Rain sensor with sigma-delta modulation and/or footprinting comparison(s)

• US 7,492,270 B2
• Filed: 01/27/2006
• Issued: 02/17/2009
• Est. Priority Date: 01/10/2006
• Status: Expired due to Fees

• Current Assignee: Guardian Glass LLC (KOCH Industries Incorporated)
• Original Assignee: Guardian Industries Corporation (KOCH Industries Incorporated)
• Inventors: Veerasamy, Vijayen S.
• Primary Examiner(s): Bugg; George A
• Assistant Examiner(s): Walk; Samuel J
• Application Number:
  US11/340,864
• Publication Number:
  US 20070157721A1
• Time in Patent Office: 1,117 Days
• Field of Search: 340/438, 340602-604, 343/713
• US Class Current: 340/602
• CPC Class Codes: B32B 17/10036 comprising two outer glass sheets
• CPC Class Codes: B32B 17/10174 Coatings of a metallic or dielectric material on a constituent layer of glass or polymer
• CPC Class Codes: B32B 17/10761 containing vinyl acetal
• CPC Class Codes: B60S 1/0818 including control systems responsive to external conditions, e.g. by detection of moisture, dirt or the like
• CPC Class Codes: B60S 1/0822 characterized by the arrangement or type of detection means
• CPC Class Codes: B60S 1/0825 Capacitive rain sensor
• CPC Class Codes: G06V 20/56 exterior to a vehicle by using sensors mounted on the vehicle

Abstract

A system and/or method for sensing the presence of moisture (e.g., rain) and/or other material(s) on a window such as a vehicle window (e.g., vehicle windshield, sunroof or backlite). In certain example embodiments of the invention, at least one sensing capacitor is supported by a window such as a vehicle windshield, the capacitor(s) having a field that is affected by moisture (e.g., rain) on a surface of the window. A sensing circuit outputs an analog signal that is based on and/or related to the capacitance(s) of the sensing capacitor(s). The analog output of the circuit may be converted to a digital signal via sigma-delta modulation, and subjected to processing (e.g., correlation) for determining whether moisture (e.g., rain, dew, fog, etc.) or the like is present on the surface of the window.

Claims

1. A rain sensor comprising:

a sensing circuit comprising at least one sensing capacitor that is sensitive to moisture on an external surface of a window;

an adder receiving, directly or indirectly, an analog output signal from the sensing circuit and determining a difference between the analog output signal from the sensing circuit and a feedback signal;

a quantizer including a comparator downstream of the adder that outputs a bitstream based at least on whether a received signal level is higher or lower than a predetermined threshold;

a lowpass digital filter downstream of the quantizer for lowpass filtering the bitstream so as to output a filtered digital signal; and

a correlation engine that performs correlation on the filtered digital signal in order to determine whether rain is present on the external surface of the window.

2. The rain sensor of claim 1, wherein the correlation is autocorrelation and/or cross-correlation.

3. The rain sensor of claim 1, wherein a feedback loop (a) receives a digital signal from between an output of the quantizer and an input of the lowpass digital filter, (b) converts the digital signal to an analog signal, and (c) provides the analog signal to the adder.

4. The rain sensor of claim 1, wherein the quantizer comprises the comparator and a latch downstream of the comparator, the latch receiving a clock signal from a clock.

5. The rain sensor of claim 1, wherein the sensing capacitor comprises a fractal geometry.

6. The rain sensor of claim 5, wherein the fractal geometry is selected from the group consisting of a Hilbert fractal and a Cantor fractal.

7. The rain sensor of claim 1, wherein first and second capacitor electrodes of the sensing capacitor each have a meandering shape and are substantially parallel to each other.

8. The rain sensor of claim 1, wherein the window is at least one of a vehicle windshield, a vehicle backlite, and a vehicle sunroof.

9. The rain sensor of claim 1, wherein the rain sensor comprises at least first and second sensing capacitors of approximately the same size that are sensitive to moisture on the external surface of the window.

10. The rain sensor of claim 1, further comprising means for autocorrelating data relating to or from the sensing capacitor to obtain autocorrelated data, and means for determining based at least on said autocorrelated data whether moisture is present on the external surface of the window.

11. The rain sensor of claim 1, wherein an opaque layer is provided on the window so as to shield at least the first sensing capacitor from a view of a passenger inside the vehicle.

12. The rain sensor of claim 1, wherein the sensing circuit further comprises at least one mimicking capacitor that mimics at least charging or discharging of the sensing capacitor, wherein a writing pulse causes at least the sensing capacitor to be charged and an erasing pulse causes each of the sensing capacitor and the mimicking capacitor to substantially discharge;

wherein presence of rain on the external surface of the window in a sensing field of the sensing capacitor causes a voltage at an output electrode of the mimicking capacitor to fluctuate in a manner proportional to fluctuation of voltage at an output electrode of the sensing capacitor even though the rain is not present in a field of the mimicking capacitor; and

wherein an output signal from the output electrode of the mimicking capacitor is sent to the adder.

13. The rain sensor of claim 1, wherein a first capacitor electrode of the sensing capacitor receives a charging signal and a second capacitor electrode of the sensing capacitor is spaced apart from the first capacitor electrode;

and wherein the second capacitor electrode is floating so that the sensing capacitor is isolated from ground.

14. The rain sensor of claim 1, further comprising at least one correlating engine that (a) autocorrelates information from, or relating to, the sensing capacitor to determine whether rain is present on the external surface of the window, and/or (b) cross-correlates information from, and/or relating to, the sensing capacitor to determine how fast to operate at least one wiper of a vehicle and/or an amount of rain on the external surface of the window.