NL2022716B1

NL2022716B1 - Sheet transfer device with an elastically deformable support surface for transferring sheets between two conveyors in a printing system

Info

Publication number: NL2022716B1
Application number: NL2022716A
Authority: NL
Inventors: G La Vos Peter
Original assignee: Canon Production Printing Holding Bv
Priority date: 2019-03-11
Filing date: 2019-03-11
Publication date: 2020-09-18
Also published as: DE102020105126A1

Abstract

A sheet transport device for a printing system comprising a first and a second sheet conveyor is provided. The sheet transfer device comprises a plurality of rotatable support rollers for supporting the sheet in between the first and second sheet conveyors. The support rollers are at least partially positioned in a suction chamber to suck the sheet against the support rollers. The support rollers are formed of an elastic material deformable under forces transmitted from at least one of the first and second sheet conveyor via the sheet to the support rollers. When one conveyor pulls on a portion of the sheet still held by the other conveyor, the elastic support rollers mitigate any displacement forces and ensure the position of the portions of the sheet on their respective conveyors is not affected.

Description

P4085NL01 1

SHEET TRANSFER DEVICE WITH AN ELASTICALLY DEFORMABLE SUPPORT SURFACE FOR TRANSFERRING SHEETS BETWEEN TWO CONVEYORS IN A PRINTING SYSTEM

FIELD OF THE INVENTION The present invention relates to a method for transporting sheets in a printing system, wherein a sheet is transferred from a first conveyor to a second conveyor, as well as to a sheet transport device for such a printing system.

BACKGROUND ART The transport path of a printing system generally comprises a plurality of different conveyors, such as air-permeable transport belts, transport pinches, drums, etc. When a sheet is transferred from a first conveyor to a second conveyor, the velocities of both conveyors may be misaligned. For example, the transport direction and/or speed of the second conveyor may differ slightly from that of the first conveyor. This may affect the position of the portion of the sheet remaining on the first conveyor, for example when the second conveyor operates pulls on the sheet in a different direction than the first conveyor. It is known to provide a sheet transfer device in between both conveyors, such that the conveyors are sufficiently spaced apart so that a sheet is never engaged by both conveyors at the same time. However, the sheet transfer device generally holds and moves the sheet, such that the sheet transfer device may pull on the portion of the sheet on the first conveyor. Likewise, the sheet transfer device may disrupt the position of a portion of the sheet on the second conveyor.

SUMMARY OF THE INVENTION It is an object of the present invention to provide sheet transfer device for transferring a sheet between two or more separate sheet conveyors in a printing system, wherein the position of the sheet on the sheet conveyors is accurately maintained during transfer.

In a first aspect of the present invention, a method for transporting a sheet through a printing system is provided. The method comprises: - transferring the sheet from a first conveyor to a second conveyor, wherein the sheet is transferred from the first to the second conveyor over an elastic support surface of a sheet transfer device; - holding the sheet onto and transporting said sheet via the elastic support surface; and

P4085NL01 2 - deforming the elastic support surface when a first conveyor velocity of the first conveyor and/or a second first conveyor velocity of the second conveyor differs from a transfer velocity of the sheet transfer device.

In order to transport the sheet, the first and second conveyors each hold and move the sheet at individual velocities, which in practice are generally not perfectly matched. Similarly a velocity difference between the sheet transfer device and one or both of the sheet conveyors generally occurs during operations. When both a sheet conveyor and the sheet transfer device hold the sheet simultaneously, a difference between a conveyor velocity and the transfer velocity can result in an undesired displacement of the sheet on the respective conveyors. An elastic support surface is provided in between the two sheet conveyors with a length in the main transport direction of the sheet that allows the sheet to be supported by the elastic support surface while being simultaneously being held by at least one of the sheet conveyors and the sheet transfer device comprising the elastic support surface. It is the insight of the inventor that by allowing the elastic support surface to deform under a force exerted on the sheet by a velocity difference between a conveyor velocity and the transfer velocity of the sheet transfer device, the force is mitigated over the elastic support surface and undesired displacement of portions of the sheet on the respective sheet conveyor is prevented.

