US 6,353,392 · Granted 2002-03-05
The Rain Sensor That Knows the Difference Between Rain and Fog
Imagine a camera on your windshield that's smart enough to tell rain from fog—so your wipers don't go crazy when the window just gets steamy. This patent uses light sensors and edge-detection smarts to figure out whether droplets are actually rain or just moisture, keeping your wipers from being annoying.
The plain-English version
What it protects
The claim covers a rain detection system that uses an imaging array sensor mounted separately from the window to analyze light patterns and edges of water droplets. What's protected here is the combination of the decoupled illumination sensor, edge detection logic that identifies droplet boundaries, a threshold-based activation method for wipers, and specifically the use of polarizing filters and illumination sources to discriminate between rain on the exterior surface and fog or condensation on the interior surface.
Why it matters
Before this patent, rain sensors often triggered false alarms when a windshield fogged up or got steamed from the inside, causing wipers to activate unnecessarily and frustrate drivers. By teaching the sensor to distinguish between exterior precipitation and interior moisture through optical filtering and edge detection, Donnelly created a more reliable automatic wiper system. This became important for premium vehicles where convenience features needed to actually work without annoying the driver.
Real-world use
When you're driving on a foggy morning and your windshield fogs up from inside the car, the wipers stay off because the system recognizes it's not real rain—only when actual raindrops hit the outside does the system spring into action.
Original USPTO abstract
A vehicular rain sensor system for detecting precipitation on an exterior surface of a window includes an illumination sensor that is decoupled from the window. The illumination sensor is preferably an imaging array sensor which communicates a signal to a control which further determines whether rain is present on the window. The control includes an edge detection function for detecting edges of precipitation droplets on the window in response to the light values sensed by the sensor and activating the windshield wipers of the vehicle when the sum of the light values exceeds a predetermined threshold value. The rain sensor system may further include a polarizing filter and an illumination source, such that the rain sensor system not only prevents false signals of rain when only fog is present on an interior surface of the window, but also actually detects fog particles on an interior surface of the window.
Patent details
- Publication number
- US 6,353,392
- Filing date
- 1998-10-30
- Grant date
- 2002-03-05
- Assignee
- Donnelly Corporation
- Inventor(s)
- SCHOFIELD KENNETH, LARSON MARK L., BOS BRENT J, LYNAM NIALL R
- CPC class
- B60H1/00785
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