GB2277952A

GB2277952A - Catch mechanism

Info

Publication number: GB2277952A
Application number: GB9309907A
Authority: GB
Inventors: Richard Weston
Original assignee: SAFESCAPE Ltd
Current assignee: SAFESCAPE Ltd
Priority date: 1993-05-14
Filing date: 1993-05-14
Publication date: 1994-11-16
Anticipated expiration: 2013-05-14
Also published as: GB2277952B; GB9309907D0

Abstract

A catch mechanism is described for mounting on the underside of a rung 12 of a collapsible ladder, comprising a bolt 18, a spring 28 acting to urge the bolt in a direction to lock two sections of one stile of the ladder to one another in the extended position of the sections and a release lever 22 mounted pivotably on the rung for retracting the bolt 18 against the action of the spring 28. The release lever 22 is pivotably connected to the bolt 18 and the spring 28 for urging the bolt 18 in its locking direction acts between the bolt 18 and the release lever 22 via a plastics bearing block 30 slidable on the bolt 18. <IMAGE>

Description

Catch Mechanism Field of the invention The present invention relates to a catch mechanism for the automatic release of the sections of a telescopically collapsible ladder.

Description of the prior art There is known, for example from PCT Application PCT/GB91/00565 , a ladder in which the stiles are made of telescopically collapsible sections. Catches having spring biassed bolts that project through the walls of the stiles and mounted on the underside of rungs are used to retain the stiles in their extended position. The catches have release levers for retracting the bolts that are automatically actuated when the rungs of the ladder are collapsed against one another.

The catch mechanisms used hitherto in such ladders have been expensive to manufacture and difficult to assemble.

Object of the invention The present invention seeks to provide an improved catch mechanism that mitigates the foregoing disadvantages.

Summarv of the invention According to the present invention, there is provided a catch mechanism for mounting on the underside of a rung of a collapsible ladder, comprising a bolt, a spring acting to urge the bolt in a direction to lock two sections of one stile of the ladder to one another in the extended position of the sections and a release lever adapted to be pivotably mounted on the rung for retracting the bolt against the action of the spring, wherein the lever is pivotably connected to the bolt and the spring for urging the bolt in its locking direction acts between the bolt and the release lever.

Because the release lever is connected to the bolt and the spring acts between the two rather than between the rung and the bolt, the components of the catch can readily be assemble to one another and offered up as a single unit to the rung. The catch is held in position on the rung only by the pin acting as the pivot for the lever on the rung and no special tools are required to keep the spring compressed while this pin is inserted.

Advantageously, the release lever is constructed as a bell crank lever with the end of one arm pivoted to the bolt and the end of the other arm acting as the means for actuating the release lever.

Preferably, the bell crank lever is formed with a stop in the form of a projection that comes to rest against bolt to limit the rotation of the bell crank lever relative to the bolt in the locking direction of the bolt in the ladder stile.

Conveniently, the spring is formed as a coil spring having one end engaging the release lever and the other end guided for sliding movement along the bolt. A bearing block of plastics material may be slidably mounted on the bolt and be provided with a bore or recess for anchoring one end of the coil spring.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial section through one rung of a collapsible ladder fitted with a catch mechanism of the invention, Figure 2 is a plan view from below of the catch mechanism shown in Figure 1, and Figure 3 is a sheet metal blank from which the release lever shown in Figure 1 is formed.

Description of the preferred embodiment The drawings show part of a telescopically collapsible ladder. The ladder is formed of several sections each comprising two tubes and a rung extending between them. The drawings show only tube 10 of one such section and part of the rung 12 connecting it to the other tube of the same section.

The tubes 10 of adjacent sections of the ladder are telescopically collapsible one inside the other and to keep the ladder extended a catch mechanism having a spring biased bolt 18 is provided. The bolt 18 projects through a hole 20 in the tube 10 to prevent the ladder from collapsing but when it is withdrawn from the tube 10, the ladder can be collapsed.

The underside of the rung 12 has upstanding walls 14 and 16 which act to strengthen the rung and also as a means for mounting the catch mechanism on the rung 12. A bell crank release lever 22 of the catch mechanism is pivoted by means of a pin 24 between these two walls. One arm of the lever 22 is connected by a pivot pin 26 to the bolt 18 and the other arm acts as the means for actuating the release lever 22. The bell crank lever 22 is formed of sheet metal, the blank from which it is made being shown in Figure 3.

When two rungs come close to one another, the lower rung comes into contact with the release lever 22 and pivots it counterclockwise, as view in Figure 1, to retract the bolt 18. In this way, when collapsing the ladder, as two pairs of rung are brought against each other, they automatically release the next section above them, thereby permitting the entire ladder to be collapsed safely, one section at a time.

A plastics bearing block 30 is slidably mounted on the bolt 18. A coil spring 28 prevented from escaping by the pin 24 has the end of one of its arms 28b anchored in the bearing block 30 and its other arm 28a leaning on the inner surface of the bell crank lever 22 to bias it clockwise, in the locking direction of the bolt 18. A projection 32 of the lever 22 acts as a stop, when it comes into contact with the bolt 18, to limit the clockwise pivoting of the lever 22 relative to the bolt 18.

The advantage of the construction of the catch mechanism described above stems from its ease of assembly. The spring 28 can be slipped under the release lever 22 and anchored in the bearing block 30 prior to the catch mechanism being fitted to the rung of the ladder. The spring 28 is held in place sufficiently by the bent end of the lever 22 and by being anchored in the bearing block 30. With these three components pre-assembled, the bolt 18 is introduced in the hole 20 in the tube 10 and the bearing block is slid between the two walls 14 and 16, where it fits snugly. The catch mechanism is moved to a position in which the holes in the release lever for the pivot pin 24 line up with corresponding holes in the walls 14 and 16 and the pin 24 is driven into position, at the same time passing through the centre of the coil spring 28 and permanently preventing its escape.The bearing block 30 now acts as a guide for the bolt 18 as well as anchoring point for the end of the coil spring 28.

The pivoting connection between the lever 22 and the bolt 18 has the effect that the bolt 18 is pivoted relative to the rung as it is retracted from the hole 20. This geometry can result in improved ladder safety in that it is possible to ensure that the bolt is slightly inclined upward (to the right as viewed) prior to the release lever being actuated and downward after it is actuated. While the stiles are under a vertical load from the weight of a person standing on it, there will be a force acting in a direction to prevent the bolts from the retracted. If a slight taper or chamfer is formed on the bolt, as shown at 34 in the drawing, the force acting to prevent inadvertent retraction of the bolt when the ladder is erected is increased.

However, when the ladder is no longer under load and the release lever is operated, the bolt will tilt the other way, the weight of the ladder will no longer oppose retraction of the bolt.

Claims

1. A catch mechanism for mounting on the underside of a rung of a collapsible ladder, comprising a bolt, a spring acting to urge the bolt in a direction to lock two sections of one stile of the ladder to one another in the extended position of the sections and a release lever adapted to be pivotably mounted on the rung for retracting the bolt against the action of the spring, wherein the lever is pivotably connected to the bolt and the spring for urging the bolt in its locking direction acts between the bolt and the release lever.

2. A catch mechanism as claimed in claim 1, wherein the release lever is constructed as a bell crank lever with the end of one arm pivoted to the bolt and the end of the other arm acting as the means for actuating the release lever.

3. A catch mechanism as claimed in claim 2, wherein the bell crank lever is formed with a stop in the form of a projection that comes to rest against bolt to limit the rotation of the bell crank lever relative to the bolt in the locking direction of the bolt in the ladder stile.

4. A catch mechanism as claimed in any preceding claim, wherein the spring is formed as a coil spring having one end engaging the release lever and the other end guided for sliding movement along the bolt.

5. A catch mechanism as claimed in claim 4, wherein a bearing block of plastics material is slidably mounted on the bolt and is provided with a bore or recess for anchoring one end of the coil spring.

6. A catch mechanism as claimed in any preceding claim, wherein a section near the end of the bolt is chamfered or tapered away from the end of the bolt.

7. A catch mechanism constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

8. A collapsible ladder fitted with catch mechanisms as claimed in any preceding claim for maintaining the ladder in its extended position until the catch mechanisms are released.