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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet recording apparatus and method
and, more particularly, to a recording apparatus and method, which heat a
liquid using electrothermal energy converting elements, and eject liquid
droplets.
2. Related Background Art
In recent years, OA equipments such as computers, wordprocessors, copying
machines, and the like have become popular, and a large number of
recording apparatuses for such equipment have been developed. An ink jet
recording apparatus allows easier high-definition recording than other
recording methods, and can realize low-noise, low-cost recording at high
speed.
An ink jet recording apparatus is designed to have various recording modes
in addition to a simple one-scan recording mode so as to solve a problem
in fixing characteristics of an ink on recording media such as a paper
sheet, an OHP film, and the like, and to prevent, e.g., density
nonuniformity inherent to recording heads.
Of these recording modes, a multi-pass print mode for performing recording
by scanning a single recording head a plurality of number of times for a
single area on a recording medium is popularly used for various purposes.
In particular, when color recording is performed by a plurality of
recording heads using different colors of inks, a thin multi-pass print
mode is executed. In this mode, in order to prevent ink overflow and image
blur on the recording medium, instead of printing all the recording data
at one time, a single scan pattern is thinned out in a checkered pattern,
and the checker pattern is recorded a plurality of number of times,
thereby finishing an image corresponding to all the recording data. Even
in a monochrome recording mode, the following print method as a
modification of the thin print multi-pass print mode is executed. For
example, in a recording head consisting of a plurality of nozzles, density
nonuniformity inherent to the recording head due to a difference in
ejection characteristics among the nozzles is often observed. In order to
eliminate such nonuniformity, half of all the recording data is printed by
a first nozzle group, and the remaining half is printed by a second nozzle
group.
In the thin multi-pass print mode, the density of a recorded image tends to
become lower than an image obtained when recording is performed at one
time without using a thinning pattern (one-pass print mode). The degree of
this phenomenon varies depending on the types of recording media. In
general, this phenomenon is less likely to occur on coated paper coated
with an ink reception layer, and is often observed on non-coated paper
such as PPC paper having no special coat. Although the details of the
mechanism of this phenomenon are unknown, this phenomenon has a strong
correlation with the ink absorption speed of ink reception
characteristics, and readily occurs on paper which has poor ink fixing
characteristics. Since this phenomenon is associated with ink absorption
in a recording medium such as paper, it also has a correlation with the
ink composition. Although paper having poor fixing characteristics
requires the thin multi-pass print mode, a decrease in density easily
occurs on such paper due to the thin multi-pass print mode.
In an ink jet recording method, ink droplets are formed by various methods,
and recording is realized by depositing ink droplets onto a recording
medium such as paper.
Of recording apparatuses adopting a recording method of this type, as an
apparatus having a structure suitable for a high-density multi-orifice
recording head, an ink jet recording apparatus of a type utilizing heat as
energy for forming ink droplets is known.
The ink jet recording apparatus, which utilizes heat as ink droplet
ejection energy, normally comprises a recording head having ink droplet
forming means for heating an ink to displace the in by causing an abrupt
increase in the volume of the ink, and ejecting the ink from orifices of a
nozzle section, thereby forming ink droplets, i.e., electrothermal energy
converting elements, which generate heat upon application of an electrical
signals and which can heat the ink.
In the ink jet recording apparatus, the ink jet characteristics,
especially, the ink droplet size, are influenced by the temperature of the
recording head, and the print density changes depending on the
temperature. Thus, temperature control for, e.g., maintaining a constant
temperature of the recording head is performed.
FIG. 22 shows an ink jet printer head for heating an ink by a heater to
generate bubbles, and ejecting ink droplets in response to the bubbles,
and in particular, shows details of an ejection element 58 as the
principal part of the head.
Heaters H.sub.1 65 and H.sub.2 66 used for heating the head and keeping the
head temperature are formed on an Si substrate 61 from the same material
as that of ejection heaters 63. Energization of the heaters H.sub.1 65 and
H.sub.2 66 is ON-OFF-controlled according to head temperature information
for a temperature detection means (thermistor 59) mounted on base plate
53, thereby controlling the head temperature. Orifices 62 for ejecting ink
communicate with corresponding nozzles 64. The nozzles 64 are supplied
with ink from an ink tank (not shown) through an ink chamber 68. A filter
69 is arranged on the ink chamber 68. The heaters 63, 65, and 66 are
connected to an electrical circuit board 54 via an Al wiring pattern 67
and bonding wires 70.
