Abstract:
A pipe torquing sprag tool comprises one or more elastomeric sprags supported on a sprag support in an arrangement lying generally in a plane that is generally perpendicular to the axis of the rotatable sprag support. Each sprag has a solid, uninterrupted side and an interrupted side, and each sprag reacts to a lateral force in the general direction tangential to the surface of the sprag support and applied near the top of the sprag to bend the elastomeric sprag either toward the interrupted side to at least partially lean, fold or collapse, or towards the substantially uninterrupted side for being deformed to a generally compressed and non-compliant configuration for gripping. The sprag tool of the present invention may comprise a sprag support for positioning an external arrangement of sprags for being inserted into the bore of an add-on pipe segment. Alternately, the sprag tool of the present invention may comprise a sprag support for positioning an internal arrangement of sprags for being received over the end of an add-on pipe segment.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to threaded oilfield tubulars. The present invention is directed to a tool for applying torque and rotation to an add-on pipe segment to make up or break out a threaded pipe connection or to rotate a pipe string. More specifically, the present invention is directed to a tool having one or more elastomeric sprags oriented on the tool for engaging and rotating an add-on pipe segment in a first rotational direction, but not in the opposite rotational direction. Additional sprags may be disposed on a separate portion of the tool for selectively providing for the capacity to rotate an add-on pipe segment in the opposite direction. 
         [0003]    2. Description of the Related Art 
         [0004]    Conventional power tongs are machines used on a rig to grip the exterior surface of an add-on pipe segment and rotate the add-on pipe segment about its axis to threadably make-up a connection between the add-on pipe segment and an aligned pipe string. The power tong generally has a throat through which the add-on pipe segment may be introduced between gripping jaws of the power tong. The gripping jaws are pivotally securable to a gripping jaw retainer that supports the jaws in position to grip, rotate and torque the add-on pipe segment by powered rotation of a surrounding ring gear. The ring gear may be rotatable using hydraulically-powered pinion gears to make up the threaded connection. After the threaded connection is torqued, a conventional power tong must generally be moved back away from well center for subsequent well operations. Conventional power tongs may be movably disposed on a track or in a groove that provides for automated advancement to and retraction from well center. 
         [0005]    A power tong may cooperate with an elevator that kicks out from well center to secure to and position an add-on pipe segment for being joined to the pipe string. Elevators may be suspended from a vertically movable top drive or a block using a pair of elongate bails. After an add-on pipe segment is joined to the proximal end of the pipe string, the elevator may be used to support the pipe string within the borehole so that the spider may disengage and the lengthened pipe string may be further installed in the borehole by lowering the elevator and the pipe string through the disengaged spider. This process may be repeated until the pipe string reaches a desired length. 
         [0006]    Conventional power tongs are generally large machines that consume a large portion of space on the rig floor, and some rigs may need to be retrofitted to accommodate conventional power tongs that operate on tracks or in grooves on the rig floor. Conventional power tongs may obstruct the view on the rig floor and often cause unwanted marks on the exterior of the add-on pipe segment and/or the pipe string. Conventional power tongs may present an obstruction on rigs equipped with elevators that kick out from well center to support and position add-on pipe segments at well center for being joined into the pipe string. 
         [0007]    Other power tongs may comprise tools that internally grip the add-on pipe segment. Internally gripping power tongs, which may include casing running tools, often employ complex mechanisms for deployment of pipe gripping jaws. Actively deployable gripping jaws may deploy by operation of cams, cylinders or axially movable mandrels. These mechanisms result in additional cost, weight and maintenance, and often require a source of external power for deployment and retraction of gripping jaws to engage and release an add-on pipe segment, respectively. 
         [0008]    What is needed is a method of rotating and torquing an add-on pipe segment to make up a threaded connection to a pipe string that utilizes substantially less rig floor space than a conventional power tong. What is needed is a power tong that can rotate and torque an add-on pipe segment using a top drive. What is needed is a power tong that can internally or externally engage and apply torque to an add-on pipe segment for making up or breaking out a threaded connection, thereby eliminating the cost, weight and maintenance of more complex actuated gripping jaws, and avoiding the need for coupling the tool to a source of power for engaging or retracting the tool. What is needed is a power tong that cooperates with elevators that kick out from well center to secure to and position add-on pipe segments at well center for being joined into the pipe string. What is needed is a tool for gripping and rotating an add-on pipe segment that does not mark or scar the pipe wall, and that does not cause damage to the threads that form the connection upon insertion of the tool into the bore of the add-on pipe segment. 
