EP3539791B1 - Printing beam for ink jet - Google Patents

Description

The present invention relates to a print bar for inkjet, comprising printheads in a row, holders each holding a printhead, and adjustment devices for adjusting the printheads to one another.

In DE 11 2015 002 942 T5 describes a so-called line-type ink jet head formed by connecting a plurality of head modules to each other along the x-direction. There is a recording head adjustment system capable of adjusting the angular deviation of the direction of rotation within the plane parallel to the recording surface of the recording head.

What is unfavorable about this is that when adjusting a head module, its nozzle plate can collide with the nozzle plate of an adjacent head module. The nozzle plates are very sensitive and can be damaged by even minor collisions.

In NL 2 008 063 C describes a positioning device in which a body with an opening for receiving a print head is connected to a base part via elastic joints. The body can be moved relative to the base by stepping motors which apply two forces in the same or opposite directions. Same directions cause translation of the body and opposite directions cause rotation.

In U.S. 2014/16201 A1 and U.S. 2016/279982A1 further prior art is described.

The object of the invention is to create a print bar in which the adjustment of the print heads is possible without the risk of collisions.

The problem is solved by a pressure bar with the features of claim 1.

In connection with the present invention, the center of gravity of the nozzle surface is understood not only as the ideal center of gravity, but also a point that lies within an imaginary, circular tolerance range, the center of which is the ideal center of gravity, the size of the area of the tolerance range being at most 20%, is in particular at most 10% and preferably at most 5% of the size of the entire nozzle area.

The advantage of the pressure bar according to the invention is that when the respective print head is adjusted, its rotation around the center of gravity of the nozzle surface is possible, as a result of which the risk of a collision is largely averted.

Various further training courses are possible:
The axis of rotation can run orthogonally to the nozzle surface through its center of gravity.

The cones can be formed on screws.

The holders can each be designed as a frame with elastic joints and lever arms.

The adjusting devices can rest against the lever arms. The lever arms can be loaded by return springs which press the lever arms against the adjustment devices.

Figur 1:

das Schema eines Druckbalkens mit mehreren Einheiten,

Figur 2:

die Detaildarstellung einer Einheit, welche einen Druckkopf nebst zugehörigen Justiereinrichtungen und einen Halter umfasst,

Figur 3:

die Einheit bei einer rotativen Justage des Druckkopfs durch die Justiereinrichtungen und

Figur 4:

die Einheit bei einer translativen Justage des Druckkopfs durch die Justiereinrichtungen.

Further developments also result from the following description of an exemplary embodiment and the associated drawing, in which shows:

Figure 1:

the scheme of a pressure bar with several units,

Figure 2:

the detailed representation of a unit, which includes a print head together with associated adjustment devices and a holder,

Figure 3:

the unit with a rotary adjustment of the print head by the adjustment devices and

Figure 4:

the unit in a translational adjustment of the printhead by the adjustment devices.

figure 1 shows a print bar 1 for full-page inkjet printing on sheets or webs as part of a digital printing machine. The printing material is transported past the printing beam 1 in the direction of the coordinate axis y. Arranged along the pressure bar 1 are holders 3 which each carry a print head 2 with a nozzle surface 6 .

Each holder 3 has a first adjustment device 4 and a second adjustment device 5 for rotating the print head 2 about the coordinate axis z and displacing the print head 2 along the coordinate axis x. The print head 2 is set relative to its adjacent print heads 2 with the adjustment devices 4 , 5 . Each adjusting device 4, 5 comprises a screw 7 with an associated drive element 14 for turning the screw 7. The drive element 14 can be a screw head for a socket wrench, a knob as a handle or preferably an electric motor. The two screws 7 of the respective holder 3 are oriented parallel to one another. Each screw 7 has a cone 12, 13 as a thrust wedge which, when the screw 7 is screwed in, pushes away a lever arm 9, 10 which bears against the thrust wedge.

figure 2 shows as an example one of the identical units from which the pressure bar 1 is composed. The first cone 12 rests on the first lever arm 9 and the second cone 13 on the second lever arm 10 of the holder 3. The print head 2 is attached to the holder 3 at a first attachment point AP1 and a second attachment point AP2.

