LEDs [LED optics] used in industrial optics can be divided into two broad categories: front-illuminated LED sources and back-illuminated LED sources.
The front-illuminated LED light source is used to detect the surface features of the object; the back-illuminated LED light source is used to detect the contour of the object or the purity of the transparent object. The front illumination VUV, UV and IR grade MgF2 optics can be divided into an annular light source, a strip light source, a coaxial light source and a square light source according to different structures. At present, ring light sources are used more commonly, including direct illumination of ring light sources, diffuse reflection ring sources, Dome sources, and the like.
Directly illuminating the ring light source, suitable for the detection of non-reflective objects; diffuse-reflecting ring light source, suitable for the detection of reflective objects; Dome light source is also a kind of diffuse reflection source, but it is repeatedly reflected by the inner wall of the hemisphere type, which can completely eliminate shadow. Mainly used to detect spherical or curved objects.
Direct illumination of the ring source
According to different illumination angles, direct illumination of the ring light source can be divided into: vertical illumination ring light source, angled ring light source, low angle ring light source and horizontal illumination ring light source. It can be simply understood that the angle between the wholesale infrared and broadband BaF2 optics of each LED and the ring lamp housing is 0°, 20°, 60° and 90° in sequence (the specific model may vary slightly).
Different lighting angles are available for different inspection requirements. Vertical illumination and angled illumination are bright-field illumination, that is, most of the reflection on the surface of the object to be measured can enter the camera, so the background is white, such as the detection of prominent features on the surface of the object. Low-angle illumination and horizontal illumination are dark-field illumination, that is, most of the reflection on the surface of the measured object does not enter the camera, so the background is black, and only the reflection of the unevenness of the object enters the camera, such as the detection of scratches on the metal surface, background. It is black and the scratch is white. At the same time, the difference between vertical illumination and angled illumination is that the former one is farther away and the latter is closer. The same is true for low-angle ring illumination and horizontal illumination ring illumination. At the same time, the diffuse reflection ring also has direct and low angle points.
Diffuse light source
Low angle diffuse reflective strip light for two applications. One is wide-width detection, two or four bars are used in combination, and the other is line-scan illumination.
Another application is line scan lighting. At present, the number of line scanning projects is gradually increasing. The line scan camera captures one line at a time, and the exposure time is short, which requires high brightness of the light source. wholesale large size infrared Silicon optics need to use a concentrating type, which is concentrated on one line, so as to accurately control image stability. There are several methods commonly used for line scanning illumination: super bright LED + concentrating mirror, fiber + concentrating mirror, high frequency fluorescent lamp + concentrating mirror. Super bright LED + concentrating mirror, long life, needless to say, but the cost is higher, the irradiation distance may be limited; the fiber brightness is high, but the cost is high; the high-frequency fluorescent lamp, the cost is lower, but it needs to change the lamp at a certain time.