FIELD OF THE INVENTION

The present invention relates to an apparatus for gripping an object having a curved surface and, in particular, though not exclusively, for gripping an object having an external diameter such as a pipe.

BACKGROUND TO THE INVENTION

In some applications it may be necessary to grip an object to be held stationary even when subjected to substantial forces. Such substantial forces my exist in forge welding applications, in which two objects are typically heated, brought into contact and subjected to large compression forces to create an interference sufficient to cause plastic deformation and material diffusion in the region of an interface between the objects. Ensuring the action of such compression forces and controlling the size of the interference with the required precision necessitates each object to be reliably gripped so as to prevent any slippage during the forge welding process.

Variations in the shapes of objects can, however, often make gripping difficult, especially when the objects are subjected to substantial forces as mentioned above. Such variations may, for example, comprise variations between the shapes of corresponding surfaces of different objects or may comprise localised variations in the shape of a surface of a single object. In the case of objects having a curved surface, variations in curvature of the curved surface between different objects or localised variations in the curvature of the curved surface of a single object may mean that such objects are particularly difficult to grip precisely. Pipes, for example, often have variations in pipe outer and inner diameters, wall thickness, concentricity and ovality and may be difficult to grip precisely, for example, with the precision required for forge welding two such pipes together. SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a gripping apparatus for gripping an object, comprising:

a body having a central axis; and

a plurality of gripping devices arranged circumferentially around the central axis wherein at least one of the gripping devices is adapted to pivot relative to the body to permit the gripping apparatus to comply with the geometry of the object being gripped.

As a result of at least one of the gripping devices being arranged to pivot relative to the body, the gripping apparatus may be used to comply with and grip objects of varying sizes and geometries or to grip an object having a surface which has localised variations in size or geometry. The gripping apparatus may have a particular application in gripping objects having a curved surface. The gripping apparatus may be particularly well suited for gripping curved objects having variations in curvature. In contrast, a gripping apparatus having a perfectly cylindrical gripping surface may only provide a single point of contact on the surface of an object such as a pipe which has a cross-section having variations in curvature such as an eccentric or elliptical cross-section. The gripping apparatus of the present invention therefore provides additional compliance with respect to the object being gripped.

At least one gripping device may be arranged so as to pivot about a gripping device pivot axis. The gripping device pivot axis may be parallel to the central axis. At least one gripping device may be arranged so as to pivot in response to engagement of one or more of the gripping devices with a surface of an object being gripped. In use, the central axis of the body may be substantially aligned with an axis, such as a longitudinal axis, of the object being gripped. The body central axis may be substantially coaxially aligned with an axis of an object being gripped.

At least one of the gripping devices may be directly mounted on the body. At least one of the gripping devices may be mounted on the body via a pivot shaft. At least one of the gripping devices may be mounted within a recess formed in or on the body.

The gripping apparatus may comprise at least two gripping devices. The gripping apparatus may comprise more than two gripping devices. The use of more than two gripping devices may have the advantage that, for a given gripping force exerted by each gripping device on the object, the total gripping force is increased.

Conversely, the total gripping force may be maintained constant by increasing the number of gripping devices but reducing the gripping force exerted by each gripping device. In the latter case, the pressure exerted by each gripping device on the object may be reduced thus conferring the advantage that any tendency of the object to deform or be damaged when gripped by the gripping apparatus is also reduced.

Two or more of the plurality of gripping devices may be pivotable about respective gripping device pivot axes. At least two of the gripping device pivot axes may be aligned parallel to each other. At least two of the gripping device pivot axes may be aligned obliquely relative to each other. Two or more of the gripping device pivot axes may be aligned parallel with the central axis of the body.

All of the gripping devices may be arranged to pivot relative to the body. This arrangement provides a significant degree of compliance of each gripping device with an object being gripped.

