Abstract:
A method of assembling a composite structure is disclosed. An illustrative embodiment of the method includes receiving and positioning at least two composite structure subassemblies on a structure assembly table by operation of at least one first device and at least one second device and compacting the at least two composite structure subassemblies into a composite structure by operation of a third device.

Description:
FIELD 
       [0001]    The present invention relates to apparatuses and methods for assembling composite structures such as aircraft stringers. More particularly, the present invention relates to a composite structure assembly table and method for the automated assembly of composite structures such as aircraft wing stringers. 
       BACKGROUND 
       [0002]    Composite structures are used extensively in aircraft and other applications in which materials having a high strength-to-weight ratio are necessary. However, composite structures are costly since fabrication of such structures requires the layering of multiple materials. Depending on the particular application, a composite structure may be formed by layering individual sheets of material either manually or using an automated apparatus. 
         [0003]    One type of composite structure which is commonly used as a support element in aircraft is the “I” beam or “T” stringer. These beam-type composite structures are generally formed by manually placing layers of composite material over a lay-up mandrel. An automated cutting machine cuts each layer of material, or prepreg, to the proper shape. The individual layers of the prepreg are then manually placed on separate lay-up mandrels. Once positioned, each layer of prepreg is manually conformed to the exterior contour of each lay-up mandrel to form two C-channels. Next, the C-channels and lay-up mandrels are rotated to facilitate joining of the C-channels to each other along their webs to form an I-beam. A radius filler is then placed in the triangular recesses formed in the center of the top and bottom flanges of the I-beam. Top and bottom composite reinforcement layers are then manually placed over the radius filler, which is then bagged and autoclave-cured. 
         [0004]    The manual I-beam or stringer fabrication process is labor-intensive, time-consuming and attended by quality control issues. Therefore, automated methods of fabricating composite structures are being developed due to the drawbacks which are associated with manual fabrication of composite structures. 
       SUMMARY 
       [0005]    The present invention is generally directed to a method of assembling a composite structure. An illustrative embodiment of the method includes receiving and positioning at least two composite structure subassemblies on a structure assembly table by operation of at least one first device and at least one second device and compacting the at least two composite structure subassemblies into a composite structure by operation of a third device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The invention will be described, by way of example, with reference to the accompanying drawings, in which: 
           [0007]      FIG. 1  is a perspective view of a table module of an illustrative embodiment of the structure assembly table, which table module includes multiple adjacent module units. 
           [0008]      FIG. 2  is an end view of a module unit of the structure assembly table, more particularly illustrating a riser block, a flipper assembly, a flopper assembly and a compactor head which in concert with each other implement automated fabrication of a composite structure. 
           [0009]      FIG. 3  is a perspective view of multiple flipper assemblies in respective module units (not shown) of the structure assembly table, with a composite structure being positioned by the flipper assemblies. 
           [0010]      FIG. 4  is a perspective view of an adjustable position flipper element of each flipper assembly. 
           [0011]      FIG. 5  is a perspective view of multiple flopper assemblies in respective module units (not shown) of the structure assembly table, with separate components of a composite structure being positioned by the respective flopper assemblies. 
           [0012]      FIG. 6  is a perspective view of a flopper assembly of a corresponding module unit of the structure assembly table. 
           [0013]      FIG. 7  is a top view of a positioning assembly of the structure assembly table. 
           [0014]      FIG. 8  is a front view of a positioning assembly of the structure assembly table. 
           [0015]      FIGS. 9-38  illustrate sequential fabrication of a composite structure in typical implementation of the structure assembly table. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring to  FIGS. 1-8 , an illustrative embodiment of the structure assembly table is generally indicated by reference numeral  1 . As shown in  FIG. 1 , the structure assembly table  1  includes a table module  2  having a generally elongated, box-shaped table module frame  3 . The table module  2  includes multiple, adjacent module units  8 , each of which is a functional subunit of the structure assembly table  1 . In the illustrative embodiment of the invention shown in  FIG. 1 , the structure assembly table  1  includes six module units  8 ; however, it is to be understood that the structure assembly table  1  may have a smaller or larger number of module units  8  depending on the application of the structure assembly table  1 . As shown in  FIG. 2 , for purposes of description herein, the structure assembly table  1  has an operator side  4  and a non-operator side  5 . 
