Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an ink jet printing system, and more
particularly to an improved method and means for maintaining a supply of ink
for the printing system.
In the operation of a synchronous ink jet printing device, the -~
ink jet nozzle is supplied with fluid ink, which is pressurized to typically
between 2 and 5 atmospheres absolute pressure. Of the ink drops directed at
a target surface, those which are not to be used in printing are captured and
removed. This unused ink is then returned to the ink supply and recirculated ~ -
through the system. The ink recirculation heretofore has been achieved by ~
using a pump to supply pressurized ink to the nozzle and draw ink from a ven- `
ted container. The returned ink would be deposited in this vented container. -
The problems which arise with this method, are those of a low mechanical -
reliability of the pumps and valves, as well as the difficulty in obtaining
chemical compatibility of different inks which are used. The pumps also
produce cyclic pressure variations, pulses, which must be minimized by means ~ ~
Qf fluid pressure regulation. In order to avoid a deterioration in print ~ ;
.... .
quality a stable stream of constant velocity droplets must be provided. For
this, an ink jet nozzle must be supplied with a nonvarying ink pressure.
Thus, the problems introduced by the pumps can adversely affect printing.
Another widely used method of fluid pressurization and recircula-
tion, is to supply a nozzle with fluid ink which is forced out of a pressure
vessel by a volume of a pressure regulated compressed gas. The returning un-
used ink is temporarily stored in another container. When the vessel from
which ink is supplied to the nozzle is empty of ink (or nearly so), the ink
recaptured from the ink drop stream is introduced into the pressure vessel,
rom the return ink container, by either automatic means, or manually while
the pressure vessel is vented to the atmosphere. This method circumvents the
problems associated with pump systems, however, the time which this type of
system can operate continuously is limited by ink pressure vessel capacity
and the number of nozzles being supplied.
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An object of this invention is to provide for an ink jet printing system,
an ink supply system which has the continuous operation capabilities of a pump
system with the constant pressure supply of the compressed gas system.
According to one aspect of this invention there is provided an ink jet
printing system of the type wherein ink is supplied from an ink reservoir to a
nozzle to be projected thereby as a stream of drops toward a target, some of ; .
the drops in said stream being deflected for printing on said target, the
remaining ink drops in said stream being captured, the improvement comprising:
a container for said captured ink, means for transferring said captured ink
into said captured ink container, means for transferring ink from said
captured ink container into said ink reservoir including, first means for
pressurizing said captured ink container to a pressure greater than the :
pressure in said ink reservoir during the transfer of ink and for discontinu-
ing the pressurization upon the termination of said ink transfer, a fresh ink
container, and means for transferring ink from said fresh ink container to
said ink reservoir, said ink transferring means including second means for
pressurizing said fresh ink container to a pressure greater than the pressure
in said fresh ink reservoir and for discontinuing the pressurization when said
transfer of ink to said ink reservoir is discontinued.
According to another aspect of this invention there is provided an ink
jet printing system of the type wherein ink is supplied from an ink reservoir
to a nozzle to be projected thereby as a stream of drops toward a target, some
of the drops in said stream being deflected for pTinting on said target, the :
remaining ink drops in said stream being captured, the improvement comprising:
a container for said captured ink, means for transferring said captured ink
into said captured ink container, means for transferring ink from said
captured ink container into said ink reservoir including first means for
pressurizing said captured ink container to a pressure greater than the
pressure in said ink reservoir during the transfer of ink and for discontinu-
ing the pressurization upon the termination of said ink transfer, a fresh ink
container, and means for transferring ink from said fresh ink container to
said ink reservoir including, means for transferring ink from said fresh ink
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container to said captured ink container when said means for transferring ink ~ ~
from said captured ink container into said ink reservoir is inoperative. -~ -
According to a further aspect of this invention there is provided an ink
jet printing system of the type wherein ink is supplied from a reservoir to a
nozzle to be projected thereby as a stream of drops toward a target, some of
the drops in said stream being deflected for printing on said target, the
remaining ink drops in said stream being captured, the improvement comprising:
means for supplying a pressurized gas, a first pressure regulator for applying
gas~at a first pressure from said means to said ink reservoir to thereby cause .
ink to flow out of said reservoir to said printing head, a captured ink
container, a first valve means connected to said captured ink container, said ; ~:
first valve having a first position for enabling captured ink to be directed
to said captured ink container, and a second position for closing said captured
ink container and for directing ink from said captured ink container into said -
ink reservoir, means for applying gas at a pressure higher than said first
pressure to said captured ink container when said valve means is in its second
position, means for operating said first valve means from i~s first, to its
second position and from its second to its first position, a container for
fresh ink, and a second valve means having a first position for enabling ink
to flow from said fresh ink container to said ink reservoir, and a second : :
position for preventing the flow of fresh ink from said fresh ink container to
said ink reservoir.
According to another aspect of this invention there is provided an ink
jet printing system of the type wherein ink is supplied from a reservoir to a
nozzle to be projected thereby as a stream of drops toward a target, some of
the drops in said stream being deflected for printing on said target, the
remaining ink drops in said stream being captured, the improvement comprising:
means for supplying a pressurized gas, a first pressure regulator for applying
gas at a first pressure from said means to said ink reservoir to thereby cause
ink to flow out of said reservoir to said printing head, a captured ink
container, a first valve means connected to said captured ink container, said
first valve having a first position for enabling captured ink to be directed
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to said captured ink container, and a second position for preventing further
input of captured ink to said captured ink container and for directing ink
from said captured ink container to be introduced into said ink reservoir,
means for applying gas at a pressure higher than said first pressure to said
captured ink container when said valve means is in its second position, means
responsive to the level of the ink in said ink reservoir for operating said
first valve means from its first to its second position, and from its second
to its first position, a container for fresh ink, a second valve means having ~-
a first position for enabling ink to flow from said fresh ink container to
said ink reservoir, and a second position for preventing the flow of fresh ink
from said fresh ink container to said ink reservoir, and means for applying
gas, at a pressure higher than the first pressure, from said source of
pressurized gas to said fresh ink container when said second valve is in its
first position, whereby ink may flow from said fresh ink container into said
ink reservoir through said second valve means.
The invention will best be understood from the following description of -~
exemplary embodiments thereof when read in conjunction with the accompanying `~
schematic drawing of the invention. ~
An ink reservoir 10 contains a supply of ink, which is fed over a supply -
hose 12, to the various printing heads represented by head 14, which are to -
use the ink. A two-way valve 16 is in the line to each printing head, for the
purpose of cutting off the printing from the ink reservoir during testing, or
when problems arise. Valve 16 is not an essential part of the invention. ~ .
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Each printing head directs a stream of ink drops toward a printing
surface, not shown. Those drops in the stream which are not used for the
purpose of printing are directed at a catcher 18. The ink in the ink reser-
voir 10 is enabled to flow through the line 12, and the printing head and to
be prajected therefrom by means of a volume of compressed gas, usually air,
` supplied from a source 20, which may be a pump. The pressurized gas is
applied to a pressure regulator 22, the output of which is supplied to the ink
reservoir 10 by means of a line 24.
~- The ink captured by the catcher 18, as well as by catchers used
with other printing heads, are returned over a line 26, through a buffer
container 28, a line 30, and a 3-way valve 34, to a captured ink container 36.
The 3-way valve has three ports, designated as N, A and S. The top of the `~ -
captured ink container is connected by a line 38 to another 3-way valve 40. ` -
This valve has three ports designated as NN, AA and SS. This 3-way valve may
- be operated so that port M , may be connected to the atmosphere through port
NN, or to a lower than atmosphere gas pressure ~vacuum) if required for ink
transer, or may be connected through port SS over a line 42 to another pres-
sure regulator 44. -~
A fresh ink supply container 50, which contains resh ink, may be
connected to the ink reservoir 10 by means of a valve 52. When the valve is
operated, it enables passage of the ink therethrough. The fresh ink container
50 may be pressurized by being connected to the source of pressurized gas,
through a valve 46, through line 42, and through pressure regulator 44.
