Patent Publication Number: US-2022212347-A1

Title: Bore metrology methods and systems, and bore locating target assemblies for use therewith

Description:
PRIORITY 
     This application claims priority from U.S. Ser. No. 63/133,465 filed on Jan. 4, 2021. 
    
    
     FIELD 
     This application relates to bore metrology and, more particularly, to apparatus, systems and methods for determining a centerline of a partially obstructed bore and, even more particularly, to apparatus, systems and methods for match drilling a bore in a second structure that obstructs an initial bore in a first structure. 
     BACKGROUND 
     Manufacturing, and particularly precision manufacturing required for industries such as the aerospace industry, requires accurate locating of workpieces, fixtures, and tools to perform various manufacturing operations and processes. Increasingly, robots are used to perform manufacturing functions that previously required manual alignment operations. However, the accuracy of the robotic work operation relies on an understanding of the location of workpieces relative to the robot and its associated tool or tools. 
     Orientation and alignment of a robot and a workpiece may conventionally be performed via coordinate measurement such as using a coordinate measuring machine or function of a robot. A tool may be aligned by a robot operator using a tool mounted camera to locate a particular feature, such as a hole or fiducial mark. Customarily, the camera is very slowly positioned close to the workpiece using numerically controlled program commands aided by manual intervention in order to accurately register a small feature against a cluttered background. However, the robotic arm on which the camera is located must be prevented from inadvertently contacting the workpiece or risk damage to any or all of the camera, the robotic arm, or the workpiece. This close proximity placement may involve the use of mechanical feelers or optical sensors, and time consuming visual inspection by the operator. When enough features have been semi-autonomously identified to derive the workpiece coordinate system in three dimensions of rotation and translation, the workpiece can be registered to the coordinate system of the robot and the operator can begin a fully autonomous robotic assembly operation, such as cutting, drilling, fastening, or welding. The semi-autonomous alignment operations described above are labor intensive and can add considerable time to the manufacturing operations cycle. Further, difficulties arise when match drilling two or more workpieces. The slight offset of the two workpieces may be problematic when both workpieces need to be robotically match drilled to a high accuracy from the inner side. 
     Accordingly, a need exists to accurately align and re-position workpieces during various manufacturing operations including those involving match drilling. 
     SUMMARY 
     Disclosed is a bore metrology method. 
     In one example, a bore metrology method includes aligning a first structure, which defines an initial bore, with a second structure, which defines a pilot bore, such that the initial bore is partially obstructed by the second structure and the pilot bore is superimposed with the initial bore. The initial bore includes a bore locating target assembly within the initial bore, the bore locating target assembly having an optical target, the optical target having a reflector and an optical absorbing feature, the optical absorbing feature defining a pattern on the optical target. At least a portion of the reflector and at least a portion of the pattern are visible through the pilot bore. The method further includes imaging the portion of the reflector and the portion of the pattern that are visible through the pilot bore. The method further includes determining a centerline of the initial bore based on the imaging. 
     Also disclosed is a bore metrology system. 
     In an example, the bore metrology system includes a bore locating target assembly positionable within an initial bore defined in a first structure. The initial bore is partially obstructed by a second structure defining a pilot bore such that the pilot bore is superimposed with the initial bore. The bore locating target assembly includes an optical target, the optical target includes a reflector and an optical absorbing feature such that the optical absorbing feature defines a pattern on the optical target. The bore metrology system further includes an automated machine including an end effector. The bore metrology system further includes a camera system mounted on the end effector, the camera system being configured to project a collimated beam of electromagnetic radiation within a field of view. In an example, the automated machine is configured to position the end effector such that the pilot bore is within the field of view. 
     Also disclosed is a bore locating target assembly. 
     In an example, a bore locating target assembly includes a self-centering insert defining a self-centering insert centerline and having a distal end and a proximal end. The bore locating target assembly further includes an optical target connected proximate the distal end of the self-centering insert such that the optical target includes a reflector and an optical absorbing feature. The optical absorbing feature defines a pattern on the optical target. 
     Other examples of the disclosed bore metrology methods and systems, and bore locating target assemblies for use therewith will become apparent from the following detailed description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some examples of the present disclosure are described with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings. 
