Patent Publication Number: US-2022214290-A1

Title: Methods and apparatus for measuring fastener concentricity

Description:
RELATED APPLICATION 
     The present application is a non-provisional of and claims priority to U.S. Provisional Patent Application No. 63/134,067, filed on Jan. 5, 2021, entitled “METHODS AND APPARATUS FOR MEASURING FASTENER CONCENTRICITY,” the complete disclosure of which is incorporated by reference. 
    
    
     FIELD 
     The present disclosure relates generally to systems and methods for inspecting fasteners, and more particularly to systems and methods for measuring concentricity and flushness of fasteners installed in a part. 
     BACKGROUND 
     Assemblies such as aircraft may include hundreds or thousands fasteners, which typically require substantial time to inspect, to verify that the fasteners are installed properly. For example, proper installation of a fastener for a given assembly may require that the fastener is perpendicular to the surfaces it joins, such that fasteners installed too oblique to the surface would be considered inadequate. When fastener installation is automated using robots to drill, install, and fasten rivets, for example, the ability to perform in-process open hole inspection may be lost. Current inspection techniques to inspect such fasteners installed in automated processes are destructive in nature. For example, rivet surface measurement is done using manual probes that give point measurements after removing fasteners for inspection. Furthermore, these techniques tend to be time-consuming, costly, and not very repeatable due to being operator-dependent. 
     SUMMARY 
     Presently disclosed systems and methods may be configured to provide nondestructive, quick, and automated inspection of installed fasteners in an assembly, such as an aircraft component. Such systems and methods may be configured to measure fastener concentricity, fastener flushness with a surface, and/or detect the presence of foreign object debris. 
     In an example, a system for inspecting a fastener installed at least partially through a hole in a part may include an x-ray imaging system, a first camera device, a second camera device, a first support structure, and at least one processing unit. The x-ray imaging system may be oriented and configured to produce an x-ray image of the fastener. The first camera device may be positioned and oriented such that it is configured to produce a first image of the fastener from a first vantage point, and the second camera device may be positioned and oriented such that it is configured to produce a second image of the fastener from a second vantage point. The x-ray imaging system, the first camera device, and the second camera device may be coupled to the first support structure. The first support structure may be configured to support and position the first camera device and the second camera device relative to the part and the fastener such that a 3D image of the fastener can be created from the first image and the second image. The at least one processing unit may be configured to create the 3D image of the fastener from the first image and the second image, and may be further configured to inspect the fastener based on the x-ray image and the 3D image, to determine concentricity and/or flushness of the fastener. 
     Disclosed methods of inspecting a fastener installed at least partially through a hole in a part generally include creating an x-ray image of the fastener via an x-ray imaging system, and measuring concentricity of the fastener, using the x-ray image. Additionally or alternatively, disclosed methods may include creating a 3D image of the fastener using a first image of the fastener and a second image of the fastener, wherein the first image is taken from a first vantage point, via a first camera device, and wherein the second image is taken from a second vantage point, via a second camera device, and measuring flushness of the fastener using the 3D image. Computer readable media having non-transitory computer readable instructions that, when executed by a processing unit, cause the processing unit to perform the disclosed methods are also disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic black box representation of examples of systems for inspecting fasteners, according to the present disclosure. 
         FIG. 2  is a schematic representation of an example of a system for inspecting fasteners, according to the present disclosure. 
         FIG. 3  is a top plan view of an example of a result from inspecting fastener concentricity, according to presently disclosed methods. 
         FIG. 4  is a top plan view of an example of a result from inspecting fastener concentricity, according to presently disclosed methods. 
         FIG. 5  is a schematic representation of the arrangement of first and second camera devices with respect to a fastener being inspected. 
         FIG. 6  illustrates results from inspecting two fasteners, illustrating one fastener that is adequately installed, and one that is inadequately installed. 
         FIG. 7  is a perspective view of one example of a support structure of presently disclosed systems. 
         FIG. 8  is a schematic flowchart diagram illustrating presently disclosed methods of inspecting installed fasteners. 
         FIG. 9  is a schematic flowchart diagram illustrating a decision tree for inspecting installed fasteners. 
     
    
    
     DESCRIPTION 
       FIGS. 1, 2, and 5  provide illustrative, non-exclusive examples of systems  10  according to the present disclosure. Elements that serve a similar, or at least substantially similar, purpose are labeled with like numbers in each of  FIGS. 1, 2, and 5 , and these elements may not be discussed in detail herein with reference to each of  FIGS. 1, 2, and 5 . Similarly, all elements may not be labeled in each of  FIGS. 1, 2 , and  5 , but reference numerals associated therewith may be utilized herein for consistency. Elements, components, and/or features that are discussed herein with reference to one or more of  FIGS. 1, 2, and 5  may be included in and/or utilized with any of  FIGS. 1, 2, and 5  without departing from the scope of the present disclosure. In general, elements that are likely to be included in a given (i.e., a particular) embodiment are illustrated in solid lines, while elements that are optional to a given embodiment are illustrated in dashed lines. However, elements that are shown in solid lines are not essential to all embodiments, and an element shown in solid lines may be omitted from a particular embodiment without departing from the scope of the present disclosure. 
     With reference to  FIGS. 1, 2, and 5 , systems  10  are configured for inspecting one or more fasteners  12  installed at least partially through one or more respective holes  14  in a part  16 . Examples will be described herein with reference to one or more fasteners  12  installed in an aircraft component (e.g., rivets in a wing panel). However, systems  10  may be used to inspect fasteners  12  installed in a wide variety of parts  16  from any industry, including but not limited to, the automotive, aerospace, marine, OEM, military, construction, transit, shipping, shelter, and cargo industries. Fasteners  12  may be configured to be at least substantially flush with one side of part  16 , at least substantially flush with both sides of part  16 , and/or may extend beyond one or both sides of part  16 , as schematically represented in  FIG. 1 . Systems  10  are configured to inspect fasteners  12  non-destructively, meaning that fasteners  12  may be inspected without being damaged or removed from part  16 . Systems  10  generally inspect fasteners  12  using a combination of radiography and image processing, combining computer vision and image processing algorithms for real-time detection and decision-making. Systems  10  further may be configured to inspect fastener  12  with only one-sided access to part  16 , in some examples. 
     Systems  10  generally include an x-ray imaging system  18 , a first camera device  20 , and a second camera device  22 . X-ray imaging system  18  is oriented and configured to produce an x-ray image of one or more fasteners  12  in part  16 . In some examples, x-ray imaging system  18  may be configured to produce an x-ray image of a single fastener  12  (e.g., fastener  12   a ) at a time, and then may be moved with respect to part  16  to produce other x-ray images of other fasteners (e.g., fastener  12   b ). In some examples, x-ray imaging system  18  may be configured to produce an x-ray image that encompasses a plurality of fasteners in a single x-ray image (e.g., fasteners  12   a,    12   b,  and  12   c ). 
     Similarly, first camera device  20  is positioned and oriented such that it is configured to produce a first image of one or more fasteners  12  in part  16 , from a first vantage point. In some examples, first camera device  20  may be configured to produce a respective first image of a single fastener  12  (e.g., fastener  12   a ) at a time, and then may be moved with respect to part  16  to produce other first images of other fasteners (e.g., fastener  12   b ). In some examples, first camera device  20  may be configured to produce a first image that encompasses a plurality of fasteners in a single first image (e.g., fasteners  12   a,    12   b,  and  12   c ). Likewise, second camera device  22  is positioned and oriented such that it is configured to produce a second image of one or more fasteners  12  in part  16 , from a second vantage point. In some examples, second camera device  22  may be configured to produce a respective second image of a single fastener  12  (e.g., fastener  12   a ) at a time, and then may be moved with respect to part  16  to produce other second images of other fasteners (e.g., fastener  12   b ). In some examples, second camera device  22  may be configured to produce a second image that encompasses a plurality of fasteners in a single second image (e.g., fasteners  12   a,    12   b,  and  12   c ). 
     Systems  10  also include at least one processing unit  24  configured to receive information (e.g., x-ray images, first images, and second images) from x-ray imaging system  18 , first camera device  20 , and second camera device  22 . Said information may be transmitted to processing unit  24  wirelessly, or processing unit  24  may be directly electrically coupled to x-ray imaging system  18 , first camera device  20 , and/or second camera device  22 . Processing unit  24  is configured to create a 3D image of one or more fasteners  12  from said information, such as using stereovision techniques. Processing unit  24  is configured to inspect fastener  12  based on the x-ray image received from x-ray imaging system  18 , and/or based on the 3D image of fastener  12 , as will be described in further detail herein. 
     Systems  10  also include a first support structure  26 , to which x-ray imaging system  18 , first camera device  20 , and second camera device  22  are coupled. First support structure  26  is configured to support and position first camera device  20  and second camera device  22  relative to part  16  and the fastener  12  being inspected such that a 3D image of fastener  12  can be created from the first image produced by first camera device  20  and the second image produced by second camera device  22 . Generally, first support structure  26  serves to position first camera device  20  and second camera device  22  such that first camera device  20  and second camera device  22  take images of fastener  12  from different angles, or vantage points. Support structure  26  generally supports x-ray imaging system  18  in a position in between first camera device  20  and second camera device  22 , though systems  10  are not limited to this arrangement. In some examples, first support structure  26  may include two or more support structures that may be linked together or that may move independently of one another, for positioning x-ray imaging system  18 , first camera device  20 , and second camera device  22  with respect to part  16  and fastener  12 . 
     First support structure  26  may be coupled to a first robot  28  that may be configured to control, orient, move, and/or position first support structure  26 , such as via a first robot arm  30  ( FIG. 2 ). First robot arm  30  may be configured to move first support structure  26  relative to part  16 , thereby adjusting a position of x-ray imaging system  18 , first camera device  20 , and second camera device  22  relative to fastener  12 . Systems  10  also may include an x-ray detector  32 , which may be coupled to a second support structure  34  and/or a second robot  36  (e.g., via a second robot arm  38  as shown in  FIG. 2 ). Second robot arm  38  may be configured to move second support structure  34  relative to part  16 , thereby adjusting a position of x-ray detector  32  relative to fastener  12 . As shown in  FIGS. 1 and 2 , x-ray imaging system  18  may be positioned on one side of part  16 , while x-ray detector  32  may be positioned on the opposite side of part  16 . Accordingly, first robot arm  30  may be positioned on one side of part  16 , while second robot arm  38  may be positioned on the opposite side of part  16 . In systems  10  including first robot  28  and second robot  36 , first robot  28  may be a commander, primary, or leader robot, that dictates movement of second robot  36 , which may be a secondary, or follower, robot. In some examples, first robot  28  and second robot  36  may be calibrated such that they move in tandem and with second robot arm  38  positioning x-ray detector  32  to face first support structure  26  and x-ray imaging system  18 , as positioned by first robot arm  30 , on the opposite side of part  16 . 
     Systems  10  are configured to measure concentricity of one or more fasteners  12  and/or flushness of one or more fasteners  12  with respect to part  16 . As used herein, “concentricity” of a fastener  12  refers to concentricity between two sides of the fastener, because fasteners  12  are configured to be perpendicular to part  16  when correctly installed in presently disclosed examples. Thus, when installed properly (i.e., such that a longitudinal axis  40  of fastener  12  is perpendicular to a plane defined by part  16 ), a circular plane defined by a first side  42  of fastener  12  is substantially concentric with a circular plane defined by a second side  44  of fastener  12 . As used herein, concentricity between first side  42  and second side  44  of fastener  12  also generally indicates concentricity with respect to hole  14  in which fastener  12  is installed. 
     With reference to  FIGS. 3-4 , processing unit  24  ( FIG. 1 ) may be configured to detect a first circle  66  and a second circle  68  from an x-ray image  70  of fastener  12 . First circle  66  corresponds to first side  42  of fastener  12  (e.g., the head of fastener  12 ), while second circle  68  corresponds to second side  44  of fastener  12  (e.g., the shaft of fastener  12 ). For example, processing unit  24  may include instructions to detect circular features whose nominal diameter is that of fastener  12  (e.g., the head or shaft of fastener  12 ). Processing steps may include basic denoising (Gaussian blurring, median filter, etc.), Canny edge detection, and/or Hough Circle detection. 
     Processing unit  24  is further configured to determine a first center  72  of first circle  66  and a second center  74  of second circle  68 , and to determine the offset, or distance, between first center  72  and second center  74 . Processing unit  24  may then determine whether the offset is within a predetermined pass/fail threshold offset distance. If first center  72  is farther from second center  74  than the predetermined pass/fail threshold offset distance, this may indicate that first circle  66  and second circle  68  are not sufficiently concentric, and therefore that fastener  12  is not adequately installed in part  16  because it is not sufficiently perpendicular to part  16 . In other words, the greater the offset between first center  72  and second center  74 , the more oblique fastener  12  may be with respect to part  16 .  FIG. 6  illustrates this concept in a different way, showing a fastener  12   d  that is adequately installed in part  16 , whereas a fastener  12   e  is oblique to part  16 , and thus inadequately installed. X-ray images  70  of each fastener  12   d,    12   e  are also shown. For example, x-ray image  70 d of fastener  12   d  illustrates that first circle  66  and second circle  68  are substantially concentric, which would correspond to a “pass” result for measuring concentricity of fastener  12   b.  On the other hand, x-ray image  70 e of fastener  12   e  reveals that first circle  66  is significantly offset from second circle  68  (due to the obliqueness of fastener  12   e  with respect to part  16 ), and thus x-ray image  70 e is an example of an image that would be interpreted as indicating an inadequately installed fastener, under certain threshold criteria. Fastener  12   e  accordingly may be indicated as inadequately installed and flagged for repair (e.g., reinstallation), removal, and/or replacement. 
     The predetermined threshold offset distance may be stored, for example, on a non-transitory computer readable memory  76  (also referred to herein as memory  76 ) ( FIG. 1 ) of system  10 . In this manner, system  10  may determine the quality of the installation of fastener  12 , as determined by concentricity of the two sides  42 ,  44  of fastener  12 . Processing unit  24  may include an x-ray image processing module for determining such concentricity of fastener  12 . Systems  10  may be said to be configured to inspect first side  42  (also referred to herein as first portion  42 ) and second side  44  (also referred to herein as second portion  44 ) of fastener  12  at least substantially simultaneously, because x-ray imaging system  18  may be configured to create an x-ray image of both first side  42  and second side  44  of fastener  12  in a single x-ray image. 
     As used herein, “flushness” refers to the degree to which the fastener  12  protrudes beyond a surface of part  16 , though systems  10  may be used to inspect fasteners  12  whether or not the fasteners are configured to be installed in hole  14  such that they are flush with part  16 . In other words, in some examples, fastener  12  may be entirely within hole  14  when properly installed, while in other examples, at least a portion of fastener  12  may be positioned externally to hole  14  when fastener  12  is properly installed. For example, fastener  12   b  is installed completely in hole  14 b in  FIG. 1 , such that first side, or first portion,  42   b  of fastener  12   b  is positioned adjacent a first surface  46  of part  16  and such that a second side, or second portion,  44 b of fastener  12   b  is positioned adjacent a second surface  48  of part  16 , with first surface  46  facing the first side of part  16  and second surface  48  facing the second side of part  16 . On the other hand, first side  42  and second side  44  of fastener  12   a  are positioned externally to its hole  14 , such that they protrude beyond first surface  46  and second surface  48 , respectively, of part  16 . 
     In some examples, system  10  is configured to inspect a height of a head of fastener  12  with respect to first surface  46  and/or second surface  48  of part  16 , thereby measuring flushness of fastener  12 . Processing unit  24  may include a 3D reconstruction module configured to determine flushness of fastener  12  by creating the 3D image of fastener  12  and the surface of part  16 . For example, once the 3D image of the fastener  12  is created from two or more images of fastener  12 , a point cloud of the 3D surface may be generated by processing unit  24 . Based on the 3D image, processing unit  24  may be configured to identify a surface of fastener  12  (e.g., the surface corresponding to first side  42 ), and to identify a surface of part  16  (e.g., first surface  46 ). Processing unit  24  may then be configured to fit a first plane to the surface of fastener  12 , and to fit a second plane to the surface of part  16 , in order to determine a height difference between the first plane and the second plane, thereby measuring flushness of fastener  12  with respect to first surface  46  of part  16 . One or more filters may be applied by processing unit  24  to the point cloud of the 3D surface of fastener  12  to identify the two surfaces, in some examples. 
     Additionally or alternatively, systems  10  may be configured to detect foreign object debris around fastener  12 , such as debris generated during installation of fastener  12 . Processing unit  24  may include a 2D processing module configured to detect foreign object debris around fastener  12 . In some examples of system  10 , processing unit  24  may be configured to identify objects with a surface area that is dissimilar to that of the head of fastener  12 , using image processing techniques (e.g., image classification algorithms), and based on the x-ray image of fastener  12 , the 3D reconstruction of fastener  12  and/or part  16 , and/or 2D images of fastener  12  and/or part  16 . For example, processing unit  24  may be configured to detect circular features having a diameter matching a known diameter of a head of fastener  12 , and to apply high pass filtering to eliminate background, and thereby detect any foreign object debris adjacent, or in the vicinity of, fastener  12 . 
     Memory  76  of processing unit  24  may store non-transitory computer readable instructions that, when executed by processing unit  24 , cause processing unit  24  to measure concentricity of fastener  12 , measure flushness of fastener  12  with respect to part  16 , and/or detect foreign object debris near fastener  12 . Threshold pass/fail criteria for fastener inspections may be stored on memory  76 . Furthermore, the instructions, when executed by processing unit  24 , may be configured to cause processing unit  24  to automatically mark, indicate, or flag any detected defective fasteners  12 . 
     Systems  10  may be configured to inspect a plurality of fasteners  12  installed in part  16 , while first robot  28  may be configured to scan part  16  as the plurality of fasteners  12  are inspected, in order to determine contours of part  16 . In this manner, processing unit  24  may determine movement of first robot arm  30 , based on the scan of part  16 , in order to position x-ray imaging system  18 , first camera device  20 , and second camera device  22  relative to the respective fastener  12  of the plurality of fasteners being inspected. In some examples, first support structure  26  is configured to be moved with respect to part  16  in between subsequent respective fastener inspections, such that x-ray imaging system  18 , first camera device  20 , and second camera device  22  are correctly positioned and oriented with respect to each respective fastener  12  being inspected. Second robot  36  may be configured to synchronously scan the part, along with first robot  28 , as the plurality of fasteners  12  are inspected, in order to determine contours of part  16 , thereby determining movement of second robot arm  38  to position x-ray detector  32  relative to the respective fastener  12  of the plurality of fasteners being inspected, or relative to first support structure  26 . 
     As shown in  FIG. 2 , commander robot  28  and/or follower robot  36  may be positioned on a sliding motion stage  90 . Sliding motion stage  90  may be configured to slide, or translate, within a workspace environment in order to position first robot  28  and second robot  36  to examine fasteners  12  in a plurality of different, spaced apart, parts  16 . Additionally or alternatively, sliding motion stage  90  may be configured to allow for movement of first robot  28  and/or second robot  36  with respect to part  16 , such that systems  10  may be positioned and oriented as desired for inspecting fasteners  12 . 
     First support structure  26  may be, or include, a first rigid linear platform, in some systems  10 . For example, first support structure  26  may be, or include, a C-beam railing. Similarly, second support structure  34  may be, or include, a second rigid linear platform, such as a C-beam railing. An example of a structure that may serve as first support structure  26  and/or second support structure  34  is illustrated in  FIG. 7 . X-ray imaging system  18 , first camera device  20 , and second camera device  22  may be coupled to first support structure  26  collinearly. 
     With continued reference to  FIGS. 1, 2, and 5 , X-ray imaging system  18  is a portable, mobile, and/or handheld x-ray imaging system  18  in some examples, though generally x-ray imaging system  18  may be any x-ray system configured to produce x-ray images of fastener  12 . First camera device  20  and/or second camera device  22  may be first and second pinhole cameras in some examples, though generally first camera device  20  and second camera device  22  may be any camera device configured to produce images of fastener  12 . System  10  in general may be portable and mounted on various robot arms in different work cells or locations. 
     Systems  10  may be configured to automatically mark, or indicate, defectively installed or unsatisfactorily installed fasteners, if any are deemed unsatisfactory as a result of inspection. Such fasteners that fail inspection may be flagged for manual inspection and/or for removal from part  16 . In some examples, systems  10  may be configured to inspect each fastener  12  in a given part  16 . In other examples, systems  10  may be configured to inspect just a subset of fasteners  12  in a given part  16 , though said systems  10  may be configured to inspect additional fasteners  12  in the vicinity of a defectively installed fastener. First robot arm  30  also may be used to install fasteners  12  in part  16 , and systems  10  may thus inspect such fasteners  12  in real-time, as they are installed. Systems  10  also may be configured for automated examination of x-ray images produced by x-ray imaging system  18 , such that fastener concentricity may be determined in real-time, at the time the fastener is installed. 
     As noted above, x-ray imaging system  18  may be positioned between first camera device  20  and second camera device  22 . In some examples, first camera device  20  and second camera device  22  are symmetrically positioned on either side of x-ray imaging system  18 , such that first camera device  20  and second camera device  22  may be at least substantially equidistant from x-ray imaging system  18 . Additionally or alternatively, first camera device  20  and second camera device  22  may be symmetrically positioned on either side of the center of hole  14  of fastener  12  being inspected. 
     With reference to  FIG. 5 , a distance  50  between first camera device  20  and second camera device  22 , a first angle  52  of first camera device  20  with respect to first support structure  26  ( FIG. 2 ), and/or a second angle  54  of second camera device  22  with respect to first support structure  26  may be selectively adjusted to position fastener  12  within a first central region  56  of a first field of view  58  of first camera device  20  and within a second central region  60  of a second field of view  62  of second camera device  22 . Distance  50  between first camera device  20  and second camera device  22  (and/or angles  52  and  54 ) may be chosen such that fastener  12  is positioned at the center of first field of view  58  and second field of view  62 . In some examples, distance  50  may be about 6 inches, about 8 inches, about 10 inches, about 12 inches, about 16 inches, about 20 inches, about 24 inches, about 28 inches, about 32 inches, about 36 inches, and/or greater than 36 inches. Distance  50  may vary depending on the size of part  16 , the size of fastener  12 , and/or first angle  52  and second angle  54 . First angle  52  and second angle  54  may be at least substantially equal in some examples. In other examples, first angle  52  may be different from second angle  54 . First angle  52  and/or second angle  54  may be about 45 degrees in some examples. In other examples, first angle  52  and/or second angle  54  may be between 0-45 degrees, between 45-90 degrees, between 90-135 degrees, and/or between 135-180 degrees. 
     Additionally or alternatively, a first standoff distance  64  between first support structure  26  and fastener  12  may be optimized for both stereographs and radiographs. For example, first standoff distance  64  may be at least 6 inches, at least 8 inches, at least 10 inches, at least 12 inches, at least 14 inches, at least 16 inches, at least 18 inches, and/or at least 20 inches. In a specific example, first standoff distance  64  may be between 12-16 inches. First standoff distance  64  may be selected or set relative to distance  50  between first camera device  20  and second camera device  22 , in view of first angle  52  and second angle  54 . First standoff distance  64  may be less than distance  50 , such as about 75% of distance  50 , about 50% of distance  50 , and/or about 25% of distance  50 . In some examples, first standoff distance  64  may be between 25-75% of distance  50 . In other examples, first standoff distance  64  may be greater than distance  50 . Additionally or alternatively, a second standoff distance between x-ray detector  32  ( FIG. 2 ) and fastener  12  may be selectively adjusted according to a desired geometric magnification of the x-ray image produced by x-ray imaging system  18 . First standoff distance  64  may be selectively adjusted via movement of first robot arm  30 , while the second standoff distance may be selectively adjusted via movement of second robot arm  38  ( FIG. 2 ). 
     Generally, system  10  includes processing unit  24 , where, in operation, processing unit  24  executes computer-readable instructions (stored on a memory  76  of processing unit  24 ) to fasteners  12  in order to detect any fasteners that are unsatisfactorily installed, in which case processing unit  24  may automatically indicate the fastener or fasteners that failed inspection. Accordingly, system  10  may serve as an automated, real-time fastener installation and inspection system. In a specific example, an onboard processing unit  24  such as Raspberry Pi can be used to provide various commands, data collection, and to perform the analysis of fasteners  12 . Processing unit  24  may be positioned on board first robot  28 , coupled to support structure  26 , and/or on board second robot  36 . In other examples, processing unit  24  may be positioned remotely from first robot  28  and second robot  36 . Processing unit  24  may be integrated into first robot  28  and/or second robot  36  at the time of manufacture. In other examples, first robot  28  and/or second robot  36  may be outfitted (e.g., retrofit) with processing unit  24  after its initial manufacture. 
     Turning now to  FIG. 7 , illustrative non-exclusive examples of first support structure  26  and/or second support structure  34 , in the form of a C-beam railing  78  are illustrated. Where appropriate, the reference numerals from the schematic illustrations of  FIGS. 1, 2, and 5  are used to designate corresponding parts in  FIG. 7  however, the examples of  FIGS. 1, 2, and 5  are non-exclusive and do not limit first support structure  26  or second support structure  34  to the illustrated example of  FIG. 7 . That is, first support structure  26  and second support structure  34  are not limited to the illustrated C-beam railing  78  and may incorporate any number of the various aspects, configurations, characteristics, properties, etc. of first support structure  26  or second support structure  34  that are illustrated in and discussed with reference to the schematic representations of  FIG. 1, 2 , or  5 , and/or the example of  FIG. 7 , as well as variations thereof, without requiring the inclusion of all such aspects, configurations, characteristics, properties, etc. For the purpose of brevity, each previously discussed component, part, portion, aspect, region, etc. or variants thereof may not be discussed, illustrated, and/or labeled again with respect to C-beam railing  78 ; however, it is within the scope of the present disclosure that the previously discussed features, variants, etc. may be utilized therewith. 
       FIG. 7  illustrates an example of first support structure  26  and/or second support structure  34 , in the form of a C-beam railing  78 . C-beam railing  78  includes a plurality of holes  80  spaced apart along a length  82  of C-beam railing  78 . For example, C-beam railing  78  may include a plurality of holes  80  along a first, or upper lip, or flange,  84  and along a second, or lower lip, or flange,  86 . One or more of holes  80  may be threaded, in some examples. Holes  80  may be said to include a first plurality of holes  80  along upper lip  84  and a second plurality of holes  80  along lower lip  86 , with the respective holes  80  being spaced relative to one another on upper lip and lower lip  84 ,  86  respectively, such that set screws may be inserted through one or more holes  80  on upper lip  84  and one or more holes  80  on lower lip  86  to limit or restrict movement of x-ray imaging system  18 , first camera device  20 , and/or second camera device  22 , via rings  88 . Rings  88  may be configured to linearly translate such that they slide longitudinally along length  82  of C-beam railing  78 , unless a set screw (or bolt, post, pin, etc.) is inserted through holes  80  to prevent such sliding movement of rings  88 . For example, a first set screw inserted through hole  80   a  and a second set screw inserted through hole  80   b  may substantially limit or prevent linear translation of ring  88   a  along C-beam railing  78 . 
