Visual Sensing Systems for Arc Welding Process

Visual sensing technology is widely used in welding practices because visual devices are decreasing in price, increasing in reliability and improving in image processing hardware and software. As the most studied welding sensor, CCD(Charge Coupled Device) is more suitable for quality control of welding process than other means of sensing devices because it can obtain both two dimensional and three dimensional information of weld pool, which directly reflect the welding dynamics of molten metal. In this chapter, according to the analysis of arc spectrum and radiation of different materials, visual sensing systems with filters are described. Based on the filtering method, clear images of weld pool are obtained during pulsed GTAW. The first step of intelligentized arc welding is to imitate the visual system of a welder to extract weld pool size. Passive visual sensing technology has seen great progress in the past years for the abundant information it extracts. Brzakovic et al. [1] obtained the weld pool image in two directions and extracted its geometry information. Wang et al. [2] attempted to get aluminium alloy image for the first time, but it is not clear enough. Zhao et al. [3] developed a passive three-dimension visual sensing method through monocular image which is processed by Shape from Shadow (SFS) algorithm to get the three-dimension geometry of the pool. In this chapter, passive visual sensing system for both aluminium alloy and low carbon steel will be discussed. 2.1 Description of the Real-Time Control Systems with Visual Sensing of Weld Pool for the Pulsed GTAW Process As one of the dominant arc weld methods, pulsed GTAW is widely used in the highquality weld manufacturing, especially for high-precise thin sheet. High-quality pulsed GTAW requires precise penetration and fine formation of the weld seam, thus real-time regulation of the welding process, i.e., regulating weld pool size, is necessary. Main influences on weld pool size involve electrical conditions, such as pulse duty ratio, peak current, base current, arc voltage, and welding speed; workpiece conditions such as the root opening or geometry of the groove, material, thickness, S.-B. Chen, J. Wu, Intelligentized Methodology for Arc Welding Dynamical Process, 35 Lecture Notes in Electrical Engineering 29, c © Springer-Verlag Berlin Heidelberg 2009 36 2 Visual Sensing Systems for Arc Welding Process Travel direction Work piece Work plate Wire feeder Manipulator SCM motion control board