EP0185311B1 - Method and apparatus for controlling an electrostatic coating system - Google Patents

Method and apparatus for controlling an electrostatic coating system Download PDF

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Publication number
EP0185311B1
EP0185311B1 EP85115801A EP85115801A EP0185311B1 EP 0185311 B1 EP0185311 B1 EP 0185311B1 EP 85115801 A EP85115801 A EP 85115801A EP 85115801 A EP85115801 A EP 85115801A EP 0185311 B1 EP0185311 B1 EP 0185311B1
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EP
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Prior art keywords
values
voltage
threshold
current
normal
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German (de)
French (fr)
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EP0185311A2 (en
EP0185311A3 (en
Inventor
Peter Henger
Fred Luderer
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Mahle Behr Industry GmbH and Co KG
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Behr Industrieanlagen GmbH and Co KG
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/02—Processes for applying liquids or other fluent materials performed by spraying
    • B05D1/04—Processes for applying liquids or other fluent materials performed by spraying involving the use of an electrostatic field
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
    • B05B5/08—Plant for applying liquids or other fluent materials to objects
    • B05B5/10—Arrangements for supplying power, e.g. charging power

Definitions

  • the invention relates to a method according to the preamble of claim 1 and to an apparatus for performing the method according to the preamble of claim 5.
  • the breakthrough field strength is achieved with an impermissible reduction in the distance between the atomizer and the workpiece, that is to say with unstable workpiece guidance or, in the case of vehicle bodies mentioned, in particular when doors and hoods are opened unintentionally. Since there is no practically usable method for directly measuring the field strength in a coating system, the operating current of the high-voltage source is instead monitored and the system is automatically switched off when a predetermined current threshold is reached, and experience shows that there is a risk of breakthrough if exceeded. Since the current flowing between the high-voltage electrodes rises steeply immediately before the breakdown field strength is reached, the risk of breakdown can be ruled out as long as the operating current does not exceed the normal value measured at the start of operation by more than a predetermined amount.
  • the operating current does not change linearly with the voltage, especially in the upper part of the range of selectable voltage values, and because the measured operating current is only partially the current flowing between the electrodes, but otherwise consists of additional components such as a shunt current flowing from the high voltage source via the paint supply system.
  • the shunt current can already be significantly higher than the electrode current at the start of operation and also gradually increase during operation, for example as a result of increasing contamination of the shunt path.
  • its size is not a measure of the field strength to be monitored; on the other hand, it is not easily possible to measure only the electrode current.
  • the high voltage with a step switch z. B. can be changed in 5 steps of 10 kV each, before starting the coating the normal operating current for the selected voltage level is measured and an associated current threshold is set by hand with a potentiometer assigned to the voltage level, which is a certain amount higher than the measured Normal current. If the voltage changes, the process is repeated with another potentiometer assigned to the new voltage level. This method is unsatisfactory for several reasons.
  • a current monitoring system for a system for the electrostatic coating of vehicle bodies with a continuously selectable voltage in which the safety switch-off only in the event of rapid current changes as a result of dangerous proximity of body parts to the atomizer being at high voltage, but not in the case of slower ones Current change should be triggered, as is possible due to gradual pollution of the system.
  • the operating current is measured in short time intervals (every 200 ms) with the aid of a sample and hold circuit measured, the measured value compared with the previous measured value stored as a reference value and finally the current measured value stored as a new reference value.
  • the reference value, with which the operating current is constantly compared, therefore increases with the gradually increasing operating current.
  • the invention is based on the object of enabling an automatic adaptation of the switch-off threshold to the respectively selected voltage in the case of a safety shutdown for a system with high voltage which can be changed in the smallest stages without excessive effort.
  • the invention eliminates the manual setting of the switch-off threshold and its likewise manual voltage-dependent change using a large number of potentiometers.
  • an electrostatic coating system for vehicle bodies supplied in series by an automatic conveyor system measures the operating current I B of the high-voltage source as a function of the freely selectable high voltage in the range up to, for example, 110 kV between the spraying device and the body to be coated, typically obtained in FIG. 1 curve shown for this current I B It is composed essentially of two components, namely a shunt current IN, which flows from the high voltage source bypassing the spray device (conventionally at high voltage potential) via its paint supply line and other shunt paths to earth, and this to add, in Fig.1 the vertical distance between the curves of the currents IN and I B corresponding electrode current between the spraying device and the workpiece.
  • a shunt current IN which flows from the high voltage source bypassing the spray device (conventionally at high voltage potential) via its paint supply line and other shunt paths to earth
  • the operating current I B can increase significantly in the course of operation, namely by reducing the shunt resistance to earth with a corresponding increase in the shunt current IN, for example as a result of increasing contamination and / or by other changes.
  • This increase, for example, to the curves I N 'and I B ', for which the switch-off curve I ' AS would then apply, can lead to a disruptive, but practically unavoidable, interruption in operation during the coating process in the known systems.
  • the normal operating current can e.g. B. correspond in one case to the curve of the current I B and in the other case to the curve t'g in FIG. 1.
  • the resulting value of the operating current I B is measured.
  • the operating current values are preferably binary coded and supplied to a microprocessor ⁇ P (FIG. 2), which calculates the current threshold values belonging to the various voltage values according to curve I AS by enlarging them by a predetermined amount (eg by 30%).
  • ⁇ P microprocessor
  • the measured operating current values and / or the threshold values calculated from them can be stored in a data memory of the microprocessor and the calculations can accordingly be carried out before, during or after the storage, or possibly only when the data is subsequently output.
  • the memory can be addressed by a binary code supplied at A (FIG. 2) and corresponding to the voltage value selected in each case.
  • the read bits of the threshold value which likewise consists of a binary code, are fed in parallel to a binary comparison switch (not shown) which is contained in the control circuit ST and which, at its other inputs, carries the bits of an operating current measured in parallel by an A / D converter corresponding corresponding binary codes received.
  • the microprocessor controlled by the comparison switching mechanism When the operating current list reaches the stored threshold value, the microprocessor controlled by the comparison switching mechanism generates a switch-off signal Ab for the high-voltage source HS.
  • the microprocessor can receive commands from a higher-level process control system, which include an on / off signal, the selected voltage at input A, a "change" signal for controlling the transfer of the voltage code at input A from a data bus of the process control system and at an input W provides signals for the selection of possibly stored different voltage / current curves.
  • the microprocessor can in turn forward a corresponding analog control signal U solI to the high-voltage source HS via a D / A converter.
  • the microprocessor can receive fault messages from the high-voltage source HS or generate them for process control.
  • the operating current 1 8 which is only valid for certain normal conditions, and consequently the curves I zs and I AS which are based thereon, change due to changed operating parameters such as, in particular, another coating material whose influence on the operating current is known, it is not absolutely necessary to restart the operation before to determine normal operating current values by measuring. In such cases, it is rather possible for the computer to calculate the now applicable threshold values itself and to store different curves for the different operating parameters. The different curves are selected as required by the signals at input W already mentioned.
  • a display device AZ controlled by the computing and control circuit ST is provided, with which the respectively measured operating current I is together with the stored threshold values associated with the respectively selected high voltage and also the actual voltage U is optically displayable.
  • the actual values are converted into binary information by A / D converters.
  • the display device can be a digital display device and / or a display device in the form of a monitor, to which the information to be displayed is supplied in the form of parallel bits at the output Z of the control circuit ST.
  • the control circuit receives command signals at input B to output the desired information. The Operating personnel can therefore get a picture of the respective operating state, especially when the warning signal appears at output V.
  • each atomizer's own high voltage should be monitored, it is advisable to install a circuit board for each atomizer, which among other things equipped with the microprocessor IlP and the control circuit ST containing integrated circuits and can be implemented with little effort.
  • the system described here of automatically adapting a cut-off current threshold to the voltage selected in each case can be easily combined with other safety shutdown systems, in particular with the system known from DE-OS-2 734 341 (mentioned at the outset). Accordingly, it may be necessary to switch off the high voltage of the coating system before reaching the cut-off current threshold mentioned, namely, for. B. if the current changes faster, ie within a given period of time by a larger amount or percentage than is permitted for safety reasons.

