Detection of raindrops on a pane by means of a camera and lighting

• US 9,335,264 B2
• Filed: 09/20/2011
• Issued: 05/10/2016
• Est. Priority Date: 11/30/2010
• Status: Active Grant

• Current Assignee: Conti Temic Microelectronic GmbH (Continental AG)
• Original Assignee: Conti Temic Microelectronic GmbH (Continental AG)
• Inventors: Kroekel, Dieter, Chivukula, Radhakrishna
• Primary Examiner(s): Chowdhury, Tarifur
• Assistant Examiner(s): Gray, Sunghee Y
• Application Number:
  US13/885,552
• Publication Number:
  US 20130235381A1
• Time in Patent Office: 1,694 Days
• Field of Search: 356/445, 348/E5.034, 348/E5.085, 348/148, 340/602, 340/601, 250/214.R, 250/574, 250/227, 250/25, 250/341.8
• US Class Current: 1/1
• CPC Class Codes: B60S 1/0844 including a camera
• CPC Class Codes: G01N 2021/435 Sensing drops on the contact surface
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G01N 21/552 Attenuated total reflection
• CPC Class Codes: G06V 20/56 exterior to a vehicle by using sensors mounted on the vehicle

Abstract

A device and a method for detecting rain on a pane, e.g. of a motor vehicle, use a camera or other light sensor and a lighting source. The camera is disposed behind an inner surface of the pane and focused onto a far range that lies in front of an outer surface of the pane. The lighting source generates a source light beam and directs it onto the inner surface of the pane such that at least one resultant reflected beam (r2; r2′) that is reflected from the outer surface of the pane impinges on the camera. The light quantity of the at least one resultant reflected beam is measured by the camera.

Claims

1. A device for detecting rain (4) on an outer surface of a pane, comprising

a camera disposed behind an inner surface of the pane (2), wherein the camera (1) is focused onto a far range that lies in front of the outer surface of the pane (2), and

a lighting source (3) adapted to generate a source light beam and configured and arranged to direct the source light beam (h;

n) through air onto the inner surface of the pane (2) so as to cause a resultant transmitted beam that is transmitted in the pane and impinges on the outer surface within the pane and is partially reflected from the outer surface (2.2) within the pane (2) to cause a partially reflected beam (r2;

r2′

) that impinges on the camera (1); and

wherein the camera is configured and adapted to measure a light quantity of the partially reflected beam (r2;

r2′

) impinging on the camera.

2. The device according to claim 1, wherein an angle of incidence of the source light beam (h;

n) onto the inner surface of the pane is set up such that the resultant transmitted beam (tl), which is transmitted in the pane and impinges on the outer surface (2.2) of the pane (2), is more reflected to form said partially reflected beam than decoupled (t2) out of the pane, when there is no rain (4) on the outer surface (2.2) of the pane (2).

3. The device according to claim 1, further comprising an evaluation unit configured to determine from the measured light quantity of the partially reflected beam whether or not there is rain (4) on the outer surface (2.2) of the pane (2).

4. The device according to claim 3, wherein the evaluation unit is configured to compare the measured light quantity of the partially reflected beam (r2;

r2′

) with a threshold value.

5. The device according to claim 3, wherein the evaluation unit is configured to determine a time variation of the measured light quantity.

6. The device according to claim 1, wherein the lighting source (3) is configured and arranged to direct the source light beam (h;

n) towards the pane (2) such that the partially reflected beam (r2 or r2′

) that is partially reflected from the outer surface of the pane and another beam (rl) that is reflected from the inner surface (2.1) of the pane respectively impinge as two spatially separated beams (rl;

r2 or r2′

) on the camera (1), and respective light quantities of the two spatially separated beams (rl;

r2 or r2′

) impinging on the camera (1) can be respectively measured by the camera (1).

7. The device according to claim 1, wherein the lighting source (3) is structurally integrated into a housing of the camera (1).

8. The device according to claim 7, wherein the lighting source (3) is arranged below a view shield (11) of the camera (1).

9. The device according to claim 8, wherein the lighting source (3) is configured to generate light of the source light beam in an infrared wavelength range and the view shield (11) is permeable in the infrared wavelength range at least in a portion of the view shield, which is located above the lighting source (3).

10. The device according to claim 7, wherein the lighting source (3) is arranged on a circuit carrier (12) of the camera (1).

