METHOD FOR CONTROLLING A WEB IN A PRINTING APPARATUS

Abstract

A method is provided for controlling a web in a printing apparatus The printing apparatus includes a transport assembly for moving the web through a transport path along a printing unit for printing an image onto a print area of the web. The method includes feeding the web from a supply roll through the transport path to the transport assembly; and switching the printing apparatus to a ready-to-print mode, wherein the printing unit does not print an image on the web and the web is maintained ready to be printed on. In a printing mode after the ready-to print mode, the following steps are performed: moving the web through the transport path in a transport direction along the printing unit by the transport assembly; and printing the image onto the print area of the web by the printing unit. The image is printed by applying an image material, which solidifies on the web during the printing step. The ready-to-print mode includes the step of: operating the transport assembly to prevent a deformation of the print area of the web in the transport path, while maintaining the web in the ready-to-print mode. The web is maintained ready to print while preventing a deformation of the print area of the web in the transport path.

Claims

1. A method for controlling a web in a printing apparatus, wherein the printing apparatus comprises a transport assembly for transporting the web over a transport path extending downstream of a supply roll and along a printing unit, said transport path comprising a web deformation zone between the roll supply and the printing unit, the method comprising the steps of: a) feeding the web from the supply roll through the transport path to the transport assembly in the transport direction; b) moving the web with the transport assembly through the transport path in the transport direction along the printing unit in a print mode of the printing apparatus; c) printing an image onto a print area of the web with the printing unit in the print mode, wherein the image is printed by applying an image material, which solidifies on the web during the printing step; d1) determining a termination of the print mode of the printing apparatus; d2) upon determination of the termination of the print mode, switching the printing apparatus to a ready-to-print mode, wherein the printing apparatus is maintained in a state to directly commence printing; and e) in the ready-to-print mode, the transport assembly transporting the print area of the web medium positioned in the deformation zone to a deformation-free zone positioned along the transport path upstream of the supply roll.

2. The method according to claim 1, wherein in the ready-to-print mode, the transport assembly in step e) transports the print area in a reverse direction opposite to the transport direction.

3. The method according to claim 2, wherein the printing apparatus comprises a web deformation device which engages and deforms the web in the web deformation zone, wherein in the ready-to-print mode, the transport assembly in step e) transports the print area from the deformation zone to the deformation-free zone, which deformation-free zone is positioned between the supply roll and the web deformation device.

4. The method according to claim 1, wherein the printing unit is positioned a predefined length along the transport path downstream of the supply roll, and the step e) further comprises the transport assembly transporting the print area in a reverse direction opposite to the transport direction over a distance less than half of the predefined length between the supply roll and the printing unit.

5. The method according to claim 1, wherein the method comprises the steps of: a) feeding the web from a supply roll through the transport path to the transport assembly; and d) switching the printing apparatus to a ready-to-print mode, wherein the printing unit does not print an image on the web and the web is maintained ready to be printed on, wherein in a printing mode after the ready-to print mode the following steps are performed: b) moving the web through the transport path in a transport direction along the printing unit by the transport assembly; and c) printing the image onto the print area of the web by the printing unit, wherein the image is printed by applying an image material, which solidifies on the web during the printing step, and wherein the ready-to-print mode comprises the step of: e) operating the transport assembly to prevent a deformation of the print area of the web in the transport path, while maintaining the web in the ready-to-print mode.

6. The method according to claim 1, wherein the image material applied in step c) comprises a phase change component, which solidifies the image when cooled to room temperature.

7. The method according to claim 1, wherein the image material applied in step c) comprises a radiation curable component, which solidifies the image in response to a curing radiation, and wherein the printing step c) further comprises applying the curing radiation to the image material on the web.

8. The method according to claim 5, wherein in the printing step c) the image is printed by an inkjet printing unit comprising ejecting droplets of image material to form the image on the web.

