Patent Publication Number: US-2022212218-A1

Title: Coating method and corresponding coating installation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage of, and claims priority to, Patent Cooperation Treaty Application No. PCT/EP2020/062240, filed on May 4, 2020, which application claims priority to German Application No. DE 10 2019 112 113.2, filed on May 9, 2019, which applications are hereby incorporated herein by reference in their entireties. 
     The disclosure relates to a coating method for coating a component (e.g. motor vehicle body component) with a coating agent (e.g. paint). Furthermore, the disclosure relates to a corresponding coating plant. 
    
    
     BACKGROUND 
     In modern coating plants for painting motor vehicle body components, rotary atomizers are usually used as application devices, which deliver a spatially extended spray jet of the paint to be applied. 
     A more recent line of development provides nozzle applicators as application devices, which are also referred to as printheads and are described, for example, in DE 10 2013 002 412 A1. In contrast to the known rotary atomizers, such nozzle applicators do not emit a spatially extended spray jet of the coating, but a spatially narrowly limited coating agent jet. This has the advantage that the applied coating is deposited almost completely on the component to be coated, so that there is little or no overspray. Another advantage of these known nozzle applicators is that patterns can also be applied to the component surface, such as graphics or lettering. However, the problem here is that the contours of the patterns are not sharp-edged. 
     When a droplet jet is applied, the coating agent droplets initially form circular coatings on the component surface, which then merge into a contiguous coating film due to the cohesive force of the applied coating. However, a droplet structure is still visible on the outer contour of the pattern. 
     The same problem occurs in a similar form if, instead of a droplet jet, a coating agent jet is applied that is contiguous in the jet direction. In this case, the coating agent jets form contiguous coating agent paths on the component surface, which usually lie next to each other and then converge due to the cohesive force of the applied coating. However, a structure can also be seen at the ends of the paths, so that the contour is not sharp-edged on all sides of the surface or pattern. 
     For the technical background of the disclosure, reference should also be made to DE 198 54 760 A1, DE 10 2010 019 612 A1, DE 10 2013 006 868 A1, EP 0 282 599 A1, DE 199 36 790 A1, EP 2 770 322 A1, FAVRE-BULLE, B.: “Automatisierung komplexer Industrieprozesse—Systeme, Verfahren and Infor-mationsmanagement”, Springer-Verlag GmbH, 2004, ISBN 978-3-7091-0562-7, DE 10 2016 014 944 A1 and DE 101 50 826 A1. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic representation of the conventional application of a pattern with a nozzle applicator that emits a coating agent jet that is contiguous in the longitudinal direction of the jet, 
         FIG. 1B  the pattern according to  FIG. 1A  after the coating agent paths have converged on the component surface, 
         FIG. 2A  a modification of  FIG. 1A  for a nozzle applicator which emits a droplet jet, 
         FIG. 2B  a modification of  FIG. 1B  for the nozzle applicator emitting a droplet jet, 
         FIGS. 3A-3D  various schematic representations of the application of a pattern according to the disclosure with a nozzle applicator that emits a coating agent jet that is contiguous in the longitudinal direction of the jet, 
         FIGS. 4A-4D  variations of  FIGS. 3A-3D  for a nozzle applicator emitting a droplet jet, 
         FIG. 5  a flow chart illustrating the coating method according to the disclosure, and 
         FIG. 6  a highly simplified schematic representation of a coating installation according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The coating method according to the disclosure firstly provides that a pattern is defined which is to be produced on the component surface of the component to be coated, the pattern being a surface region which is outlined by a contour. The concept of a pattern used in the context of the disclosure is to be understood in a general sense and includes, for example, graphics, lettering, pictures, letters, numerals and other possible designs as well as partial surfaces of a coating object (e.g. roof spar, fender, etc. of a motor vehicle body). 
     The pattern is divided into contour parts and areal parts by an operator in a suitable manner and by means of aids such as software, either semi-automatically or fully automatically. In a further step, path programs are created manually, semi-automatically or fully automatically from the information (partial surfaces) determined in this way. 
