Coating device for applying coating agent in a controlled manner

Abstract

The disclosure concerns a coating device for coating components with a coating agent, in particular for painting motor vehicle body components with a paint, with a printhead for applying the coating agent to the component, and with a coating agent supply for supplying the printhead with the coating agent to be applied, wherein the coating agent flows from the coating agent supply to the printhead at a specific coating agent pressure and a specific flow rate. The disclosure provides that the coating supply will control the coating agent pressure and/or the flow rate of the coating agent. Furthermore, the disclosure includes an associated operating method.

Claims

1. A coating device for coating components with a coating agent, comprising: a manipulator that moves the printhead along a programmed movement path at a predetermined drawing speed; a printhead supported by the manipulator and having a plurality of coating agent nozzles that eject the coating agent, the plurality of coating agent nozzles include adjacent coating agent nozzles spaced from each other by a distance along the programmed movement path; and a coating agent supply for supplying the printhead with the coating agent at a specific coating agent pressure and a specific flow rate, the coating agent supply adjusts at least one of the coating agent pressure and the flow rate of the coating agent in a controlled manner, the coating agent supply includes a coating agent pump that delivers said coating agent to said printhead, the coating agent pump defines a time constant that is a period of time which elapses between a change in desired delivery quantity and a time at which 63.2% of the desired change in delivery quantity has been implemented; wherein the distance between the adjacent coating agent nozzles spaced along the programmed movement path is greater than the predetermined drawing speed of the printhead along the programmed movement path multiplied by the time constant defined by the coating agent pump.

2. The coating device according to claim 1 wherein: the printhead is rotatable relative to the programmed movement path; the plurality of coating agent nozzles are arranged in the printhead along a nozzle line, and the nozzle line and the programmed movement path define a printhead angle; and the distance between the adjacent coating agent nozzles spaced along the programmed movement path is equal to a distance between the adjacent coating agent nozzles along the nozzle line multiplied by a cosine of the printhead angle.

3. The coating device according to claim 1, wherein the coating agent pump is a metering pump which meters and delivers the coating agent to the printhead so that the flow rate is substantially independent of pressure conditions at the inlet and outlet of the metering pump.

4. The coating device according to claim 1, further comprising a pressure sensor which measures the coating agent pressure, and a flow measuring cell which measures the flow rate, and a controller which controls the metering pump as a function of the measured coating agent pressure and as a function of the measured flow rate of the coating agent.

5. The coating device according to claim 4, further comprising a) a bypass line for bypassing the metering pump; and b) a bypass valve controlling the coating agent flow through the bypass line.

6. The coating device according to claim 4, wherein the controller controls the metering pump as a function of the measured coating agent pressure and as a function of the measured coating agent flow to control the coating agent pressure to a pre-set target pressure.

7. The coating device according to claim 4, wherein the controller controls the metering pump as a function of the measured coating agent pressure and as a function of the measured coating agent flow to control the flow rate of the coating agent to a predetermined target flow rate.

8. The coating device according to claim 4, wherein a) the controller is switchable between a pressure control mode and a flow rate control mode, b) the controller regulates the coating agent pressure to a predetermined target pressure in the pressure control mode, and c) the controller regulates the flow rate of the coating agent to a predetermined target flow rate in the flow rate control mode.

9. The coating device according to claim 8, wherein a) a control unit is provided, b) the control unit switches the controller between the pressure control mode and the flow rate control mode, c) the control unit switches the controller to the pressure control mode when the printhead is operated in a transient state in which nozzle valves of the printhead are opened or closed, d) the control unit switches the controller into the flow rate control mode when the printhead is operated in a stationary state in which no nozzle valves of the printhead are opened or closed; and e) the control unit controls a bypass valve as a function of the stationary state and the transient state or during a colour change.

10. The coating device in accordance with claim 1, wherein a) the coating agent supply has a coating agent feed to supply the coating agent, b) the coating agent supply has a coating agent return to return the coating agent, c) the coating agent supply has a pressure actuator which adjusts the coating agent flow from the coating agent feed into the coating agent return, and d) the coating agent supply has a coating agent outlet connected to the coating agent feed.

11. The coating device in accordance with claim 10, wherein the pressure actuator is a return pressure regulator which adjusts the coating agent flow into the coating agent return and thereby regulates the coating agent pressure upstream of the return pressure regulator and thus also at the coating agent outlet to the predetermined desired pressure.