9. The method according to claim 5, wherein the method after the printing step c) further comprises the steps of f) retracting the web from the transport path and g) switching the printing apparatus to a sleep mode, wherein the web is not controlled by the transport assembly.

10. The method according to claim 1, wherein the method further comprises the step of h) operating the transport assembly to deskew at least a part of the web relative to the transport path prior to the switching step d) such that the web during the ready-to-print step e) is in a predetermined orientation with respect to the transport path.

11. The method according to claim 1, wherein the transport assembly comprises a transport pinch comprising a drive roller for driving the web along the transport path and a pressure roller configured for urging against the drive roller in a pressure zone during the moving step b).

12. The method according to claim 1, wherein the printing apparatus further comprises a pre-heat unit configured for heating the web in a heating zone during the ready-to-print step e) and during the printing step c); the transport path comprising the heating zone.

13. The method according to claim 1, wherein the ready-to-print step e) is activated, when the ready-to-print mode continues for more than a predetermined time.

14. The method according to claim 1, wherein the ready-to-print step e) comprises the step of jogging the print area of the web back and forth such that the web is maintained substantially stationary in the transport direction along the transport path.

15. The method according to claim 1, wherein an image has been printed on an imaged area of the web prior to the ready-to-print step e) and the ready-to-print step e) comprises the step of repositioning the web along the transport path such that the imaged area of the web is positioned in a web deformation zone along the transport path.

16. The method according to claim 15, wherein the imaged area of the web is moved in the transport direction beyond the print unit after the ready-to-print step e) and before the subsequent printing step c).

17. The method according to claim 1, wherein the method further comprises the step of i) determining an interval area arranged between a first print area and a second print area relative to the transport direction and the ready-to-print step e) comprises the step of repositioning the web along the transport path such that the interval area of the web is positioned in a web deformation zone along the transport path.

18. The method according to claim 1, wherein the transport assembly comprises a transport pinch and a second transport device for controlling a movement of the web along the transport path and the ready-to-print step e) comprises the steps of operating the second transport device to control the web located in the transport path and opening the transport pinch.

19. A printing apparatus, comprising: a printing unit for printing an image onto a print area of a web; a transport assembly for moving the web through a transport path along the printing unit; and a control unit configured for operating the printing unit and the transport assembly to perform the method according to claim 1.

20. The method according to claim 1, wherein an image has been printed on an imaged area of the web prior to the ready-to-print step e) and the ready-to-print step e) comprises the step of repositioning the web along the transport path such that the imaged area of the web is positioned in a web deformation zone along the transport path.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] 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:

[0074] FIG. 1A shows a perspective view of an exemplary embodiment of an inkjet printing assembly;

[0075] FIG. 1B shows a schematic perspective view of a scanning inkjet printing assembly as used in the printing assembly of FIG. 1A;

[0076] FIG. 2 shows a cross-section of another exemplary embodiment of an inkjet printing system suitable for use with the method according to the present invention;

[0077] FIG. 3A-3C show cross-sections as illustrated in FIG. 2 for illustrating an embodiment of the method according to the present invention;

[0078] FIG. 4A-4B show cross-sections of a part of an embodiment of a printing assembly for illustrating a first and second detailed embodiment of the method according to the present invention, respectively;

[0079] FIG. 5 shows a cross-section of a part of an embodiment of a printing assembly for illustrating a third detailed embodiment of the method according to the present invention;

[0080] FIG. 6A-6D show cross-sections of a part of an embodiment of a printing assembly for illustrating a fourth detailed embodiment of the method according to the present invention;

[0081] FIG. 7 shows top view of a web for illustrating an example of a deformation; and

[0082] FIG. 8 shows a cross-section of a part of an embodiment of a printing assembly for illustrating a fifth detailed embodiment of the method according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0083] 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.

