Abstract:
A digital light processing (DLP) projection apparatus including an illumination system, a digital micro-mirror device (DMD) and an imaging system is provided. The DMD having a common plane and micro mirrors disposed on the common plane is disposed on a transmission path of the illumination beam to convert an illumination beam from the illumination system into an imaging beam into a screen. The imaging system includes a projection lens disposed on a transmission path of the imaging beam and a total internal reflection (TIR) prism disposed between the DMD and the projection lens. The projection lens has an optical axis, which is not parallel to a normal vector of the common plane and a chief beam of the imaging beam. At least one of the normal vectors of the surfaces of the TIR prism opposite to the projection lens and the DMD is not parallel to the optical axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority benefit of Taiwan application serial no. 95114512, filed on Apr. 24, 2006. All disclosure of the Taiwan application is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a projection apparatus, and more particularly, to a digital light processing (DLP) projection apparatus. 
         [0004]    2. Description of Related Art 
         [0005]    Referring to  FIG. 1 , a conventional digital light processing (DLP) projection apparatus  100  includes an illumination system  110 , a digital micro-mirror device (DMD)  120  and a projection lens  130 . The illumination system  110  has a light source  112 , which is suitable for providing an illumination beam  114 . The DMD  120  disposed on the transmission path of the illumination beam  114  is suitable for converting the illumination beam  114  into an imaging beam  122 . The projection lens  130  is disposed on the transmission path of the imaging beam  122  to project the imaging beam  122  onto a screen (not shown), thus forming an image on the screen. 
         [0006]    Referring to  FIGS. 1 and 2 , the DMD  120  has a plurality of micro mirrors  124  (only one is shown in  FIG. 2 ). Each of the micro mirrors  124  is suitable for tilting between angles of ±12 degrees. When one of the micro mirrors  124  rotates with the angle of +12 degrees (i.e., in an ON state), the illumination beam  114  is reflected to a pupil  132  of the projection lens  130 . The beam reflected to the pupil  132  is the imaging beam  122 . When one of the micro mirrors  124  does not rotate (i.e., in a FLAT state) or rotates with the angle of −12 degrees (i.e., in an OFF state), the beams  122   b,    122   c  reflected by one of the micro mirrors  124  deviate from the pupil  132  of the projection lens  130 . The edge portion of the beam  122   b  reflected by one of the micro mirrors  124  in the FLAT state is tend to enter the pupil  132  of the projection lens  130  to cause a decrease in contrast of the image projected on the screen by the projection lens  130 . 
         [0007]    Referring to  FIG. 3 , in order to improve the contrast of the image projected on the screen, an angle of the illumination beam  114  incident to the DMD  120  in the conventional DLP projection apparatus  100  is increased to make an inclined angle between a chief beam of the illumination beam  114  and a chief beam of the imaging beam  122  change from 24 degrees (as shown in  FIG. 2 ) to 26.5 degrees. Thus, it is avoided that the beam  122   b  reflected by one of the micro mirrors  124  in FLAT state enters the pupil  132  of the projection lens  130  to increase the contrast of the image. 
         [0008]      FIG. 4  is a schematic view showing an image  50  projected by a conventional DLP projection apparatus  100  in  FIG. 3 .  FIG. 5A  is a data diagram showing modulation transfer function (MTF) measured at position A and position B of the conventional DLP projection apparatus in  FIG. 4 .  FIG. 5B  is a data diagram showing MTF measured at position C and position D of the conventional DLP projection apparatus in  FIG. 4 . Referring to  FIGS. 3 ,  4 ,  5 A and  5 B, an axis of abscissas in  FIG. 5A  or  5 B shows a focus shift in units of millimeter, and an axis of ordinates in  FIG. 5A  or  5 B shows is the MTF. It is noted in  FIGS. 5A and 5B  that since the chief beam of the imaging beam  122  is not parallel to an optical axis X 1  of the projection lens  130 , thus resolutions of left and right sides of the image  50  projected by the conventional DLP projection apparatus  100  are not symmetrical. 
       SUMMARY OF THE INVENTION 
       [0009]    An objective of the present invention is to provide a digital light processing (DLP) projection apparatus that considers both the contrast of an image and the symmetry of the resolutions of the image. 
         [0010]    Another objective of the present invention is to provide a DLP projection apparatus to improve the symmetry the resolutions of the image. 
