Abstract:
The invention relates to a sheet transport device, preferably for arrangement on the sheet-delivery side of a printing machine, including at least two rollers that are axis-parallel with respect to each other and form between them a transport gap for the sheets for a reversible deformation and stiffening of the sheets respectively transported between them. The rollers are such that a sheet which exceeds a specific intrinsic stiffness is able to move the rollers apart against the applied force in order to avoid said sheet&#39;s deformation and/or in order to enlarge the diameter of the second roller, viewed in side elevation of the second roller, a rounded transition has been implemented in at least one section.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     Reference is made to and dual priority claimed from:  
         [0002]     German Application No. 10 2005 013 756.3, filed on Mar. 22, 2005, entitled: PAPER TRANSPORT ROLLER; and  
         [0003]     German Application No. 10 2005 013 757.1, filed on Mar. 22, 2005, entitled: PAPER TRANSPORT ROLLER.  
       FIELD OF THE INVENTION  
       [0004]     The invention relates to a sheet transport device, preferably for arrangement on the sheet-delivery side of a printing machine, specifically an electrophotographically operating printing machine, comprising at least two rollers that are axis-parallel with respect to each other and form between them a transport gap for the sheets. The relative distance between said rollers being variable in that the rollers and/or zones of the rollers can be crossed or staggered relative to each other for a reversible deformation and stiffening of sheets respectively transported between them, and a force being applied toward a magnification or increase of said crossing of the rollers and/or the roller zones, and the deformation of the sheet being pre-specified.  
       BACKGROUND OF THE INVENTION  
       [0005]     A device of the aforementioned type has been disclosed by U.S. Pat. No. 5,653,439. This patent discloses axis-parallel stiffening rollers, whereby their distances can be varied relative to each other, in which case the rollers of one of the axles are spring-biased in the direction toward the rollers of the other axle. This spring bias is intended to ensure that the slippage of the rollers adapts automatically to printing materials having different thicknesses or different weights per unit area. In so doing, all printing materials are deformed, transported, and deposited at approximately the same speed or deceleration.  
         [0006]     When using this device, however, undesirable effects may occur. For example, in particular, a thinner sheet of printing material could potentially not be sufficiently (stiffly) transported out of the inventive device, for example, before its leading edge arrives on a stack of sheets deposited on the delivery side of a printing machine, thus shifting sheets that have already been deposited on the stack, or said sheet could fold over too soon and thus cause a printing material jam; also, a thicker sheet could be irreversibly deformed and its shape or printed image could be damaged.  
         [0007]     Therefore, the object of the invention is to provide a device of the aforementioned type, which ensures sufficient stiffening of the respective sheet, on the one hand; and treats, in particular, thicker sheets in a sufficiently gentle manner, on the other hand.  
       SUMMARY OF THE INVENTION  
       [0008]     In accordance with the invention, this object has been achieved in that the rollers are arranged and configured and the application of force is set or selected in such a manner that a sheet which exceeds a specific intrinsic stiffness is able to move the rollers apart against the applied force in order to avoid said sheet&#39;s deformation.  
         [0009]     Therefore, considering the inventive stiffening device, a sheet is advantageously deformed only then, and only to an extent as is required or desirable for complementing its intrinsic stiffness, while sheets exhibiting sufficient intrinsic stiffness may remain completely undeformed and are transported flat through the device in order to avoid, in particular, damage due to an irreversible deformation of such sheets, this risk being particularly great regarding such sheets. In accordance with the invention this is achieved in that the application of force is adapted thereto in a pre-specified manner to allow the rollers to spread apart far enough in order to eliminate crossing between them altogether, if necessary.  
         [0010]     In so doing, the application of force is adjusted or selected with respect to the weight of the paper per unit area, in particular, when a sheet of paper is concerned. In particular, as regards other materials, another parameter that influences the intrinsic stiffness can be used as criterion, for example, the thickness. In so doing, the type of arrangement of the rollers and/or the application of force can be adapted to the parameter in a non-linear manner, for example, by guiding cams or power-pack staggering.  
         [0011]     In as much as a sheet must not be deformed beginning with a specific weight per unit area, because in the case of such a sheet the risk of irreversible deformation is too great, a guide value for such a sheet may be specifically determined in that the application of force is set or selected relative to the force applied to a sheet having a weight per unit area which is greater than or equal to approximately 220 grams per square meter.  
         [0012]     Likewise, a second, lower guide value can be determined for a sheet which is to be deformed to its maximum in each instance, because said sheet, in addition, must be stiffened by a deformation because its intrinsic stiffness is not sufficient, in that the application of force is set or selected in such a manner that a sheet having a weight per unit area of greater than or approximately equal to 100 grams per square meter is deformed to its maximum.  
         [0013]     A modification of the invention provides that one of the rollers is driven by a shaft, while the other roller follows on its axle, in which case the follow-roller preferably is subject to the application of pressure in the direction toward the driven roller.  
         [0014]     Preferably, force is applied to the roller in the higher location, said roller&#39;s inherent weight contributing to the applied force. The applied force can be set in such a manner that, taking into consideration the inherent weight of the roller to which the force is applied, said applied force corresponds to a weight of approximately 400 grams. Then, in particular, this force is great enough in order to sufficiently stiffen relatively thin sheets and small enough to yield appropriately to the intrinsic stiffness of relatively thick sheets, thus avoiding irreversible buckling of the sheets. If force is applied to the upper roller, its inherent weight must be considered as an increase of force; and if force is applied to the lower roller, its inherent weight must be considered as a decrease of force.  
         [0015]     A further modification of the invention provides that a plurality of rollers is arranged on each of the axles, said rollers being capable of meshing, in which case, specifically a zipper-like meshing of teeth of the rollers is conceivable, whereby respectively one roller of one axis comes into engagement with a gap between two rollers of the other axis. Of course, this meshing may also take place by following another pattern.  
         [0016]     One further modification which claims independent protection and independently achieves the object of the invention is characterized in that two rollers have profiles that are in engagement with each other in the transport gap, whereby the profile of a first roller has a reduced diameter in a central region, while the profile of a second roller has an enlarged diameter in an approximately corresponding region such that the profile engagement can serve for stiffening a respective sheet transported through the transport gap. As a result of this inventive development, it is not necessary to cross or stagger all the rollers relative to each other, but such crossing and staggering may relate to sections of the profiles of individual rollers and thus result in sufficient stiffening of the sheets. In so doing, it is also possible to improve stiffening by a pre-specified optimized roller contour and thus ensure a gentle treatment of the sheets, in particular thicker sheets.  
         [0017]     In accordance with the invention, this object has been achieved in that, in order to enlarge the diameter of the second roller, viewed in side elevation of the second roller, a rounded transition is implemented in at least one section.  
         [0018]     As a result of this, an individual sheet is transported in a gentler manner, but still preferably also better stiffened, in order to push it as far as possible out of the device, so that preferably approximately slightly more than two-thirds of its transported length project freely.  
         [0019]     Considering this inventive roller contour, the respective sheet is transported in a surprisingly simple yet effective manner, not only in a more gentle, but also in a better stiffened manner, this applying, in particular, to sheets having very different formats and/or weights per unit area.  
         [0020]     Preferably, in accordance with the invention, the second roller has a diameter maximum and is provided on both sides of said diameter maximum in at least one section with a rounded transition in order to enlarge the diameter of the second roller, viewed in side elevation of the second roller, in which case, preferably, also the first roller has a diameter maximum, and the rollers are configured symmetrically with respect to a respective diameter extreme.  
         [0021]     It has been found that different possibilities exist for providing an inventive, rounded contour of the second roller. To achieve this, a first advantageous embodiment provides that, in the case of the second roller, the rounded transition bulges toward the outside of the roller. Thus, the contour extends in an essentially convex manner toward the outside. In so doing, the second roller may overall have essentially approximately the shape of a barrel or be essentially spherical. In addition, however, in order to provide a more distinct diameter maximum, a central region may protrude outward approximately in the shape of a tire. Considering each of these described embodiments, tests have shown that such a tire should not be too narrow, in order to avoid creasing of the respective sheet. The width of such a tire, for example, could be within the size range of approximately 7 millimeters. Considering creasing of a sheet, under certain circumstances, the coefficient of friction with respect to the sheet material is also a noteworthy parameter. In conjunction with this it has been found that it is better if the coefficient of friction of the rollers, specifically the second roller, is somewhat lower. Then, creasing of the sheet is insignificant and, as a result of the deformation of the sheet, there is no excessive slippage during sheet transport. In addition, the rollers may have different coefficients of friction or have regions exhibiting relatively different coefficients of friction.  
         [0022]     A second advantageous embodiment of the inventive second roller provides that, in the case of the second roller, the rounded transition is configured in a cheek-like manner or is concavely bulging inward, in which case, preferably inward-bulging and outward-bulging rounded transitions may be provided so that successive transitions following the contour of the second roller preferably have, or result in, the shape of a bell.  
         [0023]     A third advantageous embodiment of the inventive second roller provides that the second roller has at least one bead-like thicker region. As a result of this, the second roller could also be largely cylindrical. Likewise, the second and third embodiments may provide that, in order to create a more distinct diameter maximum, a central region protrudes outward approximately like a tire. For example, the type of contour to be selected could be a function of the material used for the printing material, in which case, specifically in electrophotographic printing, a large spectrum of printing materials may potentially be used, e.g., not only paper but also film materials, for example. The inventive rollers can also be designed for easy exchange and arrangement.  
         [0024]     In order to allow the first and second rollers to be in a certain engagement with each other, the first roller must display a reduction in diameter approximately in the region where the first roller displays an enlargement in diameter, even though it is by no means necessary to achieve gapless meshing. On the contrary, it has even been found that, in particular in the central region, a larger gap between the rollers and thus a larger free space for deforming the sheet can be advantageous.  
         [0025]     In as much as, preferably in the central region, the second roller should have an enlarged diameter and, correspondingly, the first roller should have a reduced diameter, a preferred embodiment of the first roller provides, in accordance with the invention, that the first roller has approximately the shape of a dumbbell. Considering this type of shape, it is particularly easily possible to allow an appropriate gap to be left open in the central region between the rollers.  
         [0026]     The first roller, the second roller, or both rollers, may be assembled of several parts. For example, at least one of the rollers may comprise disks or disk segments, e.g., even having different coefficients of friction and consisting of different materials. Even tires, rings, linings or the like would be conceivable. In this context, it should be said, that the rollers need not necessarily be absolutely rotationally symmetrical.  
         [0027]     In particular, the dumbbell shape of the first roller, could be implemented by two spaced apart rollers, in such a manner, that the central region would be the axle or shaft itself. Even segments of the second roller could optionally spaced apart from each other. In such instances, it is of course possible to speak of several rollers, which, by interacting, form a roll profile of one metal roll, as it were.  
         [0028]     A subsequent development of the invention provides that the first roller has at least one region, which is substantially rounded in a manner approximately complementary to at least one rounded transition of the second roller. Advantageously, this results, at least in the rounded region(s), in gaps for the respective sheets, said gaps having boundaries extending in the same manner and exhibiting consistent width, in order to guide and shape the sheet in an optimal manner specifically in these regions. Considering the second roller, the affected regions may be specifically side regions, which are associated with correspondingly formed running or run-off paths. As provided by a development of the invention, these paths may be located in the regions of the dumbbell heads of the dumbbell shape of the first roller.  
         [0029]     In a preferred embodiment of the inventive device the second roller is the follow-roller.  
         [0030]     Another preferred embodiment of the inventive device provides that the device is configured for inclined upward-oriented transport or such an ejection or delivery of the respective sheet, e.g., at an angle of approximately 22 degrees. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]     Embodiments that could result in additional inventive features, which, however, do not restrict the scope of the invention, are shown by the schematic drawings. They show in:  
         [0032]      FIG. 1 a  first embodiment of rollers out of engagement with each other, in side elevation;  
         [0033]      FIG. 2  said first embodiment in engagement with each other, in side elevation;  
         [0034]      FIG. 3 a  second embodiment of rollers in engagement with each other, in side elevation;  
         [0035]      FIG. 4  said second embodiment during transport of a thicker sheet, out of engagement; and  
         [0036]      FIG. 5 a  third embodiment of an inventive roller as the contour showing an example of dimensions. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]      FIG. 1  shows a first embodiment of a region of an inventive device with rollers  1 ,  2  out of engagement with each other, in side elevation. Rollers  1 ,  2  are arranged opposite each other on axles  3 ,  4  that are parallel to each other and staggered with respect with each other. In so doing, axle  3  can be configured as the driven shaft, which supports the first rollers  1  in a drivable manner, whereas the second rollers  2  may be arranged so as to follow and be freely rotatable on axle  4 . Indicated between rollers  1 ,  2  is a thick sheet  13 , which is driven and transported by the first rollers  1 , whereas the second roller  2  in this case only rolls off the sheet and, in this manner, follow the first rollers  1  and, in so doing, act only as a type of transport boundary for forming a transport gap between the rollers  1  and  2 . In particular this thick sheet  13  is not deformed because such a deformation of a thick sheet  13  could be irreversible.  
         [0038]     In so doing, rollers  1 ,  2 , considering their (in this case, substantially oval) profile, are suitable to wave or deform sheets during transport such that said sheets are stiffened. This is clearly shown by  FIG. 2 , which, in comparison with  FIG. 1 , is meant to show a thin sheet  18  between rollers  1 ,  2 .  
         [0039]      FIG. 2  indicates that the second rollers  2  can be movably supported in axial direction in their respective hubs as indicated by double arrows  17 , or axle  4  itself could be arranged movably in the direction of a double arrow  16 . In addition, a force is applied to the second rollers  2  or to axle  4  in the direction of axle  3 .  
         [0040]     The thin sheet  18  in  FIG. 2  possesses only a relatively low intrinsic stiffness (different from thick sheet  13  in  FIG. 1 ), so that axle  4  may yield to the force exerted by said intrinsic stiffness and the thin sheet  18  is not capable of pushing back the second rollers against this force. Consequently, a wave-shaped maximum deformation of thin sheet  18  occurs during said sheet&#39;s transport between rollers  1 ,  2 . In so doing, rollers  1 ,  2  are meshing in a zipper-like manner with each other, or they are crossed or staggered relative to the respectively adjacent roller on the other axle. In order to avoid such waving in the case of a thick sheet  13 , it is specifically not only necessary to tune the application of force, but it must also be possible to push back the second rollers  2  until they are disengaged, without preventing this by an abutment stop, for example. Therefore, potentially an adjustable guide and/or abutment guide for the second roller  2  and/or its axle  4  is advantageous.  
         [0041]      FIG. 3  shows a schematic view of a second embodiment of inventive rollers in engagement with each other, in side elevation.  
         [0042]     The section of an inventive device shown in  FIG. 3  comprises a first roller and a second roller  2 , which are provided for a sheet transport and are in a certain engagement with each other by means of their profiles in order to (reversibly) deform and thus stiffen sheets transported by said rollers  1 ,  2 . The first roller  1  is rotatably supported by a axle  3 , whereas, the second roller  2  is arranged in a freely rotatable manner on an axle  4  and follows or rotates along with the first roller  1  during the transport of a respective sheet between rollers  1 ,  2 . In so doing, the second roller  2 , or its axle  4 , is arranged again so as to move in the direction of double arrows  16 ,  17  and a force is applied on said roller  2 , or said axle  4 , in the direction toward axle  3 .  
         [0043]     In  FIG. 3 , the second roller  2  has a continuously rounded contour, which leads to a maximally enlarged diameter of the second roller  2  in its central region. In said central region, the second roller  2  has an outward-bulging convex rounded section  5 . On both sides, and symmetrically thereto, the second roller  2  has cheek-like convex inward bulges in regions  6  so that, in side elevation, a type of flat bell shape results in the contour of the second roller  2 .  
         [0044]     In its central region  7 , the first roller  1  features a relative diameter reduction in order to enable an engagement of section  5  of the second roller  2  in this region and, in addition, leave a comfortable gap  12  as free space for bending a respectively transported sheet. To achieve this, the first roller  1  essentially has the approximate shape of a dumbbell and has on both sides, symmetrically adjacent to central region  7 , dumbbell heads  8  having a relatively larger diameter. In the region of said dumbbell heads  8 , the first roller  1  has running and run-off paths  9  for the second roller  2 , which, regarding their contour, are approximately complementary to the cheek-like regions  6  in their associate sections. The inventive device deforms a thin sheet  18  in such a manner that said sheet follows largely the contour of the second roller  2 , as shown in  FIG. 1 .  
         [0045]      FIG. 4  shows the device of  FIG. 3  during the transport of a thick sheet  13 . In  FIG. 4 , the same components have the same reference numbers as in  FIG. 3 .  
         [0046]     Due to its intrinsic stiffness, the thick sheet  13  is able to lift the second roller  2  against a not specifically illustrated application of force and against the force of the weight of the second roller  2  such that thick sheet  13  is transported flat and entirely without being bent between rollers  1  and  2 . In so doing, thick sheet  13  contacts the convex bulge section  5  of the second roller  2  in said roller&#39;s central region, and said sheet moves on the first roller  1  on run-off paths  14  of dumbbell heads  8 , which are located farther outside than run-off paths  9 .  
         [0047]     A sheet of medium thickness would be bent slightly by the second roller  2 , which would be located slightly lower than in  FIG. 4 , namely bent less than the extension of the contour of the second roller  2  in  FIG. 3  and bent more than the thick sheet  13  in  FIG. 4 , and would then, for example, roll off on run-off paths  15  of dumbbell heads  8  of the first roller  1 , which are provided between run-off paths  9  and  14 . Run-off paths  9 ,  14 ,  15  need not necessarily be discrete and arranged at an angle with respect to each other. Different lines of contact may result for sheets having different thicknesses and different curvatures on a continuously rounded contour of dumbbell heads  8  of the first roller  1 .  
         [0048]      FIG. 5  shows a third example of embodiment of a second roller  2 . Also, in the case of this second roller  2 , the associate first roller  1  may correspond to the first roller of  FIG. 3 .  
         [0049]     In  FIG. 5 , only the contour (for example, having the shown dimensions) of the second roller  2  has been drawn. The second roller of  FIG. 3  can be divided virtually (or also reality) into a barrel-like base element  10  and a tire-like bead  11 , in which case bead  11 , may be embodied, for example, even by a disk or by a tire. In so doing, the contour of the second roller  2  has convexly bulging regions, which, however, do not feature a continuous transition but have sudden diameter increases on the edges of bead  11 .  
         [0050]     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
       Parts List  
       [0000]    
       
           1 , 2  Rollers  
           3 ,  4  Axles  
           5  Section  
           6  Regions  
           7  Central region  
           8  Dumbbell heads  
           9  Paths  
           10  Element  
           11  Bead  
           12  Gap  
           13  Thick sheet  
           14  Path  
           15  Path  
           16  Double arrow—axial direction in their respective hubs  
           17  Double arrow—axle arranged movably  
           18  Thin sheet