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  • Electrostatic Spraying Apparatus (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)

Description

Die Erfindung betrifft ein Verfahren gemäß dem Oberbegriff des Anspruchs 1 sowie eine Vorrichtung zum Durchführen des Verfahrensgemäß dem Oberbegriff des Anspruchs 5.The invention relates to a method according to the preamble of claim 1 and to an apparatus for performing the method according to the preamble of claim 5.

Bei der elektrostatischen Beschichtung von Werkstücken, die gewöhnlich von einem automatischen Fördersystem in eine Spritzkabine oder sonstige Beschichtungsstation gebracht und dort relativ zu einem oder mehreren Farbzerstäubern bewegt werden, wird zwischen das Werkstück und jeden Zerstäuber eine Hochspannung gelegt, deren Größe zur Berücksichtigung der jeweiligen Betriebsbedingungen (Werkstück, Lacktyp, Luftbedingungen usw.) verstellbar sein muß, im Falle von Fahrzeugkarosserien etwa zwischen 60 und 110 kV. Während der Beschichtung muß aus Sicherheitsgründen unbedingt verhindert werden, daß die elektrische Feldstärke einen Wert erreichen kann, bei dem die Gefahr eines Spannungsdurchbruchs oder einer Funkenentladung besteht. Die Durchbruchfeldstärke wird bei unzulässiger Verringerung des Abstandes zwischen Zerstäuber und Werkstück erreicht, also bei unstabiler Werkstückführung oder im erwähnten Fall von Fahrzeugkarosserien insbesondere bei ungewolltem Öffnen von Türen und Hauben. Da es keine praktisch brauchbare Methode zum direkten Messen der Feldstärke in einer Beschichtungsanlage gibt, wird stattdessen der Betriebsstrom der Hochspannungsquelle überwacht und die Anlage selbsttätig bei Erreichen einer vorbestimmten Stromschwelle abgeschaltet, bei deren Überschreiten erfahrungsgemäß Durchbruchgefahr besteht. Da der zwischen den Hochspannungselektroden fließende Strom unmittelbar vor Erreichen der Durchbruchfeldstärke steil ansteigt, kann man die Durchbruchgefahr ausschließen, solange der Betriebsstrom den zu Betriebsbeginn gemessenen Normalwert um nicht mehr als ein vorbestimmtes Maß übersteigt. Eine genaue und zuverlässige Einstellung der jeweiligen Stromschwelle ist aber mit erheblichen Schwierigkeiten verbunden, weil der Betriebsstrom sich insbesondere im oberen Teil des Bereiches wählbarer Spannungswerte nicht linear mit der Spannung ändert, und weil der gemessene Betriebsstrom nur zum Teil der zwischen den Elektroden fließende Strom ist, im übrigen aber aus zusätzlichen Komponenten besteht wie vor allem einem von der Hochspannungsquelle über das Lackzuleitungssystem fließenden Nebenschlußstrom. Der Nebenschlußstrom kann schon zu Betriebsbeginn wesentlich höher sein als der Elektrodenstrom und außerdem im Laufe des Betriebes allmählich etwa infolge zunehmender Verschmutzung des Nebenschlußweges erheblich ansteigen. Seine Größe ist aber kein Maß für die zu überwachende Feldstärke; andererseits ist es nicht ohne weiteres möglich, nur den Elektrodenstrom zu messen.In the electrostatic coating of workpieces, which are usually brought into a spray booth or other coating station by an automatic conveyor system and moved there relative to one or more paint atomizers, a high voltage is applied between the workpiece and each atomizer, the size of which takes into account the respective operating conditions ( Workpiece, paint type, air conditions, etc.) must be adjustable, in the case of vehicle bodies between about 60 and 110 kV. For safety reasons, it must be absolutely prevented during the coating that the electric field strength can reach a value at which there is a risk of a voltage breakdown or a spark discharge. The breakthrough field strength is achieved with an impermissible reduction in the distance between the atomizer and the workpiece, that is to say with unstable workpiece guidance or, in the case of vehicle bodies mentioned, in particular when doors and hoods are opened unintentionally. Since there is no practically usable method for directly measuring the field strength in a coating system, the operating current of the high-voltage source is instead monitored and the system is automatically switched off when a predetermined current threshold is reached, and experience shows that there is a risk of breakthrough if exceeded. Since the current flowing between the high-voltage electrodes rises steeply immediately before the breakdown field strength is reached, the risk of breakdown can be ruled out as long as the operating current does not exceed the normal value measured at the start of operation by more than a predetermined amount. Accurate and reliable setting of the respective current threshold is associated with considerable difficulties because the operating current does not change linearly with the voltage, especially in the upper part of the range of selectable voltage values, and because the measured operating current is only partially the current flowing between the electrodes, but otherwise consists of additional components such as a shunt current flowing from the high voltage source via the paint supply system. The shunt current can already be significantly higher than the electrode current at the start of operation and also gradually increase during operation, for example as a result of increasing contamination of the shunt path. However, its size is not a measure of the field strength to be monitored; on the other hand, it is not easily possible to measure only the electrode current.