         [0011]    In order to achieve the aforementioned objectives or other objectives, a DLP projection apparatus suitable for projecting an imaging beam onto a screen is provided by the present invention. The DLP projection apparatus includes an illumination system, a digital micro-mirror device (DMD) and an imaging system. The illumination system is suitable for providing an illumination beam. The DMD having a common plane and a plurality of micro mirrors disposed on the common plane is disposed on a transmission path of the illumination beam. The micro mirrors are suitable for converting an illumination beam into an imaging beam. The imaging system includes a projection lens disposed on a transmission path of the imaging beam to project the imaging beam onto the screen and a total internal reflection (TIR) prism disposed between the DMD and the projection lens. The projection lens has an optical axis, which is not parallel to the normal vector of the common plane and a chief beam of the imaging beam. At least one of the normal vectors of the surfaces of the TIR prism opposite to the projection lens and the DMD is not parallel to the optical axis. 
         [0012]    In order to achieve the aforementioned or other objectives, the present invention provides another DLP projection apparatus suitable for projecting an imaging beam onto a screen. The DLP projection apparatus includes an illumination system, a DMD and a projection lens. The illumination system is suitable for providing an illumination beam. The DMD having a common plane and a plurality of micro mirrors disposed on the common plane is disposed on the transmission path of the illumination beam. These micro mirrors are suitable for converting the illumination beam into an imaging beam. The imaging system is disposed on the transmission path of the imaging beam to project the imaging beam onto the screen. The imaging system has an optical axis, which is the connecting line of the center of the common plane and the center of the screen. The normal vector of the common plane and the chief beam of the imaging beam are not parallel to the optical axis. The imaging system has a surface opposite to the DMD, and a normal vector of the surface is not parallel to the optical axis. 
         [0013]    The present invention changes the disposed angle of the DMD to alleviate the asymmetry problem of the resolutions of left and right sides of the image projected by the DLP projection apparatus. Moreover, one of the normal vectors of the surfaces of the TIR prism opposite to the DMD and the projection lens is not parallel to the optical axis of the projection lens, thus the optical path difference between the imaging beams resulting from the deviation of the DMD is compensated, and the image projected by the DLP projection apparatus is clear. 
         [0014]    In order to the make aforementioned and other objectives, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below. 
         [0015]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
           [0017]      FIG. 1  is a schematic view of a conventional DLP projection apparatus. 
           [0018]      FIG. 2  is an imaging schematic view of a conventional DLP projection apparatus. 
           [0019]      FIG. 3  is an imaging schematic view of another conventional DLP projection apparatus. 
           [0020]      FIG. 4  is a schematic view showing an image projected by the DLP projection apparatus in  FIG. 3 . 
           [0021]      FIG. 5A  is a data diagram showing modulation transfer function (MTF) measured at position A and position B of the conventional DLP projection apparatus in  FIG. 4 . 
           [0022]      FIG. 5B  is a data diagram showing MTF measured at position C and position D of the conventional DLP projection apparatus in  FIG. 4 . 
           [0023]      FIG. 6  is a schematic view of a DLP projection apparatus according to an embodiment of the present invention. 
           [0024]      FIG. 7  is an imaging schematic view of the DLP projection apparatus in  FIG. 6 . 
           [0025]      FIGS. 8A to 8C  are respectively the data diagrams showing the astigmatism field curves, the distortion and the lateral color to positions of the image projected by the DLP projection apparatus in  FIG. 6  according to the present invention. 
           [0026]      FIG. 9  is a diagram showing the recognizability of the DLP projection apparatus in  FIG. 6  according to the present invention. 
           [0027]      FIG. 10  is a schematic view of an image projected by the DLP projection apparatus in  FIG. 6  according to the present invention. 
           [0028]      FIG. 11  is a data diagram showing MTF measured from position E to position F of the image in  FIG. 10  according to the present invention. 
           [0029]      FIG. 12  is a data diagram showing relative illuminations measured from position E to position F of the image in  FIG. 10  according to the present invention. 
           [0030]      FIG. 13A  is a data diagram showing MTF measured at position A and position B of the image in  FIG. 10  according to the present invention. 
           [0031]      FIG. 13B  is a data diagram showing MTF measured at position C and position D of the image in  FIG. 10  according to the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0032]    Referring to  FIGS. 6 and 7 , a DLP projection apparatus  200  of an embodiment according to the present invention includes an illumination system  210 , a DMD  220  and an imaging system  230 . The illumination system  210  includes a light source  212  and a lens  214 . The light source  212  is suitable for providing an illumination beam  216  ( FIG. 6  only shows a chief beam of the illumination beam  216 ). The lens  214  is disposed between the light source  212  and the DMD  220 , and is located on a transmission path of the illumination beam  216 . In addition, the DMD  220  has a common plane  222  and a plurality of micro mirrors  224  (only one is shown in  FIG. 7 ) disposed on the common plane  222 . The DMD  220  is disposed on the transmission path of the illumination beam  216 . The micro mirrors  224  are suitable for converting the illumination beam  216  into an imaging beam  226  ( FIG. 6  only shows a chief beam L 1  of the imaging beam  226 ). 
