U.S. patent number 3,750,191 [Application Number 05/292,688] was granted by the patent office on 1973-07-31 for synchronization of multiple ink jets.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Hugh E. Naylor, III.
United States Patent |
3,750,191 |
Naylor, III |
July 31, 1973 |
SYNCHRONIZATION OF MULTIPLE INK JETS
Abstract
A method is described for sequentially determining if drop
formation for each jet in an array of ink jets is occurring at the
proper time.
Inventors: |
Naylor, III; Hugh E.
(Lexington, KY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
23125765 |
Appl.
No.: |
05/292,688 |
Filed: |
September 25, 1972 |
Current U.S.
Class: |
347/80 |
Current CPC
Class: |
B41J
2/115 (20130101) |
Current International
Class: |
B41J
2/115 (20060101); B41J 2/07 (20060101); G01d
015/18 () |
Field of
Search: |
;346/75 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hartary; Joseph W.
Claims
What is claimed is:
1. An ink jet synchronization system particularly suitable for
apparatus utilizing a plurality of ink jets, comprising:
a plurality of nozzle assemblies for forming and propelling ink
drops in respectively associated ink jet streams, each of said
nozzle assemblies incorporating driving crystals, charge
electrodes, and deflection electrodes,
means for driving said respective crystals at a predetermined
frequency in order to form streams of drops for propulsion from
said respective nozzle assemblies;
individual charge driving circuits interconnected with said charge
electrodes, respectively, for producing a charge potential on drops
passing therethrough, when required;
gutter-sensor means respectively associated with each of said
nozzle assemblies, said gutter-sensor means being positioned for
reception of drops propelled from said assemblies when said drops
carry a particular predetermined charge level and said
gutter-sensor means developing signals representative of charge
levels on drops passing therethrough;
a detector circuit responsive to signal levels developed in said
gutter-sensor means to provide a corrective signal in said system
for insuring proper relationship of said crystal driving circuits
and said charge driving circuits; and
switch circuit means interconnected for reception of signals from
each of said gutter-sensor means and operable to supply signals
from one and one only of said gutter-sensor means to said detector
circuit during each of a number of succeeding synchronization
testing intervals.
2. The apparatus of claim 1, further comprising:
control logic in said system for sequentially gating each of said
charge driving circuits in order to develop a sequence of charged
drops from each of said nozzle assemblies, each of the sequences of
drops from the respective nozzle assemblies being separated by an
inactive charge time interval;
means in said system for synchronously activating said switch
circuit to receive developed signals from said gutter-sensor means
during any time interval when charged drops are being received by
said respective gutter-sensor means; and
means responsive to output signals from said detector circuit means
for correcting the crystal drive or charge drive, as appropriate,
to insure proper synchronization of drop formation and charging in
the respective nozzle assemblies.
3. The apparatus of claim 2, wherein said switching means comprises
individual Field Effect Transistor pairs and associated switch
circuits operable in timed sequence:
a common operational amplifier; and
means interconnecting the respective switch circuits to the input
of said operational amplifier in timed sequence during
synchronization activities.
4. The apparatus of claim 1, further comprising:
control logic in said system for activating the crystal drive and
charge electrode drive circuits associated with each of said
respective nozzle assemblies and for applying corrective potentials
as required for each of said nozzle assemblies, in turn, in order
to complete the synchronization process for each respective nozzle
assembly in turn prior to any synchronization activities with
respect to the other nozzle assemblies.
5. The apparatus of claim 1, wherein individual drops are formed in
successive drop intervals comprising a finite time interval, and
further comprising:
control logic in said system for activating said charge driving
circuits during an early portion of said drop time interval and for
activating said crystal driving circuits during a later portion of
said drop interval thereby achieving synchronization.
Description
PATENT APPLICATION OF INTEREST
U. S. Patent 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.
BACKGROUND OF THE INVENTION AND PRIOR ART
A multitude of systems have been proposed in the prior art
utilizing ink jet printing techniques. Many of these devices have a
plurality of ink jet heads arranged in an array or side by side
with either simultaneous or sequential operation of the heads. In
any ink jet system, synchronization is of prime importance. This
relates to the fact that drops formed for printing need to be
formed at a proper and synchronized time particularly with respect
to charging potentials used in the system for deflection
purposes.
SUMMARY OF THE INVENTION
In a preferred embodiment of the invention, a plurality of ink jet
printing heads are monitored and controlled in a manner to obtain
accurate synchronization of drops propelled from the heads.
OBJECTS
A paramount object of the present invention is to provide a system
for synchronizing ink jet drop formation and propulsion in order to
insure high quality and accurate printing.
The foregoing and other objects, features, and advantages of the
invention will be apparent from the following more particular
description of the preferred embodiment of the invention as
illustrated in the accompanying drawings.