     Furthermore, the coating method according to the disclosure provides, in accordance with the known coating methods, that the component surface is areally coated within the predetermined contour of the desired pattern, preferably using a nozzle applicator (e.g. printhead) as already mentioned above with regard to the state of the art. 
     The coating method according to the disclosure is characterized by sharp-edged coating of the component surface with a coating agent along at least part of the contour of the pattern. In the context of the disclosure, therefore, the pattern is filled in areally within the contour, while the contour or parts of the contour (e.g. front end edge) of the pattern are traced with sharp edges. 
     It should be mentioned here that various sequences of these two coating steps are possible within the scope of the disclosure. One variant of the disclosure envisages that the areal coating of the component surface within the contour is carried out first, followed by the sharp-edged coating along the contour of the pattern. However, it is alternatively also possible that the contour of the pattern is drawn first, followed by the areal coating within the contour. 
     Furthermore, it should be mentioned that the areal coating within the contour of the predetermined pattern is preferably carried out with a greater area coating performance than the sharp-edged coating along the contour. The term area coating performance used in the context of the disclosure defines the size of the area coated on the component within a certain unit of time, i.e. the ratio of coated area and required coating time. 
     In the case of a nozzle applicator as an application device, this variation of the area coating performance can be achieved, for example, by activating or deactivating several nozzles of the nozzle applicator. Thus, the areal coating within the contour can be done with a large number of activated nozzles, whereas edge coating along the contour of the pattern can be done with a smaller number of activated nozzles. For example, sharp-edged coating along the contour of the pattern can be done with fewer than 20, 10, 5, or even just a single nozzle of the nozzle applicator. 
     However, the variation of the area coating performance for the areal coating on the one hand and for the sharp-edged coating on the other hand can also be carried out in other ways. For example, the flow rate of the applied coating agent can be changed, for which purpose the application pressure can be varied. 
     Furthermore, the applicator (e.g. nozzle applicator) is preferably moved over the component surface by a manipulator in the coating method according to the disclosure. The manipulator is preferably a multi-axis coating robot with serial robot kinematics. Another possibility of a manipulator is an x-y or x-y-z linear axis system, in which the applicator is attached to one of the axes and the axes are attached and related to each other in such a way that the applicator can be moved to any location on the surface to be coated. 
     In the aforementioned sharp-edged coating along the contour of the pattern, the manipulator moves the applicator along the contour of the pattern at a certain traversing speed, with the applicator applying a certain flow rate of the coating agent. However, depending on the shape of the pattern and the shape of the contour, it is usually not possible for the applicator to move over the component surface at a constant traversing speed. For example, the applicator must be slowed down and accelerated again at corner points, generally at points of the contour with discontinuous directional progression, turning points or kinks. With a constant flow rate of the applied coating agent, this would lead to a corresponding variation in the coating thickness on the component surface due to the variation in the traversing speed. These undesirable variations in the coating thickness on the component surface can be prevented by adjusting the flow rate of the coating agent as a function of the traversing speed. Thus, a reduction in the traversing speed then leads to a corresponding reduction in the mass flow of the coating agent, while an increase in the traversing speed also requires a corresponding increase in the mass flow of the coating agent. 
     However, the above-described adjustment of the flow rate of the coating agent as a function of the traversing speed is not sufficient in all cases to achieve a constant coating thickness on the component surface, or is not always technically feasible. For example, it is difficult for a coating robot with serial robot kinematics to realize right-angled kinks in the robot path. It can therefore also be advantageous not to traverse the contour continuously, but in several path sections that can be traversed easily by the manipulator because they have no corners, kinks or turning points. Between the successive path sections, the applicator then interrupts the delivery of the coating agent and starts the next path section during this coating pause. 
     This subdivision of the contour of the pattern to be traversed into several successive path sections is particularly useful at problem points, such as kinks in the contour. The term “problem area” used in the context of the disclosure preferably refers to the fact that the manipulator used can pass the respective problem area without interruption only with a sharp drop in the traversing speed, for example with a drop in the traversing speed of more than 50%, 70%, 80% or 90%. 
     Depending on the manipulator type, the stiffness of the manipulator and/or the overall system consisting of manipulator, traversing axis, substrate and/or the capabilities of the applicator, the possible radii and/or the acceleration distances can be different. 
     If the motion path program of the manipulator is to be created automatically, the above-mentioned parameters are entered or stored in the software required for this purpose. 
     Furthermore, it is to be mentioned that the manipulator preferably executes a kink-free start movement at the problem points between the coating of the immediately successive path sections in order to contact the immediately following path section again. 
     In one variant of the disclosure, the sharp-edged coating of the contour is carried out with a coating agent jet which is contiguous in the longitudinal direction of the jet, preferably along the entire contour. 
     In another variant of the disclosure, however, the sharp-edged coating of the contour is first carried out with a coating agent jet that is contiguous in the longitudinal direction of the jet and then with a droplet jet consisting of numerous droplets that are not contiguous in the longitudinal direction of the jet. 
     Within the scope of the disclosure, the areal coating of the pattern and/or the sharp-edged coating of the contour can be carried out alternately with a coating agent jet that is contiguous in the longitudinal direction of the jet and with a droplet jet that consists of numerous droplets that are not contiguous in the longitudinal direction of the jet. This alternation between the different jet forms (droplet jet or contiguous jet) can be temporal or alternating between the pattern within the contour and the contour itself. 
     It has already been briefly mentioned above that within the scope of the disclosure there is the possibility that first the pattern within the contour is applied over the surface and only then the contour is traced. Within the scope of the disclosure, it is possible that after the pattern has been applied to the surface, a measuring system (e.g. optical measuring system) is first used to determine the spatial orientation and position of the contour, which is initially still blurred, so that the contour can then be traced with an accurate fit. 
     Alternatively, however, the contour can be pre-drawn first and then the pattern within the contour is coated over the entire surface. In this case, it is possible that after the contour has been pre-drawn, the spatial position and orientation of the contour is first determined by means of a measuring system so that the pattern can then be coated areally within the pre-drawn contour with an accurate fit. 
     The aforementioned measuring system can be attached to the manipulator and is then moved with the manipulator. Alternatively, however, it is also possible for the measuring system to be arranged separately from the manipulator in a fixed position. 
     Preferably, the measuring system operates optically and has at least one camera and one image evaluation unit for this purpose. 
     In one variant of the disclosure, the areal coating within the contour is carried out with the same coating agent as the sharp-edged coating along the contour. 
     In another variant of the disclosure, however, different coating agents are used for this purpose, in particular coating agents with different colors. 
     Furthermore, within the scope of the disclosure, it is possible for the areal coating to be carried out with different coating agents for different patterns. Furthermore, it is also possible for the sharp-edged coating to be carried out with different coating agents for different contours. 
     It has already been briefly mentioned above that the coating agent droplets or coating agent paths applied to the component converge into a contiguous coating agent film after application due to the cohesive force of the coating agent, which is desirable in principle. However, this convergence is only possible within a certain flow time after application of the coating agent. If the same coating agent is used for the contour and for the areal coating, it is basically desirable for the contour and the inner surface to run together. In this case, the areal coating of the pattern and the sharp-edged coating along the contour are preferably carried out at a time interval that is shorter than the flow time, so that the coating agent for the contour and the surface can run together. 
     In the case of different coating agents for the contour and inner surface, and in particular in the case of differently colored coating agents for the contour and inner surface, however, this convergence of the coating agents is precisely undesirable. In this case, the areal coating of the pattern and the sharp-edged coating along the contour are preferably carried out at a time interval that is greater than the flow time, so that the different coating agents for the contour and the inner surface do not run together. 
     In general, it should be mentioned that the coating agent is preferably applied by an applicator which does not emit a spray jet, but a narrowly limited coating agent jet. The applicator can therefore be a printhead, as is known in principle from the prior art. 
     The coating agent jet can, for example, consist of coating agent droplets which are separated from one another in the longitudinal direction of the jet. Alternatively, however, it is also possible for the coating agent jet to be contiguous in the longitudinal direction of the jet. 
     It has already been briefly mentioned above that the applicator is preferably moved over the component surface by a manipulator, preferably a multi-axis coating robot with serial robot kinematics or a linear axis system. 
