Abstract:
A laser projection display apparatus includes a laser that emits a light beam. Actuators steer the light beam in horizontal and vertical directions to generate the display images. Each of the actuators includes first and second mirrors, each of which is suspended by a gimbal. Each of the mirrors rotates responsive to current flow through a coil attached to a backside of the mirror in the presence of a magnetic field. A digital signal process provides integrated control of the actuators and laser power based on the content of a display program. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
RELATED APPLICATIONS  
       [0001]     This application is related to of Ser. No. 10/170,978 filed Jun. 13, 2002 entitled, “GIMBAL FOR SUPPORTING A MOVABLE MIRROR”. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to apparatus and methods for light projection; more particularly, to optical systems that project laser light onto a screen, wall, or other object as part of an animated show or information display.  
       BACKGROUND OF THE INVENTION  
       [0003]     Modern light display systems exist in many different forms, and are implemented using a wide variety of technologies. Typical applications of light display devices include the projection display of visual information, such as for point-of-sale advertising, trade shows, corporate front-lobbies, conventions, entertainment venues (e.g., cinema projection of animated shows) and the display of various digital images. Other applications include raster-graphics data/video projection, consumer electronics devices, toys, and games.  
         [0004]     Standard laser projection display systems commonly utilize a mirror mounted to a galvanometer for scanning image lines. Examples of image display systems that use a galvanometer mounted mirror are found in U.S. Pat. Nos. 6,621,615, 6,577,429, and 6,552,702. Other conventional scanning methods employ a spinning polygon or a rotating prism. The main drawback of these types of prior art display systems is that they rely upon relatively large, massive moving components. Due to the inertia associated with these components, a large amount of electrical power is generally required for actuation of the mirrors and other optical elements. Often times, cooling fans are required to dissipate the considerable heat that is generated.  
         [0005]     The large mass and inertia also slows the response time, and hence, the performance, of the image display system. Slow movement of the laser beam, for example, makes it difficult to achieve real-time projection of high-resolution motion images. Prior art laser projectors also tend to be large, heavy, and thus lack portability. All of these drawbacks have made prior art laser display systems expensive to purchase and costly to operate.  
         [0006]     Other types of existing display technologies, such as liquid crystal display (LCD) and digital light technology (DLT), operate with a fixed number of pixels, which limits both the size and the resolution of the image being displayed. Enhancing the size and resolution of the display screen can be costly, and image display speed typically suffers.  
         [0007]     Another problem with prior art laser projection display systems is that servo control of the actuators used to move the laser beam is independent of program content of the moving image. In other words, synchronization of laser switching and servo positioning does not exist in present-day display systems. During display of an image the laser beam must be frequently turned off, and then back on again, in order to step the beam to a new scan or display position. To insure that the laser beam is not activated prior to completing the step, prior art laser projection systems operate under worst case condition assumptions. That is, if the range of the steps varies from 20 microseconds to 300 microseconds, the laser controller simply assumes a 300 microsecond step. The problem with such systems, therefore, is that for fast moving and/or high-resolution images light intensity dims significantly and performance suffers.  
         [0008]     Thus, there is a need for a robust, economical, low-power display apparatus for laser projection of images that can provide improved performance for a wide variety of applications.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention will be understood more fully from the detailed description that follows and from the accompanying drawings, which however, should not be taken to limit the invention to the specific embodiments shown, but are for explanation and understanding only.  
         [0010]      FIGS. 1A &amp; 1B  are top perspective views of two different embodiments of the image display apparatus of the present invention.  
         [0011]      FIG. 2  is a perspective view of the printed circuit board assembly and laser assembly in accordance with one embodiment of the present invention.  
         [0012]      FIG. 3  is an exploded view of the laser assembly utilized in accordance with one embodiment of the present invention.  
         [0013]      FIG. 4A  is a top perspective view of the actuator assembly utilized in accordance with one embodiment of the present invention.  
         [0014]      FIG. 4B  an exploded view of the actuator assembly shown in  FIG. 4A .  
