Method for process diagnosis and rotary atomizer arrangement

0001The invention relates to a method for process diagnosis in the coating, in particular painting of workpieces such as vehicle bodies or parts thereof and a corresponding Rotationszerstäuberanordnung according to the preamble of the independent claims. The atomizer arrangement can in particular consist of an electrostatic rotary atomizer or also of the atomizer and the forearm of a painting robot, on which the rotary atomizer is arranged via the usual wrist.

0002Electrostatic rotary atomizers are well known. In atomizers working with direct charging of the coating material, usually the electrically conductive part of the atomizer is placed under high voltage, so that the coating material can be charged by an electrode device containing all the electrically conductive parts such as bell plates, paint tubes, fittings, etc., with which it comes in contact , However, it is known that external charging of the coating material with external electrodes is also possible.

0003The usual rotary atomizers contain a pneumatic drive turbine for the Absprühelement forming bell cup whose speed z. B. can be measured by optical scanning rotating markers and transmission of the sampling pulses via optical fibers and can be kept constant by a control loop by controlling the drive air (<patcit id="pcit0001" dnum="DE4306800C2"><text>DE 43 06 800 C2</text></patcit> and <patcit id="pcit0002" dnum="EP1388372B1"><text>EP 1 388 372 B1</text></patcit>), although the problem is that at the beginning of a coating process when opening the outflow of the coating material from the atomizer controlling conventional main needle valve due to the inertia of the control system initially the speed can drop relatively sharply, which leads to coating errors and possibly be avoided by costly additional measures can.

0004In the case of the main needle valve, it is necessary to monitor the switching times for control-technical compensation of switching errors such as time delays or shifts, for example due to component wear, which lead to coating errors, especially in the case of rapid movements of a painting robot. For this purpose it is known to detect and evaluate the switching positions with optoelectronic sensors and optical waveguides (<patcit id="pcit0003" dnum="EP1245291B1"><text>EP 1 245 291 B1</text></patcit>). Fiber optic cables, however, do not always transmit the sensor signals reliably because of interfering or faulty interfaces, have only a very limited service life due to their constant bending movements in a painting robot, and due to their arrangement in the robot moreover can only be replaced with considerable effort. Also, signal evaluation may be too slow for optimal error compensation in some cases.

0005In general, there is also the problem that various process faults and other fault conditions in the coating operation are not detected at all due to the lack of appropriate sensors. Typical errors include, for example, the mounting of a wrong bell cup or the complete absence of the bell cup, contact between the bell cup and the workpiece or other surrounding objects, imbalance of the bell cup, Bearing wear or incorrect or completely missing bearing air of the rotary atomizers usually provided in the air bearing of the bell-plate shaft and incorrect volume flow of the coating material or changes in its viscosity and other properties.

0006It is already known per se to replace the air turbine commonly used in practice by an electric drive motor for the air-bearing bell-cylinder shaft of a rotary atomizer (<patcit id="pcit0004" dnum="WO2005110613A"><text>WO 2005/110613</text></patcit>). The problems described above are not solved in the known rotary atomizer. In addition, in the known Rotationszerstäuber the above-mentioned problem that it may be necessary in electrostatic coating to set the entire rotary atomizer under high voltage in the order of 100 kV. Without additional measures, an electric drive motor and its control system in an electrostatic rotary atomizer with direct charging of the coating material can not be used.

0007The potential separation measures required in an electrostatic rotary atomizer for an electromotive bell plate drive and for the signal transmission are described in the German patent application <patcit id="pcit0005" dnum="DE102007004819"><text>10 2007 004 819.1 </text></patcit>from 31.01.2007 described.

