GB2106860A - Improvements in and relating to telescopic booms - Google Patents

Abstract

A telescopic boom for a crane, access platform or the like comprises prises at least three telescopic boom sections the intermediate of which (4) is arranged to be extended by extension means (8) while the outer of which (2) is arranged to be extended by second extension means (14). Safety retaining means (30) extend from a first anchorage (32) on the outer section around a guide (34) and to a second anchorage (36) on the base section (6). The arrangement is such that when and if failure of the second extension means (14) occurs the safety retaining means (30) prevents or contains relative movement of the outer and intermediate sections (2 and 4) and thereby stops sudden and catastrophic retraction of the outer section (2). <IMAGE>

Description

SPECIFICATION Improvements in and relating to telescopic booms The present invention reiates to telescopic booms. Telescopic booms with three or more sections are often used with mobile cranes or with access or work platforms and such booms use a chain or other suitable extension means to extend and contract the outer telescopic boom section. The extension and retraction of intermediate telescopic section(s) is usually by means of a hydraulic cylinder, which in turn causes the extension or retraction of the outer telescopic section by means of the chain or other suitable extension means. Such a system is well known in the industry, and has been used successfully for many years.

The major disadvantage of the use of a chain or other suitable extension means is that mechanical failure of the extension chain or extension means itself or its end attachments may allow sudden and catastrophic retraction of the section being supported, with the possibility of causing death or serious injury to the occupants of an access platform, or others in the vicinity.

Regulatory Authorities in some countries have recognised this danger, and have dictated in particular that access platform booms which incorporate chain systems must be provided with a safety device, which in the event of extension chain failure arrests the linear motion of the boom within 100 mm and also causes tlie power source--i.e. the engine to be shut down.

An object of the present invention is to mitigate or overcome one or more of the above problems.

A telescopic boom according to the present invention comprises at least three telescopic boom sections namely an outer section, an intermediate section and a base section, extension means arranged to extend the intermediate section, second extension means arranged to extend the outer section, and flexi ble safety retaining means extending from a first anchorage on the lower portion of the outer section outwards and around a guide at or adjacent the outer end of the intermediate section and inwardly towards or beyond the foot of the intermediate section to a fixed second anchorage to prevent or contain relative movement of the outer and intermediate boom sections if failure of the second extension means occurs.

Preferably the second anchorage is on the base section at the outer end thereof. In the preferred embodiment means are provided to detect tensioning of the retaining means and consequently either lock the extension means in the extended position to prevent movement of the intermediate section relative the base section and/or immobilise the vehicle sup porting the telescopic boom.

The safety retaining means is provided with a resilient member, preferably a spring, so that the retaining means is resiliently attached to the second anchorage. A safety switch may be provided at or adjacent the second anchor age so that when the retaining means is suddenly tensioned, movement of the retain ing means relative the second anchorage is detected if failure of the second extension means occurs.

Preferably in the event of failure of the second extension means the relative move ment of the boom sections is arrested to within 0.1 m.

An embodiment of the invention will now be described by way of example with refer ence to the accompanying drawings in which: Figure 1 is a diagrammatic cross section of a telescopic boom arrangement according to the invention, and Figure 2 is a plan view of an anchorage point as viewed from direction A on the base section of the boom arrangement in Fig. 1.

In Fig. 1 there is shown a telescopic boom arrangement in which there is an outer boom section 2 telescoping within an intermediate boom section 4 which in turn telescopes within a base boom section 6. The intermedi ate section 4 is extended by first extension means namely a hydraulic ram 8 acting be tween the foot of the base section 6 at a point 10 and the base of the intermediate section at a a point 12. The outer end of the ram 8 is provided with a slipper pad which slides along the inside of the outer boom section 2 to keep apart the ram 8 and boom section 2 and prevent any friction between them.The outer boom section 2 is extended by second exten sion means namely a known chain arrange ment in which a chain 14 which may have two parts, namely an outer chain part 1 5 and an inner chain part 16. The inner chain part 1 6 is anchored to the base section at a point 18, passes around a guide, preferably a pul ley 20, at the foot of the intermediate section 4 and outwardly to an anchorage 22 at the foot of the boom section 2. The outer chain part 1 5 extends from the anchorage 22 around a guide, preferably a pulley 24 at the outer end of the intermediate section 4 and part to an anchorage point 26 at the head of the base section 6.

Chain 14 with its two parts 1 5 and 1 6 forms a flexible extension means for extending the outer section in a known way. Failure of the extension means 14 either in the chain 1 5 or at any of the anchorage points 22 or 26 without any safety device can cause cata strophic retraction of the outer boom section 2.

A flexible safety retaining means, in this case a wire rope 30 extends from an anchor age 32 on the outer boom section 2 around a guide means, in this case a deflector bracket 34 at the head of the intermediate section 4 and then from the bracket 34 inwardly and towards the foot of the intermediate section to a second anchorage 36 at the head of the base section 6. The second anchorage 36 comprises a bracket 38 to the base of which is mounted a fork member 40 having arms 42 through which a securing bolt 44 passes to secure a terminal eye 46 at the end of rope 30. The fork member 40 has a screwed shank 48 which passes through the bracket 38 and on which a spring 50 is mounted. On the end of the shank 48 there is provided a nut 52 retaining the shank on the bracket and against which spring 50 acts.

There is further provided on the shank 48 of the fork member 40 a plate 54 which acts on a switch arm 56 of a switch 58 which is arranged to interrupt a power supply (not shown) to a fail safe engine fuel solenoid (not shown). The vehicle carrying the telescopic boom is consequently immobilised as the engine is shut down.

Alternatively or additionally the switch 58 may be arranged to lock the hydraulic ram 8 in its extended position and prevent movement of the intermediate section relative the base section.

Also attached to the bracket 38 is a pair of linked drag chains 60 between which are guide hoses 62 which may be fitted to the boom arrangement for powering devices at the head of the boom arrangement or for use for controlling the boom arrangement when an access platform is fitted to the outer boom section 2 (see G.B. Patent Application Publication No. 2096568). The drag chains 60 pass around the bracket 34 to an anchorage point 64 adjacent anchorage point 32 on the outer boom section 2.

The bracket 34 has a curved surface which matches approximately the minimum natural bend radius of the drag chain 60 in its unsupported form. A clearance of approximately 10 mm is provided between the curved face of the bracket and the drag chain.

The steel rope 30 is adjusted so that in the normal operating condition the load in the rope is small and the spring 50 at the second anchorage 36 is compressed approximately 50%.

In the event of the failure of the flexible extension means 14 the weight of the outer section 2 will be taken by the steel rope causing the drag link chain to make contact with the bracket 34 and causing compression of the spring 50 at the second anchorage.

The motion of the outer section 2 will thus be arrested. The slight movement of the cable 30 relative to the bracket 38 at the second anchorage being utilized to activate the limit switch 58 which in turn shuts down the power source.

Tests carried out on the boom arrangement as above resulted in the outer boom section 2 being arrested within 55 mm of its initial position.

It will be appreciated that the safety arrangement is suitable for any telescoping boom arrangement either used for the crane or access platform or any other suitable purpose and is not restricted to use with the type of power extension means described.

The term outer section is used above as a purely relative term relative to the intermediate section or sections. That is to say there may be further outer sections, for example a telescopic boom with four sections wherein the second extension means are provided to extend the third and "outer" section will have a fourth and further outer section. In such a case the fourth section may also be extended by the second extension means. Also the invention is not limited to an arrangement having only one intermediate section but other intermediate sections may be provided.

For example a telescopic boom with four sections wherein the second extension means are provided to extend the fourth and outer section will have two intermediate sections one or both of which are extended by the first extension means.

Claims (11)

1. A telescopic boom comprising at least three telescopic boom sections namely an outer section, an intermediate section and a base section, extension means arranged to extend the intermediate section, second extension means arranged to extend the outer section, and flexible safety retaining means extending from a first anchorage on the lover portion of the outer section outwards and around a guide at or adjacent the outer end of the intermediate section and inwardly towards or beyond the foot of the intermediate section to a fixed second anchorage to prevent or contain relative movement of the outer and intermediate boom sections if failure of the second extension means occurs.

2. A boom arrangement as claimed in Claim 1 wherein the second anchorage is on the base section at the outer end thereof.

3. A telescopic boom as claimed in either Claim 1 or 2 wherein means are provided to detect tensioning of the retaining means and consequently lock the extension means in its extended position to prevent movement of the intermediate section relative the base section.

4. A telescopic boom as claimed in any preceding claim wherein means are provided to detect tensioning of the retaining means and consequently immobilise the vehicle supporting the telescopic boom.

5. A telescopic boom as claimed in either Claim 3 or 4 wherein the means is a safety switch at or adjacent the second anchorage which detects movement of the retaining means relative the second anchorage if failure of the second extension means occurs.

6. A telescopic boom as claimed in any preceding claim wherein the safety retaining means is provided with a resilient member so that the retaining means is resiliently attached to the second anchorage.

7. A telescopic boom as claimed in any preceding claim wherein in the event of failure of the second extension means the relative movement of the boom sections is arrested to within 0.1 m.

8. A telescopic boom as claimed in any preceding claim wherein the second extension means is either a hydraulic ram or chain system.

9. A telescopic boom as claimed in any preceding claim wherein the guide is a deflector bracket or pulley at or adjacent the outer end of the intermediate section.

1 0. A crane having a telescopic boom as claimed in any preceding claim.

11. An access lift platform having a telescopic boom as claimed in any preceding claim.

1 2. A telescopic boom substantially as herein described with reference to the accompanying drawings.