1. Field of the Invention
The invention relates to an edge sensor for a moving strip of material.
2. The Prior Art
The use of an active receiver element made of a plastic with light-collecting properties is known for such edge sensors. For this purpose, the receiver element is usually structured as a film or flexible sheet, which is positioned on the inside of a translucent holder which extends over the length of the receiver element and encapsulates it, with the light entry surface aligned with the light. The holder serves not only to position the receiver element and to protect it, but also, the receiver element is fixed in the edge sensor by means of the holder. It is disadvantageous in this that the translucent holder not only absorbs part of the light intended for the receiver element, but also results in a multi-part and complicated structure of the edge sensor. This is because the holder is fixed and positioned in the edge sensor with specially adapted attachment elements. Finally, the complicated structure is undesirable also in view of the usually limited space available.
The light-collecting plastic used for manufacturing the receiver element is, for example, explained in detail in data sheet KL 47310 dated Mar. 1, 1981 by the company Bayer AG. These are fluorescent-pigmented, light-collecting and light-conducting polymers of high optical purity. In this, the transparent plastic forms a system with a fluorescence pigment, which absorbs direct or diffuse light, and emits it in the plastic matrix as fluorescent radiation. If the plastic is present in sheet form, the absorbed light is transported to the edge of the sheet by total reflection, and emitted there. The good total reflection results in a relatively thin sheet thickness.