Patent Publication Number: US-10783659-B1

Title: Hole location targets and measurement systems, and methods for measuring a location of a hole

Description:
FIELD 
     The present application relates to the field of hole location targets, hole location measurement systems, and methods for measuring a location of a hole. 
     BACKGROUND 
     Touch-based coordinate measurement machines typically use a stylus to sweep an inside surface of a hole of a workpiece to determine a centerline of the hole, which takes significant time. Also, articles having holes to be measured by this technique are typically specifically designed to permit for insertion of and sweeping by a stylus of a touch-based coordinate measurement machine, thus restricting freedom of design. 
     Accordingly, those skilled in the art continue with research and development in the field of hole location targets, hole location measurement systems, and methods for measuring a location of a hole. 
     SUMMARY 
     According to a first embodiment, a hole location target includes a self-centering insert having a centerline and an optical target attached to the self-centering insert at a fixed position relative to the centerline of the self-centering insert. The optical target includes a two-dimensional pattern thereon. 
     According to the first embodiment, a hole location measurement system includes a hole location target, a camera system, and a computer system. The hole location target includes a self-centering insert having a centerline and an optical target attached to the self-centering insert at a fixed position relative to the centerline of the self-centering insert, in which the optical target includes a two-dimensional pattern thereon. The camera system is configured to capture images of the two-dimensional pattern on the optical target. The computer system is configured to measure three-dimensional locations of features of the two-dimensional pattern on the optical target and to extract a location of a cylinder axis of the cylinder surface geometry. 
     According to the first embodiment, a method for measuring a location of a hole includes centering an insert within a hole having a centerline. The optical target includes a two-dimensional pattern thereon at a fixed position relative to the centerline of the insert. The method further includes capturing images of the two-dimensional pattern on the optical target, measuring three-dimensional locations of features of the two-dimensional pattern on the optical target, and extracting a location of the centerline of the insert based on the three-dimensional locations of features of the two-dimensional pattern on the optical target and the fixed position of the optical target relative to the centerline of the insert. 
     According to a second embodiment, a hole location target includes a self-centering insert having a centerline and an optical target attached to the self-centering insert at a fixed position relative to the centerline of the self-centering insert. The optical target includes a light-emitting display. The light-emitting display includes a two-dimensional pattern thereon. 
     According to the second embodiment, a hole location measurement system includes a hole location target, a camera system, and a computer system. The hole location target includes a self-centering insert having a centerline and an optical target attached to the self-centering insert at a fixed position relative to the centerline of the self-centering insert. The optical target includes a light-emitting display having a two-dimensional pattern thereon. The camera system is configured to capture images of the two-dimensional pattern of the optical target. The computer system is configured to control modification of the two-dimensional pattern of the optical target and to determine three-dimensional coordinates of the centerline of the self-centering insert from the images of the two-dimensional pattern of the optical target. 
     According to the second embodiment, a method for measuring a location of a hole includes centering an insert within a hole having a centerline. An optical target is attached to the insert at a fixed position relative to the centerline of the insert. The optical target includes a light-emitting display having a two-dimensional pattern thereon. The method further includes capturing images of the two-dimensional pattern of the optical target, modifying the two-dimensional pattern of the optical target; and capturing images of the modified two-dimensional pattern of the optical target. 
     According to a third embodiment, a hole location target includes a self-centering insert having a centerline and a laser beam emitter attached to the self-centering insert. The axis of the emitted laser beam is concentric to the centerline of the self-centering insert. 
     According to the third embodiment, a hole location measurement system includes a hole location target, an optical system, and a computer system. The hole location target includes a self-centering insert having a centerline and a laser beam emitter attached to the self-centering insert, wherein the axis of the emitted laser beam is concentric to the centerline of the self-centering insert. The optical system senses the location of the emitted laser beam at multiple distances from the laser beam emitter. The computer system is configured to determine three-dimensional coordinates of the centerline of the self-centering insert from the sensed locations of the emitted laser beam. 
     According to the third embodiment, a method for measuring a location of a hole includes centering an insert within a hole having a centerline and emitting a laser beam from a laser beam emitter attached to the insert. The axis of the emitted laser beam is concentric to the centerline of the insert. The method further includes sensing the location of the emitted laser beam at multiple distances from the laser beam emitter and determining three-dimensional coordinates of the centerline of the self-centering insert from the sensed locations of the emitted laser beam. 
     Other embodiments of the disclosed hole location targets, hole location measurement systems, and methods for measuring a location of a hole will become apparent from the following detailed description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first exemplary hole location target according to the first embodiment of the present description in an assembled state. 
         FIG. 2  is a perspective view of a second exemplary hole location target according to the first embodiment of the present description in an assembled state. 
         FIG. 3  is an exploded perspective view of the hole location target of  FIG. 1 . 
         FIG. 4A  is cross-sectional view of the hole location target of  FIG. 1  inserted into a hole of a workpiece in a radially contracted state. 
         FIG. 4B  is cross-sectional view of the hole location target of  FIG. 4A  in a radially expanded state. 
         FIG. 5  is a representation of an exemplary hole location measurement system according to the first embodiment of the present description. 
         FIG. 6  is a flow diagram of an exemplary method for measuring a location of a hole of a workpiece according to the first embodiment of the present description. 
         FIG. 7  is a perspective view of a first exemplary hole location target according to a second embodiment of the present description in an assembled state. 
         FIG. 8  is a perspective view of a second exemplary hole location target according to the second embodiment of the present description in an assembled state. 
         FIG. 9  is an exploded perspective view of the hole location target of  FIG. 7 . 
         FIG. 10A  is cross-sectional view of the hole location target of  FIG. 7  inserted into a hole of a workpiece in a radially contracted state. 
         FIG. 10B  is cross-sectional view of the hole location target of  FIG. 10A  in a radially expanded state. 
         FIG. 11  is a representation of an exemplary hole location measurement system according to the second embodiment of the present description. 
         FIG. 12  is a flow diagram of an exemplary method for measuring a location of a hole of a workpiece according to the second embodiment of the present description. 
         FIG. 13  is a perspective view of an exemplary hole location target according to a third embodiment of the present description in an assembled state. 
         FIG. 14  is an exploded perspective view of the hole location target of  FIG. 13 . 
         FIG. 15A  is cross-sectional view of the hole location target of  FIG. 13  inserted into a hole of a workpiece in a radially contracted state. 
         FIG. 15B  is cross-sectional view of the hole location target of  FIG. 15A  in a radially expanded state. 
         FIGS. 16A and 16B  are representations of an exemplary hole location measurement system according to the third embodiment of the present description. 
         FIG. 17  is a flow diagram of an exemplary method for measuring a location of a hole of a workpiece according to the third embodiment of the present description. 
         FIG. 18  is a flow diagram of an aircraft manufacturing and service methodology. 
