Device for imaging and/or varnishing the surfaces of objects

Abstract

A device for imaging and/or varnishing the surfaces of objects or vehicles, etc. includes adapting a time lag between an application of fluid and further treatment thereof, such as drying ink or varnish, to a spreading behavior of the fluid during the application thereof. The fluid may be applied to the surface of the object in sections, firstly drying the fluid in individual sections before applying it to the next section.

Claims

1. A device for treating surfaces of objects, including vehicles, with fluids, the device comprising: a robot arm having an end; a removable receiving element supported on said end of said robot arm, said removable receiving element being a revolving head having an axis of rotation implemented by an existing robot axis or by a virtual axis created from movements about multiple axes; a print head attached to said revolving head and configured to apply a fluid to the object in an operating position; a radiation source attached to said revolving head and configured to further treat the fluid in said operating position subsequent to application; said revolving head alternately moving said print head and said radiation source into said operating position; a control computer operating one path control or simultaneously operating two path controls for said print head and said radiation source and said control computer moving said print head and said radiation source into operating positions in accordance with a rhythm adapted to a spreading time of ink; and a memory storing said path or paths to be controlled and storing displacement speeds to provide a time lag between applying the fluid and subsequently further treating the fluid, said time lag being adapted to a spreading behavior of the fluid for locations being successively passed by said print head and said radiation source.

2. The device according to claim 1, wherein said revolving head additionally carries and moves at least one of a tool for pretreating the surface to be imaged or further ink print heads into said operating position.

3. The device according to claim 1, wherein said robot arm is an articulated arm robot.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a diagrammatic, side-elevational view of a preferred exemplary embodiment of the invention on the basis of an articulated robot printing on a vehicle;

(2) FIG. 2 is an enlarged, fragmentary, side-elevational view of a print head of FIG. 1 attached to an end of a robot arm;

(3) FIG. 3 is a further enlarged side-elevational view of a region 33 of FIG. 2;

(4) FIGS. 4A-4D are diagrams of jetted inkjet droplets shown in FIG. 3 at various spreading stages;

(5) FIG. 5 is an enlarged side-elevational view of a surface shown in FIG. 3;

(6) FIGS. 6A-6C are enlarged perspective views of an end of an articulated arm shown in FIG. 4; and

(7) FIGS. 7A and 7B are perspective views of two different enlargements of an end of an alternative structure of the articulated arm.

DESCRIPTION OF THE INVENTION

(8) Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a side view of a vehicle 1 to be printed on with the aid of an articulated robot 2. The articulated robot 2 has a base 3 and a robot arm 4 formed of multiple movable members. A print head 5 is attached to an end of the robot arm 4. The base 3 may be rotatable and movable in such a way as to ensure that the arm 4 carrying the print head 5 may reach every spot of the vehicle 1. If necessary, the vehicle may be supported by a non-illustrated support, which may be used to rotate the vehicle about the vertical or tilt it about a horizontal axis.

(9) During printing, the print head 5 is only a short operating distance from the surface of the vehicle 1 and jets droplets of ink at a sufficiently high impulse for them to hit the surface of the vehicle 1 and adhere thereto. In the given example, an image 7 is printed onto the vehicle 1. The image 7 may include different areas 7a and 7b, which may differ, for example, in that they have different colors. They may also differ in that one is a screen area to be able to print halftones of different intensity and one area is solid tone to obtain a continuous surface.

(10) The vehicle 1, as the object to be printed, has a curved surface, for example a fender 8 that bulges out from a side wall, having both convex and concave curves. The curves may have a very small radius and may take the shape of bends. It is even possible to print larger, extended areas of the surface of the vehicle 1 in one color, which approximately amounts to varnishing it. However, the vehicle has preferably been varnished before, and the image is locally applied as an embellishment or as a way to convey information, for example an advertisement containing letters to convey text.

(11) The manner of imaging such a vehicle body is described, for example, in detail in German Patent Application DE 10 2012 006 371 A1, filed Mar. 29, 2012, which relates to a method for printing on an object, is owned by the Applicant of the instant application and is incorporated herein by reference in its entirety.

(12) The print head 5, which is shown in more detail in FIG. 2 and which may eject UV ink droplets at a frequency of 40 kHz, may be a print head marketed under the trademark Spectra Galaxy ja256/80 AAA by Fuji Dimatix Inc., located in Lebanon, New Hamshire. It has 256 nozzles 17. The print head 5 is received on an articulated arm 4 of a robot, for example of the KR60-3 type by the Kuka Company located in Germany. In the illustrated example, the robot arm 4 has three joints 4a, 4b and 4c, through the use of which the robot 2 moves the print head 5 across a surface 13 of the object 1. The print head 5 is further connected to an ink supply container through an ink line 16 on one hand and to a computer 19 through a data connection 6 on the other hand. The lines or connections 6, 16, which are only diagrammatically shown, may include multiple individual ink supply lines or signaling lines for controlling the individual nozzles 17 of the inkjet print head 5.

(13) In the position shown in FIG. 2, the print head 5 prints a section that has a width A on the surface 13 of the object 1. In the process, the robot moves the print head 5 into the plane of the drawing or out of the plane of the drawing, for example.

(14) As is apparent from the enlarged view of FIG. 3, immediately after hitting the surface 13 of the vehicle 1, which may be varnished, for example, the ink droplets expelled by the nozzles 17 of the print head 5 are located next to each other on the surface 13 without contacting or directly adjoining each other. Depending on the viscosity and surface tension of the ink and the surface tension or surface energy of the surface to be printed, a certain amount of time amounting to several seconds, for example between five and ten seconds, may pass until an even or uniform layer of ink forms in those areas in which the print head 5 was to print a solid area. This condition is shown in FIG. 4D at a point in time t.sub.S, which is considered the optimum spreading time. If one was to wait any longer before drying the ink, the ink would potentially continue to spread at the edges of the image, resulting in blurred contours that have a negative visual effect, for example in lettering.

(15) In accordance with a first alternative of the invention, in order to dry the jetted ink, a provision is made for the print head 5 to be followed, so to speak, by a radiation source mounted to the articulated arm of a second robot (otherwise not illustrated in the figures) that is disposed next to or behind the robot 2. While taking into account the speed, the radiation source is made to follow the print head 5 on the same path or on a path that is offset to account for different operating distances of the print head and of the radiation source in such a way that the print head 5 and the radiation source pass over the same locations on the surface 13 at a time delay corresponding to the optimum spreading time t.sub.S.

(16) Since independent motion systems, i.e. two robots, are used to move the print head 5 and the radiation source, even very curved and irregular object surfaces may be printed and dried without any collision with the surface of the object.

(17) The second alternative of the method of the invention envisages the use of only one robot as will be explained with reference to FIG. 5. In this case, the solid area to be printed onto the surface 13 by the print head 5 is divided into individual strips adjoining each other and having a width A corresponding to the width of the print head. Each strip is in turn divided into individual sections having a length t.sub.1, t.sub.2, t.sub.3, etc. The method proceeds as follows: the robot 2 initially passes the print head 5 over section t.sub.1, for example, having a length which is selected to ensure that, taking into account the printing speed, the return speed, and the time for positioning a radiation source 15 for drying the printing ink, the optimum spreading time t.sub.S elapses before the radiation tool 15 for drying the printing ink is subsequently passed over the same section at an approximately identical speed and in the same direction. Then the print head 5 is returned to the operating position to print and then dry section t.sub.2, then section t.sub.3 is first printed, then dried and so on.

(18) In this way, using only one robot, a larger portion of the surface 13 of the object is continuously imaged without excess spreading and blurring.

(19) If the solid areas in sections t.sub.1, t.sub.2, t.sub.3, . . . are to be built up out of multiple different basic colors different from the basic colors CMYK, the imaging and drying for each color in a section t.sub.1, t.sub.2, t.sub.3, . . . viewed by itself is done intermittently. In some cases, the print head on the end of the robot arm 4 is to be changed between the individual applications of ink in different colors.

(20) A very similar process can be applied if, for example, a white primer is applied prior to the application of ink or if a clear varnish is applied after imaging.

