EP0713777B1 - Arrangement of individual ink printing modules for an ink printing head - Google Patents

Description

The invention relates to an arrangement for an ink print head, which is composed of ink print modules in stacked construction, which work according to the edge shooter principle and are equipped with plate-shaped piezoelectric actuators.
The inkjet print head is intended for use in small, fast printers, which in turn are part of modern machines for franking mail or for printing addresses. Such a printer is also suitable as a product labeling device.
In contrast to the usual office printer with line-by-line printing, printing is carried out as a single franking imprint in one pass of the postal matter. Corresponding to this substantially larger print width - approximately one inch - the number of ink nozzles to be arranged one below the other and thus also the number of piezo actuators in an ink print head is considerably larger than in the case of ink print heads for office printers.

In order to meet modern convenience - clichés with word and picture symbols - for franking machines with good print quality, print resolutions of approximately 200 dpi are required, which means ink printheads with the same number of nozzles and piezo actuators with a print width of 2.54 cm (one inch). The usual nozzle openings are between 40 and 50 µm wide. With a cliché width of one inch and a resolution of 200 dpi, the adjustment errors must be kept below 10 µm.
Such ink print heads are inevitably designed in planar or stacked construction, on the one hand for reasons of the permissible dimensions and the packing density to be achieved therewith and on the other hand for reasons of economical production, see also DE 42 25 799 A1. Surface oscillators are usually used as piezo actuators in which a piezoelectric material, for example lead zirconate titanate (PZT), is arranged between two metal electrodes. The carrier plate - at the same time membrane plate over the ink pressure chambers - for the piezo actuators can consist of glass, ceramic, plastic or metal.
The way the modules are arranged in relation to one another in order to achieve a print density of 200 dpi and the contacting of the piezo actuators is a major problem.

An ink print head of the type described at the outset is known, DE 42 25 799 A1, which consists of a number of different modules, of which only one module located outside or in the middle carries the common row of nozzles on its end face. Each module consists of a central plate and membrane plates arranged on both sides of it. The ink pressure chambers are located between the membrane plates and the middle plate. All modules have ink pressure chambers for ink ejection that can be driven by piezo actuators and are connected to the assigned nozzles via correspondingly guided channels. The connection channels from module to module are inevitably orthogonal to the pressure chambers.
Spacers are arranged between the modules, which have an ink feed opening and ink feed-through openings and a cutout for the piezo actuators. The spacer parts can be in one part or two parts and consist of the same material as the piezo actuators, which are arranged on the outer wall of the ink pressure chambers and are contacted with conductor tracks running there.
Although the advantage of only a single row of nozzles is undisputed, the technological effort for producing the different modules is still considerable.
For the connecting channels running through several modules, a higher accuracy than that for the ink pressure chambers and a higher adjustment effort are required. The connection channels of different lengths require additional electronic control measures.
If individual modules are defective, an exchange of them is impossible due to the complicated assembly and adjustment, and a replacement of the complete ink print head is therefore necessary. Due to the large number of nozzles, these heads are much more expensive than inkjet print heads for conventional office printers.

It is also a printhead for inkjet printers known, EP 0 486 256 A2, which consists of several plates in Stacked construction exists. The ink pressure chambers and Nozzle channels and the nozzle openings are in Piezoelectric plates in the form of openings incorporated. It works according to the Shearing principle. To offset the nozzle openings each chamber plate in the Nozzle area opposite the required offset the previous chamber plate designed differently. That means a corresponding manufacturing effort.

The way of driving is problematic regarding acoustic decoupling and one permanent tight connection between each Plates.

An inkjet print head is also known, DE 94 04 328 U1, which consists of two outer smooth Membrane plates and a structured middle plate consists. In the middle plate are on both sides Ink chambers and the ink channels molded in Nozzles are in a row only on one side of the Middle plate, analogous to the ink suction spaces. To this The middle plate has vertical and horizontal purpose Ink channels. On the membrane plates are in the Areas above the ink chambers piezo actuators arranged. The ink chambers and the ink suction spaces are broader and deeper than that horizontal ink channels. It is consequently Recesses shallow, deeper and continuous realize. That requires a corresponding one technological effort, especially since the recesses of on both sides are. The piezo actuators have electrodes on both sides provided such that the outer electrode Piezo plate only partially covered and the inner one Electrode slightly above it. An increase in The number of nozzles inevitably increases in width and length of the print head.