0008The prior art is also to be noted <patcit id="pcit0006" dnum="EP1403746A"><text>EP 1 403 746 A</text></patcit>, <patcit id="pcit0007" dnum="DE3101193A1"><text>DE 31 01 193 A1</text></patcit>, <patcit id="pcit0008" dnum="DE3002206A1"><text>DE 30 02 206 A1</text></patcit>, <patcit id="pcit0009" dnum="DE10049506A1"><text>DE 100 49 506 A1</text></patcit>, <patcit id="pcit0010" dnum="US5629870A"><text>US 5,629,870 A</text></patcit>, <patcit id="pcit0011" dnum="US2006192508A1"><text>US 2006/192508 A1</text></patcit> and <patcit id="pcit0012" dnum="US2005067991A1"><text>US 2005/067991 A1</text></patcit>, However, the latter references generally disclose electric drives without reference to the pertinent technical field of rotary atomizers.

0009Out <patcit id="pcit0013" dnum="WO2007006325A1"><text>WO 2007/006325 A1</text></patcit> is a method and a device according to the preamble of claims 1 and 8, respectively. However, it is not possible to control the volume flow of the coating material.

0010Starting in particular from the known rotary atomizers with the previously customary air turbines, the invention has for its object to provide a method for process diagnosis and / or highly dynamic control of parameters of the coating process or the engine and a corresponding Rotationszerstäuberanordnung with which as quickly and reliably as one or more the above mentioned error conditions can be detected, so that the necessary countermeasures are possible in good time.

0011This object is solved by the features of the claims.

0012The invention is based on the finding that when using an electric drive motor for the preferably driven via a drive shaft bell cup of a rotary atomizer in a simple manner from the engine characteristics error conditions in the coating of workpieces are extremely fast and reliable detectable so that they can be corrected. The evaluation of the engine characteristics can be carried out appropriately with an electronic control system of the engine itself or with another evaluation system. The method described here can also be used for the highly dynamic control of process parameters of various types and parameters of the engine. In many cases, the detection of fault conditions is possible without the use of sensors outside the engine and its own control system. In other cases, the evaluation of engine characteristics can be done with external sensors or supported by them. For example, inadmissible robot movements can be detected and corrected with external acceleration sensors or compensated for by changing process parameters.

0013The parameters of interest in each case can be determined and analyzed during the coating or spraying process in the method described here or the corresponding atomizer arrangement, in particular also during the normal painting or coating operation or at any rate during rotation of the spray-off element at speeds with which it also during the Operating when spraying the coating material rotates. Rotary atomizers for powder coatings typically operate at speeds of about 3000 to 12000 / min, but the invention is particularly suitable for high-speed rotary atomizers with speeds that can typically be between 5000 and 80,000 rpm.

0014Furthermore, the invention is particularly suitable for electrostatic rotary atomizers, which are connected to the direct or external charging of the sprayed paint or other coating material to high voltage, for example of the order of 100 kV.

0015The parameters to be determined and analyzed according to the invention can typically be quantities which can deviate from nominal values ​​or normal conditions in the normal coating mode, while other disturbances (such as collisions of the rotating spray element with the surface to be coated) are detected or avoided in another way can be.

0016The correction of detected errors can be made dependent in particular on constantly changing parameters of the spraying process or of the bell-plate drive system, if a limit value considered to be still permissible is exceeded. In general, upon detection of errors, an alarm signal can be generated and / or intervened automatically in the monitored process for carrying out the respectively required measures.

0017Typical characteristics of the electric drive motor which can be evaluated according to the invention are the size and / or the course of its current, its electrical power, its torque or load torque, its positive or negative acceleration and / or its rotational speed, while the process or drive parameters are in particular the load of the drive system through the bell cup, the coating material supplied thereto, Imbalance of the rotating elements and / or storage of the drive shaft can be analyzed.

0018For example, it is possible to make use of the fact that, when the bell plate is wrong, for example lighter or heavier, or when the bell plate is missing, different engine torques act and a different power requirement exists than when using the correct bell plate. Due to the different torque requirements and the different acceleration behavior can be automatically close to the different moments of inertia of bell plates, which may consist of different materials such as aluminum, steel, titanium or plastic, etc. Furthermore, it is also possible to determine the different types of bell cells, which are characterized by their specific geometric dimensions and features. Based on the evaluation then the right bell cup can be selected and mounted.

