JP4122520B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including a droplet discharge head that discharges droplets onto a recording medium.

  An inkjet image forming apparatus includes a long print head (line head) in which a plurality of nozzles are arranged corresponding to the width direction of the recording medium, and conveys the recording medium relative to the print head. On the other hand, there is one that ejects droplets from a nozzle onto a recording medium to form an image on the recording medium at high speed.

  In such an image forming apparatus, when electrostatic recording is used to attract and transport a recording medium onto a transport belt, the flying droplets discharged from each nozzle 51 are charged as shown in FIG. Therefore, the flying droplets in the vicinity repel each other by the electrostatic repulsive force F, and deflect and land on the recording medium while flying away from each other.

  In particular, unlike a serial head, a line head performs recording with the head fixed in the width direction of the recording medium without scanning the head in the width direction of the recording medium. When the landing position of the flying droplet is shifted due to the force, streaks and unevenness are easily visually recognized in the paper conveyance direction of the recording medium. As a result, the print quality may be degraded.

  Therefore, various techniques have been proposed to reduce the visibility of such uneven stripes (see, for example, Patent Document 1 and Patent Document 2).

  In Patent Document 1, the distance between flying droplets ejected substantially simultaneously is increased by a droplet ejection control method that performs dispersed ejection that drives discretely selected nozzle groups substantially simultaneously, and electrostatic discharge between flying droplets is performed. The impact of the repulsive force is reduced and the landing position is prevented from shifting.

In Patent Document 2, when there are nozzles (non-discharge nozzles) that cannot discharge ink due to disconnection, ink clogging, or the like, all the nozzles corresponding to the solid portion are omitted without performing the distributed discharge as in Patent Document 1. By the droplet ejection control method in which the nozzles in the vicinity of the undischarge nozzles that are driven or specified at the same time are ejected substantially simultaneously, the visibility of the streaks in the paper conveyance direction caused by the undischarge nozzles is reduced.
JP 2001-260342 A JP 2004-42472 A

  By the way, various variations such as manufacturing variations of nozzles (position variations, discharge port processing variations, etc.), foreign matter (dirt) adhering to the vicinity of the nozzle discharge ports, and ink physical properties (viscosity, etc.) are non-uniform. Due to various reasons, variations may occur in the flying direction of the flying droplets ejected from the nozzles, and the landing position on the recording medium may be displaced. When such a landing position deviation unique to the nozzle is present in the print head, when printing is performed by the droplet ejection control method disclosed in Patent Document 1 and Patent Document 2, a stripe unevenness as described below is visually recognized. As a result, the print quality may be degraded.

  FIG. 8 is an explanatory diagram showing a printing result when solid printing is performed by the droplet ejection control method disclosed in Patent Document 1. In FIG. The nozzle 51-6 is a landing position deviation nozzle that deflects and lands on the nozzle 51-7 side. Hereinafter, the droplet ejection order of the nozzles 51-1 to 51-12 corresponding to the solid portion 130 will be described with reference to FIG.

  When the nozzles 51-1, 51-5, and 51-9 perform droplet ejection at the initial drive timing, dots 100-1, 100-5, and 100-9 are formed. When the nozzles 51-2, 51-6, 51-10 perform droplet ejection at the next driving timing, dots 100-2, 100-6, 100-10 are formed. At this time, the formation positions of the dots 100-2, 100-6, and 100-10 in the paper transport direction (sub-scanning direction) are upstream in the sub-scanning direction compared to the dots 100-1, 100-5, and 100-9. (Slightly lower in FIG. 8). When the nozzles 51-3, 51-7, 51-11 perform droplet ejection at the next drive timing, dots 100-3, 100-7, 100-11 are formed, and the nozzle 51-4 at the next drive timing. , 51-8, 51-12 are ejected, dots 100-4, 100-8, 100-12 are formed. Similarly, the nozzles 51-1,..., 51-12 sequentially perform droplet ejection.

