Description

The present invention relates to an innovative method and to an automated system for coating objects with a coating agent, in particular for painting relatively large and curved surfaces such as the surfaces of vehicle bodies and parts.

In the automated coating systems, used for example in the sector for the painting of motor vehicle bodies, it is known to use robotic arms which support heads which emit, upon command, an atomized stream of a coating agent, for example paint.

One problem of these systems is that the coating agent is emitted with a relatively wide spraying angle and, also because of the atomization, not all of it falls onto the surface to be coated and a certain quantity, known as "overspray", remains suspended in the air. For this purpose the coating system is contained inside a cabin provided with an air suction and filtering system. The overspray results, therefore, both in wastage of coating agent and costs for treatment of the air inside the cabin and the subsequent disposal of the used filters. Furthermore, the overspray may soil the walls of the cabin, the air ducts, the filtering systems, etc., with consequent further - even high - costs for maintenance of the plant and periodic shut-down thereof for cleaning.

For some time, emission devices which try to minimize the overspray have been proposed. In particular, painting heads have been proposed where the nozzles which emit the sprayed atomized paint are replaced by a plurality of adjacently arranged nozzles which emit parallel jets with a small spraying angle of each jet. Essentially, with such a system, the painting head takes the form of an inkjet printing head, with several nozzles arranged adjacent in a plane. In precisely the same manner as inkjet printing heads used for printing on paper, these systems also allow the painting of a surface with a certain degree of precision so as to form predetermined patterns, supplying the different nozzles with different streams of paint and colours.

It has, however, been noted that with the known devices, which are formed with a plurality of adjacently arranged nozzles, the result obtained is not always optimal. This is due also to the fact that the jet emitted by the single nozzles nevertheless is subject to a certain degree of dispersion which, with an increase in the distance between the surface to be painted and the painting head, results in a widening of the point of impact of the paint emitted by the single nozzle on the surface to be painted. For this reason, in the prior art, it has for example been proposed to keep the painting head at a distance which is determined beforehand as being the distance which is generally optimal for the painting operation, using the same principle adopted in inkjet printing heads where an optimum fixed distance from the surface of the sheet to be printed is established. Although this may be adequate for the heads used for printing on a sheet, which is generally flat, on vehicle body parts it is not always possible to keep all the nozzles at an optimum distance, in view also of the variable form of the surfaces to be painted. In order to minimize the problem, solutions which attempt to reduce the front area of the painting head, by moving the nozzles as close together as possible, have been proposed. The reduction in the front area of the head, however, reduces the surface area painted with each passing movement head, this making the painting process excessively slow owing to the dimensions of the surfaces which usually must be coated. It is therefore necessary to find a compromise between the minimum size of the front area of the head, optimal for minimizing the painting defects due to the form of the surfaces to be painted, and a bigger size of the front area of the head which guarantees a reasonable coating speed for large surfaces.

One solution found in the prior art is that of using several painting heads which are or can be differently oriented and which are for example mounted on the same support, or rectangular heads with one side which is much longer than the other side, so as to orient either side of the head in the direction of movement of the head over the surface depending on whether it is required to have a greater painting speed or a greater precision in terms of the distance maintained between the nozzles being operated and the surface. In addition to this possibility of orientation, there is also the selective activation of the head nozzles so as to emit the paint only in more or less limited zones of the head.

One of these systems is for example proposed in US 2020094282.

These systems, however, are unable to obtain a really satisfactory result, while complicating significantly management of the movements of the head over the surface to be coated.

The general object of the present invention is to provide a painting method and system which are able to overcome the aforementioned problems and which may be adapted also to painting surfaces with a variable form.

In view of this object the idea which has occurred is to provide, according to the invention, a system for coating objects with a coating agent, in particular for painting vehicle bodies or vehicle parts, comprising at least one coating head with a plurality of nozzles for applying the coating agent to the object to be coated and a handling robot which guides the coating head along movement paths on the surface of the object to be coated, characterized in that at least some nozzles of the plurality are supported in the head so as to have emission ends mutually movable by means of controlled actuators at least in one direction of emission of the coating agent.

Still according to the invention the idea which has occurred is to provide a method for coating objects with a coating agent, in particular for painting vehicle bodies or vehicle parts, by means of a coating head with a plurality of nozzles for applying the coating agent to the object to be coated and a handling robot which guides the coating head along movement paths on the surface of the object to be coated, characterized in that, during the guiding of the head along the movement paths on the surface of the object to be coated, at least some nozzles have an emission end which is movable, upon command, with respect to the head so as to adjust the distance of the emission end from the surface of the object to be coated.

In order to illustrate more clearly the innovative principles of the present invention and its advantages compared to the prior art, examples of embodiment applying these principles will be described below with the aid of the attached figures.

In the figures:

- Figure 1 shows a possible embodiment of a coating system employing the principles of the present invention;

- Figure 2 shows a schematic perspective view of a painting head of the device according to the invention;

- Figure 3 shows a schematic side elevation view of the head according to Figure

2; - Figure 4 shows a schematic cross-sectioned view of a possible embodiment of a painting head according to the invention;

- Figure 5 shows a schematic cross-sectioned view of a possible further embodiment of a painting head according to the invention.

With reference to the figures, Figure 1 shows a coating system or plant, denoted overall by 10, for coating surfaces of objects 11 , such as vehicle bodies or their parts.

Here, for the sake of simplicity, the terms "painting" and "paint" will be used to refer also to generic surface coating operations and to the coating agents used and will not be understood thereby as being limited to the finish-painting of surfaces, but will refer also, for example, to the application of undercoats, transparent protective varnishes or other coating agents. Moreover, the paints or coating agents may be of many known types suitable for spray or jet coating, such as water-based paints, solvent-based paints, etc.

As can be seen in Figure 1 , the system 10 may comprise at least one handling robot 12 which guides a head 13 for emitting the coating agent, along movement paths on the surface of the objects 11 to be coated. In the figure, for example, two robots 12 arranged on two sides of the object 11 are shown.

The robots 12 are of the type substantially known per se and provided with an adequate number of movement axes so as to be able to reach and travel, with their operating ends, along the surfaces to be coated. The robots may be, for example, known robots with an anthropomorphic arm having five, six or more axes. A suitable known electronic control system for the robots will position, by following the appropriate trajectories, the heads 13 along the surfaces to be coated. Each robot terminates in an operating end or wrist which carries the associated head 13.

Preferably, a known transportation line 14 is also provided for sequentially transporting objects 11 inside and outside of the operating area of the robots. The transportation line 14 may be any known sequential transportation line suitable for the purpose. For example, the transportation line may be continuous chain line, motorized rollers, etc.

Advantageously, the system 10 also comprises a containment cabin 15 inside which the operations for coating the objects 11 are performed. This cabin 15 may also have an air circulation system, for example with ducts 16 for introducing clean air from above and a grille floor 17 for extracting the air from below and conveying it into known filtering systems 18 suitable for removing overspray and other impurities and, if necessary, then recirculating it inside the cabin.

Owing to the principles of the present invention, the production of overspray is in any case very limited and the overspray filtering system may be limited in size compared to those required in the prior art or may even not be present.

Figure 2 shows in schematic form a head 13 according to the invention which is mounted on the operating end of the robot 12.

The head 13 comprises a plurality of nozzles 20 for emitting the paint from their ends 32, which are advantageously arranged alongside each other two dimensionally so as to form a matrix of adjacent nozzles. The mutual distance between the adjacent nozzles will depend on their emission range and the surface painting resolution which is required on the surface to be painted. In general the nozzles will be designed with dimensions so as to obtain slight mutual overlapping of the points painted by each nozzle, when the head is at a standstill in front of the surface to be painted. The diameter of each point will depend on the specific resolution requirements of the painted designs.