         FIG. 19  is a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1, 2, 3, 4A, 4B, 5, and 6  relate to hole location targets, hole location measurement systems, and methods for measuring a location of a hole according to a first embodiment of the present description.  FIGS. 7, 8, 9, 10A, 10B, 11, and 12  relate to hole location targets, hole location measurement systems, and methods for measuring a location of a hole according to a second embodiment of the present description.  FIGS. 13, 14, 15A, 15B, 16A, 16B and 17  relate to hole location targets, hole location measurement systems, and methods for measuring a location of a hole according to a third embodiment of the present description. 
     The hole location targets according to the first, second, and third embodiments each include a self-centering insert for inserting into a hole of a workpiece. It will be understood that the self-centering inserts of the first, second, and third embodiments can include any structures capable of inserting into the hole and self-centering a centerline of the self-centering insert to a respective centerline of the hole, such as a radially expandable bushing as shown in the illustrated examples. 
     In the illustrated examples, the hole location targets of the first and second embodiments are described below to include a radially expandable bushing in the form of expandable bellows, and the hole location target of the third embodiment is described below to include a radially expandable bushing in the form of an expandable collet. However, it will be understood that the hole location targets of the first and second embodiments can include a radially expandable bushing in the form of an expandable collet, and the hole location target of the third embodiment can include a radially expandable bushing in the form of an expandable bellows. 
     The hole location targets according to the first and second embodiments each include an optical target attached to the self-centering insert at a fixed position relative to the centerline of the self-centering insert. It will be understood that the optical targets of the first and second embodiments can have any shapes. In the illustrated examples, the optical target of the first embodiment are described below to include a cylindrical exterior surface, and the optical target of the second embodiment is described below to include flat rectangular surface. However, it will be understood that the optical target of the first embodiment can include a flat rectangular surface, and the optical target of the second embodiment can include a cylindrical exterior surface. 
       FIG. 1  is a perspective view of a first exemplary hole location target according to the first embodiment of the present description in an assembled state.  FIG. 2  is a perspective view of a second exemplary hole location target according to the first embodiment of the present description in an assembled state.  FIG. 3  is an exploded perspective view of the hole location target of  FIG. 1 .  FIG. 4A  is cross-sectional view of the hole location target of  FIG. 1  inserted into a hole of a workpiece W in a radially contracted state.  FIG. 4B  is cross-sectional view of the hole location target of  FIG. 4A  in a radially expanded state. 
     Referring to  FIGS. 1, 2, 3, 4A, and 4B , the hole location target  10  includes a first end  101  configured to be inserted into a hole H of a workpiece W and a second end  102  opposite to the first end  101 . 
     The hole location target  10  includes a self-centering insert  110  and an optical target  120  attached to the self-centering insert  110 . The self-centering insert  110  is positioned near the first end  101  and the optical target  120  is positioned near the second end  102  such that the self-centering insert  110  can be inserted into the hole H of the workpiece and the optical target  120  can remain outside of the hole H of the workpiece W. 
     The self-centering insert  110  has a centerline  111  and the optical target  120  is at a fixed position relative to the centerline  111  of the self-centering insert  110 . 
     The self-centering insert  110  is configured to be inserted into the hole H of the workpiece W and to be self-centered such that the centerline  111  of the self-centering insert  110  is positioned coaxially with a respective centerline C of the hole H of the workpiece W. By centering the centerline  111  of the self-centering insert  110  to be coaxial with the centerline C of the hole H of the workpiece W, a method that measures a location of the centerline  111  of the self-centering insert  110  can be employed to determine a location of the centerline C of the hole H of the workpiece W. Furthermore, by making the optical target  120  to be at a fixed position relative to the centerline  111  of the self-centering insert  110 , a method that measures a location of the optical target  120  can be employed to determine the location of the centerline  111  of the self-centering insert  110  and, thus, to determine the location of the centerline C of the hole H of the workpiece W. 
     In an aspect, the optical target  120  has a cylindrical exterior surface  121  that is concentric to the centerline  111  of the self-centering insert  110 . By making the cylindrical exterior surface  121  to be concentric to the centerline  111  of the self-centering insert  110 , a method that measures a location of the cylindrical exterior surface  121  can be employed to determine the location of the centerline  111  of the self-centering insert  110  and, thus, to determine the location of the centerline C of the hole H of the workpiece W. 
     In the illustrated example, the self-centering insert  110  of the first embodiment includes a radially expandable bushing  112 . It will be understood that the radially expandable bushing  112  can include any tubular structure capable of inserting into the hole H of the workpiece W and capable of radially expanding to self-center the centerline  111  of the self-centering insert  110  to the centerline C of the hole H of the workpiece W. In the illustrated example, the radially expandable bushing  112  takes the form of an expandable bellows  114 . In an alternative example, the radially expandable bushing  112  can take the form of an expandable collet such as is described below with respect to the third embodiment. 
     The expandable bellows  114  of the present description is a tubular structure in which an axial contraction of the expandable bellows  114  translates into a radial expansion of expandable bellows  114  and an axial expansion of the expandable bellows  114  translates into a radial contraction of expandable bellows  114 . In the illustrated example, the expandable bellows  114  includes a first bellows end  115  and a second bellows end  116  and one or more radial ridges  118  between the first bellows end  115  and the second bellows end  116 . By axially contracting the expandable bellows  114 , the one or more radial ridges  118  expand radially. By axially expanding the expandable bellows  114 , the one or more radial ridges  118  contract radially. 
     As shown in  FIG. 4A , by axially expanding the expandable bellows  114 , the one or more radial ridges  118  contract radially, thereby permitting the expandable bellows  114  to be inserted into a hole H of a workpiece W. As shown in  FIG. 4B , after inserting the expandable bellows into the hole H of the workpiece W, the expandable bellows  114  can be axially contracted to radially expand one or more radial ridges  118 . The one or more radial ridges  118  then contact the walls defining the hole H of the workpiece W, thus causing a self-centering of the centerline  111  of the expandable bellows  114  to the respective centerline C of the hole H of the workpiece W. 
     In the illustrated example, the optical target  120  is attached to the self-centering insert  110  such that the cylindrical exterior surface  121  is concentric to the centerline  111  of the self-centering insert  110 . By way of example, the optical target  120  can be fixedly positioned to the self-centering insert  110  such that a position of the optical target is fixed with respect to a position of centerline  111  of the self-centering insert  110 . The positioning of the optical target  120  with respect to the position of centerline  111  of the self-centering insert  110  can be permanent. In an example, the self-centering insert  110  and the optical target  120  can be combined as a monolithic body. For improved precision, the self-centering insert  110  and the optical target  120  can be unitary formed together as a monolithic body by one or more processes, such as casting, molding, and additive manufacturing. In an aspect, the cylindrical exterior surface  121  of the optical target  120  has a surface cylindricity of 5 μm or less (or a tolerance of concentricity of the cylindrical surface to the centerline that is within 5 μm) for improved precision of determining the centerline C of the hole H of the workpiece W. 
     In the illustrated example, the self-centering insert  110  includes a bore  117  for accommodating a compression device  130 . The compression device  130  is configured to axially contract the expandable bellows  114 . In the illustrated example, the compression device  130  includes a bolt  140  and a nut  160 . 
