Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-04-25
2004-06-22
Hallacher, Craig (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06752483
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to printer devices, and particularly although not exclusively to a method and apparatus for improving the detection of faulty or clogged nozzles in printer devices.
BACKGROUND TO THE INVENTION
Inkjet printing mechanisms may be used in a variety of different printing devices, such as plotters, facsimile machines or inkjet printers. Such printing devices print images using a colorant, referred to generally herein as “ink.” These inkjet printing mechanisms use inkjet cartridges, often called “pens,” to shoot drops of ink onto a page or sheet of print media. Some inkjet print mechanisms carry an ink cartridge with an entire supply of ink back and forth across the sheet. Other inkjet print mechanisms, known as “off-axis” systems, propel only a small ink supply with the printhead carriage across the printzone, and store the main ink supply in a stationary reservoir, which is located “off-axis” from the path of printhead travel. Typically, a flexible conduit or tubing is used to convey the ink from the off-axis main reservoir to the printhead cartridge. In multi-color cartridges, several printheads and reservoirs are combined into a single unit, with each reservoir/printhead combination for a given color also being referred to herein as a “pen”.
Each pen has a printhead that includes very small nozzles through which the ink drops are fired. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporisation chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energised to heat ink within the vaporisation chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energised resistor.
To print an image, the printhead is scanned back and forth across a printzone above the sheet, with the pen shooting drops of ink as it moves. By selectively energising the resistors as the printhead moves across the sheet, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text). The nozzles are typically arranged in one or more linear arrays. If more than one, the two linear arrays are located side-by-side on the printhead, parallel to one another, and substantially perpendicular to the scanning direction. Thus, the length of the nozzle arrays defines a print swath or band. That is, if all the nozzles of one array were continually fired as the printhead made one complete traverse through the printzone, a band or swath of ink would appear on the sheet. The height of this band is known as the “swath height” of the pen, the maximum pattern of ink which can be laid down in a single pass.
The orifice plate of the printhead, tends to pick up contaminants, such as paper dust, and the like, during the printing process. Such contaminants adhere to the orifice plate either because of the presence of ink on the printhead, or because of electrostatic charges. In addition, excess dried ink can accumulate around the printhead. The accumulation of either ink or other contaminants can impair the quality of the output by interfering with the proper application of ink to the printing medium. In addition, if colour pens are used, each printhead may have different nozzles which each expel different colours. If ink accumulates on the orifice plate, mixing of different coloured inks (cross-contamination) can result during use. If colours are mixed on the orifice plate, the quality of the resulting printed product can be affected. For these reasons, it is desirable to clear the printhead orifice plate of such contaminants and ink on a routine basis to prevent the build up thereof. Furthermore, the nozzles of an ink-jet printer can clog, particularly if the pens are left uncapped in an office environment.
In an off-axis pen, life goal is on the order of 40 times greater than a conventional non off-axis system, e.g. the printhead cartridges available in DesignJet® 750C color printers, produced by Hewlett-Packard Company, of Palo Alto, Calif., the present assignee. Living longer and firing more drops of ink means that there are greater probability that the printer print quality degrade and/or deviate along life. This requires finding better ways to keep functional and stable our printheads during long periods and large volumes of ink fired.
In order to maintain the quality of the printed output of the printer device it is important to improve the certainty that each instruction to the printhead to produce an ink drop from a nozzle of the plurality of nozzles does will produce such an ink drop (i.e. good servicing of the printhead and replacing nozzles out with working nozzles in performing error hiding).
In the present application, the term plot means a printed output of any kind or size produced by a printing device. For instance a plot could be a printed CAD image or a printed graphic image like a photo or a poster or any other kind of printed image reproduction.
In order to maintain the quality of the printed output of the printer device it is important that each instruction to the print head to produce an ink drop from a nozzle of the plurality of nozzles does indeed produce such an ink drop. In conventional printers it is known to attempt to detect an ink drop as it leaves the nozzle during normal operation. In conventional printers this drop detection is used to indicate the end of life the of a print head.
Referring to
FIG. 1
herein there is illustrated schematically a conventional drop detection system used in a production printer. An ink droplet
300
is ejected from a nozzle
220
and the droplet subsequently follows the path
310
. The path
310
traced by the ink droplet
300
is configured to pass between a light emitting diode (LED)
320
and a receiving photo diode
340
. The light emitted by the light emitting diode
320
is collimated by a lens
330
to produce a narrow light beam which is detected by photo diode
340
. In response to the light received, photo diode
340
produces a current which is amplified by amplifier
350
. Conventionally, the supply of current and hence the brightness of the light emitted by LED
320
is configured so as to provide a constant current output from photo diode
340
. For example, a decrease in the output current of photo diode
340
results in an increased current to LED
320
. The resulting increase and brightness of LED
320
produces an increased output current of photo diode
340
.
When an ink droplet
300
, fired from nozzle
220
, passes through the narrow light beam between LED
320
, collimating lens
330
and photo diode
340
the ink droplet
300
partially blocks the light input into photo diode
340
as a result the output current of the photo diode decreases. The decrease in the output current of photo diode
340
is detected and, as described herein before, the input current into LED
320
is increased. However, due to the comparatively slow response time of the purgatory the increase in the input current into LED
320
produces an “over shoot” in the output current of photo diode
340
. Hence, the amplified current reduced by the photo diode
340
in the presence of a ink droplet
300
is to produce a characteristic pulse shape
350
. In a conventional printer, the characteristic current pulse
350
produced by the passage of the ink droplet
300
is detected and counted by a prior art drop detection unit
370
. In a conventional printer, a drop detection process comprises sending a signal to print head
220
to fire an ink droplet
300
and attempting to detect the resulting characteristic current pulse
350
which is counted usin
Bruch Xavier
Girones Xavier
Murcia Antoni
Vega Ramon
Hallacher Craig
Hewlett-Packard Development L.P.
Lippman Peter I.
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