Title: Print control based on print head temperature
Abstract: A method and apparatus for cooling a print head of an ink jet printer before capping includes the steps of determining an ambient temperature, determining a print head temperature, and waiting a predetermined time after receipt of the last print data for the print job, ejecting a predetermined number of ink droplets from nozzles of the print head at a frequency lower than a frequency used for printing, determining a drop in print head temperature caused by ejecting the predetermined number of ink droplets, and repeating the steps of waiting a predetermined time and ejecting a predetermined number of ink droplets until the print head temperature falls below a threshold.
Patent Number: 7,025,432 Issued on 04/11/2006 to Yamada, et al.
| Inventors:
|
Yamada; Akitoshi (Irvine, CA);
Hirabayashi; Hiromitsu (Irvine, CA);
Sukigara; Akihiko (Irvine, CA)
|
| Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
148367 |
| Filed:
|
June 9, 2005 |
| Current U.S. Class: |
347/5; 347/17 |
| Current Intern'l Class: |
B41J 29/38 (20060101) |
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Nguyen; Thinh
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Parent Case Text
This application is a division of application Ser. No. 09/070,920, filed May
4, 1998 now U.S. Pat. No. 6,951,378.
Claims
What is claimed is:
1. A method of controlling a print operation of an ink jet printer, comprising
the steps of:
obtaining a parameter corresponding to a print head temperature when the ink
jet printer is down; and
performing a predetermined process based on the parameter.
2. A method according to claim 1, wherein the parameter is obtained by a calculation,
without using a measured actual temperature.
3. A method according to claim 1, wherein the parameter is obtained directly
from a measured actual temperature.
4. A method according to claim 1, wherein the predetermined process occurs in
a next print job performed by the ink jet printer.
5. A method according to claim 1, wherein the predetermined process occurs at
a next power-on for the ink jet printer.
6. A method according to claim 1, wherein the predetermined process occurs at
an end of a current print job.
7. A method according to claim 1, wherein the predetermined process is determined
based on whether a print head is capped or not.
8. A method according to claim 1, wherein the predetermined process comprises
changing a number of ink droplets ejected before a print job.
9. A method according to claim 1, wherein the predetermined process comprises
purging ink from the print head.
10. An apparatus for controlling a print operation of an ink jet printer, comprising:
a memory including a region for storing executable process steps;
a processor for executing the executable process steps; and
an interface between the processor and a print head of the ink jet printer that
allows the processor to control firing of nozzles of the print head,
wherein the executable process steps include steps of: (a) obtaining a parameter
corresponding to a print head temperature when the ink jet printer is down; and
(b) performing a predetermined process based on the parameter.
11. An apparatus according to claim 10, wherein the parameter is obtained by
a calculation, without using a measured actual temperature.
12. An apparatus according to claim 10, wherein the parameter is obtained directly
from a measured actual temperature.
13. An apparatus according to claim 10, wherein the predetermined process occurs
in a next print job performed by the ink jet printer.
14. An apparatus according to claim 10, wherein the predetermined process occurs
at a next power-on for the ink jet printer.
15. An apparatus according to claim 10, wherein the predetermined process occurs
at an end of a current print job.
16. An apparatus according to claim 10, wherein the predetermined process is
determined based on whether the print head is capped or not.
17. An apparatus according to claim 10, wherein the predetermined process comprises
changing a number of ink droplets ejected before a print job.
18. An apparatus according to claim 10, wherein the predetermined process comprises
purging ink from the print head.
19. Computer-executable process steps stored on a computer-readable medium, the
computer executable process steps to control a print operation of an ink jet printer,
the computer-executable process steps comprising:
code to obtain a parameter corresponding to a print head temperature when the
ink jet printer is down; and
code to perform a predetermined process based on the parameter.
20. Computer-executable process steps according to claim 19, wherein the parameter
is obtained by a calculation, without using a measured actual temperature.
21. Computer-executable process steps according to claim 19, wherein the parameter
is obtained directly from a measured actual temperature.
22. Computer-executable process steps according to claim 19, wherein the predetermined
process occurs in a next print job performed by the ink jet printer.
