Position Determination of a Robot End-Effector Using a 6D-Measurement System Based on the Two-View Vision

A mechatronic system based on the micro-macro-kinematic consists of an industrial robot and a piezoelectric stage mounted on the robot’s end-effector and has to carry out operations like micro-assembly or micro-milling. The piezoelectric stage has to compensate the positioning error of the robot. Therefore, the position of the robot’s end-effector has to be measured with high accuracy. This paper presents a high accuracy 6D-measurement system, which is used to determine the position and orientation of the robot’s end-effector. We start with the description of the operational concept and components of the measurement system. Then we look at image processing methods, camera calibration and reconstruction methods and choose the most accurate ones. We apply the well-known pin-hole camera model to calibrate single cameras. Then we apply the epipolar geometry to describe the relationship between two cameras and calibrate them as a stereo vision system. A distortion model is also applied to enhance the accuracy of the system. The measurement results are presented in the end of the paper

An INSPECT Measurement System for Moving Objects

published_or_final_versio

The Effect of Stem Surface Treatment and Substrate Material on Joint Replacement Stability: An In-Vitro Investigation into the Stem-Cement Interface Mechanics under Various Loading Modes

Mechanical loosening is a common mode of joint replacement failure. For cemented implants, loosening at the implant-cement interface may be affected by stem surface design. Altering the surface topography facilitates the infiltration of bone cement onto the stem, creating a mechanical interlock, improving interface stability. However, few in-vitro studies have investigated this. Therefore, the purpose of this thesis was to investigate the effect of stem surface treatments and substrate materials on stem-cement interface stability in-vitro. Four separate studies were performed to assess the stability of various stem surface treatments, with two substrate materials, under three loading modes. Titanium and cobalt chrome implant stems were custom machined and treated with one of four surfaces: smooth, sintered beads, plasma spray, and circumferential grooves. Sintered bead and plasma sprayed stems were tested in independent torsion, compression and bending; circumferential groove designs were compared in torsion and then compression. All stems were potted in aluminum tubes using PMMA, and loaded cyclically using a materials testing machine. A custom optical tracking system (resolution under 5 μm) was validated for use, and subsequently employed to measure stem-cement interface motion during loading. Overall, results showed surface treatments improved stability, but this was affected by substrate material. Across all loading modes, beaded treatments applied to titanium stems, and plasma spray treatments applied to cobalt chrome stems, improved interface stability and strength when large surface treatment areas were employed. Additionally, the machining of circumferential grooves onto the stem surface improved interface strength in compression, with no influence in torsion. A final study was performed using μ-CT imaging to observe stem and cement motion under bending loads. A custom-built loading device applied static loads to smooth titanium stems, while acquiring CT images of the stem-cement interface. Interface motion was quantified by comparing scans before and after the stem underwent cyclic loading. Results indicated the stem and the surrounding cement had displaced following loading, yet the stems remained relatively stable. These studies offer valuable information regarding the effect of stem surface treatments on stem-cement interface mechanics under various loading modes and will be used in the development of future implant systems

COMPRESSIVE IMAGING AND DUAL MOIRE´ LASER INTERFEROMETER AS METROLOGY TOOLS

Metrology is the science of measurement and deals with measuring different physical aspects of objects. In this research the focus has been on two basic problems that metrologists encounter. The first problem is the trade-off between the range of measurement and the corresponding resolution; measurement of physical parameters of a large object or scene accompanies by losing detailed information about small regions of the object. Indeed, instruments and techniques that perform coarse measurements are different from those that make fine measurements. This problem persists in the field of surface metrology, which deals with accurate measurement and detailed analysis of surfaces. For example, laser interferometry is used for fine measurement (in nanometer scale) while to measure the form of in object, which lies in the field of coarse measurement, a different technique like moire technique is used. We introduced a new technique to combine measurement from instruments with better resolution and smaller measurement range with those with coarser resolution and larger measurement range. We first measure the form of the object with coarse measurement techniques and then make some fine measurement for features in regions of interest. The second problem is the measurement conditions that lead to difficulties in measurement. These conditions include low light condition, large range of intensity variation, hyperspectral measurement, etc. Under low light condition there is not enough light for detector to detect light from object, which results in poor measurements. Large range of intensity variation results in a measurement with some saturated regions on the camera as well as some dark regions. We use compressive sampling based imaging systems to address these problems. Single pixel compressive imaging uses a single detector instead of array of detectors and reconstructs a complete image after several measurements. In this research we examined compressive imaging for different applications including low light imaging, high dynamic range imaging and hyperspectral imaging

