JP2005119291A - Image forming device and droplet jetting control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device and a recording control method that prevent an image from getting spoiled by the overlapping of dots and does not take much time in recording. <P>SOLUTION: A first dot 102 and a second dot 112 are formed so as to overlap. An ink drop 100 of a diameter D1a forming the first dot 102 is jetted and permeates a recording paper after a lapse of a prescribed time and the diameter on the surface of the recording paper becomes D1b. In that state, when an ink drop 110 forming the second dot 112 is jetted, the ink drop 100 and the ink drop 110 do not get mixed with each other. Since the ink that permeates the recording paper 16 is held in the image receiving layer in the recording paper, the mixing of the ink does not occur in the recording paper. Consequently, a desired dot shape can be obtained. Furthermore, the ink drop 110 can be jetted without waiting for the complete permeation of the ink drop 100, any reduction in the printing speed can be prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and a droplet ejection control method, and more particularly to a recording control technique in an image forming apparatus that forms an image with dots formed on a recording medium.

  In recent years, inkjet recording apparatuses (inkjet printers) have become widespread as recording apparatuses that print and record images taken by digital still cameras. An ink jet recording apparatus includes a plurality of recording elements (nozzles) in a head, and scans the recording head while ejecting ink droplets from the recording elements onto the recording medium to record an image for one line on the recording medium. The recording medium is conveyed by one line, and this process is repeated to form an image on the recording paper.

  Ink jet printers use a single serial head and perform recording while scanning the head in the width direction of the recording medium, and recording elements are arranged corresponding to the entire area of one side of the recording medium. Some use a line head. In the case of using a line head, image recording can be performed on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements. A printer using a line head does not require a transport system such as a carriage that scans a short head, and does not require complicated scanning control between the carriage movement and the recording medium. In addition, since only the recording medium moves, the recording speed can be increased as compared with a printer using a serial head.

  In an inkjet printer, one image is expressed by combining dots formed by ink ejected from a recording element (nozzle). High image quality is achieved by reducing the size of these dots and increasing the number of pixels per image. Since the dot size can be reduced by reducing the ink discharge amount, it is necessary to control the ink discharge amount finely and accurately. Further, the relative speed between the recording medium and the recording head and the ink ejection timing are controlled so that adjacent dots are ejected at a predetermined droplet ejection position.

  The ink jet recording apparatus disclosed in Patent Document 1 calculates the time during which no image distortion occurs from the ink absorption characteristics, ink penetration characteristics, ink (dot) density, ink volume, ink evaporation characteristics, and environmental temperature. Techniques to do this have been proposed. That is, the ink drying time and the like are estimated from the parameters described above, and the interval between recordings is adjusted.

Further, a method and a printing method for manufacturing a recording head for an ink jet printer described in Patent Document 2 are a method for manufacturing a print head by determining a distance between nozzles in consideration of an ink drying time, and the print head. There has been proposed a printing method using.
JP-A-3-247450 Japanese Patent Laid-Open No. 10-250059

  However, when a plurality of dots are overlapped and landed on the recording medium, the ink droplets are mixed and the original circular shape of the dot shape collapses, making it difficult to form a desired image.

  In the ink jet recording apparatus disclosed in Patent Document 1, the time during which no image disturbance occurs is obtained for each parameter, but it is very difficult to obtain the time during which image disturbance does not occur for various dot arrangement patterns. . Also, a recording method for forming mixed patterns with different dot pitches and dot diameters in one image is not sufficiently disclosed.

  In the method and the printing method for manufacturing a recording head for an ink jet printer described in Patent Document 2, it is disclosed that the second dot is landed after the drying time of the first dot has elapsed. Adjacent dots cannot be landed until these dots are completely dried, and it takes a very long time for printing. Further, since the distance between the nozzles is determined assuming a drying time based on one condition and is set to a fixed value, it is not possible to cope with a change in ink or paper.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image forming apparatus and a droplet ejection control method that prevent image disturbance due to overlapping dots and that do not require recording time.

  In order to achieve the above object, the invention according to claim 1 is a recording head for ejecting droplets onto a recording medium, droplet ejection control means for controlling droplet ejection timing of the recording head, and the recording medium. An image forming apparatus comprising: a conveying unit that moves the recording head relative to the recording medium; and a first dot that forms the first dot and the first dot formed on the recording medium. The distance Pt from the second dot formed so as to overlap the first dot after the droplet is ejected, and the second droplet forming the second dot at the time of landing on the recording medium When the diameter D2a of the surface of the recording medium and the diameter D1b of the first droplet on the surface of the recording medium when the second liquid droplets land on the recording medium, the droplet ejection control means is The first droplet satisfying D1b <2 × Pt−D2a Is characterized by controlling the droplet ejection timing as droplet ejection interval droplet diameter change time until a diameter D1b ejected droplets of said first liquid droplet to droplet ejection of the second droplet.

  That is, even if the second droplet is landed on the recording medium without waiting until the first droplet landed on the recording medium is completely held on the recording medium, the surface of the recording medium Ink mixing does not occur. Therefore, it is possible to prevent bleeding due to the mixing of the first droplet and the second droplet without reducing the printing speed, and a desired dot shape can be obtained.

  For example, in the process in which droplets penetrate into the recording medium, the droplets on the surface of the recording medium become smaller from the outside (outer periphery) toward the inside. The droplet size when landing on the recording medium is substantially the same as the size of the dots formed.

  The interval (dot pitch interval) Pt between the first dot and the second dot is substantially the same as the interval between the droplets ejected (recorded) normally from the recording head.

  In addition, D1b = 0 when the first droplet has completely penetrated, solidified, etc., so that the state where the first ink droplet does not completely penetrate satisfies D1b> 0.

  When the first dot and the second dot overlap, the sum of the radius of the first dot (D1a / 2) and the radius of the second dot (D2a / 2) is the first dot and the second dot. This is a case where the distance Pt is larger than the distance Pt between the two dots, and this satisfies the relationship Pt <(D1a / 2) + (D2a / 2).

