JP2008183771A - Inkjet printer - Google Patents

Abstract

An ink jet printer capable of suppressing a shift in ink droplet ejection timing due to a fluctuation in a moving speed of a conveying belt is provided.
When the moving belt moving speed fluctuates at a constant cycle, the conveying belt moving speed fluctuating cycle is used, and the adjacent nozzle rows formed on the same ink jet heads 4 and 5 and one printing are performed. The distance L1 between nozzles that eject ink droplets of different colors to the pixel is set to 1/10 or less of the moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation cycle, and adjacent to the same inkjet head. By setting the distance L2 between nozzles that eject ink droplets of different colors for one print pixel other than the matching nozzle row to be an integral multiple of the transport distance of the transport belt corresponding to the transport belt travel speed fluctuation cycle, Deviations in ink droplet ejection timing from each nozzle can be suppressed.
[Selection] Figure 3

Description

  In the present invention, for example, minute characters of liquid inks of a plurality of colors are ejected from a plurality of nozzles to form fine particles (ink dots) on a print medium, thereby drawing a predetermined character or image. The present invention relates to an ink jet printer.

Such an inkjet printer is generally inexpensive and can easily obtain a high-quality color printed matter. Accordingly, along with the widespread use of personal computers and digital cameras, it has become widespread not only in offices but also in general users.
In general, such an ink jet printer is configured such that a moving body called a carriage in which an ink cartridge and a print head are integrally provided reciprocates on a print medium in a direction intersecting the transport direction. By ejecting (jetting) liquid ink droplets from the nozzles to form minute ink dots on the printing medium, a desired printed matter is created by drawing predetermined characters or images on the printing medium. Yes. The carriage is equipped with four color (yellow, magenta, cyan) ink cartridges including black (black) and a print head for each color, so that not only monochrome printing but also full-color printing combining each color is easy. (Furthermore, 6 colors, 7 colors, or 8 colors in which light cyan, light magenta, etc. are added to these colors are also put into practical use).

  Further, in this type of ink jet printer in which printing is executed while reciprocating the ink jet head on the carriage in a direction intersecting with the conveyance direction of the print medium, the ink jet head is set to 10 to cleanly print the entire page. It is necessary to reciprocate several times to several tens of times. In contrast, in an inkjet printer of a type in which a long inkjet head (not necessarily integrated) having the same dimensions as the width of the print medium is disposed and the carriage is not used, the inkjet head is moved in the width direction of the print medium. There is no need, and so-called one-pass printing is possible, so high-speed printing is possible. The former inkjet printer is generally referred to as a “multi-pass (serial) inkjet printer”, and the latter inkjet printer is generally referred to as a “line head inkjet printer”. Also, in the line head type ink jet printer, a nozzle row in which a plurality of nozzles are arranged in the direction intersecting the print medium conveying direction by the width of the print medium is formed on the ink jet head, and a plurality of nozzles are formed for one print pixel. In order to eject ink droplets of different colors from each other, a plurality of nozzles must be arranged along the print medium conveyance direction.

Further, in a line head type ink jet printer, a printing medium is adsorbed to a conveyance belt and conveyed using a method such as electrostatic adsorption or air adsorption. Such a print medium conveying method is particularly effective for a line head type ink jet printer capable of high-speed printing. In the ink jet printer having such a transport mode, in the ink jet printer described in Patent Document 1 below, the nozzle row of the adjacent unit heads is a distance that is a natural number times the circumference of the drive roller that drives the transport belt. Thus, the influence of fluctuations in the moving speed of the conveying belt due to uneven rotation of the driving roller on the deviation of the ink droplet ejection timing is suppressed.
JP 2005-67127 A

