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FIELD OF THE INVENTION  
         [0001]    This invention relates to a display unit. More particularly the invention is concerned with a display unit of the kind in which a blind printed with display material is windable between a pair of rollers for presenting a selected area of the blind for display in a frame or window area.  
         BACKGROUND TO THE INVENTION  
         [0002]    Roller blind displays have been widely used for many purposes including advertising and presentation of information. In such displays a blind carries a sequence of displays along its length. It is wound between a pair of parallel spaced rollers through a display window area, the blind being wound off one roller onto the other. Various controllable drive mechanisms have been used conventionally driven by an electric motor. Such drive mechanisms including indexing means to halt the drive when a selected portion of the blind is in the display window area. The present invention seeks to provide a drive mechanism which is reliable and easy to use and, in particular, one which can be manually actuated.  
           [0003]    The present invention is applied to a display apparatus of the kind comprising first and second rollers rotatably mounted in spaced parallel relationship for winding a blind carried by the rollers therebetween through a display area to locate a selected portion of the blind thereat; and drive means for rotating one or other roller to cause lengthwise movement of the blind.  
         SUMMARY OF THE INVENTION  
         [0004]    In accordance with the present invention in display apparatus of the above kind, the drive means comprises first and second drive portions rotatable with said first and second rollers respectively, said first and second drive portions being located at opposite sides of the rollers as seen from the display area.  
           [0005]    A flexible elongate drive element is terminated at one end at the first drive portion, and is wound in a plurality of turns about the first drive portion. The drive element is terminated at the other end at the second drive portion and is wound in a plurality of turns about the second drive portion so as to be wound thereon when the drive element is wound off the first drive portion and vice versa. The is drive element has an intermediate section-supported for lengthwise movement thereof in a predetermined path between the turns wound on the first and second portions and the predetermined path includes a portion at which the intermediate section is manually actuable to apply a drive force to one or other of the rollers.  
           [0006]    The blind carried by the rollers may be a carrier for graphics, e.g. a printed display blind attached to the carrier blind. The carrier blind acts to transmit drive from the roller to which drive is applied to wind the carrier thereon to the other roller from which the blind is being wound off. The display apparatus may be constructed in the form of a light box in which the carrier blind is back lit. To this end the carrier blind is made light transmissive.  
           [0007]    In a preferred embodiment of the display apparatus of the invention the above-mentioned portion of the predetermined path is substantially parallel to and in the plane of said first and second rollers outside the space between the rollers occupied by the blind. More particularly the rollers are supported in a rectangular housing parallel to and adjacent respective ones of two opposed sides thereof and the portion of the predetermined path lies external to one of said two opposed sides to be manually accessible. One of these two opposed sides contains first and second apertures through which the flexible element extends to the external portion of the predetermined path. Manually-engageable (e.g. graspable) means is carried by the flexible element at the external portion of said predetermined path.  
           [0008]    The manually-engageable means is sized to be unable to pass through the apertures and thereby limits the extent of movement of the manually-engageable means. Preferably the manually-engageable means is a spring-loaded device acting to maintain tension on the flexible element. In the preferred embodiment of the invention the flexible element extends from the first drive portion in a direction past the second roller and extends from said second drive portion to engage a part acting as a guide pulley rotatable with the first drive roller and return towards and past the second drive portion.  
           [0009]    Furthermore in the preferred embodiment of the display apparatus the ratio of the diameter of each of the first and second rollers to the diameter of each of the first and second drive portions respectively is such that a movement of the flexible element through a distance between said apertures causes the blind to be wound over a length that is at least twice the dimension of said display area in the lengthwise direction of the blind. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a front elevation of a display unit embodying the invention with the front cover removed;  
         [0011]    [0011]FIG. 2 is an illustration to a larger scale of the means for rotatably supporting the rollers at each end, the illustration of FIG. 2 particularly pertaining to the right-hand end of the upper roller as seen in FIG. 1; and  
         [0012]    [0012]FIG. 3 is an axial section of a handle/tensioning device for the drive cord. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    There will be described an embodiment of the invention in which the invention is applied to what is known as a light-box type of display unit. A light-box provides back lighting of the displayed portion of a blind carrying display material. It will be assumed that the blind that is moved to change the display is movable in a vertical path between upper and lower rollers. Reference to the “left” and “right” and “upper” and “lower” refer to the display unit as seen in FIG. 1. The unit to be described could be mounted to provide a display in which the blind is moved horizontally.  