The gripping devices may have a uniform angular distribution around the central axis. This may permit even distribution of the gripping forces exerted on the object by the gripping apparatus, thus reducing any tendency of the object to deform when gripped by the gripping apparatus. One or more of the gripping devices may be arcuate. This arrangement may assist in achieving a sufficient grip with a curved surface of an object.

The gripping apparatus may comprise a gripping element associated with a gripping device.

The gripping element may define a gripping surface adapted to engage an object being gripped. The gripping surface may be arcuate. The gripping device may be arranged to grip an object via the gripping element. Gripping may be achieved exclusively via the gripping element. Alternatively, gripping may be achieved via both the gripping element and another component or part of an associated gripping device.

The gripping element may be pivotally mounted on the associated gripping device. This arrangement advantageously provides an additional degree of freedom within the gripping apparatus to comply with an object being gripped. The gripping element may pivot about a gripping element pivot axis. The gripping element pivot axis may be aligned parallel with the pivot axis of the associated gripping device.

Alternatively, the associated gripping element and gripping device axes may be obliquely aligned relative to each other.

The gripping element may be mounted on a surface of the associated gripping device. Alternatively, the gripping device may comprise a recessed region, within which region the gripping element is located. The recessed region may, for example, comprise a bore.

The gripping element may be pivotally mounted on the associated gripping device via a pivot shaft. The pivot shaft may be separate from the gripping element and associated gripping device. Alternatively, the pivot shaft may be integrally formed with one of the gripping element and associated gripping device. The pivot shaft may be integrally formed with the gripping element.

The gripping element may be mounted on the gripping device via a bush component. The gripping element may be retained within the associated gripping device via a retaining element.

The gripping apparatus may comprise two or more gripping elements mounted on a gripping device.

Two or more gripping devices may carry at least one respective gripping element.

The body may define an aperture adapted to accommodate an object to be gripped. The aperture may be coaxial with the central axis of the body. The gripping devices may be arranged around the aperture. Accordingly, in this arrangement, once an object to be gripped is received within the aperture the plurality of gripping devices will be arranged around the outer periphery of said object, such that the outer periphery of the object may be gripped.

The body may comprise a plurality of components arranged to be coupled together. The plurality of components may be hinged together, for example. The plurality of components may be adapted to be coupled together by, for example clamping, bolting, screwing or the like.

The body may comprise a first body part and a second body part, wherein the first body part is locatable around a first side of the object and the second body part is locatable around a second side of the object.

The plurality of components of the body may be adapted to be coupled together to configure the gripping apparatus into a gripping configuration, in which an object is gripped.

In an alternative arrangement, the body may comprise a unitary component and the gripping apparatus may comprise at least one actuator to configure the apparatus into a gripping configuration. The actuator may be arranged to establish relative movement of components of the body. The actuator may be arranged to establish relative movement of at least one gripping device relative to an object being gripped. The actuator may be arranged to translate a gripper device in a radial direction with respect to the central axis.

The gripping apparatus may comprise a plurality of actuators.

The body may be adapted to engage an object being gripped. In this arrangement, engagement of the body with the object may assist in gripping the object. Alternatively, the body may not function to grip or engage the object.

At least one of the gripping devices may be directly mounted on the body.

At least one of the gripping devices may be indirectly mounted on the body.

According to a second aspect of the present invention there is provided a welding system for welding a first object to a second object, said welding system comprising a first gripping apparatus according to the first aspect, wherein the gripping apparatus is adapted to grip at least one of the first and second objects.

In this arrangement the gripping apparatus may grip the first object during a welding operation, such as a forge welding operation in which the first and second objects may be required to be compressed together with relatively large forces. The gripping apparatus may therefore grip at least one of the objects with a force sufficient to prevent slip of the object during a welding process, while still allowing any irregularities or the like in the geometry of the object to be accommodated by compliance of the gripping apparatus.

The welding system may further comprise a second gripping apparatus according to the first aspect, wherein the first gripping apparatus is adapted to grip one of the first and second objects, and the second gripping apparatus is adapted to grip the other of the first and second objects.

