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Actuators
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Variable Stiffness Actuators
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Variable Stiffness Actuators

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

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 33167

Special Issue Editors

Prof. Steffen Leonhardt

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Guest Editor
Philips Chair for Medical Information Technology, Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Pauwelsstr. 20, D-52074 Aachen, Germany
Interests: physiological measurement techniques; personal health care systems and feedback control systems in medicine
Special Issues, Collections and Topics in MDPI journals
Dipl.-Ing. Bernhard Penzlin

E-Mail Website
Guest Editor
Helmholtz Institute of Biomedical Engineering, RWTH Aachen University, Aachen, Germany
Interests: mechatronic systems; compliant actuators; rehabilitation robotics; exoskeleton
Dr.-Ing. Chuong Ngo

E-Mail Website
Guest Editor
Medical Information Technology, Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Aachen, Germany
Interests: variable stiffness actuators; control engineering; physiological modeling; motion analysis; respiration

Special Issue Information

Dear Colleagues,

The application of compliant actuators is pursued for various reasons, including safe human-machine interactions, the imitation of physiological muscle characteristics, the reduction of peak torque, peak performance, and energy consumption. The mechanical design and technical implementation of the variable compliant actuators is a key challenge. As multivariable systems, actuator systems equipped with adjustable compliance require special control methods. Some application scenarios for these modern actuator topologies are bipedal gait, support at work or in everyday life, rehabilitation robotics, and industrial motion control.

Contributions from all areas of compliant actuators are welcome in this Special Issue, particularly the following:

  • Rehabilitation Robotics: Variable stiffness actuators to support the lower limb;
  • Design: Variable Stiffness Actuator design and experimental validation of prototypes;
  • Energy Analysis: Efficiency enhancement with actuators containing elastic elements;
  • Support in everyday life: Actuators for motion support (e.g., elderly people);
  • Control Systems: Control of systems including compliant actuators;
  • Industrial Application: VSA for use in motion support and automated processes.

Prof. Dr.-Ing. Dr. med. Dr. h. c. Steffen Leonhardt
Dipl.-Ing. Bernhard Penzlin
Dr.-Ing. Chuong Ngo
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.

Keywords

  • Control systems
  • Human robot interaction
  • Energy efficiency
  • Compliant actuators
  • Rehabilitation robotics
  • Controllable stiffness actuators
  • Actuator design

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Published Papers (6 papers)

