 |
Description  |
|
|
BACKGROUND OF THE INVENTION
The present invention relates to an ink-jet recording apparatus which
performs the recording by ejecting ink to a recording medium.
Conventionally, an ink-jet recording apparatus is developed in which ink is
heated by a heater to generate air bubbles in the ink, and the ink is
ejected with the pressure caused by the expansion of the air bubbles to a
recording medium from an ejecting port of a head, thereby performing the
recording.
With such an ink-jet recording apparatus, the heating of ink causes
temperatures of the head and ink to change during the recording. It is
observed that the temperature change of the ink causes the recorded image
density to remarkably vary.
Under a high temperature environment, the ink amount of an ink drop to be
formed increases in accordance with the decrease of the viscosity of ink.
Therefore, dots having a larger diameter are formed on a recording medium.
By contrast, under a low temperature environment, the viscosity of ink
increases so that the ink amount of an ink drop to be formed decreases.
Therefore, dots having a smaller diameter are formed on a recording
medium. Moreover, depending on the ink temperature, the ink ejection speed
also varies. As a result, the landing positions of ink drops are
scattered. This largely affects the image quality. Particularly, when the
print operation is halted for a long time period under the low temperature
environment, the temperature of the head falls, resulting in that, when
the next print operation is performed immediately after the halt, the
diameter of dots constituting an image is small and the ejection
performance is not stable, thereby producing a problem in that the image
quality is deteriorated.
From the above, it will be noted that, if the ink temperature or head
temperature is controlled so as to be kept constant throughout the
printing period and the printing halt period, the ink ejection performance
in the printing is stable and the ink amount of an ink drop can be made
uniform, thereby eliminating the problems in the image quality such as the
density variation. In the prior art, therefore, there is a problem of how
to perform the recording operation while keeping the head temperature
constant.
In order to solve the problem, some methods are hitherto proposed. One of
the methods is disclosed in Unexamined Japanese Patent Publication No.
HEI. 3-218,840. According to this method, when the recording is to be
continuously performed on a plurality of recording media, the head is
driven in such a degree that ink is not ejected, during a predetermined
time period from the end of the recording for a first recording medium to
the start of the recording for a second recording medium, thereby raising
the head temperature to a prescribed temperature. Thereafter, the
recording for the second recording medium is started. Therefore, the
density variation among recording media can be eliminated, and a stable
image quality can be always obtained even under a low temperature
environment.
However, this method has a drawback that, when a low image density printing
is to be performed under a low temperature environment, the head
temperature is raised to the prescribed temperature at the start of the
recording for one sheet, but the head temperature falls in the recording
for the end portion of the sheet, thereby causing the start and end
portions of the sheet to have different image densities. In such a case,
furthermore, the head temperature considerably falls at the end of the
printing for the sheet. This probably requires a long time period for
raising the head temperature during the predetermined time period before
the start of the printing of the next sheet. During this time period, it
is necessary to stop the print operation, and the host computer is
requested to stay in the waiting state. Therefore, this method may cause
the processing speed of the whole system to reduce.
The above-identified publication discloses also that, even in the printing
of one line, the ink flow path is kept heated by driving the recording
head with a pulse width stored in a memory by which ink can be ejected, or
by which ink cannot be ejected. However, these pulse widths are not set
for every line depending on the temperature change during the recording
for a single sheet. Therefore, the image density is also different between
lines in a single sheet.
Further, Unexamined Japanese Patent Publication No. HEI. 1-127,361
discloses another method including a first control device for generating
and supplying a drive signal for ejecting ink, and a second control device
for generating and providing a drive signal by which ink cannot be
ejected. Both the devices are simultaneously operated so that, in a
predetermined time period, the power consumption of a nozzle which ejects
ink is approximately equal to that of a nozzle which does not eject ink.
