FLAT BED PRINTING SYSTEM

Abstract

 A flat bed printing system comprising a support surface (16) for print substrates (20), a movable member (22) arranged for translational movement relative to the support surface (16) and carrying a print head assembly (24) for printing onto the print substrate on the print surface (16), and a control system (26) for controlling operations of the movable member (22) and of the print head assembly (24), characterized by a print substrate storage device (28) disposed in a working area of the movable member (22), and a substrate gripping system (32) arranged for joint movement with the movable member and capable of gripping and releasing the print substrates (20) under control of the control system (26).

Description

[0001] The invention relates to a flat bed printing system comprising a support surface for print substrates, which support surface defines a print area, a movable member arranged for translational movement relative to support surface and carrying a print head assembly for printing onto the print substrate on the print surface, and a control system for controlling operations of the movable member and of the print head assembly.

[0002] In known printing systems of this type the movable member may comprise a gantry that extends over the entire width of the support surface and may carry a page-wide print head or a carriage on which the print head assembly is mounted and which is arranged to travel along the gantry so as to scan the support surface in two dimensions.

[0003] Before a print process starts, one or more print substrates, e.g. sheets of paper, have to be placed in appropriate positions on the support surface. The operation of placing the print substrates on the support surface is in most cases performed manually. As an alternative, an expensive robot system may be used for that purpose.

[0004] US 2010/0011979 A1 describes a method for inscribing identification plates. Plates are laid by hand on a transport groove. By means of a transport pin and a carrier arm, the plate is transported to a holding device. After fixing the plate, the plate is inscribed by means of an inscription head. Drawback of the US 2010/0011979 A1 is that during operation constant operator attention is required to manually place new plates.

[0005] It is an object of the invention to provide a less expensive equipment for automating the process of placing the print substrates.

[0006] In order to achieve that object, the printing system according to the invention comprises a print substrate storage device disposed outside the print area in a working area of the movable member, and a substrate gripping system arranged for joint movement with the movable member through the print area and capable of gripping and releasing the print substrates under control of the control system. The substrate gripping system extends beyond the print area in a loading position for gripping a substrate from the print substrate storage device.

[0007] Thus, according to the invention, the movable member which carries the print head assembly is used as a tool for automatically fetching the print substrates from the storage device and placing them on the support surface. It is the insight of the inventor that by allowing the gripping system to extend outside the print area, the gripping system may be used to transfer substrates from a supply outside the print area onto the support surface.

[0008] More specific optional features of the invention are indicated in the dependent claims.

[0009] In an embodiment, the gripping system is moveable along with the movable member for positioning a gripped substrate at any desired location fitting within the print area. The gripping system can preferably be moved over substantially the entire support surface. A substrate position for a to be loaded substrate is selected or determined. The substrate position may be input by an operator or selected by the control system in by comparing dimensions of the substrate to the available area on the support surface. The control system controls the gripping system to position the substrate at the select position and then controls the print head assembly to print the substrate at the selected position. The printing system may comprise detection means such as a camera to verify or determine the position of the substrate on the support surface. The print area is defined as the area of the support surface which is within the printing range of the print head assembly so as to deposit ink on a substrate in said print area. Preferably, since the gripping system and the print head assembly are provided on the same moveable member, the working area has the same or similar size or dimensions as the printing area. However, the working area of the gripping system is offset or displaced with respect to the printing area. On the side of the print substrate storage device, the working area extends beyond the print area.

[0010] In an embodiment, the control system is configured to control the gripping system to:

• in the loading position grip a substrate on the print substrate storage device; and
• move the gripped substrate from the print substrate storage device onto the support surface. The control system determines a vacant location on the support surface with an area to fit the substrate. The gripping system is then controlled to move to the gripped substrate from outside the print area onto the support surface into the vacant location. No operator attendance is then required for loading substrates.

[0011] In an embodiment, the control system is configured to control the gripping system to:

• grip a printed substrate on the support surface; and
• move the gripped printed substrate from the support surface to an output location outside the print area. Preferably a printed substrate storage device is provided at the output location. The output location receives the substrates from the gripping system, such that no operator attendance is required for unloading substrates.

[0012] In an embodiment, the control system is configured to receive print job information defining multiple print jobs and to control the gripping system to:

• move a printed substrate from the support surface to the output location after completion of a print job; and
• load an unprinted substrate from the print substrate storage device onto a vacant location on the support surface to print a subsequent print job on said unprinted substrate. Preferably, the vacant location is the previous location of the unloaded printed substrate. Automated loading and unloading allows for unattended printing, allowing e.g. the printing system to run overnight (or until depletion of the sheet stack).

