Fire escape – ladder – or scaffold – Ladder – Extension
Reexamination Certificate
1999-04-19
2001-02-20
Chin-Shue, Alvin (Department: 3634)
Fire escape, ladder, or scaffold
Ladder
Extension
C182S212000
Reexamination Certificate
active
06189654
ABSTRACT:
SUMMARY OF THE INVENTION
This invention relates to a ladder. In particular, the invention concerns an extension ladder.
Extension ladders typically consist of a lower ladder section and an upper ladder section secured to one another so that the upper ladder section may be extended relative to the lower ladder section. The upper ladder section from the perspective of a user, is mounted in front of the lower ladder section and extends over the lower ladder section.
Each ladder section has a pair of spaced stiles with rungs extending between them. The upper ladder section usually has a width less than the width of the lower ladder section. Where this is so, the rungs of the upper ladder section are of a shorter length than the rungs of the lower ladder section.
A clutch mechanism having spaced clutch arms linked by a clutch bar is present for locking the upper ladder section at a desired extension relative to the lower ladder section. The clutch arms engage over rungs of the lower section and are pivotally mounted to the upper ladder section. In use the location of the pivot is above those parts of the clutch arms which engage over the selected rung of the lower ladder section. A rope and pulley arrangement is used to lift the upper section to release the clutch arms from the rung over which they locate and to then raise or lower the upper ladder section. The clutch arms are allowed to return to a locked position under the influence of gravity.
Such known ladders are not as strong as they could be because the ladder sections are of different widths. In addition the locking of the clutch arms under gravity does not provide a positive locking action.
By having the upper ladder section in front of the lower ladder section there is a danger that a user may miss a rung as he progresses downwardly over the transitional zone from the lower end of the upper ladder section onto the lower ladder section.
It is an object of the present invention to at least minimise some of the disadvantages referred to above
According to one aspect there is provided an extension ladder having a first ladder section adapted to provide a lower ladder section in use, a second ladder section adapted to provide an upper ladder section in use, the upper and the lower ladder sections each having a pair of spaced ladder stiles with rungs extending between each said stile of a pair of stiles at locations along the ladder sections and both said ladder sections having the same width, the lower ladder section in use being located either forwardly or rearwardly of the upper ladder section, a clutch mechanism including clutch arms extending between the ladder sections and movable between a locked position for maintaining the upper ladder section at a desired extension relative to the lower ladder section and a released position allowing for movement of the sections relative to one another and a clutch locking mechanism for biasing the clutch arms into the locked position, the stiles of each ladder section having formations for securing the sections relative to one another and allowing the upper section to be extended and retracted relative to the lower ladder section.
The formation on the stiles for securing the ladder sections to one another may consist of complementary interlocking projections and recesses which allow for relative sliding movement of the ladder sections while still securing the sections to one another. The formation in one embodiment may be provided along facing edges of the stiles in each ladder section.
In one embodiment the formations are continuous and extend along the length of the stiles. Preferably, the formations include interlocking flanges extending along the stiles. The flanges on one stile of one of the ladder section are preferably oppositely directed to the flanges of the associated stile in the other ladder section. Preferably, each stile has a pair of interlocking flanges and the flanges of the stiles are arranged in an interleaving fashion to secure the stiles to each other.
If desired, a friction reducing lining or insert may be present between the interlocking flanges of two stiles to not only assist the relative sliding action of the ladder sections but also to inhibit relative lateral movement of the stiles. In this way the tendency for the stiles to rattle may be minimised.
The ladder of the invention has a lower ladder section arranged forwardly or rearwardly of an upper ladder section. Each ladder section has two spaced longitudinally extending ladder stiles with a plurality of rungs arranged between the stiles and at spaced locations along the length of the stiles
The rungs may be present at any suitable spaced locations along the stiles either evenly spaced, unevenly spaced or at irregular spacings along the length of the stiles. It is preferred that the rungs be evenly spaced.
The stiles may have any suitable shape in transverse section. Preferably the stiles have a longitudinally extending web with the securing formation along one edge of the web. The other edge may be provided with a strengthening formation to lend rigidity to the ladder. The strengthening formation may be a strengthening flange. Alternatively an enclosed formation may be present along the other edge of the web to strengthen the ladder. Preferably, the enclosed formation is substantially rectangular in transverse cross section although other shapes are not excluded.
At least lower ends of the stiles in each ladder section may be provided with feet inserts. The feet inserts may present inclined ground engaging surfaces. For protecting a wall against which the ladder may stand or for aesthetic purposes, feet inserts may also be provided at upper ends of the stiles of both ladder sections. The feet inserts are preferably secured to the webs of the stiles. Preferably, the inserts are secured to outer faces of the webs.
The ladder sections may be provided with strengthening braces. Preferably strengthening braces are present adjacent to ends of the ladder sections The strengthening braces may consist of a pair of diagonal strengthening struts extending between the stiles of the ladder sections.
The ladder has a clutch mechanism pivotally movable between a locked position which maintains the ladder sections at a desired extension relative to one another and a released position which allows the sections to slide relative to one another.
The clutch mechanism may include two transversely spaced clutch arms fixed to a mounting axle extending across the ladder. The clutch arms and the axle are preferably secured to the lower ladder section and the axle is mounted for rotation relative to that ladder section.
The clutch mechanism may include a clutch release cord, rope, wire or chain for moving the clutch arms between the two positions mentioned above. The clutch release cord may be secured to one of the clutch arms. The other end of the clutch release cord is preferably anchored to the lower ladder section at a location spaced from the arm. The clutch arms may be mounted to the lower ladder section adjacent an upper end of the lower ladder section and the other end of the clutch release cord may be anchored to a lower most rung of the lower ladder section.
The clutch arms may engage with rungs of the ladder. Preferably the arms engage with a rung of each of the ladder sections. The location at which the arms are connected to the lower ladder section may either be above or below the rungs with which the arms may engage. Preferably, the location is below the rungs with which the arms engage.
The locking mechanisms biases the clutch arms into their locked position. The locking mechanism may have a spring for biasing the arms. In one embodiment the locking mechanism includes a gear associated with the axle which may be influenced by the spring to bias the arms. Preferably, the spring acts upon a rack which is in engagement with the gear.
The ladder may have a ladder extension rope or cord for extending and retracting the upper ladder section relative to the lower ladder section. The ladder extension rope may extend betw
Bailey Robin E.
Bailey William
Bailey Robin E.
Bailey Northern Holdings Pty Ltd.
Chin-Shue Alvin
Nixon & Vanderhye P.C.
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