The present invention is particularly advantageous when a precise and stabile position of the sheet on the first conveyor is required, for example during the printing of an image on the sheet. The position of the portion being printed on is then maintained despite velocity differences between the first conveyor and the sheet transfer device. Similarly, the second conveyor may be provided with a drying device for further fixing the ink to the sheet may then be positioned in close proximity to the print head assembly. The elastic support surface then prevents displacement of the sheet portion being dried. This is not only beneficial for the image quality, but allows for a size efficient printing system. An additional advantage is that the elastic support surface may be formed by suitable low costs material, such as an elastic polymer or rubber, resulting in a low cost solution.

Thereby the object of the present invention has been achieved.

Further embodiments are subject of the dependent claims. In an embodiment, the printing system comprises a processing device positioned over the first conveyor and the method further comprises the step of processing an upstream portion of the sheet on the first conveyor while a downstream portion of said sheet is

P4085NL01 3 engaged by the elastic support surface. The processing device is configured to perform a processing operation which alters the state of the sheet, preferably by adding and/or removing material to/and/or from the sheet. Preferably, the processing device is an inkjet print head assembly positioned over the first conveyor for jetting droplets of ink on a sheet on the first conveyor. To ensure that the processing operation is performed as desired, the position of the portion of the sheet being processed has to be maintained. The elastic support surface deforms to prevent any displacement of the portion being processed in consequence of a velocity difference between the first conveyor and the sheet transfer device, resulting in e.g. pulling on said portion.

In an embodiment, the method according to the present invention further comprises the step of holding the sheet against the support surface by means of an underpressure applied to the sheet. The elastic support surface is air permeable, such that an underpressure may be applied to a sheet on top of it. Preferably, the elastic support surface is positioned over an open ended suction chamber connected to a suction device or source. The elastic support surface preferably comprises openings for drawing air into the suction chamber. The underpressure draws the sheet against the elastic support surface. The underpressure ensures contact between the elastic support surface and the sheet, such that the elastic support surface is able to exert a friction force on the sheet. Due to the friction between the sheet and the elastic support surface the elastic support surface deforms when a conveyor velocity of the first and second conveyors does not match the transfer velocity of the sheet transfer device (or vice versa). The elasticity allows the sheet to deform accordingly to velocity differences and at the same time provides a counterforce that mitigates any pulling force.

In an embodiment, the elastic support surface is elastically deformable at least in a direction perpendicular to a main transport direction of the first conveyor. Preferably, the elastic support surface is further elastically deformable in the lateral direction perpendicular to the transport direction. The lateral direction is parallel to the plane of the sheet conveyors and/or the sheet support plane defined by the elastic support surface. In an embodiment, the support surface is formed by a plurality of rollers formed of an elastic material. The rollers are rotatable around one or more axes extending substantially perpendicular to the main transport direction of the sheet. The elastic material is elastically deformable preferably with respect to a rigid core provided

P4085NL01 4 rotatably around the rotation axes under influences of force transmitted via the sheet when there is a velocity difference between the a conveyor and the sheet transfer device. When such a velocity difference occurs, the portion of the sheet over the elastic support surface experiences a displacement force in a direction different than the transport direction of the first sheet conveyor. Due the friction between the sheet and the elastic material on the rollers, this displacement force causes the elastic material to deform in the latter direction and/or perpendicular to a transport direction of the first conveyor. The elastic material deforms instead of displacing the sheet portion on the first conveyor. Similarly, a portion on the second sheet conveyor is prevented from displacement. Due to its elasticity the elastic material exerts an opposing counter force on the sheet, which locally acts against the displacement force. As such, the elastically deformable rollers provide a displacement force mitigation zone.

In a further aspect, the present invention provides a sheet transport device for a printing system, comprising: - a first sheet conveyor positioned upstream of a second sheet conveyor; - a sheet transfer device for transferring a sheet from the first conveyor to the second conveyor, the sheet transfer device comprising an air permeable, elastic support surface for supporting the sheet in between the first and second sheet conveyors, wherein the sheet transfer device comprises a suction chamber, which suction chamber is connected to a suction source for applying an underpressure to the sheet to draw the sheet against the support surface, wherein the support surface is deformable under forces transmitted from the at least one of the first and second sheet conveyor via the sheet to the support surface when a transfer velocity of the sheet transfer device differs from a conveyor velocity of the first and/or second sheet conveyor.

