JP2010120222A - Image formation device, image forming method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image formation device, an image forming method and a program which can suppress the generation of a banding in the overlapping region formed in the joints of two or more recording heads or in the overlapping region formed between dots printed on a form and the recording head. <P>SOLUTION: The image formation device includes the recording head having two or more nozzles for discharging droplets of a recording liquid, a recording head scanning means, a conveyance means for making the recording medium scanned in the sub scan direction perpendicular to the main scan direction and a printing control means, at least. In the image formation device which forms a picture on the recording medium, when distributing printing data in the above overlapping region where two or more nozzles corresponding to one dot generation exist, the printing data is distributed so that the drive frequency may be the same as the drive frequency in a non-overlapping region. Image forming method and the program are also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, an image forming method, and a program, and more particularly to an image forming apparatus, an image forming method, and a program that suppress the occurrence of banding in an overlap region.

  As an image forming apparatus such as a printer, a facsimile machine, a copying machine, or a multifunction machine of these, for example, an apparatus including a recording head composed of a liquid discharge head that discharges liquid droplets of a recording liquid (liquid) is used. Although it is also referred to as “paper”, the material is not limited, and a recording medium (recording medium, recording medium, transfer material, recording paper, etc. is also used synonymously) and a recording liquid as a liquid (hereinafter also referred to as ink). There is a so-called ink jet type image forming apparatus in which image formation (recording, printing, printing, and printing are also used synonymously) is performed by attaching the sheet to a sheet.

  Inkjet image forming apparatuses (hereinafter referred to as “inkjet printers”) are equipped with a plurality of nozzles that eject ink (droplets) on a recording head in order to realize high-speed printing (image formation). Inkjet printers that form images on paper by ejecting ink while feeding (conveying) the paper and scanning the recording head in a direction perpendicular to the paper feed direction, A multi-pass method is employed in which an image is formed by performing a plurality of main scans (multi-scan) with the same nozzle group or different nozzle groups on the same area of the paper. However, since printing in two directions is required, the printing speed is limited, and it is desired to increase the printing speed.

  As a means for increasing the speed, for example, it is conceivable to set the scanning direction of the recording head to one direction (only in the paper feed direction). It is necessary to do more. In such a recording head, it is desirable that all the nozzles are arranged in a line at regular intervals, but from the viewpoint of cost and manufacturing technology, there is a limit to the number of nozzles that can be mounted on one recording head. is there. Therefore, a recording head equipped with a large number of nozzles by combining a plurality of recording heads having a certain number of nozzles is used.

  However, there is a limit to the joining accuracy of the recording head, and the distance between nozzles at the joining portion of adjacent recording heads cannot be made completely constant. For this reason, when the distance between the nozzles in the joint portion is long, a white streak that causes the ink to become thin occurs, and when the distance between the nozzles is short, a dark streak occurs. Such streaks are called “banding”.

  As a method of preventing the banding phenomenon, there is a method of providing an overlap as shown in FIG. 15 between the recording heads. However, since there are two nozzles corresponding to one dot in the data in the overlap portion, unless some control is performed, dots are shot from two nozzles for one dot in the data. It becomes. Therefore, there is a problem that banding occurs because the color becomes darker in the overlap portion.

  As a technique for suppressing the banding generated in the overlap portion, for example, a nozzle distribution unit that determines which of two nozzles is used for drawing based on a random number, and the nozzle distribution process are performed. Parameter determining means for determining a size parameter that defines the size of the distribution target area to be performed, and the parameter determining means determines the size parameter according to an average gradation value of an area in the vicinity of the joining area An image forming apparatus has been proposed (see Patent Document 1).

JP 2006-240043 A

  However, in the technique described in Patent Document 1, since the distribution of the print data of the overlap portion is determined by a random number, there are places where dots distributed to each nozzle are continuously / discontinuously hit. Will be mixed. As a result, there are cases where printing is performed at various drive frequencies in the overlap portion (hereinafter, also referred to as “overlap region”), and this is caused by fluctuations in the ejection droplets of the nozzle corresponding to dot generation in the overlap region. Thus, banding may occur in the overlap region.

  On the other hand, in the inkjet printer controlled to convey the paper so that the end of the recording head overlaps the dot printed on the paper, it is also caused by the deviation of the paper conveyance amount. Banding may occur in the overlap area.

  Therefore, the present invention has been made in view of the above-described problems in the prior art, and is an overlap region where a plurality of nozzles corresponding to one dot generation exist, for example, an overlap formed at a joint portion of a plurality of recording heads. An object is to provide an image forming apparatus, an image forming method, and a program capable of suppressing the occurrence of banding in a wrap region or an overlap region formed between a dot printed on a sheet and a recording head. To do.

The present invention provided to solve the above problems is as follows.
[1] A recording head having a plurality of nozzles that discharge recording liquid droplets, a recording head scanning unit that scans the recording head in the main scanning direction, and a conveyance that scans the recording medium in the sub-scanning direction orthogonal to the main scanning direction. An image forming apparatus for forming an image on the recording medium, comprising at least a printing unit and a printing control unit.
The transport means transports the recording medium such that an end region of the recording head overlaps and forms an overlap region with respect to dots recorded on the recording medium,
The image forming apparatus according to claim 1, wherein when the print control unit distributes the print data in the overlap area, the drive frequency is controlled to be the same as the drive frequency in the non-overlap area.
[2] A recording head having a plurality of nozzles that eject recording liquid droplets, a recording head scanning unit that scans the recording head in the main scanning direction, and a conveyance that scans the recording medium in the sub-scanning direction perpendicular to the main scanning direction An image forming apparatus for forming an image on the recording medium, comprising at least a printing unit and a printing control unit.
The recording head is composed of a plurality of recording head members, and the adjacent recording head members are arranged in the sub-scanning direction so as to form overlapping regions with overlapping end portions at the joint portion,
The image forming apparatus according to claim 1, wherein when the print control unit distributes the print data in the overlap area, the drive frequency is controlled to be the same as the drive frequency in the non-overlap area.
[3] The print control unit distributes the print data so that the drive frequency in the overlap region is the same as the drive frequency in the non-overlap region according to the gradation level of the image forming data. The image forming apparatus according to any one of [1] to [2].
[4] The print control means distributes the print data so that the drive frequency in the overlap region is the same as the drive frequency in the non-overlap region according to the ambient temperature of the recording head. The image forming apparatus according to [3].
[5] The print control unit distributes the print data so that the drive frequency in the overlap region is the same as the drive frequency in the non-overlap region according to the number of main scans in the same print region. The image forming apparatus according to any one of [1] to [2].
[6] Recording head having a plurality of nozzles for ejecting recording liquid droplets, recording head scanning means for scanning the recording head in the main scanning direction, and conveyance for scanning the recording medium in the sub-scanning direction orthogonal to the main scanning direction And an image forming method in an image forming apparatus for forming an image on the recording medium.
In the overlap region where a plurality of nozzles corresponding to one dot generation exist, when the print data in the overlap region is distributed, the drive frequency is distributed to be the same as the drive frequency in the non-overlap region. An image forming method.
[7] Recording head having a plurality of nozzles for ejecting recording liquid droplets, recording head scanning means for scanning the recording head in the main scanning direction, and transport for scanning the recording medium in the sub-scanning direction orthogonal to the main scanning direction An image forming apparatus that includes at least a printing unit and a printing control unit and forms an image on the recording medium, and causes the image forming method according to [6] to be executed.

  According to the present invention, an overlap region where a plurality of nozzles corresponding to one dot generation exist, for example, an overlap region formed at a joint portion of a plurality of recording heads, a region printed with paper dots, and recording. It is possible to provide an image forming apparatus, an image forming method, and a program capable of suppressing the occurrence of banding in an overlap region formed between the head and the like.

As an effect of the present invention, according to the first aspect of the present invention, a recording head having a plurality of nozzles that eject recording liquid droplets, recording head scanning means for scanning the recording head in the main scanning direction, and a recording medium are mainly used. In an image forming apparatus that includes at least a conveying unit that scans in a sub-scanning direction orthogonal to a scanning direction, and a printing control unit, and that forms an image on the recording medium, the conveying unit is recorded on the recording medium. The recording medium is transported so that the end of the recording head overlaps the dots to form an overlap area, and the print control unit is driven when distributing print data in the overlap area. Since the frequency is controlled to be the same as the drive frequency in the non-overlapping area, the overlapping area generated due to the frequency characteristics of the ejected droplet volume Bindings can be suppressed.
According to the second aspect of the present invention, a recording head having a plurality of nozzles that eject recording liquid droplets, recording head scanning means for scanning the recording head in the main scanning direction, and a recording medium in a sub-direction orthogonal to the main scanning direction. In an image forming apparatus that includes at least a conveying unit that scans in a scanning direction and a printing control unit, and that forms an image on the recording medium, the recording head includes a plurality of recording head members, and the adjacent recording heads The members are arranged in the sub-scanning direction so that the end portions overlap at the joining portion to form an overlap region, and when the print control unit distributes the print data in the overlap region, the drive frequency is non- Since the control is performed so as to be the same as the driving frequency in the overlap region, for example, a line in which a plurality of recording head members are arranged in the sub-scanning direction. Also in the printer, it is possible to suppress banding overlap region.
According to a third aspect of the present invention, in the image forming apparatus according to any one of the first to second aspects, the print control means drives the driving frequency in the overlap region in accordance with the gradation level of the image forming data. However, since the print data is distributed so as to be the same as the driving frequency in the non-overlapping area, the shadow area where the dots are densely shot at the same gradation level as in the overlapping area and the non-overlapping area. By limiting to the above, banding can be suppressed from the highlight to the middle region without impairing the overlap effect.
According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the print control means causes the drive frequency in the overlap region to be in the non-overlap region according to the ambient temperature of the recording head. Since the print data is distributed so as to be the same as the drive frequency, banding more efficiently by considering the head level and the gradation level that makes the drive frequency of the overlap area and non-overlap area the same. Can be suppressed.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to second aspects, the drive control unit has a drive frequency in the overlap area corresponding to the number of main scans in the same print area. Since the print data is distributed so as to be the same as the drive frequency in the non-overlap area, the drive frequency in the overlap area and the non-overlap area can be made the same by changing the number of print passes. Banding can be effectively suppressed.
According to the sixth aspect of the present invention, a recording head having a plurality of nozzles for discharging recording liquid droplets, recording head scanning means for scanning the recording head in the main scanning direction, and a recording medium in a sub-direction orthogonal to the main scanning direction. An image forming method in an image forming apparatus that includes at least a conveying unit that scans in a scanning direction and a print control unit, and that forms an image on the recording medium, wherein there are a plurality of nozzles corresponding to one dot generation. In the overlap area, when the print data in the overlap area is distributed, the drive frequency is distributed so as to be the same as the drive frequency in the non-overlap area. It is possible to effectively suppress the occurrence of banding in the overlap region due to the frequency characteristics of the drop amount.
According to the seventh aspect of the present invention, a recording head having a plurality of nozzles for discharging recording liquid droplets, a recording head scanning means for scanning the recording head in the main scanning direction, and a recording medium in a sub-direction orthogonal to the main scanning direction. A program for executing the image forming method according to claim 6 in an image forming apparatus that includes at least a conveying unit that scans in a scanning direction and a print control unit, and that forms an image on the recording medium. Therefore, the image forming apparatus that executes this can effectively suppress the banding of the overlap region.

Hereinafter, a configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. The image forming method and program of the present invention will also be described. 1 and 2 are views showing an example of the image forming apparatus of the present invention. FIG. 1 is an explanatory side view of the overall structure of the mechanism part, and FIG. 2 is an explanatory plan view of the mechanism part. An image forming apparatus holds a carriage 3 slidably in a main scanning direction by a guide rod 1 and a guide rail 2 which are guide members horizontally mounted on left and right side plates (not shown), and serves as a main scanning motor as a recording head scanning unit. In FIG. 2, the moving scanning is performed in the direction indicated by the arrow (main scanning direction) in FIG. 2 via the timing belt 5 stretched between the driving pulley 6A and the driven pulley 6B.
The carriage 3 includes, for example, four recording heads 7y, 7c, 7m, and 7k including liquid ejection heads that eject ink droplets of yellow (Y), cyan (C), magenta (M), and black (K), respectively. (When the colors are not distinguished, they are referred to as “recording head 7”.) A plurality of ink ejection openings are arranged in a direction crossing the main scanning direction, and the ink droplet ejection direction is directed downward. The carriage 3 is equipped with sub-tanks 8 for each color for supplying ink of each color to the recording head 7. Ink is supplied to the sub tank 8 from a main tank (ink cartridge) (not shown) via an ink supply tube 9.

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

  Here, in the image forming apparatus and the image forming method of the present invention, the “overlap region” means a region where a plurality of nozzles corresponding to one dot generation exist, and specifically, a plurality of recording heads. There are a case where the overlap region is formed at the joint portion and a case where the overlap region is formed between the region where dots are printed on the paper and the recording head. FIG. 15 is a diagram for explaining an overlap region formed at a joint portion of a plurality of recording heads. As shown in FIG. 15, a plurality of recording head members are arranged substantially in series in the sub-scanning direction, and the recording head members are arranged so that the end portions overlap each other at adjacent connecting portions to form an overlap region. A recording head can also be configured.

  In the image forming apparatus and the image forming method of the present invention, “distributing print data” means distributing data to each nozzle corresponding to generation of dots to be printed based on the print data, and a plurality of times. The printing method for performing the scan includes dividing and distributing the data for each scan.

  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 55 is detachably mounted on the back. The double-sided paper feeding unit 55 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 machine 56 is provided with caps 57 for capping each nozzle surface of the recording head 7, a wiper blade 58 as a blade member for wiping the nozzle surface, and for discharging the thickened recording liquid. An empty discharge receiver 59 for receiving droplets when performing empty discharge for discharging droplets that do not contribute to recording is provided.

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

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

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

  During printing (recording) standby, the carriage 3 is moved to the maintenance / recovery mechanism 55 side, and the nozzle surface of the recording head 7 is capped by the cap 57, and the nozzles are kept in a wet state. To prevent. In addition, the recording liquid is sucked from the nozzle in a state where the recording head 7 is capped by the cap 57, and a recovery operation is performed to discharge the thickened recording liquid and bubbles, and the ink adhered to the nozzle surface of the recording head 7 by this recovery operation. Wiping is performed with a wiper blade 58 in order to remove the cleaning. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. Thereby, the stable ejection performance of the recording head 7 is maintained.

  Next, an example of the liquid discharge head constituting the recording head 7 will be described with reference to FIGS. 3 is a cross-sectional explanatory diagram along the longitudinal direction of the liquid chamber of the head, and FIG. 4 is a cross-sectional explanatory diagram of the head along the lateral direction of the liquid chamber (nozzle arrangement direction).

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

  In addition, two rows (only one row is shown in FIG. 6) of stacked piezoelectric elements as electromechanical conversion elements that are pressure generating means (actuator means) for pressurizing ink in the liquid chamber 106 by deforming the diaphragm 102. An element 121 and a base substrate 122 to which the piezoelectric element 121 is bonded and fixed are provided. Note that a column portion 123 is provided between the piezoelectric elements 121. This support portion 123 is a portion formed simultaneously with the piezoelectric element 121 by dividing and processing the piezoelectric element member. However, since the drive voltage is not applied, the support portion 123 becomes a simple support.

  Further, an FPC cable 126 mounted with a drive circuit (drive IC) (not shown) is connected to the piezoelectric element 121.

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

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

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

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

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

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

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

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

Next, an outline of a control unit as a print control unit of the image forming apparatus will be described with reference to the block diagram of FIG.
In the control unit 200, the CPU 211 that controls the entire apparatus, the ROM 202 that stores programs executed by the CPU 211 and other fixed data, the RAM 203 that temporarily stores image data and the like, and the power supply of the apparatus are cut off. A rewritable non-volatile memory 204 for holding data in between, an image processing for performing various signal processing and rearrangement on image data, and an ASIC 205 for processing input / output signals for controlling the entire apparatus. ing.

  The control unit 200 also includes an I / F 206 for transmitting and receiving data and signals to and from the host, data transfer means for driving and controlling the recording head 7, and drive waveform generation means for generating a drive waveform. A print control unit 207; a 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 roller 34, I / O 213 for inputting detection signals from encoder sensors 43 and 35, detection signals from various sensors such as a temperature sensor that detects 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 transmits image data from the host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, an imaging device such as a digital camera, etc. via an I / F 206 via a cable or a network. Receive.

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

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

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

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

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

  The droplet control signal is a 2-bit signal that instructs each droplet to open and close an analog switch 317, which will be described later, of the head driver 208. The droplet control signal is a waveform to be selected according to the printing 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 316 that is turned on / off (opened / closed) by the output of the decoder 313 provided via the level shifter 314.

  The analog switch 316 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. Accordingly, when the analog switch 316 is turned on in accordance with the result of decoding the serially transferred image data (gradation data) and the control signals MN0 to MN3 by the decoder 313, a required drive signal constituting the common drive waveform is obtained. Passing (selected) is applied to the piezoelectric element 121.

Here, ink that is a recording liquid used in the image forming apparatus will be described.
The recording liquid has the following configurations (1) to (10).
(1) Pigment (self-dispersing pigment) 6 wt% or more (2) Wetting agent 1
(3) Wetting agent 2
(4) Water-soluble organic solvent (5) Anion or nonionic surfactant (6) Polyol or glycol ether having 8 or more carbon atoms (7) Emulsion (8) Preservative (preservative antifungal agent)
(9) pH adjuster (10) pure water That is, a pigment is used as a colorant for printing (recording), a solvent for decomposing and dispersing it as an essential component, and a wetting agent as an additive. , Surfactants, emulsions, preservatives, and pH adjusters. The reason why the humectant 1 and the humectant 2 are mixed is to make use of the characteristics of the humectant and to easily adjust the viscosity.

Hereinafter, each of the ink components will be described more specifically.
Regarding the pigment (1), inorganic pigments and organic pigments can be used without any particular limitation. As the inorganic pigment, in addition to titanium oxide and iron oxide, carbon black produced by a known method such as a contact method, a furnace method, or a thermal method can be used. Organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazines). Pigments, thioindigo pigments, isoindolinone pigments, quinofullerone pigments, etc.), dye chelates (for example, basic dye chelate, acid dye chelate, etc.), nitro pigments, nitroso pigments, aniline black, and the like.

  According to a preferred embodiment of the ink, among these pigments, those having good affinity with water are preferably used. The particle diameter of the pigment is preferably 0.05 μm to 10 μm, more preferably 1 μm or less, and most preferably 0.16 μm or less. The amount of pigment added as a colorant in the ink is preferably about 6 to 20% by weight, more preferably about 8 to 12% by weight.

Specific examples of the pigment preferably used for the ink include the following.
For black, carbon black (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, channel black, or metals such as copper, iron (CI Pigment Black 11), titanium oxide, etc. And organic pigments such as aniline black (C.I. Pigment Black 1).

  Further, for color use, CI pigment yellow 1 (fast yellow G), 3, 12 (disazo yellow AAA), 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 81, 83 (Disazo Yellow HR), 95, 97, 98, 100, 101, 104, 408, 109, 110, 117, 120, 138, 153, CI Pigment Orange 5, 13, 16 17, 36, 43, 51, CI Pigment Red 1, 2, 3, 5, 17, 22 (Brilliant First Scarlet), 23, 31, 38, 48: 2 (Permanent Red 2B (Ba)) 48: 2 (permanent red 2B (Ca)), 48: 3 (permanent red 2B (Sr)), 48: 4 (permanent red 2B (Mn)), 49 1, 52: 2, 53: 1, 57: 1 (Brilliant Carmine 6B), 60: 1, 63: 1, 63: 2, 64: 1, 81 (Rhodamine 6G rake), 83, 88, 101 (Bengara) , 104, 105, 106, 108 (cadmium red), 112, 114, 122 (quinacridone magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209 219, CI pigment violet 1 (rhodamine lake), 3, 5: 1, 16, 19, 23, 38, CI pigment blue 1, 2, 15 (phthalocyanine blue R), 15: 1, 15: 2, 15: 3 (phthalocyanine blue E), 16, 17: 1, 56, 60, 63, CI pigment green 1, 4, 7, 8, 1 , And the like 17,18,36.

  Other pigment pigments (eg carbon) treated with resin, etc., can be dispersed in water, and pigments (eg carbon) can be dispersed in water by adding functional groups such as sulfone groups and carboxyl groups to the surface. Processed pigments can be used.

  Further, a pigment may be included in a microcapsule so that the pigment can be dispersed in water.

  According to a preferred aspect of the ink, the pigment for black ink is preferably added to the ink as a pigment dispersion obtained by dispersing the pigment in an aqueous medium with a dispersant. As a preferable dispersing agent, a known dispersion used for preparing a conventionally known pigment dispersion can be used.

Examples of the dispersion include the following.
Polyacrylic acid, polymethacrylic acid, acrylic acid-acrylonitrile copolymer, vinyl acetate-acrylic acid ester copolymer, acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer Polymer, styrene-acrylic acid-alkyl acrylate ester copolymer, styrene-methacrylic acid-alkyl acrylate copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic Acid copolymer-alkyl acrylate ester copolymer, styrene-maleic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl acetate-ethylene copolymer, vinyl acetate-fatty acid vinyl ethylene copolymer, vinyl acetate -Maleate ester copolymer, vinyl acetate- Examples include crotonic acid copolymers and vinyl acetate-acrylic acid copolymers.

  According to a preferred embodiment of the ink, these copolymers preferably have a weight average molecular weight of 3,000 to 50,000, more preferably 5,000 to 30,000, most preferably 7,000 to 15. 1,000. The addition amount of the dispersant may be appropriately added as long as the pigment is stably dispersed and other effects are not lost. The dispersant is preferably in the range of 1: 0.06 to 1: 3, more preferably in the range of 1: 0.125 to 1: 3.

  The pigment used for the colorant is a particle having a particle size of 0.05 to 0.16 μm, containing 6 to 20% by weight based on the total weight of the recording ink, and is dispersed in water by a dispersant. The dispersant is a polymer dispersant having a molecular weight of 5,000 to 100,000. When at least one water-soluble organic solvent is a pyrrolidone derivative, particularly 2-pyrrolidone, the image quality is improved.

