Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2000-01-07
2002-05-21
Hallacher, Craig A. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S025000
Reexamination Certificate
active
06390618
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to ink-jet hard copy apparatus and, more specifically, to methods and apparatus for drying ink deposited on print media during real-time printing operations.
2. Description of Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the
Hewlett
-
Packard Journal
, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in
Output Hardcopy Devices
, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).
FIG. 1
(PRIOR ART) depicts an ink-jet hard copy apparatus, in this exemplary embodiment a computer peripheral printer,
101
. A housing
103
encloses the electrical and mechanical operating mechanisms of the printer
101
. Operation is administrated by an electronic controller
102
(usually a microprocessor or application specific integrated circuit (“ASIC”) controlled printed circuit board) connected by appropriate cabling to a computer (not shown). It is well known to program and execute imaging, printing, print media handling, control functions and logic with firmware or software instructions for conventional or general purpose microprocessors or with ASIC's. Cut-sheet print media
105
, loaded by the end-user onto an input tray
107
, is fed by a suitable paper-path transport mechanism (not shown, but see
FIG. 2
) to an internal printing station, or “sprint zone,” where graphical images or alphanumeric text is created. A carriage
109
, mounted on a slider
111
, scans the print medium. An encoder
113
is provided for keeping track of the position of the carriage
109
at any given time. A set
115
of individual ink-jet pens, or print cartridges,
117
A-
117
D are releasable mounted in the carriage
109
for easy access (generally, in a full color system, inks for the subtractive primary colors, cyan, yellow, magenta (CYM) and true black (K) are provided). Once a printed page is completed, the print medium is ejected onto an output tray
119
. It is common in the art to refer to the pen scanning direction as the x-axis, the paper feed direction as the y-axis, and the ink drop firing direction as the z-axis.
In essence, the ink-jet printing process involves dot-matrix manipulation of droplets of ink ejected from a pen onto an adjacent print medium (for convenience of explanation, the word “paper” is used hereinafter as generic for all forms of print media regardless of its individual constitution). An ink-jet pen includes a printhead which consists of a number of columns of ink nozzles. A column of nozzles (typically less than one-inch in total height) selectively fires ink droplets to create a predetermined print matrix of dots on the adjacently positioned paper as the pen is scanned across the media. A given nozzle of the printhead is used to address a given vertical print column position, referred to as a picture element, or “pixel,” on the paper. Horizontal positions on the paper are addressed by repeatedly firing a given nozzle as the pen is scanned. Thus, a single sweep scan of the pen can print a swath of dots. The paper is stepped to permit a series of contiguous or overlapping swaths. Dot matrix manipulation is used to form alphanumeric characters, graphical images, and even photographic reproductions from the ink drops. In the state of the art, the fired droplets of ink are measured in picoliters in volume, producing a printed dot of only about {fraction (1/600)}th inch in diameter; high-end commercial printers are know to produce a 1200 DPI (dots per inch) image.
An important factor in printing with wet ink drops is drying time. The printing of high density plots on plain paper suffers two major drawbacks. First, the saturated media is transformed into an unacceptably wavy sheet. “Ink” generally can be dye-based or pigment-based and uses water or another evaporative solvent as a carrier. When an image to be recorded has high density, a large amount of water is applied to and driven into the medium which in turn swells erratically, causing the printed regions to become wavy or wrinkled, a phenomenon generally known as “cockling.” Secondly, adjacent colors tend to run, or “bleed,” into one another. Both phenomena degrade print quality.
Preheating the media and post print zone heating of the media are both known in the prior art. In order to speed ink dot drying time on the paper surface and reduce or eliminate cockle and bleed, the print zone is sometimes heated concurrently with the printing operation. In U.S. Pat. No. 5,287,123 for a PREHEAT ROLLER FOR THERMAL INK-JET PRINTER, MEDIN (common inventor herein) et al. (hereinafter referred to as Medin '123) disclose a heating blower system for evaporating ink carriers from the print medium during real-time ink-jet printing. As illustrated summarily in
FIG. 2
(PRIOR ART), and referring simultaneously to
FIG. 1
, Medin '123 provided a cross-flow fan
201
at the exit side of a print zone subjacent a pen
117
. The cross-flow fan directs an air flow, arrows
203
, at a sheet
205
of print media
105
through the print zone (see “MEDIA DIRECTION” labeled arrows
211
) in order to cause turbulence at the medium surface being printed to thereby accelerate evaporation. An exhaust fan
207
having a duct system
209
exhausts air and ink carrier vapor away from the print zone and out of the printer. While in the Hewlett-Packard™ PaintJet™ printer model XL300 contemporary of the patented Medin device, ink drops ranged from forty to one-hundred twenty picoliters in volume, in the current state of the art drop volume has been reduced to ten picoliters. Thus, the ink droplets are much more susceptible to being affected by a cross-flow fan.
There is a need for improved methods and apparatus for scrubbing print media surface boundary layers and for preventing airstreams in the print zone from affecting ink drop flight between pen and paper, while still decreasing cockle and bleed problems inherent in ink-jet printing by improving ink dot drying time.
SUMMARY OF THE INVENTION
In its basic aspects, the present invention provides an ink-jet hard copy apparatus for printing onto a print media, including: ink-jet mechanisms for selectively printing dots of ink on an adjacently positioned print medium at a print zone of the apparatus; transport mechanisms for advancing the print medium via a print medium path through the print zone; and disposed within the apparatus proximate the print zone, airflow mechanisms for producing a substantially laminar flow of air through the print zone during printing operations.
In another basic aspect, the present invention provides a method for drying ink drops deposited on print medium by an ink-jet writing mechanisms for ejecting the ink drops from a predetermined distance between the writing mechanisms and a printing surface of the print medium at a print zone of a hard copy apparatus. The process includes the steps of: heating sequentially received sheets of the print medium such that the printing surface is higher than ambient atmospheric temperature; and providing a laminar flow of air substantially continuously across the printing surface of the sheet through the print zone.
In another basic aspect, the present invention provides an ink-jet hard copy apparatus, having a sheet media input supply and including: a paper transport for sequentially selecting a sheet of print medium from the input supply and transporting the sheet through a print zone region of the apparatus where drops of ink are deposited on a printing surface of the sheet; at least one ink-jet writing instrument for scanning the print zone substantially p
Medin Todd R.
Wotton Geoff
Hallacher Craig A.
Hewlett--Packard Company
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