EP1036660A1 - Drop-on-Demand printhead with piezo bending transducers and driving method for the same - Google Patents

Abstract

Print head has an inkjet plate with a row of jets each controlled by a piezo-bend transducer. During printing of an image each transducer receives an activation pulse according to the image to be printed. The adjacent piezo-bend transducer receives a compensation pulse to prevent interaction between the two. Independent claims are made for a piezo-bend transducer controller where in addition to an activation pulse being sent to the printing transducer a blocking pulse is sent to the adjacent transducer of a suitable duration and a printer drop on demand print head using the procedures for controlling it described above.

Description

The invention relates to a drop generator in series arranged nozzles, which are used to eject drop sequences a piezoelectric bending transducer is assigned (Piezo bending transducer drop-on-demand printhead) and one Method for controlling a piezo bending transducer drop-on-demand Printhead.

A conventional piezo bending transducer drop-on-demand printhead is known from DE 25 27 647 C3. In a nozzle plate a series of nozzles running perpendicular to the plate plane intended. Piezo bending transducers are parallel to the nozzle plate in the form of an elongated tongue clamped on one side, so-called piezo-tongue transducers, in parallel in a row arranged side by side in such a way that their not clamped free ends face each one of the nozzles. Everyone who Piezo bending transducer is designed as a piezo bimorph, the one parallel to the nozzle plate or perpendicular to the nozzles has extending bending axis. For ejecting a drop the piezo tongue is bent by applying a voltage, so that the free end moves away from the associated nozzle. The voltage is switched off and the free end snaps shut the nozzle and pushes an amount of liquid through the nozzle, so that a drop is expelled.

With a structure of this type, a pressure with a high Resolution, i.e. large number of points per length, are generated the nozzles must be arranged very close to each other. Around to achieve a clean drop output, the Piezo bending transducers, if possible, with their width, the whole Cover the assigned nozzle. If the nozzle arrangement is narrow hence the adjacent piezo bending transducers as well the nozzles assigned to them are very close together. The As a result, actuation of a piezo bending transducer also has one Fluid flow through the neighboring piezo bending transducers assigned nozzles (crosstalk). That comes in Share of the generated flow energy not the one to be printed Drops too. Furthermore, a drop may be ejected the neighboring nozzle come, which in a falsification of the desired print image results.

To eliminate the crosstalk problem, according to DE 31 14 259 A1 proposed a special design of the nozzles. The nozzles face away from the piezo bending transducers Side of the nozzle plate has a circular cross section with one of the desired drop shape dependent diameter. To the The side facing piezo bending transducers expands Nozzle funnel-shaped, but not rotationally symmetrical, but only in the direction parallel to the piezo bending transducers. The nozzle has a direction perpendicular to the piezo bending transducers a constant width, so that the nozzles lie close together can be arranged.

However, the manufacture of such nozzles requires a high one Expenditure. Furthermore, crosstalk is made with these nozzles clearly, but especially with printheads with high Resolutions not yet sufficiently reduced.

According to EP 0713 773 (Heinzl, Schullerus) is therefore proposed partition walls between each To provide piezo bending transducers. This leads to one completely eliminates crosstalk, but requires an enormous effort in production and assembly. Because of that Increasing the print resolution is always a very short distance neighboring nozzles or piezo bending transducers is sought, the partitions must comply with extreme tolerances manufactured and positioned. Furthermore, the Fluid friction in the narrow gaps between Piezo bending transducers and partitions cause considerable losses the speed of the transducer movement and the energy of the ejected drop.

The invention is based on the problem of a Piezo-bending transducer drop-on-demand print head with high resolution to create that with little manufacturing and assembly costs is producible and works without crosstalk.

According to the invention the object is achieved with a method for Control of a piezo bending transducer drop-on-demand printhead with a nozzle plate with nozzles arranged in series, which one piezo bending transducer is assigned, each of the Piezo bending transducer with a desired print image corresponding sequence of one drop ejection movement each causing triggering pulses is applied. Every trigger pulse each is assigned to that triggered by the trigger pulse Piezo bending transducers neighboring piezo bending transducers with one this deflecting compensation pulse is applied.

The deflection of the neighboring piezo bending transducer by the Compensation pulse causes locally at the neighboring Nozzle associated with piezo bending transducers fluid movement. This Fluid movement counteracts the fluid movement that occurs due to the trigger pulse and the movement of the triggered Piezobiegewandlers directly on the neighboring Piezo bending transducer adjusts the nozzle. The Fluid movements compensate each other completely or partially. A drop of droplets on the neighboring one Nozzle associated with piezo bending transducer (neighboring nozzle) does not come conditions. Falsification of the printed image is prevented. The adverse effects of crosstalk are thus switched off.

There are no partitions between adjacent ones Piezo bending transducers or special nozzle shapes required. The Nozzle plate and the wall of the printer chamber can be done easily be designed. Manufacturing and assembly costs are thus kept low.

Furthermore, adjacent piezo bending transducers can be so narrow be arranged side by side as it is the nozzle width allowed. It can therefore be a very high printhead Resolution can be achieved.

