Abstract:
Infrared radiation receivers ( 40, 72 ) of this invention include non-imaging optical concentrators ( 18, 70 ) having light exit surfaces ( 52, 86 ); a light sensor ( 46 ) having a light entrance surface that is separated from the light exit surface by a small air gap ( 53 ); and a soft, pliable, light transmissive medium ( 100, 110 ) inserted in the gap to reduce the light transmission loss across the gap. The soft, pliable medium is held in place by either a recess ( 116 ) in the concentrator or by a surrounding annular ring ( 104 ).

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to low-loss non-imaging optical concentrators and more particularly to an infrared (“IR”) receiver optical system employed in remote control systems of multimedia projectors.  
         BACKGROUND OF THE INVENTION  
         [0002]    Projection systems have been used for many years to project motion pictures and still photographs onto screens for viewing. In the recent past, slide and overhead transparency projectors were commonly used for conducting sales demonstrations, business meetings, and classroom instruction. Slide projectors were commonly controlled by a remote control unit that was electrically connected to the slide projector by a cable that allowed a presenter, such as a salesperson, instructor, or project manager, to stand next to the projector or the projection screen while conducting the slide presentation. However, the cable limited the presenter&#39;s mobility and presented a tripping hazard, especially in darkened rooms.  
           [0003]    More recently, slide and overhead presentations have been largely replaced by presentations employing multimedia projection systems. In a typical operating mode, multimedia projection systems receive video signals from a personal computer (“PC”), a tape drive, a disk drive, or some other form of image generating or storing device. The video signals may represent still, partial-, or full-motion display images of a type typically rendered by PCs. The video signals are converted in the multimedia projection system into signals that control a digitally driven imaging device that forms the image to be projected.  
           [0004]    The presenter typically controls the multimedia projection system with a wireless IR remote control device similar to ones employed to control home television receivers. This has greatly increased the mobility of the presenter and eliminated the tripping hazard. In fact, multimedia projectors have grown in popularity to the point where they are available in diverse models suited for, among others, portable, tabletop, ceiling-hung, and rear-projected applications.  
           [0005]    Because battery powered IR remote control devices are typically quite directional, the wide variety of possible projector placements and various possible presenter positions causes a dilemma. The presenter can usually point the IR remote control transmitter toward the multimedia projector, but proper placement of the IR receiver on the multimedia projector is indeterminate. Suitable IR receiver mounting positions may include top mounting when the presenter is standing close to the multimedia projector, front mounting when the presenter is standing near the projection screen, and rear mounting when the presenter is behind the multimedia projector. Top mounting may also be suitable in ceiling-hung applications in which the multimedia projector is hung upside down. Clearly no single IR receiver position was suitable for all applications, so prior workers placed multiple IR receivers on the major surfaces of the multimedia projectors, an unduly complex and costly solution.  
           [0006]    Prior IR receivers are directional primarily because the optical components coupling IR energy to an IR sensor have a limited range of angular coverage. Indeed, the most common optical component is merely an optical window having a spectral filtering property that improves the signal-to-noise ratio of the sensed IR energy. Attempts to compensate for the directionality of prior IR receivers included increasing IR transmitter power and/or IR receiver sensitivity. Unfortunately, the former solution unacceptably increased battery consumption and the latter solution was marginal because receiver sensitivity was already typically maximized.  
           [0007]    In response to this need, prior workers developed an IR receiver employing an omnidirectional optical concentrator coupled to a single IR sensor having usable sensitivity to received IR energy over a wide range of azimuthal and elevation angles. This system is described in U.S. Pat. No. 6,201,591 for NON-IMAGING OPTICAL CONCENTRATOR FOR USE IN INFRARED REMOTE CONTROL SYSTEMS, which is assigned to the assignee of this application.  
           [0008]    A problem with the above-described system is that the omnidirectional optical concentrator is mounted on the projector case and the IR sensor is mounted on a circuit board inside the projector. Manufacturing tolerances require a gap between the concentrator and the sensor, which gap creates multiple reflections of the IR signal that increases transmission loss in the system, thereby reducing the effective range of the IR remote control.  
           [0009]    What is still needed, therefore is an IR receiver having increased sensitivity to received IR energy over a wide range of azimuthal and elevation angles.  
         SUMMARY OF THE INVENTION  
         [0010]    An object of this invention is, therefore, to provide an apparatus and a method for efficiently receiving light rays propagating from multiple angles and directing them toward a light sensor.  
           [0011]    Another object of this invention is to provide a low-loss non-imaging optical concentrator apparatus.  
           [0012]    A further object of this invention is to provide an omnidirectional IR receiver usable with a remote controller in a multimedia projection application.  
           [0013]    A non-imaging optical concentrator receives light rays propagating from a wide range of elevational and azimuthal angles relative to an optical axis and directs them through a low-loss medium toward a light sensor. A first embodiment of the optical concentrator includes an optically transparent body including a substantially dome-shaped convex surface of revolution formed about the optical axis and a conical concave surface of revolution formed about the optical axis and protruding into the convex surface in a direction along the optical axis in a direction toward the light sensor. The convex surface receives light rays propagating from low elevational angles and causes them to propagate through the optically transparent body, reflect off the concave surface, and propagate generally along the optical axis toward the light sensor. The concave surface further receives light rays propagating from high elevational angles and refracts them through the optically transparent body toward the light sensor. In this embodiment, the non-imaging optical concentrator is mounted to a multimedia projector housing, and the light sensor is mounted on a circuit board within the projector housing. The concentrator and housing are separated by about a 1 millimeter gap.  
           [0014]    A second embodiment of the optically transparent body further includes a second conical concave surface of revolution formed about the optical axis and protruding from near the apex of the first conical concave surface deeper into the optically transparent body in a direction along the optical axis. The convex surface further receives light rays propagating from medium elevational angles and causes them to propagate through the optically transparent body and reflect at relatively low angles off the first and second concave surfaces in a direction generally along the optical axis toward the light sensor. In a manner similar to the first concave surface, the second concave surface further receives light rays propagating from high elevational angles and refracts them through the optically transparent body toward the light sensor. In this embodiment, the non-imaging optical concentrator is mounted to the circuit board within the projector housing and protrudes through a hole in the housing. The light sensor is also mounted to the circuit board, but because of alignment and manufacturing tolerances, is still separated from the concentrator by the gap.  
           [0015]    This invention increases light transmission between the concentrator and the light sensor inserting a soft, pliable, optically clear light transmission medium in the air gap. The light transmission medium reduces IR transmission losses by eliminating the multiple reflections caused by material-to-air interfaces. The light transmission medium is preferably a soft material, such as silicon gel or silicon glue, that is constrained by an annular ring of rigid material to hold the light transmission medium in place during the manufacture and useful lifetime of the projector.  
           [0016]    In an alternative embodiment of this invention, the optical concentrators include a recess in the surface facing the gap. The soft, pliable light transmission medium is inserted into the recess and allowed to protrude by an amount that gently compresses it against the light sensor.  
           [0017]    The low-loss non-imaging optical concentrators of this invention is advantageous because only one light sensor is required to receive IR controller data propagating from a wide range of distances, elevational angles, and azimuthal angles. They are, therefore, particularly useful for use in multimedia projector applications.  
           [0018]    Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof that proceeds with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a pictorial isometric view of a multimedia projection system employing an omnidirectional IR remote control receiver of this invention.  
         [0020]    [0020]FIG. 2 is an elevation view showing a prior art housing-mounted non-imaging optical concentrator and light sensor separated by an air gap.  
         [0021]    [0021]FIG. 3 is an elevation view showing a prior art circuit board-mounted non-imaging optical concentrator and light sensor separated by an air gap.  
         [0022]    [0022]FIGS. 4A and 4B show respective plan and elevational section views of a first embodiment of a light transmission medium of this invention.  
         [0023]    [0023]FIG. 5 is a sectional elevation view showing the light transmission medium of FIGS. 4A and 4B employed with the non-imaging optical concentrator and light sensor of FIG. 2.  
         [0024]    [0024]FIG. 6 is a sectional elevation view showing a second embodiment of a light transmission medium of this invention employed with the non-imaging optical concentrator and light sensor of FIG. 3.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]    [0025]FIG. 1 shows a projection system  10  including a multimedia projector  12  that projects an electronically generated image  14  on a projection screen  16 . Multimedia projector  12  includes a non-imaging optical concentrator  18  (hereafter “optical concentrator  18 ”) that receives light rays  20  from a remote control unit  22 . Light rays  20  preferably include IR wavelengths but may include visible, ultraviolet (“UV”), and near- and far-IR wavelengths. Optical concentrator  18  has an optical axis  24  and is mounted on or protrudes through a top surface  26  of multimedia projector  12  such that optical axis  24  extends vertically in a direction substantially normal to top surface  26 . In this mounting orientation, optical concentrator  18  can receive light rays  20  propagating from a wide range of elevational angles  28  and azimuthal angles  30 .  
         [0026]    As a labeling convention for this application, elevational angles  28  and azimuthal angles  30  are measured relative to an imaginary plane that is transverse to optical axis  24  and cuts through optical concentrator  18 . For practical purposes the imaginary plane may be considered as being substantially coplanar with top surface  26  of multimedia projector  12 . Elevational angles  28  are, therefore, expressed as angles ranging from 0 degrees (when aligned with top surface  26 ) to 90 degrees (when aligned with optical axis  24 ), and azimuthal angles  30  are expressed as 0- to 360-degree angles relative to a reference line  32  that points toward projection screen  16  and lays in top surface  26 . By way of example only, FIG. 1 shows an elevational angle  28  of about 40 degrees and an azimuthal angle  30  of about 240 degrees. However, optical concentrator  18  effectively receives light rays  20  propagating from elevational angles  28  ranging from about 0 degrees to about 90 degrees and from azimuthal angles  30  ranging from about 0 degrees to about 360 degrees.  
         [0027]    [0027]FIG. 2 shows a first optical concentrator  18  that is suitable for mounting to top surface  26  of projection system  10  (FIG. 1). Optical concentrator  18  is suitable for use in this invention as part of an IR receiver  40 . Optical concentrator  18  includes a substantially dome-shaped convex surface  42  of revolution formed about optical axis  24  and a substantially conical concave surface  44  of revolution formed about optical axis  24  and protruding into convex surface  42  in a direction along optical axis  24  toward a light sensor  46 . The apex of conical concave surface  44  is centered on optical axis  24 , and conical concave surface  44  forms a tilt angle  48  measured from optical axis  24 . Optical concentrator  18  further includes a light guide portion  50  that extends generally along optical axis  24  in a direction leading from convex surface  42  and concave surface  44  and toward light sensor  46 . Light guide portion  50  terminates in a flat surface  52 , which, for suitable coupling, is typically spaced apart by about a 1.0- to 2.0-mm air gap  53  from light sensor  46 . Light sensor  46  is mounted to a circuit board  54  that is further mounted within projection system  10 .  
         [0028]    Optical concentrator  18  is formed by injection molding from optically transparent polycarbonate material, tilt angle  48  is 45 degrees, and light sensor  46  is a 3.0 mm by 3.0 mm IR sensitive photodiode. Convex surface  42  is a truncated hemisphere having about a 5.75 mm radius of curvature and concave surface  44  is a right conic surface having about an 8.0 mm base diameter and about a 4.0 mm height. Light guide portion  50  is about a 9.3 mm long tapered cylinder having about a 5.0 mm diameter where it terminates at flat surface  52 .  
         [0029]    Optical concentrator  18  receives at convex surface  42  first light rays  55  propagating from any of azimuthal angles  30  and from first elevational angles  56  ranging from about 0 degrees to about 15 degrees. First light rays  55  enter convex surface  42 , propagate through optical concentrator  18  toward optical axis  24 , are reflected off the inside of concave surface  44  in a direction generally along the optical axis through light guide portion  50 , exit flat surface  52 , and are detected by light sensor  46 .  
         [0030]    Optical concentrator  18  further receives at concave surface  44  second light rays  58  propagating from any of azimuthal angles  30  and from second elevational angles  60  ranging from about 75 degrees to about 90 degrees. Second light rays  58  enter concave surface  44 , are refracted in a direction generally along the optical axis through light guide portion  50 , exit flat surface  52 , and are detected by light sensor  46 .  
         [0031]    [0031]FIG. 3 shows a second optical concentrator  70  that is suitable for mounting to circuit board  54  and protruding through top surface  26  of projection system  10  (FIG. 1). Optical concentrator  70  is suitable for use in this invention as part of an IR receiver  72 . Optical concentrator  70  includes a substantially dome-shaped convex surface  74  of revolution formed about optical axis  24 , a substantially conical truncated concave surface  76  of revolution formed about optical axis  24 , and a substantially conical concave surface  78  of revolution formed about optical axis  24 . Truncated concave surface  76  protrudes at a first tilt angle  80  into convex surface  74 , and conical concave surface  78  protrudes at a second tilt angle  82  further into convex surface  74 . The apex of conical concave surfaces  76  and  78  are centered on optical axis  24 , first tilt angle  80  is preferably about 45 degrees, and second tilt angle  82  is preferably about 26.6 degrees. Optical concentrator  70  further includes a light guide portion  84  that extends generally along optical axis  24  in a direction leading from conical concave surface  78  and toward light sensor  46 . Light guide portion  84  terminates in an exit surface  86 , which, for suitable coupling, is typically spaced apart by 1.0- to 2.0-mm air gap  53  from light sensor  46 . As before, light sensor  46  is mounted to circuit board  54  that is further mounted within projection system  10 .  
         [0032]    Optical concentrator  70  is formed by injection molding from optically transparent polycarbonate material. Convex surface  74  is preferably a truncated hemisphere having about a 5.75 mm radius of curvature, truncated concave surface  76  is preferably a truncated right conic surface having about a 7.990 mm base diameter and about a 2.0 mm height, and conical concave surface  78  is preferably a right conical surface having about a 3.0 mm base diameter and a 2.995 mm height. Light guide portion  84  is preferably about a 9.63 mm long cylinder having about a 4.0 mm diameter.  
         [0033]    Optical concentrator  70  receives at convex surface  74  first light rays  55  propagating from any of azimuthal angles  30  and from first elevational angles  88  ranging from about 0 degrees to about 25 degrees. First light rays  55  enter convex surface  74 , propagate through optical concentrator  70  toward optical axis  24 , are reflected off the inside of truncated concave surface  76  in a direction generally along optical axis  24  and through light guide portion  84 , exit surface  86 , and are detected by light sensor  46 .  
         [0034]    Optical concentrator  70  further receives at truncated concave surface  76  or conical concave surface  78  second light rays  58  propagating from any of azimuthal angles  30  and from second elevational angles  60  ranging from about 75 degrees to about 90 degrees. Second light rays  58  enter truncated concave surface  76  or conical concave surface  78 , are refracted in a direction generally along optical axis  24  and through light guide portion  84 , exit surface  86 , and are detected by light sensor  46 .  
         [0035]    Optical concentrator  70  still further receives at convex surface  74  third light rays  90  propagating from any of azimuthal angles  30  and from third elevational angles  92  ranging from about 25 degrees to about 45 degrees. Third light rays  90  enter convex surface  74 , propagate through optical concentrator  70 , are reflected at a first shallow angle off the inside of truncated concave surface  76 , are reflected again at a second shallow angle off the inside of conical concave surface  78 , propagate in a direction generally along optical axis  24  and through light guide portion  84 , exit surface  86 , and are detected by light sensor  46 .  
         [0036]    The materials forming optical concentrators  18  and  70  determine their spectral transmission properties. For detecting visible and near IR light rays, preferred materials include optical glasses, plastics, and, in particular, polycarbonate. For detecting UV light rays, a preferred material is quartz. For detecting IR light rays, preferred materials include quartz, zinc selenide, and germanium-doped materials. Wavelength-selective filtering dyes may be added to the materials to attenuate undesirable ambient light wavelengths, such as from fluorescent lighting. Adding such dyes or, alternatively, a discrete optical filter improves the signal-to-noise ratio of remote controller signals detected by light sensor  46 .  
         [0037]    Alternative embodiments of optical concentrators  18  and  70  may be optimized to detect light rays propagating from longer distances and smaller ranges of elevational angles or from shorter distances and larger ranges of elevational angles. The parameters of optimization available include changing the size and curvature (shape) of convex surfaces  42  and  74 ; tilt angles  48 ,  80 , and  82 ; the area, shape, size, and orientation of concave surfaces  44 ,  76 , and  78 ; the area and curvature of exit surface  86 ; and the refractive index and spectral transmission properties of the optical concentrator material. In addition to the spherical and conical surface shapes shown, cylindrical, faceted, elliptical, parabolic, hyperbolic, and combinations thereof may suit particular light detecting applications. Of course, the surfaces need not be symmetrical surfaces of revolution, but may be angularly biased to favor reception of light rays propagating from low elevational angles over a first range of azimuthal angles and to favor reception of light rays propagating from higher elevational angles over a second range of azimuthal angles.  
         [0038]    Typically tilt angles  48 ,  80 , and  82  are adjusted to optimize light ray reception over a particular range of elevational angles. In applications in which the light rays propagate from a broader range of elevational angles and a minimal range of distances is required over any azimuthal angle, a compound optical concentrator, such as the one shown in FIG. 3, is preferred.  
         [0039]    In general, optical concentrators of this invention operate in two primary modes. For receiving light rays propagating from low elevational angles (greater than the tilt angle) the optical concentrator works in reflective mode, and for receiving light rays propagating from higher elevational angles (less than the tilt angle) the optical concentrator works in refractive mode. This dual mode operation is referred to as aperture sharing, which results in a compact, relatively simple IR receiver employing a single IR sensor and having usable sensitivity to received IR energy over a wide range of azimuthal and elevation angles.  
         [0040]    It has been discovered that air gap  53  contributes to transmission loss of light rays  55 ,  58 , and  90  propagating between optical concentrators  18  and  70  and light sensor  46 . The transmission loss is caused by multiple reflections between concentrator surfaces  52  and  85  and the surface of light sensor  46 . Unfortunately, the light transmission loss reduces the useful range between remote control unit  22  (FIG. 1) and projection system  10  (FIG. 1).  
         [0041]    [0041]FIGS. 4A and 4B show a first embodiment of a light transmission medium  100  (hereafter “medium  100 ”) of this invention that reduces light transmission losses between concentrator  18  and light sensor  46 , thereby increasing the useful range between remote control unit  22  (FIG. 1) and projection system  10  (FIG. 1). Medium  100  includes a soft, pliable, optically clear material  102 , such as a silicon gel or preferably a silicon glue. Material  102  is constrained by an annular ring  104  of rigid material that holds material  102  in place during the manufacture and useful lifetime of medium  100 .  
         [0042]    [0042]FIG. 5 shows medium  100  inserted into air gap  53  between light sensor  46  and flat surface  52  of IR receiver  40 . Medium  100  effectively eliminates air gap  53 , thereby reducing IR transmission losses by eliminating the multiple reflections caused by the above-described material-to-air interfaces. Material  102  is sufficiently soft and pliable to conform to the surfaces of light sensor  46  and light guide portion  50 .  
         [0043]    Medium  100  is preferably manufactured by inserting material  102  into annular ring  104 ; pressing material  102  between a pair of substantially parallel flat surfaces coated with a release agent, such as waxed paper; allowing material  102  to cure; removing the flat surfaces; pressing and/or sticking medium  100  to either light sensor  46  or flat surface  52 ; and assembling IR receiver  40  (FIG. 2).  
         [0044]    [0044]FIG. 6 shows a second embodiment of a light transmission medium  110  (hereafter “medium  110 ”) of this invention that reduces light transmission losses between concentrator  70  and light sensor  46 , thereby increasing the useful range between remote control unit  22  (FIG. 1) and projection system  10  (FIG. 1). Medium  110  includes soft, pliable, optically clear material  102 , which in this embodiment is not constrained by an annular ring.  
         [0045]    In this embodiment, concentrator  70  includes a light guide portion  84 , an exit surface  86 , and a base  112  that includes posts  114  for mounting concentrator  70  to circuit board  54 . A recess  116  surrounding light guide portion  86  is formed in base  112 . Medium  110  is inserted into and around recess  166  and allowed to protrude a small amount, such that when assembled, medium  110  presses gently against light sensor  46 .  
         [0046]    Medium  110  is preferably manufactured by inserting material  102  into and around recess  116 ; pressing the exposed bottom surface of material  102  with a substantially parallel flat surface coated with a release agent, such as waxed paper; allowing material  102  to cure; removing the flat surface; and assembling IR receiver  72  (FIG. 3).  
         [0047]    As an alternative to the above embodiments of this invention, a suitable medium may be manufactured by flattening a substantial quantity of material  102  between a pair of substantially flat surfaces coated with a release agent; curing material  102  to form a sheet of medium; removing at least one of the flat surfaces; cutting patches of the medium from the sheet of medium; sticking the patch to either the light sensor or the concentrator; and assembling the IR receiver.  
         [0048]    Skilled workers will recognize that many changes may be made to the details of the above-described embodiments of this invention without departing from the underlying principles thereof. Accordingly, it will be appreciated that this invention is also applicable to light sensor applications other than those found in remote controls for multimedia projectors. The scope of the present invention should, therefore, be determined only by the following claims.