Abstract:
An apparatus for calibrating a laser projection device can be used to establish the deviation of known measurement points from an approved digital model or reference condition. The apparatus includes a target having a reflective portion and a mask surrounding the reflective portion. The mask includes a material that changes appearance when excited by a laser. This target eliminates or minimizes user subjectivity in laser projection calibration.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to laser projection technology and more particularly (but not exclusively) to calibrating laser projection devices.  
       BACKGROUND OF THE INVENTION  
       [0002]     Laser projection technology is in widespread use as a manufacturing aid to determine the presence or absence of features in a manufactured article. Laser projection can be useful on a factory floor to support precision assembly and manufacturing. Its usefulness, however, is contingent on accurate calibrating and positioning of the laser beam. Calibration is typically subject to an operator&#39;s determination as to whether or not the beam is at a desired location. Calibration thus can be influenced by operator bias.  
       SUMMARY OF THE INVENTION  
       [0003]     In one implementation, the invention is directed to an apparatus for use with a laser projection device. The apparatus includes a target having a reflective portion and a mask surrounding the reflective portion. The mask includes a material that changes appearance when excited by a laser.  
         [0004]     In another implementation, the invention is directed to a method of using a laser projection device relative to an article. The laser projection device and one or more targets are positioned relative to the article. A laser is projected from the projection device toward one of the one or more targets. If the beam changes an appearance of a material surrounding a reflective portion of the one target, the method includes repositioning at least one of the one target and the laser.  
         [0005]     In yet another implementation, the invention is directed to a laser projection system including a laser projection device and one or more targets for use with the laser projection device. The system includes a calibration wall having a wall surface and a plurality of target positioning stages affixed to the wall surface. Each positioning stage is configured to receive a target and operable to reposition the received target relative to the wall surface.  
         [0006]     The features, functions, and advantages can be achieved independently in various embodiments of the present inventions or may be combined in yet other embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a block diagram of a system used in relation to articles of manufacture in accordance with one implementation of the invention;  
         [0009]      FIG. 2A  is a side view of a target in accordance with one implementation of the invention;  
         [0010]      FIG. 2B  is a frontal view of the target shown in  FIG. 2A , taken in the plane of the line  2 B- 2 B indicated in  FIG. 2A ;  
         [0011]      FIG. 3  is a perspective view of a target in accordance with one implementation of the invention;  
         [0012]      FIG. 4  is a frontal view of a calibration wall in accordance with one implementation of the invention; and  
         [0013]      FIG. 5  is a perspective view of a positioning stage and target mounted thereon in accordance with one implementation of the invention.  
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0014]     The following description of various embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. The present invention, in some configurations, is directed to an apparatus for use with a laser projection device. The apparatus includes a target having a mask that covers a portion of the target while exposing a reflective portion of the target. The mask includes a material that changes appearance when excited by a laser. It should be noted that the invention can be practiced relative to many different target types, sizes, shapes and uses.  
         [0015]     A laser projection system used in relation to articles of manufacture in accordance with one implementation of the invention is indicated generally in  FIG. 1  by reference number  20 . The system  20  may be used, for example, to project illuminated lines onto the surface of an article  24 . The illuminated lines may be used to guide in configuring the article  24  with other components to produce a finished product. Additionally or alternatively, the system  20  could be used in various applications, for example, to indicate where component parts are to be cut or trimmed.  
         [0016]     The system  20  includes a laser projection device  28 , a processor (not shown) for controlling the projection device  28 , and one or more reflective targets  32  for use in aligning the projection device  28  relative to the article  24 . The target(s) may be mounted, for example, to a support for the article  24  or to another structure (not shown). Although one target  32  is shown in  FIG. 1 , generally six or more targets are used in laser projection applications. Before a laser projection application is performed, the laser projection device  28  may be aimed at each of the target(s) to obtain a set of positional coordinates for locating the article  24 . The coordinates are input to the projection device processor for subsequent use in directing the projection device  28  to project a laser beam relative to the article  24 .  
         [0017]     The target  32  is shown in greater detail in  FIGS. 2A and 2B . The target  32  includes a mounting stem  36  and body  40  made, for example, of metal. A surface  44  of the body is configured to reflect a laser. Target configurations are contemplated in which various mounting arrangements are provided. Such arrangements include using an x-y positioning stage and calibration wall for precise target repositioning as further described below. In some configurations, targets and/or target surfaces may be provided on a roll of tape, and the tape may be applied to an object as may be desired. Configurations also are contemplated in which no mounting arrangements are provided.  
         [0018]     Referring to  FIG. 2B , the surface  44  includes a central reflective portion  48 . The reflective portion  48  is, for example, part of a retro-reflective substrate  52  covering at least part of the surface  44 . A mask  56  covering part of the substrate  52  surrounds and exposes the reflective portion  48 . The mask  56  includes a material that changes appearance when excited by a laser. For example, the mask  56  may include a fluorescent material that turns from an orange to a yellow color when excited by a green laser. In some embodiments, orange fluorescent tape is used. In some other embodiments, orange fluorescent plastic and/or orange fluorescent paint could be used. In various configurations, various materials could be used which change color or otherwise change appearance when excited by a laser.  
         [0019]     One exemplary target is a modified retroflective target No. TSOR by Hubbs Machine &amp; Manufacturing, Inc. of Cedar Hill, Mo. The target body  40  is approximately 12 millimeters in length and diameter and the stem  36  is approximately 6 millimeters in diameter. Mask overlay inner diameter  60  and outer diameter  64  are application-dependent.  
         [0020]     It can be appreciated that there are many different ways to configure a target, a reflective surface and a mask. In some configurations, a mask may cover areas of reflective substrate to greater or lesser degrees than as described in the present example. In some configurations, a mask may not cover any reflective substrate. In some configurations, an appearance-changing surface could be partially overlaid by a reflective surface. Accordingly, it should be noted that the term “mask” is used herein to describe an appearance-changing surface which does not necessarily cover any part of a reflective surface. Additionally or alternatively, a reflective surface may not be centrally positioned relative to the target in some configurations but may be oriented differently to accommodate various aspects of various applications. Further, a target surface could be provided in other than in circular forms.  
         [0021]     Referring to  FIG. 1 , when the system  20  is in use, the laser projection device  28  is positioned relative to the article  24  and target(s)  32 . In calibrating the system  20 , a laser is projected toward a target  32 . If the laser is correctly aligned when it strikes the target, it strikes the central reflective portion  48 . If the beam strikes accurately, the mask  56  remains unexcited by the beam. If the laser beam strikes off-center relative to the target reflective portion and strikes an area of the mask  56 , the mask changes appearance in the stricken area. The area of appearance change can indicate a direction in which to reposition the laser beam.  
         [0022]     A perspective view of another exemplary configuration of a target is indicated generally by reference number  100  in  FIG. 3 . The target  100  includes a surface  104  configured to reflect a laser. The surface  104  includes a central reflective portion  108 . The reflective portion  108  is, for example, part of a retro-reflective substrate  112  covering at least part of the surface  104 . A mask  116  covering part of the substrate  112  surrounds and exposes the reflective portion  108 . The mask  116  includes a material that changes appearance when excited by a laser. For example, the mask  116  may include a fluorescent material that turns from an orange to a yellow color when excited by a green laser.  
         [0023]     The mask  116  includes one or more annular areas  120 , one of which is shown in the present embodiment. The annular area  120  has an inner diameter  124  and outer diameter  128  that may be configured for use with a particular laser beam thickness. For example, the inner diameter  124  may indicate a nominal diameter of an exciting laser beam and the outer diameter  128  may indicate a maximum position error of the laser beam relative to the target  100 . In one implementation, a green laser beam may be projected in a ring  132  (shown in dashed lines in  FIG. 3 ) which, if accurately projected, would encircle the reflective portion  108 . If the laser strikes the target  100  off-center, portions of the mask  116  near the diameters  124  and/or  128  may be excited to a yellow color and part of the reflective portion  108  may reflect the green color of the laser. For example, as shown in  FIG. 3 , areas  136  are excited to yellow and an area  140  of the reflective portion  108  reflects as green. The target  100  may then be moved, e.g., as further described below, to center the beam on the reflective portion  108 . When the beam is centered, depending on the beam width, the reflective portion  108  no longer reflects the laser and areas near one or both of the diameters  124  and  128  fluoresce yellow in complete circles. It can be appreciated that mask diameters could be denoted and calibrated in a laser projection device in various ways to indicate various degrees of error in beam placement.  
         [0024]     One exemplary target mounting arrangement for use, e.g., in calibrating a laser project system is indicated generally in  FIG. 4  by reference number  200 . A calibration wall  204  has a wall surface  208  and a plurality of target positioning stages  212  affixed to the wall surface  208 . Each positioning stage  212  is configured to receive a target  214  and is operable to reposition the received target  214  relative to the wall surface  208 .  
         [0025]     A positioning stage  212  is shown in greater detail in  FIG. 5 . The stage  212  has a base  216  attachable to the wall surface  208 . A platform  220  is adjustable in at least two orthogonal directions by means of a pair of micrometers  224 . The platform  220  includes one or more sockets  228  into which a target  214  may be mounted. As shown in  FIG. 5 , a single target  214  is mounted in a center socket  232 .  
         [0026]     To calibrate a laser projection device, a plurality of positioning stages  212  are placed on the calibration wall surface  208 . A target  214  may be mounted in a center socket  232  of each of the positioning stages  212 . In some implementations, more than one target  214  may be mounted on one or more of the stages  212 . Position coordinates for each of the targets  214  are entered into the laser projection device. When a target  214  is excited by the device as previously described with reference to  FIGS. 1, 2A ,  2 B and  3 , it is determined whether the beam is in alignment with the target  214 .  
         [0027]     If an alignment adjustment is to be made, the positioning stage platform  220  upon which the target  214  is mounted is moved in one or more directions to move the target  214  relative to the calibration wall  204 . Because micrometers  224  are used to move the target  214 , adjustment values are available from the micrometers  224  and can be entered into the laser projection device. In such manner, the position coordinates for the repositioned target can be adjusted to reflect the repositioning. The foregoing process may be repeated for each of the targets  214  mounted on the calibration wall to calibrate the laser projection device.  
         [0028]     The foregoing target and mask can be configured to indicate whether a laser projection device is projecting within a predetermined tolerance. The target makes it possible for a metrology inspector to tell at a glance whether or not a projected laser beam is at a location programmed in a digital part file. Inspector subjectivity in the calibration process is eliminated or minimized. In implementations in which the foregoing calibration wall is used, the ability to move targets and to update target positional coordinates with data describing relative target movement simplifies and expedites calibration. Using configurations of the invention can reduce labor time for laser projection calibration and thus can reduce costs.  
         [0029]     While various preferred embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the inventive concept. The examples illustrate the invention and are not intended to limit it. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.