JP2009045835A - Inkjet recorder and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out recording of a bidirectional multi-scanning system with density irregularities caused by a difference in recording time interval by scanning solved in an inkjet recorder. <P>SOLUTION: A unit region completed in recording by a plurality of the number of scanning is divided to 8 in a scan direction. A maximum value of an ink placement amount is set for each of the divisions. The largest value is set to the division 8. The ink placement amount is set to be a smaller value in a direction of the division 1. In other words, since the density decreases from the left towards the right because of a recording time difference in the scan direction of the unit region, the ink placement amount is increased from the left towards the right. That is, for the whole of the unit region with the 8 divisions combined, the amount of ink placed finally on a recording medium can be increased as a tendency from the left towards the right. Hence a density change corresponding to the recording time difference in the scan direction can be reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inkjet recording apparatus and an inkjet recording method, and more particularly to a configuration for reducing density unevenness that occurs when recording is performed by reciprocal bidirectional scanning.

  In recent years, OA devices such as personal computers and word processors have been widely used, and various recording devices for printing out information processed by these devices have been provided. As one tendency of such a recording apparatus, high image quality and high speed are demanded, and various techniques for that purpose are provided.

High image quality technology As an example of high image quality technology, a so-called multi-scan method is known. In this method, the same region is scanned a plurality of times by the recording head, and the plurality of times of scanning are performed in association with different ink discharge ports.

  When recording is performed using a recording head including a plurality of recording elements such as ink ejection openings, the image quality of the recorded image largely depends on the accuracy of the recording head. In the manufacturing process of the recording head, for example, the shape of the discharge port of the recording head and the disposition position of the discharge heater that generates energy for discharge may vary. Such variations appear as slight differences in ejection characteristics such as ejection amount and ejection direction between a plurality of ejection openings in the recording head, degrading image quality as density unevenness of the finally formed image. It will be.

  FIGS. 1A to 1C and FIGS. 2A to 2C are diagrams illustrating specific examples. In FIG. 1A, reference numeral 101 schematically shows a recording head, and is shown as having eight ink discharge ports 102 for the sake of simplicity of explanation. Reference numeral 103 denotes ink droplets ejected from the respective ejection ports 102. Normally, it is assumed that ink is ejected in substantially the same ejection amount and in the same direction as shown in FIG. Then, as shown in FIG. 1B, by performing such discharge, dots of substantially the same size are formed on the paper surface, and a uniform image without density unevenness is formed on the entire recorded image. Is obtained (see FIG. 1 (c)).

  However, in practice, as described above, there are many variations in the discharge characteristics of the plurality of discharge ports. For this reason, if the discharge is performed without taking any measures, as shown in FIG. 2A, the size and direction of the ink droplets discharged from the respective discharge ports vary. As a result, dots having different positions and sizes are formed on the paper as shown in FIG. In this case, in the scanning direction of the recording head, there may be a white paper portion that does not periodically satisfy the area factor of 100%, or conversely, a portion where dots overlap more than necessary, as seen in the center of the figure. White and black streaks appear. The image formed by the collection of dots in such a state has the density distribution shown in FIG. 2C in the arrangement direction of the discharge ports, and is consequently detected as density unevenness.

  The multi-scan method improves the image quality by solving the problem of density unevenness. FIGS. 3A to 3C and FIGS. 4A to 4C are diagrams for explaining this. In the multi-scan method, recording of a predetermined area is completed by a plurality of scans of the recording head, and in the example shown in FIG. That is, half of the area shown in FIG. 1B (for four pixels) is scanned twice (hereinafter also referred to as “two passes”) with an amount of recording medium transport corresponding to the half of the area interposed therebetween. To complete. In this case, the eight ink discharge ports 202 of the head 201 are divided into groups of four upper discharge ports and four lower discharge ports. At the same time, the dots formed by the ink ejected from one ejection port in one scan (scanning) are thinned out to, for example, half by using a mask in the arrangement in the scanning direction. In the second scan, the remaining half of the dots are formed using a mask that complements the mask, and the recording of the area for four pixels is completed. 4A to 4C are diagrams showing an example of the mask and a dot pattern formed using the mask. The masks or dot patterns shown in these figures are the simplest houndstooth pattern that can form dots for each pixel vertically and horizontally. The first scan (FIG. (A) or (c)) for recording the staggered pattern in the unit recording area (here, four pixels) and the second scan (FIG. 5) for recording the inverted staggered pattern. The recording is completed by (b)).

  According to the multi-scan method as described above, even if the recording head having the ejection characteristics shown in FIG. 2A is used, the influence on the recording area due to the ejection characteristics of each ejection port is reduced to ½, The recorded image is as shown in FIG. As a result, white stripes or black stripes are not so noticeable. As a result, as shown in FIG. 3C, the density unevenness is also reduced as compared with the case of FIG.

On the other hand high-speed technology, bidirectional printing is known as one example of high-speed technology. That is, in the serial type recording apparatus, after recording is performed by scanning in the forward direction of the recording head, a predetermined amount of paper is fed, and then recording scanning is performed even when the recording head is moved in the backward direction. According to this recording method, the recording speed or throughput is simply doubled compared to unidirectional recording in which recording is performed in the forward scan and recording is not performed in the return recording head movement.

  This bidirectional recording is completed by so-called one-pass recording in which a scanning area having a length corresponding to the ejection port array width of the recording head is completed by one scan, or by a plurality of scans with paper feeding interposed therebetween. It can be used for both multi-scan recording. Therefore, by performing bidirectional recording by the multi-scan method, it is possible to realize both high image quality and high speed.

  On the other hand, however, when bidirectional printing is performed by the multi-scan method, there is a problem of density unevenness (time difference unevenness) due to the difference in the time interval of recording by multiple scans depending on the position in the scanning region. Are known.

  FIG. 5 is a diagram for explaining the time difference unevenness, and shows an example in which recording is completed by two bidirectional scans (passes). In FIG. 5, paying attention to the left and right ends of the recording medium, an area where the second recording is performed immediately after the first recording and a scanning time of approximately two forward and backward scans after the first recording. After that, areas where recording is performed appear alternately. As a result, at the left end, the recording area 1 has a high image density, the recording area 2 has a low image density, and the difference in density appears alternately. Further, at the right end, the recording area 1 has a low image density, and the recording area 2 has a high image density, and the density difference appears alternately as in the left end. In each recording area, the density changes in the scanning direction. For example, in the recording area 1, the density is high on the left end side, and the density decreases as it goes to the right end side.

  Such a phenomenon varies depending on the time from when the previously recorded ink droplet penetrates into the inside of the recording medium and is adsorbed on the paper fiber or the ink receiving layer, and recording is performed with the next ink droplet. If there is enough time to adsorb to the paper fiber or ink receiving layer of the previously recorded ink, the next recorded ink droplet gradually penetrates in the direction of gravity while searching for a portion that can adsorb relatively smoothly. To go. On the other hand, when there is no time to adsorb onto the paper fiber or ink receiving layer of the previously recorded ink, the ink droplet to be recorded next merges with the previously recorded ink, and an aggregate of one ink droplet As it gradually penetrates in the direction of gravity. In the latter case, before the ink recorded earlier is sufficiently adsorbed in the vicinity of the paper surface, it merges with the ink recorded later, so that it is adsorbed further downward. As a result, the image density is relatively low. This density unevenness appears as color unevenness corresponding to the scanning time difference when secondary color recording is performed.

