311 research outputs found
Development of a Fabrication Technique for Soft Planar Inflatable Composites
Soft robotics is a rapidly growing field in robotics that combines aspects of biologically inspired characteristics to unorthodox methods capable of conforming and/or adapting to unknown tasks or environments that would otherwise be improbable or complex with conventional robotic technologies. The field of soft robotics has grown rapidly over the past decade with increasing popularity and relevance to real-world applications. However, the means of fabricating these soft, compliant and intricate robots still poses a fundamental challenge, due to the liberal use of soft materials that are difficult to manipulate in their original state such as elastomers and fabric. These material properties rely on informal design approaches and bespoke fabrication methods to build soft systems. As such, there are a limited variety of fabrication techniques used to develop soft robots which hinders the scalability of robots and the time to manufacture, thus limiting their development.
This research focuses towards developing a novel fabrication method for constructing soft planar inflatable composites. The fundamental method is based on a sub-set of additive manufacturing known as composite layering. The approach is designed from a planar manner and takes layers of elastomeric materials, embedded strain-limiting and mask layers. These components are then built up through a layer-by-layer fabrication method with the use of a bespoke film applicator set-up. This enables the fabrication of millimetre-scale soft inflatable composites with complex integrated masks and/or strain-limiting layers. These inflatable composites can then be cut into a desired shape via laser cutting or ablation. A design approach was also developed to expand the functionality of these inflatable composites through modelling and simulation via finite element analysis. Proof of concept prototypes were designed and fabricated to enable pneumatic driven actuation in the form of bending soft actuators, adjustable stiffness sensor, and planar shape change. This technique highlights the feasibility of the fabrication method and the value of its use in creating multi-material composite soft actuators which are thin, compact, flexible, and stretchable and can be applicable towards real-world application
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4D printing of shape-changing thermo-responsive textiles
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThis research reviews the state-of-the-art literature on the two-emerging material-driven
Additive Manufacturing (AM) strategies, Functionally Graded Additive Manufacturing (FGAM)
and 4D Printing (4DP) to recognise, select and implement the appropriate materials, design
and fabrication methods to produce shape-changing thermo-responsive textiles. Shapememory
polymers (SMPs) are required to provide the active properties required to sense
and self-actuate when subjected to an appropriate stimulus over time. The current
availability of SMPs for AM in the commercial market is limited and expensive. To ensure a
wider uptake of 4DP, the aim of this research is to develop a material selection framework
to discover, define and select commercially available thermoplastics as potential SMPs for
use in material extrusion (ME) 4DP. The theoretical and practical knowledge to create a
thermally actuated dual-state mechanism (DSM) active structure is described at a feasible
level for users with different backgrounds and knowledge levels in 4DP. The experiments
showed that commercial AM filaments could be used for 4DP, but not all materials exhibit
shape memory properties despite belonging to the same material type. The shape recovery
performance and repeatability of an SMP would also vary according to the programming
condition. The next stage of this research details the development and testing of polymertextile
composites using direct ME of PLA filaments on synthetic mesh fabrics. T-peel test
results revealed that the compatibility between the printing material and the textile substrate
fibre type has a dominant effect on the peel resistance of ME polymer-textile composite. The
research demonstrated the use of 4DP as an alternative and novel technique for the 3D
manipulation of textile fabrics. The shape transformation studies presented a proof-ofconcept
that the accuracy of deformation and the shape-shifting patterns of the thermoresponsive
textiles can be controlled by the geometrical dimensions and structural
arrangement of the printed SMP structure on the textile substrate. The findings will enable
researchers and designers to take advantage of the optimum parameters to discover new
shape transformations and to create potential applications in the AM fashion and textile
industry
MEMS micro-contact printing engines
This thesis investigates micro-contact printing (µCP) engines using micro-electro-mechanical
systems (MEMS). Such engines are self-contained and do not require further optical
alignment and precision manipulation equipment. Hence they provide a low-cost and
accessible method of multilevel surface patterning with sub-micron resolution. Applications
include the field of biotechnology where the placement of biological ligands at well
controlled locations on substrates is often required for biological assays, cell studies and
manipulation, or for the fabrication of biosensors.
A miniaturised silicon µCP engine is designed and fabricated using a wafer-scale MEMS
fabrication process and single level and bi-level µCP are successfully demonstrated. The
performance of the engine is fully characterised and two actuation modes, mechanical and
electrostatic, are investigated. In addition, a novel method of integrating the stamp material
into the MEMS process flow by spray coating is reported.
