Abstract:
A sheet conveyance system has at least one driven conveying shaft, with a variable spacing of the driven conveying shaft from the sheet stack. The driven conveying shaft includes at least one sheet conveyor that acts on the sheet to be conveyed with a friction coating. A toothed wheel is fixedly disposed on the conveying shaft, whereby this toothed wheel is enclosed by an outer ring that supports the friction coating and has an inner toothing constantly meshes with the outer toothing. The partial circle diameter of the toothed wheel is smaller than the inner toothing. A transferred force acts on the outer ring such that it is placed with a contact force onto the sheet. A spacer maintains a fixed spacing between the axis of rotation of the toothed wheel and the axis of rotation of the outer ring.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from German Patent Application No. 10 2004 054 021.7, which was filed on Nov. 5, 2004, and is incorporated herein by reference in its entirety.  
       TECHNICAL FIELD  
       [0002]     The present invention relates to a sheet conveyor for conveying individual sheets.  
       BACKGROUND  
       [0003]     Such a sheet conveyor is described, for example, in the patent application DE 198 44 271 C1. The essential elements of the known sheet conveyor are an outer ring having a friction coating and a toothed wheel of smaller diameter that constantly meshes with the inner toothing of the outer ring. The outer ring is set into rotation by the toothed wheel and placed onto the sheet stack by a force having a force component in order to displace the uppermost sheet of the stack. The contact point of the outer ring on the sheet in reference to the direction of conveyance TR is always behind the engagement point of the driving toothed wheel in the inner toothing of the outer ring so that the sheet is pulled. When the sheet is blocked, the outer ring is raised above the driving toothed wheel, so that the friction force between the friction coating of the outer ring and the sheet to be conveyed is reduced.  
         [0004]     The known sheet conveyor comprises two lever systems, namely a first lever system that enforces the tooth engagement between the toothed wheel and the inner toothing of the outer ring and determines the contact force on the sheet as well as a second lever system that has an effective connection with an optical sensor and serves for detecting the deflection of the outer ring. The contact force of the outer ring on the sheet varies depending on the deflection of the lever and increases continuously. The necessary contact force of the outer ring amounts to approximately IN, thus necessitating a plurality of motor steps until this force is reached. Should the sheet stack be compressed by the contact force, the contact force is reduced and the required contact force of approximately IN decreases.  
         [0005]     A similar device is known from the patent application U.S. Pat. No. 6,193,232 B1.  
       SUMMARY  
       [0006]     The object underlying the present invention is to suggest a sheet conveyor for conveying individual sheets that has a simpler design and thus can be manufactured more cost-effectively and that generates a constant contact force of the outer ring on the sheet in a wide range of the deflection of the conveyor.  
         [0007]     This object can be achieved by a sheet conveyance system for conveying individual sheets on a sheet stack, comprising at least one driven conveying shaft, whose spacing from the sheet stack is variable and that contains at least one sheet conveyor that acts with a friction coating on a sheet to be conveyed, wherein a toothed wheel having outer toothing is fixedly disposed on the conveying shaft, said toothed wheel is enclosed by an outer ring supporting the friction coating, the outer ring having an inner toothing constantly meshes with the outer toothing of the toothed wheel, a partial circle diameter of the toothed wheel is smaller than the inner toothing of the outer ring, a force transferred acts on the outer ring such that the outer ring is placed with a contact force onto on the sheet to be conveyed, and a spacer maintains a fixed spacing between an axis of rotation of the toothed wheel and an axis of rotation of the outer ring.  
         [0008]     The spacer can be disposed inside the outer ring. The conveying shaft as well as a bearing of the outer ring in the spacer can be pivoted with a fixed spacing between one another. The force can be transferred into the outer ring for generating the contact force by means of a lever resting against the outer circumference. The lever can be disposed such that the force is transferred essentially perpendicularly to the sheet to be conveyed. The lever may act together with a sensor and wherein a defined contact force is transferred onto the sheet based on the sensor information when the driven conveying shaft approaches the sheet stack. The sensor can be an optical sensor. The lever can be stressed by the force of a spring whereby the spring can be disposed such that the contact force of the outer ring on the sheet to be conveyed is essentially constant during different deflections of the lever.  
         [0009]     The essential thought of the invention is to provide an enforced coupling between the toothed wheel and the outer ring having a friction coating such that the toothed wheel meshes with the inner toothing of the outer ring independently of the position of the toothed wheel relative to that of the outer ring. A spacer is used to provide the enforced coupling, preferably inside the outer ring. The spacer preferably comprises two spaced receptacles for providing a rotative bearing for the driving conveying shaft of the toothed wheel and a central bearing for the outer ring. Of course, ball bearings can be provided in the receptacles in order to prevent friction between the conveying shaft and the spacer as well as between the bearing, e.g. bearing pin or bearing axle and the spacer. The spacing between the centers of the receptacles corresponds to the difference between the radius of the inner toothing and the radius of the toothed wheel. Since the toothing of the toothed wheel and that of the outer ring are constantly in mesh, a standard toothing can be selected between the toothed wheel and the outer ring.  
         [0010]     The toothed wheel sets the outer ring into constant rotation and the action of a defined force, is placed with a force component onto the sheet to be conveyed in order to generate the sheet conveying force.  
         [0011]     In a preferred embodiment of the present invention, the defined force is transferred into the outer ring for generating the contact force (normal force) by means of a lever, whereby the lever is disposed such that the force is transferred essentially perpendicularly to the sheet to be conveyed. For this purpose, the lever is disposed, for example, parallelly to the sheet stack and rests outwardly against the circumference of the outer ring in a region without any friction coating. By the embodiment of the sheet conveyor according to the present invention, the required contact force, and thus the working point is reached even with a small deflection of the outer ring. An additional advantage is that a compression of the sheet stack due to the contact force of the outer ring has little or no effect on the contact force of the outer ring having the friction coating on the sheet to be conveyed.  
         [0012]     It is expedient to simultaneously design the lever used for the force transmission as a sensor lever that works together with a sensor, particularly an optical sensor, whereby a defined contact force on the sheet is derived based on the sensor information when the driven conveying shaft approaches the sheet stack. Here, the point of contact between the spring acting on the lever and the lever as well as the base suspension point of the spring on a component that is fixed relative to the pivot of the lever are positioned taking into consideration that the distance of the contact point of the lever on the outer ring from the pivot of the lever increases in direct proportion to the deflection of the outer ring from its rest position. The point of contact as well as the base suspension point are selected such that the effective contact force of the outer ring on the sheet to be conveyed is largely independent of the deflection of the outer ring from its rest position. The spring force acting on the lever thus remains almost constant even in wide deflection ranges of the lever. Due to the fact that the contact force is constant, the conveying force that acts on the sheet to be conveyed and that is calculated as the product of the contact force and the friction coefficient between the friction coating and the sheet also remains constant. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The present invention is explained more elaborately in the following description on the basis of a preferred embodiment and the drawings of which:  
         [0014]      FIG. 1  is a schematic illustration of a stacking tray in an office machine for collecting and aligning individual sheets to form a sheet stack,  
         [0015]      FIG. 2   a  illustrates a sheet conveyor with a driven conveying shaft disposed centrally with respect to a sheet,  
         [0016]      FIG. 2   b  is a configuration of two sheet conveyors on the driven conveying shaft disposed symmetrically with respect to the sheet center BM,  
         [0017]      FIG. 3  is an illustration of the function elements of the sheet conveyor in a position for conveying the uppermost sheet on the sheet stack,  
         [0018]      FIG. 4  is a schematic illustration to explain the function of the sheet conveyor,  
         [0019]      FIG. 5   a  is a diagram illustrating the application of the spacing of the sheet conveyor from the sheet  10  as well as the application of the contact force F 1  over the step position of the drive motor in the prior art and  
         [0020]      FIG. 5   b  is a diagram illustrating the application of the spacing of the sheet conveyor from the sheet  10  as well as the application of the contact force F 1  over the step position of the drive motor in the sheet conveyor according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0021]     A sheet-collecting device as an additional device for a printer or for a copier is configured to collect the printed pages from the printer and deposit the pages in sorted form on a stack of up to 3000 sheets, for example.  
         [0022]     In doing so, the sheets may be deposited evenly as individual sheets, or as part of a printing job set which can be collected in a separate collection module of the device. The printing job set can be aligned flush with the edges and, if necessary, can also be stapled as a sheet.  
         [0023]      FIG. 1  illustrates the stacking tray of the stacking module having the function-determining elements.  
         [0024]     An arriving sheet is guided into the sheet guidance channel  5  along the sheet intake line  16  and conveyed by the sheet feeding rollers  4 .  
         [0025]     The sheet conveyor  2  is raised from the sheet stack  9  and is disposed in position  2 ′. The arriving sheet thus slides onto the sheet stack  9 .  
         [0026]     When the rear edge of the arriving sheet has left the sheet feeding rollers  4 , a conveying shaft  1  that is driven by a motor (not illustrated) using a toothed wheel  26 , with the sheet conveyor  2 , is lowered onto the sheet stack  9  and conveys the uppermost sheet  10  on the sheet stack  9  in the opposite direction and up to an alignment edge  8 . In addition to the sheet conveyor, it is also possible to provide a roller having rubberized fingers that is responsible for conveying the sheet  10  over the last section up to the alignment edge  8 .  
         [0027]     Through the automatically limited conveying force of the sheet conveyor  2 , the conveyed sheet  10  can automatically align itself to the alignment edge  8  and is subsequently disposed in precisely the same position as all sheets of the sheet stack  9 .  
         [0028]      FIG. 2  illustrates possible configurations of the sheet conveyor  2  on the driven conveying shaft  1 . FIG.  2   a  illustrates only a sheet conveyor disposed centrally with respect to the sheet, whereas  FIG. 2   b  illustrates two sheet conveyors  2  disposed symmetrically with respect to the sheet center. Conveyors in which the sheet conveyor is disposed asymmetrically with respect to the arriving sheets are also feasible.  
         [0029]      FIG. 3  illustrates the essential functional elements of the sheet conveyor  2 . The figure illustrates the sheet conveyor  2  placed onto the sheet stack  9  in its operating position. A toothed wheel  11  that is disposed fixedly on the driven conveying shaft  1 , meshes at the engagement point  24  with the inner toothing  12 ′ of the outer ring  12 .  
         [0030]     The partial circle diameter of the toothed wheel  11  is markedly smaller than the inner toothing  12 ′ of the outer ring  12 . Thereby the engagement point  24  of the outer ring  12  can move around in relation to the toothed wheel  11 . A lever  14 , which is supported rotatably in pivot  18  and is pre-stressed by a compression spring  15 , lies in a contact point  17  outwardly on the outer ring  12  and transfers a force F onto the outer ring  12 . The lever  14  is disposed parallelly to the sheet stack  9  so that the transferred force F is transferred onto the highest point possible of the outer ring  12  and perpendicularly to the sheet  10  to be conveyed in the outer ring  12 . Here, the compression spring  15  is disposed in such a way that the contact force F 1  of the outer ring  12  on the sheet  10  is essentially constant during the different deflections of the lever  14 . For this purpose, the point of contact  19  of the compression spring  15  as well as the base suspension point  20  on a component that is fixed relative to the pivot  18  must be selected accordingly.  
         [0031]     An enforced coupling is provided between the toothed wheel  11  and the outer ring  12  by using a spacer  27  inside the circumference of the outer ring  12 . The spacer  27  comprises two recesses  28 ,  29  whereby the driven conveying shaft is rotatably supported in the recess  28  and a bearing  30  of the outer ring  12  is rotatably mounted in the recess  29 . The spacing between the axis  31  of the toothed wheel  11  and the axis  32  of the outer ring  12  corresponds to the difference between the radius of the inner toothing and the radius of the toothed wheel  11 . Using the spacer  27 , the toothing of the toothed wheel  11  meshes with the inner toothing  12 ′ of the outer ring  12  independently of the position of the toothed wheel  11  in relation to the outer ring  12 . The lever  14  for applying the force F on the outer ring  12  is simultaneously designed as a sensor lever and it senses the position of the outer ring  12 . A sensor  22  that works together with a sensor flag  21  of the lever  14  detects whether the outer ring  12  is in contact with the sheet stack. If necessary, it can also detect the degree of the deflection of the lever  14 .  
         [0032]     In  FIG. 3  the spacing between the axis  31  of the toothed wheel  11  and the uppermost sheet  10  of the sheet stack  9  is set in such a way that the outer ring  12  having the friction coating  13  rests on the uppermost sheet  10  of the sheet stack  9 . Upon rotation of the driven conveying shaft  1  in the direction of rotation DR illustrated, a sheet conveying force F 2  is generated which moves the uppermost sheet  10  in the direction of conveyance TR.  
         [0033]     In order to attain the correct normal force component F 1  at the contact point  23  of the outer ring  12  on the sheet stack  9 , the spacing of the axis  31  from the uppermost sheet  10  is decreased until the sensor  22  over the lever  14  having the sensor flag  21  detects a predetermined deflection of the lever  14  and thus a predetermined force F exists.  
         [0034]     The basic function of the sheet conveyor  2  is explained on the basis of 4. At the contact point  23  of the friction coating  13 , the contact force F 1  results due to the force F applied perpendicularly to the sheet stack  9 . The direction and the amount of the contact force F 1  is almost identical to the force F transferred using the lever  14 .  
         [0035]     Due to the transmission of the force F perpendicularly to the sheet stack  9  into the outer ring  12 , a compression of the sheet stack caused by the contact force F 1  of the outer ring  12  has no effect on the contact force of the outer ring  12  on the sheet  10  to be conveyed. Thus the conveying force F 2  is also independent of this. An additional advantage is the constancy of the force F 1  in a wide deflection range of the lever  14  and/or of the outer ring  12 .  
         [0036]     As explained earlier, an enforced coupling is provided between the outer toothing of the toothed wheel  11  and the inner toothing  12 ′ of the outer ring  12  using the spacer  27 . They mesh with each other at the engagement point  24 .  
         [0037]     When the toothed wheel  11  is driven via the driven conveying shaft  1  in the direction of rotation DR illustrated, a force having a force component F 3  is generated in the direction of rotation onto the outer ring  12  perpendicularly away from the sheet stack  9 . The force component F 3  generates at contact point  22 , a force component F 2 , which moves the sheet  10  in the direction of conveyance TR.  
         [0038]     The contact force F 1  and the force F 3  are directed oppositely. When the coefficient of friction between the friction coating  13  and the sheet  10  to be conveyed is greater than the coefficient of friction between the sheet  10  to be conveyed and the sheet stack  9 , the force F 3  that is applied through the driven toothed wheel  11  and counteracts the contact force F 1  is always smaller than the contact force F 1 . Through the net magnitude of F 1  a force F 2  always results, which conveys the sheet.  
         [0039]     If the sheet  10  is decelerated, the force F 3 , which is applied via the toothed wheel  11 , increases. Through the increase of the force F 3 , with a constant force F, the force F 1  at contact point  23  is reduced and, via the coefficient friction, also the force component F 2  in the direction of conveyance TR of sheet  10 .  
         [0040]     The friction coating  13  thereby changes from adhering friction on the sheet  10  into sliding friction with reduced frictional force.  
         [0041]     Through the spacing d between the engagement point  24  of the toothing and the contact point  23  between the friction coating  13  and the uppermost sheet  10 , the sheet  10  is always pulled and cannot become jammed when sheet  10  is blocked.  
         [0042]     After the desired number of sheets is deposited onto the sheet stack  9 , the sheet stack  9  can be conveyed further as a set. For this purpose, the conveying shaft  1  is lowered until the friction rollers  25  engage the sheet stack  9 . Here, the outer ring  12  swings into a position of maximum deflection. The friction rollers  25  staple the sheet stack  9  using the counter rollers  3  and convey the sheet stack  9  after the alignment edge  8  moves away in the horizontal direction.  
         [0043]     The diagram in  FIG. 5   a  illustrates the application of the spacing of the sheet conveyor (BW) from the uppermost sheet  10  as well as the contact force F 1  over the step position of the drive motor that drives the conveying shaft  1  in a sheet conveyor of prior art according to the patent application DE 198 44 271 C1. First the sheet conveyor  2  is displaced from an initial position (BWa) that is spaced from the sheet  10  downwards in the direction of sheet  10 . In a step position ST 2 , the outer ring  12  of the sheet conveyor  2  reaches the sheet  10 , due to which the contact force F 1  increases somewhat linearly in an additional downward movement. In prior art, the contact force F 1  increases slowly due to which the outer ring  12  has to be deflected very widely in order to attain the desired contact force of IN. In a step position ST 3  and/or in case of a corresponding contact force F 1 , the sensor is activated via a sensor flag, and a sensor signal (stop signal for the step motor) is emitted. Due to this, the step motor and thus the sheet conveyor  2  slow down. Consequently, the step motor comes to a halt in a step position ST 4 . In the ideal case, the step position ST 4  is identical to a step position ST 4 ′ in which the desired contact force of IN is attained. In a sheet conveyor according to prior art, the sensor has to be adjusted in such a way that it is activated in time before attaining the contact force of IN in order to ensure that the step motor and thus the sheet conveyor  2  come to a halt at the desired contact force of IN in the end position BWe. If additional steps were carried out by the step motor after reaching the step position ST 4 ′, the contact force F 1  would proceed as indicated by the dashed line Fix. Thus the contact force F 1  would increase further and result in damaging the sheet  10 .  
         [0044]     The diagram in  FIG. 5   b  illustrates the application of the spacing of the sheet conveyor (BW) from the uppermost sheet  10  as well as the contact force F 1  over the step position of the drive motor of the conveying shaft  1  in the sheet conveyor according to the present invention. Here also, the sheet conveyor  2  is first displaced from an initial position (BWa), which is spaced from the sheet  10 , downwards in the direction of the sheet  10 . In a step position ST 2 , the outer ring  12  of the sheet conveyor  2  reaches the sheet  10 , due to which the contact force F 1  increases in an additional downward movement of the sheet conveyor  2 . As opposed to the prior art, in the sheet conveyor according to the present invention, the contact force F 1  increases due to the perpendicular force transfer until it corresponds to the desired contact force of IN in step position ST 4 . Even if the sheet conveyor  2  moves further downward, the contact force F 1  does not change, instead it remains constant at IN. In a desired deflection of the outer ring  12 , the sensor is activated due to which a stop signal is emitted to the step motor. The step motor initiates the method of deceleration and comes to a halt in the step position ST 4 ′. In the corresponding path of the sheet conveyor  2  in the direction of the sheet  10 , the contact force F 1  does not change. It remains constant at IN. Due to this, the precise adjustment of the sensor, which was necessary in prior art, can be omitted. If the step motor were to continue to carry out additional steps after the step position ST 4 ′ and if the sheet conveyor  2  were lowered further in the direction of the sheet  10  (dashed line), the force F 1  would continue to remain constant, as illustrated, on the basis of the embodiment of the sheet conveyor according to the present invention.  
       LIST OF REFERENCE SYMBOLS  
       [0000]    
       
           1  Driven conveying shaft  
           2  Sheet conveyor  
           2 ′ Sheet conveyor in a raised position  
           3  Lower pressure shaft with counterrollers  
           4  Sheet feeding rollers  
           5  Sheet guidance channel  
           6  Contact for collected sheets  
           7  Upper limit of the stacking tray  
           8  Alignment edge  
           9  Stack of collected sheets  
           10  Uppermost sheet of the sheet stack ( 9 )  
           11  Toothed wheel with outer toothing  
           12  Outer ring with inner toothing  
           12 ′ Inner toothing of the outer ring ( 12 )  
           13  Friction coating on the outer ring ( 12 )  
           14  Lever for applying a force (F) on the outer ring ( 12 )  
           15  Compression spring for applying the force (F) using the lever  
           16  Sheet intake line  
           17  Contact point of the lever ( 14 ) on the outer ring ( 12 )  
           18  Pivot for the lever ( 14 )  
           19  Point of contact of the compression spring ( 15 ) on the lever ( 14 )  
           20  Base suspension point of the compression spring ( 15 ) on a component  
           21  Sensor flag  
           22  Optical sensor flag  
           23  Contact point of the friction coating ( 13 ) on the uppermost sheet ( 10 )  
           24  Engagement point of the toothing of toothed wheel ( 11 ) and the outer ring ( 12 )  
           25  Friction rollers on the driven conveying shaft ( 1 )  
           26  Drive toothed wheel for the driven conveying shaft ( 1 )  
           27  Spacer  
           28  Recess in the spacer ( 27 ) for the conveying shaft ( 1 )  
           29  Recess in the spacer ( 27 ) for the bearing shaft ( 30 )  
           30  Bearing of the outer ring ( 12 )  
           31  Axis of rotation of the toothed wheel ( 11 )  
           32  Axis of rotation of the outer ring ( 12 )  
          BM Sheet center  
          d Spacing from the engagement point ( 24 ) of the toothed wheels (11) and (12) to the contact point ( 23 ) of the friction coating ( 13 ) on the uppermost sheet ( 10 )  
          DR Direction of rotation of the driven conveying shaft ( 1 )  
          TR Direction of conveyance for the uppermost sheet ( 10 )  
          F Force on the outer ring ( 12 )  
          F 1  Contact force of the sheet conveyor ( 2 ) on the sheet ( 10 )  
          F 2  Sheet conveying force  
          F 3  Force in the engagement point ( 24 ) perpendicularly away from the sheet stack  
          ON The contact force F 1  amounts to 0 Newton  
          IN The contact force F 1  amounts to 1 Newton  
          BW Spacing of the sheet conveyor ( 2 ) from the sheet ( 10 )  
          BWa Initial position of the sheet conveyor ( 2 ) before the start of the movement  
          BWe End position of the sheet conveyor ( 2 ) on the step position (ST 4 )  
          BWx Position of the sheet conveyor ( 2 ) on the step position STx  
          Fix Contact force of the sheet conveyor ( 2 ) on the sheet ( 10 ) on the position STx  
          ST Steps for the step motor that moves the sheet conveyor ( 2 ) in the direction of the sheet ( 10 )  
          ST 1  First step using which the sheet conveyor is moved to the sheet ( 10 )  
          ST 2  Step position in which the sheet conveyor comes into contact with the sheet ( 10 )  
          ST 3  Step position in which the optical sensor ( 22 ) is activated  
          ST 4  Step position in which the desired contact force is achieved  
          ST 4 ′ Stop position for the sheet conveyor ( 2 )  
          STx Random step position