Authors:
Nicolaj C. Stache
Andre´ Stollenwerk
Institute of Imaging & Computer Vision, RWTH Aachen University, 52056 Aachen, Germany

Jens Gedicke
Alexander Olowinsky
Fraunhofer Institute for Laser Technology, Steinbachstr. 15, 52074 Aachen, Germany

Achim Knepper
Til Aach
Institute of Imaging and Computer Vision, RWTH Aachen University, 52056 Aachen, Germany

In precision engineering scanners are widely used for laser beam positioning. Equipped with cameras, scanners enable process monitoring or even position recognition of the parts to be welded. To allow precise welding or position recognition, it is essential to calibrate a welding system. Instead of calibrating the whole system, most approaches only help to adjust the laser beam position. Consequently, the varying lateral offset between the laser’s focus point and the camera’s field of view, due to chromatic aberration of the scanner optics, cannot be compensated. Furthermore, these approaches require manual microscopic measurement of weld seams, which comes along with several downsides. This paper proposes two techniques for automatic calibration without these downsides by use of the system-incorporated camera. The first technique is the calibration at laser wavelength. To this end, the system automatically creates laser spots, evaluates their positions and possible offsets, and finally fits an affine model for compensation. The second technique is based on a specially coded test pattern, which is used for calibration at camera wavelengths. Experimental results confirm the accuracy of the calibration obtained.