Field of the Invention
[0001] The present invention relates generally to inkjet printing mechanisms, and more particularly
to a dual-blade wiper system for cleaning inkjet printheads, giving individual wiping
attention to an orifice plate through which ink-ejecting nozzles are formed with a
"little-brother blade," while also wiping the entire printhead, including cheek regions
of the printhead adjacent the orifice plate, using a "big-brother blade."
Background of the Invention
[0002] Inkjet printing mechanisms use cartridges, often called "pens," which eject drops
of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has
a printhead formed with very small nozzles through which the ink drops are fired.
To print an image, the printhead is propelled back and forth across the page, ejecting
drops of ink in a desired pattern as it moves. The particular ink ejection mechanism
within the printhead may take on a variety of different forms known to those skilled
in the art, such as those using piezo-electric or thermal printhead technology. For
instance, two earlier thermal ink ejection mechanisms are shown in U.S. Patent Nos.
5,278,584 and 4,683,481. In a thermal system, a barrier layer containing ink channels
and vaporization chambers is located between a nozzle orifice plate and a substrate
layer. This substrate layer typically contains linear arrays of heater elements, such
as resistors, which are energized to heat ink within the vaporization chambers. Upon
heating, an ink droplet is ejected from a nozzle associated with the energized resistor.
By selectively energizing the resistors as the printhead moves across the page, the
ink is expelled in a pattern on the print media to form a desired image (e.g., picture,
chart or text).
[0003] To clean and protect the printhead, typically a "service station" mechanism is supported
by the printer chassis so the printhead can be moved over the station for maintenance.
For storage, or during non-printing periods, the service stations usually include
a capping system which substantially seals the printhead nozzles from contaminants
and drying. Some caps are also designed to facilitate priming, such as by being connected
to a pumping unit that draws a vacuum on the printhead. During operation, clogs in
the printhead are periodically cleared by firing a number of drops of ink through
each of the nozzles in a process known as "spitting," with the waste ink being collected
in a "spittoon" reservoir portion of the service station. After spitting, uncapping,
or occasionally during printing, most service stations have an elastomeric wiper that
wipes the printhead surface to remove ink residue, as well as any paper dust or other
debris that has collected on the printhead. The wiping action is usually achieved
through relative motion of the printhead and wiper, for instance by moving the printhead
across the wiper, by moving the wiper across the printhead, or by moving both the
printhead and the wiper.
[0004] To improve the clarity and contrast of the printed image, recent research has focused
on improving the ink itself. To provide quicker, more waterfast printing with darker
blacks ad more vivid colors, pigment-based inks have been developed. These pigment-based
inks have a higher solid content than the earlier dye-based inks, which results in
a higher optical density for the new inks. Both types of ink dry quickly, which allows
inkjet printing mechanisms to form high quality images on readily available and economical
plain paper, as well as on recently developed specialty coated papers, transparencies,
fabric and other media.
[0005] As the inkjet industry investigates new printhead designs, the tendency is toward
using permanent or semi-permanent printheads in what is known in the industry as an
"off-axis" printer. In an off-axis system, the printheads carry only a small ink supply
across the printzone, with this supply being replenished through tubing that delivers
ink from an "off-axis" stationary reservoir placed at a remote stationary location
within the printer. Since these permanent or semi-permanent printheads carry only
a small ink supply, they may be physically more narrow than their predecessors, the
replaceable cartridges. Narrower printheads lead to a narrower printing mechanism,
which has a smaller "footprint," so less desktop space is needed to house the printing
mechanism during use. Narrower printheads are usually smaller and lighter, so smaller
carriages, bearings, and drive motors may be used, leading to a more economical printing
unit for consumers.
[0006] There are a variety of advantages associated with these off-axis printing systems,
but the permanent or semi-permanent nature of the printheads requires special considerations
for servicing, particularly when wiping ink residue from the printheads. This wiping
must be accomplished without any appreciable wear that could decrease printhead life,
and without using excessive forces that could otherwise un-seat the pen from the carriage
alignment datums.
[0007] In the past, the printhead wipers have been a single or dual wiper blade made of
an elastomeric material. Typically, the printhead is translated across the wiper in
a direction parallel to the scan axis of the printhead. In one printer, the wipers
were rotated about an axis perpendicular to the printhead scan axis to wipe. Today,
most inkjet pens have nozzles aligned in two linear arrays which run perpendicular
to the scanning axis. Using these earlier wiping methods, first one row of nozzles
was wiped and then the other row of nozzles was wiped. This first generation of wipers
was developed for replaceable cartridges, typically using a single elastomeric blade
which had a rectangular wiping tip, and no draft angle to the side surfaces. The term
"draft" is well known to those in the molding arts, where a part is made with a slight
angle to ease the release of the part from the mold. While these earlier wiping methods
proved satisfactory for the traditional dye based inks, unfortunately, they were unacceptable
for the newer fast drying pigment inks.
[0008] One suitable service station design for pigment-based inks was a rotary device first
sold in the Hewlett-Packard Company's DeskJet® 850C and 855C color inkjet printers,
and later in the DeskJet® 820C and 870C color inkjet printers. This rotary device
mounted the wipers, primers and caps on a motor-operated tumbler. These pens were
wiped using an orthogonal wiping technique, where the wipers ran along the length
of the linear nozzle arrays, wicking ink along the arrays from one nozzle to the next
to serve as a solvent to break down ink residue accumulated on the nozzle plate. This
rotary service station used a dual wiper blade system, with special contours on each
wiper blade tip to facilitate this wicking action and subsequent cleaning of the orifice
plate.
