Three-dimensional geometry characterization using structured light fields

Tese de doutoramento. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 200

DEVELOPMENT OF PHASE RETRIEVAL TECHNIQUES IN DISPLACEMENT AND DISPLACEMENT DERIVATIVES MEASUREMENT

Ph.DDOCTOR OF PHILOSOPH

Non-contact free-form shape measurement for coordinate measuring machines

Precision measurement of manufactured parts commonly uses contact measurement methods. A Coordinate Measuring Machine (CMM) mounted probe touches the surface of the part, recording the probe’s tip position at each contact. Recently, devices have been developed that continuously scan the probe tip across the surface, allowing points to be measured more quickly. Contact measurement is accurate and fast for shapes that are easily parameterized such as a sphere or a plane, but is slow and requires considerable user input for more general objects such as those with free-form surfaces. Phase stepping fringe projection and photogrammetry are common non-contact shape measurement methods. Photogrammetry builds a 3D model of feature points from images of an object taken from multiple perspectives. In phase stepping fringe projection a series of sinusoidal patterns, with a phase shift between each, is projected towards an object. A camera records a corresponding series of images. The phase of the pattern at each imaged point is calculated and converted to a 3D representation of the object’s surface. Techniques combining phase stepping fringe projection and photogrammetry were developed and are described here. The eventual aim is to develop an optical probe for a CMM to enable non-contact measurement of objects in an industrial setting. For the CMM to accurately report its position the probe must be small, light, and robust. The methods currently used to provide a phase shift require either an accurately calibrated translation stage to move an internal component, or a programmable projector. Neither of these implementations can be practically mounted on a CMM due to size and weight limits or the delicate parts required. A CMM probe consisting of a single camera and a fringe projector was developed. The fringe projector projects a fixed fringe pattern. Phase steps are created by moving the CMM mounted probe, taking advantage of the geometry of the fringe projection system. New techniques to calculate phase from phase stepped images created by relative motion of probe and object are proposed, mathematically modelled, and tested experimentally. Novel techniques for absolute measurement of surfaces by viewing an object from different perspectives are developed. A prototype probe is used to demonstrate measurements of a variety of objects.Engineering and Physical Sciences Research Council (EPSRC) Grant No. GR/T11289/0

A Simplified Phase Display System for 3D Surface Measurement and Abnormal Surface Pattern Detection

Today’s engineering products demand increasingly strict tolerances. The shape of a machined surface plays a critical role to the desired functionality of a product. Even a small error can be the difference between a successful product launch and a major delay. It is important to develop tools that confirm the quality and accuracy of manufactured products. The key to assessing the quality is robust measurement and inspection tools combined with advanced analysis. This research is motivated by the goals of 1) developing an advanced optical metrology system that provides accurate 3D profiles of target objects with curvature and irregular texture and 2) developing algorithms that can recognize and extract meaningful surface features with the consideration of machining process information. A new low cost measurement system with a simple coherent interferometric fringe projection system is developed. Comparing with existing optical measurement systems, the developed system generates fringe patterns on object surface through a pair of fiber optics that have a relatively simple and flexible configuration. Three-dimensional measurements of a variety of surfaces with curvatures demonstrate the applicability and flexibility of the developed system. An improved phase unwrapping algorithm based on a flood fill method is developed to enhance the performance of image processing. The developed algorithm performs phase unwrapping under the guidance of a hybrid quality map that is generated by considering the quality of both acquired original intensity images and the calculated wrapped phase map. Advances in metrology systems enable engineers to obtain a large amount of surface information. A systematic framework for surface shape characterization and abnormal pattern detection is proposed to take the advantage of the availability of high definition surface measurements through advanced metrology systems. The proposed framework evaluates a measured surface in two stages. The first step focuses on the extraction of general shape (e.g., surface form) from measurement for surface functionality evaluation and process monitoring. The second step focuses on the extraction of application specific surface details with the consideration of process information (e.g., surface waviness). Applications of automatic abnormal surface pattern detection have been demonstrated. In summary, this research focuses on two core areas: 1) developing metrology system that is capable of measuring engineered surfaces accurately; 2) proposing a methodology that can extract meaningful information from high definition measurements with consideration of process information and product functionality.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/136999/1/xinweng_1.pd

Digital Holographic Interferometry for Temperature Field Measurements in Flowing Gases and Liquids