  FIGS. 6A and 6B are diagrams for explaining the occurrence of density unevenness in accordance with such a difference in ink droplet ejection time. FIG. 6A shows a case where the time interval at which two ink droplets are ejected is long, and FIG. 6B shows a case where the time interval at which two ink droplets are ejected is short. In FIG. 6A, the first ejected ink droplets land on the recording medium, penetrate into the recording medium, and are fixed. After fixing in a relatively long time, the post-discharge ink droplets land and penetrate so as to sink under the pre-discharge ink and fix below the pre-discharge ink. On the other hand, also in the case shown in FIG. 6B, the first ejected ink droplets land on the recording medium and penetrate into the inside of the recording medium. In this case, since the time until the next ink droplet lands is short, the next post-ejection ink droplet lands in the process of fixing the first ejection ink droplet. For this reason, the unfixed ink and the post-printed ink droplet of the first ejected ink droplet permeate as an integrated ink, and finally fix. As a result, since the first ejected ink droplet is swept downward by the subsequent ejected ink droplet, the degree of penetration becomes lower on the paper surface and the density becomes lower. That is, as shown in FIGS. 6A and 6B, the penetration depth of the first ejected ink droplet, that is, the fixing position is different, and the higher the image density, the higher the image density. That is, the longer the time interval, the higher the concentration.

  As described above, a density difference is generated between the left end and the right end of the unit area where the recording is completed by a plurality of scans, according to the difference in the time interval of the plurality of recordings for recording a certain area. As shown in FIG. 5, when such unit regions are adjacent to each other, regions having different densities are alternately adjacent to each other, and this is also recognized as density unevenness (hereinafter also referred to as unevenness between bands). In particular, the difference in density is large at the left end and the right end of the unit area, and this unevenness between bands is remarkably recognized.

  As a technique for suppressing the time difference unevenness caused by the recording time difference as described above, one described in Patent Document 1 is known. This document describes that the recording mode is switched from bidirectional recording to unidirectional recording when there is a high possibility of uneven density. Specifically, the recording area is divided into a plurality of areas in the main scanning direction, and the number of dots of black ink and color ink applied to each area is counted. If there are areas where both black and color exceed the respective threshold values, the number of areas is counted, and if the number is greater than or equal to a predetermined number, there is a high possibility that time difference unevenness will occur, and switching to one-way recording is performed. This makes it possible to suppress the time difference unevenness occurring at both ends of the recorded image. The document also detects the width of image data to be recorded, that is, the width of the range scanned by the recording head, and if the width is small, the degree of unevenness in time difference is small, and the number of areas is not less than a predetermined value. It is also described that switching to one-way recording is not performed.

  As another technique for suppressing the time difference unevenness, Patent Document 2 describes that the time difference unevenness between bands is made inconspicuous by increasing the number of multi-scan passes when the recording width is long. Further, this document also describes that it is difficult to recognize the time difference unevenness by repeating the time difference unevenness at a high frequency. In addition, when the recording width is long, it is possible to shorten the multipass time difference by increasing the scanning speed of the recording head, or to reduce unevenness in time difference by switching to unidirectional recording and making the recording time in each band the same. Are listed.

JP 2003-34021 A JP 2005-144868 A

  However, switching to unidirectional recording when density unevenness is likely to occur as described in Patent Documents 1 and 2 loses the significance of bidirectional recording employed for speeding up recording. Become. Further, increasing the number of multi-scan passes causes a decrease in overall throughput. Furthermore, changing the scanning speed causes a problem that the recording resolution must be changed.

  As described above, the conventional time difference non-uniformity solving method involves a relatively large change in the content of the recording operation or processing, and accordingly, various problems as described above are derived.

  An object of the present invention is to provide an ink jet recording apparatus capable of eliminating density unevenness due to a difference in recording time interval due to scanning in bidirectional multi-scan recording without changing the recording operation as much as possible. It is to provide an ink jet recording method.

  For this purpose, the present invention uses a recording head in which a plurality of ejection openings are arranged, and scans the recording head a plurality of times in which forward scanning and backward scanning are alternately performed on a unit area of the recording medium. In an ink jet recording apparatus that performs recording of a unit area by transporting a predetermined amount of a recording medium for each of a plurality of scans and associating different ejection openings with the unit area, the position in the scanning direction in recording of the unit area According to the present invention, there is provided means for varying the maximum ink ejection amount in accordance with the recording time difference between the plurality of scans that differ depending on each other.

  In a preferred embodiment, the recording medium is transported between the last scan for recording one of the adjacent unit areas and the first scan for recording the other, and the transport amount is larger than the predetermined amount. Further comprising a transport control means, wherein the length of the unit area along the transport direction is a length corresponding to the number of ejection ports that overlap in a plurality of scans for recording the unit area. The combination of the recording time differences between a plurality of scans according to the position of the unit area in the scanning direction is the same in any of the plurality of unit areas adjacent to each other.

  Similarly, in a preferable embodiment, the recording medium is transported between the last scan for recording one of the adjacent unit areas and the first scan for recording the other, and the transport amount is expressed as (N-2q ( k-1)) · p, where N is the number of the plurality of ejection openings, q · p is the predetermined amount, k is the number of the plurality of scans, p is the arrangement pitch of the ejection opening array, and And a length of the unit area along the transport direction corresponds to the number of ejection openings that overlap in a plurality of scans for recording the unit area (N−q (k−1). )) · P, the combination of the recording time differences between a plurality of scans corresponding to the position of the unit area in the scanning direction is the same in any of the plurality of adjacent unit areas. Features.

  In addition, using a recording head in which a plurality of ejection openings are arranged, a plurality of times of scanning of the recording head in which forward scanning and backward scanning are alternately performed are performed on a unit area of the recording medium, and each of the plurality of scannings In the ink jet recording method for transporting a predetermined amount of a recording medium and associating different discharge ports with the unit area to perform recording of the unit area, the unit area is recorded depending on the position in the scanning direction. The method has a step of varying the maximum ink ejection amount in accordance with a difference in printing time between a plurality of scans.

  In a preferred embodiment, the recording medium is transported between the last scan for recording one of the adjacent unit areas and the first scan for recording the other, and the transport amount is larger than the predetermined amount. Further comprising a transport control step, wherein the length of the unit area along the transport direction is a length corresponding to the number of ejection openings that overlap in a plurality of scans for recording the unit area. A combination of recording time differences between a plurality of scans corresponding to the position of the unit area in the scanning direction is the same in any of the plurality of unit areas adjacent to each other.

  Similarly, in a preferable embodiment, the recording medium is transported between the last scan for recording one of the adjacent unit areas and the first scan for recording the other, and the transport amount is expressed as (N-2q ( k-1)) · p, where N is the number of the plurality of ejection openings, q · p is the predetermined amount, k is the number of the plurality of scans, p is the arrangement pitch of the ejection opening array, and And a length of the unit region along the transport direction corresponds to the number of ejection ports that overlap in a plurality of scans for recording the unit region (Nq (k− 1)) By using p, the combination of the recording time differences between the scanning operations of the plurality of times corresponding to the position of the unit region in the scanning direction is the same in any of the plurality of adjacent unit regions. It is characterized by.

  According to the above configuration, in multi-scan recording in which unit area recording is completed by a plurality of recording head scans in which forward scanning and backward scanning are alternately performed, a plurality of scans that differ depending on the position in the scanning direction in the unit area. The maximum ink ejection amount varies depending on the recording time difference. As a result, the difference in density according to the position in the scanning direction, which is caused by the recording time difference in the reciprocating scanning, can be offset by changing the maximum ink ejection amount, and the density difference can be reduced.

  Further, according to a preferred embodiment, the unit area where the recording is completed by a plurality of scans is recorded by the overlapping ejection ports by the plurality of scans. In this case, the conveyance amount of the recording medium between the last scan for recording one of the adjacent unit areas and the first scan for recording the other is the unit area. Is different from a predetermined amount of recording medium conveyance performed during a plurality of scans. Specifically, the conveyance amount of the recording medium between adjacent unit areas is set larger than the predetermined amount. Alternatively, the conveyance amount of the recording medium between adjacent unit areas is (N-2q (k-1)) · p. As a result, the recording time difference between a plurality of scans corresponding to the position of the unit region in the scanning direction can be made the same in any of the plurality of unit regions adjacent to each other. As a result, high-quality recording with no difference in density between unit areas can be performed, and in combination with bidirectional recording, both high-speed recording and high-quality recording can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Configuration of Recording Apparatus FIG. 7 is a perspective view schematically showing a main configuration of an ink jet recording apparatus to which the present invention can be applied. In FIG. 7, reference numerals 1A, 1B, 1C and 1D denote head cartridges in which a recording head and an ink tank are integrated, and are mounted on the carriage 2 so as to be independently replaceable. Each of the head cartridges 1A to 1D is provided with a connector for receiving a signal for driving the recording head.