Where the ink is of a type in which volatile ink base evaporation
must be compensated for in order to reuse the captured ink, a reservoir 54
for holding additive is employed. When needed the additive may be allowed to
be mixed with the incoming captured ink by means of a three-way valve 56.
Valves 34, 40, 46, 56 and 52, may be under control of a level
sensor 60, if that mode of operation is desired, or under time control, or
under any other desired control system for replenishing the ink in the ink
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reservoir. The level sensor is heing cited by~way of ex~mple. ~hen the ink
reservoir drops to a predetermined level, it applies a control signal to the
valves 34 and 40. Valve 34, when not supplying ink to the ink reservoir 10,
is set to permit captured ink to flow into the container 36. In response to
the level sensor signal, valve 34 is operated to connect port A to port S.
Valve 40, which otherwise connects the top of the container 36 to the atmos-
phere or to a source of vacuum, if desired, through ports AA and NN of the 3-
way valve 40, is also operated in response to the signal from the level
sensor, to connect the pressure regulator 44, through ports SS and AA, and the
line 38, to the top of the captured ink container 36. As a result, the cap- -
tured ink flows out of the container 36, over a line 62, into the ink reservoir
10. Check valve 61 in line 62 prevents ink backflow.
Fresh ink may be made to flow at any time into the ink reservoir
10, by operating the two-way valve 46 so that pressurized gas is applied from -
the source 20, through the pressure regulator 44 and the two-way valve 46 to ;~
the top of the fresh ink container 50. However, it may be more desirable to ~
add fresh ink when the amount-of the ink in the reservoir 10 attains a pre- -
determined value which may be different than the value at which the captured
ink is added to the contents of the container. At that time, a level sensor
60 can provide a signal which operates valves 52 and 46 to enable fresh ink
to be supplied to the ink reservoir until the level of the ink in the ink
reservoir 10 has attained a predetermined value with which time the two-way
valves 46 and 52 are operated to turn off the flow of fresh ink to the ink
reservoir 10. Level sensing arrangements for providing the indicated elec-
trical signals in response to different ink levels being attained, are well
known and therefore their details will not be described.
The buffer container 21 acts to collect the captured, or returned
ink during the interval where the captured ink container 36 is supplying ink
to the ink reservoir 10, since during that interval, port N of valve 34 is
closed. It is connected via line 29 to the atmosphere or to a suitable source
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o vacuum, i Yacuum is ~equired to draw captured ink into the captured ink
container.
Pressure regulator 44 provides a slightly higher pressure than
pressure regulator 22, in order to enable ink to flow from the containers 36
and 50 to ink reservoir 10, which at the time that inks flows from these con-
tainers is desired, ink reservoir 10 is pressurized from pressure regulator
22. The pressure in ink reservoir 10 is at all times controlled by regulator
22.
The foregoing invention enables the ink supply to the printing
heads to be maintained at a constant pressure and there is no need to interrupt
the operation for refill of the ink supply in the container 10. The invention
is not ink capacity limited. Reservoir 10 and fresh ink container 50 can be
made as large or as small as is required for the type of printing to be con-
ducted with the system.
An alternate method of adding fresh ink to the system is to connect
a vented (to atmosphere) fresh ink container 51 to the ink return line 20 via
three-way valve 56. Valve 56 may be operated to admit either additive or
fresh ink as required. While this arrangement may be slower, it eliminates `~
the need for valves 46 and 52 and eliminates the necessity of fresh ink con-
tainer 10 being a pressure vessel. With this arrangement fresh ink flows into
the captured ink container. When ink is made to flow from the captured ink
container to the ink reservoir 10, it will contain either fresh ink, or
captured ink, or a mixture of both. Of course it is possible to include both
arrangements in the same device. Operating conditions would dictate which
arrangement to use. ,
There has accordingly been described herein a novel and useful ink
supply system for an ink jet printing system.
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