Note: Descriptions are shown in the official language in which they were submitted.
-l- 1133~73
METHOD OF MAKING INK JE'r PRINT HEAD
Background of the Invention
-
In the field of ink jet printers and especially
in the matter of multiple~nozzle print heads, there has
been a problem in maintaining the ink conduits or
passaqeways in precise position and of keeping such
conduits or passageways sealed or separated from each
other in the areas of intake of the ink and of the
nozzle portion of the print head. The difficulty of
sealing the conduits from each other in the vicinity of
the nozzles is apparent from the close proximity of the
nozzles which allows or provides only a very small
sealing area.
One method of making an ink jet print head
has included a plastic casting wherein the resin or
like material is cast at room temperature and under
sufficiently high pressure to attempt to minimize the
presence of air bubbles which may cause pockets or
uneven surfaces for passage of the ink fluid.
Another method has included the use of elevated
heat temperatures and pressures in the plastic molding,
however, it has been found difficult to maintain precise
position of the parts in the mold itself.
Prior art which is representative of the
production of ink jet print heads includes British
Specification No. 1,355,915 and German Specification No.
2,164,614, which disclose that it is possible to replace
the drive elements in the print head, but with no indi-
cation in the disclosure as to how the print heads can
be produced in a simple and economic manner.
German Specification No. 2,532,Q37 discloses a
multiple nozzle ink jet print head produced through use
of ceramic plates with etching of the necessary cavities
and channels therein. Such type of print head production
however appears to be very complicated and involve
high costs, so that the disclosed method would ordinarily
be unsuitable for mass production.
~ .
673
--2--
German Specification No. 2,543,451, corres-
ponding to U.S. Patent 4,158,847, shows a piezoelec-
trically operated print head for ink printing devices
which is made of plastic in a casting procedure. Pro-
tective tubes which serve as inner electrodes are inser-
ted into ceramic tubes which serve as drive elements
Eor the print head and metal rods are then inserted into
the tubes which extend from a fluid supply cavity to
the ejection nozzles. When the plastic casting has
hardened, the metal rods are removed and the tubes act
as channels or conduits for the ink. This structure has
the disadvantage that at least a portion of the drive
element is not accessible and cannot be replaced if
found defective.
Summary of the Invention
The present invention relates to ink jet
print heads and more particularly to a method for
producing a multiple nozzle ink jet print head.
In accordance with the present invention,
there is provided a method of making an ink jet print
head comprising the steps of providing an open end mold
having an inner shape corresponding to the print head
to be cast, covering the open end of said mold with a
member having an inclined inner portion and a plurality
of apertures spaced therearound, inserting stud members
having stem portions into said apertures to cause said
stem portions to extend within said mold and terminate
along a plane spaced from the bottom thereof, each of
said stud members having a shape to form a cavity for
receipt of an ink drive element, inserting pin members
at an angle into the side of said mold to reach the low-
er portion of said stud members, filling the mold with
hardenable casting material to form the print head,
forming nozzles by boring holes in an alignment perpen-
dicular to said mold bottom plane for enabling ejectingdroplets of ink from said print head, and removing
~33673
-2a-
the stud members and the pin members to provide cavities
for insertion of said ink drive elements and to provide
passageways for flow of ink therethrough.
A mold or pattern having an inner shape of a
desired print head structure is fitted with a cover of
inverted dish-shape configuration having a plurality
of threaded holes therein which are positioned and
spaced from each other to provide a circular arrange-
ment whereby stud elements may be inserted into the
holes in a direction positioning the axis of the stud
elements toward the center of the mold and along a plane
near the lower end thereof. The stud elements include a
threaded body portion having a rod or stem secured there-
to and extending therefrom to a plane near the lower
end of the mold. A small aperture is provided from the
end of each rod or stem, such rod being spaced or main-
tained at a small distance from the lower edge of the
mold. The end of each rod or stem is conical-shaped
so as to fit with an associated aperture and to provide
a decreasing diameter channel or opening for pas~age of
drops of ink. A plurality of rods or pins are inserted
through the side walls of the mold or pattern to engage
with a portion of the threaded elements.
i
~133673
--3--
When the moldin(7 mate~ial injected into the
mold or pattern has hardened and set, the stud elements,
i.e. threade~ body portions along with the stems or
rods secure~ thereto, are removed from the mold and provide
voids forminq channels or ducts for carrying ink from
the drive elements to the nozzles of the print head.
