Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-08-16
2001-08-14
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S056000, C165S185000, C219S216000
Reexamination Certificate
active
06273555
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to ink delivery systems, and more particularly to a thermal inkjet printhead which is characterized by more efficient ink drop expulsion, controlled operating temperatures, high frequency operation, and reduced energy requirements. These goals are accomplished through the use of a novel internal design associated with the printhead as discussed in considerable detail below.
Substantial developments have been made in the field of electronic printing technology. A wide variety of highly-efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner. Thermal inkjet systems are especially important in this regard. Printing units using thermal inkjet technology basically involve an apparatus which includes at least one ink reservoir chamber in fluid communication with a substrate (preferably made of silicon [Si] and/or other comparable materials) having a plurality of thin-film heating resistors thereon. The substrate and resistors are maintained within a structure that is conventionally characterized as a “printhead”. Selective activation of the resistors causes thermal excitation of the ink materials stored inside the reservoir chamber and expulsion thereof from the printhead. Representative thermal inkjet systems are discussed in U.S. Pat. Nos. 4,500,895 to Buck et al.; 4,794,409 to Cowger et al.; 4,771,295 to Baker et al.; 5,278,584 to Keefe et al.; and the
Hewlett
-
Packard Journal,
Vol. 39, No. 4 (August 1988), all of which are incorporated herein by reference.
The ink delivery systems described above (and comparable printing units using thermal inkjet technology) typically include an ink containment unit (e.g. a housing, vessel, or tank) having a self-contained supply of ink therein in order to form an ink cartridge. In a standard ink cartridge, the ink containment unit is directly attached to the remaining components of the cartridge to produce an integral and unitary structure wherein the ink supply is considered to be “on-board” as shown in, for example, U.S. Pat. No. 4,771,295 to Baker et al. However, in other cases, the ink containment unit will be provided at a remote location within the printer, with the ink containment unit being operatively connected to and in fluid communication with the printhead using one or more ink transfer conduits. These particular systems are conventionally known as “off-axis” printing units. Representative, non-limiting off-axis ink delivery systems are discussed in co-owned pending U.S. patent application Ser. No. 08/869,446 (filed on Jun. 5, 1997) entitled “AN INK CONTAINMENT SYSTEM INCLUDING A PLURAL-WALLED BAG FORMED OF INNER AND OUTER FILM LAYERS” (Olsen et al.) and co-owned pending U.S. patent application Ser. No. 08/873,612 (filed Jun. 11, 1997) entitled “REGULATOR FOR A FREE-INK INKJET PEN” (Hauck et al.) which are each incorporated herein by reference. The present invention is applicable to both on-board and off-axis systems which will become readily apparent from the discussion provided below.
Regardless of the particular ink delivery system under consideration, an important factor involves the operating efficiency of the printhead with particular reference to the resistor elements that are used to expel ink on-demand during printhead operation. The term “operating efficiency” shall encompass a number of different items including but not limited to internal temperature levels, operational speed, operating frequency (defined below), energy requirements, and the like. The resistor elements used for ink expulsion (which are produced from a number of compositions including but not limited to a mixture comprised of elemental tantalum [Ta] and elemental aluminum [Al], as well as other comparable materials) are discussed in considerable detail in U.S. Pat. Nos. 4,535,343 to Wright et al.; 4,616,408 to Lloyd; and 5,122,812 to Hess et al. which are all incorporated herein by reference. In accordance with their ability to selectively heat the desired ink compositions so that they can be expelled on-demand from the printhead, the resistors will reach very high peak temperatures, with the term “peak temperature” being defined to involve the maximum operating temperature of the resistor which is typically measured at the end of the electrical impulse that is used to “fire” the resistor and before any cooling occurs. For example, in conventional printhead systems (including those associated with the patents mentioned above), typical peak temperatures experienced by the thin-film resistors will be around 300-1250° C., with such temperatures being reached when the resistor is activated/energized and being present when the “firing impulse” is terminated (before any cooling occurs). These high temperature values will at least partially influence the degree to which the resistors are able to cool down between sequential firing impulses (also characterized herein as “ink ejections”.) Typically, the duration between successive firing impulses in a conventional thermal inkjet printhead will be about 20-500 microseconds (&mgr;s), with the duration of each impulse being about 1-8 microseconds (&mgr;s). Thus, only a minimal amount of time is available for the resistors to satisfactorily cool-down, with typical cool-down temperatures being about 60-85° C. as discussed further below.
In accordance with the traditionally high resistor temperatures listed above and the minimal amount of available cool-down time, the overall operating frequency of the resistors in conventional printhead systems is limited. The term “operating frequency” is generally defined herein as the number of times per second that a given resistor is fired (or is able to fire) in a “black-out mode” (e.g. when the resistor is being used at a 100% rate to produce a solid zone of ink on the selected print medium). High operating frequency levels are desirable in a thermal inkjet printing system because they substantially improve printing speed which is usually expressed in pages per minute.
In conventional thermal inkjet systems including but not limited to those discussed in the U.S. patents listed above, (namely, U.S. Pat. Nos. 4,535,343 to Wright et al.; 4,616,408 to Lloyd; and 5,122,812 to Hess which are again incorporated herein by reference), each resistor is separated from the underlying substrate by an electrically-insulating layer of material. This layer (which is classified as a “dielectric” or insulator structure) is normally produced from silicon dioxide (SiO
2
) having a representative, non-limiting thickness of about 3.5 &mgr;m (see U.S. Pat. No. 4,535,343 to Wright et al.) However, the thermal conductivity of this material does not vary in a significant manner during the temperature fluctuations which occur when the resistors thereon are operating. For reference purposes, the term “thermal conductivity” is defined to involve the heat flow across a surface per unit area per unit time, divided by the negative of the rate of change of temperature with distance in a direction perpendicular to the surface. This definition shall be applicable to the present invention and the various uses of “thermal conductivity” recited herein.
In accordance with the definition of thermal conductivity provided above, the higher the thermal conductivity of a material, the better the material is able to allow the passage of heat therethrough and thereby function as a heat transfer medium. The opposite situation exists in connection with materials having a lower thermal conductivity. Compositions with low thermal conductivity values prevent thermal energy (e.g. heat) from readily passing therethrough and are appropriately characterized as thermal insulators. This information is relevant to the present invention which will become readily apparent from the specific data disclosed in the Detailed Description of Preferred Embodiments section. When each of the resistors in a thermal inkjet printhead is activated using an electrical impulse (e.g. “signal”) provi
Barlow John
Hewlett--Packard Company
Mouttet Blaise
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