Special Issue "Soft Actuators"

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A special issue of Actuators (ISSN 2076-0825).

Deadline for manuscript submissions: closed (16 December 2013)

Special Issue Editors

Guest Editor
Prof. Dr. Bram Vanderborght

Department of Mechanical Engineering, Faculty of Applied Sciences, Vrije Universiteit Brussel, Building Z - Room ZW105b, Pleinlaan, 2, B-1050 Brussels, Belgium
Website | E-Mail
Interests: variable impedance actuators; humanoids; bipedal locomotion; rehabilitation robotics; social robots; robot assisted therapies
Guest Editor
Prof. Dr. Fumiya Iida

Institute of Robotics and Intelligent Systems ETH Zurich Leonhardstrasse 27 8092 Zürich Switzerland
Website | E-Mail
Interests: biologically inspired robotics; embodied artificial intelligence; biomechanics; dynamic legged locomotion; navigation of autonomous robots; human-machine interactions
Guest Editor
Prof. Dr. Cecilia Laschi

The BioRobotics Institute Scuola Superiore Sant'Anna Piazza Martiri della Libertà, 33 56127 Pisa Italy
Website | E-Mail
Phone: +39-050-883486
Interests: soft robotics; biomimetic robotics; humanoid robotics; neurodevelopmental engineering

Special Issue Information

Dear Colleagues,

The use of soft/compliant elements is one of the oldest ways to store energy and was one of the few available to our ancestors. In ancient history they used it for their catapults and clocks and Da Vinci used his knowledge on springs to design one of the first automata driven by elastic energy. On the other hand, the start of automation/robotics was characterized with actuators that had to be as stiff as possible. For the future generation of robots however the advantages of stiff actuators like precision trajectory tracking, become less important compared to other requirements like energy efficiency, safety, force accuracy, Although recently several platforms using soft actuators like the robotic co-worker Baxter, BioRob arm, have been introduced on the market, the field of soft actuators faces still a number of fundamental scientific challenges and the optimal exploitation of their properties in applications need to be better understood. Therefore this special issue targets high quality publications spanning the following topics:

  • design of novel soft actuators
  • force, motion and stiffness control
  • safety issues in physical human-robot interaction
  • energy efficiency
  • explosive motions like throwing, kicking,..
  • applications with strong focus on role on soft actuator
  • control and actuation of continuum and/or large DOF bodies

Prof. Dr. Bram Vanderborght
Prof. Dr. Fumiya Iida
Prof. Dr. Cecilia Laschi
Guest Editors

Submission

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. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as 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 refereed through a 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 quarterly 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 300 CHF (Swiss Francs). English correction and/or formatting fees of 250 CHF (Swiss Francs) will be charged in certain cases for those articles accepted for publication that require extensive additional formatting and/or English corrections.

Keywords

  • soft actuators
  • variable impedance actuator
  • energy efficiency
  • safety
  • robustness
  • physical human robot interaction
  • control strategies

Published Papers (9 papers)

