Patent Document

[0001]    This application claims priority to Taiwan Patent Application No. 096121738 filed on Jun. 15, 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 provides a light source system and a display apparatus comprising the same, and particularly, relates to a light emitting diode (LED) light source system with high luminance and a display apparatus comprising the same. 
         [0004]    2. Descriptions of the Related Art 
         [0005]    Currently, more projection display apparatuses are adopting light emitting diodes (LEDs) as the light source in an attempt to increase the color gamut and decrease the power consumption. Because its short startup time and long life, light source of LED is used to replace high-pressure-mercury lamps in conventional projection display apparatuses. However, as a kind of divergent light source, LED is restricted by the etendue conservation law that makes the light source effective only within a limited light source area and a limited angle. Consequently, the luminance of the projection display apparatus cannot be improved by simply adding more LED light sources. As a result, it is important to improve the luminance of a projection display apparatus adopting LEDs as the light source. 
         [0006]    A light source module employing LEDs as the light source and a projection system comprising the light source module are disclosed in U.S. patent application Ser. No. 11/081,825. The light source module, a structure of which is depicted in  FIG. 1A , drives the LEDs with discrete pulses and provides increased luminance by receiving a high current input. As shown in  FIG. 1A , such a light source module  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  disposed therebetween, are disposed such that their light emitting paths are substantially orthogonal to each other. 
         [0007]    As depicted in  FIG. 1B , the mirror wheel  12  rotating about its axis  123  comprises a plurality of interleaved reflective segments  121  and transmitting segments  122 . When the power control device supplies a current to the first LED  111  to emit light, one transmitting segment  122  of the mirror wheel  12  will be rotated synchronously to a position corresponding to a direction in which the first LED  111  emits light, so that the light can transmit therethrough and exit towards the output direction. On the other hand, when the power control device supplies a current to the second LED  112  instead and switches off the current input of the first LED  111 , one reflective segment  121  of the mirror wheel  12  will be rotated to a position corresponding to a direction in which the second LED  112  emits light, so that the light from the second LED  112  is reflected and propagates in the same output direction. In this way, the two LEDs as a whole can provide the desired light beams in a fast alternating manner, resulting in an almost continuous light as perceived by the human eye. 
         [0008]      FIG. 2  is a schematic graph depicting the alternating emission duty cycle of the aforesaid light emitting structure. More specifically, the alternating emission of the two LEDs will result in a higher luminance, as well as a light flux of an On-State (i.e., the “flat peak section” labeled by symbol A) in the output light, which is adapted to form a nearly continuous light flux along the time axis as a replacement for the continuous operation mode of a single LED. 
         [0009]    However, in the practical operation of this structure, since the mirror wheel  12  consists of a plurality of reflective segments  121  and transmitting segments  122  interleaved with each other, a number of border regions will be inevitably formed therebetween. If a light beam from either of the LEDs impinges entirely or partially on such border regions, not only will light be lost, but also the instantaneous output light flux will be degraded. 
         [0010]    To avoid the aforesaid light loss, the LEDs must be controlled to not emit light in the border regions as far as possible. However, since positions for two LEDs already have fixed, the only solution is to switch off the operating LED in advance when the border region of the mirror wheel  12  is nearly approaching a light beam of a LED, after which the opposite LED will be switched on immediately. In other words, the border regions should be accompanied with an Off-State (i.e., the “narrow trough section” labeled by symbol B) as fast as possible. The opposite LED will be allowed to emit light only when the border region passes by the LED. 
         [0011]    However, as is well known, LEDs provide a highly divergent light beam, rather than a collecting light beam from an ellipsoidal lamp or a parallel light beam from a parabola lamp. As a result, the light beam projected on by an LED will actually occupy a substantial area on the mirror wheel  12 , which makes it impractical to switch the LEDs on and off in advance to achieve a desired effect. In addition, when border regions are skipped, the borders regions on the mirror wheel  12  will create a substantial unusable area on the mirror wheel  12 . This will not only undoubtedly shorten the desirable “flat peak sections” and lengthen the unwanted “narrow trough sections” in the otherwise continuous light flux, but also exacerbate the discontinuity in the light flux and degrade the usage efficiency of the mirror wheel  12  significantly. Furthermore, this structure relies entirely on a mirror wheel to integrate the light beams. Each additional mirror wheel may further increase the size of the projection display apparatus significantly. Therefore, in consideration of practical requirements on size of a projection display apparatus, luminance improvement this structure may provide is limited. 
