Abstract:
A reflective device wherein the device reflectivity is adjustable via automatic or manual means. The variable reflectance element includes a metallic mirror reflector on one side of a substrate and additional substrate layers consisting of a polarizer and a LCD whose material characteristics have been optimized for dimming. The mirror assembly provides alternate trigger mechanisms for initiating the dimming function, the dimming function being automatically referenced to ambient light levels (day or night) or manually adjusted or selected. In the automatic mode the dimming mirror assembly provides the user immediate eye protection from reflected high intensity glare by effecting near instantaneous adjustment in mirror reflectivity, such that the intensity of the reflected light impinging on the eyes is automatically adjusted so as to be at comfortable levels. The mirror assembly construction is in one piece, and allows the viewing of a display or TFT monitor located adjacent to the mirror.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a reflective device, more particularly, to such mirror systems having self-dimming mirrors and a viewable monitor placed adjacent to the reflective device for display of numerical and graphical information. 
         [0003]    2. Description of the Prior Art 
         [0004]    Automatic mirrors which automatically control the glare from bright headlights of rearward sources, or glare from a rearward sun near the horizon, (sun rising or setting) have been available for some time. Methods for controlling the glare reflected in these mirrors have included employment of motorized prismatic mirrors, utilization of liquid crystal shutters and use of electrochromic (EC) mirror reflective elements, wherein the reflectivity of the mirror is controlled via an applied voltage. The major problem with EC based devices is the relatively slow response time of the dimming function to the onset of the bright light source, typically in the range of several seconds. A number of systems have been proposed, such as in U.S. Pat. No. 3,601,614 issued to Platzer Jr. and U.S. Pat. No. 3,600,951 issued to Jordan et al., among others. Examples of control systems utilizing these type of devices include U.S. Pat. No. 5,715,093. 
         [0005]    What is desired is to provide light sensors in automatic mirror control circuits which achieve enhanced performance in response time (in the range of 10 milliseconds or less) and cost benefits relative to previously achieved technology. In addition, the option of utilizing a touch screen selection and adjustment of the dimming function, as well as a toggle switch and having numerical and graphical displays viewable on monitors located behind the mirror for user information and convenience are desired features. Providing these features will enable manufacturers to offer the comfort and advantages of glare control mirrors to the public at affordable prices. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention presents a method and process for utilizing commercially available, low cost, silicon-based light-sensing devices in automatically dimming mirror control systems as well as mirrors which may be dimmed by using a touch screen or toggle switch. The present invention also provides means for controlling the reflectivity of a mirrored surface of a vehicle rearview mirror which responds to the intensity of brightness of the light impinging on the mirror from a rearward source. In addition, the mirror provides the user with a numerical LCD display and graphical display of information on a monitor placed adjacent to the reflective device, preferably a thin film transistor (TFT) monitor. 
         [0007]    The dimming mirror system of the present invention includes a twisted nematic (TN) LCD electro-optic reflective element, at least one sensor for the ambient light level, at least one sensor for the glare light level condition, and a control circuit that responds to the current ambient and glare light levels which have been measured in order to control the reflectance level of the mirror reflective element. Additionally, a touch screen or toggle switch option is provided for selecting the dimming function. The light sensors produce an output that is proportional to the light sensed by the glare and the ambient light sensors. The controller generates an output voltage amplitude level commensurate with the glare and ambient light levels sensed, with response times in the 10 millisecond range, such that the mirror reflectivity is adjusted automatically or manually so that the intensity of the reflected light seen by the user is within his/her comfort level. 
         [0008]    The mirror system of the present invention includes an electro-optic reflective element, ambient and glare light sensors, and a circuit that generates appropriate outputs to control the reflectance level of the reflective element. This includes a charge accumulation device, a voltage difference sensing device and a controller device. The difference sensing device compares an output of the charge accumulation device with a reference. The controller device utilizes the measured ambient and glare lights levels to control the reflectance level of the mirror. The response time of the controller to the measured light levels, including generating an output proportional to the difference between the sensed output of the accumulation device relative to the ambient reference level, is in the range of a fraction of a second. 
         [0009]    Common integration elements are utilized in the various aspects of the current invention. For example, the light sensor levels are measured sequentially so that errors due to component variations correspond for both glare and ambient measurements, and track one another. This allows the use of mass-produced silicon sensors and avoids costly efforts to match components. This results in the achieving high dynamic range in the sensing of wide input light levels, utilizing commercial-off-the-shelf light sensors. 
         [0010]    The derivation of the reflectance control output signal may be referenced to the ambient light levels from a forward facing and/or a rearward facing light sensor, or from a value obtained from the amount of light impinging on the rearward facing rearview mirror surface. 
         [0011]    Due to the availability of various personal electronic devices, such as PDA&#39;s operating systems and CPU processors, various multiple functions such as GPS navigation, blue tooth functions, etc. in a single device housed within the rearview minor assembly. 
         [0012]    The present invention thus provides a dimmable rearview mirror system incorporating a control that references the brightness of the rearward scene. The mirror reflectivity is adjusted to maintain an appropriate and comfortable intensity level of the light shining into the eyes of the user in response to the rearward scene brightness level. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    For a better understanding of the present invention as well as other objects and further features thereof, reference is made to the following description which is to be read in conjunction with the accompanying drawing therein: 
           [0014]      FIG. 1  is an assembly view of the autodimming mirror of the present invention; 
           [0015]      FIG. 2  is an exploded perspective view of the dimming mirror showing its sandwich construction; 
           [0016]      FIG. 3  is a circuit diagram showing the timing and voltage signals which control the dimming function of the mirror system of the present invention; 
           [0017]      FIG. 4  is an exploded view diagram showing the liquid crystal display device of the present invention and a simplified representation of the liquid crystal molecules when the mirror is fully reflective (Voltage OFF); 
           [0018]      FIG. 5  is an exploded view diagram showing the layer construction of the liquid crystal display device of the present invention and simplified representation of the liquid crystal molecules when the mirror is dimmed (Voltage ON); 
           [0019]      FIG. 6  shows front and top views of the fully assembled auto dimming mirror of the present invention; and 
           [0020]      FIG. 7  shows the flowchart for a microprocessor utilized to control the autodimming function. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  illustrates the mirror reflector assembly  8  of the present invention, and in particular, the rearview mirror support and information display assembly  10  for vehicles. Assembly  8  is designed to be secured to the front windshield of a vehicle below the interior roof, suitable for a rearview mirror  12  to be supported on assembly  10 . Rearview mirror  12  comprises a dimmable reflective mirror element  12   a  housed in mirror housing  12   b . In addition, mirror  12  contains a video monitor  24  positioned adjacent mirror  12 , monitor  24 , utilized for display of navigational, alphanumeric, and camera images. A housing  20  is removably fitted to the mirror backing and includes an information display area  22  having a display element  24  for conveying the aforementioned information to persons inside the vehicle. Housing  20  also includes electrical circuitry for operation of the display element  24 , which circuitry includes electrical wiring  26  and a multi-connector  28  for connecting the monitor display to the vehicle&#39;s electrical system. 
         [0022]    As shown in  FIG. 1 , the vehicle operator is located so as to look outwardly through windshield W and is in position to view rearward images in the mirror element of mirror assembly  12 . An instrument panel in the vehicle dashboard is positioned below the windshield W and contains a variety of conventional instruments and displays such as a speedometer, tachometer, fuel gauge, oil pressure gauge, and alternator voltage charging indicator, as well as other instruments such as a clock, radio, CD player, AUX port, SD card slot; heater and air conditioning controls, and so on, which is available to all persons in the vehicle. Positioning of the information display  22  next to the viewing position of mirror assembly  12  has the advantage of maintaining an unobstructed view for the vehicle operator. 
         [0023]    Fitted within housing  20  is a wiring harness including electrical wires/cables and connectors  28 ,  32  as well as printed circuit board (PCB)  142  containing electronic/electrical circuitry for operating the information display element  24  and/or other functions in the supported rearview mirror assembly  8 . PCB  142  is adapted to be mounted on the front edges of interior walls  10  by means of tabs  99 ,  101  received in openings  146  (the tabs are connected by a cable having a length of approximately 125 mm to a microprocessor  145 ). PCB  142  contains the GPS  144  (PND function) and central processing unit  145  for the autodimming and power management functions, mounted within housing  10  via tabs within opening  146 . The functioning of microprocessor  145  (Signetics CDP 1802; 8-bit microprocessor or an equivalent) is detailed in the flowchart shown in  FIG. 9 . The right end of PCB  142  (as seen by the operator) is the SD card slot module  143  that stores digital map information for the vehicle navigation function. Five hard press (soft touch feel) buttons  51  (Volume on/off),  52  (Bluetooth),  53  (Power),  54  (Temperature),  55  (Guidepoint-GPS) are provided to the operator for selection of specific listed features. An auxiliary input  56 , microphone  57 , light sensor  59  and speakers  142  are also provided. Two openings  58  are provided in the rear of housing  10  to allow egress of sound from the speaker unit, housed in the speaker housing unit  143 . Power button  53  functions in two modes, a long press mode (pushing for more than 3 seconds) which turns off the device. A short press mode controls the autodimming function manually. With the power on, the default setting is the automatic mode of autodimming, controlled by the glare and light sensor  59 . If the user decides not to use the autodimming function, it is turned off by a short press of button  53 . 
         [0024]      FIG. 2(   a ) is an exploded perspective view of dimming mirror  10  showing its sandwich construction and  FIG. 2(   b ) is a top view of the assembled dimming mirror. 
         [0025]    In the voltage OFF condition, the incident light impinges on the polarizer film  80  is linearly polarized as it enters the TN-LCD liquid crystal layer  82 . The TN-LCD layer  82  rotates the polarization of the light by 90 degrees, and only allows light of the rotated polarization to be transmitted through the LCD layer. The light then is reflected from the aluminized back glass ( 84 , 86 ) and reverses path back to the front of the mirror. In the voltage off condition, the polarization of the reflected light matches the polarizer film, and the mirror is in the reflective, or light, condition. 
         [0026]    For the voltage ON condition, the LCD layer does not cause the polarization to rotate and blocks transmission of the incident polarized light. Hence in this voltage condition the mirror is in the non-reflecting or dark condition. 
         [0027]      FIG. 3  shows the autodimming activation circuit which operates on the DC input voltage as regulated by the microprocessor  145 , the voltage representing the intensity of the impinging exterior light level. This voltage adjusts the mirror reflectivity by generating a pulse output  162  which turns the mirror dimming to dark or off. 
         [0028]    The input to the circuit is from the glare and ambient as a voltage waveform (labeled “IN+5-15 volts”). The input signal is split into five parts which are applied to pins  6 ,  2 ,  7 ,  4  and  8  of integrated circuit U 1 . The circuit operates on the level and shape of the input waveforms to produce an output square wave whose peak to peak voltage is applied to the autodimming mirror to control the degree of dimming. 
         [0029]    The output of the circuit (labeled “OUT” at the extreme right of  FIG. 3 ) shows the voltage waveform that is applied relative to ground plane at four tabs located on the top edge of mirror  12   a  (indicated as reference number  61 ) of the conductive metalized reflective layer (i.e., aluminum layer  84  in the exploded view of  FIG. 2   a ). 
         [0030]    The mirror glass utilized in the autodimming mirror invention is commonly commercially available glass. The metalized reflection coatings for TN mirrors utilize aluminum. The LCD (liquid crystal) is commonly available and the same as is used for calculator displays, computer monitors, and similar applications. The polarized film  163  is a commercially available polarizer such as may be obtained in the open market for applications such as 3D movies. 
         [0031]    Typical dimensions of the mirror components shown in  FIG. 2  are as follows:
       Polarizer film  80 : 0.20 mm   Front glass  81 : 0.05 mm   Liquid crystal layer  82 : (thin, in nanometer range)   Aluminum Coating  84 : (thin, in nanometer range)   Back glass  86 : 0.05 mm   Overall length: 183.50 inches   Height: 57.60 inches   Width (depth): 2.60 mm       
 
         [0040]    The signal  162  is applied at 64 Hz and voltage applied relative to the ground plane at tabs of the conductive metalized reflective layer (i e aluminum layer  81  shown in  FIG. 2 ). Tabs  51 - 54  are located at several points around the mirror periphery. 
         [0041]    The right side diagram in  FIG. 4  illustrates the TN LCD mechanism in the “voltage on” condition. The diagram shows the anisotropic nematic liquid crystal molecules, which behave as electrical dipoles, where the orientation of the dipole in the “voltage on” condition is aligned perpendicular to substrates. In this condition the incident light is absorbed, and there is minimal reflectivity from the mirror surface, since the polarization of the reflected light is orthogonal to that of the polarizing sheet. Hence in the above (voltage off) condition the LCD is in the dimmed or absorbent state. 
         [0042]    The right side diagram in  FIG. 5  illustrates the TN LCD mechanism in the “voltage off” condition. The diagram shows the anisotropic nematic liquid crystal molecules, which behave as electrical dipoles, where the orientation of the dipole “twists” by 90 degrees from the top surface to the bottom surface, aligning with the respective direction of the electric fields at the two surfaces. The polarization of the incident light follows the polarization of the TN LCDs, so that in the above (voltage off) condition the LCD is in the reflective state. 
         [0043]      FIGS. 6A and 6B  illustrate the front and top views, respectively, of the assembled autodimming mirror  12  of the present invention. 
         [0044]      FIG. 7  is the flowchart for the 8-bit microprocessor unit  145  which controls the autodimming function. In particular, after performing an initialization function (block  100 ) the output from the back scanner (block  103 ) is read (block  102 ); if the value is greater than a first predetermined amount (block  104 ), the system enters into the high gain mode (block  106 ). If the read value is less than the predetermined amount, the system determines if the sensor output is greater than a second predetermined amount (block  110 ) and if so, the system enters into the mid-gain mode (block  108 ). If the system detects a value less than the second predetermined amount (block  110 ), the system determines if the sensor output is greater than a third predetermined value (block  112 ); if in the affirmative, the system enters the low gain mode (block  114 ). If the sensor output is less than the third predetermined value, the front sensor (element  115 ) reads the value read by a scanner (block  116 ). The same analysis on the signal from the back sensor (block  103 ) is performed on the signal from the front sensor (block  118 ,  120 ,  122 ,  124 ,  126  and  128 ). The output from the selected mode is compared (block  130 ) and if the value from the back sensor (element  103 ) is greater than the value from the front sensor (element  115 ), the output from the circuit shown in  FIG. 3  is inhibited (block  132 ). If the output from the back sensor is less than the output from the front sensor, an output (PWM) is generated (box  134 ) and the initialization sequence (block  100 ) is restarted. 
         [0045]    While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its essential teachings.