Printing method and printing system

Abstract

A printing method and a printing system are provided that can perform printing appropriately even when the transport speed of a print medium increases or decreases. [Solution] A printing method using the printing system 100 includes acquiring a first speed, which is the transport speed when the medium M passes through the target head 1, acquiring a second speed, which is the transport speed when the medium M passes through a reference head 1 located upstream of the target head 1 in the transport direction, calculating the amount of deviation in the transport direction of the landing position of the ink ejected from the target head 1 relative to the landing position of the ink ejected from the reference head 1 based on the first speed and the second speed, determining whether the transport speed is increasing or decreasing, and identifying print data to be sent to the target head 1 based on the calculated amount of deviation and the acceleration / deceleration of the transport speed.

Description

[Technical Field]

[0001] The present invention relates to a printing method and a printing system. [Background technology]

[0002] Conventionally, there exists an inkjet printing device that can continue printing even while the transport speed of the continuous paper is changing (Patent Document 1). This inkjet printing device includes a drive roller that transports the continuous paper, an encoder for measuring the distance the drive roller transports the continuous paper, and a printing unit. The printing unit has upstream nozzles located upstream of the transport path of the continuous paper, and downstream nozzles located downstream of the upstream nozzles in the transport path. This inkjet printing device also includes a printing unit controller that controls the printing unit based on the output of the encoder, and a drive roller controller that controls the drive of the drive roller to control the transport speed of the continuous paper.

[0003] The drive roller control unit controls the drive roller so that the difference between the transport speed of the continuous paper when the upstream nozzles eject ink droplets and the transport speed of the continuous paper when the downstream nozzles eject ink droplets is constant at each point in time while the speed of the drive roller is being changed. This makes it possible to maintain a constant relationship between the landing positions on the continuous paper of ink droplets ejected from the upstream nozzles and the landing positions on the continuous paper of ink droplets ejected from the downstream nozzles at each point in time while the speed of the drive roller is being changed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-160158 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, consider the case where ink droplets ejected from an upstream nozzle and ink droplets ejected from a downstream nozzle are to land at position P on the continuous paper. Assume that the time from when an ink droplet is ejected from the upstream nozzle to when it lands on the continuous paper and the time from when an ink droplet is ejected from the downstream nozzle to when it lands on the continuous paper are both t seconds. When the continuous paper is transported at a constant speed, first, in order for ink droplets ejected from the upstream nozzle to land at position P, ink droplets should be ejected from the upstream nozzle t seconds before position P arrives directly below the upstream nozzle. Then, in order for ink droplets ejected from the downstream nozzle to land at position P, ink droplets should be ejected from the downstream nozzle t seconds before position P arrives directly below the downstream nozzle.

[0006] On the other hand, if the transport speed of the continuous paper increases from the above constant speed after position P reaches directly below the upstream nozzle until it reaches directly below the downstream nozzle, the ejection timing of the downstream nozzle must be advanced to earlier than t seconds before (i.e., (t+a) seconds before). Conversely, if the transport speed of the continuous paper decreases from the above constant speed after position P reaches directly below the upstream nozzle until it reaches directly below the downstream nozzle, the ejection timing of the downstream nozzle must be delayed to later than t seconds before (i.e., (tb) seconds before).

[0007] Here, each nozzle is assigned a discharge cycle of T seconds, and in order to discharge ink droplets appropriately, it is preferable that the above (t+a) and (tb) be values ​​within the discharge cycle T. However, for example, if the acceleration amount of the continuous paper is large, the above (t+a) may become larger than the discharge cycle T, and ink droplets may not be discharged appropriately.

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a printing method and printing system that can perform printing appropriately even when the transport speed of the printing medium is changing. [Means for solving the problem]

[0009] A printing method according to an aspect of the present invention is a printing method using a printing press having a first nozzle and a second nozzle positioned apart in a transport direction of a medium, the second nozzle being positioned downstream in the transport direction from the first nozzle, the printing method including: transporting the medium in the transport direction; calculating an amount of deviation in the transport direction between a first landing position on the medium that is a landing position on the medium of a first droplet ejected from the first nozzle when a reference position on the medium passes the first nozzle; and a second landing position on the medium that is a landing position on the medium of a second droplet ejected from the second nozzle when the reference position passes the second nozzle; identifying a first pixel corresponding to the first landing position and a second pixel shifted in the transport direction from the first pixel by the amount of deviation; ejecting the first droplet from the first nozzle based on first print data corresponding to the first pixel when the reference position passes the first nozzle; and ejecting the second droplet from the second nozzle based on print data corresponding to the second pixel when the reference position passes the second nozzle.

[0010] A printing system according to an aspect of the present invention includes a first head having a first nozzle, a second head having a second nozzle, the second head being located downstream in a medium transport direction from the first nozzle, a first head controller for controlling the first head, and a second head controller for controlling the second head. The second head controller calculates a deviation in the transport direction between a first landing position on the medium where a first droplet ejected from the first nozzle lands when a reference position on the medium passes through the first nozzle and a second landing position on the medium where a second droplet ejected from the second nozzle lands when the reference position passes through the second nozzle, and identifies a first pixel corresponding to the first landing position and a second pixel shifted in the transport direction from the first pixel by the deviation. The first head controller ejects the first droplet from the first nozzle based on first print data corresponding to the first pixel when the reference position passes through the first nozzle. The second head controller causes the second nozzle to eject the second droplet based on print data corresponding to the second pixel when the reference position passes the second nozzle.