         [0012]    In summary, the LED light source structure used in the prior art projection display apparatuses has deficiencies, such as low light emission efficiency, limited room for the improvement of luminance and discontinuous light flux. In view of this, it is highly desirable to provide a light source system with higher luminance, continuous light flux and increased light emission efficiency. 
       SUMMARY OF THE INVENTION 
       [0013]    One objective of this invention is to provide a light source system and a display apparatus comprising the same. This light source system may deliver improved luminance, increased light emission efficiency and sufficient light flux, while maintaining a continuous light output as perceived by the human eye. 
         [0014]    To this end, a light source system of this invention comprises a mirror wheel and two light source modules. 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 has an inner area and an outer area. The outer area is formed at an outer edge of the inner area, and comprises one reflective segment and one transmitting segment, both arranged along the outer edge of the inner area interleavedly and continuously. The two light source modules, each comprising a plurality of light emitting diodes (LEDs) and the light collecting element, are disposed at two opposite sides of the mirror wheel respectively. The light collecting element is adapted to converge the light beams projected from the LEDs to one of the reflective segments and the transmitting segment. 
         [0015]    A display apparatus of this invention comprises the aforesaid light source system and an imaging system. The light source system is configured to provide light beams for imaging. The two light source modules included in the light source system are configured to provide two light beams respectively. These light beams are lighted up according to a predetermined integrated timing sequence to form a continuous light for transmission to the imaging system. The imaging is configured to image with the light provided from the light source system. 
         [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  illustrates the deployment relationship between a mirror wheel and light sources in the prior art; 
           [0018]      FIG. 1B  illustrates the mirror wheel of  FIG. 1A ; 
           [0019]      FIG. 2  is a graph showing the light flux versus time in the alternately light emitting structure shown in  FIG. 1A ; 
           [0020]      FIG. 3A  illustrates the display apparatus in accordance with the first embodiment of this invention; 
           [0021]      FIG. 3B  is a timing diagram for the light emission of the structure of  FIG. 3A ; 
           [0022]      FIG. 4A  illustrates a display apparatus in accordance with the second embodiment of this invention; 
           [0023]      FIG. 4B  is a timing diagram for the light emission of the structure of  FIG. 4A ; 
           [0024]      FIG. 5A  illustrates the mirror wheel in the first embodiment of this invention; and 
           [0025]      FIG. 5B  illustrates the mirror wheel in the second embodiment of this invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    A display apparatus  3  in accordance with a first embodiment of this invention is depicted in  FIG. 3A . The display apparatus  3 , which in this embodiment is a projector, comprises a light source system  31  and an imaging system  33 . The light source system  31 , which is configured to provide a light beam for imaging, comprises a mirror wheel  311 , a first light source module  313 , a second light source module  315  and a controller (not shown). 
         [0027]    As shown in  FIG. 5A , the mirror wheel  311  has a central rotating shaft  310  and a body  312  which in this embodiment is shaped like a disc, for example, a disc of 5 cm in diameter (the diameter can be adjusted depending on the actual requirements). The body  312  is disposed at an outer edge of the central rotating shaft  310 , and comprises an inner area and an outer area formed at an outer edge of the inner area. The outer area has a plurality of reflective segments  314  and a plurality of transmitting segments  316 , with the reflective segments  314  and the transmitting segments  316  arranged along the outer edge of the inner area alternately and continuously. The reflective segments  314  are equally spaced apart with one another along the outer edge of the inner area to form a hollow segment that is adapted to define each of the transmitting segments  316 . In this embodiment, there are two reflective segments  314  and two transparent segments  316  as shown in  FIG. 5A . The reflective segments  314  and the transmitting segments  316  are arranged alternately for the purpose of switching between the first light source module  313  and the second light source module  315 . Embodiments may also have one reflective segment  314  and transmitting segment  316  or more than one of them. 
