Research Of 3D Surface Measurement Based On Digital Grating Projection

Three-dimensional reconstruction has been one of the important research fields in computer vision study. Recently, the study of the three-dimensional profile reconstruction technology has made great progresses, and has been widely used in reverse engineering, machine vision, on-line product inspection, mold design, medical treatment and other fields. The measuringtechnologyof structured light projection is a core technology to realize three-dimensional reconstruction, and digital grating projection method is the mainstream optical measuring method. This method uses the digital grating as an information carrier and projectsit onto the surface. Then it usesa camera to capture grating images deformed by object height and demodulates the height information of the measured object by algorithm processing. This method has advantages of non-contact, full field and high measuringsensitivity and it can measure three-dimensional profilewith convenient steps. In this thesis, the three-dimensional surface measuring technologybased on digital grating projection is systematically studied, and the main works are as follows:(1)Various key technologiesthat determine the measurement results of phase grating projection method have been studied. Analyze in detail its system relationship model, the method to determine the height matrix, the method to acquire the real phase, and to unwrap the real phase as well as its advantages and disadvantages.(2) Improve the traditional system relationship model that determines the height matrix.This thesis adopts a straight road incidentwith a simple calibration method. This method can only use the phase-shift formula to determine the phase difference without adding any amount related to system geometry relationship. It reduces the required number of parameters to determine height matrix furthest and improvesthe immunity;(3)Propose an improved dual frequency reference grating projection technology.The technology uses a composite grating which involves only one cycle of low-frequency fringe when projecting.Compared with the traditional dual frequency technology, this method avoids the phase unwrapping errors on low-frequency gratingand finishes the calculation only by capturing five images.The experimental results prove that this method can well overcome the threaderror and measure the curve with complex profile;(4) Design and set up a measuring system with grating projection phase method. Develop the measuring software based on VC++, making the measurement of three-dimensional profile easy.