IL262709B2 - Precipitation sensor - Google Patents

Description

םיעקשמ ןשייח . Precipitation Sensor. The inventor: :איצממה Igal Zlochin ןי'צולז לאגי TECHNICAL FIELD The present invention relates to precipitation sensors, and more particularly to a rain intensity sensor. More particularly, to a rain sensor that is attached to a windshield glass of a vehicle to detect raindrops, snow and frost on the surface of the glass and output signals to control a wiper and an air conditioning system of the vehicle depending on types and amounts of substances detected and a drop cycle of raindrops as well as methods for utilizing the same.

The present invention relates, also, to condensation and moisture sensors for using in wide range of applications.

BACKGROUND OF THE INVENTION The precipitation parameters of interest may include the precipitation state (e.g. whether it is precipitating or not), the precipitation type (liquid precipitation, e.g. rain, drizzle or solid precipitation, e.g. snow, hail stones), the intensity of precipitation and/or the accumulated precipitation. Because precipitation events are in practice almost always very unevenly distributed in time and location, a single observation represents a short period time. Rain Sensors. Rain sensors have been developed for automatically detecting the presence of moisture (e.g., rain, fog, dew, sleet, snow or other condensation). A rain sensor, also called a rain detector or a rain detecting sensor, is a device which can be equipped in a vehicle to automatically sense characteristics, such as the intensity, the amount, etc., of rainwater and control operation of a wiper (e.g., the speed, the operating time, etc.) even when a driver does not manually control the wiper. Notably, if the driver attempts to control the operation or speed of the wiper while driving, the risk of an accident may increase, or the driver may experience inconvenience from having to turn away his/her eyes or have unnecessary motion while driving. The rain sensor was created to overcome the foregoing problems. It is important to accurately measure the amount of rainwater to effectively control the speed of the wiper of the vehicle. 1. Optical Sensors. An example of a known technique is an optical precipitation sensor. Optical precipitation sensors measure scattering and/or attenuation of light from the precipitation particles in a sample volume. The most common rain sensors today are those based on optoelectronic measurement. These rain sensors most often exhibit at least one light source and at least one detecting photodiode, wherein the light source sends out an optical signal, which is reflected in a predetermined detection range on the windshield, and the reflected optical signal is detected by the photodiode. Many rain sensors are optical devices that utilize internal reflection of light from a windshield. Raindrops on a windshield change the amount of reflected light and such information is used for automatically controlling the windshield wipers. Such systems are also susceptible to "dirt" distractions which may cause false reads/wipes when dirt is on the windshield Another drawback associated with part of known optical rain sensing devices is that they are typically not capable of detecting a continuous water film or a coating on a windshield. The way in which the internal reflection arrangements of known sensors operate typically depends upon individual raindrops contacting the windshield and a broader coating of water may not be detectable. On the other hand, after a wiping of the windshield by the wiper blades, a slight film of moisture as a rule remains on the sensor field. This film of moisture could lead to the wiper motor remaining in operation even though rain drops are no longer impinging on the windshield. The disadvantage, also, is that the detection range of the optoelectronic rain sensors only detects a small section usually measuring about 2 cm.sup.2 of the windshield. Therefore, rain is inaccurately detected primarily at the beginning of showers, since a larger amount of rain might already have hit the windshield without the detection range having been sufficiently wetted. Particle sizes and falling speed are estimated from the data, which is subsequently used in determining the precipitation type. Slow falling particles are characterized as snow. These types of sensors are able to detect precipitation and measure the rain intensity relatively well, while they typically have difficulties to estimate accumulated precipitation for other types of precipitation (typically expressed as water content), because the precipitation type determination is not accurate and/or reliable. Additionally, other flying particles of similar size as typical precipitation particles, such as flower seed and insects, easily cause false rain reports. An example is the Bosch vehicle windshield rain sensor (Optical Sensor U.S. Pat. No. 6,376,824 by Michenfelder et al) used to operate windshield wipers. This sensor depends on the change in refraction of a reflected light beam against glass when water is on the outer glass surface. However, it has poor sensitivity for snow, unless the glass can be heated enough to melt the snow next to the glass. This would be difficult to facilitate without making the vehicle occupants too uncomfortable and initially, in cold environments, would not work at all until the heating reached an acceptable level for the sensor to be engaged. Moreover, natural light, such as sunlight, can trigger false indications when aligned with the sensor field of view. U.S. Pat. No. 7,154,241A to Kokuryo et al. ( December 26, 2006, 318/483) describes a method for controlling an operation of a wiper by: (a) collecting water by a wiping operation; (b) detecting an amount of the collected water passing through the detection area. In optical rain sensor for controlling a vehicular wiper the detection area is extremely smaller than the wiping area of a wiper. Therefore, the detection sensitivity should be important performance for the detecting device. Particularly in the drizzling rain, since the collision probability of raindrops with the detection area is very low, it is difficult for the wiper to be precisely controlled in such a situation. To solve such a problem, WO91/03393 has disclosed a device for controlling a windscreen wiper "by the detection amount of optical energy corresponding to the size of water wall in advance of the windscreen wiper when the windscreen wiper passes through an incident point (detection area)". Also, WO91/09756 has also disclosed a rainfall response type automatic wiper control system having "means for detecting the presence of waterdrop gathered and carried to a detection region by a wiper".

