Printing method and printing system

Abstract

The present invention provides a printing method and printing system that can compensate for temporary nozzle failures caused by parameter changes during image printing while the image is being printed. [Solution] The printing method executed by the head controller 5 includes storing multiple droplet data at multiple consecutive ejection timings in the history management areas 57A to 57E, identifying ejection failure timings at which droplets cannot be ejected due to changes in ejection parameters, replacing the droplet data at the ejection timing immediately preceding the ejection failure timing, the ejection timing immediately following the ejection failure timing, or both ejection timings with complementary droplet data, and ejecting ink droplets from the nozzle N onto the medium M based on the complementary droplet data stored in the history management areas 57A to 57E, wherein the size of the droplet indicated by the complementary droplet data is larger than the size of the droplet indicated by the droplet data before replacement with the complementary droplet data.

Description

Technical Field

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

Background Art

[0002] Conventionally, there is a droplet ejection control device that detects a nozzle that temporarily stops ejecting and promotes the quick recovery of the nozzle by ejecting droplets from the nozzle (Patent Document 1). In the long paper used in this droplet ejection control device, an inspection pattern image area and a recovery pattern image area are provided between two main image areas arranged in the conveyance direction of the long paper. In the inspection pattern image area, an inspection pattern image is printed by ejecting droplets from all nozzles. Then, by reading the inspection pattern image with an in-line sensor, a nozzle that is temporarily not ejecting is detected. In the recovery pattern image area, a recovery pattern image is printed by ejecting droplets from a nozzle that is temporarily not ejecting. As a result, a nozzle that is temporarily not ejecting can be quickly recovered.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the nozzle may temporarily fail to eject not only during the printing of the inspection pattern image, but also during the printing of the main image. For example, if the relative movement speed between the paper and the nozzle changes during the printing of the main image, and the ejection parameters are changed accordingly, the nozzle may temporarily fail to eject. This is because changing the ejection parameters may require one or more ejection cycles. In the droplet ejection control device described above, if a nozzle temporarily fails to eject during the printing of the main image, it is not possible to address the temporary failure of that nozzle until the printing of the main image is completed.

[0005] The present invention was made to solve the above-mentioned problems, and aims to provide a printing method and printing system that can compensate for temporary nozzle failures caused by changes in parameters during image printing while the image is being printed. [Means for solving the problem]

[0006] According to an aspect of the present invention, a printing method is provided which is performed by a head controller electrically connected to a droplet dispensing head that dispenses droplets from a nozzle onto a conveyed medium. In this printing method, a plurality of droplet data at a plurality of consecutive dispensing timings are stored in a memory. The printing method includes, with respect to the nozzle, identifying a dispensing failure timing from the plurality of dispensing timings at which droplets can no longer be dispensed due to a change in dispensing parameters; replacing the droplet data at the dispensing timing immediately preceding the dispensing failure timing, the droplet data at the dispensing timing immediately following the dispensing failure timing, or both, with complementary droplet data; and dispensing the droplets from the nozzle onto the medium at the dispensing timing immediately preceding the dispensing failure timing, the dispensing timing immediately following the dispensing failure timing, or both, based on the complementary droplet data stored in the memory. The size of the droplets indicated by the complementary droplet data is larger than the size of the droplets indicated by the droplet data before replacement with the complementary droplet data.

[0007] According to another aspect of the present invention, a printing system is provided comprising a droplet ejection head having a nozzle and ejecting droplets from the nozzle, and a head controller for controlling the droplet ejection head. The head controller has a plurality of history management units that store droplet data indicating the size of the droplet to be ejected for each of a plurality of consecutive ejection timings for the nozzle. The head controller identifies an ejection failure timing from the plurality of consecutive ejection timings at which droplets cannot be ejected due to a change in ejection parameters, and replaces the droplet data from the ejection timing immediately preceding the ejection failure timing, the droplet data from the ejection timing immediately following the ejection failure timing, or both, from the plurality of droplet data stored in each of the plurality of history management units with complementary droplet data, and ejects the droplets from the nozzle based on the complementary droplet data stored in the plurality of history management units at the ejection timing immediately preceding the ejection failure timing, the ejection timing immediately following the ejection failure timing, or both. The size of the droplet indicated by the complementary droplet data is larger than the size of the droplet indicated by the droplet data before replacement with the complementary droplet data.