         [0015]      FIGS. 5A &amp; 5B  are side cross-sectional views of the actuator assembly shown in  FIG. 4A , without the detector bracket assembly attached.  
         [0016]      FIGS. 6A, 6B  &amp;  6 C are respective side, bottom, and perspective exploded views of the mirror-gimbal assembly utilized in accordance with one embodiment of the present invention.  
         [0017]      FIG. 7  is a cross-sectional side view of a magnet arrangement used in a mirror-gimbal assembly according to another embodiment of the present invention.  
         [0018]      FIG. 8  is a perspective view of the detector bracket assembly utilized in accordance with one embodiment of the present invention.  
         [0019]      FIG. 9  is a side cross-sectional view of the actuator assembly illustrated in  FIG. 4A  with the detector bracket assembly attached.  
         [0020]      FIG. 10 a  top perspective view of an actuator assembly utilized in accordance with an alternative embodiment of the present invention.  
         [0021]      FIG. 11  is a side view of the actuator assembly of  FIG. 10 , showing details of the light detection apparatus.  
         [0022]      FIGS. 12A &amp; 12B  are exemplary images that may be generated by the image display apparatus of the present invention.  
         [0023]      FIG. 13  is a block diagram of the integrated electronics and firmware in accordance with one embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0024]     A laser projection display device for use in displaying a variety of still or animated images is described. In the following description numerous specific details are set forth, such as angles, material types, configurations, etc., in order to provide a thorough understanding of the present invention. However, persons having ordinary skill in the light projection and optical-electronics arts will appreciate that these specific details may not be needed to practice the present invention.  
         [0025]     According to one embodiment of the present invention, a pair of actuator assemblies each having a mirror gimbal assembly are utilized to control the path of a laser beam to create line-art animation shows or other images that can be projected onto a screen, wall, or other object. By way of example, the laser display apparatus of the present invention may be used to project navigation, speed, or other information onto an area of an auto&#39;s windshield. The present invention also has numerous other consumer and industrial applications. For example, the present invention may be used for point-of-sale advertising, trade show displays, corporate front-lobby signs, helmet image display, toys, games, raster-graphics data/video displays, messaging, and mobile phone projection displays.  
         [0026]      FIG. 1A  is a perspective view of a laser projection display unit  10  in accordance with one embodiment of the present invention. In one implementation, display unit  10  comprises a box-like enclosure  11  that measures about 6×3×1 inches in size. Support legs or a mounting bracket (see  FIG. 1B ) may be attached to the bottom of enclosure  11 . Content may be downloaded into display unit  10  from a computer or other device via an interface  15  located along the rear side of enclosure  11 . Interface  15  may include a standard USB interface, serial interface, Ethernet interface, wireless connection, Firewire™ interface, etc. Display unit  10  may also be programmed and/or controlled with a handheld infrared (IR) remote device via IR input sensor  13 . Display unit  10  may also include a keypad (not shown) located along a side or top of enclosure  11  for inputting display information or controlling the shows to be displayed.  
         [0027]     In the embodiment of  FIG. 1 , laser light exits through an opening  12  located along a front side of enclosure  11 . An optional power indication LED  14  may also be mounted to the front side of enclosure  11 . Power may be supplied to display unit  10  through a standard power connector located, for example, on the rear side of enclosure  11 . Alternatively, power may be supplied by an internal battery.  
         [0028]      FIG. 1B  illustrates an alternative embodiment in which enclosure  11  is moveably mounted to a U-shaped bracket  24 . Bracket  24  may be pivoted about its base, and/or the display unit tilted up or down, in order to aim the projected laser image in a particular direction and surface.  
         [0029]      FIG. 2  is a perspective view of a printed circuit board assembly (PCBA)  17  and laser assembly  16  housed within enclosure  11  in accordance with one embodiment of the present invention. In the embodiment shown, a top cover (not shown) is attached to PCBA  17 , so that PCBA  17  comprises the bottom of enclosure  11 . Laser assembly  16  is mounted to PCBA  17  adjacent the front side where the projected laser beam exits the unit. Also mounted along the front side of PCBA  17  are power indication LED  14  and IR input sensor  13 . A standard power connector  22 , a USB interface connector  21 , and a serial interface connector  20 , which collectively comprise interface  15  in this example, are mounted along the rear side of PCBA  17 . An on/off switch  23  (partially hidden from view by laser assembly  16 ) is also mounted along a side of PCBA  17  in the embodiment of  FIG. 2 .  
