JP4768459B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming apparatus, it relates to an image forming equipment which uses a liquid discharge head in particular discharging droplets of a recording liquid to the recording head.

  Various image forming apparatuses such as printers, facsimiles, copiers, plotters, printer / fax / copier multifunction machines, etc., are recording heads composed of one or more liquid ejecting heads that eject droplets of recording liquid (for example, ink) The carriage is a recording medium (hereinafter referred to as “paper”, but the material is not limited to paper, and it means a material that can accept liquid, such as cloth, plastic film, metal plate, etc. In addition, it is also called a recording medium, recording paper, transfer material, transfer paper, etc.) and is serially scanned in a direction perpendicular to the conveying direction of the recording medium, and the recording medium is intermittently conveyed according to the recording width. A serial type image forming apparatus that forms an image on a recording medium by alternately repeating conveyance and recording (recording, printing, printing, and printing are also used synonymously). That. The recording liquid means a liquid for recording.

  In such a serial scan type image forming apparatus, when performing bi-directional printing in which an image is formed by printing in both the forward and backward directions of the carriage, the order of placing each color is reversed between the forward and backward directions. Band-shaped density unevenness (bidirectional color difference) due to the recording droplet ejection order occurs. Therefore, various proposals have conventionally been made to reduce this bidirectional color difference.

For example, as described in Patent Document 1, a head capable of arranging relatively large dots for applying cyan (C), magenta (M), and yellow (Y) ink and relatively small dots, respectively. By forming two sets of secondary color level pixels symmetrically in the scanning direction and changing the ink application order (C → M and M → C) to form a plurality of pixels arranged in the raster direction. Since a plurality of secondary color pixels arranged in the direction have different ink application orders, there is no difference in the application order regardless of whether the pixels are formed by either forward or backward scanning. Therefore, the color resulting from the ink application order An apparatus that can reduce the occurrence of unevenness is known. There are also Patent Documents 2 to 5 as similar descriptions.
JP 2001-205828 A JP 2002-137421 A JP 2001-96770 A JP 2001-96771 A JP 2001-130033 A

Further, as described in Patent Document 6, each of the first head in the order of cyan, magenta, and yellow, and the second head in the reverse order of the order of the first head, Image formation in which one black head is arranged symmetrically in the main scanning direction, and ejection is performed by the first head during forward scanning, and ejection is performed by the second head during forward scanning. There is also a device.
JP-A-8-295034

Further, as described in Patent Document 7, the image characteristic information related to the image characteristics of the input image information is acquired, arranged in the conveyance direction of the recording medium, and for each type of ink used for recording. A first head having an ejection portion, and a second head having an ejection portion for each ink that is symmetrical to the arrangement of the ejection portions for each ink of the first head, and input based on image characteristic information The recording dots based on the image information are distributed to the first recording dots and the second recording dots by the multipass / double head data generation unit, and according to the first recording dots, the first head is subjected to multipass recording control by the first head control unit, There is also an image forming apparatus in which the second head is subjected to multipass recording control by a second head control unit in accordance with the second recording dots.
JP 2000-79681 A

Further, as described in Patent Document 8, in an inkjet head used in a serial scan type inkjet recording apparatus, a plurality of nozzle rows corresponding to each type of ejectable ink are arranged in parallel in the scanning direction. Also known is an inkjet head in which at least three nozzle arrays for ejecting at least two types of ink are arranged in the same order in the forward scanning direction and the backward scanning direction.
JP 2001-113736 A

Further, as described in Patent Document 9, the first liquid and the second liquid of a different type from the first liquid are respectively ejected from different outlets while bidirectionally scanning the recording medium. A liquid discharge head that performs recording by discharging from a plurality of discharge ports arranged at a predetermined pitch in a direction different from the scanning direction, and the corresponding discharge ports are respectively in the scanning direction. A first discharge port array group that is provided in a plural number so as to match, and a second discharge port array group that is adjacent to the first discharge port array group and has the same discharge port array as the first discharge port array group And the first discharge port array group includes a first discharge port array that discharges the first liquid and a second discharge port array that discharges the second liquid, The discharge port array group includes a third discharge port array that discharges the first liquid and a fourth discharge port array that discharges the second liquid. The first discharge port row group and the second discharge port row group are discharge ports that form a first discharge port row while the first discharge port row and the third discharge port row are adjacent to each other. There is also known a liquid discharge head that is disposed so as to be displaced in the arrangement direction of the discharge ports so that the outlet and the discharge ports forming the third discharge port array complement each other in the scanning direction.
JP 2001-171119 A

Further, as described in Patent Document 10, a carriage on which a head and an ink tank for discharging ink from a plurality of nozzles and outputting input image information on the recording medium are mounted, and means for conveying the recording medium In some image forming apparatuses, the plurality of nozzles are divided to form at least two nozzle groups, and each nozzle group is connected to a different ink tank.
JP-A-7-112534

Further, as described in Patent Document 11, there is also an image forming apparatus that reduces a hue shift due to a difference in the order of ink adhesion that occurs between the forward direction and the backward direction of the print head by using gamma correction. Are known.
Japanese Patent Laid-Open No. 2003-266749

  However, as described in Patent Documents 1 to 5, the heads for applying dots having different sizes are arranged symmetrically in the scanning direction and the ink application order is changed to change the ink supply in the forward path and the return path. In a configuration in which the application order is the same, or in a configuration in which different heads or nozzle arrays are used for the forward path and the return path as described in Patent Documents 6 to 8, the amount of ink discharged due to the difference in the heads is the same even if the ink application order is the same. There is a problem that a color difference is caused between the forward path and the return path due to the difference.

  Further, as described in Patent Document 9, a first discharge port array group including a plurality of discharge port arrays such that each corresponding discharge port of the discharge port array matches the scanning direction, and a discharge port And a second discharge port array group including a plurality of discharge port arrays so that the corresponding discharge ports of the columns correspond to the scanning direction, the first discharge port array group and the second discharge port array Using the liquid discharge head in which the groups are arranged with the pitch shifted in the direction orthogonal to the scanning direction causes a problem that the head configuration becomes complicated and the manufacturing cost increases.

  Further, as described in Patent Document 10, in a configuration in which a plurality of nozzles of a head are divided into two nozzle groups and different ink tanks are connected to the nozzle groups, a mechanism for supplying ink is provided. There is a need to have two of each, and the size and complexity of the head may be increased, and the mechanism for positioning the head may be complicated and upsized. Further, since the black ink and the color ink nozzles are maintained at the same time, there is a problem that the discharge amount of the waste ink for preventing the black ink from being mixed with the color ink may increase.

  In addition, as described in Patent Document 11, in a configuration in which a hue shift due to a difference in the order of ink adhesion occurring between the forward direction and the backward direction of the print head is reduced using gamma correction, γ correction is performed. There is a problem that processing becomes complicated.

