Abstract:
A method for detecting an anomaly associated with a structure is described. The method includes obtaining a baseline scan of the structure, changing at least one condition associated with the structure which is intended to impart a movement of the structure or a movement of objects within the structure, obtaining a secondary scan of the structure, the secondary scan obtained from a same position, with respect to the structure, as the baseline scan, determining any differences between the baseline scan and the secondary scan, and identifying at least one of a foreign object proximate the structure and a structural anomaly associated with the structure based on any differences between the baseline scan and the secondary scan.

Description:
BACKGROUND 
     The field of the disclosure relates generally to foreign object debris (FOD) detection, and more specifically, to methods and systems for enhancing backscatter x-ray FOD detection. 
     As is known, aircraft and other complex structures are fabricated and subsequently modified in manners that sometimes require substantial disassembly and re-assembly of portions thereof. During fabrication, for example, it is common to place components together for a drilling operation and then separate such components for deburring operations prior to a final assembly of such components. Such operations result in FOD from the metal or composite shavings that result from the drilling and deburring operations. The tools and bits tools used to accomplish such operations, if left in a position and forgotten, may also end up as FOD. Likewise, the drilling plates used to properly align the drilling tools and bits can end up as FOD if not properly disposed of. In fact, FOD could be any type of objects unintentionally left in a fabricated structure. 
     In the aircraft example, modifications may involve the removal of exterior and/or interior panels to facilitate access to components of the aircraft that are contained within compartments located behind the panels. When such panels are removed, foreign objects are often introduced into the compartments. Items such as tools, fasteners, manufacturing material, personal objects, and other debris may be inadvertently left behind in such compartments after the modifications are complete. Such items constitute FOD. 
     Thus, is it easy to understand that during fabrication and modification of aircraft, as well as other complex assemblies such as land vehicles, water vehicles, electrical boxes and other complex machinery, there are opportunities to unintentionally leave items and other debris behind in the areas where work was performed. 
     As is easily understood, the presence of FOD in an aircraft or other complex machine is undesirable as the FOD may interfere with proper operation of such machines. However, once the fabrication and/or modifications have been completed to such machines, it is difficult to determine whether or not there is FOD present. One contemporary practice is to have technicians visually inspect work areas. However, such visual inspection is too often insufficient as FOD may be overlooked because of accessibility and inefficiency of manual inspection tools. 
     In addition, processes are known in which images taken using backscatter X-ray imaging technology are subtracted from one another, but these processes do not enhance the detection of hidden FOD. Specifically, existing X-ray processes image everything within the structure and are difficult to interpret because the multiple layers and hardware associated with such structures can mask FOD that may be hidden and not clearly visible in the image. 
     BRIEF DESCRIPTION 
     In one aspect, a method for detecting an anomaly associated with a structure is provided. The method includes obtaining a baseline scan of the structure, changing at least one condition associated with the structure which is intended to impart a movement of the structure or a movement of objects within the structure, obtaining a secondary scan of the structure, the secondary scan obtained from a same position, with respect to the structure, as the baseline scan, determining any differences between the baseline scan and the secondary scan, and identifying at least one of a foreign object proximate the structure and a structural anomaly associated with the structure based on any differences between the baseline scan and the secondary scan. 
     In another aspect, a method for determining whether any foreign object debris is associated with a structure is provided. The method includes obtaining a baseline scan of the structure, causing a movement of the structure significant enough to cause a movement of any foreign object debris that is associated with the structure, obtaining a secondary scan of the structure, the secondary scan obtained from a same position, with respect to the structure, as the baseline scan, determining any differences between the baseline scan and the secondary scan, and identifying any foreign object debris associated with the structure based on the determined differences. 
     In still another aspect, a method for detecting foreign object debris and structural anomalies associated with an aircraft is provided. The method includes interrogating a portion of an aircraft with an X-ray source, applying a physical load to the aircraft, subsequently interrogating substantially a same portion of the aircraft with the X-ray source after the application of the physical load, comparing images resulting from the X-ray interrogations to determine any differences, and identifying the objects or displacements, that resulted in the differences as one of potential foreign object debris and a structural anomaly. 
     The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow diagram of an aircraft production and service methodology. 
         FIG. 2  is a block diagram of an aircraft. 
         FIG. 3  is a flowchart illustrating a foreign object debris (FOD) detection process. 
         FIG. 4  depicts a baseline X-ray image of a portion of an aircraft with potential FOD items therein. 
         FIG. 5  depicts a second X-ray image of the same portion of the aircraft, the second X-ray image corresponding to the baseline image of  FIG. 4  after agitation of any FOD therein. 