         [0030]      FIG. 3  is an exploded perspective view of laser assembly  16  in accordance with the embodiment of  FIG. 2 . Laser assembly  16  comprises a base  25 , a barrel laser  26 , and a pair of identical actuator assemblies  27  &amp;  28 . Laser  26  and actuator assemblies  27  &amp;  28  are each mounted to various platform surfaces or block members of base  25 . For example, laser  26  is mounted to platform surface  130 , lower actuator assembly  27  is mounted to block member  132 , and upper actuator assembly  28  is mounted to block member  131  of base  25 . Base  25  is made of a durable, non-magnetic material, e.g., ceramic, polycarbonate/plastic, black anodized aluminum, etc.  
         [0031]     In the embodiment of  FIG. 3 , actuator assemblies  27  &amp;  28  are mounted in precision aligned positions with respect to one another and to laser  26  by means of a peg-to-hole mounting method. For instance, or pegs  29  on the side of actuator assembly  28  are adapted to align with and securely fit into corresponding holes  30  of upper block member  131 . Similarly, pegs  31  (only one of which is visible in  FIG. 3 ) are adapted to align with and securely fit into corresponding holes  32  of lower block member  132 . Block members  131  and  132  are arranged with their primary side surfaces orthogonal to one another such that the respective longitudinal axes of actuator assemblies  27  and  28  are oriented in a perpendicular relationship.  
         [0032]     Laser  26  may also be mounted to platform surface  130  of base  25  using a peg-to-hole alignment method. In one embodiment, laser  26  comprises an assembly manufactured by Arima Optoelectronics Corporation and commercially available as part no. ADL-63101. The assembly includes a collimating lens and a red laser diode that outputs approximately 5 mW of optical power. Other types of assemblies may be utilized, including different color (e.g., green or blue) color lasers.  
         [0033]     Laser assembly  16  operates in the following manner. The laser beam produced by laser  26  travels horizontally (i.e., parallel to the bottom of base  25 ) until it strikes mirror  33  of lower actuator assembly  27 . Actuator assembly  27  is oriented at about a 45° mechanical angle with respect to the direction of the laser beam emitted from laser  26 . That means that mirror  33 , which is mounted to a gimbal  40 , is nominally oriented at about a 45° mechanical angle to the incoming/outgoing laser beam.  
         [0034]     The flat, reflective surface of mirror  33  reflects the laser beam in an upward vertical direction (a 90° optical angle) where it strikes the gimbal-mounted mirror  34  of upper actuator assembly  28 . Upper actuator assembly  28  is also oriented at about a 45° mechanical angle with respect to the direction of the incoming/outgoing laser beam, which means that mirror  34  of actuator assembly  28  is nominally oriented at about a 45° mechanical angle with respect to the direction of the incoming/outgoing laser beam. This mirror arrangement causes the laser beam to be reflected at a 90° optical angle, i.e., back to a horizontal direction where it then exits the enclosure through opening  12  (see  FIG. 1 ).  
         [0035]     Note that lower and upper actuator assemblies  27  &amp;  28  are mounted to base  25  in a relationship wherein their longitudinal axes are perpendicular to one another. This relationship causes the laser beam to generally exit the display unit at about a 90° optical angle with respect to the direction that the laser beam is emitted from laser  26 . To reiterate, the laser beam generated by laser  26  travels in a horizontal direction until it strikes mirror  33  of lower actuator assembly  27 . Mirror  33  reflects the laser beam upward at about a 90° optical angle, where it then strikes mirror  34  of upper actuator assembly  28 . Mirror  34  reflects the laser beam at a 90° optical angle back to a horizontal direction, where it exits the enclosure in a horizontal direction that is generally perpendicular to the direction of emission from laser  26 .  
