Research On Key Techniques Of Digital Grating Projection Measurement

3D shape measurement technology has been widely used in industrial manufacturing, criminal investigation, biomedical, heritage conservation areas. Digital grating projection method is an important branch of 3D topography measurement technique. This method has advantages of non-contact, full field and high measuring sensitivity.This method uses the digital grating as an information carrier and projects it onto the surface. Then it uses a camera to capture grating images deformed by object height and demodulates the height information of the measured object by algorithm processing to achieve three-dimensional information of objects. In this thesis, the three-dimensional surface measuring technology based on digital grating projection is systematically studied. The main works are as follows:(1)The basic principle of digital grating projection measurement has been studied and analyzed.Two different models of the system are introduced respectively:Traditional triangle method system relation model and triangle method direct incidence relation model. And its advantages and disadvantages are analyzed.(2)The convolution methodof the digital grating projection method are proposed and analyzed. Including calibration, and the convolution method, FFT, phase shift method and phase extraction method in detail and analyzed.(3)An improved step calibration method is proposed. In this method, a fixed step surface is used as the calibration board, and the digital grating is projected onto the step surface, and then the reference plane fringe pattern of different position is obtained by image extension. The calibration process can be realized by the method without moving reference plane, which simplifies the calibration process and the calibration system.(4)Several factors affecting the non sinusoidal error of the grating are introduced in detail. The non sinusoidal correction of the grating is made by using the off focus projection method. This paper introduces and compares two different phase unwrapping methods:point to point method and non continuous path integral method based on quality map guidance. Achieved good results of phase unwrapping.(5)Design and set up a 3D shape measurement system with grating projection phase method. Develop the measuring software based on VC++, making the measurement of three-dimensional profile easy.