Research On Phase Shift Sinusoidal Fringe Projection Technology Based On Liquid Crystal

The technology of three-dimensional measurement,is an important measurement method to obtain the information of objects in real world.With the advent of the intelligent age,the demand of getting the three-dimensional shape information of objects easily and quickly is becoming stronger,which also promotes the vigorous development of three-dimensional measurement technology of non-contact structured light projection in each filed of world.The most widely studied structured light projection method is fringe projection profilometry.And fringe projection method of obtaining high frame rate,high precision and miniaturized has a wide range of market needs.This thesis proposes a novel miniaturized projection method,which use a liquid crystal display device with the special sinusoidal patterns,and match the optical system to generate fringes of four-step phase shifting.The method has the advantages of high precision,miniaturization,high flexibility and et al.The main research contents of this thesis are as follows:1.Comparison of phase calculation methodsThe fringe projection profilometry get the height information of objects according to the phase.In order to obtain high-precision phase and ensure the speed of fringe projection,several commonly used phase calculation methods are analyzed and compared,and the phase shifting and spatial phase unwrapping are selected as the phase calculation methods in this study.2.Research on camera calibration methodCamera calibration is very important for obtaining true fringe information.By analyzing the two imaging models of the camera and the brief classification of traditional camera calibration method,considering the simplicity,flexibility and accuracy calibration results of calibration method,the classic Zhengyou Zhang calibration method is selected as the main camera calibration method in this study.3.Design and construction of fringe projection system based on LCDAs the core device of this research,the principle and the manufacturing process of liquid crystal device are very critical to the projection system.The system designs electrode patterns based on the manufacturing process of the current commonly used TNLCD,and uses the working principle of liquid crystal optical switches to display different patterns.For the required sinusoidal patterns of the four-step phase shift method used in this study,a simple electrode pattern and an improved electrode pattern are designed in this thesis.The simple pattern has the advantage of easy process requirements,and the improved pattern can be made smaller.The produced sample has verified the feasibility of the two patterns,and the improved pattern with the advantage of smaller is selected for this research.4.Experimental research based on liquid crystal stripe projection systemThe liquid crystal fringe projection system proposed in this paper,by analyzing the fringes and compared with the binary defocus method of digital fringe projection,can also produce good sinusoidal fringes without defocusing,and has the advantage of miniaturization and the potential of high frame rate,which is expected to be used in consumer electronic products in the future.