         FIG. 6  is a difference image depicting differences between the images of  FIGS. 4 and 5 , which includes FOD that has shifted position between the time the baseline image was acquired and the time the second image was acquired. 
         FIG. 7  is a flowchart, similar to the flowchart of  FIG. 3 , and illustrating structural anomaly detection. 
         FIG. 8  further illustrates the process of  FIG. 7  through an internal crack in a riveted structure example. 
         FIG. 9  further illustrates the process of  FIG. 7  through an unbond condition in a fuel bladder example. 
         FIG. 10  further illustrates the process of  FIG. 7  through a corrosion over time condition that is associated with a wing box. 
         FIG. 11  illustrates structural displacement after pressurization that is visible if backscatter X-ray images are available at a specific view angle. 
     
    
    
     DETAILED DESCRIPTION 
     The described embodiments are directed to processes and systems for detection of foreign object debris (FOD) inside a structure by moving any entrapped FOD in between the acquisition of backscatter X-ray images. The two images are subjected to an image subtraction process to remove the overlying structure leaving a difference image based on a shifting position of any FOD. As such, a method is provided that substantially improves the probability of detecting FOD using backscatter X-ray images as only FOD remains in the subtracted image. 
     Referring more particularly to the drawings, embodiments of the disclosure may be described in the context of aircraft manufacturing and service method  100  as shown in  FIG. 1  and an aircraft  200  as shown in  FIG. 2 . During pre-production, aircraft manufacturing and service method  100  may include specification and design  102  of aircraft  200  and material procurement  104 . 
     During production, component and subassembly manufacturing  106  and system integration  108  of aircraft  200  takes place. Thereafter, aircraft  200  may go through certification and delivery  110  in order to be placed in service  112 . While in service by a customer, aircraft  200  is scheduled for routine maintenance and service  114  (which may also include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of aircraft manufacturing and service method  100  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, for example, 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. 
     As shown in  FIG. 2 , aircraft  200  produced by aircraft manufacturing and service method  100  may include airframe  202  with a plurality of systems  204  and interior  206 . Examples of systems  204  include one or more of propulsion system  208 , electrical system  210 , hydraulic system  212 , and environmental system  214 . Any number of other systems may be included in this example. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the automotive, petro-chemical, ship building or construction industries. 
     Apparatus and methods embodied herein may be employed during any one or more of the stages of aircraft manufacturing and service method  100 . For example, without limitation, components or subassemblies corresponding to component and subassembly manufacturing  106  may be fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft  200  is in service. 
     Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during component and subassembly manufacturing  106  and system integration  108 , for example, without limitation, by substantially expediting assembly of or reducing the cost of aircraft  200 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while aircraft  200  is in service, for example, without limitation, to maintenance and service  114  may be used during system integration  108  and/or maintenance and service  114  to determine whether parts may be connected and/or mated to each other. 
     The description of the different advantageous embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous embodiments may provide different advantages as compared to other advantageous embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated. 
     Turning now to  FIG. 3 , a flowchart  300  illustrating one embodiment of a FOD detection process is provided. Flowchart  300  illustrates a method to make foreign object debris (FOD) readily detectable using backscatter X-ray image. A first backscatter X-ray image is subtracted from a second backscatter X-ray image which removes the overlying structure from the resulting difference image. By imparting a movement on the structure, and therefore any FOD therein, between the acquisitions of the two images, only the difference caused by the movement of the FOD remains in the difference image. 
     Since the structure is removed from the difference image, only the FOD that has been moved remains in the difference image. Since the FOD has been moved, the FOD can easily be identified. As described above, existing backscatter X-ray image solutions require time-consuming interpretation and as a result users are often unable to detect any FOD remaining within the structure. As shown in  FIG. 3 , the overlying structure within the images that makes interpretation of such X-ray images difficult is removed. 
     Referring specifically to flowchart  300 , a baseline (first) image of the structure is obtained  310  using, for example, backscatter X-ray imaging equipment. In embodiments, the baseline image is digitally stored. The FOD is then moved  320  within the structure. One example of a mechanism to displace (move) any existing FOD includes rotating the structure in an attempt to move any FOD therein and then returning the structure to its original position. The force of gravity will generally cause any FOD within the structure being rotated to change position. Another example includes utilizing compressed air and/or pneumatics to try to move any FOD within the structure, such as, blowing forced air through or across or within the structure. Still another example is the utilization of an external device to vibrate or agitate or rotate the structure to attempt to reposition any FOD therein. These and other methods are intended to move  320  the hidden FOD within such structures. 
