Abstract:
A system fabricating composite preforms includes a layer assembly stage with a first stage for receiving new layers, such as layer N; and a second stage for holding up to K layers, such as layers N−1 to N−K. An interlayer reinforcement insertion mechanism inserts interlayer reinforcements Q through layer N and the layers N−1 to N−K, using a first layer spacing between layer N−K and layer N−K− 1  in a completed layer stage. Following the interlayer reinforcements Q insertion, the layer assembly stage transfers the layer N−K to the completed layer stage; closes the first layer spacing, bringing layers N−K and N−K−1 into contact; and transfers the layer N to the second stage. The system repeats this cycle of receiving new layers, inserting interlayer reinforcements using layer spacings between the second and completed layer stages, closing these layer spacings, and transferring layers to construct composite preforms with arbitrary numbers of layers.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/216,472, filed Mar. 17, 2014 entitled SYSTEMS FOR THREE-DIMENSIONAL WEAVING OF COMPOSITE PREFORMS AND PRODUCTS WITH VARYING CROSS-SECTIONAL TOPOLOGY which claims priority to U.S. Provisional Patent Application No. 61/788,493, filed Mar. 15, 2013 entitled SYSTEM AND METHOD FOR THREE-DIMENSIONAL WEAVING OF COMPOSITE PREFORMS AND PRODUCTS WITH VARYING CROSS-SECTIONAL TOPOLOGY which are hereby incorporated by reference as if set forth in full in this application for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to the field of fiber-reinforced composite materials, and in particular to methods and devices for manufacturing fiber preforms and finished composite products with complicated three-dimensional shapes. Fiber-reinforced composite materials, referred to herein as composites, are materials comprised of fibers embedded in a matrix material. Typical fibers include but are not limited to glass fibers, carbon fibers (e.g. graphite fibers and/or more exotic forms of carbon, such as carbon nanotubes), ceramic fibers, and synthetic polymer fibers, such as aramid and ultra-high-molecular-weight polyethylene fibers. Typical matrix materials include but are not limited to polymers, such as epoxies, vinylesters, polyester thermosetting plastics, and phenol formaldehyde resins; cement and concrete; metals; and ceramics. 
         [0003]    Composite materials often combine high-strength and relatively light weight. In typical composite products, the fibers provide high tensile strength in one or more directions and the matrix material hold the fibers in a specific shape. A set of fibers roughly in the shape of a final product is referred to as a fiber preform. Typical prior fiber preforms are comprised of layers of fibers (often woven or bound into a sheet of fabric) that are cut and arranged into a desired shape. Because fibers and fabrics made from fibers only provide high strength in specific directions, multiple layers of fiber cloth are often stacked in different orientations to provide strength and stiffness optimized for the intended usage of the final product. 
         [0004]    Most prior composite manufacturing techniques require the production of a mold, mandrel, plug, or other rigid structure in the shape of the desired preform. Sheets of fiber fabric are then cut and arranged on this rigid structure. A matrix material, such as uncured polymer resin, may be embedded in the fiber fabric or applied to the fabric during or after the fabric layup process. The matrix material is then cured or hardened, often under elevated temperature and/or pressure differentials to ensure even distribution of the matrix material and prevent voids, air bubbles, or other internal defects. Pressure and/or temperature may be applied to the composite part during curing using techniques including but not limited to compression molding, vacuum bags, autoclaves, inflatable bladders, and/or curing ovens. 
         [0005]    Unfortunately, prior techniques for manufacturing fiber preforms and final composite parts, especially for complex part shapes, are time-consuming and difficult to automate. For example, creating a mold, mandrel, or other rigid structure for supporting the preform is costly and time-consuming, especially for custom parts or small production runs where the tooling cost and time cannot be amortized over a large number of parts. In addition, the cutting and/or arranging fabric in the mold or other rigid structure is often performed by hand, due to the difficulty in draping fabric over complex forms without wrinkles or other surface defects. As a result, composite products are much more expensive than equivalent products made using conventional materials. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The invention will be described with reference to the drawings, in which: 
           [0007]      FIGS. 1A-1B  illustrate an example arrangement of the stages of a system for three-dimensional weaving of composite preforms and products with varying cross-sectional topology according to an embodiment of the invention; 
           [0008]      FIG. 2  illustrates an example progression of layers through the stages of a system for three-dimensional weaving of composite preforms and products with varying cross-sectional topology according to an embodiment of the invention; 
           [0009]      FIG. 3  illustrates a method of three-dimensional weaving of composite preforms and products with varying cross-sectional topology according to an embodiment of the invention; 
           [0010]      FIG. 4  illustrates an example weaving pattern of interlayer fibers for connecting two or more two-dimensional layers of fibers to form a three-dimensional weave according to an embodiment of the invention; 
           [0011]      FIGS. 5A-5G  illustrates the operation of an example mechanism for connecting two or more two-dimensional layers of fibers with an interlayer fibers to form a three-dimensional weave according to an embodiment of the invention; 
           [0012]      FIGS. 6A-6C  illustrate the operation of an example mechanism for consolidating two or more layers of a three-dimensional weave according to an embodiment of the invention; 
           [0013]      FIGS. 7A-7B  illustrate example staggered arrangements of interlayer fibers according to an embodiment of the invention; 
           [0014]      FIGS. 8A-8C  illustrate example open weave fabric patterns suitable for use with embodiments of the invention; 
           [0015]      FIGS. 9A-9E  illustrate an example removal of excess interlayer fibers during the consolidation of non-convex layers according to an embodiment of the invention; 
           [0016]      FIGS. 10A-10D  illustrate an example mechanism for supporting and moving layers of fabric during three-dimensional weaving according to an embodiment of the invention; and 
           [0017]      FIG. 11  illustrates a computer system suitable for controlling a system for three-dimensional weaving of composite preforms and products with varying cross-sectional topology according to an embodiment of the invention. 
       
    
    
     SUMMARY 
       [0018]    Embodiments of the invention includes a system for fabricating composite objects including a composite preform. The system includes a layer assembly stage including a first stage adapted to receive new material layers, such as a new material layer N; and a second stage adapted to hold up to K material layers, where K is a positive integer, such as one or more material layers N−1 to N−K. An embodiment of the invention includes an interlayer reinforcement insertion mechanism adapted to insert an interlayer reinforcement set Q through the material layer in the first stage, for example material layer N, and the one or more material layers located in the second stage of the layer assembly stage, for example material layers N−1 to N−K. 
         [0019]    In an embodiment, the interlayer reinforcement insertion mechanism is adapted to manipulate the interlayer reinforcement set Q within a first layer spacing between the oldest or last material layer in the second stage, such as material layer N−K, and the newest or first material layer in a completed layer stage, such as a material layer N−K−1. Following the insertion of the interlayer reinforcement set Q, the layer assembly stage transfers the material layer N−K to the completed layer stage and closes the first layer spacing to bring the material layers N−K and N−K−1 into contact. The layer assembly stage may then transfer the material layer in the first stage, such as material layer N, to the second stage. Embodiments of the system repeat this cycle of receiving new material layers, inserting interlayer reinforcement sets using additional layer spacings between the second stage and the completed layer stage, and then closing these layer spacings and transferring material layers to construct composite preforms with any arbitrary number of material layers. 
