In this paper, we develop and characterise the use of amorphous Silicon as an optically functional material in actuated devices. A novel actuator is developed which uses thin amorphous silicon film deposited on a polyimide substrate using Plasma Enhanced Chemical Vapour Deposition (PECVD). The actuator generates an active stroke via electrostatic attraction which causes the electrodes to “zip” together. The magnitude of displacement is controlled by exploiting the light-dependant resistance of an amorphous silicon (a-Si) photoreceptor integrated onto the actuator. An 8mm long actuator was prototyped and curvature changes were measured using image processing techniques to track the amorphous silicon electrode during actuation. A change of radius of 1mm was found between the ambient (22 Lux) and illuminated states (36 kLux) with an applied voltage of 5 kV.
Soft-smart functional devices and machines, made of soft-smart materials and structures, have been augmenting, supplementing, extending, and replacing their conventional hard equivalents due to the fact that they provide intrinsic compliance matching and biocompatibility. These new capabilities enable them to have safer interactions with human beings and natural environments, and better resilience and adaptability to various environments. Dielectric elastomer actuators (DEAs) and soft electroadhesion (EA) grippers are two promising soft-smart mechanisms and structures that can be used for active actuation and adhesion for soft robots. We integrate DEAs and soft EAs into monolithic soft structures capable of self-actuation and self-adhesion. These structures are fabricated by casting customized electrode materials onto dielectric elastomer membranes. Concomitant or separate actuation and adhesion can be achieved in active areas of these structures via customized control strategies. In this work, we also present a comprehensive survey of existing DEA and EA combination work. Soft-smart DEA-EA structures could impact on many fields including robotics and material handling technologies.
Optically-switched composite materials based on semiconducting materials have the potential to simplify the circuitry required to control artificial muscles. This contactless control method has the potential to improve visual technologies by enabling controllable haptic and morphing interfaces. Optically-switched active displays could provide enhanced user interaction, especially for those with visual impairments. Research into morphing interfaces with dielectric elastomer actuators (DEAs) centralizes on segmented electrode architectures that can achieve large active strains in multiple degrees of freedom. However, controlling the activation of multiple electrodes typically requires an array of discrete rigid components (e.g. MOSFETs) as well as the separation of high-voltage power lines and low-voltage control signals. In this work, we develop a photo-switched DEA system that removes the need for wired control signals, reducing complexity. Photonic switching of DEA electrodes is achieved by exploiting the light-dependent resistance of a thin film of deposited amorphous silicon (a-Si). Samples with layer thicknesses of 0.84 μm have been fabricated using plasma enhanced chemical vapor deposition. Breakdown voltages of above 6kV were obtained when using a nonconducting substrate (glass). Preliminary testing of the system shows that voltage swings of up to 865V can be achieved between ambient and direct illumination, producing an out of plane actuation of 2 μm in a weight-biased DEA disc actuator. Further tuning of the electric circuit should lead to larger actuation strains. Future work will focus on the control of multiple DEA electrodes using localized light patterns as well as testing and characterizing other materials to improve the voltage swing across the DEA.
Cephalopods employ their colour-changing skin for rapid active camouflage and signalling in complex visual environments. This is achieved with chromatophores, pigment organs which stretch under electrical stimulation to affect local skin colouration. Mimicry of the dynamic skin patterns of cephalopods in soft materials has the potential to produce novel cloaking suits and illuminated clothing. Here, we present the experimental investigation of bioinspired artificial cephalopod skin made from dielectric elastomer. Using simple local feedback mechanisms, we explore a variety of scalable dynamic patterns which include the travelling waves of the cuttlefish passing cloud display and other complex dynamic patterning.
Soft electroactive devices such as dielectric elastomer actuators have been the subject of research for several decades. One of the reasons they have not found many industrial applications to date is the challenge of manufacturing such devices cost-effectively. 3D printing is now widely used to cut manufacturing time and cost in many industries, but functional and soft materials for 3D printing are still very limited. Here we present a process that could be used to 3D print functional soft, electroactive devices like dielectric elastomer actuators and sensors. We propose a simple, low-cost 3D printing platform that uses direct ink writing of elastomer composites with low filler loading of carbon-based nanoparticles. These composites allow the deposition of smooth, uniform layers as well as rapid curing of printed materials with UV light. A diode laser is then used to induce a chemical transformation of the elastomer to create conductive patterns for electrodes with arbitrary shapes and high detail. The process is still limited by the low elasticity of the laser induced electrode material but if more suitable materials can be found, this process could dramatically reduce the time, cost and complexity involved in manufacturing dielectric elastomer devices while at the same time greatly increasing the possible geometric and functional complexity of the 3D printed devices.
