EP0094032B1 - Device for the ejection of ink droplets - Google Patents

Device for the ejection of ink droplets Download PDF

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Publication number
EP0094032B1
EP0094032B1 EP83104401A EP83104401A EP0094032B1 EP 0094032 B1 EP0094032 B1 EP 0094032B1 EP 83104401 A EP83104401 A EP 83104401A EP 83104401 A EP83104401 A EP 83104401A EP 0094032 B1 EP0094032 B1 EP 0094032B1
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EP
European Patent Office
Prior art keywords
transducer
channel
arrangement
cross
outlet opening
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP83104401A
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German (de)
French (fr)
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EP0094032A1 (en
Inventor
Joachim Prof. Dr.-Ing. Heinzl
Günter Dipl.-Ing. Rosenstock
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Siemens AG
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Siemens AG
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Publication date
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Publication of EP0094032A1 publication Critical patent/EP0094032A1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/015—Ink jet characterised by the jet generation process
    • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
    • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
    • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
    • B41J2/04581—Control methods or devices therefor, e.g. driver circuits, control circuits controlling heads based on piezoelectric elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/015—Ink jet characterised by the jet generation process
    • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
    • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
    • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
    • B41J2/04588—Control methods or devices therefor, e.g. driver circuits, control circuits using a specific waveform

