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BACKGROUND OF THE INVENTION  
         [0001]    a) Field of the Invention  
           [0002]    This invention relates to a new or improved vertically extensible mechanism for controlled displacement of a panel structure such as advertising and display signs or doors between vertically spaced deployed and retracted positions.  
           [0003]    b) Description of the Prior Art  
           [0004]    Advertising and display signs are known in many different forms. Generally, the advertiser will wish his sign to be displayed in a prominent position, which as far as outdoor signs are concerned generally means an elevated position. Thus typically advertising signs appear on billboards, trestles, and the sides and roofs of buildings.  
           [0005]    A difficulty arises with such advertising signs however, in that once they have been installed, they are not easily changed or replaced.  
           [0006]    The present invention aims to provide a display structure which can be used for advertisements, signs and other purposes which is designed to deploy the advertisement or display at an elevated location and yet can accommodate easy change or replacement of the advertisement or display without the need for steps, ladders, hoists, or the like to move workers to the elevated position of the display. On the contrary, the present invention can provide a display structure wherein the advertisement or display sign is deployed in use at an elevated location, the structure providing means for lowering the advertisement to ground level when it is to be changed or replaced.  
           [0007]    The disclosed structure also has utility in providing a mounting arrangement for other moveable panels such as overhead doors and the like. In one application the disclosed mechanism can be used to provide an overhead door for use as a so-called dock door in warehouses. Trucks and tractor trailers making deliveries and pick-ups from the warehouse are backed up to the dock door and goods are transferred to and from the warehouse by means of load-handling vehicles such as forklift trucks which can be driven into the truck body. The vertical guide tracks at the sides of the doorway for the overhead doors typically used in this application are very easily damaged through impact by the load-handling vehicles, to the extent that the door can be rendered unsafe to operate or even unserviceable. The structure disclosed herein can be used to provide an overhead door in such installations in which this problem is obviated since there is no fixed guide track at the sides of the doorway at all, but rather there is a retractable guide track at each side which is moved upwardly out of the doorway when the door is opened.  
         SUMMARY OF THE INVENTION  
         [0008]    The invention provides a display structure comprising a panel carrier and a mechanism for controlled displacement of said panel carrier between vertically spaced extended and retracted positions, said mechanism comprising a raise/lower drive system for mounting on a support at an elevated location; elongate flexible restraints connected to said drive system, and also connected to said panel carrier at laterally spaced locations thereon, said drive system being controllable selectively to retract or pay out said elongate flexible restraints to effect movement of said panel carrier between said deployed and retracted positions; a panel display frame for mounting on said support at an elevated location and configured to receive said panel carrier in the retracted position thereof and to display a panel supported on the panel carrier.  
           [0009]    The invention also provides a display structure comprising a panel carrier and a vertically extensible mechanism for controlled displacement of the panel carrier between vertically spaced raised and lowered positions, comprising: a pair of guide tracks each formed by at least first and second elongate linear track sections, each first track section being telescopically extensible with respect to the corresponding second track section; said panel carrier being positioned in a vertically orientation between said extensible first track sections; each said guide track being adapted for anchoring to a support to extend vertically thereon for guidance of said first track sections during movement of said panel carrier between the raised and the lowered positions.  
           [0010]    The display structure can include a flexible display panel connected to the panel support and include an elongate horizontal lower frame member for attachment to the lower edge of the flexible panel. The lower frame member preferably has projecting end sections that cooperate with spring loaded elements in the panel display frame so as to provide a vertical stretching force to the display panel as it approaches the raised retracted position.  
           [0011]    The panel carrier and also the lower frame member may suitably each comprise an elongate horizontal beam of constant profile, e.g. fabricated in aluminium or an aluminium alloy. The beam has a profile that includes a keyhole slot having a narrow entrance portion to accommodate the thickness of the panel and a widened interior portion sized to receive an enlarged marginal edge region of the panel. For example each of the upper and lower edges of the panel may be fixed as by bonding or welding to a generally cylindrical plastic member which is sized to be introduced longitudinally into the enlarged part of the keyhole slot but which is much too large to pass through the narrow entrance portion of the keyhole slot.  
