End element applied to the lower edge of the flexible sheet of a roller blind and roller blind using said end element

Abstract

An end element (1) comprising an end profile (4) which is connected to the lower edge (2) of the flexible sheet (3) and which comprises a pair of end flanges (5) fixed to its ends. Each end flange (5) has the outer surface (11) flat and comprises a contrast plate (10) projecting orthogonally from the outer surface (11) and arranged at a side of the contrast plate (10). The end element (1) is applied to a roller blind (50) comprising a frame (51) formed by two side uprights (52) and a box (53) in which a roller (54) for winding the flexible sheet (3) is housed. A guide slider (8) for sliding the end element (1) along the side uprights (52) protrudes from each end flange (5).

Description

[0001] END ELEMENT APPLIED TO THE LOWER EDGE OF THE FLEXIBLE SHEET OF A ROLLER BLIND AND ROLLER BLIND USING SAID END ELEMENT.

[0002] DESCRIPTION

[0003] The invention relates to an end element that is applied to the lower edge of the flexible sheet of a roller blind to keep it extended during the vertical lifting and lowering displacement.

[0004] The invention also relates to a roller blind using the aforesaid end element.

[0005] It is known that, in order to control the entry of light, air and dust into indoor environments, or to prevent them from being observed from the outside, it is customary to apply blinds of various kind to the windows, and currently the most used ones are the so-called roller blinds.

[0006] Blinds of this type comprise a frame that is applied in a window space and that comprises two uprights above which a box is arranged that accommodates therein a roller on which a flexible sheet is wound.

[0007] Inside the respective uprights there are housed guide means along which the side edges of the flexible sheet slide during lowering or lifting generated by manual or motorized driving means that rotate the roller on which the flexible sheet is wound.

[0008] The lower edge of the flexible sheet is fixed to an end element that has the ends slidably connected to longitudinal guides housed in the uprights and keeps the flexible sheet extended during lifting and lowering.

[0009] Roller blinds of the prior art that have been briefly described generally have some acknowledged drawbacks.

[0010] A first acknowledged drawback is first of all identified in the fact that the grooves to guide the sliding of the flexible sheet that are made along the longitudinal guides are large in size and unsightly, especially because they are in a very visible position as they are arranged along the uprights of the blind.

[0011] In addition, the grooves are of considerable width and this favours the entry of dust and impurities that accumulate over time and reduce the smoothness of the flexible sheet, compromising the operation of the blind.

[0012] Last but not least, an acknowledged drawback consists in the fact that along the longitudinal guides the grooves are spaced away from the ends of the end element and this aspect favours the passage of light and drafts of air.

[0013] In relation to what has been said, patent document DE 20201810515A1 is cited, in which a zip-guided awning is described in which the drawbacks that have just been listed are identified.

[0014] The aforesaid awning comprises a cross bar with mainly longitudinal development indicated with 6 in figure 2 attached to the aforesaid patent document, which is connected to the lower edge of the flexible sheet 4 and is enclosed between a pair of side guides 5 along which it slides when the flexible sheet 4 is raised or lowered.

[0015] At each end of the cross bar 6 there is a closing flange 15 which is provided with a protrusion 16 which is slidably accommodated in a corresponding longitudinal channel 14 present in the side guide 5.

[0016] It is noted that the side edge of the flexible sheet 4 is arranged in a passing through manner along a slot obtained in the protrusion 16 from which it protrudes to be engaged in the guide means that are housed in the side guide 5.

[0017] Furthermore, fixing means arranged in a passing through manner in the protrusion 16 constrain the side edge of the flexible sheet to the closing flange 15 so as to stiffen the end of the side edge projecting from the protrusion 16.

[0018] Embodiment of the aforesaid patent document, which has now been briefly described, has the drawback that the longitudinal channel 14 has a wide width that facilitates the entry of dust and impurities in general which accumulate over time and reduce the smoothness of the flexible sheet compromising the operation of the blind.

[0019] In fact, the longitudinal channel 14 is made wide since it must receive the insertion of the protrusion 16 that brings the end of the side edge of the flexible sheet closer to the guide means and which must have a sufficient width to also act as a contrast element against the skidding of the cross bar 6.

[0020] Furthermore, the wide width of the longitudinal channel 14 and of the protrusion 16 compromises the aesthetics of the roller blind.

[0021] The present invention intends to overcome the drawbacks of the prior art that have been listed.