[0084] 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, wherein the printing assembly, for example the ink jet printing assembly shown in FIG. 1B is placed. The image forming apparatus 1 also comprises a storage means for storing image receiving member 3, 4, a delivery station to collect the image receiving member 3, 4 after printing and storage means 5 for marking material. In FIG. 1A, the delivery station is embodied as a delivery tray 6. Optionally, the delivery station may comprise processing means for processing the image receiving member 3, 4 after printing, e.g. a folder or a puncher. The wide-format image forming apparatus 1 furthermore comprises means for receiving print jobs and optionally means for manipulating print jobs. These means may include a user interface unit 8 and/or a control unit 7, for example a computer.

[0085] Images are printed on an image receiving member, for example paper, supplied by a roll 3, 4. The roll 3 is supported on the roll support R1, while the roll 4 is supported on the roll support R2. Alternatively, cut sheet image receiving members may be used instead of rolls 3, 4 of image receiving member. Printed sheets of the image receiving member, cut off from the roll 3, 4, are deposited in the delivery tray 6.

[0086] Each one of the marking materials for use in the printing assembly are stored in four containers 5 arranged in fluid connection with the respective print heads for supplying marking material to said print heads.

[0087] The local user interface unit 8 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 8 is connected to a control unit 7 placed inside the printing apparatus 1. The control unit 7, for example a computer, comprises a processor adapted to issue commands to the print engine, 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 9, but nevertheless, the connection could be wireless. The image forming apparatus 1 may receive printing jobs via the network. Further, optionally, the control unit of the printer may be provided with a USB port, so printing jobs may be sent to the printer via this USB port.

[0088] FIG. 1B shows an ink jet printing assembly 10. The ink jet printing assembly 10 comprises supporting means for supporting an image receiving member 3. The supporting means 11 are shown in FIG. 1B as a platen 11, but alternatively, the supporting means 11 may be a flat surface. The platen 11, as depicted in FIG. 1B, is a rotatable drum 11, which is rotatable about its axis as indicated by arrow A. The supporting means 11 may be optionally provided with suction holes for holding the image receiving member 3 in a fixed position with respect to the supporting means 11. The inkjet printing assembly 10 comprises print heads 12a-12d, mounted on a scanning print carriage 13. The scanning print carriage 13 is guided by suitable guiding means 14, 15 to move in reciprocation in the main scanning direction B. Each print head 12a-12d comprises an orifice surface 16, 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 image receiving member 3. The platen 11, the carriage 13 and the print heads 12a-12d are controlled by suitable controlling means 18a, 18b and 18c, respectively.

[0089] The image receiving member 3 may be a medium in web or in sheet form and may be composed of e.g. paper, cardboard, label stock, coated paper, plastic, canvas, film or textile. Alternatively, the image receiving member 3 may also be an intermediate member, endless or not. Examples of endless members, which may be moved cyclically, are a belt or a drum. The image receiving member 3 is moved in the sub-scanning direction A by the platen 11 along four print heads 12a-12d 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 platen 11, such as to enable scanning of the image receiving member 3 in the main scanning direction B. Only four print heads 12a-12d are depicted for demonstrating the invention. In practice an arbitrary number of print heads may be employed. In any case, at least one print head 12a-12d per color of marking material is placed on the scanning print carriage 13. For example, for a black-and-white printer, at least one print head 12a-12d, usually containing black marking material is present. Alternatively, a black-and-white printer may comprise a white marking material, which is to be applied on a black image-receiving member 3. For a full-color printer, containing multiple colors, at least one print head 12a-12d for each of the 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.

[0090] The carriage 13 is guided by guiding means 14, 15. These guiding means 14, 15 may be rods as depicted in FIG. 1B. The rods may be driven by suitable driving means (not shown). Alternatively, the carriage 13 may be guided by other guiding means, such as an arm being able to move the carriage 13. Another alternative is to move the image receiving material 3 in the main scanning direction B.

[0091] 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 16, 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 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 zone, 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.

[0092] 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 image receiving member 3. 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.

