JP4187772B2 - Inkjet recording apparatus and recording method - Google Patents

Description

The present invention relates to an inkjet recording apparatus and a recording method .

  An inkjet head used in an inkjet recording apparatus used as an image recording apparatus (image forming apparatus) such as a printer, a facsimile machine, a copying apparatus, or a plotter has a nozzle for ejecting ink droplets, a pressurizing chamber to which the nozzle communicates, Pressure generating means for generating pressure to pressurize the ink in the pressure chamber, and by applying a driving waveform to the pressure generating means and driving, the pressure / volume in the pressure chamber is changed to eject ink droplets from the nozzles. .

  As a conventional inkjet head, a piezoelectric type that pressurizes ink in a pressure chamber by deforming and displacing a vibration plate that forms the wall surface of the pressure chamber using a piezoelectric element in terms of the method of pressure generation means, A bubble type that pressurizes ink in the pressure chamber by generating a valve by film boiling using a heating resistor provided in the pressure chamber, a diaphragm that forms the wall surface of the pressure chamber, and an electrode facing it The diaphragm is roughly classified into an electrostatic type that pressurizes the ink in the pressurized chamber by deforming and displacing the diaphragm with an electrostatic force.

  By the way, in the inkjet recording apparatus, the dot size and the resolution are greatly related to the image quality in order to form an image with dots. In other words, if the dot size is too small relative to the resolution, the image will be whitish with poor solidity. Conversely, if the dot size is too large relative to the resolution, gradation suppression will not work, and graininess will not be achieved. It will be a very bad image.

  On the other hand, dot size reduction and higher resolution are progressing in response to the demand for higher image quality. However, as the dot size decreases and the resolution increases, it takes more time to fill the unit area with dots, resulting in a decrease in printing speed. Theoretically, it is only necessary to eject ink droplets with a shorter period (high frequency driving) in accordance with the increase in resolution, but in practice it is not easy to double the driving frequency.

  Therefore, conventionally, according to the method for suppressing the decrease in the overall printing speed by increasing the number of nozzles to increase the area for forming an image at once, and the recording mode using a head that can vary the ink droplet amount. A method of switching resolution and dot size is used. The former method is very effective because the printing speed can be doubled by doubling the number of nozzles. However, this method also has limitations due to problems such as mounting area, cost, and paper pressing at the printing position. . Further, the method of changing the ink droplet amount is simply to reduce the image quality and increase the printing speed, and the printing speed in the high resolution mode remains low. Therefore, these methods are combined with an increase in driving frequency.

  Among them, the method of changing the ink droplet amount is described in, for example, a method of controlling the ink droplet amount by switching the pressure applied to the liquid chamber as described in Patent Document 1, and Patent Document 2. As described above, there is known a method of controlling the ink droplet amount by changing the volume of the liquid chamber in a pseudo manner by shifting the drive timing in accordance with the vibration of the liquid level (meniscus) of the nozzle hole. Both can be applied regardless of the pressure generating means, and these two methods can increase the number of nozzles rather than separately having units corresponding to different ink droplet amounts, and are small in size. This is advantageous in terms of the speed and printing speed.

JP-A-11-010842 Japanese Patent Laid-Open No. 11-020165

  By the way, the size of ink droplets is usually greatly affected by the size and shape of the liquid chamber in which the pressure is applied, the viscosity of the ink itself, the nozzle diameter and nozzle surface wettability, the fluid resistance of the entire unit, and the like. The optimum value varies depending on the size of the ink droplet. Therefore, when ejecting ink droplets of different sizes in the same unit, the unit that ejects ink droplets should be at an intermediate level so that it can accommodate either the larger or the smaller droplets. It will be optimized together.

  For this reason, when forming and discharging the droplet of the other size, it is necessary to create a condition for discharging the droplet of the other size by changing the pressure and timing, which causes various limitations. For example, when forming a small drop with a unit optimized for a large drop, the jet pressure is reduced or the jet speed is reduced when the meniscus is pulled toward the liquid chamber. Positional accuracy is affected, or bubbles are drawn into the liquid chamber, which tends to cause ejection abnormalities.