  Each recording head portion of the head cartridge 1 discharges cyan (C), magenta (M), yellow (Y), and black (Bk) inks, and accordingly, the corresponding ink tank portion has C, M, Y and Bk inks are stored. Each head cartridge 1 is mounted on the carriage 2 so as to be replaceable. The carriage 2 has a connector holder (electrical connection portion) for transmitting a drive signal or the like to each of the recording heads 1 via a connector. Is provided.

  The carriage 2 is guided and supported so as to be movable in the main scanning direction along a guide shaft 3 provided in the recording apparatus main body. The carriage 2 is driven by a main scanning motor 4 through a motor pulley 5, a driven pulley 6, and a timing belt 7, and its position and movement are controlled.

  A recording medium 8 such as paper or a plastic thin plate is conveyed (paper) so as to pass through a position (recording unit) facing the discharge port surface of the recording head 1 by the rotation of two sets of conveying rollers 9, 10, 11, and 12. Sent). Then, the back surface of the transported recording medium is supported by a platen (not shown) so that a flat recording surface can be formed in the recording unit. The two pairs of transport rollers (9 and 10 and 11 and 12) maintain a predetermined distance between the discharge port surface of each recording head 1 mounted on the carriage 2 and the recording medium 8 on the platen. As described above, the recording medium 8 is also supported from both sides of the recording unit.

  Although not shown in FIG. 7, an optical sensor is attached to the carriage 2. The optical sensor applied in the present embodiment is a red LED or infrared LED having a light emitting element and a light receiving element, and these elements are attached at an angle that is substantially parallel to the recording medium 8. The distance from the optical sensor to the recording medium 8 is determined according to the characteristics of the optical sensor to be used. In the present embodiment, it is assumed that the distance is set to about 6 to 8 mm. Furthermore, the optical sensor is preferably covered with a cylindrical member in order to be hardly affected by mist due to ink ejection from the recording head 1.

  FIG. 8 is a schematic perspective view for explaining the main structure of the ink discharge section 13 in the recording head section. In FIG. 8, the discharge port surface 21 is a surface facing the recording medium 8 with a predetermined gap (about 0.5 to 2 [mm] in the present embodiment), and the discharge port surface 21 has a predetermined pitch. A plurality of discharge ports (hereinafter also referred to as nozzles) 22 are formed. Each ejection port 22 communicates with the common liquid chamber 23 via a plurality of flow paths 24, and the common liquid chamber 23 to the ejection port 22 are always filled with ink intermittently. On the wall surface of each flow path 24, an electrothermal converter (such as a heating resistor; hereinafter also referred to as a discharge heater) 25 that generates energy for discharging ink is disposed.

  At the time of discharge, a predetermined voltage is applied to each electrothermal transducer 25 based on the discharge signal. As a result, the electrothermal transducer 25 converts electrical energy into thermal energy, and film boiling occurs in the ink in the flow path 24 due to the generated heat. Furthermore, ink is pushed out to the ejection port 22 by the pressure of the foam that rapidly foams, and a predetermined amount of ink is ejected as droplets. In the present embodiment, an ink jet recording head that ejects ink from the ejection port 22 by using the pressure change caused by the bubble growth and contraction due to film boiling is applied.

  In the present embodiment, the recording head 1 is mounted on the carriage 2 in such a positional relationship that the plurality of ejection ports 22 are arranged in a direction intersecting the scanning direction of the carriage 2.

Configuration of Control Circuit FIG. 9 is a block diagram showing a control configuration in the above-described inkjet recording apparatus of the present embodiment.

  In FIG. 9, reference numeral 1010 denotes an interface for exchanging recording signals and the like with the host device, and 1011 denotes an MPU. Reference numeral 1012 denotes a program ROM, and 1013 denotes a dynamic RAM. The ROM 1012 stores a control program executed by the MPU 1011. The RAM 1013 stores various data (such as the recording signal and recording data supplied to the recording head), and can also store the number of recording dots, the number of head cartridge replacements, and the like. Reference numeral 1014 denotes a gate array that controls the supply of print data to the print head 1018, and also controls the transfer of data among the interface 1018, the MPU 1011 and the RAM 1013. Reference numeral 1020 denotes a carry motor serving as a drive source for movement of the recording head 1018, and 1019 denotes a transport motor serving as a drive source for transporting the recording paper. Reference numeral 1015 denotes a head driver for driving the head based on the recording data to eject ink. Reference numerals 1016 and 1017 denote drivers for driving the carry motor 1019 and the carrier motor 1020, respectively.

  In the control configuration shown in FIG. 9 described above, when a recording signal is input to the interface 1010, processing for converting the recording signal into recording data for printing is performed between the gate array 1014 and the MPU 1011. Further, driving of motors 1018 and 1020 is controlled via motor drivers 1016 and 1017, respectively. At the same time, each recording head (unit) 1018 is driven according to the recording data of each color sent to the head driver 1015, and the recording operation is performed.

  FIG. 10 is a diagram for explaining the flow of recording data inside the recording apparatus of this embodiment. Each buffer shown in FIG. 10 is configured in the DRAM 1013 (see FIG. 9).

  Recording data from the host computer 101 and the digital camera 102 is sent to the reception buffer 1101 via the interface 1010 and stored therein. The reception buffer 1101 has a capacity of several tens of k to several hundreds of k bytes. The record data stored in the reception buffer 1101 is subjected to command analysis by the command analysis unit 1041 and then sent to the text buffer 1102. In the text buffer 1102, recording data is held as an intermediate format for one line, and processing for adding the recording position, modification type, size, character (code), font address, and the like of each character is performed. The capacity of the text buffer 1102 varies depending on the model. The serial buffer has a capacity of several lines, and the page printer has a capacity of one page. Further, the recording data stored in the text buffer 1102 is expanded by the expansion unit 1042 and stored in a binarized state in the print buffer 1103. This data is finally sent to the recording head as recording data for recording.

  In this embodiment, as will be described later, a thinning process using a mask is performed for each unit area that completes printing in a plurality of scans on binary data stored in the print buffer, and Print data is generated for each of a plurality of scans to complete the print. At the same time, a mask process is performed on the recording data corresponding to the unused nozzles. In the above configuration, the mask pattern can be set after looking at the data stored in the print buffer. Further, instead of having the text buffer instead of the above-described configuration, the recording data accumulated in the reception buffer can be developed simultaneously with the command analysis and written into the print buffer.

  FIG. 11 is a block diagram illustrating generation of recording data for performing multi-scan recording in the above-described configuration. In the figure, a data register 1201 is connected to a memory data bus, reads out recording data stored in a print buffer 1103 in the memory 1013, and temporarily stores it. In this embodiment, an unused mask process is performed on unused nozzles when reading recording data to the data register 1201. Specifically, the recording data corresponding to the unused nozzle is not read out. Of course, the unused mask processing is not limited to such a configuration. For example, the following mask registers may be provided separately corresponding to unused nozzles.

  Further, in FIG. 11, reference numeral 1202 denotes a parallel-serial converter for converting data stored in the data register 1201 into serial data, and 1203 denotes an AND gate for masking the serial data. Reference numeral 1204 denotes a counter for managing the number of data transfers.

