Inkjet printing apparatus and printing method using adjustment pattern

A print position adjustment mode is performed with high accuracy while consumption of print media is saved. An inkjet printing apparatus prints an adjustment pattern including multiple patches for adjusting print positions of dots by a print head on a print medium. Patches set next to each other in a scanning direction are printed above platen ribs at intervals based on rib pitches at which the platen ribs are arranged.

BACKGROUND

Technical Field

One disclosed aspect of the embodiments relates to an inkjet printing apparatus and a printing method using adjustment pattern in the apparatus.

Description of the Related Art

Some inkjet printing apparatus is capable of executing a print position adjustment mode for adjusting the print positions of dots on a print medium. For example, in the case of adjusting the print positions in forward and backward scans, multiple patches in which the relative print position in the forward scan and backward scan by a print head is gradually shifted are printed on a print medium in the print position adjustment mode. Then, the patch that achieved the smallest print position misalignment is selected and the print position used in the selected patch is set as an adjustment value.

Japanese Patent Laid-Open No. 2010-143123 discloses a print position adjustment method in which multiple patches having mutually different dot print positions are printed in association with respective platen ribs that support a print medium, thereby keeping small an influence due to a variation of the distance between the print head and the print medium.

In recent years, along with increases in the number of types of inks used for printing and the print resolution, the number of items for which the print positions need to be adjusted has also increased. For this reason, in the print position adjustment mode, it is necessary to further print a large number of patches in addition to the aforementioned patches for adjustment in the forward and backward scans.

However, since the printing apparatus includes only a limited number of platen ribs, the method of Japanese Patent Laid-Open No. 2010-143123 requires many print media or a print medium in a large size for printing the patches for adjustment, which is unfavorable from the viewpoint of usability.

SUMMARY

An aspect of the embodiments aims to solve the above problem. Therefore, an object of the disclosure is to execute a print position adjustment mode with high accuracy while saving consumption of print media.

In a first aspect of the disclosure, a printing apparatus includes a printing unit, a scanning unit, a conveyance unit, and a plurality of platen ribs. The printing unit is configured to print dots on a print medium by applying ink droplets. The scanning unit is configured to scan the printing unit in a scanning direction. The conveyance unit is configured to convey a print medium in a conveyance direction crossing the scanning direction. The plurality of platen ribs is configured to be arranged on a conveyance route of a print medium at positions facing the printing unit at predetermined pitches in the scanning direction and to support the print medium. The printing unit prints an adjustment pattern on a print medium in response to reception of an instruction to adjust print positions of ink droplets to be applied by the printing unit. The adjustment pattern includes a plurality of patches and is for use for adjustment. The printing unit prints the adjustment pattern such that two or more patches are printed next to each other in the scanning direction in a neighboring area around a certain one of the plurality of platen ribs and that no patches are printed in a middle area between the certain platen rib and another platen rib next to the certain platen rib in the scanning direction.

In a second aspect of the disclosure, an adjustment pattern printing method is provided for a printing apparatus that includes a printing unit, a scanning unit, a conveyance unit, and a plurality of platen ribs. The printing unit is configured to print dots on a print medium by applying ink droplets. The scanning unit is configured to scan the printing unit in a scanning direction. The conveyance unit is configured to convey a print medium in a conveyance direction crossing the scanning direction. The plurality of platen ribs is configured to be arranged on a conveyance route of a print medium at positions facing the printing unit at predetermined pitches in the scanning direction and to support the print medium. The printing unit prints an adjustment pattern on a print medium in response to reception of an instruction to adjust print positions of ink droplets to be applied by the printing unit. The adjustment pattern includes a plurality of patches and is for use for adjustment. The printing unit prints the adjustment pattern such that two or more patches are printed next to each other in the scanning direction in a neighboring area around a certain one of the plurality of platen ribs and that no patches are printed in a middle area between the certain platen rib and another platen rib next to the certain platen rib in the scanning direction.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

FIG.1is a schematic perspective view of an inkjet printing apparatus1(hereinafter, also referred to as the printing apparatus1) to which the disclosure is applicable. A carriage102is capable of reciprocating in an X direction along a guide shaft103that extends in the X direction. The carriage102is driven by a main scanning motor104via a driving mechanism including a motor pulley105, a driven pulley106, a timing belt107, and so on. An encoder1304detects the position of the carriage102moved in the X direction. A head cartridge101is mounted on the carriage102and a reflection-type optical sensor130is attached to a side portion of the carriage102.

With rotations of two sets of conveyance roller pairs109and111, a print medium P is conveyed in a Y direction crossing the scanning direction of the carriage102. A platen1301is arranged at a position opposed to a downwardly-projecting ejection port surface (not illustrated inFIG.1) of the head cartridge101and supports the print medium P being convened from the back side. The structure of the platen1301will be described later. The conveyance roller pairs109and111are part of a conveyance unit or a conveyor. The conveyor includes the conveyance roller pairs109and111and a conveying functionality provided by the CPU901(shown inFIG.6) that performs the conveying operation.

A recovery treatment unit114for maintaining good ink ejection conditions in the head cartridge101is arranged at an end portion of a movable region of the head cartridge101. The recovery treatment unit114is equipped with a cap115that caps the ejection port surface of the head cartridge101, a suction pump116, a wiper118, and so on.

