METHOD FOR LOADING A WEB; APPARATUS FOR HANDLING A WEB

Abstract

In wide format web printing the loading of a new web medium is a cumbersome process, requiring the operator to raise a very wide flexible web from the supply roll up to the print surface. The present invention provides a simple apparatus to aid in the manual loading process. The web transport assembly of the apparatus comprises a supply unit arranged for supplying the web from a media roll to a transport path and a pick-up device comprising a pick-up surface and a holding mechanism configured for releasably holding a leading edge section of the web onto the pick-up surface, wherein the pick-up device is moveable between a first position near the supply unit for attaching the leading edge section and a second position near the print surface. The leading edge section is moved upwards towards the print surface while held by the holding mechanism.

Claims

1. An apparatus for handling a web comprising a processing unit for processing the web and a web transport assembly for transporting the web through a transport path along the processing unit, the web transport assembly comprising: a supply unit arranged for mounting a media roll and for supplying the web from the media roll to the transport path; a pick-up device comprising a pick-up surface and a holding mechanism configured for releasably holding a leading edge section of the web onto the pick-up surface, wherein the pick-up device is moveable between a first position near the supply unit for attaching the leading edge section to the pick-up device and a second position positioned at an upstream end of a web supporting surface below the processing unit.

2. The apparatus according to claim 1, wherein the pick-up surface is provided at an end of a pivotable lever.

3. The apparatus according to claim 2, wherein the lever is pivotable around a shaft extending in the lateral direction of the transport path.

4. The apparatus according to claim 2, wherein the lever when in use is positioned above the transport path.

5. The apparatus according to claim 1, wherein the holding mechanism comprises a clamp for clamping the leading edge section.

6. The apparatus according to claim 1, wherein the processing unit comprises a support plate and wherein the pick-up device is positioned upstream of the support plate.

7. The apparatus according to claim 1, further comprising: an attraction mechanism configured for attracting a contact side of the web onto the pick-up surface; and a control unit configured for, during media loading, controlling the attraction mechanism to hold the leading end of the web onto the pick-up surface, wherein the control unit is configured for deactivating the attraction mechanism to release the leading end of the web from the pick-up surface in response to an operator input.

8. The apparatus according to claim 7, wherein the control unit comprises a user interface for inputting the operator input for deactivating the attraction mechanism.

9. The apparatus according to claim 1, wherein the pick-up surface is positioned at a height level higher than the supply unit when viewed in the direction of gravity.

10. The apparatus according to claim 1, wherein the web transport assembly further comprises a transport device arranged for moving the web through the transport path, and a control unit configured to activate the transport device to drive the web after releasing the leading end of the web from the pick-up surface.

11. The apparatus according to claim 7, wherein the attraction mechanism comprises a suction source for providing a suction pressure and a plurality of suction holes distributed over the pick-up surface and operatively connected to the suction source for providing the suction pressure to the contact side of the web to hold the leading end of the web.

12. The apparatus according to claim 1, wherein the pick-up surface is arranged at a height level being substantially equal to a height level of the processing unit relative to a height direction.

13. The apparatus according to claim 1, wherein the web transport assembly further comprises a foot pedal operable by the operator and operatively connected to the control unit for activating the supply unit to unwind the web from the media roll.

14. A method for loading a web into a transport path of an apparatus according to claim 1, the apparatus comprising a processing unit for processing the web and a web transport assembly being configured for transporting the web from a supply unit through the transport path along the processing unit, the web transport assembly comprising a pick-up surface arranged facing the transport path and an holding mechanism configured for releasably holding a leading edge section of the web onto the pick-up surface; the method comprising the steps of: i. mounting a media roll into the supply unit; ii. manually loading by an operator a first part of the leading end of the web onto the pick-up surface, the holding mechanism holding the first part of the leading end of the web on the pick-up surface; iii. controlling the holding mechanism to release the leading end of the web from the pick-up surface; iv. threading the leading end of the web from the pick-up surface through the transport path and beyond the processing unit.

15. The method according to claim 14, wherein step ii) comprises activating the supply unit to unwind the leading end of the web from the media roll.