At the open ended side of the suction chamber the elastic support surface is positioned, for example embodied as a plurality of support rollers provided on their respective rotation axes. The suction device is configured to draw air into the suction chambers through the open spaces between the support rollers. Thereby the sheet is held in frictional engagement with the support rollers. When a velocity difference occurs between a conveyor and the sheet transfer device the portion of the sheet over the support rollers experiences a displacement force. Said force causes the elastic material of the support rollers to deform, resulting in a counterforce. The combined counterforces of the individual rollers in frictional contact with the sheet prevent the displacement force from reaching across the sheet transfer device and affecting the position of the sheet

P4085NL01 portion on at least the first or second conveyor.

Aside from support rollers, other suitable elastic means may be provided to form the elastic support surface.

In an embodiment, the sheet transfer device comprises a plurality of support rollers 5 formed of an elastic material.

In an embodiment, each support roller comprises a rigid core rotatably supported on a rotation axis, around which core the elastic material is provided, such that the elastic material is deformable with respect to the core under the influence of forces transmitted via the sheet to the support rollers.

A layer or circumference of elastic material is provided around the rigid, which material deforms under forces transmitted via the sheet.

Said forces are parallel to the plane of the sheet.

The elasticity provides a counterforce to act against the displacement force.

The magnitude of the counterforce of each support roller is “automatically” adjusted to the displacement force due to the elastic nature of the support rollers.

No active control is required.

In an embodiment, the first and second sheet conveyors comprises holding means for holding the sheet onto the respective one of the first and second sheet conveyor.

The holding means engage and hold the sheet onto part of the conveyor.

The holding means may include suction means and/or clamping means.

Preferably the first and/or second conveyor comprise an endless transport belt provided with through-holes for drawing a sheet against the belt by means of an underpressure applied via an underlying suction chamber.

In another embodiment, the sheet transfer device comprising a drive for rotating the support wheels around rotation axes for setting the transfer velocity.

The support rollers or wheels are brought into rotation by the drive, which is controlled to operate at a predetermined speed to match the first and/or second conveyor velocity.

The elasticity of the support rollers ensures that when a velocity difference occurs between the sheet transfer device (as determined by the speed of the drive) and the first (or second) sheet conveyor, the first (or second) sheet conveyor maintains control of the velocity and position of the portion of the sheet on the first conveyor.

Basically, the due to the elasticity the support rollers conform to the first conveyor velocity, without affecting the portion of the sheet on the first conveyor.

Likewise, the elasticity of the support rollers ensures that the second conveyor at all times during operation determines the velocity and position of the sheet portion thereon.

The rotation axes preferably extend

P4085NL01 6 perpendicular to the main transport direction. Preferably a plurality of parallel rotation axes is provided spaced apart from one another in the main transport direction. In an embodiment, the elastic material forms the circumference of the support rollers and is provided with a plurality of recesses. The recesses or out-takes provide additional deformability for the elastic material. In an embodiment, the support rollers are positioned inside the suction chamber with their top portions positioned in a sheet support plane of the first and/or second sheet conveyor. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying schematical drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: Fig. 1 is a schematic side view of a sheet printing system according to the present invention; Fig. 2 is a schematic side view of a sheet transport device according to the present invention; Fig. 3 is an enlarged view of the central portion of the sheet transport device in Fig. 2; and Figs. 4 to 7 are schematic top views of the different stages of a sheet progressing over the sheet transport device in Figs. 2 and 3; Fig. 8 shows another embodiment of a sheet printing system according to the present invention.

P4085NL01 7

DETAILED DESCRIPTION OF THE DRAWINGS The present invention will now be described with reference to the accompanying drawings, wherein the same reference numerals have been used to identify the same or similar elements throughout the several views. FIG. 1 shows schematically an embodiment of a printing system 1 according to the present invention. The printing system 1, for purposes of explanation, is divided into an output section 5, a print engine and control section 3, a local user interface 7 and an input section 4. While a specific printing system is shown and described, the disclosed embodiments may be used with other types of printing system such as an ink jet print system, an electrographic print system, etc. The output section 5 comprises a first output holder 52 for holding printed image receiving material, for example a plurality of sheets. The output section 5 may comprise a second output holder 55. While 2 output holders are illustrated in FIG. 1, the number of output holders may include one, two, three or more output holders. The printed image receiving material is transported from the print engine and control section 3 via an inlet 53 to the output section 5. When a stack ejection command is invoked by the controller 37 for the first output holder 52, first guiding means 54 are activated in order to eject the plurality of sheets in the first output holder 52 outwards to a first external output holder

51. When a stack ejection command is invoked by the controller 37 for the second output holder 55, second guiding means 56 are activated in order to eject the plurality of sheets in the second output holder 55 outwards to a second external output holder 57.

