NL2032612B1

NL2032612B1 - Sheet transport device with caster wheels over a transport belt

Info

Publication number: NL2032612B1
Application number: NL2032612A
Authority: NL
Inventors: A Schulkes Joseph; P C Quirijnen Robertus
Original assignee: Canon Production Printing Holding Bv
Priority date: 2022-07-27
Filing date: 2022-07-27
Publication date: 2024-02-05
Also published as: DE102023118554A1

Abstract

100232NL01 19 Abstract 1. A sheet transport device for a printer (1), comprising a plurality of roller units (60) spaced apart from one another in a lateral direction (Y), wherein each roller unit (60) comprises : 5 - a support arm (62) extending in a transport direction (X) and being provided with urging means for pressing at least one roller (84) onto a sheet on a transport belt (33A) for transporting the sheet in the transport direction (X) which extends perpendicular to the lateral direction (Y); - a castoring hinge defining a first axis (A1) around which the respective at least one 10 roller (84) is rotatable, said first axis (a1) extending in a height direction (Z) substantially perpendicular to the transport and lateral directions (X, y), wherein an angular orientation of the least one roller (84) with respect to the first axis (A1) defines a rolling direction (RD) at a contact point with the sheet; characterized by each roller unit (60) further comprising an force equalizing hinge 15 configured for allowing the at least one roller (84) to rotate around a second axis (A2) parallel to the rolling direction (RD), such that a pressing force from the at least one roller (84) on the sheet is distributed substantially equally over a width of the at least one roller (84). 20 Fig. 5

Description

100232NL01 1

Sheet transport device with caster wheels over a transport belt

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to a sheet transport device for use in a printer. 2. Description of Background Art

Commercial and/or industrial inkjet sheet printers, specifically those for mid to high range print volumes, may be provided with an endless transport belt positioned opposite the inkjet print station. The sheet is held onto the belt by means of an underpressure applied through the belt and moves continuously along the page-wide print station to print an image thereon. To avoid artifacts in the printed image and/or contact between the print station and the sheet, the sheet is preferably held flat onto the belt. After transferring the sheet onto the belt, local deformations, such as wrinkles, folds, and/or bumps may be present in the sheet, as a result of the manner wherein the sheet lands onto the belt. It is known to provide a pinch comprising a plurality of roller units spaced apart from one another in a lateral direction. A support arm for the roller units is provided with urging means for pressing the rollers onto a sheet on the transport belt for transporting the sheet in a transport direction perpendicular to the lateral direction. Each roller unit presses onto the sheet, locally flattening the sheet. Such flattening roller units are known from e.g. EP21175373.6. Each roller unit comprises a castoring hinge defining a rotation axis around which the respective at least one roller is rotatable, the rotation axis extending in a height direction perpendicular to the transport and lateral directions of the transport belt. Thereby, the roller unit is able to conform to irregularities in the sheet.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved or alternative sheet transport device for flattening and/or smoothening sheets as these are received onto an endless transport belt.

In accordance with the present invention, a sheet transport device for a printer according to claim 1 and a printer according to claim 10 are provided. The sheet transport device comprises a plurality of roller units spaced apart from one another in a

100232NL01 2 lateral direction, wherein each roller unit comprises : - a support arm extending in a transport direction and being provided with urging means for pressing at least one roller onto a sheet on a transport belt for transporting the sheet in the transport direction which extends perpendicular to the lateral direction ; - a castoring hinge defining a first axis around which the respective at least one roller is rotatable, said first axis extending in a height direction substantially perpendicular to the transport and lateral directions, wherein an angular orientation of the least one roller with respect to the first axis defines a rolling direction at a contact point with the sheet;

The sheet transport device is characterized by each roller unit further comprising an force equalizing hinge configured for allowing the at least one roller to rotate around a second axis parallel to the rolling direction, such that a pressing force from the at least one roller on the sheet is distributed substantially equally over a width of the at least one roller.

When the direction of the sheet changes, the castoring hinge ensures the at least one roller re-orients itself parallel to that direction. The rolling direction is the circumferential direction of the at least one roller at the contact point with the sheet, and is generally parallel to a plane of the sheet and/or the underlying belt. The at least one roller therein rotates around the first axis, such that its rolling direction is brought parallel to said local direction of the sheet. Any frictional forces between the sheet and the at least one roller are thereby reduced. Additionally, force equalizing hinge allows the at least one roller to rotate out of the plane of the belt, such that it follows and/or is kept parallel to the local orientation of the sheet, especially in case of local deformations in the sheet. This prevents the edges of the at least one roller from ‘cutting into’ the sheet and leaving a permanently visible deformation. The full width of the at least one roller is homogenously applied or pressured for flattening the sheet, ensuring an highly effective smoothening of ant wrinkles therein, regardless of the sizes and/or shape of said deformations. Thereby the object of the present invention has been achieved.

