Fluorescence imaging is a powerful tool to detect the presence of processing agents, e.g., oils, lubricants, and organic coatings on metal surfaces. This imaging technique can be used in production, e.g. to determine the oil coverage on sheet metal to assure the best forming results or for inspecting the cleanliness of components before further processing like gluing, welding, coating, etc. The presented sensor is an evolution of the existing fluorescence laser scanner (F-Scanner) system1 and is optimized for measurement in motion. Adding this additional degree of freedom by mounting the scanner on a robot or gantry enables complete scans of large and complex shaped parts as well as selected areas that require special care, e.g., an increased level of cleanliness. The F-Scanner system has been improved in terms of footprint, weight, durability, and robustness. It can be operated with lightweight industrial robots and even cobots. In situations where ambient light makes fluorescence imaging challenging, a fast Fourier transform (FFT) based technique is used to ensure unperturbed measurements and high-contrast images. This work gives an overview of the advanced developments made and demonstrates the effect of FFT signal processing.
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.
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