WO2008089758A1

WO2008089758A1 - A projection screen assembly comprising a magnetic mount

Info

Publication number: WO2008089758A1
Application number: PCT/DK2007/050011
Authority: WO
Inventors: Gert Andersen
Original assignee: Dnp Denmark As
Priority date: 2007-01-24
Filing date: 2007-01-24
Publication date: 2008-07-31

Abstract

A projection screen assembly comprising a number of beams (2, 3) adapted to be assembled to a framework, and at least one projection screen panel (8) mountable on said framework when assembled, said projection screen panel comprising a front side, on which an image is to be projected, a rear side, and a number of edges, wherein at least some of said beams comprise magnets (22, 23), and wherein said screen panel (8) comprise a ferromagnetic material, the screen panel (8) being mountable on said framework by means of the magnetic attraction between said magnets (22, 23) and said ferromagnetic material.

Description

A PROJECTION SCREEN ASSEMBLY COMPRISING A MAGNETIC MOUNT

The present invention relates to a front projection screen assembly, in particular a front projection screen assembly, which may readily assembled and disassembled.

In some situations, e.g. on trade fairs, conferences or other events involving large numbers of people, there may be a need for large-sized projection screens, e.g. screen sizes with a diagonal from 120 inches and upward. Screen sizes are generally measured by their diagonal in inches, a screen of 3 by 5 meters corresponding to a 260 inch screen. If the conference is held at a place where a screen of this size is not permanently installed, or if a screen is to be located in another place that the permanently installed one, there is a need for a temporary screen. In particular for trade fairs, where people may be moving around, the screen should be rigid. Otherwise the screen may be brought into motion by people touching it or by draughts in the hall, thus deteriorating the images projected onto the screen. However, unlike a flexible screen a rigid screen cannot be rolled-up for transportation and for most situations it would be almost impossible and certainly too costly to transport a rigid screen of the above dimension, if it only has to be installed temporarily. Moreover, from a manufacturing point of view such large screens are difficult.

Thus, because of these constraints imposed on large screens by transportation and manufacture, it is not uncommon to assemble large rigid screens from several smaller screen panels, e.g. assembling a 240 inch screen from four 120 inch screen panels arranged as tiles in a 2 by 2 pattern, or a 360 inch screen from nine 120 inch screen panels arranged in a 3 by 3 pattern. Such an arrangement gives rise to new problems, e.g. the fact that visible seams may arise where the screen panels abut. Moreover, fastening means such as brackets at the edges or wires threaded through holes in the screen panels may not only also be visible, but may involve quite a lot of time consuming work. In respect of magnetic mounting of a projection screen, EP-A- 758757 discloses a back projection screen apparatus assembled from several individual back projection apparatuses. Each individual apparatus has a cabinet on which a removable back projection screen is mounted. The suggestion is made that the removable back projection screen may be mounted on the cabinet by means of magnets. However, this is merely a suggestion and no actual details are given and none of the problems, which this way of mounting the screen might involve, are discussed. Moreover, being assembled from several individual apparatuses, each with its own projector, cabinet and projection screen, such a projection screen apparatus is quite expensive, would take up quite a lot of space when not in use or transported, and would clearly display gaps between the individual sectors of the overall display screen.

In respect of easy assembly using magnets, this is known from other fields of technology not relating to projection screens. Thus, on a much smaller scale US-A-5421112 discloses a display stand assembly comprising a framework on which panels may be mounted by means of magnetic strips arranged along the framework members and magnetic strips of the opposite polarity arranged along the edges of the panels. This allows easy attachment of the panels to the framework to form a display stand. The display stand is, however, not suitable for use as a projection screen. One reason for this is that no measures are provided to minimize the gaps between the individual panels. They would thus potentially be visible to a degree disturbing the viewer, if the display stand assembly were to be used as a projection screen. Another reason is that no measures are provided in order to overcome the substantial differences in thermal expansions, which might occur if the temperature of the surrounding environment is changing.

Based on this it is the object of the invention to provide a front projection screen, which may be readily assembled and disassembled.

