Derrick Cranes And Swinging Derricks

Abstract

The invention relates to means provided in the rigging of a derrick crane for preventing or controlling a pendulum movement of the load during a slewing operation.

Description

The invention relates to derrick cranes and particularly to means for controlling such cranes during a slewing operation, that is to say, during a side-to-side movement of the jib.

The invention is of particular application in the loading and/or unloading of ships where loads have to be swung from shore to ship or vice versa and where it is important to effect the transfer as rapidly as possible, with accurate positioning of the load at the end of the slewing operation, without danger of causing damage to the surrounding structure either during or after the operation, without undue stress on the cargo handling gear, and with maximum safety to those engaged in handling the load and crane during the operation.

In the conventional form of derrick crane where the slewing wires are attached only to the jib, there is inevitably, at the end of a slewing operation, an oscillatory movement or swing of the cargo block or load because of the momentum acquired during the slewing motion and only the friction in sheaves, pulleys and/or blocks and the pull of gravity is available to check the swing which prevents positive placing of the cargo block or cargo.

Even when such swing can be controlled manually it is time taking and adds considerably to the time taken to load and/or unload a ship. Furthermore the manual control of such swing may also involve danger to those carrying out the operation.

It is among the objects of the invention to prevent or to minimize oscillation or swing of the cargo block and of the load and thereby increase the safety and reduce the time taken in a slewing operation.

According to the invention there is provided a derrick crane having means, included in the rigging effective to check a swinging movement or oscillation of the cargo block during operation of the crane, including a rigid member secured to the jib and at least one pulley member secured to the jib at a position intermediate its length, and in which the rigging connecting the cargo block to pulley members disposed adjacent the head of the jib, or to pulley members secured to the rigid member and also to pulley members at the head of the jib, defines a pyramid, the apex of the pyramid being located at the cargo block and the base of the pyramid being defined respectively by said pulley members adjacent the head of the jib or by the pulley members secured to the rigid member and the pulley members at the head of the jib.

Thus the means may comprise members including pulley sheaves secured to the jib and so disposed that the connecting rigging forms an inverted pyramid with a base having three or more sides, the apex of the pyramid being located at the cargo block.

The means according to the invention can also be readily changed to provide either a four-part or a six-part purchase on the load, that is to say, a positive effect in four lines or in six lines.

The invention is illustrated by way of example in the accompanying diagrammatic drawings, in which:

FIG. 1 shows a construction in which the rigging forms an inverted triangular pyramid using a single slewing line and providing a four-part purchase on the load;

FIG. 2 shows a construction in which the rigging forms an inverted triangular pyramid using a single slewing line and providing a six-part purchase on the load;

FIG. 3 shows an alternative pyramidal construction using a single line and providing a four-part purchase on the load, and

FIG. 4 shows a pyramidal construction using a single line and providing a six-part purchase on the load.

In the constructions illustrated in the drawings the arrows on the lines indicate the direction of movement and the direction of tension in the line during a slewing operation. When the slewing operation is in the opposite direction the arrows throughout are reversed.

In the drawings 1 denotes the jib, and in FIGS. 1 and 2, a member secured to the jib to support pulley sheaves incorporated in the rigging and connected to the cargo block is denoted by 2. In FIGS. 3 and 4, in addition to the member 2, two auxiliary members, denoted by 2a and 2b for supporting the pulley sheaves are included.

In the construction illustrated in FIG. 1 the pyramidal formation of the connecting rigging is formed by the lines connecting the pulley sheaves 5 with pulley sheaves 4a at the head of the jib and pulley sheaves 4b secured to the member 2. In the construction illustrated additional pulley sheaves 6 and 7 secured to the jib are included in the rigging.

The winch line thus passes by way of pulley block 3, to one of the pulley sheaves 4a at the head of the jib, to one of the pulley sheaves 5 located at the load block, to one of the pulley sheaves 4b secured to the member 2, and, by way of pulley sheaves 6 and 7, the other pulley sheave 4b secured to the member 2, the other pulley sheave 5 at the cargo block, and the other pulley sheave 4a at the head of the jib back to the winch, or if required to an anchor position.

The pulley sheave 7 when secured to the jib as shown provides a four-part purchase on the load, and the anti-oscillatory effect is effected in four lines.

If and when required the pulley sheave 7 may be located at the cargo block as shown in FIG. 2 and connected to pulley sheave 5 rather than secured to the jib thereby providing a six-part purchase, and the anti-oscillatory effect is effected through six lines.

The construction illustrated in FIG. 3 provides a four-part purchase and is similar to that of FIG. 1 except that the rigging connected to the cargo block has a pyramidal formation in which the base of the pyramid is formed by pulley sheaves 4a and 4b located at or near the ends of auxiliary members 2a and 2b and the apex by the cargo block.

The four-part purchase provided by the construction illustrated in FIG. 3 may be changed to a six-part purchase as shown in FIG. 4 by changing the location of pulley sheave 7 from the jib to the cargo block.

In operation the components, in the lines forming the pyramidal formation, of the slewing force exerted by the winch exert a balancing effect on the load and check any tendency for development of swing or oscillation.

Claims

I claim:

1. A derrick crane comprising:

a support surface having a mast extending outwardly therefrom;

a jib movably mounted adjacent one end of said mast and adapted to move relative thereto, said jib having load moving means, including a cargo block, associated therewith;

rigging means for controlling movement of said jib in a plane substantially parallel to the longitudinal axis of said mast and for controlling a sideward movement of said jib relative to said mast;

means, included in the rigging means, effective to check a swinging movement or oscillation of said cargo block during operation of the crane, and comprising a rigid cross member secured to the head end of the jib and extending substantially transversely thereof, first and second spaced and substantially parallel auxiliary rigid members secured to and disposed transversely of said rigid cross member, a pair of first pulley members secured to said first auxiliary rigid member adjacent the opposite ends thereof, a pair of second pulley members secured to said second auxiliary rigid member adjacent the opposite ends thereof, said first and second pulley members being spaced in a substantially rectangular configuration, and a pair of third pulley members secured to the jib at a position intermediate its length and positioned for engagement with the rigging to minimize the pendulum motion of the cargo block in the longitudinal direction of the jib, the rigging connecting the cargo block to said first and second pulley members secured to said auxiliary rigid members defining a pyramid, the apex of the pyramid being located at the cargo block and the base of the pyramid being substantially rectangular.

2. A crane according to claim 1, wherein said rigid cross member and said first and said second auxiliary rigid members define a substantially H-shaped frame fixedly secured to the head end of the jib, said jib being secured to said rigid cross member approximately midway between the ends thereof, the opposite ends of said cross members being respectively secured to said first and second auxiliary rigid member at locations disposed a substantial distance from their respective ends.

3. A crane according to claim 2, wherein said pair of third pulleys are secured to the jib at a location disposed inwardly from the head end thereof, said pair of third pulleys being disposed on substantially opposite sides of the jib but being spaced apart by a distance substantially less than the spacing between the pair of second pulleys.

4. A crane according to claim 1, wherein said rigid member is secured to said jib at a location spaced a substantial distance from the head end of the jib, and further including a pair of third pulley members secured to the jib at a position between the base end of the jib and said rigid member.