The output section 5 is digitally connected by means of a cable 60 to the print engine and control section 3 for bi-directional data signal transfer. The print engine and control section 3 comprises a print engine and a controller 37 for controlling the printing process and scheduling the plurality of sheets in a printing order before they are separated from input holder 44, 45, 46. The controller 37 is a computer, a server or a workstation, connected to the print engine and connected to the digital environment of the printing system, for example a network N for transmitting a submitted print job to the printing system 1. In FIG. 1 the controller 37 is positioned inside the print engine and control section 3, but the controller 37 may

P4085NL01 8 also be at least partially positioned outside the print engine and control section 3 in connection with the network N in a workstation N1. The controller 37 comprises a print job receiving section 371 permitting a user to submit a print job to the printing system 1, the print job comprising image data to be printed and a plurality of print job settings. The controller 37 comprises a print job queue section 372 comprising a print job queue for print jobs submitted to the printing system 1 and scheduled to be printed. The controller 37 comprises a sheet scheduling section 373 for determining for each of the plurality of sheets of the print jobs in the print job queue an entrance time in the paper path of the print engine and control section 3, especially an entrance time for the first pass and an entrance time for the second pass in the loop in the paper path according to the present invention. The sheet scheduling section 373 will also be called scheduler 373 hereinafter. The sheet scheduling section 373 takes the length of the loop into account. The length of the loop corresponds to a loop time duration of a sheet going through the loop dependent on the velocity of the sheets in the loop. The loop time duration may vary per kind of sheet, i.e. a sheet with different media properties. Resources may be recording material located in the input section 4, marking material located in a reservoir 39 near or in 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). The paper path comprises a plurality of paper path sections 32, 33, 34, 35 for transporting the image receiving material from an entry point 36 of the print engine and control section 3 along the print head or print assembly 31 to the inlet 53 of the output section 5. The paper path sections 32, 33, 34, 35 form a loop according to the present invention. The loop enables the printing of a duplex print job and/or a mix-plex job, i.e. a print job comprising a mix of sheets intended to be printed partially in a simplex mode and partially in a duplex mode.

The print head or print assembly 31 is suitable for ejecting and/or fixing marking material to image receiving material. The print head or print assembly 31 is positioned near the paper path section 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.

P4085NL01 9 While an image receiving material is transported along the paper path section 34 in a first pass in the loop, the image receiving material receives the marking material through the print head or print assembly 31. A next paper path section 32 is a flip unit 32 for selecting a different subsequent paper path for simplex or duplex printing of the image receiving material. The flip unit 32 may be also used to flip a sheet of image receiving material after printing in simplex mode before the sheet leaves the print engine and control section 3 via a curved section 38 of the flip unit 32 and via the inlet 53 to the output section 5. The curved section 38 of the flip unit 32 may not be present and the turning of a simplex page has to be done via another paper path section 35.

In case of duplex printing on a sheet or when the curved section 38 is not present, the sheet is transported along the loop via paper path section 35A in order to turn the sheet for enabling printing on the other side of the sheet. The sheet is transported along the paper path section 35 until it reaches a merging point 34A at which sheets entering the paper path section 34 from the entry point 36 interweave with the sheets coming from the paper path section 35. The sheets entering the paper path section 34 from the entry point 36 are starting their first pass along the print head or print assembly 31 in the loop. The sheets coming from the paper path section 35 are starting their second pass along the print head or print assembly 31 in the loop. When a sheet has passed the print head or print assembly 31 for the second time in the second pass, the sheet is transported to the inlet 53 of the output section 5. The input section 4 may comprise at least one input holder 44, 45, 46 for holding the image receiving material before transporting the sheets of image receiving material to the print engine and control section 3. Sheets of image receiving material are separated from the input holders 44, 45, 46 and guided from the input holders 44, 45, 46 by guiding means 42, 43, 47 to an outlet 38 for entrance in the print engine and control section 3. Each input holder 44, 45, 46 may be used for holding a different kind of image receiving material, i.e. sheets having different media properties. While 3 input holders are illustrated in FIG. 1, the number of input holders may include one, two, three or more input holders. The local user interface 7 is suitable for displaying user interface windows for controlling the print job queue residing in the controller 37. In another embodiment a computer N1 inthe network N has a user interface for displaying and controlling the print job queue of the printing system 1.