  On the other hand, the droplets ejected due to excessive pressure have long tails in the form of a string, causing satellites to occur frequently and deteriorating the dot shape, or immediately supplying the same amount as the ejected ink droplet amount into the liquid chamber Otherwise, the ink droplet amount may not be maintained at a constant value. Therefore, there is a problem that even if the ink droplet amount variable function is provided, the variable width cannot be increased so much.

The present invention has been made in view of the above problems, and an object thereof is to improve the graininess can form a fine dot.

In order to solve the above problems, an ink jet recording apparatus according to the present invention includes:
In an ink jet recording apparatus comprising a head having a nozzle that ejects ink droplets, a pressure chamber that communicates with the nozzle, and a pressure generation unit that generates pressure to pressurize the ink in the pressure chamber.
The ink droplets for forming dots identifiable with the naked eye are divided to form main dots and satellite dots of a size that cannot be recognized with the naked eye,
Center position of the satellite dots, has a structure which is formed on the separated 2 or more dots from a deposition center position of the main dot position.

Here, a configuration area before Symbol satellite dots of ink droplets are ejected becomes smaller than the area of the main dots. In addition, when the main dot and the satellite dot with respect to another main dot are at the same landing position, the ink droplet forming the main dot is not ejected.
In addition, a drive control unit that ejects ink droplets that form the main dots and satellite dots can be provided. In this case, when the dot having a size that cannot be recognized by the naked eye is formed, the drive control unit ejects an ink droplet in which the satellite dot is formed, and forms a dot other than the dot having a size that cannot be recognized by the naked eye. In some cases, the satellite dots are not generated, or the satellite dots eject ink droplets absorbed in the main dots.

Further, when the recorded image is a character or line image, an ink droplet in which the satellite dot is not formed can be ejected.
Further, only when photo ink is used, ink droplets in which the satellite dots are formed can be ejected.
In addition, it is possible to discharge ink droplets in which the satellite dots are formed only in the highlight portion of the image and the satellite dots are not formed in the shadow portion.

The recording method according to the present invention comprises:
In a recording method in an ink jet recording apparatus including a head having a nozzle that discharges ink droplets, a pressure chamber that communicates with the nozzle, and a pressure generation unit that generates pressure to pressurize ink in the pressure chamber.
The ink droplets for forming dots identifiable with the naked eye are divided to form main dots and satellite dots of a size that cannot be recognized with the naked eye,
The center position of the satellite dot is formed at a position separated by 2 dots or more from the landing center position of the main dot.

According to the ink jet recording apparatus and the recording method of the present invention, the ink droplets for forming dots that can be identified with the naked eye are divided to form main dots and satellite dots with a size that cannot be recognized with the naked eyes, Since the center position of the satellite dots is formed at a position two or more dots away from the landing center position of the main dots, it is possible to prevent the landed satellite drops from fusing with the main drops.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a mechanism portion of an ink jet recording apparatus according to the present invention.
The mechanism of this ink jet recording apparatus has a main support guide rod 3 and a sub support guide rod 4 mounted between the side plates 1 and 2 on both sides in a substantially horizontal positional relationship, and the main support guide rod 3 and the sub support guide. The carriage 5 is supported by the rod 4 so as to be slidable in the main scanning direction.

  The carriage 5 has four heads 6y, 6m, 6c, and 6k that discharge yellow (Y) ink, magenta (M) ink, cyan (C) ink, and black (Bk) ink, respectively, on the discharge surface ( The nozzle surface is mounted facing downward, and four heads are mounted on the carriage 5 above the head 6 (reference numeral “6” is any one of “6y, 6m, 6c, 6k” or a generic name). 4 ink cartridges 7 (symbol “7” is any one of “7y, 7m, 7c, 7k” or a generic name), which are ink supply bodies of each color for supplying ink to each 6, are interchangeably mounted. ing.

  The carriage 5 is connected to a timing belt 11 stretched between a drive pulley (drive timing pulley) 9 and a driven pulley (idler pulley) 10 that are rotated by the main scanning motor 8 to drive the main scanning motor 8. By controlling, the carriage 5, that is, the four heads 6 are moved in the main scanning direction.

