GB2102871A - Improvements in or relating to ladders - Google Patents

Abstract

This invention relates to ladders in which the length of at least one of the legs of the ladder is continuously adjustable within predetermined limits. To enable the, or each, leg to be adjusted it comprises a first longitudinally extending member (14) slidable in a second hollow member (1). Transverse slots (20) are provided in the second member and inclined slots (22) are provided in the first member. A pin (34) is insertable through the slot, or slots, in the second member and a selected one, or selected ones, of the slots in the first member. <IMAGE>

Description

SPECIFICATION Improvements in or relating to ladders This invention relates to ladders of the kind described and claimed in the Specification of Patent Application No. 80 39043.

Ladders of this kind include at least one pair of legs and a plurality of steps, and are capable of being used in circumstances in which it would be difficult or impossible to use a normal type of ladder. To make this possible, the length of at least one of the legs of the ladder is continuously adjustable within predetermined limits.

It is an object of the invention to provide a ladder of the kind referred to in which the means for locking the adjustable leg or legs is particularly simple and effective.

From one aspect the invention consists in a ladder comprising at least one pair of legs and a plurality of steps, wherein the length of at least one of said legs is continuously adjustable within predetermined limits, wherein the, or each, adjustable leg comprises a first longitudinally extending member slidable in a second longitudinally extending hollow member, and locking means to lock said first member relative to said second member, and wherein said locking means comprises at least one slot in said second member, a plurality of slots in said first member, said slots in said first member being inclined relative to said slots in said second member, and a pin insertable through said slot or slots in said second member and a selected one, or selected ones, of said slots in said first member.

In one embodiment of the invention the, or each, first member and the, or each, second member is a box-section member. In this embodiment, the locking means may comprise a pair of transverse slots in two opposed faces of the second box-section member, and a plurality of pairs of parallel inclined slots in two opposed faces of the first member.

In another embodiment of the invention, the first and second members are of circular or oval cross-section. In the case in which the members are of circular cross-section, the locking means may comprise a pair of diametrically-opposed, part-circumferential slots in the second member, and a plurality of pairs of diametrically-opposed, part-helical slots in the first member.

The pin may be a single longitudinally extending member insertable through the slots, or it may be in the form of a staple having two parallel longitudinally extending portions, each insertable through respective slots. In this case, of course, two parallel slots or pairs of slots are provided in the second member. In a modification of this embodiment, alternate slots or pairs of slots in the first member are inclined at different angles. When the double-pronged pin is used with alternate slots of different inclination, it is found that sufficient locking can be obtained without the necessity for slots in both sides of the two members.Thus, for example, in the case of the box-section members, two parallel transverse slots may be provided in one face of the second box-section member and a series of alternately inclined slots may be provided in one face of the first box-section member.

It is to be understood that the slot, or slots, in the second member will normally extend at right angles to the longitudinal axis of the member. It is further to be understood that the angle of inclination of the slots in the first member must be chosen in relation to the coefficients of friction between the pin and the first and second members so that, when the ladder is in use, the pin does not slide along the slots in the second member. Thus this requirement imposes a maximum value on the angle between the inclined slots and the transverse slots. On the other hand, in order that the requirement of continuous adjustment may be met, it is necessary that the upper end of one of the inclined slots should overlap the lower end of the next higher inclined slot.Thus, in order to keep the number of inclined slots to a minimum, and thus to provide the maximum amount of solid material between the inclined slots, it is desirable to make the angle of inclination between the inclined slots and the transverse slots as large as possible. it has been found that a convenient compromise between these two conflicting requirements is an angle of between 30O and 40 .

If the pin has a circular cross-section, it has been found that satisfactory locking can only be achieved with a relatively small angle of inclination between the inclined slots and the transverse slots. However, if the pin is flattened so that it is not rotatable in the transverse slots, the angle of inclination could be increased. Most satisfactory results have been achieved with a pin having a cross-section in the shape of a parallelogram, the angle of inclination between adjacent sides of the parallelogram being equal to the angle of inclination between the inclined slots and the transverse slots.

The first and second members preferably consist of aluminium, while the pin may consist, for example, of steel. However, it is of course to be understood that the angle of inclination between the inclined slots and the transverse slots can be increased by using a material for the pin which has a higher coefficient of friction with aluminium than steel. Most such materials, however, do not have sufficient strength for this purpose, and hence the pin may be a composite arrangement consisting of a hard steel core and an outer surface coating of a weaker material having a higher coefficient of friction with aluminium.

A second pair of legs may be mounted for pivotting relative to the first pair of legs, thus producing a so-called "pair of steps". Preferably the length of each of said legs is continuously adjustable within predetermined limits.

From another aspect the invention consists in any features of novelty, taken singly or in combination, of the embodiments of the invention hereinafter described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view of a pair of steps in accordance with the invention; Figure 2 is a sectional view of a part of one of the legs of the steps illustrated in Figure 1 taken on the line 2:2 looking in the direction of the arrows; Figure 3 is a perspective view on an enlarged scale of a part of one of the legs of the steps illustrated in Figure 1 showing the locking means more clearly; Figure 4 is an elevation partly in section of a part of one of the legs; Figure 5 is a scrap view illustrating the shape of one form of pin; Figure 6 is a scrap view illustrating the shape of a second form of pin:: Figures 7 and 8 illustrate the application of the invention to a ladder having only two legs; Figure 9 is a perspective view of a part of a leg having a circular cross-section; Figure 10 is an elevation, partly in section, of a part of one leg showing the use of a doublepronged pin; and Figure 11 is an elevation, partly in section, of a part of a leg having alternate slots in the first member inclined at different angles.

The steps illustrated in Figure 1 includes two legs 1 and 3 with seven steps 4 extending therebetween. The front edge of each of the steps is provided with a pair of lugs 16 and 17. Each of the lugs 1 6 is secured to the leg 3 by means of a rivet 18, and each of the lugs 17 is secured to the leg 1 by means of a rivet 1 9. The rear edge of each step is provided with two similar pairs of lugs secured to the respective legs by further rivets.

One of the additional lugs is shown at 24 in Figures 2 and 4, and one of the additional rivets is shown at 48 in Figure 4. Two further legs 5 and 6 are hingedly connected to respective ones of the legs 1 and 3, the axis of the hinge points 7 and 8 being common. As shown, the two legs 5 and 6 are maintained in parallel relationship by means of a plurality of bracing members 9. However, it is to be understood that the bracing members 9 may be arranged to hold the legs 5 and 6 at an acute angle instead of being parallel. All the legs consist of extruded or pressed metal such as aluminium having a box-section.

As shown, the lengths of all the steps 4 are equal so that the legs 1 and 3 are maintained substantially parallel. However, the length may increase progressively from the top step to the bottom step so that the legs are at an acute angle to one another as in the case of the two legs 5 and 6.

A platform 10 is hingedly mounted between the two legs 1 and 3, and includes a bar 11 which engages with the topmost one of the bracing members which is indicated by the reference 9'.

The bar 11 is provided with upstanding threaded rods which pass through slots 12 in the platform and receive wing nuts 13. Thus the position of the bar 11 below the platform 10 can be adjusted by slackening the wing nuts 13. This, of course, enables the angle between the front and rear pair of legs to be adjusted as required.

It will be understood that the device so far described constitutes a substantially conventional pair of domestic steps which are folded together or which can be maintained in the open position illustrated. However, the embodiment illustrated differs from conventional steps in that the lengths of all the legs are continuously adjustable within predetermined limits.

So far as the legs 1 and 3 are concerned, continuous adjustment is provided by two inner box-section members 14 and 1 5 which are slidable respectively in the box-section members 1 and 3. The box-section member 1 is provided with a pair of transverse slots 20, and the box-section member 3 is provided with a pair of transverse slots 21. The box-section member 14 is provided with a plurality of pairs of inclined slots 22, and the box-section member 1 5 is provided with a plurality of pairs of inclined slots 23. A pin 25 is provided to hold the box-section member 14 in position relative to the box-section member 1. As shown in Figure 2, this pin has the flattened circular shape shown more particulariy in Figure 5.

