Patent Publication Number: US-6220807-B1

Title: Tubular handling system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 08/396,204 filed Feb. 28, 1995, now abandoned, which was a continuation of application Ser. No. 07/932,683 filed Aug. 20, 1992 which issued to U.S. Pat. No. 5,458,454 (Oct. 17, 1995). 
    
    
     This invention relates to a tubular or pipe handling system and, more particularly, to a pipe handling system which moves the tubulars from a horizontal position on the piperack located adjacent the drill rig to a vertical position over the well centre and which is adapted for drill rigs used in offshore drilling. 
     BACKGROUND OF THE INVENTION 
     Conventionally, drill rigs have utilized a cable handling system for transferring a tubular such as drill pipe or casing from a piperack adjacent the well to a mousehole or well bore for connection to a previously transferred tubular or drill string. A cable extends from the drill rig and is attached to the selected pipe or tubular on the pipe rack. The tubular lies in a generally horizontal position, box end forward, such that the box end of the pipe is initially pulled from the pipe rack by the cable up the catwalk of the rig and through the V-door to assume a substantially vertical position above the drill floor. The lower end is then placed into the mousehole or well bore for connection to the previously transferred pipe and the cable is disconnected. 
     There are disadvantages inherent in the conventional cable handling technique. The manual involvement of attaching the head of a cable to the tubular and the subsequent movement of the pipe during the transfer operation in the vicinity of a worker gives rise to dangerous working conditions and pipe handling is a major source of injuries on a drill rig, particularly in offshore drilling operations. Secondly, pipe and particularly casing, is expensive. As the tubular is transferred from the pipe rack to the drill floor utilising the cable, contact between the tubular and the catwalk or other portions of the rig is made which can cause damage to the tubular and affect the integrity of the connections between successive ones of the tubulars. This is particularly true where casing is involved. 
     Prior art apparatuses other than cable handling techniques for gripping a drill pipe and transferring the pipe from a horizontal position on the piperack to a vertical position above the drill floor are known. In some of such prior art apparatuses, pipe handling apparatuses provide pipe handling without the necessity of manual interaction in grasping the pipe or transferring the pipe to the rig. One such apparatus is disclosed in U.S. Pat. No. 3,633,771 to Woolslayer et al which teaches a drill string moved by a strongback having hydraulic grasping jaws mounted a distance apart which exceed the length of a single drill pipe. This apparatus is mounted to the drilling platform and is centered in the V-door of the rig. 
     A second apparatus is that disclosed in U.S. Pat. No. 4,834,604 to Brittain et al. This patent teaches a strongback which is connected to a one-piece boom, the boom being mounted on a base located adjacent the rig and operating directly through the V-door of the rig. The strongback transfers pipe through the V-door to a vertical position and raises or lowers the pipe so that connection between the pipe and the drill string can occur. 
     Other prior art used to transfer tubulars does not provide the conventional movement of the tubular box end forward and pin end down in the vertical position; that is, the tubular is moved and must be rotated such that the pin end is in a downwardly directed direction for attachment to the drill string. This may necessitate the design of a special structure for the rig or, alternatively, it may require that the rig structure be modified to accommodate the pipe handling system. 
     A disadvantage with all of the prior art set forth above arises when breakdown of the pipe handling apparatus occurs. In this event, the breakdown may terminate the installation of the drill pipe or casing since the conventional cable handling technique for tubular transfer cannot be used as a backup. The apparatuses utilised may obstruct the catwalk or otherwise require substantial modification to the rig in order to allow conventional cable operation after breakdown. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a method of moving tubulars from a substantially horizontal position on a pipe rack to a substantially vertical position above the drill floor of a drill rig, comprising the steps of: 
     (a) simultaneously moving a bicep arm assembly pivotally connected to the structure of a drill rig, a forearm assembly pivotally connected to said bicep arm assembly, and a gripper head assembly pivotally connected to said bicep arm assembly into proximity with said tubular; 
     (b) grasping said tubular with said gripper head assembly; 
     (c) transferring said tubular box end forward into a position over the drill floor of said drill rig with said gripper head assembly, said forearm assembly and said bicep arm assembly; and 
     (d) rotating said tubular through approximately ninety (90) degrees from said horizontal to said vertical position during said transfer from said piperack to said vertical position. 