           [0012]    Preferably the two horizontally spaced guide tracks are attached to opposite ends of the panel carrier, each track comprising two or more straight track sections that are telescopically extensible/retractable. The track sections preferably have complementary profiles and have parts that are in sliding engagement with each other. The complementary sliding parts may be of plastic, aluminimum, or other suitable materials which can slide with relatively little frictional resistance. Since the loading imposed by the weight of the panel structure acts essentially in the longitudinal direction of the track sections, i.e. vertically, lateral loading of the track sections is minimal, and therefore there is no need to include rollers to achieve smooth sliding engagement between the cooperating track sections.  
           [0013]    The display structure of the invention is especially suitable for providing a mechanism for displaying an advertising panel or publicity banner in an elevated location e.g. on the side of a building, or on a free-standing support. In this case the panel structure comprises a framework that is carried between the laterally spaced guide tracks, the framework being adapted for attachment thereto of an advertising panel, or other display. The arrangement is particularly well suited to supporting flexible advertisement sheets or displays since the framework can be adapted to tension the panel slightly to maintain it in a taut vertical orientation. In this application the deployed position of the mechanism is with the guide track sections retracted so that the panel or the like is supported between them is displayed at an elevated position on the mounting structure. When it is time to remove or replace the panel, it is simply necessary to extend the mechanism to bring the panel close to the ground surface where it may be readily removed and replaced by an operative who has no need for ladders or other specialized equipment.  
           [0014]    The display structure preferably includes a vertically oriented frame for mounting on the vertical support surface, the frame defining a vertical pocket having an open ended lower side into which the display banner is movable vertically. The sides and horizontal upper parts of the frame have flanges or the like which overlie and screen the guide tracks in the vertical and upper edges of the panel carrier. Vertical movement of the panel carrier on the extensible tracks is effected by a powered drive, in the preferred embodiment this comprising a driven shaft that is mounted horizontally in the upper frame member and which is connected to the panel carrier through cables connected through the opposite ends of the latter. Rotation of the shaft in one direction permits the panel carrier to descend under the force of gravity, and rotation of the shaft in the opposite direction causes the panel carrier to rise. Power may be supplied by an electric motor or the like within the shaft, and by this means the panel carrier can readily be moved between its elevated display position and its lowered position adjacent to the grounds surface.  
           [0015]    The display structure is also susceptible of application in providing displays or advertising panels in a free-standing manner. In this application the track sections anchored to the mounting are fixed vertically at ground level. In the retracted position the panel or display is therefore at ground level, but can be raised to a selected height by extension of the track structure. In all applications the track structure can include two or more extensible track sections. In ground mounted arrangements as described, it is necessary to include a cable and pulley structure or other electrical or hydraulic drive means to effect upwards extension of the track sections.  
           [0016]    For a door installation the panel structure is a vertically movable door carried between guide tracks which are anchored to a wall or other elevated support above the doorway. The telescopically extensible track sections provide guideways for the door in moving between its retracted (raised) position wherein the doorway is open and its deployed (lowered) position wherein the doorway is closed. It will be understood therefore that when the door is in the raised position the doorway is totally unimpeded, and in particular there are no door guide tracks at the sides of the doorway in a position where they would be vulnerable to impact. Thus applicant&#39;s vertically extensible mechanism provides a structure that is eminently well suited for the provision of dock doors, completely obviating the problems as discussed above in relation to prior art dock doors.  
           [0017]    Whereas in most applications whether for doors or advertising signs or displays it will be preferable to employ a pair of guide tracks positioned at opposite ends of the panel, in principle there is no reason why one could not use a single centrally mounted guide track, or a pair of guide tracks positioned at intermediate locations in the length of the panel.  
       
    
    
       [0018]    The invention will further be described, by way of example only, with reference to the accompanying drawings wherein:  
         [0019]    [0019]FIG. 1 is a somewhat schematic perspective view showing one embodiment of the display structure as mounted on a building wall;  
         [0020]    [0020]FIG. 2 is a front elevation of the display structure drawn to a somewhat enlarged scale;  
         [0021]    [0021]FIG. 3 is a view similar to FIG. 2 but showing the display structure in an intermediate lowered or extended condition;  
         [0022]    [0022]FIG. 4 is a vertical sectional view to an enlarged scale taken on the line IV-IV in FIG. 2;  
         [0023]    [0023]FIG. 5 is an enlarged horizontal sectional view taken on the line V-V in FIG. 2;  
         [0024]    [0024]FIG. 6 is a fragmentary view taken on the line VI-VI of FIG. 4;  
         [0025]    [0025]FIG. 7 is a somewhat schematic foreshortened view showing a section of an extendible track incorporated in the structure;  
         [0026]    [0026]FIG. 8 is an enlarged view corresponding to FIG. 3 with portions omitted to show a more detailed arrangement of the panel carrier;  
         [0027]    [0027]FIG. 9 is an enlarged cross-sectional view taken on the line IX-IX in FIG. 8;  
         [0028]    [0028]FIG. 10 is an enlarged fragmentary perspective view showing a means for attachment of a panel to said panel carrier;  
         [0029]    [0029]FIG. 11 is a view similar to FIG. 2 showing a preferred modified version of the display structure embodying the invention;  
         [0030]    [0030]FIG. 12 is an enlarged view taken in the direction of the arrow  12  in FIG. 11; and  
         [0031]    [0031]FIG. 13 is an enlarged view taken in the direction of the arrow  13  in FIG. 11. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    As seen in FIG. 1, the display structure  10  is mounted on the front wall  12  of a building  14  and is movable from an elevated position (shown in full lines) to a lowered position (shown in broken lines), in the lowered position the display structure being accessible from a ground surface  15 . As will be more clearly described hereinafter, at the lowered position shown in broken lines in FIG. 1 the display structure  10  is readily accessible at ground level for servicing or for changing or replacing a banner or display carried thereon.  
         [0033]    The display in FIG. 2 is shown in retracted position in front elevation and comprises a banner or the like  16  that is stretched over a supported frame  18  (FIG. 4) that is housed within a frame  20  of inverted U-shape that is secured to the wall  12 . As seen in FIGS. 2 and 3 the frame  20  has a horizontal upper member  22  and two vertically extending side members  24 , the frame being open at its lower edge and surrounding the banner  16  and overlapping it at its upper and vertical side edges.  
         [0034]    The frame  20  is secured to the wall  12  by suitable fasteners such as capscrews or bolts  26  (FIG. 4) passing through apertures in flanges  28  and  30  provided on the horizontal upper frame member  22  and side frame members  24  respectively. The upper frame member  22  has a horizontal top wall  32  and a vertical front wall  34  which as shown in FIG. 4 overlaps the upper edge of the banner frame  18  when the latter is in the retracted display position. Similarly, as best seen in FIG. 5, each of these vertical side members  24  has a first vertical wall  36  which lies at right angles to the flange  30  that lies against the building wall surface  12  and a second vertical wall  38  which lies parallel to the building wall and which has an extent sufficient to overlap the lateral edge of the banner frame  18 .  
         [0035]    As shown in FIG. 5, the front vertical wall  38  of the side frame member  24  is detachable with respect to the lateral vertical wall  36  thereof, being secured thereto by a flexible interengaging detent structure defined by a pair of tongues  40  associated with the front wall  38  and engageable with respective teeth  42  associated with the lateral vertical wall  36 , the components having a degree of resilience to enable the tongues  42  to be passed over the teeth  40  in moving to and from the engaged position shown in FIG. 5.  
