GB2197394A - Jib cranes - Google Patents

Abstract

A jib crane comprises a fixed support pillar pivotally mounting a jib arm and a support leg 5 fixedly attached to the jib arm remote from the pillar. The base of the support leg 5 mounts a shoe 6 on the underside of which two removable tray assemblies 7 are slidably received. Each tray assembly 7 carries an air bearing pad 23 having apertures 28 through which air supplied to the pad 23 via a coupling 30 egresses to form an air film f at the base of the support leg 5 which permits movement of the support leg 5 relative to the ground 31 without friction. As a result, pivotal movement of the jib arm 3 relative to the support pillar 1 is facilitated. <IMAGE>

Description

SPECIFICATION Jib crane This invention concerns an improved jib crane.

Traditionally jib cranes comprise a pillar fixed to a suitable foundation or structure with a jib arm mounted on the pillar for controlled pivotal movement relative to the pillar. The jib arm mounts the hoist device for engaging the load to be lifted and moved, and typical hoist devices include one or more hoist pulleys with suitable hook or grapples for connection to the load. Usually the hoist device is arranged for movement lengthwise of the jib arm.

With such traditional jib cranes, the major forces are transmitted to the pillar and, to a large extent the loading is limited by the strength of the jib arm and it's connection to the pillar.

To increase the load carrying capacity of such jib cranes, it has already been proposed to provide a ground engaging support depending from the free end of the jib arm. Usually this support is a leg which has a wheel assembly for engaging the ground or a track to enable the leg to move relative to the ground when the jib arm is pivoted about the fixed pillar.

As will be appreciated, the load forces are distributed between the fixed pillar and the ground engaging wheel assembly, and considerable power is required to move the jib arm in the load carrying mode both to move the jib arm with load and to overcome the forces and frictional resistance in the wheel assembly engaging the ground or a track.

In addition to the power requirement, such ground engaging wheel assemblies are subject to wear and this applies even to installations where a track is provided.

It is an object of this invention to provide an improved jib crane which obviates high wear and friction and which avoids the use of ground engaging wheels for a dependent support leg.

According to this invention, we provide a jib crane comprising a fixed support pillar pivotally mounting a jib arm, a dependent support leg fixedly mounted on the jib arm remote from the support pillar, the base of the leg mounting a shoe arranged to receive an air bearing pad, and means for conducting air to the bearing pad when mounted in the shoe to provide an air film load support at the base of the leg.

By this invention, in use of the crane with the air bearing pad supplied with air, there is no effective friction between the base of the leg and the ground so that there is no frictional resistance to movement of the jib arm except at the pivot bearing on the support pillar. In addition, there is no wear or direct contact with the ground and no track or the like has to be provided.

Preferably, the shoe mounted on the leg is arranged to receive two air bearing pads in opposed aligned located positions.

By this arrangement the bearing area of the air film may be substantial whilst providing either a fail-safe arrangement in the event of one air film collapsing or to accommodate uneveness in the ground surface during relative movement.

Conveniently, the air supply to each air bearing pad may be conducted from the pillar support and along the jib arm and down the support leg to the location of each air bearing pad.

With this manner of conducting the air supply by suitable pipe(s) or tube(s) or hose(s), there are no trailing air supply connections associated with the dependent leg which is movable relative to the support pillar.

Preferably, mounted on the dependent leg there is a control member for actuating an air supply valve associated with the air supply and each air bearing pad so that the air supply can be controlled to provide the pressure supply, when required, to each air bearing pad.

The control member may be a simple handle device coupled to an air control valve.

Preferably, each air bearing is mounted on a tray having a peripheral rim which acts as a guard to protect the air bearing pad, and the tray is slidably mounted in the shoe.

The tray may include a detachable coupling for connection to the air supply hose or pipe.

In known manner, the air bearing comprises a rubber or like flexible diaphragm mounted on a support plate to define an air chamber into which the air is supplied under pressure. The diaphragm has a series of apertures through which air egresses to provide the load supporting air film between the ground and the air bearing pad. Various designs of such air bearings are commonly known, and can be applied to this invention.

Generally, the invented jib crane provides many practical advantages over conventional jib cranes. In particular, the foundation block for the support pillar may not be so massive, the invented jib crane can provide improved increased radius to load ratios, and the overall structure may be simplified and of less massive construction.

Other features of the invented jib crane will be described and referred to with reference to an exemplary embodiment of the invention as depicted in the accompanying drawings wherein: FIGURE 1 is an isometric general view of the jib crane and showing a removable air bearing tray; FIGURE 2 is an enlarged view of the shoe and the removal of the air bearing tray; and FIGURE 3 is a schematic sectional enlarged view of the air bearing arrangement to one side of the dependent leg support of the jib crane.

With reference to the drawings, the jib crane comprises a support pillar 1 which is rigidly mounted by means of a pedestal 2 that is bolted or otherwise secured (in known manner) to a concrete pad or like ground structure.

A jib arm 3 is mounted at one end on the upper end of the pillar 1 by a swivel or pivot bearing 4. The other end of jib arm 3 is rigidly connected to a dependent support leg 5 of which the lower end carries a shoe 6 in which two similar opposed removable air bearing tray assemblies 7 are supported.

The jib arm 3 is a conventional I-beam and has mounted thereon a hoist device 8. In known manner, the hoist 8 includes wheels 9 for rolling engagement with the I-beam for moving the hoist 8 along the length of the jib arm, and the hoist 8 has a support hook 10 on one end of a chain or rope 11 of which relative movement may be controlled by a motorised pulley block 12 in known manner.

