Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-06-12
2004-04-13
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06719410
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ink jet head using a piezoelectric body and a manufacturing method thereof, and in particular to an ink jet head using a driving source having a bimorph structure and a manufacturing method thereof.
BACKGROUND ART
An ink jet printer carries out printing on sheets by ejecting ink particles from an ink chamber. An ink jet printer has a simpler constitution than an electro-photographic printer, and hence a low-cost printer can be provided. Moreover, color printing is possible with a low-cost apparatus. Ink jet printers thus constitute the mainstream of the low-cost printer market.
Types of ink jet printer are a piezoelectric type that uses a piezoelectric element, and a thermal type that uses a heat-generating element. The piezoelectric type has advantages not seen with the thermal type, namely the response speed is high and the electrical-mechanical energy conversion efficiency is high. The piezoelectric type is thus suited to high-resolution color printers.
With a high-resolution printer, there are problems if the volume of the ink drops is too large or too small. That is, in the case that the volume of the ink drops is too large, the gradation representation ability is insufficient, and hence the resolution drops. Conversely, if the volume of the ink drops is too small, then the printing speed drops, and also the ink flying direction is disturbed due to the influence of air currents and slight electrical charging, and hence the resolution drops. With most high-resolution printers, the volume of the ink drops is thus a few pico-liters (1 pico-liter=10
−12
of a liter=10
−15
of a cubic meter).
With a piezoelectric body as the driving source for ejecting the ink drops, the mechanical energy generated (generative force) is sufficiently large, but the displacement amount is low. A displacement magnifying mechanism that increases the displacement of the piezoelectric body is thus used. A bimorph structure is most widely used as a suitable displacement magnifying mechanism in an ink jet head.
FIG.
28
(A), FIG.
28
(B) and FIG.
28
(C) are explanatory drawings of a conventional ink jet head. As shown in FIG.
28
(A), the bimorph structure has a constitution in which a plate-shaped non-piezoelectric material (metal, ceramic etc.)
91
is stuck onto a plate-shaped piezoelectric body
90
. The piezoelectric body
90
expands in the thickness direction, and at the same time contracts in the planar direction, and hence strain arises between the piezoelectric body
90
and the non-piezoelectric material
91
, and to relieve this, warping occurs. The radius of curvature due to the warping is somewhat larger on the non-piezoelectric material
91
side (the outside), and is somewhat smaller on the inside of the piezoelectric body
90
, and hence the length differs between the outside and the inside of the piezoelectric body
90
. A large deformation thus arises for a very small strain (contraction in the planar direction) in the piezoelectric body
90
.
An ink jet head using this bimorph driver is shown in FIG.
28
(B) and FIG.
28
(C). As shown in FIG.
28
(B) and FIG.
28
(C), nozzles
92
are provided in ink chambers
95
that store ink. A vibrating plate
91
is provided so as to form a wall for the ink chambers
95
. The vibrating plate
91
corresponds to the non-piezoelectric material in FIG.
28
(A). Piezoelectric bodies
90
are provided on the vibrating plate
91
in correspondence with each of the ink chambers
95
. The ink chambers
95
communicate with an ink supply chamber
94
via an ink supply hole
93
.
A voltage source
96
is connected between the vibrating plate
91
and the piezoelectric bodies
90
, and by supplying a driving voltage, the piezoelectric plates
90
and the vibrating plate
91
are displaced, and pressure is applied to the ink chambers
95
. As a result, ink drops are ejected from the nozzles
92
of the ink chambers
95
. By releasing the driving voltage, the piezoelectric bodies
90
return to their original positions, and as a result ink is supplied from the ink supply chamber
94
into the ink chambers
95
via the ink supply hole
93
.
The displacement amount depends on the width W of the piezoelectric bodies
90
as shown in FIG.
28
(B); the displacement amount is sharply reduced if the width W is narrowed. The width W of the piezoelectric bodies
90
thus cannot be made small. The dot pitch of the multi-nozzle head, in which a plurality of the nozzles are arranged in a line, i.e. the nozzle spacing d of the piezoelectric head, is determined by the width W of the piezoelectric bodies
90
. An ink jet head using such a bimorph structure is thus greatly inferior to a thermal type in terms of the nozzle installation density (the dot pitch) and the cost. For example, the installation density may be 120 dpi for the piezoelectric body bimorph type compared with 600 dpi for the thermal type, a difference of 5 times.
In the case of the piezoelectric body bimorph type, it is thus necessary to make the width W of the piezoelectric bodies
90
narrower, and hence increase the installation density. However, with the piezoelectric body bimorph type, the width W of the piezoelectric bodies
90
determines the displacement amount, and hence if the width W of the piezoelectric bodies is made narrow, then the displacement amount drops sharply, and stress increases There has thus been a problem in that it is not possible to realize the displacement required for ejecting fine ink drops having a volume suitable for printing (e.g. 1 pico-liter or more). Moreover, there has been a problem that if the driving voltage is increased to increase the displacement amount, then the stress increases, and the vibrating plate
91
breaks.
Moreover, a cantilever beam structure for increasing the displacement amount of a piezoelectric body is known (for example, Japanese Patent Application Laid-open No. 2-143861). FIG.
29
(A) and FIG.
29
(B) are drawings of the constitution of a conventional cantilever beam structure ink jet head. As shown in FIG.
29
(A), a vibrating plate
91
, a piezoelectric plate
90
and an individual electrode
98
are provided via an ink chamber
95
on a substrate
97
in which a nozzle
92
is formed. As shown in FIG.
29
(B), the piezoelectric body
90
and the vibrating plate
91
have a cantilever beam structure in which only one side is supported. With this cantilever beam structure, the three peripheral edges of the bimorph driver
90
other than the one fixed edge are free edges, and hence there is free entry and exiting of ink to and from the pressure chamber
95
. There has thus been a problem that the internal pressure in the pressure chamber does not rise to high, and hence ink drops cannot be accelerated to a sufficient speed.
To increase the pressure in the pressure chamber, one can envisage making the gap around the three edges of the bimorph piezoelectric body
90
narrower. For example, the gap suitable for ink flight is 0.5 microns or less. However, it is virtually impossible to align the various layers with high precision and form such a narrow gap around the three edges of the bimorph piezoelectric body
90
. There has thus been a problem that, with an easily realizable gap of about a few microns, ink drops fly at only a very low speed.
It is thus an object of the present invention to provide an ink jet head and manufacturing method thereof for obtaining ink drops of sufficient speed even if the width of the piezoelectric bodies is made narrow.
It is another object of the present invention to provide an ink jet head and manufacturing method thereof for narrowing the width of the piezoelectric bodies, and thus increasing the nozzle installation density of the head.
It is a further object of the present invention to provide an ink jet head and manufacturing method thereof for obtaining sufficient displacement and pressure even if the width of the piezoelectric bodies is made narrow.
Furthermore, it is an object of the present invention to provide an ink jet hea
Koike Shuji
Sakamoto Yoshiaki
Shingai Tomohisa
Armstrong Kratz Quintos Hanson & Brooks, LLP
Do An H.
Fujistu Limited
Meier Stephen D.
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