As will become clear below, the painting head according to the invention may also be significantly large in size and/or have a large number of adjacent nozzles and therefore also a relatively large front painting area and consequently a high operating speed, while ensuring an optimum painting quality.

A system 21 for supplying paint to the nozzles will provide the paint to be emitted by the head for example depending on predefined emission programs. The system 21 may also supply different paints to different nozzles or different groups of nozzles so as to cover the surfaces with predetermined patterns. For example, valves and/or closing devices (not shown) may be provided, these intercepting, upon command, the paints supplied to the nozzles or groups of nozzles, using systems which are known per se and which may be easily imagined by the person skilled in the art for the known multi-nozzle painting heads.

According to the principles of the invention, at least some of the nozzles have an emission end 32 which may be displaced, upon command, with respect to the head at least in the direction 19 of emission of the paint from their emission end 32. The displacement may be performed individually or in groups.

It is thus possible to position the emission ends 32 of the nozzles along virtual lines or surfaces which are advantageously variable and also not necessarily flat. In other words, the nozzles may be moved so as to project more or less from the front face of the head. In this way, during the movement of the head along the movement paths on the surface of the objects to be coated, the position of the nozzles may be adapted to the form of the surface to be painted.

For example, it is possible to maintain the distance between one nozzle and the surface to be painted within a range which has been predefined as being optimal, also depending on the form of the surface at the point on which this nozzle is operating. The optimal distance will depend for example on the degree of dispersion of the nozzles and the dispersion amplitude required on the surface. For example, the distance considered to be optimal may be within a range of between 5 and 50 mm or more.

The movement of the nozzles may be for example adjustable, upon command, during the painting movement so as to define with the ends of the nozzles a surface which reproduces remotely, with a desired degree of approximation, the surface to be painted which is situated in front of the front face of the paint emission head. This is clear for example already from figure 2, where the nozzles are shown arranged projecting differently from the head.

The movement of the nozzles will be performed by means of suitable actuators contained in the head and controlled by a position control system 22 which will receive the commands from an electronic coordination system 23 which will adjust the position of the nozzles depending on the position of the head on the surface to be painted. In particular, the coordination system will recognise or detect the geometry of the surface to be painted and the instantaneous position of the head on this surface, so as to control the relative forwards or backwards movement of the nozzles in the head and adapt them to the configuration of the surface which in that moment is situated in front of the head itself.

The paint supply system 21 may also be controlled by the coordination system 23 so as to adjust the emission of paint from the nozzles depending on the position of the head on the surface and the pattern which is desired in this position. Suitable control and coordination systems may be easily imagined by the person skilled in the art based on the description provided here for them and therefore will not be further described nor illustrated in detail. For example they may be suitably programmed electronic microprocessor systems.

As may be again imagined by the person skilled in the art, these electronic systems may also be integrated in or interfaced with the robot control system so as to coordinate completely the movement of the robot arms and the arrangement and operation of the head nozzles so as to perform the desired painting movement on the surfaces, adapting in each case the distance of the nozzles from the surface during the movement.

Figure 3 shows by way of example the head 13, viewed in profile, with the nozzles 20 which are arranged with their emission ends along a line (or surface) 24 so as to follow at a predetermined distance 'd' the progression of the facing line (or surface) 25 of the object 15 to be painted.

It is clear from Figure 3 that relative axial displacement of the nozzles is sufficient to arrange them along a desired line or surface 24 so as to allow optimum adaptation of the painting head to the surface, something which was impossible with the painting heads of the prior art.

Figure 4 shows schematically a first example of a possible suitable mechanism for moving the nozzles.

