WO2007028794A2

WO2007028794A2 - Shaft-ring gripper

Info

Publication number: WO2007028794A2
Application number: PCT/EP2006/066033
Authority: WO
Inventors: Malcolm Mcpherson
Original assignee: Wtb Group Ltd
Priority date: 2005-09-07
Filing date: 2006-09-05
Publication date: 2007-03-15
Also published as: WO2007028794A3; GB2429966B; GB2429966A8; GB2429966A; GB0518191D0

Abstract

A shaft-ring gripper is disclosed. The shaft ring gripper comprises a support structure having an axis and a plurality of gripping elements (9, 212, 213, 302) displaceable in a radially outward direction relative to the axis when the support structure, which has been lowered in an axial direction into an open upper end of a shaft-ring (218, 305) , is lifted, so that the gripping elements engage the inner wall of the shaft ring to lift the shaft ring together with the support structure. The shaft ring gripper further comprises guide members (9, 208, 214) on the support structure to guide the support structure into the open upper end of a shaft ring when the support structure is lowered.

Description

Shaft-ring gripper

Description

The present invention relates to an improved device for lifting a shaft ring Shaft rings are cylindrical or cone shaped hollow sections generally formed from concrete The usual method of lifting and moving such a shaft ring is to manually attach a clamping device, such as a plurality of hooks, to the shaft ring to enable a load- hfting device, such as a crane or a hoist, to be connected which can subsequently lift the shaft ring.

Recently, a device for lifting a shaft ring without the need to manually attach hooks and the like has been developed, and an example of this is known from EP 0 703 184 This patent describes a shaft ring gripper which incorporates a support structure including three arms with clamping _jaws mounted thereon which may be lowered into the open upper end of a shaft ring. The clamping jaws are displaceable in a radially outward direction so as to engage the inner cylindrical surface of the shaft ring so that, when the shaft ring gripper is lifted using, for example, a crane or a hoist, the shaft-ring is lifted together with it.

The aforementioned type of shaft ring lifting device has a known problem however, in that it can be difficult to lower the support structure of the device into a hollow shaft ring without an operator manually maneuvering the lifting device as it is lowered so as to guide the arms and clamping jaws into the open upper end of the shaft ring. Unless the shaft-ring gripper is directly above and centered with respect to the open upper end of the shaft ring before it is lowered, one or more of the clamping jaws may catch on the upper edge of the shaft ring causing the support structure to tip. The lifting device must then be lifted clear of the shaft-ring and re-positioned prior to lowering it once again. Accomplishing accurate positioning of the lifting device without manual aid can be difficult and time consuming for the driver of the crane or hoist who may not be in an optimum position to ascertain whether he has positioned the lifting device correctly prior to lowering it Having a second operator on-hand to assist in positioning the lifting device is an option but is contrary to the stated advantages of this type of shaft ring lifting device which is designed to be used by one person Furthermore, it is undesirable for an operator to be in the vicinity of a shaft-ring during lifting for reasons of safety

The present invention seeks to provide a shaft ring gripper which overcomes or substantially alleviates the problems discussed above and in which precise positioning of the support structure of the shaft ring lifting device above the open end of a shaft-ring prior to lowering of the support structure is no longer necessary

According to the invention, there is provided a shaft-ring gripper comprising a support structure having an axis and a plurality of gripping elements displaceable in a radially outward direction relative to the axis when the support structure, which has been lowered in an axial direction into an open upper end of a shaft ring, is lifted, so that the gripping elements engage the inner wall of the shaft ring to lift the shaft ring together with the support structure, the shaft ring gripper further comprising guide members on the support structure to guide the support structure into the open upper end of a shaft ring when the support structure is lowered

In one embodiment, a guide member is associated with each gripping element

Preferably, a portion of each guide member is spaced from the gripping elements in a radially outward direction, the guide members extending beyond the gripping elements in an axial direction towards the open upper end of a shaft ring disposed beneath the support structure so that, when the support structure is lowered, the wall of the shaft ring is received between the gripping elements and said guide members

In a preferred embodiment, the portion of each guide member that extends beyond the gripping elements in an axial direction is angled radially outward relative to the axis so that if said angled portion of the guide element contacts the shaft ring when the support structure is lowered, the guide element slides over the shaft ring and centres the support structure above its open upper end.