       DETAILED DESCRIPTION 
       [0020]    Embodiments of the invention include a system and method for created a composite preform with fibers and optionally other reinforcements interconnected through a three-dimensional weaving pattern. Embodiments of the invention create composite preforms by stacking layers of two-dimensional fiber fabric and then connecting two or more layers of fabric with interlayer fibers. Each layer of fabric may have a different shape than the other layers and any arbitrary topology, potentially including non-convex and/or disjoint shapes. 
         [0021]    Furthermore, embodiments of the invention may produce composite preforms comprised of any arbitrary number of interconnected layers. Further embodiments of the invention may cure composite preforms to produce completed composite parts. 
         [0022]      FIGS. 1A-1B  illustrate an example arrangement of the stages of a system for three-dimensional weaving of composite preforms and products with varying cross-sectional topology according to an embodiment of the invention.  FIG. 1A  illustrates a system  100  including one or more layer cutting stages, such as layer cutting stages  105 A and  105 B; a layer transport stage  110 ; a layer assembly stage  115 ; and a completed layer storage and/or curing stage  120 . 
         [0023]    In summary of system  100 , one or more layer cutting stages cut bulk fabric and optionally other materials into the shapes of cross-sections of the desired fiber preform. The layer transport stage  110  collects cut cross-section shapes from each of the layer cutting stages and transports them to the layer assembly stage  115 . Layer assembly stage  115  stacks cut cross-section shapes in the correct order and then joins two or more layers of cross-section shapes using interlayer weaving, as described in detail below. After the interlayer weaving process is complete for a given subset of cross-section shapes, they become part of a stack of interwoven fabric layers forming a completed section of the fiber preform and are stored in the completed layer storage stage  120 . 
         [0024]    Layer cutting stage  105 A includes a mechanism for dispensing bulk fabric, for example from a bolt or roll of fabric  106 A, over a cutting area  107 A. Bulk fabric may include any type of fibers known in the art for use with composite materials. Bulk fabric may be woven or non-woven fabric and may include different types of fibers, such as carbon fibers arranged parallel to one axis and aramid or other fibers arranged parallel to another axis. As described in detail below, embodiments of the bulk fabric is woven or otherwise assembled with gaps or holes between fibers to allow passage of interlayer fibers. Although referred to as a “layer,” each cross-section shape may be comprised of two or more physical layers of fabric, potentially bonded together, that are cut and manipulated as a unit, such as a multilayer fabric or sublaminate. 
         [0025]    A cutting head  108 A moves over the cutting area  107 A to cut one or more cross-section shapes  109 A from the bulk fabric. Cutting head  108 A may use any type of cutting mechanism known in the art and suited to cut the fibers included in the bulk fabric, including one or more static or moving blades, cutting lasers, and waterjet cutters. 
         [0026]    Each of the cross-section shapes  109 A corresponds with the shape of all or a portion of a cross-section of the desired fiber preform. As described above, the cross-section shapes may have any arbitrary topology and include non-convex and/or disjoint shapes. Furthermore, cross-section shapes associated with different layers may have different alignments with respect to the fiber orientation of the bulk fabric, so that as different layers of cross-section shapes are stacked, cross-section shapes may have fiber orientations in different directions. 
         [0027]    An embodiment of system  100  includes only a single layer cutting stage  105 A. Further embodiments of the invention include one or more additional layer cutting stages with similar components, such as layer cutting stage  105 B. Each of the optional additional layer cutting stages include similar components, including bulk fabric  106 B, cutting area  107 B, and cutting head  108 B to cut one or more cross-section shapes  109 B. Embodiments of the invention may include any arbitrary quantity of layer cutting stages operating in parallel to increase the overall speed of system  100 . 
         [0028]    In yet another embodiment, system  100  may utilize cross-section shapes cut from different materials. In one implementation, the set of layer cutting stages may be partitioned into two or more subsets, with each subset of layer cutting stages having a different type of bulk fabric material to cut. In another implementation, all or a portion of the layer cutting stages may include two or more rolls of different bulk fabric material and a mechanism for selecting one of the materials to cut. For example, layer cutting stage  105 B may include material roll  106 B and optionally roll  106 B′. 
         [0029]    In still a further embodiment, materials without fibers may also be included for cutting and incorporation into a fiber preform to support fiber layers during fabrication or to add functional characteristics to the final composite part. For example, a plastic film, such as water-soluble polyvinyl alcohol film, may be included in one or more layers of the fiber preform as a support structure for layers to be added on top of the support layers. After the fiber preform is cured, water or steam may be used to remove these support layers. Other non-fiber materials for cutting and eventual inclusion in layers may include electrically conductive and/or insulating materials; metal foils; magnetic materials; materials adapted to be removed by heat, solvents, or acid; and flexible materials. 
         [0030]    After one or more cross-section shapes for a layer have been cut from the bulk fabric by one of the cutting stages, the layer transport stage  110  moves the cross-section shapes to an initial position in the layer assembly stage  115 . In an embodiment, layer transport stage  110  includes a conveyor system for transporting cross-section shapes. In another embodiment, a mechanical arm or gantry with one or more degrees of freedom may be used to transport cross-section shapes. 
         [0031]    In an embodiment, layer transport stage includes a movable vacuum table platform for picking up cross-section shapes from one or more layer cutting stages and moving these shapes to the layer assembly stage  115 . 
         [0032]    If the cross-section shapes do not have any interior voids or openings, then any excess fabric leftover after cutting will remain attached to the roll of bulk fabric. This allows the cross-section shapes to be easily removed from the cutting stage. For more complicated fiber preforms having cross-section shapes with interior voids, embodiments of the layer transport stage  110  may include a vacuum table or gripper with selectable regions so that cut fabric corresponding with cross-section shapes may be picked up. In this implementation, pieces of cut fabric corresponding with interior voids are left behind in the cutting area and may be swept away. 
         [0033]    In still another embodiment, a moveable plate or drum with an electrostatic charge may be used to pick up cross-section shapes. In yet a further embodiment, a photoconductive plate or drum may be given a substantially uniform electrostatic charge and then exposed to a pattern of light corresponding with the inverse of the cross-section shape. The pattern of light causes the electrostatic charge to dissipate outside areas of the plate or drum corresponding with the cross-section shape. The selectively-charged plate or drum may then be used to pick up the cross-section shape while leaving behind unneeded pieces of cut fabric, such as pieces corresponding with interior voids. 