     It is advantageous here if the manipulator has a high spatial positioning accuracy and/or repeatability, which is preferably more precise than 5 mm, 2 mm or even 0.5 mm. This is useful so that the contour and the inner surface of a pattern can be applied to fit each other precisely. 
     With regard to the type of coating agent applied, the disclosure is not limited to paints, such as one-component paints, two-component paints, water-based paints or solvent-based paints. Rather, the coating agent may also be an adhesive, a bonding agent, a primer, a pasty material, a sealant, or an insulating material. 
     Furthermore, it should be mentioned that the coating agent is preferably applied with a certain application distance between the applicator and the component surface, the application distance preferably being in the range of 1 mm-80 mm, 5 mm-50 mm or 10 mm-50 mm. 
     Furthermore, it should be mentioned that the disclosure does not only claim protection for the coating method according to the disclosure described above. Rather, the disclosure also claims protection for a corresponding coating installation that carries out the coating method according to the disclosure. 
     Thus, the coating apparatus according to the disclosure firstly comprises an applicator for applying the coating agent, preferably being a nozzle applicator or a printhead. 
     Furthermore, the coating installation according to the disclosure comprises a manipulator for moving the applicator over the component surface, preferably a multi-axis coating robot with serial robot kinematics or a linear axis unit. 
     In addition, the coating installation according to the disclosure comprises a control system for controlling the manipulator and the applicator, wherein the control system can comprise hardware components and software components and can be distributed to different parts and components. The control system is designed in such a way that the coating installation executes the above-described coating method according to the disclosure. 
     For this purpose, the coating installation according to the disclosure can also comprise the measuring system already mentioned above. 
     Finally, the disclosure also claims protection for a corresponding control program which, when executed on the control system, causes the application system to carry out the coating method according to the disclosure. The control program may be stored on a computer-readable medium (e.g., computer memory, USB stick, CDROM, DVD, memory card, etc.) so that the computer-readable medium with the control program stored thereon is also protected. 
       FIGS. 1A and 1B  show schematic representations of a conventional application of a pattern in the form of the letter D to a component surface of a component, such as a motor vehicle body component. In this case, a nozzle applicator applies a coating agent jet which is contiguous in the longitudinal direction of the jet to the component surface, so that initially elongated coating agent paths  1 , which are bounded by a contour  2 , are formed on the component surface. After impact on the component surface, the coating agent paths  1  then converge due to the cohesive force of the applied coating and then form a contiguous pattern  3 . In this known type of pattern application, however, the outlines of the coating agent paths  1  are still recognizable along the contour  2 . The contour  2  is therefore not particularly sharp-edged, which is undesirable. 
       FIGS. 2A and 2B  show corresponding illustrations for the pattern application with a nozzle applicator that emits a droplet jet, i.e. a coating agent jet consisting of coating agent droplets that are not contiguous in the longitudinal direction of the jet. 
     Instead of the coating agent paths  1 , coating agent droplets  4  are formed on the component surface, which then also run together to form the contiguous pattern  3  due to the cohesive force of the applied coating agent. Here too, however, the contour  2  of the pattern  3  is not particularly sharp-edged. 
       FIGS. 3A-3D  show illustrations of pattern application according to the disclosure, these illustrations corresponding in principle to  FIGS. 1A and 1B , i.e. here, too, the pattern  3  is applied by a nozzle applicator which emits coating agent jets contiguous in the longitudinal direction of the jet, so that the coating agent paths  1  are formed on the component surface. It should be mentioned here that the reference sign  3  in  FIG. 3A  designates the desired pattern, i.e. the specification that is used in the entire process. 
     Here, the pattern  3  has an inner contour  5  and an outer contour  6 , which are sharp-edged painted to produce the desired edge sharpness of the pattern  3 . For this purpose, the nozzle applicator is guided along the inner contour  5  and along the outer contour  6  and then coats the inner contour  5  or the outer contour with edge sharpness, whereby only a single nozzle or only a few nozzles of the nozzle applicator are used to achieve the desired edge sharpness. 