       SUMMARY OF THE PRESENT INVENTION 
       [0009]    The present invention satisfies some or all of the above-referenced needs and others. The present invention is directed to a sprag tool for gripping and applying torque and rotation to an add-on pipe segment upon powered rotation of the sprag tool about its axis in a first direction. 
         [0010]    The sprag tool of the present invention may provide a ratchet-like function that is achieved by strategically shaping the sprags that are disposed on the sprag tool. Each sprag may be shaped to grip the wall of the add-on pipe segment when the sprag is moved relative to the wall in a first direction, but to slip along the wall of the add-on pipe segment when the sprag is moved relative to the wall in a second direction. In one embodiment of the present invention, a sprag tool comprises a plurality of sprags formed using an elastomeric material and having a base, a top portion, an interrupted side and a substantially uninterrupted side. The sprag is generally securable to a sprag support at its base so that the top portion extends generally radially outwardly from the surface of the sprag support. The interrupted side of the sprag may comprise a gap, a recess, a hole, a notch or void, or a plurality of these features, to permit the sprag to compliantly lean, fold or collapse in response to the application of a generally lateral force near the top portion of the sprag and in the direction of the generally interrupted side. 
         [0011]    The opposite side of the sprag is substantially uninterrupted so that the sprag deforms to a generally compressed and non-compliant configuration in response to the application of a generally lateral force near the top portion of the sprag and in the direction of the substantially uninterrupted side of the sprag by movement of the sprag support and the sprag relative to the contacted wall of the add-on pipe segment. The generally non-compliant mode of deformation of the sprag results in substantial compression of the sprag between the sprag support at its base and the wall of the add-on pipe segment at its top portion, and the compression of the sprag between these two surfaces causes the sprag to be forcibly urged against the wall of the add-on pipe segment, thereby substantially increasing the frictional grip of the elastomeric sprag on the wall of the add-on pipe segment. 
         [0012]    Consequently, a sprag tool comprising an arrangement of angularly distributed sprags disposed on the exterior of a generally cylindrical sprag support that is inserted into the interior bore of an add-on pipe segment will not grip or turn the add-on pipe segment with much torque when the sprag tool is rotated on its axis in a direction that causes the sprags to engage the interior wall of the add-on pipe segment and the resulting force on the top portion of each sprag causes it to lean, fold or collapse toward its interrupted side. However, the same sprag tool will frictionally grip the interior bore of the add-on pipe segment, and rotate and torque the add-on pipe segment, when the sprag tool is rotated on its axis in the reverse direction that causes the sprags to engage the interior wall of the add-on pipe segment in a manner that produces a lateral force applied near the top portion of each sprag that causes the sprag to deform toward the substantially uninterrupted side and to assume a generally compressed configuration between the sprag support and the wall of the add-on pipe segment. The relatively great force applied to the interior wall of the add-on pipe segment as a result of the compression of the sprag between the sprag support and the wall of the add-on pipe segment enhances frictional contact that is multiplied by the number of sprags in the arrangement that engage and contact the interior bore of the add-on pipe segment. 
         [0013]    Similarly, the sprag tool of the present invention may easily be adapted for gripping and rotating an add-on pipe segment by contacting the exterior wall. A sprag tool comprising an arrangement of angularly distributed sprags disposed on the interior bore of a generally cylindrical sprag support that is receivable over the end of a relatively smaller diameter add-on pipe segment will not grip or turn the add-on pipe segment with much torque when the sprag tool is rotated on its axis in a direction that causes each sprag to lean, fold or collapse toward its interrupted side. However, the same externally-gripping sprag tool will frictionally grip the exterior wall of an add-on pipe segment, and it will rotate and torque the add-on pipe segment, if the resulting lateral force on each sprag causes the sprag to deform toward the substantially uninterrupted side and to deform to the generally compressed configuration. The great force applied by each sprag to the exterior wall of the add-on pipe segment as a result of the compression of the sprag provides enhanced frictional contact that is multiplied by the number of sprags in the arrangement that contact the exterior bore of the add-on pipe segment. 