The recording head may be a full-line type recording head in which recording elements such as ink ejection holes are arranged over the entire printable area of the recording medium used in a direction substantially perpendicular to the relative conveying direction of the conveying means, A serial type (shuttle scan type) recording head that ejects ink droplets while moving a short recording head in a direction substantially orthogonal to the relative conveying direction of the conveying means may be used.

  A recording medium is a medium (image forming medium) that receives printing by a recording head. Specifically, a continuous sheet, a cut sheet, a sealing sheet, a resin sheet such as an OHP sheet, a film, a cloth, and other materials and shapes are used. Regardless, it includes various media.

  As a mode in which the recording medium and the recording head are relatively moved, the recording medium may be moved relative to the fixed recording head, or the recording medium may be fixed and the recording head may be moved. Further, both the recording medium and the recording head may be moved. A conveying belt, a conveying drum, or the like is applied to the recording medium conveying means.

  As shown in claim 2, in the invention described in claim 1, the recording medium at the time of landing of the recording medium on the recording medium, the interval Pt between the first dot and the second dot, and the second droplet The droplet ejection condition calculation means for obtaining the diameter D1b of the first droplet satisfying the following equation: D1b <2 × Pt−D2a, and the first droplet landed on the recording medium. And a droplet diameter change time calculating means for obtaining a droplet diameter change time from the first droplet until the diameter of the first droplet reaches D1b.

  That is, a droplet ejection condition calculating means for obtaining a condition of the first droplet capable of ejecting the second droplet, and a droplet diameter for obtaining a time until the first droplet satisfies the condition Since the change time calculation means is provided, the droplet ejection interval can be obtained in the apparatus.

  As described in claim 3, in the invention described in claim 2, a mixed pattern having a plurality of combinations of the dot interval, the diameter of the first dot, and the diameter of the second dot is formed in one image. In this case, a plurality of droplet diameter change times are calculated, and the droplet ejection control means controls the recording timing of the image using the calculated representative values of the plurality of droplet diameter change times. .

  That is, it is possible to cope with an image including a mixed pattern in which the dot interval (dot pitch) and the diameter of each dot are different, and the droplet ejection timing can be optimized for each image.

  The mixed pattern includes a plurality of dot intervals, a plurality of dot diameters, and a plurality of dot intervals and dot diameters.

  The representative value includes a maximum value, a minimum value, an average value, a value that is used most frequently, and the like, and may be appropriately used according to image quality and recording control. One representative value may be obtained per image, or a plurality of representative values may be obtained per image.

  According to a fourth aspect of the present invention, in the invention according to the third aspect, the representative value of the droplet diameter change time is at least a plurality of the droplet diameter change times calculated by the droplet diameter change time calculation means. It is characterized by containing values that are greater than the maximum value.

  In other words, since the droplet ejection timing in the image is controlled in accordance with the pattern with the longest droplet diameter change time, it is possible to reliably prevent dot bleeding, and the control system is simple and the burden on the control system is reduced. To do.

  The droplet diameter change time may be a maximum value obtained from each pattern, or may be a time obtained by adding a margin to the maximum value in anticipation of safety. However, the droplet diameter change time is less than the time when the penetration or solidification of the droplet is completely completed.

  Further, as shown in claim 5, in the invention according to any one of claims 1 to 4, the droplet ejection control means controls droplet ejection timing by one droplet ejection interval within one image. It is characterized by.

  That is, since droplet ejection control is performed by one droplet ejection interval within one image, it is possible to have a droplet ejection interval for each image.

  Further, as described in claim 6, in the invention according to any one of claims 2 to 5, information including at least one of the liquid type information and the recording medium type information is included. Provided with information providing means for providing, wherein the droplet diameter change time calculating means calculates the droplet diameter change time based on information provided by the information providing means.

  That is, even if the type of liquid or the type of recording medium (recording paper) changes, recording (image formation) is performed at the optimum droplet ejection timing, so that not only the printing speed is high but also a desired dot shape is obtained. Can do.

  In addition to the type of ink and the type of recording medium, the information may include factors that may affect environmental conditions such as temperature and humidity and the ink penetration rate. It is preferable that these conditions are converted into a data table and the data table is referred to when the droplet diameter change time is obtained.

  Further, according to a seventh aspect of the present invention, in the invention according to any one of the second to sixth aspects, the droplet change time calculating means has a dot pitch in a direction substantially orthogonal to the relative transport direction of the transport means. And the first droplet diameter change time in the direction substantially perpendicular to the relative transport direction of the transport means and the second droplet diameter change in the relative transport direction of the transport means from the dot pitch in the relative transport direction of the transport means The droplet ejection control means determines the first droplet diameter change time and the second droplet diameter change time, respectively, and the droplet ejection interval in a direction substantially perpendicular to the relative conveyance direction of the conveyance means and It is characterized in that the droplet ejection timing is controlled as a droplet ejection interval in the sub-scanning direction, which is the relative transport direction of the transport means.

  That is, it is possible to control the droplet ejection timing in the direction (main scanning direction) substantially orthogonal to the relative conveyance of the conveyance unit and the relative conveyance direction (sub-scanning direction) of the conveyance unit.

  Further, as shown in claim 8, in the invention according to any one of claims 1 to 7, the recording head has a plurality of nozzles arranged over a length corresponding to the entire width of the recording medium. It is a line head.

  The line head may be a divided head that is divided into a plurality of heads in the longitudinal direction of the head. Further, the head may include one nozzle row or a plurality of nozzle rows.

  According to a ninth aspect of the present invention, in the eighth aspect of the invention, the recording head forms odd-numbered dots among dots formed along a direction substantially perpendicular to the relative transport direction of the transport means. A first nozzle row having nozzles for ejecting liquid droplets and a second nozzle row having nozzles for ejecting liquid droplets that form even-numbered dots, and a relative transport direction of the transport means It is characterized by comprising an interval varying means for varying the interval between the first nozzle row and the second nozzle row in accordance with the droplet ejection control.

