In-process surface profile assessment of rotary machined timber using a dynamic photometric stereo technique

Machining operations have advanced in speed and there is an increasing demand for higher quality surface finish. It is therefore necessary to develop real-time surface inspection techniques which will provide sensory information for controlling the machining processes. This paper describes a practical method for real-time analysis of planed wood using the photometric stereo technique. Earlier research has shown that the technique is very effective in assessing surface waviness on static wood samples. In this paper, the photometric stereo method is extended to real industrial applications where samples are subjected to rapid movements. Surface profiles extracted from the dynamic photometric stereo method are compared with those from the static measurements and the results show that there is a high correlation between the two methods

Numerical modeling of strain localization in granular materials using Cosserat theory enhanced with microfabric properties

Finite element solution in the updated Lagrangian frame is used to investigate the strain localization phenomenon shear bands in granular materials. The micro-polar theory was used as the mathematical foundation for the continuum formulations. A laboratory testing results are used for verification and comparison with the numerical simulation. Silica sand and glass beads with different shape indices, size and surface roughness were tested under biaxial and triaxial loading conditions to investigate the physics of the problem. The shape non-uniformity and the irregular surface roughness of the grains were studied carefully to evaluate their effect on shear band characteristics. To this end, attempts have been made to bring these additional micro-properties into the constitutive equations in this study. Elasto-plastic constitutive laws with a non-associated flow rule were used in order to capture the high deformations inside the localization zones. The Micropolar theory requires two independent kinematical fields; the first is the Cosserat objective strain tensor and the second is the curvature or the rotation gradient vector. The deviation in the kinematics is performed using the classical continuum with the incorporation of the couple stress effect. A single hardening yielding model, (Lade\u27s model), with a different plastic potential function has been enhanced to account for the couple stresses and the rotations of the grains through the stress invariants. Finally, the finite element formulations in the updated Lagrangian frame were obtained. These formulations have been implemented into the finite element program ABAQUS using the user element subroutine utility (UEL). The study findings were consistent with the experimental results and the physical understanding of the phenomenon. The surface roughness of the particles was found to affect the shear band thickness and present model was able to feel such effects. The shape of the particles was found to significantly affect the shear band thickness as well. The effect of the initial void ratio, confining pressure, particle size, surface roughness and shape of particles is discussed in this dissertation. At the end, the material properties spatial distribution was mapped into the finite element mesh and the material heterogeneity effect on strain localization is shown accordingly

3D freeform surface measurement on coordinate measuring machine using photometric stereo method

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonSurface metrology has been widely used in manufacturing for many years. There has been a wide range of techniques applied for measuring surface topography. A photometric stereo technique is one of the best ways for the analysis of three-dimensional (3D) surface textural patterns. Many published works are concerned the developed approach for recovering the 3D profiles from surface normal. This research not only presents a methodology used to retrieve the profiles of surface roughness standards but also investigates the uncertainty estimation of textural measurement determined by the photometric stereo method. Various input quantities have been studied such as pixel error from recovered 3D surface textural patterns, the power of light source which involved with surface roughness average (Ra) value and the effect of room temperature. The surface roughness standards were utilized as the reference value. In term of increasing accuracy of the reference value, a contact method (stylus instrument) was used to calibrate them. Illumination angles of light source had some influence on the measurement results. A coordinate measuring machine (CMM) was used for holding the light source in order to study the effects of tilt and slant angles. The effect of tilt and slant angles were investigated. The results of these experiments successfully indicated that the angle used in photometric stereo method played an important role to the accuracy level of the roughness measurement results. The surface roughness specimen manufactured by a Computer Numerical Control (CNC) was applied to validate the capability of the photometric stereo system.The royal Thai government, ministry of sciences and technology and national institute of metrology Thailand (NIMT

