[0001] The present invention relates to continuous binary array ink jet technology and,
more particularly, to improved ink jet printhead component design and operation.
Background Art
[0002] Continuous binary array ink jet technology was first successfully commercialized
by Mead Corporation of Dayton, Ohio, in the midnineteen-seventies. In this technology,
a print head defines one or more rows of orifices which receive an electrically conductive
recording fluid, such as for instance a water base ink, from a pressurized fluid supply
manifold and ejects the fluid in rows of parallel streams. Printers using such print
heads accomplish graphic reproduction by selectively charging and deflecting the drops
in each of the streams and depositing at least some of the drops on a print receiving
medium, while others of the drops strike a drop catcher device.
[0003] In the prior art, it is known to have separate assemblies for each component of the
ink jet print head. For example, the orifice plate and the charge plate, and electronic
driving components are separate assemblies. Other systems interconnect the electronic
source of the data to be printed to the print head components which charge and deflect
the jets to accomplish the printing task. The print head components are of such precision
and sensitivity that occasionally evanescent dirt, an electrical transient of some
type, or wear causes a print head to fail. When that happens, the print head must
be returned to a central site for refurbishment. When a print head needs to be replaced
or repaired, there are several critical tolerances within the print head assembly
that need to be maintained. For instance, if a component of one assembly is replaced,
the replacement component is required to be realigned with the various other components
in the assembly. The realignment process requires specific, precise realignment tools.
The process, therefore, is time consuming and costly, and must be done in a controlled
environment. This is why print heads are sent to a central facility for overhaul.
[0004] In the design of a print head, concerted efforts are made to integrate the various
components and assemblies into a rugged structure which is capable of maintaining
alignment. In some designs, various components, such as charge plates and drop stream
generators could be disassembled and replaced in the field. However, that approach
required alignment of some components in the field as a part of the component replacement.
At the same time, market demands for improved print quality led to development of
print heads containing more jets per linear inch. As the print quality of binary array
continuous ink jet improved, the alignment tolerances became even tougher to maintain,
so that replacement of print head component parts in the field was no longer practical.
[0005] The commercial state of the art in continuous binary array ink jet technology allows
printing at 240 dots per inch (dpi). This is done with a linear array of jets, in
which the spatial density of jets is the same as the print resolution. See, for example,
U.S. Patent 4,636,808. With the ever increasing demand for improved image quality,
there is a need to further increase the print resolution. Existing systems at 240
dpi have the inherent capability to be scaled to the higher print resolutions needed.
However, practical problems have hindered the development of such systems. A 240 dpi
continuous binary array system with flat face charging scheme, as described in the
'808 patent, has 94 electrical charge leads per centimeter (240 electrical charging
leads per inch) on the charge plate. To make a practical printer, each of these leads
must be connected to external circuitry which supplies the imaging data. Making electrical
connections to these leads even at 240 dpi is a major hindrance to further improvement
of resolution.
[0006] In the prior art, conducting traces, from the face of the charge plate "fan out"
across the top of the charge plate, to an interconnection point where the leads are
much more widely spaced than they are at the active surface of the charge plate. This
is necessary because the current state of the art in connection technology, allows
only about 39 connections per centimeter (one hundred connections per linear inch).
By using the fanout technique, connections to 94 electrical charge leads per centimeter
(240 charge leads per inch) is achieved with the commercially feasible interconnection
density of 39 connections per centimeter (100 connections per inch). The cost of this
is print head space, because at the interconnection point, there are 6 cm (2.4 inches)
of connection space for each inch of active print width. It is clear that this requires
a much larger charge plate than is otherwise required for the '808 technology. Typically,
fanout causes the charge plate to be two or three times deeper than would be required
by other print head constraints. This, in turn, causes the print head to be larger
than the desirable size.
[0007] Another aspect of the interconnection problem relates to the number of connections
which need to be made between the print head and the data source. For example, the
prior art print head uses 1024 print jets at a resolution of 240 jets per inch. Although
the print width is only 10,8 cm (4.267 inches), 1024 connections to the data system
are required. To accommodate print heads with a large number of jets, it is common
practice to send data to a print head in a series of 1's and 0's, serial form, and
to convert the serial data back to "parallel" data in the print head. This raises
the rate at which data must be transferred over the "serial" connection, but dramatically
reduces the number of connections. Use of this technique means that there are some
electronic components which also reside in close proximity to the charge plate. In
the example just described of the "four inch" print head, common practice is to use
an electronic chip which contains drivers for 64 jets, and is driven through 8 input
connections. The four inch print head requires 16 such chips mounted in close proximity
to the actual charge electrodes in the print head.
