Artifact-based calibration and performance verification of the MScMS-II

Large scale measuring systems, i.e. measuring systems characterized by a measurement volume from some meters up to some hundreds of meters, are gaining importance in industry to check large parts or track the position of automated vehicles. In contrast with classical monolithic measuring systems, modern large scale measuring systems are constituted by constellations of sensors able to track the position of objects by triangulation or trilateration. This new design allows a greater system flexibility, scalability, and portability, together with a general reduction of costs. The MScMS-II is a large scale measuring system based on infrared triangulation. It has been designed to guarantee the maximum flexibility and reconfigurability, so every set-up procedure has been reduced as much as possible, so that its deployment and calibration requires a short time. However, its accuracy could benefit of a more complete volumetric calibration through the definition of a model of the volumetric error to be compensated. This work continues the one proposed at the CAT2012 conference [1]. An artifact has been developed which is constituted by a series of infrared reflective spheres, thus being well visible by the MScMS-II system. It has been calibrated with a ~1 µm uncertainty. It carries two series of balls. A pair of spheres with a reciprocal distance equal to 800 mm can be used for system calibration. A series of couples of balls with reciprocal distances equal to 200, 400, 600, 800, and 1000 mm respectively can be adopted for performance verification similarly to what is suggested in the ISO 10360 series of standards for CMMs. Experimental results are proposed for the calibration and performance verification procedure of the MScMS-II system

Fluid quantity gaging

A system for measuring the mass of liquid in a tank on orbit with 1 percent accuracy was developed and demonstrated. An extensive tradeoff identified adiabatic compression as the only gaging technique that is independent of gravity or its orientation, and of the size and distribution of bubbles in the tank. This technique is applicable to all Earth-storable and cryogenic liquids of interest for Space Station use, except superfluid helium, and can be applied to tanks of any size, shape, or internal structure. Accuracy of 0.2 percent was demonstrated in the laboratory, and a detailed analytical model was developed and verified by testing. A flight system architecture is presented that allows meeting the needs of a broad range of space fluid systems without custom development for each user

Measurement and Modelling of Soft Solid Layers in Cleaning Applications

Fouling and effective cleaning are important operating issues in the food and pharmaceutical industries, which need to be managed well to ensure process hygiene and productivity. In order to understand fouling and cleaning mechanisms, methods are required to quantify soft solid soil or deposit characteristics by measuring these in situ. This dissertation describes the development of millimanipulation and two new fluid dynamic gauging (FDG) devices, namely sideways FDG (SiDG) and integrated FDG (iFDG), and demonstrates their application for in situ measurement. Computational fluid dynamic (CFD) simulations of the flow patterns using the volume of fluid method were performed which enables previously inaccessible information to be extracted from the experimental data. The millimanipulation device reported by Magens et al., J Food Eng, 197 (2017) 48-59 measures the force experienced by a blade as it is pushed through a soil layer. The deformation of layers of viscoplastic petroleum jelly, soft white paraffin and toothpaste were studied and simulated using the regularized Bingham and the bi-viscosity models. The simulations gave good agreement with experimental results: combining visualisation and an interrupted testing mode allowed the material’s yield stress to be estimated. The SiDG device allows one to study the initial and long-term swelling of soft solid layers. The concept was implemented, commissioned and demonstrated by monitoring the swelling of gelatin, poly(vinyl acetate) (PVAc) and complex model soil layers at different pH and temperatures. All these materials underwent rapid initial hydration, followed by different longer term behaviour: gelatin and PVAc layers at pH < 11 exhibited Fickian diffusion control while at pH ≥ 11, PVAc exhibited relaxation control associated with hydrolysis. In the iFDG system the distances between the nozzle head and the soil layer, and the metallic substrate, are measured simultaneously by incorporating an inductive sensor in the gauging nozzle. The iFDG device was taken from concept to demonstration with a range of gauging liquids: water, UHT milk (opaque), a more viscous Newtonian fluid (washing-up liquid) and non-Newtonian aqueous solutions of 1 wt% and 3 wt% carboxymethyl cellulose (CMC). The CFD simulations gave good agreement with the experimental data. An ice growth experiment was performed using the iFDG device to demonstrate its application to monitoring growth of fouling layers. The CFD simulations were extended to consider the coupled flows which can arise in FDG measurements, where the stressed imposed by the gauging liquid flow can deform the soft solid soil layer. Two-fluid simulations were performed to estimate the change of topography of a petroleum jelly layer subject to FDG testing at different clearances. Acceptable agreement between the simulation results and measurements was obtained, and the observed differences were attributed to tubing-induced artefacts. A short feasibility study considered extending the approach to the three-fluid problem when a coherent liquid jet impinges horizontally on a horizontal plane coated with a soft solid soil layer. The results showed promising agreement with experiments on water jet cleaning of petroleum jelly layers.Taiwan Cambridge Scholarship (Cambridge Trust and Ministry of Education, Taiwan

