Please cite this article as: R. Pérez-San Lázaro, I. Salgado and I. Chairez, Adaptive sliding-mode controller of a lower limb mobile exoskeleton for active rehabilitation. ISA
Transactions (2020), https://doi.org/10.1016/j.isatra.2020.10.008.
ISA Transactions xxx (xxxx) xxx
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ISA Transactions
journal homepage: www.elsevier.com/locate/isatrans
Research article
Adaptive sliding-mode controller of a lower limb mobile exoskeleton
for active rehabilitation
✩
Rafael Pérez-San Lázaro
a,b
, Ivan Salgado
c,
∗
, Isaac Chairez
a,b
a
Medical Robotics and Biosignal Processing Laboratory, Unidad Profesional Interdisciplinaria de Biotecnología, Instituto Politécnico Nacional, Z.C.
07340, Mexico City, Mexico
b
Escuela de Ingeniería y Ciencias, Instituto Tecnológico de Estudios Superiores de Monterrey, Campus Guadalajara, Mexico
c
Centro de Innovación y Desarrollo Tecnológico en Cómputo, Instituto Politécnico Nacional, Z.C. 07700, Mexico City, Mexico
a r t i c l e i n f o
Article history:
Received 23 October 2019
Received in revised form 11 July 2020
Accepted 4 October 2020
Available online xxxx
Keywords:
Decentralized control
Super-twisting algorithm
Lower limb exoskeleton
Adaptive control
Active orthosis
a b s t r a c t
This study describes the design, instrumentation and control of an exoskeleton for lower limb children
rehabilitation with nine degrees of freedom. Three degrees of freedom in each leg exert the movements
of hip, knee and ankle in the sagittal plane, and three control the drive track system composed
by a caterpillar-like robot. The control scheme presents a model free decentralized output feedback
adaptive high-order sliding mode control to solve the trajectory tracking problem in each degree of
freedom of the exoskeleton. A high order sliding mode differentiator estimates the unmeasured states
and, by means of a dynamical state extension, it approximates the unknown dynamical model of the
exoskeleton. A second-order adaptive sliding mode controller based on the super-twisting algorithm
drives the exoskeleton articulations to track the proposed reference trajectories, inducing an ultimate
boundedness for the tracking error. Numerical and experimental simulation results demonstrate the
effect of the adaptive gain on the super-twisting control design. Such evaluations confirmed the
superior tracking performance forced by the adaptive law for the controller with a smaller chattering
amplitude and smaller mean tracking error.
© 2020 ISA. Published by Elsevier Ltd. All rights reserved.
1. Introduction
Biped robots are the technological basis to develop advanced
exoskeletons (EKs) aimed to help in the rehabilitation of pa-
tients who suffer injuries or/and sickness of the lower limbs [1].
However, the advanced technology (which is most of the time
expensive) of EKs restricts their benefits to patients who can use
such rehabilitation devices with the desired frequency. Besides,
EKs tend to exert motionless therapies (the EKs hold their in-
ertial displacing position throughout the rehabilitation session).
Such operating regime demotivates the patient to continue the
rehabilitation schedule.
Today, it is recognized that two main groups categorize lower
limb rehabilitation EKs: non mobile and overground rehabilita-
tion devices. Within the first group, body weight support and
treadmill mechanisms conform the device’s base. One of the
most popular non-mobile devices is Lokomat, which is already
commercially available. ReoAmbulator is another example of
✩
This document is the result of the research project funded by the Instituto
Politécnico Nacional, Mexico SIP-20200517 and SIP-20201286.
∗
Corresponding author.
E-mail addresses: rperezs1402@alumno.ipn.mx (R. Pérez-San Lázaro),
isalgador@ipn.mx (I. Salgado), jchairezo@ipn.mx (I. Chairez).
treadmill-based gait training system (marketed in the USA as
AutoAmbulator) [2]. In regard to the development of non-mobile
rehabilitation EKs, an increasing interest in overground EKs has
led to its recent research and development. Hybrid Assistive
Limb (HAL) is one of the most significant commercially available
overground lower limb EKs (developed in Japan). ReWalk is a
mobile EK from Argo Medical Technologies, which is available
in the market and offers two versions: the first one is intended
for rehabilitation therapies, while the second one is intended for
personal and assisted use [3].
Nowadays, there is a growing interest on unfolding portable
medical devices (including rehabilitation systems) as a conse-
quence of the increasing demand of assisting technologies [4–6].
Mobile rehabilitation technologies demand more complex me-
chanical designs, more efficient electronic instrumentation, reli-
able regulated mobilization of extremities articulations and effec-
tive patient-carrying mobile systems. Efficient operation of the
mobile EKs requires the assurance of the system’s robustness
against parametric uncertainties like patients weight and height
variations, as well as the severity of their health condition [7].
Such problem can be considered as a class of trajectory tracking
control design for systems with uncertain models. In this sense,
proposing an effective EK with the ability of displacing the patient
could provide a more effective treatment. Nevertheless, such
https://doi.org/10.1016/j.isatra.2020.10.008
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