Abstract:
An apparatus for fabricating a stack of adhesive plies for attaching a doubler to a surface on a structure includes a digital scanner, configured for scanning the surface and for producing a first set of digital data representing a contour of the surface, and a computer, coupled to the digital scanner, having a processor and system memory. The computer is programmed for mapping a gap between a bonding surface on the doubler and the surface on the structure using the first set of digital data and a second set of digital data representing the bonding surface, and for segmenting the mapped gap into layers corresponding to the adhesive plies.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of U.S. patent application Ser. No. 12/183,045, filed Jul. 30, 2008, which is a continuation-in-part of U.S. patent application Ser. No. 11/957,767 filed Dec. 17, 2007, now U.S. Pat. No. 8,324,911, the entire disclosures of which are incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosure generally relates to surface mapping, and deals more particularly with a method and apparatus for mapping gaps between a strengthening doubler and an uneven structure surface using digital scanning techniques, as well as a method of fitting the doubler to the uneven surface using stacked plies of adhesive. 
       BACKGROUND 
       [0003]    Pre-cured composite doublers may be used as patches to repair, reinforce and/or strengthen both metallic and polymer-matrix composite aircraft structures, such as outer skins. In some cases, the doublers may comprise metal that is preformed to the shape of a surface to which is to be applied. Doublers are also sometimes used to better distribute loads when added to a structure. The doublers may be bonded to the surface of the structure using a suitable adhesive in the form of one or more adhesive plies. It is normally important to achieve a good bond between the doubler and the structure across the entire area of the doubler. However, in some cases, the surface of the structure may be uneven, and/or contain one or more depressions which create a gap across the preformed doubler foot print onto the skin. The gap may be filled with sheet adhesive, but challenges may occur when the gap thickness varies. In order to assure a complete bond having maximum strength, the gaps should be filled with adhesive. Accordingly, it is necessary to determine the location and dimensions of the gaps in order to tailor the pattern of each ply of the adhesive in order to completely fill the gaps with adhesive. 
         [0004]    Existing techniques, including manual mapping, for measuring gaps between a structure surface and a doubler are time consuming, and measurement results may depend upon the skill of the technician who makes the measurements and interprets the results. Capacitive blankets have been proposed for use in measuring the gaps, and are effective for a variety of applications. However, capacitive blankets may not be suitable for measuring gaps over large areas or surface areas that have steep or multiple contours, since the blanket may not precisely conform to all areas of the contoured surface. 
         [0005]    Accordingly, there is a need for a method and apparatus for rapidly and reliably mapping the gaps between a doubler and the surface of a structure, especially where the surface is relatively large and/or is highly contoured. There is also a need for a method and apparatus for fabricating stacked plies of adhesive that are precisely patterned so as to completely fill all areas of the gap in order to assure a good bond between the doubler and the structural surface. 
       SUMMARY 
       [0006]    In accordance with the disclosed embodiments, gaps between a doubler and a structural surface may be mapped across the entire area of the doubler, rapidly and reliably. A three dimensional digital map is generated by digitally scanning the structural surface to which the doubler is to be applied. After aligning the structure data set and the doubler data set, the resulting three dimensional map is then segmented into layers that generally correspond to the thickness and shape of adhesive plies that are stacked and arranged so that they completely fill the gaps. The doubler may be reverse engineered if a data set is not available or if an exact representation is necessary. The three dimensional map is generated using digital files and 3-D data processing software. Digital files representing the segmented adhesive layers may be used to control an automatic cutter which cuts patterned plies from a sheet of adhesive. Alternatively, full size patterns may be printed and used as guides for manually cutting adhesive plies from a sheet of adhesive. One advantage of the disclosed embodiments lies in the highly automated nature of the method for both producing the three dimensional gap map and using it to fabricate a stack of adhesive plies that is precisely tailored to completely fill the gap. 
