Product Code: ICAL07_M804

Automatic Calibration of a Scanner-Based Laser Welding System
Authors:
André Stollenwerk, Institute of Imaging and Computer Vision, RWTH Aachen University; Aachen Germany
Nicolaj Stache, Institute of Imaging and Computer Vision, RWTH Aachen University; Aachen Germany
Alexander Olowinsky, Fraunhofer Institute for Laser Technology; Aachen Germany
Jens Gedicke, Fraunhofer Institute for Laser Technology; Aachen Germany
Achim Knepper, Institute of Imaging and Computer Vision, Rwth Aachen University; Aachen Germany
Til Aach, Institute of Imaging and Computer Vision, RWTH Aachen University; Aachen Germany
Presented at ICALEO 2007

In precision engineering scanners are widely used for laser beam positioning. Equipped with cameras, scanners enable confocal process monitoring or even position recognition of the parts to be welded. To allow precise welding and position recognition, it is essential to
calibrate this 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 lasers focus point and the cameras field-of-view, due to chromatic aberration of the scanner optic, cannot be compensated. Furthermore, these approaches require manual microscopic measurement of weld seams, which implies downsides such as tedious and error-prone manual interaction. This paper therefore proposes a two-step technique to automatically calibrate the entire welding system by use of the system-incorporated camera. First, the calibration is performed for the camera wavelengths via a specially coded test pattern, which allows determining the cameras field-of-view position accurately. Second, the scanner is calibrated at laser wavelength. Towards this end, the system creates laser spots which are captured by the camera. Then, the system detects the spots, determines the offsets to the nominal positions, and fits an affine model for compensation. Experimental results confirm the accuracy of this calibration technique.