Ink jet recording head utilizing a vibration plate having diaphragm portions and thick wall portions

An ink jet recording head formed by laminating and fixing: a flow path forming plate having through holes for defining pressure producing chambers, ink supply inlets, and a common ink chamber, a nozzle plate having nozzle openings communicating with the pressure producing chambers, and a vibration plate having diaphragm portions that are resiliently deformed in response to displacement of piezoelectric vibration elements one upon another with an adhesive so as to be watertight. The vibration plate has frame-like thick wall portions that extend as far as to the ink supply inlet side of the pressure producing chamber as well as to the inner side of the nozzle opening, and portions closer to a piezoelectric vibration element than to both ends of the pressure producing chamber are made to be supported by a base. As a result of this construction, a nonsupported region of the pressure producing chamber can be shortened, which in turn improves the rigidity of a substrate unit as a whole.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an ink jet recording head that jets droplets of 
ink by contracting a vibration plate using piezoelectric vibration 
elements of vertical vibration mode, the vibration plate constituting 
pressure producing chambers that communicate with nozzle openings and a 
common ink chamber. 
2. Related Art 
An ink jet recording head using a piezoelectric vibration element of 
vertical vibration mode as a drive source, requiring only a small area of 
abutment of the piezoelectric vibration element against the vibration 
plate, can achieve an arrangement density of a pressure producing chamber 
as high as 90 dpi or more. 
As shown in FIG. 14, such a recording head is fabricated into a single body 
by integrally fixing a substrate unit K to a base L. The substrate unit K 
is formed by laminating and fixing a flow path forming plate D, a nozzle 
plate F, and a vibration plate J with an adhesive so as to be watertight. 
The base L has a piezoelectric vibration element G, an ink supply pipe, 
and the like attached thereto. The flow path forming plate D has through 
holes defining a pressure producing chamber A, an ink supply inlet B, and 
a common ink chamber C; the nozzle plate F has a nozzle opening E 
communicating with the pressure producing chamber A; and the vibration 
plate J has a diaphragm portion H that is resiliently deformed in response 
to displacement of the piezoelectric vibration element G. 
In the thus constructed ink jet recording head, the substrate unit must be 
fixed to the base so as to cause the diaphragm portion H to confront the 
base so that the diaphragm portion H can be abutted against the tip of the 
piezoelectric vibration element G. For this reason, the substrate unit is 
fixed to the base L so as to keep away from the pressure producing chamber 
A so that the base L does not come in contact with the diaphragm portion 
H. 
To improve the pressure producing chamber arrangement density in an attempt 
to increase resolution, the length of the pressure producing chamber A 
must be increased in the axial direction since a predetermined capacity of 
the pressure producing chamber A must be ensured. However, the region 
confronting the pressure producing chamber A is a nonsupported region S1 
that is not supported by the base L, and this region is long. As a result, 
when such region is given a predetermined displacement "a" by the 
piezoelectric vibration element G to jet a droplet of ink, the 
nonsupported region S1 of the substrate unit K becomes susceptible to 
flexion as shown by the broken lines in FIG. 14, thereby imposing the 
problem of impairing printing quality. 
In addition, positional accuracy of the abutment of the tip of the 
piezoelectric vibration element G is an extremely important factor for 
such a high resolution. Therefore, to achieve the required accuracy, an 
island portion M, which is a thick wall portion formed almost in the 
middle of a region causing deformation of the pressure producing chamber, 
is formed, and the tip of the piezoelectric vibration element G is abutted 
against such island portion M, as disclosed in Japanese Unexamined Patent 
Publication No. 3-15555. 
This construction allows the displacement of the piezoelectric vibration 
element G to be transmitted through the island portion M even if the 
position of abutment of the piezoelectric vibration element G is slightly 
shifted. Therefore, a predetermined displacement can be given to the 
diaphragm portion H. 
