Robotic Materials

90 results (View BibTeX file of all listed publications)

2024

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Hexagonal electrohydraulic modules for rapidly reconfigurable high-speed robots

Yoder, Z., Rumley, E., Schmidt, I., Rothemund, P., Keplinger, C.

Science Robotics, 9, September 2024 (article)

Abstract
Robots made from reconfigurable modular units feature versatility, cost efficiency, and improved sustainability compared with fixed designs. Reconfigurable modules driven by soft actuators provide adaptable actuation, safe interaction, and wide design freedom, but existing soft modules would benefit from high-speed and high-strain actuation, as well as driving methods well-suited to untethered operation. Here, we introduce a class of electrically actuated robotic modules that provide high-speed (a peak contractile strain rate of 4618% per second, 15.8-hertz bandwidth, and a peak specific power of 122 watts per kilogram), high-strain (49% contraction) actuation and that use magnets for reversible mechanical and electrical connections between neighboring modules, thereby serving as building blocks for rapidly reconfigurable and highly agile robotic systems. The actuation performance of each hexagonal electrohydraulic (HEXEL) module is enabled by a synergistic combination of soft and rigid components; a hexagonal exoskeleton of rigid plates amplifies the motion produced by soft electrohydraulic actuators and provides a mechanical structure and connection platform for reconfigurable robots composed of many modules. We characterize the actuation performance of individual HEXEL modules, present a model that captures their quasi-static force-stroke behavior, and demonstrate both a high-jumping and a fast pipe-crawling robot. Using embedded magnetic connections, we arranged multiple modules into reconfigurable robots with diverse functionality, including a high-stroke muscle, a multimodal active array, a table-top active platform, and a fast-rolling robot. We further leveraged the magnetic connections for hosting untethered, snap-on driving electronics, together highlighting the promise of HEXEL modules for creating rapidly reconfigurable high-speed robots.

link (url) DOI [BibTex]

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Cutaneous Electrohydraulic (CUTE) Wearable Devices for Pleasant Broad-Bandwidth Haptic Cues

Sanchez-Tamayo, N., Yoder, Z., Rothemund, P., Ballardini, G., Keplinger, C., Kuchenbecker, K. J.

Advanced Science, (2402461):1-14, September 2024 (article)

Abstract
By focusing on vibrations, current wearable haptic devices underutilize the skin's perceptual capabilities. Devices that provide richer haptic stimuli, including contact feedback and/or variable pressure, are typically heavy and bulky due to the underlying actuator technology and the low sensitivity of hairy skin, which covers most of the body. This paper presents a system architecture for compact wearable devices that deliver salient and pleasant broad-bandwidth haptic cues: Cutaneous Electrohydraulic (CUTE) devices combine a custom materials design for soft haptic electrohydraulic actuators that feature high stroke, high force, and electrical safety with a comfortable mounting strategy that places the actuator in a non-contact resting position. A prototypical wrist-wearable CUTE device produces rich tactile sensations by making and breaking contact with the skin (2.44 mm actuation stroke), applying high controllable forces (exceeding 2.3 N), and delivering vibrations at a wide range of amplitudes and frequencies (0-200 Hz). A perceptual study with fourteen participants achieved 97.9% recognition accuracy across six diverse cues and verified their pleasant and expressive feel. This system architecture for wearable devices gives unprecedented control over the haptic cues delivered to the skin, providing an elegant and discreet way to activate the user's sense of touch.

DOI [BibTex]

Electrohydraulic Musculoskeletal Robotic Leg for Agile, Adaptive, yet Energy-Efficient Locomotion
Electrohydraulic Musculoskeletal Robotic Leg for Agile, Adaptive, yet Energy-Efficient Locomotion

Buchner, T. J. K., Fukushima, T., Kazemipour, A., Gravert, S., Prairie, M., Romanescu, P., Arm, P., Zhang, Y., Wang, X., Zhang, S. L., Walter, J., Keplinger, C., Katzschmann, R. K.

Nature Communications, 15(1), September 2024 (article)

Abstract
Robotic locomotion in unstructured terrain demands an agile, adaptive, and energy-efficient architecture. To traverse such terrains, legged robots use rigid electromagnetic motors and sensorized drivetrains to adapt to the environment actively. These systems struggle to compete with animals that excel through their agile and effortless motion in natural environments. We propose a bio-inspired musculoskeletal leg architecture driven by antagonistic pairs of electrohydraulic artificial muscles. Our leg is mounted on a boom arm and can adaptively hop on varying terrain in an energy-efficient yet agile manner. It can also detect obstacles through capacitive self-sensing. The leg performs powerful and agile gait motions beyond 5 Hz and high jumps up to 40 % of the leg height. Our leg’s tunable stiffness and inherent adaptability allow it to hop over grass, sand, gravel, pebbles, and large rocks using only open-loop force control. The electrohydraulic leg features a low cost of transport (0.73), and while squatting, it consumes only a fraction of the energy (1.2 %) compared to its conventional electromagnetic counterpart. Its agile, adaptive, and energy-efficient properties would open a roadmap toward a new class of musculoskeletal robots for versatile locomotion and operation in unstructured natural environments.

Press release Video (overview) Video (technical description) Article in pdf link (url) DOI [BibTex]

Buchner, T. J. K., Fukushima, T., Kazemipour, A., Gravert, S., Prairie, M., Romanescu, P., Arm, P., Zhang, Y., Wang, X., Zhang, S. L., Walter, J., Keplinger, C., Katzschmann, R. K. Electrohydraulic Musculoskeletal Robotic Leg for Agile, Adaptive, yet Energy-Efficient Locomotion Nature Communications, 15(1), September 2024 (article)

Press release Video (overview) Video (technical description) Article in pdf link (url) DOI [BibTex]

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Cutaneous Electrohydraulic (CUTE) Wearable Devices for Multimodal Haptic Feedback

Sanchez-Tamayo, N., Yoder, Z., Ballardini, G., Rothemund, P., Keplinger, C., Kuchenbecker, K. J.

Extended abstract (1 page) presented at the IEEE RoboSoft Workshop on Multimodal Soft Robots for Multifunctional Manipulation, Locomotion, and Human-Machine Interaction, San Diego, USA, April 2024 (misc)

[BibTex]

Sanchez-Tamayo, N., Yoder, Z., Ballardini, G., Rothemund, P., Keplinger, C., Kuchenbecker, K. J. Cutaneous Electrohydraulic (CUTE) Wearable Devices for Multimodal Haptic Feedback Extended abstract (1 page) presented at the IEEE RoboSoft Workshop on Multimodal Soft Robots for Multifunctional Manipulation, Locomotion, and Human-Machine Interaction, San Diego, USA, April 2024 (misc)

[BibTex]

2023

Electrochemically Controlled Hydrogels with Electrotunable Permeability and Uniaxial Actuation
Electrochemically Controlled Hydrogels with Electrotunable Permeability and Uniaxial Actuation

Benselfelt, T., Shakya, J., Rothemund, P., Lindström, S. B., Piper, A., Winkler, T. E., Hajian, A., Wågberg, L., Keplinger, C., Hamedi, M. M.

Advanced Materials, 35(45):2303255, Wiley-VCH GmbH, November 2023 (article)

Abstract
The unique properties of hydrogels enable the design of life-like soft intelligent systems. However, stimuli-responsive hydrogels still suffer from limited actuation control. Direct electronic control of electronically conductive hydrogels can solve this challenge and allow direct integration with modern electronic systems. An electrochemically controlled nanowire composite hydrogel with high in-plane conductivity that stimulates a uniaxial electrochemical osmotic expansion is demonstrated. This materials system allows precisely controlled shape-morphing at only −1 V, where capacitive charging of the hydrogel bulk leads to a large uniaxial expansion of up to 300%, caused by the ingress of ≈700 water molecules per electron–ion pair. The material retains its state when turned off, which is ideal for electrotunable membranes as the inherent coupling between the expansion and mesoporosity enables electronic control of permeability for adaptive separation, fractionation, and distribution. Used as electrochemical osmotic hydrogel actuators, they achieve an electroactive pressure of up to 0.7 MPa (1.4 MPa vs dry) and a work density of ≈150 kJ m−3 (2 MJ m−3 vs dry). This new materials system paves the way to integrate actuation, sensing, and controlled permeation into advanced soft intelligent systems.

link (url) DOI [BibTex]

2023

Benselfelt, T., Shakya, J., Rothemund, P., Lindström, S. B., Piper, A., Winkler, T. E., Hajian, A., Wågberg, L., Keplinger, C., Hamedi, M. M. Electrochemically Controlled Hydrogels with Electrotunable Permeability and Uniaxial Actuation Advanced Materials, 35(45):2303255, Wiley-VCH GmbH, November 2023 (article)

link (url) DOI [BibTex]

Hydraulically Amplified Self-healing Electrostatic Actuators
Hydraulically Amplified Self-healing Electrostatic Actuators

Keplinger, C. M., Acome, E. L., Kellaris, N. A., Mitchell, S. K.