23. Computer-executable process steps according to claim 19, wherein the predetermined
process occurs at a next power-on for the ink jet printer.
24. Computer-executable process steps according to claim 19, wherein the predetermined
process occurs at an end of a current print job.
25. Computer-executable process steps according to claim 19, wherein the predetermined
process is determined based on whether a print head is capped or not.
26. Computer-executable process steps according to claim 19, wherein the predetermined
process comprises changing a number of ink droplets ejected before a print job.
27. Computer-executable process steps according to claim 19, wherein the predetermined
process comprises purging ink from the print head.
28. A computer-readable medium which stores computer-executable process steps,
the computer-executable process steps to control a print operation of an ink jet
printer, the computer-executable process steps comprising:
an obtaining step to obtain a parameter corresponding to a print head temperature
when the ink jet printer is down; and
a performing step to perform a predetermined process based on the parameter.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to controlling a print operation for an ink jet
printer based on print head temperature. In particular, the invention pertains
to controlling the print operation so as to cool an ink jet print head before capping.
2. Description of the Related Art
Conventional ink jet printers utilize a print head with a plurality
of nozzles that are supplied with ink by internal ink supply tubes. The ink from
the ink supply tubes forms a meniscus in each nozzle. A heating element is disposed
behind each nozzle, and ink is ejected from a nozzle by firing the corresponding
heating element. The firing of the heating element boils the ink, thereby forming
a bubble of ink that is ejected from the nozzle, resulting in a dot, or pixel,
on a recording medium. Thus, by controlling the firing of the heating elements,
an image is formed on the recording medium.
Typically, at the conclusion of a print job or upon power-off, conventional
ink jet printers move their print head (or heads) to a home position where it waits
for the next print job and/or power-on. At the home position, the print head is
cleaned and capped so as to protect the sensitive print head and to keep ink from
drying on the outside of the print head. The capping mechanism also protects the
print head from damage when servicing the printer. In addition, the capping mechanism
typically includes a device for sucking ink from the print head to help keep the
print head clean.
These conventional systems suffer from a problem in that the print head is
often very hot when the print head is capped, resulting in hot ink being confined
by the cap in the nozzles and in the ink supply tubes of the print head. In some
instances, this hot ink dries out or does not form a proper meniscus in each of
the nozzles of the print head due to a change in viscosity. As a result, the confined
hot ink can form unwanted deposits in and on outer portions of the nozzles (i.e.,
beyond where the meniscus should form) and on the print head, and these ink deposits
can then thicken or dry. The thickened or dried ink deposits can interfere with
proper operation of the print head, resulting in poor print quality. Accordingly,
it is desirable to cap the print head after the ink and the print head have cooled.
SUMMARY OF THE INVENTION
The present invention addresses the foregoing problem, following a print job,
by repeatedly ejecting a predetermined number of ink droplets from nozzles of the
print head at a frequency lower than a frequency used for printing, with a pause
between each repetition, until a predetermined threshold is reached. Because the
ink is ejected intermittently and at a frequency lower than that used for printing,
the heating elements that are used to eject the ink through the nozzles do not
generate sufficient heat to heat up ink in the print head. Thus, hot ink in the
nozzles is ejected, and cool ink from the ink supply tubes is moved forward into
the nozzles, thereby cooling both the ink and the print head itself.
Accordingly, in one aspect the invention is a method of controlling
a print operation of an ink jet printer. The method includes the steps of determining
a print head temperature and controlling a capping sequence based on the determined
print head temperature. In the preferred embodiment, the determining step is repeated.
Alternatively, the determining step is performed once before the controlling step.
In another aspect, the method of controlling a print operation of an ink jet
printer
includes the steps of cooling a print head using a predetermined method and capping
the print head after the print head is cooled. In the preferred embodiment, the
cooling step is performed by ejecting ink droplets, and the ink droplets are ejected
at a frequency lower than a frequency used for printing.
In yet another aspect, the method of controlling a print operation of an ink
jet
printer includes the steps of printing an image using a print head and cooling
the print head after the end of the printing operation using a predetermined method.
