NL2032610B1

NL2032610B1 - A transport device with quadrual drive for a scanning inkjet printer

Info

Publication number: NL2032610B1
Application number: NL2032610A
Authority: NL
Inventors: A Draad Adrianus
Original assignee: Canon Kk
Priority date: 2022-07-27
Filing date: 2022-07-27
Publication date: 2024-02-05
Also published as: DE102023119622A1

Abstract

In order to avoid deformation of the belt supported on the rollers, an inkjet printer (1) is provided, which comprises a transport device (40) with an endless transport belt (4) supported on a plurality of rollers (3A, 3B, 30), such that a pair of said rollers (3A, 30) 5 define a print surface on the belt (4) facing a printhead assembly (7), characterized in that both of said rollers (3A, 30) of said pair of said rollers (3A, 30) are provided with drives (40A-40D) at either end, which drives (40A-40D) are configured for synchronously driving all ends of said rollers (3A, 30) for stepwise transport of the print medium (15, 16).

Description

11011807NL01 1

A TRANSPORT DEVICE WITH QUADRUAL DRIVE FOR A SCANNING INKJET

PRINTER

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to an inkjet printer and a method for transporting a print medium along a printhead assembly in such a printer. 2. Description of Background Art

It is known to provide printers with a belt-based transportation device. Such a transport device comprises an endless transport belt supported on a plurality of rollers, such that a pair of said plurality of rollers defines a print surface on the belt facing a scanning printhead assembly. The belt is air permeable and provided over a suction box in fluid connection with a suction source for applying an underpressure to the print medium.

The rollers are generally large in diameter to ensure sufficient rigidity to enable accurate positioning of the print medium with respect to the printhead assembly. In particular in scanning inkjet printers, due to the size of the applied print media, the rollers generally have a significant length, for example over 1.6 or even over 2.5 meters. The print medium is transported stepwise to allow for swathwise printing of images in between steps. To displace the print medium by such a step, one of the rollers is driven by a drive. It is known to apply very large and heavy rollers in order to achieve the desired image quality, as it is known that the print medium may be displaced uncontrollably and/or irregularly when the rollers lack sufficient rigidity. This results however in large, heavy, and/or costly construction.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an alternative transport device for a large format inkjet printer, preferably one that allows for a cheaper, lighter, and/or smaller transport device.

In accordance with the present invention, a printer according to claim 1 and a method according to claim 7 are provided. The printer distinguishes itself in that at least one of said rollers is provided with drives at either end, which drives are configured for synchronously driving both ends of the at least one roller for transporting the print

11011807NL01 2 medium over the suction box . By simultaneously driving both ends of an individual roller, the torsion on and resulting twisting of the roller due to the torque on the roller is kept relatively small. The inventor found that as compared to driving only one end of the roller this twisting is reduced by a factor of 4, which is in part due to the interaction of the print medium with the underpressure applied by the suction box. In consequence, the belt holding the print medium is strained less and is deformed less, resulting in a more constant transportation of the print medium. This reduces irregular deformation in the belt in the lateral direction, which is perpendicular to the transport direction of the belt. In consequence, the strain and deformation of the belt are kept relatively small and the print medium can be transported accurately, even when relatively small roller diameters are applied. Thereby the object of the present invention has been achieved.

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

In an embodiment, both rollers of said pair of rollers are provided with drives at either end, which drives are configured for synchronously driving both ends of said rollers for stepwise transport of the print medium. By simultaneously driving all ends of the rollers defining the print surface, the deformation of the belt is reduced at both the downstream and upstream side of the belt. This results in a more accurate belt transport and more precise positioning of the print medium with respect to the printhead assembly.

In an embodiment, the transport device is configured for stepwise transport of the print medium, such that a swath of an image is printed on the print medium in between consecutive steps of the print medium. The print medium is transported in discrete steps, in between which steps the scanning printhead assembly translates across the print medium in a direction perpendicular to the transport direction of the belt. It will be appreciated that the present invention may also be applied in printers comprising a page-wide printhead array, which is stationary during printing. Also in such printers does the present invention allow for a reduction of the diameters of the rollers, reducing the costs of such a system.

