Abstract:
A rear projection system includes a screen having an expandable surface that is selectively expanded to display thereon a rear projected image illuminated by a rear pico projector. The screen is selectively contracted for enhancing portability. The rear projection system includes a foldable frame that is selectively unfolded for supporting the screen and that is selectively folded for enhancing portability. A sensor is used for converting the screen to a touchscreen when the screen surface is expanded.

Description:
Field of the Invention 
       [0001]    The invention relates to a portable projection screen for a video display device. In particular, the invention relates to a portable rear projection screen. 
       BACKGROUND OF THE INVENTION 
       [0002]    A pico projector is a term directed herein to a small-format hand held projector that can be used as a standalone projector or as an integrated component in hand held portable devices. The pico projector uses similar technology to that which powers a standard projector and a rear-projection television. The small size of the pico projector can be directed for use of a single viewer and can be associated with a light weight screen. 
         [0003]    It may be desirable to include in a rear projection system a pico projector that illuminates a foldable screen installed in a foldable frame. Advantageously, rear projection system that includes a pico projector can be made to be far less sensitive than front projection system to being washed out by background lighting which can limit portable front projection system usefulness. Advantageously, the alignment of the projector of a rear projection system with respect to the screen is not critical since the user has a focus adjustment already built into the projector. With laser projection, focus would even be unnecessary. 
         [0004]    Typically, pico projectors are designed to be front projectors. When a front projector is used in a rear projection system, the displayed image on the screen, unless corrected, would be flipped left-to-right. One solution to this image flipping problem is to use a mirror for reflecting the light produced by the projector on a rear projection screen as the target for the reflected light. Another solution is to pre-process the video signal that is applied to the pico projector by employing image reversal and rotation. 
         [0005]    It may also be desirable to provide the foldable screen with a feature that makes it a touchscreen. For example, light sensors can be installed either in a front side of the screen, with respect to the viewer, looking for obstructions, or in a back side of the screen looking for screen displacements. Alternatively, touch sensing can be achieved remotely by using infra-red (IR) imaging from an imager or camera pointed at the back side of the screen. If the pico projector has already a built in camera assembly, additional cost of making it a touch screen might be merely that of providing an IR band pass filter and some software. 
       SUMMARY OF THE INVENTION 
       [0006]    A rear projection system, embodying an inventive feature, includes a display screen having an expandable surface that is selectively expanded to display thereon a rear projected image produced by a portable, hand held or pico projector. The display screen is selectively folded for enhancing portability. A foldable frame is selectively unfolded for supporting the screen, when the screen surface is expanded. The foldable frame is selectively folded for enhancing portability. A sensor makes the screen a touchscreen when the screen surface is expanded. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The preferred embodiment of the present invention will be described below in more detail with reference to the accompanying drawings in which: 
           [0008]      FIG. 1   a  illustrates a side view of a rear projection system, embodying an inventive feature; 
           [0009]      FIGS. 1   b  and  1   c  illustrate alternative ways of forming touchscreen in the arrangement of  FIG. 1   a;    
           [0010]      FIG. 2  illustrates a front view of fully assembled foldable screen assembly of  FIG. 1   a;    
           [0011]      FIG. 3  illustrates a front view of the foldable screen assembly of  FIG. 2  in which a foldable screen is completely folded; 
           [0012]      FIG. 4  illustrates a front view of the foldable screen assembly of  FIG. 2  in which the screen is pull down approximately half way down; 
           [0013]      FIG. 5  illustrates a front view of the foldable screen assembly of  FIG. 2  in which the foldable screen is completely folded and a frame is partially folded; 
           [0014]      FIG. 6  illustrates a front view of the foldable screen assembly of  FIG. 5  in which the foldable screen is completely folded and a frame is partially folded further than in  FIG. 5 ; 
           [0015]      FIG. 7   a  illustrates a front view and  FIG. 7   b  illustrates a side view of the foldable screen assembly of  FIG. 2  in which each of the foldable screen and the frame is completely folded; and 
           [0016]      FIGS. 8   a  and  8   b  illustrate corresponding solutions for an image flipping problem that occurs when a front projector is incorporated in the rear projection system of  FIG. 1   a.    
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1   a  illustrates a side view of foldable screen assembly  100 , embodying an inventive feature. In  FIG. 1   a , assembly  100  is fully unfolded and ready for displaying an image, not shown. A hand held portable projector  131  that is referred to herein as pico projector  131  is mounted on a base  132  in the back of assembly  100  to form a rear projector. Pico projector  131  is driven by a video apparatus, not shown, such as a computer. Screen assembly  100  is interposed between a viewer and pico-projector  131 . Selectively, screen assembly  100  can be rotated on its side to change from a letter to a landscape type display. 
         [0018]      FIG. 2  illustrates a front view of foldable screen assembly  100  of  FIG. 1   a  that includes a contractable or foldable screen  103  mounted in a rectangular foldable frame  104 . In  FIG. 2 , assembly  100  is fully assembled, as in FIGURE la, such that each of foldable screen  103  and foldable frame  104  is completely unfolded. Similar symbols and numerals in  FIGS. 1   a  and  2  indicate similar items or functions. In  FIG. 2 , constituent members or parts of foldable frame  104  are firmly locked to one another in a manner to form a rigid body that maintains its rectangular shape, as explained later on. 
