Robotic Materials

18 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]

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]

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]

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

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]

2022

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]

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]

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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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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]