Study On Key Techniques Of Automatic Optical Inspection System For 3D Micro Size Measurement

Automatic Optical Inspection (AOI) has advantages of advanced inspectionmethod, high measuring speed and high degree of automation. It can be applied toobtain 3D coordinate of the object surface points at the scene. Based on structuredlight vision technology, an AOI system for 3D micro size (0.01-1mm) measurement isproposed in this dissertation.The major contribution and innovations of this dissertation are as follows:1. Two mathematical models of the sensor are studied. One is the improvedmodel based on Direct Linear Transform (DLT). The other is the polynomial model.And the angle between the light plane and the measuring coordinate system isintroduced.2. A two-step calibration method for the mathematical models is studied. In thefirst step, the parameters of the mathematical model are confirmed. In the second step,the angle between the light plane and the measuring coordinate system is calculated.This method can build the measuring coordinate system directly. The process of themethod is simple and stable. It is suitable for on-site calibration.3. The errors, which maybe occurred during the calibration or the installationprocess of the sensor, are analyzed. The correction model is proposed, which canreduce the error caused by the deflection between the measuring coordinateconstructed by the calibration and the actual one. The calculation method using astandard part for the parameters in the correction model is studied.4. The adaptive adjustment method of laser light intensity is proposed, which isapplied in the developed high-precision measuring system for 3D size of solder pastesprinted on the PCBs. By using the method, the light-stripe image effect is guaranteed.And the accuracy of the light-stripe center extraction is improved while thecomplexity of image processing is reduced. The repeatability precision of the systemwas tested. The experimental result proved that the measuring precision along theheight direction is±1?m. The system was also tested on-site.5. A novel grayscale barycenter extraction algorithm along radial directions isproposed, which is applied in the developed high-precision measuring system formicro diameter. The accuracy of the measurement result can be improved obviouslyby using the algorithm. The repeatability precision of the system was tested. The experimental result proved that the measuring precision is±1.4?m. At the scene, thesystem was applied to measure the curvature radius of metal blades.