Patent Publication Number: US-2022212423-A1

Title: Drape forming apparatus and device, and method of forming a composite structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of priority to U.S. Provisional Application No. 63/133,556, filed on Jan. 4, 2021, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to a drape forming apparatus and device, and a method of forming a composite structure, with heat sources at opposing faces of the composite structure. 
     BACKGROUND 
     Composite materials, including carbon fiber epoxy impregnated laminates, are often used in applications requiring high strength and light weight, such as in the aerospace industry. At least some known composite structures are formed using a process known as hot drape forming. Hot drape forming typically includes heating one or more plies of flat pre-impregnated (i.e., prepreg) composite material, and forcing the composite material around a mandrel with a vacuum bag or a pressurized bladder device. When sufficiently heated, the plies can slide relative to one another in order to form a desired nonpianar shape. However, it is difficult and time consuming to form the sheet-like composite material into a non-planar composite structure while avoiding unacceptable buckling or wrinkling of the composite material. 
     SUMMARY 
     For relatively thick composite materials, uniform heating to a desired forming temperature using known drape forming apparatuses may be unattainable within a predetermined time threshold and/or without exceeding a predetermined maximum temperature. For example, a portion of a composite material closest to a heat source (e.g., a top ply) may quickly attain a desired forming temperature while a portion furthest from the heat source (e.g., a bottom ply) remains below the desired forming temperature. 
     A drape forming apparatus, flange forming device, and method of forming a composite material are disclosed herein that, in various embodiments, allow more uniform heating of the composite material in combination with controlled forming rate for avoiding wrinkling of the material. The composite structure may be used in a variety of implementations, especially those in which a controlled surface profile is desired (e.g., with minimal surface wrinkling), such as at an exterior of an aircraft. Representative applications include, without limitation, aeronautical components and control surfaces, including rudders, flaps, and wing surfaces. Other industries utilizing composite structures may also benefit from the improvements described herein. 
     A drape forming apparatus disclosed herein, such as for use in forming a composite structure, includes a forming tool having a first forming surface and a second forming surface nonplanar with the first forming surface. A tray is spaced apart from the forming tool and has a first side and a second side. The tray has a hinged end and a distal end, and is configured to pivot about the hinged end from a first position to a second position under an applied force such that the distal end moves away from the forming tool. The drape forming apparatus also includes a first heat source and a second heat source. The first side of the tray faces the first heat source when the tray is in the first position, and the second heat source is disposed at the second side of the tray. Accordingly, a composite material disposed on the tray is heated at both sides by the first and second heat sources, and pivots with the tray to be formed to the second forming surface. As the material is incrementally withdrawn from the tray at a controlled rate corresponding with the rate of pivoting, the portion moved furthest from the first heat source remains on the tray being heated by the second heat source until finally withdrawn. The two-sided heating provided by the drape forming apparatus may help to minimize a temperature gradient through the material, which is especially helpful when drape forming relatively thick composite materials. 
     Also disclosed herein is a device for use in forming a composite structure that includes a standoff and a tray having a first side and a second side, the tray having a hinged end and a distal end, the tray configured to pivot about the hinged end from a first position to a second position under an applied force. A heat source is secured to the second side of the tray. 
     A method of forming a composite structure, such as by utilizing the drape forming apparatus and flange forming device disclosed herein includes disposing at least one layer of composite material over a first forming surface of a forming tool so that a portion of the at least one layer of composite material is positioned on a first side of a tray coplanar with the first forming surface when the tray is in a first position, the tray having a hinged end and a distal end with the distal end nearer the first forming surface than the hinged end when the tray is in the first position. The method includes heating a first side of the at least one layer of composite material with a first heat source, the first side facing the first heat source when the tray is in the first position. The method further includes heating a second side of the at least one layer of composite material with a second heat source, the second heat source disposed at a second side of the tray. Under the method, a force is applied on the tray such that the tray pivots about the hinged end, the distal end moves away from the forming tool, and such that the portion of the at least one layer of composite material is withdrawn from the tray and is disposed against a second forming surface of the forming tool nonplanar with the first forming surface. 
     The above features and advantages, and other features and advantages, of the present teachings are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the present teachings, as defined in the appended claims, when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustrative purposes only, are schematic in nature, and are intended to be exemplary rather than to limit the scope of the disclosure. 
         FIG. 1  is a side view illustration of a first embodiment of a drape forming apparatus with two-sided heating and with pivotable trays in a first position supporting a composite material. 
         FIG. 2  is an illustration in perspective view of a first embodiment of a flange forming device included in the drape forming apparatus of  FIG. 1  showing one of the pivotable trays. 
         FIG. 3  is a side view illustration of the drape forming apparatus of  FIG. 1  at an intermediate stage of forming a composite structure. 
         FIG. 4  is a side view illustration of the drape forming apparatus of  FIG. 1  with the pivotable trays in a second position during a final curing stage of forming the composite structure. 
         FIG. 5  is a side view illustration of a second embodiment of a drape forming apparatus with two-sided heating and pivotable trays in a first position supporting a composite material. 
         FIG. 6  is a side view illustration of a second embodiment of a flange forming device for use in any of the drape forming apparatuses disclosed herein and with a pivotable tray in a first position. 
         FIG. 7  is a side view illustration of the flange forming device of  FIG. 6  with end walls removed and with the pivotable tray in a second position. 
         FIG. 8  is an illustration in perspective view of a third embodiment of a flange forming device for use in any of the drape forming apparatuses disclosed herein and with a pivotable tray in a first position. 
         FIG. 9  is an illustration in another perspective view of the flange forming device of  FIG. 8 . 
         FIG. 10  is a fragmentary side view illustration of the flange forming device of  FIG. 8 . 
         FIG. 11  is a side view illustration of a third embodiment of a drape forming apparatus including a fourth embodiment of a flange forming device and with a pivotable tray in a first position. 
         FIG. 12  is a fragmentary side view of the drape forming apparatus of  FIG. 11  with the pivotable tray in an intermediate position. 
         FIG. 13  is a fragmentary side view illustration of a fourth embodiment of a drape forming apparatus including a fifth embodiment of a flange forming device and with a pivotable tray in a first position. 
         FIG. 14  is a fragmentary side view of the drape forming apparatus of  FIG. 13  with the pivotable tray in an intermediate position. 