In a preferred embodiment, the guide means are removable The support structure may include a central shaft coaxial with the axis of the support structure and a plurality of support legs extending radially from the central shaft, the gripping elements being mounted on the support legs.

In an alternative embodiment, each support leg has a gripping element mounting arm pivotally attached thereto and gripping elements attached adjacent to each end of said arm on either side of the pivot so that the gripping elements mounted on each arm are spaced from each other in the axial direction. This arrangement has the advantage that as the mounting arm can pivot with respect to the leg to which it is attached, shaft-rings that have inner walls which are not completely cylindrical can still be gripped by the gripping elements.

Known types of shaft ring gripping devices, such as that described in EP 0703 184, each have a single gripping element attached to each support leg of the support structure. However, the inner wall surface of a shaft-ring may not be completely cylindrical and the wall may diverge or converge towards its open upper end. Consequently, it has been found that not all the gripping elements fully engage with the inner wall and hence grip the shaft ring properly, and so there is potential for the shaft ring to slip. The same problem may also occur when the shaft ring to be picked up is lying on a surface which is not completely level.

In view of the foregoing, the present invention also seeks to provide a shaft ring gripper which overcomes or substantially alleviates the problems discussed in the above paragraph and in which the gripping ability of the gripping elements is improved. It will be appreciated that this aspect of the present invention may be used independently to, or together with, the first aspect of the invention which has already been referred to above.

According to another aspect of the invention, there is provided a shaft-ring gripper comprising a support structure having an axis and a plurality of support legs each having gripping elements thereon which are displaceable in a radially outward direction relative to the axis when the support structure, which has been lowered in an axial direction into an open upper end of a shaft-ring, is Lifted, so that the gripping elements engage the inner wall of the shaft ring to lift the shaft ring together with the support structure, wherein each support leg has a gnpper element mounting arm pivotally attached thereto, and gripping elements attached adjacent to each end of said arm on either side of the pivot so that the gripping elements mounted on each arm are spaced from each other in the axial direction

In a preferred embodiment, the gripping elements are pivotally attached to said gripping element mounting arm

Preferably, one gripping element is mounted adjacent to each end of a gripping element mounting arm However, a pair of gripping elements may alternatively be mounted adjacent to each end of a gripping element mounting arm, the gripping elements of each pair being mounted on either side of the mounting arm

In one preferred embodiment, the support structure comprises first and second sets of support legs each having gripping elements thereon, wherein the second set of support legs are below the first set and are configured such that the gripping elements on one leg are disposed at a different distance from the axis to the gripping elements on the other legs of said set to counterbalance the eccentric centre of mass of a cone shaped shaft ring lifted by the gnpper.

The shaft ring gnpper disclosed in EP 0 703 184 further comprises a second set of gripping elements located below the first set of gripping elements on the end of each leg. Each of the second set of gripping elements are disposed on a shorter leg each of the same length so that the gripping elements are all disposed the same radial distance from the axis Each gripping element may be moved in a radially outward direction in the same way as the first set of gripping elements so as to engage the inner wall of a shaft ring The second set of gripping elements are primarily used to lift shaft-rings of smaller diameter and also conical shaft rings and so have a smaller gripping diameter compared to the first set of gripping elements. Cone shaped shaft-rings have an eccentric center of gravity and so hang lop sidely from known shaft-ring gnppers However, it is known from EP 0 703 184 to provide a shaft-ring gripper which enables a cone-shaped shaft ring to be lifted and maintained substantially level This is achieved by providing the lifting device with an off-centre suspension position relative to a central suspension position for lifting cylindrical shaft rings The distance between the off-centre suspension position and the central suspension position corresponds to the eccentricity of the center of mass of the shaft cone to be lifted

A disadvantage of shaft ring gnppers with this type of off-centre suspension position for lifting shaft cones is that it is necessary to move the lifting device suspension position each time a shaft cone is to be lifted.