     According to a further aspect of the invention, there is provided a pipe handling system for a drill rig comprising a bicep arm assembly pivotally connected to a base plate, a forearm assembly pivotally attached to the distant end of said bicep arm assembly, a gripper head pivotally connected to the distant end of said forearm assembly and means for mounting said bicep arm assembly to the structure of a drill rig such that said forearm assembly and said gripper head are operable to move tubulars from a piperack into a position above the drill floor of said drill rig. 
     According to yet a further aspect of the invention, there is provided a pipe handling system comprising a bicep arm assembly, a forearm assembly pivotally connected to said bicep arm assembly, the longitudinal central axis of said bicep arm assembly being offset from the longitudinal central axis of said forearm assembly such that the plane of movement of said forearm assembly and a gripper head assembly pivotally connected thereto is offset a predetermined distance from the plane of movement of said bicep arm assembly. 
     According to yet a further aspect of the invention, there is provided a pipe handling system comprising a bicep arm assembly, a forearm assembly pivotally connected to said bicep arm assembly, a gripper head assembly pivotally connected to said forearm assembly and means for mounting said bicep arm assembly to the structure of a drill rig, said mounting means comprising a base plate operable to attach to a base mounting plate connected to said structure of said drill rig, said base plate being operable to move with said bicep arm assembly, said forearm assembly and said gripper head assembly relative to the base mounting plate connected to said drill rig. 
     According to yet a further aspect of the invention, there is provided a pipe handling system comprising a bicep arm assembly, a forearm assembly pivotally connected to said bicep arm assembly and a gripper head assembly pivotally connected to said forearm assembly for gripping and moving a tubular from a horizontal position on a piperack to a near vertical position above the drill floor of a drill rig, said gripper head assembly being pivotal relative to said forearm assembly about at least two axes thereby allowing said tubular to be inclined slightly when said tubular reaches a position above said drill floor. 
     According to yet a further aspect of the invention, there is provided a gripper head assembly for a pipe handling system, said gripper head assembly comprising an upper gripper assembly, a taper lock assembly and a clamping assembly operably connected to a lower gripper assembly and means to removably connect said lower gripper assembly to said upper gripper assembly. 
    
    
     BRIEF SUMMARY OF THE SEVERAL VIEWS OF THE DRAWINGS 
     An embodiment of the invention will now be described, by way of example only, with the use of drawings in which: 
     FIG. 1 is a side view of the pipe handling system according to the invention in the process of grasping the tubular and commencing the transfer of the tubular from its horizontal position in the piperack adjacent the well bore; 
     FIG. 2 is a side view of the pipe handling system of FIG. 1 with the tubular in its vertical position over the centre of the well bore and illustrating the gripper head assembly, the forearm assembly and the bicep arm assembly in greater detail; 
     FIG. 3 is a front view of the pipe handling system of FIGS. 1 and 2 particularly illustrating the position of the forearm assembly with the tubular in moving the tubular from the piperack to the drill floor; 
     FIG. 4 is a front detail view of the base plate to which is attached the bicep arm assembly and its linear actuator; 
     FIGS. 5A and 5B are cutaway assembly views of the main and outer shafts of the bicep arm assembly and their various mounted components; 
     FIG. 6 is a diagrammatic plan view illustrating one latch of the clamping assembly used on the gripper head; 
     FIG. 7A is a plan view of the taper lock assembly used on the gripper head; 
     FIG. 7B is a cutaway sectional view taken along B—B of FIG. 7A; 
     FIG. 7C is a cutaway sectional view taken along C—C of FIG. 7A; 
     FIG. 8 is a schematic diagram illustrating the sensor and control system of the pipe handling system according to the invention; and 
     FIG. 9 is a diagrammatic side view of the pipe handling system illustrating the operating sequence of arm and gripper locations in transferring the tubular from the piperack to a vertical position on the drill floor of the rig. 
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENT 
     Referring now to the drawings, a pipe handling system according to the invention is illustrated generally at  10  in FIG.  1 . The pipe handling system  10  is connected to the structure  11  of a drill rig generally illustrated at  12  by a base plate  40  (FIG. 3) in a manner to be described. The pipe handling system  10  is used to move a tubular such as drill pipe or casing  13  from a horizontal position in the pipe rack  14  (FIG. 1) to a vertical position (FIG. 2) wherein the tubular may be connected to the drill string or previously transferred casing which extends from the well bore or mousehole as will be described in greater detail hereafter. 
