Patent Abstract:
The invention relates to a sliding clutch for torsion-limiting force transmission between a reel and a rotating part which have two bearing members disposed concentrically within one another. One of the bearing elements is formed by a circular bearing sleeve which is radially resiliently deformable transverse to its rotational axis. The bearing sleeve and the opposing bearing member abut each other in the region of a circular joint and the force transmission is effected by frictional slaving in the region of the joint. With a view to improving the frictional slaving, a tensioning element is provided on the side of the bearing sleeve opposite the side adjacent the bearing member such that the tensioning element presses against the bearing sleeve to bias the bearing sleeve against the opposing bearing member.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of the U.S. national stage designation of copending International Patent Application PCT/EP01/05671, filed May 17, 2001, which claims the benefit of European Patent Application EP 00119642.7, filed Sep. 8, 2000, the entire contents of which are expressly incorporated herein by reference thereto. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to a sliding clutch such as for a hand-held device for transferring a film from a backing tape onto a substrate.  
       BACKGROUND OF THE INVENTION  
       [0003]     A sliding clutch of this type is described in U.S. Pat. No. 4,891,090 to Lorinez et al. (corresponding to EP 0 362 697 A1). This known sliding clutch is disposed between a rotary drive member for a supply reel with the sliding clutch comprising two bearing members arranged concentrically within one another, one of these bearing members having the form of a round ring and the other bearing member being formed by a hollow cylindrical reel body. The round ring is made up of a plurality of annular segments formed by radial and axial slots which extend axially in one piece from a toothed disc while engaging concentrically in the hollow cylindrical reel body. It is guaranteed that slidable torsional slaving can be achieved by the ring segments pressing radially against the inner shell surface of the hollow cylindrical reel body with a certain amount of tensional force at its free end portions as a result of a prefabricated oversized portion.  
         [0004]     In this known sliding clutch, it is difficult to predetermine the size of the torque at which the transmission force is to be limited. This is caused by the level having to be predetermined during manufacture of the annular segments as they have to be produced with a radially oversized section so that they abut such that they are elastically pushed together with a radial bias at the inner shell surface of the reel body in the mounted position. In doing so, it has to be taken into consideration that even slight angular deviations of the annular segments can lead to a considerable radial change in position of their effective friction surfaces and a predetermined torque restriction can therefore only be implemented within a large tolerance range. In addition, in the known design, one has to expect alterations in tension caused by relatively high stress existing at the connection point between the annular segments and the toothed disc because of the desired small design which, for one thing, is inclined to decrease stress because of the material becoming fatigued and, for another thing, leans towards an unintentional increase or decrease in frictional tension as a result of changes in shape caused by differences in temperature. For reasons connected with handling and the defect-free transportation of the backing tape and the film, it is however desired to achieve as uniform a tension of the frictional surfaces on one another and as uniform a torque slaving as possible.  
         [0005]     U.S. Pat. No. 6,145,770 to Manusch et al. (corresponding to EP 0 883 564 B1) describes a sliding clutch for torque-limiting force transmission between a reel core and a reel for winding up or unwinding a tape which has two rotating parts arranged concentrically within one another, one of which has the shape of an oval ring with an annular wall which is radially elastically deformable towards the rotational axis and where the torsional force is transmitted by frictional slaving between the oval annular wall and the other bearing member provided in the form of a polygon. In this known structure, the ring is severely deformed and a concentric bearing of the rotating parts is not guaranteed either.  
         [0006]     A need exists for improving the frictional slaving of a sliding clutch of the type described above while guaranteeing a simple concentric mounting. A need also exists for the improved torque-limiting transmission of force and to make it easier to predetermine the force more precisely. Furthermore, the sliding clutch should have a long lifetime with the maximum transferable torque of the force transmission not substantially changing over a longer period of time or remaining constant.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is directed to a tensioning element provided between a circular bearing sleeve and a bearing member. The tensioning element is arranged on the side of the bearing sleeve opposite the bearing member such that it presses elastically against the bearing sleeve and is thereby resiliently deformed or bends, thus elastically biasing the bearing sleeve against the bearing member. This creates frictional slaving where the circular bearing sleeve is only very slightly resiliently deformed, namely by the amount of play of the joint, wherein this measurement is just a few tenths of a millimeter and can theoretically be zero so that the radial elastic deforming or bending of the bearing sleeve is also very small and can theoretically be zero. Consequently, the elastic deforming of the tensioning element in the sense described above found in the embodiment according to the invention is also low or non-existent. Changes in tension at the bearing sleeve and at the tensioning element caused by material fatigue are therefore slight and not damaging, thus the desired long product life is achieved. In addition, the frictional surfaces form a simple concentric pivot bearing for the bearing members during sliding of the sliding clutch.  
         [0008]     The effectiveness of the tensional force of the tensioning element can be increased or the necessary tensional force of the tensioning element can be reduced when the tensioning element is formed by a free section of the bearing sleeve which preferably extends in the longitudinal direction of the rotational axis and can be separated from the other part of the bearing sleeve by a joint or gap, especially in the form of a tongue. The partial separation from the bearing sleeve causes the free section to be connected at one end to the bearing sleeve which means that it not only cannot be lost but it is also connected in a radially resiliently flexible manner. The bearing sleeve can comprise one or several free sections which are preferably formed by one or more segments.  
         [0009]     The tensioning element is preferably formed to be ring-shaped. The annular form can serve to hold the tensioning element itself. In addition, the annular form also means that the tensioning element can essentially spread apart or press together one or more free sections or segments distributed around the periphery more or less equally. The tensioning element is preferably formed by a quartered annular spring or a helical spring in the form of a tension or compression spring. Within the boundaries of the invention, the bearing sleeve can be disposed outside or inside the other bearing member. If the bearing sleeve is disposed inside, the other bearing member is also formed by a hollow cylindrical bearing sleeve. If the circular annular wall is disposed outside, the other bearing member can also be formed as a hollow cylindrical bearing sleeve.  
         [0010]     Owing to the low deformation of the bearing sleeve and the tensioning element that follows it, especially when the tensioning element is formed in an annular fashion, frictional tension with a relatively small tolerance can be achieved by prefabricating the associated parts. In addition, the frictional tension remains constant, even after a long lifetime.  
         [0011]     The sliding clutch used in the invention is particularly suitable for torque-limiting transmission of force between a reel and a rotating member of a hand-held device for applying a film from a backing tape onto a substrate. This sliding clutch can be associated to a supply reel or a take-up reel of the handpiece. The sliding clutch used in the invention is ideally suited to such a hand-held device because it has a construction which is small and inexpensive to produce and can be integrated excellently into a hand-held device.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     [Preferred features of the present invention are disclosed in the accompanying drawings, wherein similar reference characters denote similar elements throughout the several views, and wherein:  
         [0013]      FIG. 1  shows a hand-held device for applying a film from a backing tape onto a substrate having a sliding clutch as described in the invention, the hand-held device being situated in its use position and a separable or opened housing of the hand-held device being illustrated open to one side;  
         [0014]      FIG. 2  shows a cross-sectional view along line II-II of  FIG. 1 ;  
         [0015]      FIG. 3  shows a take-up reel in a perspective side view;  
         [0016]      FIG. 4  shows a view similar to that of  FIG. 2 , but in a modified configuration;  
         [0017]      FIG. 5  shows a side view of a tensioning element of the sliding clutch in enlarged form;  
         [0018]      FIG. 6  shows a tensioning element of  FIG. 4  in a modified configuration; and  
         [0019]      FIG. 7  shows a diagram illustrating the stress course versus time. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     The hand-held device referred to as a whole as  1  serves to transfer a film F disposed on a backing tape  2  onto a substrate S, the backing tape  2  being disposed on a supply reel  4  and a take-up reel  5  in a housing  6  of the hand-held device  1 . The housing  6  has an elongated design with an essentially rectangular cross-section and is disposed in an upright position in its functioning position as per  FIG. 1 , which shall be described later. An application member  7  is provided protruding from the housing  6 , this member being arranged in the lower section of the front end of the housing and the backing tape  2  running about it. By pressing the preferably spatula-shaped application member  7  manually on the substrate S while at the same time pushing the hand-held device in the rearwards direction  3 , the lower backing tape section  2   a  can be pulled off the supply reel  4  and is automatically wound back up onto the take-up reel  5  as an upper backing tape section  2   b . In the present exemplified embodiment, the supply reel  4  and the take-up reel  5  are mounted so as to be rotatable about two rotational axes  8 ,  9  extending transversely to the deflection plane E of the backing tape  2 ; these axes are spaced apart from each other in the lengthwise direction of the housing  6  with the take-up reel  5  being disposed behind the supply reel  4 .  
         [0021]     The housing  6  is made up of two housing parts  6   a ,  6   b , the dividing joint  6   c  of which runs in or parallel to the deflection plane E of the backing tape. It is possible for the housing part  6   b , shown for example on the right hand side in  FIG. 2 , to be formed with a shell-shaped peripheral wall  6   d  and the other housing part  6   a  to be essentially flat and fulfilling the function of a lid. The reels  4 ,  5  are rotatably mounted on pivot bearing parts  10   a ,  10   b  which project from the side walls of one of the housing parts  6   a ,  6   b  and are preferably formed by hollow cylindrical bearing sleeves molded onto side walls on both sides.  
         [0022]     Between the reels  4 ,  5 , there is disposed a drive connection  11  with an integrated sliding clutch  12 . The drive connection  11  is formed such that—bearing in mind the respective effective winding diameters of the full and empty reels  4 ,  5 —it drives the take-up reel  5  at such a speed that the backing tape section  2   b  being wound up is always slightly taut. In doing so, the sliding clutch  12  prevents the backing tape  2  from being overstretched and ripping. Once a certain effective drive torque in the drive connection  11  has been exceeded, the sliding clutch  12  activates so that, although the drive connection  11  attempts to drive the take-up reel at a higher speed, it is only driven at a speed corresponding to the speed of the backing tape  2  on the take-up surface. In the present exemplified embodiment, the drive connection  11  is formed by a toothed gearing having two meshing toothed discs  11   a ,  11   b , each of which is rotatably mounted on the pivot bearing parts  10   a ,  10   b  with a small amount of play with a hollow cylindrical bearing sleeve  11   c ,  11   d . The bearing sleeve  11   c  of the toothed disc  11   a  forms the supply reel  4 . The latter is thus rigidly connected to the driving part of the drive connection  11  with the supply reel  4  and the toothed disc  11   a  having a common pivot bearing  13  which is formed by the pivot bearing parts or bearing sleeves disposed concentrically within one another.  
         [0023]     The take-up reel  5  is mounted in a rotatable manner on the driven part of the drive connection  11  by a concentric pivot bearing  14 , in this case on the driven toothed disc  11   b.  The pivot bearing  14  which is provided additionally to the pivot bearing  15  between the toothed disc  11   b  and the housing  6  is formed by two pivot bearing parts engaging concentrically within one another and in particular by hollow cylindrical bearing sleeves. The inner pivot bearing part of pivot bearing  14  is formed by the hollow cylindrical bearing sleeve  11   d  and the outer pivot bearing member is formed by a hollow cylindrical bearing sleeve  5   a  in the form of an annular wall  5   b  on the body of the take-up reel  5 , which wall is circular on at least its inside. The bearing sleeves  11   d,    5   a  extend in opposite axial directions to each other, one extending concentrically beyond the other socket-like with a small amount of bearing play and, in the embodiment exemplified in  FIG. 2 , the bearing sleeve  5   a  of the take-up reel  5  forming the outer bearing member. The bearing sleeve  5   a  is surrounded by an annular groove  5   c  which emerges from the body of the take-up reel  5  on the side facing the toothed disc  11   b  and has an axial depth which stretches over a large proportion of the width of the take-up reel  5  so that the bearing sleeve  5   a  is connected to the radially outer body part of the take-up reel  5  by a side flange wall  17  measuring for example a few millimeters in size.  
         [0024]     The bearing sleeve  5   a  has at least one free section which is separated from the other part of the bearing sleeve  5   a  by a radial gap. This can for example be formed by the wall of the bearing sleeve  5   a  being slit by at least one slot  5   d  extending in an essentially axial direction which can extend as far as the bottom region of the annular groove  5   c  and thus to the proximity of or to the flange wall  17 . The bearing sleeve  5   a  is preferably axially split into segments  5   e  by several slits  5   d  distributed along the periphery. These segments are integrally connected to the take-up reel  5  or the flange wall  17  in the region of their lower ends so that the top ends are radially resiliently flexible.  
         [0025]     The bearing sleeve  5   a  is radially biased against the inner bearing member, in this case the bearing sleeve  11   d , by a tensioning element  18  so that the inner shell surfaces of the segments  5   e  form slide faces which press against the associated bearing member, in this case the inner bearing sleeve  11   d , with the tensional force exerted on it by the tensioning element  18 . This forms the sliding clutch  12  with torque-limiting force transmission between the take-up reel S and the bearing sleeve  11   d  forming a rotary drive part.  
         [0026]     The tensioning element  18  can be a pressure element which acts in a radially elastic way and resiliently deforms the bearing sleeve  5   a  at at least one position, for example at a point-focal position, and presses the bearing sleeve  5   a  against the bearing sleeve  11   d . The tensioning element  18  can also be formed to be annular, exerting a radial force on at least one section of the circumference of the bearing sleeve  5   a.    
         [0027]     In the functioning mode, the driven drive connection part, in this case the toothed disc  11   b,  is driven by the supply reel  4  driven by the tape detachment wherein it carries the take-up reel  5  with it in the rotational direction as a result of the frictional slaving between the bearing sleeves  11   d,    5   a . When the take-up reel  5  confronts the frictional slaving with torque resistance exceeding the tape tension, the sliding clutch activates or goes into action and slides through so that the take-up reel  5  is only carried with a carrying force corresponding to the permissible tape tension and at the tape speed.  
         [0028]     The annular tensioning element  18   a  exerts an essentially uniform radial pressure on all the segments  5   e.  This tensioning element  18  can be formed by a tension or compression element which is elastic in its longitudinal direction, for example a helical spring in the form of an open or closed ring according to  FIG. 4 , the spring ends of which are connected to one another, for example are hooked to one another (tension spring) or are preferably supported on one another (compression spring). The radial force acted upon the segments  5   e  is achieved by a thus formed tensioning ring  18   a  pressing the segments  5   e  together or spreading them apart by virtue of the tensioning ring  18   a  contracting or stretching in the peripheral direction.  
         [0029]     The tensioning ring  18  can also be formed by a spring ring which acts in an elastic manner in a radial direction rather than in a circumferential direction. A spring ring made of resilient material as shown in  FIG. 6  is particularly suitable for this use, this ring having a slot  18   b  running in the transverse direction.  
         [0030]     The radial size of the tensioning element  18  in a relaxed state is to be measured such that the tensioning element  18  exerts the desired tension in a mounted and taut state.  
         [0031]     The tensioning element  18  is preferably located in the outer lengthways half of the bearing sleeve  5   a  or in the free end region thereof, as is shown in  FIG. 2 . To position the tensioning ring  18   a  axially, an annular groove  19  can be disposed in the outer shell surface of the bearing sleeve  5   a  or the segments  5   e . To make it easier to push the tensioning ring  18   a  onto the bearing sleeve  5   a , the bearing sleeve has a slanted or rounded insertion surface  21  on its free end, which, on the segments  5   e , are insertion surface parts. The radial width of the annular groove  5   c  is of such a size that there is a gap between the tensioning ring  18   a  and the groove wall surrounding it.  
         [0032]     The embodiment exemplified in  FIG. 4 , in which the same or similar parts are provided with the same reference numbers, differs from the exemplified embodiment described above in that the bearing sleeve  5   a  and the segments  5   e  are elastically biased radially outwards rather than radially inwards by the tensioning ring  18   a . In this embodiment, the bearing sleeve  5   a  or the segments  5   e  work together with a bearing part surrounding them, this bearing part being formed by a hollow cylindrical bearing sleeve  11   e  which projects axially in a concentric manner from the toothed disc  11   b  and submerges into the annular groove  5   c  made to be the appropriate size with radial play. In this embodiment, the bearing sleeve  5   a  or the segments  5   e  and the bearing sleeve  11   e  form the pivot bearing  14  for the take-up reel  5 .  
         [0033]     In this exemplified embodiment, the annular groove  19  and the insertion surface  21  are arranged on the inside of the bearing sleeve  5   a  or segments  5   e . Between the bearing sleeve  11   e  and the bearing sleeve  11   d  there is arranged an annular groove  22  open at one side. Groove  22  has such a radial width that there is a free space between the tensioning element  18  and the outer shell surface of the bearing sleeve  11   d.    
         [0034]     In the embodiment exemplified in  FIG. 3 , the tensioning ring  18   a  can be formed by a resilient pressure element which acts in its longitudinal direction, for example a compression spring in the form of a helical spring ( FIG. 5 ) or a spring ring ( FIG. 6 ) slit with a slot  18   b , this spring being radially biased outwards.  
         [0035]     The sliding surfaces of the sliding clutch  12  used in the invention abut one another at a round or hollow cylindrical joint  12   a  either directly or with a small amount of play. Only a very small radial movement—or in the case of abutment just the exertion of pressure—is required to achieve the rotational slaving based on the frictional action. Due to the low amount of radial movement, the material of the bearing sleeve  5   a  is stressed just slightly or not at all. No material fatigue or reduction of the frictional action as a result of material fatigue or aging therefore has to be expected. The tension F of a long life is made clear by  FIG. 7  given lifetime t.  
         [0036]     All the parts of the invention, including tensioning ring  18   a  and the tensioning element  18 , can be made of plastic. The tensioning ring  18   a  is preferably made of flexible metal, especially spring steel, so that the favorable spring constants can be exploited.  
         [0037]     To prevent the reels  4 ,  5  from rotating backwards, for example as a result of tensions in the backing tape  2 , one of the two reels  4 ,  5  has an associated return stop (not illustrated) which can for example be formed by a locking pawl (not illustrated) which works together with one of the toothed wheels  11   a ,  11   b.    
         [0038]     In all the exemplary embodiments, it is possible and, with a view to improving the alignment of the slide faces, favorable to arrange an annular recess in the central portion of one and/or the other of the sliding surfaces of the joint  12   a  or to contrast the sliding surfaces Z-shaped to one another as shown by  FIG. 4 . In the latter embodiment, the joining together of the bearing parts is also simplified.

Technology Classification (CPC): 1