16. The method according to claim 14, wherein the holding mechanism comprises an attraction mechanism with a plurality of suction holes distributed over the pick-up surface and the holding step of step ii) comprises providing a suction pressure through the plurality of suction holes to a contact side of the web.

17. The method according to claim 15, wherein the method further comprises the step of: v. manually loading by an operator a second part of the leading end of the web onto the pick-up surface, the attraction mechanism holding the second part of the leading end of the web on the pick-up surface by attracting the contact side of the web.

18. The method according to claim 17, wherein step ii) comprises allowing the second part of the leading end of the web to fold away from the pick-up surface before step iv).

19. The method according to claim 14, wherein step iv) comprises sliding over an outer side of the web along the pick-up surface starting from the first part of the leading end of the web to unfold the second part of the leading end of the web onto the pick-up surface.

20. The method according to claim 17, wherein step v) comprises activating the supply unit to unwind the web from the media roll.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0082] 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:

[0083] FIG. 1A shows an image forming apparatus, wherein printing is achieved using a wide format inkjet printer.

[0084] FIG. 1B shows an ink jet printing assembly.

[0085] FIGS. 2A-2E show schematically an embodiment of a web transport assembly for transporting a web along a processing unit and a method for loading the web according to the present invention.

[0086] FIGS. 3A and 3B show schematically another embodiment of a web transport assembly for transporting a web along a processing unit according to the present invention.

[0087] FIGS. 4A-4B show schematically another embodiment of a web transport assembly for transporting a web along a processing unit according to the present invention.

[0088] FIG. 5 shows a modified friction-based tensioning device of the embodiment shown in FIGS. 4A-4B.

[0089] FIG. 6 shows a plane view of another modified friction-based tensioning device of the embodiment shown in FIGS. 4A-4B.

[0090] FIG. 7 show schematically another embodiment of a web transport assembly for transporting a web along a processing unit according to the present invention.

[0091] FIG. 8 shows a plane view of a modified friction-based tensioning device of the embodiment shown in FIG. 7.

[0092] FIGS. 9A-B show schematically another embodiment of an image forming apparatus according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0093] 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. 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.

[0094] 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.

[0095] 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.

[0096] 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 controller of the printer may be provided with a USB port, so printing jobs may be sent to the printer via this USB port.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] FIG. 2A shows schematically an embodiment of a web transport assembly for transporting a web along a processing unit according to the present invention. The web transport assembly 80 may be used in a printing apparatus 1 shown in FIGS. 1A-1B. FIG. 2A shows a side view of the web transport assembly 80. FIG. 2B shows a plane view on the web transport assembly 80. The web transport assembly 80 comprises a transport device 20, which is a nip comprising a driven roller 22 and a pressure roller 24, and a pick-up device 30. The transport device 20 is arranged downstream of a processing unit 10, such as a print head assembly, and transports a web W along a transport path in a transport direction T. The web is supplied from a roll 3, which is supported by a spindle 26. The web is moved by the transport nip 20 along the transport path from the supply roll 3 along the pick-up device 30, the processing unit 10 towards a receiving roll 50. The receiving roll 50 is supported on a spindle 52. The print head assembly 10 faces a support plate 11, which is arranged to attract the web to the support plate by applying a suction force to a contact side of the web W. The web transport assembly further comprises a control unit 100, which is operatively connected to the print head assembly 10 and to the transport device 20.

[0103] The pick-up device 30 is arranged upstream of the support plate 10 and comprises a turn element 31 comprising a pick-up surface 32 for guiding a contact side of the web W while bending the web towards a path over the support plate 11 along the print head assembly 10. As shown in FIGS. 2B-2E, the pick-up device 30 further comprises an array of suction holes 34 distributed over the pick-up surface 32 and arranged along a transverse direction C across to the transport path, which extends in the transport direction T. The pick-up device 30 is operatively coupled to a suction source 40, such as a suction pump, via a tube 42, which communicates a suction pressure to the array of suction holes 34 via a manifold, which is enclosed in the turn element 31. The control unit 100 is operatively connected to the suction source 40 for controlling a suction pressure provided to the contact side of the web via the suction holes 34.

[0104] The pick-up surface 32 exerts a friction force onto the contact side of the web W, wherein the friction force is provided in response to the suction force provided to the contact side of the web via the suction holes 34.

