Many production and assembly processes in industry are subjected to particulate contamination, that could massively affect the product’s function. The detection of the particles could be a challenging task. Especially curved surfaces place high demands on the illumination system which can either be met with highly specialized setups or with a system with a high degree of flexibility. We present a cheap, fast and versatile detection system with the ability of bright and dark field illumination. Our setup offers fast and customized switching between different illumination channels adapted to the sample. The bright field illumination offers high sensitivity to scratches, whereas dark field illumination is more sensitive to particles. The system was tested on flat and curved surfaces. Since all components explicitly use standard computer interfaces, no additional hardware is needed to connect the system to a single-board computer or workstation.
Metal processing industries utilize two types of functional coatings. Conversion coatings, based on Zirconium and/or Titanium, generate corrosion resistance and paint adhesion for aluminum surfaces. Another type of functional coatings are lubricants based on mineral oil, which act as corrosion protection as well as drawing and punching oil. Efficient process development and control requires the monitoring of the thickness of these functional coatings. In this article, we present a new optical setup, which uses a rotating polygon-scanning mirror in combination with laserinduced fluorescence to monitor the spatial distribution of lubricants and conversion coatings on metal sheets. In the presented setup, the beam of a 405 nm diode laser excites auto-fluorescence of the organic molecules inside the functional coatings. By using a fast rotating scanner mirror combined with a fast analogue digital conversion, the presented setup reaches data rates of 400 lines/s consisting of 1000 data points each. Installing the scanner system at a distance of 1200 mm above the metal sheets, realizes a field of view of 2200 mm. At strip speeds of 2 m/s, the distance between two scanner lines on the surface to be investigated is 5 mm. In addition to the description of the optical system, we present different approaches for the calibration of systems for inline fluorescence measurements. For the calibration of lubricant layers in the range down to one micrometer, the reference samples are weighted. To evaluate the limit of detection of the system we use a multiphase carbon analyzer. We show the calibration results for different lubricants and metal materials with different surface textures typically used in car body manufacturing.
We present new imaging techniques for the detection and classification of particulate contamination on structured surfaces. This allows for cleanliness inspection directly on the sample. Classical imaging techniques for particle detection, such as dark-field imaging, are typically limited to flat surfaces because structures, scratches, or rough surfaces will give similar signals as particles. This problem is overcome using stimulated differential imaging. Stimulation of the sample, e.g. by air blasts, results in displacement of only the particles while sample structures remain in place. Thus, the difference of images before and after stimulation reveals the particles with high contrast. Cleanliness inspection systems also need to distinguish (often harmful) metallic particles from (often harmless) nonmetallic particles. A recognized classification method is measuring gloss. When illuminated with directed light, the glossy surface of metallic particles directly reflects most parts of the light. Non-metallic particles, in contrast, typically scatter most of the light uniformly. Here, we demonstrate a new imaging technique to measure gloss. For this purpose, several images of the sample with different angles of illumination are taken and analyzed for similarity.
We present a new optical setup, which uses scanning mirrors in combination with laser induced fluorescence to monitor
the spatial distribution of lubricant on metal sheets.
Current trends in metal processing industry require forming procedures with increasing deformations. Thus a welldefined
amount of lubricant is necessary to prevent the material from rupture, to reduce the wearing of the manufacturing
tool as well as to prevent problems in post-deforming procedures. Therefore spatial resolved analysis of the thickness of
lubricant layers is required. Current systems capture the lubricant distribution by moving sensor heads over the object
along a linear axis. However the spatial resolution of these systems is insufficient at high strip speeds, e.g. at press
plants.
The presented technology uses fast rotating scanner mirrors to deflect a laser beam on the surface. This 405 nm laser
light excites the autofluorescence of the investigated lubricants. A coaxial optic collects the fluorescence signal which is
then spectrally filtered and recorded using a photomultiplier. From the acquired signal a two dimensional image is
reconstructed in real time. This paper presents the sensor setup as well as its characterization. For the calibration of the
system reference targets were prepared using an ink jet printer.
The presented technology for the first time allows a spatial resolution in the millimetre range at production speed. The
presented test system analyses an area of 300 x 300 mm² at a spatial resolution of 1.1 mm in less than 20 seconds.
Despite this high speed of the measurement the limit of detection of the system described in this paper is better than
0.05 g/m² for the certified lubricant BAM K-009.
A new diagnostic testing device is proposed for point of care (POC) applications. It consists of a microfluidic cartridge
with a polymer biochip and an instrument for reading the biochip and controlling the microfluidics. This system allows a
very easy determination of several parameters e.g. in patients blood automatically. The biochip is made of a thin polymer
foil serving as waveguiding element and as carrier for the receptors on the biochip surface. A sensitive TIRF (total
internal reflection fluorescence) readout is realised. Optical elements for incoupling and outcoupling of light are
integrated into the foil. Beside the TIRF element, the disposable microfluidic cartridge integrates a sample inlet, several
reservoirs for reagents, fluidic microchannels and electrochemical micropumps. Sandwich assays for the detection of
clinically relevant parameters have been investigated. This hardware configuration forms the basis for a fully automated
compact low cost device using cost efficient disposables.