12. The coating device according to claim 10, wherein the pressure actuator is a controllable return valve which adjusts the coating agent flow into the coating agent return.

13. The coating device according to claim 10, wherein the pressure actuator is a double-acting control valve movable from a first position to a second position, the double-acting control valve at the first position connects the coating agent feed with the coating agent outlet and closes the coating agent return, and the double-acting control valve at the second position connects the coating agent feed with the coating agent return and closes the coating agent outlet.

14. The coating device according to claim 13, wherein a) the double-acting control valve is arranged in the printhead, and b) the coating agent outlet controlled by the double-acting control valve is a nozzle opening of the printhead, and c) the double-acting control valve has the same free flow cross-section towards the coating agent return and towards the coating agent outlet.

15. The coating device according to claim 1, wherein a) the coating agent pump is a metering pump; b) said printhead comprises a plurality of nozzle valves for controlling the flow of coating agent through said individual coating agent nozzles, and c) a control unit is provided for setting a delivery rate of the metering pump, the control unit determining the number of opened nozzle valves and setting the delivery rate of the metering pump as a function of the number of opened nozzle valves.

16. The coating device according to claim 1, wherein the coating agent supply comprises a cartridge dispenser having a coating agent-filled cartridge with a cartridge outlet for discharging the coating agent and a cartridge inlet for introducing a displacement fluid which displaces the coating agent in the cartridge and ejects it through the cartridge outlet.

17. The coating device according to claim 1, wherein the coating agent supply comprises a buffer reservoir which receives the coating agent and buffers pressure fluctuations of the coating agent.

18. The coating device according to claim 17, wherein the buffer reservoir has a cylinder with a piston which is displaceable in the cylinder.

19. The coating device according to claim 1, wherein the coating agent pump is a metering pump and further comprising a controller that controls the metering pump to deliver the coating agent to the printhead, the coating agent pressure having a maximum variation of +/−500 mbar.

20. The coating device according to claim 19, wherein the controller controls the metering pump to deliver the coating agent to the printhead such that the specified flow rate provides an exit velocity of the coating agent from the printhead that is at least 5 m/s and at most 30 m/s, and wherein the printhead has an area coating capacity of at least 0.5 m2/min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A shows a schematic diagram of a double-acting control valve for controlling the paint flow through a nozzle of the printhead in an open position,

(2) FIG. 1B the double acting control valve according to FIG. 1A in a closed position,

(3) FIG. 2 a schematic representation of a coating device according to the disclosure having a control valve for returning coating agent from the printhead, wherein the control valve is controlled in dependence on the pressure at the printhead,

(4) FIG. 3 is a modification of FIG. 2, where the control valve is controlled depending on the valves in the printhead,

(5) FIG. 4 shows another example with a flow cell and a pressure sensor,

(6) FIG. 5 another example with a color changer,

(7) FIG. 6 modification of the examples according to FIGS. 2 and 3 with a return pressure regulator,

(8) FIG. 7 a modification of FIG. 6 with an additional control unit to control the metering pump,

(9) FIG. 8 a modification of FIG. 6 with an additional buffer reservoir in the printhead,

(10) FIG. 9 a schematic diagram to illustrate the rotation of the printhead during movement, and

(11) FIG. 10 a pressure diagram to illustrate the response behavior of the coating agent pump.

DETAILED DESCRIPTION

(12) Generally, disclosure includes setting the coating agent pressure and/or the flow rate of the coating agent in a controlled manner in order to produce defined application conditions during the application of coating agents (e.g. paint, adhesive, sealant, primer, etc.) with a printhead so that high-quality coatings can be applied.

(13) The term “coating agent” used in the disclosure is to be generally understood and includes, for example, paints (e.g. water-based paint, solvent-based paint, base coat, clear coat), waxes (e.g. preservative wax), thick materials, sealants, insulating materials and adhesives.

(14) In accordance with the state of the art, the coating device according to the disclosure first has a printhead for applying the coating agent (e.g. paint, adhesive, sealant, primer, etc.) to the component (e.g. motor vehicle body component). The term “printhead” used in the context of the disclosure is to be understood in general and only serves to distinguish from atomizers (e.g. rotary atomizers, disc atomizers, airless atomizers, airmix atomizers, ultrasonic atomizers) which emit a spray of the coating agent to be applied. In contrast, the printhead emits a narrowly confined coating agent jet. Such printheads are known from the state of the art and are described for example in DE 10 2013 092 412 A1, U.S. Pat. No. 9,108,424 B2 and DE 10 2010 019 612 A1.

