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Zhou et al. Intell Robot 2023;3(1):95-112 Intelligence & Robotics
DOI: 10.20517/ir.2023.05

Research Article Open Access

Human gait tracking for rehabilitation exoskeleton: adap-
tive fractional order sliding mode control approach

Yuan Zhou 1,2 , Zhe Sun 1,2 , Bo Chen 1,2 , Guangpu Huang 1,2 , Xiang Wu 1,2 , Tian Wang 3

1 Department of Automation, Zhejiang University of Technology, Hangzhou 310023, Zhejiang, China.
2 Zhejiang Provincial United Key Laboratory of Embedded Systems, Zhejiang University of Technology, Hangzhou 310023, Zhejiang,
China.
3 Hangzhou RoboCT Technology Development Co., Ltd, Hangzhou 310000, Zhejiang, China.

Correspondence to: Prof. Bo Chen, Department of Automation, Zhejiang University of Technology, Hangzhou 310023, Zhejiang,
China. E-mail: bchen@aliyun.com; ORCID: 0000-0001-6150-3881

How to cite this article: Zhou Y, Sun Z, Chen B, Huang G, Wu X, Wang T. Human gait tracking for rehabilitation exoskeleton:
adaptive fractional order sliding mode control approach. Intell Robot 2023;3(1):95-112. http://dx.doi.org/10.20517/ir.2023.05

Received: 1 Feb 2023 First Decision: 2 Mar 2023 Revised: 16 Mar 2023 Accepted: 23 Mar 2023 Published: 31 Mar 2023
Academic Editor: Simon Yang Copy Editor: Yin Han Production Editor: Yin Han

Abstract
To improve the rehabilitation training effect of hemiplegic patients, in this paper, a discrete adaptive fractional order
fast terminal sliding mode control approach is proposed for the lower limb exoskeleton system to implement high-
precision human gait tracking tasks. Firstly, a discrete dynamic model is established based on the Lagrange system
discretization criterion for the lower limb exoskeleton robot. Then, in order to design a discrete adaptive fractional
order fast terminal sliding mode controller, the Gr¥ unwald–Letnikov fractional order operator is introduced to combine
with fast terminal attractor to construct a fractional order fast terminal sliding surface. An adaptive parameter adjust-
ment strategy is proposed for the reaching law of sliding mode control, which drives the sliding mode to the stable
region dynamically. Moreover, the stability of the control system is proved in the sense of Lyapunov, and the guide-
lines for selecting the control parameters are given. Finally, the simulations are tested on the MATLAB-Opensim
co-simulation platform. Compared with the conventional discrete sliding mode control and discrete fast terminal
sliding mode control, the results verify the superiority of the proposed method in improving lower limb rehabilitation
training.

Keywords: Lower-limb exoskeleton, adaptive discrete-time sliding mode, fractional order control, finite-time conver-
gence

© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0
International License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, shar-
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