Optical scanning sensor system with submicron resolution

In this work, autofocus and optical scanning technologies are brought together in the design of a simplified scanning microscope. The developed system uses an autofocus sensor based on the Foucault knife-edge principle and piezo-based stages for scanning the samples in axial and lateral directions. It is built with a reduced number of components and designed to offer a simple set-up for the analysis of optical aberrations. The traditional way of addressing optical aberrations in scanning system is to improve the optical system such that it works as a paraxial lens. Breaking this paradigm and observing the optics as part of a complex system, it is possible to use simpler optics and correct the resultant errors computationally. These errors are systematic and, as long as they can be measured and modelled, they can be predicted and corrected. This way, the design of the system becomes more flexible and the task of error handling can be divided between optics optimization and computational correction, reducing overall size and weight, raising system dynamics and reducing costs.Laser-Scanning Mikroskopie ist eine im Bereich der Oberflächenmessung wichtige und vielversprechende Technologie für schnelle, genaue und wiederholbare Messungen. Es ist im Grunde eine Technik zur Erhöhung von Kontrast und Auflösung in optischen Abbildungssystemen. Ein Prüfling wird punktweise abgetastet und ein dreidimensionales Bild seiner Oberfläche mit Hilfe eines Rechners erfasst und rekonstruiert. In dieser Arbeit werden Autofokus- und optische Abtastverfahren in der Entwicklung und Konstruktion eines alternativen, vereinfachten Scanning Mikroskops für Oberflächenmessungen im Millimeterbereich mit Sub-Mikrometer Auflösung zusammengebracht. Das entwickelte System verwendet einen auf dem Foucault‘sches Schneidenverfahren basierenden Autofokussensor um die Fokuslage zu bestimmen und einen Piezo-Linearantrieb für die Verschiebung des Objektivs entlang der optischen Achse und das Abtasten des Prüflings in der axialen Richtung. Die laterale Abtastung des Prüflings wird durch den Einsatz eines Piezo-Spiegels realisiert, der um zwei Achsen schwenkbar ist. Das entwickelte Mikroskop hat eine reduzierte Anzahl von optischen Komponenten und bietet einen einfachen und vielseitigen Versuchsaufbau zur Messung und Analyse von Fehlern, die durch die bewusste Verwendung von unkompensierten Optiken auftreten. Die damit verbundenen Abbildungsfehler erzeugen Asymmetrien in den Autofokussensoren und beeinträchtigen die Gesamtleistung. Die herkömmliche Lösung dieser Problematik ist das System durch Addition zusätzlicher Komponenten zu verbessern, sodass es wie ein paraxiales System wirkt. Diese Verbesserung bringt aber die Nachteile von Baugröße, Gewicht und Kosten mit sich. Durch das Brechen des Paradigmas der Verbesserung der Optik bis zu einem paraxialen System und die Betrachtung der Optik als Teil eines komplexen Systems ist es möglich, simplere Optik zu verwenden, und die resultierenden Fehler rechnerisch zu korrigieren. Diese Fehler sind systematisch und können – solange sie modelliert und gemessen werden können – vorhergesagt und korrigiert werden. Damit wird das Design des optischen Systems flexibler und die Aufgabe der Fehlerbehandlung zwischen Optimierung der Optik und rechnerischer Korrektur aufgeteilt. Baugröße, Gewicht und Kosten können dann reduziert werden und die Systemdynamik erhöht sich, ohne Einschränkung der Präzision. Das Ziel ist nicht jeden Abbildungsfehler individuell zu untersuchen, sondern deren Zusammenwirken auf die Messungen zu beobachten und zu modellieren. Verschiedene Strategien für die Behandlung dieser Messfehler werden in dieser Arbeit vorgeschlagen, diskutiert und experimentell validiert.Laser Scanning Microscopy has been used for a long time in the field of surface measurement and is today one of the most promising technologies for fast, accurate and repeatable measurements. It is technique for increasing contrast and resolution in optical imaging systems through the rejection of out-of-focus light. Images are acquired point-by-point and reconstructed with a computer, allowing three-dimensional reconstructions of objects. In this work, autofocus and optical scanning technologies are brought together in the design of an alternative simplified scanning microscope for surface measuring in millimetre range with sub-micrometer resolution. The developed system uses an autofocus sensor based on the Foucault knife-edge principle to generate a defocus signal and a piezo positioning stage for translating the objective and scanning the samples in the axial direction. For the lateral scanning, a piezo driven tip-tilt mirror is used. The developed scanning microscope is built with a reduced number of optical components and designed to offer a simple and versatile set-up for the measurement and analysis of errors induced by optical aberrations due to the use of suboptimal optics. The use of uncompensated lenses has always been avoided in scanning microscopy as it generates asymmetries in the defocus signal and deteriorates its overall performance. The traditional way of solving this problem is to improve the optical system such that it works as a paraxial lens, but that comes with the price of heavy and costly optics. By breaking the paradigm of improving the optics to a paraxial lens and observing the optics as part of a complex system, it is possible to use simpler optics and correct the resultant errors computationally. These errors are systematic and, as long as they can be measured and modelled, they can be predicted and corrected. This way, the design of the optical system becomes much more flexible and the task of error handling can be divided between optics optimization and computational correction, reducing overall size and weight, raising system dynamics and reducing costs, without losing accuracy. The goal is not to study each optical aberration individually, but to measure and model their combined influence in the measurements. Different strategies for addressing these measurement errors caused by the use of uncompensated optics are proposed, discussed and experimentally validate

Theoretical and practical aspects of robot calibration with experimental verification

One of the greatest challenges in today's industrial robotics is the development of off-line programming systems that allow drastic reduction in robots' reprogramming time, improving productivity. The article purpose is to pave the way to the construction of generic calibration systems easily adapted to any type of robot, regardless their application, such as modular robots and robot controllers specifically designed for non-standard applications. A computer system was built for developing and implementing a calibration system that involves the joint work of computer and measurement systems. Each step of this system's development is presented together with its theoretical basis. With the development of a remote maneuvering system based on ABB S3 controller experimental tests have been carried out using an IRB2000 robot and a measurement arm (ITG ROMER) with 0.087 mm of position measurement accuracy. The robot model used by its controller was identified and the robot was calibrated and evaluated in different workspaces resulting in an average accuracy improvement from 1.5 mm to 0.3 mm

Development of a tridimensional surface digitaliztion system based on computer vision and laser scanning with metrological purpose

Dissertação (mestrado)—Universidade de Brasília, Departamento de Engenharia Mecânica, Programa de pós-graduação em Ciências Mecâncias, 2008.A grande maioria dos sistemas atuais de digitalização tridimensional de superfícies baseia-se no uso de sensores de posicionamento para a medição da rotação de uma fonte emissora de luz. Esses sensores impõem restrições sobre o volume e a distância de trabalho do digitalizador e, como a reconstrução é normalmente baseada em equações de triangulação, eles também geram incertezas de medição devido à relação não-linear entre a posição angular e a distância. Para superar essas dificuldades, removendo a necessidade do uso de sensores angulares de posição de alto custo e aumentando a distância de medição, apresenta-se nesse trabalho o desenvolvimento de um sistema de digitalização tridimensional de superfícies compacto, de fácil transporte e auto-calibrável. Com o uso de técnicas de visão computacional elimina-se a necessidade de qualquer tipo de sensor de posicionamento e com o sistema de auto-calibração desenvolvido dispensa-se a necessidade de outros sistemas de medição para a calibração. Todas as técnicas de calibração de câmeras, processamento de imagens e a arquitetura completa do sistema são discutidas e apresentadas junto com um comparativo do sistema desenvolvido e sistema comerciais e em desenvolvimento em diferentes instituições de pesquisa e desenvolvimento. _______________________________________________________________________________ ABSTRACTMost of today’s 3D laser scanning systems for object model digitalization rely on angular position sensors to measure rotation of a laser diode and to reconstruct the object. However, those types of sensors restrict the object size in target and its distance from the image sensor, since reconstruction is usually based on equations for geometric triangulation, leading to high measurement errors due to the non-linear relation between angular positions and distances. In order to overcome the need of high cost angular position sensors and to increase measurement distances it is proposed here a 3D surface scanner based on computer vision that is compact, easy to transport and self-calibrated. The system calibration includes camera calibration using radial alignment constraints, image processing routines and determination of system parameters. The complete system architecture with two laser diodes and a single camera is shown, the theoretical basis, hardware implementation and practical results obtained are presented, discussed and compared with different systems available

Desenvolvimento de um sistema de digitalização tridimencional de superfícies baseado em visão computacional com varredura a laser para uso em metrologia dimensional

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2008.A grande maioria dos sistemas atuais de digitalização tridimensional de superfícies baseia-se no uso de sensores de posicionamento para a medição da rotação de uma fonte emissora de luz. Esses sensores impõem restrições sobre o volume e a distância de trabalho do digitalizador e, como a reconstrução é normalmente baseada em equações de triangulação, eles também geram incertezas de medição devido à relação não-linear entre a posição angular e a distância. Para superar essas dificuldades, removendo a necessidade do uso de sensores angulares de posição de alto custo e aumentando a distância de medição, apresenta-se nesse trabalho o desenvolvimento de um sistema de digitalização tridimensional de superfícies compacto, de fácil transporte e auto-calibrável. Com o uso de técnicas de visão computacional elimina-se a necessidade de qualquer tipo de sensor de posicionamento e com o sistema de auto-calibração desenvolvido dispensa-se a necessidade de outros sistemas de medição para a calibração. Todas as técnicas de calibração de câmeras, processamento de imagens e a arquitetura completa do sistema são discutidas e apresentadas junto com um comparativo do sistema desenvolvido e sistema comerciais e em desenvolvimento em diferentes instituições de pesquisa e desenvolvimento. _________________________________________________________________________________ ABSTRACTMost of today’s 3D laser scanning systems for object model digitalization rely on angular position sensors to measure rotation of a laser diode and to reconstruct the object. However, those types of sensors restrict the object size in target and its distance from the image sensor, since reconstruction is usually based on equations for geometric triangulation, leading to high measurement errors due to the non-linear relation between angular positions and distances. In order to overcome the need of high cost angular position sensors and to increase measurement distances it is proposed here a 3D surface scanner based on computer vision that is compact, easy to transport and self-calibrated. The system calibration includes camera calibration using radial alignment constraints, image processing routines and determination of system parameters. The complete system architecture with two laser diodes and a single camera is shown, the theoretical basis, hardware implementation and practical results obtained are presented, discussed and compared with different systems available