U.S. patent number 3,787,882 [Application Number 05/293,300] was granted by the patent office on 1974-01-22 for servo control of ink jet pump.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Gary L. Fillmore, Hugh E. Naylor, III, Donald L. West.
United States Patent |
3,787,882 |
Fillmore , et al. |
January 22, 1974 |
SERVO CONTROL OF INK JET PUMP
Abstract
An important factor in quality of printing with an ink jet
printing apparatus is the velocity of the ink jet stream. The
present case describes a number of servo systems for controlling
velocity of the stream. This can be done indirectly by sensing
pressure and/or temperature or directly by sensing velocity of the
stream and controlling the pump frequency or pump drive
currents.
Inventors: |
Fillmore; Gary L. (Lexington,
KY), Naylor, III; Hugh E. (Lexington, KY), West; Donald
L. (Lexington, KY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
23128530 |
Appl.
No.: |
05/293,300 |
Filed: |
September 25, 1972 |
Current U.S.
Class: |
347/6; 417/412;
417/32; 347/17; 347/85; 347/78; 417/43; 417/472 |
Current CPC
Class: |
B41J
2/125 (20130101); F04B 49/065 (20130101); B41J
2/17596 (20130101); F04B 43/04 (20130101) |
Current International
Class: |
B41J
2/125 (20060101); B41J 2/175 (20060101); F04B
43/04 (20060101); F04B 49/06 (20060101); F04B
43/02 (20060101); G01d 015/18 () |
Field of
Search: |
;346/75,140
;417/412,32,42,43,326 ;318/127,129,130 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hartary; Joseph W.
Attorney, Agent or Firm: Cooper; D. Kendall
Parent Case Text
RELATED PATENT APPLICATION
U. S. Pat. application Ser. No. 266,790 filed June 27, 1972,
entitled "Ink Jet Synchronization and Failure Detection System,"
and having James D. Hill, et al., as inventors.
Claims
1. In an ink printing apparatus, a servo system for monitoring and
maintaining parameters, affecting quality of printing, such as
velocity of the jet, within predetermined ranges, which determines
jet placement during printing of information, comprising:
jet forming means for forming and propelling an ink jet in a
predetermined path of travel,
pump means interconnected with said jet forming means for
maintaining a predetermined level of ink jet pressure in said jet
forming means;
sensor means proximately positioned in relation to said ink jet for
sensing a characteristic of said ink jet and for developing a
signal representative of said characteristic;
comparator means for comparing said developed signal with a
reference signal in order to further develop a corrective signal;
and
means for applying said corrective signal to said pump means in
order to maintain pressure exerted by said pump means in said jet
forming means within a predetermined range, thereby maintaining jet
velocity, jet placement, and printing of information within a
predetermined range of
2. The apparatus of claim 1, further comprising:
pump control means interconnected with said pump means for
directing corrective signals from said comparator means to said
pump means; and
timing logic interconnected with said pump control means for
controlling
3. The apparatus of claim 2 wherein said ink jet is directed to a
medium for recording of information in the form of character
intervals, each separated by an inter-character interval; and
further comprising:
recognition means interconnected with said logic means for
recognizing said inter-character intervals and for activating said
pump control means
4. The apparatus of claim 3 wherein said ink jet forming means and
said medium are relatively moved from a home position to record
information, and further comprising:
means in said recognition means for activating said pump control
means
5. The apparatus of claim 1, wherein said sensor means
comprises:
a temperature sensor for monitoring temperature characteristics of
said ink
6. The apparatus of claim 1, wherein said sensor means
comprises:
a pressure sensor for monitoring pressure characteristics of said
ink jet.
7. The apparatus of claim 1, further comprising:
a temperature sensor and a pressure sensor incorporated in said
sensor means and interconnected with said pump means for monitoring
temperature and pressure, respectively; and
circuit means responsive to signals developed by said temperature
and pressure sensors and interconnected with said pump means for
controlling pump pressure in order to maintain said pump pressure
within a
8. The apparatus of claim 1, further comprising:
a first proximity sensor and a second proximity sensor incorporated
in said sensor means and connected for input to said comparator
means, said proximity sensors being positioned a predetermined
distance apart and adjacent the path of travel of said ink jet;
means for developing signals from said proximity sensors indicative
of the passage of ink as it moves past said proximity sensors;
and
said comparator means developing a corrective signal responsive to
the signals derived from said first and second proximity sensors
for application to said pump means in order to maintain pressure in
said pump
9. The apparatus of claim 8, wherein said comparator means further
comprises:
activatable gate means;
means interconnecting said proximity sensors as inputs to said gate
means;
count means;
means interconnecting said gate means and said count means to
initiate operation of said count means under control of said gate
means during an activate mode of said gate means in order to
develop digital count representations; and
means for activating said gate means and thereby said count means
upon sensing passage of ink moving past said first proximity sensor
and for deactivating said gate means and said count means upon
sensing passage of
10. The apparatus of claim 9, wherein said comparator means further
comprises:
digital-analog converter means interconnected between said count
means and said pump means for converting digital representations
from said count
11. The apparatus of claim 8, wherein said comparator means further
comprises:
a ramp generator circuit providing a ramp signal having
predetermined slope and duration characteristics;
means interconnecting said proximity sensors as inputs to said ramp
generator;
an analog holding circuit;
means for initiating operation of said ramp generator circuit upon
sensing passage of ink by said first proximity sensor and for
terminating operation of said ramp circuit upon sensing passage of
ink by said second proximity sensor;
means interconnecting said ramp generator to said analog holding
circuit in order to provide the ramp level attained by said ramp
circuit to said analog holding circuit; and
means interconnecting said holding circuit to said pump means in
order to
12. The apparatus of claim 1 wherein said ink jet passes through a
charge electrode and between deflection electrodes for charging and
deflection within a predetermined deflection monitoring range, and
further comprising:
means for applying a charging potential to said charging electrodes
in order to deflect said ink jet into said monitoring range;
sensor means positioned adjacent the path of travel of said ink jet
for developing signals from said ink jet during passage thereof
past said sensor means indicative of velocity characteristics in
said monitoring range, and
means for applying said velocity characteristics signals to said
pump
13. The apparatus of claim 12, further comprising:
first and second sensor probes incorporated in said sensor means,
said probes being positioned a predetermined distance apart and in
proximity to said ink jet when said ink jet passes through said
monitoring range; and
means interconnected with said probes and said pump means and
responsive to signals developed by said probes for developing
corrective signals for application to said pump means in order to
increase or decrease pump pressure, as required, in order to
maintain jet velocity within a predetermined range.
Description
BACKGROUND OF THE INVENTION AND PRIOR ART
Various types of ink jet printing devices have been proposed
heretofore. In one such system, drops of ink are formed and
propelled from a nozzle toward a record medium, variably charged
according to a signal representative of a wave form or character
and deflected by deflection plates having a constant potential
applied thereto. To insure good placement of drops in forming the
waveform character, as the case may be, it is vital that the
velocity of the ink drops remain in a predetermined range. Velocity
of drops can vary considerably due to variations in temperature,
pump pressure, and the like. The primary variation is due to
temperature which causes large changes in the ink viscosity and
hence the ink velocity as it leaves the nozzle. The present
invention is intended to maintain velocity as constant as
possible.
SUMMARY OF THE INVENTION
A number of arrangements are described in the present case for
controlling velocity of ink drops in an ink jet printer either
directly or indirectly. In one case, the temperature and/or
pressure of the ink is sensed at the pump and appropriate
adjustments made to the pump driving circuit to increase or
decrease pump pressure and thereby increase or decrease velocity of
the stream. Another version contemplates the positioning of sensors
adjacent the stream of drops for inducement of a voltage as charged
drops pass by the sensors and for development of corrective signals
to again control pump pressure and velocity of the stream. This
version can be implemented in a digital or analog fashion, as
desired. In another arrangement, sensors are positioned outside the
normal range of drop deflection. During servo action, maximum
deflection of the stream occurs for development of potentials to
control the pump with corrective action, as necessary, to increase
or decrease pump pressure, and thereby change velocity of the
stream. The servo arrangements set forth make use of a highly
efficient pump structure based on voice coil driving
principles.
