Abstract:
A laser target sphere is used in conjunction with a laser scanner. The target sphere has an ideal lambertian reflectance appropriate for laser scanning systems facilitating the laser scanner finding the center of the target sphere. The target sphere includes an internal kinematic mount configured to concentrically mount the target sphere to a Spherical Mounted Retroreflector (SMR) providing a same center location of the two spheres. By adapting the target sphere to mount concentrically on the SMR, the laser scanner and target sphere system can use the same points defined for the SMR.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to precision measurements and in particular to laser target spheres. 
     Laser target spheres have become a very popular position measuring device. Laser tracking devices may be used to precisely measure the position of the center of the target sphere. However a desire is present for a target sphere which may be mounted to a second sphere and result in the two spheres having the same center point. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing a laser target sphere which is used in conjunction with a laser scanner. The target sphere has an ideal lambertian reflectance appropriate for laser scanning systems facilitating the laser scanner finding the center of the target sphere. The target sphere includes an internal kinematic mount configured to concentrically mount the target sphere to a Spherical Mounted Retroreflector (SMR) providing a same center location of the two spheres. By adapting the target sphere to mount concentrically on the SMR, the laser scanner and target sphere system can use the same points defined for the SMR. 
     In accordance with one aspect of the invention, there is provided a target sphere having an internal kinematic mount. The internal kinematic mount comprises a cavity in the target sphere containing three positioning spheres. The three positioning spheres are located in the target sphere to concentrically position the target sphere on a smaller sphere, preferably on a Spherical Mounted Retroreflector (SMR). 
     In accordance with one aspect of the invention, there is provided a target sphere having a magnet internally mounted to retain the target sphere on a Spherical Mounted Retroreflector (SMR). The magnet is positioned to attract but not touch the SMR, thus retaining the SMR against three positioning spheres to concentrically mount the target sphere on the SMR. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1A  is a top view of a scanning laser target sphere according to the present invention. 
         FIG. 1B  is a side view of the scanning laser target sphere according to the present invention. 
         FIG. 1C  is a bottom view of the scanning laser target sphere according to the present invention. 
         FIG. 2  is a cross-sectional view of the scanning laser target sphere according to the present invention taken along line  2 - 2  of  FIG. 1C . 
         FIG. 3  is a cross-sectional view of the scanning laser target sphere according to the present invention taken along line  2 - 2  of  FIG. 1C  carried on a Spherical Mounted Retroreflector (SMR). 
         FIG. 4A  is a top view of one of three positioning members according to the present invention. 
         FIG. 4B  is a side view of one of the three positioning members according to the present invention. 
         FIG. 4C  is a bottom view of one of the three positioning members according to the present invention. 
         FIG. 5A  is a cross-sectional view of one of the three positioning members according to the present invention taken along line  5 - 5  of  FIG. 4B . 
         FIG. 5B  is a cross-sectional view of one of the three positioning members according to the present invention taken along line  5 - 5  of  FIG. 4B  with an expanded post. 
         FIG. 6  shows a cross-sectional view of a hollowed out scanning laser target sphere according to the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     Where the terms “about” or “generally” are associated with an element of the invention, it is intended to describe a feature&#39;s appearance to the human eye or human perception, and not a precise measurement. The terms vertical and horizontal are with respect to the drawings, and a device rotated to different orientations is intended to come within the scope of the present invention. 
     A top view of a scanning laser target sphere  10  according to the present invention is shown in  FIG. 1A , a side view of the scanning laser target sphere  10  is shown in  FIG. 1B , a bottom view of the scanning laser target sphere  10  is shown in  FIG. 1C , and a cross-sectional view of the scanning laser target sphere  10  taken along line  2 - 2  of  FIG. 1C  is shown in  FIG. 2 . The scanning laser target sphere  10  includes a body  12  having an exterior as a truncated sphere  13  having a radius R 1  preferably between 1.75 and 8 inches and a truncation angle TA preferably less than 180 degrees, and more preferably between 116 degrees (for a 3.5 inch diameter scanner laser target sphere) and about 152 degrees (for an 8 inch diameter scanner laser target sphere). Preferably, the height H of the center of the scanner laser target sphere  10  above the base  36  is at least 0.92 inches, and more preferably between 0.92 inches and 0.98 inches, and most preferably 0.95 inches. The body  12  may be made from various materials suitable for laser scanning, and is preferably made from aluminum or titanium. The body  12  defines a recess  38  in the bottom of the body  12 , having a frusto conical portion  34 , then a cylindrical portion  32 , and a ceiling  30 . An annular ring surface  36  surrounds the annular opening  38 . 