         [0036]    Within the horizontal upper frame member  22  is housed a transverse horizontal shaft  44  (see FIGS. 4 and 8) which is rotatably mounted in bearings  46 ,  47  carried on the frame walls  36 . The shaft  44  incorporates therein an electric motor  48  by means of which the shaft can be caused to rotate in its bearings. The motor  48  is of elongate small diameter form as available from Somfy Systems,  47  Commerce Drive, Cranbury, N.J. 08512, U.S.A. One end of the motor is fixedly secured into the bearing  47 , the housing of the motor being rotatable relative to the fixed end and being secured by keys, rivets or screws (not shown) to the tubular shaft  44 . Thus when the motor is energized it drives the shaft to rotate about the axis established by the fixed bearing  47  and the rotary bearing  46 , the motor  48  being selectively driveable in opposite directions of rotation as required.  
         [0037]    As best seen in FIGS. 8 and 9, a pair of spools  50  are mounted on the shaft  44  and fixed to rotate therewith, the spools being located at spaced positions adjacent opposite ends of the shaft  44 . As shown clearly in FIG. 9, each of the spools  50  is of split construction comprising two approximately semi-cylindrical flanged shells  50 . 1 ,  50 . 2  the inner surfaces  50 . 3 ,  50 . 4  of which have a curvature that is matched to the curvature of the shaft  44 . Confronting lugs  50 . 5 ,  50 . 6  on the half shells of the spool  50  are engaged by fasteners in the form of capscrews  50 . 7  which pass through clearance holes in the lugs  50 . 6  and engage in threaded holes in the lugs  50 . 5 . It will be evident that by tightening the capscrews  50 . 7 , the spool half shells  50 . 1 ,  50 . 2  can be securely fastened together and rigidly fixed in non-rotatable fashion with respect to the shaft  44 .  
         [0038]    The banner frame  18  comprises an upper horizontal frame member  52  the opposite ends of which are attached through adjustable eye bolts  54  to respective steel cables  56  which are wound onto the spools  50 .  
         [0039]    The banner frame further comprises a lower rectangular frame section  58  comprising a horizontal upper member  60  spaced above a horizontal lower member  62  and laterally spaced vertical side members  64 , secured together to provide a rigid lightweight rectangular frame section. The frame section  58  is connected to the upper frame member  52  by adjustable lost-motion means. More specifically, adjacent each end of the frame member  52  a bolt  66  extends vertically through aligned clearance holes in the member  52  and also in the upper member  60 , this bolt being fixed with respect to the member  52  by threaded engagement with a nut that is tightened against the underside of the member  52 . The bolt  66  has an extended threaded shank  68  which passes through aligned clearance holes  70  in the horizontal upper member  60  and is engaged on the underside of the latter by a threaded nut  72 .  
         [0040]    From the foregoing it will be evident that the upper horizontal member  52  can be adjusted (to a degree) vertically with respect to the eye bolts  54  and the cables  56  by means of the nuts  55  in threaded engagement with the eye bolts on the underside of the member  52 . By adjusting the position of these nuts along the threaded eye bolts  54  the position of the member  52  relative to the eye bolts can be adjusted vertically.  
         [0041]    In a similar manner, adjustment of the position of engagement of the nuts  72  with respect to the threaded shanks  68  of the bolts  66  will limit the maximum separation between the rectangular frame section  58  and the upper horizontal frame member  52 . As will be appreciated, since the bolt shanks  68  pass through clearance holes  70  in the horizontal frame member  60 , the frame members  52  and  60  can be brought into closer relationship than the maximum separation (shown in FIG. 4) defined by the position of the nuts  72 , this possibility being demonstrated by the position shown in FIG. 8. The position shown in FIG. 4 will occur when the banner  16  in the banner frame  18  is lowered as shown in FIG. 1 into contact with the ground surface  15 . The ground surface will here support the lower frame section  58  so that continued rotation of the shaft  44  in a direction to lower the banner will result in a slight downwards movement of the upper member  52  to the relative position shown in FIG. 8.  
         [0042]    From the above it will be appreciated that rotation of the shaft  44  will be effective through the cables  56  to raise or lower the banner frame  18  and that when the latter is moved away from the position resting in the ground as shown in FIG. 1, the rectangular frame section  58  will be suspended from the frame member  52  with the horizontal upper frame member  60  in engagement with the nuts  72  in the selected adjustment position of the latter. Thus the shaft  44  can be rotated to move the banner frame  18  between the elevated position shown in full lines in FIG. 1 and the lowered position shown in broken lines therein.  