The present invention also seeks to provide a shaft ring gripper which overcomes or substantially alleviates the problems discussed in the above paragraph and in which the shaft ring gripper can more easily counteract an off centre weight It will be appreciated that this third aspect of the present invention may be used independently to, or together with, the first and second aspects of the invention which has already been referred to above.

According to a third aspect of the invention, there is provided a shaft-ring gripper comprising a support structure having an axis and a first and second set of support legs each having gripping elements thereon which are displaceable in a radially outward direction relative to the axis when the support structure, which has been lowered in an axial direction into an open upper end of a shaft-ring, is lifted, so that the gripping elements of one set of support elements engage the inner wall of a shaft ring to lift the shaft ring together with the support structure, wherein the second set of support legs are below the first set and are configured such that the gripping elements on at least one leg are disposed at a different distance from the axis to the gripping elements on the other legs of said set to counterbalance the eccentric center of mass of a cone shaped shaft ring lifted by the gripper. Embodiments 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 plan view, partly in section, of the shaft ring lifting device in accordance with the present invention,

Figure 2 is a sectional view along the line 1-1 of the shaft ring lifting device shown in Figure 1 ;

Figure 3 is a sectional view along the line 1 -1 of the shaft ring lifting device shown in Figure 2 with the gripping mechanism engaged; Figure 4 is a perspective view of the gripping elements according to a second embodiment,

Figure 5 is a plan view, partly in section, of the shaft ring lifting device according to the second embodiment shown in Figure 4,

Figure 6 is a side view of the shaft ring lifting device shown in Figures 4 and 5 with a lifting arm omitted;

Figure 7 is a side view of the shaft ring lifting device shown in Figures 4 to 6 with the gripping mechanism engaged and a lifting arm omitted,

Figure 8 is a perspective view of the shaft ring lifting device of Figures 4 to 7 engaged with a large diameter shaft ring; Figure 9 is a perspective view of the shaft ring lifting device of Figures 4 to 8 engaged with a small diameter shaft ring,

Figure 10 is a partial side view of the shaft ring contacting one of the guide members of the second embodiment of the invention,

Figure 11 is a partial side view of a shaft ring located in one of the guide members of the second embodiment of the invention; and

Figure 12 is a partial side view of a shaft ring located in one of the guide members of a third embodiment of a shaft ring lifting device.

Referring to the drawings, there is shown in Figures 1 to 3 a shaft ring lifting device 1 according to a first embodiment of the invention, comprising a support structure 2 having a horizontal triangular frame 3 which supports a guide tube 4 orientated vertically along a central axis by means of radial braces 5 extending from the midpoint of each of the three horizontal frame sections 3. A respective guide sleeve η

6 is welded onto each of the three corners of the triangular frame 3 such that each guide sleeve 6 is orientated in an approximately radial direction from the central axis, and a diagonal brace 7 extends obliquely upwards and inwards from each guide sleeve 6 to the guide tube 4

A gripping mechanism G forms part of the support structure 2 comprising a rod shaped slide 8 slidably mounted in each guide sleeve 6, wherein the guide sleeves 6 are orientated such that when the slide 8 is slideably extended outwards it extends upwards at a slight angle in the axial plane A gripping element is pivotally mounted to the distal end of each of the three slides 8 and each gripping element 9 has a contact face 10, to contact and grip the inner surface of a shaft ring 11 (as shown in Figure 3) Each contact face 10 is convexly shaped in a vertical orientation and is serrated to improve the gripping action The gripping elements 9 are pivotally mounted to rotate in a vertical plane about the distal end of each of the slides 8, such that on initial contact with a shaft ring 11 each gripping element 9 can rotate in a clockwise direction (as shown by arrow A) in order to increase the gripping action A weight arm 12 is fixably attached to each gripping element and extends backwards to position each gripping element 9 in a neutral position when not m use, wherein each respective guide sleeve 6 forms a stop

The guide tube 4 is substantially hollow such that a pull rod 13 is slideably mounted within it, wherein the pull rod 13 is longer than the guide tube 4 such that it protrudes from both ends of the guide tube 4 A vertical central axis A A is defined through the centre of the pull rod 13 and this defines the central axis of the support structure The pull rod 13 is slotted at its upper end and a vertical plate 15 is welded into the slot 14 Fixably mounted to the lower end of the pull rod 13 is a flange 16 to which three support members 17 are pivotally mounted at a proximal end of each support member 17 to extend radially outwards and obliquely upwards to pivotably mount at their distal end to a respective slide 8