(15) In addition, the coating device according to the disclosure has a coating agent supply to supply the printhead with the coating agent to be applied, resulting in a specific coating agent pressure and flow rate of the coating agent.

(16) The disclosure now provides that the coating agent supply will control the coating agent pressure and/or flow rate of the coating agent to produce defined application conditions, which is important for the application of high quality coatings.

(17) In an example of the disclosure, the coating agent supply has a metering pump that meters the coating agent and delivers it to the printhead. The term metering pump references that the flow rate is essentially independent of pressure ratios at the inlet and outlet of the metering pump. This means that a defined flow rate can be set according to the control of the metering pump, which is important for high-quality coatings.

(18) For example, the metering pump can be a gear pump, a wobble piston pump or a micro gear pump, to name just a few examples.

(19) Here it is advantageous if the metering pump can be flushed with a flushing agent to flush out coating agent residues from the metering pump. This is particularly advantageous if the metering pump is to be used to pump different colours one after the other. In the case of a colour change, the metering pump can first be flushed with a flushing agent in order to flush out coating agent residues of the old colour from the metering pump. Alternatively, the metering pump can first be blown out and then flushed. The metering pump can also be cleaned alternately with flushing agent and pulsed air.

(20) Alternatively, within the scope of the disclosure, there is the possibility that the coating agent supply has a piston metering unit in order to supply the coating agent in a controlled manner. The coating agent is pressed out of a cylinder by a sliding piston so that the piston position directly determines the amount of coating agent applied.

(21) The piston metering unit can, for example, be arranged on or in the applicator (printhead), before of the robot hand axis, behind the robot hand axis, on the distal robot arm (“Arm 2”) or on the proximal robot arm (“Arm 1”), travelling on a linear traversing axis, on the cabin wall of the painting cabin or outside the painting cabin.

(22) Another variant of the disclosure, on the other hand, provides for a cartridge dispenser with a cartridge filled with a coating agent, with a cartridge outlet for dispensing the coating agent and a cartridge inlet for introducing a displacement fluid which displaces the coating agent contained in the cartridge and ejects it through the cartridge outlet. The flow rate of the coating agent at the printhead can be precisely controlled by controlling the displacement fluid introduced into the cartridge (e.g. solvent first, then compressed air) so that defined application conditions can also be set in this way.

(23) In another variant of the disclosure, the coating agent supply has a coating agent reservoir (e.g. ring line) in order to supply the coating agent to be applied, the defined application conditions being set by a pressure regulator which regulates the coating agent pressure. A pressure sensor can also be provided to measure the coating agent pressure, whereby the measured quantity of the coating agent pressure can then be made available to the pressure regulator.

(24) In one example, the coating agent supply has a coating agent pump to convey the coating agent to the printhead. The coating agent pump is preferably a metering pump in the sense described above, but in this example another type of pump can be used as a coating agent pump.

(25) Furthermore, the coating agent supply in this example has a pressure sensor which measures the coating agent pressure at the printhead, i.e. upstream of the printhead, inside the printhead or directly at a nozzle of the printhead or at the metering pump.

(26) In the case of a pressure regulator, this example also has a flow measuring cell which measures the flow rate from the coating agent pump to the printhead, in particular the volume flow or mass flow of the coating agent being pumped.

(27) Finally, this example has a controller which controls the coating agent pump as a function of the measured coating agent pressure and/or as a function of the measured flow rate of the coating agent.

(28) Furthermore, in this example a bypass line is may be provided in order to bypass the coating agent pump. A bypass valve is also provided to control the flow of coating agent through the bypass line. The discharge of coating agent via the by-pass line also allows the pressure conditions at the printhead to be checked and can also be used for flushing and pressing.

(29) The above mentioned controller controls the coating agent pump preferably in dependence on the measured coating agent pressure and/or in dependence on the measured coating agent flow, whereby different control objectives are possible. A control objective provides that the coating agent pressure is controlled to a specified target pressure. Another control objective, on the other hand, provides that the flow rate of the coating agent is controlled to a specified target flow rate.

(30) The controller can therefore preferably be switched between a pressure control mode and a flow control mode. In pressure control mode, the controller adjusts the coating agent pressure to the specified target pressure. In the flow rate control mode, however, the controller adjusts the flow rate of the coating agent to the specified target flow rate.

