U.S. patent number 3,786,517 [Application Number 05/286,380] was granted by the patent office on 1974-01-15 for ink jet printer with ink system filter means.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Konrad A. Krause.
United States Patent |
3,786,517 |
Krause |
January 15, 1974 |
INK JET PRINTER WITH INK SYSTEM FILTER MEANS
Abstract
An ink jet printing apparatus in which a pressure generated ink
stream is produced from an opening through a piezoelectric
transducer which produces axial vibration when energized to produce
a stream of uniform ink drops. A reference electrode is provided in
electrical contact with the ink and a character designating signal
is coupled between a charge electrode placed adjacent the drop
break-off point and the reference electrode to selectively charge
individual ink drops proportional to the character designating
signals. Filter means are provided for separating the chemically
active part of the ink system from the remaining part of the ink
system. The effects of electrolysis and corrosion within the ink
system are eliminated.
Inventors: |
Krause; Konrad A. (Mt. View,
CA) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
23098362 |
Appl.
No.: |
05/286,380 |
Filed: |
September 5, 1972 |
Current U.S.
Class: |
347/74; 347/93;
347/90; 347/77 |
Current CPC
Class: |
B41J
2/17563 (20130101); B41J 2/025 (20130101) |
Current International
Class: |
B41J
2/015 (20060101); B41J 2/025 (20060101); B41J
2/175 (20060101); G01d 015/18 () |
Field of
Search: |
;346/75 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hartary; Joseph W.
Attorney, Agent or Firm: Otto Schmid, Jr. et al.
Claims
What is claimed is:
1. In an ink drop character printer of the type wherein individual
ink drops are selectively charged according to character input
information signals the improvement comprising:
an ink system having an ink reservoir composed solely of material
that is chemically inert when exposed to ink;
transducer means having piezoelectric characteristics having an
opening through said transducer means, said transducer means
forming at least part of said reservoir;
means in said ink system for supplying ink under pressure to said
reservoir to produce a stream of ink;
means for energizing said transducer means to produce a succession
of uniform ink drops from said stream of ink;
filter means in said ink system for separating that part of said
ink system which is chemically active to ink from the remaining
part of said ink system;
reference electrode means and means for mounting said reference
electrode for electrically contacting said ink under pressure;
charging electrode means mounted closely adjacent to said stream of
ink drops; and
means for coupling character information signals between said
reference electrode means and said charging electrode means so that
said ink drops are selectively charged proportional to said
information signals.
2. The apparatus according to claim 1 wherein said transducer means
comprises a single element having piezoelectric characteristics
which produces a plurality of ink jets.
3. The apparatus according to claim 1 additionally comprising means
for deflecting said ink drops proportional to the charge on said
drops.
4. The apparatus according to claim 3 wherein said deflecting means
comprises a plurality of deflecting electrodes mounted between
alternate print positions and means to energize said deflecting
electrodes with alternate fixed potentials.
5. The apparatus according to claim 3 additionally comprising means
for intercepting ink drops charged with a predetermined charge, the
remainder of said ink drops being directed to a record member to
produce the selected characters.
6. The apparatus according to claim 5 wherein said intercepting
means comprises one sump member between alternate ink jets.
7. In an ink drop character printer of the type wherein individual
ink drops are selectively charged according to character input
information signals the improvement comprising:
transducer means having piezoelectric characterisitics having an
opening through said transducer, said transducer means directly
contacting said ink and forming an ink reservoir;
nozzle means coupled at one end of said opening through said
transducer means;
an ink supply means;
electrically isolated means connected to said ink supply means for
delivering ink under pressure to the other end of said opening
through said transducer means to produce a stream of ink from said
nozzle means;
means for energizing said transducer means to produce a succession
of uniform ink drops from said stream of ink;
a first filter means having two spaced surfaces with one surface
contacting said ink supplied to said other end of the opening
through said transducer means;
reference electrode means and means for mounting said reference
electrode for contacting the other surface of said first filter
means;
a second filter means positioned between said ink supply means and
said reservoir; whereby said first and second filter means remove
the effects of electrolysis and corrosion from said ink;
charging electrode means mounted closely adjacent to said stream of
ink drops; and
means for coupling character input information signals between said
reference electrode means and said charging electrode means so that
said ink drops are selectively charged proportional to said
information signals.