         [0034]      FIG. 1B  illustrates a detail view  150  of the layer assembly stage  115  and completed layer storage and/or curing stage  120 . As shown in detail view  150 , the layer assembly stage  115  includes a new layer stage  153  and an intermediate layer stage  155 . New layer stage  153  receives new cross-section shapes  154  from the layer transport stage  110  shown in  FIG. 1A . Intermediate layer stage  115  holds at least one and optionally more than one layer. The layer assembly stage  115  uses a three-dimensional weaving technique to connect the new cross-section shapes  154  in new layer stage  153  with the one or more layers of previously received cross-section shapes in intermediate layer stage  155  using interlayer fibers. As described in detail below, after the new cross-section shapes  154  in the new layer stage  153  are connected with the cross-section shapes in the intermediate layer stage, the new cross-section shapes  154  are transferred from the new layer stage  153  to the top of the intermediate layer stage  155 . Additionally, the bottom-most layer of cross-section shapes  160  in the intermediate layer stage  155  is transferred to the completed layer storage stage  120 . 
         [0035]    To connect the cross-section shapes  154  in new layer stage  153  with the cross-section shapes in the intermediate layer stage  155 , an embodiment of the layer assembly stage  115  includes one or more pairs of interlayer weaving arms, such as interlayer weaving arm pair  157  comprised of upper interlayer weaving arm  157 A and lower interlayer weaving arm  157 B. Upper interlayer weaving arm  157 A is adapted to move over the top of new layers in new layer stage  153  in directions  158 A and  159 A. Similarly, lower interlayer weaving arm  157 B moves underneath the stack of cross-section shapes in the intermediate layer stage  155  and over the completed layer storage stage  120  in directions  158 B and  159 B. During the interlayer weaving process, the upper and lower interlayer weaving arms  157 A and  157 B move generally in unison to pass interlayer fibers through the cross-section shapes of the new layer stage  153  and intermediate layer stage  155 . 
         [0036]    In an embodiment, completed portions of the fiber preform are stored in the completed layer storage stage  120 . In a further embodiment, resin or other matrix material may be included in the bulk fabric or added to the layers of cross-section shapes during the layer cutting  105 , layer transport  110 , and/or layer assembly stages  115 . In an embodiment, the completed layer storage stage  120  may optionally include a cooling region  163  including a refrigeration or other type of cooling system to prevent resin in the preform from cooling prematurely. 
         [0037]    In yet a further embodiment, matrix material included in the fiber preform may optionally be cured or otherwise processed to produce a final product within the completed layer stage  120 . In one implementation of this embodiment, all or a portion of the completed layer stage is heated to accelerate a matrix curing process. In another implementation, the completed layer storage stage  120  includes a curing region  165  that selectively cures portions of the fiber preform as it moves through this region. The curing region  165  may include a continuous oven with one or more elevated temperature zones or any other type of curing system known in the art. In this embodiment, the rate of layer cutting and assembling is calibrated so that as new layers are added to the completed layer storage stage  120 , the completed portions of the fiber preform move through the curing region  165  at a rate appropriate for curing the matrix material. 
         [0038]    As discussed above, layers of fiber cloth, which have been cut into cross-section shapes, progress through the layer assembly stage where they are connected with each other using interlayer fibers.  FIG. 2  illustrates an example  200  of a progression of layers through the stages of a system for three-dimensional weaving of composite preforms and products with varying cross-sectional topology according to an embodiment of the invention. 
         [0039]    Example  200  begins with phase  205 . In phase  205 , a new layer, layer 1  206 , is added to the new layer stage  201 . Intermediate stage  202  and completed layer stage  203  are empty in phase  205 . Because there are no layers below layer 1  206  for weaving with interlayer fibers, phase  207  moves layer 1  206  to the intermediate layer stage  202 . 
         [0040]    Phase  209  adds layer 2  210  to the new layer stage  201 . As discussed above, each layer may be comprised of one or more cross-section shapes cut from one or more fiber fabrics. Furthermore, layer&#39;s cross-section shapes may include different shapes, different shape topologies, and different fiber orientations than those of the other layers. 
         [0041]    Phase  211  weaves interlayer fibers  212 A between layer 2  210  and layer 1  206 . As described in detail below, an upper interlayer weaving arm passes above layer 2  210  and a lower interlayer weaving arm passes below layer 1  206  to weave these two layers together with interlayer fibers. The two interlayer weaving arms pass individual fibers or untwisted bundles of fibers (sometimes referred to as tows) through layers  206  and  210 . In an embodiment, the bulk fabric used to create the cross-section shapes is woven or otherwise assembled with gaps or holes between fibers to allow passage of interlayer fibers. In a further embodiment, cross-section shapes are cut and placed in the layer assembly stage so that the gaps in adjacent fabric layers are aligned. 
         [0042]    In prior, two-dimensional weaving techniques, the fibers inserted during the weaving process (sometimes referred to as weft fibers) are normally pulled taut to bind the other fibers (sometimes referred to as warp fibers) together. In contrast, in the embodiment illustrated by example  200 , the interlayer fibers  212 A are not pulled taut at this phase so that there is sufficient space for the lower interlayer weaving arm to pass between the layers in a later phase. 
         [0043]    Following the weaving of interlayer fibers  212 A in phase  211 , phase  213  transfers layer 2  210  to the intermediate layer stage  202  and layer 1  206  to the completed layer stage  203 . In an embodiment, phase  213  may transfer these layers simultaneously so as to maintain the length and tension of interlayer fibers  212 A. 
         [0044]    Phase  215  adds layer 3  216  to the new layer stage  201  in a manner similar to phases  205  and  209 . Phase  217  weaves interlayer fibers  218 A between layer 3  216  and layer 2  210  in a manner similar to phase  211 . An upper interlayer weaving arm passes above layer 3  216  and a lower interlayer weaving arm passes below layer 2  210  to weave these two layers together with interlayer fibers. Because of the spacing left between layers 1  206  and 2  210  in the earlier interlayer weaving phase  211 , there is sufficient space for the lower interlayer weaving arm to pass between layers 1  206  and 2  210  to weave interlayer fibers  218 A between layers 3  216  and 2  210 . 
         [0045]    Following the weaving of interlayer fibers  218 A in phase  217 , phase  219  transfers layer 3  216  to the intermediate layer stage  202  and layer 2  210  to the completed layer stage  203 . In an embodiment, phase  219  may transfer these layers simultaneously so as to maintain the length and tension of interlayer fibers  218 A. Additionally, because the completed layer stage  203  already contains layer 1  206 , phase  219  now tightens interlayer fibers  212 A to form tightened interlayer fibers  212 B. This process of tightening interlayer fibers  212 A brings layers 1  206  and 2  210  into contact with each other, eliminating the space previously left between these layers for the lower interlayer weaving arm. This process of tightening a set of interlayer fibers between two layers to bring the layers into contact is referred to as layer consolidation. It should be noted that the interlayer fibers  218 A are not substantially affected by the tightening of interlayer fibers  212 A and there is still sufficient space between layers 2  210  and 3  216  to allow for the passage of the lower interlayer weaving arm. 
         [0046]    Phase  221  adds layer  4   222  to the new layer stage  201  in a manner similar to phases  205 ,  209 , and  215 . Phase  223  weaves interlayer fibers  224 A between layer 4  222  and layer 3  216  in a manner similar to phases  211  and  217 . Because of the spacing left between layers 2  210  and 3  216  in the earlier interlayer weaving phase  217 , there is sufficient space for the lower interlayer weaving arm to pass between layers 2  210  and 3  216  to weave interlayer fibers  224 A between layers 4  222  and 3  216 . 
