Abstract:
An image projector is disclosed. The image projector includes a lamp emitting light rays, a filtering unit having a first device including a plurality of color filters including a white color filter each formed to correspond to a section therein, and a second device including a plurality of color filters except a white color filter each formed to correspond to a section therein and formed at one side of the first device, and filtering the light rays emitted from the lamp through any one of the first device and the second device, a rod lens focusing and projecting the light rays separated from the filtering unit, and a digital micromirror device displaying an image through electric signals in accordance with the projected light rays.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Application No. P2003-050536, filed on Jul. 23, 2003, which is hereby incorporated by reference as if fully set forth herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a display device, and more particularly, to an image projector. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for selecting one of image brightness and color definition through a single projector, when viewing a projected image, thereby projecting the image in accordance with the user&#39;s preference.  
         [0004]     2. Discussion of the Related Art  
         [0005]     As image projection devices, also known as the projector, are being extensively introduced and provided, diverse types of product are being developed and sold on the market. Such image projection devices are under development for a structure focusing on the brightness of the projection and the compact size and light weight of the device.  
         [0006]     An optical part of a general image projection device includes a lamp as a light source, an illuminating part focusing the light emitted from the lamp, an image display device representing the focused light into an image, and a projecting part enlarging the image displayed on the image display device and projecting the enlarged image onto a screen.  
         [0007]     In the present technology, high pressure mercury lamps are most widely used as the lamp of the image projection device, and liquid crystal displays (LCDs) and digital micromirror devices (DMDs) are most widely used as the image display device of the projector. Additionally, depending upon the number of image display devices used, the image projection device can be categorized as a single-chip projector, a two (2)-chip projector, and a three (3)-chip projector.  
         [0008]     As the recent trend introduces projectors of compact size, light weight, and low cost, single-chip optical parts using only a single image display device is generally used.  
         [0009]     The single-chip image projection device includes a projector type mounting color filters of red, green, and blue, a projector type externally separating red, green, and blue light rays and simultaneously illuminating the separated light rays to the image display device, and a projector type externally and sequentially illuminating red, green, and blue light rays onto the image display device with a time interval. Herein, when using the projector type externally and sequentially illuminating red, green, and blue light rays onto the image display device with a time interval, the response speed of the image projection device is required to be three times faster than that of the three (3)-chip image projection device. In the recent technology, the digital micromirror device (DMD) most satisfies such requirements.  
         [0010]     A color separating device is formed in order to illuminate separated light rays onto the image display device. When using the projector for presentations focusing on the brightness of the screen is important, a four-sectioned color wheel should be used. On the other hand, when using the projector for viewing video images emphasizing various colors, a three-sectioned color wheel should be used. The same principle applies to a color drum.  
         [0011]     As described above, the single-chip DMD projector is disadvantageous in that an adequate color separating device emphasizing either one of brightness or color representation should be selected, depending upon whether the product is focused on the brightness of the screen or the color picture quality of the image. However, the single-chip projector used in the current technology cannot satisfy the user environment of the recent multimedia trend requiring both characteristics (i.e., brightness and color representation).  
       SUMMARY OF THE INVENTION  
       [0012]     Accordingly, the present invention is directed to an image projector that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
         [0013]     An object of the present invention is to provide an image projector using a color separating device that can selectively enhance either the brightness or the color definition of an image.  
         [0014]     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
         [0015]     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an image projector includes a lamp emitting light rays, a filtering unit having a first device including a plurality of color filters including a white color filter each formed to correspond to a section therein, and a second device including a plurality of color filters except a white color filter each formed to correspond to a section therein and formed at one side of the first device, and filtering the light rays emitted from the lamp through any one of the first device and the second device, a rod lens focusing and projecting the light rays separated from the filtering unit, and a digital micromirror device displaying an image through electric signals in accordance with the projected light rays.  
         [0016]     Herein, the first device and the second device are one of a color wheel and a color drum.  
         [0017]     The image projector according to the present invention further includes a controller selecting any one of the first device and the second device of the filtering unit.  
