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(11) | EP 0 384 628 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A louvred panel |
| (57) A louvred panel includes a frame (19) and a plurality of louvres (21,36,68) positioned
between a first and a second side of the frame. The louvres (21,36,68) are maintained
in tension. Each pair of adjacent louvres (21,36,68) defines a respective passageway
(22,34,74) having a respective transmission direction. The transmission direction
of a passageway (22,34,74) is set by a block (40,72) or peg (8) positioned in the
passageway (22,34,74). |
[0001] This invention relates to a louvred panel for permitting passage of light of incident angle within a predetermined restricted range, and in particular, to a louvred panel for use in a display device.
[0002] Louvred panels provided in accordance with the present invention may advantageously be used with equipment for projecting light onto a surface as disclosed in our copending European Patent Application No. 89301702.0 published under No. 0333333.
[0003] It is known to provide louvred panels which comprise a plastics sheet containing closely-spaced parallel louvres. Light rays with a path along a transmission direction parallel to the louvres are transmitted, the transmission of light decreasing for light incident at other angles relative to the louvres until there is zero transmission at the cut-off angle. Thus, the direction of light passing through the louvred panel can be controlled.
[0004] Us 4556913 (Van Breemen et al) discloses a baffle assembly for a rear projection television receiver. The baffle assembly is provided to prevent stray light from reaching the screen. The baffle assembly comprises a trapezoidal frame. A plurality of baffle elements are disposed between two of the sides of the frame so as to extend parallel to the other two sides. Each of the baffle elements comprises a thin elongated element which may illustratively be constructed of paper, fabric, plastics or metal; other materials may also be used. The individual baffle elements are held at each end by a sandwich type or U-shaped bracket to which a screw is mounted. A wiring nut mounted on the screw may be loosened to allow angular positioning of the baffle elements and then tightened to hold the baffle elements in place.
[0005] It is an object of the present invention to provide an improved louvred panel, particularly for use in display devices.
[0006] According to the present invention there is provided a louvred panel comprising a frame, a plurality of louvres positioned between a first and a second side of the frame with each pair of adjacent louvres defining a respective passageway having a respective transmission direction, means for maintaining tension in the louvres and a plurality of means for setting a respective transmission direction, each of the setting means being positioned in a respective passageway.
[0007] In contrast to the prior art, the inventors have appreciated the advantages of providing separate means for holding the louvres in tension and for setting the transmission directions of passageways defined by adjacent louvres in realising a practical implementation of a louvred panel suitable for use in display device.
[0008] Preferably the louvres are formed of a polyester base film which is stable with variations in temperature and humidity. Other materials which are stable with variations in temperature and humidity, such as steel or other metals, may also be used. Advantageously, the film has a thickness in the range of from 10 µm to 400 µm preferably from 12.5 µm to 50.0 µm. The thinness and consequent low mass of the film together with the aforementioned stability also alleviates the potential problem of deformation of the central part of each louvre.
[0009] Two or more setting means to define transmission directions of adjacent passageways may be set at an angle to each other. This allows light to pass through parallel to the local transmission direction of the louvred panel with minimal attenuation and alleviates the problem of variation in image intensity caused when non-parallel image-forming rays of light pass through prior art louvred panels with parallel louvres.
[0010] In projection type display devices, the image-forming rays are projected in a cone. The image forming rays cover a continuum of directions within the projected cone, such that the image forming rays from the edge of the image are at a significant angle to the image forming rays at the centre of the image, which are parallel to the cone axis. Accordingly, in one embodiment adjacent passageways positioned centrally within the panel have parallel transmission directions. Alternatively, the transmission direction of the passageways may vary gradually with separation from the centre of the panel.
[0011] Preferably the louvred panel comprises a first setting means and a second setting means in each passageway. This has the advantage of more accurately defining the transmission direction of the passageway than if only one setting means were provided in the passageway. Each pair of adjacent first or second setting means may define a groove in which a respective louvre is placed and a plurality of first setting means or a plurality of second setting means may be formed as an integral structure. The combination of these two featues provides a structure for setting the transmission directions of each passageway which can easily be made by any one of a number techniques, such as wire eroding, moulding or sawing.
[0012] In a preferred embodiment, the maintaining means comprises the combination of a structure containing an aperture and a rivet in said aperture, an end of a louvre being held in said aperture by said rivet. The inventors have found this to be an. efficient way of securing the end of a louvre and so maintaining the tension in the louvres.
[0013] More than one louvre or indeed all the louvres may be formed from a single continuous tape and so the louvred panel advantageously comprises a plurality of pegs around each of which a tape is wound, each peg determining the end of a louvre. This enables more than one louvre to be installed and tensioned at the same time.
[0014] Alternatively, more than one louvre may be formed from a single sheet of material, said single sheet including a plurality of slits, each slit corresponding to a respective passageway.
