Abstract:
A projection screen apparatus for reproducing the coherence between a visual image and associated acoustic signals. The projection screen apparatus includes a sound broadcasting device and screen that is transparent to sound waves disposed between the sound broadcasting device and the audience, whereby the projection of video and sound broadcasting are simultaneously implemented with respect to the audience. The screen includes multiple layers of white fabric that are superimposed and joined together such that the screen provides a surface that is both transparent to sound and sufficiently opaque to view a projected image.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of French Application No. 00 07372 filed Jun. 8, 2000. 
     BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The present invention relates to a projection screen of retractable type, adapted to be used in an extended position in combination with a projector, in particular a video projector, and with a sound broadcasting device. 
     More precisely, a screen according to the present invention is retracted when not in use, in order both to make it less cumbersome and to avoid the risk of its becoming dirtied and/or deteriorated. 
     Furthermore, a screen according to the present invention is of the type known as acoustically transparent, which is to say that it is permeable to sound waves. 
     This makes it possible to implement simultaneously the projection of video together with sound broadcasting coming from sound sources placed behind the acoustically transparent screen. 
     The advantage of placing the sound sources behind the screen has been known since the existence of film with sound, known as “talking pictures”. This is to procure the sensation of coherence between the projected image and the sound diffused for the spectator. 
     The simultaneous implementation of sound sources and an acoustically transparent video screen makes it possible to reproduce this sensation in a smaller environment, in particular a domestic environment. 
     Video screens combining the features mentioned above are known. Conventionally, such screens are formed from a sheet of plastics material, generally PVC, perforated with orifices of small size adapted to let through sound waves. 
     Such screens are formed from a sheet of PVC of which the perforations typically represent between 2% and 6% of their surface and let the sound through only very imperfectly. A large part of the sound is reflected, instead of passing though the orifices that perforate the screen. This phenomenon causes substantial attenuation of the sound level, particularly at high frequencies. Furthermore, the multiple reflections created initially by the full portions of the screen cause aberrations in the acoustic response, resulting in irregularities in the transfer function and in distortions that degrade the sound quality. 
     In addition, in an environment that is more restricted than a conventional movie theater, the spectator is normally placed much closer to the screen. The perforations of the screen, closer than a certain distance, become visible, and add a raster effect to the image that is bothersome. 
     Such screens are in general retractable through rolling onto a cylinder rotated by a motor, and frequent repetition of this operation gives rise to deformation either on the edges of the screen, or on the median part. This arises from the fact that screens that can be rolled up are not generally tensioned by the edges, but only by a weighting bar, that applies a vertical stretching force to the screen, towards the bottom. 
     With time, the material making up the screen can stretch in an uneven manner, thereby giving rise to deformations that risk impairing the flatness of the screen. Apart from the aesthetic drawbacks that this implies, the focusing of the projector is altered, thereby altering the quality of the image in certain zones. This defect is worse if acoustically transparent screens having perforations are used. 
     Many devices exist for tensioning the edges of screens that roll up, but they are generally both costly and unaesthetic, and can also jam due to wear. The object of the present invention is to provide an acoustically transparent retractable screen without the drawbacks mentioned above. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to a retractable projection screen that is transparent to sound waves that has at least two layers of white fabric superimposed and joined together. 
     According to a first embodiment of the present invention, the screen with at least two layers of superimposed fabric is rolled onto a rolling-up device having a weighting bar which is of sufficient weight for stretching the fabric so that the stretching compensates for the difference in diameter between the two layers when they are rolled up. 
     This makes it possible to avoid the formation of a fold in the inner layer of fabric, when the screen is rolled up. 
     According to a second embodiment of the present invention, the screen folds into a plurality of rectangles linked by folds when the weighting bar rises under the effect of traction devices that are applied to it. 
     According to a third embodiment of the present invention, a piece of fabric forming the screen is fixed by one edge defining a first end, an opposite end being affixed to a rolling-up device having a roller disposed in a fixed manner parallel to the first end, a mobile roller serving as a weighting bar being interposed between the two ends so as to tension the fabric towards the bottom by gravity. The roller is fixed to pressing members that tend to make contact between two layers of fabric which are thus disposed back to back. 
     Preferably the rolling-up device enables the simultaneous retraction of a sound broadcasting device in such a manner that the device is situated substantially at mid-height behind the screen when the latter is in the extended position. 
