JP5660269B2 - Image forming apparatus and image forming program - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming program. More specifically, the present invention relates to an image forming apparatus and an image forming program suitable for reducing banding in an image forming apparatus that performs overlap processing.

  As an image forming apparatus such as a printer (printing apparatus), a facsimile machine, a copying machine, and a multifunction machine of these, for example, a recording head (hereinafter referred to as a recording head) including a liquid discharging head that discharges droplets of a recording liquid (hereinafter also referred to as ink). A recording medium (hereinafter also referred to as paper, but the material is not limited, and the recording medium, medium, transfer material, and recording paper are also used synonymously) using an apparatus including a head) However, there is a so-called ink jet type image forming apparatus in which a recording liquid as a liquid is attached to a sheet to form an image (hereinafter, recording, printing, printing, and printing are also used synonymously).

  Inkjet image forming devices are capable of high-speed recording, can be recorded without requiring special fixing processing on so-called plain paper, and are attracting attention for office use and the like due to the small noise that can be ignored during recording. Various methods have been proposed and put into practical use. Inkjet image formation uses a recording head in which an ink liquid chamber and a nozzle communicating with the ink liquid chamber are formed, and pressure is applied to the ink in the ink liquid chamber in accordance with image information, whereby ink droplets are ejected from the nozzle. It is realized by flying and adhering to a recording medium such as paper or film. Since the image is formed in a non-contact manner, the recording can be performed on various recording media.

  By the way, there is an “image unevenness problem” as a problem that the inkjet image forming apparatus has. For example, in a serial type ink jet printer in which an image is formed by reciprocating the recording head in a direction perpendicular to the paper conveyance direction, a scanning connection part (line feed part) due to various factors such as paper feeding error and head rattling. The dot landing position may be shifted and a streak-like image failure (hereinafter also referred to as banding) may be caused.

  Further, in recent years, an image forming apparatus that has improved the printing speed by connecting a plurality of recording heads in the nozzle row direction (hereinafter also referred to as a connecting head method), and the recording head is arranged with a length that reaches the paper width. There has been proposed a line-type inkjet printer that forms an image by conveying a sheet in a direction orthogonal to the nozzle array. In these apparatuses, banding occurs in a region where the end portions of the recording head overlap (referred to as an overlap region and a head connecting portion) due to factors such as head assembly errors and head ejection characteristic differences. Since the phenomenon that occurs on the paper is the same between the head connecting portion and the scan line feed portion, the head connection portion will be described below in this specification unless otherwise specified. The same applies to the case of.

  For example, when the head joint is shifted in the direction away from the ideal position, the dot formation density of the head joint is sparse, and when the white stripe is shifted in the approaching direction, the dot formation at the head joint is formed. The density becomes dense and black streaks occur. The black and white streaks in the present specification are mainly shading unevenness caused by the landing of dots deviating from the ideal position. Black streaks with a higher density than the surroundings are black streaks, and the density is higher than the surroundings. Low streaks are described as white streaks and do not refer to color.

  In order to solve this, an overlap processing technique has been proposed. This is because the adjacent heads or scan ends overlap each other at the head joint and the line feed part of the scan, and dots are formed by overlapping multiple nozzles to disperse the dot arrangement at the joint, making streaks less noticeable. It is a technology that overlaps the head or scan ends with the head joint and scan line feed, and scatters dots from the overlapping nozzles to scatter the dots at the joint (new line), thereby reducing banding. Technology. For example, Patent Document 1 discloses that the first and second head chips in which the recording element arrays are arranged have a part of the recording area in the overlapping portion where the ends of the recording element arrays overlap each other. A recording apparatus having a recording head formed by both recording elements of a head chip is disclosed.

  However, in the technique described in Patent Document 1, while a plurality of heads are arranged in an overlapping manner, a part of the overlap portion is recorded by a plurality of heads, but is discharged from the plurality of heads. When there is no landing deviation in the ejected droplets, there is a problem that black stripes are caused due to an excessive amount of overlap. Further, in the technique described in Patent Document 1, the nozzle distribution amount decreases from the overlap start point to the end point. However, the effect is difficult to exert unless the ink amount is gently inclined. If the number of nozzles to be wrapped is not increased, the effect cannot be obtained. If this is implemented, the serial method leads to a decrease in productivity due to an increase in the number of scans, and the line method leads to an increase in cost due to an increase in the number of necessary heads. Furthermore, since the used nozzles in the overlap region are biased, there is a problem that the dispersibility is lost and it is impossible to reduce the streak caused by the jet bending.

  Further, according to the conventionally proposed overlap processing, there is a certain effect in reducing banding, but at the boundary portion between the overlap region where the overlap processing is performed and the non-overlap region where this is not performed, Since the dot formation density is likely to change, there is still a problem that streaks are still noticeable. In order to improve the streak at the boundary part, it may be possible to increase or reduce the amount of droplets at the end. According to this, one of the black and white lines is improved, but the other is deteriorated. I will.

  Therefore, the present invention has a recording head having a plurality of nozzles for discharging a recording liquid, and a part of the recording head overlaps at the time of scanning or a plurality of recording heads for discharging a recording liquid. In an image forming apparatus that includes a plurality of recording heads having nozzles, and at least two recording heads form an overlapping area by overlapping a part of the recording heads, in an area other than the end of the overlapping area, The print data is distributed to the nozzles of each recording head constituting the area other than the end, and in the end area of the overlap area, the print data corresponds to the print data to the nozzles of each recording head constituting the end area. By converting and setting the data corresponding to the droplet volume smaller than the recording liquid droplet volume, the banding is reduced, especially the overlap area and non-overlapping. And to provide an image forming apparatus and an image forming program capable of reducing banding at a boundary portion between the wrap area.

In order to achieve such an object, the image forming apparatus according to claim 1 includes a recording head having a plurality of nozzles for discharging a recording liquid, and a part of the recording head overlaps during scanning. Or an image forming apparatus having a plurality of recording heads each having a plurality of nozzles for discharging recording liquid, wherein at least two recording heads constitute an overlap region by overlapping a part of the recording heads , in a region other than the end portions in the overlap region, for the nozzles of each recording head constituting the area other than the end portion, it distributes sets the print data to be exclusively between the recording head in the scanning line, the end regions in the overlap region, for the nozzles of each recording head constituting the end portion region, the print data, droplet amount that corresponds to the indicia character data In which a control means for setting into a drop size down data smaller drop volume.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, one of the two recording heads constituting the overlap region is a first recording head and the other is a second recording head, and the control means If there is print data on the head end side of the first recording head in an area other than the end, drop size down data is set in the end area on the head end side, and if there is no print data, Similarly to the area other than the end area, the print data is distributed and set exclusively in the end area, and when print data is present on the head end side of the second recording head in the area other than the end area, Drop size reduction data is set in the end area on the head end side, and when there is no print data, the print data is exclusively distributed to the end area as in the areas other than the end. is there.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , the control means determines the amount of the recording liquid attached to each pixel in the end region of the overlap region. This is equivalent to the recording liquid adhesion amount corresponding to each pixel in the overlap region.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the control means corresponds to the droplet amount with the smallest print data in the end region of the overlap region. In this case, droplet size down data corresponding to the minimum droplet amount is set to any one nozzle corresponding to the print data.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect of the invention, the control means sets the end of the overlap region with respect to the ratio of the drop size down data corresponding to the minimum drop amount. The ratio of the print data sorting inside each recording head is increased between the end side of each recording head in the region and the inside of each recording head.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth or fifth aspect , the control means sets any one nozzle corresponding to the print data to a total discharge amount from each nozzle. Are selectively set so as to be equivalent.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, when the control unit detects that the overlap area is different from the assumed width, The conversion contents of the print data in the end area of the wrap area are changed.

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the control means sets the detected or set internal temperature and humidity, the type of recording medium, and the print mode. Accordingly, the conversion content of the print data in the end area of the overlap area is changed.

