Compact moisture sensor with efficient high obliquity optics

• US 5,898,183 A
• Filed: 10/16/1997
• Issued: 04/27/1999
• Est. Priority Date: 10/16/1997
• 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): Allen, Stephone
• Application Number:
  US08/951,922
• Time in Patent Office: 558 Days
• Field of Search: 250/574, 250/227.25, 250/239, 250/341.8, 318/483, 318/DIG. 2, 340/602
• US Class Current: 250/574
• CPC Class Codes: B60S 1/0822 characterized by the arrangement or type of detection means
• CPC Class Codes: B60S 1/0837 with a particular arrangement of the optical elements
• CPC Class Codes: B60S 1/0888 characterized by the attachment of the elements in a unit
• CPC Class Codes: G01N 21/43 by measuring critical angle

Abstract

A compact moisture sensor for mounting on the inner surface of a windshield to detect moisture, such as rain, on the outer surface of the windshield and control the windshield wipers accordingly includes a coupler having a collimator and focuser and a housing for detachably covering the coupler. A planar circuit board disposed within the housing includes emitters and detectors mounted such that the axes of emission and detection are perpendicular to the windshield when the housing is secured to the coupler. The collimator and focuser are disposed adjacent the emitter and detector respectively such that the optical axes of the collimator and focuser form oblique angles with respect to the emission and detection axes. Two emitters and two detectors are used to form four optical paths of equal length and optical efficiency. 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 which signals control circuitry for operating the windshield wipers.

Claims

1. A moisture sensor for mounting on a first surface of a sheet of glass to detect moisture in a sensing area on a second surface of the sheet of glass, said moisture sensor comprising:

a) a coupler for mounting on the first surface of the sheet of glass for optically coupling light rays into and out of the glass;

b) a housing secured to said coupler;

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

d) an emitter mounted on said device surface for emitting light rays about an emission axis extending from said emitter approximately perpendicular to said device surface;

e) a collimator optically coupled to said coupler for collimating light rays from said emitter into a collimated light beam, said collimator having a light receiving aperture with a physical center and an optical center such that an optical axis extends through said optical center and said optical center is spaced apart from said physical center, said collimator being disposed such that the optical axis forms a first oblique angle with respect to the emission axis;

f) a detector having a detection surface and a detection axis extending from the detection surface for detecting light striking the detection surface about the detection axis and for generating signals in response to the detected light, said detector mounted on the device surface of said planar circuit board such that the detection axis is approximately perpendicular to the device surface; and

g) a focuser optically coupled to said coupler for focusing the collimated light beam into a convergent fan of rays onto said detection surface, said focuser having a light transmitting aperture with a physical center and an optical center such that an optical axis extends through said optical center and said optical center is spaced apart from said physical center, said focuser being disposed such that said optical axis forms a second oblique angle with respect to said detection axis.

2. The moisture sensor of claim 1 wherein said collimator includes a collimating lens, and said focuser includes a focusing lens.

3. The moisture sensor of claim 2 wherein said coupler, said collimator, said collimating lens, said focuser and said focusing lens are formed integrally from a single piece of material.

4. The moisture sensor of claim 1 further including a signal processing circuit mounted on said circuit board and connected to said emitter and said detector for controlling the light emitted by said emitter and for processing the signals from said detector.

5. The moisture sensor of claim 1 wherein said first oblique angle is between thirty-nine and fifty-one degrees and said second oblique angle is between thirty-nine and fifty-one degrees.

6. The moisture sensor of claim 1 wherein said optical center of said collimator light receiving aperture is displaced at least 20% of the width of said light receiving aperture from said physical center of said light receiving aperture.

7. The moisture sensor of claim 1 wherein said optical center of said focuser light transmitting aperture is displaced at least 20% of the width of said light transmitting aperture from said physical center of said light transmitting aperture.

8. The moisture sensor of claim 1 wherein said collimator is disposed to collimate light rays emitted from said emitter, wherein said light rays range from approximately ten to approximately fifty degrees with respect to said emission axis.

9. The moisture sensor of claim 1 wherein said focuser is disposed to focus a collimated light beam into a convergent fan of rays onto said detection surface, wherein said fan of light rays range from approximately ten to approximately fifty degrees with respect to said detection axis.

10. The moisture sensor of claim 2 wherein said collimating lens and said focusing lens are continuous convex lenses.

11. The moisture sensor of claim 1 wherein said collimator includes a segmented collimating lens and said focuser includes a segmented focusing lens.

12. The moisture sensor of claim 2 further wherein said collimator includes a second collimating lens and said focuser includes a second focusing lens, and said moisture sensor further including a second emitter and a second detector mounted on said device surface, a second collimator optically coupled to said coupler and including third and fourth collimating lenses, and a second focuser optically coupled to said coupler and including third and fourth focusing lenses, wherein light rays from both emitters are collimated into light beams and said light beams are focused onto both detectors.