         [0019]    Foldable frame  104  includes a pair of substantially identical side portions  102  disposed at the right and left sides, respectively, of  FIG. 2 . An upper portion  105  of frame  104  is disposed perpendicularly to each of side portions  102  and forms a bridge type connection between portions  102 . Each side portion  102  includes a tubular, top section  102   a,  a tubular, middle section  102   b  and a tubular, bottom section  102   c.  An upper end  102   b   1  of middle section  102   b  is rigidly fastened to a lower end  102   a   2  of top section  102   a,  when frame  104  is unfolded. A lower end  102   b   2  of middle section  102   b  is rigidly fastened to an upper end  102   c   1  of bottom section  102   c,  when frame  104  is unfolded. Upper portion  105  has a right end  105   a  that is rigidly fastened to a top end  102   a   1  of section  102   a,  when frame  104  is unfolded. 
         [0020]    Screen  103  has a bottom edge  103   a  that is firmly attached to a lower portion  106  of frame  104 . Lower portion  106  is disposed perpendicularly to each of side portions  102  and in parallel with portion  105 , when frame  104  is unfolded. Lower portion  106  has a right end  106   a  that is rigidly fastened to a bottom end  102   c   2  of section  102   c,  when frame  104  is unfolded. This can be obtained by connecting right end  106   a  to bottom end  102   c   2  using lockable hinges, by having them fit or slide into one another or by some other suitable means. In a similar way, ends  102   c   1  and  102   b   2  can be rigidly connected to each other. The same would be applicable to the rigid connection of ends  102   a   2  and  102   b   1 . Also, the same would be applicable to the rigid connection of ends  105   a  and  102   a   1 . 
         [0021]    Side portions  102 , top portion  105  and bottom portion  106  of frame  104  are disposed symmetrically with respect to a longitudinal symmetry axis  130  to form the rectangular shape of frame  104 . Unfolded screen  103  is disposed between the pair of side portions  102 , when frame  104  is unfolded. 
         [0022]      FIG. 3  illustrates a front view of foldable screen assembly  100  of  FIG. 2  in which foldable screen  103  is completely folded and is disposed in a manner, not shown, close to upper portion  105  of frame  104 . Similar symbols and numerals in  FIGS. 1   a ,  2  and  3  indicate similar items or functions. 
         [0023]      FIG. 4  illustrates a front view of foldable screen assembly  100  of  FIG. 2  in which screen  103  is pull down approximately half way down between its completely unfolded position, shown in  FIG. 2 , and its completely folded position, shown in  FIG. 3 . Similar symbols and numerals in  FIGS. 1   a ,  2 ,  3  and  4  indicate similar items or functions. 
         [0024]      FIG. 5  illustrates a front view of foldable screen assembly  100  of  FIG. 2  in which foldable screen  103  is completely folded in the same way as in  FIG. 3  and frame  104  is partially folded. In  FIG. 5 , side portions  102  of frame  104  are partially collapsed or rotated to be no longer perpendicular to upper portion  105 . Thus, the connection of end portion  105   a  of upper portion  105  and end portion  102   a   1  of side section  102   a  is no longer rigid and perpendicular but, instead, loose in a manner to enable the pivotal rotation of section  102   a  with respect to upper portion  105 . Similar symbols and numerals in  FIGS. 1   a ,  2 ,  3 ,  4  and  5  indicate similar items or functions. 
         [0025]      FIG. 6  illustrates a front view of foldable screen assembly  100  of  FIG. 2  in which foldable screen  103  is completely folded in the same way as in  FIG. 3  and frame  104  is further folded with respect to  FIG. 5 . In  FIG. 6 , each of sections  102   a,    102   b  and  102   c  of side portions  102  is pivotally rotated to be on the opposite side of portion  105  with respect  FIGS. 2 ,  3 ,  4  and  5 . Additionally, each of sections  102   a,    102   b  and  102   c  of  FIG. 6  is inclined with respect to the corresponding adjacent section of portion  102 . In partially folded or partially unfolded frame  104 , end  102   b   1  of middle section  102   b  is no longer rigidly fastened to end  102   a   2  of section  102   a.  Instead, a junction between end  102   b   1  and end  102   a   2  forms a pivot of rotation. Similarly, a junction between end  102   b   2  and end  102   c   1  also forms a pivot of rotation. In the same way, a junction between end  102   a   1  and right end  105   a  of upper portion  105  also forms a pivot of rotation. Similar symbols and numerals in  FIGS. 1   a ,  2 ,  3 ,  4 ,  5  and  6  indicate similar items or functions. 
