Abstract:
A circular display includes a columnar waveguide plate and an image projection device. The upper width of the cross-section of the columnar waveguide plate is less than the bottom width of the cross-section of the columnar waveguide plate. The outer surface of the columnar waveguide plate is utilized for displaying an image, and the image projection device is used for projecting the image to the bottom of the columnar waveguide plate.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a circular display device, and more particularly, to a circular display device for displaying an image on an outer surface of a columnar waveguide plate with a projective light source. 
   2. Description of the Prior Art 
   Large display devices can be used to communicate information to a large number of people in advertisements. Large outdoor display devices often utilize light emitting diodes (LEDs) to be the light source. However, the maintenance of the large display device costs much due to a large number of LEDs. Otherwise, a television wall also can be utilized for advertisements, but the grid of the television wall due to the partition of televisions decreases the image quality. For solving above-mentioned problems, a 360 degrees circular display device is utilized. 
   Please refer to  FIG. 1 .  FIG. 1  is a drawing of a display apparatus  10  disclosed in U.S. Pat. No. 5,818,401. The display apparatus  10  includes a pedestal  12 , a cylindrical body  14  rotatably mounted on the pedestal  12 , and a plurality of LED arrays  16  secured on the wall of the cylindrical body  14 . Each LED array  16  includes a plurality of LEDs  18 . When the cylindrical body  14  rotates at a speed in which a viewer&#39;s eyes cannot distinguish that the individual LED array  16  and the LEDs  18  are sequentially turned on, a viewer sees the corresponding image on the rotating cylindrical body  14  due to the persistence of vision. Please refer to  FIG. 2 .  FIG. 2  is a drawing of a display apparatus  20  disclosed in U.S. Pat. No. 6,335,714. The display apparatus  20  includes a pedestal  22 , a cylindrical body  24  rotatably mounted on the pedestal  22 , and a plurality of LED sections  26  secured on the wall of the cylindrical body  24 . Each LED section  26  includes a plurality of LEDs  28 . When the cylindrical body  24  rotates at a speed in which a viewer&#39;s eyes cannot distinguish that the individual LED section  26  and the LEDs  28  are sequentially turned on, a viewer sees the corresponding image on the rotating cylindrical body  24  due to the persistence of vision. Generally, the method for displaying images using LEDs has disadvantages of large pixels and non-uniform illumination, decreasing the image quality. 
   SUMMARY OF THE INVENTION 
   It is therefore a primary objective of the claimed invention to provide a circular display device for displaying an image on an outer surface of a columnar waveguide plate with a projective light source for solving the above-mentioned problem. 
   According to claimed invention, a circular display includes a columnar waveguide plate and an image projection device. The upper width of the cross-section of the columnar waveguide plate is less than the bottom width of the cross-section of the columnar waveguide plate. The outer surface of the columnar waveguide plate is utilized for displaying an image, and the image projection device is used for projecting the image to the bottom of the columnar waveguide plate. 
   These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a drawing of a display apparatus disclosed in U.S. Pat. No. 5,818,401. 
       FIG. 2  is a drawing of a display apparatus disclosed in U.S. Pat. No. 6,335,714. 
       FIG. 3  is a drawing of a circular display of a first embodiment according to the present invention. 
       FIG. 4  is a cross-sectional view of the circular display along  4 – 4 ′ axis in  FIG. 3  according to the present invention. 
       FIG. 5  is a drawing of a circular display of a second embodiment according to the present invention. 
       FIG. 6  is a cross-sectional view of the circular display along  6 – 6 ′ axis in  FIG. 5  according to the present invention. 
   

   DETAILED DESCRIPTION 
   Please refer to  FIG. 3 .  FIG. 3  is a drawing of a circular display  50  of a first embodiment according to the present invention. The circular display  50  includes a columnar waveguide plate  54 . The columnar waveguide plate  54  is a cylindrical-shaped hollow waveguide plate, and a cross-section of the columnar waveguide plate  54  is a wedge-shaped section. The columnar waveguide plate  54  includes a light entrance plane  56  positioned on the bottom of the columnar waveguide plate  54 , and a light exit plane  58  positioned on the outer surface of the columnar waveguide plate  54 . The circular display  50  further includes an image projection device  60 . The image projection device  60  includes a base  52  installed below the columnar waveguide plate  54 , a projection module  62  installed inside columnar waveguide plate  54  for projecting a plurality of modulated light beams for forming an image, and a hemispherical reflecting surface  64  positioned on a side of the columnar waveguide plate  54  for reflecting light emitted from the projection module  62  to the light entrance plane  56  of the columnar waveguide plate  54 . The hemispherical reflecting surface  64  is formed on the base  52  by plating a reflective material, such as metal material, on a hemispherical protrusion of the base  52  or by installing a hemispherical metal structure on the base  52 . 