In cold weather conditions, frost is frequently formed on the interior side surface of the windshield glass of the vehicle due to a temperature difference between the interior and exterior of the vehicle, which may obstruct the driver's view. However, current systems lack a function to remove the frost in a convenient way. That is, although the driver can remove the frost through an air conditioning system such as a heater and/or a heating wire, there is inconvenience in that the driver manually operates the air conditioning system every time because typically once the frost starts to be generated, the frost continues to be generated even after being removed. Therefore, it is desirable to provide a rain sensor having a frost sensing function that can assist in driving the vehicle in such a manner that the frost sensing function is added to the rain sensor to detect rainfall and/or generation of frost so as to automatically operate the air conditioning system. As an example of such sensor is U.S. Pat. No. A9,682,686 to Lee et al. (June 20, 2017, 1/1). According to this patent, the rain sensor being attached to a windshield glass of a vehicle, comprising: a casing provided with a frost sensing region and an air passage formed by recessing a part of a surface of the casing which is attached to the windshield glass to contact indoor air of the vehicle; a light emitting unit configured to emit light such that the light is totally reflected from an exterior side surface of the windshield glass and the frost sensing region; a light receiving unit that receives the light reflected totally and outputs signals; and a control unit that receives the signals from the light receiving unit and analyzes a condition of raindrops on the exterior side surface of the glass and a condition of frost generated on an interior side surface of the windshield glass, wherein the air passage is formed by recessing a same surface as the frost sensing region, and connects an interior of the vehicle and the frost sensing region such that the indoor air is introduced into the frost sensing region through the air passage Error-free signal detection can then be accomplished only if the optical sensor is mounted in a region of the windshield that is cleaned by the windshield wiper system. Therefore, in some vehicle types, the sensor has to be mounted at a distance of up to 15 cm from the upper edge of the windshield. A disadvantage of this is that the sensor housing in these cases is within the field of view of the driver and is perceived as annoying because of the lack of transparency. Miniaturization is not possible, since for timely detection of wetting, for instance when it is beginning to rain, a sensor region approximately 4-5 cm.sup.2 in area is necessary.

