Patent Publication Number: US-2012026425-A1

Title: Liquid crystal display apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a liquid crystal display apparatus having a liquid crystal display panel and a light-emitting element such as a light-emitting diode for illuminating the liquid crystal display panel. 
     BACKGROUND ART 
     Various proposals have conventionally been made on head-up displays for vehicle using a liquid crystal display apparatus, and an example thereof is disclosed in Patent Document 1. Such a head-up display  1  for vehicle projects display light L onto a windshield of a vehicle or a semi-transmitting plate referred to as a combiner to display a virtual image. The head-up display  1  for vehicle is provided by putting a liquid crystal display apparatus  4  and a reflecting mirror  5  in a housing  3  having a light-transmitting window portion  2  such that the display light L emitted by the liquid crystal display apparatus  4  is reflected by the reflecting mirror  5  and then projected onto the windshield or the combiner (see  FIG. 5 ). 
     The liquid crystal display apparatus  4  has a liquid crystal display panel  6  and light-emitting diodes  7  and  8  for transmissively illuminating the liquid crystal display panel  6 . The light-emitting diodes  7  and  8  are supplied with predetermined power from a driving circuit, not shown, to emit light. The light-emitting diode  7  emits green light L 1 , whereas the light-emitting diode  8  emits red light L 2 . The liquid crystal display panel  6  is illuminated transmissively by illumination light L 3  provided by mixing the green light L 1  emitted by the light-emitting diode  7  and the red light L 2  emitted by the light-emitting diode  8 . 
     PRIOR ART REFERENCE 
     Patent Document 
     
         
         Patent Document 1: JP-A-2003-295105 
       
    
     DISCLOSURE OF THE INVENTION 
     Problems that the Invention is to Solve 
     Since the brightness of emitted light of each of the light-emitting diodes  7  and  8  varies with ambient temperature, the liquid crystal display apparatus has the problem in that the illumination light L 3  may not have a desired chromaticity but have a somewhat intense green color or red color. To solve the problem, it is contemplated that a color sensor for detecting the chromaticity of the illumination light L 3  is provided to output chromaticity data which is based on to adjust a voltage applied to the light-emitting elements  7  and  8  so that the illumination light L 3  has a desired chromaticity at all times. When the color sensor is placed between the light-emitting diodes  7  and  8  and the liquid crystal display panel  6 , however, the color sensor may obstruct the illumination light L to prevent the uniform transmissive illumination of the liquid crystal display panel  6 . 
     It is an object of the present invention to provide a liquid crystal display apparatus in which a liquid crystal display panel is uniformly illuminated transmissively and display light L has a desired chromaticity. 
     Means for Solving the Problems 
     The present invention has a liquid crystal display panel  18 , illuminating means  19  for emitting illumination light L 3  illuminating the liquid crystal display panel  18 , a polarizing member  27  reflecting the illumination light L 3 , and detecting means  28  for detecting the chromaticity of the illumination light L 3  transmitted through the polarizing member  27 . 
     The present invention has a liquid crystal display panel  18 , illuminating means  19  including a first light-emitting element  20  emitting first light L 1  having a first color and a second light-emitting element  21  emitting second light L 2  having a second color, for illuminating the liquid crystal display panel  18  with illumination light L 3  containing the first light L 1  and the second light L 2 , a polarizing member  27  reflecting the illumination light L 3 , detecting means  28  for detecting the illumination light L 4  transmitted through the polarizing member  27  to output chromaticity data, and control means  56  for adjusting power to be supplied to at least one of the first light-emitting element  20  and the second light-emitting element  21  based on the chromaticity data. 
     In the present invention, the polarizing member  27  is formed of wire grid polarizing plate. 
     Advantage of the Invention 
     Since the detecting means detects the chromaticity of the illumination light transmitted through the polarizing member, the illumination light is not obstructed by the detecting means and thus the liquid crystal display panel is uniformly illuminated transmissively. In addition, a desired chromaticity is achieved for the display light L. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  A schematic diagram showing a head-up display illustrating an embodiment of the present invention. 
         FIG. 2  A section view showing the embodiment. 
         FIG. 3  A side view of a liquid crystal display apparatus illustrating the embodiment. 
         FIG. 4  A block diagram showing the embodiment. 
         FIG. 5  A section view showing a prior art. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     An embodiment of the present invention will hereinafter be described with reference to the accompanying drawings. A head-up display  11  is placed within a dashboard  12  of a vehicle (see  FIG. 1 ). Display light L projected by the head-up display  11  is reflected by a windshield  13  toward an observer  14 . The observer  14  can visually recognize a virtual image V superimposed on a background landscape. 
     The head-up display  11  includes a liquid crystal display apparatus  15 , a reflector  16  and the like which are put in a housing  17 . The liquid crystal display apparatus  15  has a liquid crystal display panel  18 , an illuminator  19  (illuminating means), a polarizing member  27 , a color sensor  28  (detecting element), and a condensing lens  29 . 
     The liquid crystal display panel  18  is provided by adhering a polarizing plate to each of the front and back sides of a liquid crystal cell including a liquid crystal sealed in between a pair of light-transmitting substrates each having a transparent electrode film formed thereon. The liquid crystal display panel  18  digitally displays the speed of the vehicle. 
     The illuminator  19  has a light-emitting diode  20  (first light-emitting element), a light-emitting diode  21  (second light-emitting element), circuit substrates  22  and  23 , condensing lenses  24  and  25 , and dichroic mirror  26 . 
     The light-emitting diode  20  emits green light L 1  (first light) and is mounted on the circuit substrate  22 . The light-emitting diode  21  emits red light L 2  (second light) and is mounted on the circuit substrate  23 . Each of the condensing lenses  22  and  23  is formed of light-transmitting resin such as polycarbonate and is placed opposite to the light-emitting diode  20  and the light-emitting diode  21 , respectively. The dichroic mirror  26  is placed obliquely, and transmits the green light L 1  emitted by the light-emitting diode  20  and reflects the red light L 2  emitted by the light-emitting diode  21 . The liquid crystal display panel  18  is transmissively illuminated by orange light L 3  (illumination light) resulting from the mixing of the green light L 1  and the red light L 2  by the dichroic mirror  26 . 
     The polarizing member  27  is formed of wire grid polarizing plate and reflects a polarized component of a predetermined direction (for example, a direction perpendicular to the sheet) of the orange light L 3 . The polarizing plate on the back side of the liquid crystal display panel  18  has a polarization axis of the predetermined direction. The color sensor  28  detects the chromaticity of a portion L 4  of the orange light L 3  transmitted through the polarizing member  27  and outputs the chromaticity data to a microcomputer, later described. The condensing lens  29  condenses the portion L 4  of the orange light L 3  transmitted through the polarizing member  27  to the color sensor  28 . The portion L 4  of the orange light L 3  is a polarized component which does not contribute to the illumination of the liquid crystal display panel  18 . 
     The reflector  16  has a concave mirror  30 , a holding member  31 , and a stepping motor  32 . The concave mirror  30  is provided by evaporating metal (for example, aluminum) onto resin (for example, polycarbonate) to form a reflecting face  30   a . The reflecting face  30   a  is a concave face on which the display light L emitted by the liquid crystal display apparatus  15  is enlarged and the virtual image V is displayed. The concave mirror  30  is bonded to the holding member  31  by a double-faced tape. The holding member  31  is formed of resin (for example, ABS) and has a gear portion  34  and a shaft portion  35  integrally formed therewith. The shaft portion  35  of the holding member  31  is pivotally supported on the housing  17 . 
     A gear  37  is attached to a rotation shaft of the stepping motor  32 , and the gear  37  engages with the gear portion  34  of the holding member  31 . The concave mirror  30  is supported to be rotatable together with the holding member  31 . The stepping motor  32  can be used to rotate the concave mirror  30  to adjust the projection direction of the display light L. The observer  14  manipulates a press button switch (not shown) to adjust the angle of the concave mirror  30  so that the display light L is reflected to the position of his eyes (so that the virtual image V can be visually recognized). 
     The housing  17  accommodates the liquid crystal display apparatus  15  and the reflector  16 . The housing  17  is provided with a window portion  44  through which the display light L exits. The window portion  44  is formed of light-transmitting resin (for example, acrylic resin) and has a curved shape. The housing  17  is provided with a light-shield wall  17   c  to eliminate a phenomenon (wash-out) in which external light such as sunlight is incident on the liquid crystal display apparatus  15  to prevent clear recognition of the virtual image V. The light-shield wall  17   c  has a flat shape and is formed to hang obliquely from the top of the housing  17 . 
       FIG. 4  is a block diagram showing the electrical configuration of the liquid crystal display apparatus  15 . Reference numeral  51  shows a speed sensor which detects the speed of the vehicle and outputs the speed data to a microcomputer  52 . The color sensor  28  outputs the chromaticity data to the microcomputer  52 . The microcomputer  52  outputs a driving signal to the liquid crystal display panel  18  through a driving circuit  53  to cause the liquid crystal display panel  18  to display the speed of the vehicle and outputs a driving signal to the light-emitting diodes  20  and  21  through driving circuits  54  and  55 , respectively, to cause the light-emitting diodes  20  and  21  to emit light. Control means  56  is formed of the microcomputer  52  and the driving circuits  54  and  55  and adjusts a driving voltage applied to the light-emitting diodes  20  and  21  based on the chromaticity data output from the color sensor  28  so that the orange light L 3  has a desired chromaticity. 
     In the present embodiment, the portion L 4  of the orange light L 3  transmitted through the polarizing member  27  is used to detect the chromaticity of the orange light L 3  by the color sensor  28 . Since the power supplied to the light-emitting diodes  20  and  21  is adjusted on the basis of the chromaticity data output from the color sensor  28 , a desired chromaticity is achieved for the display light L. In addition, the color sensor  28  does not obstruct the orange light L 3 , so that the liquid crystal display panel is uniformly illuminated transmissively. 
     The present invention is not limited to the present embodiment, and various modifications can be made. For example, while the present embodiment employs the two light-emitting diodes  20  and  21  emitting the light of different colors, three light-emitting diodes emitting light of different colors may be used instead. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applied to a liquid crystal display apparatus having a liquid crystal display panel and a light-emitting element such as a light-emitting diode for illuminating the liquid crystal display panel. 
     DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
     
         
           18  LIQUID CRYSTAL DISPLAY PANEL 
           20  LIGHT-EMITTING DIODE (FIRST LIGHT-EMITTING ELEMENT) 
           21  LIGHT-EMITTING DIODE (SECOND LIGHT-EMITTING ELEMENT) 
           27  POLARIZING MEMBER 
           28  COLOR SENSOR (DETECTING ELEMENT) 
           56  CONTROL MEANS 
         L 1  GREEN LIGHT (FIRST LIGHT) 
         L 2  RED LIGHT (SECOND LIGHT) 
         L 3  ORANGE LIGHT (ILLUMINATION LIGHT)