Sheet stack handler with sheet stacker and / or sheet feeder for printer - Patent Application 20070122997

Abstract

To provide an improved sheet stack handler for a printer with a relatively simple and low-cost structure and a relatively small installation area.SOLUTION: The device is provided with: first and second liftable stack supports (72, 92), each configured to support a stack (89, 95) of sheets; a lift assembly configured to position the top sheet of the stack (89, 95) on the first or second liftable stack supports (72, 92) inside the stack holding volume (89, 95) at an operable (OL) level of individual sheet engagement (77) such that the individual sheet engagement (77) can stack a new sheet on the top sheet and separate the top sheet from the respective stack (89, 95); and a translation mechanism (110) configured to translate at least one of the first and second liftable stack supports (72, 92).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a sheet stack handler for a printer, to a printer comprising such a sheet stack handler, and to a method for stacking and / or feeding sheets onto and / or from a stack. [Background technology]

[0002] Sheet stack handlers are applied in sheet printers to separate individual sheets from a stack and feed them to a printing station for printing and / or forming a stack from printed sheets received from the printing station. Such sheet stack handlers comprise: a sheet stacker and / or sheet feeder; - each sheet engager comprising a sheet-to-stack feeder for stacking a sheet onto a stack of sheets on one of the first and second liftable stack supports, and / or a sheet-from-stack separator for separating a sheet from a stack of sheets on one of said first and second liftable stack supports; a lift assembly configured to move the first and second liftable stack supports between a bottom position and a top position such that a top sheet of a stack of sheets on the first or second liftable stack support is locatable at the level of the respective sheet-engaging body, the top position being adjacent the respective sheet-engaging body and the bottom position being spaced apart from the respective sheet-engaging body in a lift direction of the first or second liftable stack support, such that a stack-holding volume is defined between the top position and the bottom position; Equipped with.

[0003] One liftable stack support is lowered or raised depending on whether a sheet is to be separated from or added to the stack on the liftable stack support, so that the top surface of the stack is at an operable level where individual sheet engagers can add and / or separate sheets from the stack. The stack-holding volume defines the maximum height limit for sheets that can be separated from or stacked on the first liftable stack support. When that limit or maximum capacity is reached, the liftable stack support is unavailable for feeding or stacking additional sheets. To continue printing until the liftable stack support is again available, an alternative location for feeding or stacking sheets is required, for example, in the form of a second sheet stack handler that bypasses the first. However, such additional equipment increases the cost and footprint of the printer. This is particularly disadvantageous when the printer is configured to handle larger format sheets, such as A1 / B1 or A2 / B2 size sheets. Such larger sheets are often provided in stacks on pallets, which prevents new sheets from being easily added from the top, as is possible with certain home / office printers.

[0004] EP 3594155 A1 discloses a sheet feed module having two rotating arms, each carrying a stack support for a stack of sheets, both stack supports being vertically movable and rotatable in a horizontal plane, so that the stack supports can be changed location in a continuous cyclical motion.

[0005] US5011126A discloses a sheet feed module having a vertically movable stack support and horizontally movable pins on either side of the stack support, which may be inserted into the stack on the stack support to support the upper part of the stack, while the lower stack support returns to its starting position. Summary of the Invention

[0006] It is an object of the present invention to provide an alternative or improved sheet stack handler for a printer, preferably one which is of relatively simple and / or low cost construction and / or has a relatively small footprint.

[0007] According to the present invention there are provided a sheet stack handler as claimed in claim 1, a printer as claimed in claim 15 and a method as claimed in claim 16.

[0008] The sheet stack handler includes: a sheet stacker and / or sheet feeder; - first and second liftable stack supports, preferably mounted on a pallet, each configured to support a stack of sheets; a respective sheet engager for stacking a sheet onto a stack of sheets on one of the first or second liftable stack supports and / or for separating a sheet from a stack of sheets on one of the first and second liftable stack supports; a lift assembly for moving the first or second liftable stack support between a bottom position and a top position disposed spaced apart and adjacent to the individual sheet engagers, respectively, so that a stack-holding volume is defined between the bottom position and the top position, the lift assembly being further configured to position the top sheet of the stack on the first or second liftable stack support inside the stack-holding volume at an operable level of the individual sheet engagers so that the individual sheet engagers can stack a new sheet on the top sheet and / or separate the top sheet from their respective stacks.

[0009] The sheet stack handler further includes a translation mechanism configured to translate at least one of the first and second liftable stack supports while supporting a stack of sheets between a buffer position outside and to one side of the stack holding volume and an active position inside the stack holding volume.

[0010] The translation mechanism is configured to transport the first or second liftable stack support into and / or out of the stack-holding volume while retaining a stack of sheets on the respective liftable stack support. This allows the stack to be moved into and / or out of the stack-holding volume via a compact translation path formed, for example, by a sliding track. Outside the stack-holding volume, the respective liftable stack supports are in close proximity to the sides of the stack-holding volume. This adjacent positioning combined with translational movement results in a compact device with a relatively small footprint. When the liftable stack support inside the stack-holding volume reaches its capacity (i.e., is empty or stacked to its maximum height), another liftable stack support can be quickly and efficiently inserted into the stack-holding volume, so that operation can continue with minimal delay due to stack replacement. The liftable stack support in the buffer position is outside the stack-holding volume and thereby easily accessible for side-to-side loading and unloading of pallets thereon. This achieves the object of the present invention.

[0011] More specific optional features of the invention are set out in the dependent claims.

[0012] In one embodiment, the lift assembly includes a first lift for raising and / or lowering the first liftable stack support and a second lift for raising and / or lowering the second liftable stack support independently of the first liftable stack support. Each stack support is provided with an individual lift that allows one stack support to be raised and / or lowered independently of the other stack support. This allows for rapid stack exchange, for example, by placing the stack support at an operable level in the buffer position before inserting it into the stack-holding volume. The raising or lowering may also be performed during translation to save time. It may also allow stack supports to be moved out of each other's way before or during translation.

[0013] In one embodiment, the individual sheet engaging members are configured to transport sheets in a transport direction parallel to a transport path for supplying sheets to the individual sheet engaging members and / or receiving sheets from the individual sheet engaging members, and the translation direction of the translation mechanism is perpendicular to the transport direction and the lift direction. The transport path preferably extends in the transport direction, which is the direction in which sheets are moved onto or from a stack by the individual sheet engaging members. The stack supports are translatable parallel to their support surfaces in a direction perpendicular to the transport direction. During operation, the transport direction and the translation direction are preferably horizontal. This allows the buffer position or positions to be located laterally of the stack-holding volume with respect to the transport direction. This allows the stack supports at the buffer positions to be easily accessible.

[0014] In one embodiment, the translation mechanism is configured to move one of the first or second liftable stack supports back and forth along a straight linear track between the active position and the buffer position. The active position, when viewed in the lift direction, is inside the stack holding volume and below or overlapping a feed and / or separation module. The buffer position is to the side of, adjacent to, and / or proximate to the active position, preferably without overlapping. The translation mechanism is configured to move the stack support from the buffer position to the active position and / or vice versa along the shortest path. This reciprocating motion allows for a small footprint.

[0015] In one embodiment, the translation mechanism includes a translation frame connecting the first liftable stack support to the second liftable stack support such that the first and second liftable stack supports move simultaneously in a translation direction of the translation mechanism. The first and second liftable supports are provided together on the sliding frame, which rigidly couples the first and second liftable supports together in the translation direction of the frame. When one of the liftable stack supports is moved from a buffer position to the active position, the other stack support is moved from the active position to the buffer position, and vice versa.

[0016] In one embodiment, two buffer positions are provided on either side of the stack-holding volume, such that moving one of the first and second liftable stack supports from one of the buffer positions to the active position moves the other of the first and second liftable stack supports from the active position to the other of the buffer positions. The sliding frame is reciprocally movable between the first and second positions, such that the stack supports are alternately moved to the active positions within the stack-holding volume. Each stack support has its own buffer position, which is located on either side of the stack-holding volume in the translational direction. The sliding frames move. In one embodiment, the second liftable stack support is movable in a direction perpendicular to the lift direction of both the first and second liftable stack supports between the buffer position outside and on one side of the stack-holding volume and the active position inside the stack-holding volume above the first liftable stack support, so that the individual sheet engagers can stack and / or separate sheets onto and / or from a stack of sheets on the second liftable stack support. While the first liftable stack support is in active use, the second liftable stack support is positioned on one side of the stack-holding volume when in the buffer position. When the capacity of the first liftable support is reached, it is at or moves to its bottom position, thereby creating free space above the first liftable support within the stack-holding volume, where the second liftable support is inserted into its active position within the stack-holding volume. The second liftable support in its active position is positioned above the first liftable support and can be used to supply or stack sheets by appropriately controlling its position in the lift direction. The second liftable support is thereby maintained at the appropriate level relative to the individual sheet-engaging bodies, similar to the first liftable stack support when used to supply and / or stack sheets. A time window for providing a new stack on the first liftable support or removing a stack from the first liftable support is thus created by utilizing the capacity of the second liftable support. Because the second liftable support utilizes the same individual sheet-engaging bodies as the first liftable support without requiring adjustments to the individual sheet-engaging bodies, the structure is relatively simple and low-cost. During use, a relatively small footprint is achieved by horizontally inserting the second liftable support into the stack-holding volume from one side of the stack support.This also allows the module to be used as both a stacking module and a supply module, as the second liftable support can hold a stack of itself while in the buffer position.

[0017] In one embodiment, the second liftable support is configured to hold a second stack of sheets while in the buffer position. For stacking purposes, the second liftable support can move the stack thereon outside the stack-holding volume to the buffer position. For feeding purposes, the second liftable support can hold the second stack in the buffer position and transport it from the buffer position into the stack-holding volume. This allows the individual sheet-engaging bodies to continue printing operations utilizing the second liftable support, while the first liftable support is cleared or restocked. Preferably, the buffer position is on the opposite side of the stack-holding body from the transport path for transporting sheets to and / or from the individual sheet-engaging bodies, but the buffer position may also be provided on one of the remaining lateral sides of the stack-holding volume. Different sides of the stack-holding volume are free or open for inserting and / or removing stacks of sheets, preferably stacks provided on pallets. Since most sheet types in printing are rectangular, the stack-holding volume is typically rectangular when viewed vertically during use.

[0018] In one embodiment, the second liftable stack support is configured to move into and / or out of the stack holding volume while holding a stack of sheets, and the second liftable stack support with the stack of sheets thereon moves on the first liftable stack support in a direction perpendicular to the lift direction of both liftable stack supports. The second liftable stack support is configured to hold the stack of sheets when it is in the stack holding volume, when it is in a buffer position while it is outside the stack holding volume, and when it is moving into and / or out of the stack holding volume. This allows the second liftable stack support to move the stack into and / or out of the stack holding volume while the first liftable stack support is in a lowered position below the second liftable stack support.

[0019] In one embodiment, the lift directions of the first and second liftable stack supports are parallel to one another. In use, both lift directions preferably extend vertically or parallel to the vertical.

[0020] In one embodiment, the sheet stack handler further comprises a first lift for moving the first liftable stack support between a bottom position and a top position, and a second lift for lowering and raising the second liftable stack support independently of the first lift, the second liftable stack support being sized and positioned to be inserted into the stack-retaining volume without contacting the first lift, at least between the top and bottom positions. The first lift preferably engages the first liftable stack support at an outer and / or lateral side of the stack support surface. At least the first lift in the stack-retaining volume is spaced apart from the second liftable stack support so that the second liftable stack support, and optionally also the second lift, can move between and / or fit within the first lifts in the stack-retaining volume. This allows the second liftable stack support to be inserted onto the first liftable stack support without affecting the operation of the other. The first and second lifts are further configured to operate independently of one another such that the first liftable stack support can be positioned and / or moved independently of the position and / or movement of the second liftable stack support.

[0021] In one embodiment, the sheet stack handler further comprises a translation guide beam along which the second liftable stack support is movable as it moves into and out of the stack volume, the translation guide beam extending parallel to a horizontal direction during use. The translation beam defines a trajectory along which the second liftable stack support moves into and / or out of the stack-holding volume. The translation beam is preferably located outside the stack-holding volume, but is positioned and / or dimensioned to support the second liftable stack support even when the second liftable stack support is inside the stack-holding volume. It will be appreciated that the second lift may be provided to move with the second liftable stack support and / or may be configured to control the height of the lift beam, and thereby the height of the second liftable stack support. In another example, the second liftable stack support remains in a stationary position, and the sheet stack handler is configured to compensate for varying heights of the stack, at least within a range that is smaller than the range of the first liftable stack support.

[0022] In one embodiment, the second lift is positioned substantially outside the stack-holding volume when the second liftable stack support is inserted into the stack-holding volume. A rigid connection attaches the second lift to the second liftable stack support within the stack-holding volume. To maintain a small vertical footprint, the second lift remains outside the stack-holding volume. This allows the first lift to be positioned directly on the edge of the stack support surface of the first liftable stack support. The stack support surface has dimensions similar to or equal to the dimensions of the largest applicable sheet format. In another embodiment, the second liftable stack support does not overlap the lift line of the first lift when viewed vertically. The lift line is connected to a drive, and the first liftable stack support is raised and lowered by winding and unwinding the lift line.

[0023] In one embodiment, the sheet stack handler further includes a controller configured to determine when the number of sheets in the stack on the first liftable stack support meets or exceeds a predetermined threshold, then control the first liftable stack support to be positioned at the bottom position, subsequently control the second liftable stack support to be inserted into the stack-holding volume, and transmit the information to prompt stack support capacity information on a user interface. The controller determines when the capacity of the first liftable support is exceeded, i.e., when the stack is empty in the case of sheet feeding and / or when the stack reaches a maximum allowable height in the case of sheet stacking. The predetermined threshold can be expressed in any suitable manner, such as by number of sheets or height. In the case of sheet feeding, the threshold may be, for example, zero sheets or 0 mm or microns. When the threshold is reached, the first liftable support is controlled to lower the first liftable stack support and then move the second liftable support into the stack-holding volume. Additionally, an operator is notified via the prompt on the user interface that a stacking or unloading operation is required for the first liftable stack support. The prompt may include an estimated time before the capacity of the second liftable stack support is reached. For example, the controller is configured to apply information regarding the number of sheets on the second liftable stack support to prompt time information on the user interface indicating an estimated period until the stack on the second liftable stack support is depleted.

[0024] In another embodiment, the controller further determines on which first side of the stack-holding volume the first or second liftable stack support is located, and in response to determining that the predetermined threshold is met or exceeded, the first or second liftable stack support is moved into the stack-holding volume, thereby moving the other of the first or second liftable stack support into a buffer position on a second side of the stack-holding volume opposite the first side. The first and second stack supports move reciprocally in unison through the stack-holding volume. During printing, one of the stack supports is in a buffer position on one side of the stack-holding volume to load or unload pallets. The controller determines on which side of the printer the stack support is located for loading and unloading. When the pallet in the stack-holding volume needs to be replaced, the stack support in the buffer position is moved into the stack-holding volume. Since the other stack support is rigidly connected to the first in the translational direction, this moves the other stack support to a buffer position on the opposite side of the stack holding volume so that pallets can be loaded or unloaded, and the movement is then reversed when another pallet exchange is required.

[0025] The present invention further relates to a printer comprising the sheet stack handler described above, preferably an inkjet printer comprising a substantially straight or linear transport path portion extending between the sheet supply module and the sheet stacking module, so that relatively large format, rigid sheets such as cartons can be easily transported and printed.

[0026] The present invention further relates to a method for stacking and / or feeding sheets onto and / or from a stack, said method comprising the steps of: - controlling the height position of the first liftable stack support so that the top sheet of a stack on the first liftable stack support is at an operable level at each sheet engager so that the individual sheet engagers can stack and / or feed sheets onto and / or from the stack on the first liftable stack support; - moving a second liftable stack support from a buffer position adjacent a side of the stack-retaining volume into said stack-retaining volume along a linear trajectory; - controlling the height position of the second liftable stack support independently of the height position of the first liftable stack support so that the top sheet and / or top surface of the stack on the second liftable stack support is at the operable level at the respective sheet engagers; - stacking and / or separating sheets onto and / or from the stack on the second liftable stack support by said individual sheet engagers; Includes:

[0027] The method may be performed on the device as described above to achieve an efficient method of stacking sheets to or feeding sheets from a printer. In one embodiment, the second liftable stack support slides over the first liftable stack support within the stack-holding volume, or the sliding step includes moving the first and second liftable stack supports in translational relation.

[0028] In one embodiment, the step of interlocking the first and second liftable stack supports includes simultaneously moving the first stack support from a first buffer position on a first side of the stack-holding volume to an active position within the stack-holding volume and moving the second stack support from the active position to a second buffer position on a second side of the stack-holding volume opposite the first buffer position, and / or vice versa. The stack supports may be provided on a common sliding frame. By moving the sliding frame back and forth, one stack support is moved into the stack-holding volume and the other stack support is moved from the stack-holding volume to its respective buffer position.

[0029] In one embodiment, the method further includes adjusting the height of one of the stack supports to a level at which the individual sheet engagers can operate in its buffer position. Prior to moving into the stack-holding volume, each stack support is raised to a level at which the stack thereon can be utilized by the individual sheet engagers, thereby reducing exchange time.

[0030] The present invention further relates to a method for stacking and / or feeding sheets onto and / or from a stack, said method comprising the steps of: - controlling the height position of the first liftable stack support so that the top sheet of a stack on the first liftable stack support is at an operable level at each sheet engager so that the individual sheet engagers can stack and / or feed sheets onto and / or from the stack on the first liftable stack support; - lowering the first liftable stack support when determining that the stack height reaches or exceeds a predetermined threshold; - sliding a second liftable stack support over said first liftable stack support; - controlling a height position of the second liftable stack support so that the top sheet of a stack on the second liftable stack support is at the operable level at the individual sheet engagers so that the individual sheet engagers can stack and / or feed sheets onto and / or from the stack on the second liftable stack support disposed on the first liftable stack support; and providing a new stack on the first liftable stack support and / or removing a stack on the first liftable stack support from between the first and second liftable stack supports so that the new stack is positioned between the first and second liftable stack supports. In one embodiment, the method further includes retracting a second liftable stack support, such that the first liftable stack support thereon is free to move toward an operable level. The top of the stack or the empty stack support surface is positioned at the operable level. In another embodiment, the second liftable stack support slides directly on the first liftable stack support as the first liftable stack support passes the second liftable stack support. Preferably, the first and second liftable stack supports move vertically, and the second movable stack support slides horizontally. For example, the starting height of the stack on the first liftable stack support may be greater than the starting height of the stack on the second liftable stack support. The second liftable support acts as a temporary buffer, so that the stack provided or formed thereon is smaller than the stack on the first liftable support.

[0031] Further scope of applicability of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. [Brief explanation of the drawings]

[0032] The present invention will be more fully understood from the detailed description given herein below and the accompanying drawings, which are given by way of example only and therefore not as a limitation of the invention. [Figure 1] 1 is a schematic side view of a sheet printer according to the present invention; [Figure 2] 2 is a schematic side view of the sheet feeding device of the printer of FIG. 1. [Figure 3] 2 is a schematic side view of the sheet feeding apparatus of the printer of FIG. 1 during the step of feeding a sheet. [Figure 4] 2 is a schematic side view of a first embodiment of a sheet feeding apparatus of the printer of FIG. 1 with a first liftable stack support emptied; [Figure 5] 2 is a schematic side view of the sheet feeding apparatus of the printer of FIG. 1 with a second liftable stack support inserted into the stack-holding volume. [Figure 6] 2 is a schematic side view of the sheet feeding apparatus of the printer of FIG. 1 with sheets fed from a second liftable stack support inserted into the stack-holding volume; [Figure 7] 2 is a schematic side view of the sheet feeding apparatus of the printer of FIG. 1 with the first liftable support returned to its bottom position below the second liftable stack support onto which the sheet is being fed. [Figure 8] 2 is a schematic side view of the sheet feeding apparatus of the printer of FIG. 1, in which a first liftable support is provided with a new stack of sheets below a second liftable stack support from which sheets have been fed. [Figure 9]2 is a schematic side view of the sheet stacking device of the printer of FIG. 1 in the step of stacking a first sheet on a first liftable support; [Figure 10] 10 is a schematic side view of the sheet stacking apparatus of FIG. 9 during the step of inserting a second liftable support onto the first liftable support when the latter has reached its maximum capacity; FIG. [Figure 11] , [Figure 12] , [Figure 13] , [Figure 14] , [Figure 15] , [Figure 16] 11-16 are schematic perspective views of steps for feeding a sheet by another embodiment of a sheet feeding apparatus for the printer of FIG. [Figure 17] , [Figure 18] , [Figure 19] , [Figure 20] 17-20 show the steps of the method shown in FIGS. 11-16 in a schematic top view. [Figure 21] , [Figure 22] , [Figure 23] , [Figure 24] 21 to 24 show, in a schematic top view, steps of a method for stacking sheets by another embodiment of a sheet feeding apparatus for the printer of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be described with reference to the accompanying drawings, wherein the same reference numerals are used throughout the several views to identify the same or similar elements.

[0034] printer 1 illustrates a schematic representation of an embodiment of a printing system 1 in accordance with the present invention. For purposes of illustration, printing system 1 is divided into an output section 5, a print engine and control section 3, a local user interface 7, and an input section 4. Although a particular printing system is shown and described, the disclosed embodiments may be used with other types of printing systems, such as inkjet printing systems, electrophotographic printing systems, etc.

[0035] The output section 5 comprises an output holder for holding printed receiving material, for example a plurality of sheets. The output section 5 may comprise further output holders. The printed receiving material is transported from the print engine and control 3 via an inlet 53 to the output section 5 via rollers 54 in an output transport path 52. The output holder is included in a sheet stacking module which stacks sheets received from the output transport path 52 into a stack on the output holder.

[0036] The print engine and control 3 comprises a print engine and a controller 37 that controls the printing process and schedules the sheets in a printing order before they are separated from the stack at the input 4 .

[0037] Controller 37 is a computer, server, or workstation connected to the print engine and to the digital environment of the printing system, e.g., network N for transmitting submitted print jobs to printing system 1. In Figure 1, controller 37 is located inside print engine and control unit 3, but controller 37 may also be located at least partially outside print engine and control unit 3, relative to network N in workstation N1.

[0038] The controller 37 includes a print job receiving unit 371 that enables a user to submit a print job to the printing system 1, the print job including image data to be printed and multiple print job settings. The controller 37 includes a print job queue unit 372 that includes a print job queue for print jobs that have been submitted to the printing system 1 and are to be printed. The controller 37 includes a sheet scheduling unit 373 that determines, for each print job of multiple sheets in the print job queue, an entrance time in the paper path of the print engine and control unit 3, in particular, the entrance time of the first path in the paper path and the entrance time of the second path in the loop according to the present invention. Hereinafter, the sheet scheduling unit 373 will also be referred to as the scheduler 373.

[0039] The sheet scheduling unit 373 takes into account the length of the loop, which corresponds to the loop duration of a sheet passing through the loop, depending on the speed of the sheet in the loop, and which may differ for different types of sheets, i.e., for sheets with different media characteristics.

[0040] The resource may be recording material located in the input section 4, marking material located in a reservoir 39 near or within the print head or print assembly 31 of the print engine, or finishing material located near the print head or print assembly 31 of the print engine or located in the output section 5 (not shown).

[0041] The paper path includes a plurality of paper path sections 32, 33, 34, 35 for transporting the receiving material from an entry point 36 in the print engine and control 3 along the print head or print assembly 31 to an entrance 53 in the output section 5. The paper path sections 32, 33, 34, 35 form a loop according to the present invention, which allows printing of duplex print jobs and / or mixed jobs, i.e., print jobs containing a mix of sheets intended to be printed partly in simplex mode and partly in duplex mode.

[0042] The print head or print assembly 31 is suitable for ejecting and / or fusing marking material onto a receiving material. The print head or print assembly 31 is positioned near the paper path portion 34. The print head or print assembly 31 may be an inkjet print head, a direct imaging toner assembly, or an indirect imaging toner assembly.

[0043] As the receiving material is transported along paper path section 34 in a first path within the loop, it receives marking material through print head or print assembly 31. The next paper path section 32 is a flip unit 32 for selecting a different subsequent paper path for simplex or duplex printing of the receiving material. Flip unit 32 may also be used to flip the sheet of receiving material after printing in simplex mode before the sheet exits print engine and control section 3 through a curved portion 38 of flip unit 32 and through entrance 53 to output section 5. Curved portion 38 of flip unit 32 may not be present and turning (rotating) of single-sided pages must occur via a separate paper path section 35.

[0044] For duplex printing on a sheet, or if flexure 38 is not present, the sheet is transported along a loop through paper path section 35A to rotate the sheet to allow printing on the other side of the sheet. The sheet is transported along paper path section 35 until it reaches junction 34A, where sheets entering paper path section 34 at entry point 36 intermingle with sheets coming from paper path section 35. A sheet entering paper path section 34 at entry point 36 begins a first path along print head or print assembly 31 in a loop. A sheet coming from paper path section 35 begins a second path along print head or print assembly 31 in a loop. After the sheet passes print head or print assembly 31 a second time on the second path, the sheet is transported to entry 53 of output section 5.