[0009] Two other earlier inkjet printing mechanisms using replaceable cartridges were the
models 690C and 693C DeskJet® inkjet printers sold by the Hewlett-Packard Company
of Palo Alto, California, the present assignee. This system used dye-based color inks
and a pigment-based black ink, which had different servicing needs than the dye-based
color inks. In this earlier imaging system, the wipers had a rigid upright profile,
and were each mounted on a spring-loaded arm to avoid excessive wiping forces which
may otherwise damage the printheads. Both wipers were mounted on the same support
platform for simultaneously wiping the two pens installed in the carriage.
[0010] To maintain the desired ink drop size and trajectory, the area around the printhead
nozzles must be kept reasonably clean. Dried ink and paper fibers often stick to the
nozzle plate and the cheek areas adjacent the nozzle plate, particularly on a wide
tri-color pen, causing print quality defects if not removed. Wiping the nozzle plate
only removes excess ink and other residue accumulated near the nozzle orifices, leaving
the cheek regions unwiped to collect bits of dust, paper fibers and other debris.
This cheek debris was then moved across a printed image by the printhead, smearing
the printed ink and degrading print quality, a problem known as "fiber tracking."
[0011] To address this fiber tracking problem, a translational wiping system, using an orthogonal
wiping stroke, was first sold by the Hewlett-Packard Company as the model 890C DeskJet®
inkjet printer. To wipe the tri-color cartridge printhead, this system mounted a pair
of auxiliary "cheek wipers" (also referred to by the designers as "mud flaps") to
the wiper sled, adjacent a dual blade orifice plate wiper. There was no cheek wiping
provided for the black printhead in this printer, which only used a dual-blade orifice
plate wiper for the black pen. Thus, this system molded a total of six individual
blades onto a stainless spring steel frame to form the wiper/mud flap assembly, two
blades for the color orifice plate, two blades for the mud flaps, and two for the
black orifice plate, all to service only two pens. The multitude of wiper blades made
molding costly, not only in tooling costs, but all of these blades were difficult
to remove as a unit from the mold, even using a one degree (1°) draft on the blades.
Difficulty in removing the blades from the molds lead to a high scrap rate, and thus,
an increased cost for the parts that were successfully made, which in turn, increased
the overall cost of the printer.
Summary of the Invention
[0012] According to one aspect of the present invention, a dual-blade wiping system is provided
for cleaning an inkjet printhead in an inkjet printing mechanism, with the printhead
having an orifice plate that ejects ink therethrough and which is bordered by at least
one cheek region. The dual-blade wiping system has a first wiper blade with a width
wide enough to wipe both the orifice plate and the cheek region. The dual-blade wiping
system also has a second wiper blade with a width wide enough to wipe only the orifice
plate. A moveable platform supports both the first and second wiper blades for movement
between a rest position and a wiping position for cleaning ink residue from the printhead
with the first and second wiper blades through relative movement therebetween.
[0013] According to yet another aspect of the present invention, another wiping system is
provided as including a wide wiper blade with a width wide enough to simultaneously
wipe across both the orifice plate and the cheek region of the printhead. This wiping
system also has a moveable platform that supports the wide wiper blade for movement
between a rest position and a wiping position for cleaning ink residue from the printhead
with the wide wiper blade through relative movement therebetween.
[0014] According to a further aspect of the present invention, a wiping system is provided
for cleaning first and second inkjet printheads in an inkjet printing mechanism. Each
printhead has an orifice plate that ejects ink therethrough and which is bordered
by at least one cheek region. The wiping system includes a first dual-blade wiper
assembly that has a wide wiper blade with a width wide enough to wipe both the orifice
plate and the cheek region of the first printhead, and a narrow wiper blade with a
width wide enough to wipe only the orifice plate of the first printhead. The wiping
system also has a second dual-blade wiper assembly with a wide wiper blade having
a width wide enough to wipe both the orifice plate and the cheek region of the second
printhead, and a narrow wiper blade having a width wide enough to wipe only the orifice
plate of the second printhead. This wiping system also has a moveable platform that
supports the wide and narrow wiper blades of both the first and second wiper assemblies
for movement between a rest position and a wiping position for cleaning ink residue
from the first and second printheads with the respective first and second wiper assemblies
through relative movement therebetween.
[0015] According to a further aspect of the present invention, an inkjet printing mechanism
may be provided with a printhead wiping system as described above.
[0016] An overall goal of the present invention is to provide an inkjet printing mechanism
which prints sharp vivid images over the life of the printhead and the printing mechanism,
particularly when using fast drying pigment or dye-based inks, and preferably when
dispensed from an off-axis system.
[0017] Another goal of the present invention is to provide a wiping system for cleaning
printheads in an inkjet printing mechanism to prolong printhead life.
[0018] Still another goal of the present invention is to provide a printhead wiping system
for cleaning printheads in an inkjet printing mechanism, with the system having fewer
parts that are easier to manufacture than earlier systems, and which thus provides
consumers with a reliable, economical inkjet printing unit.
Brief Description of the Drawings
[0019]
FIG. 1 is a perspective view of one form of an inkjet printing mechanism, here, an
inkjet printer, including a printhead service station having one form of a dual-wiper
wiping system of the present invention for cleaning an inkjet printhead, and more
specifically here, for wiping a black printhead and for wiping a group of color printheads.