  Further, sub frames 13 and 14 are erected on the bottom plate 12 connecting the side plates 1 and 2, and a conveying roller 15 for feeding the paper 16 in the sub scanning direction perpendicular to the main scanning direction is provided between the sub frames 13 and 14. Holds freely. A sub-scanning motor 17 is disposed on the side of the sub-frame 14, and a gear 18 fixed to the rotation shaft of the sub-scanning motor 17 and the transporting roller 15 in order to transmit the rotation of the sub-scanning motor 17 to the transporting roller 15. And a gear 19 fixed to the shaft.

  Further, a reliability maintenance / recovery mechanism (hereinafter referred to as “subsystem”) 21 of the head 6 is disposed between the side plate 1 and the subframe 12. The sub-system 21 holds four cap means 22 for capping the ejection surface of each head 6 by a holder 23, and this holder 23 is held by a link member 24 so as to be swingable. When the carriage 5 comes into contact with the engaging portion 25 provided on the holder 23 by the movement, the holder 23 is lifted up according to the movement of the carriage 5, and the ejection surface of the head 6 is capped by the cap means 22, and the carriage 5 is printed. By moving to the region side, the holder 23 is lifted down as the carriage 5 moves, so that the cap means 22 is separated from the ejection surface of the head 6.

  The cap means 22 is connected to the suction pump 27 via the suction tube 26, forms an atmosphere opening port, and communicates with the atmosphere via the atmosphere opening tube and the atmosphere opening valve. The suction pump 27 discharges the sucked waste liquid (waste ink) to a waste liquid storage tank through a drain tube or the like.

  Further, on the side of the holder 23, a wiper blade 30, which is a wiping means made of an elastic member such as a fiber member, a foam member, or rubber, for wiping the discharge surface 6 a of the head 6 is attached to the blade arm 31. Is pivotally supported so that it can be swung by rotation of a cam that is rotated by a driving means (not shown).

  In this recording apparatus configured as described above, the paper 16 is conveyed in the sub-scanning direction while moving the head 6 (carriage 5) in the main scanning direction, and ink droplets of a desired color are ejected from the nozzles of each head. By doing so, a required color image (including a monochrome image) is recorded on the paper 16.

  Next, an example of an ink jet head constituting the head 6 in this ink jet recording apparatus will be described with reference to FIGS. 2 is a plan view showing an example of the liquid chamber configuration of the inkjet head, FIG. 3 is a cross-sectional view taken along the line AA in FIG. 2, and FIG. 4 is a transparent representation of the portion B in FIG. 2 from the nozzle side. FIG.

  The liquid chamber configuration of the inkjet head is common to the plurality of nozzles 41, the pressure chambers 42 that communicate with the nozzles 41, the common liquid chamber 43 that supplies ink to the pressure chambers 42, and the pressure chambers 42. A fluid resistance unit 44 that communicates with the liquid chamber 43 and a supply port 45 that supplies ink from the ink cartridge 7 to the common liquid chamber 43 are provided.

  Here, the plurality of nozzles 41 are formed in the nozzle plate 50, the nozzle plate 50, a vibration plate 52 that is displaced by the piezoelectric element 51 that is a pressure generating means, and between the nozzle plate 50 and the vibration plate 52. The pressurizing chamber 42, the common liquid chamber 43, and the fluid resistance portion 44 are formed by the provided ink liquid chamber forming member 53, and the supply port 45 is formed in the diaphragm 52. Here, the piezoelectric element 51 which is a pressure generating means is provided outside the pressurizing chamber 42.

Next, an outline of the control unit of the ink jet recording apparatus will be described with reference to FIG.
This control unit is used as a microcomputer (hereinafter referred to as “CPU”) 60 that also serves as a drive control means that controls the entire recording apparatus, a ROM 61 that stores necessary fixed information, a working memory, and the like. RAM 62, image memory 63 for storing data processed from image data transferred from the host, parallel input / output (PIO) port 64, input buffer 65, parallel input / output (PIO) port 66, waveform generation A circuit 67, a head drive circuit 68, a driver 69, and the like are provided.

  Here, the PIO port 64 has various information such as image data from the host side, various instruction information such as reliability recovery instruction information from an operation panel (not shown), and a detection signal from a paper presence / absence sensor that detects the start and end of the sheet. Signals from various sensors such as a home position sensor for detecting the home position (reference position) of the carriage 5 are input, and necessary information is transmitted to the host side and the operation panel side via the PIO port 64. Is done.

  The waveform generation circuit 67 generates and outputs a drive waveform to be applied to the piezoelectric element 51 of the inkjet head. The waveform generation circuit 67 uses a D / A converter to D / A convert voltage data supplied from the CPU 60 to thereby form a first drive waveform for forming a large dot and a first drive waveform for forming a small dot. A second drive waveform and a third drive waveform for forming minute dots are generated and output.

  The head drive circuit 68 applies the drive waveform output from the waveform generation circuit 67 to the piezoelectric element 51 corresponding to each nozzle 41 of the head 6 based on various data and signals given through the PIO port 66. . Further, the driver 69 drives and controls the main scanning motor 8 and the sub-scanning motor 17 in accordance with driving data given through the PIO port 66, thereby moving and scanning the carriage 5 in the main scanning direction, thereby conveying the roller 15. Is rotated to convey the paper 16 by a predetermined amount.

Next, the operation of the ink jet recording apparatus configured as described above will be described with reference to FIG.
First, the formation of minute dots according to the present invention will be described with reference to FIGS. In this recording apparatus, as shown in FIG. 6, fine dots can be formed in addition to large dots and small dots. The fine dots are divided into main dots Dm formed by landing of main droplets and satellite dots Ds formed by landing of satellite droplets, and small dots and fine dots are the same as the amount of ink droplets. .

  In this case, as shown in FIG. 7, large dots and small dots can be recognized by the naked eye, but minute dots obtained by dividing the small dot have a size that cannot be recognized by the naked eye. Thus, even if a satellite is generated in a dot that cannot be recognized by the naked eye, there is no problem in image quality.

  On the other hand, in a head using the piezoelectric element 51 as an actuator unit as in this recording apparatus, the peak value (voltage value) Vp, rise time constant tr, and fall time constant tf of the drive waveform applied to the piezoelectric element 51 are changed. By doing so, the droplet volume Mj and the droplet velocity Vj of the ink droplet ejected from the nozzle 41 can be changed.

  Therefore, from the waveform generation circuit 67 of the control unit, a first drive waveform for forming a normal large dot, a second drive waveform for forming a small dot, and a third drive waveform for forming a minute dot are provided. Generate and output a drive waveform selected according to the dot to be printed, or select a drive waveform according to the dot printed by the head drive circuit 68 from the three types of generated drive waveforms, and apply it to the piezoelectric element 51. It is trying to apply.

  Here, as the third drive waveform P3 for forming minute dots, the drive waveform P31 as shown in FIG. 8A, the drive waveform P32 as shown in FIG. ) Is generated and output, and this drive waveform is applied from the head drive circuit 68 to the piezoelectric element 51 of the head.

  When such a drive waveform is applied to the head, the main droplet Im and the satellite droplet Is are separated from the head as shown in FIG. 9A, and the main droplet Im is discharged as it is as shown in FIG. 9B. The droplet Im and the satellite droplet Is fly while being separated, and the main droplet Im and the satellite droplet Is land on a position shifted by a certain position on the sheet as shown in FIG.

  On the other hand, when the first drive waveform for forming a normal large dot and the second drive waveform for forming a small dot are given, the main droplets from the head as shown in FIG. Im and satellite droplets Is are discharged in a separated state, but satellite droplets Is merged with main droplet Im during flight as shown in FIG. 5B, and a lump as shown in FIG. And land on the paper as the main droplet Im. Alternatively, it is possible to apply a drive waveform in which ink droplet ejection is performed in the state where satellite dots are not generated in the first place.

  In this way, when forming dots other than micro dots, satellite dots are not generated or ink droplets that are absorbed by the satellite dots into the main dots are ejected, and when forming micro dots, ink droplets that are formed with satellite dots are ejected. By providing the drive control means for discharging, fine dots can be formed and the graininess of the image can be improved.

Next, the landing positions of satellite dots when forming minute dots will be described with reference to FIG.
As shown in FIG. 11A, when the satellite droplet Is obtained by dividing the small dot lands at a position very close to the main droplet Im, the satellite dot Ds and the main dot Dm are merged to form a dot D. It may be recognized as a dot larger than a small dot. Also, even if the satellite dot and main dot do not merge, if multiple satellite dots merge and become larger than the main dot, the satellite dot is more valuable as a main drop As a result, the dot coordinate data is disturbed.