The inserted rods or pins are also removed from the
side walls of the mold to form channels or ducts for
the ink supply to the drive elements. The drive elements
for ejecting the droplets of ink from the print head noz-
zles are then inserted or installed in each of the
voids formed by the stud element and the required elec-
trical wires are connected to the drive elements.
In view of the above discussion, the principal
object of the present invention is to provide a method
of making a multiple-nozzle ink jet print head in a
simple and economical manner.
Another object of the present invention is to
provide a mold or pattern for making a multiple-nozæle
ink jet print head wherein the mold includes a plurality
of parts which are precisely positioned therein and
removable therefrom for providing a number of ink-
carrying channels.
An aaditional object of the present invention ;
is to provide a method of making a multiple-nozzle ink
jet print head wherein the cover portion of the mold
receives a plurality of elements which are adjustably
attached to the cover portion for enabling an accurate
alignment of remote ends of the elements for locating
ink jet nozzles.
A further object of the present invention is
to provide a method of making a multiple-nozzle ink jet
print head wherein a plurality of elements are utilized
for forming channels and passageways within a mold and
upon hardening of the molding material, all the elements
are removed from the mold to leave channels therein for
passage of ink and to position drive elements for
.
~133673
--4--
driving ink from a supply cavity to droplet producing
nozzles.
Additional advantages and features of the
present invention will become apparent and fully understood
~rom a reading of the following description taken
together with thê annexed drawing.
Brief Description of the Drawing
Fig. 1 is a plan view of a mold or pattern
used for ~he performance of the method according to the
present inventiont
Fig. 2 is a sectional view of the mold taken
along the line 2-2 of Fig. 1:
Fig. 3 is a sectional view showing ink passage-
ways for one nozzle of a multiple-nozzle ink jet print
head as produced by means of the mold according to
Figs. 1 and 2;
Fig. 4 is an enlarged sectional view of that
portion of the print head of Fig. 3 including associated
ink drive elements as arranged according to the present
invention;
Fig. 5 is a sectional view of a portion of a
print head showing a second embodiment of the present
invention; and
Fig. 6 is a sectional view of a portion of a
print head showing a third embodiment of the present
invention.
Description of the Preferred Embodiment
Referring to Figs. 1 and 2, which respectively
show a plan view and a sectional view of a mold or
hollow form for use in making a multiple-nozzle ink jet
print head according to the present invention, and in which
corresponding parts are provided with the same reference
numbers, there is shown a mold 10 having a cylindrical
outer shape and defining a molding cavity 12 which is a
determining factor in selecting the shape of the print
.
.,' , ~ ,
.
.:
,
_5_ ~33673
head to be produced. In the preferred embodiment of the
present invention, such cavity 12 is in the form of a
frustum or cone which shape facilitates easy removal of
a print head after the hardening of the molding material.
S ~ cover portion 14 is provided to fit over the upper
open portion of the mold 10, such cover portion having
a dish-like shape with sloping or slanting sides to provide
an inclined inner form and of a size to fit beyond the
edge of the cavity 12. The cover portion 14 has on its
slanting or sloping sides preferably a plurality of
circular openings 16 which are arranged in a circle and
which receive the stud or like pluq elements necessary
for the production or forming of ink supply channels.
In the embodiment according to Figs. 1 and 2, the
openings 16 are tapped to screw-threadedly receive the
stud or plug elements 18, 20, 22, 24, 26, 28 and 30. The
elements 18 through 30 include reduced diameter portions
32, 34, 36, 38, 40, 42 and 44, although portions 40, 42
and 44 are not shown in Fig. 2, and are each provided
20 with threads so that they can be precisely positioned '
in the cavity 12 of the mold 10 by turning or rotating
same into the threaded holes 16 of the covered portion
14.