         [0043]    A track structure is provided to guide the banner frame  18  in its movement between the elevated and lowered positions. The track structure comprises telescopic track arrangements  74 ,  76  provided at respective ends of the banner frame. These track arrangements  74 ,  76  are substantially mirror images thereof and operate in an identical manner and therefore only one of them will be described.  
         [0044]    As seen in FIG. 3, each telescopic track arrangement includes four track sections  78 ,  80 ,  82  and  84  respectively, these sections being telescopically extensible and retractable in the vertical direction to guide the banner  16  for movement between the retracted raised display position, and the lowered position shown in broken lines in FIG. 1. The top track sections  78  are fixed to the vertical walls  36  of the side frame member  24  by fasteners  86  as seen in FIG. 5, and the lower track sections  48  are likewise fastened to the side members  64  of the frame section  68  also as illustrated in FIG. 5.  
         [0045]    As shown in FIGS. 5, 6 and  7 , the track sections  78 ,  80 ,  82  and  84  are of complementary profile which profile has an extended dimension D (FIG. 5) in the vertical plane at right angles to the wall  12 , this dimension being more than twice the dimension W (FIG. 5)of the track sections in a vertical plane parallel to the wall. While for reasons of strength and stability it is desirable to have the dimension D relatively large, the dimension W should be reduced as much as possible since this helps to reduce the width of the front wall  38  of the frame  20 , this being desirable to increase the visual impact of the banner  16  which will be reduced by a frame that is unnecessarily bulky.  
         [0046]    The top track section  78  and each of the second and third track sections  80  and  82  have profiles that define an oppositely directed pair of smoothly rounded longitudinal grooves  88  whereas the bottom track section and each of the intermediate track sections  80  and  82  have profiles that define a pair of oppositely directed elongate rounded ribs  90 . As is evident from FIGS. 5, 6 and  7 , the ribs  90  of one track section are arranged in close sliding engagement with the rounded grooves  88  of the next adjacent track section.  
         [0047]    At least the interengaging sliding surfaces of the elongate grooves  88  and ribs  90  are of a low-friction material sufficient to ensure smooth extension and retraction movement of the telescopic track arrangement  74 ,  76  during manipulation of the device. However since there is minimal lateral loading between the telescoping track sections, there is no need to provide roller bearings or the like. The track sections  78 ,  80 ,  82 ,  84  are conveniently formed as extrusions in aluminum or aluminum alloy.  
         [0048]    The extent to which adjacent ones of the track sections can be extended or retracted relative to one another is delimited by abutment pins. In the raised display position, see particularly FIG. 6, the track sections  78 ,  80 ,  82  and  84  are fully telescoped and fully retracted with respect to each other (FIG. 6) so that all are contained within the height of the frame  20 . FIG. 6 shows that the track sections  78 ,  80 ,  82 ,  84  are successively slightly sorter in length. In the lowered position shown in broken lines in FIG. 1 the track sections are fully extended with respect to one another. However in the lowered position there is still a degree of overlap between each track section and each adjacent lower track section since this is necessary to maintain a degree of rigidity of the track arrangements  74 ,  76  against laterally directed forces which might arise, e.g. through wind action. Thus, a first detent  92  near the upper end of each of the track sections  80 ,  82  and  84  is positioned to contact a second detent  94  positioned in confronting relationship to the first detent at a position spaced above (e.g. by 10 to 12 inches) the lower end of the respective adjacent track section  78 ,  80  and  82 . Thus when the track arrangements  74 ,  76  are extended upon lowering the banner  16 , the degree to which the track sections can be extended relative to one another is limited by interengagement of the respective detents  92 ,  94 . Furthermore, the detents  92  on the track sections  80 ,  82  project through the respective track section to act as lift detents. These lift detents are positioned to be engaged by the upper end of the next adjacent lower track section  82 ,  84  during raising of the banner  16 . The arrangement of the detents  92  and  94  are shown more clearly in FIG. 7 which illustrates one of the intermediate track sections  80 ,  82 . Each of these track sections has its upper end a detent  92  which has portions projecting on opposite sides of the track section, portion  92 . 1  being designed for engagement with the detent  94  of the next higher track section and portion  92 . 2  being positioned for engagement by the upper end of the next lower track section during raising of the banner. The uppermost track section  78  that is fixed in the frame  20  includes only the detent  94 , and the lowermost track section  84  that is affixed to the frame of the banner  16  includes only the portion  92 . 2  of a detent  92 .  
