NL2022181B1

NL2022181B1 - Web portion removal aid for wide format web printers

Info

Publication number: NL2022181B1
Application number: NL2022181A
Authority: NL
Inventors: J I Lind Jeroen; H G W Hees Marcus
Original assignee: Canon Production Printing Holding Bv
Priority date: 2018-12-12
Filing date: 2018-12-12
Publication date: 2020-07-02
Also published as: DE102019132581A1

Abstract

A wide format web printer comprising an ink treatment station for treating the inkjetted onto the web medium such that said ink hardens on the web medium. Errors may stop print operations, resulting in the presence of wet, untreated ink on the web medium. Generally manual removal of the web medium portion by cutting away a portion is required. Due to the wide format of the web medium handling of this portion is cumbersome and may lead to the wet ink contaminating the web printer or the operator. To aid the operator, the printer controller is configured to determine the occurrence of an error stopping print operation and to determine whether the error is a residual wet ink error. If the error is determined to be a residual wet ink error, an after error suction application signal is transmitted for applying suction to the web medium.

Description

P4131NL01 1 Web portion removal aid for wide format web printers

BACKGROUND OF THE INVENTION

1. Field of the invention The invention relates to a web printer comprising a print head assembly and an ink treatment station for hardening the ink jetted by the print head assembly.

2. Description of Background Art In web printers images are printed on a web medium extending continuously from an input roller to an output location, such as an output roller. Ink is jetted from the print head assembly on the web medium and is then treated by an ink treatment station to harden the ink. An example of such an ink treatment station is a UV emitter, which cures the ink by UV irradiation. In between jetting and treating, the ink is wet and transfers easily onto anything it comes into contact with. In practice the web printer may experience errors that cause the web printer to cease operations, including the ink treatment, without the possibility of resuming normal operations. A residue of wet ink may then remain on a portion of the web medium. Said portion needs to be removed from the web printer without contaminating the printer and/or the operator. In practice the portion with the wet ink is often cut from the remainder of the web medium.

Especially in wide format printing where the width of the web medium may exceed three meters this removal by the operator is cumbersome, as during cutting the web medium may move uncontrollably under the influence of gravity. It is known in the prior art to provide clamping means which engage the to be removed portion on either side of the web medium. However, such clamping means add additional components to the web printer, may deform the web medium during operation, and/or are not appropriately positioned to clamp the medium without contacting the wet ink in certain situations.

SUMMARY OF THE INVENTION It is an object of the invention to provide a simple and efficient means to reduce the risk of contamination when removing a web medium portion covered with wet ink from a web printer, in particularly a wide format web printer.

In a first aspect, the present invention provides a web printer according to claim 1. This web printer comprises: - an input roller for unwinding a web medium towards a medium holding surface

P4131NL01 2 provided with suction holes and connected to a suction device to suck the web medium against the medium holding surface; - a print head assembly positioned over the medium holding surface for jetting ink onto the web medium; - a ink treatment station for treating the ink jetted onto the web medium such that said ink hardens on the web medium; and - a printer controller configured to: - determine the occurrence of an error which error stops print operation of the printer; - determine whether the error is a residual wet ink error indicating wet ink is present on ato be removed portion of the web medium; - if the error is determined to be a residual wet ink error, transmit an after error suction application signal for applying suction to the web medium via the medium holding surface.

Due to the time delay between jetting and treating the ink, wet ink may remain on the web medium when print operations are stopped in consequence of a detected error.

The printer controller determines whether such an error occurs and controls the print head assembly and the ink treatment station to respectively cease printing and treating the image on the web medium.

The printer controller then determines whether there is a risk of wet ink being present on the web medium after the error has occurred.

This may for example be done by checking whether or not the print head assembly was printing within a predetermined time period prior to the occurrence of the error (or prior to the actual stopping of the print operations) or, in a more basic example, by checking whether a print job was being processed on the web printer at the time of the error.

When a risk of a wet ink residue on the web medium has been determined, the printer controller determines the error to be a residual wet ink error and proceeds to transmit the after error suction application signal.

The after error suction application signal is configured for applying suction to the web medium via suction holes in the medium holding surface on which the web medium portion with the wet ink resides after the error has occurred.

This suction ensures that the web medium portion is held in place during removal operations.

The operator may therein proceed to cut free the web medium portion without the risk of the web medium portion sliding off the medium holding surface and contaminating the web printer.

As such, the present invention provides a simple and low-costs solution for removing web medium portions with wet ink from a web printer.

The object of the present invention has thereby been achieved.