         [0017]    As will be hereinafter described, the structure assembly table  1  is suitable for implementing the assembly of a composite structure  87  ( FIG. 3 ) such as an aircraft wing stringer, for example. The structure assembly table  1  is highly reconfigurable via computer software modifications. The modularity of the structure assembly table  1  accommodates multiple composite structure configurations. The modular components of the structure assembly table  1  are designed to be interchangeable and serviceable through typical remove-and-replace methods. Multiple structure assembly tables  1  can be placed in end-to-end relationship with respect to each other to facilitate fabrication of composite structures having various sizes and configurations. 
         [0018]    As will be hereinafter further described, the structure assembly table  1  includes a bank of six devices or assemblies which are operable to index, lift, rotate and set individual and opposite composite structure subassemblies such as stringer mandrels, for example. Another bank of five computer-controlled shuttling or positioning devices or assemblies lifts and positions the two composite structure subassemblies relative to each other and ensures proper spacing and parallelism of the subassemblies through a series of sensing routines. A bank of six computer-controlled pneumatic compactor devices compacts the individual subassemblies together, after which a bank of flipper assemblies rotates the composite structure to the operator side  4  of the structure assembly table  1 . The flipper assemblies capture the subassemblies and position the subassemblies with respect to each other while accommodating for taper and ply thickness changes along the length of each to securely rotate the composite structure. In cases in which the composite structure is an aircraft stringer, after radius filler and cap are manually applied to one exposed side of the mandrel assembly, the flipper assembly then rotates the mandrel assembly back to the non-operator side  5  of the structure assembly table  1  where the mandrel assembly is then lifted and shuttled back to the operator side  4  for application of radius filler and cap on the opposite side of the assembly. 
         [0019]    As shown in  FIGS. 1 and 2 , each module unit  8  includes a generally elongated, rectangular module unit frame  9  which is supported by the table module frame  3 . A frame divider  10  may extend through the center portion of the module unit frame  9 . As shown in  FIG. 1 , unit connectors  11  connect the module unit frames  9  of the adjacent module units  8  to each other. A top plate  14  is provided on the table module frame  3 , between adjacent module units  8 . A module slot  16  extends between adjacent top plates  14 . 
         [0020]    As shown in  FIGS. 2 and 3 , each module unit  8  of the table module  2  includes a flipper assembly  18 . As shown in  FIG. 3 , the flipper assemblies  18  of the respective module units  8  form a bank of flipper assemblies  18  which carry out the rotating functions of the structure assembly table  1 , as will be hereinafter described. Each flipper assembly  18  is disposed beneath the module slot  16  of each corresponding module unit  8 . Each flipper assembly  18  includes a fixed position flipper device  19  typically having an electro/mechanically actuated linear positioning screw  20  which is pivotally attached to the module unit frame  9  via a pivot pin  25 . A ballscrew  21  is extendable from the ballscrew housing  20 . A flipper blade frame  22  is pivotally attached to the ballscrew  21  via a pivot pin  24 . A generally elongated, rectangular flipper blade  23  is provided on the flipper blade frame  22 . Accordingly, by selective actuation of the actuating ballscrew housing  20  and actuating ballscrew  21 , the flipper blade  23  of the fixed position flipper device  19  can be positioned between a generally horizontal position (not shown) and the generally vertical position shown in  FIG. 27 , in which vertical position the flipper blade  23  extends through the module slot  16  of the corresponding module unit  8 . A support pin  26  extends from the proximal end portion of the flipper blade  23 , in generally perpendicular relationship with respect to the longitudinal axis of the flipper blade  23 . 
         [0021]    As shown in  FIG. 3 , each flipper assembly  18  further includes an adjustable position flipper device  30  which is opposite the fixed position flipper device  19 . As shown in  FIG. 4 , the adjustable position flipper device  30  includes a containment frame  31 . The containment frame  31  is provided on a linear slide  38 , which is typically ballscrew actuated, to facilitate selective movement of the containment frame  31  toward and away from the corresponding paired or opposite fixed position flipper device  19 . A ballscrew housing  36  is provided in the containment frame  31 . A ballscrew  37  is selectively extendable from the ballscrew housing  36 . 