         FIG. 1  is a side schematic view, partially in section, of one example of the disclosed bore metrology system  100 ; 
         FIG. 2  is a front perspective view of the bore locating target assembly used in the system of  FIG. 1 ; 
         FIG. 3  is a side view, in cross-section, of the bore locating target assembly of  FIG. 2 ; 
         FIGS. 4A and 4B  are detailed front views of a first structure of the system of  FIG. 1 , shown with a bore locating target assembly inserted into an initial bore in the first structure; 
         FIGS. 5A and 5B  are detailed front views of a second structure of the system of  FIG. 1 , shown with the second structure positioned over and aligned with the first structure such that the bore locating target assembly in the first structure is partially visible through a pilot bore in the second structure; 
         FIGS. 6A and 6B  are detailed views of a portion of the system of  FIG. 1 , depicting a camera system imaging a portion of the bore locating target assembly that is visible through the pilot bore in the second structure; 
         FIG. 7  is a further detailed view of a portion of the system of  FIG. 1 , depicting a location of the pilot bore vis-a-vis the bore locating target assembly in the initial bore; 
         FIG. 8  is a side schematic view of an example camera system useful in the bore metrology system of  FIG. 1 ; 
         FIGS. 9A and 9B  are detailed views of a portion of the system of  FIG. 1 , depicting a boring spindle machining a matched bore in the second structure; 
         FIG. 10  is a flow diagram of one example of the disclosed bore metrology method; 
         FIG. 11  is a flow diagram of an aircraft manufacturing and service methodology; and 
         FIG. 12  is a perspective view of an aircraft benefiting from the disclosed bore metrology methods and systems. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description refers to the accompanying drawings, which illustrate specific examples described by the present disclosure. Other examples having different structures and operations do not depart from the scope of the present disclosure. Like reference numerals may refer to the same feature, element, or component in the different drawings. 
     Illustrative, non-exhaustive examples, which may be, but are not necessarily, claimed, of the subject matter according the present disclosure are provided below. Reference herein to “example” means that one or more feature, structure, element, component, characteristic, and/or operational step described in connection with the example is included in at least one aspect, embodiment, and/or implementation of the subject matter according to the present disclosure. Thus, the phrases “an example,” “another example,” “one or more examples,” and similar language throughout the present disclosure may, but do not necessarily, refer to the same example. Further, the subject matter characterizing any one example may, but does not necessarily, include the subject matter characterizing any other example. Moreover, the subject matter characterizing any one example may be, but is not necessarily, combined with the subject matter characterizing any other example. 
     As used herein, a system, apparatus, device, structure, article, element, component, or hardware “configured to” perform a specified function is indeed capable of performing the specified function without any alteration, rather than merely having potential to perform the specified function after further modification. In other words, the system, apparatus, device, structure, article, element, component, or hardware “configured to” perform a specified function is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the specified function. As used herein, “configured to” denotes existing characteristics of a system, apparatus, structure, article, element, component, or hardware that enable the system, apparatus, structure, article, element, component, or hardware to perform the specified function without further modification. For purposes of this disclosure, a system, apparatus, device, structure, article, element, component, or hardware described as being “configured to” perform a particular function may additionally or alternatively be described as being “adapted to” and/or as being “operative to” perform that function. 
     For the purpose of this disclosure, the terms “coupled,” “coupling,” and similar terms refer to two or more elements that are joined, linked, fastened, attached, connected, put in communication, or otherwise associated (e.g., mechanically, electrically, fluidly, optically, electromagnetically) with one another. In various examples, the elements may be associated directly or indirectly. As an example, element A may be directly associated with element B. As another example, element A may be indirectly associated with element B, for example, via another element C. It will be understood that not all associations among the various disclosed elements are necessarily represented. Accordingly, couplings other than those depicted in the figures may also exist. 
     As used herein, the terms “about,” “approximately,” “substantially,” and “generally” refer to or represent a condition that is close to, but not exactly, the stated condition that still performs the desired function or achieves the desired result. As an example, the terms “about,” “approximately,” “substantially,” and “generally” refer to a condition that is within an acceptable predetermined tolerance or accuracy. For example, the terms “about,” “approximately,” “substantially,” and “generally” refer to a condition that is within 10% of the stated condition. However, the terms “about,” “approximately,” “substantially,” and “generally” do not exclude a condition that is exactly the stated condition. 
     References throughout the present specification to features, advantages, or similar language used herein do not imply that all of the features and advantages that may be realized with the examples disclosed herein should be, or are in, any single example. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an example is included in at least one example. Thus, discussion of features, advantages, and similar language used throughout the present disclosure may, but do not necessarily, refer to the same example. 