A support pin 19 is secured to a load lifting means 20 and is slidable in a slot arrangement 18 formed in the vertical plate 15 The slot arrangement 18 comprises two suspension positions 21,22 by which the support pin 19 can suspend the support structure 2 and a path defined between them by the slot 18 along which the support pin 19 can be guided. The first suspension position 21 is located vertically above the second suspension position 22, such that they lie coaxially along the vertical central axis A-A of the guide tube 4.

When the support pin 19 is located in the second suspension position 22, the gripping mechanism G is prevented from moving relative to the rest of the support structure 2 by means of a hook 23 welded to the outer surface of the guide tube 4. The hook 23 is welded into a position such that the orientation of the hook 23 is offset but parallel to the plane of the vertical plate 15 and so the support pin 19 will support it when the support pin 19 is disposed in the second suspension position 22. The upper part of the second suspension position 22 is semicircular to correspond with the internal contour of the hook 23 and so the vertical plate 15 and the hook 23 can be simultaneously supported such that the guide tube 4 and pull rod 13 cannot move relative to each other.

Extending from each diagonal brace 7 is a guide member 24 formed from square section tube comprising a first portion 25 extending horizontally in a radial direction from each diagonal brace 7, a second portion 26 extending substantially vertically downwards from the distal end of the first portion 25 parallel to the central axis A-A, and a third portion 27 extending radially outwards and downwards from the second portion 26 at approximately 10 degrees to the vertical axis such that the distance between the inner edge 28 at the bottom of the third portion 27 and the central axis A-A, is greater than the distance between the inner edge 29 at the top of the second portion 26 and the central axis A-A. The distance between the inner edge 29 of the second portion 26 and the central axis A-A is marginally wider than the radius of the outer surface of the shaft ring required to be lifted and the second portion 26 of each guide member 24 extends below the horizontal level of the gripping elements 9.

Hereinafter, the operation of the device for lifting a shaft ring according to the first embodiment of the present invention will be described in detail. As shown in Figure 2, the shaft ring lifting device 1 is suspended in a first position by means of the support pin 19 secured to the load lifting means 20 The support pin 19 is located in the second suspension position 22 such that the gripping mechanism G is prevented from moving relative to the rest of the support structure 2 and the gripping elements 9 are in an inwardly retracted position In this state the support structure 2 is lowered towards a shaft ring to be lifted

In a situation wherein the shaft ring lifting device 1 is not directly above and centred with respect to the open upper end of the shaft ring 11 , at least one of the guide members 24 will contact the upper edge of the shaft ring as the support structure 2 is lowered due to the third portion 27 of each of the guide members 24 being angled radially outward relative to the axis A-A. When the angularly configured portion of the respective guide member 24 contacts the shaft ring, the shaft ring lifting device 1 is displaced horizontally, such that the support structure 2 is centred above the open upper end of the shaft ring. The support structure 2 can then be lowered such that the shaft ring is guided between the gripping elements 9 and the second portions 26 of each of the guide members 24.

The support structure 2 is then lowered until the support structure 2 is supported by the first portion 25 of each guide member 24 resting on the upper surface of the shaft ring If the load lifting means 20 is further lowered, the plate 15 and hence the pull rod 13 slides downwards relative to the guide tube 4 supported by the guide members 24, until the plate 15 abuts the guide tube 4 such that the pull rod 13 cannot slide any further

Referring to Figure 3, the support pin 19 is then manoeuvred out of the second suspension position 22 and guided along the slot arrangement 18 to the first suspension position 21 by manipulation of the load lifting means 20. Subsequently, the load lifting means 20 acting on the support pm 19 in the first suspension position 21 lifts the shaft ring lifting device 1 This movement causes the plate 15 and hence the pull rod 13 to slide vertically upwards relative to the guide tube 4 in the direction of arrow C as the hook 23 is no longer supported by the support pin 19 The three support members 17 pivotally mounted to the flange 16 are thereby totaled and displaced such that each tod-shaped slide 8 slides outwards in the ditection of attow D telative to theit respective guide sleeves 6 and so the gripping element 9 mounted to each slide 8 moves radially outwards to contact and grip the innet sutface of the shaft ring, in a second position As each gapping element 9 is pivotally mounted, slight adjustment of the gtipping element 9 positioning relative to the inner surface of the shaft ring can take place