         [0014]    One embodiment of the sprag tool of the present invention comprises sprags secured to the sprag support using adhesives. Another embodiment of the sprag tool of the present invention comprises sprags formed with a fastener that is releasably securable to a sprag support so that the sprags may be releasably installed on the sprag support. Yet another embodiment of the present invention comprises a sprag support having a plurality of radially outwardly protruding or inwardly protruding sprag stems, clips or retainers for securing sprags to the sprag support. In one embodiment, the sprags are installed on the sprag stems, clips or retainers when they are formed. In yet another embodiment the sprags are installed on the sprag support by being fitted into holes, apertures, grooves or channels within the sprag support. In yet another embodiment, a plurality of sprags may be coupled one to others to form a band or ring that is securable to a sprag support using fasteners, clamps or other known structures for securing a ring or band onto or within a generally cylindrical structure. 
         [0015]    The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings wherein like reference numbers represent like parts of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a perspective view of one embodiment of the sprag tool of the present invention rotatably supported above a rig floor by a top drive assembly and generally aligned with the bore of an add-on pipe segment supported by an elevator and positioned to be threadably coupled to a pipe string. 
           [0017]      FIG. 2  is an enlarged perspective view of the sprag tool of  FIG. 1  comprising two arrangements of sprags, each arrangement comprising a generally angularly distributed plurality of sprags supported on the exterior surface of a generally cylindrical sprag support. 
           [0018]      FIG. 3  is an elevation view of a top drive assembly for supporting the sprag tool of  FIGS. 1 and 2  in a position generally aligned with the bore of an add-on pipe segment suspended from the top drive assembly using an elevator supported by a pair of bails. The lower end of add-on pipe segment is received into and bears against the proximal end of a pipe string that is supported from the rig by a spider. 
           [0019]      FIG. 4  is the elevation view of  FIG. 3  after the lower portion of the sprag tool comprising the first arrangement of sprags is lowered and inserted into the bore of the add-on pipe segment at its upper end as the elevator slid downwardly along at least a portion of the length of the add-on pipe segment, and after the sprag tool is rotated about its axis to partially make-up the threaded connection between the add-on pipe segment and the pipe string. 
           [0020]      FIG. 5  is the elevation view of  FIG. 4  after the second portion of the sprag tool comprising the second arrangement of sprags is inserted into the bore of the add-on pipe segment. 
           [0021]      FIG. 6  is a top cross-sectional view of the sprag tool of  FIG. 2  showing the arrangement of relaxed sprags supported on the sprag support before insertion of the sprag tool into the bore of the add-on pipe segment. 
           [0022]      FIG. 6A  is an enlarged view of one embodiment of a sprag  12  in its generally relaxed configuration. 
           [0023]      FIG. 7A  is a cross-sectional view of  FIG. 6  as the sprag tool is inserted into the bore of the add-on pipe segment and rotated by the top drive in the direction of the arrow  60 . The sprags are shown deformed toward the complaint configuration to slide along the interior wall of the add-on pipe segment upon rotation of the sprag tool. 
           [0024]      FIG. 7B  is the cross-section view of  FIG. 7A  as the sprag tool is rotated by the top drive in the direction of the arrow  62 . The sprags are shown deformed toward their non-compliant configuration to grip the interior wall of the add-on pipe segment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]      FIG. 1  is a perspective view of one embodiment of the sprag tool  10  of the present invention rotatably supported above a rig floor  4  by a top drive assembly  17  and generally aligned with the bore of an add-on pipe segment  22  supported by an elevator  70  and positioned to be threadably coupled to a pipe string  80 . The add-on pipe segment  22  is supported from the top drive assembly  17  using a collar ring  9  and a pair of bails  68 . The add-on pipe segment  22  comprises an upper end  22 A having an internally threaded sleeve and a lower end  22 B having external threads for being received and threadably coupled to the proximal end  80 A of the pipe string  80 . The pipe string  80  is supported from the rig using a spider  25  having a set of slips  26  that cooperate to grip and suspend the pipe string within a borehole (not shown). 
