JP6638790B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method.

  2. Related Art An ink jet recording apparatus that records an image on a sheet by discharging ink droplets from a head having a nozzle hole is known. In recent years, the size and cost of inkjet recording apparatuses have been reduced. On the other hand, an inkjet recording apparatus is also required to have high image quality. For example, an inkjet recording apparatus is required to achieve high image quality by increasing the recording density in the main scanning direction.

  For example, Patent Literature 1 discloses an image forming apparatus that includes a plurality of types of masks that define a dot arrangement with a recording density equal to or higher than print image data, and performs recording at a density equal to or higher than print image data while referring to a mask selected at random. Is disclosed. Further, the image forming apparatus described in Japanese Patent Application Laid-Open No. H11-157572 differs in the mask position to be referred to for each color, so that the dot arrangement position for each color shifts, and prints at a maximum main scanning resolution of four times the print image data. Techniques that can be performed are also disclosed.

  Incidentally, in the ink jet recording apparatus, in order to increase the recording density in the main scanning direction, it is necessary to improve the accuracy of a linear encoder for detecting the position of the head in the main scanning direction. However, in the inkjet recording apparatus, when the accuracy of the linear encoder is improved, the processing cost and the like of the linear encoder increase, and the cost as a whole increases.

  The present invention has been made in view of the above, and an object of the present invention is to provide an image forming apparatus and an image forming method in which the recording density in the main scanning direction is improved at low cost.

In order to solve the above-described problem and achieve the object, the present invention is an image forming apparatus which forms an image on a recording medium by ejecting ink droplets on the recording medium, wherein A head having a plurality of nozzle holes arranged in the sub-scanning direction for discharging droplets, a main-scanning control unit for controlling movement of the head in a main-scanning direction orthogonal to the sub-scanning direction, and A scan control unit that controls the main scan control unit so that the plurality of nozzle holes are scanned N times (N is an integer of 2 or more) in the main scan direction on the position; for each, a signal generator for generating a recording pixel data representing the sub-scanning direction to extract the corresponding pixel from the image data of the corresponding line to the position, the extracted values of the pixels of the plurality of nozzle holes, wherein A main scanning encoder for generating a position signal indicating the position of the pad in the main scanning direction at predetermined intervals, and a period of the position signal for each of the N times of scanning at the same position in the sub scanning direction. A timing generation unit for generating a timing signal whose phase is shifted by 1 / N cycle , a signal output unit for outputting a recording signal having a waveform pattern corresponding to the recording pixel data at the timing of the timing signal, A head drive unit that ejects ink droplets from the plurality of nozzle holes in response to a signal, wherein the signal generation unit performs the first scan of the N scans in the sub-scanning direction on the recording medium. And ejecting ink droplets from the first nozzle hole of the plurality of nozzle holes to the first position of the plurality of nozzle holes. In scanning, ink droplets from a second nozzle hole different from the first nozzle hole of the plurality of nozzle holes with respect to a second position returning from the first position on the recording medium in a direction opposite to the sub-scanning direction. Generating the recording pixel data including a pattern for ejecting the recording pixel data.

  According to the present invention, the recording density in the main scanning direction can be improved at low cost.

FIG. 1 is a diagram illustrating a mechanical configuration of the image forming apparatus. FIG. 2 is a diagram showing the moving direction of the head (main scanning direction) and the moving direction of the paper (sub-scanning direction). FIG. 3 is a diagram illustrating a state in which the head ejects ink droplets to the paper to form dots. FIG. 4 is a diagram illustrating an electrical configuration of the image forming apparatus. FIG. 5 is a diagram showing a configuration of the main scanning encoder. FIG. 6 is a diagram illustrating a configuration of the control unit according to the first embodiment. FIG. 7 is a diagram illustrating a relationship among a position signal, a timing signal, recording pixel data, and a dot position according to the first embodiment. FIG. 8 is a diagram illustrating a configuration of a head mounted on a carriage according to the second embodiment. FIG. 9 is a diagram illustrating a configuration of a nozzle hole formed in the head according to the second embodiment. FIG. 10 is a diagram illustrating a configuration of a control unit according to the second embodiment. FIG. 11 is a diagram illustrating an example of a nozzle used in each scan in the second embodiment. FIG. 12 is a diagram illustrating a dot pattern formed on a sheet in the second embodiment. FIG. 13 is a diagram illustrating an example of a nozzle used in each scan in the third embodiment. FIG. 14 is a diagram illustrating a first pattern of dots formed on a sheet in the third embodiment. FIG. 15 is a diagram illustrating a second pattern of dots formed on a sheet in the third embodiment. FIG. 16 is a diagram illustrating an example of a nozzle used in each scan in the fourth embodiment. FIG. 17 is a diagram illustrating a first pattern of dots formed on a sheet in the fourth embodiment. FIG. 18 is a diagram illustrating a second pattern of dots formed on a sheet in the fourth embodiment. FIG. 19 is a diagram illustrating another configuration example of the nozzle holes formed in the head.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited by the embodiment.

(1st Embodiment)
FIG. 1 shows a hardware configuration of an image forming apparatus 10 according to the first embodiment. The image forming apparatus 10 forms an image on a sheet (a recording medium) by ejecting ink droplets as ink droplets on the sheet (recording medium). That is, the image forming apparatus 10 is an image recording apparatus that generates a printed material by an inkjet method.

  The image forming apparatus 10 includes a paper feed tray 11, a paper reversing unit 12, a paper transfer unit 13, a paper discharge tray 14, and an image forming unit 15.

  The sheet feed tray 11 holds sheets before an image is formed. The paper reversing unit 12 takes in the paper, reverses the taken paper, and discharges the paper.

  The paper transfer unit 13 takes in the papers one by one from the paper feed tray 11 and sends the taken-in papers to the image forming unit 15. Further, the sheet transfer unit 13 takes in the sheet on which the image formation on one side is completed from the image forming unit 15 and sends the sheet to the sheet reversing unit 12. Further, the sheet transfer section 13 takes in the inverted sheet from the sheet reversing section 12 and sends the taken sheet to the image forming section 15.

  The paper transfer unit 13 includes, for example, a paper feed roller 21, a first guide unit 23, a transfer roller 24, a pressure roller 25, a second guide unit 26, a third guide unit 27, and a pressing roller 28. And

  The paper feed roller 21 takes out one sheet from the paper feed tray 11 and moves the taken out sheet along the first guide surface 23 a of the first guide portion 23. The transfer roller 24 transfers the sheet that has moved along the first guide surface 23a to the image forming unit 15. The transfer roller 24 transfers the sheet discharged from the sheet reversing unit 12 and moved along the second guide surface 23b to the image forming unit 15. The transfer roller 24 rotates in the reverse direction and transfers the sheet discharged from the image forming unit 15 to the sheet reversing unit 12.