   Please refer to  FIG. 4 .  FIG. 4  is a cross-sectional view of the circular display  50  along  4 – 4 ′ axis in  FIG. 3  according to the present invention. As shown in  FIG. 3  and  FIG. 4 , the projection module  62  of the image projection device  60  projects the light for forming the image on the hemispherical reflecting surface  64  on the base  52 , and the hemispherical reflecting surface  64  reflects the light emitted from the projection module  62  uniformly in 360 degrees due to the symmetry in 360 degrees of the hemispherical reflecting surface  64 . The light entrance plane  56  of the columnar waveguide plate  54  is also symmetric in 360 degrees, so the light entrance plane  56  of the columnar waveguide plate  54  receives the light reflected from the hemispherical reflecting surface  64  uniformly. After the light enters the columnar waveguide plate  54  via the light entrance plane  56 , the incident angle of the light to the light exit plane  58  decreases gradually through a reflection effect performed by a wedge plane  66  so as to form the image from bottom to top by controlling the total reflection of the light transmitting inside the columnar waveguide plate  54 . Furthermore, since the incident angle of the light emitted from the projection module  62  to the hemispherical reflecting surface  64  is equal to the reflected angle of the light reflected from the hemispherical reflecting surface  64 , the incident angles of the light emitted to the light entrance plane  56  of the columnar waveguide plate  54  are different due to the different reflected angles of the light reflected from the hemispherical reflecting surface  64  corresponding to the different incident angles of the light emitted from the projection module  62  to the hemispherical reflecting surface  64 . The paths of the light of the different incident angles to the light entrance plane  56  are different, so the locations where the light passes through the light exit plane  58  of the columnar waveguide plate  54  outwardly are different. According to the above-mentioned optical characteristics, the image can be displayed on the light exit plane  58  of the columnar waveguide plate  54  correctly by controlling the angle between the columnar waveguide plate  54  and the hemispherical reflecting surface  64 , the angle between the wedge plane  66  and the light exit plane  58 , and the material of the columnar waveguide plate  54  (a refractive index of the columnar waveguide plate  54 ), and so on. 
   The image source of the circular display according to the present invention can be installed below the columnar waveguide plate. Please refer to  FIG. 5 .  FIG. 5  is a drawing of a circular display  70  of a second embodiment according to the present invention. The circular display  70  includes a columnar waveguide plate  74 . The structure of the columnar waveguide plate  74  is the same as the columnar waveguide plate  54  of the first embodiment. The columnar waveguide plate  74  is a cylindrical-shaped hollow waveguide plate, and a cross-section of the columnar waveguide plate  74  is a wedge-shaped section. The columnar waveguide plate  74  includes a light entrance plane  76  positioned on the bottom of the columnar waveguide plate  74 , and a light exit plane  78  positioned on the outer surface of the columnar waveguide plate  74 . The circular display  70  further includes an image projection device  80 . The image projection device  80  includes a projection module  82  installed on a side of the columnar waveguide plate  74  for projecting a plurality of modulated light beams for forming an image, and a lens group  84  installed between the columnar waveguide plate  74  and the projection module  82  for refracting light emitted from the projection module  82  to the light entrance plane  76  of the columnar waveguide plate  74 . 
   Please refer to  FIG. 6 .  FIG. 6  is a cross-sectional view of the circular display  70  along  6 – 6 ′ axis in  FIG. 5  according to the present invention. As shown in  FIG. 5  and  FIG. 6 , the projection module  82  of the image projection device  80  projects the light for forming the image on the lens group  84 , and the lens group  84  is capable of adjusting the paths of the light and refracting the light to the light entrance plane  76  of the columnar waveguide plate  74 . After the light enters the columnar waveguide plate  74  via the light entrance plane  76 , the incident angle of the light to the light exit plane  78  decreases gradually through a reflection effect performed by a wedge plane  86  so as to form the image from bottom to top by controlling the total reflection of the light transmitting inside the columnar waveguide plate  74 . Similarly, the image can be displayed on the light exit plane  78  of the columnar waveguide plate  74  correctly by controlling the related location of the columnar waveguide plate  74  and the lens group  84 , the optical characteristics of the lens group  84 , and so on. 
   In contrast to the conventional circular display, the circular display according to the present invention displays the image with a projection manner so as to overcome the disadvantages of large pixels and non-uniform illumination of LED light sources and to increase the image quality. Furthermore, there is only one light source in the circular display according to the present invention instead of utilizing multiple LEDs so that the cost decreases and the structure design is simplified. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.