Finally, an ink print head is known, US Pat. No. 4,703,333, in which a plurality of ink print modules which operate according to the side shooter principle are stacked at an incline one behind the other so that on the one hand the nozzle area and on the other hand the ink supply area is free. A receiving frame with inclined steps is adapted to this scale-like arrangement. In order to realize the lateral offset of the nozzles to each other, the ink printing modules are provided with elongated holes through which screws are inserted which engage in the threaded holes of the steps. The modules must be adjusted with a gauge and then locked with the screws. The individual ink printing module consists of a nozzle plate, an ink channel plate, a pressure chamber plate, a membrane plate with piezo actuators and a cover plate with a recess for a strip conductor for contacting the piezo actuators. An ink supply channel with two ink connection sockets is incorporated into the cover plate.
A replacement of individual ink printing modules is possible, but only by unsoldering the ribbon conductor and as can be seen from the description, the number of individual parts and the adjustment effort is considerable. A cleaning and sealing station adapted to this ink print head will be very complicated due to the gradation.

The purpose of the invention is to simplify the construction of the ink printhead and to improve the service properties.
The invention has for its object to provide an arrangement for an ink print head, in which the ink print modules are easily replaceable, the number of different components is reduced and adjustment effort is largely avoided.
According to the invention, this object is achieved according to the patent claims.

The proposed solution offers a number of advantages.
Since the spacer is used according to the invention both as a spacer and as an adjusting piece for the ink printing modules, complicated housings and front masks can be dispensed with.
The nozzle row offset in order to achieve the desired printing density is realized exclusively by means of the stop pieces of the spacer parts, so that the ink printing modules can be constructed completely identically. For example, with three ink printing modules, the offset t from module to module is one third of the nozzle opening distance of a module.
Since the recesses for the stop pieces in the ink printing modules always extend in depth into the nozzle plane, an exact spacing of the nozzle planes of the ink printing modules from one another is ensured. The distance s between two nozzle planes is determined exclusively by the distance between the top surfaces of opposing stop pieces of a spacer.
The recesses in the ink printing modules can be made during the manufacture of the individual plates of the module by means of laser etching or punching. The stop pieces can also be formed during the manufacture - casting - of the spacer parts from ceramic material by appropriate thickening and shaping. The casting or pressing mold only has to be designed accordingly.
If the driver circuits for the piezo actuators are housed on the ink pressure modules and the same are provided with plug connectors, the modules can be exchanged particularly easily and, moreover, individual components that are easy to test are available. This allows an effective inspection in the manufacturing process - thus an increase in the exploitation rate of the ink printhead manufacturing - and a better service. This is important, especially since the ink printing modules with their many nozzle openings are still expensive components.
Since the conductor tracks are routed from one membrane plate level to the other membrane plate level of an ink printing module via the side faces thereof, only one driver circuit and only one plug connector are required for each ink printing module.
However, it is also possible to save on the plug connectors and to integrate the driver circuits in the supply cable and / or in the external control electronics.

The assembly and contacting of the piezo actuators is simplified due to the one-piece comb-like design and the extension of all electrodes in one plane. The contact can be made using a low-melting solder, such as indium, or using bond bridges. In the first case, all electrodes of the piezo actuators face the conductor tracks.
However, it is also possible to apply the piezo actuators individually in a conventional manner. The electrodes facing the membrane plates are then expediently connected to one another by a common conductor track.

The invention is described below using the exemplary embodiment explained in more detail.