  The pressure roller 25 sandwiches the sheet between the transfer roller 24 and assists the transfer of the sheet to the image forming unit 15 by the transfer roller 24. The second guide unit 26 guides the sheet transferred to the image forming unit 15 by the transfer roller 24. The third guide unit 27 guides the sheet transferred from the image forming unit 15 to the sheet reversing unit 12 by the transfer roller 24. The pressing roller 28 sandwiches the sheet between the transfer roller 24 and assists the transfer of the sheet to the image forming unit 15 by the transfer roller 24.

  The paper output tray 14 holds sheets on which image formation by the image forming unit 15 has been completed.

  The image forming unit 15 forms an image on a sheet while conveying the sheet transferred from the sheet transfer unit 13. The image forming unit 15 has a recording unit 16 and a transport unit 17.

  The recording unit 16 forms an image on a sheet by discharging ink droplets on the sheet. The transport unit 17 transports the sheet in the direction of arrow A in FIG. 1 and moves the image forming position of the recording unit 16. Further, after image formation on the sheet is completed, the transport unit 17 further transports the sheet in the direction of arrow A in FIG. When forming images on both sides of the sheet, the transport unit 17 rotates in the reverse direction after the image formation on one side is completed, and discharges the sheet in the direction opposite to the arrow A in FIG. 1. .

  The recording unit 16 includes guide shafts 31 and 32 and a carriage 33. The guide shafts 31 and 32 are stretched over the paper conveyed by the conveyance unit 17. The guide shafts 31 and 32 hold the carriage 33 so as to be movable in a direction perpendicular to the sheet conveyance direction (the direction of arrow A in FIG. 1) and parallel to the sheet.

  The carriage 33 has a head 34 mounted thereon. The head 34 has a nozzle hole 36 for ejecting ink droplets on paper, and an ink jet mechanism 37 for ejecting (ejecting) ink from the nozzle hole 36. The ink jet mechanism 37 has energy generating means for discharging ink. The ink jet mechanism 37 may be, for example, a piezoelectric actuator such as a piezoelectric element, or a thermal actuator that uses a phase change due to film boiling of a liquid using an electrothermal conversion element such as a heating resistor. The inkjet mechanism 37 may be, for example, a shape memory alloy actuator using a metal phase change due to a temperature change, or an electrostatic actuator using an electrostatic force.

  The carriage 33 is moved along the guide shafts 31 and 32 by a driving mechanism such as a motor. Therefore, as shown in FIG. 2, the carriage 33 can move the head 34 in a direction (main scanning direction) orthogonal to the sheet conveyance direction (sub-scanning direction) and parallel to the sheet. Thus, as shown in FIG. 3, the head 34 can form dots by ejecting ink droplets from the nozzle holes 36 at arbitrary positions in the main scanning direction on the paper.

  The sheet is transported by the transport unit 17 in the sub-scanning direction. Accordingly, the head 34 can form dots by ejecting ink droplets from the nozzle holes 36 at an arbitrary position in the sub-scanning direction on the paper.

  The carriage 33 has an ink cartridge 35 mounted thereon. The ink cartridge 35 holds the ink and supplies the ink to the inkjet mechanism 37 of the head 34. The ink cartridge 35 may be detachable from the carriage 33. Further, the carriage 33 may have a configuration in which a sub-tank is mounted in place of the ink cartridge 35, and ink is supplied from the main tank to the sub-tank.

  The transport unit 17 includes a drive roller 41, a driven roller 42, a transport belt 43, a charging roller 44, a guide roller 45, and a paper discharge roller 48.

  The drive roller 41 is rotated by being driven by a motor. The driven roller 42 is a roller to which tension is applied in a direction opposite to that of the driving roller 41. The transport belt 43 is an endless belt and is stretched between the drive roller 41 and the driven roller 42. The drive roller 41, the driven roller 42, and the transport belt 43 move the paper while keeping the surface of the paper perpendicular to the ink droplets ejected from the head 34.

  The transport belt 43 may have a single-layer configuration, a two-layer configuration, or a configuration having three or more layers. As an example, the transport belt 43 has a surface layer serving as a sheet adsorption surface formed of a resin material having a pure thickness of about 40 μm, for which resistance control is not performed, for example, ETFE pure material, and a resistance control by carbon using the same material as the surface layer. It may have a two-layer structure with a back layer (medium resistance layer, ground layer).

  The charging roller 44 comes into contact with the surface layer of the conveyor belt 43 and rotates following the rotation of the conveyor belt 43. A high voltage is applied to the charging roller 44 from a high voltage circuit (high voltage power supply) in a predetermined pattern, and charges the transport belt 43. The guide roller 45 is arranged to face the charging roller 44 with the transport belt 43 interposed therebetween.

  The paper discharge roller 48 is disposed downstream of the transport belt 43 and sends out the paper on which an image is formed to the paper discharge tray 14. Further, the transport unit 17 may include a guide member (plastic template) for guiding the transport belt 43, a cleaning roller having a porous body or the like for removing ink attached to the transport belt 43, and the like.

  In such an image forming unit 15, the transport belt 43 circulates in the direction of the arrow A in FIG. 1 (transport direction), and contacts the charging roller 44 to be charged to a high potential. In this case, a voltage is applied to the charging roller 44 by switching the polarity at predetermined time intervals. Thereby, the transport belt 43 is charged in a pattern of switching the polarity at a predetermined charging pitch.

  The sheet is fed onto the conveyor belt 43 charged to such a high potential. In the sheet, charges having a polarity opposite to that of the charges on the transport belt 43 are induced on the surface in contact with the charging roller 44, and the inside of the sheet is polarized. Then, the sheet is electrostatically attracted to the transport belt 43 because the charge on the transport belt 43 and the surface of the sheet that is in contact with the transport belt 43 are electrostatically pulled toward each other. As a result, the sheet strongly adheres to the conveyor belt 43, and the warpage and the unevenness are calibrated, and the flatness is maintained.

  Then, the image forming unit 15 drives the head 34 based on a recording signal corresponding to the image data while moving the sheet in the sub-scanning direction by rotating the conveyor belt 43 and moving the carriage 33 in the main scanning direction. I do. Thus, the image forming unit 15 can form dots by ejecting (ejecting) ink droplets from the head 34 and landing them at predetermined positions on the stopped paper.

