Abstract:
A laser light projector includes a laser beam generated by a laser light source, a scanner associated with the laser light source and having one or more moving mirrors capable of scanning the laser beam along X-Y coordinates, a scan-fail monitor and a safety-lens. The safety-lens includes a plurality of powers arranged for increasing the safety of the projected light within audience areas by increasing beam divergence in the audience, while keeping beam divergence low above the heads of the audience, thus allowing mirror targeting to occur.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 61/324,014 for “Laser Projector and Safety Lens for Audience Scanning” having filing date Apr. 14, 2010, and is a continuation-in-part application of and claims priority to U.S. utility patent application Ser. No. 11/814,310 for “Laser Projector for Audience Scanning” having filing date Jul. 19, 2006 filed in a National Phase Entry from Patent Cooperation Treaty Application PCT/US2006/001988 having filing date Jan. 9, 2006, the disclosures of which are herein incorporated by reference in their entirety, and all are commonly owned. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to the field of laser projectors, and more particularly to a laser projector for safely projecting patterns and arrays of laser beams directly into an audience for entertainment display purposes. 
     BACKGROUND 
     Projectors for laser display can generally be categorized into one of three groups including graphics projectors, beam projectors, and audience scanning projectors. 
     Graphics projectors are typically those which project logos, text and other figures onto some projection surface such as a screen. To create images, these projectors employ an X-Y scanning system, usually including two small mirrors mounted on galvanometer scanners. One mirror scans the beam in one linear direction (for example, horizontally) onto the second mirror, which scans the beam in the perpendicular direction (for example, vertically). The combined X-Y motion is normally used to draw outline-type vector images, using a point-by-point “connect the dots” styled method, according to software commands from a programmable controller operably connected with the laser projector. The audience views these figures on the screen in the same way that an audience would view a movie being projected onto a screen. 
     A beam projector produces beams of light that are projected into mid-air. The beams are viewable in mid-air by virtue of fog, dust and moisture that either exists in the air or which is created by a performer or venue. The beams are often animated to produce a dynamic effect. The beams can be moved and animated in a number of ways. As described by way of example for embodiments of the invention, an X-Y scanning system is also used. The scanning system may be identical to that of graphics projectors (the projector is merely aimed into the air instead of at a screen), or the scanning system may scan more slowly than that of graphics projectors (since complex images may not be required). Use of an X-Y scanning system allows flexibility to create both simple placement of the beam to hit target mirrors or objects and also to allow more complex patterns such as circles and shapes to be projected. 
     With both graphics and beam projectors, the generated light, typically from a laser beam, does not come in contact with the audience. The light merely travels from the projector to its destination surface (in the case of graphics projectors), or along an uninterrupted path in mid air, and typically exclusively above the heads of the viewing audience (in the case of beam projectors). 
     Audience scanning projectors typically combine features of both graphics and beam projectors. Audience scanning projectors typically use X-Y scanners to project geometric figures, patterns and arrays of light beams directly into a viewing audience. As with beam projectors, when the laser is projected toward an audience, its beam also illuminates any fog, dust, and moisture in the air. The beams may create dancing sculptures that are very pleasing to audience members and the beam generally comes in direct contact with the audience. The generated effect creates an illusion of being surrounded by a tunnel of light and by other geometric shapes that are formed by the light. Such effects have been compared to being inside a fireworks display, or being at the bottom of a swimming pool filled with light. By way of example, one audience scanning projector, as known in the art, is described in the above referenced U.S. utility patent application Ser No. 11/814,310 for “Laser Projector for Audience Scanning” and herein incorporated by reference. 
     Audience scanning projectors are often placed at a height of 3 meters, which is above the heads of all audience members. This is because the typical program material (image file data and abstracts) projected by audience scanning projectors uses the concept of a “horizon” to create certain shapes. It is known by laser show programmers that audience members will not reside above the horizon, and thus, certain patterns, such as non-moving beams may be placed there which are known to be above the heads of those in the audience. Likewise, it is known that audience members will probably reside below the horizon, and therefore only sheets and cones and faster-moving patterns will typically be placed there. 
