AU662777B2 - An extension ladder - Google Patents

Description

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AUSTRALIA

S62777 Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: HILLS INDUSTRIES LIMITED A.C.N. 007 573 417 Actual Inventors: Address for Service: WILLIAM BAILEY RONALD THOMAS DELAFORCE JOSEPH BRIAN LAMB DOUGLAS BROWN 41 4

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o i- I ii CULLEN CO., e-Ma-r-I-A.Ir- evu: -c 2u*r8 er t e e 1. ,Suu

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ura:915~fte, Qld. 4-111w~ l Aucalia. R Y. OG sc"-'-es.

eiYVS'. son A Invention Title: AN EXTENSION LADDER ADDRESS FOR SERV CE Details of Associated Provisional Applicaticns: No. 9 4444 The following statement is a full description of this invention, including the best method of performing it known to us:- 44 e L r ,i 2 THIS INVENTION relates to extension ladders.

Extension ladders consist of a forward pair of stiles between which rungs extend and a rear pair of stiles between which rungs extend. The pairs of stiles are typically maintained in the proper spacial relationship by a pair of guides secured adjacent an upper end of each stile of one of the pairs of stiles. These guides hold the pairs of stiles together and facilitate relative movement between the pairs of stiles during extension and retraction of the ladder. A clutch comprising two spaced pawl members with a clutch bar extending between lower ends of the pawls is pivotally mounted near lower ends of the stiles of one of the pairs. The pawls have leading hook pro,, -tions adapted to engage about a 0 selected rung of the rungs associated with the other pairs of stiles.

In short extension ladders, the clutch is typically hand rated. To extend such ladders the pair of stiles to whici ,he clutch is attached are lifted slightly to enable the hooked projections to clear the rung about which they engage.

The clutch is weighted or balanced so that it normally tends to pivot inwardly of the ladder to engage a rung. The clutch may be pivoted outwardly by grasping the clutch bar. The Sstiles may then slide relative to one another to achieve the desired extension. The clutch bar is then released and it 2q once again pivots to engage a rung to maintain the ladder at that extension.

For longer extension ladders a rope or cord is employed to release the clutch and to enable extension and rrY-ne 3 retraction of the ladder. The rope is trained over two or three pulleys arranged at spaced locations along the ladder and secured to the clutch bar to enable the clutch to be operated. It was the practice to have the rope extend over the rungs of the ladder and this did not provide clear access to the rungs to enable the ladder to be used.

One earlier proposal involved securing the rope to the clutch bar and having the rope pass through the stile adjacent the clutch. The pulleys over which the rope was trained could then be placed on an outer face of the stile to keep a major portion of the rope clear of the rungs of the ladder.

In yet another earlier proposal one of the clutch pawls was provided with a projection spaced from the location at which the pawl was pivotally secured to the stile. One end of the rope was secured to the free end of the extension. The rope was then trained over pulleys located on an outer face of the stiles. This ensured that the rope was kept clear of the rungs.

i With all of these proposals, operation of the clutch proved difficult particularly when the ladder was fully extended. To release the clutch from the rung about which it was engaged it was necessary to pull on the rope and move it laterally of the ladder for a relatively large distance to i 25 achieve tile degree of pivotal movement necessary. In addition it we.s necessary to simultaneously maintain tension on the rope to prevent uncontrolled lowering of the extended stiles Sof the ladder.

IL- t 4 It is an object of the invention to provide an extension ladder which at least minimises the disadvantages referred to above.

According to one aspect, the invention provides an extension ladder having a first pair of stiles, a second pair of stiles, rungs extending between the stiles of each pair, a clutch having pawl means for engaging rungs of the ladder, the clutch being pivotally mounted to one of the pair of stiles, a lever arm pivotally mounting the clutch to the stiles of the one pair of stiles and a cord adjacent an outer face of the stiles fixed to the arm for pivotally moving the clutch.

The pawl means preferably comprise two spaced paw members. The pawl members being pivotally mounted to the stiles of one pair of stiles. One of the pivotal mountings being achieved by the lever arm. The pawl memoers are linked.

Preferably a clutch bar secured to each of the pawl members achieves this link. Each pawl member has a leading portion for engagement with the rungs. Preferably the leading portions are hooked projections.

The lever arm preferably is fixed to one of the pawl members and pivots with it. Alternatively, the arm may be formed integrally with one of the pawl members. The lever arm may have an attachment portion for coupling to the pawl member and a portion to which the cord may be secured. Preferably the portions are cranked relative to each other. In one embodiment the portions extend at about 900 to one another.

The cord is secured to the lever arm and trained over pulleys mounted to an exterior face of the stiles.

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Preferably two pulleys are employed although three pulleys are more preferred. Where three pulleys are present one of them is mounted to one of the stiles of one pair of stiles adjacent and above the lever arm. One of the pulleys is located adjacent an upper end of that stile while the third pulley is located adjacent a lower end of the stile of the other pair of stiles. Guides may be employed for securing the pulleys to the stiles. It is preferred that the guide to which the pulley adjacent the upper end of the stiles is mounted also acts to maintain the stiles adjacent one another to facilitate relative movement of the stiles for extension and retraction of the ladder.

11 rr i i 151 A particular preferred embodiment of the invention will now be described by way of example with reference to the drawings in which: Figure 1 is a part perspective view of an extension ladder according to an embodiment of the invention; Figure 2 is a side view of an extension ladder according to an embodiment of the invention; and Figure 3 is a sectional view taken along line A-A of Figure 2.

The ladder 10 of Figures 1, 2 and 3 has a front pair of stiles 11, 12 and a rear pair of stiles 13, 14. The stiles have rungs 15 extending between them which are swaged to the stiles. The stiles are provided with feet 16 at their lower ends.

A clutch having opposed pawls 20, 21 and a clutch bar 22 extending between the pawls and the clutch is pivotally

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i 6 attached to the stiles 11, 12. Fastener 23 attaches pawl 21 j to stile 11 while pawl 20 is piv,-tally coupled to stile 12 by lever arm 24. Each pawl 20, 21 has a forward hooked j projection 25 (only one of which is visible in Figure 1) for i 5 engagement about a desired rung 15 to maintain the ladder at ii a desired extension.

i Referring to Figure 3, bush 26 is secured in an aperture i i Sin stile 12 and receives portion 27 of arm 24. Portion 27 of Slever arm 24 is fixed relative to pawl 20 by pin 28 and thus I 10 pivotal movement of arm 24 causes the clutch to pivot relative to the stiles. Bush 26 is swaged over at 29 to fix i i i it relative to the stile 12 and enlargements 30 arranged in a i. diametrically opposed pair about the portion 27 to ensure that the arm 24 is maintained fixed relative to the stile 12.

Arm 24 has a portion 31 with an aperture 32 to which a cord 33 is fixed. As shown in Figure 2 the cord 33 is trained over pulleys 34, 35, 36. Guides 37, 38, 39 mount the pulleys to rzspective ones of the stiles 11, 12 and on an outer face of those stiles.

Operation of the ladder is as follows. By pulling downwardly on the length of the cord between pulleys 34 and 36 after the front stiles have been lifted enables the clutch

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to be moved away from the rungs. The ladder can then be t retracted. By pulling downwardly on the cord between pulleys 44 t 35 and 36, the ladder can be extended.

It can be seen that the operation of the ladder is achieved by manipulation of the cord at the side of the ladder. The lever arm is located directly at the location at r 7 which the clutch pivots relative to the stile 12 and thus the action is direct. It is not necessary for the cord to be moved laterally of the ladder. Rather tension only needs to be applied to the cord. When the tension is released the clutch moves under the influence of gravity to normally engage over a selected rung.

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Claims (7)

1. 2. The ladder of claim 1 wherein said pawl means comprises two spaced pawl members linked to each other by a clutch bar, each said pawl member has a leading portion for engagement with the rungs.
2. 3. The ladder of claim 3 wherein the lever arm has an attachment portion which is rigidly connected to the pawl member and an apertured portion to which the cord is secured.
3. 4. The ladder of claim 3 wherein portions of the lever arm It 4 2Q extend substantially at right angles to one another. 444444 The ladder of any one of claims 1 to 4 wherein the cord is trained over pulleys mounted to the outer face of the stiles by guides.
4. 6. The ladder of claim 5 wherein one of the pulleys is mounted to said one stile of the first pair of stiles and above said lever arm.
5. 7. The ladder of claim 5 or 6 wherein another of the Spulleys is mounted to said one stile of the first pair of I- 9 stiles adjacent an upper end thereof and to a guide which also acts to maintain the stiles of each said pair of stiles adjacent one another to facilitate relative movement of the stiles for extension and retraction of the ladder.
6. 8. The ladder of claim 5, 6 or 7 including a third said pulley located adjacent a lower end of one of the stiles of the second pair of stiles.
7. 9. An extension ladder substantially as herein described Swith, reference to the drawings. 0 0 DATED this 13th day of July, 1995 0 HILLS INDUSTRIES LIMITED By its Patent Attorneys R K MADDERN ASSOCIATES i Ag i a* -I I- ABSTRACT An extension ladder (10) is disclosed. The ladder has two pairs of stiles (11, 12 and 13, 14). A clutch having opposed pawls 20, 21 with a clutch bar (22) extending between them is pivotally mounted to the stiles (11, 12) of one pair of stiles by a lever arm A cord (33) trained over pulleys (34, 35, 36) on lever arm side of the ladder is operative to release the clutch. 4* 4 F' *6