     The features and advantages of the present invention will be better understood after reading the following detailed description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a front elevational view in the unrolled position of a conventional screen that can be rolled up; 
     FIG. 2 is a cross-sectional view in the unrolled position of a conventional screen that can be rolled up; 
     FIG. 3 is a front elevational view of a first embodiment of the present invention, the screen being in the unrolled position; 
     FIG. 4 is a cross-sectional view of the first embodiment of the present invention, the screen being in the unrolled position; 
     FIG. 5 is a cross-sectional view of a screen according to a second embodiment of the present invention, the screen being in the unrolled position; 
     FIG. 6 is a front elevational view of a screen according to the second embodiment of the present invention; 
     FIG. 7 shows in detail a side edge of a screen according to the second embodiment of the present invention; 
     FIG. 8 is a diagrammatic view in cross section of a third embodiment of the present invention, the screen being in a partially retracted position. 
     FIG. 9 is an enlarged detailed cross-sectional view of a portion of the third embodiment of the present invention depicted in FIG. 8; and 
     FIG. 10 is a diagrammatic side elevational view of an embodiment of the present invention associated with a retractable sound broadcasting device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A conventional retractable screen of the type that can be rolled up, such as shown in FIGS. 1 and 2, includes a band of material  10  of white color of substantially uniform width, rolled onto a roller  11 , the rotation of which is controlled by a motor  12  that rotates axially. The band of material  10  has a free end  13  that is folded and fixed so as to form a hem in which a weighting bar  14  is disposed. A split tube  15  is disposed around the weighted hem. Two detachable stoppers  16  and  16 ′ are generally provided to close the split tube  15  in order to avoid any axial displacement of the weighting bar  14  in the hem. 
     The motor  12  is generally of the type with adjustable end of travel, a reversing device (not shown) being provided for changing its direction of rotation. When the motor is activated, it rotates the roller  11  that rolls up or unrolls the band of material  10  according to the direction of rotation. 
     When the band of material  10  is unrolled, the motor  12  stops at the end of travel in a position predetermined by the adjustment. It is tensioned by the force of gravity that acts on the weighting bar  14 . When the motor  12  is started again, the reversing device reverses the direction of rotation of the motor  12 , that rolls up the band of material  10  around the roller  11  until activation of an end of travel device (not shown). The end of travel device is adjusted so as to interrupt the action of the motor  12  when the band of material  10  is sufficiently rolled up onto the roller  11 . 
     The band of material  10  is generally constituted by an opaque, white material, that reflects light and makes possible its use for a projection screen for cinematographic, photographic, computer or video applications. 
     In applications requiring sound broadcasting that is simultaneous with the image, it is generally preferred to have a source of sound behind the screen. The sound waves emitted by the source of sound, generally a loud-speaker, pass through the band of material  10 , that is generally constituted by a sheet of plastic material and perforated by a multitude of orifices provided for this purpose. 
     Such orifices are generally of a diameter in the range between 0.5 and 1.5 mm. Their total surface typically represents between 2% and 6% of the total surface of the screen. 
     This proportion of perforated surface is insufficient to permit the correct transmission of sound, a proportion of at least 40% being necessary. 
     A surface perforated to the extent of 40% or more of the surface of the screen is incompatible with an acceptable performance in cinematographic or video projection. 
     Apart from this, fabrics are known in the production of projection screens. Fabrics have the advantage, in certain textures, of being permeable to sound waves. 
     The disadvantage of fabrics that are sufficiently permeable to sound waves is their lack of opacity to light, which gives rise to a loss in the brightness of the projected images. Moreover, the lack of opacity of such fabrics can give rise to the appearance of a perceptible reflection on the screen, interfering with the projected image, when a surface situated behind the screen reflects the light. 
     If improving the opacity of a screen made of sound-permeable fabric can be achieved by using a tighter weave, and thereby increasing its density, its permeability to sound is correspondingly reduced. 
     The inventor observed that, in a surprising manner, it was possible to reconcile the need for sufficient sound permeability with sufficient opacity to light by substituting a fabric of density x, insufficiently permeable to sound, by two layers joined together of density x/2 of the same fabric of which the overall permeability to sound waves turns out to be well above that of the fabric of density x. 
     A projection screen according to the present invention, such as shown in FIGS. 3 to  10 , is free from the drawbacks and limitations mentioned above concerning conventional acoustically transparent screens that can be rolled up. 