     The pipe handling system  10  comprises four (4) principal components, namely a mounting assembly generally illustrated at  21  which includes the base plate  40  and which is adapted to connect the bicep arm assembly  22  to the structure of the drill rig  12 , the bicep arm assembly  22  which is pivotally connected to the mounting assembly  21 , a forearm assembly generally illustrated at  23  which is pivotally connected to the bicep arm assembly  22  at axis  25  and which comprises an outer forearm  30  and an inner forearm  31  movable relative to the outer forearm  30  and a gripper head assembly generally illustrated at  21  which is pivotally connected to the forearm assembly  23  by pin joint  26  as will be described in greater detail. 
     The mounting assembly  21  is best illustrated in FIGS. 3 and 4. A base mounting plate  41  is connected to the structure of the drill rig  12 . A base plate  40  is mounted thereon for sliding horizontal movement relative to the base mounting plate  41 . This is provided by a series of holes  42  extending through the lower end of the base plate  40  and bolts  43  extending through the holes  42  in base plate  40  and into threaded receiver holes  44  in base mounting plate  41 . A second series of threaded receiver holes  44  are provided in base plate  40  and a slot  45  is provided in the base mounting plate  41  to allow relative movement between the base plate  40  and the base mounting plate  41 . Bolts  51  are adapted to pass through the slot  45  in base plate  40  and are threadedly engaged with the receiver holes  44  in base mounting plate  41 . When the bolts  51  between base plate  40  and base mounting plate  41  extending through slot  45  are loosened and the bolts  43  extending through the base plate  40  into the base mounting plate  41  are removed, the base plate  40  may slide horizontally, together with the bicep arm assembly  22 , relative to the base mounting plate  41 , a distance sufficient to allow the forearm assembly  23  to move to the left and out of the area central of the catwalk  53  as best illustrated in FIG.  3 . 
     A bicep cylinder  54 , conveniently a linear actuator, is mounted between the arms  60  of base plate  40  (FIG.  4 ). The bicep cylinder  54  extends outwardly and connects with the bicep arm bracket  61  as best seen in FIG.  1 . Movement of the bicep cylinder  54  will rotate the bicep arm  22  about axis  71  relative to the base plate  40 . A second linear actuator  62  is mounted between the base plate  40  and a chain drive or actuator arm  63 . The actuator arm  63  is used to provide movement to the chain drive generally illustrated at  70  in a manner as will be more particularly described hereafter. 
     The main shaft assembly generally illustrated at  72  is illustrated in more detail in FIG.  5 A and includes the chain drive  70 . The main shaft  73  is mounted on bearings  75  in bearing housings  74  on opposite ends of the base plate  40 . A splined hub  80  is mounted to main shaft  73  and carries the actuator arm  63  (FIG. 1) which moves the main shaft  73  under the influence of aforementioned linear actuator  62 . Bearing bushings  81  are provided between the housing  64  of the bicep arm assembly  22  which bearings  81  allow rotation of the main shaft  73 . 
     Two sprockets  82  are provided which are keyed to the main shaft  73  and rotate simultaneously therewith when the actuator arm  63  moves the splined hub  80 . Chains  83  are mounted to each of the sprockets  82  and extend to sprockets  84  on the outer shaft assembly generally illustrated at  90  in FIG.  5 B. 
     The outer shaft  91  (FIG. 5B) is rotatably mounted between bush bearings  92  located within outer bearing housing  93  and inner bearing housing  94 . Each of the bearing housings  93 ,  94  is mounted to the bicep arm housing  64  by cap screws  101 . 
     Outer shaft  91  has a splined hub  102  mounted thereon which is retained by retaining ring  103 . The housing  104  of the outer forearm  30  is connected about the periphery of the splined hub  102  and a slewing ring  110  is provided between the housing  111  extending from inner bearing housing  94  and the outer forearm housing  104  to allow for relative movement therebetween. Hex bolts  112  join the flange  113  of housing  111  to the slewing ring  110  and the slewing ring  110  and outer forearm housing  104 , respectively. 