However, in a line head type ink jet printer, forming only one row of nozzles in one ink jet head is not only wasteful in space but also hinders downsizing of the apparatus. Therefore, increasing the density of nozzles formed on the ink jet head contributes to the miniaturization of the apparatus. However, in the ink jet printer described in Patent Document 1, the nozzle rows of adjacent unit heads are naturally connected to the circumference of the drive roller. It is only described that the layout is arranged so that the distance is several times. For example, when a plurality of nozzle rows are formed in one inkjet head, the deviation of the ink droplet ejection timing due to the fluctuation in the transport belt moving speed is to be suppressed. Absent.
The present invention has been made paying attention to the above-described problems. Even when a plurality of nozzle rows are formed on one inkjet head, the ink droplet ejection timing shifts due to fluctuations in the transport belt moving speed. An object of the present invention is to provide an ink jet printer capable of suppressing the above.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor obtained the following knowledge and developed the present invention. That is, the movement speed fluctuation of the conveyor belt is caused by, for example, rotation unevenness due to the roundness or eccentricity of the roller around which the conveyor belt is wound, rotation speed fluctuation of the drive motor, rotation irregularity of the drive system, etc. The rotating body has a characteristic that speed fluctuation is repeated every rotation. Variations in the moving speed of the conveyor belt due to these causes are repeated at a constant cycle. If the distance between the nozzles that eject ink droplets of different colors to one print pixel is an integral multiple of this conveyor belt movement speed fluctuation cycle, deviations in ink droplet ejection timing due to the conveyor belt movement speed fluctuation can be suppressed. It becomes possible to do. However, when trying to lay out a plurality of nozzle rows closely in the print medium conveyance direction in one inkjet head, the distance between the nozzles of these nozzle rows can be an integral multiple of the movement speed variation of the conveyance belt. Can not. On the other hand, between adjacent nozzle rows of one inkjet head, if the distance between nozzles that eject ink droplets of different colors to one print pixel is 1/10 or less of the fluctuation in the moving speed of the conveyor belt, It is possible to suppress the deviation of the ink droplet ejection timing due to the fluctuation in the conveyance belt moving speed to a level that cannot be substantially recognized.

[Invention 1] In order to solve the above-described problem, an inkjet printer according to Invention 1 has a plurality of nozzle rows arranged in a direction in which a plurality of nozzles intersect with the conveyance direction of the print medium in one inkjet head. A plurality of nozzles are arranged along the print medium conveyance direction so that ink droplets of different colors are ejected from a plurality of nozzles to a pixel, and the print medium is placed on a conveyance belt and conveyed. An ink jet printer that performs printing by ejecting ink droplets from nozzles of an ink jet head, wherein the same ink jet is used when the period when the moving speed of the conveying belt fluctuates at a constant period is a conveying belt moving speed fluctuation period. The distance between the nozzles in the adjacent nozzle rows formed on the head and ejecting ink droplets of different colors with respect to the one print pixel, Ink droplets having a color different from that of the adjacent nozzle row formed on the same ink jet head and different from the one print pixel, which is 1/10 or less of the moving distance of the conveying belt corresponding to the feeding belt moving speed fluctuation cycle The distance between the nozzles that discharge the nozzle is an integral multiple of the moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation period.
Thus, according to the ink jet printer according to the first aspect of the present invention, it is possible to suppress the deviation of the ink droplet ejection timing from each nozzle.

[Invention 2] The inkjet printer according to Invention 2 is the inkjet printer according to Invention 1, in which different colors are used with respect to the one print pixel which is an integral multiple of the moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation period. The nozzles for ejecting ink droplets are formed in different inkjet heads.
According to the ink jet printer according to the second aspect of the invention, the degree of freedom of nozzle layout in the same ink jet head is increased.

[Invention 3] The ink-jet printer of Invention 3 is the ink-jet printer of Invention 1, wherein different colors are used for the one print pixel that is an integral multiple of the moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation period. A nozzle for ejecting ink droplets is formed in one inkjet head.
According to the ink jet printer according to the third aspect, the degree of freedom in layout between different ink jet heads is increased.

[Invention 4] The inkjet printer according to Invention 4 is the inkjet printer according to any one of Inventions 1 to 3, in which the movement distance of the conveyance belt corresponding to the conveyance belt movement speed fluctuation period is set to the circumference of the roller around which the conveyance belt is wound. It is characterized by being set equal to.
According to the ink jet printer according to the fourth aspect of the present invention, it is possible to suppress the deviation of the ink droplet ejection timing due to the fluctuation in the moving speed of the conveying belt that occurs due to the uneven rotation of the rollers.

[Invention 5] The inkjet printer according to Invention 5 is an ink jet printer according to Inventions 1 to 3, in which the conveyance belt travel distance corresponding to the conveyance belt movement speed fluctuation period is a drive motor for moving the conveyance belt. It is characterized in that it is set equal to the moving distance of the conveyor belt per rotation.
According to the ink jet printer according to the fifth aspect of the present invention, it is possible to suppress the deviation of the ink droplet ejection timing due to the change in the transport belt moving speed that occurs with the change in the rotational speed of the drive motor.