As shown in Figure 5, the pin has two flat parts 26 and 27 designed to cooperate respectively with the upper and lower edges of the transverse slots 20. Curved portions 28 and 29 of the pin cooperate with the edges of one of the pairs of inclined slots 22. As shown, the angle of inclination of the slots 22 with respect to the slots 20 is 45 . However, as already stated, it is preferred that the angle should be at most 350 to 40 , and it is found that, with such an angle, the pin 25 is effective to secure the inner member 14 in relation to the outer member 1.

It Is tc, ce understood that, in use, the pin is inserted through the pair of transverse slots 20 and one of the pairs of inclined slots 22 with the member 14 in the approximate position required.

The exact position of the member 14 in the member 1 can be adjusted to sliding the pin 25 in the required direction in the transverse slots 20. If in the course of this adjustment the pin reaches one end of the pair of transverse slots and further adjustment in the same direction is required, the pin is transferred to the other end of the transverse slots where it will be found that it can pass through the next adjacent one of the pairs of inclined slots.

As has already been mentioned, a preferable shape for the cross-section of the pin 25 is a parallelogram, and a pin of this shape is shown in Figure 6. Here it will be seen that two parallel sides of the pin 30 and 31 engage the two sides of the transverse slot and two sides 32 and 33 engage the two sides of the inclined slot 22.

To enable the pin 25 to be conveniently withdrawn from, and inserted in the slots, the pin is provided with a knob 34. Furthermore, to prevent it being lost, it is provided with a chain 35 which is attached to the leg 1 by means of a rivet 36. In this connection it will be noted that the inner member 14 is shaped as shown at 37 and 38 so that it clears the heads of the rivets 19, 36 and 48.

Extension of the rear legs 5 and 6 is provided by means of box-section members 39 and 40 which are slidable respectively wthin the box-section members 5 and 6. The box-section member 5 is provided with a pair of transverse slots 41 , and the box-section member 6 is provided with a pair of transverse slots 42. Further, the box-section member 39 is provided with a plurality of pairs of inclined slots 43, and the box-section member 40 is provided with a plurality of pairs of inclined slots 44. Finally each leg is provided with a pin similar to the pin 25 described in relation to the front legs of the steps.In the particular embodiment illustrated, the box-section members 5 and 6 are considerably shorter than the box-section members 1 and 3, while the box-section members 39 and 40 are considerably longer than the boxsection members 14 and 1 5. It will be found that this is normally the most convenient arrangement to provide for a considerable adjustment of the rear legs of the steps while only a relatively small adjustment is required for the front legs. As shown in Figure 1, it will be seen that the steps can be used, for example, on a staircase, three steps of which are illustrated generally at 45, 46 and 47.

As can be seen the two rear legs may rest on a single step or, if required, may be at different levels.

The application of the invention to a twolegged ladder is illustrated generally in Figure 7.

The ladder here is of the reversible type so that only one leg needs to be adjustable. The ladder illustrated includes two legs 50 and 51, and a plurality of rungs 52. The leg 51 includes an outer box-section member and an inner box-section member 53. The inner box-section member 53 is continuously adjustable within limits within the outer box-section member, and is lockable by means of a pin, the knob on the end of which is illustrated at 54. The arrangement of the transverse and inclined slots is the same as described and illustrated with respect to the pair of steps shown in Figure 1. As can be seen from Figure 7, a ladder of this kind can be used against the wall of a building standing on an inclined surface.Since the adjustment is continuous, it can be ensured that the ladder is perfectly upright and, accordingly, an arrangement of this kind is safer than one in which a block or the like is placed under the leg 51 to correct for the slope of the ground.

Figure 8 illustrates a further ladder in accordance with the invention but, in this case, the steps 55 between the legs 56 and 57 are similar to the steps 4 of the embodiment illustrated in Figure 1. Thus, in this case, the ladder is not reversible and, accordingly, both legs 56 and 57 are made adjustable by providing them with inner box-section members 58 and 59 locked in position respectively by pins 60 and 61. Again the arrangement of the transverse and inclined slots is the same as in the previous embodiments described.