The image forming program according to claim 9 includes a recording head having a plurality of nozzles for discharging a recording liquid, and a part of the recording head overlaps at the time of scanning. There are a plurality of recording heads having a plurality of nozzles for discharging liquid, and at least two recording heads are arranged in an overlapping area in an image forming apparatus that forms an overlapping area by overlapping a part of the recording heads . in the region other than the end portion, for the nozzles of each recording head constituting the area other than the end portion, and partitioned set to be exclusively between the recording head in the print data scan line, the end in the overlap region the section area for the nozzles of each recording head constituting the end portion region, the print data, and a smaller drop volume than the droplet amount that corresponds to the indicia character data droplets Izudaun those to execute a process of setting to convert the data.

  According to the present invention, with a simple configuration, it is possible to reduce banding in the overlap processing, in particular, it is possible to reduce banding at a boundary portion between the overlap region and the non-overlap region.

1 is a side view illustrating an example of a configuration of an image forming apparatus according to the present invention. 1 is a plan view illustrating an example of a configuration of an image forming apparatus. FIG. 3 is a cross-sectional view (a liquid chamber longitudinal direction) illustrating an example of a recording head. FIG. 4 is a cross-sectional view (a liquid chamber short direction) illustrating an example of a recording head. It is a block diagram which shows the outline | summary of a control part. It is a block diagram which shows an example of a printing control part. It is explanatory drawing which shows an example of the drive waveform produced | generated and output by the drive waveform production | generation part of a printing control part. It is explanatory drawing which shows each the drive pulse selected in the case of forming a small droplet, a medium droplet, and a large droplet among the drive waveforms produced | generated and output by the drive waveform generation part of a printing control part, and a fine drive. It is explanatory drawing which shows the difference in the drive waveform by the viscosity of a recording liquid. 1 is a block explanatory diagram illustrating an example of an image forming system configured by an image forming apparatus. 1 is an explanatory block diagram illustrating an example of an image processing apparatus in an image forming system configured by the image forming apparatus. It is a block diagram which shows an image processing part roughly. It is explanatory drawing which shows the example of the printing data distribution of an overlap area | region. It is a graph which shows the change of the ejection droplet amount by a drive frequency. It is explanatory drawing which shows an example of the head connection part of two recording heads. It is explanatory drawing which shows an example of an overlap area | region. It is a flowchart which shows an example of the printing control of an overlap area | region. It is explanatory drawing which shows an example of the total ink adhesion amount by a connection head. It is explanatory drawing of the reduction effect of the banding in an edge part area | region. It is explanatory drawing which shows an example of the printing control of an overlap area | region. It is explanatory drawing which shows the other example of printing control of an overlap area | region. FIG. 6 is an explanatory diagram of a state of printing by a line type image forming apparatus. It is explanatory drawing which shows an example of the banding in a scan line feed part. It is explanatory drawing which shows the other example of printing control of an overlap area | region. It is explanatory drawing which shows the other example of printing control of an overlap area | region. It is explanatory drawing which shows the other example of printing control of an overlap area | region. It is explanatory drawing which shows the example which determines the structure pattern of a dot using the chart for a shift | offset | difference determination. It is explanatory drawing which shows the example which determines the structure pattern of a dot using the printing result of a ruled line. It is explanatory drawing which shows the example which determines the structure pattern of a dot using the printing result at the time of changing a dot structure.

  Hereinafter, the configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

(Configuration of image forming apparatus)
1 and 2 are diagrams illustrating an example of an image forming apparatus according to the present embodiment. FIG. 1 is a side explanatory view of the overall configuration of the mechanism unit, and FIG. 2 is a plan explanatory diagram of the mechanism unit.

  An image forming apparatus holds a carriage 3 slidably in a main scanning direction by a guide rod 1 and a guide rail 2 which are guide members horizontally mounted on left and right side plates (not shown), and serves as a main scanning motor as a recording head scanning unit. In FIG. 2, the moving scanning is performed in the direction indicated by the arrow (main scanning direction) in FIG. 2 via the timing belt 5 stretched between the driving pulley 6A and the driven pulley 6B. The carriage 3 includes, for example, four recording heads 7y, 7c, 7m, and 7k including liquid ejection heads that eject ink droplets of yellow (Y), cyan (C), magenta (M), and black (K), respectively. A plurality of ink ejection openings are arranged in a direction crossing the main scanning direction and the ink droplet ejection direction is directed downward. The carriage 3 is equipped with sub-tanks 8 for each color for supplying ink of each color to the recording head 7. Ink is supplied to the sub tank 8 from a main tank (ink cartridge) (not shown) via an ink supply tube 9.

  The liquid discharge head constituting the recording head 7 includes a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses a phase change caused by liquid film boiling using an electrothermal transducer such as a heating resistor, and a metal phase change caused by a temperature change. A shape memory alloy actuator using an electrostatic force, an electrostatic actuator using an electrostatic force, and the like provided as pressure generating means for generating a pressure for discharging a droplet can be used. In addition, the configuration is not limited to an independent head for each color, and may be configured with one or a plurality of liquid ejection heads having a nozzle row composed of a plurality of nozzles that eject droplets of a plurality of colors.

  Further, in the present embodiment, as shown in FIG. 15, the recording heads are arranged such that a plurality of heads are arranged substantially in series in the sub-scanning direction, and the respective heads are overlapped with each other at the connecting portion of each head. Configured. Further, the head having the configuration shown in FIG. 15 can be further connected to form a full line head. At this time, the direction in which the heads are connected may be either the main scanning direction or the sub-scanning direction.

  On the other hand, as a paper feeding unit for feeding paper 12 stacked on a paper stacking unit (pressure plate) 11 such as a paper feeding cassette 10, a half-moon roller (for separating and feeding the paper 12 one by one from the paper stacking unit 11) A separation pad 14 made of a material having a large friction coefficient is provided facing the sheet feeding roller 13 and the sheet feeding roller 13, and the separation pad 14 is urged toward the sheet feeding roller 13 side.

  Then, as conveying means for conveying the sheet 12 fed from the sheet feeding unit below the recording head 7, a conveying belt 21 for electrostatically attracting and conveying the sheet 12 and a guide 15 from the sheet feeding unit. The counter roller 22 for transporting the paper 12 sent via the belt sandwiched between the transport belt 21 and the paper 12 fed substantially vertically upward is changed by approximately 90 ° so as to follow the transport belt 21. For this purpose, a conveying guide 23 and a pressing roller 25 urged toward the conveying belt 21 by a pressing member 24 are provided. In addition, a charging roller 26 as a charging unit for charging the surface of the transport belt 21 is provided.

  Here, the conveyance belt 21 is an endless belt, is stretched between the conveyance roller 27 and the tension roller 28, and the conveyance roller 27 rotates from the sub-scanning motor 31 via the timing belt 32 and the timing roller 33. By doing so, it is configured to circulate in the belt conveyance direction (sub-scanning direction) of FIG. A guide member 29 is disposed on the back side of the conveying belt 21 corresponding to the image forming area by the recording head 7. The charging roller 26 is disposed so as to come into contact with the surface layer of the transport belt 21 and rotate following the rotation of the transport belt 21.

  Further, as shown in FIG. 2, a slit disk 34 is attached to the shaft of the transport roller 27, and a sensor 35 for detecting the slit of the slit disk 34 is provided. A rotary encoder 36 is configured.

  Further, as a paper discharge unit for discharging the paper 12 recorded by the recording head 7, a separation claw 51 for separating the paper 12 from the transport belt 21, a paper discharge roller 52 and a paper discharge roller 53, and a discharge And a paper discharge tray 54 for stocking the paper 12 to be printed.

  A double-sided paper feeding unit is detachably attached to the back. This double-sided paper feeding unit takes in the paper 12 returned by the reverse rotation of the conveying belt 21, reverses it, and feeds it again between the counter roller 22 and the conveying belt 21.

  Further, as shown in FIG. 2, a maintenance / recovery mechanism 56 for maintaining and recovering the nozzle state of the recording head 7 is disposed in the non-printing area on one side of the carriage 3 in the scanning direction. The maintenance / recovery machine 56 is provided with caps 57 for capping each nozzle surface of the recording head 7, a wiper blade 58 as a blade member for wiping the nozzle surface, and for discharging the thickened recording liquid. An empty discharge receiver 59 for receiving droplets when performing empty discharge for discharging droplets that do not contribute to recording is provided.

  In the image forming apparatus configured as described above, the sheets 12 are separated and fed one by one from the sheet feeding unit, and the sheet 12 fed substantially vertically upward is guided by the guide 15, and includes the transport belt 21 and the counter roller 22. The leading end is guided by the conveying guide 23 and pressed against the conveying belt 21 by the pressing roller 25, and the conveying direction is changed by approximately 90 °. At this time, a control unit (not shown) applies an alternating voltage that alternately repeats positive and negative to the charging roller 26 from the AC bias supply unit, and a charging voltage pattern that alternates the conveying belt 21, that is, a sub-scanning direction that is a circumferential direction. In addition, charging is performed with a pattern in which plus and minus are alternately repeated with a predetermined width. When the paper 12 is fed onto the charged transport belt 21, the paper 12 is attracted to the transport belt 21 by electrostatic force, and the paper 12 is transported in the sub-scanning direction by the circular movement of the transport belt 21.

  Therefore, by driving the recording head 7 according to the image signal while moving the carriage 3 in the forward and backward directions, ink droplets are ejected onto the stopped paper 12 to record one line. After transporting a predetermined amount, the next line is recorded. Upon receiving a recording end signal or a signal that the trailing edge of the paper 12 has reached the recording area, the recording operation is finished and the paper 12 is discharged onto the paper discharge tray 54.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 12 is fed into the double-sided paper feeding unit 61 by rotating the conveyor belt 21 in the reverse direction. The paper 12 is reversed (with the back surface being the printing surface), fed again between the counter roller 22 and the transport belt 21, controlled in timing, and transported onto the transport belt 21 as described above. Then, after recording on the back surface, the paper is discharged onto the paper discharge tray 54.

  Further, during printing standby, the carriage 3 is moved to the maintenance / recovery mechanism 56 side, and the nozzle surface of the recording head 7 is capped by the cap 57 to keep the nozzles in a wet state, thereby preventing ejection failure due to ink drying. . In addition, the recording liquid is sucked from the nozzle in a state where the recording head 7 is capped by the cap 57, and a recovery operation is performed to discharge the thickened recording liquid and bubbles, and the ink adhered to the nozzle surface of the recording head 7 by this recovery operation. Wiping is performed with a wiper blade 58 in order to remove the cleaning. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. Thereby, the stable ejection performance of the recording head 7 is maintained.

  Next, an example of the liquid discharge head constituting the recording head 7 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 A nozzle plate 103 joined to the upper surface of the plate 101 is joined and laminated, and a nozzle communication path 105 that is a flow path through which a nozzle 104 that discharges droplets (ink droplets) communicates therewith and a liquid chamber that is a pressure generation chamber. 106, an ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to the liquid chamber 106 through a fluid resistance portion (supply path) 107 is formed.

  In addition, two rows (only one row is shown in FIG. 3) of stacked piezoelectric elements as electromechanical conversion elements that are pressure generating means (actuator means) for pressurizing the ink in the liquid chamber 106 by deforming the diaphragm 102. 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 126 mounted 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 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.

  Next, an outline of a control unit as a control unit of the image forming apparatus will be described with reference to the block diagram of FIG. The control unit 200 includes a CPU 201 that controls the entire apparatus, a ROM 202 that stores programs executed by the CPU 201 and other fixed data, a RAM 203 that temporarily stores image data and the like, and a power source for the apparatus. A rewritable non-volatile memory (NVRAM) 204 for holding data in the meantime, an ASIC 205 for processing various signal processing and rearrangement for image data, and other input / output signals for controlling the entire apparatus And.

  The control unit 200 also includes a host I / F 206 for transmitting and receiving data and signals to and from the host side, a data transfer unit for driving and controlling the recording head 7, and a drive waveform generating unit for generating a drive waveform. A print control unit 207 including the head driver (driver IC) 208 for driving the recording head 7 provided on the carriage 3 side, a motor driving unit 210 for driving the main scanning motor 4 and the sub-scanning motor 31, An AC bias supply unit 212 that supplies an AC bias to the charging roller 26, I / O 213 for inputting detection signals from encoder sensors 43 and 35, and detection signals from various sensors such as a temperature sensor that detects environmental temperature. Etc. The control unit 200 is connected to an operation panel 214 for inputting and displaying information necessary for the apparatus.

  Here, the control unit 200 receives image data from a host such as an image (information) processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera via a cable or a network. Received at / F206.

  Then, the CPU 201 of the control unit 200 reads and analyzes the print data in the reception buffer included in the I / F 206, performs necessary image processing, data rearrangement processing, and the like in the ASIC 205, and this image data is head-driven. The data is transferred from the control unit 207 to the head driver 208. Note that the generation of dot pattern data for outputting an image is performed by a printer driver on the host side as will be described later.

  The print control unit 207 transfers the above-described image data to the head driver 208 as serial data, and transmits a transfer clock, a latch signal, a droplet control signal (mask signal), and the like necessary for the transfer of the image data and confirmation of the transfer. In addition to the output to the head driver 208, a drive waveform generator and a head driver composed of a D / A converter, a voltage amplifier, a current amplifier, etc. for D / A converting the pattern data of the drive signal stored in the ROM Drive waveform selection means for generating a drive waveform composed of one drive pulse (drive signal) or a plurality of drive pulses (drive signal) and outputting the drive waveform to the head driver 208.

  The head driver 208 selectively selects droplets of the recording head 7 based on image data corresponding to one line of the recording head 7 input serially, and forms a driving signal provided from the print control unit 207. The recording head 7 is driven by applying it to a driving element (for example, a piezoelectric element as described above) that generates energy to be discharged. At this time, by selecting a driving pulse constituting the driving waveform, for example, dots having different sizes such as large droplets (large dots), medium droplets (medium dots), and small droplets (small dots) can be distinguished. it can.

  Further, the CPU 201 detects a speed detection value and a position detection value obtained by sampling a detection pulse from the encoder sensor 43 constituting the linear encoder, and a speed target value and a position target value obtained from a previously stored speed / position profile. Based on this, a drive output value (control value) for the main scanning motor 4 is calculated, and the main scanning motor 4 is driven via the motor driving unit 210. Similarly, based on the speed detection value and position detection value obtained by sampling the detection pulse from the encoder sensor 35 constituting the rotary encoder, and the speed target value and position target value obtained from the previously stored speed / position profile. Then, a drive output value (control value) for the sub-scanning motor 31 is calculated, and the sub-scanning motor 31 is driven via the motor driver 210 and the motor driver.

  Next, an example of the print control unit 207 and the head driver 208 will be described with reference to FIG. As described above, the print control unit 207 generates a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within one printing cycle, and outputs a print waveform. And a data transfer unit 302 that outputs a clock signal, a latch signal (LAT), and droplet control signals M0 to M3.

  The droplet control signal is a 2-bit signal that instructs each droplet to open and close an analog switch 315, which will be described later, of the head driver 208. The droplet control signal is a waveform to be selected in accordance with the print cycle of the common drive waveform. State transition is made to level (ON), and state transition is made to L level (OFF) when not selected.

  The head driver 208 receives a transfer clock (shift clock) and serial image data (gradation data: 2 bits / CH) from the data transfer unit 302, and each register value of the shift register 311 by a latch signal. A latch circuit 312 for latching, a decoder 313 that decodes gradation data and control signals M0 to M3 and outputs the result, and a logic level voltage signal of the decoder 313 is converted to a level at which the analog switch 315 can operate. Level shifter 314, and an analog switch 315 that is turned on / off (opened / closed) by the output of the decoder 313 provided via the level shifter 314.

  The analog switch 315 is connected to the selection electrode (individual electrode) 154 of each piezoelectric element 121, and the common drive waveform from the drive waveform generation unit 301 is input thereto. Therefore, when the analog switch 315 is turned on in accordance with the result of decoding the serially transferred image data (gradation data) and the control signals MN0 to MN3 by the decoder 313, a required drive signal constituting the common drive waveform is obtained. Passing (selected) is applied to the piezoelectric element 121.

  Here, ink that is a recording liquid used in the image forming apparatus will be described. In the image forming apparatus according to the present invention, even when printing on plain paper by using an ink configuration comprising at least a pigment, a water-soluble organic solvent, a polyol or glycol ether having 8 or more carbon atoms, and water, (1 ) Good color tone (sufficient color developability and color reproducibility), (2) High image density, (3) Clear image quality without feathering or color bleeding phenomenon on characters and images, and (4) Double-sided printing Achieves high-quality images with high durability such as (5) high ink dryness (fixability) suitable for high-speed printing, and (6) light fastness and water resistance. Image density, color developability, color reproducibility, character blur, color boundary blur, double-sided printability, fixability, and the like can be greatly improved.

  Next, an example of a driving waveform preferable when such ink is used will be described with reference to FIGS.

  As shown in FIG. 7, the drive waveform generator 301 is fair within one printing cycle (one drive cycle), such as a waveform element that falls from the reference potential Ve and a waveform element that rises from the state after the fall. A drive signal (drive waveform) composed of eight drive pulses P1 to P8 is generated and output. On the other hand, the driving pulse to be used is selected by the droplet control signals M0 to M3 from the data transfer unit 302.

  Here, the waveform element in which the potential V of the drive pulse falls from the reference potential Ve is a drawing waveform element in which the piezoelectric element 121 contracts and the volume of the pressurized liquid chamber 106 expands. Further, the waveform element that rises from the state after the fall is a pressurizing waveform element that causes the piezoelectric element 121 to expand and the volume of the pressurized liquid chamber 106 to contract.

  Then, when forming a small droplet (small dot) by the droplet control signals M0 to M3 from the data transfer unit 302, the drive pulse P1 is selected as shown in FIG. 8A to form a medium droplet (medium dot). When driving, the driving pulses P4 to P6 are selected as shown in FIG. 8B, and when forming large droplets (large dots), the driving pulses P2 to P8 are selected as shown in FIG. When the meniscus is vibrated without droplet ejection, the fine drive pulse P2 is selected as shown in FIG. 8D and applied to the piezoelectric element 121 of the recording head 7 respectively.

  When forming a medium droplet, the first droplet is ejected by the drive pulse P4, the second droplet is ejected by the drive pulse P5, and the third droplet is ejected by the drive pulse P6. At this time, if the natural vibration period of the pressure chamber (liquid chamber 106) is Tc, the interval between the ejection timings of the drive pulses P4 and P5 is preferably 2Tc ± 0.5 μs. Since the drive pulses P4 and P5 are configured by simple strike waveform elements, if the drive pulse P6 is also set to the same simple strike waveform element, the ink droplet velocity becomes too large, and the landing positions of other droplet types are affected. There is a risk of shifting. Therefore, the drive pulse P6 reduces the pull-in voltage (decreasing the falling potential) to reduce the meniscus pull-in and suppress the ink drop speed of the third drop. However, the startup voltage is not reduced in order to increase the necessary ink droplet volume.

  That is, in the drawing waveform element of the final drive pulse among the plurality of drive pulses, by reducing the drawing voltage relatively, the droplet discharge speed by the final drive pulse is relatively reduced, and the landing position is set to other droplets. It can be combined with the seed as much as possible.

  The fine drive pulse P2 is a drive waveform that vibrates the meniscus without ejecting ink droplets in order to prevent drying of the meniscus of the nozzle. This fine driving pulse P2 is applied to the recording head 7 in the non-printing area. In addition, by using the drive pulse P2 which is the fine drive waveform as one of the drive pulses constituting the large droplet, it is possible to achieve a shortened (higher speed) drive cycle.

  Furthermore, by setting the interval between the ejection timings of the fine drive pulse P2 and the drive pulse P3 within the range of the natural vibration period Tc ± 0.5 μs, the volume of ink droplets ejected by the drive pulse P3 can be increased. In other words, by superimposing the expansion of the pressurized liquid chamber 6 by the drive pulse P3 on the pressure vibration of the pressurized liquid chamber 106 by the vibration cycle generated by the fine drive pulse P2, the droplet volume of the droplet that can be ejected by the drive pulse P3 is driven. It can be made larger than when applying P3 alone.

  Since the required drive waveform differs depending on the viscosity of the ink, in this image forming apparatus, as shown in FIG. 9, the drive waveform when the ink viscosity is 5 mPa · s, the same when the viscosity is 10 mPa · s. A drive waveform, similarly a drive waveform at 20 mPa · s, is prepared, and the ink viscosity is determined from the temperature detected by the temperature sensor, and the drive waveform to be used is selected.

  That is, when the ink viscosity is small, the voltage of the drive pulse is relatively small, and when the ink viscosity is large, the voltage of the drive pulse is relatively large. The volume can be discharged substantially constant. Further, the driving pulse can vibrate the meniscus without ejecting ink droplets by selecting the peak value according to the ink viscosity.

  By using a drive waveform composed of such drive pulses, it is possible to control the time until each large, medium, and small droplet lands on the paper, and the ejection start time differs for each large, medium, and small droplet. In addition, each drop can be landed at substantially the same position.

(Configuration of image forming system)
Next, referring to FIG. 10 for an embodiment of an image forming system that executes an image forming program according to the present invention stored in an image processing apparatus connected to the image forming apparatus and outputs a print image by the image forming apparatus. To explain. The image forming system includes one or a plurality of image processing apparatuses 400 such as a personal computer (PC) and an ink jet printer (image forming apparatus) 500 connected by a predetermined interface or network.

  As shown in FIG. 11, in the image processing apparatus 400, a CPU 401 and various ROMs 402 and RAM 403, which are memory means, are connected by a bus line. The bus line is connected to a storage device 406 using a magnetic storage device such as a hard disk, an input device 404 such as a mouse and a keyboard, a monitor 405 such as an LCD or a CRT, and the like via a predetermined interface. A storage medium reading device for reading a storage medium such as an optical disk is connected, and a predetermined interface (external I / F) 407 for communicating with a network such as the Internet or an external device such as a USB is connected.

  An image processing program including an image forming program according to the present invention is stored in the storage device 406 of the image processing apparatus 400. The image processing program is installed in the storage device 406 by being read from a storage medium by a storage medium reader or downloaded from a network such as the Internet. With this installation, the image processing apparatus 400 becomes operable to perform the following image processing. Note that the image processing program may operate on a predetermined OS. Further, it may be a part of specific application software.

  The image forming method (banding reduction method) described below can be performed on the ink jet printer side. In this example, the ink jet printer 500 side receives an image drawing or character print command in the apparatus. A description will be given of an example that does not have a function of generating a dot pattern to be actually recorded. That is, a print command from application software or the like executed by the image processing apparatus 400 serving as a host is subjected to image processing by a printer driver incorporated as software in the image processing apparatus 400 and can be output by the inkjet printer 500. An example in which dot pattern data (print image data) is generated, rasterized, transferred to the inkjet printer 500, and the inkjet printer 500 is printed out will be described.

  Specifically, in the image processing apparatus 400, an image drawing or character recording command from an application or operating system (for example, a description of the position and thickness and shape of a line to be recorded, a typeface of a character to be recorded, and the like) (Which describes the size, position, etc.) is temporarily stored in the drawing data memory. Note that these instructions are written in a specific print language.

  The command stored in the drawing data memory is interpreted by the rasterizer, and if it is a line recording command, it is converted into a recording dot pattern according to the designated position and thickness, etc. If there is, the outline information of the corresponding character is read from the font outline data stored in the image processing apparatus 400 and converted into a recording dot pattern corresponding to the designated position and size. Is converted to the pattern.

  Thereafter, these recorded dot patterns are subjected to image processing and stored in the raster data memory. At this time, the image processing apparatus 400 rasterizes the recording dot pattern data with the orthogonal grid as the basic recording position. Examples of the image processing include color management processing (CMM) for adjusting colors, γ correction processing, halftone processing such as dithering and error diffusion, further background removal processing, and total ink amount regulation processing. The recorded dot pattern stored in the raster data memory is transferred to the inkjet printer 500 via the interface.

  In the present embodiment, as the image forming method, so-called one-pass printing in which an image is formed on the recording medium by one main scanning may be used, or the same nozzle group or the same region of the recording medium may be used. So-called multi-pass printing in which images are formed by performing main scanning a plurality of times with different nozzle groups may be used. Further, the heads may be arranged in the main scanning direction and the same area may be divided by different nozzles. These recording methods can be used in appropriate combination.

  Hereinafter, multi-pass printing will be described. Here, a case where an image is completed by executing four main recording scans (four passes) for one recording area will be described as an example.

