Abstract:
A license plate assembly includes a frame receiving a conventional license plate and at least one blanking flash generator arranged to generate a blanking flash at the license plate in response to a monitoring flash from an external monitoring device. The monitoring device is designed to take an image of the license plate and the blanking flash is obscuring the license plate to prevent or interfere with the taking of the image.

Description:
RELATED APPLICATIONS 
     This application claims priority to provisional application Ser. No. 61/472,384 filed Apr. 6, 2011 and incorporated herein in its entirety 
    
    
     BACKGROUND OF THE INVENTION 
     A. Field of Invention 
     This invention pertains to an apparatus and method for selectively blanking a license plate, said apparatus including one or more light sources embedded in a bezel surrounding the license plate, the light sources firing on demand to illuminate the license plate, rendering it unreadable. 
     B. Description of the Prior Art 
     Motor vehicles, and, by extension, the owners of motor vehicles, are uniquely identified by their license plates. However, the license plates of motor vehicles are routinely photographed or videotaped by many entities in various locations without permission from the owners of the respective motor vehicles. Since most entities, especially private entities, do not have the right to monitor the license plates of motor vehicles, these activities often constitute flagrant violations of the expectations of privacy of the respective individuals. The present invention provides a means of preventing such privacy violations. 
     SUMMARY OF THE INVENTION 
     Briefly, the present invention provides a plate assembly that prevents an external monitoring device from making a useful image of a motor vehicle license plate. Typically, monitoring devices for performing such recording include a camera and a generator producing a monitoring flash consisting of at least one short burst of radiation that could be either in the visible light range or in the infrared range. The monitoring flash is a precursor to the actual recording and is used to insure that the motor vehicle and license plate are properly illuminated and/or to focus a camera associated with or incorporated into the monitoring device. Because it is important to obtain a clear image of the license plate, some monitoring device include means for generating a first monitoring flash used to determine the actual distance from the monitoring device (or camera) to the license plate. 
     Moreover, some monitoring device may include two cameras spaced apart from each by several feet and arranged to provide better coverage for the monitoring device. In such an arrangement, two monitoring flashes may be generated for each camera; the first being used to determine the distance to the license plate and the second for illuminating the license plate for a good image. Of course, typically, the two cameras do not take the image at exactly the same time but one may be delayed somewhat with respect to the other. 
     The present invention detects the monitoring flashes and, in response, generates a blanking flash in the form of an intense light beam directed at shallow angle at the license plate thereby blanking the license plate for a short time period. This blanking coincides with the generation of an image by the camera. 
     Specifically, after releasing the monitoring flash, the recording device triggers the camera and the camera then captures either a single image (for a photograph) or a plurality of images (for a video clip). In the present invention, the intense light pattern from the blanking flash causes the license plate to appear as a featureless or bright surface and the license plate in any image or images taken by the cameras appear blank because the camera&#39;s light sensors become oversaturated. As a result the alphanumeric characters on the license plate will be invisible, or at least partially obstructed so that they cannot be recognized. 
     If a second monitoring flash is detected within a very short time period after the first one, then it is assumed that the first monitoring flash was intended for metering and the second monitoring flash was intended to generate an image of the license plate and, accordingly, the second monitoring flash is followed by a second blanking flash. Preferably the intensity of the second flash is equal to or higher than the first. As previously mentioned, some monitoring devices may be using four sets of monitoring flashes, two for each of two cameras. Since normally there isn&#39;t enough time between the operations of the cameras to recharge the charging circuitry driving the flash generators for the blanking flashes, preferably, four separate flash generating means are provided. 
     In one embodiment, of the invention, a flash suppression means is also provided which discharges the circuitry used to drive the blanking flash generators. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows plan view of a license plate assembly constructed in accordance with this invention; 
         FIG. 2  shows a block diagram of the apparatus of  FIG. 1 ; 
         FIG. 3  shows a typical circuit used in the apparatus of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to  FIG. 1 , preferably, a license plate assembly  100  constructed in accordance with this invention assembly includes a frame  10  sized and shaped to fit around a license plate  12 . The license plate  12  is a standard license plate issued by the appropriate authorities and it bears several alphanumeric characters and/or other images. 
     The frame  10  is preferably made of a suitable plastic material and includes a bezel that forms the outside surface of the frame  10  and includes peripheral lip  14  that extends over and covers the peripheral edges  16  of plate  112  as shown. The bezel may be raised to provide sufficient room for the flash generators. Preferably, the generators may be sealed and protected by by a transparent cover of a plastic material such as acrylic, Lexan®, tampered glass, or other similar transparent materials. 
     The assembly  100  includes an electronic component  18  that can be powered by one or more batteries (not shown) dedicated for the component and included in the frame  100 . However preferably, the assembly  100  is powered from the car battery (not shown) using standard wire connectors (not shown). The assembly  100  includes a flash sensor  20  arranged and constructed to sense one or more monitoring flashes as discussed in more detail below. 
     The sensor  20  is connected to the component  18 , which also controls the operation of several flash generators  22 . In  FIG. 1 , four such flash generators  22  are shown, it being understood that their number and positions may be changed as desired. The flash generators  22  are arranged to generate blanking flashes in forms of high intensity beams of light that penetrate edgewise the plate  19  as discussed below. 
