Special Issue "New Materials and Designs for Soft Actuators"

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

Deadline for manuscript submissions: closed (31 March 2019)

Special Issue Editor

Guest Editor
Dr. Aslan Miriyev

Department of Mechanical Engineering, Columbia University in the City of New York, 500 W 120th St., Mudd 220, New York, NY 10027, USA
Website | E-Mail
Interests: soft-material robotics, soft and structural functional composites, advanced manufacturing, 3D-printing, multi-material systems

Special Issue Information

Dear Colleagues,

Soft Robotics aims to overcome one of the most significant barriers in robotics—the lack of adaptivity to the environment—by introducing soft materials that would render robots more compliant. Akin to biological organisms, such robots would be capable of soft-bodied locomotion and dexterity, necessitating the development of novel, soft actuators. The most widely known, and even successfully-commercialized soft actuation systems, presently in use, are based on inflating/deflating elastomeric chambers of various designs with fluids using compressors and pipes. The non-compliant components of these actuation systems limit miniaturization, thus introducing constraints into robotic design. This has prompted a novel research vector aimed at developing material systems for soft actuation, in particular those integrating sensing capabilities for centralized computer control of robotic motion. The goal of this exciting endeavor is replacing existing pneumatic and hydraulic soft actuators with electrically-activated functional material systems.

The synthesis and fabrication of novel actuator-sensor material systems is a technological prerequisite for engineering bio-inspired compliant robots. In the development of these critical technologies, particular attention is devoted to stimuli-responsive composite and multifunctional material systems with graded compliance and integrated flexible electronics. Such actuator–sensor materials may allow common modular design, in which nuts and bolts are used to assemble robots, to be replaced by a single-step autonomous fabrication. In addition, new actuator designs, along with advanced manufacturing methods, will further enhance the actuation performance by maximizing the actuation stress and strain. Folding, origami, fabric-embedded and 4D-robot designs may pave the way for miniaturization and multi-dimensional controlled actuation on demand.

The current Special Issue of Actuators provides insight into the latest scientific advances in the development and manufacturing of new materials for soft actuators, and their designs, aimed at improving soft actuation performance.

The following topics are of particular interest:

Materials

  • Stimuli-responsive elastomer composites
  • Multifunctional material systems for soft actuation and actuation-sensing
  • Materials with functionally-graded compliance
  • Electrically-driven soft actuators
  • Soft-material robots
  • Soft-hard actuators
  • Soft actuator-sensor material systems
  • Liquid metal alloys for soft actuation, sensing and actuation control
  • Fabric-involving actuation (including wearables)

Related fabrication and processing methods:

  • 3D- and 4D-printing techniques
  • Single-step fabrication of actuator-sensor systems
  • Micro- and nano-fabrication
  • Microfluidics

Design and manufacturing:

  • Performance-leveraging soft actuator design
  • “Bolts-and-nuts-free” soft actuator design and manufacturing
  • Bio-inspired soft actuator design
  • Soft artificial muscles
  • Origami-based design and manufacturing
  • Smart folding design and manufacturing
  • Fabric-involving actuator design and manufacturing

New! Artificial Intelligence (AI) and Computational Simulation of Soft Materials Towards Implementation in Soft Actuation

Understanding the properties and performance of soft functional materials for implementation in Soft Actuation using computer simulations and/or AI, including, but not limited to:

Materials

  • Relation between structure and function in soft materials (micro- and macro-levels)
  • Nonlinear behavior of soft materials for actuation
  • Elastic/viscoelastic behavior
  • Wave propagation in soft matter
  • Deformation of soft matter under various actuation stimuli
  • Mechanical properties of soft material systems
  • Simulation of composite material behavior
  • Simulation of manufacturing methods (including 3D-printing)

Design

  • Design of soft actuators
  • Material design for soft actuation
  • Evolutionary robotics and design automation
  • Forward and inverse kinematics in design of soft actuators
  • CAD in design of soft actuators
  • Design optimization

AI

  • AI in Soft Actuation
  • Using AI for performance prediction and control of soft actuators

I welcome you to submit your research manuscripts to this Special Issue.

Sincerely,
Dr. Aslan Miriyev
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 actuators
  • Soft-hard actuators
  • Soft artificial muscles
  • Soft actuator-sensors
  • Advanced manufacturing of soft actuators
  • 3D-Printing of soft actuators
  • Soft actuator design
  • Bio-inspired design
  • Folding, origami, 4D-robots
  • Fabric-embedded soft actuators

Published Papers (7 papers)

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Research

Open AccessArticle
A Vacuum Powered Soft Textile-Based Clutch
Actuators 2019, 8(2), 47; https://doi.org/10.3390/act8020047
Received: 25 March 2019 / Revised: 30 May 2019 / Accepted: 2 June 2019 / Published: 6 June 2019
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Abstract
We present the design, manufacturing, and characterization of a soft textile-based clutch (TBC) that uses vacuum stimulation to switch between locking and unlocking its linear displacement. The vacuum locks the relative sliding motion between two elaborated textile webbings with an elastic silicone rubber [...] Read more.
We present the design, manufacturing, and characterization of a soft textile-based clutch (TBC) that uses vacuum stimulation to switch between locking and unlocking its linear displacement. The vacuum locks the relative sliding motion between two elaborated textile webbings with an elastic silicone rubber bag. Various fabrication techniques, such as silicone casting on textiles and melt embossing for direct fabrication of miniature patterns on textile and sewing, were used to develop three groups of TBC samples based on friction and interlocking principles. Their performance was compared in a blocking configuration. The clutch with an interlocking mechanism presented the highest withstanding force (150 N) compared to that (54 N) recorded for the friction-based clutch. The simple and compact structure of the proposed clutch, together with the intrinsic adaptability of fabric with other clothing and soft materials, make it an appropriate solution for applications in soft wearable robotics and generally as a locking and variable stiffness solution for soft robotic applications. Full article
(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)
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Graphical abstract

