Measuring and testing – Moisture content or absorption characteristic of material
Reexamination Certificate
2002-12-03
2004-10-12
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Moisture content or absorption characteristic of material
C073S074000, C318S443000, C318S444000, C318S448000
Reexamination Certificate
active
06802205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to moisture detection and, more particularly, to moisture detection on a vehicle windshield.
2. Description of the Prior Art
Heretofore, the detection of moisture on a windshield of a vehicle was accomplished in four basic manners. Namely, capacitive sensor systems, resistive sensor systems, ultrasonic sensor systems and optical sensor systems.
A capacitive sensor system includes a capacitor formed on the windshield. In response to moisture on the windshield, the capacitance of the capacitor changes. A sensing circuit is connected to detect the changing capacitance and to control the operation of a windshield wiper as a function of the changing capacitance. Examples of capacitive moisture sensors include U.S. Pat. No. 5,668,478 to Buschur; U.S. Pat. No. 5,682,788 to Netzer; U.S. Pat. No. 5,801,307 to Netzer; and U.S. Pat. No. 6,094,981 to Hochstein.
A resistive measurement system includes two conductive elements disposed in spaced relation on the windshield, or another part of the vehicle, such as a conventional whip antenna. Circuitry coupled to the conductive elements measures a change in resistance thereof in response to water bridging the resistive elements and controls the operation of the windshield wiper as a function of the change in resistance. Examples of resistive measurement systems include U.S. Pat. No. 5,659,294 to Schroder; U.S. Pat. No. 5,598,146 to Schroder; U.S. Pat. No. 5,780,718 to Weber; U.S. Pat. No. 5,780,719 to VanDam; U.S. Pat. No. 5,783,743 to Weber; and U.S. Pat. No. 5,900,821 to Petzold.
An ultrasonic sensor system includes a transducer which emits an ultrasonic signal toward a first face of a sheet and receives a reflected ultrasonic signal on a second face of the sheet. The variation in the reflected signal is utilized to determine the presence or absence of foreign bodies on the second face of the sheet. Examples of ultrasonic sensor systems include U.S. Pat. No. 5,818,341 to Saurer et al. and European Publication No. EP 0638822.
An optical sensor system includes a light detector positioned to detect light reflected off a windshield from a light source. In response to the presence of moisture on the windshield, the amount of light detected by the light sensor will change due to changing reflection of the light from the light source, thus causing a change in the output of the light sensor. Detecting circuitry detects the change in output from the light detector in response to the change in light impinging thereon and operates the windshield wiper as a function of the change. Examples of light detecting systems include U.S. Pat. No. 5,694,012 to Pientka et al.; U.S. Pat. No. 5,990,647 to Zettler; U.S. Pat. No. 6,052,196 to Pientka et al.; U.S. Pat. No. 6,066,933 to Ponziana; U.S. Pat. No. 6,084,519 to Coulling et al.; U.S. Pat. No. 6,207,967 to Hochstein; U.S. Pat. No. 5,661,303 to Teder; U.S. Pat. No. 6,250,148 to Lynam; U.S. Pat. No. 6,218,741 to Braun et al.; and U.S. Pat. No. 6,232,603 to Nelson.
A problem with a capacitive sensor system includes the need to form a capacitor having sufficient capacitance whereupon the change in capacitance in response to the presence of rain on the windshield can be detected by suitable detection circuitry. Another problem with a capacitive sensor system is the change in capacitance due to heating or cooling of the metal films forming the capacitor thereby resulting in a change in the capacitance of the capacitor during use.
A problem with a resistive sensor system includes the need to have the resistive elements formed on the outer surface of the windshield whereupon the resistive elements are exposed to weather and possible deterioration. In addition, the resistive elements of a resistive sensor system are also subject to changes in resistance due to changes in the temperature.
A problem with an ultrasonic sensor system and an optical sensor system includes the need to position the transducer of the ultrasonic sensor system and the light transmitter and light receiver of the optical sensor system inside the vehicle to detect the presence of moisture at a suitable location on the windshield. However, positioning the ultrasonic sensor system or the optical sensor system at a suitable location on the windshield often results in partially blocking a driver's view through the windshield or in the positioning of such sensor system at less than an optimal location for detecting the presence of moisture on the windshield. Moreover, the sensitivity of an optical sensor to detect moisture can be compromised by the color or shade of the windshield in the path of the light propagating from the light transmitter to the light receiver.
It is, therefore, desirable to overcome the above problems and others by providing a moisture detection system having a small, nearly invisible, sensor disposed on a flexible substrate that is coupled to a sheet, such as a windshield, circuitry for stimulating the sensor, and detection circuitry for detecting a change in the resonant frequency of the sensor due to the presence of moisture on the sheet and, more particularly, the amount or rate of accumulation of moisture on the sheet. It is also desirable to provide a method for detecting the presence of moisture on a sheet by detecting a change in the resonant frequency of a sensor that is disposed on a flexible substrate that is coupled to the sheet. Still other desirable apparatus and methods may become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.
SUMMARY OF THE INVENTION
The invention is a moisture detection system that includes an electrical conductor disposed on a surface of a substrate. The electrical conductor has a resonant frequency that varies as a function of an amount of moisture present adjacent the electrical conductor. An oscillator outputs an oscillator signal at a predetermined amplitude and a predetermined frequency. A resonator circuit is coupled to the electrical conductor and is responsive to the oscillator signal for outputting a resonator signal having an amplitude related to the resonant frequency of the electrical conductor. A filter circuit is responsive to the resonator signal for outputting a rectified and filtered signal. An analog-to-digital converter is responsive to the rectified and filtered signal for outputting a digital signal related to the rectified and filtered signal. A controller is responsive to the digital signal for causing another system to operate in accordance with the digital signal.
The other system can be a wiper system that is responsive to the controller for adjusting a rate moisture is removed from adjacent the electrical conductor as a function of an amount of moisture present adjacent the electrical conductor and/or a rate moisture accumulates adjacent the electrical conductor.
The substrate can be a vehicle windshield having a plurality of transparent sheets laminated together. The electrical conductor can be sandwiched between the transparent sheets.
The substrate can be a flexible substrate. The moisture detection system can include a vehicle windshield having a plurality of transparent sheets laminated together with the flexible substrate sandwiched therebetween. The flexible substrate can include a ground conductor disposed on the flexible substrate at least partially surrounding the electrical conductor. The flexible substrate can include also or alternatively a conductive material disposed on a surface thereof opposite the electrical conductor. The conductive material can have a form that defines a faraday shield. Still further, an electrically conductive coating can also or alternatively be provided on a surface of at least one transparent sheet positioned on a side of the flexible substrate opposite an exterior surface of the vehicle windshield.
The resonator circuit can include a tank circuit having a capacitor and inductor connected in parallel between the electrical conductor and a reference voltage, and a resistor con
Barguirdjian Pascal
Haigron Michel
Hawk Allan Rex
Koram Kwaku Koi
Ellington Alandra
Lefkowitz Edward
PPG Industries Ohio Inc.
Siminerio Andrew C.
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