Therefore, the differences in temperature between the nozzles are
eliminated, and the ink amount of an ink drop is constant for both the
nozzles, thereby preventing the image quality deterioration from occurring
in a single sheet.
Also in this method, as in the above-mentioned prior art example, the ink
ejection failure and the density variation due to the variation in the ink
temperature can be prevented. However, in this method, two drive pulse
generating units are provided and simultaneously operated, so that nozzles
which are not ejecting ink are also driven. Therefore, the amount of
currents consumed by the head is increased as a whole, producing a problem
in that it requires a power source apparatus of a larger size. Moreover,
in the drive method, nozzles which are not ejecting ink and nozzles which
are ejecting ink are controlled so as to consume almost the same power.
Therefore, all the nozzles are apparently in the state of ejecting, so
that the head temperature becomes significantly high. Conversely, in this
method, unless the head temperature is made high, the variation in
temperature between the nozzles cannot be eliminated.
When the head temperature is too high, the ink pressure balance in the ink
flow path and the bubble formation balance are lost. There are problems in
that the ink ejection direction is disordered, and that external air is
introduced into the ink flow path through a nozzle to make the ink
ejection disabled. In view of these problems, under a high temperature
environment, it is necessary to inhibit the operation of the second drive
pulse generating unit, or to change the first and the second drive pulse
widths so as to reduce the applied energy. In the former method, the
second drive pulse generating unit becomes unnecessary. In the latter
method, it is necessary to determine the first and the second drive pulse
widths. When this determination is done without considering the image
density, there arises a danger that the head temperature will rise still
more. Therefore, the above-mentioned ink ejection is more dangerous to
occur a failure. As described above, the method in which the head
temperature is kept constant in a high temperature range has a problem.
Recently, it becomes possible to use a head cartridge which contains a
digital circuit to allow the interface to the body of the apparatus to be
simplified. Such a head is allowed to be driven through a few signal lines
from the body of the apparatus. Therefore, the number of cables connecting
the head to the body of the apparatus can be remarkably reduced. In such a
head cartridge containing a digital circuit, nozzles which are aligned in
a line are generally divided into groups each having several nozzles, and
the nozzles belonging in one group are simultaneously driven so that a
nozzle drive pulse width is commonly used in one nozzle group. Apparatuses
in which nozzle groups are driven are disclosed in, for example,
Unexamined Japanese Patent Publication No. SHO. 58-36,461. When such a
head is used, it is impossible to perform the control that the divided
nozzle groups are simultaneously applied with the first and second drive
pulse widths which are different from each other.
SUMMARY OF THE INVENTION
The present invention has been conducted in view of the above problems. An
object of the present invention is to provide an ink-jet recording
apparatus which can perform a stable head temperature control under any
temperature environment.
The ink-jet recording apparatus of the present invention provides a
carriage which moves relatively to a recording medium, and one or a
plurality of head cartridges which are detachably mounted on the carriage,
each of the head cartridges having a plurality of nozzles, the plurality
of nozzles being divided into a plurality of nozzle groups each having a
predetermined number of the nozzles, each of the nozzle groups
sequentially ejecting ink to perform recording for one line in an
arrangement direction of the nozzles, a temperature detecting device for
detecting a temperature of the head, a first storage device for storing a
piece of drive pulse width data for driving the nozzles, a second storage
device for storing one or more pieces of drive pulse width data for
driving the nozzles, and a drive pulse generating unit for generating a
drive pulse width for driving the nozzle groups in accordance with the
drive pulse width data stored in the first storage device or the second
storage device.
In another aspect of the present invention, the drive pulse width data
stored in the first memory device is set so as to be variable in a range
where ink can be ejected, the drive pulse width data stored in the second
memory device is set so as to be variable in a range where ink can be
ejected, in a preset temperature, and to be variable in a range where ink
cannot be ejected, at the preset temperature or a lower temperature, and
the drive pulse width data stored in the first memory device is greater
than the drive pulse width data stored in the second memory device.
