The influence of geometric errors in the nominal robot model on sensor-guided robotic laser welding

Abstract

Seam-tracking sensors can be used for teaching of seam locations prior to laser welding and for real-time tracking during laser welding. In the case of real-time tracking the sensor has to measure at least some distance in front of the laser focal point to prevent a disturbing influence from the welding process. This paper shows that for sensor-guided robotic laser welding, positional errors of the laser focal position with respect to the weld joint significantly depend on the look-ahead distance between the focal position of the laser and the seam-tracking sensor. An overview of the factors that determine the look-ahead distance is given. Special attention is paid to the influence of geometric errors in the nominal robot model that is used by the robot controller. It appears that these errors have a major effect on the obtainable accuracy during laser welding. Because the accuracy demands for positioning the laser focal point with respect to the weld joint are very strict, these geometric errors significantly limit the maximum look-ahead distance that can be chosen. It is shown that in the case of teaching instead of real-time tracking it is best to choose the look-ahead distance as small as possible (or even zero) to prevent the influence of geometric errors.