JP2024061165A - Printing device, printing method - Google Patents

Abstract

To print an image with a correct size image while reducing periodic unevenness that is easy to be visually recognized.SOLUTION: A printing device comprises: a printing part for printing an image on a medium; a print scanning part for scanning the printing part in a scanning direction; a medium conveyance part for conveying the medium in a conveyance direction crossing the scanning direction; and a control part for controlling the printing part, the print scanning part, and the medium conveyance part. The control part performs multiple printing operations for printing while scanning the printing part by the print scanning part when printing the image, and during the multiple printing operations, performs multiple conveyance operations for conveying the medium in the conveyance direction by the medium conveyance part, and controls so that although the multiple conveyance operations have a different error in a conveyance amount each time, the error becomes zero for the entire image.SELECTED DRAWING: Figure 6

Description

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

As shown in Patent Document 1, a printing method is known in which, during a scan of a print head in which multiple ink droplets are ejected in a dot matrix during a certain period, the ink droplet ejection time is varied between each scan to cause an offset of less than one dot width between each dot, thereby diffusing periodic printing errors.

Japanese Patent Application Laid-Open No. 11-10860

However, the above printing method had the problem that, if periodic printing errors accumulate, the size of the image that was originally to be printed may be shifted.

The printing device includes a printing unit that prints an image on a medium, a print scanning unit that scans the printing unit in a scanning direction, a medium transport unit that transports the medium in a transport direction that intersects the scanning direction, and a control unit that controls the printing unit, the print scanning unit, and the medium transport unit. When printing the image, the control unit performs multiple printing operations in which the printing unit is scanned while printing using the print scanning unit, and performs multiple transport operations in which the medium transport unit transports the medium in the transport direction between the multiple printing operations. Each of the multiple transport operations has a different transport amount error, and controls the error to be zero for the entire image.

When printing an image on a medium, the printing method executes multiple printing steps in which printing is performed while scanning the printing unit, and multiple transport steps in which the medium is transported in the transport direction between the multiple printing steps, and the multiple transport steps have an error in that the transport amount differs for each transport step, and the error is zero for the entire image.

FIG. 1 is a schematic diagram showing a configuration of a printing apparatus. FIG. 2 is a schematic diagram showing the configuration of a discharge head. FIG. 2 is a block diagram showing the control configuration of the printing apparatus. 11A and 11B are schematic diagrams showing examples of streaky unevenness occurring in an image. 4 is a flowchart showing a printing method. FIG. FIG. 11 is an explanatory diagram showing another printing method.

First, there will be described the configuration of the printing device 1. The printing device 1 of this embodiment is a serial large format printer that prints on a medium M by ejecting ink as a liquid.
In the following, an XYZ coordinate system is used in each figure. The direction along the Z axis is the height direction of the printing device 1. The direction along the X axis is the width direction of the medium M being transported. The direction along the X axis is referred to as the width direction or scanning direction. The direction along the Y axis is the front-rear direction of the printing device 1.

The front side of the printing device 1 is in the +Y direction, and the back side of the printing device 1 is in the -Y direction. Furthermore, when looking at the printing device 1 from the front side (looking at the printing device 1 in the -Y direction), the left side is the +X direction and the right side is the -X direction. Furthermore, the top side, upper part, top surface, etc. of the printing device 1 are in the +Z direction, and the bottom side, lower part, bottom surface, etc. are in the -Z direction.

The medium M is transported from the pay-out unit 20 to the winding unit 60, which will be described later. The direction in which the medium M is transported is referred to as the transport direction F. In addition, when referring to the positional relationship of the medium M along the transport direction F, the pay-out unit 20 side is referred to as the upstream side, and the winding unit 60 side is referred to as the downstream side.

