BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink-jet head for
printing by ejecting ink onto a record medium, and to an ink-jet
printer having the ink-jet head.
2. Description of Related Art
In an ink-jet printer, an ink-jet head distributes ink,
which is supplied from an ink tank, to pressure chambers. The
ink-jet head selectively applies pulse pressure to each
pressure chamber to eject ink through a nozzle connected with
each pressure chamber. As a means for selectively applying
pulse pressure to the pressure chambers, an actuator unit or
the like may be used in which ceramic piezoelectric sheets are
laminated. The printing operations are carried out while
reciprocating such a head at a high speed in the widthwise
direction of paper.
As for arrangement of pressure chambers in such an ink-jet
head, there are one-dimensional arrangement in which
pressure chambers are arranged in, e.g., one or two rows along
the length of the head, and two-dimensional arrangement in
which pressure chambers are arranged in a matrix along a
surface of the head. To achieve high-resolution and highspeed
printing demanded in recent years, two-dimensional
arrangement of pressure chambers is more effective. As an
example of ink-jet head in which pressure chambers are
arranged in a matrix along a surface of the head, an ink-jet
head is known in which a nozzle is disposed at the center of
each pressure chamber in a view perpendicular to the head
surface (see US Patent No. 5757400). In this case, when pulse
pressure is applied to a pressure chamber, a pressure wave
propagates in the pressure chamber perpendicularly to the head
surface. Ink is then ejected through the corresponding nozzle
disposed at the center of the pressure chamber in a view
perpendicular to the head surface.
Here, in case of ejecting ink by using a pressure wave,
there are known so-called "fill after fire" method, in which a
positive pressure is applied to a pressure chamber, and so-called
"fill before fire" method, in which at first a negative
pressure is applied to a pressure chamber and then at a
predetermined timing after a negative pressure wave has been
reversed and reflected a positive pressure is applied. In
these two methods of "fill after fire" and the "fill before
fire", it is said that the "fill before fire" generally
presents a higher energy efficiency. Moreover, in case a
pressure wave propagates in a pressure chamber perpendicularly
to the head surface as in the aforementioned conventional
example, the propagation time length of the pressure waves
(i.e., AL: Acoustic Length) is extremely short, so long as a
head is not large-sized. Furthermore, if the "fill before
fire" is performed in case of short AL, the time period for
the pressure waves to be reversed and returned becomes short,
so that a time interval between timings for a negative
pressure and for a positive pressure also becomes short.
Because of this, a highly responsive and expensive drive
circuit is necessary to be used in the ink-jet head. In
addition, if the "fill after fire" is performed in order to
avoid the above necessity, a large energy has to be inputted
to the ink-jet head, so that the problem of a poor energy
efficiency can be raised.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an ink-jet
head which can achieve a high resolution and a high
printing speed and can improve energy efficiency, and to
provide an ink-jet printer having the ink-jet head.
According to a first aspect of the present invention
provided is an ink-jet head having a passage unit including a
plurality of pressure chambers each having one end connected
with a nozzle and the other end to be connected with an ink
supply source. Each of the pressure chambers is confined in
each of a plurality of parallelogram regions and has a planar
shape of a 2n-angled shape (n: a natural number, n ≥ 3) with
no corner bulging in a direction to leave a line joining the
one end and the other end in each of the pressure chambers, in
a plane of the passage unit where the pressure chambers are
arranged. A first direction along a longer diagonal line of
the parallelogram region and a second direction joining the
one end and the other end in each of the pressure chambers are
substantially coincident with each other.
Since no corner bulges out perpendicularly to the line
joining the ends the flow can be improved.
According to a second aspect of the present invention
provided is an ink-jet printer having an ink-jet head. The
ink-jet head comprises a passage unit having a plurality of
pressure chambers each having one end connected with a nozzle
and the other end to be connected with an ink supply source.
Each of the pressure chambers is confined in each of a
plurality of parallelogram regions and has a planar shape of a
2n-angled shape (n: a natural number, n ≥ 3) with no corner
bulging in a direction to leave a line joining the one end and
the other end in each of the pressure chambers, in a plane of
the passage unit where the pressure chambers are arranged. A
first direction along a longer diagonal line of the
parallelogram region and a second direction joining the one
end and the other end in each of the pressure chambers are
substantially coincident with each other.
According to a third aspect of the present invention
provided is an ink-jet head having a passage unit including a
plurality of pressure chambers each having one end connected
with a nozzle and the other end to be connected with an ink
supply source. Each of the pressure chambers is confined in
each of a plurality of parallelogram regions and has an
elliptical planar shape with no corner bulging in a direction
to leave a line joining the one end and the other end in each
of the pressure chambers, in a plane of the passage unit where
the pressure chambers are arranged. A first direction along
the longer diagonal line of the parallelogram region and a
second direction joining the one end and the other end in each
of the pressure chambers are substantially coincident with
each other.
According to a forth aspect of the present invention
provided is an ink-jet printer including an ink-jet head. The
ink-jet head comprises a passage unit having a plurality of
pressure chambers each having one end connected with a nozzle
and the other end to be connected with an ink supply source.
Each of the pressure chambers is confined in each of a
plurality of parallelogram regions and has an elliptical
planar shape with no corner bulging in a direction to leave a
line joining the one end and the other end in each of the
pressure chambers, in a plane of the passage unit where the
pressure chambers are arranged. A first direction along the
longer diagonal line of the parallelogram region and a second
direction joining the one end and the other end in each of the
pressure chambers are substantially coincident with each
other.
In this construction, in an ink-jet head and an ink-jet
printer capable of achieving the high resolution and the high
printing speed, a second direction joining one end connected
with the nozzle and the other end connected with the ink
supply source in each of pressure chambers is substantially
parallel to a plane of the passage unit where the pressure
chambers are arranged. As a result, a pressure wave to be
generated in the pressure chamber propagates substantially
along the plane of the passage unit where the pressure
chambers are arranged. In case the pressure wave thus
propagates along the plane of the passage unit having the
pressure chambers arranged, AL can be relatively long without
increasing the head thickness (a length of the head in a
direction perpendicular to the plane). This provides a margin
in time for matching the timings of generation and reflection
of the pressure wave, and thus, "fill before fire" can be
performed, and improvement of energy efficiency is achieved
compared with the case of the "fill after fire".
BRIEF DESCRIPTION OF THE DRAWINGS
Other and further objects, features and advantages of the
invention will appear more fully from the following
description taken in connection with the accompanying drawings
in which:
FIG. 1 is a general view of an ink-jet printer including
ink-jet heads according an embodiment of the present
invention; FIG. 2 is a perspective view of an ink-jet head according
to the embodiment of the present invention; FIG. 3 is a sectional view taken along line II-II in FIG.
2; FIG. 4 is a plan view of an head main body included in
the ink-jet head of FIG. 2; FIG. 5 is an enlarged view of the region enclosed with an
alternate long and short dash line in FIG. 4; FIG. 6 is an enlarged view of the region enclosed with an
alternate long and short dash line in FIG. 5; FIG. 7 is a partial sectional view of the head main body
of FIG. 4 taken along line III-III in FIG. 6; FIG. 8 is an enlarged view of the region enclosed with an
alternate long and two short dashes line in FIG. 5; FIG. 9 is a partial exploded perspective view of the head
main body of FIG. 4; FIG. 10 is a lateral enlarged sectional view of the
region enclosed with an alternate long and short dash line in
FIG. 7; FIG. 11A is a diagram showing a first modification in a
planar shape of a pressure chamber; FIG. 11B is a diagram showing the state, in which the
pressure chambers illustrated in FIG. 11A are arranged in a 3
x 3 matrix; FIG. 12A is a diagram showing a second modification in
the planar shape of a pressure chamber; and FIG. 12B is a diagram showing the state, in which the
pressure chambers illustrated in FIG. 12A are arranged in a 3
x 3 matrix.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a general view of an ink-jet printer including
ink-jet heads according to a first embodiment of the present
invention. The ink-jet printer 101 as illustrated in FIG. 1
is a color ink-jet printer having four ink-jet heads 1. In
this printer 101, a paper feed unit 111 and a paper discharge
unit 112 are disposed in left and right portions of FIG. 1,
respectively.
In the printer 101, a paper transfer path is provided
extending from the paper feed unit 111 to the paper discharge
unit 112. A pair of feed rollers 105a and 105b is disposed
immediately downstream of the paper feed unit 111 for pinching
and putting forward a paper as an image record medium. By the
pair of feed rollers 105a and 105b, the paper is transferred
from the left to the right in FIG. 1. In the middle of the
paper transfer path, two belt rollers 106 and 107 and an
endless transfer belt 108 are disposed. The transfer belt 108
is wound on the belt rollers 106 and 107 to extend between
them. The outer face, i.e., the transfer face, of the
transfer belt 108 has been treated with silicone. Thus, a
paper fed through the pair of feed rollers 105a and 105b can
be held on the transfer face of the transfer belt 108 by the
adhesion of the face. In this state, the paper is transferred
downstream (rightward) by driving one belt roller 106 to
rotate clockwise in FIG. 1 (the direction indicated by an
arrow 104).
Pressing members 109a and 109b are disposed at positions
for feeding a paper onto the belt roller 106 and taking out
the paper from the belt roller 106, respectively. Either of
the pressing members 109a and 109b is for pressing the paper
onto the transfer face of the transfer belt 108 so as to
prevent the paper from separating from the transfer face of
the transfer belt 108. Thus, the paper surely adheres to the
transfer face.
A peeling device 110 is provided immediately downstream
of the transfer belt 108 along the paper transfer path. The
peeling device 110 peels off the paper, which has adhered to
the transfer face of the transfer belt 108, from the transfer
face to transfer the paper toward the rightward paper
discharge unit 112.
Each of the four ink-jet heads 1 has, at its lower end, a
head main body 1a. Each head main body 1a has a rectangular
section. The head main bodies 1a are arranged close to each
other with the longitudinal axis of each head main body 1a
being perpendicular to the paper transfer direction
(perpendicular to FIG. 1). That is, this printer 101 is a
line type. The bottom of each of the four head main bodies 1a
faces the paper transfer path. In the bottom of each head
main body 1a, a number of nozzles are provided each having a
small-diameter ink ejection port. The four head main bodies
1a eject ink of magenta, yellow, cyan, and black,
respectively.
The head main bodies 1a are disposed such that a narrow
clearance is formed between the lower face of each head main
body 1a and the transfer face of the transfer belt 108. The
paper transfer path is formed within the clearance. In this
construction, while a paper, which is being transferred by the
transfer belt 108, passes immediately below the four head main
bodies 1a in order, the respective color inks are ejected
through the corresponding nozzles toward the upper face, i.e.,
the print face, of the paper to form a desired color image on
the paper.
The ink-jet printer 101 is provided with a maintenance
unit 117 for automatically carrying out maintenance of the
ink-jet heads 1. The maintenance unit 117 includes four caps
116 for covering the lower faces of the four head main bodies
1a, and a not-illustrated purge system.
The maintenance unit 117 is at a position immediately
below the paper feed unit 111 (withdrawal position) while the
ink-jet printer 101 operates to print. When a predetermined
condition is satisfied after finishing the printing operation
(for example, when a state in which no printing operation is
performed continues for a predetermined time period or when
the printer 101 is powered off), the maintenance unit 117
moves to a position immediately below the four head main
bodies 1a (cap position), where the maintenance unit 117
covers the lower faces of the head main bodies 1a with the
respective caps 116 to prevent ink in the nozzles of the head
main bodies 1a from being dried.
The belt rollers 106 and 107 and the transfer belt 108
are supported by a chassis 113. The chassis 113 is put on a
cylindrical member 115 disposed under the chassis 113. The
cylindrical member 115 is rotatable around a shaft 114
provided at a position deviating from the center of the
cylindrical member 115. Thus, by rotating the shaft 114, the
level of the uppermost portion of the cylindrical member 115
can be changed to move up or down the chassis 113 accordingly.
When the maintenance unit 117 is moved from the withdrawal
position to the cap position, the cylindrical member 115 must
have been rotated at a predetermined angle in advance so as to
move down the transfer belt 108 and the belt rollers 106 and
107 by a pertinent distance from the position illustrated in
FIG. 1. A space for the movement of the maintenance unit 117
is thereby ensured.
In the region surrounded by the transfer belt 108, a
nearly rectangular parallelepiped guide 121 (having its width
substantially equal to that of the transfer belt 108) is
disposed at an opposite position to the ink-jet heads 1. The
guide 121 is in contact with the lower face of the upper part
of the transfer belt 108 to support the upper part of the
transfer belt 108 from the inside.
Next, the construction of each ink-jet head 1 according
to this embodiment will be described in more detail. FIG. 2
is a perspective view of the ink-jet head 1. FIG. 3 is a
sectional view taken along line II-II in FIG. 2. Referring to
FIGS. 2 and 3, the ink-jet head 1 according to this embodiment
includes a head main body 1a having a rectangular shape in a
plan view and extending in one direction (main scanning
direction), and a base portion 131 for supporting the head
main body 1a. The base portion 131 supporting the head main
body 1a further supports thereon driver ICs 132 for supplying
driving signals to individual electrodes 35a and 35b (see FIG.
6 and FIG. 10), and substrates 133.
Referring to FIG. 2, the base portion 131 is made up of a
base block 138 partially bonded to the upper face of the head
main body 1a to support the head main body 1a, and a holder
139 bonded to the upper face of the base block 138 to support
the base block 138. The base block 138 is a nearly
rectangular parallelepiped member having substantially the
same length of the head main body 1a. The base block 138 made
of metal material such as stainless steel has a function as a
light structure for reinforcing the holder 139. The holder
139 is made up of a holder main body 141 disposed near the
head main body 1a, and a pair of holder support portions 142
each extending on the opposite side of the holder main body
141 to the head main body 1a. Each holder support portion 142
is as a flat member. These holder support portions 142 extend
along the longitudinal direction of the holder main body 141
and are disposed in parallel with each other at a
predetermined interval.
Skirt portions 141a in a pair, protruding downward, are
provided in both end portions of the holder main body 141a in
a sub scanning direction (perpendicular to the main scanning
direction). Either skirt portion 141a is formed through the
length of the holder main body 141. As a result, in the lower
portion of the holder main body 141, a nearly rectangular
parallelepiped groove 141b is defined by the pair of skirt
portions 141a. The base block 138 is received in the groove
141b. The upper surface of the base block 138 is bonded to
the bottom of the groove 141b of the holder main body 141 with
an adhesive. The thickness of the base block 138 is somewhat
larger than the depth of the groove 141b of the holder main
body 141. As a result, the lower end of the base block 138
protrudes downward beyond the skirt portions 141a.
Within the base block 138, as a passage for ink to be
supplied to the head main body 1a, an ink reservoir 3 is
formed as a nearly rectangular parallelepiped space (hollow
region) extending along the longitudinal direction of the base
block 138. In the lower face 145 of the base block 138,
openings 3b (see FIG. 4) are formed each communicating with
the ink reservoir 3. The ink reservoir 3 is connected through
a not-illustrated supply tube with a not-illustrated main ink
tank (ink supply source) within the printer main body. Thus,
the ink reservoir 3 is suitably supplied with ink from the
main ink tank.
