ヒステリシス減衰を考慮した複素剛性ヒューマンインピーダンスモデルとカスタマイズ可能な外骨格制御
A Complex Stiffness Human Impedance Model with Customizable Exoskeleton Control
人間の関節剛性にヒステリシス減衰項を加えた複素剛性モデルを提案し、それを活用した分数階制御で外骨格の力増幅帯域と安定性を両立させる手法を示した。
著者: Binghan He, Huang Huang, Gray C. Thomas, Luis Sentis
分類: cs.RO, cs.SY, eess.SY
原文アブストラクト
The natural impedance, or dynamic relationship between force and motion, of a human operator can determine the stability of exoskeletons that use interaction-torque feedback to amplify human strength. While human impedance is typically modelled as a linear system, our experiments on a single-joint exoskeleton testbed involving 10 human subjects show evidence of nonlinear behavior: a low-frequency asymptotic phase for the dynamic stiffness of the human that is different than the expected zero, and an unexpectedly consistent damping ratio as the stiffness and inertia vary. To explain these observations, this paper considers a new frequency-domain model of the human joint dynamics featuring complex value stiffness comprising a real stiffness term and a hysteretic damping term. Using a statistical F-test we show that the hysteretic damping term is not only significant but is even more significant than the linear damping term. Further analysis reveals a linear trend linking hysteretic damping and the real part of the stiffness, which allows us to simplify the complex stiffness model down to a 1-parameter system. Then, we introduce and demonstrate a customizable fractional-order controller that exploits this hysteretic damping behavior to improve strength amplification bandwidth while maintaining stability, and explore a tuning approach which ensures that this stability property is robust to muscle co-contraction for each individual.