     According to a first embodiment of the present invention, such as shown in FIGS. 3 and 4, a projection screen  17  embodies two thicknesses of an expanse of white fabric that are permeable to air. Preferably, and in a non-limiting manner, fabric is used that has 30 to 80 threads of warp, and 20 to 40 picks of weft, per square centimeter. 
     Preferably, and in a non-limiting manner, the mass of fabric per unit area is between 150 and 200 grams per square meter. These two thicknesses, of the same dimensions and of rectangular form, can be sewn together. 
     It is also possible to fold the fabric back on itself to form two thicknesses, and to sew the side edges together, as well as the two ends of the expanse of fabric. 
     The assembly constitutes the screen and includes two visible lateral seams  18 ,  19 , an end  20  known as the roll-up end, and an opposite end  21  (FIG. 4) known as the weighting end. 
     The weighting end  21  includes, in a non-limiting manner, a hem that is open at both ends, formed in conventional manner by means of a seam  22 . 
     A weighting bar  23 , for example, a bar of solid steel, is disposed inside the hem of the weighting end  21 . Preferably, the length of the weighting bar  23  is similar to that of the width of the screen  17  such that the mechanical tension due to the mass of the weighting bar  23  is evenly distributed over the width of the screen  17 . 
     The mass of the weighting bar  23  will be proportional to the surface area of the screen  17 , and preferably at least equal to 3 kilograms per square meter of screen surface area. 
     The maximum mass of the weighting bar  23  will be determined so as to avoid tearing of the fabric around the seam  22 . 
     The assembly composed of the end  21  of the screen and the weighting bar  23  disposed inside the hem is itself disposed inside a rigid tube  24  that is split over the whole of its length. 
     Its length is at least equal to the width of the screen  17 . The screen  17  is disposed so as to pass through the split in the rigid tube  24 . Two stoppers  25  respectively block the ends of the rigid tube  24  to avoid axial displacement of the weighting bar  23  and/or hem  21  in the rigid tube  24 . 
     The roll-up end  20  of the screen  17  is fixed by a suitable device to the rolling-up device that is, for example, composed of a roller  27  that is rotationally mounted to the outer face of a driving motor  28  of generally cylindrical form (represented symbolically by a cross, FIG. 4) axially disposed inside the roller  27 . The motor  28  includes an axle (not shown) that is mounted to a fixed support  29  (FIG.  3 ). 
     The motor  28  is adapted to rotate the roller  27  in one direction or the other, according to the status of a motor control device (not shown). An end of travel device (not shown) is provided so as to interrupt the operation of the motor as soon as a set number of rotations has been achieved. 
     The end of travel device has a reversing device adapted to reverse the status of the motor control device simultaneously with the interruption of its operation. 
     The roller  27  has an axle  30  rotationally coupled to it, the end of which projecting axially from the roller  27  is supported by a fixed support  29 ′, for example, a bearing. 
     Such drive devices are known per se, particularly in devices for automatically raising blinds, and do not constitute a feature of the invention. 
     When the motor control device is operated, the motor  28  rotates the roller  27  that rolls up the screen  17  onto the roller. 
     The weighting bar  23  simultaneously tensions the two layers of the screen  17 . The rolling up of the screen onto the roller defines an inner layer and an outer layer of which the radius exceeds that of the inner layer by one thickness of fabric. For each turn rolled up, the difference in length between the two layers is thus: 
     
       
         2πe, 
       
     
     e being the thickness of the fabric. 
     The weighting bar  23  exerts, by its mass, sufficient tension to stretch the outer layer such that its elastic deformation is at least equal to the difference in length between the two layers. This avoids the formation of folds or creases by taking up the difference in length between the two layers, which folds cause visible marks on the screen and premature wear around the folds. 
     Moreover, by virtue of the elasticity of the fabric, the tension exerted by the weighting bar  23  takes up the possible non-elastic deformations that may arise in the different parts of the screen  17 , and procures sufficient flatness for the screen in the unrolled position to allow satisfactory image projection. 
     A second embodiment of the present invention is shown in FIGS. 5 to  7 . A screen  31  composed of two layers of fabric that are affixed by an edge termed the upper edge, using devices that are known per se, to an upper fixing bar  32  that is mounted to a frame (not shown), is illustrated. 
     The screen  31  is also affixed by its opposite edge, termed the lower edge, to a weighting bar  33 . 
     Two edges  34  and  34 ′ of the screen  31 , termed lateral edges, each include a sewn hem  35  and  35 ′, respectively. 
