The present invention refers to a lifting-lowering and sliding group for door or window wings.

Sliding wings doors and windows are known which, in general terms, comprise a fixed frame which defines the opening of the door or window and to which at least one wing, able to slide horizontally between a closed position and an open position of the opening and vice versa, is associated.

Conventionally, the air or water-tight seal between the wing and the respective sliding guide formed in the frame is obtained by means of so called "brush" gaskets.

"Brush" gaskets, however, do not make it possible to achieve levels of air or water seal comparable to those that can be reached, on the other hand, with gaskets made up of tubes, bands or similar, made from polymeric materials like, for example, Dutral®.

The use of such last gaskets, however, is limited by the excessive friction which would be generated during the sliding of the wing and which would make the opening and closing manoeuvres of the opening of the door or window difficult.

In order to avoid such a drawback, wings have long been known of the so called "lift and slide" type, that is, in which each wing is associated to the frame by means of a respective lifting-lowering and sliding group which is manoeuvred by a control handle.

Such a group makes it possible to lift the wing from the respective sliding guide, with consequent detachment from the latter of the sealing gasket, before being able to slidingly pull it and, subsequently, lower it again re-establishing the contact between the sealing gaskets and the sliding guide.

In general terms, such a lifting-lowering and sliding group of the known type comprises at least two carriages which are associated to the lower crossbar of a wing and of which one, that is the main or front carriage, precedes the other, that is the secondary or rear carriage, in the sliding direction of the wing for closing the opening of the door or window, wherein the two carriages are joined to one another by a connecting rod.

Each of the two carriages in turn comprises a support body provided with wheels which engage in the sliding guide of the wing and an attachment body to the lower crossbar of the wing. Such an attachment body is associated with the respective support body in a mobile manner on the vertical plane with a combined translation motion along the direction parallel to the sliding direction (horizontal direction) and along the direction orthogonal to it (vertical direction) so as to be able to be lifted and lowered with respect to it. The lifting or lowering motion of the attachment body and, therefore, of the wing to which it is fixed, with respect to the support body of the main carriage is controlled by means of a manoeuvring mechanism operated by the control handle and is transmitted to the attachment body of the secondary carriages by the rods that connect the carriages.

Starting from the closed configuration of the opening of the door or window - in which the wing is lowered with the sealing gaskets in contact with the respective sliding guide - in order to open the door or window it is necessary, in general, to rotate the handle by about 180° downwards. Such a rotation actuates, by means of transmission organs of the known type, the manoeuvring mechanism so as to move the attachment bodies of the carriages and, therefore, the wing fixed to them, away from and upwards with respect to the corresponding support bodies thus lifting the wing and detaching the sealing gaskets from the sliding guide.

It is thus possible to make the wing slide in the opening/closing direction of the door or window by means of wheels of the support bodies of the two carriages.

After having brought the wing back in the closed position of the opening of the door or window, the control handle is made to rotate by 180° upwards so as to move the attachment bodies of the two carriages towards the corresponding support bodies and, therefore, bring the wing, which is fixed to them, back in the lowered position with the sealing gaskets in contact with the sliding guide.

When the wing is in the lifted position, it tends, by action of its weight, to be brought back in the lowered position, so that its sliding is obstructed, if not even prevented.

In order to avoid such a drawback, solutions are already known which provide for the use of devices which, when the wing is in the lifted position, contrast its weight preventing its spontaneous return to the lowered position.

Some known devices are of the connecting rod and crank type and are applied to the control handle so as to prevent its return rotation to the closed position, others are of the friction type and are applied to the organs for transmitting the motion from the handle to the manoeuvring mechanism of the two carriages, again others are applied to the carriages themselves.

Amongst these latter, in particular, devices are known comprising springs interposed between the attachment body and the support body of each carriage.

These last safety devices of the known type have, however, some drawbacks.

Among these it should be reminded that such devices are active only for a fraction of the amplitude of the rotation angle of the control handle and, therefore, only for a fraction of the lifting/lowering stroke of the wing.

A further drawback consists in the fact that such devices do not make it possible to modify the degree of the springs reaction in function of the weight of the wing or to recover possible coupling clearances which can generate also in use, unless springs or the various components are replaced with laborious interventions that require the disassembly and the re-assembly of the entire window or door frame.

The main object of the present invention is that of avoiding the drawbacks of the prior art.

