A grip extension linkage to provide a gripping tool having radial gripping elements with an improved operational range. The grip extension linkage includes at least one annular body having a central internal bore and an peripheral external surface. There is provided rigid elongated spokes. Spoke guides are provided on the annular body. The spoke guides are in close fitting relation with the spokes to constrain the spokes while allowing them to move radially from a retracted position to an engaged position.

FIELD OF THE INVENTION 
     This invention relates intentionally to applications where tubulars and tubular strings must be gripped, handled and hoisted with a tool connected to a drive head or reaction frame to enable the transfer of both axial and torsional loads into or from the tubular segment being gripped. In the field of earth drilling, well construction and well servicing with drilling and service rigs this invention relates to slips, and more specifically, on rigs employing top drives, applies to tubular running tools that attach to the top drive for gripping the proximal segment of tubular strings being assembled into, deployed in or removed from the well bore. Such tubular running tools support various functions necessary or beneficial to these operations including rapid engagement and release, hoisting, pushing, rotating and flow of pressurized fluid into and out of the tubular string. This invention provides linkages to extend or improve the gripping range of such tubular running tools. 
     BACKGROUND OF THE INVENTION 
     Until recently, power tongs were the established method used to run casing or tubing strings into or out of petroleum wells, in coordination with the drilling rig hoisting system. This power tong method allows such tubular strings, comprised of pipe segments or joints with mating threaded ends, to be relatively efficiently assembled by screwing together the mated threaded ends (make-up) to form threaded connections between sequential pipe segments as they are added to the string being installed in the well bore; or conversely removed and disassembled (break-out). But this power tong method does not simultaneously support other beneficial functions such as rotating, pushing or fluid filling, after a pipe segment is added to or removed from the string, and while the string is being lowered or raised in the well bore. Running tubulars with tongs also typically requires personnel deployment in relatively higher hazard locations such as on the rig floor or more significantly, above the rig floor, on the so called ‘stabbing boards’. 
     The advent of drilling rigs equipped with top drives has enabled a new method of running tubulars, and in particular casing, where the top drive is equipped with a so called ‘top drive tubular running tool’ to grip and perhaps seal between the proximal pipe segment and top drive quill. (It should be understood here that the term top drive quill is generally meant to include such drive string components as may be attached thereto, the distal end thereof effectively acting as an extension of the quill.) Various devices to generally accomplish this purpose of ‘top drive casing running’ have therefore been developed. Using these devices in coordination with the top drive allows hoisting, rotating, pushing and filling of the casing string with drilling fluid while running, thus removing the limitations associated with power tongs. Simultaneously, automation of the gripping mechanism combined with the inherent advantages of the top drive reduces the level of human involvement required with power tong running processes and thus improves safety. 
     In addition, to handle and run casing with such top drive tubular running tools, the string weight must be transferred from the top drive to a support device when the proximal or active pipe segments are being added or removed from the otherwise assembled string. This function is typically provided by an ‘annular wedge grip’ axial load activated gripping device that uses ‘slips’ or jaws placed in a hollow ‘slip bowl’ through which the casing is run, where the slip bowl has a frusto-conical bore with downward decreasing diameter and is supported in or on the rig floor. The slips then acting as annular wedges between the pipe segment at the proximal end of the string and the frusto-conical interior surface of the slip bowl, tractionally grip the pipe but slide or slip downward and thus radially inward on the interior surface of the slip bowl as string weight is transferred to the grip. The radial force between the slips and pipe body is thus axial load self-activated or ‘self-energized’, i.e., considering tractional capacity the dependent and string weight the independent variable, a positive feedback loop exists where the independent variable of string weight is positively fed back to control radial grip force which monotonically acts to control tractional capacity or resistance to sliding, the dependent variable. Similarly, make-up and break-out torque applied to the active pipe segment must also be reacted out of the proximal end of the assembled string. This function is typically provided by tongs which have grips that engage the proximal pipe segment and an arm attached by a link such as a chain or cable to the rig structure to prevent rotation and thereby react torque not otherwise reacted by the slips in the slip bowl. The grip force of such tongs is similarly typically self-activated or ‘self-energized’ by positive feed back from applied torque load. 