[0008] According to the above embodiment of the present invention, temporary non-ejection from the nozzle caused by changes in ejection parameters during image printing can be compensated for during the printing of the image. [Brief explanation of the drawing]

[0009] [Figure 1] This is a plan view illustrating the configuration of the printing system. [Figure 2] This is a bottom view showing an example of the printing unit that makes up a printing system. [Figure 3] This is a cross-sectional view of the flow path member and actuator member that constitute the head. [Figure 4] This is a functional block diagram of the head controller. [Figure 5] This flowchart shows the processing flow performed by the head controller. [Figure 6]This figure shows an example of droplet data stored in the image data storage unit. [Figure 7] Figures (a) to (c) show the relationship between the transmission time of droplet data and parameter change information and the dispensing cycle. [Figure 8] (a) and (b) are diagrams showing examples of droplet data replacement tables. [Modes for carrying out the invention]

[0010] The printing system 100 according to an embodiment of the present invention is a digital printing press. As shown in Figure 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 includes an input unit (not shown) consisting of buttons located on the outer surface of the housing CS.

[0011] 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 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 relative to the housing CS.

[0012] The printing units 10C to 10H on the downstream side in the transport direction are supplied with inks such as yellow, orange, magenta, violet, cyan, and black, respectively. The printing units 10A and 10B on the upstream side in the transport direction are supplied with inks such as white, respectively. For these inks, for example, UV-curable inks that harden when exposed to ultraviolet (UV) light can be used.

[0013] As shown in Figure 1, ten heads 1 are positioned at the vertically lower ends of each of the printing sections 10A to 10H. The ten heads 1 are arranged in a staggered pattern in the width direction, with their lower surfaces located on the same plane. As shown in Figure 2, the lower surface of each head 1 is a nozzle surface NS from which multiple nozzles N open. On the nozzle surface NS, the multiple nozzles N are arranged in a staggered pattern in the width direction, forming two rows of nozzles aligned in the transport direction. Each nozzle row extends in the width direction. In this embodiment, each head 1 has two rows of nozzles, but there may be one row of nozzles, or three or more rows.

[0014] The conveying device 20 comprises a feed roller 20A and a recovery roller 20B shown in Figure 1, and a plurality of conveying rollers not shown. Furthermore, the conveying device 20 includes a conveying motor not shown that is connected to the feed roller 20A and the recovery roller 20B. The feed roller 20A and the recovery roller 20B are aligned in the conveying direction, with the feed roller 20A located upstream of the recovery roller 20B in the conveying direction. In the conveying direction, the printing units 10A to 10H are located between the feed roller 20A and the recovery roller 20B. The plurality of conveying rollers are located between the feed roller 20A and the recovery roller 20B in the conveying direction and are aligned in the conveying direction. The plurality of conveying rollers are located below the printing units 10A to 10H.

[0015] The feeding roller 20A, the recovery roller 20B, and the plurality of conveying rollers all extend in the width direction and rotate about a rotation axis extending in the width direction. The feeding roller 20A and the recovery roller 20B are each rotationally driven by a conveying motor. A roll-shaped medium M having a length in the conveying direction longer than the length in the width direction is attached to the feeding roller 20A. The medium M sent out from the feeding roller 20A by the rotation of the feeding roller 20A passes between the printing units 10A to 10H and the plurality of conveying rollers, and is wound around the recovery roller 20B by the rotation of the recovery roller 20B. Thereby, the medium M is conveyed in the conveying direction. The plurality of conveying rollers rotate as the medium M is conveyed. The conveying motor rotationally drives the feeding roller 20A and the recovery roller 20B so that the medium M is conveyed while contacting the upper portion of the circumferential surface of each of the plurality of conveying rollers.

