Abstract:
An system and method for improving asymmetric projection comprising a light source producing a light beam to form a light path, a projection lens disposed in the light path, a light valve inserted in the light path between the light source and the projection lens, and at least one anamorphic surface unit placed in the light path between the light source and the light valve. The anamorphic surface unit offsets a distortion of a light spot resulted from obliquely incidence on the light valve, thus an asymmetriclight spot can be improved as a more symmetric one to increase illuminating collection efficiency and uniformity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application incorporates by reference Taiwanese application Serial No.90128276, field on Nov. 15, 2001.  
         BACKGROUND OF INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a projection system and, more particularly, to an illuminating system and method for improving asymmetric projection in a projection system.  
           [0004]    2. Description of Related Art  
           [0005]    Referring to FIG. 1, a projection system  20  in a prior art is a single panel full color system having a light source  21  with a parabolic concave reflector  211  to emit a white light beam  23 . After reflected by the parabolic concave reflector  211 , the white light beam  23  passes through a converging lens  22  to converge the light beam  23  on a color wheel  24 . When rotating around a shaft, the color wheel  24  has a sequence of red, green, and blue filters to intercept the light beam  23  in order, so the light beam  23  shifts into a color light beam  25  as passing through the color wheel  24 . Then, the color light beam  25  transmits in order through an integration rod  26 , a condenser lens  27 , a stop  28 , and a relay lens  29  to impinge in a prism  30 , and a mirror  31  in the prism  30  reflects the color light beam  25  to a light valve  10 , such as Digital Micro-mirror Device (hereinafter referred to as “DMD”). Therefore, the light valve  10  modulates the color light beam  25  to generate an image light and reflects the image light into a projection lens  32  for projecting an image onto a screen (not shown).  
           [0006]    The DMD has an array of inclinable mirrors corresponding to an array of pixels constituting the image. When one of inclinable mirrors reflects a light beam to the screen, the inclinable mirrors is referred to as “on-state”; when reflecting a light beam off the screen, the pixel mirror is referred to as “off-state”; when the pixel mirror parallel the DMD board, that is between the on-state and the off-state, the pixel mirror is referred to as “flat-state”.  
           [0007]    [0007]FIG. 2 shows a second projection system  40  in a prior art. The difference, between the first projection system  20  and the second projection system  40 , is that the light source  41  of the second projection system  40  has an elliptic concave reflector  411 . The elliptic concave reflector  411  reflects and converges a light beam, emitted from the light source  41 , to a color wheel  44  without passing a converging lens. For the rest, the second projection system  40  is the same as the first projection system  20  and actually is one embodiment of the first projection system  20 . To simplify the description, the first projection system  20  was only described as an example in the following specification, but its technologies can be fully suitable for the second projection system  40 .  
           [0008]    In the first projection system  20 , from the light source  21  to the light valve  10 , the light beam passes through any optical element, such as the converging lens  22 , the color wheel  24 , integration rod  26 , the condenser lens  27 , the stop  28 , and the relay lens  29 , having the geometrically symmetric feature. Therefore, as shown in FIG. 3, before obliquely impinging onto the light valve  10 , the light beam has a rectangular cross section to form a rectangular-sectional light beam  51  with a feature of an intensely uniform illumination. If any above-mentioned optical elements and their assembly are perfect, the length of a first diagonal L 1  will be equal to that of a second diagonal L 2  on the rectangular-sectional light beam  51 , i.e. the rectangular-sectional light beam  51  has no distortion.  
           [0009]    Referring to FIG. 4, when the rectangular-sectional light beam  51 , passing through the prism  30 , obliquely impinges onto the light valve  10 , a light spot  52  is formed thereon. Consequently, the light spot  52  is distorted due to the inclined incidence, so that the length of the first diagonal L 1  isnt equal to that of the second diagonal L 2 , i.e. L 1 &gt;L 2 .  
           [0010]    The above-mentioned prior art has at least two drawbacks as follows: one reduces the uniform brightness of the light spot resulted from the unequal extension of two diagonals; the other causes the brightness loss on circumference of the light spot from the extension of the first diagonal L 1  out of the light valve and results in decreasing the illumination efficiency.  
         SUMMARY OF INVENTION  
         [0011]    One objective of the present invention is to provide a method for offsetting two asymmetric diagonals of the distorted light spot. By the use of an anamorphic surface unit of a projection system, the method will improves the asymmetric light spot resulted from the inclined incidence to achieve a more symmetric light spot.  
           [0012]    The other objective of the present invention is to use an anamorphic surface unit for producing two asymmetric orthogonal axes so that an illuminating system can generate a parabolic-sectional light beam with a smaller F-number. Thus, that can avoid the overlap of light beams between on-state and flat-state to raise the contrast. Furthermore, by amplifying the light spot, the projection system will increase the total illumination efficiency of the optic system. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic view showing a light path of a first projection system in the prior art;  
         [0014]    [0014]FIG. 2 is a schematic view showing a light path of a second projection system in the prior art;  
         [0015]    [0015]FIG. 3 is a schematic cross-sectional view showing a non-distortion rectangular light beam of a first projection system in the prior art before the light beam obliquely impinges onto the light valve;  
         [0016]    [0016]FIG. 4 is a schematic view showing a distorted rectangular light spot on the light valve in the prior art;  
         [0017]    FIGS.  5 (A)- 5 (C)is a schematic view showing an improving procedure by the use of an anamorphic surface unit;  
         [0018]    FIGS.  6 (A)- 6 (B) is a spot diagram respectively showing a brightness distribution of the light spot of the prior art and the present invention on DMD;  
         [0019]    FIGS.  7 (A)- 7 (B) is a schematic view showing the axial-extended elliptic light spot on the stop;  
         [0020]    [0020]FIG. 8 is a schematic view showing the relative positions of the open-state, off-state, and flat state of the light beam on the spot of the projection lens;  
         [0021]    FIGS.  9 (A)- 9 (B) is a spot diagram respectively showing the brightness distribution of the screen of the prior art and the present invention.  
         [0022]    [0022]FIG. 10 is an experimental data list showing the contrast between the present invention and the prior art. 
     
    
     DETAILED DESCRIPTION  
       [0023]    Referring to the drawings, the present invention will be described in a following embodiment. For solving a distortion of the prior art, the present invention is to provide an anamorphic surface unit for offsetting the distortion formed by two asymmetric diagonals of a light spot, so that the asymmetric light spot, resulting from inclined incidence of a projection system, can be improved into a more symmetric light spot.  
         [0024]    In general, the anamorphic surface unit may be formed on one surface of a lens, reflector, or mirror. Concretely, the anamorphic surface unit may be formed on any surface of the reflector  211 , converging lens  22 , condenser lens  27 , relay lens  29 , or mirror  31  of the projection system shown in FIG. 1.  
         [0025]    The anamorphic surface unit is formed on one surface of the relay lens  29  in this embodiment, for example. Referring to FIGS.  5 (A)- 5 (C), FIG. 5(B) shows a rectangular anamorphic lens having one normal surface and another convex surface with larger curvature at X-axis than Y-axis. FIG. 5(A) shows the distorted light spot on DMD, in which two diagonals at M and N direction is asymmetric each other, and the length of the N-direction diagonal is longer than that of the M-direction diagonal. When the anamorphic lens replaces the relay lens  29 , the X-axis of the anamorphic lens is in the N-direction of the distorted light spot, and the Y-axis is in the M- direction. Therefore, by means of the different amplifying rates due to the different curvature of the X-axis and the Y-axis, the length of the N-direction diagonal can be shortened to improve the asymmetric light spot on DMD for achieving a more symmetric light spot, shown in FIG. 5(C). In the same principle, by the use of the anamorphic surface unit with the different curvature, the light spot can appropriately be symmetrized or produced a predetermined distortion.  
         [0026]    Referring to FIG. 6, FIG. 6(A) shows a DMD spot diagram of the prior art without an anamorphic surface unit. Due to the inclined incidence, the light spot of the prior art generates a distortion and appears a diagonal extension from the down-left to up-right corner. That is, the length of the first diagonal L 1  is longer than that of the second diagonal L 2 , shown in FIG. 4. On the contrary, FIG. 6(B) shows a DMD spot diagram of the present invention with an anamorphic surface unit. By using an anamorphic surface unit to offset the distortion resulting from inclined incidence, a more symmetric light spot can be achieved. In contrast with the asymmetric light spot, the extension on the diagonal of the DMD light spot, shown in FIG. 6(B), have been improved obviously.  
