Special Issue "Electroactive Polymer Actuators for Soft Robotics"

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

Deadline for manuscript submissions: 30 September 2018

Special Issue Editor

Guest Editor
Dr. Andrew T. Conn

Faculty of Engineering, University of Bristol, Bristol BS8 1TR, UK Bristol Robotics Laboratory, University of the West of England, Bristol BS16 1QY, UK
Website | E-Mail
Interests: Soft robotics; Electro-active polymers; Biomedical technologies; Bio-inspired locomotion

Special Issue Information

Dear Colleagues,

The use of flexible and deformable technologies is a new paradigm in robotic design and this emerging soft robotic approach can create robots that robustly deal with uncertainty, interact more safely with humans and compliantly interact with unstructured environments. However, the requirement of many compliant actuators to be tethered to hard supply systems such as pumps or electric motors has become a technological bottleneck, which can limit the scalability, autonomy and mobility of soft robotic systems.

Electro-active polymer (EAP) actuators are a rapidly advancing class of transduction technologies that are highly scalable and operate under electrical stimuli, which frees them from bulky sub-systems. This enables their integration within inherently compliant structures for advanced soft robotic functionality such as self-sensing actuation, self-healing and embodied intelligence. EAP actuators are characterized by large active strains, which in some cases can be comparable to biological muscle, and this creates considerable potential for advanced bio-inspired and biomedical systems.

Despite these attractive characteristics, challenges such as robust control, modelling non-linear behaviour and scalable fabrication have limited the application of EAP soft robotic systems outside of laboratory conditions. This Special Issue of Actuators will present high quality publications that describe the latest advances of EAP actuators towards soft robotic systems.

Dr. Andrew T. Conn
Guest Editor

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 papers will be 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 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 350 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

  • Soft robotics
  • Artificial muscles
  • Dielectric elastomer actuators (DEAs)
  • Ionic polymer-metal composites (IPMCs)
  • Piezoelectric polymers
  • Conductive polymers
  • Ferroelectric polymers
  • Hydrogels
  • Fabrication of EAPs
  • Control of EAPs

Published Papers (4 papers)

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Research

Open AccessArticle Dielectric Elastomer Actuators with Carbon Nanotube Electrodes Painted with a Soft Brush
Actuators 2018, 7(3), 51; https://doi.org/10.3390/act7030051
Received: 5 July 2018 / Revised: 19 August 2018 / Accepted: 21 August 2018 / Published: 22 August 2018
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Abstract
We propose a simple methodology to paint carbon nanotube (CNT) powder with a soft brush onto an elastomer. A large deformation of dielectric elastomer actuator (DEA) occurs according to the small constraint of the electrodes. Uniform painting with a soft brush leads to
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We propose a simple methodology to paint carbon nanotube (CNT) powder with a soft brush onto an elastomer. A large deformation of dielectric elastomer actuator (DEA) occurs according to the small constraint of the electrodes. Uniform painting with a soft brush leads to a stable deformation, as demonstrated by the results of multiple trials. Unexpectedly, painting with a soft brush results in aligned materials on the elastomer. The oriented materials demonstrate anisotropic mechanical and electronic properties. This simple methodology should help realize innovative DEA applications. Full article
(This article belongs to the Special Issue Electroactive Polymer Actuators for Soft Robotics)
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Open AccessFeature PaperArticle Simple Controller Design Based on Internal Model Control for Twisted and Coiled Polymer Actuator
Actuators 2018, 7(3), 33; https://doi.org/10.3390/act7030033
Received: 25 May 2018 / Revised: 19 June 2018 / Accepted: 21 June 2018 / Published: 25 June 2018
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Abstract
A twisted and coiled polymer actuator (TCPA) is a novel soft actuator. TCPA is fabricated by twisting nylon fibers. The TCPA extends and contracts by heating and cooling. By applying conductive nylon fibers to the actuator, the electroactive TCPA can be driven by
[...] Read more.
A twisted and coiled polymer actuator (TCPA) is a novel soft actuator. TCPA is fabricated by twisting nylon fibers. The TCPA extends and contracts by heating and cooling. By applying conductive nylon fibers to the actuator, the electroactive TCPA can be driven by the Joule heating of the applied voltage. It has noteworthy properties such as a high power/mass ratio, large deformation, and low hysteresis. By applying conductive nylon fibers to the actuator, it can be driven by the electrical input. From these properties, many soft robots using the electroactive TCPA have been demonstrated, such as robotic hands, locomotion robots, robot skins, biomimetic robots, and so on. In this paper, to realize a simple controller design, an internal model control based on the identified model is applied. The applied controller can be designed easily without experience in parameter-tuning based on controls theory. The validity of the applied method is investigated through experiments. Full article
(This article belongs to the Special Issue Electroactive Polymer Actuators for Soft Robotics)
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Open AccessArticle Performance Optimization of a Conical Dielectric Elastomer Actuator
Actuators 2018, 7(2), 32; https://doi.org/10.3390/act7020032
Received: 24 May 2018 / Revised: 14 June 2018 / Accepted: 15 June 2018 / Published: 18 June 2018
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Abstract
Dielectric elastomer actuators (DEAs) are known as ‘artificial muscles’ due to their large actuation strain, high energy density and self-sensing capability. The conical configuration has been widely adopted in DEA applications such as bio-inspired locomotion and micropumps for its good compactness, ease for
[...] Read more.
Dielectric elastomer actuators (DEAs) are known as ‘artificial muscles’ due to their large actuation strain, high energy density and self-sensing capability. The conical configuration has been widely adopted in DEA applications such as bio-inspired locomotion and micropumps for its good compactness, ease for fabrication and large actuation stroke. However, the conical protrusion of the DEA membrane is characterized by inhomogeneous stresses, which complicate their design. In this work, we present an analytical model-based optimization for conical DEAs with the three biasing elements: (I) linear compression spring; (II) biasing mass; and (III) antagonistic double-cone DEA. The optimization is to find the maximum stroke and work output of a conical DEA by tuning its geometry (inner disk to outer frame radius ratio a/b) and pre-stretch ratio. The results show that (a) for all three cases, stroke and work output are maximum for a pre-stretch ratio of 1 × 1 for the Parker silicone elastomer, which suggests the stretch caused by out-of-plane deformation is sufficient for this specific elastomer. (b) Stroke maximization is obtained for a lower a/b ratio while a larger a/b ratio is required to maximize work output, but the optimal a/b ratio is less than 0.3 in all three cases. (c) The double-cone configuration has the largest stroke while single cone with a biasing mass has the highest work output. Full article
(This article belongs to the Special Issue Electroactive Polymer Actuators for Soft Robotics)
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Graphical abstract