(US Patent 11795979B2), October 2023 (patent)

Abstract
An electro-hydraulic actuator includes a deformable shell defining an enclosed internal cavity and containing a liquid dielectric, first and second electrodes on first and second sides, respectively, of the enclosed internal cavity. An electrostatic force between the first and second electrodes upon application of a voltage to one of the electrodes draws the electrodes towards each other to displace the liquid dielectric within the enclosed internal cavity. The shell includes active and inactive areas such that the electrostatic forces between the first and second electrodes displaces the liquid dielectric within the enclosed internal cavity from the active area of the shell to the inactive area of the shell. The first and second electrodes, the deformable shell, and the liquid dielectric cooperate to form a self-healing capacitor, and the liquid dielectric is configured for automatically filling breaches in the liquid dielectric resulting from dielectric breakdown.

link (url) [BibTex]

Keplinger, C. M., Acome, E. L., Kellaris, N. A., Mitchell, S. K. Hydraulically Amplified Self-healing Electrostatic Actuators (US Patent 11795979B2), October 2023 (patent)

link (url) [BibTex]

High Strain Peano Hydraulically Amplified Self-Healing Electrostatic (HASEL) Transducers
High Strain Peano Hydraulically Amplified Self-Healing Electrostatic (HASEL) Transducers

Keplinger, C. M., Wang, X., Mitchell, S. K.

(US Patent App. 18/138,621), August 2023 (patent)

Abstract
High strain hydraulically amplified self-healing electrostatic transducers having increased maximum theoretical and practical strains are disclosed. In particular, the actuators include electrode configurations having a zipping front created by the attraction of the electrodes that is configured orthogonally to a strain axis along which the actuators. This configuration produces increased strains. In turn, various form factors for the actuator configuration are presented including an artificial circular muscle and a strain amplifying pulley system. Other actuator configurations are contemplated that include independent and opposed electrode pairs to create cyclic activation, hybrid electrode configurations, and use of strain limiting layers for controlled deflection of the actuator.

link (url) [BibTex]

A Multifunctional Soft Robotic Shape Display with High-speed Actuation, Sensing, and Control
A Multifunctional Soft Robotic Shape Display with High-speed Actuation, Sensing, and Control

Johnson, B. K., Naris, M., Sundaram, V., Volchko, A., Ly, K., Mitchell, S. K., Acome, E., Kellaris, N., Keplinger, C., Correll, N., Humbert, J. S., Rentschler, M. E.

Nature Communications, 14(1), July 2023 (article)

Abstract
Shape displays which actively manipulate surface geometry are an expanding robotics domain with applications to haptics, manufacturing, aerodynamics, and more. However, existing displays often lack high-fidelity shape morphing, high-speed deformation, and embedded state sensing, limiting their potential uses. Here, we demonstrate a multifunctional soft shape display driven by a 10 × 10 array of scalable cellular units which combine high-speed electrohydraulic soft actuation, magnetic-based sensing, and control circuitry. We report high-performance reversible shape morphing up to 50 Hz, sensing of surface deformations with 0.1 mm sensitivity and external forces with 50 mN sensitivity in each cell, which we demonstrate across a multitude of applications including user interaction, image display, sensing of object mass, and dynamic manipulation of solids and liquids. This work showcases the rich multifunctionality and high-performance capabilities that arise from tightly-integrating large numbers of electrohydraulic actuators, soft sensors, and controllers at a previously undemonstrated scale in soft robotics.

YouTube video link (url) DOI [BibTex]

Johnson, B. K., Naris, M., Sundaram, V., Volchko, A., Ly, K., Mitchell, S. K., Acome, E., Kellaris, N., Keplinger, C., Correll, N., Humbert, J. S., Rentschler, M. E. A Multifunctional Soft Robotic Shape Display with High-speed Actuation, Sensing, and Control Nature Communications, 14(1), July 2023 (article)

YouTube video link (url) DOI [BibTex]

Capacitive Self-Sensing for Electrostatic Transducers with High Voltage Isolation
Capacitive Self-Sensing for Electrostatic Transducers with High Voltage Isolation

Correll, N., Ly, K. D., Kellaris, N. A., Keplinger, C. M.

(US Patent App. 17/928,453), June 2023 (patent)

Abstract
Transducer systems disclosed herein include self-sensing capabilities. In particular, electrostatic transducers include a low voltage electrode and a high voltage electrode. A low voltage sensing unit is coupled with the low voltage electrode of the electrostatic transducer. The low voltage sensing unit is configured to measure a capacitance of the electrostatic transducer, from which displacement of the electrostatic transducer may be calculated. High voltage drive signals received by the high voltage electrode during actuation may be isolated from the low voltage sensing unit. The isolation may be provided by dielectric material of the electrostatic transducer, a voltage suppression component, and/or a voltage suppression module comprising a low impedance ground path. In the event of an electrical failure of the transducer, the low voltage sensing unit may be isolated from high voltages.

link (url) [BibTex]

Correll, N., Ly, K. D., Kellaris, N. A., Keplinger, C. M. Capacitive Self-Sensing for Electrostatic Transducers with High Voltage Isolation (US Patent App. 17/928,453), June 2023 (patent)

link (url) [BibTex]

High Strain Peano Hydraulically Amplified Self-healing Electrostatic (HASEL) Transducers
High Strain Peano Hydraulically Amplified Self-healing Electrostatic (HASEL) Transducers

Keplinger, C. M., Wang, X., Mitchell, S. K.

(US Patent 11635094), April 2023 (patent)

Abstract
High strain hydraulically amplified self-healing electrostatic transducers having increased maximum theoretical and practical strains are disclosed. In particular, the actuators include electrode configurations having a zipping front created by the attraction of the electrodes that is configured orthogonally to a strain axis along which the actuators. This configuration produces increased strains. In turn, various form factors for the actuator configuration are presented including an artificial circular muscle and a strain amplifying pulley system. Other actuator configurations are contemplated that include independent and opposed electrode pairs to create cyclic activation, hybrid electrode configurations, and use of strain limiting layers for controlled deflection of the actuator.

link (url) [BibTex]

A Versatile Jellyfish-Like Robotic Platform for Effective Underwater Propulsion and Manipulation
A Versatile Jellyfish-Like Robotic Platform for Effective Underwater Propulsion and Manipulation

Wang, T., Joo, H., Song, S., Hu, W., Keplinger, C., Sitti, M.

Science Advances, 9(15), American Association for the Advancement of Science, April 2023, Tianlu Wang and Hyeong-Joon Joo contributed equally to this work. (article)

Abstract
Underwater devices are critical for environmental applications. However, existing prototypes typically use bulky, noisy actuators and limited configurations. Consequently, they struggle to ensure noise-free and gentle interactions with underwater species when realizing practical functions. Therefore, we developed a jellyfish-like robotic platform enabled by a synergy of electrohydraulic actuators and a hybrid structure of rigid and soft components. Our 16-cm-diameter noise-free prototype could control the fluid flow to propel while manipulating objects to be kept beneath its body without physical contact, thereby enabling safer interactions. Its against-gravity speed was up to 6.1 cm/s, substantially quicker than other examples in literature, while only requiring a low input power of around 100 mW. Moreover, using the platform, we demonstrated contact-based object manipulation, fluidic mixing, shape adaptation, steering, wireless swimming, and cooperation of two to three robots. This study introduces a versatile jellyfish-like robotic platform with a wide range of functions for diverse applications.

YouTube video link (url) DOI [BibTex]

Wang, T., Joo, H., Song, S., Hu, W., Keplinger, C., Sitti, M. A Versatile Jellyfish-Like Robotic Platform for Effective Underwater Propulsion and Manipulation Science Advances, 9(15), American Association for the Advancement of Science, April 2023, Tianlu Wang and Hyeong-Joon Joo contributed equally to this work. (article)

YouTube video link (url) DOI [BibTex]

Biodegradable Electrohydraulic Actuators for Sustainable Soft Robots
Biodegradable Electrohydraulic Actuators for Sustainable Soft Robots

Rumley, E. H., Preninger, D., Shagan-Shomron, A., Rothemund, P., Hartmann, F., Baumgartner, M., Kellaris, N., Stojanovic, A., Yoder, Z., Karrer, B., Keplinger, C., Kaltenbrunner, M.

Science Advances, 9(12), 2023, Ellen H. Rumley and David Preninger were co-first authors, and Christoph Keplinger and Martin Kaltenbrunner were shared corresponding authors. (article)

Abstract
Combating environmental pollution demands a focus on sustainability, in particular from rapidly advancing technologies that are poised to be ubiquitous in modern societies. Among these, soft robotics promises to replace conventional rigid machines for applications requiring adaptability and dexterity. For key components of soft robots, such as soft actuators, it is thus important to explore sustainable options like bioderived and biodegradable materials. We introduce systematically determined compatible materials systems for the creation of fully biodegradable, high-performance electrohydraulic soft actuators, based on various biodegradable polymer films, ester-based liquid dielectric, and NaCl-infused gelatin hydrogel. We demonstrate that these biodegradable actuators reliably operate up to high electric fields of 200 V/μm, show performance comparable to nonbiodegradable counterparts, and survive more than 100,000 actuation cycles. Furthermore, we build a robotic gripper based on biodegradable soft actuators that is readily compatible with commercial robot arms, encouraging wider use of biodegradable materials systems in soft robotics.

YouTube video DOI [BibTex]

Rumley, E. H., Preninger, D., Shagan-Shomron, A., Rothemund, P., Hartmann, F., Baumgartner, M., Kellaris, N., Stojanovic, A., Yoder, Z., Karrer, B., Keplinger, C., Kaltenbrunner, M. Biodegradable Electrohydraulic Actuators for Sustainable Soft Robots Science Advances, 9(12), 2023, Ellen H. Rumley and David Preninger were co-first authors, and Christoph Keplinger and Martin Kaltenbrunner were shared corresponding authors. (article)

YouTube video DOI [BibTex]

A Soft, Fast and Versatile Electrohydraulic Gripper with Capacitive Object Size Detection
A Soft, Fast and Versatile Electrohydraulic Gripper with Capacitive Object Size Detection

Yoder, Z., Macari, D., Kleinwaks, G., Schmidt, I., Acome, E., Keplinger, C.