     In the case of each of the three projector types described above, the X-Y signals and beam power level signals are generated by a programmable controller which generally comprises a personal computer having suitable interface hardware, and running software for generating the images, patterns and shapes. The hardware generally includes an interface circuit board that connects to the computer. This interface circuit board includes digital-to-analog converters and voltage amplifiers, so that signals can be produced which correspond to X-Y beam positions, and to beam power levels. The X-Y beam positions and beam power levels produced by the interface hardware are sometimes referred to as “command signals,” since these signals represent the software&#39;s intention for the projector to follow. The software program generates the X-Y beam positions and beam power level “command signals” and periodically transfers these as digital data to the digital-to-analog converters in the interface circuit board. Those skilled in the art know that any suitable interface hardware and software may be used to control any of the three projector types mentioned above. However, by way of example for embodiments of the present invention, hardware and software systems include the QuadMod™ series of hardware boards and Lasershow Designer™ series of laser software, both from Pangolin Laser Systems, Orlando, Fla. 
     When projecting a laser beam toward a viewer, eye safety is a major concern. If an intense laser beam were to stop scanning and stopped directly on the pupil of a viewer&#39;s eye, retinal damage can occur if the beam has sufficiently high power and a sufficiently long dwell time. Likewise, even if the beam is not stopped but is scanned across the pupil of an eye, it can still cause retinal damage if the beam power is high enough, or if the beam is scanning slowly enough. 
     In audience scanning projectors in the current state of the art, the X and Y beam position signals generated by the X-Y scanners are mathematically differentiated to produce an output equivalent to X and Y beam velocity. The X and Y beam velocities are added together to produce the total beam velocity. This total beam velocity is monitored and compared to some pre-set minimum allowable velocity to make sure that the beam velocity is sufficiently high. If the beam were to stop scanning, producing zero velocity, or if the velocity were to otherwise drop below some preset threshold, this would be considered a “scanning failure.” Under a scanning failure condition, the beam may be completely turned off by the light beam modulator or by a shutter. This type of system is called a “scan-fail monitor”. Note that a scan-fail monitor is most often implemented in the form of analog signal conditioning components, but may also be implemented with computer hardware and software. By way of further example, and with reference again to U.S. utility patent application Ser. No. 11/814,310 for “Laser Projector for Audience Scanning,” a scan-fail monitor as know in the art is described. 
     While scan-fail monitors provide some level of protection for the audience, there are a number of problems that still remain. First, a scan-fail monitor does not provide automatic power level control in different regions of the scan field. For example, scan-fail monitors are not capable of allowing a higher power level over the audience&#39;s heads or below their eyes. Second, scan-fail monitors can be easily “fooled” into believing that there is a safe condition when there is not, because they typically only monitor the rate of change of position and do not track the actual position of the beam. For example, if the beam alternates between two fixed locations, thereby concentrating 50% of the beam power in each position, the scan-fail monitor may allow this condition since the beam is technically scanning. However, in many instances, a 50% concentration of beam power could be hazardous. Therefore, improvements are still needed over the use of a scan-fail monitor alone. 
     Referring again to the above referenced audience scanning projector of the current state of the art, a laser generates a beam of light which is modulated. The modulation is performed either directly by the laser power supply, or externally by a modulator such as an acousto-optic modulator. After being modulated, the beam is directed to X-Y vector scanners and then projected directly into the audience. A scan-fail monitor may be used to detect if the scanning has stopped, or slowed to an unacceptably low level. Aside from the laser, modulator, shutter and X-Y scanners, typically no additional optical elements are used. 
     In this configuration, it could be said that the “raw laser beam” is used directly to illuminate audience members. However, a typical laser used for laser display applications has a beam diameter of 2 millimeters and divergence of around 1 milliradian. With this small size beam and low divergence, it is very possible that, during the scanning action, the entire laser beam will be smaller than 7 millimeters (which is the internationally-agreed-upon pupil diameter used for the purposes of safety evaluation) within the audience. Because the laser beam diameter is typically so small in the audience, it means that no greater than around 5 milliwatts of laser power can be used to create the laser display, regardless of the sophistication of the scan-fail monitor. If a higher power is used, the display will not be able to meet Class 1 standards for laser safety. 
     Although it is not typically done, it is known to use a lens within the beam path of an audience scanning laser projector, such as a lens whose power has approximately a −1.0 diopter. The lens may be placed between the modulated laser beam and the X-Y scanners, or immediately at the exit of the scanners. A lens whose power is negative will increase the divergence of the laser beam so that the beam diameter will be greater than 7 millimeters within the audience. When the beam is greater than 7 millimeters, the entire beam will no longer fit through the pupil of a viewer&#39;s eye and thus, not all of the laser beam&#39;s power will be delivered to the retina if the laser beam does land on someone&#39;s eye. 