The holder 3 comprises longitudinal rods 15 and transverse rods 16. The rods 15, 16 and lever arms 9, 10 are connected to one another via elastic joints (flexible joints, spring joints) 8 and together form a frame. The elastic joints 8 are tapers in which a bend occurs when the lever arms 9, 10 are pivoted in the common plane of the coordinate axes x, y or parallel to the nozzle surface 6 by the adjusting devices 4, 5. The elastic joints 8 have imaginary pivot axes which are parallel with the axes of rotation of the screws 7.

At the free end of each lever arm 9, 10, the respective cone 12, 13 acts on one side and a restoring spring 11, which presses the lever arm 9, 10 against the cone 12, 13, on the other side. The geometric center of gravity SP of the nozzle surface 6 lies in the middle of an imaginary, straight connecting line VL from the first connection point AP1 to the second connection point AP2.

figure 3 shows that the adjusting devices 4, 5 arranged between the lever arms 9, 10 push the lever arms 9, 10 apart. For this purpose, the two screws 7 are preferably screwed in a little at the same time. The respective cone 12, 13 is adjusted in a direction parallel to the coordinate axis z—axially with respect to the axis of rotation of the screw 7—and the effective diameter with which the cone 12, 13 presses on the lever arm 9, 10 increases. When the lever arms 9, 10 are pressed away from one another, the holder 3 deforms elastically in such a way that the connection points AP1, AP2 change their position relative to a fixed point FP of the holder 3. Both connection points AP1, AP2 are pivoted clockwise about the center of gravity SP when the second lever arm 10 is pivoted clockwise and the first lever arm 9 is pivoted counterclockwise.

The movement of the connection points AP1, AP2 relative to the fixed point FP results in a pivoting movement of the print head 2 about an imaginary axis of rotation RA, which runs parallel to the coordinate axis z and through the center of gravity SP. Approximately in the direction parallel to the coordinate axis x, the first connection point AP1 is shifted to the right and the second connection point AP2 to the left—that is, in the opposite direction to the first connection point AP1—to print head 2 about the axis of rotation to pan RA. The center of gravity SP does not change its position relative to the fixed point FP during the pivoting movement of the print head 2. When the print head 2 pivots or rotates about the center of gravity SP, the risk of a collision with neighboring print heads 2 is reduced.

figure 4 shows that the lever arms 9, 10 are pressed together by the return springs 11. In order to make this possible, with reference to the neutral position in figure 2 one screw 7 is screwed out a little and preferably at the same time the other screw 7 is screwed in a little. This reduces the effective diameter with which the first cone 12 bears against the first lever arm 9, so that the restoring spring 11 acting on it can pivot the first lever arm 9 clockwise. In addition, the effective diameter with which the second cone 13 presses on the second lever arm 10 increases, so that it is also pivoted clockwise against the action of the return spring 11 assigned to it. With this pivoting of the lever arms 9, 10 in the same direction, the holder 3 deforms elastically in such a way that not only the connection points AP1, AP2, but also the center of gravity SP changes its position relative to the fixed point FP.

The connection points AP1, AP2 are both - that is, in the same direction with one another - in a direction parallel to the coordinate axis x with respect figure 4 shifted to the left. As a result, the print head 2 and center of gravity SP are also shifted to the left along an imaginary translation axis TA relative to the fixed point FP. The translation axis TA is parallel to the coordinate axis x.

Various modifications are possible:
In the example described above, it is assumed that the cones 12, 13 each taper towards the tip of their screw 7.

However, it is also conceivable that the cones 12, 13 widen towards the tips. In this case, both screws 7 would have to be unscrewed slightly in order to be able to use the lever arms 9, 10 to pivot the print head 2 ( figure 3 ) to push apart.