         [0014]    [0014]FIG. 1 shows a display unit having a housing  10  formed to provide a rectangular tray in which the mechanism of the display unit is mounted. That is the housing includes a rear wall  12  and side vertical walls  14  and horizontal side walls  16  upstanding from the rear wall. Mounted in the housing parallel to and adjacent respective side walls  16  is an upper roller assembly  20  and a lower roller assembly  30  parallel to the upper roller and spaced from it. Both rollers are rotatably mounted to releasable plain bearings  18  supported on the opposed vertical side walls  14  for rotation about a horizontal axis. The structure is shown simplified in FIG. 1. A preferred arrangement for the support and rotation of the roller assemblies  20  and  30  (including their respective drive means) is described below with reference to FIG. 2. The rollers  20  and  30  receive a graphic carrier  40  which is in the form of a blind and which is windable from one roller to the other to present a portion of the blind in a display window area  22  indicated in dashed line. The display window area  22  is defined by a front cover or surround (not shown) attachable to the housing  10 . The end portions of the graphic carrier  40  are secured to respective rollers, as by pop type rivets. The carrier  40  transmits the drive applied to one roller to the other and serves to carry a display blind (not shown) on which the advertising or information to be displayed is printed. The display blind is attached to the outer surface of the carrier  40  by releasable means (not shown) such resilient plastic tongue and groove arrangements such as are well known. The front cover screens the rollers and their operating mechanism from external view so that only the wanted display portion of the blind is seen at display area  22 . The housing  10  and the front cover provide what is known as a light box. The graphics carrier  40  extends between the outer portions of the rollers, i.e. away from rear wall  12 . The carrier  40  is a translucent plastics web which supports both the tension generated in the web between the rollers  20  and  30  during movement of the carrier and diffuses light to allow back lighting of the display blind. To this end, back lighting is provided by lamps such as elongate fluorescent lamps (not shown), carried by the rear wall  12  behind the display window area  22 . The depth of the tray that is the height of the side walls  14  and  16  from the base  12 , is sufficient to allow the rollers  20  and  30  to be accommodated within the tray such that the plane of the carrier  14  therebetween is a little within the tray. This is not essential but is of advantage in the provision of a front cover or surround of straight forward construction.  
         [0015]    The roller assemblies  20  and  30  are conveniently of identical construction as exemplified by the following description of roller assembly  20 . The assembly  20  has a larger diameter portion  24  onto which the carrier  40  is wound and an integral reduced diameter portion  26  at each end of the larger diameter portion which is mounted to rotate in a plain bearing aperture of a respective bearing  18  in a construction to be described with reference to FIG. 2. All the parts of a roller assembly rotate as a unit. Not all the parts are used in the drive arrangement: it is convenient, however, to manufacture the roller assemblies to be identical and for each to be symmetrical.  
         [0016]    In order to rotate the two rollers simultaneously, a manually-operable cord drive  50  is provided as a flexible drive element. The cord drive is secured at one end  52  to the reduced diameter portion  26  at the right side of the upper roller  20  and the end portion is wound a number of turns  54  around the adjoining reduced diameter portion  26  from whence the cord extends along an intermediate path which leads down as indicated at  56  inside the adjacent side wall  14  to exit the lower side wall  16  through an apertured bush  32  (shown in cross-section) fitted in the side wall and below the reduced diameter portion at the right of the figure. The cord  50  then extends in a portion  58  exterior to the lower side wall  16  across to and through another apertured bush  34  (shown in cross-section). Having passed through the bush  34  the cord  50  passes the lower roller assembly and rises at  60  to pass round the reduced diameter portion  26  at the left of the upper roller assembly  20 —the portion  26  there acting as a guide pulley—and thence down at  62  to the reduced diameter portion  26  at the left of the lower roller assembly  30 . This end portion of the cord is treated in the same way as the other end portion  64  first described. It is wound several turns  64  around the reduced diameter portion  26  at the right of the lower roller  30  and the other end  54  of the cord  46  secured to this portion  26 . The wound portions of  54  and  64  of the cord  50  are wound in a direction enabling both rollers to rotate in the same direction, thereby winding the carrier  40  between them. The apertured bushes  32  and  34  are formed and are located below the reduced diameter portions  26  to assist a smooth longitudinal sliding motion of the cord  50  through the bushes.  
