Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1993-10-19
1995-05-09
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
318DIG2, H01J 516, H01J 4014
Patent
active
054142571
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND ART
There are instances when it is necessary to determine moisture levels on a surface such as the windscreen or windshield of a vehicle.
In the case of the windscreens of road vehicles, there has been a number of attempts in the past to determine the need to wipe the windscreen by determining the current level of rainfall or the current level of water on the windscreen. Some of these attempts, such as is described in U.S. Pat. No. 4,355,271 (Noack), have used devices which emit radiant energy from the inside of the windscreen, and direct it at the outside windscreen surface at an angle such that it will be substantially totally internally reflected from a dry screen but allowed to substantially entirely pass through a wet screen. By suitably positioning a detector that will respond to the radiant energy, it can be determined whether or not the screen is wet. However, typical examples of such devices are inefficient due to reflective losses incurred when the radiant energy beam enters and leaves the windscreen at the inside air/screen interface at a similar angle. U.S. Pat. No. 4,620,141 (McCumber et al) discloses a sensor unit of this general type but further including a light conducting rod for each emitter and detector and may overcome the problem of reflective losses. Such devices tend to be less than straight forward to manufacture and assemble. Furthermore, the required physical dimensions of the prior art devices are inconveniently large in order to obtain the required relative location of the sensor and emitter.
DISCLOSURE OF THE INVENTION
The present invention seeks to overcome the disadvantages in the prior art by providing a device which will be more easily manufactured and assembled and of compact size.
The invention provides a moisture sensor which is formed in a compact arrangement that lends itself to ready repair or replacement of its active components without removal of the entire unit from a fixed position on the interior of a windscreen and so offers a desirable alternative to existing sensor arrangements. In one embodiment the sensor provides a device to be optically coupled to the inside of a windscreen and which utilizes a radiant energy path within a transparent window, the path initially entering and finally leaving the window perpendicularly to surfaces provided for that purpose, and the proportion of radiant energy being internally reflected from the outside windscreen surface being indicative of its degree of dryness. When the outside surface is wet substantial radiant energy is transmitted through the surface and the detected signal reduced; when dry substantially total internal reflection occurs. Accordingly, throughout this specification, the terms wet and dry indicate the presence or absence of water, ice, or the like substance that will change the optical path of the radiant energy at that outside surface.
Accordingly, in one broad form, the present invention provides a moisture sensor comprising a housing incorporating window means, said window means being composed of material transparent to radiant energy from a radiant energy emitter and having at least one outermost front surface adapted to be optically coupled to an inside surface of a windscreen, a body means incorporating said emitter and a sensor for sensing radiant energy emitted by said emitter, said body means being of a stepwise shape which is a slide fit within the housing in the direction of the step so as to fit against a complementary innermost surface of said window means, and wherein said innermost surface of said window means comprises an emitter surface and a sensor surface.
Preferably the window means is a one piece window and the front surface means is a continuous front surface.
Preferably the emitter is an infra-red diode.
Preferably the window means includes a further surface positioned along the radiant energy path and providing a surface of total internal reflection to the radiant energy. It is further preferred that this further surface be intermediate the emitter surface and the fr
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patent: 4620141 (1986-10-01), McCumber et al.
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Abstract of Japanese Patent Publication No. 59-89250(A), "Liquid Detector For Automatic Windshield Wiper Controller", May 23, 1984.
Abstract of Japanese Patent Publication No. 59-85944(A), "Liquid Detector For Automatic Wind Shield Wiper Controller Device", May 18, 1984.
Abstract of Japanese Patent Publication No. 59-159053(A), "Liquid Detector for Automatic Windshield Wiper Control Apparatus", Sep. 8, 1984.
Abstract of Australian Patent Specification No. Au-A1-51,186/79, "Detecting Dust or Water on Vehicle Windscreen", Sep. 25, 1978.
Abstract of Japanese Patent Publication No. 59-100034, "Automatic Wiper Apparatus", Jun. 9, 1984.
Abstract of Japanes Patent Publication No. 59-57050, "Automatic Defrosting Control Device", Apr. 2, 1984.
Introlab Pty Limited
Nelms David C.
Nichols Steven L.
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