P4085NL01 10 Fig. 2 schematically a sheet transport device 100 according to the present invention. Such a sheet transport device 100 may for example form the transport path 33 in Fig. 1. The sheet transport device 100 in Fig. 2 comprises a first conveyor 110 upstream of a second conveyor 120, when viewed in the main transport direction T. In Fig. 2 each conveyor 110, 120 comprises a sheet support surface 111, 121 for holding and transporting sheets in the main transport direction T. Each conveyor 110, 120 in Fig. 2 comprises an air permeable, endless transport belt 111, 121 supported on a plurality of rollers 112, 123. A drive (not shown) is provided for rotating at least one of the rollers 112, 123 and driving the transport belt 111, 121. A suction chamber 115, 125 is provided adjacent the transport belt 111, 121, such that an underpressure may be applied through the transport belt 110, 120 to a sheet on the sheet support surface 111,

121. Thereto, the suction chamber 115, 125 is connected to a suction device 114, 124, such as a pump or fan. The transport belt 111, 121 is shown to illustrate the present invention, which may include different types of conveyors 110, 120, such as transport pinches, or sheet transport drums.

In the embodiment in Fig. 2 a sheet processing device 116, 126 is positioned over a respective one of the conveyors 110, 120. Each sheet processing device 118, 126 is configured to apply a process or treatment to a sheet on its respective conveyor 110,

120. The treatment alters the state of the sheet. Such sheet processing devices 1186, 126 may include an inkjet print head assembly for jetting droplets of ink on the sheet, a drying device for removing moisture from the sheet, a coating device for applying a coating to the sheet, a finisher device for performing a finishing operation such as punching, cutting, or stapling of the sheet. In the embodiment shown in Fig. 2 the first processing device 110 is a during operation stationary page-wide inkjet print head array extending over a width of the conveyor 110. The second processing device 126 in Fig. 2 is a sheet drying device 126 comprising means for drying the sheet, for example heaters and/or air blowers.

Fig. 2 further shows a sheet transfer device 130 positioned between the two conveyors 110, 120. The length of the sheet transfer device 130 in the main transport direction T is preferably less than the length of the first conveyor 110, for example less than half of said length, preferably less than a quarter of said length. The sheet transfer device 130 comprises a suction chamber 131 in fluid connection with the suction device 132, such that air may be drawn into the suction chamber 131 via its top side. The top side of the suction chamber 131 is substantially open ended. At said top side a plurality of support

P4085NL01 11 rollers 140 are provided to define a transfer support surface or plane for supporting the sheet in between the first and second conveyors 110, 120. The plurality of support rollers 140 is positioned such their top sides define a support plane which extends parallel and aligned with the support surface of the first conveyor 110 as well as with that if the second conveyor 120. The support rollers 140 are rotatably mounted on their respective rotation axes 142. A drive (not shown) is provided for rotating the support rollers 140 around their respective rotation axes 142 in Fig 2. The drive is controlled such that the angular velocity (i.e. the transfer velocity VT) in the support plane of the support rollers 140 matches the first conveyor velocity V1. The rotation axes 142 in Fig. 2 are spaced apart from another in the transport direction T. Preferably, the rotation axes 142 are positioned inside the suction chamber 131. In Fig. 2 the rotation axes 132 are aligned in a plane parallel to the support surface 111 of the first conveyor 110. Each support roller 140 comprises a rigid core 141, for example a tubular bearing 141 provided around its respective rotation axis 141. The rigid core 141 is mounted freely rotatably around the rotation axis 142. Around the rigid core 141 of each support 140 an elastic layer 143 is provided. The elastic layer 143 forms a deformable circumference around the rigid core 141, such that the outer surface of the support roller 140 is moveable with respect to the rigid core 142 under the influence of forces exerted on the sheet S. The elastic layer 143 may be formed of a suitably elastic polymer, plastic, or rubber. Further elasticity and/or deformability may be achieved by providing recesses 144 in the elastic circumference 143. Such recesses 144 may extend axially as well as radially, as shown in Figs 2 and 3.

