GB2105398A

GB2105398A - Multiple extension members

Info

Publication number: GB2105398A
Application number: GB08126614A
Authority: GB
Inventors: John Archer Haswell
Original assignee: MERRYWEATHER AND SONS AND LIMI
Current assignee: MERRYWEATHER AND SONS AND LIMI
Priority date: 1981-09-02
Filing date: 1981-09-02
Publication date: 1983-03-23
Also published as: GB2105398B; IT1154337B; IT8249057A0; DE3232299A1

Abstract

A multiple extension member in the form of a ladder or crane has two separate rope systems. A first rope system consists of a loop on each intermediate section and attached to the adjacent sections ensures synchronism of the relative movement of the sections. A second rope system consists of an extending rope zigzagging up the sections which is moved differentially with respect to a retracting rope which extends directly to the uppermost section. Duplication of ropes and safety locks is mentioned. <IMAGE>

Description

SPECIFICATION Multiple extension members This invention relates to multiple extension members and particularly but not exclusively to multiple extension ladders for use on fire escapes or fire engines.

Multiple extension ladders as used for fire fighting and fire-escape hitherto have used an extension system in which the lowest extending section is moved either by a hoisting rope or hydraulic cylinder and coupling mechanisms between the extending sections are arranged to ensure that the remaining extending sections move relative to the section on which they are carried to the same extent as the carrying section moves relative to the section on which it is carried, i.e. true proportional movement is achieved. A disadvantage of this system is that the actuating means, that is to say the hoisting rope or hydraulic cylinder has to operate at a considerable mechanical disadvantage relative to loads at the top of the ladder and the sliding friction between the sections. This mechanical disadvantage means that the actuating means must be correspondingly bulky and heavily constructed.

It is an object of the present invention to provide an improved means for proportionally extending a multiple extension member in which the heavy loads imposed on the actuating means are reduced.

According to the present invention there is provided a multiple extension member having a plurality of extension sections arranged so that each section is slidable relative to the section below it, wherein the member includes two rope systems, the first system including for each extension section having a section above it and a section below it, a loop or rope on pulleys mounted on the particular extension section, the loop being attached to both the section above it and the section below it so that the section above is constrained to project beyond the particular section by the same amount as that which the particular section projects beyond the section below it, and the second system including an extending rope and a retracting rope moved differentially, the extending rope passing in zig-zag fashion from the lower end of the lowest section to an attachment on the lower end of the uppermost section over pulleys on all but the uppermost section so that shortening of the extending rope results in extension of the member and the retracting rope passing directly from the lower end of the lowest section to an attachment on the uppermost section.

The member may be a fire escape or fire fighting ladder or it may be an extendible arm suitable for a crane or for carrying personnel in a cockpit to a required position, for example for cleaning street lamp standards or tree surgery. For safety and for balancing the loads on the sections of the member the rope systems may be duplicated or provided as an even greater plurality, so that lighter-weight ropes and pulleys can be employed.

In order that the invention may be fully understood and readily carried into effect it will now be described with reference to the accompanying drawings, of which: FIGURE 1 is a diagram of one embodiment of the invention; and FIGURE 2 shows in detail and partly in cross-section the embodiment of Figure 1 in the form of an extending ladder.

Referring now to Figure 1, the embodiment shown therein in diagrammatic form is an extending ladder having four ladder sections L1, L2, L3, and L4. L1 is the lowermost section and L4 the uppermost. In practice, the section L1 might be mounted on an elevating and rotating platform on a fire fighting appliance. For clarity the two rope systems used in Figure 1 are shown separately with the ladder sections L1 to L4 duplicated but linked together by dotted lines. The first rope system serves to synchronise the relative movement of the ladder sections so that, for example, section L3 is moved relative to section L2 by the same distance as the section L2 is moved relative to the section Li.This rope system consists of two closed loops S1 and S2 respectively mounted on the ladder sections L2 and L3 on pulleys Al and A2 and B1 and B2. The loop S1 is attached to a point P1 on the section L1 and to a point P3 on the section L3. The loop S2 is attached to a point P2 on section L2 and P4 of the section L4. It will be apparent that by virtue of the operation of the loops S1 and S2 the relative movement of the ladder sections L2, L3 and L4 will be synchronised as required.

The second rope system, forming the extending mechanism, consists of an extending rope E passing from a drum D over a pulley C1 at the top end of section L1, back to a pulley C2A at the bottom of section L2, up to a second pulley C2B on the section L2, but this time at the tip of that section, back to a pulley C3A at the bottom of section L3, forward over a pulley C3B at the top of section L3, and back to an attachment QE at the bottom of the section L4. The second rope system also includes a retracting rope R, also wound on the drum D but in the opposite sense to the extending rope E, which extends directly from the drum D to an attachment OR on the section L4 and is led over guide pulleys G on the various sections.In operation the drum D would be rotated in a clockwise direction to wind up the extending rope E and thereby reduce its length, so that the distances from pulley C1 to the pulley C2A, from the pulley C2B to the pulley C3A and from the pulley C3B to the attachment point QE are reduced.

This will result in the ladder being extended, and by virtue of the synchronising mechanism provided by the first rope system the extension of the ladder will take place uniformly. As the extending rope E is taken in by the drum D, so the retracting rope R is wound out and it will be apparent that the extension required of the rope R is substantially equal to the reduction in length of the extending rope E. The differential relationship between the lengths of the extending rope E and the retracting rope R can be maintained more accurately if the angle between the retrogressive sections of the extending rope E to the longitudinal axis of the ladder is kept as near as possible the same as the angle of the retracting rope R to the longitudinal axis of the ladder.

For use in connection with the ladder, the extension mechanism described should be arranged so that the rungs between the ladder sections are aligned with one another at each permitted extension of the ladder. Whilst it would be possible to have only one of each kind of rope system, it would be preferable for two or more to be provided to balance the loads and thereby avoid lateral forces on the sliding mechanisms provided between the ladder sections; these sliding mechanisms are not shown in Figure 1 since they do not form part of the invention and would make the Figure more difficult to understand.

Whilst the duplication of the rope systems would provide some protection against rope failure, additional security in this respect could be provided by attaching hinged brackets to the pulleys so that in the event of a reduction in the tension on a pulley a bracket would drop down to engage with the rung on a lower section of the ladder.

The advantage of the invention over the previously used arrangement can be seen in the reduction in the tension in the rope resulting from the use of the invention as set out in the table below for extension ladders having from one to six extending sections.

Ladder Arrangement Prior art This proposal 53' Single Extension 205 Ib 205 Ib 76' Double Extension 2,005 1,050 99' Triple Extension 7,487 2,618 122' Quadruple Extension 18,022 4,718 145' Quintruple Extension 39,949 8,361 168' Sextuple Extension 91,680 16,000 app.

It will be apparent that the reduction in tension resulting from the use of the invention is by a factor substantially equal to the number of extension sections.

Figure 2 shows how the rope mechanisms shown in Figure 1 could be implemented on a foursection fire fighting ladder. Figure 2 shows such a ladder in cross-section with the parts carrying the same references as in Figure 1. It should be noted that Figure 2 shows only half of the ladder but the relationship between the parts will be clear from Figure 2.

Although the invention has been described with respect to an embodiment in the form of an extending ladder, it could be applied to other forms of extending member such as crane arms or arms for carrying personnel cockpits, for example.

Claims

1. A multiple extension member having a plurality of extension sections arranged so that each section is slidable relative to the section below it, wherein the member includes two rope systems, the first system including for each extension section having a section above it and a section below it, a loop or rope on pulleys mounted on the particular extension section, the loop being attached to both the section above it and the section below it so that the section above is constrained to project beyond the particular section by the same amount as that which the particular section projects beyond the section below it, and the second system including an extending rope and a retracting rope moved differentially, the extending rope passing in zig-zag fashion from the lower end of the lowest section to an attachment on the lower end of the uppermost section over pulleys on ali but the uppermost section so that shortening of the extending rope results in extension of the member and the retracting rope passing directly from the lower end of the lowest section to an attachment on the uppermost section.

2. A multiple extension member according to claim 1 wherein at least one of the first and second rope systems is duplicated or provided as a larger plurality.

3. A multiple extension member according to claim 1 or 2 wherein at least one of the pulleys is provided with means for preventing the collapse of the member when extended in the event of a rope breaking.

4. A multiple extension member according to claim 3 wherein the means for preventing collapse comprises a bracket attached to the at least one pulley which is arranged to block downward movement of a section relative to the section below it on reduction in the tension of a rope passing round the at least one pulley.

5. A multiple extension member according to any preceding claim wherein the extending rope and the retracting rope are wound in opposite senses on a drum.

6. A multiple extension member according to claim 5 in the form of a ladder, wherein means is provided for ensuring that rotation of the drum can be stopped when rungs on adjacent sections are aligned.

7. A multiple extension member substantially as described herein with reference to the accompanying drawings.