         [0026]      FIG. 2  is an enlarged perspective view of the sprag tool shown in  FIG. 1  comprising an upper arrangement  21  and a lower arrangement  11  of sprags, each arrangement comprising a generally angularly distributed plurality of sprags  12  supported on the exterior surface of a generally cylindrical sprag support  13 . The lower arrangement  11  is positioned on the sprag support  13  a sufficient distance below the upper arrangement  21  so that the lower arrangement can be inserted into the bore of the add-on pipe segment  22  without engaging the upper arrangement  21  with the add-on pipe segment  22 . A stop plate  88  may be included to limit the extent to which the sprag tool  10  can be inserted into the bore of the add-on pipe segment  22 . 
         [0027]    In the embodiment shown in  FIG. 2 , each sprag  12  is shown extending radially outwardly from the generally cylindrical sprag support  13 , and each sprag  12  is comprised of an elastomeric material, such as rubber or polyurethane. The sprags  12  are resilient and may be deformable in multiple modes without excessive failure. The sprag tool  10  shown in  FIG. 2  is adapted for being inserted within the bore of pipe having a diameter that is substantially larger than the diameter of the sprag support  13 . 
         [0028]    The shape of each elastomeric sprag  12  provides for its ratchet-type function. For example, the lower arrangement  11  comprises a generally angularly distributed plurality of sprags  12 , when inserted into the bore of the add-on pipe segment  22  along with the sprag support  13  will conform to the annulus between the interior wall of the add-on pipe segment  22  and the sprag support  13 . As will be discussed in more detail below, the sprags  12  are shaped such that they will permit rotation of the sprag tool  10  within the bore of the add-on pipe segment  22  in a first direction, but not in the second, opposite direction. 
         [0029]    This sprag tool may have outwardly protruding sprags arranged on and secured to the exterior surface of a sprag support like those shown in the appended drawings, or it may comprise inwardly protruding sprags arranged on and secured to the interior surface of a larger pipe, such as a 24-inch pipe, to engage and grip the outside of a smaller pipe, such as a 20-inch pipe. 
         [0030]      FIG. 3  is an elevation view of a top drive assembly  17  for supporting the sprag tool  10  of  FIGS. 1 and 2  in a position generally aligned with the bore of an add-on pipe segment  22  suspended from the top drive assembly  17  using an elevator  70  supported by a pair of bails  68 . The lower end  22 B of the add-on pipe segment  22  is received into and bears against the proximal end  80 A of the pipe string  80  that is supported from the rig by the spider  25 . The elevator  70  is of the type that engages and supports the shoulder formed between the lower end of the sleeve  22 A and the pipe segment  22  and is adapted for sliding along at least a portion of the length of the pipe segment  22  when the add-on pipe segment  22  is supported to unload the elevator  70 , as in  FIG. 3 . Lowering of the top drive assembly  17 , including the collar ring  9 , the bails  68  and the elevator  70  from its position shown in  FIG. 3  will slide the elevator  70  downwardly along at least a portion of the length of the add-on pipe segment  22  and insert the sprag tool  10  into the bore of the add-on pipe segment  22 . 
         [0031]      FIG. 4  is the elevation view of  FIG. 3  after the traveling block  8  are used to lower the top drive assembly  17 , including the collar ring  9 , bails  68  and the elevator  70 , to partially insert the sprag tool  10  of the present invention into the aligned bore of the add-on pipe segment  22  and slide the elevator  70  along at least a portion of the length of the add-on pipe segment  22  from its upper end  22 A.  FIG. 4  shows that the lower arrangement  11  is inserted into the bore of the add-on pipe segment  22  through its upper end  22 A, and both the upper arrangement  21  and the stop plate  88  remain above the bore of the add-on pipe segment  22 . The sprag tool  10  has also been rotated after insertion into the bore of the add-on pipe segment  22  to threadably make up the connection between the lower end  22 B of the add-on pipe segment  22  and the upper end  22 A of the pipe string  80  to lengthen the pipe string  80 . The lengthened pipe string  80  can be lifted by raising the traveling block  8 , withdrawing the sprag tool  10  from the bore of the add-on pipe segment  22 , and reengaging the elevator  70  with the shoulder between the proximal end  22 A of the add-on pipe segment  22 , then by continuing to raise the traveling block  8  to lift the lengthened pipe string  80  and unload the spider  25  so that the lengthened pipe string  80  can be lowered further into the borehole (not shown) to position the upper end  22 A of the add-on pipe segment  22  for joining an additional add-on pipe segment  22 . 