     The disclosed methods, systems, and apparatuses address problems of existing methods for joining two indexed workpieces. An exemplary scenario involves a manufacturing condition requiring the coupling or joining of two or more indexed workpieces. In this example, the outer workpiece may have existing, full-size holes. The workpieces may be aligned such that the existing full-size holes may be obscured by an inner workpiece. The slight offset of the two workpieces may be problematic when both workpieces need to be robotically match drilled to a high accuracy from the inner side. Disclosed herein is in a bore metrology method  10  addressing the above-mentioned problems with aligning two workpieces. Further disclosed is an apparatus and system configured to project and analyze a reticle pattern to facilitate alignment of the two workpieces and match drilling of the workpieces. 
     The disclosed methods, systems, and apparatuses related to a pilot hole aligning specular reticle enable high operational efficiency machining by providing optically acquired high accuracy measurements. When observed by an active optical measurement system co-aligned with a machining spindle on a robotic end effector, each pilot hole aligning specular reticle can be measured in milliseconds at a few inches standoff distance, followed immediately by the objective matched hole machining. 
     The disclosed further enable camera systems the ability to measure a hole centerline, representing four orthogonal degrees of freedom requiring the most challenging accuracies with respect to the machine axis spindle. These four orthogonal degrees of freedom include the lateral and vertical translational axes, and the angles about these two translational axes. A required range measurement can be provided with various known methods. 
     The disclosed systems, methods, and apparatuses further enable inexpensive robotic manipulators. When hosted on an end effector with high precision staging, mounted to a robotic manipulator with stiff brakes, the disclosed pilot hole aligning specular reticle enables the robotic manipulator to be low accuracy, and therefore lower cost. 
     The disclosed pilot hole aligning specular reticle can be scaled so as to accommodate small to large holes. The reticle&#39;s specular facets are large enough to result in an extended object image, yet small enough to allow the two dimensional reticle pattern to fit within holes at least as small as 0.375″ diameter, and likely much smaller. 
     Pilot holes can be very small, thereby enabling more alignment variation between the two workpieces. As measured by an afocal active imager akin to a camera system, the pilot hole aligning specular reticle pilot hole diameter is scaled as a few dozen camera pixels. With an exemplary pixel pitch on the order of 3.5 microns, a pilot hole diameter could be about 0.035 inches or smaller. Pilot holes are cone shaped a couple degrees to enable respective unobstructed off-axis specular reflections to and from the active imaging camera. 
     Pilot hole aligning specular reticles may be manufactured at various price points including those that are essentially expendable and inexpensive. Fabricated from an optically stable plastic such as polycarbonate, pilot hole aligning specular reticles can be inexpensively mass produced akin to compact disc or digital video disc. 
     Pilot hole aligning specular reticles can protect existing, full-size holes from moisture absorption during workpiece transportation and storage. Pilot hole aligning specular reticle can be kinematically mounted to self-centering bushings and inserted into full size holes. These bushings can incorporate environmental ingress protection provisions, moister getters, etc. 
       FIG. 1  is a side schematic view, partially in section, of one example of the disclosed bore metrology system. In an example, the bore metrology system  100  includes a bore locating target assembly  120  positionable within an initial bore  104  defined in a first structure  102 . For example, the initial bore  104  may be cylindrical bore.  FIG. 2  illustrates a front perspective view and  FIG. 3  illustrates a side view, in cross-section, of the bore locating target assembly  120  used in the system of  FIG. 1 . As shown in  FIG. 1 , the initial bore  104  is partially obstructed by a second structure  112 . Second structure  112  may define a pilot bore  114 . The pilot bore  114  may be superimposed with the initial bore  104 . In an example, the bore locating target assembly  120  includes an optical target  122  wherein the optical target  122  includes a reflector  124  and an optical absorbing feature  126 . The reflector  124  may include a silver coated flat surface. The optical absorbing feature  126  may define a pattern  128  on the optical target  122 . In an example, the absorbing feature includes one or more of an etch, an ink, and a carbon-containing compound, or any combination thereof. The pattern  128  may be a polar reticle, for example. 
     The bore metrology system  100  further includes an automated machine  300  having an end effector  302 . Automated machine  300  may be in communication with a controller  400 . Controller  400  may utilize one or more numerical control programs for collection of data and analysis thereof. The automated machine  300  may be configured to position the end effector  302  such that the pilot bore  114  is within the field of view  202 . In an example, the automated machine  300  includes a robotic arm  304 . 
