Prior Art A problem in connection with self supporting step- ladders of the type defined above is that they are not adapted to be used in stairs since in such a position of use the supporting portion, having an adjustable length, must be made as short as possible. However, there is a practical restriction since when the supporting portion has a maximum length, there must be a certain overlap between the mutually, preferably telescopically, displaceable portions in order to give the supporting portion a sufficient stability when said portion has its maximum length. It is realised that such circumstances cause a restriction as regards the shortening of the length of the supporting portion.

Objectes and Features of the Invention A primary object of the present invention is to define a self supporting step-ladder of the type defined above, said step ladder being especially suitable to be used in stairs.

A further object of the ladder according to the present invention is that it should have a proper stability and fulfil pending security regulations.

Still an object of the ladder according to the present invention is that according to a preferred embodiment it should be extremely compact in its transporting position.

At least the primary object of the present invention is realised by means of a self supporting step-ladder that has been given the features defined in the appending independent

claim. Preferred embodiments of the invention are defined in the dependent claims.

Brief Description of the Drawings Below preferred embodiments of the self supporting step- ladder defined above will be described, reference being made to the accompanying drawings, where: Figure 1 shows a side view of a self supporting step-ladder according to the present invention, said step-ladder being in a position of use on a horizontal base surface, the step portion and the supporting portion of the step-ladder having maximum length; Figure 2 shows in the same scale a corresponding side view as figure 1, however, the step portion and the supporting portion of the step-ladder having minimal length; Figure 3 shows in a larger scale the step-ladder in collapsed transporting position; Figure 4 shows a section along A-A in figure 2, the section extending through only one side element of the step- ladder; Figure 5 shows in the same scale as figure 1 the self supporting step-ladder in a position of use in a flight on stairs; Figure 6 shows in a larger scale a detail of the attachment between the step portion and the supporting portion; Figure 7 shows a side view of an alternative embodiment of a step-ladder according to the present invention; and Figure 8 shows a side view of the step-ladder according to figure 7, a part of the supporting portion being used as a knee support.

Detailed Description of Preferred Embodiments of the Present Invention The general structural design of a self supporting step- ladder according to the present invention will be described, reference being made especially to figure 1. The self supporting step-ladder comprises a step portion 1 and a supporting portion 3, said portions resting on a horizontal

base surface 4. According to the preferred embodiment each of said portions 1,3 comprises two mutually displaceable elements.

The step portion 1 comprises a first step portion element 5 and a second step portion element 7, said elements 5,7 being displaceable relative to each other in the longitudinal direction of the elements 5 and 7. The first step portion element 5 comprises two first side pieces 6 and the second step portion element 7 comprises two second side pieces 8, a number of steps (not visible) extending between each pair of side pieces 6 and 8 respectively. Since the step- ladder according to the invention is shown in side view only, only one side piece 6,8 of the respective step portion element 5,7 is visible. The more detailed design of the cross section profile of the first and second side pieces 6, 8, and their mutual cooperation, will be described more in detail below, see especially figure 4.

At its lower end, in the position of use, the first side pieces 6 of the first step portion element 5 is provided with supporting means 9 that rest upon the horizontal base surface 4. Said supporting means 9 are hingedly connected to the first side pieces 6 and are also adjustable in height in the shown position of use.

At the upper end of the second step portion element 7, in the position of use, a knee support 10 is attached, the legs 11 of the knee support 10 being received in the second side pieces 8 of the second step portion element 7. The ladder according to the present invention has first means (not shown) to lock the knee support 10 in desired position, a varying length of the legs 11 being received in the side pieces 8 in dependence of how far the knee support 10 projects above the upper end of the second step portion element 7.

Said first locking means may for instance constitute locking screws.

The supporting portion 3 comprises two supporting legs of adjustable length, each of said supporting legs comprising a first tubular supporting leg portion 12 and a second tubular supporting leg portion 13, said leg portions 12,13 being displaceable in their longitudinal direction relative to each

other. In the disclosed embodiment the first supporting leg portion 12 may be received telescopically in the second supporting leg portion 13. The supporting portion 3 comprises second means 14 in order to mutually lock the first supporting leg portion 12 and the second supporting leg portion 13 relative to each other in a certain position. Preferably, said second locking means 14 being designed in such a way that locking of the portions 12 and 13 may be effected in a stepless, arbitrary position. Transverse bars (not shown) may be provided between the supporting legs in order to increase the stability and torsional rigidity of the supporting portion 3. As regards the cross sectional shape of the tubular and supporting leg portions 12,13, said cross sectional shape may in principle be arbitrary, however the cross sectional shape of the telescopically cooperating supporting leg portions should of course coincide.

The step portion 1 and the supporting portion 3 are mutually connected by means of a hinge device 15 that constitutes an important part of the present invention. Said hinge device 15 will be described more in detail below, reference being made especially to figures 5 and 6. The basic function of said hinge device 15 is to have the step portion 1 and the supporting portion 3 pivotally connected to each other, in the disclosed embodiment said hinge device 15 being provided in the area of the upper ends of the step portion 1 and the supporting portion 3 when said portions are in the position of use.