This Ph.D. dissertation introduces and elaborates the optical technique known as Digital Holographic Interferometry (DHI) in the field of applied fluid mechanics for the purpose of investigating the properties and visualization of flowing gases and liquids. The work deals mostly with the general aspects of using digital holographic interferometry as the main technique of investigation, deepening in some of its technical aspects for data treatment and visualization. It gradually present the evolving process of studying different forms of temperature fields, based on the distribution of its refractive index, starting with simple 2D distribution toward 3D distribution that is treated with tomographic approach. It brings to light main concepts and possibilities of using this technique for the field of fluid mechanics.Apart the general theoretical background introduced in the beginning of this thesis, each chapter contains an introduction to some more theoretical and technical aspects of the optical setup and data treatment that are needed for a better and full understanding of the process of capturing, treating and presenting the data. General conclusions are drawn at the end of each chapter.Throughout our work, we have achieved a deviation below tenths of degree Celsius between the temperature registered from the thermocouples, ANSYS simulations and the one measured by the optical technique for the case of heat measurements in water, falling within 5% of error margin for the case of a 2D temperature field. For the case of a 3D temperature field from a pulsatile jet with water as its working fluid, we estimated that the relative uncertainty of the temperature field measurement near the orifice is below 5%, compared to the relative uncertainty increasing up to 15% further from the orifice. We also achieved an increase of the range of measurement for the case of two-wavelength digital holographic interferometry.Each investigation is accompanied with a whole-field picture of visualizing the temperature and other important properties of the fluid/gas under study, which is one of the main advantages of this optical technique.This Ph.D. dissertation introduces and elaborates the optical technique known as Digital Holographic Interferometry (DHI) in the field of applied fluid mechanics for the purpose of investigating the properties and visualization of flowing gases and liquids. The work deals mostly with the general aspects of using digital holographic interferometry as the main technique of investigation, deepening in some of its technical aspects for data treatment and visualization. It gradually present the evolving process of studying different forms of temperature fields, based on the distribution of its refractive index, starting with simple 2D distribution toward 3D distribution that is treated with tomographic approach. It brings to light main concepts and possibilities of using this technique for the field of fluid mechanics.Apart the general theoretical background introduced in the beginning of this thesis, each chapter contains an introduction to some more theoretical and technical aspects of the optical setup and data treatment that are needed for a better and full understanding of the process of capturing, treating and presenting the data. General conclusions are drawn at the end of each chapter.Throughout our work, we have achieved a deviation below tenths of degree Celsius between the temperature registered from the thermocouples, ANSYS simulations and the one measured by the optical technique for the case of heat measurements in water, falling within 5% of error margin for the case of a 2D temperature field. For the case of a 3D temperature field from a pulsatile jet with water as its working fluid, we estimated that the relative uncertainty of the temperature field measurement near the orifice is below 5%, compared to the relative uncertainty increasing up to 15% further from the orifice. We also achieved an increase of the range of measurement for the case of two-wavelength digital holographic interferometry.Each investigation is accompanied with a whole-field picture of visualizing the temperature and other important properties of the fluid/gas under study, which is one of the main advantages of this optical technique.

A NEW METHOD OF WAVELENGTH SCANNING INTERFEROMETRY FOR INSPECTING SURFACES WITH MULTI-SIDE HIGH-SLOPED FACETS

With the development of modern advanced manufacturing technologies, the requirements for ultra-precision structured surfaces are increasing rapidly for both high value-added products and scientific research. Examples of the components encompassing the structures include brightness enhancement film (BEF), optical gratings and so forth. Besides, specially designed structured surfaces, namely metamaterials can lead to specified desirable coherence, angular or spatial characteristics that the natural materials do not possess. This promising field attracts a large amount of funding and investments. However, owing to a lack of effective means of inspecting the structured surfaces, the manufacturing process is heavily reliant on the experience of fabrication operators adopting an expensive trial-and-error approach, resulting in high scrap rates up to 50-70% of the manufactured items. Therefore, overcoming this challenge becomes increasingly valuable. The thesis proposes a novel methodology to tackle this challenge by setting up an apparatus encompassing multiple measurement probes to attain the dataset for each facet of the structured surface and then blending the acquired datasets together, based on the relative location of the probes, which is achieved via the system calibration. The method relies on wavelength scanning interferometry (WSI), which can achieve areal measurement with axial resolutions approaching the nanometre without the requirement for the mechanical scanning of either the sample or optics, unlike comparable techniques such as coherence scanning interferometry (CSI). This lack of mechanical scanning opens up the possibility of using a multi-probe optics system to provide simultaneous measurement with multi adjacent fields of view. The thesis presents a proof-of-principle demonstration of a dual-probe wavelength scanning interferometry (DPWSI) system capable of measuring near-right-angle V-groove structures in a single measurement acquisition. The optical system comprises dual probes, with orthogonal measurement planes. For a given probe, a range of V-groove angles is measurable, limited by the acceptance angle of the objective lenses employed. This range can be expanded further by designing equivalent probe heads with varying angular separation. More complicated structured surfaces can be inspected by increasing the number of probes. The fringe analysis algorithms for WSI are discussed in detail, some improvements are proposed, and experimental validation is conducted. The scheme for calibrating the DPSWI system and obtaining the relative location between the probes to achieve the whole topography is implemented and presented in full. The appraisal of the DPWSI system is also carried out using a multi-step diamond-turned specimen and a sawtooth brightness enhancement film (BEF). The results showed that the proposed method could achieve the inspection of the near-right-angle V-groove structures with submicrometre scale vertical resolution and micrometre level lateral resolution