         [0018]     Herein, one of the first device and the second device is selected from the filtering unit in accordance with one of horizontal and vertical movements of the filtering unit based on control signals of the controller.  
         [0019]     In another aspect of the present invention, an image projector includes a lamp emitting light, a first filtering unit having a plurality of color filters including a white color filter, a second filtering unit having a plurality of color filters including a white color filter, wherein any one of the color filters overlaps with any one of the color filters arranged in the first filtering unit, a rod lens focusing and projecting the light rays separated from the first and second filtering units, and a digital micromirror device displaying an image through electric signals in accordance with the projected light rays.  
         [0020]     Herein, the white color filter of the second filtering unit is smaller than the white color filter of the first filtering unit. Also, a size of the white color filter of the second filtering unit is equal to a spot size, which is a focused size of the light emitted from the lamp.  
         [0021]     The white color filter of the second filtering unit is positioned on an optical path, when a user desires to emphasize a brightness of the image. Conversely, the white color filter of the first filtering unit is positioned on an optical path, when a user desires to emphasize a color definition of the image.  
         [0022]     Also, the first filtering unit and the second filtering unit are sequentially arranged between the lamp and the rod lens. Herein, the first filtering unit is arranged between the lamp and the rod lens, and the second filtering unit is arranged behind the rod lens.  
         [0023]     Each of the first and second filtering units is a color wheel.  
         [0024]     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0026]      FIG. 1A  illustrates an optical part of an image projector according to a first embodiment of the present invention;  
         [0027]      FIG. 1B  illustrates a color wheel of the image projector according to the first embodiment of the present invention;  
         [0028]      FIG. 2A  illustrates an optical part of the image projector according to a second embodiment of the present invention;  
         [0029]      FIG. 2B  illustrates a color drum of the image projector according to the second embodiment of the present invention;  
         [0030]      FIGS. 3A and 3B  illustrate first and second color wheels of the image projector according to a third embodiment of the present invention; and  
         [0031]      FIG. 3C  illustrates an optical part of the image projector according to the third embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0033]      FIG. 1A  illustrates an optical part of an image projector according to a first embodiment of the present invention.  
         [0034]     Referring to  FIG. 1A , the projector includes a lamp  101 , a color wheel  102 , a rod lens  103 , a first illuminating lens group  104 , a second illuminating lens  105 , a digital micromirror device (DMD)  106 , a total internal reflection (TIR) prism  107 , and a projection lens  108 . The light ray emitted from the lamp  101 , which is the light source, is focused to a light incident surface of the rod lens  103  by an oval mirror. Herein, the color wheel  102  is positioned between the lamp  101  and the rod lens  103 , so as to sequentially separate the light ray into red, green, and blue light rays.  
         [0035]     In order to broaden the scope of color representation, a yellow color filter can be included in an area other than the regions corresponding to the colors red, green, and blue. Moreover, a filter of a different color can also be included herein. Based on the principles of optical science, such options can be easily understood without any additional technological explanations, and so detailed descriptions of the same will be omitted for simplicity.  
         [0036]     The color wheel  102  is formed between the lamp  101  and the rod lens  103  because the cross-sectional area of the light ray emitted from the lamp  101  is minimized when nearing the light incident surface of the rod lens  103 . Accordingly, by installing the color wheel  102  at a region whereby the cross-sectional area of the light ray is minimized, the size of the color wheel  102  can also be minimized.  
         [0037]      FIG. 1B  illustrates a color wheel of the image projector according to the first embodiment of the present invention.  
         [0038]     Referring to  FIG. 1B , the color filters of the color wheels are arranged in a double layer form. More specifically, the color wheel  102  is divided into an internal portion and an external portion. Herein, the internal portion of the color wheel  102  is formed of four sections including a red color filter, a green color filter, a blue color filter, and a white color filter. The external portion of the color wheel is formed of three sections including a red color filter, a green color filter, and a blue color filter.  