         [0047]    Following the weaving of interlayer fibers  224 A in phase  223 , phase  225  transfers layer 4  222  to the intermediate layer stage  202  and layer 3  216  to the completed layer stage  203 . Phase  225  also tightens interlayer fibers  218 A to form tightened interlayer fibers  218 B and consolidates layers 3  216  and 2  210 . This brings layers 3  216  and 2  210  into contact with each other while leaving sufficient space between layers 3  216  and 4  222  to allow for the passage of the lower interlayer weaving arm for weaving additional layers. 
         [0048]    The process outlined in phases  205  to  225 , and specifically phases  221 - 225 , may be repeated for further layers, allowing a fiber preform to be constructed from any number of fiber layers. 
         [0049]    For clarity, example  200  illustrates an intermediate layer stage  202  holding a single layer at a time. In this example, the interlayer fibers only pass through the new layer and a single intermediate layer. However, further embodiments of the invention may hold multiple layers in the intermediate layer stage  202  at the same time. In these embodiments, the interlayer fibers are woven between the new layer and all of the layers in the intermediate layer stage.  FIG. 7B  illustrate an example arrangement of interlayer fibers passing through multiple intermediate layers. In general, if the intermediate layer stage  202  is able to hold K layers simultaneously, where K is any arbitrary positive integer, then each iteration of an interlayer weaving will pass through the K layers in the intermediate layer stage and the current new layer. Exceptions to this include the first and last K layers of the preform, where the intermediate layer stage may hold less than K layers. 
         [0050]      FIG. 3  illustrates a method  300  of three-dimensional weaving of composite preforms and products with varying cross-sectional topology according to an embodiment of the invention. Method  300  begins with step  305  generating or retrieving the next cross-section of a digital representation of the preform. A digital representation of the preform may be comprised of three-dimensional computer graphics model data in the form of surface data, such as polygon or triangle meshes, higher-order surfaces such as NURBS or subdivision surfaces, or implicit surfaces; or volumetric models, such as voxel, octree, or solid geometry models. In a further embodiment, the digital representation of the preform includes specifications of fiber orientations at various locations of the preform model. These fiber orientations may be specified based on engineering analysis of the applications of the part. 
         [0051]    In an embodiment, the digital representation of the preform has already be partitioned into a set of layer specifications. Each layer specification includes a specification of the shape or shapes comprising the preform cross-section at this location. Each layer specification may optionally include a specification of the fiber orientation for this layer and/or the type of material or materials to be used for this layer (if the system has multiple types of materials installed). Step  305  retrieves this data from memory, data storage, or another computer system. 
         [0052]    In another embodiment, step  305  generates the cross-section shape of the preform itself directly from the three-dimensional model of the preform using any geometry analysis technique known in the art. For example, Boolean constructive solid geometry operations may be used to generate a cross-section shape from volumetric models and spatial partitioning, such as binary space partitioning trees, may be used to generate a cross-section shape from surface models. If fiber orientations for a specific layer or the entire preform are not specified, step  305  may specify fiber orientations based on heuristics, default patterns, or optimization algorithms using engineering simulations to optimize strength, minimize weight, and/or optimize other factors. 
         [0053]    Additionally, if the preform includes disjoint parts or has portions with large, unsupported overhangs, embodiments of step  305  may retrieve or generate specifications for support material, for example using for meltable, soluble, or otherwise easily removable material. 
         [0054]    Step  310  cuts a new layer N according to the cross-section shape and fiber orientation specified by step  305 . In this discussion of example method  300 , each layer is referred to using a sequential integer N. In some embodiments, the fiber orientation of the bulk fiber material with respect to the cutting area cannot be changed. To compensate for this, the specification of cross-section shape is rotated prior to cutting, such that the desired fiber orientation relative to the cross-section shape is achieved. Additionally, if the bulk fiber includes gaps or holes to accommodate the insertion of interlayer fibers, then step  310  may also translate the cross-section shape such that the holes in this layer will be aligned with those of previously cut layers already in the layer assembly stage. 
         [0055]    Step  315  transports the cut cross-section shapes of one or more materials to the new layer stage in the layer assembly stage. In an embodiment, step  315  rotates and translates the cut cross-section shapes of this layer so that they are aligned with respect to any previously cut layers in the intermediate layer stage of the layer assembly stage. 
         [0056]    Step  320  weaves interlayer fiber set Q between layer N and from 1 to K layers in the intermediate layer stage, where K is the maximum number of layers that may be held in the intermediate layer stage and Q is generally equal to N−1. In an embodiment, interlayer fibers are inserted only in portions of the preform where the new layer N overlaps vertically with all of the layers N−1 to N−K in the intermediate layer stage. 
         [0057]    As illustrated in  FIG. 2 , the system is initialized with an empty intermediate layer stage. In these types of situations, step  320  may be skipped. Once at least one layer is added to the intermediate layer stage, step  320  will weave interlayer fibers between the new layer N and the one or more layers in the intermediate layer stage. Once an initial run of K layers have been created, the intermediate layer stage will include K layers, and step  320  will weave interlayer fibers between the new layer N and the K layers in the intermediate layer stage, which are layers N−1 to layers N−K. The new interlayer fiber set Q is not pulled taut at this time to leave space between the layers for the passage of the lower interlayer weaving arm on subsequent interlayer weaving steps. In an embodiment, the ends of the interlayer fibers are temporarily secured for future access and tightening. 
         [0058]    Step  325  moves the new layer N to the top or first position of the intermediate layer stage, moves layer N−K from the bottom or last position of the intermediate layer stage to the completed layer stage, and moves each of the other layers N−1 to N−K+1 in the intermediate layer stage to the next adjacent position in the intermediate layer stage. 
         [0059]    Step  330  tightens a previously woven interlayer fiber set Q-K, if it exists, consolidate layers N−K and N−K−1. Layer consolidation is the process of tightening a set of interlayer fibers between two layers to bring these layers into contact and reduce or substantially eliminate the space between these fiber layers. Additionally, embodiments of step  330  may trim and remove excess interlayer fibers that are left over after tightening fiber set Q-K. 
         [0060]    Step  335  moves the set of layers in the completed layer stage down or away from the intermediate layer stage so to accommodate the addition of further layers. In an embodiment, the completed layer stage includes a moveable platform for supporting the set of interwoven and completed layers. As construction of the fiber preform progresses, the moveable platform moves away from the intermediate layer stage so that the distance between the most recent completed layer and the intermediate layer stage remains roughly constant. 
         [0061]    Step  340  determines if all of the layers of the preform have been cut and added to the layer assembly stage. If not, then method  300  returns to step  305  to process, cut, and add interlayer weaving to another layer of fabric. If all of the layers have been cut and added to the layer assembly stage, then step  345  determines if there are any layers in the intermediate layer stage left to process. If so, then method  300  proceeds back to step  325  to process additional layers in the intermediate layer stage. If step  345  determines that there are no more layers in the intermediate layer stage, then method  300  is complete. 