[Invention 6] The ink jet printer of Invention 6 is the ink jet printer of Inventions 1 to 3, wherein the moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation period is the speed of the drive system for moving the conveying belt. It is characterized in that it is set equal to the moving distance of the conveyor belt corresponding to the fluctuation period.
According to the ink jet printer according to the sixth aspect of the present invention, it is possible to suppress a deviation in the ink droplet ejection timing due to the fluctuation in the transport belt moving speed that occurs with the rotation unevenness of the drive system.

Next, a first embodiment of the inkjet printer of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of the ink jet printer of the present embodiment, FIG. 1a is a plan view thereof, and FIG. 1b is a front view thereof. In FIG. 1, a print medium 1 is a line head type ink jet printer that is transported from the right to the left in the diagram in the direction of the arrow in the diagram and printed in a print area in the middle of the transport. Incidentally, the ink jet head according to the present embodiment is arranged not only at one place but also at a plurality of places.

  Reference numeral 2 in the figure denotes a first inkjet head group provided on the upstream side in the conveyance direction of the print medium 1, and reference numeral 3 denotes a second inkjet head group provided on the downstream side, and the first inkjet head group 2. Is composed of an upstream first inkjet head 4 on the upstream side in the print medium conveyance direction and a downstream first inkjet head 5 on the downstream side, and the second inkjet head group 3 is an upstream second in the printing medium conveyance direction upstream. An inkjet head 6 and a downstream second inkjet head 7 on the downstream side are configured.

  The upstream side first inkjet head 4 and the downstream side first inkjet head 5 of the first inkjet head group 2 are disposed at a predetermined interval in the print medium transport direction, and the upstream side first inkjet heads 4 or each other. The downstream first inkjet heads 5 are also arranged at a predetermined interval in a direction intersecting the print medium conveyance direction. The upstream side second inkjet head 6 and the downstream side second inkjet head 7 of the second inkjet head group 3 are arranged at a predetermined interval in the print medium transport direction, and the upstream side second inkjet head 6. The downstream second inkjet heads 7 are also arranged at a predetermined interval in a direction intersecting the print medium conveyance direction.

  These inkjet heads 4 to 7 are provided with a plurality of nozzles for ejecting ink droplets at predetermined intervals in a direction intersecting with the conveyance direction of the print medium 1 (hereinafter also referred to as nozzle row direction). In addition, a plurality of nozzle rows are arranged in the print medium conveyance direction in each of the inkjet heads 4 to 7. For example, the upstream side and downstream side second inkjet heads 6 and 7 of the second inkjet head group 3 both intersect the print medium conveyance direction of the upstream side and downstream side first inkjet heads 4 and 5 of the first inkjet head group 2. The entire print surface of the print medium 1 can be printed by one pass with all these inkjet heads 4 to 7. The layout of the inkjet heads 4 to 7 and the nozzle layout in each of the inkjet heads 4 to 7 will be described in detail later.

  A drive roller 9 is disposed on the downstream side in the print medium conveyance direction, a driven roller 10 is disposed on the upstream side in the print medium conveyance direction, and a tension roller 11 is disposed in the middle and slightly below the sheet. The conveyor belt 8 is wound around the driving roller 9, the driven roller 10, and the tension roller 11. A conveyance belt drive motor (not shown) is connected to the drive roller 9. The driven roller 10 is grounded in order to charge the conveying belt 8 by a charging roller described later. Further, the tension roller 11 is urged downward by a spring 12, thereby applying tension (tension) to the transport belt 8. In the present embodiment, as will be described later, the print medium 1 is electrostatically attracted to the transport belt 8 and transported.

  For example, yellow (Y), magenta (M), cyan (C), and black (K) nozzles for each color are arranged in the inkjet heads 4 to 7. Ink is supplied to each of the inkjet heads 4 to 7 from an ink tank of each color (not shown) via an ink supply tube. Each of the inkjet heads 4 to 7 has a plurality of nozzles formed in a direction intersecting with the conveyance direction of the print medium 1 (that is, the nozzle row direction), and a necessary amount is simultaneously or almost simultaneously from these nozzles. By ejecting ink droplets, minute ink dots are formed and output on the print medium 1. By performing this for each color, it is possible to perform printing in a so-called one pass by passing the print medium 1 conveyed by the conveyor belt 8 once. That is, the arrangement area of these inkjet heads 4 to 7 corresponds to a printing area.