[0011] According to the aspects of the present invention, printing can be performed appropriately even when the transport speed of the print medium is increasing or decreasing. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a plan view schematically showing the configuration of a printing system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a bottom view showing an example of a printing unit included in the printing system according to the first embodiment of the present invention. [Figure 3] FIG. 2 is a cross-sectional view of a flow path member and an actuator member that constitute the head. [Figure 4](a) to (c) show the relationship between the landing position of ink ejected from the nozzle on the upstream side in the transport direction and the landing position of ink ejected from the nozzle on the downstream side in the transport direction, where (a) shows the case where the medium transport speed is constant, (b) shows the case where the medium transport speed is decreasing, and (c) shows the case where the medium transport speed is increasing. [Figure 5] FIG. 2 is a functional block diagram of a head controller according to the first embodiment of the present invention. [Figure 6] 5 is a flowchart showing a flow of processing by a head controller according to the first embodiment of the present invention. [Figure 7] 10 is a table showing an example of image data stored in an image data storage unit. [Figure 8] FIG. 10 is a functional block diagram of a head controller according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] A printing system 100 according to a first embodiment of the present invention is a digital printing press. As shown in Fig. 1, the printing system 100 mainly comprises a housing CS, printing units 10A to 10H, a transport device 20, and a controller 6. The printing units 10A to 10H, the transport device 20, and the controller 6 are arranged inside the housing CS. The printing system 100 further comprises an input unit (not shown) that is composed of buttons arranged on the outer surface of the housing CS.

[0014] The printing units 10A to 10H are arranged in this order from the upstream side in the transport direction. The transport direction is the direction in which the medium M, such as roll paper, is transported by the transport device 20. Each of the printing units 10A to 10H is long in the width direction. The width direction is the direction along the width of the medium M, and is perpendicular to the vertical direction and the transport direction. Each of the printing units 10A to 10H is a line type that ejects ink onto the medium M while its position is fixed in the housing CS.

[0015] The printing units 10C to 10H on the downstream side in the transport direction are supplied with, for example, yellow, orange, magenta, violet, cyan, and black inks, respectively. The printing units 10A and 10B on the upstream side in the transport direction are supplied with, for example, white inks, respectively. These inks may be, for example, ultraviolet curable inks (UV curable inks) that are cured by exposure to ultraviolet light (UV light).

[0016] As shown in FIG. 1, ten heads 1 are positioned at the vertically lower end of each of the printing units 10A to 10H. The ten heads 1 are arranged in a staggered pattern in the width direction with their lower surfaces on the same plane. As shown in FIG. 2, the lower surface of each head 1 forms a nozzle surface NS in which a plurality of nozzles N are opened. In the nozzle surface NS, the plurality of nozzles N are arranged in a staggered pattern in the width direction, forming two nozzle rows aligned in the transport direction. Each nozzle row extends in the width direction. In this embodiment, each head 1 has two nozzle rows formed therein, but the number of nozzle rows may be one, three, or more.

[0017] The transport device 20 includes a feed roller 20A and a recovery roller 20B shown in FIG. 1, and multiple transport rollers (not shown). The transport device 20 further includes a transport motor (not shown) connected to the feed roller 20A and the recovery roller 20B. The feed roller 20A and the recovery roller 20B are aligned in the transport direction, with the feed roller 20A located upstream of the recovery roller 20B in the transport direction. The printing units 10A to 10H are located between the feed roller 20A and the recovery roller 20B in the transport direction. The multiple transport rollers are located between the feed roller 20A and the recovery roller 20B in the transport direction, and are aligned in the transport direction. The multiple transport rollers are located below the printing units 10A to 10H.

[0018] The feed roller 20A, the recovery roller 20B, and the multiple transport rollers all extend in the width direction and rotate around a rotation axis extending in the width direction. The feed roller 20A and the recovery roller 20B are each driven to rotate by a transport motor. A roll of medium M, whose length in the transport direction is longer than its length in the width direction, is attached to the feed roller 20A. The medium M, which is sent out from the feed roller 20A by the rotation of the feed roller 20A, passes between the printing units 10A-10H and the multiple transport rollers, and is taken up by the recovery roller 20B by the rotation of the recovery roller 20B. This transports the medium M in the transport direction. The multiple transport rollers rotate as the medium M is transported. The transport motor drives the feed roller 20A and the recovery roller 20B to rotate so that the medium M is transported while contacting the upper portion of the circumferential surface of each of the multiple transport rollers.

[0019] The period during which the conveying device 20 conveys the medium M includes an acceleration period during which the conveying speed of the medium M is increased to a target value, a constant speed period during which the conveying speed of the medium M is maintained within a predetermined range including the target value, and a deceleration period during which the conveying speed of the medium M is reduced from the target value.