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Research

Open AccessArticle Robust Force Control of Series Elastic Actuators
Actuators 2014, 3(3), 182-204; doi:10.3390/act3030182
Received: 16 December 2013 / Revised: 16 May 2014 / Accepted: 30 May 2014 / Published: 9 July 2014
Cited by 4 | PDF Full-text (2091 KB) | HTML Full-text | XML Full-text
Abstract
Force-controlled series elastic actuators (SEA) are widely used in novel human-robot interaction (HRI) applications, such as assistive and rehabilitation robotics. These systems are characterized by the presence of the “human in the loop”, so that control response and stability depend on uncertain human
[...] Read more.
Force-controlled series elastic actuators (SEA) are widely used in novel human-robot interaction (HRI) applications, such as assistive and rehabilitation robotics. These systems are characterized by the presence of the “human in the loop”, so that control response and stability depend on uncertain human dynamics, including reflexes and voluntary forces. This paper proposes a force control approach that guarantees the stability and robustness of the coupled human-robot system, based on sliding-mode control (SMC), considering the human dynamics as a disturbance to reject. We propose a chattering free solution that employs simple task models to obtain high performance, comparable with second order solutions. Theoretical stability is proven within the sliding mode framework, and predictability is reached by avoiding the reaching phase by design. Furthermore, safety is introduced by a proper design of the sliding surface. The practical feasibility of the approach is shown using an SEA prototype coupled with a human impedance in severe stress tests. To show the quality of the approach, we report a comparison with state-of-the-art second order SMC, passivity-based control and adaptive control solutions. Full article
(This article belongs to the Special Issue Soft Actuators)
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Open AccessArticle Bioinspired Soft Actuation System Using Shape Memory Alloys
Actuators 2014, 3(3), 226-244; doi:10.3390/act3030226
Received: 31 December 2013 / Revised: 6 June 2014 / Accepted: 1 July 2014 / Published: 9 July 2014
Cited by 9 | PDF Full-text (897 KB) | HTML Full-text | XML Full-text
Abstract
Soft robotics requires technologies that are capable of generating forces even though the bodies are composed of very light, flexible and soft elements. A soft actuation mechanism was developed in this work, taking inspiration from the arm of the Octopus vulgaris, specifically
[...] Read more.
Soft robotics requires technologies that are capable of generating forces even though the bodies are composed of very light, flexible and soft elements. A soft actuation mechanism was developed in this work, taking inspiration from the arm of the Octopus vulgaris, specifically from the muscular hydrostat which represents its constitutive muscular structure. On the basis of the authors’ previous works on shape memory alloy (SMA) springs used as soft actuators, a specific arrangement of such SMA springs is presented, which is combined with a flexible braided sleeve featuring a conical shape and a motor-driven cable. This robot arm is able to perform tasks in water such as grasping, multi-bending gestures, shortening and elongation along its longitudinal axis. The whole structure of the arm is described in detail and experimental results on workspace, bending and grasping capabilities and generated forces are presented. Moreover, this paper demonstrates that it is possible to realize a self-contained octopus-like robotic arm with no rigid parts, highly adaptable and suitable to be mounted on underwater vehicles. Its softness allows interaction with all types of objects with very low risks of damage and limited safety issues, while at the same time producing relatively high forces when necessary. Full article
(This article belongs to the Special Issue Soft Actuators)
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Open AccessArticle A Mechanical Musculo-Skeletal System for a Human-Shaped Robot Arm
Actuators 2014, 3(2), 124-141; doi:10.3390/act3020124
Received: 20 December 2013 / Revised: 12 May 2014 / Accepted: 13 May 2014 / Published: 17 June 2014
Cited by 3 | PDF Full-text (787 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a mechanical system with a similar configuration to a human musculo-skeletal system for use in anthropomorphic robots or as artificial limbs for disabled persons. First, a mechanical module called ANLES (Actuator with Non-Linear Elasticity System) is introduced. There are two
[...] Read more.
This paper presents a mechanical system with a similar configuration to a human musculo-skeletal system for use in anthropomorphic robots or as artificial limbs for disabled persons. First, a mechanical module called ANLES (Actuator with Non-Linear Elasticity System) is introduced. There are two types of ANLES: the linear-type ANLES and rotary-type ANLES. They can be used as a voluntary muscle in a wide-range of musculo-skeletal structures in which at least double actuators work in an antagonistic setup via some elastic elements. Next, an application of the two types of ANLES to a two-degree-of-freedom (DOF) manipulator that has a similar configuration to the human elbow joint is shown. The experimental results of the joint stiffness and joint angle control elucidate that the developed mechanism effectively regulates joint stiffness in the same way as a musculo-skeletal system. Full article
(This article belongs to the Special Issue Soft Actuators)
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Open AccessArticle Robust and Accurate Closed-Loop Control of McKibben Artificial Muscle Contraction with a Linear Single Integral Action
Actuators 2014, 3(2), 142-161; doi:10.3390/act3020142
Received: 27 March 2014 / Revised: 26 May 2014 / Accepted: 28 May 2014 / Published: 17 June 2014
Cited by 2 | PDF Full-text (970 KB) | HTML Full-text | XML Full-text
Abstract
We analyze the possibility of taking advantage of artificial muscle’s own stiffness and damping, and substituting it for a classic proportional-integral-derivative controller (PID) controller an I controller. The advantages are that there would only be one parameter to tune and no need for
