EP1475161B1 - Process and device to supply metered material to a coating apparatus - Google Patents

Abstract

The method involves feeding coating and/or flushing material into a cylinder (12A,B) of a dosing unit (10A,B) and feeding it into the coating arrangement (1), especially via a line (27A,B) with a scraper. A piston is moved in the cylinder by a drive controlled to fill or empty the cylinder with a defined quantity of coating and/or flushing material. The pressure of the material in, fed to or removed from the cylinder is measured by a sensor (DSA,DSB) and coating system parameters are monitored using the resulting measurement signal. Independent claims are also included for the following: (a) a supply system for dosed material supply for a coating arrangement (b) and a dosing unit for an inventive system.

Description

The invention relates to a method and a supply system for the metered supply of material to a coating device in a system for automatically controlled series coating of workpieces according to the preamble of the independent claims. In particular, it is the electrostatic serial coating of workpieces such as vehicle bodies with electrically conductive coating material often changing color.

For example, DE 101 57 966 describes a supply system of the type considered here, in which, in the known A / B technique, two mixed color lines lead from one color changer to one piston dispenser each, which serves as a coating device via another common line Atomizers are connected. As explained in DE 101 57 966, a piston dispenser is to be understood as meaning a metering unit in the cylinder of which the piston is moved by a metering drive which is controlled as required during the coating in such a way that it displaces the coating material in the demand-metered and variable quantity into the the nebulizer leading line expresses because it is usually necessary during the coating, to change the amount of color or coating material to be supplied to the nebulizer, for example, depending on workpiece areas, size and shape of the surfaces to be coated, spray jet shape, etc. This volumetric metering, ie demand-dependent control of the volume flow with the piston feeder driven, for example, by a servomotor, also has significant advantages over other metering systems. For example, have also used in many coating systems, also volumetrically metering Zahnraddosierpumpen Although a high dosing accuracy, but they are poorly rinsed. By contrast, the color pressure regulators used for dosing in other systems (eg US Pat. No. 5,221,047) no longer satisfy today's demands on dosing accuracy. In contrast, piston dispensers are both very accurate and easily rinsed in a color change. They allow a precise metering not only of the coating material when applied by the atomizer and the filling of the piston dispenser, but also a flushing liquid to be filled with a desired volume in a line or the piston dispenser (EP 1362641). Piston dispensers can be designed to be extremely rigid (DE 102 33 633) and also allow for use as intermediate container the known since EP 0292778 advantageous potential separation between working on high voltage coating device and grounded ink supply unit such as a color changer by sections emptying the lines, the In modern coating systems is known to be realized by pigging technology (DE 199 37 426). In coupled systems, piston dispensers also have the advantage that there is no need for a gear metering pump to be present on the atomizer and, therefore, pig stations can be arranged inside the atomizer, whereby color and detergent losses can be reduced to a minimum (EP 1314480).

Problems exist in the coating systems of the type considered here, however, that for the monitoring and control of the system considerable effort is required, which often ensures neither the desired optimization of the dosing nor the required reliability. Some of these problems are due to the nature of the pigs and the elastic hoses required for them, which, for example in motor vehicle coating plants, have inside diameters between 5 and 10 mm and can be more than 15 m long. The liquids to be pumped can be both colored lacquer or other coating material as well as the thinner needed for rinsing.

From DE 100 65 608 a system for the antiseize coating of vehicle bodies with an aqueous emulsion is known, which is first pumped into an intermediate container and then conveyed from there through a line to a spraying device. The intermediate container consists of a cylinder with a piston which is driven to emptying the intermediate container by a motor. The emulsion should be fed to the spraying device with controlled pressure. For this purpose, the emulsion feed pressure is measured with a pressure sensor and the sensor signal is fed to a control device, which in turn controls the piston drive motor. With this pressure control no volumetric dosing of the coating material in the manner explained above is possible.

DE 101 20 077 discloses a color coating system in which the color print can be detected and subsequently regulated by means of a pressure sensor arranged directly in front of the atomizer. Furthermore, a pressure sensor may be located on the supply line of a dosing cylinder provided outside the ink path for a sliding medium for the coating material, which is to ensure an always sufficient supply of panning medium. A dosing unit, into which the coating material to be applied and / or a rinsing agent is passed, is not provided.