Definitions

  • the invention relates to an arrangement according to the preamble of patent claim 1.
  • an arrangement for an ink mosaic writing device in which an ejection of ink droplets is brought about by the fact that to initiate an ejection process a piezo transducer comprising an ink channel, hereinafter referred to as transducer, by applying one of the directions of polarization of the transducer
  • the voltage is first expanded, and then the voltage causing the expanding state is converted into a narrowed state by changing the polarity.
  • the pulse provided for this is always a bipolar pulse. For reasons of a simple circuit structure and a reduced power requirement, however, it is very desirable to enable safe droplet ejection with simple control impulses that fully meets the requirements of today's printing technology.
  • the ejected droplets should be shaped so that they take on a spherical shape very quickly after their ejection, and further that subsequent droplets, even if they are released at close intervals, are influenced as little as possible.
  • the object of the invention is to provide an arrangement which, using unipolar pulses and thus simple circuits, makes it possible to eject droplets which are ejected at high speed and rapidly assume the shape of a sphere.
  • Another advantage of the invention is that the supply lines and ink supplies are decoupled from the processes in the channel without the need for expensive measures.
  • the ink channel 2 shown in Fig. 1 has at one end an outlet opening 3, the diameter of which is small compared to the diameter of the ink channel.
  • a cross-sectional widening 4 is provided at its other end.
  • the cross-sectional widening 4 represents a reflection closure of the channel 2, on which pressure waves are reflected with the sign reversed. This reflection takes place almost completely, apart from physical losses.
  • the cross-sectional enlargement 4 is formed by the opening into a so-called ink supply chamber 6. This is what is not shown here, for. B. via a feed channel with an ink reservoir that is slightly lower than the outlet opening 3 of the ink channel. As long as no special influences or actions occur, this ensures that in the idle state, leakage of ink through the outlet opening 3 is reliably avoided.
  • the ink channel 2 can advantageously be formed by a recess in a plastic part 1.
  • the ink channel 2 is surrounded by a transducer 5. It is a polarized piezoceramic that changes its diameter when actuated with appropriately polarized control pulses U. A voltage applied in the direction of the polarization direction of the transducer 5 leads to a narrowing, while a pulse of opposite polarity causes the transducer to expand.
  • the converter has connections which connect it to a control circuit 7 via its electrodes. This can be controlled, for example, by the character generator of a printer and provides the correspondingly polarized control pulses U.
  • the transducer 5 comprises the ink channel 2 only over an area b and is arranged at a distance a from the cross-sectional widening 4.
  • the switching off of the pulse at time t2 has such a effect that the transducer 5 returns to its rest position and that the positive part + pa of the pressure wave w is generated, which also propagates in the ink channel 2 in both directions at the speed of sound (Fig. 2, line 2). With an assumed running time Iw, these pressure waves w arrive at the outlet opening 3 at times t4, t5 and t6 (FIG. 2, line 3).
  • the pressure wave propagating in the direction of the cross-sectional expansion is reflected on the cross-sectional expansion 4 with reversal of the sign.
  • the resulting reflected pressure waves wr also move at the speed of sound through the ink channel 2 in the direction of the outlet opening 3. There they arrive at the times t5, t6 and t7 with an assumed running time Iw + 2 Iwr (FIG. 2, line 4).
  • the pressure curve effective at the outlet opening 3 is determined by the unreflected pressure waves w and by the reflected pressure waves wr.
  • the part of the non-reflected pressure wave w arriving first (FIG. 2, line 5, phase I) causes the ink to be drawn back into the outlet opening 3.
  • the immediately following positive part of the non-reflected pressure wave w is overlaid by the also as a positive part of the incoming reflected pressure wave wr, which leads to a very high pressure increase in the area of the outlet nozzle 3 (FIG. 2, line 5, phase 11).
  • the meniscus of the ink is thereby accelerated very strongly in the direction of the outlet opening 3, so that an ink droplet begins to emerge from the outlet opening at the later flight speed.
  • the negative part of the reflected pressure wave -wr occurs (FIG. 2, line 5, phase 111), which has a negative pressure effect in the area of the outlet opening 3.
  • the amount of ink accelerated outwards during phase 11 is constricted and the droplet is separated off.
  • a new meniscus forms, which retracts to the starting position.
  • the rest position (Fig. 2, line 5, phase IV) is reached.
  • the duration of the drive pulse U i. H. the time period T between the expansion of the transducer 5 and the resetting of a greater or equal transit time of a pressure wave through the part of the ink-filled area of the ink channel enclosed by the transducer 5 corresponds to and that the time for the expansion and for resetting the transducer 5 itself is short compared to this term is.
  • the length b of the transducer 5, the pulse duration T and the distance a of the transducer from the cross-sectional expansion 4 such that the pressure wave w generated by driving the transducer 5 and the pressure wave reflected on the cross-sectional expansion 4 with reversed sign run at such a distance in the ink channel 2 that the pressure reduction in phase I, the pressure increase in phase 11, the pressure reduction in phase 111 and then the idle state in phase IV occur in succession in the region of the outlet opening 3.
  • the time for refilling the amount of ink ejected from the ink channel 2 is considerably reduced in the arrangement according to the invention, since the amount of ink required for the ejection was already largely provided during the first phase I.
  • the so-called spray frequency i.e. H. the frequency at which successive ink droplets can be ejected is essentially only limited by the ringing processes that usually take place in the ink channel.
  • the ink channel between the outlet opening and the transducer is delimited by a soft and damping channel wall.
  • the channel can also be somewhat narrowed in the area in which it emerges from the area of the transducer with its hard channel wall, so that pressure waves can propagate largely without reflection from the transducer into the ink channel while they are at the other end of the channel the cross-sectional expansion with reversed sign are reflected.
  • compensation pulses to the transducer by twice the running time of a pressure wave from the outlet opening to the cross-sectional expansion after the start of the actuation pulse, which are caused by reflection at the outlet opening and by reflection the cross-sectional expansion largely eliminate such disturbing pressure waves that reach the area of the transducer.
  • Such compensation pulses can, for. B. the derivation of the control pulse can be formed according to the time.
  • the invention has been described using an exemplary embodiment for a single ink channel. However, it is within the scope of the invention to design and activate a large number of ink channels in the manner specified control, and to arrange them overall in a multiple nozzle head. An ink mosaic pen designed according to the features of the invention can then be produced in a particularly advantageous manner using the proven injection molding process.

Description

Die Erfindung betrifft eine Anordnung gemäß dem Oberbegriff des Patentanspruches 1.The invention relates to an arrangement according to the preamble of patent claim 1.

