Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1996-08-15
1998-09-22
Le, Que
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250216, 318483, H01J 516
Patent
active
058117938
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention is based on a rain sensor in which an optical effective radiation is subjected to at least one total reflection in a sheet of glass on which the rain impinges. Disclosed in DE-PS 23 54 100 is a rain sensor of this type, which operates according to the principle of diminished total reflection. To this end the radiation emitted by a radiation source is totally reflected multiple times inside a sheet of glass on the outside and inside surface, along a measuring segment, and subsequently detected by a radiation-measuring device. Dirt particles or raindrops on the outside impair total reflection, and couple a portion of the radiation out of the sheet of glass. Each coupling-out of radiation leads to a weakening of the signal, which is detected by the radiation-measuring device. Depending on a predetermined evaluation method, for example, means for cleaning the sheet of glass are automatically activated.
In this type of rain sensor, an interfering radiation component which is emitted by the radiation source in addition to the optical effective radiation must be taken into account. An example of interfering radiation would be solar radiation, which is present particularly when the sheet of glass is disposed in a motor vehicle.
The object of the invention is to provide a rain sensor in which the influence of the interfering radiation on the result of measurement is reduced.
SUMMARY AND ADVANTAGES OF THE INVENTION
The above object generally is achieved according to the present invention by a rain sensor in which an optical effective radiation is subjected to at least one total reflection in a sheet of glass, and wherein the effective radiation coupled out of the sheet of glass at the end of a measuring segment into a coupling-out part and a present interference radiation impact at least one separating surface at which only one of the two radiations is totally reflected.
The rain sensor of the invention is equipped with a separating surface which is impacted by the effective radiation coupled out of the sheet of glass at the end of the measuring segment, as well as by an interfering radiation that may be present. The separating surface is disposed in such a manner that only one of the two radiations is totally reflected. The other radiation, in contrast, passes through the separating surface. With this measure, an effective separation of effective radiation and interfering radiation is achieved. The separation is readily possible because the effective and interfering radiations appear in different angular ranges. The effective radiation exits the sheet of glass in the region of a coupling-out part, at an angle greater than 42.degree. with respect to a line perpendicular to the surface of the sheet of glass. Regarding the angle data, it is assumed below that the refractive index of the sheet of glass and the coupling-out part are at least approximately identical, and are approximately 1.49. The interfering radiation impacts at the region of the coupling-out part, in an angular range between 0.degree. and 180.degree., which correspond to the entire half-space in front of the sheet of glass. The maximum angle of the interfering radiation in the sheet of glass and in the coupling-out part, however, is 42.degree. with respect to a line that is perpendicular to the surface of the sheet of glass. A separation of the effective radiation from the interfering radiation is therefore always possible. The measure of using a separating surface in accordance with the invention has the advantage of a simple embodiment. The separating surface is preferably a limiting surface of the coupling-out part, which is present anyway.
Advantageous modifications and embodiments of the rain sensor of the invention are disclosed.
A particularly advantageous modification provides that both the effective radiation and the interfering radiation first impact a reflective surface after being coupled out of the sheet of glass, which surface reflects the two radiations, and that the two radiations then subsequently im
REFERENCES:
patent: 4701613 (1987-10-01), Watanabe et al.
patent: 5015931 (1991-05-01), Muller
patent: 5661303 (1997-08-01), Teder
Le Que
Robert & Bosch GmbH
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