Note: Descriptions are shown in the official language in which they were submitted.
. CA 02449615 2003-12-17
PIEZOELECTRIC INK JET PRINTING SYSTEM
Background of the Tnvention
This invention relates generally to ink jet printing
systems, and more particularly to piezoelectric ink jet
printing systems.
A piezoelectric ink jet printhead is susceptible to
problems when suddenly jarred. This is because the
piezoelectric components of the printhead effect the
delivery of ink to the orifices of the printhead at
extremely low pressures. As a result, when the printhead
is subjected to vibration or impact, the flow of ink
through passages in the printhead and related supply
lines may be interrupted, causing undesirable
discontinuities in the supply of ink to the ink orifices
and often necessitating "repriming" of the printhead.
This problem is magnified when the line from the ink
supply to the printhead is relatively long because there
is a greater likelihood that vibration-induced shock
moving through the line will disrupt the flow of ink.
Previously, ink jet systems have used relatively small
ink reservoirs located close to the printhead to reduce
the length of the supply line. However, due to its small
capacity, the reservoir must be refilled manually or
replaced, at frequent intervalsf which is inconvenient
and increases downtime of the system.
Summary of the Invention
Among the several objects of this invention may be
noted the provision of an ink jet printing system having
multiple printheads which can be independently located
with respect to each other and with respect to a primary
ink supply to allow greater flexibility in the use and
application of the system; the provision of such a system
which has multiple printhead assemblies each containing a
CA 02449615 2003-12-17
2
secondary ink supply located close to the printhead to
reduce the length of an ink supply line, thus minimizing
interruptions in ink flow due to vibration; the provision
of such a system wherein the printhead and a secondary
ink supply reservoir are contained within the same
housing, and wherein the supply reservoir is adjustable
to maintain a constant orientation for proper system
operation when the printhead is rotated to print
different size indicia; the provision of such a system
which provides automatic refilling of a secondary ink
supply to eliminate the need for frequent manual
refilling; and the provision of such a system which
includes a purge system for purging individual printheads
and supply lines without overfilling the secondary ink
supply.
Briefly, a piezoelectric ink jet printing system of
this invention includes a primary ink supply and a
plurality of piezoelectric ink jet printhead assemblies.
Each assembly comprises a housing, a piezoelectric ink
jet printhead in the housing, a secondary ink supply
attached to the housing close to the printhead, and a
short ink supply line for delivery of ink from the
secondary ink supply to the printhead. The system further
includes a pump for pumping ink from the primary ink
supply to the secondary ink supply of each printhead
assembly. Each printhead assembly is operable
independently of the other printhead assemblies and is
selectively movable with respect to the other printhead
assemblies and with respect to the primary ink supply so
that each printhead assembly can be positioned at a
desired location without regard to where the other
printhead assemblies are to be positioned and without
regard to where the primary ink supply is.positioned.
In a second aspect of this invention, the ink jet
printing system includes a primary ink supply and a
plurality of piezoelectric ink jet printhead assemblies.
CA 02449615 2003-12-17
3
Each assembly includes a housing, a piezoelectric ink jet
printhead in the housing, a secondary ink supply attached
to the housing close to the printhead; and a short ink
supply line for delivery of ink from the secondary ink
supply to the printhead. The printhead of each printhead
assembly includes a linear array of ink orifices through
which ink is ejected to print indicia on a surface. Each
printhead assembly further camprises a device for
mounting the housing and printhead therein for rotation
about a first axis extending generally perpendicular to
the surface thereby to vary the height of the indicia
printed on the surface by the printhead in the housing,
and a device for locking the housing in a selected
position of rotational adjustment according to the
desired height of indicia to be printed. The secondary
ink supply of each printhead assembly is rotatably
mounted with respect to the housing of the assembly so
that when the housing of the printhead assembly is
rotated in one direction about said first axis, the
secondary ink supply may be rotated in an opposite
direction to maintain the secondary ink supply in a
selected predetermined attitude.
In a third aspect of this invention the system
comprises a primary ink supply and a plurality of
piezoelectric ink jet printhead assemblies. Each
assembly comprises a piezoelectric ink jet printhead, a
secondary ink supply close to the printhead, and a short
ink supply line for delivery of ink form the secondary
ink supply to the printhead. The system further
comprises a pump for pumping ink from the primary ink
supply to the secondary ink supply of each printhead
assembly and a purge system for each printhead assembly
for delivering ink under pressure from the primary ink
supply to the printhead of the assembly thereby to purge
air from the printhead. The purge system comprises a
purge line which bypasses the secondary ink supply of the
CA 02449615 2003-12-17
73014-9E
4
printhead assembly to prevent the delivery of ink under
pressure to the secondary ink supply during purging of the
printhead.
