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Virtual torque control combining with modal decoupling research for hydraulic-driven lower limb exoskeleton robot.

Jinsong Zhao1, Huidong Hou2, Xianwei Niu2

  • 1School of Mechanical Engineering, Yanshan University, Qinhuangdao, 066004, China; Hebei Provincial Key Laboratory of Heavy Machinery Fluid Power Transmission and Control, Yanshan University, Qinhuangdao, 066004, China; Key Laboratory of Advanced Forging & Stamping Technology and Science (Yanshan University), Ministry of Education of China, Qinhuangdao, 066004, China; State Key Laboratory of Crane Technology, Yanshan University, Qinhuangdao, 066004, China.

ISA Transactions
|February 17, 2025
PubMed
Summary

This study introduces a virtual torque control (VTC) strategy using modal decoupling to improve the performance of hydraulic-driven lower limb exoskeleton robots (HDLLERs). The method enhances precise torque tracking by addressing joint coupling disturbances and human-robot interactions.

Keywords:
H(∞) optimizationHuman–robot interaction forceHydraulic-driven lower limb exoskeleton robotModal decouplingVirtual torque control

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Area of Science:

  • Robotics
  • Biomechanics
  • Control Systems

Background:

  • Hydraulic-driven lower limb exoskeleton robots (HDLLERs) offer walking assistance.
  • Complex joint torque coupling in HDLLERs hinders precise torque tracking.
  • Human-robot interactions introduce further control challenges.

Purpose of the Study:

  • To propose a virtual torque control (VTC) strategy for HDLLERs.
  • To address joint coupling disturbances and human-robot interaction effects.
  • To enhance the precision and robustness of HDLLER control.

Main Methods:

  • Established a human-robot coupled dynamic model for the HDLLER.
  • Applied modal space decoupling based on vibration theory to diagonalize system matrices.
  • Implemented a VTC strategy to compensate for disturbances and residual terms.
  • Utilized H∞ theory to optimize VTC for robustness against model uncertainties.

Main Results:

  • Modal decoupling successfully created independent control channels.
  • The VTC strategy effectively compensated for human motion and model uncertainties.
  • H∞ optimization improved the control strategy's robustness and reduced model dependence.
  • Experimental comparisons validated the enhanced performance of the proposed method.

Conclusions:

  • The proposed VTC strategy based on modal decoupling significantly improves HDLLER performance.
  • The H∞-optimized VTC enhances robustness against parameter variations and model inaccuracies.
  • This approach offers a promising solution for precise and reliable exoskeleton control.