EP1285762B1 - Microdroplets generator in particular for ink jet printers - Google Patents

Description

The invention relates to a droplet generator for microdroplets, in particular a nozzle head for ink printers, arranged in a housing groups of piezoelectrically actuated bending transducers, which are spaced from each other on a partial length by means of wall thicknesses in recesses guided laterally, wherein extending under the bending fingers in a frame plate in the longitudinal direction Liquid longitudinal channels are arranged and in the base plate, a liquid chamber is formed, in each of which at least one nozzle opens per bending transducer.

The drop generator described at the outset is known from EP 0 713 773 A2. However, the known construction uses partitions in full length and height with corresponding wall thicknesses between the parallel adjacent bending transducers. It is therefore to start from a micro-drop generator for an ink printer, comprising a piezoelectric bending transducer in a housing, with a bending comb whose rear, passive region is provided with a transverse connecting dam and whose front, active region consists of bending tongues, which are associated with the nozzles, wherein the bending transducer consists of a carrier layer and of a connected piezoelectric layer and has on its underside in the passive portion of the carrier layer a step cutout adjacent to a hole for a pin, so that a projecting support portion is formed. This training serves the purpose that in order to avoid the so-called. Crosstalk of bending transducer chamber to bending transducer chamber in a front, the nozzle-facing portion that allows lateral fluid pressure waves to avoid disturbances in the formation of liquid droplets of the size to be observed, the ejection angle and in the frequency of the bending transducer to avoid.

Other similar drop generators are known from EP-A-0337429.

The invention has for its object to avoid crosstalk between individual chambers without consuming and difficult to control placement of partitions between the bending fingers, with a bending transducer is in each chamber, the bending tongue deflects against the associated nozzle in the common base plate, and sufficient thick chamber walls, in a manageable in the micron range for the dense assembly to achieve a high liquid flow.

The stated object is achieved in that in each case around an opening of the liquid chamber, a bead runs, which serves as a stroke limiter for the bending finger and that connects to the opening a shaft at least in the width of the bending finger and in height to the base plate. The resulting large liquid inlet to the liquid chamber causes an efficient fluid flow. This liquid flow reduces the pressures on the surrounding walls. Unwanted high pressure waves are avoided. When using the full flow width, only a low flow resistance has to be expected. Since the walls close to the bottom tight, the problem arises to dominate manufacturing tolerances in the micron range, not. A particular improvement is achieved by the edge bead: The fluid flow can be sheared off and thereby the ejected liquid quantity is sharply limited. When the bead rests on the lower edge of the bending transducer, the interior is sealed. This achieves further advantages in the event of fluctuations in pressure and temperature. The resting bending finger thus represents a seal, so that no liquid can escape through pressure and temperature fluctuations.

The liquid supply is still supported according to an embodiment in that in the housing over the group of bending fingers, a common liquid inlet is arranged.

The liquid supply is further improved further in that the liquid longitudinal channels are connected below the bending fingers in a region facing away from the nozzle to a transverse to the bending fingers (usually perpendicular) extending fluid supply line.

Depending on the exit direction of the liquid droplets, it may be advantageous for the liquid chamber in the frame plate below the edge bead to continue with the width of the (inlet) opening and to extend at right angles to the mouth of the nozzle.

An embodiment further provides that the nozzles are arranged in a nozzle plate placed on the housing and / or the frame plate and / or the base plate.

The exit direction of the liquid drops is e.g. taken into account that the nozzle plate is arranged at perpendicularly extending through the base plate nozzles on the underside of the base plate.

According to another embodiment, it is provided that in each case a separating web runs in the frame plate on the edge bead. As a result, the pressure propagation and the crosstalk to the adjacent chamber is reduced to areas of small Biegefingerauslenkungen.

In this case, the divider can be connected in each case between two adjacent edge beads.

In order to prevent the bending finger impacts on the edge bead and breakage occurs, it is advantageous that in each case centrally between two separating dividers an oppositely directed, projecting rolling surface extending between the separating webs is provided. The edge bead, the divider, the bearing point and the rolling surface lie in one plane. As a result, the damping behavior of the bending finger can be further adapted to the fluid. It is also advantageous that the surfaces are recessed around the edge bead and the rolling plane up to the dividing webs.

A further embodiment is that between each two, formed during the production by a saw cut bending fingers a Sägespalt is incorporated, which corresponds in its width to the thickness of a chamber intermediate wall or the thickness of a separating web.

In the drawings, embodiments of the invention are shown and are explained in more detail below.