(31) In this example, a control unit can be used to switch between these two operating modes (pressure control mode and flow rate control mode). Here it may be taken into account that the printhead is partly operated in a stationary state and partly in a transient state. In the stationary state (steady state) no nozzles are opened or closed at the printhead, whereby a preferably constant flow rate of the coating agent should be applied. In the transient state of the printhead, however, nozzle valves are closed or opened, which includes a corresponding dynamic adjustment of the applied quantity flow. The control unit preferably switches the controller to the flow control mode when the printhead is operated in a stationary state in which no nozzle valves of the printhead are opened or closed. The control unit, on the other hand, prefers to switch the controller to the pressure control mode when the printhead is operating in a transient state where nozzle valves of the printhead are dynamically opened or closed.

(32) The controller can calculate the different states in advance on the basis of the coating program, since it is known at any time during the coating process which nozzle is open or closed. Thus, the required coating agent volume flow can be calculated for any point in time or the points in time of the changeover from volume control operation to pressure control operation can be calculated. This significantly increases the dynamics of the control system.

(33) In addition, the control unit can also control the aforementioned bypass valve depending on the stationary or transient state of the printhead.

(34) In another example of the disclosure, the coating agent supply has a coating agent supply (e.g. ring line), a coating agent return (e.g. ring line) and a pressure actuator (e.g. control valve, pressure regulator) which adjusts the coating agent flow from the coating agent supply to the coating agent return. The return preferably leads the coating agent back to reuse, e.g. back to the ring line, to the paint tank or to another applicator. In addition, the coating agent supply in this example has a coating agent outlet (e.g. nozzle of the printhead) which can be connected to the coating agent supply or is connected to the coating agent supply.

(35) In this example, the pressure actuator—as already briefly mentioned above—can be designed as a return pressure regulator which adjusts the coating agent flow into the coating agent return and thereby regulates the coating agent pressure flow upwards upstream of the return pressure regulator and thus also at the coating agent outlet to the specified target pressure.

(36) Alternatively, as briefly mentioned above, it is possible for the pressure actuator to be a controllable return valve which adjusts the flow of coating agent to the coating agent return in order to establish defined application conditions at the coating agent outlet. As described above, the controller can also calculate the position of the return valve in advance and thus increase the control dynamics.

(37) In another variant of this example, the pressure actuator is a double-acting control valve which, depending on its valve position, either connects the coating agent supply with the coating agent outlet and closes the coating agent return, or connects the coating agent supply with the coating agent return and closes the coating agent outlet. The supplied flow of coating agent is thus directed from the pressure actuator either into the coating agent return or through the coating agent outlet, so that the flow of coating agent conveyed can remain constant in quantity and only the direction of the coating agent flow is changed, namely either into the coating agent return or through the coating agent outlet. For example, the double-acting control valve may then have a dumbbell-shaped or rocker-shaped valve element.

(38) This double-acting control valve may be located in the printhead. However, it is also possible for the double-acting control valve to be located upstream of the printhead.

(39) It should also be mentioned that the coating agent outlet controlled by the double-acting control valve may be a nozzle opening of the printhead. In this case, the double-acting control valve is located directly at the nozzle opening.

(40) It should also be mentioned that the double-acting control valve has the same free flow cross-section to the coating agent return and to the coating agent outlet, resulting in the same flow resistance in both valve positions.

(41) In a another example, the coating agent supply for conveying the coating agent has a coating agent pump with an adjustable flow rate, in particular a metering pump. The nozzle head has several coating agent nozzles for dispensing the coating agent, whereby a nozzle valve is assigned to each individual coating agent nozzle, so that the individual coating agent nozzles can be individually controlled. In addition, a control unit is provided for setting the delivery rate of the coating agent pump, the control unit determining the number of open nozzle valves and setting the delivery rate of the coating agent pump as a function of the number of open nozzle valves. The control unit can determine the number of open nozzle valves, for example by interrogating the control signals for the individual nozzle valves or as described above. The flow rate of the coating agent pump is then adjusted according to the required flow rate depending on the number of open nozzle valves. It should be noted that the control unit preferably has a very short response time of less than 100 ms, 60 ms, 10 ms, 1 ms, 100 μs or even less than 10 μs in order to be able to react sufficiently quickly to the dynamic opening and closing of the individual nozzle valves.

