METHOD FOR MANUFACTURING A PRINTING BAR UNIT FOR A PRINTING SYSTEM, AND A PRINTING BAR UNIT

Abstract

A method for manufacturing a printing bar unit for a printing system includes the steps of providing a support bar having a plurality of primary mounting positions, providing a plurality of exchangeable printheads having a plurality of inkjet nozzles, and releasably mounting the printheads to the support bar. Preceding the step of releasably mounting the printheads to the support bar, a plurality of reference organs are connected at the primary mounting positions to the support bar and undergo an alignment finishing process for forming a plurality of accurate secondary mounting positions, and then in a subsequent step the printheads are releasably mounted to the secondary mounting positions on the reference organs. A dimensional tolerance of the secondary mounting positions on the reference organs relative to each other is more accurate than a dimensional tolerance of the primary mounting positions on the support bar relative to each other.

Claims

1. A method for manufacturing a printing bar unit for a printing system, the method comprising the steps of: providing a support bar having a plurality of primary mounting positions; providing a plurality of exchangeable printheads, each printhead having a plurality of inkjet nozzles; and releasably mounting the printheads to the support bar, wherein preceding the step of releasably mounting the printheads to the support bar, a plurality of reference organs are connected at the primary mounting positions to the support bar and undergo an alignment finishing process for forming a plurality of secondary mounting positions, and then in a subsequent step the printheads are releasably mounted to the secondary mounting positions on the reference organs.

2. The method according to claim 1, wherein the alignment finishing process comprises a machining operation, in particular face milling and/or grinding.

3. The method according to claim 1, wherein the alignment finishing process of the reference organs is performed such that a dimensional tolerance of the secondary mounting positions on the reference organs relative to each other becomes more accurate than a dimensional tolerance of the primary mounting positions on the support bar relative to each other, wherein in particular the dimensional tolerance of the primary mounting positions is larger than 0.1 mm and the dimensional tolerance of the secondary mounting positions becomes smaller than 0.1 mm, in particular smaller than 0.02 mm.

4. The method according to claim 1, wherein preceding the step of releasably mounting the printheads to the support bar, reference end blocks are connected to free ends of the support bar and undergo an alignment finishing process for forming reference positioning faces destined to be placed at complementary bearing points of the printing system.

5. The method according to claim 4, wherein the alignment finishing process of the end blocks is performed such that a dimensional tolerance of the reference positioning faces of the reference end blocks relative to the secondary mounting positions on the reference organs becomes more accurate than a dimensional tolerance of the free ends of the support bar relative to the secondary mounting positions on the reference organs, wherein in particular the dimensional tolerance of the free ends is larger than 0.1 mm and the dimensional tolerance of the reference positioning faces becomes smaller than 0.1 mm, in particular smaller than 0.02 mm.

6. The method according to claim 4, wherein the alignment finishing processes of the reference end blocks and the reference organs get performed in a single simultaneous step.

7. The method according to claim 1, wherein the alignment finishing process comprises face milling and/or grinding of at least front faces of the reference organs and/or of the reference positioning faces of the end blocks.

8. The method according to claim 1, wherein the reference organs and/or end blocks are glued with a glue layer to the support bar.

9. The method according to claim 8, wherein the alignment finishing process comprises a varying of a thickness of the glue layer between the support bar and the reference organs and/or end blocks, in particular by using a glueing jig for positioning the reference organs and/or end blocks to the support bar.

10. The method according to claim 1, wherein intermediate adapter elements are mounted to the secondary mounting positions of the reference organs, and wherein the printheads are mounted to those intermediate adapter elements.

11. A printing bar unit for a printing system, in particular manufactured with a method according to claim 1, the printing bar unit comprising: a support bar having a plurality of primary mounting positions; reference organs connected at the primary mounting positions to the support bar and forming secondary mounting positions; and a plurality of exchangeable printheads, each printhead having a plurality of inkjet nozzles, and the printheads being releasably mounted to the reference organs, wherein a dimensional tolerance of the secondary mounting positions on the reference organs relative to each other is more accurate than a dimensional tolerance of the primary mounting positions on the support bar relative to each other.

12. The printing bar unit according to claim 11, wherein the reference organs have undergone an alignment finishing process comprising a machining operation, in particular face milling and/or grinding.

13. The printing bar unit according to claim 12, wherein at least front faces of the reference organs have undergone the alignment finishing process comprising the machining operation, in particular the face milling and/or grinding.

14. The printing bar unit according to claim 11, wherein the dimensional tolerance of the primary mounting positions is larger than 0.1 mm and wherein the dimensional tolerance of the secondary mounting positions is smaller than 0.1 mm, in particular smaller than 0.02 mm.

15. The printing bar unit according to claim 11, wherein the printing bar unit further comprises: reference end blocks that connect to free ends of the support bar, wherein a dimensional tolerance of the reference positioning faces of the reference end blocks relative to the secondary mounting positions on the reference organs is more accurate than a dimensional tolerance of the free ends of the support bar relative to the secondary mounting positions on the reference organs.

16. The printing bar unit according to claim 15, wherein the reference end blocks have undergone an alignment finishing process comprising a machining operation, in particular face milling and/or grinding, for forming reference positioning faces destined to be placed at complementary bearing points of the printing system.

17. The printing bar unit according to claim 16, wherein at least the reference positioning faces of the end blocks have undergone the alignment finishing process comprising the machining operation, in particular the face milling and/or grinding.

18. The printing bar unit according to claim 15, wherein the dimensional tolerance of the free ends is larger than 0.1 mm and wherein the dimensional tolerance of the reference positioning faces is smaller than 0.1 mm, in particular smaller than 0.02 mm.

19. The printing bar unit according to claim 11, wherein the support bar is made out of a ceramic material.

20. The printing bar unit according to claim 11, wherein the reference organs are made out of metal.

21. The printing bar unit according to claim 11, wherein the support bar is made out of another material than the reference organs, in particular a material having a lower coefficient of thermal expansion and/or having a higher thermal conduction and/or having a higher e-modulus and/or being more lightweight compared to the material of the reference organs.

22. The printing bar unit according to claim 11, wherein the support bar is an elongate linehead, in particular having a length of at least 1.0 meter.

23. The printing bar according to claim 11, wherein intermediate adapter elements have been mounted to the secondary mounting positions of the reference organs, and wherein the printheads have been mounted to those intermediate adapter elements.

24. A printing system comprising one or more printing bar units according to claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS:

[0025] The invention shall be explained in more detail below with reference to the accompanying drawings, in which:

[0026] FIGS. 1a, b schematically show an inkjet printing system of the single pass type respectively a scanning type system with printing bar units;

[0027] FIGS. 2a-e show subsequent manufacturing steps of a first embodiment of the method for manufacturing a printing bar unit according to the invention;

[0028] FIG. 3 shows a cross-sectional view over the line A-A in FIG. 2e;

[0029] FIGS. 4a-d show subsequent manufacturing steps of a second embodiment of the method according to the invention;

[0030] FIG. 5 shows a cross-sectional view over the line A-A in FIG. 4d; and

[0031] FIGS. 6a-c show subsequent manufacturing steps of a third embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION:

[0032] In FIGS. 1a, b two well-known types of inkjet printing systems are shown. In both cases transportation means are provided for moving a substrate 1 in a printing direction x relative to a plurality of printing bar units 2. The substrate may be of a continuous or discontinuous nature. Each printing bar unit 2 comprises a plurality of exchangeable printheads which are positioned in line or staggered next to each other. Each printhead comprises one or more arrays of individually operable inkjet nozzles for jetting ink droplets onto the substrate 1 when operated.

[0033] In FIG. 1a the inkjet printing system is of the single pass type. For this each printing bar unit 2 extends in y-direction over an entire width of the substrate 1 and is supported with its free ends at complementary bearing points of the system. With this each unit 2 is used for printing at least one colour onto the substrate 1.

[0034] In FIG. 1b the inkjet printing system is of the scanning type. For this each printing bar unit 2 has a limited length in x-direction. One or more printing bar units 2 are supported with their free ends at complementary bearing points of a shuttle 3 of the system. The shuttle 3 extends over merely a small part of the width of the substrate 1 in y direction and is movable back and forth in the scanning direction y which is perpendicular to the printing direction x. Here also each unit 2 is used for printing one colour onto the substrate 1.

[0035] Some different inventive methods for manufacturing the units 2 shall now be explained below with reference to FIGS. 2, 3 and 4.

[0036] Starting with FIG. 2. In a first step (see FIG. 2a) an elongate piece of base material is taken which forms a support bar 5. The support bar 5 here is a rectangular hollow ceramic beam with free ends 5′. If desired or deemed necessary, it is possible to machine or otherwise process one or more of the outer walls of the bar 5, for example by means of a face milling and/or grinding operation. Thus those faces can be given first dimensional tolerances, which for example can be >0.1 mm, which makes it possible to use them as reference faces for subsequent operations.

[0037] In a second step (see FIG. 2b), a plurality of primary mounting positions 6 are formed on the bar 5 by drilling holes into a front wall 5a thereof. With this use can be made of a drilling jig. It can however also be done manually. Instead of drilling holes through merely one side wall it is also possible to drill them through two opposing side walls of the bar 5.

[0038] In a third step (see FIG. 2c), reference organs 7 are connected by means of a suitable glue to the bar 5 at the primary mounting positions. With this use can be made of a glueing jig, which shall be explained in more detail below with reference to FIG. 6. The reference organs 7 here are formed by headed metal pins. With this each organ 7 is placed with an insertion part into one of the holes whereas a head part of each organ 7 remains lying projecting outside it.

[0039] In this same third step (see FIG. 2c), end blocks 8 are connected by means of a suitable glue to the bar 5 at its free ends 5′. With this use can be made of a glueing jig. The end blocks 8 here are metal caps. With this each block 8 comprises a front face 8a that is parallel to the wall 5a.

[0040] In a fourth step (see FIG. 2d), the front faces 8a of the blocks 8 and front faces 7a of the head parts of the organs 7 undergo an alignment finishing process, which here is formed by a face milling and/or grinding operation. Thus those faces 7a, 8a can be given second dimensional tolerances which are more accurate than the first ones, and for example can be <0.02 mm. The faces 7a of the organs 7 then can advantageously be used as accurate secondary mounting positions which have improved dimensional tolerances compared to the ones of the primary mounting positions (from >0.1 mm to <0.02 mm), whereas the faces 8a of the blocks 8 can be used as accurate reference positioning faces for placing them at their complementary bearing points of the printing system. Besides having the faces 7a, 8a undergo the alignment finishing process, it is also possible to have other faces or parts of the organs 7 and/or blocks 8 undergo a same or similar treatment for improving their dimensional tolerances.

[0041] In a fifth step (see FIGS. 2e and 3), printheads 9 are mounted against the secondary mounting positions that are formed by the aligned/finished faces 7a of the reference organs 7. Each printhead 9 here is mounted onto three organs 7 by means of screws 10 which get to extend from behind through holes that are present throughout the entire organs 7. With this use can be made of special positioning equipment and/or procedure, such that the printheads 9 can even be given third dimensional tolerances which may even be more accurate than the second ones, and for example can be <0.005 mm. If desired it is possible to first mount intermediate adapter elements against the secondary mounting positions of the organs 7, and then mount the printheads onto those intermediate adapter elements. As shall be clear, the shape of the reference organs 7 and any intermediate adapter elements, shall be strongly dependent on the type of printhead 9 used and its application.

[0042] In FIG. 4 a variant is shown in which same parts have been given same reference numerals. Here in a first step (see FIG. 4a) again an elongate piece of base material forms a support bar 5. A plurality of imaginary aimed primary mounting positions 6 are present on a front wall 5a of the bar.

[0043] In a second step (see FIG. 4b), reference organs 7 are connected by means of a suitable glue to the bar 5 at the primary mounting positions. With this use can be made of a glueing jig, which shall be explained in more detail below with reference to FIG. 6. The reference organs 7 here are formed by metal strips. Instead of such metal strips other shapes and profiles are also possible to be glued as reference organs 7 against the bar 5. For example FIG. 4b′ shows a variant with “boomerang” shaped organs 7′, FIG. 4b″ shows a variant with “clamp” shaped organs 7″, and FIG. 4b′″ shows a variant with “jacket” shaped organs 7′″. Moreover, such reference organs may be attached to each other by connections of low stiffness such as not to interfere with the stiffness and thermal expansion of the bar.

