Methods for printing a curved surface of an object by using an inkjet head

Abstract

A method for printing at least one section of a flat or preferably curved surface of an object includes using a relative movement between an inkjet head and the object to move the inkjet head along a first path and print a first track in the process and to move the inkjet head along a second path and print a second track in the process. A first track edge of the first track and a second track edge of the second track meet at a point and enclose an angle between about 1° and about 179° at the point. The method permits the curved surface to be printed without perceptible track connections.

Claims

1. A method for printing at least one section of a curved surface of an object, the method comprising the following steps: providing an inkjet head having a row of nozzles expelling ink; providing an articulated-arm robot for moving the inkjet head; carrying out a relative movement between the inkjet head and the curved surface of the object to move the inkjet head along a first path while printing a first track and to subsequently move the inkjet head along a second path while printing a second track, at least one of the first track or the second track having a curve; and causing a first track edge of the first track and a second track edge of the second track to intersect at a point and to enclose an angle between about 1° and about 179° at the point.

2. The method according to claim 1, wherein the angle lies between about 20° and about 70°.

3. The method according to claim 1, wherein the angle lies between about 110° and about 160°.

4. The method according to claim 1, wherein the angle lies at about 45°.

5. The method according to claim 1, wherein the angle lies at about 135°.

6. The method according to claim 1, wherein the first path and the second path overlap in an overlap area.

7. The method according to claim 6, wherein the inkjet head prints only on the first path or on the second path in at least part of the overlap area.

8. The method according to claim 6, wherein the inkjet head prints on the first path and does not print on the second path in the whole of the overlap area.

9. The method according to claim 7, wherein the second path crosses the first path in the overlap area.

10. The method according to claim 8, wherein the second path crosses the first path in the overlap area.

11. The method according to claim 9, wherein the second path and the first path cross in a plurality of overlap areas.

12. The method according to claim 10, wherein the second path and the first path cross in a plurality of overlap areas.

13. The method according to claim 11, wherein the at least one section of the surface of the object is assembled substantially from overlap areas.

14. The method according to claim 12, wherein the at least one section of the surface of the object is assembled substantially from overlap areas.

15. The method according to claim 1, which further comprises changing an orientation of the inkjet head relative to a respective one of the paths while the inkjet head is on at least one of the paths.

16. A method for printing at least one section of a curved surface of an object, the method comprising the following steps: providing an inkjet head having a row of nozzles expelling ink; providing an articulated-arm robot for moving the inkjet head; moving the inkjet head along a first path while printing a first track on the curved surface of the object; subsequently moving the inkjet head along a second path while printing a second track on the curved surface of the object; providing at least one of the first track or the second track with a curve; and changing an orientation of the inkjet head relative to a respective one of the paths while the inkjet head is on at least one of the paths.

17. The method according to claim 16, which further comprises rotating the inkjet head about an axis during a forward movement of the inkjet head on at least one of the paths.

18. The method according to claim 17, wherein the axis is perpendicular to an area of at least one of the tracks.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a diagrammatic, perspective view of a device during the performance of a preferred embodiment of the method according to the invention; and

(2) FIG. 2 is a diagrammatic, perspective view of a device during the performance of a further preferred embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) Referring now in detail to the figures of the drawings, in which mutually corresponding elements are provided with the same designations, and first, particularly, to FIG. 1 thereof, there is seen a diagrammatic, perspective illustration of a device during the performance of a preferred embodiment of the method according to the invention.

(4) An object 1 having a curved surface 2 is shown. The surface is preferably curved in two spatial directions. A section 3 can be seen on the surface. This section is intended to be printed. An inkjet head 4 is provided for the printing. The head is shown in two positions, once as head 4a and once as head 4b. The head is moved along a first path A in a first direction A′. The path A (and also a path B described below) is curved in accordance with the surface and is at a distance from the surface so that high-quality printing is possible and a collision between the head and the surface is prevented. During the movement along the first path, the head prints a first track a on the surface. The first track a (and also a track b described below) is formed of ink or ink droplets, which the head expels by using nozzles of a row of nozzles. The expulsion is carried out under control and takes into account both the onward movement of the head and also the printing image to be printed. The printing image can be a solid area or a grid. It can also include, for example, text, image or pattern.

(5) The inkjet head 4 is also moved along a second path B in a second direction B′. The movements along both paths are preferably carried out by using an articulated-arm robot, linear robot or a combined robot with rotating and sliding joints. The movements along the two paths can be made by moving the inkjet head or by moving the object or by a combination of the two movements. During the movement along the second path, the head prints a second track b on the surface 2.

(6) In FIG. 1, a first track edge a′ of the first track and a second track edge b′ of the second track are shown. These track edges meet at a point P and enclose an angle α, where α is greater than 0° and less than 180°, i.e. the two tracks do not extend in parallel. In the example shown, the angle α is about 45°.

(7) In FIG. 1, it can be seen that the two paths A and B overlap in an overlap area 5. In the example shown, the two paths cross. However, it is also possible that the second path B merely butts up against the first path A but is not continued on the opposite side of the first path. The inkjet head 4 preferably prints only on one of the two paths in the overlap area. In the example shown, the head prints only on the first path in the overlap area. The first track a is therefore an uninterrupted track and the second track b is an interrupted track, i.e. the overlap area forms a gap in the second track. However, it is also possible that printing is carried out on the first path in part of the overlap area and on the second path in a complementary part.

(8) FIG. 1 makes it also possible to see that there is at least one further overlap area 6 of the two paths A and B. In this case, the path B includes a plurality of path sections or a long, curved section which crosses the path A many times.

(9) FIG. 2 shows a diagrammatic perspective illustration of a device during the performance of a further preferred embodiment of the method according to the invention.

(10) In FIG. 2, the inkjet head 4 is once more shown in two positions, once as an inkjet head 4a and once as an inkjet head 4b. The head 4a is substantially parallel to the direction A′ of the first path A in its first orientation 7a and is substantially perpendicular to the direction A′ in its second orientation 7b. The change in the orientation is effected by a rotation of the head 4 about its axis 8 during the forward movement, preferably by using the robot. The respective orientation 7a and 7b of the head in this case is parallel to the row of nozzles of the head. The head prints the first track a during the forward movement. An appropriately adapted rotation of the head is also carried out on an adjacent second path B, on which the second track b is printed. The adaptation of the rotations (through a control system) is carried out in this case in such a way that the two tracks a and b vary in their respective width in the forward direction and their edges adjoin one another without any gaps. In the example shown, the edges exhibit a snake-like course. During the rotation of the head, the image data activation of the same has to be varied in such a way that, despite the rotation and the speeds and accelerations of the individual nozzles resulting therefrom, a high-quality printed result is achieved.