According to a third aspect of the present invention there is provided a method of gripping an object comprising using the gripping apparatus according to the first aspect.

The method according to the third aspect may therefore comprise the steps of: providing a gripping apparatus according to the first aspect; and

engaging an object to be gripped with the gripping devices of the gripping apparatus, wherein at least one of the gripping devices pivots to comply with the geometry of the object.

The object may have a curved surface.

The object may have a curved cross-section.

The object may have a perfectly circular cross-section.

The object may have a curved cross-section having variations in curvature.

The object may have an eccentric or elliptical cross-section.

The object may have a generally circular cross-section which has minor variations in curvature. The object may, for example, have a generally circular cross- section which may be slightly eccentric or elliptical.

The object may comprise a tubular portion. The object may comprise a pipe.

According to a fourth aspect of the present invention there is provided a method of welding a first object to a second object using the gripping device according to the first aspect.

Accordingly, the method according to the fourth aspect may comprise the steps of:

gripping a first object using a gripping apparatus according to the first aspect; and

welding the first object to the second object.

The method may comprise the steps of:

gripping the first object with a first gripping apparatus according to the first aspect;

gripping the second object with a second gripping apparatus according to the first aspect; and

welding the first object to the second object. The method may comprise the step of translating at least the first object with the gripping apparatus.

Welding may comprise forge welding.

The first and second objects may comprise tubular components, such as pipes or the like. For example, the objects may comprise wellbore tubulars, such as casing tubulars, drilling tubulars or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a gripping apparatus constituting a first embodiment of the present invention in which the gripping apparatus is gripping a pipe;

Figure 2 is a rear elevation of the gripping apparatus and the pipe of Figure 1 ; Figure 3 is a front elevation of the gripping apparatus and pipe of Figure 1 ;

Figure 4(a) is a front elevation of a gripping element of the gripping apparatus of Figure 1 ;

Figure 4(b) is a cross-section on AA of the gripping element of Figure 4(a);

Figure 4(c) is a cross-section on BB of the gripping element of Figure 4(a); Figure 4(d) is a cross-section on CC of the gripping element of Figure 4(a);

Figure 5(a) is a front elevation of the gripping apparatus of Figure 1 in the vicinity of a gripping device after removal of a cover plate;

Figure 5(b) is a view in the vicinity of a gripping element of Figure 5(a) looking radially outwards from a central axis of the gripping apparatus towards the gripping element;

Figure 5(c) is a cross-section on CC of Figure 5(b); Figure 6 is a front elevation of the gripping apparatus of Figure 1 after removal of the cover plates in which the gripping apparatus is gripping a pipe having a perfectly circular cross-section;

Figure 7 is a front elevation of the gripping apparatus of Figure 1 after removal of the cover plates in which the gripping apparatus is gripping a pipe having a generally circular cross-section which has minor deviations in curvature so as to be slightly elliptical; and

Figure 8 is a front elevation of an alternative embodiment of a gripping apparatus in the vicinity of a gripping device after removal of a cover plate.

DETAILED DESCRIPTION OF THE DRAWINGS

Figures 1, 2 and 3 show a gripping apparatus generally designated 2 which defines an aperture generally designated 3 which accommodates a pipe 4 wherein the gripping apparatus 2 is shown in use gripping the pipe 4. The gripping apparatus 2 has a central axis 5 which is substantially co-axial with a longitudinal axis of the pipe 4. It should be noted that in Figure 3, the left half of the gripping device 2 is shown fully assembled while the right half is shown with some components removed for brevity and clarity of the present description. The gripping apparatus 2 is particularly, though not exclusively, suitable for gripping the pipe 4 during alignment and forge welding of the pipe 4 to a further pipe (not shown). The gripping apparatus

2 may, for example, be incorporated into a forge welding system (not shown) including alignment and heating means.

