Vision-based dual feedback control of deposition height for laser consolidation

Laser consolidation is an effective way for aircraft part manufacturing and repair. The traditional open-loop laser process relies heavily on an operator's expertise in order to establish a production process. This paper presents a closed-loop control method based on dual vision feedback of deposition height. A side CCD camera is installed to detect both the substrate height in front of the meltpool and the clad height behind the meltpool in real-time. The former is fed positively (feed forward) while the latter is fed negatively (feedback) into the process controller. Based on the dual height feedback, the laser scan velocity is adjusted in real time to keep the clad height within the desired range. In this paper, a dual thresholding algorithm is proposed to determine the direction of scan velocity within one acquired meltpool image. The experiments show that the closed-loop controller can automatically compensate for the influences of process disturbances. When process parameters drift out of process window, the dual feedback controller demonstrates the ability to compensate for these changes effectively.