JP4904103B2 - Image forming apparatus and droplet ejection control method - Google Patents

Description

  The present invention relates to an image forming apparatus and a droplet ejection control method, and more particularly, to a droplet ejection control technique in a liquid ejection apparatus that ejects droplets from ejection holes to form a shape such as an image or a predetermined pattern on a medium.

  In recent years, inkjet printers have become widespread as data output devices for images and documents. An ink jet printer can drive nozzles (ejection holes) provided in a head according to data, and can form data on a recording medium by ink ejected from the nozzles. In an inkjet printer, a desired image is formed on a medium by relatively moving a head having a large number of nozzles and a recording medium and ejecting ink droplets from the nozzles.

  Up to now, ink jet printers have been used mainly as document output devices in homes and offices, but recently, they have come to be used as output devices for images taken using a digital camera or the like. There are also devices that support A3 and poster-size recording media, and can be used as output devices for advertisements and posters.

  There is a high demand for image quality when printing images taken with a digital camera, etc., and high-quality image printing is realized by achieving multiple colors (full color), multi-level tone, finer dots, higher density, etc. Has been. For example, by using multi-color ink such as light ink, multi-color and multi-step tone are realized, and by increasing nozzle density and droplet size, dot density and dot size are reduced. Realized. In addition, if droplet ejection control is performed so that ink is ejected so that adjacent dots overlap, dots can be formed on the medium with high density.

  However, when adjacent dots are formed so as to overlap each other, if the next ink lands before the previously ejected ink is fixed on the media, the shape of each dot collapses or lands later Ink droplets may approach the ink droplets that have landed first, resulting in image abnormalities such as streaks or unevenness in the resulting image. Furthermore, when inks of different colors are deposited and ejected, if a mixed color occurs, it may not be possible to realize a preferable color or gradation.

  In general, in order to prevent image abnormalities due to blurring or landing interference, it is necessary to wait until the ink droplet that has landed first penetrates to a certain extent and then perform the droplet ejection control so that the next ink droplet is ejected. There has been proposed a method of providing temperature control means for warming the medium and ink landed on the medium, and promoting the fixing of the ink using the temperature control means. Also proposed is a method of promoting the fixing of ink landed on a medium using an ultraviolet curable ink whose curing is accelerated by ultraviolet irradiation on the ink for forming an image.

  In the inkjet recording method described in Patent Document 1 and the inkjet recording apparatus using the method, different inks are used in the inkjet recording method in which recording is performed by moving a plurality of recording heads arranged in parallel relative to a recording medium. The recording timing of any one ink dot in contact with the boundary between the other ink dots and the other ink dots is shifted to prevent interference between colors.

  The ink jet recording apparatus described in Patent Document 2 includes a drum for fixing paper and a plurality of ink jet heads arranged at predetermined intervals in the circumferential direction with respect to the drum, In an ink jet recording apparatus that drives the ink jet head to perform color printing on the paper, bleeding is prevented by setting T ≧ 10 msec, which is a time T until dots of different colors contact or overlap each other at the landing position. It is configured as follows.

  In the printing method described in Patent Document 3 and the print head device used in this method, a charged ink is used, a channel for ejecting ink is provided between electrodes that generate an electric field, and an electric field is applied to the ink ejected from the channel. Is applied to deflect the ink ejection direction to prevent image deterioration such as unevenness.

In the ink jet nozzle, ink jet recording head, ink jet cartridge, and ink jet recording apparatus described in Patent Document 4, each nozzle includes a plurality of heaters that generate bubbles in the ink, and the heaters are controlled to generate different bubbles in the ink. It is configured to deflect the flying direction of ink and prevent landing interference.
JP-A-6-183129 JP 2002-120361 A JP 2000-177115 A JP 2000-185403 A

  However, in the inventions described in Patent Documents 1 and 2, high image quality is achieved by regulating the landing timing between different colors to prevent bleeding and density reduction. It is unsolved, and the problem for high-speed printing has not been solved. In addition, in the inventions described in Patent Documents 3 and 4, a method for preventing the image degradation such as unevenness by deflecting the flying direction of the ejected ink droplet is disclosed. The control method and its problem are not disclosed.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an image forming apparatus and a droplet ejection control method capable of preventing image deterioration due to blurring or landing interference and realizing preferable high-speed printing.

In order to achieve the above object, an image forming apparatus according to the present invention includes a liquid discharge head having discharge holes for discharging liquid onto a recording medium, and the liquid discharge head and the recording medium relatively in one direction. A recording medium conveying means for moving; a flying direction deflecting means for deflecting the flying direction of droplets ejected from the ejection holes in a direction having at least a component substantially parallel to the recording medium conveying direction; and the recording medium conveying When overlapping adjacent dots in the direction substantially parallel to the direction, the adjacent dots in the direction substantially parallel to the recording medium transport direction are deflected so that the flying directions of the droplets continuously ejected from the ejection holes are different. Of the discharge hole forming surface so that the difference in droplet ejection time between the first droplet and the second droplet becomes equal to or longer than the quasi-fixing time from the time of landing of the first droplet to the quasi-fixing state. Based on discharge normal direction More than three and a deflection angle setting means for setting a deflection angle with respect to the discharge hole, the deflection angle setting means, and ejection cycle Tf of the liquid ejection head is determined from said quasi fixing time To, On the scanning surface of the recording medium not considering the movement of the recording medium, the relationship between the ejection period Tf of the liquid ejection head and the semi-fixing time To is 2 or more that satisfies k ≧ (To / Tf) +1. A deflection shift amount k, which is an integer, is obtained, and the relationship between the obtained deflection shift amount k and the minimum interval Pt of the dots formed on the recording medium in the direction substantially parallel to the recording medium conveyance direction is y. = K × Pt, and the recording medium in a direction substantially parallel to the recording medium conveyance direction of two dots formed on the recording medium by two droplets ejected at successive ejection timings from the ejection holes On the scanning plane Seeking definitive deflection distance y, on the basis of the deflection distance y, and sets the deflection angle with respect to the discharge hole.

According to the present invention, the droplet ejection time difference (landing time difference) between the first droplet and the second droplet, which are adjacent dots in a direction substantially parallel to the recording medium conveyance direction, is equal to or greater than the first droplet quasi-fixing time. As described above, the flying direction of continuously ejected droplets is deflected in different directions including a direction substantially parallel to the recording medium conveyance direction, so that it is possible to avoid landing interference when overlapping adjacent dots are formed. Image quality deterioration is suppressed. In addition, the deflection distance y on the scanning surface of continuously ejected droplets is k times the minimum dot pitch Pt (the deflection distance y on the scanning surface of continuously ejecting droplets is a distance corresponding to k dots). ), A droplet ejection time difference (landing time difference, that is, a time required to move the recording medium by the pitch between dots (k-1) × Pt) on the recording medium is equal to or more than the semi-fixing time To. Since the deflection shift amount k is obtained as described above, even when the semi-fixing time To of the liquid differs depending on the type of the recording medium and the type of the liquid, A deflection shift amount k is obtained based on the ejection cycle Tf, a deflection angle is set for the ejection hole, and high image quality can be maintained regardless of the type of recording medium and the type of liquid. The droplet flying direction (deflection angle with respect to the vertical direction) θ is θ = arctan (y / Z), where Z is the distance between the liquid ejection surface and the image forming surface of the recording medium.

  There is a mode in which the liquid discharge head includes a pressure chamber that stores liquid ejected (discharged) from the discharge hole, and discharge force applying means that applies discharge force to the liquid stored in the pressure chamber. The pressure chamber applying means includes an actuator that changes the volume of the pressure chamber by deforming the pressure chamber, and a heater that heats the liquid in the pressure chamber to generate bubbles in the pressure chamber.

  In addition, the liquid ejection head includes a full-line type head having an ejection hole array having a length corresponding to the entire width of the recording medium, and a short length having an ejection hole array having a length less than the entire width of the recording medium. There is a serial type head that scans the head in the width direction of the recording medium. In a line-type inkjet head, short heads having short ejection hole arrays that are less than the length corresponding to the full width of the recording medium are arranged in a staggered manner and connected to form a length corresponding to the full width of the recording medium. Also good.

  When the sub-scanning direction is a direction substantially parallel to the recording medium conveyance direction and the main scanning direction is a direction substantially orthogonal to the recording medium conveyance direction, when a full-line head is applied to the liquid discharge head, the recording medium conveyance direction is substantially parallel. The direction (sub-scanning direction) is the width direction of the recording medium, and the direction (main scanning direction) substantially orthogonal to the recording medium transport direction is substantially orthogonal to the width direction of the recording medium. When a shuttle type head is applied to the liquid discharge head, the direction substantially parallel to the recording medium conveyance direction (sub-scanning direction) is substantially orthogonal to the width direction of the recording medium, and substantially orthogonal to the recording medium conveyance direction ( The main scanning direction) is the width direction of the recording medium.

  The recording medium is a medium to which the droplets ejected from the ejection holes are attached, and there are various kinds of materials such as continuous sheets, cut sheets, sealing sheets, resin sheets such as PHP sheets, films, cloths, and other materials and shapes. Includes media.

  Examples of the liquid ejected as droplets from the ejection holes include chemicals such as ink and resist used in the ink jet recording apparatus, and processing liquids. This liquid has physical properties (such as viscosity) that can be ejected from ejection holes provided in the liquid ejection head.

  The semi-fixing time of the liquid refers to the time from the time when the liquid droplets land on the recording medium until the semi-fixing state is reached. This refers to the state of a droplet that does not cause landing interference even when it comes into contact with a landed droplet, or that does not affect the image quality of the resulting image even if landing interference occurs. Therefore, the deflection angle may be set based on the fixing time, which is the time until the droplet landed on the recording medium is completely fixed.

  The flight direction deflecting unit includes an electric field generating unit that generates an electric field that acts on the charged liquid (droplet). A liquid that has been charged in advance may be applied to the charged liquid, or the liquid may be charged before the electric field is applied by the charging means.

  Two or more deflection angles set with respect to the ejection hole are opposite to the normal direction on the droplet ejection side of the ejection hole (for example, upstream of the recording medium conveyance direction with respect to the liquid ejection head and It may be set on the downstream side) or on the same side. In addition, any one of two or more deflection angles set with respect to the ejection hole may include an angle that is 0 degree with respect to the normal direction, or may be an angle other than 0 degree.

  In addition, when the droplet ejection time difference between the first and second dots, which are adjacent dots in a direction substantially parallel to the recording medium conveyance direction, is an integer multiple of 2 or more of the ejection interval for continuous ejection from the same ejection hole, This is preferable because synchronization between the deflection angle control and the discharge interval control can be simplified.

A deflection distance y on the recording medium scanned surface of the conveyance direction substantially parallel to the direction of dots formed on the recording medium by liquid droplets ejected successively from the previous SL discharge hole, it is formed on the recording medium And the minimum dot pitch Pt in a direction substantially parallel to the recording medium conveyance direction and the deflection shift amount k on the scanning surface of the droplets continuously ejected from the ejection holes (where k is an integer of 2 or more) Is expressed by y = k × Pt, the deflection angle setting means includes the deflection shift amount k, the ejection period Tf of the liquid ejection head, and the semi-fixing time To. There may be a mode in which the deflection shift amount k is obtained so that the relationship satisfies k ≧ (To / Tf) +1 on the scanning plane, and the deflection angle is set with respect to the ejection hole based on the deflection shift amount k. .

According to a second aspect of the invention relates to an aspect of the image forming apparatus according to claim 1 Symbol placement, the deflection angle is set to the discharge holes, and the recording medium transport direction relative to the said liquid discharging head And an angle having a component on the upstream side in the substantially parallel direction and an angle having a component on the downstream side in the parallel direction with respect to the recording medium conveyance direction with respect to the liquid ejection head.

  According to the third aspect of the present invention, the flying direction of the droplets ejected (discharged) continuously from the ejection holes is alternately deflected to the upstream side and the downstream side in the recording medium conveyance direction. Since the deflection shift amount described in (1) can be increased, it is possible to reliably avoid landing interference of droplets forming adjacent dots.

  The absolute value of the deflection angle upstream in the recording medium conveyance direction and the absolute value of the deflection angle downstream in the recording medium conveyance direction may be the same value or different values.

Before SL liquid discharge head has a plurality of discharge holes arranged in a direction substantially orthogonal to the recording medium conveyance direction, the deflection angle setting means is substantially orthogonal with said recording medium conveying direction on said recording medium There may be a mode in which different ejection angles are set for the ejection holes adjacent in the direction.

According to this aspect , the ejection holes adjacent in the direction substantially orthogonal to the recording medium conveyance direction have different deflection angles, and the droplets ejected from the adjacent ejection holes at the same timing are substantially the same as the recording medium conveyance direction. Landing at a position separated by a predetermined distance in the parallel direction avoids landing interference of droplets that form adjacent dots in a direction substantially perpendicular to the recording medium conveyance direction, can suppress deterioration in image quality, and further improve image quality Is possible.

  The aspect having a plurality of ejection holes arranged in a direction substantially orthogonal to the recording medium conveyance direction is composed of one ejection hole array in which a plurality of ejection holes are arranged in a direction substantially parallel to the recording medium conveyance direction. Or a head in which these discharge holes are formed in a staggered pattern.

A third aspect of the invention relates to an aspect of the image forming apparatus according to the first or second aspect, wherein the liquid discharge head has a plurality of discharge holes arranged in a direction substantially perpendicular to the recording medium conveyance direction. The deflection angle setting means sets a different deflection angle between the ejection holes adjacent in the direction substantially orthogonal to the recording medium conveyance direction, and among the ejection holes adjacent in the direction orthogonal to the recording medium conveyance direction, The absolute value | θa1 | of the deflection angle θa1 on the upstream side in the recording medium conveyance direction set for one ejection hole and the deflection angle θb2 on the downstream side in the recording medium conveyance direction set for the other ejection hole. The absolute value | θb2 | satisfies the following expression | θa1 | = | θb2 | and the absolute value | θa2 | of the deflection angle θa2 on the downstream side in the recording medium conveyance direction and the other ejection hole The deflection angle θ on the upstream side in the recording medium conveyance direction to be set The deflection angle is set with respect to the ejection holes adjacent to the recording medium conveyance direction so that the relationship between the absolute value of b1 and | θb1 | satisfies the following expression | θa2 | = | θb1 | And

According to the third aspect of the present invention, it is possible to simplify the control of the flying direction deflecting means for deflecting the flying direction of the droplet, which contributes to reducing the load on the control system.

According to a fourth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to third aspects, wherein the liquid discharge heads are arranged in a direction substantially orthogonal to the recording medium conveyance direction. The deflection angle setting means sets the deflection shift amount k to one of the ejection holes adjacent to the direction substantially orthogonal to the recording medium conveyance direction, and the other ejection hole. Unlike the deflection shift amount k, a droplet ejection position shift amount S having a relationship of k> S is set, and the droplet ejection position shift amount S and the recording medium conveyance direction of dots formed on the recording medium are set. A deflection distance L expressed by L = Pt × S is set as a relationship between the minimum dot pitch Pt in a substantially parallel direction and a deflection angle is set for the other ejection hole based on the deflection distance L. It is characterized by doing.

According to the fourth aspect of the present invention, the droplet ejection position shift amount S is set so that the droplet ejection time difference between the droplets forming adjacent dots in a direction substantially orthogonal to the recording medium conveyance direction becomes the semi-fixing time of the droplet. Therefore, it is possible to reliably avoid landing interference of droplets ejected at substantially the same timing in two dot rows adjacent in a direction substantially orthogonal to the recording medium conveyance direction.

A fifth aspect of the present invention relates to an aspect of the image forming apparatus according to the third aspect, wherein the deflection angle setting means includes a direction substantially parallel to the recording medium conveyance direction and a direction substantially orthogonal to the recording medium conveyance direction. The droplet ejection position shift amount S is set so that the droplet ejection time difference between droplets that are adjacent dots in different oblique directions is equal to or greater than the quasi-fixing time of the droplet, and based on the droplet ejection position shift amount S A deflection angle is set with respect to the discharge hole.

According to the fifth aspect of the present invention, the droplet ejection position shift amount S is set so that the droplet ejection time difference between the adjacent dots in the oblique direction is equal to or longer than the semi-fixing time of the droplet, and the deflection angle is set. Therefore, it is possible to avoid landing interference of droplets that are adjacent dots in an oblique direction, and it is possible to further improve image quality.

A method invention is provided to achieve the above object. That is, the droplet ejection control method according to the invention of claim 6 ejects droplets from the ejection holes provided in the liquid ejection head while relatively moving the liquid ejection head and the recording medium in one direction. A droplet ejection control method for an image forming apparatus for forming a desired image on the recording medium, wherein when forming adjacent dots in a direction substantially parallel to the recording medium conveyance direction, the dots are continuously formed from the ejection holes. The ejection time difference between the first droplet and the second droplet, which are adjacent dots in a direction substantially parallel to the recording medium conveyance direction, is deflected so that the flying directions of the ejected droplets are different. Two or more deflection angles with respect to the discharge-side normal direction of the discharge hole forming surface are set with respect to the discharge hole so that the quasi-fixing time from the time of the droplet landing until the quasi-fixing state is reached set, and ejection cycle Tf of the liquid ejection head, the quasi fixing time to The relationship between the ejection period Tf of the liquid ejection head and the quasi-fixing time To on the scanning surface of the recording medium that does not consider the movement of the recording medium is k ≧ (To / Tf) +1. A deflection shift amount k that is an integer greater than or equal to 2 is obtained, the obtained deflection shift amount k, and a minimum interval Pt of dots formed on the recording medium in a direction substantially parallel to the recording medium conveyance direction, The relationship is expressed by y = k × Pt, and the direction in which the two dots formed on the recording medium by two droplets ejected from the ejection holes at successive ejection timings is substantially parallel to the recording medium conveyance direction. A deflection distance y on the scanning surface of the recording medium is obtained, and the deflection angle is set with respect to the ejection hole based on the deflection distance y .

According to the present invention, the droplet ejection time difference between the first droplet and the second droplet that are adjacent dots in a direction substantially parallel to the recording medium conveyance direction is equal to or greater than the quasi-fixing time of the first droplet. Since the flight direction of droplets that are continuously ejected (discharged) is deflected in different directions, including the direction substantially parallel to the recording medium conveyance direction, it avoids landing interference when overlapping adjacent dots. And image quality deterioration is suppressed. Also, different deflection angles are set for the ejection holes for ejecting droplets that become adjacent dots in a direction substantially perpendicular to the recording medium conveyance direction, and droplets ejected from the adjacent ejection holes at the same timing are conveyed by the recording medium. Landing at a position separated by a predetermined distance in a direction substantially parallel to the direction can avoid landing interference of droplets that form adjacent dots in a direction substantially perpendicular to the recording medium conveyance direction, thereby suppressing image quality deterioration, and further High image quality can be achieved. Furthermore, since the droplet ejection time difference between the adjacent dots in the oblique direction is equal to or greater than the quasi-fixing time of the liquid, it is possible to avoid landing interference of the droplets that are adjacent in the oblique direction, and further increase the image quality. Can be realized. Furthermore, the deflection distance y on the scanning plane of continuously ejected droplets is set to k times the minimum dot pitch Pt (the deflection distance y on the scanning plane of continuously ejected droplets is a distance corresponding to k dots). ), A droplet ejection time difference (landing time difference, that is, a time required to move the recording medium by the pitch between dots (k-1) × Pt) on the recording medium is equal to or more than the semi-fixing time To. Since the deflection shift amount k is obtained as described above, even when the semi-fixing time To of the liquid differs depending on the type of the recording medium and the type of the liquid, A deflection shift amount k is obtained based on the ejection cycle Tf, a deflection angle is set for the ejection hole, and high image quality can be maintained regardless of the type of recording medium and the type of liquid.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Overall configuration of inkjet recording apparatus]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. As shown in the figure, the inkjet recording apparatus 10 includes a print unit 12 having a plurality of print heads 12K, 12C, 12M, and 12Y provided for each ink color, and each print head 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feeding unit 18 for supplying a recording medium (recording paper) 16, a decurling unit 20 for removing curl of the recording medium 16, and the printing A suction belt conveyance unit 22 that is arranged to face the nozzle surface (ink ejection surface) of the unit 12 and conveys the recording medium 16 while maintaining the flatness of the recording medium 16, and a print detection that reads a printing result by the printing unit 12 And a paper discharge unit 26 for discharging the printed recording medium 16 (printed material) to the outside.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When a plurality of types of recording media can be used, an information recording body such as a barcode or wireless tag that records the medium type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Thus, it is preferable to automatically determine the type of recording medium to be used and perform ink ejection control (droplet ejection control) so as to realize appropriate ink ejection according to the type of recording medium.

  The recording medium 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording medium 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration that uses roll paper, a cutter (first cutter) 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording medium 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  After the decurling process, the cut recording medium 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least portions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 are horizontal ( Flat surface).

The belt 33 has a width that is greater than the width of the recording medium 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. Then, the suction chamber 34 is sucked by the fan 35 to make a negative pressure, whereby the recording medium 16 on the belt 33 is suction-held.

  When the power of a motor (not shown in FIG. 1, described as reference numeral 88 in FIG. 6) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, the belt 33 rotates in the clockwise direction in FIG. , And the recording medium 16 held on the belt 33 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although an embodiment using a roller / nip conveyance mechanism instead of the suction belt conveyance unit 22 is also conceivable, if the roller / nip conveyance is performed in the printing area, the roller contacts the printing surface of the recording medium 16 immediately after printing, so that the image is printed. There is a problem of easy bleeding. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print region is preferable.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the recording medium conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording medium 16 by blowing heated air onto the recording medium 16 before printing. By heating the recording medium 16 immediately before printing, the ink becomes easy to dry after landing.

  The printing unit 12 is a so-called full line type head in which a line type head having a length corresponding to the maximum paper width is arranged in a direction (main scanning direction) orthogonal to the recording medium conveyance direction (see FIG. 2). Although a detailed structural example will be described later (FIGS. 3 to 5), each of the print heads 12K, 12C, 12M, and 12Y is a recording medium of the maximum size targeted by the inkjet recording apparatus 10 as shown in FIG. The line head includes a plurality of ink discharge ports (nozzles) arranged over a length exceeding at least one side of 16.

  A print head corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording medium 16 (hereinafter referred to as the recording medium conveyance direction). 12K, 12C, 12M, and 12Y are arranged. A color image can be formed on the recording medium 16 by ejecting the color inks from the print heads 12K, 12C, 12M, and 12Y while conveying the recording medium 16, respectively.