[0022] In particular, it is a first object of the invention to realize an end element that is applied to the lower edge of the flexible sheet of a roller blind and a roller blind that employs the aforesaid end element, in which blind the guide grooves of the side edges of the flexible sheet and of the ends of the end element can have a width that is contained and reduced to that of guide grooves of the prior art.

[0023] Advantageously, this aspect improves the aesthetics of the longitudinal guides and of the roller blind as a whole and also achieves the other purpose of avoiding, or at least reducing, the entry of dust and impurities in general into the guide grooves.

[0024] Advantageously, this aspect also prevents the smoothness of the flexible sheet and of the end element and therefore the proper functioning of the blind from being compromised over time.

[0025] Finally, it is desired to achieve that in the longitudinal guides the grooves are sufficiently spaced away from the ends of the end element so as to prevent or in any case effectively counteract the passage of light and drafts of air.

[0026] Advantageously, this aspect improves the functionality of the roller blind of the invention and its quality level compared to roller blinds of the prior art of equivalent type to it.

[0027] The cited objects are achieved by the end element of the invention and by the roller blind using it, the main characteristics of which are described in claim 1 to which reference will be made.

[0028] Further characteristics of the end element of the invention and of the roller blind using it are described in the dependent claims.

[0029] The aims and advantages listed will be better highlighted below during the description of a preferred, but not exclusive, embodiment of the end element of the invention and the roller blind using it, also subject matter of the invention, which are given here below, purely by way of a non-limiting example, with reference to the accompanying drawing tables, wherein:

[0030] - figure 1 represents the axonometric view of the roller blind of the invention using the end element subject matter of the invention;

[0031] - figures 2 and 3 represent exploded axonometric views of details of the end element and of the roller blind of the invention;

[0032] - figure 4 represents the axonometric view of a detail of figure 3;

[0033] - figures 5 and 6 represent views of details of the end element and of the roller blind of the invention assembled together;

[0034] - figures 7 to 9 represent axonometric views of details of the blind of the invention;

[0035] - figure 10 represents the exploded axonometric view of the end element of the invention. The end element subject matter of the invention is represented in full view in figure 1 and in the detailed views in figures 2 to 6 and 9 where it is indicated overall with 1 and is configured to be associated with the lower edge 2 of the flexible sheet 3 of a roller blind 50 represented in axonometry in figure 1 .

[0036] At each side end 2a of the flexible sheet 3 there are associated hooking means 2b which can be particularly seen in figures 3 and 5 to 6 and which are configured to be accommodated in guide means 57 for lifting and lowering the flexible sheet 3 which can also be seen in figure 9.

[0037] The end element 1 comprises an end profile 4 that identifies a longitudinal direction Y and in which there is a longitudinal channel 6, which can be particularly seen in figure 10. This longitudinal channel 6 in particular develops according to the longitudinal direction Y over the entire length of the end profile 4 and is configured to accommodate the lower edge 2 of the flexible sheet 3 that can be seen in figure 1 .

[0038] The end element 1 also comprises a pair of end flanges 5 of which one is represented in the attached figures from 2 to 6 and 10, each of which is fixed to an end of the end profile 4 and is positioned orthogonally to the longitudinal direction Y.

[0039] Furthermore, in each of the end flanges 5 there is a through hole 7 communicating with the longitudinal channel 6.

[0040] According to the invention, each end flange 5 has the outer surface 11 flat.

[0041] Furthermore, this end flange 5 comprises a contrast plate 10 projecting from the aforesaid outer surface 11 which is arranged at an end side 11a of the same outer surface 11 and is orthogonal thereto, as can be well seen in the axonometric views of figures 4 and 10.

[0042] A guide slider 8, visible in particular in figures 5 to 7 and 9, is associated with the lower edge 2 of the flexible sheet 3, at each side end 2a of the latter. Furthermore, along the entire length of the side ends 2a of the flexible sheet 3 there are associated hooking means 2b, which in turn will be associated with the guide means 57 represented in figures 2 and 9 and which will be discussed below.

[0043] Each guide slider 8 comprises a main body 9, which is accommodated in the longitudinal channel 6, and an outer body 12, which constitutes a single body with the main body 9. This outer body 12 is accommodated in the through hole 7 and protrudes from the outer surface 11 of the end flange 5, as can be seen in figures 3 and 10.

