Abstract:
An integrated front projection system has a housing assembly, a projection assembly, and an expansion assembly. The housing assembly includes a frame having a front surface that provides a front projection screen and contains other modular components. In addition, a projection assembly with a movable arm may be included, having a storage position and a projection position, and to which the front projection head may be coupled. According to one aspect, the projection assembly is modularized and has a plurality of easily replaceable component modules coupled to the housing and which operate together to project an image onto the front projection screen. According to another aspect, the integrated front projection system further has an expansion assembly coupled to the housing. The expansion assembly includes an expansion slot formed in the housing and electrically coupled to a display controller in the projection assembly and expansion modules coupled to the expansion slot. The expansion modules operate to enhance functionality of the display controller.

Description:
This is a continuation of application Ser. No. 09/616,563, filed Jul. 17, 2000, now U.S. Pat. No. 6,394,609, which is a continuation of application Ser. No. 09/261,715, filed Mar. 3, 1999, issued as U.S. Pat. No. 6,179,426. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an integrated front projection display system. In particular, the present invention relates to a low-profile integrated front projection system that coordinates specialized projection optics and an integral screen optimized to work in conjunction with the optics to create the best viewing performance and produce the necessary keystone correction. 
     Electronic or video display systems are devices capable of presenting video or electronically generated images. Whether for use in home-entertainment, advertising, videoconferencing, computing, data-conferencing or group presentations, the demand exists for an appropriate video display device. 
     Image quality remains a very important factor in choosing a video display device. However, as the need increases for display devices offering a larger picture, factors such as cost and device size and weight are becoming vital considerations. Larger display systems are preferable for group or interactive presentations. The size of the display system cabinet has proven an important factor, particularly for home or office use, where space to place a large housing or cabinet may not be available. Weight of the display system also is an important consideration, especially for portable or wall-mounted presentations. 
     Currently, the most common video display device is the typical CRT monitor, usually recognized as a television set. CRT devices are relatively inexpensive for applications requiring small to medium size images (image size traditionally is measured along the diagonal dimension of a rectangular screen). However, as image size increases, the massive proportions and weight of large CRT monitors become cumbersome and severely restrict the use and placement of the monitors. Also, screen curvature issues appear as the screen size increases. Finally, large CRT monitors consume a substantial amount of electrical power and produce electromagnetic radiation. 
     One alternative to conventional CRT monitors is rear projection television. Rear projection television generally comprises a projection mechanism or engine contained within a large housing for projection up on the rear of a screen. Back-projection screens are designed so that the projection mechanism and the viewer are on opposite sides of the screen. The screen has light transmitting properties to direct the transmitted image to the, viewer. 
     By their very nature, rear projection systems require space behind the screen to accommodate the projection volume needed for expansion of the image beam. As background and ambient reflected light may seriously degrade a rear projected image, a housing or cabinet generally encloses the projection volume. The housing may contain a mirror or mirrors so as to fold the optical path and reduce the depth of the housing. The need for “behind-the-screen” space precludes the placing of a rear projection display on a wall. 
     A new category of video presentation systems includes so-called thin Plasma displays. Much attention has been given to the ability of plasma displays to provide a relatively thin (about 75-100 nun) cabinet, which may be placed on a wall as a picture display in an integrated compact package. However, at the present time, plasma displays  3  are costly and suffer from the disadvantages of low intensity (approx. 200-400 cd/m 2  range) and difficulty in making repairs. Plasma display panels are heavy (˜80-100 lbs., ˜36-45 kg.), and walls on which they are placed may require structural strengthening. 
     A traditional type of video presentation device that has not received the same degree of attention for newer applications is front-projection systems. A front-projection system is one that has the projection mechanism and the viewer are on the same side of the screen. Front projection systems present many different optical and arrangement challenges not present in rear projection systems, as the image is reflected back to the audience, rather than transmitted. An example of front projection systems is the use of portable front projectors and a front projection screen, for use in meeting room settings or in locations such as an airplane cabin. 
     One of the advantages of front projectors is the size of the projection engine. Electronic front projectors traditionally have been designed for the smallest possible “footprint”, a term used to describe the area occupied on a table or bench, by the projector. Portable front projectors have been devised having a weight of about 10-20 lbs. (˜4.5-9 kg.). 
     Nevertheless, front projection systems have traditionally not been considered attractive for newer interactive applications because of factors such as blocking of the image by the projector or the presenter, poor image brightness, image distortion and setup  2   o  difficulties. 
     Traditional electronic front projectors typically require a room that may afford the projection volume necessary for image expansion without any physical obstructions. Although images may be projected upon a large clear flat surface, such as a wall, better image quality is achieved by the use of a separate screen. FIGS. 1 and 2 illustrate a traditional front projection system. A projector  10  is placed on a table or other elevated surface to project an image upon a screen or projection surface  20 . Those familiar with the use of electronic projectors will appreciate that tilting the projector below the normal axis of the screen produces a shape distortion of the image, known as a keystone effect. Most new electronic projectors offer a limited degree of keystone correction. However, as may be appreciated in FIG. 2, the placement of the projector may still interfere with the line of sight of the audience. 
     Of greater significance is the fact that to achieve a suitable image size, and also due to focus limitations, the projector  10  requires a certain “projection zone” in front of the screen  20 . Table A lists the published specifications for some common electronic projectors currently in the market. 
     