  Thus, according to the printing unit 12 in which the full line head that covers the entire area of the paper width is provided for each ink color, the operation of relatively moving the recording medium 16 and the printing unit 12 in the sub-scanning direction is performed once. An image can be recorded on the entire surface of the recording medium 16 only by performing it (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the print head reciprocates in the main scanning direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink are added as necessary. May be. For example, it is possible to add a print head that discharges light ink such as light cyan and light magenta.

  As shown in FIG. 1, the ink storage / loading unit 14 has tanks that store inks of colors corresponding to the print heads 12K, 12C, 12M, and 12Y, and each tank is connected via a conduit (not shown). The print heads 12K, 12C, 12M, and 12Y communicate with each other. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  The print detection unit 24 includes an image sensor for imaging the droplet ejection result of the print unit 12, and functions as a means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor.

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than at least the ink ejection width (image recording width) by the print heads 12K, 12C, 12M, and 12Y. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor is composed of a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  The print detection unit 24 reads the test pattern printed by the print heads 12K, 12C, 12M, and 12Y for each color, and detects the ejection of each print head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  A post-drying unit 42 is provided following the print detection unit 24. The post-drying unit 42 is means for drying the printed image forming surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by pressurizing the paper holes with pressure. There is an effect to.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined surface uneven shape while heating the image surface, thereby forming an uneven shape on the image forming surface. Transcript.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) that switches the paper discharge path so as to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

[Description of print head structure]
Next, the structure of the print head will be described. Since the structures of the print heads 12K, 12C, 12M, and 12Y provided for the respective ink colors are common, the print heads are represented by reference numeral 50 in the following.

  In this example, paper is exemplified as a recording medium on which ink droplets are ejected by the ink jet recording apparatus 10, but the recording medium may be a metal plate, a resin plate, wood, cloth, leather, etc. Various media that can fix the ink, can be transported relatively to the print head 50, and can secure a clearance from the print head 50 can be applied.

  3 is a plan perspective view showing an example of the structure of the print head 50, and FIG. 4A is a cross-sectional view showing a three-dimensional configuration of the ink chamber unit (a cross-sectional view taken along line IV-IV in FIG. 3). is there.

  As shown in FIG. 3, the print head 50 of this example includes a plurality of ink chamber units 53 including nozzles 51 from which ink droplets are ejected and pressure chambers 52 corresponding to the nozzles 51 along the main scanning direction. One row of nozzles having a structure arranged in a row and having a plurality of nozzles 51 (ink chamber units 53) arranged over a length corresponding to the entire width of the recording medium 16 in the main scanning direction substantially orthogonal to the recording medium conveyance direction. Full line head with rows. In the nozzle row of the print head 50, the nozzles 51 constituting the nozzle row are evenly arranged at the nozzle pitch Pnm (for example, the distance between the nozzle 51a and the nozzle 51b).

  In this example, the piezo jet method is shown in which the actuator 58 is driven to deform the pressure chamber 52 so as to apply an ejection force to the ink in the pressure chamber 52. However, the pressure chamber 52 includes a heater, It is also possible to apply a thermal method in which a heater is driven to generate bubbles in the pressure chamber 52 to give an ejection force to the ink in the pressure chamber 52.

  In the ink jet recording apparatus 10 shown in this example, a charged ink containing charged particles having a positive (or negative) charge is used. When the electric field generated in the electrode pair 1 is applied to the charged ink ejected from each nozzle 51, the flying direction of the charged ink is a predetermined angle from the vertical direction (normal direction on the ink ejection side of each nozzle 51). It is deflected in a direction that is shifted by a distance.

  The electrode pair 1 provided corresponding to each nozzle is composed of an electrode 2 and an electrode 3 arranged in a direction substantially parallel to the recording medium conveyance direction (sub-scanning direction). The nozzle 51 is provided so as to face each other.

  As a method of deflecting the flying direction of ink droplets, an ink is charged (charged ink may be used) described in Patent Document 3 (Japanese Patent Laid-Open No. 2000-177115), and an electric field is applied to the flying space of ink droplets. A method of deflecting the flying direction of ink droplets may be used, or a plurality of bubble generating heaters described in Patent Document 4 (Japanese Patent Laid-Open No. 2000-185403) are provided in the sub-scanning direction with respect to one nozzle. A method of deflecting the flying direction of ink by selectively turning on and off the heater may be used. Of course, a known method other than the above may be applied to the method of deflecting the flying direction of the ink. Details of the flight direction deflection control of ink ejected from the nozzle 51 will be described later.

  The charged ink ejected from each nozzle 51 may be precharged ink, or may be provided with a charging processing unit in the ink flow path and subjected to charging processing in the apparatus (in the head). .

  As shown in FIG. 3, the pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape, and nozzles 51 and supply ports 54 are provided at both corners on a diagonal line. Each pressure chamber 52 communicates with a common flow path 55 shown in FIG.

  As shown in FIG. 4, an actuator 58 having an individual electrode 57 is joined to a pressure plate 56 constituting the top surface of the pressure chamber 52, and the actuator 58 is applied by applying a drive voltage to the individual electrode 57. Is deformed and ink is ejected from the nozzle 51. When ink is ejected, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54. A piezoelectric element (piezoelectric actuator) such as PZT (lead zirconate titanate) or PVDF (polyvinylidene fluoride) is suitably used for the actuator 58 provided in the print head 50 shown in this example.

  In this example, the full-line type print head 50 having a nozzle row having a length corresponding to the entire width of the recording medium 16 is shown, but the present invention is a short head having a length shorter than the entire width of the recording medium 16. Scanning in the width direction of the recording medium 16 forms an image in a predetermined range along the width direction of the recording medium 16, and forms the image as described above while transporting the recording medium 16 in a direction perpendicular to the scanning direction of the short head. Thus, the present invention is also applicable to a shuttle scan (serial) method in which an image is formed on the entire surface of the recording medium 16. However, in the shuttle scan method, the width direction of the recording medium 16 (scanning direction of the short head) is the main scanning direction, and the arrangement direction of the nozzle rows provided in the short head is the sub-scanning direction.

[Description of ink supply system]
FIG. 5 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10.

  The ink supply tank 60 is a base tank for supplying ink, and is installed in the ink storage / loading unit 14 described with reference to FIG. There are two types of ink supply tank 60: a system that replenishes ink from a replenishment port (not shown) and a cartridge system that replaces the entire tank when the remaining amount of ink is low. A cartridge system is suitable for changing the ink type according to the intended use. In this case, it is preferable that the ink type information is identified by a barcode or the like, and ejection control is performed according to the ink type.

  As shown in FIG. 5, a filter 62 is provided between the ink supply tank 60 and the print head 50 in order to remove foreign substances and bubbles. The filter mesh size is preferably equal to or smaller than the nozzle diameter (generally about 20 μm).

  Although not shown in FIG. 5, a configuration in which a sub tank is provided in the vicinity of the print head 50 or integrally with the print head 50 is also preferable. The sub-tank has a function of improving a damper effect and refill that prevents fluctuations in the internal pressure of the head.

  Further, the inkjet recording apparatus 10 is provided with a cap 64 as a means for preventing the nozzle 51 from drying or preventing an increase in ink viscosity near the nozzle, and a cleaning blade 66 as a nozzle surface cleaning means.

  The maintenance unit including the cap 64 and the cleaning blade 66 can be moved relative to the print head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the print head 50 as necessary. The

  The cap 64 is displaced up and down relatively with respect to the print head 50 by an elevator mechanism (not shown). The cap 64 is raised to a predetermined raised position when the power is turned off or during printing standby, and is brought into close contact with the print head 50, thereby covering the nozzle surface with the cap 64.

  During printing or standby, if the frequency of use of a specific nozzle 51 is reduced and ink is not ejected for a certain period of time, the ink solvent near the nozzle evaporates and the ink viscosity increases. In such a state, ink cannot be ejected from the nozzle 51 even if the actuator 58 operates.

  Before such a state is reached (within the range of the viscosity that can be discharged by the operation of the actuator 58), the actuator 58 is operated, and the cap 64 (ink near the nozzle whose viscosity has increased) is discharged. Preliminary ejection (purging, idle ejection, collar ejection, dummy ejection) is performed toward the ink receiver.

  Further, when air bubbles are mixed into the ink in the print head 50 (in the pressure chamber 52), the ink cannot be ejected from the nozzle even if the actuator 58 is operated. In such a case, the cap 64 is applied to the print head 50, the ink in the pressure chamber 52 (ink mixed with bubbles) is removed by suction with the suction pump 67, and the suctioned and removed ink is sent to the collection tank 68. .

  In this suction operation, the deteriorated ink with increased viscosity (solidified) is sucked out when the ink is initially loaded into the head or when the ink is used after being stopped for a long time. Since the suction operation is performed on the entire ink in the pressure chamber 52, the amount of ink consumption increases. Therefore, it is preferable to perform preliminary ejection when the increase in ink viscosity is small.

  The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the ink discharge surface (surface of the nozzle plate) of the print head 50 by a blade moving mechanism (wiper) (not shown). When ink droplets or foreign substances adhere to the nozzle plate, the nozzle plate surface is wiped by sliding the cleaning blade 66 on the nozzle plate to clean the nozzle plate surface. It should be noted that when the ink ejection surface is cleaned by the blade mechanism, preliminary ejection is performed in order to prevent foreign matter from being mixed into the nozzle 51 by the blade.

[Description of system control system]
FIG. 6 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, a memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted. The image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the memory 74. The memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 is a control unit that controls the communication interface 70, the memory 74, the motor driver 76, the heater driver 78, and the like. The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 86, read / write control of the memory 74, and the like, and controls the motor 88 and heater 89 of the transport system. A control signal to be controlled is generated.

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heater 89 such as the post-drying unit 42 in accordance with an instruction from the system controller 72.

  The print control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from image data in the memory 74 in accordance with the control of the system controller 72, and the generated print control. A control unit that supplies a signal (print data) to the head driver 84. Necessary signal processing is performed in the print controller 80, and the ejection amount and ejection timing (droplet ejection control) of the ink droplets of the print head 50 are performed via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 6, the image buffer memory 82 is shown in a mode associated with the print control unit 80, but it can also be used as the memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with a single processor.

  The print control unit 80 includes a deflection angle setting unit 92 that sets the direction of the electric field generated in the electrode pair 1 (1K, 1C, 1M, 1Y) provided in each nozzle 51 via the electrode driving unit 90. . That is, the ink droplets ejected from each nozzle 51 based on the print data are deflected in the flight direction by the deflection angle determined by the deflection angle setting unit 92.

  That is, the electric field strength and electric field direction generated in the electrode pair 1 are obtained from the information of the deflection angle set by the deflection angle setting unit 92, and the electrode driving unit 90 applies each nozzle 51 to each nozzle 51 based on the electric field strength and the electric field direction. The corresponding electrode pair 1 is driven.

  The deflection angle setting unit 92 sets the ink deflection angle with reference to the ink type information obtained from the ink type information obtaining unit 94 and the information on the recording medium 16 obtained from the recording medium type information obtaining unit 96. The ink type information and the information on the recording medium 16 may be configured such that each information is read from an information storage body attached to an ink cartridge or a stocker (tray) of the recording medium 16, or a keyboard, a mouse, a touch panel, etc. An operator may input each information using the user interface (man machine interface).