Fig. 1

Eine Explosivdarstellung eines Tintendruckkopfes aus drei Tintendruckmodulen,

Fig. 2

eine perspektivische Ansicht des zusammengefügten Tintendruckkopfes nach Fig. 1,

Fig. 3

eine Ansicht gemäß Schnitt AA' nach Fig. 2,

Fig. 4

eine perspektivische Ansicht eines Tintendruckkopfes mit externer Ansteuerung.

Show it:

Fig. 1

An exploded view of an ink print head from three ink print modules,

Fig. 2

2 shows a perspective view of the assembled inkjet print head according to FIG. 1,

Fig. 3

3 shows a view according to section AA 'according to FIG. 2,

Fig. 4

a perspective view of an ink print head with external control.

All figures are for easy understanding drawn schematically.

According to FIG. 1, an ink print head consists of three identical ink print modules 1, 3, 5 and two spacer parts 2, 4, which are also arranged between them and are identical.
The first ink printing module 1 is composed of a first cover plate 15, a middle plate 16 and a second cover plate 17. The plates can be connected to one another by means of gluing or thermal diffusion bonding.
The cover plates 15, 17 are provided in their surface facing the central plate 16 with ink pressure chambers 151, 171, ink channels 152, 172, nozzle channels 153, 173 and ink supply channels 154, 174, see also FIG. 3.
All nozzle openings 175 of the ink printing module 1 run in a row in the second cover plate 17. For this purpose, the nozzle channels 153 are guided from the first cover plate 15 through the central plate 16 as nozzle channels 161 and on to the nozzle channels 173 in the second cover plate 17 and end there as nozzle openings 175. In this case, sixteen nozzle openings 175, 375, 575 are provided for each ink printing module 1, 3, 5. However, a real module will have 64 nozzle openings.
Piezo actuators 11, 18 are placed on the outer surfaces of the cover plates 15, 17 in the area above the ink pressure chambers 151, 171, one piezo actuator each above each ink pressure chamber. The cover plates 15, 17 are inevitably thinner in the areas above the ink pressure chambers 151, 171 and act there as a membrane. That is why the designation membrane plate is applicable. An alternative would be to design the cover plates as thin, smooth membrane plates and to shift all structures into the center plate 16.
In order to facilitate production, assembly and contacting, the piezo actuators 11, 18 are filled in the form of a comb, the back of which is designed as an inactive region and the prongs of the piezoelectric layer 113, 183. Each tine represents a single piezo actuator, the base and top surface of which are covered with electrodes 111, 112, 181, 182. An electrode 112, 182, as a common electrode of all piezo actuators 11, 18, extends over an end face or the comb back into the inactive region of the opposite side. As a result, the contact can be made from one side or using a mounting technique. Since the piezo actuators 11, 18 are combined in one component on the one hand and are spaced apart from one another on the other hand, a complex individual application and alignment over the ink pressure chambers 151, 171 is avoided. The component can be glued on as a whole using previously applied masking marks.
The electrodes 111, 112, 181, 182 are contacted by means of bond bridges with associated conductor tracks 13 which run on the surfaces of the cover plates 15, 17.
Driver circuits 12 for the piezo actuators 11, 18 in the form of a module are applied to the first cover plate 15 and also contacted with the conductor tracks 13.
So that there is an easily detachable connection to the rest of the printing electronics, a connector 14 is also attached and contacted on the cover plate 15. In order to get by with only one plug connector 14 and one driver circuit component 12 per ink printing module, the conductor tracks 13 are drawn from the second cover plate 17 over both side surfaces of the ink printing module 1 into the surface of the first cover plate 15.
The spacer 2 is designed and arranged between the ink printing modules 1 and 3 so that it is flush with the first ink printing module 1 and is offset from the second ink printing module 3 by the pressure density dimension t (for example 192 drops per inch), see also FIG. 2 The thickness of the spacer 2 is dimensioned such that there is a sufficiently large distance between the two ink printing modules 1, 3 with their attached components.
The spacer part 2 is provided on both sides with stop pieces 21, 22 which engage in the associated adapted recesses 170, 350, 360 of the ink printing modules 1, 3, see also FIG. 3.

In the example, the spacer 2 has two pairs of stop pieces 21, 22; in practical implementation there will be three pairs. Accordingly, two recesses would be designed as an elongated hole and one recess as a cylinder hole. The stop piece 21 lies with its top surface in the ink pressure module 1 on the nozzle plane 162. The stop piece 22 lies with its top surface in the ink pressure module 3 at the nozzle plane 376. The parallel spacing of the top surfaces of the opposing stop pieces 21, 22 is equal to the required spacing s of the nozzle planes 162 and 376 from one another. The plate thickness of the spacer 2 is accordingly dimensioned such that the required distance is determined exclusively by the stop pieces 21, 22.
The stop piece 21 is shorter than the stop piece 22 by a central plate thickness, since it only penetrates the cover plate 17 in the recess 170.
The stop piece 22 penetrates the cover plate 35 in the recess 350 and the middle plate 36 in the recess 360. With respect to a defined side edge of the ink printing module 3, the recesses 350 and 360 are offset more inwards by the pressure density dimension t than the stop piece 22 on the spacer part 2 In this way, the first nozzle opening 375 of the ink printing module 3 is offset from the first nozzle opening 175 of the ink printing module 1 by the pressure density dimension and, accordingly, the other nozzle openings as well.
The spacer 2 is provided with a recess 23 for the piezo actuators 18 and 31 and with a recess 24 for the driver circuits 32 and the connector 34.
Since the section AA 'according to FIG. 2 is passed through the outermost nozzle 175 of the first ink printing module 1 and the view to the adjacent outside according to FIG. 3 is shown, only the connection from the ink supply channel 154 via the ink channel 152 to the ink pressure chamber 151 is also the Nozzle duct 153, the nozzle duct 161, the nozzle duct 173 and up to the nozzle opening 175 are visible. The ink supply channels 154, 174 are orthogonal to the ink channels 152, 172 and parallel to the nozzle opening row 175.
4 shows an embodiment in which a connector is dispensed with and the driver circuits are external, for example integrated in a strip conductor. In addition, the possibility of separate application of individual piezo actuators is shown.
Since all ink printing modules 1, 3, 5 are constructed identically, and the spacers 2, 4 are also constructed identically, stacking of ink printing modules in the desired manner is possible, with equidistance and lateral offset of the rows of nozzles being ensured.
A further discussion of the other ink printing modules 3, 5 is unnecessary, corresponding information can be found in the list of reference symbols and the drawings.

