A study on automatic seam tracking in pulsed laser edge welding by using a vision sensor without an auxiliary light source

Abstract

Vision sensors adapted for automatic seam tracking in fusion welding have an auxiliary light source and a preview distance, which is the distance between the welding and the sensing position. The preview distance can generate tracking errors in automatic seam tracking, especially in micro welding of small parts. On the other hand, vision systems used for the weld pool monitoring are generally equipped with a highspeed camera and intense illumination. In this study, a vision sensor was applied to find the weld seam by monitoring the weld pool in pulsed Nd:YAG laser welding. The vision sensor observed the weld pool, and the weld seam was extracted from the image of the monitored weld pool. No auxiliary illumination source was used for monitoring the weld pool. The shape and brightness of the weld pool change temporally even in one pulse duration. To get a relatively clear image, the shutter of the CCD camera was synchronized with the start of each pulse and opened at a specific time delay from the laser pulse start. Experiments were carried out to find the appropriate moment of shutter triggering for relatively clear images. Seam tracking was successfully performed by using the information of the pool centerline in the edge joint, while the shape and brightness of the weld pool gave the first step toward the information on the status of weld quality.