[0045] The input section 4 may include one or more sheet supply modules, each with at least one input holder for holding sheets of receiving material before conveying them to the print engine and control 3. Sheets of receiving material are separated from the input holder by a sheet separating module and guided to the print engine and control 3 by guide means 42, 43, 47. Each input holder may be used to hold a different type of receiving material, i.e. sheets with different media properties.

[0046] The local user interface 7 is suitable for displaying a user interface window for controlling a print job queue present in the controller 37. In another embodiment, a computer N1 in the network N has a user interface for displaying and controlling the print job queue of the printing system 1.

[0047] Example 1 FIG. 2 shows a sheet supply module 70 included in the input section 4. It will be understood that the stack processing device shown in FIG. 2 can also be applied as a sheet stacking device in the output section 5, as described with reference to FIG. 9. The sheet supply module 70 includes a first liftable stack support 72 for holding a first stack 89 of sheets. The first liftable stack support 72 is preferably dimensioned to hold a pallet on which a stack of sheets is stacked, and its stack support surface is preferably at least the size of a standard pallet or half-pallet, e.g., at least 1200 x 800 mm or 800 x 600 mm, respectively. The first liftable stack support 72 is connected to a first lift via an attachment 74. The first sine in the example of FIG. 2 includes a lift line in the form of a lift chain 76 coupled to a drive 78 for raising and lowering the first liftable stack support 72 in a lift direction parallel to the vertical direction Z. Other lifts, such as a vertical actuator or a rack-and-pinion system, can also be applied. The first lift is configured to move the first liftable stack support 72 between a bottom position BOT shown in Figure 2 and a top position TOP shown in Figure 4 while maintaining the stack support surface horizontal. The imaginary volume between the bottom position BOT and the top position TOP is shown in Figure 2 with a dashed line to indicate a stack-retaining volume 88. The first lift is controlled to move the first liftable stack support 72 through the stack-retaining volume 89 such that the top sheet in the first stack 89 is maintained at an operable level OL of the sheet separating module 77.

[0048] The sheet separating module 77 is configured to engage and hold the top sheet from the first stack 89 and transport it onto the transport path 86. The sheet separating module 77 of FIG. 2 comprises one or more holding devices 84 that locally hold a portion of the sheet by negative pressure. While holding the sheet, the holding devices 84 guide the sheet along the transport path 86 in the transport direction X until the sheet is moved by the guide devices 82. There, the holding devices 84 release the sheet, after which the sheet is further transported in the transport direction X by rollers of the transport path 86. In the example of FIG. 2, the holding devices 84 are formed by one or more suction devices, such as suction cups or a suction conveying belt. Other holding devices may be applied, as well as separation assistance devices, such as blowers or pinchers, that help separate the top sheet from the stack 89. In another embodiment, the holding devices may be formed as an endless conveying belt with suction devices for attracting the sheet against the belt.

[0049] The first lift and sheet separation module 77 is mounted to a frame 80. The frame 80 secures the sheet feeding module 70 to the ground and provides a rigid, stationary reference against which, for example, the liftable stack supports 72, 92 are moved.

[0050] The sheet feeder 70 further includes an auxiliary stack retaining device 90. The auxiliary stack retaining device 90 includes a second liftable stack support 92 configured to hold a second stack of sheets 95. The second liftable stack support 92 has similar dimensions to the first liftable stack support 72, so that both can hold sheets of the same type (i.e., having the same dimensions and / or data). Both have at least an equally large area for the stack support surface. In FIG. 2, the second liftable stack support 92 is positioned at a buffer position B outside the stack-holding volume 88 so as not to interfere with sheet separation from the first liftable stack support 72.

[0051] The second liftable stack support 92 is configured to move from its buffer position BP into the stack-holding volume 88 by a translation mechanism 110. The translation mechanism 110 includes a horizontal drive 96. The horizontal drive 96 is configured to translate a support bearing 100, to which the second liftable stack support 92 is attached, into the stack-holding volume 88 in the conveying direction X. This guides the support bearing 100 along the frame portion 81. Furthermore, a second lift is provided to move the second liftable stack support 92 in the vertical direction Z relative to the support bearing 100. In FIG. 2 , the second lift includes a motor 93 mounted on a threaded shaft to raise and lower the second liftable stack support 92. Other suitable lifts may also be applied. It will be understood that the auxiliary stack support 90 in different embodiments may also be arranged laterally on the side to move in the direction Y into and out of the stack-holding volume 88. Another side of the stack-holding volume 88 is open so that it is accessible for moving pallets with stacks of sheets into and out of the stack-holding volume 88 .

[0052] FIG. 3 illustrates the step of separating the top sheet from the first stack 89 by the retaining device 84. The sheet is moved in the conveying direction X so that it is positioned on the conveying path 86. This causes the retaining device 84 to release its grip on the sheet, which is then conveyed further along the conveying path 86 toward the printing assembly 31. The retaining device 84 is then returned to its position at the operable level OL so that additional sheets can be separated. Alternatively, the retaining device 84 may move along an endless loop, as in the case of an endless conveyor. The first drive device 78 of the first lift is activated after the separation of one or more sheets to maintain the top sheet at the operable level OL. It will be understood that the retaining device 84 may be vertically movable to some extent and / or provide a sufficiently strong suction force so that the first drive device 78 of the first lift does not need to be activated each time a sheet is separated. As shown in Figure 4, the steps of separating one or more sheets and subsequently raising the first liftable stack support 71 are repeated until the first liftable stack support 72 is empty.

[0053] When the controller 37 determines that the stack on the first liftable stack support 72 is empty, it controls the first lift drive 78 to return the first liftable stack support 72 to the bottom position BOT. When the controller 37 determines that the first liftable stack support 72 has been lowered below the second liftable stack support 92, it activates the horizontal drive 96 to slide the second liftable stack support 92 toward and into the stack-retaining volume 88, as shown in FIGS. 5 and 6. Note that the first and second liftable stack supports 72, 92 have similar sheet stack support areas, but the second liftable stack support 92 is sized to fit between the first lifts, particularly the chains 76, at least in the lateral direction Y. The horizontal drive 96 is configured to translate the second liftable stack support 92 in the horizontal direction X. The attachment 74 is positioned to create sufficient space between the chains 76 for the second liftable support 92. The attachment 74 extends laterally and / or in the conveying directions X, Y beyond or outside the sheet stack support area so that the spacing between the chains 76 is wider than the second liftable stack support 92.

[0054] In FIG. 6 , the second liftable stack support 92 is fully inserted into the stack-holding volume 88 and is located in its active position AP. The second liftable stack support 92 is located above the first liftable stack support 72, which is at or moving toward the bottom position BOT. When viewed in the vertical direction Z, the second liftable stack support 92 entirely overlaps the first liftable stack support 92. The second lift drive 93 is controlled to position the top sheet of the second stack 95 at the sheet separation module 77 to an operational level OL. When a single sheet is present on the first stack support 72 in the active position AP, the operational level OL is preferably at and / or the same as the top position TOP.

[0055] 6 and 7 illustrate the repeated steps of separating sheets from the second stack 95 while the first liftable stack support 72 is beneath the second liftable stack support 92. In FIG. 7, the first liftable stack support 72 has reached its bottom position BOT. Printing operations can continue substantially uninterrupted despite the first stack 89 being empty. While the second stack 95 on the second liftable stack support 95 holds fewer sheets than the first stack 89, the second stack 95 still holds enough sheets to overcome at least the time required to lower the first liftable stack support 72 and restock it with a new stack. Depending on the printing speed, the second stack 95 creates a time window of at least several hours during which the first liftable stack support 72 may be refilled. When it is determined that the first stack 89 is depleted, the controller 37 sends a prompt to a user interface, for example, on a printer, computer, and / or mobile device, to notify the operator that restocking is necessary. The prompt may include an estimated time until the second stack 95 is performed, based on, for example, the number of sheets in the second stack 95 compared to the printing speed of the printer 1 .

[0056] Restoring the first liftable stack support 72 is shown in FIG. 8. A new first stack 89 is placed on the first liftable stack support 72 and below the second liftable stack support 92. Thus, printing operations can continue even while the first liftable stack support 72 is being refilled. The new first stack 89 is placed in the stack-holding volume 88 between the first and second liftable stack supports 72, 92. It will be appreciated that the operator may also choose to first retract the second liftable stack support 92 to its buffer position B before refilling the first liftable stack support 72. In either case, the second liftable stack support 92 is eventually returned to its buffer position BP when or after the new first stack 89 is provided on the first liftable stack support. Sheet supply can then continue from the new first stack 89 on the first liftable stack support 72, as shown in FIG. 1. Meanwhile, the second liftable stack support 92 may be restocked with a new second stack 95. The above steps can then be repeated.

[0057] Example 2 9 and 10 illustrate the operation of the stack processing device of FIG. 2 functioning as a sheet stacking module. Here, the sheet separating module 77 functions as the sheet stacking module 77, picking up sheets from the transport path 86 and moving them toward the operational level OL, where the sheets are ejected onto the stack 89 below. In FIG. 9, the first sheet of a new first stack 89 is placed on the first liftable stack support 72. The first liftable stack support 72 starts at the top position TP and is lowered in stages as more sheets are added to the first stack 89. When the controller 37 determines that the first liftable stack support 72 has reached the bottom position BOT (or printing / stacking is complete), a second liftable stack support 92 is inserted into the stack-holding volume 88, such that the second liftable stack support 92 is positioned above the first stack 89 on the first liftable stack support 72. The bottom position BOT here is selected so that enough space is available to insert the second liftable stack support 92 above the top sheet of the first stack 89 on the first liftable stack support 72. The second stack can then be formed on the second liftable stack support 92 while the operator removes the first stack 89 from the first liftable stack support 72. The second liftable stack support 92 is then retracted to the buffer position B so that stacking can continue on the first liftable stack support 72. After the first liftable stack support 72 is empty, the second liftable stack support 92 can be retracted to the buffer position BP so that stacking can resume on the first liftable stack support 72.

[0058] Example 3 Figure 11 shows another embodiment of a sheet stack handler, which in Figures 11-20 is configured to operate as a sheet feeder. As will be described with respect to Figures 21-24, this configuration can also be applied as a sheet stacker.

[0059] In FIG. 11 , the first and second stack supports 72, 92 are mounted together on a common sliding frame 101, forming a translation mechanism 120. The translation mechanism 120 includes a drive (not shown) configured to reciprocate the sliding frame between a first position FP and a second position SP. At either position FP, SP, one of the first and second stack supports 72, 92 is positioned inside the stack-holding volume 88 below the sheet separating module 77. The drive can move the sliding frame back and forth between the first position FP and the second position SP, such that the first stack support 72 below the sheet separating module 77 is swapped with the second stack support 92, or vice versa. The sheet separating module 77 is then configured to individually separate the top sheets from the sheet stack 89 on the respective stack supports 72, 92, place them on the transport path 86, and move the sheets in the transport direction X.

[0060] FIG. 11 shows that the frame or housing of the sheet feeder is open on both sides of the sliding frame 101 in the sliding direction Y. Thus, each stack support 72, 92 can move in and out of the housing while holding a stack of sheets. Each stack support 72, 92 is further provided with a respective lift 79, 97. The lifts 79, 97 are movable independently of each other in the lift direction Z. The lifts 79, 97 and stack supports 72, 92 on the frame have fixed, non-overlapping positions in the translational direction. Thus, when the frame is moved, the lifts 79, 97 and stack supports 72, 92 move synchronously in the translational direction.

[0061] 12 shows the initial operating state of the sheet feeder. A first stack of sheets 89 is mounted on a first stack support 72 below the sheet separating module 77. The stack of sheets 89 is mounted on a pallet 72P, which is raised intermittently or continuously by a first lift 79 to maintain the top sheet of the stack 89 at an operable level OL for the sheet separating module 77. Thus, the stream of sheets can be fed via a transport path 86 toward the printer.

[0062] A first half of the sliding frame 101, including the first stack support 72, is positioned inside the housing, while a second half, including the second stack support 92, is positioned outside the housing, allowing a second pallet 95P having a second sheet stack 95 to be stacked on the second stack support 92, as shown in FIG.

[0063] The situation in FIG. 13 is shown in a top view in FIG. 17. FIG. 17 shows that the sliding area in which the sliding frame 101 moves includes three separate areas A, B, and C. The buffer areas A and C are located to the sides of and on both sides of the active stack area B in the sliding direction Y. The buffer areas A and C are outside the housing, so that the pallets 72P and 92P can be removed from and / or placed on the stack supports 72 and 92 in the buffer areas A and C. The pallets 72P and 92P can be stacked (or unstacked) by, for example, a forklift. It will be understood that the buffer areas A and C can still be partially shielded as long as they are accessible from at least one side. When viewed from above in the vertical direction Z, the buffer areas A and C correspond to and / or overlap with the respective buffer positions BP1 and BP2, and the active stack area B is located at the active position AP.

[0064] The rigid sliding frame 101 is translatable, at least when viewed in the vertical direction Z, such that the first stack support 72 is movable between the first buffer area A and the active stack area B, and the second stack support 92 is movable between the active stack area B and another buffer area C. The sliding frame 101 rigidly couples the movement of the first stack support 72 to the movement of the second stack 92 in the translation direction Y. On the sliding frame 101, the first and second stack supports 72, 92 have fixed relative positions. The first and second lifts are similarly fixed relative to each other on the sliding frame, at least in the sliding direction. When one of the stack supports 72, 92 is moved to the active stack area B, the other of the stack supports 72, 92 is moved to its respective buffer area A, C. In this example, when the sliding frame 101 is in its first position FP, the first support stack 72 is in the active stack area B, while the second stack support 92 is in the first buffer area A. Activating the drive of the translation mechanism 120 moves the sliding frame to its second position SP, where the first stack support 72 is in the second buffer area C, while the second stack support 92 is in the active stack area B. The first and second lifts can be controlled independently of each other, so that the first and second stack supports 72, 92 can be set to any desired height, regardless of the sliding position of the sliding frame 101. Because the first and second lifts are fixed to the sliding frame in the sliding direction, the stack supports 72, 92 can move up and down as they move toward or away from the active stack area B.

[0065] 14 and 18 show the steps of emptying the first stack 89 on the first stack support 72. Before or as the first stack 89 is emptied, the second lift 97 is controlled to raise the second stack 95 to the operating level OL of the sheet feeder 77. The stack exchange time is reduced by raising the second stack 95 to the correct level before insertion. Alternatively, the lifting can occur while the sliding frame 101 is moving.

[0066] 15 and 19 show the translation of the sliding frame 101 to the second position SP. The first stack support 72 slides out of the housing into the second buffer area C. The second stack support 92 simultaneously enters the housing and is positioned at the active stack position B. Note that the second stack 95 is not perfectly aligned with the first stack 89. In this example, the second stack 95 is stacked such that it is slightly shifted relative to the first stack 89 in both the conveying direction X and the sliding direction Y. The translation of the sliding frame 101 is controlled so that each stack 89, 95 is aligned with a predetermined lateral reference position D (indicated by the arrow). This aligns the sheets in the lateral direction Y on the conveying path 86. The deviation in the conveying direction X can be corrected by controlling the movement of the sheet supply module 77, for example, so that the sheets are supplied with a constant sheet-to-sheet distance. If the stacks 89, 95 are positioned in a rotated state, the rotation can also be corrected by a combined action of positioning the sliding frame 101 and the sheet separating module 77. The position of the sheet stacks 89, 95 can be detected by one or more suitable sensors, such as a camera, a (laser) distance sensor, or other detection means. It will be understood that each correction (such as X, Y, or skew / rotation deviation) can be applied independently of each other. Thus, each stack or pallet can be loaded relatively quickly, as careful alignment is not required during loading.

[0067] Figure 16 shows the steps of lowering the first stack support 72 so that a new stack 89 can be placed on the first stack support 72, as shown in Figure 20. The above steps can then be repeated mutatis mutandis to continue the printing process with minimal interruption due to stack swapping.

[0068] Example 4 It will be understood that the configurations of Figures 11 to 16 can also be applied to a sheet stacking apparatus, as shown in Figures 21 to 24. In Figure 24, both stack supports 72, 92 include empty pallets 72P, 92P. The first stack support 72 is located in the active stack area B and rises and then lowers to maintain the top sheet of the stack 89 thereon at the level of the sheet stacking module 77. The second stack support 92 is located in the first buffer area A.

[0069] FIG. 22 shows that the first stack 89 is completed, or the first stack support 72 has reached its maximum capacity. Next, the translation mechanism 120 is actuated to slide the first stack 89 into the second buffer area C. Simultaneously, the sliding frame 101 moves the second stack support 92 to the active stack area B by moving the second position SP, where the pallet 92P is aligned with the lateral reference position D. The second lift 97 is also controlled so that the pallet 92P is in the operation OL of the sheet stacking module 77 and / or aligned with the lateral reference position D at or before the sliding frame 101 reaches the second position SP. Sheet stacking can then continue on the second stack support 92. When the capacity of the second stack support 92 is reached, an empty pallet 72P is provided on the first stack support 72, after which the sliding frame 101 can be moved to the first position FP.

[0070] While specific embodiments of the present invention have been illustrated and described herein, it will be recognized by those skilled in the art that various alternative and / or equivalent implementations exist. It should be understood that the exemplary embodiment or embodiments are examples only and are not intended to be limiting in any way in scope, applicability, or configuration. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, and it should be understood that various changes can be made in the function and arrangement of elements described in the exemplary embodiments without departing from the scope as set forth in the appended claims and their legal equivalents. In general, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

[0071] In this document, the terms "comprises," "comprising," "includes," "including," "has," "having," and any variations thereof are intended to be understood in an inclusive (i.e., non-exclusive) sense, and it will also be understood that the processes, methods, devices, apparatuses, or systems described herein are not limited to those features or portions or elements or steps that are enumerated, but may include other elements, features, portions, or steps that are not expressly enumerated or that are inherent to such processes, methods, articles, or apparatuses. Furthermore, as used herein, the terms "a" and "an" should be understood to mean one or more, unless expressly stated otherwise. Furthermore, terms such as "first," "second," and "third" are used merely as labels and are not intended to impose or establish numerical requirements on a particular ranking of the importance of those objects.

[0072] 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 which would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. 1. A sheet stack handler comprising a sheet stacker and / or a sheet feeder, - first and second liftable stack supports mounted on the pallet, each configured to support a stack of sheets; - individual sheet engagers comprising a sheet-to-stack feeder for stacking a sheet onto a stack of sheets on one of said first or second liftable stack supports and / or a sheet-from-stack separator for separating a sheet from a stack of sheets on one of said first and second liftable stack supports; a lift assembly comprising first and / or second lifts for respectively moving the first and / or second liftable stack supports between a bottom position and a top position disposed spaced apart and adjacent to the respective sheet engagers, such that a stack-holding volume is defined between the bottom and top positions, the lift assembly being further configured to position the top sheet of the stack on the first and / or second liftable stack supports inside the stack-holding volume at an operable level of the respective sheet engagers so that the respective sheet engagers can stack a new sheet on the top sheet and / or separate the top sheet from their respective stacks; a translation mechanism configured to translate at least one of said first and second liftable stack supports together with its respective first and / or second lift while supporting a stack of sheets between a buffer position outside and to one side of said stack-holding volume and an active position inside said stack-holding volume; Equipped with the first lift is a lift for raising and / or lowering the first liftable stack support, and the second lift is a lift for raising and / or lowering the second liftable stack support independently of the first liftable stack support; a sheet stack handler provided with two buffer positions on either side of the stack holding volume such that moving one of the first and second liftable stack supports from one of the buffer positions to the active position moves the other of the first and second liftable stack supports from the active position to the other of the buffer positions.

2. 2. The sheet stack handler of claim 1, wherein the individual sheet engaging members are configured to transport sheets in a transport direction parallel to a transport path for supplying sheets to the individual sheet engaging members and / or receiving sheets from the individual sheet engaging members, and the translation direction of the translation mechanism is perpendicular to the transport direction and the lift direction.

3. 3. The sheet stack handler of claim 2, wherein the translation mechanism is configured to move one of the first and second liftable stack supports back and forth along a straight linear trajectory between the active position and the buffer position.

4. 4. The sheet stack handler of claim 3, wherein the translation mechanism comprises a sliding frame connecting the first liftable stack support to the second liftable stack support such that the first and second liftable stack supports move in a direction of translation of the translation mechanism.

5. 5. The sheet stack handler of claim 4, wherein the sliding frame is a rigid frame defining fixed, non-overlapping positions thereon for the first and second liftable stack supports.

6. 5. The sheet stack handler of claim 4, wherein the first and second lifts are mounted on the sliding frame alongside one another in the translational direction.

7. 2. The sheet stack handler of claim 1, further comprising a housing enclosing the stack holding volume, the buffer position extending outside the housing, and in the buffer position, the first and second liftable stack supports are accessible for loading and / or unloading pallets therefrom.

8. The lift assembly includes: a first lift for moving the first liftable stack support between the bottom position and the top position, the second liftable stack support being movable between the buffer position and the active position in a direction perpendicular to a lift direction of both the first and second liftable stack supports and independent of the first liftable stack support, the second liftable support being inside the stack-holding volume and extending above the first liftable stack support, whereby the individual sheet engagers are able to stack sheets onto and / or separate sheets from a second stack of sheets on the second liftable stack support; a second lift for lowering and raising the second liftable stack support independently of the first lift, the second liftable stack support being dimensioned and arranged to be inserted into the stack-retaining volume without contacting the first lift at least between the top position and the bottom position; 10. The sheet stack handler of claim 1, comprising:

9. 9. The sheet stack handler of claim 8, further comprising a translation guide beam along which the second liftable stack support is movable when moving into and out of the stack-holding volume, the translation guide beam extending parallel to a horizontal direction in use.

10. 10. The sheet stack handler of claim 9, wherein the second lift is positioned outside the stack-holding volume when the second liftable stack support is inserted into the stack-holding volume.

11. 11. The sheet stack handler of claim 10, wherein the second liftable stack support does not overlap a lift line of the first lift when viewed vertically.

12. 2. The sheet stack handler of claim 1, further comprising: a controller configured to determine when a number of sheets in the stack on the first liftable stack support meets or exceeds a predetermined threshold, control the first liftable stack support to be positioned at the bottom position, subsequently control the second liftable stack support to be inserted into the stack-holding volume, and transmit stack support information to prompt the user on a user interface.

13. 1. A sheet stack handler comprising a sheet stacker and / or a sheet feeder, - first and second liftable stack supports mounted on the pallet, each configured to support a stack of sheets; - individual sheet engagers comprising a sheet-to-stack feeder for stacking a sheet onto a stack of sheets on one of said first or second liftable stack supports and / or a sheet-from-stack separator for separating a sheet from a stack of sheets on one of said first and second liftable stack supports; a lift assembly for moving the first and / or second liftable stack supports between a bottom position and a top position disposed spaced apart and adjacent to the respective sheet engagers, such that a stack-holding volume is defined between the bottom position and the top position, the lift assembly being further configured to position the top sheet of the stack on the first and / or second liftable stack supports inside the stack-holding volume at an operable level of the respective sheet engagers so that the respective sheet engagers can stack a new sheet on the top sheet and / or separate the top sheet from their respective stacks; a translation mechanism configured to translate at least one of the first and second liftable stack supports while supporting a stack of sheets between a buffer position outside and to one side of the stack-holding volume and an active position inside the stack-holding volume; Equipped with a sheet stack handler, wherein two buffer positions are provided on opposite sides of the stack holding volume, such that moving one of the first and second liftable stack supports from one of the buffer positions to the active position moves the other of the first and second liftable stack supports from the active position to the other of the buffer positions.

14. A printer comprising the sheet stack handler of claim 1.

15. 1. A method for stacking and / or feeding sheets onto and / or from a stack, comprising: - controlling the height position of the first liftable stack support by means of a first lift so that the top sheet of a stack on the first liftable stack support is at an operable level at the individual sheet engagers so that the individual sheet engagers can stack and / or feed sheets onto and / or from the stack on the first liftable stack support; - moving a second liftable stack support with a second lift from one of two buffer positions adjacent a side of the stack-holding volume to an active position within said stack-holding volume along a linear trajectory, thereby moving said first liftable stack support with said first lift from said active position to the other of said two buffer positions; - controlling the height position of the second liftable stack support by means of the second lift, independently of the height position of the first liftable stack support, so that the top sheet and / or top surface of the stack on the second liftable stack support is at the operable level at the respective sheet engager; - stacking and / or separating sheets onto and / or from said stack on said second liftable stack support by said individual sheet engagers; A method comprising:

16. 16. The method of claim 15, wherein the second liftable stack support slides on the first liftable stack support within the stack-holding volume, or wherein the sliding step includes moving the first and second liftable stack supports translationally in a coupled movement.

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