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  1. Soft robots require a complimentary control architecture to support their inherent compliance and versatility. This work presents a framework to control soft-robotic systems systematically and effectively. The data-driven model-based approach developed here makes use of Dynamic Mode Decomposition with control (DMDc) and standard controller synthesis techniques. These methods are implemented on a robotic arm driven by an antagonist pair of Hydraulically Amplified Self-Healing Electrostatic (HASEL) actuators. The results demonstrate excellent tracking performance and disturbance rejection, achieving a steady state error under 0.25% in response to step inputs and maintaining a reference orientation within 0.5 degrees during loading and unloading. The procedure presented in this work can be extended to develop effective and robust controllers for other soft-actuated systems without knowledge of their dynamics a priori. 
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  2. null (Ed.)
    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. 
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  3. 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.

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  4. 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−1are 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−1—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.

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  5. 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.

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  6. 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.

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