Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-01-06
2001-01-16
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06174046
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to ink printers and, more particularly, to the arrangement of contact pads on a print cartridge.
BACKGROUND OF THE INVENTION
Ink-jet printheads operate by ejecting a droplet of ink through a nozzle and onto a recording medium, such as a sheet of paper. When a number of nozzles are arranged in a pattern, such as one or more linear arrays, the properly sequenced ejection of ink from each nozzle causes characters or other images to be printed on the paper as the printhead is moved relative to the paper. The paper is typically shifted each time the printhead has moved across the paper. The printhead is usually part of a disposable print cartridge containing a supply of ink, where the print cartridge is easily installed in and removed from the printer.
In one design of a thermal ink-jet print cartridge, the print cartridge includes: 1) an ink reservoir and ink channels to supply ink proximate to each of the nozzles; 2) a nozzle plate in which the nozzles are formed in a certain pattern; and 3) a substrate attached to a bottom surface of the nozzle plate, where a series of thin film heaters are formed on the substrate, generally one below each nozzle. Each heater includes a thin film resistor and appropriate current leads. To print a single dot of ink, an electrical current from an external power supply is passed through a selected heater. The heater is ohmically heated, in turn superheating a thin layer of the adjacent ink. This results in explosive vaporization of the ink causing a droplet of ink to be ejected through an associated nozzle onto the paper.
One example of this type of print cartridge is shown in
FIG. 1
as print cartridge
10
. Print cartridge
10
generally includes a body
12
which acts as an ink reservoir. Body
12
may have formed on it one or more projections, such as projection
13
, to enable print cartridge
10
to be secured in place within an ink printer. The printhead portion
14
of print cartridge
10
includes a metal nozzle plate
16
(such as a gold-coated nickel plate), which has two parallel arrays of nozzles
17
formed in it using conventional photolithographic techniques. Nozzle plate
16
is attached by an adhesive to an underlying substrate (not shown) which includes heater resistors paired with each of the nozzles
17
.
A flexible insulating tape
18
has formed on it a number of conductors which terminate in contact pads
20
. The other ends of the conductors on tape
18
are connected, using tape automated bonding (TAB), to electrodes on the substrate.
When print cartridge
10
is properly installed in a moveable carriage of an ink-jet printer, pads
20
contact corresponding electrodes on the ink-jet printer which supply the energization signals to the various heater resistors on the substrate. When printing, the carriage scans print cartridge
10
across the width of a sheet of paper, and the paper is incrementally moved perpendicular to the direction of movement of print cartridge
10
.
In
FIG. 1
, some contact pads
20
are located near a middle portion of plastic body
12
. This middle portion of body
12
is prone to sinking during the injection molding process used to form body
12
. Typically, this inherent valley created in the middle portion of body
12
is approximately 7 mils deep. When print cartridge
10
is installed in an ink printer, the contact pads
20
located in this valley do not press on the corresponding ink printer electrodes with as much force as the contact pads
20
located toward the sides of body
12
. Thus, the precise degree of electrical contact between the printer electrodes and the centrally located contact pads
20
is difficult to predict. Additionally, if the sinking in the middle portion of body
12
is sufficient, the centrally located contact pads
20
may not even make electrical contact with the printer electrodes.
In a color printer, four separate print cartridges
10
are typically used and are carried by the same carriage across the sheet of paper. Typically, one of the four cartridges contains black ink, another contains cyan ink, another contains magenta ink, and another contains yellow ink.
FIG. 2
illustrates the pertinent portion of a color ink-jet printer with four print cartridges
24
,
25
,
26
, and
27
secured within a single carriage
30
. Carriage
30
is moved along stationary rod
31
back and forth across the paper sheet
32
in the direction shown by the arrow
34
. A roller
35
shifts the position of paper sheet
32
as needed. In an actual embodiment, at least two spaced rollers are used to cause paper sheet
32
to be flat along where print cartridges
24
-
27
are scanned for printing.
Each of the print cartridges
24
-
27
may have nozzles
17
(
FIG. 1
) arranged so as to print, for example, 300 dots per inch (dpi) on paper sheet
32
along an axis perpendicular to arrow
34
. This means that a nozzle
17
must be placed approximately every 3 mils along nozzle plate
16
in order to achieve 300 dpi.
In color printing, the various colored dots produced by each of the four print cartridges
24
-
27
in
FIG. 2
are selectively overlapped to create crisp images composed of virtually any color of the visible spectrum. To create a single dot on paper sheet
32
having a color which requires a blend of two or more of the colors provided by print cartridges
24
-
27
, the nozzle plates
16
on each of the cartridges
24
-
27
must be precisely aligned so that a dot ejected from a selected nozzle
17
in one cartridge overlaps a dot ejected from a corresponding nozzle
17
in another cartridge. This requires each of the nozzle plates
16
on print cartridges
24
-
27
to be aligned with respect to one another within a few tens of microns after being installed in carriage
30
.
In the prior art, the print cartridge bodies
12
of
FIG. 1
were made identical to one another so that, when multiple print cartridges
10
were installed in carriage
30
, the print cartridge bodies
12
were all aligned with one another in carriage
30
irrespective of any misalignment of the nozzle plates
16
secured to the print cartridge bodies
12
.
To align nozzle plate
16
on print cartridge
10
so that nozzle plates are positioned in ideally the same location on all the various print cartridges, nozzle plate
16
is typically glued in position on print cartridge
10
relative to a molded-in plastic datum formed on the print cartridge body
12
itself. This alignment process has a significant drawback in that the adhesive curing process causes nozzle plate
16
to slightly shift as the adhesive is being cured. In addition, molded-in stresses in plastic cartridge body
12
cause shifting of the plastic body during the thermal curing process. Since this movement is substantially unpredictable, this alignment and gluing process can only produce print cartridges whose nozzle plates were positioned to an accuracy of ±35 microns.
Other, more expensive techniques have been used to achieve higher alignment precision. One of these techniques automatically detects any misalignment of the nozzle plates once the print cartridges have been installed in a carriage and then mechanically adjusts the positions of the print cartridges in the carriage. Using another relatively expensive method, an ink drop detector within the ink printer measures the location of a drop of ejected ink after being ejected from a nozzle, and a software algorithm compensates for any misalignment of the nozzle plates. Both of these techniques significantly increase the cost of the ink printer.
Thus, what is needed is an inexpensive and reliable method and structure for improving the alignment of nozzle plates (or other forms of nozzle members) on print cartridges installed in a carriage and an improved print cartridge contact pad arrangement for improving the reliability of electrical contact between the contact pads and electrodes on a printer.
SUMMARY OF THE INVENTION
The contact pads of a print cartridge are formed on a flexible tape. Each of the uniformly sp
Azmoon Majid
Hamlin Mindy A.
Harris Donald G.
Reid W. Bruce
Wilson Arthur K.
Barlow John
Hewlett--Packard Company
Stephens Juanita
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