Drop-on-demand—coating of surfaces

Abstract

A coating of a coating medium, produced by means of a multichannel printhead (5) in a coating region (3) on a two- or three-dimensional surface (2) of an object (1), which is built up from coating points (8) along tracks (7) of one or more coating paths (6), characterized in that the starting coating point (HP) of at least one track (7) is aligned with a starting contour (AK) and an end coating point (EP) of the track (7) is aligned with an end contour (EK).

Claims

1. A method for applying a coating pattern of a coating agent to a flat or curved surface of an object by means of a print head, which ejects coating agent in jets or drops from a plurality of printing nozzles arranged in at least one row, comprising the steps of: moving the print head at a distance over the surface by means of a coating robot in a plurality of coating paths which contain tracks of coating points corresponding to the printing nozzles, the movement taking place obliquely to a starting contour AK and/or an end contour EK, wherein starting contour AK and end contour EK represent edges of a coating region, determining, for each of the tracks, a respective track length from the starting contour to the end contour, controlling the individual nozzles of the print head in such a way that the starting coating points AP of the tracks touch the starting contour AK tangentially or have a constant distance from the starting contour AK or that the end coating points EP of the tracks touch the end contour (EK) tangentially or have a constant distance from the end contour EK and that, for each of the tracks, further points are distributed depending on the respective track length between the respective starting coating point AP and the respective end coating point EP.

2. A method according to claim 1, wherein starting coating points AP of the tracks contact the starting contour (AK) tangentially or are at a constant distance from the starting contour AK, and additionally end coating points EP of the tracks contact the final contour (EK) tangentially or are at a constant distance from the final contour EK.

3. A method according to claim 2, wherein the control of the individual nozzles of the print head is carried out in such a way that the tracks between the starting coating points AP and end coating points EP contain further coating points which are arranged equidistantly and that the distances between adjacent coating points of at least two tracks are not identical.

4. A method according to claim 3, wherein the number of further coating points of the tracks between the starting coating points AP and end coating points EP is determined at least in sections in such a way that the distance between the coating points of the tracks is of the order of magnitude of the distance between adjacent tracks.

5. A method according to claim 1, wherein at least a selection of coating points additionally have an individual stochastic offset (Ad) along the track in positive or negative track direction to adjacent points.

6. A method according to claim 1, wherein the volume of the drops from the plurality of printing nozzles is adapted in such a way that the coating thickness of the coating agent is constant on average.

7. A method according to claim 1, wherein at least one section of the coating path has a curvature about a line perpendicular to the surface.

8. A method according to claim 1, wherein the coating path is reduced in its width at least in one section thereof and the volume of the drops from the plurality of printing nozzles and/or the distance of the coating points from one another is adapted in such a way that the coating thickness of the coating agent is constant on average along the coating path section of reduced width.

9. A method according to claim 1, wherein the coating paths run predominantly tangentially inwardly offset one or more times to the straight or curved edges of the coating pattern, the coating paths being connected laterally to one another without gaps.

10. A method according to claim 9, wherein at least a part of the coating pattern contains coating paths which have predominantly parallel, straight or curved coating path sections.

11. A method according to claim 1, wherein individual area elements of the coating pattern contain a free dot pattern generated by a single print nozzle of the print head.

12. A method according to claim 11, wherein the free dot pattern contains coating points which differ substantially in size from the average size of the coating points of the coating pattern.

13. A method according to claim 1, wherein the starting coating point AP and the end coating point EP of a track are identical.

14. A method according to claim 1, wherein in sections of the coating pattern which are located on the surface of the object which are rotationally symmetrically shaped at least in part with respect to an axis, the coating paths are arranged in such a way that a main direction HR of the coating paths runs tangentially to the surface in a direction of rotation about the axis at least in those sections.

15. A method according to claim 1, wherein at least in parts of the coating pattern the coating points lie on circular tracks, whose axis of rotation coincides with the axis of a print nozzle of the print head.

16. A method according to claim 1, wherein the coating paths comprise a first coating path and a second coating path that overlaps with the first coating path, whereby in an overlap area portions defined by auxiliary contours are divided between the first coating path and the second coating path.

17. A method according to claim 1, wherein the coating paths comprise a first coating path and a second coating path, and the first and second coating paths overlap laterally creating an overlap region and in the overlap region at least a first track corresponding to the first coating path and a second track corresponding to the second coating path are substantially congruent and coating points are divided among the first and second tracks and in such a way that the first and second tracks and together form a continuous coating.

18. A method according to claim 17, wherein in the overlap region at least one printing dot is at least 20% smaller than its adjacent printing dot.

19. A method according to claim 1, wherein the coating agent is glazed and the coating pattern contains graphic elements.

20. A method according to claim 1, wherein the coating pattern contains at least one further coating of a further coating agent.

21. A method according to claim 1 further comprising the following steps: execution of a print data generation in a data processing system on the basis of a first data set describing the surface of the object and a second data set describing the coating region, with the following sub-steps: loading of the data sets and establishment of geometric relationships; generating coating paths and their tracks in such a way that the coating region is at least completely covered by coating paths, taking into account a distance DD between the print head and the surface; determining the position of the starting coating points AP and/or end coating points EP of the tracks on contours which cross the tracks at an angle, so that these touch the contours tangentially and/or so that these have a constant distance to the points of intersection of the contours with the tracks; if necessary, filling up further coating points on the tracks between the starting coating point AP and the end coating point EP and determining the point spacing between adjacent coating points on the tracks; if necessary, correcting the drop size of the coating points so that a target layer thickness is achieved; generating a print data set containing coating point-specific data elements, each containing at least one time or location-related information and one volume-related information for one or more coating points; generating motion data for the control of a coating robot taking into account the distance DD; transferring the print data set to a real-time print head control; transferring the motion data to the coating robot controller; performing the coating process based on the print data and motion data.

