JP3067839B2 - Ink jet recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates meant an ink jet recording apparatus <br/>, more particularly, by using a recording head having a plurality of ink discharge ports, an ink jet recording apparatus which forms a floor Choga image.

[0002]

2. Description of the Related Art An ink jet recording system is a system in which an ink is ejected from an ink ejection port (hereinafter, referred to as a nozzle) in accordance with a recording signal to visualize an image on a recording material (recording paper). Generally, in order to perform printing at a high speed, printing is performed by discharging ink from a print head integrally formed with a large number of nozzles. In this case, if a structure in which a large number of nozzles are arranged in a straight line is used, it is relatively easy to manufacture the nozzles in terms of manufacturing technology, and the nozzles can be arranged at a high density.

[0003] In particular, when a color image is recorded, usually yellow, magenta and cyan (black as required)
Are used.

In order to express a gradation by this ink jet recording method, the size of a droplet to be ejected may be changed. However, there is no established method, and usually a known method is used. 2. Description of the Related Art The number of dots per unit area is controlled by an image processing technique. Further, there is a method in which a large number of ink droplets are ejected at substantially the same position by reducing the size of one ink droplet, and gradation is expressed by controlling the number of ink droplets. Gradation recording can be performed without reducing image quality.

[0005]

In order to perform printing at a high speed, it is effective to increase the number of nozzles. However, when the number of nozzles is increased, the width of printing performed at one time is increased.
As a result, the image density becomes uneven due to a minute difference in the ejection characteristics of each nozzle.

According to an experiment by the inventors of the present application, even a change in the ink ejection amount of at most a few percent is recognized as unevenness of the image, and there are serious drawbacks in recording an image with gradation. Become.

In particular, in a system in which a large number of ink droplets are ejected at substantially the same position on recording paper to control gradation, it is necessary to eject an extremely large number of ink droplets in order to record one image. However, since there is a limit to increasing the driving frequency of each nozzle, it is indispensable to increase the number of nozzles, and it is difficult to prevent the density unevenness of the image generated in that case.

In the method of ejecting a large number of ink droplets at substantially the same position, it is necessary to reduce the size of each ink droplet. The bleeding of the ink on the top became smaller,
There is a possibility that a gap is generated between adjacent recording pixels due to a small error of the driving position, and a streak is generated in the obtained image.

In order to prevent the occurrence of such streaks,
It is desirable that a large number of ink droplets are ejected while being shifted by a minute amount in the vertical and horizontal directions, but such control has been difficult in the past.

In view of the above, it is an object of the present invention to provide an ink jet recording apparatus which can increase the density of ink discharge ports and is suitable for obtaining a gradation image free from streaks and unevenness. is there.

[0011]

For this purpose, the present invention provides an ink jet recording apparatus which forms one pixel by discharging a number of ink droplets corresponding to the gradation data of the pixel to express gradation. A recording head having at least one row of ejection port arrays in which N ink ejection ports are arranged substantially in a straight line, and in arranging the recording head in opposition to a recording material, the ejection port array has L scans. Arranging means for arranging the scanning line and the recording head so as to face each other, input means for inputting a gradation data signal corresponding to each of a plurality of pixels, and the recording head and the recording material. The ink droplet array is configured to move relatively, and a maximum of M ink droplets (M = N / L) corresponding to the gradation data signal input from the input means in one pixel are formed in the ejection port arrangement. N a And control means for ejecting the maximum M different ink discharge ports successive corresponding to the gray-scale data signal among the click discharge port, characterized by comprising a.

[0012]

Here, when the pitch of the scanning lines is A, it is preferable to set A × L to 0.5 mm or less, or to set L to 8 or less.

[0014]

According to the present invention for [action] claim 1, by arranging the ink ejection orifice row of the printing head at an angle, the area covered by a plurality of ink discharge ports is only scan line width of a predetermined number, moreover, By shifting the relative position between the recording head and the recording material (recording paper), ink is ejected from different ink ejection ports to the same pixel, and the characteristics of the individual ink ejection ports may vary slightly. Even if it is turned on, it becomes possible to make the streak on the image inconspicuous.

According to the present invention for claim 2, despite being recorded using a recording head having N ink discharge ports, the width to be recorded is only L of scanning lines at a time. Therefore, even when the density of the image becomes uneven due to the variation of the discharge characteristics of the respective discharge ports or the like, the recording width of L scanning lines is repeated when viewed over the entire image, so that the streak becomes inconspicuous.

According to the study by the inventors of the present application, it has been found that the unevenness in image density is generally more easily recognized as the recording width becomes wider. For example, 1 per mm
When an image composed of about 6 pixels is viewed at a distance of clear vision, if the unevenness has a width of about 8 mm, it is recognized as uneven even with a density fluctuation of several%, whereas the width of about 1 mm or less is recognized. Then, even a density fluctuation of several tens% or more can be visually permissible.

As described above, according to the present invention, since the width to be recorded at a time is as small as L scanning lines, the width of the density unevenness caused by the variation of the ink ejection ports becomes small, and it becomes almost acceptable. can do. In addition, the recording speed does not decrease despite the fact that the recording width at a time is small.

Further, according to the present invention, since a plurality of ink ejection ports are used to form one pixel, even if the characteristics of each ejection port vary, it is possible to use the same. Are averaged and the variation is reduced, which also suppresses the unevenness of the image.

[0019]

Embodiments of the present invention will be described below in detail.

Embodiment 1 FIG. 1 is a schematic external view showing an embodiment of an ink jet recording apparatus to which the present invention is applied.

In the present embodiment, a recording paper 2 as a recording material is wound around a drum 4 and is rotated by a driving device 6. The recording head 101 is arranged so that its nozzle row is slightly oblique to the main scanning direction formed by the rotation of the recording paper 2 (ie, is not parallel).

When a full-color image is recorded, three (yellow, magenta, cyan) to four (black addition) recording heads are used (not shown), and color ink is supplied from each recording head. Recording is performed by discharging.

The recording head 101 performs recording while moving from left to right in the sub-scanning direction by a head driving device (not shown).

FIG. 2 shows a schematic configuration of a control system circuit in the embodiment shown in FIG. Here, reference numeral 201 denotes a main controller which controls the entire apparatus such as a discharge timing, and includes, for example, a CPU (Central Processing Unit), a program ROM (Read Only Memory), and a work RA.
A one-chip microprocessor or the like incorporating M (random access memory) or the like is usually used. The main controller 201 transmits the gradation data signal to the host computer 20.
3 and stored in the frame memory 205 for the buffer in frame units. Then, at the time of image recording (at the time of ink ejection), the main controller 201 sends the carriage feed motor 209 through the first motor driver 207.
Of the paper feed motor 213 through the second motor driver 211 and the driver controller 215 and the head driver 217 based on the gradation data read from the frame memory 205.
And discharge control of the head 101 (to be described in detail below) via the control unit, thereby performing gradation image recording on the recording paper 2.

FIG. 3 shows the relative positional relationship between the recording paper 2 and the nozzle rows included in the recording head 101. In the figure, a-17 to a + 2 on the left side of the figure indicate pixel numbers in the main scanning direction on the recording paper. The vertical lines b + 1 to b + 4 indicate main scanning lines formed by the rotation of the drum 4.

In this embodiment, the recording head 101 has 20 nozzles, and ink droplets are landed on four scanning lines (more precisely, on and around the scanning lines) by one rotation of the drum 4. Let it. In other words, the twenty nozzles linearly provided on the recording head 101 are arranged so that the arrangement direction is oblique to the main scanning direction, and the ink landing area ( The impact positions are on and around the four main scanning lines.

[0027] Thus, the nozzle array of the print head (nozzle array), since it is arranged so as to form a slight angle with the main scanning line, the pitch P _N between the actual nozzle about than the pixel pitch P _P It is about 2% longer. That is, the recording paper moves by one pixel pitch in the direction of the arrow every time the recording head discharges droplets repeatedly, so that the nozzle pitch in the main scanning direction matches the pixel pitch.

In this case, as an example, the repetitive drop ejection frequency per nozzle of the recording head is 10 kHz and the pixel density is 1
When 16 per mm, and the pitch P _P of the pixel 62.5
μm, the nozzle pitch _PN is 63.7 μm, and the recording paper speed is 0.625 m / sec.