As shown in Fig. 1, the printing device 1 is composed of a frame 15, a payout unit 20, a medium transport unit 25, a support unit 30, a printing unit 40, a print scanning unit 43, a guide unit 50, a winding unit 60, a pressure roller 70, a heater 80, a control unit 3, and the like. An operation unit 6 (Fig. 3) is provided on the front side of the printing device 1. The operation unit 6 is provided with a display means such as a liquid crystal panel. Various operation instructions can be input to the printing device 1 through the operation unit 6.
The frame 15 is composed of a base frame 16 extending in the width direction, and a pair of leg frames 17 that extend in the front-rear direction integrally with the base frame 16, support the weight of the printing device 1, and are formed at a distance in the width direction.

The heater 80, which will be described in detail later, comprises a first heater 81, a second heater 82, and a third heater 83. By driving the heater 80 and heating the printed medium M, the attached ink is quickly dried and fixed to the medium M, suppressing bleeding and blurring. In addition, the first heater 81 and the second heater 82 flatten the medium M that has swelled and deformed due to the ink, suppressing cockling.

The payout unit 20, media transport unit 25, support unit 30, guide unit 50, pressure roller 70, etc. are fixed to the base frame 16. The winding unit 60 is fixed to the leg frame 17, etc. The printing unit 40 is fixed to the base frame 16 and is disposed inside the housing 10, which is a roughly rectangular parallelepiped shape extending in the width direction. The control unit 3 is disposed inside the housing 10, and provides overall control over the operation of each part of the printing device 1.

The printing device 1 is provided with a pair of casters 18 and a pair of adjusters 19 at the lower end of each leg frame 17. After the printing device 1 is moved to the installation location by the casters 18, the height of the printing device 1 is adjusted (such as the horizontal adjustment), and the printing device 1 is fixed to, for example, the floor surface by the adjusters 19.

The payout unit 20 is provided at the bottom of the rear side of the housing 10. The payout unit 20 has a pair of holders 22 that hold both ends of the core tube 21. The holder 22 holds a roll R1 in which unused printing medium M is wound around the core tube 21 in a roll shape. One of the holders 22 is equipped with a payout motor (not shown) that supplies rotational force to the core tube 21. When the payout motor is driven to rotate in the payout direction (counterclockwise in FIG. 1), the core tube 21 rotates in response, and the medium M is paid out from the roll R1 toward the media transport unit 25. The control unit 3 controls the payout unit 20 (payout motor).

The payout unit 20 is interchangeably loaded with rolls R1 of multiple sizes with different widths and number of turns of medium M. The payout unit 20 is also interchangeably loaded with rolls R1 of multiple types (materials) of medium M.

The support section 30 includes a first support section 31, a platen 32, and a second support section 33. The first support section 31 is disposed upstream of the platen 32. The second support section 33 is disposed downstream of the platen 32. The first support section 31 guides the medium M fed from the feeding section 20 to the platen 32. The second support section 33 guides the medium M printed by the printing section 40 to the guide section 50 and the winding section 60.

The platen 32 is formed with a roughly rectangular surface whose longitudinal direction is the scanning direction, and is positioned opposite the printing unit 40 (ejection head 41). The platen 32 supports the medium M to be printed by the printing unit 40 from below. In detail, the platen 32 supports the medium M by suction to the upper surface of the platen 32 due to negative pressure applied to the platen 32. This makes it possible to suppress a decrease in print quality due to the medium M floating up.

The medium transport unit 25 transports the medium M fed from the feed unit 20 in the transport direction F. The medium transport unit 25 includes a drive roller 26, a driven roller 27, and a drive motor 28. The drive roller 26 is provided between the first support unit 31 and the platen 32. The drive roller 26 is configured to extend in a direction intersecting the transport direction F of the medium M (a direction along the X-axis).

The driven roller 27 is disposed above the driving roller 26 and is configured to be movable so as to move away from or press against the driving roller 26. When the driving motor 28 is driven and the driving roller 26 is driven to rotate, the medium M sandwiched between the driving roller 26 and the driven roller 27 is transported in the transport direction F. The control unit 3 controls the rotation of the driving roller 26 (driving motor 28).