More specific optional features of the invention are indicated in the dependent claims.

In an embodiment, the force equalizing hinge is provided at the castoring hinge. The force equalizing hinge is are preferably combined in a hinge unit. The force equalizing hinge is preferably provided at, on, and/or around the first axis of the castoring hinge.

Preferably, the castoring hinge and the force equalizing hinge are integrated in a single

100232NL01 3 hinge unit, wherein the first axis forms a support upon which is the force equalizing hinge is mounted.

In an embodiment, the urging means comprise a first spring element and the force equalizing hinge comprises a second spring element, wherein the second spring element is weaker than the first spring element. The urging means may for example be in the form of a leaf spring comprised in the support arm. The first spring element is relatively rigid and has a first spring constant. The first spring element determines the downward force by which the at least one roller presses onto the sheet. The support arm is mounted, such the first spring element is pretensioned. The rollers then exert a downward on the sheet at all time while contacting the sheet. The second spring element is weaker than the first spring element: a second spring constant of the second spring element is smaller than that of the first spring constant. In consequence, when a deformation passes under the at least one roller, the second spring element deforms more and/or faster than the second spring element. Thereby, the at least one roller rotates relatively easily around the second axis, such that the at least one roller is able to conform to any irregularities in the sheet, without substantially changing the pressing force originating from the first spring element. This provides a highly controlled manner of flattening the sheet by avoiding excessively high pressing forces.

In an embodiment, the force equalizing hinge is an elastic hinge comprising a second spring element. The at least one roller is returned to its starting position by the spring force when no deformation are present in the sheet. The second spring element provides a counter force to any lifting forces acting on the at least one roller, such that the at least one roller is kept into contact with the sheet. The at least one roller is thereby prevented from losing contact with the sheet or exerting all or the majority of its pressing force along only a portion of the width of said roller or even at a single point, such as the roller’s edge.

In an embodiment, the second spring element comprises at least one wave spring, preferably an endless and/or circular wave spring. Such a wave spring may be a circular ring with multiple sinusoidal shapes. Preferably, the wave spring is provided around the first axis. The circular shape of the wave spring allows the force equalizing hinge to facilitate the rotation around the second axis, regardless of the angular orientation of the

100232NL01 4 at least one roller. The second axis around which the at least one roller rotates may be oriented in any direction substantially perpendicular to the first axis due to the circular form of the wave spring.

In an embodiment, the support arms are rigidly mounted on a common support beam extending in the lateral direction. The support arm comprises mounting means, such that one end of the first spring element is fixed to the common support beam. Multiple roller units are mounted laterally besides one another on the common support beam over substantially the full width of the belt. This ensures sheets of all dimensions are properly flattened.

In an embodiment, at least two independently rotatable rollers are provided for each support arm. Two rollers are connected via a single hinge unit to every support arm. The rollers are provided on a common axis bearing, which comprises a spacer to prevent the rollers from contacting one another. Thereby one roller may rotate independently of the other roller. Thereby, local difference in the velocity of the sheet can be better accommodated by the roller unit and permanent deformation is reduced or prevented.

In an embodiment, the at least one roller is provided with polyoxymethylene (POM) circumferential surface. A polyoxymethylene roller or a roller coating with polyoxymethylene was found to have low interaction with the sheet material, thereby further reducing the chance of permanently deforming the sheet.

In an embodiment, the sheet transport device further comprises the endless transport belt The belt is provided with through-holes and extends over a suction box, which allows an underpressure to be applied to the sheet via the through-holes. The suction box is connected to a suction source, such as a pump or fan.

The present invention further relates to a printer comprising a sheet transport device in any of the forms above. The printer is an inkjet sheet printer, preferably one comprising a page-wide printhead array which is stationary during printing.