However, since the ink jet recording head for ejecting ink droplets by
utilizing heat energy generates heat by itself upon recording, the ink
temperature in each nozzle where the ejection heater is arranged is higher
than a temperature detected by the temperature detection means during
recording, and this temperature difference varies depending on the
recording pattern and the record density. For this reason, when data
having a high record density such as an image pattern is to be recorded,
the ink temperature in the nozzles is increased, and the print density is
increased accordingly. On the other hand, when data having a relatively
low record density such as a character pattern is to be recorded, the
print density is lowered. It is therefore difficult to always obtain a
uniform print density.
When an image pattern is recorded, a multi-pass print operation for
performing on-line recording for a plural number of times of carriage scan
operations is often performed so as to improve image quality (color
boundary blur, color misregistration, and the like). In this case, the
print density may vary due to a difference in head temperature rise caused
by different print densities in respective scan operations. When the print
density in each scan operation varies, the ink penetration state onto a
recording medium varies. In general, as compared to a case wherein the
print density is increased by a one-pass print method, when an ink is
printed a plurality of number of times at a low print density, the spread
of each ink droplet on a recording medium is decreased, and the apparent
print density is undesirably lowered.
The demand for an ink jet recording apparatus capable of performing color
recording is increasing. Such a recording apparatus uses a recording head
having an array of a plurality of recording elements obtained by
integrating a plurality of ink ejection orifices and nozzles. Some
recording apparatuses have a plurality of recording heads for respectively
ejecting cyan, magenta, yellow, and black inks for color recording. The
ink ejection orifices of such a recording head eject ink in almost an
equal quantity per pixel.
However, the ink ejection quantity is considerably influenced by the
temperature of the recording head. More specifically, when the temperature
of the recording head is high, the ejection quantity is increased; when
the temperature of the recording head is low, the ejection quantity is
decreased. Such a difference in ejection quantity largely influences the
density of a printed image. In order to stabilize the ejection quantity
independently of the environmental condition of the recording head,
temperature control must be performed for each recording head.
For this purpose, a temperature control heater is arranged near or in the
recording head in addition to ink ejection heaters, and the temperature of
the recording head is detected by a thermistor. The detected temperature
is fed back to a control mechanism to stabilize the ink ejection quantity,
thereby obtaining an image free from print density differences and which
is independent of the environmental temperature of the recording head. In
this case, temperature control is uniformly performed for recording heads.
On the other hand, when color recording is performed using ink jet
recording heads, the following method is adopted. That is, coated paper
having good ink absorbency is used as a recording medium, ink droplets
each having a relatively small drop size are ejected onto the coated
paper, and inks are absorbed in the coated paper.
When the above-mentioned coated paper is used as the recording medium, a
sufficient print density and fixing characteristics can be assured.
However, a demand has arisen for a print operation using low-cost regular
paper as a recording medium with the recent advent of low-cost information
equipment and communication equipment. When a recording apparatus is
designed exclusively for coated paper, a user must use expensive recording
media, and cannot desirably select other recording media.
Since regular paper has no special treatment for absorption of an ink as a
liquid, it cannot easily obtain a sufficient density as compared to coated
paper manufactured in consideration of ink absorbency. In particular, the
density of a black ink used for characters, ruled lines, and the like is
important in an image. Therefore, to obtain a sufficient density is an
important subject for the print operation on regular paper.
When temperature control upon ejection is uniformly performed for a
plurality of recording heads like in the above-mentioned conventional
method to perform a print operation on recording media such as regular
paper, OHP paper, and the like having inferior ink absorbency to that of
coated paper, since ink droplets to be ejected ar set to have a small drop
size, as described above, the density of black characters and black lines
is low. In addition, since inks are implanted in too much quantities on R
(red), G (green), and B (blue) portions obtained by mixing inks ejected
from the cyan, magenta, and yellow recording heads so as to obtain a color
image, the inks are considerably blurred, thus deteriorating print
quality.