The support leg 5 is of hollow box section and on the lower end there are gusset webs 13 extending to each opposed side and to secure the shoe 6 thereto by means of bolts 14 which extend through lugs 15 and 16 respectively on the gusset 13 and shoe 6. The shoe 6 has a cover top plate 17 of substantial rigid form with two opposed side walls 18 that extend parallel to each other with each side wall 18 having an internal groove or ledge 19 extending lengthwise of the wall.

Each end of the top plate 17 is curved in plan view and to the underside there is a clearance opening 20 between the two side walls 18. This clearance opening 20 provides an entry for the bearing tray assemblies 7 to be entered or removed from the shoe 6 as schematically depicted in Figures 2 and 3.

Each bearing tray assembly 7 is similar and comprises a tray member 21 of sheet steel or the like which is generally of complementary shape to the inside of the side of the shoe 6 in which it is to be received with the side edges of the tray member 21 engaging the grooves or ledges 19. The tray member 21 has an outer dependent wall 22 which serves as a guard wall and ground rest in conjunction with the side wall 18 of the shoe 6.

Each air bearing 23 is similar and is in the form of a pad comprising an annular back plate 24 having a central boss 25. A flexible annular diaphragm 26 is secured by it's peripheral edge to the back plate 24 and the centre of the diaphragm 26 is secured to and over the boss 25 by plate 27. The diaphragm 26 is formed with a series of air outlet holes 28 through which pressurised air flows from a pressure chamber 29 defined by the backplate 24 and diaphragm 26 to which air is admitted through connection(s) (not shown) communicating with an air supply block connection 30 arranged within the shoe 6. In known manner, when air pressure is applied in the chamber 29, then an air film is formed between the ground 31 and the face of the diaphragm providing a film "f" of air which is load support- ing permitting hover-like reaction, without friction.

Each bearing tray assembly 7 may be inserted or be removed from the shoe 6 by sliding the tray assembly out of the entry in the shoe, and a suitable quick release device may be incorporated in the air supply block 30 for automatic coupling and uncoupling.

The air supply pipe(s) or hose(s) are not shown in detail in the drawings but a suitable hose 32 connected to a pneumatic source such as a compressor may be conducted up the support pillar 1, over the jib arm 3 and down the dependent leg 5 to the block 30. A control valve (not shown) for controlling the supply of air to the air bearing through the block 30 may be mounted in or on the dependent leg 5 with a control handle 33 for actuating the valve being accessible to one side of the leg 5 as shown in Figure 1.

As will now be appreciated, the jib crane as just described includes the air pad bearings which, when functioning on actuation of the control handle 33, support the load transmitted to the dependent leg 5 and enable the jib arm 3 and any hoist supported load to be moved on swinging movement of the jib arm without high frictional forces acting between the ground and the dependent leg.

Thus the power requirements for load movement may be considerably less than those required for a traditional jib crane, and the pneumatic source is only required when the crane is in use.

It is envisaged that the air bearing tray assemblies may be removed when the jib crane is not in use or for servicing. When the air bearing tray assemblies are removed, then the dependent leg will be supported by the shoe engaging the ground.

Although in the preferred embodiment of the invented jib crane there are two air bearing tray assemblies, a simplified arrangement with only one air bearing could be applied.

Alternatively, more than two air bearings may be used by modification to the shoe.

Other types of air bearings may be used and the preferred type as described herein is only exemplary.

Claims (15)

1. A jib crane comprising a fixed support pillar pivotally mounting a jib arm, a dependent support leg fixedly mounted on the jib arm remote from the support pillar, the base of the leg mounting a shoe arranged to receive an air bearing pad, and means for conducting air to the bearing pad when mounted in the shoe to provide an air film load support at the base of the leg.

2. A jib crane according to Claim 1 wherein the air bearing pad is detachable from the shoe.

3. A jib crane according to Claim 1 or Claim 2 wherein the air bearing pad is mounted on a detachable tray slidably received in the shoe.

4. A jib crane according to Claim 4 wherein the tray includes a detachable coupling for connection to the air connection means.

5. A jib crane according to any one of the preceding Claims wherein the shoe and/or tray provide a peripheral guard wall for the air bearing pad.

6. A jib crane according to any one of the preceding Claims wherein the air bearing pad has a series of apertures through which the air egresses to provide the air film load support.

7. A jib crane according to Claim 6 wherein the air bearing pad comprises a flexible diaphragm mounted on a support plate to define an air chamber into which the air is supplied and the apertures are formed in the diaphragm.

8. A jib crane according to any one of the preceding Claims wherein the air conducting means includes a supply valve for controlling the air supply to the air bearing pad.

9. A jib crane according to Claim 8 wherein the supply valve is operable by a control member.

10. A jib crane according to any one of the preceding Claims wherein the air conducting means is mounted on the support leg.

11. A jib crane according to any one of the preceding Claims wherein the air conducting means is arranged to extend from the support pillar along the jib arm and down the support leg.

12. A jib crane according to any one of the preceding Claims wherein the shoe is arranged to receive two or more air bearing pads.

13. A jib crane according to any one of the preceding Claims wherein the jib arm is provided with a hoist device.

14. A jib crane according to Claim 13 wherein the hoist device is movable lengthwise of the jib arm.

15. A jib crane substantially as hereinbefore described with reference to the accompanying drawings.