Design Of Diffractive Optical Element For Three-dimensional Shape Measurement

The application of three-dimensional surface information has brought more and more convenience to our lives,and it is very important to get the information of object's three-dimensional shapes accurately and quickly.Contact measurement and non-contact measurement are two main categories of three-dimensional object shape measurement.The optical measurement technology in non-contact measurement is the most widely used in its accuracy,shortcut and limited limitation.In this paper,a diffractive optical element is designed to generate structural light in the optical three-dimensional measurement.When the diffractive optical element is illuminated by the coherent light,a predetermined random distribution point structure light can be obtained,after projecting to the surface of the object to be measured,using the digital image collected to calculate the density and size data of the light points at different positions,the system can obtain the three-dimensional information of the object.The diffractive optical element can make the measuring device miniaturized,and the obtained three-dimensional information is enough to get the motion information of the object quickly,then achieving the purpose of gesture recognition and motion direction judgement.The process of designing diffractive optical elements is discussed in detail in this paper,the specific contents of the work are as follows:(1)This thesis compares various methods for measuring the three-dimensional shape of objects,and summarizes the progress of the research on three-dimensional surface measurement for domestic and foreign scholars.On this basis,the working principle of the structured light projection method is expounded in detail.(2)The principle and related technology of two element optics are introduced,and the phase distribution of diffractive optical elements is constructed by using GS algorithm.The process is completed by MATLAB programming simulation.The characteristics of corresponding reconstructed image of the two diffractive optical elements by Fresnel diffraction and Fourier transform are compared.(3)The influence of the minimum sampling interval and the size of diffractive optical elements on the reconstructed image is analyzed,which provides the basis for parameter design of diffractive optical elements.The difference between the 4 step quantization,the 8 step quantization and the non-quantization phase distribution diffractive optical elements is compared.Through the profile map of the reconstructed image,it can be seen that the quantization processing of the phase distribution isconvenient to the processing,but the quantization noise will be introduced,The less quantified number of steps,the greater the quantization noise.(4)The phase distribution of the diffractive optical element obtained by programming is input into the liquid crystal spatial light modulator,and the reproducing effect of the designed diffractive optical element is tested by the laser beam.On the basis of theoretical analysis and experimental verification,the design scheme and the related parameters are determined.The Fourier transform diffractive optical element,which can produce the target structure light,is designed by GS algorithm.The phase distribution of the diffractive optical element is input into the liquid crystal spatial light modulator,and the experimental test is carried out by laser beam irradiation.It is proved that the clear image of the target structure light can be obtained after the imaging distance is greater than a certain value,and the design requirements are basically reached.