Preferably, the cooling step is performed by ejecting ink droplets, with the ink
droplets ejected at a frequency lower than a frequency used for printing.
In yet another aspect, the method of controlling a print operation of an ink
jet
printer includes the steps of obtaining a parameter corresponding to a print head
temperature when the ink jet printer is down and performing a predetermined process
based on the parameter. In the preferred embodiment, the parameter is obtained
by a calculation, without using a measured actual temperature. Alternatively, the
parameter is obtained directly from a measured actual temperature. The predetermined
process occurs in a next print job performed by the ink jet printer, at a next
power-on for the ink jet printer, or at an end of a current print job. The predetermined
process can be determined based on whether a print head is capped or not. The predetermined
process can include purging ink from the print head. In addition, the predetermined
process can include changing a number of ink droplets ejected before a print job.
In yet another aspect, the invention is a method of cooling a print head of an
ink jet printer before capping. The method includes the steps of determining an
ambient temperature, determining a print head temperature, and waiting a predetermined
time after receipt of the last print data for the print job. The method also includes
the steps of ejecting a predetermined number of ink droplets from nozzles of the
print head at a frequency lower than a frequency used for printing, determining
a drop in print head temperature caused by ejecting the predetermined number of
ink droplets, and repeating the steps of waiting a predetermined time and ejecting
a predetermined number of ink droplets until the print head temperature falls below
a threshold.
In the preferred embodiment, the ambient temperature is determined by using a
diode disposed in the ink jet printer. In addition, the print head temperature
after receipt of the last print data for the print job is determined by using a
calculation based on a number of ink droplets ejected from the print head during
the print job. Also in the preferred embodiment, the drop in print head temperature
caused by ejecting the predetermined number of ink droplets is determined by using
a calculation based on the predetermined number of ink droplets ejected and the
frequency that the ink droplets are ejected from the print head. Furthermore, the
predetermined time for waiting after receipt of the last print data for the print
job is between nine and twelve seconds, and the predetermined number of ink droplets
ejected from nozzles of the print head is thirty per nozzle. The frequency that
the predetermined number of droplets are ejected from the print head preferably
is approximately two kilohertz, and the frequency used for printing preferably
is at least five kilohertz.
In an alternative embodiment, the print head temperature after receipt of the
last print data for the print job is determined by using a diode disposed on the
print head. In addition, the drop in print head temperature caused by ejecting
the predetermined number of ink droplets is determined by using the diode disposed
on the print head.
In another aspect, the invention is a method of cooling a print head of an ink
jet printer. The method comprises the step of intermittently ejecting a predetermined
number of ink droplets from nozzles of the print head at a frequency lower than
a frequency used for printing.
Advantageously, the foregoing methods provide for efficient cooling
of a print head after a print job.
This brief summary has been provided so that the nature of the invention may
be understood quickly. A more complete understanding of the invention can be obtained
by reference to the following detailed description of the preferred embodiments
thereof in connection with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a perspective view of computing equipment used in connection with
the invention.
FIG. 2 is a front, cut-away perspective view of the printer shown in FIG. 1.
FIG. 3 is a block diagram showing the hardware configuration of a host processor
interfaced to a printer that can utilize the invention.
FIG. 4 is a perspective view of a printer cartridge with a print head that can
utilize the invention.
FIG. 5 is a schematic view of a print head of the type used with the printer
cartridge of FIG. 4.
FIG. 6 is a graph of an example of cooling a print head according to the invention.
FIG. 7 is a flowchart for explaining cooling of a print head according to the invention.
FIG. 8 is a flowchart for explaining excessive recovery for a print head in
a case that a method according to the invention for cooling the print head is interrupted.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a view showing an outward appearance of computing equipment used in
connection with the invention described herein. Computing equipment
1 includes
host processor
2. Host processor
2 comprises a personal computer,
preferably an IBM PC-compatible computer having a windowing environment, such as
Microsoft® Windows95. Provided with computing equipment
1 are display
screen
3 comprising a color monitor or the like, keyboard
4 for entering
text data and user commands, and pointing device
5. Pointing device
5
preferably comprises a mouse for pointing to and for manipulating objects displayed
on display screen
3.