The present invention has been made in view of the above problems, with reduced bidirectional color difference, the production of the head, so to reduce the image degradation due to variations in assembly quality image is obtained The purpose is to do.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
In an image forming apparatus in which a plurality of nozzle rows capable of ejecting recording liquid droplets are arranged in a plurality of main scanning directions and arranged in a plurality of main scanning directions.
It can eject droplets of four or more colors including at least yellow,
The nozzle row for discharging the yellow droplets is divided and arranged in different heads together with the nozzle row for discharging the other one-color droplets ,
Nozzle rows that eject droplets of at least two colors other than the yellow and the one color are arranged in the same head for each color ,
The nozzle row for discharging the yellow droplets formed on one head and the nozzle row for discharging the other color droplets are arranged so as to be shifted in the nozzle arrangement direction so as not to overlap in the main scanning direction. It was configured.

Here, the head having the nozzle row for discharging the yellow droplet and the nozzle row for discharging another color droplet is a nozzle for discharging at least two color droplets other than the yellow color and the one color. It can be configured to be arranged on both outer sides in the main scanning direction than the plurality of heads in which the rows are formed.

Moreover, even the no least be configured one color of the two colors is black. Moreover, it even said no least one color of the two colors cyan, magenta, red, and configuration is either at least blue and green. In addition , a plurality of nozzle rows that discharge droplets of the same color can be arranged so as to be shifted by (1 / nozzle row number) pitch.

The head may be configured such that the pressure generating means for generating the pressure for discharging the droplets is an electrothermal transducer. The head may be configured such that the pressure generating means for generating the pressure for discharging the droplet is an electromechanical transducer.

Further, it is possible to adopt a configuration in which the amount of displacement of the landing positions of the discharged droplets between the nozzle rows is 30 μm or less . Also, when forming an image using a plurality of colors simultaneously can to configurations without one color of the two colors even the no less. In this case, when the image to be formed has a brightness of less than 26 , all of the at least two colors can be used.

According to the image forming apparatus of the present invention, it is possible to eject droplets of four or more colors including at least yellow, and the nozzle row for ejecting yellow droplets is the nozzle row for ejecting other one color droplets. In addition, nozzle arrays that are divided and arranged in different heads and discharge droplets of at least two colors other than yellow and one color are arranged in the same head for each color, and discharge yellow droplets formed on one head. Since the nozzle row and the nozzle row that discharges another color droplet are arranged so as to be shifted in the nozzle arrangement direction so as not to overlap in the main scanning direction , the bidirectional color difference is reduced and the head Can be easily assembled, and image deterioration due to manufacturing and assembly variations is reduced.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of an image forming apparatus including an apparatus for discharging droplets according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory side view for explaining the overall structure of the mechanism section of the image forming apparatus, and FIG. 2 is a plan view for explaining the mechanism section.

  In this image forming apparatus, a carriage 4 is slidably held in a main scanning direction by a guide rod 2 and a stay 3 which are guide members horizontally mounted on left and right side plates 1A and 1B constituting a frame 1, and a main scanning motor. 5 is moved and scanned in the direction indicated by the arrow (main scanning direction) in FIG. 2 via the timing belt 7 spanned between the driving pulley 6A and the driven pulley 6B.

  For example, the carriage 4 includes four liquid ejection heads that eject recording liquid droplets (ink droplets) of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). 11a to 11d are arranged in a direction (sub-scanning direction) orthogonal to the main scanning direction in which the nozzle row of the nozzle surface 11a in which a plurality of ink discharge ports (nozzles) are formed, and the ink discharging direction is directed downward. Yes. The whole composed of a plurality of heads is referred to as “recording head 11”.

  As the liquid discharge head constituting the recording head 11, a liquid discharge head provided with a piezoelectric actuator such as a piezoelectric element as pressure generation means (actuator means) for generating pressure for discharging droplets is used. The thing using a heat generating resistor is not restricted but can be used.

  A driver IC is mounted on each head of the recording head 11 and is connected to a control unit (not shown) via a harness (flexible print cable: FPC cable) 12.

  The carriage 4 is mounted with a head tank (also referred to as a “sub tank”) 15 for each color for supplying ink of each color to the recording head 11. Each color sub-tank 15 is supplementarily supplied with ink of each color from the ink cartridge 10 of each color mounted in the cartridge loading unit 9 via the ink supply tube 16 of each color. The cartridge loading 9 is provided with a supply pump unit 17 for feeding ink in the ink cartridge 10, and the ink supply tube 16 is engaged with the rear plate 1C constituting the frame 1 in the middle of turning. It is held by a stop member 18.

  On the other hand, as a paper feed unit for feeding the paper 22 stacked on the paper stacking unit (pressure plate) 21 of the paper feed tray 20, a half-moon roller (feed) that separates and feeds the paper 22 one by one from the paper stacking unit 21. A separation pad 24 made of a material having a large friction coefficient is provided opposite to the sheet roller 23 and the sheet feeding roller 23, and the separation pad 24 is biased toward the sheet feeding roller 23 side.

  In order to feed the paper 22 fed from the paper feeding unit to the lower side of the recording head 11, a guide member 25 for guiding the paper 22, a counter roller 26, a conveyance guide member 27, and a tip pressure roller. And a holding belt 28 as a conveying means for electrostatically attracting the fed paper 22 and conveying it at a position facing the recording head 11.

  The conveyance belt 31 is an endless belt, is configured to wrap around the conveyance roller 32 and the tension roller 33 and circulate in the belt conveyance direction (sub-scanning direction). 34 is charged (charged).

  The transport belt 31 may be a single-layer belt or a multi-layer (two or more layers) belt. In the case of the conveyance belt 31 having a one-layer structure, the entire layer is formed of an insulating material because it contacts the paper 32 and the charging row 34. In the case of the transport belt 31 having a multi-layer structure, the side that contacts the paper 22 and the charging roller 34 is preferably formed of an insulating layer, and the side that does not contact the paper 22 and the charging roller 34 is preferably formed of a conductive layer. .

As an insulating material for forming the transport belt 31 having a single-layer structure or an insulating material for forming the insulating layer of the transport belt 31 having a multi-layer structure, for example, a conductive material such as PET, PEI, PVDF, PC, ETFE, or PTFE is used. It is preferable that the material does not contain a control material, and the volume resistivity is 10 ¹² Ωcm or more, preferably 10 ¹⁵ Ωcm. Further, as a material for forming the conductive layer of the transport belt 31 having a multi-layer structure, it is preferable that carbon is contained in the resin or elastomer so that the volume resistivity is 10 ⁵ to 10 ⁷ Ωcm.

The charging roller 34 is disposed so as to come into contact with an insulating layer (in the case of a multilayer belt) that forms the surface layer of the transport belt 31 and to rotate following the rotation of the transport belt 31. It is over. The charging roller 34 is formed of a conductive member having a volume resistivity of 10 ⁶ to 10 ⁹ Ω / □. As will be described later, for example, a 2 kV positive / negative AC bias (high voltage) is applied to the charging roller 34 from an AC bias supply unit (high voltage power supply). The AC bias may be a sine wave or a triangular wave, but a square wave is more preferable.