It will be appreciated that rotation herein is defined as rotational movement around an axis, and is meant to include pivoting, tilting, turning, or other similar curved movements

100232NL01 around such an axis as well.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the 5 detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the present 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 herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

Fig. 1 is a schematic side view of a sheet printer comprising a transport belt with a pinch;

Fig. 2 is a first perspective view of the roller unit of the pinch in Fig. 1;

Fig. 3 is a second perspective view of the roller unit of the pinch in Fig. 1;

Fig. 4 is a third perspective view of the roller unit of the pinch in Fig. 1;

Fig. 5 is an exploded, perspective view of the roller unit of the pinch in Fig. 1;

Fig. Bais a schematic, perspective view of the roller unit of the pinch in Fig. 1; and

Fig. 6Bis a schematic, perspective view of the roller unit of the pinch in Fig. 1 in a rotated state with respect Fig. GA.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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.

Printer layout

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

100232NL01 6 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 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,

100232NL01 7 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, which comprises an endless transport belt 33A. A pinch 60 is provided at the start of the belt for pressing sheets against the belt 33A. A sheet registration device 34A is positioned upstream of the belt 33A to adjust the lateral position and/or angle of the sheets with respect to the transport direction of the belt 33A.

The print head or print assembly 31 may be an inkjet print head, a direct imaging toner assembly or an indirect imaging toner assembly.

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

100232NL01 8 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 36 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 in the network N has a user interface for displaying and controlling the print job queue of the printing system 1.

100232NL01 9

Sheet transport device

Figs. 2 to 5 illustrate different views of a roller unit 60 of the pinch at the belt 33A in Fig. 1. In the pinch multiple such roller units 60 are provided besides one another in the lateral direction Y of the belt 33A perpendicular to the transport direction X. Each roller unit 60 comprises a support arm 62, which at one end comprises mounting means 64 for mounting the support arm 62 onto a common support beam (67 in Figs. 6A-6B). The support arm 62 further comprises an opening 85 for receiving the hinge unit 70. The mounting means 64 comprise one or more aligning recesses and/or a click mechanism that allow the support arm 62 to be quickly mounted onto the common support beam 67.

By means of a cut-out one or more smaller leaf springs are provided at the mounting means 84, which clamp the support arm 62 onto the common support beam for quick and easy assembly. In Fig. 2, the support arm 82 is formed as a leaf spring, such that the free end of the support arm 62 is rotatable around the third axis A3. The third axis

A3 is defined by the common support beam 67 and extends in the lateral direction Y, as seen in Fig. 6A-6B. The support arm 82 with the mounting means 64 and the limiter 68 {which will be discussed later on) has been integrally formed of plate metal.

The support arm 82 is connected to the roller arm 80 via the hinge unit 70. The roller arm 80 is also formed of plate metal and comprises an opening 81 for receiving the hinge unit 70. The plate metal has been folded, such that two side arms 82 extend on either side of the roller arm 82, such that the rollers 84 are positioned in between the side arms 82. The rollers 84 are provided on an axis bearing 86, which allows the rollers 84 to rotate around it independently from one another. The axis bearing 86 is also formed of plate metal, which has been cut such that the axis bearing 86 comprises two axial arms, each of which is provided with a recess at its end. These recesses allow the axis bearing 86 be quickly mounted at the side arms 82, which have been provided with corresponding protrusions 83 which can be received in said recesses. The protrusions were formed by folding the ends of the side arms. An opening is provided in the side arm at each fold to leave space for the axial arms of the axis bearing 86. The axis bearing 86 further comprises a central spacer, which prevents the rollers 84 from coming into contact with one another to ensure independent rotation of both rollers 84.

The support arm 62 ends on the roller side in a limiter 68, which is positioned between the side arms 82. Thereby, the rotation of the rollers 84 around the first axis A1 is restricted to a predetermined range. The range has been selected in correspondence

100232NL01 10 with the dimensions and operational conditions of the printer.

A hinge unit 70 is provided between the roller arm 80 and the support arm 82. The hinge unit includes the castoring hinge, which allows the roller arm 80, and thereby the rollers 84, to rotate around the first axis A1, which extends substantially in the vertical direction

Z. It will be appreciated that substantially in the vertical direction Z herein includes deviations caused by the bending of the support arm 62 around the third axis A3. The rotation of the rollers 84 around the first axis A1 determines the orientation of the rolling direction RD. The rolling direction RD is the circumferential direction of each roller 84, where said roller 82 is to contact the sheet. It is further perpendicular to the axis bearing 86. The rolling direction RD rotates with the rollers 84 and the roller arm 80 around the first axis A1 to accommodate for differences in the direction wherein the sheet moves.

The rolling direction RD is mostly parallel to the plane of the sheet and thus within the plane defined by the lateral and transport directions X, Y. The hinge unit 70 further comprises the force equalizing hinge, which allows the rollers 84 to rotate around the second axis A2. Due to the castoring hinge, the second axis A2 can remain parallel to the rolling direction RD, when the rollers 84 rotate around the first axis. Thereby, the rollers 84 are kept in full contact with the sheet over their entire widths when deformations in the sheet occur. The castoring hinge with its rotation around the first axis A1 allows the rollers 84 to adjust to a change in the sheet’s in-plane velocity, while the force equalizing hinge allows the rollers 84 to tilt around the second axis A2, so that the rollers 84 keep contact with the sheet along their full width, even when the sheet is not locally flat. The width of the rollers 84 is hereby defined as measured along their rotation axis defined by the axis bearing 86.

The workings of the hinge unit 70 are further explained schematically in Figs. 6A-6B.

The endless belt 33A conveys a sheet substantially in the transport direction X. The sheet is held onto the belt 33A by means of an underpressure applied to the sheet through openings in the belt 33A. To achieve high image quality as well to avoid contact with the printheads of the print assembly 31, the sheet is preferably held flatly against the belt 33A. Before the belt 33A receives the sheet, the sheet is registered in a predetermined lateral position and/or orientation by the registration device 34A. As the sheet is transferred from the registration device 34A onto the belt 33A, wrinkles or folds may occur in the sheet, as it lands on the belt 33A. The pinch 60 locally presses onto

100232NL01 11 the sheet to remove or reduce those deformations. Therein, no deformation should occur in the sheet that could become visible in the final printed product.

The support arm 82 is configured as a leaf spring, which is pretensioned to press the sheet against the belt 33A. The leaf spring exerts a downward force in the vertical direction Z, which is transmitted via the rollers 84 to the sheet. The force is sufficiently large to locally smoothen or flatten the sheet. The leaf spring in the support arm 62 also allows the rollers 84 to pivot around the third axis A3 parallel to the common support beam 67 to accommodate different sheet thicknesses. This pivotable or rotational movement is indicated by R1 in Figs. 6A-6B. This allows the rollers 84 to move in the vertical direction Z to avoid excessive force on a deformation in the sheet and by pre- tensioning the leaf spring of the support arm 62 a constant downward is exerted by the rollers 84 on the sheet. The support arm 62 is secured to remain perpendicular lateral direction Y, which is defined by the common support beam 67. The sheet and/or a deformation on it may however locally move non-parallel to the main transport direction

X, and/or the main transport direction of the sheet may even differ due to a re- orientation of the belt 33A. If the rollers 84 are not properly aligned with the local direction of the sheet, local forces may cause damage to the sheet. To prevent that, the hinge unit 70 allows the roller arm 80 to pivot and/or rotate around the first axis A1. This rotation R2 is indicated in Fig. 6B, wherein the rollers 84 have been rotated with respect to Fig. 6A around the first axis A1. Thereby, frictional force forces due to in-plane velocity differences are reduced and/or prevented.

The rollers 84 are further formed of a polyoxymethylene material (POM), which material which was found to leave little deformation on common sheet materials, such as paper.

The rollers 84 are cylindrical and have a certain height as measured along their axis to ensure that the rollers 84 distribute the pressing force over a sufficiently large area of the sheet. The downward pressure coming from the rollers 84 should be distributed equally along their width. Each of the two rollers 84 of each roller unit 60 are rotatable independent of one another. This further prevents or reduces forces acting on the sheet due to local differences in velocity and/or heights on the sheet.

The hinge unit 70 is further configured to allow the rollers 84 to rotate around the second axis A2 that is parallel to the roller arm 80 at all times. The roller arm 80

100232NL01 12 determines the orientation of the rollers 84, and thereby the orientation of the rolling direction RD. This rotatability around the second axis A2 prevents the edges of the rollers 84 from pressing into the sheet. The second axis A2 for this rotation R3 moves with the roller arm 80 as it rotates around the first axis A1 in the vertical direction Z.

Because the rotation R2 moves the roller arm 80 parallel to the local transport direction of respective area of the sheet, the rollers 84 are always able to tilt around an axis A2 parallel to said local transport direction. Though not shown, the hinge unit 70 may further be configured to allow the rollers 84 to rotate or pivot around an axis perpendicular to both the roller arm 80 and the vertical direction Z.

The hinge unit 70 is shown in detail in Figs. 2 to 5. The hinge unit 70 comprises top and bottom mounting caps 73, 77 comprising attaching means such as screws, clamps, etc.

The mounting caps 73, 77 are provided at either ends of the central axis 76. The bottom mounting cap 77 extends through the opening 65 in the support arm 62, such that when the bottom mounting cap 77 is secured to the central axis 76, both components are fixed with respect to the support arm 62. The roller arm 80 is rotatable around the central axis 76 with respect to the support arm 62. Thus, the rotation R2 of the castoring hinge is achieved, since the central axis 76 defines the first axis A1. The top mounting cap 73 extends through the opening 81 in the roller arm 80. A top bearing 72 in the form of a hollow cylinder is provided between the top mounting cap 73 and the roller arm 80, such that the central axis 78 extends through the top bearing 72. The central axis 76 defines the first axis A1 of the castoring hinge. The hollow cylinder of the top bearing 76 is larger than the opening 81, wherein the cross-section of the opening the top bearing 76 is larger than that of the central axis 76. A bottom bearing 78 similar to the top bearing is provided between the roller arm 80 and the support arm 62. The central axis 76 extends partially through the bottom bearing 78. The central axis 76 is provided with a support region having a wider cross-section than remainder of the central axis 76, such that the bottom bearing 78 rests on the support region. The cross-section of the support region is greater than the opening in the bottom bearing 78, which in turn is greater than the cross-section of the portion of the central axis 76 extending through it.

Thus, roller arm 80 is enable to perform the rotation R2 around an axis in the vertical direction Z.

A pair of wave springs 71, 74 separated by a spacer ring 75 are further provided around

100232NL01 13 the bottom bearing 78. The wave springs 71, 74 are rings of an elastic, preferably metal, compound, which have been deformed to comprise at least three different wave forms connected to one another. In Fig. 5 each wave spring 71, 74 comprises at least three full sinusoidal wave forms. The wave springs 71, 74 are configured to deform under the forces exerted by deformations in the sheet. In contract, the spacer ring 74 has similar dimensions as the wave springs 71, 74, but is preferably flat. The spacer ring 75 is further relatively rigid, such that it deforms little or significantly less than the wave springs 71, 74 under the same forces. The top wave spring 75 is positioned against the roller arm 80 and the bottom wave spring 74 is held against the bottom bearing 78, which in turn is held in position by the support region of the central axis 76. The wave springs 71, 74 and the spacer ring 74 extend entirely around the central axis 76, such that the force equalizing hinge formed by this wave spring assembly is able to hinge in direction around the central axis 76.

The wave springs 71, 74 form the force equalizing hinge, which is an elastic hinge that enables the rollers 84 to rotate around the second axis A2. The roller arm 80, and thereby the rollers 84, can be tilted with respect to the support arm 62. This allows for the rotation R3 in Fig. BA-6B and achieves the tilting of the force equalizing hinge. When the rollers 84 encounter a deformation, the rollers 84 are able to tilt to remain flat on the sheet, and thus apply a homogenous pressure over the full width of the rollers 84. By tilting, the wave springs 71, 74 are locally compressed on one side, while they are moved apart on the opposite side. Without any tilting forces the wave springs 71, 74 contact the spacer ring 75 and their respective arm 80 or bearing 78 at at least three space apart points. When tilting this number of contact points can be reduced, and thereby also the friction forces which act against the rotation R2. When tilting, the friction forces opposing the rotation R2 may be less than compared to the untilted situation due to the local compression of wave springs 71, 74, reducing the area of contact.

One advantage of the wave springs 71, 74 is that they form an elastic hinge that is relatively simple and low-costs to make, while still allowing for the rotation R2. Other types of elastic hinges may be applied to form the hinge unit 70. In Fig. 8A-6B, the hinge unit 70 allows for tilting around any axis parallel to the side arms 82.

100232NL01 14

Although specific embodiments of the invention are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are examples only and are not intended to limit the scope, applicability, or configuration in any way. 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, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scape as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

It will also be appreciated that in this document the terms "comprise", "comprising", “include”, "including", "contain", “containing”, "have", "having", and any variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense, such that the process, method, device, apparatus or system described herein is not limited to those features or parts or elements or steps recited but may include other elements, features, parts or steps not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms "a" and "an" used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, the terms "first", "second", "third", etc. are used merely as labels, and are not intended to impose numerical requirements on or to establish a certain ranking of importance of their objects.