The self supporting step-ladder according to the present invention, see for instance figure 1, is also equipped with a means 16 for locking the angle between the step portion 1 and the supporting portion 3 in the position of use of said ladder, a conventional technical term for said means is apart sliding safety device. In the disclosed embodiment the apart sliding safety device 16 is structurally an articulated arm having two mutually hinged subarms 17 and 18 that also are hingedly connected to the step portion 1 and the supporting portion 3 respectively.

In the position of use, shown in figure 1, of the ladder according to the present invention both the step portion 1 and the supporting portion 3 have their maximum length.

In the position of use, shown in figure 2, of the ladder according to the present invention both the step portion 1 and the supporting portion 3 have their minimum length. In this connection it should be pointed out that according to the present invention the maximum length of the supporting portion 3 is 1,5-1,75 times the minimum length of the supporting portion 3. In other words the transfer of the supporting portion 3 from the position shown in figure 2 to the position shown in figure 1 brings about a prolongation of the supporting portion with 50%-75%. The corresponding reasoning is in principle valid also for the step portion 1.

Both in the position of use according to figure 1 and the position of use according to figure 2 the articulated arm 16 is parallel to the base surface 4. In both said positions of use the step portion 1 forms an angle to the horizontal base surface 4 of 70° while the supporting portion 3 forms an angle of 69° to the horizontal base surface 4. Both these angle values are within the pending security regulations.

In order to transfer the ladder according to the present invention to the collapsed transporting position according to figure 3 it is suitable to start from the position of use according to figure 2 and then the supporting portion 3, via the hinge device 15, is swung to abut the step portion 1. In connection therewith the articulated arm 16 is collapsed and received in the space between the step portion 1 and the supporting portion 3.

A section through a first side piece 6 and a second side piece 8 is shown in figure 4, said side pieces 6,8 being mutually connected via first and second connecting portions 19 and 20 respectively, which are designed in such a way that the side pieces 6,8 are fixed relative to each other in the plane of the paper in figure 4 but are displaceable relative to each other in a direction perpendicular to the plane of the paper in figure 4. Preferably the side pieces 6,8 constitute extruded aluminium profiles.

The position of use in a flight of stairs of a ladder according to the present invention is shown in figure 5. In connection therewith the hinge device 15 has assumed a position where it is displaced upwardly relative to the step portion 1, reference being made to figure 6 in order to explain the transfer of the hinge device 15 and describe its structural design more in detail. It should be pointed out, reference being made to figure 5, that the transfer of the hinge device 15 to an upper position has the consequence that the change of length of the supporting portion 3 does not need to be equal large as if said transfer possibility was not present. Indirectly, this has an effect on the stability of the supporting portion 3, and in this connection reference is being made to what has been said above concerning the prolongation of the supporting portion 3. Due to the presence of the transferable hinge device 15 the maximum length of the supporting portion 3 has been restricted to 1,75 times the minimum length of the supporting portion 3. Such a restriction makes it possible to achieve an acceptable stability of the ladder.

The hinge device 15 comprises two links 21 having a certain length, only one of the links being visible in figure 6. In point 22 the links 21 have one end pivotally connected to the adherent second side piece 8 of the second step portion element 7 and the other end pivotally connected to an adherent second supporting leg portion 13 of the supporting portion 3 in the point 23. In order to synchronise the motion of the links 21 of the hinge device 15, when said links 21 are transferred between their positions of use a transverse bar (not visible) is provided that connects the attachment of the links 21 to the respective second supporting leg portion 13.

As is evident from figure 6 the hinge device 15 may assume two separate positions of use. The lower position of use, see also figures 1 and 2, is used when the ladder according to the present invention is located on a horizontal base surface 4. The upper position of use, see also figure 5, is used when the ladder according to the present invention is located in a flight of stairs. In order to transfer the hinge device 15 between the two separate positions of use the links

21 are brought to pivot around its attachment to the second side piece 8, this being indicated by means of the arrows 24 and 25 in figure 6 and the dotted position of the visible link 21. For the sake of clarity it should be pointed out that the arrows 24 mean that the hinge device 15 is transferred from its lower to its upper position of use while the arrows 25 mean that the hinge device 15 is transferred from its upper to its lower position of use. In order to the effect the transfer of the hinge device 15 from one position of use to the other position of use the user of the ladder grabs the transverse bar between the attachment of the links 21 to the respective second supporting leg portion 13. Pivoting of this transverse bar also induces pivoting of the links 21 around their attachment to the respective second side piece 8 in the way that is shown in figure 6.

As is evident from figure 5 each of the second step portion elements 7 are provided with a recess 26 in the edge that faces towards the supporting portion 3, said recess 26 being intended to receive the transverse bar when the hinge device 15 is located in its lower position of use, see figures 1 and 2. Possibly, a snap lock or the like may be provided in connection with said recesses 26 in order to detachably retain the hinge device 15 in its lower position of use. From security reasons this does not seem to be necessary since the force that acts in the second supporting leg portions 13 in said position of use strives to displace the hinge device 15 to abutment of the second step portion element 7.

In the position of use in a flight of stairs in figure 5 the step portion forms an angle to the horizontal plane of 70° while the supporting portion 3 forms an angle to the horizontal plane of 80°. These angles are the largest acceptable according to the pending security regulations. In said position of use the articulated arm 16 assumes a position where it forms a certain angle to the horizontal plane.

The alternative embodiment shown in figures 7 and 8 of a step-ladder according to the present invention differs principally from the embodiment described above through the design of the supporting portion 3'and the hinge device 15'.

In the embodiment according to figures 7 and 8 the supporting

portion 3'is in principle designed as a step portion, which means that both the actual step portion 1'and the supporting portion 3'are provided with steps, upon which the user may stand.

In figure 7 the hinge device 15'is shown in its uppermost position. As is evident from figure 7 the hinge device 15'comprises two bars 21', one for each side piece 8', said bars 21'being telescopically received in the adherent side piece 8'. In figure 7 the free end of the bar 21'is attached to the supporting portion 3'via an articulated attachment point 23'. Further, the bar 21'is pulled out to a maximum of the adherent side piece 8', said hinge device 15' also comprising means to lock the bar 21'relative to the side piece 8'in an extended position. The bar 21'may also be completely pushed into the side piece 8'.

In the position of use shown in figure 8, said position referring to a flight of stairs having a somewhat smaller inclination than the flight of stairs according to figure 7, one portion 12'of the supporting portion 3'has been displaced upwards in order to form a knee support for the user that stands on the step portion 1'. The lower end of the second portion 13'of the supporting portion 3'will rest against a step of the flight of stairs that the ladder is positioned in. In this connection it should be pointed out that said one portion is displaced downwards, in order to prolong the supporting portion 3', when the ladder according to the present invention is resting on a horizontal base surface, this of course under the prerequisite that the step portion 1'is prolonged to a corresponding degree. The bar 21'of the hinge device 15'is pulled out in figure 8 to a somewhat lesser degree that in figure 7. The bar 21'may be locked relative to the side piece 8'in a number of predetermined positions, said locking may for instance be effected by means of a pin (not shown) that penetrates both the bar 21'and the side piece 8'.

What has been said above regarding the adjustment possibilities concerning the length of the supporting portion 3 and the step portion 1 is valid also for the supporting

portion 3'and the step portion 1'in the embodiment according to figures 7 and 8.

As a complement to this reasoning regarding the length adjustment reference is made to the angles that the step portion 1; 1'and the supporting portion 3; 3'form with the base surface at different positions of use of the step-ladder according to the present invention. As is evident from figures 1,5,7,8 the step portion 1; 1'forms an angle to the base surface of 69° or 70° while the supporting portion 3; 3'forms an angle of 69°, 70°, 72° or 80° to the base surface.

This is valid regardless if the step-ladder according to the present invention is located on a planar base surface or in a flight of stairs. To some up it can be stated that according to the present invention the angle that the step portion 1; 1' forms with the base surface is in the interval 60-70° while the angle that the supporting portion 3; 3'forms with the base surface is in the interval 65-80°.

Due to the above described arrangement according to the present invention, i. e. to displace the hinged attachment point 23; 23'of the supporting portion 3; 3'upwards when using the step-ladder in a flight of stairs a reasonable length adjustment of said supporting portion 3; 3'is achieved. This is beneficial for the stability and the security of said supporting portion 3; 3'.

As regards the material of the self supporting step- ladder according to the present invention it has already been stated above that the side pieces 6; 6'and 8; 8'preferably are made out of aluminium. Also the rest of the ladder may in principle be manufactured from aluminium although certain details may be manufactured from other materials, e. g. plastic.

Feasible Modifications of the Invention In the embodiment described above the self supporting step-ladder comprises a step portion and a supporting portion, which are mutually connected by means of a hinge device.

However, within the scope of the present invention it is also feasible that the supporting portion is designed as a step portion, i. e. that the ladder according to the present

invention comprises two step portions that are mutually connected by means of a hinge device, that according to the principle of the present invention is transferable between at least two positions of use along the longitudinal direction of the first step portion. The second step portion, i. e. the supporting portion that is equipped with steps, is in a usual way adjustable as regards its length.

In the embodiments described above the hinge device constitutes a link mechanism that is pivoted between its two positions of use or a bar 21'that is displaceable in its longitudinal direction relative to the step portion 1'.

However, within the scope of the invention it is feasible to have other structural designs of said hinge device as long as at least two different positions of use along the step portion 1; 1'is achieved.

In the embodiment described above of the self supporting step-ladder the step portion 1 comprises two mutually displaceable step portion elements. However, within the scope of the invention it is feasible that the step portion constitutes a unit that is not adjustable to its length. In this connection it shall also be pointed out that the knee support is important from a security aspect but that said knee support does not have a direct connection with the transferring possibilities of the hinge device according to the present invention.

In the embodiment described above the apart sliding security device constitutes an articulated arm 16. However, within the scope of the invention it is feasible to have other types of apart sliding security devices, especially so-called platforms in connection with ladders of the type in question, said platforms simultaneously constituting a standing spot for the user and an apart sliding security device.