Abstract:
A projection system including a lighting system, a screen, a color filter separating light emitted from the lighting system according to wavelengths of the light, a first reflecting mirror reflecting the light passing through the color filter to change a path of the light, a display device provided in a predetermined position in the first reflecting mirror, a second reflecting mirror reflecting light reflected from the first reflecting mirror toward the display device, and a projection lens unit enlarging and projecting a color image formed by the display device onto the screen.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of Korean Patent Application No. 2002-68085, filed on Nov. 5, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a lighting system and a projection system which have an improved structure, so that the lighting system and the projection system can be made small and thin. 
   2. Description of the Related Art 
   Techniques for making projection systems small and thin have been researched and developed. In the conventional art, techniques for making a projection system small include using a mirror method and a total reflection prism. In particular, a technique using the mirror method is applied to make a projection system small and lightweight. 
   An image displaying apparatus using the mirror method is disclosed in Japanese Patent Publication No. 2000-98272. Here, as shown in  FIGS. 1 and 2 , in the image displaying apparatus, light emitted from a light source  100  is split into R, G, and B color beams by a color wheel filter  103 . The R, G, and B color beams are sequentially reflected on a first reflecting mirror  105 . Next, the R, G, and B color beams are reflected on a second reflecting mirror  107 , and then focused onto a deformable mirror device (DMD)  110 . A condenser lens  104  is further included in an optical path between the color wheel filter  103  and the first reflecting mirror  105 . 
   The DMD  110  has a plurality of micromirrors (not shown), which are two-dimensionally arranged and turned on and off according to an image signal input to each pixel. When the micromirrors are turned on, light reflected on the micromirrors is incident on a projection lens unit  113 . When the micromirrors are turned off, light reflected on the micromirros travel in a direction deviating from the projection lens unit  113 . Thus, R, G, and B color beams are incident or not incident on pixels each corresponding to the R, G, and B color beams to form a color image. 
   With reference to  FIG. 1 , light emitted from the light source  100  passes through the first reflecting mirror  105  and the second reflecting mirror  107  to the DMD  110 . In the above-described structure, the first reflecting mirror  105 , the second reflecting mirror  107 , and the DMD  110  are arranged in a triangle shape. The projection lens unit  113  is installed aside the second reflecting mirror  107 . However, the projection lens unit  113  is arranged in a proper position so that light reflected from the DMD  110  is incident on the projection lens unit  113 . In a conventional optical path, the first reflecting mirror  105 , the second reflecting mirror  107 , and the DMD  110  are arranged in different directions and different positions, respectively. Thus, an image displaying apparatus cannot be made small. 
   Light reflected from the first reflecting mirror  105  is incident on the second reflecting mirror  107 , which is disposed in a different position from the first reflecting mirror  105 . Light reflected from the second reflecting mirror  107  is incident on the DMD  110  opposite to the second reflecting mirror  107 . Thus, the optical path is complicated. Therefore, when a DMD installed in a narrow space is turned on/off, it is difficult to split a beam according to a method of driving pixels processing image data in the DMD. Also, when the DMD is turned off, light may be incident on the projection lens unit  113 . Moreover, since the second reflecting mirror  107  and the projection lens unit  113  are arranged in the same direction, an installation space is considerably limited. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention provides a projection system using a small optical system, achieved by simplifying an optical path of a reflecting mirror, and a lighting system which has an improved structure so that the lighting system is suitable for being used in the projection system. 
   Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
   According to an aspect of the present invention, there is provided a projection system including a lighting system, a screen, a color filter separating light emitted from the lighting system according to wavelengths of the light, a first reflecting mirror reflecting the light passing through the color filter to change a path of the light, a display device provided in a predetermined position in the first reflecting mirror, a second reflecting mirror reflecting light reflected from the first reflecting mirror toward the display device, and a projection lens unit enlarging and projecting a color image formed by the display device onto the screen. 