[...] Read more.
We analyze the possibility of taking advantage of artificial muscle’s own stiffness and damping, and substituting it for a classic proportional-integral-derivative controller (PID) controller an I controller. The advantages are that there would only be one parameter to tune and no need for a dynamic model. A stability analysis is proposed from a simple phenomenological artificial muscle model. Step and sinus-wave tracking responses performed with pneumatic McKibben muscles are reported showing the practical efficiency of the method to combine accuracy and load robustness. In the particular case of the McKibben artificial muscle technology, we suggest that the dynamic performances in stability and load robustness would result from the textile nature of its braided sleeve and its internal friction which do not obey Coulomb’s third law, as verified by preliminary reported original friction experiments. Comparisons are reported between three kinds of braided sleeves made of rayon yarns, plastic, and thin metal wires, whose similar closed-loop dynamic performances are highlighted. It is also experimentally shown that a sleeve braided with thin metal wires can give high accuracy performance, in step as in tracking response. This would be due to a low static friction coefficient combined with a kinetic friction exponentially increasing with speed in accordance with hydrodynamic lubrication theory applied to textile physics. Full article
(This article belongs to the Special Issue Soft Actuators)
Open AccessArticle A Novel Variable Stiffness Mechanism Capable of an Infinite Stiffness Range and Unlimited Decoupled Output Motion
Actuators 2014, 3(2), 107-123; doi:10.3390/act3020107
Received: 30 December 2013 / Revised: 1 May 2014 / Accepted: 4 May 2014 / Published: 3 June 2014
Cited by 4 | PDF Full-text (10989 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a novel variable stiffness mechanism is presented, which is capable of achieving an output stiffness with infinite range and an unlimited output motion, i.e., the mechanism output is completely decoupled from the rotor motion, in the zero stiffness configuration. The
[...] Read more.
In this paper, a novel variable stiffness mechanism is presented, which is capable of achieving an output stiffness with infinite range and an unlimited output motion, i.e., the mechanism output is completely decoupled from the rotor motion, in the zero stiffness configuration. The mechanism makes use of leaf springs, which are engaged at different positions by means of two movable supports, to realize the variable output stiffness. The Euler–Bernoulli leaf spring model is derived and validated through experimental data. By shaping the leaf springs, it is shown that the stiffness characteristic of the mechanism can be changed to fulfill different application requirements. Alternative designs can achieve the same behavior with only one leaf spring and one movable support pin. Full article
(This article belongs to the Special Issue Soft Actuators)
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Open AccessArticle Soft Pneumatic Actuators for Rehabilitation
Actuators 2014, 3(2), 84-106; doi:10.3390/act3020084
Received: 12 December 2013 / Revised: 30 April 2014 / Accepted: 4 May 2014 / Published: 26 May 2014
Cited by 7 | PDF Full-text (1310 KB) | HTML Full-text | XML Full-text
Abstract
Pneumatic artificial muscles are pneumatic devices with practical and various applications as common actuators. They, as human muscles, work in agonistic-antagonistic way, giving a traction force only when supplied by compressed air. The state of the art of soft pneumatic actuators is here
[...] Read more.
Pneumatic artificial muscles are pneumatic devices with practical and various applications as common actuators. They, as human muscles, work in agonistic-antagonistic way, giving a traction force only when supplied by compressed air. The state of the art of soft pneumatic actuators is here analyzed: different models of pneumatic muscles are considered and evolution lines are presented. Then, the use of Pneumatic Muscles (PAM) in rehabilitation apparatus is described and the general characteristics required in different applications are considered, analyzing the use of proper soft actuators with various technical properties. Therefore, research activity carried out in the Department of Mechanical and Aerospace Engineering in the field of soft and textile actuators is presented here. In particular, pneumatic textile muscles useful for active suits design are described. These components are made of a tubular structure, with an inner layer of latex coated with a deformable outer fabric sewn along the edge. In order to increase pneumatic muscles forces and contractions Braided Pneumatic Muscles are studied. In this paper, new prototypes are presented, based on a fabric construction and various kinds of geometry. Pressure-force-deformation tests results are carried out and analyzed. These actuators are useful for rehabilitation applications. In order to reproduce the whole upper limb movements, new kind of soft actuators are studied, based on the same principle of planar membranes deformation. As an example, the bellows muscle model and worm muscle model are developed and described. In both cases, wide deformations are expected. Another issue for soft actuators is the pressure therapy. Some textile sleeve prototypes developed for massage therapy on patients suffering of lymph edema are analyzed. Different types of fabric and assembly techniques have been tested. In general, these Pressure Soft Actuators are useful for upper/lower limbs treatments, according to medical requirements. In particular devices useful for arms massage treatments are considered. Finally some applications are considered. Full article
(This article belongs to the Special Issue Soft Actuators)
Open AccessArticle Sustainable Multi-Modal Sensing by a Single Sensor Utilizing the Passivity of an Elastic Actuator
Actuators 2014, 3(2), 66-83; doi:10.3390/act3020066
Received: 24 December 2013 / Revised: 29 April 2014 / Accepted: 4 May 2014 / Published: 12 May 2014
PDF Full-text (942 KB) | HTML Full-text | XML Full-text
Abstract