[0044] In particular, the lower edge 2 of the flexible sheet 3 and the main body 9 of the guide slider 8 are slidably accommodated in the longitudinal channel 6 and the outer body 12 of the guide slider 8 is slidably accommodated in the through hole 7.

[0045] This last aspect, namely that the lower edge 2 of the flexible sheet 3, the main body 9 and the outer body 12 of the guide slider 8 are slidably accommodated respectively in the longitudinal channel 6 and in the through hole 7, allows to compensate for and dampen the movement of the end element 1 along the aforesaid longitudinal direction Y, in the event that the flexible sheet 3 is urged, for example due to strong wind, to move along this direction X.

[0046] In other words, this sliding coupling prevents the end element 1 from moving integrally with the flexible sheet 3 along the aforesaid longitudinal direction X.

[0047] It is not excluded, however, that each guide slider 8, once accommodated in the longitudinal channel 6 and in the through hole 7, is fixedly arranged therein. It should be highlighted that this configuration of the end element 1 of the invention, as can be seen in particular in figures 3, 5 and 6, allows defining a sliding plane A of the flexible sheet 3 during the lifting and lowering at the outer body 12 of the guide slider 8 and a distinct holding plane B, which limits the displacement of the flexible sheet 3 according to a direction X transverse to the flexible sheet 3 itself, at the contrast plate 10.

[0048] In particular, it is noted that the sliding plane A and the holding plane B are parallel to each other and the hooking means 2b that are associated with the side end 2a of the flexible sheet 3 protrude through the through hole 7 and are arranged downstream of the outer body 12 of the guide slider 8.

[0049] As will be seen in detail below, the distinction between the sliding plane A, defined by the hooking means 2b and the outer body 12, with respect to the holding plane B, defined in turn by the contrast plate 10, allows to displace and transfer the contrast function to the contrast plate 10 alone, thus allowing to limit the thickness of the outer body 12 that retains the hooking means 2b at the lower edge 2 of the flexible sheet 3 and thus allowing to reduce the width of the guide grooves along which this flexible sheet 3 is slid.

[0050] With regard to the main body 9 of each of the guide sliders 8, with particular reference to figure 7 and also to figure 10, it is noted that it has projections 9a having the width 9b that can be seen in figure 8 and that conjugates in a guide seat 20 made inside the longitudinal channel 6 and delimited by longitudinal ribs 21 whose distance 21a is less than the width 9b of the same projections 9a.

[0051] According to the preferred embodiment of the invention, one of the aforesaid two ribs 21 belongs to a body separate from the end profile 4, which is configured to be snapped into the longitudinal channel 6 so as to define the aforesaid distance 21a between the two longitudinal ribs 21.

[0052] Therefore, the coupling in the longitudinal channel 6 of the lower edge 2 of the flexible sheet 3 to which the guide sliders 8 are associated takes place by inserting in the orthogonal direction, indicated by the arrow C in figure 10, to the longitudinal direction Y this lower edge 2 and the main bodies 9 of the same guide sliders 8 in the guide seat 20 through the opening of the longitudinal channel 6.

[0053] Obviously, this coupling operation can occur when the rib 21, defined in the aforesaid separate body, is not present inside the longitudinal channel 6. Once the aforesaid lower edge 2 has been inserted with the relative guide sliders 8 in the guide seat 20, the aforesaid rib 21 of the separate body is inserted, so as to define the distance 21a between the two ribs 21, which is less than the width 9b of the projections 9a.

[0054] In this way, when the coupling has taken place, the contrast of the projections 9a prevents the separation of the guide slider 8 from the guide seat 20 by displacement in a direction orthogonal to the longitudinal direction Y, as indicated by the arrow D.

[0055] In this way, when the lower edge 2 of the flexible sheet 3 is inserted in the longitudinal channel 6 of the end profile 4, the guide sliders 8 are inserted in the respective guide seats 20 and the lifting or lowering movement that is imposed on the flexible sheet 3 is transferred to the end profile 4 that raises or is lowered, guided by the hooking means 2b that are slidably accommodated in the guide means 57 and about which more will be said later.

[0056] With regard to the through hole 7, it has a so-called “keyhole” profile that is defined by a straight channel 14 that connects with a concave zone 15 and the width 14a of the straight channel 14 is less than the width 15a of the concave zone 15 that corresponds to the width 9b of the projections 9a of the main body 9 of each of the guide sliders 8.

[0057] With regard to the guide sliders 8, each of them, as can be seen particularly in figure 8, is formed by two parts 8a that are equal to each other, each of which has the profile corresponding to half of the entire profile of the guide slider 8 and these two parts are joined by clamping means 16 after interposing between them the lower edge 2 of the flexible sheet 3.

[0058] With regard to the roller blind indicated as a whole with 50 in figure 1 , it is noted that it comprises a frame 51 which is configured to be inserted into a window space, not represented, and in which there are identified a pair of side uprights 52 and a box 53 that overhangs the side uprights 52 and in which a roller 54 for winding the flexible sheet 3 is housed.

[0059] According to the invention, it can be seen in figures 2, 5 and 6 that in each of the side uprights 52 there is a guide shaped body 55 to guide the lifting and lowering of the end element 1.

[0060] Each guide shaped body 55 is removably associated with the respective side upright 52 by snap means 65 which can be seen in figures 5 and 6, and in the guide shaped body 55 a first longitudinal duct 56 is identified in which the guide means 57 for lifting and lowering the flexible sheet 3 are housed, which are visible in the assembly figures 2, 5, 6 and 9.

[0061] As can be seen, the guide means 57 comprise:

[0062] - a first profile 59 provided with a first longitudinal opening 60;

[0063] - a second profile 62 slidably inserted in the first profile 59 and along which there is a longitudinal slot 63 configured to slidably accommodate therein the hooking means 2b of the flexible sheet 3;

[0064] - elastic means 64 which are accommodated in the first profile 59 and are configured to constrain the second profile 62 elastically inside the first profile 59

[0065] The first profile 59 and the second profile 62, which are constrained to each other by the elastic means 64, realize a guide cartridge that is telescopically and removably coupled inside the first longitudinal duct 56.

[0066] Operationally, with reference to the cited figures and particularly to figures 5, 6 and 9, when the flexible sheet 3 is lifted or lowered, it is guided by the second profile 62 in whose longitudinal slot 63 the hooking means 2b are accommodated which are fixed to the side ends 2a of the flexible sheet 3.

[0067] Furthermore, in the event of external forces acting on the flexible sheet 3 that generate a stress component that acts on the hooking means 2b and tends to separate them from the second profile 62 to which they are coupled, the elastic means 64, as seen in figure 6, are compressed by the second profile 62 that rises with respect to the bottom of the first profile 59 and absorb the aforesaid stress component preserving the flexible sheet 3 from possible damage.

[0068] Upon cessation of the aforesaid external forces, the elastic recovery of the elastic means 64 returns the system to the initial rest condition of figure 5 in which the second profile 62 returns to be in contact with the first profile 59.

[0069] It can be observed in the already mentioned figures that the first profile 59 in which the aforesaid first longitudinal opening 60 is present is telescopically inserted in the mentioned first longitudinal duct 56 in which there is a second longitudinal opening 61 whose width 61a is less than the width 60a of the first longitudinal opening 60.

[0070] The aforesaid longitudinal openings 60, 61 also longitudinally coincide according to the longitudinal direction Y with each other and also with the longitudinal slot 63 of the second profile 62 which is slidably accommodated inside the first profile 59, as can be seen in figure 9.

[0071] As can be seen in particular in figure 8, the thickness 12a of the outer body 12 of each of the guide sliders 8 is greater than the thickness 2d of the hooking means 2b and is less than the width 61a of the second longitudinal opening 61 of the first longitudinal duct 56, and therefore the outer body 12 of the guide slider 8, together with the hooking means 2b, is accommodated in the second longitudinal opening 61 of the first longitudinal duct 56.

[0072] In addition, the measurements of the thickness 12a of the outer body 12 of each of the guide sliders 8 and of the width 61a of the second longitudinal opening 61 of the first longitudinal duct 56 are configured so that during the lifting and lowering of the flexible sheet 4 the outer body 12 of the guide slider 8 touches the edges 61b of the aforesaid second longitudinal opening 61, as can be seen in figures 5 and 6.

[0073] Figures 2, 5 and 6 show that in the guide shaped body 55 there is also a second longitudinal duct 58 which is arranged side by side with the first longitudinal duct 56 and in which the contrast plate 10 is housed, which is contained inside the second longitudinal duct 58.