Advanced Functional Materials, 23(3):2209080, 2023 (article)

Abstract
Soft robotic grippers achieve increased versatility and reduced complexity through intelligence embodied in their flexible and conformal structures. The most widely used soft grippers are pneumatically driven; they are simple and effective but require bulky air compressors that limit their application space and external sensors or computationally expensive vision systems for pick verification. In this study, a multi-material architecture for self-sensing electrohydraulic bending actuators is presented that enables a new class of highly versatile and reconfigurable soft grippers that are electrically driven and feature capacitive pick verification and object size detection. These elec-trohydraulic grippers are fast (step input results in finger closure in 50 ms), draw low power (6.5 mW per finger to hold grasp), and can pick a wide variety of objects with simple binary electrical control. Integrated high-voltage driving electronics are presented that greatly increase the application space of the grippers and make them readily compatible with commercially available robotic arms.

A Soft, Fast and Versatile Electrohydraulic Gripper with Capacitive Object Size Detection YouTube video DOI [BibTex]

2022

Hydraulically Amplified Self-healing Electrostatic Transducers Harnessing Zipping Mechanism
Hydraulically Amplified Self-healing Electrostatic Transducers Harnessing Zipping Mechanism

Keplinger, C. M., Acome, E. L., Kellaris, N. A., Mitchell, S. K., Morrissey, T. G.

(US Patent 11486421B2), November 2022 (patent)

Abstract
Hydraulically-amplified, self-healing, electrostatic transducers that harness electrostatic and hydraulic forces to achieve various actuation modes. Electrostatic forces between electrode pairs of the transducers generated upon application of a voltage to the electrode pairs draws the electrodes in each pair towards each other to displace a liquid dielectric contained within an enclosed internal cavity of the transducers to drive actuation in various manners. The electrodes and the liquid dielectric form a self-healing capacitor whereby the liquid dielectric automatically fills breaches in the liquid dielectric resulting from dielectric breakdown. Due to the resting shape of the cavity, a zipping-mechanism allows for selectively actuating the electrodes to a desired extent by controlling the voltage supplied.

link (url) [BibTex]

2022

Keplinger, C. M., Acome, E. L., Kellaris, N. A., Mitchell, S. K., Morrissey, T. G. Hydraulically Amplified Self-healing Electrostatic Transducers Harnessing Zipping Mechanism (US Patent 11486421B2), November 2022 (patent)

link (url) [BibTex]

Hydraulically Amplified Self-Healing Electrostatic (HASEL) Pumps
Hydraulically Amplified Self-Healing Electrostatic (HASEL) Pumps

Mitchell, S. K., Acome, E. L., Keplinger, C. M.

(US Patent App. 17/635,339), October 2022 (patent)

Abstract
A pumping system includes a conduit with an inlet region and an outlet region and a first pump coupled with the conduit between the inlet region and the outlet region. The first pump includes a first actuator chamber configured to house at least a first actuator, a first pump chamber aligned along a longitudinal axis of the conduit, wherein the first pump chamber is in fluid communication with the inlet region and the outlet region, and a first flexible diaphragm separating the first actuator chamber from the first pump chamber. Methods for operating the pumping system are also disclosed.

link (url) [BibTex]

Mitchell, S. K., Acome, E. L., Keplinger, C. M. Hydraulically Amplified Self-Healing Electrostatic (HASEL) Pumps (US Patent App. 17/635,339), October 2022 (patent)

link (url) [BibTex]

Hydraulically Amplified Self-healing Electrostatic Actuators
Hydraulically Amplified Self-healing Electrostatic Actuators

Keplinger, C. M., Acome, E. L., Kellaris, N. A., Mitchell, S. K.

(US Patent 11408452), August 2022 (patent)

Abstract
An electro-hydraulic actuator includes a deformable shell defining an enclosed internal cavity and containing a liquid dielectric, first and second electrodes on first and second sides, respectively, of the enclosed internal cavity. An electrostatic force between the first and second electrodes upon application of a voltage to one of the electrodes draws the electrodes towards each other to displace the liquid dielectric within the enclosed internal cavity. The shell includes active and inactive areas such that the electrostatic forces between the first and second electrodes displaces the liquid dielectric within the enclosed internal cavity from the active area of the shell to the inactive area of the shell. The first and second electrodes, the deformable shell, and the liquid dielectric cooperate to form a self-healing capacitor, and the liquid dielectric is configured for automatically filling breaches in the liquid dielectric resulting from dielectric breakdown.

link (url) [BibTex]

Keplinger, C. M., Acome, E. L., Kellaris, N. A., Mitchell, S. K. Hydraulically Amplified Self-healing Electrostatic Actuators (US Patent 11408452), August 2022 (patent)

link (url) [BibTex]

A Pocket‐Sized Ten‐Channel High Voltage Power Supply for Soft Electrostatic Actuators
A Pocket‐Sized Ten‐Channel High Voltage Power Supply for Soft Electrostatic Actuators

Mitchell, S. K., Martin, T., Keplinger, C.

Advanced Materials Technologies, 7(8), August 2022 (article)

Abstract
As soft electrostatic actuators find applications in bio-inspired robotics, compact and lightweight high voltage electronics that independently address many actuators are required. Here, a pocket-sized, battery-powered, 10-channel high voltage power supply (HVPS) is presented, which independently addresses each channel up to 10 kV. The HVPS uses one HV amplifier to create a HV rail and each output connects to the rail via custom optocouplers that are pulse-width modulated to vary their conductance. These optocouplers distribute charges to and from electrostatic devices at each output, creating a charge-controlled driving scheme that can generate independent and nearly arbitrary actuation waveforms for each channel. The HVPS weighs 250 g and measures 8.4 cm × 13.3 cm × 2 cm, about the size of a smartphone. The HVPS is characterized when driving hydraulically amplified self-healing electrostatic (HASEL) actuators. While powering a 5 nF actuator, the output of the HVPS reaches 8 kV in 100 ms and drives a 1.5 nF actuator at 100 Hz (0 to 5.4 kV). The HVPS powers an active surface consisting of an array of HASELs and generates undulatory locomotion of a soft robotic inchworm, highlighting the potential for compact HV electronics that power multi-degree-of-freedom robotic systems based on electrostatic devices.

link (url) DOI [BibTex]

Mitchell, S. K., Martin, T., Keplinger, C. A Pocket‐Sized Ten‐Channel High Voltage Power Supply for Soft Electrostatic Actuators Advanced Materials Technologies, 7(8), August 2022 (article)

link (url) DOI [BibTex]

Composite Layering of Hydraulically Amplified Self-Healing Electrostatic Transducers
Composite Layering of Hydraulically Amplified Self-Healing Electrostatic Transducers

Keplinger, C. M., Mitchell, S. K., Kellaris, N. A., Rothemund, P.

(US Patent App. 17436455), May 2022 (patent)

Abstract
A hydraulically amplified self-healing electrostatic (HASEL) transducer includes a composite, multi-layered structure. In an example, a HASEL transducer includes a dielectric layer including at least one fluid dielectric layer. The dielectric layer includes a first side and a second side opposing the first side. The HASEL transducer further includes a first electrode disposed at the first side of the dielectric layer, a second electrode disposed at the second side of the dielectric layer, a first outer layer disposed at the first electrode opposite the dielectric layer, and a second outer layer disposed at the second electrode opposite the dielectric layer. The first outer layer and second outer layer exhibit different mechanical and electrical properties from the dielectric layer.

link (url) [BibTex]

Electro-hydraulic Rolling Soft Wheel: Design, Hybrid Dynamic Modeling, and Model Predictive Control
Electro-hydraulic Rolling Soft Wheel: Design, Hybrid Dynamic Modeling, and Model Predictive Control

Ly, K., Mayekar, J. V., Aguasvivas, S., Keplinger, C., Rentschler, M. E., Correll, N.

IEEE Transactions on Robotics, 38(5):3044-3063, IEEE, May 2022 (article)

Abstract
Locomotion through rolling is attractive compared to other forms of locomotion thanks to uniform designs, high degree of mobility, dynamic stability, and self-recovery from collision. Despite previous efforts to design rolling soft systems, pneumatic and other soft actuators are often limited in terms of high-speed dynamics, system integration, and/or functionalities. Furthermore, mathematical description of the rolling dynamics for this type of robot and how the models can be used for speed control are often not mentioned. This article introduces a cylindrical-shaped shell-bulging rolling soft wheel that employs an array of 16 folded-HASEL actuators as a mean for improved rolling performance. The actuators represent the soft components with discrete forces that propel the wheel, whereas the wheel's frame is rigid but allows for smooth, continuous change in position and speed. We discuss the interplay between the electrical and mechanical design choices, the modeling of the wheel's hybrid (continuous and discrete) dynamic behavior, and the implementation of a model predictive controller (MPC) for the robot's speed. With the balance of several design factors, we show the wheel's ability to carry integrated hardware with a maximum rolling speed at 0.7 m/s (or 2.2 body lengths per second), despite its total weight of 979 g, allowing the wheel to outperform the existing rolling soft wheels with comparable weights and sizes. We also show that the MPC enables the wheel to accelerate and leverage its inherent braking capability to reach desired speeds—a critical function that did not exist in previous rolling soft systems.

link (url) DOI [BibTex]

Ly, K., Mayekar, J. V., Aguasvivas, S., Keplinger, C., Rentschler, M. E., Correll, N. Electro-hydraulic Rolling Soft Wheel: Design, Hybrid Dynamic Modeling, and Model Predictive Control IEEE Transactions on Robotics, 38(5):3044-3063, IEEE, May 2022 (article)

link (url) DOI [BibTex]

Simulating Electrohydraulic Soft Actuator Assemblies Via Reduced Order Modeling
Simulating Electrohydraulic Soft Actuator Assemblies Via Reduced Order Modeling

Hainsworth, T., Schmidt, I., Sundaram, V., Whiting, G. L., Keplinger, C., MacCurdy, R.

