Optical waveguides – Planar optical waveguide – Thin film optical waveguide
Reexamination Certificate
2000-04-18
2001-10-30
Font, Frank G. (Department: 2877)
Optical waveguides
Planar optical waveguide
Thin film optical waveguide
C385S129000
Reexamination Certificate
active
06311005
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a sensor device for determining the degree of wetting and/or soiling on window panes.
BACKGROUND INFORMATION
In motor vehicles, to measure the degree of wetting (i.e., moisture) present in the wiper field of windshields or rear windows, a rain sensor is installed on the inner side of the window. If the wiping system is switched on in the automatic operating mode, and the window is wetted with moisture at the location where the sensor is installed, a wiping operation is initiated.
The mode of operation of the sensor is based on an optical principle. In particular, a light beam of known intensity emitted by a transmitter is introduced into the pane at a certain location and is directed through a defined length of the pane by means of repeated total reflection within the pane. At a second selected location, the light beam is directed by means of optical coupling out to a receiver and to a measuring system where the residual light intensity is measured and analyzed.
When the surface of the pane is wetted with drops of water, part of the light beam is no longer completely reflected, but rather emerges from the pane. The resultant loss of intensity of the residual light is a measure of the pane surface wetting. Below a preselected threshold value, a means for cleaning the window pane is then automatically activated.
Rain sensors of this type are often installed in motor vehicles at the level of the rearview mirror to ensure that the driver's vision is not impaired by the sensor housing. In some motor vehicles, however, a light filter, e.g., a green or gray wedge tinting the upper edge of the pane, is situated at this location and is integrated in the windshield. When the wave length of the transmitter beam being used is within a range that is essentially attenuated by the light filter, it is not possible to position the optical rain sensor in the light filter, since the repeated total reflection in the pane causes the light beam to pass through the light filter several times, attenuating it to an unacceptable degree.
SUMMARY OF THE INVENTION
The sensor device of the present invention has the advantage that the transmitter beam of the rain sensor, in passing through the pane, is totally reflected or reflected at a reflecting means in the pane, such that the attenuation resulting from the optically more highly absorbent layer of the light filter is reduced.
Since the conventional windshield of an motor vehicle is comprised of a composite of a plurality of layers, and the light filter is normally designed as an optically more highly absorbent layer of the laminated glass, a reflecting means can be mounted between this layer and the external layer which faces away from the interior of the motor vehicle, so that the transmitter beam is directed through the pane, under conditions of total reflection or reflection at the outer side of the outer layer and at the reflecting means.
Another advantage of the present invention is that the reflecting means can be realized in various ways, so that for laminated glass panes that are variously manufactured or executed, optimal solutions can be found.
Yet another advantage of the present invention is that the optical paths of the light beam in the pane are shorter, the paths being generated by the reflecting means. Thus, assuming a constant length of the measuring distance of the rain sensor, the result is a larger number of reflections, so that an even (homogeneous) illumination of the measuring distance is provided. In this way, the sensitivity of the rain sensor in the area of the measuring distance is evened out (homogenized) and thus increased.
A further advantage of the present invention results from the possibility of eliminating the heating device for heating the inner side of the pane, since the wetting of the inner side of the pane, e.g., through condensation water, exerts practically no additional influence on the moisture-dependent weakening of the signal and thus on the functional reliability of the rain sensor.
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Meier Hans
Pientka Rainer
Schabanel Francois
Font Frank G.
Kenyon & Kenyon
Robert & Bosch GmbH
Stafira Michael P.
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