Patent Publication Number: US-6991228-B2

Title: Sheet depositing device

Description:
BACKGROUND OF THE INVENTION 
   This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 02076337.1 filed in Europe on Mar. 29, 2002, which is herein incorporated by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a sheet-depositing device for depositing sheets or sets of sheets fed from a paper processing apparatus sequentially onto a stacking platform and against a registration barrier. The invention relates in particular to a sheet-depositing device provided with sheet catchers. 
   BACKGROUND ART 
   U.S. Pat. No. 4,061,331 discloses a sheet depositing device having a platform upon which documents are sequentially stacked. The apparatus also has document elevatable sheet catchers which form a throat for catching or trapping the leading edge of each document during feeding of the sheets onto the platform. The platform can be raised about its receiving end for providing a base for receiving the documents in essentially the same plane in which they are fed into the apparatus. The sheet catchers have side plates and upswept tops and are slideable upwardly in guides under the influence of incoming documents. During the initial stage of a feeding cycle, the documents are fed onto the platform at a low velocity. By controlling the elevation of the platform during this stage, curling problems are minimized. The sheet catchers extend toward the incoming documents only a sufficient extent to trap the leading edge of each document before the document is totally under the influence of printing station exit rollers. When the leading edge has been trapped, the final stage of the feeding cycle begins and the document is accelerated to a high velocity by the printing station exit rollers. This causes the document to be forced under the sheet catchers and the sheet catchers to be elevated. The frictional force applied by the sheet catchers to the leading edge of the incoming sheet both decelerates the sheet until it abuts with the registration barrier, and prevents bouncing back from the registration barrier. It has been observed though, that the sheets stacked on the depositing platform tend to curl up against the registration barrier and push the sheet catchers further up. Thus, the throat is widened and therefore the leading edge of incoming sheets will not be properly placed into contact with the guide surface of the sheet catchers. Thus, the leading edge hits the registration barrier with a high velocity and tends to bounce back. The sheet is not slowed down in its reversed movement by a sufficient frictional force because it is not in proper contact with the guide surface of the sheet catchers. The result is an untidy stack. 
   U.S. Pat. No. 6,311,971 discloses a sheet depositing device in which individual sheets exiting a printer or other imaging device are moved towards an eccentric member, which rotates in coordination with the element moving the sheet. The eccentric member has a high surface and a low surface. As the sheet reaches the eccentric member, the high surface is located to contact the paper and pushes it downwards. The sheet is then moved into a clamp, the facing surface of which is at an acute angle, which guides the paper downwards. Preferably, the sheet is moved against a first reference surface before it is moved perpendicularly to the first reference surface into the clamp to encounter a second reference surface. The clamp is resiliently mounted lightly so as to allow an entering sheet to push the clamp open. Upon entering the clamp, the sheet encounters the second reference surface. Alternatively, the clamped paper may be pushed perpendicularly to the clamp surface against a reference surface. 
   Both alternatives form a uniform stack of previous and subsequent sheets, which are moved in the same manner. After the movement of a sheet to the clamp member, the eccentric member rotates so that its low surface is towards the paper exit. The low surface does not extend to encounter sheets exiting the printer, so the next sheet can fall to be moved against the clamp and the reference surface as described. This stacking apparatus flattens the curl of the sheet actually being fed onto the platform, i.e. before it has been deposited. It does, however, not solve the above-described problem that occurs when a stack curls up against the registration barrier. Further, it requires an eccentric member driven in coordination with the incoming sheet. 
   DISCLOSURE OF THE INVENTION 
   On this background, it is an object of the present invention to provide a sheet depositing device of the kind referred to initially, which overcomes the above-mentioned problem. This object is achieved by providing a sheet engaging member suspended from the sheet catcher. The suspended sheet engaging member rests on the stack even when the stack is curled up towards the registration barrier and the leading edge of the incoming sheets will be caught by the suspended sheet engaging member. 
   Preferably, the sheet engaging member is freely suspended from the sheet catcher. If required the sheet engaging member can engage the sheets with a higher force, by being resiliently suspended from the sheet catcher. 
