Coating device for coating components

Abstract

The disclosure concerns a coating device for coating components with a coating agent, in particular for painting motor vehicle body components, with a printhead, a multi-axis coating robot and with a robot control which controls the coating robot. The disclosure additionally provides for a separate printhead control which controls the printhead valve of the printhead.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage of, and claims priority to, Patent Cooperation Treaty Application No. PCT/EP2017/081102, filed on Dec. 1, 2017, which application claims priority to German Application No. DE 10 2016 014 952.3, filed on Dec. 14, 2016, which applications are hereby incorporated herein by reference in their entireties.

BACKGROUND

The disclosure concerns a coating device for coating components with a coating agent, in particular for painting vehicle body parts.

For the serial painting of car body components, rotary atomizers are usually used as application devices, which have the disadvantage of a limited application efficiency, i.e. only a part of the applied paint is deposited on the components to be coated, while the rest of the applied paint has to be disposed of as so-called overspray.

A newer development line, on the other hand, provides for so-called printheads as application device, as known for example from DE 10 2013 002 412 A1, U.S. Pat. No. 9,108,424 B2 and DE 10 2010 019 612 A1. In contrast to the known rotary atomizers, such printheads do not emit a spray of the paint to be applied, but rather a narrowly confined paint jet, which is deposited almost completely on the component to be painted, so that virtually no overspray occurs.

However, when coating a limited area (e.g. a decor) on a component surface using such a printhead, the paint jet must be controlled very precisely in terms of time and space so that the boundaries of the area to be coated are adhered to without exceeding or falling below the boundaries of the area to be coated during painting. In order to be able to produce cost-effectively and competitively or to achieve high area performances, the applicators must be moved quickly with the robot, e.g. at a drawing speed in the range of 0.5 m/s to 0.75 m/s. The combination of exact switch-on and switch-off positions of the applicators or their individual valves as well as the high painting speed results in the necessity of very short reaction times or control pulses (e.g. 1 ms, 500 μs, 100 μs, 10 μs), which are usually not possible with robot controls. For this purpose, printhead valves in the printhead must be switched on or off very precisely in order to switch the painting beam on or off accordingly. However, this is not possible with the usual robot controls, since these robot controls work with a specified cycle time, whereby the cycle time of the robot control is too long, in order to achieve the necessary temporal accuracy with the control of the printhead valves.

From EP 2 196 267 A2 a coating system is known, in which a coating robot moves a printhead over the components to be coated. The coating robot is controlled by a robot control. In addition to the robot control, a separate control unit is provided, which controls a metering unit and sets the desired paint flow. A separate printhead control is not known from this publication.

With regard to the general technical background of the disclosure, reference is made to DE 10 2010 004 496 A1 and DE 10 2014 013 158 A1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a highly simplified schematic representation of a painting installation according to the disclosure,

FIG. 2 gives a schematic representation to explain the problem underlying the disclosure and the solution in accordance with the disclosure,

FIG. 3 shows a schematic representation of a printhead moving along a programmed path across the component surface,

FIG. 4 a schematic illustration to illustrate the problem of delayed printhead valve response, and

FIG. 5 shows a schematic diagram to illustrate the interpolation of the positions in the printhead control from the positions in the robot control.

DETAILED DESCRIPTION

The disclosure comprises the general technical teaching that the printhead valves in the printhead are not controlled by the robot control that controls the coating robot. Instead, the disclosure provides for a separate printhead control which controls the printhead valves in the printhead and operates sufficiently fast to achieve the required temporal and spatial accuracy in the control of the paint jets emitted. There should be communication with the robot control in order to instruct the printhead control accordingly.

The coating device according to the disclosure is used for coating components, such as vehicle body parts. However, the disclosure is not limited to vehicle body components with regard to the type of components to be coated. Rather, the components to be coated may also be other components.

It should also be mentioned that the coating device is preferably designed for coating components with a paint, i.e. the coating agent to be applied is preferably a paint, such as a solvent-based paint, a water-based paint, a colouring base coat or a clear coat, to name just a few examples. However, the disclosure is not limited to paints with regard to the type of coating to be applied, but can also be realized with other types of coating agents, such as adhesives, insulating materials, sealants, primers, etc., to name just a few examples.