Figure 9 illustrates a part of a leg of an alternative embodiment of the invention in which the first and second members are of circular crosssection. in this case, it will be seen that there are two sets of part-helical slots 71 and 72 in the wall of the first member 70. These sets of slots are diametrically opposite to one another. In addition, there are two part-circumferential slots 73 and 74 in the wall of the second member 75. Again these two slots are diametrically opposite to each other.

A pin 76 is shown passing through the slot 73, one of the slots 71, one of the slots 72 and the slot 74.

It is to be understood that the members 70 and 75 could have oval section rather than circular section as illustrated. In either case, it will be understood that an axial load on the leg will cause a torque to be applied tending to rotate the member 70 relative to the member 75. It has been found that this torque tends to improve the locking action of the pin.

The part of the leg illustrated in Figure 10 is generally similar to that illustrated in Figure 4 except that two slots 81 and 82 are provided in the second member 80 in place of the single slot 21 illustrated in Figure 4. Furthermore, in this case, the pin is a double-pronged pin 83. The two prongs, of course, pass through respective ones of the slots 81 and 82. They also engage a respective pair of the inclined slots 84. It will be seen that, at certain relative positions of the first and second members, the two prongs will pass through adjacent slots 84 while, in the particular relative position shown in Figure 10, the two prongs pass through slots separated by a further slot.As previously stated, when a double-pronged pin is used, sufficient locking is provided by having a-single pair of slots 81 and 82 in one face of the second member 80, and a single series of inclined slots 84 in one face of the first member 85. Thus the two prongs of the pin 83 may be relatively short.

The embodiment illustrated in Figure 11 is generally similar to that illustrated in Figure 10, except that alternate slots in the first member 85 are inclined at different angles. In the particular arrangement shown, the slots 86 are inclined at an angle of 300 relative to the transverse slots 81 and 82, while the intermediate slots 87 are inclined at an angle of 350. Once again, it will be seen that, in certain positions, the prongs of the pin 83 engage parallel slots in the first member whereas, in other positions, they engage differently-inclined slots.

In all the embodiments so far described, the pin has been held in the slots largely by friction. Also, since the pin will normally be horizontal when in position, there will be no force tending to cause it to move axially out of the slots. However, there is always the possibility that vibration or movement of the person using the ladder could cause some axial movement of the pin and, under extreme conditions, it is just possible that the pin might become dislodged from the slots.

Accordingly, from another aspect of the invention, means are provided to prevent the pin from being dislodged while the ladder is in use.

For this purpose, the pin is permanently attached to a resilient member tending to urge it in the direction necessary to retain it in the respective slots. With such an arrangement, adjustment of a leg is effected by pulling the pin out of the slots against the force applied to the pin by the resilient member.

In a particular embodiment applicable, for example, to the double pronged pin shown in Figure 10 or Figure 1 lithe two prongs are rivetted to a plate so that they project perpendicularly therefrom. The plate is mounted on a flat spring member with limited rotational and translational movement relative thereto. For example, the plate may be attached to the spring member by means of a rivet which is slidable in a slot in the spring member. The spring member is longitudinally extending and the slot is located near one end of the spring member and extends parallel to the length thereof. The spring is attached to the outer member of the respective leg of the ladder, for example, by means of a rivet located near the other end thereof.

It will be understood that, with the arrangement described above, the spring member will be so located in relation to the two slots 81 and 82 that, by rotational or translational movement of the plate, the two prongs can be located in the respective slots. The two prongs can be withdrawn by pulling the plate outwardly against the action of the spring member which tends to keep the prongs in the slots.

To assist in withdrawing the prongs from the slots, the plate member may be provided with a handle or knob or it may be formed as a channel member with the two sides of the channel extending in the opposite direction to the two prongs. The plate can then be readily pulled outwardly by gripping the two sides of the channel with the thumb and two fingers.

Claims (24)

1. A ladder comprising at least one pair of legs and a plurality of steps, wherein the length of at least one of said legs is continuously adjustable within predetermined limits, wherein the, or each, adjustable leg comprises a first longitudinally extending member slidable in a second longitudinally extending hollow member, and locking means to lock said first member relative to said second member, and wherein said locking means comprises at least one slot in said second member, a plurality of slots in said first member, said slots in said first member being inclined relative to said slots in said second member, and a pin insertable through said slots or slots in said second member and a selected one, or selected ones, of said slots in said first member.

