Abstract:
The invention provides a light uniform device and a digital light processing (DLP) projection system applying the said light uniform device. The light uniform device comprises a light incident surface, a light emergent surface and a light uniform portion defined therebetween. The light incident surface and the light emergent surface have a first contour and a second contour, respectively. And a first projection image of the second contour that is projected onto a projection plane forms a rotational angle about a longitudinal axial direction corresponding to a second projection image of the first contour projected onto the projection plane. Thereby, the light sources may simply be disposed in the projection system to provide uniform light beams that entirely cover the DMD (digital micromirror device) after being uniformed by the light uniform device. Neither of the light sources need to be inclined following with the DMD, nor is additional relay lens needed in imaging.

Description:
This application claims the benefits of the priority based on Taiwan Patent Application No. 097139537 filed on Oct. 15, 2008, the disclosures of which are incorporated herein by reference in their entirety. 
     CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention provides a light uniform device for a digital light processing (DLP) projection system. 
     2. Descriptions of the Related Art 
     Projectors have become popular and more commonly used as more diversified projectors are coming onto the market. Accordingly, increasingly heightened requirements are imposed on the imaging quality of the projectors. Generally, a projection system primarily comprises an illumination subsystem and an imaging subsystem. In this industry, special emphasis has been put on improving the arrangement reliability of components, shrinking the overall volume and increasing the light source efficiency in the illumination subsystem to enhance the imaging brightness in the back-end imaging subsystem. 
     The illumination subsystem comprises a light source module, a lens and a light uniform device. To improve the imaging brightness, most conventional digital light processing (DLP) projection systems utilize a plurality of light source modules to provide ample light. As light propagates by scattering from the light source modules, a light source of non-uniform distribution results, which renders light illuminated on an imaging component of the projection system also non-uniform. Therefore, a reflecting cover is typically designed to reflect the scattered light towards a predetermined light path, and the light is then uniformed by a light uniform device to form a bright square region to be projected onto the imaging component. Thus, the imaging device can be illuminated by adequate uniform light to form a projection image. In practice, the light uniform device is an integrator, while the imaging component is a digital micromirror device (DMD). It should be noted that the bright region must cover the entire DMD completely in order for the DMD to reflect a complete projection image. 
     The projection image from the DMD is projected towards a projection lens and then forms an upstanding image on a screen for the user to watch. As required by some specifications or design requirements, the DMD needs to be installed at a certain deflection angle. This causes the DMD to be deflected with respect to the bright region to an extent that some portions of the DMD fall outside the range covered by the bright region, thereby resulting in an incomplete projection image. In this case, the bright region must be deflected along with the DMD by the same angle in order for the DMD to be covered completely by the bright region, thus a complete projection image is formed. 
     In more detail, as shown in  FIG. 1 , if the light uniform device  1  were not deflected along with the DMD, a bright region X (depicted in  FIG. 1  by oblique lines) formed by light  12  emerging from the light uniform device  1  would fail to completely cover the DMD D, making it impossible to form an image properly. To have the bright region X completely cover and uniformly illuminate the DMD D but with minimal area, the light uniform device  1  must be installed in such a way that it is deflected along with the DMD D by a certain angle. In such a case, to obtain the maximum luminous flux in the light uniform device, the illumination subsystem as a whole must be deflected by this angle accordingly, which causes the plurality of light source modules in the illumination subsystem to be inclined at an angle. 
     However, the inclination of the plurality of the light source modules not only leads to a complex and bulky design of the projection system&#39;s internal structure, but also causes poor heat dissipation performance because the inclined light source modules prevent the cooling fan from effectively generating a smooth convection flow field. Moreover, as the hot air tends to rise above, massive waste heat generated by the light source modules will accumulate above the inclined lamp bulbs and the reflecting cover at the front ends thereof. After a period of operation, the heat accumulated by the high temperature tends to shorten the service life of the bulbs and cause damage to the light source modules. 
     To deflect the light emerging from the light uniform device, another practice is to use a relatively complex relay lens at the rear end of the light uniform device to guide the light to cover the DMD completely in a uniform way. There is then no need to deflect the light uniform device and avoids the shortcomings arising from disposing the light source modules at an inclined angle. Unfortunately, this practice adds to both structural complexity and cost of the projection system. 
     Thus, in current DLP projection systems, as limited by the requirements to the plurality of light source modules, the light source modules must be installed at an inclined angle to coordinate with the deflected integrator. This leads to additional complexity of the structural design, increased overall volume and poor heat dissipation performance of the light source modules; all of which make such a solution undesirable. On the other hand, the practice of using an additional relay lens to obviate the need of inclining the light source modules is costly, degrades the optical efficiency due to an overlong light path, and also causes increased volume of the projection system due to an overly complex structural design and too many optical components. 
     Accordingly, efforts still have to be made in the art to provide a more effective imaging light source for a projection system that can obviate the shortcomings arising from deflecting the light source modules while still keeping the cost under control and reducing the overall volume of the projection system. 
