Actuators on Soft Exoskeletons

A special issue of Actuators (ISSN 2076-0825). This special issue belongs to the section "Actuators for Robotics".

Deadline for manuscript submissions: closed (30 June 2021) | Viewed by 25341

Special Issue Editors


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Guest Editor
Advanced Robotics, Istituto Italiano di Tecnologia, Via Morego, 30, 16163 Genova, Italy
Interests: exoskeletons; wearable robotics; exosuits; rehabilitation; mechatronics; human–robot interaction
Special Issues, Collections and Topics in MDPI journals
Department of Biomechanical Engineering, Faculty of Engineering Technology, University of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands
Interests: soft robotics; growing robots; soft actuation and sensing; additive manufacturing of soft robots and smart composites; bio inspired robotics

Special Issue Information

Dear Colleagues,

Soft exoskeletons, also called exosuits, are gaining great interest due to their potential benefits with respect to classical exoskeletons based on rigid structures. Their main advantages are related to their weight, comfort, and usability, thanks to their soft nature and compliant interaction with the wearer. However, the actuation of soft exoskeletons remains one of the main challenges and limiting factors of these systems. Firstly, because of the complexity of integrating an actuation system into a soft structure, and secondly, because of the limited level of assistance that they can provide. Classical actuation systems can be adapted to a soft exoskeleton using a cable-driven system, but the control of such systems is crucial. Pneumatic systems are also commonly used on soft exoskeletons due to their soft nature, however the control bandwidth can represent an issue, and the auxiliary systems (pressure generator, valves, etc.) significantly increase the weight of the system. Novel technologies based on smart materials are also possible, however due to their level of development it is difficult meet the assistance requirements.

This Special Issue aims to cover current developments in actuation on soft exoskeletons, including any aspects related to actuation technologies, design, and control for soft exoskeletons, including testing and validation. Contributions from different application areas, such as medical, rehabilitation, and industry, are welcome.

Dr. Jesús Ortiz,
Dr. Ali Sadeghi
Guest Editors

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Keywords

  • Exoskeleton/exosuit design
  • Exoskeleton/exosuit control
  • Exoskeleton/exosuit testing and validation
  • Actuation technologies
  • Actuation design
  • Actuation control
  • Rehabilitation exoskeletons
  • Industrial exoskeletons

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Published Papers (4 papers)