Polyvinyl chloride (PVC) gel is a promising, soft-smart material with electroactive properties, which can be used to make soft robotic actuators with impressive characteristics. However, until now, PVC gel actuators have always been made with rigid metal electrodes, preventing the fabrication of fully soft devices. Here, we present a novel conceptual design for PVC gel actuators. By moving the microstructure from the electrode to the gel itself, we enable PVC gels which exhibit linear contraction when sandwiched between planar electrodes made from any conductive material. We investigate four different microstructures, three of which exhibit higher displacements compared with a traditional (mesh-based) PVC gel actuator. The best performing gel achieved a displacement of 26% of the microstructure height. Finally, we demonstrate an entirely soft PVC gel actuator with thin conductive rubber electrodes. This article is a first step towards totally compliant artificial muscles made from soft electrodes and PVC gels.
Among the main issues with the implementation of Dielectric Elastomer Generators (DEGs) is the need for pre-charging to perform mechanical-to-electrical energy conversion. In cases when energy harvesting has to be performed in an environment with unpredictable characteristics (e.g., wind, waves, human walking), defining the best times for charge injection and energy extraction in a cycle is a non-trivial problem. In this paper, we present a novel Self-Sensing with Peak Detection (SSPD) method to control the charges on the material using capacitive self-sensing techniques, which defines an optimal cycle and requires no knowledge of the mechanical excitation amplitude or frequency. The effectiveness of the approach is proved by means of numerical simulations based on an highly accurate model of the DEG device.
Dielectric Elastomer Generators (DEGs) are an emerging energy harvesting technology based on a the cyclic stretching of a rubber-like membrane. However, most design processes do not take into account different excitation frequencies; thus limits the applicability studies since in real-world situations forcing frequency is not often constant. Through the use of a practical design scenario we use modeling and simulation to determine the material frequency response and, hence, carefully investigate the excitation frequencies that maximize the performance (power output, efficiency) of DEGs and the factors that influence it.
Flexible pressure sensors are crucial components for the next generation wearable devices to monitor human physiological conditions. In this paper, we present a novel resistive pressure sensor based on hybrid composites made from carbon nanotube (CNT) for the conductive coating layer and polydimethylsiloxane (PDMS) elastomers as the substrate. The high sensitivity of these sensors is attributed to the change of contact resistance caused by the variation of the contact areas between the wavy film and the electrodes. Porous electrodes were designed to increase the roughness of the interfaces, thus further enhancing the pressure sensitivity. The developed device was verified through a series of tests, and the sensor exhibited a high sensitivity of 2.05 kPa-1 under a low pressure of 35.6 Pa.
Photo-actuation, such as that observed in the reversible sun-tracking movements of heliotropic plants, is produced by a complex, yet elegant series of processes. In the heliotropic leaf movements of the Cornish Mallow, photo-actuation involves the generation, transport and manipulation of chemical signals from a distributed network of sensors in the leaf veins to a specialized osmosis driven actuation region in the leaf stem. It is theorized that such an arrangement is both efficient in terms of materials use and operational energy conversion, as well as being highly robust. We concern ourselves with understanding and mimicking these light driven, chemically controlled actuating systems with the aim of generating intelligent structures which share the properties of efficiency and robustness that are so important to survival in Nature. In this work we present recent progress in mimicking these photo-actuating systems through remote light exposure of a metastable state photoacid and the resulting signal and energy transfer through solution to a pH-responsive hydrogel actuator. Reversible actuation strains of 20% were achieved from this arrangement, with modelling then employed to reveal the critical influence hydrogel pKa has on this result. Although the strong actuation achieved highlights the progress that has been made in replicating the principles of biomimetic photo-actuation, challenges such as photoacid degradation were also revealed. It is anticipated that current work can directly lead to the development of high-performance and low-cost solartrackers for increased photovoltaic energy capture and to the creation of new types of intelligent structures employing chemical control systems.