[0105] FIGS. 2B and 2C show an embodiment of a method for loading the web W into the transport path of the web transport assembly 80. FIGS. 2B and 2C are both a side view of the web transport assembly 80 seen in a plane of the transport path arranged between the supply roll 3 and the pick-up surface 32. In this embodiment the transport path extends along the gravity direction g and across to the transport path in the transverse direction C. In a first step of the method, the leading end of the web W.sub.L is unwind from the media roll 3 supported by the spindle 26. The leading end of the web W.sub.L may be unwound manually by an operator from the media roll 3, e.g. by pulling the leading end of the web W.sub.L, or may be unwound from the media roll 3 by driving the spindle 26. In an example, the spindle 26 may be activated, such as by operating a foot pedal operatively connected to the control unit 100, to unwind the web W from the supply roll 3.

[0106] In the first step, as shown in FIG. 2A, a first part of the leading end W.sub.1 is manually loaded by the operator by raising the first part of the leading end W.sub.1 opposite to the gravity direction g onto the pick-up surface 32, as indicated by arrow M.sub.1, wherein the suction holes 34 provide a suction force to the contact side of the web W to hold the first part of the leading end W.sub.1 on the pick-up surface 32 by attracting the contact side of the web W. After the first step, the first part of the leading end W.sub.1 is held fixed at the pick-up surface 32 by the suction force provided at the pick-up surface 32. At the same time, a second part of the web W.sub.2 is allowed to hang in the gravity direction g along the transport path, while being folded away from the pick-up surface 34, as shown in FIG. 2A.

[0107] The suction force is provided by a suction pressure generated by the suction source 40. Said suction force may be activated before the first loading step. Alternatively, the suction force may be activated in response to the manually loading step. In an example, a detector is provided for detecting a presence of the web W at the pick-up surface 32 during the media loading. The detector is connected to control unit 100 to provide a signal to the control unit 100 in response to the detection of the web W at the pick-up surface 32. The control unit 100 controls the suction source 40 to increase the suction pressure at the suction holes 34 to hold the first part of the leading end W.sub.1 on the pick-up surface 32.

[0108] In a second step, as shown in FIG. 2B, a second part of the leading end W.sub.2 is manually loaded by the operator by moving the second part of the leading end W.sub.2 opposite to the gravity direction g onto the pick-up surface 32, as indicated by arrow M.sub.2, wherein the suction holes 34 provide a suction force to the contact side of the web W to hold the second part of the leading end W.sub.2 on the pick-up surface 32 by attracting the contact side of the web W, while holding the first part of the leading end W.sub.1 on the pick-up surface 32.

[0109] In particular, the second part of the leading end W.sub.2 is moved towards the pick-up surface 32 by sliding over an outer side of the web along the pick-up surface 32 starting from the first part of the leading end W.sub.1 to unfold the second part of the leading end W.sub.2 onto the pick-up surface 32, as indicated by arrow S in FIG. 2C. After the second step both the first part of the leading end W.sub.1 and the second part of the leading end W.sub.2 are held onto the pick-up surface. The operator is now free to move to any other position to further proceed the manual loading of the web W, such as shown in FIG. 2E.

[0110] FIG. 2D shows another embodiment of a method for loading the web W into the transport path of the web transport assembly 80. FIG. 2D is a side view of the web transport assembly 80 seen in a plane of the transport path arranged between the supply roll 3 and the pick-up surface 32. In this embodiment the transport path extends along the gravity direction g and across to the transport path in the transverse direction C. In a first step of the method, the leading end of the web W.sub.L is unwind from the media roll 3 supported by the spindle 26. The leading end of the web W.sub.L may be unwound manually by an operator from the media roll 3, e.g. by pulling the leading end of the web W.sub.L, or may be unwound from the media roll 3 by driving the spindle 26.

[0111] In the first step, as shown in FIG. 2E, a the leading end of the web W.sub.L is manually loaded by the operator by raising the leading end opposite to the gravity direction g onto the pick-up surface 32, as indicated by arrow M.sub.3, wherein the suction holes 34 provide a suction force to the contact side of the web W to hold the leading end W.sub.L on the pick-up surface 32 by attracting the contact side of the web W. After the first step, the whole leading end W.sub.L is held fixed at the pick-up surface 32 by the suction force provided at the pick-up surface 32. In an example of this embodiment, a width of the web W across to the transport path along the transverse direction C is not wider than a range wherein the operator can reach by using his hands. After the first step, the operator is free to move to any other position to further proceed the manual loading of the web W, such as shown in FIG. 2E.

[0112] FIG. 2E shows a further step of the embodiments shown in FIGS. 2B-2C and FIG. 2D. FIG. 2E is a plane view on the transport path over the support plate 11. In the next step, the leading end of the web W.sub.L is threaded by the operator from the pick-up surface 32 through the transport path over the support plate 11 along the processing unit 10 towards the driven roller 22 of the transport device. During the threading step the processing unit 10 may be moved away from the support plate 11, such as sideways in the transverse direction C. At the start of the threading step, the suction force at the suction holes 34 is deactivated, such as removed or at least reduced, to release the leading end of the web W.sub.L from the pick-up surface 32. In this way, the threading of the leading end of the web through the transport path beyond the pick-up surface is supported. In an example, the operator may deactivate the attraction mechanism, such as by providing an operator input to a control unit for controlling the attraction mechanism. Alternatively, the attraction mechanism may be deactivated automatically by a control unit, such as in response to a predetermined holding time.

[0113] Furthermore, during the threading step, the spindle 26 may be activated, such as by operating a foot pedal operatively connected to the control unit 100, to unwind the web W from the supply roll 3.

[0114] In a modified embodiment of the embodiment of the web transport assembly shown in FIGS. 2A-2E, the pick-up device 30 is a friction-based tensioning device 30, which is configured for further controlling a tension of the web W along the transport path between the guiding surface 32 of the friction-based tensioning device 30 and the transport nip 20 during a normal transport operation of the web through the transport path after the media loading steps shown in FIGS. 2B-2E.

[0115] In transport operation, the transport nip 20 transports the web W along the transport path in the transport direction T, such as by intermittently moving the web W in the transport direction T. As the transport nip 20 drives the web W in the transport direction T, the friction-based tensioning device 30 controls the tension of the web W in the transport direction T by controllably restraining the web in the transport direction T.

[0116] FIGS. 3A and 3B show schematically another embodiment of a web transport assembly for transporting a web along a processing unit according to the present invention. The web transport assembly 180 may be used in a printing apparatus 1 shown in FIGS. 1A-1B.

[0117] FIG. 3A shows an enlarged side view of the web transport assembly 180. FIG. 3B shows a plane view on the web transport assembly 180. The web transport assembly 180 comprises a transport roller 22, a friction-based tensioning device 130 and a control unit 100. The transport roller 22 is a driven roller, which is controlled by the control unit 100, for transporting the web w along a transport path in a transport direction T along a processing unit 10, which faces a support plate 11.

[0118] The friction-based tensioning device 130 comprises a turn bar 131, which is stationary arranged relative to the transport path and comprises a guiding surface 132 for guiding a contact side of the web W while bending the web towards a path over the support plate 11 along the processing unit 10. The guiding surface 132 comprises a plurality of suction holes 134a-134b arranged along a transverse direction C across to the transport path, which extends in the transport direction T.

[0119] The plurality of suction holes 134a-134b comprises two segments 134a-134b arranged adjacent one another along the transverse direction C. Each segment 134a-134b of the plurality of suction holes is connected to a manifold 135a-135b, respectively, which is provided inside the turn bar 131 and arranged adjacent one another along the transverse direction C.

[0120] Each manifold 135a-135b is of the friction-based tensioning device 130 is operatively coupled to a suction source 40, such as a suction pump, via a tube 42a-42b, respectively, which communicates a suction pressure to the segment of suction holes 134a-134b via the manifold 135a-135b, which is enclosed in the turn element 131.

[0121] The control unit 100 is operatively connected to the suction source 40 for controlling a suction pressure provided to the contact side of the web W via the segments of suction holes 134a-134b at each segment independently one another.

[0122] The guiding surface 132 exerts a friction force onto the contact side of the web W, wherein the friction force is provided in response to the suction force provided to the contact side of the web at each of the segments via the suction holes 134a-134b. As the suction force is controlled of each segments of the suction holes 134a-134b independently one another, the tension of the web W can be adjusted for each segment along the transverse direction C.