  FIG. 12 is a block diagram schematically showing the image processing unit 600 of the present embodiment. In the figure, 601 is an input terminal, 602 is a recording buffer, 603 is a pass number setting unit, 604 is a mask processing unit, 605 is a mask pattern table, 606 is an overlap dot control unit, 607 is a head I / F unit, and 608 is A recording head is shown.

  The bitmap data input from the input terminal 601 is stored at a predetermined address in the recording buffer 602 by the recording buffer control unit. The recording buffer 602 has a capacity capable of storing bitmap data for one scan and the paper feed amount, and constitutes a ring buffer in paper feed amount units such as a FIFO memory. The recording buffer control unit controls the recording buffer 602. When bitmap data for one scan is stored in the recording buffer 602, the printer engine is activated, and the recording buffer 602 determines the position of each nozzle of the recording head 608 from the recording buffer 602. The bitmap data is read and input to the pass number setting unit 603. When bitmap data for the next scan is input from the input terminal 601, the recording buffer 602 is controlled so as to be stored in an empty area of the recording buffer 602 (an area corresponding to the paper feed amount for which recording has been completed).

  Next, the path number setting unit 603 determines the number of divided paths and outputs the number of paths to the mask processing unit 604. In the mask pattern table 605, a necessary mask pattern is determined according to the number of divided passes determined from a mask pattern table stored in advance, for example, a mask pattern for 1-pass printing, 2-pass printing, 4-pass printing, and 8-pass printing. Select and output to the mask processing unit 604. Further, the mask processing unit 604 masks the bitmap data stored in the recording buffer 602 for each pass recording using a mask pattern, and an overlap area is controlled by an overlap dot control unit 606 (details will be described later). When the dot pattern of the inner end region and the other region is generated and output to the head driver 607, the head driver 607 rearranges the masked bitmap data in the order in which the recording head 608 uses them. Forward.

  By using multi-pass printing in this way, banding that stands out in one-pass printing can be averaged and made inconspicuous.

<Banding reduction control>
(Method by drive frequency control)
Next, a banding reduction method by controlling the drive frequency will be described. Examples of means for increasing the printing speed include the one-pass printing as described above, the connection head type, and the line type image forming apparatus. However, in one-pass printing, banding due to misalignment of the paper feed amount or banding due to misalignment of the head connecting portion occurs when a plurality of heads are arranged in the sub-scanning direction to lengthen the nozzle group. As described above, as a method for suppressing banding, there is a method in which part of the nozzles is overlapped, that is, the dot deviation is dispersed by distributing print data to each nozzle.

  In the overlap region, there are two nozzles corresponding to one dot on the data, so if no treatment is made, dots are hit from two nozzles for one dot on the data. Therefore, there is a problem that the color becomes dark at the overlap portion and banding occurs. On the other hand, the method of distributing the print data of the overlap area to each nozzle using a random number has been used, but since the random number is used, the dots distributed to each nozzle are continuous / discontinuous. Will be mixed. As a result, there are cases where printing is performed at various drive frequencies in the overlap region.

  In the image forming apparatus according to the present embodiment, the drive waveform is designed so that a target discharge amount is obtained when discharging droplets are discharged at a predetermined drive frequency. If the drive frequency changes, for example, if the one-pass printing is changed to the two-pass printing, the drive frequency is halved, so that the ejection droplet amount also fluctuates. Accordingly, when printing is performed at various drive frequencies in the overlap region, banding occurs due to fluctuations in the ejection droplet amount.

  Further, a difference in driving frequency occurs between the overlap region and the non-overlap region, and banding occurs in the overlap portion. Therefore, in this embodiment, as shown in FIG. 13, when the print data in the overlap area is distributed to the respective nozzles, the print data is distributed so that the drive frequencies in the overlap area and the non-overlap area are the same. Like to do. However, originally, in the overlap area, there has been a method of absorbing banding due to dot misalignment by dispersing the nozzles to be used, so it may be possible to see banding at that part if the dots are biased It is done.

  The drive frequency characteristics of the ejected droplets will be described with reference to FIG. In FIG. 14, the ejection droplet amount from the drive frequency of 5 kHz to 20 kHz is shown. When the 1-pass printing is 20 kHz, the 2-pass printing is 10 kHz, and the 4-pass printing is 5 kHz, the ejection droplet amount fluctuates greatly when the frequency is 20 kHz to 10 kHz, but the ejection droplet amount is varied when the frequency is 10 kHz to 5 kHz. There is no big difference.

  For this reason, when one-pass printing is performed, if the driving frequency of the non-overlapping area is half that of the overlapping area, the frequency characteristics are greatly affected. This is especially noticeable in the shadow area where dots are shot so as to fill the paper surface, but in the highlight area where dots are sparsely shot, the drive frequency in the non-overlapping area also drops, so the effect of frequency characteristics hardly occurs. .

  In the present embodiment, only the shadow area can be switched according to the gradation level so that the drive frequencies of the overlap area and the non-overlap area are the same. Since the frequency characteristic changes depending on the viscosity of the ink, the gradation level to be switched may be varied depending on the ambient temperature of the head. In particular, since banding due to a difference in driving frequency becomes remarkable during one-pass printing, the overlap area may be switched to be distributed in the multi-scan mode such as two-pass printing.

(First embodiment)
Hereinafter, an embodiment (first embodiment) of banding reduction control by the image forming apparatus according to the present invention will be described.

  As shown in FIG. 16, the image forming apparatus of the present embodiment is arranged so that a part of the first head 7a and the second head 7b overlap each other. This overlapping portion of the connection head is referred to as an overlap region 700. The processing in the overlap region 700 can reduce the banding by distributing the print nozzles to each head as described above to reduce the banding. In this embodiment, however, the end of the overlap region is further reduced. In the partial area 701, another process is performed. That is, different overlap control is performed depending on the end region (hereinafter referred to as the end region) 701 of the overlap region and the region other than the end portion of the overlap region (hereinafter referred to as the region other than the end portion) 702. I have to. The end region means a relative end portion in the overlap region, and does not necessarily mean the nozzle at the end, but depends on the size of the head or the overlap region. To a predetermined range (for one or a plurality of nozzles).

  Processing of the control unit (overlap dot control unit 606) of the image forming apparatus according to the present embodiment will be described with reference to the flowchart of FIG. First, when print data is set (S101), it is determined whether the data is an overlap area data or other non-overlap area data (S102).

  In the case of a non-overlapping area (S102: No), the process ends and is output to the head driver 607. On the other hand, if it is an overlap region (S102: Yes), it is determined whether it is an end region of the overlap region (S103).

  In a case other than the end region (S103: No), a process of distributing print data to the first head 7a and the second head 7b (S105: sorting process) is performed. On the other hand, in the case of the end region (S103: Yes), the same print data is set in the first head 7a and the second head 7b (S104), and the print data for each head is further converted to the print medium. (S106: Droplet size reduction process).

  In the drop size reduction process (S106) of the present embodiment, if the print data corresponds to a large drop, the print data corresponds to a medium drop, the print data corresponding to a medium drop, to a small drop, and the print data corresponding to a small drop Since there are no smaller droplets, the ink adhesion amount is reduced by thinning out print data from a plurality of heads.

  By performing the print control as described above, as shown in FIG. 18, even if overlapping printing is performed from a plurality of heads, the total ink adhesion amount in pixel units in the end region 701 and the region 702 other than the end portion. Can be made the same. In this embodiment, the total amount of ink adhesion is the same, but the amount of ink adhesion in the overlap region is set to be smaller than the amount of ink adhesion in the non-overlap region on the premise of gathering. Also good.

  As described above, in the edge area, the same data is distributed and the droplet size reduction process (S106) is performed. However, the same data is obtained as in the areas other than the edge area without performing the droplet size reduction process. If only the sorting is performed, if there is no landing deviation in the ejected droplets of the overlap portion, the amount of ink adhesion will be excessive by the overlap amount, resulting in ink bleeding and black streaks. Therefore, in the present embodiment, it is possible to obtain a good image by performing the droplet size down process (S106) on the edge region. In addition, since the nozzles to be used are dispersed in the region other than the end portion, even if an ejection bend occurs at a certain nozzle, another nozzle is used on the scanning line, thereby preventing complete image loss. it can.