SOFT ROBOTICS. IEEE INTERNATIONAL CONFERENCE. 5TH 2022. (RoboSoft 2022), pages: 21-28, Institute of Electrical and Electronics Engineers (IEEE), 2022 IEEE 5th International Conference on Soft Robotics (RoboSoft), April 2022 (conference)

Abstract
Soft robots compliment traditional rigid robots by expanding their capabilities to interact with the physical world. A robot made with compliant, soft materials can benefit from their inherent continuum mechanics to achieve interactions with the environment that a rigid robot may find difficult. This can include grasping delicate objects, navigating through variable terrain, or working alongside humans in a safer manner. The flexible, adaptable nature of soft robots provide these benefits, but they also make predicting their actuated response a difficult, computationally-intensive task. Here we provide a non-linear, reduced order model informed by collected data on hydraulically amplified self-healing electrostatic actuators (HASELs). With this reduced order model, we simulate robots comprised of multiple actuators in an effort to rapidly evaluate potential design candidates without the need for time-consuming manufacturing. The simulation leverages a reduced-order model of HASELs based on a parallel mass spring damper (MSD) representation, made of two non-linear springs, and a damper; this data-driven parameter identification aids model fidelity. We construct a robotic manipulator actuated via six HASELs and show that the simulations driven by the non-linear MSD models accurately predict the robot's physical behavior on a macro scale. While this work focuses on a specific actuator type, the approach shown here could be extended to other linearly expanding soft actuators. Using this method, soft robotic assemblies actuated via HASELs can be rapidly evaluated in simulation before a laborious manufacturing process, which in turn will allow for faster design iterations to create more effective robots.

link (url) DOI [BibTex]

Hainsworth, T., Schmidt, I., Sundaram, V., Whiting, G. L., Keplinger, C., MacCurdy, R. Simulating Electrohydraulic Soft Actuator Assemblies Via Reduced Order Modeling SOFT ROBOTICS. IEEE INTERNATIONAL CONFERENCE. 5TH 2022. (RoboSoft 2022), pages: 21-28, Institute of Electrical and Electronics Engineers (IEEE), 2022 IEEE 5th International Conference on Soft Robotics (RoboSoft), April 2022 (conference)

link (url) DOI [BibTex]

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Towards Enduring Autonomous Robots via Embodied Energy

Aubin, C. A., Gorissen, B., Milana, E., Buskohl, P. R., Lazarus, N., Slipher, G. A., Keplinger, C., Bongard, J., Iida, F., Lewis, J. A., Shepherd, R. F.

Nature, 602(7897):393-402, 2022 (article)

Abstract
Autonomous robots are comprised of actuation, energy, sensory, and control systems built from materials and structures that are not necessarily designed and integrated for multifunctionality. Yet, animals and other organisms that robots strive to emulate contain highly sophisticated and interconnected systems at all organizational levels, which allow multiple functions to be performed simultaneously. Herein, we examine how system integration and multifunctionality in nature inspires a new paradigm for autonomous robots that we call Embodied Energy. Currently, most untethered robots use batteries to store energy and power their operation. To extend operating times, additional battery blocks and supporting structures must be added, which increases weight and reduces efficiency. Recent advancements in energy storage techniques enable chemical or electrical energy sources to be embodied directly within the structures, materials, and mechanical systems used to create robots. This perspective highlights emerging examples of Embodied Energy, focusing on the design and fabrication principles of enduring autonomous robots.

DOI [BibTex]

Aubin, C. A., Gorissen, B., Milana, E., Buskohl, P. R., Lazarus, N., Slipher, G. A., Keplinger, C., Bongard, J., Iida, F., Lewis, J. A., Shepherd, R. F. Towards Enduring Autonomous Robots via Embodied Energy Nature, 602(7897):393-402, 2022 (article)

DOI [BibTex]

2021

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Miniaturized Circuitry for Capacitive Self-sensing and Closed-loop Control of Soft Electrostatic Transducers

Ly, K., Kellaris, N., McMorris, D., Johnson, B. K., Acome, E., Sundaram, V., Naris, M., Humbert, J. S., Rentschler, M. E., Keplinger, C., Correll, N.

Soft Robotics, 8(6):673-686, Mary Ann Liebert, Inc., publishers, December 2021 (article)

Abstract
Soft robotics is a field of robotic system design characterized by materials and structures that exhibit large-scale deformation, high compliance, and rich multifunctionality. The incorporation of soft and deformable structures endows soft robotic systems with the compliance and resiliency that makes them well adapted for unstructured and dynamic environments. Although actuation mechanisms for soft robots vary widely, soft electrostatic transducers such as dielectric elastomer actuators (DEAs) and hydraulically amplified self-healing electrostatic (HASEL) actuators have demonstrated promise due to their muscle-like performance and capacitive self-sensing capabilities. Despite previous efforts to implement self-sensing in electrostatic transducers by overlaying sinusoidal low-voltage signals, these designs still require sensing high-voltage signals, requiring bulky components that prevent integration with miniature untethered soft robots. We present a circuit design that eliminates the need for any high-voltage sensing components, thereby facilitating the design of simple low cost circuits using off-the-shelf components. Using this circuit, we perform simultaneous sensing and actuation for a range of electrostatic transducers including circular DEAs and HASEL actuators and demonstrate accurate estimated displacements with errors <4%. We further develop this circuit into a compact and portable system that couples high voltage actuation, sensing, and computation as a prototype toward untethered multifunctional soft robotic systems. Finally, we demonstrate the capabilities of our self-sensing design through feedback control of a robotic arm powered by Peano-HASEL actuators.

link (url) DOI [BibTex]

2021

Ly, K., Kellaris, N., McMorris, D., Johnson, B. K., Acome, E., Sundaram, V., Naris, M., Humbert, J. S., Rentschler, M. E., Keplinger, C., Correll, N. Miniaturized Circuitry for Capacitive Self-sensing and Closed-loop Control of Soft Electrostatic Transducers Soft Robotics, 8(6):673-686, Mary Ann Liebert, Inc., publishers, December 2021 (article)

link (url) DOI [BibTex]

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Flexible Seaweed-Like Triboelectric Nanogenerator as a Wave Energy Harvester Powering Marine Internet of Things

Wang, Y., Liu, X., Wang, Y., Wang, H., Wang, H., Zhang, S. L., Zhao, T., Xu, M., Wang, Z. L.

ACS Nano, 15(10):15700-15709, October 2021 (article)

DOI [BibTex]

Wang, Y., Liu, X., Wang, Y., Wang, H., Wang, H., Zhang, S. L., Zhao, T., Xu, M., Wang, Z. L. Flexible Seaweed-Like Triboelectric Nanogenerator as a Wave Energy Harvester Powering Marine Internet of Things ACS Nano, 15(10):15700-15709, October 2021 (article)

DOI [BibTex]

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Electriflow: Augmenting Books With Tangible Animation Using Soft Electrohydraulic Actuators

Purnendu, , Novack, S., Acome, E., Alistar, M., Keplinger, C., Gross, M. D., Bruns, C., Leithinger, D.

In ACM SIGGRAPH 2021 Labs, pages: 1-2, Association for Computing Machinery, SIGGRAPH 2021, August 2021 (inbook)

Abstract
We present Electriflow: a method of augmenting books with tangible animation employing soft electrohydraulic actuators. These actuators are compact, silent and fast in operation, and can be fabricated with commodity materials. They generate an immediate hydraulic force upon electrostatic activation without an external fluid supply source, enabling a simple and self-contained design. Electriflow actuators produce an immediate shape transition from flat to folded state which enabled their seamless integration into books. For the Emerging Technologies exhibit, we will demonstrate the prototype of a book augmented with the capability of tangible animation.

Supplemental Material link (url) DOI [BibTex]

Purnendu, , Novack, S., Acome, E., Alistar, M., Keplinger, C., Gross, M. D., Bruns, C., Leithinger, D. Electriflow: Augmenting Books With Tangible Animation Using Soft Electrohydraulic Actuators In ACM SIGGRAPH 2021 Labs, pages: 1-2, Association for Computing Machinery, SIGGRAPH 2021, August 2021 (inbook)

Supplemental Material link (url) DOI [BibTex]

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Electriflow: Augmenting Books With Tangible Animation Using Soft Electrohydraulic Actuators

Purnendu, , Novack, S., Acome, E., Alistar, M., Keplinger, C., Gross, M. D., Bruns, C., Leithinger, D.