Gemäß einer derzeit üblichen Methode wird bei einer elektrostatischen Beschichtungsanlage für Fahrzeugkarosserien, deren Hochspannung mit einem Stufenschalter schrittweise z. B. in 5 Stufen von jeweils 10 kV geändert werden kann, vor Beginn der Beschichtung der für die jeweils gewählte Spannungsstufe normale Betriebsstrom gemessen und mit einem der Spannungsstufe zugeordneten Potentiometer von Hand eine zugehörige Stromschwelle eingestellt, die um ein bestimmtes Maß höher ist als der gemessene Normalstrom. Bei Änderung der Spannung wird der Vorgang mit einem der neuen Spannungsstufe zugeordneten anderen Potentiometer wiederholt. Diese Methode ist aus verschiedenen Gründen unbefriedigend. Zunächst wäre es wünschenswert, die Spannung in wesentlich kleineren Schritten oder quasi stufenlos ändern zu können, was sich aber bei der üblichen Methode nicht realisieren läßt, da mit der Anzahl wählbarer Spannungsstufen auch diejenige der ihnen zugeordneten Potentiometer wachsen würde, die nicht nur aufwendig sind, sondern auch zu viel Platz beanspruchen würden. Dabei ist zu berücksichtigten, daß in einer Beschichtungsstation gewöhnlich mehrere gleichzeitig arbeitende Zerstäuber montiert sind und das Hochspannungsfeld jedes Zerstäubers einer eigenen Überwachung bedarf. Sind z. B. 10 Zerstäuber vorhanden und soll ihre jeweilige Betriebsspannung zwischen 60 und 110 kV in 1 kV-Schritten änderbar sein, so müßten insgesamt 500 Potentiometer installiert werden. Ein anderer Nachteil ist die Mühe und eventuelle Unzuverlässigkeit bei der manuellen Einstellung der die Stromschwelle bestimmenden Potentiometer, die außerdem in abschließbaren Steuerschränken oder auf andere Weise vor unbefugtem Verstellen geschützt werden müssen. Schließlich kann es zu unerwünschten Betriebsunterbrechungen kommen, wenn die Stromschwelle ohne Durchbruchgefahr lediglich infolge zunehmender Verschmutzung des erwähnten Nebenschlußweges oder aufgrund anderer relativ langsamer Betriebsänderungen (Erwärmung, Luftänderung usw.) erreicht wird, ohne daß das Bedienungspersonal rechtzeitig informiert wird.According to a currently common method in an electrostatic coating system for vehicle bodies, the high voltage with a step switch z. B. can be changed in 5 steps of 10 kV each, before starting the coating the normal operating current for the selected voltage level is measured and an associated current threshold is set by hand with a potentiometer assigned to the voltage level, which is a certain amount higher than the measured Normal current. If the voltage changes, the process is repeated with another potentiometer assigned to the new voltage level. This method is unsatisfactory for several reasons. First of all, it would be desirable to be able to change the voltage in substantially smaller steps or in a virtually infinitely variable manner, but this cannot be achieved with the usual method, since the number of voltage levels that can be selected would also increase that of the potentiometers assigned to them, which are not only complex, but would also take up too much space. It should be taken into account that usually several atomizers working at the same time are installed in a coating station and the high-voltage field of each atomizer requires its own monitoring. Are z. B. 10 atomizers available and if their respective operating voltage between 60 and 110 kV can be changed in 1 kV steps, a total of 500 potentiometers would have to be installed. Another disadvantage is the difficulty and possible unreliability in the manual setting of the potentiometers that determine the current threshold, which must also be protected in lockable control cabinets or in some other way against unauthorized adjustment. Finally, there may be undesirable interruptions in operation if the current threshold is reached without the risk of a breakdown simply due to increasing pollution of the above-mentioned shunt path or due to other relatively slow changes in operation (heating, air change, etc.) without the operating personnel being informed in good time.

Aus der DE-OS-2 734 341 ist ein Stromüberwachungssystem für eine Anlage zum elektrostatischen Beschichten von Fahrzeugkarosserien mit stufenlos wählbarer Spannung bekannt, bei dem die Sicherheitsabschaltung nur bei schnellen Stromänderungen infolge gefährlicher Annäherung von Karosserieteilen an den auf Hochspannung liegenden Zerstäuber, nicht aber bei langsamer Stromänderung ausgelöst werden soll, wie sie infolge allmählicher Verschmutzung der Anlage möglich ist. Zu diesem Zweck wird in kurzen Zeitabständen (alle 200 ms) mit Hilfe einer Abtast- und Halteschaltung der Betriebsstrom gemessen, der Meßwert mit dem als Referenzwert gespeicherten jeweils vorhergehenden Meßwert verglichen und schließlich der aktuelle Meßwert als neuer Referenzwert gespeichert. Der Referenzwert, mit dem der Betriebsstrom ständig verglichen wird, wächst also mit dem allmählich ansteigenden Betriebsstrom. Steigt innerhalb des genannten Zeitabstands der Strom um mehr als einen bestimmten einstellbaren Unterschiedswert an, wird die Abschaltung ausgelöst. Aber auch bei diesem bekannten System, das eine relativ aufwendige Schaltungsanordnung hat, wird außer der dynamischen Stromüberwachung statisch ein vorbestimmter Grenzstromwert, der in keinem Fall überschritten werden darf, von Hand durch das Bedienungspersonal eingestellt. Ferner besteht auch hier wie bei der bekannten Stufenmethode keine Möglichkeit einer Vorwarnung für das Bedienungspersonal, wenn sich der Betriebsstrom z. B. wegen zunehmender Verschmutzung der Anlage dem statischen Grenzwert nähert, bei dem die Betriebsunterbrechung ausgelöst wird, obwohl keine Durchbruchgefahr besteht.From DE-OS-2 734 341 a current monitoring system for a system for the electrostatic coating of vehicle bodies with a continuously selectable voltage is known, in which the safety switch-off only in the event of rapid current changes as a result of dangerous proximity of body parts to the atomizer being at high voltage, but not in the case of slower ones Current change should be triggered, as is possible due to gradual pollution of the system. For this purpose, the operating current is measured in short time intervals (every 200 ms) with the aid of a sample and hold circuit measured, the measured value compared with the previous measured value stored as a reference value and finally the current measured value stored as a new reference value. The reference value, with which the operating current is constantly compared, therefore increases with the gradually increasing operating current. If the current increases by more than a certain adjustable difference value within the specified time interval, the shutdown is triggered. But even in this known system, which has a relatively complex circuit arrangement, in addition to the dynamic current monitoring, a predetermined limit current value, which must never be exceeded, is set manually by the operating personnel. Furthermore, as in the known step method, there is also no possibility of an advance warning for the operating personnel if the operating current is, for. B. approaches the static limit value at which the interruption is triggered, although there is no risk of breakthrough due to increasing pollution of the system.

Der Erfindung liegt die Aufgabe zugrunde, bei einer Sicherheitsabschaltung für eine Anlage mit in kleinsten Stufen änderbarer Hochspannung ohne übermässigen Aufwand eine automatische Anpassung der Abschaltschwelle an die jeweils gewählte Spannung zu ermöglichen.The invention is based on the object of enabling an automatic adaptation of the switch-off threshold to the respectively selected voltage in the case of a safety shutdown for a system with high voltage which can be changed in the smallest stages without excessive effort.

Diese Aufgabe wird durch die in den Ansprüchen 1 und 5 gekennzeichnete Erfindung gelöst.This object is achieved by the invention characterized in claims 1 and 5.

Durch die Erfindung kann das manuelle Einstellen der Abschaltschwelle und deren ebenfalls manuelle spannungsabhängige Änderung mit einer Vielzahl von Potentiometern entfallen.The invention eliminates the manual setting of the switch-off threshold and its likewise manual voltage-dependent change using a large number of potentiometers.

Gemäß der Erfindung besteht ferner die Möglichkeit einer Vorwarnung des Bedienungspersonals bei Annäherung des Betriebsstroms an die Abschaltschwelle infolge sich ändernder Betriebsverhältnisse, die nicht zu erhöhter Durchbruchgefahr führen.According to the invention, there is also the possibility of pre-warning the operating personnel when the operating current approaches the switch-off threshold as a result of changing operating conditions which do not lead to an increased risk of breakthrough.

An einem Ausführungsbeispiel wird die Erfindung im folgenden näher erläutert. In der Zeichnung zeigen:

  • Fig. 1 den Stromverlauf in Abhängigkeit von der einstellbaren Betriebsspannung einer elektrostatischen Beschichtungsanlage für Fahrzeugkarosserien; und
  • Fig. 2 eine schematische Darstellung einer Anordnung zur Betriebsüberwachung der Beschichtungsanlage.
The invention is explained in more detail below using an exemplary embodiment. The drawing shows:
  • 1 shows the current profile as a function of the adjustable operating voltage of an electrostatic coating system for vehicle bodies. and
  • Fig. 2 is a schematic representation of an arrangement for monitoring the operation of the coating system.

