Abstract:
A method of forming a grout trough for a wind turbine foundation replaces the heavy and single piece template with a plurality of arc-shaped sections which are light weight and connected together to form the grout trough. The individual sections include mechanisms which enable the sections to be removed from the cured concrete by rotation of nuts on the anchor bolts which either pushes or pulls the template section away from the contact with the cured concrete. An embodiment of an individual section has a lifting bale which may be used to pick up an entire bolt package of up to twenty bolts.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     U.S. Provisional Application No. 61/487,670 for this invention was filed on May 18, 2011, for which application this inventor claims domestic priority. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to concrete foundations set within excavations or bore holes which are installed to support wind turbines. More particularly, this invention comprises an apparatus and method for configuring, installing, and setting the anchor bolts for a cylindrical foundation for a wind turbine, and installing a grout trough in the foundation. 
     U.S. Pat. Nos. 5,586,417 and 5,826,387, both by Henderson, disclose a foundation “which can be poured-on-site monolithically and is of cylindrical construction with many post-tensioned anchor bolts which maintain the poured portion of the foundation under heavy compression, even during periods when the foundation may be subject to high overturning moment.” Henderson&#39;s foundation is preferably in the shape of a cylinder, having an outer boundary shell and an inner boundary shell each formed of corrugated metal pipe. Between the outer boundary shell and the inner boundary shell elongated high strength steel bolts extend vertically up through concrete from a peripheral anchor plate, called an inbed plate, located near the bottom of the cylinder. The bolts extend upwardly from the inbed plate to a connecting plate or flange above the ground surface. The bolts extend through hollow tubes to prevent adhesion of the concrete to the bolts. The foundation typically uses no rebar reinforcing steel. This design uses the mechanical interaction with the earth to prevent over turning instead of the mass of the foundation typically used by other foundations for tower structures.  FIG. 1  schematically shows an embodiment of the Henderson foundation. 
     The “hollow tubes” of this foundation are typically elongated plastic tubes which encase the bolts substantially through the entire vertical extent of the concrete and allow the bolts to be tensioned after the concrete has hardened and cured, thereby post-tensioning the entire concrete foundation. Alternatively, the elongated bolts can be wrapped in plastic tape, or coated with a suitable lubrication, which will allow the bolts to stretch under tension over the entire operating length of the bolt through the vertical extent of the concrete. 
     Henderson further discloses the post-stressing of the concrete in great compression by tightening the high strength bolts to provide heavy tension between a heavy top flange and the inbed plate at the bottom of the foundation, thereby placing the entire foundation under high unit compression loading. The bolts are tightened so as to exceed the maximum expected overturning force of the turbine tower on the foundation. Therefore, the entire foundation withstands various loads with the concrete always in compression and the bolts always in static tension. 
     The tensioning bolts in the cylindrical foundation are preferably in side-by-side pairs, the pairs extending radially from the center of the foundation, forming an inner ring of bolts and an outer ring of bolts as shown in  FIG. 2 . As shown in  FIG. 2 , the inner ring of bolts defines a circle having a slightly shorter diameter than a circle defined by the outer ring of bolts. The bolt pattern is, of course, determined by the bolt pattern on the mounting flange of the turbine tower to be installed on the foundation. A large number of bolts in typically used for this type of foundation. Typically seventy tensioning bolts are used in the inner ring and seventy tensioning bolts in the outer ring for a total of one hundred forty bolts. In Henderson&#39;s foundation, the lower ends of the bolts are anchored to the inbed plate at the bottom of the foundation which may be constructed of several circumferentially butted and joined sections. 
     The following known procedure is typically followed in constructing the cylindrical foundation. A bore hole is drilled or excavated and an outer boundary shell of corrugated metal pipe (“CMP”) is set within the hole. Bolt bundles are lowered into the borehole. The bolt bundles typically comprise about thirty bolts, with each bolt weighing up to two hundred pounds per bolt. Workers are lowered into the CMP lined bore hole. Working from the bottom of the bore hole, the workers lift and/or position each individual bolt so it can be inserted into a template at the surface, which is suspended above the bore hole by a crane having a capacity of approximately 100 tons. Once each bolt is inserted into the template, a nut made up onto the threads extending above the template, such that the weight of each bolt is suspended by the template. 
     Once all of the bolts have been suspended from the template, the entire assembly is lifted out of the bore hole so the inbed plates may be placed at the bottom end of the bolts. As the assembly is lowered back into the bore hole, bands or rebar wraps are placed around the collective bolts to hold the bolts in position when the concrete is poured after the assembly is in position.  FIG. 3  shows such an assembly suspended by a lifting frame which is connected to the template. The entire assembly is then lowered back into the bore hole and an inner boundary shell of CMP is lowered into the bore hole such that the bolts are extending upwardly through an annulus defined by the outer boundary shell and the inner boundary shell. 
     A jig assembly is erected as generally depicted in  FIG. 4  which suspends the lifting frame, the grout template, and all anchor bolts within the bore hole. Concrete is poured into the annulus around the upwardly extending bolts, with the template at the top of the bolts used to form a “grout trough” in the upper surface of the concrete. The upwardly facing ends of the bolts extend into the grout trough and, following the hardening of the concrete, the grout trough is filled with a high strength grout upon which the tower flange is placed when the grout has adequately cured. 
     The above procedure has a number of disadvantages. For example, it requires the utilization of a very heavy jig assembly to support the extremely heavy template for leveling the template. This jig assembly requires heavy equipment to mobilize and demobilize. In addition, once the concrete has set and the grout trough formed, the template must be freed from the concrete. However, the template may substantially adhere to the concrete and heavy equipment and pry bars are often required to pry the template free. In addition, because the template supports the weight of all of the foundation bolts, each bolt must be secured to the template with a nut, thereby requiring substantial time to install the nuts. A large crane is required for lifting and suspending the bolt-template assembly, which weighs a number of tons. 
     SUMMARY OF THE INVENTION 
     Embodiments of the method and apparatus disclosed herein provide a solution to the disadvantages described above. For purposes of this disclosure, the phrase “downwardly facing end” when referencing a bolt refers to the end of a bolt facing downward within a bore hole and the phrase “upwardly facing end” refers to the end of a bolt facing upward within the bore hole. 
     An embodiment of the apparatus is utilized in combination with a method of installing bolt packages, and the bolt packages themselves, which have been previously disclosed by the present inventor, among other places, in U.S. Pat. No. 8,146,323. The following steps are taken in preparation for utilizing the present apparatus and method. First, a foundation bore hole is installed according to Henderson or other method. Thereafter, bolt packages are assembled and installed according to the &#39;323 patent. The total number of tower flange bolts to be utilized for the foundation is divided into a plurality of groups. Each of the bolts is encased within a hollow tube or other encasement (“sleeve”) which allows movement of the bolt relative to the sleeve once the bolt and sleeve are set within a concrete foundation. Each group of bolts is assembled into a bolt package where each bolt package comprises a plurality of bolts, where each bolt is either encased within a sleeve or wrapping to allow motion of the bolt with respect to the sleeve or wrapping. Within each bolt package, each bolt is retained, by position retention means, in a position, with respect to the position of adjacent bolts, which is substantially the same position as when the bolt package is later placed within the foundation bore hole. The downwardly facing ends of the bolts of each bolt package are attached to an arc-shaped in-bed plate having holes for an inner arc of bolts and an outer arc of bolts. Each assembled bolt package may thereafter be individually placed within the bore hole. The bolt packages are arranged such that the inner arc of bolts of each anchor bolt package form an inner circle of upwardly facing anchor bolts and the outer arc of each bolt package form an outer circle of upwardly facing anchor bolts. 
     The number of bolts in each bolt package will generally be about ten to twelve bolts. Of course this number may vary according to various design and installation factors, without changing the basic concept of the embodiments of the method and apparatus disclosed herein. 
     Because the present method does not require the template to support the collective weight of all of the anchor bolts, the lighter weight template of the present invention may be utilized for the formation of the grout trough and not every bolt needs to have a nut attached to the template at the upwardly facing end of the bolt. A template according to the present invention is very light relative to the known template. The pieces comprising the template of the present invention may be easily transported within the back of a small truck, with the individual template sections manually handled into the truck bed. In contrast, the known templates are extremely heavy and require relatively heavy equipment for loading and transportation. 
     In the present invention, the template for the grout trough comprises a number of sections which are fit together to form an enclosure, typically circular, for the grout trough. The sections comprise means for raising the section with respect to the upwardly facing bolts of the foundation, thereby allowing each section to be freed from the underlying concrete without the need for a crane or pry bar. For example, in one embodiment, the means for raising the arc-shaped section from the underlying concrete is a bracket, or brackets, attached to the upwardly facing surface of each arc-shaped section, where each bracket has at least one aperture into which the end of an upwardly facing anchor bolt is received. A nut on the upwardly facing anchor bolt (placed prior to placement of the arc-shaped section) underlies the bracket. Rotation of the nut in a direction which lifts the nut upwardly on the threads of the anchor bolt causes the nut to engage the underside of the bracket, thereby lifting the arc-shaped section from the concrete as rotation of the nut continues. 
     Alternatively, the arc-shaped section may also comprise a lifting bale which may be utilized in combination with an arc-shaped section. The lifting bale provides a bracket portion similar to that described above, where one or more nuts beneath the bracket section may be utilized to lift the arc-shaped section from the concrete. The lifting bale is constructed of structural steel members and capable of supporting the weight of a completed bolt package because the lifting bale attaches directly to the anchor bolts. Thus, this embodiment provides a competent lift point for lifting and positioning completed bolt packages, and also provides a mechanism for lifting the arc-shaped section from the concrete. 
     The means for raising the arc-shaped section in a third embodiment comprises a plurality of spacer tube-nut assemblies, such as four assemblies per arc-shaped section. Each spacer tube is welded to the top surface of the arc-shaped section. Each nut member comprises a bushing member depending from a nut body, where the bushing member comprises a slot. A sectioned washer or comparable structure is thereafter utilized to attach the nut member to the spacer tube, which allows the nut member to spin with respect to the spacer tube. The spacer tube-nut assemblies fit over some of the upwardly facing anchor bolts. The nuts of each arc-shaped section may thereafter be rotated on the upwardly facing anchor bolts to either position all of the arc-shaped sections at the correct level, or to lift the arc-shaped section from the concrete surface. 
     Because the arc-shaped sections are not used for lifting bolt packages, each arc-shaped section may be fabricated from light and easily handled material. In addition, the surfaces of the arc-shaped sections may be coated with polytetrafluoroethylene such as, for example, Teflon® to prevent adherence to the concrete. Once the concrete is sufficiently set, the nuts may be rotated in the appropriate direction to easily break each arc-shaped section free from the concrete, thereby eliminating any need for pry bars and heavy equipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the foundation of Henderson following installation of the anchor bolts. 
         FIG. 2  shows a completed foundation, showing an inner ring of anchor bolts and an outer ring of anchor bolts with a tower flange attached. 
         FIG. 3  shows the prior art method of placing the anchor bolts, where all of the anchor bolts are lowered into the borehole while suspended from the template. 
         FIG. 4  shows a prior art jig assembly utilized to support the extremely heavy template for leveling the template. 
         FIG. 5  shows a plurality of assembled bolt packages awaiting installation into the bore hole of a foundation. 
         FIG. 6  depicts an embodiment of a bolt package in a vertical position as it would be when lowered into position. 
         FIG. 7  depicts an embodiment of a bolt package being lowered into position within a bore hole. 
         FIG. 8  shows the top of a borehole with several bolt packages installed. 
         FIG. 9  schematically shows the configuration of one embodiment of a position retention means, referred to hereinafter as a “lattice assembly,” utilized to maintain the bolts within a bolt package in position with respect to one another. 
         FIG. 9A  shows a detailed view of how the lattice assembly in  FIG. 8  may be attached to the bolt sleeves. 
         FIG. 10  shows a perspective view of an embodiment of a lattice assembly in accord with  FIG. 9 . 
         FIG. 11  shows the lattice assembly of  FIG. 10  with bolts disposed within the bolt sleeves. 
         FIG. 12  shows an assembled grout template according to the present invention. 
         FIG. 13  shows how a plurality of the arc-shaped sections of the grout template may be stacked for transportation or storage. 
         FIG. 14  shows a lifting bracket which may be utilized as a means of lifting the arc-shaped section from the concrete surface. 
         FIG. 15  shows an embodiment of an arch-shaped section of the grout template with an optional lifting bale and alignment plate. 
