JPH06246933A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent streaks and unevenness in density from occurring by a method wherein a plurality of recording heads of the same ink color are provided and a control means which controls driving of the recording heads so that recording ink drops discharged respectively from a plurality of the recording heads of the same ink color are recorded by being superimposed on the same pixel is provided. CONSTITUTION:A plurality of recording heads 10 of the same ink color are mounted on a carriage 11. When an ink drop is recorded on recording paper 4, the carriage 11 is moved in the arrow S direction, and at first recording operation by the first ink drop is carried out on the recording paper 4 with a preceding recording head 10B1 of the first color Bk. Thereafter, by recording the second ink drop by superimposing it on a pixel recorded with the recording head 10B1 of the first color Bk with the recording head 10B2 of the second color Bk 0-2 ink drops are recorded on one pixel on the recording paper 4 by one time scan operation of the head carriage 11. Further, each pixel is recorded with ink drops from different nozzles between the recording heads B1, 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a plurality of discharge ports (nozzles).
The present invention relates to an inkjet type image forming apparatus for forming an image by printing one pixel with a plurality of dots using a recording head having the above.

[0002]

2. Description of the Related Art The ink jet recording method is a method in which ink is ejected onto a recording medium in accordance with a recording signal for recording, and is widely used because of its low running cost and quiet recording. By using a head in which a large number of nozzles are formed on a straight line perpendicular to the relative movement direction of the recording medium and the head, the width corresponding to the number of nozzles is recorded at one time by one relative scan between the head and the recording medium. Therefore, the speedup can be achieved relatively easily.

When the gradation is expressed by the ink jet recording method, the size of the ejected liquid droplets may be changed, but this method is not yet practical, and usually by pseudo halftone image processing. Controlling the number of ejected ink droplets per unit area is performed.

Further, the size of one ink droplet is reduced to form a single dot by ejecting (impacting) a plurality of ink droplets at substantially the same position, and the number of impacts (number of impacts).
There is a so-called multi-droplet method in which gradation is expressed by controlling. This method can perform gradation recording without lowering the resolution.
It is particularly effective for ink jet recording of a system in which it is difficult to change the size of each ink droplet.

[0005]

However, in the conventional multi-droplet method, since one pixel is formed by a plurality of ink droplets ejected from one nozzle, if the ink droplet volume varies from nozzle to nozzle, it is essentially uniform. There is a problem that streaks occur in the image that should be correct or density unevenness occurs.

This problem becomes noticeable when the number of nozzles is increased and the width of the recording is increased by one relative scan between the head and the recording paper as described above in order to perform recording at high speed. If the recording width is widened, the low-frequency spatial frequency components of the density unevenness increase, and the unevenness becomes more noticeable and the image quality deteriorates. When performing gradation expression, unevenness is particularly noticeable, and density unevenness is recognized even if the variation in ejection between nozzles is about several percent.

In order to avoid these problems, in the conventional multi-droplet method, the head has to be manufactured very precisely in order to minimize the variation in the discharged ink droplet volume among the nozzles, resulting in a high cost. However, there are problems such as deterioration of the production yield. Also,
As a method of eliminating density unevenness by software, a method of changing the number of ejected ink droplets so as to cancel the variation in ink droplet volume between nozzles using image processing such as an error diffusion method is also effective. However, there is a problem that the system cost is increased by incorporating such image processing. Even if such an image processing method is used, if the variation in ink droplet volume between nozzles changes over time, it is necessary to readjust the number of ejected ink droplets, resulting in poor maintainability. ing.

The present invention has been made in view of the problems of the above-mentioned conventional technique, and streaks and uneven density may occur due to variation in the amount of ink ejected between nozzles of a recording head. An object of the present invention is to realize an image forming apparatus capable of forming a high-quality image that does not exist.

[0009]

An image forming apparatus according to a first aspect of the present invention is an image forming apparatus of an ink jet system using an ink jet recording head composed of a plurality of recording heads, wherein the ink jet recording head has the same ink color. A plurality of recording heads are provided, and recording ink droplets ejected from the plurality of recording heads of the same ink color are overlapped and recorded on the same pixel.

An image forming apparatus according to a second aspect of the present invention is an image forming apparatus of an ink jet system having an ink jet recording head in which a plurality of recording heads are arranged along a conveyance direction of an object to be recorded. The recording head is divided into a predetermined number of areas, and the recording material is conveyed according to the divided areas, so that the recording ink droplets from the recording head provided in different areas on the same pixel of the recording material are recorded. The feature is that they are recorded in an overlapping manner.

In any of these cases, when a plurality of recording ink droplets are recorded on the same pixel in an overlapping manner, the amount of ink droplets of each recording head may be changed for recording.

When a plurality of recording heads are used to record a plurality of recording ink droplets on the same pixel, the amount of ink droplets ejected from the recording head is recorded later in time. It may be larger than the amount of ink droplets ejected from the recording head.

Further, the amount of ink droplets ejected from a plurality of recording heads may be controlled by controlling a pulse voltage condition applied to each recording head, which is a driving condition of each recording head.

[0014]

In the present invention, since a plurality of recording ink droplets ejected by a plurality of recording heads are superposed on the same pixel for recording, even if ejection failure occurs in a particular recording head, other Recording is performed by the ink droplets ejected from the recording head, and there is no generation of streaks and uneven density.