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE A 
               
               
                   
               
               
                   
                   
                   
                 Small- 
                 Short- 
                   
                   
               
               
                   
                   
                   
                 est 
                 est 
                   
               
               
                   
                 Lens 
                   
                 Screen 
                 Throw 
                   
                 Maximum 
               
               
                 Projector 
                 Focal 
                 Imager 
                 Diag- 
                 Dis- 
                 Throw 
                 Keystone 
               
               
                 Type 
                 Length 
                 Diagonal 
                 onal 
                 tance 
                 Ratio 
                 Correction 
               
               
                   
               
             
             
               
                 CTX Opto 
                 * 
                 163 MM 
                  1.0 m 
                 1.1 m 
                 1.1 
                 20° offset/ 
               
               
                 ExPro 580 
                   
                 Transmis- 
                   
                   
                   
                 optical 
               
               
                   
                   
                 sive LCD 
                   
                   
               
               
                 InFocus 
                 * 
                 18 mm 
                  1.3 m 
                 1.5 m 
                 1.2 
                 18° offset 
               
               
                 LP425 
                   
                 Reflective 
                   
                   
               
               
                   
                   
                 DMD 
                   
                   
               
               
                 Chisholm 
                 43-58.5 
                 23 mm 
                 0.55 m 
                 1.2 m 
                 2.2 
                 15° 
               
               
                 Dakota 
                 mm 
                 Reflective 
                   
                   
                   
                 electronic 
               
               
                 X800 
                   
                 LCD 
                   
                   
               
               
                 Epson 
                 55-72 
                 33.5 
                 0.58 m 
                 1.1 m 
                 1.9 
                 * 
               
               
                 Powerlite 
                 mm 
                 Transmis- 
               
               
                 7300 
                   
                 sive LCD 
                   
               
               
                 Proxima 
                 45-59 
                 23 mm 
                  0.5 m 
                 1.0 m 
                 2.0 
                 12° offset 
               
               
                 Impres- 
                 mm 
                 Transmis- 
               
               
                 sion A2 
                   
                 sive LCD 
               
               
                 3M 
                 167 
                 163 mm 
                  1.0 m 
                 1.2 m 
                 1.2 
                 16° offset/ 
               
               
                 MP8620 
                 mm 
                 Transmis- 
                   
                   
                   
                 optical 
               
               
                   
                   
                 sive LCD 
               
               
                   
               
               
                 *Not given in published specifications  
               
             
          
         
       