         [0007]    According to one disclosed embodiment, apparatus is provided for fabricating a stack of adhesive plies used for attaching a doubler to a surface on a structure. The apparatus comprises: a digital scanner for scanning the surface on the structure and producing a first set of digital data representing the contour of the surface; a second set of digital data representing a surface on the doubler intended to be attached to the surface on the structure; and, a computer for mapping the gap between the doubler surface and the surface on the structure using the first and second sets of digital data, and for segmenting the mapped gaps into layers corresponding to the adhesive plies. The apparatus may further include a cutter controlled by the computer for automatically cutting the adhesive plies from a sheet of adhesive, based on the pattern of the segmented layers. The digital scanner may be a laser or other optical scanner. 
         [0008]    According to a method embodiment, fabricating a stack of adhesive plies used to attach a doubler to a surface on a structure, comprises: generating a first set of digital data representing the surface of the structure; generating a second set of digital data representing a surface on the doubler that is intended to be attached to the surface of the structure; mapping the gap between the doubler surface and the surface of the structure; segmenting the mapped gap into patterned layers corresponding to the adhesive plies; and, using the patterned layers to produce the adhesive plies. Generating the first and second sets of digital data may be performed by digitally scanning the surface of the structure and the surface of the doubler, or the surface of a tool used to form the doubler. 
         [0009]    According to another method embodiment, fitting a doubler on a surface, comprises: generating a three dimensional digital map of the gap between the doubler and the surface; and, using the digital map to fabricate a stack of adhesive plies tailored to substantially fill the gap between the doubler and the surface. 
         [0010]    According to a further method embodiment, applying a doubler to a surface of the structure comprises: forming a doubler having a surface intended to be applied to the surface of the structure; generating a map of the gap between the surface of the doubler and the surface of the structure; generating a three dimensional map of the gap between the surface of the doubler and the surface of the structure; segmenting the three dimensional map into a plurality of layers, each having a pattern; using the patterns to fabricate a stack of adhesive plies that substantially fill the gap; filling the gap with the stack of adhesive plies; and, placing the doubler on the surface of the structure overlying the stack of adhesive plies. 
         [0011]    Embodiments of the disclosure satisfy a need for method and apparatus for rapidly mapping the gaps between a doubler and a structural surface that is accurate, reliable and highly automated. The disclosed embodiments also satisfy the need for a method and apparatus for fabricating multiple plies of adhesive that are precisely patterned. 
         [0012]    Other features, benefits and advantages of the disclosed embodiments will become apparent from the following description of embodiments, when viewed in accordance with the attached drawings and appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE ILLUSTRATIONS 
         [0013]      FIG. 1  is a perspective view of a composite doubler bonded to the surface of a structure. 
           [0014]      FIG. 2  is a sectional view taken along the line  2 - 2  in  FIG. 1 . 
           [0015]      FIG. 3  is a perspective view illustrating digital scanning of uneven areas on the surface of the structure shown in  FIGS. 1 and 2 . 
           [0016]      FIG. 4  is a perspective view similar to  FIG. 3  but showing digital scanning of the surface of a tool used to form the doubler shown in  FIG. 1 . 
           [0017]      FIG. 5  is a cross sectional view of a three dimensional map of the gap formed between the doubler and the uneven surface of the structure. 
           [0018]      FIG. 6  is a view similar to  FIG. 5  but showing the map having been segmented into patterned layers. 
           [0019]      FIG. 7  is a plan view of another three dimensional gap map, and illustrating the outlines of the patterned layers. 
           [0020]      FIG. 8  is a cross sectional view of a stack of plies used to fill the gap between the doubler and the uneven surface of the structure based on the map shown in  FIG. 5 . 
           [0021]      FIG. 9  is a block diagram of apparatus for generating the three dimensional gap map and for fabricating the stack of adhesive plies. 
           [0022]      FIG. 10  is a flow diagram of a method for fitting and applying a doubler on the surface of the structure. 
           [0023]      FIG. 11  is an exploded, perspective view showing how the adhesive plies may be arranged and oriented during installation of the doubler. 
           [0024]      FIG. 12  is a flow diagram of aircraft production and service methodology. 
