EP3645291B1 - Method for printing a curved surface, and device for printing three-dimensional surfaces - Google Patents

Description

The invention relates to a method for printing a curved surface by means of a digital printing process, in which defined amounts of liquid are sprayed off from several individually controllable outlet openings arranged on a flat exit surface of a print head and impinging on the curved surface as liquid droplets. The invention also relates to a device for printing three-dimensional surfaces. From the DE 10 2007 021 767 A1 a method for printing a component with two mutually inclined surface areas by means of a digital printing method is known. The mutually inclined surface areas merge into one another via a curved transition area. In a first step, the first surface area and at least part of the transition area are printed with a linear relative movement between a print head and the component. In a second printing step after pivoting the component by an angle corresponding to the angle of inclination between the surface areas, the second surface area and at least part of the transition area are printed with a linear relative movement between the print head and the component. A peculiarity of the method is that the total amount of pressure fluid reaching each surface unit of the transition area can be controlled in such a way that it corresponds to the amount reaching the flat surface areas; Because of the undefined printing conditions, however, the transition area can hardly be printed with fine patterns or lines which, for example, run obliquely over the curved transition area from one surface area to the other surface area.

Another printing process is from the DE 10 2011 086 015 A1 known. The invention is based on the object of creating a method for printing a surface with which three-dimensionally curved surfaces can also be printed in a precisely predetermined manner by means of a digital printing process. The invention is also based on the object of specifying a device for carrying out the method.

The part of the task of the invention relating to the method is achieved with a method according to claim 1. With the method according to the invention it is achieved that the amounts of liquid sprayed out of the outlet openings have sufficient time to form liquid droplets and that the liquid droplets reach the surface to be printed before they change their straight trajectory. In this way, a well-defined printing of the surface is achieved. With the specified arrangement of the exit surface relative to a convex or concave surface, an advantageous use of the existing exit openings is achieved.

With the features of claim 2, an optimal width of a printing web is achieved.

With the features of claim 3, the amount of liquid dispensed is adapted to the inclination of the surface to be printed relative to the exit surface.

With the features of claim 4 it is achieved that the liquid droplets impinge on the surface to be printed in such a way that they do not move tangentially to the surface in a disadvantageous manner, which would lead to a deterioration in the print quality.

With the features of claim 5 it is achieved that a printing path that is as wide as possible is possible with three-dimensionally curved surfaces.

Claim 6 characterizes a method according to the invention, in which the surface to be printed is printed with a plurality of webs lying next to one another, which directly adjoin one another without a visible transition and without overlapping.

Claim 7 characterizes a method according to the invention in which the surface to be printed is printed with a plurality of strips lying next to one another, which are arranged next to one another with mutual overlap without a visible transition.

Claims 8 to 10 characterize implementation forms of the method with which printing on even large, uneven surfaces is possible with excellent print quality.

Claim 11 characterizes the basic structure of a device for carrying out the method according to the invention.

Claim 12 characterizes an advantageous embodiment of the drive devices for the brackets contained in the device.

Claim 13 characterizes an advantageous further development of the device according to the invention.

Before the invention is explained with the aid of schematic drawings, for example and with further details, a few general comments on digital printing processes should be made:
The ink-jet method is preferably used as the printing method, in which predetermined amounts of liquid are sprayed digitally controlled by a computer system from outlet openings or nozzles arranged in an outlet surface of a print head. These amounts of liquid emerge from the outlet opening in the form of a column of liquid. In the course of its flight, the column of liquid changes into an essentially spherical droplet that reaches the surface to be printed.

The exit openings are generally arranged in a planar exit surface of the printhead. A number of outlet openings can be provided; it can too a plurality of rows arranged one behind the other in the direction of a relative movement between the print head and the surface to be printed may be present during a printing process, the outlet openings of which are preferably mutually offset. Several individual printheads can be combined to form a larger printhead.

The printing width of a print head (maximum distance between outlet openings in a direction perpendicular to a relative movement between the print head and a surface to be printed) is generally between 10 mm and 100 mm. The spraying of the liquid from the outlet openings is controlled by means of piezo elements. Depending on the geometry of the outlet opening and the associated piezo element, the liquid droplets have different volumes. Common volumes are between 3 pl and 160 pl. With a droplet size between 3 pl and 10 pl, high-quality decorative prints can be produced in a quality level between 600 and 1200 dpi.

For painting, for example, droplet volumes greater than 80 pl are used.

Printing fluids for white paintwork, metallic paintwork or with electrical conductivity contain particles, so that it is advantageous to use correspondingly larger outlet openings.

Very thin layers, for example, have a thickness of 1 µm, the thickness of lacquer layers is, for example, 8-20 µm.

• eine Dekorschicht,
• eine Funktionsschicht mit leitfähigen Bereichen,
• uni Farb- oder Lackschichten, transparent oder deckend,
• Haftvermittlungsschichten usw.

A wide variety of layers can be applied to a surface to be printed, preferably in successive printing steps, individually, one above the other or next to one another, for example

• a decorative layer,
• a functional layer with conductive areas,
• uni color or lacquer layers, transparent or opaque,
• Bonding layers, etc.

For a perfect quality of the applied layers it is important that the layers have a constant thickness at least in some areas and that, if the layers are applied next to one another in several strips, the strips merge seamlessly, ie without streaks.

When printing a decoration, it is advantageous to fix the sprayed-on droplets immediately by drying, for example by means of UV light, so that the positional relationship of the droplets, which defines the quality of a good decoration, is retained.

When applying paint or functional surfaces, on the other hand, it is advantageous if a drying process is only activated when the liquid droplets have bonded to form a homogeneous layer.

Furthermore, especially at high printing speeds, i.e. high speed of the relative movement between the print head and the surface to be printed, it is advantageous if the print openings or print nozzles are inclined in the direction of the relative movement, in particular are inclined in such a way that the droplets strike the surface approximately perpendicularly.

In the following, the invention is explained by way of example and with further details using schematic drawings.

Fig. 1:

einen Druckkopf mit darunter angeordneter, konvex gekrümmter, zu bedruckender Oberfläche,

Fig. 2:

einen Druckkopf mit darunter angeordnete konkav gekrümmter, zu bedruckender Oberfläche,

Fig. 3:

Skizzen zur Erläuterung der Bedruckung einer Kugel,

Fig. 4:

eine Skizze zur Erläuterung der Bedruckung einer zylindrisch gewölbten Oberfläche,

Fig. 5:

eine Skizze zur Erläuterung der Bedruckung einer dreidimensional gewölbten Oberfläche,

Fig. 6:

Ansichten zur Erläuterung der Bedruckung konkav oder konvex gewölbter Oberflächen mit überlappungsfrei aneinander angrenzenden Bahnen,

Fig. 7 und 8:

Ansichten zur Erläuterung der Bedruckung konkav oder konvex gewölbter Oberflächen mit überlappend nebeneinander angeordneten Bahnen,

Fig. 9:

Ansichten zur Erläuterung einer weiteren Durchführungsform des erfindungsgemäßen Verfahrens,

Fig. 10:

eine perspektivische Ansicht mehrerer Druckköpfe und ihrer Anordnung relativ zur zu bedruckenden Oberfläche und

Fig. 11:

eine Prinzipansicht einer Vorrichtung zur Durchführung eines erfindungsgemäßen Verfahrens.

It represent

Fig. 1:

a print head with a convexly curved surface to be printed underneath,

Fig. 2:

a print head with a concave curved surface to be printed underneath,

Fig. 3:

Sketches to explain the printing on a ball,

Fig. 4:

a sketch to explain the printing of a cylindrically curved surface,

Fig. 5:

a sketch to explain the printing on a three-dimensionally curved surface,

Fig. 6:

Views to explain the printing of concave or convex curved surfaces with non-overlapping strips adjacent to one another,

Fig. 7 and 8:

Views to explain the printing of concave or convex curved surfaces with overlapping strips arranged next to one another,

Fig. 9:

Views to explain a further embodiment of the method according to the invention,

Fig. 10:

a perspective view of several printheads and their arrangement relative to the surface to be printed and

Fig. 11:

a schematic view of a device for performing a method according to the invention.

Fig. 1 shows a surface 10 of a component, for example an interior decorative part of a motor vehicle, which is to be printed by means of a digital printing process. For this purpose, a print head 12 with a flat exit surface 14 is arranged above the surface 10. In the outlet surface 14, a plurality of outlet openings 16 or nozzles is arranged in a manner known per se, which in Fig. 1 are shown schematically in such a way as they are visible in a view from below of the exit surface 14.

A peculiarity of a digital printing process, for example an ink-jet printing process, is that predetermined amounts of liquid, controlled by piezo elements, for example, can be sprayed from the outlet openings 16, which can be individually controlled electronically in a manner known per se. These amounts of liquid emerge from the outlet openings 16 in the form of columns of liquid with a diameter approximately equal to that of the outlet openings and, as they fly, are transformed into droplets, which in general also start rotating about their axis. So that the printing of the surface takes place in a well-defined manner, the individual columns of liquid require a minimum flight distance B within which they can be converted into droplets. On the other hand, the flight path must not be too long so that the liquid droplets do not degenerate. The maximum permissible flight distance is marked with C.

For liquid droplets with a volume of 30 pl, the minimum required flight distance B is, for example, 0.5 mm. The maximum permissible flight distance C is 2 mm. If the radius of curvature of the surface 10 has the value r (mm) and the distance (C - B) is denoted by t (mm), then based on the geometric relationships for the permissible width X (mm) results when t is small in comparison to r, approximately the following value: $$\mathrm{X}=2\times {\left(\mathrm{t}\times \mathrm{r}\right)}^{0.5}$$

How out Fig. 1 As can be seen, a central region of the exit surface 14 is advantageously parallel to one that is placed tangentially on the surface 10 below the exit surface 14 Plane arranged at a distance B from the plane. The curvature of the surface 10 then determines the maximum width X according to the relationship given above, in which the surface 10 can be printed with perfect droplets corresponding to the trajectory criteria B and C during a relative movement between the surface 10 and the print head 12 perpendicular to the plane of the drawing . As can be seen, the outlet openings 16 are arranged in a larger width A overall. The outlet openings that are outside the permissible printing width X are not activated.

For a reliable determination of the distance between the exit surface 14 and the surface 10 to be printed, a schematically illustrated distance sensor 18 is provided. If printing takes place through multiple relative movements between print head 12 and surface 10 in several superimposed tracks, the thickness of the already applied printing layer can be taken into account by increasing the distance between exit surface 14 and surface 10 accordingly.

If the outlet openings 16 are controlled in such a way that, during the relative movement between the print head 12 and the surface 10, areas of the surface 10 are first printed by print openings arranged in a front row and then in the same operation from outlet openings arranged in a rear row again printing fluid is applied to one already printed surface area is applied, it is advantageous to tilt the exit surface 14 somewhat relative to the direction of the relative movement, so that the distance B of a subsequent row of exit openings 16 from the then already printed surface 10 is increased by the thickness of the already applied layer.

Other aspects that can be taken into account when determining the outlet openings to be activated and the volumes of the liquid droplets to be sprayed are the following:
How out Fig. 1 the ratio between the size of an area of the surface 10 to be printed and the size of the area of the exit surface 14 assigned to it increases in accordance with the reciprocal of the cosine of the angle between the surface area to be printed and the exit surface 14. For a uniform surface density of the printing, it is therefore advantageous if the volumes of the liquid sprayed from the corresponding areas of the exit surface also increase in accordance with the reciprocal of the cosine.

If the liquid droplets strike the surface to be printed at an angle, "blurring" can occur. It is therefore advantageous not to print surface areas which are inclined by more than 6 degrees (decoration) or 12 degrees (lacquer) to the exit surface in a respective printing step.

Fig. 2 shows one of the Fig. 1 Similar view, but with a concavely curved surface 10. As can be seen, the width X of the area that can be printed with perfect droplet quality is given by the fact that the flight distance B is minimal at the edges of the area X and the flight distance C is maximal in the middle of the area.

Based on Fig. 3 further aspects of the invention are explained.

• Wenn in Richtung der Zylinderachse Z (Fig. 4) gesehen eine gemäß Fig. 1 ermittelte zulässige Druckbreite X den gesamten zu bedruckenden Bereich überdeckt, ist es vorteilhaft die zylindrisch gekrümmten Oberfläche in einem Schritt zu bedrucken, bei dem eine Relativbewegung zwischen der Oberfläche und dem Druckkopf in Richtung der Zylinderachse Z erfolgt. Ist die zulässige Breite schmaler als die Breite der zu bedruckenden Oberfläche, so können in aufeinander folgenden Druckschritten nebeneinander liegende Bahnen gedruckt werden. Alternativ kann es vorteilhaft sein, die Bahnen B1, B2, ...BN derart zu legen, dass sie in Umfangsrichtung der zylindrischen Krümmung gerichtet sind, wie in Fig. 4 dargestellt. Es kann dann die volle Breite des Druckkopfes 12 genutzt werden, da die zu bedruckende Oberfläche senkrecht zur Richtung der Relativbewegung zwischen Druckkopf und Oberfläche nicht gekrümmt ist.
• Wenn eine Oberfläche mit zwei senkrecht aufeinander stehenden Krümmungsachsen und unterschiedlichen Krümmungsradien bedruckt werden soll (Fig. 5), und dies nicht in einer einzigen Bahn erfolgen kann, ist es für eine optimale Nutzung der Breite des Druckkopfes 12 vorteilhaft, wenn die Längsrichtung der Bahnen B1, B2 in Umfangsrichtung der Krümmung mit dem kleineren Krümmungsradius gerichtet ist und die Bahnen B1, B2 in Umfangsrichtung der Krümmung mit dem größeren Krümmungsradius benachbart sind. Die Oberfläche 10 der Fig. 5 weist quer zu ihrer Längserstreckung (von links nach rechts in der Figur) eine geringere Wölbung auf als quer zu ihrer Längserstreckung. Es versteht sich, dass die Breiten X1, X2 der Druckbahnen B1, B2 bei sich in Querrichtung der Oberfläche ändernder Wölbung aufgrund der anhand Fig. 1 erläuterten Randbedingungen unterschiedlich sein können. Der Abstand zwischen Druckkopf 12 und der Oberfläche 10 wird während der Relativbewegung zwischen der Oberfläche 10 und dem Druckkopf 12 während des Druckens derart gesteuert, dass die Bedingungen der Fig. 1 ständig erfüllt sind. Die Breite X1, X2 jeder Bahn ist längs deren gesamter Länge vorteilhaft konstant und ist dadurch durch die maximale Wölbung der Oberfläche quer zur Längsrichtung längs der gesamten Länge der Bahn gegeben.

The surface data of an object to be printed, in the example shown, a sphere 22, are stored in a computer 20. On the basis of the curvature of the surface 10 of the ball 22 to be printed, i.e. the radius of the ball, data of the print head 12, such as the diameter of the outlet openings, volumes of the amount of liquid sprayed, consistency of the pressure liquid, etc., the minimum and maximum flight distance of a droplet, as based on Fig. 1 explained, calculated. The maximum printing width X1 with which the surface of the ball can be printed is then calculated on the basis of the ball diameter. The spherical surface is divided into individual segments 24, each of which has the maximum permissible pressure width X1 in an equatorial plane of the sphere. The ball is then printed, for example, in such a way that the print head 12 is at the predetermined distance B ( Fig. 1 ) is arranged above the north pole of the sphere and the sphere is rotated through 360 ° around a horizontal axis (not shown) running in the plane of the drawing. In this case, two diametrically opposite segments 24 are printed. The control of the individual outlet openings 16 of the print head 12 is such that, starting from the poles of the sphere, the width of the printed segment increases up to the maximum width X1 and then decreases again. After the two diametrically opposite segments have been printed, the ball or the print head 12 is rotated about a vertical axis by an angle corresponding to the maximum width X1 of a segment, so that two further, opposite segments can then be printed, etc. Surfaces to be printed only rarely have a spherical or part-spherical shape. Surfaces that are cylindrically curved at least in some areas or that are curved with different radii in mutually perpendicular directions are more common. The following types of printing are advantageous for cylindrically curved surfaces:

• If in the direction of the cylinder axis Z ( Fig. 4 ) seen one according to Fig. 1 If the permissible print width X determined covers the entire area to be printed, it is advantageous to print the cylindrically curved surface in one step in which a relative movement between the surface and the print head takes place in the direction of the cylinder axis Z. If the permissible width is narrower than the width of the surface to be printed, then strips lying next to one another can be printed in successive printing steps. Alternatively, it can be advantageous to lay the webs B1, B2, ... BN in such a way that they are directed in the circumferential direction of the cylindrical curvature, as in FIG Fig. 4 shown. The full width of the print head 12 can then be used, since the surface to be printed is not curved perpendicular to the direction of the relative movement between the print head and the surface.
• If a surface is to be printed with two perpendicular axes of curvature and different radii of curvature ( Fig. 5 ), and this cannot be done in a single path, it is advantageous for optimal use of the width of the print head 12 if the longitudinal direction of the paths B1, B2 is directed in the circumferential direction of the curvature with the smaller radius of curvature and the paths B1, B2 in Circumferential direction of the curvature with the larger radius of curvature are adjacent. The surface 10 of the Fig. 5 has a smaller curvature transversely to its longitudinal extent (from left to right in the figure) than transversely to its longitudinal extent. It goes without saying that the widths X1, X2 of the printing webs B1, B2 in the case of a curvature changing in the transverse direction of the surface due to the Fig. 1 explained boundary conditions can be different. The distance between the print head 12 and the surface 10 is controlled during the relative movement between the surface 10 and the print head 12 during printing such that the conditions of the Fig. 1 are constantly fulfilled. The width X1, X2 of each web is advantageously constant along its entire length and is thereby given by the maximum curvature of the surface transversely to the longitudinal direction along the entire length of the web.

Based on Fig. 6 explains how convex and concave surfaces can be printed in such a way that printed tracks arranged next to one another are formed in a so-called multi-pass process, which merge seamlessly, ie without visible transitions.

The right half of the Fig. 6 shows a convexly curved surface area 10 with an axis of curvature M1. In a first printing step A1, a first web B1 is printed, a relative movement taking place between the print head 12 and the surface 10 in the direction of the axis of curvature M1. The effective printing width of the exit surface 14 leads to a corresponding width X of the web B1. After the web B1 has been formed, there is a relative rotation between the print head 12 and the surface 10 by an angle such that the web B2 applied by the print head 12 in a subsequent printing step A2 seamlessly adjoins the web B1 without overlapping. The control of the relative rotation between printhead 12 and surface 10 between the two printing steps is so precise that according to FIG Fig. 6 on the left edge of the web B2 on the surface 10 droplets exactly to the gem. Fig. 6 The droplets applied to the right edge of the web B1 connect as if they were part of a common wide print web. In this way, the two webs B1, B2 merge seamlessly into one another and a printed surface is created that is composed of the two webs B1 and B2 without a visible seam.

The left half of the Fig. 6 shows the relationships in the case of a concave surface 10 with an axis of curvature M2. As can be seen, after a first web of lead has been applied, relative rotation between the print head 12 and surface 10 is possible in such a way that the second web B2 is applied immediately next to the first web without overlapping with the first web B1, i.e. without a visible transition, next to the first web can.

That based on the Fig. 6 The method explained, in which adjacent webs adjoin each other without overlapping without a visible transition, is advantageously used when the rotational position between the print head 12 and the surface 10 to be printed is only slightly advantageous between the application of two adjacent print webs, for example at an angle less than 6 degrees 2-3 degrees (decor) or less than 12 degrees (paint, conductor tracks, functional surfaces, etc.) is changed. The angle of incidence of the droplets forming one edge of a printed web on the printed surface then differs from the angle of incidence of the droplets forming the adjoining edge of the adjacent web only by the small twist angle, so that the printing of the adjoining edges takes place under largely identical conditions and no change is visible.

The process of printing an adjacent web after printing a web after a slight pivoting between the print head and the surface can indeed lead to narrow webs and thus to an increase in webs in the case of strongly curved surfaces; however, this is beneficial for the print quality.

Fig. 7 shows how, as an alternative to the representation of the Fig. 6 two webs B1 and B2 with mutual overlap can be applied to the surface 10 of a component 26 next to one another. For this purpose, in an electronic data processing system, the relative rotational position between the print head 12 and the surface 10 to be printed is first established for the first printing step A1 during a first printing step A1, in which a first web B1 is applied. Furthermore, the relative rotational position between the print head 12 and the surface 10, which is to be assumed in a second printing step A2, is determined in advance in the electronic data processing system. For the sake of clarity, in Fig. 7 the position of the print head 12 in the second printing step A2 as being further removed from the surface 10 than in the first printing step. Indeed, the distance between printhead 12 and surface 10 is advantageously the same during the first and second printing steps. How out Fig. 7 As can be seen, there is an overlap region 30 between the two previously defined webs B1 and B2, within which the right edge of web B1 overlaps the left edge of web B2. The droplets applied in the second printing step A2 are not shown blackened for the sake of clarity. So that no difference is visible between the print or color intensities of the adjacent webs B1, B2, the area-related droplet density in the overlap region 30 decreases from left to right when the first web B1 is applied. The droplet density of the second printed web B2 increases accordingly from left to right in the overlap area 30, so that overall the same droplet density will exist in the overlap area 30 as in the areas of the webs B1, B2 adjacent to the overlap area 30. It goes without saying that instead of the areal density, the volume of the droplets also changes.

In Fig. 8 a layered structure of the webs B1, B2 is shown, which can be achieved by arranging the layers (4 layers in the example shown) with a single linear relative movement between the print head and the surface Exit opening rows are applied or each layer is applied by its own linear relative movement between the print head and the surface. As can be seen, each of the layers arranged one above the other is constructed differently in the overlap region 30. The areas of the left web B1 forming the overlap area 30 decrease from bottom to top, while the areas of the right web B2 forming the overlap area 30 increase from bottom to top.

For additional quality control, the print head can be provided with sensing devices that sense the color intensity or print density of the layer or web that has already been applied before a new layer or web is applied, so that if there is a discrepancy between a target value and an actual value, the area density and / or size of the droplets can be adjusted after.

That based on the Fig. 7 and 8th described method of applying adjacent webs with mutual overlap, in particular the method according to. Fig. 8 , is particularly advantageous, for example, when the paths are crossed by electrical conductors, which are produced by spraying electrically conductive liquid droplets. The electrical conductors then lead seamlessly from one track to an adjacent track without any disturbance (change in cross-section).

Based on Fig. 9 In the following, a method is explained with which, in particular, curved surfaces 10 can be printed over a large area in excellent quality. The figure shows the relative arrangement of a print head 12 relative to a curved surface 10 to be printed with successive printing steps A1 to A7. The print head 12 has an exit surface with sectors S1 to S4 which are arranged next to one another in the plane of the drawing and extend perpendicular to the plane of the drawing with a predetermined length and each have exit openings. The print head 12 is received in a holder, not shown, with which it can be moved horizontally and vertically in the plane of the drawing. A component 26 provided with the surface 10 to be printed can be tilted by means of a holder 34 about an axis running perpendicular to the plane of the drawing and can be moved perpendicular to the plane of the drawing.

In a first printing step A1, with a relative movement between the surface 10 and the print head 12 perpendicular to the plane of the drawing, a first web B1 is printed only with the activation of outlet openings of the first sector S1. After the first printing step A1, the print head (12) is moved perpendicular to the longitudinal extension of the first web (B1) (perpendicular to the plane of the drawing in the transverse direction (horizontal in the plane of the drawing)) in such a way that the second sector S2 is above the first web B1. Then, in a second printing step A2, the first web B1 is additionally printed from outlet openings of the second sector S2 and a second web B2 arranged next to the first is printed from outlet openings of the first sector S1.

The processes are repeated until, in printing step A4, a fourth web B4 is printed with exit openings of the first sector S1 and the adjacent, already printed webs B1 to B3 are printed from exit openings of sectors S4 to S2.

In further printing steps A5 to A7, no further webs are printed, but after each lateral movement of the print head 12 by the width of a sector, the number of activated sectors, beginning with sector S1, decreases by one sector, so that after the last printing step A7 all lanes B1 to B4 of all sectors S1 to S4 have been printed.

The outlet openings of the individual sectors are, as in the Figure 9 indicated, electronically controlled in such a way that they do not print the respective web with full droplet density, but complete printing of the webs is only achieved in the last printing step, after all webs from all sectors have been printed.

Advantageously, between two printing steps there is not only a linear, horizontal relative movement between the print head 12 and the component 26, but also a tilting of the surface 10 relative to the exit surface 14 such that a distance between the surface 10 and the exit surface 14 remains approximately constant.

The relative movements between print head 12 and component 26 can be adapted to the conditions given by the curvature of surface 10.

If more than that in the Fig. 9 four webs B1 to B4 shown are to be printed, the printing step A4, in which all sectors S1 to S4 are activated, after a respective Movement of the print head 12 perpendicular to the longitudinal extension of the tracks by the width of a sector and, if necessary, tilting of the component 26 can be repeated.

Overall, the procedure according to Fig. 9 achieves that a surface to be printed, after it has been completely covered by the print head through a meandering relative movement between it and the print head, with a printing step taking place during the parallel, straight passages of the meander-shaped path, can be printed homogeneously and with a precisely predetermined surface density. In this way, homogeneous conductor tracks or homogeneous conductive layers, such as. B. OLED layers can be printed without any change in cross-section or resistance.

With the based Fig. 9 The described methods can also be printed on surfaces that have two flat areas of different inclination, which merge into one another in a line-like curved area.

Fig. 10 shows a perspective representation of several print heads 12a, 12b, 12c, 12d, which are received by a common holder (not shown) and combined to form a block, which are arranged one behind the other in the longitudinal direction of the webs B1 to B4. Otherwise the arrangement corresponds to Fig. 9 , the system being in the state after the printing step A4. With the arrangement of the Fig. 10 For example, different liquids (different colors, electrically conductive, non-conductive, transparent, etc.) can be sprayed from the individual print heads simultaneously, so that the surface 10 can be printed with complex patterns and / or layers of constant thickness within a short time. The straight lines of the meandering relative movement between the print heads and the surfaces to be printed are longer than the printed tracks, so that, similar to gem. Fig. 9 the sectors, at the beginning of a path not all print heads are initially activated or the print heads are activated one after the other and at the end of a path not all print heads are activated or are deactivated one after the other.

As can be seen from the above, it is advantageous if a device that enables printing of three-dimensional surfaces largely free of restrictions by means of a digitally controlled printing process, a relative movement between the exit surface 14 of the print head 12 and the surface 10 to be printed or one of these Allows the component having surface both linearly in the three mutually perpendicular directions of the room and rotationally with three mutually perpendicular axes of rotation. It is largely irrelevant whether an electronically controlled mounting of the component and / or an electronically controlled mounting of the print head enables these movabilities.

A device or system for printing three-dimensional surfaces is in Fig. 11 shown schematically:
A holder 34 for receiving a component 26 with a surface 10 to be printed is movably attached to a frame 32. The holder 34 and with it the surface 10 to be printed is linearly movable in the three dimensions of the space by means of known drive devices, such as those used for CNC precision machine tools (not shown) and can be rotated about three mutually perpendicular axes.

A print head 12 (e.g. of the XAAR type 1003 or DIMATIX) composed of several print modules in the example shown, with a flat exit surface 14 in which individually controllable exit openings or nozzles are arranged, is together with a liquid supply 36 on a holder 38 appropriate. Similar to the holder 34, the holder 38 and with it the exit surface 14 of the print head 12 can be moved linearly in the three dimensions of the space by means of known drive devices (not shown) and can be rotated about three mutually perpendicular axes.

The liquid supply 36 can contain different liquid supplies, e.g. B. normal printing inks, special colors, functional fluids with electrically conductive particles, lacquers, primers, fluids for applying electrically insulating layers, etc.

A sensor device 40 is also attached to the holder 38, with which a distance between the exit surface 14 and the surface 10 to be printed can be determined and / or with which an optical property of the surface to be printed or already printed can be detected.

In an electronic control device 42 of a type known per se, geometrical data of the surface 10 to be printed, for example CAD data and decor data, can be stored that contain the imprints to be applied to the surface 10 with the necessary for this Fluid data included. Programs contained in the control device convert the geometric data of the surface 10 and the decor data into control data for controlling the movements of the holders 34, 38, the supply of liquids to the print head 12 and the selection and control of the outlet openings. Values determined by the sensor device 40 can be used to quickly determine target positions, to determine actual positions and printing states on the surface 10.

For example, the holder 38 for the print head 12 is advantageously movable or drivable in the Z direction (distance between the print head and the surface 10 to be printed) and in the Y direction (lateral offset of the print paths). The holder 34 for the component 26 to be printed can advantageously be driven linearly in the X direction (longitudinal direction of a printing web B1, B2) and rotatably driven about the X axis and the Y axis. It is explicitly stated that all range specifications or specifications of groups of units disclose every possible intermediate value or subgroup of units for the purpose of the original disclosure as well as for the purpose of restricting the claimed invention, in particular also as a limit of a range specification.

List of reference symbols

10

surface

12th

Printhead

14th

Exit surface

16

Outlet openings

18th

Distance sensor

20th

computer

22nd

Bullet

24

segment

26th

Component

30th

Overlap area

32

frame

34

bracket

36

Fluid supply

38

bracket

40

Sensing device

42

electronic control

A.

Width of the printhead

A1, A2

Printing steps

B1, B2

Lanes

B.

Minimum flight distance

C.

maximum permissible flight route

M1

Axis of curvature

X

permissible print width

Z

Cylinder axis

Claims (13)

1. Method for printing a curved surface (10) by means of a digital printing process in which defined amounts of liquid are sprayed off from individually controllable outlet openings (16) arranged on a plane exit surface (14) of a print head (12), wherein the amounts of liquid impinge on the curved surface (10) as liquid droplets,
   in which method the curved surface (10) and the exit surface (14) are aligned with one another in such a way that an area of the curved surface (10) is directed parallel to the exit surface (14), wherein this area with a convex curvature of the surface (10) has a minimum distance B from the exit surface (14) and with a concave curvature of the surface (10) has a maximum distance C from the exit surface (14),
   wherein during printing only outlet openings (16) for the discharge of an amount of liquid can be controlled, the distance of which from the point of impact of the liquid discharged by them onto the curved surface (10) is between the minimum distance B and the maximum distance C, wherein the minimum distance B is given by the trajectory which the amount of liquid exiting from the outlet opening (16) requires for formation of a liquid droplet, and the maximum distance C exceeds the minimum distance by a predetermined distance t along which a liquid droplet does not degenerate and its path proceeds in a straight line,
   such that with a relative movement between the exit surface (14) and the surface (10) perpendicular to the curvature of the surface (10), the surface can be printed with a track, the width X of which, with a convex curvature of the surface (10), corresponds to the distance between the outlet openings (10) spaced in the direction of the curvature of the surface (10) with maximum distance C and with concave curvature of the surface (10) corresponds to the distance between the outlet openings (10) spaced apart in the direction of the curvature of the surface (10) with a minimum distance B.
2. Method according to claim 1, wherein the width X of the track is approximately equal to 2 × (t × r)^0,5, when t is small compared to r and r is the radius of curvature of the surface (10) and t is C minus B.
3. Method according to claim 1 or 2, wherein the amount of liquid that is applied to a unit area of the surface by means of liquid droplets, increases with increasing angle between a respective unit area and the exit surface (14) such that the amount of liquid applied to the unit area is constant regardless of the angle.
4. Method according to any one of claims 1 to 3, wherein only outlet openings (16) are activated the liquid droplets of which hit the surface (10) with an impact angle of greater than 78 degrees for painting and greater than 84 degrees for decorative printing.
5. Method according to any one of claims 1 to 4, wherein when printing a surface (10) with two mutually perpendicular axes of curvature and different radii of curvature during a first printing process a relative movement between the print head (12) and the surface (10) to be printed takes place in the circumferential direction of the curvature with the smaller radius of curvature, subsequently, when the outlet openings (16) are not activated, a relative movement between the print head (12) and the surface to be printed (10) takes place in the circumferential direction of the curvature with the larger radius of curvature and then during a further printing process a relative movement between the print head (12) and the surface to be printed (10) takes place in the circumferential direction of the curvature with the smaller radius of curvature, so that tracks (B1, B2) formed during the printing processes are adjacent in the circumferential direction of the curvature with the larger radius of curvature.
6. Method according to any one of claims 1 to 5, wherein with convex or concave curvature of the surface to be printed (10) and its printing in the form of adjacent tracks (B1, B2) the positionings of the exit surface (14) with respect to the surface (10) seen in the direction of the axis of curvature during two successive relative movements between the surface (10) and the exit surface (14) for forming the respective tracks (B1, B2) are such that adjacent tracks within which the liquid can reach the surface (10) abut directly against one another.
7. Method according to any one of claims 1 to 6, wherein with concave or convex curvature of the surface to be printed (10) the positionings of the exit surface (14) relative to the surface (10) in the direction of the axis of curvature during two successive relative movements between the surface (10) and the exit surface (14) for forming a respective track (B1, B2) are such that adjacent tracks within which the liquid can reach the surface (10) overlap each other and the outlet openings (16) of the exit surface (14), from which the overlap area (30) is generated, are controlled in such a way that the amounts of liquid reaching a unit area of the surface (10) are equal in the overlap area (30) and the overlap-free areas of the tracks (B1, B2).
8. Method according to any one of claims 1 to 5, wherein
   the surface (10) is curved and is printed with a plurality of directly adjacent tracks (B1, ....., Bn) perpendicular to its length extension, the exit surface (14) comprises a plurality of directly adjacent sectors (S1, ....., Sm) with outlet openings perpendicular to the longitudinal extension of the tracks (B1, ......, Bn),
   in a first printing step (A1) a first track (B1) is printed only with the first sector (S1),
   after the first printing step the print head (12) is moved perpendicular to the longitudinal extension of the first track such that the second sector (S2) is above the first track (B1),
   then in a second printing step (A2) the first track (B1) is additionally printed with the second sector (S2) and a second track (B2) disposed adjacent to the first track is printed with the first sector (S1),
   the processes are repeated until an m-th track (Bm) is printed with the first sector (S1) and the adjacent, already printed tracks (Bm-1, ......, B1) are printed with sectors (S2, ....., Sm), and
   in further printing steps after a movement of the print head (12) perpendicular to the longitudinal extension of the tracks respectively by the width of a sector with each printing step, the number of activated sectors starting with sector S1 up to Sm decreases, so that after the last printing step all tracks are printed by all sectors (S1, ....., Sm).
9. Method according to claim 8, wherein the printing step, in which all sectors (S1, ....., Sm) are activated, is repeated after a respective movement of the print head (12) perpendicular to the longitudinal extension of the tracks by the width of one sector.
10. Method according to claim 8 or 9, wherein with a movement of the print head (12) perpendicular to the longitudinal extension of the tracks by the width of one sector in each case a tilting of the surface (10) relative to the exit surface (14) takes place such that a distance between the surface (10) and the exit surface (14) remains approximately constant.
11. Device for printing three-dimensional surfaces comprising
    a frame (32);
    a holder (34) for receiving a component (26) with a surface to be printed (10);
    a further holder (38) for receiving at least one print head (12) with an exit surface (14) which comprises outlet openings (16) for spraying off predetermined amounts of liquid;
    a drive device by means of which a relative movement between the exit surface (14) and the surface to be printed (10) can be driven;
    a liquid supply (36) for selective supplying the outlet openings (16) with a printing liquid;
    an electronic control device (42) with geometric data of the surface (10) to be printed and decoration data that include the imprints to be applied to the surface (10) with the liquid data required therefor, and with programs that convert the geometric data of the surface (10) and the decoration data in control data for controlling the drive device, for controlling the supply of liquids to the print head (12) and for selecting and controlling the outlet openings (16), wherein the device operates according to any one of claims 1 to 10.
12. Device according to claim 11, wherein the holder (38) for the print head (12) is movable in the Z direction (distance between print head (12) and surface (10) to be printed) and in the Y direction (width direction of a track (B1, B2)) and the holder (34) for the component (26) to be printed is movable in the X direction (longitudinal direction of a track (B1, B2)) and rotatable around the X axis (longitudinal direction of a track (B1, B2)) and the Y-axis.
13. Device according to claim 11 or 12, comprising a sensor device (40) for determining a distance between the exit surface (14) and the surface (10) to be printed and/or for determining an optical property of the surface to be printed or already printed.

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