Although the dot diameter may vary due to the difference in ejection time, the same dot diameter can always be obtained by varying the amount of ejected ink drops according to the ejection order. it can.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment according to the first structure of the present invention will be described with reference to the drawings.

[Embodiment 1-1] FIG. 1 is a schematic view for explaining the overall construction of an embodiment of an image forming apparatus according to the first construction of the present invention. In this embodiment, a reader unit 1 that constitutes a color image scanner that reads a document image in color and outputs digital color image data, and a reader unit 1.
The image forming apparatus of the present invention is configured by the printer unit 2 that records the digital color image data output from the printer on the recording paper.

In the reader unit 1, an exposure lamp (not shown), a lens, and an image sensor capable of reading a line image in full color (CC in this embodiment) are used.
The image of the document placed on the platen glass is read by the D sensor 3), and the main CPU 100
Controls the entire device. In addition, the main CPU 10
0 is a printer control C that controls the control operation of the printer unit 2.
PU102, reader control C that controls the reading control operation
A PU 104, a main image processing unit 106 that processes an image processing operation, and an operation unit 108 as an input unit for an operator are connected. The main image processing unit 106 described above performs image processing such as masking, black extraction, multi-valued conversion, and γ correction. A synchronous memory 110 is connected to the printer control CPU 102 and the main image processing unit 106. The synchronous memory 110 is for absorbing the time variation of the input operation and correcting the delay due to the mechanical arrangement of the recording heads described above. Then, this synchronous memory 110
Is output to the recording head 10 by controlling the head driver 115 by the printer control CPU 102.

The printer control CPU 102 is connected to a printer unit drive system 114 that controls the input drive of the printer unit.

The reader control CPU 104 also has an input system image processing unit 116 for performing necessary correction processing in the reading system such as shading correction, color correction, and γ correction, and a reader unit drive system 118 for controlling input driving of the reader. It is connected to the.

Further, the input system image processing unit 116 has a CCD
The sensor 3 is connected to the input system image processing unit 11
Reference numeral 6 is connected to the main image processing unit 106.

FIG. 2 is a schematic diagram for explaining the printer unit 2 of the image forming apparatus of the present invention, which is roughly classified into two guide rails 15a and 15b and an ink jet recording head 10.
And a carriage 11, an ink supply device, a head recovery device 20, and an electrical system (not shown).

The ink supply device is for storing ink and supplying it to the ink jet recording head 10 in a required amount, and has an ink tank 14 and an ink pump 13. The apparatus and the ink jet recording head are connected by an ink supply tube 12, and normally, the ink is ejected from the head automatically by a capillary action and is automatically supplied to the ink jet recording head 10. Further, at the time of an ink jet recording head recovery operation as described later, the ink pump 13
Ink jet recording head 1 forcibly using ink
Supply to 0.

The above-mentioned ink jet recording head and ink supply device are mounted on a carriage 11 and an ink carriage, respectively, and a belt 16 provided between pulleys 17a and 17b is connected to a shaft 18 of a motor 19 so as to rotate the motor 19. It is configured to reciprocate in the direction of arrow S along the guide rails 15a and 15b.

The head recovery device 20 includes the head 1 at the home position HP in order to maintain the stability of the head.
It is provided so as to face 0, and specifically, the following operation is performed. When not operating, the inkjet recording head 10 is capped at the home position in order to prevent the ink from evaporating from the head nozzle by moving forward in the direction of arrow f (capping operation), or bubbles or dust in the nozzle before starting image recording. It is necessary to pressurize the ink flow path in the inkjet recording head by using an ink pump for discharging the ink to forcibly discharge the ink from the nozzle (pressure recovery operation). Performs functions such as collecting ink.

FIG. 3 is a perspective view showing a schematic structure of the ink jet recording head 10. This ink jet recording head undergoes semiconductor manufacturing process steps such as etching, vapor deposition, sputtering, etc., and electrothermal conversion formed on the substrate 21. It is composed of a body 22, an electrode 23, a nozzle wall 24, and a top plate 25.

Recording ink is supplied from an ink tank 14 (not shown) into the common liquid chamber 26 of the ink jet recording head 10 through the ink supply tube 12. Reference numeral 27 in the figure denotes a supply pipe connector.

The ink supplied to the common liquid chamber 26 is supplied to the inside of the nozzle 28 due to the capillary phenomenon, and is stably held by forming a meniscus on the ejection port surface at the tip of the nozzle.

By energizing the electrothermal converter 22 here, the ink on the surface of the electrothermal converter is heated and a bubbling phenomenon occurs, and ink droplets are ejected from the ejection port surface 29 by the energy of the bubbling.

With the configuration as described above, the nozzle density is 1
With a high-density nozzle arrangement of 6 nozzles / mm, it is possible to manufacture a multi-nozzle inkjet recording head having 128 nozzles or 256 nozzles.

FIG. 4 is a diagram showing a specific structure of the ink jet recording head used in the image forming apparatus of the present invention, and FIG. 5 is a method of recording a plurality of dots on the same pixel of the recording paper 4. It is an explanatory view for explaining.

According to the present invention, a plurality of recording heads 10 of the same ink color are mounted on the head carriage 11.
In the embodiment shown in FIG. 4, recording heads 10Y ₁ and 10Y ₂ for yellow and magenta (Magent) are used.
a) recording heads 10M ₁ and 10M ₂ , cyan (Cya)
The recording heads 10C ₁ and 10C ₂ for n) and the recording heads 10B ₁ and 10B ₂ for black (B _k ) are mounted, and two recording heads are mounted for each color. By controlling the ejection operation of ink droplets by the recording heads 10 ₁ and 10 ₂ of the same ink color, the number of ink droplets per pixel on the recording paper 4 is changed in the range of 0 to 2 to perform recording. I have to.