     SUMMARY OF THE INVENTION 
     This invention provides a light uniform device for a DLP projection system comprising a plurality of light sources. With this light uniform device, light received from the plurality of light sources is adapted to cover an entire DMD in the projection system which is deflected by an angle relative to the light uniform device, thus avoiding the need of inclining the plurality of light sources. 
     The light uniform device of this invention comprises a light incident surface, a light emergent surface and a light uniform portion defined therebetween. The light incident surface has a first contour while the light emergent surface has a second contour that is substantially the same as the first contour. The projection image of the second contour projected onto a projection plane forms a rotational angle about a longitudinal axial direction of the light uniform device, the rotational angle of which is corresponding to the projection image of the first contour projected onto the projection plane. 
     With the arrangement of the light uniform device described above, light from the plurality of light sources in the DLP projection system is adapted to enter the light uniform device via the light incident surface to be reflected successively therein, and then emerge from the light emergent surface as uniform light. The resulting light is adapted to cover the DMD of the imaging system completely for imaging purposes. Thereby, the plurality of light sources may be disposed horizontally in the projection system in a simple way. Meanwhile, the light can cover the entire DMD without the need of any additional relay lens while still avoiding the adverse effect on the projection system caused by inclining the light sources. 
     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 
         FIG. 1  is the schematic view illustrating a uniform light projected by a light uniform device fails to cover an entire DMD in the prior art; 
         FIG. 2A  is the perspective view of a solid integration rod in an embodiment of a light uniform device of this invention; 
         FIG. 2B  is the perspective view of an illumination subsystem according to an embodiment of this invention; 
         FIG. 3  illustrates projections of a first contour and a second contour of the light uniform device on a projection plane according to the embodiment of this invention; and 
         FIG. 4  is the perspective view of a hollow integration rod in an embodiment of the light uniform device of this invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of this invention is a light uniform device, a schematic view of which is shown in  FIG. 2A . The light uniform device  2  is used in a DLP projection system (not shown). More specifically, the DLP projection system comprises an illumination subsystem  3  (as shown in  FIG. 2B , and only some essential components are shown for purpose of description) and an imaging subsystem (not shown). 
     In reference to  FIG. 2B , the illumination subsystem  3  comprises a plurality of light sources  33   a ,  33   b ,  33   c ,  33   d  and a light uniform device  2 , which are adapted to provide uniform light to the imaging subsystem for imaging purposes. In this embodiment, the illumination subsystem  3  further comprises a conventional light uniform device  31  extended to connect with the light uniform device  2  of this invention. The conventional light uniform device  31  comprises an upper portion  31   a  and a lower portion  31   b  for receiving light from the light sources  33   a ,  33   d  disposed in the front section and light from the light sources  33   b ,  33   c  disposed in the rear section respectively to obtain the maximum luminous flux. In this embodiment, the light uniform device  2 , and the upper portion  31   a  and the lower portion  31   b  of the conventional light uniform device  31  are all separate components; however, in other embodiments, the light uniform device  2 , and the upper portion  31   a  and the lower portion  31   b  of the conventional light uniform device  31  may be substantially formed integrally. The imaging subsystem has a DMD (not shown) and a projection lens (not shown). The DMD is adapted to receive uniform light projected by the light uniform device  2  and rotate a plurality of micromirrors (not shown) thereof to further reflect the light to the projection lens. The uniform light projected by the light uniform device  2  forms on the DMD a bright region adapted to substantially cover the entire DMD, so that the DMD can be illuminated entirely and uniformly. The projection lens comprises a plurality of lens (not shown), through which the light reflected from the DMD is projected onto a screen to form a projection image. 
     As shown in  FIG. 2A , the light uniform device  2  comprises a light incident surface  21 , a light emergent surface  23  and a light uniform portion  25  defined therebetween. The light incident surface  21  has a first contour, and the light emergent surface  23  is substantially parallel to the light incident surface  21  and has a second contour. In this embodiment, the first contour is substantially the same as the second contour, both of which have substantially the same aspect ratio and area. However, in other examples, although the first contour is also the same as the second contour, the second contour of the light emergent surface  23  is scaled up in size relative to the first contour of the light incident surface  21  to substantially have a larger area to accommodate the corresponding size of the DMD. Although not depicted individually in the figures, these still belong to applicable alternative examples. 
       FIG. 3  illustrates projections of the light uniform device  2  on a projection plane P. The projection plane P is parallel to the light incident surface  21  and the light emergent surface  23 . The second contour corresponding to the light emergent surface  23  is forward projected onto the projection plane P to form a first rectangular projection  23 ′; likewise, the first contour corresponding to the light incident surface  21  is forward projected onto the projection plane P to form a second rectangular projection  21 ′. By taking a longitudinal axis  22  of the light uniform device  2  as the center (the point where the longitudinal axis  22  intersects the projection plane P is denoted by a crossing point  22 ′ in  FIG. 3 ), the first projection  23 ′substantially forms a rotational angle θ with respect to the second projection  21 ′ in plane P. More specifically, in reference to  FIG. 3 , the rotational angle θ is an angle included between the lines drawn from the crossing point  22 ′ representing the longitudinal axis  22  to the two vertices e, e′ (corresponding to the vertices a, a′ in  FIG. 2A  respectively) at the respective top left corners of the projections  21 ′,  23 ′ respectively. The rotational angle θ is 7.25° in this embodiment, and is no greater than 90° in practical applications. 
