JP2003266667A - Ink jet imaging apparatus and ink jet imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink jet imaging apparatus and an ink jet imaging method in which a dot of a desired size can be formed at all gradations while suppressing blur of ink at the time of multi-drop system imaging. <P>SOLUTION: For a multi-drop system imaging apparatus, a maximum ejection number altering means 82 is provided to set a smaller maximum ejection number of ink drops constituting one ink dot as a recording sheet having a lower permeability of ink is employed. Furthermore, a speed alteration means 83 is provided to set a higher scanning speed of an ink jet head as the maximum ejection number of ink drops decreases. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet image forming apparatus for forming an image on a recording medium (recording paper) by ejecting ink droplets, and an inkjet image forming method executed in the image forming apparatus. In particular, the present invention relates to measures for achieving high image quality when performing multi-drop type image formation in which each ink dot formed on a recording sheet can be composed of a plurality of ink droplets.

[0002]

2. Description of the Related Art Generally, in an ink jet type image forming apparatus (hereinafter referred to as an ink jet printer), ink droplets are ejected onto the surface of a recording paper to be fed to form an image. That is, the image to be formed is multivalued to two or more, and the ink droplet ejection control from each nozzle of the inkjet head is performed based on the dot on / off signal obtained by the processing. Predetermined dots are formed on the recording paper.

Various systems have been proposed as a mechanism for ejecting the ink droplets. One of them is, for example, a system in which an electrostrictive element is used to obtain the ejection pressure of an ink droplet, as disclosed in Japanese Patent Laid-Open No. 63-247051. Specifically, as shown in FIG. 12, a plurality of grooves b, b, ... Are formed in a base plate a made of a piezoelectric material, and partition walls c, c ,. , The inside of the groove b is polarized in the depth direction of the ink chamber d, and the drive electrode e is formed in a predetermined region (for example, the upper half) of the partition wall c. Also, this groove b
The cover plate f is attached on the base plate a so as to close the upper part of the. The grooves b, b, ... Are formed by cutting with a diamond blade or the like. The drive electrode e is formed by sputtering or the like.

By applying a pulse voltage corresponding to the image signal to each of the drive electrodes e, e, ... individually, a potential difference is given between the drive electrodes e, e, and thereby an electric field orthogonal to the polarization direction. Cause The partition walls c, c, ... Shear due to the piezoelectric shear strain effect generated at this time.
Due to this deformation, a pressure wave is generated in the ink chamber d, and the pressure causes the ink droplet ejection operation.

The shearing deformation operation of each partition wall c, c, ... Generally, after applying an ejection pulse voltage to a predetermined drive electrode e so that the partition wall c operates in the direction in which the ink chamber d expands, A non-ejection pulse voltage is applied to a predetermined drive electrode e so that the partition wall c operates in a direction in which the ink chamber d contracts. As a result, a pressure wave is applied to the ink in the ink chamber d, and an ink droplet is ejected from this ink chamber d via an ink nozzle (not shown).

Further, in this type of ink droplet ejection system, it is not possible to eject ink droplets simultaneously from two adjacent ink chambers d, d. This is because the ink chambers d and d adjacent to each other share one partition wall c, and the deformation operation of the partition wall c is such that ink droplets are ejected from only one of the ink chambers d and d adjacent to each other. Because it works.

Therefore, in this type of ink jet head, generally, a plurality of ink chambers d, d, ... Arranged every predetermined number (for example, every two) are formed as a plurality of ink chamber phases. In advance, ink droplet ejection control is sequentially performed for each phase. Hereinafter, the ink ejection operation in each phase will be specifically described.

Now, as shown in FIG. 13, a plurality of ink chambers arranged at intervals of two are formed as the same phase,
Consider a case where ink droplet ejection control is performed by three phases A, B, and C. In FIG. 13, the individual phases are
It is composed of first, second, and third ink chambers 1A to 3C. In FIG. 13, the first ink chamber in the A phase is labeled 1A, the second ink chamber is labeled 2A, and the third ink chamber is labeled 3A. Further, in the B phase, reference numeral 1B is assigned to the first ink chamber and reference numeral 2B is assigned to the second ink chamber.
And the third ink chamber is denoted by reference numeral 3B. C
Similar symbols are attached to the phases.

