Abstract:
A device for successively changing elongated flexible objects from an active viewable position to a non-active, non-viewable position includes a rotatable drum to which the flexible objects are attached, a motor driving the rotatable drum in opposing rotational directions, and a controller unit controlling motor speed and direction. A balancing spring is preloaded when the flexible objects are unwound from the drum, providing a lifting force when the flexible objects are wound up on the drum. By using a freewheeling clutch, preloading only occurs in one rotational direction, the balancing spring freewheeling in the other direction, taking no load. Utilizing a magnetically interactive identification strip the device gains highly accurate information on the position of the flexible elongated objects. By pre-attaching the flexible elongated objects on each other and providing the identification strip on the designated carrier flexible object exchanging the set of flexible elongated objects is made very simple.

Description:
TECHNICAL FIELD 
     The present invention relates to a device and a method for successively changing elongated sheets or similar flexible objects from an active viewable position to a non-active, non-viewable position, said device comprising a rotatable drum to which the flexible objects are attached, a motor arranged for driving the rotatable drum in two opposing rotational directions, and a controller unit for controlling the rotational speed and direction of the motor. 
     BACKGROUND ART 
     In the commercial world of today more and more advertising is made. Stores are using advertisement posters to communicate their messages to the public. However, space is sometimes a limiting factor when it comes to exposing posters. To solve this problem it is known to use devices, which are capable of changing posters, by for instance rotating an “endless” belt or band consisting of many individual posters through a cylinder arrangement. In this fashion one surface may be used to display several different messages or advertisements. 
     However many of the known devices are usually complicated to handle, because of their complex design. For instance it might take a long time and be complicated to change a set of posters for new ones. The complexity with many different parts also contributes to the high cost for such devices. 
     One improved device is described in EP 883 875. This device comprises a drum on which different posters can be wound up and unwound. The posters are attached to the drum with the same distance therein between and by rotating the drum in a certain way and in different directions it is possible to show one poster at a time. A mechanical circuit controls the timing of the drums rotation, even if it is mentioned that it would be possible to use an electrical circuit. However, it is not further described how the electrical circuit could be realised. The mechanical circuit is complex and consists of a lot of different parts. One other aspect of the mechanical circuit is that it is noisy and different timing aspects have to be set in a mechanical way, which make it limited when it comes to set different time intervals. 
     A drawback with the device according to EP 883 875 is that it requires a strong motor when the posters or any other flexible objects become large and thereby heavy. Thus, it is important with a sufficient power supply. A large motor is of course also noisier than a small one. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a device for changing elongated flexible objects, which is much more energy efficient, silent, user friendly and reliable than today&#39;s devices. 
     The above object is according to the present invention solved by that the drum of the device comprises a balancing spring that is arranged to be preloaded during the unwinding of the flexible objects and providing a lifting force when the flexible objects are wound up whilst still allowing the device to retain the functionality of previous devices. 
     The present invention also describes a method for user-friendly attachment of the flexible objects as well as a method for self-calibration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described in more detail in relation to the enclosed drawings, in which: 
         FIG. 1  schematically shows the device for changing elongated flexible objects, partly in cross section. 
         FIG. 2  shows the device according to  FIG. 1 , having posters attached to it. The arrow indicates the preferred direction of a spectator. 
         FIG. 3  shows the device according to  FIG. 1  and  FIG. 2 , but looking at the preferred back side of the posters. 
         FIG. 4  shows a perspective view of the freewheeling balancing spring assembly. One end of the balancing spring  16  is fixed to the end cover  7 . The other end of the balancing spring  16  is connected to the journal  15  via a freewheeling clutch  17 . 
         FIG. 4A  shows a perspective view of the structural design of the freewheeling clutch  17 . 
         FIG. 4B  shows a cross section of the structural design of the freewheeling clutch  17 . 
         FIG. 4C  shows a perspective view of an alternative embodiment of a freewheeling clutch  117 . 
         FIGS. 5 to 10  depict in sequence the process by which the device changes the exposed poster. 
         FIG. 11  shows in detail how the posters may be attached according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiment of the present invention will now be described. First of all the parts comprising the device will be described as depicted in the partly cross sectional view of  FIG. 1 . 
