We report on a multifunctional four-finger gripper for soft robotics, suitable for performing delicate manipulation tasks. The gripping device is comprised of separately driven gripping and lifting mechanisms, both made from a separate single piece of smart material - ionic capacitive laminate (ICL) also known as artificial muscle. Compared to other similar devices the relatively high force output of the ICL material allows one to construct a device able to grab and lift objects exceeding multiple times its own weight. Due to flexible design of ICL grips, the device is able to adapt the complex shapes of different objects and allows grasping single or multiple objects simultaneously without damage. The performance of the gripper is evaluated in two different configurations: a) the ultimate grasping strength of the gripping hand; and b) the maximum lifting force of the lifting actuator. The ICL is composed of three main layers: a porous membrane consisting of non-ionic polymer poly(vinylidene fluoride-co-hexafluoropropene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium trifluoromethane-sulfonate (EMITFS), and a reinforcing layer of woven fiberglass cloth. Both sides of the membrane are coated with a carbonaceous electrode. The electrodes are additionally covered with thin gold layers, serving as current collectors. Device made of this material operates silently, requires low driving voltage (<3 V), and is suitable for performing tasks in open air environment.
KEYWORDS: Actuators, Electrodes, Scanning electron microscopy, Sensors, Digital image correlation, Electroactive polymers, Photomicroscopy, Mechanics, Electron microscopes, Digital imaging
Commonly, modeling of the bending behavior of the ionic electroactive polymer (IEAP) actuators is based on the classical mechanics of cantilever beam. It is acknowledged, that the actuation of the ionic electroactive polymer (IEAP) actuators is symmetric about the centroid - the convex side of the actuator is expanding and the concave side is contracting for exactly the same amount, while the thickness of the actuator remains invariant. Actuating the IEAP actuators and sensors under scanning electron microscope (SEM), in situ, reveals that for some types of them this approach is incorrect. Comparison of the SEM micrographs using the Digital Image Correction (DIC) method results with the precise strain distribution of the IEAP actuators in two directions: in the axial direction, and in the direction of thickness. This information, in turn, points to the physical processes taking place within the electrodes as well as membrane of the trilayer laminate of sub-millimeter thickness. Comparison of the EAP materials, engaged as an actuator as well as a sensor, reveals considerable differences between the micro-mechanics of the two modes.
The research is focused on lifetime and degradation of ionic electroactive polymer actuators (IEAP). The lifetime measurements were carried out using identical methodology upon the different IEAP types. The experiment conducted with large number of samples shows that two types of degradation have serious effect to the IEAPs: degradation during operation and spontaneous self-degradation. Additionally, two ways of occasional damage decrease their overall reliability. In the scope of the current paper we describe degradation of two different types of IEAP actuators: with carbonaceous electrodes and with conducting polymer electrodes. Nevertheless, the common evolutionary trends, rather than the comparative data analysis or formal statistics of all particular samples, are given. Analyzing the electromechanical and electrical impedances of the samples during their whole lifetime, we have found that observing the electric current gives adequate information about the degradation level of any IEAP actuator. Moreover, tracking this electrically measurable parameter enables detecting the occasional damage of an actuator.
Free standing conducting polymer films based on polypyrrole doped with dodecylbenzoesulfate (PPyDBS) are investigated in TBACF3SO3 (tetrabutylammonium trifluoromethanesulfonate) propylene carbonate (PC-Tf) followed in aqueous TMACl tetramethylammonium chloride (Aq-TM) with the aim to investigate actuation properties (anion or cation-driven actuation). Under isometric (constant force) conditions ECMD (electro-chemo-mechanical deformation) measurements are performed during cyclic voltammetric and chronoamperometric experiments. Electrolyte and solvent effects revealing that the actuation direction in propylene carbonate electrolyte changed from expansion at anodic potential to expansion at cathodic potentials during square wave potential steps. Finally if the PPyDBS film immersed in aqueous electrolyte the anion-driven actuation properties are maintenance. SEM measurements are implemented to reefer changes in film morphology and ion content (EDX, energy dispersive X-Ray) before and after actuation.
Comparative measurements of carbon-polymer composite micro-actuators based on room temperature ionic
liquid electrolyte were carried out in situ (1) in vacuum using a state-of-the-art scanning electron microscope, (2)
in an oxygen-free atmosphere under ambient pressure, and (3) under ambient environment. The fabricated
micro-actuators sustained their actuation performance in all three environments, revealing important implications
regarding their humidity-dependence. SEM observations demonstrate high stroke actuation of a device with submillimeter
length, which is the typical size range of actuators desirable for medical or lab-on-chip applications.