Now, the target phase of ink droplet ejection control is the B phase, and the second ink chamber 2B and the third ink chamber 3 of this B phase are used.
Consider the case where an ink droplet is ejected from B. At this time, first, the drive electrodes e1, e1, ... Of the ink chambers 2A, 2C, 3A, 3C adjacent to both sides of each of the ink chambers 2B, 3B.
Is set to a low level, and a high level voltage (the above-mentioned ejection pulse voltage) is applied to the drive electrodes e2, e2, ... Of the second ink chamber 2B and the third ink chamber 3B. This makes this second
Drive electrodes e2, e of the ink chamber 2B and the third ink chamber 3B
2, ..., and drive electrodes e1, e1, ...
A potential difference occurs between the partition walls c, c, ... Comprising the second ink chamber 2B and the third ink chamber 3B due to the action of the electric field generated at that time, and the partition walls c, c ,. The inside of 3B is enlarged (see FIG. 13B).
After that, the B-phase second ink chamber 2B and the third ink chamber 3B
The high-level voltage application to the drive electrodes e2, e2, ... Is canceled, and the drive electrodes e of the ink chambers 2A, 2C, 3A, 3C located on both sides of the ink chambers 2B, 3B are released.
A high level voltage (the above non-ejection pulse voltage) is applied to 1, e1 ,. As a result, an electric field in the opposite direction is applied between the drive electrodes e2, e2, ... Of the ink chambers 2B, 3B and the drive electrodes e1, e1 ,. 2B and third ink chamber 3
The partition walls c, c, ... Constituting B are shear-deformed to reduce the inside of these ink chambers 2B, 3B (FIG. 13).
(See (c)). As a result, a predetermined ejection pressure (wave) is generated in the ink chambers 2B and 3B, and an ink droplet is ejected from the nozzle.

FIG. 14 is a pulse waveform showing the application timing of the ejection pulse voltage and the non-ejection pulse voltage.
In this manner, by applying the non-ejection pulse voltage at the same time as the application of the ejection pulse voltage, the ink chambers 2B and 3B are continuously expanded and contracted to perform the ink droplet ejection operation.

On the other hand, in the case of the above-described ink droplet ejection operation, since the B-phase first ink chamber 1B does not eject ink droplets, the first electrodes are supplied to the drive electrodes e3, e3 of the first ink chamber 1B.
The same voltage as that of the drive electrodes e4, e4, ... Of the ink chambers 1A, 1C located on both sides of the ink chamber 1B is applied at the same timing to prevent potential difference between the electrodes so that the shear deformation does not occur. There is.

After the ink droplet ejection control operation for the B phase is performed as described above, the C phase ink chambers 1C,
The ink droplet ejection control operation for 2C and 3C is performed. In this way, control of the drive pulse voltage is controlled by A, B,
By sequentially transitioning to each phase of C, the continuous ink ejection operation is performed while effectively using all the ink chambers 1A to 3C.

Further, in this type of ink jet printer, the number of ink droplets ejected per dot on the recording paper is made variable without changing the size of the ink droplets ejected from each nozzle, and density gradation is performed. A multi-drop type image forming operation for performing the above is also generally known (see, for example, Japanese Patent Laid-Open No. 11-170521). In this method as well, ejection control of ink droplets from the ink chamber is performed by controlling the applied voltage to each drive electrode as described above.

FIG. 15 is a pulse waveform showing the application timing of each drive pulse voltage in the multi-drop method, and shows the drive pulse voltage per unit time (control time of a phase which is an ink droplet ejection control target). It shows a case where the number of ink droplets forming one dot is set by generating seven pulse waveforms for application and controlling each pulse waveform. As described above, the ink chambers in the non-ejection period (the ink chambers of the phases that are not the ejection target of the ink droplets, that is, the A-phase and C-phase ink chambers in the above-described ink droplet ejection operation) Is continuously applied with a non-ejection pulse voltage at a constant cycle (FIG. 15B).
reference). On the other hand, the ink chambers in the ejection period (the ink chambers of the phase that is the target of ink droplet ejection control, that is, the B-phase ink chambers in the ink droplet ejection operation described above) are ejected only for a predetermined period. By applying the pulse voltage, ink droplets are continuously ejected by the number of pulses of the ejection pulse voltage, and one dot on the recording paper is formed by these ink droplets. FIG. 15C shows the potential difference between the electrodes at this time. It should be noted that in the pulse waveform shown in FIG. 15, four of the seven pulse waveforms of the ink chamber in the ejection period are set as the ejection pulse waveform by setting the front four waveforms.
Ejecting ink droplets are continuously ejected. The three waveforms on the rear side are the same as the non-ejection pulse waveform. Therefore, during the period in which the pulse voltage of the three waveforms on the rear side is applied, no potential difference occurs between the electrodes, and the shear deformation does not occur, so that no ink droplet is ejected. In this way, by controlling the number of pulses of the ejection pulse voltage, dots can be formed with a density of 8 gradations (number of pulses 0 to 7).

Hereinafter, the application timing of the drive pulse voltage for sequentially controlling each phase in the multi-drop method will be specifically described with reference to FIG. This FIG.
In (a), the ejection period of the A phase is shown, (b) shows the ejection period of the B phase, and (c) shows the ejection period of the C phase.

