Optical detection of mixture ratios and impurities in viscous materials based on fluorescence imaging

This paper presents an innovative approach for an automated evaluation of mixture ratios and the detection of impurities in viscous materials. The measurement method is based on fluorescence imaging and works on a non-contact basis. The principle of the measurement setup is that three similar fluorescence images are available in different optical paths. 2D-sensor-arrays having a resolution of 1024 pixel × 1280 pixel are used for the image acquisition. A one-to-one mapping restricts the size of the fluorescence images to 5.3 mm × 6.66 mm. The vertical and horizontal resolution in the images is limited to 5.2 μm; this corresponds to the dimensions of a pixel. Due to the use of an x, y-shifting table in the measurement setup, it is possible to investigate a larger area of the measurement object. To get more information of the measurement object, each image is filtered in a different wavelength range. The center wavelength of the used bandpass filters are 405 nm, 420 nm, and 440 nm. The evaluation of the mixture ratio is realized with an acceptance range in a three-dimensional coordinate system. The determination of the number, positions, areas, and maximum dimensions of contained impurities is implemented by a dedicated threshold algorithm. The minimum detectable impurity size with the used measurement setup is 5.2 μm. Both evaluation approaches work in a real-time and automated process. Advantages of the presented system are the low level of expense for the maintenance and the universality due to the use of optical standard components.