P4131NL01 3 More specific optional features of the invention are indicated in the dependent claims. In an embodiment, the after error suction application signal is configured to control: - the suction device to apply suction to the web medium via the medium holding surface; or - a user interface to display an after error suction application indication. Web printers as known in the prior are generally configured to stop suction when print operations are stopped when a sufficiently critical error has been detected. In a preferred embodiment, the printer controller transmits the after error suction application signal to the suction device which then consecutively applies the underpressure to the web medium via holes in the medium holding surface. Suction already applied may be continued, or the suction device may be re-activated or re- connected to the medium holding surface to apply underpressure to the web medium after a limited no-suction period. In alternative embodiment or for specific error situations, it may be preferred to have the operator control the suction device to apply the suction to the web medium after occurrence of the error. In that case, the control unit is configured to stop or disconnect the suction device from the medium holding surface when the error has been detected and consecutively indicate to the operator that the suction device requires re-activation or re-connnecting. Thereto the user interface upon receipt of the after error suction application signal indicates a prompt to the operator informing him or her to control the suction device. The prompt for example may be a visualized instruction on the screen, e.g. in text or symbolic form. Preferably the latter instruction is part of a series of error resolving instructions indicating to the operator the different steps to resolve the particular error that occurred.

In another embodiment, the web printer according to the present invention further comprises a scanning inkjet print head assembly moveable over the medium holding surface and wherein the ink treatment station is a curing station or a drying station positioned downstream of the inkjet print head assembly. The scanning inkjet print head assembly comprises a carriage holding the print heads, which carriage is moveable along a beam extending laterally over the medium holding surface. A scanning web printer is preferred for wide format application as it requires a relatively small number of print heads as compared to the width of the medium holding surface. The ink treatment station is in this embodiment is an active treatment station which applies radiation to the sheet to harden the ink thereon. The radiation may be UV or infrared radiation.

P4131NL01 4 Additionally or alternatively heat may be applied to harden the ink by e.g. heating the medium support surface at the ink treatment station or by heated air nozzles blowing air towards the sheet. Active treatment allows for quick drying of the ink, resulting in fast processing and also a compact web printer.

In a preferred embodiment, the curing station comprises UV emitters for curing ink on the web medium by UV radiation. The print heads in this embodiment are connected to a UV-curable ink supply, such that during operation the print heads jet droplets of UV- curable ink. After jetting the UV radiation from the UV emitters cures the wet ink, such that the ink is hardened. In their wet state some UV curable inks are labeled as hazardous. Further UV inks generally require UV radiation to harden. The present invention is particularly advantageous for such UV-curable inks as it reduces the risks to both the web printer and the operator. The UV emitters may for example be UV emitting LEDs or lights.

In an embodiment, the printer controller comprises a memory storing an error catalogue, wherein at least one error is provided with a residual wet ink error identifier, and wherein the printer controller is configured to transmit the after error suction application signal if the determined error is provided with the residual wet ink error identifier. The error catalogue may comprise a table or list linking each error to one ar more identifiers. The error catalogue preferably comprises for each error an error name or information which may be displayed on the user interface to communicate present error to the operator. An error input identifier may be provided to allow the printer controller to determine which error in the catalogue has occurred based on input information from one or more components of the web printer. Per error the error catalogue may provide control instructions which determine specific actions to be executed by the printed controller when an error occurs. Errors in the catalogue may further be grouped together into types by associating an error type label with each error. One specific group of errors in the present invention is labeled with a residual wet ink error identifier in the error catalogue. The controller may determine that the detected error is a residual wet ink error for example from a residual wet ink identifier linked to said detected error or deduce from received error information that said error is a residual wet ink error based on predetermined criteria stored in error catalogue (for example when a paper jam is detected while the print heads are determined to be jetting). Identification of the errors via the error catalogue reliefs the workload of the operator and allows for efficient

P4131NL01 handling of errors. In a further embodiment, the error catalogue further stores a plurality of errors not associated with the residual wet ink error identifier, wherein the printer controller is 5 configured to prevent the suction device from applying suction to the medium holding surface when the determined error is one of said plurality of errors not associated with the residual wet ink error identifier. The error catalogue further holds one or more non- critical errors (e.g. low ink levels, print artifacts detected), which do not require the manual removal of a web medium with uncured ink. When such a non-critical error has been detected, print operations may be resumed, either without stopping or after intervention by the operator. Any wet ink present at the time of a non-critical error can still be transported and cured by the web printer.

In an embodiment, the printer controller is further configured to control a user interface to display a manual medium removal indication for instructing an operator that manual removal of a portion of the medium is required to resolve the determined residual wet ink error. When the printer controller detects a residual wet ink error, it controls the user interface to inform the operator of said error, e.g. by communicating the error type or name. To further aid the operator the user interface provides instructions regarding the operator acts required to resolve the detected error. These instructions may be in the form of audio or video prompts describing different actions the operator needs to perform. Thereby the operator may directly commence to resolve the error without e.g. first consulting a manual.