That is, in the present embodiment, when recording ink droplets on the recording paper 4, the head carriage 11 is scanned and moved in the direction of arrow S as shown in FIG. After the recording operation by the first ink droplet is performed on the recording sheet 4 by the first B _k color recording head 10B ₁ , as shown in FIG. 5B, the second B _k color recording head 10B ₂ The first B _k color recording head 1
As shown in FIG. 5C, by recording the second ink drop by superimposing it on the recording pixel recorded by 0B ₁ ,
By one scan operation of the head carriage 11,
Ink droplets of 0 to 2 are recorded on one pixel of the recording paper 4. In addition, each pixel has a recording head 1
Since recording is performed by ink droplets ejected from different nozzles of 0B ₁ and 10B ₂ , this apparatus allows three gradations with less streaky image deterioration due to the characteristic difference of ink droplets ejected from each nozzle of the recording head. You will be able to record high-quality images of.

Similarly, the Cyan color recording heads 10C ₁ and 10C ₂ and the Magenta color recording head 10 are used.
M ₁ , 10M ₂ , yellow color recording head 10Y ₁ ,
By controlling the ink droplet ejection operation by 10Y _2, the variation in the ink droplet ejection amount from each nozzle is averaged, and it is possible to obtain a high-quality full-color image with less streaky or uneven image deterioration. Like

By the way, when ink droplets are recorded on the same pixel of the recording paper by a plurality of recording heads at a time difference corresponding to the recording head interval at the time of scanning as in the present apparatus, the recording paper may be recorded later in time. The state of absorption of the formed ink droplets on the recording paper may differ from the state of absorption of the previously recorded ink droplets on the recording paper.

For example, as shown in FIGS. 6A and 6B, when ink droplets are recorded on a recording paper at a recording pixel pitch d (d = 63.5 μm when the recording pixel density is 400 dpi), The recording dot diameter on the paper is such that there is no gap between adjacent recording dots: d ₀ = 2 ^1/2 d (d ₀ = 89.8 μm in the case of recording pixel density 400 dpi)
Recording ink volume V ₀ from the recording head 10
However, as described above, when ink droplets are recorded on the same pixel of the recording paper at a time difference corresponding to the head interval between a plurality of recording heads, the amount of ink droplets ejected from each nozzle of each recording head. as V _N, be recorded ink total _{V 0 (V 0 = 2V N} ) to the same pixel of the recording sheet 4 by the two recording heads, the dot diameter becomes smaller than the d _0. This is because the ink droplets to be recorded later are more likely to be absorbed in the thickness direction than in the surface direction of the recording paper 4, because there is a region where the ink droplets ejected first have penetrated.

Therefore, as shown in FIGS. 6C and 6D,
The recording dot diameter d on the recording paper 4 _NIs d₀Less than
(D₀> D_N), As a result, as shown in FIG.
In addition, the recording operation for the same pixel on the recording paper
If you do it in multiple times with a time difference depending on the
Recorded image density D_NIs the ink drop amount V with one recording head₀
Image density D when ejecting ink droplets₀Compared to
There may be a problem that it becomes low due to
is there.

In view of this, in the present embodiment, even when ink droplets are recorded on the same pixel of the recording paper by a plurality of recording heads with a time difference corresponding to the recording head interval, the recording image density is not lowered, as shown in FIG. As shown in, when a plurality of recording heads record a plurality of recording ink droplets on the same pixel on the recording paper, the ink ejection amount P from the nozzle corresponding to the same pixel is determined according to the recording head. The amount P _{1 of} ink droplets ejected from the first recording head which controls the ink droplets on the recording paper _{first in time.}
In order to increase the amount of ink droplets P ₂ ejected from the second recording head for recording ink droplets later in time (P ₁ <
P ₂ ) The drive conditions of the first recording head and the second recording head are controlled.

FIGS. 9 and 10 explain the first embodiment of the first configuration of the present invention for controlling the amount of ink droplets ejected from the nozzles of each recording head of a plurality of recording heads of the same ink color. It is a model diagram for doing.

Ink jet recording head 1 shown in FIG.
When ejecting ink droplets from 0, a pulse signal having a voltage V (v) and a pulse width W (μsec) as shown in FIG. Due to the bubbling phenomenon above, ink droplets are ejected from each nozzle. This ink ejection amount P can be increased by increasing the pulse voltage value of the pulse signal applied to the electrothermal converter 22 of the recording head 10 as shown in FIG. The pulse voltage value applied to the electrothermal converter 22 of each nozzle of the first recording head and the second recording head for recording the first and second droplets is V ₁ ,
V ₂ (V ₁ <V ₂ ) and the pulse voltage value V ₁ applied to each nozzle of the first recording head for recording the first droplet is
The drive condition of each recording head is controlled so that the pulse voltage value V ₂ applied to each nozzle of the second recording head that records the second droplet with a time delay is increased.

As described above, the first recording on the recording paper
When the recording operation is performed by increasing the ejected ink droplet amount P of the second and second drops to P ₁ <P ₂ and increasing the ejected ink droplet amount from the recording head for later recording, It is possible to record a high-quality image in which the deterioration of the image does not occur and the image deterioration in the form of streaks or unevenness is small.

