Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1997-02-12
2001-11-20
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S020000, C347S070000, C347S071000
Reexamination Certificate
active
06318844
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a print head for an ink-jet printer comprising a nozzle member defining a plurality of ink channels arranged side-by-side and each terminating in a nozzle, a plurality of actuators disposed on one side of the nozzle member and respectively facing one of the ink channels for pressurizing the ink liquid therein, in order to expel ink droplets through the nozzles, support means supporting the actuators on the side opposite to the ink channels, and a plurality of connecting portions mechanically connecting the support means to the nozzle member, at least one of said connecting portions being arranged between the actuators.
DESCRIPTION OF THE INVENTION
A conventional print head of this type has been disclosed in EP-B-0 402 172. The nozzle member is formed by a nozzle plate in which recesses have been formed for defining the ink channels and the nozzles. On the side facing the actuators, the recesses are covered by a flexible plate which is sandwiched between the nozzle plate and a support plate. The actuators are formed by elongated piezoelectric plates formed integrally with and vertically projecting from the support plate, so that their edge portions engage the flexible plate. The piezoelectric actuators are provided with electrodes, and when a voltage is applied to these electrodes, the piezoelectric plate expands and presses against the flexible plate so that the latter is slightly bent and compresses the liquid in the ink channel. Thus, on demand, individual ink droplets can be expelled from nozzles by energizing the electrodes of the piezoelectric actuators.
However, when an individual actuator is energized and expands, this actuator also tends to bend the support plates so that the neighboring actuators are drawn away from the associated ink channels, with the result that the pressure in the neighboring ink channels is reduced. Thus, an undesired cross-talk phenomenon occurs, i.e., the expansion of an individual actuator has an influence not only on the ink channel associated therewith but also on the neighboring ink channels. In order to reduce this cross-talk phenomenon, the connecting portions are provided between the individual actuators.
In the conventional device, the connecting portions are shaped as continuous bars fixed on the surface of the support plate and extending lengthwise of the ink channels. These bars are fixed to the flexible plate at positions opposite to the walls of the nozzle plate which separate the individual ink channels. Since the flexible plate is also fixed to these walls of the nozzle plate, a mechanical connection with a certain tensile strength is established between the nozzle plate and the support plate. Thus, when an individual actuator is energized, the reaction force of this actuator is balanced by the tension force of the neighboring connecting portions, so that the support plate is prevented from bending and the cross-talk is suppressed.
When the print head is used with a hot melt ink system, the nozzle plate has to be heated in order to keep the temperature of the ink above the melting point. In this case the print head is subject to thermal stresses due to differential thermal expansion of the nozzle plate and the flexible plate on the one hand and the support plate on the other hand. In this respect, the conventional construction has the drawback that the bar-shaped connecting portions increase the strength of the print head only in a longitudinal direction of the ink channels but not in the direction orthogonal thereto, i.e. in the direction in which the nozzles are aligned.
The bar-shaped connecting portions intervening between the individual actuators also limit the density with which the ink channels and nozzles can be arranged and hence the spacial resolution of the print head.
SUMMARY OF THE INVENTION
The present invention has been devised in order to overcome or mitigate these problems. The print head according to the invention is characterized in that the connecting portions are spaced apart from one another in the longitudinal direction of the ink channels.
Since the connecting portions do not extend continuously over the whole length of the ink channels, the print head according to the invention is light-weight and reduces the dissipation of heat via the connecting portions. Nevertheless, the connecting portions function to absorb the reaction forces of the actuators and to prevent bending of the support plate, so that cross-talk is suppressed similarly as in the prior art.
In one embodiment of the invention, the actuating means for each individual ink channel comprise at least two separate actuators which are disposed in the gaps between the connecting portions, and the connecting portions are shaped as continuous bars extending in transverse direction of the ink channels. Thus, the connecting portions significantly increase the strength of the print head in the transverse direction, i.e. the direction, in which the nozzles are aligned. As a result, the thermal stability of the nozzle head is improved.
It has to be noted that the number of bar-shaped connecting portions can be significantly smaller than in the prior art, because each bar can absorb the reaction forces of the actuators for all ink channels, so that it is not necessary to have bars intervening in each of the clearances between the ink channels.
In addition, the spacings between the actuators and hence the spacings between the nozzles can be reduced so that a higher spacial resolution of the print head is achieved.
In another embodiment of the invention, the connecting portions are formed as separated insulae or pillars which are disposed in the intervals between the actuators. In this case, the actuators may be formed as continuous plates which extend over the whole length of the ink channels, as in the prior art. The pillars have a comparatively high tensile strength in the direction normal to the plane of the nozzle plate, but can readily be deformed in a shear mode in both directions in parallel with the nozzle plate, so that differential thermal expansion of the nozzle plate and the support plate can be absorbed by the pillars and will not lead to a substantial deformation of the nozzle plate.
This embodiment also permits a reduction in the spacing between the ink chambers. To this end, the opposing lateral surfaces of the plate-like piezoelectric actuators are formed with grooves for accommodating the pillar-shaped connecting portions.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
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Puik Erik Christian Nicolaas
Witteveen Bontko
Barlow John
Birch & Stewart Kolasch & Birch, LLP
Do An H.
OCE-Nederland, B.V.
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