In another embodiment, the manual medium removal indication further comprises cutting instructions for cutting the web medium upstream and downstream of the medium holding surface. The web medium portion with the residual wet ink needs to be manually removed from the medium holding surface. Thereto the user interface prompts the operator to manually cut said portion free of the remainder of the web medium. As the printer controller ensures that the web medium portion is held in place by suction, the operator is free to cut said portion without the risk of it contaminating the web printer.

In a further embodiment, the printer controller is configured to: - operate the web printer in an error mode when the error has been determined; and

P4131NL01 6 - control the suction device to stop suction at the medium holding surface in response to an after error suction stop signal while in the error mode and after transmission of the after error suction application signal. When a sufficiently critical error has been received, the printer controller operates the web printer in error mode, wherein web medium transport and printing are halted. When the error has been determined to be a residual wet ink error, the suction device applies suction to the medium holding surface in the error mode after the after error suction application signal has been transmitted. In this situation the printer controller is configured to maintain suction until an after error suction stop signal is received from the user interface. During cutting operations the web medium is thus secured. After cutting the web medium portion, suction is removed to allow for removal of said portion. Preferably, the user interface thereto provides instructions and after error suction stop control means.

In a preferred embodiment, the web printer is a roll-to-roll printer which further comprises an output roller for re-winding the web medium, and wherein the medium holding surface is substantially free of web medium clamping means. The web medium is unwound from the input roller and transport for rewinding at the output roller. In between the rollers the web medium extends continuously. Clamping of the web medium anywhere along its transport is undesired as it may deform or damage the web medium.

Embodiment examples will now be described in conjunction with the drawings, wherein: Fig. 1A is a schematic perspective view of a printing system; Fig. 1B is a schematic perspective view of an inkjet printing assembly the printing system in Fig. 1A; Fig. 2 is a schematic perspective view of an embodiment of a printing system according to the present invention; Fig.3 is a schematic representation of an embodiment of an error catalogue as stored on a memory of a printer controller of a web printer according to the present invention; and Fig. 4 is a schematic flow diagram of the work flow of a printer controller of a web printer according to the present invention.

P4131NL01 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.

Printing system Fig. 1A shows an image forming apparatus 1, wherein printing is achieved using a wide format inkjet printer.

The wide-format image forming apparatus 1 comprises a housing 2 holding the printing assembly 10. The image forming apparatus 1 also comprises at least one media input unit 3 for storing one or more media 8, 9 in the form of a wound-up roll of web medium.

The media 8, 9 are supplied by a roll 8, 9. The roll 8 is supported on the roll support R1, while the roll 9 is supported on the roll support R2. A transport path extends from the media input unit 3 along the printing assembly 10 to a receiving unit 4 to collect the medium 8, 9 after printing.

A storage unit 19 for marking material is provided to hold marking materials.

Each marking material for use in the printing assembly 10 is stored in one of a plurality of containers 19 arranged in fluid connection with the respective print heads for supplying marking material to said print heads to print an image on the medium 8, 9. The receiving unit 4 may comprise a take- up roller for winding up the printed medium 8, 9 or a receiving tray for supporting sheets of printed medium 8, 9. Optionally, the receiving unit 4 may comprise processing means for processing the medium 8, © after printing, e.g. a post-treatment device such as a coater, a folder or a puncher.

The wide-format image forming apparatus 1 furthermore comprises a user interface 5 for receiving print jobs and optionally for manipulating print jobs.

The local user interface unit 5 is integrated to the print engine and may comprise a display unit and a control panel.

Alternatively, the control panel may be integrated in the display unit, for example in the form of a touch-screen control panel.

The local user interface unit 5 is connected to a control unit 6 connected to the image forming apparatus 1. The control unit 6, for example a computer, comprises a processor adapted to issue commands to the image forming apparatus 1, for example for controlling the print process.

The image forming apparatus 1 may optionally be connected to a network N.

The connection to the network N is diagrammatically shown in the form of a cable 7, but nevertheless, the connection could be wireless.

The image forming apparatus 1 may receive printing jobs via the network N.

Further, optionally, the control unit 6 of the image forming apparatus 1 may be provided with a USB port, so

P4131NL01 8 printing jobs may be sent to the image forming apparatus 1 via this USB port. Printing assembly Fig. 1B shows an ink jet printing assembly 10. The ink jet printing assembly 10 comprises a medium support surface to support the medium 8, 9 during printing. The medium support surface in Fig. 1B is provided on a platen 11 in the form of a drum rotatable in direction A, but may, alternatively, be a flat support surface. The medium support surface is preferably provided with suction holes for at least temporarily holding the medium 8, 9 in a fixed position with respect to the medium support surface. The ink jet printing assembly 10 comprises print heads 12a - 12d, mounted on a scanning print carriage 13, or alternatively as a stationary page-wide array. The scanning print carriage 13 is guided by suitable guides 14, 15 to move in reciprocation in the main scanning direction B. Each print head 12a - 12d comprises an orifice surface 18, which orifice surface 16 is provided with at least one orifice 17. The print heads 12a - 12d are configured to eject droplets of marking material onto the medium 8, 9. The medium support surface, the carriage 13 and the print heads 12a - 12d are controlled by suitable controlling means 6a, 8b and 6c, respectively. The medium 8, 9 is supplied in web form and may be composed of e.g. paper, cardboard, label stock, coated paper, plastic or textile. The medium 8, 9 is moved in the sub-scanning direction A by the platen 11 along four print heads 4a - 4d provided with a fluid marking material.