0019Higher torque or power requirements or a decrease in speed can also be due to increasing wear of the bearings of the drive shaft, which not only air bearings come into consideration, but also rolling and any other bearing designs. If an impermissibly high bearing wear corresponding change of the characteristic concerned is determined, for example the storage may be replaced or repaired with other atomizer components before any major damage occurs.

0020Particularly useful may be in air bearings and a control of the bearing clearance. For this purpose, for example, it is possible first to determine the engine torque at a standstill and then to determine the air flow rate after preferably slow start of the engine as a function of the engine speed and by evaluating the engine characteristics. Important here is in particular the possible without other sensors determination as to whether the starting of the engine at all bearing clearance. Lack of clearance would be due to the friction in the bearing determined by a drastic increase in the necessary torque of the engine, so that the engine can be switched off to avoid otherwise unavoidable damage to the bearing. The control of the bearing clearance is also useful during operation with the engine running.

0021Another important possibility in practice is to measure any imbalance of the bell cup or other eccentricities of the drive shaft by evaluating the engine characteristics in order to take appropriate countermeasures for detection of improper values ​​and thus damage the storage or, for example, in blocking storage and a release and To prevent departure of the rotating bell cup from the drive shaft.

0022Another important possibility is the control of the coating material. By evaluating the acceleration and / or braking behavior of the drive motor, the volume flow of the coating material can be controlled, in particular by means of the linear increase of the acceleration or braking forces (acceleration and braking ramps). Through power or torque detection or by the effects on the speed properties of the applied paint or other coating material and its changes can be determined such as viscosity, density, adhesion, cohesion, etc.

0023It may also be useful not to evaluate the torque behavior of the engine or not only in normal operation, but instead without the spraying of coating material and in this case the load of the motor through the bell cup by an electrically generated for example according to the eddy current principle or otherwise artificial counter-torque simulate.

0024In general, the quality and precision of the application can be significantly improved by the invention, for example, in the interior and exterior painting of vehicle bodies. One reason for this is the ability to measure speed changes with the electronic control system of the electric motor much faster and can correct than with the opto-electronic and pneumatic speed control circuit of the usual air turbines, so that it eg when opening the main needle valve can not come as before to a significant drop in speed and corresponding coating errors.

0025In addition, the compensation of switching time changes of the main needle valve can be significantly improved by the invention, since the evaluation of the switching times corresponding speed curve or other engine characteristics is much more dynamic and accurate than the above-mentioned known method with opto-electronic Hauptnadelabfrage. According to another aspect, the switching time analysis according to the invention makes it possible to control coating materials mixed from two or more components, such as the 2K paints, whose components consisting of base paint and hardener are conveyed by respective metering devices to a mixing device in front of or in the atomizer. It is important that the two dosing devices are started at their right times. According to the invention, by evaluating, for example, the course of the engine torques, the load on the engine can be determined chronologically by each of the two components, so that errors can be corrected by shifting the control signals of the metering devices over time. This could also be due to the engine characteristics, the complete absence of one of the two components or incorrect viscosity or other material properties of each of the two components can be determined. Inhomogeneous or inadequate mixing could also be detected, since the motor would then be loaded differently (eg if the mixer became blocked) than if it were mixed correctly.

0026The evaluation of the engine parameters may expediently be carried out by an electronic processor, for example a microprocessor belonging to the engine control system, possibly by comparing the characteristic curve determined by the evaluation circuit with boundary conditions stored in the processor or in an external control system, for example, reference, reference or calibration curves and generation of corresponding deviation signals in the event of error conditions. It can be determined exactly, which changes of engine characteristics are due to what causes or parameters of Absprühprozesses or Glockentellerantriebs. For example, changes in viscosity of the coating material have significantly different effects on the engine behavior than the sudden loading by the coating material when opening the main needle valve, so that the respective causes of the characteristic changes can be easily discriminated.