     A plurality of elements  36  that are flat, rigid and oblong (FIG. 7) and disposed in line but not joined together are provided inside each of the hems  35 ,  35 ′. 
     All the elements  36  are identical, and four elements  37 , identical to each other and of length substantially equal to half that of an element  36 , are disposed respectively at each end of the two lines of elements  36 . 
     The elements  36  and  37  are disposed inside the hems  35 ,  35 ′, and are spaced at equal intervals. 
     Alternatively, it is possible to connect the elements  36  and  37  together by a flexible or semi-rigid band (not shown) of width substantially equal to that of the elements  36  and  37 . 
     The elements  36  are perforated in their center by an oblong hole  38 , of which the axis is perpendicular to that of the element  36 . 
     The hems include several oblong openings  39 , sewn or riveted, which are each placed over, and correspond with, one of the respective oblong holes  38  provided in the elements  36 . 
     Two straps  40  are provided, passing into each of the hems  35 ,  35 ′ through the holes  38  and openings  39 , alternating in front of and behind the screen  31 . 
     An end termed the lower end of each strap  40  is connected to the weighting bar  33 , the other end termed the upper end being fixed so as to be able to be rolled up by a rolling-up assembly  41 . 
     Two recesses (not shown) are provided in the upper fixing bar  32  to permit movement of each strap  40  without friction when it is rolled up by the rolling-up assembly  41 . 
     The rolling-up assembly  41  includes, in a manner similar to the previous embodiment, a roller  42  rotationally coupled to a motor  43  (represented symbolically by a cross in FIG.  5 ), the motor  43  being of the type with control reversal at the end of travel, as in the previous embodiment. 
     The roller  42  is provided with two pairs of circular guide flanges  44  disposed coaxially with the roller  42 , each flange of a pair being spaced from the other by a distance equal to or greater than the width of the strap  40  plus a clearance. 
     The separation between the two pair of flanges  44  is equal to the separation between the two straps  40  when they are disposed in the oblong holes  38  and openings  39 . 
     The straps  40 , the rolling-up assembly  41  and the guide flanges  44  constitute a driving device adapted to actuate the folding up of the screen. 
     When the motor  43  rotates the roller  42 , the two straps  40  roll up around the roller  42 , while being guided by the guide flanges  44 . This action pulls up the weighting bar  33  that folds up the screen  31  into a succession of rectangular parts  45  defined by the length of the elements  36  and  37  and by the width of the screen  31 . The rectangular parts  45  are connected by folds  46  that form in the gaps separating the elements  36  from each other and also in the gaps separating the elements  36  and  37 . The folds  46  are represented by gray bands in FIG.  6 . The screen  31  is thus forced to fold up in a zigzag, in the manner of a road map. 
     The end of travel device of the motor  43  is adjusted such that, when the weighting bar  33  is at a distance from the upper fixing bar  32  substantially equal to the product of the thickness of a seam of the screen  31  containing an element  36  or  37  multiplied by the number of elements  36  and  37  disposed in a seam of the screen, the end of travel device interrupts the operation of the motor  43  and operates a reversing device (not shown) that reverses the direction of rotation of the motor the next time it is started. 
     Thus, when the motor  43  starts to turn once again due to the action of a control, it unwinds the straps  40 . The weighting bar  33  pulls both the straps  40  and the screen  31  downwardly by gravity. The screen  31  unfolds until it is completely tensioned by the weighting bar  33 . 
     The end of travel device of the motor  43  is adjusted so as to interrupt the operation of the motor when the straps  40  are sufficiently unwound and are no longer tensioned by the weighting bar  33 , the weighting bar  33  being supported solely by the screen  31 . 
     The end of travel device operates a reversing device (not shown), as before. Thus, the next time the motor  43  is started, the direction of rotation of the motor  43  will cause the straps  40  to be wound up. 
     Another embodiment utilizes a rolling-up assembly  50  (FIG.  8 ), similar to those already described. 
     A band of acoustically transparent fabric  51  adapted to reflect light is fixed by one end to the rolling-up assembly  50  that includes, in a conventional manner, a drive roller (not shown) rotationally coupled to a motor (not shown) provided with an end of travel device (not shown). 