     In an example, the bore metrology system  100  includes a camera system  200  mounted on the end effector  302 . The camera system  200  may be in communication with the controller  400 . As shown in  FIG. 6A , the camera system  200  may be configured to project a collimated beam  204  of electromagnetic radiation within a field of view  202 . With reference to  FIG. 8 , camera system  200  may include a housing  210  having a boresight centerline  212 . The camera system  200  may further include a beam generator  214  configured to project a beam  216  proximate a first end  218  of the housing  210  along the boresight centerline  212 . In an example, the camera system  200  includes a quarter wave plate  222  proximate a second end  220  of the housing  210  along the boresight centerline  212 . A collimating optic  224  may be disposed between the beam generator  214  and the quarter wave plate  222  along the boresight centerline  212 . In an example, a beam-splitting half-mirror surface  226  is arranged at an angle relative to the boresight centerline  212  and positioned between the collimating optic  224  and the quarter wave plate  222 . In an example, a linear polarizing surface  228  is arranged at an angle relative to the boresight centerline  212  and positioned between the collimating optic  224  and the beam-splitting half-mirror surface  226 . In an example, the camera system  200  includes a first sensor  230  configured to receive a first input beam  232  reflected from the beam-splitting half-mirror surface  226  and a second sensor  236  configured to receive a second input beam  238  reflected from the linear polarizing surface  228 . 
     The controller  400  may be configured to determine a centerline  106  of the initial bore  104  based on a reflection of the collimated beam  204  of the electromagnetic radiation from the optical target  122  through the pilot bore  114 . In an example, the camera system  200  is configured to form an image of the reflector portion  124   a  of the reflector  124  and the pattern portion  128   a  of the pattern  128  that are visible through the pilot bore  114 . The camera system  200  may further be configured such that the controller  400  is a part of the camera system  200 . In an example, the controller  400  is configured to determine a centerline  106  of the initial bore  104  based on the formed image. In an example, illustrated in  FIG. 9A , the bore metrology system  100  further includes a boring spindle  500  mounted on the end effector  302  at a pre-determined orientation relative to the camera system  200 . 
       FIGS. 4A and 4B  illustrate a detailed front view of a first structure  102  of the bore metrology system  100 , shown with a bore locating target assembly  120  inserted into an initial bore  104  in the first structure  102 . The bore locating target assembly  120  may further include a self-centering insert  130  defining a self-centering insert centerline  132  and including a distal end  134  and a proximal end  136 . The optical target  122  may further be connected proximate the distal end  134  of the self-centering insert  130 . In an example, the optical target  122  defines an outer surface  133 . In an example, the outer surface  133  of the optical target  122  is substantially perpendicular to the self-centering insert centerline  132 . 
     In an example, multiple holes may include a bore locating target assembly  120 . Given that the full size hole pattern can be machined with precision, in an example not all the holes include a bore locating target assembly  120 .  FIG. 4A  illustrates three of the bore locating target assembly  120 . However, more or fewer of the bore locating target assembly  120  are possible. 
     In an example, the self-centering insert  130  includes a shaft  140  defining the self-centering insert centerline  132  and including a distal end portion  142  and a proximal end portion  144 . The self-centering insert  130  further including a flange  146  proximate the distal end portion  142  of the shaft  140 , a nut  148  threaded into engagement with the proximal end portion  144  of the shaft  140 , and a radially expandable bushing  150  received over the shaft  140  and positioned between the flange  146  and the nut  148 . In an example, axial compression of the radially expandable bushing  150  along the self-centering insert centerline  132  causes corresponding radial expansion of the radially expandable bushing  150 . 
     In an example, a bore locating target assembly  120  is disclosed and illustrated in  FIG. 2 . The bore locating target assembly  120  may include a self-centering insert  130 . Self-centering insert  130  may define a self-centering insert centerline  132  and include a distal end  134  and a proximal end  136 . In an example, as illustrated in  FIG. 3 , the self-centering insert  130  includes a radially expandable bushing  150  configured to center the self-centering insert  130  within a bore when the self-centering insert  130  is inserted into a bore. The radially expandable bushing  150  may be configured to radially expand in response to axial compression. The bore locating target assembly  120  may further include an optical target  122  connected proximate the distal end  134  of the self-centering insert  130 . The optical target  122  may define an outer surface  133 . In an example, the outer surface  133  of optical target  122  is substantially perpendicular to the self-centering insert centerline  132 . In another example, the outer surface  133  of the optical target  122  is substantially planar. 
     In an example, the optical target  122  includes a reflector  124  and an optical absorbing feature  126 . The reflector  124  may include a silver coated surface. The optical absorbing feature  126  may include one or more of an etch, an ink, and a carbon-containing compound, or any combination thereof. The optical absorbing feature  126  may define a pattern  128  on the optical target  122 . In an example, the pattern  128  on the optical target  122  is a polar reticle. 