         FIG. 15  is a fragmentary side view illustration of a fifth embodiment of a drape forming apparatus including a sixth embodiment of a flange forming device and with a pivotable tray in an intermediate position. 
         FIG. 16  is a fragmentary side view illustration of a sixth embodiment of a drape forming apparatus including a seventh embodiment of a flange forming device and with a pivotable tray in an intermediate position. 
         FIG. 17  is a functional block diagram flow chart illustrating aspects of an embodiment of a method of forming a composite structure. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein are various embodiments of drape forming apparatuses, flange forming devices, and methods of forming composite structures that include two-sided heating of the composite material, and specifically, two-sided heating of a portion of the composite material to be formed as a flange. Especially when forming relatively thick, multi-ply composite material, a temperature gradient through the material could lead to undesirable wrinkling. By disposing a first heat source at one face of the composite material and a second heat source at an opposite, second face of the composite material, predetermined forming temperature and time ranges can be achieved, the heat sources may be separately controlled for more uniform heating and final properties of the composite structure, and production time goals can be achieved. Additionally, the improved heating arrangement may be integrated with aspects of the drape forming apparatus that allow a rate of forming of the flange portion to be controlled. 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  is a side view illustration of a first embodiment of a drape forming apparatus  10  that includes two flange forming devices  12 , one of which is shown in perspective view in  FIG. 2 . In the implementation shown, a composite material  14  can be formed into a composite structure  15  with two flange portions, as shown in  FIG. 4 , by utilizing both of the flange forming devices  12 . The flange forming device  12  on the right side of  FIG. 1  has like components functioning in the same manner as those of the flange forming device  12  on the left side of  FIG. 1 . In some embodiments, only one of the flange forming devices  12  is included, such as when a composite structure with only one flange portion is to be formed. 
     The flange forming apparatus  10  includes a forming tool  16  that has a first forming surface  18  and a second forming surface  20  nonplanar with and extending from the first forming surface  18 . In the embodiment shown, the first forming surface  18  is an upper forming surface and the second forming surface  20  is a side forming surface that is substantially perpendicular to the first forming surface  18 . However, in an alternative implementation, the second forming surface  20  could extend from the first forming surface  18  at a different non-planar orientation. For example, the second forming surface  20  could be arcuate of otherwise contoured, could be disposed at a complementary angle to the first forming surface  18 , or could be disposed at any angle or orientation and have any shape relative to the first forming surface  18  that enables the drape forming apparatus  10  to function as described herein. 
     In the embodiment shown, the forming tool  16  also has a third forming surface  22  nonplanar with and extending from the first surface  18 , and opposite to the second forming surface  20  as another side forming surface. The description herein of utilizing the flange forming device  12  shown at the left side of  FIG. 1  to form a flange portion  14 B to the second forming surface  20  applies equally to the like flange forming device  12  shown at the right side of  FIG. 1  that is used to form a like flange portion  14 C to the third forming surface  22 . The orientation of the forming surfaces  18 ,  20 , and  22  in the embodiment of the forming tool  16  as shown can be used to form a composite structure  15  having two arm portions extending from a main portion, defining a channel. 
     As described in further detail herein, at least one layer of composite material  14  is disposed on the forming tool  16  as shown in  FIG. 1 . More specifically, a main portion  14 A of the composite material  14  rests on the forming tool  16  while opposing flange portions  14 B and  14 C extend from the main portion  14 A and are laterally outward of the first forming surface  18  in preparation for drape forming to the respective second and third side surfaces  20 ,  22  of the forming tool  16  . The flange forming device  12  includes a standoff  30  spaced apart from the forming tool  16  by a predetermined distance  32 , also referred to as a gap. Both the forming tool  16  and the standoff(s)  30  may be secured in place on a platform  31  to maintain the predetermined distance  32 . 
     The flange forming device  12  also includes a pivotable tray  34  coupled to and supported by the standoff  30 . Each flange portion  14 B,  14 C rests on a respective pivotable tray  34 . Top surface  26  of the composite material  14  is furthest from the tray  34 , while a bottom surface  28  of the composite material  14  rests on the tray  34 . More particularly, the tray  34  is supported by the standoff  30  such that the tray  34  is pivotable relative to the standoff  30  about a pivot axis  36  best shown in  FIG. 2 . The pivot axis  36  extends perpendicular to the plane of the page in  FIG. 1 . The tray  34  has a first side  38  and a second side  40  opposite to the first side  38 . In the embodiment shown, the first side  38  faces generally upward when the tray  34  is in the first position shown in  FIG. 1 , and the second side  40  faces generally downward when the tray  34  is in the first position at the beginning of the drape forming process. The tray  34  has a hinged end  42  pivotably supported by the standoff  30  and a distal end  44  opposite from the hinged end. The tray  34  is configured to pivot about the pivot axis  36  near the hinged end  42 , moving within the gap  32  from the first position to a second position (shown in  FIG. 4 ) under an applied force  76  such that the distal end  44  moves away from the forming tool  16 . 
     To achieve desired material properties of the final composite structure after drape forming, including an absence of or reduction in significant wrinkles, the drape forming apparatus  10  provides two-sided heating of the flange portion(s)  14 B,  14 C, with first and second heat sources  50 ,  52  disposed at respective opposing first and second sides  17 ,  19  of the composite material  14  (e.g., at the top surface  26  and the bottom surface  28 ). The heat sources  50 ,  52  may be independently controllable and implementable with the controlled forming rate of the composite material  14  afforded by the pivoting tray  34  of the flange forming device  12 . 
     As shown in  FIG. 1  the drape forming apparatus  10  includes a first heat source  50 . In the embodiment shown, the first heat source  50  is at least one heat lamp fixed in position relative to the forming tool  16  and the standoff(s)  30 . When the tray  34  is in the first position of  FIG. 1 , the first side  38  of the tray  34  faces the first heat source  50 . The drape forming apparatus  10  also includes a second heat source  52  disposed at the second side  40  of the tray  34 . In the embodiment shown, the second heat source  52  is a heat pad that includes a resistance heating element  54 . For example, the resistance heating element  54  may be a wire and the heat pad  52  may include a base  56 , such as a silicone rubber base, in which the resistance heating element  54  is embedded and through which heat radiates to heat the tray  34 . As an alternative to or in addition to heating via a hear pad and a resistance heating element, the second heat source may heat the second side  40  of the tray  34  by convection heating, circulating heated fluid, or otherwise. 
     The second heat source  52  may be secured directly to the second side  40  of the tray  34  as in the embodiment shown, such as with adhesive. The second heat source  52  may extend below the composite material  14  only to the far extent  64  when the tray  34  is in the first position, or may extend further laterally outward than the far extent  64 . In other embodiments, the second heat source  52  could be another mode of heating, such as at least one heat lamp disposed so that the second side  40  of the tray  34  faces the at least one heat lamp when the tray  34  is in the first position. 
     Optionally, heat output of the first heating source  50  and heat output of the second heat source  52  may be independently controlled by an electronic controller  60  operatively connected to each of the heat sources  50 ,  52  such as by controlling electrical power to each heat source. For example, the second heat source  52  can thus be controlled to provide heat uniformly along the portion of the tray  34  to which it is secured regardless of the position of the tray  34  (e.g., whether at the first position, at an intermediate position, or at the second position). Similarly, power to the first heat source  50  may be controlled by the electronic controller  60  throughout the forming process and separately from the second heat source  52 . One or more temperature sensors, such as a thermocouple, may be positioned on or in the tray  34 , on or in the second heat source  52 , and/or on a membrane  70  described herein. The second heat source  52  is fixed to and moves with the tray  34  while the first heat source  50  is fixed in position relative to the forming tool  16  and the standoff  30 . While the first side  38  of the tray  34  is moving further away from the first heat source  50  during pivoting of the tray  34  from the first position to the second position, the second side  40  of the tray  34  remains fixed in position relative to the second heat source  52 . 
     With reference to  FIG. 1 , during the drape forming process, the tray  34  is made to pivot as a result of a net force against the first side  38  of the tray  34  resulting from an applied force  76  of a membrane  70  and an opposing, resisting force  78  of a resistance device  72 . In an example, the membrane  70  may be a flexible, air-tight bladder to which a pressure differential may be applied, such as via a vacuum  74  applied at an interior surface of the membrane and/or a pressure applied at an exterior surface of the membrane, depending upon the sealing arrangement of the membrane  70  in the drape forming apparatus  10 . Alternatively or in addition, fluid pressure may be applied to the exterior of the membrane  70 . The membrane  70  is disposed over the forming tool  16 , the standoff(s)  30 , and the tray  34  on the first side  38  of the tray  34 , and therefore over the top surface  26  of the composite material  14  disposed on the forming tool  16  and the tray  34 . The membrane  70  is configured to exert the applied force  76  on the tray  34  in response to the controller  60  commanding a pressure differential on opposing sides of the membrane  70 . In  FIG. 1 , the membrane  70  is shown in a first state with dashed lines, prior to the controller  60  initiating a vacuum and/or pressure on the membrane  70 . The membrane  70  is shown in solid lines in a second state in which the membrane  70  is engaged with and exerts an applied force  76  distributed against the top surface  26  of the composite material  14 , including the flange portions  14 B,  14 C, that encourages pivoting of the tray  34  from the first position to the second position (e.g., the applied force  76  is exerted downward on the tray  34 ). 
     The resistance device  72  is coupled to the tray  34  and automatically or controllably (e.g., operable under the control of the controller  60 ) exerts a resisting force  78  on the tray  34  opposite to the applied force  76  . The resisting force  76  resists pivoting of the tray  34  from the first position to the second position. In the embodiment shown in  FIGS. 1-5 , the resistance device  72  is an adjustable resistance friction hinge having a hinge axis coincident with the pivot axis  36 . As shown in  FIG. 2 , there may be multiple resistance devices  72  disposed along the length of the tray  34  and each aligned with the pivot axis  36 . The friction within the hinge of the resistance device  72  is representable by the resisting force  78  pushing upward on the tray  34  (e.g., resisting picoting from the first position to the second position). 
     The heat sources  50 ,  52  may be controlled to ramp the temperature of the composite material  14  from room temperature to a predetermined forming temperature or to within a predetermined forming temperature range (e.g., within 10 degrees of a predetermined forming temperature), and then to maintain the composite material  14  at this temperature or within this range of temperatures for a predetermined period of time. Once the predetermined forming temperature or predetermined forming temperature range is achieved, the force  76  applied to the tray  34  may be simultaneously controlled to cause the tray  34  to pivot from the first position to the second position. The pivoting may be at a controlled rate, such as a constant rate, such as by controlling the vacuum and/or pressure acting on the membrane  70 . The resistance force  78  applied by the resistance device  72  may also be controlled or, in some embodiments, may be automatic, with only the applied force  76  of the membrane  70  controlled to control the rate of pivoting. Pivoting causes the flange portions  14 B,  14 C to withdraw from the trays  34  and form to the second and third forming surfaces  20 ,  22 , respectively, at a rate (e.g., inches withdrawn per second) that corresponds with the rate of pivoting (e.g., angles per second) of the tray  34 . A near extent  62  of the flange portion  14 B closest to the forming tool  16  when the tray is in the first position will initially withdraw, with the far extent  64  of the flange portion  14 B that is furthest from the forming tool  16  when the tray  34  is in the first position (e.g., the side edge of the flange portion  14 B) being the last to withdraw and form to the second forming surface  20  when the tray  34  is pivoted further toward the second position. The flange portion  14 B is thus heated by the second heat source  52  longer at and near the far extent  64  than at and near the near extent  62 . However, the near extent  62  moves little if at all further from the first heat source  50  during forming while the far extent  64  moves further away from the first heat source  50  according to the controlled rate of pivoting of the tray  34 . Thus, the declining contribution of heat from the first heat source  50  in the direction from the near extent  62  to the far extent  64  is countered by the increasing contribution of heat by the second heat source  52  in the direction from the near extent  62  to the far extent  64 . The ability of the controller  60  to control the rate of withdrawal of the flange portion  14 C from the tray  34  (e.g., by controlling the applied force) while also controlling the heat output of the first heat source  50  and the second heat source  52  enables control of the internal temperature profile of the composite material  14 , including the ability to prevent or limit a temperature gradient in the flange portion  14 B between a temperature at the top surface  26  of the composite material  14  and a temperature at the opposite bottom surface  28  of the composite material  14 . 
     The composite material  14  may be any composite to be formed to a desired composite structure by drape forming, and may include a first material arranged in a matrix of a second material different from the first material, with the second material softening when heated to allow the composite material to be drape formed to a desired shape. In an implementation, the composite material  14  may be carbon fiber disposed in a resin matrix such as an epoxy resin matrix. For example, the composite material  14  may be laminated plates or sheets of carbon fiber impregnated with an epoxy resin matrix. Prior to drape forming, the composite material  14  may have an overall flat shape, such as a flat sheet. During drape forming, the resin matrix must be sufficiently heated to allow the composite material  14  to form to the shape of the forming tool  16 . For example, when there are multiple layers (e.g., plies) of carbon fiber material, these layers slide relative to one another as the material  14  is formed to the shape of the forming tool  16 . Heating and softening of the resin matrix material enables this reorientation of the carbon fiber material to adopt the final formed shape composite structure. Heating of the composite material  14  to a uniform predetermined temperature or temperature range and forming the material at a controlled rate, such as a predetermined uniform rate, can best avoid the formation of wrinkles in the material. The composite material  14  may have a predetermined, designated forming temperature or temperature range (e.g., based upon prior testing) that enables the requisite pliability of the composite material  14  during forming, and may also have a predetermined maximum forming temperature and/or a predetermined maximum time above a threshold temperature that, if either is exceeded, may result in insufficient material or aesthetic properties of the final formed composite structure  15 . Additionally, an excessively long heating time adds to the manufacturing cycle time. If the composite material  14  is relatively thick (e.g., whether it is a single layer (also referred to as a single ply) that is relatively thick, or multiple layers), heating of the composite material  14  to a predetermined forming temperature or temperature range from only one side may require an unsatisfactorily long cycle time and/or may cause the side closest to the single heat source to be at an elevated temperature for longer than is optimal to attain desired material properties in the final formed composite structure. The two-sided heating solution disclosed herein solves these issues while integrating the controlled pivoting of the tray  34  to enable more uniform heating and forming of the flange portions  14 B and  14 C as described. In some implementations, heating time may be shortened by 50 percent with the two-sided heating solutions disclosed herein. 
     The flange forming device  12  may include one or more position sensors disposed on the standoff  30 , on the tray  34 , and/or on the resistance device  72  to enable the controller  60  to monitor the position of the tray  34 , and then, based on the position information, control the pressure differential acting on the membrane  70  (and, in some embodiments, control the resisting force  76  of the resistance device  72 ), to control the rate of pivoting of the tray  34  and the resulting rate of forming of the flange portion  14 B against the side surface  20  (and the flange portion  14 C against the side surface  22 ). For example, the controller  60  may implement a uniform rate of forming by control of the pressure differential acting on the membrane  70  (e.g., control of the level of vacuum  74  applied to the membrane  70 ). 
       FIG. 3  is a side view illustration of the drape forming apparatus  10  of  FIG. 1  at an intermediate stage of forming a composite structure  15  (shown in  FIG. 4 ). The trays  34  are shown pivoted from the first position of  FIG. 1  to an intermediate position, with the flange portions  14 B,  14 C of the heated composite material  14  beginning to be withdrawn from the trays  34  and change shape from the configuration in which they are coplanar with the main portion  14 A to a partially bent configuration. As discussed, the near extent  62  gradually receives less direct heating by the tray  34  via the second heat source  52  while the far extent  64  moves further from the first heat source  50  but continues in contact with the tray  34 , receiving direct heat from the tray  34  via the second heat source  52  as the tray  34  pivots in the gap between the forming tool  16  and the standoff  30 . 
       FIG. 4  is a side view illustration of the drape forming apparatus  10  with the pivotable trays  34  pivoted further than the intermediate position of  FIG. 3  to the final second position at a final stage of forming the composite structure  15 . The heat sources  50 ,  52  may each be independently controlled to continue heating according to a desired temperature profile for a predetermined time. For example, power to the heat sources  50 ,  52  may be controlled to set the heat output of each of the heat sources  50 ,  52  to zero as the composite structure  15  cools in the final shape shown in  FIG. 4 . The vacuum/and or pressure on the membrane  70  can be released and the composite structure  15  then removed from the forming tool  16  in its final, formed shape. The trays  34  can be moved to the first position in preparation for forming a subsequent composite structure with the drape forming apparatus  10 . 
       FIG. 5  is a side view illustration of a second embodiment of a drape forming apparatus  110  with two-sided heating and pivotable trays  34  in a first position supporting a composite material  14 . The drape forming apparatus  110  is identical to and functions as described with respect to the drape forming apparatus  10  except that the first heat source is a heat blanket  150  disposed on the membrane  70  rather than the at least one heat lamp  50  of the drape forming apparatus  10 . The heat blanket  150  may be sized to extend over the composite material  14  at least to the far extent  64  of the composite material  14 . The heat blanket  150  may be controlled via the controller  60 , and may provide a uniform heat output over the top surface  26  of the composite material  14 , or may provide more heat over the flange portions  14 B,  14 C or an amount of heat that differs at different areas of the flange portions  14 B,  14 C as may be desired to achieve a predetermined temperature profile through the composite material  14 . In an implementation, heat may be applied by the heat blanket  150  to heat the membrane  70  prior to applying the pressure differential (e.g., via the vacuum  74 ) to the membrane  70 . 
       FIG. 6  is a side view illustration of a second embodiment of a flange forming device  112  for use in place of flange forming device  12  in the drape forming apparatus  10  or  110 , or for use in any of the other drape forming apparatuses disclosed herein. The drape forming device  112  includes a standoff  130  with a pivotable tray  134  secured to the standoff and shown in a first position. The tray  134  is hinged to the standoff at hinges  135  and pivotable relative to the standoff  130  about pivot axis  36  at a hinged end  42 . The hinges  135  may not be friction hinges as in  FIG. 1 , as the flange forming device  112  instead includes a resistance device  172  that may be a linear actuator having one end  173  pivotably coupled to the standoff  130  and an opposite end  174  pivotably coupled to the tray  134 . Linear actuator  172  may be actuated by any suitable means such as, but not limited to, electrical and pneumatic. The resistance device  172  may be controllable by the controller  60  (shown in  FIG. 1 ) to provide the resisting force  78  on the tray  134  opposing the applied force  76  of the membrane  70  (see  FIG. 1 ), and resisting pivoting of the tray  134  from the first position of  FIG. 6  to a second position of  FIG. 7 , or may automatically resist pivoting to provide the resisting force  78 . The resistance device  172  is shown in a fully deployed position in  FIG. 6  and a fully retracted position in  FIG. 7 . 
     As shown in  FIG. 6 , the flange forming device  112  includes an end wall  180  coupled to the tray  134  and disposed between the membrane  70  and the second heat source  52  when the flange forming device  112  is used in the flange forming apparatus  10  of  FIG. 1 . The end wall  180  serves as a barrier that prevents the flexible membrane  70  from being pulled under the tray  134  during application of the pressure differential in order to prevent entanglement of the membrane  70  that would interfere with pivoting of the tray  134 , and prevent contact of the membrane  70  with the second heat source  52 . The end wall  180  is disposed inward of an end wall  182  of the standoff  130 , and pivots with the tray  134  inward of the end wall  182 .  FIG. 7  is a side view illustration of the flange forming device  112  with the end walls  180 ,  182  removed for clarity in viewing other features, and with the pivotable tray  134  in a second position. 
     Referring to  FIG. 6 , the tray  134  has a lip  136  with an aperture  138  extending therethrough. The flange forming device  112  also includes a latching device  184  secured to the standoff  130  and operable to latch the tray  134  in the second position. The latching device  184  may be secured to an inner side of the tray  134 , an inner side of the end wall  182 , or to a bracket of the standoff  130  that is disposed inward of both end walls  180 ,  182 . The latching device  184  may be operatively connected to the controller  60  and actuatable in response to a control signal provided by the controller  60  to deploy a latch  186  that extends through the aperture  138  when the tray  134  is pivoted to the second position of  FIG. 7 , thereby latching the tray  134  in the second position. Alternatively, the latching device  184  may automatically latch such as by the lip  136  triggering the latch, or otherwise. Latching of the tray  134  in the second position prevents the resistance device  172  from causing any spring back of the tray  134  toward the first position so that the tray  134  will not contact the formed composite structure  15  as it is curing on the forming tool  16 . This ability to latch the tray  134  enables the standoff  130  to be placed close to the forming tool  16  (e.g., minimizing the gap  32 ) so that the tray  134  supports the flange  14 B very close to the forming tool  16  during pivoting of the tray  134 , which may help prevent wrinkles. 
       FIGS. 8-10  show another embodiment of an alternative flange forming device  212  for use in any of the drape forming apparatuses disclosed herein. The flange forming device  212  includes many of the same components as the flange forming device  112 , such as the pivotable tray  134  shown in a first position in  FIG. 8 , the second heat source  52  configured as the heat blanket secured to the underside of the tray  134 , a standoff  230 , and a plurality of the resistance devices  172  configured as linear actuators each having one end coupled to the standoff  230  and an opposite end coupled to the tray  134 . The resistance devices  172  are shown in fully deployed positions in  FIGS. 8-10 , but may be retracted to the fully retracted position to move the tray  134  to a second position like that shown in  FIG. 7 . An end wall  280  extends from the tray  134  and serves as a barrier that prevents the flexible membrane  70  from being pulled under the tray  134  during application of the pressure differential to protect entanglement of the membrane  70  that would interfere with pivoting of the tray  134 , and prevent contact of the membrane  70  with the second heat source  52 . The end wall  280  is disposed inward of the end wall  282  of the standoff  230 , and pivots with the tray  134  inward of the end wall  282 . As best shown in  FIG. 10 , a pin  283  extends inward from the end wall  282  into a slot  285  formed in the end wall  280 . Another end wall like end wall  282  may be disposed at the opposite end of the flange forming device  212  but is not shown in  FIGS. 8 and 9 . The pin  283  and the slot  285  together function as a guide to help stabilize and limit movement of the tray  134  to the direction of pivoting. As can be seen in  FIGS. 8 and 9 , the flange forming device  212  is elongated. Although shown as relatively straight along its length, multiple flange forming devices of differing lengths and varying in width can be positioned together for manufacturing a flange portion of a nonlinear (e.g., arcuate) composite structure. Accordingly, the applied force  76  is distributed uniformly along the length of the elongated tray  134  by the multiple resistance devices  172 . Support brackets  239  are spaced along the length of the flange forming device  212  and are mounted to a front wall  241  to provide structural integrity. The resistance devices  172  extend through apertures  289  in the front wall  241 , and a variety of apertures  290  are disposed in the end wall  282 . The apertures  289 ,  290  reduce the thermal mass of the standoff  230 . The heat output of the second heat source  52  disposed on the underside of the tray  134  and of the first heat source  50  of  FIG. 1  may be controlled to provide the desired forming temperature of range of forming temperatures as described while accounting for the thermal mass of the standoff  230 . 
       FIG. 11  is a fragmentary side view illustration of a third embodiment of a drape forming apparatus  310  including a fourth embodiment of a flange forming device  312  including the standoff  330  and with a pivotable tray  334  in a first position supporting the composite material  14 .  FIG. 12  is a fragmentary side view illustration of the drape forming apparatus  310  of  FIG. 11  with the pivotable tray  334  in a second position and the composite structure  15  formed. The drape forming apparatus  310  includes many of the same components as the drape forming apparatus  10 , including the forming tool  16 , the membrane  70  (shown in fragmentary view), at least one first heat source  50 , and a standoff  330  similar to standoff  30 . The controller  60  and the vacuum  74  may also be included, and are not shown in  FIGS. 11-12 . The pivotable tray  334  has a first side  38  that faces the first heat source  50  when the tray  334  is in the first position of  FIG. 11 . The second heat source  52  is secured to the opposite second side  40  of the tray  334  and pivots with the tray  334 . The tray  334  is connected to the standoff  330  and is pivotable relative to the standoff  330  via rotatable levers  372 A,  372 B. The rotatable levers  372 A,  372 B are each pivotably connected at one end to the tray  334  and at an opposing end to the standoff  330 . The hinged tray  334  is rotatable about a first pivot axis  335 A and a second pivot axis  336 A defined between rotatable levers  372 A,  372 B and retractable hinged tray  334 , and rotatable levers  372 A,  372 B are rotatable about pivot axes  335 B,  336 B defined between rotatable levers  372 A,  372 B and standoff  330 , thereby defining a range of motion for retractable hinged tray  334  to be fully retractable within standoff  330 . The side of the standoff  330  facing the tray  334  has an open cavity into which the levers  372 A,  372 B extend and into which the tray  334  retracts when in the second position. As such, the range of motion of the tray  334  is 90 degrees, and facilitates reducing friction between at least one layer of composite material  14  and retractable hinged tray  334  as at least one layer of composite material  14  is withdrawn therefrom and, because the tray  334  withdraws into the cavity of the standoff  330 , facilitates reducing the likelihood of the membrane  70  from becoming caught between standoff  330  and retractable hinged tray  334 . The composite material  14  is also shown in fragmentary view, and may extend further to the right in the drawing as the drape forming apparatus  310  may include another flange forming device  312  disposed on the opposite side of the tool  16  as that shown for forming another flange portion. 
       FIG. 13  is a side view illustration of a fourth embodiment of a drape forming apparatus  410  including a fifth embodiment of a flange forming device  412  having a pivotable tray  434  shown in a first position.  FIG. 14  is a side view of the drape forming apparatus  410  of  FIG. 13  with the pivotable tray  434  pivoted to an intermediate position. Pivoting may continue to a second position in which the tray  434  is disposed at an angle to the standoff  30  like tray  34  in  FIG. 4 . The drape forming apparatus  410  includes many of the same components as the drape forming apparatus  10 , including the forming tool  16 , the membrane  70  (shown in fragmentary view), at least one first heat source  50 , and the standoff  30 . The controller  60  and the vacuum  74  may also be included, and are not shown in  FIGS. 13-14 . The pivotable tray  434  has a first side  38  that faces the first heat source  50  when the tray  434  is in the first position of  FIG. 13 . The second heat source  52  is secured to the opposite second side  40  of the tray  434  and pivots with the tray  434 . The tray  434  is connected to the standoff  130  and is pivotable relative to the standoff  130  via a resistance device  472  that is an integral reinforcement of the tray  434 . Stated differently, the resistance device is a reinforced portion of the tray  434  disposed at pivot axis  36 . The tray  434  is a single unitary structure, and deflects when the applied force  76  is induced against elongated tray  434  by the pressure differential over the membrane  70 . As such, reinforced portion  472  provides the counteractive resisting force  78  to the tray  434  to control the rate of pivoting of the tray  434  without having any moving parts. Reinforced portion  472  may be fabricated from the same material as tray  434 , or may be fabricated from a different stiffer material. When fabricated from the same material, the tray  434  may be thicker at the reinforced portion  472  to increase the stiffness of the tray  434  at the reinforced portion. The composite material  14  is also shown in fragmentary view, and may extend further to the right in the drawing as the drape forming apparatus  410  may include another flange forming device  412  disposed on the opposite side of the tool  16  as that shown for forming another flange portion. 
       FIG. 15  is a side view illustration of a fifth embodiment of a drape forming apparatus  510  including a sixth embodiment of a flange forming device  512  having a pivotable tray  534  in an intermediate position. The tray  534  is hinged to the standoff  30  at hinge  135  and pivotable relative to the standoff  30  about pivot axis  36  at a hinged end  42 . The hinge  135  is not a friction hinge as in  FIG. 1 . Pivoting may continue to a second position in which the tray  534  is disposed at an angle to the standoff  30  like tray  34  in  FIG. 4 . The drape forming apparatus  510  includes many of the same components as the drape forming apparatus  10 , including the forming tool  16 , the membrane  70  (shown in fragmentary view), at least one first heat source  50 , and the standoff  30 . The controller  60  and the vacuum  74  may also be included, and are not shown in  FIG. 15 . The pivotable tray  534  has a first side  38  that faces the first heat source  50  when the tray  534  is in a first position like that of  FIG. 1  (e.g., a horizontal position). The second heat source  52  is secured to the opposite second side  40  of the tray  534  and pivots with the tray  534 . A resistance device  172  that is a linear actuator like linear actuator  172  of  FIG. 7 , has one end  172 B pivotably connected to the tray and an opposite end  172 A pivotably connected to the standoff  30 . The resistance device  172  may be controllable by the controller  60  (shown in  FIG. 1 ) to provide the resisting force  78  on the tray  534  opposing the applied force  76  of the membrane  70  (see  FIG. 1 ), and resisting pivoting of the tray  534  from the first position to a second position like that of  FIG. 4 , or may automatically resist pivoting to provide the resistance force  76 . Because the pivotably connected end  172 A of the resistance device  172  is at an exterior of the standoff  30  in the gap  32  rather than within a cavity of the standoff  30  as in standoff  130  in  FIGS. 6-7  and standoff  230  in  FIG. 10 , the gap  32  is larger than when standoffs  130  or  230  are used in order to enable the tray  534  to pivot to a second position at which the composite material  14  is fully withdrawn and formed to the second surface  22 . The composite material  14  is also shown in fragmentary view, and may extend further to the right in the drawing as the drape forming apparatus  510  may include another flange forming device  512  disposed on the opposite side of the tool  16  as that shown for forming another flange portion. 
       FIG. 16  is a side view illustration of a sixth embodiment of a drape forming apparatus  610  including a seventh embodiment of a flange forming device  612  that has the pivotable tray  534  in an intermediate position. The tray  534  is hinged to the standoff  30  at hinge  135  and pivotable relative to the standoff  30  about pivot axis  36  at hinged end  42 . Pivoting may continue to a second position in which the tray  534  is disposed at an angle to the standoff  30  like tray  34  in  FIG. 4 . The drape forming apparatus  610  includes many of the same components as the drape forming apparatus  10 , including the forming tool  16 , the membrane  70  (shown in fragmentary view), at least one first heat source  50 , and the standoff  30 . The controller  60  and the vacuum  74  may also be included, and are not shown in  FIG. 16 . The pivotable tray  534  has a first side  38  that faces the first heat source  50  when the tray  534  is in a first position like that of  FIG. 1  (e.g., a horizontal position). The second heat source  52  is secured to the opposite second side  40  of the tray  534  and pivots with the tray  534 . A resistance device  672  is an inflatable bladder that is disposed between the standoff  30  and the tray  534  in the gap  32  and applies the resisting force  78  to the tray  534  opposing the applied force  76 . The resistance device  672  may be adhered to the second heat source  52  and the underside of the tray  534  not covered by the second heat source  52 . The inflatable bladder  672  may be selectively filled with any suitable fluid, which enables inflatable bladder  672  to bias against tray  534  and provide the counteractive resisting force  78  thereto. As pressure is applied by pressurized bladder  672 , tray  534  deforms inflatable bladder  672  as tray  534  pivots about pivot axis  36 . Pressure within the resistance device  672  may be varied via a valve  673  controlled by the controller  60 , or the valve  673  may automatically release fluid in response to the applied force  76  to decrease pressure, allowing the tray  534  to pivot to the second position under the applied force  76 . The composite material  14  is also shown in fragmentary view, and may extend further to the right in the drawing as the drape forming apparatus  610  may include another flange forming device  612  disposed on the opposite side of the tool  16  as that shown for forming another flange portion. 
       FIG. 17  is a functional block diagram flow chart illustrating an embodiment of a method  1000  of forming a composite structure such as composite structure  15  using any of the drape forming apparatuses and flange forming devices disclosed herein. The method  1000  may begin at block  1010 , disposing at least one layer of composite material  14  over a first forming surface  18  of a forming tool  16 . Block  1010  is accomplished so that a portion of the at least one layer of composite material  14  is positioned on a first side of a tray coplanar with the first forming surface  18  when the tray is in a first position. The tray may be any of the trays  34 ,  134 ,  234 ,  334 ,  434 , and  534 , disclosed herein having a hinged end and a distal end with the distal end nearer the first forming surface  18  than the hinged end when the tray is in the first position. 
     The method  1000  then proceeds to block  1020 , disposing a membrane  70  over the forming tool  16  and the tray. With the composite material  14  and the membrane  70  disposed as set forth in blocks  1010  and  1020 , the method  1000  proceeds to blocks  1030  and  1040 , heating a first side  17  of the at least one layer of composite material  14  with a first heat source  50  in block  1030 , the first side facing the first heat source  50  when the tray is in the first position, and heating a second side  19  of the at least one layer of composite material  14  with a second heat source  52  in block  1040 , the second heat source  52  disposed at a second side of the tray. Blocks  1030  and  1040  may be carried out simultaneously to shorten the processing time. 
     Moreover, the heating conducted in blocks  1030  and  1040  may be done in a controlled manner. For example, in optional block  1050 , the temperature may be monitored at the first side of the membrane  70 , or at the first side of the tray, or simply at the first heat source  50 , such as with one or more thermocouples operatively connected to the controller  60 . The controller  60  may determine whether a predetermined temperature has been reached or exceeded in block  1060 . If the predetermined temperature has not been reached or exceeded, the method  1000  can optionally adjust the heat output of the first heat source  50  in block  1070 , and then moves to block  1030  to continue heating the first side in block  1030  until the predetermined temperature of block  1050  is reached or exceeded. 
     Similarly, in optional block  1080 , the temperature may be monitored at the second side of the membrane  70 , or at the second side of the tray, or simply at the second heat source  52 , such as with one or more thermocouples operatively connected to the controller  60 . The controller  60  may determine whether a predetermined temperature has been reached or exceeded in block  1090 . The predetermined temperature of block  1090  may be the same as or different than the predetermined temperature of block  1060 . If the predetermined temperature has not been reached or exceeded in block  1090 , the method  1000  can optionally adjust the heat output of the second heat source  52  in block  1110 , and then continue heating the second side of the composite material  14  in block  1040  until the predetermined temperature of block  1090  is reached or exceeded. For example, adjusting the heat output in blocks  1070 ,  1110  results in controlling the heat output of at least one of the first heat source and the second heat source to limit a temperature gradient between the first side of the at least one layer of composite material and the second side of the at least one layer of composite material. 
     Once the requisite temperatures have been achieved in both blocks  1060  and  1090 , the composite material  14  is sufficiently heated for drape forming a flange portion  14 B (and, optionally,  14 C), and the method  1000  proceeds to block  1120 , applying a force  76  (e.g., applied force  76 ) on the tray such that the tray pivots about the hinged end  42 , the distal end  44  moves away from the forming tool  16 , and such that the portion  14 B of the at least one layer of composite material  14  is withdrawn from the tray and is disposed against the second forming surface  22  of the forming tool  16  that is nonplanar with the first forming surface to form a flange. As discussed, the drape forming apparatuses disclosed herein may be configured so that applied pressure is applied to an exterior surface of the membrane  70 , a vacuum is applied to an interior surface of the membrane  70  (e.g., at the side of the membrane where the tray is disposed), or both. 
     Simultaneously with block  1120 , the method  1000  may include block  1140 , exerting a resisting force  78  on the tray via a resistance device coupled to the tray to control a rate of pivoting of the tray, the resisting force  78  opposing the force applied  76  on the tray. In one example, the rate of pivoting of the tray may be controlled to be uniform (constant) and a resulting rate of forming the portion of the at least one layer of composite material against the second forming surface is therefore uniform (constant). Any of the resistance devices  72 ,  172 ,  272 ,  372 ,  472 , and  672  disclosed herein may be used. As the resistance force  78  exerted by some embodiments of the resistance devices  72 ,  172 , and  672  may be varied, optionally, the controller  60  may monitor the rate of pivoting of the tray in block  1150  with position sensors or the like, determine in block  1160  whether the rate of pivoting (e.g., angles per second) is within a predetermined range, and if not, adjust either or both of the applied force  76  or the resistance force  78  in block  1170  to control the rate of pivoting of the tray. For example, the rate of pivoting could be adjusted by increasing or decreasing the pressure differential applied to the membrane  70  (e.g., increase or decrease pressure or vacuum), increasing or decreasing the friction of the friction hinge  72 , increasing or decreasing the deployment rate of the linear actuator  172 , or increasing or decreasing the rate of deflation of the resistance device  672 . As another alternative, any of the resistance devices disclosed herein may be configured to automatically (e.g., not via the controller  60 ) provide a resistance force  78  that is not variable by the controller  60 , but that is at a predetermined magnitude that allows the tray to pivot at a rate equal to a desired forming rate of the flange portion, which may be based on prior testing, and will not pinch the composite material between the membrane  70  and the tray as it pivots. 
     Optionally, the method  1000  may include block  1180 , determining whether the tray reaches a predetermined second position, which is a final position of the tray in which the flange portion  14 B of the composite material  14  is fully withdrawn from the tray and, accordingly, in contact with the second forming surface  20  in the shape of the composite structure  15 . A contact sensor may be utilized to determine the position of the tray in block  1180 . 
     Optionally, in some implementations, the method  1000  may include activating a latching device  184  to latch the tray in the second position in block  1190 . As discussed, latching prevents spring back of resistance devices such as pneumatic linear actuators and is beneficial when the gap  32  is minimal and the tray could otherwise contact the flange portion  14 B on spring back, potentially deforming the flange portion  14 B. 
     The following Items provide example configurations of a drape forming apparatus, a device for use in forming a composite structure, and a method of forming a composite structure disclosed herein. 
     Item 1. A drape forming apparatus for use in forming a composite structure, the drape forming apparatus comprising: a forming tool having a first forming surface and a second forming surface nonplanar with the first forming surface; a tray spaced apart from the forming tool and having a first side and a second side, the tray having a hinged end and a distal end, the tray configured to pivot about the hinged end from a first position to a second position under an applied force such that the distal end moves away from the forming tool; a first heat source and a second heat source; wherein the first side of the tray faces the first heat source when the tray is in the first position; and wherein the second heat source is disposed at the second side of the tray. 
     Item 2. The drape forming apparatus of item 1, wherein the second heat source is a heat pad that includes a resistance heating element. 
     Item 3. The drape forming apparatus of any of items 1-2, wherein the first heat source is at least one heat lamp fixed in position relative to the forming tool. 
     Item 4. The drape forming apparatus of any of items 1-3, further comprising: a membrane disposed over the forming tool and the tray on the first side of the tray and configured to exert the applied force on the tray in response to a pressure differential on opposing sides of the membrane. 
     Item 5. The drape forming apparatus of item 4, wherein the first heat source is a heat blanket disposed on the membrane. 
     Item 6. The drape forming apparatus of item 4, further comprising: an end wall coupled to the tray and disposed between the membrane and the second heat source. 
     Item 7. The drape forming apparatus of any of items 1-6, further comprising: a standoff spaced apart from the forming tool, the standoff coupled to and supporting the hinged end of the tray. 
     Item 8. The drape forming apparatus of item 7, further comprising: a latching device secured to the standoff and operable to latch the tray in the second position. 
     Item 9. The drape forming apparatus of any of items 1-8, further comprising: a resistance device coupled to the tray and operable to exert a resisting force on the tray resisting pivoting of the tray from the first position to the second position. 
     Item 10 . The drape forming apparatus of item 9, wherein the resistance device is one of a linear actuator, a friction hinge, a rotatable lever, an inflatable bladder, or an integral reinforcement. 
     Item 11. The drape forming apparatus of item 9, further comprising: a membrane disposed over the forming tool and the tray at the first side of the tray; and an electronic controller operatively connected to the membrane; wherein the membrane is configured to exert the applied force on the tray in response to a pressure differential on opposing sides of the membrane; wherein the electronic controller is configured to control the pressure differential to achieve a controlled rate of pivoting of the tray. 
     Item 12. The drape forming apparatus of any of items 1-10, further comprising: an electronic controller operatively connected to the first heat source and to the second heat source and operable to control heat output of the first heat source and heat output of the second heat source. 
     Item 13. A device for use in forming a composite structure, the device comprising: a standoff; a tray having a first side and a second side, the tray having a hinged end and a distal end, the tray configured to pivot about the hinged end from a first position to a second position under an applied force; and a heat source secured to the second side of the tray. 
     Item 14. The device of item 13, wherein the heat source is a heat pad that includes a resistance heating element. 
     Item 15. The device of any of items 13-14, further comprising: an end wall coupled to the tray and extending away from the first side between the hinged end and the distal end, the end wall and the tray at least partially enclosing the heat source. 
     Item 16. The device of any of items 13-15, further comprising: a latching device secured to the standoff and operable to latch the tray in the second position. 
     Item 17. The device of any of items 13-16, further comprising: a resistance device coupled to the tray and operable to exert a resisting force on the tray that resists pivoting of the tray from the first position to the second position. 
     Item 18. The device of item 17, wherein the resistance device is one of a linear actuator, a friction hinge, rotatable levers, an inflatable bladder, or an integral reinforcement. 
     Item 19. The device of any of items 13-18, further comprising: an electronic controller operatively connected to the heat source and operable to control heat output of the heat source. 
     Item 20. A method of forming a composite structure, the method comprising: disposing at least one layer of composite material over a first forming surface of a forming tool so that a portion of the at least one layer of composite material is positioned on a first side of a tray coplanar with the first forming surface when the tray is in a first position, the tray having a hinged end and a distal end with the distal end nearer the first forming surface than the hinged end when the tray is in the first position; heating a first side of the at least one layer of composite material with a first heat source, the first side facing the first heat source when the tray is in the first position; heating a second side of the at least one layer of composite material with a second heat source, the second heat source disposed at a second side of the tray; applying a force on the tray such that the tray pivots about the hinged end, the distal end moves away from the forming tool, and such that the portion of the at least one layer of composite material is withdrawn from the tray and is disposed against a second forming surface of the forming tool nonplanar with the first forming surface. 
     Item 21. The method of item 20, further comprising: disposing a membrane over the forming tool and the tray; wherein the force is applied on the tray via the membrane. 
     Item 22. The method of item 21, wherein applying the force on the tray is by applying a vacuum on one side of the membrane. 
     Item 23. The method of item 21, wherein applying the force on the tray is by pressurizing one side of the membrane. 
     Item 24. The method of any of items 20-23, further comprising: controlling heat output of at least one of the first heat source and the second heat source to limit a temperature gradient between the first side of the at least one layer of composite material and the second side of the at least one layer of composite material. 
     Item 25. The method of any of items 20-24, further comprising: exerting a resisting force on the tray via a resistance device coupled to the tray to control a rate of pivoting of the tray, the resisting force opposing the force applied on the tray. 
     Item 26. The method of item 25, further comprising: controlling, via an electronic controller, the force applied on the tray so that a rate of pivoting of the tray is uniform and a resulting rate of forming the portion of the at least one layer of composite material against the second forming surface is uniform. 
     Item 27. The method of any of items 20-26, further comprising: activating a latching device to latch the tray in the second position. 
     The detailed description and the drawings or figures are supportive and descriptive of the present teachings, but the scope of the present teachings is defined solely by the claims. While some of the best modes and other embodiments for carrying out the present teachings have been described in detail, various alternative designs and embodiments exist for practicing the present teachings defined in the appended claims.