| The three-dimensional measurement technology based on structured light is widely used in industrial detection,quality control,reverse engineering,rapid measurement and other fields,and has the advantages of non-contact,rapid,high precision,low cost,easy popularization,and simple operation.It is widely used in high-precision manufacturing and processing sectors such as aerospace,large ships,auto bodies,and high-speed railways.With the development of industry,the demand for measuring three-dimensional topography of large work pieces has gradually increased,measurement accuracy requirements have been continuously improved,the surface of work pieces has become more complex,and the volume of work pieces has become enormous.The traditional single-plane measurement based on structured light can't meet the requirements of industrial measurement.Therefore,the research on the three-dimensional measurement and splicing method based on structured light is of great significance in obtaining three-dimensional information of large and complex work piece surfaces.Based on the structured light three-dimensional measurement system,the intersecting axis system is used,which the projector is tilted and the CCD camera is being received perpendicular to the reference plane.The coded fringes projected by the projector appear periodic fluttering on the reference surface,affecting the measurement accuracy.In large-field-of-view measurements,the CCD camera lens produces the distortion effect,and the apparent distortion of the field of view will produce the obvious distortion error.Due to the influence of the system structure,the monocular measurement system cannot obtain the complete three-dimensional appearance of large work pieces at one time,so it is necessary that the three-dimensional views need to be stitched.In the splicing process,the three-dimensional measurement is influenced by cumulative errors.For the difficulties in three-dimensional measurement,the main research contents of this paper are as follows.Cross-axis measurement systems require calibration of the system prior to measurement,including vertical calibration,parallelism calibration,alignment correction,and phase-height calibration.The mathematical model of temporal phase unwrapping method based on the fringe period correction is established.A periodic uneven stripe pattern is formed in the plane of the projector and is projected onto the reference plane,forming a uniform fringe on the reference plane.The temporal phase unwrapping method is established to overcome the difficulty of phase unwrapping due to the discontinuity of the complex surface of the work piece.The pinhole imaging model of the CCD camera was analyzed,and the internal and external parameters of the CCD camera were calibrated using Zhang Zhengyou's plane template method.Based on this,the distortion correction model of the CCD camera based on Newton iteration was established to improve the measurement accuracy of the camera and lay the foundation for the subsequent three-dimensional view stitching.After the measurement of a single three-dimensional view is completed,a three-dimensional image mosaic method based on a cylindrical coordinate system is used for the splicing,and the coordinates of the three-dimensional view of the work piece are converted into the coordinates of the cylindrical coordinate system,and then the splicing is performed.The key of this method is to determine the coordinates of the axis of rotation of the cylindrical coordinate system.During the actual measurement process,due to the imprecise positioning of the mark point,the rotation axis coordinates are inaccurate and the splicing effect is not good.The three-dimensional view stitching method is performed using three kinds of rotation axis positioning methods based on marker point fitting,vertical lines in the marker points and marker points and rotation angle.In this paper,the advantages and disadvantages of the two splicing methods are analyzed,and how to avoid the accumulated errors is solved. |
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