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Enriching micro-scale metrology with an all-optical dimensional measuring system
Abstract
Information-rich metrology (IRM) is a term that we introduce to refer to an approach where the conventional paradigm of measurement is enhanced, thanks to the introduction and active role of multiple novel sources of information. The overarching goal of IRM is to encompass and homogenise all those measurement scenarios where information available from heterogeneous sources, e.g. from the product being measured, the manufacturing process that was used to fabricate it, the internals of the measurement instrument itself, as well as from any previous measurement carried with any other instrument, is gathered and somehow incorporated with an active role into the measurement pipeline, in order to ultimately achieve a higher-quality measurement result (e.g. better metrological performance, shorter measurement times, smaller consumption of resources). A comprehensive investigation into the aspects, issues and opportunities of IRM requires a large number of test cases, and a research effort involving hardware (sensors, instrument architectures, communication networks, etc.) and software (data communication, instrument control and synchronisation, data analysis and processing), as well as significant research into mathematical and statistical modelling. As part of such an undertaking, we present here the design of an original, flexible and open-architecture, all-optical dimensional measuring system (AODMS) for measuring the geometry and surface topography of micro-scale components. The system is designed to operate in a cube of 100 mm sides, with micrometre or sub-micrometre measurement uncertainties. The key aspects of AODMS are a flexibility and open-architecture. The system is designed to accommodate a wide array of heterogeneous optical sensors, ranging from 3D measurement to 2D imaging, from prototype to commercial sensors, and is being designed to be particularly suitable to support the investigation of multi-sensor data fusion solutions [1]. The open nature of the architecture allows full flexibility in the design and configuration of the instrument control and communication software, as well as of the data analysis and processing software, thus presenting itself as an ideal platform to investigate IRM through the support to the development of solutions to enable knowledge-driven measurement, e.g. through the interaction with CAD/CAM systems, product data-management systems and any other IT-based knowledge-management solutions. The schema of the prototype AODMS are shown in Figure 1. The AODMS prototype includes a moving stage, a support and interface to a photogrammetric system dedicated to
... We present relationships between the BG properties and the geometrical parameters of the proposed IRB structure. An optimised IRB structure is then used in a case study in which a vibration isolation platform is designed to provide isolation for an all-optical dimensional measuring system (AODMS) [13]. The control of IRBs will serve as a future design tool for machines and structures with elimination of vibration waves in multiple degrees of freedom. ...
Advancements in additive manufacturing technology have allowed the realisation of geometrically complex structures with enhanced capabilities in comparison to solid structures. One of these capabilities is vibration attenuation which is of paramount importance for the precision and accuracy of metrology and machining instruments. In this project, new additively manufactured lattice structures are proposed for achieving vibration attenuation. The ability of these lattices to provide vibration attenuation at frequencies greater than their natural frequency was studied first. This is referred to as vibration isolation. For the vibration isolation study, a combination of finite element modelling and an experimental setup comprising a dynamic shaker and laser vibrometer was used. The natural frequencies obtained from the experimental results were 93 % in agreement with the simulated results. However, vibration attenuation was demonstrated only along one dimension and vibration waves were allowed to propagate, meaning the transmissibility was allowed to be greater than 0 dB. To achieve lower transmissibility, the project demonstrated that lattice structures can develop Bragg-scattering and internal resonance bandgaps. The bandgaps were identified from the lattices' dispersion curves calculated using a finite element based wave propagation modelling technique. Triply periodic minimal surface lattices and strut-based lattices developed Bragg-scattering bandgaps with a normalised bandgap frequency (wavelength divided by cell size) of ~ 0.2. The bandgap of the tested lattices was demonstrated to be tunable with the volume fraction of the lattice unit cell, thus, providing a tool to design lattice structures with bandgaps at required frequencies. An internal resonance mechanism in the form of a solid cube or sphere with struts was designed into the inner core of the unit cell of strut-based lattices. These new internal resonance lattices can provide (a) lower frequency bandgaps than Bragg-scattering lattices within the same design volume, and/or (b) comparable bandgaps frequencies with reduced unit cell dimensions. In comparison to lattices of higher normalised bandgap frequencies, lattices with lower normalised bandgap frequencies have cell sizes that are more suitable for manufacturing with the current additive manufacturing technologies and have higher periodicity within a constrained design volume, resulting in higher attenuation within the bandgaps and more homogenous structures. Similar to the Bragg-scattering lattices, the bandgaps of the internal resonance lattices were demonstrated to be tunable through modification of the geometry of the lattice unit cell. The internal resonance lattice experimentally demonstrated a bandgap of normalised frequency between 0.039 to 0.067 and an attenuation of up to -77 dB. These results are essential for engineering vibration attenuation capabilities within the macro-scale of materials for complete elimination of all mechanical vibration waves at tailorable frequencies. Future work will include further reduction of the bandgap frequencies and increasing the bandgap width by exploring new unit cell designs and new materials for additive manufacturing.