Computing equipment
1 includes floppy disk interface
6 and
a computer-readable memory medium, such as fixed disk
7. Floppy disk interface
6 provides a means whereby computing equipment
1 can access information,
such as data files, application programs, etc., stored on floppy disks. A similar
CD-ROM interface (not shown) may be provided with computing equipment
1
through which computing equipment
1 can access information stored on a CD-ROM.
Fixed disk
7 stores, among other things, application programs by which
host processor
2 generates files, manipulates and stores those files on
fixed disk
7, presents data in those files to an operator via display screen
3, and prints data in those files via printer
10. Fixed disk
7
also stores an operating system which, as noted above, is preferably a windowing
operating system. Device drivers are also stored on fixed disk
7. At least
one of the device drivers comprises a printer driver which provides a software
interface to firmware in printer
10.
In preferred embodiments of the invention, printer
10 is a multi-head
serial
printer. Accordingly, although the invention described herein is not limited to
use with such a printer, the invention will be described in the context of such
a printer.
In this regard, FIG. 2 is a front, cut-away perspective view of printer
10.
As shown in FIG. 2, printer
10 is a dual-cartridge printer which prints
images using two print heads (i.e., one head per printer cartridge). Each print
head has multiple ink jet nozzles which are used to print data upon a recording medium.
In more detail, printer cartridges
11a and lib each contain a print
head and are held in receptacles
12a and
12b, respectively.
Receptacles
12a and
12b in turn are parts of carriage
13. Carriage
13 is pulled laterally along bar
16 by belt
17,
which is driven by a carriage motor (not shown). As carriage
13 moves, heating
elements for the ink jet nozzles of the print heads are fired, thereby ejecting
ink droplets in accordance with print data. Carriage
13 can move both left
to right and right to left, providing for bi-directional printing as needed.
After print jobs, and in response to commands from host processor
2
or commands from internal printer control logic, carriage
13 moves to home
position
20 in printer
10. Disposed at home position
20 so
as to clean the print heads are ink suction devices
21a and
21b,
wiper assemblies
22a and
22b, and ink ejection receptacles
23a and
23b.
Ink suction devices
21a and
21b preferably comprise
a rotary pump and print head connection caps. The print head connection caps connect
to the print heads of printer cartridges
11a and
11b during
print head cleaning and at other times, such as when printer
10 is powered
off, so as to protect the print heads.
Wiper assemblies
22a and
22b are used to wipe access
ink from the print heads. Ink ejection receptacles
23a and
23b
preferably receive ink purged from the print heads at various times so as to
clear the ink jet nozzles. One situation when ink is purged from the print heads
is discussed below.
FIG. 3 is a block diagram showing the hardware configuration of host processor
2 interfaced to printer
10 that can utilize the invention. In FIG.
3, host processor
2 includes a central processing unit
30 such as
a programmable microprocessor interfaced to computer bus
31. Also coupled
to computer bus
31 are display interface
32 for interfacing to display
3, printer interface
34 for interfacing to printer
10 through
bi-directional communication line
36, floppy disk interface
6 for
interfacing to floppy disk
37, keyboard interface
39 for interfacing
to keyboard
4, and pointing device interface
40 for interfacing to
pointing device
5. As explained in more detail below, additionally coupled
to computer bus
31 are fixed disk
7, random access main memory (hereinafter
"RAM")
41, and read only memory (hereinafter "ROM")
42.
Fixed disk
7 includes an operating system section for storing operating
system
43, an applications section for storing application files
44,
and a printer driver section for storing printer driver
45. Also included
is an other drivers section for storing other drivers
46, such as a printer driver.
RAM
41 interfaces to computer bus
31 to provide CPU
30 with
access to memory storage. In particular, when executing stored computer-executable
process steps such as those associated with application files
44, CPU
30
loads those application instruction sequences from fixed disk
7 (or other
storage media such as media accessed via a network or floppy disk interface
6)
into RAM
41 and executes those stored program instruction sequences out
of RAM
41. RAM
41 also provides for a print data buffer used by printer
driver
45.
