Printing method, feasibility determination method, and printing system

Abstract

This prevents misidentification of impact errors caused by factors that are difficult to correct as Bi-D errors. [Solution] A method for printing a test pattern in a printing unit 2 capable of performing forward scanning, in which pigment ink is ejected onto the paper S while the print head 6 is moved forward along the main scanning direction, and return scanning, in which pigment ink is ejected onto the paper S while the print head 6 is moved back along the main scanning direction. The test pattern 31 is a density pattern having solid areas. The test pattern 31 includes at least one forward patch ja formed with the forward scanning, at least one return path patch jb formed with the return scanning, and at least one return path patch jb formed with both forward and return scanning.

Description

Technical Field

[0001] The present invention relates to a printing method, an acceptance determination method, and a printing system.

Background Art

[0002] Patent Document 1 discloses a technique for correcting a difference in landing position deviation amount in a main scanning direction in an inkjet recording apparatus. Specifically, in order to correct the landing position deviation in the main scanning direction, a plurality of patterns in which the ejection timings of the forward path and the return path are gradually different are recorded near both ends in the main scanning direction of the recording medium.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above Patent Document 1, only the elimination of the landing error between the forward and return paths is assumed, and it is impossible to cope with the landing error that occurs due to factors that are difficult to correct. In some cases, as a result of misidentifying the landing error that occurs due to factors that are difficult to correct as a Bi-D error and performing correction, there is a risk of causing inverse correction that promotes density unevenness.

Means for Solving the Problems

[0005] A forward path scan in which a liquid is ejected onto a medium while moving a print head along a forward path in a main scanning direction, A return path scan in which the liquid is ejected onto the medium while moving the print head along the return path in the main scanning direction, which is a method for printing a test pattern in a printing apparatus capable of executing, The test pattern is a density pattern having a solid area, The test pattern includes at least one forward patch formed during the forward scan, at least one return patch formed during the return scan, and at least one round-trip patch formed during the forward and return scans. Printing instructions are provided.

[0006] Forward scanning involves discharging liquid onto the medium while moving the print head along the main scanning direction, A printing system including a printing apparatus capable of performing a return scan, in which the print head is moved back along the main scanning direction while the liquid is discharged onto the medium, The printing apparatus is configured to form a test pattern which is a density pattern having solid areas, The test pattern includes at least one forward patch formed during the forward scan, at least one return patch formed during the return scan, and at least one round-trip patch formed during the forward and return scans. A printing system will be provided. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of the printing system. (First Embodiment) [Figure 2] This is a schematic diagram of the hardware configuration of the control unit. (First Embodiment) [Figure 3] This is a functional block diagram of the control unit. (First Embodiment) [Figure 4] This is an example of a test pattern image. (First Embodiment) [Figure 5] This is the control flow of the printing system. (First Embodiment) [Figure 6] This is an explanatory diagram for determining whether something is acceptable or not. (First Embodiment) [Figure 7] This shows an example where concentration fluctuations occurred in a similar manner between patches of the same type. (First Embodiment) [Figure 8]This shows an example where concentration fluctuations occurred in different ways among patches of the same type. (First Embodiment) [Figure 9] This shows an example where concentration fluctuations occurred in different ways among patches of the same type. (First Embodiment) [Figure 10] This is an example of a test pattern image. (Second Embodiment) [Figure 11] This is an example of a test pattern image. (Third Embodiment) [Figure 12] This is an example of a test pattern image. (Fourth embodiment) [Figure 13] This is an example of a test pattern image. (Fifth embodiment) [Modes for carrying out the invention]

[0008] The present invention will be described below through embodiments of the invention, but the invention claimed is not limited to the following embodiments. Furthermore, not all of the configurations described in the embodiments are necessarily essential as means of solving the problem. For clarity of explanation, the following descriptions and drawings have been omitted and simplified as appropriate. In each drawing, the same elements are denoted by the same reference numerals, and redundant explanations have been omitted where necessary.

[0009] In the following embodiments, the description will be divided into multiple sections or embodiments where necessary for convenience. Unless otherwise specified, these are not unrelated, and one may be a modification, application, detailed explanation, or supplementary explanation of part or all of the other. Furthermore, in the following embodiments, when referring to the number of elements (including number, numerical value, quantity, and range), unless otherwise specified or clearly limited to a specific number in principle, it is not limited to that specific number, and may be greater than or less than that number.

[0010] Furthermore, in the following embodiments, the components (including operation steps, etc.) are not necessarily essential unless explicitly stated or considered to be clearly essential in principle. Similarly, in the following embodiments, when referring to the shape, positional relationship, etc. of components, etc., it shall include those substantially approximated or similar to the shape, etc., unless explicitly stated and unless it is clearly not so in principle. The same applies to the above numbers (including the number, numerical value, quantity, and range).

[0011] (First Embodiment) Hereinafter, the printing system 1 will be described with reference to FIGS. 1 to 9. FIG. 1 shows a schematic diagram of the printing system 1. As shown in FIG. 1, the printing system 1 includes a printing unit 2, a reading unit 3, and a control unit 4. The printing unit 2 is a specific example of a printing device. The reading unit 3 is a specific example of a reading device. In the present embodiment, the printing system 1 is a multifunction device integrally including the printing unit 2 and the reading unit 3. However, instead of this, the printing unit 2 and the reading unit 3 may be configured as separate devices.

[0012] The printing unit 2 includes a print head 6 having a plurality of nozzle arrays 5 composed of a plurality of nozzles, a carriage 7 holding the print head 6, a carriage guide 8 that linearly reciprocally guides the carriage 7, an endless belt 9 coupled to the carriage 7, a pair of pulleys 10 that support the endless belt 9 so as to be able to run, and a carriage motor 11 that rotates one of the pulleys 10.

[0013] The printing unit 2 further includes a conveyance roller 12 rotatably supported while contacting the paper S, and a conveyance motor 13 that rotates the conveyance roller 12.

[0014] Here, the main scanning direction and the sub-scanning direction are defined.

[0015] The main scanning direction is the direction in which the carriage 7 moves back and forth. The main scanning direction includes a forward path, which is the direction away from the carriage 7's standby location (not shown), and a return path, which is the direction towards the standby location. The main scanning direction typically coincides with the width direction of the paper S. Hereinafter, the two ends in the width direction of the paper S that are relatively close to the carriage 7's standby location will be referred to as the HOME side end SH, and the end that is relatively far from the carriage 7's standby location will be referred to as the FULL side end SF.

[0016] The sub-scanning direction is perpendicular to the main scanning direction. The sub-scanning direction is parallel to the paper transport direction S.

[0017] Paper S is one specific example of a medium. The medium is not limited to paper; it may be any material such as cloth or resin film.

[0018] The printing unit 2 is a so-called serial inkjet printer that, based on commands from the control unit 4, transports the paper S in the sub-scanning direction and prints by ejecting liquid from multiple nozzle rows 5 onto the paper S while moving the print head 6 back and forth in the main scanning direction.

[0019] In this embodiment, the plurality of nozzle rows 5 include, for example, a first nozzle row 5a, a second nozzle row 5b, a third nozzle row 5c, and a fourth nozzle row 5d. The first nozzle row 5a, the second nozzle row 5b, the third nozzle row 5c, and the fourth nozzle row 5d are all formed to extend in the sub-scanning direction. The first nozzle row 5a, the second nozzle row 5b, the third nozzle row 5c, and the fourth nozzle row 5d are arranged apart from each other in the main scanning direction. The first to fourth nozzle rows 5d all eject pigment ink. The pigment ink contains at least a pigment and water. The pigment contained in the pigment ink can be, for example, color pigments such as cyan, magenta, yellow, and black, or spot pigments such as white and pearl. In this embodiment, the first nozzle row 5a ejects cyan color pigment. The second nozzle row 5b ejects magenta color pigment. The third nozzle row 5c dispenses yellow color pigment. The fourth nozzle row 5d dispenses black color pigment. Cyan color pigment is a specific example of the first colored liquid. Magenta color pigment is a specific example of the second colored liquid. The first nozzle row 5a is a specific example of the first nozzle row. The second nozzle row 5b is a specific example of the second nozzle row.

[0020] There are two types of printing methods: bidirectional printing and unidirectional printing. Hereafter, moving the print head 6 once in the main scanning direction will be referred to as one pass (abbreviated as 1 pass). The printing unit 2 in this embodiment employs the bidirectional printing method.

[0021] In the bidirectional printing method described above, the printing unit 2 moves the print head 6 forward while ejecting liquid from the print head 6 to form a partial image on the paper S corresponding to the bandwidth of the first pass. Next, the printing unit 2 performs a movement process to move the paper S by the bandwidth in the sub-scanning direction, and while moving the print head 6 back, ejects liquid from the print head 6 to form a partial image on the paper S corresponding to the bandwidth of the second pass. Thereafter, ejecting liquid onto the paper S while moving the print head 6 forward along the main scanning direction is called forward scanning, and ejecting liquid onto the paper S while moving the print head 6 back along the main scanning direction is called back scanning. Thereafter, the printing unit 2 repeats forward scanning and back scanning until the desired image is formed on the paper S. On the other hand, the unidirectional printing method described above is a method that forms the desired image on the paper S using only either forward scanning or back scanning.

[0022] The reading unit 3 is located downstream of the printing unit 2 in the paper transport direction and, based on commands from the control unit 4, reads the recording surface of the paper S ejected from the printing unit 2 and outputs the reading data to the control unit 4. The reading unit 3 is typically a CIS (Contact Image Sensor) or a CCD (Charge Coupled Device).

[0023] Figure 2 is a schematic diagram of the hardware configuration of the control unit 4. As shown in Figure 2, the control unit 4 includes a processor 4a, memory 4b, communication interface 4c, LCD 4d (Liquid Crystal Display), and input interface 4e.

[0024] The processor 4a has access to memory 4b. The processor 4a communicates with external devices, such as a personal computer, via a communication interface 4c. The processor 4a reads and executes programs stored in memory 4b. In this way, the processor 4a functions as multiple functional units that perform various functions using hardware such as the processor 4a.

[0025] LCD4d is an example of an output device. Input interface 4e is an example of an input device. Input interface 4e typically consists of a touch panel superimposed on LCD4d.

[0026] Figure 3 is a functional block diagram of the control unit 4. As shown in Figure 3, the control unit 4 includes the following multiple functional units: a print image data storage unit 20, a test pattern image data storage unit 21, a print execution unit 22, a read execution unit 23, a pass / fail determination unit 24, an output unit 25, and a density correction data generation unit 26.

[0027] The print image data storage unit 20 stores print image data input from an external device via the communication interface 4c. Typically, the print image data defines the operation of the print unit 2 for each pass.

[0028] The test pattern image data storage unit 21 stores test pattern image data that shows a test pattern image for testing the operation of the printing unit 2.

[0029] The print execution unit 22 selectively executes either the normal print mode or the test mode.

[0030] When the print execution unit 22 is executing the normal print mode, it controls the print unit 2 based on the print image data stored in the print image data storage unit 20 to form a print image on the paper S.

[0031] In response, when the print execution unit 22 executes the test mode, it controls the print unit 2 based on the test pattern image data stored in the test pattern image data storage unit 21 to form a test pattern image on the paper S. The test mode is typically performed during maintenance work on the print system 1. However, it is not limited to this, and the test mode may also be performed during the manufacturing process of the print system 1.

[0032] The test pattern image 30 in this embodiment will now be described with reference to Figure 4. In Figure 4, the paper transport direction S is shown as the paper transport direction. As shown in Figure 4, the test pattern image 30 includes a plurality of test patterns 31. The plurality of test patterns 31 are arranged without gaps in the sub-scanning direction. In this embodiment, the plurality of test patterns 31 include a cyan test pattern 31a, a magenta test pattern 31b, a yellow test pattern 31c, and a black test pattern 31d. The cyan test pattern 31a, magenta test pattern 31b, yellow test pattern 31c, and black test pattern 31d are arranged in the sub-scanning direction, specifically from the top edge SU of the paper to the bottom edge SD of the paper, in this order.

[0033] Cyan test pattern 31a is an example of the first test pattern. Magenta test pattern 31b is an example of the second test pattern. Yellow test pattern 31c is an example of the third test pattern. Black test pattern 31d is an example of the fourth test pattern.

[0034] The cyan test pattern 31a is formed by the ejection of cyan color pigment from the first nozzle row 5a. The magenta test pattern 31b is formed by the ejection of magenta color pigment from the second nozzle row 5b. The yellow test pattern 31c is formed by the ejection of yellow color pigment from the third nozzle row 5c. The black test pattern 31d is formed by the ejection of black color pigment from the fourth nozzle row 5d.

[0035] Each test pattern 31 is a density pattern with a solid area. That is, each test pattern 31 is not a line-like pattern formed as thinly as possible to measure the deviation of the impact position, but rather a pattern formed with a certain area and having a uniform density.

[0036] The test pattern image 30 is not limited to containing multiple test patterns 31, but may consist of only one test pattern 31. The multiple test patterns 31 are not limited to being arranged without gaps in the sub-scanning direction, but may be arranged with gaps between them.

[0037] Each test pattern 31 is formed over the entire area of ​​the paper S in the main scanning direction, from the HOME side edge SH to the FULL side edge SF. However, it is not limited to this, and each test pattern 31 may be formed slightly away from the HOME side edge SH, or slightly away from the FULL side edge SF.

[0038] Each test pattern 31 has the same configuration. The configuration of the test pattern 31 will be described in detail below with reference to the cyan test pattern 31a. The test pattern 31 includes a plurality of pattern units p. The plurality of pattern units p are arranged without gaps in the main scanning direction. In this embodiment, the plurality of pattern units p include a first pattern unit p1, a second pattern unit p2, a third pattern unit p3, a fourth pattern unit p4, and a fifth pattern unit p5. The first pattern unit p1, the second pattern unit p2, the third pattern unit p3, the fourth pattern unit p4, and the fifth pattern unit p5 are arranged in this order from the HOME side end SH toward the FULL side end SF. Therefore, the first pattern unit p1 can also be called the HOME side unit, which is located on the HOME side. Similarly, the fifth pattern unit p5 can also be called the FULL side unit, which is located on the FULL side, and the third pattern unit p3 can also be called the central unit, which is located in the center.

[0039] Each pattern unit p contains multiple patches j. Each patch j contains a forward patch ja, a round-trip patch jb, and a return patch jc. The forward patch ja, round-trip patch jb, and return patch jc are arranged without gaps in the main scanning direction. The forward patch ja, round-trip patch jb, and return patch jc are arranged in this order from the HOME side end SH to the FULL side end SF.

[0040] The forward path patch ja is a patch formed during the forward path scan. That is, the forward path patch ja is formed during the forward path scan. The return path patch jb is a patch formed during both the forward and return path scans. That is, the return path patch jb is formed through the cooperation of the forward and return path scans. The return path patch jc is a patch formed during the return path scan. That is, the return path patch jc is formed during the return path scan. Therefore, during the forward path scan, liquid is discharged into the areas corresponding to the forward path patch ja and the return path patch jb, and during the return path scan, liquid is discharged into the areas corresponding to the return path patch jc and the return path patch jb.

[0041] Returning to Figure 3, the print execution unit 22 may also hold density correction data 22a. If the print execution unit 22 holds density correction data 22a, it corrects the print image data based on the density correction data 22a and performs printing based on the corrected print image data.

[0042] The reading execution unit 23 controls the reading unit 3 to read the recording surface of the paper S printed by the printing unit 2 at a predetermined resolution and generate reading data.

[0043] The pass / fail determination unit 24 analyzes the read data to determine whether or not there is a significant density fluctuation in the test pattern image 30 printed on the paper S, and if there is a significant density fluctuation, whether or not density correction is possible to eliminate the density fluctuation. In this specification, density fluctuation means fluctuations in density in the sub-scanning direction. Details, including the criteria for distinguishing between significant and non-significant density fluctuations, will be described later.

[0044] The output unit 25 outputs the result of the pass / fail determination unit 24 to the LCD 4d.

[0045] The density correction data generation unit 26 generates density correction data to eliminate the significant density fluctuations detected by the pass / fail determination unit 24, and stores the generated density correction data as density correction data 22a in the print execution unit 22.

[0046] Next, the operation of the printing system 1 will be explained with reference to Figure 5. Figure 5 shows the control flow of the printing system 1.

[0047] As shown in Figure 5, first, the print execution unit 22 determines whether the print mode input via the input interface 4e is the normal print mode or the test mode (S100). If the input print mode is the normal print mode, the print execution unit 22 executes the normal print mode (S110) and terminates the process.

[0048] In contrast, when the input print mode is test mode, the print execution unit 22 executes the test mode (S120). Specifically, as shown in Figure 4, the print execution unit 22 sequentially forms a cyan test pattern 31a on the paper S (S120a), a magenta test pattern 31b on the paper S (S120b), a yellow test pattern 31c on the paper S (S120c), and a black test pattern 31d on the paper S (S120d). Note that the order in which steps S120a to S120d are executed does not particularly affect the present invention and can be performed in any order.

[0049] Next, the reading execution unit 23 controls the reading unit 3 to read the recording surface of the paper S printed by the printing unit 2 at a predetermined resolution and generate reading data (S130).

[0050] Next, the pass / fail determination unit 24 analyzes the read data to determine whether or not there is a significant density variation in the test pattern image 30 printed on the paper S, and if there is a significant density variation, whether or not it is possible to correct the density to eliminate the density variation (S140).

[0051] First, referring to Figure 6, the pass / fail determination unit 24 quantifies the density distribution c(y) of each patch j in the sub-scanning direction and determines whether or not there is a significant density fluctuation based on the amplitude of the density distribution c(y) (S140a). Figure 6 shows the process of quantifying the density distribution c(y) of patch j in the sub-scanning direction. Figure 6(a) shows the pixel section of patch j, and Figure 6(b) shows the density distribution c(y) of patch j in the sub-scanning direction. As shown in Figure 6(a), the upper left corner of patch j is taken as the origin, and the X-axis along the main scanning direction and the Y-axis along the sub-scanning direction are defined. If the number of pixels in the main scanning direction of patch j is x1 and the number of pixels in the sub-scanning direction is y1, then the density distribution c(y) of patch j in the sub-scanning direction is calculated by the following equation (1). In the following equation (1), density Q is the density of the corresponding pixel.

[0052]

number

[0053] Density Q is calculated based on RGB values ​​if the read data has RGB values ​​for each pixel. On the other hand, if the read data has Lab values ​​for each pixel, density Q is calculated based on Lab values.

[0054] Next, the pass / fail determination unit 24 calculates the average value of the density distribution c(y) in the sub-scanning direction of patch j, known as cave.

[0055] Next, the pass / fail determination unit 24 sets a first threshold Cth1 that is 20% on the darker side of the average value cave, a second threshold Cth2 that is 10% on the darker side of the average value cave, a third threshold Cth3 that is 10% on the lighter side of the average value cave, and a fourth threshold Cth4 that is 20% on the lighter side of the average value cave. For example, if the average value cave is 125, the first threshold Cth1 that is 20% on the darker side of the average value cave will be 140, which is 120% of 125. Similarly, for each patch j, the pass / fail determination unit 24 determines the concentration distribution c(y), the average value cave, and the fourth threshold Cth4 from the first threshold Cth1.

[0056] Furthermore, if the density distribution c(y) in all patches j constituting the test pattern image 30 falls between the second threshold Cth2 and the third threshold Cth3, then it is defined that there is no significant density variation in the test pattern image 30. Conversely, if the density distribution c(y) in at least one of the multiple patches j constituting the test pattern image 30 does not fall between the second threshold Cth2 and the third threshold Cth3, then it is defined that there is a significant density variation in the test pattern image 30.

[0057] If the pass / fail determination unit 24 determines that there is no significant density variation in the test pattern image 30 (S140a, NO), it determines that uniform density correction can be performed across the entire sheet of paper and proceeds to step S150. In step S150, the output unit 25 outputs a message to the LCD 4d, for example, "Uniform density correction can be performed across the entire sheet of paper," and returns to step S100.

[0058] On the other hand, if the pass / fail determination unit 24 determines that there is a significant density variation in the test pattern image 30 (S140a, YES), it determines whether the significant density variation can be corrected (S140b). Below, the correctable and uncorrectable significant density variations will be explained in order.

[0059] <Significant concentration fluctuations that can be corrected> Significant concentration fluctuations that can be corrected are those that simultaneously satisfy the following conditions (a) and (b).

[0060] Condition (a): In all patches j constituting the test pattern image 30, the density distribution c(y) falls between the first threshold Cth1 and the fourth threshold Cth4. This is because an effective method for eliminating significant density fluctuations is to increase or decrease the number of times the liquid is applied to the paper S. However, this number of applications cannot be increased or decreased indefinitely; there is a certain upper limit. Therefore, significant density fluctuations that cannot be eliminated even when the upper limit of the acceptable number of applications is used cannot be corrected.

[0061] Condition (b): Density variations occur in a similar manner between patches j of the same type. Please refer to Figure 7. Figure 7 shows an example where density variations occur in a similar manner between patches j of the same type. Figure 7 shows a sheet of paper S in which significant density variations due to transport errors were observed. In Figure 7, the significant density variation appears as a faint streak L extending linearly parallel to the main scanning direction from the HOME side edge SH to the FULL side edge SF. In Figure 7, dashed lines are drawn above and below the streak L to identify it, but these dashed lines are drawn for explanatory purposes only and do not actually exist. This streak L is thought to be caused by a transport error. Here, transport error means the error in the amount of paper S fed. The amount of paper S fed is typically constant while printing is being performed on one sheet of paper S. However, if the transport roller 12 is eccentric, the relationship between the rotation angle of the transport roller 12 and the amount of paper fed is not constant, which can cause transport errors. As a result, it is thought that a uniform misalignment of the target in the sub-scanning direction occurs in the main scanning direction.

[0062] However, if concentration fluctuations occur in a similar manner between patches of the same type j, these concentration fluctuations can be eliminated by applying a correction value d(y) obtained by inverting the concentration distribution c(y) with respect to the mean value cave, as shown in Figure 6(c). That is, by increasing or decreasing the number of injections for each pass according to the correction value d(y), the concentration distribution c(y) can be brought closer to the mean value cave.

[0063] Here, significant density fluctuations caused by transport errors are due to the eccentricity of the transport roller 12, and therefore do not occur in exactly the same way each time the normal printing mode is executed. This is because the rotational angle position of the transport roller 12 at the start of printing changes each time. However, significant density fluctuations caused by transport errors appear with a certain degree of periodicity. For example, significant density fluctuations caused by transport errors that occur on the first sheet of paper S and significant density fluctuations caused by transport errors that occur on the thirteenth sheet of paper S can occur in exactly the same way. Also, significant density fluctuations caused by transport errors that occur on the second sheet of paper S and significant density fluctuations caused by transport errors that occur on the fourteenth sheet of paper S can occur in exactly the same way. Therefore, by measuring the periodicity of the appearance of significant density fluctuations caused by transport errors in advance and adjusting the number of printing cycles by shifting the correction value d(y) in the sub-transport direction in advance according to that period, significant density fluctuations caused by transport errors can be eliminated without any problems.

[0064] <Significant concentration fluctuations that cannot be corrected> Significant concentration fluctuations that cannot be corrected satisfy at least one of the following conditions (c) and (d).

[0065] Condition (c): In at least one of the multiple patches j that make up the test pattern image 30, the concentration distribution c(y) does not fall between the first threshold Cth1 and the fourth threshold Cth4. The reason is as described above.

[0066] Condition (d): This refers to cases where concentration fluctuations occur in different ways among patches j of the same type. Please refer to Figures 8 and 9. Figures 8 and 9 show examples where concentration fluctuations occur in different ways among patches j of the same type. Figure 8 shows a sheet of paper S in which significant concentration fluctuations were observed due to transport skew. Figure 9 shows a sheet of paper S in which significant concentration fluctuations were observed due to carriage attitude fluctuations.

[0067] In Figure 8, a significant density fluctuation caused by transport skew appears as a faint streak M extending hourglass-shaped along the main scanning direction from the HOME side edge SH to the FULL side edge SF. In Figure 8, dashed lines are drawn above and below the streak M to identify it, but these are drawn for illustrative purposes only and do not actually exist. Here, transport skew refers to the tilt of the paper's orientation S. Preferably, the orientation of the paper S remains constant while printing is being performed on a single sheet of paper S. However, if local slippage occurs between the transport roller 12 and the paper S, the feed amount at the HOME side edge SH and the feed amount at the FULL side edge SF of the paper S do not match, which can cause transport skew. In this case, the impact position at the HOME side edge SH and the FULL side edge SF is shifted in the sub-transport direction, so the streak M tends to appear thicker as it approaches the HOME side edge SH or the FULL side edge SF. If transport skew occurs simultaneously with transport error, the muscle M may appear to gradually thicken from the HOME end SH towards the FULL end SF, or from the FULL end SF towards the HOME end SH.

[0068] As described above, if density fluctuations occur in different ways among the multiple forward-path patches ja included in the test pattern 31, these density fluctuations cannot be eliminated by correction because there is no correction value d(y) that can be uniformly applied in the main scanning direction. Similarly, if density fluctuations occur in different ways among the multiple return-path patches jb included in the test pattern 31, these density fluctuations cannot be eliminated by correction because there is no correction value d(y) that can be uniformly applied in the main scanning direction. Similarly, if density fluctuations occur in different ways among the multiple return-path patches jc included in the test pattern 31, these density fluctuations cannot be eliminated by correction because there is no correction value d(y) that can be uniformly applied in the main scanning direction.

[0069] In Figure 9, a significant concentration fluctuation caused by the attitude change of carriage 7 appears as a faint muscle N concentrated only in the round-trip patch jb. In Figure 9, a dashed line is drawn above and below muscle N to identify it, but this dashed line is drawn for explanatory purposes only and does not actually exist. As shown in Figure 9, the significant concentration fluctuation caused by the attitude change of carriage 7 appears only in the round-trip patch jb and not in the other patches j (forward patch ja, return patch jc). Here, the attitude change of carriage 7 mainly means that the carriage 7 tilts at a specific location due to debris adhering to the carriage guide 8 that guides the carriage 7, or damage to the carriage guide 8. Such tilting of the carriage 7's attitude occurs in opposite directions on the forward and return journeys. Therefore, the significant concentration fluctuation caused by the attitude change of carriage 7 does not appear in the forward patch ja or the return patch jc, but only in the round-trip patch jb.

[0070] When density fluctuations occur in different ways among the multiple round-trip patch jb included in the test pattern 31, as described above, there is no correction value d(y) that can be uniformly applied in the main scanning direction, so these density fluctuations cannot be eliminated by correction.

[0071] Returning to Figure 5, if in step S140b it is determined that the significant density fluctuations that appeared in the test pattern image 30 are correctable (S140b: YES), the density correction data generation unit 26 generates a correction value d(y) as density correction data (S160), saves the generated density correction data as density correction data 22a for the print execution unit 22, and the output unit 25 outputs a message to the LCD 4d, for example, "Correctable density fluctuations have been detected. Processing to correct density fluctuations will be performed in subsequent prints." (S170), and returns the process to step S100.

[0072] On the other hand, if in step S140b it is determined that the significant density fluctuations that appeared in the test pattern image 30 are uncorrectable (S140b: NO), the output unit 25 outputs a message to the LCD 4d, for example, "Uncorrectable density fluctuations detected." (S180), and returns the process to step S100.

[0073] The first embodiment has been described above. The first embodiment has the following features.

[0074] In other words, the printing method for a test pattern in a printing unit 2 (printing device) capable of performing a forward scan, in which pigment ink (liquid) is ejected onto the paper S (medium) while the print head 6 moves forward along the main scanning direction, and a return scan, in which pigment ink is ejected onto the paper S while the print head 6 moves back along the main scanning direction, has the following characteristics. As shown in Figure 4, the test pattern 31 is a density pattern having solid areas. The test pattern 31 includes at least one forward patch ja formed with the forward scan, at least one return path patch jb formed with the return scan, and at least one return path patch jb formed with both the forward and return scans. With this configuration, there is no misidentification of impact errors caused by factors that are difficult to correct as Bi-D errors, and therefore no inverse correction that exacerbates density unevenness is performed. In addition, the cause of significant density fluctuations can be isolated depending on which patch the significant density fluctuation occurred in.

[0075] Furthermore, as shown in Figure 4, at least one forward patch ja, at least one return patch jb, and at least one return patch jb are aligned in the main scanning direction. With this configuration, the size of the test pattern 31 in the sub-scanning direction can be made compact, thus reducing the printing time of the test pattern 31.

[0076] Furthermore, as shown in Figure 4, the test pattern 31 is formed over the entire area of ​​the paper S in the main scanning direction. With this configuration, any significant density fluctuation can be detected regardless of where in the main scanning direction it occurs.

[0077] Furthermore, as shown in Figure 5, the above printing method further includes reading the test pattern 31 formed on the paper S (S130), determining whether density correction is possible based on the reading result (S140), and outputting the determination result (S150, S170, S180). With this configuration, the operator can determine whether density correction is possible.

[0078] Furthermore, the print head 6 has a first nozzle row 5a (first nozzle row) capable of ejecting cyan color pigment, and a second nozzle row 5b (second nozzle row) positioned differently from the first nozzle row 5a and capable of ejecting magenta color pigment (second colored liquid), which is a different color from the cyan color pigment. The above printing method includes forming a cyan test pattern 31a (first test pattern) as a test pattern 31 using the first nozzle row 5a, and forming a magenta test pattern 31b (second test pattern) as a test pattern 31 at a different position in the sub-scanning direction relative to the cyan test pattern 31a using the second nozzle row 5b. With the above configuration, the amount of color pigment consumed can be distributed. Also, significant density fluctuations can be reliably detected regardless of the detection sensitivity of each color of the reading unit 3. Furthermore, since the presence or absence of significant density fluctuations can be determined for each nozzle row 5, it is conceivable, for example, to generate different correction values ​​d(y) for each nozzle row 5.

[0079] Furthermore, the method for determining whether concentration correction is possible using the above test pattern 31 has the following characteristics: At least one forward patch ja includes multiple forward patches ja. At least one return patch jc includes multiple return patches jc. At least one round-trip patch jb includes multiple round-trip patches jb. As shown in Figure 7, if concentration fluctuations occur in a similar manner between patches j of the same type, concentration correction is possible. As shown in Figures 8 and 9, if concentration fluctuations occur in different manner between patches j of the same type, it is determined that concentration correction is not possible. With the above configuration, it is possible to avoid mistaking concentration unevenness caused by factors that make concentration correction difficult for other factors and performing reverse correction.

[0080] (Second Embodiment) A second embodiment of this disclosure will be described below with reference to Figure 10. The following description will focus on the differences between this embodiment and the first embodiment, omitting any redundant explanations.

[0081] In the first embodiment described above, as shown in Figure 4, the multiple pattern units p are arranged without gaps in the main scanning direction.

[0082] In contrast, in this embodiment, as shown in Figure 10, the multiple pattern units p are arranged with gaps between them in the main scanning direction. That is, the multiple pattern units p include the first pattern unit p1, the third pattern unit p3, and the fifth pattern unit p5, while the second pattern unit p2 and the fourth pattern unit p4 are omitted. The first pattern unit p1 and the third pattern unit p3 are positioned apart from each other in the main scanning direction, and similarly, the third pattern unit p3 and the fifth pattern unit p5 are also positioned apart from each other in the main scanning direction.

[0083] With the above configuration, the area of ​​the test pattern image 30 is reduced, thereby lowering the consumption of pigment ink, and significant density fluctuations caused by transport errors, transport skew, and changes in the attitude of the carriage 7 can be captured without problems.

[0084] (Third embodiment) A third embodiment of this disclosure will be described below with reference to Figure 11. The following description will focus on the differences between this embodiment and the first embodiment, omitting any redundant explanations.

[0085] In the first embodiment described above, as shown in Figure 4, the multiple round-trip patches jb of the cyan test pattern 31a, the multiple round-trip patches jb of the magenta test pattern 31b, the multiple round-trip patches jb of the yellow test pattern 31c, and the multiple round-trip patches jb of the black test pattern 31d are arranged to be adjacent to each other in the sub-scanning direction and to form a row extending along the sub-scanning direction.

[0086] In contrast, in this embodiment, as shown in Figure 11, the multiple round-trip patches jb of the cyan test pattern 31a, the multiple round-trip patches jb of the magenta test pattern 31b, the multiple round-trip patches jb of the yellow test pattern 31c, and the multiple round-trip patches jb of the black test pattern 31d are formed at different positions in the main scanning direction.

[0087] Specifically, the multiple round-trip patches jb of the cyan test pattern 31a are arranged at a constant pitch in the main scanning direction. Similarly, the multiple round-trip patches jb of the magenta test pattern 31b are arranged at a constant pitch in the main scanning direction. However, the multiple round-trip patches jb of the magenta test pattern 31b are shifted toward the FULL end SF side than the multiple round-trip patches jb of the cyan test pattern 31a, and as a result, the multiple round-trip patches jb of the magenta test pattern 31b are not adjacent to any of the multiple round-trip patches jb of the cyan test pattern 31a in the sub-scanning direction. The round-trip patches jb of the magenta test pattern 31b are adjacent to the return-trip patches jc of the cyan test pattern 31a in the sub-scanning direction. The same relationship holds between the magenta test pattern 31b and the yellow test pattern 31c, and between the yellow test pattern 31c and the black test pattern 31d. As a result, the multiple round-trip patch jb in the cyan test pattern 31a, the magenta test pattern 31b, the yellow test pattern 31c, and the black test pattern 31d are arranged diagonally with respect to the sub-scanning direction, moving from the top edge SU of the paper towards the bottom edge SD and approaching the FULL side edge SF. As a result, when viewed along the main scanning direction, the round-trip patch jb appears without exception in at least one of the test patterns 31 between the HOME side edge SH and the FULL side edge SF. With this configuration, regardless of where in the main scanning direction the carriage 7's attitude changes occur, significant density changes caused by the carriage 7's attitude changes can be captured without any problems.

[0088] The third embodiment described above has the following features.

[0089] In other words, the above printing method includes forming multiple test patterns 31 in the sub-scanning direction. At least one forward patch ja, at least one return patch jc, and at least one round-trip patch jb are arranged without gaps in the main scanning direction. The multiple test patterns 31 include a cyan test pattern 31a (first test pattern) and a magenta test pattern 31b (second test pattern). At least one round-trip patch jb of the cyan test pattern 31a and at least one round-trip patch jb of the magenta test pattern 31b are formed at different positions in the main scanning direction. With this configuration, by distributing the multiple round-trip patches jb at different positions in the main scanning direction, it becomes easier to capture significant density fluctuations caused by changes in the attitude of the carriage 7.

[0090] (Fourth Embodiment) A fourth embodiment of this disclosure will be described below with reference to Figure 12. The following description will focus on the differences between this embodiment and the third embodiment described above, omitting any redundant explanations.

[0091] In the third embodiment described above, as shown in Figure 11, the forward patch ja, round-trip patch jb, and return patch jc included in the first pattern unit p1 of the cyan test pattern 31a are arranged without gaps so that they are adjacent to each other in the main scanning direction. The same applies to other pattern units p and other test patterns 31.

[0092] In contrast, in this embodiment, as shown in Figure 12, the forward patch ja, round-trip patch jb, and return patch jc included in the first pattern unit p1 of the cyan test pattern 31a are spaced apart from each other in the main scanning direction. The same applies to other pattern units p and other test patterns 31.

[0093] In this embodiment, similar to the third embodiment described above, the multiple forward patches ja of the cyan test pattern 31a, the multiple forward patches ja of the magenta test pattern 31b, the multiple forward patches ja of the yellow test pattern 31c, and the multiple forward patches ja of the black test pattern 31d are arranged diagonally with respect to the sub-scanning direction, moving from the top edge SU of the paper towards the bottom edge SD of the paper and approaching the FULL side edge SF. The same applies to the round-trip patches jb and the return-trip patches jc.

[0094] With the above configuration, compared to the case where the forward patch ja, return patch jb, and return patch jc are arranged without gaps in the main scanning direction as in the third embodiment described above, the area of ​​the test pattern image 30 is reduced, thus reducing the consumption of pigment ink. Furthermore, because multiple return patches jb are dispersed at different positions in the main scanning direction, it becomes easier to capture significant density fluctuations caused by changes in the attitude of the carriage 7.

[0095] (Fifth embodiment) A fifth embodiment of this disclosure will be described below with reference to Figure 13. The following description will focus on the differences between this embodiment and the first embodiment, omitting any redundant explanations.

[0096] In the first embodiment described above, as shown in Figure 4, the cyan test pattern 31a includes a plurality of pattern units p, which are arranged without gaps in the main scanning direction, and each pattern unit p includes a forward patch ja, a return patch jb, and a return patch jc, which are also arranged without gaps in the main scanning direction. The same applies to the other test patterns 31.

[0097] In contrast, in this embodiment, as shown in Figure 13, the cyan test pattern 31a includes a forward patch ja, a return patch jb, and a return patch jc. The forward patch ja, return patch jb, and return patch jc included in the cyan test pattern 31a all extend from the HOME side edge SH to the FULL side edge SF in the main scanning direction, and are formed over the entire area of ​​the paper S in the main scanning direction. Furthermore, the forward patch ja, return patch jb, and return patch jc are arranged in this order from the top edge SU of the paper to the bottom edge SD in the sub-scanning direction. The same applies to the other test patterns 31. In this way, since the return patch jb is formed over the entire area of ​​the paper S in the main scanning direction, even if the carriage 7's attitude changes occur anywhere in the main scanning direction, significant density changes caused by the carriage 7's attitude changes can be captured without any problems.

