Dynamics of electrohydraulic soft actuators

Rothemund, Philipp; Kirkman, Sophie; Keplinger, Christoph

doi:10.1073/pnas.2006596117

Cited by 46 publications

(50 citation statements)

References 40 publications

(70 reference statements)

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“…Optimization of the pump design would improve the performance, although the measured flow rate (13.8 μL min −1 at 1 Hz) is already comparable with other elastomeric pumps driven by DEAs [ 26,27 ] and is currently limited by the slow unzipping of the actuators, which limits the actuation frequency. The dynamics of zipping actuators with liquid dielectric is complex [ 66 ] and depends on many parameters, including the viscosity of the liquid, the geometry of the actuator, the impedance of the fluidic circuit, and the pressure in the two fluidic circuits.…”

Section: Resultsmentioning

confidence: 99%

Inkjet Printing of Complex Soft Machines with Densely Integrated Electrostatic Actuators

Schlatter

Grasso

Rosset

et al. 2020

Advanced Intelligent Systems

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Soft machines consist of distributed and interconnected actuators, sensors, logic elements, and ideally a power supply, integrated in a stretchable body. Their intrinsic compliance makes them interesting for a wide array of applications, from soft robotics [1] to organs on a chip. [2] The field has seen rapid growth, in view of the versatility of soft machines, [3] their ability to replicate animal-like motion, [4-7] their intrinsic safety for human interactions, [1] resilience, [8-10] and the ability to use material compliance and elasticity as a means to both simplify control and add function. [11] Given the highly integrated nature of complex soft machines, and the need for many different materials for functional and structural elements, additive manufacturing is an appealing method both to create soft machines with multiple independent actuators and to rapidly tailor dimensions, material properties, and device functions to different tasks. [12,13] As a fully printed soft machine requires no assembly, circuits and systems too complex for manual fabrication and assembly become possible. Printing has allowed complex soft structures with advanced materials, [14] but the focus to date has been mostly on pneumatic structures (i.e., printed chambers) and strain sensors for soft robot end effectors. [12,15] With a few exceptions such as the Octobot, [16] liquid-crystal artificial cilia, [17] or ionic electroactive polymers, [18-20] nearly all printed actuators are pneumatically driven fluidic elastomer actuator (FEAs) devices requiring external air pressure connections to inflate or deflate the bladders. [1,21] Fluidic actuation requires elastomers with well-defined channels but needs no electrical elements. In contrast, including electrically operated actuators embeds the electromechanical conversion into the device and reduces the number of external components. However, it adds important requirements, such as printing magnetic materials or metal coils for electromagnetic actuation, resistive tracks for Joule heating, or dielectrics with a high electrical breakdown, absence of pin holes, and the need for high thickness uniformity if electrostatic actuation is used. Actuators with embedded electrical actuation have been realized using printing processes, either partially printed in combination with additional fabrication methods or fully printed. The first category includes ionic electroactive polymers actuators, with printed polymer layers, but metallic electrodes deposited by other methods. [18,20] The second category includes hybrid pneumatic and shape memory polymer actuators with integrated Joule heating [22] or fully printed ionic microactuators. [19] In this work, we use inkjet printing to produce complex soft machines with integrated electrostatic zipping actuators in a single process. We use a three-material printing process which

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Section: Resultsmentioning

confidence: 99%

Inkjet Printing of Complex Soft Machines with Densely Integrated Electrostatic Actuators

Schlatter

Grasso

Rosset

et al. 2020

Advanced Intelligent Systems

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“…A major advantage of Peano-HASEL actuators is their use of a fast electrohydraulic mechanism (Kellaris et al, 2018 ). The dynamics of Peano-HASEL actuators under different loads and operating conditions were studied in detail by Rothemund et al ( 2020 ). To highlight the fundamental benefits and drawbacks of the Peano-HASEL and DC motor actuators, the dynamics of the prosthetic finger system in this work were studied under no load.…”

Section: Resultsmentioning

confidence: 99%

“…With the custom finger, maximum speed of flexion was 10.6 times greater and the bandwidth was 11.1 times greater than the DC motor actuator. Reduced pouch dimensions and lower viscosity dielectric fluids could lead to even faster actuation (Rothemund et al, 2020 ). This dynamic performance will become even more important as improved myoelectric control algorithms become available for prosthetic hands.…”

Section: Discussion and Outlookmentioning

confidence: 99%

“…Step-Voltage Response A major advantage of Peano-HASEL actuators is their use of a fast electrohydraulic mechanism (Kellaris et al, 2018). The dynamics of Peano-HASEL actuators under different loads and operating conditions were studied in detail by Rothemund et al (2020). To highlight the fundamental benefits and drawbacks FIGURE 10 | Characterizing energy consumption of Peano-HASEL actuators during grasping.…”

Section: Strokementioning

confidence: 99%

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

et al. 2020

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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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“…2 Extensive research demonstrated that the self-assembly of small-scale structures can be achieved along liquid interfaces, opening ways to inexpensive manufacture processes in between bottom-up and topdown forms of fabrication. [3][4][5][6][7][8][9] Capillary driven self-assembly consists in suspending small objects at the water-air interface. Depending on the object weight, hydrophobicity and surface tension, the interface is slightly deformed, inducing a net force between the particles.…”

Section: Introductionmentioning

confidence: 99%