The narrow gap between the piezo bending transducer and the conventionally provided partitions are eliminated. During one Recess or reset movement of the piezo bending transducer can thus the flow of hydraulic fluid past the side the piezo bending transducer faster. Another Droplet ejection is thus shorter in time previous possible. The print frequency can be increased.

According to the invention, it is possible that the piezo bending transducers with Trigger pulses are applied, the deflection of the Cause piezo bending transducer to the assigned nozzle. However, the piezo bending transducers with triggering pulses are preferred applied, the deflection of the piezo bending transducer cause the associated nozzle away. The real one Drop ejection movement of the piezo bending transducer then consists of the snap back of the piezo structure due to the during the Action of the trigger pulse and the associated Deflection built-up mechanical tension. Such Backward movement is generally faster than that Deflection movement.

Each of the adjacent piezo bending transducers is preferred a compensation pulse compared to the trigger pulse lower amplitude applied. This ensures that not due to the compensation pulse, either when deflecting or when moving backwards neighboring piezo bending transducer, a drop ejection at the Adjusts neighboring nozzle. It also prevents the Fluid movement so much energy is withdrawn that it is at the triggered nozzle no longer associated piezo bending transducer a drop of drop comes. A is preferred Compensation pulse with an amplitude of 10 to 40%, further preferably one third of the amplitude of the trigger pulse upset.

The adjacent piezo bending transducers with a Compensation pulse compared to the trigger pulse shorter duration. With a shorter pulse duration can as well as with a lower amplitude of the applied Voltage can be achieved that the deflection amplitude of the Piezobiegewandlers at the compensation pulse is less than at the trigger pulse. This can also make it more undesirable Drop ejection from the neighboring nozzle and undesirably higher fluid mechanical energy withdrawal can be avoided. Compared to the lower amplitude, the shorter pulse duration has the Advantage that the piezo bending transducer both in the trigger pulses as well as with the compensation pulses with one and the same Voltage can be operated to which the piezo bending transducer is designed. A shorter pulse duration can also be used easy to implement in terms of control technology.

The adjacent piezo bending transducers are preferred in each case delayed after the assigned trigger pulse with the Compensation pulse applied. This ensures that the fluid movement due to the trigger pulse and the Fluid movement due to the compensation pulse in time largely overlap and each other particularly well compensate. A time delay of 60 is preferred up to 100 microseconds, particularly preferably one of 80 Microseconds.

According to one embodiment, it is possible that a Compensation pulse is applied, of which the neighboring Piezo bending transducer deflected in the opposite direction becomes like the triggered piezo bending transducer. This can be done either a compensation pulse opposite to the trigger pulse Polarity. Or the other active location a bimorph or trimorph is applied. Will the triggered piezo bending transducers initially from this assigned nozzle moves away and then flips back, means this means that the neighboring piezo bending transducer first to the this associated nozzle is deflected. The actually compensating fluid movement is then by the Snapback of the neighboring piezo bending transducer triggered.

According to another embodiment, the neighboring one Piezobiewandler with a compensation pulse applied by the neighboring piezo bending transducer in the same direction deflected like the triggered piezo bending transducer. This can done by the adjacent piezo bending transducer with a Compensation pulse of the same polarity is applied as the trigger pulse. First the triggered piezo bending transducer moved away from the nozzle assigned to it and then shoots back, so will the neighboring piezo bending transducer first deflected away from the nozzle assigned to it.

According to the invention, it is possible that regardless of how many Piezo bending transducers are triggered simultaneously and like this are arranged, only one type of compensation pulse is provided is. The piezo-bending transducers triggered are preferred neighboring piezo bending transducers, however, if they have two triggered piezo bending transducers are adjacent, with a Compensation pulse of greater amplitude applied than if it are only adjacent to a triggered piezo bending transducer. This ensures that there is adequate compensation the fluid movement caused by the trigger pulse in each Trigger constellation occurs.

According to the invention, it is possible that the piezo bending transducers in three groups at different times with trigger pulses are, with every third piezo bending transducer in the Series of piezo bending transducers belonging to the same group.

According to a preferred embodiment, the Piezo bending transducers in two groups at different times Trigger pulses acted upon, adjacent to each other Piezo bending transducers belong to different groups.

In this way the printing speed is increased. By doing two different strengths of compensation pulses can also be provided in this embodiment optimal compensation can be ensured.

According to another preferred embodiment, the Piezo bending transducers in a single group with trigger pulses acted upon and the triggered piezo bending transducers with different trigger pulses, depending on whether both, one or neither of the neighboring piezo bending transducers is also triggered. In this way, the Print speed can be increased even further. The trigger pulses of different strengths ensure that even at simultaneous triggering of neighboring Piezo bending transducers deliver even drops from all Nozzles is reached.

E.g. in this embodiment, the piezo bending transducers, if one of the neighboring piezo bending transducers also is triggered with a trigger pulse of lower amplitude acts as if none of the neighboring Piezo bending transducer is also triggered, and with a Trigger pulse of even lower amplitude applied when both neighboring piezo bending transducers are also triggered become.