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23 pages, 9345 KiB  
Article
Design, Modeling, and Control of a Single Leg for a Legged-Wheeled Locomotion System with Non-Rigid Joint
by Vítor H. Pinto, José Gonçalves and Paulo Costa
Actuators 2021, 10(2), 29; https://doi.org/10.3390/act10020029 - 3 Feb 2021
Cited by 6 | Viewed by 3181
Abstract
This article presents an innovative legged-wheeled system, designed to be applied in a hybrid robotic vehicle’s locomotion system, as its driving member. The proposed system will be capable to combine the advantages of legged and wheeled locomotion systems, having 3DOF connected through a [...] Read more.
This article presents an innovative legged-wheeled system, designed to be applied in a hybrid robotic vehicle’s locomotion system, as its driving member. The proposed system will be capable to combine the advantages of legged and wheeled locomotion systems, having 3DOF connected through a combination of both rigid and non-rigid joints. This configuration provides the vehicle the ability to absorb impacts and selected external disturbances. A state space approach was adopted to control the joints, increasing the system’s stability and adaptability. Throughout this article, the entire design process of this robotic system will be presented, as well as its modeling and control. The proposed system’s design is biologically inspired, having as reference the human leg, resulting in the development of a prototype. The results of the testing process with the proposed prototype are also presented. This system was designed to be modular, low-cost, and to increase the autonomy of typical autonomous legged-wheeled locomotion systems. Full article
(This article belongs to the Special Issue Variable Stiffness Actuators)
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20 pages, 5861 KiB  
Article
Development of an Exoskeleton-Type Assist Suit Utilizing Variable Stiffness Control Devices Based on Human Joint Characteristics
by Seigo Kimura, Ryuji Suzuki, Katsuki Machida, Masashi Kashima, Manabu Okui, Rie Nishihama and Taro Nakamura
Actuators 2021, 10(1), 17; https://doi.org/10.3390/act10010017 - 18 Jan 2021
Cited by 14 | Viewed by 4116
Abstract
In this paper, the prototype of the assistive suit for lower limbs was developed. The prototype was based on an assist method with joint stiffness and antagonized angle control. The assist method comprises a system consisting of a pneumatic artificial muscle and a [...] Read more.
In this paper, the prototype of the assistive suit for lower limbs was developed. The prototype was based on an assist method with joint stiffness and antagonized angle control. The assist method comprises a system consisting of a pneumatic artificial muscle and a pull spring, which changes the joint stiffness and the antagonized angle to correspond to the movement phase and aims at coordinated motion assistance with the wearer. First, the characteristics of the developed prototype were tested. It was confirmed that the measured value of the prototype followed the target value in the relationship between torque and angle. In addition, there was hysteresis in the measured value, but it did not affect the assist. Next, the evaluation of standing-up and gait assist by measuring electromyography (EMG) of the knee extensor muscle was conducted using the prototype. In all subjects, a decrease in EMG due to the assist was confirmed. In one subject, the maximum decrease rate at the peak of the EMG was about 50% for standing-up motion and about 75% for gait motion. From the results of these assist evaluations, the effectiveness of the assist method based on the joint stiffness and antagonistic angle control using the prototype was confirmed. Full article
(This article belongs to the Special Issue Variable Stiffness Actuators)
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12 pages, 2391 KiB  
Article
Elastic Actuator Design Based on Bending of Cylindrical Beam for Robotic Applications
by Reis Murat, Nafiseh Ebrahimi and Amir Jafari
Actuators 2020, 9(3), 80; https://doi.org/10.3390/act9030080 - 8 Sep 2020
Cited by 5 | Viewed by 5030
Abstract
The lack of suitable actuators has hampered the development of high-performance machines or robots that can compete with living organisms in terms of motion, safety, and energy efficiency. The adaptation properties of biological systems to environmental variables—for example, the control performance of biological [...] Read more.
The lack of suitable actuators has hampered the development of high-performance machines or robots that can compete with living organisms in terms of motion, safety, and energy efficiency. The adaptation properties of biological systems to environmental variables—for example, the control performance of biological muscle with variable stiffness properties—exceeds the performance of mechanical devices. The variable stiffness characteristics of elastic actuators are different from the operating principle of conventional solids. Although there has been a lot of work on the design of elastic actuators in recent years, a low-cost and compact elastic actuator that can be used in place of standard rigid servo actuators is not yet available. In this study, a standard servo motor has been transformed into an elastic actuator by an elastic coupling attached to the gear system. The elastic coupling consists of four small steel beams with a cylindrical cross section placed on the circular disk, and the stiffness of the actuator is adjusted by varying the clutch length of the cylindrical beams. In this study, this innovative design is explained, then the equations expressing the variation of the torsional stiffness of the cylindrical beams with the coupling length and solutions of these equations are given. The experimental results are presented to show the ability of the proposed actuator to control position and regulate the stiffness independently. Full article