Chromatic confocal gauging for high precision dimensional metrology

Interest in the chromatic confocal microscope in the high precision dimensional metrology industry is growing rapidly. In fact, the chromatic confocal microscope offers a “stylus like” distance measurement applicable to various surface types. In addition, the chromatic confocal microscope can potentially compete in resolution with contact measurement probes, while significantly increasing the sampling rate to several kHz. Therefore, such technology is key to the Taylor Hobson Ltd. strategy. The work embodied in this thesis focuses on the design, development, and evaluation of a low cost and high resolution version of the chromatic confocal microscope. Both product are currently in pre-production phase. The low cost version the chromatic confocal microscope is designed to be a compact and cost effective system while exhibiting “state of the art” performances. In fact, the raw material cost of the system is below £500, this being achieved while exhibiting an optical head outer diameter of 8 mm, a working distance of more than 27 mm, and a resolution better than 100 nm over a measurement range exceeding 7 mm. The high resolution version of the chromatic confocal microscope is dedicated to precision. The aim of the design is to exhibit the highest achievable resolution while maintaining a measurement working distance exceeding 12 mm. By tailoring the chromatic dispersion to be appropriately low, a resolution of better than 10 nm is achieved. Both designs have been tailored within a few design cycles; this has been achieved through the development of two novel models, the spectral irradiance model and the measurement standard deviation model. The spectral irradiance model enables the analytical estimation of the chromatic confocal peak from only the optical parameters of the optical heads. Based on a geometric approach; this is more than 5 times more precise than the previously used model based on wave optics. Furthermore, by applying a fully integrated system design approach incorporating design, production, and test of optical systems, the resulting chromatic confocal system surpasses comparable commercially available chromatic confocal gauges in terms of cost, resolution, numerical aperture, range of measurement, and working distance. Such performance is further enhanced by the use of staircase diffractive surfaces. Staircase diffractive surfaces are special hybrid aspheric diffractive surfaces exhibiting insignificant manufacturing losses allowing the design to be only limited by the scalar diffraction theory used by ray tracing packages. In addition, staircase diffractive lenses permit the passively athermalisation of the optical head of the chromatic confocal microscope. The work encapsulated in this thesis extends the current understanding of the measurement environment impact on chromatic confocal gauges. This study includes the impact of the surface reflectivity, roughness, and slope onto the linearity of the chromatic confocal microscope. Using the previously described findings, methods to mitigate the linearity error induced by the surface roughness, reflectivity, and slope are presented and applied.Engineering and Physical Sciences Research Council (EPSRC) scholarshi

Methods for detailed study of detergent action in cleaning food soils

Dishwasher detergent formulations contain components which dictate the chemical environment (pH, wettability, solubility) of cleaning solutions. The role of these factors, as well as temperature, in the mechanisms controlling the cleaning of a baked heterogeneous food soil from stainless steel substrates was studied using a combination of fluid dynamic gauging, real-time imaging, millimanipulation, and solution analysis techniques. The extent of swelling, which is known to affect cleaning, was determined in situ using a fluid dynamic gauging (FDG) device developed by Wang et al. (2017). A new FDG configuration was developed which enabled measurement of swelling soon after immersion, allowing measurement of initial hydration. These studies were corroborated using a commercial point-light source confocal thickness measurement device. The onset and extent of swelling depended primarily on the solution pH. At temperatures above 35 ᵒC swelling was followed by the liberation of mobile fat present within the soil. Monitoring of droplet evolution allowed the growth and detachment of the oil droplets to be quantified and modelled. The rate of total carbonaceous material released from the soil was studied in separate tests using both stagnant and flowing solutions. The onset and volume of oil released was chiefly determined by the solution temperature and concentration of surfactant. Oil release was not directly related to deposit strength. In millimanipulation the force imposed on a blade being passed through the soil layer is measured. The device was modified to allow submersion and flow of cleaning solution across the sample so that the effect of contact time with the reagent(s) could be studied. The force required to remove the soil changed noticeably after a critical soaking time, from an almost constant value to one which decayed with time. The critical soaking time depended on the temperature, pH, and composition of the cleaning solution and in many cases was associated with a transition from cohesive to adhesive breakdown. This transition occurred on similar timescales to the swelling of the soil. Some agents promoted faster adhesive breakdown. Sinner’s circle is classically used to describe the intentions between temperature, formulation, time and mechanical forces in cleaning. The different techniques allowed these to be quantified, particularly in terms of timescales. The cleaning mechanism was broken into two parallel processes: (I) the hydration and swelling of the soil layer after exposure to aqueous solutions followed by the dewetting and displacement of oils and fats from within the soil structure towards the soil-solution interface, and (II) the ingress of solution at the soil-substrate interface, weakening the adhesive forces attaching the soil to the substrate. Temperature, pH, and surfactant type were demonstrated to act each process to a different extent, influencing the timescales of cleaning.EPSRC iCASE studentship in partnership with P&G