  In addition, a guide member 35 is disposed on the back side of the conveyance belt 31 so as to correspond to a printing area by the recording head 11. The guide member 35 has a top surface that protrudes toward the head 11 with respect to the tangent line of the two rollers (the conveyance roller 32 and the tension roller 33) that support the conveyance belt 31, thereby maintaining high-precision flatness of the conveyance belt 31. I am doing so.

  The transport belt 31 rotates in the belt transport direction of FIG. 2 when the transport roller 32 is rotationally driven by the sub-scanning motor 36 via the drive belt 37 and the timing roller 38. Although not shown, an encoder wheel having a slit is attached to the shaft of the conveying roller 32, and a transmission type photosensor for detecting the slit of the encoder wheel is provided, and the wheel encoder is configured by the encoder wheel and the photosensor. It is composed.

  Further, as a paper discharge unit for discharging the paper 22 recorded by the recording head 11 to the paper discharge tray 40, a separation claw 41 for separating the paper 22 from the transport belt 31, a paper discharge roller 42, and paper discharge The roller 43 is provided.

  A duplex unit 51 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 51 takes in the paper 22 returned by the reverse rotation of the transport belt 31, reverses it, and feeds it again between the counter roller 26 and the transport belt 31. The upper surface of the duplex unit 51 is a manual feed tray 52.

  Further, a maintenance / recovery mechanism 61 for maintaining and recovering the nozzle state of the head 11 is disposed in the non-printing area on one side of the carriage 4 in the scanning direction. The maintenance / recovery mechanism 61 includes cap members (hereinafter referred to as “caps”) 62 a to 62 d (hereinafter referred to as “caps 62” when not distinguished) and nozzles for capping the nozzle surfaces 11 a of the recording head 11. A wiper blade 63 that is a blade member for wiping the surface 11a, an empty discharge receiver 64 that receives liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid, and the like It has. Here, the cap 62a is a suction and moisture retention cap, and the other caps 62b to 62d are moisture retention caps.

  Further, in the non-printing area on the other side of the carriage 4 in the scanning direction, there is an empty space for receiving a liquid droplet when performing an empty discharge for discharging a liquid droplet that does not contribute to recording in order to discharge the recording liquid thickened during recording or the like. A discharge receiver 68 is disposed, and the idle discharge receiver 68 is provided with an opening 69 along the nozzle row direction of the recording head 11.

  In addition, an encoder scale 72 having slits is provided along the main scanning direction on the front side of the carriage 4, and an encoder sensor 73 including a transmission type photosensor that detects the slits of the encoder scale 72 on the front side of the carriage 4. These components constitute a linear encoder 74 for detecting the position of the carriage 4 in the main scanning direction.

  Next, an example of the liquid discharge head constituting the recording head in this image forming apparatus will be described with reference to FIGS. 3 is a cross-sectional explanatory diagram along the longitudinal direction of the liquid chamber of the head, and FIG. 4 is a cross-sectional explanatory diagram of the head along the lateral direction of the liquid chamber (nozzle arrangement direction).

  This liquid discharge head includes, for example, a flow path plate 101 formed by anisotropic etching of a single crystal silicon substrate, a vibration plate 102 formed by, for example, nickel electroforming bonded to the lower surface of the flow path plate 101, a flow path The nozzle plate 103 bonded to the upper surface of the plate 101 is bonded and stacked, and the nozzle communication path 105, the liquid chamber 106, and the liquid chamber 106, which are channels through which the nozzle 104 that discharges droplets (ink droplets) communicates. An ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to the liquid is formed.

  Also, two rows (only one row is shown in FIG. 4) of stacked piezoelectric elements as electromechanical conversion elements that are pressure generating means (actuator means) for deforming the diaphragm 102 to pressurize the ink in the liquid chamber 106. An element 121 and a base substrate 122 to which the piezoelectric element 121 is bonded and fixed are provided. Note that a column portion 123 is provided between the piezoelectric elements 121. This support portion 123 is a portion formed simultaneously with the piezoelectric element 121 by dividing and processing the piezoelectric element member. However, since the drive voltage is not applied, the support portion 123 becomes a simple support.

  Further, an FPC cable 12 equipped with a drive circuit (drive IC) (not shown) is connected to the piezoelectric element 121.

  The peripheral edge of the diaphragm 102 is joined to a frame member 130, and the frame member 130 serves as a through-hole 131 and a common liquid chamber 108 that house an actuator unit composed of the piezoelectric element 121 and the base substrate 122. A recess and an ink supply hole 132 for supplying ink from the outside to the common liquid chamber 108 are formed. The frame member 130 is formed by injection molding with a thermosetting resin such as an epoxy resin or polyphenylene sulfite, for example.

  Here, the flow path plate 101 is formed by, for example, subjecting the single crystal silicon substrate having a crystal plane orientation (110) to anisotropic etching using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so that the nozzle communication path 105, Although a recess or a hole serving as the liquid chamber 106 is formed, the invention is not limited to a single crystal silicon substrate, and other stainless steel substrates, photosensitive resins, and the like can also be used.

  The vibration plate 102 is formed from a nickel metal plate, and is manufactured by, for example, an electroforming method (electroforming method). Alternatively, a metal plate or a joining member between a metal and a resin plate may be used. it can. The piezoelectric element 121 and the support post 123 are bonded to the diaphragm 102 with an adhesive, and the frame member 130 is further bonded with an adhesive.

  The nozzle plate 103 forms a nozzle 104 having a diameter of 10 to 30 μm corresponding to each liquid chamber 106 and is bonded to the flow path plate 101 with an adhesive. The nozzle plate 103 is formed by forming a water repellent layer on the outermost surface of a nozzle forming member made of a metal member via a required layer. The surface of the nozzle plate 103 is the nozzle surface 34a described above.

  The piezoelectric element 121 is a stacked piezoelectric element (here, PZT) in which piezoelectric materials 151 and internal electrodes 152 are alternately stacked. An individual electrode 153 and a common electrode 154 are connected to each internal electrode 152 drawn out to different end faces of the piezoelectric element 121 alternately. In this embodiment, the ink in the liquid chamber 106 is pressurized using the displacement in the d33 direction as the piezoelectric direction of the piezoelectric element 121. However, the pressure in the d31 direction is used as the piezoelectric direction of the piezoelectric element 121. The ink in the liquid chamber 106 may be pressurized. Alternatively, a structure in which one row of piezoelectric elements 121 is provided on one substrate 122 may be employed.