     In an example, the self-centering insert  130  includes a shaft  140 . Shaft  140  may define the self-centering insert centerline  132 . In an example, shaft  140  includes a distal end portion  142  and a proximal end portion  144 . The shaft  140  may include a flange  146  proximate the distal end portion  142  of the shaft  140 . A nut  148  may be threaded into engagement with the proximal end portion  144  of the shaft  140 . In an example, the shaft  140  includes a radially expandable bushing  150 . The radially expandable bushing  150  may be configured to be received over the shaft  140  and positioned between the flange  146  and the nut  148  such that axial compression of the radially expandable bushing  150  along the self-centering insert centerline  132  causes corresponding radial expansion of the radially expandable bushing  150 . 
     As mentioned above, the camera system  200  may be configured to project a collimated beam  204  of electromagnetic radiation within field of view  202 .  FIG. 8  illustrates an exemplary camera system  200  that is configured to project an output beam (e.g., collimated beam  204 ) to be reflected back to the camera system  200  as an input beam, in accordance with example embodiments. As seen in  FIG. 8 , camera system  200  includes a housing  210  defining a boresight centerline  212 . Housing  210  may define an aperture  206  to receive a collimated input beam  208 . In an example, the camera system  200  includes an optical boresight having a boresight centerline  212 , a first sensor  230  and a second sensor  236  serially positioned relative to the boresight centerline  212  of the optical boresight, a beam-splitting half-mirror surface  226  including a beam splitter configured to split the collimated input beam  208  into a first input beam  232  and a second input beam  238 , and direct the first input beam  232  of the collimated input beam  208  to the first sensor  230 . The camera system  200  may further include a linear polarizing surface  228  including a reflective surface configured to reflect the second input beam  238  and direct second input beam  238  to the second sensor  236   
     The camera system  200  may further include a controller  400  in communication with the first sensor  230  and the second sensor  236 , controller  400  configured to monitor the camera system  200  and determine one or more offsets of the collimated input beam  208  from the boresight centerline  212  based on data received from the first sensor  230  and the second sensor  236 . The controller  400  in communication with the first sensor  230  and the second sensor  236  of the camera system  200  may be contained within the camera system  200  housing  210  or outside the housing  210 . 
     In an example, the camera system  200  is configured to project an output beam to be reflected back to the camera system  200  as the collimated input beam  208 .  FIG. 8  illustrates a camera system that includes a beam generator  214  configured to project a randomly polarized beam  216 , which includes S-aligned waves and P-aligned waves, to a collimating optic  224 . Collimating optic  224  directs a collimated output beam  240  through the camera system  200 . The collimated output beam  240  passes through a linear polarizing P-pass coating of linear polarizing surface  228 . In doing so, a portion of the collimated output beam  240 , namely the S-aligned waves of the beam, are reflected along first beam path  242  to a beam dump  244 . The beam dump  244  merely absorbs the waves without reflecting the received beams back into the optics of the camera system  200  which could affect accuracy of the measurements and data collected. 
     The portion of the collimated output beam  240  that passes through the linear polarizing P-pass coating of the linear polarizing surface  228  includes P-aligned waves of the beam  246 . A portion of the P-aligned waves of beam  246  pass through beam-splitting half-mirror surface  226  as output beam  248 , while another portion of beam  246  is split and directed along path  250  to the beam dump  244 . The remaining output beam  248  then passes through a quarter wave plate  222 , which causes the output beam from the camera system  200  to be a clockwise circularly polarized wave output beam  252  exiting the camera system  200 , directed toward bore locating target assembly  120 . Within examples, the circularly polarized wave output beam  252  corresponds to the collimated beam  204  shown in  FIGS. 6A-6B . 
     The clockwise circularly polarized wave output beam  252  is considerably more broad than the bore locating target assembly  120  as the bore locating target assembly  120  includes a very small, reflective surface. The bore locating target assembly  120  of an example embodiment is on the order of millimeters or fractions thereof, while the clockwise circularly polarized wave output beam  252  may be an order of magnitude larger or more. The bore locating target assembly  120  reflects a small portion of the clockwise circularly polarized wave output beam  252  back to the camera system  200 . The reflected beam from the bore locating target assembly  120  becomes the target input beam  254  to the camera system  200 . The target input beam  254 , as it is reflected from the clockwise circularly polarized wave output beam  252 , becomes counter-clockwise circularly polarized. The target input beam  254  passes through the quarter wave plate  222 , which causes the counter-clockwise circularly polarized wave to become S-aligned, substantially cancelling the circular polarization imparted to the clockwise circularly polarized wave output beam  252  by the quarter wave plate  222 . The S-aligned collimated input beam  208  strikes the beam-splitting half-mirror surface  226 , from which the beam is split and a portion of the beam or first input beam  232  is reflected to first sensor  230 . The portion of the beam  256  that passes through the beam-splitting half-mirror surface  226  reaches the polarizing P-pass coating of linear polarizing surface  228 . As the input beam becomes S-aligned from entering the camera system  200  through the quarter wave plate  222 , the S-aligned beam of beam  256  is reflected in its entirety off of the P-pass coating of linear polarizing surface  228  as second input beam  238  to reach the second sensor  236 . 