  A register 1205 is connected to the MPU data bus and stores a mask pattern. 1206 is a selector for selecting the digit position of the mask pattern, 1207 is a selector for selecting the row position of the mask pattern, and 1211 is a column counter for managing the digit position.

  The data transfer circuit having the above configuration serially transfers print data for the number of nozzles to the recording head in accordance with a recording signal sent from the MPU 1011. That is, the recording data stored in the print buffer 1103 is temporarily stored in the data register 1201 and converted into serial data by the parallel-serial converter 1202. The converted serial data is masked by the AND gate 1203 and then transferred to the recording head. The transfer counter 1204 counts the number of transfer bits and ends the data transfer when the value reaches the number of nozzles.

  The mask register 1205 includes four mask registers A, B, C, and D, and stores a mask pattern written by the MPU 1101. Each register stores a mask pattern of vertical 4 bits × horizontal 4 bits. The selector 1206 selects mask pattern data corresponding to the digit position by using the value of the column counter 1211 as a selection signal. The selector 1207 selects mask pattern data corresponding to the row position by using the value of the transfer counter 1204 as a selection signal. The transfer data is masked using the AND gate 1203 by the mask pattern data selected by the selectors 1206 and 1207.

  Although the present embodiment has been described with the four mask register configurations, this may be another number of mask registers. Further, the transfer data subjected to the mask processing is directly supplied to the recording head, but may be configured to be temporarily stored in the print buffer.

  Next, the bidirectional multi-scan method of the present embodiment in the ink jet recording apparatus having the configuration described above with reference to FIGS.

(Recording time difference suppression multi-scan recording method)
FIG. 12 is a diagram showing an example of multi-scan recording by bidirectional scanning according to an embodiment of the present invention. The multi-scan method described below suppresses a difference in density (unevenness between bands) between unit areas in which recording is completed by a plurality of scans.

  This figure shows an example in which recording of a unit area is completed by two scans of forward scanning and backward scanning using a recording head having 16 nozzle blocks. In the present embodiment, one nozzle block is composed of 16 nozzles. In recording according to the present embodiment, transport control is performed in which the transport amount of the recording medium transport performed between the scans is different from that of conventional multi-scan recording. That is, in the present embodiment, as shown in FIG. 12, after the first scanning in the forward direction, one nozzle block (× nozzle pitch) is transported, and then the second scanning in the backward direction forms the unit region. The recording of “recording area 1” is completed. Then, after completion of the recording of the unit area, conveyance for 14 nozzle blocks is performed. Next, the recording of “recording area 2” is completed in the same manner by the reciprocating third and fourth scans. Thereafter, the unit area is recorded by performing two reciprocating scans in the same manner.

  Further, in the above recording, the length of the unit area where the recording is completed in order such as “recording area 1” and “recording area 2” (length in the vertical direction in FIG. 12) corresponds to 15 nozzle blocks. . That is, in each scan, the recording data for one nozzle block at the upper end or the lower end of the nozzle row of the recording head is recorded with a length corresponding to the overlapping 15 nozzle blocks of the used nozzles. For example, in the first scanning in the forward direction in which “recording area 1” is recorded, the recording data corresponding to one unused nozzle block at the uppermost end is masked. Specifically, when the print data is read from the print buffer 1103, the print data is read in nozzle units of all (16 blocks) of the print head. At this time, the print data corresponding to the uppermost one nozzle block is masked. That is, as described above, the recording data corresponding to the uppermost nozzle block is not read out. Actually, the recording data to be masked is data for recording the unit area adjacent to the upper side of “recording area 1”. Since the recording has already been completed, this data is deleted from the print buffer 1103. Yes. In the next second scan, the print data corresponding to the unused nozzle block at the bottom end of the 16 nozzle blocks is masked. Similarly, in this case, when the print data is read from the print buffer in units of 16 nozzle blocks, a process for prohibiting reading of the print data corresponding to the lowermost nozzle block is performed. At this time, the recording data corresponding to the lowermost nozzle block is data for recording the next “recording area 2” and is stored in the print buffer.

  In addition to the mask processing for the above unused nozzle blocks, as described with reference to FIG. 11, mask processing using a mask pattern for performing multi-scan printing that completes printing in two scans is performed. Specifically, a mask pattern corresponding to 15 nozzle blocks for recording each unit area is prepared for every two scans to complete the recording, and the recording is thinned out by each scanning mask pattern. Generate data.

  According to the above-described recording time difference suppression multi-scan recording, the recording time difference between scans is the same position in the scanning direction in any of the “recording area 1”, “recording area 2”,. Then, it becomes the same time difference. For example, in any unit area, there is an area at the right end immediately after recording in the first scan, and recording is performed almost twice after recording in the first scan. After the scanning time has elapsed, an area where printing is performed in the second scanning is present at the left end. Thus, as shown in FIG. 12, in any unit area (recording area 1, recording area 2,...), The image density is high at the left end and the image density is low at the right end. As a result, it is difficult to recognize a difference in density between unit areas adjacent to each other in the conveyance direction of the recording medium, that is, band-to-band unevenness.

  Note that even with the above-described multi-scan recording, it is impossible to eliminate the difference in recording time according to the position in the scanning direction by each of a plurality of scans for completing recording, and hence the difference in density. For example, the density is high at the left end of the unit area, and the density decreases toward the right end. However, this difference or change in density can be reduced by controlling the ink ejection amount according to the position in the scanning direction according to an embodiment of the present invention described later. Thereby, it is possible to reduce both the density unevenness between the unit areas and the change in density in the scanning direction in each unit area.

  FIG. 13 is a diagram for explaining the details of mainly used / unused nozzle blocks in the recording of the present embodiment described with reference to FIG. As shown in FIG. 13, the recording head is composed of 16 nozzle blocks. Each block is composed of 16 nozzles, and the recording head has a total of 256 nozzles. As shown in FIG. 12, in the first scan, the uppermost block is an unused nozzle. The other 15 blocks of nozzles are used. Next, in the second scanning, an unused mask is set for one block at the lowermost end, and an unused nozzle is set. The other 15 blocks of nozzles are used for recording. The feed amount in the conveyance direction (sub-scanning direction) of the recording medium is one block between the first recording scan and the second recording scan. That is, the length (pitch) of unused nozzles set in each recording scan is used as the feed amount between scans for completing the recording of a certain unit area. On the other hand, the feed amount when moving to another unit area is 14 nozzle blocks as described above.

  The used nozzles in each scan are associated with a thinning mask that can be complemented by two printing scans. The thinning mask is not limited to the contents, and may be, for example, a staggered / reverse staggered mask or a random mask.

  As described above, when recording the same recording area (unit area), an unused mask is set for each recording scan for the nozzles of the recording head used in each scan, and related to the used nozzles. The amount of recording medium transported is performed. Accordingly, it is possible to perform recording while suppressing density unevenness between recording scans in the transport direction without causing a time difference between recording scans. In other words, since the time intervals of recording scans between adjacent recording areas can be made substantially the same, high-quality recording without band-to-band unevenness can be performed, and as a result, both high-speed recording and high-quality recording can be achieved. It becomes feasible.

  In this embodiment, nozzle control and mask control in units of blocks have been described with 16 nozzles as one block. However, the present invention is not limited to control in units of blocks, and is limited to the number of nozzles. It is not what is done. For example, the same concept can be applied even if there is one unused nozzle. The same effect can be obtained as long as the recording scan maintains the relationship between the number of unused masks and the conveyance amount of the recording medium.