In this embodiment, five ink droplets are ejected per pixel in the highest density portion. Therefore, 5
It is possible to perform six-step gradation recording of shots, four shots, three shots, two shots, one shot, and zero shots.

The process of performing such six-step gradation recording will be described in detail below.

First, the nozzle numbers 1-1 and 1 shown in FIG.
-2, 1-3, 1-4, 1-5, etc. will be described. In this nozzle number (xy), x indicates which main scanning line corresponds to the pixel. That is, x = 1 corresponds to a nozzle for forming a pixel on the main scanning line b + 1, and x = 2 corresponds to a nozzle for forming a pixel on the main scanning line b + 2 (hereinafter, omitted).

In the nozzle number (xy), y represents a nozzle used when ejecting ink droplets of "y emission" (in this embodiment, y.ltoreq.5). It does not indicate the order of ejection. For example, the main scanning line b +
In order to land three ink droplets at the position of the pixel number a-1 above the first ink droplet, first eject the first ink droplet from the nozzle 1-2 , and then move the recording paper in the direction of the arrow. 1 pixel is moved by the pitch by ejecting ink droplets of the second shot counted from the nozzle 1-1, further recording paper 1 pixel pitch by a third shot as counted from the nozzle 1 3 is moved in the direction indicated by an arrow Is ejected. In this way, ink landing as shown in FIG. 4C is performed.

In order to eject five ink droplets as shown in FIG. 4E, first, the first ink droplet is ejected from the nozzles 1-4 , and thereafter, the movement of the recording paper is performed. every time the nozzle 1 2, 1-1,1- 3, and ink ejection in the order of 1 5.

Next, other specific examples of the ink discharge control will be described in detail with reference to FIGS. In each of these figures, a small circle indicates the position of the nozzle, and a large circle indicates the impact mark (dot or ink dot) of the ink droplet.

The ink ejection states shown in FIGS.
FIG. 4 shows an ejection sequence when a maximum density pattern (5 ink ejections per pixel) of one pixel in width and three pixels in length is formed on the main scanning line b + 2 in FIG.

In this way, as shown in FIG. 11, the maximum number of ink droplet ejections (five shots) are performed at each position of the pixel numbers a, a + 1, and a + 2. In each of these figures,
In order to make the figure easier to see, the size of the dot recorded with respect to the nozzle pitch is drawn much smaller than the actual size.

By performing the above-described ink ejection control and moving the recording head 101 in the sub-scanning direction, an image is recorded while being spread in a direction perpendicular to the main scanning direction.
It is possible to prevent a gap from being formed between scanning lines even in a high density portion.

In FIG. 4, for the sake of explanation, the landing positions are shown to be arranged in a straight line, but as is already known, an ink jet recording head having a plurality of nozzles must be driven in a time-division manner. In this case, it is possible to extend the landing position in the vertical direction by shifting the driving timing between the adjacent nozzles.

In addition, the pattern of the ink droplets to be overprinted is not limited to the present embodiment. For example, in the case of only two shots, it is possible to control so as to discharge from the nozzles at both ends.

Furthermore, if the design is made in consideration of the timing of the time-division driving, the nozzle pitch may be slightly changed from that of the present embodiment, and the angle between the nozzle row and the main scanning line may be changed accordingly. it can.

According to the study of the present inventors, in general, the ability to discriminate the density of human vision depends on the cycle of the density and the roughness (resolution) of the image. When the pixels forming the image are sufficiently small, the shading cycle is several mm.
In the case of, the discrimination ability becomes the highest, and it becomes inconspicuous if it is larger or smaller.

In particular, when the shading cycle due to the unevenness of the image is 0.
When it is 5 mm or less, it suddenly becomes inconspicuous,
In the case of the period of m, the unevenness of the density of 4 to 5% can be identified, but in the case of 0.3 mm, the unevenness of the density cannot be identified unless the unevenness is about 10% or more. If it is 0.2 mm or less, it becomes almost indistinguishable regardless of the degree of density unevenness. On the other hand, 1 mm
In the case of the period, even if the density unevenness is 2% or less, it is identified.

