Back light doesn’t work: like below picture, back light has a lot of direction lighting disturbing the inspection, and it caused the double image of the thickness object, angle object, and cylinder object.
Structure: like below picture, collimated back light is under CCD camera, lens and object, like back light, it is in a line.
Main application: It is not good to use back light as the edge shape caused, we will consider collimated back light, collimated back light is used for high accurate edge test, location and measurement.
Advantages: Good parallel direction, good image result, high accuracy, very stable.
Disadvantages: The cost is higher, it has some requested for the related camera and lens(for example telecentric lens used is requested) adjust ability is higher.
Using advice: LED machine vision light and lens must be coaxial structure, If not, the image result is not good. After the structure fix, we should avoid shake to cause the position moving out.
Image result compared of back light and collimated back light
Back light has a lot of direction, when it is refracted, the lighting is still with a lot ofdirection, the whole image is uniformity, but we can’t get the bottle shape from the image, while when we use collimated back light, we can get a very clear bottle shape image.
When use back light to test the screw shape, it is very hard to get very shape edge images, this image result effects the inspection accuracy.
When use collimated back light, as the light is very parallel, so the edge is very shape and clear, if use together with telecentric lens, we can get quite good image result, this helps to enhance the test accuracy and reduce the disturbing.