One of the main challenges for the practical implementation of dielectric elastomer generators (DEGs) is supplying high voltages. To address this issue, systems using self-priming circuits (SPCs) — which exploit the DEG voltage swing to increase its supplied voltage — have been used with success. A self-priming circuit consists of a charge pump implemented in parallel with the DEG circuit. At each energy harvesting cycle, the DEG receives a low voltage input and, through an almost constant charge cycle, generates a high voltage output. SPCs receive the high voltage output at the end of the energy harvesting cycle and supply it back as input for the following cycle, using the DEG as a voltage multiplier element. Although rules for designing self-priming circuits for dielectric elastomer generators exist, they have been obtained from intuitive observation of simulation results and lack a solid theoretical foundation. Here we report the development of a mathematical model to predict voltage boost using self-priming circuits. The voltage on the DEG attached to the SPC is described as a function of its initial conditions, circuit parameters/layout, and the DEG capacitance. Our mathematical model has been validated on an existing DEG implementation from the literature, and successfully predicts the voltage boost for each cycle. Furthermore, it allows us to understand the conditions for the boost to exist, and obtain the design rules that maximize the voltage boost.
One of the greatest challenges to modern technologies is what to do with them when they go irreparably wrong or come to the end of their productive lives. The convention, since the development of modern civilisation, is to discard a broken item and then procure a new one. In the 20th century enlightened environmentalists campaigned for recycling and reuse (R and R). R and R has continued to be an important part of new technology development, but there is still a huge problem of non-recyclable materials being dumped into landfill and being discarded in the environment. The challenge is even greater for robotics, a field which will impact on all aspects of our lives, where discards include motors, rigid elements and toxic power supplies and batteries. One novel solution is the biodegradable robot, an active physical machine that is composed of biodegradable materials and which degrades to nothing when released into the environment. In this paper we examine the potential and realities of biodegradable robotics, consider novel solutions to core components such as sensors, actuators and energy scavenging, and give examples of biodegradable robotics fabricated from everyday, and not so common, biodegradable electroactive materials. The realisation of truly biodegradable robots also brings entirely new deployment, exploration and bio-remediation capabilities: why track and recover a few large non-biodegradable robots when you could speculatively release millions of biodegradable robots instead? We will consider some of these exciting developments and explore the future of this new field.
Follicular structures in skin combine sensing and actuation in a soft and compliant continuous surface. We have developed a tactile display device inspired by this structure, using a Dielectric Elastomer Actuator (DEA). DEAs allow for combined sensing and actuation, making possible two-way tactile communication between the user and the device. The device can obtain tactile information about the environment, or a user touching it, and it can also present tactile information to the user. We characterise the sensing properties of the tactile display device, and perform classification of tactile stimuli. We demonstrate two-way tactile interaction between a user and the device.
Shape memory polymers (SMP) and shape memory alloys (SMA) have both been proven important smart materials in their own fields. Shape memory polymers can be formed into complex three-dimensional structures and can undergo shape programming and large strain recovery. These are especially important for deployable structures including those for space applications and micro-structures such as stents. Shape memory alloys on the other hand are readily exploitable in a range of applications where simple, silent, light-weight and low-cost repeatable actuation is required. These include servos, valves and mobile robotic artificial muscles. Despite their differences, one important commonality between SMPs and SMAs is that they are both typically activated by thermal energy. Given this common characteristic it is important to consider how these two will behave when in close environmental proximity, and hence exposed to the same thermal stimulus, and when they are incorporated into a hybrid SMA-SMP structure. In this paper we propose and examine the operation of SMA-SMP hybrids. The relationship between the two temperatures Tg, the glass transition temperature of the polymer, and Ta, the nominal austenite to martensite transition temperature of the alloy is considered. We examine how the choice of these two temperatures affects the thermal response of the hybrid. Electrical stimulation of the SMA is also considered as a method not only of actuating the SMA but also of inducing heating in the surrounding polymer, with consequent effects on actuator behaviour. Likewise by varying the rate and degree of thermal stimulation of the SMA significantly different actuation and structural stiffness can be achieved. Novel SMP-SMA hybrid actuators and structures have many ready applications in deployable structures, robotics and tuneable engineering systems.
Chromatophores are the colour changing organelles in the skins of animals including fish and cephalopods. The ability
of cephalopods in particular to rapidly change their colouration in response to environmental changes, for example to
camouflage against a new background, and in social situations, for example to attract a mate or repel a rival, is extremely
attractive for engineering, medical, active clothing and biomimetic robotic applications. The rapid response of these
chromatophores is possible by the direct coupling of fast acting muscle and pigmented saccules. In artificial
chromatophores we are able to mimic this structure using electroactive polymer artificial muscles. In contrast to prior
research which has demonstrated monochromatic artificial chromatophores, here we consider a novel multi-colour,
multi-layer, artificial chromatophore structure inspired by the complex dermal chromatophore unit in nature and which
exploits dielectric elastomer artificial muscles as the electroactive actuation mechanism. We investigate the optical
properties of this chromatophore unit and explore the range of colours and effects that a single unit and a matrix of
chromatophores can produce. The colour gamut of the multi-colour chromatophore is analysed and shows its suitability
for practical display and camouflage applications. It is demonstrated how, by varying actuator strain and chromatophore
base colour, the gamut can be shifted through colour space, thereby tuning the artificial chromatophore to a specific
environment or application.