         [0033]    The imaging system  230  includes a projection lens  232  and a TIR prism  234  disposed between the DMD  220  and the projection lens  232 . The projection lens  232  and the TIR prism  234  are disposed on a transmission path of the imaging beam  226  to project the imaging beam  226  onto a screen (not shown). The imaging system  230  has an optical axis, which is a connecting line of a center of the common plane  222  and a center of the screen (not shown). In the embodiment, an optical axis  236  of the projection lens  232  is parallel to an optical axis of the imaging system  230 . A normal vector N 1  of the common plane  222  of the DMD  220  and the chief beam L 1  of the imaging beam  226  are not parallel to the optical axis  236 . Moreover, at least one plane of the normal vectors of a surface  234   a  opposite to the projection lens  232  and a surface  234   b  opposite to the DMD  220  of the TIR prism  234  is not parallel to the optical axis  236 . In  FIG. 6 , a normal vector N 2  of the surface  234   b  opposite to the DMD  220  of the TIR prism  234  is not parallel to the optical axis  236 . 
         [0034]    In the above DLP projection apparatus  200 , the projection lens  232  includes a plurality of lenses  232   a,  and a connecting line of central points of the lenses  232   a  is the optical axis  236 . Moreover, one of the micro mirrors  224  is suitable for tilting between angles of ±θ degrees. When one of the micro mirrors  224  tilts in an angle of +θ degrees (i.e., in an ON state), the illumination beam  216  is reflected to a pupil  231  of the projection lens  230  to project the imaging beam  226  to the projection lens  232 . When one of the micro mirrors  224  do not tilt (i.e., in a FLAT state) or tilts in an angle of −θ degrees (i.e., in an OFF state), the beams  226 b,  226 c reflected by one of the micro mirror  224  deviate from the pupil  231  of the projection lens  230 . 
         [0035]    Referring to  FIG. 7 , it is notable that in the embodiment, an inclined angle α1 between the chief beam L 2  of the illumination beam  216  incident to the DMD  220  and the chief beam L 1  of the imaging beam  226  is larger than 2θ, so as to prevent the beam  226   b  from entering the pupil  231  of the projection lens  230 . Thus, the DLP projection apparatus  200  of the embodiment projects an image with high contrast. Moreover, the above θ is, for example, 12 degrees, and α1 is, for example, 26.5 degrees. 
         [0036]    In order to improve the asymmetry problem of the resolutions of left and right sides of the image projected by the conventional projection apparatus  100  in  FIG. 1 , in the embodiment, the tilting angle of the DMD  220  is particularly changed to make an angle between the normal vector N 1  of the common plane  222  of the DMD  220  and the optical axis  236  of the projection lens  232  be an acute angle α2, and α2≧0.1 degree, whereby resolutions of left and right sides of the image projected by the DLP projection apparatus  200  are relatively more symmetric than the resolutions of the image projected by the conventional projection apparatus  100  in  FIG. 1 . In a preferred embodiment, α2 is, for example, between 0.2 degrees and 0.4 degrees. 
         [0037]    As described above, since the change of the disposed angle of the DMD  220  makes a focus position projected on a screen focal plane of the imaging beam  226  deviate along with it, the image projected on the screen by the DLP projection apparatus  200  is not clear. According to Scheimpflug principle, only when an intersection of an extension plane of the common plane  222  of the DMD  220  and an extension plane of the screen is on an extension plane of a principle plane of the imaging system  230 , the image projected on the screen is clear. Therefore, in the embodiment, the normal vector N 2  of the surface  234   b  of the TIR prism  234  is particularly not parallel to the optical axis  236  of the projection lens  232 , thereby the principle plane of the imaging system  230  is changed, and thus making the intersection of the extension plane of the common plane  222  of the DMD  220  and the extension plane of the screen on the extension plane of the principle plane of the imaging system  230 . 