[0123] In an example, any differences in tension of the web W along the transverse direction C, such as due to variations of the web W and/or the guiding surface along the transverse direction C, can be minimized by applying different suction forces to the segments of the suction holes 134a-134d.

[0124] Alternatively or additionally, a difference in tension of the web W along the transverse direction C may be induced by applying different suction forces to the segments of the suction holes 134a-134d in order to steer the web W with respect to the transport path. In an example, suction force by the left manifold segment 135a may be increased relative to the right manifold segment 135b. As a result, the friction induces on the web W by the guiding surface 132 at the segment 135a is higher than the friction induces on the web W by the guiding surface 132 at the segment 135b. In this way, the tension of the web W at the left side is higher than the tension of the web W at the right side, relative to the transport direction T, thereby rotating the web C counter-clockwise when looking from above in the plane view of FIG. 3B.

[0125] In yet another use of the web transport assembly 180 (not shown), a first web and a second web may be transported alongside one another along the transport path. The first web may be arranged at the left side of the transport path in contact with the guiding surface 132 at the segment of the suction holes 134a. The second web may be arranged at the right side of the transport path in contact with the guiding surface 132 at the segment of the suction holes 134b. The tension of the first web may be controlled by the segment of the suction holes 134a of the friction-based tensioning device 130, while the tension of the second web may be controlled by the segment of the suction holes 134b of the friction-based tensioning device 130. In this way, the friction-based tensioning device 130 supports a tandem processing of the first web and second web alongside one another while controlling a tension of each web independently one another.

[0126] FIGS. 4A-4B show schematically another embodiment of a web transport assembly for transporting a web along a processing unit according to the present invention. The web transport assembly 280 may be used in a printing apparatus 1 shown in FIGS. 1A-1B.

[0127] FIG. 4A shows an enlarged side view of the web transport assembly 280. FIG. 4B shows a plane view on the web transport assembly 280. The web transport assembly 280 comprises a transport roller 22, a friction-based tensioning device 230 and a control unit 100. The transport roller 22 is a driven roller, which is controlled by the control unit 100, for transporting the web w along a transport path in a transport direction T along a processing unit 10, which faces a support plate 11.

[0128] The friction-based tensioning device 230 is a rotatable lever assembly, which comprises a shaft 231, a guiding plate 232, a lever element 236 and a spring mechanism 238 (shown in FIG. 4B). The shaft 231 coincides with a rotation axis R of the rotatable lever assembly 230. The rotation axis R is arranged extending parallel to the transverse direction C across to the transport path. The guiding plate 232 comprises a guiding surface 233 for guiding a contact side of the web W. The lever element 236 connects the guiding plate 232 to the shaft 231. As such, the guide plate 232 is rotatably arranged around the rotation axis R of the rotatable lever assembly 230. The guiding plate 232 is rotatable around the rotation axis between a first rotation position (solid line) and a second rotation position (dashed line).

[0129] The spring mechanism 238 is coupled to the lever assembly 230 via the shaft 231 and exerts a torque force onto the guiding plate 232 via the lever element 236. The torque force depends on the rotation angle of the lever element 236 around the rotation axis. Furthermore, the torque force depends on a length of the lever element 236 between the shaft 231 and the guiding plate 232. The torque force is directed in a direction as indicated by arrow S such to restrain a rotation of the guiding plate 232.

[0130] The guiding surface 233 is arranged for guiding a contact side of the web W while bending the web towards a path over the support plate 11 along the processing unit 10. The guiding surface 233 comprises an array of suction holes 234 arranged along a transverse direction C across to the transport path, which extends in the transport direction T. Alternatively, the guiding surface 233 may comprise a plurality of arrays of suction holes 234 (not shown), each array being arranged along a transverse direction C across to the transport path.