     The camera system  200  illustrated in the exemplary embodiment shown in  FIG. 8  uses the sensed data of the first sensor  230  and the second sensor  236  to establish the translation offsets of the collimated input beam  208  from the boresight centerline  212  and angle offsets of the collimated input beam  208  from the boresight centerline  212 . 
     According to some embodiments, at least one of the first sensor  230  and second sensor  236  is a pixelated imager with the beam splitting reflective surfaces appropriately spaced. Another of the first sensor  230  and second sensor  236  of an example embodiment is a time-of-flight pixelated sensor with the beam splitting reflective surfaces appropriately spaced. The output from the time-of-flight pixelated sensor is provided to a controller  400  of the camera system  200 , where three-dimensional time-of-flight sensor electronics may be used to determine a distance of the bore locating target assembly  120  from the camera system  200 . The three-dimensional time-of-flight sensor electronics may be in communication with or in control of the beam  216  such that time-of-flight of the beam  216  is calculated through modulation of the collimated output beam  240  and processing of the reflected collimated input beam  208 . While using at least one of the first sensor  230  or the second sensor  236  as a pixelated imager with the beam splitting surfaces appropriately spaced provides for determination of five degrees of freedom of the bore locating target assembly  120 , incorporating the time-of-flight pixelated sensor with three-dimensional time-of-flight sensor electronics provides for determination of the z-axis offset or distance of the camera system  200  from the bore locating target assembly  120 . Factoring in the z-axis offset with the x- and y-axis offsets identified above, and using the three angular offsets of the three mutually orthogonal axes provides for accurate measurement of six degrees of freedom of the bore locating target assembly  120 . Incorporating time-of-flight to establish the z-axis offset requires additional calculations. 
     While the exemplary embodiment shown in  FIG. 8  includes linearly arranged optics, alternative embodiments may be made of a more compact form factor, including a form factor in which the aperture is at an angle with respect to the boresight centerline  212 . 
       FIG. 10  illustrates a flow diagram of one example of the disclosed bore metrology method  10 . In an example, the bore metrology method  10  includes positioning  20  a bore locating target assembly  120  within an initial bore  104 . The bore locating target assembly  120  may include a self-centering insert  130 . Self-centering insert  130  may define a self-centering insert centerline  132 . The bore locating target assembly  120  may further include a distal end  134  and a proximal end  136 . 
     In an example, the bore metrology method  10  includes aligning  16  a first structure  102  with a second structure  112 . First structure  102  defines the initial bore  104 . Initial bore  104  may be cylindrical in shape. Initial bore  104  may have a first diameter D 1 . First structure  102  may include any material suitable for structural integrity and material properties necessary for its intended purpose including a metallic material. Aligning  16  may occur automatically via instructions from controller  400 . 
       FIGS. 5A and 5B  illustrate a detailed front view of second structure  112  of the bore metrology system  100 , shown with the second structure  112  positioned over and aligned with the first structure  102  such that the bore locating target assembly  120  in the first structure  102  is partially visible through a pilot bore  114  in the second structure  112 . In an example, second structure  112  defines a pilot bore  114  such that the initial bore  104  of first structure  102  is partially obstructed by the second structure  112  and the pilot bore  114  is superimposed with the initial bore  104 . Pilot bore  114  may be cylindrical in shape. Pilot bore  114  may have a second diameter D 2 . In an example, second diameter D 2  is smaller than the first diameter D 1  such that it has a smaller diameter than D 1 . Second structure  112  may include any material suitable for structural integrity and material properties necessary for its intended purpose including a fiber-reinforced composite material. Positioning  20  the bore locating target assembly  120  within the initial bore  104  may occur before aligning  16  the first structure  102  with the second structure  112  or after aligning  16  the first structure  102  with the second structure  112 . 