[0020] As shown in Fig. 5, the controller 6 includes a CPU 61, a ROM 62, and a RAM 63. When the CPU 61 receives various instructions from the external device EX shown in Fig. 1 or an input unit (not shown), the CPU 61 temporarily reads data and programs stored in the ROM 62 into the RAM 63 and executes processing according to the various instructions in accordance with the read data and programs. The external device EX is, for example, a PC.

[0021] The ROM 62 stores programs and data for the CPU 61 to perform various processes. The RAM 63 temporarily stores data used by the CPU 61 when executing the programs.

[0022] 5, the controller 6 is electrically connected to a driver IC 4 via a head controller 5, which will be described later. The controller 6 is also electrically connected to each head 1 included in each of the printing units 10A to 10H via the driver IC 4. The controller 6 controls each head 1 via the head controller 5 and the driver IC 4, and ejects UV-curable ink from the multiple nozzles N of each head 1 toward the medium M being transported in the transport direction by the transport device 20. In this way, an image is printed on the medium M.

[0023] Next, we will explain the configuration of each head 1. As shown in Figure 3, the head 1 includes a flow path member 2 and an actuator member 3.

[0024] The flow path member 2 is formed by a plurality of metal plates and a nozzle plate NP stacked in the vertical direction. Ink flow paths such as individual flow paths 2B including pressure chambers P and supply manifolds 2A are formed in the plurality of metal plates by etching. The nozzle plate NP is formed from a polymer synthetic resin material such as polyimide, and is bonded to the lower surfaces of the stacked metal plates with an adhesive. The lower surface of the nozzle plate NP forms a nozzle surface NS as an ink ejection surface where the nozzles N open. The nozzle plate NP may also be formed from a metal material such as stainless steel.

[0025] Inside the flow path member 2, individual flow paths 2B communicating with each nozzle N and a supply manifold 2A communicating with the individual flow paths 2B are formed. Although not shown, the supply manifold 2A extends in the width direction (the direction perpendicular to the paper surface in FIG. 3). The supply manifold 2A is connected to a tank (not shown) located outside the head 1 via an ink supply port (not shown) formed in the flow path member 2. Ink coming out of the tank flows into the supply manifold 2A via the ink supply port, and is supplied from the supply manifold 2A to the individual flow paths 2B.

[0026] Although not shown, the flow path member 2 is formed with a plurality of individual flow paths 2B corresponding to the plurality of nozzles N, respectively. As described above, the plurality of nozzles N form two nozzle rows extending in the width direction, and the plurality of individual flow paths 2B form two individual flow path rows extending in the width direction, respectively. The supply manifold 2A is in communication with the plurality of individual flow paths 2B that make up the two individual flow path rows. The number of supply manifolds 2A formed in the flow path member 2 is adjusted according to the number of nozzles N. When a plurality of supply manifolds 2A are formed, the number of individual flow paths 2B communicating with each supply manifold 2A is also adjusted according to the number of nozzles N.

[0027] 3, the actuator member 3 is fixed to the upper surface of the flow path member 2. The actuator member 3 includes a metallic vibration plate 3A, a piezoelectric layer 3B, and a plurality of individual electrodes 3C.

[0028] The actuator member 3 is formed by sequentially depositing a thin film that will become the piezoelectric layer 3B and a thin film that will become the individual electrodes 3C on the upper surface of the diaphragm 3A.

[0029] The diaphragm 3A is disposed on the upper surface of the flow path member 2 so as to cover all of the pressure chambers P. The diaphragm 3A is a metal plate that is approximately rectangular in plan view. The upper surface of the conductive diaphragm 3A is located below the piezoelectric layer 3B. Therefore, the upper surface of the diaphragm 3A can also serve as a common electrode. The diaphragm 3A as a common electrode is connected to the ground wiring of the driver IC 4 that drives the actuator member 3, and is always maintained at ground potential. Note that the diaphragm 3A does not necessarily have to be a metal plate; for example, it may be formed from the same piezoelectric material as the piezoelectric layer 3B, with a metal film formed on its upper surface as a common electrode.

[0030] The piezoelectric layer 3B is disposed on the upper surface of the diaphragm 3A. The piezoelectric layer 3B is formed of a piezoelectric material whose main component is lead zirconate titanate (PZT), a ferroelectric solid solution of lead titanate and lead zirconate. The piezoelectric layer 3B is polarized vertically at least in the region facing the pressure chamber P (the portion sandwiched between the individual electrode 3C and the diaphragm 3A).

[0031] The individual electrode 3C is disposed on the upper surface of the piezoelectric layer 3B so as to overlap the pressure chamber P in the vertical direction. The vibration plate 3A as a common electrode, the individual electrode 3C, and the portion of the piezoelectric layer 3B sandwiched between the individual electrode 3C and the vibration plate 3A form one actuator 3X.

