EP1819517A2

EP1819517A2 - Ink jet writing head

Info

Publication number: EP1819517A2
Application number: EP05811216A
Authority: EP
Inventors: Manfred Pauly
Original assignee: REA Elektronik GmbH
Current assignee: REA Elektronik GmbH
Priority date: 2004-10-25
Filing date: 2005-10-24
Publication date: 2007-08-22
Anticipated expiration: 2025-10-24
Also published as: WO2006045572A2; DE502005004054D1; WO2006045572A3; ATE394229T1; US20090115816A1; US7824015B2; EP1819517B1

Abstract

An ink jet writing head includes a pressurized ink chamber provide with at least one ink nozzle that is closed by a mobile valve body. A piezoelectric valve actuating device that is electrically connected to a control device drives the valve body with reciprocating motions. The valve body is held by a closing spring in the closing position thereof and is connected to a connecting rod in a driving manner. At least one curved spring strip engages with the end of the connecting rod, located at a distance from the valve, the spring strip being supported on the valve-side end thereof, opposite the ink chamber. The connecting rod is subjected to the tractional prestress of a tension spring. At least one piezoelctric element is applied to the spring strip, the piezoelectric element being controlled by the control device in such a way as to perform tractile movements.

Description

Inkjet recording head

The present invention relates to an ink jet recording head having a pressurized ink chamber with at least one ink nozzle closed by a movable valve body and a piezoelectric valve actuator driving the valve body to lift and electrically connected to a driving means.

Such ink-jet recording heads are used to print characters and numbers on the surfaces moved past them. Usually, a plurality of ink nozzles are provided in an ink chamber, which are selectively actuated by a controller to briefly open the respectively driven nozzle. Under the effect of the pressure prevailing in the ink chamber, a short jet of ink is ejected from the ink nozzle, which generates a dot on the surface to be printed.

In a known ink-jet recording head (EP 0 445 137) are provided as a valve actuating elements hinged magnets whose armature are each in drive connection with the associated valve body. In this case, the mass formed essentially by the armature of the folding magnet must be accelerated and decelerated during each valve actuation process. _ 9 _

The energy required for this limits the possible operating speed of the valve actuator.

In a known ink-jet recording head of the type mentioned (DE 1 952 880 A) is to increase the

Working speed the use of piezoelectric valve actuators has been proposed. However, these ink jet recording heads do not meet the practical requirements of higher writing speeds in practice.

The object of the invention is therefore to provide an ink jet recording head of the type mentioned in such a way that it can be operated smoothly under the working speeds required in practice.

This object is achieved in that the valve body is held by a closing spring in its closed position and with a voxsteile sealed from the ink chamber movably led out drawbar is in drive connection that acts on the drawbar mindestes a curved spring strip at its end opposite the ink chamber is supported, that the drawbar under tensile prestress of a

Tension spring is and that on the spring strip at least one piezoelectric element is applied, which can be controlled by the driving device to Dehn- or contraction movements.

Preferably, flat piezo elements are used, in particular piezo elements based on films are suitable. In addition, it is also possible to use piezoelectric elements based on cier fibers or strips, for example the MFC piezoelectric elements known from WO 01/33648 A1 and available on the market (macro-fiber composite piezoelectric element).

Although high-performance piezoelectric elements are available in the form of planar piezoelectric elements, which because of their construction can not be used directly for actuating valves on ink-jet writing heads. Only through the connection with at least one curved spring strip, on which a planar piezoelectric element is applied on one side, creates a valve actuator that allows for very small footprint a sufficiently high performance and operating speed to be used in an inkjet recording head. In particular, the functionality of the valve actuator remains unrestricted even at high operating frequency over a long period.

Preferably, in each case on the curvature inside of the spring strip, a pressure biased standing, only applied to Dehnbewegungen piezoelectric element applied.