[0008] There are additional electronic components in prior art print heads. For example,
manufacturing differences between components mean that different print heads produce
best quality print output at slightly different voltages, ink pressures, operating
frequencies, etc. These "personality" differences are accommodated by putting a computer
in the print head to communicate the specific needs of the print head to the fluid
supply station which supplies power and fluids to the print head. The computer is
also useful to record any problems which may have been detected in the print head,
the length of it's use, the exact phase required for the charging voltage in relation
to the drop generation sequence for each jet, etc.
[0009] The entire electronic package must be mounted in close proximity to the operating
ink jets, and in prior art, is designed as part of the structure of the print head.
This has led to a problem because the ink jet components have a much shorter useful
life in a print head than the electronic components. When a print head is sent back
to the refurbishment center because of a problem with the ink jet components, the
electronic system which supports the print head and is part of it is sent back as
well, even though it is operating properly. This means that when hundreds of these
print heads are in service, and other hundreds are in transit to and from the refurbishment
center, there is a huge waste in the "float" of good electronic components.
[0010] It is seen then that there is a need for a print head design in which the ink jet
components can be made into a field replaceable assembly which can be quickly and
easily replaced without requiring alignment. It is also seen that there is a need
for wider print heads. It is further seen that there is a need for a print head structure
in which the ink jet components can be replaced in the field without affecting the
print head control electronics.
[0011] US-A-4847631 discloses a charge and deflection control type ink jet printer having
an inkjet section, a charging section and a deflection section configured in a single
replaceable module. In an embodiment the replaceable module has a control for adjusting
the drive voltage. The charging electrode is not loaded in the replaceable module
in this embodiment.
[0012] US-A-5455611 discloses a print-head assembly, including control capability for controlling
the flow of fluid to a drop generator and for transferring data to a charging and
collecting element. The control capability includes a microcontroller and fibre optics
for receiving data and control signals and for providing signals to an input buffer.
The print-head apparatus is capable of providing diagnostic functions and is self-contained
in a field-replaceable housing.
[0013] Accordingly, it is an object of the present invention to provide a continuous ink
jet print head with separate electronics. It is a further object of the present invention
to provide a continuous ink jet print head with refurbishable components. It is an
advantage of the present invention that parts which are sent back from the field for
refurbishment are field separable from the print head electronic components.
[0014] The invention provides a two-element print-head assembly for use in an ink jet printer
comprising a first element including means for providing fluid to a droplet generating
means, and print-head electronics for controlling drop formation; and characterised
by a second element being a field-replaceable print element apparatus including droplet
generating means; droplet charging and collecting means for charging and collecting
drops from the droplet generating means; means for receiving data signals from the
print-head electronics for controlling the means for charging and collecting drops;
and data storage means for storing a plurality of operating parameters relating to
the droplet generating means, and the droplet charging and collecting means.
[0015] Other objects and advantages of the invention will be apparent from the following
description, the accompanying drawings and the appended claims.
Fig. 1 illustrates a front view of a two element print head assembly in accordance
with the present invention; and
Fig. 2 illustrates a side view of the two element print head assembly of Fig. 1.
Detailed Description of the Preferred Embodiments
[0016] The present invention provides for a nine inch print head assembly which provides
a minimum package size and minimizes operator interventions. In operation, the nine
inch print head is similar to that of the earlier generation print head described
in U.S. Patent No. 5,455,611. Ink jet printers are typically comprised of several
components, including a fluid system, data system, and print head. The fluid system
provides electrical control of the components required to control drop formation and
maintain fluid quality. The print head, which accepts fluids from the fluid system,
generates drops and returns unused drops to the fluid system. The print head selectively
controls drop charging to allow imaging on a print medium, utilizing information prepared
by the data system. The data system accepts data in standard formats, such as ASCII,
EBCDIC, etc., along with print start and delay signals. The information is transferred
to the print head for imaging.
[0017] In the drawings, for purposes of illustration only, components within a preferred
embodiment of a print head have been expanded from what is typical for a continuous
ink jet printer print head to include all the control sensors required for maintaining
drop quality. The drawings will be described with reference to a preferred embodiment
of the present invention, wherein the preferred embodiment is a nine inch printer
which incorporates 2176 printing jets, but are not to be considered as limiting the
invention.