FIG. 2 is a side elevational view of the service station of FIG. 1, including a single
printhead dual-wiper assembly for wiping the black printhead, and a multiple printhead
dual-wiper assembly for wiping the group of color printheads.
FIG. 3 is an enlarged, front perspective view of the color wiper assembly of FIG.
2.
FIG. 4 is an enlarged, front perspective view of the black wiper assembly of FIG.
2.
FIG. 5 is an enlarged, rear perspective view of the black wiper assembly of FIG. 2.
FIG. 6 is an enlarged, side elevational view of one form of the dual-wiper assembly
of FIG. 2, showing a preferred wiping tip contour, suitable for wiping the black printhead
and the color printheads.
FIG. 7 is an enlarged, side elevational view the dual-wiper assembly of FIGS. 4-6
shown wiping the black printhead.
FIG. 8 is an enlarged, front elevational view the dual-wiper assembly of FIGS. 4-6
shown wiping the black printhead.
FIG. 9 is an enlarged, front perspective view of a first alternate embodiment of the
color wiper assembly of FIG. 2.
FIG. 10 is an enlarged, front perspective view of a second alternate embodiment of
the color wiper assembly of FIG. 2.
Detailed Description of a Preferred Embodiment
[0020] FIG. 1 illustrates an embodiment of an inkjet printing mechanism, here shown as an
"off-axis" inkjet printer 20, constructed in accordance with the present invention,
which may be used for printing for business reports, correspondence, desktop publishing,
and the like, in an industrial, office, home or other environment. A variety of inkjet
printing mechanisms are commercially available. For instance, some of the printing
mechanisms that may embody the present invention include plotters, portable printing
units, copiers, cameras, video printers, and facsimile machines, to name a few, as
well as various combination devices, such as a combination facsimile/printer. For
convenience the concepts of the present invention are illustrated in the environment
of an inkjet printer 20.
[0021] While it is apparent that the printer components may vary from model to model, the
typical inkjet printer 20 includes a frame or chassis 22 surrounded by a housing,
casing or enclosure 24, typically of a plastic material. Sheets of print media are
fed through a printzone 25 by a media handling system 26. The print media may be any
type of suitable sheet material, such as paper, card-stock, transparencies, photographic
paper, fabric, mylar, and the like, but for convenience, the illustrated embodiment
is described using paper as the print medium. The media handling system 26 has a feed
tray 28 for storing sheets of paper before printing. A series of conventional paper
drive rollers driven by a stepper motor and drive gear assembly (not shown), may be
used to move the print media from the input supply tray 28, through the printzone
25, and after printing, onto a pair of extended output drying wing members 30, shown
in a retracted or rest position in FIG. 1. The wings 30 momentarily hold a newly printed
sheet above any previously printed sheets still drying in an output tray portion 32,
then the wings 30 retract to the sides to drop the newly printed sheet into the output
tray 32. The media handling system 26 may include a series of adjustment mechanisms
for accommodating different sizes of print media, including letter, legal, A-4, envelopes,
etc., such as a sliding length adjustment lever 34, a sliding width adjustment lever
36, and an envelope feed port 38.
[0022] The printer 20 also has a printer controller, illustrated schematically as a microprocessor
40, that receives instructions from a host device, typically a computer, such as a
personal computer (not shown). The printer controller 40 may also operate in response
to user inputs provided through a key pad 42 located on the exterior of the casing
24. A monitor coupled to the computer host may be used to display visual information
to an operator, such as the printer status or a particular program being run on the
host computer. Personal computers, their input devices, such as a keyboard and/or
a mouse device, and monitors are all well known to those skilled in the art.
[0023] A carriage guide rod 44 is supported by the chassis 22 to slideably support an off-axis
inkjet pen carriage system 45 for travel back and forth across the printzone 25 along
a scanning axis 46. The carriage 45 is also propelled along guide rod 44 into a servicing
region, as indicated generally by arrow 48, located within the interior of the housing
24. A conventional carriage drive gear and DC (direct current) motor assembly may
be coupled to drive an endless belt (not shown), which may be secured in a conventional
manner to the carriage 45, with the DC motor operating in response to control signals
received from the controller 40 to incrementally advance the carriage 45 along guide
rod 44 in response to rotation of the DC motor. To provide carriage positional feedback
information to printer controller 40, a conventional encoder strip may extend along
the length of the printzone 25 and over the service station area 48, with a conventional
optical encoder reader being mounted on the back surface of printhead carriage 45
to read positional information provided by the encoder strip. The manner of providing
positional feedback information via an encoder strip reader may be accomplished in
a variety of different ways known to those skilled in the art.
[0024] In the printzone 25, the media sheet 34 receives ink from an inkjet cartridge, such
as a black ink cartridge 50 and three monochrome color ink cartridges 52, 54 and 56,
shown schematically in FIG. 2. The cartridges 50-56 are also often called "pens" by
those in the art. The black ink pen 50 is illustrated herein as containing a pigment-based
ink. While the illustrated color pens 52-56 may contain pigment-based inks, for the
purposes of illustration, color pens 52-56 are described as each containing a dye-based
ink of the colors cyan, magenta and yellow, respectively. It is apparent that other
types of inks may also be used in pens 50-56, such as paraffin-based inks, as well
as hybrid or composite inks having both dye and pigment characteristics.