Instead, it may also be provided to apply in each case to the curvature outside of the spring strip a piezoelectric element which can be excited to give contraction movements. It is particularly advantageous to apply the piezo elements on both sides of the spring strip. As a result, a particularly high actuation force is achieved. According to a preferred embodiment of the invention it is provided that at the valve remote end of the tie rod only one provided with a piezoelectric element, curved Federst attacked tires. Here, the masses to be moved are relatively small, so that a high operating frequency is achieved.

It is advantageous here, the valve distal end of the spring strip or the tie rod in a

Longitudinal guide device in the longitudinal direction of the pull rod to move.

Instead, an embodiment is possible in the valve remote end of the pull rod two curved in the opposite direction spring strip attack, which are supported at their valve-side ends against the Tintenkamme r, and wherein the piezo elements of the two spring strips by the control device like insam to the movements are controllable. Due to the symmetrical structure, a symmetrical force application is achieved on the drawbar without Führiαngseinrichtung.

The drawbar can extend at its valve distal end diαrch a bore of an upper clamping block and carry on a threaded neck of an adjusting nut, which allows adjustment of the bias. Valve eitig the pull rod extends through a hole s a lower clamping block, in which the end of the spring strip or the ends of the two spring strips is or are included. The pull rod is according to a first embodiment of the invention verbiαnden directly to the valve body. This gives an immediate force transfer from the pull rod to the valve body. This embodiment is particularly suitable if only a single T_Lntendüse is present or if there is a sufficient distance between them with multiple ink nozzles.

Instead, it is also possible that the pull rod via an operating lever with one with the

Valve connecting rod connected valve connecting rod is in drive connection. This embodiment makes it possible to arrange the valve actuators staggered on both sides of the ink chamber so that relatively narrow juxtaposed nozzle nozzles can be achieved.

Further advantageous embodiments of the inventive concept are the subject of further subclaims.

The invention will be explained in more detail below by exemplary embodiments, which are illustrated in the drawing.

It shows:

Fig. FIG. 1 shows, in a schematic, spatial representation, an ink-jet recording head with an ink nozzle and a valve actuating device, FIG.

Fig. FIG. 2 is a view in the direction of the arrow II in FIG. 1, partly in section along the line II-II, 3 is a partial sectional view corresponding to FIG. 2 of a modified embodiment of an ink-jet recording head,

4 in a section corresponding to FIG. 1, a further modified embodiment of an ink-jet recording head,

5 in a partial view, a comparison with FIG. 4 modified version,

Fig. 6 in a section corresponding to FIG. 4, a further modified embodiment.

Fig. 7 in a section corresponding to Fig. 2 shows a modified embodiment of an ink jet Schreibikopfes

Fig. 8 in a section corresponding to FIG. 2, another modified embodiment of an ink jet recording head.

91 shows in a vertical section the arrangement of two adjacent valve actuators,

10 shows a spatial representation of one of the two spring strips shown in Fig. 9 with a planar piezoelectric element.

11 is a longitudinal section of an ink-jet recording head with an ink nozzle and a

Valve actuator, which has only a curved spring strip and Fig. 12 in one. 7 shows an ink jet recording head with an ink nozzle and a valve actuator, which has two curved spring strips.

The ink-jet recording head shown in Figs. 1 and 2 serves to print characters and numbers on an area 1 indicated in Fig. 2 only while this surface 1 is moved along the ink-jet recording head. For this purpose, the ink jet scraping head to a writing ink filled, pressurized ink chamber 2, which is supplied via an ink line 3 with ink. In the bottom wall 4 of the Tintenkammeir 2 one or more ink nozzles 5 are arranged, wherein in Fig. 1, only one of these ink nozzles 5 is shown.

Each ink nozzle 5 is closed by a valve body 6 which is driven to controlled strokes. The valve body 6 is moved by a designed as a pressure spring closing spring 7 in the closed position of

Valve is pressed, via a led out of the ink chamber 2 pull rod 8 with a

Valve operating device 9 connected. The pull rod 8 may consist of a wire, a thin pull rope or a stranded stranded wire.