         [0062]    Although the steps of method  300  are shown sequentially for clarity, embodiments of the invention may perform some or all of these steps in parallel. For example, an iteration of steps  305  and  310  for a layer N+1 may be performed in parallel with interlayer weaving process of layer N in steps  315  to  335 . In further embodiments, multiple layer cutting stages M may perform steps  305  and  310  in parallel to cut multiple layers simultaneously. Cut layers are transported from their respective cutting stages to the layer assembly stage in the order of assembly. 
         [0063]    In a further embodiment, step  310  may also cut layers of non-fiber material, such as removable support material or materials with other properties, for inclusion with the fiber preform. Support material may be used to support portions of the fiber preform with large overhangs, relative to the layers underneath this portion of the preform. In an additional embodiment, fiber preforms may also be constructed with two or more disjoint parts, optionally held in place through one or more layers of removable (for example meltable or soluble) support material. Each of the disjoint parts has its own layers connected with interlayer fibers, but there are no interlayer fibers connecting the disjoint parts. 
         [0064]    An embodiment of the invention includes layers of non-fiber material, such as support material, in the fiber preform without having interlayer fibers cross open spaces between non-adjacent layers. This can be used to create overhangs within a part and separate, unconnected parts within a preform. 
         [0065]    To accomplish this, the interlayer weaving process, for example shown in phases  211 ,  217 , and  223  and step  320 , is suspended over the portion or portions of the layer assembly area where support layers and/or one or more disjoint parts are to be created after the last fiber layer before a support layer and/or a layer of a second part enters the top or first position of the intermediate layer stage. (The interlayer weaving process can continue in regions of the layer assembly stage where the second part or support layer is not going to be added.) Layers of cross-section shapes comprising one or more support layers, overhanging portions of the preform, and/or a second part are then sequentially added to the new layer stage  201  and moved down through the one or more layer positions of the intermediate layer stage  202  without any interlayer weaving until the first layer of the second part or a fiber layer of an overhanging portion of the preform reaches the bottom of the intermediate layer stage. At this point, interlayer weaving is resumed in this portion of the layer assembly stage  202  so that layers of the second part and/or overhanging portions of the preform begin to be connected with interlayer fibers. 
         [0066]    Embodiments of the invention may include intermediate layer stages having K positions, where K is any integer greater than  1 . In general, higher values of K allow for each set of interlayer fibers to span larger numbers of fiber layers, which adds strength along this axis. However, larger values of K also increase the size of the intermediate layer stage and limit minimum thickness of any portion of the fiber preform to K layers. In a further embodiment, this limitation on the minimum thickness of the fiber preform may be overcome by allowing the intermediate layer stage to hold a variable number of fiber layers from 1 to K layers. For thin portions of the fiber preform, the number of fiber layers in the intermediate layer stage is reduces to K′, where K′ is less than or equal to the thickness of a portion of the fiber preform. When the thickness of the fiber preform increases, K′ may be increased up to the maximum value of K to add strength to the preform. 
         [0067]    As described above, interlayer fibers are used to connect layers of fabric cut to cross-section shapes of a fiber preform. These interlayer fibers are not tightened at first to allow for the insertion of additional sets of interlayer fibers between subsequently added layers.  FIG. 4  illustrates an example  400  of a weaving pattern of interlayer fibers for connecting two or more two-dimensional layers of fibers to form a three-dimensional weave according to an embodiment of the invention. 
         [0068]    In example  400 , a new layer  405  is to be connected with one or more previously added layers  410  in positioned in an intermediate layer stage. Interlayer fiber  415  is used to connect layers  405  and  410 . As shown in example  400 , interlayer fiber is woven from the top surface of new layer  405  to the bottom surface of layer  410 , which would be at the bottom or last position of the intermediate layer stage. For clarity, the interlayer weaving arms passing over the top surface of layer  405  and under the bottom surface of layer  410  are omitted from this drawing. 
         [0069]    After weaving interlayer fiber  415 , the ends  420 A and  420 B are secured, but not tightened. This leaves a space  435  between the layers  405  and  410 , which will later be used to accommodate the passage of the lower interlayer weaving arm when layer  405  is at the bottom position of the intermediate layer stage. After the insertion of this subsequent interlayer fiber set, the ends  420 A and  420 B of the interlayer fiber  415  will be used to tighten the interlayer fiber  415  and remove the space  435  between layers  405  and  410 . 
         [0070]    In an embodiment, interlayer fibers such as interlayer fiber  415  are inserted in regularly spaced rows or columns. Interlayer fibers are inserted only in portions of the preform where the new layer overlaps vertically with all of the layers in the intermediate layer stage. Additionally, each interlayer weaving stage inserts interlayer fibers in only some of the available rows or columns. For example, a weaving phase may insert interlayer fiber  415  and additional interlayer fibers in alternate rows  425 A- 425 C, skipping rows  430 A- 430 D. The omitted rows will be used for interlayer fibers inserted during later weaving phases.  FIG. 7B , discussed below, illustrates an example staggered arrangement of interlayer fibers produced by skipping a portion of the rows during each interlayer weaving phase. 
         [0071]      FIGS. 5A-5G  illustrates the operation of an example mechanism for connecting two or more two-dimensional layers of fibers with an interlayer fibers to form a three-dimensional weave according to an embodiment of the invention.  FIG. 5A  illustrates a pair of fabric layers  503  and  505 . In an embodiment, layer  503  is a new layer added to the layer assembly stage and layer  505  is at the bottom position of the intermediate layer stage. 
         [0072]    Although  FIGS. 5A-5G  only show a pair of layers for clarity, additional layers may be optionally included between layers  503  and  505  if the intermediate layer stage holds more than one layer. 
         [0073]    A pair of interlayer weaving arms  507  and  509  advance in direction  513  until they reach first openings  511  and  523  in the fiber layers. In an embodiment, layers  503  and  505  are cut and positioned in the layer assembly stage so that their gaps are aligned. A variety of techniques may be used to precisely position the interlayer weaving arms  507  and  509  with respect to openings  511  and  523 . In one embodiment, layers are positioned in the intermediate layer stage so that the openings of fibers are at predetermined positions. Open loop control systems, such as stepper motors controlled by dead-reckoning, may be used to move the interlayer weaving arms to the predetermined position of openings  511  and  523 . 
         [0074]    In another embodiment, closed loop control systems may be used to move the interlayer weaving arms to predetermined or dynamically determined opening positions. Closed loop system may incorporate position sensors of any type known in the art, including both linear and rotary position and/or distance sensors. Further embodiments of the closed loop control system may include sensors for detecting openings in the fabric layers. Examples of sensors include cameras and computer vision systems and/or lasers and photodetectors mounted on opposite interlayer weaving arms to detect openings in the fabric. In still further embodiments of the invention, there may be markings or other indicators printed on or incorporated within the fabric itself to assist sensors in aligning layers of fabric and locating openings in fabric layers. In yet a further embodiment, conductive and/or magnetic fibers may be included in the fabric layer at known positions relative to the fabric openings and sensed using capacitive, inductive, and/or magnetic sensing techniques. 
