  The visual sensing system is one of the most important parts of the welding
robots to realize intelligent and autonomous welding. The active visual sensing
methods have been widely adopted in robotic welding because of their higher
accuracies compared to the passive visual sensing methods. In this paper, we
give a comprehensive review of the active visual sensing methods for robotic
welding. According to their uses, we divide the state-of-the-art active visual
sensing methods into four categories: seam tracking, weld bead defect
detection, 3D weld pool geometry measurement and welding path planning.
Firstly, we review the principles of these active visual sensing methods. Then,
we give a tutorial of the 3D calibration methods for the active visual sensing
systems used in intelligent welding robots to fill the gaps in the related
fields. At last, we compare the reviewed active visual sensing methods and give
the prospects based on their advantages and disadvantages.