         FIG. 16  shows the arc-shaped section of the grout template of  FIG. 15  with the lifting bale and alignment plate attached. 
         FIG. 17  shows how the grout templates of the present invention comprise may bushings for passage of the anchor bolts. 
         FIG. 18  shows another embodiment of an arc-shaped section of the grout template which utilizes a plurality of spacer tube-nut assemblies for lifting the section with respect to the anchor bolts. 
         FIG. 19  shows a detailed view of a portion of the arc-shaped section for the embodiment shown in  FIG. 18 . 
         FIG. 20  shows an embodiment of the arc-shaped section of the grout template being placed on the upwardly facing ends of the anchor bolts of a foundation, showing how a nut is not required for every anchor bolt. 
         FIG. 21  shows an embodiment of the arc-shaped section of the grout template attached to selected anchor bolts. 
         FIG. 22  shows how the split washer is utilized to attach the nut member to the spacer tube, but allowing the nut member to spin freely with respect to the spacer tube. 
         FIG. 23  shows a front view of a nut member. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring specifically to the figures,  FIG. 1  depicts an embodiment of a known foundation  100  utilized for installation of a relatively tall vertical structure, such as a wind turbine. It is to be appreciated that while the disclosed method and apparatus may be utilized to obtain a foundation  10  such as that depicted in  FIG. 1 , the procedure for obtaining the foundation is entirely different from the known methods. Foundation  10  comprises a bore hole  12 , an outer boundary shell  14  and an inner boundary shell  16 , each typically fashioned of corrugated metal pipe (“CMP”), set within the bore hole hole. An inner ring  18  of bolts  40  and an outer ring  20  of bolts  40  are disposed within the annulus formed between the outer boundary shell  14  and the inner boundary shell  16 , with the bolts  40  anchored at the lower end of the bore hole  12  to an inbed plate  22 . The annulus between the outer boundary shell  14  and the inner boundary shell  16  is filled with concrete  24  and the portion of the bore hole  12  inside the inner boundary shell  16  typically filled with loosely compacted soil  26 . 
       FIG. 2  depicts a typical surface view of a wind turbine base, showing the inner ring  18  of bolts  40  and the outer ring  20  of bolts  40  extending through a base flange  28  of a wind turbine tower  30  set upon a base  32  formed by concrete  24 , with nuts  15  securing the base flange to the bolts. 
       FIG. 3  depicts the currently practiced method for obtaining the configurations depicted in  FIGS. 1 and 2 . As described above, a bolt assembly is formed by first lowering individual bolts  40  into bore hole  12 , and then manually raising each bolt until it is attached to template  34 . Once all of the bolts have been attached to template  34 , the bolt assembly is lifted by a lifting assembly  36  connected to a high capacity crane  38 . A jig assembly  25  is erected as generally depicted in  FIG. 4  which suspends the lifting assembly  36 , the grout template  34 , and all anchor bolts within the bore hole. Once the bolts are in position, concrete is poured into the annulus  27  around the upwardly extending bolts, with the template  34  at the top of the bolts used to form a “grout trough” in the upper surface of the concrete. After the concrete cures, the grout template  34  must be freed from the concrete. This operation often requires the use of heavy hammers, pry bars, and a crane to break the grout template loose. 
     The present invention is utilized to obtain the general configurations depicted in  FIGS. 1 and 2  but largely avoiding the method depicted in  FIG. 3  and the jig assembly  25  depicted in  FIG. 4 . As with the known method, a bore hole  12  is drilled and lined with outer boundary shell  14 . However, rather than transferring bolt bundles into the bore hole and lifting each individual bolt  40  and inserting the bolt into template  34  according to the known method, the disclosed method utilizes prefabricated bolt packages  50  which are assembled outside of the bore hole  12  as depicted in  FIG. 5  and as taught within the present inventor&#39;s U.S. Pat. No. 8,146,323, which is incorporated herein by this reference. 
     In the method taught in the &#39;323 patent, bolt packages  50  are formed by dividing the total number of anchor bolts  40  to be installed in the foundation bore hole into a plurality of groups. Each bolt package  50  is made up of a number of individual bolts  40 . Typically, each bolt package  50  will have ten to twelve (and typically no more than twenty) individual bolts  40  which are placed in axial alignment with one another and are configured into an inner arc  52  and an outer arc  54  of bolts. Each bolt  40  in the bolt package  50  is retained in a fixed position with respect to the position of the adjacent bolts by fixing the position of each bolt by position retention means. The position of each bolt  40  within the bolt package  50 , with respect to the adjacent bolts in the package, will be substantially the same position as when the bolt package is placed within the foundation bore hole  12  and when the bolt package  50  is placed in its final disposition within the foundation. Each bolt package  50  is thereafter lowered into the bore hole  12  and arranged such that the inner arc  52  of bolts  40  of each anchor bolt package form an inner circle  18  of upwardly facing anchor bolts and the outer arc  54  of each bolt package form an outer circle  20  of upwardly facing anchor bolts as indicated by  FIGS. 7 and 8 . As indicated by  FIG. 7 , a lifting plate  56  may be utilized for lifting and lowering the bolt package  50 , but other means may also be utilized for lifting and lowering the bolt package as well, such that lifting plate  56  is optional. As described below, the lifting plate  56  may be replaced by a lifting bale  256  which is utilized together with the template sections described below. 
     Each bolt  40  contained within the bolt package  50  must be configured in such a manner as to allow tensioning of the bolt after it has been set in concrete  24 . Usually this means each bolt  40  of the bolt package  50  will be contained within a bolt sleeve  58 , where the bolt sleeves are typically elongated plastic tubes which encase the bolts substantially through the entire vertical extent of the concrete  24  and allow the bolts to be tensioned after the concrete has hardened and cured, thereby post-tensioning the entire concrete foundation. Alternatively, the bolts  40  can be wrapped in plastic tape, or coated with a suitable lubrication, which will allow the bolts to stretch under tension over the entire operating length of the bolt through the vertical extent of the concrete. 
     Each bolt package  50  further comprises an arc-shaped inbed plate  60  which is attached to what will be the downwardly facing ends of each bolt  40  when the bolt package is placed within the bore hole  12 . A nut (not shown) is made up on each downward facing end of bolts  40  to attach the inbed plate  60  to the bolts. A lifting plate  56  or lifting bale  256  may be likewise attached to the upwardly facing ends of each bolt  40 , with sufficient nuts made up on the upwardly facing ends of the bolts to adequately secure the lifting plate or lifting bale to the bolt package  50 . 
     As further taught in the &#39;323 patent, the bolt package  50  further comprises means for retaining the positions of each bolt  40  in the bolt package with respect to the other bolts in the bolt package as the bolt package is assembled and lowered into the bore hole  12 . One such means for setting the relative positions of the bolts  40  in a bolt package comprises a plurality of lattice assemblies  62 , each lattice assembly fabricated as generally depicted in  FIGS. 9-11 . 
     Once all of the bolt packages  50  are installed within the bore hole  12 , unless designed otherwise, the arcs of the adjacently positioned inbed plates  60  will form a complete circle forming the lower anchor ring, with each inbed plate of a bolt package attached to the inbed plates of the two adjacent bolt packages. In a similar manner, as best shown in  FIGS. 8 and 12 , arc-shaped sections  134  are connected to form template member  34 ′. The different embodiment of arc-shaped section  234 , as depicted in  FIGS. 15-16  or the embodiment of arc-shaped section  334  depicted in  FIGS. 20-21  may alternatively used to form template member  34 ′. 
     Arc-shaped sections  134  comprise a unitary body  140  having a first end  142  and a second end  144  generally opposite first end  142 . Unitary body  140  further comprises a top surface  146  which extends from the first end  142  to the second end  144  and a bottom surface  148  in opposite facing relation with the top surface, where the bottom surface also extends from the first end to the second end. 
     For arc-shaped sections  234 ,  334 , unitary bodies  240 ,  340  may comprise a first longitudinal wall  250 ,  350  and a second opposing longitudinal wall  252 ,  352  which extend between the first ends  242 ,  342  and second ends  244 ,  344 . However, as shown in  FIG. 17 , the unitary body  140  may simply comprise opposite facing top surface  146  and bottom surface  148  which are connected by interior bushing sleeves  154 . The surfaces of arc-shaped sections  134 ,  234 ,  334  may be coated with polytetrafluoroethylene such as, for example, Teflon® to prevent adherence to the concrete. 
     The unitary body  140 ,  240 ,  340  further comprises at least two adjacent openings  158 ,  258 ,  358  in the top surface  146 ,  246 ,  346  and at least two adjacent openings  160 ,  260 ,  360  in the bottom surface  148 ,  248 ,  348  where the openings in the top surface align with the openings in the bottom surface. These openings, into which interior bushing sleeves  154  are typically pressed as depicted in  FIG. 17 , are sized and shaped to receive an end of an anchor bolt  40 . 
       FIG. 12  depicts a surface view (without showing any of the foundation below the surface) of a grout template  34 ′ which has been assembled with a plurality of arc-shaped sections  134  (arc-shaped sections  234  and  334  may likewise be used).  FIG. 13  depicts the arc-shaped sections  134  in an unassembled configuration.  FIG. 13  shows how, in marked contrast to the extremely heavy grout template  34  utilized in the known method, the arc-shaped sections  134  are stackable, relatively light weight, and easily transported.  FIG. 14  depicts a bracket  162  which attaches to the top surface  146  of arc-shaped section  134 . The bracket  162  has openings  164  which are aligned and in facing relationship with the openings  158  in the unitary body  140 . Bracket  162  may be utilized to lift the arc-shaped section  134  from the cured concrete below the template by turning nuts  15  such that the nuts move upwardly on the anchor bolts  40 , thereby lifting bracket  162  and the attached arc-shaped section  134  from engagement with the cured concrete. This lifting mechanism, combined with the great difference in weight between the individual arc-shaped section  134  and the grout template  34  of the known method, greatly facilitates the separation of a grout template  34 ′ fabricated from the individual arc-shaped sections as compared to the grout template  34  of the known method. 
       FIG. 15  depicts an exploded view of arc-shaped section  234 . This embodiment of the template sections comprises a lifting bale  256 . As discussed above, lifting bale  256  may be utilized for lifting an entire bolt package  50 . Unlike the arc-shaped sections  134 ,  234 ,  334  which may be fabricated from relatively light materials such as aluminum, lifting bale  256  is fabricated from structural steel members comprising side members  266 ,  268 , lifting member  270  and cross-members  272 ,  274 . When lifting bale  256  is utilized to lift a bolt package  50 , bolts  40  are inserted through eight different apertures  276  which are positioned within the different structural steel members of the lifting bale, with a nut  15  securing each bolt to the lifting bale. With this configuration, the bolt package  50  is lifted by the lifting bale  256  rather than the arc-shaped section  234 . 
     As shown in  FIGS. 15-16 , arc-shaped section  234  may comprise alignment plate  278  which secures the arc-shaped section to adjacent sections. While note shown with arc-shaped sections  134 ,  334 , alignment plate  278  may be used with these embodiments as well. The alignment plate  278  insures that the grout template  34 ′ is firmly secured in place and maintaining the bolts  40  in position before the pouring of the concrete around the bolts. Once the concrete cures, arc-shaped section  234  may be lifted from the concrete by turning nuts (not shown) on anchor bolts  40 , where the nuts are located beneath cross-members  272 ,  274  in the same manner as discussed above for the embodiment without the lifting bale. 
       FIGS. 18 through 23  depict an embodiment of arc-shaped section  334  which employs a different mechanism for lifting the arc-shaped section  334  from the cured concrete. With this embodiment, a nut assembly  315  is utilized which facilitates rotation of the nut because the nut is within easy reach rather than beneath a bracket or steel frame as with the other embodiments. In this embodiment, the arc-shaped section  334  comprises a plurality of spacer tube-nut assemblies, such as four assemblies per arc-shaped section. The spacer tube  310  is welded to the top surface  346  of the arc-shaped section  334 . Each nut assembly  315  comprises a bushing member  317  depending from a nut body  319 , where the bushing member comprises a slot  321 . A sectioned washer  323  or comparable structure is thereafter utilized to attach the nut assembly  315  to the spacer tube  310 , which allows the nut assembly  315  to spin with respect to the spacer tube. The spacer tube-nut assemblies fit over some of the upwardly facing anchor bolts  40 . 
     While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. Thus the scope of the invention should not be limited according to these factors, but according to the following appended claims.