         [0075]    Continuing this example in  FIG. 5B , after aligning the interlayer weaving arms with openings  511  and  523 , a pair of rapiers or hollow needles  515  and  517  are extended from their respective weaving arms through the openings  511  and  523 . The rapiers  515  and  517  come in contact or close proximity at location  521  between the layers  503  and  505 . Rapier  515  pulls a fiber or set of fibers (such as a flat ribbon or tow of fibers)  519  from a spool or bobbin over the top surface of layer  503  and through opening  511  to location  521 . At location  521 , rapier  517  grips fiber  519  and rapier  515  releases fiber  519 . Fibers may be gripped and released using vacuum tools, mechanical grippers, or any other type of fiber handling mechanism known in the art. In a further embodiment, the end of fiber  519  includes magnetic covering so that rapiers  515  and  517  may attach and detach the fiber using electromagnets. 
         [0076]    Continuing this example in  FIG. 5C , rapiers  515  and  517  are retracted through openings  511  and  523 , respectively. During this retraction, rapier  517  pulls fiber  519  through opening  523  so that it is under the bottom surface of layer  505 . Additional fiber from a spool is released to accommodate the movement of fiber  519 . 
         [0077]    Continuing this example in  FIG. 5D , interlayer weaving arms  507  and  509  move in direction  513  along the top surface of layer  503  and the bottom surface of layer  505 , respectively, to the next openings in the fiber layers,  525  and  527 . This movement pulls fiber  519  along the bottom surface of layer  505  to opening  527 . 
         [0078]    Continuing this example in  FIG. 5E , after aligning the interlayer weaving arms with openings  525  and  527 , the rapier arms  515  and  517  are again extended from their respective weaving arms through the openings  525  and  527  to location  529 . This pulls fiber  519  through opening  527  to location  529 . At location  529 , rapier  515  grips fiber  519  and rapier  517  releases fiber  519 . 
         [0079]    Continuing this example in  FIG. 5F , rapiers  515  and  517  are retracted through openings  525  and  527 , respectively. During this retraction, rapier  517  pulls fiber  519  through opening  525  so that it is over the top surface of layer  503 . Additional fiber from a spool is released to accommodate the movement of fiber  519 . 
         [0080]    The process shown in  FIGS. 5A-5F  is repeated for the remaining openings in these rows of fabric layers  503  and  505  where the new layer  503  overlaps vertically with layer  505  and all the other layers, if any, in the intermediate layer stage.  FIG. 5G  illustrates an example of a completed row of interlayer weaving. Fiber  519  passes through a set of openings in a row of fabric layers  503  and  505 . However, a space  535  is left between the fabric layers  503  and  505  to allow for the passage of a lower interlayer weaving arm in a subsequent weaving phase. The ends of fiber  519  are secured in grippers  537  and  539 , so that the fiber  519  may be pulled taut later to place layers  503  and  505  in contact and eliminate space  535 . 
         [0081]    The above example shows a pair of interlayer weaving arms weaving a fiber between two (or potentially more) layers. After completing the weaving of this row, the pair of interlayer weaving arms may be retracted and moved to a different row of fabric openings to weave another fiber. This process may be repeated for a portion of the rows of a layer, with some rows of openings typically left open for the weaving of interlayer fibers in subsequent weaving phases between additional layers. In a further embodiment, the system may include multiple pairs of weaving arms operating in parallel to reduce the time required to perform interlayer weaving over multiple rows of openings. 
         [0082]      FIGS. 6A-6C  illustrate the operation of an example mechanism for consolidating two or more layers of a three-dimensional weave according to an embodiment of the invention. Layer consolidation is the process of tightening a set of interlayer fibers between two layers to bring these layers into contact and reduce or substantially eliminate the space between these fiber layers. 
         [0083]      FIG. 6A  illustrates a pair of layers  603  and  605  connected with interlayer fiber  607 . Interlayer fiber  607  (as well as similar interlayer fibers in other rows of layers  603  and  605 ) is secured with grippers  611  and  613 . A space  609  has been left between layers  603  and  605  to allow for the passage of a lower interlayer weaving arm during the weaving of layer  603  with one or more layers above it using a different row of openings in layer  603 . Once the weaving of layer  603  with one or more layers above has been completed, layers  603  and  605  may be consolidated to eliminate space  609 . 
         [0084]      FIG. 6B  illustrates an example of the layer consolidation process. In an embodiment, grippers  611  and  613  are pulled laterally to apply tension to interlayer fiber  607 . This tension takes of the slack space between layers  603  and  605 , bringing these two layers into contact and substantially eliminating the space  609  that existed between them. In a further embodiment, interlayer fibers and/or layer fabric may include a coating or lubricant to allow this tightening to occur without binding. 
         [0085]    After the layers  603  and  605  have been brought together, a further embodiment of the invention cuts and removes the excess interlayer fiber  615  and  617 , resulting in the layers  603  and  605  and interlayer fiber  607  as shown in  FIG. 6C . 
         [0086]    In a further embodiments, the interlayer weaving arms may insert interlayer fibers using other weaving patterns, such as satin weaves and twill weaves. In still further embodiments, alternative forms of fiber connections may be used to connect layers with interlayer fibers, such as sewing (for example using a lock stitch, chain stitch, or overlock stitch). Embodiments of the invention may be used with any type of fiber connections provided that the connection can be held open to allow for a space between layers and then later tightened to reduce or eliminate this space. 
         [0087]    As discussed above, embodiments of the invention skip rows of openings when weaving interlayer fibers between layers.  FIGS. 7A-7B  illustrate example staggered arrangements of interlayer fibers according to an embodiment of the invention.  FIG. 7A  illustrates an example  700  of staggered interlayer fibers according to an embodiment of the invention. Example  700  includes a pair of consolidated layers  703  and  705  in the completed layer stage  707 , at least one layer  709  in the intermediate layer stage  711 , and a new layer  710  in the new layer stage  712 . 
         [0088]    Consolidated layers  703  and  705  are connected with interlayer fiber  713 , which has been tightened to remove the spacing between these layers. Additionally, interlayer fiber  715  connects layer  705  and  709 . Interlayer fiber  715  has not been tightened yet, leaving a large space  717  between layers  705  and  709 . Space  717  is sufficient for allowing a lower interlayer weaving arm  719  to pass between layers  705  and  709 . Interlayer weaving arm  719  is used to weave interlayer fiber  721  between layers  709  and  710 , as well as any intervening layers. After the weaving of interlayer fiber  721  and other fibers between layers  709  and  710  is complete, layer  709  may be moved to the completed layer stage and consolidated with layer  705  by tightening interlayer fibers  715 . 
         [0089]    As shown in example  700 , each weaving phase may insert interlayer fibers in only a portion of the available rows of openings in the layer fabrics to allow each layer to be connected with layers above and below it using interlayer fibers. For example, if the intermediate layer stage only holds a single layer, then weaving interlayer fibers in alternate rows of openings, as shown in  FIG. 4 , may be suitable for connecting each layer with those layers above and below it. In  FIG. 7A , if each weaving phase uses ⅓ of the available row openings, then the intermediate layer stage may hold up to two layers. In this example  700 , each layer is connected with the two layers below it. 
