Motion Strategy of Musculoskeletal Humanoids under Environmental Contact Using Muscle Relaxation Control
Kento Kawaharazuka, Kei Tsuzuki, Moritaka Onitsuka, Yuya Koga, Yusuke Omura, Yuki Asano, Kei Okada, Koji Kawasaki, Masayuki Inaba
TL;DR
This work introduces Muscle Relaxation Control (MRC), a reflex-based method that minimizes unnecessary internal muscle tension in a musculoskeletal humanoid by exploiting environmental contact while preserving posture. MRC computes a necessary muscle tension vector $\mathbf{T}_{necessary}$ via a quadratic program and updates target muscle lengths with a bounded relaxation $\Delta \mathbf{l}$, enabling continuous movement and resting against the environment. Experiments on the Musashi humanoid show that MRC reduces internal muscle tension and temperature across basic movements, heavy object grasping, desk-supported resting, and handle operation, albeit with limitations when variable stiffness or impedance control is required. The work suggests future integration with learning controls and potential application to other soft, tendon-driven, or pneumatic systems for enhanced human-like reflexive motion.
Abstract
The musculoskeletal humanoid can move well under environmental contact thanks to its body softness. However, there are few studies that actively make use of the environment to rest its flexible musculoskeletal body. Also, its complex musculoskeletal structure is difficult to modelize and high internal muscle tension sometimes occurs. To solve these problems, we develop a muscle relaxation control which can minimize the muscle tension by actively using the environment and inhibit useless internal muscle tension. We apply this control to some basic movements, the motion of resting the arms on the desk, and handle operation, and verify its effectiveness.