     
     Throw distance is defined as the distance from the projection lens to the projection screen. Throw ratio usually is defined as the ratio of throw distance to screen diagonal. The shortest throw distance available for the listed projectors is one meter. To achieve a larger image, between 40 to 60 inches (˜1 to 1.5 meters), most projectors must be positioned even farther away, at least 8 to 12 feet (approximately 2.5 to 3.7 meters) away from the wall or screen. 
     The existence of this “projection zone” in front of the screen prevents the viewer from interacting closely with the projected image. If the presenter, for example, wishes to approach the image, the presenter will block the projection and cast a shadow on the screen. 
     Traditional integrated projectors require optical adjustment, such as focusing every time the projector is repositioned, as well as mechanical adjustment, such as raising of front support feet. Electronic connections, such as those to a laptop computer, generally are made directly to the projector, thus necessitating that the projector be readily accessible to the presenter or that the presenter runs the necessary wiring in advance. 
     Another problem with front projectors is the interference by ambient light. In a traditional front projector a significant portion of the projected light is scattered and is not reflected back to the audience. The loss of the light results in diminished image brightness. Accordingly, a highly reflective screen is desirable. However, the more reflective the screen, the larger the possible degradation of the projected image by ambient light sources. The present solution, when viewing high quality projection systems such as 35 mm photographic color slide presentation systems, is to attempt to extinguish an ambient lights. In some very critical viewing situations, an attempt has been made even to control the re-reflection of light originating from the projector itself. 
     Some screen designers have attempted to address the ambient light problem with “mono-directional reflection” screens, that is, a projection screen attempts to absorb fight not originating from the projector, while maximizing the reflection of incident light originating from the direction of the projector. Nevertheless, since portable projectors are, in fact, portable and are used at various throw distances and projection angles, it has proven very difficult to optimize a screen for all possible projector positions and optical characteristics. 
     An alternative is to design a dedicated projection facility. Such a design necessitates a dedicated conference room, in which the projector and screen position, as well as the projector&#39;s optical characteristics, are rigorously controlled and calibrated. 
     Structural elements may be used to suspend the selected projector from the ceiling. Once calibrated, such system would be permanently stationed. Such a facility may suffer from high costs and lack of portability. 
     Another issue that prevents optimal performance by front projectors is the keystone effect. If projectors are placed off-center from the screen, keystoning will occur. Keystoning is a particular image distortion where the projection of a rectangular or square image results in a screen image that resembles a keystone, that is a quadrilateral having parallel upper and lower sides, but said sides being of different lengths. 
     Methods for the reduction of keystoning again are dependent upon the position of the projector with respect to the screen. Keystone correction may be achieved by optical and by electronic methods. For large keystone correction in LCD imagers, optical methods are presently preferable, as electronic methods may suffer from pixelation distortion, as pixels become misaligned. Presently, to the applicants&#39; knowledge, the available optical keystone correction in commercially available portable electronic front projectors is between 10° to 20°. 
     The need remains for a large screen video presentation system that offers efficient space utilization, lower weight and attractive pricing. Such a system should preferably yield bright, high-quality images in room light conditions. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention comprises a front projection display system that integrates an optical engine, having control and power supply electronics, and a dedicated projection screen to provide a compact video display device. The projection engine is coupled to a high gain projection screen, having an optimized reflection pattern to give optimum optical performance in ambient light and viewing angle sensitive environments. Components of the projection engine are modularly placed in a retractable arm, pivotally connected to the screen. The arm offers precise registration to the screen apparatus and thus repeatably precisely aligns optically and mechanically to the screen. The projection wall system has an open projection position and a closed storage position. The architecture is very flat and light, having depth of less than three inches (−7.5 cm.) and a weight of less than 25 pounds (11 kilograms). Use of a radically offset projection head having matching keystone correction features allows the arm to protrude above the head of the presenter and offer a sharp and unobtrusive projection zone. 
     An exemplary integrated front projection display in accordance with the present invention includes a front projection screen, a pivoting arm coupled to the flat projection screen. the arm having a storage position and a projection position- and a front projection head coupled to the arm. When the arm is in the projection position, the front projection head is at a predetermined position with respect to the front projection screen. 
     The projection head includes projection optics having mechanical off-axis keystone correction compensation greater than or approximately equal to 22°, a throw distance of at most 800 mm, a throw-to-screen diagonal ratio of at most 1. 