(42) Another way to control the application conditions on the printhead is to provide a buffer reservoir that holds the coating agent and buffers pressure fluctuations of the coating agent.

(43) The buffer reservoir may be located directly in the printhead in order to buffer pressure fluctuations as effectively as possible. Alternatively, it is also possible to place the buffer reservoir outside the printhead and upstream of the printhead.

(44) For example, the buffer reservoir can be realized by a cylinder with a movable piston, whereby the piston can be pretensioned by a spring, compressed air, an electric actuator, a piezoelectric actuator or a magnetic actuator.

(45) It should also be mentioned that the printhead is preferably moved over the surface of the component to be coated by a manipulator (e.g. painting robot) with a serial robot kinematics along a programmed movement path at a certain drawing speed. When passing over a component edge, the individual coating agent nozzles of the printhead are then be closed or opened one after the other, which also requires a corresponding dynamic adjustment of the delivery rate of the coating agent pump. It should be noted that the required reaction time of the coating agent pump depends on the drawing speed of the printhead and on the distance of the adjacent coating agent nozzles along the programmed path of movement. The coating agent pump therefore preferably has a sufficiently short time constant, whereby the time constant of the coating agent pump indicates the time span which elapses with a change in the desired flow rate until 63.2% (1-1/e) of the desired change in the flow rate has been implemented. The following formula is therefore preferable:
s>v−τ
with: s: distance of the adjacent coating agent nozzles in the printhead along the programmed movement path, v: drawing speed of the printhead along the programmed robot path, τ: time constant of the coating agent pump.

(46) However, it should be taken into account that the distance of the adjacent coating agent nozzles along the programmed path of movement can also be influenced by a rotation of the printhead. Thus, the coating agent nozzles are usually arranged along a nozzle line in the printhead, where the printhead with the nozzle line is rotatable relative to the programmed trajectory, so that the nozzle line with the programmed trajectory includes a printhead angle. The printhead may then be rotated and moved in such a way that the following formula applies:
v.Math.τ<s=d.Math.cos α
with: s: Distance of the adjacent coating agent nozzles in the printhead along the programmed movement path, d: distance of the adjacent coating agent nozzles along the nozzle line, v: drawing speed of the printhead along the programmed robot path, τ: time constant of the coating agent pump, α: rotation angle between the nozzle line and the programmed trajectory of the printhead.

(47) In general it should be mentioned that the printhead emits a narrowly limited jet of coating agent in contrast to a spray mist, as is the case with rotary atomizers, for example.

(48) For example, the printhead can emit a droplet jet or even individual droplets in contrast to a jet of coating agent that is connected in the longitudinal direction of the jet.

(49) Alternatively, however, there is also the possibility that the printhead emits a coating agent jet being continuous in the longitudinal direction of the jet, in contrast to the droplet jet mentioned above.

(50) The control of the coating agent pressure according to the disclosure is preferably carried out with a maximum fluctuation range of ±500 mbar, ±200 mbar, ±100 mbar or even ±50 mbar at the most.

(51) It should also be mentioned that the printhead preferably has an application efficiency of at least 80%, 90%, 95% or even 99%, so that essentially the entire applied coating agent is completely deposited on the component without overspray.

(52) The printhead preferably enables a surface coating performance of at least 0.5 m.sup.2/min, 1 m.sup.2/min, 2 m.sup.2/min or at least 3 m.sup.2/min, i.e. the printhead can coat a corresponding component surface within the specified time period.

(53) It should also be mentioned that the flow rate 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.

(54) For example, the exit velocity of the coating agent can be in the range of 5 m/s to 30 m/s.

(55) The application distance between nozzle and component surface can, for example, be in the range from 4 mm to 200 mm, especially from 5 mm to 100 mm, 5 mm to 50 mm, 10 mm to 40 mm.

(56) The disclosure also offers various possibilities with regard to the applied coating agent. Preferably, however, the coating agent is a paint, such as a base coat, a clear coat, an effect paint, a mica paint or a metallic paint. For example, these coatings can be water-based or solvent-based.

(57) To eject the coating agent to be applied, the printhead may have at least one electrically controllable actuator, such as a magnetic actuator or a piezo actuator. Pneumatic valves or drives are also conceivable.

(58) The disclosure also includes a corresponding operating method, whereby the individual steps of the operating method according to the disclosure are already apparent from the above description of the coating device according to the disclosure and therefore do not have to be described in more detail.