False detections can be caused, also, by dry (non-precipitation) particles. An optical sensor with a capacitive rain detector may be applied to eliminate false detections caused by dry (non-precipitation) particles. As an example, Vaisala Present Weather Detector PWD52 uses this technique and is able to report a full set of precipitation parameters. Further in known techniques, the precipitation type may be characterized by employing a combination of optical forward scatter measurement and a capacitive detector. The optical system measures primarily the size (volume) of the precipitating particles and the capacitive measurement estimates the corresponding water content (weight). Typically, the volume/weight ratio for snow is in the order of ten times bigger than that of rain. This technique, however, has problems, when the intensity of precipitation varies a lot and/or fast or when the intensity is relatively low, because the capacitive measurement typically provides slower response to changes in precipitation intensity than the optical measurement. This may lead to false reports of precipitation type and/or intensity. Moreover, known sensors implementing this technique are relatively bulky and also expensive. Such sensors typically also require heating the whole sensor structure in order to keep it operational in changing conditions, possibly leading to excessive power consumption. There are well known, also, optical sensors for determining the moisture content of the soil in an irrigation system. They usually take the form of a prism or similar structure, in which a light beam projected into the prism is internally reflected toward a photosensor such as a photodiode or phototransistor. (The term "light" in this application is meant to include infrared radiation). The amount of light received by the photosensor depends on the amount of moisture present at the surfaces of the prism. This moisture changes the optical characteristics of the prism surface and thereby causes a portion of the beam to be refracted outwardly of the prism, instead of being reflected inwardly toward the light sensor. The amount of refraction, and thus the amount of light received by the photosensor, translates into a measurement of the wetness of the soil. Typical examples of the prior art are illustrated in U.S. Pat. No. 5,946,084 to Kubulins (a dome-shaped structure) and U.S. Pat. No. 6,079,433 to Saarem (a flat-surface prism). These devices are useful, but they are of limited efficiency because they rely on the reflection of light from the polish surfaces and their contamination changes the sensors’ sensitivity. The following patents of the optical moisture sensors are hereby incorporated by references.

The invention WO0026652 (A1) to I. Zlochin (2000) concerns dew point hygrometers based on condensation of dew on ends of optical fibers, or on surfaces of an optical prism. The surfaces of the dew forming ends are rough (grinded) and dew formed thereon increases light transmittance. In WO2005005959 to TAO SHIQUAN, et al., (2005), an optical fiber moisture sensor that can be used to sense moisture present in surrounding phase in a wide range of concentrations is provided, as well techniques for making the same. It includes a method that utilizes the light scattering phenomenon which occurs in a porous sol-gel silica by coating an optical fiber core with such silica. Thus, a porous sol-gel silica polymer coated on an optical fiber core forms the transducer of an optical fiber moisture sensor according to an embodiment. In U.S. Patent No. 7,247,837 to Zimmerman (2007) a soil moisture sensor uses a non-collimated light source and a photosensor, respectively, mounted at the foci of a transparent ellipsoidal plastic body. The dimensions of the body are such that emitted light rays are internally reflected toward the photosensor at the surface of the ellipsoid, if the surface is dry, but refracted outwardly of the body when the surface is wet. The amount of light reflected onto the photosensor is thus a measure of the amount of moisture at the surface of the sensor.

According to U.S. Patent No. 8,022,842 to Levine (2011), an optical system for detecting ice and water on the surface of an aircraft includes an elongated transparent optical element having first and second end portions. A light source and light detector are disposed in one end of the optical element and a reflective surface is disposed in the opposite end portion. The reflective surface defines a critical angle and reflects light from the light source to the light detector when the critical angle is in contact with air and refracts the light toward the external environment when the reflective surface is in contact with ice or water. The system may also incorporate an optical element wherein the reflective surface includes a continuous array of convex elements extending outwardly from and across one end of the optical element and wherein each of the convex elements defines a critical angle.

