U.S. patent number 3,761,941 [Application Number 05/297,284] was granted by the patent office on 1973-09-25 for phase control for a drop generating and charging system.
This patent grant is currently assigned to The Mead Corporation. Invention is credited to John A. Robertson.
United States Patent |
3,761,941 |
Robertson |
September 25, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
PHASE CONTROL FOR A DROP GENERATING AND CHARGING SYSTEM
Abstract
There is disclosed a phase control system for a jet drop
generator wherein the phase of drop generation is adjusted by
adjusting the amplitude of a stimulating disturbance applied to the
jet. A time varying electrical signal, preferably a binary or
ON/OFF signal, is applied to a charging electrode located near the
point of drop formation, so that newly forming drops are charged or
uncharged in correspondence to the signal. During normal operation
as a recording device, the charged drops pass through an electrical
deflection field for deflection into an appropriately placed
catcher. Drops which are uncharged pass undeflected through the
deflection field and deposit on a recording sheet. During non
recording or dead times a calibrating signal is applied to the
charging electrode and the charge carried away by the drops formed
during that period is measured by an electrometer connected to the
catcher. This measurement provides an indication of the phase of
drop generation relative to the phase of the calibrating signal.
Deviations of this relative phase from a desired relative phase are
corrected by adjusting the amplitude of the drop stimulating
disturbance.
Inventors: |
Robertson; John A.
(Chillicothe, OH) |
Assignee: |
The Mead Corporation (Dayton,
OH)
|
Family
ID: |
23145648 |
Appl.
No.: |
05/297,284 |
Filed: |
October 13, 1972 |
Current U.S.
Class: |
347/80; 239/3;
239/690; 361/226 |
Current CPC
Class: |
B41J
2/115 (20130101) |
Current International
Class: |
B41J
2/115 (20060101); B41J 2/07 (20060101); G01d
018/00 () |
Field of
Search: |
;346/75,1 ;317/3
;239/3,15 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hartary; Joseph W.
Claims
What is claimed is:
1. Method of sampling a time varying electrical signal comprising
the steps of:
1. generating a continuously flowing liquid filament,
2. applying a regular frequency drop stimulating vibration to said
liquid filament,
3. applying a drop charging electrical field to said filament in
the region where said vibration causes the filament to break up
into drops,
4. sampling said signal by modulating said field in correspondence
therewith and thereby inducing in said drops electrical charges
which represent samples of said signal,
5. detecting a deviation of the phase of said sampling from a
desired phase, and
6. correcting said deviation by adjusting the amplitude of said
vibration to alter the length of said filament and change the
timing of drop breakoff and charging.
2. In a system for control of liquid drops comprising:
means for generating a continuously flowing filament of said
liquid,
stimulation means for applying regular frequency disturbances to
said filament and causing a series of uniformly sized drops to
separate at regular intervals therefrom, and
a charging electrode responsive to an input charging signal for
inducing electrical charges in said drops during separation from
said filament;
the improvement wherein said stimulation means comprises:
means for generating an error signal related to the phase of said
drop separation relative to said charging signal, and
means responsive to said error signal generating means for
correcting said phase by adjusting the amplitude of said
disturbances to change the length of said filament and
correspondingly change the time required for said disturbances to
travel said length.
3. The improvement of claim 1 said means for generating an error
signal comprising:
means for applying a calibrating signal to said charging electrode
and thereby inducing in said drops electrical charges of magnitude
related to the magnitude of said calibrating signal at the instant
of drop separation,
means for catching the drops so charged, and
means for measuring the charge carried by the drops so caught.
4. The improvement of claim 2 said measuring means comprising means
for generating a measuring signal the voltage of which corresponds
to the effective current carried by the drops charged and caught as
aforesaid.
5. The improvement of claim 3 said means for generating an error
signal further comprising means for generating a reference voltage
and means for comparing said measuring signal voltage with said
reference voltage to create said error signal.
