98 research outputs found

    Automated Assembly Using Feature Localization

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    Automated assembly of mechanical devices is studies by researching methods of operating assembly equipment in a variable manner; that is, systems which may be configured to perform many different assembly operations are studied. The general parts assembly operation involves the removal of alignment errors within some tolerance and without damaging the parts. Two methods for eliminating alignment errors are discussed: a priori suppression and measurement and removal. Both methods are studied with the more novel measurement and removal technique being studied in greater detail. During the study of this technique, a fast and accurate six degree-of-freedom position sensor based on a light-stripe vision technique was developed. Specifications for the sensor were derived from an assembly-system error analysis. Studies on extracting accurate information from the sensor by optimally reducing redundant information, filtering quantization noise, and careful calibration procedures were performed. Prototype assembly systems for both error elimination techniques were implemented and used to assemble several products. The assembly system based on the a priori suppression technique uses a number of mechanical assembly tools and software systems which extend the capabilities of industrial robots. The need for the tools was determined through an assembly task analysis of several consumer and automotive products. The assembly system based on the measurement and removal technique used the six degree-of-freedom position sensor to measure part misalignments. Robot commands for aligning the parts were automatically calculated based on the sensor data and executed

    3D Laser Scanner Development and Analysis

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    Polarization image laser line extraction methods for reflective metal surfaces

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    In this work, we propose a novel pipeline method for laser line extraction from images with a polarization image sensor. The proposed method is specially developed for strong laser beam reflections from metal surfaces. For the pre-processing stage, we propose a demosaicing algorithm for color polarizer filter array (CPFA) sensors. This can be implemented by using either one quarter or full resolution of the sensor. In addition, we propose two methods for optimizing the information available in a 12-channel color polarization image: The first method, is based on the minimum linearly polarized irradiance, and the second method, is based on the linear polarization intensity. These pre-processing, and optimization methods are combined with laser line extraction methods. The laser line extraction is done with either the Polarized Finite Impulse Response (FIR) Center Of Gravity (COG), where the laser line coordinates are computed from the filtered laser intensity distribution, or with the Polarized FIR-Peak, where the laser line coordinates are calculated from the first derivative of the filtered laser signal. The performance of the proposed algorithms is studied experimentally using a laser line scanner assembly, made of a polarization camera, and a laser line projector operating in the blue wavelength range.acceptedVersio

    Surface scanning with uncoded structured light sources.

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    Structured Light Scanners measure the surface of a target object, producing a set of vertices which can be used to construct a three-dimensional model of the surface. The techniques are particularly appropriate for measuring the smoothly undulating, featureless forms which Stereo Vision methods find difficult, and the structured light pattern explicitly gives a dense graph of connected vertices, thus obviating the need for vertex-triangulation prior to surface reconstruction. In addition, the technique provides the measurements almost instantaneously, and so is suitable for scanning moving and non-rigid objects. Because of these advantages there is an imperative to extend the range of scannable surfaces to those including occlusions, which often reduce or prevent successful measurement.This thesis investigates ways of improving both the accuracy and the range of surface types which can be scanned using structured light techniques, extending current research by examining the role of occlusions and geometric constraints, and introducing novel algorithms to solve the Indexing Problem. The Indexing Problem demands that for every pattern element in the projected image, its counterpart, reflected from the surface of the target object, must be found in the recorded image, and most researchers have declared this problem to be intractable without resorting to coding schemes which uniquely identify each pattern element. The use of uncoded projection patterns, where the pattern elements are projected without any unique identification, has two advantages: firstly it provides the densest possible set of measured vertices within a single video timeframe, and secondly it allows the investigation of the fundamental problems without the distraction of dealing with coding schemes. These advantages educe the general strategy adopted in this thesis, of attempting to solve the Indexing Problem using uncoded patterns, and then adding some coding where difficulties still remain.In order to carry out these investigations it is necessary to precisely measure the system and its outputs, and to achieve this requirement two scanners have been built, a Single Stripe Scanner and a Multiple Stripe Scanner. The Single Stripe Scanner introduces the geometric measurement methods and provides a reference output which matches the industry standard; the Multiple Stripe Scanner then tests the results of the investigations and evaluates the success of the new algorithms and constraints. In addition, some of the investigations are tested theoretically, by using synthetic data and by the solution of geometric diagrams.These evaluations of success show that, if occlusions are not present in the recorded data, the Indexing Problem can often be completely solved if the new indexing algorithms and geometric constraints are included. Furthermore, while there are some cases where the Indexing Problem cannot be solved without recourse to a coding scheme, the addition of occlusion detection in the algorithms greatly improves the indexing accuracy and therefore the successful measurement of the target surface

    Three-dimensional geometry characterization using structured light fields

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

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

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    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

    PATTERN EVALUATION FOR IN-PLANE DISPLACEMENT MEASUREMENT OF THIN FILMS

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    The term Gossamer is used to describe ultra-lightweight spacecraft structures that solve the aerospace challenge of obtaining maximum performance while reducing the launch costs of the spacecraft. Gossamer structures are extremely compliant, which complicates control design and ground testing in full scale. One approach is to design and construct smaller test articles and verify their computational models experimentally, so that similar computational models can be used to predict the dynamic performance of full-scale structures. Though measurement of both in-plane and out-of-plane displacements is required to characterize the dynamic response of the surface of these structures, this thesis lays the groundwork for dynamic measurement of the in-plane component. The measurement of thin films must be performed using non-contacting sensors because any contacting sensor would change the dynamics of the structure. Moreover, the thin films dealt with in this work are coated with either gold or aluminum for special applications making the film optically smooth and therefore requiring a surface pattern. A Krypton Fluoride excimer laser system was selected to fabricate patterns on thin-film mirror test articles. Parameters required for pattern fabrication were investigated. Effects of the pattern on the thin-film dynamics were studied using finite element analysis. Photogrammetry was used to study the static in-plane displacement of the thin-film mirror. This was performed to determine the feasibility of the photogrammetric approach for future dynamic tests. It was concluded that photogrammetry could be used efficiently to quantify dynamic in-plane displacement with high-resolution cameras and sub-pixel target marking

    LASER RANGE IMAGING FOR ON-LINE MAPPING OF 3D IMAGES TO PSEUDO-X-RAY IMAGES FOR POULTRY BONE FRAGMENT DETECTION

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    A laser ranging image system was developed for on-line high-resolution 3D shape recovery of poultry fillets. The range imaging system in conjunction with X-ray imaging was used to provide synergistic imaging detection of bone fragments in poultry fillets. In this research, two 5 mW diode lasers coupled with two CCD cameras were used to produce 3D information based on structured lights and triangulation. A laser scattering phenomenon on meat tissues was studied when calculating the object thickness. To obtain the accurate 3D information, the cameras were calibrated to correct for camera distortions. For pixel registrations of the X-ray and laser 3D images, the range imaging system was calibrated, and noises and signal variations in the X-ray and laser 3D images were analyzed. Furthermore, the relationship between the X-ray absorption and 3D thickness of fillets was obtained, and a mapping function based on this relationship was applied to convert the fillet 3D images into the pseudo-X-ray images. For the on-line system implementation, the imaging hardware and software engineering issues, including the data flow optimization and the operating system task scheduling, were also studied. Based on the experimental on-line test, the range imaging system developed was able to scan poultry fillets at a speed of 0.2 m/sec at a resolution of 0.8(X) x 0.7(Y) x 0.7(Z) mm3. The results of this study have shown great potential for non-invasive detection of hazardous materials in boneless poultry meat with uneven thickness
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