  In the liquid discharge head having such a configuration, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential, the piezoelectric element 121 contracts, and the diaphragm 102 descends to expand the volume of the liquid chamber 106. Then, the ink flows into the liquid chamber 106, and then the voltage applied to the piezoelectric element 121 is increased to extend the piezoelectric element 121 in the stacking direction, and the diaphragm 102 is deformed in the direction of the nozzle 104, so that the volume / volume of the liquid chamber 106 is increased. By contracting the volume, the recording liquid in the liquid chamber 106 is pressurized, and droplets of the recording liquid are ejected (jetted) from the nozzle 104.

  Then, by returning the voltage applied to the piezoelectric element 121 to the reference potential, the diaphragm 102 is restored to the initial position, and the liquid chamber 106 expands to generate a negative pressure. The recording liquid is filled in 106. Therefore, after the vibration of the meniscus surface of the nozzle 104 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Note that the driving method of the head is not limited to the above example (pulling-pushing), and it is also possible to perform striking or pushing depending on the direction to which the driving waveform is given.

  In the image forming apparatus configured as described above, the sheets 22 are separated and fed one by one from the sheet feeding unit, and the sheets 22 fed substantially vertically upward are guided by the guide 25, and the conveyance belt 31 and the counter roller 26, and the leading end is guided by a conveying guide 27 and pressed against the conveying belt 31 by a leading end pressing roller 29, and the conveying direction is changed by approximately 90 °.

  At this time, a positive voltage and a negative output are alternately repeated from the AC bias supply unit (high voltage power supply) to the charging roller 34, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 31 alternates, that is, In the sub-scanning direction, which is the rotation direction, plus and minus are alternately charged in a band shape with a predetermined width. When the sheet 22 is fed onto the conveyance belt 31 that is alternately charged with plus and minus, the sheet 22 is attracted to the conveyance belt 31 by electrostatic force, and the sheet 22 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 31. Is done.

  Therefore, by driving the head 11 according to the image signal while moving the carriage 4, ink droplets are ejected onto the stopped paper 22 to record one line, and after the paper 22 is conveyed by a predetermined amount, the next Record the line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 22 has reached the recording area, the recording operation is finished and the paper 22 is discharged onto the paper discharge tray 40.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 22 is fed into the double-sided paper feeding unit 51 by rotating the conveyor belt 31 in the reverse direction. The paper 22 is reversed (with the back surface being the printing surface), fed again between the counter roller 26 and the conveyor belt 31, controlled in timing, and conveyed by the conveyor bell 31 as described above. After recording on the back surface, the paper is discharged onto the paper discharge tray 40.

Next, the relationship between the nozzle array of the recording head in this image forming apparatus and the color of the liquid droplets to be discharged will be described with reference to FIGS.
As shown in FIG. 5, the recording head in this image forming apparatus is composed of four heads 11a to 11b, and each head 11 has a main scanning direction (the forward path is indicated by arrow a2 and the backward path is indicated by arrow a1). ..) Are arranged in the main scanning direction by arranging nozzle rows N1 and N2 composed of a plurality of nozzles 11n that discharge the droplets arranged in the direction orthogonal to. Here, the nozzles 11n of the nozzle row N1 and the nozzle row N2 are arranged by shifting the pitch between the nozzles 11n (nozzle pitch) by 1/2 pitch in the sub-scanning direction.

  In this case, as shown in FIG. 6, the nozzle row N1 of the head 11a is a nozzle row Y1 that discharges yellow (Y) droplets, and the nozzle row N2 is a nozzle row that discharges magenta (M) droplets. M1 and nozzle rows N1 and N2 of the head 11b are nozzle rows K1 and K2 that discharge black (black) droplets, respectively, and nozzle rows N1 and N2 of the head 11c are respectively cyan (C) droplets. The nozzle rows C1 and C2 are ejected, the nozzle row N1 of the head 11d is a nozzle row M2 that ejects magenta (M) droplets, and the nozzle row N2 is the nozzle row Y2 that ejects yellow (Y) droplets. .

  That is, the four-color configuration of Y, M, C, and K is used, and among these three colors other than yellow, two colors are particularly weak with respect to the positional shift (the image deterioration due to the landing positional shift is large). The nozzle rows that discharge C and K droplets are not divided and arranged in different heads for each color (that is, arranged in the same head), and each of the M colors other than yellow (Y) and two colors (C, K). The nozzle rows for discharging droplets are divided and arranged in different heads.

  In this case, the nozzle rows that eject droplets of two colors (C, K) other than yellow are arranged adjacent to each other by being arranged in the same head.

  Here, focusing only on each nozzle row N1 of each of the heads 11a to 11d of the recording head 11, the recording head 11 is Y, K, C, M from the upstream side in the forward movement direction (direction a2 in FIG. 6). The heads 11a to 11d are arranged in this order. On the other hand, when attention is paid only to the nozzle rows N2 of the heads 11a to 11d of the recording head 11, the heads 11d to 11a are arranged in the order of M, K, C, and Y. That is, the arrangement of Y, M, and C forming the color image is reversed in the nozzle rows N1 and N2.

  When forming an image of a color that uses C, M, Y or K, M, Y at the same time using the recording head 11 configured in this way, the raster formed in the forward path and the backward path is interlaced. By printing, color unevenness due to the difference in the order of printing occurs at a high frequency for each recording raster, and as a result, the image looks visually uniform.

  In this case, a plurality of nozzle rows that discharge droplets of the same color, such as nozzle rows Y1 and Y2, magenta M1 and M2, and cyan C1 and C2, are arranged in a staggered manner with a (1 / nozzle row) pitch shift. Therefore, it is possible to more reliably visually suppress color unevenness during bidirectional printing.

  In this way, it is possible to eject droplets of three or more colors including at least yellow, and the nozzle rows that eject yellow droplets are divided and arranged in different heads, and eject droplets of at least two colors other than yellow. The nozzle row is configured not to be divided and arranged in different heads for each color, or at least three color droplets including yellow can be ejected, and the nozzle rows ejecting yellow droplets are different. The nozzle row that is divided and arranged in the head and discharges droplets of at least two colors other than yellow can be arranged adjacent to each color, so that the bidirectional color difference can be visually reduced. For colors with large image degradation due to landing position misalignment, the nozzle row is not divided into different heads, which facilitates head assembly and Moreover, it is possible to reduce the deterioration of the image due to variations in assembly.

  Particularly, black (black), which has a large image deterioration due to landing position deviation (weak to position deviation), is not divided and arranged in different heads, so that image deterioration due to manufacturing and assembly variations can be further reduced. .

  By the way, when forming an image using two colors other than yellow (here, C and K) in which nozzle rows are not arranged in different heads as described above, as shown in FIG. Unlike the case where neither of K and K is used, the image does not appear to be visually uniform, and band-like unevenness occurs due to the difference in the printing order during bidirectional printing.

  Therefore, as shown in FIG. 8, C and K are not used at the same time, and CMY corresponding to K in addition to C is used for color matching, so that a high frequency is complementarily set for each recording raster as described above. Thus, color unevenness due to the difference in the order of printing can be generated, and an image corresponding to the simultaneous use of C and K can be viewed visually uniformly.

