3D Measurement of Small Industrial Parts Based on the Camera-Projector System

摘要

With the development of the photogrammetry and computer science, their theories and skills are applied to all kinds of the industry. The common characteristic of industrial parts is that its surface is sleek, homogeneous and lack of the texture. So the key difficulties in 3D measurement of industrial parts are the matching and the extraction of the suitable texture and the makeup of the 3D model. According to the above difficulties and troubles, the paper proposes a method 3D measuring the small industrial parts on the principle of close-range photogrammetry which advantages are non-touched and accurate. According to the traditional method of the digital camera taking images, the projector is steered so that the projector-camera system is formed. The projector-camera system is composed of a slide projector, a digital camera, a control ground and a computer. The computer controls the other three equipments working together automatically and efficiently. The control ground is a planar grid on a rotating platform. Because of the size of the planar grid, the target industrial parts are relatively small. The planar grid is functioned as the calibration of the slide projector and the digital camera. After calibrated respectively in advance, the projector-camera system is similar with the binocular vision system on the principle of 3D reconstruction. The slide projector can project the texture characteristic onto the surface of the small industrial parts maybe lack of or without real texture suitable for matching. The digital camera takes sequential images of the small industrial parts with the projected texture characteristic. The images are taken from the different orientations when the rotating platform rotates continually. For each space feature point projected on the surface of the small industrial parts, there are two corresponding 2D points existing. One is an image point in one of the image sequences from the digital camera and another is a point in the slide from the projector. Using the image processing method, the image point can be extracted out accurately so that its 2D coordinates are gained. At the same time, the slide point is designed first so that its 2D coordinates are calculated by the known data. The 3D coordinates of the space feature point projected can be computed by the space forward intersection. Using the whole adjustment, the 3D coordinates of all space points projected on the whole surface of the small industrial parts can be computed out entirely and accurately. The precision of 3D coordinates of all projected space points is reached to ±0.1mm and it satisfied with the requirement of close-range photogrammetry and practical applications. The 3D model of the small industrial parts is acquired by connecting all neighbor space points. From the 3D model of the small industrial parts, the 3D measurements required about the small industrial parts are able to realize from it conveniently. The 3D measurement is non-touched so that it is remote and nondestructive. Because of little effect by the space factor or the time factor, the 3D measurement of the small industrial parts is flexible and practical. The 3D measurement of the small industrial parts proposed in the paper is confirmed to be correct and effective entirely by the results of the measuring experiments.