         [0049]    From the position shown in FIG. 3, when the shaft  44  is rotated to raise the banner  16 , the lower track sections  84  will move upwardly sliding freely within the intermediate track sections  82  until fully retracted whereupon the upper end  8  of the lower track section will engage the lift detent of the intermediate track section  82  so that these track sections will then travel in unison upon further lifting movement. Likewise, when the intermediate track sections  82  are fully retracted upwardly, their upper ends will engage the lift detent at the upper end of the respective next intermediate track section  80  causing the three lower track sections to move upwardly together. In the fully retracted position all the track sections are fully telescoped and the banner  16  is positioned within the frame  20 .  
         [0050]    The banner  16  itself may simply comprise a printed sheet of flexible material such as plastic having the desired information or pictorial or printed material thereon. The flexible banner  16  is connected along its upper edge to the upper horizontal frame member  52  and connected along its lower edge to the horizontal lower frame member  62 , the connection being by means of fastener clips  102  which can be slid longitudinally into undercut channels  104 ,  106  in the horizontal frame members  52  and  62  respectively. The clips  102  have bendable arms  108  which can be passed through slits or apertures (not shown) along the upper and lower ends of the banner  16  and then folded over to securely retain the associated edge of the banner with respect to the channels  104  and  106 .  
         [0051]    The vertical dimension of the banner  16  is matched to the spacing between the channels  104  and  106  such that when the banner is raised off the ground, it is held taut by the weight of the rectangular frame section  58 . To achieve this effect the positions of the nuts  72  along the threaded shanks  68  of the bolts  66  are adjusted so that the horizontal upper member  60  of the frame  58  does not engage and become seated on the nuts  72  until the banner  16  has been stretched taut. In this way it can be arranged that the flexible banner  16  does not exhibit any unsightly wrinkles or the like when it is raised to the display position. The stretching load on the banner can be varied both by adjusting the position of the nuts  72  and by adjusting the weight of the lower frame  58 .  
         [0052]    When the banner is to be removed or replaced, it is lowered from the display position to the ground position as indicated in FIG. 1. Upon reaching the ground position the banner can be relieved of stress by lowering the frame member  52  slightly with respect to the member  50 , whereupon the banner can readily be detached from the fasteners  102 .  
         [0053]    Numerous alternative methods for achieving the objects of the invention will be apparent from a reading of the foregoing description.  
         [0054]    The components of the frame  20  and the banner frame  18  and the telescopic tracks  74 ,  76  can be made of any suitable material. As with the tracks, the frames  22  and  18  could be made of aluminum or aluminum alloy members. Alternatively all of these components could be made in various compositions of plastics, glass fiber, fiber reinforced plastics etc.  
         [0055]    The banner could of course be in forms other than one of flexible material as discussed above, and in the event that the banner constitutes a rigid sheet, then there would not be any requirement for a lost motion arrangement between the upper horizontal  52  and the lower frame section  58 , and accordingly a unitary frame could be employed. Various means for attachment of the banner to the banner frame  18  other than the specific one described above are possible, e.g. by the use of cords, grommets, hooks, etc. Similarly, means other than the spools  50  and cables  56  could be employed to effect raising and lowering of the banner. For example a motor mechanism could be incorporated into the telescoping track arrangements  74 ,  76 .  