In addition, a rotary encoder 29 is provided on the drive motor 28 as a measuring means. The rotary encoder 29 is connected to the control unit 3. The rotary encoder 29 is a sensor that converts the amount of mechanical displacement of rotation into an electrical signal and processes the signal to detect the position, speed, and the like. The control unit 3 can control the transport amount in the transport direction F of the medium M by acquiring the measurement data of the rotary encoder 29.
The rotary encoder 29 is composed of a slit disk fixed to the rotating shaft of the drive motor 28, and a position detector provided at a position through which the periphery of the slit disk passes. A plurality of position detection slits are formed at equal intervals around the entire circumference of the slit disk. The position detector includes a light-emitting section made of a light-emitting diode and a light-receiving section made of a phototransistor, facing each other across the periphery of the slit disk. When light from the light-emitting section passes through the position detection slits of the slit disk and is received by the light-receiving section, an electrical signal is output from the light-receiving section.

The printing unit 40 is disposed downstream of the medium transport unit 25 and above the platen 32. The printing unit 40 includes an ejection head 41 that ejects ink toward the medium M supported on the upper surface of the platen 32.
2, the printing unit 40 of this embodiment includes a plurality of (for example, 10) ejection heads 41. The printing unit 40 also includes a carriage 42 that supports the ejection heads 41.

The ejection head 41 includes a nozzle plate 47. A plurality of nozzles 48 are formed in the nozzle plate 47. Ink is ejected from the nozzles 48. A plurality of nozzle rows in which the nozzles 48 of each ejection head 41 are arranged are arranged in the scanning direction (direction along the X-axis). Each ejection head 41 is arranged in the scanning direction for each ink color. The control unit 3 controls the operation of each ejection head 41.

The printing unit 40 is configured to be movable in the scanning direction by a print scanning unit 43. The print scanning unit 43 includes a carriage frame 45, a carriage shaft 46, a bearing 44, a carriage motor (not shown), and the like.
The carriage 42 is supported so as to be freely movable back and forth by two carriage shafts 46 that extend in the width direction and are installed on a carriage frame 45. In this embodiment, the carriage 42 and the carriage shafts 46 are engaged via two bearings 44 that are fixed to the carriage 42. The carriage 42 moves along the carriage shafts 46 by a carriage motor. The bearings 44 are configured as so-called ball bearings. The control unit 3 controls the operation of the print scanning unit 43 (carriage motor).

The winding unit 60 is disposed downstream of the guide unit 50, which will be described later. The winding unit 60 includes a pair of holders 62 that hold both ends of a core tube 61. The holders 62 hold a roll R2 formed by winding the medium M printed by the printing unit 40 onto the core tube 61. One of the holders 62 includes a winding motor (not shown) that supplies rotational force to the core tube 61. When the winding motor is driven to rotate in the winding direction (counterclockwise in FIG. 1), the core tube 61 rotates accordingly, and the medium M that has passed through the guide unit 50 is wound onto the core tube 61 to form the roll R2.

In this embodiment, the winding unit 60 winds up the medium M in synchronization with the transport operation of the medium transport unit 25 under the control of the control unit 3. The torque of the roll body R2 is optimized and the tension of the medium M is adjusted according to the speed at which the medium M is sent out, the inertia (moment of inertia) of the winding unit 60, the type of medium M, the printing conditions during printing, the environmental conditions, etc.

The guide unit 50 is disposed downstream of the second support unit 33 and upstream of the winding unit 60, and guides the printed medium M towards the winding unit 60. The guide unit 50 is composed of a hollow cylindrical cylinder 51 that is longer than the width of the medium M, and a first heater 81 that is installed inside the cylindrical portion 51. The guide unit 50 is installed on the base frame 16, with both ends of the cylindrical portion 51 supported and fixed by holding units (not shown).

In this embodiment, the guide unit 50 does not rotate. The guide unit 50 applies an appropriate tension to the printed medium M, which is conveyed in the conveying direction F by driving the winding unit 60, as the guide surface, which is the outer peripheral surface of the front side of the cylindrical portion 51, comes into contact with the medium M. Therefore, the printed medium M is conveyed in the conveying direction F by sliding in the guide unit 50 while a predetermined tension is applied to the outer peripheral surface of the front side of the cylindrical portion 51. The cylindrical portion 51 of the guide unit 50 comes into contact with the surface opposite the printed surface of the printed medium M.

The tension applied to the medium M by the guide unit 50 is generated by the winding force (rotational force) supplied to the core tube 61 by the winding motor of the winding unit 60. In other words, the control unit 3 adjusts the tension applied to the medium M by the guide unit 50 by controlling the winding force of the winding unit 60 (specifically, by controlling the winding motor).

The material of the cylindrical portion 51 can be, for example, aluminum, which has good thermal conductivity as a metal member. Therefore, heat generated by the first heater 81 installed inside the cylindrical portion 51 can be efficiently transferred to the medium M. In addition, the outer peripheral surface of the aluminum is subjected to a surface treatment such as anodizing to improve strength and corrosion resistance as well as wear resistance and smoothness.

The first heater 81 is, for example, an infrared heater that heats with infrared rays or far infrared rays. In addition to an infrared heater, the first heater 81 may be, for example, a sheath heater having a heating element (nichrome wire) inside, or a ceramic heater using ceramics as a heating element. The first heater 81 is connected to a heating drive unit (not shown) that is disposed outside the guide unit 50. The first heater 81 is heated by driving the heating drive unit, and the cylindrical portion 51 is heated from the inside thereof, thereby heating the medium M in contact with the outer circumferential surface of the cylindrical portion 51. The control unit 3 adjusts the heating temperature of the first heater 81 by controlling the heating drive unit.

The pressure roller 70 is installed on the top of the roll body R2 of the winding unit 60 and rotates in response to the rotation of the winding unit 60. The pressure roller 70 is composed of a cylindrical roller portion 71 that is longer than the width of the medium M, a rotating shaft 72 that rotates the roller portion 71, and a second heater 82 that is installed inside the roller portion 71.

The pressure roller 70 also includes a pressure mechanism (not shown). The pressure mechanism rotatably holds the rotating shaft 72 of the pressure roller 70 and rotatably supports both ends of the roller portion 71, bringing the roller portion 71 into contact with the roll body R2 and pressing the wound-up medium M. The control unit 3 can adjust the pressure applied to the roll body R2 by controlling the pressure mechanism.

More specifically, the pressure roller 70 presses the outer peripheral surface of the medium M wound around the winding unit 60. The pressure roller 70 also heats the outer peripheral surface of the medium M with the second heater 82. In this embodiment, the outer peripheral surface of the medium M to be heated is the surface opposite to the surface heated by the guide unit 50. In this manner, the pressure roller 70 presses the outer peripheral surface of the medium M wound around the winding unit 60 while heating it. In the pressure roller 70, the roller unit 71 rotates following the rotation of the winding unit 60.

The material of the roller part 71 can be, for example, aluminum, which has good thermal conductivity as a metal member. Therefore, heat generated by the second heater 82 installed inside the roller part 71 can be efficiently transferred to the medium M. The outer peripheral surface of the aluminum is subjected to a surface treatment such as anodizing.

The second heater 82, like the first heater 81, is, for example, an infrared heater that heats with infrared rays or far infrared rays. The second heater 82 is connected to a heating drive unit that is arranged on the outside of the pressure roller 70. The second heater 82 is heated by driving the heating drive unit, and the roller unit 71 is heated from the inside of the roller unit 71, thereby heating the medium M in contact with the outer circumferential surface of the roller unit 71. The control unit 3 controls the second heater 82 (heating drive unit) to adjust the heating temperature. The control unit 3 also controls the pressing mechanism to adjust the pressing force.

The third heater 83 is disposed between the printing unit 40 and the guide unit 50, facing the second support unit 33 that supports the medium M after printing. The third heater 83 heats the support surface 33a that supports the medium M of the second support unit 33, and the medium M supported by the support surface 33a. The third heater 83 is composed of an infrared heater, a housing, a duct, a suction fan, etc.

