The invention also relates to a spray coating device, that comprises at least a first and a second supply conduit for a first and a second spraying component respectively, and a spray head, which is ar- ranged at and forms a part of one of the ends of the supply conduits and from which the spraying components are sprayed towards a sub- strate.

The term spray head shall be interpreted in a wide meaning and comprises one or more nozzles but has its main function to simulta- neously, preferably via separate openings therein, conduct and direct the spraying components towards the substrate that is to be coated by the latter.

Spray coating is referred to as application of spraying components by means of spraying towards a substrate, on which at least one of the spraying components during a short or a long period forms a coating.

The at least two spraying components may have the same or different composition. Spray coating also includes, for example, lacquering, glue application, spraying of food, coating with glazing, the coating of cast or press moulds with mould lubricant, and coating of different substrates with decontamination agents, for example by removal of graffiti.

Each spraying component is not necessarily intended to form a coat- ing on the substrate. Some spraying component may for example have as its function to affect a spraying atmosphere or the geometry of the spray jet. Typically, the different spraying components are sprayed with different pressures and through different openings or different nozzles.

The invention is advantageous by devices for spray finishing, in par- ticular for stationary, automatized devices for spray lacquering of vehicles, and will therefore, by way of example, be described with reference to such a use.

THE BACKGROUND OF THE INVENTION At todays stationary, automatized devices for spray-lacquering of ve- hicles, particularly cars, spraying devices that comprise a spray head from which a jet of lacquer and at least two jets of air are directed and sprayed towards the vehicle are used. The geometry of the air jets is specially adapted in order to guarantee that the paint be applicated in a correct way against the substrate, that is the vehicle.

The spray head forms an end part of the supply conduits for the air and paint at the spraying side, the nozzle. The supply conduits are normally connected to a pressurized air source and a source for the supply of pressurized paint. Control members formed by throttle valves are often arranged in the supply conduits for the purpose of enabling an adjustment of the amounts of air and paint respectively that is sprayed out of the spray head.

When there are disturbances in the supply of paint or air by the de- vice it results in a deterioration of the quality of the paint or the ad- hesion of the paint against the substrate. According to prior art, the

adjustment of set process parameters and/or the exchange of imper- fect process control members (throttle valves, pressure generators etc) is based on a check of the quality and adhesion of the paint. This means that series of imperfect spray paintings might be executed be- fore a disturbance of the supply of paint or air is revealed by such a check, something that may result in a large production loss and in- creased production costs.

THE OBJECT OF THE INVENTION It is an object of the present invention to present a method and a de- vice that makes it possible to monitor a spray coating process in such a way that it will make it possible to establish at a later stage when a change of the predetermined process parameters has occurred with- out needing to perform a whole series of corresponding checks of the quality and/or adhesion of the coating.

It is a secondary object of the invention to preset a method and a de- vice that makes it possible to continually control the relevant process parameters and process control members based on a continuous monitoring of the spray coating process.

SUMMARY OF THE INVENTION The primary object of the invention is achieved by means of a method as initially defined, which is characterised in that a pressure or pres- sure changes in at least one of said conduits is/are continuously or frequently registered. Preferably, 1-1000 registrations per second are performed.

According to a preferred embodiment, a value of a pressure or a pres- sure change is registered in all supply conduits. In a preferred case,

the spray coating device is a spray lacquering device with air and paint supply conduits. Preferably, the pressure is then registered in both the air and the paint supply conduits.

According to another preferred embodiment, the value of the regis- tered pressure or pressure change is stored in a data memory. The memory is readable for the purpose of a subsequent representation of the pressure history in the supply conduit or conduits in which the registration has been performed.

Preferably, the value or the values of the registered pressure or the registered pressure change is emitted to a control unit, and a control of one or more process parameters of said device is performed based on said value or values. Typically, the pressure in the supply conduit in question is controlled to a desired value by controlling a valve in the conduit or by controlling the operation of a pressure generator, for example a pump (liquid) or a compressor (air) that is connected to the conduit. In this case, the storing of pressure data in a data mem- ory could be dispensed with if desired.

According to a preferred embodiment, the value of the pressure or the pressure change is registered in a region, i. e. a part of the supply conduit, downstream one or more process members that are arranged in or in connection to said conduit. Preferably, the registration is performed in a spray head, which forms an end of said supply con- duit and out of which the spraying component is sprayed through an opening. It should be realised that the different spraying components, which may comprise liquid, gas, solid particles and mixtures thereof, is ejected through separate openings in the spray head. The spray head may comprise a plurality of nozzles, each one of which is con- nected to a respective supply conduit. A supply conduit may, advan- tageously, branch off into a plurality of outlet openings. By an

arrangement of valve members in each branch respectively, the ejec- tion pressure and the ejection amount can be regulated individually for these outlet openings.

The object of the invention is also achieved by means of a device as initially defined, which is characterised in that it comprises a pres- sure sensor arranged in at least one of said conduits.

Advantageously, the device comprises a data memory which is opera- tively connected to the pressure sensor or sensors in which the val- ues of the registered pressure or pressure change are stored.

