Compact moisture sensor with collimator lenses and prismatic coupler

• US 5,661,303 A
• Filed: 05/24/1996
• Issued: 08/26/1997
• Est. Priority Date: 05/24/1996
• Status: Expired due to Term

• Current Assignee: Libbey-Owens-Ford Co. (Eaton Corporation PLC.)
• Original Assignee: Libbey-Owens-Ford Co. (Eaton Corporation PLC.)
• Inventors: Teder, Rein S.
• Primary Examiner(s): Tokar, Michael J.
• Assistant Examiner(s): HANIG, RICHARD E
• Application Number:
  US08/653,546
• Time in Patent Office: 459 Days
• Field of Search: 250/341.8, 250/227.25, 356/445
• US Class Current: 250/341.8
• CPC Class Codes: G01N 21/43 by measuring critical angle

Abstract

A compact rain sensor for mounting on the inner surface of a windshield includes collimator lenses and a detachable prismatic coupler to facilitate the mounting of emitters and detectors on a circuit board which is positioned parallel to the inner surface of the windshield. A thin optical coupler is adhesively secured to the windshield. A sensor housing is detachably secured about the outer edges of the coupler. Within the sensor housing, surface-mounted infrared emitters and detectors, as well as signal processing circuitry, are all mounted on a single printed circuit board secured in the housing. When the sensor housing is mounted on the coupler, the printed circuit board is parallel to the inner surface of the windshield and in close proximity thereto. In operation, a light beam from the emitter enters the windshield at a forty-five degree angle and is reflected back from the outer surface of the windshield to the detector, which generates a control signal based on the amount of light reflected from the outer surface. Moisture on the outer surface of the windshield reduces the amount of light reflected to the detector. Surface mounted emitters and detectors, which are very cost and space efficient, are mounted on the circuit board with an initial optical axis perpendicular to the circuit board. In order to achieve the desired forty-five degree angle of entry into the windshield, the light beam emitted from the emitter is reflected, refracted, and collimated prior to entry into the windshield by collimator lenses mounted on the circuit board and by prismatic regions formed in the coupler.

Claims

1. A moisture sensor for mounting on a surface of a sheet of glass to detect moisture on an opposite surface of the sheet of glass, said moisture sensor comprising:

a) a coupler for mounting on an inner surface of a sheet of glass, said coupler including a pair of prismatic refracting regions in spaced apart relationship;

b) a housing secured to said coupler;

c) a planar circuit board secured in said housing and having a device surface which is positioned generally parallel to the inner surface of the sheet of glass;

d) an emitter mounted on the device surface, said emitter emitting light beams with an optical axis approximately perpendicular to the device surface of said circuit board;

e) an emitter lens mounted in said housing and positioned between said emitter and a first prismatic region of said coupler, said emitter lens including a reflection surface;

f) a detector mounted on the device surface for detecting light beams striking the detector at an angle within an acceptance angle of said detector, and for generating control signals in response to the light beams; and

g) a detector lens having a reflection surface, said detector lens mounted in said housing and positioned between said detector and a second prismatic region of said coupler; and

said emitter lens, said coupler with prismatic refracting regions, and said detector lens positioned to form an optical path from said emitter to an outer surface of said glass, and back to said detector such that the light beams are emitted at an angle approximately perpendicular to said circuit board, are directed into and reflected from the sheet of glass at an angle between forty and fifty degrees, and are received at the detector at an angle within the acceptance angle of said detector.

2. The moisture sensor defined in claim 1, including a signal processing circuit mounted on said circuit board and connected to said emitter and said detector for controlling the light beams emitted by the emitter and for processing the control signals from said detector.

3. The moisture sensor defined in claim 1, including a plurality of emitters, emitter lenses, detectors, and detector lenses mounted on said circuit board and a corresponding plurality of prismatic refracting regions formed in said coupler, said emitters, emitter lenses, detectors, detector lenses, and prismatic regions being positioned to form a plurality of optical paths in which light beams are emitted at an angle approximately perpendicular to said circuit board, are directed into and reflected from the sheet of glass at an angle between forty and fifty degrees, and are received at the detector at an angle within the acceptance angle of said detector.

4. The moisture sensor defined in claim 1, wherein the prismatic refracting regions in said coupler include a convex surface for collimating the light beams.

5. The moisture sensor defined in claim 1, wherein said emitter lens and said detector lens each include a convex surface for collimating the light beams.