         [0038]    Moreover, since the disposed angle of the DMD  220  is changed, if the surface opposite to the DMD  220  of the TIR prism  234  is a surface  234   c,  i.e., the normal vector of the surface opposite to the DMD  220  of the TIR prism  234  is still parallel to the optical axis  236  of the projection lens  232 , distances between each point on the common surface  222  of the DMD  220  and the surface  234   c  of the TIR prism  234  is different. Thus, an optical path difference occurs between each of beams reflected by one of micro mirrors  224  in an ON state. Therefore, the problem of the optical path difference is alleviated by making the normal vector N 2  of the surface  234   b  of the TIR prism  234  be not parallel to the optical axis  236  of the projection lens  232 , thus improving an imaging quality of the DLP projection apparatus  200 . 
         [0039]      FIGS. 8A to 8C  are respectively the data diagrams showing the astigmatism field curves, the distortion and the lateral color to positions of the image projected by the DLP projection apparatus in  FIG. 6  according to the present invention. Referring to  FIGS. 8A to 8C , since the diagrams of the astigmatism field curves, the distortion or the lateral color are all in the range of the criteria, the DLP projection apparatus  200  of the embodiment has a good imaging quality. 
         [0040]      FIG. 9  is a diagram showing recognizability of the DLP projection apparatus in  FIG. 6  according to the present invention. In  FIG. 9 , the transverse axis represents the number of the line pairs that is shown in a distance of 1 millimeter, and the longitudinal axis represents the recognizability of the line pair number. It is noted in  FIG. 9  that even though the line pair number has reached 47 mm, the recognizability thereof is still above 0.7. Therefore, in the embodiment, the diagram between the recognizability and the line pair number is still conformed to the specification of the criterion when the tilting angle of DMD  220  is changed to make the normal vector N 2  of the surface  234   b  of the TIR prism  234  be not parallel to the optical axis  236  of the projection lens  232 . 
         [0041]      FIG. 10  is a schematic view of an image projected by the DLP projection apparatus in  FIG. 6  according to the present invention.  FIG. 11  is a data diagram showing MTF measured from position E to position F of the image in  FIG. 10  according to the present invention.  FIG. 12  is a data diagram showing relative illuminations measured from position E to position F of the image in  FIG. 10  according to the present invention. Referring to  FIGS. 11 and 12 , it is noted in  FIG. 11  that the MTF of S axis and T axis measured from position E to position F is in the range of the criterion. Moreover,  FIG. 12  shows that a uniformity corresponding to the relative illuminations measured from position E to position F of the image in the  FIG. 10  is also conformed to the criterion. 
         [0042]      FIG. 13A  is a data diagram showing MTF measured at position A and position B of the image in  FIG. 10  according to the present invention.  FIG. 13B  is a data diagram showing MTF measured at position C and position D of the image in  FIG. 10  according to the present invention. Referring to  FIGS. 5A ,  5 D,  13 A and  13 B, it is noted in comparisons of  FIG. 5A  and  FIG. 13A , and comparisons of  FIG. 5B  and FIG.  13 B that the resolutions of left and right sides of the image projected by the DLP projection apparatus  200  of the embodiment are more relative symmetrical than the resolutions of the image projected by the conventional DLP projection apparatus  100  in  FIG. 1 . 
         [0043]    Although, in the above embodiment, the asymmetry problem of the resolutions of left and right sides of the image is alleviated by making a normal vector of the surface  234   a  or  234   b  of the TIR prism  234  not parallel to the optical axis  236  of the projection lens  232 , however, the present invention improves the symmetry of the resolutions of left and right sides of the image by making at least one of the normal vectors of the surfaces of the lenses  232   a  opposite to the DMD  220  in the imaging system  230  be not parallel to the optical axis  236  of the imaging system  230 . In other words, in the present invention, the asymmetry problem of the resolutions of left and right sides of the image is alleviated by making the normal vector of the surface of at least one lens  232   a  of the projection lens  232  be not parallel to the optical axis  236  of the imaging system  230 , thus improving the imaging quality of the DLP projection apparatus  200 . 
         [0044]    To sum up, the present invention changes the disposed angle of the DMD to make the normal vector of the common plane of the DMD be not parallel to the optical axis of the projection lens, so as to alleviate the asymmetry problem of the resolutions of left and right sides of the image projected by the conventional DLP projection apparatus. Therefore, the DLP projection apparatus of the present invention considers both the contrast of the image and the symmetry of the resolutions of left and right sides of the image. Moreover, with one of the normal vectors of the surfaces of the lenses opposite to the DMD and the projection lens of the TIR prism being not parallel to the optical axis of the projection lens, the optical path difference between the imaging beams resulting from the deviation of the DMD is compensated, and the image projected by the DLP projection apparatus is clear. 
         [0045]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.