         [0032]      FIG. 5  is the elevation view of  FIG. 4  after a greater portion of the sprag tool  10  comprising both the lower arrangement  11  and the upper arrangement  21  of sprags is inserted into the bore of the add-on pipe segment  22 . The insertion of the greater portion of the sprag tool  10  comprising both the lower arrangement  11  and the upper arrangement  21  of sprags  12  into the bore of the add-on pipe segment  22  enables rotation of the add-on pipe segment  22  about its axis in either direction if the sprags  12  that comprise the upper arrangement  21  are reversed from their orientation within the lower arrangement  11 . In the event of a need to break out a threaded connection between the add-on pipe segment  22  and the pipe string  80 , simply lowering the traveling block  8  and the sprag support  13  further into the bore of the add-on pipe segment  22  until the upper arrangement  21  of sprags  12  enters the bore, and rotating the sprag support  13  in the reverse direction from that which causes the lower arrangement  11  of sprags  12  to grip, will cause the upper arrangement  21  of sprags  12  to grip the interior wall of the add-on pipe segment  22  and rotate the add-on pipe segment to break out the threaded connection. While the lower arrangement  11  is predisposed to slip within the bore of the add-on pipe segment upon rotation in a first direction, the upper arrangement  21  of sprags  12  is reversed from the lower arrangement  11 , and will grip and rotate the add-on pipe segment  22  whereas slipping would have otherwise been permitted by the lower arrangement  11 . Accordingly, a sprag tool  10  such as that shown in  FIG. 5  having two or more spaced-apart arrangements of sprags—one arrangement reversed relative to the other—enables easy switching of modes from make up to break out. 
         [0033]      FIG. 6  is a top cross-sectional view of the sprag tool  10  of  FIG. 2  revealing the shape and profile of the lower arrangement  11  of relaxed sprags  12  supported on the sprag support  13  prior to insertion of the sprag tool  10  into the bore of the add-on pipe segment  22 . The sprags  12  are arranged in a ring that is generally shaped like a ripping blade for a circular saw.  FIG. 6A  is an enlarged view of one embodiment of a sprag  12  that may be used on the sprag tool of  FIG. 6 . The sprag  12  in  FIG. 6A  is shown in a relaxed configuration. As shown in  FIG. 6A , each sprag  12  generally comprises a base  12 A, a top portion  12 B, an interrupted side  12 C and a substantially uninterrupted side  12 D. The sprag  12  is secured at its base  12 A to the sprag support  13 . The base  12 A is secured to the sprag support  13  and the top portion  12 B extends generally radially away from the base  12 A. The interrupted side  12 C comprises a large recess, gap or void portion in the sprag  12  that allows the sprag  12  to lean, fold or collapse in response to a force applied laterally to the sprag  12  near the top portion  12 B and generally along the direction of the arrow  50 . The substantially uninterrupted side  12 D of the sprag  12  is generally opposite the interrupted side  12 C and is structured to resist leaning, folding or collapsing in response to a force applied laterally to the sprag  12  near the top portion  12 B and generally along the direction of the arrow  52 . 
         [0034]    The two distinct modes of deformation of the sprag  12  described in relation to  FIG. 6A  are illustrated in  FIGS. 7A and 7B .  FIG. 7A  is a cross-sectional view of the lower arrangement  11  of deformed sprags  12 ′ shown in  FIG. 6  after the sprag tool  10  inserted into the bore of the add-on pipe segment  22  and the sprag support  13  is rotated by the top drive assembly  17  in the direction of the arrow  60 . The deformed sprags  12 ′ are shown to be compliantly deformed, each by a force applied by the interior wall  22 C of the add-on pipe segment  22  and in the direction shown by the arrow  50  in  FIG. 6A . The leaned, folded or collapsed sprag  12 ′ slides along the interior wall  22 C of the add-on pipe segment  22  during rotation of the sprag support  13  in the direction of arrow  60 . Each deformed sprag  12 ′ imparts minimal friction to the interior wall  22 C because there is little force imparted by each deformed sprag  12 ′ to the interior wall  22 C. The resulting rotational torque applied by the leaning, folded or collapsed sprags  12 ′ to the add-on pipe segment  22  is illustrated by the direction and length of arrows  64 . 
