WO1992019834A1

WO1992019834A1 - Ladder

Info

Publication number: WO1992019834A1
Application number: PCT/GB1992/000596
Authority: WO
Inventors: James Brian Clarke
Original assignee: James Brian Clarke
Priority date: 1991-04-25
Filing date: 1992-04-03
Publication date: 1992-11-12
Also published as: AU1469492A; GB2270340B; GB9108897D0; GB2270340A; GB9321146D0

Abstract

A ladder having rungs (2) extending between two stiles (1) and being fixed to the stiles by means of end parts of the rungs passing through respective holes and the stile. The inner face (3) of a stile (1) and the inner face of a rung (2) being so relatively profiled that, upon assembly, when the end part of the rung is offered into he respective holes (5) a progressively increasing annular portion of the perimeter of the leading peripheral edge of the rung end parts enters and engages within the hole. The relative peripheral shapes of the hole (5) and of the rung end part being such that the diameter of the part of the hole into which the rung (2) is initially fitted is at least as big as the corresponding diameter of the rung and the progressive engagement provides a tight fit between the rung end part and the stile.

Description

LADDER

The present invention relates to a ladder and more particularly to the connection between the stiles and rungs of a ladder.

Ladder rungs are generally made of aluminium and have hollow sections. Each end of a rung has a smaller cross section than the rest of the rung in order to provide a shoulder to abut the inner face of a stile. The end is passed through a respective hole in the stile and the end of the rung is cold formed into a lip over the immediately surrounding outer face of the stile to form a permanent joint.

Such a joint allows the rung to wear loose leading to excessive wear and lower rigidity. Racking i.e. axial movement of the stiles relatively to one another so that adjacent rungs defined with the stiles a parallelogram, may occur. After insertion of the rung into a hole in the stile some reliance is placed upon expanding the inserted rung part, and stretching the hole in the stile during the process of forming the rung lip. In practice, elastic recovery leads to both rung and hole partially returning to their original smaller size at which the rung was readily inserted into the hole, and thus the clamping force is impaired.

According to the present invention a ladder has rungs extending between two stiles and being fixed to the stiles by means comprising end parts of the rungs passing through respective holes in the stiles, the inner face of a stile and the end face of a rung being so relatively profiled that, upon assembly, when the end part of the rung is offered into the respective hole, a progressively increasing portion of the leading peripheral edge of the rung end part enters and engages within the hole; and the relative peripheral shapes of the hole and of the rung end part being such that the diameter of the part of the hole into which the rung is initially fitted is at least as big as the corresponding diameter of the rung, and at least part of the progressive engagement provides a progressively tighter fit between the rung end part and the stile.

The use of the term diameter does not necessarily require a hole of circular or other arcuate shape but applies to the dimension between opposite edge parts of a hole of any shape.

The initial engagement of the leading peripheral edge of the rung with the hole is easy as the diameter of the hole at that stage is large enough to provide a sliding fit for the rung. Thereafter the crossover points, at one side of which the edge of the rung is within the hole and at the other side of which the edge of the rung is outside the hole, provide localised zones of interference at which the necessary deformation of the rung and hole to enable the rung to advance a little further around its periphery into the hole, can be provided without excessive force. Effectively a progressive wedging action is involved. Once an extent of the rung edge has been deformed to enter the hole, that part of the rung can comparatively readily be advanced further into the hole.

This provides a ladder with joints at which the rungs have been contracted and the stile has been expanded. Thus the forces of elastic recovery work against one another and improve the rigidity of the joint.

Final securement of the rung may be achieved by conventional swaging, welding or bonding of the rung at the outer face of the stile.

The inner face of the stile may be profiled to present a concave channel, extending, e.g along the stile, in which the hole is formed. However, as long as the profiles of the inner face of the stile and the end face of the rung are appropriately different, for example either one convex or concave about one axis, and the other flat, the profiles may take many variations. However, if the final securement is to be achieved by swaging the end of the rung outwardly over the outer face of the stile, it is preferred that the end face of the rung is flat, so that the material^' can be upset evenly around the hole in the stile.

In one construction, the external cross section of the end part of the rung is substantially circular and the hole is substantially elliptical with its larger diameter horizontal, the smaller diameter of the hole being less than that of the rung end part and the larger diameter of the hole being at least as great as the diameter of the rung end part. This provides the tightest fit at the top and bottom of each hole and provides good resistance to racking. With this construction, the relative profiling may be provided by the concave channel previously described with a flat ended rung. Alternatively the rung may be concave about a vertical axis or convex about a horizontal axis with the stile face surrounding the hole being flat. Any of these arrangements will provide initial entry of the rung at the horizontally opposite edges of the hole. Lead in surfaces may be provided at the horizontally opposite edges of the hole to facilitate initial entry of the rung into the hole.

Alternatively the external cross section of the end part of the rung and the hole are substantially trapezoidal, the spacing of the parallel edges and of a part of the other two edges of the hole providing the diameter into which the rung is initially fitted.

The nip may occur across more than one diameter, for example the points of tightest engagement may occur at two points either side of the centre of the top of the rung and two corresponding points either side of the centre of the bottom of the rung.

Examples of ladders constructed in accordance with the present invention will now be described with reference to the accompanying drawings in which:

Fig. 1 is a section through a rung and stile, perpendicular to the stile;

Fig. 2 is a side view of a portion of the inside of a stile; Fig. 3 is a section of the stile along line III-III in figure 1 and a side elevation of the rung;

Fig. 4 is a section along line IV -IV in figure 3; Fig. 5 is a perspective view of a portion of a rung and a stile prior to insertion of the rung into the stile; Fig. 6 is a section similar to that shown in figure 3 with the rung fully inserted into the stile;

Fig. 7 is a section similar to that shown in figure 6 showing the finished joint; and Fig. 8 is a diagrammatic section of a first example of a rung and hole having a trapezoidal section.

The ladder comprises a pair of extended aluminium stiles 1, of which a portion of one is illustrated, interconnected by a plurality of rungs 2, of which a portion of one is illustrated. The inside face 3 of the stile has a concave channel 4 running along its length and a corresponding projection running along the outer face. Holes 5 for receiving the rungs 2 are punched through the stile 1 at regular intervals along the concave recess 4. The holes 5 are substantially elliptical with the dimension transverse to the stile being larger than the dimension in the axial direction of the stile. Two slots 6 are provided at opposite edges of the hole.

The rung 2 has a flat end and circular cross section as shown in figure 4. Two projecting flanges 7 and 8 of different lengths project upwardly from each rung. These flanges 7 and 8 in cooperation with the upper surface of the rung 2 provide a step level (A-A in figure 4) when the ladder is in use. The flanges 7 and 8 finish short of the end of the rung 2 as shown in figure 3 with only keying ribs 9 continuing to the end of the rung. When the rung and stile are fitted together, the ribs 9 fit into the slots 6 and lock the rung 2 against rotation relatively to the stile 1. On assembly of a ladder, the rung 2 is offered into the hole 5. Initial engagement occurs only between the widest part of the elliptical hole 5 which by virtue of the concavity of the hole is the part initially encountered by the leading peripheral edge of the flat end of the rung 2. The largest dimension of the elliptical hole 5 is equal to the diameter of the rung and thus initial engagement can be easily effected, Lead in surfaces may be provided on the hole 5 in order to facilitate this initial engagement. The rung 2 is inserted progressively into the hole 5 resulting in a progressively increasing angular extent of the leading peripheral edge of the rung engaging with the hole. The direction of progression of the angular engagement of the rung 2 with the hole 5 is shown by the arrows in figure 2. This progressive angular engagement is associated with a progressive resistance by virtue of the difference in cross section between the rung 2 and hole 5. The dimension of the hole 5 in the axial direction of the stile 1 is less than the diameter of the rung 2 and this will cause compression of the rung and expansion of the hole as shown in figure 6.

The tightest engagement and therefore the highest resistance to movement between the rung 2 and the stile 1 is provided in the axial direction of the stile by virtue of the hole 5 having its smallest dimension in that direction.

The rung 2 is fixed into the hole 5 by swaging the end of the rung at the outer face of the stile 1 as shown in figure 7.

In the example shown in figure 8, the rung 10 and hole 11 have trapezoidal cross sections. The flat upper surface will provide, in use, a level surface on which the user steps. The distance between the parallel edges 12, 13 of the hole is equal to the distance between the two parallel faces 14, 15 of the rung and is equivalent to the larger transverse dimension of the hole in the previous examples. The non-parallel edges 16, 17 of the hole are closer together than the non-parallel faces 18, 19 of the rung along a central part of their length at which the rung will be deformed when it is pushed into the hole. A clearance 20 is provided in each corner where the hole is larger than the rung. The end face of the rung 10 and the inner face of the stile have the same relative profiling as described in the previous examples and the difference in the sectional shape between the rung and the hole acts in the same way as previously described. This rung and hole arrangement is appropriate for use with a stile having a concave channel 4 as shown in figure 5.

Claims

1. A ladder having rungs (2) extending between two stiles (1) and being fixed to the stiles by means comprising end parts of the rungs passing through respective holes (5) in the stiles, the inner face (3) of a stile (1) and the end face of a rung (2) being so relatively profiled that, upon assembly, when the end part of the rung is offered into the respective hole (5) , a progressively increasing portion of the leading peripheral edge of the rung end part enters and engages within the hole; and the relative peripheral shapes of the hole (5) and of the rung end part being such that the diameter of the part of the hole into which the rung is initially fitted is at least as big as the corresponding diameter of the rung, and at least part of the progressive engagement provides a progressively tighter fit between the rung (2) end part and the stile (1) .

2. A ladder according to claim 1, in which the inner face (5) of the stile (1) is profiled to present a concave channel (4) in which the hole is formed.

3. A ladder according to any one of the preceding claims, in which the external cross section of the end part of the rung (2) is substantially circular and the hole (5) is substantially elliptical with its larger diameter horizontal, the smaller diameter of the hole being less than that of the rung end part and the larger diameter of the hole being at least as great as the diameter of the rung end part.

4. A ladder according to claim 1 or claim 2, in which the external cross section of the end part of the rung (10) and the hole (11) are substantially trapezoidal, the spacing of the parallel edges (12, 13) and of a part of the other two edges of the hole providing the diameter into which the rung is initially fitted.