In the variants mentioned above, both cones 12, 13 taper or widen towards the screw tips, ie in the same direction.

However, a variant is also conceivable in which the change in diameter of the two cones 12, 13 runs in opposite directions. For example, the first cone 12 tapers towards the tip of the screw 7 and the second cone 13 widens towards the tip of the screw. In this case, the first cone 12 would have to be screwed in a little and the second cone 13 would have to be screwed out a little in order to adjust the lever arms 9, 10 for the purpose of rotating the print head 2 about the pivot point SP.

An alternative design of the adjustment devices 4, 5 is also conceivable, with the screws 7 with the cones 12, 13 being replaced by pyramid-shaped thrust wedges with flat sides, for example, on which the lever arms 9, 10 rest.

Ultimately, with appropriate dimensioning of the rods 15, 16 and lever arms 10, 11, the distance between the first connection point AP1 and the center of gravity SP can be different than the distance between the second connection point AP2 and the center of gravity SP. A corresponding design of the holder 3 can nevertheless ensure that the two connection points AP1, AP2 maintain their diametrical relative position when pivoting about the pivot point SP. It is crucial that here too the nozzle surface 6 is pivoted about its geometric center of gravity SP.

Reference List

1

pressure bar

2

printhead

3

holder

4

first adjustment device

5

second adjustment device

6

nozzle area

7

screw

8th

elastic joint

9

first lever arm

10

second lever arm

11

return spring

12

first cone

13

second cone

14

drive element

15

longitudinal bar

16

crossbar

AP1

first connection point

AP2

second connection point

FP

fixed point

RA

axis of rotation

SP

main emphasis

TA

axis of translation

VL

connecting line

x

coordinate axis

y

coordinate axis

e.g

coordinate axis

Claims (6)

1. Printing bar (1) for inkjet comprising

   printing heads (2) in a row,

   mounts (3), each mount (3) holding a printing head (2), and

   adjustment devices (4, 5) for adjusting the printing heads (2) relative to one another, every printing head (2) including a nozzle surface (6) with a geometric centre of gravity (SP) and

   every printing head (2) connected to its mount (3) in two connecting points (API, AP2), which are adjustable relative to a fixed point (FP) of the mount (3) and connected to one another by an imaginary straight connecting line (VL) passing through the centre of gravity (SP) of the nozzle surface (6), wherein for every printing head (2), a first adjustment device (4) and a second adjustment device (5) are in contact with the mount (3) in such a way that adjusting the two adjustment devices (4, 5) in opposite directions causes the printing head (3) to be adjusted in a first degree of freedom and adjusting the two adjustment devices (4, 5) in the same direction causes the printing head (3) to be adjusted in a second degree of freedom, said first degree of freedom defined by a translatory axis (TA) and said second degree of freedom defined by an axis of rotation (RA),

   characterized

   in that the adjustments of the two adjustment devices (4, 5) are linear displacements along an axis of rotation and in that each one of the adjustment devices (4, 5) has a taper (12, 13).
2. Printing bar according to claim 1,
   characterized
   in that the axis of rotation (RA) is orthogonal to the nozzle surface (6) and passes through the centre of gravity (SP) of the latter.
3. Printing bar according to claim 1 or 2,
   characterized
   in that the tapers (12, 13) are formed on bolts (7).
4. Printing bar according to any one of claims 1 to 3,
   characterized
   in that each mount (3) is designed as a frame with elastic joints (8) and lever arms (9, 19).
5. Printing bar according to claim 4,
   characterized
   in that the adjustment devices (4, 5) are in contact with the lever arms (9, 10).
6. Printing bar according to claim 4 or 5,
   characterized
   in that the lever arms (9, 10) are loaded by reset springs (11) which press the lever arms (9, 10) against the adjustment devices (4, 5).

Images