FIGS.2A and2Bare perspective views illustrating the structure of the head cartridge101. The head cartridge101includes ink tanks201that store inks and a print head202that ejects the inks supplied from the ink tanks201.FIG.2Aillustrates a state where the ink tanks201are mounted on the print head202andFIG.2Billustrates a state where the ink tanks201are not mounted on the print head202. On the head cartridge101in the present embodiment, the ink tanks201of colors of black, light cyan, light magenta, cyan, magenta, and yellow are detachably mounted.

The print head202is an inkjet print head that ejects the inks by using thermal energy, and includes electric thermal conversion member. More specifically, the print head202boils the inks by using the thermal energy generated by the electric heat converters, and ejects the inks from its ejection ports to the print medium by using the bubble generating energy. Here, instead of using the electric heat converters, the print head202may use piezo elements or the like as elements for generating the ink ejection energy. The print head202is part of a printing unit or a printer which includes the print head202and a function performed by a processor or a programmable device such as the central processing unit (CPU)901shown inFIG.6.

FIGS.3A and3Bare diagrams illustrating a structure for one color in the print head202.FIG.3Aillustrates an array structure of ejection ports500in an ejection port surface510andFIG.3Billustrates a cross-sectional view taken along IIIB-IIIB.

As illustrated inFIG.3A, multiple ejection ports500from which the ink is ejectable are arranged in two arrays501and502in the ejection port surface510. The ejection port arrays501and502extend in a Y direction in which the print medium is conveyed. In each of the ejection port arrays501and502, 384 ejection ports500are formed at pitches Py, specifically, at intervals each corresponding to 600 dpi. Then, the ejection ports500in the ejection port array501are shifted in the Y direction from the ejection ports500in the ejection port array502by a half pitch (Py/2) corresponding to 1200 dpi. From the totally 768 ejection ports500in the ejection port array501and the ejection port array502, the ink of the same color is ejected, so that dots can be printed at a density of 1200 dpi in the Y direction.

As illustrated inFIG.3B, a common channel520through which the ink is supplied to the ejection port array501and the ejection port array502is formed between the ejection port array501and the ejection port array502. The ink in the common channel520is guided to each of the ejection ports500in the ejection port arrays501and502through an individual channel530. In the individual channel530, an ejection heater942formed of an electric heat converter is arranged at a position opposed to the ejection port500. When the ejection heater942driven according to a drive signal generates thermal energy, the ink in the individual channel530causes film boiling, and the bubble generating energy at that time causes an ink droplet550to be ejected from the ejection port500.

FIG.4is a diagram illustrating the array structure of the ejection ports500for six colors in the ejection port surface510. The print head202in the present embodiment supports inks of six colors of cyan (C), magenta (M), yellow (Y), black (K), light cyan (LC), and light magenta (LM). InFIG.4, C1and C2denote ejection port arrays for ejecting the ink of cyan (C) and LM1and LM2denote ejection port arrays for ejecting the ink of light magenta (LM). Then, K1and K2denote ejection port arrays for ejecting the ink of black (K) and Y1and Y2denote ejection port arrays for ejecting the ink of yellow (Y). Moreover, LC1and LC2denote ejection port arrays for ejecting the ink of light cyan (LC) and M1and M2denote ejection port arrays for ejecting the ink of magenta (M). The ejection port arrays C1, C2, LM1, and LM2are provided in a common board (chip 1), the ejection port arrays K1, K2, Y1, and Y2are provided in a common board (chip 2), and the ejection port arrays LC1, LC2, M1, and M2are provided in a common board (chip 3).

The inks of cyan (C), magenta (M), yellow (Y), and black (K) are thick inks each having a relatively high dye concentration, while the inks of light cyan (LC) and light magenta (LM) are light inks each having a dye concentration of about one-sixth of those of the thick inks. By using the print head202in which the two ejection port arrays501and502for each color are arranged, color images having a resolution of 1200 dpi are printed on print media.

FIG.5is a schematic diagram for explaining the reflection-type optical sensor130(seeFIG.1) attached to the carriage102. The reflection-type optical sensor130includes a light emitter801and a light receiver802. Incident light803emitted from the light emitter801is reflected by a print medium P and then is detected by the light receiver802. A detection signal (analog signal) of the light receiver802is transmitted to a control circuit on an electric board of the printing apparatus1through a flexible cable not illustrated, and is converted to a digital signal by an analog-to-digital (A/D) converter.

FIG.6is a block diagram for explaining a structure for control in the inkjet printing apparatus. A controller900as a main controller includes, for example, a central processing unit (CPU)901in the form of a microcomputer, a read-only memory (ROM)902that stores programs, necessary tables, and other fixed data, and a random access memory (RAM)903on which an area for developing image data, a work area, and so on are provided. The CPU901performs operations by executing a function or a program stored in the ROM902or an equivalent memory device. The operations may include functionalities of a printing unit or printer, a scanning unit or scanner, and a conveyance unit or conveyor.

A host device910is a supply source of image data, and may be in the form of not only a computer that performs creation, processing, and the like of image data for printing, but also a reader or the like for image reading. The host device910transmits and receives image data, other commands, status signals, and so on to and from the controller900via an interface (I/F)911.