In the discharge period of the phase A of FIG. 16 (a),
Two ink droplets are ejected in group 2 (see pulse waveform of 2A in the figure), while group 3 (3A in the figure)
5), five ink droplets are ejected. In this case, the group 3 (dots formed by the ink droplets ejected from the ink chamber 3A) is the group 2
Printing with darker gradation than (dots formed by ink droplets ejected from the ink chamber 2A) is performed.

In the B-phase ejection period of FIG. 16B, three ink droplets are ejected in group 2 (see the pulse waveform of 2B in the figure), whereas group 3 (3B in the figure). 6), six ink droplets are ejected. In addition, in the discharge period of the C phase of FIG.
Group 1 (see pulse waveform 1C in the figure) ejects one ink droplet, and group 2 (see pulse waveform 2C in the figure) ejects four ink droplets. In 3 (see the pulse waveform of 3C in the figure), 7 ink droplets are ejected.

Further, as shown in FIG. 16, there is a rest period (RT in FIG. 15) during the transition from the non-ejection pulse period to the ejection pulse period. This is because the vibration of the meniscus formed at the tip of the nozzle that ejects ink, the flow wave generated by ejecting the ink in the ink chamber (channel), and the like are stopped.

As an ink ejection method of this type of image forming apparatus, a thinned image is formed according to a predetermined thinning mask pattern while the recording head scans the same scanning area on a recording sheet a plurality of times. A multi-pass recording method for completing an image is also known. When this recording method is used, even when a recording head having nozzles with variations in ink ejection amount and ejection direction is used,
Since the influence on the recorded image unique to each nozzle is reduced, it is possible to reduce uneven density.

Further, in addition to the system in which the ejection pressure of the ink droplet is obtained by using the electrostrictive element as described above, an electrothermal conversion element is provided, and air bubbles are generated in the nozzle by heating the electrothermal conversion element. There is also known one in which the discharge pressure of the ink droplet is obtained by generating the.

[0021]

However, in the image forming apparatus for performing the image formation of the multi-drop method as described above, even if the same ink amount is ejected, the dot formation may be different depending on the type of recording medium and the image forming mode. There was a problem that the size and the degree of ink bleeding were different. In other words, even if a configuration that enables high-quality image formation with a large number of gradations is adopted as described above, the dot size may not be the desired one or ink There was a possibility that bleeding would occur and the image quality would be degraded.

The present invention has been made in view of the above points, and an object of the present invention is to form dots of a desired size in all gradations when performing multi-drop type image formation. It is an object of the present invention to provide an inkjet image forming apparatus and an inkjet image forming method capable of suppressing the ink bleeding.

[0023]

Means for Solving the Problems-Outline of the Invention-In order to achieve the above-mentioned object, means taken by the present invention are as follows.
When performing a multi-drop type image forming operation, the maximum number of ink droplets that make up one ink dot is limited according to the image forming conditions, so that the dot size may become larger than necessary. It is possible to avoid the occurrence of blurring. Image forming conditions that limit the maximum number of ink droplets ejected include the type of recording medium and the image forming mode.

-Solution means- Specifically, it is premised on an image forming apparatus which performs a multi-drop type image forming operation capable of forming ink dots on a recording medium by a plurality of ink droplets ejected continuously.
This image forming apparatus is provided with a maximum ejection number changing means for changing the maximum ejection number of the ink droplets forming one ink dot according to the type of recording medium.

Regarding the operation of changing the maximum number of ink drops to be ejected by the maximum ejection number changing means, one kind of recording medium is more likely to be used when the recording medium is hard for ink to permeate in the thickness direction and spreads easily in the surface direction. The maximum number of ink droplets forming an ink dot is set to be small.

Due to this specific matter, when the multi-drop type image forming operation is performed on a recording medium (for example, plain paper) on which ink hardly penetrates in the thickness direction and spreads easily in the surface direction, the maximum discharge of ink droplets is possible. If the number is the same as the conventional one (for example, the maximum ejection number is “7”), the size of the dot may become larger than necessary in the case of a dot in which the number of ejected ink droplets is relatively large. There is a high possibility that bleeding will occur. In the present solution, in such a case, the maximum ejection number of ink drops is set to be small, and the maximum ejection number is limited to a small value such as "3", whereby the dot size becomes larger than necessary. Avoiding accidental ink bleeding,
Good image formation can be performed.

In addition, as another solution, a plurality of types of image forming modes are provided for the image forming apparatus which also performs the image forming operation of the multi-drop method, and one image forming mode is selected depending on the image forming mode to be executed. A maximum ejection number changing means for changing the maximum ejection number of the ink droplets forming the ink dot is provided.

