A DEVICE FOR AUTOMATIC SPRAY APPLICATION OF PAINT

Abstract: A device for automatic spray application of paint through a spray nozzle comprises a container (5) containing paint, arranged in the immediate proximity of the spray nozzle and connected to the spray nozzle through a conduit (4) for supply of paint to the latter for said spray application. The container is arranged rotatable, and the device comprises members (8) adapted to drive the container to rotate for pressing paint (27) contained therein outwardly towards a region of the periphery thereof. The conduit emerges through an opening (18) in this region. Means are also adapted to establish an overpressure of a pressurized medium in the container for pressing paint out through the opening (18) to the spray nozzle.

Description: A DEVICE FOR AUTOMATIC SPRAY APPLICATION OF PAINT FIELD OF THE INVENTION AND PRIOR ART The present invention relates to a device for automatic spray application of paint through a spray nozzle, which comprises a container containing paint and arranged in the immediate proximity of the spray nozzle, said container being through a conduit connected to the spray nozzle for supplying paint thereto for said spray application, as well as means adapted to press the paint out of the container and through said conduit to the nozzle through a pressurized medium. Such a device may have different fields of use, but for illuminating, but not in any way restricting the invention, the use of such a device for painting objects, such as vehicle bodies, through a spray painting robot will hereinafter primarily be discussed, but the invention comprises also devices in the form of so called painting machines. "Paint" is here to be given a broad meaning and comprises all types of paints suited for spray application. It is often a desire to place such a container containing paint in spray application robots close to the spray nozzle to avoid long conduits between the source of paint and the spray nozzle, primarily to avoid a great waste of paint when colour is changed, but also to facilitate cleaning of such conduits and avoid that long conduits disturb the ability to move of the robot or otherwise constitutes obstacles. However, a problem arises when the container is arranged close to the spray nozzle should the container and the robot arm carrying the spray nozzle be moved so that the container is turned or tilted. The paint present in the container will upon such movements of the container assume a new position in the container through the gravitation and may perhaps neither be reached by said conduit in this position, so that it will not be possible to spray paint out through the spray nozzle in certain positions of the robot arm and thereby the container and nor efficiently discharge all the paint from the container should this be desired, but the problem to supply the spray nozzle with paint will instead increase with a decreasing content of paint in the container. A solution to this problem is presented in FR 2 635 990, which consists of arranging a member for mechanically dividing the container inside the container for separating the paint and the pressurized medium, such as compressed air, in which this member is formed by a piston or a flexible membrane. How- ever, an arrangement of such a membrane or piston in the container requires control means being unnecessarily complicated and makes the construction of the container unnecessarily costly. SUMMARY OF THE INVENTION The object of the present invention is to provide a device of the type mentioned in the introduction, which solves the problem discussed above in a simpler and a more advantageous way, not at least from the cost point of view, than has been achieved through the device according to the French publication mentioned above. This object is according to the invention obtained by arranging the container rotatable and provide the device with members adapted to drive the container to rotate for pressing paint contained therein outwardly towards a region of the periphery thereof, that said conduit emerges into said region through an opening, and that said means are adapted to establish an overpressure of said pressurized medium in the container for pressing paint out through said opening to the spray nozzle. Thus, it may irrespectively of the positioning in the room of the container always be ensured that paint contained in the con- tainer is present where said conduit emerges into the container and thereby paint may be supplied to the spray nozzle as long as there is any paint left in the container. This is achieved completely without any requirement of any membrane or piston inside the container. It is a matter of course that said driving member has to drive the container to rotate with such a speed that "the centrifugal force" keeps the paint against the periphery of the container. It is also within the scope of the invention that the driving member does not have to drive the container to rotate continuously, but this possibility is there and utilized when needed, so that when spray is applied for example on any object with the spray nozzle and the container in a fixed position during at least a period, it may be refrained from rotating the container should this be positioned with said region at the lowest point, so that the gravitation keeps the paint close to the opening of the conduit. Furthermore, it is emphasised that "said means are adapted to establish an overpressure of said pressurized medium in the container" is to be broadly interpreted and intended to comprise the case in which no real supply of pressurized medium to the container is car- ried out as well, but this may for example from the beginning be filled by so much pressurized medium and pressurized medium of such a high pressure, besides the paint, that this pressurized medium is sufficient for obtaining pressing of all the paint out of the container during a pressure decrease but still maintaining an overpressure in the container when all the paint has been removed. According to a preferred embodiment of the invention said opening of the conduit is located outermostly in said region at an inner wall of the container so as to enable discharging of substantially all the paint contained in the container through said opening. A possibility to complete emptying of the container with an optimum utilization of the volume thereof is ob- tained thanks to such an arrangement of the opening of the conduit in combination with rotation of the container. According to another preferred embodiment of the invention said region extends over a limited part of the extension of the container in a direction substantially in parallel with the axis for the rotation of the container. Said opening does not hereby have to be given an unproportionally large extension in this direction so as to achieve an optimum emptying of paint to "the very last drop". According to another preferred embodiment of the invention, which constitutes a further development of the embodiment last mentioned, said region is formed by a valley-like design of the container being circumferential with respect to the axis of rotation of the container and having a valley bottom with a maximum distance to the axis of rotation of the container, and said opening is located in said valley bottom. A very well defined point for collection of the paint is obtained in this way, since the extension in the axial direction will be small through this design and the paint will move in said valley in a circumferential path and thereby be caught at a point by, or more exactly be pressed out through, said opening. According to another preferred embodiment of the invention the container is substantially symmetrical with respect to the axis of rotation thereof. Such a design of the container is advantageous, since the paint hereby may be smoothly pressed outwardly towards the periphery of the container by the "centrifugal" force without any substanial formation of swirls or exerting the paint to shearing forces, which may degrade it, at the same time as a possibility to an even discharging of the paint out of the container is ensured. According to another preferred embodiment of the invention said means are adapted to press the paint out of the container through compressed air, which in most cases is to be preferred through the easiness to get access to this pressurized medium. According to another preferred embodiment of the invention said means are adapted to supply the pressurized medium to a container in the region of the axis of rotation thereof. This is advantageous since the pressurized medium is then introduced into the space being free from paint at the rotation of the container, which improves the efficiency of the device, as well as since it gets easier to arrange said means fixed with respect to rotation should this be desired. It also gets easier to ensure the possibility to remove the container from these means. According to another preferred embodiment of the invention the device comprises a first valve member arranged in said conduit and a member adapted to control the valve member to open the conduit connection between the container and the spray nozzle when spray application of the paint is to be carried out and, when not, the valve member to be closed for preventing paint from leaving the container through the conduit. It is hereby ensured that paint is only sprayed out through the spray nozzle when this is really desired, and this valve member may be arranged at any location along said conduit and may very well be located in the very spray nozzle. According to another preferred embodiment of the invention said conduit for discharging paint from the container comprises a tube extending from the region of the axis of rotation of the container outwardly towards the periphery of the container to said region for discharging paint from the container in this region and conducting the paint out of the container substantially along the axis of rotation of the container. By such an arrangement the paint may be efficiently led out where this is easiest done and nevertheless an efficient "fetching" of paint from the container takes place. According to another preferred embodiment of the invention, which constitutes a further development of the embodiment last mentioned, the device comprises a plurality of conduits emerging into said region for discharging paint from the container at a plurality of locations distributed around the periphery of the container in the direction of rotation thereof, and that each of the conduits is formed by a tube referred to. Such a construction may be advantageous so as to increase the effi- ciency of the delivery of paint from the container to the spray nozzle. According to a further preferred embodiment of the invention the device comprises members for holding the container at a carrier close to the spray nozzle, and the holding members are adapted to hold the container releasable therefrom for removal thereof from the device for exchanging it by another container or filling paint into the container and then inserting it once again in the holding members. By arranging the container in this way removable from the device an exchange to a container filled with the same paint colour or a container filled with a completely different paint colour takes place as soon as the paint in the container in question is running out or an exchange to another paint colour is to take place, so that the standing still periods of the robot or the machine for spray ap- plication may be kept short. It will then be possible to clean and/or fill the container removed in peace and quiet. Further advantages as well as advantageous features of the invention appear from the following description and the other dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a description of preferred embodiments of the invention cited as examples. In the drawings: Fig 1 is a very schematic view of a robot for spray application of paint on a vehicle body, in which this robot is provided with a device according to a preferred embodiment of the invention. Fig 2 is a view enlarged with respect to Fig 1 and partially sectioned of the device indicated in Fig 1, Fig 3 is a view corresponding to Fig 2 of a part of the de- vice shown in Fig 2 in a position for removing the container therefrom and cleaning the spray nozzle, and Fig 4 is a partially sectioned view from above of a part of a device according to an alternative embodiment of the invention. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION A device for spray application of paint in the form of a spray painting robot, which has different robot arms hingedly connected to each other, is very schematically illustrated in Fig 1. Right out on the last robot arm a spray nozzle 1 in the form of a gun is arranged, but it may also be a question of a bell, for spray application of atomized paint onto an object 2, here a vehicle body. The spray nozzle is connected to an arrangement 3 schematically indicated and adapted to atomize paint delivered to the spray nozzle 1 through a conduit 4 partially shown in Fig 2 from a container 5 containing paint and arranged in the immediate proximity of the spray nozzle. Different conduits for for example supply of compressed air or electric control of parts included in the device have for the sake of simplicity been omitted in Fig 1, and parts thereof having nothing to do with the invention have neither been shown in the other Figures. Reference is now also made to Fig 2. There it is shown that the container 5 has a mushroom hat-like appearance being also symmetrical with respect to rotation with elements 6 centrally projecting from the "mushroom hat" in parallel with the axis of symmetry, said elements being provided with circumferential engagement members in the form of a gear 7, which is in engagement with an engagement member in the form of a second gear 8 belonging to a member adapted to drive the container 5 to rotate about the symmetry axis thereof through rotating the gear 8 when desired in the spray application state of the device. The container is for this sake arranged rotatable with respect to a carrier 9, which may form a fixed part of said atomizing arrangement. It appears that the elements 6 of the container for this sake are rotatably journalled through bear- ings 10, 11 about a central part 12 arranged fixedly with re- spect to rotation with respect to the carrier 9 here and to be described more in detail further on. The container 5 may be made of different types of material de- pending upon the intended use. When an electrically conducting paint being on a high potential is applied plastic having a good insulating capacity is a suitable material, but metal may also be possible for non-conducting paints. The container has a valley-like circumferential design with respect to the axis of rotation of the container with valley bottom 13 with a maximum distance to the axis of rotation of the container, so that paint present in the container will upon rotation of the container tend to run outwardly towards said valley bottom 13 for clearly defining a paint collecting point for the conduit 4 (see further on). The device has also a means for supply of compressed air comprising a conduit 14 having a tube portion 15 emerging centrally into the container and being provided with a non re- turn valve 16 at the extremity thereof. Furthermore, the conduit 4 comprises between the container and the spray nozzle a tube 17 extending close to the axis of rotation of the container and then bent substantially radially outwardly and having an opening 18 at the periphery of the container in said valley bottom 13 for receiving paint from the container. The tube portion 15 and the tube 17 form said central part 12 being non-rotatably arranged and about which the container is intended to be brought to rotate. In an alternative embodiment it is also possible to arrange this part rotatable should that be desired. Furthermore, the device comprises members 19, here in the form of spring loaded balls, forced into engagement with recesses 20 of a part 21 rigidly connected to the part having the tubes 15 and 17. Thus, said central part and the container may be removed together from the container 9 by lifting them in the way illustrated in Fig 3, but the container is preferably also separable from said central part and held to this by holding members not shown, so that it is possible to only remove the container should that be desired. The device has also a first valve member 22 schematically indicated and arranged in the conduit 4 so as to open and close, respectively, the communication between the container and the spray nozzle. This valve member is shown in an open position in Fig 2 and in a closed position in Fig 3. A plate 24 provided with a number of holes is arranged downstream of the valve member in the conduit 4 for spreading the paint. A second valve member is arranged in the conduit 14 for supply of pressurized medium and it is schematically illustrated in Fig 3 how this valve member 23 closes the supply conduit, while it keeps this conduit open for supply of compressed air to the container in Fig 2. It is also possible that the container has any auxiliary valve arranged in the container for filling paint or compressed air. Finally, the carrier 9 has a conduit 25 emerging into the conduit 4 for supplying a cleaning medium, such as com- pressed air or a solvent, for cleaning the conduit 4 from the mouth of the conduit 25 therein and downstream to the spray nozzle. A valve member 26 is also located here for keeping this conduit 24 closed during spray application of paint through the device. The function of the device described above is as follows. When paint is to be sprayed out through the nozzle the container 5 is brought to rotate by driving the second gear 8 to rotate. Preferably, the container is then so rotated that the paint is ex- erted to a centripetal acceleration v 2 /r = about 3g (g = the gravitation), which will result in a pressing of the paint 27 outwardly as far as possible away from the axis of rotation of the container and accordingly towards said valley bottom 13. It may be a certain advantage to use a container having a comparatively small radius, since the velocity at the periphery of the container will be lowered by a factor 4 upon halving the radius, which reduces the shearing forces upon the paint and prevents it from being destroyed, primarily by formation of aggregates. The paint will by rotation of the container always be located at the periphery thereof irrespectively of the position of the con ¬ tainer in the room as a consequence of movements of the robot arm during spray application onto different surfaces of the object to be painted. The compressed air supplied centrally to the container will tend to press out the paint through the opening 18 of the conduit 4 in a region (valley bottom 13) where paint is always present as long as there is any paint at all in the container. Thus, compressed air is supplied through the conduit 14 in the position shown in Fig 2, and the valve member 22 for flow of paint to the spray nozzle is also open, while the valve member 26 is closed. It is illustrated in Fig 3 how the container may be lifted away for exchange for filling a new paint therein and/or cleaning thereof. In the position shown in Fig 3 the valve members 23 and 22 have for the rest closed the respective conduit portions, while the valve member 26 has opened the communication between the conduit 25 and the conduit 4, so that the cleaning medium may now be supplied to the conduit 4 for cleaning thereof and the spray nozzle through the conduit 25. Furthermore, the container may advantageously have an auxiliary valve arranged in the wall thereof, for example at 28, and enabling a blowing out of an optional amount of air from the container on paint filling, so that the container may be filled substantially completely with paint. A container 5 of a device according to a further embodiment of the invention is shown in Fig 4. In this embodiment a plurality of tubes 17 emerging into the region 13 for discharging paint from the container are arranged at a plurality of locations distributed around the periphery of the container. The tubes emerge close to the axis of rotation of the container into a conduit 4 in common extending to the spray nozzle. This may increase the efficiency of the delivery of paint from the container to the spray nozzle. The invention is of course not in any way restricted to the preferred embodiment described above, but many possibilities to modifications thereof will be apparent to a man skilled in the art without departing from the basic idea of the invention. The shape of the container may for example be another, and two possible shapes are a ball shape, which however does not make the collecting point as clearly defined as in the case shown above having the very accentuated valley bottom, and a discus shape, which results in a collecting point being very well defined. As already mentioned, the container may be provided with compressed air having a pressure of for example 5 bars from the beginning and then no supply of compressed air takes place, but the pressure may then fall to 2 bars when all the paint has been discharged from the container.

