Abstract:
Disclosed is a personal portable device that includes a microprojector. The microprojector creates an image for display. The image is sent to a “beam-switching element” that shunts the image toward a selected display screen (e.g., a display screen on the device or an off-device projection). The image is then displayed on the selected screen. By commanding the beam-switching element to change its configuration, different screens can be driven by the same microprojector. The combination of a single microprojector with multiple display screens gives the personal portable device the flexibility of multiple displays while preserving space within the device and, in some embodiments, lowering power consumption. In some embodiments, the microprojector simultaneously drives more than one display screen. The driven display screens may display the same or different images, and the images displayed may be of the same or of different resolutions.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related generally to projectors of optical images, and, more particularly, to optical-image projectors subject to space or power-consumption limitations. 
       BACKGROUND OF THE INVENTION 
       [0002]    A trend in personal portable devices (such as cell phones and personal digital assistants) is to add new features while keeping the devices small. Many of these new features display information visually. For example, a high-resolution, easy-to-read display screen is provided to support photograph sharing and video downloading. Many devices also include a separate, smaller or lower-resolution display screen on the outside of the device for status messages. 
         [0003]    In addition to these display screens on the device itself, some devices may soon incorporate a “microprojector.” Here, an image, either still or moving, is projected from the device onto a convenient surface (e.g., a projection screen or an office wall). The maximum size of the image is then effectively constrained only by the amount of available wall space rather than by the size of the device itself. Using a microprojector-equipped device, several people can simultaneously view a photograph, for example, or review a full page of text, neither of which can be readily done with even the largest displays on current personal portable devices. 
         [0004]    Useful as these multiple display screens are, they raise new challenges when engineers attempt to support all of them in one personal portable device. The packaging problems are exacerbated by the trend toward smaller and thinner devices. 
         [0005]    Power use is another challenge. It takes a significant amount of electrical power to simultaneously support a number of display screens, especially if one of the screens is a large display area outside the device. Designers of battery-based personal portable devices are already concerned about their power budgets and look askance at any new feature that threatens to reduce the utility of the device by reducing how long the device can operate between charges. 
       BRIEF SUMMARY 
       [0006]    The above considerations, and others, are addressed by the present invention, which can be understood by referring to the specification, drawings, and claims. According to aspects of the present invention, a personal portable device includes a microprojector that creates an image for display. The image is sent to a “beam-switching element” that shunts the image toward a selected display screen (e.g., a display screen on the device or an off-device projection surface). The image is then displayed on the selected screen. By commanding the beam-switching element to change its configuration, different screens can be driven by the same microprojector. 
         [0007]    The combination of a single microprojector driving multiple display screens gives the personal portable device the flexibility of multiple displays while preserving space within the device and, in some embodiments, lowering power consumption. For example, a device can be designed that is very thin but still incorporates multiple display screens. 
         [0008]    In some embodiments, the microprojector simultaneously drives more than one display screen. The driven display screens may display the same or different images, and the images displayed may be of the same or of different resolutions. 
         [0009]    Power consumption is lowered in some embodiments by varying the amount of power consumed by the microprojector based on the display screen (or screens) in use at any one time. For example, less power could be consumed when off-device projection is not in use. 
         [0010]    To enhance packaging flexibility, in some embodiments one or more light guides carry images from the beam-switching element to one or more display screens. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0011]    While the appended claims set forth the features of the present invention with particularity, the invention, together with its objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which: 
           [0012]      FIGS. 1   a,    1   b,  and  1   c  are block diagrams of a personal portable device with three display screens; 
           [0013]      FIG. 2   a  is a simplified schematic view of a device directing an image to a display screen on the device, according to one aspect of the present invention; 
           [0014]      FIG. 2   b  is a simplified schematic of the device of  FIG. 2   a  now projecting the image to an off-device screen; 
           [0015]      FIG. 2   c  is a simplified schematic of the device of  FIG. 2   a  simultaneously directing images to two different display screens; 
           [0016]      FIG. 3  is a flowchart of an exemplary embodiment of the present invention; and 
           [0017]      FIG. 4  is a simplified schematic of an exemplary device with a curved light guide directing an image to a display screen. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Turning to the drawings, wherein like reference numerals refer to like elements, the invention is illustrated as being implemented in a suitable environment. The following description is based on embodiments of the invention and should not be taken as limiting the invention with regard to alternative embodiments that are not explicitly described herein. 
         [0019]      FIGS. 1   a,    1   b,  and  1   c  show a personal portable device  100  (e.g., a cellphone, personal digital assistant, or personal computer) that incorporates an embodiment of the present invention in order to support multiple display screens. This particular device  100  has three display screens. First,  FIG. 1   a  shows the device  100  in an open configuration, presenting its main display  102  to a user. Typically, the main display  102  is used for most high-fidelity interactions with the user. For example, the main display  102  is used to show video or still images, is part of a user interface for changing configuration settings, and is used for viewing call logs and contact lists. To support these interactions, the main display  102  is of high resolution and is as large as can be comfortably accommodated in the device  100 . (The “resolution” of a digital image is defined as the product of its horizontal resolution and its vertical resolution. Resolution is measured in number of pixels. Note that here “horizontal” and “vertical” are merely convenient, and conventional, names for the two dimensions of a planar image and are not confined to orientations taken with respect to the direction of gravity.) 
         [0020]    When the device  100  is closed, as in  FIG. 1   b,  a secondary display  104  is readily visible. This secondary display  104  is often used for status messages (such as the time of day) and is generally of lower resolution and of smaller size than the main display  102 . 
