Raindrop sensor and wiper controller having the same

• US 20070272884A1
• Filed: 05/15/2007
• Published: 11/29/2007
• Est. Priority Date: 05/16/2006
• Status: Active Grant

• Current Assignee: DENSO Corporation, Nippon Soken, Inc.
• Original Assignee: DENSO Corporation, Nippon Soken, Inc.
• Inventors: Imanishi, Masayuki, Yamamoto, Atsushi, Michiyama, Katsunori, Utida, Akira
• Granted Patent: US 7,612,356 B2
• Time in Patent Office: Days
• US Class Current: 250/573
• 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: G06T 7/42 using transform domain methods
• CPC Class Codes: G06V 10/507 Summing image-intensity values; Histogram projection analysis
• CPC Class Codes: G06V 20/56 exterior to a vehicle by using sensors mounted on the vehicle

Abstract

A raindrop sensor includes an image sensor and an image processor. The image sensor captures an image of a windshield from inside a vehicle. The image processor performs a frequency analysis of the image to detect a high-frequency component in the image. When the high-frequency component is detected, the image processor detects a width of a change region where a change in gradation of the image occurs. When the width of the change region is within a predetermined range corresponding to a diameter of a raindrop, the image processor determines that the raindrop is on the windshield. Even when a foreign matter such as a water stain appears as the high-frequency component as a result of the frequency analysis, the raindrop and the foreign matter can be distinguished from each other based on the width of the change region.

Claims

1. A raindrop sensor for detecting a raindrop on a windshield of a vehicle, the raindrop sensor comprising:

capturing means for capturing an image of the windshield from inside the vehicle;

high-frequency component determination means for performing a frequency analysis of the image and for determining based on a result of the frequency analysis whether the image has a high-frequency component;

gradation change detection means that operates when the image has the high-frequency component to detect a width of a change region where a change in gradation of the image occurs; and

raindrop determination means for determining that the raindrop is on the windshield when the width of the change region is within a predetermined range corresponding to a diameter of the raindrop.

2. The raindrop sensor according to claim 1, wherein

the gradation change detection means detects an amount of the change in gradation within the change region, and

the raindrop determination means determines that the raindrop is on the windshield when the width of the region is within the predetermined range and the amount of the change in gradation of the image is greater than a predetermined level.

3. The raindrop sensor according to claim 1, further comprising:

a lamp for emitting a near infrared light, wherein

the gradation change detection means detects an average gradation of the image, and

the lamp emits the near infrared light to the windshield from inside the vehicle when the average gradation is less than a predetermined value.

4. The raindrop sensor according to claim 3, wherein

the capturing means includes a bandpass filter for allowing passage of the near infrared light.

5. The raindrop sensor according to claim 1, wherein

the capturing means captures a road scene ahead of the vehicle through the windshield to detect a lane or an oncoming vehicle.

6. The raindrop sensor according to claim 5, wherein

the capturing means includes a variable focus lens that focuses on the windshield to detect the raindrop on the windshield.

7. The raindrop sensor according to claim 6, wherein

the variable focus lens is one of a liquid lens and a liquid crystal lens each of which has a focal length controllable by an electric voltage or an electric current.

8. A wiper controller for controlling a windshield wiper of a vehicle, the wiper controller comprising:

capturing means for capturing an image of a windshield of the vehicle from inside the vehicle;

high-frequency component determination means for performing a frequency analysis of the image and for determining based on a result of the frequency analysis whether the image has a high-frequency component;

gradation change detection means that operates when the image has the high-frequency component to detect a width of a change region where a change in gradation of the image occurs;

raindrop determination means determining that the raindrop is on the windshield when the width of the change region is within a predetermined range corresponding to a diameter of the raindrop; and

control means for controlling the windshield wiper in accordance with an amount of the raindrop on the windshield.

9. The wiper controller according to claim 8, wherein

the gradation change detection means detects an amount of the change in gradation within the change region, and

the raindrop determination means determines that the raindrop is on the windshield when the width of the change region is within the predetermined range and the amount of the change in gradation of the image is greater than a predetermined level.

10. The wiper controller according to claim 8, further comprising:

splash detection means for detecting water splashed on the windshield, wherein

the splash detection means determines that the splashed water is on the windshield, when a first image captured at a first time has no high-frequency component, a second image captured at a second time subsequent to the first time has the high-frequency component, the second image includes at least two change regions, and the width of each of at least two of the at least two regions is outside the predetermined range, and

the control means causes the windshield wiper to wipe the splashed water from the windshield when the splash detection means determines that the splashed water is on the windshield.

11. The wiper controller according to claim 8, further comprising:

a lamp for emitting a near infrared light, wherein

the gradation change detection means detects an average gradation of the image, and

the lamp emits the near infrared light to the windshield from inside the vehicle when the average gradation is less than a predetermined value.

12. The wiper controller according to claim 11, further comprising:

the capturing means includes a bandpass filter for allowing passage of the near infrared light.

13. The wiper controller according to claim 8, wherein

the high-frequency component determination means performs the frequency analysis of a first portion of the image and determines, based on the result of the frequency analysis of the first portion of the image, whether the first portion of the image has the high-frequency component,

the gradation change detection means detects the width of the change region where the change in gradation of the first portion of the image occurs,

the raindrop determination means determines that the raindrop is on the windshield when the width of the change region is within the predetermined range, and

the first portion of the image corresponds to a second portion of the windshield, the second portion being swept by the windshield wiper.

14. The wiper controller according to claim 8, further comprising:

a lamp for emitting a near infrared light to the windshield from inside the vehicle; and

fogging determination means for detecting a fogging on an interior surface of the windshield based on the amount of the near infrared light reflected by the windshield to the capturing means, wherein

the control means activates an air-conditioner of the vehicle or switches the air-conditioner to a defrost mode when the fogging on the interior surface of the windshield is detected.