           [0025]      FIG. 13  is a block diagram of an aircraft. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Embodiments of the disclosure relate to a method and apparatus for fitting and applying a doubler  20  on the surface  24  of a structure  22  ( FIG. 1 ). In the illustrated example, the doubler  20  comprises composite materials, however, it is to be understood that the disclosed embodiments may be used to fit and apply metal doublers as well. The structure  22  may comprise, without limitation, a metallic or composite skin of an aircraft requiring repair or reinforcement in the area where the doubler  20  is applied to the structure  22 . In the illustrated example, the doubler  20  may comprise a stack of cured plies of reinforced synthetic resin, such as carbon-fiber epoxy, for example. Although both the doubler  20  and the structural surface  24  are shown as being flat in  FIGS. 1 and 2 , it is to be understood that they may be curved in one or more directions, or may comprise a combination of flat and curved surfaces. Where the doubler  20  is metal, the doubler  20  may be preformed to conform to the shape of the surface to which it is to be fitted and applied. Also, although the doubler  20  is shown as being rectangular in  FIG. 1 , it may be any of numerous other shapes to suit the particular application. 
         [0027]    As best seen in  FIG. 2 , the surface  24  of the structure  22  may include uneven surface areas  24   a  which create one or more gaps  26  at the interface  28  between the doubler  20  and the structure surface  24 . In accordance with the disclosed embodiments, the doubler  20  is bonded to the surface  24  by a suitable adhesive  42 . As will be discussed in more detail below, the adhesive  42  may comprise a built-up stack  43  of adhesive plies  44  (see  FIG. 8 ) that each have a shaped pattern such that the contour of adhesive ply stack  43  substantially matches the contour of the uneven surface  24   a  and therefore substantially completely fills the entire volume of the gap  26 . Since the three dimensional (3-D) shape of the adhesive  42  formed by the adhesive ply stack  43  substantially matches that of the gap  26 , a strong bond between the doubler  20  and the surface  24  is formed over the entire area of the interface  28 . 
         [0028]    Referring now to  FIGS. 3 and 5 , in accordance with the disclosed embodiment, a 3-D map  39  of the gap  26  ( FIG. 2 ) is generated by digitally scanning the uneven surface areas  24   a  using a digital scanner  30  that scans an energy beam  32  in a scanning pattern  34  over the surface  24  of the structure  22 . The digital scanner  30  may comprise any of various commercially available devices, such as a laser scanner of the type available, for example and without limitation, from FARO Technologies Inc., which comprises a laser line probe (not shown) mounted on a scanning arm (not shown} for movement about multiple axes. However, various other non-contact scanning devices may be employed. The digital scanner  30  generates a digital data file that represents a 3-D map  39  of the gap  26  which includes the contour  27  ( FIG. 5 ) of the uneven surface  24   a.    
         [0029]    In some cases, it may be possible that the bottom face (not shown) of the doubler  20  in the area of the interface  28  ( FIGS. 1 and 2 ) also may contain uneven surface areas  25 . Accordingly, the digital scanner  30  may be used to scan the surface  36  of a lay-up tool  38  that is used to form the doubler  20 . Any uneven surface areas in the tool  38  such as that indicated by the numeral  36   a  in surface  36  will produce a corresponding area of surface unevenness  25  ( FIG. 2 ) on the doubler  20 . Thus, by scanning the surface  36  of the tool  38 , a digital data file is generated representing the 3-D contour of the uneven surface areas  36   a , and thus of the uneven surface areas  25  on the doubler  20  that must be taken into account in determining the shape and dimensions of the adhesive  42  required to fill the gap  26  ( FIG. 2 ). Alternatively, it may be possible to scan the bonding surface of the doubler  20  directly in order to identify areas of uneven surface areas  25  which are converted into a digital data file representing the uneven surfaces  25 . In still another embodiment, a digital file representing the contours of the surface  36  of the tool  38  may be generated from a digital, 3-D CAD model of the tool  38 . 