During operation the suction device 132 applies an underpressure to the suction chamber 131, thereby drawing the sheet S against the top sides of the support rollers

140. The underpressure brings the sheet S in frictional contact with the support rollers

140. The sheet S is driven in the transport direction T over the support roller 140 from the first conveyor 110 to the second conveyor 120. The support rollers 140 are controlled to transport at the transfer velocity VT which is controlled to match or approximate the velocity V1, V2 of the first and/or second sheet conveyor 110, 120. As will be explained below, the elasticity of the support rollers 140 preserves the position of a sheet portion on the first and/or second sheet conveyor 110, 120 when velocities differences occur between the sheet transfer device 130 on one hand and at least one of the sheet conveyors 110, 120 on the other hand.

P4085NL01 12 Figs. 4 to 6 schematically illustrate the steps of the method according to the present invention. Fig. 4 shows a top down view of the sheet transport device 100 in Figs. 2 and

3. The first conveyor 110 is oriented to transport a sheet S with a velocity V1, which is different from the velocity V2 of the downstream conveyor 120 as well as from a transfer velocity VT of the sheet transfer device 130. Within the present invention the velocities V1, V2, VT may differ in direction and/or magnitude. To prevent this velocity difference from affecting the position of the sheet S on the first conveyor 110, the sheet transfer device 130 is positioned between the first and second conveyors 110, 120. The length of the sheet transfer device 130 in the main transport direction T is no more than and preferably less than a length of the sheet S to achieve compactness (the sheet S preferably being the longest sheet S available for processing by the printing system 1). In the step shown in Fig. 4, the sheet S is conveyed by the first conveyor with a velocity V1 towards the second conveyor 120.

In Fig. 4, the sheet S is moved solely by the first conveyor 110 which moves at the first conveyor velocity V1. This allows for highly accurate positioning of ink droplets on the sheet S. Fig. 5 shows the step wherein the sheet S is moved across the sheet transfer device 130. Therein the sheet S moves over the suction box 131. By means of the underpressure applied there the sheet S is drawn against the top sides of the support rollers 140, which together form the elastic support surface. Since the support rollers 140 are rotated at the transfer velocity VT, the support rollers 140 experience a force via the sheet S from the velocity difference between the first conveyor 110 and the sheet transfer device 130. Instead of displacing the portion of the sheet S on the first conveyor 110, the force deforms the support rollers 140. In Fig. 5, the force and the deformation are in the transport direction V1, since the transfer velocity VT and the first conveyor velocity V1 are parallel. Thereby, the velocity difference is prevented from acting on the portion of the sheet S still on the first conveyor 110, thus preserving the position of the portion being printed on. The elastic deformation of the support rollers 140 ensures that the first conveyor 110 at all times controls the velocity and position of the portion of the sheet S thereon when said sheet S is also engaged by the sheet transfer device 130.

In Fig. 6 the sheet S is engaged by the second conveyor 120 as well as by the sheet transfer device 130, which conveyor 120 has a conveyor velocity V2 different from that of the sheet transfer device 130. In consequence a force is exerted on the sheet S. The velocity vectors V2, VT in Fig. 5 differ in orientation, resulting in a lateral or sideways force on the sheet S. This force is however prevented from affecting the position of the