  Next, the effect of reducing the black stripes and white stripes in the edge region by the drop size reduction process (S106) in the present embodiment will be specifically described. Here, with reference to FIGS. 19A and 19B, a description will be given of a case where a head misalignment that causes black and white streaks respectively occurs. FIG. 19A shows a case where the head joint portion is shifted from the originally assumed overlap region (normal overlap region) in a direction in which the head approaches, and FIG. 19B shows that the head joint portion is normal. The case where the head is displaced in the direction away from the overlap region is shown.

  First, the occurrence of black streaks will be described with reference to FIG. The dots in the area surrounded by the ellipse in the end area are shown on the right side (a) and (b) of the arrow. Here, (a) shows the state of dots when performing the sorting process (S105) performed in the area other than the edge part, and (b) shows the droplet size reduction process (in the edge area). The state of dots when S106) is performed is shown.

  As shown in (a), when simply performing the separation process, the density per unit area increases as the non-overlapping region and the dots at the overlap end approach due to the head shifting, resulting in black streaks. Will occur. On the other hand, in (b), the non-overlapping area and the dots at the overlap end are close to each other, but by reducing the droplet size of the dot at the end area, the increase in density per unit area can be suppressed. And black lines can be suppressed.

  Next, with reference to FIG. 19B, a description will be given of when white stripes occur. Similarly, dots in an area surrounded by an ellipse in the end area are shown as (c) and (d) on the right side of the arrow. Here, (c) shows the state of dots when performing the sorting process (S105) performed in the area other than the edge part, and (d) shows the droplet size reduction process (in the edge area) (D). The state of dots when S106) is performed is shown.

  As shown in FIG. 6C, when the separation process is simply performed, the head is displaced, and the non-overlapping region and the dot at the overlapping end portion are separated from each other. The difference becomes noticeable, and as a result, white streaks are conspicuous. On the other hand, in (d), the dots in the non-overlapping area and the overlapping edge part are separated from each other, but the paper size comes out because the droplet size of the dot in the edge area is made small and no sorting is performed. Therefore, a decrease in density can be suppressed and white streaks can be suppressed.

  Next, details of print data control will be described with reference to FIGS. As shown in (A), the recording head in a state where the first head 7a and the second head 7b are overlapped so as to partially overlap corresponds to the ejection droplet size subjected to processing such as halftone processing. In the case of print data to be printed, first, as shown in (B), the data is distributed to the first head 7a and the second head 7b. That is, at this stage, data is distributed to the respective heads for the areas other than the end of the overlap area. Further, as shown in (C), a droplet size reduction process (S106) is performed on the end region of the overlap region.

  By executing the print control as described above, the dots in the end region and the region other than the end approach in the state where the banding does not occur when the head joint portion is not shifted from the state in which the banding is shifted. As a result, the amount of ink adhering increases, and black streaks appear. However, since the dots in the edge region are separated, the amount of ink adhering decreases, and both cancel out, and the ink adhering amount does not fluctuate and the banding is reduced. It becomes possible. On the other hand, in the state shifted in the white stripe direction, the dots in the end area are generated between the areas other than the end areas, and the white stripe-like extreme ink adhesion amount fluctuation does not occur. Banding can be reduced.

  Next, another embodiment of print data control will be described with reference to FIG. In the case where the minimum dots are divided in the end region, the end side of each head in the end region (tip portion, indicated by reference numeral 703) and the inside of each head (end from the center, indicated by reference numeral 704). ), It is preferable to control so that the ratio of print data placement inside each head is higher.

  The processing flow is the same as in the example shown in FIG. 20, but in the example shown in FIG. 21, the print data corresponding to the end region is a small droplet that is the minimum droplet, as shown in FIG. ing. Here, the minimum droplet is distributed to the first head 7a and the second head 7b in the droplet size reduction process shown in FIG. 6C, but the end region is distributed between the end side 703 and the inner side 704 of the head. The ratio is set so that the inner side 704 becomes higher. For example, as shown on the inner side 704a of the first head 7a and the end portion side 703b of the second head 7b, when a two-dot droplet is distributed on the inner side 704a of the first head 7a, one dot is generated at the end portion 703b of the second head 7b. It is repeated at a ratio of 2: 1 so that it can be distributed.

  In this embodiment, the sorting is repeated, but the sorting may be performed so as to be randomly distributed. In this case, it is necessary to control so that the print data is not biased. For example, when allocating at the above ratio of 2: 1, control is not performed so that 20 dots are continuously generated in the first head and 10 dots are continuously generated in the second head, and print data is not biased. Is what you do.

  As described above, the image forming apparatus having the connection head has been described as an example in the first embodiment, but the same effect can be obtained for the line type image forming apparatus by performing the above-described print control. FIG. 22 shows a state of printing by the line type image forming apparatus. In this image forming apparatus, a head unit 7u having recording heads connected to each other over the sheet width of the sheet 12 is disposed, and an image is formed by conveying the sheet in a direction orthogonal to the nozzle row. In such a line type image forming apparatus, there are a plurality of head joints, and since an image is completed in principle by one scan, the streak problem at the head joints becomes a more serious problem. However, banding can be reduced by performing the above-described control for each head joint.

(Second Embodiment)
Hereinafter, another embodiment (second embodiment) of banding reduction control by the image forming apparatus according to the present invention will be described. In addition, about the point similar to the above-mentioned embodiment, description is abbreviate | omitted suitably.

  Further, in a serial type image forming apparatus other than the line type (including those having a connecting head), banding at a line feed portion of a scan becomes a problem. In this case, the overlapping portion of the head is also called an overlap region. FIG. 23 is a diagram for explaining the occurrence of a streak at a line feed portion of a scan. FIG. 23A shows a case where there is no line feed misalignment, and FIG. An example in which the formation density is high and black lines are generated, and (C) is an example in which the dot formation density at the joint is sparse and white lines are generated because the positional relationship between scans is far from the target. is there.

  In the following embodiment, the banding reduction in the scan line feed portion will be described. However, as described above, the head joint portion can be considered in the same manner, and therefore the configuration described below in the first embodiment is more preferable. Of course, the configuration may be included as a simple configuration.

  The image forming apparatus according to the present embodiment includes an area where image formation is performed using one of the nozzles constituting the overlap area (hereinafter referred to as “area A”), and other nozzles constituting the overlap area. By providing a region (hereinafter referred to as “region B”) for ejecting droplets by using the printing, printing control having high resistance to both black stripes and white stripes is performed.

  In the present embodiment, as shown in FIG. 24A, attention is paid to the pixel closest to the head end portion in the region A. That is, it is configured to determine whether or not to perform the above-described droplet size reduction process based on the presence or absence of print data in the pixels at the end of the region A.

  If the print data is assigned to the pixel at the end of this area A, the pixel at the end of the head is further assigned to area B, and the print data is distributed to both heads and then converted into droplets of the same or smaller size. Image formation (drop size reduction process). Note that a region B is indicated by a small dot in FIG. On the other hand, when print data is not set at the end of the area A, it is only necessary to perform the sorting for the end as well as the area A (sorting process).

  For example, if the nozzle is configured to eject three types of droplets, that is, a large droplet 21 pl (pico litter), a medium droplet 9 pl, and a small droplet 3 pl, the region B is originally large in the region B. In the pixel for ejecting the droplet (21 pl), the middle droplet (9 pl) is ejected from both overlapping nozzles to form an image.

  As shown in FIG. 25A, in the case where a deviation occurs in the direction in which the scan line feed portion approaches (black stripe direction deviation), when the area B is not set as shown in FIG. The dots in the area A and the dots in the non-overlapping part approach each other, and the ink adhesion amount increases to nearly 150%, which causes black lines. On the other hand, when the region B is set as shown in (b), only half of the 9 pl droplets approach the non-overlapping dots, so the ink adhesion amount at the boundary portion is 125. The generation of black streaks can be suppressed.

  Also, as shown in FIG. 25B, when the scan line feed part is shifted in the direction away (white stripe direction deviation), when the area B is not set as shown in (a), the end of the overlap area Since the amount of dot formation is reduced, this portion becomes a white stripe. On the other hand, when the region B is set as shown in (b), half of the 9 pl droplets land on the original address, so that the occurrence of white stripes can be suppressed.