A second µCP engine formed by wafer-scale replica moulding of a polymer is developed to
further drive down cost and complexity. This system carries six complementary patterns and
allows six-level µCP with a layer-to-layer accuracy of 10 µm over a 5 mm x 5 mm area
without the use of external aligning equipment. This is the first such report of aligned
multilevel µCP.
Lastly, the integration of the replica moulded engine with a hydraulic drive for controlled
actuation is investigated. This approach is promising and proof of concept has been provided
for single-level patterning
Designing LMPA-Based Smart Materials for Soft Robotics Applications
This doctoral research, Designing LMPA (Low Melting Point Alloy) Based Smart Materials for Soft Robotics Applications, includes the following topics: (1) Introduction; (2) Robust Bicontinuous Metal-Elastomer Foam Composites with Highly Tunable Mechanical Stiffness; (3) Actively Morphing Drone Wing Design Enabled by Smart Materials for Green Unmanned Aerial Vehicles; (4) Dynamically Tunable Friction via Subsurface Stiffness Modulation; (5) LMPA Wool Sponge Based Smart Materials with Tunable Electrical Conductivity and Tunable Mechanical Stiffness for Soft Robotics; and (6) Contributions and Future Work.Soft robots are developed to interact safely with environments. Smart composites with tunable properties have found use in many soft robotics applications including robotic manipulators, locomotors, and haptics. The purpose of this work is to develop new smart materials with tunable properties (most importantly, mechanical stiffness) upon external stimuli, and integrate these novel smart materials in relevant soft robots. Stiffness tunable composites developed in previous studies have many drawbacks. For example, there is not enough stiffness change, or they are not robust enough. Here, we explore soft robotic mechanisms integrating stiffness tunable materials and innovate smart materials as needed to develop better versions of such soft robotic mechanisms. First, we develop a bicontinuous metal-elastomer foam composites with highly tunable mechanical stiffness. Second, we design and fabricate an actively morphing drone wing enabled by this smart composite, which is used as smart joints in the drone wing. Third, we explore composite pad-like structures with dynamically tunable friction achieved via subsurface stiffness modulation (SSM). We demonstrate that when these composite structures are properly integrated into soft crawling robots, the differences in friction of the two ends of these robots through SSM can be used to generate translational locomotion for untethered crawling robots. Also, we further develop a new class of smart composite based on LMPA wool sponge with tunable electrical conductivity and tunable stiffness for soft robotics applications. The implications of these studies on novel smart materials design are also discussed
Dynamics and Controls of Fluidic Pressure-Fed Mechanism (FPFM) of Nanopositioning System
Flexure or compliant mechanisms are employed in many precisions engineered devices due to their compactness, linearity, resolution, etc. Yet, critical issues remain in motion errors, thermal instability, limited bandwidth, and vibration of dynamic systems. Those issues cannot be negligible to maintain high precision and accuracy for precision engineering applications. In this thesis, a novel fluidic pressure-fed mechanism (FPFM) is proposed and investigated. The proposed method is designing internal fluidic channels inside the spring structure of the flexure mechanism using the additive manufacturing (AM) process to overcome addressed challenges. By applying pneumatic/hydraulic pressure and filling media into fluidic channels, dynamic characteristics of each spring structure of the flexure mechanism can be altered or adjusted to correct motion errors, increase operating speed, and suppress vibration. Additionally, FPFM can enhance thermal stability by flowing fluids without affecting the motion quality of the dynamic system. Lastly, the motion of the nanopositioning system driven by FPFM can provide sub-nanometer resolution motion, and this enables the nanopositioning system to have two linear motion in a monolithic structure. The main objective of this thesis is to propose and validate the feasibility of FPFM that can ultimately be used for a monolithic FPFM dual-mode stage for providing high positioning performance without motion errors while reducing vibration and increasing thermal stability and bandwidth
Investigating the effect of ultrasonic consolidation on shape memory alloy fibres
This research was driven by the capability of the Ultrasonic Consolidation (UC)
manufacturing process to create smart metal matrix composites for use within high value
engineering sectors, such as aerospace. The UC process is a hybrid additive/subtractive
manufacturing process that embeds fibres into metal matrices via the exploitation of a
high plastic flow, low temperature phenomenon encountered at ultrasonic frequency
mechanical vibrations. The research concerned an investigation of the use of the UC
process for embedding Nickel-Titanium alloy (NiTi) shape memory alloy (SMA) fibres
into Aluminium (Al) matrices which could potentially be used as vibration damping
structures, stress state variable structures, as well as other future smart material
applications.
