EP2677108B1

EP2677108B1 - Unit for stacking slats on a support ladder provided with double cross-beams for the production of venetian blinds and method for positioning a ladder

Info

Publication number: EP2677108B1
Application number: EP12195143.8A
Authority: EP
Inventors: Sergio Dallan
Original assignee: Dallan SpA
Current assignee: Dallan SpA
Priority date: 2012-02-28
Filing date: 2012-11-30
Publication date: 2014-09-17
Anticipated expiration: 2032-11-30
Also published as: EP2677108A1; PL2677108T3; PT2677108E; SI2677108T1; RS53698B1; ITPD20120055A1

Description

Field of application

The subject of the present invention is a unit for stacking slats on a support ladder provided with double cross-beams for the production of Venetian blinds and a method for positioning a ladder.

State of technique

As is known, Venetian blinds consist of a number of slats, positioned parallel to one another and held in place by support structures made of cord. These structures consist of two parallel longitudinal elements (positioned in the direction of the height of the blind) and of a plurality of cross-beams that connect the two longitudinal elements together at regular distances. Each cross-beam is associated with a slat. Due to their shape, said support structures are generally known as "support ladders".
In Venetian blinds for interior use, with double glazing for example, the support ladders are simpler, with single cross-beams, spaced apart. The single slat is inserted between one cross-beam and the other and simply rests on the cross-beam beneath it. The distance between one cross-beam and the other is equivalent to the distance required between one slat and the next (a few centimetres). This means that the insertion of the slats is very easy.
In Venetian blinds for exterior use, the support ladders have to ensure that the slats do not twist over in the wind, so they have a more complex structure, with pairs of cross-beams, positioned close together to form an eyelet. The slat is inserted into the eyelet, between the two cross-beams. In this way, the position of the slat is more stable.
The support ladders with double cross-beams which have been available on the market for some time have distances D between the two cross-beams of between 3 and 4 mm, as shown in Figure 1, substantially equal to the height of a slat with a curved section. Distances D of 3-4 mm have provided a good compromise between an effective blocking action and easy fitting of the slats onto the ladders.
These ladders are not, however, able to offer a constant guarantee of adequate blockage of the slats in the presence of strong winds.
To solve this problem, ladders with much smaller distances between the double cross-beams are proposed on the market with increasing frequency.
There are ladders with distances D of a maximum 1 mm, with versions in which the distances is as little as 0.2 mm, as shown in Figures 3 and 4 respectively.
There are also ladders with double crossed cross-beams with single cord, as shown in Figure 2. In the area where the cross-beams are attached to the vertical ribs of the ladders, the distance between the cross-beams is 3 mm; the cross between the cross-beams creates greater tension of the cords when the slat is inserted and therefore provides better blocking capacity.
Lastly, there are ladders with double cross-beams, with each cross-beam made with two or more crossed cords, as shown in Figure 5. The distance D between the cross-beams is usually 1 mm. The multi-cord structure makes the cross-beam stronger.
The systems currently known for the production of Venetian blinds have been conceived to operate with ladders with double cross-beams with distances D of 3-4 mm and are not usually reliable when used with ladders with maximum distances D of 1 mm between the cross-beams. Problems often arise also with ladders with double cross-beams with crossed cords, due to the asymmetry of the cross-beams when in tension.
In general, a reliable insertion of the slats between the eyelets of the ladders is possible only if the cross-beams are tight enough and divaricated sufficiently for the slat to enter easily.
To allow effective intervention of the divaricators, the ladder must be correctly positioned in the area of intervention of said divaricators. It is not easy to control the positioning of the ladder, because it is not rigid, meaning that it moves around, and because the ladders are often made with considerable dimensional tolerances. In said conditions, working with ladders with maximum distances D between the cross-beams of 1 mm or with asymmetrical cross-beam structures has been difficult to date.
To date, the correct positioning of the ladder on the slat insertion area is usually ensured by mechanical means. An example of this procedure is described in the European application EP2314822A1 . This document describes a unit for stacking slats equipped with a pair of rotating divaricators, shaped like a sickle and arranged specularly with respect to the longitudinal centre line of the support ladder. The ladder is held in position by a pair of guides along with the vertical ribs of the ladder slide. Each guide has two portions; a lower portion with a bigger section and an upper portion with a smaller section, connected by a step. Next to this step is a stop tooth with a spring movement, which is forced open by the cross-beams of the ladder when the latter is lifted up. The mobile stop teeth are positioned at the same height as the slat insertion plane and act as the mechanical means of reference. To correctly position the ladder, the two cross-beams that form the eyelet into which the slat has to be inserted must pass the stop teeth and allowed to rest against them. To ensure that the cross-beams rest against the teeth, the system comprises a device that uses a weight to stretch the ladder vertically, acting on the vertical ribs.
Despite being effective with regard to positioning the ladder, this system has one drawback. The vertical stretching of the ladder inevitably brings the two cross-beams closer together, reducing the space for insertion between them. This reduction does not have significant operating consequences on ladders with distances between the cross-beams in excess of 3 mm, but creates problems which are hard to overcome for ladders with distances between cross-beams below 1 mm or with crossed cords.

Presentation of the invention

Therefore, the purpose of the present invention is to eliminate all or part of the problems of the above-mentioned technique, making available a unit for stacking slats on a support ladder for the production of Venetian blinds which allows the reliable insertion of the slats on any type of ladder.
Another purpose of the present invention is to make available a unit for stacking slats which does not vertically stretch the ladders, preventing the narrowing of the cross-beams and reduction of the space for insertion between them.
Another purpose of the present invention is to make available a unit for stacking slats which allows the correct positioning of the ladder in a way that is easy to manage.
Another purpose of the present invention is to make available a unit for stacking slats which is cheap and easy to make.
Another purpose of the present invention is to make available a method for positioning a ladder in a unit for stacking slats that allows the correct positioning of the ladder in a way that is simple and reliable.

Brief description of drawings

The technical characteristics of the invention, according to the above-mentioned purposes, can be clearly seen in the contents of the claims listed below and its advantages will become more evident in the following detailed description, made with reference to the annexed drawings, which represent one or more embodiments, by way of non-restrictive example, in which:

- Figure 1 shows a ladder with double cross-beams with a single cord and distance D between the upper cross-beams of more than 3 mm;
- Figure 2 shows a ladder with double cross-beams crossed with a single cord and distance D between the cross-beams of 3 mm;
- Figures 3 and 4 show two ladders with double cross-beams with a single cord and distance D between the cross-beams of 1 mm and 0.2 mm respectively;
- Figure 5 shows a ladder with double cross-beams with crossed multiple cords and distance D between the cross-beams of 1 mm;
- Figures 6 to 13 show - for a ladder with double cross-beams with a crossed single cord - in sequence, the steps of cross-beam divarication, insertion of a slat and deposit of a slat in a loader using a stacking unit according to a preferred embodiment of the present invention;
- Figure 14 shows a plan view of the stacking unit of figure 6, without showing the slat to better highlight the parts below; and
- Figure 15 shows a lateral sectional view of the stacking unit of Figure 1 according to the sectional plan indicated with the arrow XV.

Detailed description

With reference to the drawings enclosed, the reference numeral 1 is used to indicate a unit for stacking slats on a support ladder with double cross-beams for the production of Venetian blinds according to the invention.
In particular, the stacking unit 1 is destined to be included - together with one or more identical units - in a more complex production system. In further detail, unit 1 can be moveably associated to a longitudinal support bar (not shown) at one end of which there is a slat production machine (not shown).
Here and further ahead in the description and claims, reference will be made to the stacking unit in conditions of use. In this sense, references to a higher or lower position must be considered.
According to a general embodiment of the invention, stacking unit 1 comprises at least one guide element 2 for a slat L, which defines an insertion plane m on which the slat L slide, resting on a longitudinal insertion axis X to be associated with the ladder S, slotting into the gap between a pair of cross-beams T1, T2.
This guide element 2 should preferably consist of a laminar element rigidly fastened to a support structure 3 of the stacking unit.

Stacking unit 1 comprises:

a device 20 to guide a ladder S along a positioning direction p incident the insertion plane (m); and
means 40 to divaricate at least one pair of cross-beams T1, T2 of said ladder S.

The divaricating means 40 are placed near to the guiding device 20 to divaricate substantially on the insertion plane m. In other words, the divaricating means 40 are structured and positioned with respect to the insertion plane m so that, when they have engaged a pair of cross-beams T1, T2 (correctly positioned), the two divaricated cross-beams are one above and one below the insertion plane m.
The divaricating means can be of any type suitable to the purpose.
According to the embodiment shown in the annexed figures, the divaricating means 40 comprise two sickle-shaped rotating elements 41, 42 positioned specularly with respect to the longitudinal insertion axis X of the slat L. As can be seen particularly in Figures 1, 14 and 15, both sickle-shaped elements 41 and 42 are associated to the support structure 3. Each of them is preferably provided with means of activation 43 to allow their independent activation. A more detailed description is not given as this type of divaricator is known per se to a skilled person in the art.
In operational terms, as will become clearer in the following description, the ladder S slides along the guiding device 20 in an advancement direction A (indicated in Figure 1 for example) along the positioning direction p to progressively bring each pair of cross-beams P1, P2 in front of the divaricating means 40 and allow the insertion of a slat between every pair of cross-beams. In particular, the sliding of the ladder takes place in steps, one for each pair of cross-beams.
The stacking unit 1 comprises means 20, 30 for moving the ladder S along the above-mentioned positioning direction p. Said means will be described in detail further ahead.
The stacking unit 1 comprises at least one sensor 50 to detect passage of a first cross-beam T1 of the ladder S in front of it during movement thereof along the positioning direction p.
As can be seen particularly in Figures 6 and 14, the sensor 50 is facing the guiding device 20 and is positioned at a predefined distance H from the insertion plane m with respect to the positioning direction p.
In operational terms, a pair of cross-beams T1, T2 of the ladder is therefore positionable in correspondence to the insertion plane m (ready for engagement by the divaricating means 40), if the above-mentioned movement means 20, 30 for moving the ladder by a tract equivalent to the above-mentioned predefined distance H along the positioning direction p are activated when the sensor (50) detects the passage of a first cross-beam (T1).
According to the preferred embodiment shown in the annexed Figures, the means for moving the ladder comprise the guiding device 20.
In more detail, according to said preferred embodiment, the guiding device 20 of the ladder S comprises means 25 for holding the ladder and can be moved using first movement means 60 along the above-mentioned positioning direction p. In operational terms, a pair of cross-beams T1, T2 of the ladder can be positioned in correspondence to the insertion plane m, holding the ladder S in the guiding device and moving said guiding device 20 by a tract equivalent to the predefined distance H along the positioning direction p, when the sensor 50 detects the passage of a first cross-beam of said pair.
Advantageously, the first movement means 60 of the guiding device 20 are chosen of the type that allows very precise control of the movement. Said first means 60 preferably comprise an electric piston.
According to an embodiment, the ladder holding means comprise one or more frictioning elements to brake the sliding of the ladder S. In particular, said frictioning elements can be of the preloaded spring ratchet type.
Advantageously, the means for holding the ladder comprise one or more blocking elements 25 of the ladder (S).
According to a preferred embodiment, the means for holding the ladder are made of ratchets activated by pneumatic or hydraulic pistons (25), of which the operating intensity can be controlled. Depending on the intensity of activation of the pistons, the ratchets can slow down the sliding of the ladder or block it completely.
Advantageously, the sensor 50 is of the optical type, like a micro camera or laser sensor.
As we will see further ahead, the guiding device 20 of the ladder S comprises, in particular, two positioning guides 21, 22 spaced apart, each to receive one of the longitudinal ribs P1, P2 of the ladder S, which are transversally connected by pairs of cross-beams T1, T2.
Advantageously, the sensor 50 is placed facing the device, in a position which, according to a projection parallel to the longitudinal axis X, is between the two guides 21, 22. In this way the sensor 50 is facing the area where the cross-beams pass.
According to the embodiment shown in the annexed Figures, the position of the sensor 50 is decentralised with respect to the centre line of the two guides, i.e. closer to one of the two guides, where the longitudinal ribs slide. In this way it is possible to more easily detect the passage of a ladder with double cross-beams with crossed cords. In fact, in this type of ladder, the cross-beams are visibly separate only near the longitudinal ribs, gradually coming closer together until they touch to each other, as they approach the centre.
The guiding device 20 is used to transversally tension the cross-beams T1, T2 which connect the two longitudinal ribs P1, P2 of the ladder S. In this sense, the device can be of any type suitable to the purpose, comprising two positioning guides 21, 22, each of which is used to transversally hold one of the longitudinal ribs P1, P2 of the ladder S.
According to the preferred embodiment shown in the annexed Figures, the guiding device 20 comprise a support element 23, which can be moved using the first above-mentioned movement means 60 along the positioning direction p with respect to the fixed support structure 3. Both the guides 21, 22 are hinged to this support element 23.
As shown particularly in Figures 16a and 16b, guides 21, 22 can be divaricated at two ends 21', 22' via rotations in the respective hinged points 24 to change the level of tension of the cross-beams of the ladder. The guides can each be moved by their own actuator 27, 28.
In more detail, with respect to the advancement direction A of the ladder S along the positioning direction p, each guide 21, 22 has an entrance portion 21', 22' and an exit portion 21", 22". The guides 21, 22 are hinged at the respective entrance portions 21', 22', so as to vary the distance between the exit portions 21", 22" via rotations around the respective hinging points 24 and vary the level of tension of the pair of cross-beams positioned at the exit portions.
In particular, the two guides 21, 22 rotate on the same plane, preferably vertical, with preferably horizontal hinging axes.
With respect to the guiding devices with guides opening without divarication, i.e. with permanently parallel guides, the guiding device 20 with guides 21, 21 that can be divaricated as described above, ensures that the tighter pair of cross-beams is that positioned at the exit portion, i.e. the pair of cross-beams destined to engage with the divaricating means first.
Advantageously, the guiding device comprises at least one stop tooth 26, preferably with spring activation, which engages the ladder at a cross-beam T1, T2 to prevent the sliding of the ladder S in the opposite direction to advancement. The stop tooth 26 has a function to prevent dropping and can, if necessary, be used to place the ladder S in a preliminary position. Said tooth no longer acts as a mechanical positioning reference. The possible preliminary position is in fact followed by a final positioning that brings the ladder to the correct position with respect to the insertion plane m.
As shown in the annexed Figures, the guiding device 20 comprises two stop teeth 26 positioned at the same height along the positioning direction p. Preferably, each tooth is positioned next to a guide 21, 22.
According to the embodiment shown in Figures 6 to 13, the stacking unit 1 comprises at least one slat loader 10.
The loader can be of any type suitable to the purpose. In particular, as illustrated in the annexed Figures, the loader 10 can be made up of two bars 11 and 12 provided with sprung teeth 13, 14 for the positioning of the slats already inserted in the ladder.
Advantageously, the stacking unit 1 comprises at least one lifting device 30 which is used to take a slat L from a position of insertion in the ladder S to a deposit position in the loader (see the sequence of Figures 12 and 13). The movement of the slat L moves the ladder S associated to it in the guiding device 20. In operational terms, the sliding of the ladder must be freed in the guiding device 20. To this end, the guiding device 20 is activated so as to relax the cross-beams, thus preventing friction and jamming.
The lifting device 30 can be made up, for example, of a pneumatic, hydraulic or electric cylinder.
According to the embodiment shown in the annexed Figures, the lifting device 30 is independent from the guiding device 20. It is however possible to provide an alternative solution (not shown in the annexed Figures), in which the lifting device 30 is connected to the guiding device 20 to move it along the positioning direction p.
In particular, the loader 10 is placed before the divaricating means 40 and the guiding device 20 with respect to the direction of insertion of the slats along the longitudinal axis X. In other words, the divaricating means and the guiding device are situated on the side of the loader opposite the slat entrance.
Advantageously, the stacking unit 1 can comprise an entrance element 4 for the single slats L, positioned before the loader 10 along the longitudinal axis X and preferably coplanar with the insertion plane m.
The operational steps of the stacking unit 1 as it appears from the sequence of Figures 6 to 13 are described briefly.
In Figure 6, the stacking unit 1 is in the initial condition: the ladder has been positioned in the guiding device above the stop teeth 26; the divaricating means 41, 42 are deactivated and the two guides 21, 22 are not divaricated. Subsequently, guides 21, 22 are divaricated to tension the upper pair of cross-beams T1, T2; also the means 25 for holding the ladder should preferably be activated to block it in place (Figure 7). The guiding device 20 is lifted to bring the pair of cross-beams closer to the insertion plane m; the tensioned cross-beams T1, T2 transit in front of sensor 50 which can allow control of positioning according to above description (Figure 8). As the ladder has double cross-beams with crossed cords, a first divaricator element 42, particularly of the sickle type (Figure 9), is activated, followed by the second divaricator 41 (Figure 10). The slat is inserted between the two divaricated cross-beams (Figure 11). The divaricating means are withdrawn, the means 25 for holding the ladder are deactivated and the two guides are preferably brought closer (Figure 12). The slat L not blocked by the divaricating means is lifted with the lifting device 30 inside the loader above the first sprung teeth, dragging the ladder up too, until the second pair of cross-beams moves beyond the stop teeth 26 (Figure 13). The lifting device 30 can now be lowered. The ladder is now ready for a new cycle. As shown in Figure 13, the cross-beams do not necessarily have to rest on the stop teeth.
The subject of the present invention is also a method of positioning the support ladder (comprising a plurality of pairs of cross-beams T1, T2), for the production of Venetian blinds.
Preferably, but not necessarily, the method is applied to a stacking unit 1 according to the present invention.
According to a general form of implementation, the method comprises the following operating steps:

a) providing a stacking unit 1 of slats L comprising means 40 for divaricating a pair of cross-beams; said means 40 acting on an insertion plane m which the individual slats L are made to slide on for associating to the ladder;
b) moving the ladder S along a positioning direction p incident to the insertion plane m to position a pair of cross-beams T1, T2 next to the insertion plane m and the divaricating means 40;
c) approaching the pair of cross-beams (T1, T2) in tension to the insertion plane (m) further moving the ladder along the positioning direction (p);
d) detecting during the approaching step c) by means of a sensor (50) the crossing - by a first cross-beam T1 of the above-mentioned pair - of a reference height placed at a predefined distance (H) from the insertion plane (m) with respect to the positioning direction (p);
e) after the detection step d), controlling the approaching movement of the ladder (S) to the insertion plane making the ladder and therefore the first cross-beam T1 move towards the reference plane (m) for a tract equivalent to the aforesaid predefined distance (H).

The sensor 50 is preferably of the optical type.
Advantageously, the method comprises a step f) of transversally tensioning the pair of cross-beams T1, T2. Such step f) takes place before the approach step c).
The invention allows numerous advantages, some of which have already been described.
The stacking unit 1 according to the invention allows a correct positioning of the ladder S without necessarily having to vertically stretch the cross-beams to rest them against mechanical references. This prevents the cross-beams from being brought closer together and a further reduction of the space for passage.
The stacking unit 1 can therefore be used reliably with any type of ladder, even with ladders in which the distance between the cross-beams is less than 1 mm. This is made possible by the fact that the ladder can be positioned very precisely thanks to the presence of the sensor.
The stacking unit 1 is also simple to manage using a normal PLC, as well as being affordable and easy to make. The absence of means for vertically stretching the ladders makes unit 1 easier to make and less problematic to manage in terms of maintenance.
The invention thus conceived achieves the aims set.
Obviously it can also take on, in its actual embodiment, practical forms and configurations different from those illustrated above without moving away from the present area of protection.
Moreover, all these parts can be replaced by technically equivalent elements and any dimensions, forms and materials can be used according to need.

Claims

Unit for stacking slats on a support ladder provided with double cross-beams for the production of Venetian blinds, comprising:
- at least one guide element (2) for a slat (L), which defines an insertion plane (m) on which the slat (L) slides supported along a longitudinal insertion axis (X);

- a device (20) for guiding a ladder in a positioning direction (p) incident to the insertion plane (m); and

- means (40) for divaricating at least one pair of cross-beams (T1, T2) of such ladder (S), said means being positioned in the vicinity of the guiding device (20) to operate when divaricating substantially on the insertion plane (m);
the ladder (S) being made to slide in the guiding device (20) according to a way of advancement (A) along the positioning direction (p) to progressively bring each pair of cross-beams (P1, P2) in front of the divaricator (40), characterised by the fact of comprising means (20, 30) for moving the ladder (S) along said positioning direction (p) and by the fact of comprising at least one sensor (50) to detect the transit in front of it of a cross-beam of the ladder (S) during the movement of the ladder along the positioning direction (p), the sensor (50) facing the guiding device (20) and being positioned at a predefined distance (H) from the insertion plane (m) in the positioning direction (p), a pair of cross-beams (T1, T2) of the ladder being positionable at the insertion plane (m) operating the movement means (20,30) to move the ladder by a tract equivalent to said predefined distance (H) along the positioning direction (p) at the moment in which the sensor (50) detects the transit of a first crossbeam (T1) of said pair.
Stacking unit according to claim 1, wherein the guiding device (20) of the ladder (S) comprises means (25) for holding the ladder and is movable by means of first movement means (60) along said positioning direction (p), the movement means of the ladder comprising the guiding device (20), a pair of cross-beams (T1, T2) of the ladder being positionable in correspondence of the insertion plane (m) moving the guiding device (20) by a tract equivalent to said predefined distance (H) along the positioning direction (P) at the moment in which the sensor (50) detects the passage of a first cross-beam (T1) of said pair.
Stacking unit according to claim 2, in which the holding means of the ladder comprise one or more frictioning elements (25) to brake the sliding of the ladder (S).
Stacking unit according to claim 2 or 3, in which the holding means of the ladder comprise one or more blocking elements (25) of the ladder (S).
Stacking unit according to one or more of the previous claims, in which the sensor (50) is of the optical type.
Stacking unit according to one or more of the previous claims, in which the guiding device (20) of the ladder (S) comprises two positioning guides (21,22), distanced from each other to each receive one of the two longitudinal ribs (P1, P2) of the ladder (S).
Stacking unit according to claim 6, wherein the sensor (50) is positioned facing the device in a position which according to a projection parallel to the longitudinal axis (X) is between the two guides (21,22).
Stacking unit according to claim 7, in which the position of the sensor (50) is decentralised in relation to the centreline of the two guides.
Stacking unit according to one or more of the previous claims, in which the first movement means (60) of the guiding device (20) comprise at least one electric piston to ensure accurate positioning of the guiding device (20) and of the ladder (S) supported by it.
Stacking unit according to one or more of the claims from 2 to 9, in which the guiding device (20) comprises a support element (23) which is movable by means of said first movement means (60) along said positioning direction (p) and to which both the guides (21,22) are hinged, it being possible to divaricate said guides from each other at two end portions (21',22') by means of rotation movements at the respective hinging points (24) to vary the level of tensioning of the cross-beams of the adjustable support.
Stacking unit according to claim 10, in which with respect to the way of advancement of the ladder (S) along the positioning direction (p) each guide (21,22) has an entrance portion (21',22') and an exit portion (21", 22"), the guides (21,22) being hinged in the respective entrance portions (21',22') so as to vary the distance between the exit portions (21",22") by means of rotations around the respective hinging points (24) and to vary the level of tension of the pair of cross-beams positioned at the exit portions.
Stacking unit according to one or more of the claims from 2 to 11, in which the guiding device comprises at least one stop tooth (26), elastically operated, which engages the ladder in correspondence of a cross-beam (T1, T2) to prevent the sliding of the ladder (S) in the way opposite to that of advancement.
Stacking unit according to claim 12, in which the guiding device (20) comprises two stop teeth (26) positioned at a same height along the positioning direction (p), each tooth being positioned preferably next to a guide (21, 22).
Stacking unit according to one or more of the previous claims, comprising at least one slat loader (10) and means (30) for moving a slat (L) from an insertion position in the ladder (S) in correspondence of the insertion plane (m) to a deposit position into the loader, the movement of the slat (L) making the ladder (S) associated to it advance by pulling into the guiding device (20).
Stacking unit according to one or more of the previous claims, in which the divaricating means (40) comprise two rotating, sickle-shaped divaricator elements (41, 42) positioned specularly to the longitudinal insertion axis (X) of the slat (L).
Method of positioning a support ladder for the production of Venetian blinds, said ladder (S) comprising a plurality of pairs of cross-beams (T1, T2), the method comprising the following operating steps:
- a) providing a stacking unit (1) of slats (L) comprising means (40) for divaricating a pair of cross-beams, said means (40) acting on an insertion plane (m) which the individual slats (L) are made to slide on for associating to the ladder;

- b) moving the ladder (S) along a positioning direction (p) incident to the insertion plane (m) to position a pair of cross-beams (T1, T2) next to the insertion plane (m) and the divaricating means (40);

- c) approaching the pair of cross-beams (T1, T2) in tension to the insertion plane (m) further moving the ladder along the positioning direction (p);

- d) detecting during the approaching step c) by means of a sensor (50) the crossing by a first cross-beam (T1) of a reference height placed at a predefined distance (H) from the insertion plane (m) with respect to the positioning direction (p); and

- e) after the detection step d), controlling the approaching movement of the ladder (S) to the insertion plane making the ladder move towards the insertion plane (m) for a tract equivalent to the aforesaid predefined distance (H).
Method according to claim 16, in which the sensor (50) is of the optical type.
Method according to claim 16 or 17, comprising a step f) of transversally tensioning the pair of cross-beams (T1, T2), said step f) being conducted before said approach step c).