     The positions of the component  18  and sensor  20  within frame  10  may be changed as well. If there is not enough in the frame, component  18  may be installed behind the license plate  12 . 
     Preferably, the frame  100  is formed with appropriate cavities for housing the component  18 , sensor  29  and flash generators  22 . The bezel is placed over the cavities and secured to the rest of the frame  10  thereby sealing these cavities to keep the component  18 , sensor  20  and flash generators  22  so that they will not come into contact with water (during rain and snow) and other materials, such as salt, etc. The cavities (not shown) holding the flash generators  22  can be coated with a reflective coating that directs light from the flash generator toward the license plate  12 . A portion of the bezel disposed above the sensor  20  is made of clear or transparent material that allows radiation to enter into and be sensed by sensor  20 . In an alternate embodiment, an IR filter may be placed above the sensor  20  to eliminate the effects or reduce the effects of ambient light. 
     The flash generators  22  are constructed and arranged to generate a high light pattern directed at plate  12 . In  FIG. 1 , the flash generators  22  are positioned along the lateral sides, but they may be provided above and in below the license plate  12  as well. 
     The bezel and lip  14  perform several functions. They hides and protects the circuitry shown in  FIGS. 2 and 3 . They make the frame  10  look like any other license plate frame so that the frame  10  is essentially undistinguishable from a standard license plate unless it is removed. The lip also limits the light pattern generated by flash generator  22  at license plate  12  nd prevents this light pattern from propagating into the eyes of other drivers in the vicinity. 
       FIG. 2  shows a schematic circuit diagram for the  100  apparatus and electric component  18 . As can be seen in this Figure, the component  18  includes a control circuit  30 , a charger circuit  32 , a flash power source  34 , and a switching circuit  36 . The switching circuit receives high energy pulses from the power sources  34  and directs them to one of the flash generators as required, under the control circuit  30 . It should be understood that the diagram of  FIG. 2  is somewhat schematic to describe functionally how the various elements of component  18  interact. 
       FIG. 3  shows a more detailed diagram illustrating how a particular flash generator  22  is operated. The flash generator  22  is connected to a bank of capacitors C, The capacitors C are charged under the control an electronic controller EC. When the circuit shown in FIG.  2 , 3  is disposed in a motor vehicle, when the motor vehicle is started up, the controller EC receives a CHARGE command from the control circuit  30 , and in response charges the capacitor bank C. When the capacitor bank C is charged, the controller EC generates an indication DONE to the control circuit  30 . When the control circuit sends a command FLASH, this command activates an electronic switch ES which causes through a trigger coil TC, the capacitor bank C to discharge into the flash generator  22  thereby generating a blanking flash. 
     The operation of the assembly  100  of  FIG. 1  and the circuitry of  FIGS. 2 and 3  is now described. As discussed above, once the motor vehicle is operating, the capacitor bank C is charged and ready for action. Typically monitoring device  200  starts the process of obtaining an image of license plate  12  by generating at least one monitoring flash. This monitoring flash is sensed by the sensor  20  and a flash detect signal is sent to the control circuit  30 . The control circuit  30  generates a FLASH signal to a first flash generator  22 . The respective flash generator then generates a first blanking flash. If no further monitoring flashes are detected within a couple of seconds, it is assumed that the monitoring device generates only a single flash. If a second monitoring flash is detected by sensor  20 , this information is passed on to the control circuit  30  which then triggers another flash generator  22  and a second blanking signal is generated. As mentioned above, in some instances, some monitoring devices can generate up to four monitoring flashes, a set of two for each of two cameras (not shown), and the control circuit  30  in this instance generates four sequential monitoring flashes by triggering once each of the four generators. 
     Since it is expected the first and third monitoring flashes are used to determine the distance from the cameras to the license plate and the second and fourth monitoring flashes are the ones used to illuminate the license plates, the system  100  is arranged so that the second and fourth blanking flashes have higher intensities (e.g., by 20-50%) to insure that the license plate is blanked (or, more accurately, the sensors of the cameras in the monitoring device are overloaded) and the alphanumeric characters (or any other images) on the license plate will be either invisible or at least unreadable on any images obtained by the camera. 
     The flash generators are typically strobe-type devices. 
     As soon as a blanking flash is generated, the capacitor bank is recharged by recharging circuit RC automatically to the nominal voltage value. Usually it takes about 3 seconds to recharge the bank of capacitors C. 
     The energy stored in the capacitive bank is relatively high and touching any terminals of the bank could be dangerous. Therefore safety elements (not shown) may be added that automatically discharge the capacitor bank through a dummy load (not shown) or other means. This operation may be initiated by a SUPPRESS FLASH signal the control circuit  30 . Various conditions can trigger this signal, such as turning the engine off, dismounting the frame  10 , etc. 
     Obviously numerous modifications can be made to the invention without departing from the scope of the invention as defined in the appended claims. For example, a cover plate  19  maybe provided on top of the license plate made of an active material such as an electrochromatic material that is normally transparent and becomes opaque when in the presence of an electric field or when current is passing through it (or vice versa). The cover plate may be made of other similar materials that their light transmissive characteristics in response to an electrical signal.