A Switched Systems Approach for Closed-loop Control of a Lower-Limb Cable-Driven Exoskeleton

Chen Hao Chang, Jonathan Casas, Victor H. Duenas

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Cable-driven exoskeletons are light-weight devices that can provide joint torques to assist or augment human function during locomotion. However, cable mechanisms actuating joints can experience a slacking behavior, slow response, and counteracting forces, if the electric motors are not accurately controlled. To prevent undesired joint motion, feedforward control strategies have been developed to provide cable tension and release. In this paper, the control design of a pair of electric motors is segregated into a joint-level control loop and a low-level loop to adjust cable tensions and apply torque about the knee joint. A robust sliding-mode controller is designed to track the desired knee joint kinematic trajectory, which is assigned to the lead motor to achieve leg flexion or extension. Concurrently, the low-level control objective is designed to adjust the tension of the other motor, called the follower motor, in proportion to the angular position of the lead motor. To achieve leg extension and flexion, the electric motors switch their roles between lead and follower motor. A Lyapunov-based stability analysis is developed to ensure exponential tracking for both control objectives. Moreover, an average dwell time analysis computes an upper bound on the number of motor switches to preserve exponential tracking.

Original languageEnglish (US)
Title of host publication2022 American Control Conference, ACC 2022
PublisherInstitute of Electrical and Electronics Engineers Inc.
Pages4341-4346
Number of pages6
ISBN (Electronic)9781665451963
DOIs
StatePublished - 2022
Event2022 American Control Conference, ACC 2022 - Atlanta, United States
Duration: Jun 8 2022Jun 10 2022

Publication series

NameProceedings of the American Control Conference
Volume2022-June
ISSN (Print)0743-1619

Conference

Conference2022 American Control Conference, ACC 2022
Country/TerritoryUnited States
CityAtlanta
Period6/8/226/10/22

Keywords

  • Exoskeleton
  • human-robot interaction
  • nonlinear control
  • switched systems

ASJC Scopus subject areas

  • Electrical and Electronic Engineering

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