JP2005177992A - Inkjet recording system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording system which can form images superior in the uniformity with few density irregularities and white streaks without shortening the life of a recording head more than required at the time of image formation with the use of the recording head that has many recording elements for discharging ink arranged thereat. <P>SOLUTION: Multi pass recording is carried out by applying switching by a recording scanning unit, a mask pattern which has a distribution of mutually different recording rates of blocks of a recording element array. The discharging number of times during recording can be equalized as much as possible at each block while the recording rate at both end parts prone to twist is lowered. Accordingly, a bias of a temperature distribution to be a cause of the density irregularities, and the end part twisting to be a cause of the white streaks can be reduced without shortening the life of the recording head more than required. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet recording system that forms an image by ejecting ink to a recording medium from a plurality of recording elements arranged in a recording head.

  With the spread of information processing equipment such as copying machines, word processors, computers, and communication equipment, one of the recording devices of these equipment is rapidly performing digital image recording using an ink jet recording head. It is popular. In such a recording apparatus, in order to improve the recording speed, a recording element array formed by arranging a large number of recording elements (nozzles) composed of ink discharge ports and liquid paths is used, and the above-mentioned color correspondence is provided. In general, a recording head having a plurality of recording element arrays is applied.

  Unlike a printer that records only a character as a monochrome printer, a color printer that records a color image image requires stable recording of various elements such as color development, gradation, and uniformity. In particular, the uniformity is easily affected by slight nozzle unit variations that occur in the manufacturing process of the printing element array. Such variations make the discharge amount and discharge direction of each nozzle unstable, resulting in uneven density in the recorded image. Is generated. In addition, in a serial type ink jet recording apparatus, streaks that can be visually confirmed are inevitably generated at the connecting portions between the recording scans, and such connecting streaks appear periodically. This was one of the major problems that deteriorated uniformity.

  Therefore, in the conventional serial type inkjet recording apparatus, the recording data to be recorded in the same recording area is divided into a plurality of groups, and the same recording area is recorded little by little by a plurality of recording scans with the paper feeding operation interposed therebetween. It is common to apply a so-called multi-pass recording method (see, for example, Patent Document 1). According to multi-pass printing, a printing line that can be printed by a single printing scan can be formed by a plurality of printing scans using different nozzles, so that the influence on the image unique to each nozzle is reduced. In addition, since recording is performed not only by the end nozzles but also by the central nozzles at the boundary for each recording scan, the connecting stripes are not noticeable, and density unevenness in the recorded image is reduced.

  However, even when such multi-pass printing is performed, the density unevenness is difficult to be eliminated depending on the printing rate of each printing scan, and in particular, the occurrence of new uneven stripes may be confirmed in the halftone. Therefore, a technique is also disclosed in which, when performing multi-pass printing, the amount of paper feed performed between each printing scan is changed randomly, and the pitch of each printing area is made variable to reduce such density unevenness. (For example, refer to Patent Document 2). If the configuration of Patent Document 2 is used, the period of each recording area is also randomized, so that unevenness is less noticeable and high-quality image formation is realized.

  Also, there is a method of overlapping a predetermined amount of an image recorded by one recording scan and an image recorded by the next recording scan in order to prevent a connecting stripe without performing multi-pass recording. It has been proposed (see, for example, Patent Document 3). According to Patent Literature 3, image data is masked with a random mask pattern in an area overlapping with the next recording scan in the image data recorded in the previous recording scan. Further, in the image data recorded in the next recording scan, an area overlapping with the previous recording scan is masked with a pattern obtained by inverting the random mask pattern applied last time. By adopting such a configuration, the adverse effects peculiar to the connecting portion between the scanning scans are dispersed within the region having a predetermined width, so that it is difficult to confirm strong connecting stripes on the image.

  By the way, in recent years, a technology for reducing the discharge amount per dot has been remarkably advanced, and a higher resolution image can be formed. In addition to the basic four color inks (cyan, magenta, yellow, and black), a lighter ink with a lighter density is applied to achieve the gradation similar to silver halide photography. Recording apparatuses for recording in combination with ink have already been provided.

  However, in such a recording apparatus with a small discharge amount per dot, there are cases where new adverse effects such as dot landing position deviation and discharge stability are caused. For example, according to the study by the present inventors, an image was formed using a recording head having a configuration in which 256 recording elements (nozzles) with a discharge amount of 4 pl were arranged at a pitch of 1200 dpi (dot / inch; reference value). However, it has been confirmed that the landing positions of the ink droplets ejected by the nozzles at both ends of the recording head are significantly shifted inward as compared to the landing positions by the nozzles at the center. Hereinafter, this phenomenon is referred to as “end-to-end”.

  FIG. 1 is a diagram for explaining the above-mentioned “edge shift”, and shows the state of dots on a recording medium formed by nozzles positioned at the end of the recording head. Here, for the sake of simplicity, only dots recorded by the nozzle located at the extreme end are indicated by black circles, but in reality, all the nozzles that record a predetermined color sandwich one paper feeding operation. A state where 100% printing is performed by two printing scans is shown. The paper feed boundary shown in the figure indicates the boundary between two print scans, and the dot row shown above the line is a dot row printed by the lowermost nozzle in the first print scan. is there. A dot row shown below the line indicates a dot row recorded by the uppermost nozzle in the subsequent second recording scan. The applied recording head has a configuration in which 256 nozzles capable of ejecting 4 pl ink droplets are arranged at a pitch of 1200 dpi, and ejects ink at a predetermined driving frequency while moving from left to right in the figure. It is assumed that each dot has landed on the recording medium. As can be seen in the figure, the dots recorded by the nozzles at the end, that is, the dots recorded by the uppermost and lowermost nozzles of the two recording scans, land at suitable positions in contact with each other at the start of the recording scan. However, as the scanning progresses, the landing position gradually begins to shift, and finally the distance between the landing positions of the two nozzles is about 50 μm.

  FIG. 2 is a diagram schematically showing the ejection state of the recording head when performing the recording scanning as described above. In FIG. 2, the recording head ejects ink droplets in the direction of the arrow from each nozzle toward the recording medium while moving and scanning in the direction perpendicular to the paper surface. As can be seen from the figure, the ink droplets ejected from the nozzles located at both ends of the recording head proceed while being deflected toward the center. Such a tendency is conspicuous when an image is formed with a very small ink droplet of 4 pl or less, and when the recording duty is high. Then, the dot that appears in each recording scan is recognized as a white stripe in terms of visual characteristics.

  It is also possible to make white stripes less noticeable by applying the above-described multi-pass recording or setting the number of multi-passes more than usual for such image defects. However, such a measure has not been sufficient for obtaining an image having a quality equivalent to that of a photographic image as required in recent years. Further, further increasing the number of multi-passes increases the number of printing scans, and therefore hinders speeding up.

  To solve the above problems, the nozzle array is divided into a plurality of blocks (recording element groups) at a predetermined pitch in order to reduce the image damage caused by the nozzles near the end without increasing the number of multi-passes more than necessary. A method of setting the thinning rate for each divided block to a different value is known (for example, see Patent Document 4). According to this method, for example, by applying a mask pattern as shown in FIG. 9A, the recording rate of the nozzles located at both ends in the region formed by one recording scan is set to be small in advance. I can do it. Therefore, since the number of dots that are landed at the shifted position is suppressed, the white streaks described with reference to FIG. 1 are not confirmed.

US Pat. No. 4,748,453 JP-A-7-52465 Japanese Patent Laid-Open No. 8-25693 JP 2002-096455 A JP 2002-292910 A

However, the above conventional example has the following problems to be solved.
First, if the recording rate distribution is not uniform within the nozzle array of the recording head, temperature deviation may occur and density unevenness may occur. If a block with a high recording rate and a block with a low recording rate are present in the same recording head, the temperature of the block with a high recording rate will be relatively high, and the ejection amount will increase only for that block. That is, variations in the discharge amount occur in the recording head, and this appears as density unevenness in the recorded image. Particularly in recent years, in order to improve the recording speed, the number of nozzles has been increased and the length of the recording head has been increased, making it difficult to control the temperature of the recording head uniformly. Under such circumstances, the above control that promotes the non-uniformity of the temperature distribution has been difficult to say from the viewpoint of density unevenness.

  Further, the nonuniformity of the recording rate distribution causes a difference in the number of ejections between the nozzles. In this case, the nozzle having a large number of ejections proceeds earlier in the deterioration of the ejection characteristics than the other nozzles. In the recording head, when even one nozzle has an ejection failure, it is determined that the use is inappropriate. Therefore, the method described in Patent Document 4 in which the recording frequency of some of the nozzles is locally high is used for recording. This will shorten the life of the head.

  As described above, in a recent ink jet recording apparatus using a small droplet recording head, it can be said that it is preferable to keep the number of ejections of the nozzle rows as uniform as possible from the viewpoint of density unevenness and the life of the recording head. However, on the other hand, it also has the problem of “shaft edge” as explained in the section of the prior art. Therefore, a method for solving both problems at once is desired.

  According to Patent Document 5, a method for switching the distribution of the recording rate of the nozzles in accordance with the usage amount of the recording head is disclosed. According to this method, the mask pattern to be applied is switched according to the usage amount or the durability count of the recording head while preparing in advance a plurality of mask patterns having different recording rate distributions for the nozzle rows. Therefore, from the long-term viewpoint, the number of ejections of each nozzle can be substantially equalized, and the problem of the life of the recording head can be solved to some extent.

  However, since the switching of the plurality of mask patterns is not performed during the recording of the same image and the same page, it is possible to reduce the discharge amount difference between the nozzles existing in each recording scan. Absent. In other words, in order to simultaneously solve another problem of density unevenness, it is necessary to equalize the number of ejections of each nozzle from a short-term viewpoint. It was not.

  The present invention has been made to solve the above-described problems. The object of the present invention is to achieve density unevenness and white streak while using a recording head in which a large number of recording elements for discharging small droplets of ink are arranged. It is an object of the present invention to provide an ink jet recording system that performs recording with less uniformity and excellent uniformity and does not unnecessarily shorten the life of the recording head.

  Therefore, in the present invention, a recording head in which a plurality of recording element groups each including a plurality of recording elements that eject ink is arranged in a predetermined direction is used. In an inkjet recording system for forming an image by a plurality of recording scans in a direction different from a predetermined direction, the plurality of recording element groups eject ink according to different recording rates, and the plurality of the plurality of recording elements for each recording scan Recording rate changing means for changing the recording rate in at least two recording element groups in the recording element group.

  Also, a recording head formed by arranging a plurality of recording element groups composed of a plurality of recording elements for ejecting ink in a predetermined direction differs from the predetermined direction by different recording element groups for the same region of the recording medium. In an ink jet recording system for forming an image by a plurality of recording scans in a direction, means for ejecting ink in accordance with a different recording rate from one recording element group and another recording element group in the plurality of recording element groups; A recording rate changing means for changing a recording rate in at least two recording element groups of the plurality of recording element groups between one recording scan and another recording scan among the plurality of recording scans. It is characterized by doing.

  Also, a recording head formed by arranging a plurality of recording element groups composed of a plurality of recording elements for ejecting ink in a predetermined direction differs from the predetermined direction by different recording element groups for the same region of the recording medium. In the ink jet recording system for forming an image by a plurality of recording scans in the direction, the plurality of recording element groups each eject ink according to a different recording rate, and among the plurality of recording scans, a certain recording scan Recording rate changing means for changing the distribution in the predetermined direction of the recording rate corresponding to each of the plurality of recording element groups in another recording scan.

  Also, a recording head formed by arranging a plurality of recording element groups composed of a plurality of recording elements for ejecting ink in a predetermined direction differs from the predetermined direction by different recording element groups for the same region of the recording medium. In an inkjet recording system for forming an image by a plurality of recording scans in the direction, the plurality of recording element groups ejects ink according to different mask patterns, and each of the plurality of recording element groups for each recording scan A mask pattern changing means for changing a mask pattern, wherein the mask pattern changing means has a mask pattern recording rate corresponding to the recording element group for at least two recording element groups of the different recording element groups. It is characterized by changing.

  According to the present invention, in a recording element array composed of a plurality of different recording element groups, while reducing the recording rate of the recording element groups located at both end portions where the end portion is liable to be generated, The number of ejections can be made as uniform as possible in each recording element group. As a result, it is possible to reduce the uneven temperature distribution that causes density unevenness and the edge portion that causes white stripes without shortening the life of the recording head more than necessary.

Hereinafter, a configuration example of an ink jet recording system applicable to the present invention will be specifically described.
FIG. 3 is a view for explaining the general configuration of an ink jet recording apparatus applicable to the present invention. In FIG. 3, the outer periphery of the ink jet recording apparatus main body M1000 includes an exterior member including a lower case M1001, an upper case M1002, an access cover M1003, and a discharge tray M1004, and a chassis M3019 (see FIG. 4) housed in the exterior member. Consists of

  The chassis M3019 is composed of a plurality of plate-shaped metal members having a predetermined rigidity, forms a skeleton of the recording apparatus, and holds each recording operation mechanism described later. The lower case M1001 forms a substantially lower half part of the exterior of the apparatus main body M1000, and the upper case M1002 forms a substantially upper half part of the exterior of the apparatus main body M1000. The hollow body structure which has the storage space which stores the. An opening is formed in each of the upper surface portion and the front surface portion of the apparatus main body M1000.

  One end of the discharge tray M1004 is rotatably held by the lower case M1001, and the opening formed on the front surface of the lower case M1001 can be opened and closed by the rotation. Therefore, when executing the recording operation, the discharge tray M1004 is rotated to the front side to open the opening, so that the recording medium can be discharged from the recording medium and the discharged recording media are sequentially stacked. It has come to be able to do. The paper discharge tray M1004 stores two auxiliary trays M1004a and M1004b, and the support area of the recording medium can be expanded or reduced in three stages by pulling each tray forward as necessary. It is like that.

  One end of the access cover M1003 is rotatably held by the upper case M1002, and an opening formed on the upper surface can be opened and closed. The access cover M1003 is accommodated inside the main body by opening the access cover M1003. It is possible to replace the print head cartridge H1000 or the ink tank H1900. Although not specifically shown here, when the access cover M1003 is opened and closed, the protrusion formed on the back surface rotates the cover opening and closing lever, and the rotation position of the lever is detected by a micro switch or the like. Thus, the open / closed state of the access cover M1003 can be detected.

  On the upper surface of the rear portion of the upper case M1002, a power key E0018 and a resume key E0019 are provided so that they can be pressed, and an LED E0020 is provided. When the power key E0018 is pressed, the LED E0020 lights up and recording is possible. It is to inform the operator. Further, the LED E0020 has various display functions such as notifying the operator of troubles of the recording apparatus, etc., by changing the way of blinking or the color. When the trouble is solved, the recording is resumed by pressing the resume key E0019.

FIG. 4 is a diagram for explaining the recording operation mechanism of this embodiment that is housed and held in the apparatus main body M1000.
As a recording operation mechanism in the present embodiment, an automatic feeding unit M3022 that automatically feeds a recording medium into the apparatus main body, and a recording medium that is sent one by one from the automatic feeding unit to a predetermined recording position. And a transport unit M3029 for guiding the recording medium from the recording position to the discharge unit M3030, a recording unit for performing desired recording on the recording medium transported to the recording position, and a recovery unit M5000 for performing recovery processing on the recording unit and the like. It consists of and.

  The transport unit M3029 is configured such that the transport roller is rotated by driving the transport motor E0001, and the recording medium is transported by a predetermined amount in the discharge direction by the rotation.

  The recording unit includes a carriage M4001 that is movably supported by a carriage shaft M4021, and a recording head cartridge H1000 that is detachably mounted on the carriage M4001. The carriage M4021 is driven by a carriage motor E0001 and reciprocates in a direction intersecting the recording medium conveyance direction at a predetermined speed.

  FIG. 5 is a view showing the appearance of the recording head cartridge H1000. The recording head cartridge H1000 includes an ink tank H1900 that stores ink, and a recording head H1001 that discharges ink supplied from the ink tank H1900 from nozzles according to recording information. As the ink tank H1900, black, light cyan, light magenta, cyan, magenta, and yellow are prepared independently for each color in order to enable high-quality color recording with a photographic tone.

  FIG. 6 is a configuration diagram showing how the ink tanks H1900 for the respective colors are detachably attached to the recording head H1001. By adopting a cartridge system in which the ink tanks of the respective colors can be independently replaced in this way, it is possible to appropriately replace only the ink tanks of the exhausted ink colors.

  FIG. 7 is a diagram illustrating a state in which the recording head H1001 applied in the present embodiment is observed from the ejection port side. Here, discharge ports for six colors of black (K), light cyan (LC), light magenta (LM), cyan (C), magenta (M) and yellow (Y) are arranged as shown in the figure. In each color, two ejection port arrays arranged at 640 at an interval of 600 dpi (dot / inch; reference value) in the X direction are arranged in parallel with a half-pitch (about 20 μm) shifted from each other. An image is formed on the recording medium at a recording density of 1200 dpi. The ejection port arrays for each color are arranged in parallel in the Y direction as shown in the figure, and a full color image is formed on the recording medium by ejecting ink at a predetermined frequency while the recording head H1001 moves in the Y direction. It has come to be. Note that each recording element in the present embodiment is configured by a liquid path serving as an ink passage leading to an ejection port and an electrothermal converter that gives thermal energy to the ink. When an image is recorded, a predetermined voltage is applied to the electrothermal transducer of each recording element in accordance with the image data, so that film boiling occurs in the liquid chamber, and the foaming energy causes the recording element to discharge. A predetermined amount of ink droplets is ejected from.

  FIG. 8 is a diagram showing a schematic block configuration of a control system of the ink jet recording apparatus applied in the present embodiment. The recording apparatus receives recording information as a control signal from the host computer 300. The recording information is temporarily stored in the input / output interface 301 in the recording apparatus, and at the same time, converted into data that can be processed in the recording apparatus, and input to the CPU 302 that also serves as a recording head drive signal supply unit. The CPU 302 processes data input to the CPU 302 using peripheral units such as the RAM 304 based on a control program stored in the ROM 303, and converts the data into image data that can be recorded by the recording apparatus.

In addition, the CPU 302 generates drive data for moving the recording medium and the recording head H1001 in synchronization with the image data in order to record the image data at an appropriate position on the recording medium, and the LF motor E0002 and the carriage motor E0001. Drive. The image data and the drive data of each motor are transmitted to the recording head H1001 and various motors via the head driver 307 and motor drivers 305 and 306, respectively, and an image is formed at a controlled timing.
A specific example of the most characteristic configuration of the present invention will be described below using the recording apparatus of the present embodiment described above.

  The ink jet recording apparatus according to the present embodiment employs an 8-pass multi-pass recording system in which an image is formed in the same region by a plurality of recording scans. The mask pattern applied in the present embodiment includes a random mask pattern that randomly determines the recording data of each recording scan by thinning out the image data randomly, and each recording scan by fixedly thinning out the image data. It is assumed that the final recording data is generated by multiplying both of them together with a fixed mask pattern for regularly determining the recording data.

  FIGS. 9A and 9B are diagrams for explaining the random mask patterns A and B applied in the present embodiment. Reference numeral 901 denotes a nozzle row of a certain color arranged in the recording head H1001, and it is assumed that 1280 nozzles are arranged in the nozzle row 901 in the vertical direction in the figure. The 1280 nozzles are divided into eight equal blocks (recording element groups) of 160 each, and in the figure, the recording rate in each block and the recording pixels (pixels that allow recording) corresponding to the blocks are blacked out. It is shown. A white portion indicates a non-recording pixel (a pixel that does not allow recording regardless of image data). Here, in both FIGS. 9 (a) and 9 (b), a recording pixel or a non-printing area for a total of 655360 pixels, that is, 1280 pixels in the column direction (nozzle alignment direction) and 512 pixels in the raster direction (printing head main scanning direction). A mask pattern in which recording pixels are defined is prepared.

  Both the random mask patterns A and B are random mask patterns for 4-pass multi-pass printing, and 100% of the image is completed by four printing main scans and sub-scans for 320 nozzles each. ing. More specifically, for example, in the random mask pattern A, the area (for example, the area X) on the recording medium recorded by the block a1 in the first recording scan is the block a3 in the second recording scan, and the third recording scan. Is recorded in block a5, and in the fourth recording scan, recording is performed in block a7. The arrangement of the recording pixels of the mask pattern corresponding to each block is a non-overlapping arrangement that complements each other, and the total recording rate of each block is 10%, 30%, 40%, and 20%. This recording is obtained by four recording scans. The same configuration is applied to the relationship between a2, a4, a6, and a8 and the relationship between each region of the random mask pattern B.

  The “block recording rate” refers to a plurality of blocks (for example, the blocks a1, a3, a5, and the like described above) used to complete recording on a predetermined area (for example, the area X described above) on the recording medium. This is the ratio of the number of recorded pixels of the mask pattern corresponding to each block to the total number of recorded pixels of the mask pattern corresponding to a7). For example, the total number of recorded pixels of the mask pattern corresponding to the blocks a1, a3, a5, and a7 is 327680 (= 655360/2), and the number of recorded pixels of the mask pattern corresponding to the block a1 is 32768. ing. Therefore, the recording rate of the block a1 (or the recording rate of the mask pattern corresponding to the block a1) is 10 (= 32768/327680 × 100)%.

  The “recording pixel” is a pixel that allows recording as described above. If the image data corresponding to the recording pixel is data indicating ink ejection, recording is performed. If you do not record. On the other hand, “non-recording pixels” are pixels that do not allow printing regardless of image data. Even if image data corresponding to these non-printing pixels is data indicating ink ejection, printing is performed. Absent.

The random mask pattern A and the random mask pattern B have different recording rate distributions for each block, and the random mask pattern A has a high recording rate in the central portion (block located in the center) of the nozzle row, and both end portions ( The recording rate of the blocks located at both ends is set low. In the random mask pattern B, the recording rate of the block located in the center of the nozzle row is set lower than the blocks located on both sides thereof, and the recording rate of the blocks located at both ends is the same as that of the random mask pattern A. It is set low. FIGS. 10A and 10B are diagrams for explaining the fixed mask pattern applied in the present embodiment. Both FIGS. 10A and 10B have an area of 1280 pixels in the column direction (nozzle alignment direction) and 512 pixels in the raster direction (printing head main scanning direction), as in the random mask described in FIG. However, in this example, the recording pixels (pixels that allow recording) and the non-recording pixels (pixels that do not allow recording) are arranged alternately one by one. FIGS. 10A and 10B are complementary to each other, and are configured such that a 100% image is formed by superimposing both. Here, FIG. 10A is referred to as a staggered pattern, and FIG. 10B is referred to as an inverted staggered pattern.
In the present embodiment, it is assumed that the above four types of mask patterns are all stored in the RAM 304.

  FIG. 11 is a flowchart for explaining recording data generation processing performed by the CPU 302 of the present embodiment when recording is actually performed. In this embodiment, it is assumed that 8-pass multi-pass printing is performed by reciprocating printing scanning while applying the above four types of mask patterns. In other words, in the same area on the recording medium, images are sequentially formed by eight reciprocating recording main scans by the recording head and 160 pixel sub-scans performed between each recording main scan.

  When an 8-pass multi-pass printing command is input, image data is first input from the input / output interface 301 to the CPU 302 (step S1001).

  In step S1002, −1 is added to the variable n, and in subsequent step S1003, it is determined whether n is positive or negative. Based on this result, it is possible to determine whether the next print scan is an even-numbered print scan or an odd-numbered print scan. That is, n is a variable for determining the even / odd number of printing scans, and here, it is assumed that 1 is written as an initial value. In this embodiment, odd-numbered recording scans are recorded on the forward path, and even-numbered recording scans are recorded on the backward path.

  If n> 0 is determined in step S1003, it is determined that the next scan is an even-numbered scan, and the input image data is multiplied by the inverted staggered pattern shown in FIG. 10B (step 1004). -A). In step S1005-a, the recording data obtained in step S1004-a is multiplied by the random mask pattern B shown in FIG. That is, in the even-number recording scan, the input image data is thinned out by the new mask pattern (2) obtained by multiplying the inverted staggered pattern and the random mask pattern B.

  On the other hand, if n <0 is determined in step S1003, it is determined that the next scan is an odd recording scan, and the input image data is multiplied by the staggered pattern shown in FIG. 1004-b). In step S1005-b, the recording data obtained in step S1004-b is multiplied by the random mask pattern A shown in FIG. That is, in the odd recording scan, the input image data is thinned out by the new mask pattern (1) multiplied by the staggered pattern and the random mask pattern A.

  As described above, in steps S1004 and S1005, the multiplication of the image data and the mask pattern is completed, and the final print data recorded in the next print scan is completed.

  In step S1006, the CPU 302 outputs the generated recording data to the head driver 307 and simultaneously drives the motor drivers 305 and 306. The head driver 307 drives the recording head H1001 at a predetermined timing according to the input recording data. The motor driver 305 drives the LF motor E0002 and rotates the LF roller by a predetermined amount. Further, the motor driver 306 drives the carriage motor E0001 to scan the carriage M4001 at a predetermined speed. Thereby, one recording scan is performed by the recording head.

  In step S1007, it is determined whether generation of recording data has been completed for all image data to be recorded. When it is finished, this mode is finished. If image data to be recorded still remains, the process returns to step S1002, and −1 is added to the variable n for the next recording scan.

  According to this embodiment, the mask pattern to be applied between the mask pattern (1) and the mask pattern (2) in the odd-numbered printing scan performed in the forward path and the plurality of recording scans performed in the backward path is used. An image is formed while switching.

  When 8-pass multi-pass printing is performed in this way, sub-scans of 160 pixels are performed between print scans, so that 320 scans are performed between one print pass and the next print scan. Sub-scanning for pixels is performed. That is, considering only the forward printing scan, four-pass multi-pass printing is performed. In the forward recording scan, the mask pattern (1) determined by multiplying the random mask pattern A and the staggered pattern is used, but the random mask pattern A is recorded by 100% by 4-pass multi-pass recording. As a result, a 50% image of a staggered pattern is formed by the four-pass printing on the outward path.

  Such a configuration is the same for the printing scan in the backward path. In the backward scanning scan, the mask pattern (2) determined by the multiplication of the random mask pattern B and the reverse staggered pattern is used, but the random mask pattern B is recorded at 100% by 4-pass multi-pass printing. As a result, a 50% image of an inverted staggered pattern is formed by four-pass printing on the return path.

  As described above, the zigzag pattern is recorded by the four-pass recording on the forward path, and the reverse zigzag pattern is recorded by the four-pass recording on the return path. Therefore, finally, 100% of the image is completed by complementing the forward recording scan and the backward recording scan.

  According to the above configuration, since the recording rate is 50% for each of the forward recording scan and the backward recording scan, the number of ejections of the recording head in the outward path and the number of ejections of the recording head in the backward path are as follows. Can be kept approximately the same. However, the distribution of the number of ejections of each nozzle arranged on the recording head depends on the recording rate distribution of each block described with reference to FIG. 9, and the way of distribution differs greatly between the forward path and the backward path. Understand. That is, in the forward path, the number of ejections of the block a4 and the block a5 located in the vicinity of the center of the nozzle row is the highest, but in the backward path, the number of ejections of the block a2 and the block a7 is set to be the highest.

  As described above, it is effective to set the recording rate of both ends of the recording head, that is, the blocks a1 and a8, lower than those of the other blocks as a countermeasure against the above-mentioned “end-to-end”. On the other hand, for example, when recording using only the mask pattern A is performed, the temperature in the block a4 and the block a5 is locally increased as compared with other blocks, which may cause density unevenness. explained. According to the configuration of the present embodiment, in consideration of such a situation, a recording method in which the distribution of the recording rate differs for each recording scan is realized. Therefore, the temperature distribution in the recording head can be kept substantially uniform.

  FIG. 12A is a diagram for explaining the visual evaluation results of an image recorded by applying the mask pattern shown in this embodiment and an image recorded by a conventional method. Here, in the conventional method, 1280 nozzle rows arranged in the print head are divided into 8 as in this embodiment, and the print rate of each block is 5%, 10%, 15%, 20 from the end. It is assumed that 8-pass bidirectional multi-pass printing is performed using mask patterns of%, 20%, 15%, 10%, and 5%.

  In FIG. 12A, the evaluation items are three items, that is, the durable life of the recording head, the density unevenness caused by the variation in the discharge amount, and the white stripe caused by the edge portion.

  Evaluation of the endurance life was performed by recording a predetermined number of solid images for durability continuously and recording test images for evaluation immediately before the start of recording and immediately after the end of recording. Such a study is performed in the case where the mask of this embodiment, the mask of the conventional example, and the mask having a recording rate of 12.5% uniformly in each divided block are applied. The point in time at which sudden discharge characteristic deterioration (for example, non-discharge, density unevenness, uneven stripes, etc.) occurred between test images was determined as the life of the recording head in each mask pattern. Then, the total number of ejections by all nozzles at this time is calculated for each mask, and for this example and the conventional example, the total number obtained is divided by the total number when a uniform mask of 12.5% is used. The value was multiplied by 100. That is, in the table, the lifetime of each mask is described when the lifetime when a uniform mask is applied is set to 100, and the evaluation is higher as the value approaches 100 (the lifetime is longer). Show.

  According to the table, 83.3 is obtained when the mask of this embodiment is used, and 62.5 is obtained when the mask of the conventional example is used, and the life of the recording head in this embodiment is longer than that of the conventional example. I understand that it is long. This is because when the present embodiment is applied, the mask pattern is replaced for each scanning, so that the recording rate is not concentrated in each block of the recording head, and only a specific recording element does not deteriorate particularly quickly. . On the other hand, in the conventional example, since the frequency of using the central portion of the printing element array is always high, deterioration of only the central portion is promoted, and as a result, the life of the recording head is shortened.

  Density unevenness and white stripes were evaluated by recording 100% solid images with each color recording head for 8 passes using each mask pattern, then evaluating each color, and taking the average of the evaluation results for 6 colors. It is a thing. The evaluation points are ◎, ○, △, ×, XX, where ◎ to ○ are levels at which each harmful effect cannot be discerned visually, △ is a level that can be confirmed at a visual distance of 30 cm, × ˜XX is a level that can be confirmed even at a clear visual distance of 1 m.

  Regarding density unevenness, the evaluation of this example is ◎, and the conventional example is ×. This is because when the present embodiment is applied, the mask pattern is changed for each scan, so that the recording rate is not concentrated in each block of the recording head, and local temperature rise is unlikely to occur.

  Specifically, the blocks with the highest recording rate in the forward scanning are the block a4 and the block a5 shown in FIG. 9A, and are multiplied by the staggered mask shown in FIG. The recording rate is. If recording is continued using the same mask for the backward scan in this state, the blocks a4 and a5 always maintain a high recording rate, so the temperature is likely to rise compared to the other blocks, and the discharge amount Increases and causes density unevenness. However, in the backward scan of the present embodiment, the recording rate of the blocks a4 and a5 is 10%, and the recording rate of the blocks a2 and a7 located at the end is 20%, so the temperature rises. Easy blocks are transferred, and variations in the discharge amount of the nozzle rows are equalized. On the other hand, in the conventional example, since the printing rate of the blocks a4 and a5 is kept at 20% for both the forward scanning and the backward scanning, the central portion of the nozzle row is locally high in temperature, and the discharge amount increases only in this portion. Density unevenness.

  Regarding white stripes, both the mask pattern of this embodiment and the mask pattern of the conventional example are set so that the recording rate of the two blocks at the extreme ends is lower than that of the other blocks. Therefore, white streaks due to the edge twist tend not to stand out. However, in the backward scanning using the random mask pattern B among the mask patterns in the present embodiment, the recording rates of the blocks a2 and a7 adjacent to the recording blocks a1 and a8 at the end are highest. In such a portion where the difference in recording rate is large, a condition similar to that at the end when a uniform mask is applied is provided, so that fine white stripes are likely to occur. Therefore, compared to the conventional example in which all the gentle gradation masks are applied, the white streak evaluation of this example is a slightly lower level.

  The second embodiment of the present invention will be described below. Also in this embodiment, the printing apparatus having the configuration described with reference to FIGS. 3 to 8 is applied as in the first embodiment, and an 8-pass multi-pass for forming an image in the same area by 8 printing scans. Adopt recording method. In addition, in the mask pattern to be applied, similarly to the first embodiment, the image data is randomly thinned out, and the random mask pattern for irregularly determining the print data of each print scan and the image data are fixedly thinned out. Thus, a fixed mask pattern for regularly determining print data of each print scan is used together, and final print data is generated by multiplying the two.

  FIGS. 13A and 13B are diagrams for explaining the random mask patterns C and D applied in the present embodiment. Reference numeral 901 denotes a nozzle row of a certain color arranged in the recording head H1001 as in the first embodiment, and it is assumed that 1280 nozzles are arranged in the nozzle row 901 in the vertical direction. Each of the 1280 nozzles is divided into eight equal blocks of 160, and in the figure, the recording rate in each block and the recording pixels corresponding thereto are shown as blackened portions. Here, in both FIGS. 13 (a) and 13 (b), a recording pixel or a non-printing area for a total of 655360 pixels, that is, 1280 pixels in the column direction (nozzle alignment direction) and 512 pixels in the raster direction (printing head main scanning direction) A mask pattern in which recording pixels are defined is prepared.

  Both random mask patterns C and D are random mask patterns for 4-pass multi-pass printing as in Example 1, and 100% of the image is obtained by four main printing scans and 320 sub-scans. Is completed.

  The random mask pattern C and the random mask pattern D have different recording rate distributions for each block. In both masks, the recording rate at the outermost ends is set as low as 10%. However, in the random mask pattern C, the recording rate of the blocks a2 and a3 on the relatively leading side with respect to the paper feed direction is relatively high. In the mask pattern D, the recording rate of the blocks a6 and a7 on the relatively rear side with respect to the paper feeding direction is high.

  As in the first embodiment, the mask pattern (3) obtained by multiplying the random mask pattern C and the staggered pattern in the forward scan, and the mask pattern (by masking the random mask pattern D and the inverted staggered pattern in the backward scan) Recording is performed using 4).

  FIG. 12B illustrates the visual evaluation results of the image recorded by applying the present embodiment and the image recorded by the conventional method in the same manner as FIG. 12A of the first embodiment. FIG.

  Regarding the life of the recording head, 83.3 is obtained when the mask of this embodiment is used, and 62.5 is obtained when the mask of the conventional example is used. This is because even when the present embodiment is applied, the recording rate of each block can be dispersed for each recording scan, so that only a specific recording element can be prevented from deteriorating.

  Further, regarding the density unevenness, the evaluation of this example is ◎, the conventional example is x, and the same result as that of Example 1 is obtained. Even when this embodiment is applied, the mask pattern is changed for each scanning, so that the recording rate is not concentrated in each block of the recording head, and a local temperature rise hardly occurs. In particular, in this embodiment, even in the case where a uniform mask is used, in the central portion where the temperature tends to be high, the recording rate does not increase, and the blocks located at both ends where the temperature is relatively difficult to rise. In addition, since the recording scan with a high recording rate is alternately performed, a more preferable state is obtained from the viewpoint of the uniformity of the temperature of the entire recording head, and a state in which there is almost no variation in the discharge amount is obtained. It is.

  Regarding white streaks, ◎ of higher evaluation than Example 1 is obtained. This is due to the fact that the cause of “swinging edge” appears more prominently when it is located close to a region with a high recording rate. That is, in the blocks at both ends in this embodiment, the recording scan adjacent to the block with the recording rate of 40% and the recording scan positioned at a distance of about 640 pixels are alternately performed with the block with the recording rate of 40%. It is the composition that is called. On the other hand, the blocks at both ends in the first embodiment are configured such that a recording scan adjacent to a block with a recording rate of 40% and a recording scan positioned at a distance of about 320 pixels are alternately performed. On average, the blocks at both ends of this embodiment are kept relatively far away from the higher recording rate block (here, the recording rate 40% block). It becomes. Therefore, the configuration of this example has a higher evaluation result.

  As described above with reference to the two embodiments, according to the present invention, the mask patterns having different distributions of the recording rates of the respective blocks of the printing element array can be applied while switching between the forward scanning and the backward scanning. As a result, it is possible to obtain a smooth image with less density unevenness and white stripes without shortening the life of the recording head more than necessary.

  In the above embodiment, four types of mask patterns, for example, a random mask pattern A and a staggered pattern, and a random mask pattern B and an inverted staggered pattern are stored in the ROM 303 in the recording apparatus, and each recording scan is performed. Although the description has been given of the configuration in which each multiplication is performed, the present invention is not limited to this. Each mask multiplication is performed at the time when a recording start command is received, and during the recording, the two mask patterns created are alternately read to record one page. Also good. In the ROM 303, for example, in the case of the first embodiment, the mask pattern (1) created by the random mask pattern A and the staggered pattern, and the mask pattern (2) created by the random mask pattern B and the inverted staggered pattern are stored. Two may be stored in advance. In this case, since the number of mask patterns to be stored can be limited to two, the present invention can be realized with a smaller number of memories than the above-described configuration. However, as described in the above embodiment, storing several types of mask patterns to be used in combination with each other is more often performed by another combination such as multiplication of a random mask pattern A and an inverted staggered pattern. Since this mask pattern can be generated, it can be said that this is an effective configuration means when it is desired to switch the mask according to the recording mode.

  Further, the recording rate of the portion corresponding to each block of the applied mask patterns A, B, C and D is not limited to the values shown in FIG. 9 or FIG. Furthermore, the mask pattern shown in FIG. 10 as the fixed mask is not limited to the staggered pattern or the reverse staggered pattern. The characteristics of the pattern arrangement such as the number of multipasses, the recording rate of each block, and whether or not to have randomness may be set as appropriate depending on the characteristics of the recording head, the recording mode, the recording medium, etc. The effect of the present invention can be obtained if the block having the is replaced every recording scan.

  Furthermore, in the above-described embodiment, the image forming method by bidirectional recording in which an image is formed while switching the mask pattern between the forward scan and the backward scan has been described as an example, but the present invention is not limited to this. Even in the case of unidirectional multi-pass printing, any configuration in which the mask pattern is switched in units of printing scan, such as odd-numbered scanning and even-numbered scanning, is included in the scope of the present invention.

  Furthermore, in the above embodiment, as described with reference to the block diagram of FIG. 8, the storage location of the mask to be applied and the mask multiplication processing are performed using the memory inside the printing apparatus. Although described, the present invention is not limited to this. For example, the host computer 300 connected as an external device of the recording apparatus shown in FIG. 8 is configured to have the above-described functions, and stores a mask, crosses the mask, and applies a mask pattern to the image data. Even when a series of operations such as these are performed by the host computer 300, the effect of the recording system of the present invention is not changed.

  The present invention can be applied to a serial type ink jet recording system that forms an image by ejecting ink from a plurality of recording elements.

It is a schematic diagram for demonstrating the phenomenon of edge part. It is a schematic diagram for demonstrating the phenomenon of edge part. It is a figure for demonstrating the general-view structure of the inkjet recording device applied with embodiment of this invention. It is a figure for demonstrating the internal structure of the inkjet recording device applied with embodiment of this invention. FIG. 2 is a diagram illustrating an appearance of a recording head cartridge applicable in an embodiment of the present invention. FIG. 3 is a configuration diagram illustrating a state in which an ink tank used in an embodiment of the present invention can be detachably attached to a recording head. FIG. 6 is a diagram illustrating a state in which a recording head applied in the present embodiment is observed from the discharge port side. FIG. 2 is a diagram illustrating a schematic block configuration of a control system of an ink jet recording apparatus applied in an embodiment of the present invention. (A) And (b) is a figure for demonstrating the random mask patterns A and B applied in Example 1 of this invention. (A) And (b) is a figure for demonstrating the fixed mask pattern applied in embodiment of this invention. 4 is a flowchart for explaining a recording data generation process performed by a CPU according to an embodiment applicable to the present invention. (A) And (b) is a figure for demonstrating the evaluation result by visual observation of the image recorded by applying the two Example of this invention, and the image recorded by the conventional method. (A) And (b) is a figure for demonstrating the random mask patterns C and D applied in Example 2 of this invention.

Explanation of symbols

300 Host computer 301 Input / output interface 302 CPU
303 ROM
304 Motor Driver 305 Motor Driver 307 Head Driver 901 Nozzle Row M1000 Device Main Body M1001 Lower Case M1002 Upper Case M1003 Access Cover M1004 Discharge Tray M3019 Chassis M3022 Automatic Feeding Unit M3029 Conveying Unit M3030 Discharging Unit M4001 Carriage M50001 Carriage Recovery Unit Motor E0002 LF motor E0018 Power key E0019 Resume key E0020 LED
H1000 recording head cartridge H1001 recording head H1900 ink tank

Claims (12)

Using a recording head formed by arranging a plurality of recording element groups composed of a plurality of recording elements for ejecting ink in a predetermined direction, in a direction different from the predetermined direction by different recording element groups for the same region of the recording medium. In an inkjet recording system for forming an image by a plurality of recording scans,
Means for ejecting ink in accordance with different recording rates for the plurality of recording element groups;
A recording rate changing means for changing a recording rate in at least two recording element groups of the plurality of recording element groups for each recording scan;
An ink jet recording system comprising:   The recording rate changing means alternately switches a first recording rate and a second recording rate different from the first recording rate for each recording scan as a recording rate in the recording element group. The inkjet recording system according to claim 1.   The inkjet recording system according to claim 1, wherein the recording rate changing unit performs setting so that a recording element group having the highest recording rate among the plurality of recording element groups is different for each recording scan. In the recording head, the plurality of recording elements constituting the recording element group are arranged in the same direction as the predetermined direction,
The recording rate changing means sets a recording rate of a recording element group located at both ends in the predetermined direction among the plurality of recording element groups to a value smaller than a recording rate of a recording element group adjacent to the inside. The ink jet recording system according to claim 1, wherein the ink jet recording system is an ink jet recording system.   5. The ink jet recording system according to claim 1, wherein in the plurality of recording scans, the forward recording scan and the backward recording scan of the recording head are alternately performed. 6. Using a recording head formed by arranging a plurality of recording element groups composed of a plurality of recording elements for ejecting ink in a predetermined direction, in a direction different from the predetermined direction by different recording element groups for the same region of the recording medium. In an inkjet recording system for forming an image by a plurality of recording scans,
Means for ejecting ink in accordance with a recording rate at which one recording element group and another recording element group among the plurality of recording element groups differ from each other;
A recording rate changing means for changing a recording rate in at least two recording element groups of the plurality of recording element groups in one recording scan and another recording scan among the plurality of recording scans;
An ink jet recording system comprising: Using a recording head formed by arranging a plurality of recording element groups composed of a plurality of recording elements for ejecting ink in a predetermined direction, in a direction different from the predetermined direction by different recording element groups for the same region of the recording medium. In an inkjet recording system for forming an image by a plurality of recording scans,
Means for ejecting ink according to different recording rates for each of the plurality of recording element groups;
Recording rate changing means for changing a distribution in a predetermined direction of a recording rate corresponding to each of the plurality of recording element groups between a certain recording scan and another recording scan among the plurality of recording scans. An ink jet recording system. Using a recording head formed by arranging a plurality of recording element groups composed of a plurality of recording elements for ejecting ink in a predetermined direction, in a direction different from the predetermined direction by different recording element groups for the same region of the recording medium. In an inkjet recording system for forming an image by a plurality of recording scans,
Means for ejecting ink according to different mask patterns for the plurality of recording element groups;
Mask pattern changing means for changing the mask pattern of each of the plurality of printing element groups for each printing scan,
The ink jet recording system, wherein the mask pattern changing unit changes a recording rate of a mask pattern corresponding to the recording element group for at least two recording element groups of the different recording element groups.   The mask pattern changing unit switches a first mask pattern and a second mask pattern different from the first mask pattern alternately as a mask pattern corresponding to the recording element group every recording scan. The ink jet recording system according to claim 8.   10. The mask pattern changing unit performs setting so that a printing element group corresponding to a mask pattern having the highest printing rate among the plurality of printing element groups is different for each printing scan. The inkjet recording system described in 1. In the recording head, the plurality of recording elements constituting the recording element group are arranged in the same direction as the predetermined direction,
The mask pattern changing means is a mask having a lower recording rate than the recording element group adjacent to the inside of the recording element group with respect to the recording element group located at both ends in the predetermined direction among the plurality of recording element groups. The inkjet recording system according to claim 8, wherein the pattern is made to correspond. 12. The ink jet recording system according to claim 8, wherein the mask pattern is newly generated by synthesizing a plurality of mask patterns stored in advance in a storage unit.

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