     Referring again to FIGS. 2 and 3, the forearm assembly  23  includes an outer forearm  30  and an inner forearm  31  which moves longitudinally relative to and within the outer forearm  30  under the influence of a forearm linear actuator  114  connected between bicep arm  22  and inner forearm  31  (FIG. 8) which actuator  114  is located inside outer forearm housing  104  and connected to a bracket  121  connected to the inner end of inner forearm  31 . The distant end of inner forearm  31  is pivotally connected to the gripper head assembly  21 . 
     The gripper head assembly  21  is adapted to grasp is and transfer the tubular  13  under the influence of the movement of the bicep arm assembly  22  and the forearm assembly  23 . The gripper head assembly  21  includes an upper gripper assembly  170  and a lower gripper assembly  166 . The upper gripper assembly  170  includes first and second pins  164 ,  165 , respectively, and the lower gripper assembly  166  includes recesses  167 ,  168  which are adapted to accommodate the pins  164 ,  165  when the upper gripper assembly  170  is removably mounted within the lower gripper assembly  166 . 
     The lower gripper assembly  166  also includes the taper lock assembly  142  (FIG. 7A) and the clamping assembly  136 . The taper lock assembly  142  is shown in detail in FIG.  7 . It comprises two hanger plates  144 ,  145 , the former being mounted on pin  153  and the latter being mounted on a second pin (not shown). A spring  143  is mounted between the inner surfaces  146 ,  147  of the hanger plates  144 ,  145 , respectively, in order to open the hanger plates  144 ,  145  and allow entry of a tubular  13 . 
     Slips  149 ,  150  are mounted to the hanger plates  145 ,  144 , respectively, by threaded portions of pins  153 ,  155 . The slips  149 ,  150  are operably located within a slip bowl  162  which is connected to a hanger bracket assembly  155 . The slips  149 ,  150  are adapted to move axially within the slip bowl  162  under the influence of a solenoid operated hydraulic cylinder  171  which provides movement to the slips  149 ,  150  relative to the slip bowl  162 . 
     The clamping assembly  136  shown diagrammatically in FIG. 6 includes a solenoid operated hydraulic cylinder  135 , a fixed arm  138  and a clamping arm  140 . Clamping arm  140  rotates about axis  141  under the influence of hydraulic cylinder  135 , the clamping arm  140  closing when the hydraulic cylinder  135  is retracted and the clamping arm  140  opening when the hydraulic cylinder  135  is extended. 
     Referring now to FIG. 8, the control system is illustrated generally at  200 . It comprises a sensor cluster  201  for the gripper head assembly  21 , an actuator sensor cluster  202  for the linear actuator  124 , an actuator sensor cluster  203  for the linear actuator  114  associated with the inner forearm  31 , an actuator sensor cluster  204  for the linear actuator  54  associated with the bicep arm  22  and an actuator sensor cluster  210  for the linear actuator  62  associated with the actuator arm  63  driving the chains  83 . All of the sensor clusters  201 ,  202 ,  203 ,  204 ,  210  are connected through the master controller circuit  211  to the solenoid operated taper lock assembly  142 , the clamping assembly  136 , a first linear actuator drive unit  212 , a second linear actuator drive unit  213 , a third linear actuator drive unit  214  and a fourth linear actuator drive unit  220 . 
     The sensor cluster  201  for the gripper head assembly comprises a plurality of pipe detection sensors  221 , a gripper angle sensor  222 , a plurality of pipe in claw sensors  224 , a plurality of claw closed sensors  225 , a plurality of claw open sensors  223  and a weight of pipe sensor  230 . 
     The actuator sensor cluster  202  comprises a position encoder  231  and two proximity switches  232 ,  233 . The actuator sensor cluster  203  comprises a position encoder  234  and two proximity switches  240 ,  241 .The actuator sensor cluster  204  comprises a position encoder  242  and two proximity switches  243 ,  244 . The actuator sensor cluster  210  comprises a position encoder  250  and two proximity switches  251 ,  252 . 
     Operation 
     In operation, it will be assumed that the pipe handling system  10  has been mounted to the structure  11  of the drill rig  12  by the use of mounting assembly  21  as seen in FIG. 1 such that the longitudinal axis  130  of the forearm assembly  23  is generally located directly above the central and longitudinal axis  131  of the catwalk  53  as seen in FIG.  3  and that the bolts  43 ,  44  (FIG. 1) between the base plate  40  and the base mounting plate  41  have been appropriately tightened to prevent play or movement between the base mounting plate  41  and the base plate  40 . It will further be assumed that the tubulars  13  such as drill pipe or casing located horizontally on pipe rack  14  are located a maximum distance from the structure  11  of the rig  12 . 
