Patent Publication Number: US-6334699-B1

Title: Systems and methods for diffuse illumination

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to systems and methods to generate diffuse illumination. In particular, this invention is directed to a diffuse light source for a machine vision system. 
     2. Description of Related Art 
     Uniform, diffuse illumination of a sample part is often necessary in commercial vision systems to accentuate an edge of the sample part within a designated field of view. Since most sample parts are not transparent, diffuse illumination of the sample part is also necessary so that light which is reflected from the sample part can be collected by an imaging system. Furthermore, an adjustable diffuse illumination source accommodates sample parts having a wide variety of shapes. 
     Typically, the intensity of light emitted by a light source is adjustable when the magnification of the imaging system is also adjustable. The adjustable illumination provides the ability to illuminate sample parts having different characteristics, such as, for example, shape, composition, and surface finish. 
     Also, conventional light sources project light onto the sample part at an angle from a plane which is normal to the imaging plane. This angle is referred to as the angle of incidence. Light projected at an angle of incidence which is between 0 and 90 degrees may improve the surface contrast of the image and also more clearly illuminate textured surfaces. Typically, such light sources have a prescribed range for the angle of incidence. Conventionally, the angle of incidence varies between 10° and 70° relative to the plane which is normal to the optical axis of the imaging system. Such a range is relatively broad and, therefore, provides adequate contrast in an image of a sample part. 
     Furthermore, conventional vision systems can also adjust the circumferential position of the source of diffuse lighting about an optical axis. Typically, the position of the diffuse lighting source is adjustable in, for example, addressable sectors or quadrants. As such, any combination of sectors and quadrants of such a circular light pattern can be illuminated. Additionally, the intensity level of the light source can be coordinated with the circumferential position of the light source to optimize the illumination of a sample part edge. 
     For example, some conventional vision systems include an annular light source that emits rectangular or toroidal patterns. The light source is an annulus which is divided into four quadrants. Also, other conventional vision systems include a ring light having an annulus which is subdivided into eight sectors. Additionally, some conventional vision systems have hemispherically-shaped light sources to direct light from a multitude of positions relative to an optical axis. The center of the hemisphere serves as a focal point for the light sources. Furthermore, any combination of sectors and quadrants can simultaneously be illuminated with varying illumination levels. 
     SUMMARY OF THE INVENTION 
     Recently, manufacturers of conventional vision systems have started offering a solid-state replacement for the traditional tungsten filament lamp, e.g., a halogen lamp, that has been used in conventional diffuse light sources. These manufacturers now offer light emitting diodes (LEDs) that offer higher reliability, a longer service life, greater brightness, lower cost, good modulation capabilities and a wide variety of frequency ranges. 
     Some manufacturers of such conventional vision systems provide opto-electro-mechanical designs that partially achieve the characteristics of the conventional diffuse light sources discussed above. However, these opto-electro-mechanical devices are complicated, costly, lack versatility, and do not enhance a video inspection process. For example, these light sources require overly intricate mechanical motion which results in a lower vision system throughput and an increase in cost. Other conventional solid-state light sources require a large number of discrete light sources in a two-dimensional array and an elaborate electronic cross-bar to energize them. Furthermore, other conventional solid-state light sources must accommodate at least fifty discrete light sources in a three-dimensional array housed in a large carriage. 
     Accordingly, conventional diffuse light sources are incapable of providing a full-featured, reliable, inexpensive system and method to diffusely illuminate a sample part. Moreover, conventional diff-use light sources only marginally provide the capability to alter the intensity, angle of incidence and circumferential position. Such conventional diffuse light sources do not optimally illuminate sample parts for dimensional measurements when varying construction (e.g., shape), material (e.g., absorptivity, scattering, etc.), and surface properties (e.g., color or texture) are involved. 
     The systems and methods of this invention achieves the diffuse lighting effects that are currently offered on the market. In addition, this invention offers all these features using a single solid-state source or small number of solid-state sources, such as LEDs or laser diodes. 
     Further, the systems and methods of this invention provide an economically viable way to obtain color images by assembling RGB images from a monochrome camera. A monochrome camera provides high spatial resolution that is necessary for dimensional measurements without using expensive CCD color camera technology. 
     This invention provides systems and methods that create conventional as well as more versatile diffuse illumination using a simpler, more robust device. In addition, the systems and methods of this invention allow the selection of illumination color. Therefore, the illumination color may be controlled based on the sample part properties (e.g., pigmentation) in order to improve image contrast. Also, illumination color selection is used to produce a high resolution color image using a monochrome CCD detector. Thus, the systems and methods of this invention preserve the high resolution necessary for dimensional metrology measurements without the unnecessary expense of CCD color camera technology. 
     Still further, an exemplary embodiment of the systems and methods of this invention incorporate optical source monitoring as described in U.S. patent application No. 09/220,705 filed Dec. 24, 1998 which is incorporated herein in its entirety. The optical source monitoring measures the real-time optical power output from the solid-state devices. This is possible on continuous or pulse operated systems. The measurements are taken so that power output variations may be corrected. Power output variations are due primarily to aging, drive current fluctuations and temperature drifts. The intensity measurements permit a level of calibration and instrument standardization which can yield reproducible illumination among an instrument model line. 
     One exemplary embodiment of the systems and methods of this invention includes a beam deflector that is mounted on a motor shaft. The beam deflector has a mirror. The beam deflector tilts in proportion to the centrifugal force exerted on the beam deflector when the motor shaft rotates. A light beam incident upon the mirror is deflected by an angle which is defined by the tilt of the beam deflector. 
     Additionally, because the beam deflector is rotating the deflected light beam sweeps out a cone. The deflected light beam cone is incident upon a focusing element and sweeps out a circular pattern on the surface of the focusing element. The radius of the circular pattern is dependent upon both the distance of the focusing element from the beam deflector and the angle at which the light beam is deflected. The greater the angle of deflection and the farther the focusing element is from the beam deflector, the larger the circular pattern becomes. Therefore, since the rotational speed of the motor shaft is directly proportional to the deflection angle and since the size of the circular pattern is directly proportional to the deflection angle, the size of the circular pattern is directly proportional to the rotational speed of the motor shaft. 
     Also, the speed at which the light beam traverses the circular pattern is directly proportional to the rotational speed of the motor shaft. Therefore, the rotational speed of the motor shaft controls both the size of the circular pattern and the speed with which the light beam traverses the light pattern. Thus, the motor and beam deflector control the light pattern. 
     The light beam is collimated by the focusing element to sweep out a column. This column of light is reflected by a mirror to be substantially parallel to and to encompass an optical axis of an imaging device of a vision system. The imaging device, which may include a CCD, employs optical lenses to produce an image of a sample part positioned in a field of view and located at an object plane. The collimated pattern is focused onto the same field of view using another focusing element. Reflected and scattered light from the field of view is imaged onto the CCD using optical lenses. 
     These and other objects of the invention will be described in or be apparent from the following description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: 
     FIG. 1 is a schematic diagram of an exemplary embodiment of a diffuse lighting system according to this invention; 
     FIG. 2 is a plan view of an exemplary light source according to an embodiment of this invention; 
     FIG. 3 is a sectional view of another exemplary light source according to an embodiment of this invention; 
     FIG. 4 is a sectional view of one embodiment of a beam deflector of a light pattern controller according to an embodiment of this invention; 
     FIG. 5 is a sectional view of the beam deflector of FIG. 4 taken along line V—V; 
     FIG. 6 is a partial sectional view of an exemplary focusing element according to this invention; 
     FIG. 7 is a partial sectional view of another exemplary focusing element according to this invention; 
     FIG. 8 is a partial sectional view of yet another exemplary focusing element according to this invention; 
     FIG. 9 shows another exemplary embodiment of a light pattern controller in accordance with this invention; and 
     FIG. 10 shows yet another embodiment of a light pattern controller in accordance with this invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is a schematic diagram of an exemplary diffuse illumination system  100   25  of this invention. The system  100  includes a light source  110  emitting a light beam  111 , a light pattern controller  115 , a collimating element  140 , a mirror  150  and a focusing element  160 . The light pattern controller  115  includes a motor  120  and a beam deflector  130 . FIG. 1 also shows an imaging system  200  which includes a camera  220  and an optical system  210  which produces an image of a sample part  300 . The system  100  illuminates the sample part  300  on an inspection plane  310  so that the imaging system may obtain an image of the sample part  300 . 