     In some examples, x-ray imaging system  18  may be coupled to one of rings  88  (e.g., ring  88   a ), first camera device  20  may be coupled to one of rings  88  (e.g., ring  88   b ), and second camera device  22  may be coupled to one of rings  88  (e.g., ring  88   c ). In this manner, linear translation of rings  88  thereby causes movement of the device coupled to the respective ring  88 . In some examples, the angle and position of x-ray imaging system  18  may be adjusted with respect to fastener  12  via ring  88   a.  Similarly, the angle and position of first camera device  20  may be adjusted with respect to fastener  12  via ring  88   b,  and the angle and position of second camera device  22  may be adjusted with respect to fastener  12  via ring  88   c.  When moving first camera device  20  and/or second camera device  22  (and/or when changing the focus of first camera device  20  and/or second camera device  22 , systems  10  may be configured to allow for correction of lens distortion and for calibration of first camera device  20  and/or second camera device  22  (e.g., calibration for pixels-to-inches conversion). For example, calibration of first camera device  20  and/or second camera device  22  may be performed using one or more images of a standard check-board pattern and a calibration module stored on processing unit  24 . Similarly, when moving x-ray imaging system  18 , x-ray parameters may be set to optimize image quality of resulting x-ray images. For example, image quality indicators may be placed on part  16  and/or fastener  12  to verify x-ray image quality. 
       FIGS. 8-9  schematically provide flowcharts that represent illustrative, non-exclusive examples of methods according to the present disclosure. In  FIGS. 8-9 , some steps are illustrated in dashed boxes indicating that such steps may be optional or may correspond to an optional version of a method according to the present disclosure. That said, not all methods according to the present disclosure are required to include the steps illustrated in solid boxes. The methods and steps illustrated in  FIGS. 8-9  are not limiting and other methods and steps are within the scope of the present disclosure, including methods having greater than or fewer than the number of steps illustrated, as understood from the discussions herein. 
       FIG. 8  illustrates methods  100  of inspecting a fastener (e.g., fastener  12 ) installed at least partially through a hole in a part (e.g., hole  14  of part  16 ). Methods  100  generally include creating an x-ray image of the fastener via an x-ray imaging system (e.g., x-ray imaging system  18 ), at  102 , and measuring concentricity of the fastener using the x-ray image, at  104 . Measuring concentricity at  104  may be performed by one or more processing units (e.g., processing unit  24 ). Measuring concentricity at  104  may include detecting a first circle corresponding to a first side of the fastener (e.g., a head of the fastener, such as first side  42 ), detecting a second circle corresponding to a second side of the fastener (e.g., a shaft of the fastener, such as second side  44 ), determining a first center of the first circle (e.g., first center  72  of first circle  66 ), determining a second center of the second circle (e.g., second center  74  of second circle  68 ), and determining an offset distance between the first center and the second center. Measuring concentricity at  104  also may include determining whether the offset distance is within a predetermined pass/fail threshold offset distance and/or indicating whether the offset distance is within the predetermined pass/fail threshold offset distance for each fastener inspected. 
     Methods  100  may include determining whether a particular fastener is pass/fail (e.g., whether it is installed adequately, overall, for the requirements or installation criteria of the fastener), at  120 . For example, if the measuring concentricity at  104  indicated that the offset distance is not within the predetermined pass-fail threshold offset distance, then that may be sufficient criteria for a “fail” determination at step  120 . The determining pass/fail for a given fastener at  120  generally includes determining whether the fastener is installed adequately for the given circumstances, and may be based on measuring concentricity at  104 , measuring flushness at  108 , and/or inspecting for foreign object debris at  110 . In some examples, the determining pass/fail for a given fastener at  120  includes performing a quality threshold calculation. 
     The determining pass/fail for a fastener at  120  may including indicating which fasteners have been installed adequately and/or which fasteners are inadequately installed. For example, an inadequately installed fastener may be indicated at  120  by recording or noting the location of the inadequately installed fastener, by physically marking the inadequately installed fastener, by alerting an operator of the inadequately installed fastener, by recording or noting an identification number or other identifier of the inadequately installed fastener, and/or by any other means of indicating that a particular fastener is not installed adequately. In some methods  100 , after determining that a respective fastener is installed unsatisfactorily at  120 , the respective fastener may be removed from the part at  126 , and the respective fastener may be replaced with a new fastener installed in the part. 
     Methods  100  also may include creating a 3D image, or 3D reconstruction, of the fastener using a first image of the fastener and a second image of the fastener, at  106 . The first image of the fastener is taken from a first vantage point (e.g., by first camera device  20 ), and the second image of the fastener is taken from a second vantage point (e.g., by second camera device  22 ). The 3D image of the fastener may be created at  106  by the processing unit, using stereovision, structured light projection, laser scanning, and/or any other suitable technique. For example, the creating the 3D image of the fastener at  106  may include capturing two images of the fastener (e.g., via first camera device and second camera device), reconstructing a 3D surface of the fastener, and generating a point cloud of the 3D surface using stereo vision techniques. Additionally or alternatively, the creating the 3D image of the fastener at  106  may include calibrating the first camera device and the second camera device relative to one another and relative to the fastener such that the first camera device and the second camera device are configured to take images configured to create a 3D reconstruction of the fastener installed in the part. 
     Flushness of the fastener with a surface of the part may be measured by the processing unit, using the 3D image of the fastener, at  108 . For example, the measuring flushness of a fastener at  108  may include identifying a first surface of the fastener, identifying a second surface of the part, fitting a first plane to the first surface, fitting a second plane to the second surface, and determining a height difference between the first plane and the second plane, thereby measuring flushness of the fastener. One or more filters may be applied to a point cloud of the 3D surface of the fastener to identify the first surface and/or the second surface. 
     Additionally or alternatively, a vicinity of the fastener may be inspected for foreign object debris at  110 . For example, the detecting foreign object debris at  110  may include identifying objects with a surface area that is dissimilar to that of the head of the fastener, using image processing techniques (e.g., image classification algorithms), and based on the x-ray image of the fastener, the 3D reconstruction of the fastener and part surface, and/or 2D images of the fastener and part surface. In a specific example, the inspecting for foreign object debris at  110  may include applying image processing to detect circular features having a diameter matching a known diameter of a head of the fastener, applying high pass filtering to eliminate background, and thereby detecting any foreign object debris adjacent, or in the vicinity of, the fastener. 
     In some methods  100 , the x-ray imaging system may be coupled to a first support structure (e.g., first support structure  26 ), at  112 . The coupling the x-ray imaging system to the first support structure at  112  also may include coupling the first camera device and/or the second camera device to the first support structure as well. The x-ray imaging system may be moved and/or positioned with respect to the part and/or fastener at  114 , along with the first and second camera devices, such as by coupling the first support structure to a robot arm and moving the robot arm to position the x-ray imaging system, the first camera device, and the second camera device relative to the fastener and the part. Some methods  100  may include scanning the part at  116  before the moving and/or positioning the x-ray imaging system at  114 , with the scan of the part informing the movement of the robot arm and thereby the movement of the x-ray imaging system. The scanning the part at  116  may include determining contours of the part and planning movement of the first robot arm to position the x-ray imaging system relative to a respective fastener of a plurality of fasteners being inspected. In some methods  100 , the scanning the part at  116  may be performed in tandem with the measuring concentricity at  104 , the measuring flushness at  108 , and/or the inspecting for foreign object debris at  110 . For example, the processing unit of disclosed systems may be determining concentricity at the current location, while another region of the part is being scanned in preparation for measuring concentricity at the next location of the subsequent fastener to be measured. 
     Methods  100  may include positioning the x-ray imaging system on a first side of the part via the moving the x-ray imaging system at  114 , and also coupling an x-ray detector (e.g., x-ray detector  32 ) to a second support structure at  118  and positioning the x-ray detector on the opposite side of the part from the x-ray imaging system. Coupling and positioning the x-ray detector at  118  may include selectively adjusting a stand-off distance between the x-ray detector and the part, based on, for example, the desired geometric magnification of the x-ray image. The second support structure may be coupled to a second robot arm, such as one coupled to a second robot, which may thereby control movement of the x-ray detector relative to the part and the fastener (and relative to the first robot arm and the x-ray imaging system). The second robot may be a follower robot to a commander robot controlling movement of the first support structure. In this manner, the two robot arms may be configured to move in a coordinated manner such that the x-ray imaging system and x-ray detector are positioned relative to each other and relative to the fastener to create an x-ray image of the fastener as described herein. 
     In some methods  100 , the flushness, concentricity, and/or presence of foreign object debris is measured or detected for a plurality of fasteners in a given part. In other words, the measuring concentricity at  104 , the measuring flushness at  108 , and/or the inspecting a fastener vicinity for foreign object debris at  110  may be performed a plurality of times, such as being performed for each fastener being inspected. In these examples, methods  100  may include the moving and/or positioning the x-ray imaging system at  114  between each performance of the measuring concentricity at  104 , the measuring flushness at  108 , and/or the inspecting a fastener vicinity for foreign object debris at  110 . For example, concentricity of a first fastener may be measured at  104 , flushness of the first fastener may be measured at  108 , and/or the first fastener may be inspected for foreign object debris in its vicinity at  110 , and then the x-ray imaging system may be moved and/or positioned at  114  before measuring concentricity of a second fastener may be measured at  104 , flushness of the second fastener may be measured at  108 , and/or the second fastener may be inspected for foreign object debris in its vicinity at  110 . 
     Fasteners may be inspected on a zone basis, in some methods  100 . For example, a part having a plurality of fasteners may be divided into two or more different zones, with each zone having a plurality of fasteners therein. When inspecting fasteners in a part, disclosed systems may inspect a predetermined number of fasteners (one or more) within a given zone, rather than every fastener in the zone. If the inspected fastener or fasteners in a zone are adequately installed, the system may move on to a different zone and inspect one or more fasteners in that zone, at  124 . If, on the other hand, one or more fasteners in a given zone are found to be inadequately installed, then one or more other fasteners in the same zone may be inspected, beyond the original number of fasteners inspected, at  122 . In this manner, disclosed systems may inspect a sample of fasteners in a part, and increase the sampling in areas, or zones, where one or more fasteners is determined to be inadequately installed. Thus, the measuring concentricity at  104  may include measuring concentricity of a first fastener in a first zone of the part and measuring concentricity of a second fastener within a second zone of the part. The measuring concentricity at  104  may include measuring concentricity of at least one fastener in each of a plurality of zones of the part. 
     Non-transitory computer readable instructions for performing the measuring concentricity at  104 , the moving and/or positioning the x-ray system at  114 , the scanning the part at  116 , the creating the 3D image of the fastener at  106 , the measuring flushness at  108 , the inspecting for foreign object debris at  110 , and/or the determining a pass/fail status of the fastener at  120  may be stored on a computer readable medium and/or on the memory of the processing unit of disclosed systems, and that may be executed by the processing unit of systems.  FIG. 9  schematically illustrates an example algorithm  200  that may be executed by processing unit  24  and stored on memory  76 , in order to inspect one or more fasteners  12  installed in part  16 . Briefly, the system may be positioned with respect to the fastener being inspected, as indicated by move to position at  202 . An x-ray system control module of the processing unit may be activated at  204  to trigger x-ray image collection of the faster. An x-ray image processing module of the processing unit may be activated at  206  to perform a concentricity calculation at  208 . Whether in parallel or in series, a visual camera control module of the processing unit may be activated at  210  to trigger optical image collection by the first and second camera devices. A 2D image processing module of the processing unit may be activated at  212  to perform foreign object debris detection at  214 , and a 3D reconstruction module of the processing unit may be activated at  216  to perform flushness estimation at  218 . Quality metric assessment may be performed by the processing unit at  220  to determine whether a given fastener being inspected has passed all metrics that were measured, at  224 . If all the measured metrics have a “pass” result, then the inspected fastener is deemed adequately installed, whereas if one or more of the measured metrics have a “fail” result, then the inspected fastener is deemed inadequately installed, and flagged for removal or repair. 
     Illustrative, non-exclusive examples of inventive subject matter according to the present disclosure are described in the following enumerated paragraphs: 
     A1. A system ( 10 ) for inspecting a fastener ( 12 ) installed at least partially through a hole ( 14 ) in a part ( 16 ), the system ( 10 ) comprising: 
     an x-ray imaging system ( 18 ) oriented and configured to produce an x-ray image ( 70 ) of the fastener ( 12 ); 
     a first camera device ( 20 ) positioned and oriented such that it is configured to produce a first image of the fastener ( 12 ) from a first vantage point; 
     a second camera device ( 22 ) positioned and oriented such that it is configured to produce a second image of the fastener ( 12 ) from a second vantage point; 
     a first support structure ( 26 ) to which the x-ray imaging system ( 18 ), the first camera device ( 20 ), and the second camera device ( 22 ) are coupled, wherein the first support structure ( 26 ) is configured to support and position the first camera device ( 20 ) and the second camera device ( 22 ) relative to the part ( 16 ) and the fastener ( 12 ) such that a 3D image of the fastener ( 12 ) can be created from the first image and the second image; and 
     at least one processing unit ( 24 ) configured to create the 3D image of the fastener ( 12 ) from the first image and the second image, wherein the at least one processing unit ( 24 ) is further configured to inspect the fastener ( 12 ) based on the x-ray image ( 70 ) and the 3D image. 
     A1.1. The system ( 10 ) of paragraph A1, wherein the system ( 10 ) is configured to measure concentricity of the fastener ( 12 ). 
     A1.2. The system ( 10 ) of paragraph A1 or A1.1, wherein the system ( 10 ) is configured to measure flushness of the fastener ( 12 ) with respect to the part ( 16 ). 
     A2. The system ( 10 ) of any of paragraphs A1-A1.2, further comprising an x-ray detector ( 32 ), wherein the x-ray imaging system ( 18 ) is positioned on a first side of the part ( 16 ), wherein the x-ray detector ( 32 ) is positioned on a second side of the part ( 16 ) such that the x-ray imaging system ( 18 ) and the x-ray detector ( 32 ) are on opposite sides of the part ( 16 ). 
     A3. The system ( 10 ) of paragraph A2, wherein the x-ray detector ( 32 ) is coupled to a second support structure ( 34 ). 
     A4. The system ( 10 ) of any of paragraphs A1-A3, wherein the first support structure ( 26 ) comprises a first rigid linear platform. 
     A4.1. The system ( 10 ) of any of paragraphs A1-A4, wherein the first support structure ( 26 ) comprises a C-beam railing ( 78 ). 
     A4.2. The system ( 10 ) of any of paragraphs A1-A4.1, wherein the first support structure ( 26 ) comprises a plurality of holes ( 14 ) spaced apart along a length of the first support structure ( 26 ). 
     A4.3. The system ( 10 ) of paragraph A4.2, wherein the plurality of holes ( 14 ) comprises a plurality of threaded holes ( 14 ). 
     A4.4. The system ( 10 ) of paragraph A4.2 or A4.3, wherein the plurality of holes ( 14 ) comprises a first plurality of holes ( 14 ) spaced apart along a first lip ( 84 ) of the first support structure ( 26 ), wherein the plurality of holes ( 14 ) comprises a second plurality of holes ( 14 ) spaced apart along a second lip ( 86 ) of the support structure, and wherein the first plurality of holes ( 14 ) is spaced relative to the second plurality of holes ( 14 ) such that set screws inserted through one or more of the first plurality of holes ( 14 ) and one or more of the second plurality of holes ( 14 ) may be configured to limit or restrict movement of the x-ray imaging system ( 18 ), the first camera device ( 20 ), and/or the second camera device ( 22 ). 
     A5. The system ( 10 ) of any of paragraphs A1-A4.4, wherein a/the second support structure ( 34 ) comprises a second rigid linear platform. 
     A5.1. The system ( 10 ) of any of paragraphs A1-A5, wherein a/the second support structure ( 34 ) comprises a second C-beam railing ( 78 ). 
     A5.2. The system ( 10 ) of any of paragraphs A1-A5.1, wherein a/the second support structure ( 34 ) comprises a plurality of holes ( 14 ) spaced apart along a length of the second support structure ( 34 ). 
     A6. The system ( 10 ) of any of paragraphs A1-A5.2, wherein the first support structure ( 26 ) is coupled to a first robot arm ( 30 ). 
     A7. The system ( 10 ) of paragraph A6, wherein the first robot arm ( 30 ) is configured to move the first support structure ( 26 ) relative to the part ( 16 ), thereby adjusting a position of the x-ray imaging system ( 18 ), the first camera device ( 20 ), and the second camera device ( 22 ) relative to the fastener ( 12 ). 
     A7.1. The system ( 10 ) of paragraph A7, wherein the first robot arm ( 30 ) is coupled to a commander robot ( 28 ). 
     A7.2. The system ( 10 ) of paragraph A7.1, wherein the commander robot ( 28 ) is positioned on a sliding motion stage ( 90 ). 
     A7.3. The system ( 10 ) of paragraph A7.1 or A7.2, wherein the system ( 10 ) is configured to inspect a plurality of fasteners ( 12 ) installed in the part ( 16 ), wherein the commander robot ( 28 ) is configured to scan the part ( 16 ) as the plurality of fasteners ( 12 ) are inspected, in order to determine contours of the part ( 16 ), thereby determining movement of the first robot arm ( 30 ) to position the x-ray imaging system ( 18 ), the first camera device ( 20 ), and the second camera device ( 22 ) relative to the respective fastener ( 12 ) of the plurality of fasteners ( 12 ) being inspected. 
     A7.4. The system ( 10 ) of any of paragraphs A1-A7.3, wherein the system ( 10 ) is configured to inspect a/the plurality of fasteners ( 12 ) installed in the part ( 16 ), wherein the first support structure ( 26 ) is configured to be moved with respect to the part ( 16 ) in between subsequent respective fastener ( 12 ) inspections, such that the x-ray imaging system ( 18 ), the first camera device ( 20 ), and the second camera device ( 22 ) are correctly positioned and oriented with respect to each respective fastener ( 12 ) being inspected. 
     A8. The system ( 10 ) of any of paragraphs A1-A7.4, wherein a/the second support structure ( 34 ) is coupled to a second robot arm ( 38 ). 
     A9. The system ( 10 ) of paragraph A8, wherein the second robot arm ( 38 ) is configured to move the second support structure ( 34 ) relative to the part ( 16 ), thereby adjusting a position of a/the x-ray detector ( 32 ) relative to the fastener ( 12 ). 
     A9.1. The system ( 10 ) of paragraph A9, wherein the second robot arm ( 38 ) is coupled to a follower robot ( 36 ). 
     A9.2. The system ( 10 ) of paragraph A9.1, wherein the follower robot ( 36 ) is positioned on a/the sliding motion stage ( 90 ). 
     A9.3. The system ( 10 ) of paragraph A9.1 or A9.2, wherein the system ( 10 ) is configured to inspect a/the plurality of fasteners ( 12 ) installed in the part ( 16 ), wherein the follower robot ( 36 ) is configured to synchronously scan the part ( 16 ), along with a/the commander robot ( 28 ), as the plurality of fasteners ( 12 ) are inspected, in order to determine contours of the part ( 16 ), thereby determining movement of the second robot arm ( 38 ) to position the x-ray detector ( 32 ) relative to the respective fastener ( 12 ) of the plurality of fasteners ( 12 ) being inspected, or relative to the first support structure ( 26 ). 
     A10. The system ( 10 ) of any of paragraphs A1-A9.3, wherein a/the first robot arm ( 30 ) is positioned on a/the first side of the part ( 16 ), and wherein a/the second robot arm ( 38 ) is positioned on a/the second side of the part ( 16 ). 
     A11. The system ( 10 ) of any of paragraphs A1-A10, wherein the part ( 16 ) comprises a panel. 
     A12. The system ( 10 ) of any of paragraphs A1-A11, wherein the fastener ( 12 ) is installed completely through the hole ( 14 ) such that a first portion of the fastener ( 12 ) is positioned adjacent a first surface ( 46 ) of the part ( 16 ) and such that a second portion of the fastener ( 12 ) is positioned adjacent a second surface ( 48 ) of the part ( 16 ), wherein the first surface ( 46 ) faces a/the first side of the part ( 16 ), and wherein the second surface ( 48 ) faces a/the second side of the part ( 16 ). 
     A12.1. The system ( 10 ) of paragraph A12, wherein the system ( 10 ) is configured to inspect the first portion of the fastener ( 12 ) and the second portion of the fastener ( 12 ) at least substantially simultaneously. 
     A13. The system ( 10 ) of any of paragraphs A1-A12.1, wherein the system ( 10 ) is configured to inspect the fastener ( 12 ) non-destructively. 
     A14. The system ( 10 ) of any of paragraphs A1-A13, wherein the system ( 10 ) is configured to detect fastener ( 12 ) concentricity, fastener ( 12 ) orientation, and foreign object debris generated during installation of the fastener ( 12 ). 
     A14.1. The system ( 10 ) of any of paragraphs A1-A14, wherein the system ( 10 ) is configured to inspect a height of a head of the fastener ( 12 ) with respect to a/the first surface ( 46 ) of the part ( 16 ) and/or with respect to a/the second surface ( 48 ) of the part ( 16 ). 
     A15. The system ( 10 ) of any of paragraphs A1-A14.1, wherein the system ( 10 ) is configured to inspect the fastener ( 12 ) with only one-sided access to the part ( 16 ). 
     A16. The system ( 10 ) of any of paragraphs A1-A15, wherein the x-ray imaging system ( 18 ) comprises a portable, mobile, and/or handheld x-ray imaging system ( 18 ). 
     A17. The system ( 10 ) of any of paragraphs A1-A16, wherein the first camera device ( 20 ) comprises a first pinhole camera. 
     A18. The system ( 10 ) of any of paragraphs A1-A17, wherein the second camera device ( 22 ) comprises a second pinhole camera. 
     A19. The system ( 10 ) of any of paragraphs A1-A18, wherein the system ( 10 ) is configured such that a first angle ( 52 ) and/or a first position of the x-ray imaging system ( 18 ) with respect to the fastener ( 12 ) may be selectively adjusted via one or more rings ( 88 ) and/or one or more set screws operatively coupled to the first support structure ( 26 ). 
     A19.1. The system ( 10 ) of any of paragraphs A1-A19, wherein the x-ray imaging system ( 18 ) is coupled to one or more rings ( 88 ), wherein the one or more rings ( 88 ) are configured to linearly translate along the first support structure ( 26 ), and wherein the one or more rings ( 88 ) are configured to be held in place via one or more set screws. 
     A20. The system ( 10 ) of any of paragraphs A1-A19.1, wherein the system ( 10 ) is configured such that a second angle ( 54 ) and/or a second position of the first camera device ( 20 ) with respect to the fastener ( 12 ) may be selectively adjusted via the one or more rings ( 88 ) and/or the one or more set screws operatively coupled to the first support structure ( 26 ). 
     A20.1. The system ( 10 ) of any of paragraphs A1-A20, wherein the first camera device ( 20 ) is coupled to one or more rings ( 88 ), wherein the one or more rings ( 88 ) are configured to linearly translate along the first support structure ( 26 ), and wherein the one or more rings ( 88 ) are configured to be held in place via one or more set screws. 
     A21. The system ( 10 ) of any of paragraphs A1-A20.1, wherein the system ( 10 ) is configured such that a third angle and/or a third position of the second camera device ( 22 ) with respect to the fastener ( 12 ) may be selectively adjusted via the one or more rings ( 88 ) and/or the one or more set screws operatively coupled to the first support structure ( 26 ). 
     A21.1. The system ( 10 ) of any of paragraphs A1-A21, wherein the second camera device ( 22 ) is coupled to one or more rings ( 88 ), wherein the one or more rings ( 88 ) are configured to linearly translate along the first support structure ( 26 ), and wherein the one or more rings ( 88 ) are configured to be held in place via one or more set screws. 
     A22. The system ( 10 ) of any of paragraphs A1-A21.1, wherein the x-ray imaging system ( 18 ) is positioned in between the first camera device ( 20 ) and the second camera device ( 22 ). 
     A23. The system ( 10 ) of any of paragraphs A1-A22, wherein the first camera device ( 20 ) and the second camera device ( 22 ) are symmetrically positioned on either side of the x-ray imaging system ( 18 ). 
     A24. The system ( 10 ) of any of paragraphs A1-A23, wherein the first camera device ( 20 ) and the second camera device ( 22 ) are symmetrically positioned on either side of a center line of the hole ( 14 ). 
     A25. The system ( 10 ) of any of paragraphs A1-A24, wherein the system ( 10 ) is configured such that a distance between the first camera device ( 20 ) and the second camera device ( 22 ), a first angle ( 52 ) of the first camera device ( 20 ) with respect to the first support structure ( 26 ), and a second angle ( 54 ) of the second camera device ( 22 ) with respect to the second support structure ( 34 ) may be selectively adjusted to position the fastener ( 12 ) within a first central region ( 56 ) of a first field of view ( 58 ) of the first camera device ( 20 ) and within a second central region ( 60 ) of a second field of view ( 62 ) of the second camera device ( 22 ). 
     A26. The system ( 10 ) of any of paragraphs A1-A25, wherein a first stand-off distance between the first support structure ( 26 ) and the fastener ( 12 ) is optimized for both stereographs and radiographs. 
     A27. The system ( 10 ) of any of paragraphs A1-A26, wherein the first stand-off distance is at least 6 inches, at least 8 inches, at least 10 inches, at least 12 inches, at least 14 inches, at least 16 inches, at least 18 inches, and/or at least 20 inches. 
     A28. The system ( 10 ) of any of paragraphs A1-A27, wherein the first stand-off distance is between 12-16 inches. 
     A29. The system ( 10 ) of any of paragraphs A1-A28, wherein the system ( 10 ) is configured such that a second stand-off distance between a/the x-ray detector ( 32 ) is configured to be selectively adjusted according to a desired geometric magnification of the x-ray image ( 70 ). 
     A30. The system ( 10 ) of any of paragraphs A1-A29, wherein the system ( 10 ) is configured to automatically mark defective fasteners ( 12 ) if inspection of the fastener ( 12 ) is not satisfactory. 
     A31. The system ( 10 ) of any of paragraphs A1-A30, wherein the x-ray imaging system ( 18 ), the first camera device ( 20 ), and the second camera device ( 22 ) are coupled to the first support structure ( 26 ) collinearly. 
     A32. The system ( 10 ) of any of paragraphs A1-A31, wherein a/the first robot arm ( 30 ) is configured to install the fastener ( 12 ) in the part ( 16 ), and wherein the system ( 10 ) is configured to inspect the fastener ( 12 ) in real-time. 
     A33. The system ( 10 ) of any of paragraphs A1-A32, wherein the system ( 10 ) is configured for automated examination of the x-ray image ( 70 ) to determine concentricity of the fastener ( 12 ). 
     A34. The system ( 10 ) of any of paragraphs A1-A33, wherein the at least one processing unit ( 24 ) is configured to detect a first circle ( 66 ) corresponding to a first side ( 42 ) of the fastener ( 12 ) and a second circle ( 68 ) corresponding to a second side ( 44 ) of the fastener ( 12 ), and wherein the at least one processing unit ( 24 ) is further configured to determine a first center ( 72 ) of the first circle ( 66 ) and a second center ( 74 ) of the second circle ( 68 ) and determine an offset distance between the first center ( 72 ) and the second center ( 74 ). 
     A35. The system ( 10 ) of paragraph A34, wherein the at least one processing unit ( 24 ) is configured to determine whether the offset distance is within a predetermined pass/fail threshold offset distance. 
     A35.1. The system ( 10 ) of paragraph A35, wherein the predetermined pass/fail threshold offset distance is stored on non-transitory computer readable memory ( 76 ) of the system ( 10 ). 
     A36. The system ( 10 ) of any of paragraphs A1-A35.1, wherein the at least one processing unit ( 24 ) is configured to determine a quality of installation of the fastener ( 12 ). 
     A37. The system ( 10 ) of any of paragraphs A1-A36, wherein the at least one processing unit ( 24 ) comprises an x-ray imaging processing module configured to determine concentricity of the fastener ( 12 ). 
     A38. The system ( 10 ) of any of paragraphs A1-A37, wherein the at least one processing unit ( 24 ) comprises a 2D processing module configured to detect foreign object debris around the fastener ( 12 ). 
     A39. The system ( 10 ) of any of paragraphs A1-A38, wherein the at least one processing unit ( 24 ) comprises a 3D reconstruction module configured to determine flushness of the fastener ( 12 ) with the part ( 16 ). 
     A40. The system ( 10 ) of any of paragraphs A1-A39, further comprising a memory ( 76 ) storing non-transitory computer readable instructions that, when executed by the at least one processing unit ( 24 ), cause the at least one processing unit ( 24 ) to measure concentricity of the fastener ( 12 ), measure flushness of the fastener ( 12 ) with respect to the part ( 16 ), and/or detect foreign object debris near the fastener ( 12 ). 
     A41. The system ( 10 ) of paragraph A40, wherein threshold pass/fail criteria for the fastener ( 12 ) are stored on the memory ( 76 ). 
     A42. The system ( 10 ) of paragraph A40 or A41, wherein the instructions, when executed by the at least one processing unit ( 24 ), cause the at least one processing unit ( 24 ) to automatically mark any detected defective fasteners ( 12 ). 
     B1. A method ( 100 ) of inspecting a fastener ( 12 ) installed at least partially through a hole ( 14 ) in a part ( 16 ), the method ( 100 ) comprising: 
     creating ( 102 ) an x-ray image ( 70 ) of the fastener ( 12 ) via an x-ray imaging system ( 18 ); and 
     measuring ( 104 ) concentricity of the fastener ( 12 ), using the x-ray image ( 70 ). 
     B2. The method ( 100 ) of paragraph B1, wherein the measuring ( 104 ) concentricity is performed by at least one processing unit ( 24 ). 
     B3. The method ( 100 ) of paragraph B1 or B2, further comprising creating ( 106 ) a 3D image of the fastener ( 12 ) using a first image of the fastener ( 12 ) and a second image of the fastener ( 12 ), wherein the first image is taken from a first vantage point, via a first camera device ( 20 ), and wherein the second image is taken from a second vantage point, via a second camera device ( 22 ). 
     B4. The method ( 100 ) of paragraph B3, wherein the creating ( 106 ) the 3D image of the fastener ( 12 ) is performed by at least one processing unit ( 24 ). 
     B5. The method ( 100 ) of paragraph B3 or B4, further comprising measuring ( 108 ) flushness of the fastener ( 12 ), using the 3D image. 
     B6. The method ( 100 ) of paragraph B5, wherein the measuring ( 108 ) flushness is performed by at least one processing unit ( 24 ). 
     B7. The method ( 100 ) of any of paragraphs B1-B6, further comprising inspecting ( 110 ) a vicinity of the fastener ( 12 ) for foreign object debris. 
     B8. The method ( 100 ) of any of paragraphs B1-B7, further comprising coupling ( 112 ) the x-ray imaging system ( 18 ), a/the first camera device ( 20 ), and a/the second camera device ( 22 ) to a first support structure ( 26 ). 
     B9. The method ( 100 ) of paragraph B8, further comprising moving the first support structure ( 26 ) relative to the fastener ( 12 ), via a first robot arm ( 30 ). 
     B10. The method ( 100 ) of any of paragraphs B1-B9, further comprising: 
     positioning the x-ray imaging system ( 18 ) on a first side of the part ( 16 ); and 
     positioning an x-ray detector ( 32 ) on a second side of the part ( 16 ), such that the x-ray imaging system ( 18 ) and the x-ray detector ( 32 ) are on opposite sides of the part ( 16 ). 
     B11. The method ( 100 ) of paragraph B10, further comprising coupling ( 118 ) the x-ray detector ( 32 ) to a second support structure ( 34 ). 
     B12. The method ( 100 ) of paragraph B11, further comprising moving the second support structure ( 34 ) relative to the fastener ( 12 ), via a second robot arm ( 38 ). 
     B13. The method ( 100 ) of any of paragraphs B1-B12, further comprising: 
     performing the measuring ( 104 ) concentricity of the fastener ( 12 ) a plurality of times to measure concentricity of a plurality of fasteners ( 12 ) of the part ( 16 ); and 
     moving the x-ray imaging system ( 18 ) relative to the part ( 16 ) between each performance of the measuring ( 104 ) concentricity. 
     B14. The method ( 100 ) of any of paragraphs B1-B13, further comprising scanning ( 116 ) the part ( 16 ), thereby determining contours of the part ( 16 ) and planning movement of a/the first robot arm ( 30 ) to position the x-ray imaging system ( 18 ) relative to a respective fastener ( 12 ) of a/the plurality of fasteners ( 12 ) being inspected. 
     B14.1. The method ( 100 ) of paragraph B14, wherein the scanning ( 116 ) the part ( 16 ) is performed in tandem with the measuring ( 104 ) concentricity of the fastener ( 12 ). 
     B15. The method ( 100 ) of any of paragraphs B1-B14.1, wherein the measuring ( 104 ) concentricity is performed non-destructively. 
     B16. The method ( 100 ) of any of paragraphs B1-B15, wherein the measuring ( 104 ) concentricity comprises: 
     detecting a first circle ( 66 ) corresponding to a first side ( 42 ) of the fastener ( 12 ); 
     detecting a second circle ( 68 ) corresponding to a second side ( 44 ) of the fastener ( 12 ); 
     determining a first center ( 72 ) of the first circle ( 66 ); 
     determining a second center ( 74 ) of the second circle ( 68 ); and 
     determining an offset distance between the first center ( 72 ) and the second center ( 74 ). 
     B17. The method ( 100 ) of paragraph B16, further comprising determining whether the offset distance is within a predetermined pass/fail threshold offset distance. 
     B18. The method ( 100 ) of paragraph B17, further comprising indicating the fastener ( 12 ) is defective if the offset distance is not within the predetermined pass/fail threshold offset distance. 
     B19. The method ( 100 ) of any of paragraphs B1-B18, wherein the method ( 100 ) is performed using the system ( 10 ) of any of paragraphs A1-A42. 
     B20. The method ( 100 ) of any of paragraphs B1-B19, further comprising calibrating a/the first camera device ( 20 ) and a/the second camera device ( 22 ) relative to one another and relative to the fastener ( 12 ) such that the first camera device ( 20 ) and the second camera device ( 22 ) are configured to take images configured to create a 3D reconstruction of the fastener ( 12 ) installed in the part ( 16 ). 
     B21. The method ( 100 ) of any of paragraphs B1-B20, wherein the measuring ( 104 ) concentricity of the fastener ( 12 ) comprises measuring concentricity of a first fastener ( 12 ) in a first zone of the part ( 16 ), and wherein the method ( 100 ) further comprises measuring concentricity of a second fastener ( 12 ) in a second zone of the part ( 16 ). 
     B22. The method ( 100 ) of any of paragraphs B1-B21, wherein the measuring ( 104 ) concentricity of the fastener ( 12 ) comprises measuring concentricity of at least one fastener ( 12 ) in each of a plurality of zones of the part ( 16 ). 
