Abstract:
A projection system is provided that utilizes a prism which guides color components from a light source to a display without the use of reflection, and that reflects image encoded light from the display toward a projection lens, thereby minimizing loss of luminance and improving contrast. In one embodiment, the projection system utilizes a color drum for sequentially transmitting color components of a light source towards the prism.

Description:
This application claims the benefit of the Korean Application No. P2000-85798 filed on Dec. 29, 2000, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a total reflection prism and a projector with the same. 
     2. Background of the Related Art 
     The projector enlarges, and projects a small picture by using a projection lens to a large sized screen, to display a large sized picture. The projector is provided with a color wheel for splitting a red color ‘R’, a green color ‘G’, and a blue color ‘B’ on time basis for reproducing colors. The color wheel is rotated by motor for splitting the colors in succession. FIGS. 1 and 2 illustrate related art projectors. 
     Referring to FIGS. 1 and 2, the related art projector is provided with a lamp  1 , a reflection plate  2 , a color wheel  4 , a rod lens  6 , first lenses  7  and  8 , a mirror  10 , a second lens  12 , a prism  16 , a display  14 , and a projection lens  18 . 
     Beams of lights from the lamp  1  are focused onto the color wheel  4  by the reflection plate  2 , and the color wheel  4  transmits the red, green, and blue colors in succession as motor  5  rotates the color wheel. The beams split by the color wheel  4  are incident on the rod lens  6 , and the rod lens  6  makes the beams uniform for uniform distribution of the beams on a screen. The beams passed through the rod lens  6  proceeds to the mirror  10  through the first lenses  7  and  8 , and reflected at the mirror  10  toward the second lens  12 . The second lens  12  focuses the beams from the mirror  10  onto the prism  16 , and the prism  16  guides the beams from the second lens  12  to a display  14 , and, on the same time, supplies a picture beam from the display  14  toward the projection lens  18 . The display  14  produces a picture beam loaded with picture information by using the beams from the prism  16 . The prism  16  reflects the picture beam from the display  14  toward the projection lens  18 . To do this, as shown in FIGS. 3A and 3B, the prism  16  has a first reflection surface  20  for reflecting the beams from the second lens to the display for the first time, and a second reflection surface  22  for reflecting the picture beam from the display  14  to the projection lens  18  for the second time. Finally, the projection lens  18  enlarges the picture beam, and projects the picture beam to a screen at a distance in front of the projection lens  18 . FIGS. 4A and 4B illustrate related are the color wheel in FIG.  1 . 
     Referring to FIGS. 4A,  4 B and  5 , the related art color wheel  4  is provided with color filters  26  each for transmitting a beam of light with a wavelength of a relevant color among the white beams, a coupler  24  having the color filters  26  fitted thereto, and a motor  5  having the coupler  24  fitted thereto. 
     The color filter  26  is provided with a red color filter  26 R for transmitting red beams among the white beams, a green color filter  26 G for transmitting green beams among the white beams, and a blue color filter  26 B for transmitting blue beams among the white beams. 
     The color filter  26  is attached to the coupler  24  by an adhesive, and the coupler  24  is fastened to the motor  5  by holes  25  therein. That is, the color filter  26  splits colors in succession as the motor rotates the color filters  26 . It is preferable that the beam passes a boundary  27  of the color filters within the shortest time period when the beam transmits the color wheel  4  shown in FIGS. 4A,  4 B and  5 . For an example, when it is assumed that the motor rotates at 3600 rpm for displaying 60 fields per a second, a time period required for the beam to pass the boundary will be calculated. In this instance, it is assumed that the beam is rectangular with an 8 mm width, and a 6 mm height, and the color filter  26  has an inside radius of 30 mm, and an outside radius of 40 mm. 
     Equation (1) expresses an angle when the beam passes a surface of the color filter  26 , and the equation (2) expresses a time when the beam passes the boundary  27  of the color filter  26 .                θ   =       2   ×     arctan        (     3   31     )         =     11.055      °         ,           (   1   )                                
     (where, 31 is a distance from a center of the color wheel  4  to the beam, and 3 is a half of the height of the beam).                t   =         1   60     ×     11.055   120       =     1.54                 μ                 s         ,           (   2   )                                
     (Where, 120 is a value obtained by dividing 360° by 3, a number of boundaries  27 ). 