[0015] Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings of which:
Figures 1 and 2 show steps in a method of making a louvred panel in accordance with the present invention;
Figure 3 shows a louvred panel provided in accordance with the present invention;
Figure 4 shows a view of the louvred panel of Figure 3 along the direction indicated by the arrows IV-IV in Figure 3;
Figures 5 and 6 show modifications to the louvred panel of Figures 3 and 4;
Figure 7a shows part of another embodiment of a louvred panel provided in accordance with the present invention;
Figure 7b shows a section along the line X-X of Figure 7a;
Figure 7c shows a view of a part of the structure of the louvred panel taken in the direction indicated by the arrow A in Figure 7a;
Figure 7d shows a section along the line Y-Y of Figure 7a;
Figure 8a shows a sheet of material for use in yet another embodiment of a louvred panel provided in accordance with the present invention;
and Figure 8b shows part of said yet another embodiment of a louvred panel provided in accordance with the present invention and including the sheet of Figure 8a.
[0016] Figures 1 and 2 illustrate a method of making a louvred panel in accordance with the present invention. In Figure 1 two structures 2, 4 are shown close together. Each structure 2, 4 has a plurality of digits 6 in each of which is set a peg 8. Each structure 2, 4 and its pegs 8 may be formed as a single moulding. The structures 2, 4 are sufficiently close together for the digits 6 to interlace. A tape 10 extends between two tape spools 11, 12 and respective tensioning devices 13, 14, clamping devices 15, 16 and pins 17, 18. The tape 10 is positioned between the pegs 8 of each of the structures 2, 4. The tape 10 is formed of a thin polyester base film, coated on both sides with a matt black layer; a suitable tape is that presently used for audio tape. With the clamping devices 15, 16 open, the two structures 2, 4 are then drawn apart, as shown in Figure 2, to achieve simple automatic threading of the tape.
[0017] The two structures 2, 4 are then attached by bolts or other means (not shown) to a frame 19, as shown in Figure 3 to form a louvred panel 20 of the required dimension. The louvred panel 20 comprises a plurality of louvres 21 formed by the tape 10 stretched across the frame 19. The clamping devices 15, 16 are closed to hold and maintain the ends of the tape 10 in tension. Adjacent louvres 21 are separated from one another by the pegs 8 and define adjacent passageways 22. As the tape 10 is very thin, having a thickness in the range of from 10 µm to 400 µm preferably in the range of from 12.5 µm to 50.0 µm, it has a low mass and so there is minimal deformation of the central part of each louvre 21.
[0018] The pegs 8 are positioned in the passageways with the diameter of each peg 8 defining the separation of adjacent louvres and hence the cut-off angle of the louvred panel. The transmission direction of each passageway relative to the frame 19 is given by the angle to the frame 19 of the louvres forming the passageway. As shown in Figures 4, 5 and 6 the angle of the louvres 21 is defined by the angle at which the pegs 8 are set into the structures 2, 4. Accordingly, the pegs set the transmission directions of the passageways.
[0019] In the embodiment of Figure 4, all the passageways 22 have transmission directions which are substantially parallel. In the embodiment of Figure 5, passageways 22 away from the centre of the panel 20 have transmission directions at an angle to the screen frame while those passageways 22 positioned centrally have transmission directions which are substantially parallel. In the embodiment of Figure 6, all the passageways 22 have transmission directions at an angle to the screen frame, the angle being dependent on the separation of the passageway from the centre of the panel.
[0020] Figure 7 shows parts of a louvred panel constructed in accordance with a second method. A two part assembly 30 is shown in Figures 7a and 7b. This two part assembly 30 comprises means 32 for setting the transmission directions of passageways 34 defined by adjacent louvres 36 and means 38 for maintaining the tension in the louvres 36. A two part assembly 30 is secured to each of the two verticals in a louvre screen panel (not shown).
[0021] Figure 7c shows a view of the setting means 32 in the direction indicated by the arrow A in Figure 7a. The setting means 32 is formed as an integral structure of blocks 40 defining narrow grooves 42 oriented at the angle at which the louvres 36 must be set. These grooves 42 may be made, for example, by sawing, by wire eroding, or by a process of moulding. As shown in Figure 7a, a continuous tape 44 is fed through four grooves 42 defined by adjacent blocks 42 to form two louvres 36. The tape 44 is oriented by the grooves 42 through which it is fed and a passageway 34 defined by adjacent louvres 36 formed by a tape 44 has a transmission direction set by the respective blocks 40 positioned in the passageway 34.
