Technical Field
[0001] The present invention relates to the filed of continuous ink jet printers and, more
particularly, to a device that provides a structurally sound and precision platform
that facilitates mounting of electrical, mechanical, and fluidic ink-jet printhead
components while keeping size and part count to a minimum.
Background Art
[0002] High resolution ink-jet printheads use a droplet emitter, known as a droplet generator,
and a plurality of droplet deflection electrodes, known as a catcher/charge plate,
in precise alignment to create the "ink-jet" technology area of a printhead. A bridge,
structure, chassis, or even the catcher itself is normally used as a rigid link to
hold the droplet generator and catcher/charge plate in precise alignment, as is described
and claimed in U.S. Patent Nos. 5,455,611; 5,475,411; and 5,475,409. As these components
must be critically aligned, the aligned structure is normally designed to be a customer
replaceable service component.
[0003] Printheads for long array continuous ink jet printers include, in addition to these
components, support electronics such as data handling electronics including charge
plate drivers, fluid filters, and connections. These components normally are attached
to a second frame or chassis. The structure which maintains the alignment of the ink
jet components is then attached to this second chassis. The printhead covers are also
attached to this second chassis. The printhead is typically located at the print station
by a combination of features, some associated with the first chassis and some associated
with the second chassis.
[0004] The customer replaceable printheads for short array printers, for example printers
having a print swath of about 1", typically do not include many of these fluid and
electronic support components. Rather, they are attached to a structure or chassis
which is part of a print station which is not customer replaceable. The chassis or
frame of the aligned customer replaceable printhead also attaches to the chassis of
the print station. Covers and locating features for locating the print station/printhead
are attached to this second chassis which is part of the print station.
[0005] The current art, which includes a bridge, locking structure, or chassis to maintain
alignment of the droplet generator and catcher/charge plate, and a second frame or
chassis to hold the electronic and fluid support components, exhibits many undesirable
traits and functional deficiencies. For instance, the "foot-print" (square inch area
around print array that is dedicated to the chassis that holds the droplet generator
and catcher/charge plate together) and surrounding geometry (also known as the base)
is described by dividing the square inch area at the base by the print array length.
The foot-print ratio is 14 on current wide bar products and is considered to be quite
large. A low single digit number is desirable.
[0006] Another problem with the current art is that current continuous ink-jet printheads
require a plethora of discrete electrical, mechanical, and fluidic connections to
be made by the end user. Prior art attempted to address this issue, but still required
connections to be made in several planes. This made printhead construction difficult.
[0007] A third problem with the current art is that mechanical forces that are used to constrain
ink-jet printheads in their working environment can be large. With the mix of locating
features attached to the ink jet alignment chassis and the support component chassis,
movement can and does occur between the drop generator and the catcher/charge plate.
This is a very undesirable because it will degrade printhead life and can cause a
complete printhead failure. Thermal gradients between the droplet generator, catcher/charge
plate, and the ink jet alignment chassis can also cause movement and shorten printhead
life.
[0008] Yet another problem with the existing art is that all continuous ink-jet printheads
require positive pressure purified air around the ink-jet array which improves printhead
life. This can prove difficult to achieve in current art because of the cavernous
areas created by the large foot-print described above. For the shorter array printhead,
the critical ink-jet components are exposed to a dirty environment during handling
and installation since the covers are attached to the print station, not the customer
replaceable printhead.
[0009] The use of a two chassis system is also a problem with the internal "eyelid" of a
printhead. The eyelid functions as a shutter for the ink-jet array and needs to maintain
a precise relationship to other ink-jet components. The eyelid actuation components
have been attached to the support component chassis. The alignment of the eyelid to
the ink jet components has been less than ideal as a result. Current art continuous
ink-jet printheads with two chassis have produced a system having over-constrained
or complex mechanical interfaces. An over-constrained printhead has undesirable internal
movement and can have a complex mechanical interface which will lead to difficult
mating designs.
