Abstract:
Manufacturing of a composite component, such as a composite component of an aircraft, is provided with a molding tool that includes, but is not limited to a first mold, a second mold and a pressure generator. Between the first mold and the second mold, a membrane is arranged so that between the first mold and the membrane a first region is formed, and between the second mold and the membrane a second region is formed. In the first region, a fibrous mat is arranged. In the second region with the use of the pressure generator  116  counter-pressure can be produced so that the membrane is pressed in the direction of the fibrous mat.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of International Application No. PCT/EP2010/053199, filed Mar. 12, 2010, which was published under PCT Article 21(2) and which claims priority to German patent application 10 2009 017 512.1, filed 15 Apr. 2009 and of U.S. Provisional Patent Application 61/169,624 filed 15 Apr. 2009, the disclosure of which applications is hereby incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This technical field relates to manufacturing a composite component. In particular, the invention relates to a molding tool for manufacturing a composite component, to a method for manufacturing a composite component, and to the use of a molding tool for manufacturing the composite component for an aircraft. 
       BACKGROUND 
       [0003]    Composite components may be manufactured using the resin transfer molding (RTM) method. In this type of manufacture of composite components a fibrous mat is arranged in a molding-tool cavity of a molding tool, and thereafter when the molding tool is completely closed, is impregnated with resin. The fibrous mat may be designed in various ways, for example it may comprise individual non-interwoven fibers, a woven fiber fabric or a fibrous web. The fibers may, for example, be carbon fibers. While the fibrous mat is being impregnated with resin, as a rule synthetic resin such as, for example, epoxy resin, the liquid resin fully takes up the space in the molding-tool cavity. Subsequently, the resin cures or solidifies within the molding-tool cavity, for example as a result of a chemical reaction triggered by heating the resin, and a composite component is produced that comprises the fibrous mat and the cured resin. 
         [0004]    From DE 10 2005 053 691 A1 or WO 2007 054 268 A1 a molding tool for implementing the RTM method is known. During the curing process the volume of resin is reduced up to approximately 3%. With the use of semi-finished fiber products with additional material that during infiltration by the resin dissolves with the resin, for example in order to modify mechanical characteristics of the resin, the volume of the semi-finished fiber product after infiltration may be reduced by up to approximately 20% when compared to the state before infiltration. This may result in a situation in which, above all in the case of a composite component comprising particularly thick sections, as a result of volume shrinkage the composite component no longer has the geometry defined by the molding-tool cavity. Furthermore, because the pressure in the molding tool is reduced as a result of shrinkage, blistering may occur in the composite component, which blistering reduces the local strength of the composite component. 
         [0005]    From EP 1 013 409 A2 a method is known in which instead of an inflexible counter-mold a flexible membrane is used. A fibrous mat is placed on an inflexible negative mold and is covered by means of the flexible membrane. Counter-pressure is applied to the membrane so that a molded part arises whose one side is shaped like the negative mold. No predefined geometry may be specified for the other side, which rests against the flexible membrane, of the composite component to be manufactured. 
         [0006]    In view of the foregoing it is at least one object to be able to produce composite components of uniform strength and precisely predetermined geometric shapes. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
       SUMMARY 
       [0007]    According to an embodiment of the invention, a molding tool for manufacturing a composite component is provided. The molding tool comprises a first mold, a second mold and a pressure generating means, wherein between the first mold and the second mold or further molded parts a membrane is arrangeable, so that between the first mold and the membrane a first region is formed, and between the second mold and the membrane a second region is formed, wherein in the first region a fibrous mat is arrangeable. The fibrous mat is resin-impregnated or resin-impregnable. In the second region with the use of the pressure generating means counter-pressure can be produced or counter-pressure is producible so that the membrane is being pressed or is pressed in the direction of the fibrous mat (when the counter-pressure has built up). 
         [0008]    For manufacturing a composite component a molding tool is used that comprises at least two molds, for example a first rigid mold and a second rigid mold. The molding tool may also comprise several parts. A tightly closing membrane, formed over one or several of the molding-tool surfaces, forms a pressurizable space, the second region. Counter-pressure in the second region may be generated by any desired fluid, for example a liquid, for example water, or a gas, for example air. Counter-pressure may result in that the pressure in the second region exceeds the pressure in an environment of the molding tool, or in that the pressure in the second region exceeds the pressure in the first region. Counter-pressure may also arise as a result of overpressure or may be overpressure. 
         [0009]    As a result of inflexible or stiff molding-tool surfaces that encompass the composite component or the fibrous mat on both sides a defined component thickness or precisely calibrated component areas may be manufactured. 
         [0010]    The membrane may be completely impervious to fluid. The membrane may be a foil or film, for example a plastic foil or film or a metal foil, but it may also be a membrane comprising or being of rubber. The membrane may also be partially fluid-permeable, for example by means of pores. In this case the counter-pressure in the second region may be maintained in that fluid is continuous supplied to the second region. 
         [0011]    The first mold may be a top mold and the second mold may be a bottom mold. As a result of this the membrane is pressed upwards by the counter-pressure. As a result of gravity the resin may flow through the fibrous mat in the direction of the membrane. As an alternative it is also possible for the first mold to be a bottom mold, and for the second mold to be a top mold. In this way it is possible in a simple manner for the fibrous mat to be placed on the second mold, and for the membrane to be arranged above it. 
         [0012]    The notion of the membrane being pressed in the direction of the fibrous mat may on the one hand mean that the membrane moves in the direction of the fibrous mat, and on the other hand it may also mean that the membrane exerts pressure on the fibrous mat without moving. 
         [0013]    By pressing the membrane in the direction of the fibrous mat the shrinkage resulting from the reaction of the resin during curing, or the volume change of the semi-finished fiber product during injection may be compensated for. Furthermore, in this manner already with the molding tool partly open a homogeneous filling of the first region with resin may also be achieved in the case of thickness fluctuations of the component. Likewise, a homogeneous filling is also possible in the case of components with sections that are situated normally or not normally relative to the vector of the tool closure. Thus fiber impregnation in the case of components with sudden differences in the thickness of the wall becomes better controllable. Moreover, a variation in the stroke or settlement of surfaces that are situated normally or not normally relative to the closing direction of the molding tool may be controlled better. As an alternative to introducing the resin in the molding-tool cavity, fibrous mats that are already resin-impregnated, as is the case in the pre-pregnated method, may be arranged in the molding tool. 
         [0014]    According to an embodiment the molding tool comprises a resin supply device and, for example, a closable resin outlet. By way of the resin supply device resin for impregnating the fibrous mat may be supplied to the molding tool to the first region. 
         [0015]    The fibrous mat may also be resin-impregnated with the molding tool open, because the membrane pressed in the direction of the fibrous mat prevents the resin from flowing out of the open molding tool. By means of the counter-pressure in the second region the intensity with which the membrane is pressed in the direction of the fibrous mat may be set. In this manner, despite the high flow resistance of the resin, the infusion time may be shortened when compared to that of the RTM method. By means of variation of the pressure in the pressurized second space or region the flow resistance during fiber impregnation may be set. 
         [0016]    The resin supply device may comprise a connection of the molding tool, by way of which connection resin may be conveyed under pressure by way of a line from a resin reservoir into the first region. The first region may also comprise a further connection, by way of which connection air or water or generally a fluid may be removed by suction from the first region. In this process it may be ensured that during resin impregnation of the fibrous mat no fluid remains in the first region. 
         [0017]    According to an embodiment the resin supply device is formed or situated in the first mold. To this effect the first mold may comprise one or several holes by way of which the resin is conveyed to the first region. 
         [0018]    According to a further embodiment the pressure generating means comprises a fluid supply device, wherein fluid for producing the counter-pressures may be supplied, or is suppliable, to the molding tool with said fluid supply device. The counter-pressure may be produced or may be producible by supplying a fluid with a fluid line from a fluid reservoir. 
         [0019]    According to an embodiment the fluid supply device may be formed or situated in the second mold. To this effect the second mold may comprise one or several holes by way of which the fluid may be conveyed to the second region. 
         [0020]    According to an embodiment a molding tool is provided with a section of the first mold that defines the surface geometry of a first side of the composite component, and a section of the second mold defines the surface geometry of a second side of the composite component. 
         [0021]    The geometry of the composite component may be defined completely by the opposing sections. Moreover, the surface of the composite component, which surface faces the membrane, may be defined by the interior geometry of the molding tool. Because of the geometry of the composite component, which geometry may be precisely defined by means of the molding tool, the composite component comprises a precisely determinable thickness at each position. Furthermore, the fiber volume content, in other words the ratio of resin to fibers, may be precisely set. 
         [0022]    According to a further embodiment a molding tool is provided with the first mold and the second mold that may be moved towards each other until a final position is reached in which the first mold and the second mold rest against each other. In the final position a cavity is formed between the first mold and the second mold. The final position may also be reached if there is still a small residual closing distance between the molds. 
         [0023]    If the first mold and the second mold rest against each other or abut, a cavity is formed by the sections of the first mold and the second mold, which cavity defines the geometry of the composite component. 
         [0024]    According to an embodiment the cavity defines the geometry of the composite component to be produced. This cavity may be separated into the two regions by the membrane. 
         [0025]    According to an embodiment a molding tool is provided with the first mold and the second mold that are movable towards each other up to an intermediate position in which the first mold and the second mold may be further movable towards each other. 
         [0026]    According to an embodiment in the intermediate position the first region is sealed with respect to the environment of the molding tool. In this way in the intermediate position of the molding tool a space, the first region, is created in which the fibrous mat may be resin impregnated. Resin may not leave the first region during impregnation. 
         [0027]    According to a further embodiment in the intermediate position the second region is sealed with respect to the environment of the molding tool. Already in the intermediate position the second region may be pressurized. In the intermediate position the second region is sealed with respect to the environment and in this way may be pressurized, for example by feeding a fluid at pressure, in order to generate the counter-pressure in the second region. 
         [0028]    According to an embodiment the molding tool comprises a seal for sealing the first region. In the intermediate position the first region may be sealed with respect to the environment of the molding tool by means of the seal. 
         [0029]    According to an embodiment the molding tool comprises a first seal for sealing the first region and/or the second region. The first seal may have a first protrusion over the surface of the first mold and/or the second mold. The first seal may comprise several single seals. 
         [0030]    The seal may seal the first region between the intermediate position and the final position of the molding tool. To this effect the first seal may have a high gap tolerance between the molding tool segments. This may be affected in that the seal comprises a protrusion beyond the surface of the first or the second mold. The seal may be attached to the first mold or the second mold. 
         [0031]    According to an embodiment, the seal may also seal the second region. The seal may seal the second region between the intermediate position and the final position of the molding tool with respect to the environment of the molding tool. If the seal has been affixed to the first mold, from the first intermediate position the first region may be closed off or delimited by a section of the first mold and a section of the membrane within the seal. The second region may be closed off by a section of the second mold and the section of the membrane within the seal. 
         [0032]    According to an embodiment a molding tool is provided which apart from the first seal comprises a second seal for sealing the first region and/or the second region. This may be affected in that the second seal protrudes from a surface of the first or of the second mold. The second seal may be arranged outside the first seal. In this arrangement the first seal may be attached to the first mold, and the second seal may be attached to the second mold. Both seals may comprise identical protrusions and/or may protrude identical. 
         [0033]    According to an embodiment the molding tool comprises a second seal for sealing the first region and the second region, wherein the first seal is mounted to the first mold and has the first protrusion over the surface of the first mold. The second seal is mounted to the second mold and has a second protrusion over the surface of the second mold. 
         [0034]    The first seal and/or the second seal may seal the cavity within the molding tool already at the stage in which the first and the second molds are in the intermediate positions. The seals may have a protrusion over the surfaces of the two molds, which protrusion corresponds to the gap tolerance of the molding tool in the intermediate position or is a slightly bigger. 
         [0035]    According to an embodiment, the molding tool comprises a third seal for sealing the cavity in the final position of the molding tool. The third seal may comprise a protrusion that is smaller than the protrusion of the first or of the second seal. In this manner it may be ensured that the cavity, which in the final position of the molding tool may be very highly pressurized, is also sealed off with respect to the environment when the first seal or the second seal cannot remain completely tight when exposed to these pressures. 
         [0036]    According to an embodiment the molding tool comprises a third seal for sealing the first region and the second region. The third seal may be mounted to the first mold. The third seal may comprise several single seals. According to an embodiment the third seal has a third protrusion that is smaller than the first protrusion and/or the second protrusion. 
         [0037]    According to an embodiment the third seal is arranged more outside as the first seal and/or the second seal with respect to the first region and the second region. The second seal may be arranged more outside as the first seal. 
         [0038]    According to an embodiment the membrane is mechanically connected to the second mold. The membrane may also be connected to the second mold when the molding tool is completely open and is not in the final position or in the intermediate position. 
         [0039]    On the other hand, for each manufacturing process relating to one composite component a one-way membrane may be used, such that no cleaning of residual resin from the molding tool, at least on the membrane side, is necessary. In this arrangement the membrane may also remain on the component, for example bonded to the composite component. In this manner at the same time a possibility for component lamination is provided. On the other hand, the membrane may also assume further additional functions on the composite component, for example to make it possible for the composite component to be bonded better or for it to comprise a metallic surface. 
         [0040]    A method is also provided for manufacturing a composite component. According to an embodiment the method comprises the steps of: arranging a fibrous mat in a first region between a first mold of a molding tool and a membrane arranged in the molding tool; moving the first mold and a second mold of the molding tool towards each other to an intermediate position in which a second region between the second mold and the membrane is sealed with respect to the environment of the molding tool; and generating counter-pressure in the second region so that the membrane is pressed in the direction of the fibrous mat. The fibrous mat may be resin impregnated or may be resin impregnable. 
         [0041]    Even if the molding tool in the intermediate position is not completely closed to the final dimension, the second region between the membrane and the molding tool is pressurized, such that the membrane is pressed in the direction of the fibrous mat, thus pressurizing the first region between the molding tool and the membrane and pressurizing the fibrous mat located therein. In this manner, the resin impregnating of the fibrous mat, as well as the fiber volume content of the composite component, may be set by the counter-pressure generated in the second region. 
         [0042]    According to an embodiment the method comprises supplying resin to the first region for impregnating the fibrous mat. 
         [0043]    According to an embodiment the method comprises arranging the membrane between the first mold and the second mold. 
         [0044]    According to an embodiment the method comprises moving the first mold and the second mold towards each other to a final position. In the final position between the first mold and the second mold a cavity is formed that defines the geometry of the composite component. In the final position the precise external or outer geometry of the composite component may be determined by the cavity. 
         [0045]    According to an embodiment the method comprises impregnating the fibrous mat with resin, before the first mold and second mold are moved to the final position. For example, the fibrous mat may be already impregnated with resin, when it is laid or positioned in the molding tool. Also, the fibrous mat may be impregnated with resin in the molding tool, for example in the intermediate position. 
         [0046]    According to an embodiment the method comprises connecting the membrane to the fibrous mat, for example by bonding. Bonding the membrane to the composite component may take place by means of the curing resin. 
         [0047]    According to an embodiment the method comprises a sealing of the first region and/or the second region with a first seal and/or a second seal in the intermediate position. The sealing may be achieved in that the first seal and/or the second seal has a protrusion which corresponds to the gap tolerance of the molding tool in the intermediate position or that is bigger than the gap tolerance. 
         [0048]    According to an embodiment the method comprises a sealing of the first region and/or the second region with a third seal in the end position. The third seal may have a smaller protrusion as the first seal or the second seal. 
         [0049]    A molding tool is also provided for manufacturing a composite component for an aircraft. In particular for aircraft components a predefined uniform strength while achieving the lightest possible weight is advantageous. Because the fiber volume content may be set precisely, an optimal ratio of strength to weight may be achieved. 
         [0050]    Below, the invention is described in detail with the use of exemplary embodiments with reference to the enclosed figs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0051]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
           [0052]      FIG. 1  shows a longitudinal section of a molding tool according to an exemplary embodiment; 
           [0053]      FIG. 2  shows a schematic diagram of a press arrangement in which a molding tool according to an exemplary embodiment is arranged; and 
           [0054]      FIG. 3  shows a flow chart of the sequence of a method according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0055]    The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
         [0056]      FIG. 1  shows a molding tool  100  in an intermediate position in which the molding-tool gap  102  is not completely closed to its final dimension. The molding-tool gap  102  or the molding-tool cavity  102  is formed by a first mold  104  and a second mold  106 . The molding tool may also comprise more than two molds, for example a plural number of molds or molding-tool parts. The second mold  106  is arranged in the direction of the arrow A below the first mold  104 . The two molds  104  and  106  may be moved towards each other and away from each other in the direction of the arrow A. 
         [0057]    Between the two molds  104  and  106  a membrane  108  is arranged. Between the membrane  108  and the first mold  104  a first region  110  is formed in which there is a fibrous mat  112 . Opposite the fibrous mat  112  and the first region  110 , on the other side of the membrane  108 , there is a second region  114 . The second region  114  is connected by way of an air supply device or a fluid supply device  116  as a pressure generating means in that, as indicated by the arrow B, air or fluid may be conveyed or pumped into the second region  114  in order to generate counter-pressure. 
         [0058]    In order to seal the first region  110  and the second region  114  a first seal  120  is attached to the first mold, and a second seal  118  is attached to the second mold. In relation to a central axis M of the molding tool the first seal  120  completely encompasses the fibrous mat  112 . In relation to the central axis M the second seal  118  completely encompasses the fibrous mat  112  and the first seal  120 . 
         [0059]    In this arrangement the first seal  120  protrudes beyond the surface  122  of the first mold  104  to such an extent that the first seal in the intermediate position shown in  FIG. 1  in sections presses the membrane  108  against a surface  124  of the second mold  106 . Likewise, the second seal  118  protrudes beyond the surface  124  of the second mold  106  to such an extent that the second seal in the intermediate position shown in  FIG. 1  in sections presses the membrane  108  against the surface  122  of the first mold  104 . The absolute protrusion of the two seals  118  and  120  depends on the design of the seal that is being used. 
         [0060]    The two seals  118  and  120  may comprise a foamed material or a plastic material that may be strongly compressed without suffering any damage so that the two molds may be moved towards each other up to a final position in the direction of the arrow A until the two surfaces  124  and  122  rest against each other. 
         [0061]    In relation to the center axis M, outside the two seals  118  and  120  and outside the fibrous mat  112  on the first mold a further, third seal  126  may be affixed, whose protrusion is small, for example approximately 0.2 mm, when compared to the protrusion of the two seals  118  and  120 . The third seal  126  may be to ensure that when the two molds  104  and  106  in the final position are closed to final dimensions the pressure within a cavity  128  may be maintained should the two seals  118  and  120  fail. 
         [0062]    In the final position, in which the surfaces  122  and  124  rest against each other, in the closed molding tool  100  a cavity  128  or a hollow space  128  is formed which is formed by the section  130  of the second mold  106  and the section  132  of the first mold  104 . The two sections  130  and  132  define the geometry of the composite component  129  to be manufactured. 
         [0063]    The first mold  104  has a resin supply device  134  or resin-injection gate connection  134 . Viewed from the center axis M the resin supply device  134  and a connection  117  of the fluid supply device  116  with the second region  114  are located within the two seals  118  and  120 . 
         [0064]      FIG. 2  shows a schematic diagram of a press  200  in which the molding tool  100  is arranged. The first mold  104  and the second mold  106  may be moved towards each other or away from each other by way of lifting devices, lowering devices or closing devices  202  and  204 . This movement is controlled by the control unit  206  by way of a signal line  208 . 
         [0065]    Furthermore, the first mold  104  may be heated to a predetermined temperature by way of a heating device  209 , and the second mold  106  by way of a heating device  210 . This temperature may be controlled by the control device  206  by way of the signal lines  212  and  214 . As a result of the heated molds  104  and  106 , in the resin in the molding tool a chemical reaction may be triggered or accelerated, by means of which reaction the resin cures. 
         [0066]    The press arrangement  200  has a device  216  that may comprise a fluid reservoir, a pump, a valve and/or a suction device, and which may be controlled by the control device  206  by way of the signal line  218 . By means of the pump or the suction plant in the device  216 , by way of the fluid supply device  116 , the second region  114  within the molding tool  100  may be pressurized with fluid, or the fluid may be removed from this region  114  by suction. 
         [0067]    By way of a further signal line  222  the control device  206  may control a device  220  that may comprise a resin reservoir, a further pump, a further valve, a screw-conveyor and/or a further suction device. By way of the resin supply line  224  by way of the resin supply device  134 , the device  220  may introduce resin to the first region  110  between the two tool halves or molds  104  and  106 , and, by way of a further line  226 , may lead away fluid, for example air, located in the second region  114  from the first region  110 . 
         [0068]      FIG. 3  shows a flow chart that diagrammatically shows the sequence of the method according to an exemplary embodiment. In a first step S 8  a membrane  108  is placed on the second mold  106  and a fibrous mat  112  is placed thereon. 
         [0069]    In step S 10  the molding-tool cavity will not be completely closed to the final dimension. To this effect the lifting devices, lowering devices or closing devices  202  and  204  move the two molds  104  and  106  towards each other from an open position of the molding tool until the intermediate position shown in  FIG. 1  of the two molds  104  and  106  is reached. Moreover, the molds  104  and  106  may be heated in this step or in the other steps. 
         [0070]    In the intermediate position the first region  110  and the second region  114  are then sealed, by the seals  118  and  120 , with respect to the environment of the molding tool. 
         [0071]    In step S 12  the second region  114  between the membrane  108  and the second mold  106  is pressurized by way of the air supply device or the fluid supply device  116 . To this effect the pump in the device  216  pumps air or a fluid from the fluid reservoir by way of the fluid supply device  116  into the second region  114 . 
         [0072]    In step S 14  by means of the device  220  resin is conveyed from a resin reservoir by way of the resin supply line  224  and the resin supply device  134  in the molding tool  100  to the first region  110  between the membrane  108  and the first molding tool  104 , for example by means of the pump or the screw-conveyor. At the same time the fluid located in the first region  110  or the air located therein is removed by suction, by way of the line  226 , from the first region  110  by means of the device  220 . 
         [0073]    In step S 16  the two molds  104  and  106  are moved towards each other to a final position in which the surfaces  122  and  124  of the molding tool rest against each other. 
         [0074]    Concurrently to step S 16  or after step S 16  in step S 18  the pressure in the first region  110  is increased over the pressure in the second region  114 . As a result of this the pressure pad situated in the second region  114  starts to become smaller, and the fluid situated in the second region  114  starts to leave the aforesaid through the fluid supply device  116 . 
         [0075]    In a step S 20  the fluid situated in the second region  114  is actively led away or discharged by reducing the pressure or by suction removal of the fluid. The membrane  108  then rests against the section  130  of the second mold  106 . The resin-impregnated fibrous mat  112  completely fills the cavity  128  formed between the sections  130  and  132 . While the two molds  104  and  106  move towards each other, excess resin may be pressed out by way of the resin supply device  134  or some other outlet. 
         [0076]    In the final position of the two molding tools  104  and  106  the resin-impregnated fibrous mat  112  is enclosed on both sides by the rigid molds  104  and  106 ; both surfaces of the arising composite component  129  may be geometrically calibrated by the sections  130  and  132  of the two molds  104  and  106 . 
         [0077]    In a further step S 22 , by way of the fluid supply device  116 , the resin supply device  134  or a residual closing distance of the molding tool, which distance is, for example, a few millimeters, dwell pressure or after pressure may be exerted while the molding tool  100  is closed, with the two molds  104  and  106  in the final position. In this manner the formation of pores in the composite component  129  may be prevented. 
         [0078]    In addition, it should be pointed out that “comprising” does not exclude other elements or steps, and “a” does not exclude a plural number. Furthermore, it should be pointed out that features or steps which have been described with reference to one of the above exemplary embodiments may also be used in combination with other features or steps of other exemplary embodiments described above. Moreover, while at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.