JP2014113690A - Image formation method, image formation program, and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute an overlap process with generation of density irregularity suppressed, and to ensure a high image quality.SOLUTION: An image formation method using a recording head in which at least two or more heads are arranged in a head longitudinal direction of the heads, an overlap portion 16 in which end portions of the heads adjacent in the head longitudinal direction of the heads overlap each other in the head longitudinal direction being provided, includes a step of forming dots of an image located in the overlap portion 16. In the step, three portions, i.e., a portion of forming the dots by a nozzle of one of the overlapping heads (nozzle of a head A), a portion of forming the dots by a nozzle of the other overlapping head (nozzle of a head B), and a portion of forming the dots by the nozzles of both of the heads (nozzles of the heads A and B) are provided. The portion of forming the dots by the nozzles of both of the heads is made to be present more frequently in the portion having a closer recording rate of forming the dots out of the portion of forming the dots by the nozzle of one head and the portion of forming the dots by the nozzle of the other head.

Description

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

  As an image forming apparatus such as a printer, a facsimile machine, a copying machine, or a complex machine of these, for example, a recording head (hereinafter referred to as a head or an ink jet) constituted by a liquid droplet ejection head that ejects liquid droplets of a recording liquid (hereinafter also referred to as ink) Using a device including a head) while conveying a recording medium (hereinafter also referred to as a sheet, but the material is not limited, and a recording medium, a recording sheet, and a recording sheet are also used synonymously). A so-called ink jet type image forming apparatus (also referred to as an ink jet printer) for forming an image by attaching a recording liquid as a liquid to paper (hereinafter, recording, printing, printing, and printing are also used synonymously) is known. ing.

  Inkjet image forming apparatuses have a relatively simple configuration, a small size, low cost, and low power consumption as compared with other image forming methods such as an electrophotographic method. Further, there is an advantage that high-speed recording is possible, recording can be performed on so-called plain paper without requiring a special fixing process, and operation sound during recording is very low. In addition, there is an advantage that a high-definition image can be formed because the resolution is easy to raise and dot reproducibility is good. In recent years, a wide variety of products from home use to office use and commercial printing have been developed and manufactured.

  Further, an ink jet image forming apparatus uses an ink liquid chamber and a recording head in which a nozzle communicating with the ink liquid chamber is used to apply a pressure to ink in the ink liquid chamber according to image information, thereby forming an ink droplet. Is ejected from the nozzle and attached 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.

  In such an image forming apparatus using the ink jet method, a phenomenon (banding) in which band-like color unevenness or streak-like color unevenness is generated on a recording medium due to variation in dot diameter or positional deviation is known.

  Explain banding. For example, there is known an ink jet printer called a line method in which a plurality of ink jet heads are arranged in the head length direction and a recording sheet is conveyed in a direction orthogonal to the head length direction to form an image.

  In this case, there may be a difference in ejection characteristics between the arranged heads due to manufacturing variations of the arranged heads. For example, when there is a difference in the amount of droplets to be ejected, a difference in dot diameter occurs on the recording medium, resulting in shaded strip-like color unevenness.

  Also, it is only necessary that the heads are assembled ideally. However, if misalignment occurs due to variations in assembly, etc., for example, the heads adjacent in the longitudinal direction of the heads are misaligned in the direction of approaching each other. In this case, the dot formation density is high at the boundary between the heads, and a high density streak-like image failure (called black streak) occurs. On the other hand, when the heads are displaced in the direction away from each other and assembled, the dot formation density is low at the boundary between the heads, and there is a risk of causing streak-like image defects (called white stripes) with low density.

  In order to solve the above banding, an overlap process is known in which the head ends are arranged so as to overlap each other in the longitudinal direction of the head, and the image of the overlapping portion is formed by dividing dots with overlapping nozzles to form an image. Yes.

  For example, Patent Document 1 discloses that a plurality of droplet discharge heads overlap each other in a direction intersecting the recording medium transport direction, and droplet discharge nozzles on the end side of the adjacent droplet discharge heads overlap in the recording medium transport direction. And a configuration in which the droplet discharge nozzle inside the outermost droplet discharge nozzle in the adjacent droplet discharge head is set as a droplet discharge nozzle at a boundary position where droplets can be discharged. In accordance with the amount of overlap between the droplet discharge nozzles at the boundary position set by the adjacent droplet discharge heads, the droplets are controlled by discharging droplets from the droplet discharge nozzles outside the droplet discharge nozzles at the boundary position. A droplet discharge device that suppresses the above is disclosed.

  Further, in Patent Document 2, a part of the recording area in the overlapping portion where the end portions of the recording element arrays overlap each other in the first and second head chips in which the recording element arrays are arranged is described in the first and second. A recording apparatus having a recording head formed by both recording elements of a head chip is disclosed.

  By the overlap processing, an interference zone (overlap portion) where dots of adjacent heads enter and mix is provided, and the above-described color unevenness can be reduced by reducing local deviation of dots and abrupt changes in characteristics. It becomes possible.

  In this overlap processing, in general, mask processing is performed and dots are distributed to the overlapping nozzles to form dots in the overlap portion. For this reason, by forming dots by exclusively distributing dots to overlapping nozzles, there is no change in the amount of ink ideally when no sorting process is performed.

  However, in the actual overlap process, there may be a change in the ink adhesion amount.

  This is due to the recording frequency characteristics of the head. The ink jet head uses a piezo element, a thermal element, or the like to apply pressure mechanically or thermodynamically to an ink liquid chamber, and ejects ink from a nozzle to form an image. Here, since the ink is a liquid, the characteristics such as the size and speed of the ink droplet flying vary depending on the vibration state of the ink surface (called meniscus). For this reason, even with the same ejection signal, ejection characteristics may change depending on the frequency of the signal.

  When the overlap process is performed, since the overlap portion uses a plurality of heads to share dots, the recording frequency of the head is lower than that of the non-overlap portion.

  Due to the recording frequency characteristics of the head, the dot size and flying speed of the overlap portion (influence on the landing position and shape) change, and the overlap processing effect cannot be obtained sufficiently, and images such as density unevenness can be obtained. There was a case where trouble occurred.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming method capable of obtaining an excellent image quality by performing an overlap process in which occurrence of density unevenness is suppressed.

  In order to achieve such an object, an image forming method according to the present invention is an image forming method using a recording head in which a plurality of at least two or more heads are arranged in the longitudinal direction of the head. The end portions of the heads adjacent to each other in the head length direction have overlapping portions overlapping in the head length direction, and dots are formed by one overlapping nozzle in the dot forming step of the image located in the overlapping portion. A portion where dots are formed by the other overlapping nozzle, and a portion where dots are formed by both overlapping nozzles, and the portion where dots are formed by both nozzles The ratio of the part that forms dots in either the part that forms dots with the nozzle of No. and the part that forms dots with the other nozzle is made to exist in many parts Than is.

  According to the present invention, it is possible to obtain an excellent image quality by performing an overlap process in which occurrence of density unevenness is suppressed.

1 is a side view illustrating an example of a configuration in an embodiment 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 a schematic diagram (1) of a line head array provided in a line type image forming apparatus. It is a schematic diagram (2) of a line head array provided in a line type image forming apparatus. FIG. 2 is a schematic diagram (1) of a head unit provided in a serial type image forming apparatus. It is a schematic diagram (2) of a head unit provided in a serial type image forming apparatus. FIG. 6 is an explanatory diagram of an image forming operation by a serial type image forming apparatus including a head unit having a joint portion. FIG. 10 is an explanatory diagram of an image forming operation in which scans are overlapped by a serial type image forming apparatus including a head unit having a joint portion. FIG. 10 is an explanatory diagram of an image forming operation in which scans are overlapped by a serial type image forming apparatus including a head unit having no connection portion. It is explanatory drawing of an overlap process, Comprising: (A) When there is no overlap part, (B) When it distributes with a fixed recording rate, (C) When it distributes with a recording rate gradient type. It is an example of the graph which shows a recording frequency characteristic. It is explanatory drawing about the recording frequency at the time of an overlap process. FIG. 6 is an explanatory diagram in the case where a shift occurs in the dot formation positions of head A and head B. It is explanatory drawing of the landing position shift produced by the influence of a recording frequency. It is explanatory drawing of an overlap process, Comprising: (a) The example which provides an overlapping nozzle, (b) The example which does not provide an overlapping nozzle. It is explanatory drawing of the overlap process at the time of the amount of ejected droplets changing with recording frequency characteristics, Comprising: (a) The example which provides an overlapping nozzle, (b) The example which does not provide an overlapping nozzle. It is explanatory drawing of the overlap process at the time of the shift | offset | difference in the dot formation position of the head A and the head B, Comprising: (a) The example which provides an overlapping nozzle, (b) The example which does not provide an overlapping nozzle. It is explanatory drawing of the overlap process at the time of the fluctuation | variation of a droplet quantity and speed arisen with the recording frequency characteristic, Comprising: (a) The example which provides an overlapping nozzle, (b) The example which does not provide an overlapping nozzle. It is explanatory drawing of the overlap process which changes droplet size and overlaps discharge, Comprising: (a) The example changed into the large size droplet, (b) The example changed into the small size droplet. It is explanatory drawing about the mask process of an overlap part. It is explanatory drawing about the switching process of the mask by an input gradation.

  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)
FIG. 1 and FIG. 2 are views showing the image forming apparatus according to the present embodiment. FIG. 1 is an explanatory side view of the overall structure of the mechanism unit, and FIG. 2 is an explanatory plan view 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, each composed of a droplet discharge head that discharges yellow (Y), cyan (C), magenta (M), and black (K) ink droplets. 7k (referred to as “recording head 7” when colors are not distinguished) is arranged in such a manner that a plurality of ink ejection openings intersect with 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 droplet discharge head constituting the recording head 7 includes a piezoelectric actuator such as a piezoelectric element, a thermal actuator that utilizes a phase change caused by liquid film boiling using an electrothermal transducer such as a heating resistor, and a metal phase caused by a temperature change. A shape memory alloy actuator using a change, an electrostatic actuator using an electrostatic force, or 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 by one or a plurality of droplet discharge heads having a nozzle row including a plurality of nozzles that discharge droplets of a plurality of colors.

  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 61 is detachably mounted on the back. The double-sided paper feeding unit 61 takes in the paper 12 returned by the reverse rotation of the transport belt 21, reverses it, and feeds it again between the counter roller 22 and the transport 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 mechanism 56 includes caps 57 for capping each nozzle surface of the recording head 7, a wiper blade 58 which is a blade member for wiping the nozzle surface, and a discharge unit 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.

  The image forming apparatus preferably includes a unit (patch reading unit 230) capable of acquiring image optical characteristics such as a sensor, a scanner, and a colorimeter, as will be described later. Furthermore, the image forming apparatus preferably includes a temperature / humidity sensor (not shown) for detecting the apparatus environment (temperature / humidity) of the image forming apparatus.

(Configuration of recording head)
Next, an example of a droplet 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).

  The droplet discharge head includes a flow channel plate 101 formed by anisotropic etching of a single crystal silicon substrate, a vibration plate 102 formed by nickel electroforming, for example, bonded to the lower surface of the flow channel plate 101, and a flow plate. The nozzle plate 103 bonded to the upper surface of the path plate 101 is bonded and stacked, and the nozzle communication path 105 that is a flow path through which the nozzle 104 that discharges droplets (ink droplets) communicates therewith and the liquid that is the pressure generation chamber. An ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to the chamber 106 and the liquid chamber 106 through a fluid resistance portion (supply path) 107 is formed.

  Further, two rows of stacked piezoelectric elements 121 as electromechanical conversion elements that are pressure generating means (actuator means) for deforming the diaphragm 102 to pressurize the ink in the liquid chamber 106, and the piezoelectric elements 121 And a base substrate 122 to be bonded and fixed. 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 droplet discharge head configured as described above, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential, the piezoelectric element 121 contracts, and the vibration plate 102 descends to expand the volume of the liquid chamber 106. As a result, 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. By contracting the volume / 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 how the driving waveform is given.

(Configuration of control unit)
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, each detection signal from the encoder sensor 35, an I / O 213 for inputting detection signals from various sensors such as a temperature sensor 215 that detects the environmental temperature, and the like It has. 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 hosts 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 by the I / F 206.

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

  The CPU 201 also detects a speed detection value and a position detection value obtained by sampling a detection pulse from the encoder sensor 35 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, a speed detection value and a position detection value obtained by sampling a detection pulse from the encoder sensor 35 constituting the rotary encoder 36, 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 sub-scanning motor 31 is calculated, and the sub-scanning motor 31 is driven via the motor driver 210 and the motor driver.

  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. Output to the head driver 208.

  Further, the print control unit 207 includes a drive waveform generation unit and a head driver 208 configured by a D / A converter, a voltage amplifier, a current amplifier, and the like that perform D / A conversion on the drive signal pattern data stored in the ROM 202. A drive waveform selection unit including a drive pulse (drive signal) or a plurality of drive pulses (drive signals) is generated and output 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.

(Configuration of print controller and head 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.

(Recording liquid)
Next, ink that is a recording liquid used in the image forming apparatus will be described. In the image forming apparatus according to this embodiment, for example, even when printing is performed on plain paper by using an ink configuration including 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 with no feathering or color bleeding phenomenon on characters / images, (4) Image with little ink see-through phenomenon that can withstand double-sided printing, (5) High image dryness (fixability) suitable for high-speed printing, (6) High-quality image with high fastness such as light resistance and water resistance The image density, color developability, color reproducibility, character blur, color boundary blur, double-sided printability, fixability and the like can be greatly improved.

  An example of a drive 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 pressurizing liquid chamber 106 by the driving pulse P3 on the pressure vibration of the pressurizing liquid chamber 106 by the vibration cycle generated by the fine driving pulse P2, the droplet volume of the droplets that can be ejected by the driving 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, an embodiment of an image forming system that executes an image forming program stored in an image processing apparatus connected to the image forming apparatus and outputs a print image by the image forming apparatus will be described with reference to FIG. . The image forming system is configured by connecting one or a plurality of image processing apparatuses 400 such as a personal computer (PC) and an ink jet printer (image forming apparatus) 500 via 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 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 formation described below can be performed on the ink jet printer side. In this example, however, the ink jet printer 500 side receives an image drawing or character print command in the apparatus and actually records a dot pattern. An example that does not have a function for generating the error will be described. 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 (print data) corresponding to the designated position, thickness, etc. If it is image data, the outline information of the corresponding character is called 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. Then, it is converted into a recording dot pattern as it is.

  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 ink jet printer 500 via the interface.

  In addition, when copying using the inkjet printer 500, it is necessary to perform a halftone process etc. to the recording dot pattern with the inkjet printer 500, In that case, the print control part 207 was mentioned above with respect to the scanned image data. A recording dot pattern in which halftone processing or the like is performed is generated by performing such processing.

(Image processing unit)
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 an image is 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. FIG. 12 is a block diagram schematically showing the image processing unit 600 of the present embodiment. In the drawing, reference numeral 601 denotes an input terminal, 602 denotes a recording buffer, 603 denotes a pass number setting unit, 604 denotes a mask processing unit, and 605 denotes a mask pattern table.

  Bitmap data (print data) transmitted from the image processing apparatus 400 is input from the input terminal 601 and stored in a predetermined address of 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 sets a bit according to the position of each nozzle of the recording head. The map data is read out and input to the pass number setting unit 603. In addition, when the next scan bitmap data is input from the input terminal 601, the recording buffer control unit performs recording so as to store it in an empty area of the recording buffer 602 (an area corresponding to the paper feed amount for which recording has been completed). Control the buffer 602.

  Next, a more specific configuration example of the pass number setting unit 603 in the image forming apparatus will be described. 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.

  When the mask processing unit 604 masks the bitmap data stored in the recording buffer 602 for each pass recording using the mask pattern and outputs it to the head driver 208, the head driver 208 records the masked bitmap data. They are rearranged in the order used by the head 7 and transferred to the recording head 7.

  The recording buffer 602 is realized by the RAM 203, for example, and the mask pattern table is stored in the ROM 202, for example. The pass number setting unit 603 and the mask processing unit 604 can be realized by any one of the print control unit 207, the print control unit 207 and the CPU 201, or the CPU 201. The recording buffer control unit can be realized by the CPU 201.

(Overlap control)
Next, overlap control will be described for each configuration of the recording head 7.

[Example of head configuration (1)]
The overlap control in the line type image forming apparatus will be described with reference to FIG. The recording head shown in FIG. 13 forms a line head array 7L by arranging a plurality of heads 7 (7k, 7c, 7m, 7y) in the longitudinal direction of the head, and conveys the recording paper in a direction orthogonal to the longitudinal direction of the head. Image formation. In this example, four colors of KCMY form an array for each color, and are assembled in a positional relationship in which the ends of the heads adjacent in the head length direction partially overlap each other.

  In the example of FIG. 13, the overlap portion 16 is provided for each color. However, the configuration of the line head array 7L is not limited to this. For example, as shown in FIG. A wrap portion 16 may be provided.

  Needless to say, the number of heads in the longitudinal direction of the head is not limited to the example shown in the figure. In the line type image forming apparatus, a plurality of heads are arranged in the longitudinal direction of the head, and paper is conveyed in a direction orthogonal to the head to form an image. For this reason, the number of heads in the longitudinal direction needs to be configured such that the image-forming area is equal to or larger than the corresponding recording paper in accordance with the size and overlap amount of the corresponding recording paper.

  Further, the number of heads in the direction orthogonal to the longitudinal direction is not limited to the figure, and can be set as appropriate. Although not particularly illustrated, for example, a configuration in which a plurality of heads are arranged in parallel for each color may be used, or four or more colors may be handled. Further, a configuration having two or more colors in one head may be adopted.

  In addition, as a usable head, various types such as a piezo type, a thermal type, and an electrostatic type can be used. In FIG. 13 and FIG. 14, two nozzle rows are shown in one head 7, but the nozzle layout is not particularly limited, and the number may be more or less.

[Example of head configuration (2)]
FIG. 15 shows an example of a recording head including a head unit 7U having an overlap portion 16 included in a serial type image forming apparatus.

  As for the number and configuration of the heads, various head and nozzle layout configurations can be employed as in the case of the line system, including the example shown in FIG.

  In the serial type image forming apparatus, the head unit 7U as shown in FIGS. 15 and 16 scans a plurality of times in the direction orthogonal to the recording sheet conveyance direction to form an image. For example, in the head unit 7U shown in FIG. 15, as shown in FIG. 17, the head unit 7U is reciprocally scanned to form an image while feeding the recording paper substantially by the length of the head unit.

  17 to 19 are diagrams schematically showing the relative movement of the head unit 7U and the recording paper and the image forming area in each scan. In FIGS. 17 to 19, the horizontal direction on the paper indicates the moving direction of the head unit, and the vertical direction indicates the conveyance direction of the recording paper.

  Here, when the operation shown in FIG. 17 is performed, the recording paper conveyance amount (equivalent to the length of the head unit) is made shorter than that in FIG. 17 as shown in FIG. 18, and images are formed so that the scans overlap each other. There is a case.

  As another form, FIG. 19 shows an example of a recording head of a serial type image forming apparatus using a head unit 7U that does not have an overlap portion 16. In this example as well, since it is a serial method, an image is formed by combining the scanning operation of the head unit and the sheet conveyance in the same manner as in the examples of FIGS. In this case, as in FIG. 18, an image may be formed so that the scans overlap as shown in FIG.

  Note that the head unit 7U having no overlap portion 16 is a connection head but does not have the overlap portion 16 in the head portion even if it is not a connection head configuration as shown in FIG. May be.

  As described above, the overlap process performs the head arrangement and the scanning operation so that the nozzles partially overlap.

[Nozzle classification of overlap part]
Next, the process in the overlap part (overlap part 16) in an overlap process is demonstrated. Since this process can be applied to any of the above-described head configurations, for the convenience of description, the embodiment will not be particularly distinguished and will be described in a state where two heads overlap. These two heads are referred to as head A and head B. That is, the head A and the head B include the case of different scanning with the same head.

  When the head A and the head B do not have the overlap portion 16 as shown in FIG. 20A, when the characteristics between the heads are different, the gap at the boundary portion is large.

  On the other hand, the overlap portion 16 has a nozzle overlap portion (also referred to as an overlap nozzle) in which a plurality of nozzles overlap, and there are more choices of nozzles used when forming an image of this portion than the non-overlap portion. It will be.

  As a method of distributing nozzles in the overlap portion 16, a mask describing a rule for allocating overlapping nozzles is prepared in the overlap portion 16, and the image position corresponding to the overlap portion 16 is applied by applying this mask. It is known to perform printing by distributing the data input to the overlap nozzles.

  For example, as shown in FIG. 20B, there is a method in which the head A and the head B are distributed at a constant recording rate. Further, as shown in FIG. 20C, a recording rate gradient type distribution in which dots are distributed so that the dot formation rate decreases toward the end of the head can be considered. By distributing in this way, the characteristics of the two heads are mixed and the change is moderated.

  In the classification process in the overlap unit 16, in principle, the original data may be distributed exclusively. For example, assuming that the number of dots in the area corresponding to the overlap portion 16 of the original image is 100%, when assigning to two overlapping heads, the recording rate X [% of one head (for example, head A) ], The recording rate of the other head (for example, head B) is (100−X) [%].

  In the overlap process, in general, a mask process is performed, and dots are formed in the overlap portion 16 by distributing dots to the overlapping nozzles. For this reason, by forming dots by exclusively distributing dots to overlapping nozzles, there is no change in the amount of ink ideally when no sorting process is performed.

  However, when the overlap process is actually performed, the amount of ink attached may change.

  This is due to the recording frequency characteristics of the recording head. The ink jet head uses a piezo element, a thermal element, or an electrostatic element to apply pressure to the ink liquid chamber, and ejects ink from the nozzle to form an image. Since ink is a liquid, characteristics such as the size and speed of ink droplets flying vary depending on the vibration state of the ink liquid surface (meniscus). For this reason, even with the same ejection signal, ejection characteristics may change depending on the frequency of the signal.

  In the overlap part 16, since dots are shared and formed using a plurality of heads, the recording frequency of the head is lower than that in the non-overlap part. For this reason, the dot size and the flying speed (influence on the landing position and shape) of the overlap portion 16 change depending on the recording frequency characteristics of the head, and the overlap effect may not be sufficiently obtained.

  For example, FIG. 21 shows an example of a graph showing the recording frequency characteristics, where the horizontal axis indicates the dot recording frequency (ejection frequency) [kHz], and the vertical axis indicates the ejection droplet amount (≈dot diameter) [pl]. Yes.

  Ideally, the droplet volume does not change even if the recording frequency changes, but it is difficult to eliminate this completely. For example, when printing solid dot data using a recording head having recording frequency characteristics as shown in FIG. 21, the recording frequency when dots are continuously formed is 20 [kHz]. Think about the case.

  In the overlap portion 16 as shown in FIG. 20B, when dot formation is performed by distributing 50% to each of the head A and the head B, the recording frequency of the overlap portion 16 is equivalent to 10 kHz. Will be depressed.

  For this reason, when the recording frequency characteristic as shown in FIG. 21 is present in the head, even though the overlap portion 16 intends to eject the same ink droplet amount as the non-overlapping portion, the droplet amount actually decreases. As a result, white stripe-like density unevenness occurs.

[Overlap control by overlapping nozzles]
As described above, density unevenness may occur only by dot placement exclusively in the overlap portion 16.

  Therefore, in the image forming method according to the present embodiment, a recording head (line head array 7L, head unit 7U) in which a plurality of at least two heads (heads 7) are arranged in the head length direction of the heads is used. An image forming method, wherein the head end portions adjacent to each other in the head length direction have an overlapping portion (overlap portion 16) overlapping in the head length direction, and image dots positioned in the overlapping portion In the forming step, a portion where dots are formed by one overlapping nozzle (nozzle of head A), a portion where dots are formed by the other overlapping nozzle (nozzle of head B), and both overlapping nozzles (head A) And the part where dots are formed by the nozzle of head B), and the part where dots are formed by both nozzles is formed by one nozzle. The moiety and (the ratio of the recording rate) ratio of the portion forming the dots in one of the other portion for forming dots in the nozzle portion close to, is obtained so as to present a number.

  Alternatively, an image forming method in which an image is formed by reciprocating a recording head in a direction orthogonal to a conveyance direction of a recording medium, and an area formed by the recording head using at least one scan is defined as a first image. Area (image formation area for the first scan, see FIG. 18 and the like), and an area formed by a recording head formed at a position different from the first image area using at least one scan is the second image area (Image formation area for the second scan) When the area located at the boundary between the first image area and the second image area is the third image area (scan overlap area), the third image The region corresponds to an overlapping portion (overlap portion 16) in which the first scan used for the first image region and the second scan used for the second image region overlap each other in the head longitudinal direction, Position at overlap In the dot formation step of the image to be printed, the first scan nozzle (head A nozzle) forms a dot, the second scan nozzle (head B nozzle) forms a dot, the first and first The two nozzles for both scans (the nozzles of head A and head B) are provided with three parts, and the part where dots are formed by both nozzles is the first scan nozzle. In either the portion where dots are formed or the portion where dots are formed by the nozzles of the second scan, the portion where the dots are formed (ratio of the recording rate) is present in a large amount.

  That is, it is an overlap process that selectively uses a portion where dots are exclusively arranged and a case where dots are formed using a plurality of overlapping nozzles (using two heads, head A and head B). A plurality of parts to be used are provided to suppress density unevenness due to a change in recording frequency.

  Since a plurality of overlapping nozzles are provided to reduce density unevenness due to a decrease in recording frequency, it is important to provide a large number of portions where the influence of a decrease in recording frequency is likely to occur.

  For example, this is uniformly present when the dot formation distribution rate is uniform as shown in FIG. 20B, and when the dot formation distribution rate is not uniform as shown in FIG. It is set according to the distribution rate. This will be described in detail below.

  As described above, FIG. 20C shows an example of the recording rate gradient type overlap process in which the dots are distributed so that the ratio of forming dots decreases toward the end of the head. That is, when attention is paid to one of the overlapping heads or scans, as the head or the end of the scan is approached, the ratio of dot formation in one head or scan decreases.

  In the case of this processing, as shown in FIG. 22, the recording rate of the head A is high and the recording rate of the head B is low on the side close to the head A in the overlap portion 16. This means that the recording frequency of head A is high and the recording frequency of head B tends to be low. On the other hand, on the side closer to the head B in the overlap portion 16, the recording frequency of the head A is low and the recording frequency of the head B is high. Therefore, it means that the recording frequency of the head A is low and the recording frequency of the head B tends to be high.

  In the vicinity of the middle of the heads A and B in the overlap portion 16, the recording rates of the head A and the head B are equal, and in the case of a configuration in which the recording rate is uniformly inclined at a constant rate of 0 to 100%, the recording frequency However, both heads are reduced to near 50%.

  In such a case, since either of the heads forms most of the dots on the head A side and the head B side of the overlap portion 16, the above-described recording frequency characteristics are hardly affected. In the vicinity of the middle of B (the center side of the overlap portion 16), the recording frequency of both heads is lowered, so that the influence is likely to occur.

  Therefore, in this embodiment, the portion where the recording rates of the head A and the head B are close to each other is such that there are more portions where a plurality of the overlapping nozzles are used. Therefore, in the case of distributing at a constant recording rate as shown in FIG. 20B, the portion using the overlapping nozzles is present in the overlap portion 16 at a constant rate.

  In addition, there are many portions where a plurality of overlapping nozzles are used, where a portion where dots are formed by one nozzle and a portion where dots are formed by the other nozzle are switched in the nozzle row direction or in a direction perpendicular to the nozzle row. It is preferable to do so.

  This point will be described. In the overlap process described above, the paper surface may be exposed microscopically due to landing position deviation. FIG. 23 is an explanatory diagram illustrating an example in which the paper surface is exposed microscopically due to landing position deviation.

  As shown in FIG. 23, when the dot formation positions of the head A and the head B are misaligned, the portion where the dot distribution of the dot of the head A (gray) and the dot of the head B (black) is switched is changed on this micro paper surface. Exposure is likely to occur. The cause of the landing position deviation includes various factors such as head assembly, scan position deviation, and recording sheet conveyance deviation.

  For example, when a discharge timing shift occurs between the head A and the head B, a horizontal shift as shown in FIG. 23A occurs. When an assembly shift occurs between the head A and the head B, FIG. ) May occur in the vertical direction.

  In addition, the landing position deviation may occur due to the influence of the recording frequency described above. Since the recording frequency may affect not only the droplet volume but also the droplet ejection speed, even if the above-mentioned head, scan, and recording paper conveyance misalignment do not occur, the dot misalignment will not occur. May occur. For example, the droplet ejection speed is different between the case where dots are continuously hit and the portion corresponding to the start of hitting, and landing deviation may occur.

  FIG. 24 shows an example in which dots are formed in order from the left to the right of the page. Pay attention to the dots (one of the colors) formed by one of the overlapping nozzles. If the nozzle forms a dot in the previous pixel, that is, if a dot is formed on the left side, the next pixel can form a dot at regular timing, but does not form a dot on the left side. In this case, the next dot is formed late and formed at a position shifted to the right side of the drawing.

  This is because the droplet ejection speed has a change characteristic with respect to the recording frequency. The example of FIG. 24 is an example in which the droplet ejection speed decreases as the recording frequency decreases. On the other hand, in the case of the characteristic that the discharge speed is increased, landing deviation occurs in the left direction of the sheet.

  As can be seen from FIG. 24, it is understood that the landing position deviation caused by the influence of the recording frequency is likely to occur at the switching point of the overlapping portion 16.

  This is not a deviation that occurs uniformly as a whole, such as a deviation in the landing position caused by the influence of the recording frequency, or a deviation caused by the assembly of the head, but a deviation occurs in some dots. It cannot be eliminated no matter how much misalignment is suppressed.

  In view of this, it is possible to reduce the influence of the landing position deviation caused by the influence of the recording frequency by making the dot forming portion using a plurality of overlapping nozzles more present in the boundary portion of the hitting.

  FIG. 25 shows an explanatory diagram of an example in which an overlapping nozzle is provided and an example in which no overlapping nozzle is provided. FIG. 25A is an example in which overlapping nozzles (overlapping discharge locations) are provided, and FIG. 25B is an example in which overlapping nozzles (overlapping discharge locations) are not provided.

  FIG. 25A is an example in which a portion where both the nozzles of the head A and the nozzles of the head B form dots is provided at the switching portion of the head A and the head B. Hereinafter, hatching (about the head A) is illustrated in FIG. The dots that are hatched with respect to the dots and the head B indicate overlapping dots.

  In this case, since the overlap processing is performed so that the dot recording rate decreases toward the end of the head, more overlapping discharge portions are provided on the central side of the overlap portion that is likely to be affected by a decrease in recording frequency.

  In the example shown in FIG. 25, as described above, when the drop amount is reduced due to the reduction in the recording frequency, for example, the results are as shown in FIGS.

  FIG. 26 shows an example in which images are formed in the order from the left to the right of the drawing. In the dots where dots are not formed on the left, the dots become smaller due to a decrease in the recording frequency. In FIG. 26 (a), since the overlapping dot forming portion is provided, the number of the locations itself is reduced, and the dot from the other nozzle overlapping the portion where the dot is further reduced. Since it is formed, it is possible to compensate for the drop amount drop due to the lowering of the recording frequency.

  Further, in the example shown in FIG. 25, when the positional deviation occurs between the head A and the head B as described above, for example, FIG. 27 (a), (b), FIG. 28 (a), (b) become that way.

  FIG. 27 shows an example in which the head B is displaced in the right direction, and FIG. 28 shows that a dot that did not form a dot immediately before (adjacent to the left) is delayed (shifted to the right) due to a decrease in the recording frequency. It is an example.

  In both cases of FIG. 27A and FIG. 28A, since the overlapping nozzles are provided in the vicinity of the switching of the separation, it is possible to prevent a gap caused by the positional deviation. It should be noted that such an effect cannot be obtained when a dot in the middle of continuous ejection is simply set as an overlapping ejection location.

  According to the image forming method, the image forming apparatus, and the image forming program described above, the density unevenness improvement effect in accordance with the characteristics of the image forming apparatus such as the head characteristics and the landing position deviation of the dots in consideration of the influence of the recording frequency. High overlap processing can be performed, and it becomes possible to obtain a recorded material with good image quality in which density unevenness is not conspicuous.

[Change dot data]
Up to this point, the data changed to dot data by halftone processing is basically used as it is, for example, data converted into medium droplets is distributed to heads A and B as medium droplet data. The example which provides the part which forms a dot redundantly from A and B was demonstrated.

  In the present embodiment, it is preferable that at least a part (or all) of the dots in the area responsible for dot formation by both nozzles be formed by changing the dot data to other types (drop types) of dot data. . Note that a head that divides dots of three types of sizes, large droplets, medium droplets, and small droplets, will be described as an example.

  In the example shown in FIG. 29A, medium drops are converted into large drops and discharged. This can increase the dot diameter of the overlapping portion, and is therefore effective when the drop amount is greatly decreased due to a decrease in the recording frequency, or when the positional deviation is large and the paper surface exposure can be large.

  In the example shown in FIG. 29B, medium droplets are converted into small droplets and discharged. This is effective, for example, when the characteristics of the recording frequency do not change the drop volume so much and the change in drop speed is large. In this case, if a large number of overlapping portions are provided, there is a possibility that the amount of overlap ink adhesion is increased more than necessary, and the density is increased. If the overlapping portion is reduced, the ink adhesion amount can be reduced, but in this case, the tolerance to the paper surface exposure due to the positional deviation and the fluctuation of the droplet speed of the recording frequency is weakened. In FIG. 29 (b), since the medium droplet is converted into a small droplet and discharged, an increase in the discharge amount can be suppressed as compared with hitting two medium droplets, and a large number of overlapping discharge locations can be provided. It is possible to maintain high resistance to deviation.

  In addition, the tendency of the drop amount to increase with respect to the characteristics of the recording frequency has been described so far, but this sometimes has the opposite characteristics. In other words, the recording frequency characteristics are caused by the difference in meniscus fluctuation caused by the previously input drive signal, so the waveform shape, the structure of the liquid chamber, the ink supply speed to the liquid chamber, etc. are involved in a complicated manner. This is a problem that arises. For this reason, the drop amount may decrease with respect to the recording frequency, or there may be a peak at an intermediate frequency.

  In such a case, if the droplet amount is suppressed as shown in FIG. 29 (b), it is possible to suppress the influence of the droplet amount change while enhancing the resistance to positional deviation. Although it is conceivable to provide a place where both of the overlapping nozzles do not strike, the amount of ink adhering can be suppressed, but this process leads to data loss.

  The dot data conversion is not a uniform conversion, and there may be a mixture of a portion where the medium droplet data is directly overlapped by the medium droplet and a portion where the medium droplet data is overlapped by the small droplet. It is good also as a structure which combines and overlaps different droplets like.

[Mask processing]
For the nozzle placement in the overlap portion 16, a mask that defines the placement method may be prepared, and image data may be distributed to each head using this mask.