The coating device according to the disclosure has a printhead with at least one nozzle as application device in order to deliver a coating agent jet onto the component to be coated, whereby the coating agent delivery through the nozzle is controlled by means of a printhead valve.

The term “printhead” used in the context of the disclosure is initially to be understood generally and serves only to distinguish it from conventional atomizers (e.g. rotary atomizers), which do not emit a spatially narrowly limited jet of coating agent, but a spray of the coating agent. Preferably, however, the printhead is a printhead as described for example in DE 10 2013 002 412 A1, U.S. Pat. No. 9,108,424 B2 and DE 10 2010 019 612 A1.

Furthermore, the coating device according to the disclosure includes a multi-axis coating robot that guides the printhead over the surface of the component to be coated. The coating robot preferably features serial robot kinematics with at least six or seven movable robot axes and a robot hand axis to guide the printhead over the component surface in a highly movable manner. Such coating robots are known from the state of the art and therefore do not need to be described in detail.

In addition, the coating device in accordance with the disclosure features a state-of-the-art robot control that controls the coating robot.

As already mentioned briefly above, the coating device according to the disclosure now distinguishes itself from the state of the art by a separate printhead control which is separated from the robot control and which controls at least one printhead valve, whereby the printhead control works sufficiently fast to achieve the required temporal and spatial accuracy in the control of the coating agent release.

It has already been mentioned briefly at the beginning that the robot control usually controls the coating robot with a specified first cycle time, whereby this first cycle time is too long to achieve the desired temporal and spatial accuracy of the coating release when controlling the printhead valve. The printhead control according to the disclosure works preferably clocked with a specified second cycle time, whereby this second cycle time of the printhead control is shorter than the first cycle time of the robot control, so that the printhead control can achieve the required temporal and spatial accuracy of the control of the coating release when controlling the printhead valve.

At a printhead travel speed, the position of the printhead is known only in quantized units of the robot control clock rate. At a travel speed of v=750 mm/s and a robot control clock rate of 4 ms, this position quantization is 3 mm. This is not sufficient for a more precise positioning (<1 mm, <0.1 mm) of the switch-on or switch-off point of the coating agent on the substrate, e.g. exactly at the edge of the substrate.

The second cycle time of the printhead position is therefore preferably at most 100 ms, 50 ms, 20 ms, 10 ms, 5 ms, 1 ms or even at most 100 μs.

The printhead control is preferably connected to the robot control on the input side and receives the current spatial position, the current spatial position and/or the current speed and/or the current spatial orientation of the printhead and/or the coating object as input information from the robot control at the robot control clock rate, so that the printhead control can take this information into account when controlling the printhead valve.

The printhead control interpolates or extrapolates (e.g. linear, with splines, cubically) these positions to its own time steps so that it obtains a higher position resolution. Thus the switch-on or switch-off point of the coating agent flow or coating agent drop can be set exactly.

The printhead control can also be integrated into the robot control as an independently operating module, for example.

It should also be mentioned that the coating device according to the disclosure preferably includes a colour changer which selects one of several coating agents and forwards the selected coating agent to the printhead.

In addition, the coating device according to the disclosure preferably includes a metering pump which meters the coating agent to be applied and transports it to the printhead.

In the preferred example of the disclosure, the printhead control controls not only the at least one printhead valve of the printhead, but preferably also the color changer and/or the metering pump.

It has already been mentioned above that the printhead control can switch the coating agent jet applied by the printhead on and off highly dynamically and precisely timed in order to achieve coating patterns with a very precise spatial resolution on the component surface. This is important, for example, if a surface to be coated has a sharp edge that must be adhered to exactly during the coating process. The printhead control works therefore preferably so fast and exact that the coating agent jet on the component surface reaches an exact spatial resolution of less than ±2 mm, ±1 mm, ±0.5 mm or even less than ±0.1 mm.

To achieve such an accurate coating, a measuring device is preferably provided which measures the spatial position and/or orientation of the component to be coated and transmits the determined position and/or orientation to the printhead control so that the printhead control can take this into account when controlling the printhead valves. The measuring device can be connected either directly to the printhead control or indirectly to the printhead control via the robot control. The only decisive factor in the disclosure is that the determined position or orientation of the component to be coated can be taken into account when controlling the printhead valves.