[0093] FIG. 2 illustrates schematically an image forming apparatus 1 or printing apparatus or system 1 according to the present invention. Two bearing supports 31, 32 are provided in a loading bin or tray 30 for rotatably holding a respective media roll R1, R2. From each media roll R1, R2 a respective print transport path P1, P2 extends from the media roll R1, R2 to the inkjet printing assembly 10. The print transport paths P1, P2 join together at intersection 54, after which they continue as a single main print transport path MP which extends to the inkjet printing assembly 10. The print transport paths P1, P2 and the main print transport path MP are defined by a media guide assembly 50, comprising media guide plates or conduits 51, 52, 55 for forming the respective transport paths P1, P2, MP. The main print transport MP extends further along a transport roller 61 and over a media support surface 62 or platen 62 below the inkjet printing assembly 10. The transport roller 61 is configured for driving the web provided from the respective media roll R1, R2 through the main print transport MP along the inkjet printing assembly 10. The transport device 61 may additionally comprise a pressure roller configured for urging against the transport roller 61 in a pressure zone, wherein the main print transport MP comprises the pressure zone. The transport roller and the pressure roller together form a transport pinch 61. The pressure roller enhances a control of the transport roller 61 on the movements of the web along the main print transport MP.

[0094] Downstream of the inkjet printing assembly 10 a medium 3, 4 may be guided via a guide support 63 to a take-up roller 64 for spooling the printed medium 3, 4 onto the take-up roller 64. The inkjet printing assembly 10 is configured for printing an inkjet image onto the web in a print zone located at the media support surface below the inkjet printing assembly 10.

[0095] The printing apparatus further comprises a control unit 100 for operating the inkjet printing assembly 10 for printing the inkjet image onto the web and operating the transport device 61 for controlling the web in the main print transport MP.

[0096] FIGS. 3A-3C are schematic side views of the printing system of FIG. 2 in various stages of the method according to the present invention.

[0097] In FIG. 3A a print medium 3 is loaded onto the media roll R2. In this example, the media roll R2 holds a relatively soft medium 3, such as a pressure sensitive vinyl banner material. Optionally another print medium 4 may be loaded onto the media roll R1. To increase production time, the print media 3, 4 are preferably fed into the printing system 1 by means of an automated web feeding system indicated by 280. Such a web feeding system 280 comprises for example pinches 281, 282 to transport the media, motors and motor control units to drive said pinches 281, 282 and media guides to guide the leading edge of a medium reliably to the print surface 62 at the inkjet printing assembly 10 without the assistance of an operator.

[0098] In this step, a leading edge portion of the print medium 3′ is located in the pinch 282 in the print transport path P2. The media roll R2 is rotated counter clockwise (CCVV) by driving the bearing support 32 to feed the print medium 3 in a direction F from the print transport path P2 through the main print transport MP towards the transport pinch 61.

[0099] FIG. 3B shows a second stage of the method, wherein the leading edge portion of the print medium 3′ is located in the transport pinch 61 in the main print transport path MP. The second stage is a ready-to-print mode of the printing apparatus 1.

[0100] At the second stage of the method the print medium 3 is ready to be printed on in a next printing mode, which is shown in FIG. 3C. The print medium 3 is located near to the inkjet printing assembly 10 and is arranged in a predetermined orientation with respect to the main print transport path MP, i.e. having no skew relative to the main print transport path MP. In this way, the print medium 3 is ready to be printed on in a next printing mode.

[0101] Prior to the second stage of the method, the transport pinch 61 may be operated to deskew the print medium 3 relative to the main print transport path MP. For example, the transport pinch 61 may move the print medium 3 such that the print medium 3 is pulled taut between the transport pinch 61 and the media roll R2, or between the transport pinch 61 and the pinch 282, wherein the print medium 3 is allowed to slip inside the transport pinch 61. In this way, the print medium 3 is easily aligned relative to the main print transport path MP.

[0102] During the ready-to-print mode, the print medium 3 is pressurized in the transport pinch 61. When using a relatively soft medium 3, such as a pressure sensitive vinyl banner material, the print medium 3 may become deformed when subjected to pressure for a longer period.

