Research On 3D Object Contour Fusion Technology Based On Digital Holography

Holographic technology has attracted considerable attention because it can obtain the phase information of the object,that is,the height information of the object,which is comparable to ordinary photographic technology.However,digital holography technology is also limited by the size and the total number of pixels of the Charged-Coupled Device(CCD)array,so that the imaging resolution and the imaging field of view are always mutually constrained,which limits the practicality of digital holographic topography measurement.In order to achieve high resolution and large field of view digital holography and get the three-dimensional contour of the whole object,phase stitching technology and multi-aperture stitching technology are applied to digital holography in this paper.According to the morphological characteristics of objects,objects are divided into two categories: planar three-dimensional objects and rotary three-dimensional objects.Planar three-dimensional objects are mosaic by error homogenization in Cartesian coordinate system,rotary three-dimensional objects are mosaic by cylindrical coordinate system,and particle swarm optimization(PSO)is proposed to solve the mosaic parameters.The main our researches are listed below:(1)The basic theoretical knowledge of digital holography is deeply studied,and three reconstruction algorithms of digital holography are comprehensively analyzed.The digital holograms are reconstructed separately,considering comprehensively,the angle spectrum algorithm has the best reconstruction effect.(2)In this article,we studied the principle of three commonly used unwrapping algorithms by adding the different degrees of noise,The advantages,disadvantages and application scope of the three algorithms are obtained.Although the quality map-oriented method takes a long time to calculate,it has better anti-noise ability,which provides a method for the noise of the interferogram in this paper.(3)For planar three-dimensional objects,the method of stitching in Cartesian coordinate system is adopted.We analyzed that although the procedure of two-two stitching is simple,there will be error transfer and error accumulation.So we consider the error averaging algorithm.Although the program algorithm is more complex,it can distribute the error equally to each sub-aperture,which can effectively reduce the error.The feasibility of the algorithm is verified by computer simulation.(4)For rotary three-dimensional objects,they are spliced in cylindrical coordinate system.The multi-aperture stitching technique in cylindrical coordinates in the grating projection is applied to digital holography.Particle swarm optimization algorithm is proposed to solve the problem.It not only ensures the accuracy,but also greatly simplifies the transformation of complex formulas.The feasibility of this method is verified by computer simulation.(5)The off-axis digital holographic optical path is built,and the contour fusion experiments of planar three-dimensional object(standard phase plate)and rotary three-dimensional object(hexagon nut)are carried out.The results show that the splicing effect of the phase plate is good in Cartesian coordinate system;the hexagon nut first obtains the contour of the object by oblique illumination method,and we used the gauge block to calibrate its height measurement error.The error range is from 0.1mm to 0.5mm.Particle swarm optimization is used to solve the stitching parameters.The error range after stitching is about 0.5mm.Several experiments have been carried out.The standard deviations of the error peak-to-valley values and error root mean square values are 0.039 and 0.0065,respectively.The results show that the method has good repetitive accuracy.Finally,the studs are spliced together.