     Light irradiance (which is the power per unit area) is governed by the “inverse square law”, which states that, for a given beam power, if you double the beam diameter, the power-per-unit-area will be decreased by a factor of four. Thus the power-per-unit area decreases by the inverse-square of beam diameter. Since the irradiance of the laser beam has the greatest implication to laser safety, it can be shown that decreasing the irradiance by increasing divergence is one effective means of increasing the safety of audience scanning projectors. 
     By using a lens with negative optical power to increase the divergence, this will decrease the power-per-unit area (irradiance) of the laser beam, thus making it possible to use a laser with higher than 5 milliwatts laser power, and still meet Class 1 standards for laser safety. In fact, by using a lens whose power is −1.0 diopters, the laser beam power can be increased to around 250 milliwatts for a typical size audience and a typical distance from the laser projector. 
     The increased divergence allows for a higher power laser to be used—thus, this generally provides a much more dramatic and stunning laser light show. However, this approach is also not without problems. Placing a lens with negative optical power before or after the scanners will decrease the divergence in all parts of the scan field, including above the heads of audience members. As stated above, laser projectors may be used for mirror targeting applications where the laser beam is directed to a mirror, to create a static beam sculpture. Typically a small beam is used for mirror targeting. The larger beam diameter caused by the lens makes such beam targeting virtually impossible. Another drawback is that, as the beam diameter is increased, the projected effect looks more cloudy and foggy, whereas the raw beam projected from the laser makes it look as though the light is cutting through the air like a knife. 
     It is also useful to have the lens located on a mounting arrangement external to the projector, so that if needed, the lens can be changed. However, an external mounting arrangement can also be tampered with. For example, if the laser projector is installed in a disco or night club, a rogue club operator or DJ might be tempted to completely remove the lens, thus allowing more intense and low-divergence beams to be projected everywhere, including into the audience. However, as noted above, low divergence beams projected into the audience would be potentially hazardous, especially if the power of the laser is greater than 5 milliwatts. 
     SUMMARY 
     The present invention overcomes drawbacks of known projectors by allowing the projection of laser beams with a small diameter and low divergence above the heads of the audience to aid in mirror targeting applications, while allowing the projection of laser beams with larger diameter and higher divergence within the audience, thus increasing safety. 
     Embodiments of the present invention, herein presented by way of example, increase the safety of the laser projector by making it so that if an external lens is removed, the laser projector will project high divergence beams everywhere and thus, the removal of the lens becomes a fail-safe arrangement, and also an arrangement which removes the motivation of rogue club operators and DJs to remove the external lens. 
     With the foregoing in mind, the present invention discloses a safe audience scanning projector that incorporates a laser, X-Y scanners, a scan-fail monitor and a safety lens. The safety lens may include at least two separate optical powers (curvatures)—one optical power for laser beams scanned above a horizon, and a separate optical power for laser beams scanned below the horizon. There may be an abrupt change between the optical powers, or there may be a transition region which tends to blend the optical powers. Moreover, one optical power may be effectively nearly zero, thus making that portion of the lens essentially function like a flat window. The safety lens may be the only lens used in the projector, placed at the exit of the X-Y scanners, or the safety lens may be used along with an additional lens placed before the X-Y scanners. By way of example, the present invention may be embodied in a system comprising a laser producing a beam of light, a scanner operable with the laser producing a scanned light beam, and a safety lens receiving the scanned light beam. The safety lens may comprise at least two optical powers. One optical power may project a first beam with lower divergence than a second optical power projecting a second beam. The one optical power may be more positive than the second optical power. 
     Further, the system may comprise a scan-fail monitor operable with the scanner for emitting a fault signal to the laser for reducing intensity of the beam of light coming from the laser to a level acceptable during a fault condition. The safety lens may have a plurality of optical power regions separated by at least one of a sharp split and a generally smooth transition between the optical power regions. The scanner may be an X-Y Galvanometer-based optical scanner directing the light beam along X-Y vector coordinates. 
     Yet further, the system may comprise a modifying lens receiving the light beam from the laser. The modifying lens may have a negative optical power and at least a portion of the safety lens having a positive optical power. At least a portion of the safety lens may have a negative optical power. An effective optical power of the safety lens may be about 0 diopters at a first portion and the effective optical power of the safety lens may be about negative 2 diopters at a second portion thereof. 
     First and second zones may be positioned for receiving the scanned light beam, wherein the first zone is defined above a viewing audience area and the second zone is defined to be within the viewing audience area, and wherein the scanned light beam emitted from the first portion of the safety lens is directed to the first zone and the portion of the scanned light beam emitted from the second portion of the safety lens is directed to the second zone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some of the features, advantages, and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a diagrammatical illustration of a laser beam projection system for scanning an audience, according to one possible embodiment of the present invention; 
         FIG. 2  is a cross sectional side view of one safety lens in keeping with the teachings of the present invention; and 
         FIG. 3  is a diagrammatical illustration of a laser projection system for scanning an audience, according to an alternate embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these illustrated embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     With reference to  FIG. 1 , one embodiment of the invention is herein described by way of example as a laser projection system  10 , wherein a laser  12  generates a light beam  14 , which is directed to a scanner  16 . The scanner  16  may have one or more moving mirrors capable of scanning the light beam  14  along X-Y coordinates  18 . A scan-fail monitor  20  receives an output signal  22  from the scanner  16 , the output being indicative of a scanner coordinate position and/or velocity. The scan fail monitor  20  performs a calculation on the scanner output signal  22 , and in turn outputs a fault signal  24  if the position and/or velocity of the scanner  16  would lead to a hazardous condition, such as the scanning action being too slow or stopping within an audience area  26 . The fault signal  24  reduces the power of the laser  12  to a light level that would be safe under a fault condition. 
     With continued reference to  FIG. 1 , a safety lens  28  is positioned at the output  30  of the scanner  16 . The safety lens  28  includes at least two optical powers (curvatures). One optical power is generally on an upper portion  32  (a top half, by way of example) of the safety lens  28 , and another optical power is generally on a lower portion  34  (bottom half, by way of example) of the safety lens  28 . The lower portion  34  of the safety lens  28  is intended to produce beams  36  with a higher divergence into the audience area  26  where an audience  38  will reside and thus, the optical power for the lower portion of the lens is greater than that of the upper portion  32 . The upper portion  32  of the safety lens  28  is intended to produce beams  40  with low divergence in an area  42  above the audience  38 . 
     Typical optical power for the lower portion  34  of the safety lens  28  is between −0.5 diopters and −3.0 diopters. The upper portion  32  of the safety lens  28  is intended to be scanned into the area  42  where the audience will not reside and in fact, where target mirrors (not shown) may reside. Therefore the optical power of the upper portion  32  of the safety lens  28  may be effectively nearly 0.0 diopters or possibly even slightly positive to aid in maintaining a desirably collimated projected and the scanned beam  44 . Although these are typical diopter ranges, these numbers are not intended to be limiting. 
     One possible way of manufacturing the safety lens  28  may include providing a typical round lens with an optical power of −0.5 diopters and cutting it in half. Then providing a second lens with an optical power of −1.0 diopters and cutting it in half as well. The two half-lenses are then glued together in the middle with optical cement. The portion of the lens  28  with the higher optical power would be used on the bottom, and used to project beams into the audience. The optical powers and manufacturing technique described here is only intended to be illustrative, and not limiting. 
     If the technique above were used, this would indeed create a safety lens with two separate optical powers. This manufacturing technique results in a lens that includes an abrupt change in the beam divergence as it crosses the line  46  formed where the two lenses meet. There may be undesirable beam distortions that occur within such a sharp cutoff region. 
     Therefore, one method of manufacturing the safety lens includes use of modern CNC machinery capable of producing curvatures of up to +/−18.0 diopters, and creates the safety lens out of a single piece of material, such as CR39, which is a very stable plastic monomer that can be easily machined and polished for optical applications. The manufacturing technique may provide an optical power on the upper portion  32  of the lens  28 , as illustrated with reference to  FIG. 2 , and another optical power on the lower portion  34  of the lens, and a blended optical power at an intermediate portion  48  of the lens. Note that these curvature ranges, manufacturing techniques and material are meant only to be illustrative and not limiting. 
     As noted above, generally the lower portion  34  of the safety lens  28  will effectively have greater optical power than the upper portion  32  and there may be a gradual change in lens curvature between the upper portion and lower portion, thus avoiding distortion that would be caused by the beam crossing a sharp split between the two optical powers. It is also possible that there could be three optical powers, for example, one optical power for the upper portion of the scan field, a second optical power for the central portion of the scan field, and a third optical power for the lower portion of the scan field. 