  However, in the case of a recording head having a relatively large number of nozzles, if ejection is performed simultaneously from all nozzles, voltage fluctuations are large, and ejection tends to become unstable due to ejection effects of adjacent nozzles. In general, ejection is performed by dividing a drive cycle for performing printing in one column into a plurality of drive timings. For example, 16 columns are divided into 16 columns, and the nozzles that are driven simultaneously are 16 nozzle intervals. In the case of the recording head shown in FIG. 13, 16 nozzles are ejected simultaneously, and this is repeated 16 times to complete ejection for the number of nozzles of the recording head. Such drive timing setting can be performed in a specific order (drive pattern). When this recording head driving method is used, as shown in FIG. 13, one block corresponds to one cycle of the driving pattern of the driving timing. In recording within one raster, it is preferable that the drive patterns have the same cycle. If there is a cycle shift, a slight landing shift may occur, which may cause a texture. Therefore, it is more preferable to apply the present invention in units of drive patterns.

(Dependence of density unevenness on the number of passes)
The band-to-band unevenness caused by the time difference of the reciprocal recording described so far becomes remarkable in the multi-scan of the even-numbered pass, but it is not so remarkable in the case of the odd-numbered pass. FIG. 14 is a diagram for explaining this situation, and for explaining the time difference between the printing scans.

  In FIG. 14, in the case of normal two-pass multi-scan printing, one unit area in which printing is completed in two passes is printed by the first printing scan and the second printing scan, and the second unit area is the second printing. Recording is performed by the recording scan and the third recording scan. In this case, focusing on the left end area of the recording medium, the recording time difference between the first recording scan and the second recording scan is large (A), but between the second recording scan and the third recording scan that complete the next unit area. Then, the recording time difference is small (B). In this case, the recording time difference is different between adjacent unit areas in the conveyance direction of the recording medium, and band-to-band unevenness becomes remarkable.

  On the other hand, in the case of normal 3-pass multi-scan printing, one unit area in which printing is completed in 3 passes is recorded from the first printing scan to the third printing scan, and the next unit area is the second printing. Recording is performed from the scan to the fourth recording scan. Focusing on the left end of the recording medium, in the unit area where recording is completed from the first recording scan to the third recording scan, the recording time difference between the first recording scan and the second recording scan is large (A), The recording time difference of the third recording scan is small (B). Thus, the case where the recording time difference is large (A) and the case where it is small (B) exist equally. Even in the adjacent unit area in which the recording is completed from the second recording scan to the fourth recording scan, the recording time difference between the second recording scan and the third recording scan is small (B), and the time interval between the third recording scan and the fourth recording scan is small. Is large (A) and the time difference is small and the time difference is large. As described above, in the multi-scan of three passes, the large and small numbers of the recording time differences are equal between the adjacent unit areas, and thus the density unevenness due to the recording time difference becomes inconspicuous.

  Similarly, in the case of four-pass multi-scan recording in which unit area recording is completed by four recording scans, a certain unit area is indicated by recording time differences A, B, A (hereinafter, A + B + A) at the left end of the recording medium. ) Exists. The next adjacent unit area is B + A + B. Thus, in the case of 4-pal multiscan recording, the number of large and small recording time differences differs between adjacent unit areas, and as a result, density unevenness due to the recording time difference becomes significant. On the other hand, in the case of 5-pass multi-scan printing, one unit area is A + B + A + B, and the next adjacent unit area is B + A + B + A. Thus, in the 5-pass multi-scan, the large and small numbers of recording time differences are the same between adjacent unit areas. As a result, density unevenness due to a recording time difference in reciprocal recording is not conspicuous.

  As described above, the band-to-band unevenness is remarkable when the number of passes is an even number, and the band-to-band unevenness is not noticeable when the number of passes is an odd number. Therefore, in the present embodiment, the recording time difference suppressing multi-scan recording method and the normal multi-scan recording method described in the first embodiment are switched according to the number of passes for completing the recording.

(Switching process)
FIG. 15 is a flowchart for explaining a recording process involving switching of the multi-scan recording method according to the present embodiment. In FIG. 15, first, recording data is fetched in step S1. Next, path information is acquired in step S2. This refers to information such as recording quality and recording medium included in the recording data, and refers to a combination table that the recording apparatus has in advance in a storage medium such as a ROM to determine the number of multi-scan recording passes. By doing. Alternatively, the pass number information may be directly transferred into the recording data.

  Next, in step S3, it is determined whether the path is an even path or another path, that is, an odd path based on the path number information. If it is an even-numbered pass, in step S4, the recording time difference suppression multi-scan recording method described in the first embodiment is set and executed. Thereby, as described above, the band-to-band unevenness becomes remarkable in the even-pass multi-scan recording, and the occurrence of the band-to-band unevenness can be suppressed by the above-described recording time difference suppressing multi-scan recording method. On the other hand, if it is determined in step S3 that the path is not an even-numbered pass, a normal multi-scan recording method is set and executed in step S5.

  As described above, according to the present embodiment, the recording time difference suppression multi-scan recording method is not always applied, but is applied as necessary. Thereby, by applying this method, it is possible to suppress as much as possible a decrease in throughput as compared with a normal multi-scan when the number of paths is the same.

  In the present embodiment, one type of multi-scan recording method is set for one recording data. Normally, one pass number is set for one print job. For example, when the pass number is switched depending on the type of print data for each print area, the set pass number is used. Depending on the number, a multi-scan recording method can be set for each recording area.

  In this embodiment, the multi-scan recording method is switched between the even pass and the odd pass. However, only in the case of two-pass printing where the influence of the time difference of the recording scan interval is large, the recording time difference suppressing multi-scan recording method is set. May be. In this case, it is determined whether or not there are two passes in step S3 of FIG.

  FIG. 16 is a flowchart showing a control process for implementing the above-described recording time difference suppressing multi-scan recording method. Note that the processing shown in FIG. 16 shows the case of performing two-pass multi-scan recording.

  In FIG. 16, first, recording data is fetched in step S101. Next, in step S102, it is determined whether the first recording scan or a different recording scan.

  When it is determined in step S102 that the first print scan is being performed, an unused mask for the first print scan is set in step S103 as described with reference to FIGS. Specifically, the print data is specified in correspondence with the nozzle or nozzle block, and the setting is made so as not to read the print data.

  Next, in step S104, a thinning mask for the first pass of the two-pass multi-scan is set for the nozzles used in the first recording scan. The thinning mask set here is a mask complementary to the thinning mask for the second-pass printing scan for one unit area that completes printing. Next, printing by the first scan is executed in step S105. In step S106, the feeding amount of the recording medium after the first recording scan described in FIG. 12 is set. In step S107, the recording medium is conveyed according to the feeding amount.

  Next, in step S108, it is determined whether there is recording data being recorded. Here, what is meant during recording indicates a state where multi-scan recording for one unit area is not completed. When it is determined in step S108 that there is no recording data being recorded, this sequence is terminated. If it is determined in step S108 that there is print data in the middle of printing, and if it is determined in step S102 that it is not the first print scan, it is determined in step S109 whether the print scan is the second print scan or a different print scan. .

  If it is determined in step S109 that it is the second recording scan, an unused mask for the second recording scan is set in step S110. Here, as described with reference to FIGS. 12 and 13, the unused mask set in the second recording scan has a nozzle position different from that in the first recording scan. In step S111, a thinning mask for printing is set for the nozzles used in the second printing scan. The thinning mask set here is a thinning mask having a complementary relationship with the thinning mask used in the first recording scan. Next, printing by the second scanning is executed in step S112, and the recording medium is conveyed in step S114 according to the feeding amount of the recording medium after the second recording scanning set in step S113. Here, the set feed amount is determined in relation to the number of used nozzles and unused nozzles. Next, in step S115, it is determined whether there is next recording data. If it is determined in step S115 that there is the next recording data, the process proceeds to step S101, image data is taken in again, and this process is repeated. In this case, the first recording scan and the second recording scan shown in FIG. 16 correspond to the third recording scan and the fourth recording scan described with reference to FIG. That is, in the above description, the two scans that complete the recording of the unit area are the first recording scan and the second recording scan, respectively. If it is determined in step S115 that there is no next recording data, this process is terminated.

