GB2056945A - Telescopic jib cranes - Google Patents

Abstract

A crane has a jib formed of three telescopically engaged sections 2, 4, 6 driven for outward and inward telescopic movement by a chain cable or the like 12 which is respectively connected at 56, 52, 12 to the jib sections 2, 4, 6 and movement of which by a motor 60 in one direction drives the sections 2, 4 outwardly and movement of which in the other direction drives the sections 2, 4 inwardly. <IMAGE>

Description

SPECIFICATION Endless chain drive for telescopic jib sections This invention relates to cranes,and in particular to cranes of the type having a jib formed of two or more sections which can be telescoped together.

Such cranes, which will hereafter be referred to as telescopic jib cranes, are usually mobile, i.e. the jib is mounted on a vehicle, the jib being contracted when the crane is to be moved, and extended when the crane is to be used.

Hitherto, it has been the practice to provide hydraulic rams to extend and contract the various jib sections of telescopic jib cranes. However, the provision of such rams, one often being provided for each section, is expensive and the rams which are relatively heavy, increase the weight on the vehicle of a mobile crane thus restricting the load which may be carried by the crane.

A telescopic jib crane in accordance with this invention includes a chain, cable or the like which is connected to at least two telescopic sections of the jib, which passes around at least one pulley sprocket or sheave and which is provided with drive means, the arrangement being such that on operation of the drive means in one direction, the chain or the like is moved to urge the sections outwardly relative to each other and on operation of the drive means in the other direction, the sections are urged to telescope within each other. The chain or the like is preferably an endless loop.

If a chain is employed, which is preferable for safety, then the drive means may include a motor driven chain wheel. Otherwise a winch or the like may be employed.

It will be appreciated that the provision within the telescoping sections of the jib of a single chain or the like together with its associated drive means is very much simpler to operate and is very much lighter in weight than is a number of hydraulic rams.

If the telescopic jib comprises three sections, then preferably the chain is connected at or adjacent the outer end of the base section, passes around a sprocket (which may be driven by the drive means), positioned at and connected to, the inner end of the intermediate section, passes up within the intermediate section, and is anchored to the inner end of the outer or head section of the jib, the chain then passing around a further sprocket at the outer end of the intermediate section back to the anchor point at the head of the base section. Expressed alternatively, the chain loop extends between two sprockets mounted at either end of the intermediate section and is connected to both the head and base sections.

The drive means preferably includes a reversible motor or motor and gear box to enable the direction of drive to be reversed. The motor may, for example, be a high torque low speed hydraulic motor which may be provided with an external brake.

The jib section drive means of this invention is particularly useful with a crane in accordance with the invention or our co-pending Application No.

filed co-terminously herewith, wherein the telescopic jib constitutes a strut supported by tie "ropes" and a tie rope and load compensation arrangement is provided within the jib sections. As explained in the specification of the said application, the load compensation arrangement acts so that as the jib sections are extended, the increasing tension in the tie "ropes" acts to urge the sections outwardly so that only a relatively small force is required to move the said sections outwardly.

An example of the telescopic jib crane in accordance with the invention will now be described by way of example, with reference to the accompanying drawings in which: Figure lisa diagrammatic view of one embodiment of a telescopic jib of a crane in accordance with the invention showing the jib in its erected position; Figure 2 is a diagram showing the arrangement of the means for extending the jib sections, and Figure 3 is an elevation of a mobile crane with the jib sections contracted for transport.

Referring to Figure lithe crane jib which is a "strut" jib is formed of three telescopic sections, namely, a head section 2, an intermediate section 4 and a base section 6. The base section 6 is pivotally mounted at 8 to a turntable platform 10 which may be rotatably mounted in a fixed position or which may form part of a mobile crane vehicle such as that illustrated in Figure 3.

A mobile crane having a telescopic strut jib forms the subject of our co-pending Application No.

filed co-terminously herewith.

The strut jib is supported by two tie ropes 12 of fixed length one at each side of the jib and only one of which is shown in the drawing. Each tie rope passes around a support pulley or sheave 14 carried at one end of a derrick mast 16, the other end of which is pivotally mounted at 18 to the turntable 10.

Theangleofthemastl6totheturntable 10 and hence the angle of the jib is determined by an adjustable ram 20 pivotally connected between the turntable and the head of the derrick mast 16.

A standard hoist rope 22 extends from a hoist 24 on the turntable, around a sheave at the head of the derrick mast, around pulleys 25 at the head of the outer section 2 of the jib for connection to a standard crane hook or the like (not shown).

As can be seen in Figure 2, one end of each tie rope 12 is anchored at 26 within the intermediate jib section 4 to a point adjacent the head of th at section.

The tie rope then extends around a pulley or sheave 28 extending down from, and carried by, the inner end of the outermost jib section 2 up within the jib section 2, and around a second pulley 32 extending out from, and carried by, the head of the head section 2 of the jib.