[0131] The friction-based tensioning device 230 is operatively coupled to a suction source 40, such as a suction pump, via a tube 42, which communicates a suction pressure to the array of suction holes 234 via a manifold, which is enclosed in the guiding plate 232. The control unit 100 is operatively connected to the suction source 40 for controlling a suction pressure provided to the contact side of the web via the suction holes 234. The web W is attracted to the guiding surface 233 of the guiding plate 232 by a suction force provided to the contact side of the web. In case the web W is moved in the transport direction T by the transport roller 22, the guiding plate 232 of the lever assembly 230 moves in an arched way long the transport path by rotation about the rotation axis as schematically indicated by arrow L in FIG. 4, such as from the first rotation position (solid line) to the second rotation position (dashed line). As a result, the torque force provided by the spring mechanism 238 increases, thereby increasing the tension of the web W in the transport direction T.

[0132] At the rotation position of the guiding plate 232, where the tension of the web W reaches a level equal to the friction force provided at the guiding surface 233 to the contact side of the web W, the web W starts sliding along the guiding plate 232 in the transport direction. As a result, the tension of the web is controlled to be constant, while the guiding plate 232 is held substantially stationary with respect to the transport path, thus at a constant rotation angle about the rotation axis. At this rotation angle the torque force at the guiding surface 233 of the guiding plate 232 is equal to and in opposite direction to the friction force applied by the guiding surface 233 to the web W.

[0133] The tension of the web W can easily be adjusted by adjusting the suction force provided to the web W at the guiding surface 233. When the suction force is adjusted, such as decreased, the friction force applied by the guiding surface 233 to the web W decreases. As a result, the spring element 238 will rotate the guiding plate 232 counter-clock wise (as shown in FIG. 4A). Thereby, the torque force provided by the spring mechanism 238 will decrease accordingly. The guiding plate 232 and the lever element 236 will obtain another rotation angle about the rotation axis, wherein a lower torque force balances the lower friction force at the guiding surface 233. As such, a rotation angle of the lever element 236 provides a measure of the torque force of the spring mechanism 238 and, when the web is engaged by the guiding surface 233, of the tension of the web W in the transport direction T.

[0134] FIG. 5 shows a modified friction-based tensioning device of the embodiment shown in FIGS. 4A-4B. FIG. 5 shows an enlarged side view of the web transport assembly 380. The modified friction-based tensioning device 330 comprises the lever assembly shown in FIGS. 4A-4B and additionally comprises a rotation angle measuring device 350. The rotation angle measuring device 350 comprises a rotation scale 352 mounted to the lever assembly 330. The rotation scale 352 comprises a plurality of marks for indicating a rotation angle of the lever element 236 including the guiding plate 232 about the rotation axis R which coincides with the shaft 231. The rotation scale 352 is configured to be readable by an operator. The rotation angle of the lever element 236 about the rotation axis R is a measure of the tension of the web w in the transport direction T.

[0135] In an alternative example, the lever assembly 330 may be provided with a rotatable encoder and a sensor (not shown). The rotatable encoder is mounted on the shaft 231 and comprises a plurality of marks for indicating a rotation angle of the lever element 236 including the guiding plate 232 about the rotation axis R which coincides with the shaft 231. The sensor is arranged for detecting the marks on the rotatable encoder and to send a sensor signal to the control unit 100 for indicating the rotation angle of the lever element 236 including the guiding plate 232 about the rotation axis R. In this way, the control unit 100 may determine the tension of the web W based on the detected rotation angle of the lever element 236.

[0136] FIG. 6 shows a plane view of another modified friction-based tensioning device of the embodiment shown in FIGS. 4A-4B. The modified friction-based tensioning device 430 comprises the rotatable lever assembly 330 shown in FIGS. 4A-4B, wherein the lever assembly 430 comprises a shaft 431, a first lever segment 430a and a second lever segment 430b. The first lever segment 430a and a second lever segment 430b are arranged alongside one another in the transverse direction C across to the transport path. Each of the first lever segment 430a and a second lever segment 430b is rotatable around the shaft 431 independently one another, as schematically indicated by arrows L.sub.1 and L.sub.2 in FIG. 6.

[0137] Each lever segment 430a-403b comprises a lever element (as shown in FIG. 4A) and a guiding plate 432a-432b. The lever element connects the guiding plate 432a-432b to the shaft 231. Each guiding plate 432a-432b comprises a guiding surface 433a-433b for guiding the web W and a plurality of suction holes 434a-434b for providing a suction force to a contact side of the web W to control a friction force of the guiding surface 433a-433b, respectively, to the web W. The spring mechanism 438 controls a torque force provided to each of the lever segments 430a-403b around the rotation axis R, which coincides with the shaft 431, independently one another by way of a spring element 438a-438b, respectively, which is connected to one of the lever elements (shown in FIG. 4A), respectively.