[0025] The illustrated pens 50-56 each include small reservoirs for storing a supply of
ink in what is known as an "off-axis" ink delivery system, which is in contrast to
a replaceable cartridge system where each pen has a reservoir that carries the entire
ink supply as the printhead reciprocates over the printzone 25 along the scan axis
46. Hence, the replaceable cartridge system may be considered as an "on-axis" system,
whereas systems which store the main ink supply at a stationary location remote from
the printzone scanning axis are called "off-axis" systems. In the illustrated off-axis
printer 20, ink of each color for each printhead is delivered via a conduit or tubing
system 58 from a group of main stationary reservoirs 60, 62, 64 and 66 to the on-board
reservoirs of pens 50, 52, 54 and 56, respectively. The stationary or main reservoirs
60-66 are replaceable ink supplies stored in a receptacle 68 supported by the printer
chassis 22. Each of pens 50, 52, 54 and 56 have printheads 70, 72, 74 and 76, respectively,
which selectively eject ink to form an image on a sheet of media in the printzone
25. The concepts disclosed herein for cleaning the printheads 70-76 apply equally
to the totally replaceable inkjet cartridges, as well as to the illustrated off-axis
semi-permanent or permanent printheads, although the greatest benefits of the illustrated
system may be realized in an off-axis system where extended printhead life is particularly
desirable.
[0026] The printheads 70, 72, 74 and 76 each have an orifice plate with a plurality of nozzles
formed therethrough in a manner well known to those skilled in the art. The nozzles
of each printhead 70-76 are typically formed in at least one, but typically two linear
arrays along the orifice plate. Thus, the term "linear" as used herein may be interpreted
as "nearly linear" or substantially linear, and may include nozzle arrangements slightly
offset from one another, for example, in a zigzag arrangement. Each linear array is
typically aligned in a longitudinal direction perpendicular to the scanning axis 46,
with the length of each array determining the maximum image swath for a single pass
of the printhead. The illustrated printheads 70-76 are thermal inkjet printheads,
although other types of printheads may be used, such as piezoelectric printheads.
The thermal printheads 70-76 typically include a plurality of resistors which are
associated with the nozzles. Upon energizing a selected resistor, a bubble of gas
is formed which ejects a droplet of ink from the nozzle and onto a sheet of paper
in the printzone 25 under the nozzle. The printhead resistors are selectively energized
in response to firing command control signals delivered by a multi-conductor strip
78 from the controller 40 to the printhead carriage 45.
[0027] FIG. 2 illustrates one form of a dual-blade wiping service station 80 constructed
in accordance with the present invention. The service station 80 includes a frame
82 which is supported by the printer chassis 22 in the servicing region 48 within
the printer casing 24. To service the printheads 70-76 of the pens 50-56, the service
station 80 includes a moveable platform supported by the service station frame 82.
Here, the servicing platform is shown as a rotary member supported by bearings or
bushings (not shown) at the service station frame 82 for rotation, as illustrated
by arrow 83, about an axis 84, which in the illustrated embodiment is parallel with
printhead scanning axis 46. The illustrated rotary member comprises a tumbler body
85 which may have a drive gear 86 that is driven by a conventional service station
motor and drive gear assembly (not shown). The tumbler 85 carries a series of servicing
components, such as a capping assembly 88, into position for servicing the printheads
70-76. The capping assembly 88 preferably includes four discrete caps for sealing
each of the printheads 70-76, although only a single capping unit is visible in the
view of FIG. 2. The tumbler 85 may also be mounted to the service station frame 82
for movement in a vertical direction, as indicated by the double-headed arrow in FIG.
2, to facilitate capping. Alternatively, the capping assembly 88 may be mounted to
the tumbler 85 to move upwardly away from tumbler 85 when moved into contact with
the pens 50-56 or the carriage 45, for instance, using the capping strategy first
sold by the present assignee, Hewlett-Packard Company of Palo Alto, California, in
the models 850C and 855C DeskJet® inkjet printers.
[0028] Other servicing components carried by the rotary platform 85 include a black dual-blade
wiper 90 for servicing the black printhead 70, and three color dual-blade wipers 92,
94 and 96 for servicing the respective color printheads 72, 74 and 76, although in
the side view of FIG. 2, the yellow wiper 96 obscures the view of the cyan and magenta
wipers 92, 94. Preferably, each of the wipers, 90-96 is constructed of a flexible,
resilient, non-abrasive, elastomeric material, such as nitrile rubber, or more preferably,
ethylene polypropylene diene monomer (EPDM), or other comparable materials known in
the art. For wipers 90-96, a suitable durometer, that is, the relative hardness of
the elastomer, may be selected from the range of 35-80 on the Shore A scale, or more
preferably within the range of 60-80, or even more preferably at a durometer of 70
+/- 5, which is a standard manufacturing tolerance.
[0029] By placing the black wiper 90 along a different radial location on tumbler 85 than
the radial on which the color wipers 92-96 are located, here, with the black and color
wipers being shown 180° apart for the purposes of illustration, advantageously allows
different wiping schemes to be employed for cleaning the black printhead 70 and for
cleaning the color printheads 72-76. For instance, the color pens 52-56 carrying dye-based
irks may be wiped using a faster wiping speed than required for wiping the black pen
50 which dispenses a black pigment-based ink. In the past, many service stations used
wipers that required both the black and color printheads to be wiped simultaneously,
so compromises had to be made between the optimum wiping speeds for the black pigment-based
ink ad the color dye-based inks. Problems were encountered in the past because the
slower wiping strokes required to clean the black printheads extracted excess ink
from the color printheads. When using a faster wiping stroke for the color pens, without
allowing excess time for the color ink to seep out between the orifice plate and the
wipers, the black wiper would then skip over black ink residue on the black printhead.
These problems are avoided by service station 80, which places the black wiper 90
and the color wipers 92-96 at different locations around the periphery of the tumbler
85, thus allowing wiping to be optimized for both the black printhead 70 and for the
color printheads 72-76.
[0030] As mentioned in the Background section above, the advent of permanent or semi-permanent
inkjet printheads for use in off-axis printers, such as printer 20, particularly those
using different types of ink, such as a pigment-based black ink and dye-based color
inks, has proved challenging for service station designers. New servicing approaches
were required to clean and maintain the pens without unnecessarily shortening the
printhead lifespan. In studying various servicing routines, it was felt that use of
an ink solvent may be the optimum approach to printhead cleaning. In particular, it
would be even more desirable if the ink solvent also served to lubricate the printhead
orifice plates during wiping, which would then avoid unnecessary wear or damage to
the printheads, thereby insuring a long printhead life. To this end, the service station
80 includes a solvent dispensing system 98, mounted along the lower portion of the
service station frame 82 in location where the wipers 90-96 can be coated with the
solvent prior to wiping the printheads 70-76. The solvent dispensing system 98 also
has a wiper cleaner portion to remove ink residue and any remaining solvent from the
wipers after cleaning the printheads in a wiping cycle. The inkjet ink solvent used
in system 98 may be a hygroscopic material, such as polyethylene glycol ("PEG"), Lipponic-ethylene
glycol ("LEG"), diethylene glycol ("DEG"), glycerin or other materials known to those
skilled in the art as having similar properties. These hygroscopic materials are liquid
or gelatinous compounds that will not readily evaporate during extended periods of
time because they have a large molecular size which leads to a extremely low vapor
pressure. For the purposes of illustration, the preferred ink solvent used in system
98 is PEG.
[0031] FIG. 3 shows a first embodiment of a color wiper assembly 100, constructed in accordance
with the present invention, as including a wiper mounting member or platform 102 upon
which the color wipers 92-96 are mounted, and preferably molded to the platform 102
using onsert molding techniques. While it is apparent to those skilled in the art
that the wipers 92-96 may be onsert molded directly onto the tumbler 85, in the preferred
embodiment the mounting platform 102 is used. The mount 102 is constructed of a sheet
of metal, such as a spring steel, and more preferably of a stainless spring steel
which may be bent and formed to provide a removable platform 102 for assembly onto
the tumbler 85.
[0032] The platform 102 may begin as a long strip of stainless spring steel which is first
punched in a flat state to define several features of its final construction, including
a series of holes (not shown) extending through this strip in the region under the
wipers 92-96, which are used as knit holes to onsert mold the wipers 92-96 to the
platform 102. Indeed, a series of mounting platforms 102 may be formed along a single
strip of steel, so that several sets of wipers may be onsert molded in a single step.
Then in one or more finishing operations, each of these individual platforms are severed
from one another and their sides are turned down to form ears 104 at each end, as
well as engagement tabs 105 having slots 106 therethrough. When forming the knit holes,
other mounting holes 108 may also be formed through the platform 102 to serve as assembly
points through which posts extending from the tumbler 85 are received. This manner
of mounting the wiper assembly 100 to the tumbler 85 is similar to that used to mount
the printhead wipers in the commercially available DeskJet® model 890C inkjet printer,
sold by the Hewlett-Packard Company of Palo Alto, California, the present assignee.
[0033] Each of the color wipers 92-96 is a dual-blade structure, having a little brother
wiper or blade 110 extending upwardly from a common base portion 112, constructed
of the same elastomer as the wipers 92-96, and used to strengthen the bond of the
wipers to the platform 102. Each of the little brother wipers 110 is wide enough to
wipe across the orifice plate of the color printheads 72-76. To this end, each of
the little brother wipers 110 has an outboard wiping surface 114 and an opposing inboard
wiping surface 116. Each of the wipers 110 terminates in a wiping tip 118, which has
a angular wiping edge adjacent to the inboard surface 116, and a rounded wiping edge
adjacent the outboard surface 114, as illustrated for the little brother blade 110
of wiper 92 in FIG. 3.
[0034] The other portion of the dual-blade structure of the color wipers 92-96 is a big
brother wiper or blade 120, which also extends upwardly from the base 112. Each of
the big brother wipers 120 has a width which is wide enough to not only wipe the orifice
plate, but to also wipe both cheek regions of the printhead adjacent the orifice plate,
as illustrated in further detail below with respect to FIG. 8. Each of the big brother
wipers 120 has an outboard wiping surface 124, and an opposing inboard wiping surface
126. Each of the big brother blades 120 terminates in a wiping tip 128. The illustrated
wiping tip 128 is angular along an edge adjacent the inboard surface 126, and rounded
or tapered along an edge adjacent to the outboard surface 124, as illustrated with
respect to the big brother blade 120 of wiper 96 in FIG. 3.
[0035] FIGS. 4 and 5 illustrate a black wiper assembly 130 constructed in accordance with
the present invention for wiping the black printhead 70 of pen 50. The black wiper
assembly 130 includes a mounting member or platform 132, which may be constructed
as described above for the color wiper assembly platform 102. Here, the black wiper
platform 132 is constructed with mounting ears 134, a mounting tab 135 having a slot
136 therethrough, and several mounting holes 138 used to secure the black wiper platform
132 to the tumbler 85, preferably in the same manner as described above for securing
the color wiper platform 102 to tumbler 85.