As futther radial movement of the gripping elements is restricted, further lifting of the support pin 19 by the load lifting means 20 precipitates vertical lifting of the shaft ring, as sufficient force is applied to the inner surface of the shaft ring for the friction of the gripping elements 9 thereagainst to support its weight.

Once the shaft ting has been moved to a required location, the support pm 19 is lowered such that it slides out of the first suspension position 21 and is then slid into the second support position 22. This movement releases the shaft ring by moving the gripping elements 9 radially inwards due to the pull rod 13 sliding in the opposite direction to arrow C (see Figure 3) relative to the guide tube 4. Once the support pin 19 is located in the second suspension position 22 the hook 23 prevents movement of the gripping mechanism G telative to the test of the support structure 2 such that the support structure 2 can be lifted clear of the shaft ring.

Referring now to Figures 4 to 11, an alternative second embodiment 201 of the invention will be described This second embodiment 201 operates on much the same principles as the first embodiment described above.

The second embodiment 201 of the invention comprises a central post 202 extending through a support collar 203 and skdable thereto along its axis B-B Three guide cam plates 204 are secured to, and equidistantly spaced atound, the bottom end of the central post 202 and taper radially outwards relative to the central post 202 towards their bottom ends

Three generally triangular lifting arms 205 are pivotally secured to the support collar 203 and extend radially out therefrom, equidistantly spaced atound the collar 203 corresponding to the radial positions of the cam plates 204 The lifting arms 205 of this second embodiment generally correspond to the diagonal braces and horizontal frame sections 3 of the first embodiment and a contact portion 205a of each lifting arm rests against the slanting outer tapered surface of a respective cam plate 204.

A plate 206 is secured to the upper end of the central post 202 and has a slot formed therein to allow it to be lifted by engagement with a pin 221 of a lifting means 220. A hook 207 is secured to the central collar 203 by which the central collar 203 can be lifted by engaging with said pin 221 of said lifting means 220.

A diagonally inclined section 205b and a horizontal section 205c of each lifting arm 205 each have a number of mounting holes 209a and 209b respectively formed therein, which allows a first extension arm 210 and a second extension arm 211 to be mounted to the diagonally inclined section 205b and the horizontal section 205c of each lifting arm 205 respectively Each first extension arm 210 is removably secured to the lifting arm 205 by means of a mounting pin (not shown), and can be positioned at any of the mounting holes 209a. Each first extension arm 210 is therefore moveable such that each gripping element 212 can be extended to lift shaft rings of up to a diameter of 1.8m. Each second extension arm 211 is removably secured to the lifting arm 205 by means of a mounting pin (not shown), and can be positioned at any of the mounting holes 209b.

A gripping element 212 is pivotally mounted at the point of each first extension arm 210 remote from the central post 202 and support collar 203, and a first guide member 208 extends out from each first extension arm 210 similar to the guide member 24 of the first embodiment described above.

It is to be understood that the first extension arm 210 may be omitted and alternatively a gripping element 212 may be pivotally mounted at the point of each lifting arm remote from the central post 202 and support collar 203.

Each second extension arm 211 has a gripping element 213 pivotally secured to an end of the arm 211 remote from the respective lifting arm 205. Each second extension arm 211, in any of its positions along its respective lifting arm 205, is radially closer to the axis B-B of the central post than the gripping element 212 at the remote point of the lifting arm 205 is A second guide member 214 extends out from each second extension arm 211 similar to the first guide member 208 on each first extension arm 210 described above

Each gripping element 212,213 has a weighted portion 215 (see, for example, Figure 6) located at a remote end of each gripping element 212,213 from a gripping surface 216 such that each gripping element 212,213 rotates under gravity in the direction of arrow E shown in Figure 6 to a neutral position when a shaft ring is not being lifted. Each gripping element 212,213 is prevented from rotating past the neutral position by means of a pin 217 mounted to each gripping element 212,213 which abuts the extension arm 210,211 in the neutral position.