The recent proliferation of engineered surfaces, including freeform and structured surfaces, is challenging current metrology techniques. Measurement using multiple sensors has been proposed to achieve enhanced benefits, mainly in terms of spatial frequency bandwidth, which a single sensor cannot provide. When using data from different sensors, a process of data fusion is required and there is much active research in this area. In this paper, current data fusion methods and applications are reviewed, with a focus on the mathematical foundations of the subject. Common research questions in the fusion of surface metrology data are raised and potential fusion algorithms are discussed.
By using sub-millimetre laser speckle pattern projection we show that photogrammetry systems are able to measure smooth three-dimensional objects with surface height deviations less than 1 μm. The projection of laser speckle patterns allows correspondences on the surface of smooth spheres to be found, and as a result, verification artefacts with low surface height deviations were measured. A combination of VDI/VDE and ISO standards were also utilised to provide a complete verification method, and determine the quality parameters for the system under test. Using the proposed method applied to a photogrammetry system, a 5 mm radius sphere was measured with an expanded uncertainty of 8.5 μm for sizing errors, and 16.6 μm for form errors with a 95 % confidence interval. Sphere spacing lengths between 6 mm and 10 mm were also measured by the photogrammetry system, and were found to have expanded uncertainties of around 20 μm with a 95 % confidence interval.
Although coherence scanning interferometry (CSI) is capable of measuring surface form with sub-nanometre precision, it is well known that the performance of measuring instruments depends strongly on the local tilt and curvature of the sample surface. Based on 3D linear systems theory, however, a recent analysis of fringe generation in CSI provides a method to characterise the performance of surface measuring instruments and offers considerable insight into the origins of these errors. Furthermore, from the measurement of a precision sphere, a process to calibrate and partially correct instruments has been proposed. This paper presents, for the first time, a critical look at the calibration and correction process. Computational techniques are used to investigate the effects of radius error and measurement noise introduced during the calibration process for the measurement of spherical and sinusoidal profiles. Care is taken to illustrate the residual tilt and curvature dependent errors in a manner that will allow users to estimate measurement uncertainty. It is shown that by calibrating the instrument correctly and using appropriate methods to extract phase from the resulting fringes (such as frequency domain analysis), CSI is capable of measuring the profile of surfaces with varying tilt with sub-nanometre accuracy.
Scanning white light interferometry (SWLI) is an increasingly popular method to measure the surface profile of miniature components. Although it is tolerant to step changes in profile, its capability to measure the large surface gradients that are characteristic of high-aspect-ratio surfaces is limited. This is in part due to the numerical aperture of the objective lens which restricts the spatial frequency content of both the illumination and recorded fields. More fundamentally, though, SWLI instrumentation neglects the effects of multiple scattering and assumes that the field which illuminates the object is that which would be present if the object were absent. Although this is a reasonable approximation for slowly varying surfaces, it is generally not true for those with steep gradients. In this paper the 3D theory of SWLI is presented and the approximations made by current instrumentation are discussed in this context. Using finite element methods (FEM), SWLI interferograms are calculated, for the cases of 2D Silicon V-grooves and step artefacts, and the effects of multiple scattering are illustrated. Methods to improve the capability of SWLI to measure large surface gradients, first by tilting the sample and subsequently by using an iterative FEM model to provide improved estimates of the illuminating conditions are introduced.
Design and analysis of strutbased lattice structures for vibration isolation Precision Engineering under review
- W P Syam
- W Jianwei
- B Zhao
- I Maskery
- W Elmadih
- R Leach
Syam W P, Jianwei W, Zhao B, Maskery I, Elmadih W, Leach R K 2017 Design and analysis of strutbased lattice structures for vibration isolation Precision Engineering under review
High-precision lateral distortion measurement and correction in coherence scanning interferometry using an arbitrary surface Opt
- P Ekbert
- R Su
- R Leach
Ekbert P, Su R, Leach R K 2017 High-precision lateral distortion measurement and correction in
coherence scanning interferometry using an arbitrary surface Opt. Express in press