Description

(1) Before further designs and devices, processes, possible path forms and coating strategies according to the invention are presented, the following list is intended to give an overview of the figures:

(2) FIG. 1 serves to define the nomenclatures used.

(3) FIG. 2 shows a coating result for a coating region 3 at the current prior art in grid graphics.

(4) FIG. 3a illustrates the elements of the print image according to the invention using an exemplary coating path 6 with track 7 and coating points 8 in combination with contours 4.

(5) FIG. 3b shows an example of the coating result according to the inventive principle for a coating region 3 as in FIG. 2.

(6) FIG. 4 shows a current prior art coating result in grid graphics for two adjacent coating paths 6a and 6b whose path directions have an angular difference of <5 degrees.

(7) FIG. 5 shows the coating result of the case of FIG. 4a after application of the inventive teaching and printing strategies.

(8) FIG. 6 shows the coating result after application of the inventive teaching and a printing strategy for a coating region with four curved edges. Here, the coating points 8 are distributed on tracks 7, the course of which results from a simultaneous rotation of the coating head 8 during the movement of the coating head 8 along the coating path 6.

(9) FIG. 7a illustrates three strategies for printing a coating region of any shape 3.

(10) FIG. 7b shows an example of a coating strategy for reproducing the print pattern “P” without step formation and with a coating path running around the circumference.

(11) FIG. 8 shows the detail A in FIG. 7a magnified, so that the individual print dots 8 can be identified, thus illustrating the coating path guidance and angular positions of the coating heads 5 at different times.

(12) FIG. 9 shows an example of a coating strategy for illustrating circular or even elliptical dot patterns.

(13) FIG. 10a shows an example of the lateral connection of two coating paths 6a and 6b by means of an overlap area 10 using a jagged contour (“stitching”).

(14) FIG. 10b shows an example of the connection of two coating paths 6a and 6b by means of an overlap area 10 with essentially free distribution of printing points 8 between congruent tracks 7 of the two coating paths.

(15) FIG. 11 shows essential nomenclatures in connection with printing points—generation on one track s.sub.i,j.

(16) FIG. 12 shows an example of the temporal sequence of firing times to the seven printing nozzles 8 of a coating head 5, for example, when moving along a curved coating segment.

(17) FIG. 13 schematically shows a system structure for the application of coating regions 3 to three-dimensional surfaces 2 of objects 1 according to the invention.

(18) FIG. 14 illustrates essential elements of an algorithm of a microprocessor within a real-time head control 18 for the time-asynchronous control of printing nozzles of a coating head 5.

(19) FIG. 15 shows an example of a possible data format for the communication of print data to the real-time head control 18.

(20) FIG. 16 illustrates an example of essential steps of the process flow in a data processing system for the creation of coating strategies, coating path paths and dot patterns according to the invention.

(21) FIG. 17 illustrates a further strategy for reducing the optical perceptibility of the connection between two coating paths 6 by distributing the coating points 8 over several layers L in a data processing system.

(22) FIG. 18 illustrates a sequence of coating steps BS circulating over 2 layers, where the individual structures 20 of the two layers are lines.

(23) FIG. 19 shows a hexagonal pattern of coating points to illustrate related coating strategies.

(24) FIG. 20 illustrates exemplary orientations for the coating paths 6 and an associated track 7 for a hexagonal pattern related coating strategy.

LIST OF REFERENCE SIGNS AND LETTER ABBREVIATIONS

(25) 1 Object 2 Surface 3 Coating region 4 General edge contour 5 Coating head 6 Coating sheet 6a First coating path 6b Second coating sheet 7 Track of a printing nozzle 8 Coating point 9 Edge of a coating path 10 Overlap area 11 Rotation axis 12 Firing time 14 Coating robot 15 3D measuring unit 16 DP system 17 Real-time process control 18 Real-time head control 20 Individual structure 21 Spaces, gaps HR (H1, H2, H4, H4) Main direction one coating path AK Starting contour EK End contour SKA Side edge of a coating path AP Starting coating point EP End coating point BS Coating step L Layer A Section PM Dot pattern of a layer

(26) As shown above, the coating region according to the invention can help to minimize step formation on starting and end contours as far as possible. Thus, in order to reproduce them in the described manner, the first possibility is to arrange coating paths 6, with respect to a general contour, like for example an edge of the coating region 3 or another coating path 6, that they represent starting contours AK or end contours EK of the coating path, thus that either the starting coating points AP or end coating points EP are aligned with this contour. This is advantageous if the edge to the main direction HR of a coating path 6 or of each track 7 forms an angle between preferably between 15° and 165°, especially preferably between 60° and 120° at the intersection with the contour.

(27) In principle, the coating process according to the invention (see below) allows the general use of curved coating paths 6, since different surface speeds v_S of the tracks 7 of the printing nozzles can be compensated by individual individual-nozzle control in such a way that it is possible to vary independently by adjusting the individual drop frequencies of the nozzles to their individual surface speed v_S.

(28) During the digital print preparation stage (classic: prepress), there are extensive possibilities for planning the coating paths 6 by also or predominantly using curved coating paths 6. This is particularly advantageous in the case of three-dimensional curved surfaces 2.

(29) According to the invention, it is therefore also possible to align a coating path 6 parallel to a curved contour. One side edge SKA of the coating path 6 is brought into exact alignment with the contour or has a parallel offset to it, i.e. a positive or negative offset.