The object of the invention is the disclosure of a method or dosing system of the type known from DE 101 57 966, with a simple way reliable monitoring and / or control, in particular also several factors of the system is possible.

This object is solved by the features of the claims.

The invention is based on the recognition that, with one and the same simple pressure sensor, numerous different parameters or functions of the system can be monitored, diagnosed and / or controlled both during and outside the coating operation. The size of the fluid pressure measured in the metering cylinder or in the lines connected to it can be e.g. for optimizing the speed of filling the dosing cylinder and connected lines and thus avoiding loss of time. In addition, this pressure allows conclusions to be drawn on factors as varied as the pressure and / or pressure fluctuations of the fluids in the supply system from which the dosing unit is filled (loop pressure), the viscosity of the liquids being pumped and even the state of wear of the pigs. Furthermore, the signal generated by the pressure sensor can be used to compensate for compliance of the molded hoses and other system components as well as changes in hose lengths and other system components and according to another way to report pigging positions.

In a typical embodiment of the invention, the pressure sensor first monitors the pressure prevailing in or on the cylinder during the filling of the cylinder of the dosing unit or, if appropriate, negative pressure of the coating material (or rinsing material) in order to avoid, in particular, the suction of air. The filling is preferably carried out volumetrically due to the piston movement, ie with a predetermined volume and / or volume flow, wherein the pressure monitoring system by controlling the piston drive corrective intervention when its speed is too high or will. Furthermore, the fluid pressure in the above-mentioned supply system (loop pressure) can be measured. In the subsequent application process with the required precise volumetric dosing pressure monitoring then serves mainly to protect the dosing unit downstream lines and components from impermissibly high pressures and damage caused thereby.

On the embodiment shown in the drawing, the invention will be explained in more detail. It is a molded A / B system for the metered supply of an electrostatic rotary atomizer with electrically conductive coating material of frequently changing color.

The coating material is supplied to the nebulizer 1 by a paint supply unit 2, e.g. fed to an A / B color changer, which may consist of two Farbwechselventilanordnungen per se conventional type, which are assembled into a operated according to the known A / B principle double color changing unit. The paint valves FA and FB of the unit 2 may be connected to the usual (not shown) ring lines of the paint supply system.

To the two outputs of the unit 2 are each connected via a pig station 6A and 6B gemicked hose lines 7A and 7B of insulating material connected via a respective pig station 8A and 8B respectively in the cylinder 12A and 12B of a piston dispenser 10A and 10B to lead. The piston of this doser limits the color space formed in the cylinder and is displaceable in the cylinder by a metering drive (not shown), for example a spindle drive driven by a servo motor. Preferably, the mechanical components of the piston dispenser should at least partially consist of electrically insulating material with a high modulus of elasticity, such as ceramic, as described in the already mentioned DE 102 33 633, according to which the tensile and / or flexural modulus of elasticity of the material should be greater than 10 GPa.

From the cylinder 12A and 12B, respectively, of the piston dispensers 10A and 10B, a further each pig station 28A or 28B leads to a pig station 29A or 29B respectively within the atomizer 1. The piston dispenser 10A and its pig stations 8A and 28A are conveniently assembled into a compact unit. The same applies to the piston dispenser 10B.

Depending on the mode of operation, the pig stations could be designed to accommodate one or more pigs.

For the controlled connections between the unit 2, the pig stations, the piston dispensers and the hose lines appropriate valve arrangements are provided in a conventional manner (not shown).