0027Electric motors suitable for the invention, which can drive the bell cup of a high-speed rotary atomizer with the required rotational speeds of at least 3000 and generally more than 10000 / min to eg 80000 / min, are commercially available in various types. A highly dynamic drive control system which can be used for these motors and which is specially designed for the evaluation of parameters and with which the characteristic evaluation according to the invention can be carried out, is also commercially available, in particular from Aradex AG, D-73547 Lorch, whose systems have hitherto mainly been used for the machining of workpieces and other machine tools and in particular for the highly dynamic servo drive technology can be used.

0028In the preferred example of an electrostatic rotary atomizer assembly comprising a transformer assembly containing a high voltage isolation device for electrical isolation and galvanically isolated signal transmission between the high voltage potential region of the atomizer and a low or earth potential region as disclosed in the referenced patent application <patcit id="pcit0014" dnum="DE102007004819"><text>DE 10 2007 004 819.1</text></patcit> is described, the invention is explained in detail. In the drawing show<dl id="dl0001"><dt>Fig. 1</dt><dd>the atomizer assembly according to the invention; and</dd><dt>Fig. 2</dt><dd>an inventive evaluable curve of engine performance; and</dd><dt>Fig. 3</dt><dd>schematically the inventively evaluable time course of the engine torque and the rotational speed as a function of the material flow.</dd></dl>

0029In <figref idref="f0001">Fig. 1</figref> located in the area 1 lying in operation at high voltage potential components of an electrostatic Rotationszerstäuberanordnung, namely the actual atomizer or an arrangement of the atomizer, a wrist and in the considered case with some elements also lying on high voltage forearm of a coating robot. The forearm can be made in a conventional manner of insulating material. With the exception of the primary circuits of the transformer arrangement described below, all of the components considered in region 1 can be at the high-voltage potential.

0030For the electrical supply of this area 1 leads a two- or multi-pole external supply line arrangement 2, as shown, the parallel primary coils of the three in a conventional manner as an isolation transformer with high voltage insulation paths (for more than 100 or even more than 150 kV) formed transformers T1 , T2 and T3 feeds.

0031The AC voltage of the line assembly 2 feeds the primary coil of the first transformer T1 via a converter 3 with voltage pulses on the secondary side, for example, working with frequency control drive 4 a synchronous or other electric motor M feeds, instead of the usual in rotary atomizers air turbine for driving the atomizer bell is provided. The motor M may be of a known type suitable for the drive purpose under consideration. For feeding and controlling the motor M, a correspondingly adapted control and evaluation system (drive 4) of the Aradex AG mentioned above can be used. The power supply can also be separated from a eg digital speed control. The transmission frequency of the isolation transformer can be known to be higher than the frequency at which the motor M is fed. The speed of rotary atomizers and thus of the motor M can be up to 100000 / min or more.

0032The secondary coil of the second transformer T2, however, serves to power supply components of the atomizer including actuators 6, sensors 7 and electronic elements, which are located in the high-voltage region 1. As shown, the AC voltage generated by the transformer T2 can be converted by a converter 5 into a DC supply voltage. Typical examples of the only schematically indicated at 6 and 7 components are actuators such as control and drive circuits for valves and flow, speed and other -Regelkreise and sensors such as the switching position of valves, speed, flow rate, temperature, pressure of the coating material, etc .. The actuators considered here may, for example, also include other electric motors or other motors, for example as a metering pump drive.

0033For the power supply of the sensors and actuators, a DC voltage generated in the motor drive 4 could be used in other embodiments.

0034The secondary coil of the third transformer T3 feeds a converter 9, which generates the high voltage required for the electrostatic charging of the coating material from the input AC voltage or supplies a high voltage generator, not shown, of the atomizer. The high voltage is applied to the internal or external electrode arrangements (not shown) customary for electrostatic sprayers for direct or external charging of the coating material.

