U.S. patent number 3,798,656 [Application Number 05/275,990] was granted by the patent office on 1974-03-19 for ink return system for a multijet ink jet printer.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Paul Lowy, Stanley Arthur Manning, Karl Friedrich Stroms.
United States Patent |
3,798,656 |
Lowy , et al. |
March 19, 1974 |
INK RETURN SYSTEM FOR A MULTIJET INK JET PRINTER
Abstract
A multi-jet, ink jet printer having deflection plates at a
positive or negative potential with respect to ground which
includes catch chambers for returning unused ink to an ink
reservoir. Non-information bearing ink droplets are passed
uncharged to a catch chamber and from there through a return
conduit system to the ink reservoir. To help direct the ink
droplets to the catch chambers, the catch chambers are mechanically
biased toward the trajectory of the uncharged droplets by placing
them at a slight angle with respect to the trajectory. To prevent
short-circuiting of the deflection plates to ground potential, the
return conduit system includes denebulization chambers which
convert the returning ink stream into large drops thus developing a
high resistance path between the deflection plates and the
reservoir ink at ground potential.
Inventors: |
Lowy; Paul (Peekskill, NY),
Manning; Stanley Arthur (Yorktown Heights, NY), Stroms; Karl
Friedrich (Wappingers Falls, NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
23054676 |
Appl.
No.: |
05/275,990 |
Filed: |
July 28, 1972 |
Current U.S.
Class: |
347/77;
347/90 |
Current CPC
Class: |
B41J
2/18 (20130101) |
Current International
Class: |
B41J
2/18 (20060101); G01d 015/18 () |
Field of
Search: |
;346/75,140 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Hartary; Joseph W.
Attorney, Agent or Firm: Sughrue, Rothwell, Mion, Zinn &
Macpeak
Claims
What is claimed is:
1. In an electrostatically deflected ink-jet printer providing a
continuous spray of ink droplets, a method for controlling the
interception of said ink droplets with a printing medium comprising
the steps of;
a. providing deflection plates at a non-zero potential for
generating an electrostatic field, each plate including a
catch-chamber,
b. imparting an electric charge to only those droplets which are to
intercept said printing medium,
c. directing the uncharged droplets to a catch-chamber
d. breaking the ink received by the catch-chamber into drops to
thereby cause the ink to form a high impedance return path to the
deflection plates,
e. passing each drop over a ground plate whereby the charge
acquired by the ink upon passing through the catch-chambers of the
deflection plates is neutralized and
f. collecting the neutralized drops of ink in a reservoir.
2. The method of claim 1 further including the step of disposing
said deflection plates at a slight angle with respect to the
trajectory of the uncharged droplets.
3. In an electrostatically deflected ink-jet printer of the type
including at least one nozzle for ejecting ink toward a printing
medium, a charging electrode for selectively charging ink droplets,
and an electrostatic field for deflecting the ink droplets from
their trajectory an amount proportional to the charge thereon, the
improvement comprising:
a. electrostatic deflection plate having a non-zero potential
thereon for generating said electrostatic field, each of said
deflection plates including a catch-chamber for intercepting and
collecting substantially uncharged droplets, said collected
droplets thereby assuming a charge dependent upon the potential of
said plate,
b. a reservoir, held at substantially zero potential, for storing
said ink to be fed through said at least one nozzle, and
c. a return conduit system for returning the said ink collected by
said catch-chambers to said reservoir, said return conduit system
comprising,
i. a container means, receiving said collected ink in a
substantially continuous flow, for emitting said received collected
ink in separate and discrete droplets which are relatively large
compared to said ink droplets collected by said catch-chamber, to
thereby result in a relatively large electrical impedance path
through said ink in said return conduit system between said
catch-chamber and said reservoir, and
ii. means insulating said container means from said reservoir.
4. The ink-jet printer of claim 3 wherein said deflection plates
are disposed at a slight angle with resepect to the trajectory of
said substantially uncharged droplets.
