Information
-
Patent Grant
-
6547365
-
Patent Number
6,547,365
-
Date Filed
Wednesday, October 31, 200122 years ago
-
Date Issued
Tuesday, April 15, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Pham; Hai
- Stewart, Jr.; Charles W.
-
CPC
-
US Classifications
Field of Search
US
- 347 14
- 347 19
- 347 23
- 347 12
- 347 10
- 347 20
- 347 30
- 347 33
- 347 60
- 347 7
- 347 43
- 358 296
- 400 74
-
International Classifications
-
Abstract
A method and apparatus for printing a print job includes determining which nozzles of a printhead are currently failing, estimating a number of additional printhead nozzles that will fail while printing the print job, calculating a maximum number of failing nozzles that may not be exceeded in order to maintain a specified quality level for the print job, and determining if the number of currently failing printhead nozzles added to the estimated number of additional printhead nozzles that will fail exceeds the calculated maximum number of failing nozzles. The method and apparatus also includes providing a notification in the event that the number of currently failing printhead nozzles added to the estimated number of additional printhead nozzles that will fail exceeds the calculated maximum number of failing nozzles.
Description
FIELD OF THE INVENTION
The present invention relates to printing devices, and, in particular, to a method and apparatus for predicting the end of life of a printhead.
BACKGROUND OF THE INVENTION
Inkjet printing mechanisms may be used in a variety of different printing devices, such as plotters, facsimile machines and inkjet printers, collectively referred to herein as printers. These printing mechanisms typically use a printhead to shoot drops of ink onto a page or sheet of print media. Some inkjet print mechanisms utilize a type of printhead called a cartridge that carries a self contained ink supply back and forth across the media. In the case of a multi-color cartridge, several printheads and reservoirs may be combined into a single unit, which may also be referred to as a printhead.
Other inkjet print mechanisms, known as “off-axis” systems, propel only a small amount of ink in the printhead across the media, and include a main ink supply in a separate 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 reservoir to the printhead. A printhead may also have a cap or capping mechanism such that when the printhead is not printing, the printhead is covered. This may serve to prevent the printhead from drying and/or to otherwise protect the printhead from the environment.
Each printhead 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 ejection system, a barrier layer containing ink channels and vaporization 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 energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor.
To print an image, the printhead is scanned back and forth across above the media in an area known as a print zone, with the printhead shooting drops of ink as it moves. By selectively energizing the resistors as the printhead moves across the media, the ink is expelled in a pattern on the 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 linear array is utilized, the linear arrays may be located side-by-side on the printhead, parallel to one another, and substantially perpendicular to the scanning direction. As such, 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 print zone, a band or swath of ink would appear on the sheet. The height of this band is known as the “swath height” of the printhead, the maximum pattern of ink which can be laid down in a single pass.
The orifice plate of the printhead tends to accumulate contaminants, such as paper dust, and the like, during the printing process. Such contaminants may adhere to the orifice plate for various reasons including the presence of ink on the printhead, or because of electrostatic charges that may build up during operation. In addition, excess dried ink may accumulate around the printhead. The accumulation of ink or other contaminants may impair the quality of the output by interfering with the proper application of ink to the printing medium. Also, if color printheads are used, each printhead may have different nozzles which each expel different colors. If ink accumulates on the orifice plate, a mixing of different colored inks, known as cross-contamination, can result during use. If colors are mixed on the orifice plate, the quality of the resulting printed product can be affected. Furthermore, the nozzles of an ink-jet printer can clog, particularly if the printheads are left uncapped for a period of time. For these reasons, it is desirable to service the printhead by clearing the printhead orifice plate of such contaminants and ink on a routine basis to prevent the build up thereof. This may be accomplished by a service procedure where a printhead expels ink, is brought in contact with a wiper and expels ink again, also called a spit, wipe spit procedure. In some printers this service procedure is performed at the end of a print job based on certain criteria, for example, the number of drops fired since the last spit, wipe, spit procedure, the time a printhead has been uncapped, upon a user request, when power has first been applied to the printer, etc. Service procedures such as the spit, wipe, spit procedure are desirable to maintain print quality but also contribute to increased throughput time because of the time required to perform the procedure. These types of procedures also contribute to a shorter printhead life because the wiping action may degrade the nozzle plate over time by scratching and distorting its surface.