In the example under consideration, the piston dispensers 10A and 10B may be disposed on the outside of the wall of the spray booth indicated at 3 and connected to the atomizer 1 via jointed conduits 27A, 27B passing through the arm and hand axis of a painting robot or other indicated at 4 Painting machine are passed. In other cases, the piston dispensers 10A and 10B may instead be mounted in or on one of the machine arms as in the system shown in FIG. 2 of the already mentioned DE 101 57 966, of which the structure of the A / B system described herein is adjacent to FIG Essentially, the position of the piston dispensers differs only in that the two piston dispensers 10A and 10B are connected to the atomizer 1 via the two common lines 27A, 27B instead of via a common line. In further accordance with FIG. 2 of DE 101 57 966, a separate rinsing circuit operated with potential separation (not shown here) can be provided, which contains a further piston dispenser, for example of the type described above, and a further common line, via the diluting liquid serving as rinsing agent outside the lines 27A and 27B is passed into the atomizer 1.

In operation, for example, cylinder 12A may first be filled by line pressure with a volume of a required paint material set precisely by automatically controlled backward movement of its piston by unit 2. A residual quantity of the coloring material remaining in the line 7A at the end of this process can be pressed into the cylinder 12A with a pig coming from the pig station 6A. After evacuation of the conduit 7A, the coating material from the cylinder 12A may then be pressed down to the atomizer by forward movement of the piston through the conduit 27A and then sprayed with the precise dosage effected by the automatically controlled piston actuator. For example, the coating material may in this case be conveyed by the piston dispenser 10A while filling the entire line 27A into the atomizer. The required potential separation between the grounded unit 2 and the atomizer is effected in this case by the empty line 7A. Also, if the piston dispenser 10A is to be grounded outside the cabin, the potential separation can be achieved by insulating distances in front of and behind a limited color column that can be conveyed between limiting pigs through the line 27A, as described in DE 101 31 562. In all cases, the pigs pushed through the pipes, on the one hand, provide for the emptying and cleaning of the pipe required for insulation and, on the other, for the conveyance of flushing material through the pipe. In the same way, the nebulizer 1 can be supplied by the B-circuit, wherein, according to the known A / B technique, during the spraying of a first ink from the piston dispenser 10A, a second paint is directed into the piston dispenser 10B and from there to the atomizer can be pressed.

In a manner known per se, material remaining in the system after a coating process can be pushed back into the metering cylinder and from there into the respectively connected ring line and / or be backfelt.

Incidentally, the invention can also be used for systems in which no potential separation is required.

For monitoring and controlling, in particular, a plurality of different coating system factors acting outside the piston dispensers, the piston dispensers 10A and 10B (and possibly the diluter delivering piston dispensers of the mentioned separate scavenging circuit) are provided with a pressure sensor DSA and DSB, respectively, which continuously feeds into the cylinder prevailing fluid pressure measures and a pressure corresponding to this example generates electrical signal. For example, the pressure sensor may be connected to the cylinder 12A or 12B with the pig channel connecting to the pig station 28A or 8A or 28B or 8B color channel. However, it is also possible to measure the pressure of the material received and conveyed by the dosing unit 10A or 10B, if necessary, depending on the function or system upstream or downstream of the piston dosing device. Of a larger number of different functions for which the signal of the pressure sensors can be used, some are explained below.

A first function of the pressure sensor is to monitor and control the filling pressure of the piston dispenser. This is important when the dosing cylinder is not to be filled with negative pressure in relation to the environment during the return movement of the piston, but on the other hand with only slight overpressure as close to zero, for example, to achieve maximum pressure difference to the ring line pressure, with the filling is effected. This goal can be achieved, for example, by appropriately controlling the speed of the piston drive to set and maintain a desired pressure set point and if necessary shutdown when falling below a pressure limit can be achieved. The monitoring or regulation of the filling pressure is expedient both when filling from the loop and when pushing back unused material in the metering cylinder. Here, the highest possible filling speed can be exploited.

An expedient rule also results when the material is taken from the metering cylinder by the piston drive for pressing up to the atomizer or for pushing back the material, for example in a ring line, wherein in each case the pressure with increasing filling of the downstream hose and in dependence on the piston speed (if necessary with fluctuations). On the one hand, the highest possible delivery rate, i. achieved as short a delivery time, on the other hand, however, a given in particular by the strength of the hoses or other components maximum pressure can not be exceeded. In order to make full use of the time savings possible in the system while maintaining the pressure limit, a maximum delivery rate is initially set or a volume control of the delivered material is carried out, ie volume-constant delivery, until a predetermined pressure limit is reached. Then it is switched to pressure control with the maximum allowable pressure using the pressure sensor signal as the actual value.