  That is, when an image is formed using a plurality of colors simultaneously, the image is formed without using one of at least two colors other than yellow (here, C and K). By substituting with composite black, it can be made to appear visually uniform, and a desired image can be formed while reducing the color difference.

  By the way, in the case where colors are matched using CMY corresponding to K in addition to C without simultaneously using two colors other than yellow (here, C and K) in which the nozzle rows are not dividedly arranged as shown in FIG. As shown in FIG. 4, when the total amount of ink used reaches the total amount regulation value (the maximum amount of ink that can maintain the image quality), the density is saturated before the maximum gradation is reached.

  Therefore, if the brightness is less than 26, color unevenness due to the difference in the order of placement becomes difficult to visually distinguish. Therefore, the maximum gradation can be obtained by adding (using) K instead of CMY equivalent so as not to exceed the total amount regulation. It is possible to increase the density until the image quality is maintained. In other words, when an image formed using a plurality of colors has a brightness of less than 26, by using at least two colors other than yellow, it is possible to obtain a density up to the maximum gradation without conspicuous visual color unevenness. Will be able to.

  Here, a deviation at the time of landing caused by a positional deviation or the like when the heads 11 a to 11 d are attached to the carriage 4 will be described with reference to FIGS. 10 and 11. FIG. 10 is an explanatory diagram for explaining the head mounting position deviation, and FIG. 11 is an explanatory diagram for explaining the landing position deviation.

  The positions at which the droplets ejected from the nozzles 11n of the heads 11a to 11d land on the recording medium are affected by mounting position shifts when the heads 11a to 11d are mounted on the carriage 4. In this example, there is a displacement amount y1 in the sub-scanning direction between the heads 11a and 11b, and similarly there is a displacement amount y2 in the sub-scanning direction between the heads 11a and 11c, and between the heads 11a and 11d. It is assumed that there is a deviation amount y3 in the sub-scanning direction. Further, it is assumed that the interval (nozzle pitch) of the nozzles 11n is X, and the nozzle rows N1 and N2 are formed in a staggered pattern shifted by (X / 2).

  The droplets ejected from the heads 11a and 11b (Y1, K1 droplets) should land in a straight line in the main scanning direction and land in the sub scanning direction at intervals of the nozzle pitch X. However, due to the influence of displacement of the mounting position with respect to the carriage 4, blurring of the carriage operation at the time of scanning, variation in the ejection direction of each nozzle row, etc., as shown in FIG. A displacement amount y1 ′ is generated in the scanning direction.

  Similarly, as shown in FIG. 11B, the liquid droplets discharged from the heads 11a and 11c (liquid droplets Y1 and C1) are displaced x2 ′ in the main scanning direction and displaced y2 ′ in the sub-scanning direction. As shown in FIG. 11C, the liquid droplets ejected from the heads 11a and 11d (the liquid droplets Y1 and M2) are displaced in the main scanning direction by x3 ′ and displaced by y3 ′ in the sub-scanning direction. Occurs.

  On the other hand, for the liquid droplets ejected from the nozzle row of the same head, the landing position deviation hardly occurs.

  Accordingly, when a mounting position shift occurs between the heads constituting the recording head 11, there is almost no landing position shift for K or C using only the head 11b or the head 11c, but Y using the heads 11a and 11d. When either one of the above-mentioned single color or M single color and C, M, Y, or K are used at the same time, the landing position deviation occurs.

On the other hand, a case where a conventional configuration (referred to as a comparative example) in which the ejection order in the forward path and the backward path is assigned to the nozzle arrays of the heads 11a to 11b is the same will be described with reference to FIG. To do.
In this case, the nozzle row N1 of the head 11a is a nozzle row C1 that discharges cyan (C) droplets, the nozzle row N2 is the nozzle row K1 that discharges black (K) droplets, and the nozzles of the head 11b. The row N1 is a nozzle row M1 that discharges cyan (M) droplets, the nozzle row N2 is a nozzle row Y1 that discharges yellow (Y) droplets, and the nozzle row N1 of the head 11c is a yellow (Y) liquid. A nozzle row Y2 that ejects droplets, a nozzle row N2 is a nozzle row M2 that ejects magenta (M) droplets, a nozzle row N1 of the head 11d is a nozzle row K2 that ejects black (K) droplets, The nozzle row N2 is a nozzle row C2 that discharges cyan (C) droplets.

  Here, as described above, there is a displacement amount y1 in the sub-scanning direction between the heads 11a and 11b, and similarly there is a displacement amount y2 in the sub-scanning direction between the heads 11a and 11c. It is assumed that there is a deviation amount y3 in the sub-scanning direction between 11d and 11d.

  Therefore, the landing position of the liquid droplets to be ejected between the heads 11a and 11b deviates in the main scanning direction due to the influence of this mounting position deviation and the carriage operation fluctuation during scanning, the variation in the ejection direction of each nozzle row, and the like. The amount x1 ′ is shifted by a displacement amount y1 ′ in the sub-scanning direction. Similarly, the landing position of the discharged liquid droplet between the heads 11a and 11c is the displacement amount x2 ′ in the scanning direction and the displacement amount y2 in the sub-scanning direction. Therefore, the landing position of the ejected liquid droplets is shifted by a displacement amount x3 ′ in the main scanning direction and a displacement amount y3 ′ in the sub scanning direction between the heads 11a and 11d.

  For this reason, when a single color of C, M, Y, and K and one of C, M, Y, and K are used at the same time, landing position deviation occurs.

  Therefore, in this head configuration and color assignment, sensory evaluation and colorimetric evaluation are performed on a sample prepared by adjusting landing position deviation, and the result of determining the allowable amount of landing deviation with respect to image quality by sensory evaluation is shown in FIG. It shows.

  As can be seen from this result, the image quality of black (K) and cyan (C) is more susceptible to landing position deviation than magenta (M) and yellow (Y).

  On the other hand, in the configuration according to the above-described embodiment, as described above, the black (K) and cyan (C) single colors, whose image quality is easily affected by the landing position deviation, are ejected from each nozzle row of the same head. Therefore, the landing position deviation hardly occurs (the landing position deviation which does not affect the image quality in the sensory evaluation does not occur), and the head position adjustment becomes unnecessary. From the above evaluation results, the image quality in the required sensory evaluation can be obtained by forming the nozzle rows so that the deviation amount of the landing positions between the nozzle rows of the head is 30 μm or less. That is, in the above-described embodiment, the position adjustment of the heads 11b and 11c is not necessary, and the adjustment mechanism can be simplified and the assembling time can be shortened accordingly, so that the cost can be reduced.

  Further, by adopting the configuration as in the above embodiment, it is possible to simplify the recording liquid supply system for the recording head.

