Light cut
The light section is a method of optical 3-D measurement technology that enables the measurement of a height profile along a projected line of light. It is based on the principle of triangulation . A light section sensor consists of a line projector - usually with a laser as a light source - which projects the narrowest and brightest possible line onto the measurement object, and an electronic camera that observes the projection of the line on the object. The shift of the line in the camera image is converted into 3-D coordinates using the methods of photogrammetry . The light section is therefore a special case of fringe projection . For a parallel projection of the laser line, in addition to the classic line laser, variants with telecentric optics are used to compensate for the disadvantages of a divergent point source.
Image evaluation
- Light section sensor simulated with 3D computer graphics
3. Image on the detector of the light section sensor with background lighting
4. Image on the detector without backlight
5. Image on the detector without background lighting in gray levels as height information
The series of images illustrates how a light section sensor works. The pictures show the view of the measuring camera. The projected line runs from bottom left to top right. The effect of shifting the line in the image due to level jumps on the object can be clearly seen.
Although the images were generated with a simulation, they show the typical effects of real images. Figure 3 shows the view of the measuring camera with a bright background lighting. Since it is difficult even for the human observer to follow the line in such a complex scene, one tries in practice to avoid disturbing background light. The result is shown in Fig. 4. Since the color information is not necessary for the three-dimensional evaluation and because of the higher spatial resolution with the same number of pixels, black and white cameras are normally used. Figure 5 comes closest to the image that a light section sensor has to evaluate. The difficulties in the precise localization of the line are caused by surface-related fluctuations in brightness and complicated geometries such. B. caused at object edges.
Individual evidence
- Wolter, H. Schlieren, Phase Contrast and Light Section Methods in Fundamentals of Optics 1956. SPIE MILESTONE SERIES MS 61 (1993): 69-69.