Biomimetics faces a continual challenge of how to bridge the gap between what Nature has so effectively evolved and
the current tools and materials that engineers and scientists can exploit. Kirigami, from the Japanese ‘cut’ and ‘paper’, is
a method of design where laminar materials are cut and then forced out-of-plane to yield 3D structures. Kirimimetic
design provides a convenient and relatively closed design space within which to replicate some of the most interesting
niche biological mechanisms. These include complex flexing organelles such as cilia in algae, energy storage and
buckled structures in plants, and organic appendages that actuate out-of-plane such as the myoneme of the Vorticella
protozoa. Where traditional kirigami employs passive materials which must be forced to transition to higher dimensions,
we can exploit planar smart actuators and artificial muscles to create self-actuating kirigami structures. Here we review
biomimetics with respect to the kirigami design and fabrication methods and examine how smart materials, including
electroactive polymers and shape memory polymers, can be used to realise effective biomimetic components for robotic,
deployable structures and engineering systems. One-way actuation, for example using shape memory polymers, can
yield complete self-deploying structures. Bi-directional actuation, in contrast, can be exploited to mimic fundamental
biological mechanisms such as thrust generation and fluid control. We present recent examples of kirigami robotic
mechanisms and actuators and discuss planar fabrication methods, including rapid prototyping and 3D printing, and how
current technologies, and their limitations, affect Kirigami robotics.
The article presents a working whisker structure based on dielectric elastomer actuators (DEAs). This preliminary work aims to exploit the features of the dielectric elastomer technology for use in an effective and reliable robotic application whilst accommodating the limitations of this emerging actuation technique. To this end, a modular design and structure have been conceived to simplify the building and repair process of the critical components such as the connectors, wiring, sensors and DEA membranes. This design represents the engineering and scaling of the concepts and techniques developed in previous work, and to overcome identified technical and methodological constraints that previously prohibited extensive real applications. The structure is realised as a trade-off between the unique characteristics of the DEA technology and the robotic development issues. Safety, robustness, production time and key aspects of robotic design are taken into account in the development of this prototype. The results presented show how this structure addresses the design requirement and technical constraints previously identified. The active whisking range achieved is ±14 degrees, measured using image processing of videos captured by both standard and high speed cameras. This metric will be used as one of the measures for planned improvements that are discussed in addition to the advantages and limitations of the structure and the design decisions made.
The expense and use of non-recyclable materials often requires the retrieval and recovery of exploratory robots.
Therefore, conventional materials such as plastics and metals in robotics can be limiting. For applications such as
environmental monitoring, a fully biodegradable or edible robot may provide the optimum solution. Materials that
provide power and actuation as well as biodegradability provide a compelling dimension to future robotic systems.
To highlight the potential of novel biodegradable and edible materials as artificial muscles, the actuation of a
biodegradable hydrogel was investigated. The fabricated gelatine based polymer gel was inexpensive, easy to handle,
biodegradable and edible. The electro-mechanical performance was assessed using two contactless, parallel stainless
steel electrodes immersed in 0.1M NaOH solution and fixed 40 mm apart with the strip actuator pinned directly between
the electrodes. The actuation displacement in response to a bias voltage was measured over hydration/de-hydration
cycles. Long term (11 days) and short term (1 hour) investigations demonstrated the bending behaviour of the swollen
material in response to an electric field. Actuation voltage was low (<10 V) resulting in a slow actuation response with
large displacement angles (<55 degrees). The stability of the immersed material decreased within the first hour due to
swelling, however, was recovered on de-hydrating between actuations. The controlled degradation of biodegradable and
edible artificial muscles could help to drive the development of environmentally friendly robotics.
Much research has been done on the development of tactile displays using Dielectric Elastomer Actuators (DEAs). It has been argued that they offer the potential to create low-cost full-page tactile displays — not achievable with conventional actuator technologies. All research to date has considered tactile elements moving perpendicular to the skin and thus applying a normal force distribution.
In contrast to previous work, we have investigated the use of laterally moving tactile elements that apply shear forces to the skin. This allows for the areal expansion of the DEA to be exploited directly, and a tactile display could be made with no elements moving out of the plane. There is evidence that humans are very sensitive to shear force distributions, and that in some cases a shear stimulus is indistinguishable from a normal stimulus.
We present a prototype shear tactile display actuated by a DEA, and demonstrate that the DEA can generate the necessary forces and displacements. We also present and discuss different display topologies.
Dielectric elastomer generators (DEG) provide an opportunity to harvest energy from low frequency and aperiodic sources. Because DEG are soft, deformable, high energy density generators, they can be coupled to complex structures such as the human body to harvest excess mechanical energy. However, DEG are typically constrained by a rigid frame and manufactured in a simple planar structure. This planar arrangement is unlikely to be optimal for harvesting from compliant and/or complex structures. In this paper we present a soft generator which is fabricated into a 3 Dimensional geometry. This capability will enable the 3-dimensional structure of a dielectric elastomer to be customised to the energy source, allowing efficient and/or non-invasive coupling. This paper demonstrates our first 3 dimensional generator which includes a diaphragm with a soft elastomer frame. When the generator was connected to a self-priming circuit and cyclically inflated, energy was accumulated in the system, demonstrated by an increased voltage. Our 3D generator promises a bright future for dielectric elastomers that will be customised for integration with complex and soft structures. In addition to customisable geometries, the 3D printing process may lend itself to fabricating large arrays of small generator units and for fabricating truly soft generators with excellent impedance matching to biological tissue. Thus comfortable, wearable energy harvesters are one step closer to reality.
Rodents are able to dexterously navigate confined and unlit environments by extracting spatial and textural information
with their whiskers (or vibrissae). Vibrissal-based active touch is suited to a variety of applications where vision is
occluded, such as search-and-rescue operations in collapsed buildings. In this paper, a compact dielectric elastomer
vibrissal system (DEVS) is described that mimics the vibrissal follicle-sinus complex (FSC) found in rodents. Like the
vibrissal FSC, the DEVS encapsulates all sensitive mechanoreceptors at the root of a passive whisker within an
antagonistic muscular system. Typically, rats actively whisk arrays of macro-vibrissae with amplitudes of up to ±25°. It
is demonstrated that these properties can be replicated by exploiting the characteristic large actuation strains and passive
compliance of dielectric elastomers. A prototype DEVS is developed using VHB 4905 and embedded strain gauges
bonded to the root of a tapered whisker. The DEVS is demonstrated to produce a maximum rotational output of ±22.8°.
An electro-mechanical model of the DEVS is derived, which incorporates a hyperelastic material model and Euler-
Bernoulli beam equations. The model is shown to predict experimental measurements of whisking stroke amplitude and
IPMCs are bi-polar actuators capable of large, rapid actuation in flexural configurations. The limit of actuation is defined
by the maximal voltage that can be applied to the IPMC, above which electrolysis of the electrolyte and damage to the
IPMC may occur. In this paper we present preliminary results that indicate how this actuation limit could be tuned and
even exceeded through controlled thermal cycling of gold-plated Nafion IPMCs. Thermal cycling is used to move the
centre point of the actuation stroke. Subsequent voltage stimulation actuates the structure around this new centre point.
It is shown that by further thermal cycling this centre point naturally returns to its initial position. By exploiting this
shape memory characteristic as part of a control system it is expected that more sophisticated IPMC actuation will be
Auxetic (negative Poisson's ratio) configurations have recently been used to build prototypes of deployable structures
using classical shape memory alloys (Nickel-Titanium-Copper). Chiral configurations, featuring three or more inter-connected
spiral-wound hubs, exploit efficient tensile-rotational mechanisms. These structures offer high deployability
ratios in structural elements with load-bearing characteristics. Shape memory polymers have the potential to replace
these shape memory alloys and other stored-energy actuators, and have the attractive properties of low mass, high
actuation strain, easy fabrication and tuneable thermal properties. In this work we discuss how shape memory polymers
(SMP) integrated into a chiral core could offer enhanced deployable characteristics and increase the efficiency of the
auxetic deformations in these unusual cellular structures. We consider the spiral-wound fundamental component needed
for SMP n-chiral prototypes and present test results showing actuation motion of expanding SMP deployable structures.
Applications likely to benefit from these structures include lightweight elements for structural engineering applications,
deployable structures for space applications and implantable medical devices.