         [0027]    Furthermore, because the light beam on DMD can only be reflected to the screen through the rear-end projection lens, an available rectangular region need to be defined for matching the DMD within the light spot shown in FIGS.  6 (A) and  6 (B). Owing to the producing tolerance, the available rectangular region is slightly larger than the DMD and has the same ratio of length and width as that of the DMD in order to make sure that the light beam can illuminate all DMD. Therefore, the illuminating loss area, between the peripheries of the available rectangular and the asymmetric DMD light spot in the prior art, is larger than that of the present invention, so the total light collection efficiency of the prior art is less than that of the present invention.  
         [0028]    Referring to FIGS.  7 (A) and  7 (B), FIG. 7(A) shows that the light spot on the stop of projection lens  32  is a circle spot due to the relay lens  29  without an anamorphic surface unit in prior art. FIG. 7(B) shows the light spot on the stop of projection lens  32  due to the relay lens  29  with an anamorphic surface unit. Because the relay lens  29  has the anamorphic surface with the different curvatures in X-axis and Y-axis to produce different amplifications, the light spot extends different lengths along the X-axis and Y-axis and forms an elliptic spot. Therefore, the Y-axis length of the light spot on the stop of projection lens  32  is elongated clearly, so that the shape of the light spot transforms a circular into an ellipse to increase the total light collection efficiency of projection system. The technology of the present invention will be described in detail as follows.  
         [0029]    [0029]FIG. 8 shows the relative positions of the on-state, off-state, and flat state of the light beam at the stop of the projection lens  32 . The solid line respectively represents the on-state light beam  61 , flat state light beam  62 , and off-state light beam  63  of the prior art, and the dotted line respectively represents the on-state light beam  64 , flat-state light beam  65 , and off-state light beam  66  of the present invention. In theory, the bigger the on-state light beam  61  is, the more light flex can be allowed to enter into the stop for achieving better brightness. If the on-state light beam  61  is enlarged to produce a light spot  611  having the same size as the stop  67 , the flat-state light beam  62  and off-state light beam  63  will also be enlarged as light spot  68  and  69  respectively. That causes the some overlaps between light spot  611  and light spot  68  to decrease the projection contrast. Therefore, the on-state light beam  61 , flat state light beam  62 , and off-state light beam  63  of the prior art are set to be next to each other and have no X-axial overlap between them, so that the maximum light flux can be allowed to pass without the sacrifice of contrast to achieve the best balance.  
         [0030]    The present invention uses an anamorphic surface unit for producing two asymmetric orthogonal axes to offset the distorted light spot formed by the inclined incidence of the prior art, so as to achieve a more symmetric light spot. Meanwhile, the present invention may also use the feature of two asymmetric orthogonal axes to extend the light spot of the on-state light beam  64 , flat-state light beam  65 , and off-state light beam  66  along Y-axis. Then, the diaphragm of the present invention is enlarged (i.e. the F number decreases). The on-state light beam  64 , flat state light beam  65 , and off-state light beam  66  of the present invention can respectively replace the on-state light beam  61 , flat state light beam  62 , and off-state light beam  63  of the prior art. Thus, the present invention can make sure that the elliptic light beam with the larger maximum light flux pass without any loss, and avoid the overlaps between the on-state light beam  64 , flat -state light beam  65 , and off-state light beam  66 .  
         [0031]    [0031]FIG. 9(A) and FIG. 9(B) respectively show the screen brightness distribution diagrams of the prior art and the present invention when the light beam on the DMD reflects onto the screen through the rear-end projection lens. As a result, the deep color, shown in FIG. 9(B), representing the high brightness distribution region of the present invention is larger than that of the prior art, as shown in FIG. 9(A), in the brightness region and uniformity of the screen diagram. Furthermore, the X-axis and Y-axis brightness distribution of the present invention is also indeed more uniform than that of the prior art in the screen diagram.  
         [0032]    Referring to FIG. 10, the experimental data list shows the contrast between the present invention and the prior art. The experimental datum includes the percentages of DMD efficiency DMD, overfill, the projection output efficiency of on-state, and the projection output efficiency of flat-state. The right columns of the list show the improving rate of the present invention compared with that of the prior art. As to the improving rates of the present invention, the DMD efficiency is 4.6%; the overfill loss is 16.8%; the projection output efficiency of on-state is 2.9%; the projection output efficiency of flat-state is 69.2%.  
         [0033]    Although the reflective DMD is a example for describing the above preferred embodiments, it can be replaced with a Liquid Crystal On Silicon (LCOS) or a Liquid Crystal Display (LCD) panel.  
         [0034]    The invention has been described using exemplary preferred embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.