JP2020019163A - Printing device and printing method - Google Patents

Abstract

To provide a printing device that performs printing by an inkjet system, which can perform printing more appropriately.SOLUTION: A printing device 10, which performs printing by an inkjet system, comprises a head part 12 having a nozzle row in which a plurality of nozzles for discharging ink are arranged, a main scanning driving part 18, a sub-scanning driving part 20, and a control part 30. In the nozzle row, the plurality of nozzles are arranged to be positionally shifted in a sub-scanning direction. When a dot density of ink that can be formed by one nozzle during one-time main scanning motion is defined as a printing density of the nozzle, the control part 30 sets printing densities of the respective nozzles so that printing densities of some nozzles are higher than printing densities of the other nozzles, in every main scanning motion, and makes the nozzles, which are selected as some nozzles whose printing densities are set higher, different from each other, with respect to at least two consecutive main scanning motion.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a printing device and a printing method.

  2. Description of the Related Art Conventionally, an inkjet printer that performs printing by an inkjet method has been widely used. In addition, when printing is performed by an inkjet printer, banding stripes may be a problem due to the influence of uneven feeding that occurs when a medium to be printed is conveyed. In this case, the banding fringe is, for example, a phenomenon in which a boundary portion of a band, which is an area drawn in each main scanning operation (pass), stands out in a stripe shape. On the other hand, there has been conventionally known a method of making banding stripes inconspicuous by superimposing band boundaries in a gradation shape. In this case, for example, by setting the density (print density) of printing performed by each of the plurality of nozzles in the inkjet head for each nozzle, the boundary portion of the band is formed in a gradation. In addition, regarding a configuration in which the print density is set for each nozzle, a method of setting the print density (print density) performed by each of the plurality of nozzles so as to gradually decrease toward the rear end side of the inkjet head has been conventionally known. It is known (for example, see Patent Document 1).

JP-A-2015-96315

  As described above, when printing is performed by the inkjet method, the print density may be set for each nozzle. On the other hand, the inventor of the present application has found that when setting the print density for each nozzle, a new problem may occur due to a difference in the usage rate depending on the nozzle. Therefore, conventionally, it has been desired that a printing apparatus that performs printing by an inkjet method perform printing more appropriately. Therefore, an object of the present invention is to provide a printing apparatus and a printing method that can solve the above-described problems.

  When the print density is set for each nozzle in the conventional configuration, normally, a higher load is continuously applied to some nozzles than to other nozzles. In this case, a local load becomes excessive in the ink jet head, and a problem such as missing nozzles where ink is not ejected from some nozzles may occur. More specifically, when the print density is set for each nozzle, a difference occurs between the nozzles in the amount of ink ejected from one nozzle per unit time. In this case, the flow of ink may be affected in an ink path (ink flow path) for supplying ink to each nozzle in the inkjet head. In addition, as a result, for example, the supply of ink may not be able to catch up around the nozzle where the print density becomes high, and it may be impossible to temporarily eject ink from that nozzle or nozzles around the nozzle. In addition, in this case, even in a nozzle having a low print density, for example, the timing at which the nozzle is not used may be increased, which may cause a problem such as drying of the ink in the nozzle or around the nozzle. As a result, clogging of the nozzle may easily occur.

  On the other hand, the inventor of the present application has considered that, instead of setting a fixed print density for each nozzle, the print density set for each nozzle is changed every time the main scanning operation is performed. . With this configuration, for example, it is possible to appropriately prevent a high load from continuously being applied to a specific nozzle. In this case, by appropriately changing the setting of the print density, for example, it is possible to appropriately prevent, for example, an excessive influence on the flow of the ink in the ink path in the ink jet head. This also makes it possible, for example, to properly prevent nozzle missing and the like. Further, in this case, since the nozzles having a low print density are not fixed to the specific nozzles, it is possible to appropriately prevent, for example, clogging of the nozzles having a low print density.

  Further, the inventor of the present application has found, through further intensive research, features necessary for obtaining such an effect, and has accomplished the present invention. In order to solve the above problems, the present invention is a printing apparatus that performs printing by an ink jet method, and includes a head unit having a nozzle row in which a plurality of nozzles that eject ink are arranged, and a head unit in a predetermined main scanning direction. A main scanning drive unit that causes the head unit to perform a main scanning operation of ejecting ink while moving, and a sub-scanning operation that relatively moves in a sub-scanning direction orthogonal to the main scanning direction with respect to an object to which ink is ejected A sub-scanning drive unit that causes the head unit to perform, and a control unit that controls the main scanning operation by the head unit. In the nozzle row, the plurality of nozzles are displaced in the sub-scanning direction. If the density of ink dots that can be formed by one nozzle in one main scanning operation is defined as the print density of the nozzle in one main scanning operation, the control unit performs In the main scanning operation, the print density of each of the nozzles is set so that the print density of some of the nozzles is higher than the print density of the other nozzles, and at least a portion of the print density is set. For the two main scanning operations to be performed, the nozzles selected as the partial nozzles for setting the print density high are different from each other.