  Here, in principle, the dots ejected in the region B may be ejected such that the ink adhesion amount is equivalent to that of the droplets that should have been ejected before the print data is distributed. This is particularly preferable when the configuration of the dots to be used is not switched according to the amount of deviation. For example, in the case of the dot size configuration of the present embodiment, for example, large droplet (21 pl) → medium droplet (9 pl) + medium droplet (9 pl), medium droplet (9 pl) → small droplet (3 pl) + small droplet (3 pl) By doing so, the difference from the original ink adhesion amount can be reduced, and there is no misalignment or it is difficult to cause image defects even under a small condition.

  In addition, when the smallest droplet is assigned to the print data, for example, in the case of the dot size configuration of the present embodiment, the small droplet (3pl) portion is from one of the overlapping nozzles. It is preferable to discharge these drops. In the case of small droplets, droplets of a smaller size cannot be ejected, and if ejected from both overlapping nozzles, the amount of ink adhesion doubles, causing black streaks. . Since droplets of such a size are mainly used in the highlight area, the dot formation density is low in this area, and streaks are unlikely to occur even if a deviation occurs. For this reason, it is sufficient to eject droplets from either one of the heads as described above.

  If the ejection is continuously performed from only one of the heads as described above, the area where the dots are densely distributed is biased and causes a reduction in image quality. In addition, since the ink flow does not occur in the nozzle that does not eject droplets, there is a problem that drying around the nozzle proceeds, the viscosity of the ink increases, and ejection failure is likely to occur. Therefore, it is preferable to perform control so that droplets are ejected equally from both heads. In this case, the heads may be allocated, for example, based on a specific pattern or randomly, and is not particularly limited.

  FIG. 26 shows an example in which the dot pattern of the area A is changed. FIG. 26 shows an example in which five nozzles are overlapped and the central three nozzles are set as the area A. FIG. 26A shows a staggered pattern, FIG. 26B shows a case of random scattering, FIG. 26C shows a pattern in which several dots are continuously formed in the main scanning direction, and FIG. (E) shows an example of a strip-like distribution, and various other patterns are conceivable. However, all of the dot formation positions are scattered, and the main cause is a dot misalignment. This is to reduce the formation of dots in the scanning direction. In addition, among the pixels in which one head in the region A is responsible for ejection, a pixel located on the other head side further than a pixel closer to the other head side is defined as a region B. In FIG. It is. This case also has the same effect as that shown in FIG.

  By executing the print control as described above, the overlapping discharge portion (region B) is provided at the end portion of the overlap portion which causes the occurrence of streaks. It becomes possible to suppress the generation of streaks. In addition, when there is no print data at the end, the same control (scoring process) may be performed for the entire overlap area, so that the processing amount can be reduced.

  In the above-described embodiment, an example in which dots of the same size are ejected from both nozzles constituting the overlap region (the smallest droplet is one of the nozzles) is shown. However, the dots ejected from both nozzles are different. You may make it. In particular, when the dot size configuration is more precise, it is preferable to combine different droplet sizes, since it can be made closer to the original ink deposition amount.

(Other embodiments)
The overlap control at the head joint and / or the scan line feed has been described above. In particular, in the case of the control at the head joint, the accuracy of the joint is almost fixed by the assembly of the head. By accurately grasping the state of the head connecting portion from the landing state of the head, processing corresponding to the state can be performed, and higher accuracy can be achieved.

  For example, if it is found that the target head joint portion is displaced in the black stripe direction, the effect of improving the black stripe can be further enhanced by adopting a configuration in which the ink adhesion amount is further reduced. Specifically, it is preferable that the portion of the print data with a large droplet is a medium droplet + small droplet, a medium droplet + none, a small droplet + small droplet, a small droplet + none, and the like to reduce the ink adhesion amount. Conversely, if it is known that the target head joint is displaced in the white stripe direction, the large drop portion is attached to a large droplet + small droplet, large droplet + medium droplet, large droplet + large droplet, etc. It is preferable to increase the amount. By doing so, it is possible to enhance the banding reduction effect and to form an image with a setting corresponding to the actual state of the head joint.

  For this reason, by preparing a plurality of dot configuration patterns and switching them in accordance with the state of the head connecting portion, it is possible to further enhance the handing reduction processing.

  For example, the misalignment of the head joint can be obtained by, for example, printing a chart for misalignment determination and reading it with a scanner or a photo sensor, or visually determining from the chart. An example of this chart is shown in FIG.

  Further, as shown in FIG. 28, ruled lines can be printed at the head connecting portion, and the amount of deviation can be determined from the backlash (arrow portion in FIG. 29). In the example shown in FIG. 28, a dot configuration list corresponding to the shift is provided, and the dot configuration used for the overlap portion processing is selected according to the measured shift amount.

  In addition, as shown in FIG. 29, the dot configuration may be determined by printing an image of the head joint portion when the dot configuration is changed and selecting an image in which the streak is most difficult to see. In the example shown in FIG. 29, the dot processing of the overlap portion is performed with the dot configuration (dot configuration “1”) that forms the central patch in which the streak is hardly visible.

  In addition to the displacement of the head joint, the print state of the joint varies depending on the temperature and humidity in the apparatus, the type of paper, the selected print mode, and the like. For example, when the temperature and humidity change, the ink viscosity changes, the size of the ejected droplet itself changes, and the ejection speed changes, which affects the landing position deviation on the paper surface. In addition, the spread characteristics of ink on the paper surface also change.

  Also, with regard to the type of paper, the dot bleeding method (size and shape) differs depending on the paper type, such as plain paper, coated paper, and glossy paper, and the whiteness of the paper itself also differs, so the same amount of droplets is ejected from the head. Even so, the state of dots on the paper surface and the way stripes stand out vary.

  Further, regarding the print mode, there are differences in dot formation intervals and dot configurations to be used due to differences in resolution. In serial machines, image forming operations such as pass and interlace are also involved, so the line feed accuracy itself varies depending on the paper feed amount, and even if the accuracy is the same, streaks are conspicuous in one pass. The streaks are difficult to notice because they are scattered.

  Therefore, it is also preferable to change the configuration of the dots used in accordance with these pieces of information. Specifically, for example, a plurality of droplet configuration patterns to be ejected in the edge region or region B where the droplet size reduction processing is performed may be held, and the setting pattern may be switched according to the acquired information. At this time, the pattern of the placement method may be changed for the region other than the end portion or the region A where the placement processing is performed. Regarding the acquisition of information, the temperature and humidity may be acquired by providing a sensor for detecting temperature and humidity in the image forming apparatus, for example. Further, the paper type and print mode may be acquired from, for example, setting information by the user.

  Hereinafter, an example of the dot configuration pattern switching will be described with reference to FIG. In the example shown in FIG. 27, a basic dot combination list (corresponding to patterns A to C in Table 2) is selected according to the print mode and paper type as shown in Table 1, and further, as shown in Table 2. The dot configuration is selected from the pattern list based on the shift amount and the temperature and humidity environment.

  In the example shown in FIG. 27, an example is given under the conditions of plain paper 600 × 300 dpi 1 pass, displacement −30 μm, and temperature and humidity MM. First, a pattern corresponding to the print mode is selected from Table 1. From Table 1, the pattern A is used for the plain paper 600 × 300 dpi 1 pass, so the pattern A in Table 2 is referred to. Furthermore, since the deviation amount is −30 μm and the temperature and humidity MM under the above conditions, the corresponding portion is referred to from the pattern A in Table 2. Here, since the dot configuration 2 is selected, the region B is formed with the dot configuration corresponding to the dot configuration 2 in Table 3.

From the above, under the above conditions, when large, medium, and small droplet print data are set in the area B,
-In the case of a large droplet, one head ejects a medium droplet and the other head ejects a small droplet.
In the case of medium drops, one head discharges a small drop and the other head discharges a small drop.
• In the case of small droplets, one head does not eject small droplets and the other head does not eject droplets.
Is controlled. In the example shown in FIG. 27, in the “plain paper mode” in which image formation occurs in one pass and streaks are likely to occur, the amount of droplets is adjusted with a relatively small amount of deviation and image formation is performed in multi-pass. In “Glossy paper mode”, where the amount of line breaks per scan is small and the accuracy of line breaks is high, the droplet volume is not biased so much, but these conditions are suitable for experiments. Is not particularly limited, but for example, it may be stored in advance as a parameter.

