Method and apparatus for assuring plating uniformity

A tensioning mechanism includes a frame pivotally carrying an arm at one end intermediate its length and carrying an arm fixed to the frame at its opposite end intermediate its length. Tension springs are disposed between the arms on one side of the frame and the ends of the arms on the opposite side of the frame releasably carry clamps for securing a substrate between the arms. When the substrate is clamped to the arms, the springs pivot the one arm to apply a tension to the substrate to ensure flatness and planarity of the substrate. The mechanism may then be disposed in an electrolytic bath for plating the substrate and hence defining locations for orifices to be formed in the substrate.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to apparatus and methods for forming the 
orifice plate for a fluid-jet printing device and particularly to 
apparatus and methods for assuring planarity of the orifice plate when 
disposed in an electrolytic bath whereby orifices of uniform size and 
shape through the orifice plate may be obtained. 
In fluid-jet printing technology, a linear array of fluid-jet orifices are 
formed in a substrate from which filaments of fluid issue to form a 
plurality of droplet streams for deposition on a substrate. Individually 
controllable electrostatic charging electrodes are disposed downstream of 
the orifice plate along the "drop formation" zone. In accordance with 
known principles of electrostatic conduction, these fluid filaments are 
provided an electrical charge opposite in polarity and related in 
magnitude to the electrical charge of the charging electrode. When the 
droplets separate from the filaments, the induced electrostatic charge is 
trapped on and in the droplets. The charged droplets then pass through a 
subsequent electrostatic field and are thereby deflected from a straight 
downward path toward a catcher structure. Uncharged droplets proceed along 
the straight path and are deposited upon the receiving substrate. 
Recognizing that the size of the individual orifices through the orifice 
plate is extremely small, a number of different apparatus and methods for 
forming the orifice plate have been proposed in the past. One such method 
is disclosed in U.S. Pat. No. 4,528,070, issued July 9, 1985, of common 
assignee herewith, the disclosure of which is incorporated herein by 
reference thereto. In that process, a photomask is applied to a stainless 
steel substrate to form specific images which are resistant to plating in 
the subsequent nickel-phosphorus plating steps. After the 
nickel-phosphorus plating is complete, the photomask is removed and the 
plated stainless steel is exposed to hot ferric chloride, which dissolves 
the stainless steel in the areas of the photomask not covered by the 
nickel-phosphorus plating. The resulting apertures through the plated 
substrate serve as orifices in the orifice plate of a fluid-jet printing 
apparatus. 
To assure that the fluid-jet droplets are formed regularly and precisely, 
it is important that the orifices formed in the orifice plate be as 
uniform in size and shape as possible. To achieve this uniformity, it is 
important that the coating, e.g., the nickel-phosphorus coating, is 
applied in as uniform and reproducible a manner as possible. In the 
electroplating process applying the nickel-phosphorus coating, the 
stainless steel substrate serves as a cathode in the electrolytic bath in 
which there is also disposed an anode. An electrical potential is applied 
across the anode/cathode and causes migration of ions to the cathode where 
they are reduced to nickel and phosphorus. The electrical field which 
causes the migration should be as uniform as possible across the area of 
the substrate to assure that the migration takes place uniformly toward 
the cathode surface. Additionally, the cathode should be as flat or planar 
as possible in order that the voltage over the surface being plated is as 
uniform as possible, thus assuring a uniform plating rate. 
Uniformity of the electrical field and the voltage over the surface being 
plated is achieved by making the orifice plate substrate as flat as 
possible and as parallel as possible relative to a planar anode array. 
Minor deviations from such planarity and parallelism cause irregularities 
in the amount of electroplating nickel and phosphorus, resulting in 
non-uniformity in orifice size and shape. This uniformity has proven 
somewhat difficult to achieve in practice because the stainless steel 
orifice plate, which forms the cathode in the electrolytic bath, is quite 
thin. Also, orifice plates for use in fluid-jet printers for applying ink, 
chemicals, etc. to textile fabrics are on the order of 1.8 meters long and 
thus are subject to flexing, bending and twisting, rendering achievement 
of planarity and parallelism in the electrolytic bath exceedingly 
difficult. 
In accordance with the present invention, there is provided apparatus for 
assuring the planarity of the orifice plate when in the electrolytic bath. 
To accomplish this, a tensioning mechanism for placing the 
cathode/substrate in tension during the electrolytic plating process is 
provided. Such apparatus includes an elongated frame mounting a pair of 
arms at opposite ends of the frame spaced one from the other a distance 
greater than the length of the cathode/substrate. One of the arms is 
pivoted intermediate its ends to the frame while the other arm is fixed 
intermediate its ends to the frame. Tension rods and springs extend 
between corresponding, e.g., upper, ends of the arms. The corresponding 
opposite, e.g., lower, ends of the arms are provided with a pair of spaced 
support elements which receive therebetween a pair of jaws for clamping 
the ends of the substrate. A pair of ceramic, electrical insulating, 
blocks are disposed between the jaws at each of the ends for grasping an 
end of the substrate whereby the substrate is electrically insulated from 
the tensioning mechanism. The jaws also mount a pin which is received in 
slots formed in the arms such that, when the substrate is tensioned 
between the arms, uniform tension is applied across the width of the 
substrate. 
Mounted on the frame adjacent the upper end of the pivoted arm is a toggle 
or over-center lever. The lever may be used to rotate the arm against the 
bias of the tension spring and thereby locate the lower arm in position to 
receive the pin. It will be appreciated that, upon release of the lever, 
the springs bias the arm for rotation in a direction applying tension to 
the substrate. In this manner, the flatness or planarity of the substrate 
is assured. 
It is important that the tension and hence the flatness and planarity of 
the substrate be maintained during the electroplating process. To avoid 
distortion or warpage of the tensioning mechanism when in the bath due to 
different temperature coefficients of expansion of various materials and 
to avoid the effects of the corrosive nature of the bath, the arms and the 
clamps, as well as the frame, are formed of titanium. The springs are 
formed of a different material, e.g., steel, inasmuch as they are not 
disposed in the bath. 
Prior to inserting the tensioned substrate into the bath, a plurality of 
electrical connections are spotwelded along the length of the substrate 
adjacent an edge thereof. The electrical connections are connected to a 
current control device for regulating current flow along each connection 
and hence the amount of plating in the immediate area of the substrate 
about welded electrical connection. That is, the plating is a function of 
the applied current and the hole size through the orifice plate is a 
function of the thickness of the plating. The relative thinness of the 
desired coating is about 6/10 of 1/1000 of an inch and it is desired to 
control the thickness of the plating to 1% of the thickness. To obtain 
such high accuracy and resolution, it is necessary to first 
electrolytically plate a series of substrates and measure the thickness on 
each substrate in order to ascertain the proper current flow through the 
electrical connections to the substrate, which, in turn, determines the 
thickness of the coating applied in the electrolytic bath. Once the proper 
thickness is obtained, the current controller is set and orifice plates 
may then be formed. In this manner, consistency, uniformity and 
reproducibility is achieved and the tensioning mechanism of the present 
invention contributes to those ends by maintaining the flatness or 
planarity of the substrate during the electroplating process. 
In accordance with a preferred embodiment of the present invention, there 
is provided apparatus for tensioning an elongated substrate for 
maintaining planarity thereof during an electroplating process to ensure 
substantially uniform plating, comprising a pair of means for gripping 
opposite end portions of the substrate, means connected to one of the 
gripping means for applying tension to the substrate and means for 
electrically isolating the tension applying means from the substrate. 
In accordance with a further preferred embodiment of the present invention, 
there is provided an apparatus for tensioning an elongated substrate for 
maintaining planarity thereof during an electroplating process thereby to 
ensure substantially uniform plating of the substrate, the apparatus 
comprising an elongated frame having at least one arm pivotally carried by 
the frame at one end thereof, a pair of clamps, one of the clamps being 
carried by the one arm, with the other of the clamps being carried by the 
frame adjacent the opposite end thereof such that the clamps may grip the 
opposite ends of the substrate. Means are also provided for electrically 
isolating the one arm and the frame from the substrate when clamped 
between the arms, with additional means being carried by the frame for 
pivoting the one arm in a direction for applying tension to the substrate. 
Preferably, each clamp includes a pair of jaws between which are carried a 
pair of insulator blocks for straddling the end of the substrate, the 
insulator blocks being formed of a ceramic material for electrically 
insulating the substrate from the frame. 
In accordance with a further aspect of the present invention there is 
provided a method for ensuring the planarity of an elongated substrate 
during an electroplating process and thereby ensuring substantially 
uniform plating, including the steps of clamping the opposite ends of a 
substrate in a frame, applying tension to one end of the clamped substrate 
to effect planarity thereof between its clamped ends and immersing the 
frame, while the substrate remains under tension, in an electrolytic bath 
to plate the substrate. 
Accordingly, it is a primary object of the present invention to provide 
novel and improved apparatus and methods for ensuring the planarity or 
flatness of a substrate in an electrolytic bath whereby the substrate may 
form the orifice plate of a fluid-jet printing or applicator device. 
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 the present preferred embodiment of 
the invention, an example of which is illustrated in the accompanying 
drawings. 
Referring now to the drawing figures, particularly to FIGS. 1 and 2, there 
is illustrated a tensioning mechanism constructed in accordance with the 
present invention and generally designated 10. Tensioning mechanism 10 
includes an elongated frame 12 having a length in excess of the length of 
a substrate S, e.g., an elongated orifice plate for fluid-jet printing. 
Frame 12 is formed of a pair of laterally spaced, elongated side plates 14 
and 16 secured one to the other by crosspieces 15 spaced longitudinally 
along frame 12 one from the other and bolted between side plates 14 and 
16. Elongated frame 12 includes a bottom plate 18 bolted to crosspieces 
15. As illustrated, the ends of frame 12 are disposed in the notched upper 
ends of a pair of end supports 20 and 22 and is removable from and 
portable relative to end supports 20 and 22. 
A pair of arms 24 and 26, respectively, are mounted at opposite ends of 
frame 12. The arms are identical in construction one to the other except 
that arm 24 is pivotally carried by frame 12 for pivoting movement about 
an axis 28, whereas arm 26 is rigidly secured to frame 12. Each arm 24 and 
26 includes a pair of laterally spaced elements 30 and 32 (FIG. 4) with 
suitable crosspieces 34 bolted therebetween. As best seen in FIG. 4, 
elements 30 and 32 terminate at their upper ends in laterally outwardly 
directed flanges 34 and 36, respectively, to which a crossbar 38 is 
suitably connected, for example, by bolts. As best seen in FIG. 2, a pair 
of rods 40 and 42 interconnect the opposed end edges of crossbars 38 at 
opposite ends of frame 12. More particularly, the end of each rod 40 is 
threaded at 44 (FIG. 3) and a pair of lock nuts 46, together with a 
washer, adjustably secure the rod 40 to the crossbar 38 at one end of the 
frame 12. With reference to FIGS. 1 and 2, the opposite end of each rod 40 
connects with one end of a tension spring 48, the opposite end of the 
tension spring being connected to the interior end of rod 42. The opposite 
end of each rod 42 is threaded and bolted to the corresponding end of 
crossbar 38. As best seen in FIGS. 3 and 4, each of the lower ends of 
spaced elements 30 and 32 of arms 24 and 26 are provided with a track or 
slot 50 for releasably receiving a clamping mechanism C, which will now be 
described. 
Clamping mechanism C comprises a pair of jaws 52 and 54 releasably secured 
one to the other, for example, by bolts 56 whereby the jaws can be moved 
toward and away from one another. As illustrated in FIG. 5, jaws 52 and 54 
are generally L-shaped in cross-section, and are disposed in opposition 
one to the other. The opposed legs of the jaws define a space therebetween 
for receiving a pair of ceramic insulating blocks 58 and 60, respectively. 
A pair of pins 62 and 64, respectively, mount the insulator blocks 58 and 
60 between the jaws. Thus, an end of a substrate may be inserted between 
blocks 58 and 60 and the jaws moved toward one another by action of bolts 
56 to clamp the substrate end therebetween. 
A pin 66 extends through jaws 52 and 54 in a region thereof spaced from 
blocks 58 and 60 and projects beyond the side faces of the clamp. Pin 66 
is releasably receivable in the slots 50 in elements 30 and 32. The clamps 
are therefore connected to arms 24 and 26 essentially by a single central 
pivotal contact. 
For reasons hereinafter disclosed, a support bracket is mounted at one end 
of frame 12 and carries a lever 72 for pivotal movement about a pivot 74. 
Lever 72 constitutes an over-center or toggle clamp and has a hook 76 
pivotally carried intermediate its length. It will be appreciated from a 
review of FIGS. 3 and 6 that movement of lever 72 in a counterclockwise 
direction causes hook 76 to engage crossbar 38. Further pivoting action of 
lever 72 causes hook 76 to pivot arm 24 in a counterclockwise direction 
against the bias of tension springs 48. Release of hook 76 from crossbar 
38 enables tension springs 48 to pivot arm 24 in a reverse or clockwise 
direction, as illustrated in FIG. 3. When the substrate is disengaged from 
the tension mechanism and the springs 48 have rotated arm 24 to the full 
line position illustrated in FIG. 6, it will be seen that a pair of 
openings in the frame and arm 24, respectively, lie in misalignment, one 
with the other. Upon tensioning springs 48 by movement of lever 72, these 
openings can be brought into alignment when the arm is in the position 
substantially as illustrated in FIG. 3, whereby a pin may be inserted 
through the registering openings to lock arm 24 in that position. Thus, 
prior to use, the arm 24 lies canted by springs 48 in the full line 
position illustrated in FIG. 6. 
In use, lever arm 72 is rotated to engage hook 76 with crossbar 38. Lever 
arm 72 is then pulled back to rotate arm 24 in a generally 
counterclockwise direction, as illustrated in FIG. 3, into a substantially 
vertical orientation wherein the distance between the lower ends of the 
arms is such that the substrate, when the clamps are secured to its 
opposite ends, may be attached to the arms by disposing pins 66 in slots 
50. Thus, lever 72 is used to rotate arm 24 into the position illustrated 
in FIG. 3 against the bias of springs 48. The clamps C, which are separate 
from the arm, are clamped about the ends of the substrate with the 
insulator blocks disposed between the substrate and the jaws. With the 
opposite ends of the substrate disposed within the clamps and the arm 24 
lying in the full line and dashed line positions illustrated in FIGS. 3 
and 6, respectively, pins 66 carried by clamps C are inserted into slot 
50, whereby the clamps are carried by the respective arms, with the 
substrate extending therebetween. Release of the lever 72, for example by 
rotating it past its over-center position to disengage hook 76 from 
crossbar 38, enables tension spring 48 to rotate arm 24, for example in a 
clockwise direction illustrated in FIG. 3, to tension the substrate. The 
tension applied to arm 24, in turn, displaces the lower clamp carried 
thereby in a direction away from the clamp at the opposite end of the 
frame whereby the substrate is placed under tension. The single pivotal 
point of contact between the clamp and the arm at each end of the 
tensioning mechanism affords a uniformity of tension across the width of 
the substrate. 
To ensure that the substrate is plated to a uniform thickness, a 
trial-and-error approach is afforded. Particularly, electrical leads 80 
(FIG. 7) are welded at 82 along substrates, for example every four inches, 
for connection to a current controller I.E. which regulates the current 
flow through each wire when substrate S is disposed in the electrolytic 
bath B. That is, the current flow to the various portions of substrate S 
defined by the electrical connections thereto can be selected to afford 
more or less plating to achieve the correct hole size. Thus, in use, the 
tensioning mechanism with a tensioned substrate and electrical connections 
is disposed in the electrolytic bath B and current applied. With the 
substrate serving as a cathode, ions migrate toward the cathode to provide 
the nickel phosphorus plating. The tensioning mechanism and substrate S 
are then removed from the bath and orifices are formed in the substrate by 
treating it with ferric chloride in the manner set forth in the 
above-identified patent. Because hole size is a function of the plating 
thickness, the correct hole size may be determined by applying a 
predetermined plate thickness along the plate. Thus, once it has been 
determined what areas of the plate do not have the correct hole size, the 
current controller can be adjusted to increase or decrease the current 
flow to selected areas of a plate to thereby increase or decrease the 
plate thickness, as necessary. Thus, after trial and error on different 
substrates disposed in the electrolytic bath, the appropriate current at 
each longitudinal position along the substrate may be determined. Once 
determined, substrates may be electroplated, using the tensioning 
apparatus described herein, to the proper thickness, thereby ensuring 
accuracy of the hole size in a consistent and reproducible manner. 
It will be appreciated that the tensioning mechanism assures flatness and 
planarity of the substrate disposed between the clamps. When the 
tensioning mechanism is disposed in the bath, a fixture, not shown, 
locates the mechanism and substrate a predetermined distance from the 
anode in the bath. Also, to ensure that the electrolytic bath itself, due 
to its high temperature and corrosive nature, does not distort, warp or 
otherwise effect movement of the substrate while tensioned in the frame, 
the frame, arms and clamps (excluding the ceramic blocks) are formed of 
titanium. In this manner, the effects of high temperature on different 
materials, as well as the corrosive effects of the bath on the tensioning 
mechanism, which would otherwise tend to distort or warp the frame in the 
bath, are eliminated. The springs 48 and rods associated therewith need 
not be formed of titanium and may be formed of other materials, such as 
steel, inasmuch as they are maintained outside the bath, as illustrated in 
FIG. 7. Thus, uniformity and reproducibility of the plating process is 
achieved for each substrate. 
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.