U.S. patent number 3,761,953 [Application Number 05/299,900] was granted by the patent office on 1973-09-25 for ink supply system for a jet ink printer.
This patent grant is currently assigned to The Mead Corporation. Invention is credited to Lysle D. Cahill, Gaylord A. Helgeson.
United States Patent |
3,761,953 |
Helgeson , et al. |
September 25, 1973 |
INK SUPPLY SYSTEM FOR A JET INK PRINTER
Abstract
There is disclosed an ink recirculation and replenishment system
for use in combination with an ink jet printer. Ink which is formed
into drops but not deposited on the print receiving member is
collected in a vacuum tank and thereafter recirculated by a
reciprocating pump at a steady volumetric rate. There is a pressure
tank for regulating pressure of the pumped ink and returning excess
ink directly to the pump. Means are provided for supplying an ink
replenishment liquid to the system as well as fresh ink in
volumetric amounts as required to replace fluid lost by printing
and by evaporation. The replenishment liquid contains a solvent,
which in the case of aqueous base ink will be water, and other
agents for preventing deterioration of the recirculated ink. A
depletion sensor, preferably a conductivity probe, is provided for
automatic control of replenishment liquid addition.
Inventors: |
Helgeson; Gaylord A. (Dayton,
OH), Cahill; Lysle D. (Dayton, OH) |
Assignee: |
The Mead Corporation (Dayton,
OH)
|
Family
ID: |
23156776 |
Appl.
No.: |
05/299,900 |
Filed: |
October 24, 1972 |
Current U.S.
Class: |
347/7; 137/5;
137/93; 347/89 |
Current CPC
Class: |
B41J
2/195 (20130101); Y10T 137/034 (20150401); Y10T
137/2509 (20150401) |
Current International
Class: |
B41J
2/17 (20060101); B41J 2/195 (20060101); G01d
015/18 () |
Field of
Search: |
;346/75,140
;137/5,93 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hartary; Joseph W.
Claims
What is claimed is:
1. A recirculating ink supply system for a jet drop printer
comprising:
1. an ink collection receptacle connected for collection of excess
ink from said jet drop printing system,
2. a supply line connected for recirculating reception of collected
ink from said ink collection receptacle,
3. means for supplying fresh ink to said supply line,
4. means for withdrawing the fluid content from said supply line at
a controlled volume rate,
5. pressurizing means for pressurizing the fluid withdrawn as
aforesaid from said supply line and delivering the pressurized
fluid to said jet drop printer, and
6. means for mixing a depletion correcting replenishment fluid with
the recirculated ink delivered as aforesaid to said jet drop
printer.
2. Apparatus according to claim 1 further comprising means for
sensing a depletion state of said recirculated ink and controlling
said mixing means in response thereto.
3. Apparatus according to claim 2, said mixing means being
connected to said supply line, and said sensing means being
connected for sensing the depletion state of fluid at the output
side of said withdrawing means.
4. Apparatus according to claim 2, said sensing means comprising a
conductivity sensor.
5. Apparatus according to claim 1 further comprising means for
controlling the flow of fresh ink into said supply line in
accordance with the back pressure created therein by said
withdrawing means.
6. Apparatus according to claim 5 said fresh ink supply means
comprising a fresh ink supply vessel and a feed line connecting
said vessel with said supply line, and said means for controlling
the flow of fresh ink comprising a check valve in said feed
line.
7. Apparatus according to claim 6, said mixing means comprising a
replenishment fluid supply vessel connected to said feed line and a
mixture control valve for selectively admitting fresh ink or
replenishment fluid into said feed line.
8. Apparatus according to claim 7, said pressurizing means having
an overflow line connected to said supply line.
9. Apparatus according to claim 8 further comprising a check valve
between said ink collection receptacle and said supply line, the
cracking pressure for said valve being less than the cracking
pressure for the check valve in said feed line whereby said
withdrawing means selectively withdraws from said supply line;
first the overflow ink from said pressurizing means, next the ink
from said collection receptacle, and lastly fresh ink or
replenishment fluid depending upon the position of said mixture
control valve.
10. Apparatus according to claim 9 further comprising a
conductivity sensor for sensing the conductivity of the fluid
withdrawn from said supply line and a solenoid for receiving a
sensing signal from said sensor and positioning said mixture
control valve in response thereto.
11. Apparatus according to claim 1 said pressurizing means
comprising:
1. an ink pressurizing vessel,
2. input and output connections to said vessel,
3. a standpipe mounted within said vessel and connected for
drainage to said supply line,
4. a diaphragm for covering the entrance to said standpipe, and
5. means for urging said diaphragm against said standpipe whereby
said input connection receives ink at the delivery rate of said
withdrawing means, and said output connection delivers pressurized
ink at a rate as required by said jet drop printer, with surplus
ink exiting the ink pressurizing vessel via said standpipe.
12. Apparatus according to claim 11 said means for urging said
diaphragm against said standpipe comprising a gas chamber and means
for delivering a pressurized gas thereto.
13. Apparatus according to claim 12 wherein the pressurized fluid
flowing from said pressurizing means to said jet drop printer
passes through a surge tank comprising a surge cell for pooling
said pressurized fluid under an entrapped pocket of air and input
and output connections thereto.
14. In a system for marking with individual drops of ink,
including
a supply reservoir of aqueous base marking ink containing normally
solid dissolved materials, the liquid portions of such ink being
volatizable in use whereupon the proportion of solids to liquids
changes sufficiently to cause a material change in the flow
characteristics of the ink,
a drop generator arranged to receive liquid from said reservoir and
to project a stream of discrete drops along one trajectory,
means for deflecting selected individual drops into anther
trajectory,
catcher means arranged to intercept drops following one of the
trajectories and permitting drops following the other trajectory to
proceed toward a receiving surface; and
a return connection from said catcher means to said reservoir; the
improvement comprising
means sensing the relation of volatizable to nonvolatizable
portions of the liquid in the system,
means controlled by said sensing means for replenishing volatizable
components of the marking liquid which are lost in the liquid
system,
means for combining the replenished marking liquid with fresh
marking ink,
means for circulating the combined fluid toward said drop generator
at a controlled volume rate, and
means for returning to said circulating means a portion of said
combined fluid in variable amount as required to maintain a
regulated pressure in the fluid received by said drop
generator.
15. A system as defined in claim 14 including a filter in said
return connection to remove contaminants entering the open part of
the liquid system between the drop generator and the catcher
means.
16. A system as defined in claim 14 wherein said sensing means
includes a conductivity sensor.
Description
BACKGROUND OF THE INVENTION
This invention relates to jet drop printing devices, and
particularly to the inking systems thereof. A typical construction
and arrangement of such a jet drop printing device is disclosed in
U.S. Pat. No, 3,588,906, issued June 28, 1971, and assigned to the
assignee of this application.
In the operation of such printing devices a suitable conductive ink
is directed through a drop generator for formation into a stream of
uniformly sized and regularly spaced drops. These drops are
selectively charged in accordance with an input intelligence signal
and thereafter are either deposited on a print receiving member or
caught and collected by a suitable catcher. However, for many
printing applications the ratio of printed to unprinted area is
quite small so that most of the ink passing through the drop
generator is collected by the catcher. Accordingly, it has become
desirable to achieve economy of operation by recirculating and
reusing the collected ink.
During recirculation and reuse of such ink it has been discovered
that the used ink differs from fresh ink in specific gravity,
viscosity, and conductivity. For instance in a study of aqueous
base inks of the type disclosed in copending U.S. application Ser.
No. 153,426, filed June 15, 1971, it was found that between 10 and
20 percent of the solvent was being lost during the drop forming
and catching process. The exact quantity of solvent lost is
dependent upon the vapor pressure of the solvent and hence varies
with the drop temperature, the relative humidity of the air stream
along the drop path or trajectory, the time duration of drop
exposure, and the rate of air flow through the system.
It has been observed that any loss of solvent increases the ionic
strength of the additives, particularly the electrolyte, in such
ink, up to the point of saturation. Above this point precipitation
of the dye stuff and other ink constituents occurs, causing
clogging of the fine pores of the filter in the ink recirculating
system, and also causing clogging of the small jet orifices.
Observation also indicated that not only the solvent, but other
constituents of the ink were being lost from the system. In the
case of the particular ink disclosed in said copending application
Ser. No. 153,426, the loss of the metal chelating agent
glucono-.delta.-lactone was observed to occur. The symptoms that
led to discovery of loss of this component were clogging of the
jets and the filters. Apparently the metal ion complexing agent,
the glucono-.delta.-lactone, may have complexed in the process of
circulation through various stainless steel components of the ink
conducting system.
SUMMARY OF THE INVENTION
In accordance with this invention it has been found that
deterioration of jet drop printing ink may be avoided by adding an
appropriate replenishment solution in a novel manner as hereinafter
described. In the case of the ink described in Ser. No. 153,426 an
appropriate replenishment solution has been found to comprise
distilled water; glucono-.delta.-lactone, a corrosion inhibiting
agent; 1, 2,-6 hexanetriol, an anti caking agent; and an
anti-microbial compound manufactured by Dow Chemical Company under
the name Dowicil 100. The anti-microbial compound which is known
chemically as 1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane
chloride inhibits the growth of Penicillium sp.
The replenishment liquid is packaged in a plastic bag within a
stiff cubic container and placed spout down, above a mixing valve.
A supply of fresh ink is similarly placed above the mixing valve,
and the output from the mixing valve is used to make up system
volumetric losses. This output together with recirculated ink is
pumped toward the jet drop printing head by a reciprocating pump.
The pump moves ink at a steady volumetric rate and creates a back
pressure in the pump supply lines. The output from the mixing valve
passes through a pressure operated check valve enroute to the pump
so that recirculated ink is preferentially pumped; fresh ink or
replenishment liquid being pumped only as required to make up
volumetric losses in the system. A depletion sensor, preferably a
conductivity sensor may be placed at the output side of the pump
and used to control the position of the mixing valve. The pressure
of the ink at the output side of the pump is regulated by a novel
pressure tank for delivery to the printing head. As a result there
is provided a simple reliable ink recirculation and replenishment
system requiring very few electrical controls.
Accordingly it is an object of this invention to eliminate
deterioration of ink in a recirculating ink jet printer by adding
controlled amounts of replenishing liquid thereto.
It is another object of this invention to make up volumetric losses
of ink in a recirculating ink jet printer by adding controlled
amounts of fresh ink thereto.
It is still another object of this invention to provide simple
improved apparatus for recirculating ink in an ink jet printing
system.
Another object of the invention is to provide improved pressure
regulating means for an ink supply system for an ink jet
printer.
Other objects and advantages of the invention will be apparent from
the following description, the accompanying drawings and the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The FIGURE is a schematic diagram including fluidic and electrical
controls for an ink recirculation and replenishment system for an
ink jet printer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A preferred embodiment of the invention is illustrated in the
FIGURE wherein an ink drop generator 10 generates a series of drops
18, some of which are deposited on a print receiving member 19 and
some of which are intercepted by a catcher 24. The ink which is
caught by catcher 24 is recirculated to drop generator 10 by
passing through an ink collection receptacle 11, then through a
withdrawing means such as a reciprocating pump 12, and then through
a pressurizing means such as pressure tank 13. There is an overflow
line 14 from pressure tank 13 which delivers excess ink to ink
supply line 15 which is the primary supply line for pump 12.
Pressurized ink for use by drop generator 10 leaves pressure tank
13 by an exit line 47 which leads to a filter 48 and a surge tank
49.
Drop generator 10 comprises an orifice assembly 16, a stimulator
17, a charging electrode 20, a charge signal amplifier 21 and a
pair of deflection electrodes 22 and 23. Drop formation charging
and deflection, which forms no part of this invention, is carried
out as described for instance in Van Brimer et al U.S. Pat. No.
3,588,906.
Ink collection receptacle 11 is a vacuum tank which comprises a
vessel 25 and a float valve assembly 26. Vacuum within vacuum tank
11 is created by a vacuum pump 29 and is regulated by a regulator
30 which may have a filter 31 attached thereto. Float valve
assembly 26 causes incoming ink to accumulate in vacuum tank 11
until a predetermined volume has been collected. Thereafter float
valve assembly 26 rises and permits collected ink to flow into exit
line 27 and thence through check valve 28 and supply line 15 to
pump 12. Pump 12 pumps liquid in steady constant volume pulses,
thereby creating pulses of reduced pressure in supply line 15 and
at the operating control for check valve 28. Thus collected ink is
delivered from vacuum tank 11 to pump 12 only when a predetermined
volume of ink has been collected in vessel 25 and then only if the
pressure across check valve 28 exceeds a predetermined minimum,
typically about 1/3 psid. There is also a check valve 68 for
supplying line 15 which may be set for opening upon sensing of
pressure differential of about 5 psid. Thus if vacuum tank 11 is
low on collected ink and float valve 26 is closed, pump 12 will
draw liquid for pumping through check valve 68 which provides fresh
ink or a replenishing liquid as hereinafter described. However,
check valves 28 and 68 are relatively set so that pump 12 will draw
liquid preferentially from vacuum tank 11.
Pump 12 comprises a flexible diaphragm 32, a hydraulic liquid pool
33 and a reciprocating shaft 34. Forward motion of shaft 34 extends
diaphragm 32, closes an inlet valve 35, opens an exit valve 36, and
pumps a controlled volume of ink toward pressure tank 13. Return
movement of shaft 34 causes relaxation of diaphragm 32, closing of
exit valve 36, opening of entrance valve 35, and withdrawal of a
fixed volume of fluid from line 14, check valve 28, and/or check
valve 68. Reciprocation of shaft 34 is produced by a motor 37, a
cam 38, and other linkage as illustrated.
There is a surge tank 39 connected to the exit side of pump 12 for
damping out pressure surges in the pumped ink. The pumped ink
bypasses surge tank 39 as illustrated, and does not pass
therethrough.
After leaving pump 12 the pumped ink passes through a replenishment
sensing cell 40, and thence through filter 41 enroute to pressure
tank 13. Replenishment sensing cell 40 may comprise a pair of
conductive probes 69 and 70 and a thermistor 74. Cell 40 is
configured for measurement of the conductivity of the ink flowing
therethrough, and accordingly has a driver 71 and an amplifier 72
connected respectively to probes 69 and 70. Driver 71 generates an
electrical signal which is transmitted to amplifier 72 via the ink
in cell 40. The amplitude of the signal generated by the amplifier
72 is thus a function of the conductivity of the fluid in cell 40.
The output from amplifier 72 is fed to a trigger circuit 73 which
fires when the conductivity of the ink in cell 40 is above some
predetermined level.
When trigger 73 fires, it activates solenoid 67 to position valve
66 for admission of fluid from tank 64 to line 65. However, in the
absence of a trigger signal, valve 66 is ordinarily positioned for
admission of fluid from tank 63 into line 65. Tank 63 contains
fresh ink, while tank 64 contains a replenishing solution as
hereinafter described. Thus it is seen that when pump 12
reciprocates on the backward stroke, it creates a back pressure at
the pump inlet which causes pumping first of overflow from line 14,
then collected ink from vacuum tank 11, and finally fresh ink from
tank 63 in volumetric amounts as required to augment overflow ink
and collected ink. However, if the conductivity as measured by cell
40 is above a predetermined level, then replenishing fluid replaces
fresh ink as a volumetric supplement for input to pump 12.
Conductivity variations due to temperature changes in the
recirculated ink are compensated by a temperature compensating
network 75 which is connected to thermistor 74. Temperature
variations within the ink in cell 40 cause resistance changes in
thermistor 74 and these changes are sensed by the network 75.
Network 75 generates a compensating signal which is added to the
output signal from driver 71 for application to probe 69.
After leaving cell 40, the ink flows through a filter 41, as stated
above, and thence through a line 46 into pressure tank 13. Pressure
tank 13 comprises a pressurizing vessel 42, a standpipe 43, a
diaphragm 44 and an air cavity 45. Air is supplied to cavity 45 at
a regulated pressure for urging diaphragm 44 downwardly against the
entrance to standpipe 43. Ink normally enters pressure tank 13 via
entrance line 46 and leaves via exit line 47, but the input rate is
preferably greater than the output rate. Consequently the incoming
ink fills vessel 42 and bears upwardly against diaphragm 44. When
the pressure of the ink within vessel 42 exceeds the pressure of
the air in cavity 45, the ink begins to enter standpipe 43 at the
top thereof and flows downwardly to overflow line 14. Thus the
volume and pressure of the ink delivered into line 47 for use by
drop generator 10 is carefully regulated.
The ink which leaves pressure tank 13 has been observed in some
cases to exhibit small pressure surges which would disturb the
operation of drop generator 10. Thus the ink is directed through a
surge tank 49 which comprises a surge cell 52 and input and output
collections thereto. The ink enters surge cell 52 wherein it is met
by an entrapped pocket of air 53 which absorbs minor pressure
variations therein. Thereafter the ink flows from surge cell 52 to
the orifice assembly 16 for formation into drops 18 as
aforesaid.
Pressurized air for use by pressure tank 13 is supplied by an
external high pressure air supply. The pressurized air passes
through a manually controlled inlet valve 62 thence through an air
filter 61 and an air pressure regulator 60. There is a bleed tank
54 which is connected to filters 41 and 48 by lines 57 and 58
respectively. Bleed tank 54 bleeds off air which may become
entrapped in filters 41 and 48. Bleed tank 54 is primarily
important during start-up of the system, and regulating valves 55
and 56 regulate the operation thereof.
The recirculating and replenishment system may also comprise a
series of guages 76, 77, 78 and 79, and a sampling valve as shown
in FIG. 1. Typically pump 12 may pump fixed volumes of ink at a
rate of about two pulses per second and is capable of pumping a
pressure which varies from about 75 to 90 psi. at the pump outlet.
This pressure is regulated by pressure tank 13 so that the pressure
rate at guage 78 is about 25 psi.
Containers 63 and 64 may be commercially available containers of
the bag-in-box variety comprising a flexible plastic bag within a
rigid container. Such containers are normally supplied with spouts
so that they may be readily connected to the input lines for mixing
valve 66 and thus supply liquid on demand from their inner plastic
bags. The replenishing liquid supplied by container 64 may be
tailored to meet the needs of the particular ink used by the
system. For instance, in the case of a water base anti cockling ink
as described in Ser. No. 153,426, an appropriate replenishing
liquid has been found to comprise distilled water; about 0.2
percent by weight of 1, 2, 6-hexanetriol; about 0.05 percent by
weight of glucono-.delta.-lactone; and about 0.5 grams per liter of
an anti-microbial compound manufactured by Dow Chemical Company
under the name Dowicil 100.
The 1, 2, 6-hexanetriol is an agent which is added both to fresh
ink and to the replenishing liquid for the purpose of slowing down
evaporation and inhibiting the tendency of the ink to cake in the
jet assembly. Glucono-.delta.-lactone is also added to the fresh
ink as well as to the replenisher for the purpose of preventing
precipitation of ink constitutents by metal contaminants, with the
concentration in fresh ink being about twice that in the
replenisher. The anti-microbial solution which is known chemically
as 1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride
inhibits the growth of Penicillium sp, an airborne sporific fungus
which tends to form filamentary colonies within the replenisher and
thus to clog filters 41 and 48 and orifice assembly 16.
When the water or other solvent in the ink evaporates, the direct
result is an increase in viscosity and specific gravity. However,
it has been found that the conductivity of the ink also increases
with the loss of solvent, so that increases in solids
concentrations may be observed indirectly by measuring the ink
conductivity. Accordingly the addition of replenishing liquid is
preferably controlled by solenoid 67 which in turn responds to
measurements made by the conductivity sensor 40, all as described
above. Typically trigger 73 will be set so that replenishing liquid
is delivered to the system when the measured conductivity exceeds
about 0.0390 mhos per cem. This corresponds to a specific gravity
of about 1.080. The fresh ink has a nominal specific gravity of
1.070.
It will be appreciated that while as much as 10 to 20 percent of
the solvent may be lost by ink passing through drop generator 16,
this loss over a short period of time represents only a small
fraction of the total amount of solvent in the entire system. Thus
it is not necessary that driver 71, amplifier 72, trigger 73, and
the temperature compensating network 75 operate continuously.
Accordingly the foregoing elements are conveniently packaged to
make an analyzing unit 81 which may be time shared with other jet
drop printing systems. Alternatively a single jet drop printing
system may comprise four drop generators such as drop generator 16
for printing four different colors in relative registration. Such a
printer may comprise four ink recirculation and replenishment
systems such as the system of FIG. 1 but with a single time shared
analyzing unit 81.
While the form of apparatus herein described constitutes a
preferred embodiment of the invention, it is to be understood that
the invention is not limited to this precise form of apparatus, and
that changes may be made therein without departing from the scope
of the invention.
* * * * *