         [0036]     Images are produced by laser assembly  16  by the combined rotational movements of mirrors  33  &amp;  34  associated with respective lower and upper actuator assemblies  27  &amp;  28 . Each of mirrors  33  &amp;  34  rotate about the longitudinal axis of their respective actuator assemblies under control of a software or firmware program executed by a computer or processor. By way of example, the program may rotate mirror  33  of actuator assembly  27  to perform a horizontal scan of the display image. Similarly, rotation of mirror  34  mounted on actuator assembly  28  performs a vertical scan of the display image. This aspect of the present invention is described in more detail below.  
         [0037]     According to the present invention, users can convert images from programs such as 3ds, Max, Flash, and bitmap graphics to laser line-art format using a computer-based software program. Custom shows can also be created from new programs or through software editing. Graphics and programmed shows may be downloaded and stored in memory resident on the PCBA, for subsequent stand-alone display by remote command.  FIGS. 12A &amp; 12B  are examples of just two of the types of images that may be produced by the laser projection display apparatus of the present invention.  
         [0038]      FIG. 4A  is a top perspective view of actuator assembly  28 .  FIG. 4B  is an exploded view of actuator assembly  28 , which is identical to assembly  27  according to one embodiment of the present invention. Assembly  28  comprises an elongated rectilinear actuator block  38  made of an electrically non-conductive material, such as a polycarbonate/plastic material, or anodized aluminum. A pair of pegs  29  is arranged spaced-apart on a proximate end of block  38  for mounted insertion into holes  30  of block  131  (see  FIG. 3 ) as previously described. A six-sided (see cross-section of  FIGS. 5A &amp; 5B ) permanent magnet  39  having a trapezoid-shaped top portion, which includes angled (e.g., ˜45°) upper side surfaces  42  &amp;  43  and a narrow top surface  41 , is mounted directly below mirror  34  within a centrally-located opening  36  of actuator block  38 . A pair of flux return plates  35   a  &amp;  35   b  (e.g., magnetic stainless steel or low-carbon steel) are affixed to the respective left and right sides of magnet  39 . In one implementation, magnet  39  comprises a neodymium boron iron magnet.  
         [0039]     Practitioners in the art will appreciate that the trapezoidal geometry of magnet  39  permits the generation of a relatively large magnetic field in a small space. Specifically, the trapezoidal shape of magnet  39 , which includes angled side surfaces  42  &amp;  43  leading to narrow top surface  41 , allows actuator assemblies  27  &amp;  28  to be mounted in close proximity to one another on block  25 . The close proximity between assemblies  27  &amp;  28  means that the distance between mirrors  33  &amp;  34  is minimized, which reduces problems associated with beam-mirror alignment. Minimizing the distance between mirrors  33  &amp;  34  also means that the smaller mirrors may be utilized, which translates to increased performance. The larger the distance between mirrors  33  &amp;  34 , the larger the mirror required, which means that larger magnet fields and/or larger actuator currents are needed, all of which has an adverse impact on display performance.  
         [0040]     Mirror-gimbal assembly  40  includes a mirror  34  bonded to a gimbal having ends  52   a  &amp;  52   b  mounted to opposite ends of the top surface of actuator block  38 . The gimbal suspends mirror  34  in a space between plates  35   a  &amp;  35   b  above top surface  41  of magnet  39 . This structural relationship is shown in the cross-sectional view of  FIGS. 5A &amp; 5B  taken through cut lines A-A′.  FIGS. 5A &amp; 5B  also illustrate a cross-section of a “racetrack” wire coil  45  attached to the bottom of mirror  34 . The direction of magnetization of magnet  39  is such that magnetic flux lines pass through the space between plates  35   a  &amp;  35   b  above top surface  41  in a direction perpendicular to the long axis of coil  45 . That is, the magnetic field produced by magnet  39  is perpendicular to the longitudinal axis of the coil and parallel to the top, reflective surface of mirror  34 .  