Also by this specific matter, by limiting the maximum number of ejections to a small value in accordance with the image forming mode, it is possible that the dot size becomes larger than necessary and ink bleeding occurs. It is possible to avoid and perform good image formation.

In each of the above solving means, an image is formed by ejecting ink droplets on the recording medium while the recording head moves in a predetermined scanning direction (main scanning direction), and the maximum ejection number is changed. There is provided speed changing means for changing the scanning speed of the recording head in the scanning direction in accordance with the maximum number of ink droplets changed by the means. Specifically, the smaller the maximum number of ink droplets ejected, the higher the scanning speed of the recording head in the scanning direction is set.

According to this specific matter, for example, when the maximum number of ejected ink droplets is changed from "7" to "3", the ink droplet ejection operation is reduced by "4". There will be times when is not always executed. That is, if the scanning speed of the print head is not changed, this time becomes an unnecessary waiting time. For this reason, in the present solving means, in order to eliminate this waiting time, the scanning speed of the recording head is set high in accordance with the reduction number (see the pulse waveform shown in FIG. 10). That is, the scanning speed of the recording head is set to be higher as the number of maximum ejections decreases. Therefore, the time required for one scanning can be shortened, and as a result, the time required for image formation on one recording medium can be shortened.

The specific structure of the recording head is as follows.
At least a part is composed of a piezoelectric member and is polarized in a predetermined direction, a partition wall, a plurality of ink chambers separated by the partition wall, and a drive electrode provided on the partition wall,
By selectively applying a predetermined drive pulse voltage to this drive electrode, an electric field is applied to the partition wall to cause shear deformation in the partition wall, and the number of ink droplets ejected from the ink chamber according to the number of pulses of the drive pulse voltage. Is controlled so that the dot diameter can be adjusted.

In the case of this system utilizing the piezoelectric shear strain effect, in particular, the amount of ink forming one dot can be finely controlled by an integral multiple of the minimum amount of ink to be ejected, and therefore the ink to be ejected utilizing the characteristics of the recording medium can be used. Quantity control is possible,
Further, by optimizing the maximum number of ink drops to be ejected, it is possible to achieve both high image quality and high image forming speed.

Further, a multi-drop type inkjet image forming method executed in the inkjet image forming apparatus constructed as described above is also within the technical concept of the present invention.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) First, the first embodiment will be described. First, the basic configuration of the inkjet head mounted in the inkjet printer according to the present embodiment will be described.

FIG. 1 is a perspective view showing the outer appearance of the ink jet head 1. FIG. 2 is an exploded perspective view of the inkjet head 1. As shown in these drawings, the inkjet head 1 includes a base plate 2, a cover plate 3, a nozzle plate 4, and an ink inlet 5.

As shown in FIG. 3, the base plate 2 has a bottom wall 21 and a plurality of partition walls 22, 22, ... Arranged on the upper surface of the bottom wall 21. These partition walls 2
2, 22, ... Are arranged in parallel at a predetermined interval. As a result, a plurality of grooves 23, 2 for forming an ink chamber 6 described later are provided between the partition walls 22, 22 ,.
3, ... are formed. Also, the base plate 2
The partition wall 22 is in the height direction (direction shown by an arrow in FIG. 3)
Is polarized to.

The cover plate 3 is integrally assembled to the upper part of the base plate 2 and has the grooves 23, 23,
The upper part of ... is closed. Specifically, as shown in FIG. 4 (a cross-sectional view taken along the line IV-IV in FIG. 3), the cover plate 3 is assembled on the upper portion of the base plate 2 and thus the bottom wall 21 of the base plate 2 is attached. A space surrounded by the partition wall 22 and the cover plate 3 is configured as an ink chamber 6, and the ink chamber 6 is formed by the partition wall 22.
A plurality of them are arranged in the horizontal direction across the.

A drive electrode 7 is formed on the base plate 2. As shown in FIG. 3, the drive electrode 7 is formed on approximately the upper half of the side surface of each partition wall 22 of the base plate 2. Further, the drive electrodes 7 arranged in the same ink chamber 6 are connected to each other by a connection electrode 73. Further, the external electrode 71 is connected to the connection electrode 73. By applying a pulse voltage from the pulse voltage generator 72 (see FIG. 5) to the external extraction electrode 71, the same pulse voltage is applied to both drive electrodes 7 and 7 facing each other in the ink chamber 6. Has become. Further, as shown in FIG. 1, a driver IC 12 is connected to the external extraction electrode 71 via a flexible circuit board 11.