     As shown, the bolt  140  has a first bolt end  141  and a second bolt end  142 . The bolt  140  includes a bolt shaft  143  positioned at the first bolt end  141  of the bolt  140  and a bolt head  144  positioned at the second bolt end  142  of the bolt  140 . The bolt shaft  143  includes a first shaft end  145  and a second shaft end  146 . Exterior threads  147  are positioned at the first shaft end  145  of the bolt shaft  143 , and the bolt head  144  is joined to the second shaft end  146 . The bolt head  144  includes a first bolt head end  148  and a second bolt head end  149 . A first bolt face  151  is positioned at the first bolt head end  148 , a second bolt face  152  is positioned at the second bolt head end  149 , and an outer bolt head surface  150  is positioned between the first bolt head end  148  and the second bolt head end  149 . The outer bolt head surface  150  can take the form of a plurality of faces extending around a circumference of the bolt head  144  to improve retention of the bolt  140  within the bore  117  of the self-centering insert  110 . 
     As shown, the nut  160  has a first nut end  161  and a second nut end  162 . A first nut face  163  is positioned at the first nut end  161 , a second nut face  164  is positioned at the second nut end  162 , and an outer nut surface  165  is positioned between the first nut end  161  and the second nut end  162 . In an aspect, the outer nut surface  165  can include a nut gripping surface  166  configured to improve a grip of the nut  160 . As shown, the nut gripping surface  166  can take the form of a knurled surface for manually torqueing of the nut  160 . Alternatively, the nut gripping surface  166  can take other forms, such as the of a plurality of faces for torqueing the nut  160  with a tool. The nut bore  167  passes through the nut  160  from the first nut face  163  to the second nut face  164 , and the nut bore  167  includes interior threads  168  configured to engage with the exterior threads  147  of the bolt  140 . 
     As shown, the bolt shaft  143  passes through bore  117  at a bellows end surface  119  at the first end  101  of the self-centering insert  110  to target end surface  124  at the second end  102  of the optical target  120 , and the exterior threads  147  of the bolt  140  engage with the interior threads  168  of the nut  160 . The first nut face  163  engages with the optical target  120 , and the first bolt face  151  engages with the first bellows end  115  of the expandable bellows  114 . Thus, the bolt  140  and nut  160  form a compression device  130  configured to contract the expandable bellows  114  by turning the nut  160 . However, the compression device  130  is not limited to the above-described example. In another example, the position of the bolt  140  and nut  160  can be reversed. In yet another example, the compression device  130  may take the form of a rachet or any other compression device configured to axially contract the expandable bellows  114 . 
     In the illustrated example, the hole location target  10  includes a collar  103 . The collar  103  includes a first collar end surface  104 , a second collar end surface  105 , and an outer collar surface  106  positioned between the first collar end surface  104  and a second collar end surface  105 . In an aspect, the outer collar surface  106  can include a collar gripping surface  107  configured to improve a grip of the collar  103 . As shown, the collar gripping surface  107  can take the form of a knurled surface for manually torqueing of the collar  103 . Alternatively, the collar gripping surface  107  can take other forms, such as the of a plurality of faces for torqueing the collar  103  with a tool. 
     The optical target  120  includes a two-dimensional pattern thereon  122 . In one example, the two-dimensional pattern thereon  122  can be a plurality of a pattern of dots  123  disposed around the cylindrical exterior surface  121  of the optical target  120 . In an aspect, the pattern of dots  123  can be unique such that the pattern of dots  123  on an optical target  120  of a hole location target  10  is different from the pattern of dots  123  on an optical target  120  of another hole location target  10 . In another example, the two-dimensional pattern thereon  122  can be a plurality of a two-dimensional barcodes  125  disposed around the cylindrical exterior surface  121  of the optical target  120 . In an aspect, the two-dimensional barcode  125  can be unique such that the two-dimensional barcode  125  on an optical target  120  of a hole location target  10  is different from the two-dimensional barcode  125  on an optical target  120  of another hole location target  10 . 
     In an aspect, the two-dimensional pattern  122  can have a predetermined calibration with respect to the centerline  111  of the self-centering insert  110 , such as a predetermined six degree of freedom calibration with respect to the centerline  111  of the self-centering insert  110 . The predetermined calibration of the two-dimensional pattern  122  can be used to precisely determine the centerline  111  of the self-centering insert  110  based on a determined position of the two-dimensional pattern  122 . 
     In an example, the two-dimensional pattern  122  includes a retroreflective material. By way of including a retroreflective material in the two-dimensional pattern  122 , images of the two-dimensional pattern  122  may be captured by emitting light to the retroreflective material of the two-dimensional pattern  122  on the cylindrical exterior surface  121  of the optical target  120  and capturing light reflected by the retroreflective material. 
       FIG. 5  is a representation of an exemplary hole location measurement system according to the first embodiment of the present description. 
     The hole location measurement system  100  of the first embodiment of the present description includes the hole location target  10  as described above, a camera system  40 , and a computer system  50  in communication with the camera system  40 . As shown, the camera system  40  is configured to capture images of the two-dimensional pattern  122  on the optical target  120 . As shown, the computer system  50  is configured to measure three-dimensional locations of features of the two-dimensional pattern  122  on the optical target  120  and to extract a location of a cylinder axis of the cylinder surface geometry. In an aspect, the computer system is configured to measure three-dimensional locations of features of the two-dimensional pattern on a cylindrical exterior surface of the optical target, to fit the three-dimensional locations of the features of the two-dimensional pattern to a cylinder surface geometry, and to extract a location of a cylinder axis of the cylinder surface geometry. The computer system  50  may be separate from or integrated with the camera system  40 . 
     In an aspect, hole location measurement system  100  includes a plurality of the hole location targets  10 . In another aspect, the camera system  40  is configured to capture images of the two-dimensional patterns  122  of the plurality of the hole location targets  10 . In yet another aspect, a single image captured by the camera system  40  includes the two-dimensional patterns  122  of the plurality of the hole location targets  10 . Thus, by capturing the two-dimensional patterns  122  of the plurality of the hole location targets  10  in a single image, the hole location measurement system  100  enables for single camera, single shot measurements of multiple holes at the same time. 
     In an aspect, the camera system  40  is a three-dimensional optical scanner. In another aspect, the camera system is a portable three-dimensional optical scanner. Alternatively, the three-dimensional optical scanner may be of a type supported on an articulating arm. 
     As illustrated, the portable three-dimensional optical scanner is shown as a stereo camera-styled scanner, having a pair of spaced lenses configured to acquire real-time data from a plurality of poses, utilizing a grid style coordinate system to generate and transfer  3 -D images. 
     In yet another aspect, the portable three-dimensional optical scanner includes an inertial navigation system. The inertial navigation system contained within the portable three-dimensional optical scanner provides a fixed point of reference, relative to an X-Y-Z set of common coordinates on which each scanned pose is based, irrespective of operator positioning of the physical scanner device. Thus, the angle and timing of each pose, i.e. orientation of the scanner in space and time relative to the target, is assured via the inertial navigation system to have a common frame of reference. 