[0103] According to an embodiment, a ready-to-print processing step is activated, when the ready-to-print mode continues for more than a predetermined time, such as more than 10 seconds or more than 1 minute. The control unit 100 determines when the predetermined time has lapsed and switches to the ready-to-print processing step.

[0104] An embodiment of the ready-to-print processing step is shown in FIG. 4A. FIG. 4A shows a detailed side view of the transport pinch 61 including the leading edge portion of the print medium 3′, which is located in the transport pinch 61.

[0105] The drive roller of the transport pinch 61 is operated to rotate back and forth such that the print medium 3 is jogged, i.e. conveyed back and forth, along the main print transport path MP. While jogging the print medium 3, the web is maintained substantially stationary in a transport direction along the main print transport path MP. Thus, the leading edge portion of the print medium 3′ remains substantially at the same position relative to the inkjet printing assembly 10.

[0106] In this way, the pressure provided by the transport pinch is only temporarily applied at a position of the print medium 3. Due to the jogging movement, a deformation of the print medium is substantially reduced. The jogging distance J over which the print medium 3 is conveyed back and forth may be in the range of 1 mm-20 cm, which may be selected dependent on the size of a deformation that is to be prevented by the jogging movement. For example, a deformation having a length in the web transport direction of about 1 cm may be prevented by jogging over a distance at least longer than the 1 cm, for example 2 cm. If the web needs more recovery time, the distance of jogging may even be further increased to, for example, 5 cm.

[0107] When a certain relatively soft medium 3, such as a pressure sensitive vinyl banner material, would be persistently deformed in the transport pinch within 10 seconds-20 seconds, a jogging transport pinch keeps the same soft medium 3 substantially undeformed for a time span of 15 minutes to 30 minutes.

[0108] During that time span, a chance is high that a new print job may be started.

[0109] FIG. 3C shows a third stage of the method, wherein a printing mode is started after the ready-to-print mode shown in FIG. 3B. In the printing mode, the print medium 3′, which is located in the transport pinch 61, will be driven by the transport pinch 61 and is conveyed along the inkjet printing assembly 10 and the platen 62 in a transport direction as indicated by the arrow C. At the same time the print medium 3 is supplied from the media roll R2 by rotating the bearing support 32 counter clockwise.

[0110] At the inkjet printing assembly 10 an image PA is formed onto a print area of the print medium 3. The image PA may, for example, be formed by applying a phase change ink in the form of ink droplet. The ink droplets are ejected by the inkjet printing assembly 10 at a temperature higher than room temperature. The ink droplets are cooled by the platen 62, when deposited on the print medium 3. In response to a cooling down to room temperature, the image on the print medium 3 is solidified. The print medium 3 including the solidified image is moved along the guide support 63 and is received on the take-up roller 63 by winding the print medium 3 onto the take-up roller 63.

[0111] The print medium 3 is substantially undeformed at the time of printing the image PA onto the print medium 3. As a result, the image including the print medium 3 is not deformed after printing, even when the image material (phase change ink) solidifies on the print medium 3.

[0112] When the ready-to-print mode and the ready-to-print processing step continues for more than a critical time, such as 30 minutes, the printing apparatus 1 may switch to a sleep mode (not shown), wherein the print medium 3 is retracted from the main print transport path MP and rewound on the media roll R2. However, in the sleep mode the transport pinch 61 does not control the print medium 3 and the print medium 3 is not ready to be printed on.

[0113] FIG. 4B shows an alternative embodiment of the ready-to-print processing step used for the ready-to-print mode, such as shown in FIG. 3B. FIG. 4B shows a detailed side view of the transport pinch 61 including the leading edge portion of the print medium 3′, which is located in the transport pinch 61.

