Study On Structured Light Multi-View Measurement

According to the demand for the integrated three-dimensional measurement of the parts with complex structure and features and getting real three dimensional models of them, a multi emission and multi receiving measurement system consisting of three CCD cameras and three laser linear projectors is presented. This system is implemented by using image processing, machine vision and structured-light measurement technique. Blind spots formed by occlusion are avoided effectively using this multi-view projecting and multi-direction receiving structure. Comparing to other non-contact measurement methods, this system has larger measurement scopes, measures more kinds of objects and obtains more integrated point cloud data. The main work in the dissertation includes the following aspects:1. The mapping relationship between each laser plane and its adjacent CCD camera is calibrated respectively by linear structured light technology. The relationship between computer imaging coordinates and laser plane coordinates is established based on the ideal camera imaging model. A single-tooth target is adopted to generate calibration points. Then the calibration process of intrinsic parameters is done.2. A calibration method of extrinsic parameters based on a standardized sphere is brought up. The transformation relationships among the coordinates of the measurement system are established. According to the conversion relationships, the transformation matrix of each linear structured light sensor model can be solved, and the transformation from laser plane coordinates to three dimensional world coordinates can be actualized. During the process of solving transformation matrix, the concept of"conjugate pairs"is used.3. A new method of determining the spherical center as the fixed point in space by fitting sphere is brought up in order to obtain the translation relationship among the three world coordinates. Then the point clouds obtained by different sensors can be transformed into the same world coordinate, and therefore the unification of world coordinates of the measurement system can be solved.4. This dissertation makes thorough study on the extraction algorithm of the centre line of the laser stripe, and chooses the gray centroid method to extract the centre line of the laser stripe after comparing the advantages and disadvantages of several common extraction methods. The accuracy is further improved by improving the gray centroid method.5. The software of measurement system is developed using Visual C++6.0 on Windows XP operation system. A series of calibration and measurement experiment are implemented using this software.The innovation of this dissertation is bringing up a multi emission and multi receiving measurement structure based on structured light technology, establishing the transformation relationship from computer imaging coordinates to three dimensional world coordinates for the points to be measured, and proposing a new calibration method which can finish the calibration of the whole sensor system by calibrating the intrinsic and extrinsic parameters separately.