[0018] Referring now to Fig. 1, a two element print head assembly 10 is shown in a ready
to use state attached to a print head interface controller (PIC) box 11. The separate
housing 19 is the refurbishable print head module (RPM). The RPM houses a droplet
generator means 12 which has been previously coupled to a droplet charging and collecting
means 14. Filtered fluids are provided to the droplet generator means 12 and removed
from the droplet charging and collecting means 14 via a fluid control manifold 16
located in the PIC box. The connections between the PIC box and the RPM are established
by fluidic and electrical connecting means which are mated by latching means (not
shown) when the two components are attached into an operational state. The fluid control
manifold 16 in the PIC box contains an ink temperature sensor 16a, an ambient temperature
sensor 16b, and an airflow path in the direction of arrow 16d. The airflow path 16d
is controlled by a solenoid valve 16e. The solenoid valve 16e allows air to flow into
and through the droplet generator means 12 during the print head shutdown sequence
to accelerate removal and drying of ink. To prevent drying of ink in the main filter
17a during shutdown, a second filter 17b located in the RPM 19 is provided for the
vent. This venting capability is particularly advantageous for overnight storage and
transportation. Ink supplied from the fluid manifold 16 in the PIC box is filtered
by filter means 17a prior to being supplied to the drop generator means 12.
[0019] The manifold assembly 16 also houses a pressure measuring means 16f for precisely
controlling the pressure at which drops are generated, as well as an outlet valve
16g. The outlet valve 16g is activated to provide a high flow rate through the droplet
generator means 12 during startup for dissolving ink and wetting the orifice plate
attached to the droplet generator. When the outlet valve 16g is closed, pressure builds
up sufficient for droplet formation. During each of these operations the pressure
in the droplet generator means 12 is monitored for servo control via the pressure
measuring means 16f. During cross flush conditions, a small positive pressure is maintained,
typically 3,4 kPa to 6,9 kPa (0.5 to 1.0 psig), to prevent air ingestion into the
droplet generator means 12 where air can become trapped. The trapped air would then
prevent uniform drop generation. Continuing with Fig. 1, ambient and ink temperature
sensors, 16b and 16a respectively, can be utilized by an external controller to provide
ink at a fixed temperature relative to the surroundings. This is utilized for condensate
cleaning of the drop charging and collecting means 14 during startup conditions. This
could also be utilized during normal run operations. When the RPM 19 is connected
to the PIC box 11, a plurality of electrical and fluidic connections are maintained
so that the RPM is in an operable state. In the event of a failure of the ink jet
components, the RPM 19 can be easily disconnected from the PIC box 11, so that the
print head can be returned to the refurbishment center. A replacement print head can
be immediately attached to the PIC box 11 using latching means not shown in the diagram,
and work can be resumed. The size of the combination PIC box and print head is smaller
than the prior art print heads, two of which would be needed to cover a comparable
print width. In part, this is enabled by improved interconnection technology in the
drop charging and collecting means 14.
[0020] Referring now to Fig. 2 and continuing with Fig. 1, an eyelid 24c is used in the
closed position to divert ink into the drop collection means 14 for removal via a
flow path 20 during the start up and shut down conditions. In the normal operating
(printing) condition, the eyelid 24c is opened to allow the selected drops 25 to strike
a print medium which is not shown in Fig. 2. The eyelid 24c is activated (opened)
using electromechanical means 24 in the PIC box which is connected to a link 24b,
and which pivots at pivot point 24d. A bias means 24a is used to close the eyelid
24c against the drop charging and collecting means 14 in the default state. Placement
of the activation components (in the PIC box) away from the ink usage area prevents
ink from drying on the pivots, etc. where they could cause sticking or binding of
the eyelid motion.
[0021] Both print means elements, the PIC box and the RPM are fully enclosed by housing
means 11 and 19 except for small gaps in the region of the moving eyelid 24c. The
small gaps allow positive air pressure to be maintained within the assembly 10. Positive
air is supplied to the PIC box by a fan (not shown). The positive air flows into the
PIC box through opening 22, past the PIC box electronics 27, and out through another
opening in the PIC box 35. Positive air in the RPM is provided via an air pump in
the fluid system (not shown) through two ports 34 which also serve as alignment features
for the PIC box and RPM. In the prior art, the same clean air was used for cooling
and positive air pressure in the print head. However, experience showed that the cooling
air could not be maintained clean enough for use near the ink jets 25. Cooling of
the RPM electronics is accomplished via a flow of ink which is split from the drop
generator path and returned via a path (not shown) beyond the outlet valve used for
starting jets.
