Abstract:
A sheet deposition device for the deposition of printed sheets on superimposed supports, where each support is provided with its own drive means for moving said support up and down between a deposition position, in which sheets can be deposited on that support, and a parking position, in which sheet deposition is not possible. Each support is also provided with detection means for detecting an obstacle in the space directly therebeneath, for example, sheets on a support directly therebeneath, said detection means delivering a first detection signal when the distance between the support provided with said detection means and an obstacle directly therebeneath is greater than a predetermined amount and said detection means delivering a second detection signal when said distance is equal to said predetermined amount. A control device in response to the reception of a first detection signal makes the drive means capable of activation for moving towards one another the supports between which are situated the detection means delivering the first detection signal and deactivates the drive means in response to the reception of a second detection signal.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a sheet deposition device for the selective deposition of printed sheets on a number of superimposed supports wherein each support is provided with its own drive means for moving said support up and down between a deposition position in which sheets can be deposited on that support and a parking position in which sheet deposition is not possible. 
     A sheet deposition device of this kind is known from European Patent 0 532 069. In this known sheet deposition device, when a predetermined maximum number of sheets has been deposited on one of the supports, a change-over can be made to the further deposition of sheets on one of the other supports, provided there are no sheets present on said other support, and this can be detected by a detector at the support surface of a support. During the displacement of a support, which is necessary for the purpose, with the maximum number of sheets thereon, to a lower parking position, said support will come entirely outside the deposition range of a support subsequently placed in the deposition position, in order to prevent the latter support from colliding, in its deposition position, against the sheets on the support which has been set to its lower parking position and would therefore be obstructed in its further movement. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a sheet deposition device wherein a support is movable between the deposition position and the parking position provided that there is still free space for movement between the superimposed supports and without the supports, possibly with sheets therebetween, jamming against one another. To this end, according to the present invention, a support is provided with detection means for detecting an obstacle in the space directly therebeneath, for example sheets on a support directly therebeneath, which detection means delivers a first detection signal, when the distance between the support provided with said detection means and an obstacle therebeneath is greater than a predetermined amount, and delivers a second detection signal, when said distance is equal to said predetermined amount. The sheet deposition device comprises a control device which in response to reception of a first detection signal makes the drive means capable of activation for moving towards one another the supports between which are situated the detection means delivering the first detection signal and which deactivate the said drive means in response to the reception of a second detection signal. 
     According to one aspect of the present invention, the detection means comprises a flat plate suspended beneath a support and movable between a first position in which the plate is situated at some distance from and parallel to said support and a second position in which the plate is situated at an even shorter distance from said support. The detection means further comprises switching means between the plate and the support with actuating means which are rigidly connected to the movable plate and in the first position of the plate actuate the switching means to deliver the first detection signal and in the second position of the plate actuate the switching means to deliver the second detection signal. 
     The effect of the flat plate is that an obstacle beneath a support can be detected over a relatively large range, this being important particularly if the object is a stack of sheets on a support situated directly beneath the relevant support, which does not have a flat top, for example, because the stack consists of stapled sets which have a relatively considerable thickness at the staple position. 
     Preferably, the plate is provided with fixing means near its opposite edges, which connect the plate to the support for movement in the vertical direction and switching means are provided at each of said fixing means. The effect of this is that an obstacle can be readily detected at any place beneath a support without considerable room for movement for the plate being necessary for this purpose. 
     Preferably, one of the detecting means further comprises a U-shaped strap, of which the intermediate piece connecting its arms is connected for rotation about its longitudinal axis to one of the plates or supports for connection and the ends of the arms are rotatably connected to the other plate or support for connection. The effect of this is that during its movement from the first position to the second position the plate can tip in only one direction so that for the detection of an obstacle up to the four corner points of the plate it is only necessary to use two switching means near the fixing points in a central zone of the plate. 
     This gives a compact-constructed and flexible sheet deposition device in which supports with any sheets deposited thereon cannot jam against one another. 
     According to another aspect of the present invention, the control device of the sheet deposition device comprises control means which in response to the reception of a first detection signal delivered by the detection means at a support in a deposition position or a support therebeneath, make the drive means of said supports capable of activation for moving said support(s) downwards on deposition of the subsequent sheets on said support. As a result, sheets on a support in its parking position can lie within the range of deposition positions of a support thereabove, such range being increased when sheets are removed from the support in its parking position. Another effect is that deposition of sheets can be continued as long as there is anywhere free room for movement beneath the support in the deposition position. 
     According to yet another aspect of the present invention, the control device comprises control means which, upon displacement of a support from a parking position to its deposition position and in response to the reception of a first detection signal delivered by the detection at another support situated between the said parking position and the deposition position, makes the drive means of said other support or supports capable of activation for joint downward or upward movement, with the support to be displaced into its deposition position. The effect of this is that supports with any sheets thereon which stand in the way of a support being moved into its deposition position are automatically moved out of the way provided there is still room where the support requiring to be moved away can be moved away. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the sheet deposition device according to the present invention will be explained hereinafter with reference to the accompanying drawings wherein: 
     FIG. 1 illustrates one embodiment of a printing apparatus using a sheet deposition device according to the present invention; 
     FIG. 2 shows the sheet deposition device of FIG. 1 with supports shown in their bottom positions; 
     FIG. 3 is a perspective view of detection means mounted beneath each support of the sheet deposition device show in FIGS. 1 and 2; and 
     FIG. 4 is a diagram showing a sheet deposition device with the supports in their starting position and an associated control system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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 a set of originals presented 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 a set of images presented via workstation  3  can be started by actuating a start button  7  provided on the workstation  3 , via control device  8  (hereinafter referred to as automatic printing), or by actuating a start button  6  provided on the operator control panel  5  of the printing apparatus  1  (hereinafter referred to as semi-automatic printing). 
     In the printing apparatus  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, whereafter discharge roller pairs  13  feed the set of printed sheets to a sheet deposition unit  15  forming part of a sheet deposition station  11 . 
     The sheet deposition unit  15  comprises four superimposed deposition tables  16 ,  17 ,  18  and  19 , each of which can be set to a deposition 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 . The vertical displacement of the deposition tables can be effected by means of the displacement mechanism described in European Patent Specification 0 532 069, the selected deposition table or the sheet at the top thereof always lying just beneath the discharge path formed by the discharge roller pair  13 . 
     FIG. 1 shows the bottom deposition table  16  in a bottom deposition position in which a maximum number of sheets is situated on said deposition table  16  and the deposition tables  17 ,  18  and  19  situated thereabove are in parking positions situated above the discharge path formed by the discharge roller pair  13 . 
     Since the deposition tables  17 ,  18  and  19  are adjustable as to height independently of deposition table  16 , after sheets have been removed from deposition table  16  the top deposition table  19  can if necessary also be placed in a deposition position without the bottom deposition table  16  needing to be moved further down than the bottom deposition position shown in FIG.  1 . 
     As a result, the finishing station  11  with the sheet deposition unit  15  adjacent the same is very suitable for being positioned 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 of about 100 cm. In the printing apparatus  1  with the finishing station  11  as shown in FIG. 1, the removal height for sheets delivered on deposition tables  16 ,  17 ,  18  and  19  is between 100 cm and 160 cm for a total sheet deposition capacity of about 3000 sheets. The sheet deposition level defined by the fixed discharge rollers  13  is approximately 133 cm, and this level corresponds to the deposition level wherein the bottom deposition table  16  is in its bottom deposition position. 
     The combination of high deposition capacity and limited overall height is rendered possible by using the bottom deposition table  16  solely for the deposition of prints of a first type, the printing cycle of which is initiated with a setting button on the printing apparatus, so that the operator who makes this setting can also remove the deposited prints shortly thereafter, giving the deposition tables situated thereabove the opportunity to come into their deposition position and receive prints, the printing cycle of which is initiated from a workstation  3  at a distance from the printing apparatus. 
     According to the present invention, higher-level deposition tables can also be placed in a deposition position when prints are still situated on or beneath a lower-level deposition table providing there is still room to move the higher-level support down into its deposition position. 
     Therefore, according to the present invention, each deposition table is provided with detection means which enable the higher-level deposition table to move down provided there is still free room for movement beneath said deposition table. The underside of each deposition table  17 ,  18  and  19  is for this purpose provided with the means indicated in FIG.  2 . 
     To prevent the bottom deposition table  16  from jamming, during the downward movement, against an obstacle situated beneath the bottom deposition table, for example originals or copies lying on the top of the printing apparatus  1  next to the scanning station, the bottom deposition table  16  is also provided with the same detection means as the deposition table  17 ,  18  and  19 . Accordingly, each deposition table  16 ,  17 ,  18  and  19  is provided with two straps  25 ,  26  shown in FIG. 3, to the top of which there is secured a sheet deposition plate (not shown in FIG.  3 ). 
     A U-shaped strap  27  extends from one of the adjacent straps  25  and  26  and is secured to strap  26  and is situated in the same horizontal plane as the straps  25  and  26 . 
     Looking in a direction in which sheets are fed to the deposition plate by the transport roller pair  13 , the straps  25  and  27  extend beneath the sides of the deposition plate and are rigidly connected thereto. 
     Pins  28 ,  29 ;  30 ,  31  respectively are fixed at the sides of the straps  25  and  27  extending away from one another. Looking in the sheet discharge direction, pins  28  and  29  are situated opposite one another at the upstream end of the straps  25  and  27 . A flat switch plate  32  extending parallel to the deposition plate is situated beneath the straps  25 ,  26  and  27 . Two brackets  35  and  36  are fixed on the switch plate  32 . 
     Upright parts of the brackets  35  and  36  are provided with slots  37  and  38  extending vertically and accommodating pins  28  and  29  with clearance. A hinge arm  33  bent with a U-shaped configuration is rotatably connected at the ends of its arms to pins  30  and  31  respectively. The hinge arm  33  extends around the straps  25 ,  26  and  27  and is in the same plane as the straps. 
     A U-shaped bent strip  39  is fixed on the switch plate  32 . The upright arms of the strip  39  are provided with indentations  40  and  41  in which the center piece of the hinge arm fits. The switch plate  32  is also provided with a strip which, at the top, has bent-over edges  43  which, in the position of rest of the switch plate  32 , rests on a projection  44  fixed on the strap  27 . In the position of rest of the switch plate  32 , the top edges of slots  37  and  38  rest on pins  28  and  29  respectively and the bent-over parts  43  rest on projection  44 . In this position of rest the switch plate  32  is situated a short distance, e.g. a distance of 7 mm, beneath the straps  25 ,  26  and  27  and extends parallel to the deposition plate fixed on these straps. 
     When a deposition table moves down and the switch plate  32  meets an obstacle therebeneath (e.g. a sheet stack on a deposition table therebeneath), then on the further downward movement of the deposition table the switch plate  32  is pressed in the direction of the straps  25 ,  26  and  27  until the switch plate encounters the straps. This movement of the switch plate  32  is made possible by the slots  37  and  38  and by the turning of the hinge arm  33 . The construction of the hinge arm  33  held in indentations  40  and  41  ensures that the switch plate  32  can not rotate about a line extending parallel to the sheet discharge direction. The switch plate can only tip about a line extending transversely of the sheet discharge direction. When the switch plate  32  first comes into contact with an obstacle at the upstream side, then the switch plate  32  moves upwards only at that side in the two slots  37  and  38 , even if the obstacle is situated only beneath one corner part on that side, and when the switch plate  32  first comes into contact with an obstacle on the downstream side then the switch plate  32  moves up only on that side with rotation of the hinge arm  33 , even if the obstacle is situated only beneath one corner part on that side. 
     An opto-electrical switch  45  is disposed on the upstream side of each deposition table between the straps  25  and  26  and an opto-electrical switch  46  is disposed on the downstream side of each deposition table between the straps. Each of the switches  45  and  46  cooperates with a blade  47 ,  47 ′ respectively fixed on the switch plate  32 . During movement of the switch plate  32  in the direction of a downwardly moving deposition table, blade  47  and/or blade  47 ′ will activate the associated switch or switches  45 ,  46 , in response to which the drive of the downward moving deposition table is interrupted. The switching time is so chosen that switch plate  32  can thereafter still move further before it encounters the straps. During this last movement, which can take place when the opto-electrical switch refuses to operate at the correct time, e.g., because the switch plate is pressed rapidly upwards manually, the blade actuates a microswitch (not shown) which, for protection purposes, breaks the drive to all the deposition tables. The protective microswitch does not normally respond. The above-described suspension of the switch plate ensures that the activation of the switch plate can take place at each of the corner points, and yet only two switching elements are necessary instead of four. The switch plate  32  should be sufficiently torsion-resistant and is, therefore, constructed for example from 2 mm thick aluminum. 
     The use of the switch arm  33 , situated around the straps between the deposition plate and the switch plate, ensures a flat construction which, for example, has a total overall height of only 20 mm with the required stroke length of 7 mm for the switch plate, of which, for example, 4 mm is for the opto-electrical switches and 3 mm for the protective microswitch. 
     At the drive side  48 , where they are connected to a motor which can adjust the associated deposition table as to height, the straps  25  and  26  have an elevation  49  by means of which they can come into contact with the strap of a deposition table thereabove. This elevation is of a size such that two tables between which there are no sheets cannot come so close together that the protective microswitch can respond. Only when there are sheets or some other obstacle between the deposition tables will the microswitch respond and the switching off of the motors which move the deposition tables can be rendered inoperative by the removal of the sheets which cause the microswitch to respond. 
     In FIG. 4, the four deposition tables  16 ,  17 ,  18  and  19  are shown in their starting positions. The bottom table  16  is in the lowest possible position which is at a distance beneath the transport roller pair  13  such that it can support a predetermined maximum number of sheets, e.g. 2250 sheets. A fixed sensor  50 , level with this position, detects when the support  16  is in this starting position. 
     The other deposition tables  17 ,  18  and  19  are in their starting position above the transport roller pair  13 . The support  17  is above the roller pair  13 , and supports  18  and  19  are disposed just above support  17  at distances such that each of these supports can support a predetermined maximum number of sheets, e.g. 500 sheets each. Fixed sensors  51 ,  52 ,  53  are disposed at the respective starting position level to detect when supports  17 ,  18  and  19  are in their starting positions. 
     The above indicated starting positions correspond to positions in which the sheet deposition device accommodates a maximum number of sheets. 
     Reference numeral  60  denotes a control device which sets the tables to their starting position for putting the sheet deposition device into operation. 
     First of all, by means of motor  61 , table  16  is moved down to its very lowest position at sensor  50 . Table  19  is then raised by means of motor  64  to its very highest position at sensor  53 . Table  18  is then moved up by means of motor  63  until either the position at sensor  52  is reached, in the event that the table was previously in a lower position, or sensor  57  beneath table  19  is activated in the event that table  18  was previously in a higher position than the starting position. In the latter case, table  18  then moves down until it reaches the position at sensor  52 . Table  17  is then raised by means of motor  62  until either the position at sensor  51  is reached, in the event that the table was previously in a lower position, or sensor  56  beneath table  18  is activated, in the event that table  17  was previously in a higher position than the starting position. In the latter case, table  17  then moves down until reaching the position at sensor  51 . 
     When the control device  60  determines that detectors  56 ,  57  or  58  detect an obstacle, during the upward movement of tables  17 ,  18  or  19  respectively, before the relevant table has reached its starting position, then the control device  60  delivers a signal for removal of said obstacle from the associated table, for example if more than 500 sheets have been deposited thereon. Detector  58  is provided if the sheet deposition device has a cover plate  66  which prevents a free upward movement of the top table with (too) many sheets disposed thereon. 
     Before the start of a print cycle the table selected for deposition is brought into the deposition position. 
     Starting from the starting position shown in FIG. 4, this implies the following: 
     If deposition on the bottom table  16  is selected, motor  61  moves table  16  upwards until the top of said table is level with detector  59  disposed at a fixed short distance beneath the sheet transport rollers  13 . If there are sheets on table  16  the upward movement stops when the top sheet on the table  16  reaches detector  59 . 
     If deposition on table  17  is selected, this table moves down from the starting position until the top of table  17  or the top sheet thereon comes in the range of detector  59 . When the downward movement stops before detector  59  can respond, that means that the deposition table  16  with any sheets thereon forms an obstacle and the control device  60  delivers a signal to motor  61  to lower table  16  as well. If the latter is not possible because table  16  has reached sensor  50 , the control device  60  delivers a signal to the operator to remove sheets from table  16 , for making space for further lowering of table  51  to its deposition position. 
     If a (further) downward movement of table  17  is no longer possible, while table  16  has not yet reached its extreme bottom position, then the control device  60  delivers a signal to the operator to remove sheets or some other obstacle beneath table  16 . 
     If deposition on table  18  is selected, this table moves down until the top of the table or, if sheets are present thereon, the top of the stack of sheets thereon, comes in the range of detector  59 . 
     During this movement, table  18  may first encounter table  17  and activate detector  56  in so doing. As a result, motor  62  is activated and moves table  17 , together with table  18 , downwards. Table  17  can then also meet table  16  or a sheet stack  16  thereon, so that motor  61  is also activated in the manner explained hereinbefore in connection with the selection of deposition on table  17 . When table  16  has reached its starting position and if table  17  is then already past detector  59  before table  18  reaches its deposition position, the control device  60  delivers a signal to the operator to remove sheets from table  17 . 
     If deposition on table  19  is selected, this table moves down until the top of the table or, if sheets are present thereon, the top of a stack of sheets thereon, comes in the range of detector  59 . 
     This movement can be interrupted when detector  57  responds. Table  18  then also moves down. Detector  56  can then also respond so that table  17  also moves down. The same can then also occur at table  16 . If under these conditions table  16  cannot reach its extreme bottom position, control device  60  delivers a signal for removal of sheets beneath table  16 . If table  17  cannot then fall beneath detector  59 , a signal is delivered for removal of sheets from table  17 . Finally, if table  18  also cannot fall beneath detector  59 , a signal is delivered for the removal of sheets from table  18 . 
     Before any further deposition on one of the tables  17 ,  18  and  19 , the control device  60  should, in the first instance, know where the associated table is situated, i.e. whether said table is situated beneath or above the deposition position. The reason for this is to enable the required direction of movement of the associated motor  62 ,  63  or  64  to be set. The instantaneous position of these supports can be determined by measuring the direction of displacement and the distance of each support from its starting position and storing it as memory. 
     On a change of deposition from a higher-level table (e.g. table  18 ) to a lower-level table (e.g. table  17 ), the latter table should move upwards but in so doing meets the detector beneath the higher-level table, e.g. detector  56 . When the latter responds motor  63  also moves table  18  upwards and possibly motor  64  then also moves table  19 . If the top table in the latter case reaches its extreme top position at sensor  53  before table  17  has reached its deposition position, this means that there are too many sheets on table  17  and/or table  18 . In the event of too many sheets on table  18 , table  18  has not yet reached its starting position at sensor  52  and a signal is delivered to remove sheets from table  18 . If in that case the table  18  has passed sensor  52 , that is a signal that sheets must be removed from table  17 . 
     During the deposition of sheets on a table, said table moves down stepwise to keep the top of the sheets deposited thereon in range of the detector  59 . In these conditions a detector mounted beneath the associated table can respond so that the table therebeneath is also moved down stepwise. Deposition stops when there are too many sheets on the associated table. In the case of deposition on table  16 , this occurs when said table comes into its extreme bottom starting position at sensor  50 . Deposition on table  17  stops when table  16  has moved down to its bottom-most starting position or when table  16  is already in that position in response to the detector  55 . The stopping of deposition also applies in the case of deposition on table  18  or  19 . 
     In some situations it may be convenient to be able to start deposition on a table which is still empty, e.g. in order to prevent copies for deposition from being added to sheets still on that table. 
     One solution to this problem comprises detectors on each table reacting to sheets thereon. 
     In the deposition of printed sheets of print jobs, various types of print jobs are possible in which the deposition of the printed sheets is distributed separately over different deposition tables. 
     A distinction can be made between the following in the case of separate deposition: 
     1. Next job printing 
     Successive print jobs are, as far as possible, deposited on consecutive deposition tables in their natural sequence. A user at the printer thus clearly sees when the previous job has been completed and the next job starts. Removal of the previous job is also easier. 
     2. Walk-up priority-printing 
     Print jobs initiated at the printer, i.e. not from a workstation at a distance from the printer, are deposited on a separate deposition table, e.g. on the bottom deposition table, so that the user present at the machine can see where his print job is situated. 
     3. Interrupt printing 
     In these “interim” print jobs, the current print job is interrupted for an interim job. This interim job is deposited on a different deposition table than the interrupted job, preferably the next deposition table, in order to show clearly when the printing of the interim job starts and is finished and in order to facilitate removal of the interim prints. Another advantage is that the interrupted job is delivered with out separation. 
     4. Continuous printing 
     The printer runs continuously in printing and deposits sheets provided there is still deposition space, i.e. for as long as deposition tables are emptied in good time. Deposition can start at the bottom deposition table and then continue on the deposition tables thereabove (bottom-up algorithm). Deposited prints are removed during printing and thus printing can carry on continuously. 
     5. Capacity printing 
     In order to ensure that the deposition capacity is utilised to the maximum in the case of print jobs where the user is not present at the printer, deposition is first on the top deposition table and then continues with the deposition table therebeneath (top-down algorithm). 
     6. Sorter printing 
     Print jobs are delivered sorted in respect of an adjustable feature, e.g. orders from users of group A on the bottom deposition table, of group B on the table thereabove, and so on (user groups), or orders with stapled sets on one deposition table and orders with non-stapled sets on another deliver table (stack quality printing). 
     It will be apparent that on a change of deposition from one deposition table to another, activation of the detection means suspended beneath the deposition tables plays an important role. They determine whether such change-over is possible and enable the sheet deposition device to allow such a change-over even when printed sheets are removed from deposition tables which are not in use. Without the detection means according to the present invention, the sheet deposition device would assume that the number of sheets deposited on a deposition table will always remain thereon until all the sheets have been removed from said deposition table, and this is detectable in known manner by an empty-detector on a deposition table. 
     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.