Although there are individual differences in these discrimination limits,
There is not much individual difference in the tendency to the cycle.

When the pixels constituting the image are coarse (the resolution is low), fine density fluctuations cannot be identified. When the cycle of the density unevenness is 5 pixels or less, the difference in density is not a problem because it is almost hidden by the roughness of the pixel.

If the cycle of density unevenness is about 8 pixels, 1
Density unevenness of about 0% can be identified. With 10 pixels or more, it is possible to identify unevenness of about 5% or less. This tendency is almost the same for an image coarser than about 16 pixels per mm. For example, in the case of a coarse image of about 2 pixels per 1 mm, when viewed from a very close position, only the roughness is conspicuous, so that unevenness of density having a small cycle is not recognized. In practice, such an image will be viewed at a distance greater than the clear vision distance. Therefore, the shortest distance in which a practical image is viewed depends on the roughness of the pixel. As a result, the discrimination limit of uneven density is determined by the number of pixels of the image.

In consideration of the above, in this embodiment, the pitch of the scanning lines is A, and the number of scanning lines to be simultaneously recorded is L.
When A × L is 0.5 mm or less, or
If L is set to 8 or less, even if the unevenness due to the difference in the ejection characteristics of each nozzle reaches about several percent, there is no problem on the image at all.

In particular, in the present embodiment, considering that one pixel is recorded by a plurality of nozzles, there is a problem even if the difference in the size of the ink droplet ejected from each nozzle reaches about 10%. But a beautiful image is obtained.

Further, if the above-mentioned A × L is selected to be 0.3 mm or less, or L is set to 5 or less, image unevenness due to minute variation in ejection characteristics of each nozzle can hardly be recognized, and variation in the recording head. Regardless, an extremely beautiful image can be obtained.

Embodiment 2 FIG. 12 shows a second embodiment to which the recording apparatus of the present invention is applied. In this embodiment, a recording head 101 is provided on a carriage 50 as in a normal serial printer, and recording is performed in synchronization with the movement of the carriage 50.

One scan of the carriage 50 records L scanning lines, and the recording paper 2 is fed in the direction of arrow A accordingly.

In this embodiment, the recording method is the same as that in the first embodiment. Therefore, the recording head 101 is arranged so that the nozzle arrangement direction is laid at an angle nearly horizontal.

In the apparatus of the first embodiment, when a recording head having an extremely large number of nozzles is used, the interval between the nozzle ends at both ends and the recording paper 2 must be increased.
The size of the print head that can be used is limited to a relatively small one. However, in the apparatus of this embodiment, the platen 52 is made flat so that a large print head having a relatively large number of nozzles can be used. There is an advantage of gaining.

On the other hand, the method by rotating the drum (Embodiment 1) is easier than the method by moving the carriage (Embodiment 2) to increase the relative moving speed of the recording paper and the recording head. The apparatus of Example 1 is suitable for a recording head that can be driven at a high speed with a relatively small number of nozzles.

Embodiment 3 In the third embodiment, the above-described Embodiment 1 or Embodiment 2
By using the same device as described above and making the size of the ink droplets ejected from each nozzle different, it is possible to increase the number of gradations without increasing the number of overprints.

For example, the nozzles 1-1 and 2- in FIG.
For 1,3-1,4-1, if the volume of ink is ejected almost twice as large as the other nozzles, even if the number of overlapping shots is the same, depending on the combination of which nozzle is ejected, Expression of seven gradations becomes possible.

The size of each nozzle is greatly changed, and the volume of the droplet discharged from each nozzle is, for example, a discharge volume ratio of 1, 1/2, 1/4, 1/8, and 1/16. In this case, 32 gradations can be achieved.

In order to implement this, the ejection volume of ink droplets may be made different for each nozzle. For example, as a method of an ink jet head, bubbles are generated in ink by heat energy, and In the case of using a method of ejecting ink along with the generation, the size of the heating surface of the heater and the opening area of the ejection port may be changed.

