Ladder

Abstract: The application describes a ladder comprising at least two ladder sections (A,B), including a slide section (A) and a lower section (B), the slide section having a pawl mechanism which comprises a pawl (1) pivotally mounted on the inside of one of the rungs (D1) thereof. The pawl comprises a free end (10) which extends on the inside of the slide section in order to engage the rungs (D) of the lower section (B) and an opposite end (9) extending over the said rung (D1) of the slide section (A) so that downward rotation of the opposite end is limited by the said rung. The pawl mechanism also comprises a counterbalance member (2) pivotally mounted on the slide section about a point below the said rung (D1), the counterbalance member (2) being connected to the opposite end (9) of the pawl (1) such that, upon pivoting of the pawl to allow a rung (D) of the lower section (B) to pass, the counterbalance member (2) is pivoted outwardly to maintain the centre of gravity of the pawl mechanism to the outside of the pivoting axis of the pawl (1), which ever way round the ladder is used.

Description: The present invention relates to a ladder consisting of at least two ladder sections which can slide relative to each other, the ladder including a pawl mechanism which allows one section to be moved upwards relative to another but prevents the ladder from closing accidentally. Pawl mechanisms of this type are usually provided on multi-section ladders which can be opened by means of rope operation. The pawl is connected to each upper or slide section. As the pawl passes a rung on the lower or main ladder section, it contacts the rung and pivots out of the way to allow the slide section to be raised. After the pawl clears the rung, it falls back under gravity into a position which locks against the rung of the lower or main ladder section, so that the upper or slide section cannot accidentally fall. Pawl mechanisms are known in which the pawl pivots about a point which, when the ladder sections are locked together, is above the rung of the ladder section on which the pawl catches, the pawl swinging out of the way when the ladder section, on which the pawl pivots, is raised. Pawl mechanisms are also known in which the pawl pivots about a point which, when the ladder sections are locked together, is adjacent the rung of the lower ladder section on which it catches, rotation of the pawl in one direction being prevented by the rung of the ladder section on which the pawl pivots. It is preferable that any pawl mechanism engages automatically, to prevent accidental closing of the ladder, for example if the rope being used to raise the ladder is inadvertently released or brakes. It is preferably that the pawl mechanism should act without the need for any springs, and indeed certain British standards do require that latching devices on ladders should not depend on the operation of springs and should instead simply rely on gravity. In the United Kingdom, multi-section ladders are traditionally used in such a way that the sections which slide, and are raised, are at the front, furthest from the wall. However, there is nothing to prevent the ladders being used the other way around, and indeed it is usual on the Continent for ladders to be used with the slide sections at the back, nearest to the wall. It is evident that, with such opposite inclinations of the ladder, pawl mechanisms which act purely by gravity may not always work; one way around, there is a danger that the pawl will overbalance and no longer catch on the rungs of the lower ladder sections. GB-A-110487 and GB-A-20227 describe ladders with safety pawl arrangements, that of GB-A-110487 seeming to work independently of which way up the ladder is used, but the pawl not engaging a rung of the slide section. The present invention concerns a ladder having a pawl mechanism of the type in which rotation of the pawl is prevented in one direction by one of the rungs of the ladder section on which the pawl is mounted. The object of the invention is to provide a pawl mechanism which allows the ladder to be operated safely which ever way round it is used, i.e. whether the slide sections are at the back or at the front. It is also the object of the invention that the pawl mechanism should operate under gravity, without any spring mechanism. Accordingly, the invention provides a ladder comprising at least two ladder sections, including a slide section and a lower section, the slide section having an inner side adjacent the lower section and an opposite, outer side and the slide section having a pawl mechanism which comprises a pawl pivotally mounted on the inside of one of the rungs thereof, wherein the pawl comprises a free end which extends on the inside of the slide section in order to engage the rungs of the lower section and an opposite end extending over the said rung of the slide section so that downward rotation of the opposite end is limited by the said rung, the pawl mechanism also comprising a counterbalance member pivotally mounted on the slide section about a point below the said rung, the counterbalance member being connected to the opposite end of the pawl such that, upon pivoting of the pawl to allow a rung of the lower section to pass, the counterbalance is pivoted outwardly to maintain the centre of gravity of the pawl mechanism to the outside of the vertical through the pivoting axis of the pawl, which ever way round the ladder is used. As used in this application unless otherwise clearly meant the terms "inside", "outside", "inwardly" and "outwardly" etc are used to refer to the sides of the slide section of the ladder relative to the other sections, not relative to a wall against which the ladder happens to be placed. Furthermore, a term such as "inside" is not intended to imply that something is immediately on the inner side of something else, in a direction perpendicular to the length of the ladder section, but simply to indicate that it is nearer to the inside of the ladder than that other thing. Preferably, the counterbalance member is connected to the ladder pawl by means of at least one link member. Preferably, the ladder pawl is substantially L-shaped, so that it can enclose the said rung of the slide section. Obviously, part of the ladder pawl itself, and the or each link member, can aid the counterbalancing action of the counterbalance member itself, and this application is not to be interpreted to mean that it is the action of the counterbalance member and nothing else which, under gravity, causes the ladder pawl to pivot back to its safe position, rather than overbalancing. If a ladder comprises more than two ladder sections, then each slide section will generally be provided with a pawl mechanism. A preferred embodiment of the invention is described in more detail below, by example only, with reference to the accompanying drawings, wherein: Fig. 1 is a schematic elevational view of a multi-section ladder leaning against a wall, the upper or slide sections being at the back (nearest to the wall); Fig. 2 is a schematic elevational view similar to that of Fig. 1 but with the upper or slide sections at the front (furthest from the wall); Fig. 3 is a longitudinal partial sectional view through the ladder of Fig. 1, showing the pawl mechanism in a first position; Fig. 4 is a sectional view, similar to that of Fig. 3, showing the pawl in a second position; Fig. 5 is a longitudinal partial sectional view of the ladder of Fig. 2, showing the pawl in a first position; Fig. 6 is a sectional view, similar to that of Fig. 5, showing the pawl in a second position; and Figs. 7 and 8 are partial elevational views of an upper ladder section showing alternative arrangements of the pawl mechanism. The ladder schematically illustrated in Figs. 1 and 2 consists of three ladder sections A, B and C, each of which can slide relative to the others. In practice, the two upper or slide sections are lifted relative to the third, bottom section by means of a rope in a conventional manner which need not be described here. Fig. 1 shows the ladder being used a first way round, with the upper or slide sections at the back, nearest to the wall. Fig. 2 shows the same ladder, used the other way round, with the upper or slide sections at the front, furthest from the wall. It is desirable that the ladder can be used safely both ways round, and one example of the pawl mechanism which enables this safe operation is described with reference to Figs. 3 to 6. Fig. 3 shows the three ladder sections, A, B and C, section A being the uppermost slide section, here nearest to the wall. The longitudinal sectional view of Fig. 3 shows the rungs D of the ladder sections. The pawl safety mechanism includes a ladder pawl 1, counterbalance 2 and link bar 3, connecting the ladder pawl and the counterbalance. The ladder pawl is pivotally mounted on the ladder section A by pin 4, the pivoting axis being adjacent rung D' and the edge of ladder section A nearest to the other sections. Counterbalance 2 is pivotally mounted on ladder section A by pin 5, the pivoting axis being below that of the ladder pawl. The link bar 3 is pivotally joined to both the ladder pawl and the counterbalance by pins 6, 7 respectively. The ladder pawl 1 is generally L-shaped in cross-section, with a tread section 8 which, in the "at rest" position of the ladder lies in a plane perpendicular to the length of the ladder (i.e. in a horizontal position when the ladder is directly upright). At the end of the tread section, remote from the end nearest to the other ladder sections B, C is a return section 9, extending substantially perpendicularly to the tread section 8. The free end 10 of the tread section 8 extends out of the space defined by ladder section A so that it catches on the rungs of the adjacent ladder section B, in a conventional fashion. The other end of the tread section 8 and the return section 9 lie, in the at rest position of the ladder, around rung D' of ladder section A. Rung D' prevents the free end of tread section 8 from pivoting in an upward direction. Thus, in the at rest position of the ladder, the free end 10 of tread section 8 catches on one of the rungs of ladder section B so that ladder section A cannot move downwardly. Pivot pin 6 is at the free end of return section 9 of the ladder pawl 1. In the at rest position of the ladder, pivot pin 6 is below rung D' of ladder section A; pivot pin 7, and thus the counterbalance 2, lies along the length of the ladder section from pivot pin 5. In order to extend the ladder, ladder section A is raised relative to section B and C, generally by means of a rope. Fig. 4 shows ladder section A in a higher position than in Fig. 3, the pawl mechanism passing one of the higher rungs of ladder section B. As the pawl mechanism passes one of the rungs of section B, the free end 10 of tread section 8 is pushed downwards by the relevant rung, thus lifting the other end of tread section 8 and the return section 9 of ladder pawl 1. In other words, ladder pawl 1 rotates in a clockwise direction about pivot pin 4, as seen in Fig. 4. The raising of ladder pawl 1 lifts link bar 3 which, in turn, causes counterbalance 2 to rotate. Counterbalance 3 is of course forced to move in a clockwise direction also, so that it extends, from pivot pin 5, in a direction away from the inside edge of ladder section A adjacent ladder section B. In fact, as shown in Fig. 4, when ladder pawl 1 is moved to its fullest extent by the rung of ladder section B which it is passing, the counterbalance 2 extends substantially perpendicularly to the length of ladder section A and lies beneath the rung D' of section A. After ladder section A has been raised to the desired extent, the ladder pawl 1 should revert to the position shown in Fig. 3, so that downward movement of section A is prevented (at least until such time as it is required to close the ladder, when the ladder pawl is released by means of a conventional release mechanism, for example a rope fixed to