Abstract:
To reduce the thickness of a digital light projector (DLP), a circulating tape having sequences of red, green and blue segments is used instead of a color wheel to produce a color image.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to color projectors.  
       BACKGROUND OF THE INVENTION  
       [0002]     A digital light projector (DLP) includes a Digital Mirror Device (DMD) that receives a demanded image to produce a video or still image that is projected onto a screen. Current DLP projectors use optics including mirrors and lenses to perform projection. Also, current DLP projectors have a color wheel that rotates through the projected light beam. A lamp emits light that can be reflected through a converging lens to the color wheel (usually divided into three pie slice-shaped segments of red, green and blue, or sometimes four segments including a transparent segment), and the color wheel is rotated at an adjustable speed so that the light passing through it is filtered to alternately generate red, green and blue lights. The color wheel is synchronized with a DLP processor chip that controls the components as appropriate to generate a color display.  
         [0003]     As recognized herein, for portability and other reasons it is desirable to configure the projector to be as slim as possible, but the presence of a color wheel frustrates this goal. Specifically, owing to geometry the diameter of the color wheel must be two to three times as large as the internal lens, and is thus the limiting constraint in reducing the size of the projector. Simply reducing the size of the lens (and, hence, permitting use of a smaller color wheel) sacrifices brightness and picture quality and can also add more complexity to the optics, so it is not desirable to do so. With these constraints in mind, the present invention is provided.  
       SUMMARY OF THE INVENTION  
       [0004]     In accordance with embodiments of the present invention, a projector includes a light source generating a light beam, an optics system disposed in the light beam, and a translucent tape disposed in the light beam. The tape has at least one red segment, at least one blue segment, and at least one green segment, and the segments move translationally across the light beam to establish a color image.  
         [0005]     The preferred projector is a digital light projector (DLP), and a digital mirror device (DMD) can be disposed in the light path. The tape may be endless, and it may circulate past the DMD.  
         [0006]     If desired, a fan can be disposed in a housing that holds the tape, light source, optics system, and DMD, with the tape moving in a plane and the fan exhausting air perpendicular to the plane. The tape has a flat configuration wherein the tape is rectilinear.  
         [0007]     In the preferred embodiment set forth more fully below, the tape moves around plural rollers, at least one of which is motor driven. Markers can be engaged with the tape and each marker can be associated with a respective color. The markers are sensed by a sensor to synchronize the tape movement with the operation of the DMD.  
         [0008]     In another aspect, a method for producing a demanded image using a digital mirror device (DMD) includes directing a light beam at the DMD, and altering the color of the light beam without using a color wheel.  
         [0009]     In still another aspect, a projector includes means for generating a demanded image, and non-rotating translationally-moving means juxtaposed with the means for generating for altering the color of a light beam entering the means for generating.  
         [0010]     The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic diagram looking down at the components of the present DLP with the cover removed for clarity; and  
         [0012]      FIG. 2  is an elevational view of the present color tape for DLP. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]     Referring initially to  FIG. 1 , a digital light projector (DLP)  10  is shown which includes a hollow lightweight housing  12  that holds a DLP light source  14  in accordance with DLP principles known in the art. The light source  14  emits a light beam  16  that can be reflected by a mirror  18  if desired to an optics system  20 . The optics system  20  may be a conventional DLP optics system.  
         [0014]     The light beam  16  passes through the optics system  20  and through an aperture formed by an aperture plate  22  in accordance with DLP principles known in the art before entering a digital mirror device (DMD)  24  made by, e.g., Texas Instruments. In accordance with DMD principles known in the art, the DMD  24  receives a demand for an image, and small mirrors in the DMD  24  cooperate to either pass light or not depending on the demanded image, so that, e.g., when a red light beam enters the DMD  24 , some DMD mirrors reflect the light outward through lenses  26 ,  28  to a display surface  30  outside the housing  12 , and some DMD mirrors do not, to establish red sub-pixels of an image on the display  30 . Blue and green subpixels are similarly established, with the colored subpixels together establishing the demanded image.  
         [0015]     In accordance with the present invention, unlike a conventional DLP the DLP  10  shown in  FIG. 1  does not use a rotating color wheel to establish the red, green, and blue light beams by filtering the light beam  16 . Instead, the DLP  10  uses a preferably endless, preferably flexible plastic tape  32  that moves translationally along its long dimension in the housing  12  between the DMD  24  and, e.g., the aperture plate  22  as shown. Preferably, the tape  32  circulates around a path in a constant direction, but in some embodiments the tape  32  might move back and forth in front of the DMD  24 . The tape  32  may move against plural rollers  34  that preferably have tacky surfaces, with at least one roller  34  being driven by a motor  36  that can receive signals from the DMD  24  to move the tape  32  for purposes to be shortly disclosed. If desired, the rollers  34  may tilt to facilitate replacing the tape  32 .  
         [0016]     In addition to the above structure, a marker sensor  38  can be juxtaposed with the tape  32  and connected to the DMD  24  for purposes to be shortly disclosed. Also, to cool the DLP  10 , a fan  40  may be disposed in the housing  12  to exhaust air perpendicular to the plane in which the tape  32  moves. That is, the fan  40  may have an intake grating in the cover of the DLP  10  and an exhaust grating in the bottom of the DLP  10 .  
         [0017]     Now referring to  FIG. 2 , the preferred tape  32  has plural translucent color segments and if desired for brightness plural transparent “white” segments. More particularly, the preferred tape  32  has plural red color segments  42 , each of which is followed by a similarly-sized green segment  44 , each of which in turn is followed by a similarly-sized blue segment  46 . If desired, to increase image brightness each blue segment  46  may be followed by a white or transparent segment  48 , with the pattern then repeating starting with another red segment  42 . It can be appreciated in reference to  FIGS. 1 and 2  that the tape  32  may be a flexible plastic tape that can be configured in flat configuration as shown, wherein the tape  32  is rectilinear.  
         [0018]     Preferably, in an exemplary non-limiting embodiment the speed Sn at which the motor  36  is caused to move the tape  32  may be determined as follows.  
         [0019]     Assume that S o =speed the color wheel would otherwise have if not replaced by the tape  32 , S n =speed of tape, N c =number of color segments (in the above example, four), and D=diameter of the color wheel if not otherwise replaced by the tape  32 . Then, the correct ratio CS for color segments, i.e., the ratio of the length of each color segment  42 ,  44 ,  46  to the circumference of the color wheel that would otherwise be used: 
        C s =πDS n /(N C S o ), where the speed of the tape is ½ the speed that the color wheel otherwise would have had.        
 
         [0021]      FIG. 2  also shows that if desired, plural markers  50  such as small metal tags can be attached to the tape  32  at the start of each segment. The sensor  38  shown in  FIG. 1  can sense these markers  50  as they pass in front of the sensor  38  so that the sensor  38  can feed a signal to the DMD  24  for synchronizing the tape  32  movement with DMD  24  operation by appropriately controlling the speed of the motor  36 . In one exemplary embodiment, the markers  50  may have respective electrical resistances that are correlated to respective segment colors by the sensor  38 .  
         [0022]     While the particular PROJECTOR WITH COLOR TAPE as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”. It is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. Absent express definitions herein, claim terms are to be given all ordinary and accustomed meanings that are not irreconcilable with the present specification and file history.