In this Figure 4, each nozzle (or group of nozzles, if desired) is designed so as to be axially slidable upon operation of a respective linear actuator 26 controlled by the position control system 22. The linear actuators 26 may be for example electromagnetic solenoids through which the nozzle bodies pass so that, depending on the magnetic field produced by the electromagnet, a different axial position of the corresponding nozzle is obtained. The linear actuators may however also be linear actuators of a different type. For example, they may be realized using known pneumatic linear systems (for example pistons) or electromechanical systems (for example rotary motors with suitable transmissions). The number of actuators may also be smaller than the number of nozzles depending on the spatial resolution required for adaptation of the head to the surfaces to be painted. In this case several nozzles close to each other may be moved together by means of a single actuator. In the case where the required resolution is small, a small number of actuators may also be used, each moving a group of nozzles - including a large group - all at the same time. For example, rows or columns of nozzles in the matrix of nozzles may be moved together.

The connection between the paint source and the nozzles will be realized so as to allow the desired movement of the nozzles in the painting head. For example, flexible pipes 27 may be used to supply the paint to the nozzles, in groups or individually, by means of the connection to paint dispensers 28 supplied in turn by one or more paint sources 29. The dispensers 28 may be used for example in common with rows, columns or zones of nozzles, depending on the patterns which are to be produced on the surface to be painted. If need be, if only one colour must be emitted at a time by the entire head, a single dispenser with a single paint source may be provided.

Figure 5 shows an alternative embodiment of the head 13 which allows adaptation of the head to curved surfaces using also a small number of actuators.

In this embodiment the nozzles are mounted on a flexible support 30 (for example a sheet or membrane of elastic polymer material) which may be deformed with respect to a flat arrangement by means of suitable linear actuators 31 connected to the flexible support 30. In this way, suitable operation of the actuators allows deformation of the support to be obtained so as to position the nozzles along the desired line or surface 24, in an arrangement for example with spline-like points. The flexible support 30 may also be realized with a separate set of elastic supports for groups of nozzles.

The nozzles may be guided in the head so as to remain in any case parallel to each other, or may be supported so as to allow inclination thereof depending on the deformation of the support surface, as shown by way of example in Figure 5.

In this case they may be fixed to the deformable surface of the support 30 so as to each remain generally perpendicular to the surface of the support.

As a result, the jet emitted by each nozzle may be kept generally perpendicular to the surface to be painted which is in front of the nozzle.

At this point it is clear how the objects of the invention have been achieved by providing a method and an automated system which allow suitable processing of objects such as vehicle bodies or their parts so as to ensure optimum coating or painting thereof, while keeping the distances between nozzles and surface within an optimally defined range also in the case of a head with relatively large size and surfaces to be coated which have variable and not completely flat forms.

Obviously, the above description of an embodiment applying the innovative principles of the present invention is provided by way of example of these innovative principles and must therefore not be regarded as limiting the scope of the rights claimed herein.

For example, the form and size of the heads and nozzles may vary so as to be adapted to the dimensions and form of the objects to the treated and the desired specific working requirements. In particular, the number of rows of nozzles and the number of nozzles per row and the relative arrangement of the rows and nozzles may be different from that shown, also depending on the resolution required for the patterns to be formed with the coating agent, the desired operating speeds, and the forms and dimensions of the surfaces to be coated.

The nozzles may also be arranged in concentric circular rings rather than in parallel rows and columns.

The head itself may have different dimensions in the two directions and may also have a front face which is not rectangular (for example circular), if desired or considered necessary for the particular coating requirements.

In addition to keeping the distance between the emission end of the nozzles and the surfaces to be coated relatively constant, the system according to the invention also allows the end of one or more nozzles to be moved towards or away from the surface (for example corners or edges) so as to optimize the emission or the size of the point of impact of the paint on the surface at that point.

If desired, the head may also comprise fixed nozzles and movable nozzles. The length of the nozzles may be different from that shown.

If necessary, the nozzles may also be formed as simple holes in a surface (for example the surface 30 in Figure 5) which is deformed by the actuators, without projecting from this surface.

Obviously, in the case where painting with only one colour at a time is required, it will also be possible to supply all the nozzles using a single colour source.