System and method for detecting an object on a moving web

摘要

The system includes a light source that emits light onto a web and objects that are on the web. The system further includes a lens that has a radial index of refraction gradient. The lens is positioned such that the lens only captures light above a nominal level when light from the light source is reflected by the objects and not the web. A sensor receives light from the lens and converts the light to a signal. The method includes directing light onto the objects and the web using a light source. The method further includes positioning a lens that has a radial index of refraction gradient relative to the web and the light source such that the lens only captures light above a nominal level when the light from the light source is reflected by the objects. The method further includes focusing the captured light on a sensor.