[0114] In the printing apparatus of this embodiment, a guidance assembly 80 is arranged facing the main print transport path MP between the media roll R2 and the transport pinch 61. The guidance assembly 80 comprises a guidance plate 82 extending along the main print transport path MP, which guidance plate 82 is pivotably supported at one of its ends by a supporting axle 84. The guidance plate 82 is urged towards the print medium 3 located in the print transport path MP.

[0115] When the transport pinch 61 is operated to perform a jogging movement J of the print medium 3 along the print transport path MP, the guidance plate rotates back and forth about the supporting axle 84 thereby compensating any length differences of the print medium 3 between the transport pinch 61 and the media roll R2. An outer position of the guidance plate 82′ including the print medium 3″ is indicated by dashed lines, in which outer position the longer length of the print medium 3″ between the transport pinch 61 and the media roll R2 is accommodated by a longer length of the print transport path MP. In this way, a tension is maintained in print medium 3 between the transport pinch 61 and the media roll R2 despite the jogging movement J of the print medium 3 at the transport pinch 61. As the tension is maintained in the ready-to-print processing step, the position of the print medium 3 is accurately controlled during the ready-to-print processing step.

[0116] FIG. 5 shows an alternative embodiment of the ready-to-print processing step used for the ready-to-print mode, such as shown in FIG. 3B. FIG. 5 shows a detailed side view of the transport pinch 61 including the leading edge portion of the print medium 3′, which is located in the transport pinch 61.

[0117] In the printing apparatus of this embodiment, a second medium pinch 90 is arranged at the main print transport path MP between the media roll R2 and the transport pinch 61. The second medium pinch 90 is controlled by the control unit 100. The second medium pinch 90 may comprise two rollers arranged opposite one another for holding the print medium 3 at the main print transport path MP. The second medium pinch 90 may be controlled by the control unit 100 to engage the print medium 3 in a closed state or disengage the print medium 3 in an open state.

[0118] In the ready-to-print processing step the second medium pinch 90 may be arranged in the closed state to retain the print medium 3 stationary in the main print transport path MP and to maintain a tension constant between the second medium pinch 90 and the media roll R2.

[0119] Subsequently the transport pinch 61 may be opened by the control unit 100 to disengage the print medium 3 at the transport pinch 61. In this way, during the ready-to-print processing step no pressure is provided to the print medium 3 at the transport pinch 61. The pressure at the second medium pinch 90 may be minimized by using soft material as roller components or may be minimized by applying a low pinch force between the two rollers. The second medium pinch 90 may not be provided to drive the print medium 3 along the main print transport path MP, thus a low pressure may be sufficient to retain the print medium 3.

[0120] Alternatively the second medium pinch 3 may be provided by a first plate and an opposing second plate (not shown), which are controlled by the control unit 100 to be arranged in a closed state to retain the print medium 3 or in an open state. Both plates extend along the main print transport path MP, and may additionally be provided by a high friction surface, to provide a friction force to the print medium 3, while employing a relatively low pressure to the print medium 3. In this way, the print medium 3 is maintained stationary in the main print transport path MP without deforming the print medium 3.

[0121] When switching to a printing mode, as shown in FIG. 3C, the transport pinch 61 may be closed to engage the print medium 3, may additionally be driven to control the tension of the print medium 3 between the transport pinch 61 and the second medium pinch 90, and the second medium pinch 90 may be opened to release the print medium 3. Thereafter the printing mode, as shown in FIG. 3C, may start. The print medium 3 is substantially not deformed during the ready-to-print processing step used for the ready-to-print mode.

[0122] FIGS. 6A-6D are schematic side views of a modified printing system 1 in various stages of the method according to the present invention. The printing system 1 further comprises a heating plate 70 arranged facing the main print transport path MP between the transport pinch 61 and the two bearing supports 31, 32 which are provided in the loading bin or tray 30. The heating plate 70 is controlled by the control unit 100 and is arranged for heating the print medium 3 located in the main print transport path MP at a heating zone 72.