The seven studs elements 18 through 30 provide
capillary ink cavities as well as drive element receiving
cavities or bores for the production of a multiple-
nozzle ink jet print head with the details of the
cavities being later described. In addition, the stud
elements can be precisely positioned with respect to
the cover 14 and with ink inlet and outlet channels in
the mold 10.
A plurality of ink inlet channels are provided
by inserting rods or pins 46, 48, 50, 52, 54, 56 and 58
through appropriate openings in the sides of the mold
10 and extending to positions in the molding cavity 12
whereat the ends of the rods or pins are adjacent and
engage with the reduced diameter portions 32 through 44
-6- ~3~673
of the threaded stud elements 18 through 30. In addition
to the reduced diameter portions 32 through 44 of the
threaded stud elements or members 18 through 30 for
providing the capillary ink cavities, each of such
reduced diameter portions has a stem in the form of a
rod secured thereto and identified by the stems 60, 62,
64, 66, 68, 70 and 72, which stems project downwardly
into the mold cavity 12 to terminate at a precise
distance from the bottom of such cavity 12. The slope
of the openings 16 in the cover portion 14 thus provide
the precise angular location of each of such stems 60
through 72 within the mold cavity 15, while the threads
thereof permit axial adjustment of such stems 60 through
72 with respect to the bottom of such mold cavity. Es-
sentially, the apertures or openings 16 in the cover
portion 14 are provided to permit placing of the stud
elements 18-30 therein so that the terminal ends of the
stem portions 60-72 are in a straight plane adjacent the
bottom of the mold 10.
The slope of the frustum-like cover portion
14 is chosen so that the direction of the stems 60
through 72 in the cavity 12 i5 determined in such a
manner that therefrom results the desired run or path
of the nozzle channels produced in the print head, as
illustrated in Fig. 3. The threaded holes 16 in the
cover portion 14 further extend in a suitable direction
with tips 74, 76, 78, 80, 82, 84 and 86 of the respective
stems 60 through 72 of the studs elements being conical-
shaped and directed to form a line adjacent the bottom
of the molding cavity 12 and with the tips being separated
from one another by a distance "d". The aligned nozzles
of the print head are then produced from the conical
tips of the stems 60 through 72 in a manner of drilling
or boring through a small portion of the print head
molding, after hardening thereof, from the outside of
the molding to the tips of the stems.
The method of the present invention provides
that the length of the threaded members 18 through 30 is
. . -
_7_ 113~673
chosen so that upon insertion o~ the members into the
threaded holes 16 of the cover portion 14, the lower
stems of the threaded members project be~ond the cover
portion and into the molding cavity 12. Hence, with
l:he aid of a conventional screwdriver, each of the
stud members 18-30 can be turned or rotated in the
cover 14 in a manner that the tips 74 through 86 of the
stems 60-72 have a constant distance "b" from the
bottom of the mold cavity 12.
When the studs 18 through 30 have been inserted
into the cover portion 14 and appropriately adjusted
therein, the cover portion is placed on the mold 10 and
firmly held or clamped thereon so as to remain in place
when the molding material is injected into the mold cavity
12. As illustrated (Figs. 1 and 2), a central opening
88 is provided in the cover portion 14 through which
the molding material is poured or transmitted until the
upper level of the material has reached the opening.
While the molding material may of course be in the
fluid or molten state when it is poured, the various
members and associated parts in the mold cavity 12 must
be maintained in position to provide the correctly and
precisely-positioned channels and ducts for the transmission
of the ink.
When the molding or casting material which
has been poured into the mold 10 is hardened, the studs
18 through 30 can be turned or rotated reversely with a
screwdriver and out from the cover portion 14. The cover
portion 14 can then be removed from the mold 10. A
finished multiple-nozzle ink jet print head, including
all the required channels and cavities, can thereafter
be removed from the mold 10 after removal of the inlet
channel pins 46 through 58.
Fig. 3 is a sectional view of a print head 90
showing one operating cavity and channel arrangement
after removal of the head from the mold 10, and Fig. 4
is an enlarged sectional view of a portion of the print
-8- ~133673
head 90 as produced according to the method of the
present invention.
In the sectional view of the head 90 in Fig.
3, it is the area as produced by the stud 18 and the
associated parts shown in Figs. 1 and 2 and which can
be seen as providing the cavities and channels for the
~low of the ink. The area of consideration is comprised
of the cavity or bore g2 for receipt of the ink droplet
drive elements, which bore is produced by the stud 18
of Figs. 1 and 2. The capillary pressure cavity 94,
the channel 96 and the cone 98 make up the chamber and
passageway for the ink with the capillary cavity 94 being
connected with an ink supply channel 100 which was
produced by the pin 46 of Figs. 1 and 2 and leading
laterally out of the print head 90. The ink supply
channel 100 can also be provided in a manner other than
that as previously described with respect to the pins
46 through 58, the essential thing being that same is
appropriately arranged so that a supply of ink is main-
tained at the capillary cavity 94.
It is thr~ugh the advantaqeous form of thestud or threaded elements 18 through 30 and their
special arranqement in the cover portion 14 and in the
mold 10, as seen in Figs. 1 and 2, that upon the
production of the print head 90, the bores required for
the drive elements are each provided with a threaded
portion as seen in the bore 92 in Figs. 3 and 4. In
each of the bores 92 of the print head 90, as shown in
Fig. 4, is fixed the drive elements in the form of a
membrane 102 and a piezo crystal 104 which are secured
as by bonding thereof to each other so as to form an
integral drive element. Since, as already state~ above,
the bores 92 produced by the studs 18 through 30 include
threads in the walls thereof, the drive elements can,
by an appropriate hollow screw or threaded bushing 106,
be turned or screwed into the bore 92 and be pressed
against the capillary cavity 94 for a precisé covering
~33673
of the capillary cavity. A permanent fasteninq is thus
made possible between the drive element and the portions
of the print head 90 lyinq beyond the diameter of the
capillary cavity 94.
Fig. 4 illustrates an enlarged view of the
bore 92 area of the print head 90 as seen in Fig. 3 and
as produced by the stud or threaded member 18 from
Figs. 1 and 2, and with the material area "b" of the print
head 90, as shown in Fig. 3, having been bored or drilled
to provide an outlet nozzle 108 as defined by the tip
98 to expose the ink channel 96 to the exterior of the '
print head for ejection of the droplets of ink therefrom.
The droplet producing pressure waves or pulses are
caused by the energization of the piezo crystal 104 and
the resultant bending of the membrane 102 which is thereby
caused to be moved into the capillary pressure cavity
94 there maintained full of ink. Upon pulsing the
crystal 104, ink is caused to be transmitted from the cavity
94, through the channel 96, the cone 98 and the nozzle
108, respectively, to be ejected as a droplet of ink
for impinging upon a record medium which is not shown
but which in a suitable manner is normally positioned
opposite the nozzle 108. The ink supply to the capillary
pressure cavity 94 occurs through the ink supply channel
100, which extends to the capillary cavity at an angle
of from 0 to 15 degrees as seen by the solid and the
dashed lines in Fig. 4.
In the print head 90, Fig. 3, as produced by
means of the mold 10 and the associated elements of Figs.
1 and 2, the studs 18 through 30 with the threaded
bodies were turned or rotated into the threaded holes
16 of the cover portion 14. In this manner, the bores
or cavities 92 for the drive elements include the
threaded portions for reception of the hollow screw
or cap 106 for securing the drive elements 102 and 104
in position over the capillary pressure cavity 94.
Fig. 5 is an enlarged sectional view of a
portion of a print head showing a modification or a
-lo- li33673
second embodiment thereof differing from the print head
~0 of Fig. 4. It is seen that instead of the mold 10
having a cover portion 14 including threaded holes 16 being
used, there can be used a cover portion with holes or
apertures which are not threaded and whereby the stud
elements which are to be inserted have smooth walls and
produce drive element receiving bores or cavities
without internal threads. Such a bore 110 is shown in
Fig. 5 wherein the drive elements 114 and 116 which
cover and hermetically seal a capillary pressure cavity
112 therefor must be secured in the bore in another
manner. In the embodiment shown in Fig. 5, the membrane
114 to which is bonded the piezo crystal 116 is likewise
bonded ~o the print head portion or ledge which extends
beyond the diameter of the capillary cavity 112 at the
lower side of the bore 110.
Another advantageous variation in the production
of a print head consists in the tips 74, 76, 78, 80,
82, 84 and 86 of the stems of the studs or threaded
elements 18-30 being inserted into a nozzle plate 118
which is cast integral into the print head to be produced,
thereby maintaining the tips more exactly fixed in posi-
tion. In this case, as also illustrated in Fig. 5, the
nozzles to be produced can be made with more exactness
since the nozzle plate 118 having to be cast integral
into the print head-already includes the necessary
number of nozzle openings as at 120 in an exactly pre-
determined position. A channel tip 124 of a nozzle channel
126 projects into the nozzle opening 120 and the nozzle
channel 126 leads into the capillary pressure cavity
112 which is covered by the membrane 114 with the piezo
crystal 116 bonded or otherwise secured thereto. The
lower portion of the print head 122 (Fig. 5) is provided
with a recess 128 as the nozzle plate 118 is cast
integral into the print head and the nozzle openings
120 of the nozzle plate are protected from outside
influence.
- '
~ .
133673
A further advantageous ~eature in the production
of the print head 122 provides that the supply channel
L30 ~or the capillary pressure cavity 112 be produced
with cross-sections becoming smaller in the direction
toward the pressure cavity. This reduction of the
cross-section of the supply channel 130 provides that
each such supply channel achieves a better decoupling
of the nozzle channel 126 and the capillary pressure
cavity 112 from the ink supply system whereby the print
head operates in a smoother manner and is not suhjected
to extreme fluctuations in supply and flow of ink.
Fig, 6 illustrates a sectional view of a
portion of a production variation of a print head sub-
stantially the same as Fig. 5 and which is especially
applicable in the scope of the present invention and
wherein the capillary pressure cavity 132 includes a
conical slope towards the nozzle channel 126. The
slope of such cavity 132, which is preferably at an angle
between two and five degrees as shown in Fig. 6, can be
produced in a simple manner by means of the mold 10, per
Figs. 1 and 2, since the portions of the studs 18
through 30 only have to be formed conical toward the
stems 60 through 72.
The sloping of the capillary pressure cavity
132 as seen in Fig. 6 and as per the present invention
provides that, upon the filling with ink of the capillary
pressure cavity 132 and the nozzle channel 126, the ink
flowing through the supply channel 130 is directed to
and flows along the outside wall of the capillary
pressure cavity 132 wherein any air bubbles along the
outside wall are removed by the presence of the ink.
After the outside walls are circularly surrounded by
ink, that ink which is flowing in towards the center of
the capillary pressure cavity 132 and flowing towards
the nozzle channel 126 causes any further air bubbles
which are still in the cavity 132 to be pressed towards
the nozzle channel 126 and through the channel toward
.
-12- ~33673
the nozz]e 120. The advantageous sloping of the capil-
lary pressure cavity 132 therefore enables that the
print head 122 can be filled with ink without air
bubbles beinq kept back during the filling process and
S that no additional venting means or like measures are
required during the filling of the channels and passage-
ways with the initial supply of ink. It is evident
that although the inventive formation of the capillary
pressure cavity 132, as seen in Fig. 6, is especially
suited for the print head produced according to the
present invention, the person skilled in the art can
also successfully use such a sloping of the capillary
pressure cavity with other print heads.
It is thus seen that herein shown and described
is a method for making an ink jet print head which
includes the positioning of the several elements so as
to provide for passageways and channels for droplets of
ink and for adjusting or moving the several elements to
provide for a precise positioning of the ink nozzles.
The method of producing the print head enables the
accomplishment of the objects and advantage~ mentioned
above, and while a preferred embodiment and modifications
thereof have been disclosed herein, other variations
thereof may occur to those skilled in the art. It is
contemplated that all such variations and modifications
not departing from the spirit and scope of the invention
hereof are to be construed in accordance with the
following claims.
. ` .