6. The improvement of claim 4 said means responsive to said error
signal comprising:
an integrating network for integrating said error signal to produce
a setpoint voltage.
an oscillator for generating a periodic stimulating drive signal of
continually repeating waveform,
a voltage variable attenuator for attenuating said stimulating
drive signal in accordance with the magnitude of said setpoint
voltage, and
means for generating said regular frequency disturbances in
accordance with the attenuated amplitude of said stimulating drive
signal.
7. The improvement of claim 5 said calibrating signal being a
square wave of frequency equal to the frequency of said stimulating
drive signal.
8. The improvement of claim 6 said reference voltage being selected
to correspond to the magnitude of said measuring signal voltage for
the condition when said drops separate from said filament during
transition periods for said callibrating signal.
9. In a system for control of liquid drops wherein selected drops
are removed from a stream issuing from a drop generator,
said drop generator including an orifice from which liquid is
expelled along a predetermined path as a filament to separate into
drops,
a charging electrode spaced from said orifice,
means for stimulating the liquid filament to induce regular drop
separation at a point adjacent said electrode,
and means for selectively applying charging pulses to said charging
electrode for electrostatically charging pre-determined ones of the
drops;
the improvement comprising means for attenuating the amplitude of
the stimulation energy induced into the filament by said
stimulating means,
and a control for said attenuating means responsive to the quantity
of charge on a succession of charged drops and connected to said
stimulating means to vary the amplitude of the stimulation energy
and thereby to adjust the length of said filament and produce
separation of said drops in optimal phase relationship with said
charging pulses.
10. A system as defined in claim 8, including means creating a
deflection field adjacent said path to change the trajectory of
charged drops, means for catching the charged drops, and said
control means including a detector connected to said catching means
to detect the quantity of charge on the charged drops.
11. A system as defined in claim 9, including means for driving
said stimulating means at a preselected constant frequency; said
attenuating means being responsive to changes in the output of said
detector means and connected to vary the amplitude of driving
energy supplied from said driving means to said stimulating means.
Description
BACKGROUND OF THE INVENTION
The invention relates to controlled phasing of the drop separation
from a liquid jet or stream, particularly in systems where one or
more such streams of drops are controllably placed on a receiving
surface for the purpose of image reproduction or recording. U.S.
Pat. Nos. 3,465,350, 3,465,351 and 3,596,276, all relate to systems
and devices for varying the phase relation between drop generation
and a charging signal applied to a charging electrode or tunnel
which places a predetermined electrostatic charge selectively on
individual drops separating from a continuous liquid filament. In
U.S. Pat. Nos. 3,465,350 and 3,465,351, the phase of the
stimulating vibration applied to the nozzle and the liquid filament
issuing therefrom is adjusted as necessary to control the phasing
of drop generation with respect to the application of charge
signals to the charging electrode. In U.S. Pat. No. 3,596,276 the
phase control system is applied to adjust the phase of the charging
voltage with respect to the drop generation, in order to achieve
essentially the same result. Both of these systems employ a
constant frequency, constant amplitude stimulation source, and as
noted, one type varies the phasing of the stimulation, and the
other type varies the phasing of the charging signals or
information.
In an article appearing in the British Journal of Applied Physics,
1964, Volume 15, by Crane, Birch and McCormack, entitled "The
Effect of Mechanical Vibration on the Break-Up of a Cylindrical
Water Jet in Air," at page 748, FIG. 5 and the description thereof
discloses the discovery that in a liquid jet drop forming system, a
change in amplitude of the stimulating vibration will produce a
corresponding, approximately linear, related change in the length
of the unbroken filament, or stated another way, in the point of
drop separation from the issuance of the liquid stream through the
nozzle orifice. This article deals generally with investigation of
the break-up characteristics of a liquid jet in air, and represents
modern expriences which confirm and enlarge upon the well known
19th century work of Lord Rayleigh in this field.