  Therefore, a driving waveform for ejecting ink droplets is applied so that the satellite ink droplets Is divided to generate minute dots land at positions away from the main droplet Im. In the recording device, the dot size and the dot pitch are set so that adjacent dots partially overlap so that no gap occurs during solid printing, so that the landed satellite ink droplets do not merge with the main droplets In order to achieve this, the satellite droplet Is is landed at a position at least one dot pitch away from the landing position of the main droplet Im.

  As a result, as shown in FIG. 6B, the main dot Dm and the satellite dot Ds cannot be recognized or can hardly be recognized. Also, it is necessary to reduce the number of satellite dots to one or to increase the landing position accuracy between the satellite ink droplets so that the dot size of the satellite dots Ds is at least equal to or smaller than the main dot Dm.

Next, the relationship between the interval between main dots and satellite dots and the output data will be described with reference to FIG.
As shown in FIG. 11A, in the output dots G1 and G2 (black filled dots) of the binarized image data, the coordinates of the output dot G2 are the main dot G1 as shown in FIG. When the coordinates of the satellite dot Ds1 generated when printing is performed with a minute dot (main dot Dm1), when the main dot Dm corresponding to the output dot G2 is shot, the main dot Dm of the output dot G2 is placed on the satellite dot Ds1. It will be overstruck.

  In this case, the dot size itself does not double, but the density of the dots increases, and there is a risk that the characteristics will be impaired particularly when photo ink (light color ink) is used. Therefore, when the coordinates of the output and the coordinates of the satellite dot overlap, the satellite dot is handled in the same manner as the main dot, and the main dot is not shot again at that coordinate. In this case, since printing for two dots is performed with a single ink droplet, the ink consumption can be saved slightly.

Next, the relationship with the output image data will be described with reference to FIGS.
When the image data is a character or a line drawing, isolated dots have no meaning, and dots are concentrated to form a pattern, so that satellite dots are also concentrated and combined. Therefore, even if it is a fine dot, if it adjoins and it connects, it will become easy to recognize as a pattern. For example, as shown in FIG. 13 or FIG. 14, the surplus pattern Sd in which the satellite dots are connected in the vicinity of the pattern Md by the main dots is formed, and it looks as if it is a blur or a double line. .

  Therefore, it can be dealt with by determining whether or not the image data to be output is a character or a line drawing, and switching the process so that an ink droplet in which no satellite dot is formed is ejected in the case of the character or line drawing. Further, it is also possible to discharge ink droplets in which satellite dots are formed only in the highlight portion where the granularity itself is a problem and in which no satellite dot is formed in the shadow portion. Further, when photo ink is employed, the highlight portion is almost processed with photo ink, so that ink droplets that do not form satellite dots are ejected only when photo ink is used.

  As described above, independent satellite dots can be reliably formed by ejecting ink droplets formed at positions where the satellite dots are separated by 1 dot pitch or more from the landing position of the main dots. Further, by ejecting ink droplets in which the area of the satellite dots is smaller than the area of the main dots, it is possible to prevent image degradation due to the fusion of the satellite dots.

  Furthermore, when the recorded image is a character or line image, the ink droplets on which the satellite dots are not formed are ejected, thereby preventing image deterioration due to the combination of the satellite dots. Furthermore, when the main dot and the satellite dot with respect to another main dot are at the same landing position, the occurrence of dot density unevenness can be prevented by not discharging the ink droplet forming the main dot.

  Further, by ejecting ink droplets in which satellite dots are formed only when using light-colored ink, it is possible to prevent image deterioration due to the combination of satellite dots. Further, it is possible to prevent image deterioration due to the combination of satellite dots by ejecting ink droplets in which satellite dots are formed only in the highlight portion of the image and satellite dots are not formed in the shadow portion.

  In the above-described embodiment, the present invention has been described with respect to a recording apparatus including a piezo-type ink jet head. In addition, a diaphragm that forms a wall surface of a pressurizing chamber and an electrode facing the diaphragm are provided. The same applies to an ink jet recording apparatus equipped with an electrostatic ink jet head that deforms and displaces by an electrostatic force and ejects droplets from a nozzle, a valve ink jet head that utilizes film boiling by a heating resistor in a pressure chamber, and the like. be able to.