In general, it is difficult to increase the density of the nozzle array if the nozzles are designed so as to increase the opening area of the nozzles in order to increase the discharge volume of the ink droplets. Since the overstrike is performed, the opening area of the nozzle can be designed to be smaller than that in the conventional case where no overstrike is performed, so that the density can be easily increased.

Further, in each of the embodiments described above, it is possible to arrange a nozzle having a relatively small volume of ejected ink droplets adjacent to a nozzle having a relatively large volume of ejected ink droplets. Densification is easy.
Here, as a method of making the volume of the ejected ink droplet different for each nozzle, for example, as described in JP-A-60-27548, while the meniscus of all the nozzles is vibrated by a piezo element, It is also effective to use different timings.

(Others) The present invention includes a means (for example, an electrothermal converter, a laser beam, or the like) for generating thermal energy as energy used for performing ink ejection, particularly in an ink jet recording system. An excellent effect is obtained in a recording head and a recording apparatus of a type in which the state of ink is changed by the thermal energy. This is because according to such a method, it is possible to achieve higher density and higher definition of recording.

The typical configuration and principle are described in, for example, US Pat. Nos. 4,723,129 and 4,740.
It is preferable to use the basic principle disclosed in the specification of Japanese Patent No. 796. This method is a so-called on-demand type,
It can be applied to any type of continuous type, but especially in the case of on-demand type, it can be applied to the sheet holding liquid (ink) or the electrothermal converter arranged corresponding to the liquid path. By applying at least one drive signal corresponding to the recorded information and giving a rapid temperature rise exceeding the nucleate boiling, heat energy is generated in the electrothermal transducer, and film boiling occurs on the heat acting surface of the recording head. As a result, the liquid (ink)
This is effective because air bubbles can be formed inside. The liquid (ink) is ejected through an ejection opening (ejection port) through the process of growth and contraction of the bubble to form at least one droplet. When the drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of a liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable. US Pat. No. 4,463,335 discloses a pulse-shaped drive signal.
No. 9 and No. 4,345,262 are suitable. Further, if the conditions described in US Pat. No. 4,313,124 relating to the temperature rise rate of the heat acting surface are adopted, more excellent recording can be performed.

As the configuration of the recording head, in addition to the combination configuration (a linear liquid flow path or a right-angled liquid flow path) of a discharge port, a liquid path, and an electrothermal converter as disclosed in the above-mentioned respective specifications. U.S. Pat. No. 4,558,333 and U.S. Pat. No. 44,558 which disclose a configuration in which a heat acting portion is arranged in a bending region.
A configuration using the specification of Japanese Patent No. 59600 is also included in the present invention. In addition, Japanese Unexamined Patent Application Publication No. 59-123670 discloses a configuration having a discharge section having a common slit as a discharge opening for a plurality of electrothermal transducers, and an aperture for absorbing pressure waves of thermal energy. The effect of the present invention is effective even if the configuration is based on JP-A-59-138461, which discloses a configuration in which is provided corresponding to a discharge unit. That is, according to the present invention, recording can be reliably and efficiently performed regardless of the form of the recording head.

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

Further, it is preferable to add ejection recovery means for the recording head, preliminary auxiliary means, and the like as the configuration of the recording apparatus of the present invention since the effects of the present invention can be further stabilized. To be more specific, capping means for the print head, cleaning means, pressurizing or suction means, an electrothermal transducer or a heat generating element for generating thermal energy for discharging ink droplets necessary for printing. Preheating means for performing preheating using a different heating element or a combination thereof may be used, and predischarge means for performing discharge different from recording.

The type and number of recording heads to be mounted are, for example, not only one provided for single color ink, but also a plurality of inks having different recording colors and densities. A plurality may be provided. That is, for example, the printing mode of the printing apparatus is not limited to a printing mode of only a mainstream color such as black, but may be any of integrally forming a printing head or a combination of a plurality of printing heads. The present invention is also very effective for an apparatus provided with at least one of the recording modes of full color by color mixture.

In addition, the discharge port array is not limited to one row, and it is also possible to adopt a configuration of a plurality of rows (for example, a configuration in which one row has 20 discharge ports and four rows are arranged).