     The linear actuator  54  for the bicep arm  22 , the linear actuator  114  for the inner forearm assembly  31 , the linear actuator  62  used to drive the chain sprockets  82  and, thence, chain  83  and the linear actuator  124  for the gripper head assembly  21  are all previously programmed by the master controller  211  such that angular orientation of bicep arm  22  relative to the mounting assembly  21 , the s angular orientation of the forearm assembly  23  relative to the bicep arm  22 , the extension of inner forearm  31  relative to the outer forearm  30  of the forearm assembly  23  and the angular orientation of the gripper head assembly  21  relative to the forearm assembly  23  are appropriate to bring the gripper head assembly  21  into proximity with the pipe or casing  13 . 
     As the pipe handling system  10  moves, the sensor clusters  201 ,  202 ,  203 ,  204  and  210  provide the controller  211  with positional information concerning the gripper head assembly  21  by use of the gripper angle sensor  222  and the position encoders  231 ,  234 ,  242  and  250 . These position encoders  231 ,  234 ,  242  and  250  encode the position of the respective linear actuators  124 ,  114 ,  54  and  62 , respectively. The travel limits of each member are determined by proximity switches  232 ,  233 ,  240 ,  241 , which measure the extension of the pistons of the actuators  124 ,  114 ,  54  and  62 , respectively. 
     As the gripper head assembly  21  comes into proximity with the tubular  13 , it is first detected by the pipe detection sensors  221 . The controller  211  will then check the claw open sensors  223  to ensure the taper lock assembly  142  and the clamping assembly  136  are in the open positions. 
     Based on the information from the pipe detection sensors  221 , the gripper angle sensor  222  and position encoders  231 ,  234 ,  242  and  250 , the controller  211  will activate drive units  212 ,  213 ,  214  and  220  toward the tubular  13 . 
     When the tubular  13  is within the taper lock assembly  142  and clamping assembly  136  as indicated by the pipe in claw sensors  224 , the controller  211  activates the solenoids of the hydraulic cylinders  135  (FIGS. 2 and 6) of the clamping assembly  136 . This will retract the pistons  134  relative to the cylinders  135  and rotate the clamping arms  140  about axis  141  and fit the arms about the pipe or casing  13  thereby to hold it within the circumference of the clamping arm  140  and the fixed arm  138 . Likewise, the controller  211  activates the solenoid of the taper lock assembly  142  (FIGS. 2 and 7) such that the taper lock assembly  142  will fit around the circumference of the pipe or casing by means of spring  143  which holds the hanger plates  144 ,  145  apart and which rotate about axis  151  of pin  153  and axis  152  of a second pin (not illustrated), respectively. 
     The claw closed sensors  225  will indicate when the tubular  13  is fully within the taper lock assembly  142  and the clamping assembly  136 . 
     The controller  211  then activates the drive units  212 ,  213 ,  214  and  220  and moves the pipe  13  as instructed by the controller  211  based on the weight of pipe sensor  230 , the gripper angle sensor  222 , the position encoders  231 ,  234 ,  242  and  250  and the proximity switches. 
     As viewed in FIG. 8, the pipe or casing  13  will be moved leftwardly, the box end  154  being movable forward first up the catwalk  53  without coming into contact therewith through the V-door  45  (FIG. 1) of the rig  12  and over the drill floor  46  to its final vertical position where its longitudinal axis is coincident with the axis  160  of the well bore. 
     The hydraulic cylinder  171  (FIG. 7) will then be activated to move the slip  150  relative to the slip bowl  162  and thereby release the pipe or casing  13  held therein. The hydraulic cylinders  135  (FIGS. 2 and 6) are likewise activated so that piston  134  is extended thereby opening clamping arms  140  and allowing release of pipe  13 . The gripper head assembly  21  is then moved away from the vertical standing pipe or casing  13  and back to the pipe rack  14  in order that a further pipe or casing  13  may be obtained and placed in the vertical position as described. 
     The process may, of course, be reversed; that is, the pipe handling system  10  may be used to move pipe or casing  13  from the vertical position on the axis of the well centre  160  into the horizontal position where it can be positioned on the pipe rack  14 . In this event, the various linear actuators and hydraulic cylinders are programmed by the operator to accommodate the reverse process. 