         [0039]     The structures of the internal and external portions of the color wheel  102  can also be alternated (i.e., the four-sectioned structure corresponding to the external portion and the three-sectioned structure corresponding to the internal portion of the color wheel  102 ). This is because a separate controller can arbitrarily select one of the first and second modes corresponding to each of the internal and external portions of the color wheel.  
         [0040]     In addition, the color filters are formed by dichroic coating through a masking method.  
         [0041]     Meanwhile, due to a mechanical movement of the color wheel  102  in a direction perpendicular to the axis of the light ray, the color wheel  102  can have color modes different from one another. More specifically, for example, when the brightness of the image should be emphasized, as when used in a presentation, the four-sectioned color mode is selected. On the other hand, when the color definition of the image should be emphasized, as when viewing a video image, the color mode is converted into the three-sectioned color mode. Herein, the vertical movement of the color wheel  102  can be controlled by a microprocessor of the controller.  
         [0042]     Subsequently, the light ray filtered from the color wheel  102  is incident to the rod lens  103 . The rod lens  103  is formed to have a cubic structure, and projects the light rays incident therein back to the outside through a total reflection. At this point, although the brightness of the light incident surface of the rod lens fails to be uniform, the incident light is totally reflected from the inside, thereby allowing the brightness of the light incident surface to be uniform. The uniformity of the brightness may differ depending upon the length of the rod lens or the type of light carrier.  
         [0043]     The rod lens  103  can be basically categorized into two structure types. More specifically, the rod lens  103  may include a mirror reflection structure, whereby the inside of the rod lens  103  is empty and has an inner interface formed of a mirror. The rod lens  103  may also include an internal total reflection structure, whereby the rod lens  103  is formed of a glass having a high refractive index.  
         [0044]     The DMD  106  projects the light ray having a uniform luminance distribution through the rod lens  103  through a plurality of first illuminating lenses  104  and the second illuminating lens  105 . The projected light ray is then projected to the total internal reflection (TIR) prism  107 . Herein, the TIR prism  107  is formed of two prisms joined to each other while having a fine air gap therebetween. The incident light is totally internally reflected at an interface of a first prism and, then, projected to the DMD  106 .  
         [0045]     A plurality of micromirrors (not shown) corresponding to each pixel is formed above a DMD surface of the DMD  106 . Herein, each of the micromirrors has a ±θ tilt mode depending upon an external electric signal. In the recent technology, θ is commonly set to either 10 degrees or 12 degrees.  
         [0046]     When the DMD  106  receives a white color signal, due to the tilting of the micromirrors, the light ray is reflected to an angle different from that of the incident angle. Accordingly, the reflected light ray is passed through to the projection lens  108  without a total internal reflection from the TIR prism  107 . The light ray passing through the TIR prism  107  is enlarged to form an image on a screen (not shown) through the projection lens  108 .  
         [0047]      FIG. 2A  illustrates an optical part of the image projector according to a second embodiment of the present invention.  
         [0048]     Referring to  FIG. 2A , the projector includes a lamp  201 , a color drum  202 , a rod lens  203 , a first illuminating lens group  204 , a second illuminating lens  205 , a digital micromirror device (DMD)  206 , a total internal reflection (TIR) prism  207 , and a projection lens  208 . With the exception of the color drum  202 , the structure and operation of the projector according to the second embodiment of the present invention is identical to that of the projector according to the first embodiment of the present invention, shown in  FIG. 1A , and, therefore, the detailed description of the same will be omitted for simplicity.  
         [0049]      FIG. 2B  illustrates a color drum of the image projector according to the second embodiment of the present invention.  
         [0050]     Referring to  FIG. 2B , a color drum surface of the color drum  202  is divided into an internal portion and an external portion along the vertical direction of the color drum  202 . Herein, the external portion of the color drum  202  is formed of three sections including a red color filter, a green color filter, and a blue color filter. And, the internal portion of the color drum  202  is formed of four sections including a red color filter, a green color filter, a blue color filter, and a white color filter. As described in  FIG. 1B , the structures of the internal and external portions of the color drum  202  can also be alternated (i.e., the four-sectioned structure corresponding to the external portion and the three-sectioned structure corresponding to the internal portion of the color drum  202 ).  
