Skip to main content Accessibility help
×
Home
Hostname: page-component-559fc8cf4f-z4vvc Total loading time: 0.238 Render date: 2021-02-27T23:09:49.326Z Has data issue: true Feature Flags: { "shouldUseShareProductTool": true, "shouldUseHypothesis": true, "isUnsiloEnabled": true, "metricsAbstractViews": false, "figures": false, "newCiteModal": false, "newCitedByModal": true }

Article contents

Soft robots achieve muscle-like performance, self-healing through electrohydraulic coupling

Published online by Cambridge University Press:  10 May 2018

Abstract

Image of the first page of this article
Type
Materials News
Copyright
Copyright © Materials Research Society 2018 

Robots made from soft materials have potential for use in applications that require high adaptability and conformability, or close interactions with humans. To achieve this, soft robotic actuators need to replicate the diverse capabilities and performance of natural muscles, which include high speed, power, strength, efficiency, and the ability to self-heal. Existing soft robotic systems—based on fluidic, thermal, or dielectric elastomer actuators—might exhibit outstanding performance according to certain metrics, but have critical limitations in others. To address this issue, the research team of Christoph Keplinger, a professor at the University of Colorado Boulder, has introduced a versatile actuation technology that combines high strains (>100%), high strength (0.3 MPa), high speed (>50 Hz), long lifetime (>1 million cycles), self-healing, and self-sensing capabilities. These artificial muscles, called hydraulically amplified self-healing electrostatic (HASEL) actuators, are promising especially for advancements in soft robotics.

HASEL actuators consist of a stretchable or flexible shell filled with a liquid dielectric, a vegetable oil. Electrodes, which can be made from conductive hydrogels, cover parts of the shell. When a voltage is applied to the electrodes, electrostatic forces displace the liquid deforming the soft shell. This coupling between electrostatic and hydraulic forces allows for a variety of actuation modes.

As a first design, donut-type HASEL actuators have a disc-shaped shell with electrodes located at the center (see Figure a). When a voltage is applied, the liquid is pushed to the outer region of the shell, causing a local increase in thickness. This transition from disc to donut occurs rapidly as the result of a “pull-in” instability triggered by an imbalance between the electrostatic and mechanical restoring forces. A 5-cm round disc-shaped HASEL actuator is already able to lift 150 g repeatedly over a million cycles.

A planar-type HASEL actuator is another design explored by the research team, where the electrodes cover the entire surface of the shell. When voltage is applied, the actuator reduces in thickness and expands in width. Scaling up these devices, heavy objects such as a 4-kg jug of water can be lifted (see Figure b).

In addition to the mechanical performance, what makes the technology unique is the capacity of the actuator for self-healing and self-sensing. Under high electric fields, dielectric breakdown can occur. Instead of creating a permanent conducting path between the electrodes, the liquid dielectric simply reflows and returns to an insulating state. This way, the liquid dielectric can self-heal from 50 cycles of dielectric breakdown with “the 50th breakdown event occurring at a higher voltage than the 1st breakdown event,” observes Eric Acome, the lead author of the article published in a recent issue of Science (doi:10.1126/science.aao6139). Furthermore, measure of the capacitance between the two electrodes provides self-sensing capability and can be used to monitor deformations and position without external sensors, in a closed-loop actuation control.

Hydraulically amplified self-healing electrostatic (HASEL) actuation principle (a) used to deliver high forces (b). Credit: Science.

“This work opens exciting new possibilities for soft actuation. [The self-healing capabilities of HASEL actuators] make them more practical for applications in robotics where the life cycle of components is important,” says Pablo Valdivia y Alvarado, a professor at the Singapore University of Technology and Design who was not involved in this study. Exploring new approaches to design and fabricate actuation, locomotion, and sensing mechanisms for bioinspired, multifunctional, and passive robots, he points out that “HASEL actuators can provide strains and operational bandwidths large enough for applications where mimicry of biological motion is sought.”

To exploit and further demonstrate the potential and diversity of the HASEL technology, Keplinger’s research team created so-called “Peano-HASEL” actuators—published in Science Robotics (doi:10.1126/scirobotics.aar3276)—that can be scaled up for increased force; are able to achieve precise movements; and by using the adequate index-matching liquid, they can even be made transparent. Keplinger’s team is currently investigating ways to reduce the voltage required for operation and to further improve performance. In the future, the research group hopes to enable the use of compact and portable electronics to control complex movements from arrays of such actuators.

Altmetric attention score

Full text views

Full text views reflects PDF downloads, PDFs sent to Google Drive, Dropbox and Kindle and HTML full text views.

Total number of HTML views: 88
Total number of PDF views: 198 *
View data table for this chart

* Views captured on Cambridge Core between 10th May 2018 - 27th February 2021. This data will be updated every 24 hours.

Access

Send article to Kindle

To send this article to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

Note you can select to send to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Soft robots achieve muscle-like performance, self-healing through electrohydraulic coupling
Available formats
×

Send article to Dropbox

To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

Soft robots achieve muscle-like performance, self-healing through electrohydraulic coupling
Available formats
×

Send article to Google Drive

To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

Soft robots achieve muscle-like performance, self-healing through electrohydraulic coupling
Available formats
×
×

Reply to: Submit a response


Your details


Conflicting interests

Do you have any conflicting interests? *