         [0041]      FIG. 7  is a cross-sectional side view of an alternative embodiment characterized by a magnet-return assembly that includes a pair of permanent magnets  61   a  &amp;  61   b  mounted to opposite ends of the inside surface of a U-shaped flux return member  63  (e.g., steel). Magnets  61   a  &amp;  61   b  and flux return member  63  are configured to produce a magnetic field with flux lines that are perpendicular to the longitudinal axis of coil  45  and parallel to the top, reflective surface of mirror  34 .  
         [0042]     Torque is developed on the mirror-coil assembly upon application of an appropriate current through coil  45  in the presence of the magnetic field produced by magnet  39 . Current flow through coil  45  causes mirror  34  to rotate along the long axis of actuator assembly  28 . The direction of current flow determines the direction of rotation, with the magnitude of the current determining the angle of rotation. By way of example, with the direction of the current flow in  FIG. 5B  being out of the paper in coil section  45   a  (i.e., the left side cross-section), and into the paper in coil section  45   b  (i.e., the right side cross-section), a rotational force is generated which raises the right side (the upward vertical force component is shown by arrow  48   b ) and lowers the left side (the downward vertical force component shown by arrow  48   a ) of mirror  34 . Thus, the vertical component of force produced as the current travels through coil  45  has opposing directions on opposite sides (along the transverse axis) of mirror  34 . This results in rotation of mirror  34 . Stated differently, the direction of the force is made to be opposite on each side of the mirror-coil assembly such that the resulting torque rotates or tilts the mirror attached to the gimbal. A reverse current flow in coil  45  (into coil section  45   a  and out of coil section  45   b ) generates a rotational force in the opposite rotational direction. When the applied current is interrupted or halted, the restoring spring force of the gimbal returns the assembly to a rest position (i.e., mirror  34  at 0° rotation). It is appreciated that the elongated gimbal beams  58   a  &amp;  58   b  of mirror-gimbal assembly  40  twists to accommodate rotation of mirror  34 .  
         [0043]     With reference once again to  FIGS. 4A &amp; 4B , an L-shaped detector bracket assembly  37  is attached to a distal end of block  38  using a peg-in-hole method. Detector bracket assembly  37  is utilized to detect the angle of rotation of mirror  34 , as described in more detail below.  
         [0044]     FIGS.  6 A-C show side, bottom, and exploded top perspective views of the mirror-gimbal assembly  40  utilized in accordance with one embodiment of the present invention. The gimbal of  FIG. 6  actually consists of two gimbal members  50   a  &amp;  50   b , each of which formed of a thin (e.g., 0.001 inches) flexible sheet-metal made from hard non-magnetic stainless steel material, such as 316 stainless steel, having high fatigue strength. Other materials providing similar properties may also be used. The material selected should allow the gimbal to rotate the attached mirror (or mirror-coil assembly) with a high rotational angle (e.g., +/−15°) over millions of movement cycles. The material may also be heat-treated. The sheet metal material is also preferably non-magnetic to prevent reluctance forces induced by the magnet in the actuator.  
         [0045]     In the embodiment of  FIG. 6 , each gimbal member  50  comprises an elongated beam  58  connected to a rectangular or square end  52 , which includes a circular hole  55  that may be used to mount the gimbal to actuator block  38  in accordance with the peg-in-hole mounting method previously described. Gimbal members  50  may be fabricated in a variety of shapes utilizing a variety of conventional methods, such as chemical etching, press cutting, milling, etc. Although a specific rectilinear cutout pattern is shown in these figures, it is understood that other embodiments may have different patterns or a different arrangement of beams, pads, etc., yet still provide rotational movement along the longitudinal axis in accordance with the present invention. In operation, beams  58   a  &amp;  58   b  twist about their longitudinal axis to permit mirror  34  to rotate. In certain embodiments, beams  58  may be thinned by chemical etching to facilitate rotational flexing/twisting.  