         [0017]    It will be seen that the intermediate path traversed by the cord is designed to allow ease of longitudinal movement and free winding/unwinding of the turns on drive portions  26 . The intermediate path lies essentially in a single plane and for compactness of the unit this plane is the plane in which the rollers  20  and  30  are located. The cord drive  50  extending from bush  34  -could be taken directly to the drive portion  26  at the left of lower roller  30  but by taking it up over the drive portion  24  at the right of the upper roller  20  and back down to the lower roller variation in the angle which the cord makes to the drive portion  24  of the lower roller as it winds/unwinds is reduced aiding in ensuring free movement.  
         [0018]    The section  58  of the cord outside the housing  10  provides the means by which it is manually-accessible for moving the cord lengthwise. The section  58  lies essentially in the plane of the rollers  20  and  30  and the housing  10  and is outside the spacing between the rollers within which the display area  22  is defined. A tension applied in the cord as indicated by arrow T will act to unwind the cord with respect to one roller,  30  in the case shown, and cause the carrier to be wound onto that roller. The resultant tension in the carrier  40  is communicated to the other roller and acts to wind the carrier off the other roller  20 . This in turn causes the winding up of the cord at  54  at the right of roller  20 .  
         [0019]    A means  70  is provided on the cord in the external section  58  between apertures  32  and  34  to act as a manually grippable element to move the cord and/or to act as a cord tensioning element. In the embodiment shown, the means  70  does not pass through the apertures and acts as a stop member to limit the amount of longitudinal travel of the cord  50 . Preferably it performs all three functions. In the preferred embodiment the means  70  is a spring-loaded cord tensioning device described below with reference to FIG. 3.  
         [0020]    This manual actuation requires no indexing of the blind as has been used in controlling motor-driven blind-winding systems. The person moving the cord watches the display and sets it to the required position. The system is particularly useful for displays which do not require continual change, for example menu displays which are changed at intervals during the day.  
         [0021]    The length L of carrier moved in traversing the cord tensioning device between the apertures  32  and  34  over a distance D is related to distance D by the ratio R of the diameter of the larger diameter portion  24  of a roller assembly (about which the blind is wound) to the diameter of the adjoining smaller diameter portion  26  about which the cord is wound. Thus L=RD. L is sufficient to accommodate N displays lengthwise along the blind each of which occupies the height H (in the carrier travel direction) of the display window area  22 . Thus L is not less than NH.  
         [0022]    [0022]FIG. 1 illustrates the mounting of the roller assemblies rather diagrammatically. A preferred roller support and rotational mounting will now be described, taking the right hand side of the upper roller assembly by way of example. Each roller end is supported and mounted in the same fashion. FIG. 2 also illustrates the winding of the drive cord onto the reduced diameter portion at the right hand side of the roller assembly  20 . The carrier blind  40  is not shown. In FIG. 2 parts like to those of FIG. 1 are denoted by like reference numerals.  
         [0023]    [0023]FIG. 2 shows the section of right-hand side wall  14  adjacent the right hand end of the upper roller assembly  20 . The larger diameter portion of the roller comprises a cylindrical tube  80  of aluminium whose end portion is a snug slide fit on to an inwardly projecting cylindrical portion  82  of a member  84  which is inserted into the tube until the tube abuts an outwardly directed flange  86 . Portion  82  is shown as tubular: it could be solid. The tube  80  and insert  82  may be keyed together to ensure they rotate as a unit about axis A-A. The member  84  has the drive portion  26  extending axially outwardly from flange  86 . The outer end of portion  26  carries a flange  88  and projecting from this is a raised axial boss  90 . The outer end of portion  26  has an axial blind hole extending into it through boss  90  and flange  88 . A metal spigot  92  is received in the blind hole and projects outwardly to enter the plain bearing  18 .  
         [0024]    The bearing  18  is formed in a bracket  94  fixed to and standing away from the inner surface of adjacent side wall  14 . The bracket  94  is apertured in alignment with axis A-A and an apertured bush  96  seats in the bracket aperture with an enlarged flange portion  98  axially inward to engage the facing surface of boss  90  for smooth rotational engagement therewith. The spigot  92  extends outwardly of boss  80  to enter the bearing bush  86 . The member  84  (parts  82 ,  86 ,  26 ,  88  and  90 ) is formed as an integral moulding of plastics material, e.g. Teflon, and the bearing bush  96  is likewise formed of a plastics material such as Teflon.  