  The head driver 84 drives the actuators of the print heads 12K, 12C, 12M, and 12Y for each color based on the print data given from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  Various control programs are stored in a program storage unit (not shown), and the control programs are read and executed in accordance with commands from the system controller 72. The program storage unit may be a semiconductor memory such as a ROM or EEPROM, or a magnetic disk. An external interface may be provided and a memory card or PC card may be used. Of course, you may provide several recording media among these recording media. The program storage unit may also be used as a recording unit (not shown) for operating parameters.

  As described in FIG. 1, the print detection unit 24 is a block including a line sensor, reads an image printed on the recording medium 16, performs necessary signal processing, etc. And the detection result is provided to the print control unit 80.

  The print control unit 80 performs various corrections on the print head 50 based on information obtained from the print detection unit 24 as necessary.

[Explanation of droplet ejection (discharge) control]
Next, droplet ejection (discharge) control of the inkjet recording apparatus 10 will be described in detail. In the ink jet recording apparatus 10 of this example, in order to achieve high density of the recorded image, the dots formed on the recording medium 16 by the ink that is continuously ejected from each nozzle 51 are in the main scanning direction (recording). Adjacent dots are formed so as to overlap each other in the direction substantially perpendicular to the medium conveyance direction) and the sub-scanning direction (the recording medium conveyance direction and the direction substantially parallel to the recording medium conveyance direction). Even when dots are formed at high density and high speed in this way, ink droplet ejection is controlled so as to prevent occurrence of dot abnormality due to landing interference.

  FIG. 7 shows dots formed such that dots adjacent in the main scanning direction and the sub-scanning direction overlap each other. As shown in FIG. 7, dots 100, 102, 104, and 106 formed on the recording medium 16 by ink droplets ejected from the print head 50 are dots adjacent in the main scanning direction and dots adjacent in the sub scanning direction. Are partly overlapped.

  That is, the dots 100 are formed so as to partially overlap the dots 102 adjacent in the main scanning direction, and further formed so as to partially overlap the dots 104 adjacent in the sub-scanning direction. Further, the dots 100 are formed so as not to overlap with the dots 106 adjacent in the oblique direction, and the dots 100 and the dots 106 do not overlap each other.

  FIG. 7 shows four dots formed by ink droplets ejected on the recording medium 16, but an actual image is composed of a large number of dots, and these dots are shown in FIG. The arrangement relationship of the dots 100 to 106 shown is satisfied. Further, in the main droplet ejection control, in the dots arranged in a line in the main scanning direction, the sub scanning direction, or the diagonal direction, the dots are arranged so that the dots arranged on both sides of a certain dot do not overlap each other. In other words, in the dots arranged in a line in the main scanning direction or the sub-scanning direction, each dot is formed so that three or more dots do not overlap. For example, although not shown, dots are also formed on the dot 100 of the dot 104 on the opposite side of the main scanning direction (above the dot 104 in FIG. 7), but the dot on the upper side of the dot 104 overlaps the dot 100. There is no part. Similarly, a dot is also formed on the opposite side of the dot 100 to the dot 102 (the left side of the dot 100 in FIG. 7), but the left side dot of the dot 100 does not overlap the dot 100.

  That is, if the pitch between dots in the main scanning direction is Ptm, the pitch between dots in the sub-scanning direction is Pts (where Ptm = Pts = Pt), and the diameter of the dots to be formed (hereinafter referred to as dot diameter) is D. The dots 100, 102, 104, and 106 shown in FIG. 7 have a relationship represented by the following equation [Formula 1].

[Equation 1]
D = Pt × 2 ^1/2
FIG. 8 shows an example in which dots are formed at a higher density than in the example shown in FIG. In the example shown in FIG. 8, the inter-dot pitch between adjacent dots is smaller than that in the example shown in FIG.

  That is, in the example shown in FIG. 8, the dots adjacent in the main scanning direction and the dots adjacent in the sub scanning direction overlap each other, and further, the dots adjacent in an oblique direction different from the main scanning direction and the sub scanning direction overlap each other. Is formed. Specifically, the dot 100 is formed so as to partially overlap the dot 102 adjacent in the main scanning direction, the dot 104 adjacent in the sub-scanning direction, and the dot 106 adjacent in the oblique direction. The dot pitch Ptm in the main scanning direction, the dot pitch Pts in the sub-scanning direction (where Ptm = Pts = Pt), and the dot diameter D of the dots 100, 102, 104, and 106 formed in this manner The relationship shown in Equation 2] is established.

[Equation 2]
D = Pt × 2
However, the arrangement of each dot is determined so that the dot 100 does not overlap with a dot (dot formed on the opposite side of the adjacent dot) formed so as to overlap with the adjacent dot across the adjacent dot. It has been. In the droplet ejection control shown in this example, the dot arrangement shown in FIG. 8 is applied as a dot arrangement in which dots forming a recording image such as a high image quality mode are arranged at high density. Note that the dot arrangement shown in FIG. 7 may be applied to a recorded image in which the dot density is lowered to some extent, such as in the high-speed printing mode.

  Next, droplet ejection control according to the present embodiment (in particular, droplet ejection control for forming dots arranged at high density as shown in FIG. 8 at high speed) will be described.

  As shown in FIG. 9, in the inkjet recording apparatus 10 of this example, two types of deflection angles are set for each nozzle 51, and nozzles adjacent in the main scanning direction (dots adjacent in the main scanning direction are formed). Different deflection angles are set between nozzles that eject ink droplets to be ejected. For example, θa1 and θa2 shown in FIG. 9 are deflection angles set for the nozzle 51a in FIG. 3, and θb1 and θb2 are deflection angles set for the nozzle 51b in FIG.

  That is, adjacent to the main scanning direction (direction substantially perpendicular to the recording medium conveyance direction) while taking into account the droplet ejection time difference (droplet ejection interval) of the ink droplets that form adjacent dots in the sub-scanning direction (recording medium conveyance direction). The deflection angles θa1, θa2, θb1, and θb2 shown in FIG. 9 are determined so that the droplet ejection time difference between the ink droplets that form the dots to be formed is equal to or greater than a predetermined time.

  In the nozzle 51a and the nozzle 51b (see FIG. 3) adjacent to each other in the main scanning direction, the forward deflection angle of the nozzle 51a and the nozzle 51b (the ink droplet flying direction is the vertical direction (normal direction on the ink ejection side, one-dot broken line in FIG. 9) Θa1 and θb1 (where θa1 ≠ θb1), respectively, and the backward deflection angles of the nozzles 51a and 51b (the ink droplet flight direction is recorded from the vertical direction). The angles that are deflected upstream in the medium transport direction are θa2 and θb2 (where θa2 ≠ θb2), and the ink droplets continuously ejected from the nozzle 51a are the forward deflection angle θa1 and the backward deflection angle θa2 described above. The flight direction is deflected based on the above and landed on the positions a1 and a2 on the recording medium 16.

  Specifically, when an electric field is generated in the direction from the electrode 2 to the electrode 3 shown in FIG. 9 (that is, the direction from the upstream side to the downstream side in the recording medium conveyance direction), it contains charged particles having a positive charge. The flying direction of the ink droplet is deflected by an angle θa1 to the downstream side in the recording medium conveyance direction (right direction in FIG. 9), and the landing position of the ink droplet whose flying direction is deflected is directly below the nozzle 51 (the flying direction is the same as the flying direction). The position a1 is shifted from the landing position when not deflected) to the downstream side in the recording medium conveyance direction. Further, when an electric field is generated in the direction from the electrode 3 to the electrode 2 (that is, the direction from the downstream side to the upstream side in the recording medium conveyance direction), the flight direction is the upstream side in the recording medium conveyance direction (left in FIG. 9). The landing position of the ink droplet deflected by the angle θa2 in the direction) and the flying direction is deviated from the position just below the nozzle 51 to the position a2 shifted upstream in the recording medium conveyance direction.

  The magnitudes of the deflection angles θa1, θa2, θb1, and θb2 are determined by the electric field strength generated between the electrodes 2 and 3 (voltage applied between the electrodes 2 and 3). When the electric field strength is increased, the deflection angles θa1 and θa2 , Θb1, and θb2 increase, and when the electric field strength is decreased, the absolute values of the deflection angles θa1, θa2, θb1, and θb2 decrease. That is, the direction and intensity of the electric field generated in the electrode pair 1 is determined according to the deflection angles θa1, θa2, θb1, and θb2 set for each nozzle 51.

  The absolute value of the forward deflection angle θa1 of the nozzle 51a and the absolute value of the backward deflection angle θb2 of the nozzle 51b are set to the same value, and the absolute value of the backward deflection angle θa2 of the nozzle 51a and the forward deflection angle θb1 of the nozzle 51b are set. If the absolute value is the same (that is, | θa1 | = | θb2 |, | θa2 | = | θb1 |), the electrode driver 90 controls the electric field generated between the electrode 2 and the electrode 3 (FIG. 6). Can be simplified.

  The deflection distance ya (spatial scanning width not considering the movement of the recording medium 16) of the ink droplets continuously ejected (discharged) from the nozzle 51a on the recording medium scanning surface is the deflection shift amount set for the nozzle 51a. (Deflection shift amount in the sub-scanning direction) ka and the minimum dot pitch Pt are expressed by the following equation [Formula 3].

[Equation 3]
ya = ka × Pt
Similarly, the ink droplets continuously ejected (discharged) from the nozzle 51b are deflected in the flight direction based on the forward deflection angle θb1 and the backward deflection angle θb2, and are applied to b1 and b2 of the recording medium 16. Land. The deflection distance yb on the recording medium scanning surface of the ink droplets successively ejected from the same nozzle is expressed by the following equation [Equation 4] using the deflection shift amount kb and the minimum dot pitch Pt set for the nozzle 51b. ] Is represented.

[Equation 4]
yb = kb × Pt
However, ka in [Equation 3] and kb in [Equation 4] are integers of 2 or more.

  Since the recording medium 16 moves to the downstream side in the recording medium conveyance direction by the minimum dot pitch Pt between the previous droplet ejection and the next droplet ejection, the dot pitch Pda between dots formed on the recording medium 16. , Pdb (shown in FIG. 10B) satisfies the following equations [Equation 5] and [Equation 6].

[Equation 5]
Pda = (ka + 1) × Pt
[Equation 6]
Pdb = (kb + 1) × Pt
The deflection shift amounts ka and kb set for the nozzle 51a and the nozzle 51b may be the same value or different values. In the above [Equation 5] and [Equation 6], the ink droplets successively ejected from the same nozzle have a distance (interdot pitch) of k + 1 (ka + 1 or kb + 1) dots on the recording medium 16. It shows that.

  In this way, when droplets are ejected continuously using the same nozzle, the distance between the landing positions of ink droplets by continuous droplet ejection while alternately deflecting the flying direction upstream and downstream in the recording medium conveyance direction Is shifted based on the deflection shift amount k (for example, ka, kb in FIG. 9), so that ink droplets successively ejected from the same nozzle do not form dots adjacent in the recording medium conveyance direction. Landing interference on the medium 16 can be prevented.

  In this example, one of the two types of deflection angles set for each nozzle 51 is set on the upstream side in the recording medium conveyance direction, and the other is set on the downstream side in the recording medium conveyance direction. Alternatively, it may be set downstream of the recording medium conveyance direction.