0035In addition to the sensors and actuators of the atomizer can be fed by the transformer assembly according to the invention located outside of the atomizer other components of the application technology, including actuators and sensors of the application technique, which are located at other locations of the coating machine and there high voltage potential or low or ground potential can lie. This also includes components that, depending on the system, can be at high voltage or earth potential, such as color changers. Eventually, the transformer arrangement can supply all of the application-related components present on a robot, for example, with the electrical power they require in each case.

0036By mounting relatively heavy standard constructions for the transformer assembly as separate components in the atomizer or in the robotic arm of, for example, a paint robot, they could affect its motion dynamics. It may therefore be more convenient to constructively integrate the transformer or a transformer coil into the body of the robotic arm so that it serves as a supporting element of the robotic arm and effects or at least contributes to its necessary rigidity. As a result, the transformer does not significantly increase the overall weight of the atomizer assembly, including the robotic arm.

0037The transmission of control and sensor signals to and from the high-voltage area located in the actuators and sensors 1 and the motor control system should be galvanically isolated to eliminate interference from the high voltage. For this purpose, in particular those mentioned in the<patcit id="pcit0015" dnum="DE102007004819"><text>DE 10 2007 004 819.1</text></patcit> described possibilities of optical transmission or radio transmission into consideration.

0038<figref idref="f0001">Fig. 2</figref> shows as a typical example of the evaluation of a motor characteristic according to the invention the possible (not true to scale) course of the electrical power of the motor M, as it can result in principle in a painting process. The relatively large power jump at L1 can result, for example, when opening the main needle valve, ie when loaded by the coating material. This can be, inter alia quickly and accurately determine the switching times, and by the time course and the absolute value of the power jump further process parameters can be analyzed. The recognizable inter alia at L2 relatively small power oscillations, for example, in the order of 0.01%, however, are typically due to an eccentricity of the bell cup and / or its drive shaft. The somewhat higher power oscillations (approximately 0.05%) superimposed on this can be due to mechanical shaft vibrations. According to the invention, the power curve can be determined by the motor control itself, which can generate corresponding evaluation signals in a very short time (less than 1 ms).

0039In <figref idref="f0002">Fig. 3</figref> schematically the course of the torque of the motor M (<figref idref="f0001">Fig. 1</figref>) at the beginning of the flow of material and kept constant by the engine through its control system speed. Flow of material begins when the main needle valve of the atomizer is opened at time t2 due to a main needle valve control signal generated at time t1 and loads the motor, whose torque must consequently increase to counteract the decrease in speed. Of course, the torque and speed curves in practice do not have the illustrated straight course and the speed will generally drop slightly more or less, as indicated at n. The delay between the time t1 of the control signal of the time t2, which is detected by the increase of the torque is the determined switching time of the main needle valve, which can then be corrected or compensated for deviation from predetermined desired values.

0040By automatic evaluation of the absolute value of the change in the torque, in the example considered so its increase at time t2 preferably by the engine control system itself, can be further process parameters determine such. B. right or wrong pressure of the coating material when opening the main needle valve. Incorrect pressure can be due, for example, to defective color pressure regulators or metering pumps and could result in painting errors.

0041The engine torque may also change more than once when opening the main needle valve. For example, if in 2K coatings the engine is loaded earlier by one component than by the second component, the engine torque may increase again at time t2 and then at t3, as indicated at M 'and n'. The corresponding error can then be corrected or compensated. In this case too, the absolute values ​​of the changes allow further process parameters to be analyzed, in particular the properties of the coating components.

0042Similar to the torque curve of the engine, its electrical power can also be evaluated.

0043Further evaluation options are the evaluation<ul id="ul0001" list-style="dash" compact="compact"><li>the slope (negative and positive) of each changing values ​​such. Moment, speed, power, etc .;</li><li>the absolute size of the value change of z. Moment, speed, power, etc .; and</li><li>the relative size of the value change of z. B. Moment, speed, power, etc.</li></ul>