Patent Document

[0001]    This application claims priority to Taiwan Patent Application No. 096122039 filed on Jun. 20, 2007, the disclosures of which are incorporated herein by reference in their entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a light source device; more particularly, the present invention relates to a module that employs a plurality of light emitting diodes (LEDs) as a light source, and a display system comprising the light source module. 
         [0004]    2. Descriptions of the Related Art 
         [0005]    A light emitting construction employing LEDs as a light source is disclosed in U.S. patent application Ser. No. 11/081,825. The light emitting construction emits a light beam with a high driving current in a non-continuous lighting state. This construction forms a basis for a light source module and a projection system comprising the light source module. 
         [0006]    A light source module  1  as seen in  FIG. 1  comprises a first LED  111 , a second LED  112 , a mirror wheel  12 , and a power control device (not shown). The two LEDs  111 ,  112 , with the mirror wheel  12  being disposed therebetween, are disposed such that their light emitting paths are substantially orthogonal to each other. 
         [0007]    The mirror wheel  12  rotating about its axis  123  comprises a plurality of alternately disposed reflective sectors  121  and transparent sectors  122 . Through a microscopic breakdown analysis of its operation mode, it can be shown that when the power control device supplies a current to the first LED  111  in order to make it emit light, one transparent sector  122  of the mirror wheel  12  will be synchronously rotated to a position corresponding to a direction in which the first LED  111  emits light, so that the light beam can pass through and exit toward an output direction. Subsequently, when the power control device supplies a current to the second LED  112  instead and switches off the current to the first LED  111 , one reflection sector  121  of the mirror wheel  12  will be rotated to a position corresponding to the direction in which the second LED  112  emits light, so that the light beam from the second LED  112  is reflected and propagated toward the same output direction. In this way, the light source as a whole can provide the desired light rays in a fast alternating manner, effectively resulting in continuous light as perceived by the human eye. 
         [0008]      FIG. 2  is a schematic graph depicting an alternating emission duty cycle of the aforesaid light emitting structure. More specifically, the alternating emission of the two LEDs will result in an on-state light flux (i.e., the “flat peak section” labeled by symbol A) in the output light source. This setup is adapted to implement a nearly continuous light flux along the time axis as a replacement for the continuous operation mode associated with a single LED, and provides a higher luminance. 
         [0009]    However, such an ideal structure still has a defect in practical operation. That is, since reflective sectors  121  and transparent sectors  122  of the mirror wheel  12  are alternately disposed, a number of border regions between the reflective sectors and transparent sectors will be inevitably formed therebetween. In the case that a light beam from either LED impinges entirely or partly on such border regions, not only will a portion of the light beam be lost, but also the instantaneous flux will be degraded. 
         [0010]    To avoid the aforesaid light loss, the LEDs must be controlled so that light beam will not be emitted on the border regions. However, since the two LEDs have their positions fixed, the only solution for this setup is to switch off an operating LED in advance when a border region of the mirror wheel  12  is approaching a light beam, after which the opposite LED will be switched on immediately. In other words, the border regions should be accompanied by an off-state (i.e., the “narrow trough section” labeled by symbol B), and only after the border region pass through the LED, can the opposite LED be allowed to emit a light beam. 
         [0011]    However, as is well known, a LED is a light source that provides a highly diffusive light beam, rather than an ellipsoidal lamp of collective nature or a parabolic lamp that provides a parallel light beam. As a result, the light beam projected by a LED will actually occupy a substantial area on the mirror wheel  12 , and the aforesaid solution of switching on and off for LEDs in advance is impractical to achieve the desired effect. Moreover, using this method to skip the border regions, the numerous borders regions on the mirror wheel  12  will cause a substantial area on the mirror wheel  12  that is unusable at the very onset, which will not only shorten the desirable A sections (“flat peak sections”) and lengthen the undesirable B sections (“narrow trough sections”) in the otherwise continuous light flux, but also exacerbate the discontinuity in the light flux and substantially degrade the efficiency the mirror wheel  12 . 
         [0012]    In view of this, there exists an urgent need in the art to provide a light source module that partly or completely obviates such disadvantages, and a display system comprising the light source module. 
       SUMMARY OF THE INVENTION 
       [0013]    One objective of this invention is to provide a light source module featuring higher luminescent efficiency, sufficient light flux, and sustained continuity as seen by the human eye, and to provide a display device comprising the same. 
         [0014]    To this end, a light source module of this invention comprises a mirror wheel and at least two light source submodules. The mirror wheel includes a central rotating shaft and a body. The body is disposed at an outer edge of the central rotating shaft, and comprises an inner portion and an outer portion formed at an outer edge of the inner portion. The outer portion comprises at least one reflective segment and at least one transparent segment, which are alternately arranged along the outer edge of the inner portion. The at least two light source submodules are disposed at opposite sides of the mirror wheel, each comprising a light emitting diode (LED) and at least one light collecting element. The at least one light collecting element is adapted to converge the light beam projected from the LED to the reflective segment or the transparent segment. 
         [0015]    A display system of this invention comprises a light source system, a light guiding system and an imaging system. The light source system comprises a first light source module and a second light source module, and is configured to provide light beams used for imaging. The light guiding system is adapted to guide the light beams generated by the light source system to the imaging system so as to be imaged by the imaging system. The first light source module comprises the aforesaid light source module and is configured to provide a first-color light beam, while the second light source module is configured to provide light beams having a plurality of colors different from the first color light beam. The first color light beam and the plurality of color light beams with different colors are lit and entering the light guiding system according to the predetermined integrated timing. 
         [0016]    The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1A  is a schematic view of an arrangement between a mirror wheel and a light source in the prior art; 
           [0018]      FIG. 1B  is a schematic plan view of the mirror wheel of  FIG. 1A ; 
           [0019]      FIG. 2  is a graph showing the light flux-time relationship in the alternating emission duty cycle structure shown in FIG  1 A; 
           [0020]      FIG. 3A  is a schematic view of a display system in accordance with a first embodiment of this invention; 
           [0021]      FIG. 3B  is an emission timing diagram for the structure of  FIG. 3A ; 
           [0022]      FIG. 4A  is a schematic view of a display system in accordance with a second embodiment of this invention; 
           [0023]      FIG. 4B  is an emission timing diagram for the structure of  FIG. 4A ; and 
           [0024]      FIG. 5  is a schematic view of a mirror wheel in accordance with the first embodiment of this invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    A display system  3  in accordance with a first embodiment of this invention is depicted in  FIG. 3A . The display system  3 , which in this embodiment is a digital light processing (DLP) projector, comprises a light source system  31 , a light guiding system  33 , and an imaging system  35 . 
         [0026]    The light source system  31 , comprising a first light source module  311  and a second light source module  321 , is configured to provide a light beam needed for imaging. The first light source module  311  comprises a mirror wheel  313 , two submodules, and a controller (not shown). 
         [0027]    Referring to  FIG. 5 , the mirror wheel  313  has a central rotating shaft  310  and a body  312  with, in this embodiment, a disc shape. For reference, the body  312  may be a disc of 5 cm in diameter (the diameter can be adjusted depending on actual requirement). The body  312  is disposed at an outer edge of the central rotating shaft, and comprises an inner portion and an outer portion formed at an outer edge of the inner portion. The outer portion has a plurality of reflective segments  314  and a plurality of transparent segments  316 , with these reflective segments  314  and transparent segments  316  alternately arranged along the outer edge of the inner portion. The reflective segments  314  shown in the figure are spaced apart with one another along the outer edge of the inner portion, so as to form a hollowing segment between two adjacent reflective segments  314  that is adapted to define each of the transparent segments  316 . In this embodiment, there are two reflective segments  314  and two transparent segments  316  as shown in  FIG. 5 , although implementations with only one or more than one reflective segments  314  and transparent segments  316  may occur to those skilled in this field. 
         [0028]    The first light source submodule and the second light source submodule are disposed symmetrically with respect to the mirror wheel  313 . The first light source submodule includes a first LED  3151  and a first light collecting element  3153  that is adapted to converge the light beam that is emitted from the first LED  3151  for projecting to the reflective segments  314  according to a first timing (G 1 ). The second light source submodule includes a second LED  3171  and a second light collecting element  3173  that is adapted to converge the light beam that is emitted from the second LED  3171  for projecting to the transparent segments  316  according to a second timing (G 2 ). In this embodiment, the light collective elements may be lenses, while the first LED  3151  and the second LED  3171  are both green LEDs. 
         [0029]    A controller (not shown) is electrically connected to the two light source submodules for controlling the input voltages of the first timing (G 1 ) and the second timing (G 2 ). In this embodiment, the first timing (G 1 ) and the second timing (G 2 ) are indicated that the controller provides input voltages in an alternating pulse format. 
         [0030]    It can be seen from the timing diagrams of  FIG. 3B  that the first LED  3151  and the second LED  3171  are configured to emit light beams at different times. After being reflected from the reflective segments  314  or transmitted through the transparent segments  316 , the light beams emitted from the two LEDs follow an overlapped path for providing a light beam of a first color to the light guiding system  33 , wherein the first color is green. The alternate disposition of the reflective segments  314  and the transparent segments  316  is adopted to correspond with the switching between the first light source submodule and the second light source submodule. The three pulses of the first timing (G 1 ) correspond to the light beams emitted from the first LED  3151  projecting onto the reflective segments  314  of the mirror wheel  313 , while the three pulses of the second timing (G 2 ) correspond to the light beams emitted from the second LED  3171  projecting onto the transparent segments  316  of the mirror wheel  313 . Here, an extremely high switching speed could be reached by LEDs, which depends on the number of transparent segments  316  and reflective segments  314  as well as the rotation speed of the mirror wheel  313 . 
         [0031]    The second light source module  321  is configured to provide light beams of a plurality of colors which is different from the first color, with the number of colors used in this case, but not limited to, two. The second light source module  321  comprises a third LED  3211 , a fourth LED  3213 , and a light coupling element  3215 , wherein the light coupling element  3215  is adapted to direct light beams emitted from the third LED  3211  and the fourth LED  3213  to the light guiding system  33 . In this embodiment, the third LED  3211  is configured to emit a blue light beam according to a third timing (B), and the fourth LED  3213  is configured to emit a red light beam according to a fourth timing (R). 
         [0032]    In accordance with a predetermined integrated timing comprising a first, a second, a third, and a fourth timings, as shown in  FIG. 3B , these LEDs in the first light source module  311  and the second light source module  321  emit light beams of the first color (green) and the plurality of different colors (blue and red) and project them into the light guiding system  33 . 
         [0033]    In this embodiment, the light guiding system  33  is a light coupling mirror for combining the light beams of colors from two directions into the same direction, which is adapted to guide the light beams of the first color emitted from the first light source module  311  directly to the imaging system  35 , and guide the light beams of the plurality of colors emitted from the second light source module  321  also to the imaging system  35 . Additionally, the light coupling mirror and the aforesaid light coupling element  3215  of the second light source module  321  may also be an X-plate, a dichroic mirror, a prism, or a color filter. 
         [0034]    In this embodiment, the imaging system  35  comprises a lens array assembly  37 , a digital micromirror device (DMD)  351  and a prism  39 . Hence, the light beams of the first color and the plurality of colors guided by the light guiding system  33  are then processed by the lens array assembly  37  into light beams of uniform luminance. They are then imaged by the DMD  351  before being finally projected via the prism  39  onto a screen. 
         [0035]    A display system  4  in accordance with the second embodiment of this invention is depicted in  FIG. 4 . The display system  4 , which is a LCD projector in this embodiment, comprises a light source system, a light guiding system  43 , and an imaging system. As depicted in  FIG. 4A , the display system  4  is generally similar to the display system  3  (see  FIG. 3A ), with the main difference lying in the arrangement and setup of the optical elements. In addition, as depicted in  FIG. 4B , the integrated timing applied in the display system  4  is completely different from that in the display system  3 . 
         [0036]    In the second embodiment, the light source system with a first light source module  411  and a second light source module  421  comprised therein is the same as the first embodiment, except for the arranged location of the light source modules and the timing of the second light source module  421 . In accordance with a predetermined integrated timing comprising a first, a second, a third, and a fourth timings as shown in  FIG. 4B , the LEDs in the first light source module  411  and the second light source module  421  emit light beams of the first color (green light beam) and the plurality of different colors (blue and red light beams). The light beams of the first color are then processed by a first lens array assembly  471  into beams of uniform luminance for projecting directly to the imaging system, while the light beams of the plurality of colors are processed by a second lens array assembly  473  into beams of uniform luminance for projecting into the light guiding system  43 . 
         [0037]    The light guiding system  43  comprises a beam splitter  431  and two mirrors  433 ,  435 . The beam splitter  431  is adapted to separate blue and red light beams, emitted from the second light source module  421  and combined through the light coupling elements  4215 . The separated blue and red light beams are then directed by adjacent mirrors  433 ,  435  respectively for projection to the imaging system. In this embodiment, the beam splitters and the aforesaid light coupling element  4215  of the second light source module  421  may also be an X-plate, a dichroic mirror, a prism or a color filter. The imaging system is adapted to image the green, red, and blue light beams. In this embodiment, the imaging system comprises three liquid crystal devices  451  and an x-cube  453 , with the three liquid crystal devices  451  being configured to process the green light beam emitted from the first light source module  411  and the red and blue light beams separated through the beam splitter  431  and guided by the mirrors  433  and  435 , respectively. Finally, the x-cube  453  combines the green, red, and blue light beams into an imaging beam for projecting onto the screen. 
         [0038]    In the embodiments described above, additional light collective elements may be optionally provided in the display system between the light source system and the light guiding system, between the light guiding system and the imaging system, or within the light source system. Other optical elements may also be added to modify the light path, thereby reducing the size of the display system. 
         [0039]    According to this invention, LEDs are lit at particular timings intermittently so that they can endure higher current and therefore deliver higher luminance. In these embodiments, the intermittent lighting mode endows the two LEDs of the first light source module with higher efficiency. Additionally, the converged green light beam can substantially reduce the projection area of the beam on the mirror wheel, thereby shortening the transition time compared to the large projection area on the mirror wheel in the prior art. Therefore, a display device utilizing this invention can display with optimal luminance efficiency. 
         [0040]    The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.

Technology Category: g