Matthias Rückwardt

A new method for getting the three-dimensional curve of the groove of a spectacle frame by optical measuring

Precise measuring of spectacle frames is an important field of quality assurance for opticians and their customers. Different supplier and a number of measuring methods are available but all of them are tactile ones. In this paper the possible employment of optical coordinate measuring machines is discussed for detecting the groove of a spectacle frame. The ambient conditions like deviation and measuring time are even multifaceted like quantity of quality characteristics and measuring objects itself and have to be tested. But the main challenge for an optical coordinate measuring machine is the blocked optical path, because the device under test is located behind an undercut. In this case it is necessary to deflect the beam of the machine for example with a rotating plane mirror. In the next step the difficulties of machine vision connecting to the spectacle frame are explained. Finally first results are given.

Field programmable gate array based hardware implementation of a gradient filter for edge detection in colour images with subpixel precision

Within the field of industrial image processing the use of colour cameras becomes ever more common. Increasingly the established black and white cameras are replaced by economical single-chip colour cameras with Bayer pattern. The use of the additional colour information is particularly important for recognition or inspection. Become interesting however also for the geometric metrology, if measuring tasks can be solved more robust or more exactly. However only few suitable algorithms are available, in order to detect edges with the necessary precision. All attempts require however additional computation expenditure. On the basis of a new filter for edge detection in colour images with subpixel precision, the implementation on a pre-processing hardware platform is presented. Hardware implemented filters offer the advantage that they can be used easily with existing measuring software, since after the filtering a single channel image is present, which unites the information of all colour channels. Advanced field programmable gate arrays represent an ideal platform for the parallel processing of multiple channels. The effective implementation presupposes however a high programming expenditure. On the example of the colour filter implementation, arising problems are analyzed and the chosen solution method is presented.

Fully automated measuring setup for tactile coordinate measuring machine for three dimensional measurement of freeform eyeglass frames

Coordinate measuring machines are high precession all-rounder in three dimensional measuring. Therefore the versatility of parameters and expandability of additionally hardware is very comprehensive. Consequently you need much expert knowledge of the user and mostly a lot of advanced information about the measuring object. In this paper a coordinate measuring machine and a specialized measuring machine are compared at the example of the measuring of eyeglass frames. For this case of three dimensional measuring challenges the main focus is divided into metrological and economical aspects. At first there is shown a fully automated method for tactile measuring of this abstract form. At second there is shown a comparison of the metrological characteristics of a coordinate measuring machine and a tracer for eyeglass frames. The result is in favour to the coordinate measuring machine. It was not surprising in these aspects. At last there is shown a comparison of the machine in front of the economical aspects.

Investigation, Design and Practical Testing of LED Linear Light as an Alternative to a Laser Line Generator

Abstract An interesting option for 3D object recognition is the triangulation principle. For this purpose a laser line generator is often used. But other structured linear light sources are also possible. For this the linear light has to have a defined width, brightness and sharpness. The linear light on the object, e. g. a groove, is changed by the object´s surface and is detected by digital image processing. Until now such linear light has been created with the help of a complex visual system using laser diodes. Because of some optical disadvantages of laser light, like speckles, in optical measurement applications, this paper examines the effect of using a structured LED light source instead of the laser generator. Consequently, the focus of this research lies on the necessary width, brightness, sharpness, length and depth of focus of the linear light generated by a LED light source for high-precision measuring. This research has been carried out by extensive computer-aided simulations. Several solutions are given and assessed in this paper. Zusammenfassung Das Triangulationsprinzip findet vielfach Anwendung bei der 3D-Objekterkennung. Zu diesem Zweck wird häufig ein Laserliniengenerator verwendet, aber andere strukturierte Lichtquellen sind ebenfalls möglich. Für Messaufgaben ist es notwendig, dass das Linienlicht über eine definierte Breite, Helligkeit und Schärfe verfügt. Das Erscheinungsbild des Linienlichts wird durch die Objektoberfläche, z. B. eine Nut, beeinflusst und mittels digitaler Bildverarbeitung aufgenommen. Aktuell wird das Linienlicht meist durch komplexe optische Systeme erzeugt, die Laserdioden als Lichtquelle nutzen. Gerade bei der optischen 3D-Objekterkennung besitzt Laserlicht einige Nachteile, wie z. B. Speckle. Daher erläutert dieser Artikel die Anwendung von strukturiertem Linienlicht, das LED-Lichtquellen anstelle von Laserliniengeneratoren nutzt. Folglich liegen die Forschungsschwerpunkte auf der benötigten Breite, Helligkeit, Schärfe, Länge und Tiefenschärfe des Linienlichts, sodass mit strukturierte LED-Lichtquellen ebenfalls hochgenaue Messungen möglich sind. Die Ergebnisse wurden durch umfangreiche computergestützte Simulationen realisiert. Verschiedene Lösungen werden aufgezeigt und in diesem Artikel bewertet.