Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-03-14
2002-10-08
Nguyen, Thinh (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S057000
Reexamination Certificate
active
06460979
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is in a drop-on-demand print head having a drop generator with nozzles arranged in series, respectively assigned to which there is a piezoelectric bending transducer for discharging sequences of drops and also is in a method of actuating a piezo bending transducer drop-on-demand print head.
2. Description of the Related Art
A customary piezo bending transducer drop-on-demand print head is disclosed in DE 25 27 647 C3. A series of nozzles extending perpendicularly to the plane of a nozzle plate is provided in a plate of a head. Oriented parallel to the nozzle plate are piezo bending transducers in the form of an extending reed which is restrained at one end, so-called piezo reed transducers, arranged in a series adjacent and parallel to one another in such a way that their non-restrained ends are respectively opposite one of the nozzles. Each of the piezo bending transducers is designed as a piezo bimorph, which has a bending axis extending parallel to the nozzle plate and perpendicularly to the nozzles. For discharging a drop, the piezo reed is bent by applying a voltage, so that the free end moves away from the assigned nozzle. The voltage is switched off and the free end races toward the nozzle and forces a quantity of fluid through the nozzle, so that a drop is discharged.
In a construction of this type, the nozzles must be arranged very closely together to produce a print with a high resolution, i.e. large number of dots per unit length. The piezo bending transducers must, to the extent possible, cover the entire assigned nozzle with their width to achieve a clean drop discharge. If the nozzles are closely arranged, the mutually neighboring piezo bending transducers therefore likewise lie very closely together, as do the respectively assigned nozzles. The actuation of a piezo bending transducer consequently also results in “crosstalk”—a fluid flow through the nozzles assigned to the neighboring piezo bending transducers. As a result, a proportion of the flow energy generated is not imparted to the drop to be printed. Furthermore, it may happen that a drop is discharged from the neighboring nozzle, which results in a falsification of the desired print image.
DE 31 14 259 A1 discloses a special design of the nozzles to eliminate the problem of crosstalk. The nozzles have, on the side of the nozzle plate facing away from the piezo bending transducers, a circular cross section with a diameter dependent on the desired drop shape. Toward the side facing the piezo bending transducers, the nozzle widens in a funnel-shaped manner, although not rotationally symmetrically but only in the direction parallel to the piezo bending transducers. In the direction perpendicular to the piezo bending transducers, the nozzle has a constant width, so that the nozzles can be arranged closely together.
However, the production of such nozzles requires high expenditure. Furthermore, the crosstalk reduction with these nozzles, while significant, is still not adequate, particularly in the case of print heads with high resolutions.
EP 0 713 773(Heinzl, Schullerus) proposes that partitions be provided between the individual piezo bending transducers. Although this leads to a complete elimination of crosstalk, it requires a substantial expenditure in production and assembly. Since a very small distance between neighboring nozzles or piezo bending transducers is always desired for the purpose of increasing the printing resolution, the partitions must be produced and positioned in such a way as to maintain extreme tolerances. Furthermore, the fluid friction in the narrow gaps between piezo bending transducers and partitions leads to considerable losses in the speed of the transducer movement and in the energy of the discharged drop.
SUMMARY OF THE INVENTION
The present invention is in a piezo bending transducer drop-on-demand print head with high resolution which can be produced with low production and assembly expenditure and operates without crosstalk.
The object is achieved according to the invention by a method of actuating a piezo bending transducer drop-on-demand print head with a nozzle plate with nozzles arranged in series, respectively assigned to which there is a piezo bending transducer, each of the piezo bending transducers being subjected to a sequence, corresponding to the desired print image, of triggering pulses each effecting a drop discharge movement. Assigned to each triggering pulse, each piezo bending transducer neighboring the piezo bending transducer triggered by the triggering pulse is subjected to a compensating pulse to deflect it.
The deflection of the neighboring piezo bending transducer by the compensating pulse effects a fluid movement locally at the nozzle assigned to the neighboring piezo bending transducer. This fluid movement acts counter to the fluid movement which is caused by the triggering pulse and the movement of the triggered piezo bending transducer directly at the nozzle assigned to the neighboring piezo bending transducer. The fluid movements fully or partly compensate for one another. No drop discharge occurs at the nozzle assigned to the neighboring piezo bending transducer (neighboring nozzle). Falsification of the print image is prevented. The disadvantageous effects of crosstalk are consequently eliminated.
No partitions between mutually neighboring piezo bending transducers or special nozzle shapes are required. The nozzle plate and the wall of the printer chamber can be of a simple design. Production and assembly costs are consequently kept low.
Furthermore, mutually neighboring piezo bending transducers can be arranged as closely together as the nozzle width allows. Therefore, a print head with a very high resolution is obtained.
The narrow gaps between the piezo bending transducer and the conventionally provided partitions are no longer needed. During a return or restoring movement of the piezo bending transducer, the flow of additional printing fluid laterally past the piezo bending transducer occurs more quickly. A subsequent drop discharge is consequently possible at a shorter time interval from the preceding discharge thus enabling an increase in the printing frequency.
According to the invention, the piezo bending transducers can be subjected to discharging pulses which bring about a deflection of the piezo bending transducer toward the assigned nozzle. However, the piezo bending transducers are preferably subjected to triggering pulses which cause a deflection of the piezo bending transducer away from the assigned nozzle. The actual drop discharge movement of the piezo bending transducer then comprises racing back of the piezo structure on account of the mechanical stress built up during the application of the triggering pulse and the associated deflection. Such a racing back movement is generally faster than the deflecting movement.
Each of the neighboring piezo bending transducers is preferably subjected to a compensating pulse of a lower amplitude than that of the triggering pulse. This achieves the effect that a drop discharge is not stopped at the neighboring nozzle on account of the compensating pulse itself, either during the deflecting movement or during the racing-back movement of the neighboring piezo bending transducer. Furthermore, the energy extracted from the fluid movement is not so large that a drop discharge no longer occurs at the nozzle assigned to the triggered piezo bending transducer. Preferably, the applied compensating pulse has an amplitude of 10 to 40%, and more preferably, one third of the amplitude of the triggering pulse.
The neighboring piezo bending transducers are preferably subjected to a compensating pulse of a shorter duration in comparison with the duration of the triggering pulse. With a shorter pulse duration, as with a lower amplitude of the applied voltage, it is possible to achieve the effect that the deflection amplitude of the piezo bending transducer is lower in the case of the compensating pulse than in the case of the triggering pulse.
Ederer Ingo
Heinzl Joachim
Seitz Hermann
Cohen & Pontani, Lieberman & Pavane
Nguyen Thinh
Tally Computerdrucker GmbH
LandOfFree
Piezo bending transducer drop-on demand print head and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Piezo bending transducer drop-on demand print head and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Piezo bending transducer drop-on demand print head and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2998542