According to the present invention this object is achieved by a projection screen assembly comprising a number of beams adapted to be assembled to a framework, and at least one projection screen panel mountable on said framework when assembled, said projection screen panel comprising a front side, on which an image is to be projected, a rear side, and a number of edges, wherein at least some of said beams comprise magnets, and wherein said screen panel comprise a ferromagnetic material, the screen panel being mountable on said framework by means of the magnetic attraction between said magnets and said ferromagnetic material.

In this way there is provided a projection screen assembly which is readily mountable, and which may easily be disassembled and transported. According to a preferred embodiment, said magnets are movable with respect to said beams. Making the magnets movable is advantageous as it facilitates the correct alignment of the screen panel. This is particularly advantageous when, according to an especially preferred embodiment the projection screen assembly comprises more than one screen panel.

According to a further preferred embodiment, said magnets are mounted in recesses in said beams. In this way the magnets do not protrude much from the beams, which in turn facilitates storage and transportation. According to another preferred embodiment, wherein said ferromagnetic material is arranged at said edges of the screen panel. This has shown to be sufficient for holding the screen panel in good engagement with the magnets, without adding too much weight to the screen panel. According to a specific embodiment, a number of strips comprising said ferromagnetic material are arranged along at least two of said edges. This involves material savings as the ferromagnetic material is only applied where needed.

According to another embodiment, alignment means adapted for engaging at last one edge of said screen panel are arranged on said beams. This allows proper alignment of the screen panels so as to remove any gaps between screen panels, which might influence the image projected on the projection screen assembly.

According to yet another embodiment, said screen panel is pro- vided as a sandwich construction comprising a base plate made essentially of the same material as the beams. In this way differences in thermal expansion between the framework and the screen panels is minimized. Preferably the material is aluminium, as this is light in weight and thus easy to handle during assembly and disassembly of the projection screen assembly.

According to an especially preferred embodiment, adjacent screen panels are mountable on said framework by means of the magnetic attraction between ferromagnetic material on respective adjacent screen panels and one and the same magnet. In this way the screen panels share the magnet with a neighbouring screen panel. This in turn allows the magnets to draw adjacent screen panels close together thus aiding in minimizing any visible gaps between screen panels.

The invention will now be described in greater detail based on preferred embodiments, and with reference to the drawings on which,

Fig. 1 shows a partial front view of an assembled framework for a projection screen according to the invention, but without the screen panels mounted, fig. 2 shows an end view of the assembled framework of fig. 1, also without the screen panels mounted, fig. 3 shows a detail of the front view of fig. 1, fig. 4 shows an end view of the detail of fig 3, fig. 5 shows a front view of a detail of a screen panel mounted on the framework of fig. 1, fig. 6 shows a perspective view of the detail of fig. 5, fig. 7 shows a cross sectional view of the detail of fig. 5 taken along the line VII-VII, fig. 8 shows a cross sectional view of the detail of fig. 5 taken along the line VIII-VIII, and fig. 9 shows a schematic cross section of a screen panel according to the invention.

Starting with fig. 1, a front view of a framework 1 for a front projection screen assembly is shown. For illustration purposes, parts of the right-hand side has been cut away. The framework comprises a number of horizontal beams 2 and a number of vertical beams. The horizontal beams 2 and the vertical beams 3 have been joined, preferably by means of screws, to form a number of rectangles. As is better visible in fig 2., the framework 1 of the illustrated embodiment moreover com- prises a number of uprights 4 with associated bases 5 and feet 6, for maintaining the overall front projections screen assembly in a vertical position. In order to secure the dimensions of the framework a number of stay wires 7 are connected between some of the joints of the between beams. By proper tensioning of the stay wires 7, the correct dimensions of the framework 1 to match exactly the screen panels 8 (not visible in figs. 1-4) to be mounted thereon. More specifically the stay wires are connected between fixed brackets 9 at some of the joints and tensioning means at other joints. The tensioning means for the stay wires 8 is illustrated in figs. 3 and 4. In fig. 3 two tensioning means, each one for a re- spective stay wire 7, is shown. Each tensioning means comprises an eye bolt or a hook 10 in which the stay wire 7 is guided. The stay wire 7 is connected to a tensioning bracket 11. The tensioning bracket 11 is movable up and down along to the vertical beam 3 under the influence of adjustment nut 12 and bolt 13 arrangement, so as to allow it to slide along the vertical beam 3. Preferably is the tensioning bracket 11 is guided in a recess 14 in the vertical beam 3. The vertical beams 3 and the horizontal beams are preferably extruded aluminium beams with identical cross section geometry. The cross section of the recess 14 in the vertical beam 3, is thus identical to the recess 15 in the horizontal beam 2, which is better visible in the figures, in particular in fig. 4.