     From equation (2), it can be known that the time period required for the beam to pass through the boundary  27  of the color filter  26  is 1.54 μs. As can be known from equations (1) and (2), for reducing the time period required for the beam to pass through the boundary  7  of the color filter  26 , it is necessary to make the inside radius of the color wheel  4  greater. However, the greater the inside diameter of the color wheel  4 , the larger and the heavier the projector become. 
     Moreover, the related art color wheel  4  can not be fitted overlapped with other optical system (various lenses), to require much space. Furthermore, the related art prism  16  makes two times of total reflection for transmission of the beams from the second lens  12  to the projection lens  18 , with a loss of luminance. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a total reflection prism and a projector with the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a total reflection prism and a projector with the same, which permits to fabricate a thinner projector, and enhance a luminance. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the total reflection mirror makes one time of total reflection of the beams of lights from an optical system to a projection lens. 
     In another aspect of the present invention, there is provided a projector with a total reflection prism including a light source for emitting beams of lights, a color wheel for receiving the beams from the light source, splitting color beams from the beams in succession, and transmitting the color beams, a transmission part for guiding the color beams to the prism, a display for producing a picture beam according to a video signal by using the color beams from the transmission part, a prism arranged between the transmission part and the display for guiding the color beams from the transmission part to the display, and reflecting the picture beam from the display, and a projection lens for enlarging, and projecting the picture beam. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention: 
     In the drawings: 
     FIGS. 1 and 2 illustrate related art projectors; 
     FIGS. 3A and 3B illustrate details of the related art total reflection prism in FIG. 1; 
     FIGS. 4A and 4B illustrate details of the related art color wheel in FIG. 1; 
     FIG. 5 illustrates a time required for the beam to pass through a boundary of the color wheel in FIG. 1; 
     FIG. 6 illustrates a perspective view of a cylindrical color wheel in accordance with a preferred embodiment of the present invention; 
     FIGS. 7A and 7B illustrate a time required for a beam to pass through a boundary of a cylindrical color wheel in FIG. 6; 
     FIGS. 8 and 9 illustrate projectors in accordance with a first preferred embodiment of the present invention; 
     FIG. 10 illustrates a detail of the rod lens in FIG. 8; 
     FIGS. 11A and 11B illustrate details of the prism in FIG. 8; 
     FIG. 12 illustrates a projector in accordance with a second preferred embodiment of the present invention; and, 
     FIG. 13 illustrates a projector in accordance with a third preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings  6 - 13 . FIG. 6 illustrates a perspective view of a cylindrical color wheel in accordance with a preferred embodiment of the present invention. 
     Referring to FIG. 6, the cylindrical color wheel  34  in accordance with a preferred embodiment of the present invention includes color filters  52  each for transmission of a relevant color among white beams, a coupler  50  having the color filters  52  fitted thereto, and a motor  35  coupled with the coupler  50 . 
     The color filters  52  include a red color filter  52 R for transmission of red beams among the white beams, a green color filter  52 G for transmission of green beams among the white beams, and a blue color filter  52 B for transmission of blue beams among the white beams. 
     The color filters  52  are inserted in the coupler  50  and attached thereto with adhesive, and the coupler  50  is coupled with the motor  35  by means of the holes  56  therein. That is, the color filters  52  split colors in succession as the color filters  52  are rotated by the motor  35 . 
     When it is assumed that the motor rotates at 3600 rpm to display 60 fields per a second, a time period required for the beam to pass a boundary  54  of the cylindrical color wheel  34  will be calculated. In this instance, as shown in FIGS. 7A and 7B, it is assumed that the beam is rectangular with an 8 mm width, and a 6 mm height, and the cylindrical color wheel  34  has an inside radius of 39 mm, and an one mm thickness. 
     Equation (3) expresses an angle when the beam passes a surface of the color filter  52 , and the equation (4) expresses a time when the beam passes the boundary  54  of the color filter  52 .                θ   =       2   ×     arctan        (     3   39     )         =     8.797      °         ,           (   1   )                                
     (where, 39 is the inside radius of the color wheel  34 , and 3 is a half of the height of the beam).                t   =         1   60     ×     8.797   120       =     1.22                 μ                 s         ,           (   2   )                                
     (where, 120 is a value obtained by dividing 360° by 3, a number of boundaries  54 ). 
     From equation (4), it can be known that the time period required for the beam to pass through the boundary  54  of the color filter  52  is 1.22 μs, while the time period required for the beam to pass through the boundary of the color filter in the related art color wheel is 1.54 μs. Therefore, the present invention can enhance the luminance of the projector, as the time period required for the beam to pass through the color filter  52  of the present invention is longer. Also, the radius of the color wheel  34  of the present invention can be reduced to 32 mm on the same luminance basis of the color wheels of the present invention and the related art, i.e., the projector with the color wheel  34  of the present invention can be fabricated thinner than the related art. 