  That is, in the line head, the recording timing in the direction substantially orthogonal to the recording medium can be controlled efficiently.

  Further, according to a tenth aspect of the present invention, in the invention according to any one of the first to seventh aspects, the recording head includes a plurality of nozzles arranged over a length shorter than the entire width of the recording medium. The serial head includes a moving means for moving the recording head and the recording medium relative to each other along the nozzle arrangement direction.

  In addition, as described in claim 11, in the invention according to claim 10, the recording head forms odd-numbered dots among dots formed along a direction substantially perpendicular to the relative transport direction of the transport means. A first nozzle row having nozzles for ejecting liquid droplets and a second nozzle row having nozzles for ejecting liquid droplets that form even-numbered dots, and a relative transport direction of the transport means And an interval varying means for varying the interval between the first nozzle row and the second nozzle row in accordance with droplet ejection control in a direction substantially orthogonal to the first nozzle row.

  That is, it is possible to control the recording timing in the direction substantially orthogonal to the recording medium without changing the conveyance speed and the recording frequency.

  The present invention also provides a method invention for achieving the above object. That is, the invention according to claim 12 is a droplet ejection control of an image forming apparatus comprising: a recording head that ejects droplets onto a recording medium; and a droplet ejection control unit that controls droplet ejection timing of the recording head. A first dot forming step of forming a first dot with a first droplet on the recording medium; and after the first droplet is deposited, the first dot overlaps with the first dot A second dot ejection step of ejecting a second droplet forming a second dot, and the first droplet on the surface of the recording medium when ejecting the second droplet And a droplet ejection condition calculating step for obtaining the diameter of the first droplet so that the second droplet does not overlap with the second droplet, and a value when the diameter of the first droplet is landed on the recording medium The time until a value that does not overlap the second droplet on the surface of the recording medium is obtained. It is characterized in that it comprises a droplet diameter change time calculating step.

  Software (program) for realizing the above steps can be configured, and the program can be executed using a control means such as a CPU (central processing unit). Furthermore, the program can be stored in a recording medium.

  According to the present invention, even if the second ink droplet is ejected without waiting for the complete penetration of the first ink droplet ejected first, the first ink droplet and the second ink droplet are recorded on the recording medium. Therefore, a desired dot shape can be obtained. Further, since the second ink droplet can be ejected without waiting for complete penetration of the first ink droplet, the printing speed is high.

  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 recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle of the printing unit 12 A suction belt transport unit 22 that is disposed to face a surface (ink ejection surface) and transports the recording paper 16 while maintaining the flatness of the recording paper 16, and a print detection unit 24 that reads a printing result by the printing unit 12, A paper discharge unit 26 that discharges printed recording paper (printed matter) 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 multiple types of recording paper are used, an information recording body such as a barcode or wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

  The recording paper 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 paper 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 paper 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 paper 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 paper 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 be a negative pressure, whereby the recording paper 16 on the belt 33 is sucked and 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 paper 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 a mode 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 print area, the image easily spreads because the roller contacts the printing surface of the sheet immediately after printing. There is a problem. 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 paper conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

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

  A print head 12K 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 paper 16 (hereinafter referred to as the paper transport direction). , 12C, 12M, 12Y are arranged. A color image can be formed on the recording paper 16 by discharging the color inks from the print heads 12K, 12C, 12M, and 12Y while the recording paper 16 is conveyed.

  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 paper 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 paper 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 head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like. In addition, the print detection unit 24 includes a light source that irradiates light onto the ejected dots.

  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 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 blocking the paper holes by pressurization. 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 to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. When the main image (printed target image) and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by the 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.

  Next, the structure of the print head 50 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.

  FIG. 3 (a) is a plan perspective view showing an example of the structure of the print head 50, and FIG. 3 (b) is an enlarged view of a part thereof. 3C is a perspective plan view showing another example of the structure of the print head 50, and FIG. 4 is a sectional view showing the three-dimensional configuration of the ink chamber unit (along line 4-4 in FIG. 3B). FIG.

  The print head 50 of this example includes a print head 50A and a print head 50B. The print head 50A and the print head 50B are configured to be relatively movable along the recording paper conveyance direction, and the interval between the print heads (recording). The nozzle pitch in the paper transport direction can be varied.

  For example, the print head 50A includes a motor, a transport mechanism such as a ball screw and a slide rail, and a head moving mechanism (not shown) including a guide member, and moves the print head 50A relative to the fixed second print head. There is a mode in which both the print head 50A and the print head 50B are provided with the head moving mechanism described above, and each is configured to be movable. Of course, the print head 50A may be fixed and the print head 50B may be moved.

  Further, as shown in FIG. 3A, the print head 50A and the print head 50B have a plurality of nozzles arranged in a line along a direction substantially perpendicular to the recording paper transport direction. The interval (nozzle pitch) between the nozzles 51A provided in the print head 50A and the nozzle pitch of the nozzles 51B provided in the print head 50B are the same.

  Further, the print head 50A and the second print head are substantially orthogonal to the recording paper conveyance direction so that the nozzle 51B in the second print head is positioned at a substantially intermediate position between the adjacent nozzles 51A in the print head 50A. The position of the direction is determined.

  In other words, the nozzles 51A in the first print head and the nozzles 51B in the print head 50B are arranged in a staggered manner shifted by 1/2 pitch, and each print head is in a direction substantially orthogonal to the recording paper transport direction. This is equivalent to one arranged in a straight line at 1/2 the nozzle pitch within 50.

  In this example, the print head 50A and the print head 50B have been illustrated with a single nozzle row. However, the nozzles may be two-dimensionally arranged in a matrix.