[0123] In FIG. 6A a print medium 3 is loaded onto the media roll R2. In this example, the media roll R2 holds a medium 3, such as a paper like material. Optionally another print medium 4 may be loaded onto the media roll R1.

[0124] To increase production time, the print media 3, 4 are preferably fed into the printing system 1 by means of an automated web feeding system indicated by 280, as shown in FIGS. 3A-3C. Such a web feeding system 280 comprises for example pinches 281, 282 to transport the media, motors and motor control units to drive said pinches 281, 282 and media guides to guide the leading edge of a medium reliably to the print surface 62 at the inkjet printing assembly 10 without the assistance of an operator.

[0125] In this step, a leading edge portion of the print medium 3′ is located in the print transport path P2. The media roll R2 is rotated counter clockwise by driving the bearing support 32 to feed the print medium 3 in a direction F from the print transport path P2 through the main print transport MP towards the transport pinch 61. The print medium 3 is heated to a predetermined temperature in the heat zone 72 by the heating plate 70. Subsequently the print medium 3 is engaged by the transport pinch 61.

[0126] FIG. 6B shows a second stage of the method, wherein the leading edge portion of the print medium 3′ is moved beyond the inkjet printing assembly 10. The transport pinch 61 drives the print medium 3 to convey in a transport direction C1 along the inkjet printing assembly 10. The media roll R2 supplies the print medium 3 from the print transport path P2 into the main print transport path MP by rotating the bearing support 32 counter clockwise.

[0127] The inkjet printing assembly 10 is controlled by the control unit 100 to print an image PA1 onto the print media 3 in an imaged area as indicated by dashed arrow. The image solidifies on the web during the printing process, such as by cooling down the image. The print medium 3 is pre-heated upstream of the printing zone at the inkjet printing assembly 10 in the heating zone 72 by the heating plate 70.

[0128] FIG. 6C shows a third stage of the method, which is a ready-to-print mode of the printing apparatus 1.

[0129] The third stage of the method is after the printing step shown in FIG. 6B, wherein the print media 3 is moved backwards by the transport pinch 61 as indicated by arrow R.

[0130] During the third stage of the method no image is printed onto the print medium 3. The print media 3 is repositioned such that the printed image PA.sub.1 in the imaged area is located at the heating zone 72 of the heating plate 70. The media roll is rotated clockwise to rewind a portion of the print medium 3. A leading edge portion of the print medium 3′ is located close to the inkjet printing assembly 10 and is controlled by the transport pinch 61. When the printed image PA.sub.1 in the imaged area is located at the heating zone 72 of the heating plate 70, the print medium 3 is in the ready-to-print mode. The printed image PA.sub.1 in the imaged area is heated, since the heating plate is kept at an elevated temperature in the ready-to-print mode to prevent the necessity for warming-up before printing.

[0131] For example, as shown in FIG. 7, by heating a paper like material 3 in an unprinted area, said paper like material 3 may shrink to a shortened width W1 relative to an original width W0 due to evaporation of water from the paper like material 3 at the heating zone 72. Due to the evaporation of water in the paper like material 3 at the heating zone a moisture gradient exists between the heating zone 72 and neighboring areas of the paper like material 3.sub.N in a longitudinal direction L of the main print transport path MP. This will lead to out of plane deformations of the paper like material 3.sub.N, especially on places were an expansion or a retraction of the paper like material 3 in the transversal direction T is prohibited by pinches or friction. These media deformations can also lead to the paper like material 3 touching the inkjet printing assembly 10, e.g. printheads, when moving said deformed part of the paper like material 3 along the inkjet printing assembly 10 afterwards.

[0132] When an imaged area PA1 of the paper like material 3 is positioned in the heating zone 72, the paper like material 3 may still deform as evaporation of water from the paper like material 3 still occurs in the imaged area PA1. However, such a deformation is not persistent as said deformation is not fixed onto the web afterwards by printing and solidification of ink, while the web is deformed. The imaged area PA1 has been printed on previously and the ink has solidified in an undeformed state of the web. When the deformed imaged area PA1 recovers from the deformed state due to moisturizing under room conditions, the image material will also recover to the original, flat, undeformed state.