[0032] When a predetermined drive potential is applied to a certain individual electrode 3C from the driver IC 4, a potential difference is generated between the individual electrode 3C to which this drive potential is applied and the diaphragm 3A, which serves as a common electrode and is held at ground potential. This generates an electric field in the thickness direction of the piezoelectric layer 3B sandwiched between the individual electrode 3C and the diaphragm 3A. The direction of this electric field is parallel to the polarization direction of the piezoelectric layer 3B. As a result, the region of the piezoelectric layer 3B facing the individual electrode 3C (active region) contracts in the plane direction, perpendicular to the thickness direction. Here, the diaphragm 3A below the piezoelectric layer 3B is fixed to the flow path member 2. Therefore, as the piezoelectric layer 3B located on the upper surface of the diaphragm 3A contracts in the plane direction, the portion of the diaphragm 3A covering the pressure chamber P deforms so as to become convex toward the pressure chamber P (unimorph deformation). At this time, the volume of the pressure chamber P decreases, causing the ink pressure in the pressure chamber P to increase, and ink is ejected from the nozzle N connected to the pressure chamber P. In other words, the actuator member 3 is located at a position corresponding to the pressure chamber P, and applies pressure to the ink in the pressure chamber P to eject the ink from the nozzle N.

[0033] Here, in a digital printing machine, printing is performed on a medium M, such as roll paper, that runs continuously in the transport direction during the constant speed period described above, but there are times when you want to check the print results while printing. In this case, it is necessary to slow down the transport speed of the medium M to check the print results, and then increase the transport speed back to a constant speed after checking the print results. If printing is stopped while the transport speed of the medium M is slowing down or increasing, margins will be created on the medium M. For this reason, it is desirable to be able to print appropriately even while the transport speed of the medium M is slowing down or increasing.

[0034] However, while the transport speed of the medium M is decreasing and increasing, a phenomenon occurs in which the landing position of ink ejected from the nozzle N located upstream in the transport direction and the landing position of ink ejected from the nozzle N located downstream in the transport direction are misaligned in the transport direction. This phenomenon will be described with reference to Figures 4(a) to 4(c).

[0035] In Figures 4(a) to 4(c), nozzle N A means one nozzle included in any of the heads 1 that make up the printing unit 10A. H means one nozzle included in one head 1 that constitutes the printing unit 10H. A a head 1 including a nozzle N H The head 1 including the nozzles N is at the same position in the width direction. A and nozzle N H It is assumed that the positions in the width direction are the same.

[0036] Furthermore, the medium M is transported in the transport direction, and the reference position P R Nozzle N A When passing through the nozzle N A White ink is ejected onto the medium M from the reference position P R Nozzle N H When passing through the nozzle N H It is assumed that black ink is ejected onto the medium M from the reference position P R Nozzle N A "When passing through the reference position P on the medium M" RNozzle N A It also means the timing when the reference position P R Nozzle N H "When passing through the reference position P R Nozzle N H This means the timing when the object reaches directly below the position P A is nozzle N A The position where the white ink is ejected from the H is nozzle N H This refers to the landing position of black ink ejected from the nozzle.

[0037] Also, V A is the reference position P R Nozzle N A means the transport speed of the medium M at the time when it reaches directly below V H is the reference position P R Nozzle N H This means the transport speed of the medium M at the time when it reaches directly below V. A is nozzle N A V H is nozzle N H This means the transport speed of the medium M at the timing when the ejection of black ink from the nozzles starts.

[0038] Furthermore, T A is nozzle N A After the white ink starts to be ejected from position P A This means the flight time until the missile hits the target, and T H is nozzle N H After the black ink starts to be ejected from position P H This means the flight time until the droplet hits the nozzle. A , N H Since the vertical distance from the target to the medium M is very short, the flight time T A and flight time T H is also very short, and the flight time T A and flight time T Hcan be considered to be approximately the same.

[0039] And nozzle N A After the white ink starts to be ejected from the position P A The distance that the medium M travels before hitting the target is V A T A Similarly, nozzle N H After the black ink starts to be ejected from the position P H The distance that the medium M travels before hitting the target is V H T H It can be expressed as:

[0040] As shown in FIG. 4(a), when the transport speed of the medium M is constant (V A =V H ), the distance V A T A and distance V H T H Therefore, nozzle N A The landing position P of the white ink ejected from A and nozzle N H The landing position P of the black ink ejected from H It roughly coincides with.

[0041] In contrast, as shown in FIG. 4(b), the transport speed of the medium M is reduced (V A >V H ) then distance V H T H is the distance V A T A Therefore, the nozzle N H The landing position P of the black ink ejected from H is nozzle N A The landing position P of the white ink ejected from A The position is shifted downstream in the conveying direction.

[0042] On the other hand, as shown in FIG. 4(c), the transport speed of the medium M is increasing (V A <V H ) then distance VH T H is the distance V A T A Therefore, the nozzle N H The landing position P of the black ink ejected from H is nozzle N A The landing position P of the white ink ejected from A The image is shifted to the upstream side in the conveying direction.

[0043] For this reason, the printing system 100 of this embodiment includes a head controller 5 for each head 1, and deals with deviations in the ink landing position that accompany increases and decreases in the transport speed of the medium M.

[0044] As shown in Fig. 5, the head controller 5 is electrically connected to the controller 6 and the driver IC 4. Although Fig. 5 shows only one head controller 5 and one driver IC 4, the controller 6 is electrically connected to the same number of head controllers 5 as the number of heads 1 provided in the printing system 100. The same number of head controllers 5 as the number of heads 1 are electrically connected one-to-one to the same number of driver ICs 4 as the number of heads 1.

[0045] Each head controller 5 pre-stores image data transmitted from the controller 6. The image data is raster data corresponding to the color of ink to be ejected from the target head 1. Furthermore, each head controller 5 receives ejection timing data from the controller 6. The ejection timing data instructs each head controller 5 on the pixels in the pre-stored image data where ink should land and the timing at which the ink should land on those pixels. The ejection timing data includes data on the transport speed of the medium M at the ink ejection timing. The transport speed data is acquired by the controller 6 from a rotary encoder (not shown) included in the transport device 20. Upon receiving the ejection timing data from the controller 6, each head controller 5 calculates the amount of deviation of the ink landing position at the ejection timing instructed by the ejection timing data. Then, each head controller 5 identifies print data to be read from the pre-stored image data based on the pixel specified by the ejection timing data and the calculated amount of deviation, and transmits the identified print data to the corresponding driver IC 4.

[0046] The flow of the above process will be explained below with reference to Figures 5 to 7, using one head 1 included in the printing unit 10H as an example. It is assumed that one head controller 5 and one driver IC 4 shown in Figure 5 correspond to one head 1 included in the printing unit 10H.

[0047] As shown in FIG. 5, the head controller 5 includes a first speed acquisition unit 51, a second speed acquisition unit 52, a deviation amount calculation unit 53, an acceleration / deceleration determination unit 54, an image data storage unit 55, and a conveying speed storage unit 56.

[0048] The head controller 5 is preset with a distance in the transport direction from the reference head 1 to the target head 1 controlled by the head controller 5. The reference head 1 refers to the head 1 included in the printing unit 10A that is located at the same position in the width direction as the target head 1. For example, if the target head 1 is the head 1 included in the printing unit 10H, the distance in the transport direction from the reference head 1 is 1.5 m. If the target head 1 is the head 1 included in the printing unit 10A, that is, if the target head 1 is the reference head 1, the distance in the transport direction from the reference head 1 is 0 m.

[0049] Furthermore, each head controller 5 is preset with a flight time for ink ejected from the nozzles N included in the target head 1 to land on the medium M. Note that the vertical distance from the nozzle surface NS to the medium M can be considered to be the same for all heads 1 included in the printing system 100. For this reason, the same value is set as the flight time for all head controllers 5.

[0050] 6, when the head controller 5 receives image data from the controller 6, it stores the received image data in the image data storage unit 55 (step S10). As the image data storage unit 55, for example, a DRAM can be used.

[0051] As shown in FIG. 7, the image data includes print data indicating the size of ink droplets to be ejected onto each pixel for all k nozzles N included in the target head 1. In FIG. 7, pixel ID indicates the order of each pixel in the transport direction. For example, pixel ID "1" indicates the first pixel from the downstream side in the transport direction among the pixels constituting the image, and pixel ID "100" indicates the 100th pixel from the downstream side in the transport direction. Furthermore, nozzle ID is an identification number for each of the k nozzles N included in the target head 1. Furthermore, print data "DS1," "DS2," and "DS3" indicate the size of ink droplets. For example, "DS1" indicates small droplets, "DS2" indicates medium droplets larger than "DS1," and "DS3" indicates large droplets larger than "DS2."

[0052] Next, when the head controller 5 receives the ejection timing data from the controller 6, the first speed acquisition unit 51 acquires, from the ejection timing data, transport speed data of the medium M at the specified ink ejection timing as first speed data (step S20). In other words, the first speed acquisition unit 51 of the head controller 5 that controls the target head 1 acquires transport speed data of the medium M at the timing when ink is ejected from the target head 1. Furthermore, the first speed acquisition unit 51 associates the pixel specified by the ejection timing data with the transport speed data of the medium M, and stores the association in the transport speed memory unit 56.

[0053] Next, the second speed acquisition unit 52 acquires, as second speed data from the transport speed memory unit 56, the transport speed data of the medium M at the timing when ink is ejected from the reference head 1 onto the pixel specified by the ejection timing data (step S30).

[0054] Here, the controller 6 transmits the same ejection timing data to all head controllers 5. For example, at a certain timing TM1, ejection timing data specifying the 100th pixel is transmitted to both the reference head 1 and the target head 1. However, the reference head 1 and the target head 1 are spaced apart in the transport direction. Therefore, if the reference head 1 and the target head 1 simultaneously eject ink at timing TM1, the ink ejected from the reference head 1 will land at a position on the medium M corresponding to the 100th pixel. On the other hand, the ink ejected from the target head 1 will land downstream in the transport direction from the position on the medium M corresponding to the 100th pixel. In other words, the ink ejected from the target head 1 cannot be superimposed on the ink ejected from the reference head 1. Therefore, the head controller 5 calculates the number of pixels to the reference head 1 based on the preset distance from the reference head 1 in the transport direction, and delays the ejection timing based on the calculated number of pixels.