When a robot equipped with compliant joints driven by elastic actuators contacts an object and its joints are deformed, multi-modal information, including the magnitude and direction of the applied force and the deformation of the joint, is used to enhance the performance of
[...] Read more.
When a robot equipped with compliant joints driven by elastic actuators contacts an object and its joints are deformed, multi-modal information, including the magnitude and direction of the applied force and the deformation of the joint, is used to enhance the performance of the robot such as dexterous manipulation. In conventional approaches, some types of sensors used to obtain the multi-modal information are attached to the point of contact where the force is applied and at the joint. However, this approach is not sustainable for daily use in robots, i.e., not durable or robust, because the sensors can undergo damage due to the application of excessive force and wear due to repeated contacts. Further, multiple types of sensors are required to measure such physical values, which add to the complexity of the device system of the robot. In our approach, a single type of sensor is used and it is located at a point distant from the contact point and the joint, and the information is obtained indirectly by the measurement of certain physical parameters that are influenced by the applied force and the joint deformation. In this study, we employ the McKibben pneumatic actuator whose inner pressure changes passively when a force is applied to the actuator. We derive the relationships between information and the pressures of a two-degrees-of-freedom (2-DoF) joint mechanism driven by four pneumatic actuators. Experimental results show that the multi-modal information can be obtained by using the set of pressures measured before and after the force is applied. Further, we apply our principle to obtain the stiffness values of certain contacting objects that can subsequently be categorized by using the aforementioned relationships. Full article
(This article belongs to the Special Issue Soft Actuators)
Open AccessArticle Control of a Heavy-Lift Robotic Manipulator with Pneumatic Artificial Muscles
Actuators 2014, 3(2), 41-65; doi:10.3390/act3020041
Received: 4 November 2013 / Revised: 5 April 2014 / Accepted: 10 April 2014 / Published: 24 April 2014
Cited by 3 | PDF Full-text (31822 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Lightweight, compliant actuators are particularly desirable in robotic systems intended for interaction with humans. Pneumatic artificial muscles (PAMs) exhibit these characteristics and are capable of higher specific work than comparably-sized hydraulic actuators and electric motors. The objective of this work is to develop
[...] Read more.
Lightweight, compliant actuators are particularly desirable in robotic systems intended for interaction with humans. Pneumatic artificial muscles (PAMs) exhibit these characteristics and are capable of higher specific work than comparably-sized hydraulic actuators and electric motors. The objective of this work is to develop a control algorithm that can smoothly and accurately track the desired motions of a manipulator actuated by pneumatic artificial muscles. The manipulator is intended for lifting humans in nursing assistance or casualty extraction scenarios; hence, the control strategy must be capable of responding to large variations in payload over a large range of motion. The present work first investigates the feasibility of two output feedback controllers (proportional-integral-derivative and fuzzy logic), but due to the limitations of pure output feedback control, a model-based feedforward controller is developed and combined with output feedback to achieve improved closed-loop performance. The model upon which the controller is based incorporates the internal airflow dynamics, the physical parameters of the pneumatic muscles and the manipulator dynamics. Simulations were performed in order to validate the control algorithms, guide controller design and predict optimal gains. Using real-time interface software and hardware, the controllers were implemented and experimentally tested on the manipulator, demonstrating the improved capability. Full article
(This article belongs to the Special Issue Soft Actuators)
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Open AccessArticle A Two-Degree of Freedom Variable Stiffness Actuator Based on the MACCEPA Concept
Actuators 2014, 3(2), 20-40; doi:10.3390/act3020020
Received: 30 December 2013 / Revised: 25 March 2014 / Accepted: 26 March 2014 / Published: 3 April 2014
Cited by 3 | PDF Full-text (2282 KB) | HTML Full-text | XML Full-text
Abstract
The current state-of-the-art of variable stiffness actuators consists mostly of different concepts for single-degree of freedom joints. However, in bio-inspired robotic applications, multiple degrees of freedom variable stiffness actuators are often desired. Currently, this is usually achieved by cascading single-degree of freedom actuators.
[...] Read more.
The current state-of-the-art of variable stiffness actuators consists mostly of different concepts for single-degree of freedom joints. However, in bio-inspired robotic applications, multiple degrees of freedom variable stiffness actuators are often desired. Currently, this is usually achieved by cascading single-degree of freedom actuators. The innovation presented in this work is a two-degree of freedom variable stiffness actuator using the mechanically adjustable and controllable equilibrium position actuator (MACCEPA) concept. The presented actuator is not a cascade of two single-degree of freedom actuators, but centralizes the two degrees of freedom in one single joint. Equilibrium position and stiffness of the actuator are, furthermore, independently controllable in both degrees of freedom. The design and experimental validation of the actuator are discussed in this work. The independence of adjusting the equilibrium position and stiffness of the actuator are experimentally validated. The results show that the measured characteristics of the actuator sufficiently match the theoretically calculated ones. Future work includes implementing the presented two-degree of freedom actuator in an application, like a bipedal robot or a robotic arm. Full article
(This article belongs to the Special Issue Soft Actuators)

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