     The front projection screen may have a vertically graduated reflection distribution, wherein light rays emanating from the projection position generally are reflected by the projection screen in a preselected direction, normal to the vertical axis of the screen. In the horizontal direction, the screen has a horizontal distribution, wherein the light rays generally are reflected along a predetermined illumination spread with respect to the horizontal axis. 
     The front projection display further may include modular and separate electronic and imaging modules. The imaging module may be placed inside the projection head and the electronic module is placed in the swiveling arm. 
     The electronic module may be enclosed by a honeycomb structure. A cooling fan produces a cooling air current and the honeycomb structure directs the cooling current to flow through the length of the hollow structure. The honeycomb acts as a heat exchanger and the heat generated by the projector is dissipated by convection by the cooling current. The honeycomb structure also acts as an EMI/RFI shield. The cell size, material thickness and orientation of the honeycomb structure are tuned to attenuate undesirable high electromagnetic frequencies. 
     In an alternative embodiment, the front projection display may include a light source remotely placed from the imaging components and a flexible illumination waveguide. The illumination waveguide then optically couples the light source to the imaging components in the projection head. Also in alternative embodiments, the front projection display system may include a CPU placed within the frame and digital annotation components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a traditional projection device and screen arrangement. 
     FIG. 2 is an elevation side view of the arrangement illustrated in FIG.  1 . 
     FIG. 3 is a perspective view of an integrated front projection system in accordance with the present invention in the use or projection position. 
     FIG. 4 is a perspective view of the integrated front projection system illustrated in FIG. 3 in the closed or storage position. 
     FIG. 5 is a side elevation view of the integrated front projection system illustrated in FIG. 3 in the use or projection position. 
     FIG. 6 is a schematic cut-away side elevation view of a first embodiment of the arm and projection head of the integrated front projection system illustrated in FIG.  3 . 
     FIG. 7 is a schematic cut-away side elevation view of a second embodiment of the arm and projection head of the integrated front projection system illustrated in FIG.  3 . 
     FIG. 8 is a side elevation view of a third embodiment of an integrated front projection system in accordance with the present invention in the use or projection position. 
     FIG. 9 is a schematic cut-away side elevation view of a fourth embodiment of the arm and projection head of an integrated front projection system in accordance with the present invention. 
     FIG. 10 is a schematic cut-away side elevation view of a fifth embodiment of the arm and projection head of an integrated front projection system in accordance with the present invention. 
     FIG. 11 is a top plan view of the integrated front projection system illustrated in FIG.  10 . 
     FIG. 12 is a perspective view of a sixth embodiment of an integrated front projection system in accordance with the present invention. 
     FIG. 13 is a perspective view of a seventh embodiment of an integrated front projection system in accordance with the present invention. 
     FIG. 14 is a side elevation view of the vertical reflection pattern of a controlled light distribution front projection screen in accordance with the present invention. 
     FIG. 15 is a plan view of the horizontal reflection pattern of the front projection system illustrated in FIG.  14 . 
     FIG. 16 is a vertical cross-sectional view of a controlled light distribution front projection screen in accordance with the present invention. 
     FIG. 17 is a horizontal cross-sectional view of the front projection screen illustrated in FIG.  16 . 
     FIG. 18 is a perspective view of a portion of the honeycomb structure of the integrated front projection system illustrated in FIG.  3 . 
     FIG. 19 is a detail plan view of the portion of the honeycomb structure illustrated in FIG.  18 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A preferred embodiment of the present invention comprises a front projection system that integrates an optical engine, having modular control and power supply electronics, and a dedicated projection screen to provide a compact and light video display device. FIGS. 3-6 illustrate a first exemplary embodiment of an integrated front projection system  100  in accordance with the present invention. 
     The front projection system  100  includes a dedicated high gain projection screen  102  mounted on a frame  104 . A projection head  106  is pivotally mounted by an arm  108  to a center top portion of the frame  104  at a hinge unit I 1 0. The arm  108  may be rotated out 90′ allowing the projection head  106  to pivot from a closed or storage position to an opened or projection position. 
     The screen  102  is optically coupled to the projection head. The screen  102  may be a flexible material extended over frame  104  or may be a rigid component. In an alternative embodiment, both the screen and the frame are made of an integral sheet of material. The screen  102  may include multiple-layers or special coatings, such as to allow its use as an erasable whiteboard. 
     The frame  104  contains and supports other components of the system. The frame  104  may house additional components such, as integrated speakers  112 , input and output jacks  113 , and a control panel  114 . In the present exemplary embodiment, the mechanical infrastructure of the projection system  100 , the arm  108  and the frame  104 , include lightweight materials such as aluminum magnesium or plastic composites. The entire projection system, accordingly, is relatively light (20-25 pounds, 9-11 kilograms). 