  FIG. 30A shows a place where dots are formed as “1” and a place where dots are not formed as “0”, which are assigned to the overlap portions 16 of head A and head B, respectively. is there. A pixel in which the head A and the head B are both “1” (the place of “1” described in gray in the drawing) corresponds to the overlapping discharge portion.

  FIG. 30B is an example in which numbers other than “0” and “1” are assigned to perform distribution to the head A and the head B with one mask, and “0” is a place where the head B forms a dot. , “1” corresponds to a place where dots are formed by the head A, and “2” corresponds to a place where dots are formed overlappingly by the heads A and B. In this case, processing can be performed by assigning one mask to both heads A and B.

  FIG. 30C is an example in which a number other than “0” and “1” is provided to provide a function of droplet type conversion. For example, “0” forms a dot as it is in head B, “1” forms a dot as it is in head A, “2” forms a dot as it is in heads A and B, and “3” forms a dot in heads A and B. It is possible to form an overlap by reducing the size by one.

  Further, by combining these, as shown in FIG. 30 (d), it is possible to specify more detailed conditions than hitting the heads A and B. As conditions, for example, the drop type is hit or changed as it is, or according to the drop type of the data, for example, when large drop data comes in, it is changed to a medium drop, and medium drop data comes in. In such a case, the condition can be changed, for example, the treatment can be changed depending on the type of droplet, such as hitting as it is. Also, settings may be made to change the process according to the input gradation.

  Note that a single mask may be referred to, or a reference mask may be switched according to conditions by providing a plurality of masks or a multilayered format. For example, FIG. 31 shows an example in which the mask to be referenced is changed according to the input gradation.

  This is because the method of filling the paper differs depending on the droplet type and gradation to be handled, and the influence of the recording frequency characteristic may be different. In some cases, the number of appropriate overlapping discharge locations for gradations composed of large drops may not be appropriate for gradations composed of medium drops. Is possible.

  As described above, the mask is composed of a plurality of types or at least one of the bit depths, and it is also preferable to change at least one of the type of mask to be referred to or the bit depth depending on the droplet type, input gradation, or the like. .

  In addition, regarding the selection of a mask that is a dot formation sharing pattern (dot formation pattern) for overlapping nozzles, a plurality of patterns with different placement methods and different positions and numbers of overlapping discharges are prepared. It is preferable that the selection is switched.

As a switching condition, for example, it is preferable to determine by any one of the following (1) to (8) or a combination thereof.
(1) Depends on the print mode.
(2) Varies depending on the printing paper.
(3) Varies depending on the amount of dot landing position deviation.
(4) The head overlap and the scan overlap are different.
(5) Depends on the head.
(6) Depends on the scan.
(7) Depends on the color.
(8) Varies depending on the usage environment (temperature / humidity, period of use) of the device.

  (1) is to switch according to the print mode. Since various conditions such as recording resolution, head drive signal, speed, and image processing differ depending on the print mode, it is preferable to select and apply a pattern according to this.

  In (2), even if the printing modes of the printer are common, there are a wide variety of papers in circulation. For example, even if “plain paper” is used as a bit, its properties are various. In addition, since an ink jet printer forms an image by ejecting liquid onto a recording sheet, it is known that print quality is greatly influenced by how ink spreads. Therefore, it is preferable to select and apply a suitable pattern according to the recording paper actually used by the user as well as the recommended paper.

  In (3) to (7), the ink ejection characteristics and the landing position deviation amount vary depending on the configuration of the head and the apparatus configuration that are actually used. Therefore, a pattern corresponding to this is selected and applied. Even in the same machine, the amount of landing position deviation and ejection characteristics may differ depending on the head and scan used, and the characteristics may differ slightly between the upper and lower ends of the same head.

  In addition, density unevenness is also noticeable depending on the color. In general, low brightness colors such as K and M have high contrast with the paper surface and are easily noticeable by humans, and colors such as Y are noticeable. Hateful. In addition, since the ink composition varies depending on the color, the landing characteristics themselves may differ. Therefore, it is preferable to select and apply a pattern that matches these characteristics.

  Even if the pattern is optimized in accordance with the above (1) to (7), the characteristics may change depending on the use environment of the apparatus and aging deterioration. Further, regarding the use environment of the apparatus, it largely depends on changes in temperature and humidity. Depending on the use environment, the ink ejection characteristics may change mainly due to changes in the viscosity of the ink. For example, there are examples such that a lot of ink is likely to fly under high temperature and high humidity conditions, and the ink is likely to bend under low temperature and low humidity conditions. In addition, there is a case where the nozzle driving ability is deteriorated due to deterioration over time, or the water repellency of the nozzle surface is lowered, and landing deviation is likely to occur due to discharge bending.

  Therefore, (8) It is more preferable that the optimum processing pattern is set according to the usage environment and usage time.

  These patterns may have a table in which the various printing conditions and patterns are associated with each other, and a pattern to be applied may be selectively applied by referring to the table.

  Also, there are means for forming an image under a condition that has a plurality of dot formation patterns and the sharing pattern is changed, and means for selecting a pattern from the plurality of sharing patterns, and the nozzle overlapping portion is processed by the selected pattern. It is also preferable to do this.

  For example, it is possible to form an image to which a plurality of overlap processing patterns are applied under a target condition (for example, a printing mode), select an image in which density unevenness is not conspicuous from among the images, and selectively apply the processing pattern. can give.

  Regarding the selection of the shared pattern, for example, there may be a means for receiving pattern information selected by the user, and processing may be performed by the selected pattern (for example, selecting a pattern with less density unevenness visually) An optimal image may be selected and applied by reading an image with the above sharing pattern using a scanner, a sensor, a camera, or the like.

  This can be achieved by detecting the density unevenness of the overlap portion directly or via the image luminance value and selecting a processing pattern with less density unevenness.

  As described above, it is possible to perform overlap processing suitable for the configuration and environment of the image forming apparatus.

