Abstract:
An image forming apparatus and a projection TV set having the same are provided. The image forming apparatus includes an illumination system including a light source; a color separator separating beams irradiated from the light source into separate colored beams; at least one light-path converter bending the beam irradiated from the light source upwards; and a display device processing the incident beam in response to an input signal and forming a color image; and a projection system enlarging and projecting the color image formed by the illumination system onto a screen, wherein an optical axis of the beam emitted from the light source and an optical axis of the beam reflected by the display device are disposed by the at least one light-path converter at different heights such that the illumination system and the projection system extend to be narrow in a widthwise direction and long in a lengthwise direction.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     This application claims the benefit of Korean Patent Application No. 10-2004-0034285, filed on May 14, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an image forming apparatus having a two-stage structure in which an illumination system and a projection system are disposed at different heights to be suitably mounted in a stand-shaped cabinet, and a projection TV set having the image forming apparatus.  
         [0004]     2. Description of the Related Art  
         [0005]     A projection system is largely classified into a three-panel projection system or a single-panel projection system depending on the number of display devices that perform on-off control of light emitted from a light source in units of pixels. The light source is a high-powered lamp which produces a color image. In the single-panel projection system, the structure of the optical system can be reduced, in comparison to the three-panel projection system, but white light is separated into red (R), green (G), and blue (B) colors using a sequential method. Thus, the photoefficiency of the single-panel projection system is ⅓ the photoefficiency of the three-panel projection system. Thus, efforts for increasing photoefficiency of the single-panel projection system have been made.  
         [0006]     In a conventional single-panel projection system, a beam irradiated from a white light source is separated into R, G, and B color beams using a color filter, and each color beam is sequentially transferred to a display device. The display device is operated sequentially, in the order of the colors received, so as to form an image.  
         [0007]     As shown in  FIG. 1A , the conventional single-panel projection system includes a light source  10 ; a color wheel  15  through which a beam emitted from the light source  10  passes sequentially in the order of colors; an integrator  17  which shapes the beam that has passed through the color wheel  15 ; a total reflection prism  25  which totally reflects the beam that has passed through the integrator  17 ; and a display device  27  which receives the beam reflected by the total reflection prism  25 , processes the beam according to an input image signal, and forms a color image. The system further includes a projection system  30  which enlarges and projects the color image formed by the display device  27  onto a screen.  
         [0008]     An ultraviolet interception filter  12  is disposed between the light source  10  and the color wheel  15 , and a lens group  20 , which condenses the beam that has passed through the integrator  17 , is disposed on a light path between the integrator  17  and the total reflection prism  25 .  
         [0009]     The total reflection prism  25  includes an incidence prism  25   a  which totally reflects the beam emitted from the light source  10  onto the display device  27 ; and an emission prism  25   b  which transmits the beam reflected by the display device  27  to the projection system  30 .  
         [0010]     The entire device, from the light source  10  to the projection system  30 , has a horizontal structure with a width which is, relative to its height, very large.  
         [0011]      FIG. 1B  shows a projection TV set having a cabinet  40  which contains a screen unit  35  on which a screen S is mounted. Inside the cabinet  40 , an image forming apparatus is installed. Reference numeral  42  denotes a decoration cabinet.  
         [0012]     The image forming apparatus having the horizontal structure shown in  FIG. 1A  is advantageous to be installed in the cabinet  40  extending in a horizontal direction, as shown in  FIG. 1B . The conventional image forming apparatus is suitable for a projection TV set having a shape similar to a desktop monitor.  
         [0013]     However, customers desire projection TV sets having a variety of designs. Thus, in order to change the appearance of the projection TV set, the structure of the image forming apparatus needs to be changed.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention provides an image forming apparatus that can be suitably installed in a cabinet having a stand or pillar shape extending vertically, and a projection TV set having the same.  