[0022] The ends of a tape 44 are held in the maintaining means 38. The maintaining means is formed as a structure 46 in which a plurality of holes 47 are drilled or moulded. Pop rivets 48 are inserted into the holes in such a manner that the expansion of a rivet forces the tape against the side of the hole, thus firmly securing it. Grooves 50 lead from the edge of the structure 46 to the holes 47. As the grooves 50 are tangential to the circular aspect of the holes 47, the tape can be fed through the grooves 50 and held against the walls of the holes 47 with the minimum of distorition. It is to be noted that the grooves 50 in the maintaining means 38 do not need to be aligned with the grooves 42 in the setting means 32 as the angles and transmission directions of the louvred panel are set by the setting means 32.
[0023] As shown in Figure 7, a plurality of pegs 52 are provided around which the tapes 44 are wound. This allows several louvres to be installed and tensioned at the same time. Alternatively, each louvre may be formed from a single tape with both ends of the tape being secured by rivets.
[0024] In an alternative embodiment, the holes 47 are located in the structure of the setting means. In this case, the size of the rivet would determine a lower limit to the pitch at which the grooves could be cut and hence the cut-off angle of the louvred panel. The holes in such an arrangement would advantageously be formed with their axes parallel to the length of the louvres; this will avoid problems arising out of the varying angles of the louvres and has the further advantage that the pop rivetting action during which the body of the rivet is deformed not only laterally against the side of the hole wall but also towards the head of the rivet, will tend further to tension the louvre (In principle this deformation towards the head of the rivet could cause problems with the arrangement illustrated in Figure 7 so that it might be necessary to use special rivets which deform predominantly in a lateral direction. However, in practice, the inventors found no difficulties in using ordinary rivets).
[0025] The inventors found that the construction illustrated in Figure 7 had advantages over that described with reference to Figures 1 to 6. Primarily, it was found much easier to maintain a high level of tension on the louvres at all positions on the louvred panel so that there was no visible sagging or distortion of the louvres. Another advantage is the ease of construction of the setting means as opposed to the arrangement of pegs.
[0026] Figure 8 shows part of a louvred panel constructed in accordance with a third method. The louvres are formed from a sheet 60 of e.g. polyester base film as shown in Figure 8a into which a regular grid of slits 62 has been made. Sheets of polyester base film are readily available as it is from such sheets that the thin tapes are normally manufactured.
[0027] As shown in Figure 8b, the sheet 60 is held in tension by pegs 64. The pegs 64 are mounted on two bodies 66 in linear arrays such that there is only a minimal gap between the edges of adjacent pegs 64. A tensioned louvre is formed by placing the sheet 60 over the pegs 64 such that the sections 68 of sheet material between the slits 62 pass through the gaps between the pegs 64 to form individual louvres. The bodies 66 are then separated until the required high level of tension is achieved. Finally, the two bodies 66 are attached by bolts or other means to a frame (not shown) to form a louvred panel of the required dimension.
[0028] The inventors have found the method described with reference to Figure 8 to be an effective method of obtaining and maintaining the necessary tension in the majority of the louvres. However, it will be appreciated that the louvres 68a, 68b at the edges are not properly tensioned by this method. The louvred panel may be so utilized that this is not a problem. Alternatively an additional clamping arrangement may be provided to tension these two louvres 68a, 68b in a manner known to those skilled in the art.
[0029] As shown in Figure 8b, the bodies 66 also incorporate setting means 70 comprising a plurality of grooves 72 for setting the transmission directions of respective passageways 74 defined by adjacent louvres 68. The effect of the setting means 70 is similar to the effect of the setting means 32 as described with reference to Figure 7.
1. A louvred panel comprising a frame, a plurality of louvres positioned between a
first and a second side of the frame with each pair of adjacent louvres defining a
respective passageway having a respective transmission direction, means for maintaining
tension in the louvres and a plurality of means for setting a respective transmission
direction, each of the setting means being positioned in a respective passageway.
2. A louvred panel according to Claim 1 comprising a first setting means and a second
setting means in each passageway.
3. A louvred panel according to Claim 2 wherein said first setting means delimits
a first end of said passageway and said second setting means delimits a second end
of said passageway.
4. A louvred panel according to Claims 2 or 3 wherein each pair of adjacent first
setting means defines a groove in which a respective louvre is placed.
5. A louvred panel according to any one of Claims 2 to 4 wherein a plurality of first
setting means are formed as an integral structure.
6. A louvred panel according to any one of the preceding claims wherein the maintaining
means comprises the combination of a structure containing an aperture and a rivet
in said aperture, an end of a louvre being held in said aperture by said rivet.
7. A louvred panel according to Claim 6 wherein more than one louvre is formed from
a single continuous tape.
8. A louvred panel according to any one of the preceding claims wherein all the louvres
are formed from a single continuous tape.
9. A louvred panel according to Claims 7 or 8 further comprising a plurality of pegs
around each of which a tape is wound, each peg determining the end of a louvre.
10. A louvred panel according to any one of Claims 1 to 5 wherein more than one louvre
is formed from a single sheet of material, said single sheet including a plurality
of slits, each slit corresponding to a respective passageway.