[0022] Referring again to Fig. 2, the charge electrode drivers reside on an electronic circuit
board 28 in the RPM 19 and connect to the drop charging and collecting means 14. The
PIC box electronics board 27 connects to fluid system, the data system, and the print
head. The board 27 takes print data from the data system, combines it with timing
data from the fluid system, and converts it to a format suitable for high voltage
drivers located on the electronic board 28 in the RPM 19. Also residing on the electronic
board 28 is the electronics which contains the personality module for the specific
RPM. The interface from the data system to the PIC box 11 is preferably accomplished
through a fiber optic cable means driven by a fiber optic transmitter (not shown)
in the data system. The electronic board 28 in the RPM is connected to the drop charging
and collecting means 14 via connecting means 30.
[0023] In ink jet printers, the charge and therefore the deflection of a drop depends in
the voltage on the charge plate just prior to the break off of the drops. A drop will
only be charged for catch if the charge voltage is high during the very short interval
just prior to break off. Conversely, a drop will be left uncharged for print only
if the charge voltage is near zero during this time interval. To ensure proper selection
of the print drops, it is necessary to maintain proper phase between the print pulses
and the break off of drops. To aid the operator in selecting the optimum phase, a
microprocessor in the PIC box electronics 27 can generate a diagnostic plot of the
stimulation break off phase for each array of jets. From this plot, the operator can
readily select the desired operating phase. This plot also provides a check on stimulation
uniformity which may indicate a degradation in the drop generator 12.
[0024] The PIC box electronics 27 includes the microcontroller which does status monitoring,
and selftest control, and monitors the personality module in the RPM for specific
fluid system parameters. The microcontroller communicates with the fluid system over
a bidirectional serial link. The microcontroller is used to provide a serial interface
to the fluid system, transfer status and commands to and from the fluid system, and
to control analog components in PIC box.
[0025] In the preferred embodiment of the present invention, the PIC box and the RPM assembly
are controlled by a fluid system utilizing parameters within the personality module
within the RPM. The two member print head apparatus accepts data via a fiber optic
link from a data system to ultimately control print drop selection.
[0026] Although the preferred mode of practicing the invention has been described with reference
to an ink jet print head for a continuous ink jet printer, the principle of the present
invention can also be applied to a wide variety of ink jet printers.
Industrial Applicability and Advantages
[0027] The RPM and PIC box apparatus according to the present invention are useful in continuous
ink jet printers. The apparatus of the present invention provides for a separable
print head and drive electronics assembly so that the ink jet components can be returned
for refurbishment without including the support electronics. The RPM of the present
invention has the further advantage of being able to store operating (initial and
final) parameters, so that the replacement RPM can work with the same PIC box electronics.
The combined PIC box and RPM of the present invention is smaller than the prior art
print head, and prints a larger swath than two prior art print heads.
1. A two-element print-head assembly for use in an ink jet printer comprising:
a first element including means (16) for providing fluid to a droplet generating means,
and print-head electronics (27) for controlling drop formation; and
a second element being a field-replaceable print element apparatus (19) including:
droplet generating means (12);
droplet charging and collecting means (14) for charging and collecting drops from
the droplet generating means;
means (28) for receiving data signals from the print-head electronics for controlling
the means (12, 14) for charging and collecting drops; and characterised by
data storage means (28) for storing a plurality of operating parameters relating to
the droplet generating means (12), and the droplet charging and collecting means (14).
2. A two-element print-head assembly as claimed in claim 1, wherein the field-replaceable
print element apparatus (19) comprises control electronics having:
a. a microcontroller (28);
b. fiber optic means for receiving data and control signals and providing the signals
to an input buffer;
c. a random access memory (28) for providing data memory;
d. latch and shift register means (28) for latching and shifting data from the random
access memory;
e. high voltage driver means (28) for receiving data from the latch and shift register
means; and
f. a control state machine (28) which communicates with the microcontroller, for handling
generation of all control signals for the input buffer, the random access memory,
and the latch and shift register means.
3. A two-element print-head assembly as claimed in claim 2, wherein the field-replaceable
print element apparatus (19) further comprises means (28) for controlling print quality
by controlling externally supplied ink pressure, ink temperature, and stimulation
level in accordance with internally stored parameters, and utilising previously measured
hole size information to control a number of drops printed on a spot for use in colour
adjustment.
1. Zwei-Elemente-Druckkopfanordnung für einen Tintenstrahldrucker, enthaltend:
ein erstes Element, welches Mittel (16) zum Bereitstellen eines Fluids an einem Tröpfchenerzeugungsmittel
und eine elektronische Druckkopfsteuerschaltung (27) zum Steuern der Tropfenbildung
enthält;
ein zweites Element, das eine austauschbare Druckelementeinrichtung (19) ist, welche
aufweist:
Tröpfchenerzeugungsmittel (12);
Tröpfchenauflade- und -sammelmittel (14) zum Aufladen und Sammeln von Tropfen aus
den Tröpfchenerzeugungsmitteln;
Mittel (28) zum Empfang von Datensignalen aus der elektronischen Druckkopfsteuerschaltung
zum Steuern der Mittel (12, 14) zum Aufladen und Sammeln der Tropfen; und gekennzeichnet durch
Datenspeichermittel (28) zum Speichern einer Vielzahl an Betriebsparametern, die die
Tröpfchenerzeugungsmittel (12) und die Tröpfchenauflade- sowie -sammelmittel (14)
betreffen.