A scanning print carriage 13 carries the four print heads 12a - 12d and may be moved in reciprocation in the main scanning direction B parallel to the medium support surface, such as to enable scanning of the medium 8, 9 in the main scanning direction B. Any number of print heads may be employed. Preferably, at least one print head 12a - 12d per color of marking material is placed on the scanning print carriage 13, for example one for print head 12a - 12d for each of the applied colors, usually black, cyan, magenta and yellow is present. Often, in a full-color printer, black marking material is used more frequently in comparison to differently colored marking material. Therefore, more print heads 12a - 12d containing black marking material may be provided on the scanning print carriage 13 compared to print heads 12a - 12d containing marking material in any of the other colors. Alternatively, the print head 12a - 12d containing black marking material may be larger than any of the print heads 12a - 12d, containing a differently colored marking material.

The carriage 13 is guided by guides 14, 15 in the form of guide rails or rods 14,

P4131NL01 9 15, as depicted in Fig. 1B. The carriage 13 may be driven along the guides 14, 15 by a suitable driving actuator (not shown). An alternative is to move the medium 8, 9 in the main scanning direction B. Print heads Each print head 12a - 12d comprises an orifice surface 16 having at least one orifice 17, in fluid communication with a pressure chamber containing fluid marking material provided in the print head 12a - 12d. On the orifice surface 18, a number of orifices 17 is arranged in a single linear array parallel to the sub-scanning direction A.

Eight orifices 17 per print head 12a - 12d are depicted in Fig. 1B, however obviously in a practical embodiment at least several hundreds of orifices 17 may be provided per print head 12a - 12d, optionally arranged in multiple arrays. As depicted in Fig. 1B, the respective print heads 12a - 12d are placed parallel to each other such that corresponding orifices 17 of the respective print heads 12a - 12d are positioned in-line in the main scanning direction B. This means that a line of image dots in the main scanning direction B may be formed by selectively activating up to four orifices 17, each of them being part of a different print head 12a - 12d. This parallel positioning of the print heads 12a - 12d with corresponding in-line placement of the orifices 17 is advantageous to increase productivity and/or improve print quality. Alternatively multiple print heads 12a - 12d may be placed on the print carriage adjacent to each other such that the orifices 17 of the respective print heads 12a - 12d are positioned in a staggered configuration instead of in-line. For instance, this may be done to increase the print resolution or to enlarge the effective print area, which may be addressed in a single scan in the main scanning direction. The image dots are formed by ejecting droplets of marking material from the orifices 17.

Upon ejection of the marking material, some marking material may be spilled and stay on the orifice surface 16 of the print head 12a - 12d. The ink present on the orifice surface 16, may negatively influence the ejection of droplets and the placement of these droplets on the medium 8, 9. Therefore, it may be advantageous to remove excess of ink from the orifice surface 16. The excess of ink may be removed for example by wiping with a wiper and/or by application of a suitable anti-wetting property of the surface, e.g. provided by a coating.

Ink curing In the preferred embodiment shown in Fig. 2 the print heads 12a-d of the print

P4131NL01 10 head assembly 110 are configured for the emission of UV-curable ink.

Each print head 12a-d is therein connected to a UV-curable ink supply.

UV-curable ink offers a wide color range as well as the possibility of gloss control, which makes these inks particularly interesting for graphic art applications.

As the name implies UV-curable inks (or UV-inks for short) require curing by UV-radiation to cure or harden the liquid ink after it has been jetted by the print-heads 12a-d onto the web medium 8. Thereto a curing station 150 is positioned downstream of the print head assembly 110. The curing station 150 may in one example be mounted on the same carriage as the print head assembly 110 and/or be a separate unit 150 spaced apart from the print head assembly 110 in the transport direction of the web medium 8. The curing station 150 comprises UV emitters, such as UV lights, preferably LEDs.

The UV radiation cures or hardens the wet UV ink, making the printed web medium suitable for further handling by an operator or medium handling devices.

Web transport system Fig. 2 discloses a printing system 100 according to the present invention.

It will be appreciated that any features of the printing system 1 may be incorporated in the printing system 100 in Fig. 2. The printing system 100 is a roll-to-roll printing system 100, wherein a web 8 is unwound from a first media roll on an input roller R1 to a second media roll on an output roller R3. The web 8 is unwound from the input roller R1 in substantially the horizontal direction H towards a first dancer 131. The first dancer 131 is a roller 131 rotatable around its central axis and moveable in substantially the vertical direction V.

