Abstract:
In a method for transporting sheets of paper the individual sheets are conveyed successively in a conveying direction to a stop unit and at least one sheet is held at the stop unit to form a set at the stop unit. The stop unit is activated for conveying the set formed at the stop unit when a sheet of a next set to be formed at the stop unit overlaps the set formed at the stop unit. The device for performing the method has a collector with transport elements for transporting sheets along a transport path and a stop unit positioned in the transport path and operated intermittently for forming sets of sheets and further transporting the sets formed thereat. A control device is connected to the stop unit. The collector further has a first sensor device connected to the control device which sends an activation signal to the stop unit when a sheet of a next set to be formed overlaps a set already formed at the stop unit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for transporting sheets which are conveyed successively to a stop unit and are held there until a stack is formed which is comprised of at least one sheet which stack is subsequently transported farther by the stop unit. The invention also relates to a device for performing the method, wherein the device comprises transport elements, preferably transport belts, for the sheets, and a stop unit which is positioned in the transport path of the sheets and can be driven in a cycled fashion and is connected to a control device. 
     2. Description of the Related Art 
     In a known device of this kind, the sheets are supplied by a feeder. In the feeder, the sheets are stacked and are then individually gripped by rollers and read. The sheets are transported by the transport elements to the stop unit where they are held until the sheets coming from the feeder stack have been compiled as sets. As soon as these sheet sets or sheet stacks have been generated, the stop unit is switched on so that this set of sheets is transported to a processing station arranged downstream. When switching on the stop unit, the feeder is also switched on so that the sheets of the next set to be formed are transported to the stop unit. As soon as the previously formed stack has been transported away, the stop unit is switched off so that the subsequently arriving sheets coming from the feeder again can form a stack at the stop unit. In this way, the corresponding sheet sets at the stop unit are formed successively and are then transported in a cycled fashion. The sheet sets are formed with considerable temporal spacing successively at the stop unit and then further transported by it. With this procedure and device it is therefore not possible to achieve high output. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to further develop the method according to the aforementioned kind such that a high output can be achieved without compromising the reliability of the sheet feeding action. 
     In accordance with the present invention, this is achieved in that the further transport of the sheet stack is carried out as soon as a sheet of the next stack to be formed overlaps the sheet stack resting against the stop unit. With respect to the device this is achieved in that the control device has a sensor device connected thereto which during transport of a sheet, belonging to the stack to be newly formed, sends a signal for switching on the stop unit when the transported sheet overlaps the stack resting against the stop unit. 
     In the method according to the invention the further transport of the stack formed at the stop unit and the feeding of the sheet of the next stack to be formed are carried out so that overlap occurs. Accordingly, during the stack formation there is no delay, resulting from the wait for the finished stack to be transported farther by the stop unit, before the first sheet of the next stack to be formed is supplied. The further transport of the stack formed at the stop unit is carried out as soon as the first sheet of the respective next stack to be formed overlaps the stack resting against the stop unit. In this way, very high cycle times and thus very high output is produced. The device according to the invention has a sensor device which, during the transport of the sheet belonging to the next stack to be formed, supplies a signal for switching on the stop unit when this sheet overlaps the finished stack resting against the stop unit. Because of this embodiment the device according to the invention has a high output. 
     In the simplest case, the stack (set) is comprised of only a single sheet. Of course, the stack can also be comprised of two or more sheets. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawing: 
     FIG. 1 is a schematic representation of the sequence of method steps when using the device according to the invention; 
     FIG. 2 is a side view of the device according to the invention; 
     FIG. 3 is a plan view of the device according to FIG. 2, wherein, in order to simplify the drawing, parts that are positioned above one another are illustrated adjacent to one another. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The device serves to collect individually fed documents to form sets and the sets of sheets are subsequently transported farther to an after processing station. In FIG. 1 the steps of the method sequence are schematically illustrated. The device  1  is a collector which at its intake side has two shafts  2  positioned above one another about which transport belts  3  are guided, respectively. With these transport belts, the documents such as sheets are transported through the collector  1 . At the exit side the collector is provided with shafts  4  positioned above one another about which the transport belts  3  are guided. In the area between the shafts  2  and  4 , a stop unit  5  is provided which in the shown embodiment is comprised of rollers arranged above one another and rotating in opposite directions. Advantageously, this stop unit  5  is adjustable in the transport direction of the sheets so that the collector  1  can be adjusted to different sheet sizes. 
     In the transport direction a ramp  6  is provided downstream of the shafts  2  which ensures that the sheet coming from the supply system  7  is lifted. The sheets run onto the slanted side of the ramp  6  and are thus lifted in this area. Such ramps  6  are known in connection with such collectors  1  and will therefore not be described in detail in this context. At least one reading system  8  is correlated with the supply system  7  with which the individual sheets, before being fed to the collector  1 , are read. The reading system  8  of the illustrated embodiment is arranged in the area between the supply system  7  and the collector  1 . The reading system  8  detects the individual sheets and ensures that those sheets that belong to a set are compiled and formed into a stack. In the simplest case, the stack or set is comprised of only a single sheet. However, it is possible to combine two or more sheets to a set or stack. The supply system  7  can, for example, be a feeder. 
     At the beginning of the collecting process a first sheet  9  is transported via the transport belts  3  from the supply system  7  until it reaches with its leading edge in the transport direction the stop unit  5 . The rollers of the stop unit  5  are standing still so that the sheet  9  remains in this stop position until the subsequent sheet  10  is supplied. In FIG. 1 a scenario is illustrated in which each set is comprised of only a single sheet. In FIG. 1 three positions of the sheets  9  passing through the collector  1  are illustrated. In the middle position, the sheet  9  rests with its leading edge in the transport direction at the stop unit  5 . The next sheet  10 , which in this embodiment belongs to the next set, is being transported by the supply system  7  via the transport elements into the collector  1 . Via the ramp  6  the leading edge of the sheet  10  is lifted in the transport direction such that it can overlap the sheet  9  resting against the stop unit  5 . As soon as overlap has occurred, the rollers are driven such by the stop unit  5  that the sheet  9  is transported in the direction toward the after processing station  12 . Preferably, the following sheet  10  is transported with the same speed as the sheet  9 . As soon as the leading edge of the next sheet  10  comes to rest against the stop unit  5  in the transport direction, the rollers of the stop unit  5  are stopped. This makes it possible that the first sheet  9  is transported with a portion of its length in the direction toward the after processing unit  12  and that the successively supplied sheet  10  remains in the stop position (lower representation of FIG.  1 ). At this point, in the manner disclosed above, the next sheet  11  is supplied by the supply system  7 . It is again read by the reading system  8  and moved into the collector  1 . Its leading edge also reaches the ramp  6  so that the edge of this sheet  11  is lifted. As soon as the sheet  11  overlaps the sheet  10 , the drive of the rollers of the stop unit  5  is again started. This causes the sheet  9 , which is still positioned between the rollers of the stop unit  5 , to be completely transported out of the collector  1  while the sheet  10  is transported farther until the sheet  11  comes to rest against the rollers of the stop unit  5 . At this point, the stop unit  5  is switched off again. In this way, the individual sheets are transported through the collector  1  in sequence. 
     Because of the described method, the supply system  7  must not be switched off but can be operated continuously. This results in extremely short time periods for the sheets  9  to  11  to pass through the collector  1 . The collector  1  has a very high output because of this process sequence. 
     In order to obtain an optimal passage time of the sheets  9  to  11  through the collector  1 , they are each transported after their contact at the stop unit  5  by half their length, respectively. 
     The switching off of the stop unit  5  is carried out when the leading edge of the respective sheets  9  to  11  in the transport direction reaches the photoelectric barrier  13  which is advantageously provided at the after processing unit  12 . As soon as one of the sheets  9  to  11  has reached with its leading edge the light barrier or photo electric barrier  13 , the latter sends a switch-off signal to the stop unit  5  so that its rollers are then stopped. 
     In the same way, the rollers of the stop unit  5  are switched on when the sheets  9  to  11  supplied by the supply system  7  reach the ramp  6  and overlap the sheet stack by a certain amount. The collector  1  is provided with a photoelectric barrier  14  for this purpose which in the illustrated embodiment is positioned immediately behind the ramp  6  in the transport direction of the sheets. As soon as the respective following sheet  10 ,  11  has overlapped the respective sheet  9 ,  10  in front, the photoelectric barrier  14  sends a corresponding signal to the stop unit  5  which is thus switched on. 
     The after processing unit  12  is provided at the intake side with a transport device  15  which is, for example, formed by rollers positioned atop one another. This transport device  15  can be driven continuously since the respective sheets  9  to  11  are stopped by means of the light barrier  13  shortly before reaching the transport device  15 . 