ROM
42 in host processor
2 stores invariant instruction sequences,
such as start-up instruction sequences or basic input/output operating system (BIOS)
sequences for operation of keyboard
4.
Printer
10 includes controller
51 and print engine
52.
Controller
51 includes CPU
53 such as an 8-bit or a 16-bit microprocessor,
ROM
54, control logic
55, and I/O ports unit
56 connected
to bus
57. Connected to control logic
55 is RAM
59. Control
logic
55 includes controllers for print image buffer storage in RAM
59
and for print engine
52, including controllers for line feed motor
61
and carriage motor
62. Control logic
55 also provides control signals
and print data for print heads
64a and
64b of print
engine
52, including heat pulse generation control signals, and receives
data from temperature sensors (not shown) optionally disposed on print heads
64a
and
64b. In addition, control logic
55 receives temperature
data from ambient temperature sensor
65 through I/O ports unit
56.
In the preferred embodiment, the temperature sensors are diodes.
FIG. 4 is a perspective view of printer cartridge
11a with one
type of print head that can utilize the invention. As shown in FIG. 4, print head
64a and ink supply portion
67 of printer cartridge
11a
are integrated. In other words, print head
64a and ink supply
portion
67 are integral parts of printer cartridge
11a. However,
the invention is equally applicable to printer cartridges that have separately
removable and replaceable ink supply portions and print heads. In addition, printer
cartridge
11b shown in FIG. 2 can be of the same type as printer
cartridge
11a or of a different type.
FIG. 5 is a schematic view of print head
64a that is part of printer
cartridge
11a. Depicted in FIG. 5 is a heater board made from a silicon
wafer that is disposed in print head
64a. Heater board
71
is of a type used in a color print head. Accordingly, heater board
71 has
yellow nozzle group
72, magenta nozzle group
73, cyan nozzle group
64 and black nozzle group
75. In a typical print head, yellow, magenta
and cyan nozzle groups
72 through
74 each have
24 nozzles;
black nozzle group
75 has
64 nozzles. In FIG. 5, far fewer nozzles
(represented by the small circles) are shown for the sake of clarity. It should
be noted that the invention is equally applicable to print heads that have a different
number and type of nozzles, such as a print head that has 128 black nozzles and
no color nozzles.
Also shown in FIG. 5 are ink supply tubes
76. Each of these ink supply
tubes feeds ink of the appropriate color to the nozzles. Before reaching the nozzles,
ink supply tubes
76 branch so as to provide a separate ink supply tube branch
for each nozzle. It should be noted that other arrangements of ink supply tubes
are possible, and the present invention is equally applicable to print heads that
utilize those arrangements.
Temperature sensor
79 is optionally provided for measuring a temperature
of print head
64a. If this sensor is present, it preferably comprises
a diode.
Small heating elements, depicted by the rectangles behind the nozzle groups
in FIG. 5, are disposed behind the nozzles. While one rectangle is shown behind
each nozzle group in FIG. 5, a separate heating element actually is disposed behind
each nozzle. In operation, a meniscus forms at the boundaries of the ink with air
in the nozzles. When print head
64a is commanded to eject an ink
droplet from a nozzle, the heating element behind that nozzle fires. This firing
of the heating element causes the ink to boil, forcing a small ink droplet to fly
from the nozzle. The remaining ink in the nozzle re-forms a new meniscus, and the
process is repeated as necessary.
In order for the above process of ejecting ink droplets to work properly, the
nozzles must be unclogged and a meniscus must be able to form properly at each
nozzle. Otherwise, control over the ink droplets degrades or becomes impossible.
As mentioned above, ink jet printers move their print head (or heads) to a home
position after a print job is finished. At the home position, the print head is
cleaned with the wiper assemblies and capped so as to keep ink from drying on the
inside and the outside of the print head. However, if the print head is too hot
when capped, heat from the print head and hot ink cannot readily dissipate, possibly
resulting in a change of viscosity of the ink and/or drying of the ink. Ultimately,
the confined hot ink can form unwanted deposits on outer portions of the nozzles
(i.e., beyond where the meniscus should have formed) and on the print head, and
these ink deposits can then thicken or dry. The thickened or dried ink deposits
can interfere with proper operation of the print head. In particular, the ink deposits
can either interfere with proper formation of a meniscus in a nozzle or can block
a nozzle completely, resulting in poor print quality.
The invention addresses the foregoing problems by cooling the print head before
capping. For the sake of brevity, the invention is described with reference to
print head
64a of printer
10. However, as will be apparent
to those skilled in the art, the invention is equally applicable to any type of
print head used in an ink jet printer.
Briefly, the method for cooling the print head according to the invention
includes the steps of determining an ambient temperature, determining a print head
temperature, and waiting a predetermined time after receipt of the last print data
for a print job. The method also includes the steps of ejecting a predetermined
number of ink droplets from nozzles of the print head at a frequency lower than
a frequency used for printing, determining a drop in print head temperature caused
by ejecting the predetermined number of ink droplets, and repeating the steps of
waiting a predetermined time and ejecting a predetermined number of ink droplets
until the print head temperature falls below a predetermined threshold.
Shown in FIG. 6 is graph
84 of an example of cooling a print head according
to the invention. The horizontal axis of graph
84 is time, and the vertical
axis is print head temperature T
head. Solid line
85 shows the
temperature of print head
64a according to the invention.
Before printing, the temperature of print head
64a is at T
amb,
the ambient temperature. The ambient temperature preferably is determined by taking
a measurement from temperature sensor
65 in printer
10. When printing
starts at time
88, firing of the heating elements causes rise ΔT
print
in print head temperature T
head.
In the preferred embodiment, ΔT
print is calculated using a mathematical
model. According to this model, ΔT
print is equal to the sum of
values for changes in print head temperature ΔT
n calculated at
periodic intervals during the printing operation. The value for ΔT
n
preferably are calculated every 50 milliseconds. In an alternative embodiment,
ΔT
n is calculated once for the entire printing operation.
In the case of a color print head, ΔT
n can be calculated using
the following equation:
##EQU1##
where coeff1 is a heat-up coefficient based on the effect of the number of
black ink droplets ejected, coeff2 is a heat-up coefficient based on the effect
of the number of color droplets ejected, coeff3 is a heat-up coefficient based
on the effect of the heater duty cycle (i.e., heater frequency), coeff4 is a heat
diffusion coefficient, ΔT
n-1 is the last calculated change in
print head temperature, and coeff5 is a cool-down coefficient.
In more detail, coeff1 through coeff3 relate to the effect of firing the heating
elements on print head temperature. Heat diffusion coefficient coeff4 relates to
heat diffusion through the print head due to the difference between print head
temperature T
head and ambient temperature T
amb. The cool-down
coefficient coeff5 represents cooling of print head
64a due to inactivity,
including inactivity between the ejection of successive ink droplets, and the passage
of cooler ink into print head
64a from ink supply tubes
76.
The values of coeff1 through coeff4 are typically positive, and the value of
coeff4 is typically less than 1. The value of coeff5 is negative, representing
cooling of the print head.
When calculating the first value of ΔT
n for ΔT
print,
ΔT
n-1 has a value of zero, eliminating the heat diffusion coefficient
coeff4 from the calculation. The heat diffusion coefficient is eliminated because
the print head is at T
amb the first time ΔT
n is calculated.
Thus, there is no significant heat diffusion.
Of course, the actual coefficients and calculations used depend on the head/ink/resolution
combination for the print head. For example, the calculation given above is suitable
for a four-color print head, whereas an all-black print head would use a different
calculation that excludes, for example, dependence on the number of color droplets ejected.
Alternatively, the rise in print head temperature ΔT
print
can be determined by taking a reading from temperature sensor
79 on print
head
64a of the actual print head temperature. However, the mathematical
model is preferred because measurements taken from temperature sensor
79
can fluctuate widely, possibly resulting in an incorrect T
head after printing.
Print head
64a is capped after printing so as to protect the
print head. According to the invention, print head
64a is cooled
down to T
cap before capping. T
cap is equal to the ambient
temperature, as measured with temperature sensor
65, plus an acceptable
difference ΔT
cap, which in the present invention is 10° C.
over T
amb (i.e., T
cap equals T
amb plus ΔT
cap,
and ΔT
cap is 10° C.).
Print head
64a preferably is not cooled all the way down to T
amb
for at least two reason. First, cooling all the way down to T
amb may
take too much time for efficient operation. Second, print head operation actually
can be improved if print head
64a is warmer than the ambient temperature,
so long as the nozzles in print head
64a are not hot enough to cause
the problems discussed above.
When printing stops at time
90 in FIG. 6, heating of print head
64a
due to firing of the heating elements levels off, and print head
64a
begins to cool down. Thus, the first step in cooling print head
64a
according to the invention is to wait a predetermined amount of time, preferably
between nine and twelve seconds. Thus, at time
92, print head
64a
has cooled somewhat. However, in the example shown in FIG. 6, print head
64a
has not cooled down to T
cap after the predetermined wait.
In order to accelerate cooling of print head
64a, print head
64a
at time
92 is commanded to eject a predetermine number of ink droplets
from its nozzles at a frequency lower than a frequency used for printing. Print
head
64a is positioned over ink ejection receptacle
23a
for the ink ejection operation. In the preferred embodiment, the predetermined
number of ink droplets that are ejected is thirty per nozzle, at a frequency of
approximately two kilohertz. This frequency is lower than the frequency used for
printing, which is at least five kilohertz.
Because so few droplets are ejected, firing the heating elements to eject
the droplets does not cause a significant rise in print head temperature T
head.
In fact, because of the low frequency of heating element firing and the motion
of cooler ink into the nozzles from ink supply tubes
76, print head
64a
is actually cooled down by ejecting the ink droplets.
Mathematically, in the equation given above for ΔT
n,
coeff5 is adjusted to account for the low frequency and the movement of cool ink
into the print head. As a result, coeff5 dominates the equation, indicating that
print head
64a is cooled. Thus, after the ink droplets have been
ejected from print head
64a, print head temperature T
head
has fallen, as shown at time
93 in graph
84.
The above waiting and ejecting steps are repeated until print head temperature
T
head falls below T
cap. The drop in print head temperature
T
head is either computed mathematically, based on the above mathematical
model for ΔT
n (with coeff5 adjusted accordingly), or by taking
a reading from temperature sensor
79 on print head
64a of
the actual print head temperature.
The calculated temperature approach is preferred over the actual temperature
of the print head because temperature sensor
79 may not accurately measure
the temperature of print head
64a around the nozzles, where the temperature
matters most. Instead, temperature sensor
79 measures the temperature at
a point removed from the nozzles. In addition, temperature measurements taken with
temperature sensor
79 can fluctuate widely. This fluctuation is detrimental
because it can result in a false low print head temperature reading. Such a false
low can result in capping before print head
64a cools sufficiently,
leading to the problems discussed above with respect to capping hot print heads.
At time
97, print head temperature T
head has fallen below T
cap,
so print head
64a is capped. After a time, if no other printing operations
occur, print head temperature T
head falls to T
amb, shown
at time
98.
For comparison, line
99 in graph
84 shows print head temperature
in a case that low frequency ejection of ink from the nozzles of print head
64a
is not used. In that case, the print head temperature takes longer to fall to T
amb,
at least partly because the print head is capped while it is still hot (i.e., just
after printing stops at time
92). This capping traps the heat in the print
head and prevents the heat from dissipating.
FIG. 7 is a flowchart for explaining cooling of a print head according to the
invention. In step S
701, a print job starts. The print jobs causes print
head
64a to heat up. In step S
702, the print jobs ends. The
ambient temperature is determined in steps S
703, preferably by taking a
reading of temperature sensor
65. The ambient temperature can be determined
in advance of the print job or at any time during the print job. However, in the
preferred embodiment, the ambient temperature is determined just after the print
job, as shown.
In step S
704, a wait of preferably nine to twelve seconds occurs. This
waits allows the print head to cool somewhat without further action. In the case
that the print job was short, this wait may allow for sufficient cooling of the
print head.