Furthermore, since the recording heads suffer from variations in ejection
quantity, the print density varies in units of recording heads. As a
result, especially in a color recording mode, different color tones are
obtained in units of color ink jet recording apparatuses.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the problems of the
related arts, and from a new viewpoint that is not expected in the
conventional methods.
Thus, it is the first object of the present invention to provide an ink jet
recording apparatus, which can prevent a decrease in density in a thin
multi-pass print mode, and can satisfactorily record an image according to
the types of recording media.
In order to achieve the above object, an ink jet recording apparatus
according to the present invention, comprises print method control means
for switching a print mode between a thin multi-pass print mode for
controlling the number of times of recording head scan operations for a
single recording area, and sequentially performing divided recording data,
and a one-pass print mode for recording all recording data in a single
head scan operation, and ejection quantity control means for controlling
an ink ejection quantity. The ejection quantity control means is
controlled so that a total ink quantity per unit recording area in the
thin multi-pass print mode is larger than that in the one-past print mode.
Thus, image recording suitable for various recording media can be
attained.
It is the second object of the present invention to provide an ink jet
recording apparatus, which can eliminate print density differences caused
by differences in recording modes.
In order to achieve this object, according to the present invention, an ink
jet recording apparatus for performing recording using a recording head
for ejecting an ink, comprises discrimination means for discriminating a
type of recording data recorded by the recording head, and ejection
quantity control means for controlling an ejection quantity of an ink
ejected from the recording head according to the type of recording data
discriminated by the discrimination means. The target temperature of the
recording head is switched according to the recording mode, thereby
eliminating print density differences due to a difference in recording
modes.
It is the third object of the present invention to provide an ink jet
recording method and apparatus, wherein even when a print operation is
performed not only on coated paper but also on a recording medium such as
regular paper or OHP paper, which has inferior fixing characteristics to
that of the coated paper, and cannot obtain a sufficient OD (average
optical density), use temperature ranges of recording heads are
individually set, so that, in a color recording mode, the print density of
black characters is increased, improvement in fixing characteristics and
prevention of blur are attained by suppressing ink implantation quantity
of a color recording unit, and image recording can be performed with high
print quality.
It is the fourth object of the present invention to provide an ink jet
recording method and apparatus, wherein print density characteristics of
each recording head are measured to set an optimal use temperature range
for each recording head.
In order to achieve the above objects, according to the present invention,
an ink jet recording apparatus for performing recording using a plurality
of recording heads for ejecting inks onto a recording medium, comprises
temperature detection means for detecting temperatures of the recording
heads, and temperature control means for controlling the temperatures of
the recording heads on the basis of the temperature information detected
by the temperature detection means so that the temperatures of the
recording heads do not fall outside predetermined temperature ranges which
are set in correspondence with the recording heads.
According to the present invention, there is also provided an ink jet
recording apparatus for performing recording using a plurality of
recording heads for ejecting inks onto a recording medium, comprising
temperature range setting means for setting temperature ranges of the
recording heads for respective recording heads, and control means for
controlling temperatures of the recording heads according to the
temperature ranges set by the temperature range setting means.
According to the present invention, there is also provided an ink jet
recording apparatus for performing recording using a plurality of
recording heads for ejecting inks onto a recording medium, comprising
temperature range setting means for setting predetermined temperature
ranges of the recording heads according to a type of recording medium to
be used for respective recording heads.
According to the present invention, there is also provided an ink jet
recording method comprising the step of preparing a plurality of recording
heads for performing recording by ejecting inks onto a recording medium,
and the step of performing recording by controlling temperatures of the
recording heads so as not to fall outside predetermined temperature
ranges, which are set in correspondence with the recording heads.
According to the present invention, there is also provided an ink jet
recording apparatus for performing recording using a plurality of
recording heads for ejecting inks onto a recording medium, comprising
density detection means for detecting densities of test patterns formed on
a recording medium by the recording heads, temperature setting means for
setting temperatures of the recording heads in units of recording heads on
the basis of the densities of the test patterns detected by the density
detection means, and control means for controlling the temperatures of the
recording heads according to the temperatures set by the temperature
setting means.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view for explaining an ink jet recording apparatus
which can adopt the present invention;
FIG. 2 is a block diagram showing the ink jet recording apparatus which can
adopt the present invention;
FIGS. 3A to 3D are views for explaining a method of generating thinned
print signals;
FIG. 4 is a table showing print control modes and target head temperatures
according to the first embodiment of the present invention;
FIG. 5 is a flow chart showing a target temperature setting routine for a
recording head;
FIG. 6 is an explanatory view of recording patterns of the first
embodiment;
FIG. 7 is a graph showing the correlation between the target temperature
and the ejection quantity of a recording heard;
FIG. 8 is a graph showing the correlation between the ejection quantity and
the record density according to recording modes and recording media;
FIG. 9 is a chart showing an ejection quantity setting state under the PWM
control according to the second embodiment of the present invention;
FIG. 10 shows a PWM table of the second embodiment;
FIG. 11 is a graph showing ejection quantity control based on table
conversion;
FIG. 12 is a flow chart showing a head driving control routine of the
second embodiment;
FIGS. 13A to 13C are explanatory views showing recording processes in a
recording method according to the third embodiment of the present
invention;
FIG. 14 is an explanatory view showing a state upon completion of recording
by the recording method of the third embodiment;
FIG. 15 is a flow chart showing a head temperature control routine
according to the fourth embodiment of the present invention;
FIG. 16A to 16C re explanatory views of an image recording method;
FIG. 17 is a flow chart showing a head temperature control routine
according to the fifth embodiment of the present invention;
FIG. 18 is a flow chart showing a head temperature control routine
according to the sixth embodiment of the present invention;
FIG. 19 is a partially cutaway perspective view of an ink jet recording
apparatus which can adopt the present invention;
FIG. 20 is a block diagram of a control unit of the ink jet recording
apparatus which can adopt the present invention;
FIG. 21 is a schematic view of an ink jet recording head which can adopt
the present invention;
FIG. 22 is a sectional view showing principal parts of the ink jet
recording head which can adopt the present invention;
FIG. 23 is a graph showing the correlation between the target head
temperature and the ejection quantity of the recording head;
FIG. 24 is a flow chart showing a processing sequence for setting a use
temperature range of the recording head;
FIG. 25 is a flow chart showing a temperature control operation of the
recording head;
FIG. 26 is a perspective view showing an arrangement of a recording section
of the ink jet recording apparatus;
FIG. 27 is a schematic view showing an arrangement of an ink jet recording
head unit;
FIG. 28 is a block diagram showing an arrangement of a control system of
the ink jet recording apparatus;
FIG. 29 is a block diagram showing an arrangement obtained by integrating a
driver, a temperature control heater, and a temperature measurement sensor
to a recording head itself;
FIG. 30 is a schematic perspective view showing an arrangement of a
recording head 102A;
FIG. 31 shows a print sample;
FIG. 32 is a graph showing use temperature ranges of recording heads;
FIG. 33 is a view showing a density detection means;
FIG. 34 is a graph showing an example of a print density comparison table;
FIG. 35 is a flow chart showing an example of a density detection sequence,
and a temperature range setting sequence;
FIG. 36 is a table showing use temperature ranges of the recording heads in
units of print modes and density characteristics of the recording heads;
FIG. 37 is a flow chart showing another example of a density detection
sequence, and a temperature range setting sequence;
FIG. 38 is a schematic block diagram showing an arrangement obtained when
the recording apparatus of the present invention is applied to an
information processing apparatus;
FIG. 39 is a perspective view showing the outer appearance of the
information processing apparatus shown in FIG. 38; and
FIG. 40 is a perspective view showing another information processing
apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention will be described in
detail hereinafter with reference to the accompanying drawings.
The first embodiment of the present application will be described below.
(First Embodiment)
FIG. 1 is a schematic view of an ink jet recording apparatus, which can
adopt the present invention. An ink jet cartridge C has an ink tank unit
in its upper portion, and a recording head 23 (not shown) in its lower
portion. The cartridge C also has a connector for receiving signals for
driving the recording head 23. A carriage 2 aligns and carries four
cartridges C1, C2, C3, and C4 (which store different color inks, e.g.,
yellow, magenta, cyan, and black inks). The carriage 2 is provided with a
connector holder, electrically connected to the recording heads 23, for
transmitting, e.g, signals for driving recording heads.
The ink jet recording apparatus includes a scan rail 11, extending in the
main scan direction of the carriage 2, for slidably supporting the
carriage 2, and a drive belt 32 for transmitting a driving force for
reciprocally moving the carriage 2. The apparatus also includes pairs of
convey rollers 15 and 16, and 17 and 18, arranged before and after the
recording positions of the recording heads, for clamping and conveying a
recording medium, and a recording medium P such as a paper sheet, which is
urged against a plated (not shown) for flattening a recording surface of
the recording medium P. At this time, the recording head 23 of each ink
jet cartridge C carried on the carriage 2 projects downward from the
carriage, and is located between the convey rollers 16 and 18 for
conveying the recording medium. The ejection orifice formation surface of
each recording head faces parallel to the recording medium P urged against
the guide surface of the platen (not shown). Note that the drive belt 32
is driven by a main scan motor 29, and the pairs of convey rollers 15 to
18 are driven by a sub-scan motor 26 (not shown).
In the ink jet recording apparatus of this embodiment, a recovery system
unit is arranged at the home position side (at the left side in FIG. 1).
The recovery system unit includes cap units 300 arranged in correspondence
with the plurality of ink jet cartridges each having the recording head
23. Upon movement of the carriage 2, the cap units 300 can be slid in the
right-to-left direction and be also vertically moved. When the carriage 2
is located at the home position, the cap units 300 are joined to the
corresponding recording heads 23 to cap them, thereby preventing an
ejection error of the ink in the ejection orifices of the recording heads
23. Such ejection error is caused by evaporation, which results in
increased viscosity and solidification of the attached inks.
The recovery system unit also includes a pump unit 500 communicating with
the cap units 300. When the recording head 23 causes an ejection error,
the pump unit 500 is used for generating a negative pressure in suction
recovery processing executed by joining the cap unit 300 and the
corresponding recording head 23. Furthermore, the recovery system unit
includes a blade 401 as a wiping member formed of an elastic material such
as rubber, and a blade holder 402 for holding the blade 401.
In the four ink jet cartridges carried on the carriage 2, the cartridge C1
stores a black (to be abbreviated to as K hereinafter) ink, the cartridge
C2 stores a cyan (to be abbreviated to as C hereinafter) ink, the
cartridge C3 stores a magenta (to be abbreviated to as M hereinafter) ink,
and the cartridge C4 stores a yellow (to be abbreviated to as Y
hereinafter) ink. The inks overlap each other in this order. Intermediate
colors can be realized by properly overlapping C, M, and Y color ink dots.
More specifically, red can be realized by overlapping M and Y; blue, C and
M; and green, C and Y. Black can be realized by overlapping three colors
C, M, and Y. However, since black realized by overlapping three colors C,
M, and Y has poor color development and precise overlapping of three
colors is difficult, a chromatic edge is formed, and the ink implantation
density per unit time becomes too high. For these reasons, only black is
implanted separately (using a black ink).
FIG. 2 is a control block diagram of the ink jet recording apparatus which
performs a thinning multi-pass print operation that can adopt the present
invention. In FIG. 2, the recording head 23 has a plurality of ink
ejection orifices, and a plurality of electrothermal converting elements
as ejection energy generation elements arranged in correspondence with the
ejection orifices. In the recording head 23, an ejection signal according
to recording data is supplied to the electrothermal converting elements,
and bubbles formed by these elements cause a change in state of the ink,
thereby ejecting ink droplets from the ejection orifices. The main scan
motor 29 drives the drive belt 32. A print mode selector 20 switches a
print mode automatically or by a manual switch operation by a user. A thin
print signal generator 21 generates a thin print signal for performing the
thinning multi-pass print operation from an input image signal (to be
referred to as a print signal thereinafter) S when the print mode selector
20 selects a thinning multi-pass print mode. A head driver 22 drives the
recording head 23 according to a signal from the thin print signal
generator 21, and changes the driving condition of the recording head 23
according to the selected print mode, as will be described later. A main
scan motor driving signal generator 27 generates a signal for driving the
main scan motor 29. The generator 27 sequentially generates driving
signals corresponding in number to passes when the thinning multi-pass
print mode is selected by the print mode selector 20. A main scan motor
driver 28 controls the driving operation of the main scan motor 29
according to a signal from the main scan motor driving signal generator
27. A sub-scan motor | | |
