JP2011005875A - Method for correcting sub-scanning feed of printing medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for improving the image quality by correcting paper feeding errors of a printer.SOLUTION: Under the condition that, as the test pattern for deciding correction values of the sub-scanning feeds of printing media, test patterns including a plurality of color patches respectively printed by employing each correction value different from one another are printed with one kind of ink in the ink duty of <100% are printed, such as a test pattern in the ink duty of about 80% with black ink is printed, the sub-scanning feed is corrected on printing according to the correction value set in response to the printed result of the test pattern.

Description

  The present invention relates to a technique for performing printing by recording ink dots on a print medium while moving a print head in a main scanning direction.

  As computer output devices, ink jet printers and laser printers that eject ink from a head have become widespread. In particular, in recent years, color printers using color inks have been widely used.

  Various print media for inkjet printers are commercially available. Since different inks have different color developability, there is a great difference in image quality. In addition, the type of print medium also affects the accuracy of sub-scan feed (hereinafter referred to as “paper feed”) of the print medium. For example, an actual feed amount may be considerably different between a print medium having a slippery surface and a print medium having a less slippery surface even if the same feed operation is performed. Further, the accuracy of paper feeding tends to vary considerably from printer to printer.

  The quality of the paper feeding accuracy has a great influence on the image quality. However, in a printer that performs printing in a so-called interlaced recording mode, it is possible to suppress deterioration in image quality due to a paper feed error to some extent by appropriately setting the paper feed amount. Here, the “interlace recording mode” means a printing method performed using a print head having nozzles arranged at a nozzle pitch that is twice or more the dot pitch in the sub-scanning direction (that is, main scanning line pitch). Yes. When such a print head is used, a gap is generated between main scanning lines (raster lines) that can be recorded by one main scanning. In order to eliminate this gap, the number of main scans equal to the number of main scan lines included in the gap is further required. It is known that various feed amounts can be adopted in such an interlace recording mode. Therefore, conventionally, by appropriately selecting the paper feed amount in the interlaced recording mode, the influence of image quality due to variations in paper feed accuracy has been suppressed to a small level.

  For the reasons described above, direct correction of paper feed error has not been considered much in interlaced recording mode printers. However, with the recent progress of high image quality of printers, there has been a demand for further improving image quality by appropriately correcting paper feed errors in printers that perform printing in the interlaced recording mode. Such a demand is not only increasing for printers using only the interlaced recording mode but also for printers using the non-interlaced recording mode.

  SUMMARY An advantage of some aspects of the invention is to provide a technique capable of improving image quality by correcting a paper feeding error of a printer.

  To achieve the above object, the method of the present invention corrects the sub-scan feed amount of a print medium in a printing apparatus that performs printing by recording ink dots on the print medium while moving the print head in the main scanning direction. (A) As a test pattern for determining a correction value of the sub-scan feed amount of the printing medium, one type of test pattern including a plurality of color patches respectively printed using different correction values (B) a step of correcting the sub-scan feed amount according to a correction value set according to the print result of the test pattern when performing printing. It is characterized by providing.

  According to this method, since a color patch is printed with an ink duty of less than 100% using one type of ink, it is possible to print a color patch that easily finds image deterioration due to a paper feed error. As a result, the image quality can be improved by correcting the sub-scan feed error of the printer with an appropriate correction value.

  The ink duty may be changed according to the type of the print medium.

  In general, if the ink duty is excessively increased, the ink is liable to bleed, and conversely if it is excessively low, it tends to be difficult to find image quality deterioration due to a paper feed error. Also, the ease of ink bleeding usually varies depending on the type of print medium (particularly its surface characteristics). Therefore, if the ink duty is changed according to the type of print medium, it is possible to print a test pattern suitable for each type of print medium.

  The plurality of color patches may be gray patches reproduced with black ink. The ink duty of the gray patch may be a value in a range from about 70% to about 90%.

  According to this configuration, it is possible to print a test pattern that makes it easy to determine an appropriate correction value for paper feed error.

  The plurality of color patches are preferably arranged along the sub-scanning direction on a single print medium.

  In this way, since many color patches can be printed on one print medium, the print medium can be saved.

  The print head may include a color nozzle row in which a plurality of color nozzle groups are arranged in a predetermined order along the sub-scanning direction, and a black nozzle row arranged in parallel with the color nozzle row. . At this time, it is preferable that the plurality of color patches be printed using only some of the plurality of black nozzles included in the black nozzle row.

  According to this configuration, since the gap between the color patches can be made relatively small, it is possible to print more color patches on one print medium.

  The present invention can be realized in various forms, for example, a sub-scan feed amount (paper feed amount) correction method and apparatus, a sub-scan feed control method and apparatus, and a sub-scan feed amount correction. Printing method and apparatus in consideration of printing, printing control apparatus and method for controlling printing apparatus in consideration of correction of sub-scan feed amount, computer program for realizing the method and apparatus, and recording medium on which the computer program is recorded It can be realized in various forms such as a data signal including the computer program and embodied in a carrier wave.

1 is a block diagram showing the configuration of a printing system as an embodiment of the present invention. 1 is a schematic perspective view showing a main configuration of a color inkjet printer 20. FIG. FIG. 2 is a block diagram showing an electrical configuration of the printer 20. The perspective view which shows the structure of a subscanning drive mechanism. FIG. 4 is an explanatory diagram showing a nozzle arrangement on the lower surface of the print head. 6 is a flowchart illustrating a procedure for paper feed correction before shipment of the printer. Explanatory drawing which shows the example of a test pattern. Explanatory drawing which shows two types of dot recording methods of a gray patch. 6 is a flowchart illustrating a procedure for paper feed correction by a user. Explanatory drawing which shows the example of the user interface window W1 which permits a user to print the test pattern. Explanatory drawing which shows the example of the user interface window W2 which permits a user to set a patch number. Explanatory drawing which shows the 1st example of the paper feed used when printing a test pattern. Explanatory drawing which shows the 2nd example of the paper feed used when printing a test pattern. Explanatory drawing which shows actual paper feeding. Explanatory drawing which shows the method of printing a gray patch using only black ink. Explanatory drawing which shows the method of printing a gray patch using composite black. FIG. 6 is an explanatory diagram showing a relationship between a paper feed amount F and a correction value δ.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Overall configuration of the device:
B. Content of paper feed correction:
C. Details on how to print test patterns and how to determine paper feed correction values:
D. Variation:

A. Overall configuration of the device:
FIG. 1 is a block diagram showing the configuration of a printing system as an embodiment of the present invention. This printing system includes a computer 90 and a color inkjet printer 20. The printing system including the printer 20 and the computer 90 can be called a “printing apparatus” in a broad sense.

  In the computer 90, an application program 95 operates under a predetermined operating system. A video driver 91 and a printer driver 96 are incorporated in the operating system, and print data PD to be transferred to the printer 20 is output from the application program 95 via these drivers. The application program 95 that performs image retouching or the like performs desired processing on the image to be processed, and displays an image on the CRT 21 via the video driver 91.

  When the application program 95 issues a print command, the printer driver 96 of the computer 90 receives the image data from the application program 95 and converts it into print data PD to be supplied to the printer 20. The printer driver 96 includes a resolution conversion module 97, a color conversion module 98, a halftone module 99, a rasterizer 100, a user interface display module 101, a test pattern supply module 102, and a color conversion lookup table LUT. And are provided.

  The resolution conversion module 97 plays a role of converting the resolution of the color image data formed by the application program 95 into the print resolution. The image data thus converted in resolution is still image information composed of three color components of RGB. The color conversion module 98 converts RGB image data into multi-tone data of a plurality of ink colors that can be used by the printer 20 for each pixel while referring to the color conversion lookup table LUT.

  The color-converted multi-gradation data has, for example, 256 gradation values. The halftone module 99 performs so-called halftone processing to generate halftone image data. The halftone image data is rearranged in the order of data to be transferred to the printer 20 by the rasterizer 100, and output as final print data PD. The print data PD includes raster data indicating the dot formation state during each main scan and data indicating the sub-scan feed amount.

  The user interface display module 101 has a function of displaying various user interface windows related to printing, and a function of receiving user input in these windows.

  The test pattern supply module 102 has a function of reading a test pattern print signal TPS used for determining a correction value for the sub-scan feed amount (also referred to as “paper feed amount”) from the hard disk 92 and supplying the read test pattern print signal TPS to the printer 20. Have. When the test pattern print signal TPS is stored as compressed data, the test pattern print signal TPS has a function of expanding the compressed data.

  The printer driver 96 corresponds to a program for realizing a function of supplying the print data PD and the test pattern print signal TPS to the printer 20. A program for realizing the function of the printer driver 96 is supplied in a form recorded on a computer-readable recording medium. Such recording media include flexible disks, CD-ROMs, magneto-optical disks, IC cards, ROM cartridges, punch cards, printed matter on which codes such as bar codes are printed, computer internal storage devices (such as RAM and ROM). A variety of computer-readable media such as a memory) and an external storage device can be used. It is also possible to download such a computer program to the computer 90 via the Internet.

  A computer 90 having a printer driver 96 functions as a print control device that supplies the print data PD and the test pattern print signal TPS to the printer 20 to perform printing.

  FIG. 2 is a schematic perspective view showing the main configuration of the color inkjet printer 20. The printer 20 includes a paper stacker 22, a paper feed roller 24 driven by a step motor (not shown), a platen 26, a carriage 28, a carriage motor 30, a traction belt 32 driven by the carriage motor 30, and a carriage. And a guide rail 34 for 28. A print head 36 having a large number of nozzles is mounted on the carriage 28.

  The printing paper P is taken up by the paper feed roller 24 from the paper stacker 22 and fed on the surface of the platen 26 in the sub-scanning direction. The carriage 28 is pulled by a pulling belt 32 driven by a carriage motor 30 and moves in the main scanning direction along the guide rail 34. The main scanning direction is perpendicular to the sub-scanning direction.

  FIG. 3 is a block diagram showing an electrical configuration of the inkjet printer 20. The printer 20 includes a reception buffer memory 50 that receives a signal supplied from a computer 90, an image buffer 52 that stores print data, a system controller 54 that controls the overall operation of the printer 20, a main memory 56, and an EEPROM 58. And. The system controller 54 is further connected to a main scanning drive circuit 61 that drives the carriage motor 30, a sub-scanning drive circuit 62 that drives the paper feed motor 31, and a head drive circuit 63 that drives the print head 36. .

  The main scanning drive circuit 61, the carriage motor 30, the traction belt 32 (FIG. 2), and the guide rail 34 constitute a main scanning drive mechanism. The sub-scanning drive circuit 62, the paper feed motor 31, and the paper feed roller 24 (FIG. 2) constitute a sub-scanning drive mechanism (or “feed mechanism”).

  The print data transferred from the computer 90 is temporarily stored in the reception buffer memory 50. In the printer 20, the system controller 54 reads necessary information from the print data from the reception buffer memory 50, and sends control signals to the drive circuits 61, 62, and 63 based on the read information.

  The image buffer 52 stores print data of a plurality of color components received by the reception buffer memory 50. The head drive circuit 63 reads the print data of each color component from the image buffer 52 in accordance with a control signal from the system controller 54 and drives the nozzle array of each color provided in the print head 36 in response to this.

  FIG. 4 is a perspective view showing the configuration of the sub-scanning drive mechanism. The power of the paper feed motor 31 is transmitted to the paper feed roller 24 and the paper discharge roller 42 via the gear train 40. The paper feed roller 24 is provided with a driven roller 25, and the paper discharge roller 42 is also provided with a jagged roller 44 as its driven roller. The printing paper P is fed while being sandwiched by these rollers, and moves on the platen 26.

  A rotary encoder 46 composed of a code plate 46a and a photo sensor 46b is provided on the shaft of the paper feed roller 24. The paper feed amount (sub-scan feed amount) is determined according to the pulse signal from the rotary encoder 46.

  FIG. 5 is an explanatory diagram showing the nozzle arrangement on the lower surface of the print head 36. The print head 36 has a black nozzle row and a color nozzle row arranged on a straight line along the sub-scanning direction SS. In this specification, the “nozzle row” is also referred to as “nozzle group”.

  The black nozzle row (indicated by white circles) has 180 nozzles # 1 to # 180. These nozzles # 1 to # 180 are arranged at a constant nozzle pitch k · D along the sub-scanning direction. Here, D is the dot pitch in the sub-scanning direction SS, and k is an integer. The dot pitch D in the sub-scanning direction is a value depending on the printing resolution in the sub-scanning direction, and is equal to the pitch of the main scanning line (raster line). Hereinafter, the integer k representing the nozzle pitch k · D is simply referred to as “nozzle pitch k”. The unit of the nozzle pitch k is [dot], which means the dot pitch in the sub-scanning direction.

  In the example of FIG. 5, the nozzle pitch k · D is a value corresponding to 180 dpi. When the printing resolution in the sub-scanning direction (that is, the dot pitch D) is 360 dpi, the nozzle pitch k is 2 dots. When the printing resolution in the sub-scanning direction is 720 dpi, the nozzle pitch k is 4 dots. The nozzle pitch k can take an arbitrary integer of 1 or more.

  The color nozzle array includes a yellow nozzle group Y (indicated by white triangles), a magenta nozzle group M (indicated by white squares), and a cyan nozzle group C (indicated by white rhombuses). In this specification, the nozzle group for chromatic ink is also referred to as a “chromatic nozzle group”. Each chromatic nozzle group has 60 nozzles # 1 to # 60. Further, the nozzle pitch of the chromatic nozzle group is the same as the nozzle pitch k of the black nozzle row. The nozzles of the chromatic color nozzle group are arranged at the same sub-scanning position as the nozzles of the black nozzle row.

  In the present specification, like the print head of FIG. 5, a print head including a color nozzle row in which a plurality of chromatic color nozzle groups are arranged in order along the sub-scanning direction and a black nozzle row parallel to the color nozzle row. Is called “vertical array head”. On the other hand, a print head in which nozzle groups for a plurality of colors are present at substantially the same sub-scanning position and arranged in order along the main scanning direction is referred to as a “horizontal array head”. In the horizontal array head, a plurality of nozzles constituting each nozzle group are arrayed along the sub-scanning direction. In the embodiment described below, the vertically arranged head shown in FIG. 5 is used.

  At the time of printing, ink droplets are ejected from each nozzle while the print head 36 is moving at a constant speed in the main scanning direction together with the carriage 28 (FIG. 2). However, depending on the printing method, not all nozzles are always used, and only some nozzles may be used.

  In normal monochrome printing, almost all 180 black nozzles are used. On the other hand, in color printing, 60 nozzles are used for each color of CMY, and 60 black nozzles are also used. The 60 black nozzles used in color printing are, for example, nozzles # 121 to # 180 arranged at the same sub-scanning position as the 60 cyan nozzles.

B. Outline of paper feed correction:
As will be described below, the paper feed error is corrected before shipment of the printer 20 and can be corrected by the user after shipment.

  FIG. 6 is a flowchart showing a procedure for paper feed correction before the printer 20 is shipped. In step S1, the type of printing paper (printing medium) scheduled to be used by the printer 20 is sequentially selected. Examples of types of printing paper include plain paper, glossy film, photographic paper, and roll-type photographic paper. In step S2, the print resolution is selected. In this embodiment, two print resolutions of a low resolution of 360 × 360 dpi and a high resolution of 720 × 720 dpi can be used as the print resolution. In this specification, the print resolution is expressed as (main scanning direction resolution) × (sub-scanning direction resolution).

  In step S3, the selected printing paper is set in the printer 20, and a predetermined test pattern is printed. FIG. 7 shows an example of a test pattern. In this test pattern, nine color patches having different paper feed correction values δ are arranged on one A4 size printing paper P along the sub-scanning direction (vertical direction in FIG. 7). The height (2 × LB) of each color patch and the value of the gap G between the color patches are set so that all the color patches fit on one printing paper P. These values (2 × LB, G) will be further described later.

  The patch number printed beside each color patch is associated in advance with the paper feed correction value δ. However, the paper feed correction value δ is drawn for convenience only and is not actually printed. Each color patch is a gray patch in which a gray region having a uniform density is reproduced using only black ink.

  The relative positions of the upper half and the lower half of each gray patch are adjusted according to the paper feed correction value δ. As a result, black stripes and white stripes parallel to the main scanning direction appear in each gray patch in accordance with the relationship between the paper feed error of the printer 20 and the correction value δ. The test pattern shown in FIG. 7 corresponds to a test pattern printed when the printer 20 has no paper feed error. At this time, the gray patch with patch number 5 (correction value δ = 0) has no black stripes or white stripes, and it can be observed that this correction state is optimal. If a paper feed error occurs, the correction state of the other patches becomes optimum.

  FIG. 8 is an explanatory diagram showing two types of dot recording methods for gray patches. In FIG. 8, rectangular grids indicate pixels, and circles hatched with diagonal lines indicate ink dots. In the first method shown in FIG. 8A, the dot size is a solid size (100% size) and the dot recording rate is 80%. Here, “solid size” means a dot size that can form a solid region (an image region that is filled with ink without a gap) when the dot is recorded in all pixels. In general, the solid size is determined in advance for each print resolution. “Dot recording rate” means the proportion of pixels in which dots are recorded.

  The reason why the dot recording rate is set to 80% in the dot recording method of FIG. 8A is to make it easier to detect black and white lines in each gray patch of FIG. In other words, if the dot recording rate is set to an excessively high value (for example, 100%), ink bleeding tends to occur, and it may be difficult to observe black and white lines. On the other hand, if the dot recording rate is set to an excessively low value (for example, 60%), the ink dots become too sparse, and it may be difficult to observe black and white stripes. On the other hand, if the dot recording rate is set to about 80%, there is little ink bleeding and the dots are arranged quite densely, so that black stripes and white stripes can be easily found. In addition, the dot recording rate of the gray patch when using plain paper may be less than 100%, but a value in the range of about 70% to about 90% is preferable, and a value of about 75% to about 85% is preferable. More preferred is about 80%.

  In the first method shown in FIG. 8B, the dot size is 80% of the solid size, and the dot recording rate is 100%. Also with this dot recording method, it is possible to record a gray patch that easily finds black stripes and white stripes, as in the method of FIG.

  In this specification, the product of the dot size (area% when the solid size is 100%) and the dot recording rate is referred to as “ink duty”. In both methods shown in FIGS. 8A and 8B, the ink duty is 80%. When plain paper is used, the ink duty of the gray patch of the test pattern may be less than 100%, but a value in the range of about 70% to about 90% is preferable, and a value of about 75% to about 85%. Is more preferred, with about 80% being most preferred. Note that the value of the gray patch ink duty is preferably set to a different value depending on the type of print medium (difference in surface material).

  As the test pattern, various patterns other than those shown in FIG. 7 can be used. For example, other types of color patches, ruled line patterns, and the like can be used. In particular, color patches are not limited to gray patches, and color patches using other inks can be used. In the present specification, “color patch” means an image area reproduced in a substantially uniform color. When using a color patch, it is preferable to print the color patch using only one type of ink in order to easily detect black stripes and white stripes. Details of the test pattern printing method will be described later.

  The main factor of the paper feed error in the printer 20 is a manufacturing error of the paper feed roller 24 (FIG. 4). This manufacturing error includes an outer diameter error and a surface roughness error. For example, if the outer diameter of the paper feed roller 24 is larger than the design value, the feed error becomes positive, and if it is smaller, it becomes negative. In this embodiment, correction of the paper feed error due to the manufacturing error of the paper feed roller 24 is performed for each printer before shipment. Therefore, even if the tolerance of the paper feed roller 24 is set to be slightly large, the paper feed error during actual printing can be made almost zero. Further, since the yield of the paper feed roller 24 is increased as the tolerance for the manufacturing error of the paper feed roller 24 is relaxed, there is an advantage that the cost of the printer 20 is reduced.

  In step S4 in FIG. 6, the color patch with the highest image quality is selected from the plurality of printed color patches, and the patch number is set in the EEPROM 58 (FIG. 3) of the printer 20. In the example of FIG. 7, the patch number (= 5) of the central color patch without black stripes or white stripes is stored in the EEPROM 58. The paper feed correction value set by the inspection before shipment is referred to as a “reference correction value”.

  In step S5, it is determined whether or not steps S1 to S4 have been completed with respect to combinations of all printing papers scheduled to be used by the printer 20 and all printing resolutions. If not, the process returns to step S1. . Here, “all print sheets scheduled to be used by the printer 20” means types of sheets that can be selected by the user in the property window of the printer driver 96 (FIG. 1). The same applies to “all print resolutions”. In this way, the paper feed reference correction value is set for all combinations of printing paper and printing resolution.

  FIG. 9 is a flowchart showing a procedure of paper feed correction by the user. In steps S11 and S12, the user selects the type of print paper and the print resolution, and in step S13, the test pattern is printed by inputting a test pattern print command. FIG. 10 is an explanatory diagram illustrating an example of a user interface window W1 that allows a user to issue a test pattern print instruction. This window W1 is a utility window in the printer properties, and is provided with a button B1 for inputting a print instruction for a paper feed adjustment test pattern. When the user clicks the button B1, the test pattern supply module 102 (FIG. 1) reads the test pattern print signal TPS from the hard disk 92 and supplies it to the printer 20, and the printer 20 prints the test pattern accordingly. This test pattern may be the same as the test pattern (FIG. 7) used for paper feed correction before shipment, or may be a different test pattern. In this embodiment, the test pattern shown in FIG. 7 is also used for paper feed correction by the user.

  In step S14 of FIG. 8, a color patch with the highest image quality is selected from a plurality of printed color patches, and the patch number is set. FIG. 11 is an explanatory diagram showing an example of a user interface window W2 that allows the user to set a preferable patch number. This window W2 is automatically displayed by the user interface display module 101 (FIG. 1) when the test pattern is printed. In this window W2, a plurality of buttons B11 to B19 for selecting a preferred patch number are provided. When the user clicks one of these buttons B11 to B19, a preferred patch number is set in the EEPROM 58 (FIG. 3) of the printer 20. The patch number may be registered in the EEPROM 58 as a replacement for the reference correction value set in step S4 of FIG. 6, or may be registered in the EEPROM 58 as a value for further correcting the reference correction value. Further, the patch number indicating the feed correction value by the user may be registered in the printer driver 96 instead of the EEPROM 58.

  In step S15 in FIG. 9, actual printing is executed in accordance with a user instruction. At this time, the operation of the paper feed motor 31 (FIG. 3) is controlled in accordance with the paper feed correction value set in step S14.

  As described above, in this embodiment, only black ink is used and a gray patch having an ink duty of about 80% is printed as a test pattern. Therefore, it is easy to find black stripes and white stripes due to a paper feed error of the printer 20. There is an advantage. Further, since all the gray patches are sequentially arranged on the printing paper P along the sub-scanning direction, there is an advantage that it is not necessary to use many printing papers P for printing the test pattern. is there.

C. Details on how to print test patterns and how to determine paper feed correction values:
FIG. 12 shows an example of paper feeding used when printing a test pattern in step S3 of FIG. 6 and step S13 of FIG. This paper feed is for a 360 × 360 dpi low resolution printing mode. As described with reference to FIG. 5, the nozzle pitch k · D is 180 dpi. Therefore, when the print resolution in the sub-scanning direction is 360 dpi, the integer k that defines the nozzle pitch is 2.

  FIG. 12 shows the positions of the print head 36 in the sub-scanning direction in the four passes of pass 1 to pass 4, respectively. Here, “pass” means one main scan. In FIG. 12, for convenience of illustration, the number of nozzles of the print head 36 is illustrated to be small, the number of black nozzles is nine, and the number of chromatic nozzles for one color is three. Further, a black-filled graphic indicates a nozzle used for printing a test pattern, and a white graphic indicates a nozzle that is not used. In this embodiment, since the gray patch is reproduced using only the black ink, the chromatic nozzle is not used, and only three nozzles # 7 to # 9 out of the nine black nozzles are used. The reason why only some of the black nozzles # 7 to # 9 are used is that the gray patch height (width in the sub-scanning direction) is lowered and a large number of gray patches are placed on one printing paper P. This is to enable printing.

  In the example of FIG. 12, since the nozzle pitch k is 2 dots, there is a gap for one line between raster lines (main scanning lines) recorded in one pass. The paper feed amount F1 after pass 1 is one dot. Therefore, in pass 2, a gap line not recorded in pass 1 is recorded. The raster line positions recorded in passes 1 and 2 are shown at the right end of FIG. As can be understood from this, six consecutive lines are recorded with black ink in passes 1 and 2. Here, the six lines recorded with black ink in passes 1 and 2 are referred to as “black band BB”. This black band BB is the same as a raster line printed in one pass using a virtual dense nozzle row 36a having six nozzles arranged with a nozzle pitch k of 1 dot. In other words, passes 1 and 2 are equivalent to a single pass using the dense nozzle row 36a as shown at the right end of FIG. The height LB (referred to as “band width”) of the dense nozzle row 36a is defined by (number of used nozzles N) × (nozzle pitch k). In the example of FIG. 12, the bandwidth LB is set equal to the height Lc1 of the chromatic nozzle group for one color.

  The paper feed amount F2 after pass 2 is 5 dots. By this paper feed, the uppermost nozzle in the black nozzles used is placed at the uppermost end of the area where black dots are not recorded at the end of pass 1. Positioned. It can be understood that such a recording method is substantially equivalent to a recording method in which the paper is fed by the bandwidth LB for each pass using the virtual dense nozzle row shown at the right end of FIG. Therefore, paper feeding as shown in FIG. 12 is called “pseudo band feeding”. The feed amount F2 after pass 2 is equal to the value obtained by subtracting the previous feed amount F1 (= 1 dot) from the bandwidth LB. Accordingly, the total ΣFi of the feed amounts F1 to F2 for two times is equal to the bandwidth LB.

  In passes 1 and 2, the upper half of one gray patch shown in FIG. 7 is printed, and in passes 3 and 4, the lower half of the gray patch is printed. Therefore, the height of each gray patch in FIG. 7 in the sub-scanning direction is about twice the bandwidth LB. When each color patch is printed, the value of the feed amount F2 after the second pass is adjusted according to the paper feed correction value δ. That is, each color patch simulates a different paper feed error.

  FIG. 13 shows an example of paper feed for a high-resolution print mode of 720 × 720 dpi. At this time, since the integer k that defines the nozzle pitch is 4, raster lines can be recorded without any gaps by four passes of passes 1 to 4. The right end of FIG. 13 shows a dense nozzle row 36b that can record raster lines recorded in passes 1 to 4 in one pass. The height LB of the dense nozzle row 36b is also equal to the height Lc1 of the chromatic nozzle group for one color.

  In the examples of FIGS. 12 and 13, the number of nozzles to be used is 3 for convenience of explanation, but the number of nozzles to be actually used is several tens or more. FIG. 14 shows an example of the actual paper feed amount in the two print modes. Such an actual paper feed amount is preset in the printer driver 96. FIG. 14A shows an example of paper feeding used for the test pattern in the low resolution printing mode. In this mode, the nozzle pitch k is 2 dots, and the number N of used nozzles is 60. The first feed amount F1 is 1 dot, and the second feed amount F2 is 119 dots. The total of these two feed amounts F1 to F2 is equal to the bandwidth N × k (= 120). FIG. 12 is a simplified drawing of this paper feed.

  FIG. 14B shows an example of the paper feed amount in the high resolution printing mode. In this mode, the third feed amount F1 to F3 is 1 dot, and the fourth feed amount F4 is 117 dots. The total of these four feed amounts F1 to F4 is equal to the bandwidth N × k (= 120). FIG. 13 is a simplified drawing of this paper feed.

  When a test pattern is printed using pseudo band feeding as shown in FIGS. 12 and 13, banding is likely to occur at the boundary of each color band due to a paper feeding error, so that it is easy to detect a paper feeding error. is there. Here, “banding” means a streak-like image degradation portion along the main scanning direction. For example, in the upper four test patterns in FIG. 7, dark banding (black stripes) occurs at the boundary between the upper half and the lower half, and in the lower four test patterns, thin banding (white stripes) occurs. . White streaks occur when the paper feed is insufficient, and black streaks occur when the paper feed is excessive. Banding detection may be performed with the naked eye, or may be performed automatically by imaging a test pattern and performing image processing.

  As described above, when the test pattern (color patch) is printed by the pseudo band feed using the print head 36 having the nozzle pitch k of 2 or more, there is an advantage that the paper feed error can be easily detected. In particular, in this embodiment, since the ink duty is set to about 80%, it is easier to detect the paper feed error.

  In the present embodiment, one of the reasons for printing the test pattern using only one type of ink (black ink) is to reduce the gap G (FIG. 7) between the color patches and to make one print sheet. This is because a large number of color patches can be printed on P. 15 and 16 show a comparison between a method of printing a gray patch using only black ink and a method of printing a gray patch using composite black. Here, “composite black” means an achromatic color reproduced using three colors of CMY inks.

  FIG. 15 shows how two gray patches GP1 and GP2 are printed using the virtual dense nozzle array 36a shown in FIG. The upper half of the gray patch GP1 is printed by one pass using one dense nozzle row 36a, and the lower half is printed by the next one pass. Note that one pass of the dense nozzle row 36a corresponds to two passes (for example, pass 1 and pass 2) of the print head 36 shown in FIG.

  The difference ΔL1 between the positions of pass 1 and pass 2 of the dense nozzle row 36a is set equal to the bandwidth LB. However, strictly speaking, this position difference ΔL1 is equal to a value obtained by adding the bandwidth LB and the paper feed correction value δ (FIG. 7) of the gray patch GP1. Similarly, the second gray patch GP2 is printed by pass 3 and pass 4 of the dense nozzle row 36a.

  The gap G1 between the two gray patches GP1 and GP2 is equal to a value obtained by subtracting the bandwidth LB from the difference ΔL2 between the positions of the dense nozzle row 36a in pass 2 and pass 3. Since the value of the position difference ΔL2 can be set arbitrarily, the gap G1 can also be set arbitrarily.

  On the other hand, as shown in FIG. 16, when a gray patch is printed using composite black, there are the following restrictions on the gap G2 between the two gray patches GP3 and GP4. When a gray patch is printed with composite black, three passes of CMY ink dots are formed in the upper half of the gray patch by performing three passes using the dense nozzle array 36a. In the example of FIG. 16, the upper half of the gray patch GP3 is recorded by pass 1 to pass 3, and the lower half is recorded by pass 2 to 4.

  Printing of the next gray patch GP4 can start from pass 4. The gap G2 at this time is equal to the bandwidth LB. By the way, if so-called back feed (reverse paper feed) is not performed, this gap G2 = LB is the minimum gap between gray patches. When back feed is performed, a feed error due to a backlash of the gear mechanism or the like occurs. Therefore, back feed is not performed in normal printing. Therefore, when printing gray patches with composite black, it is difficult to make the gap G2 between the gray patches equal to or less than the bandwidth LB. Therefore, in terms of reducing the gap between gray patches, it is preferable to use monochromatic black rather than composite black.

  When printing a test pattern, it is preferable to save paper resources by arranging as many color patches as possible on one printing paper P as described in FIG. For this purpose, the gap between the color patches should be set as small as possible. In this sense, it is preferable to print a test pattern using only one type of ink (for example, only black ink) without using a plurality of types of ink as in composite black. However, when the print head is not a vertical array head as shown in FIG. 5 but a horizontal array head (a head in which nozzle groups of each color are arranged in order along the main scanning direction), it will be described with reference to FIG. There are no gap limitations. Therefore, in this case, the test pattern may be printed with a plurality of types of ink.

  The test pattern print signal TPS representing the test pattern is registered in the printer driver 96 (FIG. 1) and stored as a file for the printer driver 96 in the hard disk 92 of the computer 90. The test pattern print signal TPS has the same format as the print data PD (raster data + paper feed amount) transmitted from the printer driver 96 to the printer 20. However, the test pattern print signal TPS is preferably stored in a data-compressed format. When the user gives an instruction to print a test pattern, the test pattern print signal TPS is called by the test pattern supply module 102, decompressed as necessary, and transferred to the printer 20. As described above, in this embodiment, the test pattern print signal TPS is registered in the printer driver 96 in a format that can be transferred to the printer 20 as it is, so that there is an advantage that the test pattern can be printed in a short time. . This advantage is particularly remarkable when a test pattern having a two-dimensional spread is used, such as the color patch shown in FIG.

  In this embodiment, since the test pattern print signal TPS is stored as a file of the printer driver 96, when the specification of the printer driver 96 is changed, the test pattern print signal TPS is simultaneously sent together with the printer driver 96. There is an advantage that the version can be upgraded. Accordingly, a test pattern suitable for the paper feed amount actually used by the printer driver 96 can be used for correcting the paper feed amount.

  Incidentally, the normal printer 20 can use a plurality of types of paper feed amounts. Therefore, in this embodiment, the correction value δ is determined for each paper feed amount. FIG. 17A shows the relationship between the paper feed amount F and the correction value δ. Here, the unit of the feed amount F is [dot], and the unit of the correction value δ is [pulse]. FIG. 17B shows a unit of the correction value δ. Here, it is assumed that one cycle of the A-phase and B-phase signals of the rotary encoder 46 (FIG. 4) of the paper feed mechanism corresponds to 1440 dpi. Therefore, in this embodiment, a distance corresponding to one period (1440 dpi) of the A phase and B phase signals of the encoder 46 is used as a unit [pulse] of the correction value δ.

  In a normal encoder, the phases of the A phase signal and the B phase signal are shifted by a quarter period, so that the position can be commanded in units of 1/4 of one period (1440 dpi). Therefore, a distance corresponding to a quarter of one period (1440 dpi) of the A phase and B phase signals of the encoder 46 may be used as a unit [pulse] of the correction value δ. Moreover, you may employ | adopt 1/2 of 1 period of the output signal of an encoder as a unit of correction value (delta). Further, when a step motor is used as the paper feed motor 31, one step pulse can be used as a unit of the correction value δ.

  The feed amount correction value is predicted by, for example, setting in advance the shape of a curve G1 as shown in FIG. 17A or a characteristic curve (prediction curve) such as a straight line G2 passing through the origin. Is possible. In general, a correction value for a feed amount other than a typical feed amount may be predicted according to a predetermined prediction curve. Here, the “prediction curve” has a broad meaning including a straight line.

  The correction value δ shown in FIG. 17 is registered in a nonvolatile memory (EEPROM 58) in the printer 20 or a printer driver 96 (specifically, a hard disk of the computer 90). During actual printing, a value obtained by correcting the paper feed amount F with the correction value δ is given as a command value from the system controller 54 to the sub-scanning drive circuit 62.

  As described above, in this embodiment, since the paper feed amount is corrected using the correction value δ determined according to the test pattern print result, it is possible to perform high-quality printing with little paper feed error. is there. In particular, since only one type of ink (black ink) is used and a color patch with an ink duty of about 80% is printed as a test pattern, it is easy to detect banding due to a paper feed error, resulting in a paper feed error. It is possible to easily determine an appropriate correction value.

E. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

E1. Modification 1:
In the above embodiment, a color ink jet printer has been described. However, the present invention can be applied to a monochrome printer, and can also be applied to printers other than the ink jet system. The present invention is generally applicable to a printing apparatus that records an image on a print medium, and can also be applied to, for example, a facsimile machine and a copier.

E2. Modification 2:
In the above-described embodiments, the case where printing in the interlace recording mode is performed using a print head having a nozzle pitch k of 2 dots or more is generally described. It is also applicable when printing using

E3. Modification 3:
In the above embodiment, as shown in FIG. 5, the case where the vertical array head having the two-row configuration of the black nozzle row and the color nozzle row is used has been described. It is also applicable to a laterally arranged head that is located in the sub-scanning direction position and is sequentially arranged along the main scanning direction.

E4. Modification 4:
In the above embodiment, the correction value is determined by one type of test pattern, but the correction value may be determined by using a plurality of types of test patterns. For example, the coarse correction value may be determined using the first test pattern for coarse adjustment, and the final fine correction value may be determined using the second test pattern for fine adjustment. For example, a coarse correction value can be set at an interval of 10 steps, and a fine correction value can be set at an interval of 1 step. In this way, if a plurality of adjustments are performed, it is possible to efficiently determine a fine correction value.

E5. Modification 5:
In the above embodiment, the gray patch reproduced only with the black ink is used as the test pattern color patch. However, other color patches may be used. For example, it is also possible to use a single color patch that is reproduced with cyan ink or magenta ink.

E6. Modification 6:
In the above embodiment, the correction value is determined by observing the test pattern by a human. Instead, the image quality of the test pattern is mechanically measured to reduce the image quality of the sub-scan feed error. It is also possible to measure the influence of the correction and the correction unit corrects the sub-scan feed according to the measurement result. In this way, it is possible to appropriately correct the sub-scan feed error without requiring manual work.

20 ... Color inkjet printer 21 ... CRT
22 ... paper stacker 24 ... paper feed roller 25 ... driven roller 26 ... platen 28 ... carriage 30 ... carriage motor 31 ... paper feed motor 32 ... traction belt 34. ..Guide rail 36 ... Print heads 36a, 36b ... Virtual dense nozzle array 40 ... Gear train 42 ... Discharge roller 44 ... Giza roller 46 ... Rotary encoder 46a ... Code plate 46b ... Photo sensor 50 ... Reception buffer memory 52 ... Image buffer 54 ... System controller 54a ... Paper feed control unit 56 ... Main memory 58 ... EEPROM
61 ... Main scan drive circuit 62 ... Sub scan drive circuit 63 ... Head drive circuit 90 ... Computer 91 ... Video driver 92 ... Hard disk 95 ... Application program 96 ... Printer Driver 97 ... Resolution conversion module 98 ... Color conversion module 99 ... Halftone module 100 ... Rasterizer 101 ... User interface display module 102 ... Test pattern supply module

Claims (8)

A method of correcting a sub-scan feed amount of a print medium in a printing apparatus that performs printing by recording ink dots on the print medium while moving the print head in the main scanning direction,
(A) As a test pattern for determining the correction value of the sub-scan feed amount of the print medium, a test pattern including a plurality of color patches respectively printed using different correction values is used with one type of ink. Printing with less than 100% ink duty;
(B) a step of correcting the sub-scan feed amount according to a correction value set according to the print result of the test pattern when performing printing;
A correction method comprising: The correction method according to claim 1,
The correction method, wherein the ink duty is changed according to a type of the print medium. The correction method according to claim 1, wherein:
The correction method, wherein the plurality of color patches are gray patches reproduced with black ink. The correction method according to claim 3,
The gray patch ink duty is a correction method in a range of about 70% to about 90%. The correction method according to any one of claims 1 to 4,
The correction method, wherein the plurality of color patches are arranged along a sub-scanning direction on a single print medium. The correction method according to claim 5, wherein
The print head includes a color nozzle row in which a plurality of color nozzle groups are arranged in a predetermined order along the sub-scanning direction, and a black nozzle row arranged in parallel with the color nozzle row,
The correction method, wherein the plurality of color patches are printed using only some of the plurality of black nozzles included in the black nozzle row. A printing apparatus that performs printing by recording ink dots on a print medium while moving a print head in a main scanning direction,
A print head having a plurality of nozzles;
A main scanning drive unit that moves the print head in the main scanning direction;
A sub-scanning drive unit that moves the print medium in the sub-scanning direction by intermittent multiple times of feeding;
A head drive unit that ejects ink droplets from the plurality of nozzles during main scanning of the print head;
A control unit for controlling the main scanning driving unit, the sub-scanning driving unit, and the head driving unit;
With
The controller is
(A) As a test pattern for determining the correction value of the sub-scan feed amount of the print medium, a test pattern including a plurality of color patches respectively printed using different correction values is used with one type of ink. It has a test pattern printing mode that prints with an ink duty of less than 100%,
(B) When performing printing, the sub-scan feed amount is corrected according to the correction value set according to the print result of the test pattern, and a command value indicating the corrected sub-scan feed amount is supplied to the sub-scan driving unit. A printing apparatus characterized by supplying. A computer program for causing a computer including a printing apparatus that performs printing by recording ink dots on a print medium while moving the print head in the main scanning direction to correct the sub-scan feed amount of the print medium. ,
(A) As a test pattern for determining the correction value of the sub-scan feed amount of the print medium, a test pattern including a plurality of color patches respectively printed using different correction values is used with one type of ink. Printing with less than 100% ink duty;
(B) a step of correcting the sub-scan feed amount according to a correction value set according to the print result of the test pattern when performing printing;
A computer program comprising a program for causing the computer to realize the above.

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