Disadvantages of Optical Sensors. • High sensitivity to the contamination of the optical elements. Such systems are also susceptible to "dirt" distractions which may cause false reads/wipes when dirt is on the windshield • In optical rain sensor for controlling a vehicular wiper the detection area is extremely smaller than the wiping area of a wiper. Therefore, the detection sensitivity should be important performance for the detecting device. Particularly in the drizzling rain, since the collision probability of raindrops with the detection area is very low, it is difficult for the wiper to be precisely controlled in such a situation. • The detection range of the optoelectronic rain sensors only detects a small section usually measuring about 2 cm.sup.2 of the windshield. Therefore, rain is inaccurately detected primarily at the beginning of showers, since a larger amount of rain might already have hit the windshield without the detection range having been sufficiently wetted. • Part of known optical rain sensors typically not capable of detecting a continuous water film or a coating on a windshield. The way in which the internal reflection arrangements of known sensors operate typically depends upon individual raindrops contacting the windshield and a broader coating of water may not be detectable. • On the other hand, after a wiping of the windshield by the wiper blades, a slight film of moisture as a rule remains on the sensor field. This film of moisture could lead to the wiper motor remaining in operation even though rain drops are no longer impinging on the windshield. • Poor sensitivity for snow, unless the glass can be heated enough to melt the snow next to the glass. This would be difficult to facilitate without making the vehicle occupants too uncomfortable and initially, in cold environments, would not work at all until the heating reached an acceptable level for the sensor to be engaged. • Natural light, such as sunlight, can trigger false indications when aligned with the sensor field of view. • A conventional rain sensing method using internal light guiding phenomenon inside of the windshield requires a complicated optical system and brings on difficulties in mounting; in a method measuring reflecting light from the raindrops wherein the light source and the light receiving element are located apart opposing each other, the SNR is degraded due to the reflection from the surface of the windshield; a reflection type method wherein a light source and a light receiving element are serially arranged, has a narrow and small raindrop sensing area. • The sensing efficiency is getting, also, worse since it is affected by headlights from another person's vehicle as well as is susceptible to interference from external light sources and thus provides inadequate performance. 2. Image Sensors U.S. Pat. No. 5,923,027 to Stam , et al. (July 13, 1999, 250/208.1) describes a moisture sensor and windshield fog detector using an image sensor, wherein the light source is positioned such that, when moisture is present on the surface, the light spot is reflected into the image sensor field of view. The sensor is adapted to detect the level of fog both on the interior of the windshield as well as the exterior of the windshield. By providing a system for automatically detecting the presence of fog on the interior and exterior of the windshield, serious performance limitations of known automatic rain sensors are eliminated. Disadvantage of this sensor is a relatively small sampling area that can be illuminated in proper manner. U.S. Pat. No. 6,313,454 to Bos , et al. (November 6, 2001, 250/208.1) describes a vehicular rain sensor system for detecting precipitation on an exterior surface of a window including 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 preferably includes an edge detection function for detecting edges of precipitation droplets on the window and activating the windshield wipers of the vehicle when the number of edges detected exceeds a predetermined threshold value. A smoothing algorithm or filter is provided to account for surface irregularities on the window, thereby substantially precluding such irregularities from being erroneously detected as rain droplets by the edge detection function. The rain sensor system may further include a polarizing filter and an illumination source, such that the rain sensor system may not only prevent false signals of rain when only fog is present on an interior surface of the window, but also allows the rain sensor system to actually detect fog particles on an interior surface of the window, thereby allowing the control to further be connected to a ventilation blower within the vehicle for the purpose of activating the blower to eliminate the fog. U.S. Pat. No. 6,768,422 to Schofield , et al. (July 27, 2004, 340/602) describes a vehicular precipitation sensor, decoupled from the windshield, which detects precipitation on a vehicle window that includes an imaging array sensor directed at the vehicle window from inside the vehicle, and a control operable to detect precipitation at a surface of the vehicle window in response to an output of the imaging array sensor. The imaging array sensor is operable to detect precipitation which includes water droplets at an exterior surface of the vehicle window and fog particles at an interior surface of the vehicle window. The sensor includes an illumination device for illuminating the vehicle window in an area near said imaging array sensor. U.S. Pat. No. 7,199,346 to Stam et al. (April 3, 2007, 250/208.1) describes a windshield wiper control system for a vehicle comprising: an image sensor; an optical system operative to image at least a portion of the surface of the windshield onto the image sensor; an illuminator for providing supplemental illumination across substantially all of the imaged portion of the windshield surface; and a processing system in communication with the image sensor and the illuminator and operative to analyze images from the image sensor to detect moisture on the windshield and to activate the windshield wipers when moisture is detected. The system further including a rearview mirror assembly adapted for attaching to a vehicle, wherein said image sensor is supported by said rearview mirror assembly. U.S. Pat. No. 7,259,367 B2, to Reime (August 21, 2007, 250/227.25), which is incorporated by reference, proposes a method for sensing rain by means of a camera, wherein a large area of the window of view, which is defined by the camera's angular aperture and the windowpane, is illuminated. The camera is almost set to infinity focus and can thus be used for driver assistance applications at the same time. As an image of the far range is produced, raindrops can only be noticed as faults in the image, which are detected by complex difference measurements of the images recorded using light that is pulsed or modulated in synchronization with the pixel frequency. • The focusing optics of the camera are adjusted between almost infinite and the screen surface.

• The light from the light source is coupled directly into the screen and, given a wetting, a reflection towards the camera occurs on the side opposite the coupling, wherein the coupling of the light is effected laterally into the screen or with a prism into the surface of the screen. • The light source is a first light source the device further comprising a second light source whose light impinges under total reflection on the inside of the screen to detect wetting thereon, wherein both light sources are driven separately for a separate detection of wetting on the outside of the screen and fogging on the inside of the screen. Disadvantage of this scheme is difficulty of preventing light reflections that not caused by the wetting. U.S. Pat. No. 7,646,889 to Tsukamoto (January 12, 2010, 382/104) describes a rain sensor provided in a vehicle includes a camera and a processor. The camera takes an image of a scene outside of the vehicle through a windshield of the vehicle with an infinite focal length. The processor detects rain based on a variation degree of intensities of pixels in the image from an average intensity of the pixels. The rain sensor described above detects the external substances on the windshield by executing edge extraction of the original image. In heavy rain where the amount of the rain drops is huge, borders between the rain drops quickly disappear and, thereby, the entire windshield is covered with the rain. In this case, it is difficult for the controller to extract edges of the rain drops. In another case that a mud splash causes a large amount of mud to be attached to the windshield, it is also difficult for the controller to extract edges of the mud. In this context, the conventional rain sensor has room for improvement. U.S. Patent Application No. 20110204206 to Taoka; Tetsuo (August 25, 2011, 250/208.1) provides a rain sensor capable of adequately detecting raindrops in a captured image. The rain sensor includes: a surface light source 14 which emits light to a windshield G to cause light to be incident on a raindrop detection region T set on the windshield G at a critical angle or more; a camera 15 which is arranged on the optical path of light totally reflected by the detection region T and captures the detection region T; and a detection unit which detects raindrops adhering to the detection region T from contrast in the image captured by the camera 15.

Disadvantages of this scheme are inability to detect mist in the interior surface of the windshield, a relatively small sampling area, as well as low signal to noise ratio caused by high level of the reflected background light. Also, the necessity to match to different windshield configurations. U.S. Patent Application No. 20110273564 to Seger; Ulrich ; et al. (November 10, 2011, 348/148) describes a camera system for detecting the surroundings of a vehicle through a vehicle window pane, having a camera having an image sensor for recording images, a first optical radiation generated by the vehicle surroundings being detectable by a sensor surface of the image sensor, and having a radiation source for emitting a second optical radiation. At least a portion of the emitted second optical radiation is detectable by the sensor surface of the image sensor, and the portion of the second optical radiation detected by the sensor surface is a function of a state of the vehicle window pane. A portion of the second optical radiation which has been reflected multiple times on the surfaces of the vehicle window pane is coupled out and coupled into the camera. First coupling means and second coupling means are each formed by a prism situated at interior surface of the window pane. A change in particular at outer surface of the vehicle windowpane, for example, as the result of wetting of this surface by water droplets, results in a reduction of the total reflections and a decrease in the intensity of the portion of second optical radiation detected by the camera. Disadvantages of this scheme are measurement absolute value of the light intensity that depends also on the windowpane contamination, as well as mist in the interior surface of the windowpane?????? In order to detect raindrops also at night, it is proposed in WO 2010/072198 A1 to couple light via a coupling element into the windscreen and to guide it via total reflection in the pane. By a decoupling element the totally reflected light is decoupled in the direction of the camera. When there are water drops on the windscreen, a part of the light is decoupled and is no longer totally reflected to the decoupling element. It is also disadvantageous here that for each modified pane inclination the integrated camera lighting unit must be mechanically adapted to the modified installation condition. Disadvantages of Image Sensors.