8. The apparatus according to claim 7 additionally comprising means
for deflecting said ink drops proportional to the charge on said
drops.
9. The apparatus according to claim 8 wherein said deflecting means
comprises a plurality of deflecting electrodes mounted between
alternate print positions and means to energize said deflecting
electrodes with alternate fixed potentials.
10. The apparatus according to claim 8 additionally comprising
means for intercepting ink drops charged with a predetermined
charge, the remainder of said ink drops being directed to a record
member to produce the selected characters.
11. The apparatus according to claim 10 wherein said intercepting
means comprises one sump member between alternate ink jets.
Description
BACKGROUND OF INVENTION
This invention relates to an electrically operated character
printer and more particularly to an improved printer of the type
which utilizes selectively charged ink drops to print characters on
a suitable record member.
In the prior art is has been known to utilize selectively charged
ink drops to print characters; however, these printers have not
been suitable for usage as an output printer for a data processing
system, since they require maintenance at relatively short
intervals. The usage as a computer output printer requires great
reliability of operation over extended periods of time.
One factor which contributes to the reliability problem is a
tendancy for the ink nozzles to clog, thereby causing a shutdown of
the system. This is due in part to electrolysis of metal parts in
the system as a result of electrical potential being applied across
the ink and the metal parts. Another factor which contributes to
the problem has been found to be variation in characteristics
between jets and changes in these characteristics with time.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an improved
ink jet printer in which the effects of electrolysis are
eliminated.
It is another object of this invention to provide an ink jet
printer in which manufacturing costs and maintenance time are
minimized so that the resulting printer is capable of operating for
extended periods as a computer output printer.
It is another object of the invention to provide an ink jet print
head of simplified construction so that the transducer works
directly on the ink stream.
It is a further object of this invention to provide an ink jet
printer in which a plurality of ink jets are produced from a single
electromechanical member.
Briefly, according to the invention there is provided improved ink
jet printing apparatus in which a pressure generated ink stream is
passed through an opening in a transducer means having
piezoelectric characteristics suitable energization of which causes
the ink stream to break up into uniform drops which are
individually charged proportional to a character designating input
signals placed between a reference electrode in contact with the
ink stream and a charging electrode placed adjacent the ink stream
at the point at which drop break-off occurs so that action of a
constant electric field through which the drops pass causes the ink
drops to be deflected proportional to the charge placed on the
drops to print characters designated by the input signals on a
record member.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a diagrammatic schematic view of an ink jet line
printer embodying the present invention;
FIG. 2 shows a section view of a single ink jet print head of an
alternate embodiment of the invention.
FIG. 3 shows a specific embodiment of a multi-jet line printer
embodying the present invention;
FIG. 4 shows a schematic block diagram of the electronic control
circuitry for the multi-jet line printer of FIG. 3;
FIG. 5 is a voltage waveform on a time scale for the voltage
applied to the charge electrode to print the last scan for
characters 81 and 83 as shown in FIG. 3;
FIG. 6 is a voltage waveform on a time scale for the voltage
applied to the charge electrode to print the last scan for
characters 85 and 87 as shown in FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 there is shown an ink drop printing apparatus
in accordance with the invention. This apparatus has a transducer
means 10 having a plurality of openings 11 which form spaced ink
jet printing means. Transducer means 10 comprises a transducer
member having piezoelectric characteristics and a nozzle means 12
is fastened to one side of the transducer member so that a nozzle
is aligned with one end of each of the openings 11 in transducer
means 10. An ink supply means 14 is provided for supplying ink
under pressure to each of openings 11 so that a stream of ink 16 is
produced from each of nozzle means 12. Transducer means 10 is
energized by a suitable source of oscillations 24 and the
application of the signal from source 24 causes transducer means 10
to expand and contract axially, thereby vibrating nozzle means 12.