     In the present exemplary embodiment, the arm  108  is rigid and hollow. The arm  108  comprises die cast aluminum or magnesium, or other suitable materials, surrounded by a hard plastic shell. At the top and center of the frame  104 , the hinge unit  10  allows the projection arm  108  and head  106  to pivot between a closed (storage) position and an open (use) position. FIG. 4 illustrates the projection system  100  in a closed or storage position. When not in use, the arm  108  may be kept in the closed position as to be substantially parallel with the frame  104 , and thus present no obstruction to objects that may be moving in the space in front of the frame  104 . Although the arm is shown folded back to an audience left position, the system may be adaptable to allow storage of the arm and projection head to an audience fight position. An ability to select storage position may be valuable in avoiding obstacles present in the projection area prior to the installation of the system. The ability of the arm  108  to rotate contributes to the projection system&#39;s minimal thickness, approximately 2-3 inches (5-7.5 cm.), in the storage position. 
     The system  100  allows for the projection head  106  to be placed in an exact pivotal registration in the operating or projection mode in relation to the optical screen  102 . In system  100 , use position is at a normal arm angle with respect to the screen and generally above the screen. However, other embodiments may be designed around other predetermined positions. Movement between the two positions may be assisted manually or may be motor-driven. 
     In the present embodiment, an electrical motor  116  residing within the hinge unit  110  controls the movement of the arm  108 . The motor  116  may be AC, DC, manually driven by détentes, over-center-cam (spring loaded) or any other suitable type that provides reliable repeatable positioning. The motor  116  is a precision guided gear drive motor having two limit sensor switches to accurately position the arm  108 , and accordingly, the projection head  106 , in precise and repeatable closed and open positions. 
     The movement of the arm  108  and the functions of the projector system  100  may be controlled through the control panel  114 , a remote control (not shown), or other control mechanism. While the arm  108  of the projection system  100  is pivotally fixed at a single point, those skilled in the art will readily appreciate that a variety of different linkage and/or pivoting mechanisms may be implemented within the spirit of the present invention. In alternative embodiments, the head and arm may include additional hinge or telescopic movement and the arm may be coupled to other portions of the frame or to a wall or post. 
     As explained in more detail in relation to FIGS. 14-17, the system  100  optimizes the coupling of the projection engine with the exact positioning of the head  106  in relation to the screen  102  to yield high contrast, brightest enhancement, image uniformity, optimal image position, and sharp focus. Since the optical parameters of the projection engine are known and selected for compatibility and the exact position of the projector head  106  in the use position is known and predetermined, the exemplary screen  102  may be designed and optimized to provide maximum illumination for the audience while reducing interference by ambient light. 
     When active, the projection system  100  generates a beam of light having a plurality of light rays  162 . In relation to a coordinate system wherein the screen defines a z-plane, each fight ray  162  includes components along both the horizontal x-plane and the vertical y-plane. The angle of incidence of each light beam  162  upon the screen  102  depends on the optical characteristics of the projector, such as F/#, and the position of the projection head  106  in relation to the screen  102 . 
     FIG. 14 is a side elevation of a vertical axis ray diagram, illustrating the reflection of tight beams  162  emitted by projection system  100 . Point  60  is the known precise location of the ideal point source for projection lens  140  (illustrated in FIG. 6) when the projection head  106  is in the “USE” position. The angles of incidence of the light beams  162  on the screen increase along the positive x-direction (see directional axis in FIG.  14 ). 
     In a traditional screen, the light rays  162  would each be reflected in accordance with their angle of incidence. Especially at the sharp projection angle of system  100 , the resulting light pattern would be scattered, with only a portion of the light rays reaching the audience. To compensate for the graduated increase in incidence angles, the screen  102  includes a vertically graduated reflection pattern oriented to receive the projected light rays  162  at the expected incidence angle for each point on the screen  102  and to reflect the rays approximately at normal angle along the vertical plane. The light beams  162  are reflected in a direction vertically close to normal because that corresponds to the expected location of the audience. In alternative embodiments where the audience is expected to be in a different position, a different reflection pattern may be implemented. 
     FIG. 15 illustrates a top plan view of the horizontal distribution of the light emanating from point  60 . As the audience is expected to be horizontally distributed, the horizontal reflection pattern of the screen is arranged to provide a wider illumination spread in the horizontal direction. 
     FIG. 16 illustrates an expanded view of a vertical cross-section of the projection screen  104 . FIG. 17 illustrates an expanded plan view of a horizontal cross section of the screen. The projection screen comprises a multi-layer material. The screen  104  includes a first linear Fresnel lens element  170 , a second linear Fresnel element  172 , and a reflective component  174 . First and second spacer elements  171  and  173  may be placed between the Fresnel elements  170  and  172  and between the second Fresnel element  172  and the reflective element  174  respectively. The linear Fresnel lens elements  170  and  172  include a planar side,  176  and  178  respectively, and a prismatic side,  180  and  182  respectively. The first Fresnel element  170  includes a thin isotropic diffusing layer  184  on its planar side  176 . The diffusing layer  184  functions as an image-receiving surface. The prismatic side  180  includes a plurality of linear grooves  186  running horizontally in a graduated pattern. The grooves  186  are designed to control the vertical light spread. The lens center is positioned near the top of the projection screen. 