     The light source  110  has one or more solid-state light emitting devices that are stable and have a long service life. The solid-state light emitting devices may include LEDs or laser diodes. Further, the solid state light emitting devices may emit radiation in the visible and/or near-infrared regions of the electromagnetic spectrum. The solid-state light emitting devices are selected because they emit radiation in the spectral regions in which charge coupled devices (CCDs) of the camera  220  are known to be photosensitive. 
     LEDs are also used as the light emitting devices because LEDs are more amenable to precise optical power regulation than halogen lamps. This is at least partially due to the smaller drive currents needed to operate the LEDs. In addition, the discrete nature of LEDs allows the wavelength of the emitted light to be more flexibly selected. Also, when driven electronically within the working parameters of the LEDs, the repeatability and reliability of the light output by the LEDs are both very high. In addition, some LEDs are capable of emitting light in the ultra-violet A frequency range, which improves the resolving power of imaging optics. 
     Still further, the light source  110  has one or more optical power monitoring devices incorporated within the light source  110 . Preferably, these devices are silicon photodiodes whose spectral responsivity is matched to the spectral emission of the solid-state devices within light source  110 . These optical power monitoring devices are not restricted by material or design. Any device capable of measuring the optical output of the solid-state devices within light source  110  can be used. Lastly, in the configuration where light source  110  can multiplex between illumination colors, each color has a dedicated device to monitor optical power incorporated within light source  110 . 
     As shown in FIG. 1, the light source  110  emits the light beam  111  which is incident upon the beam deflector  130  of the light pattern controller  115 . The beam deflector  130  is mounted on a shaft  121  of the motor  120 . The beam deflector  130  tilts relative to the axis of the shaft  121  in proportion to the centrifugal force exerted on the beam deflector  130  when the motor shaft  121  rotates. The light beam  111  from the light source  110  is directed onto a mirror  134  (shown in FIG. 4) of the beam deflector  130 , and is reflected from the mirror  134  by an angle which is defined by the tilt of the beam deflector  130 . 
     Additionally, because the beam deflector  130  is rotating, the light beam  111  sweeps out a cone  113 . The deflected light beam cone is incident upon the collimating element  140  and sweeps out a circular pattern on the surface of the collimating element  140 . The collimating element  140  may be, for example, a condenser lens, a Fresnel lens, or a set of reflective louvers. The radius of the circular pattern is dependent upon both the distance of the collimating element  140  from the beam deflector  130  and also the angle at which the light beam  111  is deflected by the beam deflector  130 . The greater the angle of deflection and the farther the collimating element  140  is from the beam deflector  130  the larger the circular pattern swept by the light beam  111  will be on the surface of the collimating element  140 . Therefore, since the deflection angle is directly proportional to the rotational speed of the motor shaft  121  and since the size of the circular pattern is directly proportional to the deflection angle, the size of the circular pattern is directly proportional to the rotational speed of the motor shaft  121 . 
     Also, the speed at which the light beam  111  traverses the circular pattern is directly proportional to the rotational speed of the motor shaft  121 . Therefore, the rotational speed of the motor shaft  121  controls both the size of the circular pattern and the speed with which the light beam  111  traverses the circular pattern. Thus, the light pattern controller  115  controls the pattern swept by the light beam  111  on the collimator  140 . 