A similar rule possibility also exists when filling the metering cylinder from the ring line and when pushing back unused color material from the atomizer into the metering cylinder. Here as well, a maximum delivery rate can first be set or a volume control can be carried out until the pressure sensor reaches a still permissible lower pressure limit (close to zero), and then switched over to pressure regulation to maintain the achieved pressure value.

One of the further realizable with the pressure sensor monitoring options is that it is determined, for example, in the Andrückvorgang with the pressure sensor, if the friction occurring in particular of the pigs and due to the viscosity of the pumped material pressure losses are within the normal range.

With the pressure sensor can be measured and monitored during filling of the piston meter also the ring line pressure, i. the color printing in the case of filling the metering cylinder via the color changer 2 each connected loop and its possible variations. The pressure in the metering cylinder corresponds after reaching the Kolbenendstellung the ring line pressure.

Furthermore, the viscosity of the respective coating material can be determined from the pressure measured in the metering cylinder, since the pressure in the metering cylinder changes according to generally known physical laws (inter alia Hagen-Poiseulles law) according to the viscosity in the case of other known system parameters.

The u.a. The pressure in the metering cylinder based on the flow rate and viscosity of the material conveyed may change undesirably, in particular due to the resilience of the molded hoses and possibly also of the piston meter (DE 101 48 097, DE 102 33 633). These pressure changes can also be measured by the pressure sensor, and due to the measurements, e.g. compensation of the "hose breathing" or other system softnesses can be carried out or supported by appropriate control of the piston drive.

Further, the pressure sensor may also detect the length or volume of tubing contained in the system and, for example, its signal after installation or replacement Incorrect hose length determined by hoses will be compensated if the measured pressure changes in a defined manner with hose length.

Another way to use the pressure sensor signal is the finding that a pig in operation reaches one of its end positions. If a pig loaded by the piston feeder is e.g. against a stop in the pig station, this is noticeable by a sudden increase in pressure in the metering cylinder. This can be saved in some cases, otherwise necessary for known reasons external pig sensors that respond to magnetic or iron cores of the pigs and in particular in the high voltage range electrostatic sprayer require considerable effort. With the signal of the pressure sensor reporting the pig end position, it is expedient to trigger further signals, in particular for valve control of the system.

During or even outside the normal operation of the dosing system, the pressure sensor can be used to detect or verify critical properties of the system and its components. An important example of this is the determination of the state of the pigs used, whose function is impaired in particular by wear. Faulty newts can u.a. insufficient cleaning of the lines and thus not only undesirable contamination of the paint material, but also insufficient electrical insulation in the potential separation result. If the pressure values measured by one of the hoses during operation or for diagnostic purposes deviate from the specified normal values, this deviation can serve as a measure of the state of wear of the relevant pig.

Regardless of its other diagnostic, monitoring or control functions, the DSA, DSB pressure sensor is always used for overpressure monitoring the system, for example, to reliably avoid the risk of damage to the hose lines or other components of the system by impermissibly high pressure. The pressure sensor signal can be used as a control or warning signal and possibly as a shutdown signal and also for continuous visual pressure display.

If it is necessary depending on the application, the pressure sensor can be arranged or formed high voltage resistant, so that it is not disturbed by the high voltage required in electrostatic coating equipment and / or its signals can be easily led out of the high voltage range.