     The prismatic side  182  of the second linear Fresnel lens element  172  includes a plurality of vertical grooves  188  (FIG. 17) facing the plurality of grooves  186  of the first Fresnel lens element  170 . The second linear Fresnel lens element  172  has a lens center positioned on a vertical line extending through the center of the screen. The planar surface  178  of second Fresnel element  172  faces a back reflector  174 , having a vertical linear structure reflecting the light back in the direction of the audience. The grooves of the structure back reflector  174  preferably have a cylindrical shape, such as a lenticular structure, or may be a repeating groove pattern of micro facets that approximate a cylindrical shape. An incident surface  175  of the back reflector  174  may be specular or diffuse reflecting, metallic, or white coated, depending on the amount of screen gain and type of screen appearance desired. Second linear Fresnel element  172 , in conjunction with the structured back reflector  174 , provides control of light distribution spreading in the horizontal direction to accommodate viewers who are positioned horizontally in front of the screen. Alternatively, the reflector structure  174  may be embossed into the planar surface  178 , reducing the number of screen elements. 
     Alternative embodiments of the screen may comprise 3M multi-layer film technology. 
     As may be appreciated in FIG. 5, the projection system  100  places the projection head  106  at an extreme angle and close distance to the screen  102 , thus minimizing the possibility of the presenter&#39;s interference. Placement of the optical head  106  at the end of a radically offset projection arm  108  presented unique mechanical and optical challenges. Even the lightest and most compact conventional portable projectors at about 7 lb. (3.2 kg.), may have leveraged unbalanced strain upon the structure components. Optically, the throw distance necessary to even focus the image would have necessitated a long arm, further creating lever amplified stresses on the structure. Even if structurally sound, the system would have projected a severely keystone distorted and relatively small image. 
     An electronic optical engine includes imaging and electronic components. As better illustrated in FIG. 6, in projection system  100  the arm  108  is a rigid hollow structure surrounded by an outer plastic shell  118 . The structure of arm  108  defines an arm chamber  122  and allows for the modular and separate placement of a control and power electronics module  118  and an imaging module  120 . The control and power electronics module  118  includes control boards, ballast, and other electronic components. The electronic elements are internally connected through an array of internal power and data connections. The imaging module  120  includes a light source, projection optics, color wheel and imager. By distributing components of the projection system along the arm and the frame, a lesser load is placed on the hinge and the arm. Also, a smaller projector head size becomes possible. Those skilled in the art will recognize that a variety of different modular arrangements may be possible within alternative embodiments of the present invention. For example, alternatively, components of the electronics module may be placed inside of frame  104 . 
     A considerable amount EMI/RFI shielding is required in traditional projector designs to reduce EM crosstalk between the lamp and the electronic components and to have radio frequency containment. The separate placement of electronic components  20  within the arm  108  naturally reduces EMI/RFI interference. Furthermore, in the exemplary system  100 , the power supply and control electronics module  118  is enclosed by a honeycomb structure  124  including a plurality of hexagonal cells  125 . The honeycomb structure surrounds the power supply and electronics module  118  and provides both EMI/RFI shielding and thermal management characteristics. FIGS. 18 and 19 illustrate details of the honeycomb structure  124 . As described in co-pending and co-assigned U.S. patent application Ser. No. 08/883,446, entitled, “Honeycomb Light and Heat Trap for Projector”, which is hereby incorporated by reference, the shape, orientation, thickness and size of the hexagonal cells may be tuned to attenuate specific electromagnetic frequencies. In the present exemplary embodiment, the hexagonal cells  125  are aligned generally longitudinally along the arm  108  and are oriented at a predetermined specific angle φ to attenuate high electromagnetic frequencies. The honeycomb structure  124  is an aluminum hexagonal core having 0.25-0.0625 inch (0.635 -0.159 cm.) cell size S, 0.002 inch (˜0.005 cm.) foil thickness T, and a corrosion resistant coating. The physical separation of the electronic components and the honeycomb structure  124  provide sufficient attenuation to reduce the need for other traditional coatings or shields. 
     The present arrangement also offers an efficient thermal management system. An air intake  126  is located in the housing of the hinge unit  110 . A fan  130 , located in the projection head  106 , draws air through the air intake  126 , through the interior of the hollow projection arm  108 , cooling the electronic and power supply components  118  located therein. The air exits the projection head  106  through an air outlet  127 . Air also may be drawn through the projection head  106 . The flow of cooling air also may be used to cool components located in the projector head  106  or a separate cooling air flow or heat management elements may be employed. 
