scholarly journals Dynamics of electrohydraulic soft actuators

2020 ◽  
Vol 117 (28) ◽  
pp. 16207-16213 ◽  
Author(s):  
Philipp Rothemund ◽  
Sophie Kirkman ◽  
Christoph Keplinger
Keyword(s):  
Electric Fields ◽  
High Speed ◽  
Scaling Analysis ◽  
Self Healing ◽  
Electrostatic Actuator ◽  
Fundamental Physics ◽  
Soft Actuators ◽  
External Loads ◽  
Electrohydraulic Actuators ◽  
Inertial Regime

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.

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

2020 ◽  
Vol 7 ◽  
Author(s):  
Zachary Yoder ◽  
Nicholas Kellaris ◽  
Christina Chase-Markopoulou ◽  
Devon Ricken ◽  
Shane K. Mitchell ◽  
...  
Keyword(s):  
High Speed ◽  
Kinematic Model ◽  
Electrical Energy ◽  
Dc Motor ◽  
Self Healing ◽  
Force Output ◽  
Prosthetic Limbs ◽  
Neuromuscular Systems ◽  
Soft Actuators ◽  
Prosthetic Finger

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.

Hydraulically amplified self-healing electrostatic actuators with muscle-like performance

Science ◽  
2018 ◽  
Vol 359 (6371) ◽  
pp. 61-65 ◽  
Author(s):  
E. Acome ◽  
S. K. Mitchell ◽  
T. G. Morrissey ◽  
M. B. Emmett ◽  
C. Benjamin ◽  
...  
Keyword(s):  
High Speed ◽  
Dielectric Breakdown ◽  
Artificial Muscle ◽  
Robotic Arm ◽  
Soft Robotics ◽  
Self Healing ◽  
Electrostatic Actuators ◽  
Robotic Devices ◽  
Soft Actuators ◽  
Wide Potential

Existing soft actuators have persistent challenges that restrain the potential of soft robotics, highlighting a need for soft transducers that are powerful, high-speed, efficient, and robust. We describe a class of soft actuators, termed hydraulically amplified self-healing electrostatic (HASEL) actuators, which harness a mechanism that couples electrostatic and hydraulic forces to achieve a variety of actuation modes. We introduce prototypical designs of HASEL actuators and demonstrate their robust, muscle-like performance as well as their ability to repeatedly self-heal after dielectric breakdown—all using widely available materials and common fabrication techniques. A soft gripper handling delicate objects and a self-sensing artificial muscle powering a robotic arm illustrate the wide potential of HASEL actuators for next-generation soft robotic devices.

scholarly journals A self-healing ferroelectric liquid crystal electro-optic shutter based on vertical surface-relief grating alignment

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Peter J. M. Wyatt ◽  
James Bailey ◽  
Mamatha Nagaraj ◽  
J. Cliff Jones
Keyword(s):  
Adaptive Optics ◽  
Electric Fields ◽  
Surface Relief ◽  
High Speed ◽  
Spatial Light Modulators ◽  
Smectic Layer ◽  
Self Healing ◽  
Surface Relief Grating ◽  
Light Modulators ◽  
Induced Flow

AbstractFerroelectric liquid crystals remain of interest for display and spatial light modulators because they exhibit significantly faster optical response times than nematics. However, smectic layers are sensitive to shock-induced flow and are usually permanently displaced once a well-aligned sample is disrupted, rendering such devices inoperable. We introduce a vertical alignment geometry combined with a surface-relief grating to control both the smectic layer and director orientations. This mode undergoes “self-healing” of the smectic layers after disruption by shock-induced flow. Sub-millisecond switching between optically distinct states is demonstrated using in-plane electric fields. Self-healing occurs within a second after being disrupted by shock, wherein both the layer and director realign without additional external stimulus. The route to material improvements for optimised devices is discussed, promising faster spatial light modulators for high-speed adaptive optics, micro-displays for virtual/augmented reality and telecommunications with inherent shock stability.