         [0015]     Consistent with an aspect of the present invention, there is provided an image forming apparatus including: an illumination system including: a light source; a color separator separating beams irradiated from the light source into separate colored beams; at least one light-path converter bending the beam irradiated from the light source upwards; and a display device processing the incident beam in response to an input signal and forming a color image; and a projection system enlarging and projecting the color image formed by the illumination system onto a screen, wherein an optical axis of a beam emitted from the light source and an optical axis of a beam reflected by the display device are disposed by the at least one light-path converter at different heights such that the illumination system and the projection system extend to be narrow in a widthwise direction and long in a lengthwise direction.  
         [0016]     Consistent with another aspect of the present invention, there is provided a projection TV set including a screen unit and a cabinet having an image forming apparatus, wherein the image forming apparatus disposed in a vertical direction is installed in the cabinet and the cabinet has a smaller width than the screen unit and a pillar shape extending vertically. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The above aspects and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0018]      FIG. 1A  is a schematic diagram of a conventional image forming apparatus;  
         [0019]      FIG. 1B  shows the appearance of a projection TV set having the conventional image forming apparatus;  
         [0020]      FIG. 2  shows the appearance of a projection TV set having an image forming apparatus consistent with an exemplary embodiment of the present invention;  
         [0021]      FIG. 3  is a schematic diagram of a structure of an image forming apparatus consistent with another exemplary embodiment of the present invention;  
         [0022]      FIG. 4  is a right-side view of  FIG. 3 ;  
         [0023]      FIG. 5  shows the structure and coordinate system of a deformable micromirror device (DMD) used in the image forming apparatus consistent with another exemplary embodiment of the present invention;  
         [0024]      FIG. 6A  shows a light path of a beam reflected upwards by a first light-path converter used in the image forming apparatus shown in  FIG. 3 ;  
         [0025]      FIG. 6B  is a schematic diagram of the gradient of the first light-path converter, at which a beam is reflected upwards by the first light-path converter used in the image forming apparatus shown in  FIG. 3 ;  
         [0026]      FIG. 7A  is a schematic diagram of the arrangement of a second light-path converter and a display device which allows a beam to be incident on the display device at a predetermined angle after reflecting from the second light-path converter used in the image forming apparatus shown in  FIG. 3 ; and  
         [0027]      FIGS. 7B, 7C , and  7 D are schematic diagrams of the gradient of the second light-path converter at which a beam incident on the second light-path converter, used in the image forming apparatus shown in  FIG. 3 , is reflected at a predetermined angle. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]      FIG. 2  shows a projection TV set having an image forming apparatus consistent with an exemplary embodiment of the present invention. The projection TV set of  FIG. 2  includes a screen unit  90  having a screen S; and a cabinet  95  having a stand or pillar shape extending vertically disposed under the screen unit  90 .  
         [0029]      FIGS. 3 and 4  are schematic diagrams of an image forming apparatus consistent with another exemplary embodiment of the present invention. The image forming apparatus of  FIGS. 3 and 4  includes an illumination system  100  which radiates a beam and forms a color image; and a projection system  150  which enlarges and projects the color image onto a screen S. The illumination system  100  and the projection system  150  are disposed at different heights extending vertically.  
         [0030]     Also, the illumination system  100  and the projection system  150  are installed in the cabinet  95 . The present invention is an improved structure relative to a prior-art structure in which the illumination system  100  and the projection system  150  are suitably installed in the cabinet  95  having a stand shape, as shown in  FIG. 2 .  
         [0031]     The illumination system  100  includes a light source  103  which radiates a beam; a color separator  110  which separates the beam irradiated from the light source  103  into separate colors; and a display device  130  which processes the color beam that has passed through the color separator  110  in response to an input signal and forms a color image. In addition, in order to arrange the illumination system  100  to extend vertically, the illumination system  100  further includes at least one light-path converter which bends the beam irradiated from the light source  103  upwards. The projection system  150  enlarges and projects the color image formed on the display device  130  onto the screen S.  