The nozzle plate 4 is attached to the front surface side (front side in FIG. 2) of the base plate 2 and the cover plate 3 to close the ink chamber 6, and corresponds to each ink chamber 6, 6 ,. , Nozzles 41, 41, ... Are formed. That is, when a pressure for ejecting ink is generated in the ink chamber 6, the nozzle 4 facing the ink chamber 6
1 to a predetermined amount of ink drops in the horizontal direction (see arrow in Fig. 2)
It is designed to be discharged.

The ink inlet 5 is attached to the upper surface of the cover plate 3 having an ink introduction opening, and has a filter member 51 for filtering the ink supplied from an ink tank (not shown) to the ink chambers 6, 6 ,. It is provided.

Specifically, in the ink jet head 1 according to this embodiment, each ink chamber 6 has a length (active length) of 1.1 mm, a height dimension of 300 μm, and a width dimension of 84 μm. The width dimension is 85 μm, and the pitch of the ink chambers 6 is 150 dpi. The drive electrode 7 is made of an Al film formed by the oblique vacuum evaporation method from the upper end of the partition wall 22 to a position of 150 μm. As the operation of forming the drive electrode 7, the upper surface film of the Al film adhered over the substantially upper half and the upper surface of the side surface of the partition wall 22 by the oblique vacuum deposition is removed by polishing to remove the side surface of the partition wall 22. After the Al films are separated, the Al films facing each other in the ink chamber 6 are electrically connected to each other. The cover plate 3 is adhered to the upper surface of the partition wall 22 with an adhesive, and the thickness of the adhesive layer (not shown) is set to 1 μm or less. Furthermore,
The diameter of the nozzle 41 formed on the nozzle plate 4 on the discharge side is 17 μm. This nozzle plate 4 has a plurality of nozzles 41, 41, which are through holes formed by excimer laser after coating a water-repellent film on a polyimide film.
It is obtained by forming ... This nozzle 41,4
The pitch of 1, ... Is 150 dpi, which is the same as the pitch of the ink chambers 6, 6 ,. The above-mentioned dimensions and manufacturing method are not limited to these.

As a basic operation of ejecting ink droplets in the present ink jet head 1, as in the case described with reference to FIGS. 13 and 14, the plurality of ink droplets are arranged every predetermined number (for example, every two). The ink chambers 6, 6, ... Have a plurality of phases, each of which constitutes one ink chamber phase,
Ink ejection control is sequentially performed for each phase. Specifically, as shown in FIG. 13, a plurality of ink chambers arranged at intervals of two are configured as one phase, and ink droplet ejection control is performed by three phases A, B, and C. .

FIG. 6 shows a state in which the partition walls forming the ink chambers NA, NB, NC are deformed and ink is ejected from the ink chamber NB. FIG. 6A shows a state in which the drive pulse voltage is not applied to all the channels. This state is called a rest period. FIG. 6B shows a state where ink is sucked into the channel NB by expanding the channel NB. In FIG. 6C, the channel NB is contracted so that the channel N
The state where ink is ejected from the nozzle of B is shown.

Further, FIG. 7A shows the waveform of the drive pulse voltage for ejecting ink from the nozzle of the channel NB. FIG. 7B shows a waveform of a drive pulse voltage for preventing ink from being ejected from the nozzle of any channel. Here, when the channel NB shown in FIG. 6B is expanded, and when the channel N shown in FIG.
The pulse waveform of B when contracted is shown in FIG. Since the ink ejection operation by applying the voltage of the pulse waveform is the same as the above-mentioned case, the description thereof is omitted here.

When the ejection pulse voltage is applied to the drive electrode 7 to operate the partition wall 22 in the direction in which the ink chamber 6 expands,
The application maintaining time of the ejection pulse voltage (pulse width of the ejection pulse) is the time L / a during which the pressure wave in the ink chamber 6 propagates in one direction in the longitudinal direction of the ink chamber 6 (L is the length dimension of the ink chamber 6, When a is a sound velocity in the ink), the pressure fluctuation can be most effectively increased, the ejection efficiency can be improved, and the ejection speed of the ink droplet can be increased. In the present embodiment, as shown in FIG. 14, as the application time of each drive pulse voltage, when the time during which the pressure wave for ejecting the ink droplet propagates from the rear end portion of the ink chamber to the ink ejecting portion at the front end is AL. , Application time of discharge pulse voltage is AL,
The application time of the non-ejection pulse voltage is set to 2AL, and the ink droplet ejection cycle is set to 3.5AL. In addition, the voltage values of the drive pulse voltages are set to be equal to each other, so that the power supply is shared.