The general operation of the second embodiment 201 is similar to that of the first embodiment, and will now be described The device 201 is positioned over the shaft ring to be lifted and lowered such that the guide members 208/214 can locate the gripping elements 212/213 as described previously within the inside of the shaft ring. A pin 221 of a lifting means 220 engages both the plate 206 and hook 207, so holding the central post 202 and the support collar 203 in a fixed position relative to each other. In this position the gripping elements 212/213 are spaced from the inside surface of the shaft ring.

Referring to Figures 10 and 11, in a situation wherein the shaft ring lifting device 201 is not directly above and centred with respect to the open upper end of the shaft ring 218, at least one of the guide members 208/214 will contact the upper edge of the shaft ring 218 as the support structure is lowered due to the third portion 219/220 of each of the guide members 208/214 being angled radially outward relative to the axis B-B (as shown in Figure 6). When this angularly configured portion of the respective guide member 219/220 contacts the shaft ring 218, the shaft ring lifting device 201 is displaced horizontally, such that the support structure is centred above the open upper end of the shaft ring 218 The support structure can then be lowered such that the shaft ring 218 is guided between the gripping elements212/213 and the second portions 221 /222 of each of the guide members 208/214 (as shown in Figures 6 and 8)

To lift the shaft ring, the hook 207 is disengaged from the lifting pin 221 and only the plate 206 is lifted. This pulls the central post 202 upwards relative to the support collar 203 and in doing so, the cam plates 204 move upwards relative to the lifting arms 205, thereby pushing against the contact portions 205a and pivoting the lifting arms 205 about the support collar 203 so that the gripping elements 212/213 are displaced radially outward into contact with the inner surface of the shaft ring 218, as shown in Figure 7 As described previously, further lifting of the plate 206 causes the weight of the shaft ring to force the gripping elements 212/213 radially outwards with greater force, to increase the friction of the gripping elements 212/213 with the inner surface of the shaft ring 218, to allow the shaft ring to be lifted

The major advantage provided by this second embodiment of the invention is that each second extension arm 211 can be independently positioned on the respective lifting arm 205 to enable the device 201 to be adapted to lift smaller diameter shaft rings (see Figure 9), and also irregularly shaped shaft rings which have an eccentric centre of gravity, such as, cone shaped shaft rings This is achieved by positioning each second extension arm 211 individually in such a way that when presented to the irregular shaft ring to be lifted, the centre of gravity of the shaft ring corresponds to the axis B-B of the central post 202. For example, one secondary arm 211 may need to be positioned at a greater radial distance from the central post 202 This enables the present invention to overcome the problems associated with the prior art discussed above

A third embodiment of the lifting device of the present invention incorporating an alternative gtippmg element arrangement 301 will now be described with reference to Figure 12. The support structure of the third embodiment is substantially the same as that described with reference to the second embodiment shown in Figures 4 to 11 , and so will not be described in detail hereinafter. However, the difference of this third embodiment is that each gripping element 302 does not mount directly to the distal end of each lifting arm 303. Instead, a gripping element mounting arm 304 is pivotally attached at its mid-point to the end of each lifting arm 305 remote from the central post. The gripping element 302 is pivotally mounted to each end of each gripping element mounting arm 303, such that two gripping elements 302 are mounted to each lifting arm 303 and are spaced from each other in the axial direction. Each gripping element mounting arm 304 is pivotally attached to its respective lifting arm 303 such that it can rotate about the lifting arm 304 to align with the inner surface of a shaft ring 305, and so fully engage thereto and hence grip the shaft ring 305 properly.

The operation of the third embodiment of the invention is similar to that described above in relation to the second embodiment and so will not be described in any detail. The support structure is lowered in an axial direction into an open upper end of a shaft ring 305 and lifted so that the lifting arms 303 are radially extended as in the previous method. Gripping element mounting arms 304, pivotally attached to each of the lifting arms 303, are free to rotate such that the two gripping elements 302 mounted to each gnpper element mounting arm 304 can adjust dependent on the alignment of the inner surface of the shaft ring 305 to correspond thereto, such that both gripping elements 302 fully engage with the inner wall and hence grip the shaft ring 305 properly.