The gripping apparatus 2 comprises a body, generally designated 6 (see e.g. Figure 2), having a first part 8 and a second part 10. The gripping apparatus 2 further comprises gripping devices 12, gripping elements 14, bushes 16, retention elements 18, a first cover plate 20 and a second cover plate 22. As will be described in further detail below, each gripping device 12 is pivotally mounted on the body 6 and a pair of gripping elements 14 are pivotally mounted in each gripping device 12 in respective bushes 16. The gripping elements 14 are each held in respective bushes 16 by respective retention elements 18. The gripping devices 12 are held in place by one of the cover plates 20,22.

An individual gripping element 14 is shown in isolation in Figures 4(a) to 4(d). The gripping element 14 has an associated gripping element pivot axis 30 and is symmetric about a plane 31 that contains the gripping element axis 30. The gripping element 14 comprises a shaft portion 32 which is partially cylindrical and has a partially cylindrical surface 33 having an associated principal diameter 0. The gripping element 14 also includes a head portion 34 integrally formed with the shaft portion 32. The shaft portion 32 and the head portion 34 collectively define a concave surface 38 that is arranged to engage an external surface of the pipe 4. The head portion 34 comprises shoulder portions 40 that extend radially with respect to the gripping element axis 30 beyond the principal diameter 0 , of the shaft portion 32. A recess 42 is formed in an upper and outer periphery of the head portion 34. As shown in Figure 4(b), the recess 42 comprises a step surface 44 and side walls 46 which taper or flare outwardly towards the outer periphery of the head portion 34.

An individual gripping device 12 is shown in situ in Figure 5(a). Figures 5(b) and 5(c) show corresponding views in the vicinity of an individual gripping element 14. The gripping device 12 is generally arcuate and comprises a head portion 51 having an aperture 52 and two shoulders 54. The gripping device 12 is pivotally mounted on the body 6 (body half 8 in the example shown) via a pivot shaft (not shown) of an external system such as a forge welding system, which pivot shaft extends through the aperture 52 such that the gripping device 12 is pivotable with respect to the pivot shaft and the body 6. . The gripping device 12 further comprises a concave surface 56 that faces radially-inwards towards the central axis 5 and which has a corresponding diameter that is greater than the nominal external diameter of the pipe 4. It should be noted that in Figure 5(c), the curvature of the surface 56 has been exaggerated for clarity of illustration. Two recesses 58 are formed in the surface 56 of the gripping device 12. As indicated in Figure 5(c), each recess 58 comprises a bore hole having a diameter 0 ₂ and a bore hole axis 60 that is aligned parallel to the central axis 5. Each bore hole axis 60 is positioned sufficiently close to the surface 56 of the gripping device 12 such that a curved sidewall of each bore hole intersects the surface 56 of the gripping device 12 so as to form a recess opening.

Fitted into each recess 58 is a corresponding bush 16. Each bush 16 is rotatably fixed within a respective recess 58. Each bush 16 is generally C-shaped and has an internal diameter in which a shaft portion 32 of a corresponding gripping element 14 is fitted, wherein the shaft portion 32 of the gripping element 14 is coaxial with and rotatable with respect to the bush 16. The partially cylindrical surface 33 of the shaft portion 32 of the gripping element 14 circumferentially extends for more than 180°, and similarly the internal surface of the bush 16 also circumferentially extends for more than 180°, such that the shaft portion 32 may be retained within the bush 16. Also, the outer surface of the bush 16 and the inner surface of the recess

58 each circumferentially extend for more than 180° to ensure that the bush 16 is retained within the recess 58.

The radially-inner surface 38 of the gripping element 14 protrudes radially inwards towards the central axis 5 beyond the surface 56 of the gripping device 12. It should also be noted that in Figures 5(a) to 5(c), each gripping element 14 is shown in a nominal position in which the radially-inner surface 38 of the gripping element 14 is substantially coaxial with the central axis 5.