6. The moisture sensor defined in claim 5, wherein the convex surfaces are aspheric surfaces.

7. The moisture sensor defined in claim 1, wherein the combined reflection of the light beams by the emitter lens and refraction of the light beams by the first prismatic region deflects the light beams in the range between forty and fifty degrees, and the combined refraction of the light beams by the second prismatic region and reflection of the light beams by the detector lens deflects the light beams in the range between forty and fifty degrees.

8. The moisture sensor defined in claim 7, wherein the light beams are deflected approximately forty-five degrees by reflection in the emitter lens and refraction in the first prismatic region, and wherein the light beams are deflected approximately forty-five degrees by refraction in the second prismatic region and reflection in the detector lens.

9. The moisture sensor defined in claim 8, wherein the light beams are reflected approximately sixty degrees by said emitter lens and refracted approximately fifteen degrees by the first prismatic region, and wherein the light beams are refracted approximately fifteen degrees by the second prismatic region and reflected approximately sixty degrees by said detector lens.

10. The moisture sensor defined in claim 1, wherein said coupler has a thickness of 5 mm or less.

11. The moisture sensor defined in claim 1, wherein said emitter and said detector are surface mounted devices.

12. The moisture sensor defined in claim 1, wherein the prismatic refracting regions on said coupler include a surface formed at an angle of approximately twenty-one degrees with respect to the inner surface of the sheet of glass.

13. The moisture sensor defined in claim 1, wherein said coupler includes light blocking grooves.

14. The moisture sensor defined in claim 1, including light blockers mounted on said circuit board and positioned in proximity to said detector.

15. The moisture sensor defined in claim 1, wherein the light beams are received at said detector at an angle approximately perpendicular to said circuit board.

16. A moisture sensor for mounting on a surface of a sheet of glass to detect moisture on an opposite surface of the sheet of glass, said moisture sensor comprising:

a) a coupler for mounting on an inner surface of a sheet of glass, said coupler including three prismatic refracting regions in spaced apart relationship;

b) a housing secured to said coupler;

c) a planar circuit board secured in said housing and having a device surface which is positioned generally parallel to the inner surface of the sheet of glass;

d) a first emitter and a second emitter mounted on the device surface in spaced apart relationship, said emitters emitting light beams with an optical axis approximately perpendicular to the device surface of said circuit board;

e) a first emitter lens mounted in said housing and positioned between said first emitter and a first prismatic region, and a second emitter lens mounted in said housing and positioned between said second emitter and a second prismatic region, said emitter lenses including a reflection surface;

f) a detector mounted on the device surface for detecting light beams striking the detector at an angle within an acceptance angle of said detector, and for generating control signals in response to the light beams;

g) a detector lens having a reflection surface, said detector lens mounted in said housing and positioned between said detector and a third prismatic region of said coupler; and

said emitter lenses, said coupler with prismatic refracting regions, and said detector lens positioned to form a first optical path from said first emitter to an outer surface of said glass and back to said detector, and a second optical path from said second emitter to an outer surface of said glass and back to said detector, such that the light beams from said first and second emitters are emitted at an angle approximately perpendicular to said circuit board, are directed into and reflected from the sheet of glass at an angle between forty and fifty degrees, and are received at the detector at an angle within the acceptance angle of said detector.

17. The moisture sensor defined in claim 16, including a signal processing circuit mounted on said circuit board and connected to said emitters and said detector for controlling the light beams emitted by the emitters and for processing the control signals from said detector.

18. The moisture sensor defined in claim 16, wherein the light beams are received at said detector at an angle of approximately sixteen degrees with respect to a perpendicular axis extending from said detector on said circuit board.

19. The moisture sensor defined in claim 16, wherein the light beams are reflected approximately sixty degrees by said emitter lenses and refracted approximately fifteen degrees by the first prismatic region, and wherein the light beams are refracted approximately fifteen degrees by the second prismatic region and reflected approximately sixty degrees by said detector lens, and wherein the light beams are rotated within a plane of the windshield approximately eleven degrees by said emitter lenses and approximately five degrees by the third prismatic region of said coupler.

20. The moisture sensor defined in claim 16, including at least one additional optical set mounted on said circuit board, said optical sets comprising at least two emitters, a equivalent number of emitter lenses, a detector, and a detector lens, and a including a corresponding plurality of prismatic refracting regions formed in said coupler such that said emitters, emitter lenses, detectors, detector lenses, and prismatic regions being positioned to form a plurality of optical paths in which light beams are emitted at an angle approximately perpendicular to said circuit board, are directed into and reflected from the sheet of glass at an angle between forty and fifty degrees, and are received at the detectors at an angle within the acceptance angle of said detectors.