Method of fabricating an ink jet apparatus

A method of fabricating an ink jet apparatus of the type having a plurality of variable volume chambers arranged in an array, each of the chambers adaptive to receive ink from a reservoir and including an orifice for ejecting droplets of ink-on-demand, is facilitated by utilizing a ganged array of transducer feet which are inserted into the chambers, joined to the respective transducer and unganged by lapping off an interconnecting web flushed with the forward face of the image head.

BACKGROUND OF THE INVENTION 
This invention relates generally to ink jet arrays which include a 
plurality of ink jet channels with each channel having a chamber, an inlet 
to the chamber, an orifice from the chamber, and transducer means coupled 
to the chamber for ejecting droplets of ink from the chamber as a function 
of the state of energization of the transducer. More particularly, this 
invention relates to an efficient method of fabricating a high-density ink 
jet array. 
Within the art of ink jet printing, it is often desirable to employ a print 
head configuration which permits the utilization of a plurality of ink 
jets in a densely packed array such that a reasonably large area of a copy 
medium may be printed simultaneously. This is especially the case in the 
printing of alphanumeric information in which the resolution of individual 
characters as well as the speed of printing are of utmost importance. 
One suitable such printer is described in U.S. Pat. No. 4,459,601, issued 
July 10, 1984 to Stuart D. Howkins, assigned to the assignee of the 
present invention and incorporated herein by reference. In that 
arrangement, an ink jet apparatus of the demand or impulse type comprises 
a chamber and an orifice in which droplets of ink are ejected in response 
to the state of energization of a transducer which communicates with the 
chamber through a foot forming a movable wall. The transducer expands and 
contracts, in a direction having at least one component extending parallel 
with the direction of droplet ejection through the orifice, and is 
elongated in such direction, the electric field resulting from the 
energizing or drive voltage being applied transversely to the axis of 
elongation. 
One problem common to all high-speed, high-resolution, drop-on-demand ink 
jet printers occurs because the jets of an array are spaced very close to 
one another. That is, the response of one jet in an array to its drive 
voltage can be affected by the simultaneously application of a drive 
voltage to another nearby jet. This can result in a phenomenon, known in 
the art as "mechanical cross-talk", where pressure waves are transmitted 
through the solid material in which the jets are formed, or in another 
phenomenon known in the art as "electrical cross-talk", where relatively 
large drive voltages necessary for substantial displacement of transducers 
utilized in the prior art cause the subsequent pulsing of an inappropriate 
jet. 
While the risk of electrical cross-talk between ink jets in an array 
utilizing the teachings of U.S. Pat. No. 4,459,601 as discussed above will 
be minimized, the risk of mechanical cross-talk remains. One approach 
which alleviates this problem, however, is discussed in U.S. Pat. No. 
4,439,780, issued Mar. 27, 1984 to Thomas W. DeYoung and Viacheslav B. 
Maltsev, assigned to the assignee of the present invention and 
incorporated herein by reference. In that arrangement, an ink jet array 
comprises a plurality of elongated transducers coupled to a plurality of 
ink jet chambers, the transducers being supported only at their 
longitudinal extremities. The support at the extremity remote from the 
chamber is provided such that no longitudinal motion along the axis of 
elongation of the transducers occurs, while the support at the other 
extremity includes bearings which substantially preclude lateral movement 
of the transducers transverse to the axis of elongation but permit the 
longitudinal movement thereof along the axis, thus minimizing mechanical 
cross-talk between jets within the array. 
As is more fully disclosed in the aforedescribed U.S. Pat. No. 4,439,780, 
the coupling means may comprise a foot attached to the transducer and the 
bearing means may comprise a hole receiving the foot. Preferably, the foot 
is cylindrical in cross-section and the hole is also cylindrical in 
cross-section with the hole slightly larger relative to the foot so as to 
assure no more than a line contact therebetween. The foot is subsequently 
"potted" within the hole by a viscoelastic material. 
Other characteristic problems which are encountered in the implementation 
of high-speed, high-resolution impulse ink jet printers do not impact so 
much upon their operation, but indeed impact on their fabrication. For 
example, the relatively small sizes of transducer elements used in densely 
packed arrays make them difficult to handle. A unitary transducer array 
is, therefore, preferred. 