[Embodiment 1-2] FIG. 11 shows recording of a plurality of recording heads of the same ink color when recording a plurality of recording heads by recording a plurality of recording ink droplets on the same pixel on a recording sheet. FIG. 6 is a model diagram for explaining a second embodiment of the first configuration of the present invention for controlling the amount of ink droplets ejected from the nozzles of the head.

In the present embodiment, the pulse voltage applied to the electrothermal converter 22 of each nozzle of the first recording head and the second recording head for recording the first and second drops on the recording paper. Pulse width W (μsec) of W ₁ , W ₂ (W ₁ <W ₂ )
And the pulse width W ₁ applied to each nozzle of the first recording head for recording the first droplet is applied to each nozzle of the second recording head for recording the second droplet with a time delay. The drive conditions of each recording head are controlled so as to increase the pulse width W ₂ , and the ejected ink droplet amounts P of the first and second droplets recorded on the recording paper are temporally set to P ₁ <P _2. The recording operation is performed by increasing the amount of ink droplets ejected from the recording head for later recording.

[Embodiment 1-3] FIGS. 12 and 13 show a first structure of the present invention for controlling the amount of ink droplets ejected from the nozzles of each recording head of a plurality of recording heads of the same ink color. It is a model figure for demonstrating the Example of 3.

In this embodiment, the electrothermal converter 22 of each nozzle of the first recording head and the second recording head for recording the first and second drops on the recording paper is shown in FIG. A pulse voltage composed of two pulse signals as shown is applied.

Of the pulse voltages, the first pulse voltage applied to the electrothermal converter 22 first is set to a pulse width w which gives energy to the extent that ink bubbling does not occur on the electrothermal converter surface. After the ink on the surface of the electrothermal converter is heated by the first pulse voltage as the sub heat pulse and the temperature rises, the pulse width W as the second pulse voltage as the main heat pulse is obtained.
A pulse voltage of (W> w) is applied to the electrothermal converter to foam ink and eject ink droplets from the recording head.

At this time, the pulse width w of the first pulse voltage as the sub-heat pulse is recorded later on the first recording head and the second recording head as w ₁ <w ₂ later. The ink temperature on the surface of the electrothermal converter can be controlled to be high by controlling the recording head so that it becomes larger, and the ink is ejected from each nozzle of the second recording head when the second pulse voltage is applied. It becomes possible to increase the ejected ink droplet amount P.

Further, the pulse width W of the second pulse voltage that causes the ink bubbling phenomenon in the first recording head and the second recording head as shown in the second embodiment.
By controlling the pulse widths of both the pulse voltage of the first pulse voltage and the pulse width w of the first pulse voltage and the application interval time t of the first pulse voltage and the second pulse voltage, ink ejected from each nozzle of the recording head is controlled. The control range of the ink amount P of the drop amount can be selected wider.

[Embodiment 1-4] FIGS. 14 and 15 show a first configuration of the present invention for controlling the amount of ink droplets ejected from the nozzles of each recording head of a plurality of recording heads of the same ink color. It is a model figure for demonstrating the Example of FIG.

In the present embodiment, the electrothermal converter 22 of each nozzle of the first recording head and the second recording head for recording the first and second drops on the same pixel of the recording paper, A pulse voltage composed of a plurality of sub heat pulse voltages and a main heat pulse voltage as shown in FIG. 14 is applied.

Then, as in this embodiment, the electrothermal converter 2
2 is applied with M pulses of a sub-heat pulse voltage having a pulse width w (μsec) of energy that does not cause the ink bubbling phenomenon, and then a main heat pulse voltage having a pulse width W (μsec) is applied. The pulse number M of the sub heat pulse voltage of (μsec) is controlled to be smaller than the sub heat pulse number M ₁ applied to each nozzle of the first recording head that records the first droplet on the same pixel of the recording sheet. The drive condition of each recording head is controlled so that the number M _{2 of} sub-heat pulses applied to each nozzle of the second recording head that records the second droplet with a time delay is increased (M ₁ <M ₂ ). The amount of ejected ink droplets P of the first and second drops recorded on the recording paper is set to P ₁ <P ₂ so that the recording head that records later in time increases.

[Embodiment 2-1] Next, an embodiment according to the second configuration of the present invention will be described.

FIG. 16 shows a recording head for one pixel in order to perform recording by changing the number of ink droplets per pixel in the range of 0 to 3 by using the apparatus according to the second structure of the present invention. FIG. 6 is a schematic diagram for explaining a recording method of forming an image by scanning three times.

In the second configuration of the present invention, the case where an image is recorded on a recording sheet using the recording head 10 having 128 nozzles has been described. For convenience, the nozzle numbers of the recording head 10 are 1, 2, ..., 128 from the top to the bottom of the drawing.

When an image is recorded on the recording paper by the recording head 10, the recording head is scanned three times with respect to one pixel on the recording paper so that the number of ink drops per pixel is 0 to 3 times. Record. Therefore, the nozzles of the recording head 10 having 128 nozzles are divided into blocks (I), (II), (III) for every 42 nozzles excluding the nozzles located at both ends, as shown in FIG. After one recording operation is performed in units of 42 nozzles in one scan operation, the recording paper is conveyed by 42 pixels (upward in the figure), and similarly 4
The second scanning operation is performed in units of two nozzles, the recording paper is conveyed again by 42 pixels, and then the third scanning operation is performed.

That is, as shown in FIG. 16B, the pixel A is No. 1 in the block (III) of the recording head 10 due to the first scanning operation. After printing is performed with the nozzles of No. 86, as shown in FIG. 16C, the second scan operation causes No. 2 of the block (II) of the print head 10. 44
The recording is performed by the nozzles of No. 1 and the third scanning operation is performed as shown in FIG.
No. 0 of block (I). Since recording is performed by two nozzles, and as a result, the pixel A is recorded by ink droplets of 0 to 3, each pixel is recorded by a different nozzle of the recording head 10 each time. ,
It becomes possible to record a high-quality image of four gradations with less streaky image deterioration due to the characteristics of ink droplets ejected from each nozzle of the recording head. Similarly, by repeating the recording operation by the recording head 10 in units of 42 nozzles and the conveyance of the recording paper, the variation in the ink liquid amount from each nozzle is averaged over the entire screen, resulting in a streak-like or uneven image. An image with little deterioration can be obtained.

Even when such recording is performed, the first aspect of the present invention
As in the case of the configuration of 1, the normal one-time recording
Simply divide the amount of ink used and print later
The formed ink droplets are in the thickness direction rather than the surface direction of the recording paper 4.
On the recording paper 4 because it is easily absorbed into
Recording dot diameter d_NIs d₀Smaller than (d ₀
> D_N), As a result, as shown in FIG.
Of multiple recording operations for the same pixel
In case of scan recording, the recorded image density is
It is lower than in the case of normal recording without recording
There is a problem that it will happen.

Therefore, in the present invention, even when ink droplets are recorded on the same pixel of the recording paper with a time difference corresponding to the scanning interval by the multi-scan recording method, the recorded image density is prevented from lowering as shown in FIG. As shown in FIG. 4, when recording ink droplets are overlapped and recorded on the same pixel on the recording paper a plurality of times, the pixel on the recording head is recorded on the same pixel according to the number of recording scans by the recording head 10 for the same pixel. Ink ejection amount P from the corresponding nozzle
To control the ink ejection amount P for the same pixel.
The larger the number of scans of the recording head, the more (P
₁ <P ₂ <P ₃ ).

That is, as shown in FIG. 18, the discharge area (III) for recording the first droplet of the recording head 10 on the recording paper 4 by scanning the recording head once in the direction of arrow S.
When ink droplets are recorded by the nozzles of _{No. 2, the} amount of ink ejected from each nozzle in the ejection area (III) of the recording head 10 is set to P ₁ (pl), and then the recording paper 4 is moved in the direction of arrow H. Of the discharge area (III), the second scan operation is performed by the recording head, and recording is performed on the recording sheet 4 in the area where the first droplet is recorded. When ink droplets are recorded by the nozzles of the ejection area (II) for recording the second droplet of the head 10, the amount of ink ejected from each nozzle of the ejection area (II) of the recording head 10 is P ₂ (pl). (P ₁ <P ₂ )
Similarly, the third scan operation by the recording head is performed, and the discharge area (I) of the recording head 10 for recording the third droplet is recorded in the area where the second droplet is recorded on the recording sheet 4. When ink droplets are printed by the nozzles, the amount of ink ejected from each nozzle in the ejection area (I) of the recording head 10 is set to P ₃ (pl) (P ₁ <P ₂ <P ₃ ) and Therefore, the driving conditions of the nozzles in the ejection areas (1), (II), and (III) of the recording head are controlled so that the amount of ejected ink droplets recorded on the recording sheet is increased.

FIGS. 19 and 20 are model diagrams for explaining the first embodiment of the second configuration of the present invention for controlling the amount of ink droplets ejected from each nozzle depending on the ejection area of the recording head 10. When ejecting ink droplets from the ink jet recording head 10 used in the present embodiment shown in FIG. 3, a voltage V (v) and a pulse width shown in FIG. A pulse signal of W (μsec) is applied to cause ink droplets to be ejected from each nozzle due to the bubbling phenomenon on the surface of the electrothermal converter. However, as shown in FIG. Since the ink ejection amount P from each nozzle of the recording head 10 can be increased as the pulse voltage value of the pulse signal applied to the recording head 10 is increased, the first droplet, the second droplet, and the third droplet on the recording paper.
Ejection areas (I) (II) of the recording head 10 for recording droplets
The pulse voltage values applied to the electrothermal converter 22 of each nozzle in (III) are V ₃ , V ₂ , and V ₁ (V ₁ <V ₂ <V ₃ ) and the first
The pulse voltage value V ₁ for each nozzle in the ejection area (II) of the recording head 10 for recording the second droplet is larger than the pulse voltage value V ₁ for each nozzle in the ejection area (III) for recording the droplet. ₂ is increased, and the drive condition of the recording head is controlled so that the pulse voltage value V ₃ for each nozzle in the ejection area (I) of the recording head 10 for recording the third droplet is further increased, and the recording head is controlled to print on the recording paper. By increasing the ejected ink droplet amount P for recording the first, second, and third droplets to be recorded as P ₁ <P ₂ <P _3, and increasing the amount of ink droplets to be recorded later, the present invention As described above, even when performing the multi-scan recording in which the recording operation on the same pixel on the recording paper is divided into a plurality of times, the density of the recorded image does not decrease. Further, it becomes possible to record a high-quality image with less streaky or uneven image deterioration.