       FIG. 6  is a flow diagram of an exemplary method for measuring a location of a hole H of a workpiece W according to the first embodiment of the present description. 
     The method  1000  includes, at block  1002 , centering an insert within a hole H having a centerline C. The insert can be the self-centered insert  110  or can be a different insert that is centered by any external means. 
     An optical target  120  is attached to the insert at a fixed position relative to the centerline  111  of the self-centering insert  110 . The optical target  120  includes a two-dimensional pattern  122  thereon. 
     The method  1000  further includes, at block  1004 , capturing images of the two-dimensional pattern  122  on the optical target  120 . The images can be captured by the camera system  40  as described above. In an aspect, the step of capturing images, at block,  1004 , includes emitting light to a retroreflective material of the two-dimensional pattern  122  on the optical target  120  and capturing light reflected by the retroreflective material. 
     The method  1000  further includes, at block  1006 , measuring three-dimensional locations of features of the two-dimensional pattern  122  on the optical target  120 , at block  1008 , extracting a location of the centerline  111  of the self-centering insert  110  based on the three-dimensional locations of features of the two-dimensional pattern  122  and the fixed position of the optical target  120  relative to the centerline  111  of the self-centering insert  110 . Each of these steps can be performed by the camera system  40 , the computer system  50 , or the camera system  40  integrated with the computer system  50 . 
     The step  1006  of measuring three-dimensional locations of features of the two-dimensional pattern  122  on the optical target  120  is performed by analysis of the of the images captured by the camera system  40 , to identify the two dimensional pattern of the optical target within the acquired image and to determine distance relative to the optical target based on a measure of target features within the image. 
     In an example, measuring three-dimensional locations of features of the two-dimensional pattern  122  on the optical target  120  includes measuring three-dimensional locations of dot centroids of a pattern of dots  123  of the two-dimensional pattern  122  shown in  FIG. 1 . Each dot of the pattern of dots  123  has a centroid which can be determined from the images captured by the camera system  40 , and each centroid has a specific three-dimensional location. Thus, by measuring the three-dimensional locations of each dot centroid as captured by the camera system  40 , a plurality of precise three-dimensional locations on the optical target  120  can be found. 
     In another example, measuring three-dimensional locations of features of the two-dimensional pattern  122  on the optical target  120  includes measuring three-dimensional locations of intersections of a two-dimensional barcode  125  of the two-dimensional pattern  122  shown in  FIG. 2 . Each line of the two-dimensional barcode  125  defines a one-dimensional vector in three-dimensional space, which can be determined from the images captured by the camera system  40 , and the intersection of two lines of the two-dimensional barcode  125  defines a specific three-dimensional location. Thus, by measuring the three-dimensional locations of intersections of a barcode pattern as captured by the camera system  40 , a plurality of precise three-dimensional locations on the optical target  120  can be found. 
     The step  1008  of fitting the three-dimensional locations of the features of the two-dimensional pattern  122  to a cylinder surface geometry can be performed by, for example, calculating a best fit of the three-dimensional locations of the features to a cylinder surface geometry. Thus, the plurality of precise three-dimensional locations on the optical target  120  can be used to accurately find a cylinder surface geometry of the optical target  120 . 
     The step  1010  of extracting a location of a cylinder axis of the cylinder surface geometry can be performed by, for example, calculating a best fit of a cylinder axis to the cylinder surface geometry. By extracting the location of the cylinder axis, the extracted cylinder location of the cylinder axis can be precisely equated to a centerline of the hole H of the workpiece W. 
     In an aspect, the method  1000  further includes comparing the three-dimensional locations of features of the two-dimensional pattern  122  on the optical target  120  to a database of three-dimensional locations of features of known optical targets. As shown in  FIG. 5 , the two-dimensional pattern  122  on the optical target  120  can be unique. Thus, the method  1000  can correlate a unique optical target  120  to a unique location of the hole H of the workpiece W. 
       FIG. 7  is a perspective view of a first exemplary hole location target according to a second embodiment of the present description in an assembled state.  FIG. 8  is a perspective view of a second exemplary hole location target according to the second embodiment of the present description in an assembled state.  FIG. 9  is an exploded perspective view of the hole location target of  FIG. 7 .  FIG. 10A  is cross-sectional view of the hole location target of  FIG. 7  inserted into a hole of a workpiece W in a radially contracted state.  FIG. 10B  is cross-sectional view of the hole location target of  FIG. 10A  in a radially expanded state. 
     Referring to  FIGS. 7, 8, 9, 10A, 10B, 11, and 12 , the hole location target  20  includes a first end  201  configured to be inserted into a hole H of a workpiece W and a second end  202  opposite to the first end  201 . 
     The hole location target  20  includes a self-centering insert  210  and an optical target  220  attached to the self-centering insert  210 . The self-centering insert  210  is positioned near the first end  201  and the optical target  220  is positioned near the second end  202  such that the self-centering insert  210  can be inserted into the hole H of the workpiece and the optical target  220  can remain outside of the hole H of the workpiece W. 
     The self-centering insert  210  has a centerline  211  and the optical target  220  is attached to the self-centering insert  210  at a fixed position relative to the centerline  211  of the self-centering insert  210 , and the optical target  220  includes a light-emitting display  270 . By attaching the optical target  220 , including the light-emitting display  270 , to the self-centering insert  210  at a fixed position relative to the centerline  211  of the self-centering insert  210 , a method that measures a location of the light-emitting display  270  can be employed to determine a location of the centerline  211  of the self-centering insert  210 , which can be correlated to the location of the centerline C of the hole H of the workpiece W. 
     The self-centering insert  210  is configured to be inserted into the hole H of the workpiece W and to be self-centered such that the centerline  211  of the self-centering insert  210  is positioned coaxially with a respective centerline C of the hole H of the workpiece W. By centering the centerline  211  of the self-centering insert  210  to be coaxial with the centerline C of the hole H of the workpiece W, a method that measures a location of the centerline  211  of the self-centering insert  210  can be employed to determine a location of the centerline C of the hole H of the workpiece W. Furthermore, by making the optical target  220  at a fixed position (or known offset) relative to the centerline  211  of the self-centering insert  210 , a method that measures a location of the optical target  220  can be employed to determine the location of the centerline  211  of the self-centering insert  210  and, thus, to determine the location of the centerline C of the hole H of the workpiece W. In an aspect, the self-centering insert  210  can include a bore  217  for accommodating a compression device  230 . 
     In the illustrated example, the self-centering insert  210  of the first embodiment includes a radially expandable bushing  212 . It will be understood that the radially expandable bushing  212  can include any tubular structure capable of inserting into the hole H of the workpiece W and capable of radially expanding to self-center the centerline  211  of the self-centering insert  210  to the centerline C of the hole H of the workpiece W. In the illustrated example, the radially expandable bushing  212  takes the form of an expandable bellows  214 . In an alternative example, the radially expandable bushing  212  can take the form of an expandable collet such as is illustrated with respect to the third embodiment below. 