     Before the collecting process is started, the position of the stop unit  5  relative to the light barrier  13  or to the shafts  4  is adjusted to the size of the sheets  9  to  11  to be transported. When the paper size changes, the stop unit  5  is adjusted in the direction of the double arrow  16  in FIG. 1 such that the sheets come to rest between the ramp  6  and the stop unit  5 . The spacing  17  between the axes of the rollers of the stop unit  5  and the ramp corresponds to the length of the sheets  9  to  11  to be transported. Also, the ramps  6  are adjusted accordingly in the transport direction of the sheets  9  to  11 . When, for example, in the shown embodiment a shorter sheet size is to be processed, the spacing between the stop unit  5  and the shafts  4  at the exit side of the collector  1  must be shortened. Accordingly, the ramp  6  must also be horizontally adjusted in the direction toward the shafts  4 . When, on the other hand, longer sheet sizes are used, the stop unit  5  and the ramp  6  are adjusted in the other direction. 
     The collector  1  operates fully automatically. The reading system  8 , the rollers of the stop unit  5 , the shafts  2 ,  4 , and the corresponding photoelectric barriers  13  and  14  are connected to the control device. The control device comprises at least one micro controller which can be provided in the supply system  7 , in the collector  1 , or in the after processing unit  12 . 
     The supply system  7  can have any suitable configuration. Also, the after processing unit  12  can be any suitable device, for example, a folding machine, a packaging machine, which may be a part of an inserter, a stapling device, a welding device etc. The sheets  9  to  11  transported through the collector  1  can thus be further processed in different ways. 
     In FIG. 1, for reasons of simplifying the drawings, it is surmised that each set is comprised of a single sheet  9  or  10  or  11 . For sets which are comprised of several sheets, which may be identical or different, the individual sheets are stacked at the stop unit  5  to form the respective set. The stop unit is not switched on during this collecting period. Only when the respective set has been formed at the stop unit  5  and the first sheet of the next set overlaps the already stacked set, the stop unit  5  is switched on as disclosed above. With this intermittent operation of the stop unit  5 , the respective sets are formed sequentially at the stop unit  5  and individual sets are then supplied in the manner described above to the after processing unit  12 . The reading system  8  detects when a sheet of the next stack is supplied and a sensor signal is then sent to the stop unit  5 . 
     With the aid of FIGS. 2 and 3, the collector  1  will be explained in more detail. It has a frame  18  in which a motor  19  is arranged. Its drive shaft  20  is in driving connection by means of an endless drive  21  with an intermediate shaft  22  which is rotatably supported in the sidewalls  23 ,  24  (FIG. 3) of the frame  18 . As is illustrated in FIG. 3, a pulley  25  is provided on the end of the intermediate shaft  22  projecting from the sidewall  23  and the endless drive member  21  (FIG. 2) is guided about this pulley  25 . The end of the intermediate shaft  22  projecting past the sidewall  24  of the frame  18  supports a pulley  26  about which the endless belt  27  is guided. The endless belt  27  connects the intermediate shaft  22  with the shaft  28  and the shafts  2 . The ends of the shafts  2 ,  28  are rotatably supported in the sidewalls  23 ,  24  of the frame  18 . The required tension of the endless belt  27  is provided by two tension rollers  29 ,  30  which are rotatably supported on the external side of the sidewall  24 . In FIG. 3, for reasons of simplification, only one tension roller  30  is illustrated which is positioned adjacent to the upper shaft  2 . The tension roller  29 , as illustrated in FIG. 2, is positioned immediately adjacent to the shafts  2 ,  28 . 
     As is illustrated in FIG. 2, the upper shaft  2  is positioned forwardly, relative to the lower shaft  2 , in the transport direction of the sheets  9  to  11 . However, this staggered placement is only so great that in a plan view onto the collector  1  the two shafts  2  do overlap one another. 
     Pulleys  31 ,  32  are fixedly connected to the two shafts  2  for common rotation and the endless transport belts  3  are guided about the pulleys  31 ,  32 . The pulleys  31 ,  32  have an axial spacing to one another. The non-carrying run of the upper transport belts  3  and the carrying run of the lower transport belts  3  are arranged such that, viewed in the axial direction of the shafts  2 ,  4 , they contact one another, and optionally overlap slightly. This ensures that even thin sheets can be transported reliably between the transport belts  3  of the collector  1 . The axial spacing of the pulleys  31 ,  32  on the shafts  2  is so great that different sheet sizes can be reliably transported through the collector. The transport belts  3  are comprised advantageously of an elastic material and are formed as a round belt. The endless drive members  21 ,  27  provided for the drive action, on the other hand, are strip-shaped belts. 
     The upper transport belts  3  connect the upper shaft  2  with the upper shaft  4  which is provided with corresponding pulleys  33 . Accordingly, the lower transport belts  3  connect the lower shaft  2  with the lower shaft  4  also having corresponding pulleys  34 . 
     The axes of the two shafts  4 , in contrast to the axes of the shafts  2 , are positioned in a common vertical plane. The two ends of the shafts  4  are supported in the sidewalls  23 ,  24  of the frame  18 . 
     The ramp  6  extends between the two sidewalls  23 ,  24  and is adjustable in the transport direction of the sheets  9  to  11 . The sidewalls  23 ,  24  of the frame  18  are provided with slots extending in the transport direction. Axles  35 ,  36  provided at the end face of the ramp  6  project through the slots. As is illustrated in FIG. 2, the ramp  6  has at least on one end, preferably on both ends, brackets  37  extending parallel to the sidewalls  23  and  24  of the frame  18 , wherein the brackets  37  are each engaged by an end of an endless circulating chain  38 , respectively. When viewed in a side view (FIG.  2 ), the chains  38  are guided on chain wheels  40 , fixedly seated on horizontal axles  39  for common rotation, to chain wheels  41 , which are fixedly seated on a horizontal shaft  42  for common rotation, between the runs of the lower transport belts. The shaft  42  is in an area below the transport belts  3  and its ends are supported rotatably in the frame sidewalls  23 ,  24 . The axles  39  are mounted in the sidewalls  23 ,  24  of the frame  18 . The chain wheels  40 ,  41  are positioned on the outer sides of the frame sidewalls  23 ,  24  facing away from one another. The chains  38  extends from the chain wheels  41  to further chain wheels  43  which are seated on the shaft  44  between the two runs of the lower transport belts  3 . Their two ends are supported in the frame sidewalls  23 ,  24 . The shaft ends project through slots  45  provided in the frame sidewalls  23 ,  24  and extending in the transport direction of the sheets  9  to  11 . The shaft  4  is secured in a suitable way relative to the frame sidewalls  23 ,  24  in a selected position. With a corresponding movement of the shaft  44  in the slots  45  the tension of the chains  38  can be adjusted by a desired amount. The chains  38  are fastened with their other ends on the brackets  37  of the ramp  6 . As is shown in FIG. 3, one end of the shaft  42  is extended past the frame sidewall  24  and supports a manual actuator  46 , preferably a turn wheel, with which the shaft  42  can be rotated about its axis. The shaft  42  is secured by clamping with a clamping device  47  provided on the frame in a selected rotational position. The clamping device  47  has a sleeve or bushing  48  provided on the frame  18  through which the shaft  42  projects. A clamping bolt  49  is screwed into the bushing  48  in a radial direction with which the shaft  42  can be securely clamped in the bushing  48  and thus relative to the frame  18 . 
     For moving the ramp  6 , it is possible to fasten rail-like strips on the inner sides of the frame sidewalls  23 ,  24  facing one another on which the carriage of the ramp  6  can be horizontally guided. 
     Also, the stop unit  5  can be adjusted in the transport direction of the sheets  9  to  11  in order to adjust the collector  1  to different papers sizes. The stop unit  5  has two shafts  50 ,  51  positioned atop one another and arranged at the same level as the neighboring shafts  4 . They extend between the runs of the upper and the lower transport belts  3 . The two shafts  50 ,  51  engage one another at their ends in the vicinity of the frame sidewall  23  by respective gear wheels  52 ,  53 . The gear wheel  52  seated on the shaft  50  meshes also with a gear wheel  54  which is supported rotatably in a support plate  55  through which the one ends of the shaft  50 ,  51  extend and in which they are rotatably supported. 
     At the other end neighboring the frame sidewall  24 , the shaft  50  is rotatable supported by means of a bearing  56  in the support plate  57 . The lower shaft  51  extends through this support plate  57  and supports on its projecting end a pulley  58  which is in driving connection by means of a drive belt (not shown) with a pulley  60  mounted on a motor shaft  59 . The motor  61  for driving the shafts  50 ,  51  of the stop unit  5  is fastened on the support plate  57  which extends, like the oppositely positioned support plate  55 , in a vertical plane. As is illustrated in FIG. 2, the support plate  57  projects downwardly past the transport belt  3 . The motor  61  is fastened in the area below the transport belt  3  on the support plate  57  on the side facing away from the frame sidewall  24 . At the lower edge the oppositely positioned support plates  55 ,  57  are connected by an axle  62  to one another. The axle  62  extends with its ends through the support plates  55 ,  57  and engages horizontal slots  63  in the frame sidewalls  23 ,  24 . The two support plates  55 ,  57  are also supported with the oppositely positioned edge area on the frame. 
     The upper shaft  50  is spring-loaded toward the lower shaft  51  so that it can be radially moved relative to the shaft  51  to a limited extent. This is necessary when the sheet stack to be transported has a greater thickness. In order to ensure this movability, the openings  64  in the support plates  55 ,  57  are wider than the shaft  50 . The ends of the shaft  50  are received in a sleeve which projects through the openings  64 . A tension spring  65  is connected to a radial projection of these sleeves (bushings), respectively, and the end of the spring is fastened to the support plate  55  or  57 . 
     The support plates  55 ,  57  are provided at their lower edge with a respective projection  66 ,  67  extending counter to the transport direction  16  through which the ends of the axle  62  project. The projections  66 ,  67  are bracket-shaped (FIG. 2) and are positioned in the area between the two frame sidewalls  23 ,  24 . At the free end of the projection  67  a bracket  68  is mounted on which the two ends of the circulating chain  69  are fastened (FIG.  2 ). The chain  69  is guided about two chain wheels  70 ,  71  on a shaft  72  and a shaft  42 . While the chain wheels  41  are positioned external to the frame  18  (FIG.  3 ), the chain wheels  71  are positioned within the frame  18 . The two chain wheels  70 ,  71  have the same diameter which is smaller than the diameter of the chain wheels  41  on the shaft  42  via which the chains  38  for adjusting the ramp  6  are guided. The diameter of the chain wheels  41  and  71  on the shaft  42  are selected such that during rotation of the shaft  42  the ramp  6  is adjusted by a distance twice that of the displacement of the stop unit  5 . In this way, the stop unit  5  and the ramp  6  are adjusted simultaneously with one adjusting process to the desired paper size. For rotation of the shaft  42  it is only required that the clamping bolt  49  be unscrewed such that the shaft  42  can be freely rotated in the bushing  48 . With the manual actuator  46  the shaft  42  can then be rotated by the desired amount wherein via the described chain drive the stop unit  5  and the ramp  6  are adjusted simultaneously in the same direction. Subsequently, the clamping bolt  49  is again tightened and the shaft  42  is then fixedly clamped in the bushing  48 . 
     Rollers  73 ,  74  are positioned fixedly for common rotation on the two shaft  50 ,  51  of the stop unit  5 . They have an axial spacing to one another and are advantageously provided on their periphery with friction coatings  75 ,  76 . The rollers  73 ,  74  are resting against one another via these coatings by the force of tension springs  65 . The rollers  73 ,  74 , as can be seen in the plan view according to FIG. 3, are arranged in the area between the transport belts  3 . 
     When adjusting the stop unit  5 , the axle  62  with its two ends is moved in the slots  63  extending in the transport direction  16 . The support plates  55 ,  57  are also guided at the oppositely positioned edge in a suitable way on the frame. The ramp  6  is guided in the described manner on the frame sidewalls  23 ,  24  during movement so that a problem-free adjustment of these components of the collector  1  is ensured. 
     The photoelectric barrier  14  in the area of the ramp  6  triggers in the way disclosed above the working cycle for the two shafts  50 ,  51  of the stop unit  5 . As soon as the respective following sheet  10 , 11  has passed the photoelectric barrier  14 , the motor  61  receives a corresponding activation signal so that the shafts  50 ,  51  are rotated and their rollers  73 ,  74  transport the sheet  9  or set of sheets resting against the stop unit  5  to the after processing unit  12 . The light barrier  13  arranged in the transport direction downstream of the shafts  4  provides an additional safety feature because it allows monitoring of the set separation. In this way, it is ensured that the individual sets, which may be comprised of a single or of several sheets, are checked and supplied precisely separated from one another to the after processing unit  12 . 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.