         [0030]    As will be discussed below in more detail, commercially available software such, without limitation, Polyworks and Geomagic may be used to compare the two digital data files respectively representing the contours of the uneven surface areas  25  on the doubler  20  and those  24   a  on the structure surface  24 , and to generate a 3-D map  39  of the gap  26 , as shown in  FIG. 5 , and thus of the void that is to be filled with the adhesive  42 . 
         [0031]    Referring now to  FIGS. 6 and 7 , the 3-D map  39  of the gap  26  is then segmented into patterned layers  40  each having a predefined thickness “D” and a distinct outer boundary pattern  43  (see  FIG. 7 ). The thickness D may generally correspond to the thickness of each adhesive ply  44  in the ply stack  43 , however, in some applications it may be useful to vary the thickness D for at least certain of the patterned layers  40  in order to more closely fit the patterned layers  40  to the contour of the uneven surface areas  24   a . Segmenting the 3-D map  39  of the gap  26  results in a segmented 3-D map  39  ( FIGS. 6 and 7 ) which is in effect, a topographic map wherein the boundary patterns  43  form the topographic lines of each layer  40 . 
         [0032]    Referring now also to  FIG. 8 , using the pattern, thickness and position of each of the segmented layers  40 , individual plies  44  of adhesive may be cut from a sheet (not shown) of adhesive and arranged to form a stack  43  substantially matching the contours of the 3-D map  39 . Thus, the ply stack  43  has surface contours substantially matching that of the gap  26  between the doubler  20  and the structure surface  24 . During installation, the ply stack  43  is placed between the doubler  20  and the structure  22 , thereby contacting essentially the entire surface areas of the interface  28  ( FIGS. 1 and 2 ). 
         [0033]      FIG. 9  illustrates apparatus generally indicated by the numeral  46  for fitting the doubler  20  to the structure  22 . The apparatus  46  includes a computer  48  coupled with memory  50  for storing files and programs that are accessed and used by the computer  48 . For example, the digital data sets  35  gathered from the digital scanner  30  or 3-D CAD models  54 , may be processed with commercially available, imaging processing programs that may be used to manipulate digital data and carryout processes necessary to measure the gaps, generate the 3-D map, segment the layers  40  and output data representing the size, shape and location of the adhesive plies  44 . The digital scanner  30  sends the scanned digital data set  35  to the computer  48  where it may be used in various calculations. 
         [0034]    In one embodiment, the adhesive plies  44  may be automatically cut from a sheet (not shown) of adhesive material using a cutter  60  operated by a controller  58  which receives data and control instructions from the computer  48 . In some applications, where the thickness D of the patterned layers  40  varies ( FIG. 6 ), the adhesive plies  44  may be cut from more than one sheet of adhesive having differing thicknesses. In another embodiment, a printer  62  is coupled with the computer  48  and is operative to print full size physical patterns that may be cut out and/or followed in order to manually cut the adhesive plies  44  from a sheet of adhesive material. 
         [0035]    Attention is now directed to  FIG. 10  which illustrates the steps of a method for fitting the doubler  20  on the structure  22 . Beginning at step  64 , the surface  24  is digitally scanned in order to produce a first digital data file that represents the contour of the uneven surface areas  24   a  on structure surface  24 . At step  66 , a second digital data file is generated which represents the surface contour of the doubler tool  38 , or the doubler  20  itself. As previously discussed, this second digital data file may be developed using a CAD file representing a 3-D model of the doubler tool  38 , or by scanning the surface  36  of the doubler tool  38 , as described above in connection with  FIG. 4 . 
         [0036]    At step  68 , the digital data files generated in steps  64  and  66  are compared, and the results are used to generate the 3-D map  39  of the gap  26 , at step  70 . 
         [0037]    At step  72 , the thickness of the adhesive plies  44  may be selected, which generally corresponds to the thickness D of the segmented layers  40  shown in  FIG. 6 . As discussed above, more than one thickness may be selected for the adhesive plies  44 . Based on the ply thickness selected at  72 , the 3-D map  39  is segmented into layers that form flat patterns, as shown at step  74 . 