Also visible in figs. 1, 3 and 4 is a number of alignment means 16, for the horizontal and vertical alignment of the screen panels 8. As mentioned above the screen panels 8 are not shown in those figures. Moreover, the alignment means 16 for horizontal alignment is only being visible in fig 1. Apart form their orientation, the alignment means 16 for vertical and horizontal alignment, respectively, are basically identical, and a description will only be given for the vertical alignment means 16, as best seen in figs. 3 and 5 to 7. In respect of figs. 5 to 7 as well as fig. 8, it should be noted that for illustration purposes these figures show only parts of the screen assembly, the rest being cut away. Each alignment means 16 comprises a flat plate 17 with two elongate holes 18. The flat plate 17 may be secured to the horizontal beam 2 by means of screws or bolts 19 passing through a respective one of said elongate holes 18, and into threaded bores 20 in the horizontal beam 2. The vertical location of the flat plates 17 with respect to the horizontal beam 2 may be adjusted by loosening the bolts 19 sliding the flat plate 17 along the bolt 19, using the elongate hole 18 as a guide, and securing the flat plate 17 again in a desired position. This in turn allows the vertical alignment of the screen panel resting on the top edge 21 of the flat plate 17. It should be noted that not all beams 3 have associated alignment means 16. Rather, only those beams forming the outer perimeter of the framework 1 have associated alignment means 16. Thus if a projection screen assembly comprises a large number of screen panels 8, say nine in a three by three arrangement or sixteen in a four by four arrangement, only those screen panels 8 forming the edge of the overall screen with engage the alignment means. In particular it should be noted that a screen panel 8 forming part of the perimeter preferably abuts, at least two alignment means 16, if any - alignment means at the top of the framework 1 are not considered necessary. Thus, by the individual adjustment of the two alignment means 16, the screen panel 8 abutting them may be turned slightly in orientation with respect to the framework 1, if necessary. Turning a screen panel 8 this way the orientation will propagate to adjacent screen panels 8, and thus effectively overall screen from one side to another and from bottom to top of the overall screen, thus obviating the need for alignment means at the top of the screen.

The alignment means 16 however, do not secure the screen panels 8 to the framework 1 of the projection screen assembly, they merely server the alignment purpose. As illustrated in figs. 5, 6 and 8, the screen panels 8 are attached to the framework 1 using magnets 22, 23. The magnets 22, 23 are preferably permanent magnets. In particular, the magnets are ring-shaped magnets 22 located in recesses 24. In fig. 3 an empty recess 24 for accommodating such a ring shaped magnet 22. The ring shaped magnet 22 is held in a floating manner is said recess 24. That is to say in a manner allowing limited motion with respect to the vertical beam 3, in which it is mounted. Preferably this is achieved by use of a mounting bolt 25 and a securing nut 26, which are not tight- ened, but allow some axial motion along the axis of the bolt 25. Moreover this allows the ring-shaped magnet 22 to protrude only slightly over from the vertical and horizontal beams. The magnets will thus not hinder the efficient storage of the beams 2, 3 when the screen assembly is disassembled and stored. Preferably, the bore in which the bolt 25 is mounted has a slightly larger diameter than the bolt 25 so as to also allow some lateral motion. This allows the magnet 22 to move slightly and thereby take up tolerances, thermal expansion differences between the framework 1 and the screen panels 8, etc.