In SIGGRAPH ’21: ACM SIGGRAPH 2021 Labs, pages: 8, ACM, New York, NY, Special Interest Group on Computer Graphics and Interactive Techniques Conference (SIGGRAPH 2021), July 2021 (inproceedings)

Abstract
We present Electriflow: a method of augmenting books with tangible animation employing soft electrohydraulic actuators. These actuators are compact, silent and fast in operation, and can be fabricated with commodity materials. They generate an immediate hydraulic force upon electrostatic activation without an external fluid supply source, enabling a simple and self-contained design. Electriflow actuators produce an immediate shape transition from flat to folded state which enabled their seamless integration into books. For the Emerging Technologies exhibit, we will demonstrate the prototype of a book augmented with the capability of tangible animation.

link (url) DOI [BibTex]

Purnendu, , Novack, S., Acome, E., Alistar, M., Keplinger, C., Gross, M. D., Bruns, C., Leithinger, D. Electriflow: Augmenting Books With Tangible Animation Using Soft Electrohydraulic Actuators In SIGGRAPH ’21: ACM SIGGRAPH 2021 Labs, pages: 8, ACM, New York, NY, Special Interest Group on Computer Graphics and Interactive Techniques Conference (SIGGRAPH 2021), July 2021 (inproceedings)

link (url) DOI [BibTex]

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Electriflow: Soft Electrohydraulic Building Blocks for Prototyping Shape-changing Interfaces

Purnendu, , Novack, S. M., Acome, E., Keplinger, C., Alistar, M., Gross, M. D., Bruns, C., Leithinger, D.

In DIS ’21: Designing Interactive Systems Conference 2021, pages: 1280-1290, ACM, New York, NY, Designing Interactive Systems Conference (DIS 2021), June 2021 (inproceedings)

Abstract
We present Electriflow: a new class of soft electrohydraulic actuators as building blocks for prototyping shape-changing interfaces. These actuators are silent and fast in operation and can be fabricated with commodity materials. Electriflow generates an immediate hydraulic force upon electrostatic activation without an external fluid supply source, enabling a simple and compact self-contained design. This paper describes the materials and mechanisms of these shape-changing building blocks, as well as the underlying fabrication process, which includes a software tool that assists in their design, shape visualization and construction. Finally, we explore four classes of application prototypes: tangible animation, actuating origami creases, shape-changing phone, and shape-changing bowl.

link (url) DOI [BibTex]

Purnendu, , Novack, S. M., Acome, E., Keplinger, C., Alistar, M., Gross, M. D., Bruns, C., Leithinger, D. Electriflow: Soft Electrohydraulic Building Blocks for Prototyping Shape-changing Interfaces In DIS ’21: Designing Interactive Systems Conference 2021, pages: 1280-1290, ACM, New York, NY, Designing Interactive Systems Conference (DIS 2021), June 2021 (inproceedings)

link (url) DOI [BibTex]

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Soft Electrohydraulic Actuators for Origami Inspired Shape-Changing Interfaces

Purnendu, , Acome, E., Keplinger, C., Gross, M. D., Bruns, C., Leithinger, D.

In CHI EA ’21: Extended Abstracts of the 2021 CHI Conference on Human Factors in Computing Systems, pages: 377, ACM, New York, NY, Conference on Human Factors in Computing Systems (CHI 2021), May 2021 (inproceedings)

Abstract
In this paper, we present electrohydraulic actuators for origami inspired shape-changing interfaces, which are capable of producing sharp hinge-like bends. These compliant actuators generate an immediate hydraulic force upon electrostatic activation without an external fluid supply source, are silent and fast in operation, and can be fabricated with commodity materials. We experimentally investigate the characteristics of these actuators and present application scenarios for actuating existing objects as well as origami folds. In addition, we present a software tool for the design and fabrication of shape-changing interfaces using these electrohydraulic actuators. We also discuss how this work opens avenues for other possible applications in Human Computer Interaction (HCI).

link (url) DOI [BibTex]

Purnendu, , Acome, E., Keplinger, C., Gross, M. D., Bruns, C., Leithinger, D. Soft Electrohydraulic Actuators for Origami Inspired Shape-Changing Interfaces In CHI EA ’21: Extended Abstracts of the 2021 CHI Conference on Human Factors in Computing Systems, pages: 377, ACM, New York, NY, Conference on Human Factors in Computing Systems (CHI 2021), May 2021 (inproceedings)

link (url) DOI [BibTex]

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Hydraulically amplified self-healing electrostatic actuators

Keplinger, C. M., Acome, E. L., Kellaris, N. A., Mitchell, S. K.

(US Patent 10995779), May 2021 (patent)

Abstract
Hydraulically-amplified, self-healing, electrostatic actuators that harness electrostatic and hydraulic forces to achieve various actuation modes. Electrostatic forces between electrode pairs of the actuators generated upon application of a voltage to the electrode pairs draws the electrodes in each pair towards each other to displace a liquid dielectric contained within an enclosed internal cavity of the actuators to drive actuation in various manners. The electrodes and the liquid dielectric form a self-healing capacitor whereby the liquid dielectric automatically fills breaches in the liquid dielectric resulting from dielectric breakdown.

link (url) [BibTex]

Keplinger, C. M., Acome, E. L., Kellaris, N. A., Mitchell, S. K. Hydraulically amplified self-healing electrostatic actuators (US Patent 10995779), May 2021 (patent)

link (url) [BibTex]

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Hydraulically Amplified Self-Healing Electrostatic Transducers Harnessing Zipping Mechanism

Keplinger, C. M., Acome, E. L., Kellaris, N. A., Mitchell, S. K., Morrissey, T. G.

(US Patent 20210003149A1), January 2021 (patent)

Abstract
Hydraulically-amplified, self-healing, electrostatic transducers that harness electrostatic and hydraulic forces to achieve various actuation modes. Electrostatic forces between electrode pairs of the transducers generated upon application of a voltage to the electrode pairs draws the electrodes in each pair towards each other to displace a liquid dielectric contained within an enclosed internal cavity of the transducers to drive actuation in various manners. The electrodes and the liquid dielectric form a self-healing capacitor whereby the liquid dielectric automatically fills breaches in the liquid dielectric resulting from dielectric breakdown. Due to the resting shape of the cavity, a zipping-mechanism allows for selectively actuating the electrodes to a desired extent by controlling the voltage supplied.

link (url) [BibTex]

Keplinger, C. M., Acome, E. L., Kellaris, N. A., Mitchell, S. K., Morrissey, T. G. Hydraulically Amplified Self-Healing Electrostatic Transducers Harnessing Zipping Mechanism (US Patent 20210003149A1), January 2021 (patent)

link (url) [BibTex]

HASEL Artificial Muscles for a New Generation of Lifelike Robots—Recent Progress and Future Opportunities
HASEL Artificial Muscles for a New Generation of Lifelike Robots—Recent Progress and Future Opportunities

Rothemund, P., Kellaris, N., Mitchell, S. K., Acome, E., Keplinger, C.

Advanced Materials, 33(19):2003375, 2021, Nicholas Kellaris, Shane K. Mitchell, and Eric Acome contributed equally to this publication. (article)

Abstract
Future robots and intelligent systems will autonomously navigate in unstructured environments and closely collaborate with humans; integrated with our bodies and minds, they will allow us to surpass our physical limitations. Traditional robots are mostly built from rigid, metallic components and electromagnetic motors, which make them heavy, expensive, unsafe near people, and ill-suited for unpredictable environments. By contrast, biological organisms make extensive use of soft materials and radically outperform robots in terms of dexterity, agility, and adaptability. Particularly, natural muscle—a masterpiece of evolution—has long inspired researchers to create “artificial muscles” in an attempt to replicate its versatility, seamless integration with sensing, and ability to self-heal. To date, natural muscle remains unmatched in all-round performance, but rapid advancements in soft robotics have brought viable alternatives closer than ever. Herein, the recent development of hydraulically amplified self-healing electrostatic (HASEL) actuators, a new class of high-performance, self-sensing artificial muscles that couple electrostatic and hydraulic forces to achieve diverse modes of actuation, is discussed; current designs match or exceed natural muscle in many metrics. Research on materials, designs, fabrication, modeling, and control systems for HASEL actuators is detailed. In each area, research opportunities are identified, which together lays out a roadmap for actuators with drastically improved performance. With their unique versatility and wide potential for further improvement, HASEL actuators are poised to play an important role in a paradigm shift that fundamentally challenges the current limitations of robotic hardware toward future intelligent systems that replicate the vast capabilities of biological organisms.

DOI [BibTex]

Rothemund, P., Kellaris, N., Mitchell, S. K., Acome, E., Keplinger, C. HASEL Artificial Muscles for a New Generation of Lifelike Robots—Recent Progress and Future Opportunities Advanced Materials, 33(19):2003375, 2021, Nicholas Kellaris, Shane K. Mitchell, and Eric Acome contributed equally to this publication. (article)

DOI [BibTex]

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A Triboelectric-Nanogenerator-Based Gas–Solid Two-Phase Flow Sensor for Pneumatic Conveying System Detecting

Wang, Y., Liu, D., Hu, Z., Chen, T., Zhang, Z., Wang, H., Du, T., Zhang, S. L., Zhao, Z., Zhou, T., Xu, M.

Advanced Materials Technologies, 6(5):2001270, 2021 (article)

DOI [BibTex]

Wang, Y., Liu, D., Hu, Z., Chen, T., Zhang, Z., Wang, H., Du, T., Zhang, S. L., Zhao, Z., Zhou, T., Xu, M. A Triboelectric-Nanogenerator-Based Gas–Solid Two-Phase Flow Sensor for Pneumatic Conveying System Detecting Advanced Materials Technologies, 6(5):2001270, 2021 (article)

DOI [BibTex]

Shaping the future of robotics through materials innovation
Shaping the future of robotics through materials innovation

Rothemund, P., Kim, Y., Heisser, R. H., Zhao, X., Shepherd, R. F., Keplinger, C.