         [0028]    The first light source module  313  and the second light source module  315  are disposed symmetrically with respect to the mirror wheel  311 . A controller (not shown) is electrically connected to the two light source modules to control the voltage levels of a first main timing sequence and a second main timing sequence inputted to the two light source modules respectively. The first light source module  313  includes a first LED  3131 , a second LED  3133 , a third LED  3135 , a first light coupling element  3137  and a first light collecting element  3139 . The first LED  3131 , the second LED  3133  and the third LED  3135  are lit up to emit light according to the first main timing sequence. The first light coupling element  3137  is adapted to redirect light beams projected by the LEDs to the first light collecting element  3139 . The first light collecting element  3139  is adapted to converge the light beam from the first coupling element  3137  to form a first light beam for projecting onto the reflective segments  314 . The first LED  3131 , the second LED  3133  and the third LED  3135  are green, red and blue respectively. 
         [0029]    As shown in the timing diagram of  FIG. 3B , the first main timing sequence comprises three timing subsequences, i.e., a first timing sequence G 11 , a second timing sequence R 11  and a third timing sequence B 11 , according to which the first LED  3131 , the second LED  3133  and the third LED  3135  project light beams to the first light collecting element  3139  successively. The main timing sequence and the timing subsequences are configured to provide input voltages in an interleaved pulse format. 
         [0030]    The second light source module  315  includes a fourth LED  3151 , a fifth LED  3153 , a sixth LED  3155 , a second light coupling element  3157  and a second light collecting element  3159 . The fourth LED  3151 , the fifth LED  3153  and the sixth LED  3155  are lit up to emit light according to the second main timing sequence. The second light coupling element  3157  is adapted to redirect light beams projected by each of these LEDs to the second light collecting element  3159 . The second light collecting element  3159  is adapted to converge the light beam from the second coupling element  3157  to form a second light beam for projecting onto the transmitting segments  316 . The fourth LED  3151 , the fifth LED  3153  and the sixth LED  3155  are green, red and blue respectively. In this embodiment, the first light coupling element  3137  and/or the second light coupling element  3157  is an X-plate respectively. The first light collecting element  3139  and/or the second light collecting element  3159  comprises a lens respectively. It should be noted that the number of the LEDs, color and location of the light coupling elements, as well as the number, type and location of the light collecting elements are not just limited to those described above. For example, in other embodiments, the first light coupling element  3137  and/or the second light coupling element  3157  may also be a prism. 
         [0031]    As shown in the timing diagram of  FIG. 3B , the second main timing sequence comprises three timing subsequences, i.e., a fourth timing sequence G 12 , a fifth timing sequence R 12  and a sixth timing sequence B 12 , according to which the fourth LED  3151 , the fifth LED  3153  and the sixth LED  3155  project light beams to the second light collecting element  3159  successively. These timing sequences are configured to provide input voltages in an interleaved pulse format. 
         [0032]    It can be seen from the timing diagram of  FIG. 3B  that the first LED  3131 , the second LED  3133  and the third LED  3135  of the first light source module  313 , and the fourth LED  3151 , the fifth LED  3153  and the sixth LED  3155  of the second light source module  315  are configured to emit light at different times. In other words, the controller is configured to light up the first light beam and the second light beam according to a preset integrated timing sequence depicted in the timing diagram. Specifically, in the first main timing sequence, there are three pulses for each of the three subsequences thereof. The total duration of the nine pulses included in a main timing sequence constitutes a so-called duty cycle. Driven by the nine pulses, the LEDs of the first light source module  313  are lit up successively for projecting a light beam onto the reflective segments  314  of the mirror wheel  311 . Similarly, in the second main timing sequence, there are three pulses for each of the three subsequences thereof, and the LEDs are driven by the nine pulses. The LEDs of the second light source module  315  are lit up successively for projecting a light beam onto the transmitting segments  316  of the mirror wheel  311 . Here, the LEDs of these light source modules have an extremely high switching speed, which depends on the number of transmitting segments  316  and reflective segments  314  as well as the rotation speed of the mirror wheel  313 . 
         [0033]    The first light source module  313  and the second light source module  315  operate alternately in respective duty cycles to produce the first and the second light beams which, as a whole, appear as a continuous light beam to the human eye. Then, the first and the second light beams propagate into the imaging system  33  through the reflective segments  314  and the transmitting segments  316  of the mirror wheel  311  respectively. 
