Patent Grant
11912015
The present invention generally pertains to sheet printer and a method for transferring a sheet between conveyors in such a printer.
A sheet printer, specifically a sheet printer for high productivity or large volumes, comprises a transport path which transports sheets from a sheet input module, such as a sheet feeder, along a print station for deposition of an image on said sheet, to a sheet output module, for example a sheet stacker. The transport path generally comprises a plurality of conveyors, such as transport pinches and conveyor belts. A conveyor belt allows the sheet to be adhered flatly to its sheet support surface by means of an underpressure applied through the belt to the sheet. Also, the sheet is transported without contacting one of its faces, which allows it be transported while the image has not yet been fully fixed to the sheet. For those reasons belt conveyors may be applied at or near the print station. When a belt conveyor receives a sheet from an upstream conveyor, a controlled landing of the sheet on the belt conveyor is desired to avoid deforming the sheet. An air knife forming unit may be used to control the landing of the sheet, specifically for preventing the leading edge of the sheet from curling and/or wrinkling. Such an air knife forming unit is known for example from EP 3224167 B1. EP 3224167 B1 proposes further controlling the landing of the sheet by controlling the underpressure applied to the leading edge of the sheet as it lands on the belt conveyor.
It is an object of the present invention to provide an air knife assembly to assist in the transfer of sheets, wherein the chance of deforming the leading edge during landing is reduced. The present invention seeks to provide an alternative solution to EP 3224167 B1, which solution preferably requires less components, costs, and/or space.
Thereto, the present invention relates to a sheet printer comprising:
The insight of the inventors is illustrated in
It is the further insight of the inventors that the above issues may be avoided if the respective air current and air flows are directed substantially perpendicular to the transport direction. When, for example, an air curtain 74, 76 which is longitudinal in the transport direction and perpendicular to said transport direction X is applied, as shown in
Further advantageous embodiments are subject of the dependent claims.
It will be appreciated that substantially perpendicular may comprise the majority of the air flows being directed perpendicular to the transport direction. A small or minor portion of the air current and/or the resulting air flows may be directed non-perpendicular to the transport direction. Said portion is however significantly less (for example less than 20%) than the amount of air flowing perpendicular to the transport direction in terms of velocity and/or volumetric rates. The majority of the air current is aimed to flow perpendicular to the transport direction, as well to direct the resulting air flows perpendicular to the transport direction.
In an embodiment, the air knife assembly is configured for emitting an air curtain substantially longitudinal in said transport direction. The air curtain as emitted by the air knife assembly extends longitudinally in the transport direction. The air curtain when viewed perpendicular to a sheet support plane of the downstream conveyor is substantially parallel to or at a small angle (for example between 0 and 30°) with respect to the transport direction. Preferably, in said view the air curtain is substantially straight, though it may comprise minor bending.
In an embodiment, the air knife assembly is configured for emitting at least two laterally spaced apart air curtains which extend longitudinally in said transport direction. The air knife assembly preferably comprises a first and a second air knife forming unit at different lateral positions. Each air knife forming unit is configured for jetting an air curtain, preferably synchronously with one another. In an advantageous embodiment, the first and second air knife forming units are positioned symmetrically with respect to a center or central plane of the downstream conveyor and/or or the sheet, for example offset at the same spacing with respect to a central line of the conveyor in the transport direction. Using two air curtains provides added control over the air flow.
In an embodiment, the air knife assembly comprises an elongated air knife forming unit which extends substantially longitudinally in said transport direction. The air curtain is formed and determined by the air knife forming unit. Preferably, the air knife forming unit is formed of a row of nozzles extending substantially in said transport direction, though a single elongated nozzle may be applied within the present invention. The nozzles are preferably spaced sufficiently adjacent to create a substantially continuous air curtain.
In an embodiment, said air knife assembly comprises two air knife forming units, each formed of a row of nozzles extending substantially in said transport direction. The air knife assembly comprises two rows of nozzles which extend in the transport direction and are laterally spaced apart from one another. Each row of nozzles is configured for forming an air curtain. Pressurized gas is provided to the rows of nozzles, preferably such that both air curtains are formed simultaneously and mirror-symmetrically with respect to a central plane passing through a center of the downstream conveyor or the sheet.
In an embodiment, the nozzles of each row are aimed at an angle with respect to an out-of-plane direction of a sheet support surface of said conveyors, and wherein each row of nozzles is angled towards its respective adjacent lateral side of said conveyors. The air flow generated by the nozzles is directed sideways towards the nearest lateral edges of the conveyors. Thereby, the majority of the air flow from the row of nozzles is directed to the adjacent lateral edge of the conveyor, while a smaller portion passes towards the center and/or remote lateral edge of the downstream conveyor. When two air knife forming units are positioned as such, the majority of the generated air flow is thus directed laterally towards the closest outer sides of the conveyor. In the region in between the air knife forming units (when viewed from above) the resulting air flows from the first and second air knife forming units may substantially cancel each other out in the lateral direction, as a consequence of the mirror-symmetric positioning of the air knife forming units in another embodiment. The Bernoulli forces in the central region may thus be relatively small, while the sheet in said region is pressed firmly downward by the combined air flows.
In an embodiment, the air knife assembly extends from and over an upstream end of said downstream conveyor to and over a downstream end of said upstream conveyor. The air knife assembly, specifically the air knife forming unit and its generated air curtain, extends over the length of the transfer region in the transport direction. The generated air curtain covers the last end of the upstream and the first end of the downstream conveyor as well as the gap intermediate the conveyors in the transport direction. Preferably, the jetting of the air curtains is timed with the arrival of the leading edge at the downstream conveyor. Allowing the air knife assembly to extend across the transfer region allows for an effective pressing down on the sheet, especially compared to a lateral air knife forming unit pressing only very locally on the leading edge.
In an embodiment, a sheet drying station is positioned over the downstream conveyor, said drying station comprising an air blower for supplying pressurized air, wherein the air knife assembly is supplied by said air blower. The sheet drying station comprises one or more air nozzles for applying a drying and/or heating air flow to the sheet. Pressurized gas is supplied to the nozzles of the drying station by means of an air blower. Said blower may further be connected to the air knife assembly to supply pressurized gas to the air knife assembly. The first conveyor is preferably sufficiently adjacent the sheet drying station to allow for a simple and low air resistance connection between the air blower and the air knife assembly. In another embodiment, the sheet drying station transitions into the air knife assembly, at least along the transport direction. The air knife forming unit may thus be formed from similar or the same components as the sheet drying station, reducing the overall costs of the printer.
In an embodiment, the sheet drying station is generally positioned downstream or adjacent the print station, which comprises the upstream conveyor. The sheet is printed while on the upstream conveyor and transferred to the downstream conveyor, which is comprised in the sheet drying station. This results in a very compact embodiment, wherein the sheet may be dried rapidly after printing, reducing the chance of print artifacts due to a relative long exposure of the sheet to wet ink.
In an embodiment, the drying station comprises an impingement dryer which comprises a plurality of nozzles of emitting high velocity air jets, wherein the impingement dryer extends towards the transfer region where it transitions into the air knife assembly. Impingement drying of sheets is an efficient method of drying printed sheets. The high velocity nozzles and suitable air blower for supplying pressurized gas of impingement dryer may be shared and/or utilized in the air knife assembly. This allows for costs reduction as similar and/or less components may be used. Also, the air knife assembly may be formed as an extension of the sheet drying station, resulting in a space efficient design. The transitioning may be achieved by mounting a support for the air knife assembly on the support for the impingement dryer, or a single support may be shared between the impingement dryer and the air knife assembly.
In an embodiment, said upstream conveyor and/or said downstream conveyor comprises an air-permeable endless belt positioned over a suction chamber through which an underpressure is applicable for holding sheets against said endless belt. The respective conveyor holds the sheet flatly against the belt by suction applied to the sheet through the belt. The suction chamber is connected to a suction source for drawing in air through the belt and the suction chamber. The endless belt is suspended on at least two rollers, one which is provided with a motor for rotating said roller and thereby moving the belt.
In an embodiment, the sheet printer according to the present invention further comprises a controller for controlling the air knife assembly to emit the air current timed to an arrival of a sheet in the transfer region. The air knife assembly is controlled for intermittently jetting air curtains, for example by means of a valve controlled by the controller. The air curtains are applied as the leading edge of the sheet arrives at the downstream conveyor. The air curtains are therein preferably applied along the length of the transfer region to provide a sufficient pressing force on the sheet. The timing may be varied dependent on the requirements of the print media type applied.
In an embodiment, the air knife assembly is positioned over and facing a sheet support surface of said conveyors. The air knife assembly is during operation position above the conveyors.
The invention further relates to a method for transferring a sheet between a downstream conveyor positioned to receive a sheet from an upstream conveyor, comprising the step of applying an air current to the sheet as it is transferred between said conveyors, characterized by the air current extending substantially longitudinal in a transport direction of said conveyors. The air current may be applied as described above.
Additionally, the present invention may further relate to a sheet conveyor assembly for transporting a sheet in a transport direction along a print station for printing an image on said sheet and along a detector downstream of said print station for inspecting said printed sheet, wherein an air blowing assembly is provided downstream of the detector for generating an air current between the conveyor assembly and detector which air current flows upstream against the transport direction. This configuration has the advantage to provide reliable inspection of printed images in a sheet printer, especially during prolonged operation. In an advantageous embodiment, the air knife assembly may be embodied in the air blowing assembly of said printer, though as will be explained below the object of said printer may also be achieved with a different air blowing assembly, such as a sheet drying station.
It was found that the reduced reliability of the detector was a consequence of particulates contaminating the surface of the detector facing the sheet. The particulates were found to originate from the print station, where a fine ink mist is generated during the jetting of the ink jet print heads. It was further found that particulates from this ink mist traveled in the transport direction of the sheets towards the detector. At the detector the particulates would adhere to the sensor surface of the detector, providing spots in the image data, which did not correspond to the printed image. This resulted in erroneous conclusion and/or results as to the quality of the printed image. This in turn resulting in unnecessary downtime of the printer as cleaning of the detector was required.
The present invention prevents the particulates from the ink mist from substantially reaching the detector by providing an air flow opposite to the transport direction. The air flow flows from the air blowing assembly along the detector towards the print station and forms an effective barrier against ink particulates originating from the print heads. As such, ink contamination of the detector is reduced or even prevented, resulting in a prolonged reliable operation of the detector.
In an embodiment, the print station is connected to a suction system for drawing air from the print station, said suction system comprising a filter and being connected to the air blowing assembly, such that filtered air is supplied from the suction system to the air blowing assembly. The upstream air flow should be free of ink particulates. A similar requirement is generally or often placed on the surroundings of the printer. Thereto the printer is provided with a suction system connected to a filter for withdrawing and filtering air from the print station, such that said filtered air may be vented to the ambient of the printer. The same suction system and filter may be applied for providing ink-free air to the air blowing assembly, resulting in a compact and low-cost embodiment.
In an embodiment, the air blowing assembly is positioned sufficiently adjacent the detector, such that its generated local overpressure in combination with a local underpressure applied by the suction system at the print station results in the upstream air flow. The air flow is formed due to the pressure gradient between the overpressure provided by the air blowing assembly and the relative underpressure at the print station due to the suction system. Underpressure and overpressure herein being relative terms dependent on the operating conditions of the printer, which are generally at atmospheric pressure. Preferably, the air blowing assembly is directly downstream of the detector.
In an embodiment, the print station comprises plurality of ink jet print heads for generating ink droplets, an wherein the upstream air flow substantially prevents ink particulates from the ink jet print heads from reaching and covering the detector. The air flow between the air blowing assembly and the print station and/or its suction system is sufficiently large and/or strong to prevent ink particulates to travel from the print region below the print station onto the detector. In another embodiment, operation of the print heads results in an ink mist at least between the conveyor assembly and the print station, which ink mist is substantially prevented from reaching the detector by the upstream air flow. The ink mist is formed of very fine droplets or particulates created during the jetting of the ink droplets intended to form the image on the sheet. The ink particulates may be sufficiently small to be less affected by gravity, allowing these particulates to travel relatively far in the transport direction. The upstream air flow provides a convective flow which will return particulates to the print station and/or forms a pressure front beyond which the particulates substantially do not pass.
In an embodiment, the print heads during operation extend stationary over a majority of the width of the conveyor assembly. This allows the conveyor assembly to transport the sheet along the print station without stopping during printing. The sheets thus travel with a relatively high speed along the print station, which could create an air flow in the transport direction and bring particulates onto the detector. It should be noted that the print gap between such a pagewide print head array and the conveyor assembly is relatively small to allow for accurate positioning of the ink droplets on the sheets. This is avoided by the air blowing assembly providing a sufficiently large air flow and/or overpressure, such that the air flow beneath the detector is substantially opposite to the transport direction.
In an embodiment, the air blowing assembly comprises an air knife assembly positioned in a transfer region between upstream and downstream conveyors of the conveyor assembly for emitting an air current to control the landing of an edge of said sheet on the downstream conveyor, wherein the air knife assembly is positioned adjacent the detector. In another embodiment, the air blowing assembly comprises a sheet drying station comprising a plurality of nozzles for blowing air towards the sheet for drying an image printed on said sheet, wherein the sheet drying station is positioned adjacent the detector. Specifically, the sheet drying station may in another embodiment formed by an impingement dryer for delivering jets of high velocity air onto the sheet to provide fast and efficient drying of the printed sheets.
The present invention further relates to a method for ink jet printing of sheets, comprising the steps of:
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.
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:
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.
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
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 printer, for example a network N for transmitting a submitted print job to the printer 1. In
The controller 37 comprises a print job receiving section 371 permitting a user to submit a print job to the printer 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 printer 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 near or in the print station 39 of the print engine, or finishing material located near the print station 39 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 station 39 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 station 39 is suitable for ejecting and/or fixing marking material to image receiving material. The print station 39 is positioned near the paper path sections 33, 34. The print station 39 comprises an inkjet print head assembly, preferably formed as a page wide array. Downstream of the print station 39 a print quality inspection device in the form of detector 31 is provided for determining a compliance between the printed image and the input print job. The detector 31 may comprise a camera, such as a CCD or line scanner with sufficient resolution to analyze the printed image for example for the occurrence of non-jetting or deviating jetting nozzles of the print station 39. A treatment station 60 is provided downstream of the print station 39, and preferably downstream of the detector 31. The treatment station 60 is arranged for fixing the jetted ink to the image receiving. The treatment station 60 thereto may comprise heaters and/or emitters for emitting (heated) air and/or radiation for drying and/or curing the ink on the image receiving member.
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 station 39. 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 station 39 in the loop. The sheets coming from the paper path section 35 are starting their second pass along the print station 39 in the loop. When a sheet has passed the print station 39 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
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 printer 1.
Above the transfer region T an air knife assembly 70 is provided. The air knife assembly 70 extends over the adjacent ends of the conveyors 33A, 33B as well as over the intermediate area. The air knife assembly 70 in
Pressurized air is supplied to the air knife forming unit 72 to generate the air current 74. The emitted air current 74 is shaped as an air curtain 74 which is longitudinal in the transport direction X, while being relatively narrow in the lateral direction Y, at least until the current 74 contacts a sheet 41 and/or conveyors 33A, 33B. The air curtain 74 need not be continuous, though it is preferred that the jets emitted by the individual nozzles 73 overlap and/or are in close proximity when forming the air curtain 74. Preferably, the jetting of the air current 74 is timed or pulsed in accordance with the arrival of a sheet 41 in the transfer region T. To ensure a controlled landing of the sheet 41 on the downstream conveyor 33B, the air current 74 may for example be jetted as the leading edge of the sheet 41 arrives at the downstream conveyor 33B or when said leading edge leaves the upstream conveyor 33A. The nozzles 73 may be controlled to jet simultaneously, but also subsequently with a timing that matches the speed of the sheet 41, such that a leading edge of the air curtain moves at a similar speed as the leading edge. The jetting of air may be stopped after a predetermined period from the landing of the leading edge on the downstream conveyor 33B. The timing, speeds, and volumetric rates of the air currents differ per print media type and may be selected from a predetermined lookup table stored on the controller's memory.
Downstream of the air knife assembly 70 a sheet treatment station 60 is positioned. In
In the present invention, the air knife assembly 70 extends longitudinally in the transport direction X, as illustrated in
As shown in
As shown in
The page-wide print head array ensures high productivity as the sheets 41 may continue moving on the conveyor 33A during printing. Further, the conveyor 33A holds the sheet flat against the belt 33F during printing, reducing the risk of print artifacts from occurring. Additionally, a print quality detector 31 is positioned over the same conveyor 33A as over which the print station 39 is positioned. The printed image is thereby inspected after printing for the occurrence of print defects, for example due to the failing of print head nozzles. The detector 31 is positioned between the air knife assembly 70 and the print station 39. The detector 31 is preferably an optical detector 31, such as a camera or line scanner, which acquires an image from the printed sheet 41. The acquired image is converted to data which is compared to previously stored image date (which may be a test pattern or image data defining the printed image). As such any defects in the printed image may be de identified and appropriate actions may be scheduled, such as reprinting, print head cleaning, issuing operator notifications, etc.
The air knife assembly 70 is provided with filtered air from the filter 84 via channel 85, which is also used for cleaning the air drawn in from below the print station 39. Different sources of air may be applied, such as clean ambient air or a different gas supplied from a different source, such as a pressurized line or container. Connecting the filter 84 and suction source 81 to both the air knife assembly 70 and the print station 39 however results in a compact and low cost embodiment, as shown in
A sufficiently large and/or strong flow 74A for pushing back the ink mist 90 from the detector 31 may be formed by an appropriate configuration of the respective components. The flow 74A may be increased by closely positioning the air knife assembly 70, detector 31, and print station 39 with respect to one another. The air knife assembly 70 may be configured to blow a portion of its jetted air towards and/or underneath the detector 31. The air flow 84A is further dependent on the power of the suction source 81 as well the dimensions of the channels 39A, 80, 83, 85. Shielding may be provided around the detector 31 and/or air knife assembly 70 to direct the air flow 74A. The skilled person will take into consideration that the air flow underneath the print station 39 should not excessively disturb the positioning of the jetted droplets and/or will compensate for this by other means, such as adjusting the timing of the jetting of the droplets.
It will be appreciated that the embodiment in the
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, 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20183271 | Jun 2020 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20130156473 | Boesten | Jun 2013 | A1 |
| 20160152045 | La Vos | Jun 2016 | A1 |
| 20160152429 | La Vos | Jun 2016 | A1 |
| 20190283470 | Okayama | Sep 2019 | A1 |
| Number | Date | Country |
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| 3 224 167 | Oct 2018 | EP |
| 9-142429 | Jun 1997 | JP |
| 2002-128038 | May 2002 | JP |
| 3770640 | Apr 2006 | JP |
| 2006334943 | Dec 2006 | JP |
| 2009160886 | Jul 2009 | JP |
| 2010083599 | Apr 2010 | JP |
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| Search Report issued in European priority application 20183271 dated Dec. 14, 2020. |
| Number | Date | Country | |
|---|---|---|---|
| 20210402806 A1 | Dec 2021 | US |