         [0026]      FIG. 7   a  illustrates a front view of foldable screen assembly  100  of  FIG. 2  in which foldable screen  103  is completely folded in the same way as in  FIG. 3 . Additionally, frame  104  is completely folded in that each of sections  102   a,    102   b  and  102   c  of each side portions  102  is rotated to be parallel disposed with respect to each of the other sections of portion  102  and with respect to portions  105  and  106 . As in  FIG. 6 , each of sections  102   a,    102   b  and  102   c  of side portions  102  is rotated to be on the opposite side of portion  105  with respect  FIGS. 2 ,  3  and  4 .  FIG. 7   b  illustrates a side view of completely folded screen assembly  100  of  FIG. 7   a . Similar symbols and numerals in  FIGS. 1   a ,  2 ,  3 ,  4 ,  5 ,  6 ,  7   a  and  7   b  indicate similar items or functions. 
         [0027]      FIG. 1   b  illustrates a front view of system  100  of  FIG. 1   a . In carrying out an inventive feature, screen  103  of  FIG. 1   b  forms a user interface touchscreen adapted to interact with a video apparatus, not shown, such as, for example, a computer or an electronic tablet. Similar symbols and numerals in  FIGS. 1   a ,  1   b ,  2 ,  3 ,  4 ,  5 ,  6 ,  7   a  and  7   b  indicate similar items or functions. 
         [0028]    In  FIG. 1   b , a corresponding part of each sensor element  110  of a series of sensor elements  110  is built into an edge of each of frame side portions  102 , an edge of portion  105  and an edge portion  106 . Each sensor element  110  of the series of sensor elements  110  associated with side portions  102  of frame  104  includes a light source part that is installed on, for example, left side portion  102  and a corresponding light sensor part that is installed on right side portion  102 . 
         [0029]    As long as the user/viewer does not interrupt a ray of light emitted from the light source part of sensor element  110 , the light sensor part of element  110  is illuminated. On the other hand, when, for example, a finger of the user/viewer is interposed in the path of the ray of light, the light sensor part of element  110  is not illuminated. Accordingly, a vertical position Y of the finger with respect to screen  103  can be evaluated by a processor, not shown. 
         [0030]    Similarly, each sensor element  110  of the series of sensor elements  110  associated with upper portion  105  and lower portion  106  of frame  104  includes a light source part that is installed on, for example, upper portion  105  and a corresponding light sensor part that is installed on lower portion  106 . Accordingly, a horizontal position X of the finger with respect to screen  103  can be evaluated by the processor, not shown. 
         [0031]    Sensor elements  110  may be disposed in a front of screen  103  with respect to a viewer of  FIG. 1   a  so as to detect the aforementioned blocking of light by, for example, a finger of the user/viewer; alternatively, light sensor elements  110  of  FIG. 1   b  may be disposed in a back of screen  103  with respect to the viewer of  FIG. 1   a  so as to detect deflection of screen  103  when touched by the viewer. Thus, screen  103  forms a user interface touchscreen adapted to interact with a video apparatus, not shown, such as, for example, a computer or an electronic tablet that is responsive to light sensor elements  110  of  FIG. 1   b.    
         [0032]    Instead of using light sensor elements  110  of  FIG. 1   b , a camera  133  of  FIG. 1   a , operating as an IR light sensor, may be combined in the same assembly with pico-projector  133 . When a finger of, for example, a user/viewer touches screen  103 , the touching finger sets up an abrupt change in an IR energy of a camera captured thermal image  135  that is shown in  FIG. 1   c . Thermal image  135  is mapped onto the pixel array, not shown, of camera  133  of FIGURE la that senses the user finger touch on screen  103 . Thus, screen  103  forms a user interface touchscreen. Similar symbols and numerals in  FIGS. 1   a ,  1   b ,  1   c ,  2 ,  3 ,  4 ,  5 ,  6 ,  7   a  and  7   b  indicate similar items or functions. 
         [0033]    Pico projector  131  is, typically, the type designed to be used as a front projector. Without correction, pico projector  131 , utilized as a rear projector such as in  FIG. 1   a  would produce a projected image that needs image flipping correction.  FIG. 8   a  is provided for explaining the need for such image correction and a first correction solution for such problem.  FIG. 8   b  is provided for explaining a second correction solution for such problem. Similar symbols and numerals in  FIGS. 1   a ,  1   b ,  1   c ,  2 ,  3 ,  4 ,  5 ,  6 ,  7   a,    7   b,    8   a  and  8   b  indicate similar items or functions. 
         [0034]    Unlike in a front projector situation, the viewer looks into the direct light produced by projector  131 , instead of at the reflected light from screen  103 . Without correction, the image produced by the direct light from pico projector  131  would be improperly flipped left side-to-right side, and vice versa, with respect to an axis of symmetry  130  of  FIG. 8   a . In a first solution to this problem, demonstrated in  FIG. 8   a  , an image contained in a memory, not shown, of pico projector  131  would be electronically processed by a signal processor, not shown, so as to be flipped left side-to-right side, and vice versa. In this way, the viewed image would no longer be incorrectly flipped. In an alternative solution to this problem, a mirror  150  of  FIG. 8   b  would reflects the image to be optically flipped left side-to-right side, and vice versa, so that the viewed image would no longer be incorrectly flipped.