Using a digital holographic microscope setup, it is possible to measure dynamic volume changes in living cells. The cells were investigated time-dependently in transmission mode for different kinds of stimuli affecting their morphology. The measured phase shift was correlated to the cellular optical thickness, and then of the cell volume as well as the refractive index were calculated and interpreted. For the characterization of the digital holographic microscope setup, we have developed a transparent three-dimensional (3-D) reference chart that can be used as a lateral resolution chart and step-height resolution chart included in one substrate. For the monitoring of living cells, a biocompatible and autoclavable flow chamber was designed, which allows us to add, exchange, or dilute the fluid within the flow chamber. An integrated changeable coverslip enables inverse microscopic applications. Trypsinization, cell swelling and shrinking induced by osmolarity changes, and apoptosis served as model processes to elucidate the potential of the digital holographic microscopy (DHM).
We present a phase-shifting holographic set-up for the microscopic imaging of adherent cells. The superposition of an object wave field and a reference wave is recorded on a digital sensor with three reference wave phases. The reference phases are then recovered by statistical analysis of the recorded intensities. Subsequently, the object wave phase is calculated by the generalized phase shifting algorithm. After phase unwrapping and background subtraction, the phase shift introduced by the adherent cell culture is reconstructed. As the interferograms are recorded in the image plane of the microsope objective, the full lateral resolution is achieved in contrast to off-axis holography where the reconstruction requires numerical propagation for the separation of 0th and 1st order. Our approach uses three arbitrary unknown reference phases and poses thus minimum requirements on the mechanical and thermal stability of the set-up. We give preliminary results of images from a Vero cell line and pollen grains.
We report on a recently developed highly sensitive instrument for label-free detection of biomolecules based on the principle of a Young interferometer. With this technology, biomolecular interactions can be detected in real-time without elaborate sample preparation using a planar waveguide as sensing element. The binding reaction of the antibody-antigen pair immunoglobulin G and protein G has been studied and an affinity constant of K=2.6*107 M-1 has been determined.
For the measurement of biomolecular interactions such as immunoreactions it is often necessary to prepare reporter molecules to detect small biomolecules. In many cases fluorescence markers are used to detect the binding between molecules. These markers, however, can influence the examined reaction. A label-free optical detection method based on the principle of a Young interferometer offers an alternative solution. This technology allows real-time, kinetic analysis of antigene-antibody reactions or the detection of a specific analyte without elaborate sample preparation. Especially reactions where it is inconvenient or impossible to use markers can be detected with this method. In this paper, an interferometric device based on a planar waveguide as sensing element is presented. The system yields a high resolution with respect to surface mass coverage and a low sensitivity towards undesired external influences. Interferometric sensors theoretically have the highest detection limits among label-free bionsensors.
We report the application of nematic liquid crystals for the optical sensing of organic solvents using two different evanescent field probes. Liquid crystals with different nematic ranges are used as sensitive coating materials on integrated optical reflection grating couplers and on integrated optical Mach-Zehnder interferometers as well. A non-linear behavior was observed when the liquid crystal coated IO transducers were exposed to various concentrations of toluene, meta-xylene and para-xylene. The calibration over a wide range pointed out a phase transition of the liquid crystal due to the penetration by the analyte. The birefringend liquid crystal and an isotropic polymer coating are compared by their responses to the xylene isomeres. The data indicate that the liquid crystal's response is mainly given by a decrease of the order parameter S. Furthermore, we take advantage from the non-linearity and the clearing point in order to improve the performance of the sensor system.
The development of integrated optical interferometers for chemical sensing and refractometry is reviewed. The optical configurations are Mach-Zehnder-, polarization-, and Young- interferometer. The problems of signal processing -- ambiguity and signal fading -- are discussed. Applications are gas sensing, immunosensing, and differential refractometry. The chemical and biochemical sensors base on evanescent wave sensing.
An integrated optical sensor for the detection of gases like CO2 and SO2 is described. The working principle is as follows: The gas to be measured is absorbed by a sensitive film, which changes its refractive index with gas absorption. The sensitive film is deposited onto an integrated optical interferometer. As the intensity distribution of waveguide modes is not totally confined to the waveguide, interferometer phase changes with the refractive index of the film. Tests have been made with interferometers of the Fabry-Perot-type. Interferometer phase is measured continuously using the serrodyne detection scheme. Organically modified silicates are used as sensitive films. These glassy films are prepared by the solgel technique, which allows the incorporation of functional organic groups within a network of siloxane bonds. The ability of selective gas absorption of these materials is determined by chosing appropriate functional groups. Films sensitive toward CO2 and SO2 have been fabricated and tested under different gas atmospheres. Temperature dependence of the sensor signal and cross sensitivities toward other gases and humidity have been investigated.
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