  As a method for discharging and outputting ink from each nozzle of the ink jet head, there are an electrostatic method, a piezo method, a film boiling ink jet method, and the like. In the electrostatic system, when a drive signal is given to the electrostatic gap, which is an actuator, the diaphragm in the cavity is displaced, causing a pressure change in the cavity, and ink drops are ejected from the nozzle by the pressure change. It is. In the piezo method, when a drive signal is given to a piezo element that is an actuator, the diaphragm in the cavity is displaced to cause a pressure change in the cavity, and ink droplets are ejected from the nozzle by the pressure change. . In the film boiling ink jet method, there is a minute heater in the cavity, the ink is instantaneously heated to 300 ° C. or more, the ink becomes a film boiling state, bubbles are generated, and ink droplets are ejected from the nozzle by the pressure change. That's it. The present invention can be applied to any ink output method.

  On the upstream side of the driven roller 10, two pairs of gate rollers 13 are provided for adjusting the feeding timing of the printing medium 1 supplied from the feeding unit and correcting the skew of the printing medium 1. The skew is a twist of the print medium 1 with respect to the transport direction. In addition, a feed roller 14 for supplying the print medium 1 from the paper feeding unit is provided further upstream of the gate roller 13. A pressure roller 15 that presses the print medium 1 against the conveyance belt 8 is disposed above the driven roller 10.

  Below the driven roller 10, as described above, a belt charging device for charging the conveyor belt 8 is disposed. This belt charging device is composed of a charging roller 16 that is in contact with the conveying belt 8 with the driven roller 10 interposed therebetween, and an AC power source 17 that applies charge to the charging roller 16. To charge them. The AC power supply 17 applies an AC voltage having a frequency of about 10 to 50 Hz, for example. In general, these belts are composed of a medium / high resistance body or an insulator. Therefore, when charged by a belt charging device, the charge applied to the surface is also composed of a high resistance body or an insulator. The print medium 1 is caused to generate dielectric polarization, and the print medium 1 can be adsorbed to the belt by electrostatic force generated between the charge generated by the dielectric polarization and the charge on the belt surface. Further, as the belt charging means, a so-called corotron for dropping a so-called charge may be used.

  A control device for controlling itself is provided in the ink jet printer. As shown in FIG. 2, for example, the control device controls the printing device, the paper supply / discharge device, and the like based on print information input from an external device 60 such as a personal computer or a digital camera. The printing process is performed. Then, a print information storage unit 31 that stores print information input from the external device 60, a CPU (Central Processing Unit) 32 that executes various processes such as a print process, and the feed roller 14 based on instructions from the CPU 32. A feed roller controller 33 for controlling the feed roller drive motor 34 for driving, a gate roller controller 35 for controlling the gate roller drive motor 36 for driving the gate roller 13 based on a command from the CPU 32, and the CPU 32 From the AC power supply control unit 38 that controls the AC power supply 17 based on a command from the CPU, the conveyance control unit 41 that controls the conveyance belt drive motor 40 for driving the driving roller 9 based on the command from the CPU 32, and the CPU 32 Inkjet head control for controlling the inkjet heads 4 to 7 based on the command 42, and a separator controller 44 for controlling the separation device 43 of the discharge unit based on a command from the CPU 32.

  Therefore, according to this ink jet printer, the surface of the conveying belt 8 is charged by the charging roller 16 of the charging device, the printing medium 1 is fed from the feed roller 14 in this state, and the posture control of the printing medium 1 is performed by the gate roller 13. After performing the above, when the printing medium 1 is supplied above the first conveying belt 8 and the printing medium 1 is pressed against the first conveying belt 8 by the pressure roller 15, the printing medium 1 is first conveyed by the action of the dielectric polarization described above. Adsorbed on the surface of the belt 8. In this state, when the driving roller 9 is rotationally driven by the conveying belt driving motor, the rotational driving force is transmitted to the driven roller 10 via the conveying belt 8.

  In this way, the conveyance belt 8 is moved downstream in the conveyance direction with the print medium 1 adsorbed, the print medium 1 is moved below the first inkjet head group 2, and the upstream and downstream of the first inkjet head group 2. Printing is performed by ejecting ink droplets from the nozzles formed on the side first inkjet heads 4 and 5. When printing by the first inkjet head group 2 is completed, the print medium 1 is moved below the second inkjet head group 3 on the downstream side in the transport direction, and the second inkjet head 6 on the upstream / downstream side of the second inkjet head group 3. , 7 to perform printing by ejecting ink droplets from the nozzles. When printing by the second ink jet head group 3 is completed, the print medium 1 is further moved downstream in the transport direction, and discharged to the paper discharge section while separating the print medium 1 from the surface of the transport belt 8 by a separation device (not shown). To do.

  Next, as a representative of the layout of the inkjet heads 4 to 7 and the nozzle or nozzle row layout in the inkjet heads 4 to 7 of the present embodiment, the upstream side first inkjet head 4 and the downstream side of the first inkjet head group 2 are shown. 2 shows the nozzle surface of the inkjet head 5, and FIG. 4 shows the details of the nozzle layout. In the figure, symbol K corresponds to black, C corresponds to cyan, M corresponds to magenta, and Y corresponds to yellow. In FIG. 3, the nozzle rows of the respective colors are drawn in a line, but actually, as shown in FIG. 4, a large number of nozzles are arranged at predetermined intervals.

  In this embodiment, for example, assuming that the right side in the drawing is the upstream side in the printing medium conveyance direction and the left side in the drawing is the downstream side in the printing medium conveyance direction, black K from the upstream side in the printing medium conveyance direction of the upstream first inkjet head 4 is used. , Cyan C, black K,..., A total of 8 nozzle rows are formed. On the other hand, in the first inkjet head 4 on the downstream side, a total of eight nozzle rows are formed in the order of magenta M, yellow Y, and magenta M from the upstream side in the print medium conveyance direction. Among these, when considering a set of nozzle rows of black K and cyan C or a set of nozzle rows of magenta M and yellow Y, a total of four nozzle rows are arranged from the upstream side in the print medium conveyance direction. It will be. Therefore, the first set, the second set,... Are called from the upstream side in the print medium conveyance direction.

  Next, when the nozzles formed in each nozzle row are viewed in terms of print pixels in the nozzle row direction, for example, in order from the top of the figure, the first set, the third set, the second set, and the fourth set. Nozzles are formed in order. That is, for example, in the example of FIG. 4, in the uppermost print pixel in the figure, black K and cyan C ink droplets are ejected from the first set of nozzle rows of the upstream first inkjet head 4, and then the downstream first inkjet is performed. Magenta M and yellow Y ink droplets are ejected from the first set of nozzle rows of the head 5. In this way, full color printing is possible by ejecting ink droplets of various colors onto one printing pixel. That is, in the present embodiment, a plurality of nozzles are arranged along the print medium conveyance direction so that different color ink droplets are ejected from a plurality of nozzles to one print pixel.

  In this embodiment, for example, the first set of black K and cyan C in the upstream first inkjet head 4 is adjacent to the adjacent nozzle row or the first set of magenta M and yellow Y in the downstream first inkjet head 5. The distance L1 between the matching nozzle rows was set to a predetermined value equal to or less than 1/10 of the circumferential length of the drive roller 9. The distance L2 between the first set of black K nozzle rows of the upstream first ink jet head 4 and the first set of magenta M nozzle rows of the downstream first ink jet head 5 is defined as the circumferential length of the drive roller 9. A predetermined value that is an integer multiple of.

  The fluctuation of the moving speed of the conveyor belt 8 due to the rotation unevenness of the driving roller 9 is restored every time the driving roller 9 makes one rotation. That is, the circumferential length of the driving roller 9 is the moving distance of the conveying belt 8 corresponding to the fluctuation cycle of the moving speed of the conveying belt 8. For example, FIG. 5 shows a case where the drive roller 9 is eccentric and the moving speed of the conveyor belt 8 varies. In the figure, the fluctuation of the moving speed is 60 μm in amplitude. FIG. 6 shows an arrangement example of nozzle rows of a conventional general inkjet head using the same reference numerals as those in FIG. 7 and the present embodiment. In the same figure, each of the inkjet heads 4 and 5 is provided with 8 nozzle rows, but the uppermost print pixel in the drawing is upstream of the upstream first inkjet head 4 in the print medium conveying direction. Black K from the first nozzle row, cyan C from the third nozzle row, magenta M from the fifth nozzle row, and yellow Y ink droplets from the seventh nozzle row are discharged, respectively. The second print pixel from the top includes black K from the first nozzle row on the upstream side in the print medium conveyance direction of the first inkjet head 5 on the downstream side, cyan C from the third nozzle row, and the fifth row. Magenta M is ejected from the nozzle row, and yellow Y ink droplets are ejected from the seventh nozzle row, and two rows on the upstream side in the print medium conveyance direction of the upstream first inkjet head 4 are arranged on the third print pixel from the top. From the nozzle row of the eye Ink droplets click K is ejected. In this example, the distance between the upstream first inkjet head 4 and the downstream first inkjet head 5 is not defined, but the distance is, for example, that of the conveyor belt 8 where the fluctuation amplitude of the moving speed of the conveyor belt 8 is maximized. If it is equal to the moving distance, the positions of the printing pixels adjacent in the nozzle row direction are shifted by 60 μm at the maximum. For example, at a resolution of 720 dpi, the ink dot pitch is about 35 μm, but if the movement speed of the conveyor belt 8 fluctuates as much as 60 μm, ink droplets cannot be ejected to an appropriate position. That is, the ink droplet ejection timing is shifted due to the movement speed fluctuation of the transport belt 8.