However, for such an extremely high resolution as 180 dpi or more, 
inaccuracies in relative position between the island portion M and the 
pressure producing chamber A occur easily, causing the pressure producing 
chamber A to be deformed inconsistently, thereby giving rise to the 
problem of impaired printing quality. 
Further, to reduce the pitch of the pressure producing chamber A, the 
partition wall defining the pressure producing chamber A becomes thin, 
which in turn reduces rigidity. As a result, one pressure producing 
chamber is deformed by contraction and expansion of a piezoelectric 
vibration element that drives another pressure producing chamber adjacent 
to such one pressure producing chamber, causing a so-called satellite. 
Moreover, the degree of deformation of the pressure producing chamber by 
the expansion of the piezoelectric vibration element is reduced, thereby 
imposing the problem of dropping ink jetting efficiency. 
SUMMARY OF THE INVENTION 
The invention has been made in consideration of the aforementioned problems 
and an object of the invention is, therefore, to provide an ink jet 
recording head in which the nonsupported region of the pressure producing 
chamber is made as short as possible so as to increase the rigidity of the 
substrate unit. 
Another object of the invention is to provide a novel ink jet recording 
head capable of reducing the effect of fabrication inaccuracies upon 
printing quality to the smallest possible degree. 
To achieve the above objects, the invention is applied to an ink jet 
recording head formed by fixing a substrate unit to a base, the substrate 
unit being formed by laminating and fixing a flow path forming plate, a 
nozzle plate, and a vibration plate with an adhesive so as to be 
watertight, the flow path forming plate having through holes defining 
pressure producing chambers, ink supply inlets, and a common ink chamber, 
the nozzle plate having nozzle openings communicating with the pressure 
producing chambers, and the vibration plate having diaphragm portions, 
each diaphragm portion being resiliently deformed in response to 
displacement of a piezoelectric vibration element. In such ink jet 
recording head, the vibration plate has a frame-like thick wall portion 
formed close to a side of the ink supply inlet of the pressure producing 
chamber and to a side of the nozzle opening, the thick wall portion being 
thicker than the diaphragm portion and extended so as to be island-like 
toward the piezoelectric vibration element, and a region confronting the 
frame-like thick wall portion is made to serve as a region for bonding the 
substrate unit to the base. 
The frame-like thick wall portion extending toward the piezoelectric 
vibration element is supported by the base. As a result of this 
construction, the nonsupported region of the pressure producing chamber 
can be made as short as possible, which in turn allows the base to receive 
force applied by the piezoelectric vibration element and thereby increases 
the rigidity of the substrate unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Details of the invention will now be described with reference to the 
embodiments shown in the drawings. 
FIG. 1 shows the general aspect of a recording head of the invention. In 
FIG. 1 reference numeral 2 denotes a nozzle plate having nozzle openings 1 
formed therein; 3, a flow path forming plate having through holes 3a 
defining pressure producing chambers 9, through holes or grooves 3b 
defining ink supply inlets 10, and a through hole 3d defining a common ink 
chamber formed therein; and 4, a vibration plate that is resiliently 
deformed while abutted against the tips of piezoelectric vibration 
elements 6. A substrate unit 5 is formed by fixing the nozzle plate 2 and 
the vibration plate 4 to both surfaces of the flow path forming plate 3 so 
as to be watertight. 
Reference numeral 7 denotes a base into which the piezoelectric vibration 
elements 6 are inserted so that the piezoelectric vibration elements can 
vibrate therein. The ink jet recording head is fabricated into a single 
body by fixing the piezoelectric vibration elements 6 and the substrate 
unit 5 with the vibration plate 4 abutted against the tips of the 
piezoelectric vibration elements 6 exposed from openings of the base. It 
should be noted that reference numeral 12 in FIG. 1 denotes an ink supply 
pipe for supplying ink from a not shown ink tank to the substrate unit 5, 
reference numeral 7a denotes a mount for the elements 6, and 8 denotes the 
overall base unit. 