     B23. The method ( 100 ) of paragraph B22, wherein the measuring ( 104 ) concentricity comprises measuring concentricity of additional fasteners ( 12 ) within a respective zone of the plurality of zones if a different fastener ( 12 ) within the respective zone is determined to be defective. 
     B24. The method ( 100 ) of any of paragraphs B1-B23, further comprising selectively adjusting a stand-off distance between an/the x-ray detector ( 32 ) and the part ( 16 ), based on desired geometric magnification of the x-ray image ( 70 ). 
     B25. The method ( 100 ) of any of paragraphs B1-B24, further comprising: 
     determining ( 120 ) that a respective fastener ( 12 ) of the part ( 16 ) is installed unsatisfactorily; 
     removing ( 126 ) the respective fastener ( 12 ) from the part ( 16 ); and 
     replacing the respective fastener ( 12 ) with a new fastener ( 12 ) installed in the part ( 16 ). 
     B26. The method ( 100 ) of any of paragraphs B1-B25, further comprising creating a 3D reconstruction of the fastener ( 12 ) installed in the part ( 16 ). 
     B27. The method ( 100 ) of paragraph B26, wherein the creating the 3D reconstruction comprises stereo imaging with a/the first camera device ( 20 ) and a/the second camera device ( 22 ). 
     B28. The method ( 100 ) of paragraph B26 or B27, wherein the creating the 3D reconstruction comprises structured light projection. 
     B29. The method ( 100 ) of any of paragraph B26-B28, wherein the creating the 3D reconstruction comprises laser scanning. 
     B30. The method ( 100 ) of any of paragraphs B1-B29, further comprising: 
     capturing two images of the fastener ( 12 ); 
     reconstructing a 3D surface of the fastener ( 12 ); and 
     generating a point cloud of the 3D surface using stereo vision techniques. 
     B31. The method ( 100 ) of any of paragraphs B1-B30, further comprising: 
     identifying a first surface of the fastener ( 12 ); 
     identifying a second surface ( 48 ) of the part ( 16 ); 
     fitting a first plane to the first surface; 
     fitting a second plane to the second surface ( 48 ); and 
     determining a height difference between the first plane and the second plane, thereby measuring ( 108 ) flushness of the fastener ( 12 ). 
     B32. The method ( 100 ) of paragraph B31, wherein the identifying the first surface comprises applying one or more filters to a/the point cloud of a/the 3D surface of the fastener ( 12 ). 
     B33. The method ( 100 ) of paragraph B31 or B32, wherein the identifying the second surface comprises applying one or more filters to a/the point cloud of a/the 3D surface of the part ( 16 ). 
     B34. The method ( 100 ) of any of paragraphs B1-B33, further comprising: 
     applying image processing to detect circular features having a diameter matching a known diameter of a head of the fastener ( 12 ); 
     applying high pass filtering to eliminate background; and 
     detecting foreign object debris adjacent the fastener ( 12 ). 
     B35. The method ( 100 ) of paragraph B34, wherein the detecting foreign object debris comprises identifying objects with a surface area that is dissimilar to that of the head of the fastener ( 12 ). 
     C1. A computer readable medium, comprising: 
     non-transitory computer readable instructions that, when executed by a processing unit ( 24 ), cause the processing unit ( 24 ) to perform the method ( 100 ) of any of paragraphs B1-B35. 
     C2. A computer readable medium, comprising: 
     non-transitory computer readable instructions that, when executed by a processing unit ( 24 ), cause the processing unit ( 24 ) to measure concentricity of a fastener ( 12 ) installed in a part ( 16 ), using an x-ray image ( 70 ) of the fastener ( 12 ). 
     C3. The computer readable medium of paragraph C2, wherein the non-transitory computer readable instructions, when executed by the processing unit ( 24 ), further cause the processing unit ( 24 ) to: 
     create a 3D reconstruction of a fastener ( 12 ) installed in a part ( 16 ), using a first image of the fastener ( 12 ) and a second image of the fastener ( 12 ); and 
     measure flushness of the fastener ( 12 ) with a surface of the part ( 16 ), using the 3D reconstruction. 
     C4. The computer readable medium of paragraph C2 or C3, wherein the non-transitory computer readable instructions, when executed by the processing unit ( 24 ), further cause the processing unit ( 24 ) to detect foreign object debris in a vicinity of the fastener ( 12 ). 
     D1. The use of the system ( 10 ) of any of paragraphs A1-A42 to measure concentricity of a fastener ( 12 ) with a hole ( 14 ) in which the fastener ( 12 ) is installed. 
     D2. The use of the system ( 10 ) of any of paragraphs A1-A42 to measure flushness of a fastener ( 12 ) with a surface of part ( 16 ) in which the fastener ( 12 ) is installed. 
     D3. The use of the system ( 10 ) of any of paragraphs A1-A42 to detect foreign object debris near a fastener ( 12 ) installed in a part ( 16 ). 
     As used herein, the terms “selective” and “selectively,” when modifying an action, movement, configuration, or other activity of one or more components or characteristics of an apparatus, mean that the specific action, movement, configuration, or other activity is a direct or indirect result of dynamic processes and/or user manipulation of an aspect of, or one or more components of, the apparatus. The terms “selective” and “selectively” thus may characterize an activity that is a direct or indirect result of user manipulation of an aspect of, or one or more components of, the apparatus, or may characterize a process that occurs automatically, such as via the mechanisms disclosed herein. 
     As used herein, the terms “adapted” and “configured” mean that the element, component, or other subject matter is designed and/or intended to perform a given function. Thus, the use of the terms “adapted” and “configured” should not be construed to mean that a given element, component, or other subject matter is simply “capable of” performing a given function but that the element, component, and/or other subject matter is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the function. It is also within the scope of the present disclosure that elements, components, and/or other recited subject matter that is recited as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa. Similarly, subject matter that is recited as being configured to perform a particular function may additionally or alternatively be described as being operative to perform that function. 
     As used herein, the phrase “at least one,” in reference to a list of one or more entities should be understood to mean at least one entity selected from any one or more of the entities in the list of entities, but not necessarily including at least one of each and every entity specifically listed within the list of entities and not excluding any combinations of entities in the list of entities. This definition also allows that entities may optionally be present other than the entities specifically identified within the list of entities to which the phrase “at least one” refers, whether related or unrelated to those entities specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) may refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including entities other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including entities other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other entities). In other words, the phrases “at least one,” “one or more,” and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B, and C,” “at least one of A, B, or C,” “one or more of A, B, and C,” “one or more of A, B, or C” and “A, B, and/or C” may mean A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B, and C together, and optionally any of the above in combination with at least one other entity. 
     A processing unit may be any suitable device or devices that are configured to perform the functions of the processing unit discussed herein. For example, the processing unit may include one or more of an electronic controller, a dedicated controller, a special-purpose controller, a personal computer, a special-purpose computer, a display device, a logic device, a memory device, and/or a memory device having computer readable media suitable for storing computer-executable instructions for implementing aspects of systems and/or methods according to the present disclosure. Additionally or alternatively, the processing unit may include, or be configured to read, non-transitory computer readable storage, or memory, media suitable for storing computer-executable instructions, or software, for implementing methods or steps of methods according to the present disclosure. Examples of such media include CD-ROMs, disks, hard drives, flash memory, etc. As used herein, storage, or memory, devices and media having computer-executable instructions as well as computer-implemented methods and other methods according to the present disclosure are considered to be within the scope of subject matter deemed patentable in accordance with Section 101 of Title 35 of the United States Code. 
     As used herein, the phrase “at least substantially,” when modifying a degree or relationship, includes not only the recited “substantial” degree or relationship, but also the full extent of the recited degree or relationship. A substantial amount of a recited degree or relationship may include at least 75% of the recited degree or relationship. For example, a first direction that is at least substantially parallel to a second direction includes a first direction that is within an angular deviation of 22.5° relative to the second direction and also includes a first direction that is identical to the second direction. 
     The various disclosed elements of apparatuses and steps of methods disclosed herein are not required to all apparatuses and methods according to the present disclosure, and the present disclosure includes all novel and non-obvious combinations and subcombinations of the various elements and steps disclosed herein. Moreover, one or more of the various elements and steps disclosed herein may define independent inventive subject matter that is separate and apart from the whole of a disclosed apparatus or method. Accordingly, such inventive subject matter is not required to be associated with the specific apparatuses and methods that are expressly disclosed herein, and such inventive subject matter may find utility in apparatuses and/or methods that are not expressly disclosed herein. 
     As used herein, the phrase, “for example,” the phrase, “as an example,” and/or simply the term “example,” when used with reference to one or more components, features, details, structures, embodiments, and/or methods according to the present disclosure, are intended to convey that the described component, feature, detail, structure, embodiment, and/or method is an illustrative, non-exclusive example of components, features, details, structures, embodiments, and/or methods according to the present disclosure. Thus, the described component, feature, detail, structure, embodiment, and/or method is not intended to be limiting, required, or exclusive/exhaustive; and other components, features, details, structures, embodiments, and/or methods, including structurally and/or functionally similar and/or equivalent components, features, details, structures, embodiments, and/or methods, are also within the scope of the present disclosure.