  That is, in the case of the configuration of the above embodiment, as shown in FIG. 14, in order to supply the recording liquid to the yellow (Y) nozzle rows Y1 and Y2 and the magenta (M) nozzle rows M1 and M2. For example, the supply paths 19y and 19m from the yellow sub tank 15y and the magenta sub tank 15m need to be divided into two systems in order to supply the recording liquid to the different heads 11a and 11d. In order to supply the recording liquid to the rows K1, K2 and the cyan (C) nozzle rows C1, C2, for example, the supply paths 19k, 19c from the black sub tank 15k and the cyan sub tank 15c may be one system. . Since the heads for supplying different recording liquids are equipped with the sub tanks 15 for each color, in this example, the heads 11a and 11d are each equipped with two sub tanks 15.

  On the other hand, in the case of the configuration shown in FIG. 12 described above, as shown in FIG. 15, each of the heads 11a to 11d ejects different recording liquids from each nozzle row. Either two supply paths 19 from 15 are required, or each head 11a to 11d is equipped with two sub tanks.

Next, another embodiment of the present invention will be described with reference to FIG.
This embodiment is an example in which recording liquids of four colors C, M, Y, and K are used in the above embodiment, whereas C, M, Y, K, R, G, or C, M, Y , K, R, and B recording liquids are used.
Here, the nozzle row Y1 that discharges yellow (Y) droplets and the nozzle row M1 that discharges magenta (M) droplets are ejected to the head 11a, and the cyan (C) droplets are ejected to the head 11b. The nozzle row C1 and the nozzle row G1 that discharges green (G) droplets (or the nozzle row B1 that discharges blue (B) droplets) and black (black: K) droplets are respectively applied to the head 11c. The nozzle rows K1 and K2 for discharging, the nozzle rows R1 and R2 for discharging red (R) droplets to the head 11d, and the nozzle row G2 for discharging green (G) droplets to the head 11e (or A nozzle row B2) that discharges blue (B) droplets and a nozzle row C2 that discharges cyan (C) droplets, and a nozzle row M2 that discharges magenta (M) droplets to the head 11f and yellow (Y) droplets are ejected The nozzle column Y2 are arranged, respectively.

  Therefore, in this head configuration and color assignment, sensory evaluation and colorimetric evaluation are performed on a sample prepared by adjusting landing position deviation, and the result of determining the allowable amount of landing deviation with respect to image quality by sensory evaluation is shown in FIG. It shows.

  As can be seen from this result, the image quality of black (K) and red (R) is more susceptible to landing position deviation than other colors. Therefore, for these black (K) and red (R), by using the nozzle row of the same head as described above, it becomes difficult to be affected by the landing position deviation, and the image quality is improved.

  Here, the description is given with a four-color or six-color head. However, even when seven or more colors are arranged at the same time, the same effect as that of the above embodiment can be obtained.

Next, another embodiment of an image forming apparatus including an apparatus for discharging droplets according to the present invention will be described with reference to FIGS. 18 is a perspective explanatory view of a carriage portion of the image forming apparatus, and FIG. 19 is a cross-sectional explanatory view of a main part for explaining an example of a liquid discharge head mounted on the carriage.
Here, as shown in FIG. 18, a recording head 211 including a liquid discharge head is mounted on the carriage 4. As shown in FIG. 19, this liquid discharge head includes a discharge energy generator 511 (electrodes for applying a discharge signal to the generator and a protective layer provided on the generator as necessary) are omitted. A flow path forming member 515 that constitutes a side wall of the flow path 513 is stacked on the substrate 512 that is provided, and a nozzle plate 516 having a nozzle 514 formed thereon is stacked on the flow path forming member 515. In this head, as indicated by a one-dot chain line 517, the direction of ink flow to the ejection energy operating portion in the flow path 513 is perpendicular to the opening center axis of the nozzle 514.

  By adopting a configuration such as this liquid ejection head, the energy from the ejection energy generator 511 can be more efficiently converted into the formation of ink droplets and the kinetic energy of the flight, and the meniscus can be quickly restored by supplying ink. This is particularly effective when a heating element is used as the discharge energy generator. In addition, a so-called cavitation phenomenon in which the discharge energy generating body is gradually destroyed by the impact when bubbles that are a problem in the edge shooter disappear can be avoided by the side shooter method. That is, in the side shooter system, when bubbles grow and reach the nozzle, the bubbles are brought into the atmosphere, and the bubbles do not contract due to a temperature drop, so the life of the head is relatively long.

Next, the nozzle array arrangement of the recording head 211 will be described with reference to FIG.
The recording head 211 is arranged with the nozzle rows 216 a to 216 h in the vertical direction in the moving direction (main scanning direction) of the carriage 4. When the nozzle rows 216a to 216h of the recording head 211 are viewed on the side facing the sheet (droplet ejection port side), the nozzle rows 216a to 216h are even rows 216b, 216d with respect to the odd rows 216a, 216c, 216e, 216g. , 216f, 216h are arranged in a staggered manner with a shift of X / 2 pitch. The recording liquids of the same color are ejected from the nozzle arrays 216c and 216d, and 216e and 216f, and the recording liquids of different colors are ejected from the nozzle arrays 216a and 216b and 216g and 216h, respectively.

  Specifically, focusing only on the odd nozzle rows of the recording head 211, the recording head 211 has nozzle rows in the order of Y, K, C, M from the upstream side in the forward movement direction (the direction of arrow a2 in FIG. 20). It becomes the arranged configuration. On the other hand, when paying attention only to the even nozzle rows, the order is M, K, C, and Y, and the arrangement of Y, M, and C forming the color image is reversed in the odd and even nozzle rows.

  With this configuration, in an image printed using C, M, Y or K, M, Y at the same time, printing is performed so that the rasters printed in the forward path and the backward path are interlaced, so that they are complementarily recorded. Color unevenness due to the difference in the order of printing occurs at a high frequency for each raster, and the image looks visually uniform.

  Thus, for the two color nozzle rows other than the yellow nozzle row, the same color nozzle rows are arranged without interposing another color nozzle row therebetween, that is, the same color nozzle rows are adjacent to each other. Since the required nozzle position accuracy and mounting position accuracy are relaxed, the manufacturing yield can be improved and the cost can be reduced.

  In particular, for black (black), which has a large image degradation due to landing position deviation (weak to position deviation), the nozzle position accuracy and mounting accuracy are eased by arranging the nozzle rows adjacent to each other, thereby improving the manufacturing yield. And cost reduction.

  By the way, here again, as described above, since the above does not apply to the simultaneous use of two colors other than yellow (here, C and K), C and K are simultaneously used as shown in FIG. Then, unevenness due to the difference in driving order occurs. Therefore, an image corresponding to the simultaneous use of C and K as shown in FIG. 8 described above by matching colors using CMY corresponding to K in addition to C without using C and K at the same time. Will also look visually uniform.