One early approach towards the resolution of the above-described problem is 
disclosed in U.S. Pat. No. 4,072,959, which issued to Rune Elmqvist. As 
discussed therein, a recorder operating with drops of liquid includes a 
comb-shaped piezo electric transducer arranged such that individual teeth 
of the comb are associated respectively to a densely-packed array of ink 
jet chambers. Each of the transducers is immersed in a common reservoir 
such that energization of one transducer associated with one chamber may 
produce cross-talk with respect to an adjacent chamber or chambers. In 
other words, there is no fluidic isolation from chamber to chamber between 
the various transducers, or more accurately, segments of the common 
transducer. In addition to such cross-talk problems, the construction 
shown in the Elmqvist patent poses a requirement for a non-conductive ink. 
It has been generally observed, however, that transducer-driven ink jets of 
apparently identical construction do not all operate over a single 
operating voltage range. This variation in operating voltage may result 
from such factors as variations in transducer material from piece to 
piece, variations in the acoustical coupling between the transducer and 
the remainder of the jet, or from other variations in structure which are 
not simple to control on a dimensional basis. These variations are 
troublesome in a manufacturing environment because they require the 
transducer driving electronics to be tuned to the jets on an individual 
basis where variations in transducer performance alone can be on the order 
of 15% to 20%. As a result, electronic configurations such a "resistor 
packs" which are well known in the art and used to individually tune the 
jets are desirably eliminated in an ink jet apparatus. 
One means of reducing the variations in transducer from piece to piece is 
disclosed in copending application Ser. No. 902,473, filed Aug. 29, 1986, 
which is assigned to the assignee of the present invention and 
incorporated herein by reference. In that arrangement, a transducer array 
is produced in unitized fashion for ready assembly within an ink jet 
apparatus. The ink jet apparatus, in the preferred embodiment of that 
invention, includes a plurality of variable volume chambers, each of which 
is coupled to a respective element of the transducer array for ejection of 
ink through an associated orifice or jet. In order to fabricate the array, 
a monolithic slab of piezoelectric material, for example, lead zirconate 
titanate (PZT) is laminated to a rigid substrate such as glass by a 
selected thermoplastic cement. This lamina is then sized according to the 
desired number and dimensions and individual transducer elements and 
element spacing, and is subsequently diced to produce those elements. 
After such sizing and dicing, typically accomplished by a "dicing saw", 
the lamina is positioned PZT-side down with one end thereof being bonded 
by a structural-type electrically conductive epoxy to a shelf formed in 
the printer head. The other end is then operatively coupled to the 
variable volume chambers, and the resulting assembly is placed within an 
oven to cure. Once the structural-type electrically conductive epoxy has 
cured the oven's temperature is elevated to a point at which the 
thermoplastic cement will readily flow, thus facilitating the removal of 
the rigid substrate. Thereafter, the transducer elements can be 
electrically coupled by conventional means. 
While the above described copending application Ser. No. 902,473, filed 
Aug. 29, 1986, reduces the variations in transducer material from piece to 
piece by producing a transducer array from a monolithic slab of 
piezoelectric material, variations in the acoustical coupling between the 
transducer and the remainder of the jet are still possible. One means of 
alleviating this problem, as disclosed in the aforedescribed U.S. Pat. No. 
4,439,780, includes the use of a coupling means comprising a foot attached 
to the transducer and bearing means comprising a hole which receives the 
foot. Preferably, the foot is cylindrical in cross-section and the hole is 
also cylindrical in cross-section with the hole slightly larger relative 
to the foot so as to assure no more than a line contact therebetween. The 
coupling means further comprises a diaphragm between the chamber and the 
foot with a viscoelastic material sandwiched between the foot and the 
diaphragm assisting in the maintenance of the lateral position of the 
transducer at the diaphragm. 
It will be appreciated, however, that an individual foot may be secured 
within the hole simply by means of a viscoelastic material such as 
silicone which is marketed under the name RTV. The ends of the transducers 
may be cemented to the feet by means of suitable adhesive such as an epoxy 
and the diaphragm may be eliminated. This "potted foot" configuration is 
presently preferred over the diaphragm designs illustrated herein for 
reasons of reliability and durability. Effective coupling of an individual 
transducer within a multichannel array is, nevertheless, hampered because 
of variations in structure which are not simple to control on a 
dimensional basis. A more efficient means of coupling is therefore 
desirable. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general and object of the present invention to provide 
a means for use in an ink jet printing apparatus for the effective 
coupling of a transducer array to a corresponding number of variable 
volume chambers. More specifically, it is an object of this invention to 
provide an ink jet printer which is easily fabricated, capable of 
producing a high-resolution image at high rates of speed, and which 
minimizes cross-talk between jets in a multichannel array. 
Another object of this invention is to provide an improved method for 
incorporating a unitized transducer array within an ink jet printer while 
minimizing variations in the acoustical coupling between the array and the 
remainder of the jet. 
Still another object of this invention is to provide an ink jet printer 
with a minimum of parts. 
Briefly, these and other objects of the present invention are accomplished 
by an ink jet apparatus including a plurality of variable volume chambers, 
each of which is coupled to a respective element of a transducer array for 
the ejection of ink through an associated orifice or jet. In accordance 
with one important aspect of this invention, each of the transducer 
elements in the array are coupled to a respective one of the plurality of 
variable volume chambers by attaching it to a transducer foot which is 
"potted" within the chamber. The transducer foot in the preferred 
embodiment is but one of an array of ganged transducer feet joined 
together by a common web and inserted through the orifice side of the 
variable volume chamber. Thereafter, in accordance with a method 
consistent with the invention, the transducer feet are inserted through 
the chambers, affixed to the end of the transducer elements, separated 
each from the other by lapping off their interconnecting web, and potted 
within the variable volume chambers with a viscoelastic material. 
In accordance with yet another important aspect of the invention, the 
ganged foot array is utilized to connect a transducer array comprised of a 
monolithic slab of piezoelectric material, for example, lead zirconate 
titanate, which is laminated to a rigid substrate such as glass by a 
selected thermoplastic cement. This lamina is then sized according to the 
desired number and dimension of individual transducer elements and 
interelement spacing, and is subsequently diced to produce those elements. 
After such sizing and dicing the lamina is positioned PZT-side down with 
one end thereof being bonded by a structural-type electrically conductive 
epoxy to a shelf formed in the printer head. The other end is then 
operatively coupled by joining each transducer element to a respective one 
of the transducer feet within the array, thereby coupling the transducer 
elements to the variable volume chamber. 
Other objects, advantages and novel features of this invention will become 
apparent from the following detailed description of a preferred embodiment 
when considered in conjunction with the accompanying drawings:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, wherein like characters designate like or 
corresponding parts through the several views, there is shown in FIG. 1 a 
lamina 10 having a first layer 12 of piezo electric material which is 
bonded by a layer 14 of thermoplastic cement to a second layer 16 
comprising a rigid substrate. The piezoelectric layer 12 comprises a 
conventionally poled ferroelectric ceramic, such as a lead zirconate 
titanate (PZT) which has been exposed to an original DC polarizing field. 
As is well known in the art, the polar axis of such piezoelectric ceramics 
is parallel to the original DC polarizing field. It will appreciated from 
the following discussion, therefore, that the piezoelectric layer 12 
includes a negative or ground plane which, according to the invention, 
faces out when incorporated within the lamina 10. The lamina 10, as shown 
in FIG. 2, is then sized and diced by a conventional saw to produce an 
array of transducer elements 18. In accordance with an important aspect of 
this invention, the sizing step determines the outside dimensions of the 
transducer array: that is, the overall length and width of the lamina 10 
is determined by the desired number and length of the transducer elements 
18. Thereafter, the dicing step produces the individual transducer 
elements 18 and ensures a proper element width and spacing therebetween 
within the array. 
Referring now to FIG. 3, the sized and diced lamina 10 is shown ready for 
positioning within a printer head 20. The printer head 20 includes at one 
end thereof a plurality of chambers 22, and at the other end a shelf 
portion 24 upon which the lamina 10 will be supported. As discussed thus 
far, the above method of fabricating an ink jet printer is consistent with 
the disclosure of copending application Ser. No. 902,473, filed Aug. 29, 
1986. In accordance with a preferred embodiment of this invention, a 
ganged array of transducer feet 26 as shown more clearly in FIG. 3a is 
inserted through the chambers 22 thereby providing a second point of 
attachment for each of the transducer elements 18. A layer of 
structural-type conductive epoxy 28 is applied to the shelf 24 and each of 
the feet 26. The lamina 10 is then attached to the printer heads 20 such 
that each of the transducer elements 18 is aligned with a respective foot 
26 and supported upon the shelf 24. 
Referring now to FIG. 3a, there is shown a preferred embodiment of the 
present invention. Comprised of a molded assembly of individual feet 26 
joined together by an interconnecting web 26a, the ganged array 26' may be 
fabricated from a plastic or ceramic material which is capable of being 
bonded to the transducer elements 18. It will be understood that the 
individual feet 26, after separation, form a movable wall at the rear of 
the variable volume chambers formed by the chambers 22 within the print 
head 20. The array 26' may be formed as shown in FIG. 3a. Each of the feet 
26 generally comprise a substantially cylindrical portion 26b having a 
horizontal shelf 26c molded therein. The shelf 26c is adapted to hold an 
individual transducer element 18 as well as a suitable adhesive 28 bonding 
the two together. 
Referring now to FIG. 3b, there is shown an alternative embodiment of the 
present invention. As in the preferred embodiment of FIG. 3a, the 
individual transducer feet 26 may be generally comprised of a subtantially 
cylindrical portion 26a having the shelf 26d formed at their distal ends 
as shown in FIG. 3. It will be readily apparent from FIG. 3b that the 
individual transducer feet 26 are not joined together by a rigid 
interconnecting web as in the preferred embodiment of FIG. 3a. Instead, a 
thin rod 26e having a plurality of fine, flexible fingers 26f connected 
between the transducer feet 26 and the rod 26e. The ganged array 26" as 
shown in FIG. 3b is, accordingly, inserted through the holes 22 from the 
back side of the print head 20 in a manner opposite to that shown in FIG. 
3. Thereafter, the individual feet 26 are joined to respective transducer 
elements 18 and the feet 26 are potted with a viscoelastic material or 
elastomeric potting compound 38. In this manner, no post assembly 
processes are required to remove the interconnection of individual feet, 
since the fine flexible fingers 26f permit the movement of individual 
transducer 26 as attached to the transducer elements 18 without causing 
substantial loading. It should be noted, however, that the array 26" must 
be flexible enough to permit movement of the foot 26 within the holes 22 
without substantially loading its respective transducer element 18, 
thereby requiring the individual transducer elements 18 to be tuned and 
adjusted for a common drive voltage through the installation of suitable 
electronics such as a resistor pack. 
The epoxy 28 may then be cured in an oven 30 as shown in FIG. 4. In 
accordance with another important aspect of the invention, the 
thermoplastic cement 14 and epoxy 28 must be carefully selected to ensure 
they provide the proper bond strengths. For example, the thermoplastic 
cement 14 must provide a tenacious bond between the PZT layer 12 and the 
rigid substrate 16 in order to effectively size and dice the lamina 10 for 
production of uniform transducer elements 18. Moreover, the thermoplastic 
cement 14 must be capable of withstanding temperatures required to cure 
the epoxy 28 without melting, must itself be chemically compatible with 
the epoxy 28, and must be readily soluble in standard cleaning solutions. 
One suitable such thermoplastic cement 14 is Struers Lakeside 70c cement, 
a registered trademark of H. Courtright and Company, Chicago, Ill. A 
suitable compatible epoxy 28 which was used in a preferred embodiment 
invention is EPO-TEK-H20E, a two component, silver filled epoxy produced 
by Epoxy Technology, Inc., Billerica, Mass. Referring again to FIG. 4, it 
will be appreciated that the temperature of the oven 30 which is selected 
to cure the epoxy 28 must also prevent the melting of the thermoplastic 
cement 14 once the epoxy 28 is cured. The temperature of the oven 30 is 
elevated to a point at which the thermoplastic cement 14 will readily 
flow, thereby freeing the rigid substrate 16 from the array of transducer 
elements 18 as shown if FIG. 5. After the rigid substrate 16 is removed, 
the transducers 18 and printer head 20 are cleaned using such standard 
solvents as alcohol, acetone, or a solution of borax and water. 
Upon cleaning, subsequent assembly operations may be carried out as shown 
is FIG. 6, and as more fully described in copending application Ser. No. 
902,473 filed Aug. 29, 1986. Most importantly, the interconnecting web 
joining the transducer feet 26 of the array 26 prime as shown in FIG. 3a 
must be lapped off flush with the surface of the forward face of the 
printer head 20. Thereafter, fluidic supply and ejection means, such as a 
restricter plate 40, a chamber plate 42, and an orifice plate 44 may be 
attached to complete the assembly of an exemplary ink jet printer. 
As utilized herein, the term elongated is intended to indicate that the 
length is greater than the width. In other words, the axis of elongation 
has utilized here and extends along the length which is greater than the 
transverse dimension across which the electric field is applied. Moreover, 
it will be appreciated that the particular transducer may be elongated in 
another direction which might be referred to as the depth and the overall 
depth may be greater than the length. It will, therefore, be understood 
that the term elongation is a relative term. Moreover it will be 
understood that the transducer will expand and contract in other 
directions in addition to along the axis of elongation but such expansion 
and contraction is not of concern because it is not in the direction of 
coupling provided by the ganged array 26'. In the embodiments shown 
herein, the axis of coupling is the axis of elongation. 
Although particular embodiments of the invention have been shown and 
described, other embodiments will occur to those of ordinary skill in the 
art which fall within the true spirit and scope of the appended claims.