GB2066763A - Polar crane - Google Patents

Abstract

In many applications polar cranes have to be repeatedly positioned with high accuracy. A guidance system is disclosed which has two pairs of guides 20, 22 and 24, 26. Each guide consists of two rollers carried by a sheave rotatably mounted on the crane bridge 12, the rollers being locatable one on each side of a guideway, e.g. the circular track 14 on which the bridge runs. The pairs of guides 20, 22 and 24 and 24, 26 are interconnected by respective rope loops 58 and 60 which pass around and are locked to the respective pairs of sheaves in such a manner that movement of one guide results in equal movement of the other guide in a sense to maintain the repeatability of positioning of the centre C of the bridge 12. A hydraulically-linked guide system is also described. <IMAGE>

Description

SPECIFICATION Polar crane The invention relates to polar cranes.

Polar cranes are cranes of the kind in which a crane bridge is rotatably mounted on a circular track and may be used, for example in the reactor dome of a nuclear reactor.

In such an application, the crane is operable to remove and replace the reactor cover and to replace spent fuel elements with fresh fuel elements. That type of duty imposes a requirement on the crane of high repeatability of positioning of the centre of the crane bridge (e.g.

to within 6 millimetres (mm)) in relation to the notional working area of the crane.

However, allowance has to be made in the guidance system of that type of crane for expansion of the crane bridge. For a bridge having a 40 metre (m) span, expansion in the region of 25 mm can be expected under normal working conditions and in the region of 62 mm under reactor "explosion" conditions when the bridge temperature could rise rapidly to around 1 500C.

Additionally, in order to maintain repeatability of location, bridge expansion should be accommodated symmetrically with respect to the bridge centre.

It will be clear that a conventional roller guidance system, in accommodating the abovementioned expansions, will allow considerable movement of the bridge. For example, one end only may then move along the track some 1 to 2 m. Consequently, repeatability of location will not be very good. Also with a conventional system, expansion is not necessarily accommodated symmetrically of the bridge centre.

A further requirement of that type of crane is for the load to be shared equally, if possible, by all the guidance points so that the crane has a greater chance of surviving shock loads from, for example, reactor "explosion" or earth tremors. With the conventional guidance system, it will be apparent that generally only two, and often only one, of the guidance points will bear the load.

UK Patent No. 1120949 discloses a system for guiding a linear crane, i.e. one travelling on parallel tracks, which involve mechanically or hydraulically linking a pair of guide members so that they move equally and opposite to one another. A further pair of guide members may be provided in a position spaced from the first pair in the direction of travel of the crane.

It will be apparent, however, that that system would not guide a polar crane. It would allow the crane bridge to move linearly (instead of only rotationally) to take up the maximum movement allowed by the guidance system.

It is an object of the invention to provide a polar crane with a guidance system which at least in part fulfills the above requirements.

A polar crane, in accordance with the invention comprises a bridge, load-bearing wheels mounted on the bridge engaging a circular track, two pairs of guides, the guides in each pair being mounted on opposite end halves of the bridge, circular guideway surfaces for interaction with the guides and mechanical or hydraulic linkage means interconnecting the guides of each pair whereby movement of one guide results in movement of the other guide of the pair in a sense to maintain the repeatability of positioning of the centre of the bridge.

Preferably, the guides each comprise two rollers between which the track or a separate guideway extends, the opposite sides of the track or guideway providing said guideway surfaces.

Alternatively, the guides each comprise one roller between two guideway surfaces provided by the track and a guideway; or by two guideways; or by a channel-shaped track or guideway.

Two forms of polar crane will now be described to illustrate the invention by way of example only with reference to the accompanying drawings, in which: Figure 1 is a view from underneath a first form of polar crane; Figure 2 is a view on line Il-lI in Figure 1; Figures 3 and 5 are views on lines Ill-Ill and V-V in Figures 4 and 6, respectively; Figures 4, 6 and 7 are, respectively, enlarged plan view of the areas circled and labelled IV, VI and VII, respectively, in Figure 1; Figure 8 is a view similar to Figure 1 of a second form of polar crane; Figure 9 is an enlarged underneath of the area circled and labelled IX in Figure 8; and Figure 10 is a view on arrow X in Figure 9.

