EP2062730A1 - Flexible print head - Google Patents

Abstract

The head has a set of print modules (2, 2a) including a tip (24) formed with a nozzle orifice (23). An ejecting unit ejects ink droplets from the orifice. A flexibly deformable mounting element has a set of seats holding the tip, where the element fits a substrate to be printed. An ink supply is connected to the print modules, where the ink supply holds inks of different colors and feeds different colors to different modules. The mounting element is made of elastomer e.g. rubber, silicone and acrylic.

Description

The invention relates to a printhead for an inkjet printer having a plurality of printing nozzles.

The marking of products by means of freely programmable labeling systems has been known for a long time and is used industrially in many areas. Thus, for a variety of applications, among others, ink jet printers are used, which enable contactless marking of products by ejecting drops of ink from one or a plurality of nozzles of a printhead in such a way that a printed image in the form of a dot matrix is built up on the surface to be printed can.

Essentially, two different techniques are known, one being continuous inkjet technology and the other being drop-on-demand technology.

In the continuous inkjet technique, a continuously emerging ink jet is usually only modulated from a single nozzle by means of a modulation element for generating pressure fluctuations, for example by means of a piezoelectric vibrator, so that it emerges from the nozzle at a certain distance from the nozzle break up equal drops.

The resulting ink drops can be charged differently electrostatically from the ink jet immediately before their detachment and can then be deflected in a subsequent electric field of a plate capacitor according to their respective electrostatic charge, resulting in different trajectories for the respective ink drops at least in a deflection.

This makes it possible to select different positions of the differently charged ink droplets at least in one direction transversely to the direction of propagation of the ink droplets, whereby a punctiform printed image can be generated with a simultaneous and synchronized relative movement of a product to be marked to the print head.

Since this principle works well over a certain distance between the print head and the surface to be printed with good quality, it is also possible to mark, for example, moderately structured surfaces. The disadvantage, however, is that the maximum height of a printing line generated thereby system can be only about 10 mm to 20 mm, which for example it is not possible to produce a larger label with only a single printhead or labeling such as a pipe or a cable so To perform that the lateral surface of the pipe or cable can be printed in an angular range of more than 120 degrees or even in an angular range of 360 degrees.

In these cases, it is necessary to use a plurality of printheads and / or printing systems and to arrange them appropriately, for example, to arrange for a 360 ° printing circularly around the object to be printed, wherein the printed image are distributed to the number of printing system used must and must be printed synchronously. Such a method is naturally complex and error prone and costly.

In contrast to the continuous inkjet method, a print head of a drop-on-demand printing system has a multiplicity of individual nozzles, each of which can be controlled independently of one another, which are generally arranged in a line in a nozzle plate and each have the same spacing.

The generation of individual ink droplets is carried out in principle by the fact that each nozzle with its associated nozzle chamber and a modulation element associated with it represents its own independently controllable pressure module. For this purpose, for example, all the nozzle chambers present in a print head are connected via common ink feeds to a common ink reservoir, so that in operation the nozzle chambers are each filled with ink.

The respective modulation elements are attached to the respective nozzle chamber in such a way that they can impulsively build up a positive pressure in the respective nozzle chambers with a corresponding electrical activation, whereby an ink droplet is thrown out of the nozzle to the outside. As a result of the fact that the printing modules can be controlled essentially independently of one another, it is thus possible to produce a complete printing line with a single common control pulse, wherein the control pulse simultaneously triggers all required nozzles via corresponding drive circuits.

Depending on the type and design of the printheads, the respective pressure chambers are connected to each other via the said ink supply line and, depending on the mode of operation of the modulation elements, the nozzles can be driven, for example, only in certain groups for droplet generation by, for example, injecting the nozzles 1, 4, with a first pressure impulse. 7, ... be driven, in a second pressure pulse, the nozzles 2, 5, 8, .. are controlled and in a third pressure pulse, the nozzles 3, 6, 9, are driven, resulting in a continuous movement of an object to be printed on the print head along a sawtooth Pressure line results.

Due to the system, it is not possible with drop-on-demand printheads to produce a high-quality printing over a greater distance on, for example, a curved or structured surface of a product, since the ink drops produced by this method have a relatively low ejection speed and a small diameter and thus have a low mass and thus already after a short distance through the air resistance and external air movements, such as those caused by a movement of the object to be labeled, can be distracted uncontrolled from their respective trajectory and thus increasing with the distance deterioration of the printed image established.

However, since it is usually desirable to achieve high print quality, it is also necessary to provide a high number of print channels, while at the same time the spacing of adjacent nozzles must be small and the ejected ink drops each must be small. Technically, this is achieved in that the construction of a complete print head is more or less monolithic, for example by all the nozzle chambers whose corresponding ink supply lines and the respective modulation elements are combined in a common body and form a rigid block.

Corresponding printheads, which operate according to the drop-on-demand method, are industrially manufactured and sold, for example, by the companies Spectra, Xaar, Konika Minolta, Hewlett Packard or Epson.

A disadvantage of the mentioned printheads, however, is that more curved surfaces can be printed only unsatisfactory or not at all in a single operation, or only with the use of a plurality of printheads, which means a high investment.

In the published patent application DE 40 33 816 A1 On the other hand, a flexible printhead is described, with which it is possible to print a curved surface within a portion of the curvature, however, the shape of the printhead is adjustable only as a circular segment around a fixed center and thus only with a curvature in a plane and therefore not suitable for the printing of differently shaped surfaces. In addition, a 360 ° printing with such a printhead is not possible.

The object of the invention is to provide a printhead with which it is possible to print the surface of a molded body substantially independently of the shape of the surface of the body along a given direction without rotating the body or printhead during printing ,

The object is achieved according to the invention in that the print head has a plurality of adjacent printing modules, each with at least one pressure nozzle, wherein two adjacent printing modules are interconnected by a flexible material and / or element at least in the connecting direction, preferably in all spatial directions.

For example, the printhead may comprise a plurality of individual printing modules which can be controlled substantially independently of one another or which can be jointly controlled, which can be combined in such a way that the nozzle openings of the respective printing modules form a common nozzle arrangement. The nozzle arrangement can be designed according to the invention in that the nozzles of the printing modules lie on a common three-dimensionally formed nozzle surface, in particular which can be curved in several dimensions or can be curved and have substantially the same distance from one another independently of the respective shape of the nozzle surface.

The arrangement of the nozzles of the printing modules to a nozzle surface can be formed according to the invention so that the nozzles of the printing modules, for example, form essentially a linear arrangement or a planar arrangement.

In order to be able to adapt a nozzle surface formed in this way to a labeling of differently shaped product surfaces, it can be provided according to the invention in a preferred embodiment, at least the nozzles of the printing modules, or the end regions of the printing modules which have the at least one nozzle and thus at least To summarize the so-called nozzle plates of the printing modules in a consisting of a flexible material, for example, an elastomeric, especially rubber-like material receiving device to a specific nozzle surface.

This makes it possible to adapt the thus formed nozzle surface due to the flexibility of the material of the receiving device of a surface of a three-dimensional product to be labeled, for example, the surface of a cylindrical product so that all nozzles from the surface of the product have a substantially equal distance, so that a constant printing quality independent of a printing distance can be achieved. In this case, an elastomeric material for the receiving device can preferably be selected, which has isotropic properties in terms of its flexibility.

With such a receiving device, it is also possible to deform the nozzle surface in a radius of for example 360 ° and / or in addition to twist, so as to form a circle or a spiral, for example, whereby a cylindrical product completely on its outer surface or at a tubular material whose inner surface can be printed.

Each individual printing module can in this case comprise, for example, a main body which has an ink feed, an ink chamber with a downstream nozzle opening and electrical drive elements for generating a single ink droplet and electrical connection elements for connection to a higher-level control.

According to the invention, the individual printing modules can be connected, for example, to each other by means of the aforementioned recording device or generally a flexible and / or deformable material so that their respective nozzle plates form a common surface in a basic position and their nozzles are arranged for example in a line or form a line, whereby it is possible to bring a nozzle row thus created into any shape by deformation of the flexible and / or deformable material, for example to form a circle or arc or to deform it into a spiral or a serpentine line. Under this basic position can thus be understood such an arrangement of the nozzle modules to each other, which automatically occupy this without deforming forces. Thus, the material used can be elastic and self-restoring in terms of shape.

It may further be provided according to the invention that the pressure modules are interconnected by means of a plastically deformable, in particular a thermoplastic material, wherein a formation of a specific three-dimensional nozzle arrangement can be achieved, for example, that the exemplary thermoplastic material by a Heating can be brought into a deformable state, so that it can be brought into a desired shape. A subsequent cooling fixes the material permanently, for example. Depending on the material used, the deformation may for example be irreversible or be reversible by re-heating the material.

It may further be provided according to the invention that the row of nozzles along an axis, for example along its longitudinal axis, in particular thus that axis along which the nozzle plates are arranged one behind the other, rotatable, whereby the respective ejection directions of the ink drops from the respective nozzles, for example, from said longitudinal axis in have different directions radially outward, so as to print, for example, the interior of a hollow body in whole or in part.

It can further be inventively provided to deform the row of nozzles by an example perpendicular and in particular spaced from the said longitudinal axis of a nozzle row working axis, whereby the respective ejection directions of the ink droplets from the respective nozzles, for example, radially inwardly to the exemplified working axis have, so for example To print the exterior of a body in whole or in part.

It may further be provided according to the invention to deform the row of nozzles by an example perpendicular and in particular spaced from said longitudinal axis of a nozzle row working axis, whereby the respective ejection directions of the ink droplets from the respective nozzles, for example, radially outward relative to the exemplified working axis have, for example to print all or part of the inside of a body.

It can further be inventively provided to equip the respective pressure modules with respective valves, for example, check valves and / or respective pumps, for example, micropumps in their ink supply lines and / or respective ink reservoir, whereby, for example, mechanical pressure fluctuations in a common ink supply are not transmitted to the print modules and thereby the Reliability of such a printhead significantly increased.

In addition, this makes it possible to emptying or filling individual printing modules with ink in a simple manner, so that, for example, for service purposes, individual printing modules can be exchanged without impairing the functionality of the other printing modules. In addition, this also makes it possible, for nozzle cleaning of individual nozzles targeted eject a certain amount of ink, which, for example, penetrated air or interfering impurities can be selectively ejected from the respective nozzle.

A printhead according to the invention can be constructed from a number of individual printing modules as described above. It is irrelevant according to the invention, whether the individual printing modules represent only electrically or pneumatically controllable valves, or whether each individual printing module is a separate print head with at least one nozzle.

According to the invention, the individual printing modules can preferably be connected to one another with a deformable material along a longitudinal axis, for example by means of a rubber material or for example by means of a thermoplastic material or for example via one or more spring elements to which the individual printing modules are fastened.

Since the respective printing modules have to be supplied with ink or another means to be printed for operation, the supply can be supplied with them Means according to the invention, for example via individual external leads or in a corresponding embodiment of the printing modules and the connecting material via a common feed line.

This can be done when using a said elastomeric, in particular rubber-like compound in a preferred embodiment in the interior of the elastomeric material, which in this case also has the function of a supply system and / or reservoir for the agent, in particular the ink.

Accordingly, when using one or more coil springs as connecting elements, these can be made hollow and thus also serve as supply hoses. The required electrical leads to the individual printing modules are suitably guided in each case by means of cables to a common control electronics and / or a higher-level control.

For example, when using inks, these may be conventional low viscosity oil based inks or UV curable inks, but also other low viscosity liquids such as adhesives or oils or reaction liquids as required. If the pressure modules additionally each have valves and / or corresponding pumps, for example micropumps, this eliminates known problems with foreign air in the supply lines when using the mentioned inks to be printed, since these are effectively conveyed from the ink system by the conveying action of said pumps and the nozzle elements can thus have a self-cleaning function; on the other hand, there is the additional possibility of conveying gases instead of liquids, in particular reactive gases, and to bring them targeted and metered to individual positions of a surface within a production process in order, for example, to trigger chemical or physical reactions or support.

Figur 1:

eine erste erfindungsgemäße Ausführung eines Druckkopfes

Figur 2:

eine zweite erfindungsgemäße Ausführung eines Druckkopfes

Figur 3:

eine Rückansicht einer ersten oder zweiten Ausführung eines Druckkopfes

Figur 4:

eine erste mögliche Form eines erfindungsgemäßen Druckkopfes gemäß Figur 1 oder Figur 2

Figur 5:

eine zweite mögliche Form eines erfindungsgemäßen Druckkopfes gemäß Figur 1 oder Figur 2

Figur 6:

eine dritte mögliche Form eines erfindungsgemäßen Druckkopfes gemäß Figur 1 oder Figur 2

Embodiments of the invention are illustrated in the following figures. Show it:

FIG. 1:

a first embodiment of a printhead according to the invention

FIG. 2:

a second embodiment of a printhead according to the invention

FIG. 3:

a rear view of a first or second embodiment of a printhead

FIG. 4:

a first possible form of a printhead according to the invention FIG. 1 or FIG. 2

FIG. 5:

a second possible form of a printhead according to the invention FIG. 1 or FIG. 2

FIG. 6:

a third possible form of a printhead according to the invention FIG. 1 or FIG. 2

A first embodiment of a printhead according to the invention shows FIG. 1 , A printhead according to the invention has, for example, a receiving plate 1 which consists of a flexible, eg elastomeric material and in which a number of receiving openings 1a are provided for accommodating printing modules 2 which can be controlled independently of one another. The receiving plate forms the receiving device mentioned above and may in a preferred embodiment have a thickness such that the receiving device is at least largely self-supporting, so at least not significantly deformed under the action of gravity, but only by external forces applied.

The openings 1 a can be designed so that, for example, at the pressure modules 2 each existing formations 24 accurately fit into the openings and clamp, for example, in this, which is easily possible especially when using a rubber-like material for the receiving plate 1. Alternatively or in addition thereto It may be provided to provide corresponding fastening devices, not shown, on the receiving device 1 to hold the printing modules 2 in their respective openings 1 a, regardless of a required for a specific application deformation of the receiving plate 1. It may be provided according to the invention, for example, the printing modules. 2 to glue in their receiving openings 1a accordingly.

It can further be inventively provided that the respective pressure modules are introduced into the receiving openings 1a of the receiving plate 1, that the respective nozzle plates 22 form at least in a basic form a substantially closed surface with the surface 1 b. In the case of an undeformed basic shape, this surface may be e.g. lie in one plane.

The arrangement of the nozzle plates 22 in the receiving device 1 can be such that the respective nozzles 23 form a line, for example, as in FIG FIG. 1 shown, wherein the distance between adjacent nozzles 23 is preferably equal to each other at least in a basic position of the receiving device.

According to the invention, the printing modules 2 can consist, for example, of a base body 21 in which, depending on the type and design of the printing module, micropumps, valves, ink filters, pressure generating elements, ink feeds and optionally electronic control circuits can be provided and which at one end face a nozzle plate 22 with at least one Nozzle 23 has.

For controlling the respective pressure modules 2 by means of a higher-level control, not shown, the pressure modules 2 each have electrical connections 26, whereby it is possible to operate each pressure module independently. In addition, each printing module 2 has at least one connection 25 for supplying ink, the respective connections 25 being connected to one another, for example common supply, not shown, can be summarized.

It can be inventively further provided that the printing modules 2 as in FIG. 2 shown, in turn each represent printheads, which have on their respective the receiving device 1 side facing a nozzle plate 22 with a certain number of individual nozzles 23a. Depending on the type and design of the printheads 2, the individual nozzles 23a of each printhead 2 can be controlled independently of one another in groups or in each case. By arranging a certain number of printheads 2 in a common receiving plate 1 and their respective substantially plan completion of the respective nozzle plates 22 with the surface 1 b, a common area 1b is thereby created as a common nozzle plate, due to the flexibility of the material used as a nozzle plate the receiving plate 1, the common nozzle plate 1 b is deformable.

The Figures 1 and 2 also show schematically a way to exchange individual print modules 2, for example, by individual print modules 2a can be removed from the common recording device 1 or added.

A rear view of an embodiment of a printhead according to the invention with a plurality of individual printing modules 2 according to FIG FIG. 1 or FIG. 2 is in FIG. 3 shown. The individual printing modules 2, 2a have, for example, for electrical control via a higher-level control, not shown, each electrical connections 26, via which the respective printing modules can be controlled according to a total image to be printed.

The supply of an ink to be printed in each case takes place, for example, via feeders 25 which, for example, by means of corresponding connecting elements to a common ink supply supply line can be summarized. It is also possible according to the invention to supply different printing modules with different inks from different ink reservoirs, which makes it possible, for example in the case of all-round printing of a cylindrical printing material such as a cable or a tube, to have different printings with different printing inks in different areas in one operation produce.

FIG. 4 shows by way of example a first possible deformation of a printhead according to the invention, for example for printing a concave shape of an object to be printed. For this purpose, for example, the end faces 1 c, 1 d of the receiving plate 1 along one, for example, formed by the nozzle assembly of the printing modules longitudinal axis 110 against each other in the direction of rotation 100a or 100b twisted that the desired nozzle arrangement and a desired ejection direction of the respective ink droplets from the nozzles 23 can train. In this case, this longitudinal axis preferably extends exactly through the mouth openings of the nozzles.

Another possible deformation of a printhead according to the invention shows FIG. 5 , wherein in this deformation of the receiving plate 1 shown by way of example only part of the receiving plate 1 is deformed about an axis 111, for example perpendicular to an axis formed by the nozzle assembly of the printing modules in the direction 100c, whereby for example the printing of a rounded edge of an object to be printed is made possible.

Another possible deformation of a printhead according to the invention shows FIG. 6 , wherein in this deformation of the receiving plate 1 shown by way of example, this is bent substantially to a 100, for example, perpendicular to an axis 112 formed by the nozzle assembly of the printing modules substantially circular in the direction 100d in particular here, for example, the now facing frontal surfaces 1 c , 1 d in addition can be shifted against each other, so that the receiving plate 1 is deformed substantially helically. This makes it possible, for example, to provide a cylindrical substrate such as cables or tubes in one operation with an all-round printing.

With regard to all embodiments, it should be noted that the technical features mentioned in connection with one embodiment can be used not only in the specific embodiment, but also in the other embodiments. All disclosed technical features of this invention description are to be classified as essential to the invention and arbitrarily combined or used alone.

Claims (15)

Printhead, in particular for an inkjet printer having a plurality of printing nozzles, characterized in that it comprises a plurality of adjacent printing modules (2) each having at least one printing nozzle (23), wherein two adjacent printing modules (2) with each other by at least in the connecting direction, in particular in all spatial directions flexible Material (1) and / or element (1) are connected. Printhead according to claim 1, characterized in that the orientation of the printing jets of the printing nozzles (23) to each other and / or the distance of the printing nozzles (23) to each other due to the flexibility of the material connecting the printing modules, in particular in a plurality of spatial directions is adjustable. Printhead according to one of the preceding claims, characterized in that the pressure jets of adjacent pressure nozzles (23) are at least partially convergent or divergent to one another. Printhead according to one of the preceding claims, characterized in that the pressure jets of adjacent pressure nozzles (23) are at least partially perpendicular to the direction of the alignment of the pressure nozzles (23) adjustable, in particular the orientation of the pressure nozzles (23) about the longitudinal axis (110) of the pressure nozzle row rotatable is. Printhead according to one of the preceding claims, characterized in that all the printing modules (2) have a common pressure medium supply line. Printhead according to one of claims 1 to 4, characterized in that all the pressure modules (2) have separate pressure medium supply lines. Printhead according to one of the preceding claims, characterized in that the connection between two adjacent printing modules (2) is hollow, in particular to transport through the hollow connection a pressure medium to the pressure nozzles (23). Printhead according to one of the preceding claims, characterized in that it is the flexible material (1) is an elastomeric material, in particular a rubber, silicone or acrylic. Printhead according to one of Claims 1 to 7, characterized in that the flexible element (1) is a spring element. Printhead according to one of claims 1 to 7, characterized in that it is the flexible material (1) is a reversible in particular thermoplastically deformable material Printhead according to one of the preceding claims, characterized in that the individual pressure nozzles (23) can be arranged around an axis (111, 112) in an angular range of at least 360 degrees. Printhead according to one of the preceding claims, characterized in that the individual pressure nozzles (23) are arranged spirally about an axis (110, 112), in particular wherein the pressure beams are oriented on the axis (110, 112) or away from it. Printhead according to one of the preceding claims, characterized in that a pressure nozzle (23) has a controllable valve. Printhead according to one of the preceding claims, characterized in that the printing modules (2) are detachably combined in a receiving device (1) made of flexible, in particular elastomeric material. Printhead according to one of the preceding claims, characterized in that the receiving device (1) is formed in particular completely from the flexible material, in particular in the manner of a mat and a plurality, in particular in a line adjacent openings (1 a) each having in particular the form-fitting Recording a print module (2).

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