Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1999-08-30
2001-12-18
Nguyen, Judy (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06331055
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to inkjet printers, and more particularly to inkjet printers with thermal inkjet printheads.
BACKGROUND OF THE INVENTION
Inkjet printers employ pens having printheads that reciprocate over a media sheet and expel droplets onto the sheet to generate a printed image or pattern. A typical printhead includes a silicon chip substrate having a central ink hole that communicates with an ink filled chamber of the pen when the rear of the substrate is mounted against the pen. An array of firing resistors is positioned on the front of the substrate, within a chamber enclosed peripherally by a barrier layer surrounding the resistors and the ink aperture. An orifice plate connected to the barrier just above the front surface of the substrate encloses the chamber, and defines a firing orifice just above each resistor. Additional description of basic printhead structure may be found in “The Second-Generation Thermal Inkjet Structure” by Ronald Askeland et al. in the Hewlett-Packard Journal, August 1988, pages 28-31; “Development of a High-Resolution Thermal Inkjet Printhead” by William A. Buskirk et al. in the Hewlett-Packard Journal, October 1988, pages 55-61; and “The Third-Generation HP Thermal Inkjet Printhead” by J. Stephen Aden et al. in the Hewlett-Packard Journal, February 1994, pages 41-45, which are hereby incorporated by reference.
For a single color pen, the resistors are arranged in two parallel elongated arrays that each extend nearly the length of the substrate to provide a maximum array length for a given substrate chip size. The resistor arrays flank opposite sides of the ink aperture, which is typically an elongated slot or elongated array of holes. To ensure structural integrity of the substrate, the ink aperture does not extend too close to the substrate edges, or as close to the edges as the endmost several firing resistors. Therefore, several resistors at each end of each array extend beyond the end of the ink supply aperture or slot.
While a reasonably effective configuration, it has been found that the end firing elements, that is, those that include the end resistors, are more susceptible to failure than are the multitude of firing elements that adjoin the length of the ink supply slot. It is believed that small air bubbles come primarily from two sources: those that arise from outgassing of ink components during normal operation, and those left behind after completion of pen assembly. These bubbles tend to aggregate and coalesce into larger bubbles in ends of the ink chamber. This occurs in the portions beyond the ends of the ink supply slots, and in the vicinity of the end resistors. Small bubbles present are normally tolerated because they can usually be “ejected,” with only a single ink droplet being omitted from printed output; the firing element then continues properly following the momentary tolerable failure. However, it is believed that when the small tolerable bubbles are permitted to coalesce, they become large enough to permanently block one or more firing elements, preventing ink from reaching a firing resistor.
Thus, there is a need for an inkjet printhead that provides bubble management for facilitating moving bubbles away from the firing element region and promoting migration and coalescence of small bubbles away from the inkjet apertures.
SUMMARY OF THE INVENTION
Since bubbles tend to grow and expand into less constraining regions, the present invention provides grooves or depressions in a top plate that extend from the bubble collection area near the firing chambers toward the slot region. The present invention overcomes the limitations of the prior art by providing an inkjet printhead with an orifice plate connected to the barrier layer, spaced apart from the substrate second major surface, enclosing the ink manifold, and defining a plurality of orifice apertures, each associated with a respective ink energizing element, such that the orifice plate has a planar plate defining the plurality of orifice apertures and a plurality of grooves. At least two grooves each extend from an ink feed slot region of the inkjet printhead to a bubble collection area adjacent to an end firing chamber located beyond the ink feed slot region. The grooves collect bubbles and guide the bubbles away from critical areas, thus avoiding formation of larger bubbles that may permanently block ink from reaching one or more firing elements.
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Hume Garrard
Miller Michael D.
Hewlett--Packard Company
Nguyen Judy
LandOfFree
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