In addition, in the above-described embodiments of the present invention, the ink is described as a liquid. However, even if the ink solidifies at room temperature or lower, it can be softened or liquefied at room temperature. Since it can be used in liquid form when recording is performed, it can be used in the present invention. Alternatively, in the ink jet system, in some cases, the temperature is adjusted so that the ink itself is kept within a range of 30 ° C. or more and 70 ° C. or less, and the temperature is controlled so that the viscosity of the ink is in a stable ejection range. 30 ° C in this case
An ink that is liquid at a temperature of 70 ° C. or lower can be used. In addition, the ink is liquefied for the first time by heating in order to positively prevent the temperature of the ink itself from rising due to thermal energy or to prevent the ink from evaporating by using the energy as the energy of the state change from the solid state to the liquid state of the ink. May be used. In any case, the application of heat energy causes the ink to be liquefied by the application of the heat energy according to the recording signal and the liquid ink to be ejected, or to start solidifying when it reaches the recording medium. The present invention is also applicable to a case where an ink having a property of liquefying for the first time is used. In such a case, the ink
JP-A-54-56847 or JP-A-60-7
It may be used for recording while being held as a liquid material or a solid material in concave portions or through holes of a porous sheet as described in JP-A-1260. In the present invention, it is most effective to execute the above-described method of causing film boiling for each ink.

Further, the form of the ink jet recording apparatus according to the present invention is not only used as an image output terminal of an information processing apparatus such as a computer, but also a copying apparatus combined with a reader or the like, and further, a facsimile having a transmission / reception function. It may be in the form of an apparatus.

[0069]

As described above, according to the present invention, the recording head is arranged so that the nozzle row of the recording head and the scanning line are oblique, and a plurality of ink droplets respectively ejected from different ink ejection ports. To form one pixel, it is possible to obtain a high-gradation image free from streaks and unevenness due to variations in the ink ejection amount. Further, since there is a great degree of freedom in designing the ink discharge amount, it is easy to increase the density of the ink discharge ports.

[Brief description of the drawings]

FIG. 1 is a schematic external view showing an inkjet recording apparatus according to one embodiment of the present invention.

FIG. 2 is a block diagram illustrating a control unit according to one embodiment of the present invention.

FIG. 3 is a diagram illustrating a positional relationship between a recording sheet as a recording material and a recording head having a plurality of ink discharge ports (nozzles).

FIG. 4 is a diagram showing a state when a plurality of ink droplets land on one pixel in the present embodiment.

FIG. 5 is a diagram showing a specific process of ink ejection control.

FIG. 6 is a diagram showing a specific process of ink ejection control.

FIG. 7 is a diagram showing a specific process of ink ejection control.

FIG. 8 is a diagram illustrating a specific ink ejection control process.

FIG. 9 is a diagram illustrating a specific ink ejection control process.

FIG. 10 is a diagram showing a specific process of ink ejection control.

FIG. 11 is a diagram illustrating a specific process of ink ejection control.

FIG. 12 is an external view showing an inkjet recording apparatus according to another embodiment of the present invention.

[Explanation of symbols]

 2 Recording paper as recording material 4 Drum 6 Drum driving device 50 Carriage 52 Platen 101 Recording head

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/205 B41J 2/04-2/065

Claims (2)

(57) [Claims] 1. An ink jet recording apparatus for forming a pixel by discharging a number of ink droplets corresponding to the gradation data of the pixel to express a gradation, wherein the N ink discharge ports are substantially straightforward. A recording head having at least one row of ejection port arrays arranged on a line, and arranging the recording head so as to face a recording material so that the ejection port arrangement faces the L scanning lines, Arranging means for arranging a recording head; input means for inputting a gradation data signal corresponding to each of a plurality of pixels; relatively moving the recording head and the recording material;
A maximum of M (M = N / L) ink droplets corresponding to the gradation data signal input from the input means in one pixel are applied to N ink ejection ports forming the ejection port array. Control means for discharging from a maximum of M different continuous ink discharge ports in accordance with the gradation data signal. 2. The method according to claim 1, wherein A × L is 0.5 mm or less, wherein A is a pitch of the scanning lines.
Is set to 8 or less.