  The image forming method (banding reduction method) in the image forming apparatus described in the above embodiment can be executed by a program stored in a main body memory such as a ROM. A program for executing this image forming method can be provided, for example, by downloading from the Internet, and can be installed from the image processing apparatus to the image forming apparatus. The processing of the present invention may be configured to be performed by a printer driver of the image processing apparatus. The present invention is also applied to an aspect of a recording medium on which a program for executing the density correction method is recorded so as to be executable by the image forming apparatus.

  Further, according to the image forming method (banding reduction method) in the image forming apparatus described in the above embodiment, in the image forming apparatus using the serial head, the continuous head connected to the head, and the line head, It is possible to create an ink-jet recorded product as a printing result with less unevenness than before.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

  For example, in the above-described embodiment, the number of nozzles constituting the overlap region and the number of nozzles constituting the end region or the B region are not limited to the illustrated example, and the number of nozzles of the entire recording head What is necessary is just to set suitably according to etc., and it does not restrict | limit in particular.

  Further, in a serial type image forming apparatus having a connection head, since there are both a head connection part and a scan line feed part, it is preferable to divide the control contents at the head connection part and the line feed part. For example, the amount of ink attached to the overlap portion is controlled at the head connecting portion, and the amount of ink attached to each pixel in the non-overlapping region so that the scan line feed portion may be shifted to either black stripes or white stripes. It is preferable to control the ink adhesion amount so that the ink adhesion amount does not easily change.

  Further, for example, in the image forming apparatus of the above-described embodiment, the recording head is described as an example of a piezoelectric head using a piezoelectric element, but a thermal head that discharges droplets by film boiling using an electrothermal conversion element. Of course, it is also good. As described above, the piezoelectric head can eject droplets having different sizes depending on the driving waveform, and it is easy to form a gradation image. On the other hand, the thermal type head is advantageous in printing an image with high resolution at a high speed because it is easy to highly integrate nozzles.

  Examples of the thermal head include an edge shooter type head and a side shooter type head. The edge shooter type head has the advantage that it is very easy to miniaturize each part with precision, make the nozzles multi-sized, or downsize, and has high productivity. In addition, the side shooter type head can convert the energy from the discharge energy generator more efficiently into the formation of ink droplets and the kinetic energy of the flight, and the meniscus can be quickly restored by supplying ink. It is particularly effective when a heating element is used as the discharge energy generator. In addition, the so-called cavitation phenomenon in which the discharge energy generator is gradually destroyed by the impact when the bubbles that are problematic in the edge shooter method disappear can be avoided by the side shooter method. In other words, in the side shooter method, 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.

1 guide rod 2 guide rail 3 carriage 4 main scanning motor 5 timing belt 6A drive pulley 6B driven pulley 7, 7y, 7c, 7m, 7k recording head 7a first head 7b second head 7u head unit 8 sub tank 9 ink supply tube 10 Paper cassette 11 Paper stacking unit (pressure plate)
12 Paper (Recording medium)
13 Half-moon roller (feed roller)
14 Separation pad 15 Guide 21 Conveying belt 22 Counter roller 23 Conveying guide 24 Pressing member 25 Pressing roller 26 Charging roller 27 Conveying roller 28 Tension roller 29 Guide member 31 Sub-scanning motor 32 Timing belt 33 Timing roller 34 Slit disk 35, 43 Encoder Sensor 36 Rotary encoder 51 Separation claw 52 Paper discharge roller 53 Paper discharge roller 54 Paper discharge tray 56 Maintenance recovery mechanism 57 Cap 58 Wiper blade 59 Empty discharge receptacle 61 Double-sided paper feed unit 101 Channel plate 102 Vibration plate 103 Nozzle plate 104 Nozzle 105 Nozzle communication path 106 Liquid chamber 107 Fluid resistance section (supply path)
108 Common Liquid Chamber 109 Ink Supply Port 121 Piezoelectric Element 122 Base Substrate 123 Support Column 126 FPC Cable 130 Frame Member 131 Through Port 132 Ink Supply Hole 151 Piezoelectric Material 152 Internal Electrode 153 Individual Electrode 154 Common Electrode 200 Controller 201 CPU
202 ROM
203 RAM
204 Nonvolatile memory (NVRAM)
205 ASIC
206 Host I / F
207 Print control unit 208 Head driver (driver IC)
210 Motor drive unit 212 AC bias supply unit 213 I / O
214 Operation Panel 301 Drive Waveform Generation Unit 302 Data Transfer Unit 311 Shift Register 312 Latch Circuit 313 Decoder 314 Level Shifter 315 Analog Switch 400 Image Processing Device 401 CPU
402 ROM
403 RAM
404 Input device 405 Monitor 406 Storage device 407 External I / F
500 Inkjet printer 600 Image processing unit 601 Input terminal 602 Recording buffer 603 Pass number setting unit 604 Mask processing unit 605 Mask pattern table 606 Overlap dot control unit 607 Head driver 608 Recording head 700 Overlap region 701 End region 702 Other than the end Area 703 end area side 704 edge area side 704 inside edge area

JP 2008-143065 A

Claims (9)

A recording head having a plurality of nozzles for discharging a recording liquid, and having a plurality of nozzles for discharging a recording liquid when a part of the recording head overlaps at the time of scanning In the image forming apparatus in which at least two of the recording heads constitute an overlapping region by overlapping a part of the recording heads,
Wherein in the region other than the end portions in the overlap region, for the nozzles of each recording head constituting the area other than the end portion, set distributes the print data to be exclusively between the recording head in the scanning line,
The end region of the overlap region, for the nozzles of each recording head constituting the end portion region, the print data, the drop size down data smaller drop volume than the droplet amount that corresponds to the indicia character data An image forming apparatus comprising control means for converting and setting. One of the two recording heads constituting the overlap area is a first recording head, the other is a second recording head,
The control means includes
When there is print data on the head end side of the first recording head in a region other than the end portion, the drop size down data is set in the end region on the head end side, and there is no print data Is set to distribute the print data exclusively to the end area in the same manner as the area other than the end,
When there is print data on the head end side of the second recording head in a region other than the end portion, the drop size down data is set in the end region on the head end side, and there is no print data The image forming apparatus according to claim 1 , wherein the print data is distributed and set exclusively in the end area, similarly to the area other than the end area . The control means includes
2. The recording liquid adhesion amount with respect to each pixel in the end region of the overlap region is equal to the recording liquid adhesion amount corresponding to each pixel in the non-overlap region of the recording head. Or the image forming apparatus according to 2; The control means includes
When the print data in the end region of the overlap region corresponds to the minimum droplet amount, drop size down data corresponding to the minimum droplet amount is set to any one nozzle corresponding to the print data. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The control means includes
With respect to the ratio of the drop size data corresponding to the minimum droplet amount, the recording head end side of each of the recording heads in the end region of the overlap region and the inside of each recording head 5. The image forming apparatus according to claim 4, wherein a ratio of the print data to be arranged inside is increased. The control means includes
6. The image forming apparatus according to claim 4, wherein any one nozzle corresponding to the print data is selectively set so that a total discharge amount from each nozzle is equal. . The control means includes
7. The conversion content of print data in an end area of the overlap area is changed when it is detected that the overlap area is different from an assumed width. The image forming apparatus described. The control means includes
8. The conversion content of the print data in the end area of the overlap area is changed according to the detected temperature and humidity in the apparatus, the type of recording medium, and the print mode. The image forming apparatus according to any one of the above. A recording head having a plurality of nozzles for discharging a recording liquid, and having a plurality of nozzles for discharging a recording liquid when a part of the recording head overlaps at the time of scanning A plurality of the recording heads, and at least two of the recording heads form an overlapping region by overlapping a part of the recording heads.
Wherein in the region other than the end portions in the overlap region, for the nozzles of each recording head constituting the area other than the end portion, set distributes the print data to be exclusively between the recording head in the scanning line,
The end region of the overlap region, for the nozzles of each recording head constituting the end portion region, the print data, the drop size down data smaller drop volume than the droplet amount that corresponds to the indicia character data An image forming program for executing a conversion and setting process.