  FIG. 4 is a diagram illustrating an electrical configuration of the image forming apparatus 10 according to the first embodiment. The image forming apparatus 10 includes a CPU (Central Processing Unit) 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, a host I / F 54, an operation panel 55, a head driving unit 61, A main scanning drive unit 62, a main scanning encoder 63, a sub scanning driving unit 64, a sub scanning encoder 65, and a control unit 66 are provided.

  The CPU 51 controls the entire image forming apparatus 10. The ROM 52 is a nonvolatile storage device that stores programs executed by the CPU 51 and other parameters. The RAM 53 is a volatile storage device that stores image data and the like and serves as a work area for data processing of the CPU 51. The host I / F 54 transmits and receives image data and the like to and from an external computer and the like. The operation panel 55 inputs operation information by the user and displays various information provided to the user.

  The head driving unit 61 is mounted on the carriage 33 together with the head 34. The head driving unit 61 inputs a recording signal from the control unit 66. Then, the head driving unit 61 drives the ink jet mechanism 37 of the head 34 according to the waveform pattern of the input recording signal, and ejects ink droplets from the nozzle holes 36 of the head 34.

  The main scanning drive unit 62 receives a control signal from the control unit 66 and moves the carriage 33 in the main scanning direction according to the input control signal. More specifically, the main scanning drive unit 62 includes a motor that rotates according to a control signal from the control unit 66, a belt that converts the rotation of the motor into a linear movement in the main scanning direction, and the like.

  The main scanning encoder 63 generates a position signal indicating the position of the head 34 in the main scanning direction at predetermined intervals. As an example, the main scanning encoder 63 outputs a position signal of a pulse waveform every time the head 34 moves a predetermined interval in the main scanning direction. The interval at which the main scanning encoder 63 generates a pulse corresponds to the accuracy of position detection by the main scanning encoder 63 in the main scanning direction. In the present embodiment, the main scanning encoder 63 generates a pulse waveform every time the head 34 moves by an interval corresponding to 1200 dpi. Such a main scanning encoder 63 outputs a position signal having a pulse waveform of a constant cycle as the head 34 moves at a constant speed in the main scanning direction.

  As shown in FIG. 5, the main scanning encoder 63 includes a scale 67 fixed and arranged in parallel with the main scanning direction, and a sensor 68 mounted on the carriage 33. Scale lines (for example, optical or magnetic scales) are formed on the scale 67 at regular intervals (for example, intervals corresponding to 1200 dpi) in the main scanning direction. The interval between the scale lines corresponds to the accuracy of the main scanning encoder 63. The sensor 68 optically or magnetically reads a scale line formed on the scale 67 by moving the head 34 in the main scanning direction, and generates a pulse at a position where the scale line is read. The main scanning encoder 63 may be of an optical type, a magnetic type, or another type.

  The sub-scanning drive unit 64 receives a control signal from the control unit 66 and moves the paper in the sub-scanning direction according to the input control signal. More specifically, the sub-scanning drive unit 64 includes a motor that rotates the driving roller 41 so that the sheet held on the transport belt 43 moves in the sub-scanning direction.

  The sub-scanning encoder 65 generates a sub-scanning position signal indicating the position of the sheet in the sub-scanning direction at predetermined intervals. As an example, the sub-scanning encoder 65 outputs a position signal of a pulse waveform every time the paper moves a predetermined interval in the main scanning direction. The interval at which the sub-scanning encoder 65 generates a pulse corresponds to the accuracy of position detection in the sub-scanning direction by the sub-scanning encoder 65. In the present embodiment, for example, the sub-scanning encoder 65 outputs a sub-scanning position signal having a pulse waveform every time the paper is rotated by a rotation amount corresponding to 1200 dpi.

  The control unit 66 receives image data to be printed from the CPU 51, generates a recording signal of a waveform pattern corresponding to the input image data, and supplies the recording signal to the head driving unit 61. The control unit 66 supplies a control signal to the main scanning drive unit 62 and the sub-scanning drive unit 64 in accordance with the position signals from the main scanning encoder 63 and the sub-scanning encoder 65, and the position of the head 34 in the main scanning direction and the paper Is controlled in the sub-scanning direction. Then, the control unit 66 supplies the recording signal to the head driving unit 61 so that ink droplets corresponding to the recording signal are supplied from the nozzle holes 36 of the head 34 at the respective positions in the main scanning direction and the sub-scanning direction of the paper. Discharge.

  According to the image forming apparatus 10 described above, an image corresponding to image data input from an external computer or the like can be formed on a sheet.

  FIG. 6 is a diagram illustrating a configuration of the control unit 66 according to the first embodiment. The control unit 66 includes a scan control unit 70, a buffer unit 71, a main scan control unit 72, a sub-scan control unit 73, a timing generation unit 74, a mask generation unit 75, a signal generation unit 76, and a signal output unit. And a portion 77.

  The scan control unit 70 controls the position at which the head 34 discharges ink droplets. That is, the scan control unit 70 controls the position of the nozzle hole 36 of the head 34 with respect to the sheet in the sub-scanning direction and the position in the main scanning direction. In the present embodiment, the scan control unit 70 controls the buffer unit 71 and the main scanning unit so that the nozzle hole 36 is scanned N times (N is an integer of 2 or more) in the main scanning direction at the same position in the sub-scanning direction. The controller 72, the sub-scanning controller 73, the timing generator 74, the mask generator 75, and the signal generator 76 are controlled.

  The buffer unit 71 receives image data from the outside and temporarily stores the image data. The buffer unit 71 outputs the image data of the line corresponding to the position of the nozzle hole 36 of the head 34 in the sub-scanning direction to the signal generation unit 76 under the control of the scan control unit 70.

  The main scanning control section 72 supplies a control signal to the main scanning driving section 62 based on the position signal output from the main scanning encoder 63 and the control by the scanning control section 70 to control the movement of the head 34 in the main scanning direction. . The main scanning control unit 72 moves the head 34 at a predetermined speed in the main scanning direction according to a position signal from the main scanning encoder 63, for example.

  The sub-scanning control unit 73 supplies a control signal to the sub-scanning driving unit 64 based on the position signal output from the sub-scanning encoder 65 and the control by the scan control unit 70 to control the movement of the sheet in the sub-scanning direction. The sub-scanning control unit 73 moves the sheet in the sub-scanning direction outside the moving period of the head 34 in the main scanning direction. That is, the main scanning control unit 72 moves the head 34 in the main scanning direction while the paper is stopped. Note that the sub-scanning control unit 73 can move the sheet with the accuracy of detecting the position in the sub-scanning direction by the sub-scanning encoder 65. In the present embodiment, the accuracy of the sub-scanning encoder 65 is 1200 dpi. Therefore, the sub-scanning control unit 73 can move the paper in the sub-scanning direction with an accuracy of 1200 dpi.