[Embodiment 2-2] FIG. 21 shows a recording head 10
FIG. 5 is a model diagram for explaining a second embodiment of the second configuration of the present invention for controlling the amount of ink droplets ejected from each nozzle according to the ejection area of the first embodiment. The pulse width W of the pulse voltage applied to the electrothermal converters 22 of the respective nozzles in the ejection regions (I), (II), and (III) of the recording head 10 for recording the first, second, and third drops.
(Μsec) is W ₃ , W ₂ , W ₁ (W ₁ <W ₂ <W ₃ ),
Ejection area of recording head 10 for recording the first droplet (III)
The pulse width W ₂ for each nozzle of the ejection area (II) of the recording head 10 for recording the second droplet is made larger than the pulse width W ₁ for each nozzle of the recording head for recording the third droplet. The driving conditions of the recording head are controlled so as to further increase the pulse width W ₃ for each nozzle in the ten ejection regions (I), and the first droplet and the second droplet are recorded on the recording sheet.
The ejected ink droplet amount P for recording the droplet and the third droplet is P ₁ <P ₂
<P _3, and the amount of ink drops to be recorded later is increased.

[Embodiment 2-3] FIGS. 22 and 23 show a third embodiment according to the second configuration of the present invention for controlling the amount of ink droplets ejected from each nozzle depending on the ejection area of the recording head 10. FIG. 3 is a model diagram for explaining, in the present embodiment, the amount of ink droplets ejected from each nozzle in the ejection region of the recording head 10 for recording the first droplet, the second droplet, and the third droplet on the recording paper. In order to control P, a pulse voltage composed of two pulse signals is applied to the electrothermal converter 22 of each nozzle of the recording head as shown in FIG.

Of the pulse voltages, the first pulse voltage applied to the electrothermal converter 22 first has a pulse width w that gives energy to the extent that ink bubbling does not occur on the electrothermal converter surface. After setting, the ink on the surface of the electrothermal converter is heated by the first pulse voltage as the sub heat pulse to raise the temperature, and then the pulse width W (W>w> w) as the second pulse voltage as the main heat pulse. Pulse voltage is applied to the electrothermal converter to foam the ink and eject ink droplets from the recording head.

At this time, the pulse width w of the first pulse voltage as the sub-heat pulse is set to w ₁ <w ₂ <w ₃ for the ejection areas (I), (II), and (III) of the recording head. It is possible to control the ink temperature on the electrothermal converter surface by controlling the nozzles to be recorded to be larger, and increase the amount of ink droplets ejected from each nozzle when the second pulse voltage is applied. In addition, the pulse width W of the second pulse voltage and the pulse width w of the first pulse voltage that cause the ink bubbling phenomenon, as shown in the second embodiment, can be increased or decreased. By controlling the pulse widths of both pulse voltages and the application interval time t of the first pulse voltage and the second pulse voltage, the control width of the ink amount P of the ink droplet amount ejected from each nozzle of the recording head can be further improved. Wide choice Become.

[Embodiment 2-4] FIGS. 24 and 25 show a fourth embodiment of the second configuration of the present invention for controlling the amount of ink droplets ejected from each nozzle depending on the ejection area of the recording head 10. FIG. 3 is a model diagram for explaining, in the present embodiment, the amount of ink droplets ejected from each nozzle in the ejection region of the recording head 10 for recording the first droplet, the second droplet, and the third droplet on the recording paper. In order to control P, a pulse voltage composed of a plurality of sub heat pulse voltages and a main heat pulse voltage as shown in FIG. 24 is applied to the electrothermal converter 22 of each nozzle of the recording head.

Then, as in this embodiment, the electrothermal converter 2
2 is applied with M pulses of a sub-heat pulse voltage having a pulse width w (μsec) of energy that does not cause the ink bubbling phenomenon, and then a main heat pulse voltage having a pulse width W (μsec) is applied. By controlling the pulse number M of the sub-heat pulse voltage of (μsec), the second droplet is generated more than the sub-heat pulse number M ₁ for each nozzle in the ejection area (III) of the recording head 10 for recording the first droplet. The sub-heat pulse number M ₂ for each nozzle in the ejection area (II) of the recording head 10 for recording is increased, and
The first droplet to be recorded on the recording paper by controlling the driving condition of the recording head so as to further increase the sub heat pulse number M ₃ for each nozzle in the ejection area (I) of the recording head 10 for recording the droplet, Controlling the ejection ink droplet amount of the recording head by increasing the ejection ink droplet amount P for recording the second and third drops to P ₁ <P ₂ <P ₃ and increasing the ink droplet amount to be recorded later. The accuracy is further improved, and even when performing multi-scan recording in which the recording operation on the same pixel on the recording paper is divided into a plurality of times as in the present invention, the density of the recorded image does not decrease. Further, it becomes possible to record a high-quality image with less streaky or uneven image deterioration.

In the embodiment described above, when recording with a plurality of ink droplets, the dot diameter of the ink droplet recorded earlier in time is the dot diameter of the ink droplet recorded later in time. Although it has been described that the amount of ink droplets to be recorded later is increased because it is larger than the above, the opposite may occur depending on the type of recorded matter and ink. In this case, it is possible to obtain the same effect as each of the above-described embodiments by reducing the amount of ink droplets that are recorded later in time, and such a configuration is also possible.

The present invention is particularly effective in an ink jet recording head and a recording apparatus for recording by forming flying droplets by utilizing thermal energy among the ink jet recording systems.

Regarding its typical structure and principle, see, for example, US Pat. Nos. 4,723,129 and 4740.
What is done using the basic principles disclosed in 796 is preferred. This method can be applied to both the so-called on-demand type and continuous type, but especially in the case of the on-demand type, liquid (ink)
By applying at least one drive signal to the electrothermal converter arranged corresponding to the sheet or liquid path in which is stored, which corresponds to the recorded information and causes a rapid temperature rise exceeding nucleate boiling. , It is effective because it generates heat energy in the electrothermal converter and causes film boiling on the heat-acting surface of the recording head, resulting in the formation of bubbles in the liquid (ink) corresponding to this drive signal on a one-to-one basis. Is. The liquid (ink) is ejected through the ejection openings by the growth and contraction of the bubbles 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 ejection port, the liquid passage, and the electrothermal converter (the straight liquid passage or the right-angled liquid passage) as disclosed in the above-mentioned respective specifications, The present invention also includes configurations using US Pat. No. 4,558,333 and US Pat. No. 4,459,600, which disclose a configuration in which a heat acting portion is arranged in a bending region.

In addition, JP-A-59-123670 discloses a structure in which a common slit is used as a discharge portion of the electrothermal converter for a plurality of electrothermal converters, and a pressure wave of thermal energy is absorbed. The present invention is also effective as a configuration based on Japanese Patent Application Laid-Open No. 59-138461, which discloses a configuration in which an opening corresponds to a discharge portion.

Further, as a full line type recording head having a length corresponding to the maximum recording medium width that can be recorded by the recording apparatus, the length can be increased by combining a plurality of recording heads as disclosed in the above-mentioned specification. The present invention can exert the above-mentioned effects more effectively, although it may have a configuration that satisfies the above requirement or a configuration as one recording head integrally formed.

In addition, by being attached to the apparatus main body, it can be electrically connected to the apparatus main body and can be supplied with ink from the apparatus main body by a replaceable chip type recording head or the recording head itself. The present invention is also effective when a cartridge-type recording head provided with an ink tank is used.

Further, it is preferable to add recovery means for the recording head, preliminary auxiliary means, etc., which are provided as a configuration of the recording apparatus of the present invention, because the effects of the present invention can be further stabilized. If you list these specifically,
Capping means, cleaning means, pressurizing or sucking means for the recording head, preheating means using an electrothermal converter or another heating element or a combination thereof, and a preliminary ejection mode for performing ejection other than recording It is also effective to perform stable recording.

Further, as the recording mode of the recording apparatus, not only the mainstream color such as black but not only the recording mode, the recording head may be integrally formed or a plurality of them may be combined. The present invention is also extremely effective for a device provided with at least one of full colors by color mixing.

In the embodiments of the present invention described above, the ink is described as a liquid, but it is an ink that solidifies at room temperature or lower and that softens at room temperature, or is a liquid, or the above-mentioned liquid. In the inkjet method, the temperature of the ink itself is generally adjusted within a range of 30 ° C. or higher and 70 ° C. or lower to control the temperature of the ink so that the viscosity of the ink is within a stable ejection range. It may be in a liquid form.

In addition, the temperature rise due to the thermal energy is positively prevented by using it as the energy for changing the state of the ink from the solid state to the liquid state, or the ink is solidified in the standing state for the purpose of preventing evaporation of the ink. In some cases, such as ink that is liquefied by applying heat energy according to a recording signal and ejected as a liquid ink, or one that has already started to solidify when it reaches a recording medium. The use of an ink having a property of being liquefied only by heat energy is also applicable to the present invention. In such a case, the ink is disclosed in JP-A-54-5684.
No. 7 or JP-A-60-71260, a mode in which the porous sheet is opposed to the electrothermal converter in the state of being held as a liquid or solid in the recess or through hole of the porous sheet. May be 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 a form of the recording apparatus according to the present invention, in addition to the one provided integrally or separately as an image output terminal of information processing equipment such as a word processor or a computer, a copying apparatus combined with a reader or the like, May take the form of a facsimile machine having a transmission / reception function.

[0080]

As described above, according to the present invention,
In an image forming apparatus that forms an image using an inkjet type recording head having a plurality of ejection ports (nozzles), in order to form one pixel on a recording sheet with a plurality of dots, a recording head of the same ink color is used. A plurality of recording inks are formed on the same pixel of the recording paper by controlling the ejection operation of the plurality of recording heads to form a recording image by dividing the recording operation into a plurality of times. There is no occurrence of streaks or uneven density due to the variation between the nozzles. Further, it becomes possible to provide an image forming apparatus capable of recording a high-quality image with less image deterioration such as a decrease in recorded image density.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an overall configuration of an embodiment of an image forming apparatus according to a first configuration of the present invention.

FIG. 2 is a schematic diagram for explaining a printer unit 2 in FIG.

3 is a perspective view showing a schematic configuration of the inkjet recording head 10 in FIG.

FIG. 4 is a diagram showing a specific configuration of an inkjet recording head used in the image forming apparatus of the present invention.

5A to 5C are views for explaining a method of recording a plurality of dots on the same pixel by the image forming apparatus of the present invention.

FIGS. 6A to 6D are diagrams for explaining a difference in an absorption state caused by a time difference when recording with a plurality of ink droplets.

FIG. 7 is a diagram showing a difference in recording density caused by a difference in absorption state shown in FIG.