In a further aspect of the present invention, the ink-jet recording
apparatus further comprises a print data processing control unit for
controlling print data and setting data so as to be printed, when there is
no data to be printed in nozzle groups to be driven, during a print
recording operation under an environment of a preset temperature or a
lower temperature, one of the pieces of drive pulse width data stored in
the second memory device is selected, and the nozzle groups in which there
is no data to be printed is also driven.
In a still further aspect of the present invention, the print data
processing control unit is controlled so as to operate at the preset
temperature or a lower temperature, to generate data for causing at least
one nozzle in the nozzle group to be driven, to print, and to selectively
determine the number of data pieces to be generated and the position of
the nozzle.
In a still further aspect of the present invention, the ink-jet recording
apparatus further comprises a print density detecting unit for detecting a
print density in the nozzle group to be driven, during a print operation
under an environment at the preset temperature or a higher temperature,
and either of the drive pulse width data stored in the first memory device
and the drive pulse width data stored in the second memory device is
selected on the basis of a detected result to sequentially generate a
drive pulse, and to sequentially drive the plurality of nozzle groups.
In a still further aspect of the present invention, when either of the
drive pulse width data stored in the first memory device and the drive
pulse width data stored in the second memory device is selected by the
print density detecting unit based on the detected result, a reference for
the selection is variable.
In a still further aspect of the present invention, during a recording
operation under an environment in a preset temperature range, only the
drive pulse width data stored in the first memory device is used, and the
selection of the drive pulse width data stored in the second memory device
and the generation of the print data in the print data processing control
unit is inhibited.
In a still further aspect of the present invention, the number of nozzles
to be simultaneously driven is at least one.
According to the present invention, the temperature detecting device, the
first and storage devices each for storing a drive pulse width data, and a
drive pulse generating unit are provided for each of the heads, and one of
the drive pulse width data is selected at a high speed for each of
simultaneously driven nozzle groups. Therefore, by a relatively simple
circuit, the drive control for each of the nozzle groups in accordance
with the head temperature can be realized and the head temperature control
can be stably performed.
In the other aspect of the present invention, the drive pulse width data
stored in the first memory device is set so as to be variable in a range
where ink can be ejected, and the drive pulse width data stored in the
second memory device is set so as to be variable in a range where ink can
be ejected, in a preset temperature, and to be variable in a range where
ink cannot be ejected, at the preset temperature or a lower temperature.
Accordingly, the head temperature control can be performed in the
following manner: when the apparatus is used under a high temperature
environment, the drive pulse width is shortened so as to reduce the heat
generation; and, when the apparatus is used under a low temperature
environment, a nozzle which is not used for printing is heated.
In the further aspect of the present invention, in the print recording
operation under an environment of a preset temperature or a lower
temperature, a drive pulse width data by which ink is not ejected is set
in the second storage device. When there is no print data in the nozzle
group to be driven, the print data processing control unit sets print data
to be printed by the head and drives the nozzle group which does not
perform the printing. Therefore, even when an image of a low print density
is to be printed under a low temperature environment, the head temperature
is prevented from falling.
In the still further aspect of the present invention, the print data
processing control unit is controlled so as to operate at the preset
temperature or a lower temperature, to generate data for causing at least
one nozzle in the nozzle group to be driven, to print, and to selectively
determine the number of data pieces to be generated and the position of
the nozzle. Therefore, the variation in temperature between nozzles can be
suppressed to a low level, and the head temperature under a low
temperature environment can be controlled so as to be constant.
In the still further aspect of the present invention, in a print operation
under an environment at the preset temperature or a higher temperature,
the print density detecting unit detects a print density in the nozzle
group to be simultaneously driven, and either of the drive pulse width
data stored in the first memory device and the drive pulse width data
stored in the second memory device is selected on the basis of the
detected print density. When the print density is high, the data of the
narrower drive pulse width is selected. This can reduce the heat
generation so that the heat accumulation under a high temperature
environment can be prevented from occurring.