  The timing generator 74 acquires a position signal from the main scanning encoder 63 and generates a timing signal in which the acquired position signal is shifted in phase. For example, the timing generation unit 74 generates a signal when the sensor 68 of the main scanning encoder 63 detects a scale line formed on the scale 67 while the head 34 is moving at a constant speed in the main scanning direction. The position signal is delayed by a time shorter than the period of the pulse to be generated to generate a timing signal.

  In the present embodiment, the timing generator 74 generates timing signals having different phases for each of N scans on the same position in the sub-scanning direction. More specifically, the timing generation unit 74 shifts the phase of the timing signal by 1 / N with respect to the generation cycle of the pulse of the position signal for each of N scans on the same position in the sub-scanning direction. Generate

  For example, when N = 4, the timing generation unit 74 includes a first delay unit 81-1, a second delay unit 81-2, a third delay unit 81-3, and a fourth delay unit 81 -4 and a switching unit 82. The first delay unit 81-1 outputs a first timing signal having no phase shift from the position signal. Second delay section 81-2 outputs a second timing signal whose phase is shifted by 1/4 cycle from the position signal. Third delay section 81-3 outputs a third timing signal whose phase is shifted by 周期 cycle from the position signal. The fourth delay section 81-4 outputs a fourth timing signal shifted in phase by 3/4 from the position signal.

  The switching unit 82 outputs any one of the first to fourth timing signals according to the control by the scan control unit 70 and supplies the signal to the signal output unit 77. For example, the switching unit 82 outputs the first timing signal in the first scan of the N scans, outputs the second timing signal in the second scan, and outputs the third timing signal in the third scan. A timing signal is output, and a fourth timing signal is output in the fourth scan. The timing generation unit 74 having such a configuration can output the first to fourth timing signals whose phases are shifted by 1 / N cycle with respect to the generation cycle of the pulse of the position signal.

  The mask generation unit 75 stores N types of mask patterns generated in advance, and selects and outputs a mask pattern corresponding to each of N scans in accordance with control by the scan control unit 70. More specifically, the mask generation unit 75 determines the pixel at the position corresponding to the phase of the timing signal from the image data output from the buffer unit 71 every N scans on the same position in the sub-scanning direction. , A mask pattern for thinning out pixels in the main scanning direction to 1 / N is generated.

  The signal generation unit 76 determines the number of pixels specified by the mask pattern generated by the mask generation unit 75 from the image data output from the buffer unit 71 for each of N scans on the same position in the sub-scanning direction. A value is extracted, and recording pixel data representing the value of the extracted pixel is generated. That is, for each of N scans on the same position in the sub-scanning direction, the signal generation unit 76 calculates a pixel corresponding to the phase of the timing signal from the image data of the line corresponding to the position of the nozzle hole 36 in the sub-scanning direction. Is extracted, and recording pixel data representing the value of the extracted pixel is generated. Then, the signal generation unit 76 supplies the generated recording pixel data to the signal output unit 77.

  The signal output unit 77 inputs the timing signal output from the timing generation unit 74 and the recording pixel data generated by the signal generation unit 76 for each of N scans on the same position in the sub-scanning direction. . Then, the signal output unit 77 outputs a recording signal having a value corresponding to the recording pixel data generated by the signal generating unit 76 in synchronization with the timing of the timing signal.

  Then, the control unit 66 supplies the recording signal output from the signal output unit 77 to the head driving unit 61.

  FIG. 7 is a diagram illustrating a relationship among a position signal, a timing signal, recording pixel data, and a dot position when N = 4 in the first embodiment.

  When N = 4, the first timing signal output in the first scan has, for example, no delay with respect to the position signal. The second timing signal output in the second scan is delayed by 1/4 cycle with respect to the position signal. The third timing signal output in the third scan is delayed by 周期 cycle with respect to the position signal. The fourth timing signal output in the fourth scan is delayed by ／ cycle with respect to the position signal.

  The signal output unit 77 sets the recording signal to a high level, for example, when the recording pixel data is “1” and the timing signal rises. Then, when the recording signal is at the high level, the head driving unit 61 causes the nozzle holes 36 to eject ink droplets. Therefore, the head driving unit 61 ejects ink droplets from the nozzle holes 36 of the head 34 at the timing when the recording pixel data is “1” and the timing signal rises, for example.

  In each of the first to fourth scans, the phase of the timing signal is shifted by １ ／ cycle. Accordingly, the positions of the dots formed in the first to fourth scans are shifted in phase by 1/4 cycle. Accordingly, the control unit 66 can form dots in the main scanning direction with an accuracy four times as high as the accuracy of the position signal output from the main scanning encoder 63.

  As described above, the image forming apparatus 10 according to the present embodiment can improve the recording density in the main scanning direction without changing the main scanning encoder 63. Thereby, according to the image forming apparatus 10, the recording density in the main scanning direction can be improved at low cost.

(2nd Embodiment)
Next, an image forming apparatus 10 according to the second embodiment will be described. Since the image forming apparatus 10 according to the second embodiment has substantially the same configuration as the first embodiment, members having substantially the same functions are denoted by the same reference numerals, and description thereof will be omitted except for differences.

  FIG. 8 is a diagram illustrating a configuration of a head 34 mounted on a carriage 33 according to the second embodiment. FIG. 9 is a diagram illustrating a configuration of a nozzle hole 36 formed in the head 34 according to the second embodiment.

  The head 34 mounted on the carriage 33 according to the second embodiment includes N nozzle units 90 that eject ink droplets of different colors. Each of the N nozzle units 90 includes L (L is an integer of 2 or more) nozzle holes 36. The L nozzle holes 36 are arranged at least in a row at predetermined intervals in the sub-scanning direction.

  The N nozzle units 90 are arranged side by side in the main scanning direction. Thus, the N × L nozzle holes 36 included in the N nozzle units 90 are arranged in a matrix in the main scanning direction and the sub-scanning direction.

  In the present embodiment, N = 4, and the head 34 includes a nozzle unit 90-K that ejects K color ink droplets, a nozzle unit 90-C that ejects C color ink droplets, and a M color ink. It includes a nozzle unit 90-M for discharging droplets and a nozzle unit 90-Y for discharging ink droplets of Y color. In the present embodiment, the L nozzle holes 36 included in each nozzle unit 90 are arranged at intervals corresponding to, for example, 1200 dpi. The number of colors, the arrangement order, and the interval between the nozzle holes 36 are not limited to these.