  In the present embodiment, when the cycle when the moving speed of the conveyor belt 8 fluctuates at a constant period is defined as the conveyor belt moving speed fluctuation period, the adjacent nozzle rows formed in the same inkjet heads 4 and 5 and one The distance L1 between the nozzles that eject ink droplets of different colors to one print pixel was set to 1/10 or less of the moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation period. As shown in FIG. 5, for example, if the distance L1 between adjacent nozzle rows of black K and cyan C in FIGS. 3 and 4 is about 1/10 of the conveying belt moving speed fluctuation period, the conveying belt moving speed fluctuation amplitude is 60 μm. Even so, the difference in the movement speed fluctuation of the conveyor belt generated at the black K and cyan C nozzle portions is about 17.6 μm, which is less than about half of the resolution, so that the deviation of the ink droplet ejection timing is suppressed. can do.

  Further, the distance L2 between the first set of black K nozzle rows of the upstream first inkjet head 4 and the first set of magenta M nozzle rows of the downstream first inkjet head 5, that is, the same inkjet heads 4, 5 The distance L2 between nozzles that eject ink droplets of different colors with respect to the one print pixel other than the adjacent nozzle rows formed in (1) is the transport belt travel distance corresponding to the transport belt travel speed fluctuation period. By making it an integral multiple, fluctuations in the moving speed of the conveyor belt 8 can be restored, and thus deviations in ink droplet ejection timing can be suppressed.

  As described above, according to the ink jet printer of this embodiment, one ink jet head 4, 5 has a plurality of nozzle rows in which a plurality of nozzles are arranged in a direction intersecting the transport direction of the print medium 1, and one print pixel. The plurality of nozzles are arranged along the print medium conveyance direction so that different color ink droplets are ejected from the plurality of nozzles, and the print medium 1 is placed on the conveyance belt 8 and conveyed. In the case of an ink jet printer that performs printing by ejecting ink droplets from the nozzles of the ink jet heads 4 and 5, the period when the moving speed of the conveying belt 8 fluctuates at a constant period is set as the conveying belt moving speed fluctuation period The distance L1 between the nozzles that are adjacent to each other in the same inkjet heads 4 and 5 and eject ink droplets of different colors to one print pixel Ink of different colors for one print pixel other than adjacent nozzle rows formed in the same inkjet head, which is 1/10 or less of the moving distance of the conveying belt 8 corresponding to the conveying belt moving speed fluctuation cycle By setting the distance L2 between the nozzles for ejecting droplets to be an integral multiple of the moving distance of the conveying belt 8 corresponding to the conveying belt moving speed fluctuation period, it is possible to suppress the deviation of the ink droplet discharging timing from each nozzle. .

Further, nozzles that eject ink droplets of different colors to one print pixel that is an integral multiple of the moving distance of the conveying belt 8 corresponding to the conveying belt moving speed fluctuation cycle are formed in different ink jet heads 4 and 5. As a result, the degree of freedom of nozzle layout in the same inkjet heads 4 and 5 is increased.
Further, since the moving distance of the conveying belt 8 corresponding to the conveying belt moving speed fluctuation period is set equal to the circumferential length of the driving roller 9 around which the conveying belt 8 is wound, the rotation of the driving roller 9 is accompanied. Deviations in the ink droplet ejection timing due to fluctuations in the transport belt moving speed that occur can be suppressed.

  The moving distance of the conveying belt 8 corresponding to the conveying belt moving speed fluctuation cycle is set equal to the moving distance of the conveying belt 8 per one rotation of the drive motor 40 for moving the conveying belt 8, for example. It may be set equal to the moving distance of the conveying belt 8 corresponding to the speed fluctuation period of the driving system for moving the conveying belt 8, and in this way, the conveying that occurs with fluctuations in the rotational speed of the driving motor. Deviations in ink droplet ejection timing due to fluctuations in the belt movement speed and deviations in ink droplet ejection timing due to fluctuations in the conveyance belt movement speed caused by uneven rotation of the drive system can be suppressed.

  Next, a second embodiment of the ink jet printer of the present invention will be described with reference to FIGS. The schematic configuration of the inkjet printer of this embodiment and the configuration of the control device are the same as those in FIGS. 1 and 2 of the first embodiment. In this embodiment, the layout of the inkjet heads 4 to 7 and the nozzle or nozzle row layout in the inkjet heads 4 to 7 are different from those of the first embodiment. In FIG. 8, the nozzle surfaces of the upstream first inkjet head 4 and the downstream second inkjet head 5 of the first inkjet head group 2 are shown as representatives of these inkjet heads 4 to 7, and the nozzle layout is shown in FIG. Details are shown. In FIG. 8, the nozzle rows of the respective colors are drawn in a linear shape, but actually, as shown in FIG. 9, a large number of nozzles are arranged at predetermined intervals.

  In this embodiment, for example, assuming that the right side of the drawing is the upstream side in the printing medium conveyance direction and the left side of the drawing is the downstream side in the printing medium conveyance direction, both the upstream first inkjet head 4 and the downstream first inkjet head 5 are A total of eight nozzle rows are formed in the order of black K, cyan C, black K, cyan C, magenta M, yellow Y, magenta M, and yellow Y from the upstream side in the print medium conveyance direction. Among these, when considering a set of nozzle rows of black K and cyan C or a set of nozzle rows of magenta M and yellow Y, a total of four nozzle rows are arranged from the upstream side in the print medium conveyance direction. It will be. Therefore, the first set, the second set,... Are called from the upstream side in the print medium conveyance direction.

  Next, when the nozzles formed in the respective nozzle rows are viewed in terms of print pixels in the nozzle row direction, for example, in order from the top of the figure, the first set and the third set of the upstream first inkjet head 4, Nozzles in order of the first set and the third set of the downstream first inkjet head 5, the second set and the fourth set of the upstream first inkjet head 4, and the second set and the fourth set of the downstream first inkjet head 5. Is formed. That is, for example, in the example of FIG. 4, black K and cyan C ink droplets are ejected from the first set of nozzle rows of the upstream first inkjet head 4 in the uppermost print pixel in the diagram, and then the upstream first Magenta M and yellow Y ink droplets are ejected from the third set of nozzle rows of the inkjet head 4. In this way, full color printing is possible by ejecting ink droplets of various colors onto one printing pixel. That is, in the present embodiment, a plurality of nozzles are arranged along the print medium conveyance direction so that different color ink droplets are ejected from a plurality of nozzles to one print pixel.

  In the present embodiment, for example, the first set of black K and cyan C adjacent to the first ink jet head 4 on the upstream side or the third set of magenta M and yellow Y adjacent to the first ink jet head 4 on the upstream side. The distance L1 between the nozzle rows to be matched is set to a predetermined value equal to or less than 1/10 of the moving distance of the conveying belt 8 per one rotation of the conveying belt drive motor 40. Further, the distance L2 between the first set of black K nozzle rows and the third set of magenta M nozzle rows of the upstream first ink-jet head 4 is defined as the transfer belt 8 per rotation of the transfer belt drive motor 40. A predetermined value that is an integral multiple of the moving distance.

  Since the moving distance of the conveying belt 8 per one rotation of the conveying belt drive motor 40 is shorter than the circumferential length of the driving roller 9 of the first embodiment, even the distance between nozzles in the same inkjet heads 4 and 5 is the same. It is possible to set an integral multiple of the moving distance of the conveying belt 8 per one rotation of the conveying belt drive motor 40. Further, when printing is performed using two or more inkjet heads 4 and 5 as in the present embodiment, it is not necessary to regulate the distance between the inkjet heads 4 and 5, so that the individual inkjet heads 4 and 5 The degree of layout freedom increases.