According to the invention it is possible that the compensation pulses as Rectangular signals are provided. Preferably the neighboring piezo bending transducers, however, with compensation pulses with a gentle falling edge. This will achieved that due to the movement of the neighboring Piezo bending transducer towards the neighboring nozzle, i.e. depending on Polarity either at the deflection due to the Compensation pulse or when jumping back after action of the compensation pulse, no droplet ejection at the neighboring nozzle sets, but a gentle decay of the flow movement is achieved.

According to an alternative embodiment of the invention, a Method for controlling a piezo bending transducer drop-on-demand Printhead with a nozzle plate arranged in series Nozzles, each of which is assigned a piezo bending transducer, proposed, each of the piezo bending transducers with a sequence of one desired print image Trigger pulses causing drop ejection movement and each trigger pulse is assigned to everyone with it applied piezo bending transducers adjacent piezo bending transducers is applied with a closing control pulse, of which the Piezo bending transducer deflected towards the associated nozzle and is held there for a period during the drop ejection.

The deflection of the neighboring piezo bending transducers and their Holding on to the associated nozzles ensures that the nozzles against the one filled with hydraulic fluid Print head chamber wholly or partially fluid-mechanically be sealed off. As a result, none of these nozzles Leak drop. The printed image will be falsified prevented.

The neighboring piezo bending transducers with the Closing control pulse timed to the assigned trigger pulse acted upon previously or simultaneously. In this way it is ensured that the foreclosure when the Drop-ejecting movement of the trigger pulse applied piezo bending transducer has already occurred.

According to the invention, the adjacent piezo bending transducers can also be used a closing control pulse are applied, the Amplitude that comes close to a trigger pulse. To be favoured them with a close control pulse of an amplitude acted on, the maximum one sixth, the amplitude of the Trigger pulse is. This enables the use of Piezo bending transducers of two-pole type, i.e. Piezobimorph with passive position or monomorph. Since the trigger pulse the Piezo bending transducers are usually deflected away from the nozzle Tripping pulse and closing control pulse each other opposed. Two-pole piezo bending transducers can actually only in one direction, namely its preferred direction be deflected. If the amplitude is low, it is also two-pole piezo bending transducers a deflection against the Preferred direction possible.

Both in the embodiments of the invention Procedure with compensation pulses as well alternative embodiment with closing control pulses preferred, before or when starting up the piezo bending transducer Drop-on-demand printhead to perform a trimming process. I.e. for each of the piezo bending transducers is before commissioning Amplitude, duration and / or time delay of Compensation pulses or closing control pulses with one Trimming procedure determined, for the intended Constellations of trigger pulses each applied Compensation pulses or closing control pulses regarding Amplitude, duration and / or time delay varies and below Measurement of drop ejection or crosstalk behavior optimized become. In this way, manufacturing inaccuracies or Inhomogeneities of the piezoceramic are taken into account. The Compensation pulse is individual to the individual Piezo bending transducer adapted. This way, too existing manufacturing inaccuracies Drop discharge on all nozzles or piezo bending transducers be ensured. If the trimming process is not only with individual trigger pulses but with pulse combinations, i.e. simultaneous triggering of several piezo bending transducers different constellations can be carried out interactions of manufacturing or Material inaccuracies of several piezo bending transducers be worn.

Only duration is preferred in the trimming process and / or time delay of compensation pulses or closing control pulses varies. This enables the Trimming procedure is carried out with little effort. Further the piezo bending transducers can only be used with the Voltage amplitudes are operated for which they are designed are.

According to the invention, the measurements can be carried out within the Trimming process with one of the piezo bending transducers independent device. To be favoured in the trimming process, the piezo bending transducers as sensors used by voltages that result from triggering a Piezo bending transducer, the fluid movement caused thereby and the deflection of the neighboring piezo bending transducers in them be induced, measured and to optimize the Drop ejection or crosstalk behavior can be evaluated. This allows and without additional equipment thus inexpensively determine the crosstalk behavior. Thereby, that effects can be recorded in the printhead itself can Crosstalk behavior can be determined particularly precisely.

The piezo-bending transducers triggered are preferred neighboring piezo bending transducers during operation Compensation pulses or closing control pulses are applied, determined for the amplitude, duration and / or time delay be caused by tensions caused by the triggering of a Piezo bending transducer, the fluid movement caused thereby and the deflection of the neighboring piezo bending transducers in them be induced, measured and processed. So one serves Adjacent piezo bending transducer after application of a trigger pulse initially as a sensor. The recorded data are evaluated and Amlitude, duration and / or time delay of the optimal Compensation pulse are determined. Then the serves Adjacent piezo bending transducers as an actuator and around the determined one Time delay after the trigger pulse becomes the corresponding one Compensation pulse to the neighboring piezo bending transducer created. Interactions between the data recorded on several piezo bending transducers be taken into account. It can also be taken into account which piezo bending transducers are applied at the same time.

Such a comparison of the pulses during operation can in addition to the irregularities of droplet ejection caused by Manufacturing and material inaccuracies are caused, irregularities of the Drop output compensated by adjusting the pulses become. For example, Differences in temperature conditions Be taken into account. For example, Irregularities of the fluidic initial conditions at the beginning of the Trigger pulse are compensated, such as a residual flow due to the previous droplet discharge. E.g. can also Shocks are compensated. The one in operation Integrated adjustment of the pulses thus leads to a considerable Improvement of the printing result, especially to a extensive independence of the print result from external Influences.