  FIG. 10 is a diagram illustrating a configuration of a control unit 66 according to the second embodiment. In the present embodiment, the signal generator 76 includes L K signal generators 76K-1 to 76K-1L, L C signal generators 76C-1 to 76C-1L, and L M signal generators 76M. -1 to L and L signal generation units for Y 76Y-1 to 76Y-L. The signal output unit 77 includes L signal output units 77K-1 to 77K-1L, L signal output units 77C-1 to 77C-1L, and L signal output units 77M-1 to 77M-1. L and L number of Y signal output units 77Y-1 to 77Y-L.

  The L K signal generation units 76K-1 to 76K-1L and the L K signal output units 77K-1 to 77L correspond to the L nozzle holes 36 of the K nozzle unit 90-K. The L C signal generation units 76C-1 to 76C-L and the L C signal output units 77C-1 to 77C correspond to the L nozzle holes 36 of the C nozzle unit 90-C. The L M signal generation units 76M-1 to 76M-L and the L M signal output units 77M-1 to 77M correspond to the L nozzle holes 36 of the M nozzle unit 90-M. The L Y signal generators 76Y-1 to 76Y-1L and the L Y signal output units 77Y-1 to 77L correspond to the L nozzle holes 36 of the Y nozzle unit 90-Y.

  In the present embodiment, the image data of the K, C, M, and Y planes is input to the buffer unit 71.

  The buffer unit 71, under the control of the scan control unit 70, converts the line data corresponding to the position of each of the L nozzle holes 36 in the sub-scanning direction from the K plane image data into L K signal signals. Output to the generating units 76K-1 to 76K-L. The buffer unit 71, under the control of the scan control unit 70, converts the line data corresponding to the position of each of the L nozzle holes 36 in the sub-scanning direction from the C plane image data into L C signal signals. Output to the generating units 76C-1 to 76C-L. The buffer unit 71, under the control of the scan control unit 70, converts the line data corresponding to the position of each of the L nozzle holes 36 in the sub-scanning direction from the M plane image data into L M signal signals. Output to the generating units 76M-1 to 76M-L. The buffer unit 71, under the control of the scan control unit 70, converts the line data corresponding to the position of each of the L nozzle holes 36 in the sub-scanning direction out of the Y plane image data into L Y signal signals. Output to the generation units 76Y-1 to 76Y-1L.

  In the present embodiment, the timing generation unit 74 generates N timing signals whose phases are shifted by 1 / N cycle with respect to the generation cycle of the pulse of the position signal. In the present embodiment, N = 4. The timing generation unit 74 provides a first timing signal having no phase shift from the position signal to the K signal output units 77K-1 to 77K-L. The timing generation unit 74 provides the second timing signals, which are shifted in phase by 1/4 cycle from the position signals, to the C signal output units 77C-1 to 77C-L. The timing generation unit 74 provides a third timing signal having a phase shifted by 周期 cycle from the position signal to the M signal output units 77M-1 to 77M-L. The timing generation section 74 provides a fourth timing signal having a phase shifted by 3/4 cycle from the position signal to the Y signal output sections 77Y-1 to 77Y-L.

  The mask generation unit 75 extracts the value of the pixel at the position of the corresponding nozzle hole 36 from the K plane image data output from the buffer unit 71, corresponding to each of the K signal generation units 76K-1 to 76L. To generate a mask pattern. The mask generation unit 75 extracts the value of the pixel at the position of the corresponding nozzle hole 36 from the C plane image data output from the buffer unit 71 corresponding to each of the C signal generation units 76C-1 to 76C-L. To generate a mask pattern. The mask generation unit 75 extracts the value of the pixel at the position of the corresponding nozzle hole 36 from the M plane image data output from the buffer unit 71, corresponding to each of the M signal generation units 76M-1 to 76M-L. To generate a mask pattern. The mask generation unit 75 extracts the value of the pixel at the position of the corresponding nozzle hole 36 from the Y plane image data output from the buffer unit 71, corresponding to each of the Y signal generation units 76Y-1 to 76L. To generate a mask pattern.

  Each of the K signal generation units 76K-1 to 76L is configured to convert a pixel of the line of the corresponding nozzle hole 36 from the K plane image data output from the buffer unit 71 based on the mask pattern generated by the mask generation unit 75. Is extracted, and recording pixel data representing the value of the extracted pixel is generated. Based on the mask pattern generated by the mask generation unit 75, each of the C signal generation units 76C-1 to 76C-L converts the pixel of the line of the corresponding nozzle hole 36 from the C plane image data output from the buffer unit 71. Is extracted, and recording pixel data representing the value of the extracted pixel is generated.

  Each of the M signal generation units 76M-1 to 76L is configured to convert a pixel of the line of the corresponding nozzle hole 36 from the M plane image data output from the buffer unit 71 based on the mask pattern generated by the mask generation unit 75. Is extracted, and recording pixel data representing the value of the extracted pixel is generated. Each of the Y signal generation units 76 </ b> Y- 1 to 76 </ b> L converts the pixel of the line of the corresponding nozzle hole 36 from the Y plane image data output from the buffer unit 71 based on the mask pattern generated by the mask generation unit 75. Is extracted, and recording pixel data representing the value of the extracted pixel is generated.

  Each of the K signal output sections 77K-1 to 77K-L receives the first timing signal and the recording pixel data generated by each of the K signal generation sections 76K-1 to 76L. Then, each of the K signal output units 77K-1 to 77K-L outputs a K recording signal at a level corresponding to the corresponding recording pixel data at the timing of the first timing signal.

  Each of the C signal output sections 77C-1 to 77C-L receives the second timing signal and the recording pixel data generated by each of the C signal generation sections 76C-1 to 76C-L. Then, each of the C signal output units 77C-1 to 77C-L outputs a C recording signal at a level corresponding to the corresponding recording pixel data at the timing of the second timing signal.

  Each of the M signal output units 77M-1 to 77M-L receives the third timing signal and the recording pixel data generated by each of the M signal generation units 76M-1 to 76M-L. Then, each of the M signal output units 77M-1 to 77M-L outputs a recording signal for M at a level corresponding to the corresponding recording pixel data at the timing of the third timing signal.

  Each of the Y signal output units 77Y-1 to 77L receives the fourth timing signal and the recording pixel data generated by each of the Y signal generation units 76Y-1 to 76L. Then, each of the Y signal output sections 77Y-1 to 77Y-L outputs a Y recording signal at a level corresponding to the corresponding recording pixel data at the timing of the fourth timing signal.

  Then, the control unit 66 supplies the recording signal for K, the recording signal for C, the recording signal for M, and the recording signal for Y to the head driving unit 61, and the corresponding nozzle hole 36 The ink of the desired color is ejected.

