1,721,300 research outputs found
Fiber pumps for wearable fluidic systems
No full textIncorporating pressurized fluidic circuits into textiles can enable muscular support, thermoregulation, and haptic feedback in a convenient wearable form factor. However, conventional rigid pumps, with their associated noise and vibration, are unsuitable for most wearables. We report fluidic pumps in the form of stretchable fibers. This allows pressure sources to be integrated directly into textiles, enabling untethered wearable fluidics. Our pumps consist of continuous helical electrodes embedded within the walls of thin elastomer tubing and generate pressure silently through charge-injection electrohydrodynamics. Each meter of fiber generates 100 kilopascals of pressure, and flow rates approaching 55 milliliters per minute are possible, which is equivalent to a power density of 15 watts per kilogram. The benefits in design freedom are considerable, which we illustrate with demonstrations of wearable haptics, mechanically active fabrics, and thermoregulatory textiles
Peeling in electroadhesion soft grippers
Full text linkElectroadhesion endows robots with super-human abilities: mechanical geckoes that climb vertical walls and soft grippers that grasp the most delicate objects. Based on electrostatics, the adhesion forces are turned on and off by an electrical signal, promising extremely fast operation, from silent fully solid-state devices. Practical applications of electroadhesion have however been limited to date by two main challenges: (1) the adhesion forces can vary over 1000x by simply changing the angle between the electroadhesive tape and the object, (2) release is often slow due to residual adhesion when voltage is removed.This paper describes a solution to both these issues by understanding and leveraging peeling in electroadhesion. We present simple models for peeling of electroadhesive tapes, predicting a change in peeling force from < 1 mN to over 1 N by changing the angle between the tape and the object from 90 degrees to 0 degrees. The models are in excellent agreement with our peeling experiments with 30 mm long, 20 mm wide, 300 tm thick electroadhesion tapes made of silicone rubber with carbon electrodes.We demonstrate an electroadhesion soft gripper that uses motorized fingers to control the peeling angle, as a practical application of our peeling models. By moving the fingers to ensure a low peeling angle (0 degrees) when grasping, the same gripper can successfully pick up from a 10 g cherry tomato (2.5 cm wide) to a 600 g Mango (9 cm wide). By then setting a high peeling angle (> 30 degrees), the gripper reliably and rapidly (< 300 ms) releases those objects, despite residual adhesion.Electroadhesion soft grippers have many advantages, including grasping without squeezing, silent operation, low power consumption (< 1 W) and low weight (1 g per soft finger). Understanding and modelling contact mechanics in electroadhesion devices was an essential missing step for practical applications of electroadhesion in robots and grippers. This paper sheds light on how peeling influences electroadhesion and provides practical tools to design and operate electroadhesion systems
Delicate yet strong: characterizing the electro-adhesion lifting force with a soft gripper
No full textCompliant grippers are one of the most promising soft robotic devices for industrial tasks. Soft grippers dramatically simplify grasping control because the gripper automatically conforms to the object's shape. A common limitation of soft structures is that they can only generate low forces, limiting grasping ability. One approach to increase the holding force is to increase the shear force by using controlled adhesion: the lifting force is thus increased, while the clamping force can be kept low, important for manipulating delicate objects. In this work, we explore the lifting force generated with a soft gripper using electroadhesion. We show that this force is highly dependent on the holding posture, which depends on both the shape of the gripper and the shape of the object. For a 1 cm(2) electroadhesion area, we measure maximum lifting forces up to 16 N, strongly dependent on object's shape. Reliability is also an essential feature to move soft robots into industrial scenarios. The gripper survived over 100 cycles at high load with no damage, showing its high robustness. Combining electroadhesion and dielectric elastomers actuators, our soft gripper generates grasping forces so high that we reach the structural limits of the rigid plastic frame, yet it is delicate enough to gently pick up and release a cherry tomato.LMT
Actuating droplets with electrowetting: Force and dynamics
Full text linkAbstract Electrowetting on dielectric (EWOD) allows rapid movement of liquid droplets on a smooth surface, with applications ranging from lab‐on‐chip devices to micro‐actuators. The in‐plane force on a droplet is a key indicator of EWOD performance. This force has been extensively modeled but few direct experimental measurements are reported. We study the EWOD force on a droplet using two setups that allow, for the first time, the simultaneous measurement of force and contact angle, while imaging the droplet shape at 6000 frames/s. For several liquids and surfaces, we observe that the force saturates at a voltage of approximately 150 V. Application of voltages of up 2 kV, that is, 10 times higher than is typical, does not significantly increase forces beyond the saturation point. However, we observe that the transient dynamics, localized at the front contact line, do not show saturation with voltage. At the higher voltages, the initial front contact line speed continues to increase, the front contact angle temporarily becomes near zero, creating a thin liquid film, and capillary waves form at the liquid–air interface. When the localized EWOD forces at the contact line exceed the capillary forces, projectile droplets form. Increasing surface tension allows for higher droplet forces, which we demonstrate with mercury
Printing electrodes for P(VDF-TrFE-CTFE) actuators using a consumer grade inkjet printer