  Regarding the wetting agents 1 and 2 and the water-soluble organic solvent (2) to (4), in the case of an ink, water is used as a liquid medium in the ink. In order to prevent drying and to improve dissolution stability, for example, the following water-soluble organic solvents are used. A plurality of these water-soluble organic solvents may be used in combination.

Specific examples of the wetting agent and the water-soluble organic solvent include the following.
Ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetraethylene glycol, hexylene glycol, polyethylene glycol, polypropylene glycol, 1,5-pentanediol, 1,6-hexanediol, glycerol, Polyhydric alcohols such as 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, and petriol; ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether , Diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether Polyhydric alcohol alkyl ethers such as propylene glycol monoethyl ether; Polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl Nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, 1,3-dimethylimidazolidinone, ε-caprolactam, γ-butyrolactone; amides such as formamide, N-methylformamide, N, N-dimethylformamide; monoethanol Amines such as amine, diethanolamine, triethanolamine, monoethylamine, diethylamine and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane and thiodiethanol; propylene carbonate Over bets is ethylene carbonate.

  Among these organic solvents, diethylene glycol, thiodiethanol, polyethylene glycol 200 to 600, triethylene glycol, glycerol, 1,2,6-hexanetriol, 1,2,4-butanetriol, petriol, 1,5-pentane Diol, 2-pyrrolidone and N-methyl-2-pyrrolidone are preferred. These are excellent in solubility and prevention of poor jetting characteristics due to water evaporation.

  The other wetting agent preferably contains sugar. Examples of saccharides include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides) and polysaccharides, preferably glucose, mannose, fructose, ribose, xylose, arabinose, galactose, maltose, cellobiose, Examples include lactose, sucrose, trehalose, and maltotriose. Here, the polysaccharide means a saccharide in a broad sense, and is used to include a substance that exists widely in nature such as α-cyclodextrin and cellulose.

In addition, the derivatives of these saccharides are represented by the reducing sugars of the saccharides described above (for example, sugar alcohol (general formula HOCH ₂ (CHOH) nCH ₂ OH (where n represents an integer of 2 to 5)). ), Oxidized sugars (eg, aldonic acid, uronic acid, etc.), amino acids, thioic acids, etc. Particularly preferred are sugar alcohols, and specific examples include maltitol, sorbit and the like.

  The content of these saccharides is suitably 0.1 to 40% by weight, preferably 0.5 to 30% by weight of the ink composition.

  The surfactant (5) is not particularly limited, but examples of the anionic surfactant include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, laurate, and polyoxyethylene alkyl ether sulfate. And the like.

  Nonionic surfactants include, for example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl amines, polyoxyethylene alkyl amides, and the like. Can be mentioned. The surfactants can be used alone or in combination of two or more.

The surface tension in the ink is an index indicating the permeability to paper, and in particular shows the dynamic surface tension in a short time of 1 second or less after the surface is formed, and is different from the static surface tension measured by the saturation time. Any measuring method can be used as long as it can measure a dynamic surface tension of 1 second or less by a conventionally known method described in JP-A-63-31237 or the like. In the present invention, a Wilhelmy type suspension is used. It measured using the plate type surface tension meter. When the value of the surface tension is preferably 40 mJ / m ² or less, more preferably 35 mJ / m ² or less, excellent fixing properties and drying properties can be obtained.

Regarding the polyol or glycol ether having 8 or more carbon atoms of (6), a partially water-soluble polyol and / or glycol ether having a solubility of less than 0.1 to 4.5% by weight in water at 25 ° C. Is added in an amount of 0.1 to 10.0% by weight based on the total weight of the recording ink, thereby improving the wettability of the ink with respect to the heat element, and even when added in a small amount, ejection stability and frequency stability can be obtained. I found out that
(A) 2-ethyl-1,3-hexanediol Solubility: 4.2% (20 ° C.)
(B) 2,2,4-Trimethyl-1,3-pentanediol Solubility: 2.0% (25 ° C.).

  A penetrant having a solubility of less than 0.1-4.5% by weight in water at 25 ° C. has the advantage of very high permeability instead of low solubility. Therefore, an ink having a very high permeability in a combination of a penetrant having a solubility of less than 0.1 to 4.5% by weight in water at 25 ° C. with another solvent or another surfactant. Can be produced.

  It is preferable that a resin emulsion is added to the ink as the emulsion (7). The resin emulsion means an emulsion in which the continuous phase is water and the dispersed phase is the following resin component. Examples of the resin component in the dispersed phase include acrylic resins, vinyl acetate resins, styrene-butadiene resins, vinyl chloride resins, acrylic-styrene resins, butadiene resins, and styrene resins.

  According to a preferred embodiment of the ink, the resin is preferably a polymer having both a hydrophilic part and a hydrophobic part. The particle size of these resin components is not particularly limited as long as an emulsion is formed, but is preferably about 150 nm or less, more preferably about 5 to 100 nm.

  These resin emulsions can be obtained by mixing resin particles in water, optionally with a surfactant. For example, an acrylic resin or styrene-acrylic resin emulsion can be obtained by adding (meth) acrylic acid ester or styrene, (meth) acrylic acid ester, and optionally (meth) acrylic acid ester, and a surfactant to water. It can be obtained by mixing. The mixing ratio of the resin component and the surfactant is usually preferably about 10: 1 to 5: 1. When the amount of the surfactant used is less than the above range, it is difficult to form an emulsion, and when it exceeds the above range, the water resistance of the ink tends to be lowered or the penetrability tends to deteriorate.

  The ratio of the resin as the dispersed phase component of the emulsion and water is 60 to 400 parts by weight, preferably 100 to 200 parts by weight with respect to 100 parts by weight of the resin.

  Commercially available resin emulsions include Microgel E-1002, E-5002 (styrene-acrylic resin emulsion, manufactured by Nippon Paint Co., Ltd .: both trade names), Boncoat 4001 (acrylic resin emulsion, Dainippon Ink & Chemicals, Inc.) Company: trade name), Boncoat 5454 (styrene-acrylic resin emulsion, Dainippon Ink and Chemicals Co., Ltd .: trade name), SAE-1014 (styrene-acrylic resin emulsion, made by Nippon Zeon Co., Ltd .: trade name) , Cybinol SK-200 (acrylic resin emulsion, manufactured by Syden Chemical Co., Ltd .: trade name), and the like.

The ink preferably contains a resin emulsion such that the resin component is 0.1 to 40% by weight of the ink, more preferably 1 to 25% by weight.
The resin emulsion has the property of thickening and aggregating, has the effect of suppressing the penetration of the coloring components, and further promoting the fixing to the recording material. Further, depending on the type of resin emulsion, a film is formed on the recording material, and the printed material has an effect of improving the abrasion resistance.

  In addition to the colorant, solvent, and surfactant described above, conventionally known additives can be added to the ink. (8) Preservative (antifungal agent), (9) pH adjuster, etc. Is mentioned.

  For example, as an antiseptic / antifungal agent, sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, sodium pentachlorophenol and the like can be used.

  As the pH adjuster, any substance can be used as long as the pH can be adjusted to 7 or more without adversely affecting the ink to be prepared. Examples thereof include amines such as diethanolamine and triethanolamine, hydroxides of alkali metal elements such as lithium hydroxide, sodium hydroxide and potassium hydroxide, ammonium hydroxide, quaternary ammonium hydroxide, and quaternary phosphonium. Examples thereof include carbonates of alkali metals such as hydroxide, lithium carbonate, sodium carbonate, and potassium carbonate. Examples of the chelating reagent include sodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, sodium uramil diacetate, and the like.

  Examples of the rust inhibitor include acidic sulfite, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

  Thus, even when printing on plain paper by using an ink composition comprising at least a pigment, a water-soluble organic solvent, a polyol or glycol ether having 8 or more carbon atoms, and water, (1) good color tone ( (2) High image density, (3) Clear image quality without feathering or color bleeding on characters / images, (4) Ink back that can withstand double-sided printing It is possible to achieve an image with little missing phenomenon, (5) high image dryness (fixability) suitable for high-speed printing, and (6) high image quality with high fastness such as light resistance and water resistance. Density, color developability, color reproducibility, character bleeding, color boundary bleeding, double-sided printing property, fixing property, etc. can be greatly improved.

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

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

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

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

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

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

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

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

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

  That is, when the ink viscosity is small, the voltage of the drive pulse is relatively small, and when the ink viscosity is large, the voltage of the drive pulse is relatively large. The volume can be discharged substantially constant. Further, the driving pulse 2 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.

  Next, an image forming method according to the present invention for outputting a print image by the image forming apparatus according to the present invention and an image forming apparatus in which a program according to the present invention is installed in a computer will be described below.

  An example of a printing system including an ink jet printer (ink jet recording apparatus) which is an image forming apparatus according to the present invention and an image processing apparatus equipped with an image forming method program according to the present invention will be described with reference to FIG.

  The printing system (image forming system) is configured by connecting one or a plurality of image processing apparatuses 400 such as a personal computer (PC) and the ink jet printer 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 a CRT, and the like via a predetermined interface. A storage medium reading device for reading a storage medium such as an optical disk is connected, and a predetermined interface (external I / F) 407 for communicating with a network such as the Internet or an external device such as a USB is connected.

  An image processing program including a program according to the present invention is stored in the storage device 406 of the image processing apparatus 400. This 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 this image processing program may operate on a predetermined OS. Further, it may be a part of specific application software.

  The image processing method according to the present invention can also be performed on the ink jet printer side, but here, on the ink jet recording apparatus side, a dot pattern that is actually recorded upon receiving an image drawing or character print command in the apparatus. 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 the printer driver according to the present invention incorporated as software in the image processing apparatus 400 (host computer), and then an inkjet printer. An example in which multi-value dot pattern data (print image data) that can be output by 500 is generated, rasterized, transferred to the inkjet printer 500, and the inkjet printer 500 is printed out will be described.

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

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

  Thereafter, image processing is performed on these recorded dot patterns (image data 410) 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 recording dot pattern stored in the raster data memory is transferred to the ink jet recording apparatus 500 via the interface.

  As an image recording method by the image recording apparatus of the present invention, 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 may be used for the same area of the recording medium. So-called “multi-pass printing” in which an image is formed by performing main scanning a plurality of times with groups or different nozzle groups may be used. Further, a plurality of heads may be arranged in the main scanning direction, and the same area may be divided by different nozzles. These recording methods can be used in appropriate combination.

Hereinafter, multi-pass printing will be described.
Here, a case where an image is completed by executing four main recording scans (four passes) for one recording area will be described as an example.
FIG. 12 is a block diagram schematically showing an image processing unit in this embodiment. In the figure, 601 is an input terminal, 602 is a recording buffer, 604 is a pass number setting unit, 605 is a mask processing unit, 606 is a mask pattern table, 607 is a head I / F unit, and 608 is a recording head. The bitmap data input from the input terminal 601 is stored at a predetermined address in the recording buffer 602 by the recording buffer control unit. The recording buffer 602 has a capacity capable of storing bitmap data for one scan and the paper feed amount, and constitutes a ring buffer in paper feed amount units such as a FIFO memory. The recording buffer control unit controls the recording buffer 602. When bitmap data for one scan is stored in the recording buffer 602, the printer engine is activated, and the recording buffer 602 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 604. When bitmap data for the next scan is input from the input terminal 601, the recording buffer 602 is controlled so as to be stored in an empty area of the recording buffer 602 (an area corresponding to the paper feed amount for which recording has been completed).

  Next, a more specific configuration example of the pass number setting unit in the image processing unit will be described. The path number setting unit 604 determines the number of divided paths and outputs the number of paths to the mask processing unit 605. In the mask pattern table 606, 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 mask processing 605. When the mask processing unit 605 masks the bitmap data stored in the recording buffer 602 for each pass recording using a mask pattern and outputs it to the head driver, the head driver records the masked bitmap data. They are rearranged in the order used by the head 608 and transferred to the recording head 608.

  By using multi-pass printing in this way, banding that stands out in one-pass printing can be averaged and made inconspicuous. One means for speeding up printing is a one-pass printing or a printer having a head with a size larger than the paper width (generally a line head type printer). In one-pass printing, banding due to deviation of the paper feed amount, In the case where a plurality of heads are arranged in the sub-scanning direction and the nozzle group is lengthened, banding due to a shift of the head connecting portion occurs.

  As a method of suppressing such banding, there is a method of overlapping a part of the nozzles, which distributes the dot deviation by distributing the print data to each nozzle.

  In the overlap area, there are two nozzles corresponding to one dot in the data. Therefore, if no treatment is made, dots will be hit from two nozzles for one dot in the data, and overlap will occur. The color becomes dark at the part and banding occurs. In contrast, a method of distributing print data in the overlap area to each nozzle using a random number has been used, but since the random number is used, the dots distributed to each nozzle are continuous / non-continuous. Will be mixed. As a result, there are cases where printing is performed at various drive frequencies in the overlap region. That is, when the ejection droplets of the nozzle are ejected at a predetermined drive frequency, the drive waveform is designed so as to achieve the target ejection amount, so that the ejection droplet amount also varies when the drive frequency changes. . For example, when changing from 1-pass printing to 2-pass printing, the drive frequency is halved. For this reason, if printing is performed at various drive frequencies in the overlap region, banding occurs due to fluctuations in the amount of ejected droplets. Furthermore, a drive frequency difference also occurs between the overlap region and the non-overlap region, and banding occurs in the overlap portion.

  Therefore, when the image forming apparatus, the image forming method, and the program according to the present invention distribute the print data in the overlap area, for example, as shown in FIG. By distributing the print data to each nozzle in each scan so as to be the same as the drive frequency, the occurrence of banding can be suppressed.

  However, originally, in the overlap area, there has been a method of absorbing banding due to dot misalignment by dispersing the nozzles to be used, so it may be possible to see banding at that part if the dots are biased It is done.

Here, the drive frequency characteristics of the ejected droplets will be described with reference to FIG.
FIG. 14 shows the ejection droplet amount when the drive frequency is 5 kHz to 20 kHz. The 1-pass printing is 20 kHz, the 2-pass printing is 10 kHz, and the 4-pass printing is 5 kHz. When the frequency is 20 kHz to 10 kHz, the ejected droplet amount fluctuates greatly, but when the frequency is 10 kHz to 5 kHz, there is no significant difference in the ejected droplet amount. That is, when one-pass printing is performed, if the drive frequency of the non-overlap region is half that of the overlap region, the frequency characteristics are greatly affected.
In particular, the effect of frequency characteristics becomes significant in the shadow area where dots are shot so as to fill the paper, but in the highlight area where dots are shot sparsely, the driving frequency in the non-overlapping area has also dropped, so the effect is almost impossible. No longer occurs.

  Therefore, in the image forming apparatus of the present invention, the print control unit causes the drive frequency in the overlap region to be the same as the drive frequency in the non-overlap region according to the gradation level of the image formation data. More specifically, it is preferable to distribute the print data. Specifically, in the image forming apparatus of the present invention, only the shadow area can be switched according to the gradation level so that the driving frequency of the overlap area and the non-overlap area is the same. It is said.

  In addition, since the frequency characteristic changes depending on the viscosity of the ink, in the image forming apparatus of the present invention, the print control unit has a driving frequency in the overlap region according to the ambient temperature of the recording head. It is preferable to distribute the print data so as to be the same as the drive frequency in the non-overlap region. That is, the gradation level of the image forming data whose distribution is switched may be changed depending on the ambient temperature of the head.

  Furthermore, in the image forming apparatus according to the present invention, the print control unit causes the drive frequency in the overlap area to be the same as the drive frequency in the non-overlap area according to the number of main scans in the same print area. It is preferable to distribute the print data. Specifically, since banding due to a difference in driving frequency becomes significant during one-pass printing, the overlap area may be switched to be distributed in the multi-scan mode such as two-pass printing.

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

Here, different examples of the thermal head will be described with reference to FIGS.
The head shown in FIG. 16 is an edge shooter type head, and an ejection energy generator 501 (electrodes for applying an ejection signal to the generator and a protective layer provided on the generator as needed) are omitted. ) And a top plate 506 constituting a cover of the flow path 503 and a side wall of the flow path 503 and a wall material 505 constituting the nozzle 504. In this head, ink travels straight from the flow path 503 toward the nozzle 504 as indicated by a one-dot chain line 507.

  In this head, when a recording signal is applied to the ejection energy generator 501 through an electrode (not shown) in a state where the ink is stored in the flow path 503 from a liquid chamber (not shown) in which ink is stored, the generator 501 is applied. The discharge energy generated from the nozzles acts on the ink in the flow path 503 above the discharge energy generator 501 (discharge energy operation unit), and as a result, the ink is discharged from the nozzle 504 as droplets.