Wenn man in der Spritzkabine z. B. einer elektrostatischen Beschichtungsanlage für serienweise von einem automatischen Fördersystem zugeführte Fahrzeugkarosserien den Betriebsstrom IB der Hochspannungsquelle in Abhängigkeit von der im Bereich bis beispielsweise 110 kV frei wählbaren Hochspannung zwischen der Sprühvorrichtung und der zu beschichtenden Karosserie mißt, erhält man typisch die in Fig.1 dargestellte Kurve für diesen Strom IB Er setzt sich im wesentlichen aus zwei Komponenten zusammen, nämlich einen Nebenschlußstrom IN, der von der Hochspannungsquelle unter Umgehung der (konventionell auf dem Hochspannungspotential liegenden) Sprühvorrichtung über deren Lackzuführungsleitung und sonstige Nebenschlußwege nach Erde fließt, und dem hierzu zu addierenden, in Fig.1 dem vertikalen Abstand zwischen den Kurven der Ströme IN und IB entsprechenden Elektrodenstrom zwischen Sprühvorrichtung und Werkstück. Weder der Elektrodenstrom noch der Nebenschlußstrom IN können ohne weiteres jeweils für sich allein gemessen werden. Die Kurven der Ströme IN und IB gelten für einen gegebenen Elektrodenabstand zwischen Werkstück und Sprühvorrichtung und für normale Betriebsbedingungen. Bei Verkleinerung des Elektrodenabstands würde der Elektrodenstrom und damit der Betriebsstrom 18 bis zu einem Durchbruchwert ansteigen, der in Abhängigkeit von der eingestellten Spannung auf einer ähnlichen (nicht dargestellten) Kurve liegt wie der Betriebsstrom selbst. Zur Vermeidung der Durchbruchgefahr ist es bekanntlich erforderlich, die Hochspannungsanlage bei Erreichen einer vorbestimmten Stromschwelle entsprechend der Kurve IAS abzuschalten. Aber auch ohne Änderung des Elektrodenabstands, also ohne Durchbruchgefahr kann der Betriebsstrom IB im Laufe des Betriebes erheblich ansteigen, und zwar durch Verringerung des Nebenschlußwiderstands gegen Erde mit entsprechendem Anstieg des Nebenschlußstroms IN etwa infolge zunehmender Verschmutzung und/oder durch sonstige Änderungen. Dieser Anstieg beispielsweise auf die Kurven IN' und IB', für die dann eigentlich die Abschaltkurve I'AS gelten würde, kann bei den bekannten Systemen zu einer störenden, jedoch praktisch nicht vermeidbaren Betriebsunterbrechung während des Beschichtungsvorgangs führen.If you in the spray booth z. B. an electrostatic coating system for vehicle bodies supplied in series by an automatic conveyor system measures the operating current I B of the high-voltage source as a function of the freely selectable high voltage in the range up to, for example, 110 kV between the spraying device and the body to be coated, typically obtained in FIG. 1 curve shown for this current I B It is composed essentially of two components, namely a shunt current IN, which flows from the high voltage source bypassing the spray device (conventionally at high voltage potential) via its paint supply line and other shunt paths to earth, and this to add, in Fig.1 the vertical distance between the curves of the currents IN and I B corresponding electrode current between the spraying device and the workpiece. Neither the electrode current nor the shunt current IN can be easily measured individually. The curves of the currents IN and I B apply for a given electrode distance between the workpiece and the spraying device and for normal operating conditions. If the electrode spacing were reduced, the electrode current and thus the operating current 1 8 would rise to a breakdown value which, depending on the voltage set, lies on a curve (not shown) similar to the operating current itself. As is known, to avoid the risk of breakdown, it is necessary to use the Switch off the high-voltage system when a predetermined current threshold is reached in accordance with curve I AS . But even without changing the electrode spacing, i.e. without the risk of breakdown, the operating current I B can increase significantly in the course of operation, namely by reducing the shunt resistance to earth with a corresponding increase in the shunt current IN, for example as a result of increasing contamination and / or by other changes. This increase, for example, to the curves I N 'and I B ', for which the switch-off curve I ' AS would then apply, can lead to a disruptive, but practically unavoidable, interruption in operation during the coating process in the known systems.

Ferner können sich auch für geänderte Normalbedingungen, etwa für andere Elektroden-Normalabstände oder anderen Lacktyp, erheblich anders verlaufende Spannungs/Strom-Kurven ergeben. Im Falle unterschiedlicher Lacksorten, die hinsichtlich ihres elektrischen Widerstands stark voneinander abweichen können, kann der normale Bestriebsstrom z. B. im einen Fall der Kurve des Stroms IB und im anderen Fall der Kurve t'g in Fig 1 entsprechen.Furthermore, voltage / current curves which run significantly differently can also result for changed normal conditions, for example for other electrode normal distances or other paint types. In the case of different types of lacquer, which can differ greatly in terms of their electrical resistance, the normal operating current can e.g. B. correspond in one case to the curve of the current I B and in the other case to the curve t'g in FIG. 1.