  FIG. 11 is a diagram illustrating an example of a nozzle used in each scan in the second embodiment. In the present embodiment, the scan control unit 70 scans the same position on the paper in the sub-scanning direction N times (four times in the present embodiment) in the main scanning direction so that ink droplets are ejected from the nozzle holes 36. Next, each part is controlled.

  Specifically, in the first scan, as shown in FIG. 11A, the scan control unit 70 sends the K color ink through the L nozzle holes 36 included in the K nozzle unit 90-K. Is discharged. In the second scan, as shown in FIG. 11B, the scan control unit 70 ejects the C color ink from the L nozzle holes 36 included in the C nozzle unit 90-C.

  In the third scan, as illustrated in FIG. 11C, the scan control unit 70 ejects M color ink from the L nozzle holes 36 included in the M nozzle unit 90-M. In the fourth scan, as shown in FIG. 11D, the scan control unit 70 ejects the Y color ink from the L nozzle holes 36 included in the Y nozzle unit 90-Y.

  FIG. 12 is a diagram illustrating a dot pattern formed on a sheet in the second embodiment. The image forming apparatus 10 according to the present embodiment can form dots at intervals in the sub-scanning direction of the nozzle holes 36 (intervals equivalent to 1200 dpi) in the sub-scanning direction.

  In addition, the image forming apparatus 10 according to the present embodiment shifts the K, C, and C by １ ／ intervals (4800 dpi) of the scale line cycle of the scale 67 of the main scanning encoder 63 in the main scanning direction. M and Y dots can be recorded in order. As a result, the image forming apparatus 10 according to the present embodiment can form dots with a density four times the scale line of the scale 67 of the main scanning encoder 63 in the main scanning direction.

  As described above, the image forming apparatus 10 according to the present embodiment can improve the recording density in the main scanning direction without changing the main scanning encoder 63. Thereby, according to the image forming apparatus 10, the recording density in the main scanning direction can be improved at low cost. Further, in the image forming apparatus 10 according to the present embodiment, since the dot formation positions are shifted for each color, the colors can be expressed with high definition.

(Third embodiment)
Next, an image forming apparatus 10 according to the third embodiment will be described. Since the image forming apparatus 10 according to the third embodiment has substantially the same configuration as the second embodiment, members having substantially the same functions are denoted by the same reference numerals, and description thereof will be omitted except for differences.

  FIG. 13 is a diagram illustrating an example of a nozzle used in each scan in the third embodiment. In the third embodiment, the interval in the sub-scanning direction between the L nozzle holes 36 included in the nozzle unit 90 is an interval corresponding to 1 / P (P is an integer of 2 or more) of the accuracy of the sub-scanning encoder 65. ing. That is, the interval between the L nozzle holes 36 in the sub-scanning direction is longer than the accuracy of the sub-scanning encoder 65. Accordingly, the sub-scanning control unit 73 controls the movement of the sheet in the sub-scanning direction by a distance unit shorter than the interval between the nozzle holes 36 in the sub-scanning direction.

  In the third embodiment, the scan control unit 70 moves the sheet in the sub-scanning direction by an interval corresponding to the accuracy of the sub-scanning encoder 65, and scans the same position on the sheet in the main scanning direction N times. Is repeated P times. Thus, the image forming apparatus 10 can form an image by a distance corresponding to the length of the L nozzle holes 36 of the sheet.

  For example, when N = 4 and P = 4 and the accuracy of the sub-scanning encoder 65 is a length equivalent to 1200 dpi, the interval in the sub-scanning direction of the L nozzle holes 36 included in the nozzle unit 90 is as follows. The length is equivalent to 300 dpi. In this case, the scan control unit 70 scans the head 34 N times (four times) at the same position in the sub-scanning direction after moving the paper by a length corresponding to 1200 dpi in the sub-scanning direction. Then, the scan control unit 70 repeats this process P times (four times). As a result, the scan control unit 70 repeats the scan N × P times = 16 times. Thus, the image forming apparatus 10 can form an image on a sheet by a length of 300 dpi × L in the sub-scanning direction.

  FIG. 14 is a diagram illustrating a first pattern of dots formed on a sheet in the third embodiment. The image forming apparatus 10 according to the present embodiment has an interval of 1 / P of the interval of the nozzle holes 36 in the sub-scanning direction with respect to the sub-scanning direction, that is, an interval corresponding to the accuracy of the sub-scanning encoder 65 (1200 dpi equivalent). At intervals).

  In addition, the image forming apparatus 10 according to the present embodiment shifts the K, C, and C by １ ／ intervals (4800 dpi) of the scale line cycle of the scale 67 of the main scanning encoder 63 in the main scanning direction. M and Y dots can be recorded in order. Accordingly, the image forming apparatus 10 can form dots with a density four times as high as the scale line of the scale 67 of the main scanning encoder 63 in the main scanning direction.

  As described above, the image forming apparatus 10 according to the present embodiment can improve the recording density in the main scanning direction without changing the main scanning encoder 63. Thereby, according to the image forming apparatus 10, the recording density in the main scanning direction can be improved at low cost. Further, in the image forming apparatus 10 according to the present embodiment, since the dot formation position is shifted for each color, the color can be expressed with high definition.

  FIG. 15 is a diagram illustrating a second pattern of dots formed on a sheet in the third embodiment. If it is an integral multiple of the detection accuracy of the sub-scanning encoder 65, the scan control unit 70 can move the sheet to an arbitrary position in the sub-scanning direction. In addition, the scan control unit 70 can cause the head 34 to scan in the main scanning direction an arbitrary number of times at the same position in the sub-scanning direction.

  Therefore, the signal generation unit 76 generates the recording pixel data of the pattern in which the ink liquid is ejected from each of the nozzle holes 36 in the order in which the adjacent dots are not formed in two consecutive scans. For example, the signal generator 76 generates recording pixel data for forming dots in a pattern in which ink droplets are ejected in the order shown in FIG.

  In this case, the scan control unit 70 moves the head 34 in the sub-scanning direction and moves the head 34 at the same position in the sub-scanning direction so that dots are formed on the paper in a pattern as shown in FIG. Of the head 34 is controlled. The mask generating unit 75 stores a plurality of mask patterns in advance in accordance with the movement and scan patterns in the sub-scanning direction, and sets an appropriate mask pattern in accordance with the position of the head 34 in the sub-scanning direction and the number of scans. Is given to the signal generation unit 76.

  As a result, according to the image forming apparatus 10 of the third embodiment, dots formed on the sheet attract each other to cause bleeding at a color boundary, and dry unevenness (color unevenness) of ink called beading occurs. Generation can be suppressed.