[0098] The fifth embodiment described above has the following features: at least one forward patch ja, at least one return patch jc, and at least one round-trip patch jb are aligned in the sub-scanning direction. Even when various patches j are aligned in the sub-scanning direction in this way, as with the first embodiment described above, there is no misidentification of impact errors caused by factors that are difficult to correct as Bi-D errors, and therefore no inverse correction that exacerbates density unevenness is performed.

[0099] Although the present invention has been described above with reference to embodiments, the present invention is not limited thereto. Various modifications to the structure and details of the present invention can be made that are understandable to those skilled in the art within the scope of the invention.

[0100] Some or all of the above embodiments may also be described as follows, but are not limited to the following:

[0101] In the above example, the program can be stored and supplied to the computer using various types of non-transitory computer-readable medium. Non-transitory computer-readable medium includes various types of tangible storage medium. Examples of non-transitory computer-readable medium include magnetic storage media (e.g., flexible disks, magnetic tapes, hard disk drives) and magneto-optical storage media (e.g., magneto-optical disks). Examples of non-transitory computer-readable medium further include CD-ROM (Read Only Memory), CD-R, CD-R / W, and semiconductor memory (e.g., mask ROM; examples of non-transitory computer-readable medium further include PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, and RAM (random access memory)). Alternatively, the program may be supplied to the computer by various types of transient computer-readable medium. Examples of transient computer-readable medium include electrical signals, optical signals, and electromagnetic waves. Temporary computer-readable media can supply programs to a computer via wired communication channels such as electric wires and optical fibers, or via wireless communication channels. [Explanation of Symbols]

[0102] 1…Printing system, 2…Printing unit, 3…Reading unit, 4…Control unit, 4a…Processor, 4b…Memory, 4c…Communication interface, 4e…Input interface, 5…Nozzle row, 5a…First nozzle row, 5b…Second nozzle row, 5c…Third nozzle row, 5d…Fourth nozzle row, 6…Print head, 7…Carriage, 8…Carriage guide, 9…Endless belt, 10…Pulley, 11…Carriage motor, 12…Conveyor roller, 13…Conveyor motor, 20…Print image data storage unit, 21…Test pattern image data storage unit, 22…Print execution unit, 22a…Density correction data, 23…Reading execution unit, 24…Pass / fail determination unit, 25…Output unit, 26…Density correction data generation unit, 30…Test pattern image, 31…Test pattern, 31a…Cyan test pattern, 31b…Magenta test pattern, 31c…Yellow test pattern, 31d…Black test pattern

Claims

1. Forward scanning involves discharging liquid onto the medium while moving the print head along the main scanning direction, A method for printing a test pattern in a printing apparatus capable of performing a return scan, in which the print head is moved back along the main scanning direction while the liquid is discharged onto the medium, The aforementioned test pattern is a concentration pattern having a solid region. The test pattern includes at least one forward patch formed during the forward scan, at least one return patch formed during the return scan, and at least one round-trip patch formed during the forward scan and the return scan. Printing method.

2. The at least one forward patch, the at least one return patch, and the at least one round-trip patch are aligned in the main scan direction. The printing method according to claim 1.

3. The at least one forward patch, the at least one return patch, and the at least one round-trip patch are aligned in the sub-scanning direction. The printing method according to claim 1.

4. The test pattern is formed over the entire area of ​​the main scanning direction of the medium. The printing method according to any one of claims 1 to 3.

5. Reading the test pattern formed on the medium, The determination of whether or not density correction is possible based on the reading results, Output the judgment result, This also includes, The printing method according to claim 1.

6. The print head includes a first nozzle row capable of ejecting a first colored liquid, and a second nozzle row positioned differently from the first nozzle row and capable of ejecting a second colored liquid of a different color from the first colored liquid. Using the first nozzle array, a first test pattern is formed as the test pattern, Using the second nozzle row, a second test pattern is formed as the test pattern at a position different from the first test pattern in the sub-scanning direction, including, The printing method according to claim 1.

7. This includes forming multiple test patterns in the sub-scanning direction, The at least one forward patch, the at least one return patch, and the at least one round-trip patch are arranged without gaps in the main scanning direction. The aforementioned plurality of test patterns include a first test pattern and a second test pattern, The at least one round-trip patch of the first test pattern and the at least one round-trip patch of the second test pattern are formed at different positions in the main scanning direction. The printing method according to claim 1.

8. This includes forming multiple test patterns in the sub-scanning direction, The at least one forward patch, the at least one return patch, and the at least one round-trip patch are arranged apart from each other in the main scanning direction. The aforementioned plurality of test patterns include a first test pattern and a second test pattern, The at least one round-trip patch of the first test pattern and the at least one round-trip patch of the second test pattern are formed at different positions in the main scanning direction. The printing method according to claim 1.

9. A method for determining whether or not concentration correction can be performed using the test pattern described in claim 1, The aforementioned at least one forward patch includes multiple forward patches, The aforementioned at least one return patch includes multiple return patches, The aforementioned at least one round-trip patch includes multiple round-trip patches, If concentration fluctuations occur in a similar manner among patches of the same type, concentration correction is possible. If concentration fluctuations occur in different ways among patches of the same type, it is determined that concentration correction is impossible. Method of determining availability.

10. Forward scanning involves discharging liquid onto the medium while moving the print head along the main scanning direction, A printing system including a printing apparatus capable of performing a return scan, in which the print head is moved back along the main scanning direction while the liquid is discharged onto the medium, The printing apparatus is configured to form a test pattern which is a density pattern having solid areas, The test pattern includes at least one forward patch formed during the forward scan, at least one return patch formed during the return scan, and at least one round-trip patch formed during the forward scan and the return scan. Printing system.

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