Development and Characterisation of a Multi-material 3D Printed Torsion Spring

Compliant actuation methods are popular in robotics applications where interaction with complex and unpredictable environments and objects is required. There are a number of ways of achieving this, but one common method is Series Elastic Actuation (SEA). In a recent version of their Unified Snake robot, Choset et al. incorporated a Series Elastic Element (SEE) in the form of a rubber torsional spring. This pa- per explores the possibility of using multi-material 3D printing to produce similar SEEs. This approach would facilitate the fabrication and testing of different spring variants and minimise the assembly required. This approach is evaluated by characterizing the behavior of two printed SEEs with different dimensions. The springs exhibit predictable viscoelastic behavior that is well described by a five element Wiechert model. We find that individual springs behave predictably and that multiple copies of the same spring design exhibit good consistency

MEMS micromirrors for imaging applications

Strathclyde theses - ask staff. Thesis no. : T13478Optical MEMS (microelectromechanical systems) are widely used in various applications. In this thesis, the design, simulation and characterisation of two optical MEMS devices for imaging applications, a varifocal micromirror and a 2D scanning micromirror, are introduced. Both devices have been fabricated using the commercial Silicon-on-Insulator multi-users MEMS processes (SOIMUMPs), in the 10 m thick Silicon-on-Insulator (SOI) wafer. Optical MEMS device with variable focal length is a critical component for imaging system miniaturisation. In this thesis, a thermally-actuated varifocal micromirror (VFM) with 1-mm-diameter aperture is introduced. The electrothermal actuation through Joule heating of the micromirror suspensions and the optothermal actuation using incident laser power absorption have been demonstrated as well as finite element method (FEM) simulation comparisons. Especially, the optical aberrations produced by this VFM have been statistically quantified to be negligible throughout the actuation range. A compact imaging system incorporating this VFM has been demonstrated with high quality imaging results. MEMS 2D scanners, or scanning micromirrors, are another type of optical MEMS which have been widely investigated for applications such as biomedical microscope imaging, projection, retinal display and optical switches for telecommunication network, etc. For large and fast scanning motions, the actuation scheme to scan a micromirror in two axes, the structural connections and arrangement are fundamental. The microscanner introduced utilises two types of actuators, electrothermal actuators and electrostatic comb-drives, to scan a 1.2-mm-diameter gold coated silicon micromirror in two orthogonal axes. With assistance of FEM software, CoventorWare, the structure optimisation of actuators and flexure connections are presented. The maximum optical scan angles in two axes by each type of actuator individually and by actuating the two at the same time have been characterised experimentally. By programming actuation signals, the microscanner has achieved a rectangular scan pattern with 7° 10° angular-scan-field at a line-scan rate of around 1656 Hz.Optical MEMS (microelectromechanical systems) are widely used in various applications. In this thesis, the design, simulation and characterisation of two optical MEMS devices for imaging applications, a varifocal micromirror and a 2D scanning micromirror, are introduced. Both devices have been fabricated using the commercial Silicon-on-Insulator multi-users MEMS processes (SOIMUMPs), in the 10 m thick Silicon-on-Insulator (SOI) wafer. Optical MEMS device with variable focal length is a critical component for imaging system miniaturisation. In this thesis, a thermally-actuated varifocal micromirror (VFM) with 1-mm-diameter aperture is introduced. The electrothermal actuation through Joule heating of the micromirror suspensions and the optothermal actuation using incident laser power absorption have been demonstrated as well as finite element method (FEM) simulation comparisons. Especially, the optical aberrations produced by this VFM have been statistically quantified to be negligible throughout the actuation range. A compact imaging system incorporating this VFM has been demonstrated with high quality imaging results. MEMS 2D scanners, or scanning micromirrors, are another type of optical MEMS which have been widely investigated for applications such as biomedical microscope imaging, projection, retinal display and optical switches for telecommunication network, etc. For large and fast scanning motions, the actuation scheme to scan a micromirror in two axes, the structural connections and arrangement are fundamental. The microscanner introduced utilises two types of actuators, electrothermal actuators and electrostatic comb-drives, to scan a 1.2-mm-diameter gold coated silicon micromirror in two orthogonal axes. With assistance of FEM software, CoventorWare, the structure optimisation of actuators and flexure connections are presented. The maximum optical scan angles in two axes by each type of actuator individually and by actuating the two at the same time have been characterised experimentally. By programming actuation signals, the microscanner has achieved a rectangular scan pattern with 7° 10° angular-scan-field at a line-scan rate of around 1656 Hz

A Biologically Inspired Controllable Stiffness Multimodal Whisker Follicle

This thesis takes a soft robotics approach to understand the computational role of a soft whisker follicle with mechanisms to control the stiffness of the whisker. In particular, the thesis explores the role of the controllable stiffness whisker follicle to selectively favour low frequency geometric features of an object or the high frequency texture features of the object.Tactile sensing is one of the most essential and complex sensory systems for most living beings. To acquire tactile information and explore the environment, animals use various biological mechanisms and transducing techniques. Whiskers, or vibrissae are a form of mammalian hair, found on almost all mammals other than homo sapiens. For many mammals, and especially rodents, these whiskers are essential as a means of tactile sensing.The mammalian whisker follicle contains multiple sensory receptors strategically organised to capture tactile sensory stimuli of different frequencies via the vibrissal system. Nocturnal mammals such as rats heavily depend on whisker based tactile perception to find their way through burrows and identify objects. There is diversity in the whiskers in terms of the physical structure and nervous innervation. The robotics community has developed many different whisker sensors inspired by this biological basis. They take diverse mechanical, electronic, and computational approaches to use whiskers to identify the geometry, mechanical properties, and objects' texture. Some work addresses specific object identification features and others address multiple features such as texture and shape etc. Therefore, it is vital to have a comprehensive discussion of the literature and to understand the merits of bio-inspired and pure-engineered approaches to whisker-based tactile perception.The most important contribution is the design and use of a novel soft whisker follicle comprising two different frequency-dependent data capturing modules to derive more profound insights into the biological basis of tactile perception in the mammalian whisker follicle. The new insights into the biological basis of tactile perception using whiskers provide new design guidelines to develop efficient robotic whiskers

Development of design criteria for novel 3D-printed quadric-surfaced sludge digesters for wastewater infrastructure

The quadric-surfaced sludge digester (QSD), also known as the egg-shaped sludge digester, has proven its advantages over traditional cylindrical digesters recently. A reduction in operational cost is the dominant factor. Its shell can be described as a revolution of a parabola with the apex and base being either tapered or spherical. This shape provides a surface free of discontinuities, which is advantageous regarding the efficiency during mixing. Since the shape does not produce areas of inactive fluid motion within the tank, sludge settlement and an eventual grit build-up are avoided. The stresses developed in the shell of the sludge digester, vary along the meridian and equatorial diameters. A non-dimensional parameter, ξ, defines the height-to-diameter aspect ratio which is used to delineate the parametric boundary conditions of the shell’s surface. Three groups of analyses were conducted to determine the orthogonal stresses in the shell of the QSD. The first-principles numerical models ran reasonably quickly, and many iterations were made during the study. The results showed that they were in within the range 5.34% to 7.2% to 2D FEA simulations. The 3D FEA simulations were within the range of 8.3% to 9.2% to the MATLAB time-history models. This is a good indicator that the first principles numerical models are an excellent time-saving method to predict the behaviour of the QSD under seismic excitation. Upon examining the criteria for the design, analysing the results for the 2D FEA simulations showed that the fill height is not a significant variable with sloshing however the 3D FEA showed that the hydrostatic pressure is a significant variable. With the maximum tensile stress of the 3D-printed ABS being 24.4 MPa, the overall maximum stress of 5.45 MPa, the material can be a viable option for the use of QSD construction in small island developing states (SIDS)

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

Atomic Scale Microscopy of Zr-based Bulk Metallic Glasses Processed by Various Routes

Bulk metallic glasses (BMGs) exhibit a rare combination of strength and toughness that is difficult to achieve by other materials. These properties make them favourable for a diverse range of engineering applications. However, their disordered amorphous structure invokes catastrophic failure with shear bands localisation, limiting their industrial development as structural materials. Moreover, it is not yet clear how to quantitatively link their microstructural features to processing and mechanical properties. The aim of this thesis was to quantitatively analyse the structural features contributing to local hardness variations in thermomechanically processed zirconium (Zr)-based BMGs. Advanced atom probe tomography (APT) techniques were used to observe structural and chemical changes in these BMGs. APT operational parameters were optimised and tested for robust data outcomes. APT cluster analysis was effectively utilised in the characterisation of nanoscale heterogeneities in the BMG microstructure. The chemical composition of the nanoscale heterogeneities was roughly Zr27Cu29Al21Ni19Nb4 (at. %) in Zr63.96Cu13.36Ni10.29Al11.04Nb1.25 (at. %), and Zr22Cu29Al17Ni23Ti9 (at. %) in Zr52.5Cu17.9Ni14.6Al10Ti5 (at. %). Their chemistry was experimentally reported herein for the first time. Additionally, an ab-initio molecular dynamic (AIMD) simulation was used to simulate the atomistic distribution in a Zr-based BMG. Clusters observed in APT assigned as MRO regions were found synonymous to the shear band nucleation zones. Beyond the novel methodological rigor introduced here, the findings provide a new, independent validation of the inverse correlation between local hardness and size of the MRO regions, with their chemical compositions, providing a novel handle on the quest for understanding microstructure- property-processing relationship in BMGs