Printer, control method of the same, and program

Abstract

To provide a printer which can suppress lowering of image quality caused by density unevenness.SOLUTION: A printer executes printing processing of allowing a control device to drive a driving element by driving frequency according to relative moving speed between a medium to be printed and a head, while relatively moving the medium to be printed and the head on the basis of image data according to a velocity profile, to discharge ink to the medium to be printed from nozzles, and to print an image onto the medium to be printed, which includes discharging the ink at such a density unevenness frequency band that an ink discharge volume is different from a discharge volume based on the image data, out of the driving frequency, where the printing processing relatively moves the medium to be printed and the head so that at least a part of a density unevenness moving section which is a moving section between the medium to be printed relatively moved at the relative moving speed corresponding to the density unevenness frequency band and the head, and the specific image region are made to overlap each other when the image includes a blank region, and a specific image region having a low duty region or a character region.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a printing apparatus that performs printing while relatively moving a head and a printing medium, a control method thereof, and a program.

Background Art

[0002] As a conventional printing apparatus, the recording apparatus of Patent Document 1 is known. This recording apparatus includes a recording head that performs recording on a recording medium, and a carriage that moves the recording head. By moving the recording head by this carriage, recording is performed on paper.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the recording apparatus of Patent Document 1 described above, in recording on paper, when ink is ejected from the nozzles of the recording head based on recording data, residual vibration occurs in which the meniscus of the ink formed at the nozzles vibrates due to the ejection. Further, since recording is performed in the acceleration / deceleration section of the carriage, as the moving speed of the recording head changes due to acceleration / deceleration, the ejection frequency of the recording head changes. In this case, the residual vibration of the meniscus and the pressure wave corresponding to the ejection frequency of the recording head may overlap, and the ejection volume of the ink from the nozzles may be less than the ejection volume based on the recording data. Such a decrease in the ejection volume of the ink may cause a low-density region to occur in the image, resulting in a possible deterioration in image quality.

[0005] The present invention has been made to solve such problems, and an object thereof is to provide a printing apparatus, a control method thereof, and a program that can suppress a deterioration in image quality caused by density unevenness.

Means for Solving the Problem

[0006] A printing apparatus according to an aspect of the present disclosure includes a nozzle that discharges ink onto a printing medium, a head having a drive element that applies pressure to discharge ink from the nozzle, a relative movement device that relatively moves the printing medium and the head, and a control device. The control device drives the drive element at a drive frequency corresponding to the relative movement speed between the printing medium and the head while relatively moving the printing medium and the head according to a speed profile based on image data, and discharges ink from the nozzle onto the printing medium to print an image on the printing medium. In the printing process, a printing process including discharging ink in a density unevenness frequency band in which the discharged volume of ink is different from the discharged volume based on the image data among the drive frequencies is executed. In the printing process, when the image includes a specific image area having a blank area, a low duty area, or a character area, at least a part of a density unevenness movement section, which is a movement section between the printing medium and the head that relatively moves at a relative movement speed corresponding to the density unevenness frequency band, and the specific image area are overlapped, and the printing medium and the head are relatively moved.

[0007] A method for controlling a printing apparatus according to an aspect of the present disclosure is a method for controlling a printing apparatus including a head having nozzles for discharging ink onto a printing medium and drive elements for applying pressure to discharge the ink from the nozzles, and a relative movement device for relatively moving the printing medium and the head. The method includes performing a printing process of discharging ink from the nozzles onto the printing medium by driving the drive elements at a driving frequency corresponding to the relative movement speed between the printing medium and the head while relatively moving the printing medium and the head according to a speed profile based on image data to print an image on the printing medium. The printing process includes performing a printing process including discharging ink in a density unevenness frequency band where the discharged volume of the ink is different from the discharged volume based on the image data among the driving frequencies. In the printing process, when the image includes a specific image area having a blank area, a low duty area, or a character area, the printing medium and the head are relatively moved so that at least a part of a density unevenness movement section, which is a movement section of the printing medium and the head moving relatively at a relative movement speed corresponding to the density unevenness frequency band, overlaps with the specific image area.

[0008] A program according to an aspect of the present disclosure is for a printing apparatus including a head having a nozzle that discharges ink onto a printing medium and a driving element that applies pressure for discharging ink from the nozzle, and a relative movement device that relatively moves the printing medium and the head. Based on image data, while relatively moving the printing medium and the head according to a speed profile, the driving element is driven at a driving frequency corresponding to the relative movement speed between the printing medium and the head to discharge ink from the nozzle onto the printing medium, and perform a printing process of printing an image on the printing medium. Among the driving frequencies, a printing process including discharging ink in a density unevenness frequency band where the discharged volume of ink is different from the discharged volume based on the image data is executed. In the printing process, when the image includes a specific image area having a blank area, a low duty area, or a character area, at least a part of a density unevenness movement section, which is a movement section of the printing medium and the head that relatively move at a relative movement speed corresponding to the density unevenness frequency band, and the specific image area are overlapped, and the printing medium and the head are relatively moved.

Advantages of the Invention

[0009] Due to the overlap between the residual signal caused by ink discharge and the pressure wave caused by driving the driving element, the discharged volume of ink may be different from the discharged volume based on the image data. Even in such a case, the printing apparatus relatively moves the printing medium and the head so that at least a part of the density unevenness movement section and the specific image area overlap. As a result, the density unevenness movement image formed by the head moving in the density unevenness movement section overlaps with the specific image area. Therefore, the density unevenness image area becomes less noticeable, and a decrease in image quality due to density unevenness can be suppressed.

[0010] The above object, other objects, features, and advantages of the present disclosure will become apparent from the following detailed description of the preferred embodiments with reference to the accompanying drawings.

Brief Description of the Drawings

[0011]

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Embodiments for Carrying Out the Invention

[0012] <Printing Apparatus> As shown in FIG. 1, a printing apparatus 10 according to an embodiment of the present disclosure is an apparatus that discharges ink from a head 20 onto a printing medium A to print an image on the printing medium A, and is, for example, an inkjet printer of a serial head type. The printing medium A is, for example, a sheet such as paper and cloth.

[0013] Hereinafter, the moving direction in which the head 20 moves is referred to as the left-right direction. A direction that intersects (for example, is orthogonal to) this moving direction and in which the printing medium A is conveyed is referred to as the front-rear direction. Also, a direction that intersects (for example, is orthogonal to) the moving direction of the head 20 and the conveying direction of the printing medium A is referred to as the up-down direction. However, the directions related to the printing apparatus 10 are not limited to this.

[0014] The printing apparatus 10 includes a head 20. The head 20 has a plurality of nozzles 21 and a plurality of drive elements 22 (FIG. 2). The plurality of nozzles 21 are arranged in the front-rear direction to form a nozzle row, and the plurality of nozzle rows are arranged in the left-right direction. The nozzle 21 opens to a discharge surface 23 which is the lower surface of the head 20. The drive element 22 is a piezoelectric element, a heating element, an electrostatic actuator, etc., is provided for each nozzle 21, and applies pressure for discharging ink droplets from the nozzle 21 to the ink in the head 20. This pressure wave acts on the meniscus of the ink formed in the nozzle 21, and the ink is discharged from the nozzle 21.

[0015] Furthermore, the printing apparatus 10 includes a tank 11 and a platen 12. The tank 11 communicates with the nozzles 21 of the head 20, stores ink, and supplies it to the nozzles 21. The platen 12 is positioned at a predetermined distance below the head 20. The flat upper surface of the platen 12 is arranged to face the discharge surface 23 of the head 20 and supports the printing medium A from below.

[0016] Furthermore, the printing apparatus 10 includes a moving device 30 that moves the head 20 in the left-right direction. The moving device 30 has a carriage 31, two guide rails 32, an endless belt 33, and a moving motor 34. The carriage 31 is box-shaped and mounts the head 20. The two guide rails 32 extend left and right across the platen 12 disposed directly below, are arranged front and rear apart so as to sandwich all the nozzles 21 therebetween, and support the carriage 31 movably. The endless belt 33 is connected to the carriage 31 and is connected to the moving motor 34 via a pulley 35 provided on the guide rail 32. Therefore, when the moving motor 34 rotates and drives, the endless belt 33 runs, and the carriage 31 and the head 20 mounted on the carriage 31 are moved in the left-right direction along the guide rail 32. Thereby, the moving device 30 is a relative moving device that relatively moves the printing medium A and the head 20. In this case, the relative moving direction in which the printing medium A and the head 20 relatively move is the left-right direction.

[0017] Furthermore, the printing apparatus 10 includes a conveyance device 40 that conveys the printing medium A in the front-rear direction. The conveyance device 40 has, for example, conveyance rollers 41 and a conveyance motor 42 (FIG. 2). The conveyance rollers 41 have an axis extending in the left-right direction, and the conveyance motor 42 is connected to the axis of the conveyance rollers 41. When the conveyance motor 42 is rotationally driven, the conveyance rollers 41 rotate about their axis, and convey the printing medium A in the front-rear direction on the platen 12.

[0018] Furthermore, as shown in FIG. 2, the printing apparatus 10 includes a control device 50, and a communication interface 53, a head drive circuit 54, a movement drive circuit 55, and a conveyance drive circuit 56 that are electrically connected to the control device 50. The control device 50 is configured by, for example, a computer, and has an arithmetic unit 51 and a storage unit 52.

[0019] The storage unit 52 is a memory accessible from the arithmetic unit 51, and has at least one of, for example, RAM, ROM, E2PROM, and NVRAM. The storage unit 52 stores data input from the communication interface 53, and computer programs and various data used for data processing by the arithmetic unit 51.

[0020] The arithmetic unit 51 includes, for example, a processor such as a CPU, an integrated circuit such as an ASIC, or both circuits. By the arithmetic unit 51 executing a computer program while referring to the stored data in the storage unit 52, the control device 50 controls the operations of each part of the printing apparatus 10. Thereby, the printing apparatus 10 executes various processes such as a printing process for printing an image and a speed change process for changing the relative speed of the head 20 in the printing process. Note that these processes will be described later.

[0021] Note that the control device 50 may be constituted by a single device, or a plurality of devices may be distributed and configured to cooperate to perform the operations of the control device 50. For example, the printing device 10 may be configured to include an information processing unit such as a personal computer or a mobile terminal device, and a printing execution unit having the head 20. In this case, the information processing unit and the printing execution unit are formed separately so as to be communicable with each other. In such a case, the control device 50 may be constituted by the control device of the information processing unit and the control device of the printing execution unit. These control devices cooperate to perform the operations of the control device 50 of the printing device 10.

[0022] The communication interface 53 is a connecting device that connects to an external device existing independently from outside the printing device 10, and may be connected to the external device by wired communication such as a USB cable or wireless communication such as a LAN. Examples of the external device include a computer, a mobile terminal device, a server, a storage medium, and a camera. Thereby, the control device 50 acquires data such as image data from the external device via the communication interface 53. The image data is data representing an image to be printed, and is, for example, raster data.

[0023] The head drive circuit 54 is electrically connected to the drive element 22 of the head 20. The control device 50 generates a control signal for driving the drive element 22 based on image data or the like, and the head drive circuit 54 generates a drive signal for the drive element 22 based on this control signal. Then, the drive element 22 is driven based on the drive signal so as to apply pressure to the ink in the head 20 at the ejection timing based on the image data. Thereby, ink droplets are ejected from the nozzles 21 of the head 20.

[0024] The movement drive circuit 55 is electrically connected to the movement motor 34 of the moving device 30. The control device 50 generates a control signal for driving the movement motor 34 based on image data or the like, and the movement drive circuit 55 generates a drive signal for the movement motor 34 based on this control signal. Then, the movement motor 34 drives based on the drive signal so as to move the carriage 31 on which the head 20 is mounted in the left - right direction at a variable speed and stop the carriage 31 at an arbitrary position within its movable range.

[0025] The conveyance drive circuit 56 is electrically connected to the conveyance motor 42 of the conveyance device 40. The control device 50 generates a control signal for driving the conveyance motor 42 based on image data or the like, and the conveyance drive circuit 56 generates a drive signal for the conveyance motor 42 based on this control signal. Then, the conveyance motor 42 drives based on the drive signal so as to intermittently or continuously convey the printing medium A on the platen 12 in the front - rear direction and stop the printing medium A at a predetermined position on the platen 12.

[0026] Furthermore, the printing apparatus 10 includes a display device 13 and an input device 14 that are electrically connected to the control device 50. The display device 13 is a device that displays information such as printed images, for example, a liquid crystal display or the like. The input device 14 is a device that receives input of external information, for example, a touch panel, a physical switch, and a communication interface 53, etc., receives an operation by the user, and transmits the received operation information to the control device 50.

[0027] <Printing process> The control device 50 acquires the image data of the print image which is the target of the printing process, executes data processing such as halftone processing on the image data, and generates image data in a printable format by the printing device 10. Then, the control device 50 executes the printing process based on the image data of the print image. In this printing process, the control device 50 executes a pass operation based on a partial image data which is a part of the image data, and while moving the head 20 to the right or left, ejects ink droplets from the nozzles 21 of the head 20 onto the print medium A. Thereby, dots are formed on the print medium A, and as shown in FIG. 3B, a partial image D composed of dots is formed on the print medium A. The relative movement of the head 20 with respect to the print medium A is performed according to a speed profile. The speed profile will be described later.

[0028] Then, the control device 50 executes a conveyance operation to convey the print medium A forward. In this way, the control device 50 executes the pass operation and the conveyance operation, so that a plurality of partial images D are formed along the front-rear direction, and a print image composed of the plurality of partial images D is formed on the print medium A. This partial image D is a part of the print image and is an image formed on the print medium A by one pass operation. The partial image data is a part of the image data of the print image and is data representing the partial image D.

[0029] <Speed Profile> The relative movement between the print medium A and the head 20 in the pass operation of such a printing process is performed according to a speed profile such as the first speed profile in FIG. 3A. This speed profile represents the relative movement distance between the print medium A and the head 20 in the left-right direction on the horizontal axis, and represents the relative movement speed between the print medium A and the head 20 on the vertical axis. This relative movement distance is set based on the horizontal dimension of the partial image D formed in the pass operation, and the relative movement speed is set based on the print duty etc. of this partial image D.

[0030] Note that, as the speed profile used for the pass operation, instead of the first speed profile, a second speed profile different from the first speed profile may be used. The second speed profile will be described later.

[0031] Also, in the serial head type printing apparatus 10 of the example in FIG. 1, the head 20 is moved without moving the printing medium A in the left - right direction. Therefore, hereinafter, the relative movement speed between the printing medium A and the head 20 is referred to as the movement speed of the head 20. Also, the relative movement acceleration, which is the change rate of the relative movement speed between the printing medium A and the head 20, is referred to as the acceleration of the head 20. Also, the relative movement distance between the printing medium A and the head 20 is referred to as the movement distance of the head 20. Further, the movement of the head 20 with positive acceleration may be referred to as acceleration movement, and the movement of the head 20 with negative acceleration may be referred to as deceleration movement.

[0032] In the pass operation, according to the speed profile of the example in FIG. 3A, after starting the movement, the head 20 accelerates from the speed V0 to a higher speed V1 in the acceleration movement section Cb. Then, the head 20 moves at a constant speed V1 in the constant speed movement section Cc. Further, the head 20 decelerates from the speed V1 to the speed V0 in the deceleration movement section Cd and stops moving. While the head 20 is moving in this acceleration movement section Cb, constant speed movement section Cc, and deceleration movement section Cd, ink is ejected from the head 20. By this pass operation, as shown in FIG. 3B, a partial image D is formed in the printing area A1 of the printing medium A. Note that hereinafter, the processing for the acceleration movement section Cb will be described. However, for the deceleration movement section Cd, since the movement speed of the head 20 changes in the same way as the acceleration movement section Cb, the same processing as the acceleration movement section Cb can be executed.

[0033] <First determination process> In such a pass operation, the head 20 moves according to the speed profile, and ink is ejected by driving the driving element 22. Depending on the highest frequency among the driving frequencies of the driving element 22 corresponding to the moving speed of the head 20, the ink ejection volume by driving the driving element 22 may decrease. For this reason, the control device 50 executes a first determination process for determining whether the highest frequency among the driving frequencies of the driving element 22 in the printing process is less than the low density frequency band F. As shown in FIG. 4B, this low density frequency band F is a frequency band in which the ink ejection volume among the driving frequencies of the driving element 22 decreases compared to the ejection volume based on the image data.

[0034] That is, as shown in FIG. 3A, in the acceleration movement section Cb by the pass operation, ink is ejected from the head 20 while the moving speed of the head 20 changes. Here, in order to eject ink so as to form dots at regular intervals, the driving element 22 is driven at a driving frequency corresponding to the moving speed of the head 20. Therefore, as shown in FIG. 4A, the driving frequency of the driving element 22 changes in proportion to the moving speed of the head 20.

[0035] When the driving element 22 is driven, the meniscus of the ink formed in the nozzle 21 vibrates due to the pressure wave, and the ink is ejected from the nozzle 21. If the driving element 22 performs the next driving with vibration remaining in the meniscus after this ejection, the pressure wave corresponding to this driving overlaps with the residual vibration of the meniscus, and the ink ejection volume from the nozzle 21 may decrease compared to the ejection volume based on the image data. For example, as shown in FIG. 4B, the ink ejection volume in the low density frequency band F among the driving frequencies of the driving element 22 becomes smaller than the ejection volume based on the image data indicated by the alternate long and short dash line.

[0036] Incidentally, the relative relationship between the driving frequency of the driving element 22 in FIG. 4B and the ejection volume of the ink is acquired in advance, and the low-concentration frequency band F among the driving frequencies is stored in the storage unit 52. This relative relationship is acquired by experiment or calculation. In the experiment, while changing the driving frequency of the driving element 22, ink is ejected from the nozzle 21. Then, by measuring the weight of the ejected ink with a balance, the ejection volume of the ink corresponding to the weight is acquired. Alternatively, the ejection volume of the ink is acquired by performing image processing on the dots formed by the ejected ink. Further, in the calculation, based on the electric circuit model of the head 20, the ejection volume of the ink corresponding to the driving frequency of the driving element 22 is acquired by calculation or simulation.

[0037] However, if the highest frequency among the driving frequencies of the driving element 22 in the pass operation is less than the low-concentration frequency band F, the ejection volume of the ink does not decrease. Therefore, the control device 50 executes the first determination process to determine whether the highest frequency is less than the low-concentration frequency band F. The highest frequency is the product of a predetermined driving frequency and the printing duty of the partial image D based on the partial image data. For example, when the predetermined driving frequency is 50 kHz and the printing duty of the partial image D targeted for the pass operation is 60%, the highest frequency of that pass operation is 30 kHz.

[0038] The printing duty is the ratio of the size of the dots constituting the partial image D to the size of the partial image D. The size of the dots is obtained based on the number and type of the dots. The types of dots include, for example, no dot, small dot, medium dot larger than the small dot, and large dot larger than the medium dot. When all the dots constituting the partial image D are large dots, the printing duty of the partial image D is 100%. When all the dots constituting the partial image D are no dots, the printing duty of the partial image D is 0%.

[0039] In this first determination process, when the highest frequency of the driving element 22 is less than the low-concentration frequency band F, the driving element 22 does not drive at the driving frequency of the low-concentration frequency band F. Therefore, the ejection volume of the ink does not decrease from the ejection volume based on the partial image data, and the partial image D formed based on this partial image data has the decrease in density due to the decrease in the ejection volume suppressed. On the other hand, when the highest frequency is the low-concentration frequency band F or greater than the low-concentration frequency band F, the driving element 22 drives at the driving frequency of the low-concentration frequency band F. Due to the driving of the driving element 22 in this low-concentration frequency band F, the ejection volume of the ink decreases from the ejection volume based on the partial image data. Therefore, as shown in FIG. 5B, in the partial image D, a low-concentration image region Da, which is a region where the density has decreased due to the decrease in the ejection volume, is generated.

[0040] <Second determination process> Thus, even when the low-concentration image region Da is generated in the partial image D, if the low-concentration image region Da overlaps with a specific image region Db in the partial image D, where the low-concentration image region Da is a region where the low-concentration image region Da is difficult to visually recognize, the deterioration of the image quality caused by the low-concentration image region Da can be suppressed. Therefore, the control device 50 executes a second determination process for determining whether the image includes the specific image region Db based on the image data. This specific image region Db has a blank region, a low-duty region, or a character region.

[0041] In this second determination process, the control device 50 acquires the size and position of the dots constituting the partial image D based on the partial data, and determines whether the partial image D includes the specific image region Db based on the size and position of the dots. The blank region is a region in the partial image D where no dots are formed, and is a region where the number of consecutive dotless pixels is equal to or greater than a predetermined value. The low-duty region is a region where the duty is less than a predetermined value. The character region is a region where characters are formed by dots. And when the partial image D includes the specific image region Db, the control device 50 acquires the position of the specific image region Db and stores it in the storage unit 52.

[0042] <Fourth determination process> Thus, even if the specific image region Db is included in the partial image D, depending on its position, the specific image region Db may not overlap with the low-concentration image region Da. The position of the low-concentration image region Da changes according to the speed profile. For this reason, the control device 50 executes the fourth determination process for the position of the low-concentration image region Da according to the first speed profile and the third determination process for the position of the low-concentration image region Da according to the second speed profile. The third determination process will be described later.

[0043] In the fourth determination process, when the highest frequency in the first determination process is not less than the low-concentration frequency band F and the image includes the specific image region Db in the second determination process, the control device 50 determines whether all of the first low-concentration movement section Ca1 corresponding to the low-concentration image region Da and the specific image region Db can be overlapped.

[0044] That is, in the pass operation, in the acceleration movement section Cb of FIG. 5A, the movement speed of the head 20 changes according to the first speed profile. The first low-concentration movement section Ca1 in this acceleration movement section Cb is the movement section between the print medium A and the head 20 that relatively moves in the low-concentration speed band Va in the printing process according to the first speed profile. As shown in FIG. 4A, the low-concentration speed band Va is the movement speed of the head 20 when the drive element 22 is driven in the low-concentration frequency band F. As shown in FIG. 4B, when the drive element 22 is driven in the low-concentration frequency band F, the ejection volume of the ink ejected from the nozzles 21 of the head 20 decreases compared to the ejection volume based on the image data. Therefore, as shown in FIGS. 5A and 5B, in the low-concentration image region Da, which is the region formed while the head 20 is moving in the first low-concentration movement section Ca1 among the partial images D formed by the pass operation, the density is lower than that of other regions.

[0045] The first speed profile is obtained based on, for example, the moving distance of the head 20 based on the dimensions of the partial image D in the left - right direction, the moving speed V1 of the head 20 based on the print duty of the partial image D, etc., and a predetermined acceleration. When all of the first low - density moving section Ca1 based on this first speed profile overlaps with the specific image area Db based on the partial image data, all of the low - density image area Da corresponding to the first low - density moving section Ca1 overlaps with the specific image area Db. In this case, the first speed profile is used as the speed profile in the printing process. Thereby, the low - density image area Da becomes less conspicuous due to the specific image area Db, and it is possible to suppress a decrease in the image quality of the partial image D caused by a density decrease.

[0046] <Third determination process> However, as shown in FIG. 6A, there may be a case where part or all of the first low - density moving section Ca1 according to the first speed profile does not overlap with the specific image area Db. In this case, when changing the speed profile of the printing process from the first speed profile to the second speed profile, at least a part of the second low - density moving section Ca2 according to the second speed profile may be made to overlap with the specific image area Db.

[0047] Therefore, the control device 50 executes a third determination process to determine whether at least a part of the second low - density moving section Ca2 overlaps with the specific image area Db. The second low - density moving section Ca2 is a section in the acceleration moving section Cb where the head 20 moves at the moving speed in the low - density speed band Va in the second speed profile. And when at least a part of the second low - density moving section Ca2 overlaps with the specific image area Db, the control device 50 executes a speed change process to change the speed profile of the printing process from the first speed profile to the second speed profile.

[0048] For example, the following three second speed profiles can be targets of this third determination process. As shown in FIG. 6A, the first second speed profile is obtained when the dimension of the first low-concentration movement section Ca1 in the left-right direction is equal to or less than the dimension of the specific image region Db. In this case, as shown in the examples of FIGS. 6B and 6C, in the second speed profile, one end of the second low-concentration movement section Ca2 in the left-right direction overlaps with one end of the specific image region Db. In the speed profile, along the direction in which the acceleration movement section Cb and the constant speed movement section Cc are arranged, in the acceleration movement section Cb, the side closer to the constant speed movement section Cc may be referred to as the right, and the side farther from the constant speed movement section Cc may be referred to as the left.

[0049] As shown in FIG. 6A, when the specific image region Db is located to the left of the first low-concentration movement section Ca1, as shown in FIG. 6B, the right end of the second low-concentration movement section Ca2 overlaps with the right end of the specific image region Db. On the other hand, when the specific image region Db is located to the right of the first low-concentration movement section Ca1 in the left-right direction, as shown in FIG. 6C, the left end of the second low-concentration movement section Ca2 overlaps with the left end of the specific image region Db. As a result, the entire second low-concentration movement section Ca2 and the specific image region Db overlap.

[0050] Furthermore, as shown in FIGS. 6B and 6C, the acceleration, which is the change rate of the relative movement speed in the second low-concentration movement section Ca2, is set to be the same as the acceleration in the first low-concentration movement section Ca1 (FIG. 6A). As a result, in the second low-concentration movement section Ca2, the position and movement speed at its left end become (C1, Va1), and the position and movement speed at its right end become (C2, Va2). Here, Va1 indicates the minimum speed of the low-concentration speed band Va, and Va2 indicates the maximum speed of the low-concentration speed band Va. C1 indicates the left end position of the second low-concentration movement section Ca2, and C2 indicates the right end position of the second low-concentration movement section Ca2.

[0051] Furthermore, the right end in the section Cl to the left of the second low-concentration moving section Ca2 in the acceleration moving section Cb overlaps with the left end (C1, Va1) of the second low-concentration moving section Ca2. Also, the left end in the section Cr to the right of the second low-concentration moving section Ca2 in the acceleration moving section Cb overlaps with the right end (C2, Va2) of the second low-concentration moving section Ca2. Thereby, the moving speeds in the second low-concentration moving section Ca2 and the other sections Cl, Cr are continuous.

[0052] Furthermore, the left end of the left section Cl in the second speed profile is aligned with the start position (C0, V0) of the acceleration moving section Cb, similar to the left end of the first speed profile. Also, the right end of the right section Cr in the second speed profile is aligned with the end position (C3, V1) of the acceleration moving section Cb, similar to the right end of the first speed profile. Thereby, the accelerations of the sections Cl, Cr other than the second low-concentration moving section Ca2 in the second speed profile are different from those of the first speed profile. V0 indicates the start speed of the acceleration movement, and V1 indicates the end speed of the acceleration movement.

[0053] In this way, the first second speed profile is obtained. The absolute value of the acceleration in this second speed profile is limited to a predetermined value or less in terms of the performance and image quality of the moving device 30. Therefore, the control device 50 determines whether the absolute value of the acceleration of the second speed profiles in FIGS. 6B and 6C is less than or equal to the predetermined value. Here, when the absolute value of the acceleration of the second speed profile is less than or equal to the predetermined value, the control device 50 determines that all of the second low-concentration moving section Ca2 of the second speed profile and the specific image area Db are overlapped.

[0054] In this first second speed profile, one end of the second low-concentration moving section Ca2 overlaps with one end of the specific image region Db. As a result, since the entire low-concentration image region Da corresponding to the second low-concentration moving section Ca2 overlaps with the specific image region Db, it is possible to suppress a decrease in the image quality of the partial image D caused by a decrease in concentration. Also, since the change between the acceleration of the first low-concentration moving section Ca1 in the acceleration moving section Cb and the accelerations of the sections Cl and Cr is suppressed to be small, it is possible to suppress a decrease in the image quality caused by a change in acceleration.

[0055] Also, as shown in FIG. 7A, the second second speed profile is obtained when the dimension of the first low-concentration moving section Ca1 in the left-right direction is larger than the dimension of the specific image region Db. In this case, as shown in FIG. 7B, in the second speed profile, both ends of the second low-concentration moving section Ca2 in the left-right direction are respectively overlapped with both ends of the specific image region Db. As a result, the entire second low-concentration moving section Ca2 and the specific image region Db overlap. Also, the second low-concentration moving section Ca2 has its left end position and moving speed become (C1, Va1), and its right end position and moving speed become (C2, Va2). The acceleration in this second low-concentration moving section Ca2 is different from the acceleration in the first low-concentration moving section Ca1 (FIG. 7A).

[0056] Furthermore, the right end of the left section Cl is overlapped with the left end (C1, Va1) of the second low-concentration moving section Ca2. Also, the left end of the right section Cr is overlapped with the right end (C2, Va2) of the second low-concentration moving section Ca2. As a result, the moving speeds in the second low-concentration moving section Ca2 and the other sections Cl and Cr are continuous.

[0057] Furthermore, the left end of the left section Cl in the second speed profile is aligned with the start position (C0, V0) of the acceleration movement section Cb, similar to the left end of the first speed profile. Also, the right end of the right section Cr in the second speed profile is aligned with the end position (C3, V1) of the acceleration movement section Cb, similar to the right end of the first speed profile. As a result, since the accelerations of sections Cl and Cr are different from those of the first speed profile, the acceleration throughout the entire acceleration movement section Cb in this second speed profile is different from that of the first speed profile.

[0058] In this way, the second second speed profile is obtained. The control device 50 determines whether or not the absolute value of the acceleration in the second speed profile of FIG. 7B is less than or equal to a predetermined value. Here, when the absolute value of the acceleration of the second speed profile is less than or equal to the predetermined value, the control device 50 determines that all of the second low-concentration movement section Ca2 of the second speed profile and the specific image region Db are to be overlapped.

[0059] In the second second speed profile obtained in this way, both ends of the second low-concentration movement section Ca2 are overlapped with both ends of the specific image region Db. As a result, the dimension of the second low-concentration movement section Ca2 in the left-right direction becomes smaller than the dimension of the first low-concentration movement section Ca1 and becomes the same as the dimension of the specific image region Db. For this reason, it is possible to overlap all of the low-concentration image region Da corresponding to the second low-concentration movement section Ca2 and the specific image region Db, and suppress a deterioration in the image quality of the partial image D caused by the density reduction.

[0060] However, there may be cases where the absolute values of the accelerations in the first and second second speed profiles are greater than a predetermined value. In this case, these second speed profiles are not used as the speed profile for the printing process. For this reason, the control device 50 determines that all of the second low-concentration movement section Ca2 and the specific image region Db cannot be overlapped with these second speed profiles.

[0061] Therefore, as the third second-speed profile, a speed profile is obtained such that a part of the second low-concentration moving section Ca2 overlaps with the specific image area Db. In this case, as shown in FIG. 8B, the acceleration of the second low-concentration moving section Ca2 is set to be the same as the acceleration of the first low-concentration moving section Ca1, and the absolute value of the acceleration in the sections Cl and Cr is set to be equal to or less than a predetermined value.

[0062] Furthermore, the right end of the left section Cl is overlapped with the left end (C1, Va1) of the second low-concentration moving section Ca2, and the left end of the right section Cr is overlapped with the right end (C2, Va2) of the second low-concentration moving section Ca2. Furthermore, the left end of the left section Cl is aligned with the start position (C0, V0) of the acceleration moving section Cb, and the right end of the right section Cr is aligned with the end position (C3, V1) of the acceleration moving section Cb.

[0063] In such a state, the center of the second low-concentration moving section Ca2 in the left-right direction is brought closer to the center of the specific image area Db than the center of the first low-concentration moving section Ca1, and the third second-speed profile is obtained. In this third second-speed profile, the control device 50 determines whether or not a part of the second low-concentration moving section Ca2 overlaps with the specific image area Db. If these overlap, in the second-speed profile, the center of the second low-concentration moving section Ca2 is closer to the center of the specific image area Db than the center of the first low-concentration moving section Ca1. Therefore, the overlap range between the second low-concentration moving section Ca2 and the specific image area Db can be made wider than the overlap range between the first low-concentration moving section Ca1 and the specific image area Db. Thus, the overlap range between the low-concentration image area Da corresponding to the second low-concentration moving section Ca2 and the specific image area Db can be made as wide as possible, and a deterioration in the image quality of the partial image D due to a decrease in concentration can be suppressed.

[0064] <Control Method of Printing Device> The printing device 10 is controlled by the control device 50 according to the flowchart showing an example of the control method in FIG. 9. For example, the printing device 10 starts the process in FIG. 9 in accordance with a start instruction from the user using the input device 14. In the process of FIG. 9, the control device 50 acquires the partial image data of the path operation among the image data of the print image to be printed from the communication interface 53 or the storage unit 52 (step S10). Then, the control device 50 executes a first determination process to determine whether the maximum frequency of the drive element 22 in the printing process is less than the low-density frequency band F (step S11).

[0065] If the maximum frequency is less than the low-density frequency band F in the first determination process (step S11: YES), the low-density image area Da caused by driving the drive element 22 in the low-density frequency band F does not occur in the partial image D. Therefore, the control device 50 executes the path operation of the printing process based on the partial image data using the first speed profile as the speed profile of the printing process (step S12).

[0066] On the other hand, if the maximum frequency is not less than the low-density frequency band F in the first determination process of step S11 (step S11: NO), the control device 50 executes a second determination process to determine whether the partial image D based on the partial image data includes the specific image area Db (step S13). Here, when the partial image D does not include the specific image area Db (step S13: NO), the low-density image area Da based on the low-density frequency band F cannot overlap with the specific image area Db. Therefore, the control device 50 executes a correction process to correct the density in the low-density image area Da based on the data corresponding to the low-density image area Da in the partial image data (step S14).

[0067] In the correction process, for example, the partial image data is corrected so that the density of the low-density image area Da increases by increasing the size of the dots constituting the low-density image area Da or increasing the number of dots. Then, the control device 50 executes a path operation based on the partial image data on which the correction process has been performed using the first speed profile (step S12). As a result, the decrease in density in the low-density image area Da is reduced, and the deterioration of the image quality due to the density decrease can be suppressed.

[0068] Also, when the partial image D includes the specific image area Db in the second determination process of step S13 (step S13: YES), the control device 50 executes a fourth determination process to determine whether all of the first low-density movement section Ca1 corresponding to the low-density speed band Va in the first speed profile and the specific image area Db can be overlapped (step S15).

[0069] In this fourth determination process, when all of the first low-density movement section Ca1 and the specific image area Db can be overlapped (step S15: YES), the control device 50 executes a path operation based on the partial image data using the first speed profile (step S12). In this way, without executing the speed change process, in the path operation, ink is ejected while moving the head 20 according to the first speed profile to form the partial image D. In this partial image D, since all of the low-density image area Da corresponding to the first low-density movement section Ca1 overlaps the specific image area Db, the low-density image area Da is less conspicuous, and the deterioration of the image quality of the partial image D due to the density decrease can be suppressed.

[0070] When all of the first low-density movement section Ca1 and the specific image area Db cannot be overlapped in step S15 (step S15: NO), the control device 50 executes a third determination process to determine whether at least a part of the second low-density movement section Ca2 and the specific image area Db can be overlapped in the printing process according to the second speed profile (step S16).

[0071] The third determination process is executed by the control device 50 according to, for example, the flowchart of the example in FIG. 10. In the third determination process, the control device 50 determines whether or not the dimension of the first low-concentration movement section Ca1 in the first speed profile is equal to or less than the dimension of the specific image area Db (step S20).

[0072] For example, as shown in FIG. 6A, when the dimension of the first low-concentration movement section Ca1 is equal to or less than the dimension of the specific image area Db (step S20: YES), the control device 50 acquires the first second speed profile shown in the examples of FIGS. 6B and 6C (step S21). In this second speed profile, one end of the second low-concentration movement section Ca2 in the left-right direction is overlapped with one end of the specific image area Db. Also, the acceleration of the second low-concentration movement section Ca2 is determined to be the same as the acceleration of the first low-concentration movement section Ca1. Further, the movement speeds and accelerations of the sections Cl and Cr are determined so that the movement speeds of the second low-concentration movement section Ca2 and the other sections Cl and Cr are continuous.

[0073] Then, the control device 50 determines whether or not the absolute value of the acceleration in the first second speed profile acquired in S21 is equal to or less than a predetermined value (step S22). Here, when the absolute value of the acceleration in the second speed profile is equal to or less than the predetermined value (step S22: YES), the control device 50 determines that all of the second low-concentration movement section Ca2 and the specific image area Db can be overlapped in the printing process according to this second speed profile (step S23).

[0074] Also, in step S20, for example, as shown in FIG. 7A, when the dimension of the first low-concentration movement section Ca1 is larger than the dimension of the specific image area Db (step S20: NO), the control device 50 acquires the second second-speed profile shown in the example of FIG. 7B (step S24). In this second second-speed profile, both ends of the second low-concentration movement section Ca2 are respectively overlapped with both ends of the specific image area Db. Further, the movement speeds and accelerations of the sections Cl and Cr are determined so that the movement speeds of the second low-concentration movement section Ca2 and the other sections Cl and Cr are continuous. Note that the second second-speed profile in step S24 is different from the first second-speed profile in step S21 in that the acceleration of the second low-concentration movement section Ca2 is different from the acceleration of the first low-concentration movement section Ca1.

[0075] Then, the control device 50 determines whether or not the absolute value of the acceleration in the second second-speed profile acquired in S24 is equal to or less than a predetermined value (step S22). Here, when the absolute value of the acceleration in the second-speed profile is equal to or less than the predetermined value (step S22: YES), the control device 50 determines that all of the second low-concentration movement section Ca2 and the specific image area Db can be overlapped in the printing process according to this second-speed profile (step S23).

[0076] Also, in step S22, when the absolute value of the acceleration in the second speed profile obtained in step S21 or S24 is greater than a predetermined value (step S22: NO), the entire second low-concentration movement section Ca2 of the second speed profile and the specific image area Db cannot be overlapped. In this case, the control device 50 acquires the third second speed profile shown in the example of FIG. 8B (step S25). In this third second speed profile, the acceleration of the second low-concentration movement section Ca2 is determined to be the same as the acceleration of the first low-concentration movement section Ca1. Also, the movement speeds and accelerations of the sections Cl and Cr are determined so that the movement speeds of the second low-concentration movement section Ca2 and the other sections Cl and Cr are continuous. Further, the absolute value of the acceleration of the sections Cl and Cr is equal to or less than the predetermined value, and the center of the second low-concentration movement section Ca2 in the left-right direction is brought closer to the center of the specific image area Db than the center of the first low-concentration movement section Ca1.

[0077] Then, the control device 50 determines whether or not the second low-concentration movement section Ca2 in the third second speed profile acquired in S25 overlaps with the specific image area Db (step S26). Here, when the second low-concentration movement section Ca2 and the specific image area Db overlap (step S26: YES), the control device 50 determines that a part of the second low-concentration movement section Ca2 and the specific image area Db can be overlapped in the printing process according to this second speed profile (step S27). On the other hand, when the second low-concentration movement section Ca2 and the specific image area Db do not overlap (step S26: NO), the control device 50 determines that the second low-concentration movement section Ca2 and the specific image area Db cannot be overlapped in the printing process according to this second speed profile (step S28).

[0078] In this way, when the control device 50 executes the third determination process, it returns to the process of step S16 in FIG. 9. If it is determined in this step S16 that at least a part of the second low-density movement section Ca2 and the specific image area Db cannot be overlapped in the printing process according to the second speed profile (step S16: NO), the control device 50 executes a correction process of correcting the density in the low-density image area Da based on the data corresponding to the low-density image area Da in the partial image data (step S17). This correction process is the same as the correction process in step S14.

[0079] Then, the control device 50 executes a pass operation based on the partial image data on which the correction process has been performed using the first speed profile (step S12). That is, the control device 50 is not executing the speed change process. As a result, the pass operation according to the first speed profile is executed without executing the speed change process. In this pass operation, since the density in the low-density image area Da is corrected by the correction process, the decrease in the density of the low-density image area Da is reduced, and the deterioration of the image quality due to the density decrease can be suppressed.

[0080] Also, if it is determined in step S16 that at least a part of the second low-density movement section Ca2 and the specific image area Db can be overlapped in the printing process according to the second speed profile (step S16: YES), the control device 50 executes a speed change process (step S18). In the speed change process, the control device 50 changes the speed profile from the first speed profile to the second speed profile.

[0081] This second speed profile is the second speed profile that is determined to overlap at least a part or all of the second low-density movement section Ca2 and the specific image area Db among the second speed profiles obtained in steps S21, S24, or S25 in the third determination process of FIG. 10. According to this second speed profile, the printing medium A and the head 20 relatively move so that at least a part or all of the second low-density movement section Ca2 and the specific image area Db overlap.

[0082] Then, the control device 50 executes the path operation of the printing process using the second speed profile as the speed profile of the printing process based on the partial image data (step S12). In this path operation, ink is ejected while moving the head 20 according to the second speed profile to form the partial image D. In this partial image D, since at least a part of the low-concentration image area Da corresponding to the second low-concentration movement section Ca2 overlaps with the specific image area Db, the low-concentration image area Da is less conspicuous, and the deterioration of the image quality of the partial image D due to the density decrease can be suppressed.

[0083] After the control device 50 executes the path operation in step S12, it determines whether all the path operations in the printing process have been executed (step S19). Here, if there are still path operations to be executed (step S19: NO), the control device 50 returns to the process of step S10 and executes the subsequent processes. On the other hand, if all the path operations have been executed (step S19: YES), the control device 50 ends the process.

[0084] <Modification Example 1> In the above configuration, when the entire second low-concentration movement section Ca2 and the specific image area Db can be overlapped in the third determination process, in the speed change process, the speed profile is changed from the first speed profile to the second speed profile in which one end of the second low-concentration movement section Ca2 in the left-right direction is overlapped with one end of the specific image area Db as shown in the examples of FIGS. 6B and 6C. However, the second speed profile is not limited to this. For example, in the printing apparatus 10 according to Modification Example 1, in the speed change process, the speed profile may be changed from the first speed profile to the second speed profile in which the center of the second low-concentration movement section Ca2 in the left-right direction is overlapped with the center of the specific image area Db as shown in the example of FIG. 11B.

[0085] Specifically, as shown in the example of FIG. 11A, at least a part of the first low-concentration moving section Ca1 of the first speed profile does not overlap with the specific image region Db, and the dimension of the first low-concentration moving section Ca1 in the left-right direction may be equal to or smaller than the dimension of the specific image region Db. In this case, the second speed profile is obtained by the control device 50 as follows.

[0086] As shown in the example of FIG. 11B, in the second speed profile, the center of the second low-concentration moving section Ca2 in the left-right direction is overlapped with the center of the specific image region Db. Further, the acceleration, which is the change rate of the relative moving speed in the second low-concentration moving section Ca2, is set to be the same as the acceleration in the first low-concentration moving section Ca1 (FIG. 11A). Further, the right end in the left section Cl is overlapped with the left end (C1, Va1) of the second low-concentration moving section Ca2, and the left end in the right section Cr is overlapped with the right end (C2, Va2) of the second low-concentration moving section Ca2. Further, the left end of the left section Cl is aligned with the start position (C0, V0) of the acceleration moving section Cb, and the right end of the right section Cr is aligned with the end position (C3, V1) of the acceleration moving section Cb.

[0087] In this way, the second speed profile is obtained. The control device 50 determines whether or not the absolute value of the acceleration of the second speed profile is equal to or less than a predetermined value. Here, when the absolute value of the acceleration of the second speed profile is equal to or less than the predetermined value, the control device 50 determines that all of the second low-concentration moving section Ca2 of the second speed profile and the specific image region Db can be overlapped. As a result, since all of the low-concentration image region Da corresponding to the second low-concentration moving section Ca2 overlaps with the specific image region Db, it is possible to suppress the deterioration of the image quality of the partial image D caused by the density reduction.

[0088] <Modification 2> In the printing apparatus 10 according to Modification 2, in the above-described embodiment and Modification 1, the character region of the specific image region Db includes a first character group Db1 and a second character group Db2 different from the first character group Db1. In the third determination process, the control device 50 determines whether or not the second low-density movement section Ca2 can be duplicated with the second character group Db2 without being duplicated with the first character group Db1 in the printing process according to the second speed profile.

[0089] Specifically, as shown in FIG. 5C, the character region of the specific image region Db has a first character group Db1 and a second character group Db2. Each of the first character group Db1 and the second character group Db2 is a single unified region including one or more characters. The first character group Db1 and the second character group Db2 are arranged at different positions from each other in the left-right direction without overlapping each other. The first character group Db1 and the second character group Db2 may be classified according to the size of the characters. For example, the characters constituting the first character group Db1 may be smaller than the characters constituting the second character group Db2.

[0090] Also, the first character group Db1 and the second character group Db2 may be specified by the user. For example, the control device 50 performs image processing of a print image based on image data and acquires a plurality of character groups. Then, the control device 50 displays the plurality of character groups on the display device 13 as options for the first character group Db1. When the user designates the first character group Db1 from the plurality of character groups using the input device 14, this designation information is input from the input device 14 to the control device 50. The control device 50 acquires the designated character group as the first character group Db1 based on the designation information, and acquires the other character groups as the second character group Db2.

[0091] And in the example of FIG. 12A, when at least a part of the first low-concentration moving section Ca1 in the first speed profile does not overlap with the first character group Db1 of the specific image area Db and does not overlap with the second character group Db2 of the specific image area Db, as shown in the example of FIG. 12B, the control device 50 overlaps one end (for example, the right end) of the second low-concentration moving section Ca2 in the second speed profile in the left-right direction with one end (for example, the right end) of the second character group Db2 of the specific image area Db without overlapping the second low-concentration moving section Ca2 with the first character group Db1 of the specific image area Db. Then, the control device 50 makes the acceleration in the second low-concentration moving section Ca2 the same as the acceleration in the first low-concentration moving section Ca1 and acquires the second speed profile in the same manner as the first second speed profile in the examples of FIGS. 6B and 6C.

[0092] In addition, when the dimension of the first low-concentration moving section Ca1 in the left-right direction is larger than the dimension of the specific image area Db, the control device 50 may overlap both ends of the second low-concentration moving section Ca2 in the left-right direction with both ends of the second character group Db2 respectively and acquire the second speed profile in the same manner as the second second speed profile in the example of FIG. 7B. Further, when the dimension of the first low-concentration moving section Ca1 in the left-right direction is less than or equal to the dimension of the specific image area Db, the control device 50 may acquire the second speed profile in the same manner as the second speed profile in the example of FIG. 11B, with the second low-concentration moving section Ca2 not overlapping the first character group Db1 of the specific image area Db and the center of the second low-concentration moving section Ca2 in the left-right direction overlapping the center of the second character group Db2. Also, the control device 50 may acquire the second speed profile in the same manner as the third second speed profile in the example of FIG. 8B, with the second low-concentration moving section Ca2 not overlapping the first character group Db1 of the specific image area Db and the center of the second low-concentration moving section Ca2 in the left-right direction approaching the center of the second character group Db2 more than the center of the first low-concentration moving section Ca1.

[0093] When the absolute value of the acceleration in the second speed profile thus obtained is equal to or less than a predetermined value, in the printing process according to the second speed profile, all or part of the second low-concentration movement section Ca2 and the second character group Db2 of the specific image area Db can be overlapped. As a result, the low-concentration image area Da corresponding to the second low-concentration movement section Ca2 overlaps with the second character group Db2, thereby suppressing a decrease in image quality caused by the low-concentration image area Da. Further, since the low-concentration image area Da does not overlap with the first character group Db1, it is possible to suppress a situation where, for example, the first character group Db1 consisting of small characters becomes difficult to see due to the low-concentration image area Da.

[0094] <Modification Example 3> The printing apparatus 10 according to the above-described embodiment and Modification Examples 1-2 was a serial head type as shown in the example of FIG. 1, but may be a line head type as shown in the example of FIG. 13. In this case, as shown in FIG. 13, the printing apparatus 10 does not include a moving device that moves the head 20 along the left-right direction. The arrangement range of the nozzles 21 in the head 20 extends longer in the left-right direction than the printing area A1 of the printing medium A.

[0095] In the printing process, based on the image data, while the printing medium A is being conveyed forward on the platen 12 by the conveying device 40 without the head 20 moving in the front-rear direction, ink is ejected from the nozzles 21 onto the printing medium A, whereby an image is printed on the printing medium A. In this case, the conveying device 40 is a relative moving device that relatively moves the printing medium A and the head 20. In this case, the relative moving direction in which the printing medium A and the head 20 relatively move is the front-rear direction. Note that the relative moving device may move both or either one of the head 20 and the printing medium A as long as the head 20 and the printing medium A can be relatively moved.

[0096] Thus, also in the line head type printing apparatus 10, in the printing process, the control device 50 relatively moves the printing medium A and the head 20 according to a speed profile based on the image data, and drives the drive element 22 at a drive frequency corresponding to the relative movement speed between the printing medium A and the head 20 as shown in FIG. 4A. As a result, as shown in FIG. 4B, when the maximum frequency of the drive element 22 is not less than the low density frequency band F, the ejection volume of the ink decreases from the volume based on the image data.

[0097] Therefore, when the image includes the specific image area Db, the control device 50 relatively moves the head 20 and the printing medium A so that at least a part of the second low density movement section Ca2 of the second speed profile overlaps with the specific image area Db. As a result, since at least a part of the low density image area Da corresponding to the second low density movement section Ca2 overlaps with the specific image area Db, it is possible to suppress a decrease in the image quality of the image due to the density decrease. Further, when the image does not include the specific image area Db, the control device 50 relatively moves the head 20 and the printing medium A according to the first speed profile.

[0098] For example, the line head type printing apparatus 10 is controlled by the control device 50 according to a flowchart showing an example of the control method in FIG. 9. In this case, in step S10, the image data of the print image to be printed is acquired. In steps S12 and S13, the printing process is executed based on the image data. Further, in step S16 of FIG. 9, the third determination process of FIG. 10 is executed.

[0099] <Modification Example 4> In the above-described embodiments and Modifications 1 to 3, the density unevenness where the ejection volume of the ink is different from the ejection volume based on the image data has been described as the low density where the ejection volume of the ink decreases from the ejection volume based on the image data. However, the density unevenness is not limited thereto, and may be a high density where the ejection volume of the ink increases from the ejection volume based on the image data. For this reason, among the drive frequencies of the drive element 22, the density unevenness frequency band where the ejection volume of the ink is different from the ejection volume based on the image data includes at least one of the low density frequency band F and the high density frequency band E as shown in FIG. 4B.

[0100] The density unevenness moving section is a moving section between the printing medium A and the head 20 that relatively moves at a relative moving speed corresponding to the density unevenness frequency band. The first density unevenness moving section is the density unevenness moving section in the first speed profile, and includes at least one of the first low density moving section Ca1 and the first high density moving section. Further, the second density unevenness moving section is the density unevenness moving section in the second speed profile, and includes at least one of the second low density moving section Ca2 and the second high density moving section.

[0101] The first high density moving section is a moving section between the printing medium A and the head 20 that relatively moves in the high density speed band Vb in the printing process according to the first speed profile. The second high density moving section is a moving section between the printing medium A and the head 20 that relatively moves in the high density speed band Vb in the printing process according to the second speed profile. As shown in FIG. 4A, the high density speed band Vb is the relative moving speed between the printing medium A and the head 20 when driving in the high density frequency band E of the drive element 22, and corresponds to the high density frequency band E. As shown in FIG. 4B, the high density frequency band E is a frequency band in which the ejection volume of the ink increases from the ejection volume based on the image data among the drive frequencies of the drive element 22. A high density image area with a high density is generated in the image due to this increase in the ejection volume.

[0102] Similar to the flowchart of FIG. 9 regarding the low-concentration frequency band F and the low-concentration movement interval, the control device 50 performs processing on the density unevenness frequency band and the density unevenness movement interval. For example, when the highest frequency of the driving element 22 is less than the density unevenness frequency band, a density unevenness image area caused by driving the driving element 22 in the density unevenness frequency band does not occur in the printed image. Therefore, the control device 50 executes printing processing based on the image data using the first speed profile as the speed profile of the printing processing.

[0103] Also, when the image does not include the specific image area Db and when the entire second density unevenness movement interval and the specific image area Db cannot be overlapped, the control device 50 executes the printing processing with the first speed profile without performing the speed change processing. In this printing processing, by using the image data on which the correction processing has been performed, the density unevenness in the density unevenness image area is reduced, and the deterioration of the image quality due to the density unevenness can be suppressed.

[0104] Also, when the entire first density unevenness movement interval and the specific image area Db can be overlapped, the control device 50 executes the printing processing with the first speed profile without performing the speed change processing. Thereby, since the density unevenness image area corresponding to the first density unevenness movement interval is overlapped with the specific image area Db, the density unevenness image area becomes less conspicuous, and the deterioration of the image quality due to the density unevenness can be suppressed.

[0105] Also, when the highest frequency of the driving element 22 is not less than the density unevenness frequency band, the image includes the specific image area Db, a part or all of the first density unevenness movement interval and the specific image area Db do not overlap, and at least a part of the second density unevenness movement interval and the specific image area Db can be overlapped, the control device 50 executes the speed change processing and executes the printing processing with the second speed profile. Thereby, since the density unevenness image area corresponding to the second density unevenness movement interval is overlapped with the specific image area Db, the density unevenness image area becomes less conspicuous, and the deterioration of the image quality due to the density unevenness can be suppressed.

[0106] The control device 50 performs processing on the density unevenness frequency band and the density unevenness movement section in the same way as the flowchart of FIG. 10 regarding the low-concentration frequency band F and the low-concentration movement section. For example, when the dimension of the first density unevenness movement section is equal to or less than the dimension of the specific image area Db, in the second speed profile, one end of the second density unevenness movement section in the left-right direction is overlapped with one end of the specific image area Db. Also, the acceleration of the second density unevenness movement section is determined to be the same as the acceleration of the first density unevenness movement section.

[0107] Also, when the dimension of the first density unevenness movement section is larger than the dimension of the specific image area Db, in the second speed profile, both ends of the second density unevenness movement section may be respectively overlapped with both ends of the specific image area Db. Further, when the absolute value of the acceleration in these second speed profiles is larger than a predetermined value, in the second speed profile, the center of the second density unevenness movement section in the left-right direction may be brought closer to the center of the specific image area Db than the center of the first density unevenness movement section while the absolute value of the acceleration is below the predetermined value.

[0108] <Other Modification Examples> In the above-described embodiment and all modification examples, the image may include a plurality of types of specific image areas Db, and the plurality of types of specific image areas Db may be at least two of a blank area, a low-duty area, and a character area. In this order of the blank area, the low-duty area, and the character area, the second low-concentration movement section Ca2 can be made less conspicuous. Therefore, when at least a part of the plurality of types of specific image areas Db and the second low-concentration movement section Ca2 are overlapped, the priority order of overlapping is the blank area, the low-duty area, and the character area.

[0109] In the above-described embodiment and all modification examples, the image may include a plurality of specific image areas Db, and there may be a case where the plurality of specific image areas Db are overlapped with the second low-concentration movement section Ca2. In this case, among the plurality of specific image areas Db, the specific image area Db in which the change in acceleration in the acceleration movement section Cb is minimized is overlapped with the second low-concentration movement section Ca2. Thereby, it is possible to suppress the deterioration of the image quality due to the change in acceleration.

[0110] The above-described embodiments and modifications may be combined with each other as long as they do not exclude each other. Also, from the above description, many improvements and other embodiments of the present disclosure will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and provided for the purpose of teaching those skilled in the art the best mode of carrying out the present disclosure. Without departing from the spirit of the present disclosure, the details of its structure and / or function can be substantially changed.

Explanation of Reference Numerals

[0111] 10: Printing device 20: Head 21: Nozzle 22: Driving element 30: Moving device (relative moving device) 40: Conveying device (relative moving device) 50: Control device

Claims

1. A head having a nozzle for discharging ink onto a printing medium and a driving element for applying pressure to discharge ink from the nozzle, a relative movement device for relatively moving the printing medium and the head, and a control device, wherein the control device performs a printing process of discharging ink from the nozzle onto the printing medium by driving the driving element with a driving frequency corresponding to the relative movement speed between the printing medium and the head while relatively moving the printing medium and the head according to a speed profile based on image data, and printing an image on the printing medium, and among the driving frequencies, executes a printing process including discharging ink in a density unevenness frequency band where the discharged volume of ink is different from the discharged volume based on the image data, in the printing process, when the image includes a specific image area having a blank area, a low duty area, or a character area, relatively moves the printing medium and the head so that at least a part of a density unevenness movement section, which is a movement section of the printing medium and the head moving relatively at a relative movement speed corresponding to the density unevenness frequency band, overlaps with the specific image area, a printing apparatus.

2. The speed profile includes a first speed profile and a second speed profile different from the first speed profile, wherein the control device performs a determination process of determining whether the image includes the specific image area based on the image data, and in the printing process, when the image does not include the specific image area in the determination process, relatively moves the printing medium and the head according to the first speed profile, and when the image includes the specific image area in the determination process, relatively moves the printing medium and the head so that at least a part of the density unevenness movement section overlaps with the specific image area according to the second speed profile, The printing apparatus according to Claim 1.

3. The speed profile includes a first speed profile and a second speed profile different from the first speed profile, wherein the control device performs a first determination process of determining whether the highest frequency among the driving frequencies in the printing process is less than the density unevenness frequency band, and a second determination process of determining whether the image includes the specific image area based on the image data, When the highest frequency in the first determination process is not less than the density unevenness frequency band and the image includes the specific image area in the second determination process, a third determination process is performed to determine whether at least a part of the density unevenness movement section overlaps with the specific image area in the printing process according to the second speed profile. When at least a part of the density unevenness movement section overlaps with the specific image area in the third determination process, a speed change process is performed to change the speed profile from the first speed profile to the second speed profile. The printing apparatus according to claim 1.

4. The control device When the density unevenness movement section does not overlap with the specific image area in the third determination process, the speed change process is not executed. The printing apparatus according to claim 3.

5. The control device When all of at least a part of the density unevenness movement section overlaps with the specific image area in the third determination process, in the speed change process, the speed profile is changed from the first speed profile to the second speed profile in which the end of the density unevenness movement section in the relative movement direction in which the printing medium and the head move relative to each other overlaps with the end of the specific image area. The printing apparatus according to claim 3.

6. The control device When all of at least a part of the density unevenness movement section overlaps with the specific image area in the third determination process, in the speed change process, the speed profile is changed from the first speed profile to the second speed profile in which the center of the density unevenness movement section in the relative movement direction in which the printing medium and the head move relative to each other overlaps with the center of the specific image area. The printing apparatus according to claim 3.

7. The change rate of the relative movement speed in the density unevenness movement section of the second speed profile is the same as that of the first speed profile. The printing apparatus according to claim 5 or 6.

8. The control device When, in the third determination process, all of the density unevenness movement section among at least a part of the density unevenness movement section and the specific image area overlap each other, in the speed change process, the speed profile is changed from the first speed profile to the second speed profile in which both ends of the density unevenness movement section in the relative movement direction in which the medium to be printed and the head move relative to each other are overlapped with both ends of the specific image area, The printing apparatus according to claim 3.

9. The second speed profile is a speed profile in which the center of the density unevenness movement section in the relative movement direction in which the medium to be printed and the head move relative to each other is closer to the center of the specific image area than the first speed profile, The control device, When, in the third determination process, a part of the density unevenness movement section and the specific image area overlap each other, in the speed change process, the speed profile is changed from the first speed profile to the second speed profile, The printing apparatus according to claim 3.

10. The control device, When the highest frequency is not less than the density unevenness frequency band in the first determination process and the image includes the specific image area in the second determination process, a fourth determination process is executed to determine whether or not all of the density unevenness movement section and the specific image area overlap each other in the printing process according to the first speed profile, When all of the density unevenness movement section and the specific image area overlap each other in the fourth determination process, the speed change process is not executed, The printing apparatus according to claim 3.

11. The control device, When all of the density unevenness movement section and the specific image area do not overlap each other in the fourth determination process, the third determination process is executed, The printing apparatus according to claim 10.

12. The character area of the specific image area includes a first character group and a second character group different from the first character group, The control device, In the third determination process, it is determined whether or not the density unevenness movement section can be overlapped with the second character group without overlapping with the first character group in the printing process according to the second speed profile, In the speed change process, when the density unevenness movement section can be overlapped with the second character group without overlapping with the first character group, the speed profile is changed from the first speed profile to the second speed profile, The printing apparatus according to claim 3.

13. A printing apparatus control method comprising: a head having a nozzle for discharging ink onto a printing medium and a driving element for applying pressure to discharge the ink from the nozzle; a relative movement device for relatively moving the printing medium and the head; wherein, while relatively moving the printing medium and the head according to a speed profile based on image data, the driving element is driven at a driving frequency corresponding to the relative movement speed between the printing medium and the head to discharge ink from the nozzle onto the printing medium, and a printing process for printing an image on the printing medium is performed, and among the driving frequencies, a printing process including discharging ink in a density unevenness frequency band where the discharged volume of the ink is different from the discharged volume based on the image data is executed, in the printing process, when the image includes a specific image area having a blank area, a low duty area, or a character area, the printing medium and the head are relatively moved so that at least a part of a density unevenness movement section, which is a movement section of the printing medium and the head moving relatively at a relative movement speed corresponding to the density unevenness frequency band, overlaps with the specific image area. A printing apparatus control method.

14. A printing apparatus comprising: a head having a nozzle for discharging ink onto a printing medium and a driving element for applying pressure to discharge the ink from the nozzle; a relative movement device for relatively moving the printing medium and the head; wherein, while relatively moving the printing medium and the head according to a speed profile based on image data, the driving element is driven at a driving frequency corresponding to the relative movement speed between the printing medium and the head to discharge ink from the nozzle onto the printing medium, and a printing process for printing an image on the printing medium is performed, and among the driving frequencies, a printing process including discharging ink in a density unevenness frequency band where the discharged volume of the ink is different from the discharged volume based on the image data is executed, in the printing process, when the image includes a specific image area having a blank area, a low duty area, or a character area, the printing medium and the head are relatively moved so that at least a part of a density unevenness movement section, which is a movement section of the printing medium and the head moving relatively at a relative movement speed corresponding to the density unevenness frequency band, overlaps with the specific image area. A program. ​ ​

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