         [0034]    In this embodiment, the imaging system  33  comprises a lens array assembly  331 , a digital micromirror device (DMD)  333  and a prism  335 . Hence, after the light beams projected via the first light collecting element  3139  and the second light collecting element  3159  to the mirror wheel  311  are reflected from/transmitted through the mirror wheel  311 , the resulting continuous light beams are processed by the lens array assembly  331  into light beams of uniform luminance and then reflected from the prism  335  to the DMD  333  for imaging. Finally, an image is projected via the prism  335  onto a screen (not shown). 
         [0035]    In this embodiment, the two light source modules operate alternately to emit light beams so a duty cycle of either the light source modules is equal to a time period in which the mirror wheel  311  accomplish a quarter of the rotation. This time period in turn corresponds to the time periods when the first and the second light beams impinge on the reflective segments  314  and the transmitting segments  316  respectively. As individual LEDs are lighted up discretely according to a specific timing sequence in each duty cycle, the LEDs are able to withstand a higher current, thus giving rise to an increased overall luminance of the display apparatus  3 . 
         [0036]    A second embodiment of this invention, which is also a display apparatus  4 , is depicted in  FIG. 4A . Similarly, the display apparatus  4  comprises a light source system and an imaging system  43 . In this embodiment, the display apparatus  4  is a projector. However, unlike the first embodiment, the light source system of this embodiment comprises three light source modules, i.e., a first light source module  413 , a second light source module  415  and a third light source module  417  respectively. Additionally, in consideration of the additional third light source module  417 , although a mirror wheel  411  in this embodiment still comprises two reflective segments  414  and two transmitting segments  416 , both the reflective segments  414  thereof are further divided into a first reflective segment  414 A and a second reflective segment  414 B respectively, as shown in  FIG. 5B . Here, the first reflective segment  414 A, the second reflective segment  414 B and the transmitting segment  416  are arranged alternately for switching between the first light source module  413 , the third light source module  417  and the second light source module  415 . It should be noted herein that to adapt to different incident directions of the first light beam from the first light source module  413  and the third light beam from the third light source module  417 , the mirror wheel  411  should have different reflection angles (not shown) in the cross-sections of the first reflective segment  414 A and the second reflective segment  414 B so that these light beams are reflected in the same direction. 
         [0037]    In the light source system of this embodiment, the first light source module  413  and the second light source  415  are just the same as the first light source module  313  and the second light source module  315  of the first embodiment, and hence will not be described in detail again. The three light source modules are disposed with respect to the mirror wheel  411  in such a way that light beams projected by these light source modules will impinge exactly on the first reflective segment  414 A, the transmitting segment  416  and the second reflective segment  414 B respectively. 
         [0038]    The third light source module  417  includes a seventh LED  4171 , an eighth LED  4173 , a ninth LED  4175 , a third light coupling element  4177  and a third light collecting element  4179 . The seventh LED  4171 , the eighth LED  4173  and the ninth LED  4175  are lit up to emit a plurality of light beams according to a third main timing sequence. The third light coupling element  4177  is adapted to redirect light beams projected by each of these LEDs to the third light collecting element  4179 . The third light collecting element  4179  is adapted to converge the light beam from the third coupling element  4177  to form a third light beam for projecting onto the second reflective segments  414 B. The seventh LED  4171 , the eighth LED  4173  and the ninth LED  4175  are green, red and blue respectively. In this embodiment, the third light coupling element  4177  is an X-plate, while the third light collecting element  4179  comprises a lens. It should be noted that the number of LEDs, color and location of the light coupling elements, as well as the number, type and location of the light collecting elements are not just limited to what described above. For example, in other embodiments, the third light coupling element  4177  may also be a prism. 
         [0039]    As shown in the timing diagram of  FIG. 4B , the third main timing sequence comprises three timing subsequences, i.e., a seventh timing sequence G 23 , an eighth timing sequence R 23  and a ninth timing sequence B 23 , according to which the seventh LED  4171 , the eighth LED  4173  and the ninth LED  4175  project light beams to the third light collecting element  4179  successively. These timing sequences are configured to provide input voltages in an interleaved pulse format. 