     The gripper head assembly  21  is designed to accommodate the change in diameters of tubulars  13  and may be used with drill pipe and casing of various diameters. In the event a change in the pipe or casing size is required, the gripper head assembly  21  is designed to allow a change in the clamping assembly  136  and the taper lock assembly  142 . To this end, reference is made to FIG. 2 wherein the lower gripper assembly  166  which includes the taper lock assembly  142  and the clamping assembly  136  is removable from the upper gripper assembly  170  which is connected to the inner forearm  31 . A locking pin  163  is manually removed and the recesses  167 ,  168  of the lower gripper assembly  166  move out of engagement with pins  164 ,  165  of the upper gripper assembly  170  by moving the inner forearm  31  connected to the gripper head assembly  21 . A replacement lower gripper assembly (not shown) can then be connected by moving the inner forearm  31  to a position where the recesses  167 ,  168  of the replacement gripper assembly are aligned with the pins  164 ,  165  of the upper gripper assembly  170  and then locking the pins  164 ,  165  into the recesses  167 ,  168  with a manually insertable locking pin  163 . The replacement lower gripper assembly  166  will then move with the upper gripper assembly  170  and will accommodate pipe sizes different from the pipe sizes accommodated by the initial lower gripper assembly  166 . 
     It is desirable to service tubulars ranging from a minimum outside diameter of 2¾ inch. To that end, it has been found that three lower gripper assemblies are necessary to cover the operating ranges. 
     In the event that the pipe handling system  10  breaks down or otherwise becomes inoperable, the conventional cable handling system may be used to reduce or forestall any downtime of the drill rig. To this end, the bolts  43  between the base plate  40  (FIG. 3) and the base mounting plate  41  are removed and the bolts  51  passing between the slot  45  in the base mounting plate  40  and into the base plate  40  are loosened. The base plate  40  is then moved relative to the base mounting plate  41  by use of the slot  45  which allows such movement. As illustrated in FIG. 3, the base plate  40  can be moved leftwardly relative to base mounting plate  41  by the use of slot  45 . The forearm assembly  23  will also move leftwardly out of proximity with the catwalk  53  and the centre of the V-door  45  so that the tubulars  13  may be retrieved by the conventional cable system from the horizontal position on piperack  14  to the vertical position on drill floor  46  over the well bore axis  160  (FIG.  9 ). When the pipe handling system  10  is repaired or otherwise put back into service, the operation is reversed; that is, the base plate  40  will be moved horizontally relative to base mounting plate  41  until the forearm assembly  23  is again aligned with and over the axis of the catwalk  53 . The bolts  51  are secured and the bolts  42  are inserted and secured. The pipe handling system  10  will again be operable as described. 
     It is likewise a relatively simply operation to replace the bicep arm  22  illustrated in FIG.  1  and the forearm assembly  23  with members having an extended length shorter or longer than the lengths illustrated depending on the configuration of the rig and the position of the pipe rack which holds the pipe or casing  13 . In this regard, reference is made to FIGS. 5A and 5B where the capscrews  85  can be removed which will thereby allow the housing  64  of the bicep arm  22  to be removed. Likewise, it is relatively convenient to remove the hex bolts  112  and the cap screws  115  in order to allow the outer forearm housing  104  and the inner forearm  31  to be removed and replaced. The length of the chains  83  will be appropriately adjusted in this event by removing or adding the necessary links. 
     It is also intended that the pipe handling system  10  move the pipe or casing  13  from a horizontal to a vertical position not in line with the well centre but in line with a mousehole (not illustrated) located a relatively short distance away from the well centre. The mousehole is a vertical, elongate cylindrical container adjacent the rotary table of the drill floor which is used to separate the pipe temporarily and is used to form drill strings prior to inserting such drill strings into the well bore. 
     Likewise, if the mouse hole is inclined, it is contemplated that by giving the gripper head assembly  21  a further degree of movement such as by providing a second axis of rotation  27  at right angles to the axis of rotation of pin joint  26  as illustrated at  37  in FIG. 3, the tubular  13  could be inclined as desired to coincide with the off-centre axis of the mousehole. 
     Many further embodiments will readily occur to those skilled in the art to which the invention relates and the specific embodiments described should be taken as illustrative of the invention only and not as limiting its scope as defined in accordance with the accompanying claims.