The ongoing adjustment when operating the piezo bending transducer drop-on-demand Print head can be used instead of the invention Trimming or in addition to trimming before commissioning.

Furthermore, the object is achieved with a Piezo bending transducer with drop-on-demand printhead Nozzle plate with nozzles arranged in a row, each one Piezobie transducer is associated with the ejecting one Dripping from the respective nozzle with a trigger pulse is acted upon, and a control device, each of which the piezo bending transducer according to one of the above inventive method with trigger pulses and Compensation pulses can be applied.

According to the invention it is possible that the control device suitably designed, e.g. as a computer with a corresponding control software. The is preferred Control device designed as an integrated circuit.

According to the invention, the piezo bending transducers can e.g. than on both Elongated stretched piezo strips are formed at the ends be (piezo bridge transducer). Those are preferred Piezo bending transducers as elongated, one-sided clamps Tongues formed (piezo tongue transducer). Are further preferred the nozzles associated with the piezo-tongue transducers in the region of the Free ends of the piezo-tongue transducer arranged.

According to the invention, the piezo bending transducers can be monomorphs, as bimorphs with one passive layer each, as bimorphs with each two active layers or be formed as trimorphs. Further you can use the longitudinal effect of the piezoceramic or the transverse effect be made use of the piezoceramic. You can as Single-layer converter or constructed as a multi-layer converter his.

The piezo bending transducers are preferred as bimorphs with two active layers or as trimorphs and is the Control device designed so that the neighboring Piezo bending transducer deflected in the opposite direction are like the triggered piezo bending transducer by the each other active position of the piezo transducer with the compensation pulse is applied. This will reduce the risk of destroying the Piezo bending transducer switched off. This would exist if the Deflection of the neighboring piezo bending transducer in the opposite direction by creating an opposite polarized voltage at the same position of a monomorph would be done. Contrary to the direction of polarization, a Piezoceramic only subjected to approx. 10% of the maximum voltage become.

According to the invention, the nozzles can e.g. be arranged so that the nozzle axis parallel to the longitudinal direction of the Piezobiegewandlers runs and the nozzle in the extension of the piezo bending transducer is arranged (edge shooter) According to the invention, the nozzles can e.g. also be arranged that the nozzle axis perpendicular to the longitudinal direction of the Piezobiegewandlers and perpendicular to its bending axis and the nozzle in the area of the free end of the piezo bending transducer is arranged (sideshooter).

Furthermore, a piezo bending transducer drop-on-demand printhead proposed having a nozzle plate with in series arranged nozzles, each of which has a piezo bending transducer is associated with the ejecting a drop from the each nozzle can be acted upon with a trigger pulse, and a control device, each of which is the piezo bending transducer according to one of the methods according to the alternative embodiment the invention with trigger pulses and closing control pulses is acted upon.

In this case too, the types of Piezo bending transducers or control devices are used.

In this case, the piezo bending transducer has drop-on-demand Print head preferably has at least three-pole piezo bending transducers Two piezoceramic layers each on and from the control device the trigger pulses to the one piezoceramic layer and the Closing control pulses to the other piezoceramic layer of the Piezo bending transducer created. In this way it is achieved that the closing control pulse also have a larger amplitude can without the risk of destroying the Piezobiegewandlers exists, as is the case with a monomorph Would be the case.

According to the invention, patterns of pulses can also be provided, where not only the one triggered piezo bending transducer immediately adjacent piezo bending transducer, but also the the next but one or the next but one piezo bending transducer Compensation pulses, closing control pulses or modified Trigger pulses are applied.

Figuren 1a bis 1e schematisch die Arbeitsweise eines mit dem erfindungsgemäßen Verfahren angesteuerten Piezobiegewandler Drop-on-Demand Druckkopfes bzw. eines erfindungsgemäßen Piezobiegewandler Drop-on-Demand Druckkopfes;

Figuren 2a bis 2d schematisch die Arbeitsweise eines mit der alternativen Ausführungsform des erfindungsgemäßen Verfahrens angesteuerten Piezobiegewandler Drop-on-Demand Druckkopfes bzw. eines nach diesem Verfahren arbeitenden erfindungsgemäßen Piezobiegewandler Drop-on-Demand Druckkopfes;

Figur 3 schematisch den Aufbau eines erfindungsgemäßen Piezobiegewandler Drop-on-Demand Druckkopfes;

Figuren 4a bis 4d schematisch den Aufbau von Piezobiegewandlern mit unterschiedlichen Schichtanordnungen gemäß unterschiedlichen Ausführungsformen des erfindungsgemäßen Piezobiegewandler Drop-on-Demand Druckkopfes;

Figuren 5a und 5b schematisch den Aufbau von Piezobiegewandlern mit unterschiedlichen Kontaktierungsanordnungen gemäß unterschiedlichen Ausführungsformen des erfindungsgemäßen Piezobiegewandler Drop-on-Demand Druckkopfes;

Figur 6 schematisch den Aufbau eines Piezobiegewandlers mit einer Mehrschichtanordnung gemäß einer Ausführungsform des erfindungsgemäßen Piezobiegewandler Drop-on-Demand Druckkopfes;

Figur 7 in perspektivischer Darstellung drei als Bimorph aufgebaute Piezobiegewandler mit dreipoliger Kontaktierung;

Figur 8 schematisch im Querschnitt einen als Bimorph aufgebauten Piezobiegewandler mit dreipoliger Kontaktierung;

Figur 9 schematisch die Arbeitsweise eines Piezobiegewandlers beim Ausstoßen eines Tropfens zusammen mit dem zugehörigen Verlauf der an dem Piezobiegewandler anliegenden Spannung; und

Figuren 10a und 10b schematisch Aufbau und Anordnung eines Piezozungenwandlers bzw. eines Piezobrückenwandlers.

Embodiments of the invention will be described in connection with the drawing. The drawing shows:

FIGS. 1 a to 1 e schematically show the mode of operation of a piezo bending transducer drop-on-demand print head or a piezo bending transducer drop-on-demand print head according to the invention;

FIGS. 2a to 2d schematically illustrate the mode of operation of a piezo bending transducer drop-on-demand print head controlled by the alternative embodiment of the method according to the invention or of a piezo bending transducer drop-on-demand print head working according to this method;

FIG. 3 schematically shows the structure of a piezo bending transducer according to the drop-on-demand print head;

Figures 4a to 4d schematically the structure of piezo bending transducers with different layer arrangements according to different embodiments of the piezo bending transducer according to the invention drop-on-demand print head;

FIGS. 5a and 5b schematically show the structure of piezo bending transducers with different contacting arrangements according to different embodiments of the piezo bending transducer according to the invention drop-on-demand print head;

FIG. 6 schematically shows the structure of a piezo bending transducer with a multilayer arrangement according to an embodiment of the piezo bending transducer according to the invention drop-on-demand print head;

FIG. 7 shows a perspective view of three piezo-bending transducers constructed as bimorphs with three-pole contacting;

FIG. 8 shows schematically in cross section a bimorph piezoelectric transducer with three-pole contact;

FIG. 9 shows schematically the mode of operation of a piezo bending transducer when ejecting a drop together with the associated profile of the voltage applied to the piezo bending transducer; and

Figures 10a and 10b schematically structure and arrangement of a piezo tongue transducer or a piezo bridge transducer.

The principle of the invention is shown in FIGS. 1a to 1e Procedure evident. Each of the figures shows schematically a section of a piezo bending transducer drop-on-demand Printhead. In a nozzle plate 1 are three in a row Nozzles 11 extending perpendicular to the plane of the plate are provided. Three piezo bending transducers 2 in are parallel to the nozzle plate 1 a row arranged side by side in parallel so that their free ends 21 not clamped in each case one of the nozzles 11 face each other. Each of the piezo bending transducers 2 is one parallel to the nozzle plate 1 or perpendicular to the nozzles 11 extending bending axis bendable.

The position of the three is shown in each of FIGS. 1a to 1e Piezo bending transducer 2 in a different stage of the sequence of movements apparent that expires when the middle of the three Piezobiewandler 2 is acted upon by a trigger pulse.

In Figure 1a, all three piezo bending transducers 2 are in the rest position.

In Figure 1b, the middle piezo bending transducer 2 is due to the Action of the trigger pulse in the deflection movement, so that whose free end 21 moves away from the associated nozzle 11 will (see arrow).

In Figure 1c, the trigger pulse is completed, the deflecting Voltage no longer works and the middle piezo bending transducer 2 soars as a result of the structure built up during deflection mechanical stresses so that the free end 21 to the assigned nozzle 11 is moved (see arrow).

In Figure 1d, the two outer piezo bending transducers 2 with the Compensation pulse is applied and are consequently deflected so that the free ends 21 of each assigned nozzles 11 are moved away (see arrows) while the middle piezo bending transducer 2 continues as a result of mechanical stresses so that its free End 21 is moved toward the associated nozzle 11 (cf. Arrow). The from the middle piezo bending transducer 2 to the outer piezo bending transducers 2 associated with nozzles 11 displaced liquid is due to the deflection movements the outer piezo bending transducer 2 from the assigned nozzles 11 sucked away and does not emerge from the nozzles 11. It comes from that not to falsify the printed image.

In Figure 1e, the compensation pulses are also completed or in the decaying phase and the outer piezo bending transducers 2 snap back due to the mechanical stresses, so that the free ends 21 of which are moved toward the associated nozzles 11 be (see arrow). Due to the lower amplitude of the Compensation pulses or a suitable decay edge leads the backward movement of the outer piezo bending transducer 2 is not to overcome the surface tension on the assigned nozzles 11 and thus not to a drop exit.

Specific exemplary embodiments are described.

It becomes a printhead with piezo ceramic actuators from PI Ceramic, leather pants used. A piezo bending transducer has one Length of 5 mm, height of 0.32 mm and width of 0.4 mm. The free length is 3.2 mm. The nozzle plate is out Silicon and has a thickness of 400 microns. The Nozzle diameter is 60 µm. The nozzle channel length is 380 µm. The distance between the slats, i.e. the Piezo bending transducer in the rest position, and the nozzle plate is 20 µm. Diethyl succinate is used as the test medium for printing used.

Auslösepuls:
Impulsbreite 50 µs, Rechteckimpuls, Amplitude 55 V

Kompensationspuls:
Impulsbreite 17 µs, Rechteckimpuls, Amplitude 55 V,
Zeitverzögerung zum Auslöseimpuls: 67 µs

According to one embodiment, the control works with the following pulses:

Trigger pulse:
Pulse width 50 µs, rectangular pulse, amplitude 55 V

Compensation pulse:
Pulse width 17 µs, rectangular pulse, amplitude 55 V,
Time delay to trigger pulse: 67 µs

Auslösepuls:
Impulsbreite 50 µs, Rechteckimpuls, Amplitude 55 V

Kompensationspuls:
Impulsbreite 7 µs, Rechteckimpuls, Amplitude 55 V,
Zeitverzögerung zu Auslöseimpuls: 64 µs

According to another embodiment, the control works with the following pulses:

Trigger pulse:
Pulse width 50 µs, rectangular pulse, amplitude 55 V

Compensation pulse:
Pulse width 7 µs, rectangular pulse, amplitude 55 V,
Time delay to trigger pulse: 64 µs

The principle of the invention is shown in FIGS. 2a to 2d Method according to the alternative embodiment can be seen. Each of the figures schematically shows a section of one Piezo bending transducer drop-on-demand printhead. In a Nozzle plate 1 are three in a row perpendicular to the plane of the plate extending nozzles 11 are provided. Parallel to the nozzle plate 1 are three piezo bending transducers 2 in a row in parallel arranged side by side in such a way that their not clamped free ends 21 each face one of the nozzles 11. Each of the piezo bending transducers 2 is parallel to the one Nozzle plate 1 or perpendicular to the nozzles 11 Bending axis bendable.

The position of the three is shown in each of FIGS. 2a to 2d Piezo bending transducer 2 in a different stage of the sequence of movements apparent that expires when the middle of the three Piezobiewandler 2 is acted upon by a trigger pulse.

In Figure 2a, all three piezo bending transducers 2 are in the rest position.

In Figure 2b, the middle piezo bending transducer 2 is due to the Action of the trigger pulse in the deflection movement, so that whose free end 21 moves away from the associated nozzle 11 will (see arrow). At the same time, the two outside Piezo bending transducer 2 is acted upon by the closing control pulse and are consequently deflected so that their free ends 21 are moved towards the respectively assigned nozzles 11 (cf. Arrows). The two outer piezo bending transducers 2 are so moved far to the associated nozzles 11 that the Nozzles 11 against the one filled with hydraulic fluid Print head chamber wholly or partially fluid-mechanically be sealed off.

In Figure 2c the trigger pulse is completed, the deflecting Voltage no longer works and the middle piezo bending transducer 2 soars as a result of the structure built up during deflection mechanical stresses so that the free end 21 to the assigned nozzle 11 is moved (see arrow). This will on the nozzle 11 assigned to the middle piezo bending transducer 2 the drop ejection causes. The two outer ones Piezo bending transducers 2 are still with the closing control pulse acted upon. As a result, their free ends 21 become wider in a position near the respectively assigned nozzles 11 held. The two outer Piezobiegewandlern 2 associated nozzles 11 continue against printhead chamber completely or filled with hydraulic fluid partially partitioned off by fluid mechanics. As a result the backward movement of the middle piezo bending transducer 2 to a flow movement in the area of the outer Piezo bending transducers 2 associated nozzles 11 result, as a result of Fluidic partitioning occurs at these nozzles 11 does not lead to a drop.

In Figure 2d, the middle piezo bending transducer 2 is due to the mechanical deflection built up in the structure during deflection Tensions have completely flipped back to their original position. The two outer piezo bending transducers 2 are no longer further acted upon by the closing control pulse and are consequently also as a result of the deflection in the Mechanical stresses built up entirely in structure their starting positions have receded.

The structure of an inventive device is shown schematically in FIG Piezobiewandler drop-on-demand print head visible. The Nozzle plate 1 and the piezo bending transducer 2 corresponds the structure of the representation according to Figures 1a to 1e, with more Nozzles 11 and piezo bending transducers 2 are shown. Everyone who Piezo bending transducer 2 is connected to a via a signal line 4 Control device 3 connected. The control device 3 is designed so that according to the inventive method Compensation pulses delayed with each trigger pulse those adjacent to the triggered piezo bending transducer 2 Piezo bending transducer 2 are given. This is with the arrows indicated along the signal lines 4. The control device 3 is designed as an integrated circuit.

4a to 4d, 5a and 5b and 6 are different types of piezo bending transducers can be seen that in different embodiments of the invention Piezo bending transducers drop-on-demand printhead are provided. All of the piezo bending transducers 2 shown are each in Side view with the clamped end on the left shown. The axis around which the piezo bending transducer 2 is bent is perpendicular to the plane of the drawing.

FIG. 4a shows a piezo bimorph with a passive position evident. The piezo bending transducer 2 consists of two layers of piezoceramic, an active layer 22 and a passive layer 23. A voltage is only applied to the active layer 22, so that their length is changed. Because the length of the passive layer 23 remains constant, the Piezo bending transducer 2.

FIG. 4b shows a piezo monomorph in which the passive layer 23 by a non-piezoceramic Layer 24 is replaced.

FIG. 4c shows a piezo bimorph in which two active layers 22 are present. These are opposite polarized and are polarized with oppositely Voltage is applied so that the one layer shortens and the other extended.

FIG. 4d shows a piezo trimorph in which two active layers 22 are present, between which one is not off Piezoceramic layer 24 is arranged. Such a Construction enables greater deflections with the same tension.

FIG. 5a shows a structure in which the cross effect the piezoceramic is used. The polarization of the Piezoceramic runs in the direction perpendicular to the layers. A positive voltage applied along this polarization an elongation of the material in the direction of polarization. Because of the mechanical cross contraction occurs simultaneously Contraction in the longitudinal direction of the piezo bending transducer 2, the leads to bending because of the rigid other layer.

From Figure 5b, a structure can be seen in which the Longitudinal effect of the piezoceramic is used. The polarization of the Piezoceramic runs in the longitudinal direction of the piezo bending transducer 2. A positive voltage applied along this polarization causes the material to expand in the direction of polarization. Because of the rigid other layer, the Piezo bending transducer 2.

FIG. 6 shows a multilayer structure of a piezoceramic layer evident. Instead of a uniformly polarized and the two opposite ends with contacts Several layers are provided, each one are alternately provided with opposite polarization. Between the layers are alternately on the plus or on contacts connected to the negative pole. To this Way is a large longitudinal effect of the small size Piezoceramic achieved.

According to the invention, each of FIGS. 4a to 4d visible designs with longitudinal effect according to FIG. 5a, possibly Multi-layer structure according to Figure 6, or with cross effect according to Figure 5b for the piezo bending transducer of the piezo bending transducer drop-on-demand Printhead can be used.

From Figures 7 and 8 it can be seen how the three-pole Contacting a piezo bending transducer constructed as a bimorph 2 is formed. A cross section of a bimorph piezoelectric transducer is shown in FIG 2 with three-pole contact, which is designed as a multilayer piezo bending transducer. The Piezo bending transducer 2 has an upper and a lower active Location 22 on.

The bimorph piezo bending transducer 2 is over its entire thickness made up of layers of piezoceramic. Adjacent layers are each provided with opposite polarization. Contact foils 26 are arranged between the layers Every second one of the contact foils 26 is at one end of the Piezo bending transducer 2 connected to a ground contact bridge. The ground contact bridge is at the ground contact 27 connected to the top of the piezo bending transducer 2 at a distance from the other end of the piezo bending transducer 2 is arranged. The ground contact 27 is via a signal line 4 to the control device 3 (not shown here) connected. The other contact foils 26 are the two assigned to active layers 22. In the area of the upper active layer 22 are these contact foils 26 at one end of the other Piezo bending transducer 2 running contact bridge connected, which is connected to a first signal contact 28, the on the top of the piezo bending transducer 2 near the other end of the piezo bending transducer 2 is arranged. The first Signal contact 27 is via a signal line 4 to the Control device 3 (not shown here) connected. in the These contact foils 26 are in the area of the lower active layer 22 to one at the other end of the piezo bending transducer 2 running further contact bridge connected to a second signal contact 29 is connected to the Bottom of the piezo bending transducer 2 near the other end of the Piezobiegewandlers 2 is arranged. The second signal contact 29 is to the control device 3 via a signal line 4 (not shown here) connected.

From Figure 7 is the spatial representation in perspective Arrangement of ground contact 27, first signal contact 28 and second signal contact 29 can be seen. In particular is can be seen that the ground contact 27 and the first Signal contact 28 both on the top of the piezo bending transducer 2 are arranged and isolated from each other

For a trigger pulse, FIG. 9 shows the time profile of the voltage applied directly to the piezoceramic during the deflection phase, during the phase of the recoil Piezo bending transducer and during the subsequent phase of Swinging out of the piezo bending transducer can be seen.

From Figure 10a is a schematic structure and arrangement of a Piezo-tongue transducer used according to the invention can be seen.

From Figure 10b is a schematic structure and arrangement of a Piezo bridge transducer used according to the invention can be seen.

Claims (21)

Method for controlling a piezo bending transducer drop-on-demand Printhead with a nozzle plate in series arranged nozzles, each of which has a piezo bending transducer is assigned, wherein each of the piezo bending transducers with a the sequence of each corresponding to the desired print image trigger pulses causing a drop ejection movement is applied, and assigned to each trigger pulse the piezo bending transducer triggered by the trigger pulse Adjacent piezo bending transducers with a deflecting one Compensation pulse is applied. The method of claim 1, wherein each of the adjacent ones Piezo bending transducer with a compensation pulse in the Compared to the trigger pulse of lower amplitude, preferred an amplitude that is two thirds lower becomes. A method according to claim 1 or 2, wherein each of the neighboring piezo bending transducer with a compensation pulse a shorter duration compared to the trigger pulse is applied. A method according to any one of claims 1 to 3, wherein each of the neighboring piezo bending transducers delayed, preferred delayed by 80 microseconds after the assigned Trigger pulse with the compensation pulse is applied. A method according to any one of claims 1 to 4, wherein each of the neighboring piezo bending transducer with a compensation pulse is acted upon by the adjacent piezo bending transducer is first deflected in the opposite direction like the triggered piezo bending transducer. Method according to one of claims 1 to 5, wherein the triggered piezo bending transducers neighboring Piezo bending transducers when they triggered two Piezo bending transducers are adjacent to one Compensation pulse of greater amplitude can be applied as if they were just a triggered piezo bending transducer are neighboring. Method according to one of claims 1 to 6, wherein the Piezo bending transducers in two groups at different times Trigger pulses are applied to each other neighboring piezo bending transducers each different Belong to groups. Method according to one of claims 1 to 6, wherein the Piezo bending transducers in a single group with trigger pulses be applied and the triggered piezo bending transducers different trigger pulses are applied, depending on whether both, one or neither of the neighboring ones Piezo bending transducer is also triggered. The method of claim 8, wherein the piezo bending transducer when one of the neighboring piezo bending transducers as well is triggered with a trigger pulse of lower amplitude is applied as if none of the neighboring Piezo bending transducer is also triggered, and with a Trigger pulse of even lower amplitude is applied, if both neighboring piezo bending transducers also to be triggered. Method according to one of claims 1 to 9, wherein the neighboring piezo bending transducers with compensation pulses be applied to a gently sloping flank. Method for controlling a piezo bending transducer drop-on-demand Printhead it in line with a nozzle plate arranged nozzles, each of which has a piezo bending transducer is assigned, wherein each of the piezo bending transducers with a the sequence of each corresponding to the desired print image trigger pulses causing a drop ejection movement is applied, and assigned to each trigger pulse the applied piezo bending transducer Piezo bending transducer with a closing control pulse is acted upon by the adjacent piezo bending transducer deflected towards the associated nozzle and there for a duration is held. The method of claim 11, wherein the adjacent ones Piezo bending transducer with a closing control pulse Amplitude is applied, which is at most one sixth, the amplitude of the trigger pulse is. Method according to one of claims 1 to 12, before Commissioning of the piezo bending transducer drop-on-demand Printhead whereby for each of the piezo bending transducers amplitude, Duration and / or time delay of compensation pulses or Closing control pulses determined using a trimming process in which, for the intended constellations of Trigger pulses the compensation pulses respectively applied Closing control pulses with regard to amplitude, duration and / or Time delay varies and under measurement of the Drop ejection or crosstalk behavior can be optimized. The method of claim 13, wherein the trimming method only duration and / or time delay of Compensation pulses or closing control pulses vary become. Method according to one of claims 13 or 14, wherein at the piezoelectric transducers as sensors be used by voltages resulting from the Triggering a piezo bending transducer, the result caused fluid movement and the deflection of the neighboring piezo bending transducers are induced in these measured and to optimize the drop or Crosstalk behavior can be evaluated. Method according to one of claims 1 to 15, wherein the triggered piezo bending transducers neighboring Piezo bending transducer during operation with Compensation pulses or closing control pulses are applied for the amplitude, duration and / or time delay can be determined by stresses resulting from the Triggering a piezo bending transducer, the result caused fluid movement and the deflection of the neighboring piezo bending transducers are induced in these be measured and processed. Piezo bending transducer with drop-on-demand printhead Nozzle plate (1) with nozzles (11) arranged in series, which each a piezo bending transducer (2) is assigned, the under Ejecting a drop from the respective nozzle (11) with a trigger pulse is applied, and a Control device (3), of which each of the piezo bending transducers (2) according to the method according to one of claims 1 to 10, 13 or 14 with trigger pulses and compensation pulses is acted upon. Piezo bending transducer with drop-on-demand printhead a nozzle plate (1) with nozzles (11) arranged in series, which each have a piezo bending transducer (2) assigned to it while ejecting a drop from the respective nozzle (11) can be acted upon with a trigger pulse, and a Control device (3), of which each of the piezo bending transducers (2) by the method according to any one of claims 11 to 14 trigger pulses and closing control pulses can be applied is. Piezo bending transducer drop-on-demand printhead according to claim 18, the at least three-pole piezo bending transducer (2) with each two active layers (22) made of piezoceramic and one Control device (3), from which the trigger pulses the an active position (22) and the closing control pulses the other active position (22) of the piezo bending transducer (2) be created. Piezo bending transducer drop-on-demand printhead according to one of the Claims 17 to 19, wherein the piezo bending transducer (2) as Piezo-tongue transducers are formed. Piezo bending transducer drop-on-demand printhead according to one of the Claims 17 to 19, wherein the piezo bending transducer (2) as Piezo bridge transducers are formed.

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