  In addition, as described above, when two colors other than yellow (here, C and K) are not used at the same time and colors are matched using CMY corresponding to K in addition to C, the total amount of ink used is the total amount regulation value. When this value is reached, the density is saturated before the maximum gradation is reached. Therefore, when the brightness is less than 26, it is difficult to visually identify color unevenness due to the difference in the order of placement. Therefore, as shown in FIG. 9 described above, an image with brightness 26 or more is equivalent to K so as not to exceed the total amount regulation. By adding K in place of CMY, it is possible to increase the density to the maximum gradation and maintain the image quality. In other words, when an image formed using a plurality of colors has a brightness of less than 26, by using at least two colors other than yellow, it is possible to obtain a density up to the maximum gradation without conspicuous visual color unevenness. Will be able to.

  Here, a deviation at the time of landing caused by a deviation at the time of nozzle formation of the recording head 211 will be described with reference to FIGS. 21 and 22. FIG. 21 is an explanatory diagram for explaining the positional deviation at the time of nozzle formation, and FIG. 22 is an explanatory diagram for explaining the landing positional deviation.

  The positions at which the droplets ejected from the nozzle arrays 216a to 216h land on the recording medium are affected by the positional deviation when the nozzle arrays 216a to 216h are formed. Note that the interval (nozzle pitch) between the nozzles 216n is X, and the nozzle rows 216a and 216b (the same applies to the other nozzle rows) are formed in a zigzag pattern shifted by (X / 2).

  The droplets ejected from the nozzle rows 216a and 216b (Y1 and K1 droplets) originally land in a straight line with respect to the main scanning direction, and must land at intervals of the nozzle pitch X in the sub scanning direction. However, due to the influence of nozzle position misalignment, carriage movement blur during scanning, and variations in the ejection direction of each nozzle array, as shown in FIG. A displacement amount y1 ′ is generated in the direction.

  Similarly, the droplets (Y1, C1 droplets) ejected from the nozzle rows 216a and 216e are displaced x2 'in the main scanning direction and displaced y2 in the sub-scanning direction, as shown in FIG. 22B. ′, And the droplets (Y1, M2 droplets) ejected from the nozzle rows 216a and 216g are displaced in the main scanning direction by x3 ′ and displaced in the sub-scanning direction, as shown in FIG. y3 'is generated.

  Therefore, almost no landing deviation occurs in the single colors of C and K, and landing deviation occurs when any of the single colors of Y and M and C, M, Y, and K are used at the same time.

On the other hand, a case where a conventional configuration (referred to as a comparative example) in which a plurality of nozzle arrays are assigned with the same discharge order in the forward path and the backward path will be described with reference to FIG.
In this case, the nozzle row 218a is a nozzle row C1 that discharges cyan (C) droplets, the nozzle row 218b is a nozzle row K1 that discharges black (K) droplets, and the nozzle row 218c is cyan (M). The nozzle row M1 that discharges droplets, the nozzle row 218d is the nozzle row Y1 that discharges yellow (Y) droplets, the nozzle row Y2 that discharges yellow (Y) droplets, and the nozzle row 218f. Is a nozzle row M2 that ejects magenta (M) droplets, nozzle row 218g is a nozzle row K2 that ejects black (K) droplets, and nozzle row 218h2 is a nozzle that ejects cyan (C) droplets Let it be column C2.

  Here, discharge is performed between the nozzle rows 218a and 218c and between the nozzle rows 218b and 218d due to the influence of the deviation of the nozzle row formation position, the carriage operation blur at the time of scanning, the variation in the ejection direction of each nozzle row, and the like. The landing position of the liquid droplet is shifted by a displacement amount x1 ′ in the main scanning direction and a displacement amount y1 ′ in the sub-scanning direction. Similarly, between the nozzle rows 218a and 218e, between 218b and 218f, the landing positions of the ejected liquid droplets are shifted by a displacement amount x2 ′ in the scanning direction and a displacement amount y2 ′ in the sub-scanning direction, and the nozzle row 218a. Between the nozzle row 218g and between the nozzle rows 218b and 219h, the landing positions of the ejected droplets are shifted by a displacement amount x3 ′ in the main scanning direction and a displacement amount y3 ′ in the sub-scanning direction.

  For this reason, when a single color of C, M, Y, and K and one of C, M, Y, and K are used at the same time, landing position deviation occurs.

  Therefore, in this head configuration and color assignment, sensory evaluation and colorimetric evaluation are performed on a sample prepared by adjusting landing position deviation, and the result of determining the allowable amount of landing deviation with respect to image quality by sensory evaluation is shown in FIG. It shows.

  As can be seen from this result, the image quality of black (K) and cyan (C) is more susceptible to landing position deviation than magenta (M) and yellow (Y).

  On the other hand, in the configuration according to the above-described embodiment, as described above, the black (K) and cyan (C) single colors that are easily affected by the landing position deviation are discharged from the adjacent nozzle rows. Landing position deviations are unlikely to occur (the landing position deviations that affect the image quality in sensory evaluation do not occur), and deterioration in image quality due to landing position deviations can be suppressed. From the above evaluation results, the image quality in the required sensory evaluation can be obtained by forming the nozzle rows so that the deviation amount of the landing positions between the nozzle rows of the head is 30 μm or less. In other words, by making the amount of droplet landing position deviation between nozzle rows 30 μm or less, the required nozzle position accuracy and mounting position accuracy are eased, so that the manufacturing yield is improved and the cost is reduced. Is possible.

  Further, by adopting the configuration as in this embodiment, it is possible to simplify the recording liquid supply system for the recording head.

  That is, in the case of the configuration of this embodiment, as shown in FIG. 25, two systems are arranged from the head tanks (or recording liquid cartridges) 215y, 215k, 215c, and 215m to the nozzle rows corresponding to the nozzle rows 216a to 216h. Recording liquid is supplied. In this case, since the black nozzle arrays 216c and 216d and the cyan nozzle arrays 216e and 216f are adjacent to each other, the supply paths for these nozzle arrays are arranged without intersecting with the supply paths for the recording liquids of other colors. it can.

  On the other hand, in the configuration shown in FIG. 23 described above, as shown in FIG. 26, only the yellow nozzle rows are adjacent to each other. It becomes relatively complicated.

Next, another example of this embodiment will be described with reference to FIG. In the above example, the recording liquids of four colors C, M, Y, and K are used, whereas the recording liquids of seven colors C, M, Y, K, R, G, and B are used. It is an example.
Here, the nozzle row Y1 ejects yellow (Y) droplets to the nozzle row 220a, the nozzle row M1 ejects magenta (M) droplets to the nozzle row 220b, and cyan (to the nozzle row 220c. Nozzle row C1 for discharging C droplets, Nozzle row B1 for discharging blue (B) droplets for the nozzle row 220d, and Nozzle row for discharging green (G) droplets for the nozzle row 220e. G1, nozzle rows K1 and K2 for discharging black (K) droplets to the nozzle rows 220f and 220g, and nozzle rows for discharging red (R) droplets to the nozzle rows 10h and 220i, respectively. R1, R2, nozzle row G2 for ejecting green (G) droplets to nozzle row 220j, nozzle row B2 for ejecting blue (B) droplets to nozzle row 220k, and nozzle row 220l to nozzle row 220l The nozzle row C2 that discharges the An (C) droplet, the nozzle row M2 that discharges the magenta (M) droplet to the nozzle row 220m, and the yellow (Y) droplet to the nozzle row 220n are discharged. Nozzle rows Y2 are arranged respectively. FIG. 28 illustrates the assignment of colors to the nozzle rows 222a to 222n of the comparative example.