     The expandable bellows  214  of the present description is a tubular structure in which an axial contraction of the expandable bellows  214  translates into a radial expansion of expandable bellows  214  and an axial expansion of the expandable bellows  214  translates into a radial contraction of expandable bellows  214 . In the illustrated example, the expandable bellows  214  includes a first bellows end  215  and a second bellows end  216  and one or more radial ridges  218  between the first bellows end  215  and the second bellows end  216 . By axially contracting the expandable bellows  214 , the one or more radial ridges  218  expand radially. By axially expanding the expandable bellows  214 , the one more radial ridges  218  contract radially. 
     As shown in  FIG. 10A , by axially expanding the expandable bellows  214 , the one or more radial ridges  218  contract radially, thereby permitting the expandable bellows  214  to be inserted into a hole H of a workpiece W. As shown in  FIG. 10B , after inserting the expandable bellows  214  into the hole H of the workpiece W, the expandable bellows  214  can be axially contracted to radially expand one or more radial ridges  218 . The one or more radial ridges  218  then contact the walls defining the hole H of the workpiece W, thus causing a self-centering of the centerline  211  of the expandable bellows  214  to the respective centerline C of the hole H of the workpiece W. 
     In the illustrated example, the optical target  220  is attached to the self-centering insert  110  such that the optical target  220  is at a fixed position relative to the centerline  211  of the self-centering insert  210 . The fixed positioning of the optical target  220  with respect to the position of centerline  211  of the self-centering insert  210  can be permanent. As shown, the self-centering insert  210  and a target support  203  for supporting the optical target  220  can be combined as a monolithic body. For improved precision, the self-centering insert  210  and the target support  203  can be unitary formed together as a monolithic body by one or more processes, such as casting, molding, and additive manufacturing. 
     In the illustrated example, the self-centering insert  210  includes a compression device  230  configured to axially contract the expandable bellows  214 . In the illustrated example, the compression device  230  includes a bolt  240  and a nut  260 . 
     As shown, the bolt  240  has a first bolt end  241  and a second bolt end  242 . The bolt  240  includes a bolt shaft  243  positioned at the first bolt end  241  of the bolt  240  and a bolt head  244  positioned at the second bolt end  242  of the bolt  240 . The bolt shaft  243  includes a first shaft end  245  and a second shaft end  246 . Exterior threads  247  are positioned at the first shaft end  245  of the bolt shaft  243 , and the bolt head  244  is joined to the second shaft end  246 . The bolt head  244  includes a first bolt head end  248  and a second bolt head end  249 . A first bolt face  251  is positioned at the first bolt head end  248 , a second bolt face  252  is positioned at the second bolt head end  249 , and an outer bolt head surface  250  is positioned between the first bolt head end  248  and the second bolt head end  249 . The outer bolt head surface  250  can take the form of a plurality of faces extending around a circumference of the bolt head  244  to improve torqueing of the bolt  240 . 
     As shown, the nut  260  has a first nut end  261  and a second nut end  262 . A first nut face  263  is positioned at the first nut end  261 , a second nut face  264  is positioned at the second nut end  262 , and an outer nut surface  265  is positioned between the first nut end  261  and the second nut end  262 . As shown, the nut gripping surface  266  can take the form of a plurality of faces for improve retention with the self-centering insert  210 . The nut bore  267  passes through the nut  260  from the first nut face  263  to the second nut face  264 , and the nut bore  267  includes interior threads  268  configured to engage with the exterior threads  247  of the bolt  240 . 
     As shown, the bolt shaft  243  passes through bore  217  at the first bellows end  215  through the expandable bellows  214  to the second bellows end  216 , and the exterior threads  247  of the bolt  240  engage with the interior threads  268  of the nut  260 . The bolt  240  engages with the first bellows end  215  and the nut  260  engages with the second bellows end  216 . Thus, the bolt  240  and nut  260  form a compression device  230  configured to contract the expandable bellows  214  by turning the bolt  240 . However, the compression device  230  is not limited to the above-described example. In another example, the position of the bolt  240  and nut  260  may be reversed. In yet another example, the compression device  230  may take the form of a rachet or any other compression device configured to axially contract the expandable bellows  214 . 
     As previously mentioned, the optical target  220  includes a light-emitting display  270 . The light-emitting display  270  includes, for example, a liquid crystal display (LCD), a light emitted diode (LED), an organic light-emitting diode (OLED), or a quantum dot light emitting diodes (QLED). The light-emitting display  270  includes a two-dimensional pattern  222  thereon. By measuring a location of the light-emitting display  270 , a location of the centerline  211  of the self-centering insert  210  can be determined, which can be correlated to the location of the centerline C of the hole H of the workpiece W. In an aspect, the two-dimensional pattern  22  can have a predetermined calibration with respect to the centerline  211  of the self-centering insert  210 , such as a predetermined six degree of freedom calibration with respect to the centerline  211  of the self-centering insert  210 . The predetermined calibration of the two-dimensional pattern  222  can be used to precisely determine the centerline  211  of the self-centering insert  210  based on a determined position of the two-dimensional pattern  222 . Furthermore, by way emitting light from the light-emitting display  270 , the two-dimensional pattern  222  thereon can be more easily captured by a camera system. 
     In the example shown in  FIG. 7 , the two-dimensional pattern  222  thereon can a plurality of a pattern of dots  223 . In an aspect, the pattern of dots  223  can be displayed to be unique such that the pattern of dots  223  on an optical target  220  of a hole location target  20  is different from the pattern of dots  223  displayed on an optical target  220  of another hole location target  20 . The three-dimensional locations of dot centroids of the pattern of dots  223  of the two-dimensional pattern  222  can be determined. Each dot of the pattern of dots  223  has a centroid which can be determined from the images captured by a camera system, and each centroid has a specific three-dimensional location. Thus, by measuring the three-dimensional locations of each dot centroid, a plurality of precise three-dimensional locations of the light-emitting display  270  of the optical target  220  can be found. 
     In another example shown in  FIG. 8 , the two-dimensional pattern  222  thereon can a plurality of a two-dimensional barcode  225  displayed by the optical target  220 . In an aspect, the two-dimensional barcode  225  can be displayed to be unique such that the two-dimensional barcode  225  on an optical target  220  of a hole location target  20  is different from the two-dimensional barcode  225  displayed on an optical target  220  of another hole location target  20 . Each line of the barcode pattern defines a one-dimensional vector in three-dimensional space, which can be determined from the images captured by a camera system, and the intersection of two lines of the barcode pattern defines a specific three-dimensional location. Thus, by measuring the three-dimensional locations of intersections of a barcode pattern, a plurality of precise three-dimensional locations on the light-emitting display  270  of the optical target  220  can be found. 
     Furthermore, by way of including a light-emitting display  270  in the optical target  220 , the optical target  220  can preferably modify the two-dimensional pattern  222  of the optical target  220 . Modifying the two-dimensional pattern  222  can include, for example, changing a size of the two-dimensional pattern, modifying an intensity of light of the light-emitting display  270 , modifying a wavelength of light of the light-emitting display  270 , and temporal modulation of light of the light-emitting display  270 . 
       FIG. 11  is a representation of an exemplary hole location measurement system according to the second embodiment of the present description. 
     The hole location measurement system  200  includes the hole location target  20 , a camera system  40  configured to capture images of the two-dimensional pattern  222  of the optical target  220 , and a computer system  50  in communication with the camera system  40  and in communication with hole location target  20 . The computer system  50  is configured to control modification of the two-dimensional pattern  222  of the optical target  220  and to determine three-dimensional coordinates of the centerline  211  of the self-centering insert from the images of the two-dimensional pattern  222  of the optical target  220 . The computer system  50  may be separate from or integrated with the camera system  40 . 
     In an aspect, hole location measurement system  200  includes a plurality of the hole location targets  20 . In another aspect, the camera system  40  is configured to capture images of the two-dimensional patterns  222  of the plurality of the hole location targets  20 . In yet another aspect, a single image captured by the camera system  40  includes the two-dimensional patterns  222  of the plurality of the hole location targets  20 . Thus, by capturing the two-dimensional patterns  222  of the plurality of the hole location targets  20  in a single image, the hole location measurement system  200  enables for single camera, single shot measurements of multiple holes at the same time. 
     In an aspect, the camera system  40  is a three-dimensional optical scanner. In another aspect, the camera system is a portable three-dimensional optical scanner. Alternatively, the three-dimensional optical scanner may be of a type supported on an articulating arm. 
     As illustrated, the portable three-dimensional optical scanner is shown as a stereo camera-styled scanner, having a pair of spaced lenses configured to acquire real-time data from a plurality of poses, utilizing a grid style coordinate system to generate and transfer  3 -D images. 
     The portable three-dimensional optical scanner can include an inertial navigation system. The inertial navigation system contained within the portable three-dimensional optical scanner provides a fixed point of reference, relative to an X-Y-Z set of common coordinates on which each scanned pose is based, irrespective of operator positioning of the physical scanner device. Thus, the angle and timing of each pose, i.e. orientation of the scanner in space and time relative to the target, is assured via the inertial navigation system to have a common frame of reference. 
     In an aspect, the light-emitting display  270  and the camera system  40  can include at least one of matching polarized filters and matching wavelength filters. By way of matching a polarized filter and/or a wavelength filter of the light-emitting display  270  and the camera system  40 , a capability of a hole location measurement system  200  to capture images of the two-dimensional patterns  222  of the plurality of the hole location targets  20  can be enhanced. 
       FIG. 12  is a flow diagram of an exemplary method for measuring a location of a hole H of a workpiece W according to the second embodiment of the present description. 
     The method  2000  for measuring a location of a hole H includes, at block  2002 , centering an insert within a hole having a centerline. The insert can be the self-centered insert  210  or can be a different insert that is centered by any external means. The optical target  220  is attached to the insert at a fixed position relative to the centerline  211  of the insert. The optical target  220  includes the light-emitting display  270  comprising a two-dimensional pattern  222  thereon. In an example, the two-dimensional pattern  222  can include, for example, the pattern of dots  223  or the two-dimensional barcode  225 . 
     The method  2000  further includes, at block  2004 , capturing images of the two-dimensional pattern  222  of the optical target. The images can be captured by the camera system  40  as described above. 
     The method  2000  further includes, at block  2006 , modifying the two-dimensional pattern  222  of the optical target  220 . 
     The method  2000  further includes, at block  2008 , capturing images of the modified two-dimensional pattern  222  of the optical target  220 . The images can be captured by the camera system  40  as described above. 
     In step  2006 , modifying the two-dimensional pattern  222  can include, for example, changing a size of the two-dimensional pattern, modifying an intensity of light of the light-emitting display  270 , modifying a wavelength of light of the light-emitting display  270 , and temporal modulation of light of the light-emitting display  270 . 
     Changing a size of the two-dimensional pattern  222  can include, for example, increasing or decreasing size of each dot of the pattern of dots  223  or increasing or decreasing a size of a bar of the two-dimensional barcode  225 . By way of increasing or decreasing a size of the two-dimensional pattern  222 , the method  2000  can compensate for a distance between the camera system  40  and the hole location target  20 . In an exemplary aspect, the camera system  40 , alone or by way of the computer system  50 , can control a size of the two-dimensional pattern  222 . Thus, the method  2000  can provide for an interactive control of the size of the two-dimensional pattern  222  based on real-time feedback from the camera system  40  capturing the images of the two-dimensional pattern  222 . 
     By way of modifying an intensity of light of the light-emitting display  270 , the method  2000  can compensate for environmental conditions, e.g. intensity of background light. In an exemplary aspect, the camera system  40 , alone or by way of the computer system  50 , can control an intensity of light of the two-dimensional pattern  222 . Thus, the method  2000  can provide for an interactive control of the intensity of the two-dimensional pattern  222  based on real-time feedback from the camera system  40  capturing the images of the two-dimensional pattern  222 . 
     By way of modifying a wavelength of light of the light-emitting display  270 , the method  2000  can compensate for environmental conditions by distinguishing the wavelength of light emitted from the light-emitting display  270 . In an exemplary aspect, the camera system  40 , alone or by way of the computer system  50 , can control a wavelength of light of the two-dimensional pattern  222 . Thus, the method  2000  can provide for an interactive control of the wavelength of the two-dimensional pattern  222  based on real-time feedback from the camera system  40  capturing the images of the two-dimensional pattern  222 . 
     By way of temporal modulation of light of the light-emitting display  270 , the method  2000  can compensate for environmental conditions. Temporal modulation of light can include, for example, a blinking of light of the light-emitting display  270 . In an exemplary aspect, the camera system  40 , alone or by way of the computer system  50 , can control a of temporal modulation of light of the two-dimensional pattern  222 . Thus, the method  2000  can provide for an interactive control of the phase of the two-dimensional pattern  222  based on real-time feedback from the camera system  40  capturing the images of the two-dimensional pattern  222 . 
     Thus, as described above, modifying the two-dimensional pattern  222  of the optical target  220  by the camera system  40 , alone or by way of the computer system  50 , can provide for method  2000  that adjusts the optical target  220  to the conditions at the time of taking the measurements. 
     In another aspect, modifying the two-dimensional pattern  222  of the optical target  220  can communicate a status of the hole location target  20 . Thus, modifying the two-dimensional pattern  222  can communicate a signal with a status of the hole location target  20 , which can include correlating the signal with an identity of the hole location target. 
       FIG. 13  is a perspective view of an exemplary hole location target according to a third embodiment of the present description in an assembled state.  FIG. 14  is an exploded perspective view of the hole location target of  FIG. 13 .  FIG. 15A  is cross-sectional view of the hole location target of  FIG. 13  inserted into a hole of a workpiece W in a radially contracted state.  FIG. 15B  is cross-sectional view of the hole location target of  FIG. 15A  in a radially expanded state. 