Aus der DE-AS 2 548 691 ist eine Anordnung für eine Tintenmosaikschreibeinrichtung bekannt, bei der ein Ausstoß von Tintentröpfchen dadurch bewirkt wird, daß zur Einleitung eines Ausstoßvorganges ein einen Tintenkanal umfassender Piezowandler, im folgenden Wandler genannt, durch Anlegen einer der Polarisationsrichtung des Wandlers entgegengerichteten Spannung zuerst erweitert, und dann durch Polaritätswechsel der den erweiternden Zustand hervorrufenden Spannung in einen verengten Zustand übergeführt wird. Der hierzu vorgesehene Impuls ist stets ein bipolarer Impuls. Es ist aber aus Gründen eines einfachen Schaltungsaufbaues und eines reduzierten Leistungsbedarfs sehr erwünscht, mit einfachen Ansteuerimpulsen einen sicheren und den Anforderungen der heutigen Drucktechnik voll genügenden Tröpfchenausstoß zu ermöglichen. In diesem Zusammenhang spielt es auch eine Rolle, daß die ausgestoßenen Tröpfchen so geformt sein sollen, daß sie sehr rasch nach ihrem Ausstoß Kugelgestalt annehmen, und weiterhin, daß nachfolgende Tröpfchen, auch wenn sie in dichtem zeitlichen Abstand ausgelöst werden, möglichst wenig beeinflußt werden.From DE-AS 2 548 691 an arrangement for an ink mosaic writing device is known in which an ejection of ink droplets is brought about by the fact that to initiate an ejection process a piezo transducer comprising an ink channel, hereinafter referred to as transducer, by applying one of the directions of polarization of the transducer The voltage is first expanded, and then the voltage causing the expanding state is converted into a narrowed state by changing the polarity. The pulse provided for this is always a bipolar pulse. For reasons of a simple circuit structure and a reduced power requirement, however, it is very desirable to enable safe droplet ejection with simple control impulses that fully meets the requirements of today's printing technology. In this context, it also plays a role that the ejected droplets should be shaped so that they take on a spherical shape very quickly after their ejection, and further that subsequent droplets, even if they are released at close intervals, are influenced as little as possible.

Aufgabe der Erfindung ist es, eine Anordnung anzugeben, die unter Verwendung unipolarer Impulse und damit einfacher Schaltungen den Ausstoß von Tröpfchen ermöglicht, die mit hoher Geschwindigkeit ausgestoßen werden und rasch die Kugelgestalt annehmen.The object of the invention is to provide an arrangement which, using unipolar pulses and thus simple circuits, makes it possible to eject droplets which are ejected at high speed and rapidly assume the shape of a sphere.

Gelöst wird diese Aufgabe gemäß den kennzeichnenden Merkmalen des Patentanspruches 1.This object is achieved in accordance with the characterizing features of patent claim 1.

Weitere vorteilhafte Ausgestaltungen sind in den Unteransprüchen angegeben.Further advantageous refinements are specified in the subclaims.

Die mit der Erfindung erreichbaren Vorteile bestehen vor allem darin, daß mit einem unipolaren Impuls mit gleichen Flanken, ein Tröpfchenausstoß erfolgt, wodurch eine Verringerung der Ansteuerspannung, d. h. eine Reduzierung der Leistung erreichbar ist, daß weiterhin die einen Tröpfchenausstoß bewirkenden Druckphasen und damit auch die den Tröpfchenausstoß auslösenden Vorgänge exakt definiert sind, was zu einer sehr raschen Ausbildung von kugelförmigen Tröpfchen führt. Ein weiterer, mit der Erfindung verbundener Vorteil besteht darin, daß durch die exakte Ausbildung der einzelnen Druckphasen im Bereich der Austrittsöffnung des Kanals die Ergänzung der durch das ausgestoßene Tröpfchen verlorengegangenen Flüssigkeit innerhalb sehr kurzer Zeit geschieht, wobei die dafür notwendigen Vorgänge nicht durch den Einfluß von Oberflächenspannungen bewirkt wird. Auf diese Weise wird vermieden, daß kapillare Kräfte das Wiederauffüllen bewirken müssen, wodurch der Ruhezustand schneller erreicht und die Beeinflussung nachfolgender Tröpfchen erheblich reduziert wird.The advantages that can be achieved with the invention consist primarily in the fact that droplet ejection takes place with a unipolar pulse with the same edges, as a result of which a reduction in the drive voltage, i. H. a reduction in performance can be achieved that the pressure phases causing droplet ejection and thus also the processes triggering droplet ejection are precisely defined, which leads to a very rapid formation of spherical droplets. Another advantage associated with the invention is that the exact formation of the individual pressure phases in the region of the outlet opening of the channel means that the liquid lost due to the ejected droplet is replenished within a very short time, the processes necessary for this not being influenced by Surface tension is caused. In this way it is avoided that capillary forces have to bring about the refilling, as a result of which the idle state is reached more quickly and the influence of subsequent droplets is considerably reduced.