  That is, the image quality of black (K) and red (R) is more susceptible to landing position deviation than other colors. Thus, for these black (K) and red (R), by using adjacent nozzle rows as described above, it becomes difficult to be affected by the landing position deviation, and the image quality is improved.

  Here, the description is given with a head having a four-color configuration or a seven-color configuration, but the same effects as those of the above embodiments can be obtained even in the case of a head that discharges eight or more colors.

  In the above embodiment, an image forming apparatus having a printer configuration has been described as an example. However, the present invention can be similarly applied to a multifunction type image forming apparatus in which a printer / fax / copier is combined. Further, the present invention can be similarly applied to a recording liquid other than ink, a device that ejects liquid droplets that use liquid, or an image forming apparatus that includes a device that ejects liquid droplets.

1 is an explanatory side view illustrating an overall configuration of a mechanism unit of an image forming apparatus according to the present invention. It is a plane explanatory view of the mechanism part. FIG. 4 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber showing an example of a liquid discharge head constituting the head of the image forming apparatus. FIG. 6 is a cross-sectional explanatory view along the lateral direction of the liquid chamber of the liquid discharge head. FIG. 2 is a schematic explanatory diagram viewed from a nozzle surface side for explaining a head of the image forming apparatus. FIG. 6 is a schematic explanatory diagram for explaining the color assignment. It is explanatory drawing with which it uses for description of a bidirectional | two-way color difference at the time of using only the color arrange | positioned at the same head. It is explanatory drawing with which it uses for description of reduction of a bidirectional | two-way color difference when not using the color arrange | positioned at the same head. It is explanatory drawing with which it uses for description of the relationship between the case where the color arrange | positioned in the same head is not used, and a total amount regulation value. It is a typical explanatory view of a head used for explanation of variation in a head attachment position. It is explanatory drawing similarly used for description of landing position dispersion | variation. It is a typical explanatory view of a head used for explanation of variation in a mounting position of a head in a comparative example. It is explanatory drawing which shows an example of the result of having determined the allowance of the landing deviation with respect to image quality in the case of a 4 color structure by sensory evaluation. It is explanatory drawing with which it uses for description of the recording liquid supply system about the head structure of this invention. It is explanatory drawing with which it uses for description of the recording liquid supply system about the head structure of a comparative example. It is a typical explanatory view of a head for explanation of other embodiments of the present invention. It is explanatory drawing which shows an example of the result of having determined the allowance of the landing deviation with respect to the image quality in the case of 6 color structure by sensory evaluation. FIG. 6 is a perspective explanatory view of a carriage portion for explaining another embodiment of the image forming apparatus according to the present invention. FIG. 3 is an explanatory cross-sectional view of a main part for explaining the recording head of the same embodiment. FIG. 4 is a schematic explanatory diagram for explaining color assignment to a nozzle row of the recording head. It is a typical explanatory view of a head used for explanation of variation in a nozzle formation position of the head. It is explanatory drawing similarly used for description of landing position dispersion | variation. It is a typical explanatory view of a head used for explanation of variation in a nozzle row formation position in a comparative example. It is explanatory drawing which shows an example of the result of having determined the allowance of the landing deviation with respect to image quality in the case of a 4 color structure by sensory evaluation. It is explanatory drawing with which it uses for description of the recording liquid supply system with respect to each nozzle row of the head. It is explanatory drawing with which it uses for description of the recording liquid supply system with respect to each nozzle row of the head of a comparative example. It is typical explanatory drawing with which it uses for description of the example of this invention made into 7 color structure. It is typical explanatory drawing with which it uses for description of the comparative example made into 7 color structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 4 ... Carriage 5 ... Main scanning motor 11 ... Head 11a-11f head N1, N2 ... Nozzle row 22 ... Recording medium (paper)
DESCRIPTION OF SYMBOLS 31 ... Conveyance belt 32 ... Conveyance roller 36 ... Sub scanning motor 121 ... Piezoelectric element 211 ... Recording head 216a-216h, 220a-220n ... Nozzle row

Claims (10)

In an image forming apparatus in which a plurality of nozzle rows capable of ejecting recording liquid droplets are arranged in a plurality of main scanning directions and arranged in a plurality of main scanning directions.
It can eject droplets of four or more colors including at least yellow,
The nozzle row for discharging the yellow droplets is divided and arranged in different heads together with the nozzle row for discharging the other one-color droplets ,
Nozzle rows that eject droplets of at least two colors other than the yellow and the one color are arranged in the same head for each color ,
The nozzle row for discharging the yellow droplets formed on one head and the nozzle row for discharging the other color droplets are arranged so as to be shifted in the nozzle arrangement direction so as not to overlap in the main scanning direction. and has <br/> that the image forming apparatus according to claim. 2. The image forming apparatus according to claim 1, wherein a head having a nozzle row that discharges the yellow droplets and a nozzle row that discharges another one-color droplet includes at least two other than the yellow and the one color. An image forming apparatus, wherein the image forming apparatus is disposed on both outer sides in the main scanning direction with respect to a plurality of heads in which nozzle rows for discharging colored droplets are formed . The image forming apparatus according to claim 1 or 2, before the image forming apparatus characterized by even without Kisukuna one color of the two colors is black. The image forming apparatus according to any one of claims 1 to 3, the image even before Kisukuna without the one color of the two colors is characterized cyan, magenta, red, blue and green that at least either Forming equipment. The image forming apparatus according to any one of claims 1 to 4, a plurality of nozzle rows for discharging liquid droplets of the same color, characterized in that a relationship which is staggered pitch (1 / number of nozzle arrays) Image forming apparatus. The image forming apparatus according to any one of claims 1 to 5, wherein the head is an image forming apparatus, wherein the pressure generating means for generating a pressure for ejecting the droplets are electrothermal transducers. The image forming apparatus according to any one of claims 1 to 5, wherein the head is an image forming apparatus, wherein the pressure generating means for generating a pressure for ejecting the droplets is an electromechanical conversion element.   8. The image forming apparatus according to claim 1, wherein a landing position deviation amount of the discharged droplets between the nozzle rows is 30 [mu] m or less. The image forming apparatus according to any one of claims 1 to 8, when forming an image using a plurality of colors simultaneously, characterized in that it does not use one color of the two colors even before Kisukuna without Image forming apparatus. The image forming apparatus according to claim 9 , wherein when the image to be formed has a brightness of less than 26 , all the at least two colors are used.

Images