The pull rod 8 extends through the

Valve operating device 9 and carries at its upper end remote from the valve on a threaded portion 10 a

Adjusting nut 11. The drawbar 8 extends at its valve distal end through a bore 12 of an upper Clamping blocks 13. At the valve remote end of the pull rod 8 engage in the opposite direction convex curved spring strips 14, which consist for example of spring steel. The upper ends of the two spring strips 14 are in the upper. Clamping block 13 was added.

The lower ends of the two spring strips 14 are received in a lower clamping block 15. The pull rod 8 extends on the valve side through a bore 16 of the lower clamping block 15, which sits in the embodiment of FIGS. 1 and 2 directly on the ink chamber 2. In the embodiment of FIG. 3, the lower clamping block 15 is also in a fixed position to the ink chamber. 2

In this way, the two curved Fedeitrstreif s 14, which act on the valve remote end to the tie rod 8, valve side opposite the ink chamber 2 supported.

The Zugst ange 8 is under tensile prestress one

Spannfede r. In the embodiment according to the F ¹ Ig. 1 and 2 forms di e closing spring 7, which presses on the valve body 6, at the same time the tension spring of the pull rod. 8

The two curved spring strips 14 each carry a piezo element 17 on the inside of the arch. These are preferably planar piezoelectric elements, in particular piezoelectric elements based on films are suitable. In addition, the use of pie zoelementen on the basis of fibers or strips is possible - both piezo elements 17 are connected by an electrical drive means 18 together to Dehnbewegungen controllable. The two piezo elements 17 are due to the bias of the valve actuator 9 and the resulting curvature of the spring elements 14 on the concave Völbungsinnenseiten under a mechanical compression bias. They are going through the

Control device 18 electrically driven exclusively in such a way that they perform a Dehnbewegiαng.

With dash-dotted lines is only indicated in Fig. 3 that in addition to the piezoelectric element 17 (or independently) on the vault outer side of the spring strip 14, a further planar piezoelectric element 17a may be applied, which is electrically connected so that it stimulated only to contraction movements and therefore exercises traction.

In Ausfühxungsbeispiel according to FIGS. 1 and 2, the pull rod 8 is connected directly to the valve body 6. Notwithstanding this is in the embodiment of FIG. 3, the pull rod 8 via a unilaterally mounted on the lower clamping block 15 actuating lever 19 with a connected to the valve closing member 6 valve connecting rod 20 in Antriebsverüoindung. The valve pull rod 20, which is also abgedichtet in this embodiment from the inks, chamber 2, carries on an upper gewiαdeabschnitt 21 an adjusting nut 22, which allows a length adjustment on the actuating lever 19.

At the lower end of the pull rod 8 is designed as a compression spring, separate tension spring 23 is arranged, which is connected to the pull rod 8 actuating lever 19 after cärückt down and exerts the desired tensile prestress on the pull rod 8. Thus, this engages the pull rod 8 a separate, separated from the closing spring 7 tension spring 23.

The embodiment illustrated in FIG. 4 differs from the exemplary embodiment according to FIG. 1 primarily in that, instead of the two spring strips 14 at the valve-distal end of the drawbar 8, only a single, curved spring strip 14 provided with a piezo element 17 acts.

The valve distal end 14a of the spring strip 14 is in this case longitudinally movably guided in a longitudinal guide device in the longitudinal direction of the pull rod 8. For this purpose, the

Longitudinal guide device on a stationary ETührungsschlitz 24, engages in the at least one upper longitudinal extension 25 of the spring strip 14 movable. The guide slot 24 is formed on a guide plate 26 which is fastened at its one end to the clamping block 15, for example screwed and angled at the other end to a horizontal plate 27. The longitudinal extensions 24 of the spring plate 14 are formed, for example, by the two upward side strips, ie in the longitudinal direction of the tie rod 8, of the side strips of the spring plate 14. A between these two longitudinal extensions 25 horizontally angled tab 28 is below the adjusting nut 11 and transmits the movements of the FederbILechs 14 on the pull rod 8. Since the masses to be moved in this case are relatively low, very high operating frequencies are achieved. The longitudinal guide device can also be designed so that the valve distal end of the pull rod 8 in the longitudinal guide device in the longitudinal direction of: pull rod is guided movably, for example, all in a guide bore in the plate 27th