  Note that the recording time difference-suppressing multi-scan recording method described in each of the above embodiments relates to two-pass printing, but it goes without saying that the application of the present invention is not limited to two passes. It is possible to execute a multi-scan recording method that suppresses the recording time difference for any number of passes of 3 passes or more, such as 3 passes and 4 passes. In this case, in the even number of passes, the recording of each unit area starts with scanning in a fixed direction of forward or backward, but in the odd number of passes, the scanning of forward and backward is alternately performed at the start of recording of each unit area. The only difference is.

  FIG. 17 is a diagram for explaining a 4-pass printing time difference suppressing multi-scan printing method, which is the same as FIG. Similar to the example shown in FIG. 12, this is an example using a recording head having 16 nozzle blocks, and shows an example in which recording of a unit area is completed by four reciprocating scans. One nozzle block is composed of 16 nozzles.

  As shown in FIG. 17, after the first scan in the forward direction, the recording medium is conveyed by one nozzle block (× nozzle pitch). Next, the second scanning in the backward direction is performed, and thereafter, the conveyance for one nozzle block is performed in the same manner. Further, the third scan is performed in the forward direction, and thereafter the same one nozzle block is conveyed, and finally the fourth scan in the reverse direction is performed, thereby completing the recording of “recording region 1” as a unit region. Then, after completion of the recording of this unit area, 10 nozzle blocks are conveyed. Next, the printing of “printing area 2” is completed in the same manner by the fifth reciprocating scan, the sixth scan in the backward direction, the seventh scan in the forward direction, and the eighth scan in the backward direction. Thereafter, the unit area is recorded by performing four reciprocal scans in the same manner.

  Further, in the above recording, the length of the unit area where the recording is completed in order such as “recording area 1” and “recording area 2” (length in the vertical direction in FIG. 17) corresponds to 10 nozzle blocks. . That is, in the first scan for recording “recording area 1”, the recording data corresponding to the three nozzle blocks on the upper end side are masked. In the next second scanning, print data corresponding to the two nozzle blocks on the upper end side and the one nozzle block on the lower end side is masked. Further, in the third scan, print data corresponding to one nozzle block on the upper end side and two nozzle blocks on the lower end side are masked. In the final fourth scan, print data corresponding to the three nozzle blocks on the lower end side is masked. As a result of masking in this way, each unit area is recorded with a length corresponding to 10 nozzle blocks, which are overlapping portions of the used nozzles of each scan.

  Of course, in addition to the mask processing for the unused nozzle block, mask processing using a mask pattern for performing multi-scan recording in which recording is completed by four scans is performed.

  Generalizing the recording medium conveyance amount in the multi-scan recording of each embodiment described above is as follows. In the case where a unit area is completed by k times of scanning, that is, in the case of k-pass multi-scanning, in each of the above-described embodiments, the conveyance amount for each of k times of scanning is one nozzle block. In this case, when a recording head having N nozzle blocks is used, the transport amount when moving to the next unit area is represented by (N−2 (k−1)) · p. Here, p is a transport amount corresponding to one nozzle block. Even if the transport unit is not a nozzle block but a nozzle unit, the transport amount can be expressed by the same equation if p is the nozzle arrangement pitch. It is clear that the following amounts are also true. Further, the sum of the mask amounts of the print data is k-1 nozzle blocks in any of the k scans, and the mask amount on the upper end side of the m-th scan is (k-1)-(m-1). It is a block. Furthermore, the nozzles used, that is, the nozzles that overlap in k scans are N- (k-1) blocks.

  Next, if the conveyance amount for each of the k scans is not equal to one nozzle block, but more generalized to q nozzle blocks, the above relationship is as follows. The transport amount when moving to the next unit area is represented by (N-2q (k-1)) · p. Further, the sum of the mask amounts of the print data is q (k−1) nozzle blocks in any of the k scans, and the mask amount on the upper end side of the m-th scan is q ((k−1) − (M-1)) It is for a block. Furthermore, the nozzles used, that is, the nozzles that overlap in k scans, are Nq (k-1) blocks.

  For example, in the case shown in FIG. 12, the transport amount between the two scans (the first scan and the second scan) is half that of the nozzle row of the recording head, as in the normal multi-scan. 8 nozzle blocks (q = 8). In this case, the transport amount (between the second scan and the third scan) for shifting to the adjacent “recording region 2” is 0 nozzle block from the above formula. Further, in the case shown in FIG. 17, the transport amount between the four scans (first scan to fourth scan) is ¼ of the nozzle row of the recording head, as in the normal multi-scan. Assume 4 nozzle blocks (q = 4). In this case, the transport amount (between the fourth scan and the fifth scan) for shifting to the adjacent “printing area 2” is -8 nozzle blocks from the above equation, and in this case, in the reverse direction. Will be transported. Thus, in normal multi-scan printing, the transport amount (N−2q (k−1)) · p when moving to the first scan for recording the next unit area is a plurality of scans that complete the unit area. Is the same as the transport amount q · p. On the other hand, in the method of the present embodiment, these transport amounts are different in many cases. In practice, the throughput (N−2q (k−1)) · p when moving to the next unit area is larger than the conveyance amount q · p during a plurality of scans in consideration of throughput and the like. It is desirable to satisfy the relationship.

  However, q which satisfies q · p = (N−2q (k−1)) · p exists, and the configuration thereof is also included in the present invention. In this case, if q that satisfies the condition of q = N / k, which is one of the conditions of normal multi-scan, is considered, q = N, that is, the case of recording by one pass. Therefore, the multi-scan recording condition is not satisfied. Therefore, in the case of multi-scan recording (2 passes or more), when the transport amount for shifting to an adjacent unit area is defined as (N-2q (k-1)) · p, these conditions are usually The multi-scan is not included.

  It should be noted that the mask processing of the recording data corresponding to the unused nozzles is not necessarily performed when the present invention is applied. From the beginning, print data may be generated in units of used nozzles set to exclude unused nozzles, and may be associated with the used nozzles of each of the multiple scans. For example, in the example shown in FIG. 12, print data is generated in units of 15 nozzle blocks, which is one block less than the nozzle row corresponding to the length of the unit area. In the first scan, this data is associated with the nozzles from the second nozzle block to the lowest nozzle block from the upper end side, and in the second scan, from the uppermost nozzle block to the second nozzle block from the lower end. It is made to correspond to this nozzle.

  Next, the normal multi-scan recording method in step S5 shown in FIG. 15 will be described. FIG. 18 is a flowchart showing this type of recording process. First, recording data is fetched in step S201. Here, as described in FIG. 15, the number of paths has already been determined. Next, a thinning mask is set according to the number of passes determined in step S202, mask processing is performed, and recording is executed in step S205 based on the recording data generated thereby. Next, according to the feed amount set in step S204, the recording medium is conveyed in step S205. In step S205, it is determined whether there is next recording data. If it is determined in step S205 that there is the next recording data, the process proceeds to step S201, image data is captured again, and this sequence is repeated. If it is determined in step S205 that there is no next recording data, this process ends.

  In the case of a normal multi-scan recording method, if the number of passes is determined, recording can be performed by setting a thinning mask and a feed amount. On the other hand, in the multi-scan recording method with the recording time difference suppression, the difference is that an unused nozzle is set, and further, the feed amount is determined in relation to the number of unused nozzles.

  As described above, the embodiment of the present invention switches between the recording time difference suppressing multi-scan method and the normal multi-scan method according to the number of passes for completing multi-scan recording. Thereby, the band nonuniformity between unit regions can be reduced. In the following, some embodiments will be described in which density change due to a recording time difference according to the position in the scanning direction in each unit region is further reduced.

(First embodiment)
In the first embodiment of the present invention, in accordance with the switching between the recording time difference suppression multi-scan method and the normal multi-scan method described above with reference to FIG. Processing for suppressing the resulting density change is performed. Specifically, the ink ejection amount represented by the recording data is changed according to the density that will change.

