针对基于SMT技术生产的PCB板产品的三维缺陷检测问题, 设计了一款高分辨率、高远心度及低畸变的双光路双远心光学系统。它通过远心投影物镜经共光路物镜将DMD数字条纹均匀投影至待测物面, 同时经由共光路物镜和成像物镜收集物面反射条纹光至CMOS接收面。使用ZEMAX光学软件分别对三部分镜组进行优化设计, 分析了系统的像差和调制传递函数。设计结果表明: 共光路物镜部分采用长工作距离、大视场角及物方远心结构, 空间频率50lp/mm处, 各视场的MTF接近衍射极限; 投影光路畸变小于0.1%, 在投影面上全视场范围MTF在6lp/mm处大于0.8且条纹周期均匀; 成像光路畸变小于0.05%, 在全视场范围MTF在80lp/mm处大于0.3。仿真成像结果表明,在离焦量为+/-6mm时仍能达到景深范围内分辨率要求, 能有效提高3D AOI检测质量。且双光路双远心系统所用材料基本为普通玻璃且重复率较高, 利于加工和节省成本。

According to the 3D Automatic Optical Inspection (AOI) of print circuit boards (PCB) produced by surface mounted technology (SMT), the design of a bi-telecentric optical system with high resolution, high telecentricity and low distortion was introduced . The fringes produced by digital micro-mirror device (DMD) are projected uniformly onto the object plane by telecentric projection lens and common-path lens. Concurrently, the reflected fringes are collected to CMOS by common-path and imaging lens. The three parts of the system designed and optimized respectively by ZEMAX and their aberration and MTF were analyzed. The design result shows that the common-path lens have long work distance, large field of view (FOV) and object telecentic structure, the MTF of each FOV approaches the diffraction limit at 50lp/mm. The distortion of projection path is less than 0.1%, its MTF at 6lp/mm is more than 0.8 in the whole FOV and the fringe period is uniform. The distortion of imaging path is less than 1%, its MTF is more than 0.3 at 80lp/mm in the whole FOV and the reflected fringes remain clear within a depth of focus of +/-6mm. The optical system can effectively improve the test quality of 3D AOI. Besides, ordinary material was used in the system in order to facilitate machining and cut costs.