In an embodiment, a length of said rollers is at least 1.6 meters, preferably at least 2.5 meters, and very preferably at least 3 meters. The rollers are relatively long, as a consequence of which twisting due to torque at the ends is relatively large. Such rollers are applied in large format graphic printers, for example for printing banners, panels,

11011807NL01 3 displays, or foils.

In an embodiment, the belt is air permeable and provided over a suction box in fluid connection with a suction source for applying an underpressure to the print medium.

The print medium is sucked against the belt via openings in the belt, though air may pass through the belt and into the suction box. The suction source may be a fan or pump. This ensures a secure holding of the print medium onto the belt, such that the print medium may be accurately transported by the belt.

In an embodiment, the printer comprises: - a sensor for determining the displacement of the belt and/or print medium with respect to the scanning printhead assembly and; - a controller configured to determine based upon data from said sensor a subsequent control pulse corresponding to a displacement step size and to apply said control pulse simultaneously to all drives.

In practice, the actual displacement of the print medium during a step may vary from the intended value. The controller is configured to compensate for such variations and seeks to maintain a constant (average) step size. When the controller determines from sensor data that a previous step exceeded the intended step size, the controller will correct the control signals for the drives to apply a smaller step (as compared to the previous step), or vice versa. Thereby, the swath width is kept constant, which improves the image quality.

In an embodiment, said pair of said rollers have a relatively small diameter, preferably no greater than 1/10" of a length of said rollers. The rollers are relatively thin or narrow, which allows for a compact, light, and/or low costs structure. Such rollers are more prone to twisting under torsion as compared to large diameter rollers, but the four drives are able to keep any twisting of the rollers sufficiently small.

The present invention further relates to a method for transporting a print medium along a printhead assembly comprising the steps of: - adhering the print medium by means of an underpressure against an endless belt supported on a pair of rollers defining a print surface facing the scanning printhead assembly; - controlling at least two drives each positioned at a different end of the at least one

11011807NL01 4 roller, such that each end of the at least one roller is driven synchronously with the others.

It was found that by simultaneously applying the driving torque to both ends of the roller, the twisting of the roller in its center is reduced by a factor of four. In consequence, the belt is deformed less as compared to driving the roller at a single end. The displacement of the print medium per step is more constant along its full width, resulting in a more accurate positioning and higher print quality.

In an embodiment, both rollers are driving synchronously at each end of either roller. By driving the four ends of the rollers simultaneously, the required torque is applied to the ends at the same time. Since the torque is applied symmetrically to each roller, the twisting is reduced, as compared to applying the total torque only on one end. Since both rollers are actuated synchronously, the torque in each roller is further reduced which minimizes belt deformation and reduces the risk of slippage between belt and rollers at high loads. This ensures an accurate displacement of the print medium.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

Fig. 1 is a schematic perspective view of a printing system according to the present invention in a first printing mode;

Fig. 2 is a schematic perspective view of a printing system in Fig. 1 in a second printing mode;

Fig. 3 is a schematic diagram of a control unit of a printer according to Fig. 1 or 2;

Fig. 4 is a schematic, top-down view of a transport device of a printer in Fig. 1 or 2;

Fig. 5 is a schematic graph illustrating the sensor data and control signals applied by the controller of the printer in Fig. 1 and 2; and

11011807NL01

Fig. 6 is a block diagram illustrating the steps of printing on the printer in Fig. 1 or 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference to the accompanying 5 drawings, wherein the same reference numerals have been used to identify the same or similar elements throughout the several views.

Printing system

Fig. 1 & 2 show a wide format inkjet printer 1. The wide-format printer 1 comprises an inkjet printing assembly 7 for printing on a print medium 15, 16. The print medium 15in Fig. 1 is a relatively rigid substrate, such as a panel. The print medium 15, 16 is supplied from a media input unit 14, which may be configured for storing a plurality of such print media 15, 16 and supplying these to the printer 1. The printer 1 comprises transport means for receiving and transporting the print medium 15, 16 along the inkjet printing assembly 7. In Fig. 1, the transport means comprise an endless transport belt 4 supported on a plurality of support rollers 3A, 3B, 3C. At least one of the support rollers 3A, 3B, 3C is provided with driving means for moving the belt 4. Additionally, one or more one of the support rollers 3A, 3B, 3C may be configured to be moved and/or tilted to adjust and control the lateral position of the belt 4. The inkjet printing assembly 7 may be provided with a sensor 8, such as a CCD camera, to determine the relative position of belt 4 and/or the print medium 15, 16. Data from said sensor 8 may be applied to control the position of the belt 4 and/or the print medium 15, 16. The belt 4 is further provided with through-holes and a suction box 5 in connection with a suction source (not shown), such that an underpressure may be applied to the print medium 15, 16 via the through-holes in the belt 4. The underpressure adheres the print medium 15, 16 flatly to the belt 4 and prevents displacement of the print medium 15, 16 with respect to the belt 4. Due to this holding the belt 4 is able to transport the print medium 15, 16. It will be appreciated that other suitable transport means, such as rollers, steppers, etc, may alternatively be applied. The print medium 15, 16 may be transported stepwise and/or in continuous movement.