the return section 9 of the ladder pawl, or to the link bar 3, which rope passes over a pulley above rung D' and then down to the ground so that the pawl can be lifted in order to allow the ladder sections to close on one another). As explained in the opening passages of this application, the ladder pawl should return to the position shown in Fig. 3, catching on the rungs of section B, under gravity and without the need for any special spring means etc. It is evident from a study of Fig. 4 that the centre of gravity of ladder pawl 1, even in its pivoted position, is to the left of pivot pin 4, i.e. on the wall side of pivot pin 4. Thus, the ladder pawl 1 will fall back to the position shown in Fig. 3 without the need of a counterbalance. However, it should be noted that the movement of the counterbalance from the at rest position of the ladder shown in Fig. 3 to the pivoted position shown in Fig. 4 shifts the centre of gravity of the complete pawl mechanism to the left, i.e. nearer to the wall, in view of the fact that the counterbalance itself rotates towards the wall. It can therefore be seen that the counterbalance assists the return of the ladder pawl to the safe position in which it catches on the rungs of ladder section B. To use the ladder in its alternative orientation, i.e. with the upper or slide sections at the front, furthest from the wall, the ladder is simply turned around so that what was the back of the ladder becomes the front of the ladder. This position is shown in Figs. 5 and 6, as well as Fig. 2. Fig. 5 corresponds to the view of Fig. 3, i.e. showing the ladder in an at rest position with ladder pawl 1 catching on one of the rungs of ladder section B. Fig. 6 corresponds to the view of Fig. 4, showing the ladder pawl 1 in the tilted position which it assumes as it passes one of the rungs of ladder section B, upon ladder section A being raised. It is evident that the ladder pawl 1, the link bar 3 and the counterbalance 2 can assume the same positions, relative to the rung D' of ladder section A, whatever orientation the ladder is in. However, with the ladder being used the other way around as shown in Figs. 5 and 6, the position of the ladder pawl mechanism relative to the vertical alters substantially, by 80° if the ladder is used at an angle of 50° to the horizontal, as in Figs. 3 to 6. A consideration of Fig. 6 shows that, in the tilted position of the ladder pawl mechanism, the centre of gravity of ladder pawl 1 is above or to the left of pivot pin 4. In other words, the centre of gravity moves closer to the wall as the ladder pawl rotates in an anticlockwise direction (in the view of Fig. 6) which would lead to a risk of the ladder pawl 1 itself overbalancing. If it did overbalance, it would not return to the position shown in Fig. 5 after the rung of section B passed by; ladder section A would thus be in an inherently unsafe, freefall position should the rope being used to raise the ladder be accidentally released. However, a consideration of Fig. 6 also shows that although the centre of gravity of ladder pawl 1 moves to the left, nearer to the wall, the centre of gravity of the counterbalance 1 moves to the right, away from the wall. Overall, the centre of gravity of the complete ladder pawl mechanism thus remains on the side of the vertical away from the wall, so that the ladder pawl 1 will return to the position of Fig. 5 without any risk of it overbalancing. Of course, with the ladder being used at a steeper angle (as is usual), the centre of gravity of the pawl mechanism is even further to the non-wall side of the vertical so that again there is no possibility of the ladder pawl overbalancing. As illustrated in Fig. 7, the pawl 1, link bar 3 and counterbalance 2 extend across substantially the full width of the ladder section A, between the stiles. In this case, the pawl, link bar and counterbalance may be formed of extruded aluminium. In Fig. 8, it is seen that as an alternative a pawl 1 and counterbalance 2 can be provided on either side of the ladder section, linked by steel pins 6, 7 extending across the ladder. In this case, the pawl and counterbalance pieces may be formed of, for example, either extruded aluminium or cast steel.

Claims: A ladder comprising at least two ladder sections (A,B), including a slide section (A) and a lower section (B), the slide section having an inner side adjacent the lower section and an opposite, outer side and the slide section having a pawl mechanism which comprises a pawl (1) pivotally mounted on the inside of one of the rungs (D') thereof, wherein the pawl comprises a free end (10) which extends on the inside of the slide section in order to engage the rungs (D) of the lower section (B) and an opposite end (9) extending over the said rung (D') of the slide section (A) so that downward rotation of the opposite end is limited by the said rung, the pawl mechanism also comprising a counterbalance member (2) pivotally mounted on the slide section about a point below the said rung (D'), the counterbalance member (2) being connected to the opposite end (9) of the pawl (1) such that, upon pivoting of the pawl to allow a rung (D) of the lower section (B) to pass, the counterbalance is pivoted outwardly to maintain the centre of gravity of the pawl mechanism to the outside of the vertical through the pivoting axis of the pawl (1), which ever way round the ladder is used. A ladder according to claim 1, wherein the counterbalance member (2) is connected to the ladder pawl (1) by means of at least one link member (3). A ladder according to claim 1 or 2, wherein the ladder pawl (1) is substantially L-shaped, so that it can enclose the said rung (D') of the slide section. A ladder according to claim 1, 2 or 3, which comprises more than two ladder sections, each slide section being provided with a pawl mechanism.

Inventors: MITCHELL TREFOR, MITCHELL, TREFOR
Applicants: SGB HOLDINGS LTD, SGB HOLDINGS LIMITED
Application year: 1995
Main classification: E06C7
IPC codes: E06C7, E06C1