         [0032]     The illumination system  100  further includes a first light-path converter  120  which is disposed between the color separator  110  and the display device  130  and converts the path of an incident beam into a first direction; a second light-path converter  125  which converts the path of the beam reflected by the first light-path converter  120  into a second direction; and a condensing element  127  which directs the beam reflected by the second light-path converter  125  to the display device  130  and directs the beam reflected by the display device  130  toward the projection system  150 .  
         [0033]     The light source  103  is disposed under the cabinet  95  so that the optical axis of the light source  103  is parallel to a bottom surface of the cabinet  95 . A beam, which is emitted from the light source  103  and proceeds parallel to the bottom surface of the light source  103 , is reflected by the first light-path converter  120  upwards. In addition, the second light-path converter  125  directs the beam reflected by the first light-path converter  120  to the condensing element  127 . The color separator  110  may be, for example, a color wheel.  
         [0034]     An ultraviolet interception filter  105  is disposed on a light path between the light source  103  and the color separator  110 , and an integrator  112 , which shapes the beam emitted from the light source  103 , is disposed between the color separator  110  and the first light-path converter  120 . The integrator  112  shapes the beam so that the beam has a cross section corresponding to the shape of the display device  130 .  
         [0035]     Lenses for condensing beams are disposed on a light path between the integrator  112  and the condensing element  127 . For example, a first condensing lens  114  is disposed between the integrator  112  and the first light-path converter  120 . Second and third condensing lenses  115  and  116  are disposed between the first light-path converter  120  and the second light-path converter  125 . A fourth condensing lens  117  is disposed between the second light-path converter  125  and the condensing element  127 .  
         [0036]     The condensing element  127  creates different optical paths for the beam incident on the display device  130  and the beam reflected by the display device  130 . The condensing element  127  may be a total reflection prism having first and second prisms  127   a  and  127   b  opposite one another. The first prism  127   a  which is an incidence prism, totally reflects an incident beam directly to the display device  130 , and the second prism  127   b,  which is an emission prism, transmits the beam reflected by the display device  130  directly to the projection system  150 . Alternatively, the condensing element  127  may include a concave mirror or lens for condensing the beam from the second light-path converter  125  onto the display device  130 .  
         [0037]     The display device  130  may be a reflection type liquid crystal display (LCD) or a deformable micromirror device (DMD).  
         [0038]     The projection system  150  includes a projection lens group  155  which makes a color image direct to a screen; and a reflection mirror  157  which directs the path of a beam properly.  
         [0039]     In the present exemplary embodiment, the first light-path converter  120  which directs the beam emitted from the light source upwards so that the image forming apparatus can be suitably installed in the cabinet having a stand shape, and the second light-path converter  125  which makes the beam incident on the display device  130  at an optimum angle, are mounted.  
         [0040]     As shown in  FIG. 5 , in order to transfer the beam emitted from the light source  103  upwards, the first light-path converter  120  may be disposed at an angle which will be described later. In the DMD  130 , a plurality of micromirrors  130   a  are arranged two-dimensionally, and the micromirrors  130   a  can be rotated separately. The incident beam proceeds toward the projection system  150  or deviates from the projection system  150  depending on the direction of the micromirrors  130   a  such that the incident beam is on-off in units of micromirrors.  
         [0041]     Here, it is assumed that the direction perpendicular to the plane of the DMD  130  is the X-axis, the Z-axis is vertical and the Y-axis is defined by the conventions of a right-handed system. A coordinate system based on theses conventions is also used in  FIG. 3 .  
         [0042]     First, referring to  FIG. 6A , in order to direct the beam reflected by the first light-path converter  120  upwards, an area in which the beam reflected by the first light-path converter  120  should exist, and that area should be in an upper part of the X-axis. For explanatory convenience,  FIG. 6A  shows a group of optical elements disposed on a path from the light source  103  to the first light-path converter  120 .  