[0013] In another embodiment, the substrate gripping system comprises an actuator for moving the substrate gripping system perpendicular to the support surface. After releasing a substrate, the gripping system is preferably raised to avoid it displacing or damaging the substrate. Thereto, the printing system comprises an actuator to raise and lower the gripping system with respect to the support surface. In another embodiment, the actuator is further configured to raise the print head carriage. The gripping system and the print head assembly are mounted together on said carriage. A single actuator then suffices for ensuring that the gripping system and the print head assembly do not contact the substrates loaded on the support surface. The actuator is controlled to set the height of the gripping system based on a substrate thickness parameter provided to the control system. The control system may e.g. comprise a media catalogue comprising thickness information for various substrate types.

[0014] In an embodiment, the actuator is configured for vertical movement of the gripping system. Preferably, the actuator is configured to vertically move the print head carriage with the gripping system mounted thereon. The print head assembly and the gripping system can thereby be moved in synchronous movement over the print area as well as perpendicular thereto.

[0015] In an embodiment, the substrate storage device and the gripping system are configured for vertical movement of a substrate on the substrate storage device next to the support surface. The vertical movement range of the gripping system may be limited, especially when said actuator is also used for adjusting the height of the print head assembly. The substrate storage device then comprises e.g. a lift system for bringing a top substrate up to the level of the support surface.

[0016] The movable member may comprise a gantry that is movable relative to the support surface in one direction. It may also comprise a carriage that carries the print head assembly and is movable along the gantry in a second direction orthogonal to the first direction.

[0017] In one embodiment, the gripping system is mounted directly on the gantry, and the print substrate storage device may be disposed adjacent to an edge of the support surface that extends orthogonally to the direction of movement of the gantry, so that the gantry may be moved to a position in the area of the storage device for taking up a print substrate from the storage device, and the gantry may then be moved over the support surface for dragging the print substrate over the support surface and dropping it in a desired position. Preferably, the gripping system is moveable with respect to the gantry perpendicular to the support surface to allow the gripping system to move over the substrates e.g. during printing.

[0018] Of course, the system may comprise a plurality of print substrate storage devices placed side by side, and the gantry may comprise a plurality of gripping systems which may preferably be operated independently of one another, so that the print substrates may be taken up selectively from one of the storage devices.

[0019] In another embodiment, the gripping system may be mounted to the print head carriage so that it is capable of moving and positioning the print substrates in two dimensions.

[0020] In an embodiment, the printing system according to the present invention further comprises a print substrate storage device positioned on a first side of the support surface in the first direction, wherein the substrate gripping system is mounted on said first side of the gantry facing the print substrate storage device. Thereby, the working area of the gripping device extends beyond the print area towards the print substrate storage device.

[0021] In an embodiment, the print substrate storage device comprises a lift system for controlling a height of a stack of substrates such that the topmost substrate is positioned in a suitable height in which it can be taken up by substrate gripping system in the loading position.

[0022] Optionally, the gripping system may be arranged to be detachable from the movable member. In that case a magazine may be disposed adjacent to the support surface, and the movable member may be arranged to take up the gripping system from the magazine when it is needed and to return it into the magazine when a print substrate or substrates have been placed. In particular in cases where the gripping system is carried on the print head carriage this has the advantage that the mass of inertia of the print head carriage can be reduced during the print process.

[0023] The gripping system may comprise one or more suction heads for attracting and dropping the print substrates by means of a controlled suction pressure.

[0024] In an embodiment, the printing system according to the invention may comprise a print substrate unloading system for transferring printed substrates from the support surface to an unloading position, preferably positioned at an opposite side of the support surface with respect to the print substrate storage device.