5. The ink jet printer of claim 3 wherein there are a plurality of
nozzles, a pair of said deflection plates being associated with
each nozzle, each deflection plate being either at a positive or
negative potential with respect to ground, said conduit system
comprising a first conduit coupled to the catch chambers of said
negative potential deflection plates and a second conduit coupled
to the catch chambers of said positive potential deflection plates,
further including first and second of said containers for receiving
ink from said conduit system, said first container receiving ink
from said first conduit said second container receiving ink from
said second conduit.
6. The ink jet printer of claim 5 wherein at least one plate of
each pair of deflection plates associated with a nozzle forms one
plate of another pair of deflection plates associated with another
nozzle.
7. The ink-jet printer of claim 3 wherein each of said deflection
plates is hollow, the hollow portion of the deflection plate
forming the catch-chamber.
8. In an electrostatically deflected ink-jet printer of the type
including at least one nozzle for ejecting ink toward a printing
medium, a charging electrode for selectively charging ink droplets,
and an electrostatic field for deflecting the ink droplets from
their trajectory an amount proportional to the charge thereon, the
improvement comprising:
a. electrostatic deflection plates having a non-zero potential
thereon for generating said electrostatic field, each of said
deflection plates being provided with a catch-chamber for
intercepting substantially uncharged droplets;
b. an ink return conduit system receiving the ink collected by said
catch-chamber,
c. a container for receiving ink from said conduit system in a
substantially continuous flow, said container comprising a
compartment including means for collecting the received ink and
emitting it in the form of drops, so that the ink forms a high
impedance return path to said deflection plates, said container
further comprising another compartment including a grounded
conductive plate for receiving said ink drops whereby the charge on
the ink drops acquired upon passing through the catch-chambers of
the deflection plates is neutralized, and
d. an ink collecting reservoir for receiving the ink drops after
they pass through said container.
9. The ink-jet printer of claim 8 wherein said container is formed
from non-conductive materials and wherein said compartment includes
high surface tension material and said another compartment includes
an inlet port for receiving dry air and an outlet port coupled to
said reservoir.
10. The ink jet printer of claim 9 wherein said reservoir includes
an air outlet port for connection to subatmospheric pressure and an
ink outlet port for returning ink to said nozzle.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is in the field of the ink jet printers and more
particularly in ink return systems for such printers.
2. Description of the Prior Art
Ink jet printers have created much interest in the area of high
speed printing. For example, in computer systems, it is often
desirable to print out information at speeds of up to 4,000
characters per second. Ink jet printers have this capability and
may be used in conjunction with or in place of conventional CRT
type display units.
In ink jet printing, one or more ink jet producing nozzles,
connected to an ink reservoir through a pressure pump, receive
fluid ink under pressure and eject the ink in fine continuous
sprays, each of which comprises a string of droplets. The
continuous ink spray inherently breaks up into very small droplets.
In some systems, the rate and size of these droplets are controlled
by vibrating the nozzles. The particular vibration frequency is
controlled to control the size and spacing of the droplets. The
stream breaks up into droplets as it passes through a charging
electrode. The potential on the charging electrode is varied in
accordance with the information to be printed. As the droplets pass
through the electrode, a charge is transferred to the individual
droplets, this charge being a function of the potential applied to
the charging electrode to thereby produce information bearing
droplets. Between the charging electrode and the moving printing
medium upon which the information bearing droplets impinge, there
is generated a fixed electrostatic field which changes the
trajectory of the droplets passing therethrough, in accordance with
the charge thereon, whereby the droplets are directed to selected
points on the moving printing medium. An example of such a printer
is illustrated in the article by R.L. Gamblin et al, Electrostatic
Ink Deflection Bar Code, Printer, IBM Technical Disclosure
Bulletin, Volume 11, No. 9, May 1969, pages 1736-1737.