[0074] During the lifting and lowering of the flexible sheet 3 the contrast plate 10 defines the holding plane B which, in case of stresses, for example due to strong wind, limits the displacement of the flexible sheet 3 according to a direction X transverse to the sliding plane A of the flexible sheet 3. As mentioned above, the fact that the contrast function has been delegated to the contrast plate 10, lying on the holding plane B, in turn distinct from the sliding plane A, allows the aforesaid longitudinal openings 60, 61 to be realized for the insertion of the outer body 12 of the guide slider 8, which retains the lower portion of the side edge 2 of the flexible sheet 3, of reduced thickness and lower than the solutions proposed by the prior art, thus obtaining all the advantages and aims highlighted in the present description.

[0075] In particular, based on what has been set forth, it is understood that the end element 1 and the roller blind 50 using it achieve the aims of the invention.

[0076] In particular, it has been seen that the width 61a of the second longitudinal opening 61 of the first longitudinal duct 56 associated with a respective side upright 52 is very reduced since it slidably accommodates the outer body 12 of the guide slider 8, associated with the end profile 4, also of reduced thickness. Furthermore, it has been said that at each end of the end profile 4 an end flange 5 having the flat outer surface 11 is applied and this allows to approach each end flange 5 to the second longitudinal opening 61 of the first longitudinal duct 56 until touching it.

[0077] Therefore, the reduced thickness of the outer body 12 of the guide slider 8 and the reduced width of the second longitudinal opening 61 that accommodates it improve the aesthetic appearance of the roller blind 50 of the invention compared to roller blinds of the prior art equivalent thereto.

[0078] In particular, the reduction in the width of the longitudinal openings that develop along the uprights makes them less visible and therefore more aesthetically acceptable and their small width limits the entry and accumulation of dust or other impurities that over time can compromise the use of the roller blind.

[0079] Furthermore, the presence of the flat surfaces in a position close to the longitudinal openings, together with the small width of these, also reduces the entry of light and drafts of air.

[0080] Finally, it can be observed that the presence of the contrast plate 10 limits the displacement of the flexible sheet 3 in the direction X orthogonal to the lifting and lowering direction and prevents its damage.

[0081] In fact, the contrast plate 10 cooperates inside the second longitudinal duct 56 which, in the presence of wind, limits its displacement in the aforesaid orthogonal direction X. This limited displacement prevents the outer body 12 of each of the guide sliders 8 from creeping along the edges 61b of the second longitudinal opening 61 of the first longitudinal duct 56, even if it is of limited width 61a, during the lifting and lowering of the flexible sheet 3.

[0082] In summary, it is the presence of the contrast plate 10 that allows realizing the longitudinal opening 61 of width 61a less than the width of the corresponding sliding slits of the flexible sheet that are present in the roller blinds of the prior art.

[0083] In the execution phase, modifications and variants that have not been described and represented in the drawings may be made to the end element 1 and to the roller blind 50 of the invention.

[0084] If such modifications or variants should fall within the claims that follow, they must certainly be considered all falling within and protected by this patent.