Electrokinetic instability due to streamwise conductivity gradients in microchip electrophoresis

2021 ◽  
Vol 925 ◽  
Author(s):  
Kaushlendra Dubey ◽  
Sanjeev Sanghi ◽  
Amit Gupta ◽  
Supreet Singh Bahga
Keyword(s):  
Electric Field ◽  
Numerical Simulations ◽  
Electric Fields ◽  
Quantitative Measure ◽  
Underlying Mechanism ◽  
Scaling Analysis ◽  
Recirculating Flow ◽  
Electrokinetic Instability ◽  
Spatial Features ◽  
Proper Orthogonal Decomposition Technique

We present an experimental and numerical investigation of electrokinetic instability (EKI) in microchannel flow with streamwise conductivity gradients, such as those observed during sample stacking in capillary electrophoresis. A plug of a low-conductivity electrolyte solution is initially sandwiched between two high-conductivity zones in a microchannel. This spatial conductivity gradient is subjected to an external electric field applied along the microchannel axis, and for sufficiently strong electric fields an instability sets in. We have explored the physics of this EKI through experiments and numerical simulations, and supplemented the results using scaling analysis. We performed EKI experiments at different electric field values and visualised the flow using a passive fluorescent tracer. The experimental data were analysed using the proper orthogonal decomposition technique to obtain a quantitative measure of the threshold electric field for the onset of instability, along with the corresponding coherent structures. To elucidate the physical mechanism underlying the instability, we performed high-resolution numerical simulations of ion transport coupled with fluid flow driven by the electric body force. Simulations reveal that the non-uniform electroosmotic flow due to axially varying conductivity field causes a recirculating flow within the low-conductivity region, and creates a new configuration wherein the local conductivity gradients are orthogonal to the applied electric field. This configuration leads to EKI above a threshold electric field. The spatial features of the instability predicted by the simulations and the threshold electric field are in good agreement with the experimental observations and provide useful insight into the underlying mechanism of instability.

scholarly journals Phase-transformation-induced lubrication of earthquake sliding

2017 ◽  
Vol 375 (2103) ◽  
pp. 20160008 ◽  
Author(s):  
Harry W. Green
Keyword(s):  
Phase Transformation ◽  
Dry Friction ◽  
High Speed ◽  
Frictional Resistance ◽  
Low Pressure ◽  
Self Healing ◽  
Strength Recovery ◽  
Endothermic Reactions ◽  
Shear Heating ◽  
Fast Motion

Frictional failure is not possible at depth in Earth, hence earthquakes deeper than 30–50 km cannot initiate by overcoming dry friction. Moreover, the frequency distribution of earthquakes with depth is bimodal, suggesting another change of mechanism at about 350 km. Here I suggest that the change at 30–50 km is from overcoming dry friction to reduction of effective stress by dehydration embrittlement and that the change at 350 km is due to desiccation of slabs and initiation by phase-transformation-induced faulting. High-speed friction experiments at low pressure indicate that exceeding dry friction provokes shear heating that leads to endothermic reactions and pronounced weakening. Higher-pressure studies show nanocrystalline gouge accompanying dehydration and the highest pressure experiments initiate by exothermic polymorphic phase transformation. Here I discuss the characteristic nanostructures of experiments on high-speed friction and high-pressure faulting and show that all simulated earthquake systems yield very weak transformation-induced lubrication, most commonly nanometric gouge or melt. I also show that phase-transformation-induced faulting of olivine to spinel can propagate into material previously transformed to spinel, apparently by triggering melting analogous to high-speed friction studies at low pressure. These experiments taken as a whole suggest that earthquakes at all depths slide at low frictional resistance by a self-healing pulse mechanism with rapid strength recovery. This article is part of the themed issue ‘Faulting, friction and weakening: from slow to fast motion’.

Vitrimer-based soft actuators with multiple responsiveness and self-healing ability triggered by multiple stimuli

Matter ◽  
2021 ◽  
Author(s):  
Yang Yang ◽  
Huimin Wang ◽  
Shuai Zhang ◽  
Yen Wei ◽  
Xiangming He ◽  
...  
Keyword(s):  
Self Healing ◽  
Soft Actuators

scholarly journals A Self-Healing Polymer with Fast Elastic Recovery upon Stretching

Molecules ◽  
2020 ◽  
Vol 25 (3) ◽  
pp. 597 ◽  
Author(s):  
Pei-Chen Zhao ◽  
Wen Li ◽  
Wei Huang ◽  
Cheng-Hui Li
Keyword(s):  
Room Temperature ◽  
Elastic Recovery ◽  
Self Healing ◽  
Original Length ◽  
Healing Efficiency ◽  
Recovery Behavior ◽  
Long Time ◽  
Highly Stretchable ◽  
Soft Actuators

