Research On Fast 3D Measurement Based On Color Composite Grating

Optical 3-D measurement technology is based on modern optics, optoelectronics, image and graphics computing, and computer control technology. And it is one of the modern non-contact measurement methods which is developed by the rapid development of science and engineering technology. Due to its high precision and speed, it has broad application prospects in many fields such as industrial product detection, medical diagnosis and space remote sensing.Fourier transform profilometry (FTP) and phase measurement profilometry (PMP) are two of the most important ways of grating projection measurement. FTP can rebuild the 3D shape of the object by acquiring only one frame of grating image on the object. This method is fast, but the precision of FTP is not as good as PMP. To rebuild the profile of the object, PMP needs N frames of phase shift grating images on the object according to the different algorithm. The algorithm of PMP does not involve the calculation of Fourier transform, the precision is high but with a low detection speed.To keep a high precision and detection speed, this paper mainly focus on PMP based on color composite grating. The basic principle of PMP is described. The measurement system based on PMP was built up which used a projection of color grating. The influence of the nonlinear system on the measurement is studied, and two different correction methods based on transfer function for the system was proposed. The main contents of the study are as follows:1. The basic principle of PMP was analyzed and discussed. The influence of the quality of the grating image on the accuracy was briefly described. And the correction methods were also introduced.2. Measurement system was built using a CCD camera and a projector as the main instruments. Based on three steps phase shifting technique, the three frame of phase shift map was fixed in the projector of the red, green and blue three channel, in advance. The image of color grating was projected and received into the computer for processing.3. According to the problem that the images of the color grating the CCD got was in bad sinusoidal property. The influence of grating projection quality on measurement error is investigated. The concept of transfer function is introduced to the correction of the color composite grating, and two new methods of establishing transfer function was proposed to correct the projection grating.4. The calibration principle of the measurement system was discussed, and the calibration of the height direction was carried out. A face model was rebuilt with only one images of color grating.Experimental results shows that the method of grating correction can effectively improve the image quality of the system and then improve the measurement accuracy of the system. The method is simple and fast. The color composite grating projection can also improve the speed of the measurement. Therefore, the improved PMP has a broad application prospect in the high-speed and online measurement such as the surface topography of the wheel and rail.