     Referring to  FIGS. 13, 14, 15A, and 15B , the hole location target  30  includes a first end  301  configured to be inserted into a hole H of a workpiece W and a second end  302  opposite to the first end  301 . 
     The hole location target  30  includes a self-centering insert  310  and a laser beam emitter  320  attached to the self-centering insert  310 . The self-centering insert  310  is positioned near the first end  301  and the laser beam L is emitted near the second end  302  such that the self-centering insert  310  can be inserted into the hole H of the workpiece and the laser beam L can be emitted outside of the hole H of the workpiece W. The self-centering insert  310  has a centerline  311  and the axis of the emitted laser beam L is concentric to the centerline  311  of the self-centering insert  310 . 
     The self-centering insert  310  is configured to be inserted into the hole H of the workpiece W and to be self-centered such that the centerline  311  of the self-centering insert  310  is positioned coaxially with a respective centerline C of the hole H of the workpiece W. By centering the centerline  311  of the self-centering insert  310  to be coaxial with the centerline C of the hole H of the workpiece W, a method that measures a location of the centerline  311  of the self-centering insert  310  can be employed to determine a location of the centerline C of the hole H of the workpiece W. Furthermore, by making the axis of the emitted laser beam L to be concentric to the centerline  311  of the self-centering insert  310 , a method that measures the location of the emitted laser beam L can be employed to determine the location of the centerline  311  of the self-centering insert  310  and, thus, to determine the location of the centerline C of the hole H of the workpiece W. In an aspect, the axis of the emitted laser beam is concentric to the centerline of the self-centering insert to 5 μm or less. 
     In the illustrated example, the self-centering insert  310  of the first embodiment includes a radially expandable bushing  312 . It will be understood that the radially expandable bushing  312  can include any tubular structure capable of inserting into the hole H of the workpiece W and capable of radially expanding to self-center the centerline  311  of the self-centering insert  310  to the centerline C of the hole H of the workpiece W. In the illustrated example, the radially expandable bushing  312  takes the form of an expandable collet  314 . In an alternative example, the radially expandable bushing  312  can take the form of an expandable bellows such as is illustrated with respect to the first and third embodiments above. 
     The expandable collet  314  of the present description is a tubular structure in which radially outward force applied to the expandable collet  314  radially expands the expandable collet  314 . 
     In the illustrated example, the expandable collet  314  includes a first collet end  315  and a second collet end  316  and axial beams  318  between the first collet end  315  and the second collet end  316 . By applying a radially outward force to the expandable collet  314 , the axial beams  318  circumferentially separate and expand radially outward. 
     As shown in  FIG. 15A , reducing the radially outward force applied to the expandable collet  314 , the axial beams  318  contract radially, thereby permitting the expandable collet  314  to be inserted into a hole H of a workpiece W. As shown in  FIG. 15B , after inserting the expandable collet  314  into the hole H of the workpiece W, the radially outward force is applied to the expandable collet  314  and the axial beams  318  radially expand. The axial beams  318  then contact the walls defining the hole H of the workpiece W, thus causing a self-centering of the centerline  311  of the expandable collet  314  to the respective centerline C of the hole H of the workpiece W. 
     In the illustrated example, the laser beam emitter  320  is attached to the self-centering insert  310  such that the emitted laser beam L is concentric to the centerline  311  of the self-centering insert  310 . By way of example, the laser beam emitter  320  can be fixedly positioned to the self-centering insert  310  such that a position of the laser beam emitter  320  is fixed with respect to a position of centerline  311  of the self-centering insert  310 . The positioning of the laser beam emitter  320  with respect to the position of centerline  311  of the self-centering insert  310  can be permanent. 
     In the illustrated example, the self-centering insert  310  includes an expansion device  330  configured to apply a force to radially expand the expandable collet  314 . In the illustrated example, the expansion device  330  includes a first wedge  340 , a second wedge  350 , and a collar  360 . 
     As shown, the first wedge  340  has a first wedge lower end  341 , a first wedge upper end  342  opposite to the first wedge lower end  341 , and a first hollow shaft  343  between the first wedge lower end  341  and the first wedge upper end  342 . A first inclined wedge surface  344  is positioned at the first wedge lower end  341  of the first wedge  340 . The first inclined wedge surface  344  is configured to engage with an inclined collet surface of the expandable collet  314 . Exterior threads  345  are positioned on an exterior surface of the first hollow shaft  343 , and a wedge grip  346  is positioned at the first wedge upper end  342  of the first wedge  340 . The wedge grip  346  can include a wedge gripping surface  348 . The wedge gripping surface  348  can take the form of a knurled surface for improved manually torqueing of the wedge grip  346 . Alternatively, the wedge gripping surface  348  can take other forms, such as the of a plurality of faces for torqueing the wedge grip  346  with a tool. The first wedge  340  is sized to pass through an first end of a hollow interior of the expandable collet  314  such that the first inclined wedge surface  344  engages with the inclined collet surface  319  and such that the exterior threads  345  and wedge grip  346  extend past a second end of the hollow interior of the expandable collet  314 . 
     As shown, the second wedge  350  has a second wedge lower end  351 , a second wedge upper end  352  opposite to the second wedge lower end  351 , and a second hollow shaft  353  between the second wedge lower end  351  and the second wedge upper end  352 . A second inclined wedge surface  354  is positioned at the second wedge upper end  352  of the second wedge  350 . The second inclined wedge surface  354  is configured to engage with an inclined collet surface  319  of the expandable collet  314 . The second hollow shaft  353  is sized to pass through the hollow interior of the expandable collet  314  such that the second inclined wedge surface  354  engages with the inclined collet surface  319 . 
     By engagement of the first inclined wedge surface  344  and the second inclined wedge surface  354  with the inclined collet surfaces  319 , an axial movement of the first wedge  340  towards the second wedge  350  results in a radially outward force applied to the expandable collet  314  to circumferentially separate and radially expand the axial beams  318 . 
     The collar  360  can provide axial movement of the first wedge  340  towards the second wedge  350 . As shown, the collar  360  includes a first collar portion  361  and a second collar portion  366 . 
     The first collar portion  361  has a first collar lower end  362  and a first collar upper end  363 . The first collar upper end  363  can include a wavy upper surface  364  configured to engage with a corresponding wavy surface of the second collar portion, and a first collar bore  365  passes through the first collar portion  361  from the first collar lower end  362  to the first collar upper end  363 . 
     The second collar portion  366  has a second collar lower end  367  and a second collar upper end  368 . The second collar portion  366  can include a second collar gripping surface  369 . The second collar gripping surface  369  can take the form of a knurled surface for improved manually torqueing of the second collar gripping surface  369 . Alternatively, the second collar gripping surface  369  can take other forms, such as the of a plurality of faces for torqueing the second collar gripping surface  369  with a tool. The second collar portion  366  includes interior threads  370  in a bore passing through the second collar portion  366  from the second collar lower end  367  to the second collar upper end  368 . The interior threads  370  of the second collar portion  366  are configured to engage with the exterior threads of the first wedge  340  to axially move the first wedge  340  towards the second wedge  350 . 