  In the case of such a configuration, the position of the peak (peak) can be changed with respect to the print density of each nozzle in the nozzle row by changing the nozzle for which the print density is set high. The print density peak is, for example, a portion where the print density setting becomes a mountain-like shape when a higher print density is set for one of the nozzles than the surroundings. In this case, by changing the position of the peak of the print density, for example, it is possible to appropriately prevent a high load from continuously being applied to some of the nozzles. Further, thereby, for example, it is possible to appropriately prevent the ink flow from being excessively affected in the ink path in the ink jet head, and to properly prevent nozzle missing. Further, in this case, since the nozzle whose print density is lowered also changes due to the change in the position of the mountain, it is possible to appropriately prevent the nozzle clogging due to the lowered print density of a specific nozzle. Therefore, with this configuration, for example, printing can be performed more appropriately in a printing apparatus that performs printing by an inkjet method.

  Here, in this configuration, the target from which ink is ejected is, for example, a medium to be printed. In this configuration, the printing apparatus performs, for example, multi-pass printing (multi-pass printing). In this case, the control unit causes the head unit to perform a plurality of main scanning operations for the same position on the medium, for example. In this case, if the number of main scanning operations to be performed on the same position is defined as the number of passes, the control unit may determine, for example, at least one of the main scanning operations included in the number of consecutively performed main scanning operations. For two consecutive main scanning operations, the nozzles selected as some of the nozzles for setting a high print density are different from each other. With this configuration, for example, it is possible to more appropriately prevent a high load from being continuously applied to some of the nozzles. It is more preferable to change the print density setting every time one main scanning operation is performed. In this case, for example, every time the head unit performs one main scanning operation, the control unit changes the nozzles to be selected as some of the nozzles for setting a high print density. With this configuration, for example, it is possible to more appropriately prevent a high load from being continuously applied to some of the nozzles.

  In each main scanning operation, the control unit sets the print density of each nozzle based on, for example, a preset pattern. In this case, for example, it is conceivable to prepare a plurality of patterns different from each other in advance and use each of the plurality of patterns in order each time the head unit performs one main scanning operation. With such a configuration, for example, the nozzles selected as some of the nozzles for setting a high print density can be appropriately changed.

  Further, it is preferable to set the print density so that the print density gradually changes near the end of the nozzle row, for example. More specifically, in this case, for example, in at least a part of the main scanning operation, the control unit gradually changes the print density for a plurality of nozzles existing at the end of the nozzle row in the sub-scanning direction. Thus, the print density of each nozzle is set. With this configuration, for example, banding stripes can be appropriately prevented from being noticeable. In this case, it is conceivable that the print density is set in a gradation at least near the end of the nozzle row. The setting of the gradation print density may be performed for the entire nozzle array. Further, it is more preferable to set the print density in all the main scanning operations.

  In this configuration, the head unit may include a plurality of inkjet heads that eject the same color ink. In this case, each of the plurality of inkjet heads has a plurality of nozzles that are arranged at different positions in the sub-scanning direction. In addition, the plurality of inkjet heads are arranged at different positions in the sub-scanning direction, for example, such that the nozzle rows in the head unit are formed by aligning the nozzles of each inkjet head. More specifically, in this case, the plurality of inkjet heads are arranged, for example, in a staggered manner.

  In this case, it is preferable to set the print density for each of the inkjet heads so that the print density of the nozzles near the ends gradually changes. More specifically, in this case, in at least a part of the main scanning operation, for example, the control unit may control the arrangement of the nozzles in each inkjet head with respect to the arrangement of the nozzles in the sub-scanning direction. The print density of each nozzle is set so that the print density changes gradually. With this configuration, for example, when a plurality of inkjet heads that eject ink of the same color are used, it is possible to appropriately prevent streaks or the like corresponding to the boundary portions of the inkjet heads from being conspicuous. In this case, the streak or the like corresponding to the boundary portion of the ink jet head is, for example, a streak or the like generated in a printing result due to the influence of individual differences of the ink jet head.

  Further, as a configuration of the present invention, a printing method or the like having the same characteristics as described above may be used. In this case, for example, the same effect as described above can be obtained.

  According to the present invention, for example, printing can be performed more appropriately in a printing apparatus that performs printing by an inkjet method.

FIG. 1 is a diagram illustrating a printing device 10 according to an embodiment of the present invention. FIG. 1A illustrates an example of a configuration of a main part of the printing apparatus 10. FIG. 1B shows an example of the configuration of the head unit 12 in the printing apparatus 10. FIG. 4 is a diagram illustrating an example of setting of print density. FIG. 4 is a diagram for describing setting of print density performed in the present example. An example of setting of print density in the case of three passes is shown. FIG. 4 is a diagram for describing setting of print density for each color head 102 configured by a plurality of inkjet heads. FIG. 5A shows an example of the configuration of the head 102 for each color. FIG. 5B shows an example of the print density for each color head 102 constituted by a plurality of inkjet heads 302.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a printing apparatus 10 according to an embodiment of the present invention. FIG. 1A illustrates an example of a configuration of a main part of the printing apparatus 10. FIG. 1B shows an example of the configuration of the head unit 12 in the printing apparatus 10. Note that, except for the points described below, the printing apparatus 10 may have the same or similar features as a known inkjet printer. For example, the printing apparatus 10 may further have the same or similar configuration as a known inkjet printer, in addition to the configuration described below.

  The printing apparatus 10 is an inkjet printer that performs printing on a medium 50 to be printed by an inkjet method. In this case, the medium 50 is an example of a target from which ink is ejected. Further, in the present example, the printing apparatus 10 includes a head unit 12, a platen 14, a guide rail 16, a main scanning drive unit 18, a sub-scanning drive unit 20, and a control unit 30. The head section 12 is a section that ejects ink onto the medium 50, and has a plurality of heads 102 for each color, for example, as shown in FIG. In this case, each color head 102 is a portion including an ink jet head that discharges ink of each color used for printing, has a nozzle row in which a plurality of nozzles that discharge ink to the medium 50 are arranged, and has different colors from each other. Is ejected. More specifically, in this example, the head unit 12 ejects inks of yellow (Y), magenta (M), cyan (C), and black (K), respectively. A plurality of heads 102 for each color. Further, in the present example, as shown in the figure, the plurality of heads 102 for each color align the positions in the sub-scanning direction (X direction in the figure) preset in the printing apparatus 10 and are orthogonal to the sub-scanning direction. In the main scanning direction (Y direction in the figure). In this case, the head unit 12 holds a plurality of heads 102 for each color by, for example, a carriage not shown.

  The platen 14 is a trapezoidal member that supports the medium 50 at a position facing the head unit 12. The guide rail 16 is a rail-shaped member extending in the main scanning direction, and guides the movement of the head unit 12 in the main scanning direction.

  The main scanning drive unit 18 is a driving unit that causes the head unit 12 to perform a main scanning operation (scan operation). In this case, the main scanning operation is, for example, an operation of ejecting ink while moving in the main scanning direction. Further, causing the head unit 12 to perform the main scanning operation means, for example, causing the inkjet head in the head unit 12 to perform the main scanning operation. Further, in the present example, the printing device 10 executes the printing operation in the serial system by causing the head unit 12 to perform the main scanning operation. Further, in this example, the printing apparatus 10 executes a printing operation by a multi-pass method. In this case, the operation of the multi-pass method is, for example, an operation of performing a plurality of main scanning operations on the same position on the medium 50. During the main scanning operation, the head unit 12 moves in the main scanning direction along the guide rail 16. In the main scanning operation, the movement of the head unit 12 in the main scanning direction refers to a relative movement with respect to the medium 50. Therefore, in a modified example of the printing apparatus 10, the position of the head unit 12 may be fixed, and the medium 50 may be moved by moving the platen 14, for example.

  The sub-scanning driving unit 20 is a driving unit that causes the head unit 12 to perform a sub-scanning operation. In this case, the sub-scanning operation is, for example, an operation of moving relatively to the medium 50 in the sub-scanning direction. Further, causing the head unit 12 to perform the sub-scanning operation means, for example, causing the inkjet head in the head unit 12 to perform the sub-scanning operation. In this example, the sub-scanning drive unit 20 performs the sub-scanning operation on the head unit 12 by transporting the medium 50 in a transport direction parallel to the sub-scanning direction using, for example, a roller (not shown). Let In this case, the medium 50 is transported by a feed amount set in accordance with the number of printing passes between each main scanning operation. In this case, the number of passes refers to, for example, the number of main scanning operations performed on the same position on the medium 50. The feed amount set in accordance with the number of passes is, for example, a feed amount corresponding to a distance obtained by dividing the length of the nozzle row (length in the sub-scanning direction) in the head unit 12 by the number of passes. .

  The control unit 30 is, for example, a CPU of the printing device 10 and controls the operation of each unit of the printing device 10. More specifically, the printing apparatus 10 causes each nozzle of the head unit 12 to eject ink according to an image to be printed, for example, when controlling the main scanning operation by the head unit 12. In this case, the control unit 30 sets the print density of each nozzle. The setting of the print density and the like will be described later in more detail.

  Here, as described above, the printing apparatus 10 of the present example may have the same or similar features as a known inkjet printer, except for the points described above and below. For example, it is conceivable to use various known types of ink as the ink ejected from each color head 102 in the head unit 12. In this case, it is preferable that the printing apparatus 10 further include a fixing unit or the like for fixing the ink on the medium 50 according to the type of the ink to be used. More specifically, when an ink that is fixed to the medium 50 by evaporating a solvent (evaporation-drying type ink) is used as the ink, a heater or the like that heats the medium or the ink may be used as the fixing unit. In this case, the heater is disposed, for example, in the platen 14 at a position facing the head unit 12 with the medium 50 interposed therebetween. Further, as such an evaporative drying type ink, for example, various known aqueous inks, solvent inks (solvent inks), and the like may be used. Further, as the ink, for example, an ultraviolet curable ink (UV ink) that is cured by irradiation with ultraviolet light may be used. In this case, it is conceivable to use an ultraviolet irradiation unit such as a UV LED as the fixing unit. Further, in this case, it is conceivable that the ultraviolet irradiation means is arranged at a position adjacent to the plurality of color heads 102 (a position adjacent in the main scanning direction) in the head unit 12.

  Further, as described above, in this example, each head 102 for each color is a portion including the inkjet head. In this case, one head 102 for each color may be configured with one inkjet head, or may be configured with a plurality of inkjet heads that eject ink of the same color. Further, the inkjet head included in each color head 102 may have one nozzle row, or may have two or more nozzle rows. In addition, when one head for each color 102 includes a plurality of inkjet heads, or when one inkjet head has a plurality of nozzle rows, a plurality of nozzle rows exist in each one head for color 102. Will be. In such a case, for example, a virtual nozzle array obtained by synthesizing the plurality of nozzle arrays can be considered, and the virtual nozzle array can be considered as a nozzle array of the head 102 for each color. In this case, the virtual nozzle row is, for example, a nozzle that focuses on the position in the sub-scanning direction without considering the difference in the position in the main scanning direction for a plurality of nozzles present in one color head 102. Column. In this case, the nozzle row of each color head 102 can be considered to be, for example, a row in which a plurality of nozzles are shifted in position in the sub-scanning direction.

  Next, the setting of the print density for each nozzle in each color head 102 will be described. First, for the sake of convenience of explanation, items common to the conventional setting of print density will be described.

  FIG. 2 is a diagram showing an example of the print density setting, and is an example of the same print density setting as that shown in FIG. 6 of JP-A-2015-96316 cited as Patent Document 1 above. Is shown. In this example, the print density of the nozzle is the density of ink dots that can be formed by one nozzle in one main scanning operation. The ink dot that can be formed by one nozzle in one main scanning operation is, for example, an ink dot that is formed when ink is ejected at the minimum dischargeable interval. The minimum dischargeable interval is, for example, an interval corresponding to a cycle of a drive signal that is a signal for discharging ink from each nozzle. The drive signal is, for example, a signal for driving a drive element (for example, a piezo element) corresponding to each nozzle.

  Further, the print density of the nozzle can be considered to be, for example, a density corresponding to the density of ink dots that can be formed side by side in the main scanning direction by the nozzle in one main scanning operation. In this case, the density corresponding to the dot density is, for example, a density corresponding to the number of ink dots that can be formed per unit length. The number of ink dots that can be formed per unit length is, for example, the number of ink dots that are formed when solid printing is performed on a medium. In addition, solid printing refers to, for example, performing printing such that ink is ejected to all ejection positions corresponding to the printing resolution by performing a main scanning operation for the number of passes. In addition, the print density of the nozzle may be considered to be, for example, a density corresponding to a matter described in the print density performed by the nozzle in Patent Literature 1, and the like.

  In FIG. 2, the arrangement of circles shown on the left side indicates the nozzle row of each color head 102. As described above, this nozzle row is a row having a plurality of nozzles 202 arranged at different positions in the sub-scanning direction. Further, this nozzle row can be considered, for example, as a virtual nozzle row in the head 102 for each color. In FIG. 2, the graph on the right side shows the print density of each nozzle 202 in the nozzle row. More specifically, in the case shown in the figure, the print density at the center of the nozzle row is the highest, and the print density gradually decreases toward the front end side and the rear end side of each color head 102. The print density is set so that In this case, the front end side and the rear end side of each color head 102 are one end side and the other end side of each color head 102 in the sub-scanning direction. In the illustrated case, the front end side of each color head 102 is located upstream in the medium transport direction. The rear end of each color head 102 is located downstream in the medium transport direction. Further, such setting of the print density can be considered to be, for example, a gradation-like setting in which the print density is reduced at both ends of the heads 102 for each color.

  In such a configuration, band boundaries, which are regions drawn in each main scanning operation (pass), overlap in a gradation state, so that banding stripes can be made less noticeable. However, in this case, as the amount of ink ejected from the nozzles near the center of the nozzle row continues to be larger than the amount of ink ejected from the nozzles near both ends, as shown in the figure as a load on the nozzles, A higher load will continue to be applied to some of the nozzles in the nozzle row than to other nozzles.

  More specifically, in an inkjet head, ink is usually supplied to each nozzle via an ink path (ink flow path) formed in the inkjet head. In this case, the ink path is formed along the positions of the plurality of nozzles, and supplies ink to each nozzle. In this case, supplying ink to the nozzles means, for example, supplying ink to an ink chamber formed before the nozzles. The ink chamber is, for example, a space in the vicinity of each nozzle for accommodating a driving element (for example, a piezo element) corresponding to each nozzle. In this case, if there is a nozzle such as the nozzle near the center of the nozzle row in the case shown in FIG. 2 in which the amount of ink ejected per unit time is large, the flow of ink in the ink path near that position May be affected. Further, as a result, for example, the supply of ink may not be able to catch up around the nozzle where the print density becomes high, and it may not be possible to temporarily eject ink from that nozzle or nozzles around the nozzle.

  Here, in this regard, it is considered that such a problem is unlikely to occur if, for example, the amount of ink that can flow in the ink path is sufficiently large. In addition, for example, when performing a multi-pass operation with a certain number of passes or more, such a problem hardly occurs because the amount of ink ejected in one main scanning operation is reduced. However, for example, when printing is performed with a small number of passes (for example, four passes or less), the amount of ink increases in one main scanning operation, so it is difficult to sufficiently secure the amount of ink that can flow in the ink path. In some cases. In addition, as a result, a phenomenon (nozzle missing) in which ink cannot be temporarily ejected from some nozzles is likely to occur. In addition, when the position of the nozzle where the load is increased is fixed, the nozzle where the print density is low is also fixed, and a problem may occur even in the nozzle where the print density is low. More specifically, in this case, in a nozzle having a low print density, for example, the timing at which the nozzle is not used is increased, which may cause a problem that the ink dries in the nozzle or around the nozzle. As a result, clogging of the nozzle may easily occur.

  On the other hand, in this example, by setting the print density so as not to fix the position of the nozzle where the load becomes high, the load on each nozzle in each color head 102 is dispersed, and such a problem occurs. Is preventing. Therefore, the setting of the print density performed in this example will be described in more detail below. FIG. 3 is a diagram for explaining the print density setting performed in this example, and shows an example of the print density setting when printing is performed with two passes (two passes).

  In this example, the control unit 30 (see FIG. 1) sets the print density of each nozzle so that the print density of some nozzles is higher than the print density of other nozzles in each main scanning operation. I do. In addition, the print density is set so that a peak (peak) of the print density is formed at any position of the nozzle row of each color head 102. In this case, the peak of the print density is, for example, as shown in the figure, a portion where the print density is set to a mountain shape by setting a higher print density for one of the nozzles than the surroundings. is there. Further, in this example, at least in part of the main scanning operation, the print density is set so that a plurality of peaks are formed, for example, as shown in the drawing.

  In addition, in FIG. 3, the diagram on the left side shows an example of the print density when the first main scanning operation (first main scanning operation) is performed for any position on the medium. In addition, the diagram on the right shows an example of the print density in the case where the second main scanning operation (second main scanning operation) is performed on the position. As can be seen from the figure, in this example, the setting of the print density differs between the first pass and the second pass. More specifically, in this case, nozzles to be selected as some of the nozzles for setting high print density are different between the first pass and the second pass. As a result, as shown in the drawing, the position of the peak of the print density is changed between the first pass and the second pass.

  In this case, in each main scanning operation, the control unit 30 sets the print density of each nozzle based on, for example, a preset pattern. In this case, setting the print density based on the pattern means, for example, using a mask based on a predetermined pattern as a mask used when determining a position where ink is ejected in each main scanning operation in a multi-pass method. . Further, in this case, a plurality of different patterns are prepared in advance, and each of the plurality of patterns is used in turn each time the head unit 12 (see FIG. 1) performs one main scanning operation. .

  More specifically, in this example, a first pattern and a second pattern that are different from each other are used as such patterns. In this case, the first pattern is a pattern used when setting the print density as in the case shown as the first pass in the drawing. The second pattern is a pattern used when setting the print density, for example, as shown in the second pass in the drawing. Then, the control unit 30 alternately uses, for example, each of the first pattern and the second pattern each time the head unit 12 performs one main scanning operation. In such a configuration, the position of the peak of the print density is shifted by half of the feed amount in the sub-scanning operation every time one main scanning operation is performed, as shown in the drawing. At the time of printing, the operations shown as the first pass and the second pass in the figure are repeated thereafter, so that the printing operation of the multi-pass method is executed for each position of the medium.

  With such a configuration, for example, the nozzles selected as some of the nozzles for setting a high print density can be appropriately changed for each main scanning operation. In addition, for example, the position of the peak of the print density can be appropriately changed each time the main scanning operation is performed. In this case, by changing the position of the peak of the print density, for example, it is possible to appropriately prevent a high load from continuously being applied to some of the nozzles. More specifically, as shown in the drawing, the load applied to the nozzle changes according to the print density. In this case, by changing the position of the peak of the print density, it is possible to change the nozzles to which a high load is applied. Therefore, according to the present example, for example, it is possible to appropriately prevent a high load from continuously being applied to some of the nozzles. In addition, for example, it is possible to appropriately prevent the ink flow in the ink path in the inkjet head constituting each color head 102 from excessively affecting the flow of ink, and to properly prevent nozzle missing. Further, in this case, by changing the position of the peak of the print density, it is possible to appropriately prevent the nozzles whose print density decreases from being fixed. In addition, this can appropriately prevent, for example, nozzle clogging caused by a decrease in the print density of a specific nozzle. Therefore, according to the present example, for example, in the printing apparatus 10 that performs printing by the inkjet method, printing can be performed more appropriately.

  In this example, the print density can be easily and appropriately changed by changing the print density setting every time the main scanning operation is performed. More specifically, when considering only changing the position of the peak of the print density, instead of changing the print density every time the main scanning operation is performed, it is possible to change the print density during the main scanning operation. Is also conceivable. However, in this case, it is conceivable that the control for establishing the complementary relation of the print density becomes complicated. To establish the complementary relation of the print density means, for example, to set the print density in each main scan operation so that the total print density for the main scan operations for the number of passes becomes a predetermined density at each position on the medium. That is. Further, when the print density is changed during the main scanning operation, an unintended change or the like occurs in the way of ink ejection at the timing when the print density is changed, which may affect print quality. On the other hand, in the present embodiment, the position of the peak of the print density can be appropriately changed while appropriately preventing such a problem from occurring.

  In addition, when the position of the peak of the print density is changed as described above, it is usually necessary to set the print density in each main scanning operation so that the complementary relationship described above is satisfied. become. On the other hand, when performing printing in two passes, for example, by setting the print density as shown in the figure, it is possible to appropriately change the position of the peak of the print density while establishing a complementary relationship. .

  In this case, it is preferable that the print density in at least a part of the main scanning operation be set in a gradation at least in the vicinity of the end of the nozzle row of each color head 102 as shown in the drawing. . In this case, setting the print density in a gradation means, for example, setting the print density so that the print density gradually changes along the sub-scanning direction. With this configuration, for example, banding stripes can be appropriately prevented from being noticeable.

  In this case, setting the print density in the vicinity of the end of the nozzle row of each color head 102 in a gradation form means that a plurality of nozzles existing at the end of the nozzle row of each color head 102 in the sub-scanning direction are This is to set the print density in a gradation form. The plurality of nozzles existing at the end of the nozzle row are, for example, about 10 (for example, about 5 to 15) nozzles arranged at the end of the nozzle row. In this case, it is preferable that the print density is set in a gradation form for the nozzles near both ends of the nozzle row. Further, it is preferable that the number of nozzles for setting the print density in a gradation manner at the end of the nozzle row is 20 or more (for example, about 20 to 40). Further, as can be seen from the drawing, in this example, in all the main scanning operations, gradation print density is set for the entire nozzle row of each color head 102. . With this configuration, for example, banding stripes can be more appropriately prevented from being noticeable.

  Further, the method of setting the print density and the number of printing passes are not limited to those described above, and can be variously changed. FIG. 4 shows an example of print density settings when printing is performed with three passes (three passes).

  As shown in the figure, in this case as well, the print density is set so that the print density peaks at any position of the nozzle row of each color head 102 in each main scanning operation. Further, in this case, the peak portion is not a mountain shape in which the top is dotted like in the case shown in FIG. 3, but the portion having the highest print density has the same print density over a certain range. It is shaped like a mountain with a flat top. Also in this case, the print density setting is changed each time the head section 12 (see FIG. 1) performs the main scanning operation, so that the complementary relationship of the print density is established and the position of the peak of the print density is established. Is changing. More specifically, also in the case shown in FIG. 4, as shown in the figure, each time one main scanning operation is performed, the position of the peak of the print density becomes half the feed amount in the sub-scanning operation. Only, it will be shifted. Also in this case, at the time of printing, the operations shown as the first pass, the second pass, and the third pass in the drawing are repeated thereafter, so that the printing operation of the multi-pass method is performed for each position of the medium. Execute

  Also in the case of such a configuration, for example, it is possible to appropriately prevent the problem that occurs when a high load is continuously applied to some of the nozzles. Also in this case, the print density near the end of the nozzle row of each color head 102 is set in a gradation form as shown in the figure. Therefore, also in this case, for example, banding stripes can be appropriately prevented from being noticeable.

  Further, it is possible to further change the setting method of the print density and the number of printing passes. For example, the number of printing passes may be four or more. As for the setting of the print density, for example, it is conceivable to make various settings so as to appropriately change the position of the mountain while establishing a complementary relationship. In this case, it is preferable that, for the setting of the print density, for example, it is preferable that, for at least a part of two consecutive main scanning operations, the nozzles selected as some of the nozzles for setting a high print density be different from each other. You can think. Further, in this case, the two consecutive main scanning operations are, for example, any two consecutive main scanning operations included in the main scanning operations for the number of consecutive passes. With this configuration, for example, it is possible to appropriately prevent a high load from continuously being applied to some of the nozzles. It is more preferable to change the print density setting every time one main scanning operation is performed. In this case, for example, each time the head unit 12 performs one main scanning operation, the control unit 30 changes the nozzles to be selected as some of the nozzles for setting a high print density. With this configuration, for example, it is possible to appropriately prevent a high load from continuously being applied to some of the nozzles.

  Here, as described above, in this example, each color head 102 may be constituted by a plurality of inkjet heads that eject ink of the same color. In this case, it is preferable to set the print density in consideration of the arrangement of a plurality of inkjet heads included in one color head 102. Therefore, an example of setting the print density in the case of using each color head 102 including a plurality of inkjet heads will be described below.

  FIG. 5 is a diagram illustrating the setting of the print density for each color head 102 configured by a plurality of inkjet heads. FIG. 5A shows an example of the configuration of the head 102 for each color. In this case, each head 102 for each color in the head unit 12 (see FIG. 1) has a plurality of inkjet heads 302 that eject ink of the same color. Further, as shown in the drawing, these inkjet heads 302 are arranged in a staggered manner with their positions in the sub-scanning direction shifted. In this case, the arrangement of the plurality of inkjet heads 302 may be the same as that of a known staggered head. The staggered head is, for example, a composite head configured by arranging a plurality of inkjet heads that eject ink of the same color in a staggered manner. More specifically, in this case, each of the plurality of inkjet heads 302 constituting one inkjet head 302 has a plurality of nozzles that are arranged at different positions in the sub-scanning direction. The plurality of inkjet heads 302 are arranged at different positions in the sub-scanning direction such that the nozzle rows of each inkjet head 302 are combined to form a nozzle row of each color head 102.

  Also, in the case where the heads 102 for each color having such a configuration are used, the nozzle rows of the heads 102 for each color are the same as or similar to the case described above with reference to FIGS. It is conceivable to set the print density. With this configuration, for example, the position of the peak of the print density can be appropriately changed while establishing the complementary relation of the print density. In addition, for example, it is possible to appropriately prevent a high load from continuously being applied to some of the nozzles. When each color head 102 including a plurality of inkjet heads 302 is used, it is preferable to further set the print density in consideration of the influence of the boundary between the inkjet heads 302. In this case, the boundary portion between the inkjet heads 302 is, for example, a portion corresponding to a joint between two inkjet heads 302 adjacently arranged in the sub-scanning direction.

  FIG. 5B is a diagram illustrating an example of the print density for each color head 102 configured by the plurality of inkjet heads 302, and illustrates an example of the print density setting in the case of two passes. The example shown in the figure is an example in which the print density is set in consideration of the influence of the boundary portion of the inkjet head 302.

  When a plurality of inkjet heads 302 are used, it is usually difficult to completely match the characteristics (e.g., ejection characteristics) of each inkjet head 302. Therefore, when the heads 102 for each color are configured by the plurality of inkjet heads 302, the amount of ink ejected by the inkjet head 302 on one side of the boundary is reduced by the influence of the difference in characteristics (individual difference) between the inkjet heads 302. May be greater than the number of the inkjet heads 302, or the reverse. As a result, an unintended and noticeable streak may occur at a portion corresponding to the boundary of the inkjet head 302 on the medium.

  On the other hand, in the case shown in FIG. 5B, each of the plurality of inkjet heads 302 constituting one color head 102 is formed in a gradation form in which the print density of the nozzle near the end gradually changes. Set the print density so that In this case, the nozzles near the ends are nozzles near the ends in the sub-scanning direction of the respective inkjet heads 302. More specifically, in this case, for example, in each main scanning operation, the control unit 30 (refer to FIG. 1) determines a plurality of nozzles at the end in the sub-scanning direction with respect to the arrangement of the nozzles in each inkjet head 302. The print density of each nozzle is set such that the print density of each nozzle gradually changes. In this case, for example, as shown in the drawing, the print density is set so that at least one peak of the print density is formed in a range corresponding to each ink jet head 302. In addition, such setting of the print density can be considered as, for example, setting a print density in which at least the vicinity of the end portion is in a gradation form for each of the plurality of inkjet heads 302 arranged in a staggered manner. Also in this case, the nozzles selected as a part of the nozzles for setting the print density to be higher are changed every main scanning operation to change the position of the peak of the print density. With this configuration, for example, it is possible to appropriately prevent a high load from continuously being applied to some of the nozzles.

  In this case, the print density of the nozzles at the end portions of the respective inkjet heads 302 changes in a gradation manner at the boundary portions of the inkjet heads 302, for example, as indicated by a portion surrounded by an oval drawn by a broken line in the drawing. become. In this case, it is possible to appropriately prevent the streaks and the like corresponding to the boundary portion of the inkjet head 302 from being conspicuous as compared with a case where the same print density is set for all the nozzles, for example. The streak or the like corresponding to the boundary portion of the inkjet head 302 is, for example, a streak or the like generated in a printing result due to the influence of the individual difference of the inkjet head 302 or the like.

  Here, in order to prevent streaks or the like corresponding to the boundary portion of the inkjet head 302 from becoming conspicuous, for example, as shown in the print density of the first pass in FIG. It is particularly effective to use a print density setting that reduces the print density of a set. However, if the print density setting is the same in all the printing passes, as described above, a high load will continue to be applied to some of the nozzles. On the other hand, in the case of the above-described configuration, as described above, by changing the position of the peak of the print density, the load on each nozzle in the inkjet head 302 is dispersed, and a high load is applied to some of the nozzles. Properly can be prevented from continuing. Also, in this case, in at least a part of the printing passes, by using a print density setting that reduces the print density at the end of the inkjet head 302, the stripes or the like corresponding to the boundary portion of the inkjet head 302 stand out. It is possible to make it difficult. For this reason, with such a configuration, for example, it is possible to appropriately prevent continuous streaking or the like corresponding to the boundary portion of the inkjet head 302 while appropriately preventing a high load from continuously being applied to some of the nozzles.

  In FIG. 5, in the case where one head 102 for each color is formed of two inkjet heads 302, two or more print densities are set for each nozzle constituting the nozzle row of the head 102 for each color. An example is shown in which a print density having peaks is set. Further, in a modified example of the configuration of the head for each color 102, it is conceivable to configure one head for each color 102 with three or more inkjet heads 302. In this case, it is conceivable that the print density set for each nozzle constituting the nozzle row of each color head 102 is set so as to have peaks equal to or larger than the number of ink jet heads 302. More specifically, for example, when the number of the ink jet heads 302 constituting one head for each color 102 is three, the number of peaks is set to three, and the number of the ink jet heads 302 constituting the head for each color 102 is three. When the number is four, the number of peaks may be set to four and the position of the peak may be changed for each main scanning operation. With this configuration, the same effect as described above can be appropriately obtained by using the print density setting according to the number of the inkjet heads 302.

  Subsequently, a supplementary explanation and the like regarding each configuration described above will be given. In addition, for convenience of description, each configuration described above is collectively referred to as a present example below.

  In the above description, as an example of a problem that occurs when a high load continues to be applied to some of the nozzles, a phenomenon (nozzle missing) in which some of the nozzles cannot temporarily eject ink has been described. In this case, the missing nozzle can be considered to be, for example, a temporary ejection failure that occurs during use of the inkjet head. However, when a high load continues to be applied to some of the nozzles, it is conceivable that not only temporary ejection failure and the like, but also deterioration of the inkjet head and the nozzles and the like are likely to occur. On the other hand, according to the present example, by dispersing the load on each nozzle as described above, it becomes possible to appropriately prevent the deterioration of the inkjet head and the nozzle, and the like.

  Further, as described above, the problem of nozzle missing, which occurs when the print density setting is not changed, is particularly likely to occur when the number of printing passes is small. Therefore, the setting of the print density as in the present example can be particularly preferably used when the number of printing passes is small (for example, 4 passes or less). More specifically, the number of printing passes may be, for example, about 2 to 3. With this configuration, for example, high-speed printing can be appropriately performed while appropriately preventing the occurrence of a problem such as nozzle missing. When the setting of the print density is changed for each main scanning operation as in this example, as described above, the position of the peak of the print density is changed while establishing the complementary relation of the print density. Will be. Therefore, it is conceivable that the print density is set in a pattern corresponding to the number of passes.

  In the above description, the configuration of the printing apparatus 10 (see FIG. 1) mainly in the case where ink is ejected to a medium has been described. In this case, the printing apparatus 10 can be considered as an inkjet printer or the like that draws a two-dimensional image on a medium. However, in a modified example of the printing apparatus 10, a 3D printer (3D printing apparatus) that forms a three-dimensional object may be used as the printing apparatus 10. Also, in this case, a modeling table that supports the modeled object being modeled and a modeled object that is being modeled can be considered as objects to which ink is ejected. Also in this case, by setting the print density in the same manner as described above, it is possible to appropriately prevent a high load from continuously being applied to some of the nozzles. Further, the printing apparatus 10 can be considered as an example of a liquid ejection apparatus, for example. In this case, the ink can be considered as an example of the liquid ejected by the liquid ejection device.

  INDUSTRIAL APPLICATION This invention can be used suitably for a printing apparatus, for example.

DESCRIPTION OF SYMBOLS 10 ... Printing apparatus, 12 ... Head part, 14 ... Platen, 16 ... Guide rail, 18 ... Main scanning drive part, 20 ... Sub scanning drive part, 30 ... Control Part, 50: medium, 102: head for each color, 202: nozzle, 302: inkjet head

Claims (7)

A printing device that performs printing by an inkjet method,
A head unit having a nozzle row in which a plurality of nozzles that eject ink are arranged,
A main scanning drive unit for causing the head unit to perform a main scanning operation of discharging ink while moving in a preset main scanning direction,
A sub-scanning drive unit that causes the head unit to perform a sub-scanning operation of relatively moving in a sub-scanning direction orthogonal to the main scanning direction with respect to a target from which ink is to be ejected;
A control unit for controlling the main scanning operation by the head unit,
In the nozzle row, the plurality of nozzles are arranged while being shifted in position in the sub-scanning direction.
When the density of ink dots that can be formed by one nozzle in one main scanning operation is defined as the print density of the nozzle,
The control unit sets the print density of each of the nozzles so that the print density of some of the nozzles is higher than the print density of the other nozzles in each main scanning operation.
In addition, the printing apparatus is characterized in that, for at least some of the two successive main scanning operations, the nozzles selected as the some of the nozzles for setting the print density high are different from each other. The control unit causes the head unit to perform the main scanning operation a plurality of times for the same position in the target where the ink is ejected,
When the number of times of the main scanning operation to be performed on the same position is defined as the number of passes, at least one of the two consecutive main scanning operations included in the main scanning operation for the number of passes performed continuously. 2. The printing apparatus according to claim 1, wherein, in the main scanning operation, the nozzles selected as the partial nozzles for setting the print density high are different from each other.   The said control part changes the said nozzle selected as the said some nozzle which sets the said print density high, every time the said head part performs the said one main scanning operation, The Claim 1 characterized by the above-mentioned. Or the printing device according to 2. In each main scanning operation, the control unit sets the print density of each nozzle based on a preset pattern,
And the nozzles selected as the partial nozzles for setting the print density high by sequentially using each of the plurality of patterns different from each other each time the head portion performs the main scanning operation once. The printing apparatus according to claim 3, wherein the printer is changed.   In at least a part of the main scanning operation, for the plurality of nozzles present at the end of the nozzle row in the sub-scanning direction, the control unit, so that the print density gradually changes, The printing apparatus according to claim 1, wherein the print density of the nozzle is set. The head unit has a plurality of inkjet heads that eject ink of the same color,
Each of the plurality of inkjet heads has a plurality of nozzles arranged at different positions in the sub-scanning direction, and the nozzle row in the head unit is configured by aligning the nozzles in each of the inkjet heads. In such a manner, the positions are shifted from each other in the sub-scanning direction,
In at least a part of the main scanning operation, the control unit may control the print density of each of the plurality of nozzles existing at the end in the sub-scanning direction with respect to the arrangement of the nozzles in each of the inkjet heads. The printing apparatus according to any one of claims 1 to 5, wherein the print density of each of the nozzles is set so as to change gradually. A printing method for performing printing by an inkjet method,
In a head portion having a nozzle row in which a plurality of nozzles for ejecting ink are arranged,
A main scanning operation of ejecting ink while moving in a preset main scanning direction,
A sub-scanning operation of relatively moving in a sub-scanning direction orthogonal to the main scanning direction with respect to a target for discharging ink,
In the nozzle row, the plurality of nozzles are arranged while being shifted in position in the sub-scanning direction,
When the density of ink dots that can be formed by one nozzle in one main scanning operation is defined as the print density of the nozzle,
In each main scanning operation, the print density of each of the nozzles is set so that the print density of some of the nozzles is higher than the print density of the other nozzles,
A printing method, wherein at least a part of the two successive main scanning operations, the nozzles selected as the partial nozzles for setting the print density high are different from each other.

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