         [0046]     A tab  51  located at the end of beam  58  is bonded to the bottom of one end of mirror  34 . For example, tab  51   a  is bonded to the left end, and tab  51   b  is bonded to the right end, of mirror  34  in the completed mirror-gimbal assembly of  FIG. 6 . Mirror  34  may be bonded to tabs  51  with adhesive. Alternatively, gold pads formed on the bottom ends of mirror  34  may be aligned with and bonded ultrasonically (e.g., 60-70 kHz) to gold pads formed on tabs  51  of gimbal members  50 . Similarly, coil  45  may be adhesively or ultrasonically bonded to the bottom of mirror  34  with gold pads on the bottom of mirror  34  aligned to corresponding pads located on opposite ends of coil  45 . (Reference numerals appended with the letter “a” denote elements of the left-hand gimbal member  50   a , with the appended letter “b” denoting elements of the right-hand gimbal member  50   b .)  
         [0047]     Mirror  34  is made of a Pyrex® substrate that is coated with a reflective metal (e.g., aluminum, silver, gold, etc.) covered with a thin protective layer of silicon dioxide. In the exemplary embodiment shown, mirror  34  is about 2.2 mm wide, 0.2 mm thick and about 6.7 mm long.  
         [0048]      FIG. 6  also shows coil  45  bonded to the bottom (i.e., backside) of mirror  34 . In the embodiment of  FIG. 6  coil  45  comprises an elongated “racetrack” shaped wire coil that is about the same size as mirror  34 . Coil  45  is made of insulated  48  gauge copper wire and has approximately 70 turns. Current is delivered/conducted to coil  45  through gimbal members  50   a  &amp;  50   b . By way of example, contact pads  54   a  &amp;  54   b  (˜1-2 microns of gold) may be formed on a top portion of respective ends  52   a  &amp;  52   b  of gimbal members  50   a  &amp;  50   b  using conventional lithographic printing methods. A seed layer of nickel (˜1-2 microns thick) may be added to contact pad  54  to facilitate soldering of wires (not shown in  FIG. 6 ) to each of contact pads  54 . Standard soldering or wire-bonding techniques may be used to bond wires to contact pads  54 . In one direction, current to coil  45  flows into contact pad  54   a , through gimbal beam  58   a , coil  45 , gimbal beam  58   b , and out of contact pad  54   b . It is appreciated that each end of the wrapped wire that comprises coil  45  is electrically connected with tabs  51 . Ultrasonic bonding or soldering coil wires to gold pads located on the bottom of mirror  34  may be utilizing to achieve electrical connection.  
         [0049]     In an alternative embodiment, coil  45  may be printed onto the backside of mirror  34  by plating or sputtering methods, e.g., utilizing standard semiconductor processing techniques. In yet another embodiment, mirror  34  may be integrated with gimbal members, with each being formed from a single wafer of silicon or thin piece of metal (e.g., steel). In still other embodiments, instead of utilizing two separate gimbal members, the gimbal may be fabricated from a single piece of thin material having ends connected by an elongated beam. In this latter embodiment, the mirror and/or coil may be bonded onto (or integrated with) the single piece of material.  
         [0050]     Servo control of the actuator assemblies is achieved through position feedback of mirrors  33  &amp;  34 .  FIG. 8  is a bottom perspective view of detector bracket assembly  37  utilized for position feedback in accordance with one embodiment of the present invention. Assembly  37  includes an L-shaped rigid bracket member  64 , one end of which comprises a flat, side plate  65  having two or more holes  66  used for aligned mounting to corresponding pegs protruding from the one side of actuator block  38  (see  FIG. 4 ). The other end of bracket member  64  comprises a top plate  69  that supports an LED  70 . Note that top plate  69  includes an optional opening  67  that reduces weight and which may be useful for permitting visual inspection of the underlying mirror-gimbal assembly.  