U.S. Pat. No. 5,455,608 describes how a printer may schedule service on a printhead based on the result of a drop detection step. Before starting a plot the printer performs a drop detection on all printheads present to detect if any nozzles are non-firing, also referred to as a “nozzle out” condition. If a nozzle out condition is detected in a printhead, the printer triggers an automatic recovery servicing process for servicing the malfunctioning printhead to clear or otherwise recover the malfunctioning nozzle.
This process includes a sequence of nozzle recovery or clearing procedures of increasing severity. At the end of each procedure a new drop detection test is performed on the printhead, to detect if the printhead is fully recovered. If the drop detection test indicates that a nozzle out condition continues to exist, another servicing procedure is performed. If, after a predetermined number of procedures, the printhead is still not fully recovered (i.e. at least one nozzle is still out) the user is instructed to replace the printhead or to discontinue the current nozzle check. Thus, a “nozzle health” detection is performed before each print job and recovery procedures are performed based on a fixed threshold, in this example, at least one nozzle remaining non-firing.
If the printer is not able to fully recover the failing nozzles or if some nozzles are intermittent, the system may attempt to use error hiding techniques to compensate for these failures. However, there is a maximum number of failing nozzles for which the system will not be able to compensate. If the system is unable to compensate for the failing or intermittent nozzles, the system may run the recovery servicing process at the beginning of each print job, whenever the nozzle health indicates that a servicing process is required, or in response to a user request. This may continue until the printhead has been fully recovered or replaced. This may lead to an unacceptable loss of throughput and a loss of printer productivity because the automatic recovery process is very time consuming, and consumes a large quantity of ink, particularly if a priming function is included in the recovery process. In some instances, before each plot the printer may direct the user to replace the printhead or to discontinue the current nozzle check.
It is possible for a nozzle to fail during printing. If this happens, the maximum number of nozzles out, for which the system is unable to compensate, may be exceeded. This could result in less than desirable overall image quality. The probability of a nozzle failing during a print job is made more likely by certain trends. There is a trend toward wider printing areas, and thus wider plotters, to accommodate wider media. At the present time plotters accommodating sixty inch wide media are commonly available. In addition to larger printing widths, the length of print jobs continues to increase. The number of ink compositions available for use is also proliferating in order to provide the number of colors and quality desired by users. Correspondingly, the number of printheads present in a plotter to deliver these inks is also increasing. As the number of printheads increases, the number of ink reservoirs is also increasing, with a trend toward having one reservoir per printhead for increased ink capacity. An additional trend is an increase in job density, that is, the complexity of plots requested by users.
It would be advantageous to alert a user about the probability of finishing a print job within a given set of quality criteria, preferably before the print job begins. It would also be advantageous to alert a user before starting a job in the event that there is a low probability of meeting the minimum quality requirements for a print job, allowing the user either to ignore the alert, or to take action to correct the problem. In this way, time, media, ink, etc. are less likely to be wasted.
SUMMARY OF THE INVENTION
The invention provides for a method and apparatus for printing a print job including determining which nozzles of a printhead are currently failing, estimating a number of additional printhead nozzles that will fail while printing the print job, calculating a maximum number of failing nozzles that may not be exceeded in order to maintain a specified quality level for the print job, and determining if the number of currently failing printhead nozzles added to the estimated number of additional printhead nozzles that will fail exceeds the calculated maximum number of failing nozzles. The invention also includes providing a notification in the event that the number of currently failing printhead nozzles added to the estimated number of additional printhead nozzles that will fail exceeds the calculated maximum number of failing nozzles.
BRIEF DESCRIPTION OF THE DRAWINGS
The above set forth and other features of the invention are made more apparent in the ensuing Detailed Description of the Invention when read in conjunction with the attached Drawings, wherein:
FIG. 1
is a perspective view of a printer in accordance with the invention in cut-away form.
FIG. 2
is a perspective view of a printhead service station.
FIG. 3
is a diagram of a printhead showing the placement of nozzles on an orifice plate.
FIG. 4
illustrates a drop detection device;
FIG. 5
illustrates schematically a block diagram of the printer;
FIG. 6
shows the probability of finishing a print job using a number of printheads with different life times and for various ink fluxes; and
FIG. 7
shows a flow diagram of the operation of a printer in accordance with the teachings of this invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1
shows an example of a large format inkjet printer
20
, also called a plotter. Plotters are usually used for printing conventional engineering and architectural drawings as well as high quality poster-sized images, and the like, in an industrial, office, home, or other environment.
Inkjet printing mechanisms are commercially available in many different types of products. For instance, some of the commercially available products that may embody the present invention include desk top printers, portable printing units, copiers, cameras, video printers, facsimile machines, etc.
The printer
20
in this example includes a chassis
22
surrounded by an enclosure
24
, forming a printer assembly
26
. The printer assembly
26
may be supported on a desk or tabletop, but is preferably supported by a pair of leg assemblies
28
. The printer
20
also has a controller, illustrated schematically as a processor
30
, that receives instructions from a host device, typically a computing device, for example, a personal computer, a mainframe, etc.
The printer
20
may also include a key pad and display panel
32
, which provides a user interface where the display provides information to a user and the keypad accepts input from the user. A monitor (not shown) coupled to the host device may also be used to display visual information to an operator, such as printer status, service requirements, error conditions, etc.
A conventional print media handling system (not shown) may be used to advance a continuous sheet of print media
34
through a print zone
35
. The print media may be any type of suitable sheet material, such as paper, poster board, fabric, transparencies, mylar, etc. A carriage guide rod
36
is mounted to the chassis
22
to define a scanning axis
38
, with the guide rod
36
slideably supporting a printhead carriage
40
for travel back and forth, reciprocally, across the print zone
35
. A conventional carriage drive motor (not shown) may be used to propel the carriage
40
in response to a control signal received from the controller
30
. To provide carriage position information to controller
30
, a conventional metallic encoder strip (not shown) may be extended along the length of the print zone
35
and over the servicing region
42
. A conventional optical encoder reader may be mounted on the back surface of printhead carriage
40
to read positional information provided by the encoder strip, for example, as described in U.S. Pat. No. 5,276,970, also assigned to Hewlett-Packard Company, the assignee of the present invention. The manner of providing positional feedback information may also be accomplished in a variety of other ways. Upon completion of a print job, the carriage
40
may be used to drag a cutting mechanism across the final trailing portion of the media to sever the printed portion of the media from the remainder of the continuous sheet
34
. Moreover, the printer
20
may also be capable of printing on pre-cut sheets, rather than on continuous sheet media
34
.
In the print zone
35
, the media
34
receives ink from at least one printhead, for example, a black ink printhead
50
and three monochrome color ink printheads
52
,
54
and
56
, as shown in FIG.
2
.
The black ink printhead
50
is illustrated herein as containing a pigment based ink while the color printheads
52
,
54
and
56
are each described as containing a dye based ink of the colors yellow, magenta and cyan, respectively. It should be understood that the color printheads
52
,
54
,
56
may also contain pigment based inks and that other types of inks may be used in the printheads
50
,
52
,
54
,
56
such as paraffin based inks, hybrid inks having both dye and pigment characteristics, and any other type of ink suitable for plotting applications. In a this example the printer
20
uses an “off axis” ink delivery system, having main reservoirs (not shown) for each ink (black, cyan, magenta, yellow) located in an ink supply section
58
. In this off axis system, the printheads
50
,
52
,
54
,
56
may be replenished by ink conveyed through a conventional flexible tubing system (not shown) from the stationary main reservoirs, so only a small ink supply is propelled by the carriage
40
across the print zone
35
which is located “off axis” from the path of printhead travel.