Reference symbols used

1

first ink printing module

11

Piezo actuator / s on the top of the ink printing module 1

111

Individual electrodes or control electrodes of the piezo actuators 11

112

common electrode of the piezo actuators 11

113

Piezo layer of the piezo actuators 11

12th

Ink circuit module driver circuit 1

13

Conductor tracks on the ink printing module 1

14

Ink module connector 1

15

first cover plate or membrane plate of the ink printing module 1

151

Ink pressure chamber / s in the cover plate 15

152

Ink channel between the ink pressure chamber 151 and the ink supply channel 154

153

Nozzle channel in the cover plate 15

154

Ink supply channel in cover plate 15

16

Center plate of the inkjet print module 1

161

Nozzle channel in the middle plate 16

162

Nozzle level in the ink printing module 1

17th

second cover plate or membrane plate of the ink printing module 1

170

Bore or recess in the cover plate 17 for Stop pieces 21

171

Ink pressure chamber / s of the cover plate 17

172

Ink channel between ink pressure chamber 171 and Ink supply channel 174

173

Nozzle channel in the cover plate 17

174

Ink supply channel in cover plate 17

175

Nozzle opening / s in the ink printing module 1

176

Nozzle level in the ink printing module 1

18th

Piezo actuator / s on the underside of the ink printing module 1

181

Individual electrodes or control electrodes of the piezo actuators 18th

182

common electrode of the piezo actuators 18

183

Piezo layer of the piezo actuators 18

2nd

first spacer

21

Stop piece on spacer 2 to the ink printing module 1

22

Stop piece on spacer 2 to the ink printing module 3rd

23

Recess in spacer 2 for piezo actuators 18 and 31

24th

Recess in spacer 2 for driver circuit 32 and for connector 34

3rd

second ink printing module

31

Piezo actuator / s on the top of the ink printing module 3rd

311

Individual electrodes or control electrodes of the piezo actuators 31

312

common electrode of the piezo actuators 31

313

Piezo layer of the piezo actuators 31

32

Ink circuit module driver circuit 3

33

Conductor tracks on the ink printing module 3

34

Connector on the inkjet print module 3

35

first cover plate or membrane plate of the ink printing module 3rd

350

Bore or recess in the cover plate 35 for Stop piece 22

351

Ink pressure chamber / s in the cover plate 35

352

Ink channels between ink pressure chamber 351 and Ink supply channel 354

353

Nozzle channel in cover plate 35

354

Ink supply channel in cover plate 35

36

Middle plate of the ink printing module 3

360

Bore or recess in the middle plate 36 for Stop piece 22

361

Nozzle channel in the middle plate 36

362

Nozzle level in the ink printing module 3

37

second cover plate or membrane plate of the ink printing module 3rd

370

Bore or recess in the cover plate 37 for Stop piece 41

371

Ink pressure chamber / s in the cover plate 37

372

Ink channel between ink pressure chamber 371 and Ink supply channel 374

373

Nozzle channel in the cover plate 37

374

Ink supply channel in the cover plate 37

375

Nozzle opening / s in the ink printing module 3

376

Nozzle level in the ink printing module 3

38

Piezo actuator / s on the underside of the ink printing module 3rd

381

Individual electrodes or control electrodes of the Piezo actuators 38

382

common electrode of the piezo actuators 38

383

Piezo layer of the piezo actuators 38

4th

second spacer

41

Stop piece on the spacer 4 to the ink printing module 3rd

42

Stop piece on the spacer 4 to the ink printing module 5

43

Recess in spacer 4 for piezo actuators 38 and 51

44

Recess in the spacer 4 for the driver circuit 52 and for connectors 54

5

third ink printing module

51

Piezo actuator / s on the top of the ink printing module 5

511

Individual electrodes or control electrodes of the Piezo actuators 51

512

common electrode of the piezo actuators 51

513

Piezo layer of the piezo actuators 51

52

Ink circuit module driver circuit 5

53

Conductor tracks on the ink printing module 5

54

Connector on the inkjet print module 5

55

first cover plate or membrane plate of the ink printing module 5

550

Bore or recess in cover plate 55 for stop piece 42

551

Ink pressure chamber / s in cover plate 55

552

Ink channel between ink pressure chamber 551 and Ink supply channel 554

553

Nozzle channel in cover plate 55

554

Ink supply channel in cover plate 55

56

Middle plate of the ink printing module 5

560

Bore or recess in the middle plate 56 for Stop pieces 42

561

Nozzle channel in the middle plate 56

562

Nozzle level in the ink printing module 5

57

second cover plate or membrane plate of the ink printing module 5

571

Ink pressure chamber / s in cover plate 57

572

Ink channel between ink pressure chamber 571 and Ink supply channel 574

573

Nozzle channel in cover plate 57

574

Ink supply channel in cover plate 57

575

Nozzle opening / s in the ink printing module 5

576

Nozzle level in inkjet print module 5

58

Piezo actuator / s on the underside of the ink printing module 5

581

Individual electrodes or control electrodes of the piezo actuators 58

582

common electrode of the piezo actuators 58

583

Piezo layer of the piezo actuators 58

s

Nozzle plane distance

t

Print density (dpi = dots per inch)

Claims (7)