[0133] It is noted that the web is not heated to a temperature that liquefies the image material. Further, it is noted that the image material may have been cured by suitable curing means, such as but not limited to UV radiation, which prevents that the image material may liquefy again.

[0134] Even further, it is noted that the presence of the image material may suppress any deformation of the web e.g. due to a moisture gradient in the web as described in relation to FIG. 7.

[0135] FIG. 6D shows a fourth stage of the method, which is a printing mode started right after the ready-to-print mode of the printing apparatus 1. During the fourth stage, the transport pinch 61 conveys the print media 3 including the imaged area PA1 along the inkjet printing assembly 10 in a direction C1, while the inkjet printing assembly 10 is not printing. The printing media 3 is fed from the media roll R2 by rotating the bearing support 32 counter clockwise. The inkjet printing assembly starts printing a second image on a print area PA2 behind the imaged area PA1 with respect to the transport direction C1. The second image in said print area PA2 is printed on a part of the print media 3, which is not deformed during the ready-to-print mode shown in FIG. 6C. Additionally or alternatively to the ready-to-print step described in reference to FIG. 6C, the transport pinch 61 may be operated to move the print media 3 in a jogging movement, i.e. back and forth as shown in FIG. 4A, along the heating zone 72 in the media print transport path MP in the ready-to-print mode. For example, the imaged area

[0136] PA1 may be moved in a jogging movement along the heating zone 72. In another example, a print area of the print medium 3, which is not imaged, may be moved in a jogging movement along the heating zone 72.

[0137] In this way a moisture gradient of the print media 3 along the media print transport path MP is reduced. As a result, the deformation of the print media 3 at the heating zone 72 is reduced.

[0138] FIG. 8 shows an alternative embodiment of the ready-to-print processing step used for the ready-to-print mode of the printing apparatus as shown in FIG. 3B.

[0139] In the ready-to-print mode the leading edge part of the print medium 3′ is fed towards the transport pinch 61 to be engaged by the transport pinch 61.

[0140] The control unit 100 is configured to determine a first print area PA3 close to the leading edge part of the print medium 3′, is further configured to determine a second print area PA4 upstream of the first print area PA3 and an interval area I.sub.3-4 arranged in between the second print area PA4 and the first print area PA3. For example the second print area PA4 and the first print area PA3 and the interval area I.sub.3-4 are derived from a print job, which is processed by the control unit 100, such as a ripping process of the images to be printed after the ready-to-print mode. Optionally, the control unit 100 may be configured to determine a first print area PA3 close to the leading edge part of the print medium 3′ and an interval area I.sub.3-4 without determining the size of the second print area PA4.

[0141] In this embodiment of the ready-to-print processing step, the control unit 100 controls the transport pinch 61 to reposition the print medium 3, such that the interval area I.sub.3-4 is located at the transport pinch 61. The first print area PA3 is located downstream of the transport pinch 61, i.e. at the platen 62, and the second print area PA4 is located upstream of the transport pinch 61 in the main print transport path MP. In this way, only the interval area I.sub.3-4 is deformed by the transport pinch 61 during the ready-to-print mode.

[0142] After the ready to print mode, the leading edge part of the print medium 3′ is moved backwards to the start of the inkjet printing assembly 10, the first image is printed in the first print area PA3 and the second image is printed in the second print area PA4, while moving the print medium 3 in the transport direction along the inkjet printing assembly 10. Both print areas PA3, PA4 were not deformed during the ready-to-print mode. As a result no deformation of the print medium 3 is fixed by application of the image material on the print medium, none withstanding the solidification of the image by the image material during the printing step on the print medium 3.

[0143] 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 is herewith disclosed.

[0144] 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.

[0145] 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.

[0146] 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.