Claims: Claims 1. A device for automatic spray application of paint through a spray nozzle (1), which comprises a container (5) containing paint and arranged in the immediate proximity of the spray nozzle, said container being through a conduit (4) connected to the spray nozzle for supplying paint thereto for said spray application, as well as means (14-16) adapted to press the paint out of the container and through said conduit to the nozzle through a pressurized medium, characterized in that the container is rotatably arranged and that the device comprises members (8) adapted to drive the container to rotate for pressing paint contained therein outwardly towards a region (13) of the periphery thereof, that said conduit emerges into said region through an opening (18), and that said means are adapted to establish an overpressure of said pressurized medium in the container for pressing paint out through said opening to the spray nozzle. 2. A device according to claim 1, characterized in that said opening (18) of the conduit (4) is located outermostly in said region at an inner wall of the container so as to enable discharging of substantially all the paint contained in the container through said opening. 3. A device according to claim 1 or 2, characterized in that said region (13) extends over a limited part of the extension of the container in a direction substantially in parallel with the axis for the rotation of the container. 4. A device according to claim 3, characterized in that said region is formed by a valley-like design of the container being circumferential with respect to the axis of rotation of the container and having a valley bottom (13) with a maximum distance to the axis of rotation of the container, and that said opening (18) is located in said valley bottom. 5. A device according to any of claims 1-4, characterized in that the container (5) is substantially symmetrical with respect to the axis of rotation thereof. 6. A device according to any of claims 1-5, characterized in that said means (14-16) are adapted to press the paint out of the container through compressed air. 7. A device according to any of claims 1-6, characterized in that said means (14-16) comprise a source of pressurized medium adapted to supply said pressurized medium into the inte- rior of the container. 8. A device according to claim 7, characterized in that said means (14-16) are adapted to supply the pressurized medium to the container in the region of the axis of rotation thereof. 9. A device according to any of claims 1-8, characterized in that it comprises a first valve member (22) arranged in said conduit and a member adapted to control the valve member to open the conduit connection between the container (5) and the spray nozzle (1) when spray application of the paint is to be carried out and, when not, the valve member to be closed for preventing paint from leaving the container through the conduit. 10. A device according to claim 7 or 8, characterized in that it has a second valve member (23) arranged in a conduit (14) for supply of pressurized medium from said source to the container (5) and a member adapted to control the second valve member to open and close, respectively, the communication between the source of pressurized medium and the container. 11. A device according to any of claims 1-10, characterized in that said conduit (4) for discharging paint from the container (5) comprises a tube (17) extending from the region of the axis of rotation of the container outwardly the periphery of the container to said region (13) for discharging paint from the container in this region and conducting the paint out of the container substantially along the axis of rotation of the container. 12. A device according to claim 11, characterized in that it comprises a plurality of conduits emerging into said region for discharging paint from the container (5) at a plurality of locations distributed around the periphery of the container in the direction of rotation thereof, and that each of the conduits is formed by a tube referred to (17). 13. A device according to claim 12, characterized in that said tubes (17) emerge close to the axis of rotation of the container into a conduit (4) in common extending to the spray nozzle (1). 14. A device according to any of claims 1-13, characterized in that it comprises members (19, 20) for holding the container at a carrier (9) close to the spray nozzle (1), and that the holding members are adapted to hold the container releasable therefrom for removal thereof from the device for exchanging it by another container or filling paint into the container and then inserting it once again in the holding members.

Inventors: ANFINDSEN OLE ARNT, ANFINDSEN, OLE, ARNT
Applicants: ABB FLEXIBLE AUTOMATION AS, ANFINDSEN OLE ARNT, ABB FLEXIBLE AUTOMATION A/S, ANFINDSEN, OLE, ARNT
Application year: 1998
Main classification: B05B3
IPC codes: B05B3, B05B5, B05B9, B05B12, B05B13