(59) In the following, FIGS. 1A and 1B are first explained, which show a double acting nozzle valve in a nozzle head of a coating device according to the disclosure, whereby the nozzle valve either releases (FIG. 1A) or blocks (FIG. 1B) the coating agent flow through a nozzle 1 in the printhead.

(60) The coating agent to be applied is fed into the printhead via a coating agent feed 2 and can either leave the nozzle head through the nozzle 1 or be returned to a coating agent return 3 depending on the position of the nozzle valve, the flow path from the coating agent feed 2 to the coating agent return 3 leading through a return opening 4 which is either released (FIG. 1B) or blocked (FIG. 1A) by the control valve.

(61) The control valve is only schematically shown here and has a valve needle 5 which can be shifted in the direction of the double arrow by an actuator not shown (e.g. solenoid actuator).

(62) A seal 6, 7 is fitted to each of the two opposite ends of the valve needle 5 in order to be able to close the nozzle 1 or the return opening 4.

(63) In the valve position shown in FIG. 1A, the control valve closes the return opening 4 with the seal 6 so that no coating agent can flow from the coating agent feed 2 to the coating agent return 3.

(64) Instead, the control valve releases the nozzle 1 so that coating agent can escape from the coating agent feed 2 through the nozzle 1.

(65) In the valve position shown in FIG. 1B, however, the control valve with the seal 6 releases the return opening 4 so that coating agent can flow from the coating agent feed 2 into the coating agent return 3.

(66) In this valve position, on the other hand, the control valve closes the nozzle 1 with the seal 7 so that no coating agent can escape from the nozzle 1.

(67) The control valve is therefore double-acting, since the control valve controls not only the coating agent flow through the nozzle 1, but also the coating agent flow from the coating agent feed 2 to the coating agent return 3.

(68) It should be mentioned here that the return opening 4 essentially has the same free flow cross-section as the nozzle 1 and thus also has the same flow resistance. This means that the coating agent flow through the coating agent feed 2 is not influenced by the position of the control valve, since the coating agent flow supplied is discharged either through the return opening 4 or through the nozzle 1 without changing the flow resistance. This is advantageous because switching the control valve will not result in unwanted pressure surges which could affect the coating quality. The recirculation should generate a similar back pressure or be almost pressureless so that the flow conditions remain constant.

(69) FIG. 2 shows a schematic representation of a coating device according to the disclosure with a coating agent feed 8, which can be connected, for example, to a ring line and supplies a metering pump 9 with the coating agent to be applied. The metering pump 9 delivers the coating agent to be applied at a defined flow rate to a printhead 10 with numerous nozzles N1, N2, N3, N4, . . . , Nn, where each nozzle N1-Nn is assigned a control valve V1-Vn in order to control the coating agent flow through the respective nozzle N1-Nn.

(70) The control valves V1-Vn are each individually controlled by control signals S1-Sn, whereby the generation of the control signals S1-Sn is not shown here for simplification.

(71) In addition, the coating device shown has a coating agent return 11 in order to circulate unneeded coating agent or to divert it into a return.

(72) The coating agent flow through the coating agent return is adjusted by a return valve VR, whereby the return valve VR is controlled by a control unit 12.

(73) In addition, the coating device shown has a pressure sensor 13 which measures the coating agent pressure in the printhead 10, i.e. immediately in front of the nozzles N1-Nn.

(74) The pressure sensor 13 is connected on the output side with the control unit 12, which controls the return valve VR depending on the measured pressure. The aim of controlling the return valve VR by the control unit 12 is to set the coating agent pressure in the printhead 10 as constant as possible, regardless of the valve position of the V1-Vn control valves. Thus, opening the control valves V1-Vn leads to a larger coating agent flow through the respective nozzles N1-Nn, which without countermeasures initially leads to an undesired pressure drop of the coating agent pressure in the printhead 10. The control unit 12 can counteract this by closing the return valve VR accordingly, so that less coating agent is diverted via the coating agent feedback 11. The reduced coating agent flow into the coating agent return 11 then compensates, if possible, for the increased coating agent flow through the open control valves V1-Vn. Ideally, this compensation should be such that the flow of coating agent into the printhead 10 remains constant regardless of the valve position of the control valves V1-Vn, which also results in a constant coating agent pressure in the printhead 10. This compensation therefore leads to a constant coating agent pressure even when the control valves V1-Vn are opened or closed dynamically, thus contributing to a good coating result.