The inkjet printing assembly 7 is configured to translate along a first guide beam 6 in a scanning direction. The scanning direction is perpendicular to the direction in which the print medium is transported by the belt 4. The inkjet printing assembly 7 holds a plurality of print heads (not shown), which are configured to jet a plurality of different marking

11011807NL01 6 materials (different colors of ink, primers, coatings, etc.) on the print medium 15, 16.

Each marking material for use in the printing assembly 7 is stored in one of a plurality of containers arranged in fluid connection with the respective print heads for supplying marking material to said print heads to print an image on the print medium 15, 16.

The ejection of the marking material from the print heads is performed in accordance with data provided in the respective print job. The timing by which the droplets of marking material are released from the print heads determines their position on the print medium 15, 16. The timing may be adjusted based on the position of the inkjet printing assembly 7 along the first guide beam 6. The above mentioned sensor 8 may therein be applied to determine the relative position and/or velocity of the inkjet printing assembly 7 with respect to the print medium 15, 16. Based upon data from the sensor 8, the release timing of the marking material may be adjusted.

Upon ejection of the marking material, some marking material may be spilled and stay on a nozzle surface of the print heads. The marking material present on the nozzle surface, may negatively influence the ejection of droplets and the placement of these droplets on the print medium 15, 16. Therefore, it may be advantageous to remove excess of marking material from the nozzle surface. The excess of marking material 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.

The marking materials may require treatment to properly fixate them on the print medium. Thereto, a fixation unit 10 is provided downstream of the inkjet printing assembly 7. The fixation unit 10 may emit heat and/or radiation to facilitate the marking material fixation process. In the example of Fig. 1, the fixation unit 10 is a radiation emitter, which emits light of certain frequencies, which interacts with the marking materials, for example UV light in case of UV-curable inks. The fixation unit 10 in Fig. 1 is translatable along a second guide beam 9. Other fixation units 10, such as page-wide curing or drying stations may also be applied. Further, the inkjet printing assembly 7 may be provided with a further fixation unit on the same carriage which holds the print heads. This further fixation unit can be used to (partially) cure and/or harden the marking materials, independent of or interaction with the fixation unit 10.

After printing, and optionally fixation, the print medium 15, 16 is transported to a

11011807NL01 7 receiving unit (not shown). The receiving unit may comprise a take-up roller for winding up the print medium 15, 16, a receiving tray for supporting sheets of print medium 15, 18, or a rigid media handler, similar to the media input unit 14. Optionally, the receiving unit may comprise processing means for processing the medium 8, 9 after printing, e.g. a post-treatment device such as a coater, a folder, a cutter, or a puncher.

The wide-format printer 1 furthermore comprises a user interface 11 for receiving print jobs and optionally for manipulating print jobs. The local user interface unit 11 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 11 is connected to a control unit 12 connected to the printer 1. The control unit 12, for example a computer, comprises a processor adapted to issue commands to the printer 1, for example for controlling the print process. The printer 1 may optionally be connected to a network.

The connection to the network can be via cable or wireless. The printer 1 may receive printing jobs via the network. Further, optionally, the control unit 12 of the printer 1 may be provided with an input port, such as a USB port, so printing jobs may be sent to the printer 1 via this input port.