2D and 3D computer vision analysis of gaze, gender and age

Human-Computer Interaction (HCI) has been an active research area for over four decades. Research studies and commercial designs in this area have been largely facilitated by the visual modality which brings diversified functionality and improved usability to HCI interfaces by employing various computer vision techniques. This thesis explores a number of facial cues, such as gender, age and gaze, by performing 2D and 3D based computer vision analysis. The ultimate aim is to create a natural HCI strategy that can fulfil user expectations, augment user satisfaction and enrich user experience by understanding user characteristics and behaviours. To this end, salient features have been extracted and analysed from 2D and 3D face representations; 3D reconstruction algorithms and their compatible real-world imaging systems have been investigated; case study HCI systems have been designed to demonstrate the reliability, robustness, and applicability of the proposed method.More specifically, an unsupervised approach has been proposed to localise eye centres in images and videos accurately and efficiently. This is achieved by utilisation of two types of geometric features and eye models, complemented by an iris radius constraint and a selective oriented gradient filter specifically tailored to this modular scheme. This approach resolves challenges such as interfering facial edges, undesirable illumination conditions, head poses, and the presence of facial accessories and makeup. Tested on 3 publicly available databases (the BioID database, the GI4E database and the extended Yale Face Database b), and a self-collected database, this method outperforms all the methods in comparison and thus proves to be highly accurate and robust. Based on this approach, a gaze gesture recognition algorithm has been designed to increase the interactivity of HCI systems by encoding eye saccades into a communication channel similar to the role of hand gestures. As well as analysing eye/gaze data that represent user behaviours and reveal user intentions, this thesis also investigates the automatic recognition of user demographics such as gender and age. The Fisher Vector encoding algorithm is employed to construct visual vocabularies as salient features for gender and age classification. Algorithm evaluations on three publicly available databases (the FERET database, the LFW database and the FRCVv2 database) demonstrate the superior performance of the proposed method in both laboratory and unconstrained environments. In order to achieve enhanced robustness, a two-source photometric stereo method has been introduced to recover surface normals such that more invariant 3D facia features become available that can further boost classification accuracy and robustness. A 2D+3D imaging system has been designed for construction of a self-collected dataset including 2D and 3D facial data. Experiments show that utilisation of 3D facial features can increase gender classification rate by up to 6% (based on the self-collected dataset), and can increase age classification rate by up to 12% (based on the Photoface database). Finally, two case study HCI systems, a gaze gesture based map browser and a directed advertising billboard, have been designed by adopting all the proposed algorithms as well as the fully compatible imaging system. Benefits from the proposed algorithms naturally ensure that the case study systems can possess high robustness to head pose variation and illumination variation; and can achieve excellent real-time performance. Overall, the proposed HCI strategy enabled by reliably recognised facial cues can serve to spawn a wide array of innovative systems and to bring HCI to a more natural and intelligent state

3D Multi-Scale Behavior of Granular Materials using Experimental and Numerical Techniques

Constitutive modeling of granular material behavior has generally been based on global response of laboratory-size specimens or larger models with little understanding of the fundamental mechanics that drive the global response. Many studies have acknowledged the importance of micro-scale and meso-scale mechanics on the constitutive behavior of granular materials. However, much knowledge is still missing to develop and improve robust micromechanical constitutive models. The research in this dissertation contributes to this knowledge gap for many potential applications using novel experimental techniques to investigate the three-dimensional (3D) behavior of granular materials. Critical micromechanics measurements at multiple scales are investigated by combining 3D synchrotron micro-computed tomography (SMT), 3D image analysis, and finite element analysis (FEA). At the single particle level (micro-scale), particle fracture was examined at strain rates of 0.2 mm/min and 2 m/s using quasi-static unconfined compression, unconfined mini-Kolsky bar, and x-ray imaging techniques. Surface reconstructions of particles were generated and exported to Abaqus FEA software, where quasi-static and higher rate loading curves and crack propagation were simulated with good accuracy. Stress concentrations in oddly shaped particles during FEA simulations resulted in more realistic fracture stresses than theoretical models. A nonlinear multivariable statistical model was developed to predict force required to fracture individual particles with known internal structure and loading geometry. At the meso-scale, 3D SMT imaging during in-situ triaxial testing of granular materials were used to identify particle morphology, contacts, kinematics and interparticle behavior. Micro shear bands (MSB) were exposed during pre-peak stress using a new relative particle displacement concept developed in this dissertation. MSB for spherical particles (glass beads) had larger thickness (3d50 to 5d50) than that of angular sands (such as F35 Ottawa sand, MSB thickness of 1d50 to 3d50). Particle morphology also plays a significant role in the onset and growth of shear bands and global fabric evolution of granular materials. More spherical particles typically exhibit more homogeneous internal anisotropy. Fabric of particles within the shear band (at higher densities and confining pressures) exhibits a peak and decrease into steady-state. Also, experimental fabric produces more accurate strength and deformation predictions in constitutive models that incorporate fabric evolution