     The initial bore further includes a bore locating target assembly  120  within the initial bore  104 . In an example, the bore locating target assembly  120  further includes an optical target  122 . In an example, the optical target  122  is connected proximate the distal end  134  of the self-centering insert  130  of bore locating target assembly  120 . In an example, the optical target  122  defines an outer surface  133 . The outer surface  133  of the optical target  122  may be substantially perpendicular to the self-centering insert centerline  132 . The optical target  122  may further include a reflector  124  and an optical absorbing feature  126 . 
       FIGS. 6A and 6B  illustrate a detailed view of a portion of the bore metrology system  100 , depicting camera system  200  imaging a portion of the bore locating target assembly  120  that is visible through the pilot bore  114  in the second structure  112 . The optical absorbing feature  126  may be configured to define a pattern  128  on the optical target  122 . For example, the pattern  128  may be a polar reticle or the like. In an example, at least a reflector portion  124   a  of the reflector  124  and at least a pattern portion  128   a  of the pattern  128  defined on the optical target  122  are visible through the pilot bore  114 . Reflector  124  may include a silver coated polished surface (e.g., mirror) or any other material suitable for reflection. In an example, the optical absorbing feature  126  includes one or more of an etch, an ink, and a carbon-containing compound, or any combination thereof. 
       FIG. 7  illustrates a detailed view of a portion of the bore metrology system  100 , depicting a location of the pilot bore  114  vis-a-vis the bore locating target assembly  120  in the initial bore  104 . In an example, the bore metrology method  10  further includes imaging  22  the reflector portion  124   a  of the reflector  124  and the pattern portion  128   a  of the pattern  128  that are visible through the pilot bore  114 . Data captured during imaging  22  may be communicated to a controller  400  for analysis. The bore metrology method  10  further includes determining  24  a centerline  106  of the initial bore  104  based on the imaging  22 . Determining  24  may be performed by controller  400 . The determining  24  the centerline  106  of the initial bore  104  may include determining an angular orientation of the initial bore  104 . 
     In an example, the bore metrology method  10  may further include machining  12  ( FIG. 10 ) the initial bore  104  in the first structure  102 . The machining  12  of the initial bore  104  may be performed prior to the aligning  16  using a machining tool, such as a mill end or the like. The machining  12  of the initial bore  104  may be performed at the same location as the aligning  16  or at a different location. 
     In an example, the bore metrology method  10  may further include machining  14  ( FIG. 10 ) the pilot bore  114  in the second structure  112 . The machining  14  of the pilot bore  114  may be performed prior to the aligning  16  using a machining tool, such as a mill end or the like. The machining  14  of the pilot bore  114  may be performed at the same location as the aligning  16  and/or the machining  12 , or at a different location. 
     In an example, the bore metrology method  10  may further include fixing  18  the first structure  102  relative to the second structure  112 . Fixing  18  may occur after aligning  16  the first structure  102  with the second structure  112 . In an example, the imaging  22  may include positioning a camera system  200  having a field of view  202  such that the pilot bore  114  is within the field of view  202 . In an example, the imaging  22  may include projecting a collimated beam  204  of electromagnetic radiation onto the reflector portion  124   a  of the reflector  124  and the pattern portion  128   a  of the pattern  128  that are visible through the pilot bore  114 . Positioning the camera system  200  may be performed by an automated machine  300 . The determining  24  the centerline  106  of the initial bore  104  may include determining a surface vector V of the optical target  122  based on specular reflection of the collimated beam  204  of the electromagnetic radiation from the optical target  122 . 
     In an example, the self-centering insert  130  further includes a shaft  140 . Shaft  140  may define the self-centering insert centerline  132  and may further include a distal end portion  142  and a proximal end portion  144 . The self-centering insert  130  may further include a flange  146  proximate the distal end portion  142  of the shaft  140 . In an example, the self-centering insert  130  includes a nut  148  threaded into engagement with the proximal end portion  144  of the shaft  140 . The self-centering insert  130  may include a radially expandable bushing  150  that may be received over the shaft  140  and may further be positioned between the flange  146  and the nut  148 . In an example, axial compression of the radially expandable bushing  150  along the self-centering insert centerline  132  may cause corresponding radial expansion of the radially expandable bushing  150 . 