     The orientation of the honeycomb structure  124  also is designed to act as a convection heat sink to absorb the thermal energy generated by the electronic module  118  and transfers the heat by convection into the flow of cooling air drawn by the fan  130 . The honeycomb structure is oriented to direct airflow over sensitive components. Different portions of the honeycomb structure  124  may have different inclination angles φ direct air flow to different components. The chamber  122  may also include exterior or interior fins,  127  and  128  respectively, to act as high efficient heat exchangers for both lamp and electronics cooling. The ability to direct the flow of cooling air with the honeycomb structure  124  into the interior fins  128  allows for better convection cooling, thus enabling the use of a low CFM fan  130  or even the use of naturally created convection. The cooling arrangement offered by the arm and the honeycomb structure also allows for very low overall power consumption and low audible noise. 
     Commercially available electronic front projectors are designed to project a specified screen diagonal (D) at a specified throw distance (TD). The throw ratio (TR) of a projector is defined as the ratio of throw distance to screen diagonal. Magnification is measured as screen diagonal/imager diagonal. Optically, the unobtrusive arrangement of the projection head  106  of projection system  100  requires that the image simultaneously accommodate three very demanding requirements: (1) short-throw distance, (2) high magnification, and (3) large keystone correction. To minimize image shadowing, in the present exemplary embodiment, the projector head  106  is located at a projection angle &gt;22° and the arm measures about 36 in. (˜91.4 cms). The screen  102  has a screen diagonal between 42 to 60 inches (˜107-152 cms.). Accordingly, the design goals for the exemplary display system  100  included (1) a throw distance ≦800 mm; (2) a magnification ≧ 50 ×; and (3) keystone correction for a projection angle ≧22°. 
     Referring to FIG. 6, the projection head  106  includes a lamp unit  132 , an imager or light valve  134 , condensing optics  136 , a color wheel  138 , a condensing mirror  139  and a projection lens  140 . The projection head may also include polarization converters (for polarization rotating imagers), infrared and ultraviolet absorption or reflection filters, an alternative light source possibly coupled with a lamp changing mechanism, reflector mirrors, and other optical components (not shown). The lamp unit  132  includes a reflector  131  and a lamp  133 . The reflector  131  focuses the light produced by the lamp  133  through the color wheel  138 . The beam of light then is condensed by the condensing optics  136  and the condensing mirror  139 . The now condensed beam of light is reflected off the condensing mirror and is directed towards the reflective imager  134 , which in turn reflects the light onto the projection lenses  140 . 
     The lamp unit  132  includes an elliptic reflector  131  and a high intensity arc  15  discharge lamp  133 , such as the Philips UHP type, from Philips, Eindhoven, The Netherlands, or the OSRAM VIP-270 from Osram, Berlin, Germany. Other suitable bulbs and lamp arrangements may be used, such as metal halide or tungsten halogen lamps. 
     In the present exemplary embodiment, the imager  134  comprises a single XGA digital micromirror device (DMD) having about a 22 mm diagonal, such as those manufactured by Texas Instruments, Inc., Dallas, Tex. The color wheel  138  is a spinning red/green/blue (RGB) color sequential disc producing 16.7 million colors in the projected image. In alternative embodiments, the color wheel and the imager  134  may be replaced by different suitable configurations, such as a liquid crystal RGB color sequential shutter and a reflective or transmissive liquid crystal display (LCD) imager. Those skilled in the art will readily recognize that other optical components and arrangements may be possible in accordance with the spirit of the present invention. 
     The imager  134  and the lamp  132  may be cooled by the airflow generated by the fan  130 . A further thermal advantage of the arrangement of the present embodiment is that the warmer components, such as the lamp, are located at an end portion of the cooling air flow path, thus preventing the intense heat from the lamp from affecting delicate electronic components. 
     Traditional projector lenses proved unsuitable to accomplish the simultaneous requirements of the display system  100 . Accordingly, the present invention addresses this problem by the innovative conversion of 35 mm camera lenses having a small f-number and a large field of view into projection lenses. The projection lens  140  has a focal length about 14 to 20 mm, and a speed of f/2.8 or less. Suitable lenses include Nikon 18 mm., f/2.8 D Nikkor from Nikon, Japan, or Canon Photo EF 14 mm. f/2.8 L USM from Canon, Japan. The focus of the lens  140  is preset for optimal resolution on screen  102 . 
     To provide 22° keystone correction, the light valve center is shifted from the projection lens center by an amount equal to the projection angle. Such a large degree of keystone correction is possible because the projection angle is known and is repeatable. At projection angles exceeding 22°′, the projection lens is selected to have a full field coverage angle exceeding 90°. In alternative embodiments, even larger keystone correction are possible, thus enabling the use of even a shorter projection arm. The keystone correction features need not be limited only to the optics. Keystone corrected optics, electronic keystone correction means, and screen inclination may be combined to achieve a suitable image. In an alternative embodiment, the screen may be motor driven, to reach an inclined projection position at the time that the arm is placed in the open position. 