  In this example, the droplet ejection (ejection) timing and the ink droplet landing timing due to the droplet ejection (ejection) are handled as substantially the same timing. Actually, the ink droplets land on the recording medium 16 after a predetermined flight time from the droplet ejection timing, but the flight time of each ink droplet is substantially the same, and this flight time depends on the droplet ejection cycle Tf and the recording medium 16. This time is sufficiently shorter than the transport time per unit feed amount, and the droplet ejection timing and the landing timing can be handled as substantially the same timing.

  FIGS. 10A and 10B show an example of dots formed on the recording medium 16 by the droplet ejection control described above.

  10A and 10B, the dot row 200a is composed of dots formed by ink droplets ejected from the nozzle 51a shown in FIG. 3, and the dot row 200b is a nozzle shown in FIG. It is composed of dots formed by ink droplets ejected from 51b.

  The numbers described in the dots shown in FIG. 10 represent the relative droplet ejection timing with reference to a certain droplet ejection timing. For example, the dot described as 2 indicates the droplet ejection cycle from the reference timing. A dot formed by an ink droplet ejected at the second droplet ejection timing of Tf is shown.

  Further, the dots constituting the actual dot row 200a and the dot row 200b are arranged in a line along a direction substantially parallel to the recording medium conveyance direction, and adjacent dots overlap, but FIG. Therefore, the adjacent dots in each dot row are drawn with their positions shifted in the vertical direction in FIG. The upper stage of FIG. 10A is dots by ink droplets ejected at odd-numbered droplet ejection timings, and the lower stage is dots by ink droplets ejected at even-numbered droplet ejection timings. It is.

  For example, the dot (the rightmost dot in the second row from the top) 202a that is ejected at the second droplet ejection timing of the droplet ejection period Tf from the reference timing is the ink that was ejected at the droplet ejection timing 9. It is located between a dot 209a by the droplet (the rightmost dot in the uppermost row) and a dot (second dot from the right in the uppermost row) 211a that has been ejected at the droplet ejection timing 11. Similarly, in the dots constituting the dot row 200b, the dot 202b is located between the dot 209b and the dot 211b.

  Also, in FIG. 10B, the adjacent relationship between the dots is maintained, and each dot is drawn without actually overlapping adjacent dots. Note that Pda and Pdb shown in FIG. 10B are substantially parallel to the recording paper conveyance direction of dots formed by ink droplets successively ejected from the same nozzle shown in [Equation 5] and [Equation 6]. Pt is the minimum inter-dot pitch in the direction substantially parallel to the recording paper conveyance direction.

  Although only two dot rows are shown in FIGS. 10A and 10B, the image formation width of the recording medium 16 can be reduced by repeatedly forming these two dot rows over a predetermined image formation width. A desired image can be formed over the entire area.

  Next, a description will be given of the droplet ejection time difference of ink droplets that form dots adjacent in the direction substantially parallel to the recording medium conveyance direction in the droplet ejection control of this example. As shown in FIG. 10A, in the dot row 200a formed by the ink droplets ejected from the nozzle 51a, the dots (for example, the dots 209a and 202a) adjacent in the direction substantially parallel to the recording medium conveyance direction are as follows. It is formed by ink droplets ejected from the nozzle 51a at a predetermined droplet ejection time difference (droplet ejection interval) Ts. The droplet ejection time difference Ts between the ink droplets forming the adjacent dots is expressed by the following equation [Formula 7] using the deflection shift amount k and the droplet ejection period Tf.

[Equation 7]
Ts = Tf × (k−1)
By setting the deflection shift amount k so that the droplet ejection time difference Ts shown in the above [Expression 7] is larger than the semi-fixing time To, droplets are ejected continuously from the same nozzle. Ink droplet landing interference can be avoided. That is, the relationship between the droplet ejection time difference Ts of ink droplets continuously ejected from the same nozzle and the semi-fixing time To of the ink satisfies the following equation [Equation 8], and ink droplets ejected continuously from the same nozzle The landing interference is avoided.

[Equation 8]
Ts ≧ To
From the above [Equation 7] and [Equation 8], the deflection shift amount k is expressed by the following equation [Equation] using the droplet ejection time difference Ts of ink droplets continuously ejected from the same nozzle and the semi-fixing time To of the ink. 9].

[Equation 9]
k ≧ (To / Tf) +1
The semi-fixing time To described above is the time from when the ink droplets land on the recording medium 16 until the semi-fixing state is reached. In addition, the semi-fixed state of the ink droplets referred to here means that even if an ink droplet that has been ejected first comes into contact with an ink droplet that has been ejected earlier, landing interference that affects the image quality of the recorded image does not occur. This is a state where ink droplets that have been ejected to a certain extent are fixed on the recording medium 16.

  That is, in the droplet ejection control shown in this example, even if the landing interference occurs, this is allowed as long as the bleeding or unevenness generated in the recorded image due to the landing interference is not visually recognized, and high-speed printing is given priority. Ink droplet ejection is performed. The speed of image printing can be increased by performing ink droplet ejection that comes into contact with the recording medium 16 and the ink droplet by the previous ejection without waiting for complete fixation of the previously ejected ink.

  FIG. 10A shows an example in which k = 8. That is, the deflection distance on the recording medium scanning surface (spatial scanning width not considering the movement of the recording medium 16) is ya = 8 × Pt. However, since the recording medium 16 is conveyed by one pitch (Pt) while the flight deflection angle is changed from θa1 to θa2, the scanning distance between dots on the recording medium 16 is ya = (8-1) × Pt. It becomes. Therefore, the droplet ejection time difference Ts for forming adjacent dots on the recording medium 16 is Ts = Tf × (8-1) from the above [Equation 7].

  FIG. 11 shows an example of the semi-fixed state of ink droplets. FIG. 11A shows the ink droplet 220 immediately after landing on the recording medium 16. In the case of permeation type fixing, the permeation amount V2 (pl) to the recording medium 16 immediately after the landing is expressed by the following equation [Equation 10] with respect to the volume V1 (pl) of the ink droplet 220 on the recording medium 16 immediately after the landing. ], It is considered that the influence on the image quality is almost eliminated even if the landing interference is not completely eliminated.

[Equation 10]
V2 = V1 x 0.7
That is, the volume V2 of the ink 222 that has penetrated into the recording medium 16 shown in FIG. 11B is approximately 70% or 70% or more (V2 ≧ V1) of the volume V1 of the ink droplet 220 immediately after landing shown in FIG. X 0.7) (that is, the volume V3 of the ink droplet 200 ′ remaining on the recording medium 16 shown in FIG. 11B is approximately 30% or 30% or less of the volume V1 of the ink droplet 220 upon landing). Then, even if an ink droplet that becomes a dot formed so as to overlap with a dot formed by the ink droplet 220 lands, the ink droplet landed first (volume V2 corresponding to 30% of the volume V1 at the time of landing) Ink landing) 224 does not cause any landing interference. That is, the shape of the dots formed by the ink 222 that has penetrated into the recording medium 16 is maintained.

  In other words, it can be said that the volume V2 corresponding to 70% of the ink droplet 220 having the volume V1 immediately after landing passes through the recording medium 16 when the semi-fixing time (semi-penetration time) To elapses. The state in which the volume V1 of the ink droplet 220 immediately after landing on the recording medium 16 has completely penetrated into the recording medium 16 is referred to as a complete fixing (penetration) state, and the ink that has landed on the recording medium 16 has changed from the landing state to the complete penetration state. This time is called complete fixing (penetration) time.

  In the case of curable fixing using UV curable ink or the like, if the viscosity of the previously ejected ink droplet becomes larger than a predetermined value, the ink becomes an adjacent dot of the dot formed by the ink. A drop is hit.

  In the UV curable ink, the viscosity of the ink droplet immediately after landing on the recording medium 16 is about 20 (mPa · s) or less. By applying curing energy by UV light or the like immediately after landing, the curing reaction is promoted mainly on the surface of the recording medium 16, and the viscosity of the ink droplets increases. In the state where the viscosity of the ink droplet is about 1000 (mPa · s) or more, it is considered that the influence on the quality of the recorded image is almost eliminated even if the landing interference is not completely eliminated.

  That is, a state where the viscosity of the ink on the recording medium 16 is 1000 (mPa · s) or more is called a semi-fixed state, and the viscosity of the ink from the timing when the ink droplets land on the recording medium 16 (from the timing when the curing energy is applied). Is defined as a semi-curing time (quasi-fixing time) To. A state where the viscosity of the ink is 1000 (mPa · s) or more includes, for example, a state where the ink droplet is cured to such an extent that the ink droplet does not move from a predetermined landing position.

  Since the semi-fixing time To varies depending on the type of ink, the type of the recording medium 16, the dot diameter, and the like, the semi-fixing time To is stored in advance as a data table using the ink type, the type of the recording medium 16, the dot diameter, and the like as parameters. It is preferable to store the data in a medium (memory such as the image memory 74 and the image buffer memory 82 in FIG. 6) and read the data according to the use conditions.

  Next, a description will be given of the droplet ejection time difference between the ink droplets that form dots adjacent in the direction substantially orthogonal to the recording medium conveyance direction. In the droplet ejection control shown in this example, ink droplets that are ejected at substantially the same timing between nozzles that eject ink droplets that are adjacent in a direction substantially orthogonal to the recording medium conveyance direction are substantially the same as the recording medium conveyance direction. The flying direction of the ink droplet is deflected so as to land at a predetermined distance (with a predetermined phase difference) in the parallel direction.

  As shown in FIG. 10A, the dots 213a of the dot array 200a formed by ink droplets ejected from the nozzle 51a and the dots 209b of the dot array 200b formed by ink droplets ejected from the nozzle 51b. Are dots adjacent to the recording medium conveyance direction in a direction substantially perpendicular to the recording medium conveyance direction. The dots 213a formed by the ink droplets ejected in the thirteenth period of the droplet ejection period Tf from the reference timing and the droplet ejection period Tf from the reference timing. There is a droplet ejection time difference corresponding to four cycles of the droplet ejection cycle Tf between the dots 209b formed by the ink droplets ejected in the ninth cycle. Similarly, the ink droplets forming the dots 206a and 202b that are adjacent in the direction substantially orthogonal to the recording medium conveyance direction have a droplet ejection time difference corresponding to four droplet ejection cycles Tf.

  In other words, dots formed by ink droplets ejected at substantially the same timing between nozzles that eject ink droplets that are adjacent to each other in a direction substantially perpendicular to the recording medium conveyance direction (for example, dots 202a and 202b). ) Has a distance of 4 dots (a deflection distance L corresponding to a time corresponding to 4 cycles of the droplet ejection period Tf) in a direction substantially parallel to the recording medium conveyance direction.

  That is, the droplet ejection time difference Tsm (Tsm = Pdm / V (transport speed of the recording medium 16)) corresponding to the dot pitch Pdm in the direction substantially parallel to the recording medium transport direction shown in FIG. If it is longer than the fixing time To (ie, Tsm ≧ To), it is possible to prevent landing interference of ink droplets that form dots adjacent in the direction substantially perpendicular to the recording paper transport direction.

  In this example, the deflection distance L (see FIG. 9) between the ink droplet ejected from the nozzle 51a and the ink droplet ejected from the nozzle 51b at substantially the same droplet ejection timing (substantially simultaneously) is expressed as the droplet ejection position. It is defined as the shift amount S multiplied by the minimum dot pitch Pt in the recording medium conveyance direction.