     Thus, the first wedge  340 , the second wedge  350 , and the collar  360  form an expansion device  330  configured to apply a radially outward force to the expandable collet  314  by turning the collar  360 . However, the expansion device  330  is not limited to the above-described example. In another example, the position of the first wedge  340 , the second wedge  350 , and the collar  360  can be reversed. In yet another example, the expansion device  330  may take the form of a spring or any other expansion device configured to radially expand the expandable collet  314 . 
     As shown, the hole location target  30  further includes a power device  380 . In the illustrated example, the power device  380  includes a battery  381 , a power switch  382 , and a conduit  383 . However, the power device  380  is not limited to the above-described example. In another example, the power device  380  could include a wire connected to an electricity supply. 
       FIG. 16A  is a representation of an exemplary hole location measurement system according to the third embodiment of the present description, including an optical sensor at a first distance d 1  from the laser beam emitter.  FIG. 16B  is a representation of the exemplary hole location measurement system according to the third embodiment of the present description, including the optical sensor at a second distance d 2  from the laser beam emitter. 
     The hole location measurement system  300  includes the hole location target  30 , in which the axis of the emitted laser beam L is concentric to the centerline  311  of the self-centering insert  310 , an optical system  41  sensing the location of the emitted laser beam L at multiple distances from the laser beam emitter  320 , and a computer system  50  in communication with the hole location target  30  and optionally the optical system  41 . The computer system  50  is configured to determine three-dimensional coordinates of the centerline  311  of the self-centering insert  310  from the sensed locations of the emitted laser beam L. The optical system  41  includes any optical system capable of sensing the location of the emitted laser beam L at multiple distances from the laser beam emitter  320 . The computer system  50  may be separate from or integrated with the camera system  40 . 
     In an aspect, hole location measurement system  300  includes a plurality of the hole location targets  30 . In another aspect, the optical system  41  is configured to sense the location of multiple emitted laser beams L at the same time. Thus, by sensing the location of multiple emitted laser beams L at the same time, the hole location measurement system  300  enables for measurements of multiple holes at the same time. 
     The optical system  41  can be a portable optical system. Alternatively, the optical system  41  is of a type supported on an articulating arm. 
     In an aspect, the laser beam emitter  320  is configured to modulate a power of the emitted laser beam L. By controlling modulation of the emitted laser beam L, laser beam emitter  320  can compensate for environmental conditions, e.g. intensity of background light. 
     In another aspect, the optical system  41  and/or the computer system  50  is configured to control the modulation of the emitted laser beam L. By controlling modulation of the emitted laser beam L, the hole location measurement system  300  can compensate for environmental conditions, e.g. intensity of background light, by modulating the emitted laser beam L to facilitate sensing of the emitted laser beam L by the optical system  41 . Thus, the hole location measurement system  300  can provide for an interactive control of the modulation of the emitted laser beam L based on real-time feedback from the optical system  41  sensing the location of emitted laser beam L. 
     Furthermore, in an aspect, the emitted laser beam L is modulated to send a signal, and the computer system  50  is configured to extract a signal from the modulated powder of the emitted laser beam L. The signal can be indicative of a status of the hole location target, an identity of the hole location target, or a status of the laser beam emitter. 
     In an aspect, the laser beam emitter  320  and the optical system  41  can include at least one of matching polarized filters and matching wavelength filters. By way of matching a polarized filter and/or a wavelength filter of the laser beam emitter  320  and the optical system  41 , a capability of a hole location measurement system  300  to sense the location of the emitted laser beam L can be enhanced. 
       FIG. 17  is a flow diagram of an exemplary method for measuring a location of a hole of a workpiece W according to the third embodiment of the present description. 
     The method  3000  for measuring a location of a hole H includes, at block  3002 , centering an insert within a hole having a centerline. The insert can be the self-centered insert  310  or can be a different insert that is centered by any external means. 
     The method  3000  further includes, at block  3004 , emitting a laser beam from a laser beam emitter attached to the insert, wherein the axis of the emitted laser beam is concentric to the centerline of the insert. 
     The method  3000  further includes, at block  3006 , sensing the location of the emitted laser beam at multiple distances from the laser beam emitter. 
     The method  3000  further includes, at block  3008 , determining three-dimensional coordinates of the centerline of the self-centering insert from the sensed locations of the emitted laser beam. 
     In an aspect, the method  3000  further includes modulating a power of the emitted laser beam and extracting a signal from the modulated powder of the emitted laser beam. In another aspect, the method  3000  further includes correlating the signal with a status of the hole location target. 
     In an aspect, the method  3000  further includes correlating the signal with an identity of the hole location target. 
     In an aspect, the method  3000  further includes correlating the signal with a status of the laser beam emitter. 
     In an aspect, the method  3000  further includes rotating an article having the hole therein, emitting the laser beam from the laser beam emitter during the rotating, sensing the location of the emitted laser beam at multiple distances from the laser beam emitter during the rotating, and determining three-dimensional coordinates of the centerline of the self-centering insert throughout the rotation from sensed locations of the emitted laser beam. 
     Examples of the present disclosure may be described in the context of an aircraft manufacturing and service method  4000 , as shown in  FIG. 18 , and an aircraft  4002 , as shown in  FIG. 19 . During pre-production, the aircraft manufacturing and service method  4000  may include specification and design  4004  of the aircraft  4002  and material procurement  4006 . During production, component/subassembly manufacturing  4008  and system integration  4010  of the aircraft  4002  takes place. Thereafter, the aircraft  4002  may go through certification and delivery  4012  in order to be placed in service  4014 . While in service by a customer, the aircraft  4002  is scheduled for routine maintenance and service  4016 , which may also include modification, reconfiguration, refurbishment and the like. 
     Each of the processes of method  4000  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     The hole location targets, hole location measurement systems, and methods for measuring a location of a hole of the present disclosure may be employed during any one or more of the stages of the aircraft manufacturing and service method  1000 , including specification and design  4004  of the aircraft  4002 , material procurement  4006 , component/subassembly manufacturing  4008 , system integration  4010 , certification and delivery  4012 , placing the aircraft in service  4014 , and routine maintenance and service  4016 . 
     As shown in  FIG. 19 , the aircraft  4002  produced by example method  4000  may include an airframe  4018  with a plurality of systems  4020  and an interior  4022 . Examples of the plurality of systems  4020  may include one or more of a propulsion system  4024 , an electrical system  4026 , a hydraulic system  4028 , and an environmental system  4030 . Any number of other systems may be included. The hole location targets, hole location measurement systems, and methods for measuring a location of a hole of the present disclosure may be employed for any of the systems of the aircraft  4002 . 
     Although various embodiments of the disclosed hole location targets, hole location measurement systems, and methods for measuring a location of a hole have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.