     Within the embodiment illustrated with reference to the system  10 , it is preferable that at least the lower portion  34  of the safety lens  28  be made with negative optical power, because a negative optical power will increase divergence at all points between the output of the safety lens and the audience. However, it is also possible to configure the safety lens  28  using a positive optical power, even in the lower portion  34 . However, there will be a converging effect before the beam begins to diverge, again providing beams with higher divergence in the audience  38 . Thus, positive optical powers can be used as long as the audience is located at a sufficient distance from the laser projector to ensure that they are beyond the point of convergence. 
     The safety lens  28  may additionally be coated with a multi-layer, reflection free coating  50  optimized for transmittance in the visible wavelengths. 
     The system  10  described above with reference to  FIG. 1  provides a straight forward and thus desirable approach to create laser beam projection for safe audience scanning, because it places the safety lens  28  at the output  30  of the scanner  16 , and no additional lenses or adjustments are needed. 
     However, yet further desirable performance characteristics are achieved with the system  11  illustrated with reference to  FIG. 3 . For the system  11  herein described by way of example, the laser  12  produces the light beam  14  which is directed through a modifying lens  52  before being directed to the scanner  16 . The scanner  16  includes one or more moving mirrors capable of scanning the laser beam along the X-Y coordinates, described earlier with reference to  FIG. 1 . The scan fail monitor  20  performs a calculation on the scanner output signal  22 , which in turn outputs a fault signal  24  if the position and/or velocity of the scanner  16  would lead to a hazardous condition, such as the scanning action being too slow or stopping in the audience  38 . The safety lens  28  is as earlier described with reference to  FIG. 1 . 
     Within the system  11 , it is desirable for the lens  52  to be configured to provide a negative optical power of, for example −2.0 diopters. It is also desirable to configure the upper portion  32  of the safety lens  28  to have a positive optical power of, for example +2.1 diopters, thus beams with low divergence  42  will be projected above the audience  38 . The upper portion  32  may be configured to provide completely collimated beams as long as the lens  52  is spaced appropriately from the scanner  16 . In this configuration, the lens  52  having a negative optical power and the upper portion  32  of the safety lens  28  having a positive optical power that is greater than or equal to the negative power of lens  52  will form an up-collimator. An up-collimator reduces divergence even further when compared with that of the laser  12  itself. This is desirable for mirror targeting applications. 
     Up-collimators that comprise two lenses are known in the art, and are typically placed before the scanner. However, placing the single lens  52  before the scanner  16  and the safety lens  28 , a second lens, after the scanner  16  provides a dual benefit. In this system  11 , the moving mirror on the scanner  16  does not have to be as big as it would be in the case for well known up-collimator methods. Yet further, another benefit is provided by the lower portion  34  of safety lens  28 . 
     Unlike the upper portion  32  of the safety lens  28 , the lower portion  34  is configured with an optical power that does not quite collimate the light and in fact, within the system  11 , the lower portion of the safety lens may provide no optical power at all, in which case it will provide beams with higher divergence into the audience  38  because of the optical power of the lens  52 . 
     Since it may be desirable for the safety lens  28  to be located external to the components carried within a common housing  54  and more easily removable so that different optical powers may be used for different venues. However, it should be understood that there is added safety for the system above described when all components are within a common housing because the safety lens becomes an integral fail-safe component. By way of example for the system  11  above described, if the safety lens is removed, then high divergence beams may be projected everywhere because of the optical power of lens  52 . 
     As noted above, within the system  11 , it is preferable to have the lens  52  configured to provide a negative optical power, and at least the upper portion  32  of safety lens  28  configured to have a positive optical power. However, it is possible for modifying lens  52  to provide a positive optical power, and also possible to configure the safety lens  28  to provide negative optical power. Many lenses and optical configurations are possible and still remain within the scope of this invention as long as the beams with lower divergence  42  are directed above the heads of the audience  38  and the beams with greater divergence  38  directed into the audience  29 . 
     It will be understood by those of skill in the art that embodiments of the present invention may be driven by a computer or other pattern generator, not herein described because such devices are common and well known to those of ordinary skill in the art. 
     Accordingly, within the drawings and specification, there have been disclosed typical preferred embodiments of the invention, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The invention has been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the invention as described in the foregoing specification and as defined in the appended claims.