OBJECTS
The primary object of the present invention, of course, is to sense
various parameters in an ink jet printing system in order to
develop corrective signals for controlling pump pressure and/or
frequency to ultimately maintain velocity of the ink jet stream
within a desired velocity range.
The foregoing and other objects, features, and advantages of the
invention will be apparent from the following more particular
description of the preferred embodiments of the invention as
illustrated in the accompanying drawings.
DRAWINGS
In the Drawings
FIG. 1 is a system representation illustrating servo control of a
pump in an ink jet system.
FIG. 2 illustrates velocity control by sensing of temperature and
pressure.
FIG. 3a illustrates an arrangement for sensing velocity of an ink
drop stream to develop digital count levels and conversion to
analog for pump control, while FIG. 3b is essentially the same
system wherein analog levels are developed directly.
FIG. 4 illustrates servo control involving the sensing of the
maximum deflection of an ink jet stream.
FIG. 5 is a cross-sectional view of a voice-coil pump that is
useful in the various embodiments of FIGS. 1-4.
DETAILED DESCRIPTION
FIG. 1 is a generalized version representative of the various
systems set forth in greater detail in FIGS. 2-4. An ink jet system
1, usually comprising an ink jet printing device, or the like, has
an associated sensor 2, such as a temperature sensor. The ink jet
system may be of the type set forth in the Hill, et al., patent
application referred to previously. An output developed by sensor 2
is provided to an amplifier circuit 3 and from there to a
comparator circuit 4. Another input to comparator circuit 4 is a
reference signal on line 5. The output of comparator 4 is applied
to pump control circuit 7 and is used to develop a control signal
by lines 10 and 11 to coil 12 of pump 13. Servo action may be
provided under ordinary circumstances from machine clock 16 through
machine logic 17 in conjunction with recognition block 6. Thus the
operation of the servo system shown in FIG. 1 would usually take
place during non-printing intervals such as during a carrier return
(CR) interval, or home position between printing of characters that
is, inter-character intervals, and the like, as recognized by block
6. As an alternative and as will be described shortly, a pressure
sensor 20 associated with pump 13 provides inputs to amplifier
circuit 3 instead of sensor 2. If pressure is sensed by sensor 20,
as an example, provision is made to develop a corrective signal
from pump control circuit 7 in order to increase or decrease
pressure of pump 13 from the input signals related to pressure in
pump 13. If the velocity of the stream is too slow, indicated by a
low pump pressure, it may be increased by increasing the voltage
applied to coil 12 of pump 13. Further, the frequency of signal
applied to coil 12 may be changed to change pump pressure.
This is further illustrated in FIG. 2 where pump 13 is shown with
associated coil 12. The pump assembly is further associated with
nozzle 22 emitting a stream of ink drops 23 directed toward a
record medium 25 for printing of characters or waveforms. In the
event drops are not required for printing they are directed to a
gutter 27. Ink is supplied through pump 13 to nozzle 22 from ink
supply 29 by conduit 30. Pump 13 is a pump which is controlled by
coil 12 such that the pressure is a function of coil current.
Pressure sensor 32 monitors pump pressure and feeds a voltage
analogous to pressure to amplifier 35. Amplifier 35 compares the
pressure signal to the reference signal provided by amplifier 36
and adjusts a voltage controlled oscillator 38 so that current "I"
to pump 13 minimizes the difference between the reference input and
the sensor 32 output, thus holding pressure constant. A manually
set adjustment at oscillator 38 allows an initial factory pressure
adjustment to be made. Amplifier 36 compares temperature reference
voltage from block 40 with temperature sensor voltage from sensor
41 and adjusts the pressure reference voltage input for amplifier
35. This causes pressure to follow temperature change to hold
velocity constant.
An ink jet system, without initial adjustments, could have as much
as a 10 to 1 variation in deflection sensitivity. This is due, in a
large part, to variation in fluid flow through the nozzle.
Adjusting pressure to obtain a constant velocity reduces this to a
5 to 1 variation. Adjusting for zero temperature effect could
further reduce this variation to 1.5 or 2 to 1. At that point,
including other system tolerances, an adjustment of deflection
voltage would hold the machine to an acceptable level of
performance.
By servo controlling pressure and automatically adjusting for
temperature variation, electrical parameters are monitored rather
than mechanical parameters. The system can easily compensate for
different ink characteristics. Also, less precise tolerances are
possible in the nozzle and in ink batch to batch variation.
Instead of controlling coil current to adjust pressure, a constant
current but variable frequency oscillator could be utilized to
operate the pump. A wide variety of sensors can be used for
pressure sensor 32 and temperature sensor 41. As an example, a
thermocouple gauge may serve for temperature sensor 32.
In summary, the circuit of FIG. 2 holds pressure in an ink jet
printer constant by means of a servo loop. It further allows the
reference pressure of the servo loop to be temperature compensated
so that constant ink jet velocity is maintained with time and
temperature variation. The servo loop eliminates the dependence
upon relatively wide range and difficult to control mechanical
tolerances and replaces them with more stable and easily controlled
electrical tolerances.
If desired, either a pressure sensor or a temperature sensor could
be used alone in conjunction with the pump for monitoring and
changing pump pressure to thereby control velocity. The servo
system of FIG. 2 could be set up to maintain a constant pressure
for a given temperature and thereafter simply adjust pressure up or
down in order to compensate for temperature changes. The converse
is also true.
FIG. 3a illustrates a system for monitoring drop velocity directly
and developing signals to control pump pressure in order to change
the velocity of the drops, as required. FIG. 3a makes use of
digital techniques. FIG. 3b is related to FIG. 3a using essentially
the same sensor arrangement but developing analog signals to change
pump pressure rather than digital signals that have to be converted
to analog signals.
In FIG. 3a, a stream of drops 43 is emitted from nozzle 44 passing
through a charge electrode 45. Gutter 46 is positioned for
receiving drops in stream 43. Two sensors 48 and 49 are positioned
a predetermined distance apart and in proximity to the path of
travel of the drops in stream 43. The two sensors 48 and 49 feed
respectively associated comparator circuits 50 and 51. The
comparator circuits have reference potentials applied by lines 53
and 54, respectively. During testing of drop velocity, as when the
nozzle 44 is at home position, or in between characters, gate
circuit 56 is activated in a synchronous fashion by machine clock
pulses on line 58. The comparator outputs are fed to gate 56 by
lines 60 and 61 through interface connections 62 and 63,
respectively.
In operation, a group of drops is emitted from nozzle 44, such as
six (6) in number, or the like. The group of drops passes sensor 48
developing a voltage which ultimately activates gate 56 to gate
counter circuit 65 to start a counting operation. When the sequence
of drops passes sensor 49, another potential is developed that is
also applied to gate 56 but that turns off counter 65 instead. Thus
a number of count pulses is developed in counter 65 that is
directly representative of the time required for passage of the
drops from sensor 48 to sensor 49. The count status of counter 65
is applied to the digital-analog converter circuit 67 in order to
derive a correction signal by line 68 that ordinarily would be
applied to a pump control circuit similar to circuit 7 in FIG. 1 in
order to vary pump pressure as required. As noted before, either
the frequency or current drive of the pump can be changed in order
to change pump pressure.
FIG. 3b is an analog approach utilizing various elements in FIG.
3a. The circuit of FIG. 3b is substituted for elements 56, 65, and
67 in FIG. 3a by appropriate connection of interface connectors 62a
and 63a with connectors 62 and 63, respectively, in FIG. 3a.
Outputs developed by sensors 48 and 49 in this case are applied to
a ramp generator 70. Upon detection of a potential on line 60a,
FIG. 3b, the ramp generator is activated. Ramp generator 70
develops a ramp signal at a known rate and range of voltage levels.
Upon detection of another output on lines 61a, FIG. 3b, the output
from ramp generator 70 is deactivated. The level attained is stored
in the holding circuit 71 and applied by line 72 to vary pump
pressure in a manner similar to that described before.
By using the foregoing techniques, the velocity of the ink stream
43 may be maintained constant. As a result, since the deflection
sensitivity of stream 43 is proportional to 1/(Vel).sup.3, the
deflection of stream 43 required during printing of information is
also maintained in a tightly controlled manner. Using the servo
techniques previously described, tolerances on other elements of
the system, such as on the nozzle, temperature, etc. need not be
maintained as tightly as would otherwise be required.
In FIG. 4, the actual deflection of a stream of drops is tested in
order to determine velocity characteristics. Nozzle 75 emits a
stream of drops 76 passing through charge electrode 77 and between
deflection plates 78 and 79. During printing of information, the
drops in stream 76 are directed to a record medium, not shown. When
not required for printing, drops are directed to gutter 80. During
testing of velocity of the stream, maximum deflection of drops is
initiated by appropriate charging by charge electrode 77 and
deflection by plates 78 and 79 in order that the drops reach the
area of two proximity sensors 82 and 83 representing maximum
deflection of the stream. As an example, a group of six drops can
be used as before. Gutter 85 is positioned to receive drops
directed between sensors 82 and 83. Potentials are developed by
sensors 82 and 83 as the stream of drops passes by. It is assumed
that a normal deflection for test purposes of the drops in stream
76 is between sensors 82 and 83. If drops pass close to sensor 83
representing an increase in velocity of the drops, an output is
developed that is applied to amplifier circuit 90 and in turn to
comparator circuit 91 for development of appropriate correction
signal by line 92 to control pump pressure. In this case, since the
velocity of the drops is somewhat high, the pump pressure is
reduced. If drops pass in proximity to sensor 82, an output is
developed that is applied to amplifier circuit 94 and again applied
to comparator 91. In this case, the stream of drops is moving at a
relatively lower velocity and the output signal by line 92 would be
of an appropriate level to increase pump pressure.
FIG. 5 illustrates a highly efficient pump structure 100 that is
useful in the various servo circuits previously described. Pump 100
includes a pump supporting structure 101 housing a number of
elements. A flat spring member 102 is mounted for oscillatory
movement in structure 101. Spring member 102 is driven by coil 104
that in turn is excited by an oscillator 106. Attached to member
102 is connecting rod 108 that in turn is connected to a bellows
110. Pump 100 further includes an input conduit 112 through which
ink is supplied from an ink supply not shown. An output conduit 114
supplies ink to a nozzle, not shown, but that would be similar to
those previously described. Control of ink passage and pumping is
exerted by an input valve 115 and an output valve 116. The action
of the pump is similar to that of a voice coil normally found in
radio and television equipment, or the like. The metal diaphragm
102 and associated bellows 110 change the volume of the pump cavity
120. Valves 115 and 116 control the flow of ink in and out of the
pump.
The pressure produced by pump 100 is related to the force imparted
to bellows 110 by diaphragm 102 which in turn is related to the
frequency and current conditions established in coil 104. With
these characteristics, pump 100 is readily incorporated in the
various servo circuits previously discussed and controllable as
required insofar as maintaining a desired pressure range. This in
turn, as mentioned, controls drop velocity.
In operation, as bellows 110 moves to the left in FIG. 5, flap 115
opens thereby drawing ink through conduit 112 into chamber 120.
Valve 116 remains closed at this time. As bellows 110 moves to the
right and expands, valve 115 remains closed and ink is forced
through valve 116 and out of way by conduit 114 to the ink jet
nozzle.
While the invention has been particularly shown and described with
reference to several embodiments, it will be understood by those
skilled in the art that various changes in form and detail may be
made without departure from the spirit and scope of the
invention.
* * * * *