Actuation Solutions for Wearable Robots

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

Deadline for manuscript submissions: closed (10 December 2023) | Viewed by 16935

Special Issue Editors

Gogoa Mobility Robots S.L., 48220 Abadiño, Spain
Interests: wearable exoskeletons; wearable robotics; rehabilitation robotics; neural rehabilitation; gamification for rehabilitation; gait
Department of Information Systems Engineering, University San Pablo CEU, Boadilla del Monte, 28688 Madrid, Spain
Interests: gait; trainer; partial weight suspension; induction of movements; disability; Exoskeleton; lower body rehabilitation; robotic rehabilitation
Neuralrehablitation group, Cajal Institute, Spanish, National Research Council (CSIC), Spain
Interests: actuators; wearable robots; exoskeletons; control; neurorehabilitation
Department of Mechanical Engineering, University of Melbourne, Melbourne, Australia
Interests: assistive and rehabilitation robotics; wearable robots; human learning; computational modelling
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Special Issue Information

Dear Colleagues,

Recent years have seen significant progress in the field of wearable robots, owing to the advancements in both existing technologies and breakthrough developments. These new advancements have opened up a door for new and exciting applications that allow for improved personalisation and co-adaptation frameworks, which are slowly becoming the new norm in the field of human–wearable robot interaction. 

In wearable robots, several technological aspects need to be at their best: compact, lightweight and high performance actuation systems, effective and comfortable physical interfaces, wearable and accurate sensing technologies, and adaptive and intrinsically safe control approaches. In this context, and now more than ever before, it is crucial that actuation systems deliver robust, reliable, repetitive, and biologically relevant performance while minimally adding to the robot’s footprint, complexity, and weight/inertia. While many different and exciting actuators have been developed so far in the literature, a large number of them are limited to research labs and are in the proof-of-concept phase, a stage most of them will never move forward from. Constant innovations in sensor technologies, material science, and motor performance provide new momentum to bringing the best of actuation technologies outside labs in a form that is compact, modular, wearable, and, most importantly, safe.

This Special Issue aims to exhibit these latest research achievements, findings, and ideas in the field of actuation technology designed for use in wearable robotics. In particular, this Special Issue focuses on presenting new advances in design, control, characterization and/or testing of actuation systems technologies—integrated and isolated—for rehabilitation, assistive and/or power augmentation exoskeletons, prostheses and/or orthoses applicable both in the upper and lower limbs. This Special Issue encourages the submission of manuscripts related but not limited to the following topics:

  • Compliant actuators
  • Variable Impedance Actuators
  •  Soft actuation technologies
  • Wearable actuation systems
  • Orthotic and prosthetic actuators
  • Advanced actuation systems
  • Integrated actuation solutions
  • Remote actuation systems
  •  Direct-drive actuators

Dr. Guillermo Asín-Prieto
Dr. Eloy José Urendes Jiménez
Dr. David Rodríguez Cianca
Dr. Tomislav Bacek
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Actuators is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (8 papers)

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Research

21 pages, 13554 KiB  
Article
A Bimodal Hydrostatic Actuator for Robotic Legs with Compliant Fast Motion and High Lifting Force
by Alex Lecavalier, Jeff Denis, Jean-Sébastien Plante and Alexandre Girard
Actuators 2023, 12(12), 452; https://doi.org/10.3390/act12120452 - 07 Dec 2023
Viewed by 1114
Abstract
Robotic legs, such as for lower-limb exoskeletons and prostheses, have bimodal operation: (1) within a task, like for walking (high speed and low force for the swing phase and low speed and higher force when the leg bears the weight of the system); [...] Read more.
Robotic legs, such as for lower-limb exoskeletons and prostheses, have bimodal operation: (1) within a task, like for walking (high speed and low force for the swing phase and low speed and higher force when the leg bears the weight of the system); (2) between tasks, like between walking and sit–stand motions. Sizing a traditional single-ratio actuation system for such extremum operations leads to oversized heavy electric motor and poor energy efficiency at low speeds. This paper explores a bimodal actuation concept where a hydrostatic transmission is dynamically reconfigured using custom motorized ball valves to suit the requirements of a robotic leg with a smaller and more efficient actuation system. First, this paper presents an analysis of the mass and efficiency advantages of the bimodal solution over a baseline solution, for three operating points: high-speed, high-force, and braking modes. Second, an experimental demonstration with a custom-built actuation system and a robotic leg test bench is presented. Control challenges regarding dynamic transition between modes are discussed and a control scheme solution is proposed and tested. The results show the following findings: (1) The actuator prototype can meet the requirements of a leg bimodal operation in terms of force, speed, and compliance while using smaller motors than a baseline solution. (2) The proposed operating principle and control schemes allow for smooth and fast mode transitions. (3) Motorized ball valves exhibit a good trade-off between size, speed, and flow restriction. (4) Motorized ball valves are a promising way to dynamically reconfigure a hydrostatic transmission while allowing energy to be dissipated. Full article
(This article belongs to the Special Issue Actuation Solutions for Wearable Robots)
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13 pages, 1205 KiB  
Article
Exploring the Just Noticeable Interaction Stiffness Differences of an Impedance-Controlled Series Elastic Actuator
by Rodrigo J. Velasco-Guillen, Felix Schofer, Adna Bliek and Philipp Beckerle
Actuators 2023, 12(10), 378; https://doi.org/10.3390/act12100378 - 05 Oct 2023
Cited by 1 | Viewed by 1066
Abstract
The integration of a passive elastic element in series between a motor and its load is popular in many human–robot interaction scenarios. By virtually imposing elastic behavior on the motor, an impedance control can act as a second stiffness to such an actuator. [...] Read more.
The integration of a passive elastic element in series between a motor and its load is popular in many human–robot interaction scenarios. By virtually imposing elastic behavior on the motor, an impedance control can act as a second stiffness to such an actuator. In this study, we investigated how participants perceived the different stiffness settings in a series elastic actuator by measuring the Just Noticeable Difference (JND) of the real stiffness of the elastic element and the virtual stiffness introduced by impedance control. We conducted a user study during which participants interacted with an impedance-controlled Series Elastic Actuator through a lever. During the user study, we varied the real stiffness of the elastic element and the virtual stiffness. We found that participants seem to perceive both the virtual stiffness and the real stiffness in the same way and in accordance to Weber’s law, which states that the stiffness JND is always equal to a fraction of the initial stiffness. Following these findings, we concluded that the impedance controller can implement an effective virtual stiffness with a behavior comparable to a real torsional spring. Therefore, a system combining real and virtual stiffness can simulate a single combined stiffness for a user interacting with it. Full article
(This article belongs to the Special Issue Actuation Solutions for Wearable Robots)
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15 pages, 14382 KiB  
Article
Design, Control, and Assessment of a Synergy-Based Exosuit for Patients with Gait-Associated Pathologies
by Ashwin Jayakumar, Javier Bermejo-García, Daniel Rodríguez Jorge, Rafael Agujetas, Francisco Romero-Sánchez and Francisco J. Alonso-Sánchez
Actuators 2023, 12(8), 309; https://doi.org/10.3390/act12080309 - 28 Jul 2023
Viewed by 1048
Abstract
With ever-rising population comes a corresponding rise in people with mobility issues who have difficulty handling tasks in their daily lives. Such persons could benefit significantly from an active movement assistance device. This paper presents the design of a lower-limb exosuit designed to [...] Read more.
With ever-rising population comes a corresponding rise in people with mobility issues who have difficulty handling tasks in their daily lives. Such persons could benefit significantly from an active movement assistance device. This paper presents the design of a lower-limb exosuit designed to provide the wearer with useful gait assistance. While exoskeletons have existed for a while, soft exoskeletons or exosuits are relatively new. One challenge in the design of a gait-assistance device is the reduction of device weight. In order to facilitate this, the concept of kinematic synergies is implemented to reduce the number of actuators. In this prototype, the exosuit can actuate the hip, ankle, and knee of both legs using just one single motor, and a transmission system consisting of gears and clutches. The implementation of these synergies and their advantages are detailed in this paper, as well as preliminary tests to assess performance. This was performed by testing the exosuit worn by a subject on a treadmill while taking EMG readings and measuring cable tension produced. Significant reductions by up to 35% in certain muscle activations were observed, demonstrating the validity of this prototype for gait assistance. Full article