  The above-described image processing relating to overlap can be performed by mounting a dot formation program (image formation program) in a host computer (image processing apparatus) connected to the image formation apparatus, for example. The host computer may be physically connected to the image forming apparatus via a USB or the like, or may be connected via a network such as a wireless LAN.

  Further, if the program is directly installed in the image forming apparatus so that it can be executed, the overlap processing can be applied even when the image forming apparatus is implemented in a stand-alone manner. In general, the image forming apparatus main body is equipped with an inexpensive arithmetic unit and has a low calculation processing capacity compared to the host computer. For example, when the image forming apparatus main body has the above two processing systems and performs image printing from the host computer. From the point of view of printing productivity, etc., it is possible to use a program installed in the host computer to perform processing in the main unit when copying and printing with a digital camera or tablet PC connected. preferable.

  In addition, image processing of a general printer, for example, color matching processing and halftone processing may be performed by a host computer, and overlapping processing may be performed by the main body. The image forming program may be implemented by software, or may be implemented by hardware coding such as ASIC.

  According to the image forming method, the image forming apparatus, and the image forming program according to the present embodiment described above, according to the characteristics of the image forming apparatus and the printing conditions such as the head characteristics and the dot landing position deviation in consideration of the influence of the recording frequency. In addition, it is possible to perform an overlap process with a high density unevenness improvement effect, and it is possible to obtain a recorded product with good image quality in which density unevenness is not conspicuous.

  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.

DESCRIPTION OF SYMBOLS 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 (head)
7L Line head 7U Head unit 8 Sub tank 9 Ink supply tube 10 Paper feed cassette 11 Paper stacking section (pressure plate)
12 Paper (recording medium)
13 Half-moon roller (feed roller)
14 Separation pad 15 Guide 16 Overlap portion 21 Conveying belt 22 Counter roller 23 Conveying guide 24 Holding member 25 Holding 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 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 Receiver 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 portion (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 220 Patch Output Unit 230 Patch Reading Unit 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

JP 2006-35731 A JP 2008-143065 A

Claims (10)

An image forming method using a recording head in which at least two or more heads are arranged in the head length direction of the head,
In the dot forming step of the image located at the overlapping portion, the end portions of the head adjacent to each other in the head length direction of the head have an overlapping portion overlapping in the head length direction.
A part that forms dots with one overlapping nozzle;
A portion where dots are formed by the other overlapping nozzle;
Provide the three parts, the part that forms dots with both overlapping nozzles,
The part where dots are formed by both of the nozzles is mostly a part where the ratio of the part where dots are formed by either the part where dots are formed by the one nozzle or the part where dots are formed by the other nozzle is close. An image forming method characterized in that it exists. An image forming method for forming an image by reciprocating a recording head in a direction orthogonal to a conveyance direction of a recording medium,
An area formed by the recording head using at least one scan is a first image area,
An area formed by the recording head formed at a position different from the first image area using at least one scan is a second image area,
When the region located at the boundary between the first image region and the second image region is a third image region,
The third image region corresponds to an overlapping portion in which the first scan used for the first image region and the second scan used for the second image region overlap each other in the head length direction. In the dot formation step of the image located in the overlapping portion,
A portion for forming dots with the nozzle of the first scan;
A portion for forming dots with the nozzle of the second scan;
A portion for forming dots with both nozzles of both the first and second scans, and three portions;
The ratio of the portion where dots are formed by either of the nozzles of the first scan and the portion where dots are formed by the nozzle of the first scan or the portion where dots are formed by the nozzle of the second scan is close. An image forming method characterized in that a large amount exists in a portion. The recording head has a length equal to or greater than the width of the recording medium in the head length direction,
The image forming method according to claim 1, wherein the image is formed by conveying the recording medium in a direction orthogonal to the longitudinal direction of the head.   The image forming method according to claim 1, wherein the recording head reciprocates in a direction orthogonal to a recording medium conveyance direction to form an image. The part where dots are formed by both the nozzles,
Either the part that forms dots with the one nozzle or the part that forms dots with the nozzles of the first scan; and
Either the part that forms dots with the other nozzle or the part that forms dots with the nozzles of the second scan,
5. The image forming method according to claim 1, wherein a large number of the nozzles are present in a nozzle row direction or a portion switched in a direction orthogonal to the nozzle row. At least a part of a portion where dots are formed by both the nozzles,
6. The image forming method according to claim 1, wherein the dot data is formed after being changed to dot data of another drop type.   The image forming method according to claim 1, wherein a dot formation pattern in a portion where dots are formed by both the nozzles is performed by mask processing.   The image forming method according to claim 1, wherein a dot formation pattern in a portion where dots are formed by the both nozzles is performed by a pattern selected by a user. An image forming program for causing an image forming apparatus including a recording head in which at least two or more heads are arranged in the head length direction of the head to execute processing,
The recording head has an overlapping portion in which head ends adjacent to each other in the head length direction overlap in the head length direction,
When executing the dot formation processing of the image located in the overlapping portion,
A part that forms dots with one overlapping nozzle;
A portion where dots are formed by the other overlapping nozzle;
Provide the three parts, the part that forms dots with both overlapping nozzles,
The part where dots are formed by both of the nozzles is mostly a part where the ratio of the part where dots are formed by either the part where dots are formed by the one nozzle or the part where dots are formed by the other nozzle is close. An image forming program characterized in that it exists. An image forming apparatus comprising a recording head in which at least two or more heads are arranged in the head length direction of the head,
The recording head has an overlapping portion in which head ends adjacent to each other in the head length direction of the head overlap in the head length direction,
Comprising dot forming means for forming dots of an image located in the overlapping portion;
The dot forming means
A part that forms dots with one overlapping nozzle;
A portion where dots are formed by the other overlapping nozzle;
Provide the three parts, the part that forms dots with both overlapping nozzles,
The part where dots are formed by both of the nozzles is mostly a part where the ratio of the part where dots are formed by either the part where dots are formed by the one nozzle or the part where dots are formed by the other nozzle is close. An image forming apparatus characterized in that the image forming apparatus exists.