   The lighting system may include a lamp light source radiating the light, a reflector reflecting the light emitted from the lamp light source to emit the light in one direction, and an intercepting unit reflecting a portion of the light emitted from the lamp light source toward the reflector so that the light emitted from the reflector has an annular light distribution. 
   The intercepting unit may be convex, the surface thereof curving toward the lamp light source. 
   Uniform light forming units may be provided in an optical path between the lighting system and the first reflecting mirror, wherein the uniform light forming units convert the light passing through the color filter into uniform light. Shielding plates may be provided in the centers of the uniform light forming units, shielding incident light from proceeding. 
   The first reflecting mirror and the second reflecting mirror may be symmetrical with respect to an optical axis. 
   According to another aspect of the present invention, there is also provided a lighting system including a lamp light source radiating light, a reflector reflecting the light emitted from the lamp light source to emit the light in one direction, and an intercepting unit reflecting a portion of the light emitted from the lamp light source toward the reflector so that the light emitted from the reflector has an annular light distribution. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a plan view of an image displaying apparatus disclosed in Japanese Patent Publication No. 2000-98272; 
       FIG. 2  is a front view of the image displaying apparatus shown in  FIG. 1 ; 
       FIG. 3  is an exploded perspective view of a small-sized projection system according to the present invention; 
       FIG. 4  is a front view of the small-sized projection system shown in  FIG. 3 ; 
       FIG. 5A  is a view of a lighting system according to an embodiment of the present invention; 
       FIG. 5B  is a view of a lighting system according to another embodiment of the present invention; 
       FIG. 6  is a view of a uniform light forming unit used in a projection system according to the present invention; and 
       FIG. 7  is a X-Z plane view of a projection system according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
   Referring to  FIG. 3 , a projection system according to the present invention includes a light system  5 , a first reflecting mirror  20  on which light emitted from the lighting system  5  is reflected, a display device  23  which is installed in the surface of the first reflecting mirror  20 , and a second reflecting mirror  25  which reflects light reflected from the first reflecting mirror  20  onto the display device  23 . 
   A color filter  10 , collimating lenses  13 , and uniform light forming units  15  are disposed in an optical path between the lighting system  5  and the first reflecting mirror  20 . The color filter  10  sequentially splits light emitted from the lighting system  5  into R, G, and B color beams. The collimating lenses  13  converts light passing through the color filter  10  into parallel light. The uniform light forming units  15  forms incident light into uniform light. 
   In the present invention, the display device  23  is installed in the surface of the first reflecting mirror  20 . The second reflecting mirror  25  receives light reflected from the first reflecting mirror  20  and reflects the received light toward the display device  23 . 
     FIG. 4  shows the arrangement structure and an optical path of the first reflecting mirror  20 , the display device  23 , and the second reflecting mirror  25 . Here, since the display device  23  is installed inside the first reflecting mirror  20 , only spaces for installing the first and second reflecting mirrors  20  and  25  are necessary. It is easily seen from  FIG. 4  that the arrangement structure of the first reflecting mirror  20 , the second reflecting mirror  25 , and the display device  23  is different from the triangle arrangement of the first reflecting mirror  105 , the second reflecting mirror  107 , and the DMD  110  according to the conventional art (see  FIG. 1 ). Thus, the arrangement structure according to the present invention contributes to a remarkable reduction in a space for installing the optical components, compared with the arrangement structure according to the conventional art. 
   The first reflecting mirror  20  is inclined at a predetermined angle with an optical axis of light made uniformly incident by the uniform light forming units  15 . The second reflecting mirror  25  is arranged so that light reflected from the first reflecting mirror  20  is reflected on the second reflecting mirror  25  and focused onto the display device  23 . 
   The first and second reflecting mirrors  20  and  25  may be elliptic mirrors, plane mirrors, spherical mirrors, or aspherical mirrors. The first and second reflecting mirrors  20  and  25  may be symmetrical or asymmetrical, depending on the positions thereof. 
   The display device  23  may be inserted into a hole  21  formed in the first reflecting mirror  20 . A drive  22  driving the display device  23  may be disposed on the back surface of the first reflecting mirror  20 . The display device  23 , for example, may be a moveable mirror device, which realizes a color image due to the on-off switching operation of a micromirror, or a liquid crystal display device, which realizes a color image by modulating incident light to polarized light. 
   When light emitted from the lighting system  5  is incident on the first reflecting mirror  20 , the light must not be incident on the display device  23 . Since the intensity of light emitted from the light system  5  is non-uniform, image quality may be deteriorated when light is directly incident on the display device  23 . To prevent this, a unit which intercepts light emitted from the lighting system  5  from being incident on the display device  23 , is required. Here, light emitted from the lighting system  5  is uniformly formed by the uniform light forming units  15 . However, since this cannot provide sufficient image quality, light is made further uniform via the first and second reflecting mirrors  20  and  25 , and then incident on the display device  23 . 
   A method of modifying the structure of the lighting system  5  so that light is not emitted from the center of the lighting system  5  will be described. 
   As shown in  FIG. 5A , the lighting system  5  includes an intercepting unit  7  intercepting light emitted from the center of the lighting system  5 . The lighting system  5  includes a lamp light source  6 , a reflector (not shown) which reflects light emitted from the lamp light source  6  in a predetermined direction, and the intercepting unit  7 , which intercepts a portion of light emitted from the lamp light source  6 . 
   The reflector, for example, may be an elliptic mirror  8  shown in  FIG. 5A , or a parabolic mirror  9  shown in  FIG. 5B . In  FIG. 5A , the lighting system  5  includes the lamp light source  6 , the intercepting unit  7 , and the elliptic mirror  8 . A portion of light in a radial shape emitted from the lamp light source  6  is reflected on the elliptic mirror  8  and emitted via an opening of the elliptic mirror  8 . Light reflected from the intercepting unit  7  is further reflected on the elliptic mirror  8  and emitted. Here, since a middle portion of light emitted from the lamp light source  6  is intercepted by the intercepting unit  7 , light L emitted from the lighting system  5  becomes annular. 
   It is preferable that light reflected from the intercepting unit  7  goes toward the elliptic mirror  8  and thus is used as effective light so that the intercepting unit  7  does not cause loss of light. For this, it is preferable that the intercepting unit  7  is convex, the surface thereof curving toward the lamp light source  6 . The elliptic mirror  8  generally has a first focal point F 1  and a second focal point F 2 . The lamp light source  6  is disposed at the first focal point F 1 , and light reflected from the elliptic mirror  8  is focused at the second focal point F 2 . 
   In  FIG. 5B , the lighting system  5  has the parabolic mirror  9 . The intercepting unit  7  is installed in a predetermined position inside the parabolic mirror  9 . As described previously, the intercepting unit  7  reflects a portion of light emitted from the lamp light source  6  toward the parabolic mirror  9  and allows the light to go toward the periphery of the lighting system  5 , so that light is not emitted from the center of the lighting system  5 . In other words, the intercepting unit  7  induces light going toward the periphery of an optical axis C so as to intercept light emitted from the center of the lighting system  5  and use the intercepted light as effective light, so that loss of light can be prevented. Light reflected from the parabolic mirror  9  is annularly distributed. 
   Unlike light reflected from the elliptic mirror  8 , light reflected from the parabolic mirror  9  advances as parallel light. Thus, in a case where the parabolic mirror  9  is used, it is preferable that a focusing lens (not shown) focusing light onto the color filter  10  is further included. 
   The uniform light forming units  15 , which form light emitted from the lighting system  5  into uniform light, are further installed in the optical path between the lighting system  5  and the first reflecting mirror  20 . The uniform light forming units  15 , for example, may be integrating rods or an array of fly eye lenses. Shielding plates  14  may be placed in the center of the uniform light forming units  15 , so that light emitted from the lighting system  5  is not directly incident on the display device  23 . 
   The shielding plates  14  may be coated so that light does not pass through the uniform light forming units  15 . The lighting system  5  may include the shielding plates  14  instead of the intercepting units  7 , so that light emitted from the lighting system  5  is prevented from being directly incident the display device  23 . Here, it is preferable that the shielding plates  14  are formed in the centers of the uniform light forming units  15 . As shown in  FIG. 6 , the shielding plates  14  may be cross-shaped to prevent loss of light. 
   More preferably, the lighting system  5  includes the intercepting unit  7 , the uniform light forming units  15 , and the shielding plates  14 . As a result, light travelling through the intercepting unit  7  along the optical axis can be intercepted and loss of light can be prevented. Also, a portion of light that the intercepting unit  7  fails to completely intercept is shielded by the shielding plates  14 . Thus, the possibility that a portion of light reflected from the elliptic mirror  8  or the parabolic mirror  9  would travel along the optical axis c and be incident on the display device  23  can be excluded. 
   The intercepting unit  7  or the shielding plates  14  prevent light emitted from the lighting system  5  from being incident on the display device  23 , so that light that is made uniform via the first and second reflecting mirrors  20  and  25  is incident on the display device  23 . In other words, light emitted from the lighting system  5  is made uniform by the uniform light forming units  15 , made further uniform by the first and second reflecting mirrors  20  and  25 , and then made incident on the display device  23 . 
   The operation of the small-sized projection system having the above-described structure will be described below. 
   Light emitted from the lighting system  5  is split into R, G, and B color beams, according to a wavelength, by the color filter  10 , and the R, G, and B color beams sequentially move toward the collimating lenses  13 . Here, light having the annular intensity is formed due to the intercepting unit  7 . Light that the collimating lenses  13  form into parallel light has a uniform intensity due to the uniform light forming units  15 . If the uniform light forming units  15  are an array of fly eye lenses, each lens cell of the array of fly eye lenses corresponds to each pixel of the display device  23 . 
     FIG. 7  is a X-Z plane view of the projection system shown in  FIG. 3 . Light passing through the uniform light forming units  15  is incident on the first reflecting mirror  20 , and then reflected toward the second reflecting mirror  25 . Here, since the intercepting unit  7  of the lighting system  5  and the shielding plates  14  of the uniform light forming units  15  intercept light from going to the center of the optical axis C, light is not incident on the display device  23 . 
   It is preferable that the first reflecting mirror  20  and the second reflecting mirror  25  are symmetrical on the basis of the optical axis C. In other words, it is preferable that the lighting system  5 , the color filter  10 , the collimating lenses  13 , the uniform light forming units  15 , and the first reflecting mirror  20  are arranged in line, and the second reflecting mirror  25  is disposed in an upper space between the uniform light forming units  15  and the first reflecting mirror  20  so that they are not inclined to one side of the optical axis C. It is preferable that the first and second reflecting mirrors  20  and  25  are symmetrical on the y-z plane in  FIG. 7 . Then, a space for installing the first and second reflecting mirrors  20  and  25  can be minimized and the projection system can be made small and lightweight. 
   Light reflected from the second reflecting mirror  25  proceeds to the display device  23 . The display device  23  is turned on and off in each pixel according to an image signal input from the drive  22  to form a color image. The color image is enlarged and projected onto a screen (not shown) via a projection lens unit  30 . The projection lens unit  30  is installed close to the second reflecting mirror  25 , so that light is incident on each pixel when the display device  23  is turned on. 
   As described above, in an optical path in a projection system according to the present invention, a path of light reflected from the first reflecting mirror  20  to the second reflecting mirror  25 , and a path of light reflected from the second reflecting mirror  25  to the display device  23 , are included between the first and second reflecting mirrors  20  and  25 . Thus, the space occupied by the optical components is reduced. 
   Also, in the projection system according to the present invention, the arrangement structure of reflecting mirrors is improved to reduce the whole size of the system. In detail, an installation space is much more reduced by installing a display device in the surface of a reflecting mirror than when the reflecting mirror and the display device are installed in different positions. Furthermore, an optical path from a first reflecting mirror to a second reflecting mirror to the display device, and an optical path from the display device to a projection lens unit, is simplified to easily perform an optical design. 
   Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.