FIG. 8 is a diagram showing the amounts of a plurality of ink droplets for recording.

FIG. 9 is a model diagram of an embodiment for controlling the amount of ink droplets ejected from a plurality of recording heads.

FIG. 10 is a model diagram of an example for controlling the amount of ink droplets ejected from a plurality of recording heads.

FIG. 11 is a model diagram for explaining a second embodiment according to the first configuration of the present invention.

FIG. 12 is a model diagram for explaining a third embodiment according to the first configuration of the present invention.

FIG. 13 is a model diagram for explaining a third embodiment according to the first configuration of the present invention.

FIG. 14 is a model diagram for explaining a fourth embodiment according to the first configuration of the present invention.

FIG. 15 is a model diagram for explaining a fourth embodiment according to the first configuration of the present invention.

16 (a) to (d) are each the second aspect of the present invention.
FIG. 6 is a schematic diagram for explaining a recording method in the apparatus having the above configuration.

FIG. 17 is a diagram showing the amounts of a plurality of ink droplets for recording.

FIG. 18 (A) and (B) are respectively the second aspect of the present invention.
FIG. 6 is a schematic diagram for explaining a recording method in the apparatus having the above configuration.

FIG. 19 is a model diagram for explaining the first embodiment according to the second configuration of the present invention.

FIG. 20 is a model diagram for explaining the first embodiment according to the second configuration of the present invention.

FIG. 21 is a model diagram for explaining a second embodiment according to the second configuration of the present invention.

FIG. 22 is a model diagram for explaining a third embodiment according to the second configuration of the present invention.

FIG. 23 is a model diagram for explaining a third embodiment according to the second configuration of the present invention.

FIG. 24 is a model diagram for explaining a fourth embodiment according to the second configuration of the present invention.

FIG. 25 is a model diagram for explaining a fourth embodiment according to the second configuration of the present invention.

[Explanation of symbols]

 1 Reader Part 2 Printer Part 3 CCD 10 Inkjet Recording Head 11 Carriage 12 Ink Supply Tube 13 Pump 14 Ink Tank 15a, 15b Guide Rail 16 Belt 17a, 17b Pulley 18 Shaft 19 Motor 20 Head Recovery Device 21 Board 22 Electrothermal Converter 23 Electrode 24 Nozzle wall 25 Top plate 26 Common liquid chamber 28 Nozzle 29 Discharge port surface 100 Main CPU 102 Printer control CPU 104 Reader control CPU 106 Main image processing unit 108 Operation unit 110 Synchronous memory 114 Printer drive unit 115 Head driver 116 Input image processing Section 118 Leader section drive system

Claims (10)

[Claims] 1. An inkjet image forming apparatus for performing recording using an inkjet recording head comprising a plurality of recording heads, wherein the inkjet recording heads have a plurality of recording heads of the same ink color. An image forming apparatus comprising: a control unit that controls driving of the recording head so that recording ink droplets ejected from the recording heads of ink colors are recorded on the same pixel in an overlapping manner. 2. The image forming apparatus according to claim 1, wherein when the plurality of recording heads of the same ink color record a plurality of recording ink droplets on the same pixel, the ink droplet amount of each recording head is increased. An image forming apparatus characterized by changing and recording. 3. The image forming apparatus according to claim 2, wherein when a plurality of recording heads record a plurality of recording ink droplets on the same pixel in an overlapping manner, ejection ink of the recording head is recorded later in time. An image forming apparatus characterized in that the amount of droplets is larger than the amount of ink droplets ejected from a recording head that records earlier in time. 4. The image forming apparatus according to claim 2, wherein controlling the amount of ink droplets ejected from the plurality of recording heads is applied to each recording head which is a driving condition of each recording head. The image forming apparatus is performed by controlling a pulse voltage condition to be applied. 5. The recording head is a recording head that ejects ink by using thermal energy, and is an inkjet recording head that includes a thermal energy converter for generating thermal energy applied to the ink. The inkjet recording apparatus according to any one of claims 1 to 4, which is characterized. 6. An inkjet type image forming apparatus for performing recording using an inkjet recording head in which a plurality of recording heads are arranged along a conveyance direction of a recording medium, wherein the plurality of recording heads are arranged at a predetermined number. The recording medium is divided into regions, and the recording medium is conveyed in accordance with the divided regions, and recording ink droplets from recording heads provided in different regions on the same pixel of the recording medium are overlapped and recorded. An image forming apparatus comprising: a control unit that controls driving of a recording head. 7. The image forming apparatus according to claim 6, wherein when recording a plurality of recording ink droplets on the same pixel in an overlapping manner, recording is performed by changing the ink droplet amount of each recording head. Image forming apparatus. 8. The ink forming apparatus according to claim 7, wherein when a plurality of recording heads record a plurality of recording ink droplets on the same pixel in an overlapping manner, the recording head ejects ink later in time. An image forming apparatus characterized in that the amount of droplets is larger than the amount of ink droplets ejected from a recording head that records earlier in time. 9. The image forming apparatus according to claim 7, wherein controlling the amount of ink droplets ejected from the plurality of recording heads is applied to each recording head, which is a driving condition of each recording head. The image forming apparatus is performed by controlling a pulse voltage condition to be applied. 10. The recording head is a recording head that ejects ink by utilizing thermal energy, and is an inkjet recording head including a thermal energy converter for generating thermal energy applied to the ink. The ink jet recording apparatus according to any one of claims 6 to 9, which is characterized.