Ink writing head with piezoelectrically excitable membrane

Details Ink writing head with piezoelectrically excitable membrane Ink writing head with piezoelectrically excitable membrane

1988-10-11

1989-12-19

Miller, Jr., George H.

Recorders

Markers and/or driving means therefor

With ink supply to marker

346 11, G01D 1518

Patent

active

048885983

DESCRIPTION:

BRIEF SUMMARY
The invention is directed to an in writing head and to a method for the manufacture of an ink writing head according to the preamble of patent claims 1 and 13.
Piezoelectrically operated drive elements in ink printers are generally known. Thus, German Published Application No. 21 64 614 discloses an arrangement in printing units for writing on paper with colored fluid wherein a fluid situated in an ink chamber is ejected from a printer jet via a piezoelectrically operated drive element. The volume change in the chamber is effected by an electrically driven piezoceramic that is seated on a metal plate and that arcs into the chamber. The employed piezo drive element is composed of a continuously polarized piezoceramic layer that is arranged on a metal plate, whereby the metal plate serves as cooperating electrode. When a suitable voltage pulse is applied, the piezoceramic constricts. Since the ceramic is secured to a metal plate, a bending moment acts on this plate. This results therein that the middle part of the plate arcs into the fluid chamber.
The length changes that can be directly piezoelectrically produced are disappearingly small. They are also limited by the electrical field strengths that dare be applied to the ceramic without this leading to punch-throughs or arc-overs. Further, the applied field strengths dare not lead to a re-polarization; they must also be switchable via appropriate drive circuits.
It is therefore standard to not exceed a voltage of about 200 V. The field strength should thereby be lower than 1 V/.mu.m in the direction opposite the polarization. The distances between electrodes at air, moreover, should not be smaller than 1 .mu.m/V. The direct length change that can be achieved in this way is thus about 0.1% or about 0.2 .mu.m given a layer thickness of 200 .mu.m, assuming that the ceramic is active through and through and is not partly inactive due, for instance, to a firing skin. In ink printing the drive elements, whether they are small piezo tubes or piezo laminae, are needed for a whole series of functions. They should accelerate controllably small ink quantities, eject them as droplets and replenish ink from a reservoir. If possible, however, they should also close the ejection openings in order to prevent the runout and the drying of the ink. Finally, the ink channels and the discharge openings should be capable of being cleaned and aerated with such elements.
Only a part of these functions are fully met in the known drive elements comprising acoustic drop formation. Sound waves in the ink channel can in fact form rapidly flying drops, but static pressure for eliminating impediments in the channel cannot be generated. Air inclusions in the ink channel limit the propagation of the pressure waves in the channel and channels that have emptied can only be refilled with an outside intervention. Given acoustic drop formation, the closure of the discharge openings can likewise only ensue mechanically from the outside.
It is therefore an object of the invention to fashion an ink head of the species initially cited such that, first, it can be simply manufactured in a galvanoplastic method and that, second, it exhibits a high degree of efficiency.
In an apparatus of the species initially cited, this object is achieved in accord with the characterizing part of the first patent claim.
Advantageous embodiments of the invention are characterized in the subclaims.
An especially large stroke derives in that the membrane comprises a piezoelectrically excitable peripheral region and a piezoelectrically excitable central region that are driven such for producing a membrane excursion that the membrane is shortened in its peripheral region by transversal contraction and is lengthened in its central region. This stroke is the result of exploiting two actions, namely the exploitation of the transversal contraction in the ceramic itself and the curvature of layers adjacent to the composite that dilate differently. Due to the transversal contraction, the stroke of the membrane can be increased

REFERENCES:
patent: 4539575 (1985-09-01), Nilsson
patent: 4672398 (1987-06-01), Kuwabara et al.

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