Within this general object, one object of the present invention is that of making a lifting-lowering and sliding group for door or window wings which makes it possible to contrast the spontaneous rotation of the control handle from the open position to the closed position for the entire amplitude of its rotation angle, i.e. for the entire lifting-lowering stroke of the wing.

A further object of the present invention is that of making a lifting-lowering and sliding group for door or window wings that allows to reduce the force that a user must apply to the control handle in order to bring the wing from the lowered position to the lifted position and vice versa.

Yet another object of the present invention is that of making a lifting-lowering and sliding group for door or window wings which makes it possible to modify the degree of reaction of the springs in a simple and rapid manner even when the door or window frame is in the mounted configuration and without requiring disassembly and re-assembly operations.

Yet another object of the present invention is that of making a lifting-lowering and sliding group for door or window wings having a low number of components, assembled with one another in a particularly simple and functional manner.

These and yet other objects are achieved with a lifting-lowering and sliding group for door or window wings as defined in claim 1.

Further characteristics are specified in the dependent claims.

The characteristics and the advantages of a lifting-lowering and sliding group for door or window wings according to the present invention shall become clearer from the following description, given as an example and not for limiting purposes, with reference to the attached schematic drawings, in which:

• figure 1 is a schematic view of a window with sliding wing with a lifting-lowering and sliding group according to the present invention applied to it;
• figure 2a is an axonometric and exploded view of a lifting-lowering and sliding group according to the present invention;
• figures 2b and 2c are two details on an enlarged scale of figure 2a;
• figures 3a and 3b show, respectively in a side elevation view and in a longitudinal section view, the lifting-lowering and sliding group according to the present invention applied to a wing in a first configuration;
• figures 4a and 4b show, respectively in a side elevation view and in a longitudinal section view, the lifting-lowering and sliding group according to the present invention applied to a wing in a second configuration;
• figures 5 and 6 show on an enlarged scale a first detail of the lifting-lowering and sliding group in the two configurations according to figures 3a and 4a;
• figures 7 and 8 show on an enlarged scale a second detail of the lifting-lowering and sliding group in the two configurations according to figures 3b and 4b.

With reference to the attached drawings a lifting-lowering and sliding group of door or window wings has been wholly indicated with reference numeral 10.

In figure 1 the group 10 is schematically represented in the configuration assembled in a window frame 100 of the so-called "lift and slide" type.

The window frame 100 comprises a fixed frame 101 that defines the opening of a door or of a window and at least one wing 102 which is mounted on the fixed frame 101 in a sliding manner horizontally along a sliding direction A, which is defined by a sliding guide obtained in the fixed frame 101, between a closed position, represented in figure 1, and an open position, not represented, of the opening of the door or window and vice versa.

In the figures, with the arrows A1 and A2, there have been indicated the sense and direction of the sliding of the wing 102 for opening and closing the opening, respectively.

A sealing gasket 103 is fixed to the lower crossbar 104 of the wing 102, so that, when the wing 102 is in the closing position of the door or window opening, an air and/or water tight seal is created between the wing 102 and the respective sliding guide.

The group 10 comprises at least one carriage and, in general, at least two carriages 11a and 11b arranged in series along the sliding direction A. One of such two carriages, generally indicated as the front or main carriage 11a, precedes the other one, generally indicated as the rear or secondary carriage 11b, with respect to the sliding direction A2 for closing the wing 102.

Between the main carriage 11a and the secondary carriage 11b there could be at least one further intermediate carriage.

The main carriage 11a has an end associated to a manoeuvring mechanism 12 that is operated by a control handle 105 that is mounted on the wing 102.

Moreover, there are provided organs for locking the wing 102 in the closed position, these organs are not represented since they are of the known type and are operated by the same control handle 105.

For the sake of clarity and simplicity, in the rest of the description, the two carriages shall be indicated as "main carriage" and "secondary carriage", it being understood that one of them is directly connected to the manoeuvring mechanism that is operated by the control handle and the other one is at the opposite end of the series of carriages which can be arranged to support the wing 102.

The end of the main carriage 11a opposite to that associated to the manoeuvring mechanism 12 is fixed at the end of a connecting rod 13 extending parallel to the sliding direction A and the opposite end of which is fixed to an end of the secondary carriage 11b.

The connecting rod 13 acts as a transmission and manoeuvre mechanism between the main carriage 11a and the secondary carriage 11b.

In the present description elements that are common to the two carriages shall be indicated with the same reference numerals followed by the letter "a", if they refer to the main carriage 11a, and by the letter "b", if they refer to the secondary carriage 11b.

Each of the two carriages, main 11a and secondary 11b, comprises in turn a support body 14a, 14b which is provided with support and rolling elements made up of wheels 15a, 15b which are pivotally mounted on it around respective pins 16a, 16b orthogonal to the lying plane of the wing 102 and which are housed in the sliding guide, schematically indicated by the line 106 in figures from 3a to 8, so as to allow the translation of the wing 102 along the sliding direction A.

Each of the two carriages, main 11a and secondary 11b, moreover, comprises an attachment body 17a, 17b to the wing 102, which, in particular, can be fixed, for example through screws 18a, 18b, to the lower crossbar 104 of the wing 102.

Each attachment body 17a, 17b is associated with a respective support body 14a, 14b in a mobile manner on a plane parallel to the lying plane of the wing 102 with a relative combined translation motion along the sliding direction A and along a direction B orthogonal to it for lifting and lowering the wing 102 with respect to the support body 14a, 14b and, therefore, with respect to the sliding guide 106.

Considering the group 10 in the configuration assembled onto a wing 102, the sliding direction A is horizontal and the direction B orthogonal to it is the vertical one.

One particular characteristic of the present invention consists in the fact that the support body 14a, 14b of each carriage, main 11a and secondary 11b, comprises a guide body 19a, 19b of respective elastic means 20a, 20b which act between the support body 14a, 14b itself and a respective counter element 21a, 21b associable to the lower crossbar 104 of the wing 102.

Wherein the counter element 21a, 21b is made up of a body that is distinct and separate from the attachment body 17a, 17b of the respective carriage and is associated to the respective guide body 19a, 19b in a mobile manner in translation along the sliding direction A and along the direction B orthogonal to it. Advantageously, the guide bodies 19a, 19b are defined at the end of the respective support body 14a, 14b opposite to the end of the latter which is associable to the respective manoeuvring mechanism.

That is, the guide body 19a of the main carriage 11a is defined at the end of the respective support body 14a opposite to that associated to the manoeuvring mechanism 12.

The guide body 19b of the secondary carriage 11b is defined at the end of the respective support body 14b opposite to that fixed to the connecting rod 13.

Both guide bodies 19a, 19b moreover, extend in a direction that is parallel to the sliding direction A of the wing 102; i.e. they extend horizontally so that the elastic force exerted by the respective elastic means 20a, 20b that are guided on them is directed parallel to the sliding direction A of the wing 102. Advantageously, each guide body 19a, 19b consists of a guide rod which extends from the end of the respective support body 14a, 14b opposite to the end of the latter that is associated to the respective manoeuvring mechanism.

As shall become clearer from the following detailed description, the guide rod that integrates the guide body 19a of the main carriage 11a coincides with a length of the connecting rod 13.

As schematically represented in figures from 3a to 4b, the main carriage 11a and the secondary one 11b assume a first operative configuration and a second operative configuration respectively "with the wing 102 lowered" and "with the wing 102 lifted".

In the first configuration ("with the wing 102 lowered", figures 3a and 3b), the attachment bodies 17a, 17b are in a lowered position with respect to the corresponding support bodies 14a, 14b and the elastic means 20a, 20b are compressed between the respective support body 14a, 14b and counter element 21a, 21b in a first compression state.

In such a first configuration, the wing 102, which is fixed to the attachment bodies 17a, 17b is in the position lowered with respect to the sliding guide 106 with the gasket 103 in seal contact with the latter.

In the second configuration ("with the wing 102 lifted", figures 4a and 4b), the attachment bodies 17a, 17b are in a lifted position with respect to the corresponding support bodies 14a, 14b and the elastic means 20a, 20b are compressed between the respective support body 14a, 14b and counter element 21a, 21b in a second compression state.

In such a second configuration, the wing 102, which is fixed to the attachment bodies 17a, 17b is in a lifted position with respect to the sliding guide 106.

As can be noted in the attached figures, the second compression state of the elastic means 20a, 20b (that assumed in the second configuration "with a lifted wing 102") is less than that of the first compression state, so that the elastic means 20a, 20b assist the passage of the main and secondary carriages 11a and 11b from the first configuration ("with the wing 102 lowered") to the second configuration ("with the wing 102 lifted") and contrast the weight of the wing 102 when the carriages are in the second configuration ("with the wing 102 lifted"), preventing its spontaneous return to the first configuration ("with the wing 102 lowered").

According to a further particular characteristic of the present invention, at least one of the two carriages, main 11a and secondary 11b, in particular at least the secondary carriage 11b, comprises adjusting means 22a, 22b of the first compression state of the respective elastic means 20a, 20b.

In greater detail and with reference to figure 2, the support body 14a of the main carriage 11a consists of two side walls 140a facing one another and parallel to the lying plane of the wing 102 and between which are arranged the wheels 15a, the pins 16a of which are supported in holes 141a obtained in the two side walls 140a.

Each of the two side walls 140a comprises, at one end, a hole 142 in which the manoeuvring mechanism 12 articulates and, at the opposite end, holes 143, in which the pins 23 of a spacer 24 are fitted in.

The attachment body 17a of the main carriage 11a is L-shaped with one branch extending parallel to the sliding direction A and which is intended to be fixed to the lower crossbar 104 of the wing 102 and the other branch extending orthogonal to the first and which is intended to be fixed to the rib of the wing 102.

The attachment body 17a has an appendage 170a which extends towards the support body 14a and in which a slot 171a is defined, the slot being rectilinear, parallel to the lying plane of the wing 102 and inclined with respect to the forward movement direction A.

Along the slot 171a a pin 172a is mobile, the pin 172a being fixedly attached to the support body 14a.

In practice, the slot 171a is a through slot formed in the appendage 170a and the pin 172a consists of a pin the opposite ends of which are fixed in holes 144a obtained in the two side walls 140a.

At the angle portion of the attachment body 17a a further hole 173 is obtained for the articulation of the manoeuvring mechanism 12, as described later on in the description.

One end of the connecting rod 13 is fixed inside the spacer 24, by means of dowels 25.

The same connecting rod 13, or better, a length thereof extending from the end of the support body 14a opposite to that associated to the manoeuvring mechanism 12, acts as a guide body 19a of the elastic means 20a.

The latter advantageously consist of at least one cylindrical or conical-spiral torsion spring coaxially mounted to the connecting rod 13 with one end resting on an abutment surface defined by the spacer 24 of the support body 14a and with the opposite end resting on the respective counter element 21a.

The counter element 21a is fixed to the lower crossbar 104 of the wing 102 by means of dowels 210a and projects at the bottom in a plate that is orthogonal to the lying plane of the wing 102 and in which a slot 211a is obtained extending parallel to the direction B and in which the connecting rod 13 is inserted with a clearance, so that between the counter element 21a and the connecting rod 13 (guide rod of the elastic means 20a) there can be a relative sliding motion along the sliding direction A (horizontal) of the wing 102 and along the direction B orthogonal to it (vertical).

The adjusting means 22a of the compression state, or better, of the first compression state, of the elastic means 20a are defined at the end of the support body 14a opposite to the end of the latter associated to the manoeuvring mechanism 12 and are suitable for modifying the position of the counter element 21a with respect to the support body 14a when the main carriage is in the first configuration (figures 3a and 3b) before that the counter element 21a is mounted on the wing 102.

In particular, the adjusting means 22a comprise an adjusting organ that consists of a nut 220 which is screwed on at least one threaded length of the guide body 19a (connecting rod 13) and that, in the mounting phase of the group 10 and when the main carriage 11a is in the first configuration, rests against the counter element 21a on the side opposite with respect to the elastic means 20a.

In such conditions and before fixing the counter element 21a to the lower crossbar 104 of the wing 102, by acting on the nut 220 it is possible to modify the first compression state (pre-load) of the elastic means 20a.

After having adjusted the first compression state (pre-load) of the elastic means 20a to the desired value, temporarily keeping the nut 220 in position, the assembly of the group 10 is completed by fixing the counter element 21a to the lower crossbar 104 of the wing 102.

Once it has been mounted, the nut 220 is unscrewed and removed from the counter element 21a by a distance equal to at least the relative sliding between it and the guide body 19a (connecting rod 13; figures 5 and 6).

Again with reference to figure 2, the support body 14b of the secondary carriage 11b consists of two side walls 140b facing one another and parallel to the lying plane of the wing 102 and between which are arranged the wheels 15b, the pins 16b of which are supported in holes 141b obtained in the two side walls 140b.

Each of the two side walls 140b comprises, at each of the two opposite ends, respective holes 145 and 146 in which the pins 26, 27, of a respective spacer 28, 29, are respectively fitted.

The attachment body 17b of the secondary carriage 11b consists of a plate intended to be fixed to the lower crossbar 104 of the wing 102.

In a completely similar way to the attachment body 17a of the main carriage 11a, also the attachment body 17b has an appendage 170b which extends towards the support body 14b and in which a slot 171b is defined, the slot being rectilinear, parallel to the lying plane of the wing 102 and inclined with respect to the forward movement direction A completely identical to the slot 171a.

Along the slot 171b a pin 172b is mobile, the pin being fixedly attached to the support body 14b.

In practice, the slot 171b is a through slot formed in the appendage 170b and the pin 172b consists of a pin the opposite ends of which are fixed in holes 144b formed in the two side walls 140b.

One end of the connecting rod 13 is fixed, by means of dowels 30, inside the spacer 28.

The guide body 19b of the elastic means 20b consists of a guide rod that has one end fixed inside the spacer 29 by means of dowels 31.

The elastic means 20b advantageously consist of at least one cylindrical or conical-spiral torsion spring coaxially mounted to the guide body 19b with one end resting on an abutment surface defined by the spacer 29 of the support body 14b and with the opposite end resting on the respective counter element 21b.

The counter element 21b is fixed to the lower crossbar 104 of the wing 102 by means of dowels 210b and projects at the bottom in a plate that is orthogonal to the lying plane of the wing 102 and in which a slot 211b is formed extending parallel to the direction B and in which the guide body 19b is inserted with clearance, so that between the counter element 21b and the guide body 19b (guide rod of the elastic means 20b) a relative sliding movement can occur along the sliding direction A (horizontal) of the wing 102 and along the direction B orthogonal to it (vertical).

The end of the guide body 19b opposite to the one fixed to the spacer 29 has a collar 190 for stopping the relative sliding of the counter element 21b.

The counter element 21b is associated with an attachment block 32 that is fixed to the lower crossbar 104 of the wing 102 with the interposition of the adjusting means 22b of the compression state, or better of the first compression state, of the elastic means 20b.

In greater detail, the adjusting means 22b are configured in order to modify the position of the counter element 21b with respect to the attachment block 32.

Such adjusting means 22b comprise an adjusting screw 221 extending parallel to the guide body 19b (guide rod) and that passes a through hole 212 obtained in the counter element 21b.

Said adjusting screw 221 has an end engaged in a threaded hole 33 which is obtained in the attachment block 32 and the opposite end provided with an abutment element consisting of the head 222 whereon the counter element 21b stops (figure 7 and 8).

In the head 222 a seat 223 is formed for engaging with a manoeuvring tool.

As can be seen from the attached figures, considering the group 10 in the assembled configuration on a door or window wing, the adjusting means 22b of the compression state of the elastic means 20b of the secondary carriage 11b are accessible from the outside. It is not excluded that the adjusting means 22a of the compression state of the elastic means 20a of the main carriage 11a, can be configured in a completely identical manner to that of the adjusting means 22b of the compression state of the elastic means 20b of the secondary carriage 11b, i.e. of the outermost carriage. The manoeuvring mechanism 12 comprises a ternary element consisting of two plates 120 facing one another and parallel to the lying plane of the wing 102 and each of which has three holes, first holes 121, second holes 122 and third holes 123, respectively.

The first holes 121 house the ends of a first pin 124 around which the end of a connecting rod 125 is articulated, the opposite end of the connecting rod 125 is articulated to the support body 14a of the main carriage 11a by means of a second pin 126 mounted in the holes 142 of the side walls 140a.

The second holes 122 house the ends of a third pin 127 around which the attachment body 17a of the main carriage 11a is articulated by means of the hole 173.

The third holes 123 house the ends of a fourth pin 128 inserted in a hole 129 of a control rod 130 associable to the upright of the wing 102 in a sliding manner along the direction B orthogonal to the sliding direction A and controlled, by means of transmission organs which have not been represented since they are of the known type, by the handle 105.