     Three rollers termed lower rollers  54 ,  55  and  56  (FIGS. 8 and 9) are parallel to the rolling-up assembly  50  and are fixed by their ends to a support  57 , their axes substantially forming an isosceles triangle with the vertex at the bottom. A first roller  54  is fixed, and a second roller  55 , of which the axis defines the vertex of the triangle, is also fixed. Advantageously, the second roller is of greater diameter than the first roller. 
     A third roller  56 , substantially of the same diameter as the first roller  54 , is connected to the supports  57  in order for its axis to be able to move in a path limited by the support  57 . 
     Elastic members (not shown) are provided to move the mobile third roller  56  toward the first roller  54 . The action of the elastic members is represented by an arrow shown in FIG.  9 . 
     The first and third rollers  54 ,  56 , in combination with the elastic members constitute a device for pressing together the two layers of the band of fabric  51  and  51 ′, coupled in their movement to the second roller  55 . 
     The part  51 ′ of the band of fabric indicates that which rises up to the rolling-up assembly  50 . It is fixed at its end by a seam  52 , parallel to the rolling-up assembly  50 . 
     In order to visualize the two layers of the band of fabric  51  and  51 ′, they are represented separately in FIGS. 8 and 9, but it should be understood that they are in fact joined together. 
     The first and third rollers  54 ,  56  can, in accordance with a further feature of the present invention, be replaced by any device of parallel guidance, for example permitting the band of fabric to slip. 
     The combination of such a guide device with elastic members moving them toward each other defines the device for pressing the two layers of the band of fabric  51  and  51 ′ together. 
     The part  51 ′ of the band of fabric is disposed so as to pass between the first and third lower rollers  54 ,  56 , to pass around the second lower roller  55 , to pass a second time between the first and third lower rollers  54  and  56 , and to be fixed at its end by the seam  52  to its other part of the band of fabric  51 , itself fixed to the rolling-up assembly  50 . 
     The assembly  58  constituted by the three lower rollers  54 ,  55  and  56  and by their supports  57  is mobile and of sufficient mass to tension the band of fabric  51  and  51 ′ by gravity. 
     When the rolling-up assembly  50  rolls up the band of fabric  51  and  51 ′, the part that is not rolled up reduces, pulling the assembly  58  upwardly. The end of travel device provided in the rolling-up assembly  50  is adjusted so as to interrupt the action of the rolling-up assembly and to reverse it at the next control operation when the assembly  58  arrives at a predetermined position, near to the rolling-up assembly  50 . 
     When the rolling-up assembly  50  unrolls the band of fabric  51  and  51 ′ it is drawn downwardly and tensioned by the mass of the mobile assembly  58 . 
     The first and third rollers  54 ,  56  press the two thicknesses  51  and  51 ′ of the band of fabric against each other so as to form an acoustically transparent projection screen composed of two layers of white fabric. 
     A further variant of the embodiments of the present invention illustrates a fixed support  65  (FIG. 10) extending substantially horizontally behind the screen  31 , and a roller  66  disposed parallel to the roller  42  supported, for example, by bearings. A drive device for rotating the roller  66  includes, for example, a transmission belt  47  that rotationally couples the roller  42  with the roller  66 . Advantageously, in this case, the diameter of the roller  66  is half that of the roller  42 . 
     Any other device for driving the roller  66  can be envisioned, of which the action is synchronized with the rotation of the roller  42 . 
     A pair of straps  48  is fixed by one end to the roller  66 , the other end being mounted by any suitable device  49  to a sound broadcasting device  60  including at least one loudspeaker  61 . 
     Preferably the sound broadcasting device  60  has three independent acoustic units that are brought together to form a mechanically connected assembly that is adapted to be displaced vertically by the winding or unwinding of the straps  48 . 
     When the roller  42  rolls or folds up the screen  31  (according to the embodiment of the invention), it drives around the roller  66  which winds up the strap  48 , thus raising the sound broadcasting device  60 . 
     Conversely, on extension of the screen  31 , the roller  42  rotates the roller  66  in the other direction, which unwinds the straps  48 , so lowering the sound broadcasting device  60  following a path that is substantially half that of the weighting bar  33 . 
     Thus, when the screen that is permeable to sound waves is in the extended position, the sound broadcasting device  60  is located behind it substantially at mid-height. 
     This is the position that is most favorable to its correct operation. 
     The embodiments given in the present invention are non-limiting examples of the present invention that has been described above. It will be apparent to those skilled in the art that suitable modifications may be made to the invention without departing from the spirit thereof, that is defined by the claims that follow hereinafter.