FIG. 2 is a schematic perspective explanatory view of a mechanism portion of the ink jet recording apparatus according to the present invention. It is a top view which shows an example of the liquid chamber structure of an inkjet head. It is sectional drawing which follows the AA line of FIG. FIG. 3 is an enlarged explanatory diagram transparently expressing a portion B of FIG. 2 from the nozzle side. FIG. 2 is a block diagram illustrating an overview of a control unit of the recording apparatus. FIG. 6 is an explanatory diagram for explaining dot formation in the recording apparatus. It is explanatory drawing about the visual recognition possibility of the dot in the recording device. FIG. 6 is an explanatory diagram illustrating different examples of drive waveforms for forming minute dots in the recording apparatus. It is explanatory drawing explaining the process from droplet discharge to the time of landing when the drive waveform of FIG. 8 is applied. It is explanatory drawing explaining the process from droplet discharge to the landing at the time of applying the drive waveform for forming dots other than a micro dot. It is explanatory drawing with which it uses for description of the landing position of a satellite droplet and a main droplet. It is explanatory drawing with which it uses for description of the relationship between image data and a printing dot. It is explanatory drawing explaining the example of the surplus image formation by the coupling | bonding of a satellite dot. Explanatory drawing explaining other examples of surplus image formation by combination of satellite dots

Explanation of symbols

DESCRIPTION OF SYMBOLS 5 ... Carriage 6 ... Head 41 ... Nozzle 42 ... Pressurizing chamber 51 ... Piezoelectric element 67 ... Waveform generation circuit 68 ... Head drive circuit.

Claims (9)

In an ink jet recording apparatus comprising a head having a nozzle that ejects ink droplets, a pressure chamber that communicates with the nozzle, and a pressure generation unit that generates pressure to pressurize the ink in the pressure chamber.
The ink droplets for forming dots identifiable with the naked eye are divided to form main dots and satellite dots of a size that cannot be recognized with the naked eye,
The inkjet recording apparatus, wherein the center position of the satellite dot is formed at a position separated by 2 dots or more from the landing center position of the main dot. The inkjet recording apparatus according to claim 1, wherein
An ink jet recording apparatus, wherein an ink droplet having an area of the satellite dot smaller than that of a main dot is ejected. The inkjet recording apparatus according to claim 1 or 2,
An ink jet recording apparatus, wherein an ink droplet forming the main dot is not ejected when the main dot and a satellite dot with respect to another main dot are in the same landing position. The inkjet recording apparatus according to any one of claims 1 to 3,
An ink jet recording apparatus comprising drive control means for ejecting ink droplets that form the main dots and satellite dots. The inkjet recording apparatus according to claim 4, wherein
The drive control means ejects ink droplets in which the satellite dots are formed when forming dots having a size that cannot be recognized by the naked eye, and the satellites when forming dots other than dots having a size that cannot be recognized by the naked eye. An ink jet recording apparatus, wherein no dot is generated or an ink droplet in which the satellite dot is absorbed in the main dot is ejected. The inkjet recording apparatus according to any one of claims 1 to 5,
An ink jet recording apparatus that discharges ink droplets in which the satellite dots are not formed when the recorded image is a character or line image. The inkjet recording apparatus according to any one of claims 1 to 6,
An ink jet recording apparatus, wherein ink droplets on which the satellite dots are formed are ejected only when photo ink is used. (
In the ink jet recording apparatus according to any one of claims 1 to 7,
An ink jet recording apparatus, wherein an ink droplet in which the satellite dot is formed only in a highlight portion of an image and the satellite dot is not formed in a shadow portion is ejected. In a recording method in an ink jet recording apparatus including a head having a nozzle that discharges ink droplets, a pressure chamber that communicates with the nozzle, and a pressure generation unit that generates pressure to pressurize ink in the pressure chamber.
The ink droplets for forming dots identifiable with the naked eye are divided to form main dots and satellite dots of a size that cannot be recognized with the naked eye,
The recording method according to claim 1, wherein the center position of the satellite dots is formed at a position two dots or more away from the landing center position of the main dots.

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