[0138] Each guide plate 432a-432b is operatively coupled to a suction source 40, such as a suction pump, via a tube 42a-42b, respectively, which communicates a suction pressure to the segment of suction holes 434a-434b, respectively. The control unit 100 is operatively connected to the suction source 40 for controlling a suction pressure provided to the contact side of the web W via the suction holes 434a-434b at each lever segment independently one another.

[0139] The guiding surface 433a-433b of each lever segment exerts a friction force onto the contact side of the web W, wherein the friction force is provided in response to the suction force provided to the contact side of the web at each of the lever segments via the suction holes 434a-434b.

[0140] As the suction force is controlled of the suction holes 434a-434b of each lever segment 430a-430b independently one another, the tension of the web W can be adjusted for each lever segment 430a-430b along the transverse direction C.

[0141] In this way, the tension of the web W in the transport direction T may be varied along the transverse direction C by the spring mechanism 438.

[0142] FIG. 7 show schematically another embodiment of a web transport assembly for transporting a web along a processing unit according to the present invention. The web transport assembly 580 may be used in a printing apparatus 1 shown in FIGS. 1A-1B.

[0143] FIG. 7 shows an enlarged side view of the web transport assembly 580. FIG. 4B shows a plane view on the web transport assembly 580. The web transport assembly 580 comprises a transport roller 22, a friction-based tensioning device 530 and a control unit 100. The transport roller 22 is a driven roller, which is controlled by the control unit 100, for transporting the web W along a transport path in a transport direction T along a processing unit 10, which faces a support plate 11.

[0144] The friction-based tensioning device 530 is a rotatable roller 532 comprising a guiding surface 533 at its circumference. The roller 532 is mounted on a shaft 531, which coincides with the rotation axis of the roller 532. The roller 532 further comprises suction holes 534 distributed over the guiding surface 533 for providing a suction force to a contact side of the web W, while the guiding surface 533 of the roller 530 is in rolling contact to the contact side of the web W. For this purpose, the suction holes 534 are distributed over the guiding surface 533 along the circumference direction of the roller 530.

[0145] The suction holes 533 are connected to a suction source 40 via a tube 42. The suction source 40 provides a suction pressure to the suction holes 534 for attracting the web onto the guiding surface 533. The control unit 100 is operatively connected to the suction source 40 for controlling a suction pressure provided to the contact side of the web via the suction holes 534.

[0146] The friction-based tensioning device 530 further comprises a friction mechanism 536 coupled to the shaft 531 of the rotatable roller 532. The friction mechanism 536 is a journal bearing, which is configured for controlling a friction force acting on the shaft 531 for restraining a rotation of the roller 532 around its rotation axis. The control unit 100 is operatively connected to the friction mechanism 536 for controlling the friction force acting on the shaft 531.

[0147] The friction force provided to the contact side of the web W via the guiding surface 533 is selected higher than the friction force provided by the friction mechanism 536 onto the shaft 531 of the roller 532. As such, the web pulls the roller 532, thereby driving a rotation of the roller 532 around its rotating axis, when the web W is moved in the transport direction T along the transport path by the transport roller 22.

[0148] In this way, the friction mechanism 536 determines the tension of the web W, when the roller 532 is held in rolling contact to the contact side of the web W.