  Next, a description will be given of a droplet ejection time difference between ink droplets forming dots adjacent in an oblique direction. In the droplet ejection control of this example, in order to arrange the dots with high density, each dot is formed such that adjacent dots overlap in an oblique direction as shown in FIG.

  As shown in FIG. 10B, the dot 206a is adjacent to the dot 209b and the dot 211b in an oblique direction, and the difference in droplet ejection time between the ink droplet forming the dot 206a and the ink droplet forming the dot 209b is the droplet ejection. The droplet ejection time difference between the ink droplet forming the dot 206a and the ink droplet forming the dot 211b is 5 cycles of the droplet ejection cycle Tf. In this way, in the droplet ejection control shown in this example, it is possible to give a droplet ejection time difference between ink droplets forming dots adjacent in an oblique direction, and this droplet ejection time difference is equal to or greater than the semi-fixing time To of the ink droplet. By setting the deflection angle of the ink droplets ejected from each nozzle so as to become, it becomes possible to prevent landing interference of ink droplets forming dots adjacent in the oblique direction.

  That is, in the droplet ejection control shown in this example, the droplet ejection time difference Ts of ink droplets that form adjacent dots by deflecting the flying direction of the ink droplets ejected from each nozzle in a direction substantially parallel to the recording medium conveyance direction is obtained. Dots formed from ink droplets that are ejected at substantially the same ejection timing within a dot row that is adjacent in the direction substantially perpendicular to the recording paper transport direction so that the ink droplet quasi-fixing time To is equal to or longer than A shift amount (droplet position shift amount) S, which is a distance between them, is set, and ink that forms dots adjacent to each other in a direction substantially orthogonal to the recording medium conveyance direction, a direction substantially parallel to the recording medium conveyance direction, and an oblique direction. Drop landing interference is prevented, and dots arranged at high density on the recording medium 16 can be formed at high speed.

  FIG. 12 shows a flowchart of control for setting the deflection shift amount k and the droplet deposition position shift amount S in the droplet ejection control described above. When the control is started (step S10), a calculation process of a deflection shift amount (flight change shift amount in the sub-scanning direction) k in a direction substantially parallel to the recording medium conveyance direction (sub-scanning direction) k is executed (step S12). ).

  In step S12, the deflection shift amount k is obtained from the conditions of the droplet ejection period (ejection period) Tf and the droplet ejection time difference Ts of the ink droplets that form adjacent dots in the sub-scanning direction, and is temporarily stored in a predetermined memory. The

  The deflection shift amount k may be obtained in consideration of a predetermined margin while satisfying the condition shown in the above [Formula 9]. When the deflection shift amount k is provisionally determined in step S12, the process proceeds to step S14.

  In step S14, the dot positions adjacent to each other in the direction substantially perpendicular to the recording paper conveyance direction, which is the relative positional relationship between dots adjacent in the recording medium conveyance direction (main scanning direction), are substantially the same. A shift amount (droplet position shift amount S) that is a distance between dots formed from the ink droplets to be ejected is set. That is, in step S14, an optimum value of the phase difference (droplet ejection time difference) in the sub-scanning direction of ink droplets that form dots adjacent in the main scanning direction is obtained.

  In step S14, first, S = 2 (or S = 3) is set as an initial value of the droplet ejection position shift amount S (step S100). Based on the initial value of the droplet deposition position shift amount S, the droplet ejection time difference T1 for forming the dots adjacent in the main scanning direction is obtained (step S102), and further, the dots adjacent in the oblique direction are formed. A minimum value T2min of the ink droplet ejection time difference T2 is obtained (step S104).

  If the initial value of the droplet ejection position shift amount S is S = 1, the dots formed by the ink droplets ejected at the same timing are adjacent to each other in the oblique direction. The value is set to 2 or more.

  The minimum value of the droplet ejection time difference T1 for forming ink dots adjacent in the main scanning direction obtained in step S102 and the ink droplet ejection time difference T2 for forming ink dots adjacent in the oblique direction obtained in step S104. T2min is temporarily stored as a set in a predetermined memory (step S106), and the process proceeds to step S108.

  It should be noted that there is a difference in the main scanning direction between the droplet ejection time difference T1 of the ink droplets forming dots adjacent in the main scanning direction and the minimum value T2min of the droplet ejection time difference T2 of forming ink dots adjacent in the oblique direction. Increasing the drop ejection time difference T1 between the ink droplets forming the adjacent dots decreases the minimum value T2min of the drop ejection time difference T2 between the ink droplets forming the adjacent dots in the diagonal direction, while the dots adjacent in the diagonal direction are reduced. When the minimum value T2min of the droplet ejection time difference T2 of the ink droplets to be formed is increased, there is a relationship that the droplet ejection time difference T1 of the ink droplets that form dots adjacent in the main scanning direction is decreased.

  That is, the optimum droplet ejection time is adjusted by adjusting the droplet ejection time difference T1 of ink droplets forming dots adjacent in the main scanning direction and the minimum value T2min of the droplet ejection time difference T2 of ink droplets forming dots adjacent in the oblique direction. It is necessary to obtain the droplet position shift amount S.

  In step S108, it is determined whether or not the droplet ejection position shift amount S is equal to or less than the deflection shift amount k. In step S108, if the droplet ejection position shift amount S is equal to or less than the deflection shift amount k (YES determination). Then, the droplet ejection position shift amount S is increased by a predetermined value (step S110), and the droplet ejection time difference T1 for forming the dots adjacent in the main scanning direction and the ink droplets forming the dots adjacent in the oblique direction are described above. The minimum value T2min of the droplet ejection time difference T2 is obtained again.

  Specifically, in step S110, 2 is added to the droplet ejection position shift amount S, and the process proceeds to step S100, where the minimum value of the droplet ejection time differences T1 and T2 described above is based on the counted droplet ejection position shift amount S. T2min is determined.

In FIG. 13A, the deflection shift amount k = 8 (initial value, the minimum value of the droplet ejection time difference Ts for forming the adjacent dots in the sub-scanning direction is the time corresponding to 7 cycles of the droplet ejection period Tf), The dot arrangement when the droplet ejection position shift amount S = 2 (initial value) is shown. FIG. 13B shows the deflection shift amount k.
= 8, droplet placement position shift amount S = 4 (when droplet ejection position shift amount S is counted up by 2), FIG. 13 (c) shows S = 6 (droplet ejection position shift amount S). The dot arrangement in the case of counting up by 4) is shown.

  In the case of the droplet ejection position shift amount S = 2, 4, 6,... (An even number of 2 or more), the droplet ejection time difference T1 for forming the dots adjacent in the main scanning direction is obtained by the following equation [Equation 11]. It is done.

[Equation 11]
T1 = S
Further, the minimum value T2min of the droplet ejection time difference T2 of the ink droplets forming dots adjacent in the oblique direction can be obtained by the following equation [Equation 12].

[Equation 12]
T2min = k-S-1
As shown in FIG. 13 (a), when the droplet ejection position shift amount S = 2, the droplet ejection time difference T1 of the ink droplets forming the adjacent dots in the main scanning direction is a time corresponding to two cycles of the droplet ejection cycle Tf. is there. At this time, the minimum value T2min of the droplet ejection time difference T2 of the ink droplets forming the dots adjacent in the oblique direction is a time corresponding to 5 cycles of the droplet ejection cycle Tf. is there.

  Further, as shown in FIG. 13B, when the droplet ejection position shift amount S = 4, the droplet ejection time difference T1 of the ink droplets forming the adjacent dots in the main scanning direction is equivalent to 4 cycles of the droplet ejection cycle Tf. It's time. At this time, the minimum value T2min of the droplet ejection time difference T2 of the ink droplets forming dots adjacent in the oblique direction is a time corresponding to three droplet ejection cycles Tf, and an example of a combination of the dots is a dot 209a and a dot 206b. is there.

  Further, when the droplet ejection position shift amount S is incremented by 2 and the droplet ejection position shift amount S = 6, as shown in FIG. 13C, the droplet ejection of ink droplets forming dots adjacent in the main scanning direction. The time difference T1 is a time corresponding to six periods of the droplet ejection period Tf. At this time, the minimum value T2min of the droplet ejection time difference T2 of the ink droplets forming dots adjacent in the oblique direction is one cycle of the droplet ejection cycle Tf, and an example of the dot combination is the dot 209a and the dot 208b.

  In the dot arrangement shown in FIG. 13 (c), ink droplets forming dots adjacent in an oblique direction are ejected at successive timings, and landing interference between the ink droplets is caused in high-speed printing as shown in this example. Since this cannot be prevented, the deflection shift amount k = 8 and the droplet ejection position shift amount S = 6 are not set, and other combinations are set for the deflection shift amount k and the droplet ejection position shift amount S.

  14A to 14C show dot arrangements when the deflection shift amount k = 8 and the droplet ejection position shift amount S = 3, 5, 7,... (Odd number of 3 or more). When the droplet ejection position shift amount S = 3, the droplet ejection time difference T1 of the ink droplets that form adjacent dots in the main scanning direction is obtained by the following equation [Equation 13].

[Equation 13]
T1 = k-S
Further, the minimum value T2min of the droplet ejection time difference T2 of the ink droplets forming dots adjacent in the oblique direction can be obtained by the following equation [Formula 14].

[Formula 14]
T2min = S-1
As shown in FIG. 14 (a), when the droplet ejection position shift amount S = 3, the droplet ejection time difference T1 of the ink droplets forming adjacent dots in the main scanning direction is a time corresponding to 5 cycles of the droplet ejection cycle Tf. is there. At this time, the minimum value T2min of the droplet ejection time difference T2 of the ink droplets forming dots adjacent in the oblique direction is a time corresponding to two droplet ejection cycles Tf, and an example of a combination of the dots is a dot 202a and a dot 204b. is there.

  Further, as shown in FIG. 14B, when the droplet ejection position shift amount S = 5, the droplet ejection time difference T1 of the ink droplets forming the adjacent dots in the main scanning direction is equivalent to 3 cycles of the droplet ejection cycle Tf. It's time. At this time, the minimum value T2min of the droplet ejection time difference T2 of the ink droplets forming the dots adjacent in the oblique direction is the time corresponding to the four droplet ejection cycles Tf. An example of a combination of the dots is the dot 209a and the dot 206b. is there.

  Further, when the droplet ejection position shift amount S is incremented by 2 and the droplet ejection position shift amount S = 7 as shown in FIG. 14C, the droplet ejection of ink droplets forming adjacent dots in the main scanning direction. The time difference T1 is a time corresponding to two periods of the droplet ejection period Tf. At this time, the minimum value T2min of the droplet ejection time difference T2 of the ink droplets forming dots adjacent in the oblique direction is equivalent to six droplet ejection cycles Tf, and an example of a combination of the dots is the dot 202a and the dot 208b.

  In this manner, the droplet ejection position shift amount S is changed from 2 to 7, and the droplet ejection time difference T1 for forming the adjacent dots in the main scanning direction and the ejection of the ink droplets forming the adjacent dots in the oblique direction. The minimum value T2min of the drop time difference T2 is determined as a set, and the combination of the deflection shift amount k and the droplet ejection position shift amount S is determined so that these are longer than the semi-fixing time To of the ink.