     Three positioning members  18   a ,  18   b , and  18   c  threadedly reside in cavities  20  and reach down from the ceiling  30  into the cavity  38 . The positioning members  18   a ,  18   b , and  18   c  are preferably spaced 120 degrees apart and are vertically positioned in a common horizontal plane H. A magnet  14  threadedly resides in a cavity  16  in the ceiling  30  and reach down from the ceiling  30  into the cavity  38 . While the positioning members  18   a ,  18   b , and  18   c  and magnet  14  preferably threadedly engage the body  12 , those skilled in the art will recognize various way to attach the positioning members  18   a ,  18   b , and  18   c  and magnet  14  to the body, and a scanning laser target sphere  10  having the positioning members  18   a ,  18   b , and  18   c  and magnet  14  attached in other manners is intended to come within the scope of the present invention. 
     A second cross-sectional view of the scanning laser target sphere  10  taken along line  2 - 2  of  FIG. 1C  carried on a Spherical Mounted Retroreflector (SMR)  40  is shown in  FIG. 3 . Those skilled in the art will recognize an SMR as a commonly used reflective target, having a radius R 2  of preferably 0.75 inches. The positioning members  18   a ,  18   b , and  18   c  are configured to concentrically position the scanning laser target sphere  10  on the SMR  40 , thereby taking advantage of the positioning characteristics of the SMR  40 . Thus, determining the position of the scanning laser target sphere  10  also determines the position of the SMR  40 . The magnet  14  retains the scanning laser target sphere  10  on the SMR  40  but is adjusted to avoid touching the SMR  40  which resides against the three positioning members  18   a ,  18   b , and  18   c.    
     A top view of the positioning member  18   a  is shown in  FIG. 4A , a side view of the positioning member  18   a  is shown in  FIG. 4B , and a bottom view of the positioning member  18   a  is shown in  FIG. 4C . The positioning members  18   b  and  18   c  are of the same design. The positioning member  18   a  includes a spherical portion  42  and threaded cylindrical post  44 . The spherical portion  42  is preferably attached to the post  44  by brazing  46 . A non-round, preferably hexagonal, passage  48  aligned with the post  44  extends through the spherical portion  42 . The passage  48  is configured to accept a tool, for example an Allen wrench, to rotate the position member to adjust the depth of the positioning member in the cavity  38  to concentrically position the scanning laser target sphere  10  on an SMR  40 . 
     A cross-sectional view of the positioning member  18   a  taken along line  5 - 5  of  FIG. 4B  is shown in  FIG. 5A  and a second cross-sectional view of the positioning member  18   a  taken along line  5 - 5  of  FIG. 4B  with an expanded post  44  is shown in  FIG. 5B . The post  44  has a hollow threaded interior  50  having a narrowing end  50   a  opposite to the spherical portion  48 . The post  44  further includes at least one lengthwise cut  56 , and preferably two centered lengthwise cuts  56 . A ball  52  resides between the narrowing end  50   a  and a set screw  54 . A tool may be inserted through the passage  48  into a shaped recess  49  (preferably a hexagonal cross-section) to advance the set screw  54  and the ball  50  against the narrowed end  50   b . The advancing of the ball  52  expands the post  44  to retain the position of the positioning member  18   a  after adjustment. 
     A cross-sectional view of a hollowed out scanning laser target sphere  12   a  is shown in  FIG. 6 . The hollowed out scanning laser target sphere  12   a  is lighter in weight and provides advantages in larger diameter laser target spheres. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.