         [0051]     However, unlike the color wheel  102  shown in  FIG. 1A , the color drum  202  is formed to make mechanical movements in a direction horizontal to the axis of the light ray. More specifically, unlike the color wheel  102 , the first mode and the second mode of the color drum  202  are connected to each other three-dimensionally. Therefore, a user can select a desired mode only when the color drum  202  is moved along a horizontal direction of the axis of the light ray.  
         [0052]     Herein, a microprocessor of a separate controller controls the movements of the color drum.  
         [0053]      FIGS. 3A and 3B  illustrate first and second color wheels of the image projector according to a third embodiment of the present invention. And,  FIG. 3C  illustrates an optical part of the image projector according to the third embodiment of the present invention.  
         [0054]     Referring to  FIG. 3A , the first color wheel  302  is formed of a red color filter, a green color filter, a blue color filter, and a white color filter each adequately arranged into four sections. And, as shown in  FIG. 3B , the second color wheel  303  is formed of a red color filter, a green color filter, a blue color filter, and a white color filter arranged in four sections, wherein the red, green, and blue color filters are arranged to have an adequate size and the white color filter is formed to be smaller than the other color filters. It is preferable that the white color filter is minimized to the size to which the light emitted from the lamp is focused (i.e., a spot size).  
         [0055]     The optical part of the image projector having the above described first and second color wheels applied thereto will now be described in detail with reference to  FIG. 3C .  
         [0056]     Referring to  FIG. 3C , the first and second color wheels  302  and  303  are sequentially arranged between the lamp  301 , which is the light source, and the rod lens  304 . At this point, the second color wheel  303  is arranged so that any one of the color filter sections thereof overlaps with any one of the color filter sections of the first color wheel  302 . Then, the first and second color wheel is selectively operated based on the selection of the user. In other words, when the first color wheel is operated, the second color wheel is stopped, and when the second wheel is operated, the first wheel is stopped.  
         [0057]     More specifically, when the first color wheel  302  is operated, the white color filter section of the second color wheel  303  is fixed within an effective area of the optical path. On the other hand, when the second color wheel  303  is operated, the white color filter section of the first color wheel  302  is fixed within the effective area of the optical path. Herein, the effective area of the optical path refers to a cross-sectional area of the color wheel, when the light ray emitted from the lamp passes through the color wheel.  
         [0058]     When the user desires to focus on the brightness of the image displayed through the projector, the white color filter section of the second color wheel  303  is positioned on the optical path. Then, the first color wheel  302  is rotated. Accordingly, the image projector can produce a bright image due to the relatively larger white color filter section of the first color wheel  302 .  
         [0059]     Conversely, the user desires to focus on the color definition of the image displayed through the projector, the white color filter section of the first color wheel  302  is positioned on the optical path. Then, by rotating the second color wheel  303 , the image projector can produce an image represented by more natural and vivid colors.  
         [0060]     Meanwhile, as shown in  FIG. 3C , the first and second color wheels  302  and  303  are sequentially arranged between the lamp  301  and the rod lens  304 . Alternatively, the first color wheel  302  can be arranged between the lamp  301  and the rod lens  304 , and the second color wheel  303  can be arranged between the rod lens  304  and the first illuminating lens group  305 .  
         [0061]     The aforementioned image projector according to the third embodiment of the present invention does not require a separate controller to mechanically move the first and second color wheels. Nevertheless, the motor operation for each of the first and second color wheels should be controlled so as to represent the image desired by the user.  
         [0062]     As described above, the image projector according to the present invention has the following advantages.  
         [0063]     By representing a time-division color separating device in a plurality of color modes, the user can select one of image brightness and color definition through a single projector, when viewing a projected image.  
         [0064]     Furthermore, the plurality of color modes can be selected according to the user&#39;s preference without distortion of the projected image.  
         [0065]     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.