The design of polymers that exhibit both good elasticity and self-healing properties is a highly challenging task. In spite of this, the literature reports highly stretchable self-healing polymers, but most of them exhibit slow elastic recovery behavior, i.e., they can only recover to their original length upon relaxation for a long time after stretching. Herein, a self-healing polymer with a fast elastic recovery property is demonstrated. We used 4-[tris(4-formylphenyl)methyl]benzaldehyde (TFPM) as a tetratopic linker to crosslink a poly(dimethylsiloxane) backbone, and obtained a self-healing polymer with high stretchability and fast elastic recovery upon stretching. The strain at break of the as-prepared polymer is observed at about 1400%. The polymer can immediately recover to its original length after being stretched. The damaged sample can be healed at room temperature with a healing efficiency up to 93% within 1 h. Such a polymer can be used for various applications, such as functioning as substrates or matrixes in soft actuators, electronic skins, biochips, and biosensors with prolonged lifetimes.

scholarly journals The Fabrication and Characterization of InAlAs/InGaAs APDs Based on a Mesa-Structure with Polyimide Passivation

Sensors ◽  
2019 ◽  
Vol 19 (15) ◽  
pp. 3399 ◽  
Author(s):  
Jheng-Jie Liu ◽  
Wen-Jeng Ho ◽  
June-Yan Chen ◽  
Jian-Nan Lin ◽  
Chi-Jen Teng ◽  
...  
Keyword(s):  
Electric Fields ◽  
High Speed ◽  
Gain Bandwidth ◽  
Mesa Structure ◽  
Multiplication Gain ◽  
Data Rates ◽  
Field Control ◽  
Side Walls ◽  
Speed Response

This paper presents a novel front-illuminated InAlAs/InGaAs separate absorption, grading, field-control and multiplication (SAGFM) avalanche photodiodes (APDs) with a mesa-structure for high speed response. The electric fields in the InAlAs-multiplication layer and InGaAs-absorption layer enable high multiplication gain and high-speed response thanks to the thickness and concentration of the field-control and multiplication layers. A mesa active region of 45 micrometers was defined using a bromine-based isotropic wet etching solution. The side walls of the mesa were subjected to sulfur treatment before being coated with a thick polyimide layer to reduce current leakage, while lowering capacitance and increasing response speeds. The breakdown voltage (VBR) of the proposed SAGFM APDs was approximately 32 V. Under reverse bias of 0.9 VBR at room temperature, the proposed device achieved dark current of 31.4 nA, capacitance of 0.19 pF and multiplication gain of 9.8. The 3-dB frequency response was 8.97 GHz and the gain-bandwidth product was 88 GHz. A rise time of 42.0 ps was derived from eye-diagrams at 0.9 VBR. There was notable absence of intersymbol-interference and the signals remained error-free at data-rates of up to 12.5 Gbps.

Friction Torque Measurement in Partial Hybrid S-C Angular Contact Ball Bearings

2014 ◽  
Vol 658 ◽  
pp. 339-344
Author(s):  
Viorel Paleu ◽  
Ioan Damian ◽  
Cristel Stirbu
Keyword(s):  
Silicon Nitride ◽  
High Speed ◽  
Equilibrium Temperature ◽  
Friction Torque ◽  
Ball Bearings ◽  
Self Healing ◽  
Testing Device ◽  
Torque Measurement ◽  
Steel Balls ◽  
Partial Hybrid

To monitor the friction torque evolution in tandems of angular contact ball bearings, a new testing device is developed. New partial hybrid bearings from 7206C series are obtained by combining 8 steel balls with 4 silicon nitride balls of the same diameter equally spaced in the cage, these bearings being denoted hereafter as 8S-4C type. For comparison, tests are carried-out also on conventional all-steel bearings and hybrid bearings with all the steel balls replaced by silicon nitride balls. The equilibrium temperature of the all-steel, hybrid and 8S-4C ball bearings is determined by tests. At high speed and light axial load, the 8S-4C ball bearings withstand to an oil shut-off test of one minute, while the similar all-steel bearings seized. The 8S-4C partial hybrid ball bearings can be an advantageous solution comparative to more expensive all hybrid bearings, avoiding the scuffing due to the self-healing effect induced by the higher hardness of the silicon nitride balls.

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