No full textTo facilitate smart material transducer research and application, it is important to develop fabrication processes that are widely accessible and compatible with additive manufacturing (AM) techniques. This work addresses inkjet printing and material selection in the fabrication of bending cantilever actuators based on the P(VDF-TrFE-CTFE) relaxor ferroelectric polymer. It investigates the effects of three different substrates (PEN, polyimide and a PET-based) and four different conductive inks (metal- and carbon-based) on the actuator fabrication and performance, to minimize process complexity and need for specialized equipment. First, electrode samples are manufactured for the feasible substrate-ink combination, their sheet resistances are measured, and their feasibility for actuator electrodes is analysed. Then, the simplest viable process is employed to fabricate the actuator samples, and their performance is measured in quasi-static and dynamic experiments. The least complex fabrication process was achieved with the resin-coated PET substrate (IJ-220) and carbon black electrodes (JR-700LV), only requiring a consumer-grade inkjet printer, a spin-coater and a thermal oven. The electrode samples showed 2.29 · 103 Ω/□ sheet resistance at 10 print repetitions, indicating an actuator’s electrical bandwidth of 9.36 kHz. The manufactured actuators achieved 206 µm tip deflections in response to 1 Hz 300 V excitation, and up to 3 mm deflections in resonant operation at 115 Hz. Therefore, manufacturing flexible designs of well-performing smart material actuators is viable using widely available and low-budget equipment.Dynamics of Micro and Nano SystemsMicro and Nano Engineerin
Soft Robotic Grippers
Full text linkAdvances in soft robotics, materials science, and stretchable electronics have enabled rapid progress in soft grippers. Here, a critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures. Soft gripping can be categorized into three technologies, enabling grasping by: a) actuation, b) controlled stiffness, and c) controlled adhesion. A comprehensive review of each type is presented. Compared to rigid grippers, end-effectors fabricated from flexible and soft components can often grasp or manipulate a larger variety of objects. Such grippers are an example of morphological computation, where control complexity is greatly reduced by material softness and mechanical compliance. Advanced materials and soft components, in particular silicone elastomers, shape memory materials, and active polymers and gels, are increasingly investigated for the design of lighter, simpler, and more universal grippers, using the inherent functionality of the materials. Embedding stretchable distributed sensors in or on soft grippers greatly enhances the ways in which the grippers interact with objects. Challenges for soft grippers include miniaturization, robustness, speed, integration of sensing, and control. Improved materials, processing methods, and sensing play an important role in future research
MicroThrust MEMS electrospray emitters - integrated microfabrication and test results
No full textWith the growth of interest in small satellites (<10kg), there is a particular need to provide a propulsion element for this class of spacecraft. Microfabricated electrospray thrusters offer a solution to this problem. By using ionic
liquids as the propellant solely ions can be emitted, resulting in a large specific
impulse[1] . The thrust from an individual emitter is though a fraction of a N. However by using well-established MEMS technologies thousands
of capillary emitters can be manufactured within an area of a few cm2, increasing the thrust to the mN level. We report on results from the Microthrust FP7 Project1,where the aims are to manufacture and test a complete breadboard thruster system based upon microfabricated thruster chips, alongside the design of a flight system that could enable a CubeSat to leave earth orbit. Prior to this
project we had developed a number of manufacturing processes for specific thruster elements[2,3] .
We report here on a new generation of microfabricated emitters, and their relative performance. The emitters consist of 70μm high etched-Silicon capillaries with outer diameters tapering to less than 10μm. Previous designs included 5μm silica microspheres within the 18 to 24μm internal diameter of the emitter to increase the hydraulic impedance[4]. However the filling factor of these microspheres in individual emitters differed; therefore a new generation of emitters having more similar impedance and with 5 -10μm internal diameters and hole depths of 100μm have been manufactured. Previously the etched-Silicon extractor chip was aligned to the emitter chip using 200μm ruby spheres
[2] . Due to assembly difficulties this has been replaced with a polymer-
based wafer bonding interface, allowing for simplified assembly and a wafer
-scale fabrication process.
These emitters have been tested in both uni-polar and bi-polar mode, using the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4). The tests
herein have been achieved without an acceleration stage. The Time-of-Flight data shows a mixed ion-droplet regime, approaching a Purely Ionic Regime (PIR) at low flow rate
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Optimization of the force and power consumption of a microfabricated magnetic actuator
Full text linkThe force (F) and the power consumption (P ) of a magnetic actuator are modeled, measured and optimized in the context of developing micro-actuators for large arrays, such as in portable tactile displays for the visually impaired. We present a novel analytical approach complemented with finite element simulation (FEM) and experiment validation, showing that the optimization process can be performed considering a single figure of merit. The magnetic actuator is a disc-shaped permanent magnet displaced by planar microcoil. Numerous design parameters are evaluated, including the width and separation of the coil traces, the trace thickness, number of turns and the maximum and minimum radius of the coil. We obtained experimental values ranging from 2 to 12 mN/ sqrt(W) using up to 2-layer coils of both microfabricated and commercial printed circuit board (PCB) technologies. This performance can be further improved by a factor of two by adopting a 6-layer technology. The method can be applied to a wide range of electromagnetic actuators.LMT
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