2. Zwel-Elemente-Druckkopfanordnung nach Anspruch 1, bei der die austauschbare Druckelementeinrichtung
(19) eine elektronische Steuerschaltung enthält, die aufweist:
a) einen Mikrokontroller (28);
b) Glasfasermittel zum Empfangen von Daten und von Steuersignalen sowie zum Bereitstellen
der Signale an einen Eingabebuffer;
c) einen Direktzugriffsspeicher (28) zum Bereitstellen eines Datenspeichers;
d) Verriegelungs- und Schieberegistermittel (28) zum Verriegeln und Verschieben von
Daten aus dem Direktzugriffsspeicher;
e) Hochspannungs-Steuermittel (28) zum Empfangen von Daten aus den Verriegelungs-
und Schieberegistermitteln; und
f) eine Steuerzustandsmaschine (28), welche in Kommunikationsverbindung mit dem Mikrokontroller
steht, um die Erzeugung aller Steuersignale für den Eingabebuffer, den Direktzugriffsspeicher
und die Verriegelungs- und Schieberegistermittel durchzuführen.
3. Zwei-Elemente-Druckkopfanordnung nach Anspruch 2, bei der die austauschbare Druckelementeinrichtung
(19) weiterhin Mittel (28) zum Steuern der Druckqualität durch Steuern eines von außen
zugeführten Tintendruckes, der Tintentemperatur und des Stimulationspegels in Übereinstimmung
mit den intern gespeicherten Parametern und durch Verwenden von im voraus erfassten
Lochgrößeninformationen enthält, um die Zahl an Tropfen zu steuern, die auf einem
Punkt zum Zwecke der Farbeinstellung gedruckt werden.
1. Ensemble de tête d'impression à deux éléments pour une utilisation dans une imprimante
à jet d'encre, comprenant :
- un premier élément comprenant des moyens (16) pour fournir un fluide à un moyen
de génération de gouttelettes, et un circuit électronique de tête d'impression (27)
pour commander la formation des gouttes; et
- un second élément constitué par un dispositif d'élément d'impression remplaçable
par l'utilisateur (19), comprenant :
- un moyen de génération de gouttelettes (12);
- un moyen de chargement et de collecte de gouttelettes (14) pour charger et pour
collecter des gouttelettes à partir du moyen de génération de gouttelettes;
- un moyen (28) pour recevoir des signaux de données à partir du circuit électronique
de tête d'impression pour commander les moyens (12, 14) pour le chargement et la collecte
des gouttelettes; et
caractérisé par un moyen de stockage de données (28) pour stocker une pluralité de paramètres de
fonctionnement concernant le moyen de génération de gouttelettes (12) et le moyen
de chargement et de collecte de gouttelettes (14).
2. Ensemble de tête d'impression à deux éléments selon la revendication 1, dans lequel
le dispositif d'élément d'impression remplaçable par l'utilisateur (19) comprend un
circuit électronique de commande possédant :
a) un microprocesseur (28);
b) un moyen à fibre optique pour recevoir des données et des signaux de commande et
pour fournir les signaux à une mémoire cache d'entrée;
c) une mémoire vive (28) pour constituer une mémoire de données;
d) un moyen de registre à bascule et à décalage (28) pour basculer et décaler des
données à partir de la mémoire vive;
e) un moyen de circuit d'attaque à haute tension (28) pour recevoir des données du
moyen de registre à bascule et à décalage; et
f) une machine d'état de commande (28) communiquant avec le microprocesseur pour manier
la génération de tous les signaux de commande pour la mémoire cache d'entrée, la mémoire
vive et le moyen de registre à bascule et à décalage.
3. Ensemble de tête d'impression à deux éléments selon la revendication 2, dans lequel
le dispositif d'élément d'impression remplaçable par l'utilisateur (19) comprend,
de plus, un moyen (28) pour commander la qualité d'impression en commandant une pression
externe d'encre fournie, une température d'encre et un niveau de stimulation selon
des paramètres stockés, de façon interne, et utilisant une information de dimension
de trous mesurée précédemment pour commander le nombre de gouttes imprimées sur un
point pour un réglage de couleur.