     The areal coating of the pattern  3  within the contour  2  is then carried out in a separate processing step, for example with a higher area coating performance. 
     The nozzle applicator is guided over the component surface by a multi-axis coating robot with serial robot kinematics. Although such a coating robot enables high-precision positioning of the nozzle applicator, kinks with an angle (greater than a limit angle), in particular right-angled ones, of the robot path are problematic. Thus, the outer contour  6  has two problem areas  7 ,  8 , where the outer contour  6  shows a rectangular kink. Correspondingly, the inner contour  5  also has problem areas  9 ,  10  where the inner contour  5  shows a rectangular kink. It is therefore difficult for a coating robot with serial robot kinematics to guide the nozzle applicator exactly over the problem areas  7 - 10 , since the traversing speed would have to be greatly reduced (limit value zero) for this. 
     The coating method according to the disclosure provides for the outer contour  6  to be divided into two path sections BA 1 , BA 4 , just as the inner contour  5  is divided into two path sections BA 2 , BA 3 . During the sharp-edged coating of the outer contour  6 , the path section BA 1  is coated first, starting from an starting point P 1 A and ending at a departure point P 1 E. No large angles (sharp kinks) occur on the path section BA 1 , so that the coating robot can guide the nozzle applicator along the path section BA 1  at an almost constant traversing speed. 
     The path section BA 2  of the inner contour  5  is coated accordingly, starting from an starting point B 2 A and ending with a departure point P 2 E. Here, too, there are no kinks on the path section BA 2 , which allows an almost constant traversing speed within the path section BA 2 . 
     The path section BA 3  starts at the starting point P 3 A and ends at the departure point P 3 E and is completely linear, which also allows a constant traversing speed on the path section BA 3 . 
     Finally, the path section BA 4  starts at the starting point P 4 A and ends at the departure point P 4 E. The path section BA 4  is also completely linear and therefore enables a constant traversing speed. 
       FIGS. 4A-4D  show modifications of  FIGS. 3A-3D  for a nozzle applicator that emits a droplet jet. To avoid repetition, reference is therefore made to the description of  FIGS. 3A-3D . 
       FIG. 5  shows a flow chart to illustrate the coating method according to the disclosure. 
     After the program start, the manipulator type is first defined in a step S 1 , i.e. the type of the multi-axis coating robot used or, for example, the type of the linear axis system. Depending on the manipulator type, an associated parameter set is then loaded, which reflects the properties of the respective manipulator. 
     In a step S 2 , the applicator type is then determined and a corresponding parameter set is loaded that reflects the properties of the respective applicator type, as well as optional parameters, such as the spacing of the nozzles, the nozzle diameter and the number of nozzles. 
     In a step S 3 , parameters for a path program algorithm are then defined, such as maximum and/or minimum coating path width, minimum possible curve radius, minimum and/or maximum coating volume flow and maximum path speed. 
     In a step S 4 , a graphic is then read in, which is to be applied as a pattern. 
     In a step S 5 , the graphic is then analyzed, for example with regard to the inner surface, the contour, the assigned colors and with regard to matching with the available colors. 
     In a step S 6 , a path program is then calculated that defines starting and departure paths as well as switch-on and switch-off points. 
     In a step S 7 , the path program is then visualized and a simulation of the path program is performed. The operator of the program can then evaluate the result. If the path program is not acceptable, a corresponding adjustment follows in step S 3 . Otherwise, the path program is released for control. 
       FIG. 6  shows a highly simplified schematic representation of a coating installation according to the disclosure with a measuring system  11 , a manipulator  12 , an applicator  13  and a control system  14 . The control system  14  can have hardware components and software components and can be distributed over various parts and components. 
     The control system  14  controls the manipulator  12  and the applicator  13  in the manner described above so that the monitoring method according to the disclosure is carried out. 
     Here, the measuring system  11  can determine the spatial position and orientation of the contour and the inner surface of the pattern, so that the contour and the inner surface can be applied with an accurate fit to each other. 
     The disclosure is not limited to the preferred embodiments described above. Rather, a large number of variants and variations are possible which also make use of the inventive idea and therefore fall within the scope of protection.