[0036] The black wiper assembly 130 includes a little brother wiper or blade 140 which extends
upwardly from a base portion 142. The base 142 is integrally molded of the same elastomer
as the blade 140, ad used to secure the blade to platform 132 during the onsert molding
process, as described above for the color base 112. The little brother wiper 140 is
wide enough to wipe across the orifice plate of the black printhead 70. The blade
140 includes an outboard wiping surface 144, and an opposing inboard wiping surface
146. The little brother blade 140 terminates in a wiping tip 148, which has an angular
edge adjacent to the inboard surface 146, and a rounded or tapered edge blending into
the outboard surface 144.
[0037] The black wiper assembly 130 is a dual-blade structure, and includes a big brother
wiper or blade 150 which also extends upwardly from base 142, and is formed integral
therewith, to secure the big brother blade 150 to the black wiper platform 132. The
big brother blade 150 is wide enough to wipe across the entire surface of the black
printhead 70, including the orifice plate and both cheek regions along each side of
the orifice plate. The big brother blade 150 includes an outboard wiping surface 154,
and an opposing inboard wiping surface 156. The big brother blade 150 terminates in
a wiping tip 158, which has an angular junction with the inner wiping surface 156,
and a rounded or tapered edge blending into the outer wiping surface 154.
[0038] FIG. 6 shows a side view of the black wiper assembly 130 to better illustrate a preferred
contour for the wiping tips 148, 158 of blades 140, 150. Preferably, the inboard and
outboard surfaces 144, 146 ad 154, 156 of blades 140 and 150 are each molded with
a large draft angle, preferably on the order of 1.5 degrees. This large draft angle
advantageously helps reduce the force the wiper tips 148, 158 apply against the printheads
70-76, since this force is proportional to the cube of the cross sectional blade thickness
T shown in FIG. 6, e.g., F ∝ T
3. Use of a tapered configuration advantageously maintains a secure mount at the base
portions 112, 142 while reducing the wiping force seen by the printheads 70-76. Additionally,
use of this large draft angle aids in filling the molds, as well as removing the wiper
assembly 130 from the wiper molds, so fewer parts are scrapped out, leading to overall
economies in producing the wiper assemblies. Preferably, the color wiper assembly
100 is also constructed with each of the blades 110, 120 of wipers 92-96 having the
same contours as illustrated in FIG. 6 for blades 140 and 150, to achieve these advantages.
[0039] FIG. 7 illustrates the black wiper assembly 130 being carried by tumbler 85 to wipe
printhead 70 of the black pen 50. It is apparent that tumbler 85 may rotate either
in the direction indicated by arrow 83, or in the opposite direction to first present
the little brother blade 140 to the printhead, followed by wiping with the big brother
blade 150. In the preferred wiping scheme, the tumbler 85 rotates in the direction
of arrow 83 to first wipe printhead 70 with the big brother wiper 150.
[0040] FIG. 8 shows a rear elevational view of the preferred wiping process. Here, the printhead
70 is shown as having an orifice plate 160 of a width A, which is roughly the width
of little brother wiper 140, and a pair of cheek regions 162 having substantially
equal widths B ad C, located to each side of the orifice plate 160. The ink-ejecting
nozzles are formed through the orifice plate 160, preferably arranged in two substantially
linear, mutually parallel arrays. The little brother wiper 140 preferably has a width
which is wide enough to sweep across both nozzle arrays in a direction parallel thereto
(sweeping along the length of both arrays simultaneously), with enough extra width
to accommodate for any manufacturing or assembly tolerances typically encountered,
to assure adequate wiping contact with each nozzle of the orifice plate 160. The color
printheads 72-76 have a similar geometry, each having a pair of cheeks flanking the
orifice plate, so the wiping operation of FIG. 8 is also representative of the wiping
process for the color wipers 92-96. During the preferred wiping process in the direction
of arrow 83 (which would point into the drawing sheet in the view of FIG. 8), the
leading edge of the big brother wiping tip 158 is rounded, while the trailing little
brother blade 140 has the angular portion of the wiping tip 148 contacting the printhead
70. When wiping in the opposite direction, the leading edge of the little brother
wiping tip 148 is rounded, while the trailing big brother blade 150 has the angular
portion of the wiping tip 158 contacting the printhead 70.
[0041] As illustrated in FIG. 7, the rounded wiping edge 158 of the leading blade 150 forms
a capillary passageway 164 into which ink is wicked, or extracted through capillary
forces, from the printhead nozzles into the small crevice between the orifice plate
and the rounded leading edge of blade 158. This wicked ink then acts as a solvent
to dissolve ink residue remaining on the orifice plate 160. The angular portion of
the trailing wiper tip 148 is then used to scrape clean the orifice plate, removing
any of this wicked ink and dissolved residue from the orifice plate 160. The big brother
and little brother blades 110, 120 of the color wipers 92-96 may be constructed with
wiping tips 118, 128 to function as described with respect to FIGS. 7 and 8 for the
black wiper assembly 130. It is apparent that other contours may be used for the wiping
tips 118, 128, 148 and 158, such as use of a rectangular wiping tip, or tips having
other contours, but the preferred embodiment for these wiping tips is illustrated
herein.
[0042] FIG. 9 illustrates another embodiment comprising an alternating wiper assembly 100'
which may be substituted for assembly 100 to clean the color printheads 72-76. Here,
the alternating wiper assembly 100' has a platform 102 which may constructed as described
above, and a wiper base 112' which may also be fashioned as described above for base
112. The color wiper assembly 100' has cyan and yellow wipers 92 and 96 as described
above, but a modified wiper assembly 94' for cleaning the magenta printhead 74. Here,
the magenta wiper 94' has the locations of the big brother and little brother wipers
120, 110 reversed from that shown for the magenta wiper 94 of assembly 100 in FIG.