SUMMARY OF THE INVENTION
The present invention relates to a novel system for controlling the
break-up phasing of a liquid filament in the jet of a recording or
printing system using individual drops. A constant frequency,
variable amplitude drop stimulating disturbance is applied to the
liquid filament, and the amplitude of the stimulating distubrance
is adjusted to change the length of the liquid filament and thereby
correct the phase of drop breakoff relative to a system clock
signal. The system clock signal also controls the phase of
application of charge signal pulses to a charging electrode which
is located downstream from the nozzle orifice at a location where
drops separate from the liquid filment. Typical systems in which
the invention is applicable are disclosed in U.S. Pat. Nos.
3,560,641 and 3,656,174, all assigned to the assignee of the
present application.
In general, each of these systems utilizes an electronic printing
control accomplished by electrostatically switching the trajectory
of uniform drops of printing liquid, such as a conductive liquid
ink. The drops are produced from one or more liquid jets, and the
break-up of the continuous filament of the jets is induced or
stimulated by the application of regular frequency disturbances
upstream of the desired drop separation point. The charging
electrode(s) is located near the point of drop separation, and a
time varying electrical signal is applied thereto. This creates a
correspondingly varying electrical field at the tip of the filament
thereby inducing charges in the newly forming drops which represent
samples of the charging signal. The phase at which this sampling
occurs depends upon the phase of drop separation relative to the
phase of the applied signal.
For jet drop generators of the type herein involved, the amplitude
of the applied stimulating disturbances controls the nominal
filament length which in turn controls the time required for the
disturbances to travel from the orifice down to the drop separation
point. This travel time dictates the phase of drop separation
relative to the stimulation control signal and hences the phase of
drop separation relative to the drop charging signal. In a typical
system the nominal filament length and hence the drop separation
phase may change with time due to slight drifts in operating
parameters such as liquid surface tension, viscosity, liquid supply
pressure and extraneous environmetal noise.
Automatic phase regulation is achieved according to the present
invention by applying a calibrating charge signal to the charging
electrode during a non-printing period or so called "dead time."
This calibrating signal may be a square wave having a sharp rise
time and a slow decay time and generated in synchronism with the
drop stimulating disturbances. The stimulation energy then may be
deliberately decreased to lengthen the liquid filament and cause
the drops to separate therefrom during the decay time of the square
wave. The drops which are so stimulated all receive a partial
charge and are all caught by an appropriately placed catcher. An
electrometer is connected to the catcher and measures the jet
current during this dead time calibration.
The output of the electrometer is compared with a reference voltage
to generate an error signal for adjustment of the amplitude of the
stimulation energy. This adjustment continues until drop separation
occurs precisely at a predetermined point within the decay of the
calibrating square wave. Thereafter at the end of the dead time the
stimulation energy level is increased a predetermined amount to
shorten the liquid filament and produce drop separation in correct
phase relation with the normal print charging signal.
Accordingly, the primary object of the invention is to provide a
phase control system for a liquid jet drop recording or printing
device, in which the amplitude of the stimulation applied to the
jet or jets, is varied in accordance with the phase relation
between the drop separation and the application of charge signals
to a charging electrode near the drop separation point.
Other features and advantages of the invention will be apparent
from the following description, the accompanying drawing and the
appended claims.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic diagram illustrating the phase control system
applied to a single drop generator;
FIGS. 2, 3 and 4 are similar drawings of a single liquid filament,
showing the change in length of the continuous filament with
changes in the magnitude of the applied constant frequency
stimulation; and
FIG. 5 is an illustration of the wave forms of the signals
appearing at test points A through H of the system of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, a suitable supply of conductive liquid marking
material, such as an ink 10 is maintained within a reservoir 11 to
which is attached an orifice plate 12. There is an orifice 14 in
orifice plate 12, and ink 10 which is maintained under pressure
passes through orifice 14 to form a continuous filament 15 on the
exit side thereof. A stimulation transducer 20, which may be a
piezoelectric crystal or other convenient vibrating transducer,
vibrates orifice plate 12. These vibrations are transmitted to
filament 15 causing it to break up into uniformly sized and
regularly spaced drops 16.