In the lower face 145 of the base block 138, the vicinity
of each opening 3b protrudes downward from the surrounding
portion. The base block 138 is in contact with a passage unit
4 (see FIG. 3) of the head main body 1a at the only vicinity
portion 145a of each opening 3b of the lower face 145. Thus,
the region of the lower face 145 of the base block 138 other
than the vicinity portion 145a of each opening 3b is distant
from the head main body 1a. Actuator units 21 are disposed
within the distance.
To the outer side face of each holder support portion 142
of the holder 139, a driver IC 132 is fixed with an elastic
member 137 such as a sponge being interposed between them. A
heat sink 134 is disposed in close contact with the outer side
face of the driver IC 132. The heat sink 134 is made of a
nearly rectangular parallelepiped member for efficiently
radiating heat generated in the driver IC 132. A flexible
printed circuit (FPC) 136 as a power supply member is
connected with the driver IC 132. The FPC 136 connected with
the driver IC 132 is bonded to and electrically connected with
the corresponding substrate 133 and the head main body 1a by
soldering. The substrate 133 is disposed outside the FPC 136
above the driver IC 132 and the heat sink 134. The upper face
of the heat sink 134 is bonded to the substrate 133 with a
seal member 149. Also, the lower face of the heat sink 134 is
bonded to the FPC 136 with a seal member 149.
Between the lower face of each skirt portion 141a of the
holder main body 141 and the upper face of the passage unit 4,
a seal member 150 is disposed to sandwich the FPC 136. The
FPC 136 is fixed by the seal member 150 to the passage unit 4
and the holder main body 141. Therefore, even if the head
main body 1a is elongated, the head main body 1a can be
prevented from being bent, the interconnecting portion between
each actuator unit and the FPC 136 can be prevented from
receiving stress, and the FPC 136 can surely be held.
Referring to FIG. 2, in the vicinity of each lower corner
of the ink-jet head 1 along the main scanning direction, six
protruding portions 30a are disposed at regular intervals
along the corresponding side wall of the ink-jet head 1.
These protruding portions 30a are provided at both ends in the
sub scanning direction of a nozzle plate 30 in the lowermost
layer of the head main body 1a (see FIG. 7). The nozzle plate
30 is bent by about 90 degrees along the boundary line between
each protruding portion 30a and the other portion. The
protruding portions 30a are provided at positions
corresponding to the vicinities of both ends of various papers
to be used for printing. Each bent portion of the nozzle
plate 30 has a shape not right-angled but rounded. This makes
it hard to bring about clogging of a paper, i.e., jamming,
which may occur because the leading edge of the paper, which
has been transferred to approach the head 1, is stopped by the
side face of the head 1.
FIG. 4 is a schematic plan view of the head main body 1a.
In FIG. 4, an ink reservoir 3 formed in the base block 138 is
imaginarily illustrated with a broken line. Referring to FIG.
4, the head main body 1a has a rectangular shape in the plan
view extending in one direction (main scanning direction).
The head main body 1a includes a passage unit 4 in which a
large number of pressure chambers 10 and a large number of ink
ejection ports 8 at the front ends of nozzles are formed (as
for both, see FIGS. 5, 6, and 7), as described later.
Trapezoidal actuator units 21 arranged in two lines in a
staggered shape are bonded onto the upper face of the passage
unit 4. Each actuator unit 21 is disposed such that its
parallel opposed sides (upper and lower sides) extend along
the longitudinal direction of the passage unit 4. The oblique
sides of each neighboring actuator units 21 overlap each other
in the lateral direction of the passage unit 4.
The lower face of the passage unit 4 corresponding to the
bonded region of each actuator unit 4 is made into an ink
ejection region. In the surface of each ink ejection region,
a large number of ink ejection ports 8 are arranged in a
matrix, as described later. In the base block 138 disposed
above the passage unit 4, an ink reservoir 3 is formed along
the longitudinal direction of the base block 138. The ink
reservoir 3 communicates with an ink tank (not illustrated)
through an opening 3a provided at one end of the ink reservoir
3, so that the ink reservoir 3 is always filled up with ink.
In the ink reservoir 3, pairs of openings 3b are provided in
regions where no actuator unit 21 is present, so as to be
arranged in a staggered shape along the longitudinal direction
of the ink reservoir 3.
FIG. 5 is an enlarged view of the region enclosed with an
alternate long and short dash line in FIG. 4. Referring to
FIGS. 4 and 5, the ink reservoir 3 communicates through each
opening 3b with a manifold channel 5 disposed under the
opening 3b. Each opening 3b is provided with a filter (not
illustrated) for catching dust and dirt contained in ink. The
front end portion of each manifold channel 5 branches into two
sub-manifold channels 5a. Below a single one of the actuator
unit 21, two sub-manifold channels 5a extend from each of the
two openings 3b on both sides of the actuator unit 21 in the
longitudinal direction of the ink-jet head 1. That is, below
the single actuator unit 21, four sub-manifold channels 5a in
total extend along the longitudinal direction of the ink-jet
head 1. Each sub-manifold channel 5a is filled up with ink
supplied from the ink reservoir 3.
FIG. 6 is an enlarged view of the region enclosed with an
alternate long and short dash line in FIG. 5. Either of FIGS.
5 and 6 is a vertical view of a plane in which many pressure
chambers 10 are arranged in a matrix in the passage unit 4.
Pressure chambers 10, apertures 12, nozzles 8, sub-manifold
channels, etc., as components of the passage unit 4, are
disposed at different levels from one another perpendicularly
to FIGS. 5 and 6 (see FIG. 7).
As shown in FIG. 6, a number of rhombic regions 10x (as
shown by alternate long and short dash lines) are so arranged
adjacent to each other in a matrix in two directions, a first
arrangement direction and a second arrangement direction as
indicated by arrows in FIG. 6, that they do not overlap each
other but share their individual sides. The first arrangement
direction and the second arrangement direction are parallel to
the plane of a trapezoidal ink ejection region, as shown in
FIG. 5. The first arrangement direction is coincident with the
longitudinal direction of the passage unit 4, whereas the
second arrangement direction is coincident with the direction
along one oblique side of the rhombic region 10x. The
pressure chamber 10 has a substantially elliptic planar shape
slightly smaller than the rhombic regions 10x and is
individually housed in the region 10x.
Each of the pressure chambers 10 is connected at its one
end with the nozzle and at its other with the sub-manifold
channel 5a, as will be described in detail. The one end
connected with the nozzle and the other end connected with the
sub-manifold channel 5a in each pressure chamber 10 are
disposed separately at the two ends of the longer diagonal of
each rhombic region 10x. In other words, the direction taken
along the longer diagonal line of the rhombic region 10x
(i.e., the diagonal direction: a first direction) and the
direction joining the one end and the other end of each
pressure chamber 1 (i.e., the two-end direction: a second
direction) are coincident with each other, as shown in FIG. 6.
Of the pressure waves which are generated in the pressure
chamber 10 when a pressure is applied to the pressure chamber
10 by the actuator unit 21, therefore, the pressure wave
propagating in the direction joining the one end and the other
end of the pressure chamber 10 (i.e., the two-end direction:
the second direction) is used as to contribute to the ejection
of ink.
In case the propagating direction of the pressure wave
used for ejection (as will be shortly called the "pressure
wave") is perpendicular to the plane, it is usual that the
planar shape of the pressure chamber 10 is symmetrically with
respect to an origin, such as a circle or a polygon. In case
the propagation direction of the pressure wave is along the
plane of the passage unit 4 as in this embodiment, however,
for elongating the propagation time length of the pressure
waves (i.e., AL: Acoustic Length), it is preferable that the
planar shape of the pressure chamber 10 is slender along the
propagation direction of the pressure waves, i.e., the
direction joining the one end and the other end (i.e., the
two-end direction: the second direction). For this reason,
the planar shape of the pressure chamber 10 shown in FIG. 6 is
elliptical, in which the length in the two-end direction (the
second direction) is longer than the length in the direction
perpendicular thereto.
As shown in FIG. 6, the first arrangement direction and
the second arrangement direction of the matrix arrangement of
the pressure chambers 10 do not intersect at a right angle but
make an acute angle 'theta'. As a result, the spacing between
each of the ink ejection ports 8 in the scanning direction of
the ink-jet head 1 is narrowed. Thus, the image formation of
a high resolution by the printing method described
hereinafter.
FIG. 6 illustrates pairs of individual electrodes 35a and
35b each overlapping the corresponding pressure chamber 10 in
a plan view and having a shape in a plan view similar to that
of the pressure chamber 10 and somewhat smaller than the
pressure chamber 10.
FIG. 7 is a partial sectional view of the head main body
1a of FIG. 4. As apparent from FIG. 7, each ink ejection port
8 is formed at the tip end of a tapered nozzle. Between a
pressure chamber 10 and a sub-manifold channel 5a, an aperture
12 extends substantially in parallel with the surface of the
passage unit 4, like the pressure chamber 10. This aperture
12 is for restricting the ink flow to give the passage a
suitable resistance, thereby achieving the stabilization of
ink ejection. Each ink ejection port 8 communicates with a
sub-manifold channel 5a through a pressure chamber 10 (length:
900 µm, width: 350 µm) and an aperture 12. Thus, within the
ink-jet head 1 formed are ink passages 32 each extending from
an ink tank to an ink ejection port 8 through an ink reservoir
3, a manifold channel 5, a sub-manifold channel 5a, an
aperture 12, and a pressure chamber 10.
When viewing perpendicularly to FIG. 6, the aperture 12
communicating with a pressure chamber 10 is disposed so as to
overlap another pressure chamber 10 neighboring that pressure
chamber 10. A cause making this arrangement possible is that
the aperture 12 is disposed on the sub-manifold channel 5a
side of the pressure chamber 10 with respect to a direction
perpendicular to FIG. 6 and it is provided at the different
level from the pressure chamber 10. Referring to FIG. 7, each
of the pressure chamber 10, the aperture 12, and the sub-manifold
channel 5a is formed within layered sheet members.
In a view perpendicular to the surface of the passage unit 4,
they are disposed so as to overlap one another.
In FIGS. 5 and 6, to make it easy to understand the
drawings, the pressure chambers 10, the apertures 12, etc.,
are illustrated with solid lines though they should be
illustrated with broken lines because they are below the
actuator unit 21.
In the plane of FIGS. 5 and 6, pressure chambers 10 are
arranged within an ink ejection region in two directions,
i.e., a direction along the length of the ink-jet head 1 (a
first arrangement direction) and a direction somewhat
inclining from the width of the ink-jet head 1 (a second
arrangement direction). The first and second arrangement
directions form an angle 'theta' somewhat smaller than the
right angle. The ink ejection ports 8 are arranged at 50 dpi
(dots per inch) in the first arrangement direction. On the
other hand, the pressure chambers 10 are arranged in the
second arrangement direction such that the ink ejection region
corresponding to one actuator unit 21 may include twelve
pressure chambers 10. The shift to the first arrangement
direction due to the arrangement in which twelve pressure
chambers 10 are arranged in the second arrangement direction,
corresponds to one pressure chamber 10. Therefore, within the
whole width of the ink-jet head 1, in a region of the interval
between two ink ejection ports 8 neighboring each other in the
first arrangement direction, there are twelve ink ejection
ports 8. At both ends of each ink ejection region in the
first arrangement direction (corresponding to an oblique side
of the actuator unit 21), the above condition is satisfied by
making a compensation relation to the ink ejection region
corresponding to the opposite actuator unit 21 in the width of
the ink-jet head 1. Therefore, in the ink-jet head 1
according to this embodiment, by ejecting ink droplets in
order through a large number of ink ejection ports 8 arranged
in the arrangement directions A and B with relative movement
of a paper along the width of the ink-jet head 1, printing at
600 dpi in the main scanning direction can be performed.
Next, the construction of the passage unit 4 will be
described in more detail with reference to FIG. 8. Referring
to FIG. 8, pressure chambers 10 are arranged in lines in the
first arrangement direction at predetermined intervals at 500
dpi. Twelve lines of pressure chambers 10 are arranged in the
second first arrangement directions the whole, the pressure
chambers 10 are two-dimensionally arranged in the ink ejection
region corresponding to one actuator unit 21.
The pressure chambers 10 are classified into two kinds,
i.e., pressure chambers 10a in each of which a nozzle is
connected with the upper acute portion in FIG. 8, and pressure
chambers 10b in each of which a nozzle is connected with the
lower acute portion. Pressure chambers 10a and 10b are
arranged in the first arrangement direction to form pressure
chamber rows 11a and 11b, respectively. Referring to FIG. 8,
in the ink ejection region corresponding to one actuator unit
21, from the lower side of FIG. 8, there are disposed two
pressure chamber rows 11a and two pressure chamber rows 11b
neighboring the upper side of the pressure chamber rows 11a.
The four pressure chamber rows of the two pressure chamber
rows 11a and the two pressure chamber rows 11b constitute a
set of pressure chamber rows. Such a set of pressure chamber
rows is repeatedly disposed three times from the lower side in
the ink ejection region corresponding to one actuator unit 21.
A straight line extending through the upper acute portion of
each pressure chamber in each pressure chamber rows 11a and
11b crosses the lower oblique side of each pressure chamber in
the pressure chamber row neighboring the upper side of that
pressure chamber row.
As described above, when viewing perpendicularly to FIG.
8, two first pressure chamber rows 11a and two pressure
chamber rows 11b, in which nozzles connected with pressure
chambers 10 are disposed at different positions, are arranged
alternately to neighbor each other. Consequently, as the
whole, the pressure chambers 10 are arranged regularly. On
the other hand, nozzles are arranged in a concentrated manner
in a central region of each set of pressure chamber rows
constituted by the above four pressure chamber rows.
Therefore, in case that each four pressure chamber rows
constitute a set of pressure chamber rows and such a set of
pressure chamber rows is repeatedly disposed three times from
the lower side as described above, there is formed a region
where no nozzle exists, in the vicinity of the boundary
between each neighboring sets of pressure chamber rows, i.e.,
on both sides of each set of pressure chamber rows constituted
by four pressure chamber rows. Wide sub-manifold channels 5a
extend there for supplying ink to the corresponding pressure
chambers 10. In this embodiment, in the ink ejection region
corresponding to one actuator unit 21, four wide sub-manifold
channels 5a in total are arranged in the first arrangement
direction, i.e., one on the lower side of FIG. 8, one between
the lowermost set of pressure chamber rows and the second
lowermost set of pressure chamber rows, and two on both sides
of the uppermost set of pressure chamber rows.
Referring to FIG. 8, nozzles communicating with ink
ejection ports 8 for ejecting ink are arranged in the first
arrangement direction at regular intervals at 50 dpi to
correspond to the respective pressure chambers 10 regularly
arranged in the first arrangement direction. On the other
hand, while twelve pressure chambers 10 are regularly arranged
also in the second arrangement direction forming an angle
'theta' with the first arrangement direction, twelve nozzles
corresponding to the twelve pressure chambers 10 include ones
each communicating with the upper acute portion of the
corresponding pressure chamber 10 and ones each communicating
with the lower acute portion of the corresponding pressure
chamber 10, as a result, they are not regularly arranged in
the second arrangement direction at regular intervals.
If all nozzles communicate with the same-side acute
portions of the respective pressure chambers 10, the nozzles
are regularly arranged also in the second arrangement
direction at regular intervals. In this case, nozzles are
arranged so as to shift in the first arrangement direction by
a distance corresponding to 600 dpi as resolution upon
printing per pressure chamber row from the lower side to the
upper side of FIG. 8. Contrastingly in this embodiment, since
four pressure chamber rows of two pressure chamber rows 11a
and two pressure chamber rows 11b constitute a set of pressure
chamber rows and such a set of pressure chamber rows is
repeatedly disposed three times from the lower side, the shift
of nozzle position in the first arrangement direction per
pressure chamber row from the lower side to the upper side of
FIG. 8 is not always the same.
In the ink-jet head 1 according to this embodiment, a
band region R will be discussed that has a width (about 508.0
µm) corresponding to 50 dpi in the first arrangement direction
and extends perpendicularly to the first arrangement
direction. In this band region R, any of twelve pressure
chamber rows includes only one nozzle. That is, when such a
band region R is defined at an optional position in the ink
ejection region corresponding to one actuator unit 21, twelve
nozzles are always distributed in the band region R. The
positions of points respectively obtained by projecting the
twelve nozzles onto a straight line extending in the first
arrangement direction are distant from each other by a
distance corresponding to 600 dpi as resolution upon printing.
When the twelve nozzles included in one band region R are
denoted by (1) to (12) in order from one whose projected image
onto a straight line extending in the first arrangement
direction is the leftmost, the twelve nozzles are arranged in
the order of (1), (7), (2), (8), (5), (11), (6), (12), (9),
(3), (10), and (4) from the lower side.
In the thus-constructed ink-jet head 1 according to this
embodiment, by properly driving active layers in the actuator
unit 21, a character, a figure, or the like, having a
resolution of 600 dpi can be formed. That is, by selectively
driving active layers corresponding to the twelve pressure
chamber rows in order in accordance with the transfer of a
print medium, a specific character or figure can be printed on
the print medium.
By way of example, a case will be described wherein a
straight line extending in the first arrangement direction is
printed at a resolution of 600 dpi. First, a case will be
briefly described wherein nozzles communicate with the same-side
acute portions of pressure chambers 10. In this case, in
accordance with transfer of a print medium, ink ejection
starts from a nozzle in the lowermost pressure chamber row in
FIG. 8. Ink ejection is then shifted upward with selecting a
nozzle belonging to the upper neighboring pressure chamber row
in order. Ink dots are thereby formed in order in the first
arrangement direction with neighboring each other at 600 dpi.
Finally, all the ink dots form a straight line extending in
the first arrangement direction at a resolution of 600 dpi.
On the other hand, in this embodiment, ink ejection
starts from a nozzle in the lowermost pressure chamber row 11a
in FIG. 8, and ink ejection is then shifted upward with
selecting a nozzle communicating with the upper neighboring
pressure chamber row in order in accordance with transfer of a
print medium. In this embodiment, however, since the
positional shift of nozzles in the first arrangement direction
per pressure chamber row from the lower side to the upper side
is not always the same, ink dots formed in order in the first
arrangement direction in accordance with the transfer of the
print medium are not arranged at regular intervals at 600 dpi.
More specifically, as shown in FIG. 8, in accordance with
the transfer of the print medium, ink is first ejected through
a nozzle (1) communicating with the lowermost pressure chamber
row 11a in FIG. 8 to form a dot row on the print medium at
intervals corresponding to 50 dpi (about 508.0 µm). After
this, as the print medium is transferred and the straight line
formation position has reached the position of a nozzle (7)
communicating with the second lowermost pressure chamber row
11a, ink is ejected through the nozzle (7). The second ink
dot is thereby formed at a position shifted from the first
formed dot position in the first arrangement direction by a
distance of six times the interval corresponding to 600 dpi
(about 42.3 µm) (about 42.3 µm × 6 = about 254.0 µm).
Next, as the print medium is further transferred and the
straight line formation position has reached the position of a
nozzle (2) communicating with the third lowermost pressure
chamber row 11b, ink is ejected through the nozzle (2). The
third ink dot is thereby formed at a position shifted from the
first formed dot position in the first arrangement direction
by a distance of the interval corresponding to 600 dpi (about
42.3 µm). As the print medium is further transferred and the
straight line formation position has reached the position of a
nozzle (8) communicating with the fourth lowermost pressure
chamber row 11b, ink is ejected through the nozzle (8). The
fourth ink dot is thereby formed at a position shifted from
the first formed dot position in the first arrangement
direction by a distance of seven times the interval
corresponding to 600 dpi (about 42.3 µm) (about 42. 3 µm × 7 =
about 296.3 µm). As the print medium is further transferred
and the straight line formation position has reached the
position of a nozzle (5) communicating with the fifth
lowermost pressure chamber row 11a, ink is ejected through the
nozzle (5). The fifth ink dot is thereby formed at a position
shifted from the first formed dot position in the first
arrangement direction by a distance of four times the interval
corresponding to 600 dpi (about 42.3 µm) (about 42. 3 µm × 4 =
about 169.3 µm).
After this, in the same manner, ink dots are formed with
selecting nozzles communicating with pressure chambers 10 in
order from the lower side to the upper side in FIG. 8. In
this case, when the number of a nozzle in FIG. 8 is N, an ink
dot is formed at a position shifted from the first formed dot
position in the first arrangement direction by a distance
corresponding to (magnification n = N - 1) × (interval
corresponding to 600 dpi). When the twelve nozzles have been
finally selected, the gap between the ink dots to be formed by
the nozzles (1) in the lowermost pressure chamber rows 11a in
FIG. 8 at an interval corresponding to 50 dpi (about 508.0 µm)
is filled up with eleven dots formed at intervals
corresponding to 600 dpi (about 42.3 µm). Therefore, as the
whole, a straight line extending in the first arrangement
direction can be drawn at a resolution of 600 dpi.
FIG. 9 is a partial exploded view of the head main body
1a of FIG. 4. Referring to FIGS. 7 and 9, a principal portion
on the bottom side of the ink-jet head 1 has a layered
structure laminated with ten sheet materials in total, i.e.,
from the top, an actuator unit 21, a cavity plate 22, a base
plate 23, an aperture plate 24, a supply plate 25, manifold
plates 26, 27, and 28, a cover plate 29, and a nozzle plate
30. Of them, nine plates other than the actuator unit 21
constitute the passage unit 4.
As will be described later in detail, the actuator unit
21 is laminated with five piezoelectric sheets and provided
with electrodes so that three of them may include layers to be
active when an electric field is applied (hereinafter, simply
referred to as "layer including active layers") and the
remaining two layers may be inactive. The cavity plate 22 is
made of metal, in which a large number of substantially
rhombic openings are formed corresponding to the respective
pressure chambers 10. The base plate 23 is made of metal, in
which a communication hole between each pressure chamber 10 of
the cavity plate 22 and the corresponding aperture 12, and a
communication hole between the pressure chamber 10 and the
corresponding ink ejection port 8 are formed. The aperture
plate 24 is made of metal, in which, in addition to apertures
12, communication holes are formed for connecting each
pressure chamber 10 of the cavity plate 22 with the
corresponding ink ejection port 8. The supply plate 25 is
made of metal, in which communication holes between each
aperture 12 and the corresponding sub-manifold channel 5a and
communication holes for connecting each pressure chamber 10 of
the cavity plate 22 with the corresponding ink ejection port 8
are formed. Each of the manifold plates 26, 27, and 28 is
made of metal, which defines an upper portion of each sub-manifold
channel 5a and in which communication holes are
formed for connecting each pressure chamber 10 of the cavity
plate 22 with the corresponding ink ejection port 8. The
cover plate 29 is made of metal, in which communication holes
are formed for connecting each pressure chamber 10 of the
cavity plate 22 with the corresponding ink ejection port 8.
The nozzle plate 30 is made of metal, in which tapered ink
ejection ports 8 each functioning as a nozzle are formed for
the respective pressure chambers 10 of the cavity plate 22.
These ten plates 21 to 30 are put in layers with being
positioned to each other to form such an ink passage 32 as
illustrated in FIG. 7. The ink passage 32 first extends
upward from the sub-manifold channel 5a, then extends
horizontally in the aperture 12, then further extends upward,
then again extends horizontally in the pressure chamber 10,
then extends obliquely downward in a certain length to get
apart from the aperture 12, and then extends vertically
downward toward the ink ejection port 8.
Next, the construction of the actuator unit 21 will be
described. FIG. 10 is a lateral enlarged sectional view of
the region enclosed with an alternate long and short dash line
in FIG. 7. Referring to FIG. 10, the actuator unit 21
includes five piezoelectric sheets 41, 42, 43, 44, and 45
having the same thickness of about 15 µm. These piezoelectric
sheets 41 to 45 are made into a continuous layered flat plate
(continuous flat layers) that is so disposed as to extend over
many pressure chambers 10 formed within one ink ejection
region in the ink-jet head 1. Since the piezoelectric sheets
41 to 45 are disposed so as to extend over many pressure
chambers 10 as the continuous flat layers, the individual
electrodes 35a and 35b can be arranged at a high density by
using, e.g., a screen printing technique. Therefore, also the
pressure chambers 10 formed at positions corresponding to the
individual electrodes 35a and 35b can be arranged at a high
density. This makes it possible to print a high-resolution
image. In this embodiment, each of the piezoelectric sheets
41 to 45 is made of a lead zirconate titanate (PZT)-base
ceramic material having ferroelectricity.
Between the uppermost piezoelectric sheet 41 of the
actuator unit 21 and the piezoelectric sheet 42 neighboring
downward the piezoelectric sheet 41, an about 2 µm-thick
common electrode 34a is interposed. The common electrode 34a
is made of a single conductive sheet extending substantially
in the whole region of the actuator unit 21. Also, between
the piezoelectric sheet 43 neighboring downward the
piezoelectric sheet 42 and the piezoelectric sheet 44
neighboring downward the piezoelectric sheet 43, an about 2 µ
m-thick common electrode 34b is interposed having the same
shape as the common electrode 34a.
In a modification, many pairs of common electrodes 34a
and 34b each having a shape larger than that of a pressure
chamber 10 so that the projection image of each common
electrode projected along the thickness of the common
electrode may include the pressure chamber, may be provided
for each pressure chamber 10. In another modification, many
pairs of common electrodes 34a and 34b each having a shape
somewhat smaller than that of a pressure chamber 10 so that
the projection image of each common electrode projected along
the thickness of the common electrode may be included in the
pressure chamber, may be provided for each pressure chamber
10. Thus, the common electrode 34a or 34b may not always be a
single conductive sheet formed on the whole of the face of a
piezoelectric sheet. In the above modifications, however, all
the common electrodes must be electrically connected with one
another so that the portion corresponding to any pressure
chamber 10 may be at the same potential.
Referring to FIG. 10, an about 1 µm-thick individual
electrode 35a is formed on the upper face of the piezoelectric
sheet 41 at a position corresponding to the pressure chamber
10. The individual electrode 35a has a nearly elliptical
shape (length: 850 µm, width: 250 µm) in a plan view similar
to that of the pressure chamber 10, so that a projection image
of the individual electrode 35a projected along the thickness
of the individual electrode 35a is included in the
corresponding pressure chamber 10 (see FIG. 6). Between the
piezoelectric sheets 42 and 43, an about 2 µm-thick individual
electrode 35b having the same shape as the individual
electrode 35a in a plan view is interposed at a position
corresponding to the individual electrode 35a. No electrode
is provided between the piezoelectric sheet 44 and the
piezoelectric sheet 45 neighboring downward the piezoelectric
sheet 44, and on the lower face of the piezoelectric sheet 45.
Each of the electrodes 34a, 34b, 35a, and 35b is made of,
e.g., an Ag-Pd-base metallic material.
The common electrodes 34a and 34b are grounded in a not-illustrated
region. Thus, the common electrodes 34a and 34b
are kept at the ground potential at a region corresponding to
any pressure chamber 10. The individual electrodes 35a and
35b in each pair corresponding to a pressure chamber 10 are
connected to a driver IC 132 through an FPC 136 including
leads independent of another pair of individual electrodes so
that the potential of each pair of individual electrodes can
be controlled independently of that of another pair(see FIGS.
2 and 3). In this case, the individual electrodes 35a and 35b
in each pair vertically arranged may be connected to the
driver IC 132 through the same lead.
In the ink-jet head 1 according to this embodiment, the
piezoelectric sheets 41 to 43 are polarized in their
thickness. Therefore, the individual electrodes 35a and 35b
are set at a potential different from that of the common
electrodes 34a and 34b to apply an electric field in the
polarization, the portions of the piezoelectric sheets 41 to
43 to which the electric field has been applied works as
active layers and the portions are ready to expand or contract
in thickness, i.e., in layers, and to contract or expand
perpendicularly to the thickness, i.e., in a plane, by the
transversal piezoelectric effect. On the other hand, since
the remaining two piezoelectric sheets 44 and 45 are inactive
layers having no regions sandwiched by the individual
electrodes 35a and 35b and the common electrodes 34a and 34b,
they can not deform in their selves. That is, the actuator
unit 21 has a so-called unimorph structure in which the upper
(i.e., distant from the pressure chamber 10) three
piezoelectric sheets 41 to 43 are layers including active
layers and the lower (i.e., near the pressure chamber 10) two
piezoelectric sheets 44 and 45 are inactive layers.
Therefore, when the driver IC 132 is controlled so that
an electric field is produced in the same direction as the
polarization and the individual electrodes 35a and 35b are set
at a positive or negative predetermined potential relative to
the common electrodes 34a and 34b, active layers in the
piezoelectric sheets 41 to 43 sandwiched by the individual
electrodes 35a and 35b and the common electrodes 34a and 34b
contract in a plane, while the piezoelectric sheets 44 and 45
do not contract in themselves. At this time, as illustrated
in FIG. 10, the lowermost face of the piezoelectric sheets 41
to 45 is fixed to the upper face of partitions partitioning
pressure chambers 10 formed in the cavity plate 22, as a
result, the piezoelectric sheets 41 to 45 deform into a convex
shape toward the pressure chamber side by contracting in a
plane by the transversal piezoelectric effect (unimorph
deformation). Therefore, the volume of the pressure chamber
10 is decreased to raise the pressure of ink. The ink is
thereby ejected through the ink ejection port 8. After this,
when the individual electrodes 35a and 35b are returned to the
original potential, the piezoelectric sheets 41 to 45 return
to the original flat shape and the pressure chamber 10 also
returns to its original volume. Thus, the pressure chamber 10
sucks ink therein through the manifold channel 5.
In another driving method, all the individual electrodes
35a and 35b are set in advance at a different potential from
that of the common electrodes 34a and 34b so that the
piezoelectric sheets 41 to 45 deform into a convex shape
toward the pressure chamber 10 side. When an ejecting request
is issued, the corresponding pair of individual electrodes 35a
and 35b is once set at the same potential as that of the
common electrodes 34a and 34b. After this, at a predetermined
timing, the pair of individual electrodes 35a and 35b is again
set at the different potential from that of the common
electrodes 34a and 34b. In this case, at the timing when the
pair of individual electrodes 35a and 35b is set at the same
potential as that of the common electrodes 34a and 34b, the
piezoelectric sheets 41 to 45 return to their original shapes.
The corresponding pressure chamber 10 is thereby increased in
volume from its initial state (the state that the potentials
of both electrodes differ from each other), to suck ink from
the manifold channel 5 into the pressure chamber 10. After
this, at the timing when the pair of individual electrodes 35a
and 35b is again set at the different potential from that of
the common electrodes 34a and 34b, the piezoelectric sheets 41
to 45 deform into a convex shape toward the pressure chamber
10. The volume of the pressure chamber 10 is thereby
decreased and the pressure of ink in the pressure chamber 10
increases to eject ink.
In case that the polarization occurs in the reverse
direction to the electric field applied to the piezoelectric
sheets 41 to 43, the active layers in the piezoelectric sheets
41 to 43 sandwiched by the individual electrodes 35a and 35b
and the common electrodes 34a and 34b are ready to elongate
perpendicularly to the polarization. As a result, the
piezoelectric sheets 41 to 45 deform into a concave shape
toward the pressure chamber 10 by the transversal
piezoelectric effect. Therefore, the volume of the pressure
chamber 10 is increased to suck ink from the manifold channel
5. After this, when the individual electrodes 35a and 35b
return to their original potential, the piezoelectric sheets
41 to 45 also return to their original flat, shape. The
pressure chamber 10 thereby returns to its original volume to
eject ink through the ink ejection port 8.
As described above, in the ink-jet head 1 of this
embodiment, as shown in FIG. 6, the two-end direction (or the
second direction) joining the one end connected with the
nozzle and the other end connected with the sub-manifold
channel 5a of the pressure chamber 10 is substantially
parallel with the plane of the passage unit 4 where the
pressure chambers 10 are arranged. Therefore, the pressure
wave to be generated in the pressure chamber 10 propagates
substantially along the plane of the passage unit 4. In case
the pressure wave propagates in the direction perpendicular to
the plane of the passage unit 4, the AL is shortened so long
as the thickness of the head 1 (i.e., the length of the head 1
in the direction perpendicular to the plane) is not increased.
In case the pressure wave propagates along the surface of the
passage unit 4 as in this embodiment, however, the AL can be
relatively long without increasing the thickness of the head
1. This provides a margin in time for matching the timings of
generation and reflection of the pressure wave, and thus, the
so-called "fill before fire" higher in energy efficiency than
the "fill after fire" can be performed.
The "fill before fire" is a method, in which a voltage is
applied in advance to all the individual electrodes 35a and
35b to reduce the volumes of all pressure chambers 10, in
which the voltage on the individual electrodes 35a and 35b is
released only from the pressure chamber 10 for the ink
ejecting action to enlarge its volume thereby to generate
negative pressure waves, and in which the voltage is applied
again to the individual electrodes 35a and 35b to reduce the
volume of the pressure chambers 10 thereby to superpose the
positive pressure waves at a timing for the negative pressure
waves generated beforehand to reach after inverted and
reflected, so that the ejection pressure is efficiently
applied to the ink by using the pressure waves propagating in
the pressure chambers 10. In short, according to the
aforementioned construction, it is possible to improve the
energy efficiency in the ink-jet head 1.
Moreover, the pressure chamber 10 has the elliptical
planar shape having no corner bulging in the direction to
leave the line joining the one end and the other. Therefore,
the spacing between the adjoining pressure chambers 10 can be
enlarged to suppress the crosstalk which might otherwise raise
a problem in case the pressure chambers 10 are arranged
adjacent to each other.
Moreover, the planar shape of the pressure chamber 10 is
formed into the elliptical shape having no corner as a whole
so that the spacing between the adjoining pressure chambers 10
can be enlarged to suppress the crosstalk which might
otherwise cause a problem in case the pressure chambers 10 are
arranged close to each other. Moreover, the flow of ink is
smoothed, and the discharge of air bubbles in the ink by the
purge is made easy so that the bubbles are hard to accumulate
in the ink. Therefore, it is possible to eliminate the
problem that the normal discharge of ink is obstructed by the
bubbles.
Moreover, the direction along the longer diagonal line of
the rhombic region 10x confining the pressure chamber 10
(i.e., the diagonal direction: the first direction) and the
direction joining the one end and the other of the pressure
chamber 10 (i.e., the two-end direction: the second direction)
are coincident to achieve the high integration of the pressure
chambers 10 and the smooth flow of ink and to enlarge the AL
effectively. As the AL is the larger, moreover, it is the
easier to control the "fill before fire".
Moreover, the effect to enlarge the AL can also be
obtained because the planar shape of the pressure chamber 10
on the surface of the passage unit 4 is slender along the
direction joining the one end and the other (i.e., the two-end
direction: the second direction) or the propagation direction
of the pressure waves.
Moreover, the planar shape of the pressure chamber 10 is
symmetrical with respect to the axis in the propagation
direction of the pressure wave or the direction joining the
one end and the other (i.e., the two-end direction: the second
direction). Therefore, the pressure waves to be generated in
the pressure chamber 10 are symmetrically reflected to provide
an effect that the discharge of ink is stabilized.
Further, since the passage unit 4 is formed with nine
sheet members 22 to 30 laminated each other and each having
corresponding openings, the manufacture of the passage unit 4
is easy.
Further, in the head main body 1a of the ink-jet head 1,
separate actuator units 21 corresponding to the respective ink
ejection regions are bonded onto the passage unit 4 to be
arranged along the length of the passage unit 4. Therefore,
each of the actuator units 21 apt to be uneven in dimensional
accuracy because they are formed by sintering or the like, can
be positioned to the passage unit 4 independently from another
actuator unit 21. Thus, even in case of a long head, the
increase in shift of each actuator unit 21 from the accurate
position on the passage unit 4 is restricted, and both can
accurately be positioned to each other. Therefore, as to even
an individual electrodes 35a and 35b being relatively apart
from a mark, the individual electrodes 35a and 35b can not
considerably be shifted from the predetermined position to the
corresponding pressure chamber 10. As a result, good ink
ejection performance can be obtained and the manufacture yield
of the ink-jet heads 1 is remarkably improved. On the other
hand, differently from the above, if a long-shaped actuator
unit 4 is made like the passage unit 4, the more the
individual electrodes 35a and 35b are apart from the mark, the
larger the shift of the individual electrodes 35a and 35b is
from the predetermined position on the corresponding pressure
chamber 10 in a plan view when the actuator unit 21 is laid
over the passage unit 4. As a result, the ink ejection
performance of a pressure chamber 10 relatively apart from the
mark is deteriorated and thus the uniformity of the ink
ejection performance in the ink-jet head 1 is not obtained.
Further, in the actuator unit 21, since the piezoelectric
sheets 41 to 43 are sandwiched by the common electrodes 34a
and 34b and the individual electrodes 35a and 35b, the volume
of each pressure chamber 10 can easily be changed by the
piezoelectric effect. Besides, since the piezoelectric sheets
41 to 45 are made into a continuous layered flat plate
(continuous flat layers), the actuator unit 21 can easily be
manufactured.
Further, the ink-jet head 1 has the actuator units 21
each having a unimorph structure in which the piezoelectric
sheets 44 and 45 near each pressure chamber 10 are inactive
and the piezoelectric sheets 41 to 43 distant from each
pressure chamber 10 include active layers. Therefore, the
change in volume of each pressure chamber 10 can be increased
by the transversal piezoelectric effect. As a result, in
comparison with an ink-jet head in which a layer including
active portions is provided on the pressure chamber 10 side
and a non-active layer is provided on the opposite side,
lowering the voltage to be applied to the individual
electrodes 35a and 35b and/or high integration of the pressure
chambers 10 can be achieved. By lowering the voltage to be
applied, the driver for driving the individual electrodes 35a
and 35b can be made small in size and the cost can be held
down. In addition, each pressure chamber 10 can be made small
in size. Besides, even in case of a high integration of the
pressure chambers 10, a sufficient amount of ink can be
ejected. Thus, a decrease in size of the head 1 and a highly
dense arrangement of printing dots can be realized.
Further, in the head main body 1a of the ink-jet head 1,
each actuator unit 21 has a substantially trapezoidal shape.
The actuator units 21 are arranged in two lines in a staggered
shape so that the parallel opposed sides of each actuator unit
21 extend along the length of the passage unit 4, and the
oblique sides of each neighboring actuator units 21 overlap
each other in the width of the passage unit 4. Since the
oblique sides of each neighboring actuator units 21 thus
overlap each other, in the length of the ink-jet head 1, the
pressure chambers 10 existing along the width of the passage
unit 4 can compensate each other. As a result, with realizing
high-resolution printing, a small-size ink-jet head 1 having a
very narrow width can be realized.
Here, the planar shape of the pressure chamber on the
passage unit 4 may not be slender along the direction joining
the one end connected with the nozzle and the other end
connected with the sub-manifold channel 5a(i.e., the two-end
direction: the second direction). In this case, however, it
is impossible to expect the high integration of the pressure
chambers.
Moreover, the matrix arrangement direction of the
pressure chambers on the surface of the passage unit 4 may not
be limited to the first arrangement direction and the second
arrangement direction, as shown in FIG. 6, but may take
various directions, as long as it is along the surface of the
passage unit 4.
Moreover, the region for confining the pressure chamber
10 may be a parallelogram but may not be limited to the
rhombic shape. The planar shape of the pressure chamber 10
itself contained in that region may be suitably changed in
various shapes, as long as it is confined in that region and
it is an elliptical shape or a 2n-angled shape (n: a natural
number, n ≥ 3) having no corner bulging in the direction to
leave the line joining the one end and the other. For
example, a modification of the planar shape of the pressure
chamber is shown in FIG. 11A and FIG. 12A. In FIG. 11A, a
first modification is exemplified by a pressure chamber 60
having a substantially hexagonal planar shape, in which the
corners corresponding to the obtuse portions of a rhombic
region 60x are cut off substantially in parallel to the
direction joining the one end and the other of the pressure
chamber 10 (i.e., the two-end direction: the second
direction). In FIG. 12A, a second modification is exemplified
by a pressure chamber 70 having a substantially elliptical
planar shape more slender than that of the aforementioned
embodiment along the direction joining the one end and the
other of the pressure chamber 10 (i.e., the two-end direction:
the second direction). Each of individual electrodes 65a and
65b and individual electrodes 75a and 75b has respectively a
substantially hexagonal shape and a elliptical shape, which is
substantially similar to and slightly smaller than the
pressure chambers 60 and 70. Here, FIGS. 11A and 11B and
FIGS. 12A and 12B show neither a nozzle connected with the one
end of the pressure chamber 60 nor a sub-manifold channel
connected with the other end of the pressure chamber 60.
However, a nozzle and a sub-manifold channel are formed
respectively at the two ends on the longer diagonal line of
rhombic region 60x and 70x. Each of the arrows in FIGS 11A and
11B shows the propagation direction of the pressure wave.
FIG. 11B and FIG. 12B show the states, in which the
pressure chambers 60 and 70 according to the first and second
modifications illustrated in FIG. 11A and 12B are arranged in
a 3 x 3 matrix, respectively. when the pressure chambers 60
having a substantially hexagonal plane according to the first
modification are arranged in the matrix, as shown in FIG. 11B,
the spacing, as taken in the direction parallel to the shorter
diagonal line of the rhombic region 60x, between the adjoining
pressure chambers 60 and 60 is designated by d1. Likewise,
the aforementioned spacing in the pressure chambers 70 having
the substantially elliptical plane according to the second
modification and arranged in the matrix shown in FIG. 12B is
designated by d2. It will be understood that the spacing
between the adjoining pressure chambers is larger than that of
the case in which the individual pressure chambers have shapes
similar to and slightly smaller than those of the rhombic
regions 60x and 70x. With this enlarged spacing, such a
crosstalk hardly occurs as might otherwise raise a problem in
case the pressure chambers are arranged close to each other.
Particularly for the pressure chambers 60 according to
the first modification, as shown in FIGS. 11A and 11B, the
spacing between the pressure chambers 60 arranged in the
matrix can be efficiently enlarged by cutting off the corners
substantially in parallel to the direction joining the one end
and the other end of the pressure chambers 60 (i.e., the two-end
direction: the second direction). In other words, the
spacing between the pressure chambers 60 can be enlarged to
suppress the crosstalk without drastically reducing the area
of the pressure chambers 60. Moreover, the pressure chambers
60 have a relatively simple planar shape such as the
substantially hexagonal shape, so that they can be formed
relatively easily.
Moreover, the planar shape of the pressure chambers may
also be a pentagonal, decagonal or deformed elliptical shape,
for example.
Further, the passage unit 4 may not be formed with
laminated sheet members.
Further, the material of each of the piezoelectric sheets
and electrodes is not limited to those described above, and it
may be changed to another known material. Each of the
inactive layers may be made of an insulating sheet other than
a piezoelectric sheet. The number of layers including active
layers, the number of inactive layers, etc., may be changed
properly. For example, although piezoelectric sheets as
layers including active layers included in an actuator unit 21
are put in three or five layers in the above-described
embodiment, piezoelectric sheets may be put in seven or more
layers. In this case, the numbers of individual and common
electrodes may properly be changed in accordance with the
number of layered piezoelectric sheets. Although each
actuator unit 21 includes two layers of piezoelectric sheets
as inactive layers in the above-described embodiment, each
actuator unit 21 may include only one inactive layer.
Alternatively, each actuator unit 21 may include three or more
inactive layers as far as they do not hinder the expansion or
contraction deformation of the actuator unit 21. Although
each actuator unit 21 of the above-described embodiment
includes inactive layers on the pressure chamber side of
layers including active layers, a layer or layers including
active layers may be disposed on the pressure chamber 10 side
of the inactive layers. Alternatively, no inactive layer may
be provided. However, by providing the inactive layers 44 and
45 on the pressure chamber 10 side of the layers including
active layers, it is expected to further improve the
deformation efficiency of the actuator unit 21.
Further, although the common electrodes are kept at the
ground potential in the above-described embodiment, this
feature is not limitative. The common electrodes may be kept
at any potential as far as the potential is in common to all
pressure chambers 10.
Further, in the above-described embodiment, as
illustrated in FIG. 4, trapezoidal actuator units 21 are
arranged in two lines in a staggered shape. But, each
actuator unit may not always be trapezoidal. Besides,
actuator units may be arranged in a single line along the
length of the passage unit. Alternatively, actuator units may
be arranged in three or more lines in a staggered shape.
Further, not one actuator unit 21 is disposed to extend over
pressure chambers 10 but one actuator unit 21 may be provided
for each pressure chamber 10.
Further, a large number of common electrodes 34a and 34b
may be formed for each pressure chamber 10 so that a
projection image of the common electrodes in the thickness of
the common electrodes includes a pressure chamber region or
the projection image is included within the pressure chamber
region. Thus, each of the common electrodes 34a and 34b may
not always be made of a single conductive sheet provided in
the substantially whole region of each actuator unit 21. In
such a case, however, the parts of each common electrode must
be electrically connected with one another so that all the
parts corresponding to the respective pressure chambers 10 are
at the same potential.