     The device comprises a drum  1  with rotational freedom between two end holding means  2 ,  3 , preferably in the shape of discs. At each end the drum  1  is fitted with end covers  6  and  7  respectively. From a first end holding means  2  a motor holding bar  10  protrudes through the end cover  6 . A motor  11  for rotating the drum  1  of the device is provided inside the drum  1  and is held in place by the motor holding bar  10 . A controller unit  13  for controlling the speed and direction of the motor  11  as well as other aspects of the operation of the device is mounted on the motor holding bar  10 . The motor  11  exerts its torque to the drum  1  via a driving disc  14 . An output shaft  12  from the motor  11  is connected to the driving disc  14  in such a way that when the shaft  12  rotates the driving disc  14  also rotates. At the opposite end of the drum  1  a journal  15  protrudes from a second end holding means  3  through the end cover  7 . The journal  15  is rigidly connected to the second end holding means  3 . A freewheeling clutch  17  is provided towards the end of the journal  15 . A balancing spring  16  is connected to the end cover  7  at one end and to the freewheeling clutch  17  at the other end. 
     The motor holding bar  10  and the first end holding means  2  are fixed connected and may be produced as a single part, e.g. welded. The same applies to the second end holding means  3 , which may be combined with the journal  15  into a single part. In order to minimize friction as the drum  1  rotates bearings  8  and  9  are housed in the end covers  6  and  7 . The end holding means  2  and  3  must not be allowed to rotate more than a small distance with reference to each other and may therefore be directly locked to each other or even produced as a single part. 
     Protruding from the first end holding means  2  is a girder  18  containing a magnet  19  and identifying means  20 . 
     Suspension means  4  and  5 , e.g. in the shape of hooks, may be added to the device in order to facilitate installation from ceiling, wall or a particular stand. The suspension means  4  and  5  engage the holding means  2  and  3 . In order to use the device for its main purpose, flexible elongated objects  100 - 400 , referred to as posters, are attached to the drum  1 , as depicted in  FIGS. 2 and 3 . Expecting that the posters  100 - 400  are fully wound out, one of them will be exposed to a viewer in front of the device. Arrow  80  in  FIG. 2  indicates this viewable direction. In order to provide a means for the controller unit  13  to calibrate the position of the posters or derive other necessary information about the system, an identifiable magnetically attractable object  110 , referred to as identification strip, is attached to at least one of the posters, e.g. the poster  100  as depicted in FIGS.  3 , 5 , 6 , 7 , 8  and  10 . The identification strip  110  may however be integrated into the very fabric of the poster  100 , e.g. by use of special thread or printing ink. 
     The principle of operation will be described below. 
     In order to describe the new functionality introduced by the present invention it is necessary to summarize the main function of changing and displaying posters. This function is in itself not unique to the present invention and can be found in the existing invention, EP 883 875. However the additional new functionality added by the present invention is clearly described below. 
     According to  FIG. 5  poster  400  is in an exposed state. The device is depicted with 4 posters, but the device can easily be used with other numbers of posters attached to the drum  1 . In order to display another poster the device will start to turn the drum  1  counterclockwise around its axis according to the arrow  90  in  FIG. 6  thus winding up the attached posters  100 - 400 . Eventually, as the objects are fully wound up, the one object that was furthest back when starting to wind up, in this case poster  100 , will fall over the top as depicted by arrow  94  in  FIG. 9  and thereby become the front object. As this happens the device reverses the rotation of the drum  1 , winding the posters  100 - 400  down clockwise which is indicated by the arrow  95  seen in  FIG. 10 . This motion continues until the newly exposed poster  100  is fully exposed. The device then stops, exposing the object for an arbitrarily set amount of time after which the cycle repeats for the next poster to be shown and so on. The device can however be interrupted at any time, during any part of the cycle, without affecting the function of the device as long as this does not cause any loss of information regarding the exact position of the posters. For instance it may be preferred to halt the device as the newly exposed poster falls over the top of the drum  1  or pause the unwinding midways. This can be achieved either by direct input from the user or as part of a pre-programmed procedure, but it is outside the scope of this text to describe this any further as it is easily realized by a person skilled in the art. 
     It should be noted that even though the motion consists of both clockwise and counterclockwise rotation the total sum of all rotation has to be counterclockwise with reference to  FIGS. 5 to 10 . In order to successively change the posters the drum  1  is turned a certain amount more counterclockwise than clockwise for every object. For a set of two posters that amount is ½ of a revolution, for a set of three it is ⅓ of a revolution and so on. A prerequisite for this is that the elongated flexible objects  200 - 400  are attached to the carrier flexible object  100  at distances of ½ the drum circumference for a number of two posters, ⅓ the drum circumference for a number of three posters, ¼ for a number of four posters and so on. 
     Below the function of the balancing spring assembly is described in detail. In order to wind up the posters  100 - 400  it is necessary that the motor  11  driving the system produces a lifting force to overcome the weight of the poster  100 - 400 . By introducing a spring  16  that is connected to the drum  1 , via the end cover  7 , at one end and to the journal  15 , via the freewheeling clutch  17 , at the other end it is possible to preload the device in such a way that the force of the spring  16  balances the weight of the posters  100 - 400  to a high degree. The spring  16  is therefore referred to as a balancing spring. When the posters  100 - 400  are completely wound up the balancing spring  16  is not loaded at all, i.e. has no inherent load. As the posters  100 - 400  are wound down the balancing spring  16  is spun and thereby continuously gets preloaded enough to balance the weight of the posters  100 - 400 . Similarly as the posters  100 - 400  are wound up the balancing spring  16  continues to provide this lifting force. 
     This means that instead of having to lift the entire weight of the objects the motor only has to provide enough force for acceleration. Thereby the physical requirements of the motor are reduced significantly, indirectly reducing noise and power consumption as well. 
     The balancing spring  16  is fixed connected to the drum  1  via end cover  7 . At the start of winding down a poster the balancing spring  16  is supposed to provide no lifting force. This also has to comply with the inherent function of the device to successively rotate the drum  1  slightly more counterclockwise than clockwise for every poster changed. Therefore the balancing spring  16  is connected via a freewheeling clutch  17  to the journal  15 . This allows the balancing spring, end cover, drum-package to freewheel counterclockwise without preloading the balancing spring  16  whereas clockwise rotation is clutched meaning that the balancing spring  16  is preloaded. In this way the device is allowed continuous counterclockwise motion whilst still benefiting from having the weight of the posters  100 - 400  balanced. In  FIG. 4  the balancing spring  16  is depicted as a torsion spring as this is the preferred embodiment, but it should be realized that other types of springs may be used to achieve the objective of balancing the weight of the posters. 
     In  FIGS. 4A and 4B  the structural design of the freewheeling clutch  17  is shown schematically. The freewheeling clutch  17  thus constitutes of a so called one way needle clutch. The outer ring  21  is provided with a number of segments  22  on its inner side, said segments  22  defining rolling surfaces for a number of rollers/needles  23  that are included in the one way needle clutch  17 . The segments  22  have a varying distance in relation to the center of the one way needle clutch  17  in the circumferential direction of the outer ring  21 . Therefore, adjacent segments  22  are connected by radial steps  24 . By studying  FIG. 4B  it is realized that when the outer ring  21  is rotated in counter clockwise direction/CCW the rollers  23  abut the steps  24  and the rotation is permitted. If the outer ring  21  is rotated in a direction opposite to CCW the rollers  23  will be jammed between the outer ring  21  and a central cylindrical body  25  of the one way needle clutch  17 . Thus rotation is prohibited. 
     If the balancing spring  16  was directly fixed to both the journal  15  and drum  1 , i.e. no freewheeling clutch was present, it would in order to comply with the incremental counterclockwise rotation be increasingly preloaded in the wrong direction and the device would eventually either break down from destroying the balancing spring  16  or stall due to insufficient motor torque. 
     In  FIG. 4C  an alternative design of a freewheeling clutch  117  is shown. In this connection it should be pointed out that the arrangement shown in  FIG. 4C  is reversed compared to the arrangement shown in  FIG. 4 . Thus, the freewheeling clutch  117  is integrated with the end cover  107  and one end of the balancing spring  116  is in engagement with said freewheeling clutch  117 . The other end of the balancing spring  116  is fixedly connected to the journal  115  at a distance from the end cover  107  that generally corresponds to the length of the balancing spring  116 . The freewheeling clutch  117  comprises a number of bosses  140  distributed around the journal  115 . The bosses  140  comprise an end surface  141  and a sloping surface  142  that extends from the end surface  141  to the inner surface of the end cover  107 . As the posters are unwound from the drum the balancing spring  116  will abut against the end surface  141  of the bosses  140  of the end cover  107  and thereby taking load, contributing a lifting force countering some or all of the weight of the posters. Then as the posters are wound up on the drum this abutment will still be in effect and the balancing spring  116  will continue to provide a lifting force. When the posters are once again fully wound up the balancing spring  116  will reach an unloaded state. Continuing in this winding up direction there are however no bosses to obstruct the movement of the balancing spring  116 . Hence during any further movement in the winding up direction the balancing spring  116  will be free to slide on the sloping surfaces  142  of the bosses  140  and no preloading of the balancing spring  116  will be effected. 
     In order to accomplish the proper function of the device according to the preferred embodiment described earlier we may define the degrees of freedom of the internal parts as follows.
         The end covers  6  and  7  are provided freely rotatable with reference to journal  15  and motor holding bar  10  allowing the integration of ball bearings  8 ,  9  for lower friction or simply relying on sleeve bearings.   The end covers  6  and  7  as well as the driving disc  14  are all fixed connected to the drum  1 . The motor axis  12  is also fixed connected to the drum  1  via the driving disc  14 .   The motor  11  is fixed connected to the first end holding means  2  via the motor holding bar  10  to which also the controller unit  13  may be attached.   The journal  15  and motor holding bar  10  are fixed connected to the first and second end holding means  2  and  3  respectively.   The end holding means  2  and  3  need with reference to each other to allow no more than a few degrees of rotational freedom. This can either be achieved by providing the device with a crossbar or relying on the mounting of the device, i.e. letting the wall, ceiling or other device support restrict the rotation of the end holding means  2  and  3 .   The balancing spring  16  is fixed connected to the end cover  7 . The other end of the balancing spring  16  is via the freewheeling clutch  17  allowed free rotation around the axis of the journal  15  in only one direction.       

     The function of the magnet assembly will be described below. 
     In order to successively change the posters  100 - 400  in a correct manner it is of utmost importance that the reversal of the rotation of the drum  1  occurs at the right position according to  FIGS. 9 and 10 . The posters  100 - 400  can be pre-arranged on the drum  1  for this to be accomplished and the controller unit  13  can be programmed to function according to these fixed positions. This does however require the user of the device to manually calibrate the device to the posters  100 - 400  and leaves the device completely unable to self-correct any shift from this calibration. 
     According to the function of the device, as the end of the poster to be exposed reaches the position on the drum  1  where it will fall over, the rotational direction of the drum  1  is reversed in order to expose this poster. It is necessary that this reversal occurs at a specific point in order to guarantee the function of the device. If the reversal is performed too early the next poster will not fall over and be exposed. If the reversal is too late there is a risk that the succeeding poster will also fall over, compromising the function of the device. The device therefore needs to be calibrated with the posters. The calibration signal can also be used by the controller unit  13  to determine whether the device is functioning properly and take care of any such detected problems should they arise. 
     One such means of calibration is depicted in  FIGS. 3 ,  5 ,  6 ,  7 ,  8  and  10 . An identification strip  110  is attached to one of the posters near or at the end of the poster. The device is fitted with a magnet  19  on the protruding girder  18 . On this girder  18  close to the magnet  19  are means for identifying the end of the poster, referred to as identifying means  20 . As the magnetically attractable identification strip  110  comes into proximity of the magnet  19  it is pulled towards the magnet and the accompanying identifying means  20  as depicted by arrow  91  in  FIG. 6  whereby a signal is sent to the controller unit  13 , indicating that one of the posters is near the top of the drum  1 . There are several different techniques available for constructing the identifying means  20 . They may for instance comprise an inductive sensor or one or more electric contact points, integrate an optic sensor device etc. but by bringing the end of the poster so close to the identifying means  20 , precision and functionality is increased regardless of the method used for identification. 
     As the drum  1  is turning counterclockwise/CCW winding up the posters it will stretch the end of the poster  100  as the identification strip  110  is held back by the magnet  19 . Eventually the poster  100  cannot be stretched any further and is released from the magnet  19  as depicted in  FIG. 8 . This point of release is of very high accuracy and is preferably the one used for calibrating the position of the posters. 