(21) A robot arm suitable for the purpose described above is shown in FIGS. 6A-6C. A mounting plate 12 is fixed to the end of the robot arm 4. Three different tools jutting out in different directions are mounted to the mounting plate 12. A tool 26 is used for generating a plasma discharge to pretreat the surface to improve ink reception qualities. Reference numeral 5 indicates a four-color inkjet print head, which is only diagrammatically shown and may include ink supply lines and signaling lines located inside or outside the mount. Reference numeral 15 denotes an ultraviolet radiation source that has approximately the same width as the inkjet print head 5. Due to a robot axis 4c, the three different heads may be successively rotated into an aligned position relative to the surface 13 of the object to be printed. When the path of the robot arm 4 is planned, the entire sequence of motions for pretreating, printing and curing the ink on the surface 3 of the object is stored. This sequence may include the steps of initially pretreating the entire surface 13 using the processing head or tool 26 (e.g. plasma treatment) and applying UV radiation, IR radiation, or radiation in the visible range or subjecting it to corona treatment or hot-air treatment.

(22) This stage is shown in FIG. 6A. Then the print head 5 is rotated into the operating position to print a first color such as black or cyan onto section t.sub.1 of the surface 13 (FIG. 6B). In the illustrated position, the robot arm stops its sequence of motions, moves to the beginning of section t.sub.1, where it rotates the UV radiation source 15 into the operating position and subsequently passes over section t.sub.1 to dry the ink in this section (FIG. 6C). Then the robot arm 4 returns to the beginning of section t.sub.1 and rotates the inkjet head 5 back into position to apply the next color to section t.sub.1 and subsequently to cure the ink and so on. When all of the inks required for section t.sub.1 have been printed and cured, the sequence is repeated in section t.sub.2, etc. until the desired image is provided on the entire surface 13.

(23) In accordance with an alternative of the method, it is possible to successively print one color onto sections t.sub.1, t.sub.2, . . . , to intermittently dry the corresponding ink in sections, and then to return to section t.sub.1 to start with the next color. However, if larger areas of the surface 13 are imaged in this way, the position of the tools at the end of the robot arm will have to be recalibrated to ensure that the different colors are printed on top of each other in register.

(24) A further exemplary embodiment of a robot arm suitable for carrying out the method of the invention is shown in FIGS. 7A and 7B. In this case, a mounting plate 112 attached to an end of a robot arm 104 carries a carrier structure 117 to which an application tool 105 and a further treatment tool 115 are attached in a manner that becomes apparent from the detailed view in accordance with FIGS. 7A and 7B. The application tool 105 is a four-color inkjet print head formed of four individual print heads 105a, 105b, 105c, 105d. Using guides that are not illustrated in any detail herein, each of these individual print heads may be slid towards the surface 13 to be imaged in a direction parallel to a bar 127 of the carrier structure 117. An advantage of this feature is that the inkjet print heads 105a to 105d may be moved into narrow recesses, corrugations, etc. to reach surface areas therein while maintaining the minimum distances required for sharp images. The treatment or dryer tool 115 does not have to meet this requirement to the same extent because sufficient energy density may also be achieved by an extended exposure time or by increasing the intensity of the radiation.

(25) The dryer tool 115 is connected to the carrier structure 117 and thus also to the application tool, i.e. the inkjet heads 105a to 105d, by multiple adjustable movement axes indicated by arrows 131 to 134. An L-shaped carrier 120 is movably supported about an articulated joint 119 by a first carriage 118, which is movable along a (not further illustrated) guide on the carrier structure 117 in the direction of the surface 113 to be treated as indicated by the arrow 131. On its underside, the L-shaped carrier 120 is equipped with a (otherwise non-illustrated) linear guide along which the dryer tool 115 may be moved in the direction of the inkjet heads 105a to 105d. In this way, the distance and thus taking into account the moving speed of the carrier 117 attached to the robot arm 104, the time lag between the imaging of the surface 13 by one of the four inkjet heads 105a to 105d and the subsequent drying with the aid of an UV lamp, for example, that is received in the dryer tool 115 may be adjusted. The combined rotary/pivoting movements indicated by the arrows 132 and 133 and made possible by the articulated joint 119 and the movement of the carriage 118 allow only one robot arm 104 to move the carrier 120 over the surface 13 in such a way that the dryer tool 115 follows the imaged strip created by the inkjet heads 105a to 105d without contact. For this purpose, one needs to take into account drives (not illustrated in FIG. 7b) for the movement axes 131 to 134 and positions thereof when the path of the robot arm 104 is being planned.