Patent Publication Number: US-6663097-B2

Title: Devices for feeding sheets of a recording medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a United States national phase application of pending German Application Serial No. 100.16 793.4, filed Apr. 5, 2000, and herein claims priority of to the afore-referenced pending application. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable 
     REFERENCE TO A “MICROFICHE APPENDIX” 
     Not applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a device for feeding sheets of a recording medium from a stack to an office machine according to the definition of the species of claim 1. 
     In the case of office machines which process individual sheets of a recording medium, in particular paper sheets, it is necessary to feed the sheets which are kept in a stack individually to the office machine. 
     To do so, it is known that separating rollers can be made to act in a frictionally engaged manner on the top sheet of the stack, pushing the top sheet against separation comers so that the top sheet springs over the separation corners and is separated from the following second sheet of the stack. This single feed by means of separation corners depends greatly on the properties of the sheet, in particular the stiffniess of the sheet. Therefore, this device is suitable only for a relatively narrow range of sheet qualities. 
     The sheet quality, i.e., its stiffness, the paper weight, etc., are less influential in separation and single feed of sheets where pressure is applied over the top sheet of the stack to cause the sheet to form a wave (wave generator), thereby releasing it from the following second sheet of the stack. The top sheet released from the second sheet in this way is at the same time advanced forward away from the stack and sent to the office machine. 
     2. Related Art 
     A device of the generic type defined in the preamble based on this principle is known from German Patent 178,765. With this device, shingling parts made of steel are mounted on a continuously rotating chain and are guided over the top sheet of the stack under pressure and supported by a guide skid. Such shingling parts guided over a sheet under pressure may cause pressure marks and traces on the surface of the sheet. This is a disadvantage especially when working with grades of paper having a sensitive surface, e.g., supercalendered paper. In addition, it is known that rollers which are mounted so they can rotate may be passed over the top sheet as shingling elements. To do so, the rollers are mounted on the periphery of a rotationally driven disk. According to German Patent 205,058, the disk rotates about an axis parallel to the plane of the sheet and perpendicular to the direction of feed. According to German Patent 164,228, the disk is arranged in the same way, and the rollers mounted on its periphery are also spring-mounted radially. According to U.S. Pat. No. 4,165,870, the disk can rotate about an axis perpendicular to the plane of the sheet and the direction of feed, whereby the rollers running in the direction of feed can be brought in contact with the top sheet of the stack by tilting the axis. The use of rotationally mounted rollers as shingling elements reduces the problem of pressure marks and traces, but it cannot completely eliminate it in the case of sensitive paper surfaces. Because of the arrangement of rollers on the periphery of a disk, the rollers engage with the top sheet of the stack only over a very short distance in the direction of feed. Therefore, to generate a flexing effect sufficient to loosen the top sheet, a relatively high pressure of the rollers on the sheet is necessary, but this in turn results in more pressure marks. 
     A device of is disclosed which may enable a wide range of sheet qualities to be separated for single feed and fed to the machine reliably, while preventing most pressure marks on a surface of the sheets. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention is explained in greater detail below on the basis of an embodiment which is illustrated in the drawings, which show: 
     FIG.  1 : a perspective view of the device with the housing removed, 
     FIG.  2 : an exploded diagram of the device, 
     FIG.  3 : a side view of the device, 
     FIG.  4 : a view of the device from the rear end, and 
     FIG.  5 : a top view of the device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The device may use as the shingling elements rollers which are mounted to rotate freely on an axle. The axles are attached at both ends to continuously rotating traction means and are supported on guide skids. This makes it possible to use wide rollers which can press on the top sheet of the stack over their entire width without a tendency to tilt. The rollers may act over a longer distance. This yields an intense flexing effect, even if the contact pressure of the rollers is relatively low. Therefore the device can be used for a wide range of paper varieties, i.e., for papers with a wide range of different stiffniess values and weights. There are fewer pressure marks due to the reduction in the required contact pressure of the rollers. 
     In an advantageous embodiment, the development of pressure marks can be further reduced by the fact that the rollers or the guide skids supporting their axles have two successive and connected sections in the direction of movement of the rollers, namely a first section which approaches the plane of the top sheet, and a second section running parallel to this plane of the sheet. The rollers are first supported by the first section, so that at their periphery they approach the surface of the top sheet at first slowly, then come in contact with this surface gently and apply increasing pressure to the surface of the sheet only with further movement. The intense flexing effect with the full contact pressure of the rollers then takes place in the second section. It has been found that the development of pressure marks can be reduced significantly by this asymptotic action of the rollers on the sheet surface. Therefore, this device is especially suitable for sheets having a highly sensitive surface such as supercalendered grades of paper. Since the rollers do not suddenly come in contact with the surface of the sheet in this embodiment, annoying noise production is also avoided. 
     In addition, the prevention of pressure marks can also be promoted by the fact that the rollers are designed with a slight camber. The contact pressure then decreases continuously from the center of the roller toward its axial ends, and there is no sudden change in contact pressure which would promote the development of pressure marks at the axial ends of the rollers in particular. In addition, the rollers may have a jacket or a shell coating of a soft elastic material to further reduce the development of pressure marks. In an expedient embodiment, the axles of the rollers are mounted on the traction means in such a way that the axles are in a plane in which the traction means exert a tensile force on the axle. This ensures that no tilting moment will be exerted on the rollers due to the tensile force, in particular when the rollers are placed on the sheet. 
     The number of rollers and thus their mutual spacing are selected by taking into account two conditions in particular. First, the distance should be great enough so that the sheet can bulge between the rollers, thus permitting a good flexing effect. Secondly, the distance between the rollers should be only great enough so that two rollers are always sitting on the surface of the sheet. This guarantees that the support of the device on the sheet surface will always be uniform and noise-generating rattling of the device on the stack of sheets is prevented. 
     A flexible safety belt rotating continuously may also be wrapped around the rollers. The rollers may then pass over this safety belt in the same manner as the crawler chain of a track-laying vehicle. The safety belt runs loosely with the rollers as the rollers move, and thus it causes the top sheet of the stack to be entrained. The pressure of the rollers is exerted on the safety belt and acts on the top sheet through this safety belt. The safety belt distributes the pressure of the rollers and also makes it more uniform, thus further reducing sudden changes in contact pressure which lead to pressure marks. 
     To feed single sheets of a recording medium, e.g., paper sheets, to an office machine (not shown in the drawing) such as a printer, a copier or the like, these sheets are kept in a supply stack  10 . Sheets  11 ,  12 ,  13 , etc. are pulled individually from the top of the stack and fed to the office machine (at the right in the diagram in FIG.  1 ). As soon as the top sheet  11  has been shifted a sufficient distance away from the stack, this sheet is picked up by the conveyer rollers (not shown) which convey the sheet  11  further. 
     A device which is provided for separating and feeding of sheets  11 ,  12 ,  13  is placed on the top of the top sheet  11  of the stack  10  and is held in this position by a holder (not shown in the drawing). This device is enclosed in a box-shaped housing  20  which is open on the bottom side facing stack  10 . 
     A supporting part  22  having a plate parallel to the plane of the top sheet  11  is arranged at the bottom of housing  20 . One guide skid  24  is mounted on each of the two longitudinal sides of supporting part  2  running in the direction of feed of sheets  11 ,  12 ,  13 . Guide skids  24  each project beyond the front end (at the right in the drawing) and the rear end (at the left in the drawing) of the supporting part  22 . A bearing hole  26  is provided in the ends of the guide skids  24  projecting above the supporting part  22 . Shafts  28  and  30  are mounted in the bearing holes  26 . Shafts  28  and  30  run parallel to the front and rear transverse edges of the supporting part  22  and project beyond the guide skids  24  on both sides. Deflecting toothed disks  32  are placed on the ends of shafts  28  and  30  and are secured so that they cannot rotate. 
     Continuous toothed belts  34  with internal toothing run as traction means over deflecting toothed disks  32  and engage with the deflecting toothed disks  32 . Toothed belts  34  are held tightly by the deflecting toothed disks  32  and rotate in a vertical plane adjacent to guide skids  24  and outside said guide skids  24 . 
     Bearing bushes  36  are placed on toothed belts  34 . Bearing bushes  36  are slotted axially in their outer area so that two gripping jaws  38  are formed. The bearing bushes are pushed from the side of supporting part  22  onto the toothed belt  34  with these gripping jaws  38 ; the gripping jaws  38  engage in a form-fitting manner with the teeth of the toothed belt  34 , so that bearing bushes  36  are undisplaceably and unpivotably secured on toothed belt  34 . The bearing bushes  36  are designed as a sliding block  40  connected to the gripping jaws  38  facing outward. Sliding block  40  is essentially in the shape of a cube. A bearing bore  42  is shaped in the inside end face of each sliding block  40  facing the supporting part  22 . Bearing bushes  36  with gripping jaws  38  and sliding block  40  are each produced as a one-piece plastic injection molded part. 
     Bearing bores  42  are arranged in bearing bushes  36  in such a way that their axis is in the plane of toothed belt  34  when bearing bush  36  is pushed onto the respective toothed belt  34 . In their crown rim, each deflecting toothed disk  32  has recesses  44  with which the gripping jaws  38  of the bearing bushes  36  placed on the toothed belt  34  can engage when the area of toothed belt  34  which is equipped with a bearing bush  36  passes over the respective deflective toothed disk  32 . 
     In assembly of the device, bearing bushes  36  are placed on the respective toothed belt  34  in such positions that opposing bearing bushes  36  are aligned axially with their bearing bores  42  on the two toothed belts  34 . An axle  46  is inserted into the bearing bores  42  of the opposing bearing bushes  36 . A roller  48  is mounted so it can rotate freely on each axle  46 . Rollers  48  are designed with a slight camber, so their greatest diameter is in the central axial area, with the diameter decreasing toward the axial ends. Rollers  48  extend axially from one bearing bush  36  to the other bearing bush and thus over the entire width of supporting part  22  between guide skids  24 . Rollers  40  are preferably covered or coated with a jacket made of a soft elastic material such as a rubber. 
     The continuously rotating toothed belts  34  are driven by the deflecting toothed disk  32  sitting on the front shaft  28 . Therefore, housing  20  contains an electric motor  50 , with a driven gear wheel  52  that engages with a gearing toothed wheel  54 , which in turn drives the deflecting toothed disk  32 , sitting on its driven shaft. Deflecting toothed disks  32  sitting on the front shaft  28  are driven in this way and in turn drive the toothed belt  34 . Deflecting toothed disks  32  sitting on the rear shaft  30  are entrained by the toothed belt  34  so they run freely. 
     When the toothed belts  34  are driven to rotate by electric motor  50 , the bearing bushes  36  placed on toothed belt  34  slide with their respective sliding block  40  on the upper or lower peripheral surfaces of guide skids  24 . The lower peripheral surface of guide skids  24  facing the stack  10  has two sections in its longitudinal direction, i.e., in the direction of feed of sheets  11 ,  12 ,  13 , said two sections being interconnected, one developing into the other. The first section  56 , i.e., the left section in the drawing, is inclined slightly toward the plane of the top sheet  11  of the stack  10  so that the guide skid  24  maintains a slightly greater distance from the top sheet  11  at its left end than in the middle area of guide skid  24  where the first section  56  develops into the second section  58 . The second section  58  which extends slightly over the right half of guide skid  24  in the drawing is designed to be parallel to the surface of the top sheet  11 . 
     Preferably four rollers  28  are mounted at equal mutual spacing on toothed belt  34 . This guarantees that in any position of toothed belts  34 , two rollers  48  will be on the lower part of the rotating toothed belt  34  facing the stack. 
     Finally, the housing  20  also contains an electromagnetically operable braking device  60 . Braking device  60  is mounted at the rear end of housing  20  (at the left in the drawing). Braking device  60  has a brake element  62  which can move down toward the stack  10  in a process that is controlled by braking device  60 , and then it can sit on stack  10  with frictional engagement. 
     This device may function as follows: 
     After inserting stack  10  into the magazine of the office machine, the device is placed on the top sheet  11  of stack  10 . The position of the device with respect to the plane of the top sheet  11  is secured by its holder. In the vertical direction, the device sits on stack  10  under its own weight. A means for relieving the weight may be provided if necessary to reduce the contact pressure of the device on the stack, or a spring bias tension can increase the contact pressure. 
     To feed the sheets from stack  10  individually to the office machine, electric motor  50  is started to drive the toothed belt  34 , which rotates counterclockwise in the drawing. Rotating toothed belts  34  entrain rollers  48  which are attached to the toothed belts, so the rollers move from the top part of toothed belt  34  around the rear deflector toothed disks  32 . Then rollers  48  reach the bottom side facing stack  10 . Bearing bushes  36  first slide along the first section  56  of the guide skids  24  with the respective sliding block  40 . Since the guide skids  24  are at first a greater distance away from top sheet  11  in this first section  56 , rollers  48  do not yet come in contact with the top sheet  11  immediately after their movement about deflector toothed disk  32 . However, when the rollers then move forward along the first section  56  (toward the right in the drawing), rollers  48  slowly approach the surface of top sheet  11  and are set down gently on this surface. With further movement, the contact pressure of roller  48  on the top sheet  11  increases due to the reduction in distance of guide skids  24  from top sheet  11 . In the area where the first section  56  develops into the second section  58 , the roller has reached its full contact pressure. This contact pressure is maintained over the entire length of the second section  58  of guide skids  24 . In doing so, roller  48  exerts the desired flexing shingling effect on the top sheet  11 . Due to this flexing motion, the top sheet  11  is loosened from the following second sheet  12  and is displaced by the rollers  48  toward the right the direction of feed toward the office machine, as illustrated in FIG.  1 . Since the second section  59  of the guide skids  24  takes at least about half of the length of the guide skids  24  and since four rollers  48  are arranged on toothed belt  34 , this guarantees that one roller  48  will always be in the area of the second section  58  of the guide skids  24  in the rotation of toothed belt  34 . This roller  48  defines the distance of the device from the surface of the top sheet  11 . This guarantees that the device will always be held at the same distance from the top sheet  11  and that no vertical “vibrating” movement of the device will occur due to the transition in engagement from one roller  48  to the next roller  48 . 
     As soon as the top sheet  11  has been displaced due to the flexing shingling motion of rollers  48  so far from stack  10  in the direction of feed that its trailing edge (at the left in the drawing) has pulled out beneath brake element  62  of braking device  60 , the braking device is actuated by means of, for example, optoelectric scanning of the front edge of top sheet  11 . This lowers the brake element  62  so that it then sits on the rear edge of the second sheet  12  which is then exposed, and presses it against the stack  10 . The second sheet  12  is secured by brake element  62  in this way, while the top sheet  11  is conveyed further and is picked up and removed by the downstream conveyer rollers. 
     Optionally, the device may also be lifted up from the top sheet  11  of the stack  10  by means of the braking device  60  as soon as the forward edge of the top sheet  11  is gripped by the downstream conveyer rollers, as described in German Patent 196 41 973 A1, for example. As soon as the top sheet  11  has been removed from the stack and the device is sitting with the rollers  48  on the second sheet  12 , the braking device  60  releases this second sheet  12  which is then the top sheet of the stack  10  so that it can be isolated for single feed and fed then either continuously or in response to an appropriate command in the same way. 
     A continuously rotating safety belt not shown made of a flexible material may also be placed around rollers  48 . The width of the safety belt corresponds to the width of rollers  48 , so that they do not act directly on top sheet  11 , but instead they act on top sheet  11  only through the safety belt. The safety belt is wrapped loosely around the rollers  48  in the manner of a crawler chain with a track-laying vehicle. Then rollers  48  do not run on the top sheet  11  but instead run on the safety belt, which is in turn in contact with the top sheet  11  and is located between the rollers  48  and top sheet  11 . 
     List of Reference Notation 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 10 
                 stack 
               
               
                 11 
                 top sheet 
               
               
                 12 
                 second sheet 
               
               
                 13 
                 third sheet 
               
               
                 20 
                 housing 
               
               
                 22 
                 supporting part 
               
               
                 24 
                 guide skid 
               
               
                 26 
                 bearing holes 
               
               
                 28 
                 shaft 
               
               
                 30 
                 shaft 
               
               
                 32 
                 deflecting toothed disks 
               
               
                 34 
                 toothed belt 
               
               
                 36 
                 bearing bushes 
               
               
                 38 
                 gripping jaws 
               
               
                 40 
                 sliding block 
               
               
                 42 
                 bearing bore 
               
               
                 44 
                 recesses 
               
               
                 46 
                 axles 
               
               
                 48 
                 rollers 
               
               
                 50 
                 electric motor 
               
               
                 52 
                 driven gear wheel 
               
               
                 54 
                 gear wheel 
               
               
                 56 
                 first section of 24 
               
               
                 58 
                 second section of 24 
               
               
                 60 
                 braking device 
               
               
                 62 
                 brake element