Since the flow of liquid ink is continuous, a catch basin must be
used to gather unused ink. The unused ink is that ink which does
not carry an information indicative charge. For the purpose of
describing this invention, ink jet printers will be classified into
two groups, those which position the catch basin between the
deflection plates and the printing medium and those in which the
catch basin is integral with the deflection plates. In the former
type system, exemplified by U.S. Pat. No. 3,484,793, to G.A. W.
Weigl, issued Dec. 16, 1969, the droplet trajectory length is long,
creating problems of aerodynamic instability of the droplets.
A technique for improving droplet stability is to shorten the
trajectory path. A convenient means for accomplishing this is to
make the catch basin integral with the deflection plates thereby
permitting the printing medium to be placed close to the deflection
plates. Such a system is described in U.S. Pat. No. 3,512,173 to
D.E. Damouth, issued May 12, 1970. In the Damouth system a pair of
deflection plates are associated with each nozzle, with one of the
plates being placed at ground potential. The grounded deflection
plate has associated therewith an intercepting plate which together
with the deflection plate forms a return channel for the unused
ink. A high voltage source is coupled to the other deflection plate
to provide a potential difference in the area of 3000 volts between
the two plates. To direct non-information bearing ink droplets into
the return channel, a uniform bias charge is applied thereto. Thus
each droplet, whether it carries information or not, is provided
with a charge. The problem with this technique is that the charge
on the unused droplets affects the charge on the information
bearing droplets. Further, by requiring one of the deflection
plates to be at ground potential, a separate pair of deflection
plates must be utilized with each nozzle. This requirement results
from manufacturing difficulties associated with the positioning of
the plurality of nozzles relatively close together. Still further,
very high potential sources must be used with the system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved
multi-jet, ink jet printing apparatus which includes a novel ink
return system of the type which includes deflection plates formed
with catch chambers integral therewith.
To accomplish the above objective, there is provided a multi-jet,
ink jet printing apparatus wherein fluid ink stored in an ink
reservoir is supplied under pressure to a plurality of nozzles to
produce a continuous ink spray from each nozzle. A moving printing
medium is positioned to receive the ink. Associated with each
nozzle is a charging electrode and a pair of deflection plates. The
ink ejected from the nozzles breaks up into small droplets as these
droplets pass through a charging electrode. The charging electrodes
are caused to assume a potential indicative of the information to
be printed. When no printing is to take place, the charging
electrode is placed at ground potential so that no charge is
imparted to the droplets passing therethrough. As droplets pass
through a charging electrode at a potential indicative of
information to be printed, a charge is developed on the droplet,
the charge being a function of the potential applied to the
charging electrode. The droplets pass through an electrostatic
field created by a pair of deflection plates whereby charged
droplets impinge upon the printed medium at selected locations.
Non-information bearing droplets remain uncharged so that they do
not interfere with the charge on the information carrying droplets.
The deflection plates are formed with a hollow portion acting as a
catch chamber for the uncharged, non-information bearing droplets.
To assist in the catching of uncharged droplets, the deflection
plates are disposed at a small angle with respect to the trajectory
of these droplets.
Adjacent deflection plates are given respectively a positive and
negative potential with respect to ground and adjacent ink jet
nozzles share a common deflection plate thus reducing the total
number of plates needed. For example, in a system utilizing 60
nozzles and 60 charging electrodes, only 61 deflection plates are
required. In that none of the deflection plates is at ground
potential, the magnitude of the potential applied to any one plate
can be greatly reduced thus permitting the use of less expensive,
lower potential sources. That is, instead of using for example a
3000 volt source coupled to a deflection plate, the other plate
being at ground potential, one plate is coupled to a +1500 volt
source while the other plate is coupled to a -1500 volt source.
An opening is provided at the end of each deflection plate to
receive fluid collected by the catch chamber. The opening is
coupled to a return conduit system for carrying the unused ink back
to the ink reservoir. However, as the ink enters a catch chamber,
it assumes a charge which corresponds to the potential on the
plate. So that the returning fluid does not provide a low
resistance path between the reservoir ink at ground potential, and
the deflection plates, thereby presenting a short-circuit path from
the deflection plate to ground, denebulization chambers are
provided within the return conduit system. As used herein
denebulization refers to the breaking up of a fluid stream into
relatively large drops. These chambers convert the returning
substantially continuous flow of ink into relatively large drops
which present a high impedance to current seeking to flow between
the deflection plates and the ink reservoir.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE illustrates the improved non-shorting ink return system
of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the FIGURE, information received from information
sources 15 is to be printed on a printing medium 3 by selectively
deflecting inking droplets produced by a plurality of nozzles 6. To
this end, ink 2, stored in ink reservoir 4 is supplied in a
conventional manner to the nozzles 6. Ink pump 8 is provided to
introduce the ink into the nozzles 6 under pressure. The ink forced
into the nozzles 6 is then ejected therefrom toward the printing
medium 3. Due to the natural instability of the liquid stream 10,
the ink inherently breaks up into small droplets 12 a short
distance from the nozzle. In the vicinity of the ink break-up there
is positioned a charging electrode 14 coupled to an information
signal source 15. The information signal source provides a
potential on its associated charging electrode indicative of the
information which is to be printed. In its simplest form, the
information signal source may be a ramp generator selectively
turned on or off. As the ink droplets 12 pass through a charging
electrode 14, they assume a charge which is a function of the
potential on the charging electrode. The ink stream 10 is
continuous and when no information is to be printed on document 3,
the potential on a charging electrode 14 is at ground and thus
uncharged ink droplets emerge from the charging electrode. To
collect the uncharged ink droplets, each deflection plate 17 is
provided with a catch chamber 16 for receiving the uncharged
droplets. Each nozzle 6 is mechanically aimed at a catch chamber
16. Two deflection plates are associated with each nozzle and
create a fixed electrostatic field which alters the trajectory of
charged droplets. One of these plates is at a potential positive
with respect to ground while the other is at a potential negative
with respect to ground. To aid in the catching process, the
deflection plates are positioned at a slight angle with respect to
the trajectory of the droplets. As illustrated in the FIGURE, each
of the deflection plates 17 is positioned at an angle of
approximately 3.degree. with respect to the trajectory of uncharged
droplets.
Ink collected by the catch chambers 16 flows through openings 18
into either the return conduit 20 or 22 depending upon whether the
fluid has emerged from a positive or negative potential deflection
plate. The conduits may be formed of insulating material for safety
reasons. However, as uncharged droplets enter a catch chamber, they
assume a charge corresponding to the potential on that plate 17.
Ink flows out of a deflection plate through return conduit 20 or 22
in the form of a substantially continuous flow which if it were
connected would present a low resistance path between the
deflection plate and the reservoir ink at ground potential. If such
a low resistance path occurs, shorting out the deflection plates
might result.
To prevent this, there are provided denebulization chambers 24, one
coupled in line with each conduit 20 and 22. Each chamber, made of
insulating material, is divided into two compartments 26 and 27. In
the first compartment 26 there is provided material having a high
surface tension such as metal wool. The returning ink stream enters
this compartment and is emitted therefrom in large drops 28 which
impinge upon a grounded conductive plate 30 in the second
compartment 27. The conversion of the substantially continuous ink
stream into separated large drops produces an extremely high
impedance path to the deflection plate 17. In fact, the impedance
between the ink reservoir 4 and the deflection plates increases to
a value greater than 100 megohms. After impinging upon grounded
conductive plate 30 the fluid passes through conduit 32 to the ink
reservoir 4. In order to aid the return flow of ink there is
provided the vacuum pump 36 to evacuate air in the reservoir 4.
To dry the denebulization chambers for preventing conduction of
electrical current from taking place, each chamber 24 includes an
aperture 34 through which dry air is forced using any suitable air
pump (not shown). The introduction of the dry air dries the chamber
thus decreasing the humidity in the chamber to prevent electrical
current flow.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that various changes in form and
details may be made therein without departing from the spirit and
scope of the invention.
* * * * *