         [0025]    The structure described above with reference to FIG. 2 is designed for ease of rotation bearing in mind that ease of manual actuation is required.  
         [0026]    To complete the drive portion  26  shown in FIG. 2, there is also shown the rising cord portion  56  which engages the portion  26  at the rear (as seen in the figure) and is wound in a plurality of turns  54  of which only the first and last  54   a,    54   b  are shown for clarity of illustration. The end of turn  54   b  is then taken through an aperture in flange  88  and is suitably terminated for example in a knot  55  to retain the end in place and anchor the turns  54  to portion  26 . The flange  88  acts to prevent the wound cord from sliding off the drive portion  26 .  
         [0027]    The flange  86  acts to locate the carrier and the display blind affixed thereto against any tendency for axial displacement. Preferably the aperture in the bracket  94  is provided with a releasable side portion so that the bush  96  and the spigot  92  within it are releasable from the bracket in order to remove the roller assembly as a unit. This provision is made on all four apertured brackets.  
         [0028]    The construction of the combined handle/tensioning device  70  is illustrated in FIG. 3. It is considered to be novel in its own right. The device  70  comprises a tubular body  72  closed at one end. The closed end has a central aperture  73  allowing the cord  40  to enter the body from one side (FIG. 1). The other end of body  72  is interiorly threaded to receive a screw-in cap  74  which is also centrally apertured at  75  to allow the cord  40  to enter the handle from the other side. Within the body  72  are two helical springs  76   a,    76   b  aligned in the body  72 , their outer ends bearing against the inner surfaces of the closed end of the body  72  and the cap  74 . The cord  40  is separated into two within the handle. One end portion  40   a  of the cord passes through the helical spring  76   a  and through the aperture of a washer  77   a  engaging the inner end of the spring  76   a.  The end of cord portion  40   a  is tied into a knot  78   a  interiorly of washer  77   a  so that the cord end is retained by the washer. Similarly the other end portion  40   b  of cord passes through the helical spring  76   b  and through the aperture of a washer  77   b  engaging the inner end of the spring  76   b.  The end of cord portion  40   b  is tied into a knot  78   b  interiorly of washer  77   b  so that the cord end is retained by the washer. The washers are axially movable in the body  72  to compress the respective springs. This construction has the advantage that by unscrewing the cap  74 , the interior assembly can be removed from body  72 . The handle effectively provides a continuous drive cord  40  in which a tension-maintaining resilience is incorporated.  
         [0029]    In practice the handle can be set up to have the cord knots  78   a,    78   b  a little separated to establish tension in the cord  40  and provide a degree of yielding enabling tension to be maintained in use of the apparatus. It is preferred to have the cord exit the lower side of the housing with the handle  70  accessible below the lower side, so that similar display units can be placed side by side in close proximity.  
         [0030]    It will be appreciated that the rollers could be journalled to bearings provided directly in the side walls  14 . The apertures  32  and  34  could be substituted by curved cord guides extending out of the lower side wall. The embodiment described utilises a graphic carrier which is affixed to the roller assemblies  20  and  30 . With the aluminium roller tubes, e.g.  80 , described the carrier  40  can be affixed thereto by pop rivets. While it is preferred to have a graphics carrier by which the display blind is carried in a two layer composite, a single layer display blind could be used. A light box type of construction is not essential for the practice of the invention.

Summary:
An advertising display unit has a blind wound between a pair of spaced rollers rotatably mounted for bringing a selected portion of the blind into a display window area. A mechanism for longitudinally moving the blind is provided which is easily accessed and actuated manually. Each roller comprises an assembly having a larger diameter portion onto which the blind is wound and a smaller diameter portion that rotates with it. A cord drive is secured to and wound a number of turns round the smaller diameter portion of one roller. The cord drive follows a path a section of which extends externally of a housing in which the rollers are mounted. The cord drive passes to the other roller where it is wound a number of turns about and secured to the small diameter portion of the other roller. The cord is wound about the small diameter portion so as to wind off one and onto the other with the rollers rotating in the same direction. The blind serves to transmit drive from the wind-up roller to the wind-off roller. The external section of the path includes a manually-graspable handle in which the cord is secured by a spring-loaded mechanism to maintain tension in the cord.