Optical detection of water droplets using light refraction with a mask to prevent detection of unrefracted light
First Claim
1. An optical droplet detector apparatus for determining the degree of vision impairment through a window due to an accumulation of water or other precipitation on the window comprising:
- a first light source for illuminating water droplets on said window with a first light beam transmitted through said window to the inside of said window;
a photo-detector located inside said window; and
a masking device positioned in front of said photo-detector to effectively block the direct transmission of light rays from said first light source to said photo-detector, but allowing said photo-detector to receive light rays from said first source which have been refracted by droplets on said window for the purpose of determining the amount of water on said window so that the output signal of said photo-detector increases with an increase in water droplets on said window.
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Accused Products
Abstract
An optical detection system for detecting rain or other water droplets on the outer surface of a window and fog on the inner surface with a single photo-detector. The invention measures the accumulation of water droplets on the window by light refraction of a first light beam with droplets to redirect a first light beam to the photo-detector. A masking device prevents light from reaching the photo-detector directly without refraction. As a result the rain measurement output signal of the photo-detector increases with an increasing accumulation of water droplets on the window. The fog accumulation is measured by a second light beam reflected off the inner surface of the window to the photo-detector so that the output signal of the photo-detector decreases with increasing amounts of fog since fog scatters the light to reduce the amount of light reflected to the photo-detector. A third light source is focused directly on the photo-detector to bias it into an operating point of high sensitivity to infrared light and is connected in a negative feedback circuit from the output of the photo-detector amplifier. The photo-detector output is connected to a narrowband amplifier that is tuned to the frequency of an oscillator which pulses the first and second light sources at different times. As a result of this negative feedback, changes in the output signal due to external factors are cancelled so they do not produce errors.
90 Citations
20 Claims
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1. An optical droplet detector apparatus for determining the degree of vision impairment through a window due to an accumulation of water or other precipitation on the window comprising:
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a first light source for illuminating water droplets on said window with a first light beam transmitted through said window to the inside of said window; a photo-detector located inside said window; and a masking device positioned in front of said photo-detector to effectively block the direct transmission of light rays from said first light source to said photo-detector, but allowing said photo-detector to receive light rays from said first source which have been refracted by droplets on said window for the purpose of determining the amount of water on said window so that the output signal of said photo-detector increases with an increase in water droplets on said window. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A water droplet detector for determining the degree of vision impairment through a windshield of a vehicle due to an accumulation of water on said windshield comprising:
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a first sensor incorporating a first light source and a photo-detector for the purpose of determining the degree of water accumulation on the outside surface of said windshield; a second sensor incorporating a second light source and said photo-detector for the purpose of determining the degree of fog accumulation on the inside surface of said windshield; a third light source for the purpose of optically driving said photo-detector to its bias operating point; a drive circuit for providing pulsed drive current to said first light source and to said second light source; an output circuit connected to the photo-detector including a tuned amplifier for providing narrowband amplification closely tuned to the frequency of said pulsating drive currents for the purposes of amplifying the pulsating output current produced by said photo-detector and rejecting other, potentially interfering currents produced by said photo-detector; and a feedback circuit connected from said output circuit to said third light source for providing attenuation and additional phase shift to the output signal of said output circuit to provide a negative feedback signal to modulate said third light source for the purpose of gain stabilization of said output circuit. - View Dependent Claims (11, 12, 13)
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14. A method of optical detection of water or other precipitation on a window to determine the degree of vision impairment through the window due to the accumulation of water on said window, comprising the steps of:
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transmitting a first light beam from a first light source through said window to the inside of said window; detecting the first light beam with a photo-detector inside said window; blocking the direct transmission of light rays from said first light source to said photo-detector by a light masking device; and refracting said first light beam with water droplets or other precipitation on said window to cause a portion of said first light beam to be redirected from said water droplets to said photo-detector so that the detector output signal of said photo-detector increases with an increase in water droplets on said window. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification