JPH0747698A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To enable enlargement of the gradation reproducing range without sacrifice of the reliability or cost of recording head when recording is effected by multiscan system in an ink jet recorder. CONSTITUTION:The ink jet recorder comprises a recording head 1-1 having a plurality of ports for jetting a light color ink and a recording head 1-2 having a plurality of ports for delivering a dark color ink. An image is formed by superposing a plurality of ink droplets jetted from a plurality of jet ports in the recording head substantially at one point and the gradation of picture element is represented by appropriate combination of the number and the density of a plurality of ink droplets.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus, and more particularly to gradation expression of a recorded image.

[0002]

2. Description of the Related Art In recent years, high resolution and high gradation have been demanded as a means for improving the quality of recorded images in an ink jet recording system. As a technique for enhancing gradation, a plurality of relatively small ink droplets (small droplets) are landed at substantially the same location on the recording material in a short time to form one pixel, and the number of ink droplets to be ejected is set. A so-called multi-droplet method is known in which gradation is expressed by changing the gradation. This multi-droplet method is a method that can obtain a high-density and high-gradation image in an inkjet recording method in which it is difficult to greatly modulate the size of one ink droplet.

However, in the conventional multi-droplet method, since one pixel is formed by continuously ejecting a plurality of times from the same ejection port, the volume of ejected ink droplets varies from ejection port to ejection port. If there are variations in the discharge direction and the discharge direction, these variations are reflected as they are on the image and appear as streaks (white streaks, black streaks) or density unevenness.

In order to avoid these problems, conventionally, it is necessary to precisely manufacture the recording head, which increases the manufacturing cost and reduces the yield.

Although a method for solving the above-mentioned problem of streaks and uneven density by using image processing has been proposed, a system for the above processing causes a cost increase and a change over time of the recording head. There was a problem that it was difficult to deal with.

Further, as a method for solving the above problem,
A so-called multi-scan method in which one pixel is formed by ink droplets ejected from a plurality of different ejection ports has also been proposed. However, the ink jet recording method that uses thermal energy and ejects ink along with the generation of bubbles generated by this causes the ejection volume to fluctuate due to the environmental temperature and the self-heating of the recording head accompanying recording, so it always responds to image signals It may not be possible to perform stable gradation recording for each pixel. That is, the volume of each droplet fluctuates due to the temperature change, and as a result, even if a pixel composed of a plurality of ink droplets is formed by multi-scan, the formed pixel may not exhibit a predetermined density. In such a case, for example, a difference in density between the left and right of the image or density unevenness for each scan width due to a density change for each scan occurs, and the image quality is degraded.

This tendency is remarkable when the number of gradations is increased in the multi-scan system or the burst system because the volume of the ink droplet must be reduced, and the droplet is reduced in size. Becomes
Volume fluctuation, discharge direction deviation, reliability (discharging recovery, etc.)
It is to promote the decrease of. In addition, it is often difficult to achieve multi-nozzle by the above method.

On the other hand, the conventional recording head is used as it is,
Although a method has been proposed in which the number of recording heads is increased to use dark and light inks, gradation is expressed by this, and graininess is reduced, the amount of ink shot increases, resulting in an increase in running cost. Increasing the occurrence of cockling, fixing problems, and the like, and pseudo contours that occur when switching between dark and light inks are problems.

[0009]

SUMMARY OF THE INVENTION A first object of the present invention is a technique capable of expanding the gradation reproduction range in the multi-scan system without lowering the reliability of the recording head and increasing the cost. The present invention is to provide an inkjet recording apparatus.

Another object of the present invention is to provide an ink jet recording apparatus which can reduce the pseudo gradation when switching dark and light ink, which is a problem of the gradation multi-valued system, by increasing the number of gradations. To do.

[0011]

Therefore, according to the present invention,
An inkjet that uses a recording head that has a plurality of ejection ports and ejects inks of the same color system but different densities, and performs recording by combining pixels formed by ejecting the inks on a recording medium. In the recording apparatus, a moving unit that relatively moves the recording head with respect to the recording medium and a movement of the recording head by the moving unit are controlled, and ejection from a plurality of ejection ports of the recording head is controlled, And a recording control means capable of forming a pixel by superposing a plurality of ejected ink droplets containing ink droplets having mutually different densities at substantially the same location on the recording medium.

[0012]

According to the above construction, a plurality of ink droplets ejected from a plurality of ejection ports land at substantially the same location to form a pixel. Since the ink droplets forming these pixels include inks having different densities,
The gradation range of pixels can be increased by combining the number of landed ink drops and the combination of darkness and lightness.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a perspective view of an ink jet recording apparatus applicable to the present invention.

In FIG. 1, reference numeral 1-1 indicates a recording head having 128 ejection ports, and a light ink (dye density:
(0.8%) is discharged. Reference numeral 1-2 similarly denotes a recording head having 128 ejection ports, which ejects dark ink (dye density: 3: 0%).
Reference numeral 4 denotes a carriage on which the recording heads 1-1 and 1-2 are mounted to move, and the movement of the carriage 4 has two guide shafts 5 which are slidably engaged at a part thereof.
It will be performed while being guided by A and 5B. Reference numerals 6-1 and 6-2 denote ink supply tubes for supplying the above-described light and dark inks to the recording heads 1-1 and 1-2 from an ink tank (not shown), respectively, and reference numerals 7-1 and 7-. Reference numeral 2 transmits a drive signal and a control signal to each head drive circuit provided in a part of the recording heads 1-1 and 1-2 from a main body device control unit (not shown) based on recording data (image signal). Shows a flexible cable for. The ink supply tubes 6-1 and 6-2 and the flexible cables 7-1 and 7-2 are both configured by members that can follow the movement of the carriage 4.

The carriage 4 has guide shafts 5A and 5B.
Connected to a part of a belt (not shown) provided in parallel with
The belt can be moved by being driven by a carriage motor (not shown). Reference numeral 3 indicates a platen whose longitudinal direction extends parallel to the guide shafts 5A and 5B, and reference numeral 2 indicates a recording medium such as recording paper. The recording heads 1-1 and 1-2 can perform recording by ejecting light and dark ink droplets onto the recording medium 2 as the carriage 4 moves.

A method of recording 9 gradations on plain paper using this apparatus will be described. The combination of dark and light ink will be described later with reference to FIGS. That is, recording is performed by changing the number of ink droplets per pixel within a range of 0 to 4 (ink ejection amount per pixel: within a range of 30 to 90 (ng / dot)).

2 and 3 are conceptual diagrams for explaining the recording method of this embodiment.

In the figure, 1-1 (1-2) is a schematic representation of a recording head, and the recording head 1-1 (1-2)
As described above, 128 discharge ports for light (dark) ink are arranged in the vertical direction of FIG. For convenience, the discharge port numbers are numbered from top to bottom in the figure. 1, No.
2, ..., No. 128.

First, in the first scan (scan), both the dark ink head 1-2 and the light ink head 1-1 are used for the respective No. 97 to 128 (No. 97 'to N
o. Recording is performed while moving the carriage in the main scanning direction at a speed of about 282 mm / sec using only the ejection openings 128 ').

As a result, as shown in FIG. 3A, the 1st to 32nd pixels at the upper end of the recording medium are first recorded with dark ink as ink droplets of 0 or 1 based on the image signal, and immediately after that, light pixels are printed. Ink will be recorded with 0 or 1 ink drops. It should be noted that FIG. 3 illustrates pixel formation using only one of dark ink and light ink.

Next, the recording medium is moved upward by 32 pixels (sub-scanning direction, arrow direction in FIG. 2), and the recording heads 1-1,
1-2 using No. From 65 (No. 65 ') to 128
Recording is performed using the (128 ') ejection port. As a result,
As shown in FIG. From 65 (65 ') to 96
The discharge port of (96 ′) was No. 97 (97 ') to 1
The 1st to 32nd pixels recorded by the 28 (128 ') discharge port are recorded, and the No. 97 (97 ') to 128 (12
The 8 ') ejection port newly records the 33rd to 64th pixels. As a result, the 1st to 32nd pixels are recorded with the number of ink drops from 0 to 2 per pixel.

Next, the recording medium is moved upward again by 32 pixels and No. Recording is performed using 33 (33 ') to 128 (128') ejection ports. As shown in FIGS. 3C and 3D, if the recording is sequentially repeated in the same manner as described above, when the fourth recording is completed, the 1st to 32nd pixels have 0 to 4 drops for each of the dark and light inks. Since recording is performed with ink, recording with 9 gradations can be obtained. If recording is repeated from the fifth time onward in the same manner as above, an image with 9 gradations is obtained over the entire surface. Contrary to the start of recording, at the bottom end of the image, 32 nozzles are sequentially stopped from the lower side for each scanning to form the image end.

The image thus obtained, for example, 1
Focusing on the second pixel, this pixel has a discharge port No.
1 (1 '), 33 (33'), 65 (65 '), 97
(97 ′) is formed by ink droplets of 0 or 1 which are respectively ejected from a total of 4 ejection openings, so that the variations in the ink droplet capacities of the ejection openings are averaged and an image with no noticeable streaks or unevenness is obtained. You can

When various images are recorded using the above recording method, the gradation is higher than that of the conventional one in which a plurality of ink droplets are ejected from the same ejection port (multi-droplet method). Excellent, high-definition images without streaks and unevenness were obtained. In addition, as a result of performing an environmental test from a low temperature and low humidity environment (15 ° C / 10%) to a high temperature and high humidity environment (35 ° C / 90%) as an environmental condition by using the recording method of the present example, fixation, ejection It was found that the response performance and the like, that is, the performance of preventing the recording head from being clogged and twisted, are equivalent to or better than those of the conventional recording head.

Next, the recording head driving method according to this embodiment will be described.

A so-called pulse width modulation driving method is used for driving the recording head. In the driving pulse shown in FIG.
V _OP is the drive voltage, P ₁ is the preheat pulse width, P ₂ is the interval time, and P ₃ is the main heat pulse width. T ₁ , T ₂ and T ₃ indicate times for determining P ₁ , P ₂ and P ₃ . The voltage V _OP is an index of electrical energy required to generate thermal energy, and is the area, resistance value, film structure of the electrothermal conversion element (hereinafter, also referred to as ejection heater), film structure, ejection port of the recording head, ink path structure. Is determined by

The pulse width modulation driving method is based on P ₁ , P ₂ , P ₃
Pulse is given in order. P ₁ represents the width of the preheat pulse, and mainly controls the ink temperature distribution and viscosity distribution in the nozzle. The width P ₁ (which also controls P ₂ and P ₃ at the same time) is controlled according to the temperature detection using the temperature sensor of the recording head. At this time, the width is set so that the ejection heater does not excessively apply thermal energy and pre-foaming or bubble through phenomenon occurs in the ink. The interval time P ₂ has a function of providing a constant time interval so that the pre-heat pulse and the main heat pulse do not interfere with each other, and controlling and equalizing the temperature distribution of the ink in the ejection port. The main heat pulse causes a bubbling phenomenon on the ejection heater due to its width P ₃ to eject an ink droplet from the ejection port. These pulse widths can be determined by the area of the ejection heater, the resistance value, the film structure, the ejection port of the head, the ink path structure, and the physical properties of the ink.

FIG. 5 shows the structure of the recording head according to this example. The driving condition of the light ink in the environment of the head temperature T _H = 25.0 (° C.) is V _OP = 15.0 (V). P ₁ =
1.0 (μsec), P ₂ = 4.0 (μsec), P ₃
When a pulse of 2.0 (μsec) is given, optimum driving conditions are set and a stable ink ejection state is obtained. The ejection characteristic at this time is that the ink ejection amount V _D = 4.7.
(Ng / dot), discharge speed V = 14.0 ± 0.2 (m
/ Sec). The driving condition for dark ink is V _OP = 1
When 5.0 (V), P ₁ = 1.2 (μsec), P ₂ =
When a pulse of 4.0 (μsec) and P ₃ = 2.0 (μsec) is given, optimum driving conditions are established and a stable ink ejection state is obtained. The ejection characteristic at this time is the ink ejection amount V
_D = 5.0 (ng / dot), discharge speed V = 15.0 ±
0.2 (m / sec). The reason why the driving condition is changed depending on the shade is to reduce the granularity of dots in the highlight portion in the present embodiment, and it is possible to optimize it according to the resolution, the number of gradations, the ink, the recording medium, etc. Well this is not the case.

Incidentally, the maximum ink ejection amount per pixel (determined by the combination of dark and light inks) is about 90 (ng / dot) with 8 drops, and the maximum drive frequency of the recording head is fr = 4.0 KHz, which is 360 dpi. With a resolution of 128, and 128 outlets are divided into 16 blocks and 1 Bl
Drives sequentially from the lock.

That is, the first block is 1, 2, 3, ..., 8 The second block is 9, 10, 11, ..., 16 ... ...
The blocks are sequentially driven in the order of first, second, third, ..., Sixteenth.

Next, the ejection amount control method using the preheat pulse width P ₁ (or the interval P ₂ can be similarly controlled) will be described in detail.

FIG. 6 shows the relationship between the preheat pulse width P ₁ and the ejection amount V _{D under} the condition that the head temperature (T _H ) is constant.

As shown in the figure, as the pulse width P ₁ increases, the width up to the width P _1LMT is linear (However, this is not the case depending on the design of the recording head and the setting of the main pulse width P ₃ . In some cases, a preheat pulse longer than that causes pre-foaming (or a bubble-through phenomenon; a phenomenon in which bubbles communicate with the atmosphere before ink droplet ejection), and foaming of the main heat pulse is disturbed. Further width P
_When it exceeds _1MAX , the discharge amount tends to decrease.

As described above, the ejection amount can be changed by appropriately setting the value of the preheat pulse width P ₁ .

FIG. 7 shows the relationship between the head temperature T _H (environmental temperature T _R ) and the ejection amount V _{D under} the condition that the preheat pulse width P ₁ is constant. As shown in FIG. 7, it tends to increase linearly as the head temperature T _H increases.

The coefficients of the regions showing the linearity in FIGS. 6 and 7 are the preheat pulse dependence coefficient of the discharge amount: K _P = ΔV _DP / Δ
P ₁ (ng / μs · dot) Head temperature dependence coefficient of ejection amount: K _TH = ΔV _DT / ΔT _H (n
g / C ・ dot).

In the case of the recording head structure shown in FIG. 5, K
_P = 1.5 (ng / μsec · dot), K _TH = 0.0
5 (ng / deg · dot).

When these two relations are effectively used as described below, the head temperature changes due to various factors such as a change in environmental temperature and a change due to self-heating accompanying recording, as shown in FIG. Even in this case, it is possible to provide a method of controlling the ejection amount that can always keep the ink ejection amount constant.

The discharge amount control shown in FIG. 8 is constructed under the following three conditions.

1) T _H ≦ T ₀ The ejection amount compensation at low temperature is performed by temperature control using a sub heater of the recording head.

Here, T ₀ is the target temperature for the above temperature control.

2) T ₀ <T _H ≤T _{L The} ejection amount control is performed by the above-mentioned pulse width modulation method (hereinafter also referred to as PWM).

3) T _L <T _H (<T _C ) A single pulse is used to control this width.

The control shown in 1) above is mainly for securing the ejection amount in the low temperature environment in the temperature control region shown in FIG. 8, and is performed when the recording head temperature T _H = 25.0 ° C. or less. By keeping the head temperature T _H constant at the controlled temperature T ₀ = 25.0 (° C.), the ejection amount V _D0 = 5.0 (ng / d when T _H = T ₀ ).
ot). The temperature control temperature T _{0 is set} to 25.0 ° C. in order to eliminate adverse effects caused by temperature control, such as ink thickening, ink sticking, or temperature control ripple. Each pulse width at this time is P ₁ / P ₂ / P ₃ = 1.0 / 4.0 / 2.0
(Μsec).

The control shown in 2) is performed in the PWM region shown in FIG. 8 and when the head temperature T _H is between 26.0 ° C. and 56.0 ° C. That is, the temperature sensor detects the self-temperature rise or the environmental temperature change due to recording, and the preheat pulse width P ₁ is changed every 2.0 ° C. according to the table shown in FIG. 9 for each block. This control follows the sequence shown in FIG. A temperature sensor for detecting the temperature may be provided for each block, and in this case, more accurate control can be performed.

In this sequence, in order to prevent erroneous head temperature detection and more accurate temperature detection, step S8 is performed.
2 in the last three temperature _{(T n-3, T n} -2, T n-1) and newly detected temperature T _n of the temperature averaged by adding the head temperature _{T n = (T n-3} + T n- ₂ + T _n-1 + T _n ) / 4. In the next step S83, the previous average value T _n-1
And a head temperature T _n measured this time are compared and determined with a predetermined value ΔT, and if the relationship between the difference and the predetermined value ΔT is (1) | T _n −T _n-1 | ≦ ΔT, the temperature is Change ±
Since the change is within ΔT ° C and is within the range of one table, the pulse width of P ₁ is not changed (step S85).

(2) When T _n -T _n-1 > ΔT, the temperature change is shifted to the high temperature side, so the table is lowered by _one to narrow the pulse width of P ₁ (step S86).

(3) When T _n -T _n-1 <-ΔT, the temperature change is shifted to the low temperature side, so the table is moved up by ₁ to widen the pulse width of P ₁ (step S84).

Here, the table allows only one change.

Control is performed while changing the table as described above. The cycle (feedback time) T _F for changing one table during recording is 20 msec.

Therefore, the recording time required for one line (about 8
(00 msec), it is possible to change the table about 40 times independently for each outlet block, so it is possible to cope with the temperature rise of 30.0 deg at the maximum and reduce the occurrence of density change. ing.

The use of the average of four times for temperature detection is to prevent erroneous detection due to prevention of sensor noise and interference with other blocks, and to perform feedback smoothly.
This is because the density change due to the control is minimized and the density change (connection unevenness) in the connection by the serial recording method is inconspicuous.

When this discharge amount control method is used, the target discharge amount V _D0 of plain paper is 5.0 (ng / do) within the above temperature range.
Control is possible within a range of ± 0.08 (ng / dot) with respect to t). Therefore, even at the time of maximum ink ejection,
± 1.28 with respect to V _D0 = 80.0 (ng / dot)
The control becomes possible within the range of (ng / dot). If the discharge amount variation within this range is accommodated, the density variation occurring during recording of one sheet can be suppressed to about ± 0.05 even in the case of 100% duty recording, which is remarkable in the serial recording method. Occurrence of density unevenness and connecting lines are not a problem.

If the average number of times of temperature detection is increased, the temperature becomes stronger against noise and the like, and a smoother temperature change can be made, but conversely, in real-time control, the detection accuracy is impaired and accurate control cannot be performed. Further, if the average number of temperature detections is reduced, the temperature becomes weaker and a sudden change occurs, but conversely, in real-time control, the detection accuracy increases and accurate control becomes possible.

Next, in the control shown in 3) above, the drive pulse is a single pulse, and the self-heating suppression control is performed by this pulse width modulation. As a result, the amount of heat generated by recording can be reduced as much as possible. This control area is the head temperature T _H
= 56.0 ° C or higher is assumed, and this temperature is
For example, the temperature reached momentarily when recording continuously at 100% duty, but the head structure design and head driving conditions are set so that the entire head temperature (A ₁ substrate base temperature) does not always reach this temperature. ing. In the unlikely event that this state occurs continuously, it is determined to be a high temperature abnormal state, and the high temperature abnormal operation process is performed by using a known technique such as suction and stop, which is a countermeasure.

The control sequence of the area shown in 1) above will be described below. In this embodiment, control is performed using sub-heaters arranged on the left and right of the ejection port side of the recording head substrate and sensors arranged in the immediate vicinity thereof.

FIG. 11 shows the positional relationship between the temperature sensor, the sub heater and the discharge heater.

For the temperature detection, an average value of four times is used as in the above pulse width modulation method. At this time, the head temperature T _H
Uses the average value of the temperature T _L and T _R which has detected the temperature sensor 20A, the 20B and _{(T H = (T L +} T R) / 2). Depending on the detected temperature, the sub heaters 30A, 30B
At the same time, a voltage V _OP equal to that in the case of the discharge heater is applied, and at the same time, a short pulse having a width that does not cause discharge to the discharge heater is continuously applied until the target temperature is reached, and temperature control is performed in a short time. The short pulse heating condition in this example is the driving frequency:
f = 8 (KHz), drive voltage: V _OP = 15.0 (V),
The pulse width is P _W = 0.5 (μsec), and after the target temperature is reached, only the temperature control by the sub heater is switched. This is to suppress deterioration of the ejection heater due to short pulses. The control method by the sub-heater is basically an on / off method. That is, the target temperature T
Maximum power until reaching ₀ = 25.0 ° C (1.
2W) is turned on, the current is cut off when the target temperature is reached, and the current is passed when the target temperature is decreased. The cycle of this control is 40m
sec. When this timing is lengthened, the width of the ripple is increased and the cycle of temperature change is extended. Further, if this timing is shortened, the width of ripple becomes small and the above cycle becomes short. With this method, the temperature control ripple width at the target temperature is about 2 ° C., but since temperature detection based on four-time averaging is used, the temperature control ripple has almost no effect on the discharge amount control. If necessary, an expensive control method such as PID control may be used.

The image density (reflection density OD for each gradation of 0 to 16) on plain paper recorded by the monochrome recording ink jet recording apparatus of the present example by the temperature control method shown in FIG. 8 and each environment (low temperature and low humidity: (5 From (.degree. C./10%) to high temperature and high humidity: (35.degree. C./90%)), almost no density change (including print duty) within the page occurs.
By the way, the dye concentration of the ink is 3.5%.

As can be seen from the above description, an image having no streaks or unevenness is obtained which has very little change in density due to ambient temperature or recording temperature rise and has gradation reproducibility.

(Embodiment 2) FIG. 12 is a perspective view of an ink jet recording apparatus according to a second embodiment of the present invention.

In this example, the present invention is applied to a high speed full color printer. 4 on special paper using this device
A method of performing full-color recording of 9 gradations using dark and light inks of each color (Bk, C, M, Y) will be described below.

The ejection order of the recording heads of the respective colors is as follows: black Bk1 (dark) and Bk2 (light), cyan C1 (dark).
And C2 (light), magenta M1 (dark) and M2
(Light), Y1 (dark) and Y2 (light) for yellow (however, in order to form one pixel by four scans, the ink landing order at each pixel is the image signal and the dark and light ink and drop). It is not limited to this because it depends on the gradation data of the number of let.). In order to express gradation, the number of ink droplets of each color per pixel is changed in the range of 0 to 4 for recording.

The recording heads Bk1, C1, M1 and Y1 of this example have 512 ejection ports, and N from the lower end.
o. 1 to 256 heads (Bk1-1, C1-1,
M1-1, Y1-1), No. 257 to 512 are light ink heads (Bk1-2, C1-2, M1-
2, Y1-2).

The recording method of this example will be described below with reference to FIGS. 13 and 14.

First, in the first scan, No. 1 to 6
Carriage about 5 carriages in the main scanning direction using only 4 ejection ports
Recording is performed while moving at a speed of 08 mm / sec.

For simplification, one color will be described here. As a result, as shown in FIGS. 13A and 14, the 1st to 64th pixels on the recording medium are recorded with 0 or 1 ink droplet of dark ink based on the image signal.

Next, the recording medium is moved upward by 64 pixels,
No. Recording is performed using 1 to 128 ejection ports. As a result, as shown in FIG. 13 (B) and FIG. 6
Nos. 5 to 128 are the same as the previous No. The 1st to 64th pixels recorded respectively from the 1 to 64 ejection ports are recorded,
No. The 1st to 64th ejection ports newly record the 65th to 128th pixels. As a result, the dark ink is recorded with the number of ink drops of 0 to 2 on the first to 64th pixels, respectively.

Next, the recording medium is moved upward again by 64 pixels and No. Recording is performed using the ejection ports 1 to 192.
As shown in FIGS. 13C, 13D, and 14, when the same recording as described above is sequentially repeated, when the image formation with the dark ink is completed and the fourth recording is completed, the first to 64th recording is completed. A pixel will be recorded with 0-4 drops of ink. From the fifth time onward, four scans were performed in the same manner as above, and the light ink No. Recording with the ejection ports 257 to 512 is repeated. As a result, as shown in FIG. 14, the 1st to 64th pixels are recorded with 0 to 4 drops of light ink, and a total of 8 drops of dark and light ink, that is, recording of 9 gradations is obtained.

When recording is performed in this order based on the image data, an image with 9 gradations is obtained over the entire surface. On the contrary to the start of recording, at the lower end of the image, the discharge is sequentially stopped from the bottom by 64 discharge ports for each scanning to form the image end.

Focusing on, for example, the first pixel of the image obtained in this manner, this pixel has a discharge port No.
1,65,129,193,257,321,385
By using 0 or 1 ink droplets respectively ejected from a total of 8 ejection outlets of 449, reduction of graininess due to light ink, maximum density due to dark ink, and averaging of variations in ink droplet volume at each ejection port are achieved. As a result, it is possible to obtain an image with high gradation and high contrast with no noticeable stripes or unevenness.

The number of dark and light ink droplets for realizing each gradation is determined according to the density distribution table shown in FIG. 15, and the result of the combination is shown in FIG.
It becomes what is shown in (A)-(C). That is, the number of ink droplets of each light ink is ejected up to 1 to 4 gradations and 5
Up to 7 gradations are combinations of dark ink and light ink, and the maximum 8 gradations are for discharging and recording dark ink.

Although one color has been described above, other colors may be similarly discharged, and a full color image is recorded by discharging all colors.

When various images were recorded using the above recording method, as compared with the conventional multi-droplet method,
The number of gradations can be increased without lowering the reliability of the recording head, and an extremely high-definition, high-contrast image without streaks and unevenness can be obtained.

Next, the features of the ejection drive control method of this embodiment will be described.

Basically, the same drive system as that of the first embodiment is adopted, but since the length of the recording head is long and the distributed block drive system as described below is used, feedback by a plurality of temperature sensors is performed. In this method, it is often difficult to control the discharge amount stabilization corresponding to each discharge port. Therefore, it is necessary to eliminate the head temperature distribution in the ejection port array direction.

The pulse width modulation driving method is used for driving the recording head, and a description thereof is omitted here. In the recording head of this example, the driving conditions for the dark and light inks are the same, and the dark and light inks in FIG.
(A) has the same head structure shown in _{~ (C), V OP =} 20.0 at ambient head temperature T _H = 35.0 (℃)
When (V), P ₁ = 1.0 (μsec), P ₂ = 4.0
When a pulse of (μsec) and P ₃ = 3.0 (μsec) is given, optimum driving conditions are established and a stable ink ejection state is obtained. The ejection characteristic at this time is that the ink ejection amount V _D =
8.0 (ng / dot), discharge speed V = 14.0 ± 0.
It was 2 (m / sec). By the way, the maximum ink ejection amount per pixel is about 32 (ng / do) with 4 drops.
t), the maximum drive frequency of the recording head is fr = 8.0 KH
z, which has a resolution of 400 dpi, 512 ejection ports are dispersedly divided into 8 blocks (1 block: 64 segments), and are sequentially driven in the following order.

That is, the first block is 1, 9, 17, ..., 489, 49
7,505 The second block is 2,10,18, ..., 490,4
98,506 ······· The eighth block is 8,16,24, ..., 496,5
No. 04, 512, and the driving order is distributed driving in the order of the first, fourth, seventh, second, fifth, eighth, third and sixth blocks.

In the first embodiment, control is performed so that no pulse is applied to the ejection port having no ejection signal (P ₁ and P _3).
= 0 (μsec)), but in the present embodiment, a pulse that does not eject is continuously supplied to an ejection port having no ejection signal. 1) If there is an image signal, a normal pulse is given.

Pulse condition: P ₁ (PWM) / P ₂ / P ₃ 2) When there is no image signal, P ₁ (P ₃ = 0: control not to give foaming or ejection without giving main pulse. Yes.)

In the control of 2), pulse width modulation of a single pulse of P ₁ only when there is no discharge signal (the same pulse width as that of the discharge port having a discharge signal: P ₁ (PWM) is added)
The same heating control as the single pulse heating by the control is performed, and the temperature is controlled so as to minimize the temperature difference between the ejection port or the ejection port group having the ejection signal and the ejection port or the ejection port group having no ejection signal. is there. Further, in order to reduce the amount of heat generated by heating by the preheat pulse width P ₁ as much as possible, the device is devised so that P ₁ is PWM-controlled according to the head temperature in the same manner as the ejection port where the ejection signal is generated.

The control sequence of this embodiment is performed using the left and right temperature sensors, as in the first embodiment. Further, the temperature is detected by using an average value of four times as in the above-mentioned discharge amount control method.

That is, the head temperature T _H is the temperature T _HL , T detected by the sensors arranged on the left and right every 10 (ms).
_HR is read and these average values ( _TH = ( _THL + _THR ) /
2) is calculated. Next, the temperature of the past three times (T _n-3 , T
_n-2 , T _n-1 ) and the newly detected temperature T _n are added and the averaged temperature is calculated as head temperature T _n = (T _n-3 + T _n-2 + T _n-1)
+ T _n ) / 4. Further, based on this value T _n , the pulse width P ₁ is determined by referring to the table similar to FIG.

Next, after the presence or absence of the ejection signal of each ejection port is judged, the ordinary divided pulses: P ₁ , P ₂ , P ₃ are given to the ejection port having the ejection signal, and the ejection port having no ejection signal is given. For, only the preheat pulse: P ₁ is given.

The time (feedback time) required to change one table during the above sequence is T _F
= 20 msec. Therefore, one line (about 400m
sec), it is possible to change the table about 20 times independently for each block, and it is possible to reduce the occurrence of concentration change corresponding to a temperature rise of 20.0 deg at the maximum.

(Embodiment 3) FIG. 18 is a plan view showing a circuit on a substrate of a recording head according to this embodiment. In addition, FIG.
FIG. 3 is an exploded perspective view of a recording head according to this example.

Using this apparatus, four colors (Bk,
A method of performing full-color recording of 5 gradations for each of C, M, and Y) will be described. That is, the number of ink droplets of each color per pixel is in the range of 0 to 4 (range of ink ejection amount per pixel, 1 color: 12 to 48 (ng / dot): provided that the maximum ink ejection amount is 96 per image. (Ng /
dot); 2.0 colors (for R / G / B printing) are suppressed by pixel processing. ) To change and record.

This recording head, as shown in FIG.
The four colors of Bk, C, M, and Y are configured to be recorded by one recording head.
By using one piece, the same operation as that of light and shade + multi-pass can be performed by one scanning. That is, the first two recording heads eject the dark ink of each color, and the remaining two recording heads eject the light ink.

The number of ejection ports for each color in one recording head is Bk: 64, C: 24, M: 24, Y: 24. An A ₁ sensor is used as the temperature sensor 20, and Bk
One is arranged between the discharge port arrays of C and C. This A ₁ sensor 2
0 is used to monitor the average temperature of the recording head, and the temperature in the vicinity of the ejection port for each color is calculated from the separately provided dot count for each color and is independently controlled. Therefore, one sensor can control a plurality of colors at the same time.

In the apparatus used in this embodiment, the maximum drive frequency of the recording head is fr = 8.0 KHz (actual drive is 5.4 KHz) and has a resolution of 360 dpi.

First, the black: 64 discharge ports are divided into 8 blocks, and the first block (1, 9, 17, 25, ...
.., 57 segments) to the second, ..., Eighth block sequentially.

The drive interval of each block is 8.5 (μse
It is set to c). This block interval is set in order to obtain linearity especially when recording vertical ruled lines by using 1 to 8 segments in the above-mentioned distributed division driving. 8 × 8.5 (μsec) up to segment = 68 (μse
Carriage speed: 381 for the ejection time difference of c)
The misalignment of the dots ejected from the recording head that moves at (mm / sec) does not occur. Desirably, half of the resolution: in the case of (360 dpi) that needs to be suppressed to about 35 (μm) or less. It is preferable to use such a recording head because the color order of the ejected ink does not change even when reciprocal recording is performed. It should be noted that the order of shading does not easily relate to the tint. The 24 ejection ports for each of cyan, magenta, and yellow are divided into three blocks and driven in the same manner.

Further, the color image recording method of this example will be described with reference to FIG.
It shows in 0.

In the first scan, Bk (N1 / N2, T
1 / T2: Hereinafter, Ni represents dark ink, and Tj (i, j
= 1, 2) represents light ink), and the first line (1 pass) is recorded using only 24 ejection ports. Here, 5 gradations are recorded for each color by combining dark and light inks based on the image density signal.

In the same manner, the recording paper is shifted by 24 ejection ports in the same manner, and in the second scan, C (N1 / N2, T
1 / T2) is recorded using only eight ejection ports. 2 pass is also B
Recording is performed with 24 ejection ports of k (N1 / N2, T1 / T2). Further, the recording paper is shifted by 24 ejection openings, and in the third scan, the 1st pass is printed by 16 ejection openings of C (N1 / N2, T1 / T2), and at the same time, the 3rd pass is Bk.
(N1 / N2, T1 / T2) 24 outlets, 2 passes are C
Recording is performed with eight (N1 / N2, T1 / T2) ejection ports.

Similarly, in the fourth scan, M (N
Recording is performed with 24 discharge ports of 1 / N2, T1 / T2), 4 passes are 24 discharge ports of Bk (N1 / N2, T1 / T2), and 3 passes are 8 discharges of C (N1 / N2, T1 / T2). The exit and 2 passes are recorded with 16 ejection openings of C (N1 / N2, T1 / T2).

The recording paper is shifted by 24 ejection ports, and one pass of Y (N1 / N2, T1 / T2) is made for one pass in the fifth scan.
Recording with 6 ejection ports and 5 passes for Bk (N1 / N
2, T1 / T2) 24 outlets, 4 passes are C (N1 / N
2, T1 / T2) 8 outlets, 3 passes are C (N1 / N)
2, T1 / T2) 16 outlets, 2 passes are M (N1 / N)
(2, T1 / T2) is recorded with 24 ejection ports.

The recording paper is shifted by 24 ejection ports, and in the sixth scan, one pass is Y (N1 / N2, T1 / T2) 8 times.
Recording at the discharge port, and 6 passes for Bk (N1 / N
2, T1 / T2) 24 discharge ports, 5 passes are C (N1 / N
2, T1 / T2) 8 outlets, 4 passes are C (N1 / N
2, T1 / T2) 16 outlets, 3 passes M (N1 / N)
2, T1 / T2) 24 outlets, 2 passes Y (N1 / N)
(2, T1 / T2) 16 ejection ports for recording.

According to the above method, data is distributed in order from the first recording head by a data distribution circuit (not shown) so that the data is evenly distributed to the respective recording heads, and four-pass recording is performed using the four recording heads. Further, this embodiment is characterized by the head drive control method and the printing method. A distributed block drive / divided pulse (double pulse) drive method is used for driving the head, and the same control as in the first embodiment is performed.

The pulse width modulation drive control method of this embodiment is
A pulse is applied in the order of P ₁ , P ₂ , and P ₃ , and P ₁ is based on the output value from the temperature sensor 20 of A ₁ and the head temperature _TH (K · C · M · Y) described above. After the pulse width is determined before the start of recording and the recording is started, the driving is performed based on the data obtained through the dot counter, that is, the data of the print head temperature rise (ΔT (K · C · M · Y)). The PWM drive method is used in which the drive is performed while changing the conditions. The method of controlling the ejection amount by P ₁ is the same as that of the first embodiment, and therefore the description thereof is omitted here.

By the way, the coefficient of the region showing each linearity is the preheat pulse dependence coefficient of the discharge amount: K _P = ΔV _DP / Δ
P ₁ (ng / μs · dot) Head temperature dependence coefficient of ejection amount: K _TH = ΔV _DT / ΔT _H (n
g / C ・ dot).

In the structure of the recording head shown in FIG. 18,
The above coefficient is

[0104]

[ _Formula 1] K _PBk = 8.25 (ng / μsec · dot) K _THBk = 0.7 (ng / μsec · dot) K _PCMY = 4.12 (ng / μsec · dot) K _THCMY = 0.36 ( ng / μsec · dot).

As for the ejection characteristics of the recording head driven by using the driving method as described above, in the case of black, V _OP = 2 in the environment of head temperature T _H = 25.0 (° C.)
When 5.6 (V), P ₁ = 1.25 (μsec), P ₂
= 2.0 (μsec) and P ₃ = 2.50 (μsec), optimum driving conditions are obtained and a stable ink ejection state is obtained. The ejection characteristics at this time are: ink ejection amount V _D = 20.0 (ng / dot), ejection speed V = 1
It was 4.0 (m / sec).

As for the ejection characteristics, in the case of color, V _OP = 2 in the environment of head temperature T _H = 25.0 (° C.) for each color
When 5.6 (V), P ₁ = 1.00 (μsec), P ₂
= 2.0 (μsec) and P ₃ = 2.00 (μsec), optimum driving conditions are achieved and a stable ink ejection state is obtained. The ejection characteristics at this time are as follows: ink ejection amount V _D = 10.0 (ng / dot), ejection speed V = 1
It is 4.0 (m / sec).

Next, a method for simultaneously independently driving a plurality of colors with one sensor in this embodiment will be described.

The ink jet printer shown in FIG.
The number of dots for one line for each color of a recording signal such as characters and images sent from a host computer (not shown): about 300
A counter for independently counting 0 pixels x the number of ejection openings of each color is provided. It also has the function of counting the number of dots per unit time. Based on the value counted by this counter, the temperature rise of the discharge port of each color per unit time is previously calculated and determined by a table: T _DOT (K, C, M, Y) (this embodiment) Then, the calculation was performed assuming that the temperature rise of each color does not affect the other colors, but it is known from the experimental data that the influence of the other colors can be ignored. Since the temperature rises affect each other and become complicated and there are few other influences from the experimental results, they were made independent, but they may be created considering other influences in calculation). The ejection amount of each color is controlled independently according to the sequence shown in FIG.

Here, a method of simultaneously controlling four colors with one temperature sensor will be described in detail.

As shown in FIG. 18, the recording head has A ₁
One temperature sensor 20 is installed at the center.

First, the sensor 20 is used to detect the temperature every 5 msec, and the average of 10 times of this detection is set as the head temperature. Next, the ejection port temperature of each color is initialized based on this temperature. Furthermore, the ejection signals for each ejection port of each color are counted for 50 msec, and these are counted as N _Ki , N _Ci ,
N _Mi and N _Yi .

The time interval used here is preferably set so that the temperature rise of the head is substantially constant no matter what pattern is printed in this time interval.

Next, the ratio to the total number of dots (N _K0 , N _C0 , N _M0 , N _Y0 ) for 50 msec for each color: α _ji
(Discharge duty) is calculated.

[0114]

[ _Mathematical formula-see original _document ] α _Ki = N _Ki / N _Ko α _Ci = N _Ci / N _Co α _Mi = N _Mi / N _Mo α _Yi = N _Yi / N _Yo Furthermore, the above ratio: α _{ji is} preliminarily tested and calculated. The relationship between the printing ratio: α _ji and the temperature rise: ΔT _{ji obtained in step 1} is converted into the ejection port temperature for each color.

[0115]

## _EQU00003 ## T _Ki = T _B0 + ΔT _Ki T _Ci = T _B0 + ΔT _Ci T _Mi = T _B0 + ΔT _Mi T _Yi = T _B0 + ΔT _Yi Next, the driving parameter corresponding to the above temperature of each color, that is, the pulse width P ₁ (T _ji ) is assigned by the PWM table.

Thereafter, the above sequence is repeated every 50 msec to set the drive parameters according to the ejection signal of each color.

Even in the complicated recording method as described above,
When the above control method is used, even if various patterns are printed, it is possible to change the driving conditions for each color according to the ejection duty of each row and keep the ejection amount constant. Printing with no change and excellent gradation and color reproducibility is possible.

In this embodiment, the above control method is adopted,
From low temperature and low humidity environment (15 ℃ / 10%),
Results of recording test under high temperature and high humidity environment (35 ° C./90%) Bk driving condition: P ₁ : PWM (P ₁ = 1.25 (μ when T _H = 25 ° C.)
_{sec)) P 2: 2.00 (} μsec) P 3: 2.50 (μsec) ( provided that the discharge amount under the condition of changing at individual difference of the _{head): V dBk = 20.0 ± 1.0} (ng / Dot)
(Between pages / inside) Reflection density fluctuation: OD _BK = 1.35 ± 0.05 (between pages / inside). However, the data is after 4 scans printing (4 drops printing).

C, M, Y drive conditions: P ₁ : PWM (P ₁ = 1.00 (μ at T _H = 25 ° C.
sec)) ※ feedback by the temperature sensor of the head control method _{P 2: 2.00 (μsec) P} 3: 2.00 (μsec) ( provided that the discharge amount under the condition of changing at individual difference of the _head): V dCMY = 10.0 ± 0.75 (ng / dot) Reflection density fluctuation: OD _C = 1.20 ± 0.05 (between pages / inside) Reflection density fluctuation: OD _M = 1.20 ± 0.05 (between pages / inside) inner) reflection density variation: became OD _Y = 1.15 ± 0.05 (in the inter-page-). However, the data is after 4 scans printing (4 drops printing).

As described above, very stable density stability, gradation reproducibility, and even image characteristics were exhibited. In addition, even when reciprocal recording was performed, good image characteristics were exhibited without a change in color tone or a connecting line due to serial recording.

In each of the above embodiments, the PWM control of P ₁ is performed in the discharge amount control method, but the same effect can be obtained by PWM control of P ₂ , so either P ₁ or P ₂ is used. You may control it. Further, P ₃ may also be modulated depending on the ambient temperature and other conditions. Further, temperature control or the like may be performed at the same time in order to further increase the variation range of the discharge amount.

Further, in the above embodiment, the gradation is expressed by using two kinds of ink, dark ink and light ink, but the dye density of the ink may be further divided to increase the number of gradations. The combination of dark and light ink and the number of ink drops can be determined in relation to the gradation reproducibility within the range of the maximum ink ejection amount. Further, the number of gradations can be further increased in combination with pseudo gradation, and the gradation distribution table may be non-linear.

Further, in the above embodiment, the number of ink droplets of dark and light inks is set by using the distribution table, but it may be set by the host computer or other control device, and the gradation can be reproduced. Any known method can be used as long as it is available.

(Others) The present invention is provided with a means (for example, an electrothermal converter or a laser beam) for generating heat energy as energy used for ejecting ink, particularly in the ink jet recording system. The present invention brings about excellent effects in a recording head and a recording apparatus of the type in which the state of ink is changed by the heat energy. This is because such a system can achieve high density recording and high definition recording.

Regarding its typical structure and principle, see, for example, US Pat. No. 4,723,129 and US Pat. No. 4,740.
What is done using the basic principles disclosed in 796 is preferred. This method is a so-called on-demand type,
It can be applied to any of the continuous type, but especially in the case of the on-demand type, it can be applied to the sheet holding the liquid (ink) or the electrothermal converter arranged corresponding to the liquid path. By applying at least one drive signal corresponding to the recording information and giving a rapid temperature rise exceeding nucleate boiling, heat energy is generated in the electrothermal converter, and film boiling is caused on the heat acting surface of the recording head. Liquid (ink) corresponding to this drive signal in a one-to-one correspondence
It is effective because bubbles can be formed inside. Due to the growth and contraction of the bubbles, the liquid (ink) is ejected through the ejection opening to form at least one droplet. It is more preferable to make this drive signal into a pulse shape, because the bubble growth and contraction are immediately and appropriately performed, so that the ejection of the liquid (ink) with excellent responsiveness can be achieved. As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. If the conditions described in US Pat. No. 4,313,124 of the invention relating to the rate of temperature rise on the heat acting surface are adopted, more excellent recording can be performed.

As the constitution of the recording head, in addition to the combination constitution of the discharge port, the liquid passage, and the electrothermal converter (the linear liquid passage or the right-angled liquid passage) as disclosed in the above-mentioned respective specifications, US Pat. No. 4,558,333, US Pat. No. 4,558,333, which discloses a configuration in which a heat acting portion is arranged in a bending region.
The structure using the specification of No. 59600 is also included in the present invention. In addition, Japanese Unexamined Patent Publication No. 59-123670 discloses a configuration in which a common slit is used as a discharge portion of the electrothermal converter for a plurality of electrothermal converters, and an opening for absorbing a pressure wave of thermal energy is provided. The effect of the present invention is effective even if the configuration corresponding to the ejection portion is disclosed in JP-A-59-138461. That is, according to the present invention, recording can be surely and efficiently performed regardless of the form of the recording head.

Further, the present invention can be effectively applied to a full line type recording head having a length corresponding to the maximum width of a recording medium which can be recorded by the recording apparatus. Such a recording head may have a configuration that satisfies the length by a combination of a plurality of recording heads or a configuration as one recording head integrally formed.

In addition, even in the case of the serial type as in the above example, the recording head fixed to the apparatus main body or the electrical connection to the apparatus main body or the ink from the apparatus main body by being attached to the apparatus main body. The present invention is also effective when a replaceable chip-type recording head that can be supplied or a cartridge-type recording head in which an ink tank is integrally provided in the recording head itself is used.

Further, as the constitution of the recording apparatus of the present invention, it is preferable to add the ejection recovery means of the recording head, the auxiliary auxiliary means and the like because the effects of the present invention can be further stabilized. Specifically, heating is performed by using a capping unit, a cleaning unit, a pressure or suction unit for the recording head, an electrothermal converter or a heating element other than this, or a combination thereof. Examples thereof include a preliminary heating unit for performing the discharge and a preliminary discharge unit for performing discharge different from the recording.

Regarding the type and the number of recording heads to be mounted, for example, only one is provided corresponding to a single color ink, or a plurality of inks having different recording colors and densities are supported. A plurality of pieces may be provided. That is, for example, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, but it may be either the recording head is integrally formed or a plurality of combinations may be used. The present invention is also extremely effective for an apparatus provided with at least one of full-color recording modes by color mixing.

In addition, in the embodiments of the present invention described above, the ink is described as a liquid, but an ink that solidifies at room temperature or lower and that softens or liquefies at room temperature may be used. Or, in the inkjet system, it is common to control the temperature of the ink itself within the range of 30 ° C. or higher and 70 ° C. or lower to control the temperature so that the viscosity of the ink is within the stable ejection range. Sometimes, a liquid ink may be used. In addition, the temperature rise due to thermal energy is positively prevented by using it as the energy of the state change of the ink from the solid state to the liquid state, or in order to prevent the evaporation of the ink, it is solidified and heated in the standing state. You may use the ink liquefied by. In any case, by applying thermal energy such as ink that is liquefied by applying thermal energy according to the recording signal and liquid ink is ejected, or that begins to solidify when it reaches the recording medium. The present invention can be applied to the case where an ink having a property of being liquefied for the first time is used. In this case, the ink is
JP-A-54-56847 or JP-A-60-7
As described in Japanese Patent No. 1260, it may be configured to face the electrothermal converter in a state of being held as a liquid or a solid in the concave portion or the through hole of the porous sheet. In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.

In addition, as the form of the ink jet recording apparatus of the present invention, besides the one used as an image output terminal of an information processing apparatus such as a computer, a copying apparatus combined with a reader or the like, and a facsimile apparatus having a transmission / reception function are provided. It may be a form or the like.

[0133]

As described above, according to the present invention,
A plurality of ink droplets respectively ejected from the plurality of ejection ports land at approximately the same location to form a pixel. Since the ink droplets forming these pixels include inks having different densities, the gradation range of the pixel can be increased by combining the number of landed ink droplets and the combination of dark and light.

As a result, it is possible to perform high-gradation recording while maintaining low cost and high reliability, it is possible to increase the number of gradations without lowering the reliability of the recording head, and by increasing the number of gradations. It is possible to reduce the pseudo gradation generated when the dark and light inks are switched, and it is possible to achieve high image quality without density unevenness and streaks.

[Brief description of drawings]

FIG. 1 is a perspective view of an inkjet recording apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining a recording operation of the first embodiment.

FIG. 3 is an explanatory diagram showing a pixel forming process according to the first embodiment.

FIG. 4 is a schematic waveform diagram showing a recording head drive pulse used in the first embodiment.

5A and 5B are a longitudinal sectional view and a front view showing the structure of the recording head used in Example 1. FIG.

FIG. 6 is a diagram showing the relationship between the pre-pulse width P ₁ and the ejection amount V _d shown in FIG.

FIG. 7 is a diagram showing a relationship between environmental temperature and discharge amount.

FIG. 8 is an explanatory diagram showing discharge amount control applied to the first embodiment.

FIG. 9 is a schematic diagram of a table used in the discharge amount control.

FIG. 10 is a flowchart showing a discharge amount control sequence of the first embodiment.

FIG. 11 is a plan view showing the configuration on the substrate of the recording head used in the first embodiment.

FIG. 12 is a perspective view showing a color inkjet recording apparatus according to a second embodiment of the invention.

FIG. 13 is an explanatory diagram illustrating a pixel forming process according to the second embodiment.

FIG. 14 is an explanatory diagram showing a pixel forming process according to the second embodiment.

FIG. 15 is a schematic diagram showing a density distribution table used in the second embodiment.

16 (A) to 16 (C) are explanatory diagrams illustrating combinations of gradations of dark and light ink droplets in the second embodiment.

17A, 17B and 17C are cross-sectional views showing the structure of the recording head according to the second embodiment.

FIG. 18 is a plan view showing the configuration on the substrate of the recording head according to the third embodiment of the invention.

FIG. 19 is an exploded perspective view of the recording head according to the third embodiment.

FIG. 20 is an explanatory diagram illustrating a recording operation according to the third embodiment.

FIG. 21 is a perspective view showing an ink jet recording apparatus according to a third embodiment.

[Explanation of symbols]

 1 Recording Head 2, P Recording Medium 3 Platen Roller 4, 32, 502 Carriage 20A, 20B Sub Heater 30, 30A, 30B Temperature Sensor

Claims (2)

[Claims] 1. A combination of pixels formed by ejecting ink onto a recording medium, using a recording head having a plurality of ejection ports for ejecting inks of the same color and different densities from the plurality of ejection ports. In an ink jet recording apparatus for recording by means of a recording means, a moving means for moving the recording head relative to a recording medium, a movement of the recording head by the moving means are controlled, and A recording control means capable of controlling ejection and forming a pixel by superimposing a plurality of ejected ink droplets containing ink droplets having mutually different densities at substantially the same location on a recording medium; An inkjet recording device characterized by the above. 2. The ink jet recording apparatus according to claim 1, wherein the recording head uses the thermal energy to generate bubbles in the ink and ejects the ink based on the generation of the bubbles.