In the in Fig. 5 embodiment shown in a partial view engages the valve remote end 14a of the spring strip 14, a spring 29, which leads out here as a compression spring is. The spring 29 is supported on the underside of the plate 27 and biases the spring strip 14 in Bewegu.ngsrich.tung the pull rod 8 before. The required bias of the piezoelectric element 17 is in this case essentially by the spring 29, so that on the one hand, the bias of the piezoelectric element 17 can be specified precisely and on the other hand, the closing spring 7 can be designed weaker.

Fig. 6 shows a valve actuating device similar to FIG. 4, wherein j edoch in the already in Fig. 3 described on the outside of the curvature of the spring strip 14 a stimulable to contraction movements planar piezoelectric element 17a is applied.

In Fig. 7 are shown in a vertical section two immediately adjacent to one another arranged in an ink jet recording valve actuation devices, which in each case have a curved spring strip 14 'and an end of the spring strip 14' angxeifende drawbar 8 at venti. At the Wölbungsaußens eite of the spring strip 14 'is a flat Piezoel ement 17' appli graced. The connection of the upper, distal end of each spring strip 14 'is similar in the embodiment of FIG. 6. Deviating from this, however, the pull rod 8 extends through a passage opening 30 of the

Spring strip 14 'and the planar piezoelectric element 17'. As can be seen particularly clearly from FIG. 8, the passage opening 30 for the drawbar 8 is a longitudinal slot open towards the valve end of the spring strip 14 '.

The implementation of the pull rod 8 through the passage opening 30 of the spring strip 14 'allows a space-saving arrangement. The distance between two adjacent tie rods 8 and thus between two adjacent ink nozzles 5 can be very narrow despite relatively large peak height of the curved spring strips 14 'because the support of the valve end of each spring strip 14' - as in Fiςr. 7 - may be in the vicinity of the respective adjacent tie rod 8. Starting from a predetermined for each application, mutual spacing of the ink nozzles 5, a favorable for the efficiency of the piezoelectric valve actuator, relatively strong curvature of the spring strip 14 'gewäh.lt be.

Fig. 8 also shows that the Fedeirstreifen 14 'is laterally constricted in its central region. This results in the central region of the spring strip 14 'an increased bending elasticity. This is favorable for the drive behavior. In the embodiment according to FIG. 9, at the end of the pull rod 108 protruding into the valve actuating device 109, a curved or curved spring strip 114, which consists for example of spring steel, fiber-reinforced plastic or similar resilient material, engages. The domed spring strip 114 is attached at its valve distal (in the drawing upper) end 114a to a bow-shaped support 113, which is attached for example to the upper wall of the ink chamber 2. The pull rod 108 extends in the illustrated embodiment through a bore 115 in the upper. Wall of the ink chamber 2 and through a bore 116 of an angled tab 117 at the valve near end 118 of Fedeαrstreifens 114th

A extending in Bewegungsrichtuncj the pull rod 8 tongue 119 at the valve near end 118 of the spring strip 114 is guided in a serving as a longitudinal guide means recess 120 in the longitudinal direction of the tie rod 108 movable.

The curved spring strip 114 carries in the embodiment shown in Fig. 9 on its curvature inside a piezoelectric element 121. This is preferably a flat piezoelectric element, in particular piezoelectric elements are suitable based on film. In addition, the use of piezoelectric elements based on fibers or strips is possible.

The piezoelectric element 121 is through, an electrical

Control device 122, which is indicated only schematically in the drawing, to a contraction movement controllable. As the electrically driven piezoelectric element 121 shortens, the curvature or curvature of the spring strip 114 is enhanced. As a result, a tensile force is exerted on the pull rod 108; the valve is opened. The valve closes again under the action of the closing spring 7, as soon as this tensile force is no longer effective.