Nature Materials, 20(12):1582-1587, 2021 (article)

Abstract
New classes of functional soft materials show promise to revolutionize robotics. Now materials scientists must focus on realizing the predicted performance of these materials and developing effective and robust interfaces to integrate them into highly functional robotic systems that have a positive impact on human life.

link (url) DOI [BibTex]

Rothemund, P., Kim, Y., Heisser, R. H., Zhao, X., Shepherd, R. F., Keplinger, C. Shaping the future of robotics through materials innovation Nature Materials, 20(12):1582-1587, 2021 (article)

link (url) DOI [BibTex]

Spider-Inspired Electrohydraulic Actuators for Fast, Soft-Actuated Joints
Spider-Inspired Electrohydraulic Actuators for Fast, Soft-Actuated Joints

Kellaris, N., Rothemund, P., Zeng, Y., Mitchell, S. K., Smith, G. M., Jayaram, K., Keplinger, C.

Advanced Science, 8(14):2100916, 2021 (article)

Abstract
The impressive locomotion and manipulation capabilities of spiders have led to a host of bioinspired robotic designs aiming to reproduce their functionalities; however, current actuation mechanisms are deficient in either speed, force output, displacement, or efficiency. Here—using inspiration from the hydraulic mechanism used in spider legs—soft-actuated joints are developed that use electrostatic forces to locally pressurize a hydraulic fluid, and cause flexion of a segmented structure. The result is a lightweight, low-profile articulating mechanism capable of fast operation, high forces, and large displacement; these devices are termed spider-inspired electrohydraulic soft-actuated (SES) joints. SES joints with rotation angles up to 70°, blocked torques up to 70 mN m, and specific torques up to 21 N m / kg are demonstrated. SES joints demonstrate high speed operation, with measured roll-off frequencies up to 24 Hz and specific power as high as 230 W/kg—similar to human muscle. The versatility of these devices is illustrated by combining SES joints to create a bidirectional joint, an artificial limb with independently addressable joints, and a compliant gripper. The lightweight, low-profile design, and high performance of these devices, makes them well-suited toward the development of articulating robotic systems that can rapidly maneuver.

DOI Project Page [BibTex]

Kellaris, N., Rothemund, P., Zeng, Y., Mitchell, S. K., Smith, G. M., Jayaram, K., Keplinger, C. Spider-Inspired Electrohydraulic Actuators for Fast, Soft-Actuated Joints Advanced Science, 8(14):2100916, 2021 (article)

DOI Project Page [BibTex]

Electromechanics of Planar {HASEL} Actuators
Electromechanics of Planar HASEL Actuators

Kirkman, S., Rothemund, P., Acome, E., Keplinger, C.

Extreme Mechanics Letters, 48, pages: 101408, 2021 (article)

DOI Project Page [BibTex]

Kirkman, S., Rothemund, P., Acome, E., Keplinger, C. Electromechanics of Planar HASEL Actuators Extreme Mechanics Letters, 48, pages: 101408, 2021 (article)

DOI Project Page [BibTex]

Liquid Crystal Elastomers with Enhanced Directional Actuation to Electric Fields
Liquid Crystal Elastomers with Enhanced Directional Actuation to Electric Fields

Fowler, H. E., Rothemund, P., Keplinger, C., White, T. J.

Advanced Materials, 33(43):2103806, 2021 (article)

Abstract
The integration of soft, stimuli-responsive materials in robotic systems is a promising approach to introduce dexterous and delicate manipulation of objects. Electrical control of mechanical response offers many benefits in robotic systems including the availability of this energy input, the associated response time, magnitude of actuation, and opportunity for self-regulation. Here, a materials chemistry is detailed to prepare liquid crystal elastomers (LCEs) with a 14:1 modulus contrast and increase in dielectric constant to enhance electromechanical deformation. The inherent modulus contrast of these LCEs (when coated with compliant electrodes) directly convert an electric field to a directional expansion of 20%. The electromechanical response of LCE actuators is observed upon application of voltage ranging from 0.5 to 6 kV. The deformation of these materials is rapid, reaching strain rates of 18% s−1. Upon removal of the electric field, little hysteresis is observed. Patterning the spatial orientation of the nematic director of the LCEs results in a 2D–3D shape transformation to a cone 8 mm in height. Individual and sequential addressing of an array of LCE actuators is demonstrated as a haptic surface.

DOI Project Page [BibTex]

Fowler, H. E., Rothemund, P., Keplinger, C., White, T. J. Liquid Crystal Elastomers with Enhanced Directional Actuation to Electric Fields Advanced Materials, 33(43):2103806, 2021 (article)

DOI Project Page [BibTex]

Scientific Report 2016 - 2021
Scientific Report 2016 - 2021
2021 (mpi_year_book)

Abstract
This report presents research done at the Max Planck Institute for Intelligent Systems from January2016 to November 2021. It is our fourth report since the founding of the institute in 2011. Dueto the fact that the upcoming evaluation is an extended one, the report covers a longer reportingperiod.This scientific report is organized as follows: we begin with an overview of the institute, includingan outline of its structure, an introduction of our latest research departments, and a presentationof our main collaborative initiatives and activities (Chapter1). The central part of the scientificreport consists of chapters on the research conducted by the institute’s departments (Chapters2to6) and its independent research groups (Chapters7 to24), as well as the work of the institute’scentral scientific facilities (Chapter25). For entities founded after January 2016, the respectivereport sections cover work done from the date of the establishment of the department, group, orfacility. These chapters are followed by a summary of selected outreach activities and scientificevents hosted by the institute (Chapter26). The scientific publications of the featured departmentsand research groups published during the 6-year review period complete this scientific report.

Scientific Report 2016 - 2021 [BibTex]

2020

Design of a High-Speed Prosthetic Finger Driven by Peano-HASEL Actuators
Design of a High-Speed Prosthetic Finger Driven by Peano-HASEL Actuators

Yoder, Z., Kellaris, N., Chase-Markopoulou, C., Ricken, D., Mitchell, S. K., Emmett, M. B., Segil, J., Keplinger, C.

Frontiers in Robotics and AI, 7, pages: 586216, Frontiers, November 2020 (article)

Abstract
Current designs of powered prosthetic limbs are limited by the nearly exclusive use of DC motor technology. Soft actuators promise new design freedom to create prosthetic limbs which more closely mimic intact neuromuscular systems and improve the capabilities of prosthetic users. This work evaluates the performance of a hydraulically amplified self-healing electrostatic (HASEL) soft actuator for use in a prosthetic hand. We compare a linearly-contracting HASEL actuator, termed a Peano-HASEL, to an existing actuator (DC motor) when driving a prosthetic finger like those utilized in multi-functional prosthetic hands. A kinematic model of the prosthetic finger is developed and validated, and is used to customize a prosthetic finger that is tuned to complement the force-strain characteristics of the Peano-HASEL actuators. An analytical model is used to inform the design of an improved Peano-HASEL actuator with the goal of increasing the fingertip pinch force of the prosthetic finger. When compared to a weight-matched DC motor actuator, the Peano-HASEL and custom finger is 10.6 times faster, has 11.1 times higher bandwidth, and consumes 8.7 times less electrical energy to grasp. It reaches 91% of the maximum range of motion of the original finger. However, the DC motor actuator produces 10 times the fingertip force at a relevant grip position. In this body of work, we present ways to further increase the force output of the Peano-HASEL driven prosthetic finger system, and discuss the significance of the unique properties of Peano-HASELs when applied to the field of upper-limb prosthetic design. This approach toward clinically-relevant actuator performance paired with a substantially different form-factor compared to DC motors presents new opportunities to advance the field of prosthetic limb design.

link (url) DOI [BibTex]

2020

Yoder, Z., Kellaris, N., Chase-Markopoulou, C., Ricken, D., Mitchell, S. K., Emmett, M. B., Segil, J., Keplinger, C. Design of a High-Speed Prosthetic Finger Driven by Peano-HASEL Actuators Frontiers in Robotics and AI, 7, pages: 586216, Frontiers, November 2020 (article)

link (url) DOI [BibTex]

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Miniaturized circuitry for capacitive self-sensing and closed-loop control of soft electrostatic transducers

Ly, K., Kellaris, N., McMorris, D., Johnson, B. K., Acome, E., Sundaram, V., Naris, M., Humbert, J. S., Rentschler, M. E., Keplinger, C., Correll, N.