   The sheet catcher rests on the depositing platform or the stacked sheets via a roller that allows relative lateral movement between the depositing platform and the sheet catcher without applying any substantial lateral force to the sheets. The roller is preferably shaped as a spherical segment or as a conical frustum for providing a sloping surface guiding the leading edge of incoming sheets under the roller. 
   The sheet engaging member may comprise a tongue, which is preferably pivotally suspended from the end portion of the sheet catcher. The sheet engagement surface of the tongue is preferably sloped to form a throat for trapping the leading edge of incoming sheets. 
   According to one embodiment of the present invention, the sheet engagement surface of the sheet engaging element is covered with a felt fabric having a low friction coefficient in the direction in which the sheets are fed and a high friction coefficient in the opposite direction to improve the deceleration and anti-bounce back characteristics of the sheet catcher. The sheet catcher may be movable along a guide. Also the sheet depositing platform may be movable along the guide. The sheet depositing device may comprise two or more parallel guides, and be provided with a plurality of superposed depositing platforms and sheet catchers. 
   Further objects, features, advantages and properties of the bearing, shell and production methods according to the present invention will become apparent from the detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
       FIG. 1  illustrates one embodiment of the a sheet depositing device in combination with a printing apparatus; 
       FIG. 2  is a side view, in detail, of the sheet depositing device; 
       FIG. 3  is a top view, in detail, of a mechanism for creating stepped stacks; 
       FIG. 4  is a view, in detail, of a sheet catcher; 
       FIG. 5  is a view, in detail, of a sheet catcher when the stack is curled up against the registration barrier; 
       FIG. 6  shows a first embodiment of the sensor arrangement; 
       FIG. 7  shows a detail of the sensor arrangement in a first embodiment; 
       FIG. 8  shows a second and third embodiment of the sensor arrangement; 
       FIG. 9  shows a detail of the sensor arrangement in a second embodiment; 
       FIG. 10  shows a detail of the sensor arrangement in a third embodiment; and 
       FIG. 11  is a side view in detail on the sheet depositing device illustrating height sensors and curl of the stack in the feed side. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Expediently, the sheet depositing device is located at the output of a paper processing machine. The sheet depositing device will hereinafter be illustrated with a paper processing machine in the form of a printing apparatus. It is evident, that the sheet depositing device could be operated together with any other type of paper processing apparatus, such as copiers, imaging devices, etc. 
   The printing apparatus  1  shown in  FIG. 1  comprises means known per se for printing an image on a receiving sheet. These images for printing may be present on original documents which are fed to a scanning station  2  situated at the top of the printing apparatus  1 . Images for printing can also be fed in digital form from a workstation  3  connected via a network  4  to a control device  8  of the printing apparatus  1 . A printing cycle for copying an original set fed via the scanning station  2  is started by actuating a start button  6  on the operator control panel  5  of the printing apparatus  1 . 
   A printing cycle for printing an image set fed via workstation  3  can be started by actuating a start button  7  provided on the workstation  3 , via control device  8  or by actuating a start button  6  provided on the operator control panel  5  of the printing apparatus  1 . 
   In the printing apparatus  1  shown in  FIG. 1 , the sheet transport path  10  forms the path for delivering to a sheet finishing station  11  the sheets printed in the printing apparatus. 
   The finishing station  11  contains a sheet collecting tray  12  (not shown in detail) in which a number of printed sheets belonging to a set can be collected and stapled by a stapler  14 , whereafter discharge roller pairs  13  feed the set to a sheet depositing device  15  forming part of a sheet depositing station  11 . 
   The sheet depositing device  15  shown in  FIG. 2  comprises two superimposed depositing platforms  16  and  17 , upon which sheets are sequentially stacked. The depositing platforms are guided along a pair of guide rails  21 , 22  in the form of two hollow aluminum profiles that serve also as a registration barrier for supplied sheets. Each of the depositing platforms  16 , 17  can be set to a depositing position with respect to the horizontal discharge path formed by the discharge roller pair  13 , to receive sheets discharged by the discharge roller pair  13 . Each depositing platform is provided with two sheet catchers  71  for preventing incoming sheets from bouncing back, as will be described below in connection with  FIGS. 4 and 5 . 
   The vertical displacement of the depositing platforms is effected by a spindle drive system associated with each depositing platforms  16 , 17  ( FIG. 2 ). Each spindle drive comprises a DC motor (not shown) driving a spindle-shaft through a reduction gearing  32 . The spindle-shafts  33  driving the platforms extend vertically next to the depositing platforms. A nut  35  translating relative rotation of the spindle shaft  33  in a vertical movement embraces each spindle-shaft  33  through threaded engagement. Each nut  35  carries respective depositing platforms  16 ,  17 . 
   The vertical position of the selected depositing platforms  16 , 17  or the sheet at the top thereof, is always just beneath the discharge path formed by the discharge roller pair  13 .  FIG. 2  shows the lower depositing platform  16  in a bottom depositing position in which a number of sheets are situated on the depositing platform  16  and the depositing platform  17  thereabove is in a parking position situated above the discharge path formed by the discharge roller pair  13 . 
   Since the depositing platform  17  is adjustable as to height, independently of depositing platform  16 , the depositing platform  17  can be placed in a depositing position without the lower depositing platform  16  needing to be moved further down than the bottom depositing position shown in  FIG. 2 . 
   As a result, the finishing station  11  with the sheet depositing device  15  adjacent the same, is very suitable for being disposed at the top of a printing apparatus  1 , the top of which, with the scanning station  2 , is situated at a normal working height for a standing operator, i.e., at about 100 cm. In the printing apparatus  1  with the finishing station  11  as shown in  FIG. 1 , the removal height for sheets deposited on depositing platforms  16  and  17  is between 100 cm and 160 cm for a total sheet depositing capacity of about 2400 sheets. The sheet depositing level defined by the fixed discharge rollers  13  is at approximately the 133 cm level and this level corresponds to the depositing level at which the bottom depositing platform  16  is in its bottom depositing position. 
   A knocker  51  is provided to produce a smooth-sided stack of sheets by knocking the edged of the stack towards the registration barrier formed by the guide rails  21 ,  22 . An excenter mechanism  52  drives the knocker. The knocker moves rapidly and if necessary repeatedly towards the stack. 
   The depositing device is equipped with a mechanism ( FIG. 3 ) for forming stepped stacks. Hereto, the depositing platforms  16 , 17  move horizontally in a direction perpendicular to the feed direction between two offset positions. The depositing platform is moved to its two offset positions by an electric motor (not shown) coupled to an ordinary crank mechanism for converting the rotary movement of the electric motor into a reciprocating movement. The crank  43  is mounted on the drive shaft of the electric motor and is pivotally connected to one end of a connecting member  41 . The connecting member  41  is shaped as three superimposed rings thus creating a longitudinal flexibility that allows it to function as a resilient member. The connecting member  41  is on its other end pivotally connected to a lever  45 . The lever  45  is provided with a pivot rod  47  at its free end that is engaged by a hook shaped rod  49 . The hook shaped rod  49  is connected to each of the depositing platforms  16 , 17 . The pivot rod  47  extends upwardly along the full lifting height of the depositing platforms  16 , 17 . The hook shaped rods  49  slide along the pivot rod  47  when the depositing platforms  16 , 17  move vertically. Half a revolution of the electric motor corresponds to a movement from one offset position to another. The position of the crank is optically detected by sensor  63 . The signal of sensor  63  is send to the control device  8 . The control device  8 , in turn signals to stop movement, when or shortly before, an offset position has been reached. 
   Each depositing platform, shown in detail in  FIGS. 4 and 5 , is provided with two sheet catchers  71 . The sheet catchers are passively movable upwards and downwards along the guide rails and rest with their weight on the depositing platforms  16 ,  17 , or, on a stack of sheets on the depositing platforms  16 , 17 . A major part of the weight of the sheet catchers  71  rests on the stacked sheets/depositing surface through a roller  73 . The roller  73  allows movement of the sheets relative to the sheet catchers  71  in a direction substantially perpendicular to the feed direction of the incoming sheets without applying a lateral force to the stacked sheets. This insures that the integrity of the stacked sheets remains undisturbed as the depositing platform moves laterally to offset successive sets of sheets from one another as explained with reference to  FIG. 3 . The rollers  73  are preferably shaped as a spherical segment or as a conical frustum for providing a sloping surface guiding the leading edge of incoming sheets under the roller. 
   The sheet catchers  71  are provided with a sloping surface to form a throat for trapping the leading edge of sheets fed onto the depositing platforms  16 , 17 . The sheets are fed with a high velocity towards the sheet catchers  71 . This causes the sheet to be forced under the sheet catchers  71  and the sheet catchers  71  to be elevated. 
   A tongue  75  is pivotally suspended from a pivot axis  76  placed towards the tip of each of the sheet catchers  71 . The freely movable end of the tongue  75  rests on the stacked sheets or on the depositing platforms  16 , 17 . Alternatively, the tongue  75  may be resiliently suspended from the sheet catcher  71  (not shown). The rotational movement of the tongue  75  is limited by a pin  77  fixed to the sheet catcher and protruding into an aperture  78  in the tongue  75 . 
   The sheet engagement surface of the tongue is similarly sloped as the sheet catcher  71 , and preferably slightly curved. The sheet engaging surface of the tongue  75  protrudes from the sheet engaging surface of the sheet catcher  71  so as to engage the leading edge of incoming sheets. The sheet catchers  71  and their tongues  75  guide the leading edge of the incoming sheet down towards the depositing platforms  16 , 17  or the stack on the depositing platforms  16 ,  17  until it abuts with the registration barriers  21 , 22 . 
   The sheet engagement surface of the tongue is covered with a fabric  74  that has a low coefficient of friction in one direction and a high coefficient of friction in the opposite direction. The fabric  74  is arranged on the tongue  75  such that the incoming sheets will be exposed to the low coefficient of friction in the feed direction and to the high coefficient of friction in the opposite direction. The fabric  74  preferred for use with the present invention has sloping bristles of pile fabric. The pile fabric  74  which is preferably used on the contact surface of the tongue  75  is produced with nylons strings woven through a cotton backing to provide the intended front of the fabric, the nylon string extending between stitch apertures which are double the pile length required. These strings are then cut to produce the piles that are “panned”, which is the application of a heated surface to the piles in one sense to produce a slant. As the piles have the same slant, the coefficient of friction in the slant direction is substantially lower than the coefficient of friction in the direction opposite to the slant. 
   The fabric  74  is placed on the tongue  75  with the slant in the paper feed direction. As the sheets are fed with high velocity, they may tend to bounce back from the depositing registration barrier after they abut with the registration barrier which is, in this embodiment formed by surfaces  51  and  52  of the two guide rails  21 , 22 . The high coefficient of friction of the felt fabric in the direction opposite to the feed direction ensures that the sheets do not bounce back, even if they abut with the registration barriers  21 , 22  with some velocity. 
   The sheets stacked on the depositing platform tend sometimes to curl up against the registration barrier (cf.  FIG. 5 ). The curled up stack pushes the sheet catchers further up and thus the throat is widened. In conventional sheet catchers  71  this will create a throat that is too wide to apply sufficient frictional force to prevent the sheet from bouncing back from the registration barrier. Because the tongue  75  is freely movable, its sheet engaging surface rests on the top of the stacked sheets, and will thus also be in contact with the leading edge of incoming sheets when the stacked sheets are curled up against the registration barriers  21 , 22 . 
   As shown in  FIG. 6  through  FIG. 10 , the sheet depositing device is provided with a sensor arrangement for detecting the positions of the depositing platforms  16 , 17  and the sheet catchers  71 , shown in  FIG. 2 . The sensor arrangement comprises an array of active elements  80 , that may be arranged within the guide rails  21 , 22 . In a first embodiment shown in  FIGS. 6 and 7 , the sensor arrangement operates by capacitive detection. The array of active elements  80  is formed by regularly spaced conductive fields  81 . The pitch between the conductive fields depends on the required measuring accuracy. In the exemplary arrangement, a pitch of 5 mm or less proves satisfactory. A non-conductive area is provided between consecutive conductive fields  81 . A strip of conductive material  82  extends in parallel to the array of conductive fields  81 . The array  80  can e.g. be manufactured on a print board. The print board  85  is placed inside guide rail  21 . The upper and lower depositing platforms  16 , 17  and the respective sheet catchers  71  are provided with the passive element of the sensor arrangement in the form of a conductive plate  83 . The conductive plates  83  are arranged such that their horizontal extension is sufficient to cover substantially the conductive strip  82  and a conductive field  81 . The vertical extent of the conductive plates  83  determines the reliability and the resolution of the measured value. A vertical dimension of twice the pitch between the conductive fields proved to give satisfactory results. The conductive plates  83  are guided in guide rail  21 . The conductive plates  83  on the sheet catchers  71  are directly attached to a member of the sheet catcher that protrudes into the guide rail  21 . The conductive plates  83  that move in unison with the depositing platforms  16 , 17  are attached to a carrier member  79  ( FIG. 4 ). The carrier member  79  is guided in the guide rail  21 . A pin  65  extends from the carrier member  79  into a nut  64  in the respective depositing platforms  16 ,  17 . The laterally extending nut allows the depositing platform to move laterally for creating stepped stacks as described above. When the conductive plate  83  moves up or down with the respective depositing platforms  16 , 17  or sheet catcher  71  it moves at a short distance over the conductive strip  82  and alternately over conductive fields  81  and the non-conductive areas between the conductive fields  81 . 
   A sub-control unit  86  measures the electrical capacity between each of the conductive fields  81  and the conductive strip  82 . When the conductive plate  83  covers a conductive field  81  and the conductive strip  82 , the electrical capacity associated with that specific conductive field is much larger than the capacity associated with a non-covered conductive field. The sub control unit  86  measures the electrical capacity associated with each conductive field  81  and converts the signals from the sensor array  80  to a position signal which is sent to the control device  8 . Alternatively, the strip of conductive material  82  may be replaced by a second array of conductive fields extending in parallel with the first array of conductive fields (not shown). In this embodiment the sub control unit  86  measures the capacities of the pairs of conductive fields from the arrays  81  and  82 , respectively. 
   In a second preferred embodiment shown in  FIGS. 8 and 9 , the sensor arrangement operates with the Hall effect. The array of active elements is built up of an array of regularly spaced hall sensors  81 . The upper and lower depositing platforms  16 , 17  and the respective sheet catchers  71  are provided with the passive element of the sensor arrangement in the form a magnet  84 . When the magnet  84  moves up or down with the respective depositing platforms  16 , 17  or sheet catcher  74 , it moves at a short distance over the hall sensors  81 . In the sub control  86  unit the signals from the hall sensors are converted to a positional signal and sent to the control device  8 . 
   In an alternative embodiment shown in  FIGS. 8 and 10 , the sensor arrangement operates with light. The array of active elements is built up of an array of regularly spaced sensors  81 , each comprising an LED  90  and a photocell  91 . The upper and lower depositing platforms  16 ,  17  and the respective sheet catchers  71  are provided with the passive element of the sensor arrangement in the form a reflector  89 . When the reflector  89  moves up or down with the respective depositing platforms  16 , 17  or the sheet catcher  71 , it moves over the sensors and reflects the light emitted by the LED  90  of the sensor that it is facing to the respective photocell  91 . The photocells  89  are connected to the sub control unit  86 , which converts the signals into a positional signal and sends it to the control device  8 . Although the LED-photocell-pairs are shown as vertical arrangements in  FIG. 10 , it will be clear that they may also be arranged horizontally or in any other direction. 
   The catchers  71  will always rest on the stack. Both the position of the sheet catchers  71  and the depositing trays  16 ,  17  are known. Thus, the distance between the depositing platforms  16 ,  17  and the sheet catcher  71  can be used to determine the stack height. This information is used by the control device  8  to determine when a depositing platforms  16 , 17  is full, e.g. to change to the other depositing platforms  16 , 17 , or when both depositing platforms are full, to issue an alarm that the stacking device needs to be emptied. 
   Height detectors as shown in  FIG. 11  ensure that the upper edge of a stack of deposited sheets on the active depositing platforms  16 ,  17  is always at the correct height to receive a new sheet from the discharge roller pair  13  by adjusting the position of the depositing platforms  16 ,  17 . The height detectors are formed by two superimposed sensors. One sensor comprises a pair of LEDs  93 , 93 ′ and a single photocell  95 , and the other sensor comprises a pair of LEDs  94 , 94 ′ and a single photocell  96 . Other numbers of photocells may be contemplated, e.g. one photocell for each LED, or a single photocell for all four LEDs (that would then be operated in a phase-shifted pulsated manner). The pair of LEDs  93 , 93 ′ ( 94 , 94 ′) of the respective sensor direct a substantially horizontal light bundle from the feed side of the stack towards the respective photocell  95  ( 96 ) at the registration barrier side of the stack. The LEDs  93 , 93 ′ ( 94 ,  94 ) in one pair are spaced laterally apart. The respective photocell  95  ( 96 ) is arranged in the lateral midpoint of the stack. The LEDs  93 , 93 ′ ( 94 ,  94 ′) therefore direct two light beams diagonally over the stack towards each of the photocell  95  ( 96 ). The output of the photocell  95  ( 96 ) is active only when it receives light from both LEDs  93 , 93 ′ ( 94 , 94 ′). 
   The photocells  95 , 96  are connected to the control device  8 . A first pair of LEDs  94 , 94 ′ and first photocell  96  are arranged at the minimum depositing height, whereas a second pair of LEDs  93 , 93 ′ and second photocell  95  are arranged at the maximum depositing height. When the output of the first photocell  96  is active, the control device  8  powers the respective DC motor to raise the active depositing platforms  16 , 17  until the first photocell  96  becomes inactive. When the second photocell  95  becomes inactive, the control device  8  powers the respective DC motor to lower the active depositing platforms  16 , 17  until the second photocell  95  becomes active. When the depositing platforms  16 , 17  is in the correct position, the output of the first photocell  96  should be inactive and output of the second photocell  95  should be active. 
   While feeding a sheet onto the stack, the height detectors are deactivated for a short period because the incoming sheet will obstruct the LEDs  93 , 93 ′,  94 , 94 ′. 
   The stacked sheets sometimes tend to form a curl on the feed side of the stack, which is aggravated by e.g. staples which make the stack grow faster on the staple side. The effect is illustrated in  FIG. 11 . The height detectors ensure that the active depositing platforms  16 , 17  will be lowered to compensate for the curl to ensure that the sheets fed by the discharge roller pair  13  do not hit the side of the stack. This may lead however to a situation, e.g. when the curl on the feed side is large, in which the sheet catchers  71  are positioned too low with respect to the discharge roller pair  13 , and the leading edge of the incoming sheets will not be caught under the sheet catchers  17 , but instead pass above the sheet catchers  71 . In this situation the control over the stacking process will be completely lost. The control device  8  compares therefore the height of the sheet catchers  71  with the height of the feed roller pair  13 , and if the height difference between the sheet catchers  71  and the feed roller pair exceeds a preset threshold, the feeding process is stopped and an alarm is set. 
   Although the present invention has been described by an embodiment with two depositing platforms and two guide rails, it is clear to those skilled in the art, that this is merely an example of a preferred embodiment of the present invention. It is e.g. possible to use only one guide rail, one platform, or to use more than two guide rails or more than two platforms. 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.