Gemäß dem hier beschriebenen Überwachungsverfahren wird vor Beginn des eigentlichen Beschichtungsbetriebes zunächst unter Normalbedingungen für jeden der wählbaren Spannungswerte, die vorzugsweise in kleinen Schritten von z. B. 1 kV oder 0,5 kV, also quasi stufenlos eingestellt werden, der sich ergebende Wert des Betriebsstroms IB gemessen. Die Betriebsstromwerte werden vorzugsweise binär codiert und einem Mikroprozessor µP (Fig. 2) zugeführt, der hieraus durch Vergrösserung um ein vorbestimmtes Maß (z. B. um 30 %) die zu den verschiedenen Spannungswerten gehörenden Stromschwellwerte gemäß der Kurve IAS errechnet. Hierbei können in einem Datenspeicher des Mikroprozessors die gemessenen Betriebsstromwerte und/oder die hieraus errechneten Schwellwerte gespeichert und demgemäß die Rechnungen vor, während oder nach der Speicherung oder evtl. auch erst bei der späteren Datenausgabe durchgeführt werden.According to the monitoring method described here, before the actual coating operation begins, first of all under normal conditions for each of the selectable voltage values, which are preferably carried out in small steps of, for. B. 1 kV or 0.5 kV, that is to say quasi continuously, the resulting value of the operating current I B is measured. The operating current values are preferably binary coded and supplied to a microprocessor µP (FIG. 2), which calculates the current threshold values belonging to the various voltage values according to curve I AS by enlarging them by a predetermined amount (eg by 30%). In this case, the measured operating current values and / or the threshold values calculated from them can be stored in a data memory of the microprocessor and the calculations can accordingly be carried out before, during or after the storage, or possibly only when the data is subsequently output.

Es können ohne weiteres auch die Werte verschiedener, für unterschiedliche Normalbedingungen wie z. B. unterschiedliche Lacksorten geltender Spannungs/Strom-Kurven gespeichert und später entsprechend den jeweils geltenden Bedingungen ausgewählt werden.The values of different, for different normal conditions such as e.g. B. Different varnish types of applicable voltage / current curves are saved and later selected according to the applicable conditions.

Ungeachtet der erwähnten anderen Möglichkeiten erscheit es zweckmässig, unmittelbar die vom Mikroprozessor errechneten Schwellwerte zu speichern. Zum Lesen kann der Speicher durch einen bei A (Fig.2) zugeführten, dem jeweils gewählten Spannungswert entsprechenden Binärcode adressiert werden. Während des Beschichtungsbetriebes werden die gelesenen Bits des ebenfalls aus einem Binärcode bestehenden Schwellwertes parallel einem in der Steuerschaltung ST enthaltenden binären Vergleichsschaltwerk (nicht dargestellt) zugeführt, das an seinen anderen Eingängen die parallel von einem A/D-Wandler zugeführten Bits eines dem laufend gemessenen Betriebsstrom list entsprechenden weiteren Binärcodes empfängt. Wenn der Betriebsstrom list den gespeicherten Schwellwert erreicht, erzeugt der vom Vergleichsschaltwerk gesteuerte Mikroprozessor ein Abschaltsignal Ab für die Hochspannungsquelle HS.Regardless of the other possibilities mentioned, it makes sense to immediately store the threshold values calculated by the microprocessor. For reading, the memory can be addressed by a binary code supplied at A (FIG. 2) and corresponding to the voltage value selected in each case. During the coating operation, the read bits of the threshold value, which likewise consists of a binary code, are fed in parallel to a binary comparison switch (not shown) which is contained in the control circuit ST and which, at its other inputs, carries the bits of an operating current measured in parallel by an A / D converter corresponding corresponding binary codes received. When the operating current list reaches the stored threshold value, the microprocessor controlled by the comparison switching mechanism generates a switch-off signal Ab for the high-voltage source HS.

Der Mikroprozessor kann Befehle von einer übergeordneten Prozess-Steuerung erhalten, die ihm u.a. ein Ein/Aus-Signal, die gewählte Spannung am Eingang A, ein Signal "Ändern" zur Steuerung der Übernahme des Spannungscodes am Eingang A von einem Datenbus der Prozess-Steuerung sowie an einem Eingang W Signale für die Auswahl ggf. gespeicherter verschiedener Spannungs/Strom-Kurven liefert. Aufgrund des Spannungscodes am Eingang A kann der Mikroprozessor seinerseits über einen D/A-Wandler ein entsprechendes analoges Steuersignal UsolI an die Hochspannungsquelle HS weitergeben. Ferner kann der Mikroprozessor Störmeldungen von der Hochspannungsquelle HS empfangen bzw. für die Prozess-Steuerung erzeugen.The microprocessor can receive commands from a higher-level process control system, which include an on / off signal, the selected voltage at input A, a "change" signal for controlling the transfer of the voltage code at input A from a data bus of the process control system and at an input W provides signals for the selection of possibly stored different voltage / current curves. On the basis of the voltage code at input A, the microprocessor can in turn forward a corresponding analog control signal U solI to the high-voltage source HS via a D / A converter. Furthermore, the microprocessor can receive fault messages from the high-voltage source HS or generate them for process control.