         [0056]    The dimensions of the banner  16  can be varied widely to suit numerous applications as can the length of the track arrangements and the extent to which they can raise and lower the banner. In the particular example illustrated the banner has a dimension of approximately 4 feet by 12 feet and is moved vertically between its upper and lowered positions through a distance of approximately 9 feet using track arrangements each having four track sections of an approximate length of 4 feet, each of the lower track sections  80 ,  82 ,  84  being capable of producing an extension of approximately 36 to 38 inches depending upon the minimum degree of overlap as determined by the detents  94 . The number and configuration of the track sections can be modified to suit any particular installation. For particularly wide or heavy banners or other displays a third suspension cable and spool arrangement could be provided at an intermediate location in the length of the shaft  44 .  
         [0057]    Control of the display structure through operation of the motor can be arranged in any convenient way. Typically, a switch (not shown) will be provided on the exterior or interior of the building wall and will have three positions, one to effect rotation of the motor in a first direction to effect lowering of the structure, a second to effect rotation of the motor in the opposite direction to effect raising of the structure, and a third locked position wherein the motor is de-energized. Alternative means for control of the motor could be provided so that it can be done remotely, e.g. through the use of a microwave or radio link using well known techniques.  
         [0058]    A simplified and preferred configuration of the display structure is shown in FIGS. 11 through 13. As in the previous embodiment, the display structure  110  includes a frame  120  mounted at an elevated location on a surface  112  of a wall. The frame  120  is similar to the frame  20  described in relation to the embodiment of FIGS.  1  to  10  having a horizontal top section, vertical side sections, and an open lower side. The top section and the side sections have flange like extensions  122 ,  124  respectively which overlap respective edges of the banner  116  when the latter is in its raised position.  
         [0059]    As in the previous embodiment the banner  116  is moved between raised and lowered positions by means of flexible straps  156 , (three of which are shown in FIG. 11) which are wound around spools  150  on a horizontal shaft  144  mounted between bearings  146  and  147  in the upper member of the frame  120 . As before, the shaft  144  incorporates an electric motor by means of which it is driven in rotation in one direction or the other as desired.  
         [0060]    The structure of the banner  116  is different in that there is no rectangular frame section, but rather only an upper horizontal frame member  160  and a lower horizontal frame member  162 . However these frame members are not directly interconnected. The form of the frame members appears more clearly in FIG. 12 which shows these frame members to an enlarged scale as having identical profiles, formed as aluminium extrudates. Each frame member  160 ,  162  is of hollow box profile having along one edge a vertically arranged flange  164 ,  166  positioned opposite to a keyhole slot  168 ,  170  formed in the frame member profile and extending throughout the length thereof and having open ends at opposite ends of the frame member. As is clear from FIG. 12, each keyhole slot has a narrow slit-shaped entrance portion  172 ,  174  opening into an enlarged interior portion  176 ,  178 .  
         [0061]    The banner itself comprises a flexible rectangular sheet the upper and lower horizontal edges of which have enlargements  180 ,  182  sized to fit within the widened interior portions  176 ,  178  of the keyhole slots, but much too large to pass through the slot entrance portions  168 ,  170 . These enlargements are suitably formed by wrapping each of the upper and lower marginal regions of the banner  116  to a rod-shaped member such as a plastic rope and bonding these marginal regions to the rod-shaped members, for example by heat welding.  
         [0062]    Thus it will be seen that there is no direct connection between the upper and lower frame members  160 ,  162 , but rather these are only linked through the material of the banner itself so that the lower frame member is in effect suspended from the upper frame member by the banner.  
         [0063]    As seen in FIG. 11, at opposite ends of the lower frame member  162  there are laterally projecting pins  184 ,  186 , these pins being integrally attached to the frame member  162 .  