         [0021]      FIG. 1   c  illustrates a third display screen. In the figure, a user  106  is projecting an image  108  from her personal portable device  100 . The image  108  could be, for example, a photograph, a video, or a computerized display from a word processor or an Internet browser. The image  108  may be projected onto a screen or even onto a wall or ceiling. By projecting the large, high resolution image  108  rather than presenting it on a (necessarily small) display screen  102  or  104  of her personal portable device  100 , the user  106  can invite others to share the image  108  with her. 
         [0022]    Prior to the present invention, the personal portable device  100  would have to incorporate within it three sets of display electronics, one set for each of the three display screens  102 ,  104 , and  108 . These three sets of display electronics increase the cost of the device  100  and consume significant amounts of its limited volume. 
         [0023]    According to aspects of the present invention,  FIGS. 2   a,    2   b,  and  2   c  show alternatives to having these multiple sets of display electronics.  FIG. 3  presents an exemplary method of operation of the personal portable device  100  of  FIGS. 2   a,    2   b,  and  2   c.  In the schematic of  FIG. 2   a,  the device  100  contains control logic and display memory  200 . In order to display an image, the control logic  200  sends the image to a microprojector  202 . The microprojector  202  modulates light in order to imprint image information into a projected light beam (step  300  of  FIG. 3 ). 
         [0024]    The projected light beam, modulated to incorporate the image information, is directed to a “beam-switching element”  204  (step  302  of  FIG. 3 ). The beam-switching element  204 , under the direction of the control logic  200 , can direct the light to one or more display screens (step  304 ). In  FIG. 2   a,  the beam-switching element  204  directs the image to a rear-projection display screen  206 . This image is then viewable by the user  106  of the personal portable device  100  (step  306 ). In some embodiments, this rear-projection display screen  206  is the same as the main display  102  or the secondary display  104  of the device  100 . 
         [0025]      FIG. 2   b  shows the same personal portable device  100  of  FIG. 2   a  but in a different operational mode. In  FIG. 2   b,  the control logic  200  tells the beam-switching element  204  to send the image to an external surface for a projection-display screen. This image passes through an optically clear window  208  on the surface of the device  100  and is projected against a screen or wall, as shown in  FIG. 1   c.  Because one microprojector  202  supports multiple display screens, the device  100  can be built more cheaply and smaller than before. 
         [0026]    Several technologies can be used for the microprojector  202 . Depending upon economic and engineering factors, the microprojector  202  can incorporate an imager (either reflective or transmissive) or a laser or can be a hybrid. 
         [0027]    There are also a number of ways of building the beam-switching element  204 . A physically movable mirror can be used where the mirror moves between a first position when the display screen  206  is in use to a second position when the projection display is used. Semi-transparent and electrically configurable mirrors are also usable. 
         [0028]      FIG. 2   c  shows an embodiment of the personal portable device  100  where the beam-switching element  204  is able to simultaneously send images to two different display screens  206  and  208 . In one case, the beam-switching element  204  is electrically configurable, and in the scenario of  FIG. 2   c  it is configured to reflect part of the light incident on it to the rear-projection display screen  206  while passing the remainder of the light to the projection display  208  (step  304  of  FIG. 3 ). 
         [0029]    In another case, the beam-switching element  204  and the microprojector  202  are configured to simultaneously display a first image on the display screen  206  and a different image on the display  208 . The microprojector  202  creates both images, possibly on different portions of its display area, and the beam-switching element  204  is directed to separate the images and to send them to the appropriate displays screens  206  and  208 . 
         [0030]    When different images are displayed simultaneously, they may be of the same or of different resolutions. For example, the image on the projection display  208  may be of high resolution, while a low-resolution status message is shown on the local display screen  206 . The images, different or the same, and their resolutions, different or the same, are under the control of the control logic  200 . The control logic  200  can direct the microprojector  202  so that some of its pixels are allocated to the projection display  208 , while others are allocated to the local display screen  206 . In some embodiments, the microprojector  202  has VGA resolution, that is, 640×480 pixels. Embodiments of the present invention are compatible with other image resolutions. 
         [0031]    In some embodiments, the control logic  200  also varies the amount of power used by the microprojector  202  depending upon which, and how many, displays are in use at any one time. Because a projected image  108  is usually rather large and is often shown on a less-than-ideal surface, it often requires more light than is necessary to show an image on a local display screen  206 . Thus, the control logic  200  may decrease the power used by the microprojector  202  whenever the projection display  208  is not in use. This feature gives the personal portable device  100  the ability to project images without incurring the cost of always driving the microprojector  202  at full power. 
         [0032]    The embodiment in  FIG. 4  illustrates the packaging flexibility provided by some aspects of the present invention. In  FIG. 4 , the microprojector  202  and the beam-switching element  204  are located on one side of the personal portable device  100 . Images can be directed to a projection display  208  on this same side of the device  100 . The beam-switching element  204  can also direct images to a display  402  located on the other side of the device  100 . To bring images from the beam-switching element  204  across the width of the device  100  to the display  402 , a curved light guide  400  is provided. 
         [0033]    Light guides can be used in conjunction with other embodiments (such as those of  FIGS. 2   a,    2   b,  and  2   c ) in order to enhance flexibility in locating components such as the displays  206 ,  208 , and  402  and the microprojector  202 . For example, the microprojector  202  and the beam-switching element  204  can be located in a base of the personal portable device  100 , while a flexible light guide can carry image information across a hinge to a display on a cover portion of the device  100 . 
         [0034]    In view of the many possible embodiments to which the principles of the present invention may be applied, it should be recognized that the embodiments described herein with respect to the drawing figures are meant to be illustrative only and should not be taken as limiting the scope of the invention. For example, the light paths in the figures are only meant to illustrate the functions of the various components and are not meant to be definitive. Other arrangements of the optical components shown in the figures and the addition of other known optical components are possible and may be called for in various environments. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof.