Note: Descriptions are shown in the official language in which they were submitted.
1319561
,
INK FLOW CONTROL SYSTEM AND METHOD
FOR AN INK JET PRINTER
Technical Field
This invention relates generally to ink jet
printing systems and more particularly to such systems
employing auxiliary ink pumping means for improving
operational performance. These systems are operative to
maintain a positive pressure within an ink cavity and
ink channel of an ink jet pen for extending its maximum
operating frequency.
Backqround Art and Related Appllcation
In certain types of ink jet printing systems, such
as thermal ink jet (TIJ) printers, the maximum
achievable operating frequency, FmaX, is inherently
limited by: 1) the inability of the natural capillary
action in the ink ~eed apparatus to adequately supply
ink to the ink reservoir chamber (the ink cavity) of the
printhead and 2) by oscillations of the ink meniscus at
the orifice plate of the printhead which persist for
some time, To, after drop ejection has occurred. One
approach to extending FmaX as well as providing other
operational improvements in thermal ink jet printheads
is disclos~d and claimed in copending Canadian
25 application Serial No. 572,430 of Marzio A. Leban et al
entitled "Integral Thin Film Injection System For
Thermal Ink Jet Heads and Method of Operation", filed
July 19, 1988, assigned to the present assignee~
Thermal ink jet printers having these operational
characteristics are now generally well known in the art
and are described, for example, in the Hewlett-Packard
Journal, Volume 38, No. 5, May 1985. These printers
employ printhead devices having resistive heater
elements ~resistors~ which are normally aligned with
corresponding ink ejection orifices in an adjacent
orifice plate and are operative to receive electrical
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drive pulses from an external source. These pulses
rapidly heat the heater resistors and thereby cause ink
in an adjacent ink reservoir to vaporize and be forced
out of the orifice plate during an ink jet printing
operation. Thus, as the operating frequency of the
printhead is extended out beyond a certain limit, there
is a tendency for the nakural capillary action of the
ink feed system of the TIJ printer to inadequately
supply the required volume of ink to the ink reservoirs
associated with the heater resistors, the adjacent ink
cavity and ink channel feeding the cavity.
This "ink starvation effect" becomes even more
pronounced as the viscosity of the ink is increased. In
many applications it is desirable to increase the ink
viscosity in order to achieve an improved print quality
on a variety of paper types and particularly plain
paper. In addition to the above limitations imposed by
this ink starvation effect, natural meniscus
oscillations of the ink at the orifice further place a
20 limitation on FmaX and persist for some time, To,
immediately after a drop is ejected. ~uring this time,
To, further drop ejection is greatly restrictedO
Disclosure of Invention
Ascor~Lngly, it is an object of an a~ of this
25 invention to overccme the above inability of the natural
ink feed capillary action to adequately supply ink to
the ink jet printhead during high frequency operation
and thereby extend FmaX beyond its present limits.
An object of an aspect of the invention is to
provide a new and improved printhead of the type
described which is operative to generat~ meniscus
oscillations of the ink at the orif ice of a controlled
frequency, Fm, and a controlled amplitude, Im. This
action allows f iring of ink drops of varying volume ~rom
the same orifice by timing the drop firing with meniscus
height. Small drops are ejected when firing occurs at
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low meniscus levels, and large drops are ejected when
firing occurs at high meniscus levels.
An object of an aspect of the invention is to
extend the upper limit of the usable ink viscosity.
This is accomplished by employing the pumping action o-E
a piezoelectric system to produce a positive pressure
over and above the natural capillary force within the
ink capillary cavity and ink capillary channel of the
ink j~t printhead.
To achieve the above objects and attendant
advantages of thi~ invention, we have discovered and
developed a new and improvecl ink eed system and method
of operation for an ink jet printhead wherein the
amplitude and frPquency of oscillations of the meniscus
at a fluid ejection orifice are controlled by ejecting
fluid through an orifice and at a natural resonant
frequency and amplitude with respect to an equilibrium
position. The frequency or amplitude or both of the
fluid ~eniscus at the orifice are modulated in a
controlled phase relation with respect to the phase
position o~ the oscillations of the meniscus above or
below the equilibrium position.
Other aspects of this invention are as follows:
A method for pumpîng ink to an opening in an inkjet
printhead orifice plate to overcome the inability of the
natural ink feed capillary action to adequately supply
ink to the inkiet printhead and to extend the maximum
operational frequency thereof while simultaneously
controlling and varying the ink drop volume ejected from
said orifice plate, which comprises the steps of:
a. providing an ink flow path to an opening in
said orifice plate,
b. pulsing a first transducer in or adjacent to
said ink flow path and disposed on said printhead to
provide a pumping action in a direction parallel to said
ink flow path to enable said printhead to operate with
~,.
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4a
inks having a lower surface tension and a higher
viscosity or both and to contxol the oscillations of an
ink meniscus at said opening in said orifice plate, and
c. pulsing a second transducer in said ink flow
path so that the pulsing of said second transducer
ejects ink drops of varying volume from said orifice
opening by timing said drop ejection with the height of
said meniscus at said orifice plate opening, whereby
small drops are ejected when the firing of said second
transducer occurs at low meniscus levels, and large
drops are ejected when the firing of said second
transducer occurs at high meni~cus levels.
An inkjet printhead operable for provicling a
pumping action useful for producing a positive pressure
over and above the natural capillary force within an ink
capillary cavity and associated ink feed channel of said
ink jet printhead and for extending the maximum
operating frequency of ink ejection therefrom and for
simultaneously varying the drop volume of ink ejected
from said printhead, comprising:
a. a substrate having an ink supply channel
therein for receiving ink from a remote source,
b. an orifice plate mounted above said substrate
and having an orifice opening therein for receiving ink
from said ink supply channel,
c. a first transducer positioned adjacent said
channel and being operative to flex in a direction
perpendicular to said substrate and parallel with the
flow of ink through said ink feed channel for pumping
ink through said ink supply channel and overcoming the
inability of the natural ink feed capillary action to
adequately supply ink to said ink jet printhead, said
first transducer also being operative to pump ink toward
and said opening in said orifice plate and allowing said
printhead to operate with inks having a lower surface
tension and a higher viscosity or both,
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4b
d. a second transducer positioned adjacent said
orifice opening for controlling the ejection and drop
volume of ink through said orifice openiny, whereby said
first transducer is operative to simultaneously control
the oscillations of an ink meniscus at said orifice
opening and to pump ink thereto, and said second
transducer is operative to generate a firing pulse at a
chosen phase position of an oscillating ink meniscus at
said orificP opening with respect to an ink meniscus
equilibrium position at said opening to control the drop
volume of ink ejected from said orifice opening.
In a preferred embodiment of the invention, a
resistive heater element is aligned with respect to an
orifice plate, and an ink flow path supplies ink into a
chamber or reservoir between the resistive heater
element and the orifice plate. This improved system
includes, among other things: 1) a piezoelectric system
which is mounted internal to the ink cavity of an ink
jet printhead; 2) an external piezoelectric system which
is mounted directly on the orifice plate of an ink jet
printhead; 3) dual independent piezoelectric systems
which are both mounted internal to the ink cavity of the
printhead; and 4) dual piezoelectric systems with one
being intsrnal to the ink cavity of the printhead and
the other being external and mounted directly on the
orifice plate of the printhead. The above described ink
feed systems may be used to: 1) produce oscillations of
controlled frequency, Fm, and controlled amplitude, Im,
of the ink meniscus at the ink ejection orifice and
produce the ejection of ink drops from a single orifice
with varying and controlled volumes; 2) extend the
maximum frequency of operation, FmaX, of the ink jet
printhead; and 3) extand the viscosity range of inks
which may be used.
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The above brief summary of invention will become be~ter
understood and appreciated from the following description of the
accompanying drawing.
Brief Description of the Drawinqs
5Figure 1 is an abbreviated perspective view showing a
typical mounting arrangement of a heater resistor within an ink
feed channel.
Figure 2 is an abbreviated cross section view showing
the position of the heater resistor with respect to the main ink
feed channel, the ink cavity and the orifice plate of the thermal
ink jet printhead.
Figures 3A-3C show, in abbreviated cross-section, three
different meniscus positions during its oscillation at an orifice
opening.
15Figures 4A-4B compare the natural meniscus oscillation
with the induced meniscus oscillation provided in accordance with
the present invention.
Figure 5 is an abbreviated cross section view of an ink
jet printhead which shows the piezoelectric pump material mounted
within the ink cavity of the printhead.
Figure 6 is an abbreviated cross section view of an ink
jet printhead which shows the piezoelectric pump material mounted
on the orifice plate of the printhead.
Figure 7 is an abbreviated cross section view of an ink
jet printhead which shows two (2) separate piezoelectric pump
transducers mounted within the ink cavity of the printhead.
Figure 8 is an abbreviated cross section view of an ink
jet printhead which shows the piezoelectric pumps mounted on both
the orifice plate outside the ink cavity and within the ink
cavity of the printhead.
Figures 9A-9B show the shifting of the induced meniscus
oscillation about the meniscus equilibrium position by an amount
contxolled by the timing of pressure pulses generated by the
piezoelectric pump or pumps of the ink jet printhead.
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Detailed Description
Referring now to Figure 1, thexe is shown a
perspective view of a single heater element (resistor)
11 surrounded by a barrier material 12 forming an ink
channel 13 immediately adjacent to the resistor 11. The
barrier material 12 also forms an ink cavity region 14
exterior to the ink channel 13. This type of three
sided barrier layer construction is generally well
known in the art and is disclosed for example in U.S.
Patent Nos. 4,794,410 and 4,794,411, both issued
December 12, 1988, of Howard H. Taub et al assigned to
the present assignee.
Figure 2 is a cross section view which would be
taken through the center of the resistor in Figure 1
when the printhead structure therein, including the
orifice plate, is completed. Figure 2 further
illustrates that the ink cavity 14 is formed between an
underlying substrate 15 and an outer orifice plate 16.
An orifice 17 is positioned immediately above the
resistor 11, and ink from an ink feed system 18 is drawn
into the ink cavity 14 and into the ink channel 13
regions by a capillary force.
As the resistor 11 is fired by a suitable pulse
applied thereto, a drop of ink is ejected from the
orifice 17. An ink jet printhead operating in this
manner is considered to be operating in tha "equilibrium
mode". Immediately after drop ejection in the
equilibrium mode, the meniscus of the ink at the
orifice 17 will oscillate fr~m the equilibrium positicn
3 n 19 as indicated in Figure 3A and achieves a maximum
extension 20 and a minimum extension 21 as indicated in
Figures 3B to 3C. These "natural oscillations" continue
for a length of time, labeled the "dead time';, To, with
a decaying amplitude as shown in Figure 4A. During this
time, ejection of an additional drop of ink is not
permitted.
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~(
a
In accordance wikh the present invention, a
piezoel~ctric material 22 such as quartz or barium
titanate crystals or a kynar piezoelectric film is
introduced into the ink cavity 14 as shown in Figure 5,
or is mounted externally on the outer surface of the
orifice plate 16 as shown in Figure 6. The
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material 22 is connected in such a manner that it can be
energized with a controlled electrical signal, and this signal
induces oscillations, of controlled frequency and magnitude,
within the material 22. This action in turn produces a positive
ink pressure within the ink cavity 14 and the ink channel 13 and
thereby behaves as an ink pump. Both internally and externally
mounted piezoelectric systems function in an equivalent manner.
There are various available piezoelectric driving
circuits suitable for providing the piezoelectric drive siynals
described herein, and the choice of circuit design of these
drivers is considered well within the skill of the art.
Therefore, a detailed description of specific driver circuit
design has been omitted for sake of brevity. However,
piezoelectric driver circuits have been described in many U.S.
Patents, such as U.S. Patents 4,714,935, 4,717,927, 4,630,072,
4,498,089 and 4,521,786. Piezoelectric driver circuits have also
been enclosed in the following four textbook references:
1. Precision Frequencv Control; E. A. Gerber, Ed. Academic
Press, 1985.
2. Acoustic Waves: Devices Imagina and Analoque Siqnal
Devices; Gordon Kino, Prentice-Hall, 1987.
3. Standard Methods for the Measurement of E~uivalent
Circuits, American National Standards, Electronic
Industries Association, 1985.
4. VF2 - Models, Measurements~ Device Ideas, John
Linvill, Stanford Technical Report number 4834~3,
Stanford University, 1978.
The oscillations of the piezoelectric material 22
produce a constant, symmetric and continuous oscillation of the
ink meniscus as shown in Figure 4B. These continuous, induced,
symmetric and controlled meniscus oscillations of frequency, Fm,
and amplitude, Im, in Figure 4B are superimposed on the "natural
oscillations" in Figure 4A. The net result of this superposition
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of these two kinds of meniscus oscillations is a vir-tual
"swamping out" of the natural meniscus oscillations in Figure ~A,
and the virtual elimination of the "dead time", To, which is
responsible for limiting the maximum operating frequency, FmaX,
of the ink jet printhead.
The timing of the firing of resistor 11 with respect
to the meniscus amplitude, Im, o~ the induced meniscus
oscillations is crucial. I~ the resistor 11 is fired at the
equilibrium position, or points (T) in Figure 4B, the ink jet
printhead is operating in the "equilibrium mode" and medium
volume ink drops, Veq, are ejected. These ejected ink drops are
of a volume equal to the case where the piezoelectric material
is not pulsed. The maximum achievable operating frequency, FmaX~
of the ink jet printhead operating in the "equilibrium mode" is
limited only by the frequency of induced meniscus oscillations,
Fm. If the resistor ll is fired at the maximum meniscus
extension position, namely at points (U) in Figure ~B, then the
ink jet printhead is operating in the "rich mode" and maximum
volume ink drops, Vmax, are ejected. If the resistor 11 is fired
at the minimum meniscus extension position, which is point (V)
in Figure 4B, then the ink jet printhead is operating in the
"lean mode" and minimum volume ink drops, Vmin, are ejected.
Firing the resistor 11 at different points between the rich and
lean modes will cause ink drops to be ejected in varying and
controlled volumes.
The range of ejected ink drop volume may be extended
by employing dual independently controlled piezoelectric systems
within an ink jet printhead. Figure 7 illustrates such a system
where both independently controlled piezoelectric drivers 22 are
incorporated within the ink cavity 14.
Fiyure 8 illustrates another system where the
pie~oelectric drivers 22 are incorporated both inside and outside
the ink cavity 14, with the outside driver mounted on the orifice
plate 16. The method of operation of both these systems in
Figures 7 and 8 is the same.
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Each independently driven piezoelectric driver 22 may
be energized with a controlled signal and caused to oscillate
whieh in turn induces a symmetrie meniscus oseillation as
described above. If both piezoeleetrie drivers within an ink jet
printhead are caused to oscillate in phase with each other and
with equivalent amplitudes, then the induced meniscus oscillation
remains symmetric as described above with reference to Figure 4B.
Within the ink jet printhead, both piezoelectric
drivers 22 may be caused to: 1) oscillate out of phase with each
other at the same frequency and amplitude; or 2~ oscillate out
of phase with each other at the same amplitude and with a
different frequency. The combination of frequency, amplitude and
phase shift may be selected to induce a meniscus oscillation
which is asymmetric as shown in Figures 9A and 9B.
If the induced asymmetric meniscus osciliation is
skewed to the positive as shown in Figure 9A, the maximum volume
ink drop, Vmax, ejected may be further extended from the
symmetric case due to the greater meniscus extension in the
asymmetric case. The limiting situation is attained when the
asymmetric positive meniscus extension is so great that actual
drop ejection begins to occur. Large positive asymmetric
meniscus extensions may be favored by suitable choice of ink
viscosity and surface energy of the ink.
Alternatively, if the asymmetric meniscus oscillation
is skewed to the negative as shown in Figure 9B, the minimum
volume ink drop, Vmin, ejected may be further extended from the
symmetric case. The limiting situation is attained when the
asymmetric negative meniscus extension is so great that the
printhead will begin to aspirate air through an orifice opening
in the orifice plate of the printhead. Air aspiration may be
modified by suitable choice of ink viscosity and ink surface
energy.
The pumping action of the added piezoelectric system
deseribed above enables the ink jet printhead to be used not only
with eurrent inks, with their low viscosities (< about 3 cps) and
higher surface tensions (> about 55 dyne/cm), but also with inks
1 31 q561
having a lower surface tension and a higher viscosity.
Generally, higher viscosity inks penetrate slower into the
surface of paper such that the print quality on a variety of
papers, and particularly on xerographic or bond papers, is
improved. Printheads using higher viscosity inks therefore print
more consistently on a wider set of plain papers. The ability
to use both high viscosity and low surface tension inks yield
faster drytimes on plain papers as well.
The ability to use higher viscosity inks with a lower
surface tension has significant advantages over current
technology. Standard ink technology, which employs soluble dyes
in a usually aqueous based vehicle, could be expanded to use a
much larger group of allowable solvents. For example, higher
molecular weight glycols, ethers, ketones, and the l:ike could be
used in conjunction with water to obtain the desired vehicle
properties. This expanded group of solvents allow dyes to be
used in the new printhead described herein which are not
currently acceptable because of solubility or reactivity with the
ink vehicle. These additional dyes improve contrast, color, hue
and print quality on the printed medium. Besides the improved
print quality inherent in higher viscosity inks, other solvent
and dye mixtures could yield improved waterfastness, reliability,
smearfastness, lightfastness and archivability. Also, additional
color dyes could be used, with a possible attendant improvement
in color gamut and bleed characteristics.
The ability to lower the requirements of surface
tension and raise the allowable limit on viscosity would enable
the printhead to be used with "non standard" ink jet inks (e.g.
non-aqueous, dye based). For example, pigment based,
microemulsion or encapsulation inks could be used. These new
colorant systems would offer higher waterfastness, improved
smearfastness, better color gamut, better reliability and better
lightfastness and bleed.
Various modifications may be made to the above
described embodiments without departing from the scope of this
invention. For example, the present invention is not strictly
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limited to the specific printhead cross-section geometries shown
and may be practiced using various printhead geometries including
the well known "side shooter", "face shooterl' and "edge-shooter"
constructions and the use of offsets between heater resistor
center lines and orifice centers. Additionally, the geometries
of the ink feed channel and the ink reservoir cavities may be
modified in accordance with the design constraints applicable to
a variety of thermal ink jet printhead applications, and may
include various state of the art hydraulic tuning and crosstalk
reduction features.