In a preferred embodiment of the disclosure, the measuring device has a camera which takes an image of the component to be coated, whereby this image is evaluated by an image evaluation unit which determines the spatial position or orientation of the component to be coated. Within the scope of the disclosure, it is also possible that several cameras are arranged at different positions in order to increase the accuracy of the position determination.

In one example of the disclosure, the measuring device can determine the spatial position and/or orientation of the component to be coated with a very high accuracy and a correspondingly low position tolerance, whereby the position tolerance is preferably smaller than ±2 mm, ±1 mm, ±0.5 mm, ±0.25 mm or even smaller than ±0.1 mm.

In one example of the disclosure, the coating device has, in addition to the printhead control and the robot control, an additional metering control for the aforementioned metering device (e.g. metering cylinder, metering pump, etc.), which meters the coating agent and conveys it to the printhead.

The metering control is preferably connected to the printhead control in order to synchronize the control of the metering pump with the control of the printhead valves of the printhead. If, for example, numerous printhead valves are suddenly opened, the consumption of coating agent suddenly increases, so that the metering pump should also be operated at a higher capacity.

In addition, the metering control is preferably also connected to the robot control in order to synchronize the control of the metering pump with the control of the coating robot. If, for example, the robot control controls the coating robot in such a way that the printhead is moved over the component surface at a high drawing speed, a large coating quantity usually also has to be conveyed by the metering pump, so that synchronisation of the robot control on the one hand and the metering control on the other hand is advantageous.

It has already been mentioned several times that the disclosure enables a highly dynamic and precise control of the printhead valves by providing a separate printhead control that works sufficiently fast. However, this only makes sense if the printhead valves themselves work sufficiently fast. The printhead valves therefore preferably have a very short switching time of at most 100 ms, 50 ms, 20 ms, 5 ms, 1 ms or even at most 100 μs. A very good reproducibility or repeatability of the switching times of all valves is even more important in order to correct them individually if necessary.

It should also be mentioned that the coating device according to the disclosure may have a first data interface for communicating with production planning, but this is known from the state of the art and therefore does not need to be described in detail.

In addition, the disclosure-based coating device may have a second data interface for recording a control file, whereby the control file may, for example, specify a graphic that is to be applied to the component surface by the coating device. This second data interface can, for example, be implemented using a USB stick reader (USB: Universal Serial Bus) or a memory card reader, to name just a few examples.

Furthermore, the disclosure offers the possibility of maintaining paint statistics. Furthermore, a paint requirement quantity calculation can follow within the framework of the disclosure. In addition, it is possible to communicate with a graphic visualization computer. Furthermore, the disclosure offers the possibility of communication with a safety control. In this case, a paint release can be carried out by a higher-level control system, which also checks whether a supply air system is in operation and whether there are any safety-relevant malfunctions. In addition, the printhead control can also release the paint if it determines that the colour print is in order, the metering pump is working, the coating robot is in its initial position, the optical measurement is complete, the vehicle has been measured and a position correction has been carried out.

It is also worth mentioning that the printhead preferably emits a narrowly limited jet of coating agent as opposed to a spray mist, as is the case with conventional atomizers (e.g. rotary atomizers).

In a variant of the disclosure, the printhead emits a droplet jet consisting of numerous droplets separated from each other in the longitudinal direction of the droplet jet, as opposed to a jet of coating agent hanging together in the longitudinal direction of the jet.

In another variant of the disclosure, the printhead, on the other hand, emits a coating medium jet being continuous in the longitudinal direction of the jet, in contrast to a droplet jet.

These two variants (droplet jet and continuous coating agent jet) can also be combined within the scope of the disclosure. For example, the printhead can alternately emit a droplet jet and a continuous coating agent jet. Furthermore, in the frame of the disclosure there is the possibility that a part of the nozzles of the printhead emits a droplet jet, while at the same time another part of the nozzles of the same printhead emits a continuous coating agent jet in the longitudinal direction of the jet.