     Once the structure is returned to its original position, a secondary (second) backscatter X-ray image is obtained  330  with the area of interest of the structure in the same position as when the baseline image was obtained  310 . The secondary image is also digitally stored. While described as being in the original position when the secondary image is obtained, it is merely necessary that the position of the structure is in the same position with respect to the backscatter X-ray imaging device when the two images are obtained  310 ,  330 . For example, one method used to ensure the position of the structure is in the same position with respect to the backscatter X-ray imaging device during the acquisition of the two images is to use fiduciary position markers on the structure. 
     The original digitally stored image (the baseline image) is subtracted  340  from the secondary digitally stored image using one or more image processing software applications to reveal the differences between the images. In certain applications, the second image may be subtracted from the first image. In an embodiment, the differences are stored as what is referred to herein as a difference image. The difference image is interpreted to identify  350  articles (i.e., FOD) that have changed position. For example, the original position of a particular foreign object and a new position for the foreign object can be determined based upon the negative or positive shading within the difference image(s) created by the subtraction process. 
     With regard to FOD detection, the process illustrated by  FIG. 3  provides a capability to find hidden FOD including manufacturing debris, lost tools, bits, misplaced components and/or hardware such as nuts, washers and bolts, as well as metallic and non-metallic materials that could potentially be inadvertently misplaced during fabrication or modification of an aircraft or other complex structure. 
       FIG. 4  is a representation of an image  400  of a portion  402  of an aircraft. For correlation with the method illustrated by  FIG. 3 , image  400  may be considered a baseline image. As shown in image  400 , the X-ray has indicated potential FOD, including rivets  410 , drill plate  420 , and shavings  430 . Image  400  is an exaggeration for purposes of illustration as in the typical case; such FOD is not so easily identifiable. 
     After the aircraft portion  402  is moved and/or forces are applied to the aircraft portion as described herein, a second image  500  is obtained, as shown in  FIG. 5 . Image  500  may be considered a second X-ray image of the portion  402  of the aircraft, and as described herein, the second X-ray image corresponds to the baseline image of  FIG. 4 . As can be seen in this image depiction, rivets  410 , drill plate  420 , and shavings  430  have shifted in position due to one or both of a movement of the aircraft portion  402  and a force (compressed air, etc.) being applied to the aircraft portion. 
       FIG. 6  is a difference image  600  depicting differences between image  400  and image  500  of  FIGS. 4 and 5 . As easily seen from the exaggeration of  FIGS. 4-6 , image  600  includes the various FOD (rivets  410 , drill plate  420 , and shavings  430 ) that has shifted position between the time the baseline image  400  was acquired and the time the second image  500  was acquired. Notably, since the FOD has shifted position, each instance of FOD will appear twice in the difference image. 
     Similar to detection of FOD in a broader sense, the described embodiments are also useful in detection of structural anomalies and any other defects within such structures. A typical example would be treating the structural crack or deformation as a form of foreign object debris created after the introduction of physical stresses or forces. In some applications, if a structure, for example a tank assembly, is stressed, the underlying structure may move if there is an anomaly within either the tank or the underlying structure. By positioning a backscatter X-ray system at the correct orientation before and after (or during) the application of the stress, the internal movement within the structure can be assessed utilizing subsequent backscatter X-ray difference images. Methods such as vacuum application, pressurization, and loading are used to apply the stress. While systems are known that measure external surface displacement, the described embodiments are operable to visualize any internal displacements caused by the application of the stress by providing an inside view of the structure. 
     Structural anomaly detection is further illustrated by flowchart  700  of  FIG. 7 . A baseline (first) image of the structure is obtained  710  using, for example, backscatter X-ray imaging equipment. In embodiments, the baseline image is digitally stored. The structure is then stressed  720  using some form of loading such as application of a vacuum, air/pneumatics pressurization, application of structural loading, and/or application of heating/thermal loading. An alternative to stressing the structure is using time-based images such as monitoring corrosion over time on subsequent backscatter X-ray images. 
     A secondary (second) backscatter X-ray image is obtained  730  with the area of interest of the structure in the same position as when the baseline image was obtained  710  and either with the load applied or after loading and digitally storing that image. The secondary image is also digitally stored. While described as being in the original position when the secondary image is obtained, it is merely necessary that the position of the structure is in the same position with respect to the backscatter X-ray imaging device when the two images are obtained  710 ,  730 . For example, one method used to ensure the position of the structure is in the same position with respect to the backscatter X-ray imaging device during the acquisition of the two images is to use fiduciary position markers on the structure. 
     The original digitally stored image (the baseline image) is subtracted  740  from the secondary digitally stored image using one or more image processing software applications to reveal the differences between the images. In certain applications, the second image may be subtracted from the first image. In an embodiment, the differences are stored as what is referred to herein as a difference image. The difference image is interpreted to identify  750  structure or materials in the image field of view that have moved position. The resultant subtracted image is then evaluated  760  for to identify structural anomalies or potential defects that were displaced due to the loading. 
       FIG. 8  further illustrates the process of  FIG. 7  through an internal crack in a riveted structure example. Riveted structure  800  includes three layers  802 ,  804 , and  806 , though only layer  802  is visible. A closed crack  808  is in layer  806 , though crack  808  is not readily found, due to layer  806  being non-accessible. A baseline image  810  is obtained with an X-ray unit  820  with structure  800  in the unstressed state. 
     A stress is applied to structure  800 , and a secondary image  850  is obtained, in which an image item  852  associated with crack  808  is plainly visible. Subtraction of image  810  and  850  results in a subtracted image  860  where the background of structure  800  is removed and illustrating an image item  862  that is associated with crack  808  and caused by displacement of the structure  800 . 
       FIG. 9  further illustrates the process of  FIG. 7  through an unbond condition in a fuel bladder example. In a static condition, fuel bladder  900  includes an unbonded portion  902  that is not visible, due to the portion being non-accessible. A baseline image  910  is obtained with an X-ray unit  920  with fuel bladder  900  in the unstressed state. 
     A stress, for example, in the form of a vacuum, is applied to structure  900 , and a secondary image  950  is obtained, in which an image item  952  associated with unbonded portion  902  is plainly visible. Subtraction of image  910  and  950  results in a subtracted image  960  where the background of fuel bladder  900  is removed and illustrating an image item  962  that is associated with unbonded portion  902  and caused by displacement of the fuel bladder  900  by application of the vacuum. 
       FIG. 10  further illustrates the process of  FIG. 7  through a corrosion over time condition that is associated with a wing box  1000 . In a static condition, wing box  1000  includes a small corroded area  1002 . A baseline image  1010  is obtained with an X-ray unit  1020  in which an image item  1022  associated with small corroded area  1002  is plainly visible, though not considered to be an issue with operation of wing box  1000 . An amount of time passes, and a secondary image  1050  is obtained, in which an image item  1052  associated with an enlarged corroded area  1060  is plainly visible. Subtraction of image  1010  and  1050  results in a subtracted image  1070  where the background of wing box  1000  is removed and illustrating an image item  1072  that is associated with a growth in the corroded area of wing box  1000  caused by passage of time. 
       FIG. 11  illustrates structural displacement after pressurization that might be visible if backscatter X-ray images are available at a specific view angle. Simply, in a structure  1100  bonds are to be made everywhere trusses  1102 ,  1104 ,  1106 , and  1108  are adjacent to a skin  1110 . While denoted by the upper illustration, but not visible, non-bonded region  1120  includes an area where upper members  1134  and  1136 , respectively, of trusses  1104  and  1106  are not bonded to skin  1110 . Application of pressure to structure  1100  causes a separation area  1150  to occur as shown in the lower illustration, in which the non-bond area  1120  is clearly seen as is the separation between skin  1100  and upper truss members  1134  and  1136 . 
     The described embodiments are adaptable to other image acquisition technologies. For example, further embodiments utilize a traditional X-ray process whereby a digital detector is used to capture both a baseline image and a secondary image after the FOD has been moved within the structure or an internal component has been stressed that moves the underlying structure. As such, alternate X-ray technologies other than backscatter X-ray are also used to generate difference images of the internal structure. 
     The embodiments described herein are useful to all complex machine manufacturers and repair organizations, including, but not limited to, major aerospace manufacturers, water vehicle manufacturers, land vehicle manufacturers, and maintenance facilities. As described above, variations to movement of the structure to displace FOD embodiments include embodiments directed to non-destructive evaluation of structures. Examples of such non-destructive evaluation include, for example, a pressure or vacuum applied to a structure prior to acquisition of a second image to determine if a disbonding or other structural anomaly has occurred. More generally, a pre-stressed condition backscatter X-ray and a post-stressed condition backscatter X-ray may be utilized to determine if a movement has occurred with regard to the structure, for example, visualizing changes that occur internal to the structure and/or visualizing surface deformations caused by subsurface anomalies 
     The embodiments described herein significantly increase the capability for detecting FOD and therefore reduce production costs associated with FOD as minimizing the amount of FOD left within products improves safety, customer relationships and improves the work process. 
     This written description uses examples to disclose various embodiments, which include the best mode, to enable any person skilled in the art to practice those embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.