     FIGS. 8 and 9 illustrate projectors in accordance with a preferred embodiment of the present invention. 
     Referring to FIGS. 8 and 9, the projector in accordance with a preferred embodiment of the present invention includes a lamp  30 , a reflection plate  32 , a cylindrical color wheel  34 , a rod lens  36 , first lenses  37  and  38 , a mirror  40 , a second lens  42 , a prism  46 , a display  44 , and an enlarging and projecting lens  48 . 
     The beams from the lamp  30  are focused on the cylindrical color wheel  34  by the reflection plate  32 , and the cylindrical color wheel  34  transmits red, green, and blue beams in succession, as the motor  35  rotates the cylindrical color wheel  34 . The beams color split by the cylindrical color wheel  34  are incident on the rod lens  36 , and the rod lens  36  makes distribution of the beams uniform for uniform distribution of the beams on the screen, and deflects a path of the beams. 
     To do this, referring to FIG. 10, the rod lens  36  has an incident surface  58  sloped at an angle with respect to the beam from the reflection plate  32 . Also, the incident surface  58  is a total reflection mirror, or has a coat of total reflection material applied thereto. 
     As an alternative to this, referring to FIG. 12, a rod lens the same with the rod lens  6  in the related art may be used, when a mirror  39  is required in front of the incident surface of the rod lens  6  for deflecting the path of the beams, additionally. 
     The beams reflected at the rod lens  36  proceeds to the mirror  40  by the first lenses  37  and  38 , and reflected at the mirror  40  to the second lens  42 . The second lens  42  receives the beams from the mirror  40 , and focuses onto the prism  46 , and the prism  46  guides the beams from the second lens  42 , and supplies a picture beam from the display  44  to the projection lens  48 . 
     A prism of the present invention will be explained in detail with reference to FIGS. 11A and 11B. 
     Referring to FIGS. 11A and 11B, the prism  46  of the present invention includes a first sub-prism  100  having a top surface  108  and a bottom surface  110 , both in triangular forms, and a second sub-prism  102  having a top surface  106  in a form of triangle, and a bottom surface  104  in a form of a parallelogram. 
     There is a display  44  on a side surface of the first sub-prism  100 . The first prism and the second prism are disposed with a minute air gap between them. A contact surface  60  of the first sub-prism  100  and the second sub-prism  102  refracts the beams from the second lens  42  to the display  44 , and reflects the picture beam from the display  44  to the projection lens  48 , thereby deflecting the path of the beams from the second lens  42  to a preset angle. 
     The prism  46  of the present invention is compared to the related art prism  16  in FIGS. 3A or  3 B, to find that, though the related art prism  16  totally reflects the beams from the second lens  12  for two times for directing the beams toward the projection lens  18 , the prism  46  of the present invention totally reflects the beams only once for directing the beams from the second lens  42  toward the projection lens  48 , thereby minimizing a loss of luminance caused by the total reflection. Moreover, though the related art prism  16  is required to be arranged three dimensionally owing to a complicated optical path from the lamp to the projection lens, the prism  46  of the present invention is arranged two dimensionally in parallel with the projection lens  48 , the prism  44 , the cylindrical color wheel  34 , the rod lens  36 , the first lenses  37  and  38 , and the mirror  40 , to allow fabrication of a thinner projector. 
     Furthermore, though the related art projector is difficult to fabricate a thinner projector owing to a high optical system caused by the display  14  arranged under the prism  16 , the projector of the present invention permits to fabricate a thinner projector because the display  44  is arranged at a side of the prism  46 . 
     The projection lens  48  receives the picture beam from the prism  46 , and enlarges, and projects to a screen in front of the projection lens  48  at a distance. 
     In the meantime, the present invention may employ the color wheel  4  and the rod lens  6  identical to the related art in FIG.  13 . 
     As has been explained, according to the total reflection prism and the projector with the same of the present invention, the prism makes total reflection only once for directing the beams from an optical system to the projection lens, that minimizes a loss of luminance caused by the total reflection. 
     Moreover, the arrangement of the display and the prism side by side, both parallel with the color wheel, the optical system, the prism, and the projection lens permits to fabricate a thinner projector. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the total reflection prism and the projector with the same of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.