Francis Lilley | Liverpool John Moores University (original) (raw)

Papers by Francis Lilley

Applied Optics - APPL OPT, 2010

Three-dimensional (3D) surface shape measurement is a vital component in many industrial processe... more Three-dimensional (3D) surface shape measurement is a vital component in many industrial processes. The subject has developed significantly over recent years and a number of mainly noncontact techniques now exist for surface measurement, exhibiting varying levels of maturity. Within the larger group of 3D measurement techniques, one of the most promising approaches is provided by those methods that are based upon fringe analysis. Current techniques mainly focus on the measurement of small and mediumscale objects, while work on the measurement of larger objects is not so well developed. One potential solution for the measurement of large objects that has been proposed by various researchers is the concept of performing multipanel measurement and the system proposed here uses this basic approach, but in a flexible form of a single moveable sensor head that would be cost effective for measuring very large objects. Most practical surface measurement techniques require the inclusion of a calibration stage to ensure accurate measurements. In the case of fringe analysis techniques, phase-to-height calibration is required, which includes the use of phase-to-height models. Most existing models (both analytical and empirical) are intended to be used in a static measurement mode, which means that, typically, a single calibration is performed prior to multiple measurements being made using an unvarying system geometry. However, multipanel measurement strategies do not necessarily keep the measurement system geometry constant and thus require dynamic recalibration. To solve the problem of dynamic recalibration, we propose a class of models called hybrid models. These hybrid models inherit the basic form of analytical models, but their coefficients are obtained in an empirical manner. The paper also discusses issues associated with all phase-to-height models used in fringe analysis that have a quotient form, identifying points of uncertainty and regions of distortion as issues affecting accuracy in phase maps produced in this manner.

Optics and Lasers in Engineering - OPT LASER ENG, 2009

This paper presents a thorough discussion on the application of the one-dimensional continuous wa... more This paper presents a thorough discussion on the application of the one-dimensional continuous wavelet transform (1D-CWT) in order to retrieve phase information in temporally and spatially tilted fringe patterns and highlights recent progress and challenges. The paper also suggests some possible future developments for this method. The advantages and drawbacks of the one-dimensional continuous wavelet transform technique are discussed here and in this context are compared to the widely used methods of Fourier fringe analysis, phase stepping and the windowed Fourier transform. A description is given of the manner in which the CWT phase gradient and phase estimation methods may be used to extract the phase of fringe patterns, and these two methods are compared and contrasted. Five different ridge extraction algorithms are explained and the performance of three of these is evaluated. To alleviate the distortions that may occur at the image borders and at regions close to holes in fringe patterns, two methods are described and evaluated for extending the image edges and for filling in holes within fringe patterns. A novel mother wavelet is presented which has been designed to improve the ability of the continuous wavelet transform to analyse fringe patterns that contain sudden phase variations. The sampling and structural conditions that are required to obtain ‘correct’ phase are also discussed.

Optical Engineering - OPT ENG, 2000

Robust fringe analysis system for human body shape measurement. [Optical Engineering 39, 187 (200... more Robust fringe analysis system for human body shape measurement. [Optical Engineering 39, 187 (2000)]. Francis Lilley, Michael J. Lalor, David R. Burton. Abstract. This paper describes the development and practical application ...

Optics and Lasers in Engineering, 2016

Optics Communications, 2016

Pre-requisite: In order to understand this tutorial it is necessary for you to have already studi... more Pre-requisite: In order to understand this tutorial it is necessary for you to have already studied and completed the "one-dimensional phase unwrapping problem" tutorial before reading this document. There are many applications that produce wrapped phase images. Examples of these are synthetic aperture radar (SAR), magnetic resonance imaging (MRI) and fringe pattern analysis. The wrapped phase images that are produced by these applications are not usable unless they are first unwrapped so as to form a continuous phase map. This means that the development of a robust phase unwrapping algorithm is an important topic for all these applications. In this article, we will not discuss phase unwrapping only in the specific context of these applications, but we will instead explain the concept of the 2D phase unwrapping problem in general terms.

IAENG International Journal of Computer Science

Export Date: 3 December 2012, Source: Scopus

In this paper, we suggest a novel system that is capable of measuring absolute distances with an ... more In this paper, we suggest a novel system that is capable of measuring absolute distances with an uncertainty of one micrometer, or better, over a distance of up to 20 meters. This system consists of a Michelson interferometer, a tunable external cavity diode laser, a wavelength meter, a digital camera and a computer. The Michelson interferometer contains a reference arm mirror, a target arm mirror, a coherent light source, a white screen and a beam-splitter. The distance between the beam-splitter and the reference arm is known a priori with one-micrometer accuracy. The distance between the beam-splitter and the required measurement target arm is initially known with only a low precision accuracy of one-millimeter. The distance between the beam-splitter and the target arm is required to be measured with one micrometer uncertainty, or better. Index Terms— Absolute distance measurement, external cavity tunable diode laser, Fourier fringe analysis, Michelson interferometer, synthetic wa...

Microscopy research and technique, Jan 25, 2015

Tapping mode atomic force microscopy (AFM) provides phase images in addition to height and amplit... more Tapping mode atomic force microscopy (AFM) provides phase images in addition to height and amplitude images. Although the behavior of tapping mode AFM has been investigated using mathematical modeling, comprehensive understanding of the behavior of tapping mode AFM still poses a significant challenge to the AFM community, involving issues such as the correct interpretation of the phase images. In this paper, the cantilever's dynamic behavior in tapping mode AFM is studied through a three dimensional finite element method. The cantilever's dynamic displacement responses are firstly obtained via simulation under different tip-sample separations, and for different tip-sample interaction forces, such as elastic force, adhesion force, viscosity force, and the van der Waals force, which correspond to the cantilever's action upon various different representative computer-generated test samples. Simulated results show that the dynamic cantilever displacement response can be divi...

Applications of Digital Image Processing XIV, 1991

ABSTRACT

Optics and Lasers in Engineering, 1997

If structured light consisting of parallel stripes, or fringes, is projected onto a surface, then... more If structured light consisting of parallel stripes, or fringes, is projected onto a surface, then the surface acts as a phase modulator, with the amount of modulation at any point depending upon the height of the surface at that point. In recent years considerable effort has been devoted to the problem of fringe demodulation, with prominence given to techniques using

International Conference on Medical Information Visualisation--BioMedical Visualisation (MedVis'06), 2006

Research into high performance surface measurement using continuously structured light projection... more Research into high performance surface measurement using continuously structured light projection and Fourier transform profilometry is described. It is shown that the capture of single-colour interferometer fringes, modulated by the surface variations of either test phantoms or human volunteers can yield body surface height maps in the high radiation environment of the radiotherapy clinic. The 3D surfaces are reconstructed from

Circuit World, 1990

ABSTRACT Electronics manufacturing throughout the world now uses an increasing percentage of Surf... more ABSTRACT Electronics manufacturing throughout the world now uses an increasing percentage of Surface Mount Technology (SMT). The compact and light-weight surface-mounted components offer a number of advantages to manufacturers. Unfortunately, however, these same beneficial characteristics make the quality of the product difficult to guarantee. As miniaturisation continues, the inspection problem becomes worse, and so advanced methods of inspection are required. Automatic inspection systems already exist, although an effective, inexpensive and reliable system has yet to be found. Recent work carried out within the Coherent and Electro-Optics Research Group at Liverpool Polytechnic has looked at the feasibility of applying some of its established inspection methods to the problem of solder joint inspection. Extensive development must still take place; however, the methods employed have shown promise. The system uses structured light techniques to add height information to an image of the solder joint under inspection. In this way a 3-D image of the joint may be built up, digitised and processed in a computer at high speed in order to determine its quality.

Computer Vision for Industry, 1993

ABSTRACT This paper describes a non-contact system for surface shape measurement of manufactured ... more ABSTRACT This paper describes a non-contact system for surface shape measurement of manufactured parts. The technique consists of a coherent optical system combined with powerful parallel processing hardware, thus allowing rapid inspection rates to be realized. A `structured lighting' system is employed involving the projection of a multi-stripe fringe pattern onto the object surface thus enabling 3D data to be obtained. Phase measuring techniques are applied in order to increase accuracy and resolution. A comparison is made between two different phase measuring methodologies. These techniques require computationally intensive algorithms and processing of large amounts of image data. Image processing hardware should be fast enough to achieve results within a reasonable time scale. A parallel image processing system has been designed for such applications based on the Texas Instruments digital signal processor type TMS320C40. The system is based on MIMD message passing architecture and uses an EISA bus for the host interface. The issues of speed of data acquisition and processing, reliability and robustness of the technique and accuracy are discussed.

Microscopy research and technique, 2013

Understanding how the mechanical properties of cells alter with disease may help with the develop... more Understanding how the mechanical properties of cells alter with disease may help with the development of novel diagnostics and treatment regimes. The emergence of tools such as the atomic force microscope (AFM) has enabled us to physically measure the mechanical properties of cells. However, suitable models for the analysis of real experimental data are either absent, or fail to provide a simple analysis tool in which experimental data can be analyzed quickly and reliably. The Hertz model has been widely used to study AFM data on living cells, however it makes assumptions that are untrue for cells, namely that cells behave as linear elastic bodies. This article presents and evaluates an alternative nonlinear Hertz model, which allows the Young's modulus to vary according to a second order polynomial function of indentation depth. Evaluation of the model revealed that prostate cancer cells (PC3) responded more uniformly to force compared to the normal PNT2 cells. Also, more energ...

ABSTRACT The sensing and visualisation of 3D body surface information is being researched for cli... more ABSTRACT The sensing and visualisation of 3D body surface information is being researched for clinical use in the radiation treatment of cancer, where accurate patient set-up and positional monitoring is essential. Where 3D measurement is based on the projection of structured light onto the patient it is necessary to remove background detail prior to extracting patient surface topology. Rapid background changes render a single pre-emptive determination of background useless. Instead it becomes necessary to update background information at video-rates. This precludes disruptive pauses for the physical collection of background data. This paper describes a method of generating background data from the video images of the structured light projection itself. Results are presented to show that image frame processing that includes a randomised element of structural spreading is the key to successfully implementing real-time background correction.

Optics Express, 2012

We present a novel system that can measure absolute distances of up to 300 mm with an uncertainty... more We present a novel system that can measure absolute distances of up to 300 mm with an uncertainty of the order of one micrometer, within a timeframe of 40 seconds. The proposed system uses a Michelson interferometer, a tunable laser, a wavelength meter and a computer for analysis. The principle of synthetic wave creation is used in a novel way in that the system employs an initial low precision estimate of the distance, obtained using a triangulation, or time-of-flight, laser system, or similar, and then iterates through a sequence of progressively smaller synthetic wavelengths until it reaches micrometer uncertainties in the determination of the distance. A further novel feature of the system is its use of Fourier transform phase analysis techniques to achieve sub-wavelength accuracy. This method has the major advantages of being relatively simple to realize, offering demonstrated high relative precisions better than 5 × 10(-5). Finally, the fact that this device does not require a continuous line-of-sight to the target as is the case with other configurations offers significant advantages.