Hybrid printing system

The printer 1 in Fig. 1 is a so-called hybrid printer, capable of handling both flexible media and rigid substrates. In Fig. 1, the printer 1 operates in a first print mode, wherein the printer 1 is configured for transporting rigid substrates, such as the print medium 15. Such rigid print media 15 may be panels for doors, walls, etc., corrugated media, plates formed of plastic or metal, etc. To handle these rigid print media 15 the printer 1 in Fig. 1 is configured with a substantially linear transport path: from the media input device 14, the print medium 15 moves forward along the inkjet printing assembly 7 at a at substantially constant height. The media input unit 14 and the receiving unit are positioned at the level of the medium support surface of the belt 4. In Fig. 2, a flexible web medium 16 is supplied to the printer 1, which web medium 16 may be composed of e.g. paper, label stock, coated paper, plastic or textile. The web medium 16 is supplied from the input roller 2A and extends across the belt 4 to the take-up roller 2B, where the web medium 16 is re-wound. The printer 1 is configured to swiftly and efficiently switch between print modes.

11011807NL01 8

Contrel

An embodiment of the control unit 12 is in more detail presented in Fig. 3. As shown in

Fig. 3, the control unit 12 comprises a Central Processing Unit (CPU) 31, a Graphical

Processor Unit (GPU) 32, a Random Access Memory (RAM) 33, a Read Only Memory (ROM) 34, a network unit 36, an interface unit 37, a hard disk (HD) 35 and an image processing unit 39 such as a Raster Image Processor (RIP). The aforementioned units 31 - 37 are interconnected through a bus system 38. However, the control unit 12 may also be a distributed control unit.

The CPU 31 controls the printing system 1 in accordance with control programs stored in the ROM 34 or on the HD 35 and the local user interface panel 5. The CPU 31 also controls the image processing unit 34 and the GPU 32. The ROM 34 stores programs and data such as boot program, set-up program, various set-up data or the like, which are to be read out and executed by the CPU 31. The hard disk 35 is an example of a non-volatile storage unit for storing and saving programs and data which make the CPU 31 execute a print process to be described later. The hard disk 35 also comprises an area for saving the data of externally submitted print jobs. The programs and data on the HD 35 are read out onto the RAM 33 by the CPU 31 as needed. The RAM 33 has an area for temporarily storing the programs and data read out from the ROM 34 and

HD 35 by the CPU 31, and a work area which is used by the CPU 31 to execute various processes. The interface unit 37 connects the control unit 12 to the client devices 21 - 24 and to the printing system 1. The network unit 36 connects the control unit 12 to the network N and is designed to provide communication with the workstations 22 - 24, and with other devices 21 reachable via the network N. The image processing unit 39 may be implemented as a software component running on an operation system of the control unit 12 or as a firmware program, for example embodied in a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC). The image processing unit 39 has functions for reading, interpreting and rasterizing the print job data. Said print job data contains image data to be printed (i.e. fonts and graphics that describe the content of the document to be printed, described in a Page Description Language or the like), image processing attributes and print settings.

Belt drive

Fig. 4 illustrates a top-down view of the transport device 40 of the scanning inkjet printer 1in Figs. 1 and 2. The print medium 15, 16 is adhered to the endless belt 4 by means of

11011807NL01 9 the underpressure applied through the air permeable belt 4 by means of the suction box 5. The portion of the belt 4 suspended between the drive rollers 3A and 3C defines the flat or planar print surface on which the print medium 15, 16 is supported during printing.

A drive 40A-40D is provided at each end of the drive rollers 3A, 3C. In consequence, the upstream and downstream drive rollers 3A, 3B between which the print surface extends are each provided with two drives 40A-40D, one at each at end of the respective roller 3A, 3C. It is noted that the drive rollers 3A, 3C are rigid rollers, which are preferably of a constant structure along their lengths (with the possible exception of the end regions).

Each of the drives 40A-40D is connected to the controller 12. The controller 12 is configured to drive all drives 40A-40D at the end of one at least one of the drive rollers 3A, 3C simultaneously. In the example described below, both drive rollers 3A, 3C will be driven synchronously at both their ends, though it is within the present invention to apply drive both ends of only one of the drive rollers 3A, 3C as well. The drive torque is thus provided at both ends of the respective drive roller 3A, 3C simultaneously. In consequence, the torsion on each drive roller 3A, 3C is relatively small, reducing the twisting of the drive rollers 3A, 3C. Excessive twisting results in an inhomogeneous displacement of the print medium, 15, 16, since the central portion of the belt 4 is displaced differently than at the lateral edges of the belt 4. Since the drive rollers 3A, 3C deform less during the drive action, the belt 4 is also deformed less. This results in a more accurate transportation of the print medium 15, 16. This allows for the use of drive rollers 3A, 3C with a relatively small diameter. This diameter may be smaller than 1/10" of the length of the rollers 3A, 3C, which length is generally be at least 2.5 meters to 3 meters.