Preferably, the device comprises a control unit, which is operatively connected to the pressure sensor or sensors and which is arranged to control one or more process control members based on the values registered by the pressure sensor or sensors.

In a preferred embodiment, the device comprises one or more process control members arranged in or in connection with said supply con- duit or conduits, the pressure sensor or sensors being arranged downstream the process control members.

The invention also relates to the use of a device according to the in- vention for spray-painting, in particular spray-painting of vehicles, in particular cars. It is particularly preferred that the device is used as a stationary, automatized device for the spray-painting of vehicles.

Further features and advantages of the invention will be seen from the following detailed description and from the remaining dependent patent claims.

BRIEF DESCRIPTION OF THE DRAWING A preferred embodiment of the invention will, hereinafter, be de- scribed with reference to the annexed drawing, on which the only figure shows: a schematic representation of essential components in a device according to the invention, and how these components are connected with each other.

DETAILED DESCRIPTION OF THE INVENTION The only figure shows an embodiment of a spray coating device according to the invention. The device is a spray-painting device and comprises a spray head 1, a source 2 for a first, liquid spraying com- ponent, in this case consisting of paint, to the spray head 1, a con- duit 3 for the supply of the first spraying component from the source 2 to the spray head 1, and a pump 4 for pumping the first spraying component through the supply conduit 3 from the source 2 to the spray head 1. Further, it comprises at least one process control member 5 formed by a throttle valve for the regulation of the flow of the first spraying component through the supply conduit 3.

The device also comprises a source for a second, gaseous spraying component, in this case air, for affecting the physical properties (the degree of distribution) of the first component and the spray geometry of the first component. Said source could comprise any type of gas holder if the second spraying component is constituted by other gas than air. However, in this case, the atmosphere is the air source. The device comprises at least one second conduit 6 for the supply of air to the spray head 1, a compressor 7 or the like for the compression of the air and for feeding the latter through the supply conduit 6 to the

spray head 1. The second conduit is, in this case, branched off into separate branches 6a, 6b, each one of which leads to the spray head 1. Process control members 8a, 8b formed by at least one valve for the regulation of the flow of air in each of the branches 6a, 6b of the supply conduit 6 are also present as a part of the device.

The spray head 1 is connected with and forms a part of the supply conduits 3,6a, 6b. The spray head comprises two nozzles 9,10, one of which 9 comprises one or more openings for the ejection of air exclusively for the purpose of controlling the width of the jet of paint and air that is ejected through the second nozzle 10. In the second nozzle 10, air is ejected together with paint through different open- ings for the air and the paint, the air jet having as its task to finely distribute, atomatize, the first spraying component, in this case the liquid/paint. Accordingly, the air supply conduit 6 is branched off for the purpose of leading with a first branch 6a into the first nozzle 9 and a second branch 6b into the second nozzle 10. The opening or openings of the first nozzle 9 are, preferably, arranged in front of and around the opening or openings of the second nozzle 10.

In each supply conduit 2,6a, 6b there is provided a pressure sensor 11. Preferably, the pressure sensor 11 is arranged downstream all other process control members in the respective supply conduit 2,6a, 6b. The pressure sensors 11 are arranged in that part of the supply conduits that extends as channels in the spray head 1. A pressure sensor 11 is provided in each branch 6a, 6b of the air supply conduit 6. In the preferred embodiment, the individual pressure sensor 11 is a piezoresitive element, the electrical signal of which, as an answer of pressure changes, is used, in a way known per see, for determination of the pressure in the supply conduit in question. The pressure in the supply conduit 2,6a, 6b in this embodiment is above 0 bar and less than or equal to 25 bar.

The device also comprises a control unit 12 for controlling process parameters by controlling individual process control member 4,5, 7, 8a, 8b. The control unit 12 is operatively, that is either wirelessly or by wire, connected with the pressure sensors 11. The control is based on the pressure values or pressure change values that are registered by the pressure sensors 11 and that, by signals, are emitted to the control unit 12. Advantageously, the control unit 12 comprises a memory for storing the registered pressure values or pressure change values. It is also conceivable to completely dispense with the control unit and only provide a memory out of which the registered values can be subsequently retrieved for an evaluation of the process. The immediate feed back and on line control which is made possible by means of the control unit 12 is however advantageous and preferred.

The control unit may be a PC with suitable software for the gathering of registered values, comparison of actual values with desired values of the pressures in the supply conduits and the possible branches thereof, evaluation of such comparisons, and for the control of rele- vant process control members as a result of the evaluation. Accord- ingly, the control unit is operatively connected with the existing proc- ess control members 4,5, 7,8a, 8b.

It should be realised that a plurality of alternative embodiments will be obvious for the man skilled in the art without thereby going be- yond the scope of the invention. The extent of protection of the in- vention shall therefore not be delimited to the specific embodiment that has been described above, but to the extent of protection which is defined by means of the annexed patent claims supported by the description and the drawing.

In particular, it should be realised that a large number of different designs of spray heads, nozzles, nozzle openings, supply conduits and branches of such supply conduits, and of the existing process control members as well as the location thereof may occur within the scope of the invention.