Accurate depth from defocus estimation with video-rate implementation

The science of measuring depth from images at video rate using „defocus‟ has been investigated. The method required two differently focussed images acquired from a single view point using a single camera. The relative blur between the images was used to determine the in-focus axial points of each pixel and hence depth. The depth estimation algorithm researched by Watanabe and Nayar was employed to recover the depth estimates, but the broadband filters, referred as the Rational filters were designed using a new procedure: the Two Step Polynomial Approach. The filters designed by the new model were largely insensitive to object texture and were shown to model the blur more precisely than the previous method. Experiments with real planar images demonstrated a maximum RMS depth error of 1.18% for the proposed filters, compared to 1.54% for the previous design. The researched software program required five 2D convolutions to be processed in parallel and these convolutions were effectively implemented on a FPGA using a two channel, five stage pipelined architecture, however the precision of the filter coefficients and the variables had to be limited within the processor. The number of multipliers required for each convolution was reduced from 49 to 10 (79.5% reduction) using a Triangular design procedure. Experimental results suggested that the pipelined processor provided depth estimates comparable in accuracy to the full precision Matlab‟s output, and generated depth maps of size 400 x 400 pixels in 13.06msec, that is faster than the video rate. The defocused images (near and far-focused) were optically registered for magnification using Telecentric optics. A frequency domain approach based on phase correlation was employed to measure the radial shifts due to magnification and also to optimally position the external aperture. The telecentric optics ensured pixel to pixel registration between the defocused images was correct and provided more accurate depth estimates

Three-Dimensional Shape Measurements of Specular Objects Using Phase-Measuring Deflectometry

The fast development in the fields of integrated circuits, photovoltaics, the automobile industry, advanced manufacturing, and astronomy have led to the importance and necessity of quickly and accurately obtaining three-dimensional (3D) shape data of specular surfaces for quality control and function evaluation. Owing to the advantages of a large dynamic range, non-contact operation, full-field and fast acquisition, high accuracy, and automatic data processing, phase-measuring deflectometry (PMD, also called fringe reflection profilometry) has been widely studied and applied in many fields. Phase information coded in the reflected fringe patterns relates to the local slope and height of the measured specular objects. The 3D shape is obtained by integrating the local gradient data or directly calculating the depth data from the phase information. We present a review of the relevant techniques regarding classical PMD. The improved PMD technique is then used to measure specular objects having discontinuous and/or isolated surfaces. Some influential factors on the measured results are presented. The challenges and future research directions are discussed to further advance PMD techniques. Finally, the application fields of PMD are briefly introduce

Structured-light based sensing using a single fixed fringe grating: Fringe boundary detection and 3-D reconstruction

Advanced electronic manufacturing requires the 3-D inspection of very small surfaces like the solder bumps on wafers for direct die-to-die bonding. Yet the microscopic size and highly specular and textureless nature of the surfaces make the task difficult. It is also demanded that the size of the entire inspection system be small so as to minimize restraint on the operation of the various moving parts involved in the manufacturing process. In this paper, we describe a new 3-D reconstruction mechanism for the task. The mechanism is based upon the well-known concept of structured-light projection, but adapted to a new configuration that owns a particularly small system size and operates in a different manner. Unlike the traditional mechanisms which involve an array of light sources that occupy a rather extended physical space, the proposed mechanism consists of only a single light source plus a binary grating for projecting binary pattern. To allow the projection at each position of the inspected surface to vary and form distinct binary code, the binary grating is shifted in space. In every shift, a separate image of the illuminated surface is taken. With the use of pattern projection, and of discrete coding instead of analog coding in the projection, issues like texture-absence, image saturation, and image noise of the inspected surfaces are much lessened. Experimental results on a variety of objects are presented to illustrate the effectiveness of this mechanism. © 2008 IEEE.published_or_final_versio

Integración de Proyección de Franjas y Correlación digital de imagines 2D para la medida de deformaciones y desplazamientos