(30) Basically, the track lengths of the tracks 7 of a coating path 6 differ according to the radius of curvature of the track curve. Inner tracks 7 are shorter than outer tracks. According to the invention, so many coating points are inserted on track 7 between the start and end coating points of each track 7, that the dot pitch d_k is approximated as close as possible to the original dot pitch p_xy. In this way, the layer thickness of a coating path 6 remains constant over the entire width, even with curvatures.

(31) A rotation of the coating head, which causes the row of nozzles of a coating head to change its orientation relative to the main direction HR of a coating path over time, automatically results in a change of the width of the applied coating path. FIG. 5 illustrates this possibility, with reference to the print image and process according to the invention. In order to avoid an increase in the coating thickness when the printing width is reduced, the application of the print image and process according to the invention thus includes the possibility that the width of the coating path 6 is reduced at least in one section and that the drop volume and/or the distance of the coating points 8 from each other is adapted to this section. Thus, the two parameters dot pitch and drop volume are available for a coating thickness correction.

(32) These possibilities result in a variety of coating strategies to coat arbitrarily shaped coating region 3 using curved coating paths 6. FIG. 7a illustrates 2 the use of two possible strategies. In the vicinity of the edges of coating region 3, the coating paths 6 are mainly tangentially offset inward one or more times to the straight or curved edges 4 of coating region 3, with the coating paths 6 being adjacent to each other without gaps.

(33) There are different ways in which the different coating paths 6 can be connected to each other, especially in the start and end areas. A small selection is shown in FIG. 7a in details A, B, C. and in FIG. 7b in detail D.

(34) If the side edge SKA of a first coating path 6a coincides with a first contour and the side edge SKA of a second coating path 6b coincides with a second contour and the two contours enclose an angle of preferably between 60° and 120°, then the connection of the two coating paths shown in detail A is advantageous. This is shown enlarged in FIG. 8. In this case, the second contour is preferably used as starting AK or end contour EK of coating path 6. In the case of FIG. 7a and FIG. 8, the first and second contours are each edge contours 4 of the coating region 3. As shown in FIGS. 7a and 8, the second coating agent path 6b, which connects to a first coating agent path 6a, is attached with its starting contour AK to the side edge SKA of the first coating agent path 6a. The side edge SKA of the second coating agent path 6b and the end contour of the first coating agent path 6a are on a common contour which coincides with the edge contour 4 of the coating agent area.

(35) If the side edge SKA of a first coating path 6a coincides with a first contour and the side edge SKA of a second coating path 6b coincides with a second contour and the two contours enclose an angle of preferably between 120° and 180°, then the connection of the two coating paths shown in detail B in FIG. 7a is advantageous. In this case, the connection of the two coating paths 6a and 6b is designed in such a way that the end contour EK of the first coating sheet 6a coincides with the starting contour AK of the first coating path 6a. Detail D in FIG. 7b is intended to demonstrate that it is also possible to realize small radii within a coating path 6. In this case, it is not necessary to connect a further coating path.

(36) As shown in the center of FIG. 7a, another part of the coating region 3 contains coating paths 6, which have predominantly parallel, straight or curved coating path pieces 6. These have start and end contours, which in the example shown are predominantly side edges SKA of other coating paths 6.

(37) Despite the many possibilities of using curved coating agent paths 6, it may still be possible that individual smaller areas, especially in corners, cannot be optimally coated in the form of coating agent paths 6. According to the invention, it is suggested here that individual area elements of the coating region 3 contain a free dot pattern, which is generated by a single printing nozzle of the coating head 5. It may be advantageous to use coating points 8 of different sizes and to select the position of the coating points and their individual drop volume in such a way that the area element is coated with a given coating thickness, taking into account the flow. Thus, the coating contains areas with a free dot pattern containing coating points 8 that differ significantly in size from the average size of the coating points 8 of coating region 3; see detail C in FIG. 7a.

(38) According to the invention, parts of the coating on a surface 2 of the object 1 may have a dot pattern 8 which is arranged in a circle about an axis 11. This can, for example, as shown in FIG. 9, be perpendicular to surface 2, but can also be at any angle in space. Thus, for example, surface 2 in a subarea can itself be the result of the rotation of a one-dimensional surface contour about an axis 11 in space. Examples are a sphere, a pyramid, a cone or a cigar, or the fuselage of an airplane. In order to coat these surfaces, individual coating paths 6 run parallel to each other and circularly about the rotation axis 11, whereby at least individual coating paths 6 can perform a full rotation of 360 degrees, so that the end contour EK coincides with the starting contour AK of the same coating path 6a or 6b (FIG. 9). According to the invention, the coating paths 6 can then also be arranged in such a way that they are also rotationally symmetrical about rotation axis 10 relative to surface 2. Thus, according to the invention, a coating is proposed, characterized in that in coating regions 3, which are located on a surface 2 of the object 1, which is rotationally symmetrically formed at least in parts about an axis 11, the coating paths 6 are arranged in such a way that the main direction HR is tangential to the surface 2 at least in areas in the direction of rotation.

(39) A special case is characterized in that at least parts of the coating region 3 contain a rotation pattern, whereby at least in parts of the coating region 3 the printing points 8 lie on circular tracks 7, the axis of rotation 11 of which coincides with the axis of a printing nozzle of the coating head 5. In this case, a pure rotation of the coating head takes place; see coating path 6b in FIG. 9.

(40) In a special case, a coating is further characterized in that the starting coating point AP and end coating point EP of a track 7 are identical. In this case, the resulting round, but preferably elongated or line-shaped coating point 8 can be aligned to a starting contour AK and an end contour EK in such a way that it is touched by these contours on opposite sides.

(41) A variety of other coating strategies are conceivable, for example based on segmental arc patterns, hexagonal patterns, or coating in spiral or elliptical paths. All these are made possible by the inventive basic idea defined by the features of claim 1.