  In this example, when the droplet ejection position shift amount S is changed by two, the droplet ejection time difference T1 for forming ink dots adjacent in the main scanning direction and the droplet ejection time difference T2 for forming ink dots adjacent in the oblique direction. Since the mathematical formula for calculating the minimum value T2min is shared, in step S110 of FIG. 12, the droplet ejection position shift amount S is changed by two. Of course, the droplet ejection position shift amount S may be changed by 1 in step S110 of FIG. In a mode in which the droplet ejection position shift amount S is changed by one, the deflection shift amount k is obtained by alternately using [Equation 11] and [Equation 13], and [Equation 12] and [Equation 14] are used alternately. Thus, the droplet ejection position shift amount S is obtained.

  In step S108, when the droplet ejection position shift amount S is greater than or equal to the deflection shift amount k (when S ≧ 9) (NO determination), the process proceeds to step S18 and is adjacent to the main scanning direction stored in step S106. It is determined whether or not the droplet ejection time difference T1 of the ink droplets forming the dots and the minimum value T2min of the droplet ejection time difference T2 of the ink droplets forming the diagonally adjacent dots are greater than the quasi-fixing time To. The minimum droplet ejection time difference T1 between the ink droplets forming the dots adjacent in the main scanning direction and the droplet ejection time difference T2 between the ink droplets forming the dots adjacent in the oblique direction stored in (2) is larger than the semi-fixing time To. In other words, that is, when it is determined that the minimum value T2min of the droplet ejection time differences T1 and T2 is a droplet ejection time difference that does not affect the image quality (YES determination), the deflection shift amount k and the droplet ejection position shift are determined. Set the amount S in a set, the setting control of the deflection shift amount k and the droplet ejection position shift amount S is ended (step S18).

  On the other hand, when the minimum values T1min and T2min of the droplet ejection time difference are smaller than the semi-fixing time To, that is, the minimum values T1min and T2min of the droplet ejection time difference are determined to be a droplet ejection time level at a level that affects the image quality. (NO determination), returning to step S12, the deflection shift amount k is reset.

  In this way, the deflection shift amount k and the droplet ejection position shift amount S are set so that the droplet ejection time difference between the ink droplets forming dots adjacent in the main scanning direction, the sub-scanning direction, and the oblique direction is equal to or greater than the semi-fixing time To. Is set, and ink ejection is controlled based on the deflection shift amount k and the droplet ejection position shift amount S.

[Application example]
Next, an application example according to the present embodiment will be described. FIG. 15 is a schematic diagram illustrating the nozzle arrangement of the print head 300 according to this application example. In FIG. 15, a part of the structure shown in FIG. 3 (for example, the electrode pair 1 and the pressure chamber 52) is omitted.

  As shown in the figure, the head 300 has a nozzle arrangement structure in which the nozzles 51 are arranged on a staggered pattern, and nozzles that eject ink droplets that form adjacent dots in a direction substantially perpendicular to the recording paper conveyance direction ( For example, the nozzle pitch in the direction substantially orthogonal to the recording paper conveyance direction of the nozzles 51a ′ and 51b ′ in FIG. 15 is Pnm, and the nozzles adjacent in the direction substantially parallel to the recording paper conveyance direction (for example, FIG. 15). The nozzle pitch between the nozzles 51a ′ and 51b ′) in the direction substantially parallel to the recording paper conveyance direction is Pns.

  As described above, the head 300 having two nozzle rows in which the nozzles 51 are arranged in a staggered manner is substantially a nozzle substantially in the direction perpendicular to the recording paper conveyance direction, as compared with the head 50 having one nozzle row shown in FIG. The density can be increased, and high quality of the recorded image can be achieved.

  Next, droplet ejection control in the print head 300 in which the nozzles 51 as shown in FIG. 15 are arranged on a staggered pattern will be described with reference to FIGS. 16 and 17. As shown in FIG. 16, the ink droplets ejected from the nozzle 51a ′ are deflected by the forward deflection angle θa1 and the backward deflection angle θa2 with reference to the normal direction 320a on the ejection side of the nozzle 51a ′ indicated by the one-dot broken line. Land on a1 and a2 of the recording medium 16. Further, the ink ejected from the nozzle 51b ′ is deflected by the forward deflection angle θb1 and the backward deflection angle θb2 with reference to the normal direction 320b on the discharge side of the nozzle 51b ′ indicated by a one-dot broken line, and b1 and Land on b2. The deflection angles θa1, θa2, θb1, and θb2 described above are the forward direction in the recording medium conveyance direction downstream with respect to the normal directions 320a and 320b (vertical direction) of the surfaces on which the nozzles 51a ′ and 51b ′ are formed. The upstream side is the backward direction.

  An ink droplet ejected at an odd droplet ejection timing of the droplet ejection cycle Tf from a certain reference timing is deflected in the flight direction by the forward deflection angles θa1 and θb1 (or the backward deflection angles θa2 and θb2). The ink droplets ejected at the even-numbered droplet ejection timing are deflected in the flying direction by the backward deflection angles θa2, θb2 (or backward deflection angles θa1, θb1).

  In this example, the landing position a2 in which the ink droplet ejected from the nozzle 51a ′ is deflected based on the backward deflection angle θa2 and the ink droplet ejected from the nozzle 51b ′ are deflected based on the backward deflection angle θb1. The deflection angles of the nozzle 51a ′ and the nozzle 51b ′ are set so that the landing positions b1 are substantially the same position.

  That is, in the droplet ejection control of this application example, a nozzle that ejects dots adjacent to the deflection distance ya (= ka × Pt) on the scanning surface of the nozzle 51a ′ and the direction substantially perpendicular to the recording medium conveyance direction (FIG. 16). The deflection distance L (= S × Pt) of the ink droplets ejected from the nozzles 51a ′ and 51b ′) at the same timing is substantially the same.

  In other words, a dot row 200a (shown in FIG. 17) formed by ink ejected from the nozzle 51a ′ and a dot row 200b (shown in FIG. 17) formed by ink ejected from the nozzle 51b ′. , Has a phase difference corresponding to a deflection distance ya (= L) on the scanning surface in a direction substantially parallel to the recording paper conveyance direction.

  Of course, the landing position a2 of the ink droplet deflected by the backward deflection angle θa2 of the nozzle 51a ′ and the landing position b1 of the ink droplet deflected by the forward deflection angle θb1 of the nozzle 51b ′ are different from each other. The backward deflection angle θa2 of the nozzle 51a ′ and the forward deflection angle θb1 of the nozzle 51b ′ may be set.

  FIG. 17 shows the arrangement of dots by the droplet ejection control described in FIG. Note that, in the dot row 200a ′ and the dot row 200b ′ shown in FIG. 17, as in FIG. 10A, the dots formed by the ink droplets that are ejected in odd cycles with reference to a certain droplet ejection timing are in the upper row. The dots formed by the ink droplets ejected in the even-numbered cycles are drawn on the lower stage.

  In the droplet ejection arrangement shown in FIG. 17, the droplet ejection time difference T1 of the ink droplets that form adjacent dots in the sub-scanning direction is the time corresponding to 7 cycles of the droplet ejection cycle Tf (ie, deflection shift amount k = 8). The minimum value T2min of the droplet ejection time difference T2 of the ink droplets forming dots adjacent in the main scanning direction is a time corresponding to 8 cycles of the droplet ejection cycle Tf (that is, the droplet ejection position shift amount S = 8). By applying droplet ejection control that realizes the dot arrangement shown in FIG. 17, ink droplets that are adjacent to the recording paper conveyance direction, in a direction substantially parallel to the recording paper conveyance direction, in a direction substantially orthogonal to the recording paper conveyance direction, and in a diagonal direction are given predetermined ejection. The deflection shift amount k and the droplet ejection position shift amount S are set such that the droplet ejection time difference Ts has a droplet ejection time difference Ts that is equal to or greater than the quasi-fixing time To of the ink droplet.

[About droplet ejection conditions]
Next, an example of the droplet ejection conditions of this example is shown. If the resolution (dot density) of the recorded image is 600 dpi (dot / inch), the minimum dot pitch Pt is approximately 42.2 (μm). At this time, if the conveyance speed of the recording medium 16 is 1.67 (mm / sec), the droplet ejection period Tf is approximately 25.3 (msec).

  If the semi-fixing time 20 (msec) in the combination of the general ink and the recording medium 16 can be applied to the semi-fixing (penetration) time of the medium (recording medium 16) to be used, the droplet ejection control according to the present invention is applied. Therefore, it is possible to perform printing without causing landing interference while maintaining the transport speed of 1.67 (mm / sec).

  Here, in order to increase the production capacity, when the transport speed is set to about 10 (mm / sec) (about 6 times the above example), the droplet ejection cycle Tf is about 4.2 (msec), and the droplet ejection according to the present invention. When the control is not applied, landing interference occurs and there is a concern about the quality deterioration of the recorded image.

  When the droplet ejection control according to the present invention is applied under such printing conditions, the droplet ejection time difference of the ink droplets that form dots adjacent in the main scanning direction, the sub-scanning direction, and the oblique direction is equal to five droplet ejection cycles Tf. As described above, by setting the deflection shift amount k and the droplet ejection position shift amount S, landing interference can be avoided even during high-speed printing, and a high-quality recorded image can be formed.

  If the resolution of the recorded image is 1200 dpi, the minimum dot pitch Pt is approximately 21.1 (μm). When the conveyance speed of the recording medium 16 is 1.67 (mm / sec), the droplet ejection period Tf is approximately 12.6 (msec), and landing interference occurs when the above-described general ink and the recording medium 16 are used. May occur and the quality of the recorded image may be degraded.

  When the droplet ejection control according to the present invention is applied under such printing conditions, the droplet ejection time difference between the ink droplets forming dots adjacent in the main scanning direction, the sub-scanning direction, and the oblique direction is equal to or more than two cycles of the droplet ejection cycle. Thus, by setting the deflection shift amount k and the droplet ejection position shift amount S, landing interference can be avoided even when dots are arranged at high density, and a high-quality recorded image can be formed. .

  In this way, even if single-pass printing is performed while maintaining a constant droplet ejection period Tf and a constant transport speed without changing the relative relationship between the print head 50 (300) and the recording medium 16, landing interference occurs. Therefore, predetermined printing conditions can be ensured. When the droplet ejection control such as the droplet ejection period (discharge period) Tf and the conveyance speed of the recording medium 16 is changed, the deflection condition of the droplet flight direction is changed accordingly.

  An example of the flight deflection amount (flying angle) is also shown. As shown in FIG. 17, the distance z (clearance) between the nozzle forming surface of the print head 50 and the image forming surface of the recording medium 16 is approximately 300 (μm). From the deflection distance y on the scanning surface in the sub-scanning direction of the ink droplets continuously ejected from the same nozzle and the distance z between the nozzle formation surface of the print head 50 and the image formation surface of the recording medium 16, the deflection angle θ of the ink droplet is Is expressed by the following equation [Equation 15].

[Equation 15]
θ = arctan (y / z)
That is, when the dot density is 600 dpi, the minimum dot pitch Pt is 42.2 μm, and when the deflection shift amount k is 4, the deflection of the ink droplets continuously ejected from the same nozzle on the scanning surface in the sub-scanning direction. The distance y is (4-1) × 42.2 (μm) ≈0.127 (mm), and the deflection angle θ is approximately 7.2 (degrees).

  When the deflection shift amount is 8, the deflection distance y on the scanning surface in the sub-scanning direction of ink droplets continuously ejected from the same nozzle is (8-1) × 42.2 (μm) ≈0.295. (Mm), and the deflection angle θ at this time is 16.4 (degrees).