(75) The example shown in FIG. 3 largely corresponds to the example described above and shown in FIG. 2, so that reference is made to the above description to avoid repetitions, using the same reference signs for the corresponding details.

(76) One difference between this example and the example shown in FIG. 2 is that the control unit 12 is not connected to the pressure sensor 13, but receives the control signals S1-Sn for controlling the control valves V1-Vn as input signals. The control unit 12 is thus informed about a dynamic opening or closing of the control valves S1-Sn and can react thereupon with a corresponding closing or opening of the return valve VR in order to be able to compensate an increased or reduced coating agent flow through the nozzles N1-Nn by a corresponding opening or closing of the return valve VR in order to keep the coating agent pressure in the printhead 10 as constant as possible.

(77) FIG. 4 shows another example of a coating device according to disclosure with a printhead 14 with numerous control valves controlled by a control unit 15.

(78) The coating agent to be applied is supplied to the printhead 14 via a coating agent feed 16, a metering pump 17 and a flow measuring cell 18, whereby the flow measuring cell 18 measures the flow rate Q of the coating agent.

(79) In addition, the coating device has a pressure sensor 19 which measures the coating agent pressure p in the printhead 14.

(80) The pressure sensor 19 and the flow measuring cell 18 are connected on the output side to a controller 20 which controls the metering pump 17.

(81) In addition, a bypass valve 21 is provided which is controlled by the control unit 15.

(82) During operation of this coating device, a distinction is made between a stationary state and a transient state.

(83) In the stationary state, no control valves are dynamically opened or closed in the printhead 14, so that the system is in the stationary state.

(84) In the transient state, however, control valves in the printhead 14 are dynamically closed or opened so that the system is not in the stationary state.

(85) Depending on these two states, the controller 20 is then operated either in a flow control mode or in a pressure control mode.

(86) In the pressure control mode, the controller 20 controls the metering pump 17 in such a way that a coating agent pressure p that is as constant as possible is provided at the input of the printhead 14.

(87) In the flow rate control mode, however, the controller 20 controls the metering pump 17 in such a way that the flow rate Q of the coating agent is as constant as possible.

(88) The control unit 15 switches the controller 20 between the pressure control mode and the flow rate control mode in such a way that in the transient state it switches to the pressure control mode, whereas in the stationary state it switches to the flow rate control mode.

(89) FIG. 5 shows another example of a coating device according to the disclosure with a printhead 22 as application device.

(90) The printhead 22 is supplied with the paint to be coated via a ring line arrangement 23 with several lines for different colours F1, F2, . . . , Fn.

(91) The desired color F1-Fn is selected by a color changer 24 from the ring line arrangement 23, whereby the color changer 24 feeds the selected color to a metering pump 25, which feeds the selected coating agent with a defined flow rate to the printhead 22.

(92) In addition, the color changer 24 is connected to a ring line arrangement 26, which forms a coating agent return.

(93) The color changer 24 therefore not only has the function of selecting the desired paint F1-Fn from the ring line arrangement 23 and feeding it to the metering pump 25 and thus also to the printhead 22. Rather, the color changer 24 also has the task of returning excess coating agent to the ring line arrangement 26 depending on the valve position of the control valves in the printhead 22 in order to prevent pressure fluctuations in the printhead 22 as far as possible or if no coating agent of a certain color is required.

(94) In addition, the coating device has a pressure sensor 27, which measures the paint pressure in the printhead 22 or at the metering pump and is connected on the output side to a control unit 28. The control unit 28 now controls the color changer 24 in such a way that pressure fluctuations in the printhead 22 are avoided as far as possible. For this purpose, the control unit 28 opens or closes the return to the ring line arrangement 26 in order to compensate for a dynamic increase or decrease in the applied coating agent flow. The control unit 28 thus ensures controlled printing conditions in the printhead 22, which contributes to a good coating result.

(95) FIG. 6 shows a modification of FIG. 2 so that to avoid repetitions, reference is first made to the above description of FIG. 2, using the same reference signs for corresponding details.

(96) A feature of this example is that a return pressure regulator 29 controls the coating agent flow into the coating agent return 11 instead of the return valve VR. The return pressure regulator 29 regulates the coating agents pressure upstream of the return pressure regulator 29 and thus within the printhead 10 to a specified set pressure. The return flow regulator 29 can compensate for an increase or decrease in the applied coating agent flow if the control valves V1-Vn are opened or closed dynamically. Thus the return pressure regulator 29 ensures an essentially constant coating agent pressure in the printhead 10.