         [0043]     In order to satisfy these conditions, the angle between the normal of the first light-path converter  120  and the Z-axis (θ  1 ) is between 0° and 90°. Referring to  FIG. 6B , when the first light-path converter  120  is parallel to the X-axis, θ  1  has a minimum value ( θ  1  min) of 0, θ  1  min=0°. When the first light-path converter  120  is parallel to the Z-axis, θ  1  has a maximum value, θ  1  max=90°. The position of the first light-path converter  120 , which transfers the beam emitted from the light source  103  upwards, is indicated by θ  1 , and defined by relation 1. 
 
0&lt;θ 1 &lt;90 (°)   (1) 
 
         [0044]     Next, referring to  FIG. 7A , the beam reflected by the second light-path converter  125  is incident on the condensing element  127  at a predetermined angle α with respect to the Z-axis. In order to satisfy incident angle requirements, the gradient angle of the second light-path converter  125  is obtained as follows. That is, since the incident beam has been reflected by the first light-path converter  120  upwards, an area in which a beam incident on the second light-path converter  125  may exist, and that area is a lower portion of the X-Y plane.  
         [0045]     Here, the beam reflected from the second light-path converter  125  has an angle α with respect to the Z-axis, and the angle between the Z-axis and normal of the second light-path converter  125  is referred to as θ 2 .  
         [0046]      FIG. 7B  shows the case where the beam incident on the second light-path converter  125  from the (+)Y-axis. In this case, θ 2  is (45+α/2) degrees.  FIG. 7C  shows the case where the beam incident on the second light-path converter  125  is parallel to the Z-axis. In this case, θ 2  is (90+α/2) degrees.  
         [0047]      FIG. 7D  shows the case where the beam incident on the second light-path converter  125  from the (−)Y-axis. In this case, θ 2  is (45−α/2) degrees.  
         [0048]     Referring to  FIGS. 7B, 7C , and  7 D, in order to direct the beam reflected by the second light-path converter  125  at an angle α with respect to the Z-axis, the following conditions may apply:  
               45   -     α   2       &lt;     θ   2     &lt;     90   +       α   2     ⁢     (   °   )                 (   2   )             
 
         [0049]     For example, when the display device  130  is a DMD, the beam reflected by the second light-path converter  125  is incident on the condensing element  127  at an angle of 45 degrees, with respect to the Z-axis, θ 2  is given by relation 2. 
 
22.5&lt;θ 2 &lt;112.5 (°)   (3) 
 
         [0050]     Consistent with the present invention, a cabinet in which an illumination system and a projection system are received can extend in a lengthwise direction, and thus, the appearance of the image forming apparatus can be different from the appearance of a prior art image forming apparatus. In other words, the illumination system and the projection system can be easily mounted in a cabinet having a stand or pillar shape, as shown in  FIG. 2 .  
         [0051]     Referring to  FIG. 4 , when a vertical distance from an arc center of the light source  103  to a plane parallel to the ground passing the center of the display device  130  is P and a horizontal distance from the arc center of the light source  103  to the first light-path converter  120  of the at least one light-path converter which is first placed on the light path from the light source  103  is Q, the ratio of Q to P may range from 1.5 to 2.0.  
         [0052]     The illumination system  100  has the above structure and the illumination system  100  and the projection system  150  have a two-stage structure to be suitably mounted in a post-shaped cabinet.  
         [0053]     As described above, in the image forming apparatus consistent with the present invention, the illumination system and the projection system for radiating beams are disposed to extend in a vertical direction and thus, can be easily mounted in a cabinet having a stand or pillar shape extending vertically.  
         [0054]     Accordingly, the projection TV set having the image forming apparatus consistent with an exemplary embodiment of the present invention has a stand shape, so in the same, the projection TV set can have a variety of designs in order to satisfy customers&#39; desires.  
         [0055]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims.