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.
Dielectric elastomer (DE) actuators such as conventional double cone configurations have demonstrated that coupled DE membranes can be rigidly-coupled to execute antagonistic out-of-plane actuation. This paper presents experimental analysis of the compliant coupling in the emerging magnetically-coupled DE actuator (MCDEA) design, which exploits contactless magnetic repulsion to create a frictionless coupling between DE membranes. The compliance of this coupling enables the advantage of having two different actuation modes: antagonistic reciprocation and bi-directional expansion. However, since this compliance adds an additional degree-of-freedom, it increases the complexity of the actuator’s dynamics because the coupling distance can exhibit oscillatory behavior that is distinct from each of the actuator’s output oscillations in terms of phase difference and frequency. In this work, the relationship between DEA membrane stiffness and required magnetic force is experimentally analyzed before we present an investigation into the phase space of the compliant coupling and its relationship with the stroke amplitude. It is shown that the fundamental frequency of the MCDEA’s output stroke (46.1 Hz) corresponds to a super-harmonic frequency of the magnetic coupling that is double that of the output. The fundamental frequency of the coupling (87.6 Hz) is found to correspond to a second resonant peak in the MCDEA’s output with a much lower amplitude than at 46.1 Hz. This suggests that the dynamics can be exploited by controlling the excitation frequency for unidirectional push/pull or bidirectional expansion/contraction actuation, which creates potential for new compliant DE actuator and generator designs.
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.
The inherent elasticity of dielectric elastomer actuators (DEAs) gives this technology great potential in energy efficient locomotion applications. In this work, a modular double cone DEA is developed with reduced manufacturing and maintenance time costs. This actuator can lift 45 g of mass (5 times its own weight) while producing a stroke of 10.4 mm (23.6% its height). The contribution of the elastic energy stored in antagonistic DEA membranes to the mechanical work output is experimentally investigated by adding delay into the DEA driving voltage. Increasing the delay time in actuation voltage and hence reducing the duty cycle is found to increase the amount of elastic energy being recovered but an upper limit is also noticed. The DEA is then applied to a three-segment leg that is able to move up and down by 17.9 mm (9% its initial height), which demonstrates the feasibility of utilizing this DEA design in legged locomotion.
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.
In recent studies, stack based Dielectric Elastomer Actuators (DEAs) have been successfully used in haptic feedback and sensing applications. However, limitations in the fabrication method, and materials used to con- struct stack actuators constrain their force and displacement output per unit volume. This paper focuses on a fabrication process enabling a stacked elastomer actuator to withstand the high tensile forces needed for high power applications, such as mimetics for mammalian muscle contraction (i.e prostheses), whilst requiring low voltage for thickness-mode contractile actuation. Spun elastomer layers are bonded together in a pre-strained state using a conductive adhesive filler, forming a Laminated Inter-Penetrating Network (L-IPN) with repeatable and uniform electrode thickness. The resulting structure utilises the stored strain energy of the dielectric elas- tomer to compress the cured electrode composite material. The method is used to fabricate an L-IPN example, which demonstrated that the bonded L-IPN has high tensile strength normal to the lamination. Additionally, the uniformity and retained dielectric layer pre-strain of the L-IPN are confirmed. The described method is envisaged to be used in a semi-automated assembly of large-scale multi-layer stacks of pre-strained dielectric layers possessing a tensile strength in the range generated by mammalian muscle.
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.
Robotic devices typically utilize rigid components in order to produce precise and robust operation. Rigidity becomes a
significant impediment, however, when navigating confined or constricted environments e.g. search-and-rescue,
industrial pipe inspection. In such cases adaptively conformable soft structures become optimal. Dielectric elastomers
(DEs) are well suited for developing such soft robots since they are inherently compliant and can produce large musclelike
actuation strains. In this paper, a soft segmented inchworm robot is presented that utilizes pneumatically-coupled DE
membranes to produce inchworm-like locomotion. The robot is constructed from repeated body segments, each with a
simple control architecture, so that the total length can be readily adapted by adding or removing segments. Each
segment consists of a soft inflatable shell (internal pressure in range of 1.0-15.9 mBar) and a pair of antagonistic DE
membranes (VHB 4905). Experimental testing of a single body segment is presented and the relationship between drive
voltage, pneumatic pressure and active displacement is characterized. This demonstrates that pneumatic coupling of DE
membranes induces complex non-linear electro-mechanical behaviour as drive voltage and pneumatic pressure are
altered. Locomotion of a two-segment inchworm robot prototype with a passive length of 80 mm is presented. Artificial
setae are included on the body shell to generate anisotropic friction for locomotion. A maximum locomotion speed of 4.1
mm/s was recorded at a drive frequency of 1.5 Hz, which compares favourably to biological counterparts. Future
development of the soft inchworm robot are discussed including reflexive low-level control of individual segments.
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
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.
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°.
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.