P4085NL01 13 sheet S on the second conveyor 120 due to the elasticity of the support rollers 140 as the support rollers 140 elastically deform in response to the force. As the outer surface of the support rollers 140 is able to deform, the sheet S is free to adapt to the force within the area of the sheet transfer device 130. The force is as such gradually mitigated across the sheet transfer device 130, similarly to what was described with respect to Figs. 4 and 5. In Fig. 7, the sheet S clears the sheet transfer device 130 and is transported solely at the second conveyor velocity V2. The sheet transfer device 130 ensures that when a sheet S is held simultaneously by a conveyor 110, 120 and the sheet transfer device 130 the respective conveyor 110, 120 determines and controls the velocity and position of the sheet portion thereon. It will be appreciated that the length of the sheet transfer device 130 may be selected dependent on a sheet length of a sheet to be printed as compared to the distance between a processing device on one conveyor and the adjacent end of the other conveyor. For example, once a sheet S has passed the first processing device 116 on the first conveyor there may no longer be a need for accurate position control on the first conveyor 110, allowing for an even more compact embodiment of the sheet transfer device 130. Should the printing system 1 be configured to hold or process multiple sheet types, then the sheet type with the greatest length in the transport direction T should be used to determine suitable dimension for the sheet transfer device 130.

Fig. 8 shows another embodiment of the sheet transfer device 230 according to the present invention. The elastic support surface in Fig. 8 is formed by an endless transport belt 242 provided with an elastically deformable support surface. The support surface in Fig. 8 is formed by a plurality of elastic fingers or other suitable maze structure mounted onto the belt 242. A suction chamber 231 connected to a suction source 232 is provided below the belt 242 to draw in air via through-holes in the belt

242. Thereby, the sheet S is sucked against the top surface of the elastically deformable fingers 241. The fingers 241 are configured to deform via forces acting on the sheet S when a velocity difference occurs between the transport belt 242 and the first or second conveyors 110, 120. In other embodiment, the elastic support surface on the belt 242 may be formed by a porous layer of suitable elasticity or elastic protrusions on the belt 242 spaced apart to permit the passage of air between them towards the suction chamber 231. Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention,

P4085NL01 14 which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination and any advantageous combination of such claims are herewith disclosed. Further, it is contemplated that structural elements may be generated by application of three-dimensional (3D) printing techniques. Therefore, any reference to a structural element is intended to encompass any computer executable instructions that instruct a computer to generate such a structural element by three-dimensional printing techniques or similar computer controlled manufacturing techniques. Furthermore, such a reference to a structural element encompasses a computer readable medium carrying such computer executable instructions.

Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly.

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.

P4085NL01 15

EMBODIMENTS

1. A method for transporting a sheet (S) through a printing system (1), comprising: - transferring the sheet (S) from a first conveyor (110) to a second conveyor (120), characterized in that the sheet (S) is transferred from the first conveyor (110) to the second conveyor (120) over an elastic support surface of a sheet transfer device (130; 230) and by the sheet (S) deforming the elastic support surface when a first conveyor velocity (V1) of the first conveyor (110) and/or a second conveyor velocity (V2) of the second conveyor (120) differs from a transfer velocity (VT) of the sheet transfer device (130; 230).

2. The method according to embodiment 1, wherein the printing system (1) comprising a processing device (116) positioned over the first conveyor (110) and the method further comprises the step of processing an upstream portion of the sheet (S) on the first conveyor (110) while a downstream portion of said sheet (S) is engaged by the sheet transfer device (130; 230).

3. The method according to embodiment 1 or 2, further comprising the step of holding the sheet (S) against the support surface (130; 230) by means of an underpressure applied to the sheet (S).

4. The method according to any of the previous embodiments, wherein the support surface is formed by a plurality of rollers (140) formed of an elastic material.

5. A sheet transport device (100) for a printing system (1), comprising: - afirst sheet conveyor (110) positioned upstream of a second sheet conveyor (120); - a sheet transfer device (130; 230) for transferring a sheet (S) from the first sheet conveyor (110) to the second sheet conveyor (120), the sheet transfer device (130; 230) comprising an air permeable, elastic support surface (for supporting the sheet (S) in between the first and second sheet conveyors (110, 120), characterized in that the sheet transfer device (130; 230) comprises a suction chamber (131) wherein the support rollers (140) are at least partially positioned, which suction chamber (131) is connected to a suction source (132) for applying an underpressure to the sheet (S) to draw the sheet (S) against the support surface, wherein the support surface is formed of an elastic material deformable under forces transmitted from the at least one of the first and second sheet conveyors (110, 120) via the sheet (S) to the

P4085NL01 16 support surface when a transfer velocity (VT) of the sheet transfer device (130; 230) differs from a conveyor velocity of the first and/or second sheet conveyor.