[0055] For example, assume that the distance of the target head 1 from the reference head 1 in the transport direction is 1.5 m, which corresponds to 20,000 pixels. Assume also that the controller 6 transmits ejection timing data specifying the 100th pixel and timing TM1 to all head controllers 5. At this time, the reference head 1 ejects ink at timing TM1 to a position on the medium M corresponding to the 100th pixel. In response, when the target head 1 receives ejection timing data specifying the 20,100th pixel, which is the 100th pixel plus 20,000 pixels, and ejection timing TM2 to the 20,100th pixel, it ejects ink at timing TM2 to a position on the medium M corresponding to the 100th pixel. This allows the ink ejected from the reference head 1 and the ink ejected from the target head 1 to land at the position on the medium M corresponding to the 100th pixel.

[0056] Therefore, in step S30 described above, the second speed acquisition unit 52 identifies a pixel obtained by subtracting the number of pixels from the target head 1 to the reference head 1 from the pixel specified by the ejection timing data. Then, the transport speed data of the medium M associated with the identified pixel is read from the transport speed storage unit 56. For example, if the ejection timing data specifies the 20,100th pixel, the second speed acquisition unit 52 identifies the 100th pixel obtained by subtracting 20,000 pixels from the 20,100th pixel. Then, the second speed acquisition unit 53 reads the transport speed data of the medium M associated with the 100th pixel from the transport speed storage unit 56. In this way, the second speed acquisition unit 52 can acquire, as the second speed data, the transport speed data of the medium M at the timing when ink is ejected from the reference head 1 onto the pixel specified by the ejection timing data.

[0057] Then, the deviation amount calculation unit 53 calculates the deviation amount in the transport direction of the landing position of the ink ejected from the target head 1 relative to the landing position of the ink ejected from the reference head 1 based on the first speed data acquired by the first speed acquisition unit 51 in step S20 and the second speed data acquired by the second speed acquisition unit 52 in step S30 (step S40). The transport speed acquired by the first speed acquisition unit 51 is referred to as V H , the conveying speed acquired by the second speed acquisition unit 52 is V A If the flight time of ink ejected from the target head 1 and the reference head 1 is T, the distance in the transport direction between the landing position of the ink ejected from the reference head 1 and the landing position of the ink ejected from the target head 1 is (V H TV A T). The deviation in the transport direction between the landing position of the ink ejected from the reference head 1 and the landing position of the ink ejected from the target head 1 can be expressed as the above distance (V H TV A T) by the size of one pixel. In other words, the above-mentioned deviation amount means how many pixels the distance in the transport direction between the landing position of the ink ejected from the reference head 1 and the landing position of the ink ejected from the target head 1 corresponds to. For example, if the image resolution is 1200 dpi, the size of one pixel is approximately 21.16 μm. Note that the above distance (V H TV A If the value obtained by dividing T) by the size of one pixel does not become an integer, it can be obtained as an integer by, for example, rounding off to the first decimal place.

[0058] Then, the acceleration / deceleration determination unit 54 compares the first speed data acquired by the first speed acquisition unit 51 in step S20 with the second speed data acquired by the second speed acquisition unit 52 in step S30, and determines whether the transport speed of the medium M is increasing or decreasing (step S50). If the first speed data is smaller than the second speed data, the acceleration / deceleration determination unit 54 determines that the transport speed of the medium M is decreasing. On the other hand, if the first speed data is greater than the second speed data, the acceleration / deceleration determination unit 54 determines that the transport speed of the medium M is increasing.

[0059] Then, the head controller 5 specifies the print data to be read from the image data storage unit 55 based on the amount of deviation calculated in step S40 and the result of the acceleration / deceleration determination in step S50 (step S60).

[0060] For example, assume that the ejection timing data transmitted from the controller 6 specifies the 100th pixel, and that the amount of deviation calculated by the deviation amount calculation unit 53 in step S40 is four pixels. Furthermore, assume that the acceleration / deceleration determination unit 54 determines in step S50 that the transport speed of the medium M is decreasing. In this case, the head controller 5 identifies print data to be ejected onto the 96th pixel, which is shifted four pixels downstream in the transport direction from the 100th pixel, from the image data stored in the image data storage unit 55. That is, in the example shown in FIG. 7, for nozzle N with a nozzle ID of "m," print data "DS1" to be ejected onto the 96th pixel is identified.

[0061] Meanwhile, assume that the ejection timing data sent from the controller 6 specifies the 100th pixel, and that the amount of deviation calculated by the deviation amount calculation unit 53 in step S40 is four pixels. Furthermore, assume that the acceleration / deceleration determination unit 54 determines in step S50 that the transport speed of the medium M is increasing. In this case, the head controller 5 identifies print data to be ejected onto the 104th pixel, which is shifted four pixels upstream from the 100th pixel in the transport direction, from the image data stored in the image data storage unit 55. That is, in the example shown in FIG. 7, for nozzle N with a nozzle ID of "m," print data "DS3" to be ejected onto the 104th pixel is identified.