2. A ladder as claimed in Claim 1, wherein the, or each, first member and the, or each, second member is a box-section member.

3. A ladder as claimed in Claim 2, wherein the locking means comprises a pair of transverse slots in two opposed faces of the second box-section member, and a plurality of pairs of inclined slots in two opposed faces of the first member.

4. A ladder as claimed in Claim 1 ,wherein the, or each, first member and the, or each, second member is of circular or oval cross-section.

5. A ladder as claimed in Claim 4, in which the first and second members are of circular crosssection and in which the locking means comprise a pair of diametrically-opposed, partcircumferential slots in the second member, and a plurality of pairs of diametrically-opposed, parthelical slots in the first member.

6. A ladder as claimed in any of the preceding Claims, wherein the locking means include two parallel slots in said second member spaced apart in the axial direction of the member, and wherein the pin is in the form of a two-pronged member, the spacing between the prongs being such that they can be inserted through respective ones of said parallel slots in the second member.

7. A ladder as claimed in Claim 6, wherein alternate slots, or pairs of slots, in the first member are inclined at different angles.

8. A ladder as claimed in any of the preceding Claims, wherein the slot, or slots, in the second member extend at right angles to the longitudinal axis of the member, and wherein the slots in the first member are inclined with respect to the slots in the second member at an angle between 300 and 400.

9. A ladder as claimed in any of the preceding Claims, wherein the pin has, or the two prongs of the pin have, a circular cross-section.

10. A ladder as claimed in any of Claims 1 to 8, wherein the pin, or each of the prongs of the pin, has a cross-section in the shape of a parallelogram, the angle of inclination between adjacent sides of the parallelogram being substantially equal to the angle of inclination between the slots in the first member and the slots in the second member.

11. A ladder as claimed in any of the preceding Claims, wherein the first and second members consist of aluminium.

12. A ladder as claimed in any of the preceding Claims, wherein the pin consists of steel.

13. A ladder as claimed in any of Claims 1 to 11, wherein the pin consists of a hard steel core and an outer surface coating of a material having a higher coefficient of friction than steel with the material of the first and second members.

14. A ladder as claimed in any of the preceding Claims, wherein a second pair of legs is mounted for pivotting relative to the first pair of legs.

1 5. A ladder as claimed in Claim 14, where the length of each of the four legs is continuously adjustable within predetermined limits.

16. A ladder as claimed in any of the preceding Claims, including means for preventing the pins from being dislodged from the slots while the ladder is in use.

1 7. A ladder as claimed in Claim 16, wherein the pin is attached to a resilient member which is itself attached to the respective second member, the arrangement being such that the resilient member urges the pin in the direction necessary to retain it in the respective slots.

18. A ladder as claimed in Claim 17, wherein the resilient member is a flat spring.

19. A ladder as claimed in Claim 1 8 and in Claim 6 or Claim 7, wherein the two prongs are secured to a plate so that they project perpendicularly therefrom, said plate being mounted on said flat spring with limited rotational and translational freedom of movement relative thereto.

20. A ladder as claimed in Claim 19, wherein the plate is attached to the flat spring by means of a rivet which is slidable in a slot in the spring.

21. A ladder as claimed in Claim 20, wherein the spring is longitudinally extending and the slot is located near one end of the spring and extends parallel to the length thereof, the spring being attached to the respective second member by means of a rivet located near the other end thereof.

22. A ladder as claimed in Claim 21, wherein the plate is formed by the base of a channel member, the two sides of which extend in the opposite direction to the two prongs so that the plate can be readily pulled outwardly by gripping the two sides of the channel.

23. A ladder substantially as hereinbefore described with reference to, and as illustrated in, the accompanying diagrammatic drawings.

24. Any features of novelty, taken singly or in combination, of the ladder as hereinbefore described with reference to the accompanying diagrammatic drawings.