Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-03-25
2003-02-11
Hallacher, Craig (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S023000
Reexamination Certificate
active
06517183
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
It is known to produce paper copies, also known as “hard” copies, of files stored on a host device, e.g., a computer using a printer device. The print media onto which files may be printed includes paper and clear acetates for use in lectures, seminars and the like.
Referring to
FIG. 1
herein, there is illustrated a conventional host device
100
in this case a personal computer, linked to a printer device
120
via a cable
110
. Amongst the known methods for printing text and the like onto a print medium such as paper it is known to build up an image on the paper by spraying droplets of ink from a plurality of nozzles.
Referring to
FIG. 2
herein, there is illustrated schematically part of a prior art printer device comprising an array of printer nozzles
220
arranged into parallel rows. The unit comprising the arrangement of printer nozzles is known herein as a printer head. In a conventional printer of the type described herein the printer head
210
is constrained to move in a direction
260
with respect to the print medium
200
e.g. a sheet of A4 paper. In addition, the print medium
200
is also constrained to move in a further direction
250
. Preferably, direction
260
is orthogonal to direction
250
. During a normal print operation, printer head
210
is moved into a first position with respect to the print medium
200
and a plurality of ink droplets are sprayed from a same plurality of printer nozzles
220
contained within printer head
210
. This process is also known as a print operation. After the completion of a print operation the printer head
210
is moved in a direction
260
to a second position and another print operation is performed. In a like manner, the printer head is repeatedly moved in a direction
260
across the print medium
200
and a print operation performed after each such movement of the print head
210
. When the printer head
210
reaches an edge of the print medium
200
, the print medium is moved a short distance in a direction
250
, parallel to a main length of the print medium
200
, and another print operation is performed. The printer head
210
is then moved in a direction
260
back across the print medium
200
and another print operation is performed. In this manner, a complete printed page is produced.
In order to maintain the quality of the printed output of the printer device it is important that each instruction to the printer head to produce an ink drop from a nozzle of the plurality of nozzles does indeed produce such an fin 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 printer head
210
. Drop detection is known to be performed by a drop detection assembly
270
. It is known to locate the drop detection assembly
270
outside of the region used for printing onto said print medium
200
and the drop detection assembly
270
is known to be located substantially close to an edge of said print medium
200
.
Referring to
FIG. 3
herein there is illustrated schematically a conventional drop detection system used in a production printer. An ink droplet
300
is sprayed 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 printer head
220
to fire an ink droplet
300
and attempting to detect the resulting characteristic current pulse
350
which is counted using drop detection device
370
. The steps of firing a droplet and counting that the resulting characteristic current pulse is repeated six times. If four characteristic pulses
350
are counted from the six attempts to spray an ink droplet
300
then, in a conventional system, the printer nozzle
220
is considered to be functioning correctly.
However, because of the need for three separate optical components to produce the collimated light beam in conventional drop protection systems there is a greater possibility for misalignment between the various components. Any misalignment between the LED
320
, collimating lens
330
and photo diode
340
results in the width of the region in which an ink droplet
300
may be detected being reduced. In addition, because prior art drop detection systems require that a plurality of droplets are sprayed and detected individually this results in a comparatively long detection time for a nozzle and waste of ink.
U.S. Pat. No. 5,430,306 (Hewlett Packard) discloses an opto electronic test device for detecting the presence of thermal-inkjet ink drops from a print head. The device includes an illumination-source, a collimating aperture, a lens for focusing a collimated light beam on to a detector which converts varying illumination intensities into a varying output electrical signal. The output signal of the detector is converted to a digital signal by an aialogue-to-digital converter (A/D) and the digitized output is stored as a series of samples in a memory device. Drop detection is effected by triggering an ink droplet to be sprayed from a pen nozzle, and after a delay of approximately 100 &mgr;s, the droplet enters the collimated light beam. Occultation of the light input into the detector by the droplet causes a decrease in the output signal of the detector. The A/D converter samples the output signal of the detector and stores the sequence of digitized measurements in a memory. After a time delay, which is substantially longer than 100 &mgr;s, a second ink drop is triggered to be ejected from the pen nozzle and after a delay the output of the detector is again digitized. These measurements are repeated for a sequence of, typically, 8 ink droplets and an average time-profile of the output of the detector is formed by a micro-processor. A drop signal is determined to be present if, for example, the peak-to-peak voltage of the average signal is greater than a threshold value.
In order to average out noise fluctuations and derive a usable drop signal it is necessary to repeat the steps o
Bruch Xavier
Girones Xavier
Murcia Antoni
Serra Albert
Vega Ramon
Hallacher Craig
Hewlett--Packard Company
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