  Thus, according to the ink jet printer of the present embodiment, in addition to the effects of the first embodiment, one print pixel that is an integral multiple of the moving distance of the conveying belt 8 corresponding to the conveying belt moving speed fluctuation period. In contrast, since the nozzles for ejecting ink droplets of different colors are formed in one inkjet head 4, 5, the degree of freedom in layout between different inkjet heads is increased.

Further, the movement distance of the conveyance belt 8 corresponding to the conveyance belt movement speed fluctuation period is set equal to the movement distance of the conveyance belt 8 per one rotation of the conveyance belt drive motor 40 for moving the conveyance belt 8. Further, it is possible to suppress the deviation of the ink droplet ejection timing due to the fluctuation in the conveyance belt moving speed that occurs with the fluctuation in the rotation speed of the conveyance belt drive motor 40.
Note that the movement distance of the conveyance belt 8 corresponding to the conveyance belt movement speed fluctuation cycle may be set equal to the movement distance of the conveyance belt 8 corresponding to the speed fluctuation period of the drive system for moving the conveyance belt 8, for example. In this case, it is possible to suppress deviations in the ink droplet ejection timing due to fluctuations in the transport belt moving speed that occur with the rotation unevenness of the drive system.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows 1st Embodiment of the inkjet printer of this invention, (a) is a top view, (b) is a front view. It is a block block diagram of the inkjet printer of FIG. It is explanatory drawing of the layout of the inkjet head of FIG. 1, and a nozzle row. FIG. 4 is a detailed view of the layout of the nozzle row in FIG. 3. It is explanatory drawing of the fluctuation | variation of a conveyance belt moving speed. It is explanatory drawing of the layout of the conventional common inkjet head and nozzle row. FIG. 7 is a detailed view of the layout of the nozzle row in FIG. 6. It is explanatory drawing of the layout of the inkjet head and nozzle row which shows 2nd Embodiment of the inkjet printer of this invention. FIG. 9 is a detailed view of the layout of the nozzle row in FIG. 8.

Explanation of symbols

  1 is a print medium, 2 is a first inkjet head group, 3 is a second inkjet head group, 4 is an upstream first inkjet head, 5 is a downstream first inkjet head, 6 is an upstream second inkjet head, and 7 is Second downstream ink jet head, 8 is a conveying belt, 9 is a driving roller, 10 is a driven roller, 11 is a tension roller, 12 is a spring, 13 is a gate roller, 14 is a feed roller, 15 is a pressure roller, 16 is a charging roller , 17 is an AC power source

Claims (6)

  A single inkjet head has a plurality of nozzle rows in which a plurality of nozzles are arranged in a direction intersecting the conveyance direction of the print medium, and ink droplets of different colors are ejected from the plurality of nozzles to one print pixel. An ink jet printer that performs printing by disposing a plurality of the plurality of nozzles along a print medium conveyance direction and ejecting ink droplets from the nozzles of the ink jet head onto a print medium that is placed on a conveyance belt and conveyed. When the period when the moving speed of the conveying belt fluctuates at a constant period is the conveying belt moving speed fluctuation period, the adjacent nozzle rows formed on the same inkjet head and the one print pixel The distance between nozzles that eject ink droplets of different colors is 1/10 or less of the movement distance of the conveyance belt corresponding to the conveyance belt movement speed fluctuation cycle. In addition, the distance between nozzles that eject ink droplets of different colors with respect to the one print pixel other than adjacent nozzle rows formed in the same inkjet head corresponds to the conveyance belt moving speed fluctuation period. An inkjet printer characterized by being an integral multiple of the moving distance of the conveyor belt.   The nozzles for ejecting ink droplets of different colors to the one print pixel, which is an integral multiple of the moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation period, are formed in different ink jet heads. The inkjet printer according to claim 1.   A nozzle that ejects ink droplets of different colors to the one print pixel, which is an integral multiple of the moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation period, is formed in one ink jet head. The inkjet printer according to claim 1.   4. The moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation period is set equal to the circumferential length of a roller around which the conveying belt is wound. 5. Inkjet printer.   2. The moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation period is set equal to the moving distance of the conveying belt per one rotation of the drive motor for moving the conveying belt. The inkjet printer according to any one of 3.   The moving distance of the conveying belt corresponding to the conveying belt moving speed fluctuation period is set equal to the moving distance of the conveying belt corresponding to the speed changing period of the drive system for moving the conveying belt. The inkjet printer according to any one of 1 to 3.

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