  When droplets are ejected in such a droplet ejection order, the distance between droplets ejected almost simultaneously increases, so the influence of electrostatic repulsion between flying droplets is reduced and the effect of electrostatic repulsion When the landing position shift nozzle 51-6 unique to the nozzle exists, as shown in FIG. 8, the dot row 120-6 formed by the landing position shift nozzle 51-6 and the landing position are prevented. Straight stripes in the sub-scanning direction can be visually recognized between the dot row 120-5 formed by the adjacent nozzle 51-5 on the opposite side to the deviation direction.

  FIG. 9 is an explanatory diagram showing a printing result when solid printing is performed by the droplet ejection control method disclosed in Patent Document 2. In FIG. The nozzle 51-6 is a landing position deviation nozzle that deflects and lands on the nozzle 51-7 side.

  When the nozzles 51-1,..., 51-12 corresponding to the solid portion 130 are ejected at substantially the same drive timing, the flying droplets of the nozzles 51-1,. Is affected by electrostatic repulsion force F (see FIG. 10). However, as shown in FIG. 11, when at least three adjacent nozzles eject droplets substantially simultaneously, the flying droplet of the middle nozzle receives the electrostatic repulsive force F from the flying droplets of the nozzles on both sides, but its influence. Are offset, so that they land at the original landing position directly below the nozzle 51.

  Accordingly, as shown in FIG. 9, dot rows 120-2,..., 120- formed by nozzles 51-2,. 11 (except for the dot row 120-6) is formed at the original landing position in the direction (main scanning direction) substantially orthogonal to the paper conveyance direction of the recording medium.

  By the way, the flying droplet of the landing position misalignment nozzle 51-6 receives electrostatic repulsion force from the flying droplets of the adjacent nozzles 51-5 and 51-7 on both sides, but the flying of the nozzle 51-7 in the landing position misalignment direction. Since the distance to the droplet is shorter, the electrostatic repulsive force from the flying droplet of the nozzle 51-7 is larger than that of the flying droplet of the nozzle 51-5. Therefore, since the dot row 120-6 formed by the landing position misalignment nozzle 51-6 is shifted back to the original landing position in the main scanning direction, the dot row 120-5 is compared with the case shown in FIG. And the visibility of stripes occurring between the dot rows 120-6 are reduced.

  On the other hand, the nozzles 51-1 and 51-12 corresponding to the ends of the solid part 130 have only adjacent nozzles 51-2 and 51-11 on one side, respectively, so that the dot row 120 formed by the nozzle 51-1. -1 shifts to the opposite side of the dot row 120-2 formed by the adjacent nozzle 51-2, and the dot row 120-12 formed by the nozzle 51-12 is formed by the adjacent nozzle 51-11. Shift to the opposite side to the dot row 120-11 side. As a result, stripes can be visually recognized between the dot row 120-1 and the dot row 120-2 and between the dot row 120-11 and the dot row 120-12. In some cases, both edges of the image are observed in a blurred state.

  Further, in the droplet ejection control method disclosed in Patent Document 2, the power for driving all the nozzles corresponding to the solid portion 130 at substantially the same drive timing (simultaneous drive power) tends to increase, and the simultaneous drive power is insufficient. There is a risk of doing. As a result, all the nozzles corresponding to the solid portion 130 cannot be driven at substantially the same drive timing, and there may be a case where the non-uniformity in the sub-scanning direction due to the nozzle having a unique landing position shift is visually recognized.

  In addition, Patent Document 2 discloses a droplet ejection control method for ejecting nozzles in the vicinity of both of the specified ejection failure nozzles substantially simultaneously. However, unlike the ejection failure nozzle, the nozzle landing position deviation nozzle specific in real time is disclosed. Is difficult to apply because it is difficult to identify.

  The present invention has been made in view of such circumstances, and provides an image forming apparatus that reduces the visibility of uneven stripes generated in the paper conveyance direction when performing solid printing.