     FIG. 7 illustrates a second exemplary embodiment of the present invention. The same last two digits in the reference numerals designate similar elements in all exemplary embodiments. To decrease the size of the light engine even further and to reduce the size and weight of projector head  206  and arm  208 , lamp  232  and fan  230  are placed within hinge unit  210  or within frame  204 . Power supply and electronic components  218  are located inside frame  204  and behind screen  202 . A sequential color wheel  238 , a projection lens  240 , and condensing optics  236 , including a condensing mirror  239 , remain within the projector head  206 . A flexible illumination waveguide  242  is channeled through the projection arm  208  and couples the illumination from the lamp or light source  232  to the condensing optics  236 . The lamp  232  focuses light into an entrance aperture  244  of the illumination waveguide  242 . The light is transmitted by the illumination waveguide  242  up to an exit aperture  245 , where the light is then directed through the color wheel  138  to the condensing optics  236  and  239 . In the present embodiment, the illumination waveguide  242  is a solid large core plastic optical fiber, such as Spotlight type LF90FB from Sumitomo 3M Company, Ltd., Japan, or Stay-Flex type SEL 400-from Lumenyte International Corp., of Irvine, Calif. 
     Cooling in system  200  is performed in a reverse direction than in system  100 . The cooling mechanism or fan  230  draws air from the air intake  226  located in the projection head  206  and exhausts air through the air exhaust  227  located on the hinge unit  210 . 
     FIG. 8 illustrates a third exemplary embodiment of a projection system  300  in accordance with the present invention. The projection system  300  includes a projection head  306  mounted along the mid-span of a pivoting arm  308 . The projection head  306  is substantially similar to the projection head  106  in system  100 . The image projected by a projection lens  340  of the projection head  306  is reflected off a mirror or reflective surface  346  onto a screen  302 . The arrangement of optical system  300  allows for an increased throw distance and magnification while maintaining the same arm length or for the same throw distance and magnification with a shorter pivoting arm. 
     FIG. 9 illustrates a fourth exemplary embodiment of a projection system  400  in accordance with the present invention, having a screen  402 , a frame  404 , a projection head  406 , and an arm  408 . The projection head  406  of the projection system 400 includes a lamp  432  optically aligned with a transmissive color wheel  438  and condensing optics  436 . After passing through the color wheel  438  and the condensing optics  436 , a light beam is focused upon a reflective imager  434 , which, in turn, directs the light beam towards a retrofocus projection lens  440 . The projector system  400  includes modular power supply and system electronics  418  and a separate modular driver board  448  for the imager  434 . 
     FIG. 10 illustrates a fifth exemplary embodiment of a projection system  500  in accordance with the present invention. In the projection system  500 , the power supply electronics  519  are positioned inside of a frame  504 . A hinge  510  couples an arm  508  holding a projector head  506  to the frame  504 . Electronic control boards  550  are positioned within the arm  508 . The projection head  506  includes a lamp unit  532 , a polarizer  535 , optics  536 , a transmissive LCD imager  534 , and projection lens  540 , all aligned in a straight optical path. A fan  530  provides ventilation. As illustrated in FIG. 11, the arm  508  may be rotated a ±90° for storage on the right or the left side. 
     FIGS. 12 and 13 illustrate the versatility of the projection system of the present invention. FIG. 12 illustrates a digital whiteboard system  601  including a projection system  600  in accordance with the present invention and an input device, such as a stylus,  653 . The projection system  600  includes integrated electronics for an annotation system  652 , as well as LTV, K laser or other type of sensors  654 . The sensors  654  are calibrated to track the movement of the stylus  653  on the surface of the screen. The stylus  653  similarly may include transmitters and/or sensors to aid in tracking and to coordinate timing or control signals with electronics  652 . The screen  602  may be coated to allow for erasable whiteboard use. The integrated electronics  652  may include a CPU. 
     FIG. 13 illustrates a videoconferencing and/or dataconferencing system  701 , including a projection system  700  in accordance with the present invention. A camera  756 , such as a CMOS or CCD camera, is mounted on the projection head  706  or on the frame  704 . The camera  756  may pivot to capture a presenter or to capture documents placed on the screen  702 . Alternatively, additional cameras may be directed to the presenter and to the screen. Again, the screen may be coated to act as an erasable whiteboard. The camera  756  is directly coupled to a CPU  758  integrally placed within the frame  704 . A microphone  760  also is placed within the frame  704 . Additional electronic modules, such as a tuner, network card, sound card, video card, communication devices, and others may be placed within the frame  704 . 
     Those skilled in the art will readily appreciate that elements of the present invention may be combined, separately or in one system, to provide videoconferencing, data-conferencing, and electronic whiteboard functions, as well a any other function where a light and compact display system may be useful. 
     As the system of the present invention is designed to optimize the projection image at the predetermined projection position, no set-up adjustments are necessary to the optics, mechanics, or electronics and optimal on-screen performance is consistently offered. The integral structure of the system  100  allows for easier storage and portability and avoids cabling and positioning associated with the use of traditional projectors. 
     Those skilled in the art will appreciate that the present invention may be used with a variety of different optical components. While the present invention has been described with a reference to exemplary preferred embodiments, the invention may be embodied in other specific forms without departing from the spirit of the invention. Accordingly, it should be understood that the embodiments described and illustrated herein are only exemplary and should not be considered as limiting the scope of the present invention. Other variations and modifications may be made in accordance with the spirit and scope of the present invention.