     In an example, the determining  24  the centerline  106  of the initial bore  104  includes determining a two-dimensional coordinate location of a center  129  of a portion of the optical target  122  that is visible through the pilot bore  114 . In an example, the determining  24  further includes determining translational offsets corresponding to a difference between the two-dimensional coordinate location of the center  129  of the portion of the optical target  122  that is visible through the pilot bore  114  and a two-dimensional coordinate location of a center  123  of the optical target  122 .  FIG. 7  illustrates a difference between an X-coordinate location of center  129  and an X-coordinate location of center  123 , as well as a difference between a Y-coordinate location of center  129  and a Y-coordinate location of center  123 . The determining the two-dimensional coordinate location of the center  129  of the portion of the optical target  122  that is visible through the pilot bore  114  may include applying a pattern matching algorithm to the portion of the optical target  122  that is visible through the pilot bore  114 . A controller  400  may be utilized to apply a pattern matching algorithm to the portion of the optical target  122  that is visible through the pilot bore  114 . 
     The bore metrology method  10  may further include machining  26  a matched bore  116  in the second structure  112  along the centerline  106  of the initial bore  104 . The machining  26  may be performed using the boring spindle  500  shown in  FIGS. 9A and 9B , or like apparatus. In an example, the machining  26  of the matched bore  116  in the second structure  112  further includes machining the second structure  112  without contacting the first structure  102 .  FIG. 9B  shows the boring spindle  500  drill location for when boring spindle  500  drills matched bore  116  in the second structure  112 . For illustrative purposes, portions of the second structure  112  are transparent so that the center of optical target  122  can be seen. 
       FIG. 11  is a flow diagram of an aircraft manufacturing and service methodology. Examples of the disclosure may be described in the context of an aircraft manufacturing and service method  1100 , as shown in  FIG. 11 , and an aircraft  1102 , as shown in  FIG. 12 . During pre-production, the aircraft manufacturing and service method  1100  may include specification and design  1104  of the aircraft  1102  and material procurement  1106 . During production, component/subassembly manufacturing  1108  and system integration  1110  of the aircraft  1102  takes place. Thereafter, the aircraft  1102  may go through certification and delivery  1112  in order to be placed in service  1114 . While in service by a customer, the aircraft  1102  is scheduled for routine maintenance and service  1116 , which may also include modification, reconfiguration, refurbishment and the like. 
     Each of the steps of method  1100  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. 
       FIG. 12  is a perspective view of an aircraft benefiting from the disclosed bore metrology methods and systems. As shown in  FIG. 12 , the aircraft  1102  produced by example method  1100  may include an airframe  1118  with a plurality of systems  1120  and an interior  1122 . Examples of the plurality of systems  1120  may include one or more of a propulsion system  1124 , an electrical system  1126 , a hydraulic system  1128 , and an environmental system  1130 . Any number of other systems may be included. 
     The disclosed methods and systems may be employed during any one or more of the stages of the aircraft manufacturing and service method  1100 . As one example, components or subassemblies corresponding to component/subassembly manufacturing  1108 , system integration  1110  and/or maintenance and service  1116  may be assembled using the disclosed methods and systems. As another example, the airframe  1118  may be constructed using the disclosed methods and systems. Also, one or more apparatus examples, method examples, or a combination thereof may be utilized during component/subassembly manufacturing  1108  and/or system integration  1110 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  1102 , such as the airframe  1118  and/or the interior  1122 . Similarly, one or more of system examples, method examples, or a combination thereof may be utilized while the aircraft  1102  is in service, for example and without limitation, to maintenance and service  1116 . 
     Aspects of disclosed examples may be implemented in software, hardware, firmware, or a combination thereof. The various elements of the system, either individually or in combination, may be implemented as a computer program product tangibly embodied in a machine-readable storage device for execution by a processor. Various steps of examples may be performed by a computer processor executing a program tangibly embodied on a computer-readable medium to perform functions by operating on input and generating output. The computer-readable medium may be, for example, a memory, a transportable medium such as a compact disk or a flash drive, such that a computer program embodying aspects of the disclosed examples can be loaded onto a computer. 
     The above-described methods and systems are described in the context of an aircraft. However, one of ordinary skill in the art will readily recognize that the disclosed methods and systems are suitable for a variety of applications, and the present disclosure is not limited to aircraft manufacturing applications. For example, the disclosed methods and systems may be implemented in various types of vehicles including, for example, helicopters, passenger ships, automobiles, marine products (boat, motors, etc.) and the like. Non-vehicle applications are also contemplated. 
     Also, although the above-description describes methods and systems that may be used to manufacture an aircraft or aircraft component in the aviation industry in accordance with various regulations (e.g., commercial, military, etc.), it is contemplated that the disclosed methods and systems may be implemented to facilitate manufacturing of a part in any industry in accordance with the applicable industry standards. The specific methods and systems can be selected and tailored depending upon the particular application. 
     Although various examples of the disclosed bore metrology methods and systems, and bore locating target assemblies for use therewith 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.