[0062] Then, the head controller 5 reads out the print data for all the nozzles identified in step S60 from the image data storage unit 55, and sends it to the corresponding driver IC 4 (step S70). Then, the driver IC 4 drives the actuator 3X included in the corresponding head 1 based on the print data sent from the head controller 5, causing ink to be ejected at the timing specified by the print data.

[0063] As described above, the landing position of ink ejected from each head 1 may be shifted by several pixels due to changes in the transport speed of the medium M. In this case, the head controller 5 of this embodiment does not shift the ejection timing of the head 1, but rather causes the head 1 to eject ink based on print data corresponding to pixels that are shifted by several pixels. Therefore, printing can be performed appropriately even while the transport speed of the medium M is changing.

[0064] Next, a second embodiment of the present invention will be described. The second embodiment of the present invention differs from the first embodiment in that the head controller 5 includes a plurality of history management units. The following description will focus on the differences from the first embodiment.

[0065] As shown in Fig. 8, the head controller 5 includes a plurality of history management units. In Fig. 8, nine history management units 57A to 57I are shown as an example. The history management units 57A to 57I store print data for nine consecutive pixels read from the image data storage unit 55. The nine consecutive pixels include a pixel specified by the ejection timing data. For example, if the pixel specified by the ejection timing data is the 100th pixel, the history management units 57A to 57I store print data corresponding to the 96th to 104th pixels.

[0066] The head controller 5 then executes the processes of steps S10 to S50 in the first embodiment. Thereafter, the head controller 5 identifies the history management unit from which to read print data from among the history management units 57A to 57I, based on the amount of deviation calculated in step S40 and the result of the acceleration / deceleration determination in step S50. For example, if the amount of deviation calculated in step S40 is four pixels and it is determined in step S50 that the conveying speed is increasing, the head controller 5 identifies the 104th pixel, which is shifted four pixels upstream in the conveying direction from the 100th pixel specified by the ejection timing data. The head controller 5 then reads the print data corresponding to the 104th pixel from the history management unit 57I in which the print data corresponding to the 104th pixel is stored, and transmits the print data to the driver IC 4. On the other hand, if the amount of deviation calculated in step S40 is four pixels and it is determined in step S50 that the conveying speed is decreasing, the head controller 5 identifies the 96th pixel, which is shifted four pixels downstream in the conveying direction from the 100th pixel specified by the ejection timing data. Then, the head controller 5 reads out the print data corresponding to the 96th pixel from the history management unit 57A in which the print data corresponding to the 96th pixel is stored, and transmits it to the driver IC 4.

[0067] In the second embodiment, drive waveforms corresponding to the print data "DS1," "DS2," and "DS3" in the first embodiment, respectively, and drive waveforms corresponding to the print data "DS4," "DS5," and "DS6," respectively, may be preset in the history management units 57A to 57I. The print data "DS4," "DS5," and "DS6" indicate the size of the ink droplets. For example, "DS4" means a small droplet, "DS5" a medium droplet, and "DS6" a large droplet. The drive waveforms corresponding to "DS4," "DS5," and "DS6," respectively, are drive waveforms that cause ink to land 0.5 pixels earlier or later than the drive waveforms corresponding to "DS1," "DS2," and "DS3," respectively. Then, in step S40, if the value obtained by dividing the distance in the transport direction between the landing position of the ink ejected from the reference head 1 and the landing position of the ink ejected from the target head 1 by the size of one pixel is not an integer, the history management units 57A to 57F may replace "DS1", "DS2", and "DS3" with "DS4", "DS5", and "DS6", respectively, depending on the value of the decimal part.

[0068] For example, suppose the distance in the transport direction between the landing position of ink ejected from the reference head 1 and the landing position of ink ejected from the target head 1, divided by the size of one pixel, is a value greater than or equal to 4.33 and less than 4.66. In this case, the head controller 5 identifies the 104th pixel, which is shifted by the integer part of this value, or "4" pixels. Then, because the decimal part of this value is greater than or equal to 0.33 and less than 0.66, the head controller 5 replaces the print data corresponding to the 104th pixel stored in the history management unit 57I with one of "DS4," "DS5," or "DS6." For example, if the print data "DS1" is stored in the history management unit 57I, the head controller 5 replaces "DS1" stored in the history management unit 57I with "DS4." The head controller 5 then reads the replaced print data "DS4" from the history management unit 57I and sends it to the driver IC 4.

[0069] The second embodiment described above can also provide the same effects as the first embodiment.

[0070] (Variation) The above-described embodiment is illustrative in all respects and is not restrictive. Not all of the components shown in the above-described embodiment are essential, and the components can be changed or omitted as necessary.

[0071] The number and arrangement of the heads 1 included in each printing unit can also be changed as appropriate. Furthermore, the number and arrangement of the nozzles N included in each head 1 can also be changed as appropriate.

[0072] Furthermore, in the above embodiment, white, yellow, orange, magenta, violet, cyan, and black inks are ejected from the printing units 10A to 10H, but this is not limitative and inks of any appropriate color may be ejected.

[0073] In the above embodiment, the transport device 20 is not subject to control by the controller 6, but this is not limiting. The controller 6 may also control the transport of the medium M by the transport device 20.

[0074] In the above embodiment, roll paper was used as the medium M, but a medium of an appropriate material can be used as needed. For example, the medium M may be a resin film or cloth wound into a roll.

[0075] The controller 6 does not have to be disposed inside the case CS, and may be a PC or the like disposed outside the case CS. [Explanation of symbols]

[0076] 1 head 2 Flow path components 3 Actuator member 4 Driver IC 5 head controller 6 Controller 10A~10H Printing section 20. Conveyor 20A Feeding Roller 20B Collection roller 51 1st speed acquisition section 52 2nd speed acquisition section 53 Deviation amount calculation unit 54 Acceleration / deceleration judgment section 55 Image data storage unit 56 Conveying speed memory unit 57A~57I History Management Department 100 Printing Systems

Claims

1. A printing method using a printing machine having a first nozzle and a second nozzle positioned apart in a transport direction of a medium, the second nozzle being positioned downstream of the first nozzle in the transport direction, transporting the medium in the transport direction; calculating a deviation amount in the transport direction between a first landing position, which is a landing position on the medium of a first droplet ejected from the first nozzle when a reference position on the medium passes through the first nozzle, and a second landing position, which is a landing position on the medium of a second droplet ejected from the second nozzle when the reference position passes through the second nozzle; Identifying a first pixel corresponding to the first landing position and a second pixel shifted from the first pixel by the shift amount in the transport direction; When the reference position passes through the first nozzle, the first droplet is ejected from the first nozzle based on first print data corresponding to the first pixel; When the reference position passes the second nozzle, the second droplet is ejected from the second nozzle based on print data corresponding to the second pixel.

2. The method further includes acquiring a first speed, which is a transport speed of the medium when the reference position passes through the first nozzle, and acquiring a second speed, which is a transport speed of the medium when the reference position passes through the second nozzle, identifying the first landing position based on the first velocity and the flight time of the first droplet; The printing method according to claim 1 , wherein the second landing position is determined based on the second velocity and a flight time of the second droplet.

3. The printing machine further includes a memory unit; the storage unit stores a plurality of pieces of print data for the second nozzles, the print data corresponding to a plurality of pixels arranged in the transport direction, the plurality of pixels including the first pixels and the second pixels; 3. The printing method according to claim 2, further comprising, when an instruction to read print data corresponding to the first pixel is received, identifying the second pixel based on the calculated amount of deviation, and reading print data for the second nozzle corresponding to the second pixel from the memory unit.

4. When the first speed is greater than the second speed, the second pixel is shifted downstream in the transport direction relative to the first pixel. The printing method according to claim 3 , wherein when the first speed is lower than the second speed, the second pixel is shifted upstream in the transport direction relative to the first pixel.

5. The printing machine further includes a memory unit; a plurality of history management units; the storage unit stores a plurality of pieces of print data for the second nozzles, the print data corresponding to a plurality of pixels arranged in the transport direction, the plurality of pixels including the first pixels and the second pixels; The plurality of history management units each sequentially store a plurality of print data read from the storage unit, 3. The printing method according to claim 2, further comprising: when an instruction to read out print data corresponding to the first pixel is received while print data corresponding to the first pixel is stored in one of the plurality of history management units, reading out print data corresponding to the second pixel as the second print data from a history management unit in which print data corresponding to a second pixel shifted by a number of pixels equivalent to the calculated shift amount from the history management unit in which the print data corresponding to the first pixel is stored.

6. When the first speed is greater than the second speed, the second pixel is shifted downstream in the transport direction relative to the first pixel. The printing method according to claim 5 , wherein when the first speed is lower than the second speed, the second pixel is shifted upstream in the transport direction relative to the first pixel.

7. If the number of pixels corresponding to the calculated amount of deviation is not an integer, a history management unit that is shifted by the largest integer that does not exceed the number of pixels corresponding to the calculated amount of deviation from the history management unit in which the print data corresponding to the first pixels is stored is identified as the history management unit in which the second print data is stored; The printing method according to claim 5 , wherein the ejection waveform indicated by the second print data stored in the identified history management unit is replaced with a replacement ejection waveform that lands with a 0.5 pixel shift.

8. The printing method according to claim 7 , wherein the ejection waveform indicated by the second print data and the replacement ejection waveform are preset in each of the plurality of history management units.

9. 1. A printing system comprising: a first head having a first nozzle; a second head having a second nozzle, the second nozzle being located downstream of the first nozzle in a medium transport direction; a first head controller that controls the first head; a second head controller that controls the second head, The second head controller calculating a deviation amount in the transport direction between a first landing position, which is a landing position on the medium of a first droplet ejected from the first nozzle when a reference position on the medium passes through the first nozzle, and a second landing position, which is a landing position on the medium of a second droplet ejected from the second nozzle when the reference position passes through the second nozzle; identifying a first pixel corresponding to the first landing position and a second pixel shifted from the first pixel by the shift amount in the transport direction; the first head controller ejects the first droplet from the first nozzle based on first print data corresponding to the first pixel when the reference position passes through the first nozzle; The second head controller causes the second droplet to be ejected from the second nozzle based on print data corresponding to the second pixel when the reference position passes the second nozzle.

Images