Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-05-13
2002-12-10
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06491379
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an inkjet recording apparatus for providing output images on recording media, which can satisfy a wide range of needs in the printing industry wherein high quality images must be output at a high speed, needs in the printer industry that are based on requirements in offices and personal requirements and, further, needs in consumer product industries wherein inexpensive and versatile output equipment and the like utilizing various types of recording paper for various purposes are required.
As a conventional electrostatic type inkjet recording system, a slit-jet recording system has been disclosed (Susumu Ichinose et al.: “Slit-Jet Recording System”, Paper at the First Symposium on Non-Impact Printing Techniques, pp. 119-124, 1984). A description will be made on the slit-jet system based on the side view in
FIG. 9
a
and the perspective view in
FIG. 9
b.
As shown in
FIGS. 9
a
,
9
b
, a recording head is constituted by a head portion
911
and a counter electrode portion
912
proposed in a face-to-face relationship with said head portion
911
. The head portion
911
is constituted by an ink ejection port
901
formed like a slit, an upper substrate
902
and a lower substrate
903
that form said ink injection port
901
, recording electrodes
904
provided on said lower substrate
903
in units of pixels, a control circuit
907
for switching the ejection of ink from the position of each of the recording electrodes
904
based on a recording signal, and a high voltage power supply
906
for supplying a constant voltage pulse to electrodes selected from among said recording electrodes
904
, to cause a potential difference between the counter electrode portion
912
and them when the voltage is applied.
The counter electrode portion
912
is constituted by a support body
917
and a common electrode
905
provided on the support body
917
and is provided in a face-to-face relationship with said ink ejection port
901
with a predetermined microscopic gap therebetween and, further, recording paper
910
is inserted in said microscopic gap.
Ink
908
having high resistance is charged in the ink ejection port
901
of said head portion
911
, and the head portion
911
and counter electrode portion
912
are driven. Then, as a result of the application of a constant voltage pulse to said recording electrodes
904
as shown in
FIG. 9
a
, charges are supplied from the recording electrodes
904
to the ink in regions where the ink is to be ejected, and an electric field is generated between the recording electrodes
904
and common electrode
905
. The ink
908
receives a Coulomb force in the electric field thus generated to be ejected toward the counter electrode portion
912
, and flown ink
909
sticks on to and penetrates into recording paper
910
to provide a desired image output.
According to such a conventional slit-jet recording system, it is possible to avoid limitations on resolution placed by nozzles and to facilitate the cleaning of said ink ejection port
901
by replacing nozzles used for inkjet recording with said ink ejection port
901
in the form of an elongate slit.
Further, according to the slit-jet recording system, color output printing can be easily achieved by using a plurality of said recording heads and supplying each of the ink ejection ports
901
with said ink
908
in a different color and driving it based on a recording signal.
However, conventional recording heads and recording apparatuses according to the slit-jet recording system have had the following problems.
(1) The head portion has integrated functions of wiring to recording electrode patterns divided on the basis of recording pixels and to the circuit for controlling and driving said electrodes independently, an ink chamber for storing a predetermined amount of ink and ink supply means such as an ink tank or ink supply path; the head portion has a very complicated structure which reduces the yield of production.
(2) The durability of the head portion is low because the divided recording electrodes at the head portion are always in direct contact with ink to supply electric charges thereto and because the electrodes have such small divisions that they can be easily corroded by reactions such as electrolysis and oxidation.
(3) Since the constant voltage pulse is applied only to recording electrodes which are to cause the ejection of ink during printing, a large potential difference occurs between the recording electrodes which cause the ejection of ink and those which does not cause the ejection of ink. No insulation treatment can be performed on the surface of the recording electrodes because they supply electric charges to ink and, in addition, adjoining recording electrodes are electrically connected through ink. As a result, a voltage drop can occur between the adjoining electrodes, which disables the generation of the potential difference required for the ejection of ink to reduce the selectivity of ink ejecting positions. A possible solution to this is to increase the potential difference supplied between the electrodes in advance. In this case, however, there is a risk of discharge between adjoining recording electrodes or between the recording electrodes and the common electrode on the counter electrode portion.
(4) Since the electric field generated in the recording head is generated by applying a voltage to divided recording electrodes at the head portion and the common electrode at the counter electrode portion, the electrostatic fields in the regions to which the voltage is applied during the operation concentrate at the head portion where the divided thin electrodes are arranged and spread in the form of a plane at the counter electrode. Therefore, while the ink ejecting positions at the ink ejection port in the head portion is accurately positioned, the landing positions of ink flying toward the counter electrode portion are unstable because of the spread of the electric field. This increases the possibility of misalignment of ink dots as an output image for an apparatus, which makes it difficult to provide a high quality output.
(5) Multi-color printing such as color printing can be performed at least by arranging recording heads associated with respective colors and by driving them independently. However, since this necessitates a recording head and a driving circuit for each color and, the cost and size of an apparatus are increased.
(6) When adjoining recording electrodes are simultaneously driven, i.e., when voltages having the same polarity are applied to adjoining recording electrodes, an interaction occurs between ejected ink droplets, which results in a phenomenon wherein recorded pixels are displaced from normal positions to reduce the quality of the image. Possible causes of this include the fact that turbulence occurs at electric fields generated simultaneously between adjoining electrodes toward the counter electrode as a result of significant mutual influence and the electric fields are not concentrated at the counter electrode which is a common electrode and the fact that physical continuation of ink attributable to ejection port formed like a slit has significant influence. Therefore, in order to avoid such an interaction between adjoining electrodes, divided driving methods have conventionally been used in which recording electrodes are sequentially driven at intervals of several lines, which has inevitably resulted in a reduction of recording speed.
(7) The principle behind the ejection of ink during electrostatic type inkjet recording is the fact that ink in the vicinity of said recording electrodes is charged when a voltage is applied between the recording electrodes and common electrodes, and the ink in said region receives a Coulomb force from electric fields generated between both of the electrodes to be ejected toward the counter electrode.
A Coulomb force F that acts when ink is ejected depends on the strength E of the electric fields generated between both of the electrodes and the amoun
Kawaguchi Koji
Kuwahara Seiji
Muramatsu Hiroyuki
Sato Tatsuru
Adams & Wilks
Gordon Raquel Yvette
Seiko Instruments Inc.
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