[0010] Yet another problem with the existing art is that EMI shielding and "skins" are attached
to the support component chassis which also supports the ink-jet alignment chassis.
These shielding covers have been found to distort the support component chassis, which
in turn can distort the ink-jet alignment chassis, resulting in movement between critical
ink-jet components.
[0011] It is seen, therefore, that it would be desirable to have an ink jet printhead chassis
system capable of overcoming the problems associated with the prior art.
Summary of the Invention
[0012] This need is met by the monolithic ink jet printhead chassis that allows ink-jet
printhead mechanical, electrical, and fluidic functions to be precisely and rigidly
tied together.
[0013] In accordance with one aspect of the present invention, the problems with the prior
art are overcome by using a single highly rigid frame or chassis which serves to maintain
the alignment of the ink-jet components and to which all the electronic and fluid
components are attached. The central location of this chassis serves to isolate the
electronic support components from the fluid related components, minimizing the risk
to the electronic components due to a catastrophic failure of an ink jet component.
It further serves to improve the flow of clean air around the critical ink jet components.
[0014] Accordingly, it is an advantage of the present invention that it provides a structurally
sound and precision platform for the ink jet printhead. It is a further advantage
of the present invention that the monolithic ink jet printhead chassis facilitates
mounting of electrical, mechanical, and fluidic printhead components. Finally, it
is an advantage of the present invention that it minimizes part numbers and structure
size.
[0015] Other objects and advantages of the invention will be apparent from the following
description, the accompanying drawing and the appended claims.
Brief Description of the Drawing
[0016] Fig. 1 is an exploded view of a printhead with monolithic printhead chassis, constructed
in accordance with the present invention.
Detailed Description of the Preferred Embodiments
[0017] The novel design of the present invention enhances ink-jet performance, increases
printhead ruggedness, and serves as a precision chassis. Referring to Fig. 1, a structural
beam or monolithic frame 10 has been created that is similar in length to the drop
generator 12 and catcher of assembly 14. This beam 10, which comprises the monolithic
frame, has a fairly large vertical axis, as indicated by z-axis direction arrow 16,
so that the rectangular moment of inertia is large. This beam attaches to the top
of the catcher charge plate assembly 14 and its length along the z axis, perpendicular
to the plane of the catcher, is quite large. One manner by which the catcher-charge
plate assembly can be attached to the frame is described and claimed in commonly assigned,
co-pending patent application Serial No.
(Attorney Docket SDP216PA), totally incorporated herein by reference.
[0018] The long z-axis length of the frame 10 makes the frame very stiff and, therefore,
immune to distortion caused by loads to the top surface. The value of this will be
discussed later. The beam depth along the x axis indicated by arrow 18 is shallow,
yet sufficient as the external loads in this direction are minimal. This allows for
an incredibly small foot print ratio, for example a foot print ratio of only five.
[0019] The accessible, and rigid monolithic printhead frame 10 solves the problem of different
electrical, mechanical, and fluidic connections being in several different planes,
which has heretofore required the end user to make many different connections. As
a result of the large z axis extension of the monolithic frame, the new structure
10 has enough stiffness to allow all of these connections simultaneously. The new
structure has the necessary rigidity as a result of locating all these connection
at the upper surface of the frame, and orienting all these connections so that the
insertion forces are directed down, parallel to the large z axis of the frame. Furthermore,
by locating these connections and the mounting features at the top of the monolithic
frame and locating the mounting features for the charge plate/catcher assembly and
the droplet generator near the bottom of the frame, the risk of the critical alignment
of the drop generator to the charge plate/catcher assembly being altered by a printhead
installation is minimized.
[0020] The force required to mate all the fluid and electrical connections is applied to
the printhead by means of a lift mechanism with engages dovetail grooves on each end
of the monolithic frame. Clearance holes are provided in the cover, so that the lifting
force is applied only to the monolithic frame. The lifting mechanism is part of a
suitable printhead latch mechanism, such as is described and claimed in commonly assigned,
co-pending application Serial No.