  Here, for convenience, the recording paper conveyance direction is sometimes referred to as a sub-scanning direction, and the direction substantially orthogonal to the recording paper conveyance direction is sometimes referred to as a main scanning direction.

  Further, as shown in FIG. 3 (c), short two-dimensionally arranged heads 50 'may be arranged in a staggered manner and connected to form a length corresponding to the entire width of the print medium.

  The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape, and the nozzle 51 and the supply port 54 are provided at both corners on the diagonal line. Each pressure chamber 52 communicates with a common flow channel 55 through a supply port 54.

  An actuator 58 having an individual electrode 57 is joined to the pressure plate 56 constituting the top surface of the pressure chamber 52, and the actuator 58 is deformed by applying a driving voltage to the individual electrode 57, and the nozzle 51 Ink is ejected. When ink is ejected, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54.

  When the nozzles are driven by a full line head having a nozzle row corresponding to the entire width of the paper (recording paper 16), (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially moved from one side to the other. (3) The nozzles are divided into blocks, and each block is sequentially driven from one side to the other. One row of dots is formed in the paper width direction (direction perpendicular to the paper conveyance direction). Nozzle driving that prints a line or a line composed of a plurality of rows of dots is defined as main scanning.

  When driving the nozzles 51 arranged in a matrix as shown in FIG. 3A, the main scanning as described in the above (3) is preferable. That is, one line is printed in the width direction of the recording paper 16 by driving the nozzle 51A and the nozzle 51B at different timings according to the conveyance speed of the recording paper 16 like the nozzles 51A, 51B, 51A,.

  On the other hand, the sub-scan is defined as the above-described full-line head and the paper are moved relative to each other to repeatedly print a line composed of one row of dots or a line composed of a plurality of rows of dots formed by the above-described main scan. To do.

  In the implementation of the present invention, the nozzle arrangement structure is not limited to the illustrated example. In the present embodiment, a method of ejecting ink droplets by deformation of an actuator 58 typified by a piezo element (piezoelectric element) is employed. In implementing the present invention, an actuator other than the piezoelectric element can be applied to the actuator 58.

  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 ink remaining amount 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. The ink supply tank 60 of FIG. 5 is equivalent to the ink storage / loading unit 14 of FIG. 1 described above.

  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 51 and a cleaning blade 66 as a means for cleaning the surface of the nozzle 51. Yes.

  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 51 surface (ink ejection 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, brim 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.

  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, an image 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, IEEE 1394, Ethernet, and 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. 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 image memory 74. The image 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 image 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 each unit such as the communication interface 70, the image memory 74, the motor driver 76, and the heater driver 78. 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 image memory 74, and the like, as well as a transport system motor 88 and heater 89. A control signal for controlling 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 the image data in the image memory 74 according to the control of the system controller 72, and the generated print A control unit that supplies a control 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 of the ink droplets of the print head 50 are controlled 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 form associated with the print control unit 80, but it can also be used as the image 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 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.

(Control of droplet ejection timing)
The droplet ejection timing control (droplet ejection control) of the inkjet recording apparatus 10 will be described with reference to FIGS. In the ink jet recording apparatus 10, when dots formed on the recording paper 16 overlap, the ink droplet 110 (the ink droplet 100 (the ink droplet 100 previously ejected) is ejected next before the penetration of the recording paper 16 is finished). The droplet ejection (recording) timing is controlled so as to perform the droplet ejection shown in FIG.

  FIG. 7 shows the ink droplet 100 previously ejected. The droplet diameter of the ink droplet 100 on the surface of the recording paper 16 is D1a.

  When the dye-based ink is ejected onto the penetrating recording paper 16 (recording medium), the ink droplet 100 that has landed on the surface of the recording paper 16 penetrates into the image receiving layer (not shown) of the recording paper 16 over time. The permeation is completed from the outside to the inside of the ink droplet 100, so that the diameter of the ink droplet gradually decreases toward the center.

  When the predetermined time T elapses, the solvent on the surface of the recording paper 16 runs out, and the ink droplet 100 completely penetrates into the recording paper 16. Here, dots having a predetermined size (in this embodiment, the same diameter as the diameter of the ink droplet upon landing) are formed. This time T is defined as a complete penetration time.

  FIG. 8 is a cross-sectional view taken along line 8-8 in FIG. 7, and shows a state immediately after the ink droplet 100 has landed on the recording paper 16. FIG.

  FIG. 9 shows a state in which, after the ink droplet 100 has landed on the recording paper 16, a predetermined time less than the complete penetration time T has elapsed, and the diameter of the ink droplet 100 on the surface of the recording paper 16 becomes D1b. .

  A circle indicated by a broken line in FIG. 9 indicates the dot 102 formed by the ink droplet 100, and the size thereof is substantially the same as the size of the ink droplet when the ink droplet 100 lands on the recording paper 16. In other words, the ink droplet 100 forms a dot 102 having a diameter D1a.

  FIG. 9 shows a state in which an ink droplet 110 having a diameter D2a is ejected to form a dot 112 having a dot diameter D2a at an interval (dot pitch interval) Pt from the dot 102.

  The diameter D1b after the passage of time δT after the previously ejected ink droplet 100 landed on the recording paper 16, the diameter D2a of the ink droplet 110 when landed on the recording paper 16, the ink droplet 100 and the ink When the relationship between the distance from the droplet 110 (corresponding to the pitch of the dots formed by the ink droplet 100 and the ink droplet 110) Pt satisfies the following equation [Equation 1], the ink droplet 100 and the ink on the surface of the recording paper 16 Since the ink droplets are not mixed with the droplets 110, the shapes of the ink droplets 100 and the dots 102 and the dots 112 (formed in the same position and in the same size as the ink droplets 110 in FIG. 9) do not collapse. Therefore, a desired dot shape can be obtained.