Preferably, is dancer 131 is controlled to adjust its vertical position as the web 8 is unwound from the input roller R1, such that the web 8 leaves the input roller R1 in substantially the horizontal direction H regardless amount of media remaining on the input roller R1. This positional adjustment may be done by applying an appropriate force by means of a roller actuator for driving the input roller R1. The first dancer 131 during operation is adjusted in correspondence with the decreasing diameter of the media roll on the input roller R1 to keep the web horizontal between the input roller R1 and the first dancer 131. The web 8 then curves around the first dancer 131 towards the substantially vertical direction towards the turn element 153. The web 8 thus curves around the first dancer 131 over a substantially straight angle (i.e. circa 909). By adjusting the vertical position of the first dancer 131, this angle is kept constant while the diameter of the media roll on the input roller R1 decreases.

Maintaining a substantially straight angle allows for force decoupling of forces acting on the web 8 on

P4131NL01 11 the input roller side of the first 131 dancer from the web 8 on the print surface side of the first dancer 131. This increases the inaccuracy of the step-wise displacement of the web 8 as well as its positional stability in between displacement steps.

Preferably, the first dancer 131 is positioned such that the web 8 extends substantially horizontally between the input roller R1 and the first dancer 131. The weight of wide media rolls (e.g. over meters wide) causes the middle section of the input roller 131 to sag.

Due to said sagging the input roller 131 is in practice not perfectly straight, but comprises a parabolic curvature with a lowest point in the middle of the input roller 131 (if the media roll is positioned centrally on the input roller 131). The media roll during unwinding is not fully cylinder symmetric, which results in inaccuracy in the positioning of the web 8. By allowing the web 8 to unwind from the top of the media roll in a substantially horizontal direction D towards the first dancer 131, the effect of the sagging are removed or significantly reduced.

The web 8 between the input roller R1 and the first dancer 131 comprises a substantially homogeneous tension in both the length and width directions of the web 8. In consequence, the media positioning accuracy is improved.

The turn element 153 curves the web 8 from its vertical orientation towards the substantially horizontal print surface 111. The turn element 153 is preferably a stationary turn bar 153 provided with a low friction surface such that the web 8 slides over said surface with minimum resistance.

The print surface 111 is provided with suction holes {not shown) through which an underpressure is applied to the web 8 to adhere the web to the print surface 111. The underpressure is achieved by the suction device 112 is fluid connection with the holes in the print surface 111. Thereby flatness of the web 8 on the print surface 111 is improved.

Above the print surface 111 the inkjet printing assembly 110 is provided.

As explained previously in Fig. 1B, the inkjet printing assembly 110 comprises a print head carriage moveable in a width direction over the web 8 for swath-wise printing an image on the web 8. Downstream of the print surface 111 a stepping roller 151 is provided.

The stepping roller 151, for example a capstan roller, is provided with a high friction surface (such as a rubber surface) for engaging the web 8. The stepping roller 151 is driven by an actuator (not shown) configured to move the stepping roller 151 over a predetermined angle to move the web 8 a predetermined distance over the print surface 111. The low friction of the stationary turn element 153 combined with the force decoupling of the 90° turn by means of the first dancer 131 improve the accuracy by which the web 8 can be

P4131NL01 12 stepwise moved. The rotation of the stepping roller 151 determines the displacement of the web 8 over the print surface 111. For illustrative purposes the elasticity 8A or stiffness 8A has been visually indicated as a spring 8A. Rotating the stepping roller 151 affects the tension in the web 8 upstream of the stepping roller 151. To accurately displace the web 8 with respect to the printing assembly 110 accurate control over the web tension is required. It is further noted that the stiffness 8A may vary greatly between different media types, such as paper, foil, textile, etc. Downstream of the stepping roller 151, the web 8 curves around the second dancer

141. The second dancer 141 is moveable in substantially the horizontal direction H. From the second dancer 141 the web 8 extends to the output roller R3 which winds the web 8 into a media roll. The first and second dancers 131, 141 are configured to locally tension the web 8. The first dancer 131 tensions the web between the input roller R1 and the turn element 133. The second dancer 141 tensions the web 8 between the stepping roller 151 and the output roller R3. Each dancer 131, 141 is supported by its respective dancer suspension assembly 130, 140. Both dancers 131, 141 are connected to an actuator 135B, 145B via a wire element 133, 143. A spring element 137, 147 is provided along the wire element 133, 143. The motor or actuator 135B, 145B pulls on the respective dancer 131, 141 via the respective spring element 137, 147. The spring element 137, 147, when stationary, provides a tension force on the respective dancer 131, 141 even when the dancer 131, 141 is stationary. As such the tension in the web 8 can be controlled to a desired value.

Preferably, the printing system 100 includes a position sensor (not shown) to determine the position of each dancer 131, 141. The position sensor may be an encoder provided in the respective dancer support pulley 135A, 145A, as the rotation of the dancer support pulley 135A, 145A provides a measure for the displacement of the dancer 131,

141. The displacement of each dancer 131, 141 is preferably limited to linear movement. In an advantageous embodiment, the dancers 131, 141 are suspended on either end by a rod mechanism. The rod mechanism is in an exemplary embodiment a four rod mechanism, wherein the dancer 131, 141 is mounted on a central one of the four rods. While the outer two rods are preferably straight, the central rod preferably comprises a curvature such that the dancer 131, 141 is restricted to substantially linear

P4131NL01 13 movement. The rod mechanism provides a low friction solution for limiting the movement of the dancer 131, 141. Additionally, contact sensors 139, 149 may be provided to collaborate with the position sensor. The contact sensors 139, 149 provide a fixed position with respect to the frame of the printing system 100 and transmit a signal when the dancer 131, 141 is positioned at said position. By determining the displacement from said position, e.g. by means of the encoders, the position of the dancer 131, 141 can be determined swiftly and accurately after a new web 8 has been loaded on the printing system 100.

Further, one or more spring sensors 138, 148 may be provided which spring sensors 138, 148 are configured to determine the force exerted by the spring element 137, 147. Preferably, the spring sensor 138, 148 comprises an array of individual detectors positioned to detect the spring element 137, 147 at different positions in the length direction of the spring element 137, 147. The spring force of the spring element 137, 147 is determined by the spring constant and the spring length (specifically by the spring stretching). The length of the spring element 137, 147 as determined by the spring sensors 138, 148 thus provides an accurate measure for the spring force, which in turn determines the tension in the web 8.

Inthe embodiment in Fig. 2 separate actuators 135B and springs elements 137 are provided for controlling the spring force on either side of the dancer 131. As such different forces can applied to the different ends of the dancer 131. This allows the dancer suspension assembly 130, 140 to compensate for tension variations in the width directions of the web 133.

The web transport system in Fig. 2 has the advantage that it avoids clamping the web medium 8, thereby locally deforming or damaging the web medium 8, which could lead to print artifacts.

Error handling Fig. 4 illustrates schematically the steps of an embodiment of a method of operating the web printer 100 according to the present invention. Prior to commencing operations the web medium 8 from the input roller R1 is connected to the output roller R3. A print job comprising one or more images is received by the printer controller 8 or control unit 6 in step a after which printing commences. The images are printed in consecutive swaths

P4131NL01 14 on the web medium 8 by the scanning print head carriage 110. In between swaths, the web medium 8 is moved a step in its transport direction by driving the roller 151. During printing and transportation the control unit 6 controls a suction device 112 to apply an underpressure to the web medium 8 via the print surface 111 or medium holding surface

111. Thereby the web medium 8 is drawn against the print surface 111.

During operations the control unit 6 monitors for the occurrence of errors. Errors may be received from any of the printer's components, such as the transport system or the print head carriage assembly 110. Without errors the printer 100 continues its operation (step m). When in step d an error is detected by the control unit 6, the control unit 8 determines the type of the error. Thereto, the control unit 6 comprises a memory storing an error catalogue (EC in Fig. 3) or table EC which comprises a list of errors E1-E4 and their corresponding characteristics In1-In4, WI, T1-T4, Ac1-Ac4. The error catalogue EC lists each error E1-E4 and one or more error determination factors In1-In4 for each error. The error determination factors In1-In4 may include input signal characteristics that allow the control unit 6 to identify or classify the error E1-E4. In a basic example for each error E1-E4 an input signal characteristic In1-In4 or identifier In1-In4 may be stored in the error catalogue EC, against which input signal characteristic In1-In4 a received error signal may be compared to determine the error E1-E4. The error catalogue EC may then provide further characteristics E1-E4, WI, T1-T4, Ac1-Ac4 for the identified error E1-E4, such as a text string E1-E4 containing a name E1-E4 for the error E1-E4 to be displayed on the user interface 5 or control instructions Ac1-Ac4 for initializing appropriate actions to resolve said error E1-E4.

In the error catalogue EC errors E1-E4 may share a common identifier WI, T1-T3. Errors E1-E4 may as such be linked or grouped together in a particular error class WI, T1-T3 or type. For example, certain errors E1, E2 may be tagged as non-critical error T1 which allow for continuation of the print operations, but trigger the control unit 6 to transmit an error message Ac1, Ac2 to the user interface 5. Critical errors E3-E4, T2-T3 result in the control unit 8 stopping print operations. The web transport is halted as is the ink jetting of the print heads 12a-d. Critical errors E3-E4, T2-T3 may include a web medium jam, an excessive lateral position deviation of the web medium 8, or other operational deviations that are incorrigible by the web printer 100 itself. When a critical error E3-E4, T2-T3 occurs and print operations are suddenly halted uncured ink may remain between on the web medium 8, for example on printed portions of the web

P4131NL01 15 medium 8 that have not yet reached the curing station 150 or have been insufficiently exposed to UV-radiation to fully harden.

UV-curable inks generally do not harden by exposure to air, So care is required to remove the uncured from the web printer 100 without said wet ink contaminating the web printer 100 and/or the operator.

Certain types of uncured UV-curable inks are further considered hazardous, so these should be handled with appropriate care.

In case there is no risk of wet ink on the web medium 8 at the moment print operations are halted by the control unit 6 (error E3 under error type T2), the control unit 6 proceeds to step k and also stops the suction at the print surface 111, for example by stopping the suction device 112 or controlling a valve to disconnect the suction device 112 from the print surface 111. The control unit & may derive the presence of uncured ink from the active status of the print head assembly 110. When the print-heads 12a-d are jetting when the critical error E4, T3 is determined and print operations are halted, residual wet ink will likely be present on the web medium 8. The control unit 6 then further determines the error E4 to be a residual wet ink error WI.

The control unit 6 then proceeds to step i, wherein the control unit 6 transmits an after error suction application signal Ac4. As can be seen in Fig. 3, the residual wet ink error may be identified via a dedicated identifier WI.

In a preferred embodiment, the control unit 6 applies the error suction application signal Ac4 to apply suction to the web medium 8 via the print surface 111 after the residual wet ink error WI has been determined and print operations have been stopped.

The control unit & may therein initially stop the suction device 112 and activate it later for environmental reasons, e.g. after a predetermined time or when the presence of an operator at the user interface 5 has been detected.

As such, when the operator is present at the web printer 100 with the residual wet ink error WI, suction is applied to the web medium 8 via the print surface 111. Thereby the web medium 8 is held or secured onto the print surface 111. Via the user interface 5 the operator is instructed via visual prompts to cut the web medium 8 on either side of the print surface 111. Since the portion of the web medium 8 with the wet ink is secured by suction onto the print surface 111 there is no risk of said portion moving uncontrollably and contaminating the web printer 100. After stabilizing the cut portion on the print surface 111, for example by folding the leading and or trailing edges of the web medium portion over its wet ink

P4131NL01 16 section, the suction may be removed said cut portion of the web medium 8. Thereto, the user interface 5 indicates a suction stop button after having completed showing the prompts for cutting the web medium 8. In this manner, the operator may easily remove the portion with the residual uncured ink without the risk of contamination.

In an alternative embodiment, the after error suction application is transmitted to the operator via the user interface 5. Instead of directly controlling the suction device 112, the user interface provides or indicates a control means such as a button for prompting the operator to active the suction device 112. For example, upon detecting the residual wet ink error the control unit may cease operation of the web printer 100 including the suction device 112 and display an error message identifying the residual wet ink error WI on the user interface 5 as well as a user instruction to activate the suction device 112 before proceeding with the above discussed cutting and removal of the web medium 8.

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 scope 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

P413TNL01 17 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.

P4131NL01 18 Embodiments

1. A web printer (100) comprising: - an input roller (R1) for unwinding a web medium (8) towards a medium holding surface (111) provided with suction holes and connected to a suction device (112) to suck the web medium (8) against the medium holding surface (111); - a print head assembly (110) positioned over the medium holding surface (111) for jetting ink onto the web medium (8); - a ink treatment station (150) for treating the ink jetted onto the web medium (8) such that said ink hardens on the web medium (8); and - a printer controller (6) configured to: - determine the occurrence of an error (E3-E4) which error (E3-E4) stops print operation of the web printer (100); - determine whether the error (E3-E4) is a residual wet ink error (WI) indicating wet ink is present on a to be removed portion of the web medium (8); - if the error (E4) is determined to be a residual wet ink error (WI), transmit an after error suction application signal (Ac4) for applying suction to the web medium (8) via the medium holding surface (111).

2. The web printer (100) according to claim 1, wherein the after error suction application signal (Ac4) is configured to control: - the suction device (112) to apply suction to the web medium (8) via the medium holding surface (111); or - a user interface (5) to display an after error suction application indication to an operator.

3. The web printer (100) according to claim 1 or 2, wherein the inkjet print head assembly is a scanning inkjet print head assembly (110) moveable over the medium holding surface (111) and wherein the ink treatment station (150) is a curing station (150) or a drying station positioned downstream of the inkjet print head assembly (110).

4. The web printer (100) according to claim 3, wherein the curing station (150) comprises UV emitters for curing ink on the web medium by UV radiation. 5 The web printer (100) according to any of the previous claims, wherein the printer

P4131NL01 19 controller (6) comprises a memory storing an error catalogue (EC), wherein at least one error (E4) is provided with a residual wet ink error identifier (WI), and wherein the printer controller (8) is configured to transmit the after error suction application signal (Ac4) when the determined error (E4) is provided with the residual wet ink error identifier (WI).

6. The web printer (100) according to claim 5, wherein the error catalogue (EC) further stores a plurality of errors (E1-E3) not associated with the residual wet ink error identifier (WI), wherein the printer controller (6) is configured to prevent the suction device (112) from applying suction to the medium holding surface (111) when the determined error (E1-E3) is one of said plurality of errors (E1-E3) not associated with the residual wet ink error identifier (WI).

7. The web printer (100) according to any of the previous claims, wherein the printer controller (6) is further configured to control a user interface (5) to display a manual medium removal indication for instructing an operator that manual removal of a portion of the web medium (8) is required to resolve the determined residual wet ink error.

8. The web printer (100) according to claim 7, wherein the manual medium removal indication further comprises cutting instructions for cutting the web medium (8) upstream and downstream of the medium holding surface (111).

9. The web printer (100) according to any of the previous claims, wherein the printer controller (6) is configured to: - operate the web printer (100) in an error mode when the error (E3-E4) has been determined; and - control the suction device (112) to stop suction at the medium holding surface (111) in response to an after error suction stop signal while in the error mode and after transmission of the after error suction application signal (Ac4).

10. The web printer (100) according to any of the previous claims, wherein the web printer (100) is a roll-to-roll printer (100) further comprising an output roller (R3) for re- winding the web medium (8), and wherein the medium holding surface (111) is substantially free of web medium clamping means.

Claims

P4131EN01 20 Conclusions

Web printer (100) comprising: - an input roller (R1) for unwinding a web medium (8) to a medium holding surface (111) provided with suction holes and connected to a suction device (112) around the web medium (8) suction against the medium holding surface (111); - a printhead assembly (110) positioned above the medium holding surface (111) for spraying ink onto the web medium (8); - an ink treatment station (150) for treating ink sprayed on the web medium (8) such that the ink cures on the web medium (8); and - a printer operating system (8) adapted to: - determine the occurrence of an error (E3-E4), which error (E3-E4) stops the printing process of the web printer (100); - determining whether the error (E3-E4) is a wet ink residue error (WI) indicating that wet ink is present on a part of the web medium (8) to be removed; - when the error (E4) is determined to be a wet ink residue error (WI), sending a post-error suction application signal (Ac4) for applying suction to the web medium (8) via the media holding plane (111).

The web printer (100) according to claim 1, wherein the post-fault suction application signal (Ac4) is arranged to control: - the suction device (112) for applying suction to the web medium (8) via the medium holding plane (111); or - a user interface (5) for displaying a post-suction suction application indication to a user.

The web printer (100) of claim 1 or 2, wherein the inkjet printhead assembly is a translating inkjet printhead assembly (110) movable over the media holding surface (111) and wherein the ink treatment station (150) is a curing station (150) or a downstream station of the inkjet printhead assembly (110) is positioned.

The web printer (100) according to claim 3, wherein the curing station (150) comprises UV radiators for curing ink on the web medim (8).

P4131EN01 21

The web printer (100) according to any of the preceding claims, wherein the printer operating system (6) comprises a memory on which an error catalog (EC) is stored, in which at least one error (E4) is provided with a wet ink residue error identifier (WI), and wherein the printer control system (8) is arranged to send the post-fault suction application signal (Ac4) when the determined error (E4) includes the wet ink residue error identifier (WI).

The web printer (100) of claim 5, further comprising a plurality of errors (E1-E3) stored on the error catalog (EC), which errors (E1-E3) are not associated with the wet ink residue error identifier (WI), wherein the printer operating system (6) adapted to prevent the suction device (112) from applying suction to the medium holding surface (111) when the determined error (E1-E3) is one of the plurality of errors concerned (E1-E3), which errors (E1 -E3) are not connected to the wet ink residue error identifier (WI).

The web printer (100) according to any of the preceding claims, wherein the printer operating system (6) is further adapted to control a user interface (5) for displaying a manual media removal indication for instructing a user to manually delete a portion of the web medium {8) is required to resolve the determined wet ink residue error (E4).

The web printer (100) according to claim 7, wherein the manual media removal indication further comprises cutting instructions for cutting the web media (8) upstream and downstream of the media holding surface (111).

Web printer (100) according to any of the preceding claims, wherein the printer operating system (6) is arranged for: - controlling the web printer (100) in an error mode when the error (E3-E4) is determined; and - controlling the suction device (112) to stop the suction on the medium holding surface (111) in response to a post-fault suction stop signal during the fault mode and after sending the post-fault suction application signal (Ac4).

The web printer (100) according to any of the preceding claims, wherein the

P413TNL01 22 web printer (100) is a roll-to-roll printer (100), further comprising an output roller (R3) for winding up the web medium (8) and wherein the medium retaining surface (111) is substantially free of web medium clamping means.