Multi-scale metrology for automated non-destructive testing systems

This thesis was previously held under moratorium from 5/05/2020 to 5/05/2022The use of lightweight composite structures in the aerospace industry is now commonplace. Unlike conventional materials, these parts can be moulded into complex aerodynamic shapes, which are diffcult to inspect rapidly using conventional Non-Destructive Testing (NDT) techniques. Industrial robots provide a means of automating the inspection process due to their high dexterity and improved path planning methods. This thesis concerns using industrial robots as a method for assessing the quality of components with complex geometries. The focus of the investigations in this thesis is on improving the overall system performance through the use of concepts from the field of metrology, specifically calibration and traceability. The use of computer vision is investigated as a way to increase automation levels by identifying a component's type and approximate position through comparison with CAD models. The challenges identified through this research include developing novel calibration techniques for optimising sensor integration, verifying system performance using laser trackers, and improving automation levels through optical sensing. The developed calibration techniques are evaluated experimentally using standard reference samples. A 70% increase in absolute accuracy was achieved in comparison to manual calibration techniques. Inspections were improved as verified by a 30% improvement in ultrasonic signal response. A new approach to automatically identify and estimate the pose of a component was developed specifically for automated NDT applications. The method uses 2D and 3D camera measurements along with CAD models to extract and match shape information. It was found that optical large volume measurements could provide suffciently high accuracy measurements to allow ultrasonic alignment methods to work, establishing a multi-scale metrology approach to increasing automation levels. A classification framework based on shape outlines extracted from images was shown to provide over 88% accuracy on a limited number of samples.The use of lightweight composite structures in the aerospace industry is now commonplace. Unlike conventional materials, these parts can be moulded into complex aerodynamic shapes, which are diffcult to inspect rapidly using conventional Non-Destructive Testing (NDT) techniques. Industrial robots provide a means of automating the inspection process due to their high dexterity and improved path planning methods. This thesis concerns using industrial robots as a method for assessing the quality of components with complex geometries. The focus of the investigations in this thesis is on improving the overall system performance through the use of concepts from the field of metrology, specifically calibration and traceability. The use of computer vision is investigated as a way to increase automation levels by identifying a component's type and approximate position through comparison with CAD models. The challenges identified through this research include developing novel calibration techniques for optimising sensor integration, verifying system performance using laser trackers, and improving automation levels through optical sensing. The developed calibration techniques are evaluated experimentally using standard reference samples. A 70% increase in absolute accuracy was achieved in comparison to manual calibration techniques. Inspections were improved as verified by a 30% improvement in ultrasonic signal response. A new approach to automatically identify and estimate the pose of a component was developed specifically for automated NDT applications. The method uses 2D and 3D camera measurements along with CAD models to extract and match shape information. It was found that optical large volume measurements could provide suffciently high accuracy measurements to allow ultrasonic alignment methods to work, establishing a multi-scale metrology approach to increasing automation levels. A classification framework based on shape outlines extracted from images was shown to provide over 88% accuracy on a limited number of samples

Study and Characterization of a Camera-based Distributed System for Large-Volume Dimensional Metrology Applications

Large-Volume Dimensional Metrology (LVDM) deals with dimensional inspection of large objects with dimensions in the order of tens up to hundreds of meters. Typical large volume dimensional metrology applications concern the assembly/disassembly phase of large objects, referring to industrial engineering. Based on different technologies and measurement principles, a wealth of LVDM systems have been proposed and developed in the literature, just to name a few, e.g., optical based systems such as laser tracker, laser radar, and mechanical based systems such as gantry CMM and multi-joints artificial arm CMM, and so on. Basically, the main existing LVDM systems can be divided into two categories, i.e. centralized systems and distributed systems, according to the scheme of hardware configuration. By definition, a centralized system is a stand-alone unit which works independently to provide measurements of a spatial point, while a distributed system, is defined as a system that consists of a series of sensors which work cooperatively to provide measurements of a spatial point, and usually individual sensor cannot measure the coordinates separately. Some representative distributed systems in the literature are iGPS, MScMS-II, and etc. The current trend of LVDM systems seem to orient towards distributed systems, and actually, distributed systems demonstrate many advantages that distinguish themselves from conventional centralized systems