Use of sensors in robotic welding for controlling the weld quality leads to replacement of manual welding operation in dangerous work environment in presence of high temperature and fumes even in small or medium scale enterprises. The seam tracking operation is very essential for extracting weld seam position which can be fed to robot controller for instructing robot along the weld seam path. The seam tracking operation can be executed by different types of sensors having their own merits and demerits. In this paper, different sensors and techniques used for seam tracking task in robotic welding have been discussed in detail. Each sensor has different method or technology of weld seam feature extraction which have been described by different authors in different ways. The chief tasks for seam tracking have been found to be weld starting and end point detection, weld edge detection, joint width measurement and weld path position determination with respect to robot co-ordinate frame. Thus sensors have a very important role in robotic welding for fully automating the system with in process real time monitoring of weld process parameters with the sensor feedback. In further discussion the practical use of different sensors in industries with a comparison of their advantages and disadvantages have been discussed. This Paper presents the role of sensors in robotic welding and a detail study of methodologies of weld seam position and geometry feature extraction by different sensors typically used for weld seam tracking.

Advances in weld seam tracking techniques for robotic welding: A review

Gas metal arc welding (GMAW) process is one of the most widespread welding processes used in industries for their excellent quality, reliability, productivity, and cost-effectiveness. To develop an automatic GMAW system, vision capability in the system is a necessary component supplying real-time information about weld pool and seam tracking. In this research work, an automatic seam tracking system is presented, where the automatic tracking of welding path and torch positioning are performed by a newly developed image acquisition system. The system aims to add a vision capability to the GMAW system. A CCD camera is configured with a welding torch to acquire real-time images. The acquired images are processed through newly developed software for real-time detection of welding seam location and characteristics. The software encapsulates the acquired image input facility, image filtering technique, strategy to measure the seam gap, strategy to position torch at the starting point of welding, user interface for automatic guide, and the strategy to correct the torch movements. The seam recognition accuracy was verified during several welding experiments on linear weld seam. Real-time measurements of the seam gap and the seam tracking have achieved a high accuracy.

An image acquisition system for real-time seam tracking

Application of circular laser vision sensor (CLVS) on welded seam tracking

Non-intrusive and real-time monitoring techniques are increasingly required by manufacturing industry in order to detect flaws in arc welding processes. In this work the development of an optical inspection system, for monitoring the manual gas tungsten arc welding (GTAW) process of steel pipes, is described. The arc plasma visible emission produced during the process was acquired and spectroscopically analysed. Measuring the intensities of selected argon emission lines allowed real time calculation and recording of the axial electron temperature of the plasma. Experimental results showed that the temperature signal varies greatly in the case of instabilities of the weld pool that cause weld defects. A suitable algorithm, based on a statistical analysis of the signal, was developed in order to real time flag defective joints. It is shown that several weld defects such as porosity, dropout, lack of fusion, solid inclusions and craters were successfully detected in a production environment. The performances of the optical sensor were compared with the results of state-of-the-art post-weld controls such as x-rays and penetrating dyes, showing good agreement and thus demonstrating the validity of this quality monitoring system.

http://iopscience.iop.org/article/10.1088/0957-0233/15/12/010/pdf

A sensing torch for on-line monitoring of the gas tungsten arc welding process of steel pipes

Detection of GTA welding quality and disturbance factors with spectral signal of arc light

This paper presents a detailed series of measurements of the spectrum of the light emitted from a MIG welding arc. This work was done in the framework of a larger project concerning the development of a seam tracking sensor. Detailed measurements and analysis of the spectrum produced from welding arcs have been performed. The measurements extend from the ultraviolet region of the spectrum (150 nm) to the near infrared region (970 nm) and have revealed the presence of many strong emission lines in the spectrum. The results are of great importance for the design of any optical or vision system working close to a welding arc, because the wavelength of the optical system can be selected to be close to a value where the spectrum of the arc causes the minimum interference to the laser light.

G Agapiou

Papers

A detailed analysis of the MIG spectrum for the development of laser-based seam tracking sensors