Ein weiterer Vorteil der Erfindung besteht darin, daß die Versorgungsleitungen und Tintenzuführungen von den Vorgängen im Kanal abgekoppelt sind, ohne daß dafür aufwendige Maßnahmen erforderlich sind.Another advantage of the invention is that the supply lines and ink supplies are decoupled from the processes in the channel without the need for expensive measures.

Einzelheiten der Erfindung werden im folgenden anhand der Zeichnungen erläutert. Dabei zeigt

  • Fig. 1 als Beispiel einen Tintenkanal,
  • Fig. 2 in Form einiger Ablaufdiagramme den Zusammenhang zwischen einem Ansteuerungsimpuls und den, den Kanal durchlaufenden Druckwellen.
Details of the invention are explained below with reference to the drawings. It shows
  • 1 shows an ink channel as an example,
  • Fig. 2 in the form of some flow diagrams the relationship between a control pulse and the pressure waves passing through the channel.

Der In Fig. 1 dargestellte Tintenkanal 2 weist an seinem einen Ende eine Austrittsöffnung 3 auf, deren Durchmesser gegenüber dem Durchmesser des Tintenkanals klein ist. An seinem anderen Ende ist eine Querschnittserweiterung 4 vorgesehen. Die Querschnittserweiterung 4 stellt einen Reflexionsabschluß des Kanals 2 dar, an dem Druckwellen unter Vorzeichenumkehr reflektiert werden. Diese Reflexion erfolgt nahezu vollständig, sieht man von physikalisch bedingten Verlusten ab. Im Beispiel ist die Querschnittserweiterung 4 durch die Einmündung in eine sog. Tintenvorsorgungskammer 6 gebildet. Diese steht, was hier nicht dargestellt ist, z. B. über einen Zuführkanal mit einem Tintenreservoir in Verbindung, das etwas tiefer liegt als die Austrittsöffnung 3 des Tintenkanals. Solange keine besonderen Einflüsse oder Einwirkungen auftreten, ist damit gewährleistet, daß im Ruhezustand ein Austreten von Tinte über die Austrittsöffnung 3 sicher vermieden wird. Der Tintenkanal 2 kann vorteilhafterweise durch eine Ausnehmung in einem Kunststoffteil 1 gebildet sein.The ink channel 2 shown in Fig. 1 has at one end an outlet opening 3, the diameter of which is small compared to the diameter of the ink channel. A cross-sectional widening 4 is provided at its other end. The cross-sectional widening 4 represents a reflection closure of the channel 2, on which pressure waves are reflected with the sign reversed. This reflection takes place almost completely, apart from physical losses. In the example, the cross-sectional enlargement 4 is formed by the opening into a so-called ink supply chamber 6. This is what is not shown here, for. B. via a feed channel with an ink reservoir that is slightly lower than the outlet opening 3 of the ink channel. As long as no special influences or actions occur, this ensures that in the idle state, leakage of ink through the outlet opening 3 is reliably avoided. The ink channel 2 can advantageously be formed by a recess in a plastic part 1.

In Nähe der Querschnittserweiterung 4 ist der Tintenkanal 2 von einem Wandler 5 umfaßt. Dabei handelt es sich um eine polarisierte Piezokeramik, die bei Ansteuerung mit entsprechend gepolten Steuerimpulsen U ihren Durchmesser verändert. Eine in Richtung der Polarisationsrichtung des Wandlers 5 an diesen angelegte Spannung führt zu einer Verengung, während ein Impuls entgegengesetzter Polarität eine Erweiterung des Wandlers bewirkt. Der Wandler besitzt Anschlüsse, die ihn über seine Elektroden mit einer Ansteuerschaltung 7 verbinden. Diese kann beispielsweise vom Zeichengenerator eines Druckers gesteuert werden, und stellt die entsprechend gepolten Steuerimpulse U zur Verfügung. Der Wandler 5 umfaßt den Tintenkanal 2 nur über einen Bereich b und ist im Abstand a von der Querschnittserweiterung 4 angeordnet.In the vicinity of the cross-sectional expansion 4, the ink channel 2 is surrounded by a transducer 5. It is a polarized piezoceramic that changes its diameter when actuated with appropriately polarized control pulses U. A voltage applied in the direction of the polarization direction of the transducer 5 leads to a narrowing, while a pulse of opposite polarity causes the transducer to expand. The converter has connections which connect it to a control circuit 7 via its electrodes. This can be controlled, for example, by the character generator of a printer and provides the correspondingly polarized control pulses U. The transducer 5 comprises the ink channel 2 only over an area b and is arranged at a distance a from the cross-sectional widening 4.