It was hypothesised that the fibre volume fraction within a UC matrix was limited due to
a reduction in foil/foil bonding, caused by increased fibre numbers, as opposed to the
total level of plastic flow of the matrix material being insufficient to accommodate the
increased fibre numbers.
This hypothesis was tested by increasing the NiTi SMA fibre volume fraction, within an
Al 3003 (T0) metal matrix, beyond that of previous UC work. The metal matrix and the
fibre matrix interface of these samples was then microscopically analysed and the
overall UC sample integrity was tested via mechanical peel testing. It was found that a
fibre volume fraction of ~9.8% volume (30 X Ø100 µm SMA fibres) was the maximum
achievable using an Al 3003 (T0) 100 µm thick foil material and conventional UC fibre
embedding.
A revised hypothesis was postulated that the interlaminar structure created during UC
was affected by the process parameters used. This interlaminar structure contained
areas of un-bonded foil and the increase of UC process parameters would reduce this
area of un-bonded foil. Areas of this interlaminar structure were also thought to have
undergone grain refinement which would have created harder material areas within the
structure. It was suggested that maximum plastic flow of the matrix had not been
reached and thus the use of larger diameter NiTi SMA fibres were embedded to
increase the effective SMA fibre volume fraction within Al 3003 (T0) UC samples. It was
suggested that the embedding of SMA fibres via UC had an abrasive effect on the SMA
fibres and the SMA fibres had an effect on the Al 3003 (T0) microstructure. It was further
suggested that the activation of UC embedded SMA fibres would reduce the strength of
the fibre/matrix interface and the matrix would impede the ability of the SMA fibres to
contract causing a forceful interaction at the fibre to matrix interface, weakening the UC
structure.
The investigation to test the revised hypothesis was broken down into three sections of
study.
Study 1 was a methodology to determine the characteristics of the interlaminar surface
created via UC and how this surface affected the nature of the consolidated sample. UC
samples of Al 3003 (T0) were manufactured using a range of process parameters. The
analysis involved optical microscopy to determine the UC weld density and the
interlaminar surface; mechanical peel testing to quantify the interlaminar bond strength;
white light interferometry to measure the interlaminar surface profile and microhardness
measurements to determine the hardness of the interlaminar material.
Study 2 was a methodology to allow the analysis of the microstructural and mechanical
interactions at the fibre/matrix interface, post-UC. Al 3003 (T0) samples were
manufactured via UC using a range of process parameters with various NiTi SMA fibre
diameters embedded. The analysis involved using mechanical peel testing to determine
the interlaminar bond strength; optical microscopy to determine the level of fibre
encapsulation; scanning electron microscopy and focussed ion beam analysis to
analyse the fibre and matrix grain structures and microscopic interactions.
Study 3 was a methodology to investigate the fibre usage as would be expected from
envisaged applications of an SMA containing metal matrix composite. Samples were
manufactured using a range of UC process parameters with various SMA fibre
diameters embedded and the embedded SMA fibres were subjected to different
extension/contraction cycle numbers. The analysis involved using mechanical peel
testing to determine the interlaminar bond strength; optical microscopy to determine the
level of fibre encapsulation and the interlaminar effect of fibre activation; fibre pullout
testing to measurement the strength of the fibre/matrix interaction and load rate testing
of the activated SMA fibres to monitor performance.
The interlaminar surface was found to affect the strength and density of interlaminar
bonding during the UC process and the use of higher UC process parameters affected
this interlaminar structure. Levels of un-bonded material were found within the
interlaminar structure and these levels were found to decrease with increasing
sonotrode amplitude and pressure with reducing speed. It was suggested that a
specifically texture sonotrode could be developed to modify the interlaminar structure to
the requirements of the intended sample application. The measurement of the
interlaminar material hardness was unsuccessful and future work would likely require a
different methodology to measuring this.
The work identified a grain refining effect of the embedded SMA fibres on the Al 3003
(T0) matrix material, (grain sizes were reduced from ~15 µm to <1 µm within 20 µm of
the SMA fibres), as well as localised damage caused by the UC process to the SMA
fibres. The performance of the activated SMA fibres established that this damage did not
prohibit the ability of the SMAs to function however the compressive nature of the Al
3003 (T0) matrix was identified as reducing the ability of the SMA fibres to contract.