[0149] FIG. 8 shows a plane view of a modified friction-based tensioning device of the embodiment shown in FIG. 7. In the modified friction-based tensioning device 630, the rotatable roller 630 comprises a first roller segment 632a and a second roller segment 632b. The first roller segment 632a and a second roller segment 632b are arranged alongside one another along a transverse direction C across to the transport path. The first roller segment 632a and a second roller segment 632b are rotatably mounted on a first shaft 631a and a second shaft 631b independently one another. The first shaft 631a and second shaft 631b are both arranged coinciding with a mutual rotation axis R. Each of the roller segments 632a-632b has a guiding surface 633a-633b arranged at its circumference and comprises suction holes 634a-634b distributed over the guiding surface 633a-633b over the whole circumference of the roller segments 632a-632b, respectively, for providing a suction force to a contact side of the web W. The suction holes 634a-634b are connected to a suction source 40 via a tube 42a-42b, respectively. The suction source 40 provides a suction pressure to the suction holes 634a-634b for attracting the web onto the guiding surface 633a-633b. The control unit 100 is operatively connected to the suction source 40 for controlling a suction pressure provided to the contact side of the web via the suction holes 634a-634b of the first roller segment 632a and a second roller segment 632b independently one another.

[0150] The friction-based tensioning device 630 comprises a first journal bearing 636a and a second journal bearing 636b. The first journal bearing 636a is coupled to the first shaft 631a for control a friction force acting on the first shaft 631a for restraining a rotation of the first roller segment 632a. The second journal bearing 636b is coupled to the second shaft 631b for control a friction force acting on the second shaft 631b for restraining a rotation of the second roller segment 632b.

[0151] The control unit 100 is operatively connected to the first journal bearing 636a and the second journal bearing 636b for adjusting the friction force acting on the shafts 631a-631b, respectively, independently one another.

[0152] In this way, the tension of the web W in the transport direction T at both sides of the web W across the transport path may be controlled by each roller segment 632a-632b independently one another.

[0153] FIG. 9 A shows a further embodiment, wherein the lever 736 is provided as a media cover plate 736. The media loading cover 736 in the first position shown in FIG. 9A shields part of the web W on the transport path from accidental access e.g. by an operator. The media cover plate 736 is pivotably connected to the support beam 713 via intermediate element 714. The support beam 713 moveably supports the translating print carriage 710. The free end of the media cover plate 736 is provided with a holding mechanism 740 in the form of a clamp 740. The intermediate element 714 positions the media cover plate 736 such that in the first position in FIG. 9A the holding mechanism is positioned near the supply unit (now shown). This allows for easy attachment of the leading edge section L of the web W to the holding mechanism 740. After securing the leading edge section L to the holding mechanism 740, the media cover plate 736 is pivoted to its second position shown in FIG. 9B. The intermediate element 714 positions the media cover plate 736 such that in the second position in FIG. 9B the holding mechanism 740 is positioned near the upstream end of the print surface 711. The pivot axis of the media cover plate 736 is thereby positioned above the transport path. The distance between the transport path and the pivot axis is preferably at least the length of the lever or plate 736. Thereby the horizontal spacing between the surfaces 711, 712 and the pivot axis is sufficient to let the media cover plate 736 pass unhindered along the surfaces 711, 712. This further allows the media cover plate 736 to hang freely in the first position without overlapping the transport path. In FIG. 9B a curved support surface 712 is positioned at this upstream end. The curved support surface 712 guides the web W from a vertical to a horizontal orientation on the print surface 711. The curved surface 712 may be a stationary curved plate 712 or a roller. The leading edge section L attached to the media cover plate 736 is thereby easily brought from the supply unit to the print surface 711. Preferably, the upwards pivoting of the media cover plate 736 is aided by an urging device such as a spring or one or more gas struts, such that the operator may raise the web medium W to the print surface 711 with relatively little effort. The urging devices are preferably configured to drive the media cover plate 736 to one of the first and the second positions as the media cover plate passes halfway through the angle between the two positions. Dependent on the direction of motion, i.e. upwards or downwards, the urging device forces the media cover plate into the respective position after an initial push by the operator in the respective direction. In the second position in FIG. 9B, the leading edge section L is released from the holding mechanism 740 and positioned onto the print surface 711 or the curved surface 712. From there the web is fed to the receiving roller (not shown) downstream of the print surface 711. After loading, the media cover plate is returned to its first position shown in FIG. 9A wherein it protects the web medium W from damage and contamination. The media cover plate 736 is preferably a page-wide plate extending over the width of the transport path. The holding mechanism 740 need only engage the web at sufficient positions to facilitate a secure holding of the web during the pivoting of the media cover plate 736.

[0154] Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination and any advantageous combination of such claims are herewith disclosed.

[0155] 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.

[0156] 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.

[0157] 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.