11. The device according to claim 1, wherein the lighting source (3) is configured to generate the source light beam with only light having a wavelength in a specific wavelength range, and wherein a first spectral filter is arranged in the beam path of the camera (1) in a region, through which the partially reflected beam (r2;

r2′

) passes, and wherein the first spectral filter is permeable to light having a wavelength in the specific wavelength range.

12. The device according to claim 11, wherein the lighting source (3) is configured and arranged to direct the source light beam (h;

n) towards the pane (2) such that the partially reflected beam (r2 or r2′

) and another beam (rl) that is reflected from the inner surface (2.1) of the pane respectively impinge as two spatially separated beams (rl;

r2 or r2′

) on the camera (1), and respective light quantities of the two spatially separated beams (rl;

r2 or r2′

) impinging on the camera (1) can be respectively measured by the camera (1), wherein a second spectral filter is arranged in a region of the beam path, through which the two spatially separated beams (r1;

r2 or r2′

) do not pass, and wherein the second spectral filter blocks light having a wavelength in the specific wavelength range.

13. The device according to claim 12, wherein the camera (1) comprises an image sensor (5), and wherein the first spectral filter or the first and second spectral filters are applied directly on pixels of the image sensor (5).

14. The device according to claim 1, wherein the lighting source (3) is configured to generate a focused light beam (h) as the source light beam.

15. The device according to claim 1, further comprising a light guide, wherein the source light beam (h) generated by the lighting source (3) is directed by the light guide (13) and emitted from the light guide through the air onto the inner surface of the pane (2).

16. A method for detecting rain (4) on the outer surface (2.2) of the pane (2) by the device according to claim 1, comprising the steps:

with the camera, recording a first image with the lighting source (3) turned off,

with the camera, recording a second image with the lighting source (3) turned on,

forming a difference image from the second and first images, and

in the difference image, evaluating a light quantity of the partially reflected beam (r2;

r2;

′

) to detect whether there is rain (4) on the outer surface (2.2) of the pane.

17. The device according to claim 1, wherein the pane and the lighting source are configured and arranged so that the source light beam is directed through the air directly onto the inner surface of the pane, and wherein the inner surface of the pane forms an air-pane-interface for the source light beam.

18. The device according to claim 1, not including an optical coupling element on the inner surface of the pane for coupling the source light beam into the pane.

19. The device according to claim 1, wherein the light source is configured and arranged to direct the source light beam onto the inner surface of the pane at an incidence angle such that the resultant transmitted beam is always only partially reflected from the outer surface within the pane including when there is rain on the outer surface and when there is no rain on the outer surface.

20. A method for detecting rain (4) on an outer surface (2.2) of a pane (2), comprising the steps:

providing a camera (1) disposed behind an inner surface of the pane (2) and focused onto a far range in front of the outer surface of the pane,

with a lighting source (3), generating a source light beam (h;

n), and directing the source light beam (h;

n) through air onto the inner surface of the pane (2) so as to cause a resultant transmitted beam that is transmitted in the pane and impinges on the outer surface within the pane and is partially reflected from the outer surface (2.2) within the pane (2) to cause a partially reflected beam that impinges on the camera (1),

using the camera, measuring a light quantity of the partially reflected beam (r2;

r2′

), and

evaluating the measured light quantity of the partially reflected beam (r2;

r2′

) to detect whether there is rain (4) on the outer surface (2.2) of the pane (2).

21. A device for detecting rain on an outer surface of a pane, comprising:

a light source arranged behind an inner surface of said pane, adapted to generate a source light beam, and configured and arranged to direct said source light beam through air onto said inner surface of said pane at an incidence angle so as to cause a resultant first transmitted beam that is transmitted within said pane and impinges on said outer surface within said pane, and such that said first transmitted beam is only partially reflected from said outer surface internally in said pane to cause a second reflected beam that is emitted through said inner surface out of said pane; and

a camera that is arranged behind said inner surface of said pane, and is focused onto a far range that lies in front of said outer surface of said pane, and is configured and arranged to receive said second reflected beam and measure a light quantity of said second reflected beam.

22. The device according to claim 21, wherein said pane and said light source are configured and arranged so that said source light beam is directed through said air directly onto said inner surface of said pane, and wherein said inner surface of said pane forms an air-pane-interface for said source light beam.

23. The device according to claim 21, not including an optical coupling element on said inner surface of said pane for coupling said source light beam into said pane.

24. The device according to claim 21, wherein said light source is configured and arranged to direct said source light beam onto said inner surface of said pane at such a value of said incidence angle such that said first transmitted beam is always only partially reflected from said outer surface internally in said pane including when there is rain on said outer surface and when there is no rain on said outer surface.