[Equation 1]
D1b <2 × Pt -D2a
Here, the condition in which the dot 102 and the dot 112 overlap is represented by Pt <(D1a / 2) + (D2a / 2). In other words, the condition where the dot 102 and the dot 112 overlap is when the sum of the radius of the dot 102 and the radius of the dot 112 is larger than the dot pitch Pt.

  The dots 102 shown in FIG. 9 are recorded after the ink droplet 100 has not penetrated into the recording paper 16 (the region indicated as the ink droplet 100) and the ink droplet 100 has penetrated into the recording paper 16. There is a region in which the ink coloring matter (solute) is held inside the image receiving layer of the paper 16 (a region obtained by excluding the region shown as the ink droplet 100 from the region of the dot 102 shown by the broken line). Of the two regions, the other ink droplets 110 can be landed on the region where the ink droplet 100 has penetrated into the recording paper 16.

  FIG. 10 is a cross-sectional view (corresponding to FIG. 8) showing a cross section of the ink droplet 100 and the ink droplet 110. When the ink droplet 110 permeates the recording paper 16, even if the ink droplet 100 and the ink droplet 110 are mixed in the image receiving layer of the recording paper 16 at the portion where the dot 102 and the ink droplet 110 overlap, the ink droplet Since 100 has already penetrated into the image receiving layer and the ink coloring matter (solute) is retained in the image receiving layer, the shape of the dot 102 inside the image receiving layer hardly changes.

  When the above-described complete penetration time T elapses after the ink droplet 110 has landed on the recording paper 16, the penetration of the ink droplet 110 into the recording paper 16 is finished, and as shown in FIG. D2a dots 112 are formed.

  12 is a cross-sectional view showing a cross section of the dot 102 and the dot 112 shown in FIG.

  Therefore, when two dots overlap, the next ink can be ejected without waiting for the complete permeation time T for the permeation of the previously ejected ink droplet to finish (in the state of D1b> 0). .

  That is, the diameter P1 of the ink droplet 100 that satisfies the following [Equation 1] from the interval Pt between the ink droplet 100 that has landed first and the ink droplet 110 that has landed next, the diameter D2a when the ink droplet 110 landed, and D1b is obtained, and the permeation time δT is obtained from the obtained diameter D1b of the ink droplet 100 and the diameter D1a when the ink droplet 100 is landed. The droplet ejection timing of the ink droplet 100 and the ink droplet 110 is controlled with the penetration time δT thus determined as the droplet ejection interval.

  In the above-described embodiment, the dye-based ink in which the ink coloring matter is retained by the permeation in the image receiving layer of the penetrating recording paper 16 has been described. However, the present invention is also applicable to pigment-based ink that solidifies on the surface of the recording paper 16 or ultraviolet curable ink (UV curable ink).

  In the case of ink that has a large molecular structure of the ink dye and is mixed in the solvent without dissolving in the solvent (many pigment types are this type), when the ink droplets land on the surface of the recording paper 16, the solvent penetrates into the image receiving layer. Although some of the dye penetrates into the image receiving layer, most of the dye is solidified on the paper surface. Also in the case of UV curable ink, most of the ink droplets that have landed on the surface of the recording paper 16 are solidified (cured) on the surface of the recording paper 16 when irradiated with ultraviolet rays.

  At that time, the portion of the ink on the recording paper 16 that has landed as droplets becomes smaller from the outside toward the inside as the solidification (curing) progresses. Therefore, the present invention can be applied to prevent mixing of ink droplets on the surface of the recording paper 16.

  FIG. 13 is a block diagram illustrating details of the droplet ejection control unit 200 that executes the droplet ejection control described above. The droplet ejection control unit 200 is included in the system (print control unit 80) shown in FIG.

  When the image data 202 is acquired from the host computer 86 shown in FIG. 6, the dot data generation unit 210 performs conversion from RGB data to CMY data, distribution of dark and light inks, and generation of CMYK dot data.

  Next, in the inequality calculation unit 212, the pitch Pt of two dots (for example, the ink droplet 100 and the ink droplet 110 shown in FIG. 11) and the diameter D2a of the ink droplet (ink droplet 110 of FIG. 11) to be ejected later. From this, D1b is obtained as the diameter of the previously ejected ink droplet (ink droplet 100 in FIG. 11).

  On the other hand, the information regarding the time change of the ink droplet size to be used stored in the dot diameter calculation / storage unit 214 is referred to, and the timing calculation unit 216 determines when the ink droplet that forms the previously ejected dot is landed. The permeation time δT (droplet ejection interval) from the droplet diameter D1a to the aforementioned D1b is obtained. Further, timing control parameters in the sub-scanning direction (recording paper conveyance speed, etc.) and timing control parameters in the main scanning direction (interval L between the print head 50A and the print head 50B, etc.) are determined from the penetration time δT.

  Note that in a mixed pattern in which dots having different dot diameters exist, the representative value calculation unit 217 uses a representative value of the penetration time δT in the mixed pattern, timing control parameters in the sub-scanning direction (recording paper conveyance speed, etc.), A representative value of a timing control parameter (such as an interval L between the print head 50A and the print head 50B) in the scanning direction is obtained.

  For this representative value, the penetration time δT, the control parameter in the main scanning direction, the maximum value of the control parameter in the sub-scanning direction may be applied, or the minimum value, the average value, the most frequently used value, etc. can be applied as appropriate It is.

  Based on the penetration time δT thus obtained, the timing control parameter in the sub-scanning direction, and the timing control parameter in the main scanning direction, the nozzle driving signal generation unit 218 generates a driving signal 220 for each nozzle.

  Here, the speed at which the ink droplet permeates the recording paper 16 mainly depends on the type of ink, the type of the recording paper 16, the environmental temperature, the humidity, and the like.

  The dot diameter calculation / storage unit 214 stores these pieces of information in a data table and provides the timing calculation unit 216 with parameters for determining the permeation time δT calculated by the calculation.

