Structure: like below pictures, back light is under the inspected object, and the CCD camera, lens, inspected object and back light is in a line.
Main application: exist detection, account, film edge inspection, location, and measurement, surface inspection and foreign parts and defects inspection of transparent object, deform and defects, print code inspection of transparent and semi-transparent object.
Advantages: Structure is simple, cost is rather low, the image result is stable and reliable. Under normal situation, the image result is just black and white, and the camera is easy to grab the picture and it is good for algorithm.
Disadvantages: It is not very good for line scan application, it will cause double image if the object is too thickness or the edge is round, cylinder, and the test result is not accuracy.
Using advice: Illumination area is better to just match the FOV, if the illumination is too big, it will effect the double image of the edge. It is better to get some long distance between object and light, this can help to get better image result. If use object telecentric lens, the test result is more stable. As for the intensity, it doesn’t need to brightness.
Back light used in account, measurement, scratch inspection, configure inspection and so on