In the still further aspect of the present invention, the print density
detecting unit operates in such a manner that the criterion of selecting
the drive pulse width data stored in the first and second memory devices
can be changed. Therefore, the heat accumulation can be prevented and the
heating control can be performed not only under a high temperature
environment but also under the optimum environment.
In the still further aspect of the present invention, during a recording
operation in a preset range, only the drive pulse width data stored in the
first memory device is used. The head temperature is prevented from
rapidly falling or rising.
In the still further aspect of the present invention, the number of nozzles
to be simultaneously driven is at least one whereby the temperature
control suitable for the structure of the used head can be realized.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing the system configuration of an embodiment of
the ink-jet recording apparatus according to the present invention;
FIG. 2 is a schematic diagram showing the configuration of the vicinity of
a carriage in one embodiment of the ink-jet recording apparatus according
to the present invention;
FIG. 3 is a diagram showing the configuration of an embodiment of a head
drive control operation unit of the ink-jet recording apparatus according
to the present invention;
FIG. 4 is a diagram showing the configuration of another embodiment of the
head drive control operation unit of the ink-jet recording apparatus
according to the present invention;
FIG. 5 is a diagram showing the configuration of an embodiment of an
internal circuit of a head of the ink-jet recording apparatus according to
the present invention;
FIG. 6 is a drive timing chart for nozzle groups in the head of the ink-jet
recording apparatus according to the present invention;
FIG. 7 is an output timing diagram of the head drive control operation unit
in the case where the head temperature is in the optimum temperature range
A;
FIG. 8 is an output timing diagram of the head drive control operation unit
in the case where the head temperature is in the optimum temperature range
B;
FIG. 9 is an output timing diagram of the head drive control operation unit
in the case where the head temperature is in the optimum temperature range
C;
FIG. 10 is an output timing diagram of the head drive control unit in the
case where the head temperature is in the optimum temperature range B
under a low environmental temperature condition;
FIG. 11 is an output timing diagram of the head drive control unit in the
case the head temperature falls to the optimum temperature range A under
the low temperature environment;
FIG. 12 is a diagram showing the temperature rising tendency of the head
under an environment in the optimum temperature range;
FIG. 13 is a diagram showing the temperature rising tendency of the head
under a lower temperature environment;
FIGS. 14 to 20 are flowcharts illustrating exemplary temperature control
operations in the ink-jet recording apparatus according to the present
invention; and
FIG. 21 is a schematic diagram showing the configuration of another
embodiment of the carriage according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a diagram showing the system configuration of an embodiment of
the ink-jet recording apparatus of the present invention. In the FIG. 1,
reference numeral 1 denotes an ink-jet recording apparatus, 2 denotes a
host computer, 3 denotes a CPU, 4 denotes a work RAM, 5 denotes a font
ROM, 6 denotes a program ROM, 7 denotes an EEPROM, 8 denotes an interface,
9 denotes an operation panel, 10 denotes a memory controller, 11 denotes
an image RAM, 12 denotes a head controller, 13 denotes recording heads, 14
denotes a motor controller, 15 denotes a motor, 16 denotes an I/O
controller, 17 denotes sensors, and 18 denotes a common bus.
The ink-jet recording apparatus 1 is connected to the host computer 2 so
that data are transmitted therebetween. The CPU 3 is connected to the work
RAM 4, the font ROM 5, the program ROM 6 and the EEPROM 7. The CPU 3
operates in accordance with programs stored in the program ROM 6 while
referring to preset values stored in the EEPROM 7 such as correction data
for high quality recording. The CPU 3 is connected also to the common bus
18, so as to control various units of the ink-jet recording apparatus 1
via the common bus 18. The work RAM 4 is used as a work memory area for
the CPU 3, and also as a memory for storing various kinds of information
used in the system. The font ROM 5 stores image data of characters to be
printed. The program ROM 6 stores programs for instructing the operation
of the CPU 3. The EEPROM 7 is a nonvolatile memory which can retain the
contents thereof even if the power is off. For this reason, various preset
values such as correction data for high quality recording and operation
modes of the system are stored in the EEPROM 7. In some cases, such data
are set through the operation panel 9.
The interface 8 is connected to the common bus 18 and the host computer 2,
so that data are directly sent to and received from the host computer 2.
The operation panel 9 is connected to the common bus 18 so as to accept
various inputs from the user and display various conditions and messages
to the user.
The memory controller 10 is connected to the image RAM 11, the common bus
18 and the head controller 12, and controls the image RAM 11. Data to be
recorded are stored in the image RAM 11 with the form of an image. The
memory area of the image RAM 11 can be divided into regions respectively
corresponding to the recording heads.
The head controller 12 is connected to the recording head 13, the common
bus 18 and the memory controller 10, and controls the recording heads 13.
The controls of the recording heads 13 include at least controls of the
timing of ejecting ink from each nozzle of the recording heads, and the
temperature of the ink, etc. In place of the CPU 3, the head controller 12
can perform some of the controls such as the selection of used nozzles on
the basis of the nozzle selection data which will be described later. The
recording heads 13 consist of a plurality of heads each having N nozzles.
For example, in the case of color printing, the recording heads 13 consist
of four heads for black (K), cyan (C), magenta (M), and yellow (Y).
The motor controller 14 is connected to the motor 15 and the common bus 18,
and controls the motor 15. The motor 15 moves a carriage on which the
recording heads 13 are mounted, in a relative manner to a recording
medium, e.g., a recording sheet. The I/O controller 16 is connected to the
various sensors 17 and the common bus 18, and controls the various sensors
17 and receives data detected therefrom. The sensors 17 include those for
detecting, for example, the end of a recording sheet, the width of the
recording sheet, and the amount of ink.
The common bus 18 connects the CPU 3, the interface 8, the operation panel
9, the memory controller 10, the head controller 12, the motor controller
14 and the I/O controller 16 to each other, to transmit various kinds of
data and control signals therebetween.
With the above-described configuration, the units are separately installed
so as to perform different functions. This configuration can be modified
so that, for example, the image RAM 11 and the work RAM. 4 is realized
with a single RAM.
The operation of the system shown in FIG. 1 will be described. The CPU 3
operates in accordance with the programs stored in the program ROM 6 while
referring to the preset values and the like stored in the EEPROM 7. During
the operation, the work RAM 4 is used as required. Values and the like to
be stored in the EEPROM 7 are input through the operation panel 9.
Furthermore, the CPU 3 receives data from the sensors 17 via the I/O
controller 16. The CPU 3 checks the conditions as to whether the recording
can be performed or not, and instructs the motor controller 14 to move the
carriage and transport a recording sheet, thereby performing the position
setting or the like for the recording.
When the host computer 2 sends out data to be recorded such as image data
and character codes, the data are received by the interface 8 which in
turn transfers the received data to the CPU 3. The CPU 3 converts the
received data into image data suitable for the recording, e.g., a bit map,
depending on the print format. For example, if the received data are
character codes, the data are converted into image data of the
corresponding characters by using the font ROM 5. The converted image data
are stored into the image RAM 11 through the memory controller 10.
After the image data are stored, a head drive pulse width and a drive
operation mode are determined based on the temperatures detected by
temperature detecting elements (hereinafter referred to as "thermistor")
incorporated in the printer body and in the heads, and various set values
are set to the head controller 12. Particularly, a low head temperature
adversely affects the ink ejection characteristics at an instance
immediately before the start of the printing. In order to prevent this
from occurring, an operation for raising the head temperature is performed
until the head temperature reaches an optimum temperature range in which
the ink ejection characteristics are relatively stable. Next, the CPU 3
instructs the motor controller 14 to move the carriage and performs the
scanning operation. An encoder for generating a print timing signal is
mounted on the carriage on which the recording heads 13 are mounted. The
print timing signal depending on the carriage scanning speed is supplied
to the CPU 3 and the head controller 12. The CPU 3 determines a printing
start position on the basis of the timing signal, and provides a gate
signal for enabling the printing to be started, to the head controller 12.
In response to the print enable gate signal and the print timing signal,
the head controller 12 outputs a head drive signal to the recording heads
13. The above operation is continuously performed. When the printing for
one scan is completed, an interrupt is produced from the memory controller
10, and input into the CPU 3. Upon receiving the interrupt signal, the CPU
3 requires the motor controller 14 to transport the recording medium by a
print recording width and to scan the carriage again. In this manner, the
printing for one scan is repeated several times until the print recording
operation for the recording medium in the transporting direction is
completed. In the embodiment, the head temperature and the environmental
temperature are detected before every printing for one scan, so that the
head drive pulse and the drive operation mode are determined for every
printing.
When the print operation for one recording medium is completed in this way,
the CPU 3 requires the motor controller 14 to discharge the recording
medium. At the same time, in order to prevent the ink from drying, the
carriage is moved to a position where a cap member for covering the nozzle
portion is provided, and the capping operation is performed. Then, the CPU
3 waits the next print operation. As a result of the above series of
operations, the print operation for one recording medium is completed.
FIG. 2 is a schematic diagram showing the configuration of the vicinity of
a carriage in one embodiment of the ink-jet recording apparatus of the
present invention. In the FIG. 2, reference numeral 21 denotes recording
head units, 22 denotes a carriage, 23 denotes a recording medium, and 24
denotes a transport roller. On the carriage 22, one or a plurality of
recording head units 21 are mounted in such a manner that they are
detachable from the carriage 22 separately or as a single unit. Each of
the recording head units 21 is provided with a plurality of nozzles. While
the carriage 22 is scanned laterally, ink is ejected from the nozzles to
perform the printing. In the case where a plurality of recording head
units 21 are mounted on the carriage 22, ink is ejected from the recording
head units 21 so that ink dots are superposed to form an image. For
example, four recording heads for black, cyan, magenta and yellow can be
provided for each of the recording head units 21, thereby enabling a color
image to be formed.
When one scan operation of the carriage 22 is finished, the recording
medium 23 is transported by a predetermined distance by the transport
roller 24. This operation is repeated so as to complete the printing for
one recording sheet.
In the embodiment, the movement of a recording medium in the vertical
direction is conducted by moving the recording medium itself.
Alternatively, the vertical movement can be achieved by moving the
carriage 22. The moving distance can correspond to a printing pitch of one
scanning, or a predetermined line-feed pitch. A recording medium can be
moved in a single step by a distance corresponding to several scans and
including a line-feed pitch for a blank line. Moreover, during the
operation of feeding a recording medium, or when a recording medium is
positioned for the recording in accordance with a predetermined format,
for example, the recording medium can be transported in accordance with
instructions from the CPU 3, and the moving distance can be varied by
instructions from the host computer 2.
FIG. 21 is a schematic diagram showing the configuration of another
embodiment of the carriage according to the present invention. In the FIG.
21, reference numeral 201 denotes a recording head, 210 denotes a head
mounting member, 211 denotes a carriage, 212 denotes a projection disposed
on an upper surface of the carriage, 214 denotes rods for supporting the
carriage, 225 denotes a thermistor, and 227 denotes a power control
circuit for the thermistor.
FIG. 3 is a diagram showing the configuration of an embodiment of a head
drive control operation unit of the ink-jet recording apparatus of the
present invention. In the FIG. 3, reference numeral 31 denotes a device
for storing an adjacent nozzle group printing period, 32 denotes a counter
for setting an adjacent nozzle group printing period, 33 denotes a print
timing control unit, 34 denotes a print drive pulse generating unit, 35
denotes a print dot number counter, 36 denotes a counter for setting a
print drive pulse width, 37 denotes a data selecting device, 38 denotes a
first storage device, 39 denotes a second storage device, 40 denotes an
image density detecting unit, and 41 denotes a print data processing unit.
The head drive control operation unit constitutes a part of the head
controller 12 shown in FIG. 1. In the driving of the plurality of nozzles
provided for the heads, the plurality of nozzles are divided into groups
each having several nozzles, the nozzles belonging to one nozzle group are
simultaneously driven, and the nozzle groups are sequentially driven. In
the following description, such a nozzle group is referred to as a
dividedly and simultaneously driven nozzle group.
The device 31 for storing the adjacent nozzle group printing period stores
the value of an adjacent nozzle group printing period which corresponds to
a time period between the dividedly and simultaneously driven nozzle
groups. This value is determined on the bases of data sent from the CPU 3,
etc., and set in the storage device in response to a signal WR. In
accordance with instructions of the print timing control unit 33, the
counter 32 for setting the adjacent nozzle group printing period generates
a period time signal based on the adjacent nozzle group printing period
stored in the device 31 for storing the adjacent nozzle group printing
period, and sends the period time signal to the printing timing control
unit 33 and the print dot number counter 35. The print dot number counter
35 which receives the period time signal from the counter 32 for setting
the adjacent nozzle group print period counts the number of nozzle groups,
and, when the counted number reaches the total nozzle number, informs the
print timing control unit 33 of this.
The print timing control unit 33 generates various timing signals. In
response to a clock signal and a gate signal from other control units, the
period time signal from the counter 32 for setting the adjacent nozzle
group printing period, and the signal indicative of the number of print
nozzle groups from the print dot number counter 35, the print timing
control unit 33 performs the following operations. The print timing
control unit 33 provides a counted value fetching instruction and a count
clock signal, to the counter 32 for setting the adjacent nozzle group
printing period and the counter 36 for setting the print drive pulse
width. The print timing control unit 33 instructs the print drive pulse
generating unit 34 to start the driving. The print timing control unit 33
provides an image data read clock signal to the image density detecting
unit 40, and outputs the same signal to the external. The print timing
control unit 33 provides a print data transfer clock signal to the print
data processing unit 41, and outputs the same signal to the print heads.
The print drive pulse generating unit 34 performs an ON/OFF control of a
drive pulse for the print heads, in response to the drive start
instruction from the print timing control unit 33 and the count end signal
from the counter 36 for setting the print drive pulse width. The counter
36 for setting the print drive pulse width fetches the drive pulse width
data selected by the data selecting device 37, in accordance with the
instruction from the print timing control unit 33, and performs the count
operation on the basis of the count clock signal from the print timing
control unit 33 until the counted value reaches the drive pulse width
data. Then, the counter 36 for setting the print drive pulse width
provides an end signal to the print drive pulse generating unit 34. The
data selecting device 37 selects either of the drive pulse width data
stored in the first storage device 38 and that stored in the second
storage device 39, depending on the image density information from the
image density detecting unit 40. The first and second storage devices 38
and 39 store the drive pulse width data which are to be set in the counter
36 for setting the print drive pulse width. These data are sent from the
CPU 3, etc., and stored in response to the signal WR.
The image density detecting unit 40 includes a print data buffer for
storing print data which are to be subjected to one division and
simultaneous driving operation, and detects the number of printing dots in
the print data buffer as the print density. Image data externally provided
are stored in the print data buffer in accordance with the image data read
clock signal supplied from the print timing control unit 33. Moreover, a
density reference value which is externally fed, e.g., from the CPU 3 is
fetched in accordance with the timing of the signal WR. The density
reference value is compared with the print density of the data stored in
the print data buffer, and the comparison result is supplied to the data
selecting device 37. The print data stored in the print data buffer are
fed to the print data processing unit 41. The print data processing unit
41 receives the print data from the image density detecting unit 40 in
accordance with the print data transfer clock signal supplied from the
print timing control unit 33, and transfers the print data to the heads.
When the information indicating that there is no data to be printed by the
dividedly and simultaneously driven nozzle group is sent from the image
density detecting unit 40, the print data processing unit 41 sets print
data to an arbitrary position corresponding to at least one nozzle in the
dividedly and simultaneously driven nozzle group. The data indicative of
the number of the nozzles and the nozzle positions are sent from the CPU
3, etc., and fetched in response to the signal WR.
FIG. 4 is a diagram showing the configuration of another embodiment of the
head drive control operation unit of the ink-jet recording apparatus of
the present invention. In the FIG. 4, 42, 43 and 44 denote second storage
devices. Elements similar to those of FIG. 3 are denoted by the same
reference numerals, and their description is omitted. The configuration
shown in FIG. 4 is different from that in FIG. 3 in the configuration of
the second storage device. In this embodiment, the second storage device
consists of three units of second storage device 42, 43 and 44. Therefore,
in the second storage device, a plurality of data pieces can be stored. In
the case where such plural units of second storage device are used, the
data selecting device 37 can select one among the data pieces respectively
stored in the first storage device 38 and the second storage devices 42,
43 and 44.
FIG. 5 is a diagram: showing the configuration of an embodiment of the
internal circuit of a head of the ink-jet recording apparatus of the
present invention. In the FIG. 5, 51 denotes a 4-bit shift register, 52
denotes a 4-bit latch, 53 denotes a 32-bit shift register, R1 to R128
denote heaters, T1 to T128 denote switching transistors, IV1 to IV128
denote inverters, and NA1 to NA128 denote NAND circuits. In FIG. 5, the
total number of the nozzles of the head is 128, and one nozzle group
consists of four nozzles, or the nozzles are divided into 32 groups to be
driven. The nozzles are provided with the heaters R1 to R128,
respectively. One end of each of the heaters R1 to R128 is connected to a
common power source. The other end of each of the heaters R1 to R128 is
grounded via the corresponding one of the switching transistors T1 to
T128. When one of the switching transistors is turned "ON", a current
flows through the respective heater, so that the nozzle is driven. The
switching transistors T1 to T128 are turned "ON" or "OFF" in accordance
with a logical product signal of the drive pulse and the print data which
are input to the respective NAND circuits NA1 to NA128. The logical
product signals are produced by the NAND circuits NA1 to NA128 and the
inverters IV1 to IV128.
The shift register 51 sequentially receives the print data from the print
data processing unit 41 in synchronization with the print data transfer
clock signal from the print timing control unit 33, and outputs parallel
print data corresponding to the four nozzles of one nozzle group. In
synchronization with the drive pulse from the print drive pulse generating
unit 34, the 4-bit latch 52 temporarily stored the print data from the
4-bit shift register 51, and outputs print data toward the nozzles. The
print data output from the 4-bit latch 52 are respectively input to the
NAND circuits corresponding to the nozzles in each nozzle group. More
specifically, a first data line from the 4-bit latch 52 is connected to
the NAND circuit NA1 corresponding to the first nozzle of the first nozzle
group, the NAND circuit NA5 corresponding to the first nozzle of the
second nozzle group, . . . , and the NAND circuit NA125 corresponding to
the first nozzle of the 32th nozzle group. The second data line is
connected to the NAND circuits corresponding to the second nozzles of the
nozzle groups. The third and the fourth data lines are connected to the
NAND circuits in the same manner. The 32-bit shift register 53 has output
lines corresponding to the nozzle groups. The output lines are
sequentially switched over by the shift operation, so that one nozzle
group is sequentially selected from the 32 nozzle groups, and a drive
| | |