The third heater 83 faces the medium M that is supported and transported on the support surface 33a of the second support unit 33, and dries and fixes the ink by applying heat from the printing surface side of the medium M. The control unit 3 controls the third heater 83.

Next, the control configuration of the printing device 1 will be described.
3, the printing device 1 includes a control unit 3. The control unit 3 includes a CPU 3a, a memory 3b, a control circuit 3c, and an I/F (interface) 3d. The CPU 3a is an arithmetic processing device. The memory 3b is a storage device that secures an area for storing various programs or a working area, and includes memory elements such as a RAM and an EEPROM.

When the control unit 3 receives print data or the like from an information processing terminal or the like via the I/F 3d, the CPU 3a executes calculations in accordance with various programs and controls each driving unit and the like via the control circuit 3c.
In the printing device 1 of this embodiment, a control signal is sent from the control unit 3 to each drive unit, and a printing operation in which ink is ejected as ink droplets from the ejection head 41 while moving the printing unit 40 in the scanning direction, and a transport operation in which the medium transport unit 25 transports the medium M a predetermined amount in the transport direction F are alternately repeated. Ink dots are thereby formed on the medium M, and an image or the like is printed on the medium M.

Here, as shown in FIG. 4, streaky unevenness Er may occur in an image printed on the medium M. The streaky unevenness Er in this embodiment is unevenness that occurs locally in the image and extends along the transport direction F. The streaky unevenness Er occurs when the landing position of the ink ejected from the nozzle 48 periodically shifts in the transport direction F due to factors such as the assembly accuracy of the printing unit 40 and the print scanning unit 43. In other words, even if there is a slight change in how the ink dots are filled, it becomes unevenness that has periodicity in the transport direction F because the ink is transported at a constant amount without error, and it is thought that the streaky unevenness Er is likely to occur. In addition, in the area where the streaky unevenness Er occurs, the ink dots are filled differently from other areas, so it is easy to visually recognize it as streaky unevenness.
Therefore, in the printing device 1 of this embodiment, the driving units are controlled so that the ink dots are filled irregularly in the image. In other words, in the printing device 1, the driving units are controlled so that the occurrence of periodicity in the filling of the ink dots in the transport direction F is reduced.

Next, a printing method in the printing device 1 will be described.
5, the control unit 3 receives print data from an information processing terminal such as a personal computer via the I/F 3d. The control unit 3 analyzes the contents of various commands included in the received print data, and transmits control signals to each drive unit for a transport operation to transport the medium M and for forming ink dots.

Next, in the feeding process (step S12), the control unit 3 supplies the medium M in the transport direction F and positions the medium M at the print start position (also called the cue position). The control unit 3 drives the medium transport unit 25 and other components to transport the medium M to the print start position.

Next, in the printing process (step S13), the control unit 3 executes printing while moving the printing unit 40 in the scanning direction. The control unit 3 drives the printing unit 40 and the print scanning unit 43 to eject ink from the ejection head 41 moving along the scanning direction to form ink dots on the medium M. As ink is continuously ejected from the moving ejection head 41, a dot row (raster line) consisting of multiple ink dots along the scanning direction is formed on the medium M. Here, the movement (scanning) of the printing unit 40 along the same raster line is called a pass, and one scan is called one pass. Furthermore, when one raster line is completed with n scans, it is called n-pass printing.

Next, in the transport step (step S14), the control unit 3 moves the medium M along the transport direction F. The control unit 3 drives and controls the drive motor 28, and rotates the drive roller 26 to transport the medium M in the transport direction F. The transport amount by which the medium M is transported in the transport direction F is specified for each pass. The control unit 3 calculates the transport amount using a transport program related to the transport, and drives and controls the drive motor 28. The control unit 3 also acquires measurement data from the rotary encoder 29, and controls the rotation of the drive motor 28. This controls the transport amount of the medium M.
This transport operation changes the position of the medium M that the ejection head 41 faces, making it possible to form ink dots at positions different from the positions of the ink dots formed by the previous printing operation. The transport amount of the medium M in each pass will be described later.

Next, in step S15, the control unit 3 determines whether printing has ended. If the control unit 3 determines that printing has ended, it ends printing. On the other hand, if printing is to continue, it proceeds to step S13.

When the process proceeds to step S13, the control unit 3 executes printing while moving the printing unit 40 in the scanning direction. Then, the process proceeds to step S14, where the control unit 3 moves the medium M along the transport direction F.

Thereafter, the control unit 3 repeats the printing operation (step S13) and the transport operation (step S14) until there is no more data to be printed.
Furthermore, a transport operation of the medium M is performed for each pass. An image is formed by performing multiple passes. The number of passes is determined by the resolution of the image; for example, when a high-resolution image is formed, the number of passes is greater, and when a low-resolution image is formed, the number of passes is smaller. By changing the number of passes, it is possible to change the density of the ink dots that form the raster lines.

Next, as an example of forming a high-resolution image, a printing method of 8-pass printing in which an image is formed by 8 passes will be described.
In the example of Figure 6, the control unit 3 controls the printing unit 40 and the medium transport unit 25, and when printing an image, performs multiple (8) printing operations (step S13) in which printing is performed while scanning the printing unit 40 by the print scanning unit 43, and performs multiple (8) transport operations (step S14) in which the medium M is transported in the transport direction F by the medium transport unit 25 between the multiple (8) printing operations.

In the multiple (eight) transport operations, the transport amount varies with each transport operation, and the control unit 3 controls the transport operation so that the error becomes zero over the entire image.
The medium transport unit 25 transports the medium M by a transport amount that includes a different error from a specified transport amount for each pass. The specified transport amount is the same for each pass. However, the error in the transport amount differs for each pass.
The error in the transport amount is set appropriately depending on the pitch dimension between the nozzles 48 in the ejection head 41. For example, if the pitch dimension between the nozzles 48 is 40 μm, the maximum error is equal to or less than the pitch dimension between the nozzles 48 of 40 μm. Here, it is preferable to set the error in the transport amount to ±20 μm. If the maximum error exceeds the pitch dimension between the nozzles 48 (for example, 40 μm), it will fall outside the ink dot formation region between the targeted passes, reducing the effect on streak unevenness Er.

The CPU 3a calculates error data for each pass according to a program related to the error in the transport amount, and transmits the transport amount data, which is a specified transport amount plus an error, to the medium transport unit 25 via the control circuit 3c. This drives the medium transport unit 25, and the medium M is transported by the specified transport amount plus an error.
Furthermore, the CPU 3a performs calculations so that the error in the transport amount is zero for the entire image. Specifically, in n-pass printing, calculations are performed so that the error is zero after n transports, where n is an integer equal to or greater than 1. In this embodiment, calculations are performed so that the error is zero after eight transports in eight-pass printing. In other words, calculations are performed so that the accumulated error is zero when eight passes are considered as one unit.
Furthermore, the CPU 3a performs calculations so that the error is different for every eight transports (every pass), and prevents the same error value from continuing for a plurality of transports.

In the example of Figure 6, for the first to eighth passes, the error in the transport amount for the first pass is +20 μm, the error in the transport amount for the second pass is -10 μm, the error in the transport amount for the third pass is 0 μm, the error in the transport amount for the fourth pass is +10 μm, the error in the transport amount for the fifth pass is -20 μm, the error in the transport amount for the sixth pass is +20 μm, the error in the transport amount for the seventh pass is 0 μm, and the error in the transport amount for the eighth pass is -20 μm. The cumulative error for the first to eighth passes is zero. Also, the error in the transport amount for each pass is different.

Next, for the second to ninth passes, the error in the transport amount for the second to eighth passes is the same as above. The error in the transport amount for the ninth pass is +20 μm. The cumulative error for the second to ninth passes is zero. Also, the error in the transport amount for each pass is different.

From then on, the cumulative error is zero for every 8 passes, and the transport operation is performed so that the error in the transport amount varies for each pass.

Therefore, the feeding accuracy of the medium M in 8-pass 1 unit is ensured. In other words, the full-length feeding accuracy for transporting the medium M to print an image of a predetermined size is ensured. This results in an image of the predetermined size being formed. Also, the error in the transport amount differs for each pass. This makes the ink dots filling in the transport direction F irregular, reducing periodic ink dot filling, and thus reducing the occurrence of easily noticeable periodic unevenness (streaky unevenness Er).
Since the image is completed in the last pass of the entire image, there is no need to consider errors in the transport after the last pass. Therefore, the CPU 3a performs calculations so that the accumulated error up to the transport before the last pass becomes zero.

Next, another printing method will be described.
Specifically, as an example of forming a low-resolution image, a two-pass printing method in which n is 2 and an image is printed in two passes will be described assuming that the predetermined number is 6 and six passes are one unit, and the entire image is printed in multiple units. The predetermined number can be set arbitrarily, but is preferably an integer multiple of n. Here, the predetermined number refers to the number of transport operations in one cycle that reduces the accumulated error to zero.
In the example of Figure 7, the control unit 3 controls the printing unit 40 and the medium transport unit 25, and when printing an image, performs multiple (two) printing operations (step S13) in which printing is performed while scanning the printing unit 40 with the print scanning unit 43, and performs multiple (two) transport operations (step S14) in which the medium M is transported in the transport direction F by the medium transport unit 25 between the multiple (two) printing operations.

Although there is an error in the multiple (two) transport operations, the control unit 3 controls so that the error becomes zero for each of six transport operations, which is one unit.
The medium transport unit 25 transports the medium M by a transport amount including a different error from the specified transport amount for each pass. The specified transport amount is the same for each pass. However, the error in the transport amount differs for each pass. The setting of the error in the transport amount is the same as above.

The CPU 3a calculates error data for each pass according to a program related to the error in the transport amount, and transmits the transport amount data, which is a specified transport amount plus an error, to the medium transport unit 25 via the control circuit 3c. This drives the medium transport unit 25, and the medium M is transported by the specified transport amount plus an error.
Furthermore, the CPU 3a performs calculations so that the error in the transport amount is zero for the entire image. In this embodiment, calculations are performed so that the accumulated error is zero when six passes are regarded as one unit.
Furthermore, the CPU 3a performs calculations so that the fluctuation pattern of the error in the transport amount for every two transports (every pass) is different.
In the following example, a case will be described in which printing of one unit is completed in the sixth pass.

In the example of Figure 7, the error in the transport amount in the first pass and the second pass is +20 μm, and the error in the transport amount in the second pass is -10 μm. The cumulative error in the first and second passes is +10 μm.

Next, in the second and third passes, the error in the transport amount in the second pass is -10 μm, and the error in the transport amount in the third pass is 0 μm. The cumulative error in the second and third passes is -10 μm. In addition, the fluctuation patterns of the transport amount error are different between the first and second passes and the second and third passes.

Next, in the third and fourth passes, the error in the transport amount in the third pass is 0 μm, and the error in the transport amount in the fourth pass is +10 μm. The cumulative error in the third and fourth passes is +10 μm. In addition, the fluctuation pattern of the transport amount error is different between the second and third passes and the third and fourth passes.

Next, in the fourth and fifth passes, the error in the transport amount in the fourth pass is +10 μm, and the error in the transport amount in the fifth pass is 0 μm. The cumulative error in the fourth and fifth passes is +10 μm. In addition, the fluctuation patterns of the transport amount error are different between the third and fourth passes and the fourth and fifth passes.

Next, in the fifth and sixth passes, the error in the transport amount in the fifth pass is 0 μm, and the error in the transport amount in the sixth pass is -20 μm. The cumulative error in the fifth and sixth passes is -20 μm. In addition, the fluctuation patterns of the transport amount error are different between the fourth and fifth passes and the fifth and sixth passes.

In the example shown in this figure, a cumulative error occurs every two passes, but the overall cumulative error is zero up to the sixth pass, when one unit is printed. This ensures full-length feed accuracy for transporting the medium M to print an image of a specified size. Therefore, an image of the specified size is formed.

Furthermore, because two-pass printing has fewer passes than eight-pass printing, the number of times the error in the transport amount fluctuates every two passes is reduced, and the effect on periodic unevenness (streaky unevenness Er) is reduced. Therefore, in low-pass printing such as two-pass printing, the accumulated error is not set to zero every two passes, but an error is generated, and the accumulated error is set to zero every six passes, which is one unit. This increases the variation in the fluctuation pattern of the error in the transport amount, and makes it possible to reduce the occurrence of periodicity in the way ink dots are filled in the transport direction F.
Also, as explained in the printing method for 8-pass printing, there is no need to consider errors in the transport after the last pass of the entire image. Therefore, the last unit of the entire image is controlled so that the accumulated error up to the transport before the last pass is zero. When printing the entire image in one unit, in this embodiment, control is performed so that the accumulated error of five transports is zero.
When printing the entire image, if passes less than one unit occur, control is performed so that the cumulative error in the transport amount becomes zero in the range printed using passes less than one unit.

As described above, according to this embodiment, by imparting irregular errors to the transport amount of the medium M, the appearance of periodicity in the arrangement of ink dots in the transport direction F is reduced. This makes image unevenness in the transport direction F less visible, thereby improving image quality.
Furthermore, since the cumulative error in transporting the medium M during the image to be printed is zero, full-length feed accuracy is ensured, and an image of the desired size can be printed.

In addition, even if there are areas on the medium M where the ink landing position changes due to the occurrence of wavy wrinkles (cockling) on the medium M, the periodic arrangement of ink dots in the transport direction F of the medium M is reduced, so visible unevenness can be suppressed.

In addition, even if streaky unevenness Er occurs due to, for example, individual differences in the ejection head 41 or the assembly accuracy of the print scanning unit 43, the occurrence of streaky unevenness Er can be easily suppressed by adding irregular errors to the transport amount of the medium M.

1...printing device, 3...control unit, 3a...CPU, 3b...memory, 3c...control circuit, 3d...I/F, 6...operation unit, 20...feeding unit, 25...medium transport unit, 26...driving roller, 27...driven roller, 28...driving motor, 29...rotary encoder, 30...support unit, 31...first support unit, 32...platen, 33...second support unit, 33a...support surface, 40...printing unit, 41...ejection head, 42...carriage, 43...print scanning unit, 44...bearing, 45...carriage frame, 46...carriage shaft, 47...nozzle plate, 48...nozzle, 50...guide unit, 60...winding unit, 70...pressure roller, 80...heater, M...medium.

Claims (7)

A printing unit that prints an image on a medium;
A print scanning unit that scans the print unit in a scanning direction;
a medium transport unit that transports the medium in a transport direction that intersects with the scanning direction;
a control unit that controls the printing unit, the print scanning unit, and the medium transport unit,
The control unit, when printing the image, performs multiple printing operations in which printing is performed while scanning the printing unit using the print scanning unit, and performs multiple transport operations in which the medium transport unit transports the medium in the transport direction between the multiple printing operations, and the multiple transport operations have an error in the amount of transport that varies from one operation to the next, and is controlled so that the error is zero for the entire image. 2. The printing device according to claim 1,
The control unit controls the printing device so that an error becomes zero after n conveyances in n-pass printing. 2. The printing device according to claim 1,
The control unit changes an error fluctuation pattern for each of the n conveyances in n-pass printing. 4. The printing device according to claim 3,
The control unit performs control so that an error becomes zero for each unit, the unit being a scan accompanied by a predetermined number of conveyances. 5. The printing device according to claim 4,
A printing device, wherein the predetermined number is an integer multiple of n. 6. The printing device according to claim 4, further comprising:
The control unit is configured to print the entire image in one or more units. When printing an image on a medium, a printing process is performed multiple times while scanning a printing unit;
a plurality of transport steps of transporting the medium in a transport direction between the plurality of printing steps;
A printing method, characterized in that the conveying steps each have a different conveying amount error, and the error becomes zero over the entire image.

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