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在金属激光熔覆自由三维成形中,不断生长的成形面与成形喷头之间的距离应保持恒定值,以保证生长表面上处于聚焦激光焦点附近熔池的离焦量基本不变。以光学三角法为原理,提出了一种基于嵌入式机器视觉的激光自由成形熔池离焦量在线测控系统,推导出了镜头焦距设计公式,给出了系统硬件方案以及软件方案,同时为高效稳定处理熔池图像,提出了一种基于面积的熔池灰度阈值估计算法。经测试,此测量系统能实时准确地测得熔池离焦量,将该系统运用至实际薄壁圆环成形中,实时调节光头提升速度以保持离焦量恒定,使得薄壁圆环成形精度得到明显提高。
In free-form metal cladding laser, the distance between the continuously growing forming surface and the forming nozzle should be kept constant to ensure that the amount of defocus in the weld pool near the focus of the focused laser on the growth surface remains essentially constant. Based on the principle of optical trigonometry, an on-line measurement and control system of laser free-form weld pool defocusing volume based on embedded machine vision is proposed. The design formula of lens focal length is deduced, and the system hardware solution and software solution are given. Stabilization of weld pool image, an area-based threshold estimation algorithm for weld pool gray level was proposed. After testing, the measuring system can measure the defocusing amount of the molten pool in real time and accurately. The system is applied to the forming of the actual thin-walled ring. The raising speed of the bald is adjusted in real time to keep the defocusing constant and the forming accuracy of the thin-walled ring is obviously improved.