  The penetration time δT may be obtained by referring to the data of the diameter D1b from a database in which the diameter D1b is calculated and registered in advance from the diameter D1a, the diameter D2a, and the dot interval Pt. The database may be provided inside the inkjet recording apparatus 10 or may be provided outside.

  For example, the ink type information 230 may be read when the ink cartridge is loaded, the ink type information 230 may be stored, and the ink information may be provided to the timing calculation unit 216 when printing is performed. Similarly, the paper type information 232 can be read and stored when the recording paper 16 is loaded.

  The ink type information 230 and the paper type information may be automatically read at the time of loading from a wireless tag or a barcode attached to an ink cartridge or a paper tray, or may be input by an operator via a keyboard or a touch panel.

  A change in ink droplet diameter over time for each ink type and paper type will be described with reference to FIGS.

  FIG. 14 is a graph 300 showing a change in ink droplet diameter over time when ink A1 and paper B1 are used. In the graph 300, a curve 302 indicates a case where the diameter of the ink droplet upon landing is 100 μm, and a curve 304 and a curve 306 indicate the case where the diameter of the ink droplet upon landing is 60 μm and 30 μm, respectively.

For example, in curve 302, it can be seen that the time from the ink droplet diameter of 100 μm at the time of landing to 40 μm is approximately 3.9 msec. On the other hand, in the curve 304, the time from the ink droplet diameter of 60 μm to 0 μm (that is, the end of permeation) at the time of landing is 7.0 msec, and the change amount of the ink droplet diameter is the same as that described with reference to the curve 302. Although it is 60 μm, the time required for this varies depending on the diameter of the ink droplet upon landing.

  Therefore, in the graph 300, it is preferable to provide a curve for each ink droplet diameter at the time of landing, in addition to the curve 302, the curve 304, and the curve 306.

  FIG. 15 is a graph 320 showing changes in ink droplet diameter over time when the ink droplet diameter upon landing is 100 μm for three types of ink and paper. In the graph 320, a curve 321 indicates a combination of the ink A1 and the sheet B1, a curve 322 indicates a combination of the ink A2 and the sheet B2, and a curve 323 indicates a combination of the ink A3 and the sheet B3.

  As described above, when a penetrating recording paper 16 is used for the combination of a plurality of ink types and a plurality of recording paper materials, the landed ink droplets may penetrate into the image receiving layer in the recording paper 16 or may not. When the penetrating recording paper 16 is used, the time required for ink droplet size change accompanying the solidification (curing) on the surface of the recording paper 16 (that is, the penetrating time, the solidifying time, and the curing time δT) is determined in advance through experiments or simulations. It is obtained and stored in the dot diameter calculation / storage unit 214.

  The storage form may be a graph (an arithmetic expression such as an approximate expression for each curve), but a mode in which each curve is stored in a data table is preferable.

  In addition to the ink type and the paper type, there may be representative values under some conditions depending on the environmental temperature, humidity, and the like, and it may be estimated by complementation that corresponds to the actual environmental conditions.

  Furthermore, when ink or paper of a type that is not stored is set, a change in the ink droplet that has actually landed may be imaged by an imaging means or the like and measured, and the penetration time δT may be obtained each time. A line sensor, an area sensor, or the like may be used as the image pickup means, and the image detecting unit can also be used as the print detection unit 24 shown in FIG.

  In this example, as shown in FIG. 16, the dot pitch Pts in the recording paper conveyance direction (sub-scanning direction) and the dot pitch Ptm in the direction substantially orthogonal to the recording paper conveyance direction (main scanning direction) are divided as necessary. It can be handled separately. As a result, the droplet ejection timing δT obtained from D1b obtained by applying [Equation 1] can also be handled by distinguishing the droplet ejection interval δTm in the main scanning direction and the droplet ejection interval δTs in the sub-scanning direction. .

  Further, for example, the present invention can also be applied to the droplet ejection timing of dots adjacent in an oblique direction that is not adjacent in the main scanning direction and the sub-scanning direction like the dot 250 and the dot 256 in FIG.

  As shown in FIG. 3A, the ink jet recording apparatus 10 includes a print head 50A and a print head 50B arranged in the sub-scanning direction, and the interval L between the print head 50A and the print head 50B is variable. Is possible. Therefore, by adjusting the interval L between the print head 50A and the print head 50B and the conveyance speed of the recording paper 16, it is possible to control the droplet ejection interval δTm of dots adjacent in the main scanning direction in the line head.

  That is, when the dot 252 adjacent to the dot 250 ejected from the print head 50A is ejected from the print head 50B, the main scanning is performed from the conveyance speed Vs of the recording paper 16 and the distance L between the print head 50A and the print head 50B. The droplet ejection interval δTm in the direction is obtained by the following equation [Equation 2].

[Equation 2]
δTm = L / Vs
On the other hand, the droplet ejection interval δTs in the sub-scanning direction is obtained from the recording paper transport speed Vs and the droplet ejection interval Pts in the sub-scanning direction according to the following equation [Equation 3].

δTs = Pts / Vs
In this example, the full-line type line head has been described, but the present invention is also applicable to a serial head (shuttle scan type head). The serial head has two nozzle rows in the sub-scanning direction (distance between column centers: Ls), and one nozzle row and the other nozzle row are arranged in a staggered manner with a half pitch shift. Has been. Furthermore, the interval between the nozzle rows can be varied.

  The droplet ejection interval δTm in the main scanning direction is obtained from the following equation (4) from the main scanning direction speed (scanning speed) Vm of the print head and the dot pitch Ptm in the main scanning direction.

[Equation 4]
δTm = Ptm / Vm
In order to satisfy the above [Equation 4], a dot 252 is ejected onto the dot 250, and similarly a dot 256 is ejected onto the dot 254.

  Similarly, the droplet ejection interval δTs in the sub-scanning direction is obtained by the following equation [Equation 5] from the recording paper transport speed Vs and the interval Ls in the sub-scanning direction of the nozzle row.

[Equation 5]
δTs = Ls / Vs
In order to satisfy the above [Equation 5], a dot 254 is ejected onto the dot 250, and similarly a dot 256 is ejected onto the dot 252.

  The present invention is also applicable to the case where mixed patterns having different dot pitches and dot diameters are formed in one image. In the mixed pattern, the droplet ejection interval δTm in the main scanning direction and the droplet ejection interval δTs in the sub-scanning direction are obtained for all combinations of the inter-dot pitch and the dot diameter, respectively, and the maximum values of the obtained droplet ejection intervals δTm and δTs are obtained. If δTmax-m and δTmax-s are the representative droplet ejection interval values, the control operation can be simplified.

  That is, the droplet ejection interval of the image is set according to the pattern having the longest droplet ejection interval in the image. Based on the ink droplet ejection timing of the overlapping portion with the most severe bleeding condition, the other regions are also unified at the droplet ejection timing.

  Further, in consideration of safety, the droplet ejection interval of the image may be larger than the maximum values δTmax-m and δTmax-s.

  FIG. 17 is a flowchart showing the flow of the droplet ejection timing control described above.

  When image data is input and printing control is started (step S10), the inter-dot pitch Pt between the first dot (for example, dot 102 in FIG. 11) and the second dot (for example, dot 112 in FIG. 11) The diameter D1b of the ink droplet 100 forming the first dot 102 is calculated from the diameter D2a of the second dot and using the above-described [Equation 1] (step S12 in FIG. 17).

  Next, the first dot is formed according to the ink type and the paper type (refer to the data table, graph 300, and graph 320 stored in the dot diameter calculation / storage unit 214 shown in FIG. 13). The penetration time δT, which is the difference between the landing time of the first dot and the second dot, is determined from the diameter D1a at the time of landing of the ink droplet (the ink droplet landed first) and D1b obtained in step S12. (Step S14).

  Subsequent to step S14, timing control in the sub-scanning direction is executed. When the permeation time δT is obtained, the sub-scanning direction speed (recording paper conveyance speed) Vs is obtained by the above-described [Equation 3] in the timing calculation unit 216 shown in FIG. 13 (step S16).

  Subsequently, timing control in the main scanning direction is executed. From [Equation 2] described above, the distance L between the print head 50A and the print head 50B shown in FIG. 16 is obtained and adjusted to this (step S18).

As described above, timing control in the sub-scanning direction and main-scanning direction is performed, and when one image is formed, the print control ends (step S20).
Note that the interval L between the print head 50A and the print head 50B may be set slightly larger with a margin, and the recording paper conveyance speed may be set and changed according to the ink type and the paper type.

  The scope of application of the present invention is such that the dot formed by the ink droplet landed later (dot 112 in FIG. 11) overlaps the center of the dot formed by the ink droplet landed first (dot 102 in FIG. 11). This is a small range, which satisfies the following equation [Formula 6].

[Equation 6]
D2a / 2 <Pt
It is possible to configure a program (software) that realizes the droplet ejection control described above and install the program in the inkjet recording apparatus 10. The program can also be recorded on a recording medium (magnetic recording medium, optical recording medium, etc.), distributed, or installed on a device using the recording medium.

  In the inkjet recording apparatus 10 configured as described above, when overlapping dots are formed, the ink droplets ejected earlier and later are determined from the inter-dot pitch Pt and the diameter D2a of the droplets ejected later. The diameter D1b of the previously ejected ink droplet is determined so that the ejected ink droplet does not mix on the surface of the recording paper 16.

  Further, a permeation time δT until the diameter of the previously ejected ink droplet reaches the landing diameter D1a to D1b is obtained, and this permeation time δT is determined as the ink droplet ejected earlier and the ink droplet ejected later. The droplet ejection control with the droplet ejection interval is performed.

  The next droplet can be ejected without waiting for the complete permeation time T for the permeation of the previously ejected ink droplets to the recording paper 16, and the printing time can be shortened. In addition, on the surface of the recording paper 16, the ink droplet previously ejected and the ink droplet ejected next are not mixed, and the ink droplet previously ejected also in the image receiving layer of the recording paper 16. The ink droplets ejected next time are not mixed with each other, so that a desired dot shape can be obtained without breaking the dot diameter.

  Since the droplet ejection interval depends on environmental conditions such as ink type, paper type, temperature, and humidity, it is calculated according to these conditions. Further, the droplet ejection interval can be obtained for each of the main scanning direction and the sub-scanning direction, and can be controlled for each of the main scanning direction and the sub-scanning direction. Therefore, a line head or a serial head can be applied to the print head.

  In mixed patterns with different dot diameters and inter-dot pitches, the droplet ejection interval is obtained for each pattern, and the maximum droplet ejection interval may be used as the droplet ejection interval of the image. An added value may be used.

  In the above embodiment, an inkjet recording apparatus has been described as an example of an image recording apparatus, but the scope of application of the present invention is not limited to this. The present invention can also be applied to liquid discharge apparatuses such as dispensers and coating apparatuses that discharge liquids such as water, chemicals, and processing liquids onto a medium to be discharged.