  Such an edge shooter type head has the advantage that it is extremely easy to miniaturize each part with precision, to make the nozzles multi-sized or to be miniaturized, and to increase mass productivity. On the other hand, there is a limit to the response frequency and droplet flying speed during droplet ejection. In addition, bubbles are generated in the ink due to the heat generated by the electrothermal conversion element. The bubbles contract due to a decrease in temperature, and the discharge energy generator 501 is gradually destroyed by an impact when the bubbles disappear in the vicinity of the discharge energy generator 501. The so-called cavitation phenomenon occurs, and there is a disadvantage that the lifetime is relatively short.

  The head shown in FIG. 17 is a side shooter type head, and an ejection energy generator 511 (an electrode for applying an ejection signal to the generator and a protective layer provided on the generator as needed) are omitted. ) And a nozzle plate 516 in which nozzles 514 are formed on the flow path forming member 515 are stacked. In this head, as indicated by a one-dot chain line 517, the direction of ink flow to the ejection energy operating portion in the flow path 513 is perpendicular to the opening center axis of the nozzle 514.

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

  In the above embodiment, the printer driver as a program according to the present invention is configured to cause the computer to execute the image processing method according to the present invention, but the image forming apparatus itself has been described above. Means for executing the image processing method may be provided. Further, an application specific integrated circuit (ASIC) for executing the image forming method according to the present invention can be mounted on the image forming apparatus.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. Can be changed within the range that can be conceived, and any embodiment is included in the scope of the present invention as long as the effects and advantages of the present invention are exhibited.

1 is a side view showing a configuration in an embodiment of an image forming apparatus according to the present invention. 1 is a plan view showing a configuration in an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a cross-sectional view (longitudinal direction of the liquid chamber) showing an example of a recording head of the image forming apparatus according to the present invention. FIG. 3 is a cross-sectional view (a liquid chamber short direction) illustrating an example of a recording head of the image forming apparatus according to the present invention. 1 is a block diagram illustrating an overview of a control unit in an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a block diagram illustrating an example of a print control unit in an embodiment of an image forming apparatus according to the present invention. 6 is an explanatory diagram illustrating an example of a drive waveform generated and output by a drive waveform generation unit of a print control unit of the image forming apparatus. FIG. Description of drive pulses selected in the case of forming small droplets, medium droplets, large droplets, and fine drive among the drive waveforms generated and output by the drive waveform generation unit of the print control unit of the image forming apparatus FIG. 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 according to the present invention. 1 is a block diagram illustrating an example of an image processing apparatus in an image forming system configured by an image forming apparatus according to the present invention. 1 is a block diagram schematically showing an image processing unit in an image forming system configured by an image forming apparatus according to the present invention. In the image forming method according to the present invention, it is an explanatory diagram showing an example of print data distribution in the overlap area. It is a graph which shows the change of the ejection droplet amount by a drive frequency. It is explanatory drawing which shows an example of arrangement | positioning of the connection part of a several head. It is explanatory drawing which shows the head of the edge shooter system which is another example of a thermal type head. It is explanatory drawing which shows the head of the side shooter system which is another example of a thermal type head.

Explanation of symbols

3 Carriage 7 Recording head 104 Nozzle 200 Print control means (control unit)

Claims (7)

A recording head having a plurality of nozzles for discharging droplets of recording liquid, a recording head scanning means for scanning the recording head in the main scanning direction, a conveying means for scanning a recording medium in a sub-scanning direction perpendicular to the main scanning direction, and In an image forming apparatus that includes at least a print control unit and forms an image on the recording medium,
The transport means transports the recording medium such that an end region of the recording head overlaps and forms an overlap region with respect to dots recorded on the recording medium,
The image forming apparatus according to claim 1, wherein when the print control unit distributes the print data in the overlap area, the drive frequency is controlled to be the same as the drive frequency in the non-overlap area. A recording head having a plurality of nozzles for discharging droplets of recording liquid, a recording head scanning means for scanning the recording head in the main scanning direction, a conveying means for scanning a recording medium in a sub-scanning direction perpendicular to the main scanning direction, and In an image forming apparatus that includes at least a print control unit and forms an image on the recording medium,
The recording head is composed of a plurality of recording head members, and the adjacent recording head members are arranged in the sub-scanning direction so as to form overlapping regions with overlapping end portions at the joint portion,
The image forming apparatus according to claim 1, wherein when the print control unit distributes the print data in the overlap area, the drive frequency is controlled to be the same as the drive frequency in the non-overlap area.   The print control unit distributes the print data so that the drive frequency in the overlap region is the same as the drive frequency in the non-overlap region according to the gradation level of the image forming data. The image forming apparatus according to claim 1.   The print control unit distributes print data so that a drive frequency in the overlap region is the same as a drive frequency in a non-overlap region according to the ambient temperature of the recording head. The image forming apparatus according to 3.   The print control unit distributes print data so that a drive frequency in the overlap region is the same as a drive frequency in a non-overlap region according to the number of main scans in the same print region. Item 3. The image forming apparatus according to any one of Items 1 to 2. A recording head having a plurality of nozzles for discharging droplets of recording liquid, a recording head scanning means for scanning the recording head in the main scanning direction, a conveying means for scanning a recording medium in a sub-scanning direction perpendicular to the main scanning direction, and An image forming method in an image forming apparatus that includes at least a print control unit and forms an image on the recording medium,
In the overlap region where a plurality of nozzles corresponding to one dot generation exist, when the print data in the overlap region is distributed, the drive frequency is distributed to be the same as the drive frequency in the non-overlap region. An image forming method.   A recording head having a plurality of nozzles for discharging droplets of recording liquid, a recording head scanning means for scanning the recording head in the main scanning direction, a conveying means for scanning a recording medium in a sub-scanning direction perpendicular to the main scanning direction, and A program for executing the image forming method according to claim 6 in an image forming apparatus that includes at least a print control unit and forms an image on the recording medium.

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