An operation unit920is a switch group that accepts input of instructions by an operator, and includes a power supply switch921, a printing start switch922for making an instruction to start printing, and a recovery switch923for making an instruction to activate a recovery operation for the print head202. Moreover, the operation unit920includes a print position adjustment start switch924for starting a print position adjustment mode to be described later. In the present embodiment, execution of the print operation, the recovery operation for the print head202, and the print position adjustment mode can be instructed through the switches in the operation unit920. Instead, these operations may be executed based on instructions from the host device910.

A sensor group930includes the reflection-type optical sensor130described with reference toFIG.5, a photocoupler931for detecting a home position, a temperature sensor932provided at an appropriate position for detecting an environment temperature, and so on.

A head driver940is a driver that drives the ejection heaters942in the print head202according to print data or the like. The head driver940includes a shift register that aligns print data with the positions of the ejection heaters942, a latch circuit that performs a latching action at an appropriate timing, and a logic circuit element that operates the ejection heaters942in synchronization with drive timing signals.

The print head202includes sub-heaters941for temperature adjustment of the ink before ejection in addition to the ejection heaters942described with reference toFIG.3B. The sub-heaters941may be provided on the same board as the ejection heaters942or provided at a portion other than the board in the print head202.

A main scanning motor driver950is a driver that drives the main scanning motor104. A sub scanning motor driver960is a driver that drives a sub scanning motor961that rotates the conveyance roller pairs109and111. A recovery motor driver970is a driver that operates the suction pump116, the wiper118, and so on in the recovery treatment unit114.

Hereinafter, description will be given of a print position adjustment mode in the present embodiment.

FIG.7is a flowchart for explaining steps in processing of the print position adjustment mode in the present embodiment. This processing is processing that the CPU901executes according to a program stored in the ROM902by using the RAM903as a work area. This processing is started in the case where a user presses down the print position adjustment start switch924or a command for print position adjustment is inputted from the host device910.

Upon start of this processing, the CPU901first executes adjustment pattern print processing for printing a predetermined adjustment pattern on a print medium P at S1. The adjustment pattern includes multiple patches for each of items for which the print positions are to be adjusted, which will be described in detail later.

At S2, the CPU901measures an optical density of each of the patches included in the adjustment pattern by using the reflection-type optical sensor130.

At S3, the CPU901determines a print position adjustment value for each of the items based on the optical densities of the corresponding patches obtained at S2.

At S4, the CPU901stores the adjustment values determined at S3in association with the respective items in the ROM902. This processing is completed at the end of this step.

The adjustment values stored at S4are used in following print operations, and enable the printing apparatus1to output an image having no print position misalignment.

FIGS.8A to8Care diagrams illustrating an example of the patches printed at S1inFIG.7. Here, a case where an adjustment value is obtained for the print positions in the forward and backward scans as an item is described as an example. In the case of adjusting the print positions in the forward and backward scans, one patch includes a first dot group1000printed in the forward scan and a second dot group1001printed in the backward scan. In the present embodiment, each of the first dot group1000and the second dot group1001is a pattern in which four pixels where dots are printed consecutively and four pixels where any dots are not printed consecutively are alternately repeated in a main scanning direction. Then, at S1inFIG.7, multiple patches where a shift amount in the X direction between these two dot groups is gradually changed are printed on the print medium. More specifically, a timing for applying a voltage to the ejection heaters942to print the second dot group in the backward scan is shifted on a patch-by-patch basis relative to a timing for applying a voltage to the ejection heaters942to print the first dot group in the forward scan.

FIGS.8A to8Cillustrate three patches among which the aforementioned ejection timings are different.FIG.8Aillustrates a state where the print positions of the first dot group1000and the second dot group1001are aligned with each other, in other words, the case where the ejection timing in the forward scan and the ejection timing in the backward scan are in favorable conditions. On the other hand,FIG.8Billustrates a state where the second dot group1001is misaligned with the first dot group1000in the right direction andFIG.8Cillustrates a state where the aforementioned misalignment is further greater than inFIG.8B.

Here, these three drawings are compared. In the case of the patch inFIG.8A, all the dots are arranged at approximately equal intervals in the main scanning direction, and a coverage ratio of dots to a print medium (area factor) is approximately 100%. In contrast, in the case of the patch inFIG.8B, portions where the sheet surface is exposed appear at boundaries between the first dot group1000and the second dot group1001, and the area factor decreases as compared withFIG.8A. InFIG.8Chaving the greater misalignment than inFIG.8B, the area factor further decreases. InFIGS.8B and8C, portions where the density increases as compared withFIG.8Adue to overlapping of dots are also generated, but the decrease in the area factor has a greater influence on the optical density than the dot overlapping has. For this reason, in the case of measuring the densities of the entire patches, the optical density decreases in the order of the patch inFIG.8A, the patch inFIG.8B, and the patch inFIG.8C, that is, in ascending order of the misalignment.

FIG.9is a diagram illustrating a relation between the print position misalignment and the optical density. The horizontal axis indicates the misalignment of the second dot group1001relative to the first dot group1000in a patch, and the vertical axis indicates the optical density of the patch. The optical density is a detected density D obtained by using the reflection-type optical sensor130described with reference toFIG.5.

