System for detecting droplets on a translucent surface

• US 7,253,898 B2
• Filed: 03/31/2005
• Issued: 08/07/2007
• Est. Priority Date: 03/31/2005
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Oho, Shigeru, Saikalis, George
• Primary Examiner(s): Chowdhury; Tarifur
• Assistant Examiner(s): Cartoon; Daniel
• Application Number:
  US11/096,172
• Publication Number:
  US 20060221342A1
• Time in Patent Office: 859 Days
• Field of Search: 356/239.1, 356/4, 356/5, 356/7, 356/8, 356335-343, 356/432, 356/221, 356/226, 356/227, 356/223, 356/230, 250/227.25, 250/559.4, 250/573, 250/208.1, 250/205, 250/201.1, 250/206, 340/601, 340/602, 345/8
• US Class Current: 356/338
• CPC Class Codes: B60S 1/0822 characterized by the arrangement or type of detection means
• CPC Class Codes: B60S 1/0833 Optical rain sensor
• CPC Class Codes: B60S 1/0844 including a camera
• CPC Class Codes: G01N 21/958 Inspecting transparent materials or objects, e.g. windscreens for conveyed flat sheet or rod G01N21/896
• CPC Class Codes: G06V 20/56 exterior to a vehicle by using sensors mounted on the vehicle

Abstract

A system which detects droplets on a translucent surface having a camera which, upon activation, acquires an image of a portion of the surface. A radiation source, upon activation, illuminates the portion of the translucent surface while a control circuit selectively activates both the camera and the radiation source. A processor receives a captured image from the camera and, through image processing, generates an output signal representative of the number of droplets on the portion of the translucent surface.

Claims

1. A system for detecting droplets on a translucent surface comprising:

a camera which, upon activation, acquires an image of at least a portion of the translucent surface and generates an output signal representative of said image,

a radiation source which, upon activation, illuminates the at least a portion of the translucent surface,

a control circuit which selectively activates said camera and said radiation source,

a processor which receives said camera output signal and, through image processing, generates an output signal representative of the magnitude of droplets on the at least a portion of the translucent surface,

wherein said radiation source comprises a visible light source, and

wherein during activation of said radiation source, said control circuit activates said radiation source for a sufficiently short period of time so as to be undetectable to a human eye.

2. The invention as defined in claim 1 wherein said control circuit activates said camera to produce a first and a second sequential image, said control circuit deactivating said radiation source during one of said first and second sequential image and activating said radiation source during the other of the first and second sequential image, said processor output signal representing the difference between said first and said second sequential image.

3. The invention as defined in claim 1 wherein said control circuit iteratively activates said camera and said radiation source.

4. The invention as defined in claim 1 wherein said camera comprises a charge coupled device.

5. The invention as defined in claim 4 wherein said control circuit activates said radiation source a predetermined time period after activation of said camera.

6. The invention as defined in claim 1 wherein said control circuit comprises a brightness control circuit which varies the brightness of the radiation source.

7. The invention as defined in claim 1 wherein said control circuit comprises a pulse width circuit which varies the duration of activation of said radiation source.

8. The invention as defined in claim 1 wherein said processor generates an output signal representative of the size of the droplets in the at least a portion of the translucent surface.

9. The invention as defined in claim 1 wherein said magnitude of droplets comprises the number of droplets on said portion of the translucent surface.

10. The invention as defined in claim 1 wherein said magnitude of droplets comprises the proportion of area coverage of said droplets on said portion of said translucent surface.

11. For use in conjunction with a translucent windshield and a variable speed windshield wiper which, when activated, wipes droplets from the windshield, a system for detecting droplets on the windshield comprising:

a camera which, upon activation, acquires an image of at least a portion of the windshield and generates an output signal representative of said image,

a visible light radiation source which, upon activation, illuminates the at least a portion of the windshield,

a control circuit which selectively activates said camera and said radiation source,

a processor which receives said camera output signal and, through image processing, generates an output signal representative of the magnitude of droplets on the at least a portion of the translucent surface,

a wiper speed control circuit which receives said processor output signal and varies the speed of the windshield wiper as a function of said processor output signal,

wherein said control circuit comprises a brightness control circuit which varies the brightness of the radiation source, and

wherein during activation of said radiation source, said control circuit activates said radiation source for a sufficiently short period of time so as to be undetectable to a human eye.

12. The invention as defined in claim 11 wherein said control circuit activates said camera to produce a first and a second sequential image, said control circuit deactivating said radiation source during one of said first and second sequential image and activating said radiation source during the other of the first and second sequential image, said processor output signal representing the difference between said first and said second sequential image.

13. The invention as defined in claim 11 wherein said radiation source comprises a light source.

14. The invention as defined in claim 11 wherein said radiation source comprises an infrared radiation source.

15. The invention as defined in claim 11 wherein said control circuit iteratively activates said camera and said radiation source.

16. The invention as defined in claim 11 wherein said camera comprises a charge coupled device.

17. The invention as defined in claim 16 wherein said control circuit activates said radiation source a predetermined time period after activation of said camera.

18. The invention as defined in claim 11 wherein said control circuit comprises a pulse width circuit which varies the duration of activation of said radiation source.

19. The invention as defined in claim 11 wherein said processor generates an output signal representative of the size of the droplets in the at least a portion of the windshield.

20. The invention as defined in claim 11 wherein said magnitude of droplets comprises the number of droplets on said portion of the translucent surface.

21. The invention as defined in claim 11 wherein said magnitude of droplets comprises the proportion of area coverage of said droplets on said portion of said translucent surface.

22. The invention as defined in claim 11 wherein said processor generates said output signal representative of a rolling average of the magnitude of droplets on said portion of said translucent surface.

23. A method for detecting droplets on a translucent surface comprising the steps of:

acquiring an image of at least a portion of the translucent surface,

generating an output signal representative of said image,

illuminating the at least a portion of the translucent surface with a pulse of visible light having a duration undetectable to a human eye,

image processing said image to generate an output signal representative of the magnitude of droplets on the at least a portion of the translucent surface.

24. The invention as defined in claim 23 wherein said image acquiring step further comprises the steps of acquiring two sequential images wherein only one of said images is acquired during said illuminating step, and wherein said image processing step comprises the step of determining differences between said two sequential images.

25. The invention as defined in claim 23 and further comprising the step of varying the brightness of said illuminating step.

26. The invention as defined in claim 23 wherein said image processing step comprises the step of determining the size of droplets on the translucent surface.

27. The invention as defined in claim 23 wherein said image processing step comprises the step of determining the number of droplets on the translucent surface.