It should also be mentioned that the coating medium pressure is preferably controlled with a relatively small fluctuation range of maximum ±500 mbar, ±200 mbar, ±100 mbar or even ±50 mbar.

The advantage of using a printhead as an application device is the high application efficiency, which is preferably greater than 80%, 90%, 95% or even 99%, so that the printhead is essentially overspray-free.

It should also be mentioned that the printhead preferably has a sufficiently high area coating performance to be able to paint vehicle body components efficiently. The printhead therefore preferably has a surface coating performance of at least 0.5 m²/min, 1 m²/min, 2 m²/min or even 3 m²/min.

It should also be mentioned that the volume flow of the applied coating agent and thus the exit speed of the coating agent is preferably adjusted in such a way that the coating agent does not bounce off the component after hitting it or does not penetrate the lower paint layer wet-on-wet or push it to the side or displace it in the case of a paint application.

The coating agent exit velocity from the printhead can therefore be in the range of 5 m/s to 30 m/s, for example, and any intermediate intervals are possible.

The application distance (i.e. the distance between nozzle and component surface) is preferably in the range of 4 mm to 200 mm.

It should also be mentioned that the printhead valve preferably has an electrically controllable actuator, such as a magnetic actuator or a piezo actuator, to enable the desired fast response.

FIG. 1 shows a highly simplified schematic representation of a painting system according to the disclosure for painting car body components 1 with a paint.

The car body components 1 are conventionally conveyed by a conveyor along a painting line through the painting installation, which is known from the state of the art and is therefore not shown for simplification.

The painting is done by a multi-axis painting robot 2 with a serial robot kinematics and several robot arms and a highly movable robot hand axis, which guides a printhead 3 as application device. The printhead 3 then emits coating agent jets 4 onto the surface of the vehicle body part 1, as shown schematically.

It should be mentioned here that the painting robot 2 is arranged in a painting booth, which typically contains several such painting robots 2 on both sides of the painting line, whereby only one single painting robot 2 is shown for simplification.

The painting robot 2 can be controlled in a conventional way by a robot control 5, whereby the robot control 5 operates with a specified cycle time and therefore only allows positioning with a limited spatial resolution according to the cycle time. The spatial resolution that can be achieved in this way, however, is not sufficiently accurate to allow the printhead 3 to coat the component surface with local accuracy.

The coating device according to the disclosure therefore additionally has a camera 6, which takes a picture of the motor vehicle body component 1 and the painting robot 2 in order to enable an exact relative positioning of the painting robot 2 with the printhead 3 relative to the motor vehicle body component 1.

The image captured by camera 6 is then evaluated by an image evaluation unit, whereby the image evaluation unit is not shown here for simplification.

It should also be mentioned that within the scope of the disclosure there is the possibility that several such cameras 6 are provided, which record the painting robot 2 and the vehicle body part 1 from different perspectives and thus enable a higher accuracy in position determination.

It has already been mentioned above that the robot control 5 has a relatively long cycle time which does not allow the required spatial accuracy to control the printhead 3 with high accuracy. The coating device according to the disclosure therefore preferably has a separate printhead control 7, which controls the printhead valves located in the printhead 3, which are not shown for simplification, highly precisely and highly dynamically.

The printhead control 7 is connected on the input side to the robot control 5 and receives from the robot control 5 the current position and orientation of the vehicle body series component 1 relative to the printhead 3, in order to be able to take this input information into account when controlling the printhead valves in the printhead 3.

It should also be mentioned that the coating device has, among other things, a colour changer and a metering pump, which are not shown for simplification. The colour changer and the metering pump are controlled by an additional metering control 8, which is connected to the printhead control 7 and the robot control 5.

In addition, a data interface to production planning 9 is provided.

Production planning 9 in turn has a data interface, for example in the form of a USB stick reader, so that a control file can be read in using a USB stick 10, which defines a graphic (e.g. a decor) that is to be applied to the component surface of the vehicle body component.

Here it is possible for the control file to be transferred directly from the end customer to the factory via the car dealerships. In the production software, the graphic is then assigned to the number of the car body. Data is then transferred to the robot control via an interface of the production software and identification is usually carried out via reading points and data carriers on the body. Not only the serial number can be stored on the data carrier, but also other data, if necessary the graphic data.

