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The dissertation presents two approaches for novel and improved measurement techniques, in the area of optical confocal surface metrology.
Firstly, a highly miniaturized endoscopic point distance sensor based on a spatial confocal measurement principle is presented. The sensor utilizes a new technique called spatial confocal point distance measurement. A special feature of the proposed sensor design is the high degree of miniaturization through femto-second direct laser writing and the use of optical fiber bundles, which enable an endoscopic application.
The second part of the dissertation will present a novel method for chromatic confocal metrology, that enables high-speed and high-resolution one-shot areal surface metrology without the need for a spectrometer. After deriving the theoretical basis of the approach, an optical design is conducted and verified using a preliminary optical simulation, After the design of a suitable housing and implementation of a calibration and processing algorithm, the experimental validation and the acquired results will be presented.
In summary, this work adds two novel measurement techniques to the field of fast in-line optical confocal metrology.
The spectrometer-free chromatic confocal measurement technique enables 3D surface measurements with just one exposure and without scanning. To reduce the need for a spectrometer for the spectral analysis of the reflected light composition and thus the extraction of the local surface height, an optical spectral analysis unit is used. This unit determines the first momentum of the spectral composition reflected from the surface under probe for a large number of lateral measurement points simultaneously. This work investigates the impact of the spectral composition and light power of the light source on the sensitivity and accuracy of this method. A thorough optimization of the light source will be conducted, demonstrating the impact of various spectral compositions and light source power on the system performance, taking into account the system-related etendue. In addition, the optimization of the spectral transmission filter used in the optical spectral analysis unit and its influence on the accuracy and sensitivity of the system over the entire measurement range is shown.
The spectrometer free areal chromatic confocal metrology (ChromaCAM) is an optical 3D surface measurement technology, which allows a simultaneous measurement of a large array of measuring points within a single exposure. In this work, we investigate the accuracy of a first prototype sensor system utilizing this new singleshot 3D measurement technique. It is found that surface height measurement errors smaller 1μm within a total measurement range of about 1000 μm are achievable. Furthermore, several influential factors are investigated showing the advantages and limits of the presented system. Investigating different surface materials it is found that frame rates up to approximately 800 fps for highly reflecting surfaces and up to 30 fps for ceramics, aluminum, and plastics are achievable.
Increasing miniaturization requires improved and highly miniaturized optical 3D metrology systems. In this paper a basic measurement principle and a proposed optical design of a highly miniaturized endoscopic spatial confocal point distance sensor are presented. The sensor uses a, to our knowledge new technique called spatial confocal point distance measurement. A special feature of the proposed sensor design is the high degree of miniaturization, through femtosecond direct laser writing and the use of optical fiber bundles, which enable an
endoscopic application.
Chromatic confocal metrology suffers from a limitation in the number of measurement points that can be measured simultaneously in a single frame acquisition. We propose chromatic confocal areal metrology (ChromaCAM), in which the surface height for each point in a 2D grid of measurement spots, generated by a rectangular micro-lens array, is parallely analyzed through the utilization of a pinhole multiplexer unit, an analog optical analysis unit, and postprocessing algorithms. An experiment shows the viability of the simultaneous acquisition of multiple measurement points and the advantages over exisiting areal chromatic confocal approaches. Compared with conventional chromatic confocal metrology, the increase in the acquisition rate is significant and enables one-shot measurements.
We present a highly miniaturized endoscopic point distance sensor based on a spatial confocal measurement principle. The sensor uses a new technique called spatial confocal point distance measurement. A special feature of the proposed sensor design is the high degree of miniaturization through femtosecond direct laser writing and the use of optical fiber bundles, which enable an endoscopic application. We show the complete sensor measurement principle, sensor head design, experimental setup, and experimental results.
Chromatic confocal metrology is a widely established optical metrology technique, that allows for non-contact high-speed three-dimensional surface profiling without the need of mechanical depth scanning. However current methods are limited by the use of some sort of surface scanning method with mechanically moving parts. Furthermore the setups involve a spectrometer setup, either through prisms, gratings or multi-spectral cameras. This drastically limits the simultaneously measureable positions in lateral direction, as the spectrometer setup
will utilize one spatial dimension for the wavelength domain. We present a novel method for chromatic confocal metrology, that enables high-speed and high resolution one-shot aerial surface metrology. This method is scalable with respect to measurement range in axial as well as in lateral direction and in the number of measurement points that can be measured simultaneously. After deriving the theoretical basis of the approach a virtual optical design with a FOV of 10mm by 10mm and a depth range of 1.5mm with roughly 1000 measurement points, based mainly on off-the-shelf components will be presented. This virtual system design was used to perform various simulations and explain the design process and considerations as well as the expected system response of the proposed system.
Purposefully induced axial chromatic aberration is the core of the chromatic confocal metrology technique.Through the resulting generation of separated focal planes for each wavelength of a broadband light sourcea measurement volume is created and a three-dimensional reconstruction of the topography of technical and biomedical surfaces and layers can be performed. Based on the chromatic confocal metrology technique various metrology sensors and measurement systems have been developed, with high axial and lateral resolution, accuracy and precision. For a significant increase in measurement points, that can be measured simultaneously and the resulting reduction in measurement time, a chromatic confocal method utilizing a micro-lens array in combination with a improved spectral peak detection, has been developed. Through a single image acquisition, the object topography can be measured for multiple points simultaneously and therefore mitigating the need for axial aswell as lateral scanning of the object. For this reason in-situ applications have become a viable domain. First preliminary results of testing a laboratory setup of the proposed system design are presented.