FIG. 2 shows an embodiment of the piezoelectric vibration element 6. A 
plurality of layers, each being formed by interposing a piezoelectric 
material layer 60 between electrode layers 61, 62, are laminated one upon 
another to form a laminated member. Ends of the electrode layers 61 and 
ends of the electrode layers 62 are exposed to ends of the laminated 
member so as to be connected to a segment electrode 63 and a common 
electrode 64, respectively, so that the piezoelectric vibration element 6 
can expand and contract in directions parallel with the electrode layers 
61, 62. 
FIG. 3 is a diagram showing how the substrate unit 5 and the piezoelectric 
vibration elements 6 are mounted. The nozzle plate 2 and the vibration 
plate 4 bracket the flow path forming plate 3 and are fixed to both 
surfaces of the flow path forming plate 3 with an adhesive so as to be 
watertight, so that the pressure producing chambers 9 are formed so as to 
extend along the arrays of the nozzle openings 1. 
On the other hand, in the vibration plate 4 an island portion 4a is formed 
so as to be positioned almost in the middle of a region confronting the 
corresponding pressure producing chamber 9, and a first thick wall portion 
4b, and second and third thick wall portions 4c, 4d are also formed. The 
island portion is abutted against the tip of the piezoelectric vibration 
element 6. The first thick wall portion 4b is formed so as to confront a 
partition wall 3c partitioning the adjacent pressure producing chambers 9 
and either coincide with the boundary of the pressure producing chamber 9 
or slightly overhang the pressure producing chamber 9 as shown in FIG. 5. 
The second and third thick wall portions 4c, 4d are formed so as to 
slightly overhang both ends of the pressure producing chamber 9. A region, 
which is a thin wall portion surrounded by the first, second, and third 
thick wall portions 4b, 4c, 4d, is defined as a diaphragm portion 4e. The 
diaphragm portion 4e is deformed by the piezoelectric vibration element 6. 
If the diaphragm portion 4e is formed to a size smaller than the opening of 
the pressure producing chamber 9, so that the thick wall portions 4b, 4c, 
4d of the vibration plate 4 overhang the pressure producing chamber 9, 
then the first thick wall portion 4b overhangs the pressure producing 
chamber 9 by .DELTA.L1 from the wall 3c defining the pressure producing 
chambers (FIG. 5), and the second and third thick wall portions 4c, 4d 
also overhang the pressure producing chamber by .DELTA.L2 in the 
vicinities of both ends of the pressure producing chamber (FIG. 6). 
Let us take a specific example, in which the width W1 of the pressure 
producing chamber 9 is set to 200 .mu.m; the width W2 of the partition 
wall 3c is set to 80 .mu.m; and the width W3 of the first thick wall 
portion 4b is set to 140 .mu.m. Then, an overhanging length .DELTA.L1 of 
30 .mu.m can be provided in the case where the flow path forming plate 3 
and the vibration plate 4 are bonded to each other with the center line of 
the pressure producing chamber 9 aligned with that of the island portion 
4a. 
As a result, when the diaphragm portion 4e is positioned so as to confront 
the pressure producing chamber 9 with a positioning error .DELTA.L3 
between the flow path forming plate 3 and the vibration plate 4 being 
equal to, e.g., 20 .mu.m as shown in FIG. 7, an adhesive P overflow region 
.DELTA.L4 of as large as 10 .mu.m can be provided. As a result, even if 
the adhesive P overflows from the partition wall 3c, such overflown 
adhesive P is absorbed by the first, second, and third thick wall portions 
4b, 4c, 4d to thereby block the adhesive P from further overflowing to the 
diaphragm portion 4e, which in turn allows the diaphragm portion 4e to 
maintain a consistent resilient characteristic. 
That is, if the vibration plate 4 and the flow path forming plate 3 are 
misaligned with the thick wall portion 4b formed so as to coincide with 
the width of the partition wall 3c of the pressure producing chamber 9, 
the adhesive P overflows into the diaphragm portion 4e (as shown in FIGS. 
13(A) and 13(B)), making the vibration characteristic of the diaphragm 
portion 4e erratic. 
In general, when the width W3 of the first thick wall portion 4b 
confronting the partition wall 3c is increased by about 5 to 50% with 
respect to the width W2 of the partition wall 3c defining the adjacent 
pressure producing chambers 9, fabrication errors can be absorbed, and the 
ink jetting performance can therefore be maintained consistent. 
On the other hand, the diaphragm portion 4e is defined by the frame-like 
second and third thick wall portions 4c, 4d, whose thicknesses are 
substantially the same as that of the island portion 4a, as well as by the 
first thick wall portion 4b, which is integrally formed with the second 
and third thick wall portions and extends in parallel with the partition 
wall 3c of the pressure producing chamber 9. As a result, the partition 
wall 3c defining the pressure producing chamber 9 is reinforced not only 
by the nozzle plate 2 but also by the first thick wall portion 4b of the 
vibration plate 4, which in turn increases the rigidity of the substrate 
unit 5 as a whole with respect to the displacement of the piezoelectric 
vibration element 6. Hence, the flexion of the substrate unit 5 at the 
time the ink is jetted can be minimized, thereby preventing crosstalks. 
Further, as shown in FIG. 8, the second and third thick wall portions 4c, 
4d formed on both ends of the pressure producing chamber 9 extend toward 
the piezoelectric vibration element 6 so as to go along with the partition 
wall 3c of the pressure producing chamber 9, and the extended regions (the 
dotted regions in FIG. 3) are supported by the base 7 while fixed to the 
base 7 with the adhesive. Therefore, a nonsupported region S2 can be 
rendered shorter than the nonsupported region S1 (FIG. 14) in the 
conventional example, making flexion of the substrate unit 5 due to 
displacement of the piezoelectric vibration element 6 less. 
The vibration plate 4 may be formed by electroforming nickel, chromium, or 
the like (for forming the island portion 4a and the thick wall portions 
4b, 4c, 4d) on a high molecular film such as polyimide, polysulfone, 
polycarbonate, polyetherimide, polyethylene, polyalamide, or polyester; or 
by laminating the high molecular film on a metal film such as nickel, 
chromium, stainless steel, gold, silver, copper, or titanium by casting or 
the like and etching the metal film so as to match the profiles of the 
island portion 4a and the thick wall portions 4b, 4c, 4d; or by using a 
metal film such as silicon, nickel, chromium, stainless steel, or titanium 
and partially etching a region for forming the diaphragm portion 4e. 
A 40 .mu.m-thick stainless steel film and a 3 .mu.m-thick polyimide film 
were laminated by bonding, and the stainless steel film was etched to 
prepare the vibration plate 4 in this particular embodiment. 
FIG. 9 shows a second embodiment of the invention. The second embodiment is 
characterized as causing only portions close to both ends of the pressure 
producing chamber 9 (regions A, B in FIG. 9) of the first thick wall 
portion formed on the vibration plate 4 to overhang the pressure producing 
chamber, and causing the width of a region (a region C in FIG. 9) of the 
first thick wall portion confronting the island portion 4a to coincide 
with the width of the partition wall 3c defining the pressure producing 
chamber 9. 
According to the second embodiment, the area of the diaphragm portion 4e 
can be increased only if accuracy in aligning the vibration plate 4 with 
the flow path forming plate 3 is improved. In addition, the region fixed 
by the base 7 can be made as large as possible, i.e., the nonsupported 
region S2 can be shortened to reduce flexion of the substrate unit 5. 
FIG. 10 shows a third embodiment of the invention. The third embodiment is 
characterized as extending those portions of the second and third thick 
wall portions 4c, 4d that are close to both ends of the pressure producing 
chamber 9 to form peninsulas extending out to both ends of the island 
portion 4a (regions A, B in FIG. 10), and replacing the first thick wall 
portion 4b with a thin wall portion 4f. According to the third embodiment, 
the region supported by the base 7 is made as long as possible to reduce 
flexion of the substrate unit 5. If the adhesive for bonding the substrate 
unit 5 to the base 7 is applied by transferring, the region to which the 
adhesive is applied can be limited within the semiisland-like thick wall 
portions, thereby preventing the adhesive for fixing the base 7 from 
overflowing as far as to the diaphragm portion 4e. 
In this embodiment, a bonding process between the base 7 and the thick wall 
portions 4c and 4d is performed at a region defined between an inner side 
of the pressure producing chamber 9 and outer sides of both ends of the 
island portion 4a in order to prevent the base 7 and the island portion 4a 
from contacting each other by a vibration of the vibration plate 4 when 
the ink expelling operation is performed. 
FIG. 11 shows a fourth embodiment of the invention. The fourth embodiment 
is characterized as forming the first thick wall portion 4b in a region (a 
region C in FIG. 11) confronting the island portion so as to be continuous 
to the aforementioned semi-island-like second and third thick wall 
portions 4c, 4d so that the width of the first thick wall portion 4b is 
slightly smaller than that of the partition wall 3c. 
According to the fourth embodiment, not only is the rigidity of the 
substrate unit as a whole improved and the area of the diaphragm portion 
4e made as large as possible, but also the region supported by the base 7 
can be increased to prevent flexion of the substrate unit 5. 
While the aforementioned embodiments have been described as using 
piezoelectric vibration elements having a vertical vibration mode as their 
drive source, piezoelectric vibration elements of flexion vibration mode 
may also be used. 
That is, as shown in FIG. 12, a piezoelectric vibration element 20 of 
flexion vibration mode is bonded onto the surface of the diaphragm portion 
4e defined by the thick wall portions 4b, 4c, 4d so as not to come in 
contact with the thick wall portions 4b, 4c, 4d. The island portion 4a is 
not formed. As a result of this construction, the diaphragm portion 4e is 
contracted to thereby contract a pressure producing chamber 23 formed of a 
flow path forming plate 21, a second cover plate 24, and a vibration plate 
4, which in turn causes ink to be jetted out of a nozzle opening 22 
communicating with the pressure producing chamber 23. In this embodiment 
also, the propagation of vibrations to the adjacent pressure producing 
chambers 23 can be prevented by the thick wall portions 4b, 4c, 4d. It 
should be noted that reference numeral 25 denotes an ink supply inlet. 
As described in the foregoing, the ink jet recording head of the invention 
is formed by fixing a substrate unit to a base, the substrate unit being 
formed by laminating and fixing a flow path forming plate, a nozzle plate, 
and a vibration plate with an adhesive so as to be watertight, the flow 
path forming plate having through holes defining pressure producing 
chambers, ink supply inlets, and a common ink chamber, the nozzle plate 
having nozzle openings communicating with the pressure producing chambers, 
the vibration plate having diaphragm portions, each diaphragm portion 
being resiliently deformed in response to displacement of a piezoelectric 
vibration element, and in such ink jet recording head, the vibration plate 
has frame-like thick wall portions formed close to a side of the ink 
supply inlet of the pressure producing chamber and to a side of the nozzle 
opening, the thick wall portions being thicker than the diaphragm portion 
and extended so as to be island-like toward the piezoelectric vibration 
element, and a region confronting the frame-like thick wall portions is 
made to serve as a region for bonding the substrate unit to the base. As a 
result of this construction, the nonsupported region of the pressure 
producing chamber can be shortened without disturbing the displacement of 
the diaphragm portion, which in turn reduces flexion of the substrate unit 
attributable to displacement of the piezoelectric vibration element.