DRAWINGS
In the Drawings
FIG. 1 represents an ink jet system including a character generator
and three ink jet nozzles or head assemblies with associated
synchronizing circuitry.
FIG. 2 is an electronic switch circuit that is useful in the
circuit of FIG. 1.
FIG. 3a illustrates the fundamentals of detector circuit while FIG.
3b illustrates the preferred embodiment of the detector circuit.
The switching circuit of FIG. 2 is ultimately derived from the
circuit of FIG. 3b.
FIG. 4 illustrates various timing relationships during a single
drop interval in the system of FIG. 1.
DETAILED DESCRIPTION
The system of FIG. 1 includes a number of ink jet nozzle assemblies
1, 2, and 3 for forming and propelling drops of ink toward a record
medium, not shown. The respective nozzle assemblies 1, 2, and 3
include crystals 6-8, charge electrodes 10-12, deflection
electrodes 14-16, and sensor gutters 18-20. Each nozzle has a
respectively associated charge electrode driver, designated 22-24.
The charge electrode drivers 22-24 are controlled by the
synchronization pulse generator 26 as well as a character generator
28. Initial control of the circuits is from master clock 30 and
control logic 31.
As is known in the art, drops are formed by the respective nozzle
assemblies in the form of streams of drops designated 33-35. During
synchronization, a sequence of drops which, numerically, can be in
a wide range as from only several drops to a hundred drops are
directed to the respective gutters 18-20. Drops passing in the
gutters 18-20 develop signals on lines 37-39 that are applied to
the electronic switch circuit 40. Associated with switch circuit 40
is a detector amplifier circuit 41, the output of which is returned
by line 42 to control logic 31.
Synchronization of the individual streams of drops formed by the
nozzle assemblies 1-3 may be formed in a sequential fashion. That
is, all of the synchronizing efforts for one nozzle assembly may be
completed prior to initiation of efforts for any of the other
nozzle assemblies. However, it is preferable to synchronize the
respective nozzle assemblies in what might be characterized as a
semi-parallel fashion.
With a semi-parallel arrangement, control signals are directed to
the individual nozzle assemblies 1-3 in such a way that sequences
of drops are propelled from the respective nozzle assemblies in
rotation during drop synchronization procedures with signals
developed from each assembly and corrective action taken with all
assemblies, if and as required.
As is known, synchronization, may be achieved by varying the phase
of the crystals with respect to the charging potentials applied to
the respective charge electrodes 10-12. In the semi-parallel mode,
all crystals are driven with the same phase signal initially. To
start synchronization, a sequence of drops 33a, such as three
drops, is formed and propelled, charged in nozzle assembly 1 and
directed to gutter 18. This results in a signal on line 37 to
switch circuit 40. Shortly thereafter separated by a few drops
perhaps, a sequence of drops 34a is formed, propelled, and charged
in nozzle assembly 2 and directed to gutter 19 to develop a signal.
The signal is applied by line 31 to switch circuit 40. Shortly
after that, and after a short interval of several drops, as before,
another sequence of drops 35a is formed, propelled and charged in
nozzle assembly 3 and directed to gutter 20 in order to develop a
signal on line 39 for application to switch circuit 40. In this
manner only a slight interval exists between the checking of each
nozzle assembly and while a determination is made by control logic
31 as to the correction required to achieve synchronization for any
particular nozzle, signals are developed for the other nozzles as
well to at least initiate corrective action.
The charging of drops for synchronization purposes is customarily
carried out in a manner similar to regular printing of characters
and as described in the Hill, et al, application referred to
previously.
Some of the relationships during a typical drop interval are
illustrated in FIG. 4. One drop time is assumed to be 10
micro-seconds with a first portion of 2.5 micro-seconds
constituting a forbidden time interval when drops should not be
formed. Synchronization of drop formation with respect to charging
preferably occurs in a 3 micro-second interval in the latter
portion of the 10 micro-second drop interval. The forbidden time
interval corresponds to the time when the charge electrode voltage
is changing and thus drop formation should not occur at this time.
If a drop is formed during the synchronization time illustrated
then formation will occur in a correct relationship with respect to
the charge electrode voltage and at a stable time.
In operation, if drops landing in the gutters 18-20 create no
output, as an example, then the drops were formed outside of the
synchronization time, that is improperly. Corrective action can
then be taken by control logic 31 to change drop formation by
either shifting the phase of the crystal device frequency for
crystals 6-8 or changing the amplitude of the voltages applied to
crystals 6-8, or by changing the phase of the voltage pulse
(applied to the charge electrode) with respect to the crystal.
Comparable corrective action is required of course in the event of
relatively low signals developed from gutters 18-20 and applied
through switch circuit 40 and detector circuit 41 to logic 31. If a
sufficient number of properly charged drops pass into gutter 18-20,
then signal levels are developed that are of sufficient magnitude
to indicate proper synchronization of drop formation and charging
by charge electrodes 10-12. Thus, under such circumstances, no
corrective action is required.
Some of the switching logic useful in the circuit of FIG. 1 and
particularly in the switch circuit 40 is illustrated in FIGS. 2,
3a, and 3b.
The basic circuit of FIG. 3a uses an operational amplifier 45 with
an FET (Field Effect Transistor) input which draws a negligible
current, less than 0.5NA (nanoamperes) at 55.degree.C. Resistor 46
(R1) is a high value resistor such as 50 m.OMEGA. .+-. 5 percent
carbon. Resistors 47 and 48 (R2 and R3) serve to increase the
apparent feedback resistance as seen by amplifier A1. The voltage
applied across R1 is determined by the ratio of R2 and R3 (minus
input of amplifier 45 is at virtual ground). If R2 is 300.OMEGA.
and R3 is 2.7k.OMEGA., 10 percent of the op-amp's output voltage is
fed back to R1. The effective feedback resistance R.sub.FB is thus
given by Equation 1:
R.sub.FB = R1 (R2 + R3/R2 ) (1)
as an example, if gutter current I.sub.G = 4NA and resistor R1 =
50m.OMEGA., V1 is virtual ground, then, neglecting bias current
into amplifier 45, all the gutter current flows through R1. V2 =
50m.OMEGA. .times. 4NA = 0.2V if R2 = 300.OMEGA. and R3 =
2.7k.OMEGA., V3 must be as follows:
V3 = (.2V/R2) (R2 + R3)
= .2 (300 + 2700)/300 = 2.0 volts (2)
Capacitors 50 and 51 (C1 and C2) are chosen so that the gain of
amplifier 45 tapers off at an appropriate frequency.
The circuit of FIG. 3b operates on the same basic principle as that
in FIG. 3a except that a non-FET input, less expensive, amplifier
53 is used. A matched pair of junction Field Effect Transistors 55
and 56 provides a high input impedence buffer for amplifier 53. The
matched pair of transistors is needed because of the wide variation
of FET characteristics with currently available manufacturing
procedures.
The method of synchronization is extended to synchronize "N" ink
jets by using the circuits of FIG. 3b and "N" analog switches, as
shown in FIG. 2. Using the principles of the circuits of FIGS. 3a
and 3b, electronic logic determines if drop formation is occurring
at the proper time. If it is not, the magnitude or the phase of the
signal applied to the respective crystals 6-8, FIG. 1, is changed
to shift drop formation to the desired point in time. Inputs on
lines 37-39 are derived from FIG. 1 for the circuit of FIG. 2. The
circuit of FIG. 2 includes matched pairs 60-62 of Field Effect
Transistors, designated Q11 and Q21, Q12 and Q22, and Q13 and Q23,
respectively, each pair having a respectively associated resistor
63-65 and a switch circuit 66-68.
The outputs of the switch circuits 66-68 are directed to the
detector amplifier circuit 41. Resistors 63-65 correspond to
resistor R1 designated 57 in FIG. 3b. The matched pairs 60-62 of
Field Effect Transistors serve as high impedence buffers between
the high impedence sensor inputs 37-39 (sensing gutters) and the
lower impedence input to operational amplifier 70 on line 72.
Switches 66-68, which are analog switches, serve to isolate the
Field Effect Transistor pair 60-62 from one another. Switches 66-68
are operated by control logic 31 on line 44 representative of a
cable operable in a timed sequence at inputs 44a, 44b and 44c,
respectively. Preferably, only one switch 66-68 is coupled to
amplifier 70 at any given time, the other switches being opened. By
appropriate sequential closure of switches 66-68, the signals
developed in gutters 18-20 reflected on lines 37-39 are
sequentially scanned in order to determine what corrective action
is required for synchronizing the ink jet strams of drops from the
respective nozzle assemblies.
While not shown, it may be feasible to operate several ink jets
from one crystal. One ink jet in a group attached to a single
crystal could be used for synchronization. Then sufficient crystal
assemblies could be used to provide the required number of jets. By
combining the multiple jet per crystal technique with the
sequential synchronizing cricuitry described above a significant
reduction in the cost of multi-jet synchronization appears
feasible.
Although the methods shown herein utilize the technique of sensing
the stream current by means of a DC measurement, the same basic
approach used here could work utilizing a non-contacting sensor.
This would result in an AC measurement. The detector senses the
sequence of charged drops passing by a small electrically isolated
sensor near the gutter. This method has the advantage of not
requiring direct sensor contact with the ink. Thus it is not as
subject to contamination.
While the invention has been particularly shown and described with
reference to a preferred embodiment, it will be understood skilled
in the art that various changes in form and detail may be made
without departure from the spirit and scope of the invention.
* * * * *