Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-01-25
2001-06-12
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06244682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to ink-jet printing and, more specifically to a method and apparatus for automated optical determination of optimized energy requirements for firing ink droplets from an ink-jet printhead, producing high quality printing while preserving printhead life.
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 [sic] Devices
, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).
FIG. 1
depicts an ink-jet hard copy apparatus, in this exemplary embodiment, a computer peripheral, color printer,
101
. A housing
103
encloses the electrical and mechanical operating mechanisms of the printer
101
. Operation is administrated by an electronic controller (usually a microprocessor or application specific integrated circuit (“ASIC”) controlled printed circuit board, not shown, but see
FIGS. 1A and 3
) 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 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) to an internal printing station where graphical images or alphanumeric text are created using state of the art color imaging and text rendering techniques. A carriage
109
, mounted on a slider
111
, scans the print medium. An encoder strip and its appurtenant devices
113
are 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 releasably mounted in the carriage
109
for easy access and replacement; generally, in a full color system, inks for the subtractive primary colors, cyan, yellow, magenta (CYM) and true black (K) are provided. Each pen or cartridge has one or more printhead mechanisms (not seen in this perspective) for “jetting” minute droplets of ink to form dots on adjacently positioned print media. Once a printed page is completed, the print medium is ejected onto an output tray
119
.
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). An ink-jet pen
117
x
includes a printhead which consists of a number of columns of ink nozzles. Each column (typically less than one-inch in total height) of nozzles selectively fires ink droplets (typically only several picoliters in liquid volume) from addressed nozzles that are directed 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 across its width. Thus, a single sweep scan of the pen can print a swath of dots. The paper is stepped to permit a series of contiguous swaths. Dot matrix manipulation is used to form alphanumeric characters, graphical images, and even photographic reproductions from the ink drops. Generally, the pen scanning axis is referred to as the x-axis, the paper transport axis is referred to as the y-axis, and the ink drop firing direction is referred to as the z-axis.
Within a thermal ink-jet printhead—in the state of the art having such small dimensions that thin film, integrated circuit fabrication techniques are employed in manufacture—a set of ink drop generators includes individually activated ink heater resistors subjacent the ink firing nozzles. An attribute of printing is the minimum energy required for a given printhead to eject an ink drop, also known as turn-on energy, “TOE.” Due to design manufacturing tolerance variations, TOE can vary significantly for a particular pen design specification. Therefore, a printer must provide ink drop firing pulses to fire a compatible pen having the highest TOE. Use of a pen with a lower TOE requires that pen to dissipate the difference in the energy required and the energy delivered—viz., highest specified TOE—in the form of heat. The greater the variation in TOE, the greater the excessive energy, i.e., heat buildup. The amount of excess heat that a given pen can tolerate is a function of the operating temperature range and the acceptable reliability for the particular application. The relationship of TOE to the ability to dissipate heat is known as a particular pen design “energy budget.” Moreover, as drop generator density increases on the printhead—e.g., from 150 nozzles to 300 nozzles in substantially the same size circuit—the ability to dissipate heat decreases. While most of the energy is carried away by the ejected ink drop, the increase in drop generator density decreases the overall energy budget.
The goal therefore is to control electrical firing pulses such that the printhead is operated at a pulse energy that is approximately at or greater than the turn-on energy of the resistor and within a range that provides the desired print quality while avoiding premature failure of the heater resistors due to variation in TOE becoming great relative to a pen's ability to dissipate heat.
There is a need to measure actual TOE for a given pen-printer combination to calculate an operating energy given an energy budget and to set dynamically a TOE-related operating energy to optimize printing operations. The variation in TOE and printers is thereby adjusted out, increasing the margin for reliability and operating temperature range, and increasing the energy budget.
In the prior art TOE determination is known to be done with thermal sensing, a process referred to as “TTOE.” Referring now to
FIG. 1A
(PRIOR ART), shown is a simplified block diagram of a thermal ink-jet hard copy engine. A controller
11
receives print data
10
input and processes the print data to provide print control information to a printhead driver circuit
13
. A controlled voltage power supply
15
provides to the printhead driver circuit
13
a controlled supply voltage, Vs, whose magnitude is controlled by the controller
11
. The printhead driver circuit
13
, as controlled by the controller
11
, applies driving or energizing voltage pulses of voltage, VP, to a thin film integrated circuit thermal ink jet printhead
19
that includes thin film ink drop firing heater resistors
17
. The voltage pulses VP are typically applied to contact pads that are connected by conductive traces to the heater resistors
17
, and therefore the pulse voltage received by a resistor is typically less than the pulse voltage VP at the printhead contact pads. Since the actual voltage across a heater resistor
17
cannot be readily measured, thermal turn-on energy for a heater resistor as described herein will be with reference to the voltage applied to the contact pads of the printhead cartridge associated with the heater resistor. The resistance associated with a heater resistor
17
will be expressed in terms of pad-to-pad resistance of a heater resistor and its interconnect circuitry (i.e., the resistance between the printhead contact pads associated with a heater resistor). Th
Lundsten Kerry
Walker Steven H
Barlow John
Hallacher Craig A.
Hewlett--Packard Company
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