[0025] In an embodiment, the support surface comprises a plurality of suction holes in fluid connection with a vacuum source for holding the substrate against the substrate surface. During printing the substrates are held in place by an underpressure applied by the vacuum source via the suction holes. The underpressure prevents substrates from curling and coming into contact with the print head assembly, thereby damaging the image on the substrate and/or the print head assembly. The control system is configured to control the gripping system to move a substrate when the vacuum source is prevented from applying an underpressure to the suction holes. To prevent the substrates from sticking to the support surface even in absence of an underpressure, the gripping system can be controlled to raise a substrate slightly above the support surface before horizontally moving said substrate. Thereby, friction between the substrate and the support surface is also reduced, resulting in an easier movement of the substrate. Preferably, the full print area is provided with suction holes to accommodate a wide variety of media sizes. The suction holes may for example be provided in a regular or continuous pattern filling the print area. Local interruptions in the suction hole pattern would result in locally poor holding of the substrate which is undesired. Practically, it is preferred that both the gripping system and the print head assembly are positioned above (i..e. higher than) the support surface.

[0026] Embodiment examples will now be described in conjunction with the drawings, wherein:

Fig. 1

is a schematic view of a printing system according to the invention;

Figs. 2 and 3

are partial side views of a printing system according to a modified embodiment in two different operational states;

Fig. 4

is a top plan view of the printing system shown in Figs. 2 and 3;

Figs. 5 and 6

are enlarged partial front views of a printing system according to yet another embodiment in two different operational states; and

Figs 7A-D

are partial side views of a printing system according to a further embodiment in different states of unloading a printed substrate.

[0027] Fig. 1 shows a printing system comprising a flat bed printer 10 and a workstation 12 connected to the printer via a network 14 and permitting to compile and edit print jobs to be executed with the printer 10.

[0028] The printer 10 has a flat bed with a rectangular support surface 16 in which a regular pattern of suction holes 18 has been formed. The suction holes are connected to a vacuum source, so that a print substrate 20, e.g. a rectangular sheet of paper, can be sucked against the support surface so as to be immobilized on the flat bed.

[0029] A gantry 22 extends across the print surface 16 in a main scanning direction x and is itself movable relative to the support surface in a sub-scanning direction y. A print head assembly 24, comprising for example one or more ink jet print heads, is driven for reciprocating movement along the gantry 22 in the main scanning direction x and is controlled to eject ink, e.g. UV-curable ink, onto the print substrate 20.

[0030] The movements of the gantry 22 and of the print head assembly 24 and the ejection of ink by the print heads are controlled by a print controller 26.

[0031] A print substrate storage device 28 is disposed at the rear edge of the support surface 16 in Fig. 1 and carries a stack 30 of print substrates. A gripping system 32 for taking up the print substrates from the stack 30 comprises at least two cantilevered arms 34 which extend from the gantry 22 towards the storage system 28 and have suction heads (not visible in Fig. 1) on the bottom sides.

[0032] When a new print substrate is to be placed on the support surface 16, the suction system for the suction holes 18 is switched off and the gantry 22 is moved to the position shown in Fig. 1, so that the arms 34 assume a position above an edge portion of the topmost print substrate on the stack 30. Then the suction heads attached to the arms 34 are activated und control of the print controller 26 so that the topmost substrate sheet is attracted against the arms 34. Then, the gantry 22 is moved in the negative y-direction in Fig. 1 so as to drag the topmost sheet from the stack 30 over the support surface 16 until it has reached the position that has been shown in Fig. 1 for the print substrate 20. Then, the suction heads of the arms 34 are switched off, so that the substrate sheet is dropped onto the support surface 16 and is immobilized on the support surface by re-activating the suction holes 18. Then the print process may be performed in the usual way by two-dimensionally scanning the print substrate 26 with the print head assembly 24.

[0033] Optionally, a guide system for guiding the movement of the gantry 22 in ± y-direction may be extended beyond the front edge of the support surface 16 in Fig. 1, so that the gantry and the gripping system 32 may also be used for removing the print substrate 20 on which an image has been formed from the support surface 16 and dropping it on an output stack. The printing system would then be capable of unattended operation for printing images onto a plurality of print substrates.

[0034] Figs. 2 and 3 show a side view of a rear part of the support surface 16 of a printing system according to a modified embodiment. A print head assembly 24' is mounted on a bottom side of a print head carriage 36 which travels along the gantry 22. In this embodiment, a gripping system 32' is constituted by arms 34' which are mounted on the print head carriage 36. Suction heads 38 are visible in the drawing.

[0035] The print substrate storage system 28 comprises a lift system 40 which controls the height of the stack 30 such that the topmost print substrate 20 is always positioned in a suitable height in which it can be taken up by the suction heads 38, as has been shown in Fig. 2.

[0036] In Fig. 3, the gantry 22 moves to the left (in negative y-direction), and the gripping system 32' drags the print substrate 20 onto the support surface 16.