In Fig.1 ist zwischen der Kurve des Betriebsstroms 18 und der Abschaltkurve [AS eine weitere Kurve Izs dargestellt. Hierbei handelt es sich um Zwischenschwellwerte, die ähnlich wie die Abschaltschwellwerte gemäß der Kurve IAS vom Mikroprozessor aufgrund der zunächst gemessenen Normalwerte des Betriebsstroms IB errechnet, gespeichert und ständig mit dem tatsächlichen Betriebsstrom list verglichen werden. Bei Überschreiten der Zwischenschwellwerte der Kurve Izs (die z. B. um 15 % höher sein können als der normale Betriebsstrom IB) wird aber nicht die Hochspannungsquelle HS abgeschaltet, sondern nur am Ausgang V der Steuerschaltung ST ein akustisches und/oder optisches Vorwarnsignal für das Bedienungspersonal erzeugt. Das Bedienungspersonal erhält dadurch die Möglichkeit, bei einem allmählichen Anstieg des Betriebsstroms zu einem geeigneten Zeitpunkt wie etwa nach Fertigbeschichtung einer Karosserie die Anlage zu überprüfen und ggf. bei fortgeschrittener Verschmutzung oder anderen relativ langsamen Betriebsänderungen vor Fortsetzung des Beschichtungsbetriebes zunächst wieder den Normalzustand herbeizuführen. Dadurch können überraschende Betriebsunterbrechungen zu einem ungünstigen Zeitpunkt, die nicht wegen Durchbruchgefahr erforderlich wären, auf einfache Weise vermieden werden. Der dem vertikalen Abstand zwischen den Kurven Izs und IAS in Fig. 1 entsprechende Vorwarnbereich ist so groß bemessen, daß dem Personal genügend Zeit bleibt, einen geeigneten Zeitpunkt für die Überprüfung abzuwarten.In Figure 1, the operating current and the trip curve 1 8 [AS is another curve I shown zs between the curve. These are intermediate threshold values which, like the switch-off threshold values according to curve I AS , are calculated by the microprocessor on the basis of the initially measured normal values of the operating current I B , stored and constantly compared with the actual operating current list. Exceeding Zwischenschwellwerte the curve I zs (z. B. 15% may be higher than the normal operating current I B) but is not turned off the high voltage source HS, but only at the output V the control circuit ST, an audible and / or visual warning signal generated for the operating personnel. This gives the operating personnel the opportunity to check the system if the operating current increases gradually at a suitable point in time, such as after a body has been completely coated, and if necessary, to restore normal operation before continuing the coating operation in the event of advanced contamination or other relatively slow changes in operation. This makes it easy to avoid surprising interruptions in operation at an unfavorable time, which would not be necessary due to the risk of breakthrough. The warning area corresponding to the vertical distance between the curves I zs and I AS in FIG. 1 is so large that the personnel have enough time to wait for a suitable time for the check.

Wenn sich der nur für bestimmte Normalbedingungen geltende Betriebsstrom 18 und folglich die darauf beruhenden Kurven Izs und IAS aufgrund geänderter Betriebsparameter wie insbesondere eines anderen Lackmaterials ändert, deren Einfluß auf den Betriebsstrom bekannt ist, ist es nicht unbedingt notwendig, erneut vor Betriebsbeginn die normalen Betriebsstromwerte durch Messen zu ermitteln. In solchen Fällen ist es dem Rechner vielmehr möglich, die nun geltenden Schwellwerte selbst zu errechnen und unterschiedliche Kurven für die unterschiedlichen Betriebsparameter zu speichern. Die unterschiedlichen Kurven werden durch die schon erwähnten Signale am Eingang W je nach Bedarf ausgewählt.If the operating current 1 8 , which is only valid for certain normal conditions, and consequently the curves I zs and I AS which are based thereon, change due to changed operating parameters such as, in particular, another coating material whose influence on the operating current is known, it is not absolutely necessary to restart the operation before to determine normal operating current values by measuring. In such cases, it is rather possible for the computer to calculate the now applicable threshold values itself and to store different curves for the different operating parameters. The different curves are selected as required by the signals at input W already mentioned.

Bei der hier beschriebenen Vorrichtung hat das Personal noch weitere bisher nicht bestehende Überprüfungsmöglichkeiten. Insbesondere ist eine von der Rechen- und Steuerschaltung ST gesteuerte Anzeigeeinrichtung AZ vorgesehen, mit der der jeweils gemessene Betriebsstrom list zusammen mit den zu der jeweils gewählten Hochspannung gehörenden gespeicherten Schwellwerten und außerdem die tatsächliche Spannung Uist optisch anzeigbar sind. Die IstWerte werden durch A/D-Wandler in Binärinformationen umgewandelt. Bei der Anzeigeeinrichtung kann es sich um ein Digitalanzeigegerät und/oder ein Sichtgerät in Gestalt eines Monitors handeln, denen die anzuzeigende Information in Form paralleler Bits am Ausgang Z der Steuerschaltung ST zugefüht wird. Zu diesem Zweck erhält die Steuerschaltung am Eingang B Befehlssignale zur Ausgabe der gewünschten Information. Das Bedienungspersonal kann sich daher vor allem auch bei Erscheinen des Warnsignals am Ausgang V ein Bild vom jeweiligen Betriebszustand machen.In the case of the device described here, the personnel still have other verification options that have not existed to date. In particular, a display device AZ controlled by the computing and control circuit ST is provided, with which the respectively measured operating current I is together with the stored threshold values associated with the respectively selected high voltage and also the actual voltage U is optically displayable. The actual values are converted into binary information by A / D converters. The display device can be a digital display device and / or a display device in the form of a monitor, to which the information to be displayed is supplied in the form of parallel bits at the output Z of the control circuit ST. For this purpose, the control circuit receives command signals at input B to output the desired information. The Operating personnel can therefore get a picture of the respective operating state, especially when the warning signal appears at output V.

