A study of the precision factors of large-scale object surface profile laser scanning measurement

In this paper, the authors present a method of using laser scanning triangulation for the non-contact 3D surface profile measurement of a large-scale object. The characteristics of large-scale object non-contact measurement are analyzed and a measuring method is proposed. Experimental work was performed to analyze the main factors influencing measurement precision such as image distortion and the accurate designation of a speckle center, and methods of solving these problems are proposed. To solve the problem of image distortion the authors designed a combined filter by which pulse noise and the Gaussian noise of the speckle image can be eliminated efficiently. Using the characteristics of the intensity distribution of the laser speckle image they proposed a new approximating method that can locate the center of the laser speckle image at the sub-pixel level. The auxiliary variables are set to linearize the relationship between the image displacement and the distance, accurate values of the laser triangulation system parameters can be calibrated accurately, and the measuring precision increased remarkably. Using the above techniques, a measuring system based on laser scanning triangulation was designed. The results of the experiment show that these methods can increase the measuring precision of a large-scale 3D surface profile effectively.