Here, in the case where Iin denotes the intensity of the incident light803and Iref denotes the intensity of the reflected light804inFIG.5, the reflectance R is
R=Iref/Iin.

The detected density D is a logarithmic function of the reciprocal of the reflectance R, and can be calculated in accordance with the following equation using the reflectance R.
D=Log10(1/R)

If the misalignment between the print position in the forward scan and the print position in the backward scan is 0 μm, the area factor on the print medium is approximately 100% as inFIG.8Aand the detected density is the highest value. Then, as the misalignment between the print positions in any of the right and left directions increases, the area factor decreases and accordingly the detected density becomes lower. At S3inFIG.7, the CPU901compares the detected densities of the patches with each other, and determines the print position in the patch with the highest detected density as the adjustment value.

FIG.10is a top view illustrating a layout of platen ribs1303in a platen1301that extend in the X direction. Although a scanning region of the head cartridge101is actually right above the platen1301, the scanning region is shifted in the Y direction inFIG.10for the purpose of explaining the positional relationship between them in the X direction.

The position of the head cartridge101in the X direction during a printing scan is managed by the encoder1304.FIG.10illustrates a state where the head cartridge101is located at the recovery treatment unit114outside a printable region W where the head cartridge101can actually print images.

The platen1301is a plate that extends in the X direction. The platen1301is provided in two rows at a predetermined interval in the Y direction, and an ink absorber1302for absorbing the ink flowing out of the edges of a print medium during a print operation is provided between the two rows of the platen1301. On the platen1301, multiple platen ribs1303projecting upward are formed at predetermined pitches in the X direction. More specifically, these platen ribs1303are arranged on a conveyance route of the print medium and support the print medium being conveyed from the back side. The position of each of the platen ribs1303in the X direction is managed in association with a coordinate in the encoder1304.

The platen ribs1303are arranged symmetrically with respect to a center line1305of the printable region W. For convenience, R1denotes the platen rib1303located closest to the recovery treatment unit114and R2, R3, . . . , R14denote the platen ribs1303in ascending order of the distance from the recovery treatment unit114.FIG.10indicates the distance between the center line1305and each platen rib1303.

The print medium P being conveyed on the platen ribs1303in the Y direction is conveyed with the center of the print medium P aligned with the center line1305irrespective of the size of the print medium. The layout of the platen ribs1303is determined depending on the size of a print medium supposed to be conveyed and the rib pitches between the two neighboring platen ribs1303are not constant. For example, in the case where a print medium is in A4 size, the print medium is conveyed in the Y direction at an internal position between the platen ribs1303of R3and R12while being supported by the eight platen ribs1303of R4to R11.

FIG.11is a diagram illustrating a state where the three platen ribs1303of R7, R8, and R9support a print medium P being conveyed. The platen ribs1303have a height of approximately 2 mm, and their tip ends come into contact with the back side of the print medium P and thereby support the print medium P. The pitch between R7and R8and the pitch between R8and R9are both 24 mm.

In the print medium P, a portion supported by each of the platen ribs1303is in an upwardly-projecting form and a portion between the two platen ribs1303is in a recessed form. Here, an intra-sheet maximum variation is defined as a difference between the projecting portion and the lowest point of the recessed portion. This intra-sheet maximum variation in a print medium having a low stiffness such as a plain sheet, for example, is approximately 200 μm. In other words, a distance between the ejection port surface of the print head202and the print medium P (a head-to-paper distance) has a variation of 200 μm in the X direction.

FIGS.12A and12Bare diagrams for explaining print position misalignment between the forward scan and the backward scan due to a difference in the head-to-paper distance. In the forward scan, the print head202ejects the ink to the print medium P at an ejection velocity Vz while moving at a velocity Vx in the +X direction. In this ejection, an ink droplet ejected also has the velocity Vx in the +X direction and is landed to form the dot at a position shifted in the +X direction from the position where the print head202ejects the ink droplet. On the other hand, in the backward scan, the print head202ejects the ink to the print medium P at the ejection velocity Vz while moving at the velocity Vx in the −X direction. In this ejection, an ink droplet ejected also has the velocity −Vx in the −X direction and is landed to form the dot at a position shifted in the −X direction from the position where the print head202ejects the ink droplet.

FIG.12Aillustrates a state where the position of the ink landed in the forward scan and the position of the ink landed in the backward scan coincide with each other with a head-to-paper distance d1. On the other hand,FIG.12Billustrates a case where ejection actions are performed with a head-to-paper distance d2(>d1) at the same timings as inFIG.12A. In the case ofFIG.12B, in proportion to the increase in the head-to-paper distance, a time from the ejection to the landing of the ink droplet increases, and accordingly the traveling distance in the X direction also increases. For this reason, even though the ejection actions are performed at the same timings as inFIG.12A, the dot printed in the forward scan and the dot printed in the backward scan are formed at different positions and thus a misalignment with a distance s occurs between the two dots.