Each gripping element 14 is retained axially within the corresponding bush 16 by a corresponding retention element 18 having a first end which is attached to the gripping device 12 and a second end that is shaped and sized so that it fits within the recess 42 of the corresponding gripping element 14 and engages the corresponding recess step surface 44 (see Figure 4(b)). The retention element 18 thus exerts an axial force on the corresponding gripping element 14 urging the shoulders 40 of the gripping element 14 into axial engagement with the corresponding bush 16. Due to the flared nature of the recess srdewalls 46, the gripping element 14 may only pivot over a limited angular range about the corresponding pivot axis 60 as indicated by the arrows 80 in Figure 5(a).

As indicated by the arrow 82 in Figure 5(a), each gripping device 12 is rotatable with respect to the body 6 about a pivot axis 86 coaxial with each aperture 52 to provide an additional degree of pivot for the gripping elements 14. As shown most clearly in Figure 5(a), to accommodate the gripping devices 12 and the movement of the shoulders 54 of the gripping devices 12 during this pivoting motion, the corresponding body parts 8,10 have recesses 88 formed therein.

As shown most clearly in Figures 1 and 3, the gripping devices 12 are sandwiched axially between the body 6 and the cover plates 20,22 which are connected to the body 6 by fasteners 88. The cover plates 20,22 have recesses 90 formed therein through which the gripping elements 14 and the retention elements 18 extend. The recesses 90 are sized and shaped so as to accommodate rotation of the gripping elements 14.

The first and second body parts 8,10 each comprise a first lug 92 having a slot 94 formed therein (see Figure 1). When attached to an external system such as a forge welding system, the first lugs 92 of the first and second body parts 8,10 are located adjacent to one another and bolts or pins (not shown) from the external system extend through the slots 94 such that the first and second body parts 8,10 are both independently slidable and pivotable with respect to the external system. In addition, the first and second body parts 8,10 each comprise a second lug 96 which is diametrically opposed to a corresponding first lug 92.

In use, the gripping apparatus 2 is capable of gripping objects having a perfectly circular cross-section and objects having a generally circular cross-section which has deviations in curvature such as an eccentric or elliptical cross-section. In Figure 6, for example, the gripping apparatus 2 is shown gripping an external surface of a pipe 104 having a perfectly circular cross-section. In use, the first and second body parts 8, 10 are swivelled apart or otherwise separated to admit the circular pipe 104 into the space formed between the gripping elements 14. The first and second body parts 8,10 are swivelled back into position around the circular pipe 104 such that the longitudinal axis of the circular pipe 104 is approximately coaxial with the central axis 5 of the gripping apparatus 2. As indicated by the arrows 106 in Figure 6, the second lugs 96 are urged and ultimately clamped together thus fixing the first and second body parts 8,10 around the circular pipe 104 and urging the radially-inner surfaces 38 of the gripping elements 14 to contact and grip the external diameter of the circular pipe 104. Depending on the initial orientation of each gripping element

14, each gripping element 14 may also pivot in response to being urged into contact with the circular pipe 104 so that the radially-inner surface 38 of the gripping element 14 complies with and grips the external diameter of the circular pipe 104. In addition, depending on the initial orientation of each gripping device 12, each gripping device 12 may also pivot in response to at least one of the corresponding gripping elements

14 being urged into contact with the circular pipe 104 so as to provide an additional degree of pivot for the corresponding gripping elements 14.