     In this embodiment, the primary imaging component in the DLP projection system is a DMD having a rectangular profile, so both the first contour of the light incident surface  21  and the second contour of the light emergent surface  23  assume a rectangular form for applying to the DMDs currently used. 
     Furthermore, as shown in  FIG. 2A , the light uniform portion  25  defined between the light incident surface  21  and the light emergent surface  23  is composed of a plurality of continuous outer surfaces  2   a . In this embodiment, the plurality of continuous outer surfaces  2   a  is a plurality of triangular surfaces adjoining each other. In more detail, unlike the outer surface of the light uniform portion of the conventional light uniform device  1  shown in  FIG. 1  (which is composed of four rectangles adjoining and perpendicular to each other), the light uniform portion  25  of the light uniform device  2  is composed of eight triangular surfaces adjoining each other. 
     In more detail, as shown in  FIG. 2A , the light incident surface  21  of the light uniform device  2  has four vertices, i.e., a, b, c and d respectively; likewise, the light emergent surface  23  also has four vertices corresponding to those of the light incident surface  21 , i.e., a′, b′, c′ and d′, in which d′ is shaded from view. The profile of the light uniform portion  25  is substantially defined between the light incident surface  21  and the light emergent surface  23  by lines connecting paired vertices (i.e., a paired with a′, b paired with b′, c paired with c′, and d paired with d′). In this embodiment, the light uniform portion  25  is composed of eight triangular surfaces; however, instead of being limited to this embodiment, the light uniform portion  25  may also be composed of a plurality of arbitrary polygonal planes or curved surface based on the above relationships in other embodiments, as long as the corresponding relationships between the projections  21 ′,  23 ′ of the contours of the light incident surface  21  and the light emergent surface  23  in the projection plane P with respect to the crossing point  22 ′ representing the longitudinal axis  22  can be maintained as shown in  FIG. 3 . 
     The light uniform device  2  of this embodiment is a solid integration rod as shown in FIG.  2 A, which is coated with a reflection coating on the outer surface  2   a  thereof; however, in other embodiments, the light uniform device  2 ′ may also be a hollow integration rod as shown in  FIG. 4 . The hollow integration rod has a shell body  27  and a light tunnel  29  formed in the shell body  27 . A space formed by the light tunnel  29  has a profile like that of the solid integration rod shown in  FIG. 2 , although the detailed structural lines of the space are not shown herein. The shell body  27  of the hollow integration rod is coated with a reflection coating on an inner surface  2   b  thereof. In this way, whether the light uniform device  2  is in the form of a solid integration rod or the light uniform device  2 ′ is in the form of a hollow integration rod may utilize the reflection coating applied on respective surfaces  2   a ,  2   b  to reflect light successively, thus accomplishing the effect of projecting the incident light out of the light uniform device uniformly. 
     On the other hand, to accommodate the use of different optional light sources in the DLP projection system, the light uniform device may be made of a material selected from a group consisting of glass, quartz and plastic depending on the intensity of the light sources. For example, a light uniform device made of quartz is used for high-power light sources such as xenon lamps or some mercury lamps, a light uniform device made of a BK7 material may be used for mercury lamps of lower power, and a light uniform device made of a plastic material may be used for other light sources such as LEDs. It should be noted that the reflection coating may be provided depending on the practical needs, and the material of the light uniform device is not limited to what is described above. 
     With the above structure and features, the light uniform device of this invention is disposed in the DLP projection system so that when light from the plurality of light sources projects on the light incident surface  21 , the light is adapted to enter the light uniform device  2  via the light incident surface  21 , and then reflected in the light uniform portion  25  successively to form uniform light before emerging from the light emergent surface  23 . Because both the contours and the projections of the contours on the projection plane P assume a rectangular form, the light emerging from the light emergent surface  23  having the second contour forms a rectangular bright region that is adapted to accommodate to the rectangular DMD. This bright region substantially covers the entire DMD to form a complete projection image. 
     In summary, with the structure and features of the light uniform device of this invention, light projects on the light incident surface is adapted to be uniformed by the light uniform portion and then emerges from the light emergent surface to cover the entire DMD. Consequently, in the DLP projection system incorporating the light uniform device of this invention, the illumination subsystem may have a plurality of light sources disposed horizontally in a simple way instead of being deflected along with the DMD as in the prior art solutions. This may avoid, not only the increase in volume of the system due to the complex mechanical structures, but also the degradation in heat dissipation performance arising from inclining the illumination subsystem. On the other hand, the light uniform device of this invention may improve the shortcomings of the prior art, in which an additional relay lens must be used in order for the light to cover the entire DMD, thereby shortening the optical path, enhancing the optical efficiency and saving costs. 
     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.