The printheads
50
,
52
,
54
,
56
each have an orifice plate
60
,
62
,
64
,
66
, respectively. As shown in
FIG. 3
, each orifice plate
60
,
62
,
64
,
66
includes a plurality of nozzles
150
. The nozzles
150
of each orifice plate
60
,
62
,
64
,
66
are typically formed in at least one, but typically two linear arrays
152
,
154
along the orifice plate. Each linear array is typically aligned in a longitudinal direction substantially perpendicular to the scanning axis
38
, with the length of each array determining the maximum image swath for a single pass of a printhead.
FIG. 2
shows the carriage
40
positioned with the printheads
50
,
52
,
54
,
56
ready to be serviced by a replaceable printhead cleaner service station
70
, constructed in accordance with the present invention. The service station
70
includes a translationally moveable pallet
72
, which is selectively driven by motor
74
through a rack and pinion gear assembly
75
in a forward direction
76
and in a rearward direction
78
in response to a drive signal received from the controller
30
. The service station
70
includes a number of print head cleaner units corresponding to the number of printheads. In this example, the service station
70
includes four replaceable printhead cleaner units
80
,
82
,
84
,
86
for servicing the respective printheads
50
,
52
,
54
,
56
.
Each printhead cleaner unit
80
,
82
,
84
,
86
also includes a spittoon chamber
108
. The spittoon
108
may be filled with an ink absorber
124
, preferably of a foam material, although any suitable absorbing material may be used. The absorber
124
receives ink spit from the printheads
60
,
62
,
64
,
66
and holds the ink while the volatiles or liquid components evaporate, leaving the solid components of the ink trapped within the chambers of the foam material. In one embodiment, the spittoon
108
of the black printhead cleaner unit
80
is supplied as an empty chamber, which then fills with a tar like black ink residue over the life of the cleaner unit.
Each printhead cleaner unit
80
,
82
,
84
,
86
may include a dual bladed wiper assembly which has two wiper blades
126
and
128
, which are preferably constructed with rounded exterior wiping edges, and an angular interior wiping edge.
The black printhead cleaner unit
80
, used to service black printhead
50
, which may include a pigment based ink, may also include an ink solvent chamber (not shown) which holds an ink solvent. To deliver the solvent from the reservoir to the orifice plate
60
, the black cleaner unit
80
preferably includes a solvent applicator or member
135
, which underlies the reservoir block.
FIG. 4
shows a schematic representation of a printhead and a drop detection device. A printhead
400
, which may include any one of printheads
60
,
62
,
64
,
66
comprises an array of printer nozzles
410
. Preferably, the printhead
400
includes of two rows of printer nozzles
410
, with each row having
524
printer nozzles.
The printhead
400
is configured to spray or eject a single droplet or a sequence of droplets of ink
480
from the nozzle
410
in response to commands issued by the controller
30
. An emitter
464
is mounted in an emitter housing
460
and a detector
454
is mounted in a detector housing
450
. An elongate, substantially straight, rigid member
470
connects the two housings
450
,
460
. The emitter housing
460
, member
470
and detector housing
450
all comprise a substantially rigid assembly
466
configured to actively locate the emitter
464
with respect to the detector
454
.
The printhead
400
, rigid assembly
466
, emitter
464
, and detector
454
are orientated with respect to each other such that a path traced by the ink droplet
480
passes between the emitter
464
and the detector
454
.
A collimator
468
is provided either as part of the emitter
464
or as a separate item so as to collimate radiation emitted by the emitter
464
into a radiation beam which exits the emitter housing
460
via aperture
461
. The collimated radiation beam is admitted into detector housing
450
by way of aperture
451
and impinges on detector
454
. The ink droplet
480
sprayed from nozzle
410
enters the collimated radiation beam and causes a change in the beam impinging on detector
454
.
Various techniques may be employed to detect ink droplets using the drop detection device
466
. These may include, for example, spraying a specific number of ink drops from individual nozzles in turn in specific timing sequences to account for the speed of the drops, accounting for the distance between the nozzle and the radiation beam, determining the time the drop spends in the radiation beam etc.
The ink drop detector may also be a “print on media and scan” type drop detector or nozzle health detector where a pattern is printed on the media and then scanned to determine nozzle functionality.
It is important to note that the ink drop detection device is at least able to determine parameters related to the health of each nozzle. Some examples may include parameters related to whether a nozzle is fully functional or not ejecting ink at all (a “nozzle out” condition).
FIG. 5
shows a block diagram of printer
20
. Printer
20
includes the processor
30
for directing printer operations and front panel
32
including a display
200
and keypad
205
for displaying messages to a user and receiving user inputs, respectively. The printer
20
also includes a carriage motor drive
210
for positioning the carriage
40
, a media drive
215
that operates to position the media
34
, and printhead drive circuitry
220
for controlling the individual nozzles on each printhead
50
,
52
,
54
,
56
. Printer
20
also includes a cleaning device drive
225
for positioning the printhead cleaner service station
70
, and memory
230
for storing programs, including a printer operating system, temporary system operating parameters and temporary data.
The processor
30
executes the programs in memory
230
either automatically, in response to user inputs from front panel
32
, or in response to inputs from the host device. The programs executed by the processor
30
may include routines for checking the status of various printer components at power up, receiving print jobs, displaying information and receiving commands from a user, and performing various maintenance and recovery actions. For example, in the event that the ink drop detection systems detects that a certain nozzle is in a “nozzle out” condition, a program may be executed that causes the nozzle that is out and printhead cleaning device
70
to operate together to clear the condition. An example procedure may include operating the nozzle to expel ink, operating the printhead cleaning device to wipe the nozzle and operating the nozzle to expel ink again, as in the spit, wipe, spit procedure described above.
The printer
20
also includes ink drop detection circuitry
250
to operate and receive information from the ink drop detector
466
. The ink drop detection circuitry
250
may also be configured to store history information about a particular nozzle in memory
230
. This may include an indication of whether or not a nozzle is presently fully functional or is in a “nozzle out” condition, information related to the types of previous failures, the time between failures, the number and type of recovery actions, and any other information regarding the nozzles that may be suitably stored.
The programs executed by the processor
30
preferably include routines for analyzing the quality requirements of incoming print jobs and for calculating the probability that, for each printhead to be utilized, the minimum number of nozzles required to maintain the quality requirements for the job will be available during the print job. In other words, the probability that the maximum number of nozzles out will not be exceeded during the particular print job may be calculated by the processor
30
.
If a printhead experiences a series of nozzle failures, these failures will typically be distributed over a number of nozzles. Nozzle failures are due to various factors, including printhead lot and/or age, printer age, environmental conditions, number of droplets ejected, type of ink, etc. For purposes of this invention, these factors are assumed to contribute randomly to nozzle failure. In addition, nozzle failures have some dependency upon each other. As one example, residue build up on the nozzle plate may affect a number of nozzles at the same time. Therefore, for purposes of the teachings herein, the nozzle failures are assumed to occur randomly and to have some dependence upon one another.
In order to ensure that the probability of reaching the maximum number of nozzles out in an unpredictable way is minimized, the total ink flux for the particular print job can be utilized with a prediction model. Total ink flux may be defined as an average ink volume distributed over an area of media. Ink flux may typically be measured as cc/m
2
(cubic centimeters over square meters). Ink flux is an important factor for determining nozzle failures because the expected mean life of a printhead is typically measured as the total volume of ink in cubic centimeters expelled by the printhead.
FIG. 6
shows example data of the relative probability of finishing a print job with respect to plot length.
FIG. 6
shows generally that the probability of finishing a print job without exceeding the maximum number of nozzles out decreases as the plot length increases. In particular, for an incoming print job having an ink flux of 27 cc/m
2
, line
610
shows the relative probability of finishing the print job when utilizing a printhead with an expected mean life of 1400 cc's. Line
620
shows the relative probability of finishing a print job having the same ink flux when utilizing a printhead with an expected mean life of 700 cc's. Lines
630
and
640
show the relative probability of finishing a print job with an ink flux of 60 cc/m
2
for printheads with expected mean lives of 1400 and 700 cc's respectively. Thus, it can also be seen that generally, the probability of completing a print job decreases as the ink flux increases.
A printhead may be considered as a combination of repairable and non-repairable systems because recovery procedures and masking techniques may “repair” some nozzle problems while some failure mechanisms are incapable of being recovered. The nozzle out process may be modeled assuming that each nozzle out represents a failure of a printhead system.
Table 1 shows example data of the distribution of the number of nozzle outs over time for a particular printhead, including the time of each failure occurrence and the time between subsequent failures, also known as the inter-arrival time.
TABLE 1
|
|
Number of Nozzle Outs
Failure Time (Ti)
Inter-Arrival Time (Xi)
|
|
1
260
260
|
2
400
140
|
3
1250
850
|
. . .
. . .
|
n
2000
|
|
Let Ti represent the arrival time for the i
th
failure and Xi represent the time between (i−1) and the ith failure. An estimate of the rate at which failures are occurring is a useful means of predicting future failures. The inter-arrival times between failures are not considered independent nor identically distributed because the failures themselves may be dependent upon each other and are thought to occur randomly, as mentioned above. Because the failures are dependent upon one another, the inter-arrival times between failures may follow trends based upon the failure dependencies.
To account for this complex relationship, a stochastic point process model, may be utilized. Stochastic processes, also known as random processes, relate to sequences of events constrained by probability. A stochastic point process is a stochastic process that is realized by a series of discrete data instead of a continuous path. One type of stochastic point process that yields a distribution of intervals between changes in data points that are not independent and are not independently distributed is a non-homogeneous Poisson process. Because the inter-arrival times between nozzle failures cannot be considered independent nor identically distributed, a non-homogeneous Poisson process is a suitable process model for the instant application. The following are some of the more important relationships of the distribution.
The rate of failure occurrence may be described as v(t)=λβ
β−1
, where the change in v(t) over an interval (v(t)dt) represents the probability that a failure will occur in the interval (t, t+dt).
If N(t) is used to denote the number of failures that have occurred at t, then the probability that a system, such as a printhead, will experience j failures in the interval (t
1
, t
2
) is given by the Poisson expression:
For the purposes of these teachings it is important to calculate the expected number of failures E during the interval (t
1
, t
2
). This is derived from Equation A above, and represented by:
If, for a given incoming print job, this predicted number of failures plus the number of nozzles out at the beginning of the print job exceeds the maximum number of nozzles out, beyond which image quality cannot be assured, then the user may be notified that the proper image quality cannot be assured.
The parameters λ and β are obtained from nozzle failure data gathered over time by applying Crow maximum likelihood estimators to the interarrival times, assuming that a single system at the time of its m
th
failure may be represented as:
Maximum likelihood estimation is used to find the population that is most likely to produce the observed sample. Crow maximum likelihood estimators are specific types of estimators defined by the equations above.
Because the failure data over time is collected for more than one system, a set of parameters (λ, β) is obtained for each printhead each time there is a nozzle out. These parameters belong to a distribution of mean {overscore (λ)} and standard deviation σ
λ
, and mean {overscore (β)} and standard deviation σ
β
, respectively.
An example analysis begins with the data shown in Table 2 where the maximum number of nozzles out is 4 and three printheads are analyzed.
TABLE 2
|
|
Cc's for given
Printhead
Printhead
Printhead
Standard
|
nozzle out
1
2
3
Mean
Deviation
|
|
|
Nozzle outs = 1
130
150
200
160
36
|
Nozzle outs = 2
450
600
500
517
76
|
Nozzle outs = 3
1500
800
1000
1100
361
|
Nozzle outs = 4
1600
1500
1300
1467
153
|
|
Using the equations above, {circumflex over (λ)} and {circumflex over (β)} are calculated where m=number of nozzles out, in this example 4, T
m
=cc's when the number of nozzles out is 4, and T
i
=cc's when the number of nozzles out is 1. The mean and standard deviation of {circumflex over (λ)} ({overscore (λ)}, σ
λ
) and {circumflex over (β)} ({overscore (β)}, σ
β
) are also calculated.
TABLE 3
|
|
Printhead
Printhead
Printhead
|
1
2
3
{overscore (λ)}, σ
λ
{overscore (β)}, σ
β
|
|
|
{circumflex over (λ)}
1.0407
1.03964
1.2946
(1.12, 0.14)
—
|
{circumflex over (β)}
0.00185
0.001996
0.000372
—
(0.0014, 0.00089)
|
|
When a new printhead is installed in the printer, ideally there are no failures, that is, no nozzle outs, and the expected number of failures is the number of nozzles out at the beginning of the print job. Once the printhead has experienced a nozzle out, the set of parameters (λ,β) may be calculated from the relationship: λ={overscore (λ)}+kσ
λ
and β={overscore (β)}+kσ
β
for the printhead, where K=(cc's for number of nozzles out—mean cc's for number of nozzles out)/standard deviation for number of nozzles out (from Table 2).
As an example, for a new printhead installed in the system described by Tables 2 and 3 above, if the cc's for a first nozzle out is 170, then K=(170−160)/36=0.27.
The parameters (λ,β) may then be determined.
Upon the occurrence of each subsequent nozzle out, the parameters (λ,β) are recalculated in order to update the probability of failure.
At the beginning of each print job, the updated parameters (λ,β) are plugged into Equation B above, where t
1
is the volume of ink expelled by the printhead thus far, and t
2
is t
1
plus the volume of ink for the incoming print job determined from the print job's ink flux. This predicted number of failures from Equation B plus the number of nozzles out at the beginning of the print job are compared to the maximum number of nozzles out, beyond which image quality cannot be assured. If the predicted number of failures plus the number of nozzles out at the beginning of the print job exceed the maximum number of nozzles out, then the operator or user may be alerted that the proper image quality cannot be assured.
A method of utilizing the techniques described above in conjunction with an incoming print job is described with reference to FIG.
7
.
In step
500
, at some time during normal operations, the printer
20
executes a series of procedures to determine if any nozzles are out for a particular printhead. If the printer determines that no nozzles are out, normal printing operations continue as in step
510
. In the event that a nozzle is out, the number of droplets ejected by the nozzle are determined in step
520
. In step
530
, the rate of occurrence of the failure (as shown in Table 2) and the parameters (λ,β) are determined.
Upon receiving a print job, step
540
, the ink flux for each color and the plot length are calculated as shown in step
550
. The number of nozzles that are going to fail during the print job are then estimated utilizing Equation B, the ink flux, and the plot length of the print job (step
560
). In step
570
, the estimated number of nozzles that are going to fail (n
t1
) is added to the actual number of nozzles currently “out” (n
t1
+n
t<t1
) and compared to the maximum number of nozzles out that can be permitted for a given image quality (N). If the maximum number of nozzles out will be exceeded during the plot, the user is alerted as shown in step
580
. The user may optionally permit printing, or may initiate a service routine (step
600
). In the event that the maximum number of nozzles out will not be exceed, the print job is plotted in step
590
.
It can thus be appreciated that while the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of the invention.
Claims
- 1. A method of printing a print job comprising:determining which nozzles of a printhead are currently failing; estimating a number of additional printhead nozzles that will fail while printing said print job; calculating a maximum number of failing nozzles that may not be exceeded in order to maintain a specified quality level for said print job; and determining if said number of currently failing printhead nozzles added to said estimated number of additional printhead nozzles that will fail exceeds said calculated maximum number of failing nozzles.
- 2. The method of claim 1, further comprising providing a notification in the event that said number of currently failing printhead nozzles added to said estimated number of additional printhead nozzles that will fail exceeds said calculated maximum number of failing nozzles.
- 3. The method of claim 1, wherein determining which nozzles of a printhead are currently failing comprises determining the health of the printhead nozzles.
- 4. The method of claim 1, wherein estimating a number of additional printhead nozzles that will fail comprises utilizing a stochastic point process model.
- 5. The method of claim 4, wherein said stochastic point process model comprises a non-homogeneous Poisson process.
- 6. The method of claim 1, wherein estimating a number of additional printhead nozzles that will fail comprises utilizing the ink flux and print length of said print job in combination with a stochastic point process model.
- 7. A printer for printing a print job comprising:an ink drop detector for determining which nozzles of a printhead are currently failing; a processor for estimating a number of additional printhead nozzles that will fail while printing said print job; first circuitry for calculating a maximum number of failing nozzles that may not be exceeded in order to maintain a specified quality level for said print job; and second circuitry for determining if said number of currently failing printhead nozzles added to said estimated number of additional printhead nozzles that will fail exceeds said calculated maximum number of failing nozzles.
- 8. The printer of claim 7, further comprising circuitry for providing a notification in the event that said number of currently failing printhead nozzles added to said estimated number of additional printhead nozzles that will fail exceeds said calculated maximum number of failing nozzles.
- 9. The printer of claim 7, wherein said ink drop detection circuitry determines the health of the printhead nozzles.
- 10. The printer of claim 7, wherein said processor estimates a number of additional printhead nozzles that will fail utilizing a stochastic point process model.
- 11. The printer of claim 10, wherein said stochastic point process model comprises a non-homogeneous Poisson process.
- 12. The printer of claim 7, wherein said processor estimates a number of additional printhead nozzles that will fail utilizing the ink flux and print length of said print job in combination with a stochastic point process model.
- 13. A printer comprising:A printer including a processor that performs the following operations: determining which nozzles of a printhead are currently failing; estimating a number of additional printhead nozzles that will fail while printing said print job; calculating a maximum number of failing nozzles that may not be exceeded in order to maintain a specified quality level for said print job; and determining if said number of currently failing printhead nozzles added to said estimated number of additional printhead nozzles that will fail exceeds said calculated maximum number of failing nozzles.
- 14. The printer of claim 13, wherein said operations further comprise:providing a notification in the event that said number of currently failing printhead nozzles added to said estimated number of additional printhead nozzles that will fail exceeds said calculated maximum number of failing nozzles.
- 15. The printer of claim 13, wherein said operations further comprise:determining which nozzles of a printhead are currently failing comprises determining the health of the printhead nozzles.
- 16. The printer of claim 13, wherein the operation of estimating a number of additional printhead nozzles that will fail comprises utilizing a stochastic point process model.
- 17. The printer of claim 16, wherein said stochastic point process model comprises a non-homogeneous Poisson process.
- 18. The printer of claim 13, wherein the operation of estimating a number of additional printhead nozzles that will fail comprises utilizing the ink flux and print length of said print job in combination with a stochastic point process model.
US Referenced Citations (16)
Foreign Referenced Citations (6)
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EP |
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EP |
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Sep 1998 |
EP |
63221050 |
Sep 1988 |
JP |
63224956 |
Sep 1988 |
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Sep 1992 |
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