Similarly, in Figure 7, the gripping apparatus 2 is shown gripping an external surface of a pipe 204 which has a slightly elliptical cross-section. As indicated by the arrows 206 in Figure 7, the second lugs 96 are urged and clamped together thus fixing the first and second body parts 8,10 around the elliptical pipe 204 and the urging the radially-inner surfaces 38 of the gripping elements 14 to contact and grip the external surface of the elliptical pipe 204. Depending on the initial orientation of the gripping elements 14 at the time of gripping, the gripping elements 14 may also pivot in response to being urged into contact with the elliptical pipe 204 so that the radially-inner surfaces 38 of the gripping elements 14 can comply with and grip the external surface of the elliptical pipe 204. In addition, depending on the initial orientation of each gripping device 12, each gripping device 12 may also pivot in response to at least one of the corresponding gripping elements 14 being urged into contact with the elliptical pipe 204 so as to provide an additional degree of pivot for the corresponding gripping elements 14. In contrast to the gripping action of the gripping apparatus 2 depicted in Figure 6 for a round pipe 104, however, the body parts 8 and/or 10 may also contact the elliptical pipe 204 e.g. at positions 208 and

210 thus providing a gripping force additional to the gripping force provided by the gripping elements 14.

An alternative embodiment 302 of a gripping device is shown in Figure 8. The gripping apparatus 302 has many of the same or similar features to the gripping apparatus 2 and, as such, like features of the gripping apparatus 302 are identified with reference numerals given by incrementing the reference numerals of the corresponding features of the gripping apparatus 2 by 300. The gripping apparatus 302 comprises gripping devices 312 and gripping elements 314 which are all pivotable in the same way as the gripping devices 12 and the gripping elements 14 of the gripping apparatus 2. In contrast to the gripping apparatus 2, however, the gripping devices 312 of the gripping apparatus 302 are movable in a radial direction as indicated by the arrow 398 in Figure 8. The body 306 also comprises recesses 388 which accommodate both rotation and radial translation of the gripping devices 312. The gripping apparatus 302 may comprise first and second body parts 308 and 310 which are arranged and are operable in the same way as body parts 8 and 10 of the gripping apparatus 2. When it is desired to grip an object such as a pipe, the gripping devices 312 are translated radially inwards until the radially-inner surfaces 338 of gripping elements 314 contact and grip an external surface of the object. As for the gripping apparatus 2, the gripping elements 314 may also pivot in response to being urged into contact with the external surface of the object so that the radially- inner surfaces 338 of the gripping elements 314 can comply with and grip the external surface of the object. In addition, depending on the initial orientation of each gripping device 312, each gripping device 312 may also pivot in response to at least one of the corresponding gripping elements 314 being urged into contact with the object so as to provide an additional degree of pivot for the corresponding gripping elements 314. By translating the gripping devices 312 in this way, the gripping apparatus 302 is, therefore, capable of gripping objects having perfectly circular cross-sections and objects which have cross-sections which are generally circular but which have variations in curvature such as eccentric or elliptical cross-sections. Alternatively, the body 306 of the gripping apparatus 302 may comprise a single annular part which has an internal diameter that, in use, is fitted over the end of the object to be gripped with the gripping devices 312 in a retracted position. The internal diameter of such an alternative unitary annular body would, however, have to be chosen so as to exceed a nominal external diameter of the object to be gripped. Such an alternative unitary annular body would not, therefore, in general contact the object or provide grip additional to the grip provided by the gripping elements 314. Once such an annular body 306 is fitted over the object, the gripping devices 312 may be advanced radially until the radially-inner surfaces 338 of the gripping elements 314 comply with and grip the external surface of the object. The gripping apparatus 302 may, for example, comprise actuators (not shown) for the translation of the gripping devices 312. The actuators may, for example, be independently operable so that the gripping devices 312 may be translated independently. The actuators may be driven by any suitable means including, but not limited to, electrical, hydraulic, or pneumatic means or the like.

It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made without departing from the scope of the present invention. For example, a selection of the gripping elements 14 or gripping devices 12 may be arranged to pivot. Additionally, any number of gripping devices 12 and gripping elements 14 may be provided. The gripping devices 12 and/or the body 6 may also engage a surface of the object to be gripped to provide further grip. In alternative embodiments, the gripping elements 14 may be omitted altogether and the gripping devices 12 may grip the object to be gripped by engaging a surface of the object to be gripped.