Open AccessFeature PaperArticle Experimental Characterisation of a Flat Dielectric Elastomer Loudspeaker
Actuators 2018, 7(2), 28; https://doi.org/10.3390/act7020028
Received: 24 April 2018 / Revised: 18 May 2018 / Accepted: 5 June 2018 / Published: 11 June 2018
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Abstract
Conventional loudspeakers are often heavy, require substantial design spaces and are hard to integrate into lightweight structures (e.g., panels). To overcome these drawbacks, this paper presents a novel extremely flat loudspeaker which uses dielectric elastomer actuators with natural rubber for the elastomeric layers
[...] Read more.
Conventional loudspeakers are often heavy, require substantial design spaces and are hard to integrate into lightweight structures (e.g., panels). To overcome these drawbacks, this paper presents a novel extremely flat loudspeaker which uses dielectric elastomer actuators with natural rubber for the elastomeric layers and metal electrodes as transduction mechanism. To facilitate the deformation of the elastomer, the electrodes are perforated. The microscopic holes lead to a macroscopically compressible stack configuration despite the elastomer incompressibility. The design is developed and the materials are chosen to guarantee low mechanical and electrical losses and a high efficiency in the entire frequency range up to several kilohertz. The loudspeaker was designed, built and afterwards experimentally investigated and characterised. Laser measurements of the surface velocity were performed to find dynamic effects present at the diaphragm. To further characterise the device, a semi anechoic chamber as used. Sound pressure levels emitted by the device were recorded at different bias and alternating voltages to study their influence. The nonlinearity of the loudspeaker, which is inherent for this kind of actuators, was quantified considering the total harmonic distortion. Here, a dependence on the amplitude of the alternating voltage is observed. Further, the distortion decreases rapidly the higher the frequency is, which qualifies the loudspeaker concept to properly work at high frequencies. Transfer functions between supplied voltage and on-axis sound pressure were measured and showed in principle potential for high frequency application. Further, the behaviour of the diaphragm changing from rigid piston to resilient disk with respect to frequency for different configurations was observed. Additionally, the directivity of the loudspeaker was investigated at several frequencies, and was in accordance with previously found research outcomes. The results, especially in the high frequency range, prove the usability of this design concept for practical applications. Full article
(This article belongs to the Special Issue Electroactive Polymer Actuators for Soft Robotics)
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