FIGS.13A and13Bare diagrams illustrating an influence of a difference in the head-to-paper distance on the detection accuracy of the reflection-type optical sensor130.FIG.13Aillustrates a case where an optical density of the print medium P is measured under the condition that a distance between the reflection-type optical sensor130and the print medium P is d3. The incident light803emitted from the light emitter801is reflected by the print medium P and the reflected light804is incident on the substantially center of the light receiver802. On the other hand,FIG.13Billustrates a case where an optical density of the print medium P is measured under the condition that the distance between the reflection-type optical sensor130and the print medium P is d4(>d3). Due to the longer distance between the reflection-type optical sensor130and the print medium P, the reflected light804is shifted in the X direction and is incident on an edge portion of the light receiver802. Thus, even if the measurement is performed on the same image, the optical density detected by the reflection-type optical sensor130varies betweenFIGS.13A and13B.

As discussed above, a variation of the head-to-paper distance illustrated inFIG.11is a factor that reduces the accuracy of the print positions and the measurement accuracy of the optical density. In other words, in the print position adjustment mode in the present embodiment in which multiple patches are printed and the optical density of each of the patches is measured, the head-to-paper distance at each of the positions on the print medium where the multiple patches are arranged is required to be stable in the process of conveying the print medium. From this point of view, it can be said that the printing of multiple patches in association with the respective platen ribs as in Japanese Patent Laid-Open No. 2010-143123 is effective for maintaining the accuracy of the print position adjustment.

However, if all the patches necessary for adjustment are arranged above the platen ribs1303, a print medium in, for example, A4 size allows only eight patches above R4to R11to be arranged in the X direction (seeFIG.10). Meanwhile, the inkjet printing apparatus1requires print position adjustments for various items including not only the above-described print positions in the forward and backward scans, but also the print positions of the inks of different colors (seeFIG.6), the print positions of the ejection port arrays (seeFIG.3A), and so on. Under such circumstances, printing of all the patches for all the items on a print medium or print media requires a print medium in a large size having no versatility or consumes multiple print media for the print position adjustment mode, which is unfavorable in terms of the usability.

In view of the above circumstances, the present inventors considered that it is effective to confirm in advance ranges on both sides of each platen rib1303where the influence of the print position misalignment due to a variation of the head-to-paper distance is tolerable and to arrange a plurality of the above patches within the confirmed ranges. Then, in the case ofFIG.11, the studies by the present inventors confirmed that a variation of the head-to-paper distance within a range of 25% of the distance from R8to R7or R9, specifically, within a 6 mm area on either of the right and left sides is kept as low as approximately 100 μm, which is half of the intra-sheet maximum variation of 200 μm. If the variation of the head-to-paper distance is kept as low as 100 μm, the influence on the accuracy of the print position adjustment is only at a level of several μm and the influence on image quality in the inkjet printing apparatus of the present embodiment that prints images at a print resolution of 1200 dip can be kept within a tolerable range. Thus, in the print position adjustment mode of the present embodiment, one patch is printed within a 6 mm area on one side of the platen rib1303and another patch having a shift amount different from that in the former patch is printed within a 6 mm area on the other side of the platen rib1303. As a result, the number of patches printable in the width direction of the print medium can be increased as compared with a case in the related art.

To this end, the present inventors first confirmed the size of a patch necessary to normally measure the optical density.

FIGS.14A and14Bare diagrams each depicting a relation between one patch1700and a spot diameter1702of the incident light803of the reflection-type optical sensor130(seeFIG.5) on a print medium. In order to measure the density of the patch accurately, it is desirable that the spot diameter1702be within the area of the patch1700as inFIG.14Afor the following reason. If the spot diameter1702protrudes from the area of the patch1700as illustrated inFIG.14B, the detected density tends to be affected by a variation of the light incident position, and may not have the clear maximum value as illustrated inFIG.9. Thus, in the present embodiment, the spot diameter of the incident light803is narrowed by a lens not illustrated, and the size of the patch in the X direction is set to 4.7 mm, which is the size to which the spot diameter thus narrowed can be fully confined. This makes it possible to arrange two patches next to each other within the 6 mm areas on both sides of one platen rib1303.

FIGS.15A and15Bare views illustrating a layout of patches in the X direction in the print position adjustment mode of the present embodiment.FIG.15Adepicts an overall view in the X direction andFIG.15Bdepicts an enlarged view of an area around the rib R4. Here, an adjustment pattern for adjusting the print positions in the forward scan and the print positions in the backward scan by using a print medium P in A4 size is illustrated as an example. InFIGS.15A and15B, 13 patches are illustrated with reference signs of1401to1413, respectively.

As illustrated inFIG.15B, the patch1401and the patch1402are arranged next to each other on both sides of the platen rib1303of R4, and the two patches1401and1402each have a width of 4.7 mm in the X direction, that is, totally have a width of 9.4 mm in the X direction. Thus, these two patches are confined to the 6 mm areas on the right and left sides of the platen rib1303, and therefore can be used favorably for the print position adjustment under the condition that a variation of the head-to-paper distance is in a tolerable range. In the present embodiment, such a patch set is printed in association with each of the platen ribs1303of R5to R9. InFIG.15A, the leftmost patch1413is arranged right above the platen rib1303of R10.