Additionally it was found that the activation of SMA fibres within an Al 3003 (T0) matrix
resulted in a reduction of the fibre/matrix interface strength which allowed fibres to be
pulled from the composite with greater ease (a loss of ~80% was encountered after a
single activation and extension cycle). The use of larger SMA fibre diameters allowed for
the fibre volume fraction to be increased however the activation of these SMA fibres had
a delaminating effect on the Al 3003 (T0) structure due to the size of the radial
expansion of the SMA fibre.
The work furthered the understanding of the effect of UC on SMA fibres and highlighted
the importance of the interlaminar surface in UC and that to increase the SMA fibre
volume fraction to a useable level (25-50%) then an alternative fibre embedding method
within UC is required. The fibre/matrix interface interactions during SMA activation have
implications in the ability of UC SMA embedded smart metal matrix composites to
function successfully due to weakening effects on fibre matrix interface strength and the
ability to achieve SMA fibre activation within the metal matrix
A Digital Manufacturing Process For Three-Dimensional Electronics
Additive manufacturing (AM) offers the ability to produce devices with a degree of three-dimensional complexity and mass customisation previously unachievable with subtractive and formative approaches. These benefits have not transitioned into the production of commercial electronics that still rely on planar, template-driven manufacturing, which prevents them from being tailored to the end user or exploiting conformal circuitry for miniaturisation. Research into the AM fabrication of 3D electronics has been demonstrated; however, because of material restrictions, the durability and electrical conductivity of such devices was often limited.
This thesis presents a novel manufacturing approach that hybridises the AM of polyetherimide (PEI) with chemical modification and selective light-based synthesis of silver nanoparticles to produce 3D electronic systems. The resulting nanoparticles act as a seed site for the electroless deposition of copper. The use of high-performance materials for both the conductive and dielectric elements created devices with the performance required for real-world applications.
For printing PEI, a low-cost fused filament fabrication (FFF); also known as fused deposition modelling (FDM), printer with a unique inverted design was developed. The orientation of the printer traps hot air within a heated build environment that is open on its underside allowing the print head to deposit the polymer while keeping the sensitive components outside. The maximum achievable temperature was 120 °C and was found to reduce the degree of warping and the ultimate tensile strength of printed parts. The dimensional accuracy was, on average, within 0.05 mm of a benchmark printer and fine control over the layer thickness led to the discovery of flexible substrates that can be directly integrated into rigid parts.
Chemical modification of the printed PEI was used to embed ionic silver into the polymer chain, sensitising it to patterning with a 405 nm laser. The rig used for patterning was a re-purposed vat-photopolymerisation printer that uses a galvanometer to guide the beam that is focused to a spot size of 155 µm at the focal plane. The positioning of the laser spot was controlled with an open-sourced version of the printers slicing software. The optimal laser patterning parameters were experimentally validated and a link between area-related energy density and the quality of the copper deposition was found. In tests where samples were exposed to more than 2.55 J/cm^2, degradation of the polymer was experienced which produced blistering and delamination of the copper. Less than 2.34 J/cm^2 also had negative effect and resulted in incomplete coverage of the patterned area. The minimum feature resolution produced by the patterning setup was 301 µm; however, tests with a photomask demonstrated features an order of magnitude smaller. The non-contact approach was also used to produce conformal patterns over sloped and curved surfaces.
Characterisation of the copper deposits found an average thickness of 559 nm and a conductivity of 3.81 × 107 S/m. Tape peel and bend fatigue testing showed that the copper was ductile and adhered well to the PEI, with flexible electronic samples demonstrating over 50,000 cycles at a minimum bend radius of 6.59 mm without failure. Additionally, the PEI and copper combination was shown to survive a solder reflow with peak temperatures of 249°C. Using a robotic pick and place system a test board was automatically populated with surface mount components as small as 0201 resistors which were affixed using high-temperature, Type-V Tin-Silver-Copper solder paste.
Finally, to prove the process a range of functional demonstrators were built and evaluated. These included a functional timer circuit, inductive wireless power coils compatible with two existing standards, a cylindrical RF antenna capable of operating at several frequencies below 10 GHz, flexible positional sensors, and multi-mode shape memory alloy actuators
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