         [0022]    A pair of spaced-apart frame flanges  32  extends from the containment frame  31 . A pivot rod  33  extends between the frame flanges  32 . An elongated flipper blade frame  34  is pivotally mounted on the pivot rod  33 . As further shown in  FIG. 4 , on one side of the pivot rod  33 , the ballscrew  37  pivotally engages a first end of the flipper blade frame  34  via a pivot pin  33   a . A generally elongated, rectangular flipper blade  35  extends from a second end of the flipper blade frame  34  on the opposite side of the pivot rod  33 . Accordingly, by selective actuation of the ballscrew housing  36  and ballscrew  37 , the flipper blade  35  of the adjustable position flipper device  30  can be positioned between a generally horizontal position (not shown) and the generally vertical position shown in  FIG. 27 , in which vertical position the flipper blade  35  extends through the module slot  16  of the corresponding module unit  8 . A support pin  39  extends from the proximal end portion of the flipper blade  35 , in generally perpendicular relationship with respect to the longitudinal axis of the flipper blade  35 . A controller (not shown) is connected to the ballscrew housing  20  of each fixed position flipper device  19  and the ballscrew housing  36  of each adjustable position flipper device  30  to facilitate operation of the flipper assemblies  18  of the module units  8  in concert with each other. 
         [0023]    As shown in  FIGS. 2 ,  5  and  6 , each module unit  8  of the table module  2  further includes a flopper assembly  44  which is adjacent to the corresponding flipper assembly  18 . The flopper assemblies  44  are adapted to index, lift, rotate and set opposing composite structure subunits in a simple linear actuation preparatory to fabrication of the composite structure. As shown in  FIG. 2 , the flipper assembly  18  and the flopper assembly  44  are typically located on opposite sides of the frame divider  10 . The flopper assemblies  44  of the respective module units  8  form a bank of flopper assemblies  44  which carry out relative placement or positioning of the composite structure component subunits with respect to each other in operation of the structure assembly table  1 , as shown in  FIG. 5  and will be hereinafter described. As shown in  FIG. 6 , each flopper assembly  44  includes a three-walled cabinet  55  having a track plate  59  which is attached to the module unit frame  9  of each module unit  8  according to the knowledge of those skilled in the art. A pair of spaced-apart side plates  54  extends from respective ends of the track plate  59 . At least one carriage track  58  is provided on the track plate  59 . As shown in  FIG. 6 , a pair of generally parallel, spaced-apart carriage tracks  58  may be provided on the track plate  59 . A linear rail carriage  57  slidably engages the carriage tracks  58 . A yoke assembly  56  is provided on the linear rail carriage  57 . As shown in  FIG. 2 , a pair of jack screw housing servo motors (I/O) includes a pair of jack screw housings  63  provided on the module unit frame  9 . A pair of jack screws and ball nuts  63   a  is extendable from the stabilizing jack screw housings  63 , respectively. The stabilizing jack screws and ball nuts  63   a  engage the linear rail carriage  57  through a gang connection  62  and actuate movement of the linear rail carriages  57  of the flopper assemblies  44  in concert along the respective pairs of carriage tracks  58 . 
         [0024]    As shown in  FIG. 6 , a flopper frame  45  includes an elongated crosspiece  46  which is provided on the yoke assembly  56 . A slotted cradle support  47  extends from each end of the crosspiece  46 . Cradle position blocks  49  and  51  are pivotally attached to each cradle support  47 . Accordingly, a curved track groove  50  provides tracking on cradle position block  49 . A ball plunger  53  extends through a plunger opening (not shown) provided in the cradle support  47  and through to the track groove  50 . An elongated slider link  48  is attached to each side plate  54  of the cabinet  55 . Each cradle position block  49  is pivotally attached to the corresponding slider link  48  typically via a pivot pin (not shown) located above a ball detent  52  which extends through the slider link  48  and position block  49 . 
         [0025]    An L-shaped mandrel cradle  51  is provided on each cradle position block  49 . Accordingly, each mandrel cradle  51  is selectively positional between a first position shown in  FIG. 11  and a second position shown in  FIG. 13 , in which second position the mandrel cradle  51  has been rotated 90 degrees with respect to the first position, according to a technique which will be hereinafter described. Depending on the position of the linear rail carriage  57  and yoke assembly  56  on the carriage tracks  58  of the cabinet  55 , each pair of mandrel cradles  51  extends through the module slot  16  of the corresponding module unit  8 , as shown in  FIGS. 13 and 14 , or is disposed beneath the top surface of the module unit  8 , as shown in  FIG. 15 . At least one pivot stop pin  64  may extend from each cradle support  47  to prevent each mandrel cradle  51  from pivoting beyond the position shown in  FIG. 6 . 