  Note that, for example, the dots formed in the fifth scan from the dots formed in the fourth scan in FIG. 15 return in the direction opposite to the sub-scanning direction. However, in each nozzle unit 90, a plurality of nozzle holes 36 are formed side by side in the sub-scanning direction. If the sheet is returned in the reverse direction, the dots can be formed in an order including a portion returning in the reverse direction of the sub-scanning direction without returning the sheet.

(Fourth embodiment)
Next, an image forming apparatus 10 according to a fourth embodiment will be described. Since the image forming apparatus 10 according to the fourth embodiment has substantially the same configuration as the second embodiment, members having substantially the same functions are denoted by the same reference numerals, and description thereof will be omitted except for differences.

  FIG. 16 is a diagram illustrating an example of a nozzle used in each scan in the fourth embodiment. In the fourth embodiment, the interval between the L nozzle holes 36 included in the nozzle unit 90 in the sub-scanning direction is equal to the interval corresponding to the accuracy of the sub-scanning encoder 65 (in the present embodiment, the interval corresponding to 1200 dpi). Has become. In the present embodiment, the signal generating unit 76 forms dots on the paper using the L nozzle holes 36 in one scan.

  Here, in the present embodiment, in one scan, the signal generation unit 76 simultaneously uses the nozzle holes 36 included in the plurality of nozzle units 90 to form dots on the paper. In this case, the signal generator 76 uses only one nozzle hole 36 for the same line in the sub-scanning direction. At the same time, the signal generation unit 76 uses only one color plate nozzle hole 36 for the same ink ejection timing in the main scanning direction.

  For example, it is assumed that the head 34 has four nozzle units 90 for K, C, M, and Y. In this case, as shown in FIG. 16A, in the first scan, the signal generation unit 76 determines that L / 2 of the L nozzle holes 36 included in the K nozzle unit 90-K Minutes are selected and used one by one in the sub-scanning direction. Further, in the first scan, the signal generation unit 76 uses the nozzle holes 36 included in the K nozzle unit 90-K at every single ink ejection timing in the main scanning direction.

  Also, as shown in FIG. 16A, in the first scan, the signal generation unit 76 sets the K nozzle unit 36 out of the L nozzle holes 36 included in the M nozzle unit 90-M. Select and use L / 2 of unused lines in 90-K. Further, in the first scan, the signal generation unit 76 sets the nozzle holes 36 included in the M nozzle unit 90-M in the main scanning direction at the same ink ejection timing as the K nozzle unit 90-K. use.

  Also, as shown in FIG. 16A, in the first scan, the signal generation unit 76 assigns L / 2 of the L nozzle holes 36 included in the C nozzle unit 90-C to the sub-unit. Select and use one by one in the scanning direction. Further, in the first scan, the signal generation unit 76 uses the nozzle holes 36 included in the nozzle unit 90-C for C at a different ink ejection timing from the nozzle unit 90-K for K in the main scanning direction. I do.

  Also, as shown in FIG. 16A, in the first scan, the signal generation unit 76 sets the C nozzle unit out of the L nozzle holes 36 included in the Y nozzle unit 90-Y. Select and use L / 2 of unused lines in 90-C. Further, in the first scan, the signal generation unit 76 sets the nozzle holes 36 included in the Y nozzle unit 90-Y in the main scanning direction at the same ink ejection timing as the C nozzle unit 90-C. use.

  In addition, as shown in FIG. 16B, in the second scan, the signal generation unit 76 sets the nozzle holes 36 of the four nozzle units 90 for the K, C, M, and Y nozzles. First, the nozzle holes 36 not used in the first scan are used at a different ink ejection timing from that in the first scan. Thereafter, the signal generator 76 repeats the same processing as the first scan and the second scan.

  FIG. 17 is a diagram illustrating a first pattern of dots formed on a sheet in the fourth embodiment. The image forming apparatus 10 according to the present embodiment can form dots at intervals in the sub-scanning direction of the nozzle holes 36 (intervals equivalent to 1200 dpi) with respect to the sub-scanning direction.

  Further, the pattern of the ink droplets formed on the paper differs for each line. For example, as shown in FIG. 17, a line in which dots are formed in the order of K → M → C → Y from the left in the main scanning direction, and a line where dots are formed in the order of M → K → Y → C from the left in the main scanning direction. Are formed alternately in the sub-scanning direction.

  As described above, in the image forming apparatus 10 according to the present embodiment, in one scan, the number of the nozzle holes 36 for ejecting the ink droplets from one nozzle unit 90 is determined in each of the main scanning direction and the sub-scanning direction. Can be thinned out. Therefore, according to the image forming apparatus 10, it is possible to stably eject the ink droplets by eliminating the bias of the nozzle holes 36 used in one scan.

  FIG. 18 is a diagram illustrating a second pattern of dots formed on a sheet in the fourth embodiment. In the fourth embodiment, the distance between the L nozzle holes 36 included in the nozzle unit 90 in the sub-scanning direction is 1 / P (P is an integer of 2 or more) of the accuracy of the sub-scanning encoder 65 (for example, , 300 dpi).

  In this case, the signal generation unit 76 may generate the recording pixel data of the pattern in which the ink liquid is ejected from each nozzle hole 36 in the order in which the adjacent dots are not formed in two consecutive scans. Good. For example, the signal generation unit 76 determines a region of 4 dots (K, C, M, and Y) in the main scanning direction and 4 × 4 dots of four lines in the sub-scanning direction on the paper as shown in FIG. Print pixel data of a pattern in which ink droplets are ejected in the order shown may be generated.

  As a result, according to the image forming apparatus 10 of the fourth embodiment, dots formed on the sheet attract each other to cause bleeding at the color boundary, and dry unevenness (color unevenness) of ink called beading occurs. Generation can be suppressed.

  FIG. 19 is a diagram showing another configuration example of the nozzle hole 36 formed in the head 34. As shown in FIG. 19, the L nozzle holes 36 formed in the plurality of nozzle units 90 may be shifted from each other in the sub-scanning direction.

  For example, the position of the L nozzle holes 36 formed in the K nozzle unit 90-K in the sub-scanning direction and the position of the L nozzle holes 36 formed in the C nozzle unit 90-C in the sub-scanning direction May deviate from the position. In the present embodiment, the interval between the nozzle holes 36 in the sub-scanning direction is a length equivalent to 300 dpi, and the shift amount between adjacent nozzle units 90 is a length equivalent to 600 dpi.

  By having a deviation between the nozzle units 90 in this manner, the control unit 66 can reduce the number of movements of the paper in the sub-scanning direction, for example, when forming dots in the pattern shown in FIGS. It is possible to reduce the number of sheets and to perform printing efficiently.