Since simultaneous drive torque is applied to all ends of both driving rollers 3A, 3C, the deformation of the belt 4 is reduced even further. The actuation forces on the belt 4 at the upstream and downstream drive rollers 3A, 3C are similar in size and synchronous in timing. Distribution of the total required drive torque over both driving roller 3A, 3C further reduces the twist of the rollers compared to only one driven roller. This also reduces the deformation of the belt 4.

Fig. 5 illustrates the signals SD, SA, SB, SC, DS applied in the method schematically illustrated in Fig. 6. In step i, the print medium 15, 16 and/or the belt 4 are sensed for

11011807NL01 10 example by means of sensor 8 and/or an encoder provided on any of the rollers 3A-3C.

By sensing the print medium 15, 16 and/or the belt 4, the sensor 8 generates sensor data SD, which is transmitted to the controller 12. The transport device 40 transports the print medium 15, 16 stepwise, as indicated by the steps in the sensor data SD. In practice the steps may vary in size, which variations can be accurately determined using e.g. the sensor 8. In Fig. 5, the sensor data SD shows three steps, wherein the second (middle) step is greater than the first (left) and the last (right) step is smaller than the first and second.

In step ii, the controller 12 analyzes the sensor data SD to determine appropriate control signals for the drives 40A-40D. The controller 12 herein strives towards a constant (average) value of the displacement steps. Fig. 5 illustrates the different control signals

SA-SD. Since in this example the drives 40A-40D are identical the control signals SA-

SD are also identical. Each control signal SA-SD comprises three pulses, corresponding to the intended displacement after each of the sensed steps in the sensor data SD. The controller 12 in step iii transmits these signals SA-SD to the drives 40A-40D. In step iv, the drives 40A-40D are controlled to simultaneously apply the corresponding torque to the ends of the drive rollers 3A, 3C. The method is then repeated from step i until completion of the print job.

In the example in Fig. 5, the initial sensed displacement in the sensor data SD corresponds to the intended step size. The controller 12 then applies the first pulses as shown in the signal data SD and the belt 4 moves the print medium 15, 16 by a step.

These control pulses in Fig. 5 are the same in size and shape for each step, and configured to synchronously apply the respective torque to the rollers 3A, 3C. After completing this displacement step, the actual displacement is sensed again, resulting in the middle displacement step in the sensor data SD. This middle displacement step in the sensor data SD is larger than the previous step. The controller 12 compensates for this increase in step size by adjusting the next control pulses. In Fig. 5, these are the middle control pulses (which are reduced in size as compared to the first pulses) in the control signals SA-SD. Based on that the drive rollers 3A, 3C are actuated another step.

This final step is also sensed corresponding to the last step in the sensor data SD. The last step is determined to be smaller than the other steps. Consequently, the controller 12 adjusts the next control pulses in the control signals 40A-40D to be greater than the previous pulses in order to maintain an on average constant step size.

11011807NL01 11

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 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.