6. The sheet transport device (100) according to embodiment 5, wherein the sheet transfer device comprises support rollers (140), which each comprises a rigid core (142) rotatably supported on a rotation axis, around which core (142) the elastic material is provided, such that the elastic material is deformable with respect to the core (142) under the influence of forces transmitted via the sheet to the support rollers (140).

7. The sheet transport device (100) according to embodiment 5 or 6 , wherein the first and second sheet conveyors (110, 120) comprises holding means for holding the sheet (S) onto the respective one of the first and second sheet conveyors (110, 120).

8. The sheet transport device (100) according to any of the embodiments 5 to 7, wherein the support rollers (140) are driveable around their rotation axes by means of a drive for setting the transfer velocity (VT).

9. The sheet transport device (100) according to any of the embodiments 5 to 8, wherein the elastic material forms the circumference of the support roller (140) and is provided with a plurality of recesses.

10. The sheet transport device (100) according to any of the embodiments 5 to 9, wherein the support rollers (140) are positioned inside the suction chamber (131) with their top portions positioned in a sheet support plane of the first and/or second sheet conveyor.

Claims

P4085EN01 17 CONCLUSIONS

A method for transporting a sheet (S) through a printing system (1), comprising the steps of: - transferring the sheet (S) from a first conveyor (110) to a second conveyor (120), with the characterized in that the sheet (S) is transferred from the first conveyor (110) to the second conveyor (120) via an elastic support surface of a sheet transfer device (130; 230) and that the sheet (S) deforms the elastic support surface when a first conveying speed (V1) of the first conveyor (110) is different and / or second conveying speed (V2) of the second conveyor (120) is different from a transfer speed of the sheet transfer device (130; 230).

The method of claim 1, wherein the printing system (1) comprises a processing device (118) positioned over the first conveyor (110) and the method further comprises the step of processing an upstream portion of the sheet (S) on the first conveyor (110) while a downstream portion of the sheet (S) is engaged by the sheet transfer device (130; 230).

A method according to claim 1 or 2, further comprising the step of holding the sheet (S) against the support surface by applying an underpressure to the sheet (S).

The method of any preceding claim, wherein the support surface is formed by a plurality of rollers (140) formed of an elastic material.

A sheet transport apparatus (100) for a printing system (1), comprising: - a first sheet transporter (110) positioned upstream of a second sheet transporter (120); - a sheet transfer device (130; 230) for transferring a sheet (S) from the first sheet conveyor (110) to the sheet second conveyor (120), the sheet transfer device (130; 230) comprising an air permeable elastic support surface for supporting the sheet (S) between the first and second sheet conveyors (110, 120), characterized in that the sheet transfer device (130; 230) comprises a suction chamber (131) within which the support rollers (140) are at least partially located, the suction chamber (131) ) is connected to a suction source (132) for applying a negative pressure

P4085NL01 18 on the sheet (S) to urge the sheet (S) against the support surface, the support surface being formed of an elastic material which is deformable under the influence of forces transmitted from at least one of the first and second sheet conveyors ( 110, 120) through the sheet (S) at the support surface, when a transfer speed (VT) of the sheet transfer device (130; 230) differs from a conveyor speed (V1, V2) of the first and / or second sheet conveyor (110; 120) ).

The sheet transport device (100) of claim 5, wherein the sheet transfer device (130; 230) comprises a plurality of support rollers (140), each of which includes a rigid core (142) rotatably disposed on an axis of rotation, the elastic material being such It is provided around the core (142) that the elastic material is deformable relative to the core (142) under the influence of forces transmitted through the sheet (S) to the support rollers (140).

A sheet transport apparatus (100) according to claim 5 or 6, wherein the first and second sheet transporters (110, 120) include holding means for holding the sheet (S) on the first and second sheet transporters (110, 120), respectively.

A sheet transport apparatus (100) according to any one of claims 5 to 7, wherein the support rollers (140) are drivably mounted on their rotational shafts for driving by a motor to adjust the transfer speed (VT).

The sheet transport device (100) of any of claims 5 to 8, wherein the elastic material defines the periphery of the support rollers (140) and includes a plurality of recesses.

A sheet transport apparatus (100) according to any one of claims 5 to 9, wherein the support rollers (140) are located in the suction chamber (131) with their upper parts located in a support surface of the first and / or second sheet transporter.