基于机器视觉的贴片安装锡膏三维检测

【作者】 张丽云；

【导师】 罗兵；

【作者基本信息】 五邑大学 ， 通信与信息系统， 2011， 硕士

【摘要】 电子制造业的印刷电路板上元器件安装采用表面贴片安装技术(SMT, Surface Mounted Technology)后,元器件密度、生产自动化水平、产品质量都得到很大提高。但检测技术的不足却影响了产品质量和生产自动化水平。而引起电子产品质量缺陷的一个重要原因就是贴片安装时锡膏印刷的缺陷。锡膏印刷质量检测包括对所印刷锡膏面积、位置的二维检测,还包括对锡膏厚度、体积和形状的三维测量。传统的借助放大镜的人工目检无法适应高集成度、细间距、微小元件的锡膏检测。采用激光三角法半自动锡膏检测也无法满足贴片安装生产的精度和速度要求。目前,国内贴片安装生产线使用的锡膏三维测试仪器完全依靠进口,设备的价格非常昂贵。因此,研发具有自主知识产权的三维锡膏检测设备,对于提高电子制造业自动化水平、降低生产成本、提高电子产品质量都具有重要意义。三维测量的方法有很多,传统的机械接触式测量法(如探针式),由于存在测量力、测量时间长、需进行测头半径的补偿、不能测量较软质材料等局限性,为此人们寻求能够克服上述缺陷的三维测量方法,非接触的光学投影式三维轮廓术正是在这一要求下出现的。光学投影式三维轮廓术有多种,其中,相位法三维测量轮廓术,简称相位测量轮廓术,是属于投影式光学投影式三维轮廓术的一种,它以其非接触、高速度、高精度、大数据量等一系列优点而日益受到人们的重视和研究,另外该方法还具有受环境电磁场影响小、工作距离大、可测量非金属面及较软质材料等特点。相位测量轮廓术根据观察物体上结构光的灰度被调制变化情况来测量物体的三维形貌。它通过多幅相移条纹图来计算得到截断的相位,再通过相位展开算法将截断相位展开为连续相位,最后根据物体高度对结构光相位的调制关系从计算得到的相位中恢复物体的表面三维高度。本论文的工作是在已有的研究工作基础上,重点研究了相位测量轮廓术中的条纹投影及获取,相位展开,相位-高度映射关系,测量系统标定等关键技术,分析了影响相位测量轮廓术测量精度的因素。用结构光投形进行机器视觉三维测量可以快速有效检测电子产品贴片生产线锡膏印刷质量。图像采集系统的设计其中主要环节,通过选取合适的摄像机、镜头和投影仪,建立了三维测量系统。通过标定板,完成对图像采集系统的准确标定。实验结果初步验证了设计的图像采集系统经标定后可以满足三维检测的精度要求。本文还详细分析了相位展开算法的基本原理,讨论和比较了各种算法的设计方法、计算公式和适用范围,对相位展开方法的最新进展和应用前景进行了较全面的分析和评述。更多还原

【Abstract】 After using surface Mounted Technology (SMT) installed components, the components density, production automation level, product quality of the electronic manufacturing printed circuit boards are improved. But testing technology deficiency badly affects the quality of products and production automatization level. An important reason of Electronic product quality defects is the solder paste printing defects when Surface Mounted. The printing quality testing including the two-dimensional detection of the area、position and the 3d measurement of the thickness、volume and shapes of solder paste printing. The traditional using a magnifying glass artificial visual inspection can’t adapt the solder paste testing of high level of integration, fine spacing, tiny components. By using the laser triangulation semi-auto solder paste test can’t satisfy the patch installation precision and speed production requirements. At present, the domestic PCB (Printed Circle Board) installation of the line completely dependent on imports of 3d test instrument.3D measurement systems of solder paste completely rely on imports, But the imported equipments are more expensive. So that, developing 3D measurement systems of solder paste with independent intellectual property to enhance electronic manufacturing automation level, reduce the production cost, improve electronic product quality is very significant.There are a lot of methods for 3D shape measurement. Because the traditional mechanical contact profilometry has many limitations, for example, the measurement speed is low, it exists measuring power and need compensate the size of the probe, it can’t measure the soft material. Therefor, the People seek a better kind of profilometry which is able to overcome these limitations, untouched optical profilometry based on light pattern Projection is such an profilometry. Untouched optical profilometry based on light pattern projection has many types. One is grating projection phase measurement method. It has many advantages such as untouched, high speed, high precision, more data. It also isn’t affected by the electromagnetic wave in the surrounding environment. It can measure the nonmetal object and soft material. Phase measurement method is becoming more and more important for his advantages. 3D shape of objects is measured by observation the change of structure light gray of the object contour based on objects in PMP.The wrapped phase of fringe pattern is calculated from more than three frames of images containing phase shifted fringe pattern. Then, the continuous phase is obtained through unwrapping algorithm. Finally, Finally,according to the objects height on the structure light phase modulation relationship from the calculated phase to recover the 3d surface height objects. In this dissertation, the key technologies in PMP such as casting and acquiring fringe pattern, phase unwrapping, Phase-height mapping and system calibrating etc. The factors affecting measurement accuracy in PMP are analyzed.Structured light based machine vision three-dimensional measurement can quickly and effectively inspect solder paste defaults in SMT assembly line. Image acquisition designing is an important part of the system, which was composed of proper selected camera, suited lens and sinusoidal grating projector. Image acquisition subsystem calibration is also necessary and was proposed by standard calibration block. Experiment results verify the designed of image collection system can satisfy the calibration of the 3D measurement precision requirements. In the dissertation we also analyzed the basic principle of the phase unwrapping algorithm in detail, and we also discussed and compared the designing method, formula and applying range of each algorithm. At last, we analyzed and gave comments on the new development and its application.更多还原