The present 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 present 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.

100232NL01 15

Embodiments 1. A sheet transport device for a printer (1), comprising a plurality of roller units {60) spaced apart from one another in a lateral direction (YY), wherein each roller unit (60) comprises : -a support arm (62) extending in a transport direction (X) and being provided with urging means for pressing at least one roller (84) onto a sheet on a transport belt (33A) for transporting the sheet in the transport direction (X) which extends perpendicular to the lateral direction (Y); - a castoring hinge defining a first axis (A1) around which the respective at least one roller (84) is rotatable, said first axis (a1) extending in a height direction (Z) substantially perpendicular to the transport and lateral directions (X, Y), wherein an angular orientation of the least one roller (84) with respect to the first axis (A1) defines a rolling direction (RD) at a contact point with the sheet; characterized by each roller unit (60) further comprising an force equalizing hinge configured for allowing the at least one roller (84) to rotate around a second axis (A2) parallel to the rolling direction (RD), such that a pressing force from the at least one roller (84) on the sheet is distributed substantially equally over a width of the at least one roller (84). 2. The sheet transport device according to claim 1, wherein the force equalizing hinge is provided at the castoring hinge. 3. The sheet transport device according any of the previous claims, wherein the urging means comprise a first spring element and the force equalizing hinge comprises a second spring element (71, 74), wherein the second spring element (71, 74) is weaker than the first spring element.

A4. The sheet transport device according to claim 3, wherein the second spring element (71, 74) comprises at least one wave spring. 5. The sheet transport device according to claim 3 or 4, wherein the first spring element comprises a leaf spring. 6. The sheet transport device according any of the previous claims, wherein the support arms (62) are rigidly mounted on a common support beam (67) extending in the lateral direction (Y).

100232NL01 16 7. The sheet transport device according any of the previous claims, wherein at least two independently rotatable rollers (84) are provided for each support arm (62). 8. The sheet transport device according any of the previous claims, wherein the at least one roller (84) is provided with polyoxymethylene (POM) circumferential surface. 9 The sheet transport device according any of the previous claims, further comprising the endless transport belt (33A). 10. A printer (1) comprising a sheet transport device according to any of the previous claims.

Claims

100232EN01 17 Conclusions

A sheet transport device for a printer (1), comprising a plurality of lateral direction (Y} spaced roller units (60), each roller unit (80) comprising: -a support arm (62) extending in a transport direction (X) extending and provided with a forcing means for pressing at least one roller (84) onto a sheet on a conveyor belt (33A) for conveying the sheet in the conveying direction (X) extending perpendicular to the lateral direction (Y} ; - a pivot hinge that determines a first axis (A1) around which the respective at least one roller (84) is rotatable, wherein the relevant first axis (A1) extends in a height direction (2), which height direction is substantially perpendicular to the conveyor belt and lateral direction (X, Y), wherein an angular orientation of the at least one roller (84) relative to the first axis (A1) determines a rolling direction (RD) at a point of contact with the sheet; characterized in that each roller unit (60) further comprises a force-distributing hinge adapted to rotate the at least one roller (84) about a second axis (A2) parallel to the rolling direction (RD), so that a pressing force of the at least one roller (84) on the lot is evenly distributed over a width of the at least one roller (84).

2. Sheet transport device according to claim 1, wherein the force-distributing hinge is provided on the swivel hinge.

Sheet transport device according to any one of the preceding claims, wherein the forcing means comprises a first spring element and wherein the force-distributing hinge comprises a second spring element (71, 74), wherein the second spring element (71, 74) is weaker than the first spring element.

The sheet transport device according to claim 3, wherein the second spring element (71, 74) comprises at least one wave spring.

5. Sheet transport device according to claim 3 or 4, wherein the first spring element comprises a leaf spring.

100232NL01 18

Sheet transport device according to any one of the preceding claims, wherein the support arms (62) are fixedly provided on a common support beam (67) that extends in the lateral direction {Y).

Sheet transport device according to any one of the preceding claims, wherein at least two rollers (84) that can rotate depending on each other are provided for each support arm (62).

A sheet transport device according to any one of the preceding claims, wherein the at least one roller (84) is provided with a peripheral surface of polyoxymethylene (POM).

A sheet transport device according to any one of the preceding claims, further comprising the endless conveyor belt (33A).

A printer (1) comprising a sheet transport device according to any one of the preceding claims.