The print head temperature T
head is determined in step S
705,
either mathematically, as discussed above, or by taking a reading of temperature
sensor
79. The mathematical approach is preferred. In step S
706,
it is determined if print head temperature T
head is less than or equal
to T
amb plus ΔT
cap.
If print head temperature T
head has not fallen below or to T
amb
plus ΔT
cap, then flow proceeds to step S
707, where
accelerated cooling is achieved by ejecting a predetermined number of ink droplets
from print head
64a at a frequency lower than that used for printing.
Then, flow returns to step S
704 for another waiting period. The result of
these steps is that ink droplets are ejected from print head
64a repeatedly
at the lower frequency, with a pause between each repetition, until print head
temperature T
head falls below the threshold defined by T
amb plus ΔT
cap.
When it is determined in step S
706 that T
head has fallen to
or below this threshold, flow proceeds to step S
708, where print head
64a
is capped.
It should be noted that other cleaning operations, such as wiping of print head
64a with wiper assembly
22a, can occur at any point
throughout the above operation. In the preferred embodiment, head wiping occurs
just after the print job and every time ink droplets are ejected from print head
64a into ink ejection receptacle
23a.
In actual operation, the above method can take some time. During that time, the
cooling operation can be interrupted. For example, a user could switch printer
10 off before cooling is complete. In that case, at the start of the next
print job, printer
10 should perform an excessive recovery operation to
ensure that the nozzles of print head
64a are clear. FIG. 8 is a
flowchart for explaining excessive recovery for a print head in this case.
Briefly, steps S
801 through S
804 correspond to obtaining a
parameter corresponding to a print head temperature when the ink jet printer is
down and performing a predetermined process (e.g., forced cooling of the print
head) based on the parameter. In the preferred embodiment of the invention, steps
S
801 through S
804 replace step S
701 of FIG. 7.
In step S
801, a print job starts after printer
10 has been, for
example, turned off. In step S
802, it is determined if a prior cooling operation
was interrupted. This determination can be made by checking a non-volatile memory
location in printer
10, by querying host processor
2 which can store
the information on fixed disk
7, by sensing a position of print head
64a
(e.g., if the print head is in the middle of the carriage, proper cooling was
not performed), by checking if the print head is capped, etc. The determination
can also be made by obtaining, when the ink jet printer is down (e.g., after soft
power-off), a calculated print head temperature or an actual print head temperature
measurement. Again, obtaining a calculated print head temperature is preferred
over obtaining an actual print head temperature measurement. All of the above-described
determinations are based on parameters the reflect whether the print head was cooled
before an interruption in operation, and thus directly or indirectly correspond
to print head temperature during the interruption (e.g., when the ink jet printer
is down).
If the prior cooling operation was interrupted, flow proceeds to step S
803,
where ink is purged from print head
64a into ink ejection receptacle
23a. This purging operation comprises ejecting sufficient ink from
print head
64a so as to clear the nozzles of any thickened or dried
ink deposits. After purging, or if the prior cooling operation was not interrupted,
flow proceeds to step S
804, and printer
10 is ready to print.
In the case that printer
10 automatically ejects a number of ink droplets
before a print job, step S
803 can be replaced with a step of changing a
number of ink droplets ejected before the print job. This alternative embodiment
is shown parenthetically in step S
803 of FIG. 8. In another embodiment,
step S
802 through S
804 are performed at power-on for the ink jet
printer, without waiting for a print job to start.
By virtue of the above operation, the invention provides for an efficient way
to cool a print head of an ink jet printer, such as before capping.
It should be noted that the invention can be embodied in various forms. For example,
the invention can be embodied in printer driver
45 on fixed disk
7,
in ROM
54 of printer
10, and in control logic
55 of printer
10. As will be understood by those skilled in the art, these examples are
not an exhaustive list of possible embodiments, and many other possible embodiments exist.
Accordingly, while the present invention is described above with respect
to what is currently considered its preferred embodiments, it is to be understood
that the invention is not limited to that described above. To the contrary, the
invention is intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
*