A further aspect of the present invention provides
a piezoelectric ink jet printing system comprising a primary
ink supply, a plurality of piezoelectric ink jet printhead
assemblies, each assembly comprising a piezoelectric ink jet
printhead, a secondary ink supply adjacent the printhead,
and an ink supply line for delivery of ink from the
secondary ink supply to the printhead, a pump for pumping
ink from the primary ink supply to the secondary ink supply
of each printhead assembly, and a purge system for each
printhead assembly for delivering ink under pressure from
the primary ink supply to the printhead of the assembly
thereby to purge air from the printhead, said purge system
comprising a purge line which bypasses the secondary ink
supply of the printhead assembly to prevent the delivery of
ink under pressure to the secondary ink supply during
purging of the printhead.
Other objects and features will be in part
apparent and in part pointed out hereinafter.
Brief Description of the Drawings
Fig. 1 is a perspective view of a piezoelectric
ink jet printing system of the present invention;
Fig. 2 is a perspective view of a printhead
assembly of the ink jet printing system of Fig. 1;
Fig. 2A is a rear perspective view of the
printhead assembly of Fig. 2;
Fig. 3 is a perspective view of components of the
printhead assembly of Fig. 2;
' CA 02449615 2003-12-17
73014-9E ,
4a
Fig. 4 is a perspective view of a secondary ink
supply mounted within a lower part of a housing of the
printhead assembly of Fig. 2;
Fig. 5 is a plan view of the printhead assembly of
Fig. 2 with an upper part of the housing removed;
Fig. 6 is a hydraulic schematic of the ink jet
printing system of Fig. 1;
Fig. ? is a cross-sectional view taken along line
7--7 of Fig. 3; and
Fig. 8 is an electrical schematic of the printhead
controller.
Corresponding parts are designated by
corresponding reference numerals in the several views of the
drawings.
Description of Preferred Embodiments
Referring now to the drawings, and first to
Figs. 1-3, a piezoelectric ink jet printing system is
generally indicated at 10. The system comprises a primary
ink supply, generally designated 12, and a plurality of
piezoelectric ink jet printhead assemblies 14, each of which
includes a printhead 16 and a housing 18 for both the
printhead and a secondary ink supply 20. As shown in
Fig. 6, a pump 22 is provided for pumping ink from the
CA 02449615 2003-12-17
73014-9E
primary ink supply 12 to the secondary ink supply 20 of
each printhead assembly 14. The printheads 16 may be any
suitable piezoelectric printhead, such as a printhead
available from Trident, Inc, of Brookfield, CT., in
5 which the ejection of ink droplets through multiple
nozzles is effected by-the reciprocation of plungers
driven by piezoelectricity. U.S. Patent No. 4,714,934,
describes such a printhead.
The printhead assemblies 14 are typically arranged
on opposite sides of a conveyor 24. The printhead 16 of
each assembly 14 has a linear array of ink orifices 26
(Figs. 2 and 3) through which ink is ejected to print
indicia on a surface 28 such as the side of a carton or
other product travelling along the conveyor 24The
printhead assemblies 14 may be mounted in various
configurations and any number of printhead assemblies may
be used. The primary ink supply 12 is preferably located
in the general vicinity (e. g:, 40 feet) of the printhead
assemblies 14 to reduce the length of ink supply lines 30
and associated pressure drop. As shown in Fig. 6, the
primary ink supply 12 preferably includes a reservoir 32
and a large ink supply bottle 34 (1 liter or 500 ml for
example) having an opening (nat shown) connected.to the
reservoir. The reservoir 32 includes a level~detector
(not shown) which senses when the ink bottle 34 is empty
and sends a signal to a low level light 36 (Fig. 1); to
notify someone to replace the ink supply. bottle. In
addition to illuminating the low level light 36, the
level detector also sends a signal to shut off the pump
22 so that the reservoir 32 is not completely emptied of
ink. This prevents possible damage .to the pump 22 from
running without.ink and allows for replacement of the ink
bottle 34 without interruption of operation of the
printheads 16. The ink bottle 34, reservoir 32 and pump
22 are all located within a single enclosure 38 adjacent
CA 02449615 2003-12-17
6
to an electronic controller 40 (Fig. 1) which controls
the operation of the system 10. It is to be understood
that other pump, reservoir and controller arrangements
may be used without departing from the scope of this
invention.