Although embodiments of the invention have been shown and described, it will be appreciated by those skilled in the art that these are preferred embodiments only and that changes may be made to these embodiments, or alternative embodiments are included, within the scope of the invention which is defined in the claims hereafter.

Claims

1. A shaft-ting gripper comprising a support structure having an axis and a plurality of gripping elements displaceable in a radially outward direction relative to the axis when the support structure, which has been lowered in an axial direction into an open upper end of a shaft-ring, is lifted, so that the gripping elements engage the inner wall of the shaft ring to lift the shaft ring together with the support structure, the shaft ring gripper further comprising guide members on the support structure to guide the support structure into the open upper end of a shaft ring when the support structure is lowered.

2. A shaft-ring gripper according to claim 1 , wherein a guide member is associated with each gripping element.

3. A shaft-ring gripper according to claim 1 or claim 2, wherein a portion of each guide member is spaced from the gripping elements in a radially outward direction, the guide members extending beyond the gripping elements in an axial direction towards the open upper end of a shaft ring disposed beneath the support structure so that, when the support structure is lowered, the wall of the shaft ring is received between the gripping elements and said guide members.

4. A shaft-ring gripper according to claim 3, wherein at least said portion of each guide member that extends beyond the gripping elements in an axial direction is angled radially outward relative to the axis so that if said angled portion of the guide element contacts the shaft ring when the support structure is lowered, the guide element slides over the shaft ring and centres the support structure above its open upper end.

5. A device for lifting a shaft ring according to any preceding claim wherein the guide members are removable.

6. A shaft-ring gripper according to any preceding claim, wherein the support structure includes a central shaft coaxial with the axis of the support structure and a plurality of support legs extending radially from the central shaft, the gripping elements being mounted on the support legs.

7. A shaft-ring gπpper according to claim 6, wherein each support leg has a gripping element mounting arm pivo tally attached thereto and gripping elements attached adjacent to each end of said arm on either side of the pivot so that the gripping elements mounted on each arm are spaced from each other in the axial direction.

8. A shaft-ring gπpper comprising a support structure having an axis and a plurality of support legs each having gripping elements thereon which are displaceable in a radially outward direction relative to the axis when the support structure, which has been lowered in an axial direction into an open upper end of a shaft-ring, is lifted, so that the gripping elements engage the inner wall of the shaft ring to lift the shaft ring together with the support structure, wherein each support leg has a gripping element mounting arm pivo tally attached thereto, and gripping elements attached adjacent to each end of said arm on either side of the pivot so that the gripping elements mounted on each arm are spaced from each other in the axial direction.

9. A shaft-ring gnpper according to claim 8, wherein the gripping elements are pivotally attached to said gripping element mounting arm.

10. A shaft-ring gnpper according to claim 9, wherein one gripping element is mounted adjacent to each end of a gripping element mounting arm.

11. A shaft-ring gnpper according to claim 9, wherein a pair of gripping elements are mounted adjacent to each end of a gripping element mounting arm, the gripping elements of each pair being mounted on either side of the mounting arm.

12. A shaft-ring gripper according to any of claims 6 to 11, wherein the support structure comprises first and second sets of support legs each having gripping elements thereon, wherein the second set of support legs are below the first set and are configured such that the gripping elements on one leg are disposed at a different distance from the axis to the gripping elements on the other legs of said set to counterbalance the eccentric centre of mass of a cone shaped shaft ring Lifted by the gripper

13. A shaft-ring gripper comprising a support structure having an axis and a first and second set of support legs each having gripping elements thereon which are displaceable in a radially outward direction relative to the axis when the support structure, which has been lowered in an axial direction into an open upper end of a shaft-ring, is lifted, so that the gripping elements of one set of support elements engage the inner wall of a shaft ring to lift the shaft ring together with the support structure, wherein the second set of support legs are below the first set and are configured such that the gripping elements on at least one leg are disposed at a different distance from the axis to the gripping elements on the other legs of said set to counterbalance the eccentric center of mass of a cone shaped shaft ring lifted by the gripper.