In general it should be mentioned that the robot control 5, the printhead control 7 and the metering control 8 are preferably designed as separate hardware components and are separated from each other.

Within the scope of the disclosure, however, there is also the possibility that the robot control 5, the printhead control 7 and the metering control 8 can only be implemented as separate software components in an otherwise uniform control unit.

In the following, the schematic representation in FIG. 2 is explained. FIG. 2 shows a programmed movement path 11 in the upper area, whereby the printhead 3 is moved along the programmed movement path 11 over the surface of the motor vehicle body component 1.

In addition, FIG. 2 shows in the upper area a limited area 12 to be coated, which is covered by the printhead 3 along the programmed movement path 11. At the time t=t1 the printhead 3 then passes the left boundary of the area 12 to be coated, so that the coating should also begin at this time. At the time t=t2 the printhead 3 then passes the opposite boundary of the surface 12 to be coated, so that the printhead 3 should stop the coating at exactly this time.

FIG. 2 shows in the middle area the actual opening times 13 of the printhead valves of the printhead 3. For simplification it is assumed that the printhead 3 has six nozzles in a row. In practice, however, printhead 3 actually has a larger number of nozzles and a larger number of nozzle rows, which is irrelevant for the principle of the disclosure.

If the printhead valves of printhead 3 are controlled exactly in time, the actual opening times 13 of the printhead valves of printhead 3 are exactly within the area 12 to be coated, as shown in FIG. 2, bottom right.

In fact, however, the printhead valves in printhead 3 would open with a time offset Δt when controlled by the relatively slow robot control 5 when printhead 3 passes the boundary of the area to be coated 12 along the programmed movement path 11. This means that the surface 12 to be coated is only coated with a corresponding spatial offset Δs=v·Δt, as shown in FIG. 4. The spatial offset Δs and thus the achievable spatial resolution during coating depends here on the drawing speed v of the printhead 3 along the programmed movement path 11 and the temporal offset Δt. The offset can, for example, be compensated by a lead time. One problem, however, is the timing of the control, which generates a repeat error (“jitter”). It is therefore important that the control of the printhead valves in the printhead 3 is highly dynamic and highly precise in terms and timing.

FIG. 3 shows a simplified schematic representation of the printhead 3 with six nozzles 14 arranged in a single nozzle row. In practice, however, the printhead 3 typically has a larger number of nozzles 14 per nozzle row and a larger number of nozzle rows, which is not significant for the disclosure.

FIG. 5 shows a schematic diagram to illustrate the interpolation of the printhead control positions from the robot control positions.

The upper part of the drawing shows the positions stored in the robot control along a time axis, whereby the positions are represented as time markers ♦ or time markers ⋄. Below this, the drawing shows the positions along the time axis stored in the printhead control.

The filled-in time markers ♦ each illustrate a time at which coating agent is applied, while the blank time markers ⋄ each symbolize a time at which no coating agent is applied.

It can be seen from the drawing that the temporal resolution and thus also the spatial resolution of the positions in the robot control is considerably coarser and thus less accurate than in the printhead control.

The printhead control enables this finer spatial resolution of the positions by the printhead control interpolating finer positions from the relatively coarse positions of the robot control.

The printhead is moved along a given movement path over the component surface, where the coating should start at time t=t1 and end again at time t=t2. It can be seen from the drawing that the coating is started or finished very precisely at the desired points in time t=t1 or t=t2, which is made possible by the aforementioned interpolation.

The disclosure is not limited to the embodiment described above. Rather, the disclosure also claims protection for the subject-matter and the features of the dependent claims independently of the referenced claims and in particular also without the features of the main claim.

Claims

1. Coating device for coating components with a coating agent, with a) a printhead with a plurality of nozzles for delivering a coating agent jet to the component to be coated, anda plurality of printhead valves controlling the release of coating agent through the plurality of nozzles,b) a multi-axis coating robot which guides the printhead over the surface of the component to be coated,c) a robot control which controls the coating robot, andd) a printhead control that controls the printhead valves, the printhead control connected on the input side to the robot control and receives from the robot control at least one of a current spatial position, a current speed, and a current spatial orientation of the printhead as input information.