     Both of the signals mentioned above can be used as information for the controller unit  13  to determine the exact position of the posters. However, preferably the latter signal is used since the disengagement point of the identification strip  110  and the magnet  19  can easily achieve far greater accuracy than the engagement point. This is due to the very controlled nature of a stretched poster compared to the uncontrolled nature of an unstretched poster. 
     The device will in this way use the signal in order to determine the correct position at which to reverse the direction of the drum  1 . Preferably this position is slightly after the identification strip  110  has disengaged the magnet  19  in order to ensure that the identification strip  110  is no longer influenced by the magnet and there is no chance of it being pulled back towards the magnet  19  as the rotation of the drum  1  is reversed. 
     For the next poster the position of reversal can easily be calculated by the controller unit  13  by adding ⅓, ¼ drum revolution etc. counterclockwise rotation according to the method described earlier. An identification strip  110  is therefore only necessary on one of the posters. It should however be understood that an identification strip can be attached to each and every of the posters e.g. in order to further enhance reliability of the device. 
     Although the most likely setup is having the identification strip  110  made of a passive material that will interact with the magnetic field of a magnet  19  it is also possible to make an identification strip  110  that is permanently magnetic whereby the magnet  19  can be replaced with a magnetically attractable material, e.g. soft iron. It is also possible to make the entire fabric of a poster or a part of it magnetic by use of special thread or printing ink. Furthermore the magnetic field provided either by the magnet  19  or by the identification strip  110  can be produced by means of an electro magnet having the benefit of being possible to turn on and off. 
     The advantages given to the device by magnetically attracting the posters towards the identifying means  20  can be summarized as improving the cost-efficiency, accuracy and reliability of calibration. It also has a self-cleaning effect as the identification strip  110  is forced to slide across the surface of the girder  18  thereby keeping surfaces free from corrosion or dust. 
     A method for attaching the posters to the device will be described below. 
     The posters  100 - 400  can be attached to the drum  1  in a variety of ways. In one preferred embodiment of the present invention the posters  100 - 400  are attached to each other as a separate package as depicted in  FIG. 11  before being fixed to the drum  1 . The first poster  100  being the carrier for the other posters needs to be a certain amount longer than the other posters in order to achieve proper exposure. The other posters are then attached to this carrier poster  100  at certain distances determined by the diameter of the drum  1  and the total number of posters. 
     Preferably, the posters are attached at the same mutual distance around the drum  1  in order to make it easier to program the controller unit  13  and also enhance the changing of the posters. However, it is also possible to provide the posters at different mutual distances to each other. The posters themselves might also be provided, if necessary, with weights such that the posters always appear in a stretched state. 
     When using a single identification strip  110  it can be provided on any of the posters  100 - 400  in order to achieve calibration of the poster position. By placing it on the carrier poster  100  as depicted in  FIG. 11  it can however fulfill yet another objective. When a user wishes to switch the set of posters  100 - 400  for another set of posters and the principle of a carrier poster  100  is applied it is necessary that the carrier poster  100  is the front-most poster being exposed. The particular carrier poster  100  can be sorted out by the device given that the identification strip  110  is attached to said poster  100 . During calibration as the identification strip  110  is recognized by the device and the poster  100  subsequently is changed to being the front-most poster the user can easily stop the device and efficiently make the desired switch of poster sets. 
     It should be understood that the design of the device can differ from the schematic view of  FIG. 1 . The drum  1  may for instance be made very narrow or even solid forcing the motor and balancing spring mechanisms to be outside the drum  1 . It is however believed to be very advantageous both in a practical, economical and design sense to use the drum  1  as a housing for motor, balancing mechanisms, controller units etc. The balancing spring  16  and freewheeling clutch  17  as well as identifying means  20  and the identification strip  110  can be physically realized in a number of ways but in order to be utilized properly by the device they need to interact with each other in the ways described earlier. It shall be understood that even if the invention has been described with reference to preferred embodiments the invention is not limited thereto. Features from one embodiment may for example be used together with other embodiments. Thus, the features described above may be combined in any desired combination. There are many embodiments and variations that are within the scope of the invention, which are best defined by the accompanying claims. 
     FEASIBLE MODIFICATIONS OF THE INVENTION 
     In the embodiment described above the girder  18  is provided with one magnet  19 . However, within the scope of the present invention it is feasible to have more than one magnet.