[0044] In this same second step (see FIG. 4b), end blocks 8 are connected by means of a suitable glue to the bar 5 at its free ends 5′. With this use can be made of a glueing jig. The end blocks 8 here again are formed by metal caps.

[0045] In a third step (see FIG. 4c), the front faces 8a of the blocks 8 and front faces 7a of the organs 7 undergo an alignment finishing process, which here is formed by a face milling or grinding operation.

[0046] In a fourth step (see FIGS. 4d and 5), printheads 9 are mounted against the secondary mounting positions that are formed by the aligned/finished front faces 7a of the reference organs 7.

[0047] The possible use of the glueing jig in steps 2c and 4b shall now be explained in more detail with reference to FIG. 6. Firstly (see FIG. 6a), the reference organs 7 are accurately placed lined up against a jig 15. Subsequently, the support bar 5, of which the front wall 5a has been provided with glue layers 16, is placed against the reference organs 7 on the jig 15. The bar 5 here has been drawn over exaggerated as being somewhat irregularly curved. As can be seen in FIG. 6b the glue layer now is well able to overcome those irregular curves of the bar 5 by varying thicknesses of the glue layers 16 between the support bar 5 and the reference organs 7. After the glue layers 16 have sufficiently hardened, it is then possible to remove the jig 15 and start to perform the aimed face milling and/or grinding operations on the reference organs 7. The face milling and/or grinding now can be performed rather quickly because the use of the jig 15 and the varying thicknesses of the glue layers 16 already have improved the accuracy of the organs 7 to a certain extent.

[0048] Besides the embodiments shown, numerous variants are possible. For example the materials, various dimensions and/or shapes of the distinctive components may differ. Instead of drilling holes in the support bar, it is also possible to already provide those holes in the support bar during manufacturing thereof. If for example the support bar is made out of ceramic material, then the holes can already be made therein while the ceramic material is still in its green phase. Despite the fact that such holes then are likely to be rather inaccurate because of shrinkages of the material during hardening, this is no problem, since according to the invention, the position accuracy of the printheads on the support bar can be greatly and easily improved during the subsequent connection and alignment finishing process of the reference organs. Instead of using a rectangular hollow beam as support bar, it is also possible to use a strip-shaped, T-shaped or L-shaped support bar or any other profile. This shall be dependent on the type of printheads that need to be mounted thereto and on the required rigidity. In the case of the hollow beam, the hollow inside the beam may be used for supplying fluids such as inks and/or steering signals, and/or gasses towards and from the respective printheads and their neighbourhood. Instead of glueing or otherwise connecting reference organs to the support bar that already comprise a through-going mounting opening therein, it is also possible to accurately drill such through-going mounting openings in the reference organs during the alignment finishing process. This then makes it possible to obtain through-going mounting openings with improved dimensional tolerances relative to the ones of the support bar with its first mounting positions. Instead of glueing, the organs and/or blocks can also be connected in other manners to the support bar, for example by clamping or screwing. It is also possible to obtain the support bar by means of a 3D-printing operation. In the alternative or in addition thereto it is also possible to perform a 3D-printing operation for making the reference organs on top of the support bar. Those 3D-printed reference organs then can be printed out of another material than the support bar, and those 3D-printed reference organs then in a subsequent step can undergo the alignment finishing operation according to the invention.

[0049] Thus according to the invention a manufacturing method and printing bar unit is obtained with which reference positioning faces and mounting positions for printheads can be optimally defined relative to each other, while being able to use all kinds of support bars, even ones which are rather inaccurate in their dimensions and which are difficult to directly machine such that they get more accurately defined. The invention advantageously can be used for both single pass and scanning types of printing systems, and for example can be used in the field of textile printing, decor printing, packaging printing, label printing, document printing above a flat track or above a curved track on which a continuous or discontinuous substrate is transported. When used in single pass printing systems, the printing bar unit according to the invention can advantageously form an elongate linehead, in particular one having a length of at least 1.0 meter which gets equipped with tens of printheads in line or staggered next to each other. Even at such long lengths, very high accuracies can be obtained for the positioning of the printheads. When used in scanning printing systems, the printing bar unit according to the present invention can advantageously also be formed with relative long support bars such that wider strokes can be made in one scanning movement of a shuttle to which the printing bar units are mounted.