  FIG. 19 is a diagram showing a change in density in the scanning direction in a certain unit area in the printing result by the printing time difference suppressing multi-scan method shown in FIG.

  In FIG. 19, the horizontal axis indicates the position in the scanning direction, and the vertical axis indicates the density. Here, the density is an optical reflection density of an image recorded on a recording medium, and is an area factor that is maximum, that is, a density of an image in a state where one pixel is completely filled with ink without a gap. As shown in FIG. 19, the density decreases from left to right within the recording range. This is because the density is low in the area where the recording by the second scanning is performed immediately after the recording by the first scanning, and the second scanning after the scanning time of about two times of the scanning time has elapsed after the recording by the first scanning. This is because the image density is high in the area where the recording is performed. As the cause, as shown in FIG. 6, the penetration depth of the ink component changes depending on a plurality of inks, that is, the recording time difference, so that the image density is different. For the above reasons, in the example shown in FIG. 19, the density decreases from the left side recorded with a long time difference between the two scans to the right side recorded with a short time difference in the recording range.

  Of course, such a change in density also occurs in the normal multi-scan method. However, as shown in FIG. 5, the direction of density change is the density change shown in “Recording area 1” (left side; high → right side; low) and the density change shown in “recording area 2” (left side; Low → right; high). Accordingly, the control of the driving amount described below is performed in two directions when applied to a normal multi-scan.

  In the present embodiment, for the density change described above, the maximum value of the ink ejection amount is set according to the position in the scanning direction.

  FIG. 20 is a diagram for explaining the maximum value of the ink ejection amount corresponding to the position in the scanning direction corresponding to the density change shown in FIG. As shown in FIG. 20, there is shown a characteristic that the ink hit amount increases from the left to the right within the recording range. This shows a tendency opposite to the density change shown in FIG. That is, the density is made uniform by correcting the ink ejection amount with the change characteristic opposite to the density change shown in FIG.

  FIG. 21 is a diagram illustrating an example of a result of such density correction. In FIG. 21, the density change before correction shows a characteristic that decreases from the left to the right within the recording range, whereas the density change after correction is almost independent of the position in the scanning direction. It can be seen that it has a flat density characteristic. That is, the density difference in the unit area due to the time difference of the printing scan is reduced by limiting the maximum value of the ink ejection amount.

  Specifically, the unit area is divided into a plurality of partial areas, and a maximum driving amount is set for each of the divided areas.

  FIG. 22 is a diagram showing an example of a table for setting the maximum value of the ink ejection amount, which is in accordance with the characteristics of the ejection amount shown in FIG. As shown in FIG. 22, the unit area is divided into eight in the scanning direction, and the maximum value of the ink ejection amount is set for each divided area. Then, the largest value is set in the divided area 8 and the smaller value is set in the direction of the divided area 1. That is, in the case of the density change as shown in FIG. 19, the density decreases as it goes from the left to the right within the recording range, so that the ink shot amount is increased as it goes from the left to the right. In other words, by using the setting table for the maximum value of the ink ejection amount as shown in FIG. 22, the total amount of ink finally deposited on the recording medium is shown as a trend in the entire unit area including the eight divided areas. As shown in FIG. As a result, density correction as shown in FIG. 21 can be performed.

  Here, the ink ejection amount is set for the recording data before being quantized. Specifically, first, image data represented by a gradation value of 0 to 255 in which one pixel is 8 bits is set as recording data for each unit area. The recording data for each unit area is divided into eight divided recording data corresponding to the eight divided areas. Further, (e) with respect to each divided recording data, the table shown in FIG. Then, for a pixel having a gradation value exceeding the maximum value, processing for changing the gradation value to the acquired maximum value is performed. For example, when a pixel in “divided region 1” has a gradation value exceeding 255 × 93%, a process of changing the gradation value to 255 × 93% is performed.

  Note that the table used for gamma correction may be changed instead of the setting of the upper limit value of the driving amount described above. For example, eight gamma correction tables are prepared in which the maximum output value corresponds to each of the maximum implantation amounts shown in FIG. FIG. 23 is a diagram showing a table for selecting this gamma correction table according to the divided areas.

  By using the gamma correction table in this way, it is possible to perform density correction not only in a portion where the ink shot amount is large in a recorded image but also in a halftone.

  As described above, by setting the maximum value of the ink ejection amount according to the divided areas in the scanning direction, it is possible to reduce changes in density due to the recording time difference in the scanning direction of the unit areas.

As described above, this is applied to both the recording time difference suppressing multi-scan and the normal multi-scan. Thereby, in the multi-scan recording with suppressed recording time difference, the band-to-band unevenness is remarkably reduced, and the density change in the scanning direction can be reduced in each unit region. Further, in normal multi-scan recording, the density change in the scanning direction in each unit area can be reduced, and as a result, the density difference at the same position in the scanning direction between adjacent unit areas (bands) can also be reduced. .
(Second Embodiment)
The influence of the time difference on the density differs depending on the relative characteristics of the ink with respect to the recording medium. Therefore, in the second embodiment of the present invention, the maximum value of the ink ejection amount is set according to the type of the recording medium.

  FIG. 24 is a diagram illustrating the maximum value of the ink ejection amount in the scanning direction for each type of recording medium. As shown in FIG. 24, in any recording medium, the maximum value of the ink ejection amount is increased from left to right for each divided region. As described above in the first embodiment, this shows a tendency opposite to the density change shown in FIG. 19, and thus the density in the scanning direction can be made uniform. Further, the “recording medium 1” has a characteristic that the recording time difference is relatively insensitive and the density difference hardly occurs even if the recording time difference exists. For this reason, the maximum value of the ink ejection amount does not have to be changed greatly. On the other hand, the “recording medium 3” is relatively sensitive to the time difference, and has a characteristic that the influence of the recording time difference is large and the density difference appears. Therefore, the maximum value of the ink ejection amount is greatly changed. “Recording medium 2” has intermediate characteristics between “recording medium 1” and “recording medium 3”. Thus, by setting the maximum value of the ink ejection amount in a different manner for each type of recording medium, it is possible to reduce the density change in the scanning direction due to the recording time difference regardless of the type of recording medium. That is, the density difference in the recording area due to the time difference of the recording scan can be suppressed by limiting the maximum value of the ink ejection amount.

  Note that the characteristics for each type of recording medium described above are related to the phenomenon of ink permeation into the recording medium, and thus may be affected by environmental temperature, humidity, and the like. More preferably, by having a setting table for correcting the environmental temperature and humidity, it is possible to suppress the density difference in the print area due to the time difference of the print scan with higher accuracy.

  Also in this embodiment, the gamma correction table may be set for each divided region in accordance with not only the upper limit value of the driving amount but also the type of recording medium.

  As described above, even if the type of the recording medium to be used is changed by setting the maximum ink ejection amount according to the type of the recording medium, the scanning direction caused by the recording time difference by the bidirectional multi-scan method The density change can be reduced satisfactorily.

(Other embodiments)
In each of the above-described embodiments, the driving amount represented by the print data is changed according to the position in the scanning direction, but the application of the present invention is not limited to such a form. For example, the discharge amount of each nozzle in the recording head may be changed. For example, in a head that discharges ink by generating bubbles using an electrothermal transducer, the ejection amount can be changed by changing the waveform of an electrical pulse supplied to the electrothermal transducer. Further, in a method in which ink is ejected by pressure generated by electromechanical conversion using a piezo element, the ejection amount can be changed by changing a voltage applied to the piezo element. As described above, the amount of ink finally ejected into a certain region can be changed also by changing the ink amount itself ejected from the recording head in accordance with the position in the scanning direction. The time difference unevenness according to the position at can be reduced.

  Each of the above-described embodiments relates to a bidirectional multi-scan of unit areas having a length corresponding to the nozzle row obtained by dividing the nozzle array of the recording head. That is, for each of a plurality of scans, the recording medium is conveyed by a predetermined amount relative to the recording head, and recording is performed in association with different nozzles. However, the application of the present invention is not limited to this form. It is obvious that the present invention can also be applied to a mode in which recording of the unit area is completed by performing reciprocal scanning of the recording head at the same position with respect to the unit area of the recording medium without conveying the recording medium.

(A), (b) and (c) is a figure which shows an example of the ideal recording state in an inkjet recording device. (A), (b), and (c) are diagrams showing a recording state with density unevenness in the ink jet recording apparatus. (A), (b), and (c) are diagrams illustrating recording in which density unevenness is suppressed by a conventional example of a multi-scan method in an inkjet recording apparatus. (A), (b) and (c) is a figure explaining the recording for every scanning in a multi-scan system. It is a figure explaining the density nonuniformity resulting from the time difference in one prior art example of a multi-scan system. (A) And (b) is sectional drawing which shows the mode of fixation of the two ink droplets discharged continuously. 1 is a perspective view schematically showing a main part configuration of an ink jet recording apparatus according to an embodiment of the present invention. It is a typical perspective view for demonstrating the main structures of the ink discharge part of the recording head used with the apparatus of FIG. It is a block diagram which shows the control structure in the said apparatus. It is a figure explaining the flow of the recording data in the said apparatus. FIG. 10 is a block diagram showing a data transfer circuit configured in the gate array shown in FIG. 9. It is a figure which shows an example of the multiscan recording by the bidirectional | two-way scanning which concerns on 1st embodiment of this invention. FIG. 13 is a diagram for explaining details of mainly used / unused nozzle blocks in the recording of the present embodiment described in FIG. 12. It is a figure explaining that the band non-uniformity resulting from the time difference of reciprocating recording differs in the case of an even-numbered pass and the case of an odd-numbered pass. It is a flowchart explaining the recording process accompanied by the switching of the multi-scan recording system concerning 2nd embodiment of this invention. 6 is a flowchart showing a control process for implementing the recording time difference suppressing multi-scan recording method described in the first embodiment with respect to the switching. It is a figure explaining the 4-pass recording time difference suppression multi-scan recording system based on one Embodiment of this invention. It is a flowchart which shows the recording process of a normal multiscan recording system. It is a figure which shows the density change of the scanning direction in a certain unit area | region in the printing result by the printing time difference suppression multiscan system shown in FIG. FIG. 20 is a diagram for explaining the maximum value of the ink ejection amount corresponding to the position in the scanning direction corresponding to the density change shown in FIG. 19. It is a figure which shows an example of the result of having performed the density | concentration correction | amendment by the amount of ink placement. It is a figure which shows an example of the table for setting the maximum value of the ink placement amount which concerns on 1st embodiment of this invention. It is a figure which shows the table for selecting the gamma correction table for setting the wink driving amount which concerns on the modification of said 1st embodiment according to a division area. FIG. 10 is a diagram illustrating a maximum value of ink ejection amount in a scanning direction for each type of recording medium according to a second embodiment of the present invention.

Explanation of symbols

1, 1A, 1B, 1C, 1D, 1018 Recording head 1011 MPU
1012 ROM
1013 DRAM
1014 Gate array 1201 Data register 1203 AND gate 1204 Transfer counter 1205 Register 1206 Selector 1207 Selector 1211 Column counter 1230 Print buffer

Claims (12)

Ink jet recording, which uses a recording head in which a plurality of ejection openings are arranged, and performs recording of the unit area by scanning the recording head a plurality of times in which forward scanning and backward scanning are alternately performed. In the device
An ink jet recording apparatus comprising: means for differentiating a maximum ink ejection amount in accordance with a recording time difference between the plurality of scans, which differs depending on a position in a scanning direction in the recording of the unit area.   2. The ink jet recording apparatus according to claim 1, wherein a recording medium is transported by a predetermined amount for each of the plurality of scans, and recording is performed on the unit area by associating different discharge ports with the unit area.   The means may vary the maximum ink ejection amount in accordance with a maximum ink ejection amount value set for each of a plurality of divided areas obtained by dividing the unit area according to a position in a scanning direction. Item 3. The ink jet recording apparatus according to Item 1 or 2.   4. The ink jet recording apparatus according to claim 3, wherein the means varies the maximum ink ejection amount in accordance with a gamma correction table set for each of the divided areas.   5. The apparatus according to claim 1, wherein the means changes the maximum ink ejection amount in accordance with a printing time difference between the plurality of scans, which differ depending on the position in the scanning direction, in a different manner for each type of printing medium. Any one of the inkjet recording apparatuses. Means for conveying the recording medium between the last scan for recording one of the adjacent unit areas and the first scan for recording the other, wherein the conveyance amount is greater than the predetermined amount. Further comprising
The length of the unit region along the transport direction is a length corresponding to the number of ejection openings that overlap in a plurality of scans for recording the unit region, so that the unit region is positioned at the position in the scan direction. 6. The ink jet recording apparatus according to claim 2, wherein the combination of the corresponding recording time differences between the plurality of scans is the same in any of the plurality of unit regions adjacent to each other. A means for transporting the recording medium between the last scan for recording one of the adjacent unit areas and the first scan for recording the other, wherein the transport amount is
(N-2q (k-1)) · p,
Here, N is the number of the plurality of ejection openings, q · p is the predetermined amount, k is the number of the plurality of scans, p is the arrangement pitch of the ejection opening array,
Further comprising a transport control means,
The length of the unit area along the transport direction is (Nq (k-1)) · p corresponding to the number of ejection openings that overlap in a plurality of scans for recording the unit area. 6. The combination of the recording time differences between a plurality of scans corresponding to the position of the unit area in the scanning direction is the same in any of the plurality of unit areas adjacent to each other. Any one of the inkjet recording apparatuses.   The apparatus further comprises a judging means for judging whether or not the number of times of scanning a plurality of times for recording the unit area is an even number, and when the judging means judges that the number of times is an even number of times, carrying by the carrying control means and 8. The inkjet recording according to claim 6, wherein the length of the region along the transport direction is a length corresponding to the number of ejection openings that overlap in a plurality of scans for recording the unit region. apparatus. Using a recording head in which a plurality of ejection openings are arranged, a unit area of a recording medium is scanned with the recording head a plurality of times in which forward scanning and backward scanning are alternately performed to perform recording on the unit area. In the inkjet recording method,
An ink jet recording method comprising: a step of varying the maximum ink ejection amount in accordance with a recording time difference between the plurality of scans, which differs depending on a position in a scanning direction, in the recording of the unit area.   10. The ink jet recording method according to claim 9, wherein a recording medium is transported by a predetermined amount for each of the plurality of scans, and recording is performed in the unit area by associating different ejection openings with the unit area. A transport control step for transporting the recording medium between the last scan for recording one of the adjacent unit areas and the first scan for recording the other, wherein the transport amount is larger than the predetermined amount. Further comprising
The length of the unit region along the transport direction is a length corresponding to the number of ejection openings that overlap in a plurality of scans for recording the unit region, so that the unit region is positioned at the position in the scan direction. 11. The ink jet recording method according to claim 10, wherein the combination of the corresponding recording time differences between the plurality of scannings is the same in any of the plurality of unit regions adjacent to each other. A means for transporting the recording medium between the last scan for recording one of the adjacent unit areas and the first scan for recording the other, wherein the transport amount is
(N-2q (k-1)) · p,
Here, N is the number of the plurality of ejection openings, q · p is the predetermined amount, k is the number of the plurality of scans, p is the arrangement pitch of the ejection opening array,
Further having a conveyance control step
The length of the unit area along the transport direction is (Nq (k-1)) · p corresponding to the number of ejection openings that overlap in a plurality of scans for recording the unit area. The combination of the recording time differences between a plurality of scans according to the position of the unit area in the scanning direction is the same in any of the plurality of unit areas adjacent to each other. Inkjet recording method.

Images