In order to achieve the object, the invention according to claim 1 is a long droplet discharge head in which a plurality of nozzles are arranged along a main scanning direction orthogonal to a sub-scanning direction that is a paper transport direction; A conveying unit that adsorbs and conveys a recording medium by electrostatic adsorption, and a printing liquid that divides a print area into a plurality of blocks according to power that can be driven simultaneously , and that is ejected from end nozzles in the divided blocks A dividing unit that performs the division so that the non-uniform stripes generated by the influence of electrostatic repulsion force from flying droplets discharged from other nozzles in the block are inconspicuous; and the dividing unit. Corresponding to each block at a driving timing such that the flying droplets discharged from the nozzles in the block are affected by the electrostatic repulsion force from the flying droplets discharged from the other nozzles in the block. Control means for driving all nozzles for each block, and a boundary line that divides the main scanning direction of the block is a boundary line that divides the main scanning direction of a block adjacent to the sub-scanning direction; An image forming apparatus is provided that is not continuous in the sub-scanning direction.

  According to the present invention, since the boundary line dividing the main scanning direction of each block does not continue in the sub-scanning direction in blocks adjacent to the sub-scanning direction, when the nozzles corresponding to each block are driven substantially simultaneously, In the boundary region that divides the main scanning direction, the unevenness in the sub-scanning direction is not continuous between blocks adjacent in the sub-scanning direction, and the visibility of the unevenness in the entire printing region is reduced.

  In addition, by dividing the printing area into a plurality of blocks and driving the nozzles corresponding to each block substantially simultaneously, even if there are nozzle-specific landing position deviation nozzles that are difficult to identify, the landing position deviation nozzles The flying droplet is deflected and landed on the recording medium so as to return to the original landing position in the main scanning direction due to the influence of electrostatic repulsive force. Visibility is reduced.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the control unit includes a plurality of blocks divided in the main scanning direction divided by the dividing unit. All the nozzles corresponding to each block are driven for each block at a driving timing such that the flying droplets discharged from the other nozzles are not affected by the electrostatic repulsion force from the flying droplets discharged from the nozzles in other blocks. It is characterized by driving .

  According to the aspect of the second aspect, the simultaneous drive power of the nozzles can be suppressed by changing the drive timing for each block existing in the same main scanning direction.

  According to the present invention, since the boundary line dividing the main scanning direction of each block does not continue in the sub-scanning direction in blocks adjacent to the sub-scanning direction, when the nozzles corresponding to each block are driven substantially simultaneously, In the boundary region that divides the main scanning direction, the unevenness in the sub-scanning direction is not continuous between blocks adjacent in the sub-scanning direction, and the visibility of the unevenness in the entire printing region is reduced.

  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 showing an outline of an embodiment of an ink jet recording apparatus as an image forming apparatus according to the present invention. As shown in FIG. 1, the ink jet 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, and 12Y. An ink storage / loading unit 14 for storing ink to be supplied to the paper, a paper feeding unit 18 for supplying the recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle surface of the printing unit 12 An adsorption belt conveyance unit 22 that is arranged opposite to the (ink ejection surface) and conveys the recording paper 16 while maintaining the flatness of the recording paper 16, a print detection unit 24 that reads a printing result by the printing unit 12, and a print And a paper discharge unit 26 for discharging the 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.

  In the case of an apparatus configuration using roll paper, a 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 arranged on the print surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  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.

  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 electrostatic suction belt 33 is wound between rollers 31 and 32, and at least a portion facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24. Are configured to form a flat surface (flat surface).

  The electrostatic attraction belt 33 has a width that is greater than the width of the recording paper 16, and an electrode (not shown) is provided therein, and the electrode is configured to come into contact with the roller 31. Further, a DC high voltage generator 46 is connected to the roller 31, and when a DC high voltage is applied to the roller 31 from the DC high voltage generator 46, the electrostatic attraction belt 43 wound around the roller 31. Is charged and the recording paper 16 is attracted and held on the electrostatic attracting belt 43 by the electrostatic attracting effect.

  When the power of a motor (not shown) is transmitted to at least one of the rollers 31 and 32 around which the electrostatic attraction belt 33 is wound, the electrostatic attraction belt 33 is driven clockwise in FIG. The recording paper 16 held on the electroadsorption belt 33 is conveyed from left to right in FIG.

  Since ink adheres to the electrostatic attraction belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the electrostatic attraction belt 33 (an appropriate position other than the printing 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 blowing method of spraying 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.

  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 transport direction (sub-scanning direction) ( (See FIG. 2).

  As shown in FIG. 2, the print heads 12K, 12C, 12M, and 12Y constituting the printing unit 12 discharge ink over a length that exceeds at least one side of the maximum-size recording paper 16 targeted by the inkjet recording apparatus 10. It is composed of a line type head in which a plurality of outlets (nozzles) are arranged.

  Printing corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side (left side in FIG. 1) along the conveyance direction (paper conveyance direction) of the recording paper 16 Heads 12K, 12C, 12M, and 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 width of the paper is provided for each ink color, the recording paper 16 and the printing unit 12 are relatively moved in the paper transport direction (sub-scanning direction). It is possible to record an image on the entire surface of the recording paper 16 by performing this operation only once (that is, by one sub-scan). Accordingly, high-speed printing is possible as compared with a shuttle type head in which the print head reciprocates in a direction (main scanning direction) orthogonal to the paper transport 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 has a pipeline that is 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, etc.) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. is doing.

  The print detection unit 24 includes an image sensor (line sensor or the like) for imaging the droplet ejection result of the print unit 12, and means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor. Function as.

  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 includes 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 patterns 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 the dot size, 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 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 uneven surface 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. 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 sorting means (not shown) for switching the paper discharge path in order 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. ing. 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, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

  Since the structures of the print heads 12K, 12C, 12M, and 12Y provided for each ink color are the same, the print head is represented by the reference numeral 50 below.

[Explanation of control system]
FIG. 3 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. 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 to the communication interface 70. 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 composed of semiconductor elements, 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 control unit 80, and the ejection amount and ejection timing of droplets (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. 3, the image buffer memory 82 is shown in a mode accompanying 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 one processor.

  The head driver 84 drives the heat generating elements (not shown in FIG. 3, described as reference numeral 58 in FIG. 5) of the print head 50 of 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.

  As described with reference to FIG. 1, the print detection unit 24 is a block including a line sensor (not shown), reads an image printed on the recording paper 16, performs necessary signal processing, etc. Presence / absence, variation in droplet ejection size, etc.) and the detection result is provided to the print controller 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.

  The print area dividing means and the drive timing control means, which are the features of the present application, are implemented by the print controller 80.

[Print head structure]
Next, the structure of the print head 50 will be described.

  FIG. 4 is a plan view of the print head 50 as viewed from the nozzle surface. As shown in FIG. 4, a number of nozzles 51 that eject droplets (ink droplets) are formed in the print head 50 along the longitudinal direction. Note that such a nozzle row is not limited to one row, and it is also possible to improve the recording density as a plurality of nozzle rows.

  FIG. 5 is a cross-sectional view taken along line 5-5 in FIG. As shown in FIG. 5, the print head 50 is provided with a common liquid chamber 55 that communicates with the nozzles 51 via the ink supply path 53 and the nozzle flow path 60. The common liquid chamber 55 is connected to an ink supply tank (not shown) and stores ink to be supplied to each nozzle 51.

  The print head 50 is provided with heating elements 58 corresponding to the nozzles 51 on a one-to-one basis. The heating element 58 is configured such that the nozzle 51 is arranged directly above (upward in FIG. 5), and the direction substantially perpendicular to the heating element 58 coincides with the droplet flying direction of the nozzle 51. The heating element 58 is electrically connected to a power supply wiring (not shown) disposed in the print head 50, and the heating element 58 generates heat when a drive signal corresponding to image data is supplied to the heating element 58. It is configured as follows.

  In implementing the present invention, the arrangement of the heating elements 58 is not limited to the illustrated example. For example, as in another example of the structure of the print head 50 shown in FIG. 6, a configuration in which the direction substantially parallel to the heating element 58 is the droplet flying direction of the nozzle 51 may be used.

  Next, the operation of the print head 50 configured as described above will be described with reference to FIG.

  The ink stored in the common liquid chamber 55 passes through the ink supply path 53 and is filled into the nozzle flow path 60. When a drive signal corresponding to the image data is sent from the head driver 84 (see FIG. 3) to the heat generating element 58, the drive signal is supplied to the heat generating element 58 through a power supply wiring (not shown). Generates heat. When bubbles are generated in the ink by the heat energy from the heating element 58, a part of the ink is discharged from the nozzle 51 to the outside of the print head 50 by the pressure at the time of the bubble generation, and is discharged outside the print head 50. Dots are formed on the top. By repeating such a process, a predetermined image is formed on the recording paper 16.

  In this embodiment, a thermal jet method is employed in which bubbles are generated in the nozzle by the heating element 58 and the liquid droplet (ink droplet) is ejected by the pressure. However, in implementing the present invention, the liquid droplet (ink) is used. The method of ejecting droplets is not limited, and a piezoelectric method of ejecting droplets (ink droplets) from nozzles by applying pressure to the ink in the pressure chamber by deformation of an actuator represented by a piezoelectric element (piezoelectric element), etc. Various methods can be applied.

[Method of droplet ejection control]
FIG. 7 is an explanatory view showing a printing result by the droplet ejection control method according to the present invention. The nozzle 51-11 is a landing position deviation nozzle that deflects and lands on the nozzle 51-12 side. For convenience of explanation, a case where 24 nozzles 51-1,..., 51-24 are driven to perform solid printing will be described, but the number of nozzles is not limited to the illustrated example.

  In the present embodiment, the deformed T-shaped solid portion 130 is divided into a plurality of blocks 110A, 110B, 110C, 110D, and 110E in the main scanning direction and the sub-scanning direction, and a plurality of blocks 110A,. The nozzles are driven almost simultaneously. At this time, the boundary line 150 dividing the main scanning direction of each block 110A,..., 110E is not continuous in the sub-scanning direction in blocks adjacent to the sub-scanning direction. For example, the left and right boundary lines in FIG. 7 of the block 110B are not continuous in the sub scanning direction with the left and right boundary lines in FIG. 7 of the blocks 110D and 110E adjacent in the sub scanning direction. The shape of the solid portion 130 is not limited to the illustrated example. The solid portion refers to a region printed with a substantially constant density or a gradation region accompanied by a density change, and so on.

  The size of the divided blocks is determined from the power that can drive the nozzles simultaneously in the main scanning direction. The size in the sub-scanning direction is determined from the visibility of unevenness, and is desirably suppressed to about 5 mm or less.

  In FIG. 7, first, at the first drive timing, the nozzles 51-1,..., 51-8 corresponding to the block 110A are driven substantially simultaneously to form dots 100-1,.

  At this time, since the nozzles 51-1 and 51-8 are positioned at the end of the nozzle group that ejects droplets substantially simultaneously, they are deflected to the opposite side of the nozzles 51-2 and 51-7 due to the influence of electrostatic repulsion. Dots 100-1 and 100-8 are formed at the positions, respectively.

  On the other hand, since the nozzles 51-2,..., 51-7 are located at positions other than the end of the nozzle group that ejects droplets at substantially the same time, the influence of electrostatic repulsion on the flying droplets is offset and the original in the main scanning direction Dots 100-2,..., 100-7 are formed at the landing positions.

  Subsequently, the nozzles 51-9,..., 51-16 corresponding to the block 110B are driven substantially simultaneously at the second drive timing slightly delayed from the first drive timing. The drive timing between the blocks is a time difference that does not affect the electrostatic repulsion between the flying droplets that are ejected adjacently between the blocks.

  Since the nozzles 51-9 and 51-16 are located at the end of the nozzle group that ejects droplets substantially at the same time, the nozzles 51-9 and 51-16 are deflected to the opposite side to the nozzles 51-10 and 51-15 due to the influence of electrostatic repulsion. Dots 100-9 and 100-16 are formed respectively.

  On the other hand, since the nozzles 51-10,..., 51-15 (excluding the nozzle 51-11) are located outside the end of the nozzle group that ejects droplets substantially simultaneously, the influence of electrostatic repulsive force on the flying droplets is offset. Thus, dots 100-10,..., 100-15 (excluding the dot 100-11) are formed at the original landing positions in the main scanning direction.

  By the way, the flying droplet of the landing position misalignment nozzle 51-11 is larger than the flying droplet of the adjacent nozzle 51-10 opposite to the landing position misalignment direction, and the flying droplet of the adjacent nozzle 51-12 in the landing position misalignment direction. And the distance will be closer. For this reason, the electrostatic repulsive force of the flying droplets of the nozzle 51-12 is larger than the electrostatic repulsive force of the flying droplets of the nozzle 51-10. Accordingly, the flying droplets of the landing position misalignment nozzle 51-11 are deflected and landed on the recording paper so as to return to the original landing position in the main scanning direction, thereby forming dots 100-11.

  Subsequently, at the third driving timing slightly delayed from the second driving timing, the nozzles 51-17,..., 51-24 corresponding to the block 110C are driven substantially simultaneously, and the dot 100 is driven as in the block 110A. -17, ..., 100-24 are formed.

  In the fourth to twelfth drive timings, the same droplet ejection operation as the first to third drive timings is repeated for each nozzle corresponding to each of the blocks 110A, 110B, and 110C. The repetition of these droplet ejection operations is realized by shifting the phase of the drive timing within the droplet ejection cycle in the sub-scanning direction in each of the blocks 110A, 110B, and 110C. In the example shown in FIG. 7, the number of droplets ejected by each nozzle 51-1,..., 51-24 is four, and four dots are formed in the sub-scanning direction. In carrying out the present invention, the number of droplet ejections in each block is not limited to four.

  At the thirteenth drive timing, the nozzle nozzles 51-5,..., 51-12 corresponding to the block 110D are driven substantially simultaneously, and at the fourteenth drive timing, the nozzles 51-13,. 51-20 are driven almost simultaneously. In block 110D, drive timing of the same phase as block 110A is applied, and in block 110E, drive timing of the same phase as block 110B is applied. At this time, the flying droplets of the nozzles corresponding to the ends of the blocks 110D and 110E shift to the outside of each block due to the influence of electrostatic repulsion, and the flying droplets of the landing position misalignment nozzle 51-11 As in the case of the block B, the deflection landing is made on the recording paper so as to return to the original landing position in the main scanning direction.

  In this way, by driving the nozzles corresponding to the respective blocks obtained by dividing the solid portion 130 in the main scanning direction and the sub-scanning direction substantially simultaneously, the electrostatic repulsive force is obtained except for the boundary portion dividing the main scanning direction of each block. It is possible to prevent landing position deviation due to the influence of.

  In particular, the flying droplets of the landing position misalignment nozzles 51-11 unique to the nozzle, which are difficult to specify, are driven at the same time by the nozzles in each block at the same time. Since the deflection landing is made on the recording paper so as to return to FIG. 8, the visibility of the uneven stripes in the sub-scanning direction is reduced as compared with the case shown in FIG.

  Also, by changing the drive timing for each block existing in the same main scanning direction, the number of nozzles driven at substantially the same drive timing can be reduced, so that the simultaneous drive power of the nozzles can be suppressed.

