Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-08-20
2001-09-04
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S227250
Reexamination Certificate
active
06285037
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid drop detection method and an apparatus therefor, for detecting liquid such as drops of rain adhering upon a front windshield of an automobile, so as to drive a wiper and so on corresponding thereto.
2. Description of Prior Art
An optical type liquid drop detector (a rain sensor) was already proposed and disclosed in Japanese Laid-Open Patent No. Hei 9-68616 (1997) filed by the inventors of the present invention.
This detector has a construction wherein a light emitting element and a light receiving element are attached on one side surface of a glass plate, and wherein a light beam emitted from the light emitting element is guided into the glass plate through a light guiding body and enters into a light receiving element after undergoing total internal reflection within the glass plate. When such the light beam undergoing total internal reflection within the glass plate enters into the light receiving element, it is reduced in an amount (intensity) by loss from the total internal reflection if water drops are adhered at surface points where the total internal reflection is taking place, thereby enabling detection of the adhesion of water drops on the surface of the glass plate on the basis of the reduced amount of received light.
SUMMARY OF THE INVENTION
When applying the liquid drop detect or as mentioned above to an automobile, it must be attached on an interior side surface of the front windshield. In such a case, it is necessary that the attachment of the liquid drop detector does not obstruct driving and does not decrease the sensitivity in detection thereof. However, such liquid drop detector as mentioned above has been applied only for the purpose of trial, wherein incomplete consideration was paid to the details of applying it to an automobile practically.
According to the present invention, for dissolving the drawback mentioned above, there is provided a liquid drop detecting method, comprising steps of:
introducing a light beam emitted from a light emitting means into a glass plate; and
detecting presence of liquid drops adhering upon said glass plate by detecting the light beam experiencing total internal reflection on both inner surfaces within said glass plate, wherein a wavelength of the light beam emitted from said light emitting means is selected to be from 700 nm to 780 nm.
Further, according to the present invention, there is provided a liquid drop detecting apparatus, comprising:
light emitting means for emitting a light beam;
a glass plate, into which the light beams emitted from said light emitting means is introduced; and
light receiving means for detecting the light beam experiencing total internal reflection on both inner surfaces within said glass plate, wherein a wavelength of the light beam emitted from said light emitting means is selected to be from 700 nm to 780 nm.
The reason for using light being 700 nm to 780 nm in wavelength thereof for detection is that, first of all, as shown in TABLE 1 below, comparison luminosity factor increases gradually if the wavelength is shorter than 700 nm, i.e., the detection light can be easily recognized by the naked eye, thereby introducing obstruction or distraction.
TABLE 1
Standard
Comparison
Wavelength
Luminosity
(nm)
Factor
500
0.323
510
0.503
520
0.710
530
0.862
540
0.954
550
0.995
560
0.995
570
0.962
580
0.870
590
0.757
600
0.631
610
0.503
620
0.361
630
0.265
640
0.175
650
0.107
660
0.061
670
0.032
680
0.017
690
0.0082
700
0.0042
710
0.0021
720
0.00105
730
0.00052
740
0.00025
750
0.00012
760
0.00006
The front windshield presently in common use contains a relatively large amount of iron components for the purpose of cutting down ultraviolet rays and for absorbing heat rays thereof. Since the absorbing region of the iron components lies from 900 nm to 1,000 nm, then the absorption comes to be larger in an infrared region exceeding 780 nm and the luminosity factor at such wavelengths is decreased. In particular, if trying to improve reliability in detection by means of the number of measuring points (i.e., the total internal reflection points) of the liquid drop detector, the number of reflections must be equal or more than 2 times. However, the larger the number of total internal reflections, the more the attenuated light beam is weakened, and thus the reliability is decreased.
Also, most of the recent front windshields for automobiles have shading in an upper portion thereof for the purpose of protection from blinding or dazzling light. A line A in
FIG. 3
shows the relationship between wavelength and permeability of the front shield for automobiles, which includes an intermediate film of polyvinyl butyral, while a line B shows the relationship between wavelength and permeability of the same front shield for automobiles, in particular in a shaded portion at the top region of the windshield.
From the graph, it can be seen that the light rays from 470 nm to 700 nm in wavelength are selectively absorbed in the shaded portion. If the liquid drop detector is provided on the interior side of the front windshield being formed with the shading in the portion of the intermediate film and as the detection light of the detector is used the light being from 470 nm to 700 nm in wavelength, the detection light is absorbed by the shaded portion, therefore the luminosity factor is decreased greatly.
Therefore, according to the present invention, the light from 700 nm to 780 nm in wavelength is used, which lies in a region of visible light but is small in the luminosity factor thereof, therefore being unlikely to cause obstruction or distraction, and is also small in a level of absorption into the glass.
REFERENCES:
patent: 5181645 (1993-01-01), Yoshimi et al.
patent: 10-268066 (1998-09-01), None
Koyama Tadashi
Tanaka Shuhei
Tsunetomo Keiji
Le Que T.
Nippon Sheet Glass Co. Ltd.
Pillsbury & Winthrop LLP
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