         [0026]    The jack screws and ball nuts  63   a  can be extended from the respective jack screw housings  63  of the respective pair of jack screw housing servo motors (I/O to raise each yoke assembly  56 , via the linear rail carriage  57 , through the corresponding module slot  16  ( FIG. 1 ) in the table module  2 . At a certain point during the lift, one leg of each mandrel cradle  51  indexes one of a left hand mandrel  88  and a right hand mandrel  88   a , as shown in  FIG. 5 , during fabrication of a stringer  93  ( FIG. 38 ), which will be hereinafter described. Continuing through the lift, a certain point is reached upon which the slider links  48  and the yoke assembly  56  reach their slide limit and force the mandrel cradles  51  to rotate. The halfway point of this rotation of the mandrel cradles  51  is shown in  FIG. 5 . Once the mandrel cradles  51  have rotated opposite one another and are locked into position by the ball detents  52 , actuation of the jack screws and ball nuts  63   a  is reversed and the linear rail carriage  57  travels downwardly on the carriage tracks  58 . As the linear rail carriage  57  continues its downward travel on the carriage tracks  58 , the mandrel cradles  51  bump against the fixed cabinet  55  to release the ball detents  52 , such that gravity returns the mandrel cradles  51  to the upright position. 
         [0027]    As shown in  FIGS. 1 ,  2 ,  7  and  8 , the table module  2  of the structure assembly table  1  further includes multiple positioning assemblies  70  which facilitate selective positioning of the composite assembly and composite assembly components along the transverse axis of the table module  2  during fabrication of a stringer  93 . In a typical embodiment, the structure assembly table  1  includes five positioning assemblies  70 . As shown in  FIG. 1 , each positioning assembly  70  is typically provided between adjacent module units  8 . 
         [0028]    As shown in  FIGS. 7 and 8 , each positioning assembly  70  typically includes a pair of generally parallel, spaced-apart vertical carriage supports  71 . A vertical carriage  72  is slidably mounted on each vertical carriage support  71 . An I/O capable vertical servo motor  73  is provided on each vertical carriage support  71  and operably engages each corresponding vertical carriage  72  to facilitate vertical travel of each vertical carriage  72  on the corresponding vertical carriage support  71 . Fasteners  74  attach each vertical carriage support  71  of the positioning assembly  70  to a corresponding unit connector  11  which connects the adjacent module units  8  of the table module  2  to each other. 
         [0029]    An elongated transverse carriage support  76  extends between the vertical carriages  72 . The transverse carriage support  76  may be attached to the vertical carriages  72  via a pair of gusseted angle attach brackets  75 , for example. A transverse carriage  77  is slidably mounted on the transverse carriage support  76 . A riser block  78  is provided on the transverse carriage  77 . A cover  79 , such as a delrin cover, for example, is provided on the riser block  78 . An I/O capable transverse servo motor  80  operably engages the transverse carriage  77  to facilitate selective travel of the transverse carriage  77  along the transverse carriage support  76 . As shown in  FIG. 7 , a photoelectric sensor  81  is provided on the cover  79 , which is adapted to detect the edge of a composite structure subassembly on the riser block  78  at five different locations of the composite structure subassembly during fabrication of the composite structure, as will be hereinafter described. In an illustrative embodiment of the structure assembly table  1 , the photoelectric sensors  81  are spaced at forty (40) inch centers per table module  2 . By operation of the vertical servo motors  73 , the vertical carriages  72  travel vertically on the respective vertical carriage supports  71  and raise and lower the transverse carriage support  76  and riser block  78  with respect to the top surface of the table module  2 . By operation of the transverse servo motor  80 , the transverse carriage  77  and riser block  78  travel in a selected direction along the transverse carriage support  76 . 
         [0030]    As further shown in  FIGS. 1 and 2 , a compactor head  84  extends through the module slot  16  of each module unit  8 . A compactor assembly (not shown) is typically supported by the module unit frame  9  of each module unit  8 , beneath the top plate  14 . The compactor assembly typically includes a pneumatically-actuated cylinder (not shown) which engages the compactor head  84  to facilitate selective bidirectional travel of the compactor head  84  along the module slot  16  of the corresponding module unit  8 . Accordingly, responsive to operation of the compactor assembly, the compactor head  84  is capable of travel between the far right position shown in  FIG. 23  and the position shown in  FIG. 24  for purposes which will be hereinafter described. 
         [0031]    A computerized controller (not shown) is connected to the actuating ballscrew housing servo motor (I/O)  20  and the actuating ballscrew housing servo motor (I/O)  36  of each flipper assembly  18 ; the actuating jack screw housing servo motor (I/O)  63  ( FIG. 2 ) of each flopper assembly  44 ; and the servo motors (I/O)  73  and the servo motor (I/O)  80  ( FIG. 8 ) of each positioning assembly  70  to facilitate automated fabrication of a composite structure  87 , as will be hereinafter described with respect to  FIGS. 9-38 . 
         [0032]    Referring next to  FIGS. 9-38 , implementation of the composite structure assembly table  1  in the fabrication of a composite aircraft stringer  93  ( FIG. 38 ) will be described. It will be recognized and understood that the composite structure assembly table  1  can be configured to fabricate a variety of composite aircraft stringers  93 . Furthermore, the composite structure and assembly table  1  can be readily re-configured to accommodate stringers of various sizes and configurations, as needed. Multiple table modules  2  can be placed in end-to-end relationship with respect to each other to form a composite structure assembly table  1  of selected length depending on the length of the aircraft stringer  93  to be fabricated using the composite structure assembly table  1 . 
         [0033]    In  FIG. 9 , operation of the composite structure assembly table  1  begins by controller input of table configuration, depending on the type of aircraft stringer  93  ( FIG. 38 ) which is to be fabricated, into the computerized controller (not shown). The table configuration includes such parameters as the length of the stringer  93  and the variations in thickness along the length of the stringer  93 , for example. In  FIG. 10 , the flopper assemblies  44  are operated to extend the pairs of mandrel cradles  51  through the respective module slots  16  ( FIG. 1 ) in the table module  2  of the structure assembly table  1 . In  FIG. 11 , a left hand mandrel  88  and a right hand mandrel  88   a , each of which receives a pair of respective C-shaped stringer charges  89 , is placed on the mandrel cradles  51  of the flopper assemblies  44 . The left hand mandrel  88  and right hand mandrel  88   a  extend in generally parallel relationship with respect to the longitudinal axis of the table module  2  and each other. 
         [0034]    In  FIGS. 12 and 13 , the mandrel cradles  51  of the respective flopper assemblies  44  are rotated outwardly to turn the left hand mandrel  88  and right hand mandrel  88   a  and respective stringer charges  89  away from each other in a horizontal orientation, as shown in  FIG. 13 . The flopper assemblies  44  are shown with the mandrels  88 ,  88   a  and stringer charges  89  in the raised position in  FIG. 5 . In  FIG. 14 , the mandrel cradles  51  are lowered to rest the mandrels  88 ,  88   a  onto the top plates  14  ( FIG. 1 ) or top surface of the table module  2 . In  FIG. 15 , the mandrel cradles  51  are lowered beneath the surface of the table module  2 . 
         [0035]    In  FIG. 16 , left hand mandrel  88  and composite charge  89  are sensed for location then lifted. A traverse move of the riser blocks  78  positions  88  and  89  next to support pins  26  of fixed flipper  19  as shown in  FIG. 17 . In  FIG. 18 , the riser blocks  78  of the positioning assemblies  70  have sensed position relative to the right-hand mandrel  88   a  and  89  by operation of the photoelectric sensors  81 . Then, the right-hand mandrel  88   a  is lifted above the surface of the table module  2 . The left-hand mandrel  88  remains on the top surface of the table module  2 , as previously located. In  FIG. 19 , the positioning assemblies  70  are operated to move the riser blocks  78 , and the right-hand mandrel  88   a , toward and adjacent to the left-hand mandrel  88 . In  FIG. 20 , the riser blocks  78  ( FIG. 7 ) have been lowered beneath the top surface of the table module  2  to rest the right-hand mandrel  88   a  on the table module  2 . Next, the photoelectric sensors  81  ( FIG. 7 ) on the respective riser blocks  78  sense the location of the edge of the right-hand mandrel  88   a . This location is used by the system controller to calculate straight-line final placement of the right-hand mandrel  88   a.    
         [0036]    In  FIG. 21 , the riser blocks  78  have located the right-hand mandrel  88   a  and lifted the right-hand mandrel  88   a  above the top surface of the table module  2 . This step begins final placement of the right-hand mandrel  88   a . In  FIG. 22 , the riser blocks  78  have moved the right-hand mandrel  88   a  toward and immediately adjacent to the left-handed mandrel  88 , with the webbing of the stringer charges  89  on the respective mandrels  88 ,  88   a  typically disposed in contact with each other. In  FIG. 23 , the riser blocks  78  have been lowered beneath the top surface of the table module  2 . 