         [0038]    In one embodiment, full size flat patterns are printed out at step  86  and are then used at step  88  as guides to manually cut each of the adhesive plies  44 . Alternatively, files representing the segmented 3-D map  39  may be exported to an automatic adhesive cutter  60 , at step  76 . The cutter  60  then automatically cuts each of the adhesive plies  44  to the predetermined size and shape. 
         [0039]    The adhesive plies  44 , having been cut to the appropriate size and shape, may then be arranged and stacked according to the 3-D map  39  ( FIGS. 6 and 7 ), and the stack  43  is then placed between the doubler  20  and the surface  24  of the structure  22 , as shown at step  82 . The doubler  20  having been fitted to the surface  24  of the structure  22 , the doubler  20  and the surface  24  surrounding the doubler  20  are vacuum bagged and are cured in place, as shown at step  84 . 
         [0040]    In some applications, as those skilled in the art will recognize, darts may be added to some of the adhesive layers  44  in order to accommodate the material properties of the adhesive layers  44 . On nearly flat surfaces, the adhesive stacks  43  can be formed by laying down essentially flat layers of adhesive. With more contoured structure surfaces, however, the bulk of the adhesive layers  44  may require darting in order to minimize the number of layers  44  needed to produce the required shape. The darting may be automatically generated using pattern software. 
         [0041]    It should be noted here that although the steps of the method embodiments disclosed above have been described as being carried out in a particular order for illustrative purposes, it is possible to perform the steps of these methods in various other orders. 
         [0042]      FIG. 11  illustrates, in exploded form, the stack  43  of adhesive plies  44  that may be placed between the doubler  20  and the surface  24 , wherein the footprint of the doubler  20  on the surface  24  is indicated by the dashed line  85 . The adhesive plies  44  may be assembled as a stack  43  before being placed between the doubler  20  and the surface  24 , or they may be sequentially applied to either the doubler  20  or to the surface  24  (or a combination of both) before the doubler  20  is applied to the surface  24 . As previously discussed the 3-D map  39  ( FIG. 7 ) may be used as a guide to arrange and orient the adhesive plies  44 , both relative to each other and relative to the intended placement position on surface  24 . In order to assure proper placement and orientation of the adhesive plies  44 , a coordinate system  87  may be used as a reference to locate the adhesive plies  44  within an XY plane corresponding the plane of the surface  24 , and to properly orient their rotational position about a Z axis of the coordinate system  87 , which in the illustrated example, extends normal to the surface  24 . Additionally, in order to assist in the orientation process, each of the adhesive plies  44  may carry marks or indicia, indicated as “F” and “A” in  FIG. 11 , for example, to respectively designate fore and aft directions of orientation for each of the adhesive plies  44 . 
         [0043]    Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace and automotive applications. Thus, referring now to  FIGS. 12 and 13 , embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method  90  as shown in  FIG. 12  and an aircraft  92  as shown in  FIG. 13 . Aircraft applications of the disclosed embodiments may include, for example, without limitation, composite stiffened members such as fuselage skins, wing skins, control surfaces, hatches, floor panels, door panels, access panels and empennages, to name a few. During pre-production, exemplary method  90  may include specification and design  94  of the aircraft  92  and material procurement  96 . During production, component and subassembly manufacturing  98  and system integration  100  of the aircraft  92  takes place. Thereafter, the aircraft  92  may go through certification and delivery  102  in order to be placed in service  104 . While in service by a customer, the aircraft  92  is scheduled for routine maintenance and service  106  (which may also include modification, reconfiguration, refurbishment, and so on). 
         [0044]    Each of the processes of method  90  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
         [0045]    As shown in  FIG. 13 , the aircraft  92  produced by exemplary method  90  may include an airframe  108  with a plurality of systems  110  and an interior  112 . Examples of high-level systems  110  include one or more of a propulsion system  114 , an electrical system  116 , a hydraulic system  118 , and an environmental system  120 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the automotive industry. 
         [0046]    Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service method  90 . For example, components or subassemblies corresponding to production process  98  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  92  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  98  and  100 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  92 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  92  is in service, for example and without limitation, to maintenance and service  106 . 
         [0047]    Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.