Further, in the present ink jet head 1, the number of ink droplets to be ejected for one dot on the recording paper is made variable without changing the size of ink droplets ejected from the nozzles 41, 41, .... A multi-drop method is employed in which density gradation is performed by using this method. That is, similarly to the case described with reference to FIG. 15 above, the partition wall 22 is applied in the direction in which the ink chamber 6 is expanded by applying the ejection pulse voltage to the predetermined drive electrode 7.
After activating, the ink droplet ejection operation of applying a non-ejection pulse voltage to a predetermined drive electrode 7 to activate the partition wall 22 in the direction in which the ink chamber 6 contracts is performed according to the number of ink droplets ejected for one dot. By repeating the above, the required number of ink droplets are continuously ejected from the nozzle 41. The plurality of ink liquids thus ejected are applied onto the recording paper so as to combine during flight or to form one dot at the same time when landing on the recording paper.

This ink jet printer is provided with a drive pulse controller 81 for generating the above-mentioned ejection pulse voltage and non-ejection pulse voltage (see FIG. 5).

A feature of this ink jet printer is that it has a maximum ejection number changing means 82 for changing the maximum ejection number of ink droplets forming one ink dot according to the type of recording paper used. In particular (see FIG. 5). In other words, the recording paper that is the target of image formation is
The maximum number of ink droplets that can be ejected is changed depending on whether the type is “glossy paper for exclusive use of inkjet”, “coated paper for exclusive use of inkjet”, or “plain paper”. Specifically, as the type of recording paper, the maximum ejection number of ink droplets forming one ink dot is set to be smaller as the recording paper is more difficult to penetrate in the thickness direction and more likely to spread in the surface direction. ing. In other words, the ink droplets that form one ink dot are more likely to be formed when the image is formed on “inkjet-dedicated coated paper” or “plain paper” than when the image is formed on “inkjet-dedicated glossy paper”. It is set so that the maximum number of discharges of is reduced. Hereinafter, specific numerical values will be described.

FIG. 8 shows the result of an experiment carried out to determine the maximum number of ink droplets to be ejected. When two types of ink jet heads, head A and head B, were used to perform image forming operations, respectively. The results of measuring the dot diameters on various types of paper are shown in FIG.

Here, the head A has the above-mentioned structure and the diameter of the nozzle 41 is 17 μm. The amount of one ink droplet ejected by this head A is 2p
It is l. On the other hand, the head B differs from the head A only in the diameter of the nozzle 41, and the diameter thereof is 19 μm. The amount of one ink droplet ejected by the head B is 3 pl.

On the other hand, as the paper used here, "A glossy paper for exclusive use of inkjet" is used as A paper, "Coated paper for exclusive use of inkjet" as B paper, and "Plain paper" as C paper.

For example, when the printing resolution is 600 dpi, the ideal dot diameter is 59.8 μm. For this reason,
The maximum ejection number (maximum number of ink droplets forming one dot) required for each sheet based on FIG. 8 is as shown in Table 1 below.

[0054]

[Table 1] In this way, the maximum ejection number changing means 82 sets the maximum ejection number required for each sheet.

As means for identifying the type of recording paper in this apparatus, information input from the user (setting operation on the driver setting screen of the personal computer or input operation on the printer), The automatic detection method of recording paper by the light detection method (a method of irradiating the recording paper with light and detecting the reflected light to detect the presence or absence of the coating layer and the gloss state of the surface) is listed.

Another feature of the present inkjet printer is that the scanning speed (the scanning speed of the carriage) of the inkjet head 1 in the scanning direction (main scanning direction) is determined according to the maximum number of ink droplets obtained as described above. (Corresponding to the above) is provided (see FIG. 5). Specifically, the smaller the maximum ejection number of the ink droplet changed by the maximum ejection number changing means 82, the higher the scanning speed of the inkjet head 1 in the scanning direction is set. Hereinafter, the operation of changing the scanning speed will be specifically described.

The drop cycle (the time required to generate one drop (one ink drop)) of the ink jet head 1 configured as described above is generally determined by the ink chamber length and is, for example, 7 μs. In this case, the drive frequency f (Hz) is f = 1000000 / (7 x "maximum number of ink drops ejected" x 3) (1), and the carriage scanning speed when image formation is performed at a resolution of 600 dpi. V (ips: inch / sec) is V = (1/600) × f (2) Therefore, the drive frequency f under each of the above conditions
(Hz) and carriage scanning speed V (ips) are obtained as shown in Tables 2 and 3 below. In practice, the carriage scanning speed V is set with a margin of about 10% in consideration of the carriage speed fluctuation.

[0058]

[Table 2]

[0059]

[Table 3] As described above, the maximum ejection number of ink droplets is set according to the type of recording paper, and the carriage scanning speed (scanning speed of the inkjet head 1 in the scanning direction) is set according to the set maximum ejection number of ink droplets. By setting the image formation, it is possible to form dots of a desired size and suppress ink bleeding at all gradations (the number of gradations of "the changed maximum ejection number + 1"). The operation can be performed at high speed. As a result, it is possible to achieve both high quality of the formed image and high speed of the image forming speed.

