Note: Descriptions are shown in the official language in which they were submitted.
CA 022039~2 1997-04-29
-1 -
BRAZING PROCESS FOR A
CONTINUOUS INK JET PRINTHEAD
Technical Field
The present invention relates to
continuous ink jet printers and, more particularly, to
a brazing process for joining machined resonator
portions to yield a single resonator body for a
continuous ink jet printhead
Backqround Art
Ink jet printing systems are known in
which a printhead defines one or more rows of orifices
which receive an electrically conductive recording
fluid from a pressurized fluid supply manifold and
eject the fluid in rows of parallel streams. Printers
using such printheads accomplish graphic reproduction
by selectively charging and deflecting the drops in
each of the streams and depositing at least some of
the drops on a print receiving medium, while others of
the drops strike a drop catcher device.
Droplet generators are one of the major
components in a continuous ink jet printhead. Droplet
generators often use a nozzle plate attached to a
resonant body to stimulate the j ets . In a resonator
body design where the inlet and outlet ports are not
directly in line with the nozzle plate channel,
machining from a solid metal block is essentially
impossible.
It is seen then that it would be desirable
to eliminate the problems associated with the prior
art resonator body design by providing a resonator
body design which is particularly useful where the
inlet and outlet ports are not directly in line with
the nozzle plate channel
CA 022039~2 l997-04-29
-2 -
SummarY of the Invention
This need is met by the system according
to the present invention, wherein the resonator body
of a continuous ink jet printhead is fabricated from
S two precision machined halves which are brazed
together in a process to yield an integral unit. The
integral unit comprises the inlet and outlet f luid
ports as well as the fluid channel which directs the
fluid into the bonded nozzle plate
In accordance with one aspect of the
present invention, a brazing process is provided for
joining machined resonator portions to yield a single
resonator body for a continuous ink jet printhead. A
first resonator body portion and a second resonator
body portion are provided, each resonator portion
having partial fluid ingress, fluid egress, and nozzle
plate channel fluid cavities. A braze preform is then
insertable between the f irst and second resonator body
portions to join the first and second resonator body
portions. Alignment pins secure and align the first
resonator body portion to the second resonator body
port ion .
Accordingly, it is an object of the
present invention to yield a single resonator body for
a continuous ink jet printhead. It is a further
object of the present invention to provide a resonator
body design where the inlet and outlet ports are not
directly in line with the nozzle plate channel. It is
an advantage of the present invention that it provides
a viable resonator body design which addresses the
packaging constraints of some printheads.
Other objects and advantages of the
invention will be apparent from the following
description, the accompanying drawings and the
3 5 appended c 1 a ims .
CA 022039~2 1997-04-29
-3 -
Brief Description of the Drawinqs
Fig. lA is a partially cutaway view
illustrating two joined halves forming a resonator
body in accordance with the present invention;
Fig. lB is a view along section line B-B
of Fig. lA;
Fig. 2 illustrates a brazed foil-resonator
preform used to braze the two resonator halves into
the single resonator body of Fig. lA; and
Fig. 3 is a side view of a brazing
alignment pin used in the joining of the two resonator
halves .
Detailed Description of the Preferred Embodiments
The present invention provides brazing
process whereby two machined resonator halves are
brazed together in a manner that yields a single
resonator body for a continuous ink jet printhead. In
co-pending, commonly assigned patent application
Serial No. 08/640,180 (docket number SDP163PA),
totally incorporated herein by reference, a top feed
droplet generator assembly is disclosed, which has an
integral f luid cavity wherein f luid ingress and egress
to and from the resonator body is on the side of the
resonator body opposite the nozzle plate. The brazing
process according to the present invention is
particularly useful when used to join two resonator
halves into the top feed droplet generator described
and claimed in co-pending, commonly assigned patent
application Serial No.
08/640 ,180 (docket number SDP163PA) .
Referring now to the drawings, in Fig. lA
there is illustrated a partially cutaway view of two
resonator halves joined to form a resonator body in
accordance with the present invention; and in Fig. lB
CA 022039~2 1997-04-29
-4--
there is illustrated a front section view of one of
the resonator halves. The resonator is a top feed
resonator, wherein inlet and outlet ports are located
at the top of the resonator body and communicate with
a nozzle plate channel located at the bottom of the
resonator body
Resonator 1 comprises f luid ingress and
egress on a surface 7 opposite nozzle plate 2. A
counterbore 3 feature permits an effective means to
secure fittings 6 to the droplet generator 1. A fluid
passage 4 allows fluid to travel from an ingress point
8 down to the nozzle plate 2. A narrow fluid trench
5 redirects fluid flow from the fluid passage 4 to an
in-line direction with the nozzles (not shown)
lS associated with nozzle plate 2. Since fluid passage
4 is not directly in line with the nozzle plate
channel, machining from a solid metal block is
impractical and, essentially, impossible.
To provide such a design using machining,
the present invention proposes a two piece resonator
design, wherein two pieces lA and lB are brazed
together to form a single resonator. Each
symmetrically machined portion lA and lB preferably
comprises half of inlet 8, outlet 9 and nozzle plate
2 channel fluid cavity. For a continuous ink. jet
printhead design, the resonator body 1 is fabricated
from the two precision machined portions lA and lB
which are brazed together to yield an integral unit.
The integral unit comprises the inlet 8 and outlet 9
fluid ports and the fluid channel 4 which directs the
fluid into the bonded nozzle plate 2. After brazing,
a complete resonator body 1 with properly sized fluid
channels is achieved.
In the prior art, such as a one inch, 120
drops per inch ink jet printer resonator body, the
CA 022039~2 l997-04-29
-5-
fluid channels can be machined in one portion of the
resonator body, with the second resonator portion
being a solid cover. A rectangular braze foil
material without fluid channel cutouts was placed
S between the two halves, with the fluid cavity half
being placed on top to avoid flow of the braze foil
into the f luid channels .
In a one inch, 240 drops per inch printing
system, each resonator portion lA and lB comprises
part of the inlet 8, the outlet 9 and the nozzle plate
2 channel fluid cavity. With two fluid channel
symmetrical halves, there is a greater chance for
thin, rectangular braze foil to flow into the fluid
channels, especially if a solid braze foil, i.e., one
without fluid channel cutouts, is used.
Braze material in the fluid cavities is
undesirable for several reasons One, braze material
that has melted and solidified presents a rough,
almost grit blasted appearance, which can be a source
of fluid flow disturbances and can create sites for
air bubble attachment. Either of these problems can
severely affect the resonator body performance. Also,
the added nonsymmetrical mass due to the excess braze
foil in one of the portions lA or lB may be another
source of poor resonator body performance.
In an effort to greatly reduce the amount
of braze material which can flow into the fluid
channels, a braze foil preform 10, as shown in Fig. 2,
is used. By the proper, standard mechanical use of
brazing alignment pins 11, as illustrated in Fig. 3,
insertable into apertures 12 of Fig. 2, the two
portions lA and lB can be accurately aligned. In a
preferred embodiment of the present invention, the
pins 11 are machined from round stock and have break
edges 14 at each end, to provide relief for ease of
CA 022039~2 1997-04-29
--6 -
insertion into apertures 12. Preferably, one of the
resonator sections lA or lB, has alignment apertures
designed for a press fit; while the other resonator
portion lB or lA, has alignment apertures designed for
a slip fit.
The braze preform 10 of the present
invention comprises fluid channel cutout 13. The
preform shape allows for 5 to 15 mils of overhang into
the fluid channels for tolerancing and to ensure
adequate braze coverage at the melt temperature. With
the insertion of the braze preform 10, the resulting
resonator body 1 minimizes braze material in the fluid
channels as the preform melts when the braze
temperature is applied. This reduces poor resonator
performance attributed to the existence of braze
material. In a preferred embodiment of the present
invention, the pins 11 are of the same material as the
resonator portions lA and lB, to eliminate differences
in thermal expansion at the braze temperature. If
thermal expansion rates differ between the pin 11 and
the resonator portions lA and lB, the upper resonator
portions would "hang" up, when the upper resonator
portion is actually required to float during the
brazing process to obtain perfect braze integrity.
Industrial AP,olicabilitY and
Advant aqe s
The present invention is useful in the
field of ink jet printing, and has the advantage of
addressing packaging constraints of certain
printheads. The present invention provides the
further advantage of providing an integral resonator
body by brazing two separate resonator body portions.
Finally, the present invention provides the advantage
of minimizing braze material in the fluid channels.
CA 022039~2 1997-04-29
-- 7 --
Having descrlbed the invention in detail
and by reference to the preferred embodiment thereof,
it will be apparent that other modifications and
variations are possible without departing from the
scope of the invention defined in the appended claims