The polar crane 10 in Figures 1 to 7 has a bridge 12 which spans a circular track 14. The track 14 is mounted on a support girder 16 which is secured to the walls of a building or to some other support structure (not shown) The bridge 12 is of conventional construction and carries on its upper surfaces, a movable carriage (not shown) from which a load can be suspended and other usual control and auxiliary equipment (not shown).

The bridge 12 has four load-bearing wheels 18 which engage the circular track 14.

The bridge 12 is guided relative to the track 14 by two pairs of guides 20, 22 and 24, 26, respectively, which interact with guideway surfaces provided by opposite sides 1 4a of the track 14. As can be seen from the drawing, the pairs of guides 20, 22 and 24, 26 are positioned at the ends of respective horizontal straight lines which, as viewed in plan, intersect at their centres at the centre C of the bridge 12.

The guides 20, 22, 24 and 26 are all the same and only guide 20 is described below. Guide 20 consists of a sheave 28 (see Figures 3 and 4). The sheave 28 has an enlarged position 30 which is provided with three through-bores 32, 34 and 36.

A pivot pin 38, carried by the bridge 12, engages the bore 32 through bearing sleeves to rotatably mount the sheave 28 on the bridge 12.

Pins 40, 42, which have eccentric shafts 44 and 46, respectively, extending from their lower ends, are locked in the bores 34, 36, respectively.

Guide rollers 48 and 50 are mounted on the shafts 44 and 46, respectively, by roller bearings. The shafts 44 and 46 are eccentric to the pins 40 and 42 to allow adjustment of the clearance between the rail and the respective guide rollers 44 and 46 which are located one on each side of the track 14. Typically, the roller clearance from the guideway surfaces 1 4a is 1 mm.

The sheave 28 has a shaped portion 52 against which a steel wire rope passing round the sheave 28 is locked by locking plates 54 and bolts 56.

The pairs of guides 20, 22 and 24, 26 are linked together by respective steel wire ropes 58 and 60 formed into a closed loop. The ropes 53 and 60 are connected together and tensioned by respective turnbuckles 62 and 64. The ropes 58 and 60 pass around guide pulleys 66 (see Figures 5 and 6) to keep them clear of the centre of the bridge 12. The pulleys 66 are mounted on the mounting pins 68 by roller bearings.

In an alternative construction, the turnbuckles at2, 64 could be replaced by self-tightening devices so that the ropes are maintained at substantially constant tension.

As can be seen from Figure 1, pivotal movement (say clockwise) of one guide 20, say of a pair will result in the equal, clockwise pivotal movement of the other guide 22 of the pair, the guides being connected by the rope 58. Thus, the rollers of the guides 20, 22 all move away from the centre of the bridge.

It will be appreciated that the bridge 12 is positively guided with respect to the track 14 by the guides 20, 22, 24 and 26 which accommodate thermal expansions and track defects without affecting the repeatability of positioning of the centre of the bridge 12 by the crane. The guides also tend to share loads substantially equally between themselves.

The polar crane 110 in Figures 8 to 10 is similar to that shown in Figures 1 to 7 except that the pairs of guides 120, 122 and 124, 126 are linked together hydraulically.

The guides 120, 122, 124 and 126 are all the same and only guide 126 is described below. The guide 126 consists of a member 128 having three through-bores 132, 134 and 136. A pivot pin 138, carried by the bridge 112, engages the bore 132 through bearing sleeves to pivotally mount the member 128 on the bridge 112.

Pins 140 and 142, which have eccentric shafts 144 and 146, respectively, extending from their lower ends, are locked in the bores 134 and 136, respectively. Guide rollers 148 and 150 are mounted on the shafts 144 and 146, respectively, by roller bearings. The guide rollers 148 and 150 are located on either side of the track 114 for interaction with the guideway surfaces 1 1 4a and are adjustable with respect to the track 114 similarly to the rollers 48 and 50 of the first embodiment.

A web 152 on the member 128 has one end of a link 154 pivotally attached to it. The other end of the link 1 54 is pivotally attached to the piston rod 156 of a double-acting hydraulic unit. The cylinder 1 58 of the unit is secured to the bridge 112.

Operation of the unit causes the member 128 to pivot about pin 138.

As can be seen from Figure 8, the piston and cylinder units of the pairs of guides 120, 122 and 124, 126 are linked by pairs of hydraulic lines 160, 162 and 164,166 so that pivotal movement of one guide of the pair will result in equal and opposite movement of the other guide of the pair.