1. An arrangement for an ink print head of a stack design composed of individual ink print modules (1, 3, 5) having a row of nozzles (175, 375, 575) each, that are provided with a spacer (2, 4) arranged between each of them and with plate-shaped piezoactuators (11, 18, 31, 38, 51, 58) having electrodes (111, 112, 181, 182, 311, 312, 381, 382, 511, 512, 581, 582) on either side, said piezoactuators being fitted on the outside on cover plates (15, 17, 35, 37, 55, 57) serving as membrane plates over ink pressure chambers (151, 171, 351, 371, 551, 571) for ejecting ink and being contacted by means of strip conductors (13, 33, 53) running on the outside on the cover plates (15, 17, 35, 37, 55, 57),
   characterized by the following features:

   the in print modules (1, 3, 5) are of an identical design and are arranged in an offset manner with their nozzles (175, 375, 575) being in a staggered relation with one another;

   the spacers (2, 4) are also of an identical plate-shaped design and, for ensuring the required distance (s) between neighbouring ink print modules (1, 3 or 3, 5, respectively) as well as for exactly fixing the ink print modules (1, 3, 5) with an offset (t) to each other, are on either side provided with positioning pieces (21, 22, 41, 42) that engage with associated adapted recesses (170, 350, 360, 370, 550, 560) of neighbouring ink print modules (1, 3 or 3, 5, respectively);

   the strip conductors (13, 33, 53) extend on each module (1, 3, 5) from a cover plate (15, 35, 55) over at least one side face of the module (1, 3, 5) up to the other cover plate (17, 37, 57).
2. An arrangement according to Claim 1, characterized in that

   the piezoactuators (11, 18, 31, 51, 58) are of an identical design and have both an active and an inactive area each,

   one of the electrodes extending, as a joint electrode (112, 182, 312, 382, 512, 582) of all piezoactuators arranged on the same cover plate (15, 17, 35, 37, 55, 57), from one level over a side face of the piezo layer (113, 183, 313, 383, 513, 583) to the level of the other electrodes;

   that the piezoactuators are contacted by means of placing their electrodes on the strip conductors (13, 33, 53);

   that on the one cover plate (15, 35, 55) of each ink print module (1, 3, 5), a driver circuit (12, 32, 52) is fixed for the piezoactuators and contacted with the assigned strip conductors; and

   that each print module is provided with a plug-type connector (14, 34, 54) that is contacted with assigned strip conductors, too.
3. An arrangement according to Claim 1, characterized in that the piezoactuators (11, 18, 31, 38, 51, 58) are designed as single-piece chamber-shaped parts.
4. An arrangement according to Claim 1, characterized

   in that each of the spacers (2, 4), on the one hand, with their positioning pieces arranged on the one side (21, 41), abuts on the middle plate (16, 36) of the adjacent ink print module (1, 3) in the area of a nozzle level (162, 362) and, on the other hand, with their positioning pieces (22,42) arranged on the other side, abuts on the second cover plate (37, 57) of the adjacent (231) ink print module (3, 5) in the area of a nozzle level (376, 576); and

   that the distance between the top surfaces of opposite positioning pieces (21, 22 or 41, 42, respectively) of each spacer (2, 4) is equal to the distance (s) of neighbouring nozzle levels (162, 362 or 376, 562 or 576, respectively).
5. An arrangement according to Claims 1 and 4, characterized in that, in order to provide for the required offset between the nozzles (175, 375, 575) of neighbouring ink print modules (1 and 3 or 3 and 5, respectively), the positioning pieces (22, 42) facing towards the following ink print module (3, 5) of the spacer (2, 4) aligned with the preceding ink print module (1, 3) are further offset by the printing density value ( t ) in relation to a defined lateral edge of the ink print module (1, 3, 5) than the assigned adapted recesses (350, 360, 550, 560).
6. An arrangement according to Claims 1 and 2, characterized in that the spacers (2, 4) are provided with cutouts (23, 24, 43, 44) for the assigned piezoactuators (18, 31, 38, 51) and, if applicable, for driver circuits (12, 32, 52) and plug connectors (14, 34, 54).
7. An arrangement according to Claim 1, characterized in that the spacers (2, 4) are made of ceramic material and that the positioning pieces (21, 22, 41, 42) are formed by respective thickening and forming during the manufacturing of the ceramic plates.

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