         [0051]     In one embodiment of the completed actuator assembly, LED  70  is suspended directly over about 25% of one end of the mirror mounted on top of actuator block  38 . A pair of photodetectors  68   a  &amp;  68   b  is mounted to top plate  69  on opposite sides of LED  70 .  FIG. 9  is a cross-sectional side view (taken through cut lines A-A′) of actuator assembly  28  showing the position of LED  70  and photodetectors  68   a  &amp;  68   b  relative to mirror  34 . In one implementation, photodetectors  68  comprise part number S-4VL manufactured by UDT Sensors, Inc., of Hawthorne, Calif.; and LED  70  comprises part number BL-HF035A-TR manufactured by American Bright Optoelectronics Corp., of Brea, Calif. Solder pads  72   a  &amp;  72   b  allow a wire to be connected to each of respective photodetectors  68   a  &amp;  68   b . Each photodetector  68  produces an electrical signal proportional to the intensity of the incident light.  
         [0052]     During operation LED  70  produces light that is reflected off the surface of mirror  34  (or  33 ). In certain embodiments, the light from LED  70  may be focused or otherwise directed toward the mirror at side angles (e.g., 30-45°) depending on the particular LED used and the location of photodetectors  68 . In any case, the intensity of the reflected light is detected by each photodetector  68 . As the mirror rotates in a particular direction, the intensity of light decreases on one side of LED  70  and increases on the other side. This difference in light intensity on opposite sides of LED  70  is sensed by photodetectors  68 . Together, photodetectors  68   a  &amp;  68   b  produce a rotational position feedback signal that is input to servo control circuitry, details of which are discussed below.  
         [0053]      FIG. 10  is a perspective view of another embodiment of an actuator assembly  80  in accordance with the present invention. Actuator assembly  80  comprises a block  82  of electrically non-conductive material having a beveled (45°) bottom surface  83  and a pair of mounting holes  84  for securing assembly  80  to the base of the laser assembly. Ordinary securing methods, e.g., screws, rivets, pins, etc., may be employed. In this embodiment, a mirror-gimbal assembly  81  is attached to opposite ends of a top surface of block  82  for rotationally suspending a mirror  87  (with backside mounted coil  85 ) directly above a permanent magnet (not shown). Rotation of mirror-coil assembly  87  is achieved in the same manner as that described in conjunction with previous embodiments.  
         [0054]     Position feedback is achieved in the embodiment of  FIG. 10  through the use of a pair of photodetectors  88   a  &amp;  88   b  mounted to mounting plates  86   a  &amp;  86   b , respectively attached to opposite sides of block  82 . A LED  91  is mounted on the top of a pedestal  90  underneath one end of mirror  87 , as best seen in the cross-sectional side view of  FIG. 11 . In this embodiment, light produced by LED  91  is blocked by the bottom of mirror  87 , but passes through the openings on both sides of mirror  87 . This arrangement causes shadows to be cast on the vertically mounted photodetectors  88 , which are laterally spaced apart on opposite sides above the top, reflective surface of mirror  87 . Depending on the rotational angle of mirror  87 , the shadow (or light intensity) sensed by one photodetector  88  is greater relative to that sensed by the photodetector positioned on the opposite side of mirror  87 . The difference between the light intensities sensed by the two photodetectors is a measure of the rotation of mirror  87 . The signal output from photodetectors  88  may be input to a servo control circuit.  
         [0055]     With reference now to  FIG. 13 , there is shown a block diagram of the electronics architecture according to one embodiment of the present invention.  FIG. 13  illustrates personal computer (PC) based software  100  for creating and downloading display programs or shows into the laser projection display apparatus of the present invention through USB port  21 , coupled to USB communications block  114  of digital signal process (DSP)  110 . As explained previously, display programs may also be downloaded to the display device through a variety of other connections and methods, including wireless connection, Ethernet, serial interface, etc. Alternatively, the display device of the present invention may include one or more drive units, such as hard magnetic disc, floppy, CD-ROM drive, or DVD disk drive units for receiving display program content. Input commands may be entered by a hand-held remote control device  101  through IR port  13 , which is coupled to a remote control decoder  115 , which may comprise software or firmware embedded within DSP  110 . Input commands may also be input through an alternative keypad source, such as a conventional keypad incorporated into or mounted onto the device enclosure.  
         [0056]     Content memory access is managed by block  111  of DSP  110 , which interfaces with content flash memory  104  and boot flash memory (e.g., EEPROM)  105 . Downloaded program shows or display images created with pushbutton keypad strokes may be stored in the display device in flash memory unit  104  coupled to DSP  110 . In an alternative embodiment, flash memory  104  and/or boot flash  105  may be embedded within DSP  110 .  
         [0057]     Position feedback signals generated by the photodetectors associated with the laser beam steering actuators are input into DSP  110 , which, in one implementation, comprises part number ADSP 21990 manufactured by Analog Devices Corporation of Norwood, Mass. As shown in  FIG. 13 , position sensor block  37  of laser assembly  16  produces position feedback signals coupled to analog-to-digital (A/D) converter  116  embedded in DSP  110 . Feedback power and light intensity signals from laser  26  are also coupled to DSP  110  to control laser light intensity and for automatic power control. A/D converter  116  converts the analog feedback signals received from actuator assemblies  27  &amp;  28  and laser assembly  16 , and converts them into digital signals for processing by DSP  110 .  
         [0058]     By way of example, in order to move the laser beam to a new position responsive to the content of a downloaded program, DSP  110  performs calculations and generates digital signals that are output to a digital-to-analog (D/A) converter  120 . D/A converter  120  converts the digitals signals received from DSP  110  into analog signals coupled to actuator drivers  124  and laser driver  122 . These analog signals are used by drivers  122  and  124  to generate currents (i.e., coil currents) that are used to change the rotational position of the mirrors associated with actuators  27  &amp;  28  of laser assembly  16 , as well as control the power and intensity of laser  26 . Actuator servo control is shown occurring in block  113  of DSP  110 . Similarly, control of laser  16  (e.g., intensity and power) is performed in block  112 .  
         [0059]     It should be understood that in the embodiment shown, laser  26  includes a photodetector that produces a signal useful for automatic power control. According to the architecture of the present invention, automatic power control, laser intensity control, and on/off switching of the laser diode are performed by DSP  110 . Furthermore, control of each of these functions is integrated with program content and servo actuation of the mirrors. Laser intensity and power feedback signals are coupled to A/D converter  116  of DSP  110 , which may be determine, for example, that the content program requires the laser beam to turn off and move to a new position before turning on again. To perform this operation, laser control block  112  of DSP  110  outputs signals through D/A converter  120  and laser driver  122  that turns laser  26  off, and then turns laser  26  back on again at the precise time that position sensors  37  indicate to DSP  110  that the mirrors of actuators  27  &amp;  28  are at the desired rotational position. Thus, on/off switching of the laser diode is synchronized with the servo loop that controls actuation of the mirrors, all of which is based on program content.  
         [0060]     According to the present invention, the output power of laser  26  may also be controlled to vary laser intensity based upon show content. For example, when projecting a real-time animated show that moves rapidly from one image to another image, or one that has many display points or pixels, DSP  110  may increase the light intensity of the laser beam to avoid dimming of the projected display. Conversely, when projecting a static image or one that changes slowly, DSP  110  may decrease the intensity of the laser beam. In other words, DSP  110  controls the laser output, both in terms of light intensity and on/off switching, depending upon the execution instructions of the display program, i.e., show content. In the embodiment of  FIG. 13 , DSP  110  controls the servo actuation of mirrors  33  &amp;  34 , light intensity and on/off control of laser  26 , as well as content control for the projection shows in an integrated manner. The electronics architecture of the present invention thus integrates servo control of laser light switching/intensity and mirror position with program content (firmware), all in a single processor to greatly improves performance over prior art laser projectors.  
         [0061]     It should be understood that elements of the present invention may also be provided as a computer program product which may include a machine-readable medium having stored thereon instructions which may be used to program a computer (or other electronic device) to perform a process. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, elements of the present invention may be downloaded as a computer program product, wherein the program may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection).  
         [0062]     Additionally, although the present invention has been described in conjunction with specific embodiments, numerous modifications and alterations are well within the scope of the present invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.