For optimal performance, actuators designed for biologically-inspired robotics applications need to be capable of
mimicking the key characteristics of natural musculoskeletal systems. These characteristics include a large output stroke,
high energy density, antagonistic operation and passive compliance. The actuation properties of dielectric elastomer
actuators (DEAs) make them viable for use as an artificial muscle technology. However, much like the musculoskeletal
system, rigid structures are needed to couple the compliant DEA layers to a load. In this paper, a cone DEA design is
developed as an antagonistic, multi-DOF actuator, viable for a variety for biologically-inspired robotics applications. The
design has the advantage of maintaining pre-strain through a support structure without substantially lowering the overall
mass-specific power density. Prototype cone DEAs have been fabricated with VHB 4910 acrylic elastomer and have
characteristic dimensions of 49mm (strut length) and 60mm (DEA diameter). Multi-DOF kinematical outputs of the cone
DEAs were measured using a custom 3D motion tracking system. Experimental tests of the prototypes demonstrate
antagonistic linear (±10mm), rotational (±25°) and combined multi-DOF strokes. Overall, antagonistic cone DEAs are
shown to produce a complex multi-DOF output from a mass-efficient support structure and thus are well suited for being
exploited in biologically-inspired robotics.
This paper presents two new methods for the segmentation of ionic polymer metal composites (IPMCs) in order to create
sophisticated multi-segment sensor-actuators. The first method is based on the application of a heated stylus which,
through a combination of water vaporization and melting of the Nafion substrate removes and redistributes electrode
material. The second method is based on spark discharge machining; a process used in industry to machine extremely
hard conducting materials such as titanium and pre-hardened steel. In contrast to previous segmentation methods
including laser ablation, machining and manual scraping these methods are extremely inexpensive, safe, accurate and
quick. Spark discharge segmentation in particular is an attractive method due to its self-limiting nature, which makes it
robust to variations in segmentation speed and applied pressure. These two methods are presented and assessed through
the fabrication of a series of multi-segment actuators. Actuation results are presented for a two segment spark-discharge
segmented cilia-like IPMC actuator.
This paper presents a bio-inspired, dielectric elastomer (DE) based tubular pumping unit, developed for eventual use as a
component of an artificial digestive tract onboard a microbial fuel cell powered robot (EcoBot). The pump effects fluid
displacement by direct actuation of the tube wall as opposed to excitation by an external body.
The actuator consists of a DE tube moulded from silicone, held in a negative pressure chamber, which is used for
prestraining the tube. The pump is coupled with custom designed polymeric check valves in order to rectify the fluid
flow and assess the performance of the unit. The valves exhibited the necessary low opening pressures required for use
with the actuator. The tube's actuation characteristics were measured both with and without liquid in the system. Based
on these data the optimal operating conditions for the pump are discussed. The pump and valve system has achieved
flowrates in excess of 40μl/s.
This radially contracting/expanding actuator element is the fundamental component of a peristaltic pump. This 'soft
pump' concept is suitable for biomimetic robotic systems, or for the medical or food industries where hard contact with
the delivered substrate may be undesirable. Future work will look at connecting multiple tubes in series in order to
Dielectric elastomer actuators (DEAs) offer numerous benefits as high displacement smart material actuators. The
output of a DEA film is typically characterised by a large area expansion and a smaller transverse displacement.
Consequently, their application is often limited by difficulties in resolving area expansion strain into a usable output.
Certain DEAs also require pre-strain in order to achieve optimal performance. In this paper, Hoberman's radially
expanding mechanism is used to form a novel DEA structure. The mechanism is composed of a number of repeating
angulated scissor-links which resolve area expansion into a uniaxial displacement and have intrinsic pre-straining
capabilities. This allows the Hoberman mechanism to be exploited as an actuator or as a pre-straining device. The
stress distribution induced in the elastomer film when the mechanism is expanded was analysed using photoelasticity,
which showed a 6 segment mechanism produces a significantly more uniform strain pattern compared to 4 segments.
Prototype DEA mechanisms demonstrated that the Hoberman linkage does resolve area expansion strain into a uniaxial
displacement (which can be linear or rotary) at the cost of mechanical friction losses. The 4 segment DEA prototype
produced a maximum stroke of 3.13 mm (6.88% planar strain) with a tensile load of 1.46 N. The 6 segment DEA
prototype demonstrated improved performance with a maximum stroke of 4.52 mm (7.51% planar strain) and a
maximum rotation of 4.98°.
Although dielectric elastomer actuators (DEAs) are becoming more powerful and more versatile, one disadvantage of
DEAs is the need to continuously supply electrical power in order to maintain an actuated state. Previous solutions to this
problem have involved the construction of a bistable or multi-stable rigid mechanical structure or the addition of some
external locking mechanism. Such structures and mechanisms add unwanted complexity and bulk. In this paper we
present a dielectric elastomer actuator that exhibits zero-energy fixity. That is, the actuator can be switched into a rigid
state where it requires no energy to maintain its actuated shape. This is achieved without any additional mechanical
complexity. This actuator relies on changes to the elastic properties of the elastomer material in response to a secondary
stimulus. The elastomer can be switched from a rigid glass-like state to a soft rubber-like state as required. We present a
dielectric elastomer actuator that utilizes shape-memory polymer properties to achieve such state switching. We call this
a dielectric shape memory polymer actuator (DSMPA). In this case control of the elastic properties is achieved through
temperature control. When the material is below its glass transition temperature (Tg) it is in its rigid state and dielectric
actuation has no effect. When the temperature is elevated above Tg the material becomes soft and elastic, and dielectric
actuation can be exploited. We present preliminary results showing that the necessary conditions for this zero-energy
fixity property have been achieved. Applications are widespread in the fields of robotics and engineering and include
morphing wings that only need energy to change shape and control valves that lock rigidly into position.
In nature, unidirectional fluid flows are often induced at micro-scales by cilia and related organelles. A controllable
unidirectional flow is beneficial at these scales for a range of novel robotic and medical applications, whether the flow is
used for propulsion (e.g. swimming robots) or mass transfer (e.g. prosthetic trachea). Ionic Polymer Metal Composites
(IPMCs) are innovative smart materials that can be used directly as active propulsive surfaces rather than a traditional
motor and propeller. IPMC actuators with two segmented electrodes that attempt to mimic the motion of cilia-like
organelles have been realized. In this paper the optimization of these actuators towards producing unidirectional flows is
A parametric study of the kinematic and hydrodynamic effect of modulating the drive signal has been
conducted. As with eukaryotic cilia and flagella found in mammals, the segmented IPMC actuator can generate both
flexural (asymmetric) and undulatory (symmetric) motions from the same physical structure. The motion is controlled
by applying profiles of driving frequencies and phase differences. Kinematic analysis using a camera and laser
displacement sensor has been used to measure and classify different motion types. The hydrodynamic forces produced
by each motion type have been estimated using particle-tracking flow visualization. This allows drive signal profiles to
be ranked in terms of fluid flow momentum transfer and directionality. Using the results of the parametric study, the
IPMC motion is optimized towards producing unidirectional flow via repeatable cilia-inspired motion.
When McKibben artificial muscle actuators are applied to robotic joints, the joints are driven by pairs of actuators
located antagonistically to increase the joint stiffness. However, the force for shape fixity is not large. Therefore, the
objective of this study is to develop a McKibben artificial muscle using a shape-memory polymer (SMP). SMPs can be
deformed above their glass transition temperature (Tg) by applying a small load. They maintain their shape after they
have been cooled to below Tg. They then return to the predefined shape when heated above Tg. Exploiting these
characteristics, we coated the braided mesh shell of a commercial McKibben artificial muscle and made a prototype of
the actuator using the SMP. When this new actuator is warmed above Tg, the SMP deforms. Then, when the internal
bladder is pressurized, the actuator shortens and/or produces a load. After the actuator becomes the desirable length, the
actuator is cooled to below Tg and the SMP is fixed in a rigid state even without the air supply. Consequently, this
actuator can maintain its length more rigidly and accurately. The experimental results conducted on this prototype
confirm the feasibility of this new actuator.
We present a new approach to the fabrication of soft dielectric elastomer actuators using a 3D printing process.
Complete actuators including active membranes and support structures can be 3D printed in one go, resulting in a great
improvement in fabrication speed and increases in accuracy and consistency. We describe the fabrication process and
present force and displacement results for a double-membrane antagonistic actuator. In this structure controlled prestrain
is applied by the simple process of pressing together two printed actuator halves. The development of 3D printable
soft actuators will have a large impact on many application areas including engineering, medicine and the emerging field
of soft robotics.
Ionic polymer metal composite (IPMC) is an ideal material for underwater biomimetic robots. Its softness is very helpful
for generating biomimetic motion. Because IPMCs naturally contain water they do not require extra sealing. The
resulting robot can be soft and lightweight. Previous research on swimming robots is focused on robots swimming in
water. In our study we compare the suitability of two different locomotion patterns - tail oscillation and body undulation,
for swimming in viscous fluid. We found that in water both patterns could propel the robot by generating vortices behind
the robot body. In viscous fluid the robot could be propelled only by body undulation without much disturbance of
nearby fluid. Unlike tail oscillation, the whole body undulation was shown to be a suitable pattern for locomotion in both
water and viscous fluid.
We consider the embodiment of a microbial fuel cell using artificial muscle actuators. The microbial fuel cell digests
organic matter and generates electricity. This energy is stored in a capacitor bank until it is discharged to power one of
two complimentary artificial muscle technologies: the dielectric elastomer actuator and the ionic-polymer metal
composite. We study the ability of the fuel cell to generate useful actuation and consider appropriate configurations to
maximally exploit both of these artificial muscle technologies. A prototype artificial sphincter is implemented using a
dielectric elastomer actuator. Stirrer and cilia mechanisms motivate experimentation using ionic polymer metal
composite actuators. The ability of the fuel cell to drive both of these technologies opens up new possibilities for truly
biomimetic soft artificial robotic organisms.
The emergence of soft polymer actuators brings a great deal of excitement in the robotics and biomedical engineering
community because of the possibilities to easily mimic the motion of living organisms and ability to manipulate living
tissue and cells without damaging it. Some of the applications of soft polymer actuators, such as micropumps, require
them to operate at high frequency and large displacement, which usually achieved near resonance. It would be beneficial
for the designer, if he could easily tailor the frequency response and the resonance frequency to suit the operating
conditions. We propose such an effective method of modification of the frequency response of ionic polymer metal
composite (IPMC) actuators by introducing an anisotropic roughness on their surface.
We present a novel linear actuator made from a single Ionic Polymer-Metal Composite (IPMC) strip. In its simplest
form the device activates into the shape of a double-clamped buckled beam. This structure was chosen following
observation of the buckle failure modes of axially compressed beams. The practical realization of this device is made
possible by the development of new manufacturing techniques also described. The benefit of this buckled beam
structure is that bending moments in the two halves of the beam cancel each other out. As a result, only one bending
actuator is needed to form a single linear actuator and there is no need for mechanical joining of separate actuators - a
disadvantage of previous linear actuator designs. The non-rotating nature of the end fixing in the double-clamped
buckled beam also means that joining multiple elements to increase displacement or force is trivial. We present initial
experimental results of a single linear actuator and a balanced, pair-connected linear actuator.
Ionic polymer-metal composites (IPMC) are soft actuators with potential applications in the fields of medicine and
biologically inspired robotics. Typically, an IPMC bends with approximately constant curvature when voltage is applied
to it. More complex shapes were achieved in the past by pre-shaping the actuator or by segmentation and separate
actuation of each segment. There are many applications for which fully independent control of each segment of the
IPMC is not required and the use of external wiring is objectionable. In this paper we propose two key elements needed
to create an IPMC, which can actuate into a complex curve. The first is a connection between adjacent segments, which
enables opposite curvature. This can be achieved by reversing the polarity applied on each side of the IPMC, for
example by a through-hole connection. The second key element is a variable curvature segment. The segment is
designed to bend with any fraction of its full bending ability under given electrical input by changing the overlap of
opposite charge electrodes. We demonstrated the usefulness of these key elements in two devices. One is a bi-stable
buckled IPMC beam, also used as a building block in a linear actuator device. The other one is an IPMC, actuating into
an S-shaped curve with gradually increasing curvature near the ends. The proposed method of manufacturing holds
promise for a wide range of new applications of IPMCs, including applications in which IPMCs are used for sensing.
Demands from the fields of bio-medical engineering and biologically-inspired robotics motivate a growing interest in
actuators with properties similar to biological muscle, including ionic polymer-metal composites (IPMC), the focus of
this study. IPMC actuators consist of an ion-conductive polymer membrane, coated with thin metal electrodes on both
sides and bend when voltage is applied. Some of the advantages of IPMC actuators are their softness, lack of moving
parts, easy miniaturization, light weight and low actuation voltage. When used in bio-mimetic robotic applications, such
as a snake-like swimming robot, locomotion speed can be improved by increasing the bending amplitude. However, it
cannot be improved much by increasing the driving voltage, because of water electrolysis. To enhance the bending
response of IPMCs we created a "preferred" bending direction by anisotropic surface modification. Introduction of
anisotropic roughness with grooves across the length of the actuator improved the bending response by a factor of 2.1.
Artificially introduced cracks on the electrodes in direction, in which natural cracks form by bending, improved bending
response by a factor of 1.6. Anisotropic surface modification is an effective method to enhance the bending response of
IPMC actuators and does not compromise their rigidity under loads perpendicular to the bending plane.