         [0037]    In  FIG. 24 , the compactor assembly (not shown) has moved the compactor head  84  from the far right-hand “home” position at the non-operator side  5  of the table module  2 , as shown in  FIG. 23 , toward and then against the right-hand mandrel  88   a , as shown in  FIG. 24 . The left-hand mandrel  88  engages the support pins  26  on the respective flipper blades  23  ( FIG. 2 ) of the flipper assemblies  18 . Therefore, the webbing of the C-shaped stringer charges  89  on the respective mandrels  88 ,  88   a  are pressed against and joined to each other under pressure for a time. In  FIG. 25 , the compactor head  84  has returned to the far right-hand “home” position at the non-operator side  5  of the table module  2 . 
         [0038]    In  FIGS. 26 and 27 , the flipper assemblies  18  have begun to raise the fixed position flipper device  19  and the adjustable position flipper device  30  above the plane of the top surface of the table module  2 . The flipper blade  23  of the fixed position flipper device  19  rotates the mandrels  88 ,  88   a  and connected stringer charges  89  about ninety degrees. At the end of the lifting or rotating movement, the mandrels  88 ,  88   a  and connected stringer charges  89  are positioned between the flipper blade  23  of the fixed position flipper device  19  and the flipper blade  35  of the adjustable position flipper device  30 , as shown in  FIG. 27 . In  FIG. 28 , the mandrels  88 ,  88   a  and stringer charges  89  have been transferred from the flipper blade  23  of the fixed position flipper device  19  to the flipper blade  35  of the adjustable position flipper device  30 . In  FIG. 29 , the flipper blade  23  and the flipper blade  35  have been lowered beneath the top surface of the table module  2 , with the mandrels  88 ,  88   a  and stringer charges  89  resting on the operator side top surface of the table module  2 . It will be appreciated by those skilled in the art that the independent adjustment capability of the adjustable position flipper device  30  of each flipper assembly  18  are capable of compensating for taper and ply thickness variations along the length of the mandrel assembly. Referring again to  FIG. 2 , the linear slide  38  facilitates positioning of each adjustable position flipper device  30  with respect to the corresponding paired fixed position flipper device  19  during repositioning of the mandrel assembly in order to compensate for these taper and ply thickness variations. 
         [0039]    In  FIG. 30 , a radius filler  91  is applied to the triangular crevice which extends between and along the connected stringer charges  89 . A bottom cap  90  is applied to the stringer charges  89 , over the radius filler  91 . Application of the radius filler  91  and bottom cap  90  to the stringer charges  89  can be carried out using a manual process, according to the knowledge of those skilled in the art. 
         [0040]    In  FIGS. 31-33 , the mandrels  88 ,  88   a  and connected stringer charges  89  are raised from the surface of the table module  2  and rotated 90 degrees as they are transferred from the flipper blade  35  of the adjustable position flipper device  30  to the flipper blade  23  of the fixed position flipper device  19 . The mandrels  88 ,  88   a  and stringer charges  89  are additionally shown engaged by the flipper assemblies  18  in the raised position in  FIG. 3 . The mandrels  88 ,  88   a  and stringer charges  89  are then rotated another 90 degrees as the flipper blade  23  of the fixed position flipper device  19  rests the mandrels  88 ,  88   a  and stringer charges  89  on the top surface of the table module  2 , respectively. In  FIG. 34 , the riser blocks  78  of the positioning assemblies  70  have located and raised the mandrels  88 ,  88   a  and stringer charges  89  above the surface of the table module  2  and support pin  26 . In  FIG. 35 , the riser blocks  78  have moved the mandrels  88 ,  88  and stringer charges  89  to the operator side  4  of the table module  2 . 
         [0041]    In  FIG. 36 , the riser blocks  78  have lowered the mandrels  88 ,  88   a  and stringer charges  89  onto the top surface of the table module  2 . In  FIG. 37 , a radius filler  91  is applied to the triangular crevice between the stringer charges  89 . A top cap  92  is applied to the stringer charges  89 , over the radius filler  91 . Application of the radius filler  91  and top cap  92  to the stringer charges  89  can be carried out using a manual process, according to the knowledge of those skilled in the art. As shown in  FIG. 38 , application of the radius filler  91  and top cap  92  to the stringer charges  89  completes fabrication of the stringer  93 . The completed stringer  93  is then readied for access by an operator for transport from the structure assembly table  1  to a subsequent processing station (not shown). 
         [0042]    Although this invention has 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 ordinary skill in the art.