Automated shape analysis and visualization of the human back.

Spinal and back deformities can lead to pain and discomfort, disrupting productivity, and may require prolonged treatment. The conventional method of assessing and monitoring tile de-formity using radiographs has known radiation hazards. An alternative approach for monitoring the deformity is to base the assessment on the shape of back surface. Though three-dimensional data acquisition methods exist, techniques to extract relevant information for clinical use have not been widely developed. Thi's thesis presentsthe content and progression of research into automated analysis and visu-alization of three-dimensional laser scans of the human back. Using mathematical shape analysis, methods have been developed to compute stable curvature of the back surface and to detect the anatomic landmarks from the curvature maps. Compared with manual palpation, the landmarks have been detected to within accuracy of 1.15mm and precision of 0.8111m.Based on the detected spinous process landmarks, the back midline which is the closest surface approximation of the spine, has been derived using constrained polynomial fitting and statistical techniques. Three-dimensional geometric measurementsbasedon the midline were then corn-puted to quantify the deformity. Visualization plays a crucial role in back shape analysis since it enables the exploration of back deformities without the need for physical manipulation of the subject. In the third phase,various visualization techniques have been developed, namely, continuous and discrete colour maps, contour maps and three-dimensional views. In the last phase of the research,a software system has been developed for automating the tasks involved in analysing, visualizing and quantifying of the back shape. The novel aspectsof this research lie in the development of effective noise smoothing methods for stable curvature computation; improved shape analysis and landmark detection algorithm; effective techniques for visualizing the shape of the back; derivation of the back midline using constrained polynomials and computation of three dimensional surface measurements.

Optoelectronic speckle shearing interferometry

This thesis describes the implementation of enhanced signal processing techniques in electronic speckle shearing interferometry, including two-wavelength slope measurement, phase stepping, and heterodyning and stroboscopic illumination in vibration analysis. All the techniques were achieved using laser diode emission wavelength modulation. Slope measurement using two-wavelength illumination can generate slope fringes in a mechanically passive manner and the fringe visibility is better compared to other illumination-shifting and object-tilting methods. Three simple geometric objects were measured using an x shear of 4 mm and AX ~ 0.45 nm. The results are in agreement with a theoretical analysis. The measurement accuracy can be further improved by calculating the simple equations of parameters in the fringe function. A novel phase stepping technique has been demonstrated using laser diode injection current modulation. An imbalanced Michelson-interferometer arrangement, with a perspex block of 25 mm thickness inserted into the longer interferometer arm to maintain equal image magnification for the two images, was used to obtain a 2n phase shift for an optical frequency change of 7.25 GHz. The technique provides an additional phase stepping method in shearography with the advantages of removing an active phase-shifting component from the interferometer and a greater linearity in the phase shifts through the diode wavelength modulation. In vibration measurement, heterodyning and stroboscopic illumination have also been successfully achieved in a mechanical passive manner. For shearing systems using a Michelson interferometer, heterodyning was originally difficult to perform. With the unbalanced optical configuration as used in the phase stepping work, heterodyning has been demonstrated to measure vibration motion ~5.5 kHz and the diode optical frequency modulation ~15 GHz. By pulsing the laser diode with an 11% duty cycle, stroboscopic illumination was performed to obtain cosine fringes along with greatly improved visibility. Phase stepping methods were then incorporated to automate the fringe analysis.Ph