(42) One difficulty can always be to join two coating paths 6a and 6b together in such a way that no coating defects are visible. The eye is particularly sensitive to even faint signs of lines, which should be avoided, if possible. “Stitching,” a technique known from printing technology, can also be applied to the process according to the invention: here, two adjacent paths 6a and 6b are positioned in such a way that they overlap each other in an overlap area 10. An auxiliary contour is then inserted into this overlap area, which does not correspond to an elongated line. In stitching, for example, this is a zigzag line. The coating points in this area are then divided between the two coating paths 6a and 6b. This case is shown in FIG. 10a.

(43) Thus, according to the invention, a coating is proposed, characterized in that two coating paths 6a and 6b overlap, whereby in an overlap area 10 areas defined by auxiliary contours are divided between the first coating path 6a and the second coating path 6b. Any edge contours of a coating path 6a can be overlapped with any edge contour of another coating path 6b. Also, individual tracks 7 of the two coating paths 6a and 6b within the overlap area need not be congruent.

(44) FIG. 10b shows as an example that in an overlap area 10 individual coating points 8 or groups of coating points can be freely assigned to a coating path 6a or 6b. For this purpose, it is advantageous if the coating paths 6a and 6b overlap in such a way that at least one track 7a of the coating path 6a is congruent with a track 7b of the coating path 6b and coating points 8 of these tracks are divided among the coating paths 6a and 6b. Thus, according to the invention, a coating is proposed, characterized in that two coating paths 6a and 6b laterally overlap in such a way that in the overlap area 10 at least one track 7a of the first coating path 6a and one track 7b of the second coating path 6b are substantially congruent and coating points 8 of these tracks are divided among the tracks 7a and 7b in such a way that the tracks 7a and 7b together form a continuous coating. At least one coating point 8 in the overlap area 10 can be at least 20% smaller than its neighboring coating point.

(45) In a further embodiment according to the invention, the coating agent is glazed, i.e. at least partially transparent, for example a glazed paint or glazed varnish. In particular, this can also be a varnish or ink in one of the primary colors yellow, magenta, black or cyan. In particular, it can also contain any graphic pattern within coating region 3. If a glazed coating agent is used, optical properties of the substrate or other coatings present underneath the coating may shine through the coating. In this context, a coating agent should also be regarded as glazed if it contains pigments or scattering particles that are significantly larger than the scattered light wavelength, but are only present in the coating agent in such a small load that the coating produced from it is at least partially transparent.

(46) According to the invention, a coating according to one of the preceding claims can then be characterized in that coating region 3 contains at least one further coating of a further coating agent.

(47) At this point, it should be noted that the coating according to the invention can serve both functional purposes such as the protection of the surface against environmental influences or the modification of the physical or chemical properties of the surfaces (wettability, gloss, reflectivity, electrical conductivity or insulation, smoothing and filling, stone impact resistance, and many others), but essentially also for the optical decoration or graphic design of the abovementioned surfaces 2. Thus, the inventive teaching is also transferable to the field of inkjet printing, provided that the processes for print data preparation and control of print heads described below are also implemented. In this way, the effective resolution of today's printing processes can be increased by means of intelligent motion automation and coating process technology alone, or a desired resolution can be achieved using more cost-effective print heads that only offer a lower resolution.

(48) For this purpose, it is not necessary to apply the invention's methods to all details of an image. It is sufficient to extract selected high-contrast graphic elements such as corners, borders and edges using pattern recognition algorithms and to assign them to the contours according to the invention for the application of the inventive teaching.

(49) The generation of the coating according to the invention requires devices and processes that are presented in the following: To explain the inventive process for producing the coating according to the invention, the nomenclatures in FIG. 11 are based on a track s.sub.i,j of a coating path Bi, on which coating points P.sub.i,j,k are located, which have a distance d.sub.i,j,k to their subsequent coating points P.sub.i,j,k+1. The track s.sub.i,J extends from an starting coating point AP to and including an end coating point EP. The indices have the following meaning:

(50) Path index: i=1 . . . m

(51) Track index on the path: j=1 . . . b

(52) Index of a coating point 8 on the: k=1 . . . n

(53) The number b of tracks corresponds to the number of printing nozzles of a coating head 5, wherein several track segments can be present within a track 7, as in the case of track 7a of path 6a in FIG. 10a, which consists of three track segments. In this case, the method for placing the coating points 8 according to the invention can be applied to each of these track segments.

(54) The index k shows that the number of coating points n on the different tracks 7 is not a constant but a variable. In the case of circular tracks, for example, the track with the largest track radius has the most coating points. Tracks that cross one or more contours that define coating-free areas have a smaller number n of coating points 8.

(55) The basic principle for the temporal control is illustrated in FIG. 12 using a short path segment for a curvature. The coating of this segment takes place between a start time t1 and an end time t2. The individual printing nozzles are shown as circles within the coating head 5. Within the time interval the coating head 5 has moved and rotated. The firing times 12 were calculated in such a way that the coating points of each track have a constant distance d.sub.i,j,k to their following point. This corresponds to the value d_p derived above. The circular motion results in different time intervals Δt between the firing times 12 for each printing nozzle on each track. The time sequence of the firing times 12 for the nozzles or tracks s1 to s7 is shown in 7 diagrams.