         [0064]    At the lower end of each vertical part of the frame  120  in a location that is shielded by the side flange  124 , there is a tensioning arrangement  190  for applying a loading tension to the banner  116  when the latter is in its raised deployed position to maintain the banner in taut condition. The tensioning arrangement is best seen in FIG. 13 as comprising a vertically oriented plunger  192  having a widened pocket structure  194  downwardly oriented at its lower end, the plunger being vertically slidable in a guide  196  that is fixedly attached near the lower end of a vertical wall at one side of the frame  20 . The guide  196  defines a hollow interior channel with a closed upper end  198 , and an open lower end through which the plunger  192  extends. Within this channel and compressed between the closed upper end  198  and the upper end  200  of the plunger is a coiled compression spring  202 . It will be envisaged that the plunger  192  is movable vertically from the position shown in full lines in FIG. 13 compressing the spring  202  in the process, the force of the spring  202  varying in proportion to the extent of the upwards displacement of the plunger. In the position shown in FIG. 13 an abutment structure acting between the plunger  192  and the guide  196  prevents the former from passing completely out of the guide in the downwards direction.  
         [0065]    The tensioning arrangement  190  is positioned at each side of the banner  160  to be engaged by the respective pins  184 ,  186  as the banner approaches its fully raised position, this being the position represented in full lines in FIG. 13 indicating the pin  186  moving upwardly into engagement with the pocket  194  of the plunger. From this position, further upwards movement of the banner will cause the pins  184 ,  186  to raise the respective plungers  192  against the force of their springs  202  until the position shown in broken lines in FIG. 13 is reached with the plungers  192  fully retracted. In this position, the force of each of the springs  202  acts on the lower frame member  162  through the respective pins  184  and  186  and applies a vertical tensioning force to the banner  116  to maintain it in taut condition so that it has no tendency to form folds or wrinkles. Furthermore, the force of the compression springs will prevent any tendency for the various parts to rattle or otherwise create noise.  
         [0066]    The strength of the compression springs  202  and the range of travel of the plunger  192  can of course be selected to suit the overall dimensions of the display structure and the composition or material of the banner  116  itself. Typically the parts are dimensioned to accommodate a displacement of the plungers  192  at a magnitude of between about 5% and 10% of the height of the panel  116 .  
         [0067]    When the banner  116  is fully raised as discussed above the motor which drives the shaft  144  is in locked up condition and will hold the banner in position against the force of the springs without any slackening of the banner, until such time as the motor is actuated to rotate the shaft to lower the banner.  
         [0068]    In situations where a supply of electrical power is not available, a mechanical means could be used to control movement of the structure, e.g. a clockwork mechanism or a spring system as used in conventional roller blinds.  
         [0069]    It is also feasible to adapt the disclosed mechanism to provide banner display systems which operate in the reverse mode e.g. in which the operating mechanism is positioned at ground level, and this would be particularly suitable for providing banners and advertisements in situations such as exhibition halls. In this arrangement however it will evidently be necessary to include guide track structure as shown in FIGS.  1  to  10  and provide a floor mounted drive system whether mechanical, electrical or hydraulic to effect raising of the banner to the elevated display system.  
         [0070]    Thus while specific embodiments of the invention have been disclosed in the foregoing and illustrated in the drawings, various modifications in the structure and components are possible and all such are intended to be comprehended within the scope of the appended claims.

Summary:
A vertically extensible mechanism for controlling displacement of a panel such as an advertising sign, moves the structure between vertically spaced raised and lowered positions. The mechanism comprises a pair of vertically oriented laterally spaced guide tracks each having two or more elongate track sections that are telescopically extensible. The panel is carried in a vertical orientation between the guide tracks which are anchored to a mounting to extend vertically thereon. The mounting can be an elevated one, e.g. in a roof structure, or in a building wall above a door opening, or a low level mounting, e.g. on a ground surface or floor. In an alternative arrangement that is particularly suitable for the provision of elevated display signs and banners, the guide tracks are dispensed with and the panel is supported on a plurality of flexible straps or the like which are wound around a shaft extending horizontally at an elevated location. Rotation of the shaft in one direction is effective to lower the panel and rotation in the reverse direction is effective to raise the panel. The shaft can be driven remotely, and for use with flexible panels a tensioning mechanism is provided to ensure that the panel when raised and deployed is in a tautly stretched condition.