11011807NL01 12

EMBODIMENTS

1. A printer (1) comprising a transport device (40) with an endless transport belt (4) supported on a plurality of rollers (3A, 3B, 3C) wherein the belt (4) is air permeable and provided over a suction box (5) in fluid connection with a suction source for applying an underpressure to the print medium (15, 16), such that a pair of the plurality of rollers (3A, 3C) defines a print surface on the belt (4) facing a printhead assembly (7), characterized in that at least one of said pair of said rollers (3A, 3C) is provided with drives (40A-40D) at either end, which drives (40A-40D) are configured for synchronously driving both ends of said roller (3A, 3C) for transporting the print medium (15, 18) over the suction box (5). 2. The printer (1) according to claim 1, wherein both rollers (3A, 3C) of said pairs of rollers (3A, 3C) are provided with drives (40A-40D) at either end, which drives (40A- 40D) are configured for synchronously driving both ends of said rollers (3A, 3C) for stepwise transport of the print medium (15, 16). 3. The printer (1) according to claim 1 or 2, wherein the transport device (40) is configured for stepwise transport of the print medium (15, 16), such that a swath of an image is printed on the print medium (15, 16) in between consecutive steps of the print medium (15, 16). 4. The printer (1) according to any of the previous claims, wherein a length of said rollers (3A, 3B, 3C) is at least 2 meters, preferably at least 2.5 meters, and very preferably at least 3 meters. 5. The printer (1) according to any of the previous claims, further comprising: - a sensor (8) for determining the displacement of the belt (4) and/or print medium (15, 16) with respect to the printhead assembly (7) and; - a controller (12) configured to determine based upon data (SD) from said sensor (8) a subsequent control pulse (SA, SB, SC, SD) corresponding to a displacement step size and to apply said control pulse (SA, SB, SC, SD) simultaneously to all drives (40A- 40D). 6. The printer (1) according to any of the previous claims, wherein said pair of said rollers (3A, 3C) have a relatively small diameter, preferably no greater than 1/10" of a

11011807NL01 13 length of said rollers (3A, 3C). 7. A method for transporting a print medium (15, 16) along a printhead assembly (7) comprising the steps of:

- adhering the print medium (15, 16) by means of an underpressure against an endless belt (4) supported on a pair of rollers (3A, 3C) defining a print surface facing the scanning printhead assembly (7);

- controlling at least two drives (40A-40D) each positioned at a different end of at least one of the rollers (3A, 3C) of the pair of rollers (3A, 3C), such that each end of said at least one roller (3A, 3C) is driven synchronously with the other end.

Claims

11011807EN01 14 CONCLUSIONS

A printer (1) comprising a transport device (40) with an endless conveyor belt (4), the belt (4) being air-permeable and provided over a suction box (5) in fluid communication with a suction source for applying a underpressure on the print medium (15, 186), which conveyor belt (4) is provided on a plurality of rollers (3A, 3B, 3C), so that a pair of the plurality of rollers (3A, 3C) determines a printing surface on the belt (4) , facing a print head assembly (7), characterized in that at least one pair of rollers (3A, 3C) of the pair of rollers (3A, 3C) is provided with drives (40A-40D) at each end, which drives (40A-40D) are designed to synchronously drive both ends of the relevant roller (3A, 3C) for stepwise transport of a print medium (15, 16) over the suction box

(5).

The printer (1) according to claim 1, wherein both rollers (3A, 3C) of the pairs of rollers (3A, 3C) are provided with drives (40A-40D) at each end, which drives (40A-40D) are arranged for synchronously driving both ends of the relevant rollers (3A, 3C) for stepwise transport of the print medium (15, 16).

The printer (1) according to claim 1 or 2, wherein the transport device (40) is adapted for stepwise transport of the print medium (15, 16), so that a line of an image is printed on the print medium (15, 16) between successive steps of the print medium (15, 16} in.

The printer (1) according to any of the preceding claims, wherein a length of the rollers (3A, 3B, 3C) is at least 1.6 meters, preferably at least 2.5 meters, and particularly preferably at least 3 meters .

The printer (1) according to any one of the preceding claims, further comprising: - a sensor (8) for determining the displacement of the belt (4) and/or the print medium (15, 16) with respect to the print head assembly (7) and; - a control unit (12) designed to determine a subsequent control pulse (SA, SB, SC, SD) from data (SD) from the sensor (8), which corresponds to a displacement step size and to determine the control pulse (SA, SB, SC, SD) can be applied simultaneously to all drives (40A-40D).

11011807NL01 15

The printer (1) according to any one of the preceding claims, wherein the pair of rollers (3A, 3C) has a relatively small diameter, not greater than 1/10" of the length of the rollers (3A, 3C).

7. A method for transporting a print medium (15, 16) along a print head assembly (7) comprising the steps of: - sucking the print medium (15, 18) against an endless belt (4) provided on an underpressure a pair of rollers (3A, 3C), defining a printing plane facing the printhead assembly (7); - controlling at least two drives (40A-40D), each provided at one end of at least one of the rollers (3A, 3C), so that each end of the at least one roller (3A, 3C) is synchronized with the other end is driven.