Reconstructing Geometry from Its Latent Structures

Our world is full of objects with complex shapes and structures. Through extensive experience humans quickly develop an intuition about how objects are shaped, and what their material properties are simply by analyzing their appearance. We engage this intuitive understanding of geometry in nearly everything we do.It is not surprising then, that a careful treatment of geometry stands to give machines a powerful advantage in the many tasks of visual perception. To that end, this thesis focuses on geometry recovery in a wide range of real-world problems. First, we describe a new approach to image registration. We observe that the structure of the imaged subject becomes embedded in the image intensities. By minimizing the change in shape of these intensity structures we ensure a physically realizable deformation. We then describe a method for reassembling fragmented, thin-shelled objects from range-images of their fragments using only the geometric and photometric structure embedded in the boundary of each fragment. Third, we describe a method for recovering and representing the shape of a geometric texture (such as bark, or sandpaper) by studying the characteristic properties of texture---self similarity and scale variability. Finally, we describe two methods for recovering the 3D geometry and reflectance properties of an object from images taken under natural illumination. We note that the structure of the surrounding environment, modulated by the reflectance, becomes embedded in the appearance of the object giving strong clues about the object's shape.Though these domains are quite diverse, an essential premise---that observations of objects contain within them salient clues about the object's structure---enables new and powerful approaches. For each problem we begin by investigating what these clues are.We then derive models and methods to canonically represent these clues and enable their full exploitation. The wide-ranging success of each method shows the importance of our carefully formulated observations about geometry, and the fundamental role geometry plays in visual perception.Ph.D., Computer Science -- Drexel University, 201

Quantifying subglacial roughness and its link to glacial geomorphology and ice speed

The shape of subglacial bed topography, termed its roughness, is a recognised control on basal ice-flow. Although glaciologists have observed patterns of variations in ice speed over beds with different roughness values, the strength of this relationship has rarely been quantified, and measurements of roughness are based on just a few methods. Moreover, the shape of topography can vary in a number of ways, but how this influences roughness and the quantification of roughness is largely unknown. This project investigates methods of measuring roughness, and how such measurements might be related to spatial patterns in ice speed in both contemporary and palaeo-settings. Roughness of ice-sheet beds has traditionally been summarised using spectral analysis. The first part of this projected was aimed at reviewing this method. The influence of the number of data points was explored by developing a new technique for re-digitising radio-echo sounding records, which remain the most extensive source of bed data from Antarctica. This yielded measurements with a resolution (c.250 m) eight-times higher than those used in previous work, and allowed assessment of roughness over short window lengths. Significantly, subjective decisions about, for example, the choice of window length can lead to differing results using spectral analysis. The second part of this project was, therefore, to identify and evaluate 36 alternative methods of quantifying roughness, many of which had never before been used to analyse subglacial beds. The project looked at the broader approach to quantifying roughness, exploring the benefits of 2D versus 3D techniques for investigating subglacial data. The relationship between roughness and ice speed was tested using these alternative techniques in isolation, but also in a combination. Indeed, the use of generalised linear models (GLMs) allowed the strength of this relationship to be quantified for the first time, and permitted the roughness variables most related to ice speed to be identified. Testing the agreement between patterns in roughness in ice speed for the Siple Coast showed a pattern of increasing ice speed as roughness decreased. Modelling revealed a 98% fit between ice speed and roughness for the MacAyeal Ice Stream indicating that roughness is a strong control on basal ice flow. It was revealed that the measures of roughness most related to ice speed were those that summarised changes in the vertical height of the surface, rather than the shape or wavelength of the features. It was also found that the lateral margin of the MacAyeal Ice Stream corresponds with an area of high bed roughness. Analysis of formerly glaciated areas of Britain showed that the size and frequency of subglacial bedforms influence parameter results as do subtle changes in the orientation of 2D profiles across bedform fields. It was demonstrated how this might be used to identify subglacial features beneath contemporary ice sheets. In conclusion, alternative roughness parameters were found to be less restrictive and arguably more informative than spectral analysis, because they have the advantage of allowing differing characteristics of the topography to be measured. Conversely, this meant that no single parameter could provide a complete summary. Thus, a key conclusion of this work is that the most suitable approach to quantifying roughness is to use a suite of roughness parameters, designed to summarise a range of variables that are most relevant to the specific investigation