  In the present embodiment, a full-line type print head provided with a nozzle row having a length corresponding to the recordable width of the recording medium 16 is illustrated, but the scope of the present invention is limited to the above-described full-line type print head. However, the present invention is also applicable to a shuttle type print head that has a nozzle row having a length shorter than the recording width of the recording paper and forms an image in a predetermined area while scanning in the width direction of the recording medium 16. In particular, the one-pass shuttle method (single-pass shuttle method) that completes the formation of the image of the area scanned by the print head in one shuttle scan is particularly effective.

  On the other hand, the effect of the present invention can also be obtained by a method of printing the same image area by scanning a plurality of times by making the intermittent feed amount of the recording paper smaller than the print length of the print head in the sub-scanning direction.

  A method for printing on the recording medium 16 using the single pass shuttle method will be described with reference to FIG. FIG. 18 shows a print area of the recording medium 16 to be printed using the shuttle type print head. As shown in FIG. 18, the shuttle scanning width (scanning width in the main scanning direction) of the print head is set larger than the printable width in the main scanning direction.

  In the first shuttle scan, the print area 501 is printed. The length of the print area 501 in the sub-scanning direction is substantially the same as the print effective length of the print head. In the second shuttle scan, the print area 502 is printed, and then the print area 503 is printed. When the print head is scanned once in the main scanning direction in this way, the print head and the recording medium 16 are relatively moved in the sub-scanning direction, and printing is sequentially performed.

  When the print area 504 is printed by the (i-1) th shuttle scan, and when the print area 505 is printed by the i-th shuttle scan, printing is performed on the entire surface of the recording medium 16, and the recording medium 16 has a desired print. An image is formed.

  In one movement in the main scanning direction, the print head may be moved in one direction to perform printing in the main scanning direction of the print area, or the print head may be moved back and forth to move the print area. Printing in the main scanning direction may be performed.

  That is, when printing the print area 501, the print head is moved in one of the main scanning directions (for example, from the left to the right in FIG. 18), and when printing the printing area 502, the main scanning direction. It may be controlled to move in the other direction (for example, the direction from right to left in FIG. 18).

  The shuttle type print head is provided with a main scanning direction moving means for relatively moving the head and the recording medium 16 in the main scanning direction. The main scanning direction moving means may move the print head relative to the fixed recording medium 16 or may move the recording medium 16 relative to the fixed print head. Further, both the print head and the recording medium 16 may be moved. Further, control is performed so that the print areas do not overlap at the boundary between adjacent print areas (for example, print area 501 and print area 502).

  In this embodiment, an inkjet head used in an inkjet recording apparatus is exemplified as a droplet ejection head. However, the present invention is not limited to liquids (water, chemicals) on an ejection medium such as a wafer, a glass substrate, or an epoxy substrate. In addition, the present invention can be applied to a discharge head used in a liquid discharge apparatus that discharges a resist, a processing liquid) to form a three-dimensional shape such as an image, a circuit wiring, or a processing pattern.

  The inkjet recording apparatus 10 configured as described above deflects the flying direction of ink droplets successively ejected from each nozzle provided in the print head 50 by a predetermined angle in the recording medium conveyance direction (sub-scanning direction). As a result, the ink droplet ejection is controlled so that the droplet ejection time difference between the ink droplets forming dots adjacent in the main scanning direction, the sub-scanning direction, and the oblique direction is equal to or greater than the semi-fixing time To of the ink to the recording medium 16. Even in high-speed printing in which dots are arranged at high density, landing interference does not occur on the recording medium 16, and a preferable image can be obtained.

1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. FIG. 1 is a plan view of a main part around a printing unit of the ink jet recording apparatus shown in FIG. Plane perspective view showing structural example of print head Sectional view along line IV-IV in FIG. 1 is a conceptual diagram showing the configuration of an ink supply system in the ink jet recording apparatus shown in FIG. 1 is a principal block diagram showing the system configuration of the ink jet recording apparatus shown in FIG. The figure explaining the dot arrangement | positioning formed with the inkjet recording device shown in FIG. The figure explaining the other aspect of dot arrangement | positioning shown in FIG. The figure explaining the deflection | deviation of the flight direction of the ink droplet which was ejected from the printing head of the inkjet recording device shown in FIG. The figure explaining droplet ejection control concerning the present invention Diagram explaining the semi-fixed state The flowchart which shows the flow of the flight direction deflection | deviation amount setting control in the droplet ejection control which concerns on this invention The figure explaining flight direction deflection amount setting control shown in FIG. The figure explaining flight direction deflection amount setting control shown in FIG. The top view which shows the schematic structural example of the print head which concerns on the application example of this invention FIG. 15 is a diagram for explaining deflection in the flight direction of ink droplets ejected from the print head shown in FIG. The figure explaining the droplet ejection control which concerns on the application example of this invention Diagram for explaining droplet ejection control in a shuttle type print head

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,1K, 1C, 1M, 1Y ... Electrode pair, 2,3 ... Electrode, 10 ... Inkjet recording apparatus, 12 ... Printing part, 50, 300 ... Print head, 16 ... Recording medium, 51 ... Nozzle, 80 ... Print control , 90: Electrode control unit, 92: Deflection angle setting unit, θa1, θa2, θb1, θb2 ... Deflection angle, k: Deflection shift amount, S ... Droplet position shift amount, Ts ... Droplet ejection time difference

Claims (6)

A liquid ejection head having ejection holes for ejecting liquid onto the recording medium;
A recording medium conveying means for relatively moving the liquid ejection head and the recording medium in one direction;
Flight direction deflecting means for deflecting the flight direction of droplets ejected from the ejection holes in a direction having at least a component in a direction substantially parallel to the recording medium conveyance direction;
When overlapping adjacent dots in a direction substantially parallel to the recording medium conveyance direction are formed so as to be deflected so that the flying directions of the droplets continuously ejected from the ejection holes are different, the direction is substantially parallel to the recording medium conveyance direction. The ejection is performed so that the difference in droplet ejection time between the first droplet and the second droplet that are adjacent dots in the direction is equal to or longer than the quasi-fixing time from the landing of the first droplet to the quasi-fixing state. A deflection angle setting means for setting two or more deflection angles with respect to the ejection hole with respect to the ejection side normal direction of the hole forming surface;
Equipped with a,
The deflection angle setting means is obtained from the ejection period Tf of the liquid ejection head and the semi-fixing time To, and the ejection of the liquid ejection head on the scanning surface of the recording medium that does not consider the movement of the recording medium. A deflection shift amount k in which the relationship between the period Tf and the semi-fixing time To is an integer of 2 or more satisfying k ≧ (To / Tf) +1 is obtained.
The relationship between the obtained deflection shift amount k and the minimum interval Pt of dots formed on the recording medium in a direction substantially parallel to the recording medium conveyance direction is expressed by y = k × Pt, and the ejection A deflection distance y on the scanning surface of the recording medium in a direction substantially parallel to the recording medium transport direction of two dots formed on the recording medium by two droplets ejected from the holes at successive ejection timings is obtained. ,
An image forming apparatus , wherein the deflection angle is set with respect to the ejection hole based on the deflection distance y . The deflection angle set with respect to the ejection hole includes an angle having a component upstream in a direction substantially parallel to the recording medium conveyance direction with respect to the liquid ejection head, and the recording medium with respect to the liquid ejection head. the image forming apparatus according to claim 1 Symbol mounting, characterized in that it comprises a an angle having a component in the conveying direction and substantially parallel to the downstream side. The liquid ejection head has a plurality of ejection holes arranged in a direction substantially orthogonal to the recording medium conveyance direction,
The deflection angle setting means sets a different deflection angle between the ejection holes adjacent in the direction substantially orthogonal to the recording medium conveyance direction, and one of the ejection holes adjacent in the direction orthogonal to the recording medium conveyance direction. The absolute value | θa1 | of the deflection angle θa1 upstream of the recording medium conveyance direction set with respect to the ejection hole and the absolute value of the deflection angle θb2 downstream of the recording medium conveyance direction set with respect to the other ejection hole Value | θb2 | is represented by the following formula: | θa1 | = | θb2 |
And the absolute value | θa2 | of the deflection angle θa2 downstream in the recording medium conveyance direction and the absolute value | θb1 | of the deflection angle θb1 upstream of the recording medium conveyance direction set for the other ejection hole Is the following formula: | θa2 | = | θb1 |
3. The image forming apparatus according to claim 1, wherein a deflection angle is set with respect to an ejection hole adjacent to the recording medium conveyance direction in a direction substantially orthogonal to the recording medium conveyance direction. The liquid ejection head has a plurality of ejection holes arranged in a direction substantially orthogonal to the recording medium conveyance direction,
The deflection angle setting means sets the deflection shift amount k to one of the ejection holes adjacent in the direction substantially orthogonal to the recording medium conveyance direction, and differs from the deflection shift amount k to the other ejection hole, k Set a droplet ejection position shift amount S having a relationship of> S,
The relationship between the droplet ejection position shift amount S and the minimum dot pitch Pt in the direction substantially parallel to the recording medium conveyance direction of dots formed on the recording medium is expressed by L = Pt × S. set the distance L, the image forming apparatus according to any one of claims 1 to 3, characterized in that to set the deflection angle with respect to the other of the discharge hole based on the deflection distance L. The deflection angle setting means is configured such that a droplet ejection time difference between adjacent droplets in a direction substantially parallel to the recording medium transport direction and an oblique direction different from the recording medium transport direction is substantially perpendicular to the recording medium transport direction. 4. The image formation according to claim 3 , wherein the droplet ejection position shift amount S is set so as to be equal to or longer than the time, and the deflection angle is set with respect to the ejection hole based on the droplet ejection position shift amount S. apparatus. An image forming apparatus that forms a desired image on a recording medium by ejecting liquid droplets from an ejection hole provided in the liquid ejection head while relatively moving the liquid ejection head and the recording medium in one direction. A droplet ejection control method,
When overlapping adjacent dots in a direction substantially parallel to the recording medium conveyance direction are formed so as to be deflected so that the flying directions of the droplets continuously ejected from the ejection holes are different, the direction is substantially parallel to the recording medium conveyance direction. The ejection is performed so that the difference in droplet ejection time between the first droplet and the second droplet that are adjacent dots in the direction is equal to or longer than the quasi-fixing time from the landing of the first droplet to the quasi-fixing state. Two or more deflection angles with respect to the discharge-side normal direction of the hole forming surface are set with respect to the discharge hole,
The ejection cycle Tf of the liquid ejection head and the semi-fixing are obtained from the ejection cycle Tf of the liquid ejection head and the semi-fixing time To, and on the scanning surface of the recording medium not considering the movement of the recording medium. A deflection shift amount k whose relationship with the time To is an integer of 2 or more satisfying k ≧ (To / Tf) +1 is obtained,
The relationship between the obtained deflection shift amount k and the minimum interval Pt of dots formed on the recording medium in a direction substantially parallel to the recording medium conveyance direction is expressed by y = k × Pt, and the ejection A deflection distance y on the scanning surface of the recording medium in a direction substantially parallel to the recording medium transport direction of two dots formed on the recording medium by two droplets ejected from the holes at successive ejection timings is obtained. ,
A droplet ejection control method , wherein the deflection angle is set with respect to the ejection hole based on the deflection distance y .

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