In light of the attached figures and of the description made above, a man skilled in the art will not have any difficulty in understanding how the present invention operates and its advantages.

In particular, with reference to figures 3a-3b and 4a-4b in these, the group 10 according to the present invention is illustrated respectively in the first configuration ("with the wing 102 lowered") and in the second configuration ("with the wing 102 lifted").

In the first configuration (figures 3a and 3b), the first and the fourth pin 124 and 128 of the manoeuvring mechanism 12 are substantially aligned with the support bodies 14a, 14b of the main carriage 11a and of the secondary carriage 11b.

The attachment bodies 17a, 17b of the main carriage 11a and of the secondary one 11b are in a lowered position with respect to the corresponding support body 14a, 14b with the pins 172a, 172b in abutment at the upper end of the respective slot 171a, 171b.

In said first configuration, the elastic means 20a, 20b are in their first compression state (pre-load).

From such a first configuration, by rotating the handle 105 by around 180° downwards, as indicated by the arrow F1 in figure 3a, the rotation of the ternary element is generated, as indicated by the arrow F2 in figure 3b. Since the wing 102, which, in such a first configuration is positioned to close the opening of the door or window, is constrained by the fixed frame 101, such a rotation generates the sliding of the support bodies 14a, 14b of the main carriage 11a and of the secondary one 11b in the closing direction of the wing 102 and, thanks to the coupling between slots 171a, 171b and pins 172a, 172b, the lifting of the attachment bodies 17a, 17b and, therefore, of the wing 102 to which they are fixed, with respect to the support body 14a, 14b of the main carriage 11a and secondary one 11b.

The group 10 and, therefore, the wing 102 to which it is applied thus assume the second configuration ("with lifted wing 102"; figures 4a and 4b) in which the first and the fourth pin 124 and 128 of the manoeuvring mechanism 12 are substantially aligned along the direction B.

The attachment bodies 17a, 17b of the main carriage 11a and of the secondary one 11b are in a lifted position with respect to the corresponding support body 14a, 14b with the pins 172a, 172b in abutment at the lower end of the respective slot 171a, 171b.

In said second configuration, the elastic means 20a, 20b are in their second compression state, in which they are stretched with respect to the first compression state.

The passage from the first to the second configuration is assisted by the thrust exerted by the elastic means 20a, 20b which pass from the first compression state (pre-load) to the second compression state.

Once the second configuration ("with lifted wing 102") has been reached, the elastic means 20a, 20b contribute to support the weight of the wing 102 preventing its return to the lowered position.

The elastic reaction of the elastic means 20a, 20b is adjusted as a function of the weight of the wing 102 thanks to the adjusting means 22a, 22b, of which, those applied to the secondary carriage 11b are accessible from the outside also when the group 10 is in the assembled configuration on the window frame.

In practice it has been seen how the subject-matter of the present invention makes it possible to achieve the predetermined objects.

The lifting-lowering and sliding group according to the present invention, indeed, thanks to the particular location and arrangement of the elastic means, makes it possible to facilitate the opening manoeuvre of the wing, reducing the force that a user must exert on the control handle in order to bring the wing from the lowered position to the lifted one and, consequently, to reduce the dimensions of the arm of the control handle itself.

Thanks to the particular location and arrangement of the elastic means, the lifting-lowering and sliding group according to the present invention makes it possible to effectively contrast the spontaneous return of the wing from the lifted position to the lowered position for the entire lifting/lowering stroke thereof, i.e. the entire amplitude of the corresponding rotation angle of the control handle.

Thanks to the provision of the adjusting means of the compression state of the elastic means it is, moreover, possible to adjust the elastic reaction as a function of the weight of the wing.

The particular configuration and arrangement of the adjusting means of the compression state of the elastic means mounted on the secondary carriage - that is of the carriage at the end of the wing opposite to that whereon the control handle is mounted - allow to adjust the elastic reaction even when the group is in the assembled configuration, in a simple and rapid manner, without it being necessary any disassembly and reassembly operation.

Such adjusting means, indeed, are easily accessible below the wing and it is sufficient to use a manoeuvring tool to carry out the adjustment intervention.

The lifting-lowering and sliding group for door or window wings thus conceived is subject to numerous modifications and variants, all covered by the invention; moreover, all the details can be replaced by technically equivalent elements. In practice the materials used, as well as the dimensions, can be any according to the technical requirements.