  Further, since the boundary line dividing the main scanning direction of each block is not continuous in the sub-scanning direction in the block adjacent to the sub-scanning direction, the main block of each block is driven when the nozzles corresponding to each block are driven substantially simultaneously. Since the non-uniformity in the sub-scanning direction that occurs in the boundary region (edge and its vicinity) that divides the scanning direction does not continue in the sub-scanning direction between the blocks, the solid portion 130 is compared with the case shown in FIG. The overall visibility of stripes is reduced.

  Further, when printing in the high image quality mode, it is desirable to slow down the conveyance speed of the recording paper 16. When the conveyance speed of the recording paper 16 is fast and the ejection cycle of each nozzle is short, for example, the ejection intervals of the nozzles 51-9, 51-10, 51-11, 51-12 when the blocks 110B and 110D are switched are further shortened. As a result, the ink refill is not in time, and the droplet discharge amount is disturbed. By slowing down the conveyance speed of the recording paper 16, the discharge cycle of each nozzle can be increased to such an extent that it does not affect the refill, so that it is possible to perform printing without causing a disturbance in the droplet discharge amount. Become.

  In carrying out the present invention, the number of nozzles corresponding to each block is not limited to eight as in the example shown in FIG. The number of nozzles corresponding to each block may be different for each block.

  Although the image forming apparatus of the present invention has been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the spirit of the present invention. Of course.

1 is an overall configuration diagram showing an outline of an embodiment of an ink jet recording apparatus as an image forming apparatus according to the present invention. FIG. 2 is a plan view of a main part around a printing unit of the inkjet recording apparatus shown in FIG. 1. It is a principal block diagram showing the system configuration of the ink jet recording apparatus. It is a top view at the time of seeing a print head from a nozzle surface. It is sectional drawing which follows the 6-6 line in FIG. It is sectional drawing which shows the other structural example of a print head. It is explanatory drawing which showed the printing result by the droplet ejection control method which concerns on this invention. It is explanatory drawing which showed the printing result by the conventional droplet ejection control method. It is explanatory drawing which showed the printing result by the conventional droplet ejection control method. It is explanatory drawing when a droplet is discharged from two adjacent nozzles simultaneously. It is explanatory drawing when a droplet is discharged simultaneously from three adjacent nozzles.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device 50 ... Print head 50A ... Nozzle surface 51 ... Nozzle 53 ... Ink supply path 55 ... Common liquid chamber 58 ... Heating element

Claims (3)

A long droplet discharge head in which a plurality of nozzles are arranged along a main scanning direction orthogonal to a sub-scanning direction that is a paper conveying direction;
Conveying means for adsorbing and conveying the recording medium by electrostatic adsorption;
A printing droplet is divided into a plurality of blocks according to power that can be driven simultaneously, and flying droplets ejected from the end nozzles in the divided blocks are ejected from other nozzles in the block. Dividing means for performing the division so as to make the uneven stripes generated by being affected by electrostatic repulsion force inconspicuous ,
Each block at a driving timing such that the flying droplets ejected from the nozzles in the block divided by the dividing means are affected by the electrostatic repulsion force from the flying droplets ejected from the other nozzles in the block. And a control means for driving all nozzles corresponding to each block,
The image forming apparatus according to claim 1, wherein a boundary line dividing the main scanning direction of the block is not continuous with a boundary line dividing the main scanning direction of a block adjacent to the sub scanning direction in the sub scanning direction.   The control means is a flying liquid in which flying droplets ejected from nozzles in one block among a plurality of blocks existing in the main scanning direction divided by the dividing means are ejected from nozzles in another block. The image forming apparatus according to claim 1, wherein all the nozzles corresponding to each block are driven for each block at a driving timing so as not to be affected by the electrostatic repulsion force from the droplet.   The image forming apparatus according to claim 1, wherein the print area is an area that is printed at a substantially constant density or a gradation area that accompanies a density change.

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