Citation: Pan, C.-T.; Lee, M.-C.;
Huang, J.-S.; Chang, C.-C.; Hoe, Z.-Y.;
Li, K.-M. Active Assistive Design and
Multiaxis Self-Tuning Control of a
Novel Lower Limb Rehabilitation
Exoskeleton. Machines 2022, 10, 318.
https://doi.org/10.3390/
machines10050318
Academic Editors: Raffaele Di
Gregorio and Dan Zhang
Received: 26 March 2022
Accepted: 26 April 2022
Published: 28 April 2022
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Article
Active Assistive Design and Multiaxis Self-Tuning Control of a
Novel Lower Limb Rehabilitation Exoskeleton
Cheng-Tang Pan
1,†
, Ming-Chan Lee
2,†
, Jhih-Syuan Huang
1
, Chun-Chieh Chang
3
, Zheng-Yu Hoe
4,
*
and Kuan-Ming Li
2,
*
1
Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University,
Kaohsiung 804, Taiwan; pan@mem.nsysu.edu.tw (C.-T.P.); andyhuang@mem.nsysu.edu.tw (J.-S.H.)
2
Department of Mechanical Engineering, National Taiwan University, Taipei 106, Taiwan;
d08522019@ntu.edu.tw
3
GreenEpoxy Technology Corporation, Kaohsiung 824, Taiwan; jay.chang@mem.nsysu.edu.tw
4
Department of Physical Medicine and Rehabilitation, Kaohsiung Veterans General Hospital,
Kaohsiung 813, Taiwan
* Correspondence: jhoe@vghks.gov.tw (Z.-Y.H.); kmli@ntu.edu.tw (K.-M.L.)
† These authors contributed equally to this work.
Abstract:
This paper presented the mechanical design and control of a lower limb rehabilitation
exoskeleton named “the second lower limb rehabilitation exoskeleton (LLRE-II)”. The exoskeleton
with a lightweight mechanism comprises a 16-cm stepless adjustable thigh and calf rod. The LLRE-II
weighs less than 16 kg and has four degrees of freedom on each leg, including the waist, hip, knee,
and ankle, which ensures fitted wear and comfort. Motors and harmonic drives were installed on the
joints of the hip and knee to operate the exoskeleton. Meanwhile, master and slave motor controllers
were programmed using a Texas Instruments microcontroller (TMS320F28069) for the walking gait
commands and evaluation boards (TMS320F28069/DRV8301) of the joints. A self-tuning multiaxis
control system was developed, and the performance of the controller was investigated through
experiments. The experimental results showed that the mechanical design and control system exhibit
adequate performance. Trajectory tracking errors were eliminated, and the root mean square errors
reduced from 6.45 to 1.22 and from 4.15 to 3.09 for the hip and knee, respectively.
Keywords: exoskeleton; mechanical design; multiaxis control; master–slave control; tuning
1. Introduction
The mobility of the aging population is restricted owing to sarcopenia or physical
disabilities. An exoskeleton is a wearable orthosis that provides human body assistance
via integrated robotic mechanisms. Exoskeletons started being investigated many decades
ago and have garnered significant interest owing to the current development of the aging
society [1–5].
In the 1960s, the exoskeleton “Hardiman”, which is powered by electrical motors
and a master–slave control system, was the first exoskeleton to be developed by General
Electric Company; however, it failed to operate as intended owing to its complex and heavy
structure [
6
]. Recently, researchers at Tsukuba University developed a hybrid assistive
limb (HAL) for patients with lower-limb illnesses. The HAL comprises posture and power-
assist control and is powered by motors and a hybrid controller. Electromyography (EMG)
sensors were installed on the HAL to capture foot reaction forces and detect the walking
intention of the wearer [
7
]. Meanwhile, the Berkeley lower-extremity exoskeleton is an
anthropomorphic model comprising seven degrees of freedom (DOFs) per leg, four of
which are powered by linear hydraulic actuators. The exoskeleton enables the wearer to
carry significant loads with minimal effort over different terrains. Furthermore, it allows
various payloads to be mounted on a backpack-like frame [8,9].
Machines 2022, 10, 318. https://doi.org/10.3390/machines10050318 https://www.mdpi.com/journal/machines