Fig. 1

eine Längsschnitt durch den Biegewandler mit Grundplatte, Rahmenplatte, Flüssigkeitskammer und Düse,

Fig. 2

denselben Schnitt wie Fig. 1 mit einem Gehäuse,

Fig. 3

denselben Schnitt mit einer angeformten Düse,

Fig. 4A

einen Teilschnitt in Richtung der Düsen mit Flüssigkeitskammer und Trennstegen,

Fig. 4B

einen Teilschnitt in Richtung der Düsen in einer Ebene, in der Flüssigkeit in eine Nachbar-Flüssigkeitskammer gelangen kann,

Fig. 4C

einen Teilschnitt in Richtung der Düsen bei Aufliegen der Biegefinger auf der Flüssigkeitskammer,

Fig. 5A

eine Draufsicht auf die Rahmenplatte mit den Trennstegen,

Fig. 5B

einen Schnitt durch Fig. 5A in der Ebene der Flüssigkeitskammer und

Fig. 6

eine Draufsicht auf die Rahmenplatte mit den Abrollflächen.

Show it:

Fig. 1

a longitudinal section through the bending transducer with base plate, frame plate, liquid chamber and nozzle,

Fig. 2

the same section as FIG. 1 with a housing,

Fig. 3

the same section with a molded nozzle,

Fig. 4A

a partial section in the direction of the nozzle with liquid chamber and dividers,

Fig. 4B

a partial section in the direction of the nozzles in a plane in which liquid can enter a neighboring liquid chamber,

Fig. 4C

a partial section in the direction of the nozzle when the bending fingers rest on the liquid chamber,

Fig. 5A

a top view of the frame plate with the dividers,

Fig. 5B

a section through Fig. 5A in the plane of the liquid chamber and

Fig. 6

a plan view of the frame plate with the rolling surfaces.

The drop generator has a plurality of bending transducers 1 arranged in series, each of which is formed from a piezo plate 3 adhered to a frame plate 2 and subsequently separated by sawing into individual bending transducers 1 as a function of the distance between two nozzles 7. The frame plate 2 has areas for fixing the piezoelectric plate 3, which form a bearing edge 4 for a bending finger 5 and other areas in which the bending fingers 5 move rapidly from a prestressed position to a relaxed position to each liquid drop 6 by a Let nozzle 7 escape. Instead of a planar, bimorph multilayer piezo plate 3a (passive type - in contrast to the multilayer piezo plate 3b in active design) can also be a bending comb in which the piezo plate 3 is provided with a connecting dam 9 and then the individual bending fingers 5 by sawing be prepared, on.die provided with cutouts, paragraphs, approaches and edges (so-called structures) frame plate 2 are placed. The connecting dam 9 is aligned, centered and fixed, e.g. by gluing or clamping. The adhesive surface for the bending transducer 1 is about 1/3 of its total length. This results in an alignment effect on the free-standing bending finger. 5

The frame plate 2 has the bearing 10 for the bending transducer 1 and tools for aligning the articulated into individual bending transducer 1 group. The group of bending transducers 1 is tightly enclosed by a housing 11.

Below the bending fingers 5 in the frame plate 2 extending longitudinally longitudinal liquid channels 12 are arranged, which end in the base plate 1 a in a liquid chamber 13. Each liquid chamber 13 has at least one nozzle 7.

The hydration is u.a. influenced by an opening 14. The opening 14 has the largest possible square (or rectangular) cross section, which results from the constructive dimensions between the bending fingers 5 and the nozzle intervals. Around the opening 14 of the liquid chamber 13 extends an edge bead 15, which is located in the region of the largest deflection of the bending finger 5, which consequently serves as a stroke limiter for the bending finger 5. To the opening 14 includes a shaft 16 at least in the width of the bending finger 5 and in height to the base plate 1a. The shaft 16 is guided without substantial narrowing to the nozzle 7. At the front-side drop outlet (Fig. 1 - 3), the fluid flow is deflected.

A sufficiently large amount of liquid is basically provided by arranging a common liquid inlet 17 in the housing 11 above the group of bending fingers 5 (FIG. 2). In addition, the liquid longitudinal channels 12 are connected below the bending fingers 5 in a region facing away from the nozzles 7 to a transverse to the bending fingers 5 or perpendicular fluid supply line 18.

The liquid chamber 13 in the frame plate 2 continues below the edge bead 15 with the width 14a and extends in the embodiment of FIG. 2 at right angles to the mouth 19 of the nozzle. 7

The nozzle 7 may be arranged in a nozzle plate 20 placed on the housing 11 and / or the frame plate 2 and / or the base plate 1a.

In perpendicular through the base plate 1 a extending nozzles 7, the nozzle plate 20 is disposed on the underside of the base plate 1 a. Thus, the nozzle geometry can be optimized without restrictions.

Furthermore, in each case a separating web 21 runs in the frame plate 2 at the edge bead 15. The deep shafts 16 are separated from one another by these separating webs 21. With small nozzle openings directly under the bending finger 5, a large part of the liquid is pressed laterally to an adjacent bending transducer 1 (see Fig. 4B) The arrangement of a plunger at the tip of the bending finger 5 increases the introduction of force without affecting the liquid Nachfluss.

According to FIG. 5A, in each case between two separating webs 21, an oppositely directed, projecting rolling surface 22 with web width is formed between the separating webs 21. Basically, by such dividers in or on the frame plate 2, a leakage of a pressure wave in the area of action of an adjacent bending transducer 1 can be further reduced. It is expedient to form the separating webs only in the region of the liquid chamber 13 and not to lead to the bearing edge 4. Characterized the liquid flow is ensured under the bending fingers 5 and a washable filler under the piezoelectric plate 3 can be easily introduced and removed after a saw cut 23 again. When gluing the piezoelectric plate 3, this can be supported on the dividing webs 21, so that an accurate distance of the piezoelectric plate 3 is achieved.

Between each two, formed during the preparation by a saw cut 23 bending fingers 5, a kerf 23a is incorporated, which corresponds in width to the thickness of a chamber intermediate wall 8 or the thickness of a separating web 21. The sawing of the piezo plate 3 in the plane of the separating webs 21 or the chamber intermediate wall 8 up to the height (the beginning) of the separating webs 21, which are easily sawed, results in an exact assignment of the bending fingers 5 to the liquid chamber 13 and to the separating webs 21st Between the dividers 21 and the edge of the piezo-plate 3, a lateral air gap can be generated when sawing, so that the fluid is not trapped under the bending finger 5 when actuated and dampens the movement. The bending fingers 5 are narrower by a minimum tolerance than the distance of the separating webs 21st

LIST OF REFERENCE NUMBERS

1

bending transducer

1a

baseplate

2

frame plate

3

Piezo plate

3a

Multilayer (passive)

3b

Multilayer (active)

4

bearing edge

5

bending fingers

6

Drop of liquid (microdrops)

7

jet

8th

Chamber partition

9

connection dam

10

depository

11

casing

12

Liquid longitudinal channels

13

liquid chamber

14

opening

14a

width

15

bead

16

shaft

17

liquid inlet

18

fluid supply line

19

Mouth of the nozzle

20

nozzle plate

21

divider

22

rolling surface

23

Saw cut

23a

kerf

Claims (10)

1. Drop generator for micro drops, in particutar a jet head for ink jet printers, with groups of bending converters (1) which can be operated piezo-electrically and which are arranged in a casing (11), separated by each other on a partial length by means of wall thicknesses separately in recesses, in which case longitudinally arranged longitudinal liquid channels (12) are running below the bending fingers (5) in a frame plate (2) and where a liquid chamber (13) is formed in the base plate (1 a). At least one nozzle each (7) leads into the bending converters (1) each,
   characterized by the fact
   that a bead (15) each runs around an aperture (14) of the liquid chamber (13). This bead (15) serves as a stroke limitation device for the bending finger (5)d; and that a shaft (16) is connected with the aperture (14), at least in the width of the bending finger (5) and in the height up to the base plate (1a).
2. Drop generator according to Claim 1,
   characterized by the fact
   that a mutual liquid inlet (17) is arranged in the casing (11) above the group of bending fingers (5).
3. Drop generator according to one of the Claims 1 or 2,
   characterized by the fact
   that the longitudinal liquid channels (12) are connected below the bending fingers (5) to a fluid inlet (18) which is arranged diagonally to the bending fingers (5) and positioned in an area separated from the nozzles (7).
4. Drop generator according to one of the Claims 1 to 3,
   characterized by the fact
   that the liquid chamber (13) is extended in the base plate (2) below the bead (15) with the width (14a) of the aperture (14) and extends at right angles to the mouth (19) of the aperture (7).
5. Drop generator according to one of the Claims 1 to 4,
   characterized by the fact
   that the nozzles (7) are arranged on a nozzle plate (20) positioned on the casing (11) and/or on the frame plate (2) and/or on the base plate (1 a).
6. Drop generator according to one of the Claims 1 to 4,
   characterized by the fact
   that the nozzle plate (20) is positioned at the underside of the base plate (1a) while the nozzles (7) are arranged running vertically through the base plate (1a).
7. Drop generator according to one of the Claims 1 to 6,
   characterized by the fact
   that there is at each of the beads (15) a separating web (21) in the frame plate (2).
8. Drop generator according to Claim 7
   characterized by the fact
   that the separating web (21) is connected in each case between two beads (15) running parallel along each other.
9. Drop generator according to one of the Claims 1 to 8,
   characterized by the fact
   that a protruding rolling-off surface is provided in each case in the centre between two adjacent separating webs (21), reaching between the separating webs (21) in the opposite direction.
10. Drop generator according to one of the Claims 1 to 9,
    characterized by the fact
    that a sawing slit (23a) has been worked in between two bending fingers (5), formed during the manufacture by a sawing cut (23).This sawing slit (23a) corresponds in its width to the thickness of the dividing wall of the chamber (8) or to the thickness of a separating web (21).

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