Three dimensional measurement of specular surfaces and its application in welding process

Observation and the study of the weld pool surface can provide information related to the welding process, which can ultimately be used to develop a control procedure. This study presents a new sensing technique for measuring the state of weld pool and calculating the depth of depression. A compact sensor and algorithm for calibration and sensing the weld pool was created as a result of this study. In order to develop the sensing system a computer simulation was first created to understand the physics involved in observing the weld pool surface. This simulation incorporated the properties of laser, weld pool, and camera optics to describe the mechanism of observing the weld pool from specular reflection. The simulation could be used to predict the outcome of experiments with grids placed in front of the laser and to determine the position where the camera should be placed to acquire the best image.; Systematic experiments were performed to build the knowledge base needed for developing the compact sensor. Experiments were performed to determine the positioning of the lens, its focal length, and size. A study of the illumination system helped understand the dispersion of laser light under welding environment. Experiments are performed to determine the position where the laser light needs to hit the weld pool and how it is reflected from various points of the weld pool.; Finally a technique is developed which uses a calibrated CCD sensor and structured light to extract the surface information as depth of pool from captured images. It projects a laser line from a pre-determined position onto the weld pool surface. Reflected laser beam from the weld pool surface is captured by a calibrated CCD sensor to form the image. The image is then processed based on ray-tracing technique to calculate the depth of the weld pool surface using the position of laser and its fan angle along with the intrinsic parameters and extrinsic parameters of the CCD sensor. Experiments are performed using the technique to measure the depth of weld pool and reconstruct its profile. The reconstruction experiments were performed on a varying weld pool shape due to change in current or speed of the welding process. The change in the welding parameters were reflected on the weld pool and the reconstructed profile reflected these changes. A analysis of the system error was also performed by measuring heights of specular objects using the proposed system and comparing it to the actual height of the object.