Research On 3D Measurement Technology Based On Structured Light Projection

Three-dimensional information or accurate 3D measurement of the object is often needed in industrial automation production. There are plenty ways to obtain 3D information, such as non-contact measurement, which has been widely used because of its higher speed and higher precision. For example, structured light 3D measurement technology has been widely used in electronic SMT production. Laser triangulation is a traditional structured light measurement method, whose speed and accuracy can not meet the requirements of real-time detection in SMT production line. This paper studied 3D measurement technology based on phase measuring profilometry(PMP), including phase unwrapping in SPI, image mosaic, window planning and path optimization problem.And the relationship between phase and real height is also studied to improve the accuracy in SPI 3D measurement.Before the SPI online detection, a full picture of the PCB though image mosaic is need to decide window planning and detection path optimization. The high frequency coefficients of wavelet decomposition can reflect the change of image contour. And this can be used for the image mosaic to reduce the effects of uneven illumination. Then random search method based on prior knowledge is designed for the detection window planning and the ant colony algorithm to the detection path planning to get better results.Phase unwrapping is always a key problem and also a difficult problem in PMP because of noise, shadows and other reasons. This paper proposed a global phase unwrapping method based on plain fitting. Firstly, the phase of PCB base board can be fitted by plain fitting and quadratic surface fitting, then other area phases of PCB board can be unwrapped approaching to the fitting base board and an offset of fitting surface according to counting is necessary to set up to get the right unwrapping phase. Finally,the accurate phase can be obtain through quadratic surface fitting.Finally, the relationship between phase and real height is analysised in detail and the error is also calculated in detail.The research work of this paper can improve the performance of 3D measurement based on PMP, especially the SPI 3D measurement in electronic SMT.