Monocular-vision-based method for online measurement of pose parameters of weld stud

With the rapid development of stud welding technology, weld studs are extensively used in automobile industry. A weld stud differs from a regular stud in that it has special external features. This study develops a novel non-contact, fast, and high-precision method based on monocular vision for measuring the position and attitude parameters of a weld stud. Under this method, the measuring principle for the weld stud's position and attitude parameters is derived and an accurate mathematical model is set up. Based on this mathematical model, a precise calibration method for the projective transformation's corresponding relationship parameters is developed and an optimal observation condition is then introduced as the constraint into the measurement process so as to enhance the location precision. The experiment results show that the proposed method is fast and accurate, and it satisfies the requirement of online, flexible, fast, and high-precision measurement of weld studs' pose parameters in automobile and other manufacturing industries. (C) 2014 Elsevier Ltd. All rights reserved.