Da bei jedem vorhandenen Zerstäuber dessen eigene Hochspannung überwacht werden soll, ist es zweckmässig, für jeden Zerstäuber eine Schaltungsplatte zu installieren, die u.a. mit den Mikroprozessor IlP und die Steuerschaltung ST enthaltenden integrierten Schaltkreisen bestückt und mit wenig Aufwand realisierbar ist.Since each atomizer's own high voltage should be monitored, it is advisable to install a circuit board for each atomizer, which among other things equipped with the microprocessor IlP and the control circuit ST containing integrated circuits and can be implemented with little effort.

Das hier beschriebene System der selbsttätigen Anpassung einer Abschaltstromschwelle an die jeweils gewählte Spannung kann ohne weiteres mit anderen Sicherheitsabschaltsystemen kombiniert werden, insbesondere mit dem aus der (eingangs erwähnten) DE-OS-2 734 341 bekannten System. Demgemäss kann es erforderlich sein, die Hochspannung der Beschichtungsanlage schon vor Erreichen der erwähnten Abschaltstromschwelle abzuschalten, nämlich z. B. dann, wenn sich der Strom schneller, also innerhalb einer gegebenen Zeitspanne um einen größeren Betrag oder Prozentwert ändert, als aus Sicherheitsgründen zulässig ist.The system described here of automatically adapting a cut-off current threshold to the voltage selected in each case can be easily combined with other safety shutdown systems, in particular with the system known from DE-OS-2 734 341 (mentioned at the outset). Accordingly, it may be necessary to switch off the high voltage of the coating system before reaching the cut-off current threshold mentioned, namely, for. B. if the current changes faster, ie within a given period of time by a larger amount or percentage than is permitted for safety reasons.

Claims (6)

1. Method for controlling the operation of an electrostatic coating installation, operated by a selectably variable highvoltage, for large workpieces, especially those fed by an automatic conveyor-system, for example vehicle-bodies, the method including first determining , for each of the different selectable high-voltage values, the normal operating current of the high-voltage source and a higher current threshold-value, there being a danger of voltage-breakdown between the coating installation and the workpiece if this threshold-voltage is exceeded; and the operating current being then, during coating, continuously measured and compared with a stored value, and the high-voltage being automatically switched off when the current-threshold , existing in response to the high- voltage selected, is reached,
characterized in that the normal current-values measured prior to coating for the respective voltage-values and/or the threshold-values determined on the basis of the normal values, are stored jointly; and in that the operating current, measured during the coating operation, is compared with the stored value automatically selected according to the adjusted voltage.
2. Method according to claim 1, characterized in that the normal- and threshold-values of the current are stored as binary data, and in that the current-threshold-values are calculated digitally from the normal values.
3. Method according to claim 1 or 2, characterized in that, based upon the stored values and as a function of the selected voltage values, a respective intermediate threshold value, between the normal value and the shut-off- threshold-value, is automatically adjusted, a warning signal being produced when this is exceeded.
4. Method according to one of claims 1 to 3, characterized in that the respective normal- and threshold-values for different kinds of enamel, or other operating conditions, are stored jointly, and the stored values are selected on the basis of the respective actual operating conditions.
5. Apparatus for the implementation of the method according to one of claims 1 - 4, comprising a computing- and control circuit (ST) including memory means and a comparison circuit connected to the output of the memory means, characterized in that the computing- and control circuit (ST) contains a microprocessor (liP) and a data memory, addressable by the selected highvoltage values, for binary data corresponding to the predetermined normal values and/or threshold-values; and in that, connected to the data-outputs from the memory, is a binary comparison circuit to which the measured operating current (lactual) is fed through an A/D converter.
6. Apparatus according to claim 5, characterized in that an indicating device (AZ), controlled by the computing- and control-circuit (ST), is provided, by means of which the respective measured operating current (lactual), and the stored threshold values pertaining to the high-voltage selected, may be displayed optically.
EP85115801A 1984-12-17 1985-12-11 Method and apparatus for controlling an electrostatic coating system Expired EP0185311B1 (en)

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DE3445946A DE3445946A1 (en) 1984-12-17 1984-12-17 METHOD AND DEVICE FOR MONITORING THE OPERATION OF AN ELECTROSTATIC COATING SYSTEM
DE3445946 1984-12-17

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EP0185311A2 EP0185311A2 (en) 1986-06-25
EP0185311A3 EP0185311A3 (en) 1986-12-30
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EP0966084B2 (en) † 1998-06-18 2012-10-17 SAMES Technologies Method for controlling the triggering of a safety device in a high voltage generator and high voltage generator using such method
CN106413910A (en) * 2014-04-04 2017-02-15 固瑞克明尼苏达有限公司 Electrostatic spray gun having external charge points
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CN102355955A (en) * 2009-03-17 2012-02-15 杜尔系统有限责任公司 Monitoring method and monitoring device for an electrostatic coating plant
CN102355955B (en) * 2009-03-17 2015-09-09 杜尔系统有限责任公司 For method for supervising and the watch-dog of electrostatic spraying apparatus
CN106413910A (en) * 2014-04-04 2017-02-15 固瑞克明尼苏达有限公司 Electrostatic spray gun having external charge points
US10926275B1 (en) 2020-06-25 2021-02-23 Graco Minnesota Inc. Electrostatic handheld sprayer
US11738358B2 (en) 2020-06-25 2023-08-29 Graco Minnesota Inc. Electrostatic handheld sprayer

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DE3569485D1 (en) 1989-05-24
US4764393A (en) 1988-08-16
CA1246401A (en) 1988-12-13
ES8704762A1 (en) 1987-04-16
EP0185311A2 (en) 1986-06-25
ES550975A0 (en) 1987-04-16
EP0185311A3 (en) 1986-12-30
DE3445946A1 (en) 1986-06-19

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