Specifically, FIG. 9 shows the application timing of the drive pulse voltage when the maximum number of ink droplets ejected is set to "5". That is, according to Table 1, this pulse waveform shows the application timing when the paper B is used in the head A. FIG. 10 shows the application timing of the drive pulse voltage when the maximum number of ink droplets ejected is set to “3”. That is, according to Table 1, this pulse waveform shows the application timing when B paper or C paper is used in the head B. As shown in FIGS. 9 and 10, when the maximum number of ink droplets to be ejected is set to be small, the ejection period of each phase is set to be short so that the carriage scanning speed can be set high. Therefore, compared with the conventional application timing of the drive pulse voltage as shown in FIG. 16, that is, the maximum ejection number of ink droplets is fixed to “7” regardless of the type of recording paper, the image forming operation is performed. Higher speed can be achieved.

(Second Embodiment) Next, a second embodiment will be described. In the above-described first embodiment, the maximum number of ink droplets ejected is set according to the type of recording paper, and the scanning speed of the inkjet head 1 in the scanning direction is set according to the set maximum number of ink droplets ejected. It was This form is
Instead, the maximum ejection number of ink droplets is set according to the image forming mode, and the scanning speed of the inkjet head 1 in the scanning direction is set according to the set maximum ejection number of ink droplets. Since other configurations and operations are similar to those of the first embodiment, only the setting operation of the maximum number of ink droplets and the scanning speed setting operation of the inkjet head 1 will be described here.

The ink jet image forming apparatus of the present invention has "speed priority mode (draft mode)", "normal mode",
"Image quality priority mode (high image quality mode)" can be selected. For example, in the case of the "speed priority mode", the image resolution is reduced to increase the image forming speed. On the other hand, in the case of the "image quality priority mode", in general, a multi-pass operation is performed to make image defects due to variations and banding unique to the nozzles inconspicuous.

Therefore, for example, as shown in Table 4 below, the image resolution, the maximum number of ink drops to be ejected, the scanning speed of the carriage, depending on the combination of selection of the recording paper and the image forming mode,
The number of multi-pass is set.

[0064]

[Table 4] In Table 4, the first stage shows the image resolution, the second stage shows the maximum number of ink drops ejected, the third stage shows the scanning speed of the carriage, and the fourth stage shows the number of multi-passes.

As described above, the maximum number of ink drops to be ejected is set according to the image forming mode, and the scanning speed (carriage scanning speed) of the ink jet head 1 in the scanning direction is set according to the set maximum number of ink drops to be ejected. ), The image forming operation capable of forming dots of a desired size in all gradations and suppressing ink bleeding can be performed at high speed in this embodiment as well. You can

-Other Embodiments- In each of the above-described embodiments, the case where the present invention is applied to an ink jet printer for forming an image of a multi-pass recording system has been described. The present invention is not limited to this, and can also be applied to an inkjet printer that forms an image by a single-pass printing method.

Further, according to the present invention, bubbles are generated in the nozzle by heating the electrothermal conversion element to obtain the ejection pressure of ink droplets (so-called bubble jet (registered trademark)).
It is also possible to apply it to an inkjet printer which forms an image of the (method).

Further, in each of the above-described embodiments, the scanning speed of the ink jet head 1 in the scanning direction is changed according to the changed maximum number of ejected ink droplets. That is, the scanning speed of the inkjet head 1 in the scanning direction is set to be higher as the maximum number of ejected ink droplets is smaller, so that the high quality of the formed image and the high speed of the image forming speed are compatible with each other. It was The present invention is not limited to this, and includes the technical idea of changing only the maximum number of ink droplets to be ejected without changing the scanning speed of the inkjet head 1 in the scanning direction. For example, the one shown in FIG. 11 shows the application timing of the drive pulse voltage when the maximum ejection number of ink droplets before change is “7” and the maximum ejection number is set to “5”. There is. In this case, there is a time period in which the ink droplet ejection operation is not always executed by the reduction number “2” of the maximum ejection number.

[0069]

As described above, according to the present invention, when performing the multi-drop type image forming operation, the maximum number of ink droplets constituting one ink dot is changed according to the type of recording medium and the image forming mode. By limiting the size of the dots, it is possible to prevent the dot size from becoming larger than necessary and ink bleeding to occur. Therefore, high-quality image formation can be performed by a simple control operation such as setting the maximum number of ink droplets to be ejected.

Further, the scanning speed of the recording head in the scanning direction is changed according to the changed maximum number of ejected ink droplets. Specifically, the smaller the maximum number of ink droplets ejected, the higher the scanning speed of the recording head in the scanning direction is set. Therefore, the time required for one scan can be shortened, and as a result, the time required for forming an image on one recording medium can be shortened, and the image forming operation can be speeded up. .