3. Such an alternating color wiper assembly 100' may be particularly advantageous
for use in a wiping system which wipes bi-directionally across the printheads 92-96.
Alternatively, the alternating color wiper assembly 100' may be useful where the magenta
ink in pen 54 has different properties than the cyan and yellow inks in pens 52 and
56.
[0043] FIG. 10 illustrates a third embodiment which may be substituted for assemblies 100
and 100', here shown as a unified blade color wiper assembly 100'', constructed in
accordance with the present invention. The unified blade wiper assembly 100'' includes
a platform 102 which may be constructed as described above, and a wiper base 112''
serving the same functions as discussed above with respect to base 112 in FIG. 3.
Here, the unified blade assembly 100'' has wipers 92'', 94'' and 96'' for wiping the
color printheads 72, 74 and 76, respectively. Each of the wipers 92'', 94'', 96''
includes a little brother wiper or blade 110, for wiping the orifice plates of printheads
72-76. However, rather than having three individual big brother wiper blades 120,
wipers 92'', 94'' and 95'' each share a portion of a unified wiper blade 170, which
has a first portion 172, a second portion 174, and a third portion 176, dedicated
to wiping the orifice plates and cheeks of printheads 72, 74, and 76, respectively.
The unified wiper blade 170 has a outboard surface 124', an inboard surface 126',
and a wiping tip 128', Which may be constructed to have the same contours as described
above for surfaces 124, 126 and tip 128 of the big brother blade 120.
[0044] Use of the unified blade 170 in wiper assembly 100'' may be preferred over the big
brother blades 120 of the color wiper assemblies 100 and 100' because fewer parts
are required to form the unified assembly 100''. That is, use of the unified blade
170, while requiring slightly more in material cost, may prove to be a more economical
design than illustrated for assemblies 100 and 100', because fewer mold cavities need
to be made. The unified assembly 100'' only needs four mold cavities (three for blades
110, and one for blade 170), which results in a more economically manufactured mold.
Additionally, the unified blade 170 may be easier to remove from the mold than the
individual big brother blades 120, yielding lower scrap rates and more acceptable
parts, which then may be produced more economically. Additionally, use of the unified
blade 170 may be helpful in removing any debris or fibers clinging between the pens
50-56, which may otherwise trail down onto the printed image creating fiber tracks,
a problem discussed above in the Background section.
Conclusion
[0045] A variety of advantages are realized using the dual-blade, big brother/little brother
wiping systems 100, 130, 100' and 100'' described herein, and several of these advantages
have been noted above. For example, these dual-blade wiping systems have been found
to reduce the forces exerted on printheads 70-76, in both a normal direction, that
is, directly upright into the surface of the orifice plates, and in a tangential or
wiping direction, using the rotary platform 85 as the wipers are moved in a arc across
printheads 70-76. This reduction in both normal and tangential forces applied to the
pens 50-52 during wiping is important, because excessive forces during wiping could
potentially unseat the pens 50-56 from their alignment datums inside the printhead
carriage 45.
[0046] Another advantage realized using the dual-blade wiping systems 100, 130, 100' and
100'' is that the normal and normal tangential forces experienced by the printheads
70-76 during wiping are reduced. This reduction in force is important, because otherwise
the substrate forming the orifice plates of printheads 70-76 could potentially be
damaged under excessive forces. Additionally, it is important that the wipers do not
scratch the orifice plate, or damage the individual orifice holes, which would then
effect the ink ejection trajectory and ruin print quality. Avoiding orifice plate
damage is of particular concern for printheads constructed using plastic orifice surfaces,
where the nozzles themselves could be easily damaged through a deformation known as
"ruffles," where a portion of the orifice plate adjacent the nozzle is deflected upwardly
so the nozzle orifice no longer resides in a single plane, leading to misdirected
droplet ejection.
[0047] A further advantage noted above, is the use of the big brother wipers 120, 150, 170
to clean not only the orifice plate, but also to clean the cheek regions adjacent
the orifice plates, such as cheek regions 162 in FIG. 8. Cleaning of the cheek regions
then removes any dust, debris or fibers which may be clinging to the cheeks, to avoid
the fiber tracking problem described in the Background section above. This fiber tracking
problem is of particular concern when using long-life printheads, such as those of
pens 50-56 in the illustrated off-axis printer 20.
[0048] Finally, the illustrated dual-blade wiper systems 100, 130, 100' and 100'' are believed
to be easier to manufacture than their predecessor wiper systems described in the
Background above. Ease of molding and manufacture not only leads to lower tooling
costs in initially preparing the molds, but also in a lower scrap rate, as more acceptable
quality parts are produced. Use of the tapered cross sectional configuration of the
blades facilitates the mold filling process, decreases the cooling time and thus the
overall molding cycle time, as well as leaving less elastomer debris in the molds,
so less down-time is required to clean the molds. Basically, by having fewer blades
molded to service each pen 50-56, the parts are easier to mold, further leading to
a lower scrap-out rate, and ultimately to a more economical and reliable inkjet printing
unit 20 for consumers.