As a result of this vibration, each ink stream 16 breaks up into
uniform drops. The spacing of the ink drops in the drawings is
greatly exaggerated for illustrative purposes. However, the actual
spacing is normally a few thousandths of an inch so that high
printing rates can be obtained. A charging electrode means 20 is
mounted at a position adjacent the point at which ink stream 16
breaks up into drops and the charging electrode is energized by a
signal from character input information source 22. The character
input signal is connected between a reference electrode means 18
mounted in contact with the ink stream and charging electrode means
20. As a result of the character input signal the ink drops receive
a charge dependent on the amplitude of the signal applied to the
charge electrode 20. After passing through charge electrode 20, the
charged ink drops pass into deflection means 26 which comprises a
static electric field. As a result, the charged drops required to
print the characters are deflected from the stream path and reach
the surface of print medium 32 to form the desired character. The
drops which are not required to produce the desired character are
directed to sump means 28 by the signals applied to the ink drops
while passing charging electrode 20.
Although only six character positions are shown in FIG. 1, it is
usual in a computer output printer to have a much longer line
comprising up to 132 characters, for example. Each of the ink jets
shown in the drawing is positioned to print two adjacent character
positions by deflecting the ink drops horizontally along the print
medium by means of suitable voltages applied to the charge
electrode. The vertical dimension of the character is provided by
the vertical motion of the print medium. Alternatively, printing
can be accomplished by electrically deflecting the ink jet to
produce the vertical dimension while the print medium moves to
produce the horizontal dimension of the characters. Sump means 28
comprises an opening for each pair of print positions so that
unneeded drops enter the sump opening from both of the adjacent ink
jets. Deflection means 26 comprises spaced conductive plates with
one plate adjacent each side of the ink stream. In this manner,
each deflection plate, except the end one, is shared between two
adjacent ink jet nozzles. To accomplish proper deflection in this
manner, the polarity of each of the deflection plates is
alternated. This in turn means that the polarity of the voltage to
the charge electrodes must be alternated along the print line.
The embodiment of the invention shown in FIG. 2 comprises a
manifold having an opening which connects to each of the ink jets
in the system. An electromechanical transducer 10 such an a
piezoelectric ceramic is mounted in alignment with the opening from
the manifold 36. An individual nozzle member 38 is fixed to the
other end of the opening in the piezoelectric material and an ink
pressure means 40 is provided to supply ink to the manifold under
pressure so that a stream of ink 41 is produced from nozzle 38.
Each of the faces of the piezoelectric material has an electrode 43
formed thereon and a source of oscillations 24 is connected to
these electrodes 43 to produce a mechanical vibration in the
piezoelectric material so that a vibration is produced in the axial
direction of the ink jet opening to break up ink stream 41 into a
series of uniformly spaced uniform ink drops 45. The charge
electrode is positioned adjacent the point at which ink drops 45
break off from the ink stream 41. A voltage is applied to the
charge electrode which is derived from a character generator 50
which is controlled by signals on input signal line 42. A reference
electrode means such as grounding electrode 44 is positioned
adjacent the ink path through manifold 36. Filter means 34 is
positioned between electrode 44 and the ink path through manifold
36 so that any particles resulting from electrolysis action on
electrode 44 are prevented from reaching the ink stream by filter
means 34. One terminal of the character generator 50 is maintained
at the reference potential such as ground and the other terminal is
electrically connected to charge electrode 20. Thus, the electrical
path for charging ink drops 45 is established from reference
electrode 44 through filter means 34 through the ink stream 41 and
to the charge electrode 20. As each ink drop is being formed, the
charge electrode 20 in the vicinity of the jet stream 41 is used to
induce a charge on that drop. For example, if the charge electrode
20 is driven to a positive voltage, electrons are attracted to the
end of the jet stream so that the tip of the jet becomes negative.
When breakoff of the drop occurs, this negative charge is trapped
so that the drop is subject to the action of a subsequent
electrostatic field. The charged ink drops are then directed
through a static electric field produced by high-voltage supply 46
connected between deflection plates 48. In this manner, the drops
forming the characters are deflected to the proper position on
print medium 32 and the other drops are directed to ink sump 28.
The ink from sump 28 is directed for filtering and recirculation to
the ink supply system 40.
To produce reliable operation, the proper materials must be
utilized in the apparatus. In addition to the electrolysis problem
previously mentioned, there may be an additional chemical corrosion
problem if some materials are exposed to the ink over a prolonged
period of time. For this reason, the preferred material for the
manifold 36 is a plastic material such as plexiglass, for example,
since this material has sufficient mechanical strength yet is inert
chemically when exposed to the ink over an extended period. In a
specific embodiment which was successfully operated, the printer
was constructed by using for transducer means 10 a piezoelectric
ceramic polarized for axial vibration. A 0.040 hole was drilled
through the piezoelectric material at the position for each ink
jet. The opening was counter-bored to relieve each side of the hole
and, in addition, to insure that the electrode surface 43 of the
piezoelectric material did not extend into the hole area in which
case they would be shorted by the conducting ink. A quartz nozzle
was attached to one end of the hole using a suitable adhesive. It
was found that a semielastic epoxy adhesive was suitable for this
purpose, since this adhesive had suitable thermal expansion
characteristics. One suitable material is sold under the trade name
of Glasshesive by Adhesive Engineering, 1411 Industrial, San
Carlos, Calif. The reference material used to attach the
piezoelectric material to the manifold which was constructed from
plexiglass was an epoxy adhesive sold under the trade name of
Epoxylite by Epoxylite Corp., 1428 North Tyler Ave., South El
Monte, Calif. The reference electrode member 44 was a stainless
steel plug threaded into an opening in manifold 36 which connects
with the ink stream. The filter member 34 comprises a nonconductive
porous disk 52 and a nonconductive support screen 54. The filter
member may suitably comprise filters sold under the trade name of
Millipore Filter by Millipore Corp., Ashby Road, Bedford, Mass. The
filter comprises mixtures of cellulose composed of inert esters of
cellulose and the pre-filter material is a pure glass fiber with an
acrylic binder. Thus, it can be seen that this construction permits
an electrical circuit from the reference electrode to the charge
electrode through the ink stream which is only a fraction of an
inch. However, the filter prevents any particles resulting from
electrolysis from entering the ink stream, thereby resulting in
reliable operation.
The embodiment of the printer shown in FIG. 3 comprises a multi-jet
printer in which a plurality of print heads 60 are provided with
each print head operable to print two adjacent print positions.
Each print head 60 is formed with an opening through a suitable
piezo-ceramic material 58 polarized for axial vibration. Individual
nozzles 62 are fastened to one end of the opening through the
piezoceramic material. Alternatively, the nozzles may be formed by
a suitably shaped orifice in a common plate as shown in FIG. 1 or
by an orifice jewel for each print head. Ink under pressure is
provided from ink reservoir 64 by means of ink pump 66, filter 68
and pressure regulator 70 to common manifold 72. An opening 74 is
provided from manifold 72 to transmit ink under pressure to each
print head 60 so that an ink stream 76 is formed. A source of
oscillation such as 100KHz, for example, is provided to terminals
78, 80 of the piezo-ceramic 58 so that a continuous stream of ink
drops 82 is formed due to the vibration of nozzles 62 by the
piezo-ceramic transducer 58.
The individual ink drops are charged by the signal voltage applied
between charge electrodes 84 and ground electrode 65. In the
embodiment shown, the charge electrodes are formed from a
continuous insulator material which has an opening surrounded by
conductive material which leads to terminals 86. The charging
voltage is generated in response to digital input signals from an
associated data processing system, for example. An embodiment of
the necessary components to derive the charging voltage is shown in
FIG. 4. In cases where a data processing system is used to control
the printer, the clock 93 and storage 94 are included in the
processor system. The control means 95 may comprise either wired
circuits or the functions may be performed by programmed
instructions in the procesor. Control means 95 provides the
electrical signals to control the operation of the remaining
electrical circuits. The data from storage 94 includes the code for
each of the characters to be printed in a line in the character set
being used by the printer. This coded data is directed to character
generator 96 which serves as an appropriate decoding device. One
suitable character generator is a Read-only storage device which
produces signals corresponding to dot positions within the chosen
print matrix. The matrix coded data is transferred into line print
buffer 97 which has one byte of storage for each print position for
each scan. In the embodiment shown, seven bytes of storage are
provided for each character to be printed. The timing for scans of
the print matrix is derived from emitter 98 which is mounted on the
same shaft as the tractor which drives print sheet 90 by power
supplied from motor 92. The signals from emitter 98 are utilized in
control means 95 to generate control signals which are coupled to
buffer accessing control means 101. Buffer accessing control means
may comprise a shift register which has a number of stages equal to
the vertical matrix positions. A signal is provided to the shift
register from control means 95 at the time for each scan. The
signal energizes the next stage of the shift register so that all
the bytes of the data in buffer 97 for that scan are transferred in
parallel to a digital to analog converter 99, one of which is
provided for each print position. An analog output circuit 100 is
utilized to hold the voltage on terminal 86 of the charge
electrodes 84 for a predetermined time as shown in FIGS. 5 and
6.
The matrix illustrated in FIG. 3 is a 5 by 7 matrix. This means
that a character is formed by a selection of one or more of 5 ink
drops for each horizontal scan of the print sheet 90 and a
horizontal scan is made at each of 7 vertical positions as the
paper 90 is driven vertically in the direction of the arrows by
means of paper drive motor 92. The charge electrode voltage for
scan of the print positions 81 and 83 as shown in FIG. 3 is shown
in FIG. 5. This voltage applied to charge electrode 84, produces
the seventh scan of the two print positions. The upper level V is
the charge necessary to direct ink drops to ink sump 56 while
succeeding steps of voltage direct ink drops to adjacent positions
horizontally along the print axis to print the last scan of
character 81. The voltage is returned to the sump level to cover
the position between characters and the succeeding levels of
voltage direct drops to complete the last scan of character 83.
The charged drops go through a static electric field set up between
deflection plates 71, 73 by a suitable high voltage supply from
high voltage source 79. The positive terminal of source 79 is
connected to support means 75 and to each of deflection plates 71
due to their rigid mounting upon support means 75. The negative
terminal of source 79 is connected to support means 77 and to each
of deflection plates 73 due to their rigid mounting upon support
means 77. This arrangement means that alternately polarized
voltages must be provided to adjacent print heads. For example,
adjacent print heads in FIG. 3 print the same data, but the voltage
to the charge electrode is different as shown in FIGS. 5 and 6.
This difference can be easily accommodated on a one-time basis when
setting up the character patterns in the Read-only Storage device.
There is an advantage from a mechanical standpoint, however, since
this arrangement permits one sump means 56 to service four print
positions. This construction requires less vacuum from vacuum
source 88 to insure that ink does not collect in the sump, but is
returned to the in reservoir for filtering for recirculation in the
system. The deflection plates are mounted so that electrical shorts
are prevented in the event that ink accumulates around these plates
in operation. In addition, the electrolysis problem is solved since
there is no metal in the ink path between filters 67 and 68.
While the invention has been particularly shown and described with
reference to preferred embodiments thereof, it will be understood
by those skilled in the art that various changes in the form and
details may be made therein without departing from the spirit and
scope of the invention. For example, a multi-jet array can be
constructed of individual nozzles similar to those shown in FIG. 2.
This has the advantage that individual nozzles can be replaced and
in this case the mounting must provide for alignment of individual
jets. One suitable construction is to provide a spherical surface
on the manifold end of the nozzle so that the newly installed
nozzle can be accurately adjusted and then fixed into position with
suitable mounting screws. In addition, the nozzle structure shown
in FIG. 3 may be attached with screws if desirable so that the
nozzles can be removed for ease in cleaning the nozzles and the
manifold, if necessary.
* * * * *