Open AccessArticle
Mechanical Simplification of Variable-Stiffness Actuators Using Dielectric Elastomer Transducers
Actuators 2019, 8(2), 44; https://doi.org/10.3390/act8020044
Received: 29 March 2019 / Revised: 1 May 2019 / Accepted: 15 May 2019 / Published: 20 May 2019
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Abstract
Legged and gait-assistance robots can walk more efficiently if their actuators are compliant. The adjustable compliance of variable-stiffness actuators (VSAs) can enhance this benefit. However, this functionality requires additional mechanical components making VSAs impractical for some uses due to increased weight, volume, and [...] Read more.
Legged and gait-assistance robots can walk more efficiently if their actuators are compliant. The adjustable compliance of variable-stiffness actuators (VSAs) can enhance this benefit. However, this functionality requires additional mechanical components making VSAs impractical for some uses due to increased weight, volume, and cost. VSAs would be more practical if they could modulate the stiffness of their springs without additional components, which usually include moving parts and an additional motor. Therefore, we designed a VSA that uses dielectric elastomer transducers (DETs) for springs. It does not need mechanical stiffness-adjusting components because DETs soften due to electrostatic forces. This paper presents details and performance of our design. Our DET VSA demonstrated independent modulation of its equilibrium position and stiffness. Our design approach could make it practical to obtain the benefits of variable-stiffness actuation with less weight, volume, and cost than normally accompanies them, once weaknesses of DET technology are addressed. Full article
(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)
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Open AccessArticle
A Soft Master-Slave Robot Mimicking Octopus Arm Structure Using Thin Artificial Muscles and Wire Encoders
Actuators 2019, 8(2), 40; https://doi.org/10.3390/act8020040
Received: 31 March 2019 / Revised: 30 April 2019 / Accepted: 4 May 2019 / Published: 13 May 2019
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Abstract
An octopus arm with a flexible structure and no rigid skeleton shows a high degree of freedom and flexibility. These excellent features are suitable for working in an environment having fragile and unknown-shaped objects. Therefore, a soft robot arm resembling an octopus arm [...] Read more.
An octopus arm with a flexible structure and no rigid skeleton shows a high degree of freedom and flexibility. These excellent features are suitable for working in an environment having fragile and unknown-shaped objects. Therefore, a soft robot arm resembling an octopus arm can be useful as a harvesting machine without damaging crops in the agricultural field, as a rehabilitation apparatus in the welfare field, as a safe surgery tool in the medical field, and so on. Unlike industrial robots, to consider the applications of the soft robot arm, the instructions for it relating to a task cannot in many cases be given as a numerical value, and the motion according to an operator’s sense and intent is useful. This paper describes the design and feedback control of a soft master-slave robot system. The system is configured with two soft rubber machines; one is a slave machine that is the soft robot arm mimicking the muscle arrangement of the octopus arm by pneumatic artificial muscles, and the other is a master machine that gives the target motion to the slave machine. Both are configured with soft materials. The slave machine has an actuating part and a sensing part, it can perform bending and torsional motions, and these motions are estimated by the sensing part with threads that connect to wire encoders. The master machine is almost the same configuration, but it has no actuating part. The slave machine is driven according to the deformation of the master machine. We confirmed experimentally that the slave machine followed the master machine that was deformed by an operator. Full article
(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)
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Open AccessArticle
Conductive Fabric Heaters for Heat-Activated Soft Actuators
Actuators 2019, 8(1), 9; https://doi.org/10.3390/act8010009
Received: 28 December 2018 / Revised: 11 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
We examine electrically conductive fabrics as conductive heaters for heat-activated soft actuators. We have explored various fabric designs optimized for material properties, heat distribution and actuation/de-actuation characteristics of the soft actuators. We implemented this approach in the silicone/ethanol composite actuators, in which ethanol [...] Read more.
We examine electrically conductive fabrics as conductive heaters for heat-activated soft actuators. We have explored various fabric designs optimized for material properties, heat distribution and actuation/de-actuation characteristics of the soft actuators. We implemented this approach in the silicone/ethanol composite actuators, in which ethanol undergoes a thermally-induced phase change, leading to high actuation stress and strain. Various types of conductive fabrics were tested, and we developed a stretchable kirigami-based fabric design. We demonstrate a fabric heater that is capable of cyclic heating of the actuator to the required 80 °C. The fabric with the special kirigami design can withstand temperatures of up to 195 °C, can consume up to 30 W of power, and allows the actuator to reach >30% linear strain. This technology may be used in various systems involving thermally-induced actuation. Full article
(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)
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Open AccessArticle
Design of Soft Origami Mechanisms with Targeted Symmetries
Actuators 2019, 8(1), 3; https://doi.org/10.3390/act8010003
Received: 16 November 2018 / Revised: 19 December 2018 / Accepted: 20 December 2018 / Published: 24 December 2018
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Abstract
The integration of soft actuating materials within origami-based mechanisms is a novel method to amplify the actuated motion and tune the compliance of systems for low stiffness applications. Origami structures provide natural flexibility given the extreme geometric difference between thickness and length, and [...] Read more.
The integration of soft actuating materials within origami-based mechanisms is a novel method to amplify the actuated motion and tune the compliance of systems for low stiffness applications. Origami structures provide natural flexibility given the extreme geometric difference between thickness and length, and the energetically preferred bending deformation mode can naturally be used as a form of actuation. However, origami fold patterns that are designed for specific actuation motions and mechanical loading scenarios are needed to expand the library of fold-based actuation strategies. In this study, a recently developed optimization framework for maximizing the performance of compliant origami mechanisms is utilized to discover optimal actuating fold patterns. Variant patterns are discovered through exploring different symmetries in the input and output conditions of the optimization problem. Patterns designed for twist (rotational symmetry) yield significantly better performance, in terms of both geometric advantage and energy requirements, than patterns exhibiting vertical reflection symmetries. The mechanical energy requirements for each design are analyzed and compared for both the small and large applied displacement regimes. Utilizing the patterns discovered through optimization, the multistability of the actuating arms is demonstrated empirically with a paper prototype, where the stable configurations are accessed through local vertex pop-through instabilities. Lastly, the coupled mechanics of fold networks in these actuators yield useful macroscopic motions and can achieve stable shape change through accessing the local vertex instabilities. This survey of origami mechanisms, energy comparison, and multistability characterization provides a new set of designs for future integration with soft actuating materials. Full article
(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)
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Open AccessArticle
Directional Stiffness Control Through Geometric Patterning and Localized Heating of Field’s Metal Lattice Embedded in Silicone
Actuators 2018, 7(4), 80; https://doi.org/10.3390/act7040080
Received: 1 October 2018 / Revised: 13 November 2018 / Accepted: 21 November 2018 / Published: 27 November 2018
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Abstract
This research explores a new realm of soft robotic materials where the stiffness magnitude, directionality, and spatial resolution may be precisely controlled. These materials mimic biological systems where localized muscle contractions and adjustment of tissue stiffness enables meticulous, intelligent movement. Here we propose [...] Read more.
This research explores a new realm of soft robotic materials where the stiffness magnitude, directionality, and spatial resolution may be precisely controlled. These materials mimic biological systems where localized muscle contractions and adjustment of tissue stiffness enables meticulous, intelligent movement. Here we propose the use of a low-melting-point (LMP) metal lattice structure as a rigid frame using localized heating to allow compliance about selectable axes along the lattice. The resulting shape of the lattice is modeled using product of exponentials kinematics to describe the serial chain of tunably compliant axes; this model is found to match the behavior of the physical test piece consisting of a Field’s metal (FM) lattice encased in silicone rubber. This concept could enable highly maneuverable robotic structures with significantly improved dexterity. Full article
(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)
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Open AccessArticle
Force-Amplified Soft Electromagnetic Actuators
Actuators 2018, 7(4), 76; https://doi.org/10.3390/act7040076
Received: 1 October 2018 / Revised: 22 October 2018 / Accepted: 23 October 2018 / Published: 31 October 2018
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Abstract
Electrically-driven direct current (DC) motors are the core component of conventional robots thanks to the ease of computer control and high torque for their size. However, DC motors are often manually attached and soldered into robotic assemblies, and they are not flexible. For [...] Read more.
Electrically-driven direct current (DC) motors are the core component of conventional robots thanks to the ease of computer control and high torque for their size. However, DC motors are often manually attached and soldered into robotic assemblies, and they are not flexible. For soft robotics, researchers have looked to new, compliant materials that are compatible with 3-D printing or other automated assembly methods. In this work we use a computer-controlled embroidery machine to create flat motor windings in flexible fabrics. We model their electromagnetic fields and present them as linear actuators that move a permanent magnet attached to a cable. The fabrication method puts some constraints on the coil design, which are discussed. However, the planar nature of the embroidered sheets enables the designer to use laminar fabrication methods, such as stacking or layering into parts, during 3-D printing. The soft motor windings produced static holding forces of up to 0.25 N and could lift a 0.3 g mass several cm using direct drive. A 3-D printed mechanical amplifier with two stages was able to quadruple the lifting mass, reducing the travel by a factor of 4. Machine embroidery-installed cables and motor coils could lead to “bolts and nuts free” fabrication of thin, electrically-driven cable actuators. Full article
(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)
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