The magnets 22 engage a ferromagnetic material arranged on the back of the screen panels 8. The back is understood as the opposite side of the side of the screen panel 8 with respect to the side on which an image is to be projected. As can best be seen from the schematic cross-section of fig. 9, the screen panel 8 is preferably a layered construction. Typically the top layer is a lens film 26 giving high contrast when an image is projected thereon. The lens film 26 is adhered to a sandwich support plate comprising two plastic layers 27, 28 on opposite sides of an aluminium layer 29. To the opposite side of sandwich support plate, a steel or iron band 30 is adhered in order to provide the ferromagnetic material used in connection with the invention. Aluminium as part of the support plate is preferred, because the beams 2, 3 would normally be of the aluminium. By choosing the same material for the various parts, the differences in thermal expansion between the framework 1 and the screen panels 8 can be reduced when the temperature of the surrounding environment is changing. Apart from the stated advan- tages of aluminium and the use of an iron or steel band 30, such screen panels 8 are per se well known and do not form part of this invention.

In addition to or, albeit less preferred, as an alternative to the floating magnets 22 fixed magnets 23 may be provided. The fixed magnets 23 are preferably in the form of strips adhered to the vertical and horizontal beams 3, 2. Such magnets are generally flat and do not protrude much over the surface of the vertical and horizontal beams 2, 3.

The magnets 22 and, if used, the magnets 23 are arranged along a centre line on the vertical and horizontal beams 2, 3 the lengths thereof. This allows adjacent screen panels 8 to share one magnet 22. Thus as can be seen in e.g. fig. 6 the screen panel adheres magnetically to the invisible half of the magnet 22, whereas the other visible half would be used together with another adjacent panel 8, to be attached thereto by the magnetic attraction. This aids in minimizing any possible gap between the screen panels, because the magnet 22 will tend to close the magnetic circuit, i.e. removing the gap, between the respective ferromagnetic strips on the adjacent panels. Thus, it is not necessary to use any further means to bring the screen panels 8 together. In particular the alignment means 16 are not used for this, thus obviating the need for any alignment means at the top of the framework, as indicated in fig. 1 and mentioned above. Though not shown in the figures, it may even be possible to have the corners of four screen panels sharing one and the same magnet each overlapping approximately one quarter of the magnet. Remaining at fig. 1 it should be noted that the projection screen assembly may optionally comprise a number of powerful springs 31 arranged between vertical beams 3 and an upright 4 to allow some thermal expansion between the upright 4 and the framework 1.

Though the above description as been made with reference to specific embodiments, it should be noted that the scope of the invention is not restricted to those embodiments. Rather, the skilled person will realize that numerous variations are possible. In particular he will realize that the beams of the frameworks and the support plates of the screen panels could be made of different materials such as plastic or steel. The latter would obviate the need for the attached steel band, but the screen panel would likely be heavier. The skilled person will also realize that even though the screen assembly is highly advantageous for temporary screens, the starting point for the invention is the general desire to provide large rigid front projection screens. The invention is thus not only relates to temporarily assembled front projection screens, but is in fact also applicable in relation to permanently assembled front projection screens, which thus also fall within the scope of the invention as defined in the claims.

Claims

P A T E N T C L A I M S

1. A projection screen assembly comprising a number of beams adapted to be assembled to a framework, and at least one projection screen panel mountable on said framework when assembled, said pro- jection screen panel comprising a front side, on which an image is to be projected, a rear side, and a number of edges, wherein at least some of said beams comprise magnets, and wherein said screen panel comprise a ferromagnetic material, the screen panel being mountable on said framework by means of the magnetic attraction between said magnets and said ferromagnetic material.

2. A projection screen assembly according to claim 1, wherein said magnets are movable with respect to said beams.

3. A projection screen assembly according to claim 1 or 2, wherein said magnets are mounted in recesses in said beams.

4. A projection screen assembly according to any one of the preceding claims, wherein said ferromagnetic material is arranged at said edges.

5. A projection screen assembly according to claim 4, wherein a number of strips comprising said ferromagnetic material are arranged along at least two of said edges.

6. A projection screen assembly according to any one of the preceding claims, wherein alignment means adapted for engaging at last one edge of said panel are arranged on said beams.

7. A projection screen assembly according to any one of the preceding claims wherein said screen panel is provided as a sandwich construction comprising a base plate made essentially of the same material as the beams.

8. A projection screen according to claim 7, wherein said mate- rial is aluminium.

9. A projection screen assembly according to any one of the preceding claims, comprising more than one panel.

10. A projection screen assembly according to claim 7 wherein adjacent screen panels are mountable on said framework by means of the magnetic attraction between ferromagnetic material on respective adjacent panels and one and the same magnet.