In the present embodiment, the relative print position of the first dot group1000printed in the forward scan and the second dot group1001printed in the backward scan (seeFIG.8) is gradually changed in the arrangement order of the patches. For example, for the center patch1407, the first dot group1000and the second dot group1001are printed with the ejection timings in the forward scan and the backward scan matched each other according to the design. Then, the ejection timing is changed gradually from that of the center patch1407such that the ejection timing in the backward scan is advanced more as the patch is located closer to the leftmost and the ejection timing in the backward scan is delayed more as the patch is located closer to the rightmost. However, the relation between the arrangement order and the ejection timings of the patches is not limited to the above. For example, the patches with the most-advanced and most-delayed ejection timings in the backward scan may be arranged next to each other in the vicinity of the same platen rib1303.

FIG.16is an overall view of an adjustment pattern printed in the print position adjustment mode of the present embodiment. The adjustment pattern in the present embodiment includes a first pattern1800for adjusting the print positions in the forward and backward scans, a second pattern1801for adjusting the print positions of the ejection port arrays of the same color, and a third pattern1802for adjusting the print positions of the ejection port arrays of different colors. Then, all of these patterns are printed on one print medium P in A4 size.

Hereinafter, each of the patterns will be briefly described. The first pattern1800is a pattern for adjusting the print positions in the forward scan and the backward scan. Six rows each including 13 patches arrayed in the X direction as described with reference toFIG.15are printed in Y direction for the respective inks of six colors. The second pattern1801is a pattern for adjusting the print positions of the ejection port arrays that eject the ink of the same color, such as the ejection port arrays501and502inFIG.3A. Six rows each including 13 patches in which the shift amount between the dot group printed by the ejection port array501and the dot group printed by the ejection port array502is gradually changed are printed in Y direction in association with the respective inks of six colors. The third pattern1802is a pattern for adjusting the print positions of the ejection port arrays that eject the inks of different colors as illustrated inFIG.4. For example, five rows each including 13 patches in which the shift amount between the dot group printed by the ejection port arrays of the reference color (K1) and the dot group printed by the ejection port arrays of an adjustment color (C1) is gradually changed are printed in Y direction in association with the respective five adjustment colors.

Thus, according to the present embodiment, all of the 221 patches included in the three patterns can be placed on one print medium in A4 size. In other words, it is possible to execute the print position adjustment mode with high accuracy while saving consumption of print media.

Although the present embodiment is described on the assumption that the patches are printed within the 6 mm areas on both sides of the platen rib1303in order to limit the influence due to a variation of the head-to-paper distance to the tolerable range, such areas can be changed as appropriate as a matter of course. The degree of variation of the head-to-paper distance also varies depending on the type of the print medium, use environment, the width of the platen rib1303, and so on. Moreover, even with the same degree of the print position misalignment, the influence on an image changes depending on whether the image is a text image or a photograph image or depending on the print resolution of the image or the like. For the reasons discussed above, the patch printable areas on both sides of the platen rib1303may be adjusted as appropriate depending on these various kinds of information.

Second Embodiment

FIG.17is an overall view of an adjustment pattern to be used in the print position adjustment mode of the present embodiment. The adjustment pattern of the present embodiment also includes a first pattern1950for adjusting the print positions in the forward and backward scans, a second pattern1951for adjusting the print positions of the ejection port arrays of the same color, and a third pattern1952for adjusting the print positions of the ejection port arrays of the different colors. Then, all of these patterns are printed on one print medium P in A4 size.

A difference of the adjustment pattern in the present embodiment from that in the first embodiment is a combination of two patches above the same platen rib1303. For example, in the present embodiment, patches1901to1913are patches for adjusting the print positions in the forward and backward scans for the cyan ink. Then, patches1921to1933are patches for adjusting the print positions in the forward and backward scans for the light cyan ink. In other words, in the present embodiment, two patches arranged above the same platen rib1303are patches printed by different colors, that is, by different ejection port arrays. The same applies to the second pattern1951and the third pattern1952.

According to the disclosure, the ejection port arrays can be driven at more dispersed locations in the print medium P than in the first embodiment. This makes it possible to print the adjustment pattern while maintaining the stable ejection conditions of the respective ejection port arrays, and thereby to further enhance the adjustment accuracy.

Third Embodiment

In the print position adjustment mode of the present embodiment, coarse adjustment of the print positions is performed prior to the print position arrangement processing described in the first embodiment.

FIG.18is an overall view of an adjustment pattern to be used in the print position adjustment mode of the present embodiment. The adjustment pattern in the present embodiment includes a coarse adjustment pattern2000in addition to the first pattern1800, the second pattern1801, and the third pattern1802described in the first embodiment. Then, all of these patterns are printed on one print medium P in A4 size.

The coarse adjustment pattern2000is printed at the head in the conveyance direction (Y direction) prior to the first to third patterns1800to1802for fine adjustment. Then, before printing of the first to third patterns1800to1802, the coarse adjustment pattern2000is read, and a range of the dot shift amount (ejection timing) is set for the multiple patches to be printed in the first to third patterns.

FIG.19is a flowchart for explaining steps in processing in the print position adjustment mode of the present embodiment. Hereinafter the steps will be described with reference to the adjustment pattern inFIG.18.

Upon start of this processing, the CPU901first prints the coarse adjustment pattern2000on a print medium P at S11. As illustrated inFIG.18, the coarse adjustment pattern2000is printed at the head of the print medium P in the conveyance direction (Y direction).

As illustrated inFIG.18, the coarse adjustment pattern2000includes pattern groups2001to2006for the respective inks of six colors. Each of the pattern groups2001to2006includes five columns and three rows of patches. In the coarse adjustment, the influence of the print position misalignment due to the variation of the head-to-paper distance does not have to be considered to the same degree as in the fine adjustment. Therefore, in the present embodiment, the pattern groups2001to2006are arranged at equal intervals in the X direction irrespective of the positions of the platen ribs1303.

Here, the pattern group2001for the cyan ink is focused. The five patches in the patch row2007are printed by the ejection port array C1(seeFIG.4) in the forward scan. The five patches in the patch row2008are printed by the ejection port array C1in the backward scan. The five patches in the patch row2009are printed by the ejection port array C2in the forward scan. The same applies to the other pattern groups2002to2006for the different ink colors.

At S12, the CPU901performs processing of reading the patches included in the coarse adjustment pattern2000by using the reflection-type optical sensor130. Specifically, the CPU901conveys the print medium P such that the printed coarse adjustment pattern2000is located within a region readable by the reflection-type optical sensor130, and causes the reflection-type optical sensor130to perform the reading processing while scanning the carriage102.

At S13, the CPU901sets median adjustment values for the fine adjustment pattern based on the image read at S12. Here, the median adjustment value is a value equivalent to a median value of the print positions in the 13 patches for the same adjustment item in the fine adjustment pattern. Specifically, an average value of the amounts of misalignment between the edge positions of the patches in the patch row2007in the X direction and the edge positions of the patches in the patch row2008in the X direction is obtained. Then, the print position in the forward and backward scans for correcting this amount of misalignment is set as the median adjustment value for cyan in the first pattern1800. In addition, at S13, the CPU901sets the median adjustment values for the second pattern1801based on the edge positions in the patch row2007and the patch row2008. Further, the CPU901sets the median adjustment values for the third pattern1802based on the edge positions of the patch groups of the different colors.

At S14, the CPU901prints the adjustment pattern for fine adjustment, that is, the first pattern1800, the second pattern1801, and the third pattern1802based on the median adjustment values set at S13.

At S15, the CPU901measures the optical density of each of the patches included in the first pattern1800, the second pattern1801, and the third pattern1802by using the reflection-type optical sensor130.

At S16, the CPU901determines the adjustment value of the print position for each of the aforementioned items based on the optical densities of the patches obtained at S15.

At S17, the CPU901stores the adjustment values determined at S16in the ROM902in association with the respective adjustment items. This processing is completed at the end of this step.

The adjustment values stored at S17are used afterwards to print actual images and enable the printing apparatus1to output images without print position misalignment.

The execution of the coarse adjustment processing prior to the fine adjustment processing as in the present embodiment makes it possible to reduce the adjustment range, that is, the number of patches actually printed on a print medium in the fine adjustment processing. For this reason, even if a print head having a large variation of the print position misalignment is used, the print positions can be adjusted appropriately only by printing a predetermined number of patches.

Although the adjustment pattern in the first embodiment described with reference toFIG.16is used above for the fine adjustment processing, the adjustment pattern for fine adjustment may be the adjustment pattern in the second embodiment described with reference toFIG.17as a matter of course.

Fourth Embodiment

In the above embodiments, two patches with different shift amounts are arranged within the 6 mm areas on both sides of each platen rib1303symmetrically in the right-left direction in order that the variation of the head-to-paper distance can be kept within 100 μm. In contrast to this, the patches in the present embodiment are arranged at positions that can coincide with the sampling cycles of the reflection-type optical sensor130while satisfying the condition that the positions should be within the 6 mm areas on both sides.

FIGS.20A and20Bare diagrams for comparing the print positions of the patches in the present embodiment with the print positions in the aforementioned embodiments.FIG.20Aillustrates the patch print positions without consideration of the sampling cycles andFIG.20Billustrates the patch print positions in the present embodiment in consideration of the sampling cycles.FIGS.20A and20Billustrate enlarged views of the platen ribs1303of R6and R7and patches1404to1407printed around these platen ribs1303.

A lower portion ofFIG.20Bindicates sampling timings2200of the reflection-type optical sensor130that moves in the X direction at a predetermined velocity. A region where the reflection-type optical sensor130moves within a period of pulse application is each of sampling sections2201to2206.

For example, in the sampling section2201, the spot diameter of the reflection-type optical sensor130moves from2207to2208, and this movement region is a sampling region. In the sampling section2202, the spot diameter of the reflection-type optical sensor130moves from2209to2210, and this movement region is a sampling region. The sampling regions in the sampling section2201and the sampling section2202are located at positions approximately symmetric with respect to the platen rib1303of R6.

However, the sampling cycles of the reflection-type optical sensor130are not synchronized with the positions where the platen ribs1303are arranged. For example, the sampling regions in the sampling section2205and the sampling section2206are not located at positions symmetric with respect to the platen rib1303of R7.

For this reason, inFIG.20Ain which two patches are printed symmetrically in the right-left direction with respect to each platen rib1303without consideration of the sampling cycles, the sampling regions protrude from the patches. In this case, the detection accuracy of the reflection-type optical sensor130may decrease.