[0037] In this embodiment the gripping system 32' can move along the gantry 22 together with the print head carriage 36, so that the substrate sheet that has been taken up by the gripping system can not only be moved in the negative y-direction but also in positive or negative x-direction so as to position the substrate sheet accurately on the support surface 16 in two dimensions. A camera 42 has been mounted above the support surface 16 for capturing the position of the print substrate and feedback-controlling the movements of the gantry 22 and the print head carriage 36.

[0038] As can be seen in the top plan view in Fig. 4, the gripping system 32' has a plurality (at least two) of arms 34' and suction heads 38 holding the print substrate 20 at two or more different points so as to prevent the substrate sheet from rotating when it is moved in the x-direction (along the gantry 22).

[0039] In this embodiment, a second print substrate storage device 28' has been provided for accommodating print substrates 20' of a different format. Thus, by controlling the movement of the print head carriage 36, it is possible to select the storage device 28 or 28' from which the next print substrate shall be supplied.

[0040] Of course, it is possible with the printing system shown in Figs. 2 to 4 to place a plurality of print substrates on the support surface 16 at a time, so that images can be formed on the plurality of print substrates in a common print process.

[0041] Figs. 5 and 6 show an embodiment in which the print head carriage 36 has a chuck 44 for holding a detachable gripping system 32". The gripping system 32" has only a single suction head 38 for taking up print substrates 20" of a smaller size. The gripping system 32" has a drive mechanism 46 for rotating the suction head 38 and the print substrate held thereat about a vertical axis, and preferably also for adjusting the suction head in height. Thus, when the print head carriage 36 and/or the gantry 22 are moved, the suction head 38 may be held in a lifted position so as to reliably prevent a collision with print substrates which have been placed earlier. When a print substrate is to be taken up in the storage system, the suction head 38 is temporarily lowered. By rotating the suction head 38 it is possible to control the orientation of the print substrate. This system can be used for example for nesting a plurality of print substrates with irregular shapes on the support surface 16 in accordance with a known nesting algorithm.

[0042] A magazine 48 for storing a plurality of gripping systems of different types (for print substrates with different shapes and dimensions) has been installed along one side of the support surface 16 that extends at right angles to the gantry 22. When all print substrates 20" have been placed on the support surface and the print process is to start, the movements of the gantry 22 and the print head carriage 36 can be controlled so as to move the gripping system 32" to the magazine 48.

[0043] Fig. 6 shows a condition where the gripping system 32" has been passed-over to a chuck 50 of the magazine 48. When the print process has been completed and new print substrates to be placed on the support surface 6, the chuck 44 on the print head carriage 36 can be moved to the magazine 48 again so as to select and take up a gripping system that will be needed for the next task.

[0044] Fig. 7A illustrates a print substrate unloading device 60 for transferring printed substrates 20'" from the support surface 16 to an off loading position outside the support surface 16, e.g. a further print substrate storage system (not shown). Preferably, the print substrate unloading device 60 is positioned at an opposite side of the support surface 16 with respect to the print substrate storage system 28. This allows for simultaneous loading and unloading of print substrates 20'" on and from the support surface 16. In this embodiment, the print substrate unloading device 60 comprises an unloading gripping system 62. The unloading gripping system 62 in Fig. 7A comprises suction heads 63 for engaging and holding the printed substrate 20"'. The unloading gripping system 62 is moveable along a beam 61. The beam 61 is perpendicular to the edge of the support surface 16 over which it extends. Preferably, the beam 16, and thereby the movement range of the unloading gripping system 62, extends over only an edge region of the support surface 16. In Fig. 7A, the unloading gripping system 61 is in a non-active state and positioned as not to impede movement of the print head carriage 36.

[0045] As shown in Fig. 7B, after printing, the unloading gripping system 62 is moved along its beam 61 over the printed substrate 20"'. The suction heads 61 then engage a region of the printed substrate 20'" located near the print substrate unloading device 60. Preferably, the support surface 16 comprises one or registering stops (not shown) near the unloading edge of the support surface 16. The print substrate 20'" may then be accurately positioned by aligning the print substrate 20'" against the registering stops. During the engagement step in Fig. 7B, the under-pressure applied to the printed substrate 20'" via the vacuum holes in the support surface 16 has been removed.