     The light cone  113  is collimated by the collimator  140  to sweep out a cylinder. The light cylinder is reflected by the mirror  150  to be substantially parallel to and to surround an optical axis  212  of the imaging system  200 . The imaging system  200  employs optical lenses  210  to image a field of view located at an object plane onto the image plane of the camera  220  (e.g., pixel array). The collimated pattern is focused onto the same field of view using the focusing element  160 . 
     The motor  120  may be a direct current motor (DC), an alternating current motor (AC) or a stepper motor. Any other known or later developed motor can also be used as the motor  120  to provide accurate rotational position and speed control information. Preferably, the speed control of the rotary motor should be better than 1%. 
     The mirror  150  is angled relative to the optical axis  212  and has an aperture  151  positioned where the optical axis  212  passes through the plane of the mirror  150 . The aperture  151  is sized to permit unobstructed transmission of an image of the sample part  300  to the camera  220 . 
     The cylinder of light is then reflected by the mirror  150  toward the focusing element  160 . The focusing element  160  can be a condenser lens, a Fresnel lens or the like. The focusing element  160  can also be a set of annular rings of mirrored louvers which are individually angled as a function of radius. The gradation in the angle of incidence of the light beam onto the sample part as a result of individual louvers or annular reflectors positioned at discrete radial locations in the focusing element  160  is discrete. It should be appreciated that any known or later developed element capable of collimating or focusing a light beam can also be used. It should also be appreciated that the collimator  140  may be identical to the focusing element  160 . 
     The light beam  111  is then directed by the focusing element  160  onto the sample part  300  on the inspection plane  310 . The focusing element  160  has a focal distance which coincides with an average working distance of the objective lenses  210 . For example, if the objective lenses  210  image at magnification levels of 1×, 3×, 5×, and 10× and have corresponding effective working distances of 59.0 mm, 72.5 mm, 59.5 mm, and 44.0 mm, respectively, with a resulting average working distance of 58.75 mm, then selecting a nominal focal length of approximately 59.0 mm for the focusing element  160  will coincide with the average working distance of the objective lenses  210  to yield good performance within the operational magnification range. 
     As shown in FIG. 2, the light source  110  may include an array of solid-state devices  112 ,  114  and  116 , which each have different characteristics. The LEDs  112 - 116  operate in the red, green and blue spectral regions, respectively. In another exemplary embodiment, the LEDs  112 - 116  can emit radiation in the near infrared or other spectral regions which are compatible with observation of the sample part  300 . A light source  110  having multiple solid-state devices can multiplex among the individual solid-state devices to optimally illuminate the sample part. In addition, a multi-wavelength addressable light source can match or avoid the average spectral absorption properties of the sample part to enhance the image contrast. 
     As shown in FIG. 3, the solid-state devices  112 - 116  may also be surface mounted in an acrylic-encapsulated package  118  to form the light source  110 . For example, surface-mounted solid-state devices  112 - 116  can be combined with a collection and/or collimation lens to form the light source  110 . 
     FIG. 4 shows a sectional view of the beam deflector  130 , which deflects the light beam  111  from the light source  110 . The beam deflector  130  includes a cylindrically-shaped barrel  131  having a first end  132  and a second end  133 . The second end  133  has a mirror  134 . An internal cavity  135  of the beam deflector  130  defines an area in which the motor shaft  121  is received. 
     The motor shaft  121  is aligned with a transmitting axis  122 . The motor shaft  121  also includes a hole  123  that accepts a clevis pin  124  about which the beam deflector  130  pivots. 
     As shown in FIG. 4, the center of mass of the beam deflector  130  is located to the left of the transmitting axis  122 . Thus, when the motor shaft  121  rotates, a centrifugal force operates through the center of mass of the beam deflector  130  to push the center of mass away from the motor shaft  121 . 
     A spring  136  within the beam deflector  130  counteracts the centrifugal force. Although the spring  136  is shown to provide a counteracting force, any known or subsequently developed device for applying a counteracting force can be used in accordance with this invention. 
     A position adjuster  137  is disposed, within the cavity  135  of the barrel  131 . The position adjuster  137  adjusts an angle between the longitudinal axis of the barrel  131  and the transmitting axis  122  of the motor shaft  121  within a predetermined range. In one exemplary embodiment, the adjuster  137  adjusts the angle such that the angle is substantially equal to zero when the angular velocity of the shaft  121  is below a threshold velocity ω 0 . 
     The mirror  134  shown in FIG. 4 is a concave, spherical mirror having a center that is coincident with the transmitting axis  122 . The mirror  134  may also be a planar or convex mirror. It should be understood that the mirror  134  may be any known or later developed reflector capable of reflecting electromagnetic radiation of the wavelengths emitted by the light emitting devices of the light source  110 . 
     FIG. 5 shows a sectional view of the beam deflector  130  taken through line V—V in FIG.  4 . The cavity  135  forms a transverse slot to permit the barrel  131  to pivot inside about the clevis pin  124 . 
     Accordingly, the beam deflector  130  generates two-dimensional circular patterns of light. The two-dimensional patterns of light have a variable radius that is a function of the angular velocity ω at which the beam deflector  130  rotates. 
     As discussed above, the mirror  134  reflects the light output by the light emitting devices of the light source  110 . Furthermore, the focal length of the mirror  134  is chosen to provide a light beam having a predetermined diameter. The focal length of the mirror  134  is also chosen based on the performance of the light source  110 . The diameter of the light beam  111  incident on the inspection plane  310  is chosen to provide adequate image brightness and field of view-conformity. For example, a mirror  134  having a diameter of approximately 12.5 mm can be used to provide a focal length of approximately 12 mm to 40 mm. The focal length of the mirror  134  is chosen to provide the clearest image of the sample part  300 . The direction and/or divergence of the light beam  111  must be taken into consideration when choosing the mirror  134 . 
     As discussed above, after the light beam  111  reflects off the mirror  150 , the light beam  111  must be redirected onto the sample part  300 . The focusing element  160  redirects the light beam  111  onto the sample part  300 . 
     FIG. 6 shows a second exemplary embodiment of a focusing element  160  which has a plurality of mirrored surfaces  161 - 165 . Each mirrored surface  161 - 165  reflects the light beam  111  that circumscribes a circle having a corresponding radius R 1 -R 5 . The larger the radius of the cylinder swept by the light beam  111 , the larger the R 1 -R 5  radii of the mirrored surfaces  161 - 165  that reflect the light beam  111 . Each mirrored surface  161 - 165  reflects the light beam at a different angle of incidence a onto the sample part  300 . The light beam  111  has a nominal diameter d. The inner flat surfaces of the mirrored surfaces  161 - 165  are first-surface mirrors optimized for spectral reflection in the visible and near-infrared portions of the electromagnetic spectrum. 
     In an exemplary embodiment of this invention, the mirrored surfaces  161 - 165  are injection-molded engineering plastic parts with a reflective coating deposited onto the inner flat surface. The ensemble of all mirrored surfaces  161 - 165  that make up the focusing element  160  are spatially rigid with respect to each other and the objective lens  210 . The rigidity of the mirrored surfaces  161 - 165  is achieved using a transparent, donut-shaped base  166 . Further, a bracket  167  fixes the assembly relative to the objective lens  210 . Lastly, an angle of each mirrored surface  161 - 165  relative to the optical axis  212  is slightly different, to compensate for a change in the optical pathlength that results from the light beam  111  being refracted through the transparent material of the base  166 . 
     It should be understood that it is possible to manually exchange the objective lens  210  with another objective lens of differing numerical aperture to increase or reduce the magnification. Typically, for machine vision instruments, the working distance WD of such lenses vary slightly (±25%) within the line of commonly-used microscope objective lenses. To this end, diffuse illumination with a variable angle of incidence a requires the illumination focal point of the mirrored surfaces  161 - 165  to be coincident with the focal point of the objective lens  210 . One manual method of achieving this is to provide a unique detent positioner  211  near the focusing element  160  for each objective lens  210 . This results in coincident foci at the focal point  250 . The element  160  can then be correctly positioned when the objective lens  210  is exchanged. 
     FIG. 7 shows a third exemplary embodiment of a focusing element  260  which has a plurality of annular, parabolic mirrored surfaces  261 - 265 . Each mirrored surface  261 - 265  reflects the light beam  111 , which sweeps a cylinder with corresponding radius, onto a focal point  250 . As the radius of the cylinder varies throughout a corresponding range for a particular mirrored surface  261 - 265 , the corresponding mirrored surface  261 - 265  reflects the light beam  111  onto the focal point  250  at a continuously varying angle of incidence. 
     The interior surfaces of focusing element  260  are first-surface mirrors created by deposition of an appropriately reflecting metal onto plastic. The parabolic shape enables the light beam  111  to be focused onto the focal point  250 . This focusing increases the incident energy per unit area on the focal point  250 . 
     In the exemplary embodiment shown in FIG. 8, the focusing element  360  is a Fresnel lens. The Fresnel lens has focal length chosen such that it&#39;s focal point coincides with the focal point  250 . 
     The sample part  300  is imaged by the camera  220  using the objective lenses  210 . The optical axis  212  is perpendicular to the sample part  300  and is substantially perpendicular with the transmitting axis  122 . After reflecting off of the mirror  150 , light that was directed along the transmitting axis  122  is now substantially parallel to the optical axis  212 . The optical axis  212  and the transmitting axis  122  intersect and have intersection substantially at the center of the aperature  151 . 
     The focal point  250  has two symmetric areas of interest that surround the focal point  250 . The first area corresponds to the field of view  251 . Scattered and reflected light within the field of view  251  is imaged by the objective lens  210  onto the camera  220 . Although a first linear dimension of the field of view area  251  is depicted, it should be understood that a second linear dimension is normal to the plane of the figure. The second area is larger than the first area and corresponds to an illumination field  252  which encompasses the field of view  251 . Both the field of view  251  and the illumination field  252  also have a geometric center located at the focal point  250 . 
     In the exemplary embodiment shown in FIG. 8, a variable angle of incidence a is created in like manner to the exemplary embodiment shown in FIGS. 6 and 7, except that the Fresnel lens is replaced with a suitable spherical or aspherical lens. Again, the spherical or aspherical lens has focal length chosen such that it&#39;s focal point coincides with the focal point  250 . Also, differing working distances can be accommodated manually by providing a different detent positioner  211  for the lens  210  that will result in coincident foci at point  250 . 
     FIG. 9 shows a second exemplary embodiment of a light pattern controller  215  which includes a beam deflector  230  in accordance with this invention. The beam deflector  230  is a two-dimensional scanning galvanometer. To achieve illumination symmetry about the optical axis  212 , the swept pattern is made circular. Further, this circular pattern is created using two angular scanning galvanometers whose scan axes are orthogonal to each other. A circular pattern is created by the input drive signals (V x  and V y ) to each scanning galvanometer. The two scanning input waveforms are sinusoids described by: 
      V x =A x sin(2 πƒ x t+θ x ); and  (1) 
     
       
         V y =A y sin(2 πƒ y t+θ y ).  (2) 
       
     
     where: 
     θ x =phase angle of sinusoid V x  with respect to a reference sine wave (V x  is designed to follow the reference sine wave faithfully with zero phase difference); 
     θ y =phase angle of sinusoid V y  with respect to V x ; 
     ƒ x =angular scanning frequency of galvanometer X; and 
     ƒ y =angular scanning frequency of galvanometer Y. Additionally, to obtain a symmetric, circular pattern, the input waveforms must be controlled such that: 
     
       
         (θ x −θ y )=π/2, 3π/2  (3) 
       
     
     Also, the drive frequencies ƒ x  and ƒ y  are controlled to provide the proper number of circular sweep cycles per video field integration in the CCD of the camera  200 . A minimum execution of two whole sweep cycles per field integration will minimally assure meeting the Nyquist criteria of the camera  220 . Further, all sweep cycles per field integration should be whole numbers to ensure that interlaced fields produce spatially similar illumination patterns in assembled frames. The drive frequencies are controlled according to: 
     
       
         f x =f y   (4) 
       
     
     where: 
     
       
         f min ≦f i ≦f resonant   (5) 
       
     
     In the case of an RS  170  camera with interlaced fields, f min  is twice as fast as the overlap time period between odd and even fields. This overlap period is 16⅔ msec. Therefore, f min  would correspond to a sweep rate occurring at least 2 times within this period or every 8⅓ msec (120 Hz). Choice of the XY scanner and the inertia of each mirror restrict the upper limit, f resonant . Input of equivalent drive frequencies meets the final requirement for a symmetric, circular sweep pattern. 
     The amplitude of each waveform is also controlled based on the angle of incidence a which is desired by the user. Essentially, the waveform amplitudes are chosen such that: 
     
       
         A x =A y   (6) 
       
     
     where: 
     A i  represents the peak amplitude (or sweep circle radius) for each specific desired angle of illumination incidence α. This radius or amplitude is selectable within the mirror scan angle range ζ i , where−ζ max ≦ζ i ≦+ζ max . 
     As a result, the diameter of the circularly scanned pattern is controlled by the choice of waveform amplitudes. 
     In an exemplary embodiment of the invention, a lookup table which translates between the angle of incidence and the input voltage values to the scanning galvanometer is used. As discussed with the above parameters, illumination conditions selected by the user dictate the specific input settings to each scanner axis. 
     FIG. 10 shows another exemplary embodiment of a light pattern controller  315 . A light source  310  emits a diverging light stream which impinges upon the light pattern controller  315 . The light pattern controller  315  is a liquid crystal device. The liquid crystal device includes an array of addressable sectors which are controllable to block portions of the light from the light source  310  from impinging upon the collimator  340 . For example, a light ray  31  IA impinges upon the light pattern controller  315  and passes through to impinge and be collimated by the collimating element  340 . By contrast, a light ray  311 B impinges upon the light pattern controller  315  but is blocked to prevent the light ray  311 B from passing through and impinging upon the collimator  340 . Therefore, the liquid crystal shutter of the light pattern controller  315  controls the pattern of light from the light source  310  that impinges upon the collimator  340 . 
     It should be appreciated that the addressable sectors can be in any desired shape, such as a square pixel-like shape or a arcuate sector-like shape. 
     It should be understood that the liquid crystal device may also include an array of addressable pixels and may also operate in a reflective mode rather than the blocking mode described above. 
     It is to be understood that while the detailed description described light deflectors for projecting a prescribed pattern onto a collimating element in a serial manner that generation of a prescribed pattern may also be accomplished in a parallel manner. Two means to realize parallel pattern generation is with the use of addressable liquid crystal displays (LCDs) and addressable holographic light splitting elements. Any known or later developed structure for and/or method of directing a prescribed pattern onto a surface of a collimating element may be used. 
     It is also to be understood that while the detailed description described a beam deflector and a two-dimensional scanning galvanometer for projecting a prescribed pattern onto a collimating element that any known or later developed structure for and/or method of sweeping a pattern onto a surface of a collimating element may be used. 
     While the description set forth above refers generally to light being emitted from a light source having a solid state device, it should be understood that the invention may also utilize more conventional light sources such as a filament-type. Additionally, it should be understood that the light source of the invention may also emit radiation outside of the visible spectrum in useful regions capable of being sensed. Specifically, these spectral regions include the ultra-violet A and near infrared portions of the spectrum. 
     While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations are apparent to those skilled in the art. Accordingly, the embodiments of the invention as set forth above are intended to be illustrative and not limiting. Various changes may be made without departing from the spirit and scope of the invention.