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Open AccessArticle
Robust Sliding-Mode Control of a Two-DOF Lower-Limb Exoskeleton Using a Cascade-Adaptive Super-Twisting Observer
by
Sahbi Boubaker
Sahbi Boubaker
,
Habib Dimassi
Habib Dimassi
Salim Hadj Said
Salim Hadj Said
Souad Kamel
Souad Kamel
1
Department of Computer and Network Engineering, College of Computer Science and Engineering, University of Jeddah, Jeddah 21959, Saudi Arabia
2
King Salman Center for Disability Research, Riyadh 11614, Saudi Arabia
3
Laboratory of Automatics, Electrical Systems and Environment (LASEE), Electrical engineering department, National Engineers School of Monastir, University of Monastir, Monnastir, Tunisia
*
Author to whom correspondence should be addressed.
Actuators 2025, 14(10), 503; https://doi.org/10.3390/act14100503 (registering DOI)
Submission received: 6 August 2025
/
Revised: 6 September 2025
/
Accepted: 12 September 2025
/
Published: 18 October 2025
Abstract
This paper presents an output-feedback sliding-mode control strategy for a two-DOF lower-limb exoskeleton system aimed at rehabilitation assistance for disabled individuals. The core of the approach is a cascade super-twisting observer, beginning with a super-twisting differentiator (STD) that estimates unmeasured angular velocities from measured joint angles. These velocity estimates feed into a second-stage adaptive super-twisting sliding-mode observer (ASTSMO), which accurately reconstructs external load torque disturbances affecting the system. Using these estimates, a sliding-mode controller robustly tracks the exoskeleton’s desired trajectories despite external disturbances. The stability of the proposed control scheme is rigorously established through Lyapunov-based analysis within a sliding-mode framework. Numerical simulations conducted in Matlab R2022/Simulink demonstrate the method’s effectiveness in accurately estimating unmeasured states and unknown disturbances, as well as achieving robust tracking performance in the presence of system uncertainties.
Share and Cite
MDPI and ACS Style
Boubaker, S.; Dimassi, H.; Said, S.H.; Kamel, S.
Robust Sliding-Mode Control of a Two-DOF Lower-Limb Exoskeleton Using a Cascade-Adaptive Super-Twisting Observer. Actuators 2025, 14, 503.
https://doi.org/10.3390/act14100503
AMA Style
Boubaker S, Dimassi H, Said SH, Kamel S.
Robust Sliding-Mode Control of a Two-DOF Lower-Limb Exoskeleton Using a Cascade-Adaptive Super-Twisting Observer. Actuators. 2025; 14(10):503.
https://doi.org/10.3390/act14100503
Chicago/Turabian Style
Boubaker, Sahbi, Habib Dimassi, Salim Hadj Said, and Souad Kamel.
2025. "Robust Sliding-Mode Control of a Two-DOF Lower-Limb Exoskeleton Using a Cascade-Adaptive Super-Twisting Observer" Actuators 14, no. 10: 503.
https://doi.org/10.3390/act14100503
APA Style
Boubaker, S., Dimassi, H., Said, S. H., & Kamel, S.
(2025). Robust Sliding-Mode Control of a Two-DOF Lower-Limb Exoskeleton Using a Cascade-Adaptive Super-Twisting Observer. Actuators, 14(10), 503.
https://doi.org/10.3390/act14100503
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