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New Materials and Designs for Soft Actuators

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

Deadline for manuscript submissions: closed (31 March 2019) | Viewed by 85191

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Dr. Aslan Miriyev

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Guest Editor

Physical AI (PAI) Laboratory, Department of Mechanical Engineering, Ben-Gurion University of the Negev, Be'er Sheva, Israel
Interests: physical AI (PAI); material intelligence; soft-material robotics; bio-hybrid robotics; soft actuation; bio-hybrid actuation; soft and structural functional composites; multi-material systems; advanced manufacturing; 3D printing
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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 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 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

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

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Published Papers (9 papers)

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Editorial

Jump to: Research

13 pages, 789 KiB

Open AccessEditorial

A Focus on Soft Actuation

by Aslan Miriyev

Actuators 2019, 8(4), 74; https://doi.org/10.3390/act8040074 - 23 Oct 2019

Cited by 14 | Viewed by 9501

Abstract

The present editorial paper analyzes the hundred recent research works on soft actuation to understand the current main research focus in the light of the grand challenges in the field. Two characteristic paper types were obtained: one focuses on soft actuator design, manufacturing and demonstration, while another includes in addition the development of functional materials. Although vast majority of the works showcased soft actuation, evaluation of its robustness by multi-cyclic actuation was reported in less than 50% of the works, while only 10% described successful actuation for more than 1000 cycles. It is suggested that broadening the research focus to include investigation of mechanisms underlying the degradation of soft functional material performance in real cyclic actuation conditions, along with application of artificial intelligence methods for prediction of muscle behavior, may allow overcoming the reliability issues and developing robust soft-material actuators. The outcomes of the present work might be applicable to the entire soft robotics domain. Full article

(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)

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Research

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18 pages, 5333 KiB

Open AccessFeature PaperArticle

Shape Memory Polymer Composite Actuator: Modeling Approach for Preliminary Design and Validation

by Salvatore Ameduri, Monica Ciminello, Antonio Concilio, Fabrizio Quadrini and Loredana Santo

Actuators 2019, 8(3), 51; https://doi.org/10.3390/act8030051 - 27 Jun 2019

Cited by 7 | Viewed by 7927

Abstract

The work at hand focuses on the modeling, prototyping, and experimental functionality test of a smart actuator based on shape memory polymer technology. Particular attention is paid to the specific modeling approach, here conceived as an effective predictive scheme, quick and, at the same time, able to face those nonlinearity aspects, strictly related to the large displacements shape memory polymers usually undergo. Shape memory polymer composites (SMPCs) may play a critical role for many applications, ranging from self-repairing systems to deployable structures (e.g., solar sails, antennas) and functional subcomponents (e.g., pliers, transporters of small objects). For all these applications, it is very important to have an effective tool that may drive the designers during the preliminary definition of the main parameters of the actuation system. For the present work, a SMPC plate sample has been conceived and realized in view of aerospace applications. An external fibre optic sensor has been then fixed with special adhesive. The temperatures needed for the activation of the Shape Memory Polymer (SMP) and strain storing have been provided by a thermo-gun and complete load–unload cycles, including strain storing, have been performed. Experimental displacements and strains have been used to validate a dedicated predictive theoretical approach, suited for laminates integrated with SMP layers. Full article

(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)

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13 pages, 6064 KiB

Open AccessArticle

A Vacuum Powered Soft Textile-Based Clutch

by Ali Sadeghi, Alessio Mondini and Barbara Mazzolai

Actuators 2019, 8(2), 47; https://doi.org/10.3390/act8020047 - 6 Jun 2019

Cited by 15 | Viewed by 10056

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 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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19 pages, 3682 KiB

Open AccessArticle

Mechanical Simplification of Variable-Stiffness Actuators Using Dielectric Elastomer Transducers

by David P. Allen, Edgar Bolívar, Sophie Farmer, Walter Voit and Robert D. Gregg

Actuators 2019, 8(2), 44; https://doi.org/10.3390/act8020044 - 20 May 2019

Cited by 13 | Viewed by 8688

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 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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13 pages, 6418 KiB

Open AccessArticle

A Soft Master-Slave Robot Mimicking Octopus Arm Structure Using Thin Artificial Muscles and Wire Encoders

by Shota Furukawa, Shuichi Wakimoto, Takefumi Kanda and Hiroki Hagihara

Actuators 2019, 8(2), 40; https://doi.org/10.3390/act8020040 - 13 May 2019

Cited by 27 | Viewed by 10139

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 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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28 pages, 11227 KiB

Open AccessEditor’s ChoiceArticle

Conductive Fabric Heaters for Heat-Activated Soft Actuators

by Mark Cartolano, Boxi Xia, Aslan Miriyev and Hod Lipson

Actuators 2019, 8(1), 9; https://doi.org/10.3390/act8010009 - 21 Jan 2019

Cited by 28 | Viewed by 14258

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 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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16 pages, 3883 KiB

Open AccessArticle

Design of Soft Origami Mechanisms with Targeted Symmetries

by Andrew Gillman, Gregory Wilson, Kazuko Fuchi, Darren Hartl, Alexander Pankonien and Philip Buskohl

Actuators 2019, 8(1), 3; https://doi.org/10.3390/act8010003 - 24 Dec 2018

Cited by 9 | Viewed by 8873

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 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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8 pages, 1397 KiB

Open AccessArticle

Directional Stiffness Control Through Geometric Patterning and Localized Heating of Field’s Metal Lattice Embedded in Silicone

by Emily A. Allen and John P. Swensen

Actuators 2018, 7(4), 80; https://doi.org/10.3390/act7040080 - 27 Nov 2018

Cited by 9 | Viewed by 5770

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 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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11 pages, 4091 KiB

Open AccessArticle

Force-Amplified Soft Electromagnetic Actuators

by Stanley R. Doerger and Cindy K. Harnett

Actuators 2018, 7(4), 76; https://doi.org/10.3390/act7040076 - 31 Oct 2018

Cited by 10 | Viewed by 8395

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 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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