Carbide–derived Carbon (CDC) material is applied for super capacitors due to their nanoporous structure and their high
charging/discharging capability. In this work we report for the first time CDC linear actuators and CDC combined with
polypyrrole (CDC-PPy) in ECMD (Electrochemomechanical deformation) under isotonic (constant force) and isometric
(constant length) measurements in aqueous electrolyte. CDC-PPy actuators showing nearly double strain under cyclic
voltammetric and square wave potential measurements in comparison to CDC linear actuators. The new material is
investigated by SEM (scanning electron microscopy) and EDX (energy dispersive X-ray analysis) to reveal how the
conducting polymer layer and the CDC layer interfere together.
In comparison to other ionic electromechanically active polymers (ionic EAP), carbon-polymer composite (CPC) actuators are considered especially attractive due to possibility of producing completely metal-free devices. However, mechanical response of ionic EAP-s is, in addition to voltage and frequency, dependent on environmental variables such as humidity and temperature. Therefore, similarly to other EAPs, one of the major challenges lies in achieving controlled actuation of the CPC sample. Due to their size and added complexity, external feedback devices (e.g. laser displacement sensors and video cameras) tend to inhibit the application of micro-scale actuators. Hence, self-sensing EAP actuators – capable for simultaneous actuation and sensing – are often desired. A thin polyvinylidene fluoride-cohexafluoropropylene film with ionic liquid (EMIMBF4) was prepared and masked coincidently on opposite surfaces prior to spray painting carbide-derived carbon electrodes. The purpose of masking was to create different electrically insulated electrodes on the same surface of polymer in order to achieve separate sections for actuator and sensor on one piece of CPC material. Solution of electrode paint consisting of carbide-derived carbon, EMIMBF4 and dimethylacetamide was applied to the polymer film. After removing the masking tape, a completely metal-free CPC actuator with sophisticated electrode geometry was achieved to foster simultaneous sensing and actuation, i.e. self-sensing carbon-polymer actuator was created.
There is still emerging need for more effective and technologically simple electrode materials for low voltage ionic EAP
materials. Most extensively used carbon materials for bending and linear actuators are different types of carbon
nanotubes. We have used for the electrode layers carbide-derived carbon (CDC) and several carbon aerogels. The
differences in actuation performance were analyzed in the context of pore characteristics of carbons, electromechanical
and electrochemical (EIS) properties. Quantum chemistry and molecular dynamics simulations were used to analyze in
detail the actuation/sensor processes in material.
High surface area carbon, ionic liquid and polymer are incorporated in an electromechanically active composite. This
laminate bends when voltage (typically less than 3 V) is applied between the electrodes, and generates voltage and
current when bent with an external force. By suitable optimization, the material can be used either as an actuator, energy
storage element (supercapacitor) or sensor. Strain caused by bending promotes dislocation of ions in the micropores of
carbon. As a result, the charge separation occurs because ions of ionic liquid are likely trapped in the micropores of
diameters close to the ion sizes.
In this work we report an actuator material, that consist of carbon aerogel, 1-ethyl-3-methylimidazolium
tetrafluoroborate (EMIBF4) and poly(vinylidene-co-hexafluoropropylene) (PVdF(HFP)). Actuators were made by using
layer-by-layer casting method and they work as a bending actuators. Carbon aerogel is synthesized from 5-
methylresorcinol, which is a waste product in oil-shale industry. It makes the material "environmentally green". Carbon
aerogels have a very low density and considerable specific surface area. It is generally understood that the large
interfacial surface area of electrodes gives rise to better actuation performance; therefore, designing actuators with high
specific surface area electrodes is of interest. The assembled three layer actuators require low voltage to operate and
work steadily in open air due to non-volatile electrolyte. The electromechanical and electrical characteristics of prepared
actuators were examined and compared to our previously reported actuators based on the carbide-derived carbon and
activated carbon electrodes. The differences in actuation performance were analyzed in the context of pore
characteristics and degree of graphitization of carbons. The gas sorption measurements were performed to characterize
pore size distribution. These actuators show high strain, low back-relaxation and low power consumption and they are
good for slow-response applications compared to carbon nanotube actuators.
An electromechanical actuator was prepared using non-ionic polymer, ionic liquid and carbide-derived carbon (CDC).
Recently, simple layer-by-layer casting method for actuator production was discovered, using "bucky gel" mixture as the
precursor of actuator electrode layers. In this paper we investigate carbide-derived carbon as a new alternative to carbon
nanotubes to replace nanotubes in the electrode layer of the actuator. At the initial stage of the study, the ratio of
nanoporous high surface TiC-derived carbon powder, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) and
polymer (PVdF(HFP)) was varied and each formed electrode was analyzed to find the optimal composition. The results
revealed that the optimal component ratio for electrodes is: 35 wt% PVdF(HFP), 35 wt% EMIBF4 and 30 wt% CDC.
The assembled three layer actuators were characterized by measuring blocking force, maximum strain, speed, power
consumption and capacitance. The synthesized actuator showed very good force and capacitive characteristics and it is
preferable for slow-response applications compared to actuators based on carbon nanotubes.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.