         [0040]    The first light source module  413  and the second light source module  415  of this embodiment are the same in structure as those of the previous embodiment. However, the first timing sequence G 21 , the second timing sequence R 21  and the third timing sequence B 21  followed respectively by the first LED  4131 , the second LED  4133  and the third LED  4135  of the first light source module  413 , as well as the fourth timing sequence G 22 , the fifth timing sequence R 22  and the sixth timing sequence B 22  followed respectively by the fourth LED  4151 , the fifth LED  4153  and the sixth LED  4155  of the second light source module  415  are different from the first timing sequences G 11 , the second timing sequence R 11 , the third timing sequence B 11 , the fourth timing sequence G 12 , the fifth timing sequence R 12  and the sixth timing sequence B 12  of the previous embodiment. 
         [0041]    Furthermore, it can be seen from the timing diagram of  FIG. 4B  that the first LED  4131 , the second LED  4133  and the third LED  4135  of the first light source module  413 , the fourth LED  4151 , the fifth LED  4153  and the sixth LED  4155  of the second light source module  415 , and the seventh LED  4171 , the eighth LED  4173  and the ninth LED  4175  of the third light source module  417  are configured to emit light at different times. In other words, a controller is configured to light up the first, the second and the third light beams according to the preset integrated timing sequence depicted in the timing diagram. Specifically, in the first main timing sequence, there are three pulses for each of the three subsequences thereof. The total duration of the nine pulses included in a main timing sequence constitutes a so-called duty cycle. Driven by the nine pulses, the LEDs of the first light source module  413  are lit up successively for projecting a first continuous light beam onto the first reflective segments  414 A of the mirror wheel  411 . In the second main timing sequence, there are three pulses for each of the three subsequences thereof, thus constituting another duty cycle. Driven by the nine pulses, the LEDs of the second light source module  415  are lit up successively for projecting a second continuous light beam onto the transmitting segments  416  of the mirror wheel  411 . Similarly, driven by the third main timing sequence, the LEDs of the third light source module  417  are lit up successively for projecting a third continuous light beam onto the second reflective segments  414 B of the mirror wheel  411 . Here, the LEDs described above have an extremely high switching speed, which depends on the number of transmitting segments  416  and reflective segments  414  as well as the rotation speed of the mirror wheel  411 . 
         [0042]    Briefly speaking, the first light source module  413 , the second light source module  415  and the third light source module  417  are configured to operate one-by-one repeatedly. The first, the second and the third light beams emitted by these light source modules are projected onto the first reflective segment  414 A, the transmitting segment  416  and the second reflective segment  414 B respectively in such a way that the light paths they follow when propagating to the imaging system  43  overlap with each other. 
         [0043]    In this embodiment, the imaging system  43  comprises a lens array assembly  431 , a digital micromirror device (DMD)  433  and a prism  435 . Hence, after the light beams projected via the first light collecting element  4139 , the second light collecting element  4159  and the third light collecting element  4179  to the mirror wheel  411  are reflected from/transmitted through the mirror wheel  411 , the resulting continuous light beams are processed by the lens array assembly  431  into light beams of uniform luminance and then reflected from the prism  435  to the DMD  433  for imaging. Finally, an image is projected via the prism  435  onto a screen (not shown). 
         [0044]    In this embodiment, there are three light source modules operating alternately to produce light beams, so each individual light source module operates with a shorter duty cycle compared to those of the first embodiment. As a result, it is possible to drive each individual LED of the light source modules with a higher current, thus giving rise to an increased overall luminance of the display apparatus  4 . 
         [0045]    In conclusion, according to this invention, the LEDs are lit up discretely and alternately according to a specific timing sequence, so each individual LED is able to withstand a higher current, thereby giving rise to improved luminance. Furthermore, each additional light source module may contribute to further improved light emission efficiency and luminance. Moreover, with the configuration of the reflective segments and transmitting segments in combination with two or more interleaved timing sequences used for light source modules, light will not be lost during the switching of the light sources. In addition, of the instantaneous output light flux will also not be degraded. Therefore, the display apparatus of this invention is capable of displaying an image with optimal light emission efficiency, higher luminance and more uniform light flux. 
         [0046]    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: 5