  Although an ink jet image forming apparatus has been described as an embodiment, the present invention relates to, for example, a color material liquid used for manufacturing a color filter for a liquid crystal display or an electrode liquid material used for manufacturing an electrode film for an organic EL display. For example, the present invention can be applied to a droplet discharging apparatus having another configuration for discharging a special liquid such as a liquid.

  The ink droplets ejected from the nozzle holes 36 are not particularly limited, and may be, for example, liquids including the following various materials (including dispersions such as suspensions and emulsions). That is, an ink containing a filter material of a color filter, a light emitting material for forming an EL light emitting layer in an organic EL (Electro Luminescence) device, a fluorescent material for forming a phosphor on an electrode in an electron emission device, PDP (Plasma). A fluorescent material for forming a phosphor in a display panel device, a migrating material for forming a migrating body in an electrophoretic display device, a bank material for forming a bank on the surface of the substrate W, various coating materials, and forming an electrode A liquid electrode material, a particle material forming a spacer for forming a minute cell gap between two substrates, a liquid metal material for forming a metal wiring, a lens material for forming a microlens, A resist material, a light diffusion material for forming a light diffuser, Various test liquid material to be used for the biosensor, such as NA chip or a protein chip or the like.

  In addition, the droplet acceptor from which droplets are to be ejected is not limited to paper such as recording paper, but may be other media such as films, woven fabrics and nonwoven fabrics, and various substrates such as glass substrates and silicon substrates. Work.

REFERENCE SIGNS LIST 10 image forming apparatus 11 paper feed tray 12 paper reversing unit 13 paper transfer unit 14 paper discharge tray 15 image forming unit 16 recording unit 17 transport unit 21 paper feed roller 23 first guide unit 24 transfer roller 25 pressure roller 26 second guide Part 27 third guide part 28 pressing roller 31 guide shaft 32 guide shaft 33 carriage 34 head 35 ink cartridge 36 nozzle hole 37 ink jet mechanism 41 drive roller 42 driven roller 43 transport belt 44 charging roller 45 guide roller 48 discharge roller 51 CPU
52 ROM
53 RAM
54 Host I / F
55 operation panel 61 head drive unit 62 main scan drive unit 63 main scan encoder 64 sub scan drive unit 65 sub scan encoder 66 control unit 67 scale 68 sensor 70 scan control unit 71 buffer unit 72 main scan control unit 73 sub scan control unit 74 Timing generation unit 75 Mask generation unit 76 Signal generation unit 77 Signal output unit 81 Delay unit 82 Switching unit 90 Nozzle unit

JP 2004-209765 A

Claims (5)

An image forming apparatus that forms an image on the recording medium by discharging ink droplets on the recording medium,
A head having a plurality of nozzle holes arranged in the sub-scanning direction, each of which ejects ink droplets to the recording medium,
A main scanning control unit that controls movement of the head in a main scanning direction orthogonal to the sub scanning direction,
A scan control unit that controls the main scan control unit to scan the plurality of nozzle holes N times (N is an integer of 2 or more) in the main scan direction at the same position in the sub-scan direction;
For each of the N scans, a corresponding pixel is extracted from image data of a line corresponding to the position of the plurality of nozzle holes in the sub-scanning direction, and recording pixel data representing the value of the extracted pixel is generated. A signal generation unit for
A main scanning encoder that generates a position signal indicating the position of the head in the main scanning direction at predetermined intervals,
A timing generation unit that generates a timing signal whose phase is shifted by 1 / N cycle with respect to the cycle of the position signal for each of the N scans on the same position in the sub-scanning direction;
A signal output unit that outputs a recording signal having a waveform pattern corresponding to the recording pixel data at the timing of the timing signal ,
A head drive unit that ejects ink droplets from the plurality of nozzle holes according to the recording signal,
With
The signal generator,
In a first scan of the N scans, ink droplets are ejected from a first nozzle hole of the plurality of nozzle holes to a first position in the sub-scanning direction on the recording medium,
In a second scan after the first scan of the N scans, the second position of the plurality of nozzle holes with respect to a second position returning in the reverse direction of the sub-scanning direction from the first position on the recording medium. An image forming apparatus that generates the recording pixel data including a pattern for ejecting ink droplets from a second nozzle hole different from the first nozzle hole. The image forming apparatus according to claim 1, wherein the signal generation unit generates the recording pixel data in a pattern in which ink droplets corresponding to two adjacent pixels are not ejected in two consecutive scans. The main scanning control unit, an image forming apparatus according to the head to claim 1 or 2 causes movement at a predetermined velocity in the main scanning direction. The head has N nozzle units that eject ink droplets of different colors,
Each of the N nozzle units includes L (L is an integer of 2 or more) nozzle holes arranged in at least one line at predetermined intervals in the sub-scanning direction,
The N nozzle units are arranged side by side in the main scanning direction,
The head drive unit, for each of the N scans of the same position in the sub-scanning direction, to any one of claims 1 to 3, to eject ink droplets from one nozzle hole of a different color The image forming apparatus according to claim 1. An image forming method executed by an image forming apparatus that forms an image on the recording medium by discharging ink droplets on the recording medium,
The image forming apparatus includes:
A head having a plurality of nozzle holes arranged in the sub-scanning direction, each of which ejects ink droplets to the recording medium,
A main scanning control unit that controls movement of the head in a main scanning direction orthogonal to the sub scanning direction,
A scan control unit that controls the main scan control unit to scan the plurality of nozzle holes N times (N is an integer of 2 or more) in the main scan direction at the same position in the sub-scan direction;
For each of the N scans, a corresponding pixel is extracted from image data of a line corresponding to the position of the plurality of nozzle holes in the sub-scanning direction, and recording pixel data representing the value of the extracted pixel is generated. A signal generation unit for
A main scanning encoder that generates a position signal indicating the position of the head in the main scanning direction at predetermined intervals,
A timing generation unit that generates a timing signal whose phase is shifted by 1 / N cycle with respect to the cycle of the position signal for each of the N scans on the same position in the sub-scanning direction;
A signal output unit that outputs a recording signal having a waveform pattern corresponding to the recording pixel data at the timing of the timing signal ,
A head drive unit that ejects ink droplets from the plurality of nozzle holes according to the recording signal,
With
The signal generator,
In a first scan of the N scans, ink droplets are ejected from a first nozzle hole of the plurality of nozzle holes to a first position in the sub-scanning direction on the recording medium,
In a second scan after the first scan of the N scans, the second position of the plurality of nozzle holes with respect to a second position returning in the reverse direction of the sub-scanning direction from the first position on the recording medium. An image forming method for generating the recording pixel data including a pattern for ejecting ink droplets from a second nozzle hole different from the first nozzle hole.

Images