Claims (15)

1. Method of volumetrically metered supply of material to a coating device (1) in an installation for the automatically controlled series coating of workpieces, in which the coating material to be applied by the coating device (1) and/or a flushing material is first of all led into a cylinder (12A, 12B) of a metering unit (10A, 10B) and is then delivered to the coating device (1) via line (27A, 27B) which is in particular pigged, wherein in the cylinder (12A, 12B) a piston is moved by a controlled drive for filling or emptying the cylinder (12A, 12B) with a predetermined quantity of the coating or flushing material, and wherein the coating material is applied with the precise volumetric metering effected by the piston drive, characterised in that the pressure of the coating or flushing material which is located in the cylinder (12A, 12B) of the metering unit (10A, 10B) or delivered to the cylinder or removed from the cylinder is measured by a pressure sensor (DSA, DSB) which generates a measurement signal corresponding to the pressure, and that one or several operating parameter(s) is (are) monitored and/or controlled as a function of the measurement signal.
2. Method as claimed in Claim 1, characterised in that the speed of the piston drive of the metering unit (10A, 10B) is controlled or switched off as a function of the measurement signal when the cylinder (12A, 12B) is filled and/or when material from it is forced back into a supply system or is forced only as far as the coating device (1).
3. Method as claimed in Claim 2, characterised in that in the closed feedback loop the piston drive is adjusted for setting of the pressure according to a desired value.
4. Method as claimed in Claim 3, characterised in that for conveying material during forcing gout of the material from the metering unit (10A, 10B) and/or during introduction of the material into the metering unit first of all a maximum conveying rate is set or an adjustment of the conveying volume is carried out until a limiting value for pressure is reached and then the pressure regulation is carried out.
5. Method as claimed in Claim 1, characterised in that the pressure and/or pressure fluctuations of the material in the supply system from which the metering unit (10A, 10B) is filled is determined from the measurement signal.
6. Method as claimed in Claim 1, characterised in that the viscosity of the material with which the metering unit (10A, 10B) is filled is determined from the measurement signal.
7. Method as claimed in Claim 1, characterised in that pressure losses caused by pig friction in the line (7A, 7B, 27A, 27B) and/or by the viscosity of the conveyed material are determined from the measurement signal.
8. Method as claimed in Claim 1, characterised in that a control signal is obtained from the measurement signal for the compensation of changes in pressure which are due to changes of system components such as for example the flexibility and/or the length or the volume of a hose line (7A, 7B, 27A, 27B) and/or of some other component of the metering system.
9. Method as claimed in Claim 1, characterised in that a sensor signal which reports the pig position is generated from the measurement signal when a pig which is acted on by the metering unit (10A, 10B) strikes a stop.
10. Method as claimed in Claim 1, characterised in that the state of wear of a pig conveying through the line (7A, 7B, 27A, 27B) is determined from the measurement signal.
11. Supply system for the volumetrically metered supply of material to a coating device (1) in an installation for the automatically controlled series coating of workpieces with a line (27A, 27B) which is in particular piggable and through which the coating material and/or a flushing material can be delivered to the coating device (1) which applies the coating material, and with a metering unit (10A, 10B) which includes a cylinder (12A, 12B) to receive the coating or flushing material to be delivered to the line (27A, 27B) and in which a piston can be moved by a controlled drive for filling or emptying the cylinder (12A, 12B) with a predetermined quantity of the material, wherein the coating material is applied with the precise volumetric metering effected by the piston drive, characterised in that a pressure sensor (DSA, DSB) is provided which measures the pressure of the coating and flushing material located in the cylinder (12A, 12B) of the metering unit (10A, 10B) or delivered to the cylinder or removed from the cylinder and which generates a measurement signal corresponding to the pressure, and that a means is provided by which one or several operating parameter(s) of the coating installation is (are) monitored and/or controlled as a function of the measurement signal of the pressure sensor (DSA, DSB).
12. Supply system as claimed in Claim 11, characterised in that the piston of the metering unit (10A, 10B) is driven by a reversible servomotor via a spindle drive or another gear unit.
13. Metering unit (10A, 10B) for a system as claimed in Claim 11 or 12 with a cylinder (12A, 12B), a piston which is or can be driven by a controlled motor, and a connection for a pressure sensor (DSA, DSB) which measures the fluid pressure in the cylinder (12A, 12B).
14. Metering unit as claimed in Claim 13 with at least one attached pigging station (8A, 28A, 8B, 28B).
15. Metering unit as claimed in Claim 13 or 14, in which the cylinder (12A, 12B) is made from ceramic material or other insulating material with a modulus of elasticity in tension and/or a flexural modulus of elasticity which is greater than 10 GPa.

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