Soft Robotics, Mary Ann Liebert, Inc., publishers, October 2020 (article)

Abstract
Soft robotics is a field of robotic system design characterized by materials and structures that exhibit large-scale deformation, high compliance, and rich multifunctionality. The incorporation of soft and deformable structures endows soft robotic systems with the compliance and resiliency that makes them well adapted for unstructured and dynamic environments. Although actuation mechanisms for soft robots vary widely, soft electrostatic transducers such as dielectric elastomer actuators (DEAs) and hydraulically amplified self-healing electrostatic (HASEL) actuators have demonstrated promise due to their muscle-like performance and capacitive self-sensing capabilities. Despite previous efforts to implement self-sensing in electrostatic transducers by overlaying sinusoidal low-voltage signals, these designs still require sensing high-voltage signals, requiring bulky components that prevent integration with miniature untethered soft robots. We present a circuit design that eliminates the need for any high-voltage sensing components, thereby facilitating the design of simple low cost circuits using off-the-shelf components. Using this circuit, we perform simultaneous sensing and actuation for a range of electrostatic transducers including circular DEAs and HASEL actuators and demonstrate accurate estimated displacements with errors <4%. We further develop this circuit into a compact and portable system that couples high voltage actuation, sensing, and computation as a prototype toward untethered multifunctional soft robotic systems. Finally, we demonstrate the capabilities of our self-sensing design through feedback control of a robotic arm powered by Peano-HASEL actuators.

link (url) DOI [BibTex]

Ly, K., Kellaris, N., McMorris, D., Johnson, B. K., Acome, E., Sundaram, V., Naris, M., Humbert, J. S., Rentschler, M. E., Keplinger, C., Correll, N. Miniaturized circuitry for capacitive self-sensing and closed-loop control of soft electrostatic transducers Soft Robotics, Mary Ann Liebert, Inc., publishers, October 2020 (article)

link (url) DOI [BibTex]

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Rapid 3D Printing of Electrohydraulic (HASEL) Tentacle Actuators

O’Neill, M. R., Acome, E., Bakarich, S., Mitchell, S. K., Timko, J., Keplinger, C., Shepherd, R. F.

Advanced Functional Materials, 30(40):2005244, August 2020 (article)

Abstract
A comprehensive material system is introduced for the additive manufacturing of electrohydraulic (HASEL) tentacle actuators. This material system consists of a photo-curable, elastomeric silicone-urethane with relatively strong dielectric properties (εr ≈ 8.8 at 1 kHz) in combination with ionically-conductive hydrogel and silver paint electrodes that displace a vegetable-based liquid dielectric under the application of an electric field. The electronic properties of the silicone material as well as the mechanical properties of the constitutive silicone and hydrogel materials are investigated. The hydraulic pressure exerted on the dielectric working fluid in these capacitive actuators is measured in order to characterize their quasi-static behavior. Various design features enabled by 3D printing influence this behavior—decreasing the voltage at which actuation begins or increasing the force density in the system. Using a capacitance change of >35% across the actuators while powered, a demonstration of self-sensing inherent to HASELs is shown. Antagonistic pairs of the 3D printed actuators are shown to exert a blocked force of over 400 mN. An electrohydraulic tentacle actuator is then fabricated to demonstrate the use of this material and actuation system in a synthetic hydrostat. This tentacle actuator is shown to achieve motion in a multi-dimensional space.

link (url) DOI [BibTex]

O’Neill, M. R., Acome, E., Bakarich, S., Mitchell, S. K., Timko, J., Keplinger, C., Shepherd, R. F. Rapid 3D Printing of Electrohydraulic (HASEL) Tentacle Actuators Advanced Functional Materials, 30(40):2005244, August 2020 (article)

link (url) DOI [BibTex]

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A Lesson from Plants: High‐Speed Soft Robotic Actuators

Baumgartner, R., Kogler, A., Stadlbauer, J. M., Foo, C. C., Kaltseis, R., Baumgartner, M., Mao, G., Keplinger, C., Koh, S. J. A., Arnold, N., Suo, Z., Kaltenbrunner, M., Bauer, S.

Advanced Materials, 7(5):1903391, March 2020 (article)

Abstract
Rapid energy-efficient movements are one of nature's greatest developments. Mechanisms like snap-buckling allow plants like the Venus flytrap to close the terminal lobes of their leaves at barely perceptible speed. Here, a soft balloon actuator is presented, which is inspired by such mechanical instabilities and creates safe, giant, and fast deformations. The basic design comprises two inflated elastomer membranes pneumatically coupled by a pressurized chamber of suitable volume. The high-speed actuation of a rubber balloon in a state close to the verge of mechanical instability is remotely triggered by a voltage-controlled dielectric elastomer membrane. This method spatially separates electrically active and passive parts, and thereby averts electrical breakdown resulting from the drastic thinning of an electroactive membrane during large expansion. Bistable operation with small and large volumes of the rubber balloon is demonstrated, achieving large volume changes of 1398% and a high-speed area change rate of 2600 cm2 s−1. The presented combination of fast response time with large deformation and safe handling are central aspects for a new generation of soft bio-inspired robots and can help pave the way for applications ranging from haptic displays to soft grippers and high-speed sorting machines.

link (url) DOI [BibTex]

Baumgartner, R., Kogler, A., Stadlbauer, J. M., Foo, C. C., Kaltseis, R., Baumgartner, M., Mao, G., Keplinger, C., Koh, S. J. A., Arnold, N., Suo, Z., Kaltenbrunner, M., Bauer, S. A Lesson from Plants: High‐Speed Soft Robotic Actuators Advanced Materials, 7(5):1903391, March 2020 (article)

link (url) DOI [BibTex]

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Identification and Control of a Nonlinear Soft Actuator and Sensor System

Johnson, B. K., Sundaram, V., Naris, M., Acome, E., Ly, K., Correll, N., Keplinger, C., Humbert, J. S., Rentschler, M. E.

IEEE Robotics and Automation Letters, 5(3):3783-3790, March 2020 (article)

Abstract
Soft robots are becoming increasingly prevalent, with unique applications to medical devices and wearable technology. Understanding the dynamics of nonlinear soft actuators is crucial to creating controllable soft robots. this letter presents a system identification process and closed-loop control of foldable HASEL (hydraulically amplified self-healing electrostatic) soft actuators. We characterized foldable HASELs with linear frequency response tests and modeled them using a linear superposition of static and dynamic terms. We also identified two responses of the system: an activation and relaxation response. Based on these two responses, we developed a dual-mode controller which was validated through closed-loop control using a capacitive elastomeric strain sensor wrapped around the actuator. Using this integrated sensor, we achieved step response rise times as fast as 0.025 s and settling times as fast as 0.17 s while under load. These system identification and control techniques can be applied to any HASEL-driven soft robot and could be applied to other soft actuators to enable controllable soft robots.

link (url) DOI [BibTex]

Johnson, B. K., Sundaram, V., Naris, M., Acome, E., Ly, K., Correll, N., Keplinger, C., Humbert, J. S., Rentschler, M. E. Identification and Control of a Nonlinear Soft Actuator and Sensor System IEEE Robotics and Automation Letters, 5(3):3783-3790, March 2020 (article)

link (url) DOI [BibTex]

High-Strain Peano-HASEL Actuators
High-Strain Peano-HASEL Actuators

Wang, X., Mitchell, S. K., Rumley, E. H., Rothemund, P., Keplinger, C.

Advanced Functional Materials, 30(7):1908821, 2020 (article)

Abstract
Soft robots are intrinsically safe for use near humans and adaptable when operated in unstructured environments, thereby offering capabilities beyond traditional robots based on rigid components. Soft actuators are key components of soft robots; recently developed hydraulically amplified self-healing electrostatic (HASEL) actuators provide a versatile framework to create high-speed actuators with excellent all-around performance. Peano-HASEL actuators linearly contract upon application of voltage, closely mimicking the behavior of muscle. Peano-HASEL actuators, however, produce a maximum strain of ≈15%, while skeletal muscles achieve ≈20% on average. Here, a new type of HASEL is introduced, termed high-strain Peano-HASEL (HS-Peano-HASEL) actuator, that achieves linear contraction up to ≈24%. A wide range of performance metrics are investigated, and the maximum strain of multiunit HS-Peano-HASEL actuators is optimized by varying materials and geometry. Furthermore, an artificial circular muscle (ACM) based on the HS-Peano-HASEL acts as a tubular pump, resembling the primordial heart of an ascidian. Additionally, a strain-amplifying pulley system is introduced to increase the maximum strain of an HS-Peano-HASEL to 42%. The muscle-like maximum actuation strain and excellent demonstrated all-around performance of HS-Peano-HASEL actuators make them promising candidates for use in artificial organs, life-like robotic faces, and a variety of other robotic systems.

DOI [BibTex]

Wang, X., Mitchell, S. K., Rumley, E. H., Rothemund, P., Keplinger, C. High-Strain Peano-HASEL Actuators Advanced Functional Materials, 30(7):1908821, 2020 (article)

DOI [BibTex]

Dynamics of Electrohydraulic Soft Actuators
Dynamics of Electrohydraulic Soft Actuators

Rothemund, P., Kirkman, S., Keplinger, C.

Proceedings of the National Academy of Sciences of the United States of America, 117(28):16207-16213, 2020 (article)

Abstract
Nature has inspired the design of robots in which soft actuators enable tasks such as handling of fragile objects and adapting to unstructured environments. Those tasks are difficult for traditional robots, which predominantly consist of hard components. Electrohydraulic soft actuators are liquid-filled shells that deform upon the application of electric fields; they excel among soft actuators with muscle-like force outputs and actuation strains, and with actuation frequencies above 100 Hz. However, the fundamental physics that governs the dynamics of electrohydraulic soft actuators is unexplored. Here, we study the dynamics of electrohydraulic soft actuators using the Peano-HASEL (hydraulically amplified self-healing electrostatic) actuator as a model system. Using experiments and a scaling analysis, we discover two dynamic regimes: a regime in which viscous dissipation reduces the actuation speed and a regime governed by inertial effects in which high-speed actuation is possible. For each regime, we derive a timescale that describes the influence of geometry, materials system, and applied external loads on the actuation speed. We also derive a model to study the dynamic behavior of Peano-HASEL actuators in both regimes. Although this analysis focuses on the Peano-HASEL actuator, the presented results may readily be generalized to other electrohydraulic actuators. When designed to operate in the inertial regime, electrohydraulic actuators will enable bio-inspired robots with unprecedented speeds of motion.