1. A wiping system (100; 100'; 100''; 130) for cleaning an inkjet printhead (70, 72,
74, 76) in an inkjet printing mechanism (20), with the printhead having an orifice
plate (160) that ejects ink therethrough and which is bordered by at least one cheek
region (162), comprising:
a first wiper blade (120; 150; 170) having a width wide enough to wipe both the orifice
plate (160) and the cheek region (162);
a second wiper blade (110; 140) having a width wide enough to wipe only the orifice
plate (160); and
a moveable platform (85) that supports both the first and second wiper blades (110,
120; 140, 150; 110, 170) for movement between a rest position and a wiping position
for cleaning ink residue from the printhead (70, 72, 74, 76) with the first and second
wiper blades (110, 120; 140, 150; 110, 170) through relative movement therebetween.
2. A wiping system according to claim 1 wherein the first and second wiper blades (110,
120; 140, 150; 110, 170) are spaced apart to define a interior region therebetween,
with the first and second wiper blades each having opposing inboard and outboard surfaces
(126, 124; 116, 114; 156, 154; 146, 144; 126', 124'), with the inboard surfaces (126;
116; 156; 146; 126') of each blade facing toward the interior region, wherein each
blade terminates in a wiping edge (128, 118; 158, 148) having a rounded surface joining
the outboard surface (124; 114; 154; 144; 124'), and the wiping edge of each blade
terminates angularly with the inboard surface (126; 116; 156; 146; 126').
3. A wiping system according to claims 1 or 2 for cleaning an inkjet printhead having
two cheek regions (162) adjacent opposing sides of the orifice plate (160), wherein
the width of the first wiper blade (120; 150; 170) is wide enough to wipe the orifice
plate (160) and the two cheek regions (162).
4. A wiping system for cleaning an inkjet printhead (70, 72, 74, 76) in an inkjet printing
mechanism (20), with the printhead having an orifice(120; 150; 170) plate (160) that
ejects ink therethrough and which is bordered by at least one cheek region (162),
comprising:
a wide wiper blade (120; 150; 170) having a width wide enough to simultaneously wipe
across both the orifice plate (160) and the cheek region (162); and
a moveable platform (85) that supports the wide wiper blade (120; 150; 170) for movement
between a rest position and a wiping position for cleaning ink residue from the printhead
(120; 150; 170) with the wide wiper blade (120; 150; 170) through relative movement
therebetween.
5. A wiping system according to claim 4, further including a narrow wiper blade (110;
140) having a width wide enough to wipe only the orifice plate (160), with the narrow
wiper blade (110; 140) supported by the platform (85) for movement between a rest
position and a wiping position for cleaning ink residue from the printhead (70, 72,
74, 76) with the narrow wiper blade (110; 140) through relative movement therebetween.
6. A wiping system according to claims 4 or 5 for cleaning another printhead in the inkjet
printing mechanism (20), with said another printhead also having an orifice plate
(160) that ejects ink therethrough and which is bordered by at least one cheek region
(162), wherein the width of the wide wiper blade (170) is wide enough to simultaneously
wipe across the orifice plates and cheek regions of said printhead and said another
printhead.
7. A wiping system (100; 100'; 100'') for cleaning first and second inkjet printheads
(72, 74, 76) in an inkjet printing mechanism (20), with each printhead having an orifice
plate (160) that ejects ink therethrough and which is bordered by at least one cheek
region (162), comprising:
a first dual-blade wiper assembly (92, 94, 96; 92, 94', 96; 92'', 94'', 96'') having
(a) a wide wiper blade (120; 170) having a width wide enough to wipe both the orifice
plate (160) and the cheek region (162) of the first printhead (72, 74, 76), and (b)
a narrow wiper blade (110) having a width wide enough to wipe only the orifice plate
(160) of the first printhead (72, 74, 76);
a second dual-blade wiper assembly (92, 94, 96; 92, 94', 96; 92'', 94'', 96'') having
(a) a wide wiper blade (120; 170) having a width wide enough to wipe both the orifice
plate (160) and the cheek region (162) of the second printhead (72, 74, 76), and (b)
a narrow wiper blade (110) having a width wide enough to wipe only the orifice plate
(160) of the second printhead (72, 74, 76); and
a moveable platform (85) that supports the wide ad narrow wiper blades of both the
first and second wiper assemblies for movement between a rest position and a wiping
position for cleaning ink residue from the first and second printheads with the respective
first and second wiper assemblies through relative movement therebetween.
8. A wiping system (100) according to claim 7 wherein the wide wiper blades (120) of
both the first and second wiper assemblies (92, 94, 96) are arranged side-by-side
in a first line along the moveable platform (85), and the narrow wiper blades (110)
of both the first and second wiper assemblies (92, 94, 96) are arranged side-by-side
in a second line along the moveable platform (85).
9. A wiping system (100') according to claim 7 wherein the wide wiper blade (120) of
the first wiper assembly (92, 94, 96) and the narrow wiper blade (110) of the second
wiper assembly (92, 94, 96) are arranged side-by-side in a first line along the moveable
platform (85), and the narrow wiper blade (110) of the first wiper assembly (92, 94,
96) and the wide wiper blade (120) of the second wiper assembly (92, 94, 96) are arranged
side-by-side in a second line along the moveable platform (85).
10. An inkjet printing mechanism (20), comprising:
an inkjet printhead (70, 72, 74, 76) having an orifice plate (160) that ejects ink
therethrough and which is bordered by at least one cheek region (162);
a carriage (45) that reciprocates the printhead (70, 72, 74, 76) through a printzone
(25) for printing and to a servicing region (48) for printhead servicing; and
a wiping system according to any of claims 1 through 9.