The paper presents a novel method for monitoring and estimating the depth of a laser-drilled hole using machine vision. Through on-line image acquisition and analysis in laser machining processes, we could simultaneously obtain correlations between the machining processes and analyzed images. Based on the machine vision method, the depths of laser-machined holes could be estimated in real time. Therefore, a low cost on-line inspection system is developed to increase productivity. All of the processing work was performed in air under standard atmospheric conditions and gas assist was used. A correlation between the cumulative size of the laser-induced plasma region and the depth of the hole is presented. The result indicates that the estimated depths of the laser-drilled holes were a linear function of the cumulative plasma size, with a high degree of confidence. This research provides a novel machine vision-based method for estimating the depths of laser-drilled holes in real time.
Strgar, S.; Mo？ina, J. An optodynamic determination of the depth of laser-drilled holes by the simultaneous detection of ultrasonic waves in the air and in the workpiece. Ultrasonics 2002, 40, 791–795.
Bredice, F.O.; Orzi, D.J.O.; Schinca, D.; Sobral, H.; Villagran-Muniz, M. Characterization of pulsed laser generated plasma through its perturbation in an electric field. IEEE Trans. Plasma Sci. 2002, 30, 2139–2143.
Bredice, F.O.; Sobral, H.; Villagran-Muniz, M.; Di Rocco, H.O.; Cristoforetti, G.; Legnaioli, S.; Palleschi, V.; Salvetti, A.; Tognoni, E. Real time measurement of the electron density of a laser generated plasma using a RC circuit. Spectrochim. Acta Part B 2007, 62, 836–840.
Madjid, S.N.; Kitazima, I.; Kobayashi, T.; Lee, Y.I.; Kagawa, K. Characteristics of induced current due to laser plasma and its application to laser processing monitoring. Jpn. J. Appl. Phys. 2004, 43, 1018–1027.
Idris, N.; Madjid, S.N.; Ramli, M.; Kurniawan, K.H.; Lee, Y.I.; Kagawa, K. Monitoring of laser processing using induced current under applied electric field on laser produced-plasma. J. Mater. Process. Technol. 2009, 209, 3009–3021.
Walter, D.; Michalowski, A.; Gauch, R.; Dausinger, F. Monitoring of the Micro-Drilling Process by Detection of Laser-Induced Shock Waves in Air. Proceeding of the 26th International Congress on Applications of Lasers & Electro-Optics, Orlando, FL, USA, 29 October–1 November 2007.