DOI [BibTex]

Rothemund, P., Kirkman, S., Keplinger, C. Dynamics of Electrohydraulic Soft Actuators Proceedings of the National Academy of Sciences of the United States of America, 117(28):16207-16213, 2020 (article)

DOI [BibTex]

2019

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An Easy‐to‐Implement Toolkit to Create Versatile and High‐Performance HASEL Actuators for Untethered Soft Robots

Mitchell, S. K., Wang, X., Acome, E., Martin, T., Ly, K., Kellaris, N., Venkata, V. G., Keplinger, C.

Advanced Science, 6(14):1900178, June 2019 (article)

Abstract
For soft robots to have ubiquitous adoption in practical applications they require soft actuators that provide well-rounded actuation performance that parallels natural muscle while being inexpensive and easily fabricated. This manuscript introduces a toolkit to rapidly prototype, manufacture, test, and power various designs of hydraulically amplified self-healing electrostatic (HASEL) actuators with muscle-like performance that achieve all three basic modes of actuation (expansion, contraction, and rotation). This toolkit utilizes easy-to-implement methods, inexpensive fabrication tools, commodity materials, and off-the-shelf high-voltage electronics thereby enabling a wide audience to explore HASEL technology. Remarkably, the actuators created from this easy-to-implement toolkit achieve linear strains exceeding 100%, a specific power greater than 150 W kg−1 , and ≈20% strain at frequencies above 100 Hz. This combination of large strain, extreme speed, and high specific power yields soft actuators that jump without power-amplifying mechanisms. Additionally, an efficient fabrication technique is introduced for modular designs of HASEL actuators, which is used to develop soft robotic devices driven by portable electronics. Inspired by the versatility of elephant trunks, the above capabilities are combined to create an untethered continuum robot for grasping and manipulating delicate objects, highlighting the wide potential of the introduced methods for soft robots with increasing sophistication.

link (url) DOI [BibTex]

2019

Mitchell, S. K., Wang, X., Acome, E., Martin, T., Ly, K., Kellaris, N., Venkata, V. G., Keplinger, C. An Easy‐to‐Implement Toolkit to Create Versatile and High‐Performance HASEL Actuators for Untethered Soft Robots Advanced Science, 6(14):1900178, June 2019 (article)

link (url) DOI [BibTex]

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Stretchable ionics for transparent sensors and actuators

Sun, J. Y., Keplinger, C. M., Suo, Z., Whitesides, G. M.

(US Patent 10302586 B2), May 2019 (patent)

Abstract
A class of devices enabled by ionic conductors is highly stretchable , fully transparent to light of all colors , biocompatible or biodegradable , and capable of operation at frequencies beyond 10 kilohertz and voltages above 10 kilo volts . These devices enabled by ionic conductors can be used as large strain actuators , full - range loudspeakers , as strain or pressure sensors and as stretchable interconnects . The electromechanical transduction is achieved without electrochemical reaction . When large stretchability and high optical transmittance are required , the ionic conductors have lower sheet resistance than all existing electronic conductors .

link (url) [BibTex]

Sun, J. Y., Keplinger, C. M., Suo, Z., Whitesides, G. M. Stretchable ionics for transparent sensors and actuators (US Patent 10302586 B2), May 2019 (patent)

link (url) [BibTex]

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Mechanical‐to‐Electrical Energy Conversion with Variable Electric Double Layers

Morrissey, T. G., Mitchell, S. K., Jaros, A. T., Ambos, E., Keplinger, C.

Energy Technology, 7(4):1801007, WILEY-VCH, March 2019 (article)

Abstract
The electromagnetic generator requires sophisticated power take-off systems to effectively capture low-frequency mechanical motion such as ocean waves and human gait. Conversely, electrostatic generators are variable capacitors, which harness charge separation processes that can directly capture low-frequency mechanical energy. The fundamentals of mechanical-to-electrical energy conversion with an electrostatic generator that exploits the high energy density of electric double layer (EDL) capacitors and varies capacitance by physical manipulation of the electrode–electrolyte interfacial area are elucidated. A model system is designed where all experimental parameters are easy to access in order to gain a detailed understanding of the energy flow in this conversion process. The system, termed a variable EDL generator, is based on titanium electrodes in NaCl aqueous electrolyte and operated as a charge pump. The net positive electrical energy generation of the system in the voltage–charge work-conjugate plane is analyzed, and it shows that the variable EDL generator can be scaled-up to spin an electric motor and increase the output power of the generator through the use of waste heat. The detailed analysis of this energy conversion principle suggests multiple avenues to enhance the performance of the variable EDL generator.

link (url) DOI [BibTex]

Morrissey, T. G., Mitchell, S. K., Jaros, A. T., Ambos, E., Keplinger, C. Mechanical‐to‐Electrical Energy Conversion with Variable Electric Double Layers Energy Technology, 7(4):1801007, WILEY-VCH, March 2019 (article)

link (url) DOI [BibTex]

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Area-of-effect softbots (aoes) for asteroid proximity operations

McMahon, J., Mitchell, S. K., Oguri, K., Kellaris, N., Kuettel, D., Keplinger, C., Bercovici, B.

In 2019 IEEE Aerospace Conference (AERO 2019), pages: 1554-1569, IEEE, Piscataway, NJ, IEEE Aerospace Conference (AERO 2019), 2019 (inproceedings)

Abstract
This paper will provide an introduction and overview of Area-of-Effect Softbots (AoES), which are currently in development under a Phase 2 NASA Innovative Advanced Concepts (NIAC) project. AoES are designed to operate in proximity to, and on the surface of, small asteroids to support mining and planetary defense missions. Their unique design and capabilities are dependent on the incorporation of soft, compliant, and lightweight materials. AoES have a large area-to-mass ratio which allows them to take advantage of the peculiarities of the dynamical environment around small asteroids. Specifically, AoES will use solar radiation pressure to sail to the surface of the target asteroid after being deployed at a safe altitude from a mothership around the asteroid. This capability and the associated control laws will be demonstrated, removing the need for propulsion systems. Furthermore, the large, flexible surface area allows for robustness with respect to uncertainty about the asteroid surface structure - it can provide flotation to prevent sinking into a very loose, dusty regolith, and also provide anchoring to the surface through natural and electroadhesion forces. The enabling technology that will allow the AoES design loop to close is a new class of soft actuators known as HASEL actuators. These actuators harness an electrohydraulic mechanism, whereby electrostatic forces generate hydraulic pressure to drive shape change in a soft fluidfilled structure. HASELs provide an extremely power- and mass-efficient mechanism for actuating the large flexible surface areas that are the essential components defining AoES. Current system design, requirements, and key tradeoffs will be discussed - with a particular focus on the actuation, mobility, anchoring, materials, and power systems/components. The nominal mission profile and concept of operations for using

link (url) DOI [BibTex]

McMahon, J., Mitchell, S. K., Oguri, K., Kellaris, N., Kuettel, D., Keplinger, C., Bercovici, B. Area-of-effect softbots (aoes) for asteroid proximity operations In 2019 IEEE Aerospace Conference (AERO 2019), pages: 1554-1569, IEEE, Piscataway, NJ, IEEE Aerospace Conference (AERO 2019), 2019 (inproceedings)

link (url) DOI [BibTex]

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Simulation-driven design to reduce pull-in voltage of donut HASEL actuators

Panwar, S., Gandhi, U., Acome, E., Keplinger, C., Rowe, M.

Proceedings of SPIE, 10966, pages: 1096622, SPIE, March 2019 (article)

Abstract
Soft robotics research has been motivated in part by the versatility and functionality of human muscle. Researchers have tried to mimic the speed and performance of human muscle by using soft fluid actuators; however, these actuators are often slow and bulky. Research conducted in the use of dielectric elastomers has proven to be promising. These dielectric elastomers can produce large strains using high voltage electrical input. However, the development of these dielectric elastomer actuators has been inhibited due to their susceptibility to dielectric breakdown and electrical aging. One recent technology that can solve these issues and advance the field of soft actuators, is that of the hydraulically amplified self-healing electrostatic (HASEL) actuator. Such actuators are comprised of a liquid dielectric enclosed in an elastomer shell with electrodes on either side of the shell. Incorporating a liquid dielectric dramatically reduces the impact of dielectric breakdown on the performance of HASEL actuators and allows for hydraulically-coupled modes of actuation. However, the voltages that are required to operate these actuators are still challenging for commercial applications. Our work uses a simulation-driven approach to determine design parameters for donut HASEL actuators that provide a high actuation strain at a reduced pull-in voltage. We outline a modeling approach that is comprised of calibrating the properties of a multiphysics finite element model using actual HASEL actuator experimental data. The model is validated using a donut-shape HASEL actuator from literature. The model is then applied to determine the optimal electrode size and fluid dielectric permittivity for achieving a low operating voltage. This simulation-driven design assists in the fabrication of soft actuators with potential application to a variety of industries. Keywords: Electroactive polymer, soft actuator, artificial muscles, simulation, finite element method, HASEL

link (url) DOI [BibTex]

Panwar, S., Gandhi, U., Acome, E., Keplinger, C., Rowe, M. Simulation-driven design to reduce pull-in voltage of donut HASEL actuators Proceedings of SPIE, 10966, pages: 1096622, SPIE, March 2019 (article)

link (url) DOI [BibTex]