         [0090]      FIG. 7B  illustrates another example  750  of a staggered interlayer fiber arrangement. In example  750 , new layer stage  753  includes layer  759 . Intermediate layer stage  755  includes four layers, layers  761 A- 761 D. Completed layer stage  757  may include any number of layers, including in this example layer  763 . 
         [0091]    In example  750 , because there are four layers in the intermediate layer stage  755 , interlayer fibers are woven into each new layer at every fifth row of openings. In a general implementation of this embodiment, if there are K layers in an intermediate layer stage, then interlayer fibers are added to each new layer at every K+1 row of openings. To this end, interlayer fibers  765 A and  765 B are woven between new layer  759  and layer  761 D, passing through unused openings in layers  761 A- 761 C as well. 
         [0092]    As new layer  759  progresses through intermediate layer stage  755 , its unused rows of openings will be gradually filled by interlayer fibers connecting with subsequent layers. For example, layer  761 A in the first position of the intermediate layer stage  755  has interlayer fibers in two of every five adjacent rows of openings: such as interlayer fibers  765 A and  767 . Layer  761 B in the second position of the intermediate layer stage  755  has interlayer fibers in three of every five adjacent rows of openings: such as interlayer fibers  765 A,  767 , and  769 . Layer  761 C in the third position of the intermediate layer stage  755  has interlayer fibers in four of every five adjacent rows of openings: such as interlayer fibers  765 A,  767 ,  769 , and  771 . Layer  761 D in the fourth position of the intermediate layer stage  755  has interlayer fibers in all five of every five adjacent rows of openings: such as interlayer fibers  765 A,  767 ,  769 , and  773 . 
         [0093]    Following the addition of interlayer fibers  765 A and  765 B, all of the rows of openings in layer  761 D are now occupied by interlayer fibers (at least for those openings that vertically overlap with the layers above it). Thus, layer  761 D is ready for consolidation with layer  763  and interlayer fibers such as  773  may be tightened to eliminate the space between these two layers. 
         [0094]    As shown in this example  750 , by weaving interlayer fibers in every K+1 row of a new layer when the intermediate layer stage has K layers, all of the rows of openings of each layer are occupied with interlayer fibers by the time this new layer progresses through the intermediate layer stage. For each new layer added, the relative phase or offset of the interlayer fiber pattern is changed, but the K+1 interval between rows of interlayer fibers added remains unchanged. In this implementation, interlayer fibers each typically connect K+1 layers. 
         [0095]    In an embodiment illustrated by example  750 , interlayer fibers are woven in regular K+1 intervals. However, further embodiments may use other patterns for distributing interlayer fibers, including stochastic patterns of interlayer fibers with statistical distributions corresponding to an average interval of K+1 rows. 
         [0096]    As described above, interlayer fibers are woven through openings of two or more layers.  FIGS. 8A-8C  illustrate example open weave fabric patterns suitable for use with embodiments of the invention.  FIG. 8A  illustrates an example open plain weave pattern  800 . Unlike typical plain weaves where the warp and weft fibers are arranged in close contact with each other, open plain weave pattern  800  includes numerous openings suitable for allowing passage of interlayer fibers, such as openings  805 A- 8051 . 
         [0097]      FIG. 8B  illustrates an open satin weave pattern  820 . Satin weaves typically have higher strength than plain weaves because the warp fibers are not bent or crimped in every row of the weave. Example open satin weave pattern  820  is referred to as a four thread satin weave; however, embodiments of the invention may be used with any variation of an open satin weave. Unlike typical satin weaves where the warp and weft fibers are arranged in close contact with each other, open satin weave pattern  820  includes numerous openings suitable for allowing passage of interlayer fibers, such as openings  825 A- 825 L. 
         [0098]      FIG. 8C  illustrates an open leno weave pattern  840 . Many open weave patterns allow warp fibers to move positions easily, which can lead to uneven distributions of fibers, referred to as bruising. Leno weave patterns prevent this by twisting warp fibers after one or more weft fibers have been inserted. The twisted warp fibers hold the weft fibers in place while still leaving large spaces between the fibers, such as spaces  841 A- 841 I. 
         [0099]    The open leno weave pattern  840  includes large primary fibers  843 A- 843 D. Primary fibers are intended to provide high tensile strength along their axes. The leno weave pattern  840  also includes twisted secondary fibers  845 A- 845 D intended to hold primary fibers  843  in place. The secondary fibers may be made of the same material as the primary fibers or a different material, such as a less expensive material. When manufactured using traditional weaving processes, the primary fibers  843  will often be weft fibers and the secondary fibers  845  will be warp fibers. 
         [0100]      FIG. 8C  illustrates a basic leno weave pattern  840 . However, further embodiments of the invention may use more complicated leno weaves, such as leno weave patterns where the warp fibers are twisted only after multiple weft fibers have been inserted. In another example, Karamiori or Japanese leno weave patterns may be used to place and hold primary fibers in wide variety of different distributions. Normally, such patterns are used for aesthetic purposes; however, embodiments of the invention may use these patterns to increase or decrease the spacing between primary fibers. 
         [0101]    The preceding weave patterns are shown for purposes of illustration and embodiments of the invention may use these and/or any other open fabric patterns known in the art, such as twill weaves, basket weaves, unidirectional weaves, bonded directional weaves, and non-woven fabrics, where fibers or tows are bonded instead of woven together. Additionally, secondary or filling fibers may be included in fabrics to provide support during the weaving process. In a further embodiment, secondary fibers may be adapted to melt, dissolve, or burn away during the curing process. 
         [0102]    As discussed above, following the consolidation of two or more layers, excess interlayer fibers may be cut and removed from the fiber preform.  FIGS. 9A-9E  illustrate an example removal of excess interlayer fibers during the consolidation of non-convex layers according to an embodiment of the invention.  FIG. 9A  illustrates an example top view  900  of two layers: a lower layer  902  and an upper layer comprised of two disjoint shapes  904  and  906 . Prior to layer consolidation, interlayer fibers  908  pass over the upper layer, including the empty region  905  between shapes  904  and  906 . 
         [0103]      FIG. 9B  illustrates an example top view  910  of the two layers following layer consolidation. The interlayer fibers  908  have been trimmed so that they no longer cross gap  905 . 
         [0104]      FIGS. 9C-9E  illustrate a detailed side view of the trimming of excess fibers during layer consolidation. In  FIG. 9C , layers  912  and  914  are connected with an interlayer fiber  916 . Layer  912  includes two disjoint portions, separated by a gap  918 . Before layer consolidation, this gap  918  is spanned by the interlayer fiber  916 . 
         [0105]    In  FIG. 9D , the interlayer fiber  916  has been tightened to bring layers  912  and  914  into contact. However, gap  918  is still spanned by the interlayer fiber  916 . 
