Research On Dynamic3-D Profilometry Technology Based On Digital Grating Projection

With the development of the digital technology, the3-D profilometry technology plays a more and more important role in the manufacturing industry, medical domain, computer science, homeland security and environment. At present, to obtain the3D information of the static object is not a technical problem, and while the dynamic measurement with high speed and high measurement accuracy which has bright prospects in application, is the hot research topic.The sinusoidal grating projection which is used by3-D profilometry technology based on the digital fringe projection techniques is mainly a gray image. But in the rapid measurement, it has to face the following problems:(1) To be limited by the refresh rate of the projector, the projecting speed of the8-bit sinusoidal grating image is low and insufficient for the rapid measurement;(2) The nonlinear error is introduced by the Gamma effect of the projector;(3) The camera and the projector must be precisely synchronized for high-quality measurement, and the operation is difficult. The measurement method based on the defocused binary patterns was studied in this paper.The main research contents are as follows:(1) Several kinds of the defocused binary patterns were studied and analyzed. In a certain defocused condition, the binary patterns would be approximate to the sinusoidal patterns. Compared with the sinusoidal fringe, the binary fringe only has two values:0and1, and it is not affected by the Gamma effect and projecting speed is greatly improved. The simulations and experiments have been done to verify the square wave, PWM patterns and the binary dithered patterns and analyze their advantages and disadvantages.(2) A Fourier method based on the orthogonal patterns was studied. It removes the carrier frequency, double sizes filter windows and improves the measurement accuracy. A method was proposed to improve the single image orthogonal fringe technique. A calibration of the periods or the orthogonal fringes was done in advance and to scale the image to make the periods into integers. The operation makes the single method more practicable.(3) The multi-frequency heterodyne principle was applied to the binary patterns method. The method not only has the advantages of high projecting speed, not affected by the Gamma effect, but also achieves fast and global phase unwrapping. It is very good for the dynamic measurement.(4) Aimed at removing the carrier, an auto carried removal method based on the digital image processing method was proposed. Through the digital image processing, it confirms the object area after a series of digital image processing operations. And then according to the phase of the reference area, it used the series-expansion approach to build the global carrier and obtained the object absolute phase after removing the carrier. This method doesn’t need the manual intervention and improve the speed of the measurement system.