(56) To illustrate the indexing, the time intervals Δt.sub.i,j,k are given for selected firing times, for example Δt.sub.111 and Δt.sub.112 in track s1 or Δt.sub.171 or Δt.sub.171 in track s7. The time intervals Δt.sub.i,j,k result from the track velocities v.sub.i,j,k, which are derived vectorially from the track velocity in main direction H and coating head rotation before in a way known to the average person skilled in the art. v.sub.i,j,k is the velocity of the printing nozzle of the coating path i of track j, when the coating point k is applied. This results in:
Δt.sub.i,j,k=d.sub.i,j,k/v.sub.i,j,k

(57) To determine the target time 12 for the delivery of a single coating point 8 of each track j, the value Δt.sub.i,j,k is added to the firing time of the previous dot. The implementation of the procedure requires the adherence to an exact time and sequence plan for all movements and rotations of the coating head, which has to be ensured by the coating robot. The process runs in real time, so that usually the values v.sub.i,j,k(t) or Δt.sub.i,j,k(t) are tracked as a function of a global running variable “time” t in a computing unit. In addition or alternatively, the movement and synchronization of the delivery points for coating points 8 can include the real-time tracking of the actual movement kinematics (time, location, speed) e.g. from sensor measurements, i.e. from actual data of the movement processing, or basically on the basis of a track-specific running variable ξ (see FIG. 11), which can be either a time variable or can represent a covered distance.

(58) In total, various system components are required to be able to implement the coating process according to the invention. In FIG. 13, the most important components are only shown in a simplified form. In a data processing system 16, a programmer carries out the coating path planning offline according to the teachings of the present invention. This process can also be called pre-press. For this purpose, data of the surface 2 of the object 1 and the coating region 3 are processed. Data of the surface 2 may already exist in digital form from the design documents of the object 1. Alternatively, they can also be obtained by surface measurement using an optical 3D measurement 15. As a result of the prepress stage, at least one print data set is transmitted to the real-time head control 18, which contains the path-related print data, the format of which is suggested in the context of the invention below. Motion data and control data for the coating robot 17 are transmitted to a real-time data processing system 17 and further configuration and control data are transmitted to the real-time head control 18.

(59) The real-time process comprises the motion control of the coating robot 14, the control of the printing nozzles in the coating head by means of the real-time head control 18, as well as all functions of the coating agent supply,—pressure regulation—temperature control, the coating agent change and rinsing steps, the coating head maintenance and cleaning, and the real-time monitoring of the coating processes, preparation of the surface and drying of the coating.

(60) According to the invention, a data format is proposed which can be called an asynchronous printing process. Since in the inkjet printing technology all the nozzles in a row in a coating head 5 are fired synchronously, purely pixel-based data sets are sufficient. Usually, only the color values of the individual pixels are transmitted to the nozzles in such a way that they can be processed quickly enough in parallel at the next firing time.

(61) The method according to the invention requires at least one data pair of information for each coating point 8: A first value is a temporal information Θ.sub.i,j,k regarding the firing time of a coating point k on a track j on a path i. This value can be an absolute value T.sub.i,j,k, which increases continuously with each coating point, or an incremental value, such as the abovementioned time interval Δt.sub.i,j,k. The second value is, as in the conventional data format, a value defining the drop volume V.sub.i,j,k. Thus, each coating point 8 with the data pair (Θ.sub.i,j,k, V.sub.i,j,k) is uniquely determined.

(62) There are many possibilities to store the data pairs in a data format, which can be retrieved serially as efficiently and easily as possible.

(63) One possibility is to store all tracks of all paths for all coating points in e.g. this hierarchical way. Or it is always possible to store a number n of consecutive identical data pairs for example by the data triplet (n, Θ.sub.i,j,k, V.sub.i,j,k). This is for example the case with straight or constantly curved coating paths 6, which already covers many cases.

(64) In general, a coating path can be divided into several segments in such a way that the most efficient data representation in the form of data blocks is achieved. In FIG. 14, a format is proposed that includes a simple classification in the form of path segment types, thus enabling resource-saving real-time processing. It should be noted here that due to the division into path segments in the following description of FIG. 15, path segment-related data pairs are assumed which use the segment index i instead of the path index i: (Θ.sub.ξ,j,k, V.sub.ξ,j,k). Different segments of a path are treated like different paths in terms of data technology. After a header, which may contain project data (objects, surface, template coating region, customer, coating agent, thinner, print parameters . . . ) or detailed information about the print job (number of paths, segments, tracks, coating points, calibration values, type of graphic, data format, coding), the file is structured, for example, according to coating paths, including path segments ξ.

(65) The data block of a path segment contains the type specification (type 1: rectangular pattern, type 2 circular arc, type 3 any pattern) followed by the number n of dots of each track followed by the data pairs (Θ.sub.ξ,j,k, V.sub.ξ,j,k) in each case.

(66) In the simplest case of a rectangular pattern, for example, it is sufficient to specify the number of coating points for a track 7, since all tracks are identical, as well as a single data pair (Θ.sub.ξ,j,k, V.sub.ξ,j,k), if it is a coating region without any other internal patterns (.fwdarw.type 1). In the case of a circular arc, a data pair (Θ.sub.ξ,j,k, V.sub.ξ,j,k) must be specified for each track s.sub.j so that despite different track speeds, individual constant dot pitches d_p are given on each track, if this is planned (.fwdarw.type 2). The path segment type 3 is reserved for the general case, where each coating point 8 is assigned an individual drop volume and an individual firing time.

(67) It should be noted that only individual segment types are worked out and given here as examples and that the multitude of possibilities cannot be dealt with exhaustively. All these are based on the inventive generation of coating points 8 of all tracks 7 of all coating paths 6.

(68) The following is a description of the real-time coating head control process: in order to achieve a low-delay processing of the data pairs, they must first be temporarily stored in a working memory, buffer or data buffer, where they can be quickly retrieved. In contrast to the conventional coating head control, the coating head control according to the invention has a separate time control for each printing nozzle, which is able to convert the individual firing times into delay-free firing commands. Before each delivery of a coating point 8, an individual firing time can be defined. The principle of time control is explained at an individual printing nozzle: in a first step a data pair from a time information and drop size indication (Θ.sub.ξ,j,k, V.sub.ξ,j,k) is loaded. The time information is already available here in simplified form as fire time T_next. In a loop the system time of a microprocessor is continuously compared with the target firing time T_next with microsecond accuracy (“polling”) and a drop release is triggered immediately after exceeding this time. Then the data pair for the next coating point on the track is loaded and the process is repeated.

(69) If the coating head has a larger number of printing nozzles, the time queries are performed sequentially in a sub-loop for all printing nozzles and after firing a nozzle j the corresponding data pair for this nozzle is reloaded; see here the flow chart in FIG. 14. Depending on the number of printing nozzles, this may already require a powerful microcontroller. In particular, the firing and reloading of new print data always requires a higher number of clock cycles, which can lead to an impairment of the print image, if the firing times of two print nozzles are very close together. Therefore, parallel computers, e.g. FPGAs, are generally better suited for this purpose. It should also be mentioned that real-time trigger signals for given programmed events are always transmitted from the real-time process control to the real-time coating head control, for example to start, pause or stop the print drop generation process, or to initiate pre-programmed process cycles for cleaning or changing the coating agent or for changing parameter sets.

(70) Thus, according to the invention, methods for producing a coating on a two- or three-dimensional surface 2 of an object 1 in the form of a coating region 3 with the aid of a coating head 5, which is introduced along one or more coating paths 6, consisting of one or more tracks 7 of coating points 8 of a coating agent, are also guided over the surface 2 at a distance DD, characterized in that the starting coating point AP of at least one track 7 is applied in alignment with a starting contour AK and the end coating point EP of track 7 is applied in alignment with an end contour EK. Further coating points 8 on track 7 can be applied between a start coating point AP and an end coating point EP of at least one track 7 in a fitted manner, which can be done in such a way that a coating according to claims 1 to 19 results.

(71) The technical process from the generation of coating data to the application of the coating can be described approximately by the following steps:

(72) (a) The implementation of a print data generation in a data processing system on the basis of a first data set describing the surface 2 of the object and a second data set describing the coating region 3, with the following sub-steps; see also FIG. 16:

(73) Loading of the two data sets and establishment of geometrical relations. These describe the geometric position of the coating region in relation to the geometric data of surface 2. The generation of coating paths Bi and their tracks s.sub.j in such a way that the coating region 3 is at least completely covered by coating paths, taking into account the number and distance of the printing nozzles in the coating head and the distance DD to be maintained between coating head 5 and surface 2. For further use, the intended coating head velocities vj(ξ) and curvatures φj(ξ) are calculated for all tracks sj. Determining the starting coating points APi and end coating points EPi of all tracks 7 on contours 4 that cross tracks 7. If necessary, filling up further coating points 8 on tracks 7 between the start coating point AP and the end coating point EP and determining the dot pitches between adjacent coating points 8 on tracks 7. If, as in most cases, the coating points on track 7 are distributed equidistantly, then, in a subsequent step, first the path lengths Lj of the track segments sj of all printing paths i are determined, then the dot pitches dj of adjacent coating points 8 are calculated for all tracks j printing paths i; the dot pitches are converted into control times for the firing of the printing nozzles for droplet delivery; the speeds vj(ξ) and curvatures φj(ξ) of all tracks sj calculated above are used for this. If necessary, a correction of the drop size of the coating points 8 is made so that a target coating thickness is achieved. The generation of a print data set, which contains coating point-specific data elements, each containing at least one time or location-related information and one volume-related information for one or more coating points 8. The generation of motion data for the control of a coating robot under consideration of the distance DD.
(b) Transferring the print data set to the real-time coating head control.
(c) Transferring the motion data to the control of the coating robot.
(d) Finally, performing the coating process based on the print data and motion data including drying processes.

(74) The coating process is performed with a device for producing a coating on a two- or three-dimensional surface 2 of an object 1 in the form of a coating region 3, composed of coating points 8 of a coating agent, which are arranged along one or more tracks 7 one or more coating paths 6, characterized in that

(75) a data processing system 16 for generating a print data record, which contains coating point-specific data elements, each of which contains at least one time or location-related information and one volume-related information on one or more coating points 8, and for generating the path and control data of the coating process,
a real-time process control 17,
a coating robot 14 to move the coating head at a distance DD above the surface 2 of the object 1,
a real-time coating head controller configured to asynchronously control at least two print nozzles of the coating head, so that the starting coating points AP and end coating points EP of tracks 7 are adapted to contours 4 crossing tracks 7,
a coating head 5 with at least one row of printing nozzles suitable for applying the coating agent in discrete quantities to the surface without contact.

(76) In addition to the measures described in FIG. 10a and FIG. 10b for reducing the optical perceptibility of the connection between two coating paths 6 within a coating region 3, such as 6a and 6b, other strategies in accordance with the invention are suitable, which are described below:

(77) The basic idea of these further strategies is that the coating points 8 of the coating region 3 are distributed in a first process step A (FIG. 17: Example dot pattern) to n virtual coating layers, in the following briefly called layer L. The distribution of the coating points 8 to different layers L.sub.i, i=1 . . . n, is done in a data processing system or a printer driver. Thus, each layer L.sub.i contains a subset of all coating points 8 of the coating region 3, which is called dot pattern PM.sub.i of layer L.sub.i. The dot patterns PM.sub.i of all layers L.sub.i complement each other after processing all layers L to a complete coating.

(78) As illustrated in FIG. 17, dot patterns PM are composed of dots, dot groups or lines (FIG. 18), preferably arranged in regular intervals over the coating region 3, in the following referred to as individual structures 20, between which gaps 21 are located, which are filled by individual structures 20 of the remaining layer L.

(79) An essential feature is that the dot patterns PM.sub.i of the individual layer L.sub.i are such that they occupy the gaps in the dot patterns PM.sub.j of the other layer L.sub.j, and that coating points 8 of different layers do not coincide locally, i.e. do not have the same position. Thus, the dot patterns PM of the different layer L are complementary. A complete coating requires the processing of all layers L.sub.i.

(80) The different layers L.sub.i are applied to the surface 2 in a second process step B (FIG. 18: Example line pattern), the application step, with one or more, but usually a multitude of n coating steps BS.sub.1 to BS according to a processing strategy using a coating head 5. A coating step BS includes exclusively all individual structures 20 of a single layer L. For example, a coating step BS includes all individual structures 20 of a single coating path 6 from a layer L, if a coating head 5 is guided over the object.

(81) Coating points 8 associated with the same layer L can have identical or different dot sizes on the surface 2, corresponding to lines of identical or different line widths. Similarly, coating points 8 associated with different layers L.sub.i may have identical or different dot sizes on surface 2, corresponding to lines of identical or different line widths. Dot size and line width result from the drop-on-demand drop size, the kinetics and the surface condition.

(82) The aim should be that the drop size or line width of the first coating step BS.sub.1 applied at one point on surface 2 in the processing sequence is selected small enough that the individual structures 20 (dots or lines) of the layer L.sub.i associated with BS.sub.1 are imaged on the surface as isolated individual structures 20, i.e. as isolated dots and/or lines that do not or only slightly touch each other and do not or only slightly run into each other. It should be ensured that, due to tolerances of, for example, the drop-on-demand technology, the application processes or the substrate properties (e.g. surface texture or local differences in wettability), isolated or increased contact between the mentioned printing dots or lines may occur.

(83) It may also be advantageous if the drop size or line width of the last coating step BS.sub.n applied at a point on surface 2 in the processing sequence is larger than the drop size or line width applied at this point in the previous coating steps BS.sub.i and is selected large enough to ensure that any gaps in the coating are completely filled with coating material.

(84) Preferred processing strategies are described below. It is essential that the individual structures 20 processed during a coating step BS originate from only one individual layer L.

(85) Preferably, a coating head 5 is guided over the surface 2 of a (3-dimensional) object 1 due to its limited width in adjoining coating paths 6. Preferably, all individual structures 20 of a layer L, which are covered by a respective coating path 6, are applied. The individual structures 20 applied to the surface 2 in a coating step BS originate from a single layer L.

(86) According to a first processing strategy, all individual structures 20 of a layer L.sub.i are first applied by one or more coating steps BS, followed by those of the remaining layers. This means, for example, that in the case of two layers L (n=2), the individual structures 20 of both layers L.sub.1 and L.sub.2 are applied completely one after the other to the surface 2, e.g. by a multitude of coating paths 6.

(87) Since the coating of surfaces in the drop-on-demand process is based on the fact that adjacent coating points must come into contact with each other while still wet in order to form a coherent layer by the mutual interlacing (flow) of the coating agent, the processing strategy just described can only be applied if it is ensured that the individual structures 20 of the first layer L.sub.1 applied in the first step are still sufficiently wet. As a rule, this means that coating region 3 must be sufficiently small for this.

(88) According to the invention, a gradient therefore always takes place between an isolated individual structure 20 of a first layer L.sub.1 and a second layer L.sub.2, and there is a requirement at each point of the coating region 3 that the time t.sub.L2-L1 that elapses between the application of an individual structure 20 of the first layer L.sub.1 and an individual structure 20 of the second layer L.sub.1 adjacent to it must be shorter than an open time to of the coating agent on surface 2, above which no sufficient gradient can take place any longer. It is therefore preferable to try to determine a processing strategy in such a way that for each point of the coating region 3 the following applies:
t.sub.L2-L1<t.sub.0 is fulfilled,
where t.sub.0 is in the order of a few seconds or minutes. This requirement leads to further processing strategies:

(89) Basically, a coating region 3 is coated by means of a drop-on-demand coating head 5 in at least two coating steps BS, which contain complementary dot patterns PM, preferably evenly distributed over the coating region 3, each containing dots or lines isolated from each other.

(90) The application of the coating points 8 in the individual coating steps BS is performed serially in preferably parallel coating paths 6, or with the aid of coating strategies as described above and in FIGS. 3 to 10, for example guided by a multi-axis coating robot 14.

(91) The further processing strategies are better suited for large coating regions 3 and are characterized by the fact that in successive coating steps BS individual structures 20 are applied to the surface 2 alternately from different layers, whereby these individual structures 20 represent a subset of the dot patterns PM of the corresponding layer L from which they originate.

(92) The principle is illustrated in FIG. 18. In the example, the coating points 8 of the coating region 3 are distributed on two layers L.sub.1 and L.sub.2; the individual structures 20 are lines. This selection is made with regard to a serial processing by means of four coating steps BS.sub.1, BS.sub.2, BS.sub.3 and BS.sub.4, which correspond, for example, to coating paths 6 using a coating head 5, with the lines corresponding to tracks 7 of the printing nozzles. These are n=2 layers; the individual structures (lines) applied in the coating steps are alternately from layer L1 and layer L2:

(93) TABLE-US-00001 Coating step Individual structure 20 from layer BS.sub.1 L.sub.1 BS.sub.2 L.sub.2 BS.sub.3 L.sub.1 BS.sub.4 L.sub.2

(94) According to the invention, in this process, in a first coating step BS.sub.1 at least a first section A.sub.1 of the coating region 3 is coated with individual structures 20 of the first layer L.sub.1, which do not yet form a closed layer. In a second coating step BS.sub.2, individual structures 20 of the second layer L.sub.2 are used to coat the first section A.sub.1 and additionally a second section A.sub.2, whereby in section A.sub.1 a closed coating now results from the individual structures 20 of L.sub.1 and L.sub.2 and in section A.sub.2 an unclosed layer of individual structures 20 of layer L.sub.2. In a third coating step BS.sub.3, individual structures 20 of the first layer L.sub.1 are again used to coat the second section A.sub.2 and additionally a third section A.sub.2, whereby a closed coating is now also produced in section A.sub.2 from the individual structures 20 of L.sub.2 and L.sub.1 and an unclosed layer of individual structures 20 of layer L.sub.1 is produced in section A.sub.3. This alternating coating with individual structures 20 of L.sub.1 and L.sub.2 can now be continued analogously infinitely and thus large coating regions can be coated using this method. Only 4 coating steps BS are shown in FIG. 18. In the last (fourth) coating step BS.sub.n (BS.sub.4), individual structures 20 of the last resulting layer L.sub.1 or 2 (here L.sub.2) are used to coat the penultimate (here third) section A.sub.n-2 (here A3), so that now also in the last section A.sub.n-2 from the individual structures 20 of L.sub.1 and L.sub.2 a closed coating is present.

(95) Thus, within a sequential coating process consisting of several coating steps BS, at least one coating step BS is carried out, with which regularly arranged individual structures 20 such as dots or lines interrupted by spaces 21 are applied to a surface of an object in two sections A.sub.i and A.sub.i+1, characterized in that in the first section A.sub.i an incomplete layer previously applied is completed by the regularly arranged individual structures 20 to form a closed coating and in a second section A.sub.i+1 an incomplete layer of individual structures 20 is applied which has complementarily arranged interspaces 21.

(96) FIG. 19 exemplarily describes a distribution of the coating points 8 of the coating region 3 to three layers L.sub.1, L.sub.2 and L.sub.3 in a first process step A. As shown in the top of the figure, here the point arrangement of the coating points 8 is a hexagonal arrangement. This becomes clear by displaying the points as hexagons. The distribution of the coating points 8 on the layers 1 to 3 is illustrated by the hatching. Thus, the total layer (upper picture) is composed of the layers L.sub.1, L.sub.2 and L.sub.3, which are shown below.

(97) The application of the layer in the second process step B runs analogously, as described above for the case with two layers. In FIG. 20, two possible orientations, in particular main directions, for coating paths 6 and an associated track 7 are shown as an example and purely schematic.

(98) While in an orthogonal arrangement of the coating points 8 in rows and columns only two main directions and two diagonals are possible as directions of movement of the coating head 5 or the coating tracks 6, in a hexagonal arrangement there are three main directions and three diagonals, whereby the diagonal is always the bisector of the angle to two main directions.

(99) When applying individual structures 20 of a layer L.sub.i with a coating path 6, the coating path 6 can basically be aligned along any main direction or diagonal, depending on the nozzle distance of the coating head. For example, in the case of the hexagonal dot arrangement, coating steps BS or coating paths 6 of all layers L.sub.1 can be aligned along the same main direction or diagonal, which has the advantage that a coating region 3 can basically be coated starting from one side with long and parallel coating paths 6 towards the opposite side, which has the advantage that a coating region 3 can basically be coated from one side with long and parallel coating tracks 6 towards the opposite side. It is possible to work with coating steps BS, which use the individual structures 20 circulating in the layers L.sub.1 to L.sub.3:

(100) TABLE-US-00002 Coating step Individual structure 20 from layer BS.sub.1 L.sub.1 BS.sub.2 L.sub.2 BS.sub.3 L.sub.3 BS.sub.4 L.sub.1 . . . . . .

(101) FIG. 19 shows a special feature of a hexagonal point pattern (Detail D): Depending on the angular position of an edge contour 4, coating points of two layers may alternately protrude or recede. In order to obtain a straight edge nevertheless, it is suggested according to the invention to place coating points 8 of reduced size between those coating points in the last applied coating step BS.sub.n; see enlargement in FIG. 19, which protrude from the edge contour 4.

(102) It should be noted that the inventive methods and the proposed arrangements of coating points 8 are basically not limited to the examples given here, but represent general solutions that can be linked together. For example, dot arrangements according to FIGS. 3 to 10 can be distributed to different layers L and the individual structures of layers L.sub.i, i=1 . . . n, serially or section by section can be applied to a surface 2 to be coated by coating steps BS.sub.j, j=1 . . . k, especially coating paths 6. The dot size of each coating point 8 to be applied can be varied.

(103) As described above, a coherent coating in coating region 3 essentially consists of coating points 8 of the individual structures 20 of a first layer L.sub.1 running together with coating points 8 of the individual structures 20 of a second layer L.sub.2 and forming a layer. Since the individual structures 20 are substantially arranged or distributed regularly over the entire coating region 3, the way in which the coating points 8 run over the coating region 3 is always the same and independent of the coating paths.

(104) In contrast, the coating agent is always applied over the entire surface in parallel paths 6 according to the prior art. This results in visible differences in the course between areas in the middle of each path 6, where adjacent coating points 8 are applied almost simultaneously and can run optimally, and the edges 9 of the coating paths 6, where adjacent paths, which are applied with a larger time offset of seconds to minutes, connect to each other and due to the time offset, a worse course between the adjacent tracks 7 of the two adjacent coating paths 6 takes place.