         [0106]    In  FIG. 9E , interlayer fiber  916  has been cut into pieces  916 A and  916 B, and the excess portion of the interlayer fiber  916  has been removed from the gap  918 . In a further embodiment, excess fiber at the ends of pieces  916 A and/or  916 B may be folded over or under layer  912 . 
         [0107]    As described above, layers of cut fabric cross-section shapes are moved through the layer assembly stage during interlayer weaving. One mechanism to accomplish this movement is through sets of pins, with each set forming a shelf to support a layer and having openings to accommodate the passage of interlayer fibers. Each set of pins moves down through the positions of the new layer and intermediate layer stages As layer consolidation is performed, the pins retract to the side to allow the layers to contact. 
         [0108]      FIGS. 10A-10D  illustrate another example mechanism for supporting and moving layers of fabric during three-dimensional weaving according to an embodiment of the invention.  FIG. 10A  illustrates an example mechanism in an initial configuration  1000 . The example mechanism includes end pieces  1003  and  1005 . Each of the end pieces  1003  and  1005  includes a set of vertical supports, such as supports  1004  and  1006 , respectively. End piece  1005  is connected with sliding rails  1007 A and  1007 B, which allow end piece  1005  to move to the opposite side of end piece  1003 . The vertical supports  1004  and  1006  are offset from each other to allow end pieces  1003  and  1006  to pass by each other. Example mechanism also includes a spool  1009  of high strength fiber, such as nylon fiber, which will be used to form a supporting shelf for a fiber layer in the layer assembly stage. 
         [0109]      FIG. 10B  illustrates the example mechanism in a second configuration  1020 . In this configuration, the end piece  1005  has moved along sliding rails  1007 A and  1007 B to the opposite side of end piece  1003 . Following this movement, a fiber anchor  1013  draws a fiber  1011  from the spool  1009  across the width of end pieces  1003  and  1005 . Fiber  1011  is surrounded on either side by the vertical supports  1004  and  1006 . 
         [0110]      FIG. 10C  illustrates the example mechanism in a third configuration  1040 . In this configuration, the end piece  1005  has moved along sliding rails  1007 A and  1007 B back to the opposite side of end piece  1003 . In doing so, the vertical supports  1006  of end piece  1005  have drawn additional amounts of fiber  1011  from spool  1009 . Fiber  1011  is held taut using a tension mechanism included in spool  1009  and/or fiber anchor  1013  and forms a shelf  1045  for supporting a fabric layer. 
         [0111]    The end pieces  1003  and  1004  may move vertically through the layer assembly stage to move shelf  1045  and the fabric layer that it supports to different positions of this stage. During layer consolidation, fiber  1011  may be released from anchor  1013  and pulled back on to spool  1009 . This causes shelf  1045  to disappear and lets the previously supported fabric layer contact the layer below it. 
         [0112]      FIG. 10D  illustrates an example mechanism  1060  for moving retractable fiber support shelves, as described in  FIGS. 10A-10C , vertically through a layer assembly stage. according to an embodiment of the invention. In this example  1060 , each set of vertical supports can be detached from its respective end piece and attached to a vertically moving chain or conveyor belt in a continuous loop, such as conveyor belt loop  1065 . For example, each of the sets of vertical supports, such as supports  1004 A and  1004 B, are attached to conveyor belt loop  1065 , which moves vertically through the layer assembly stage. (The conveyor belt loop for supports  1006 A and  1006 B has been omitted from  FIG. 10B  for clarity.) Supports may be attached and detached from end pieces and conveyor belt loops using hooks, latches, magnets, and/or other attachment mechanisms. The conveyor belt loops move in unison through the layer assembly stage, pulling shelves  1045 A and  1045 B via their respective supports  1004 A and  1006 A and  1004 B and  1006 A. At the bottom of the layer assembly stage, each of the shelves may be retracted by releasing the associated fiber from its anchor and pulling it back on to its spool. 
         [0113]      FIG. 11  illustrates a computer system suitable  1100  for controlling a system for three-dimensional weaving of composite preforms and products with varying cross-sectional topology according to an embodiment of the invention. The computer system  1100  includes one or more general purpose or specialized processors  1105 , which can include microprocessors, microcontrollers, system on a chip (SoC) devices, digital signal processors, graphics processing units (GPUs), ASICs, and other information processing devices. The computer system  1100  also includes random access memory  1110  and non-volatile memory  1115 , such as a magnetic or optical disk drive and/or flash memory devices. 
         [0114]    The computer system  1100  may optionally includes one or more visual display devices  1120 . The computer system  1100  may also optionally include an audio processor  1125  for generating and receiving sound via speakers, microphone, or other audio inputs and outputs  1130 ; and optional sensors and input devices  1140  such as keyboards; scroll wheels; buttons; keypads; touch pads, touch screens, and other touch sensors; joysticks and direction pads; motion sensors, such as accelerometers and gyroscopes; global positioning system (GPS) and other location determining sensors; temperature sensors; such as mechanical, optical, magnetic or other types of position detectors and/or limit switches for detecting the current positions of the various components of the above-described systems; voltage, current, resistance, capacitance, inductance, continuity, or any other type of sensor for measuring electrical characteristics of the various components of the above-described systems; force, acceleration, stress or strain, and/or tension sensors; and/or any other type of input device known in the art. Computer system  1100  may optionally include one or more cameras or other optical measurement devices  1135  for capturing still images and/or video. 
         [0115]    The computer system  1100  may also include one or more modems and/or wired or wireless network interfaces  1145  (such as the  802 . 11  family of network standards) for communicating data via local-area networks  1150 ; wide-area networks such as the Internet; CDMA, GSM, or other cellular data networks of any generation or protocol; industrial networks; or any other standard or proprietary networks. The computer system  1100  can also include a peripheral and/or data transfer interface, such as wired or wireless USB, IEEE 1394 (Firewire), Bluetooth, or other wired or wireless data transfer interfaces. 
         [0116]    The computer system  1100  can include a power system  1155  for obtaining electrical power from an external source, such as AC line current or DC power tailored to the computer system  1100  via an external power supply, as well as one or more rechargeable or one-time use batteries, fuel cells, or any other electrical energy generation device. Additionally, power system  1155  may provide energy in the form of compressed gas, vacuum, and/or hydraulic systems to power various actuators and components of embodiments of the invention. 
         [0117]    Computer system  1100  may be implemented in a variety of different form factors, including desktop and laptop configurations as well as embedded and headless forms. 
         [0118]    Embodiments of the invention use a variety of motors and actuators, such as brushed or brushless DC motors, AC synchronous and induction motors, stepper motors, servomotors, solenoids, and/or pneumatic and hydraulic actuators. In an embodiment, computer system  1100  include motor and actuator controls  1060  for providing power and control signals to these motors and actuators. 
         [0119]    Further embodiments can be envisioned to one of ordinary skill in the art. In other embodiments, combinations or sub-combinations of the above disclosed invention can be advantageously made. The block diagrams of the architecture and flow charts are grouped for ease of understanding. However it should be understood that combinations of blocks, additions of new blocks, re-arrangement of blocks, and the like are contemplated in alternative embodiments of the present invention. 
         [0120]    The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims.