Fire escape – ladder – or scaffold – Ladder – Slidable nested single rung units
Patent
1996-09-12
1998-04-14
Chin-Shue, Alvin C.
Fire escape, ladder, or scaffold
Ladder
Slidable nested single rung units
182207, E06C 100
Patent
active
057381860
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an extensible ladder.
Various types of extensible ladder have been proposed hitherto. U.S. Pat. No. 1,712,942 discloses one such ladder comprising a plurality of sections each having a pair of tubular uprights connected at their upper ends by a rung, with the tubular uprights of each section being a sliding fit with the corresponding uprights of the adjacent sections.
The adjacent uprights need to be a tight fit with each other, so that the ladder is rigid when it is erected. However, this tight fit makes the ladder extremely difficult to extend and collapse. The sliding areas of contact between adjacent upright sections wear with prolonged use, and thus the ladder becomes increasingly less rigid. Any dust or swarf that gets trapped between the uprights will cause the ladder to jam when it is being collapsed or extended.
We have now devised an extensible ladder which alleviates the above-mentioned problems.
In accordance with this invention there is provided an extensible ladder comprising a plurality of sections, each section having a pair of uprights connected by a rung, with the uprights of each section being slidably engaged with the corresponding uprights of an adjacent section, the uprights being formed with longitudinally extending grooves which reduce the area of sliding contact between adjacent uprights.
The friction between adjacent uprights is greatly reduced owing to the grooves reducing the area of sliding contact between them. This makes the ladder very much easier to extend or collapse than conventional extensible ladders. The areas of sliding contact between adjacent uprights do not wear as badly as conventional extensible ladders, and thus the ladder does not suffer from the problems of poor rigidity. Any dust or other particles that get caught between the uprights will collect in the grooves rather than between the areas of sliding contact. The ladder is thus less prone to jamming.
Preferably the uprights are tubular or channel-section, the grooves being formed on the inside surfaces of the uprights, so that they are hidden from view.
It is known to apply oil or other liquid lubricants to the uprights of extensible ladders to reduce the sliding friction, thereby making the ladder easier to extend and collapse. This lubrication is messy, since it gets on the hands and clothes of persons climbing the ladder. Furthermore, in time the lubrication becomes discoloured, and thus stains any objects which come into contact with the ladder.
Thus, preferably a dry friction-reducing coating, such as polytetrafluoroethylene (PTFE), is applied to the areas of sliding contact of the uprights of the ladder sections.
Preferably the sections of the ladder can be separated from each other, so that they can be cleaned, and so that damaged sections can be replaced.
When a person climbs a ladder, a considerable amount of downwards force is applied to the rungs. Thus, the rungs need to be securely attached to the uprights. Generally in conventional non-extensible ladders, the rungs extend through tubular uprights so as to form a rigid connection therebetween. It is not possible to construct extensible ladders in this way, since the rungs would obstruct the sliding action of the uprights. Preferably the rungs are therefore attached to the outside of the tubular uprights by welding. Some materials, particularly aluminium, are not easy to weld whilst maintaining necessary tolerances. It will be appreciated that the tolerances involved in constructing extensible ladders are critical, for example if the distance between the opposite uprights of each section is not exactly correct, then the sections of the ladder will not fit together properly. However, these accurate tolerances can be achieved using jigs and robotic welding apparatus.
The rungs of U.S. Pat. No. 1,712,942 are welded to the uprights, and it will be appreciated that the welds need to penetrate into respective areas of the uprights and rungs, so that a strong connection is formed therebetween. A disadvantage of weld penetration
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Chin-Shue Alvin C.
Foxdale Developments Limited
Schindler Edwin D.
Smith Richard M.
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