Each printhead assembly 14 is operable independently
of the other printhead assemblies and is selectively
moveable with respect to the other printhead assemblies
and with respect to the primary ink supply 12 so that
each printhead assembly can be positioned at a desired
location without regard to where the other printhead
assemblies are to be positioned and without regard to
where the primary ink supply is positianed. A typical
arrangement of printhead assemblies 14, primary ink
supply 12 and conveyor 24 is shown in Fig. 1. Two
mounting bars, each designated 42, are located on
opposite sides of the conveyor 24 and extend generally
parallel to the conveyor fox mounting the printhead
assemblies l4 along the conveyor. Each mounting bar 42
is attached to a respective side of the conveyor 24 by
two arms 44 extending out from the conveyer frame 46.
Clamps 48 are provided to connect the printhead
assemblies 14 to the bar 42 at selected locations along
the bar. Each clamp 48 includes a first part 50 which
clamps onto the bar 42 and a second part 52 which
slidably receives the lower end of a support post 54
connected at its upper end to a respective printhead
assembly 14. The elevation of each printhead assembly 14
may be adjusted by loosening the second part 52 of the
clamp 48, slidably moving the support post 54 vertically
within the clamp to the desired elevation, and then
tightening the second part of the clamp. The position of
the printhead assembly 14 is also adjustable in a
direction parallel to the conveyor 24 by loosening the
first part 50 of the clamp 48, sliding the clamp and
CA 02449615 2003-12-17
7
associated printhead assembly 14 along the mounting bar
42, and tightening the first part of the clamp.
It will be observed from Fig. 2 that the printhead
housing 18 includes a lower part 60, an upper part 62 and
a pair of end caps 64. The upper part 62 is releasably
attached to the lower part 60 and the end caps 64 are
attached to the lower and upper parts by screws 68 or any
other suitable fasteners. To remove the upper part 62 of
the housing 60, two upper screws 68 must be removed from
each end cap 64. The upper part 62 may be removed from
the printhead assembly l4 without removing the end caps
64. As shown in Figs. 4 and 5, components within the
housing 18 are secured to the lower part 60 of the
housing 18.
As shown best in Fig. 2A, a bracket 70 is used to
mount the housing 18 of each printhead assembly 14 on its
respective support post 54 for rotation of the assembly
about a first axis A generally perpendicular to the
surface 28 upon which indicia is to be printed. This
rotation allows an operator to match the incline or
decline of the conveyor 24, or to vary the height of the
indicia to be printed on surface 28, since rotation of
the assembly changes the angular position (and thus the
effective printing height) of the linear array of
printhead orifices. A fastener 72 is provided for
locking the housing 18 in a selected position of
rotational adjustment according to the desired height of
indicia to be printed. The bracket 70 includes a base 74
and two legs 76 extending down from the base on opposite
sides of the upper end of the support post 54. The
fastener 72 extends through holes in both legs 76 and the
support post 54. A clamp-up bushing (not shown) is
provided between one of the legs 76 and the support post
54 to hold the printhead assembly in a set angular
position when the fastener 72 is tightened.
CA 02449615 2003-12-17
8
The position of the printhead assembly 14 can be
adjusted in a direction generally perpendicular to the
conveyor 24 by sliding the housing 18 of the assembly
relative to the bracket 70. It will be noted in this
regard that the base 74 of the bracket 70 is generally U-
shaped and forms a channel 78 having an open top for
receiving two parallel ribs 80 projecting along a lower
surface of housing (see Fig. 2A). The two ribs are
spaced apart a distance such that they have a close
sliding fit within the channel 78, thus enabling
adjustment of the printhead assembly 14 relative to the
bracket 70. The ribs 80 are preferably angled outward
and the sides 84 of the channel 78 are preferably angled
inward to form a dovetail sliding connection which
prevents movement of the housing 18 in a vertical
direction relative to the bracket 70. A set screw 86
holds the printhead assembly 14 in a set linear position.
It is to be understood that other mounting and adjustment
configurations may be used without departing from the
scope of this invention.
The secondary ink supply 20 inside the housing
comprises a small receptacle 88 defining a reservoir 92
for the ink supply, a removable top 94 fastened to the
receptacle, an inlet 96, an outlet 98, a vent 100 and a
level detector generally designated 102. A short ink
supply line 104 connects the outlet 98 to the printhead
16. The secondary ink supply 20 is attached to the lower
part 60 of the housing 18 close to the printhead 16 to
minimize the length of 104. The secondary ink supply 20
is rotatably mounted with respect to the housing 18 so
that when the housing is rotated in one direction about
axis A, the reservoir 92 of the secondary ink supply may
be rotated in an opposite direction about a second axis B
to maintain the reservoir in a selected predetermined
attitude, usually one in which the top 94 of the
reservoir is horizontal and level. In the preferred
CA 02449615 2003-12-17
9
embodiment, axis B passes through or closely adjacent to
the lowest ink orifice 106 in the linear array of
orifices 26 of the printhead 16 (Fig. 3). The
arrangement is such as to maintain the fluid level iri the
reservoir at a height sufficient to provide flow from the
outlet 98 of the reservoir to the printhead without
causing weepage of ink from the orifices 26 when the
printhead is not printing due to head pressure in the
reservoir 92.
As shown in Figs: 3, 4 and 7, the receptacle 88 of
the secondary ink supply 20 is rotatably carried by a
leveling bracket 108 so that the reservoir 92 can be
rotated to accommodate the angle at which the housing and
printhead 16 oriented. The secondary ink supply 20 is
preferably rotated so that the top 94 of the reservoir 92
is maintained in a horizontal and level position to allow
for proper operation of the level detector 102: The
leveling bracket 108 comprises a base 110 and two arms
112 angling up from the base. The base 110 of the
bracket 108 is attached to the lower part 60 of the
housing 18 by four screws 114. Each arm 112 has a hole
at its upper end for receiving a screw 115 having a major
diameter slightly smaller than the diameter of the hole.
The arms 112 are sized and spaced for receiving the
receptacle 88 of the secondary ink supply 20
therebetween. The holes in the arms 112 are aligned with
openings located in opposite side walls 116 of the
receptacle (Fig. 7). These openings extend only
partially through the walls 116 of the receptacle 88 and
do not extend into the reservoir 92 of the secondary ink
supply 20. Screws 115 extend through the holes in the
arms 112 of the leveling bracket 108 and are threaded
into the openings in the receptacle 88. The screws 114
are tightened sufficient to fractionally hold the
receptacle 88 in a set position while still permitting
manual rotation of the receptacle about axis B without
' CA 02449615 2003-12-17
l
loosening the screws. In order to adjust the attitude of
the receptacle 88 following adjustment of the printhead
assembly 14 about axis A, the upper part 62 of the
housing 18 is removed and the receptacle is manually
rotated about axis B so that the top 94 of reservoir 92
remains in a horizontal and level position. Means other
than that shown in the drawings and described above may
be provided for mounting the receptacle 88 for rotation
on axis B.
As illustrated in Fig. 6, the pump 22 supplies ink
to each printhead assembly via a main ink supply line 118
and a plurality of ink feed lines 120 which branch from
the main line and feed ink to the individual printhead
assemblies l4. The downstream end 122 of each feed line
120 is connected to the inlet 96 of the secondary ink
supply 20 of a respective printhead assembly 14. A
normally closed feed valve 124 mounted in the housing 18
of the printhead assembly 14 controls flow of ink through
the feed line 120 to the reservoir 92 of the secondary
ink supply 20. The feed valve 124 is moveable from its
normally closed position in which flow of ink into the
secondary ink supply 20 is blocked, to an open position
allowing flow to the secondary ink supply. The feed
valve 124 is an electronically controlled, two-position
solenoid valve that responds to a signal received from
the level detector 102 located within the reservoir 92.
The solenoid valve may be of conventional design, one
such valve being commercially available from Angar
Scientific under trade designation AM195.
As shown in Fig. 7, the level detector 102
comprises a magnetic float 126 and a reed switch 128.
