| 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. |
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