(Attorney Docket SDP208PA), totally incorporated herein by reference.
[0021] To dock or mate printheads with other ink-jet hardware, prior art used "tooling balls"
and "vees" that would contact multiple planes, and rectangular shapes that would nest
and couple with multiple planes. This required complex mating structures to be developed.
The monolithic frame structure 10 of the present invention allows the printhead to
be located to a rigid three area (flat) reference plane 24 on the top of the monolithic
frame. This facilitates a simple tripod type mating surface on the printhead docking
station. Pins that pilot into apertures machined into the monolithic frame 10 are
used to help guide the fluid and electrical connection to engage properly. It should
be noted that the printhead cover 26 is not used to locate or hold the printhead in
place, as has been required in the prior art. As mentioned earlier, the cover has
openings to allow the lift mechanism to engage the frame directly, as can be seen
in the exploded view of Fig. 1. Furthermore, the cover has clearance holes so that
contact to the reference plane of the frame, not to the cover, determines the printhead
location. These printhead locating features are also described more fully in commonly
assigned, co-pending application Serial No.
(Attorney Docket SDP208PA).
[0022] The drop generator is mounted to the frame at 42 by means of freeze blocks 28. These
freeze blocks are attached to the drop generator by means of thin wall tubing which
is bonded into dovetail grooves in the top of the drop generator. The freeze blocks
are typically cyanoacrylate bonded to mating surfaces on the monolithic frame. These
freeze blocks and the manner in which they are bonded to the frames are described
and claimed in commonly assigned, co-pending application Serial No.
(Attorney Docket SDP223PA), totally incorporated herein by reference. This structure
has resulted in a printhead which is much more rugged than the prior art. Accelerations
as small as 15g's, for example, could cause permanent deformation to the two chassis
structures of the prior art, producing alignment shifts of precision parts. The monolithic
frame 10 of the present invention can sustain "g" loads as high as, for example, 70g's,
without any associated movement, thereby providing a design which yields extremely
high shock load capacity for the continuous ink-jet printhead.
[0023] With the structure and configuration proposed by the present invention and illustrated
in Fig. 1, the ink-jet components are on one side 24 of the frame 10, and the electronics
and the their required cooling system, including cooling device 30, are on the other
side 20 of the frame 10. This configuration simplifies assembly while allowing for
a smaller printhead size. The centrally located frame also isolates the electronic
components from the ink, In the prior art the electronics could be exposed detrimentally
to ink mist produced during normal operation or to ink from a printhead failure.
[0024] Continuous ink-jet printheads run at high frequencies and emit electrical "noise".
EMI shielding is required to contain this noise that could cause failures in other
sensitive electronic devices. Current art has resolved this dilemma with metal covers
on the printhead. As the prior art did not isolate the electronic components from
the ink jet ones, it was necessary to install these EMI shielding covers after the
printhead was completely aligned, to provide the necessary access for alignment. When
cover pieces were fastened to the printhead chassis, the chassis could be twisted,
causing undesirable movement in critical ink-jet components. Furthermore, the numerous
seams between the cover pieces and the printhead chassis tended to allow excessive
electrical noise leak out of the printhead.
[0025] These problems are resolved by the present invention. The monolithic frame 10 of
the present invention is extremely rigid and resolves the movement issues related
to the prior art. Furthermore, the cover, which is a one piece unit, attaches to the
printhead only at two locations on the top of the frame. It therefore does not induce
any shift of the critical ink jet components. The monolithic frame 10 bisects the
printhead into two sections, an electronics side 20 and an ink jet side 24. This allows
the noise emitting "charge driver board" 22 to be isolated by a wall of metal, i.e.,
the frame 10. The single piece cover 26, eliminating all seams, is attached to the
monolithic frame 10. Flexible EMI shielding gaskets or seals between the frame and
the cover and around the cover ports complete the EMI shielding of the electronics
without affecting the alignment of the ink jet components.