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Research

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16 pages, 4274 KiB  
Article
Friction Prediction and Validation of a Variable Stiffness Lower Limb Exosuit Based on Finite Element Analysis
by Zhuo Ma, Siyang Zuo, Baojun Chen and Jianbin Liu
Actuators 2021, 10(7), 151; https://doi.org/10.3390/act10070151 - 2 Jul 2021
Cited by 2 | Viewed by 2975
Abstract
The variable stiffness exosuit has great potential for human augmentation and medical applications. However, the model of the variable stiffness mechanism in exosuits is far from satisfactory for the accurate prediction and control of friction force. This paper presents a friction prediction model [...] Read more.
The variable stiffness exosuit has great potential for human augmentation and medical applications. However, the model of the variable stiffness mechanism in exosuits is far from satisfactory for the accurate prediction and control of friction force. This paper presents a friction prediction model of a variable stiffness lower limb exosuit, verifies its prediction performance, and identifies its applicability. The friction force model was established by the Coulomb friction hypothesis. The equivalent coefficient, which is the core parameter of the model, was determined based on friction and squeezing force data obtained by tests and an ANSYS simulation. Experiments show that the prediction error of the proposed model can reach 15% with a proper structural dimension change constraint. The friction force control test showed that the achieved model can shorten the settling time of the step response by 26% and eliminate the steady-state error. Verifications indicate that the proposed method can provide guidance to the modeling of other friction/stiffness structures, especially friction-based wearable robot structure models and predictions. Full article
(This article belongs to the Special Issue Actuators on Soft Exoskeletons)
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10 pages, 3606 KiB  
Article
Pneumatic Artificial Muscle Based on Novel Winding Method
by Disheng Xie, Zhuo Ma, Jianbin Liu and Siyang Zuo
Actuators 2021, 10(5), 100; https://doi.org/10.3390/act10050100 - 10 May 2021
Cited by 10 | Viewed by 4383
Abstract
This paper proposes a pneumatic artificial muscle based on a novel winding method. By this method, the inflation of silicone tubes is transformed to the contraction of muscle, whereas the expansion keeps on one side of the muscle, i.e., the expansion of the [...] Read more.
This paper proposes a pneumatic artificial muscle based on a novel winding method. By this method, the inflation of silicone tubes is transformed to the contraction of muscle, whereas the expansion keeps on one side of the muscle, i.e., the expansion of the actuator does not affect the object close to it. Hence the muscle is great for wearable robots without squeezing on the user’s skin. Through necessary simplification, the contraction ratio model and force model are proposed and verified by experiments. The prototype of this paper has a maximum contraction ratio of 35.8% and a maximum output force of 12.24 N with only 5 mm thickness. The high compatibility proves it excellent to be the alternative for wearable robots. Full article
(This article belongs to the Special Issue Actuators on Soft Exoskeletons)
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17 pages, 25523 KiB  
Article
Design of a 2DoF Ankle Exoskeleton with a Polycentric Structure and a Bi-Directional Tendon-Driven Actuator Controlled Using a PID Neural Network
by Taehoon Lee, Inwoo Kim and Yoon Su Baek
Actuators 2021, 10(1), 9; https://doi.org/10.3390/act10010009 - 4 Jan 2021
Cited by 21 | Viewed by 5869
Abstract
Lower limb exoskeleton robots help with walking movements through mechanical force, by identifying the wearer’s walking intention. When the exoskeleton robot is lightweight and comfortable to wear, the stability of walking increases, and energy can be used efficiently. However, because it is difficult [...] Read more.
Lower limb exoskeleton robots help with walking movements through mechanical force, by identifying the wearer’s walking intention. When the exoskeleton robot is lightweight and comfortable to wear, the stability of walking increases, and energy can be used efficiently. However, because it is difficult to implement the complex anatomical movements of the human body, most are designed simply. Due to this, misalignment between the human and robot movement causes the wearer to feel uncomfortable, and the stability of walking is reduced. In this paper, we developed a two degrees of freedom (2DoF) ankle exoskeleton robot with a subtalar joint and a talocrural joint, applying a four-bar linkage to realize the anatomical movement of a simple 1DoF structure mainly used for ankles. However, bidirectional tendon-driven actuators (BTDAs) do not consider the difference in a length change of both cables due to dorsiflexion (DF) and plantar flexion (PF) during walking, causing misalignment. To solve this problem, a BTDA was developed by considering the length change of both cables. Cable-driven actuators and exoskeleton robot systems create uncertainty. Accordingly, adaptive control was performed with a proportional-integral-differential neural network (PIDNN) controller to minimize system uncertainty. Full article
(This article belongs to the Special Issue Actuators on Soft Exoskeletons)
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Review

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26 pages, 62480 KiB  
Review
Soft Exoskeletons: Development, Requirements, and Challenges of the Last Decade
by Alan Francisco Pérez Vidal, Jesse Yoe Rumbo Morales, Gerardo Ortiz Torres, Felipe de Jesús Sorcia Vázquez, Alan Cruz Rojas, Jorge Aurelio Brizuela Mendoza and Julio César Rodríguez Cerda
Actuators 2021, 10(7), 166; https://doi.org/10.3390/act10070166 - 19 Jul 2021
Cited by 52 | Viewed by 10871
Abstract
In this article, various investigations on soft exoskeletons are presented and their functional and structural characteristics are analyzed. The present work is oriented to the studies of the last decade and covers the upper and lower joints, specifically the shoulder, elbow, wrist, hand, [...] Read more.
In this article, various investigations on soft exoskeletons are presented and their functional and structural characteristics are analyzed. The present work is oriented to the studies of the last decade and covers the upper and lower joints, specifically the shoulder, elbow, wrist, hand, hip, knee, and ankle. Its functionality, applicability, and main characteristics are exposed, such as degrees of freedom, force, actuators, power transmission methods, control systems, and sensors. The purpose of this work is to show the current trend in the development of soft exoskeletons, in addition to specifying the essential characteristics that must be considered in its design and the challenges that its construction implies. Full article
(This article belongs to the Special Issue Actuators on Soft Exoskeletons)
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