To avoid this situation, the sampling timings of the reflection-type optical sensor130may not be set in fixed cycles but may be set according to the positions where the platen ribs1303are arranged. In this case, however, a new electric circuit, memory capacity, and firmware processing time are required, which causes an increase in cost.

For this reason, in the present embodiment, each of the patches is shifted to a position including the sampling region with a limitation of the 6 mm area on either side of the corresponding platen rib1303while the sampling cycles of the reflection-type optical sensor130are kept constant. Specifically, as illustrated inFIG.20B, two patches1406and1407in the vicinity of the platen rib1303of R7are arranged to include the sampling regions in the two sampling sections2205and2206closest to the platen rib1303of R7. As a result, in the case ofFIG.20B, the two patches1406and1407are not arranged symmetric with respect to the platen rib1303of R7, but are shifted to the right by approximately 0.2 mm with respect to the platen rib1303. Even in such a situation, the two patches are confined to the 6 mm areas on both sides of the platen rib1303. Thus, it is possible to perform the print position adjustment mode with high accuracy while keeping the variation of the head-to-paper distance within 100 μm.

In sum, according to the present embodiment, it is possible to perform the print position adjustment mode with high accuracy while keeping the sampling cycles of the reflection-type optical sensor130constant and saving consumption of print media.

Fifth Embodiment

A degree of unevenness on a print medium P varies depending on various conditions such as the type of the print medium, an environment temperature, and an environment humidity. In other words, an area where the patch can be arranged is not limited to the 6 mm area from the platen rib1303but is also adjustable depending on the above conditions. The present embodiment intends to change the number of patches arranged in the vicinity of the platen rib1303in the adjustment pattern as appropriate.

FIGS.21A to21Care diagrams for explaining processing of setting the number of patches. In this processing, N same test patches are printed above one platen rib1303and on both sides of this platen rib1303as illustrated inFIG.21A. The N test patches are the same as the patch described with reference toFIG.8, and are printed according to the adjustment value set at this time point.FIG.21Bis a top view of the N test patches. Here, N is 5 and the test patches 1 to 5 are illustrated.

Next, the optical density of each of the test patches is measured by using the reflection-type optical sensor130. In this example, it is assumed that the optical densities as illustrated inFIG.21Care obtained. The test patch 3 above the platen rib1303where no print position misalignment occurs has the highest density, and the density of the test patch becomes lower as the distance from the platen rib1303increases.

In the present embodiment, a density difference ΔD corresponding to a tolerable range of print position misalignment is determined in advance and patches can be printed only at positions corresponding to test patches each having a density difference ΔD or less in the actual print position adjustment mode. In the case ofFIG.21C, patches can be arranged at three areas corresponding to the test patches 2 to 4.

FIGS.22A and22Bare diagrams illustrating how patches are printed in the X direction in the print position adjustment mode of the present embodiment.FIG.22Adepicts an overall view in the X direction andFIG.22Bdepicts an enlarged view of an area around the platen rib1303of R4. Here, an adjustment pattern for adjusting the print positions in the forward scan and the print positions in the backward scan by using a print medium P in A4 size is illustrated as an example. Regarding each of the platen ribs1303of R4to R7, three patches2401to2403each having a width of 4.7 mm are arranged next to each other with the platen rib1303centered. The positions of these three patches are included in an area around the position of the platen rib1303where the print position misalignment due to the variation of the head-to-paper distance is confirmed sufficiently small. Therefore, the print position misalignment is within the tolerable range, and the favorable print position adjustment can be performed.

In the adjustment pattern ofFIG.22A, the width in the X direction for printing the same numbers of patches is narrower than in the adjustment pattern inFIG.15A. For this reason, in the print position adjustment mode using the adjustment pattern inFIG.22A, the movement range of the carriage is narrower than in the case of using the adjustment pattern inFIG.15A, so that the mode itself can be completed within a shorter time. In addition, if the patches are shifted as a whole to the center (the left side inFIG.22A) in the adjustment pattern inFIG.22A, a print medium in a size smaller than A4 can be used. This also makes it possible to further save consumption of print media.

OTHER EMBODIMENTS

In the embodiments described above, the description is given on the assumption that the print medium P in A4 size is used. Instead, needless to say, the adjustment patterns described in the above embodiments may be also printed on print media larger than the A4 size.

FIGS.23A and23Bare diagrams illustrating cases where the pattern inFIG.18is printed on a print medium P in A4 size and a print medium P′ in A3 size. In each ofFIGS.23A and23B, an alternate long and short dash line corresponds to an area supported by the platen rib1303of R7in the course of conveying a print medium P.

As described above, the printing apparatus1in the above embodiments conveys a print medium P with the center of the print medium P aligned with the center line1305of the printable region W irrespective of the size of the print medium used. For this reason, in the print position adjustment mode, the relative positional relation between the patches included in the adjustment pattern and the platen ribs1303is stable irrespective of the size of a print medium. In sum, use of a print medium in a predetermined size or larger in the print position adjustment mode makes it possible to perform stable print position adjustment while avoiding a variation of the adjustment accuracy.

This application claims the benefit of Japanese Patent Application No. 2019-236668 filed Dec. 26, 2019, which is hereby incorporated by reference wherein in its entirety.