Claims (9)

CLAIMS. What is claimed is:

1. A capacitive precipitation sensor for measuring precipitation rate based on an electrical capacitor, including: a) a window, having an internal surface and an external surface; b) at least one external first electrode structure, made of uncoated electrically conductive material, attached to the external surface of said window; c) at least one internal second electrode structure, made of insulated electrically conductive material, attached to the internal surface of said window; d) a measuring circuit is responsive to provide an output signal indicative dynamic changes in capacitance between said first and second electrodes’ structures when precipitation fall on said window; e) electric leads connecting said two electrodes’ structures to said measuring circuit for applying an electrical field to them; f) a central processing unit connected to said measuring circuit, programmed to compute the rate of precipitation falling on said capacitor every given time frame; g) a wireless data transmitter to transmit the precipitation rate to a central controller, wherein, the area of said at least one first electrode structure is part of the area of said at least one second electrode structure, the area of said first electrode structure is dynamically increased due the precipitation falling on the window, being in electrical communication via moisture with said uncoated electrically conductive material, that, in turn, causes the capacitance increasing and fluctuations in time during the precipitation, which amplitude and frequency during every given time frame are correlated with the precipitation rate, that measured by said measuring circuit.

2. The capacitive precipitation sensor according to claim 1, wherein said first electrode structure is built-in a hydrophobic film attached to the external surface of said window, while said at least one second electrode structure is made of an insulated electrically conductive film, attached to the internal surface of said window.

3. The capacitive precipitation sensors according to claims 1 or 2, wherein said window is a vehicle’s windshield and said central controller controls operation of a wiper, e.g., the speed and the operating time.

4. The capacitive precipitation sensor according to any one of claims 1-3, wherein said external first electrode structure electrically connected to a metal vehicle’s body.

5. The capacitive precipitation sensor according to any one of claims 1-4, wherein said external first electrode structure is in form of a grid, spiral or other structure, formed by electric conductors.

6. The capacitive precipitation sensor according to any one of claims 1-5, wherein during wipers operation water is collected at said first electrode structure and an amount of the collected water passing through it is detected; the wiping operation control is carried out based on the detected water amount.

7. The capacitive precipitation sensor according to claim 1 based on near-field electro-magnetic tagging technology, wherein said external first electrode structure is served as an external tag antenna and said internal second electrode structure is served as a reader, wherein a voltage across the reader structure induces a voltage across the tag antenna structure; when rain drops fall on the window, they change the impedance of the external tag antenna and, as a result, the reader output signal is changed accordingly.

8. A capacitive precipitation sensor, for measuring precipitation rate of precipitation falling on a window, having external and internal surfaces, including: a) an electrical capacitor in form of a tube attached to said window’s external surface; b) at least one external first electrode structure, made of uncoated electrically conductive material, attached to the external surface of said tube; c) at least one internal second electrode structure, made of insulated electrically conductive material, placed inside said tube; d) a measuring circuit is responsive to provide an output signal indicative dynamic changes in capacitance between said first and second electrodes’ structures when precipitation fall on said tube; e) electric leads connecting said two electrodes’ structures to said measuring circuit for applying an electrical field to them; f) a central processing unit connected to said measuring circuit, programmed to compute the rate of precipitation falling on said capacitor every given time frame; g) a wireless data transmitter to transmit the precipitation rate to a central controller, wherein, the area of said at least one first electrode structure is part of the area of said tube external surface, the area of said first electrode structure is dynamically increased due the precipitation falling on the tube, being in electrical communication via moisture with said uncoated electrically conductive material, that, in turn, causes the capacitance increasing and fluctuations in time during the precipitation, which amplitude and frequency during every given time frame are correlated with the precipitation rate, that measured by said measuring circuit.

9. The capacitive precipitation sensors according to any one of claims 1-8, wherein said window is a vehicle’s windshield and said central controller controls operation of a wiper, e.g., the speed and the operating time. The inventor: Igal Zlochin, 41/7 Shoshanat HaCarmel Str. Haifa, 34323