[0046] In the subsequent step shown in Fig. 7C, the unloading gripping system 62 is moved in the opposite direction as in Fig. 7B towards the unloading edge of the support surface 16. The print substrate unloading device 60 further comprises an unloading transport device 64 for transporting the printed substrate 20'" from the support surface 16 to its unloading position, for example a printed substrate stack holder positioned at the unloading edge of the support surface 16. In Fig. 7A-D, the unloading transport device 64 is shown as a transport pinch, but may in other embodiments be configured as a transport belt or other suitable transport device. The unloading gripping system 62 positions the printed substrate 20'" in the unloading transport device 64, such that the unloading transport device 64 engages and transports the printed substrate 20'" to the unloading position, as shown in Fig. 7D. The above indicated steps may be performed by a controller to allow for unattended loading and unloading of print substrates 20"'.

[0047] 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.

[0048] 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.

[0049] 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.

Claims

1. A flat bed printing system comprising a support surface (16) for print substrates (20; 20'; 20"; 20"') wherein the support surface (16) defines a print area, a movable member (22; 36) arranged for translational movement relative to the support surface (16) and carrying a print head assembly (24; 24') for printing onto the print substrate on the print surface (16), and a control system (26) for controlling operations of the movable member (22, 36) and of the print head assembly (24; 24'), a print substrate storage device (28; 28') disposed outside the print area in a working area of the movable member (22; 36), and a substrate gripping system (32; 32'; 32") arranged for joint movement with the movable member over the print area and capable of gripping and releasing the print substrates (20; 20'; 20"; 20"') under control of the control system (26), characterized in that the substrate gripping system (32; 32'; 32") extends beyond the print area in a loading position for gripping a substrate (20) from a print substrate storage device (28).

2. The printing system according to claim 1, wherein the control system (26) is configured to control the gripping system (32; 32'; 32") to:

- in the loading position grip a substrate (20) on the print substrate storage device (28); and

- move the gripped substrate (20) from the print substrate storage device (28) onto the support surface (16).

3. The printing system according to claim 2, wherein the control system (26) is configured to control the gripping system (32; 32'; 32") to:

- grip a printed substrate (20) on the support surface (28); and

- move the gripped printed substrate (20) from the support surface (16) to an output location outside the print area.

4. The printing system according to claim 3, wherein the control system (26) is configured to receive print job information defining multiple print jobs and to control the gripping system (32; 32'; 32") to:

- move a printed substrate (20) from the support surface (28) to the output location after completion of a print job; and

- load an unprinted substrate (20) from the print substrate storage device (28) onto a vacant location on the support surface (16) to print a subsequent print job on said unprinted substrate (20).

5. The printing system according to any of the preceding claims, wherein the substrate gripping system (32; 32'; 32") comprises an actuator for moving the substrate gripping system (32; 32'; 32") perpendicular to the support surface (16).

6. The printing system according to any of the preceding claims, wherein the movable member comprises a gantry (22) arranged to move relative to the support surface (16) in a first direction (y).

7. The printing system according to claim 6, wherein the movable member comprises a print head carriage (36) arranged to move along the gantry (22) in a second direction (x) orthogonal to the first direction (y).

8. The printing system according to claim 6 or 7, wherein the gripping system (32) is mounted directly on the gantry (22).

9. The printing system according to claim 6 or 7, wherein the gripping system (32'; 32") is mounted on the print head carriage (36).

10. The printing system according to claim 6 or 7, further comprising a print substrate storage device (28) positioned on a first side of the support surface (16) in the first direction (y), wherein the substrate gripping system (32; 32'; 32") is mounted on said first side of gantry (22) facing the print substrate storage device (28).

11. The print system according to claim 10, wherein the print substrate storage device (28) comprises a lift system (40) for controlling a height of a stack (30) of substrates (20) such that the topmost substrate (20) is positioned in a suitable height in which it can be taken up by substrate gripping system (32; 32'; 32") in the loading position.

12. The printing system according to any of the preceding claims, wherein the gripping system (32") is detachable from the movable member (36).

13. The printing system according to claim 12, comprising a magazine (48) disposed adjacent to the support surface (16) and arranged to store the gripping system (32").

14. The printing system according to any of the preceding claims, wherein the gripping system (32; 32'; 32") comprises at least one suction head (38) controlled by the control system (26).

15. The printing system according to any of the preceding claims, wherein the support surface (16) comprises a plurality of suction holes in fluid connection with a vacuum source for holding the substrate against the substrate surface.

Drawing