There is provided a charging electrode 25 which surrounds filament
15 near the point of drop break off. For normal printing operations
a series of charge pulses are generated in synchronism with a data
clock signal and applied to electrode 25 to produce selective
charging of drops 16. Any drop which breaks off from filament 15
during a time when a charge is being applied to electrode 25 will
be charged to a polarity opposite the charge on electrode 25. All
of drops 16 fall between a pair of deflection electrodes 27 and 28
which create a steady state electrical field across the path of the
falling drops. Those of drops 16 which are charged are deflected
into a catcher 30 and are caught. Uncharged drops pass undeflected
between plates 27 and 28 and impact on a recording medium 31 which
may be mounted on a rotating drum 32.
Stimulation transducer 20 is driven in synchronism with the data
clock signal, and ideally each drop separation should occur
precisely at the mid-time of a clock pulse period. Furthermore each
drop should separate at the same point in space. This does not
ordinarily happen, and thus there appears a charging phase error as
above described. As a consequence there may be printing errors due
to drop flight times which are greater or less than anticipated or
drops which are improperly charged due to being generated either
before the associated charging pulse has reached its proper
charging level or after decay of the pulse has begun. Similar
errors may occur, as also mentioned above for other types of
recorders wherein the charging electrode is charged to various
levels for scanning deflection of the drops.
In accordance with the practice of this invention the charging
phase error is corrected by adjusting the amplitude of the driving
signal applied to stimulation transducer. Thus phase errors in one
direction are corrected by increasing the amplitude of the
stimulation and accordingly shortening filament 15. For phase
errors in the other direction the amplitude of the stimulation
signal is decreased to lengthen filament 15. These adjustments are
made during a dead time when printing signals are not being
generated.
For making the above described adjustments there may be provided a
scanner 13 which observes the rotation of drum 32. Scanner 13 scans
a narrow track which may be provided with a strip of colored tape
or other indicating medium within a dead area 63 corresponding to
the space between the top and bottom of recording medium 31. When
scanner 13 senses the presence of the dead area,it transmits a
signal to the dead time sensing circuit 17 which in turn gates off
FET 51. This removes a ground from line 35 which connects catcher
30 with electrometer 36. During this dead period all drops are
charged so that the drops will be caught by catcher 30 and current
will be measured by an electrometer 36. The output from
electrometer 36 is fed to a level detector 38 which drives an
integrating network 40. The output from integrating network 40
adjusts a voltage variable attenuater 42 which in turn drives
stimulation signal amplifier 22.
In order to make an accurate adjustment of the stimulation signal
amplitude, a square wave calibrating signal is applied to charging
electrode 25, and filament 15 is deliberately lengthened to produce
drop separation during the decay time of the calibrating signal.
The drops then are all charged by a partial charge and adjustments
are made to the stimulation amplitude to make the output from
electrometer 36 correspond to a reference voltage V.sub.Ref. At
this point the drop separation time is accurately known with
respect to the trailing edge of the square cailbrating wave.
Thereafter at the end of the dead period, the stimulation energy is
increased a predetermined amount to shorten filament 15 and produce
drop separation at the midpoint of the calibrating square waves.
The calibrating signal is clocked by the same signal as the print
data so that drop separation then occurs in correct phase with
normal print charging.
FIGS. 2, 3, and 4 show the shifting of the drop separation point as
above described. FIG. 2 is the initial condition where the
separation point should be located a distance X from orifice plate
12, but deviates therefrom by an error distance .DELTA.X. FIG. 2
illustrates the condition after the separation has been adjusted to
occur at a predetermined time during the square wave decay. In this
case the square wave has a 50 percent duty cycle and the
predetermined adjustment distance is about a quarter of a wave
length. FIG. 4 illustrates the condition after calibration is
complete.
Lengthening of filament 15 for the above mentioned purpose is
accomplished by gating on FET 53 with the output from dead time
sensing network 17. Driving signals for amplifier 22 are generated
by an oscillator 45 which oscillates in synchronism with the
charging pulses applied to electrode 25. The output from oscillator
45 is attenuated by voltage variable attenuator 42 under the
control of output signals from integrating network 40, and closing
of FET 53 provides a path through resistor 56 for abruptly
decreasing the amplitude of the signal applied to amplifier 22.
Resistor 56 is manually adjustable to provide for diverse operating
conditions.
The output from dead time sensing network 17 is also applied to AND
gate 33 and through a resistor 57 to FET 52, the function of which
will be explained presently. A data clock signal which is in
synchronism with the output of oscillator 45, is applied to AND
gate 33 so that AND gate 33 will provide data clock signals to OR
gate 34 whenever scanner 13 is viewing dead area 63. The output
from OR gate 34 is fed to the base of switching transistor 67. A
charging voltage, as for instance 100 volts, is applied across
resistor 66 to the collector of transistor 67 and also to charging
electrode 25 whenever transistor 67 is gated off by application of
a pulse to the base thereof. Typically the 100 volt pulse generated
by the opening of transistor 67 will have a fairly fast rise time
in the order of about 0.3 microseconds. However, the pulse control
network comprising diode 68, resistor 65 and capacitor 64 prevents
a sharp cut off of the 100 volt pulse when transistor 67 is gated
back ON. Consequently the 100 volt pulses applied to charging
electrode 25 are characterized by a fast rise time and a rather
slow trailing edge decay in the order of about 3 microseconds.
These pulses comprise the above mentioned calibrating signal.
During normal printing periods control pulses for the base of
transistor 67 are provided by a print data signal applied to OR
gate 34 as one input thereof. This signal consists of a series of
"NO PRINT" pulses generated in synchronism with the data clock,but
only for those clock periods during which no printing mark is
desired. For clock periods when a printing mark is desired, the
print data signal is clamped to zero thereby disabling OR gate 34,
gating ON transistor 67, and grounding the +100 volt input at the
collector thereof. Consequently no charge is applied to drops
generated during such clock periods. These drops avoid deflection
and catching and are able to deposit on the paper 31.
Level detector 38 comprises an operational amplifier 58 having one
input terminal grounded and the other input terminal connected to a
summing junction to which are also connected a feedback path and a
reference voltage V.sub.Ref. Thus the output of level detector 38
provides an error signal which varies with the variation of the
output of electrometer 36 from the reference voltage. During normal
printing periods FET 52 is gated ON so that the output from level
detector 38 is grounded. However, during the dead time FET 52 is
gated OFF and the output from level detector 38 drives integrator
40. Resistor 57 and capacitor 69 provide a switching time delay for
FET 52 during which the desired error signal is being achieved.
Integrator 40 comprises a conventionally connected operational
amplifier 59, a starting switch 60 and potential source 61. Switch
60 is initially closed to produce a starting output from amplifier
59 and thereafter is opened. Within voltage variable attenuator 42
there is a FET 54 which operates in the variable resistance mode.
The gate of FET 54 is connected to resistor 62 which in turn is
connected to integrating network 40. Thus the conductivity of FET
54 varies in accordance with the output from amplifier 59. FET 54
is connected in the feedback path around operational amplifier 55,
so that variations in the conductivity of FET 54 cause variations
in the gain of amplifier 55. Amplifier 55 is the driver for the
stimulation amplifier 22 and supplies signals thereto from
oscillator 45 at a magnitude which varies in accordance with the
conductivity variations in FET 54.
The operation of the network illustrated in FIG. 1 can be
understood further by referring to FIG. 5 wherein are shown a
series of time varying signal wave forms as may be observed at test
points A through H of FIG. 1. The signal at point A is the data
clock signal which is in synchronism with the oscillator output
signal observed at point B. The signal at point C is the output of
the dead time sensing circuit which is applied to FET 51, FET 52,
and FET 53 as above described. The output of electrometer 36 as
viewed at point D begins rising as soon as the output from the dead
time sensor goes from zero to a positive non-zero value. For a
typical phase error the electrometer output may rise from zero to a
reference voltage, overshoot the reference voltage, and thereafter
reapproach the reference voltage as the stimulation phase error is
corrected. The corresponding output wave forms from the level
detector 38 and the integrating network 40 may be observed at
points E and F respectively.
The charging pulses which are applied to charging electrode 25 may
be observed at test point G as also illustrated in FIG. 5. Further
illustrated with the wave form for point G are a series of arrows
positioned at various locations along the charging pulses. Each
arrow corresponds to the separation instant for a drop being
charged in response to the charging signal. Thus the charge signal
may comprise a series of pulses a through s including the pulses b
through k which are generated during the system dead time. Ideally
for normal non dead time operation the drop separation times should
correspond precisely with the mid points for the charging pulses.
For the error illustrated in FIG. 5 the system initially generates
drops slightly after the mid point of the charging pulses (as shown
for pulse a).
When the dead time sensor gates on FET 53, the stimulation drive
signal as seen at point H decreases, thus lengthening filament 15
from a nominal length X+.DELTA.X as shown in FIG. 2 to a nominal
length X+K as shown in FIG. 3. (The actual filament lengths varies
cyclically a small amount about the nominal filament length with
the generation of each drop). If no phase error is present when FET
53 is gated on, the pulse arrows as illustrated in FIG. 5 for the
point G wave form will move from the mid point of the last print
data pulse to the mid point of the trailing edges of the dead time
pulses. However, for the phase error illustrated in FIG. 5, the
pulse arrows move from a point within the right hand side of pulse
a to a point on the right hand side of the trailing edge of pulse
b. This means that phase correction may be accomplished by
adjusting the length of filament 15 to bring the pulse arrows to
the mid points of the trailing edges of the dead time pulses. For
the illustrated case, the observed phase error causes the level
detector output (point E) to go negative (after an initial positive
transient) and thereafter to approach zero as the system phase
error is corrected. Concomitantly the changing length of filament
15 causes the phase of the drop separation relative to the system
clock to change such that the pulse arrows as illustrated for wave
form G approach the mid points of the trailing edges of the dead
time pulses. Thus for pulses b, c, d, e and f the pulse arrows
progressively move left until for pulse g full correction is
achieved. The pulse arrows remain in the corrected position for
pulses h, i, j and k. Thereafter at the end of the dead time, FET
53 is gated OFF, filament 15 shortens to the corrected length X as
shown in FIG. 4, and the pulse arrows shift to the center of the
print data pulses as illustrated for pulses l through s.
The effect of the above described correction process upon the
stimulation drive signal (as seen at point H) is also shown on FIG.
5. Thus the stimulation drive signal changes abruptly from some
peak-to-peak magnitude U.sub.1 to a smaller magnitude U.sub.2 when
FET 53 becomes conductive. Thereafter the drive signal gradually
increases from the magnitude U.sub.2 to a corrected magnitude
U.sub.3 as the system phase error is corrected. The stimulation
drive signal then maintains the magnitude U.sub.3 until FET 53 is
opened. At this time the stimulation drive signal abruptly
increases from the level U.sub.3 to a corrected operating level
U.sub.4. It will be understood that a stimulation drive signal of
magnitude U.sub.1 produces a nominal filament length X+.DELTA.X as
seen in FIG. 2 while drive signal magnitudes U.sub.3 and U.sub.4
correspond respectively to filament lengths X+K and X as shown
respectively in FIGS. 3 and 4.
It will be appreciated that the invention as above described for
use with an ON/OFF jet drop recording system, is also applicable to
other types of jet drop recorders characterized by having charging
phase control problems. Accordingly the above described apparatus
is only a preferred embodiment and it is to be understood that
changes may be made therein without departing from the scope of the
invention.
* * * * *