2. Coating device according to claim 1, wherein a) the robot control controls the coating robot with a specific first cycle time in a clocked manner, andb) the printhead control controls a printhead valve of the plurality of printhead valves of the printhead in a clocked manner with a specific second cycle time,c) the second cycle time of the printhead control is shorter than the first cycle time of the robot control.

3. Coating device according to claim 2, wherein the second cycle time of the printhead control is at most 100 ms.

4. Coating device according to claim 1, wherein the printhead control controls at least one of the following in addition to the plurality of printhead valves of the printhead: a) a color changer which selects one of a plurality of coating means and forwards the selected coating means to the printhead,b) a metering device which meters the coating agent to be applied.

5. Coating device according to claim 1, wherein the printhead control can switch on and switch off the coating agent jet applied by the printhead in a time-controlled manner with a spatial resolution on the surface of the component to be coated of less than ±2 mm.

6. Coating device according to claim 1, further comprising: a) a measuring device for measuring the spatial position of the component to be coated, the measuring device being connected on the output side to the printhead control and transmitting the spatial position of the component to be coated to the printhead control, andb) a mechanical positioning device for precise positioning of the component to be coated.

7. Coating device according to claim 6, wherein the measuring device comprises the following: a) at least one sensor for position determination, andb) an evaluation unit which evaluates a sensor signal of the sensor and determines therefrom the spatial position of the component to be coated.

8. Coating device according to claim 6, wherein the measuring device determines the spatial position of the component to be coated with a position tolerance of less than ±2 mm.

9. Coating device according to claim 1, wherein a) the coating device has a metering control for controlling a metering device which meters the coating agent and conveys it to the printhead, andb) the metering control is connected to the robot control in order to synchronize the control of the metering device with the control of at least one printhead valve of the plurality of printhead valves of the printhead, andc) the metering control is connected to the robot control in order to synchronize the control of the metering device with the control of the coating robot.

10. Coating device according to claim 1, wherein the at least one printhead valve of the printhead has a short switching time of at most 100 ms.

11. Coating device according to claim 1, further comprising a first data interface for communication with a production planning.

12. Coating device according to claim 11, further comprising a second data interface for receiving a control file for coating the component with a graphic, the graphic being predetermined by the control file.

13. Coating device in accordance with claim 1, wherein the printhead emits a continuous jet of coating medium in a longitudinal direction or a droplet jet consisting of numerous droplets separated from each other in the longitudinal direction and aligned along the longitudinal direction, in contrast to a spray mist.

14. Coating device according to claim 1, wherein coating agent pressure is controlled with a maximum variation of ±500 mbar.

15. Coating device according to claim 1, wherein the printhead has an application efficiency of at least 90% so that substantially all of the applied coating agent is completely deposited on the component without overspray.

16. Coating device according to claim 1, wherein the printhead has a surface coating performance of at least 0.5 m2/min.

17. Coating device according to claim 1, wherein a printhead valve of the plurality of printhead valves has an electrically controllable actuator in order to eject drops of the coating agent from the printhead.

18. Coating device according to claim 6, wherein the measuring device for measuring the spatial position of the component to be coated is a camera.

19. Coating device according to claim 18, further comprising an evaluation unit that evaluates a picture of the component to be coated and the printhead taken by the camera to extract the position of the printhead relative to the component to be coated.

20. Coating device for coating components with a coating agent, with a) a printhead with a plurality of nozzles for delivering a coating agent jet to the component to be coated, anda plurality of printhead valves controlling the release of coating agent through the plurality of nozzles,b) a multi-axis coating robot which guides the printhead over the surface of the component to be coated,c) a robot control which controls the coating robot, andd) a printhead control that controls the printhead valves and at least one of a color changer which selects one of a plurality of coating means and forwards the selected coating means to the printhead and a metering device which meters the coating agent to be applied.

21. Coating device in accordance with claim 20, wherein the printhead emits a continuous jet of coating medium in a longitudinal direction or a droplet jet consisting of numerous droplets separated from each other in the longitudinal direction and aligned along the longitudinal direction, in contrast to a spray mist.