The ink-jet recording head shown in Fig. 10 differs from the writing head of Fig. 7 in that the tie rod 108 is engaged by two oppositely-curved spring strips 114 each arranged as already described in the example of Fig. 9 has been. Both spring strips 114 are attached to their valve remote ends 112 and connected at their valve-near ends 118 with each other and with the tie rod 108. A longitudinal guide device, as described in FIG. 9, is dispensed with in this double arrangement of the spring strips 114.

The embodiment shown in FIG. 11 differs from the exemplary embodiment according to FIG. 1 only in that, in addition to the flat piezo element 121 already described, a further, planar piezoelement 123 is applied to the outside of the curvature of the spring strip 114 on the inside of the curvature of the spring strip 114. While the piezoelectric element 121 on the inside of the buckle in the already beschirriebenen manner by the electrical drive means 122 is driven to contraction movements, the planar piezoelectric element 123 on the vault outer side of the spring strip 114 is designed so that it through the electrical control device 122 can be controlled to Ausdehn- movements. The contraction of the piezoelectric element 121 on the concavity inside and the stretching movement of the piezoelectric element 123 on the vault outside of the spring strip 114 cause a reinforcement of the curvature oc the curvature of the spring strip 114 and thereby the exertion of a tensile force on the tie rod 108th

The embodiment of FIG. 12 differs from the embodiment of FIG. ILl only in that here the piezoelectric element on the curvature inside of the spring strip 114 has been omitted, so that the spring strip 114 carries only the piezoelectric element 123 excitable to Ausdehn movements on the vault outside.

Claims

Inkjet Writing Head Pats

An ink-jet recording head having a pressurized ink can (2) with at least one ink nozzle (5) which is closed by a movable valve body (6), O and with a valve body for lifting motions driving, piezoelectric

Valve actuating device (9) which is electrically connected to a control device (18, 122), characterized in that the valve body (6) by 5 a closing spring (7) is held in its closed position and with a pull rod (8, 108) in drive connection is that at the tie rod (8, 108) at least one curved spring strip (14, 14 ', 114) engages, which is supported at its end opposite the ink chamber (2), that the pull rod (8, 108) under tensile prestress of a Tensioning spring (7, 23) is and that on the spring strip (14, 14 ', 114) at least one piezoelectric element (17,17a, 17') is applied, which by the driving means (18, 122) can be driven to expand or contractions , 5

2. ink-jet recording head according to claim 1, characterized in that the curved spring strip (14, 14 ') with its valve distal end (112) on the drawbar (8, 108) engages and at its valve-side end (118) O opposite the ink chamber (2) is supported.

3. An ink-jet recording head according to claim 1, characterized in that the domed spring strip (114) is fastened to its end remote from the valve (112), and that the at least one piezo element (121, 123) applied to the spring strip (114) can be actuated by the actuation device (122) to change its length reinforce the curvature of the spring strip (114) so that a pulling force is exerted on the pull rod (108).

4. ink-jet recording head according to one of claims 1-3, characterized in that the piezoelectric element (17) is a planar piezoelectric element.

5. ink-jet recording head according to claim 4, characterized in that the piezoelectric elements (17, 17 a, 17 ', 121, 123) are carried out on the basis of films.

6. An ink-jet recording head according to claim 4, characterized in that the piezoelectric elements (17, 17 a, 17 ', 121, 123) are made on the basis of fibers or strips.

7. An ink-jet recording head according to claim 4, characterized in that the piezoelectric elements (17, 17a, 17 ', 121, 123) are MFC piezoelectric elements.

8. ink-jet recording head according to one of claims 1-7, characterized in that the piezoelectric element (17, 121) in each case on the curvature inside of the spring strip (14, 114) is applied.

9. ink-jet recording head according to one of claims 1-7, characterized in that the piezoelectric element (17a, 123) in each case on the Völbungsamßenseite the spring strip (14, 114) is applied.

10. An ink-jet recording head according to any one of claims l- ~ 7, characterized in that the piezoelectric elements (17, 17a,

121, 123) are applied on both sides of the spring strip (14, 114).

11. An ink-jet recording head according to claim 2, characterized in that at the valve distal end of the tie rod (8) only one with a piezo element (17, 17 ') versehener, curved spring strip (14, 14') engages.

12. An ink-jet recording head according to claim 2, characterized in that at the valve distal end of the pull rod (8) engage two curved in the opposite direction spring strips (14) which are supported at their valve-side ends gegenüloer the ink chamber (2) and that the piezoelectric elements ( 17) of the two spring strips (14) by the driving means (18) are controllable together to Dehnbewegungen.

13. An ink-jet recording head according to claim 12, characterized in that the two spring strips (14) are convexly curved in opposite directions.

14. ink-jet recording head according to claims 3, characterized in that the piezoelectric element (121) in each case on the curvature inside of the spring strip (114) and applied to contraction movements can be controlled.

15. An ink-jet recording head according to claim 3, characterized in that the piezoelectric element (123) is in each case applied on the outside of the curvature of the spring strip (114) and can be actuated for expansion movements.

16. An ink-jet recording head according to claim 2 or 3, characterized in that on the tie rod (108) niαr a unilaterally or on both sides with a piezoelectric element (121, 123) versehener, curved spring strip (114) engages.

17. An ink-jet recording head according to claim 3, characterized in that on the pull rod (108) two curved in the opposite direction spring strips (114) engage, which are attached to their valve remote ends, and that the piezo elements (121, 123) of the two spring strips (114) by the driving means (122) are controllable together to changes in length.

18. An ink-jet recording head according to claim 3, characterized in that only a single spring strip (.L14) is used and that the valve-near end (118) of the

Spring strip (114) ± n a Längsführungseinrichtuncj in the longitudinal direction of the tie rod (108) is movably guided.

19. An ink-jet recording head according to any one of claims 2-14, characterized in that the pull rod (8) erstxeckt valve side by a bore (16) of a lower clamping block (15) and that the end of the spring strip (14) or the ends the two spring tires (14) is or are received in the lower clamping block (15).

20. An ink-jet recording head according to claim 11, characterized in that the valve distal end (14 a) of the Spring strip (14) in a longitudinal guide device in the longitudinal direction of the drawbar (8) is movably guided.

21. An ink-jet recording head according to claim 20, dadurcti characterized in that the longitudinal guide means comprises a stationary guide slot (24) into which an upper longitudinal extension (25) of the spring strip (14) engages movable.

22. An ink-jet recording head according to claim 1, characterized in that the pull rod (8) is directly connected to: the valve body (6).

23. An ink-jet recording head according to claim 1, characterized in that the pull rod (8) via a

Actuating lever (19) with a connected to the valve closing body (6) connected valve connecting rod (20) is in drive connection.

24. An ink-jet recording head according to claim 1, characterized in that the closing spring (7) of the valve body at the same time forms the tension spring of the drawbar (8).

25. An ink-jet recording head according to claim 1, characterized in that on the pull rod (8) a separate, of the closing spring (7) separate tension spring (23) engages.

26. An ink-jet recording head according to claim 1, characterized in that the spring strip (14) is biased by a force acting on its valve remote end spring (29) in the direction of movement of the drawbar (8).

27. ink-jet recording head according to claim 2, characterized in that the pull rod (8) through a passage opening (30) in the valve-side half of the spring strip (14 ') and the applied thereon piezoelectric element (17').

28 ink jet writing head according to claim 27, characterized in that the passage opening (30) for the tie rod (8) is an open longitudinal slot to the valve end of the spring strip.

29. ink jet write head according to claim 1, characterized in that the spring strip (14 ') is constricted laterally in its central region.