Fluid distribution bar for fluid-jet printing

A fluid distribution bar has a plurality of superposed channels with the lower channel in communication with an orifice plate for issuing fluid droplets for deposition on a substrate. The bar is formed from identically cast sections having channel portions opening through a side face thereof which open into one another when the sections are secured each to the other. The channels have a plurality of longitudinally spaced ports providing communication one between the other, the ports communicating between the lower and the intermediate channels being longitudinally offset from the ports communicating between the intermediate and upper channels. The upper surfaces of the lower and intermediate channels are shaped to guide air bubbles in the fluid to the ports such that, as fluid is supplied to the orifice plate, the air bubbles rise in the fluid and pass from one channel to the next through the ports and out of the bar.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to the field of non-contact fluid marking 
devices commonly known as "ink-jet" or "fluid-jet" devices. More 
particularly, the present invention relates to a fluid-jet distribution 
bar and to methods for forming and assembling a fluid distribution bar 
used in such non-contact fluid marking devices for flowing fluid through 
an orifice plat. 
Fluid-jet devices in and of themselves are well known. Typically, prior art 
fluid-jet devices provide a linear array of fluid-jet orifices formed in 
an orifice plate from which filaments of pressurized fluid (e.g., ink, 
dye, etc.) are caused to issue from a fluid supply channel. A controllable 
electrostatic charging electrode is disposed downstream of the orifice 
plate along the so-called "drop formation" zone. In accordance with 
well-known principles of electrostatic induction, the fluid filament is 
caused to assume an electrical potential opposite in polarity and related 
in magnitude to the electrical potential of its respective charging 
electrode. When a droplet of fluid separates from the filament, the 
induced electrostatic charge is then trapped on and in the droplet. Thus, 
subsequent passage of the charged droplet through an electrostatic field 
having the same polarity as the droplet charge will cause the droplet to 
be deflected away from a normal droplet path twoards a droplet catching 
structure. Uncharged droplets, on the other hand, proceed along a normal 
path and are eventually deposited upon a substrate. 
It will be appreciated that the orifice plate has a linear array of very 
small orifices having diameters in the range, for example, of about 
0.0013-0.01 inches. In fabricating fluid-jet devices of this general type, 
there is provided a fluid distribution bar having a plenum which supplies 
fluid to the orifice plate at uniform pressure and minimal turbulence. 
However, when the orifice array extends a substantial distance, for 
example 1.8 meters, and recognizing the extremely small orifice size, 
technical difficulties obtain in providing a uniform fluid supply for 
distribution through the orifices. For example, air bubbles in the fluid, 
when confronting the orifices of the orifice plate, have a tendency to 
prevent the fluid from flowing or distort the fluid flowing through the 
orifices. This results in a non-uniform flow curtain below the orifice 
plate, possible interference between adjacent flow streams issuing from 
the orifices, and possible canting of the flow streams from their desired 
direction perpendicular to the orifice plate. 
Additionally, sagging in the middle of the distribution bar and, hence, the 
orifice plate, because of their relatively long lengths, must be avoided. 
Thus, structural problems are a consideration in the design of a 
distribution bar. 
The present invention is directed to a fluid distribution bar and methods 
of assembly and operation of a fluid distribution bar for use in a 
fluid-jet printing apparatus. The present invention provides a fluid 
distribution bar having fluid distribution channels in communication with 
the orifice plate constructed such that uniform pressure and minimum 
eddies and turbulence occur in the fluid, the fluid being provided 
substantially free of air bubbles. To accomplish this, preferably three 
superposed distribution channels are provided along the bar. Each channel 
has a separate inlet and outlet. The lowermost and intermediate channels 
have upper surfaces which are shaped to direct gas, e.g., air bubbles, 
rising in the fluid in the channels to high points or apices located at 
longitudinally spaced positions along the channels. These high points are 
in communication through ports with the next higher channel whereby the 
air bubbles flow from the lower channel(s) into the higher channel(s). 
Additionally, the upper surfaces of the intermediate and lower channels 
are shaped and the ports located to minimize movement of the fluid and, 
hence, minimize eddy currents and turbulence. Additionally, those ports 
serve as fluid inlet ports for the lower channel which feeds fluid to the 
orifice plate for flow through the orifices. Baffles are provided in the 
form of bosses in the lower channel to avoid direct impingement of the 
fluid entering the lower chamber through the ports on the orifice plate. 
The channels are also formed to have smooth continuous uninterrupted 
surfaces throughout their lengths whereby corners, sharp turns and the 
like in the channels are avoided, as well as the turbulence and eddy 
currents associated with such flow paths 
Additionally, in view of the substantial length of the distribution bar, 
the need to form the channels as indicated above, and to avoid deflections 
caused by the weight of the bar, the bar is preferably formed of cast 
metal. Preferably, the bar is formed from identically cast half-sections 
of stainless steel. Each half-section has portions of a plurality of 
internal channels configured, when the bar sections are mated to provide a 
non-turbulent, substantially damped, flow to the orifice plate. The 
identically cast half-sections of stainless steel are preferably formed in 
a conventional casting mold, such as a sand mold. These two half-sections 
are then joined together along longitudinally extending side faces 
thereof, for example, by bolts. 
A significant feature of the present invention resides in the ability to 
rapidly change the type or color of the fluid flowing through the channels 
and orifice plate without stopping fluid flow through the orifices. 
Shutdown of the flow through the orifices causes substantial problems, 
both in cleaning the channels and in starting the flow of fluid through 
the orifice plate. However, it is essential to ensure that the changeover 
from one fluid type or color to another is accomplished without leaving 
any residue of the first fluid in the distribution bar. The multiple 
channels permit such changeover without shutdown, without causing any 
change in the flow of the fluid filaments through the orifice plate (other 
than the transition from the first fluid to the second), and without any 
apparent change from normal operation during the changeover of fluids. 
In normal operation, the inlet and outlet for the lower channel are closed, 
the outlet for the intermediate channel is closed, and a vacuum is applied 
to the upper channel. Thus, fluid is supplied through the inlet to the 
intermediate channel and gas is removed from the upper channel. In 
changeover, however, all three channels are opened at one end of the bar 
to serve as inlets for receiving the new fluid and all three channels are 
opened at the other end of the bar to serve as outlets for the old fluid 
and any mixture of the old and new fluids. Atmospheric or a slightly 
elevated pressure is maintained in the bar during changeover so that the 
fluid jets still run. Thus, there is horizontal flow across the bar as the 
fluid continues to issue through the orifices of the orifice plate. 
Changeover is in about 50 seconds with acid dyes for a bar about 1.8 
meters long, much shorter than if only the middle level channel was used 
for changeover. Such quick changes can be of importance when using the 
fluid jet device to apply dyes to fabrics, since multiple color changes 
may be needed in a relatively short period of time. Thus, fluid of a 
different type or color may be introduced to one end of the bar into the 
multiple channels. As the new fluid enters, the old fluid is removed by 
continuing to issue through the orifices, as well as by flow through the 
channel outlets at the opposite end of the bar. A restriction is 
preferably located in the outlets to elevate the pressure in the bar 
during changeover in order to maintain sufficient pressure to continue the 
flow through the orifices. The new fluid simply replaces the old fluid as 
the latter runs out of the bar without the need for shutdown or first 
draining the old fluid before replacing it with the new fluid. Also, the 
continuous, smooth nature of the channels permits the new fluid 
essentially to flush the old fluid from the bar without leaving any 
residue. 
Accordingly, in accordance with the present invention, apparatus is 
provided for supplying fluid to the orifice plate of a fluid-jet 
applicator comprising an elongated fluid distribution bar having a pair of 
elongated channels extending from adjacent one end of the bar to adjacent 
the opposite end of the bar, one of the channels being disposed above the 
other channel. Means are carried by the bar defining an inlet for 
supplying fluid to the channels. Means are additionally provided for 
defining an elongated slot for flowing the fluid outwardly of the other 
channel for flow through the orifice plate. Means are also provided 
defining at least one port providing communication between the channels 
and further means are provided for directing gases entrained in the fluid 
in the other channel to the port for flow through the one channel 
outwardly of the bar. 
Preferably, the gas-directing means includes shaped upper surfaces in the 
other or lower channel which includes a plurality o f high points spaced 
longitudinally along the upper surface of such other channel coincident 
with a plurality of ports which are spaced longitudinally one from the 
other along the bar providing communication between the channels. 
Additionally, a third channel is disposed above the one or intermediate 
channel and has a plurality of ports spaced longitudinally therealong 
providing for communication between the third channel and the one channel, 
the ports being out of phase with the ports providing communication 
between the intermediate and lower channels. 
In a preferred form of the present invention, the fluid distribution bar is 
formed of tow identically cast sections, each defining a portion of each 
channel, together with means for securing the cast sections one to the 
other to lie on opposite sides of the longitudinal centerline of the bar, 
with the cast channel portions in opposition one to the other. 
In accordance with the present invention, there is also provided a method 
for forming a fluid distribution bar for use in flowing fluid to an 
orifice plate in a fluid-jet printing device wherein the bar has at least 
a pair of channels, one superposed over the other, including the steps of 
casting two identical elongated sections each defining portion of each 
channel, with each channel portion opening through a side face of the cast 
section, providing communication between the channels and securing the 
cast sections one to the other with the side faces abutting one another 
and the channel portions opening into one another to form the superposed 
channels. 
In accordance with a further aspect of the present invention, there is 
provided a method of changing from one type of fluid to another in the 
fluid distribution bar of a fluid-jet printing device, the bar having at 
least a pair of channels, one superposed over the other, in communication 
with one another and an orifice plate comprising the steps of flowing a 
first fluid into the channels to form a fluid-jet curtain issuing from the 
orifices through the orifice plate, maintaining the fluid-jet curtain 
formed by the first fluid, while introducing into the channels a second 
fluid of a different type, and continuing to maintain the fluid-jet 
curtain as the second fluid displaces the first fluid in the channels of 
the distribution bar and in the formation of the fluid-jet curtain whereby 
the fluid forming the fluid-jet curtain changes from the first fluid to 
the second fluid. 
In a still further aspect of the present invention, there is provided a 
method of operating the fluid distribution bar of a fluid-jet printing 
device, the bar having at least a pair of channels, one superposed over 
the other, in communication with one another and an orifice plate, 
comprising the steps of flowing a fluid into the channels to form a 
fluid-jet curtain issuing from the orifice through the orifice plate, 
applying a vacuum to the fluid in the distribution bar and flowing gases 
entrained in the fluid from the lower channel into the superposed channel 
for removal from the distribution bar. 
Accordingly, it is a primary object of the present invention to provide a 
novel and improved fluid distribution bar for use in a fluid-jet device 
and methods for forming and using such fluid distribution bar for flowing 
fluid through an orifice plate in a manner enabling gas entrained in the 
fluid to be removed before it reaches the orifice plate, providing 
non-turbulent, damped flow of fluid to the orifice plate, and affording 
quick changeover of fluids from one to another. 
These and further objects and advantages of the present invention will 
become more apparent upon reference to the following specification, 
appended claims and drawings

DETAILED DESCRIPTION OF THE DRAWING FIGURES 
Reference will now be made in detail to a preferred embodiment of the 
invention, an example of which is illustrated in the accompanying 
drawings. 
Referring now to the drawing figures, particularly to FIG. 1, there is 
illustrated a fluid distribution bar, generally designated 10, constructed 
in accordance with the present invention, having fluid distribution 
channels for distribution of fluid through orifices in an orifice plate 12 
disposed along the underside of bar 10. Clamps 14 are disposed along the 
underside of the orifice plate, to clamp the orifice plate to the 
distribution bar. A longitudinally extending opening is left between the 
clamps 14, enabling passage of fluid filaments and drops between the 
clamps. The distribution bar 10, orifice plate 12 and clamps 14 form part 
of a printhead assembly, generally designated 16. 
Referring again to FIG. 1, there is provided along the underside of the 
distribution bar a charge electrode 18, a deflection electrode 20, and a 
droplet catcher 22 opposite deflection electrode 20. Underlying the 
deflection electrode and droplet catcher is a substrate S on which fluid 
is deposited. 
As understood by those familiar with fluid-jet printing devices, fluid is 
supplied from the fluid distribution bar to the orifice plate and flows 
through orifices in the orifice plate to emerge on the underside thereof 
in the form of fluid filaments directed in a downward direction 
perpendicular to the orifice plate. These filaments receive a charge 
potential, by means of charge electrode 18, opposite in polarity and 
related in magnitude to the electrical potential of the charging electrode 
18. Charged droplets separated from the fluid filaments are deflected by 
deflection electrode 20 towards droplet catcher 22, while the uncharged 
droplets continue downwardly onto the substrate. The present invention 
provides a novel and improved distribution bar, as well as a method for 
forming, assembling and using the bar. 
In accordance with the present invention, distribution bar 10 comprises a 
molded stainless steel bar formed of a pair of identical castings 20 and 
22, respectively. Each cast section is mated with an identical cast 
section along opposed longitudinally-extending lateral faces. The castings 
may be formed in conventional sand molds and joined together as 
hereinafter explained. 
Referring now to FIGS. 4 through 12, and initially to FIGS. 4 through 6, 
the cast sections each have channel sections, particularly upper, 
intermediate and lower channel sections 24s, 26s and 28s, respectively, 
which open through the longitudinally extending side face of the bar 
section, which is to be butted against the side face of the adjoining 
identically cast bar section. It will be appreciated from a review of FIG. 
2 that the channel sections 24s, 26s and 28s, in final assembly of the 
identically cast half-sections of the bar, define upper, intermediate and 
lower channels 24, 26 and 28, respectively. While an elongated slot 29 is 
illustrated between opposite mating bar sections 20 and 22 at the lower 
end of channel 28, as illustrated in FIG. 2, for distribution fluid from 
the bar to orifice plate 12, slot 29 is formed by machining after the bars 
are secured one to the other, rather than in the casting process. 
Adjacent one end of the bar section as illustrated in FIG. 5, each channel 
section 24s, 26s and 28s extends laterally into the bar section to a 
greater extent at transitions 24t, 26t and 28t, respectively, to define 
passages 24p, 26p and 28p, which remain open to the side as shown in FIG. 
5. That is, the channel sections 24s, 26s and 28s form transitions 24t, 
26t and 28t with the passages 24p, 26p and 28p at locations along the 
mating face of the cast half-section where the latter passages angle 
laterally or more deeply into the associated bar section. The passages 
24p, 26p and 28p within bar section 20 then curve upwardly. Openings 29 
are later machined and tapped to open through the upper surface of the 
corresponding bar section to provide communication with the respective 
passages 24p, 26p and 28p and threaded connections for receiving various 
fittings, not shown. Tapped openings 29 lie wholly within the bar section 
and do not open through the side face thereof. A void 30 is provided at 
the end of the casting to reduce the mass of metal of the bar, as well as 
to preclude distortions during cooling of the casting. 
FIGS. 7 through 9 illustrate portions of the distribution bar intermediate 
its opposite ends while the channel sections 24s, 26s and 28s thereof are 
illustrated in FIG. 8. A plurality of fluid communication ports 32 are 
spaced longitudinally along the bar section providing for communication 
between the upper and intermediate channels 24s and 26s, respectively. 
Similarly, a plurality of fluid communication ports 34 are provided 
between the intermediate and lower channels 26s and 28s, respectively, at 
longitudinally spaced positions along the length of the bar. From a review 
of FIG. 8, it will be appreciated that ports 32 and 34 are longitudinally 
offset one from the other. It will be appreciated that the ports 32 and 34 
illustrated in FIG. 8 are, when the casting is made, half-cylindrical 
recesses which form complete cylindrical ports upon mating assembly of the 
bar sections. 
Also in FIG. 8, the upper surface of intermediate channel section 26s is 
shaped to provide alternating linear upwardly sloping and downwardly 
sloping upper wall surfaces 36 and 38, respectively, terminating at an 
upper high point or apex 40 coincident with the axis of port 32. The 
juncture of the upwardly sloping and downwardly sloping walls 36 and 38 
form low points or lower apices 42. Somewhat similarly, the upper surface 
of lower channel section 28 has linear upwardly sloping and downwardly 
sloping surfaces 44 and 46, respectively. The surfaces 44 and 46 meet at 
an upper apex 48, which lies coincident with the axis of ports 34, and 
also meet at a lower apex 50 intermediate ports 34. Ports 32 between the 
upper and intermediate channel sections 24 and 26, respectively, are 
spaced one from the other twice the longitudinal distance that ports 34 
between intermediate and lower channels 26 and 38, respectively, are 
longitudinal spaced one from the other. Additionally, it will be seen that 
the surfaces 36 and 38, respectively, of the intermediate channel 26 
extend linearly between the lower apices 50 of the upper surface of the 
lower channel 28. 
FIG. 8 also shows bosses 52 which extend toward the centerline of the bar 
from the inner side wall of lower channel 28. While apertures 54 for 
receiving fasteners are illustrated in FIGS. 5, 8 and 11, the openings 
through bosses 52 and the apertures 54 are not formed in the casting 
process. Rather, such openings are later formed by machining when the bar 
sections are joined one to the other to ensure accurate fit. 
Referring now to FIGS. 10-12, there is illustrated the opposite end of cast 
bar section 20. In FIG. 11, channel sections 24s, 26s and 28s terminate in 
transitions 24t, 26t' and 28t' which open through the mating face of bar 
section 20 into the transition sections 24t, 26t and 28t of the opposite 
mating bar section 22 for communication with the passages 24p, 26p and 28p 
thereof, respectively. A void 30' is provided in the opposite end of the 
bar section for like reasons as void 30. 
Referring now to FIGS. 13, 14 and 15, the transition sections and the 
passages 24p, 26p and 28p formed at the lefthand end of the bar, as 
illustrated in FIG. 5, are clearly shown in relation to the upper, 
intermediate and lower channel sections, respectively. Additionally, the 
bar is shown prior to machining. For example, in FIG. 13, upper channel 24 
has its transition illustrated by the dashed lines extending downwardly 
and to the right, the passage 24p being illustrated by the vertical dashed 
lines extending through the upper edge of section 20. Similarly, the FIG. 
14, intermediate channel section 26 has its transition in bar section 20 
in communication with the passage 26p, which extends upwardly to open 
through the upper face of section 20. FIG. 15 illustrates the lower 
channel 28 and its transition illustrated by the dashed lines to the 
passage 28p opening through the upper face of section 20. Additionally, 
bosses 52 of the adjoining sections 20 and 22 are illustrated. 
In FIGS. 13, 14 and 15, the bar sections 20 and 22 are illustrated in full 
line prior to machining, with the lower channel's exit slot 29 illustrated 
in FIG. 15 being illustrated by dashed lines subsequent to machining. 
As indicated previously, each bar section 20 and 22 is formed of an 
identical casting, for example, in a sand mold. Once formed, the castings 
are machined to assure flatness of their mating surfaces. The cast 
sections are then disposed end-to-end and joined, using an anaerobic 
sealant. In joining the sections one to other, it will be seen that the 
channel sections, ports, transitions and bosses are aligned one with the 
other. Holes 54 are then drilled through the combined bar sections and the 
sections are bolted one to the other. Holes 55 (FIG. 8) in the lowermost 
portion of the bar sections are also drilled through bosses 52 formed in 
the mated casting. Once the bar sections are secured one to the other 
using bolts, not shown, passing through the openings 54 and 55, the lower 
face of the bar is machined to remove excess metal along the side margins, 
to form the elongated slot 29 in communication with lower channel 28, and 
to form a pair of side-by-side elongated recesses 58 for receiving seals 
60. 
To form the fluid distribution bar 10, the bar sections 20 and 22 are cast 
of stainless steel in a conventional sand mold. The molds are identical 
one with the other and, hence, the cast sections are identical. As 
illustrated in FIG. 15, the bar sections once formed are machined in part 
prior to assembly and in part subsequent to assembly. In FIG. 15, it will 
be seen that a portion of the lower chamber 28 is defined by a casting 
surface 61, which is machined before assembly of the bar sections one to 
the other to obtain the machined surface 62. The bar section passages 24p, 
26p and 28p at the locations where they open through the upper faces of 
the bars are tapped prior to assembly to provide the connections with 
various fluid lines. The bar sections are then mated along their 
longitudinally opposed faces such that the bar channel sections 24s, 26s 
and 28s open one into the other to complete the channels 24, 26 and 28, 
respectively. The ports 32 and 48 likewise mate with opposing ports to 
form cylindrical openings between the channels. 
Note that the grooves 58 for seal 60 form a continuous groove about the 
slot 29. Seal 60 thus extends continuously about opening 29. Referring to 
FIG. 13, lower opposite edge portions 64 of the bar sections are also 
machined to provide elongated recesses which cooperate with the clamp 
structure 14, as shown in FIGS. 1-3. 
To use the fluid distribution bar hereof, the orifice plate 12 is clamped 
along the underside of the bar, with its orifices in communication with 
the slot 29 and, hence, in communication with the channels of the bar. 
Once the bar is in position in the fluid-jet printing device, fluid is 
supplied to the channels through inlet openings at one end of the channels 
opening into passages 24p, 26p and 28p, respectively. As explained in 
another patent application filed on behalf of assignee, a vacuum is 
applied to the underside of the orifice plate to draw the fluid in the 
channels through the orifices and into a catcher tray in order to start 
the fluid filaments. Thus, it will be appreciated that fluid flows into 
the three channels simultaneously. Significantly, the bosses 52 lie in 
vertically spaced position below the ports 48 to prevent direct 
impingement of the fluid flowing through ports 48 downwardly into lower 
channel 28 onto the orifice plate 12. Thus, a more uniform application of 
the fluid to the orifice plate is provided. Also, it will be appreciated 
that the upwardly and downwardly sloping surfaces 44 and 46 of the lower 
channel and corresponding channels 36 and 38 of the intermediate channel 
tend to direct the gas entrained in the fluid upwardly to the high points 
or apices of the upper surfaces of the respective channels. It will be 
noted that such high points lie coincident with the ports whereby 
entrained gas escapes through the ports into the channel above the port. 
Each port therefore serves as a fluid communication channel for supplying 
fluid from one channel to the underlying channel, as well as a port for 
enabling egress of gas from the underlying channel to the overlying 
channel. In this manner, gas entrapped in the fluid and which is 
deleterious to the effective formation and continued flow of fluid 
filaments in a direction perpendicular to the orifice plate is removed 
from the channels without causing significant eddies or turbulence within 
the channels. 
Once starting is achieved, the ports of the lower channel 28 are closed, 
the outlet port of channel 26 is closed and chamber 24 is put in 
communication with a vacuum through either of its ports, to take away air 
reaching chamber 24 as bubbles from the fluid. Thus, fluid flows into 
intermediate channel 26 through its inlet port at one end for flow through 
the intermediate and lower channels to the orifice plate. 
To change fluids, all three chambers have their respective ports at one end 
open to drain and the opposite ports opened to receive the new fluid. The 
vacuum pressure is also removed. This causes a sweeping away of the old 
fluid across the length of the bar and its replacement with new fluid. 
Once the new fluid has completely replaced the old fluid, the lower 
chamber ports may be reclosed, the outlet port of the intermediate chamber 
may be closed and the upper chamber is re-connected to the vacuum. 
It will be understood that although the fluids being discharged from the 
orifice plate during changeover contaminate one another, they may all be 
collected in the catcher 22 and directed to waste. Since changeover is 
accomplished rapidly, the amount of waste is minimal. thus, color changes 
of dyes for fabric as a substrate S may be accomplished quite rapidly. 
Thus, it will be seen that the objectives of the present invention are 
fully accomplished in that there has been provided a novel and improved 
fluid distribution chamber for an fluid-jet printing device and a method 
of forming and operating the bar which affords improved flow of the fluid 
through the chamber and orifices. 
While the invention has been described in connection with what is presently 
considered to be the most practical and preferred embodiment it is to be 
understood that the invention is not to be limited to the disclosed 
embodiment, but on the contrary, is intended to cover various 
modifications and equivalent arrangements included within the spirit and 
scope of the appended claims.