(97) FIG. 7 shows a modification of the example in FIG. 6, so that to avoid repetitions, reference is first made to the above description, using the same reference signs for appropriate details.

(98) A feature of this example is that a control unit 30 controls the metering pump 9 depending on the control signals S1-Sn for the control valves V1-Vn of the printhead 10.

(99) For example, if one or more of the control valves V1-Vn are closed dynamically, the control unit 30 can reduce the flow rate of the metering pump 9 to prevent the coating agent pressure in the printhead 10 from overshooting. In this example, not only does the return pressure regulator 29 contribute to achieving the desired pressure conditions in the printhead 10, but also the control of the metering pump 9 by the control unit 30.

(100) FIG. 8 shows a modification of the example according to FIG. 6, so that to avoid repetitions, reference is first made to the above description, using the same reference signs for the corresponding details.

(101) A feature of this example is that the printhead 10 contains an integrated buffer reservoir 31 which buffers pressure fluctuations in the printhead 10.

(102) For example, the buffer reservoir 31 may have a cylinder with a sliding piston, where the piston can be preloaded by a spring or compressed air.

(103) Due to its buffer effect, the buffer reservoir 31 also contributes to ensuring that no significant pressure fluctuations occur in the printhead 10 even when the control valves V1-Vn are opened or closed dynamically, as these are buffered by the buffer reservoir 31.

(104) FIGS. 9 and 10 are described below. FIG. 9, for example, shows in very simplified form the movement of a printhead 32 along a programmed movement path 33 over a component surface, whereby the printhead 32 is moved over the component surface by a multi-axis painting robot with a serial robot kinematics or by a machine or a linear unit at a drawing speed v. The printhead 32 is moved over the component surface by a multi-axis painting robot with a serial robot kinematics.

(105) In the printhead 32, several nozzles 34 are arranged next to each other along a nozzle line 35, which is very simplified. The nozzles 34 are arranged along the nozzle line 35 at a distance d from each other.

(106) The nozzle head 32 can be rotated each time by the multi-axis painting robot, whereby the nozzle head 32 with the nozzle li-nie 35 encloses an angle α relative to the programmed movement path 33. Depending on the rotation angle α of the printhead 32, a certain distance s between the adjacent nozzles 34 along the programmed movement path 33 is set.

(107) In the above example the nozzles 34 in the printhead 32 are be closed one after the other as the printhead 32 approaches the boundary of an area to be coated. If the printhead 32 reaches the end of an area to be coated along the programmed trajectory 33, the nozzles 34 of the printhead 32 are closed one after the other from front to rear.

(108) This closing of the nozzles 34 leads to a dynamic reduction of the applied coating agent flow, so that the associated coating agent pump should be shut down accordingly in order to avoid excess coating agent delivery and the associated excess coating agent pressure. However, a coating pump usually has a certain inertia and cannot react immediately to a change in the desired flow rate, but only with a certain delay, as shown in FIG. 10. FIG. 10 shows the change of the desired flow rate from a nominal value Q1 to a lower nominal value Q2. From this it can be seen that the desired change in the flow rate is implemented with a certain time constant τ.

(109) If possible, the coating agent pump should now be able to react so quickly that the coating agent pump with its flow rate can follow the dynamic opening and closing of the nozzles 34 of the nozzle head 32. The coating device should therefore fulfil the following formula:
v.Math.τ<s=d.Math.cos α
with: s: Distance of the adjacent coating agent nozzles in the printhead along the programmed movement path, d: distance of the adjacent coating agent nozzles along the nozzle line, v: drawing speed of the printhead along the programmed robot path, τ: time constant of the coating agent pump, α: rotation angle between the nozzle line and the programmed trajectory of the printhead.

(110) If this formula is fulfilled, the coating agent pump can approximately track the amount of coating agent pumped to the dynamic opening or closing of the nozzles 34.

(111) The disclosure is not limited to the examples described above. Rather, a large number of variants and modifications are possible which also make use of the inventive idea and therefore fall within the scope of protection. The feature of a control of the coating agent pressure or the flow rate of the coating agent is therefore not a necessary feature in the context of the further aspects of disclosure.