Single exposure 3D imaging of dusty plasma clusters

We have worked out the details of a single camera, single exposure method to perform three-dimensional imaging of a finite particle cluster. The procedure is based on the plenoptic imaging principle and utilizes a commercial Lytro light field still camera. We demonstrate the capabilities of our technique on a single layer particle cluster in a dusty plasma, where the camera is aligned inclined at a small angle to the particle layer. The reconstruction of the third coordinate (depth) is found to be accurate and even shadowing particles can be identified.Comment: 6 pages, 7 figures. Submitted to Rev. Sci. Inst

A Laser-Based Vision System for Weld Quality Inspection

Welding is a very complex process in which the final weld quality can be affected by many process parameters. In order to inspect the weld quality and detect the presence of various weld defects, different methods and systems are studied and developed. In this paper, a laser-based vision system is developed for non-destructive weld quality inspection. The vision sensor is designed based on the principle of laser triangulation. By processing the images acquired from the vision sensor, the geometrical features of the weld can be obtained. Through the visual analysis of the acquired 3D profiles of the weld, the presences as well as the positions and sizes of the weld defects can be accurately identified and therefore, the non-destructive weld quality inspection can be achieved

Measurement method for 2-dimensional coordinate system

The subject of this Master’s of Science Thesis is to study suitability of predefined technologies and development of a measurement system for measuring Cartesian style robot’s positioning accuracy within its x/y-plane. The methods currently used for measuring and calibrating robot positioning are based on commercial solutions or measurement systems developed internally. Both of these have their non-beneficial properties that lead to the commissioning of this thesis work. The commercial system provides a high accuracy and repeatability performance but are often costly and difficult or impossible to integrate to the robot system in question. The second mentioned measurement system has much lower building costs but it only measures in one axis at a time and thus, it doesn’t see the possible orthogonality errors. This problem was approached with three methodologies covering the theoretical background of the main geometrical error sources, some basics of the theory of measurement uncertainty, evaluation procedure for evaluating suitability of technologies for measuring positioning and developing a measurement system with the selected technology based on the evaluation results. The technologies are evaluated with a scoring system based on criterion that sets a range of requirements for e.g. accuracy performance and other functionality. The goal of this thesis was to develop a low cost, system integrable positioning measurement system and study its performance and usability by comparing it to commercial measurement systems and systems design and developed internally. After conducting evaluation of the technologies, a camera-based technology was selected for development phase. This technology solution includes a camera and optics that are the robots standard equipment and thus won’t add any additional costs. This solution requires a measurement target which is used with the camera to detect motion and algorithms for camera calibration and for calculating motion increments from the captured images. With the combination of camera, optics and the measurement target a value of 55.2 pixels per millimeter was obtained which translates to 17.9 μm ± 0.001-pixel size in the measurement images

A calibration method for a laser triangulation scanner mounted on a robot arm for surface mapping

This paper presents and discusses a method to calibrate a specially built laser triangulation sensor to scan and map the surface of hydraulic turbine blades and to assign 3D coordinates to a dedicated robot to repair, by welding in layers, the damage on blades eroded by cavitation pitting and/or cracks produced by cyclic loading. Due to the large nonlinearities present in a camera and laser diodes, large range distances become di cult to measure with high precision. Aiming to improve the precision and accuracy of the range measurement sensor based on laser triangulation, a calibration model is proposed that involves the parameters of the camera, lens, laser positions, and sensor position on the robot arm related to the robot base to find the best accuracy in the distance range of the application. The developed sensor is composed of a CMOS camera and two laser diodes that project light lines onto the blade surface and needs image processing to find the 3D coordinates. The distances vary from 250 to 650 mm and the accuracy obtained within the distance range is below 1 mm. The calibration process needs a previous camera calibration and special calibration boards to calculate the correct distance between the laser diodes and the camera. The sensor position fixed on the robot arm is found by moving the robot to selected positions. The experimental procedures show the success of the calibration scheme

High-performance long-range laser scanner with calibrated digital camera: a hybrid 3D laser sensor system

Peer Reviewe

A new method to determine multi-angular reflectance factor from lightweight multispectral cameras with sky sensor in a target-less workflow applicable to UAV

A new physically based method to estimate hemispheric-directional reflectance factor (HDRF) from lightweight multispectral cameras that have a downwelling irradiance sensor is presented. It combines radiometry with photogrammetric computer vision to derive geometrically and radiometrically accurate data purely from the images, without requiring reflectance targets or any other additional information apart from the imagery. The sky sensor orientation is initially computed using photogrammetric computer vision and revised with a non-linear regression comprising radiometric and photogrammetry-derived information. It works for both clear sky and overcast conditions. A ground-based test acquisition of a Spectralon target observed from different viewing directions and with different sun positions using a typical multispectral sensor configuration for clear sky and overcast showed that both the overall value and the directionality of the reflectance factor as reported in the literature were well retrieved. An RMSE of 3% for clear sky and up to 5% for overcast sky was observed

High-performance long-range laser scanner with calibrated digital camera: a hybrid 3D laser sensor system

Peer Reviewe

Precision angle measurement of MEMS scanning systems

MEMS mirrors and its laser scanning systems have received much attention in high precision scanning systems, for various applications such as lidars and augmented reality head up displays in automotive markets. High accuracy and precision are required for high resolution and reliable operation of the MEMS-based laser scanning system. To achieve such high accuracy and precision, an appropriate characterisation of MEMS mirror is crucial. This thesis discusses the development of an accurate and precise characterisation system for MEMS-based laser scanning systems. A new characterisation system is designed to allow an accurate mechanical angle measurements for a large mechanical range with a large tolerance of the working distance errors. The new characterisation system is composed by a lens system with a 2/3 inch CMOS image sensor, which allows the required performance. For three-lens systems, conventional lens disposition (CLD) and unusual lens disposition (ULD) are considered for the chosen lens system configuration. Once the lenses are properly selected, the parameters of the characterisation system arrangement are determined for each lens disposition case, using the software Zemax OpticStudio and Matlab. Then, the characterisation system designed for both lens disposition cases is developed in the laboratory and aligned in an experimental setup so that it is possible to perform the measurement of the mechanical angle of a galvanometer-based scanning mirror. For two lens disposition cases, numerical simulation by Zemax OpticStudio and experimental results by the characterisation system are analysed and compared to evaluate the developed lens-based characterisation system. Finally, only the ULD case allows mechanical angle measurements up to +-7º with a tolerance of working distance error for +-5mm, which corresponds to 16.17% where the maximum error in the mechanical angle measurement does not surpass the required accuracy of 0.1º, which is verified by both numerical and experimental results. The mechanical angles +-7º are larger than the maximum mechanical angles that the 2/3 inch sensor can measure when it is placed at the same working distance of the characterisation system. This show that the lens-based characterisation system with ULD of the three lens system configuration enables a proper mechanical angle measurement for a large mechanical range with high tolerance against the errors in working distance.Espejos en MEMS y sus sistemas de escaneo láser reciben mucha atención para sistemas de escaneo de alta precisión en varias aplicaciones como "lidars" o "headup displays" en el mercado del automóvil. Se requiere alta precisión y exactitud para una alta resolución y operación fiable de un sistema de escaneo láser basado en espejo de MEMS. Con el fin de conseguir tal precisión y exactitud, una adecuada caracterización de los espejos de MEMS es crucial. En este TFG se discute el desarrollo de un sistema de caracterización preciso y exacto para los sistemas de escaneo láser basados en espejos de MEMS. Un nuevo sistema de caracterización es diseñado para obtener medidas del ángulo mecánico para un rango de ángulos mecánicos extenso con una tolerancia de los errores de la distancia de trabajo considerable. El nuevo sistema de caracterización está compuesto por un sistema de lentes y un sensor CMOS de tamaño 2/3 pulgadas, permitiendo el funcionamiento requerido. Para sistemas de tres lentes, se considera una disposición convencional de las lentes (CLD) y una disposición inusual de las lentes (ULD) para la configuración escogida del sistema de tres lentes. Una vez que las lentes se han elegido adecuadamente, los parámetros de la disposición del sistema de caracterización se determinan para las dos disposiciones de las lentes consideradas, utilizando el software Zemax OpticStudio y el Matlab. Entonces, el sistema de caracterización diseñado para las dos disposiciones de las lentes se establece en el laboratorio y se alinea en un montaje experimental de forma que sea posible medir el ángulo mecánico de un espejo que oscila. Para las dos disposiciones de lentes, los resultados numéricos por simulaciones utilizando Zemax OpticStudio y los resultados experimentales del sistema de caracterización son analizados y comparados para evaluar el sistema de caracterización basado en lentes que se ha diseñado. Finalmente, sólo el caso ULD permite la medida de ángulos mecánicos hasta +-7º con una tolerancia del error de la distancia de trabajo de +-5 mm, que corresponde a un 16.17% donde el máximo error en la medida de ángulos mecánicos no sobrepasa la exactitud requerida de 0.1º, verificado por los resultados numéricos y experimentales. Los ángulos mecánicos +-7º son mayores que los máximos ángulos mecánicos que el sensor de tamaño 2/3 pulgadas puede medir cuando está a la misma distancia de trabajo del sistema de caracterización. Esto muestra que el sistema de caracterización basado en lentes, cuando se considera el caso ULD por el sistema de tres lentes, permite una medida adecuada de los ángulos mecánicos para un rango de ángulos mecánicos extenso con una tolerancia contra los errores de la distancia de trabajo considerable.Miralls en MEMS i els seus sistemes d'escaneig làser reben molta atenció per sistemes d'escaneig d'alta precisió en varies aplicacions com "lidars" o "head up displays" en el mercat de l'automòbil. Es requereix alta precisió i exactitud per una alta resolució i operació fiable d'un sistema d'escaneig làser basat en mirall de MEMS. Per tal d'aconseguir tal precisió i exactitud, una adequada caracterització dels miralls de MEMS és crucial. En aquest TFG es discuteix el desenvolupament d'un sistema de caracterització precís i exacte pels sistemes d'escaneig làser basats en miralls de MEMS. Un nou sistema de caracterització és dissenyat per obtindre mesures de l'angle mecànic per un rang d'angles mecànics extens amb una tolerància dels errors de la distància de treball considerable. El nou sistema de caracterització està compost per un sistema de lents i un sensor CMOS de mida 2/3 polzades, permetent el funcionament requerit. Per sistemes de tres lents, es considera una disposició convencional de les lents (CLD) i una disposició inusual de les lents (ULD) per la configuració escollida del sistema de tres lents. Un cop les lents s'han triat adequadament, els paràmetres de l'arranjament del sistema de caracterització es determinen per les dues disposicions de les lents considerades, utilitzant el software Zemax OpticStudio i el Matlab. Llavors, el sistema de caracterització dissenyat per les dues disposicions de les lents s'estableix en el laboratori i s'alinea en un muntatge experimental de manera que sigui possible mesurar l'angle mecànic d'un mirall que oscil·la. Per les dues disposicions de lents, els resultats numèrics per simulacions utilitzant Zemax OpticStudio i els resultats experimentals del sistema de caracterització són analitzats i comparats per evaluar el sistema de caracterització basat en lents que s'ha disenyat. Finalment, només el cas ULD permet la mesura d'angles mecànics fins a +-7º amb una tolerància del error de la distància de treball de +-5 mm, que correspon a un 16.17% on el màxim error en la mesura d'angles mecànics no sobrepassa l'exactitud requerida de 0.1º, verificat pels resultats numèrics i experimentals. Els angles mecànics +-7º són majors que el màxims angles mecànics que el sensor de mira 2/3 polzades pot mesurar quan és a la mateixa distància de treball del sistema de caracterització. Això mostra que el sistema de caracterització basat en lents, quan es considera el cas ULD pel sistema de tres lents, permet una mesura adequada dels angles mecànics per un rang d'angles mecànics extens amb una tolerància contra els errors de la distància de treball considerable

Rotorcraft Blade Angle Calibration Methods

The most vital system of a rotorcraft is the rotor system due to its effects on the overall flight quality of the vehicle. Therefore, it is of importance to be able to accurately determine blade position during flight so that fine adjustments can be made to ensure a safe and efficient flight. In this study, a current calibration method focusing on the pitch, flap, and lead-lag blade angles is analyzed and found to have larger than acceptable error associated with the sensor calibrations. A literature review is conducted which reveals four novel methods that can potentially increase the accuracy of the sensor calibrations. An uncertainty analysis is conducted aiding in the decision of which of the four methods would best improve the calibration accuracy. The results conclude that a simpler method can be applied and calibration times can greatly be reduced while increasing the accuracy of the calibration. Finally, a new calibration method is proposed utilizing the newly chosen sensor that can be later implemented into the system

Optical Tool Setting and Control for Precision Lathe

The focus of this research was on the development of a machine vision system to provide automatic tool offset and tool nose radius compensation on a lathe used on the shop floor. To accomplish this work, a T-bed lathe which utilized a PC-based Computer Numerical Control was used. National Instruments Vision Builder for Automated Inspection was utilized to develop the machine vision software. A machine vision based optical tool setter was developed for checking the radius of lathe tools. A collimated blue light source along with a 5X microscope objective were used. Software written in Microsoft Visual Basic 2005 enabled software updates of offsets and tool nose radius. Overall, the system had an average repeatability of 8.2 µm, with an accuracy average of 2.5 µm, providing an opportunity for improved part tolerance