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 Enlarged view of the main part of Fig. 3 (a) Plane perspective view showing another structural example of the print head Sectional view along line 4-4 in Fig. 3 (b) Block diagram of the ink supply unit of the ink jet recording apparatus shown in FIG. System configuration diagram of the ink jet recording apparatus shown in FIG. The figure explaining the droplet ejection control of the inkjet recording device which concerns on embodiment of this invention Sectional drawing which follows the 8-8 line in FIG. The figure explaining the principal part of droplet ejection control shown in FIG. Cross section of FIG. The figure explaining the result of droplet ejection control shown in FIG. Sectional view of FIG. 1 is a block diagram of a droplet ejection control unit of an ink jet recording apparatus according to an embodiment of the present invention. Graph showing the relationship between elapsed time after landing and ink drop diameter Modification of the graph shown in FIG. The figure explaining the droplet ejection interval of a main scanning direction and a subscanning direction 6 is a flowchart showing a flow of droplet ejection control of the ink jet recording apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 16 ... Recording paper, 50, 50A, 50B ... Print head, 51, 51A, 51B ... Nozzle, 72 ... System controller, 80 ... Print control part, 100, 110 ... Ink droplet, 102, 112, 250, 252, 254, 256 ... dot, 200 ... droplet ejection control unit, 212 ... inequality calculation unit, 214 ... dot diameter calculation / storage unit, 21
6 ... timing calculation unit, 230 ... ink type information, 232 ... paper type information, D1a, D1b, D2a, D2b ... dot diameter, δT ... penetration time

Claims (12)

A recording head for ejecting droplets on a recording medium, a droplet ejection control means for controlling the ejection timing of the recording head, and a transport means for moving the recording medium and the recording head relative to the recording medium An image forming apparatus comprising:
The distance between the first dot formed on the recording medium and the second dot formed so as to overlap the first dot after the first droplet forming the first dot is deposited. Pt, the diameter D2a of the surface of the recording medium when the second droplet forming the second dot is landed on the recording medium, and the target when the second droplet has landed on the recording medium When the diameter D1b of the first droplet on the surface of the recording medium is set, the droplet ejection control means is
D1b <2 × Pt -D2a
The droplet ejection timing is defined by the droplet diameter change time until the diameter D1b of the first droplet satisfying the condition is reached as the droplet ejection interval from the droplet ejection of the first droplet to the droplet ejection of the second droplet. An image forming apparatus that controls the image forming apparatus. The distance Pt between the first dot and the second dot, and the diameter D2a of the surface of the recording medium when the second droplet lands are as follows:
D1b <2 × Pt -D2a
Droplet ejection condition calculating means for obtaining a diameter D1b of the first droplet satisfying
Droplet diameter change time calculating means for obtaining a droplet diameter change time from when the first droplet has landed on the recording medium until the diameter of the first droplet reaches D1b;
The image forming apparatus according to claim 1, further comprising:   When a mixed pattern having a plurality of combinations of the dot interval, the first dot diameter, and the second dot diameter is formed in one image, a plurality of droplet diameter change times are calculated, and the droplet ejection control is performed. 3. The image forming apparatus according to claim 2, wherein the means controls the recording timing of the image using the calculated representative values of the plurality of droplet diameter change times.   4. The representative value of the droplet diameter change time includes at least a value equal to or larger than a maximum value of the plurality of droplet diameter change times calculated by the droplet diameter change time calculating unit. The image forming apparatus described.   5. The image forming apparatus according to claim 1, wherein the droplet ejection control unit controls droplet ejection timing by one droplet ejection interval within one image. 6. Comprising information providing means for providing at least liquid type information or information including any one of the recording medium type information,
The said droplet diameter change time calculation means calculates the said droplet diameter change time based on the information provided by the said information provision means, The any one of Claims 2 thru | or 5 characterized by the above-mentioned. Image forming apparatus. The droplet change time calculation unit is configured to detect a dot pitch in a direction substantially perpendicular to a relative conveyance direction of the conveyance unit and a dot pitch in a relative conveyance direction of the conveyance unit in a direction substantially orthogonal to the relative conveyance direction of the conveyance unit. Obtaining a first droplet diameter change time and a second droplet diameter change time in the relative transport direction of the transport means;
The droplet ejection control means is configured to set the first droplet diameter change time and the second droplet diameter change time to a droplet ejection interval in a direction substantially orthogonal to a relative conveyance direction of the conveyance means and a relative relationship between the conveyance means, respectively. The image forming apparatus according to claim 2, wherein the droplet ejection timing is controlled as a droplet ejection interval in the sub-scanning direction that is the transport direction.   8. The image forming apparatus according to claim 1, wherein the recording head is a line head in which a plurality of nozzles are arranged over a length corresponding to the entire width of the recording medium. . The recording head includes a first nozzle row having nozzles for ejecting droplets that form odd-numbered dots among dots formed along a direction substantially orthogonal to the relative transport direction of the transport unit; A second nozzle row having nozzles for ejecting droplets forming the second dots,
9. The image according to claim 8, further comprising an interval varying unit that varies an interval between the first nozzle row and the second nozzle row in accordance with droplet ejection control in the relative carrying direction of the carrying unit. Forming equipment.   The recording head includes a moving unit in which a plurality of the nozzles are arranged over a length shorter than the entire width of the recording medium, and the recording head and the recording medium are relatively moved along the arrangement direction of the nozzles. The image forming apparatus according to claim 1, wherein the image forming apparatus is a serial head. The recording head includes a first nozzle row having nozzles for ejecting droplets that form odd-numbered dots among dots formed along a direction substantially orthogonal to the relative transport direction of the transport unit; A second nozzle row having nozzles for ejecting droplets forming the second dots,
An interval varying means is provided for varying the interval between the first nozzle row and the second nozzle row in accordance with droplet ejection control in a direction substantially orthogonal to the relative carrying direction of the carrying means. Item 15. The image forming apparatus according to Item 10. A droplet ejection control method for an image forming apparatus, comprising: a recording head that ejects droplets on a recording medium; and a droplet ejection control unit that controls droplet ejection timing of the recording head,
A first dot forming step of forming a first dot with a first droplet on the recording medium;
A second dot depositing step of depositing a second droplet that forms a second dot that overlaps the first dot after depositing the first droplet;
When the second droplet is ejected, a droplet ejection for determining the diameter of the first droplet so that the first droplet and the second droplet do not overlap on the surface of the recording medium. A condition calculation step;
Droplet diameter change for obtaining a time from a value when the diameter of the first droplet lands on the recording medium to a value that does not overlap the second droplet on the surface of the recording medium A time calculation step;
A droplet ejection control method comprising:

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