Near-infrared vision system for monitoring arc welding processes

Abstract

Throughout the years, vision, human beings' favourite sense, along with our great capacity to obtain, process and interpret a great amount of visual data, has been a great inspiration for development of techniques and technological devices that reproduce it into a computational system. In welding processes, vision can supply information on inspection and quality of the welded joint, monitoring of parameters, trajectory correction and even study of the phenomena involved in the process. However, the light radiation emitted from the weld arc is a barrier to studies based on the viewing process. One form currently used to visualize the process, without the interference of the arc's light, consists of illuminating the process with the near-infrared (NIR) light and using interference (band pass) filters, around this same wavelength, during acquisition of the images. One solution for the NIR light that is being increasingly used involves the use of high-power laser diodes, of low-cost and less complex installation than conventional lasers. The proposal of this study is the design, construction and assessment of a low-cost, highly flexible vision system for welding processes. It is based on characterization of the spectrum of the weld arc, definition of a drive topology for the high-power laser diode in NIR within its limitations of use, and maximizing the light power emitted, creation of control circuits, selection of optical equipment and components and, finally, design and apply a prototype for visualization of welding processes. As a whole, the limitations of the viewing system were encountered through their application with tungsten inert gas and metal inert gas/metal active gas welding. In these trials, although it had not been capable of overcoming the arc radiation, the system developed provided homogenous lighting synchronized with the camera, whereby the main limitation was long exposure time of the camera. In conclusion, the use of employing the system to assist with joint tracking is suggested.