Die durch die erfindungsgemäße Anordnung des Wandlers 5 sowie die durch dessen Ansteuerung mittels unipolarer Ansteuerimpulse ausgelösten Vorgänge, d. h. also die Wirkungsweise der erfindungsgemäßen Anordnung, werden im folgenden auch unter Bezugnahme auf Fig. 2 beschrieben.The processes triggered by the arrangement of the converter 5 according to the invention and the processes triggered by its control by means of unipolar control pulses, i. H. that is, the mode of operation of the arrangement according to the invention are also described below with reference to FIG. 2.

Es wird angenommen, daß ein unipolarer Ansteuerimpuls U mit gleicher Steilheit der Anstiegs- und Abfallflanke und einer, der Polarisationsrichtung des Wandlers 5 entgegengesetzt gerichteten Polarität zum Zeitpunkt t1 an den Wandler gelegt wird, und daß dieser Impuls zum Zeitpunkt t2 wieder abgeschaltet wird (Fig. 2, Zeile 1). Das hat zur Folge, daß im Tintenkanal 2 im vom Wandler 5 umfaßten Bereich durch dessen Ausweitung, bedingt durch die der Polarisationsrichtung des Wandlers entgegengesetzt gerichteten Polarität des Ansteuerimpulses U, ein negativer Teil -pa der Welle w erzeugt wird, der sich ausgehend von den Austrittsquerschnitten 8 und 9 des Wandlers 5 sowohl in Richtung zur Austrittsöffnung 3 als auch in Richtung zur Querschnittserweiterung 4 hin ausbreitet. Diese Ausbreitung erfolgt mit Schallgeschwindigkeit. Die Abschaltung des Impulses zum Zeitpunkt t2 wirkt sich in einer solchen Weise aus, daß der Wandler 5 wieder seine Ruhelage einnimmt, und daß damit der positive Teil +pa der Druckwelle w erzeugt wird, die sich ebenfalls mit Schallgeschwindigkeit in beide Richtungen im Tintenkanal 2 ausbreitet (Fig. 2, Zeile 2). Diese Druckwellen w treffen bei einer angenommenen Laufzeit Iw zu den Zeitpunkten t4, t5 und t6 an der Austrittsöffnung 3 ein (Fig. 2, Zeile 3).It is believed that a unipolar An Control pulse U with the same steepness of the rising and falling edge and a polarity opposite to the direction of polarization of the converter 5 is applied to the converter at time t1, and that this pulse is switched off again at time t2 (FIG. 2, line 1). The result of this is that a negative part -pa of the wave w is generated in the ink duct 2 in the area encompassed by the transducer 5 due to its expansion, due to the polarity of the drive pulse U directed in the opposite direction to the polarization of the transducer 8 and 9 of the transducer 5 spreads both in the direction of the outlet opening 3 and in the direction of the cross-sectional widening 4. This propagation takes place at the speed of sound. The switching off of the pulse at time t2 has such a effect that the transducer 5 returns to its rest position and that the positive part + pa of the pressure wave w is generated, which also propagates in the ink channel 2 in both directions at the speed of sound (Fig. 2, line 2). With an assumed running time Iw, these pressure waves w arrive at the outlet opening 3 at times t4, t5 and t6 (FIG. 2, line 3).

Die sich in Richtung der Querschnittserweiterung ausbreitende Druckwelle wird an der Querschnittserweiterung 4 unter Vorzeichenumkehr reflektiert. Die dabei entstehenden reflektierten Druckwellen wr bewegen sich ebenfalls mit Schallgeschwindigkeit durch den Tintenkanal 2 in Richtung zur Austrittsöffnung 3. Dort treffen sie bei angenommener Laufzeit Iw + 2 Iwr zu den Zeitpunkten t5, t6 und t7 ein (Fig. 2, Zeile 4). Der an der Austrittsöffnung 3 wirksame Druckverlauf ist dabei durch die unreflektierten Druckwellen w und durch die reflektierten Druckwellen wr bestimmt. Der zuerst eintreffende Teil der nicht reflektierten Druckwelle w (Fig. 2, Zeile 5, Phase I), bewirkt ein Zurückziehen der Tinte in die Austrittsöffnung 3 hinein. Der unmittelbar darauf folgende positive Teil der nicht reflektierten Druckwelle w wird von dem ebenfalls als positiven Teil der ankommenden reflektierten Druckwelle wr überlagert, was zu einem sehr hohen Druckanstieg im Bereich der Austrittsdüse 3 führt (Fig. 2, Zeile 5, Phase 11). Der Meniskus der Tinte wird dadurch in Richtung der Austrittsöffnung 3 hin sehr stark beschleunigt, so daß ein Tintentröpfchen bereits mit der späteren Fluggeschwindigkeit aus der Austrittsöffnung auszutreten beginnt. Unmittelbar darauf tritt der negative Teil der reflektierten Druckwelle -wr ein (Fig. 2, Zeile 5, Phase 111), der sich im Bereich der Austrittsöffnung 3 in Form eines Unterdrucks auswirkt. Dadurch wird die während der Phase 11 nach außen beschleunigte Tintenmenge eingeschnürt und das Tröpfchen wird abgetrennt. Gleichzeitig bildet sich dabei ein neuer Meniskus aus, der sich bis zur Ausgangsstellung zurückzieht. Die Ruhestellung (Fig. 2, Zeile 5, Phase IV) ist damit erreicht.The pressure wave propagating in the direction of the cross-sectional expansion is reflected on the cross-sectional expansion 4 with reversal of the sign. The resulting reflected pressure waves wr also move at the speed of sound through the ink channel 2 in the direction of the outlet opening 3. There they arrive at the times t5, t6 and t7 with an assumed running time Iw + 2 Iwr (FIG. 2, line 4). The pressure curve effective at the outlet opening 3 is determined by the unreflected pressure waves w and by the reflected pressure waves wr. The part of the non-reflected pressure wave w arriving first (FIG. 2, line 5, phase I) causes the ink to be drawn back into the outlet opening 3. The immediately following positive part of the non-reflected pressure wave w is overlaid by the also as a positive part of the incoming reflected pressure wave wr, which leads to a very high pressure increase in the area of the outlet nozzle 3 (FIG. 2, line 5, phase 11). The meniscus of the ink is thereby accelerated very strongly in the direction of the outlet opening 3, so that an ink droplet begins to emerge from the outlet opening at the later flight speed. Immediately afterwards, the negative part of the reflected pressure wave -wr occurs (FIG. 2, line 5, phase 111), which has a negative pressure effect in the area of the outlet opening 3. As a result, the amount of ink accelerated outwards during phase 11 is constricted and the droplet is separated off. At the same time, a new meniscus forms, which retracts to the starting position. The rest position (Fig. 2, line 5, phase IV) is reached.

Es ist vorteilhaft, daß die Dauer des Ansteuerimpulses U, d. h. die Zeitdauer T zwischen dem Erweitern des Wandlers 5 und dem Rückstellen größerer oder gleicher Laufzeit einer Druckwelle durch den vom Wandler 5 umschlossenen Teil des mit Tinte gefüllten Bereichs des Tintenkanals entspricht, und daß die Zeit für das Erweitern und für das Rückstellen des Wandlers 5 selbst kurz im Vergleich zu dieser Laufzeit ist.It is advantageous that the duration of the drive pulse U, i. H. the time period T between the expansion of the transducer 5 and the resetting of a greater or equal transit time of a pressure wave through the part of the ink-filled area of the ink channel enclosed by the transducer 5 corresponds to and that the time for the expansion and for resetting the transducer 5 itself is short compared to this term is.

Weiterhin ist es vorteilhaft, die Länge b des Wandlers 5, die lmpulsdauer T und den Abstand a des Wandlers von der Querschnittserweiterung 4 derart aufeinander abzustimmen, daß die durch Ansteuerung des Wandlers 5 erzeugte Druckwelle w und die an der Querschnittserweiterung 4 unter Vorzeichenumkehr reflektierte Druckwelle wr in einem solchen Abstand im Tintenkanal 2 verlaufen, daß sich im Bereich der Austrittsöffnung 3 aufeinanderfolgend die Druckverminderung der Phase I, die Druckerhöhung der Phase 11, darauf wiederum die Druckverminderung der Phase 111 und anschließend der Ruhezustand der Phase IV einstellt.Furthermore, it is advantageous to coordinate the length b of the transducer 5, the pulse duration T and the distance a of the transducer from the cross-sectional expansion 4 such that the pressure wave w generated by driving the transducer 5 and the pressure wave reflected on the cross-sectional expansion 4 with reversed sign run at such a distance in the ink channel 2 that the pressure reduction in phase I, the pressure increase in phase 11, the pressure reduction in phase 111 and then the idle state in phase IV occur in succession in the region of the outlet opening 3.

Die Zeitdauer für ein Wiederauffüllen der aus dem Tintenkanal 2 ausgestoßenen Tintenmenge wird bei der Anordnung nach der Erfindung erheblich reduziert, da die für den Ausstoß benötigte Tintenmenge bereits während der ersten Phase I weitgehend bereitgestellt wurde. Das bedeutet praktisch, daß die sog. Spritzfrequenz, d. h. die Frequenz mit der aufeinanderfolgende Tintentröpfchen ausgestoßen werden können, im wesentlichen nur durch die im Tintenkanal üblicherweise ablaufenden Nachschwingvorgänge begrenzt ist. Gemäß einer Ausgestaltung der Erfindung wird dazu weiter vorgeschlagen, daß der Tintenkanal zwischen der Austrittsöffnung und dem Wandler durch eine weiche und dämpfende Kanalwand begrenzt ist. Der Kanal kann aber auch in dem Bereich, in dem er aus dem Bereich des Wandlers mit seiner harten Kanalwand austritt, etwas verengt sein, so daß sich Druckwellen weitgehend reflexionsfrei vom Wandler in den Tintenkanal hinein ausbreiten können, während sie am anderen Ende des Kanals an der Querschnittserweiterung mit Vorzeichenumkehr reflektiert werden.The time for refilling the amount of ink ejected from the ink channel 2 is considerably reduced in the arrangement according to the invention, since the amount of ink required for the ejection was already largely provided during the first phase I. This means practically that the so-called spray frequency, i.e. H. the frequency at which successive ink droplets can be ejected is essentially only limited by the ringing processes that usually take place in the ink channel. According to one embodiment of the invention, it is further proposed that the ink channel between the outlet opening and the transducer is delimited by a soft and damping channel wall. However, the channel can also be somewhat narrowed in the area in which it emerges from the area of the transducer with its hard channel wall, so that pressure waves can propagate largely without reflection from the transducer into the ink channel while they are at the other end of the channel the cross-sectional expansion with reversed sign are reflected.

Gemäß weiterer Ausgestaltung ist es zur Reduzierung bzw. Eliminierung der Nachschwingvorgänge auch möglich, an dem Wandler um zweimal die Laufzeit einer Druckwelle von der Austrittsöffnung bis zur Querschnittserweiterung nach dem Beginn des Ansteuerimpulses verzögert, Kompensationsimpulse anzulegen, die durch Reflexion an der Austrittsöffnung und durch Reflexion an der Querschnittserweiterung solche störende Druckwellen, die in den Bereich des Wandlers gelangen, weitgehend auslöschen. Derartige Kompensationsimpulse können z. B. der Ableitung des Ansteuerimpulses nach der Zeit entsprechend gebildet werden.According to a further embodiment, in order to reduce or eliminate the ringing processes, it is also possible to apply compensation pulses to the transducer by twice the running time of a pressure wave from the outlet opening to the cross-sectional expansion after the start of the actuation pulse, which are caused by reflection at the outlet opening and by reflection the cross-sectional expansion largely eliminate such disturbing pressure waves that reach the area of the transducer. Such compensation pulses can, for. B. the derivation of the control pulse can be formed according to the time.

Die Erfindung wurde anhand eines Ausführungsbeispieles für einen einzigen Tintenkanal beschrieben. Es liegt jedoch im Rahmen der Erfindung, eine Vielzahl von Tintenkanälen in der angegebenen Weise auszugestalten und anzusteuern, und diese insgesamt in einem Mehrfachdüsenkopf anzuordnen. Ein nach den Merkmalen der Erfindung ausgestalteter Tintenmosaikschreiber kann dann in besonders vorteilhafter Weise im bewährten Spritzgußverfahren hergestellt werden.The invention has been described using an exemplary embodiment for a single ink channel. However, it is within the scope of the invention to design and activate a large number of ink channels in the manner specified control, and to arrange them overall in a multiple nozzle head. An ink mosaic pen designed according to the features of the invention can then be produced in a particularly advantageous manner using the proven injection molding process.

Claims (9)

1. In arrangement for ejecting droplets from a channel which has an outlet opening and is filled with liquid, where the channel is surrounded over a part of its length by a piezoelectric transducer, the diameter of which changes when it is driven by drive pulses, and where a pulse poled oppositely to the direction of polarisation of the transducer is applied to the transducer to initiate the ejection of droplets, characterised in that at its end remote from its outlet opening (3),
the channel (2) has a cross-sectional widening (4) at which a pressure wave (pa), produced when the transducer (5) is driven, is fully reflected (pr) with a reversal of sign;
that the transducer (5) surrounds the channel (2) in the vicinity of the cross-sectional widening (4); and that the transducer (5) is driven by unipolar pulses having symmetrical leading and trailing edges.
2. An arrangement as claimed in claim 1, characterised in that the length (b) of the transducer (5), the pulse duration (T) and the distance (a) of the transducer (5) from the cross-sectional widening (4) are matched to one another in such a way that the pressure wave (pa) produced when the transducer (5) is driven and the pressure wave (pr) reflected at the cross-sectional widening (4) with a reversal of sign, run in the channel (2) with a spacing which is such that in the region of the outlet opening (3), first a pressure reduction (Phase I), then a pressure increase (Phase II) and then again a pressure reduction (Phase III) and subsequently the rest state (Phase IV) successively occur.
3. An arrangement as claimed in claim 1 and 2, characterised in
that the period of time (T) between the expansion of the transducer (5) and the restoration is greater than or equal to the transit time of a pressure wave through that part (b) of the channel (2) which is surrounded by the transducer (5); and that the time for the expansion and the restoration of the transducer itself is short in comparison with this transit time.
4. An arrangement as claimed in one of the preceding claims, characterised in that, after the initiation of a droplet ejection (Phase I), the ejection of a droplet from the outlet opening (3) takes place as a result of the disconnection of the pulse (U) (Phases II and III).
5. An arrangement as claimed in one of claims 1 to 4, characterised in that the channel (2) is made of an elastic material having damping properties.
6. An arrangement as claimed in claim 5, characterised in that in the region surrounded by the transducer (5), the channel (2) has a slightly increased diameter.
7. An arrangement as claimed in claim 1 to 6, characterised in
that the transducer (5) can be driven by compensation pulses which are delayed relative to a drive pulse (U);
that the time delay is determined by twice the transit time of a pressure wave between the outlet opening (3) and the cross-sectional widening (4);
and that the compensation pulses have a lower energy than the drive pulses.
8. An arrangement as claimed in claim 7, characterised in that the compensation pulses correspond in their shape to the time-dependent derivative of the drive pulses.
9. An arrangement as claimed in one of claims 1 to 8, characterised in
that a plurality of channels (2) are provided which each have an outlet opening (3) and which at their ends remote from the outlet openings (3) are connected to a common zone (6) which is preferably designed as a supply chamber and is filled with liquid, these connections representing the cross-sectional widening (4);
that in the vicinity (spacing a) of the cross-sectional widening (4), each channel (2) is surrounded by a transducer (5) over a part (b) of its length;
and that each transducer (5) is connected to a drive circuit emitting the drive pulses and, if necessary, compensation pulses.
EP83104401A 1982-05-07 1983-05-04 Device for the ejection of ink droplets Expired EP0094032B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3217248 1982-05-07
DE3217248A DE3217248C2 (en) 1982-05-07 1982-05-07 Arrangement for ejecting ink droplets

Publications (2)

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EP0094032A1 EP0094032A1 (en) 1983-11-16
EP0094032B1 true EP0094032B1 (en) 1985-09-11

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EP (1) EP0094032B1 (en)
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DE (1) DE3217248C2 (en)

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Also Published As

Publication number Publication date
DE3217248A1 (en) 1983-11-10
JPH0252626B2 (en) 1990-11-14
EP0094032A1 (en) 1983-11-16
US4716418A (en) 1987-12-29
DE3217248C2 (en) 1986-01-02
JPS58203064A (en) 1983-11-26

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