Thus, the bridge 112 is positively guided by the guides similarly to the bridge 12.

A hydraulic accumulator 1 68 is connected to each of the hydraulic lines 160, 162, 1 64 and 166 through check valves 170 to ensure that she pressure in each of the lines is maintained constant. Each pair of hydraulic lines 160, 162 and 164, 166 are interconnected by by-pass valves 172 and 174, respectively. The valves 172, 174 are normally closed but can be opened to enable the pairs of guides to be centralised.

In a modification, the positions of the pistons and cylinders can be reversed, i.e. the piston can be secured to the bridge. Other combinations of pistons and cylinders are also possible.

The repeatability of location of the centres of the bridges 12 and 112 using the guide systems described is better than the required 6 mm. With a roller/track clearance of 1 mm and an angle of 250 for (b (i.e. the angle between the end of the bridge and the tangent to the track at the pivot point of the guide means), the repeatability in the longitudinal direction (arrow A in Figure 1) is +0.5 mm and in the transverse direction (arrow B in Figure 1) is +0.5 sin sJ = + 1.2 mm.

The value of 9 is not critical but too small an angle should be avoided. That is because at small angles the track approximates to parallel rails and the guidance systems described will not then positively guide the bridge.

In a modification of the embodiments described, a single guide roller can replace the two guide rollers of the guides, the single guide rollers being located between concentric rails or between the concentric limbs of a U-shaped track.

t will be appreciated that other forms of guides may be used (not necessarily pivotal types) provided that the guide roller of each guide move substantially normally to the track. In applications where relatively large movements can occur owing, for example, to out-of-roundness of the track, then provision would have to be made to maintain the pair of guide rollers of each guide substantially normal to the track.

In a further modification (not shown) the linkage between the guides in any pair may be arranged to cause one guide to move in the opposite angular sense to the other guide instead of moving in the same angular sense, provided the rollers are so arranged in relation to the pivotal axes of the guides that the movements of the guides in any pair always produce equal and opposite reactions at the mountings of the guides on the bridge.

The guides may move rectilinearly instead of angularly.

Whatever the arrangement, the rollers are arranged so that the movement of one guide in any pair caused by expansion of the bridge or by non-circularity in the track always causes movement of the other guide in the pair such that at the guide mountings the bridge is subjected to equal and opposite reactions. The one guide thus causes the other guide to move in a sense such as to maintain the repeatability of positioning of the centre of the bridge in relation to the notional working area of the crane.

Claims (9)

1. A polar crane comprising a bridge, loadbearing wheels mounted on the bridge engaging a circular track, two pairs of guides, the guides in each pair being mounted on opposite end halves of the bridge, circular guideway surfaces for interaction with the guides and mechanical or hydraulic linkage means interconnecting the guides of each pair whereby movement of one guide results in movement of the other guide of the pair in a sense to maintain the repeatability of positioning of the centre of the bridge.

2. A crane according to clairn 1, in which the guides each comprise two rollers between which the track or a separate guideway extends, the opposite sides of the track or guideway providing said guideway surfaces.

3. A crane according to claim 1, in which the guides each comprises one roller between two guideway surfaces provided by the track and a guideway; or by two guideways; or by a channelshaped track or guideway.

4. A crane according to claim 2 or claim 3, in which the guides each comprise a member rotatably mounted on the bridge and carrying said roller or rollers.

5. A crane according to claim 4, in which each member comprises a sheave, said linkage means comprising, for each pair of guides, a loop of rope located around and locked to each pair of sheaves.

6. A crane according to claim 4, in which said linkage means comprises, for each pair of guides, two double-acting hydraulic piston-and-cylinder units, the pistons or cylinders of the units being secured to the bridge adjacent the members of each pair of guides, the cylinder or piston, respectively, of the units being secured to said adjacent member for movement with said member, the cylinder of the units being interconnected by hydraulic lines whereby said movement of one guide resulting from movement of the other guide of the pair is achieved.

7. A polar crane according to claim 1 substantially as hereinbefore described with reference to the accompanying drawings.

8. A polar crane according to claim 1 substantially as hereinbefore described with reference to Figures 1 to 7 of the accompanying drawings.

9. A polar crane according to claim 1 substantially as hereinbefore described with reference to Figures 8 to 10 of the accompanying drawings.