     In general terms, the gripping tool of PCT patent application CA 2006/00710 and U.S. national phase application Ser. No. 11/912,665, may be summarized as a gripping tool which includes a body assembly, having a load adaptor coupled for axial load transfer to the remainder of the body, or more briefly the main body, the load adaptor adapted to be structurally connected to one of a drive head or reaction frame, a gripping assembly carried by the main body and having a grip surface, which gripping assembly is provided with activating means to radially stroke or move from a retracted position to an engaged position to radially tractionally engage the grip surface with either an interior surface or exterior surface of a work piece in response to relative axial movement or axial stroke of the main body in at least one direction, relative to the grip surface. A linkage is provided acting between the body assembly and the gripping assembly which, upon relative rotation in at least one direction of the load adaptor relative to the grip surface, results in relative axial displacement of the main body with respect to the gripping assembly to move the gripping assembly from the retracted to the engaged position in accordance with the action of the activating means. 
     This gripping tool thus utilizes a mechanically activated grip mechanism that generates its gripping force in response to axial load or axial stroke activation of the grip assembly, which activation occurs either together with or independently from, externally applied axial load and externally applied torsion load, in the form of applied right or left hand torque, which loads are carried across the tool from the load adaptor of the body assembly to the grip surface of the gripping assembly, in tractional engagement with the work piece. 
     It will be apparent that the utility of this or other similar gripping tools is a function of the range of work piece sizes, typically expressed as minimum and maximum diameters for tubular work pieces, which can be accommodated between the fully retracted and fully extended grip surface positions of a given gripping tool, i.e., the radial size and radial stroke of the gripping surface. The utility of a given gripping tool can be improved if it can accommodate a greater range of work pieces sizes. The present invention is directed toward meeting this need in applications where greater radial size and radial stroke are beneficial such as often occurs when adapting gripping tools for running oilfield tubulars. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention there is provided a grip extension linkage to provide a gripping tool having radial gripping elements with an improved operational range. The grip extension linkage includes at least one annular body having a central internal bore and a peripheral external surface. There is provided rigid elongated spokes. Spoke guides are provided on the annular body. The spoke guides are in close fitting relation with the spokes to constrain the spokes while allowing them to move radially from a retracted position to an engaged position. 
     According to another aspect of the present invention there is a method in which the above described grip extension linkage is used to improve the operational range of the gripping tool having radial gripping elements. This involves positioning one of a work piece or a cylindrical gripping tool within the central internal bore of the at least one annular body and the other of the work piece or the cylindrical gripping tool around the peripheral external surface of the at least one annular body. This places the spokes in an annular space between the gripping elements of the gripping tool and the work piece. A first end of each of the spokes engages the gripping elements and a second end of each of the spokes either directly or indirectly engages the work piece. When the gripping elements of the gripping tool are moved radially to apply pressure on the first end of each of the spokes, the spokes moving radially from a retracted position to an extended position and act as radial extensions of the gripping elements of the gripping tool. 
     As noted above, the spokes can act either directly or indirectly upon the work piece. There will hereafter be further described a configuration in which the spokes indirectly engage the work piece. In that embodiment, slave gripping elements are positioned at a second end of each of the spokes. Radial movement of the gripping elements of the gripping tool are transferred via the spokes to the slave gripping elements. 
     As noted above, either the work piece or the gripping tool may be positioned within the central internal bore. When the work piece is positioned within the central internal bore, an interior surface of the gripping tool is positioned around the periphery of the body and the second end of each of the spokes directly or indirectly engage an exterior surface of the work piece. When the gripping tool is positioned within the central internal bore, an interior surface of the work piece is positioned around the periphery of the body and the second end of each of the spokes directly or indirectly engage the interior surface of the work piece. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to in any way limit the scope of the invention to the particular embodiment or embodiments shown, wherein: 
         FIG. 1  is a schematic of a grip surface extension linkage located internal to a tubular work piece. 
         FIG. 2  is an external view of an internal grip tubular running tool with grip surface extension linkage assembly. 
         FIG. 3  is an external trimetric view of a grip surface extension linkage assembly. 
         FIG. 4  is an external trimetric view of a primary guide plate. 
         FIG. 5  is an external trimetric view of a secondary guide plate. 
         FIG. 6  is a cross section view of a grip surface extension linkage assembly. 
         FIG. 7  is a cross section view of a spoke assembly. 
         FIG. 8  is an axial cross section view of a grip surface extension linkage shown as it would appear located internal to and coaxially with a work piece. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     General Principles 
     Referring now to  FIG. 1  showing a schematic of a cross section through a radial plane of grip surface extension linkage  50  comprised of spokes  51  and spoke guides  52  shown as a plurality of elements disposed inside tubular work piece  53  and are understood to act together as a rigid body (attached to each other out of the two dimensional plane of view). Spokes  51  are arranged with extended grip surface  54  close fitting with tubular work piece  53  and gripping tool grip or interface surface  55 . Force vectors as might typically be applied at gripping tool interface surface  55  by a gripping tool to apply torque through grip surface extension linkage  50  to work piece  53  and the resultant forces at grip surface  54 , are shown on one spoke  51 , where it will be apparent to one skilled in the art that the tangential force vectors “T i ” and “T o ” will most typically be less than the radial force vector “R i ” and “R o ” as required to meet typical frictional grip/work piece interfacial properties, and as such relatively short radial spokes will tend to be stable while relatively tall radial spokes may tend to roll and apply excessive prying loads as rolling is prevented by a radial non-uniform load distribution at interface  56  between the spoke  51  and work piece  53  and interface  55  between spoke  51  and gripping tool (not shown). To stabilize and prevent excessive radial prying loads, extension linkage  50  is provided with at least one rigid spoke guide  52  arranged to act between adjacent spokes  51  and providing a parallel guide contact face  57  at each spoke guide interface  58  that is sufficiently close fitting with spokes  51  and also sufficiently rigid such that any tendency of spoke  51  to roll will be prevented by contact with spoke guide interfaces  58  resulting in moment reaction contact stress illustrated by vectors “w i ” and “w o ” acting at radially inner and outer locations respectively, while guide contact face  57  is sufficiently smooth so as to facilitate radial sliding engagement at spoke guide interface  58  and to allow for radial motion of the spoke  51  under load and consequently allowing extended grip surface  54  to move radially and engage work piece  53 . It will now be evident that grip surface extension linkage  50  provides a structure that transfers radial and torsional load from gripping tool interface  55  to extended grip surface  54  and prevents the tendency of spokes  51  to rotate or impose undue reaction moments at either spoke guide interface  58  or at the work piece  53  interface with extended grip surface  54 . 
     Grip Surface Extension Linkage 
     Referring to  FIGS. 2 through 8 , there will now be described a preferred embodiment of the present invention referred to here as a grip surface extension linkage, previously described in principal with reference to  FIG. 1 . Referring first to  FIG. 2 , internal gripping tubular running tool  100  is shown configured with grip surface extension linkage assembly  400  adapted to mate with and be carried by lower end  109  of grip assembly  120 . Assembly  400  is comprised of a plurality of radial oriented spokes  480  (shown here as five (5) matching the number of jaws  160 ), primary and secondary spoke guide plates  460  and  470  respectively, segmented retainer ring  520 , and threaded retainer ring  530 . Primary spoke guide plate  460  is coaxially located at the upper ends  481  of spokes  480  and similarly secondary spoke guide plate  470  is located at the lower ends  482  of spokes  480 , where the spokes  480  engage with inward facing primary and secondary radial grooves,  465  and  475  respectively, provided in guide plates  460  and  470 , respectively to thus form spoke guides as previously described with reference to  FIG. 1 . Referring still to  FIG. 2 , slots  497  can be provided for the placement of garter springs  507  (see  FIG. 6  and  FIG. 7 ) to facilitate spoke  480  refraction. Referring now to  FIG. 3 , showing a trimetric external view of grip surface extension linkage assembly  400  provided separate from the running tool, spokes  480  are provided as assemblies of radially inner web elements  490  rigidly connected to radially outer die elements  500  carrying extended grip surface  504  configured to engage with a work piece (not shown). 
     Referring now to  FIG. 4 , which shows primary guide plate  460  in an external trimetric view, primary guide plate  460  has top end  461 , bottom end  462 , internal bore  463  and external surface  464 . Primary guide plate  460  has a plurality of radial grooves  465 , in this case five, each defined by load faces  466  and  467  on the bottom end  462  extending from internal bore  463  to external surface  464 . Located adjacent to and concentric with internal bore  463  and at the bottom end  462  of guide plate  460  is garter spring groove  468  and stroke limit rib  469 . On the top end  461  of guide plate  460  located concentric with and adjacent to internal bore  463  is retaining ring locating groove  459 . 
     Referring again to  FIG. 3 , grip surface extension linkage assembly  400  is provided with a retainer ring  520  comprised of a plurality of retainer ring segments  521 , in this case five, having upper face  522 , lower face  523 , inner face  524  and outer face  525 . Retainer ring  520  is located adjacent to primary guide plate  460  such that lower face  523  mates with and is rigidly attached to retaining ring locating groove  459  on top face  461  of guide plate  460  by bolts (not shown). Inner face  524  of retainer ring  520  has internal upset section  526  designed to engage, referring now to  FIG. 1 , axial retention groove  148  to thus constrain relative axial movement of primary guide plate of  460  on gripping tool  100 . 
     Referring now to  FIG. 5 , showing secondary guide plate  470  in an external trimetric view, having top end  471 , bottom face  472 , internal bore  473  and external surface  474 . Secondary guide plate  470  has a plurality of radial grooves  475 , in this case five, each defined by load faces  476  and  477  on the top end  471  extending from internal bore  473  to external surface  474 . Located adjacent to and concentric with internal bore  473  and at the bottom end  472  of guide plate  470  is retaining spring guide shoulder  478  and stroke limit rib  479 . 
     Referring now to  FIG. 6 , showing a cross section view of assembly  400 , threaded retainer ring  530  with top face  531 , inside surface  532  and bottom face  533 , has seal element  534  on top face  531  and thread element  535  on inside surface  532 . Threaded retainer ring  530  is arranged concentrically with secondary guide plate  470  having thread element  535  designed to threadingly engage, referring now to  FIG. 2 , cage  144  of tubular running tool  100 . Referring again to  FIG. 6 , top face  531  of ring  530  engages bottom face  472  of guide plate  470 , thereby axially constraining relative downward movement of secondary guide plate  470  and grip surface extension linkage assembly  400 . 
     Referring now to  FIG. 7 , a single spoke assembly  480  is shown in a section view, which in this embodiment of the present invention consists of web  490  and die  500 . However, it is understood that the present invention is not limited to this arrangement. The number of spoke components may be selected as desired, to provide ease of manufacture, interchange of parts between sizes, component strength as required by and specifically relating to radial extent of die and length of circumferential overhang. Referring still to  FIG. 7 , generally elongate web  490  has top end  491 , bottom end  492 , internal surface  493 , and external surface  494 . External surface  494  is provided with a plurality of axial load lugs  496  generally arranged between the top end  491  and the bottom end  492 , while internal surface  493  is provided with a plurality of axial load grooves  495  arranged between the top end  491  and bottom end  492 . Web  490  has a plurality of circumferential retaining spring grooves  497 , in this case four, located one at top end  491 , one at bottom end  492  (both of which accommodate garter springs  507  that directly retains the web  490 ), and two located along internal surface  493  which provide clearance for additional garter springs that directly retain the jaw  160  of tubular running tool  100  (not shown), and two retaining lips  498 , one on either side, axially oriented and extending between top end  491  and bottom end  492 . The thickness of web  490  is generally governed by the thickness of jaw  160  and by the requirement to have some non-zero cage thickness between said jaw  160  while maximizing mandrel contact area. 
     Referring still to  FIG. 7 , die  500  with top end  501 , bottom end  502 , internal face  503  and external grip surface  504 , has a plurality of laterally oriented axial retaining grooves  505  generally arranged on internal surface  503  between top end  501  and bottom end  502 . Referring now to  FIG. 3 , die  500  is attached to web  490  by bolts (not shown) arranged in bolt holes  509 . Referring now to  FIG. 7 , internal surface  503  of die  500  mates and interlocks with external surface  494  of web  490 , such that axial retaining grooves  505  of die  500  engage axial load lugs  496  of web  490 , and referring now to  FIG. 8 , which shows an axially oriented section view of grip surface extension linkage assembly  400 , lateral retaining lips  506  of die  500  overhang and engage with lateral faces  511  of web  490  which collectively provide means to transfer axial, circumferential and radial load between web  490  and die  500 . Referring now to  FIG. 2 , internal surface  493  of web  490  is designed to mate and interlock with the external gripping surface  164  of jaw  160  of tubular running tool  100  (not shown) and provide means to transfer load between the tubular running tool  100  and web  490  in a manner analogous to the load transfer between web  490  and die  500 . 
     Referring again to  FIG. 8 , extended grip surface  504  of die  500  is generally configured with a friction enhancing surface (not shown) designed to provide a balance between surface penetration and friction characteristics and to provide a relatively large contact area to distribute radial contact load and consequently minimize deformation of work piece  401  while tractionally engaging internal surface  402  of work piece  401 , and providing means to transfer axial, circumferential and radial load between die  500  and work piece  401 . 
     Referring again to  FIG. 6 , stroke limit rib  469  and  479  on guide plate  460  and,  470  respectively act in conjunction with spring retaining grooves  497  on top end  491  and bottom end  492  of web  490  and function as rigid stops by engaging if spoke assemblies  480  move radially past the design stroke limit. Referring now to  FIG. 3 , spokes  480  of grip surface extension linkage assembly  400  are located axially between primary guide plate  460  and secondary guide plate  470  and aligned in guide grooves  465  and  475  respectively such that lateral faces  511  of web  490  slidingly engage said guide grooves and function to react lateral forces resultant on spoke assemblies  480  due to torsion applied to tubular running tool interface  499  on inner surface  493  of web  490  as previously described with reference to  FIG. 1 . 
     Referring again to  FIG. 2 , grip surface extension linkage assembly  400  is located external to and co-axial with tubular running tool  100 , where gripping tool interface surfaces  499  of spokes  480  are engaged with the gripping surface  164  of jaws  160  of the grip assembly  120  and where spokes  480  can be circumferentially aligned with the jaws of tubular running tool  100 . It is understood also that the number of spokes  480  can be equal to the number of jaws  160  on the tubular running tool  100 . Referring now to  FIG. 8 , it will be apparent to one skilled in the art that the grip surface extension linkage is not necessarily associated with or attached to a specific tubular running tool, and as such said linkage assembly  400  can be provided with an integral link between primary and secondary guide plates  460  and  470  respectively to prevent relative axial movement but allow some relative rotation of each guide plate about the axis of linkage assembly  400 . In this case assembly  400  can be provided a means of axial retention in a work-piece  401  such that the grip surface extension linkage assembly  400  would first be inserted into said work-piece and to grip said work-piece, a tubular running tool (not shown) would subsequently be inserted into the grip surface extension linkage assembly  400  and activation of said tubular running tool would activate the grip surface extension linkage assembly  400 . It will be apparent that an arrangement such as this might be beneficial in an application where multiple work-pieces of different sizes were being gripping in quick succession. 
     In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. 
     It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the spirit and scope of the invention as hereinafter defined in the Claims.