(This article belongs to the Special Issue Variable Stiffness Actuators)
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21 pages, 8269 KiB  
Article
A Concentric Design of a Bypass Magnetorheological Fluid Damper with a Serpentine Flux Valve
by Muhammad Hafiz Idris, Fitrian Imaduddin, Ubaidillah, Saiful Amri Mazlan and Seung-Bok Choi
Actuators 2020, 9(1), 16; https://doi.org/10.3390/act9010016 - 6 Mar 2020
Cited by 36 | Viewed by 7164
Abstract
This work presents a new concentric design structure of a bypass magnetorheological (MR) damper with a serpentine flux valve type. In this design, the serpentine valve is installed not in the middle of the piston but on the bypass channel of the damper. [...] Read more.
This work presents a new concentric design structure of a bypass magnetorheological (MR) damper with a serpentine flux valve type. In this design, the serpentine valve is installed not in the middle of the piston but on the bypass channel of the damper. However, to make it less bulky, the location of the valve installation is chosen to be in line with the cylinder axis, which is different from the common configuration of the bypass damper. With the proposed design concept, the performance flexibility of the bypass configuration and the compactness of the piston valve configuration can be accomplished. In this study, these benefits were demonstrated by firstly deriving an analytical model of the proposed MR damper focusing on the bypass concentric valve structure, which is vital in determining the damping force characteristics. The prototype of MR damper was also fabricated and characterized using the dynamic test machine. The simulation results show that the damping force could be adjusted from 20 N in the off-state to around 600 N in the on-state with 0.3 A of excitation current. In the experiments, during low piston velocity measurement, the on-state results from the simulation were generally in good agreement with the experimental results. However, with the increase in piston velocity, the deviation between the simulation and the experiment gets higher. The deviations are most probably due to seal frictions that were not accounted for in the model. The seal friction is probably dominant as the seals in the prototype need to be prepared for handling higher fluid pressure. As a result, the frictions are quite prevalent and significantly affect the measured off-state damping forces as well, where it was recorded ten times higher than the predicted values from the model. Nevertheless, although there were deviations, the dynamic range of the concentric bypass structure is still 1.5 times higher than the conventional structure and the new structure can be potentially explored more to achieve an improved MR damper design. Full article
(This article belongs to the Special Issue Variable Stiffness Actuators)
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16 pages, 3429 KiB  
Article
Design and Analysis of a Clutched Parallel Elastic Actuator
by Bernhard Penzlin, Mustafa Enes Fincan, Yinbo Li, Linhong Ji, Steffen Leonhardt and Chuong Ngo
Actuators 2019, 8(3), 67; https://doi.org/10.3390/act8030067 - 5 Sep 2019
Cited by 20 | Viewed by 7685
Abstract
Various actuator topologies are discussed for the purpose of powering periodic processes and particularly walking robots. The Clutched Parallel Elastic Actuator (CPEA) is proposed to reduce the energy consumption of active exoskeletons. A nonlinear model of the CPEA is presented in addition to [...] Read more.
Various actuator topologies are discussed for the purpose of powering periodic processes and particularly walking robots. The Clutched Parallel Elastic Actuator (CPEA) is proposed to reduce the energy consumption of active exoskeletons. A nonlinear model of the CPEA is presented in addition to the mechanical design. The CPEA prototype is operated with a passive load on the walking trajectory of the hip joint. The actuator is controlled with a cascaded position control and a superimposed Iterative Learning Controller (ILC). The controller was chosen to ensure comparability between active and deactivated spring operation. The application of the CPEA has the potential to increase efficiency in the design of exoskeletons. Full article
(This article belongs to the Special Issue Variable Stiffness Actuators)
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13 pages, 3356 KiB  
Letter
Analysis of the Possibilities of Using a Driver’s Brain Activity to Pneumatically Actuate a Secondary Foot Brake Pedal
by Ryszard Dindorf and Piotr Wos
Actuators 2020, 9(3), 49; https://doi.org/10.3390/act9030049 - 1 Jul 2020
Cited by 3 | Viewed by 4490
Abstract
The study deals with the use of the driver’s brain activity for wireless remote control of the pneumatic actuator exerting pressure on the secondary foot brake pedal. The conducted experimental tests confirm that bioelectrical signals (BES) induced by muscle tension within the head [...] Read more.
The study deals with the use of the driver’s brain activity for wireless remote control of the pneumatic actuator exerting pressure on the secondary foot brake pedal. The conducted experimental tests confirm that bioelectrical signals (BES) induced by muscle tension within the head can be used for wireless remote control of a pneumatic actuator to exert a pressure force on a foot brake pedal for disabled drivers during car emergency braking. It has been shown that the BES artefacts generated by muscular tension inside the head (e.g., movement of the face and eyelids, clenching of jaws, and pressing the tongue on the palate) are the easiest to control of the pneumatic systems. The proposed car braking assistance system controlled by the driver’s brain activity can improve the driving safety of disabled people, e.g., by reducing the reaction time of pneumatically assisted emergency braking. Full article
(This article belongs to the Special Issue Variable Stiffness Actuators)
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