The reed switch 128 may be any suitable design, such as
one commercially available from National Magnetic under
trade designation TLS-10NPS. The reed switch 128 is
actuated when the ink in the reservoir 92 reaches a low
level (switch open) and, during filling, when the ink in
CA 02449615 2003-12-17
11
the reservoir reaches a full level (switch closed). The
low level is preferably about 0.125 in. below the
elevation of the lowest orifice 26 of the printhead, and
the full level is preferably about 0.125 in. above the
elevation of the lowest orifice of the printhead, the
arrangement being such that the level of ink in the
reservoir is not so high as to cause weeping through the
orifices and not so low as to risk interruption of the
ink supply to the printhead. Upon actuation of the reed
switch 128 by a low level condition, a signal is sent to
an electronic printhead controller 130 (Figs: 5 and 6),
contained within the housing 18 of the printhead assembly
14, and after a one minute delay, the controller sends a
signal to turn on the pump 22 and open the feed valve
124, thus allowing pressurized ink supplied from the ink
feed line 120 to flow into the reservoir 92 of the
secondary ink supply 20. The feed valve 124 remains open
until the magnetic float 126 reaches its full position at
which time the reed switch 128 is actuated to send a
signal to the printhead controller 130 to shut off the
pump 22 and close the feed valve 124. The one minute
delay is provided to extend pump life by reducing the
number of on/off cycles due to transient flow. The
secondary ink supply 20 further includes a vent line 125
to prevent over-pressurization of the secondary ink
supply reservoir 92 in case the reservoir is
inadvertently overfilled due to a failure in the
electronics or to a feed valve 124 which does not
properly close.
It will be understood from the foregoing that the
level detector 102 and printhead controller 130
constitute a system for effecting operation of the pump
22 to deliver ink from the primary ink supply 12 to the
secondary ink supply 20 of the printhead assembly 14 in
response to a decrease in the quantity of ink in the
CA 02449615 2003-12-17
12
secondary ink supply 20 thereby automatically to refill
the secondary ink supply.
In accordance with this invention, each printhead
assembly 14 has a purge system, generally indicated at
132 (Fig. 6), associated with it for delivering ink under
pressure from the primary ink supply 12 to the printhead
16 of the assembly thereby to purge air from the
printhead. This system 132 includes a purge line 134
connected at its upstream end 136 to the feed line 120
for the printhead assembly 14 and at its downstream end
138 to the short ink supply line 104, and a normally
closed purge shutoff valve 140 in the housing 18 of the
printhead assembly for controlling the flow of ink
through the purge line. The purge line 134 bypasses the
secondary ink supply 20 to prevent the delivery of ink
under pressure to the secondary ink supply during a purge
cycle. The shutoff valve 140 is similar to the feed
solenoid valve 104 and is movable between a closed
position for blocking flow through the purge line 134 and
an open position permitting flow through the line to
deliver ink to the printhead 16 in a quantity sufficient
to force ink through the printhead to purge air from the
printhead. The purge operation is also effective for
purging the short ink supply line 104 downstream of its
juncture with the purge line 134. Purging of the
printhead 16 is accomplished by pushing a purge manually
operated switch 142 (Fig. 2A) located on the housing l8
of the printhead assembly 14. Actuation of this switch
142 signals the printhead controller 130 to turn on the
pump 22 and to open the purge valve 140, thereby causing
ink to be delivered under pressure to the printhead 16.
The purge switch 142 may be manually operated or it may
be electronically controlled to operate automatically
upon start-up and/or at specified intervals of time, for
example.
CA 02449615 2003-12-17
Both the feed valve 124 and purge valve 140 may be
solenoid operated, in which case the solenoids may be attached
to a solenoid manifold 144 connected to the lower part 60 of
the housing 18 of the printhead assembly 14, as shown in Fig. 7.
The solenoid manifold 144 provides a connection for the ink
lines and electrical wires.
The short ink supply line 104 includes two check
valves, the first 146 located upstream of the purge line 134
and the second 148 located downstream of the purge line (Fig.
6). The upstream check valve 146 is provided to prevent ink
from flowing from the purge line 134 into the reservoir 92 of
the secondary ink supply 20 during a purge cycle.- The down-
stream check valve 148 is provided to prevent back flow of ink
or air from the printhead 16 into the short ink supply line 104.
As noted above, the controller 130 of each printhead
assembly interfaces with the electronic controller 40 of the
ink jet printing system for operation of the pump 22 upon
receiving a low level signal from the level detector 102 of
the secondary ink supply 20. An electrical schematic of the
printhead controller 130 is provided in Fig. 8.~ The printhead
controller controls the purge shutoff valve 140 solenoid upon
actuaticn-of the purge switch 142 and controls the feed valve
124 solenoid upon receiving a low level signal from the level
detector 102 .of the secondary ink supply 20.
In view of the above, it will be seen that the
several objects of the invention are achieved and other
advantageous results attained.
13
CA 02449615 2003-12-17
As various changes could be made in the above
constructions without departing from the scope of the
invention, it is intended that all matter contained in the
above description or shown in the accompanying drawings shall
be interpreted as illustrative and not in a limiting sense.
13a
