Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1991-04-16
1992-11-24
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
25022731, G01V 904
Patent
active
051665328
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
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.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an edge sensor for a moving strip of material, which is characterized by a space-saving and significantly simplified structure, and an improved utilization of light.
The self-supporting, elongated element made of light-collecting plastic can be directly held without noteworthy structural effort, which eliminates an additional holder for positioning and supporting the receiver element. Thanks to its self-supporting property, the elongated element does not require any protection against contact with the strip, because it deals easily with any forces which occur in that connection. The self-supporting structure of the tube-shaped element has the further advantage of an increased light-collection and amplification effect. Together with the measure of placing the self-supporting element made of light-collecting plastic opposite the strip to be scanned directly, i.e. without any protective element, the unhindered incident light results in greater performance of the receiver element, so that less energy is required than before. The additional material needed for the self-supporting structure of the element is certainly justified by the savings in separate holders and mounting parts. In addition, assembly and maintenance are made simple, because the self-supporting element can be handled like a rigid element in the receiver. Unexpectedly, the self-supporting element made of light-collecting plastic yields an improved response behavior to light changes and a high resistance to mechanical wear. It can be cut off from a continuous profile in any desired length, and adapted to the conditions of use in each case. In this manner, the production effort and the production costs are drastically reduced.
An especially important embodiment is the following. With regard to the effort to manufacture edge sensors in as simple, cost-effective and robust a manner as possible, the use of a commercially available fluorescent tube holder to hold the hollow element fulfills all requirements. Such light fixtures, which are commercially available in different sizes, are inexpensive and easy to install. The hollow element made of light-collecting plastic is inserted instead of the fluorescent tub
REFERENCES:
patent: 4002919 (1977-01-01), Linard
patent: 4157477 (1979-06-01), Kall et al.
patent: 4827120 (1989-05-01), Stauffer
patent: 5021674 (1991-06-01), Brunner
Brunner Gerhard
Krauth Wolfgang
Erhardt & Leimer GmbH
Le Que T.
Nelms David C.
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