13. A moisture sensor for mounting on a first surface of a sheet of glass to detect moisture in a plurality of sensing areas on a second surface of the sheet of glass, said moisture sensor comprising:

a) a housing;

b) first and second emitters disposed in said housing for emitting light rays;

c) a first detector disposed in said housing for detecting light rays traveling along a first optical path extending from said first emitter to the second surface of said glass at one of the sensing areas and back to said first detector and for detecting light rays traveling along a second optical path extending from said second emitter to the second surface of said glass at one of the sensing areas and back to said first detector, wherein the length of said second optical path is approximately equal to the length of said first optical path; and

d) a second detector disposed in said housing for detecting light rays traveling along a third optical path extending from said first emitter to the second surface of said glass at one of the sensing areas and back to said second detector and for detecting light rays traveling along a fourth optical path extending from said second emitter to the second surface of said glass at one of the sensing areas and back to said second detector, wherein the lengths of said third and fourth optical paths are approximately equal to the length of said first optical path.

14. The moisture sensor of claim 13 further including a coupler having collimators for collimating a portion of light rays emitted from said emitters about emission axes extending perpendicularly with respect to the first surface of the sheet of glass into collimated light beams traveling along said optical paths, and focusers for focusing said collimated beams into convergent rays onto said detectors having detection axes extending perpendicularly with respect to the first surface of the sheet of glass.

15. The moisture sensor of claim 14 wherein said collimators include a light receiving aperture with a physical center and an optical center such that an optical axis extends through said optical center and said optical center is spaced apart from said physical center, said collimators being disposed such that said optical axes form first oblique angles with respect to said emission axes, and wherein said focusers include a light transmitting aperture with a physical center and an optical center such that an optical axis extends through said optical center and said optical center is spaced apart from said physical center, said focusers being disposed such that said optical axes form second oblique angles with respect to said detection axes.

16. A moisture sensor for mounting on a first surface of a sheet of glass to detect moisture in a plurality of sensing areas on a second surface of the sheet of glass, said moisture sensor comprising:

a) a first emitter for emitting light rays disposed at a first corner of a square;

b) a second emitter for emitting light rays disposed at a second corner of the square, opposite the first corner;

c) a first collimator disposed adjacent said first emitter for collimating light rays emitted from said first emitter into a first and second collimated light beam;

d) a second collimator disposed adjacent said second emitter for collimating light rays emitted from said second emitter into a third and fourth collimated light beam;

e) a first detector disposed at a third corner of the square for detecting said first collimated light beam traveling along a first optical path between said first emitter and said first detector and said third collimated light beam traveling along a second optical path between said second emitter and said first detector, said second optical path having a length approximately equal to said first optical path, and for generating signals in response to the detected light beams; and

f) a second detector disposed at a fourth corner of the square opposite the third corner for detecting said second collimated light beam traveling along a third optical path between said first emitter and said second detector and said fourth collimated light beam traveling along a fourth optical path between said second emitter and said second detector, said third and fourth optical paths each having a length approximately equal to said first optical path, and for generating signals in response to the detected light beams.

17. A moisture sensor for mounting on a first surface of a sheet of glass to detect moisture in a sensing area on a second surface of the sheet of glass, said moisture sensor comprising:

a) a coupler having a mounting surface for mounting on the first surface of the sheet of glass for coupling light rays into and out of the glass;

b) a sleeve disposed about the perimeter of said coupler and extending from said coupler opposite said mounting surface;

b) tabs extending outwardly from said sleeve;

c) a housing for fitting over said sleeve having a base and side walls extending from said base, said side walls having interior surfaces with grooves formed therein, said housing detachably fitting over said sleeve such that said tabs extend into said grooves for securing said housing to said coupler;

d) a planar circuit board secured in said housing and having a device surface for receiving electronic components;

e) an emitter mounted on said device surface for emitting light rays symmetrically about an emission axis; and

f) a detector mounted on said device surface having a detection surface for detecting light emitted by said emitter and for generating control signals in response to said detected light.

18. The moisture sensor of claim 17 further including a collimator extending from the surface of said coupler opposite said mounting surface for collimating light rays emitted from said emitter into a collimated light beam, and a focuser extending from the surface of said coupler opposite said mounting surface for focusing the collimated light beam into a convergent fan of light rays onto said detection surface.

19. The moisture sensor of claim 18 wherein said emitter includes an emission axis extending from said emitter approximately perpendicular to said device surface, and said detector includes a detection axis extending from said detection surface approximately perpendicular to said device surface.

20. The moisture sensor of claim 19 wherein said collimator includes a light receiving aperture with a physical center and an optical center such that an optical axis extends through said optical center and said optical center is spaced apart from said physical center, said collimator being disposed such that the optical axis forms a first oblique angle with respect to the emission axis, and said focuser includes a light transmitting aperture with a physical center and an optical center such that an optical axis extends through said optical center and said optical center is spaced apart from said physical center, said focuser and said detector being disposed such that said optical axis forms a second oblique angle with respect to said detection axis.