         [0035]    It should be noted that there are a variety of sprag shapes that may provide the ratchet-like function of the sprag tool. The shape of the sprag, in additional to its elastomeric properties, provides for its ratchet-like function in the present invention. One embodiment of a sprag used on a tool of the present invention comprises a base for being secured to a sprag support, a top of the sprag generally opposite the base for contacting the wall of an add-on pipe segment, and two sides generally intermediate the base and the top of the sprag. The sprag is generally flexible to enable it to be placed into an annular space between the sprag support and the wall of an add-on pipe segment. 
         [0036]    One side of the sprag is generally interrupted to allow the sprag to lean, fold or generally collapse when a generally lateral force is applied by movement of sprag support relative to the contacted wall of the add-on pipe segment, near the top of the sprag, and in the direction toward the generally interrupted side of the sprag. The leaning, folding or collapsing of each sprag in response to the lateral force applied as a result of movement of the sprag tool relative to the wall of the add-on pipe segment results in relatively little force applied by the sprag to the wall of the add-on pipe segment and, as a result, little frictional resistance to sliding movement of the wall of the add-on pipe segment relative to the sprag. It should be appreciated that the frictional force applied by the sprag to resist relative movement of the wall of the add-on pipe segment is a function of the force applied by the sprag to the wall, the area of contact between the sprag and the wall, and the coefficient of friction between the sprag material and the wall. 
         [0037]      FIG. 7B  is the cross-section view of the lower arrangement  11  of deformed sprags  12 ″ shown in  FIG. 6  after the sprag tool  10  inserted into the bore of the add-on pipe segment  22  and the sprag support  13  is rotated by the top drive assembly  17  in the direction of the arrow  62 . The deformed sprags  12 ″ are shown to be deformed to a generally non-compliant configuration, each by a force applied by the interior wall  22 C of the add-on pipe segment  22  and in the direction shown by the arrow  52  in  FIG. 6A . The generally collapse-resistant sprag  12 ″ bends to a configuration that compresses between the interior wall  22 C of the add-on pipe segment  22  during rotation of the sprag support  13  in the direction of arrow  62 . Each non-compliant and compressibly deformed sprag  12 ″ imparts substantial friction to the interior wall  22 C because there is a great force imparted by each compressibly deformed sprag  12 ″ to the interior wall  22 C. The resulting rotational torque applied by the sprags  12 ″ to the add-on pipe segment  22  is illustrated by the direction and length of arrows  66 . 
         [0038]    The embodiment of the sprag tool  10  shown in the appended drawings is rotatably suspended from a rotatable quill of a top drive assembly  17 , and positionable above and alignable with a pipe string  80  suspended in a borehole (not shown) using a spider  25 . It should be understood that any tool that provides for supporting and rotating the sprag tool  10  may be substituted without loss of function. 
         [0039]    It should be understood that the capacity of a sprag tool to impart torque to an add-on pipe segment may vary according to the number, size and shape of the sprags. Also, additional torquing capacity may be achieved by including multiple rows or rings of sprags within an arrangement. For example, an arrangement of sprags resembling those shown in the lower arrangement  11  in  FIG. 2  that were secured on the exterior surface of a 16-inch cylindrical support produced 4,200 ft-lbs of torque on a 20-inch add-on pipe segment when the sprag tool was inserted into the bore of the add-on pipe segment and rotated using a simulated top drive. This amount of torque may be readily doubled by securing two adjacent rows or rings of sprags into a single arrangement. In this manner, unless the add-on pipe segment is somehow obstructed or is extremely short, almost any reasonable torque may be attained using a sprag tool of the present invention. 
         [0040]    The terms “comprising,” “including,” and “having,” as used in the claims and specification herein, indicate an open group that includes other elements or features not specified. The term “consisting essentially of,” as used in the claims and specification herein, indicates a partially open group that includes other elements not specified, so long as those other elements or features do not materially alter the basic and novel characteristics of the claimed invention. The terms “a,” “an” and the singular forms of words include the plural form of the same words, and the terms mean that one or more of something is provided. The terms “at least one” and “one or more” are used interchangeably. 
         [0041]    The term “one” or “single” shall be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as “two,” are used when a specific number of things is intended. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention. 
         [0042]    It should be understood from the foregoing description that various modifications and changes may be made in the preferred embodiments of the present invention without departing from its true spirit. The foregoing description is provided for the purpose of illustration only and should not be construed in a limiting sense. Only the language of the following claims should limit the scope of this invention.