[0026] It is known in the art to be desirable for continuous ink-jet printheads to maintain
purified positive air pressure around the print array. The positive air chamber shape
and size around the print array affects the uniformity of this air flow. The positive
air chamber should closely match the array in length and, if designed effectively,
print head life and performance will be greatly enhanced. The monolithic frame 10
facilitates this by reducing the volumetric area to be pressurized to 99 cubic inches
versus 717 cubic inches on current art. The primary structure of the monolithic frame
is also aligned parallel to the array so that the air flow can be more readily distributed
down the length of the array. The use of a single piece cover 26 eliminates the possibility
of air leaks at any seams so that the supplied air can be more effectively used. This
positive air chamber is described and claimed in commonly assigned, co-pending application
Serial No.
(Attorney Docket SDP222PA), totally incorporated herein by reference.
[0027] Thermal gradients in the printhead structure can cause differential movement in critical
ink-jet printhead hardware. In accordance with the present invention, these thermal
gradients have been greatly reduced. This is accomplished by circulating the printing
fluid that normally flows through the drop generator and catcher/charge plate assembly
also through the monolithic frame 10. In this way, the temperature of the frame 10
tracks that of the drop generator and the catcher due to the flow of the same ink
through each component. This is facilitated by the size and rigidity of the frame
10 which allow it to serve as a fluid manifold. The proximity of the frame 10 to the
print array also helps in reducing the thermal gradients in the printhead. Ideally,
the frame should be made of a material having a similar thermal expansion to that
of the catcher charge plate assembly and of the drop generator. In this way distortions
of the printhead caused by thermal gradients are minimized.
[0028] A shutter device known as an "eyelid" 14 is used for maintenance and as an air flow
control tool. The eyelid registration to other ink-jet printhead components is critical.
In the prior art, the eyelid was located though a sheet metal support component chassis
or with loosely tied linkage. As a result of poor alignment, there have been problems
with leaky eyelid seals. The monolithic frame 10 has built in registration pins 32
and pads that are rigidly coupled to other critical ink-jet components. This facilitates
improved registration and rigidity which improves printhead performance and reliability.
[0029] The invention has been described in detail with particular reference to certain preferred
embodiments thereof, but it will be understood that modifications and variations can
be effected within the spirit and scope of the invention.
1. A printhead alignment apparatus for a continuous ink jet printer having a droplet
generator and a catcher/charge plate assembly, the alignment apparatus comprising:
a single chassis for maintaining alignment of the droplet generator and the catcher/charge
plate assembly; and
attachment means for attaching electronic and fluidic components to the single chassis.
2. A printhead alignment apparatus as claimed in claim 1 wherein the single chassis separates
electronic and fluid related functions of the printhead.
3. A printhead alignment apparatus as claimed in claim 2 wherein connections for the
electronic and fluid related functions are in a plane parallel to a plane of the catcher.
4. A printhead alignment apparatus as claimed in claim 3 wherein printhead mounting features
and connections are separated from mounting features for the catcher and the droplet
generator.
5. A printhead alignment apparatus as claimed in claim 1 wherein the single chassis comprises
means for accurate location of an eyelid mechanism relative to the droplet generator
and the catcher/charge plate assembly.
6. A printhead alignment apparatus as claimed in claim 1 wherein the single chassis comprises
a fluid manifold.
7. A printhead alignment apparatus as claimed in claim 1 wherein the single chassis has
a z-axis length larger than its x-axis depth, with the z-axis length being perpendicular
to a plane of the catcher.
8. A printhead alignment apparatus as claimed in 7 further comprising insertion forces
for making multiple fluidic and electrical connections to the printhead, the insertion
forces being directed parallel to the large z axis.
9. A printhead alignment apparatus as claimed in claim wherein the single chassis further
comprises all printhead installation features to install the printhead at a print
station.