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3D/6D calibration and real-time focus shift compensation for automated 30 kW laser remote scanner

: Cerwenka, G.; Wollnack, J.; Krähling, T.; Jayaprakash, R.; Emmelmann, C.


Journal of laser applications : JLA 31 (2019), Nr.2, Art. 022607
ISSN: 1042-346X
ISSN: 1938-1387
Fraunhofer IAPT ()

Laser remote scanner (LRS) technology is one of the most promising topics in industrial manufacturing. To overcome current limitations for large-scale applications, an automated scanner system with 30 kW laser power has been developed. This system includes a stereo camera-based 3D vision for part detection as well as for task estimation. For this purpose, precise 3D/6D laser tool calibration has been conducted. To control the effect of focus shift due to high laser power level, additively manufactured lens holders and an easy to compute real-time focus shift compensation model have been investigated and are presented. Section II briefly introduces the 30 kW LRS concept, which includes demands and limitations. Furthermore, approaches for optical design and mechanical solutions, such as a gimbal-mounted mirror, are shown. The integration of the stereo camera system is considered. Section III describes laser tool calibration in 3D/6D, which is a prerequisite for absolute high-precision laser tool positioning of self-teaching automated LRS. A feasibility study has been performed. Laser beam induced thermal behaviors in the 30 kW LRS optics are discussed in Sec. IV, which causes refraction index and geometry changes that lead to focus shift. Additive manufactured internal cooled lens holder structure has been studied. A model for real-time compensation of focus shift has been investigated. It combines thermo-optic, stress-optic, and geometric effect with ABCD matrix analysis for optics. The topics are summarized, and an outlook is given on further applications for high-power LRS.