Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1998-10-29
2001-05-15
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S227250, C250S341800
Reexamination Certificate
active
06232603
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention generally relates to a sensor for detecting the presence of moisture. More particularly, the present invention is directed to an optoelectric sensor for detecting the presence of moisture and/or rain on the outside surface of a variety of energy modifying glass windshields.
2. Discussion
Rain sensors that rely on light or infrared (IR) energy reflecting off of the outside surface of a windshield operate under the well understood phenomenon of total internal reflection, and are generally known within the art. In a typical vehicle configuration, the rain sensor is electrically interconnected with the windshield wiper control circuit. Thus, when the presence of moisture or rain is detected on the windshield surface, a signal can be generated for triggering operation of the windshield wipers. These conventional rain sensors also have the capability of detecting the intensity of rain accumulation and may in turn control the windshield wiping frequency.
With reference to
FIG. 1
, a conventional rain sensor
10
which is optically coupled to a solar absorptive glass windshield
20
is shown. Rain sensor
10
is shown as including an energy source or emitter
12
which emits light energy
28
, and using an optical lens
16
, directs this energy through inside surface
24
, and toward the outside surface
26
of the windshield
20
at an incident angle of principally 45 degrees. This light energy
28
is reflected at the outside surface
26
, back through the inside surface
24
, and focused by an optical lens
18
onto a photo sensitive detector
14
, such as a photo transistor or photo diode. The presence of moisture or rain on the outside surface
26
of the windshield causes a change in the angle of reflection of the incident light energy
28
. This change in the angle of reflection results in less light energy
28
being reflected back to the photodetector
14
. The electronics controlling rain sensor
10
are capable of detecting moisture and/or rain
22
on the outside surface
26
of the windshield
20
by monitoring and analyzing the amount of light energy
28
returning to photodetector
14
.
Advances in windshield technology have allowed the introduction of high performing glasses, such as IR reflective glass. A cross section of this type of IR reflective glass
30
is schematically represented in
FIG. 2
, and is shown to include an inner reflective layer
32
made up of a material that reflects energy in the IR spectrum. The inner reflective layer
32
is typically a microscopic layer of silver or other suitable reflective material which is situated between an inner glass layer
33
and an outer glass layer
35
. This type of windshield glass is highly reflective at IR wavelengths, which assists in keeping the interior of the vehicle cooler when subjected to sunlight. At the same time, this IR reflective glass has a transmissivity level of greater than 75% of the visible spectrum. The transmissivity level of IR reflective glass is typically greater than that of solar absorbing glass in the visible spectrum. Thus, IR reflective glass is favored in many automotive markets since government regulations will not allow solar absorbing glasses to be used because they do not meet the regulated transmissivity levels for visible light.
With continued reference to
FIG. 2
, this inner reflective layer
32
of windshield
30
creates a significant challenge for IR based rain sensors, such as rain sensor
10
, because the inner reflective layer
32
tends to reflect a large amount of the incident light energy
28
to the photodetector
14
before it reaches the outside surface
36
of the glass. The light energy
28
reflected from outside surface
36
is represented as dashed line ray traces
39
, and the light energy
28
reflected from inner layer
32
is represented as solid line ray traces
38
, both illustrated in FIG.
2
. This reflection of light energy
38
from reflective layer
32
reduces the sensitivity and effectiveness of the rain sensor
10
because a larger percentage of the incident energy
28
transmitted by the emitter
12
is reflected from the inner reflective material layer
32
and not the target area of outside surface
36
. For example, in a typical IR reflective windshield having an inner reflective layer
32
, calculations show that this inner reflective layer causes a sensitivity reduction of the sensor of over 28 dB. Thus, a rain drop
22
landing on the windshield's outside surface
36
has a smaller effect on the change in total energy seen by the photodetector
14
.
This change could be compensated for by means of electrically amplifying the signal or by changing multiplying factors in the control and analysis software. However, these methods are undesirable in that a sensor which is modified to work on reflective glass, such as IR reflective glass
30
would be too sensitive on non-reflective or solar absorptive glass, such as windshield
20
. Alternatively, separate sensors would need to be incorporated within rain sensor
10
to detect the inner reflective layer
32
allowing the control and analysis software to adapt or switch between operating modes. However, this method adds complexity and cost to the system.
Additionally, this problem is difficult to solve using only an electrical or electronic approach because of the already high gain levels used in the circuitry of these rain sensors. Moreover, if a rain sensor is customized for a particular type of windshield, there is no assurance that the vehicle will not have its windshield replaced in the future with a different type of windshield, thus causing unknown results, including the rain sensor not working on the glass at all. Accordingly, a contemplated solution is to modify the windshield optical coupling device associated with the rain sensor, which is typically supplied with the windshield. To this end, the problems associated with glass replacement and customizing rain sensors for particular windshield reflective layer characteristics are eliminated.
In view of these problems, it is desirable to provide a device and technique for minimizing the effects of the reflective properties of the inner reflective layer associated with IR reflective windshields. In addition, it is desirable to create a rain sensing system that has similar performance using the same sensor on a variety of IR reflective and solar absorptive glass windshields, requiring only a different optical attachment coupler to be bonded to the windshield. It is also desirable to provide an electronic rain sensor system in which a common optoelectric configuration can be used with both IR reflective and solar absorptive glass windshields. Furthermore, it is desirable that this common optoelectric configuration work on a variety of IR reflective glass windshields having different transmissivity levels. Such a device would allow the same rain sensor to be used on a replacement windshield having different reflective properties or physical characteristics without recalibrating the sensor. Finally, it is desirable to provide an optical attachment coupler which is designed for a specific windshield curve, which also includes a standard mounting configuration for receiving and securing the rain sensor in optical contact with the inside surface of the windshield.
SUMMARY OF THE INVENTION
Pursuant to the present invention an optical coupling device for maintaining a moisture sensor in optical contact with a windshield having a reflective layer disposed therein is disclosed. The optical coupling device includes a substrate. A first lens is formed within the substrate for transmitting light energy into the windshield. A second lens is also formed within the substrate for receiving light energy reflected from an outside surface of the windshield. An energy absorbing member is disposed between the first lens and the second lens. The energy absorbing member is positioned for absorbing light energy reflected from the reflective layer.
REFERENCES:
patent: 4620141 (1986-10-
Gabor Otilia
Hannaher Constantine
Harness & Dickey & Pierce P.L.C.
Kelsey-Hayes Co.
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