Claims

CLAIMS1 ) End element (1 ) configured to be associated with the lower edge (2) of the flexible sheet (3) of a roller blind (50), to each side end (2a) of said flexible sheet (3) there being associated hooking means (2b) which are configured to be accommodated in guide means (57) for lifting and lowering said flexible sheet (3), said end element (1 ) comprising:- an end profile (4) that identifies a longitudinal direction (Y) and in which there is a longitudinal channel (6) that develops according to said longitudinal direction (Y) over the entire length of said end profile (4) and is configured to accommodate said lower edge (2) of said flexible sheet (3);- a pair of end flanges (5) each of which is fixed to an end of said end profile(4) orthogonally to said longitudinal direction (Y), in each of said end flanges(5) there being a through hole (7) communicating with said longitudinal channel (6), where each of said end flanges (5) has the outer surface (11 ) flat, characterized in that it comprises guide sliders (8) associated with said lower edge (2) of said flexible sheet (3) at each side end (2a), each guide slider (8) comprising a main body (9) which is accommodated in said longitudinal channel (6) and an outer body (12) which is accommodated in said through hole (7) and protrudes from said outer surface (11 ) of said end flange (5).2) End element (1 ) according to claim 1 , characterized in that each of said end flanges (5) comprises a contrast plate (10) projecting from said outer surface (11 ).3) End element (1 ) according to claim 2, characterized in that said contrast plate (10) is orthogonal to said outer surface (11 ).4) End element (1 ) according to any one of the preceding claims, characterized in that said lower edge (2) of said flexible sheet (3) and said main body (9) of said guide slider (8) are slidably accommodated in said longitudinal channel (6) and said outer body (12) of said guide slider (8) is slidably accommodated in said through hole (7).5) End element (1 ) according to any one of the preceding claims, characterized in that said outer body (12) of said guide slider (8) defines the sliding plane (A) of said flexible sheet (3) during lifting and lowering and said contrast plate (10) defines the holding plane (B) that limits the displacement of said flexible sheet (3) according to a direction (X) transverse to said slidingplane (A) of said flexible sheet (3).6) End element (1 ) according to claim 5, characterized in that said sliding plane (A) and said holding plane (B) are parallel to each other.7) End element (1 ) according to any one of the preceding claims, characterized in that said hooking means (2b) protrude through said through hole (7) and are arranged downstream of said outer body (12) of each respective guide slider (8).8) End element (1 ) according to any one of the preceding claims, characterized in that said main body (9) of each of said guide sliders (8) has projections (9a) that conjugate in a guide seat (20) present inside said longitudinal channel (6) and delimited by longitudinal ribs (21 ), the distance (21a) between said ribs (20) being less than the width (9b) of said projections (9a).9) End element (1 ) according to any one of the preceding claims, characterized in that said through hole (7) is defined by a straight channel (14) that connects with said concave zone (15), the width (14a) of said straight channel (14) being less than the width (15a) of said concave zone (15).10) End element (1 ) according to any one of the preceding claims, characterized in that each of said guide sliders (8) is composed of two parts (8a) that are equal to each other, where each of which has the profile corresponding to half of the entire profile of said guide slider (8), said two parts (8a) being joined by clamping means (16) after interposing between them said lower edge (2) of said flexible sheet (3).11 ) Roller blind (50) comprising a frame (51 ) configured to be inserted into a window space and in which a pair of side uprights (52) and a box (53) overlying said side uprights (52) are identified and in which a roller (54) for winding a flexible sheet (3) is housed, characterized in that in each of said side uprights (52) there is a guide shaped body (55) for lifting and lowering said flexible sheet (3) coupled to an end element (1 ) according to any one of the preceding claims.12) Roller blind (50) according to claim 11 , characterized in that said guide shaped body (55) is removably associated with said side upright (52) by snap means (65).13) Roller blind (50) according to any one of claims 11 or 12, characterized in that in said guide shaped body (55) there are identified:- a first longitudinal duct (56) in which said guide means (57) for lifting and lowering said flexible sheet (3) are housed;- a second longitudinal duct (58) arranged side by side with said first longitudinal duct (56) and in which said contrast plate (10) is housed during the lifting and lowering of said flexible sheet (3).14) Roller blind (50) according to claim 13, characterized in that said guide means (57) comprise:- a first profile (59) provided with a first longitudinal opening (60) and telescopically inserted in said first longitudinal duct (56) in which there is a second longitudinal opening (61 ) whose width (61a) is less than the width (60a) of said first longitudinal opening (60), said longitudinal openings (60, 61 ) longitudinally coincide with each other and being configured to accommodate the sliding insertion of said hooking means (2b) of said flexible sheet (3) and of said outer body (12) of the corresponding guide slider (8);- a second profile (62) slidably inserted in said first profile (59) along which there is a longitudinal slot (63) longitudinally coinciding with said longitudinal openings (60, 61 ) and configured to slidably accommodate therein said hooking means (2b) of said flexible sheet (3);- elastic means (64) which are accommodated in said first profile (59) and are configured to constrain said second profile (62) elastically inside said first profile (59), wherein said first profile (59) and said second profile (62), constrained to each other by said elastic means (64), realize a removable guide cartridge.15) Roller blind (50) according to claim 14, characterized in that the thickness (12a) of said outer body (12) of each of said guide sliders (8) is greater than the thickness (2d) of said hooking means (2b) and is less than the width (61a) of said second longitudinal opening (61 ) of said first longitudinal duct (56), and therefore said outer body (12) of said guide slider (8) together with said hooking means (2b) is accommodated in said second longitudinal opening (61 ) of said first longitudinal duct (56) and the measurements of said thickness (12a) of said outer body (12) of each of said guide sliders (8) and of said width (61a) of said second longitudinal opening (61 ) of said first longitudinal duct (56) are in relation to each other so that during the lifting and lowering of said flexible sheet (3) said outer body (12) of said guide slider (8)touches the edges (61b) of said second longitudinal opening (61 ).

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