[ES] En esta tesis se presenta un novedoso sistema que permite medir los desplazamientos en las direcciones X-, Y- y Z- ocurridos en la superficie de un objeto sometido a deformación. El método seguido se basa en combinar las técnicas 2D-DIC y FP. Éste sistema propuesto obtiene dichos resultados a partir de la adquisición de tan sólo una imagen por cada etapa de la deformación del objeto, lo que permite la adquisición de datos en tiempo real. Además, permite una completa y sencilla calibración de los parámetros necesarios para la corrección de los desplazamientos medidos en el plano. Para ilustrar el potencial del sistema propuesto, se ha realizado una serie de experimentos estáticos y dinámicos. Los resultados se han comparado con los obtenidos empleando un sistema Correlación Digital de Imágenes 3D comercial, manifestando un nivel de concordancia muy alto con diferencias menores del 5%.[EN]This thesis presents a novel system to measure displacements in X-, Y-and Z-directions occurring on the surface of an object under deformation. The employed method is based on combining 2D-DIC and FP techniques. This proposed system obtains those results from the acquisition of only one image per each stage of the deformation of the object, enabling real time data acquisition. In addition it allows a complete and simple calibration procedure of the required parameters for the correction of the measured in the plane displacements. To illustrate the potential of the proposed system it has been performed a series of static and dynamic experiments. The results were compared with those obtained using a Digital Mapping 3D images commercial system, showing a high level of concordance with differences lower to 5%.Tesis Univ. Jaén. Departamento de Ingeniería Mecánica y Minera, leída el 25 de marzo de 201

Accurate depth from defocus estimation with video-rate implementation

The science of measuring depth from images at video rate using „defocus‟ has been investigated. The method required two differently focussed images acquired from a single view point using a single camera. The relative blur between the images was used to determine the in-focus axial points of each pixel and hence depth. The depth estimation algorithm researched by Watanabe and Nayar was employed to recover the depth estimates, but the broadband filters, referred as the Rational filters were designed using a new procedure: the Two Step Polynomial Approach. The filters designed by the new model were largely insensitive to object texture and were shown to model the blur more precisely than the previous method. Experiments with real planar images demonstrated a maximum RMS depth error of 1.18% for the proposed filters, compared to 1.54% for the previous design. The researched software program required five 2D convolutions to be processed in parallel and these convolutions were effectively implemented on a FPGA using a two channel, five stage pipelined architecture, however the precision of the filter coefficients and the variables had to be limited within the processor. The number of multipliers required for each convolution was reduced from 49 to 10 (79.5% reduction) using a Triangular design procedure. Experimental results suggested that the pipelined processor provided depth estimates comparable in accuracy to the full precision Matlab‟s output, and generated depth maps of size 400 x 400 pixels in 13.06msec, that is faster than the video rate. The defocused images (near and far-focused) were optically registered for magnification using Telecentric optics. A frequency domain approach based on phase correlation was employed to measure the radial shifts due to magnification and also to optimally position the external aperture. The telecentric optics ensured pixel to pixel registration between the defocused images was correct and provided more accurate depth estimates.EThOS - Electronic Theses Online ServiceUniversity of Warwick (UoW)GBUnited Kingdo

Optimisation of the Dielectrophoretic Well System for Cell-Based Assays.

Dielectrophoresis (DEP), the induced motion of cells in an inhomogeneous electric field, can be measured by studying the motion of the cells at different frequencies. This work uses a light absorption method to determine the DEP force and extract the dielectric properties of cell populations. Previously, light intensity changes in a 3D well electrode have been measured with a microscope and a single channel signal generator. This work sets out to enable real time measurement of cell populations by implementing a digital camera, lens and light source alongside a 20 channel signal generator in one machine, the DEP well instrument, to measure light intensity changes for 20 wells simultaneously. Optimisation of the optics is carried out through the evaluation of different cameras, lenses and light sources and measuring the light intensity changes of yeast populations in 4 wells that are energized with the same frequency, in order to ensure that the system is able to give consistent results. Finally, the application of the DEP well instrument for detection of drug cytotoxicity and rapid detection of apoptosis, both important in the development of new chemotherapeutic drugs, was studied. Both apoptosis and cytotoxicity of drugs can be characterized by changes in the membrane and cytoplasm properties of cells resulting in various distinct sub-populations within a sample. Rapid detection of apoptosis was examined by inducing HeLa cells with the well known chemotherapeutic agent staurosporine and comparing the results obtained with DEP and those obtained with the gold standard method of measuring apoptosis, Annexin V assay with flow cytometry. The ability of the DEP well instrument to test drug cytotoxicity on suspension and adherent cells was studied by inducing cells with the chemotherapeutic agent doxorubicin and measuring cell viability with DEP after different incubation times. The results were compared with the colorimetric assay 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) and trypan blue experimental results, as well as with previously published values