The tie rope then passes around the support pulley or sheave 14 carried by the head of the derrick mast 16, jib and then around a pulley 34 extending out from, and carried by, the head of the second or intermediate jib section 4. The tie rope then passes down the second jib section and out from the bottom thereof, around a pulley 38 extending from, and carried by, the inner end of the second or intermediate jib section.

The tie rope finally extends out from the base section around a further pulley 42 extending out from, and carried by, the head of the base section 6 of the jib, to an anchor point 46 at the lower end of the intermediary or second jib section 4.

When the head jib section 2 is telescoped into the intermediate section 4, the length of tie rope extending between the pulley 28 and the anchor point 26 is extended to compensate for the extent of telescopic movement of the head jib section 2 within the intermediate jib section 4. Equally, when the section 4 is telescoped into the base section 6, the length of tie rope extending between the pulleys 38 and 42 is extended to compensate for the movement ofthe two sections together. The length of tie rope bet- ween the pulley 42 and the anchor 46 also increases to compensate for the movement of the jib section 2 towards the base section 6.Thus the length of tie rope extending between the support pulley 14 at the derrick mast head, and the pulleys 32 and 34 is reduced to compensate for the shorter jib length whilst maintaining the angle of the jib approximately constant.

Equally, when the jib sections are extended the length of tie rope taken up within the jib length is reduced allowing the length of jib ropes between the pulleys 32,34 and 14to extend, again maintaining the jib angle approximately constant.

When the jib is subjected to load, the load increases the tension in the tie ropes 12 and this increases in tension, as can readily be appreciated from Figure 2, acts to urge the jib sections to move out from each other which compensates for the ten- dency of the applied load to drive the jib sections back within each other.

When the jib sections are being moved outwardly from each other, it will be appreciated that the further the extension, the greater the tension in the tie rope 12, and the greater the tension, the greater the force supplied by the tie ropes on the pulleys 28 and 38 tending to move the sections outwardly. This arrangement therefore has the advantage that the means provided to move the jib sections outwardly need be less powerful than what otherwise would be the case.

The jib sections are moved inwardly and outwardly relative to each other by an endless loop of chain 50 anchored at 52 adjacent the head ofthe base section 6, and then passing up outside the intermediate or second jib section 4 to pass around a sprocket 54 positioned at the top of the intermediate section 4. The chain then passes down within the intermediate section and is anchored at 56 to the inner end ofthe outermost or head section 2.

The chain then passes around a chain wheel or sprocket 58 attached to a bracket extending from the innermost end of the intermediate or second section 4 before returning to be anchored at 52.

The chain wheel 58 is driven by a motor generally indicated at 60 which is either reversible or which is provided with a gear box enabling the direction of movement of the chain loop to be reversed.

The motor 60 may be a high torque low speed hydraulic motor If an external brake is fitted to the motor, the sections may be telescoped when carry ing a load, and held in a retracted position by the brake.

When the motor 60 is driven to rotate the chain loop in a clockwise direction as seen in Figure 2, the head section 2 ofthejib is moved within the intermediate section 4 due to the connection of the chain at 56 and the loop surrounding the chain wheel 58 its extended allowing the intermediate section 4 to move within the base section 6.

Equally, whereth direction of drive is reversed so that the chain is r%roved in an anti-clockwise direction as seen in Figure 2"the head section 2 is urged outwardly from the inrermediate section 4 and intermediate section 4 isi itself moved outwardly from the base section 6.

The outward movementof the various sections is aided by the load compensation arrangement as described above.

The invention thusproMd'es a low cost, low weight, jib section drive system Referring to Figure 3, the rib sections are shown in their collapsed condition carried on a vehicle 62, with the turntable 10 mounted on the vehicle for rotation about an axis indicated by the dot and dash line 65.

The jib may be moved from the erected position shown in Figures 1 and 2 to the contracted position in the manner described in our co-pending Application No. (filed co-terminously herewith).

In the collapsed position, the jib sections rest on supports 65, 66 and a counterweight 68, which in use is mounted at the rearofturntable 10 (see Figure 1 ) is carried on a platform 70.

Claims (6)

1. A crane having a jib formed of at least three telescopically engaged sections wherein the drive means to move the sections out from each other comprises a cable, chain or the like, which is connected to the head and base sections and which passes around a pulley sprocketorwheel on the central section, means being provided to drive the chain.

2. A crane as claimed in Claim 1 in which the chain is a closed loop connected both to the head and base sections and extending between two sprockets mounted at eith er end ofthe intermediate section.

3. A crane as claimed in eiberClaim 1 1 or Claim 2 in which the drive means is reversible and includes a driven chain wheel.

4. Acraneorthelikeasclaimed in Claim 3 in which the drive means includes a high torque low speed hydraulic motor.

5. A crane as claimed in any of the preceding claims wherein the telescopic jib is a "strut" sup ported in use by tie ropes.

6. A crane substantially as hereinbefore described with referent to the accompanying draw ings.