(This article belongs to the Special Issue Actuation Solutions for Wearable Robots)
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15 pages, 4373 KiB  
Article
Design of a Quasi-Direct Drive Actuator with Embedded Pulley for a Compact, Lightweight, and High-Bandwidth Exosuit
by Jaeha Yang, Junyoung Moon, Jaewook Ryu, Jehyeok Kim, Kimoon Nam, Sungjin Park, Yoosun Kim and Giuk Lee
Actuators 2023, 12(1), 21; https://doi.org/10.3390/act12010021 - 03 Jan 2023
Cited by 1 | Viewed by 2666
Abstract
Although exosuits have several advantages compared to exoskeleton type of wearable robots, they have limitations, such as bulkiness and low control performance. This study addresses the design and evaluation of a compact, lightweight, and highly responsive actuator to be used for exosuits, based [...] Read more.
Although exosuits have several advantages compared to exoskeleton type of wearable robots, they have limitations, such as bulkiness and low control performance. This study addresses the design and evaluation of a compact, lightweight, and highly responsive actuator to be used for exosuits, based on the Quasi-Direct Drive (QDD) actuation. The design requirements of the actuator were set based on the actuation system used in the state-of-the-art exosuit from Harvard University (HE) so that it could be an improvement compared to HE. Several design concepts were comparatively evaluated to select the optimal design, and a design for the pulley embedded QDD (PEQDD) actuator was selected. The PEQDD was fabricated using mechanical components selected based on the design constraints or designed through mechanical analysis. Using a dynamometer, the efficiency map of the PEQDD was drawn. The control bandwidth comparison test with the motor originally used for HE showed improved bandwidth from 6.25 Hz to 20 Hz. Preliminary testing was done in walking and running conditions using an exosuit utilizing PEQDD. The test results showed that the actuator performance met all the design requirements. Full article
(This article belongs to the Special Issue Actuation Solutions for Wearable Robots)
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24 pages, 8530 KiB  
Article
Design, Development, and Control of a Novel Upper-Limb Power-Assist Exoskeleton System Driven by Pneumatic Muscle Actuators
by Hsien-Ru Chu, Shean-Juinn Chiou, I-Hsum Li and Lian-Wang Lee
Actuators 2022, 11(8), 231; https://doi.org/10.3390/act11080231 - 10 Aug 2022
Cited by 2 | Viewed by 1960
Abstract
An innovative wearable upper-limb power-assist exoskeleton system (UPES) was designed for laborers to improve work efficiency and reduce the risk of musculoskeletal disorders. This novel wearable UPES consists of four joints, each comprising a single actuated pneumatic muscle actuator (PMA) and a torsion [...] Read more.
An innovative wearable upper-limb power-assist exoskeleton system (UPES) was designed for laborers to improve work efficiency and reduce the risk of musculoskeletal disorders. This novel wearable UPES consists of four joints, each comprising a single actuated pneumatic muscle actuator (PMA) and a torsion spring module driven via a steel cable. Unlike most single-joint applications, where dual-PMAs are driven by antagonism, this design aims to combine a torsion spring module with a single-PMA via a steel cable for a 1-degree of freedom (1-DOF) joint controlled by a proportional-pressure regulator. The proposed four driving degrees of freedom wearable UPES is suitable for power assistance in work and characterizes a simple structure, safety, and compliance with the motion of an upper limb. However, due to the hysteresis, time-varying characteristics of the PMA, and non-linear movement between joint flexion and extension, the model parameters are difficult to identify accurately, resulting in unmeasurable uncertainties and disturbances of the wearable UPES. To address this issue, we propose an improved proxy-based sliding mode controller integrated with a linear extended state observer (IPSMC-LESO) to achieve accurate power-assisted control for the upper limb and ensure safe interaction between the UPES and the wearer. This control method can slow the underdamped dynamic recovery motion to tend the target trajectory without overshoots from large tracking errors that result in actuator saturation, and without deteriorating the power assist effect during regular operation. The experimental results show that IPSMC-LESO can effectively control a 4-DOF wearable UPES, observe the unknown states and total disturbance online of the system, and adapt to the external environment and load changes to improve system control performance. The results prove that the joint torsion spring module combining the single-PMA can reduce the number of PMAs and proportional-pressure regulators by half and obtain a control response similar to that of the dual-PMA structure. Full article
(This article belongs to the Special Issue Actuation Solutions for Wearable Robots)
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14 pages, 4475 KiB  
Article
Development of a Series Elastic Tendon Actuator (SETA) Based on Gait Analysis for a Knee Assistive Exosuit
by Hee Don Lee, Heejin Park, Dae Han Hong and Tae Hun Kang
Actuators 2022, 11(6), 166; https://doi.org/10.3390/act11060166 - 15 Jun 2022
Cited by 6 | Viewed by 2444
Abstract
An exosuit is a wearable robot that assists the muscular strength of a human that wears it by using multiple wires with similar functions to human muscles. This study focuses on the development of a series elastic tendon actuator (SETA) for the actuation [...] Read more.
An exosuit is a wearable robot that assists the muscular strength of a human that wears it by using multiple wires with similar functions to human muscles. This study focuses on the development of a series elastic tendon actuator (SETA) for the actuation of an exosuit. A gait analysis was performed for walking on stairs to deduce the design requirements of SETA, and the necessary performances were then determined based on these requirements. The SETA is designed to assign compliance to rigid wires using linear springs. The deformation in linear springs generated during tension was measured through an encoder to calculate the human robot interaction (HRI) force. By utilizing the HRI force as feedback of an admittance controller, the SETA was capable of providing wire tensions required by an exosuit. The performance of the SETA was verified through series elastic component (SEC) deformation and force control experiments. The SEC deformation increased from 0 to 3.86 mm when the wire tension increased from 0 to 100 N. This force controller demonstrated a slight vibration owing to the mechanical properties of the springs constituting the SEC during the step input; however, the value gradually converged to 100 N. The developed SETA was applied to an exosuit system for supporting knee strength of the elderly when walking on stairs. Full article
(This article belongs to the Special Issue Actuation Solutions for Wearable Robots)
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23 pages, 6157 KiB  
Article
Design and Experiment Evaluation of Load Distribution on the Dual Motors in Cam-Based Variable Stiffness Actuator with Helping Mode
by Fanghua Mei, Shusheng Bi, Yueri Cai and Hanjun Gao
Actuators 2022, 11(6), 153; https://doi.org/10.3390/act11060153 - 08 Jun 2022
Viewed by 1950
Abstract
This paper presents a novel cam-based variable stiffness actuator (VSA). It significantly differs from its counterparts in that the external load distributes on its two motors with a small difference. It is a feasible method to improve VSA’s output power, especially in compact [...] Read more.
This paper presents a novel cam-based variable stiffness actuator (VSA). It significantly differs from its counterparts in that the external load distributes on its two motors with a small difference. It is a feasible method to improve VSA’s output power, especially in compact joints, such as rehabilitation devices. The stiffness adjustment involves a spring-balanced crank-slider mechanism with a variable-length base frame. Its tunable node is the common node for force decomposition, synthesis, stiffness adjustment, and position control by setting it at the common groove of two differential variable-pitch cams. The paper establishes analytical expressions among the pressure angle of the cam pitch curve, load distribution, and its crucial design indexes and constraints. Based on this, the pitch curve synthesis method is put forward to optimize the load distribution. In addition, a reasonable tradeoff can be easily made by locally adjusting the cam pressure angle. So, the dual motors can work against the output load together in the same direction with a close amount. In the fabricated prototype, current stratification caused by the unstable friction direction has been observed. The estimation results of motor frictionless current matched the designed load distribution behavior. Full article
(This article belongs to the Special Issue Actuation Solutions for Wearable Robots)
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14 pages, 4678 KiB  
Article
Single Actuator with Versatile Controllability of 2-DOF Assistance for Exosuits via a Novel Moving-Gear Mechanism
by Jaewook Ryu, Seungtae Yang and Giuk Lee
Actuators 2022, 11(5), 135; https://doi.org/10.3390/act11050135 - 13 May 2022
Cited by 1 | Viewed by 2871
Abstract
Decreasing the system weight while maintaining the assistance performance can help reduce the metabolic penalty in exosuits. Various researchers have proposed a bi-directional cable-driven actuator that can provide two degrees of freedom (2-DOF) assistance by using a single motor. However, such systems face [...] Read more.
Decreasing the system weight while maintaining the assistance performance can help reduce the metabolic penalty in exosuits. Various researchers have proposed a bi-directional cable-driven actuator that can provide two degrees of freedom (2-DOF) assistance by using a single motor. However, such systems face limitations associated with the controllability of the assistance force. This study proposes a novel cable-driven system, that is, a dual pulley drive, that can provide versatile controllability of 2-DOF cable actuation by using a single motor via a novel moving gear mechanism. The moving gear winds the cable by switching both the side pulleys, which are then used for 2-DOF cable actuation. The spiral springs embedded between the pulley and base shaft work to release the cable. Results of experiments demonstrate that the dual pulley drive provides a versatile range of motion. The proposed system can provide 34.1% of overlapping motion per cable round trip time and support the non-overlapping motion. The preliminary integration of the dual pulley drive to the exosuit confirms that the novel exosuit is considerably lighter than the state-of-the-art exosuit. The calculations indicate that the operating cable speed and force generated using the proposed design are higher than the existing exosuit. Full article
(This article belongs to the Special Issue Actuation Solutions for Wearable Robots)
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