In particular, when the present invention is applied to a system utilizing the piezoelectric shear strain effect capable of finely controlling the ink amount forming one dot by an integral multiple of the minimum ejected ink amount, the characteristics of the recording medium are It is possible to make good use of the control of the amount of ejected ink, and it is possible to achieve both high image quality and high image forming speed by optimizing the maximum number of ink droplets ejected.

[Brief description of drawings]

FIG. 1 is a perspective view showing an appearance of an inkjet head according to an embodiment.

FIG. 2 is an exploded perspective view of an inkjet head.

FIG. 3 is a cross-sectional view of the inkjet head as seen from the ink ejection direction.

4 is a cross-sectional view of the inkjet head at a position corresponding to line IV-IV in FIG.

FIG. 5 is a diagram showing a control block for applying a voltage to drive electrodes.

FIG. 6 is a diagram for explaining a deformation operation of a partition wall forming the ink chamber.

FIG. 7 is a diagram for explaining changes in drive pulse voltage and potential difference between electrodes for each channel.

FIG. 8 is a diagram showing the results of measuring the dot diameters on various types of paper when performing image forming operations using two types of inkjet heads.

FIG. 9 is a diagram showing an example of the drive pulse voltage application timing in each phase ejection period when the maximum number of ink droplets ejected is set to “5”.

FIG. 10 is a diagram showing an example of the drive pulse voltage application timing in the ejection period of each phase when the maximum ejection number of ink droplets is set to “3”.

FIG. 11 is a diagram showing an example of a drive pulse voltage application timing when the maximum number of ink drops is set to “5” and the scanning speed of the inkjet head is not changed.

FIG. 12 is a view corresponding to FIG. 3 in a conventional example.

FIG. 13 is a diagram corresponding to FIG. 3 for explaining an ink droplet ejection control operation of each ink chamber.

FIG. 14 is a diagram showing application timings of an ejection pulse voltage and a non-ejection pulse voltage.

FIG. 15 is a diagram showing the application timing of each drive pulse voltage in the conventional multi-drop method.

FIG. 16 is a diagram showing an example of drive pulse voltage application timing in each phase ejection period in the conventional multi-drop method.

[Explanation of symbols]

1 Inkjet head (recording head) 22 partition 6 ink chamber 7 Drive electrode 82 Maximum discharge number changing means 83 Speed change means

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Claims (7)

[Claims] 1. An image forming apparatus for performing a multi-drop type image forming operation capable of forming ink dots on a recording medium by a plurality of ink droplets ejected continuously, wherein one ink is used depending on the type of the recording medium. An inkjet image forming apparatus comprising: a maximum ejection number changing means for changing the maximum ejection number of ink droplets forming a dot. 2. The ink jet image forming apparatus according to claim 1, wherein the maximum ejection number changing means is a recording medium of which the ink is less likely to permeate in the thickness direction and more easily spread in the surface direction. An inkjet image forming apparatus characterized in that the maximum number of ink droplets forming one ink dot is set to be small. 3. An image forming apparatus for performing an image forming operation of a multi-drop method capable of forming ink dots on a recording medium by a plurality of ink droplets continuously ejected, having a plurality of kinds of image forming modes and executing the same. An inkjet image forming apparatus, comprising: a maximum ejection number changing means for changing the maximum ejection number of ink droplets forming one ink dot according to the image forming mode. 4. The inkjet image forming apparatus according to claim 1, 2 or 3, wherein an image is formed by ejecting ink droplets onto a recording medium while the recording head moves in a predetermined scanning direction. An inkjet image forming apparatus is provided with a speed changing unit that changes a scanning speed of a recording head in a scanning direction according to the maximum number of ejected ink droplets that is changed by the maximum ejection number changing unit. 5. The inkjet image forming apparatus according to claim 4, wherein the speed changing unit sets the scanning speed of the recording head in the scanning direction to be higher as the maximum number of ink droplets ejected is smaller. apparatus. 6. The inkjet image forming apparatus according to any one of claims 1 to 5, wherein the recording head includes a partition wall which is at least partially formed of a piezoelectric member and is polarized in a predetermined direction, and the partition wall. A plurality of ink chambers separated from each other and a drive electrode provided on the partition wall are provided. By selectively applying a predetermined drive pulse voltage to the drive electrode, an electric field is applied to the partition wall to shear the partition wall. An inkjet image forming apparatus, which is configured to generate deformation and control the number of ink droplets ejected from an ink chamber according to the number of pulses of a drive pulse voltage so that a dot diameter can be adjusted. 7. An inkjet image forming method of a multi-drop method which is executed in the inkjet image forming apparatus according to claim 1. Description: