AU723701B2

AU723701B2 - Foldable ladder with high strength

Info

Publication number: AU723701B2
Application number: AU28678/97A
Authority: AU
Inventors: Ik Woo Lee
Original assignee: IG CORP Co Ltd
Current assignee: IG Corp Co Ltd
Priority date: 1996-08-01
Filing date: 1997-07-16
Publication date: 2000-09-07
Anticipated expiration: 2017-07-16
Also published as: EP0822317A2; EP0822317A3; KR100210012B1; DE822317T1; AU2867897A; KR19980013622A

Description

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AUSTRALIA

Patents Act 1990 IG CORPORATION COMPANY LTD.

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Foldable ladder with high strength The following statement is a full description of this invention including the best method of performing it known to us:- BACKGROUND OF THE INVENTION 1. Field of the Invention -The present invention relates, in general, to high strength foldable ladders made of aluminum and, more particularly, to a structural improvement in such ladders for providing a reinforcing part to each hinged joint of a foldable ladder thereby improving the durability of the ladder.

2. Description of the Prior Art U.S. Patent No. 4,947,959 disclosed an aluminum folding ladder.

The folding ladder disclosed in the above U.S. Patent comprises a plurality of ladder sections, which are pivotally connected together by means of hinged joints. Each ladder section consists of two uprights, 5 each of which is provided with at least one rung hole. If each upright has two or more rung holes, the rung holes are equally spaced. Each ladder section also has at least one rung which is fitted in and held by the holes of the uprights. Korean U.M. Laid-open Publication No.

95-6677 disclosed a foldable mechanism which can be preferably used with aluminum foldable ladders.

Fig. 1 is a perspective view of a typical aluminum foldable ladder.

As shown in Fig. 1, the typical foldable ladder includes a plurality of ladder sections 1, which are pivotally connected together by means of 1/1 hinged joints 2. Each ladder section 1 consists of two uprights 11, each of which is provided with at least one rung hole 111. Each ladder section 1 also has at least one rung 12 which is fitted in and held by the holes 111 of the uprights 11. In order to fix the above rung 12 to the uprights 11, both ends of the rung 12 are fitted into the holes 111 of the uprights 11 so that they penetrate the holes 111.

The ends-of the rung 12 are, thereafter, compressed so as to fix the rung 12 to the uprights 11.

In the above ladder, two outer ladder sections 1 have a symmetric construction, while two intermediate ladder sections 1 have the same construction.

However, the above foldable ladder has a problem in that the *above ladder is made of aluminum so that the uprights of the ladder may be easily deformed or unbalanced when the ladder is used for a lengthy period of time or is overloaded.

2 Summary of the Invention In accordance with a first aspect, the present invention provides a foldable ladder with high strength comprising a plurality of ladder sections pivotally connected together by means of hinged joints, each ladder section having two uprights with respective rung holes and at least one rung fitted into and fixed to the rung holes of said uprights, further comprising: first and second reinforcing parts provided on opposite side surfaces of each upright, respectively, said first and second reinforcing parts extending from each hinged joint to a predetermined length along each upright, and wherein said reinforcing parts are provided with reinforcing holes aligned with the rung hole of each upright.

Embodiments of the invention may provide a high strength foldable ladder in which the above problems can be overcome and which is provided with inner and outer reinforcing parts on both side surfaces of each upright, the reinforcing parts being formed by axially extending each hinged joint to a predetermined length along an upright and being used for unifomly distributing the vertical or lateral load to all directions of the upright thus giving high strength to the ladder.

Further embodiments of the present invention may provide a high 20 strength foldable ladder in which both ends of a rung are compressed to integrate the upright, rung and reinforcing parts into a single body thus 0. giving an operational safety to the ladder and lengthening the expected life span of the ladder.

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0 9-0.6 o555 Brief Description of the Drawings The above and other features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a perspective view of a typical foldable ladder; Fig. 2 is a perspective view of a foldable ladder in accordance with a preferred embodiment of the present invention; Fig. 3 is an exploded perspective view showing the reinforcing part of the foldable ladder of this invention; and Figs. 4A and 4B are sectional views of the foldable ladder of Fig. 2, in which: Fig. 4A is a sectional view taken along the line A-A of Fig. 2; and Fig. 4B is a sectional view taken along the line B-B of Fig. 2.

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o SS S *o *o oo o DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 2 is a perspective view of a foldable ladder in accordance with a preferred embodiment of the present invention. As shown in Fig. 2, the foldable ladder of this invention includes a plurality of ladder sections 1, which are pivotally connected together by means of hinged joints 2'.

Each ladder section 1 consists of two uprights 11, each of which is provided with at least one rung hole 111 (see Fig. Each ladder 10 section 1 also has at least one rung 12 which is fitted in and held by holes 111 of the uprights 11. In the same manner as the typical

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foldable ladders, the ladder sections 1 are made of aluminum, while the hinged joints 2' are formed of a high strength material such as stainless steel or high strength aluminum alloy. The foldable ladder of this invention is invented according to the fact that the hinged joints are made of the high strength material. That is, the hinged joints 2' of the ladder of this invention longitudinally extend to a predetermined length along the respective uprights 1 1 differently from the typical joints 2 of Fig. i, thus forming reinforcing parts 21. Both side 0, surfaces of each upright 11 are sided by the inner and outer reinforcing parts 21 as best seen in Figs. 4A and 4B. Due to the above reinforcing parts 21, the rungs 12 are more strongly held by the uprights 11 so that the strength of the ladder sections 1 is remarkably improved.

Fig. 3 is an exploded perspective view showing the reinforcing parts 21 of the foldable ladder of this invention.

In the prior art, the rung 12 is fixed to the uprights 11 by fitting the rung 12 into the holes 111 of the uprights 11 prior to compressing both ends of the rung 12. A reinforcing hole 211:is formed on each reinforcing part 21 so that the reinforcing hole 211 is aligned with the rung hole 111. of the upright 11. Therefore, when the rung 12 is fixed to the uprights 11 of a ladder section 1 of this invention, the rung 12 passes through the reinforcing hole 211 of the inner reinforcing part 21 and the rung hole 111 of the upright 11 prior to penetrating the /O reinforcing hole 211 of the outer reinforcing part 21. A reinforcing boss 212 is provided on the edge of the reinforcing hole 211 of each outer reinforcing part 21. The ends of the rung 12 are curled around the reinforcing bosses 212 when the rung 12 is compressed outside the outer reinforcing parts 21. When the ends of the rung 12 are 15 compressed, the upright 11, rung 12 and reinforcing parts 21 are integrated into a single body. Therefore, the rung 12 is more strongly fixed to the uprights 11.

Figs. 4A and 4B are sectional views of the ladder of this invention taken along the lines A-A and B-B of Fig. 2, respectively. Figs. 4A c and 4B show, in detail, the ends of the rung 12, which are curled around and wrapped about the bosses 212 of the reinforcing holes 211 of the outer reinforcing parts 21. As best seen in Fig. 4B, the inside surfaces of the inner' and outer reinforcing parts 21 are knurled to form a plurality of reinforcing protrusions 213.

0215 The above reinforcing protrusions 213 made of stainless steel thus eat into the opposite side surfaces of the aluminum upright 11 when both ends of the rung 12 .are curled around the reinforcing bosses 212 of the outer reinforcing parts 21. The integration strength of the junctions between the upright 11 and the inner and outer reinforcing parts 21 is thus improved.

As described above, the present invention provides a high strengthl foldable ladder provided with reinforcing parts. Each reinforcing part of the abov ladder is formed by axially extending the high strength hinged joint along the aluminum upright to a 10 predetermined length and is provided with a reinforcing hole, boss and protrusions, thus remarkably improving the strength of the ladder without using any separate reinforcing member. Due to the above reinforcing parts, the foldable ladder of this invention is not only free from deformation when it is used for a lengthy.period of time or is overloaded, the ladder is also free from causing a safety accident during a work using the ladder.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are o possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A foldable ladder with high strength comprising a plurality of ladder sections pivotally connected together by means of hinged joints, each ladder section having two uprights with respective rung holes and at least one rung fitted into and fixed to the rung holes of said uprights, further comprising: first and second reinforcing parts provided on opposite side surfaces of each upright, respectively, said first and second reinforcing parts extending from each hinged joint to a predetermined length along each upright, and wherein said reinforcing parts are provided with reinforcing holes aligned with the rung hole of each upright.

2. The foldable ladder according to claim 1, wherein a reinforcing boss is formed on the edge of each reinforcing hole and is adapted for more strongly fixing the rung to the upright.

3. The foldable ladder according to claim 1 or claim 2, wherein each end of said rung is compressed to integrate said upright, rung and reinforcing parts into a single body.

4. The foldable ladder according to any one of claims 1 to 3, wherein the inside surfaces of said inner and outer reinforcing parts are provided with a 20 plurality of reinforcing protrusions.

5. A foldable ladder substantially as herein described and with reference to Figures 2 to 4 of the accompanying drawings. Dated this twenty-ninth day of June 2000. o* *I G CORPORATION COMPANY LTD Patent Attorneys for the Applicant: F B RICE CO