[0016] During the period when the conveying device 20 conveys the medium M, an acceleration period for increasing the conveying speed of the medium M to a target value, a constant speed period for maintaining the conveying speed of the medium M within a predetermined range including the target value, and a deceleration period for decreasing the conveying speed of the medium M from the target value are included.

[0017] As shown in FIG. 4, 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 and an input unit (not shown), it temporarily reads out the data and programs stored in the ROM 62 to the RAM 63, and executes processing corresponding to the various instructions according to the read data and programs. The external device EX is, for example, a PC.

[0018] Programs and data for the CPU 61 to perform various processes are stored in the ROM 62. Data used when the CPU 61 executes a program is temporarily stored in the RAM 63.

[0019] As shown in FIG. 4, the controller 6 is electrically connected to the driver IC 4 via a head controller 5 described later. The controller 6 is electrically connected to each head 1 included in each of the printing units 10A to 10H via the head controller 5 and the driver IC 4. The controller 6 controls each head 1 via the head controller 5 and the driver IC 4, and causes the UV curable ink to be ejected from a plurality of nozzles N of each head 1 toward the medium M conveyed in the conveyance direction by the conveyance device 20. Thereby, an image is printed on the medium M.

[0020] Next, the configuration of each head 1 will be described. All the heads 1 included in the printing system 100 have the configuration described below. As shown in FIG. 3, the head 1 includes a flow path member 2 and an actuator member 3.

[0021] The flow path member 2 is formed by a plurality of metal plates and a nozzle plate NP laminated 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 of a polymer synthetic resin material such as polyimide, for example, and is joined to the lower surface of the laminated metal plates with an adhesive. The lower surface of the nozzle plate NP is a nozzle surface NS as an ink ejection surface where the nozzles N open. Note that the nozzle plate NP may be formed of a metal material such as stainless steel.

[0022] Inside the flow path member 2, an individual flow path 2B communicating with each nozzle N and a supply manifold 2A communicating with the individual flow path 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. The ink discharged from 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 path 2B.

[0023] Although not shown in the diagram, the flow channel member 2 has multiple individual flow channels 2B, each corresponding to one of the multiple nozzles N. As described above, the multiple nozzles N each form two rows of nozzles extending in the width direction, and similarly, the multiple individual flow channels 2B each form two rows of individual flow channels extending in the width direction. The supply manifold 2A communicates with the multiple individual flow channels 2B that constitute the two rows of individual flow channels. The number of supply manifolds 2A formed in the flow channel member 2 is adjusted to match the number of nozzles N. Furthermore, when multiple supply manifolds 2A are formed, the number of individual flow channels 2B communicating with each supply manifold 2A is also adjusted to match the number of nozzles N.

[0024] As shown in Figure 3, the actuator member 3 is fixed to the upper surface of the flow channel member 2. The actuator member 3 includes a metal diaphragm 3A, a piezoelectric layer 3B, and a plurality of individual electrodes 3C.

[0025] The actuator member 3 is formed by sequentially depositing a thin film that will become a piezoelectric layer 3B and a thin film that will become individual electrodes 3C on the upper surface of the diaphragm 3A.

[0026] The diaphragm 3A is positioned on the upper surface of the flow channel member 2 so as to cover all of the pressure chambers P. The diaphragm 3A is a metal plate that is approximately rectangular in shape when viewed from above. 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. As a common electrode, the diaphragm 3A 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 to serve as a common electrode.

[0027] The piezoelectric layer 3B is located on the upper surface of the diaphragm 3A. The piezoelectric layer 3B is formed from 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 electrodes 3C and the diaphragm 3A).

[0028] The individual electrodes 3C are positioned on the upper surface of the piezoelectric layer 3B so as to overlap the pressure chamber P vertically. The diaphragm 3A, which acts as a common electrode, the individual electrodes 3C, and the portion of the piezoelectric layer 3B sandwiched between the individual electrodes 3C and the diaphragm 3A form a single actuator 3X.

[0029] When a predetermined driving potential is applied to an individual electrode 3C from the driver IC 4, a potential difference is created between the individual electrode 3C to which this driving potential is applied and the diaphragm 3A, which is a common electrode held at ground potential. As a result, an electric field acts in the thickness direction on 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. Therefore, the region of the piezoelectric layer 3B facing the individual electrode 3C (active region) contracts in a planar direction perpendicular to the thickness direction. Here, the diaphragm 3A below the piezoelectric layer 3B is fixed to the flow channel member 2. Therefore, as the piezoelectric layer 3B located on the upper surface of the diaphragm 3A contracts in the planar direction, the portion of the diaphragm 3A covering the pressure chamber P deforms so that it becomes convex toward the pressure chamber P (unimorph deformation). At this time, the volume inside the pressure chamber P decreases, the ink pressure inside the pressure chamber P increases, and ink is ejected from the nozzle N that communicates with this pressure chamber P. In other words, the actuator member 3 is located in a position corresponding to the pressure chamber P and applies pressure to the ink in the pressure chamber P in order to eject ink from the nozzle N which communicates with the pressure chamber P.

[0030] Next, the head controller 5 will be described. As shown in Figure 4, the head controller 5 is electrically connected to the controller 6 and the driver IC 4. Although Figure 4 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 there are heads 1 in the printing system 100. Furthermore, the same number of head controllers 5 as there are heads 1 and the same number of driver IC 4 as there are heads 1 are electrically connected one-to-one. In other words, each head controller 5 is electrically connected to the head 1 to be controlled via the driver IC 4.

[0031] All head controllers 5 included in the printing system 100 have the same configuration. Therefore, the following explanation will use one head controller 5 as an example. As shown in Figure 4, the head controller 5 is a circuit board on which a history management unit 51, a parameter change instruction receiving unit 52, an ejection failure timing identification unit 53, a droplet data replacement unit 54, an image data storage unit 55, a droplet data replacement table 56, and history management areas 57A to 57E are examples of memory.

[0032] The head controller 5 stores image data transmitted from the controller 6 in advance. The head controller 5 also receives ejection timing data from the controller 6. The ejection timing data instructs the head controller 5 to identify the pixels from the pre-stored image data where ink should be deposited and the ejection timing of the ink to be deposited on those pixels. Furthermore, if, for example, a change in ejection parameters is necessary due to a change in the transport speed of the medium M, the head controller 5 receives a parameter change instruction from the controller 6. The parameter change instruction instructs the head controller 5 to identify the ejection timing where the parameter change is necessary and to provide parameter change information. The parameter change information includes, for example, information on changes in the drive voltage of the actuator 3X and information on changes in the drive timing of the actuator 3X.

[0033] After storing the image data, the head controller 5 receives a parameter change instruction from the controller 6 and identifies the ejection failure timing. The ejection failure timing is the moment when ink cannot be temporarily ejected from the nozzle in order to change the ejection parameters. The head controller 5 then replaces the droplet data from the ejection timing immediately preceding the identified ejection failure timing, the droplet data from the ejection timing immediately following the identified ejection failure timing, or both, with complementary droplet data indicating larger droplets. The head controller 5 then transmits the replaced complementary droplet data to the corresponding driver IC 4.

[0034] The above processing flow will be explained below with reference to Figure 5. First, when the head controller 5 receives image data from the controller 6, the history management unit 51 stores the received image data in the image data storage unit 55 (step S10). For example, DRAM can be used as the image data storage unit 55.

[0035] The image data is raster data and corresponds to the color of the ink ejected from the controlled head 1. As shown in Figure 6, the image data includes droplet data indicating the size of the ink droplet to be ejected to each pixel for all k nozzles N included in the target head 1. In Figure 6, the pixel ID means the order of each pixel in the transport direction. For example, pixel ID "1" means the first pixel from the downstream side in the transport direction among the pixels that make up the image, and pixel ID "100" means the 100th pixel from the downstream side in the transport direction. The nozzle ID is the identification number of the k nozzles N included in the target head 1. The print data "DS1", "DS2", and "DS3" indicate the size of the ink droplet; for example, "DS1" means a small droplet, "DS2" means a medium droplet larger than a small droplet, and "DS3" means a large droplet larger than a medium droplet. The print data "DS0" means no ejection of ink.

[0036] Next, the history management unit 51 reads droplet data for k nozzles N in ascending order of pixel ID from the image data storage unit 55 and stores it in the history management areas 57A to 57E for each pixel ID (step S20). For example, before receiving the first ejection timing data, the history management unit 51 stores the droplet data for pixel ID "1" to pixel ID "5" in the history management areas 57A to 57E, respectively.

[0037] Next, when the history management unit 51 receives discharge timing data from the controller 6 (step S30), the parameter change instruction receiving unit 52 determines whether it has received a parameter change instruction from the controller 6 (step S40).

[0038] If the parameter change instruction receiving unit 52 determines that it has not received a parameter change instruction from the controller 6 (step S40: NO), the history management unit 51 transmits the droplet data stored in the history management area 57A to the driver IC 4 (step S70).

[0039] In step S70, after transmitting droplet data to the driver IC 4, the history management unit 51 determines whether it has transmitted droplet data for all pixels stored in the image data storage unit 55 to the driver IC 4 (step S80). If it determines that it has not transmitted droplet data for all pixels to the driver IC 4 (step S80: NO), the history management unit 51 executes the process in step S20. That is, the history management unit 51 moves the droplet data stored in history management areas 57B to 57E to history management areas 57A to 57D, respectively. Then, the history management unit 51 reads the droplet data for the smallest pixel ID from the image data storage unit 55 and stores it in history management area 57E. For example, if droplet data for pixel IDs "2" to "5" is stored in history management areas 57B to 57E, respectively, the history management unit 51 moves the droplet data for pixel IDs "2" to "5" to history management areas 57A to 57D, respectively. Then, the history management unit 51 reads the droplet data for pixel ID "6" from the image data storage unit 55 and stores it in the history management area 57E. After that, the history management unit 51 sequentially executes the processes from step S30 onwards described above. In step S80, if it determines that droplet data for all pixels has been sent to the driver IC4 (step S80: YES), the head controller 5 terminates the above series of processes.

[0040] In step S40, if the parameter change instruction receiving unit 52 determines that it has received a parameter change instruction from the controller 6 (step S40: YES), the dispensing failure timing identification unit 53 executes the dispensing failure timing identification process (step S50).

[0041] The following explains the process for identifying the timing of ejection failure, referring to Figures 7(a) to 7(c). In Figures 7(a) to 7(c), for example, "T(99)" means the timing for ejecting an ink droplet according to the droplet data of pixel ID "99". The periods T(99) to T(100), T(100) to T(101), T(101) to T(102), and T(102) to T(103) each represent one ejection cycle. "Droplet data" means the transmission time of the droplet data, and "setting" means the transmission time of the parameter change information. Figures 7(a) to 7(c) assume, as an example, that a parameter change is required at the ejection timing T(100).

[0042] As shown in Figure 7(a), if the sum of the droplet data transmission time and the parameter change information transmission time is shorter than one discharge cycle, the head controller 5 can transmit droplet data and parameter change information between discharge timing T(100) and discharge timing T(101). Then, at discharge timing T(101), the head controller 5 can transmit the droplet data that should be transmitted at discharge timing T(101). For this reason, the discharge failure timing identification unit 53 does not identify discharge timing T(101) as a discharge failure timing.

[0043] On the other hand, as shown in Figure 7(b), if the discharge cycle becomes shorter compared to Figure 7(a) due to an increase in the transport speed of the medium M, for example, the sum of the droplet data transmission time and the parameter change information transmission time may be between 1 and 2 discharge cycles. In this case, at discharge timing T(101), the head controller 5 is transmitting parameter change information, and therefore cannot transmit the droplet data that should be transmitted at discharge timing T(101). For this reason, the discharge failure timing identification unit 53 identifies discharge timing T(101) as a discharge failure timing.

[0044] Furthermore, as shown in Figure 7(c), depending on the content of the parameter change information, if the transmission time of the parameter change information becomes longer compared to Figure 7(b), the sum of the droplet data transmission time and the parameter change information transmission time may be 2 or more but less than 3 discharge cycles. In this case, at discharge timing T(101) and discharge timing T(102), the head controller 5 is transmitting parameter change information, and therefore cannot transmit the droplet data that should be transmitted at discharge timing T(101) and discharge timing T(102). For this reason, the discharge failure timing identification unit 53 identifies discharge timing T(101) and discharge timing T(102) as discharge failure timings.

[0045] Returning to the flowchart in Figure 5, after the dispensing failure timing identification unit 53 performs the dispensing failure timing identification process (step S50), the droplet data replacement unit 54 performs the droplet data replacement process (step S60). More specifically, when the droplet data for the dispensing timing identified as a dispensing failure timing in the dispensing failure timing identification process (step S50) is stored, for example, in the history management area 57C, the droplet data replacement unit 54 performs the droplet data replacement process (step S60).

[0046] The droplet data replacement process will be explained below using the specific examples in Figures 6, 8(a), and 8(b). In Figures 8(a) and 8(b), droplet data after replacement where the droplet size is larger than before replacement is shown with shading. First, let's focus on nozzle ID "m" in Figure 6 and assume that the timing at which ink droplets should be ejected according to the droplet data of pixel ID "101" has been identified as an ejection failure timing. In other words, let's assume that one ejection timing T(101) has been identified as an ejection failure timing.

[0047] In Figure 6, the droplet data for the discharge timing T(101), which was identified as a discharge failure timing, is "DS2". Furthermore, the droplet data for the discharge timing T(100), which is one step prior to the discharge failure timing, and the discharge timing T(102), which is one step following, are both "DS1". In Figure 6, these droplet data are shown with shading.

[0048] In this case, the droplet data replacement unit 54 searches the droplet data replacement table 56 shown in Figure 8(a) for a pattern in which, before replacement, the droplet data at the previous timing is "DS1", the droplet data at the dispensing failure timing is "DS2", and the droplet data at the next timing is "DS1". Then, pattern ID "34" is found to be a match. According to pattern ID "34", the droplet data at the previous timing is replaced with "DS2", and the droplet data at the next timing is also replaced with "DS2". Accordingly, the droplet data replacement unit 54 replaces the droplet data at dispensing timing T(100) stored in the history management area 57B with "DS2", and also replaces the droplet data at dispensing timing (T102) stored in the history management area 57D with "DS2". In other words, the droplet data replacement unit 54 replaces the droplet data at the timing immediately before and immediately after the dispensing failure timing with complementary droplet data indicating a larger droplet size.

[0049] In the example above, both the droplet data from the previous timing and the droplet data from the next timing were replaced with complementary droplet data, but this is not the only example. Depending on the droplet data at the ejection failure timing and the timings immediately before and after it, for example, as in pattern ID "1", only the droplet data from the previous timing may be replaced with complementary droplet data, or for example, as in pattern ID "36", only the droplet data from the next timing may be replaced with complementary droplet data. Note that if the droplet data at the ejection failure timing is "DS0", no ink droplets are ejected at that timing in the first place. Therefore, there is no need to replace the droplet data at the timings immediately before and after the ejection failure timing.

[0050] Furthermore, while the above specific example assumed that only one dispensing timing was identified as a non-dispensing timing, as shown in Figure 7(c), there are also cases where two consecutive dispensing timings are identified as non-dispensing timings. In this case, the droplet data replacement unit 54 searches for droplet data patterns for the previous timing, non-dispensing timing 1, non-dispensing timing 2, and the next timing from the droplet data replacement table shown in Figure 8(b), not Figure 8(a). In Figure 8(b), the previous timing refers to the timing immediately preceding non-dispensing timing 1, and the next timing refers to the timing immediately following non-dispensing timing 2. Then, as in the case where only one dispensing timing is identified as a non-dispensing timing, the droplet data replacement unit 54 replaces the droplet data for the previous timing, the next timing, or both timings with complementary droplet data according to the matching pattern. Note that the droplet data replacement table 56 shown in Figures 8(a) and 8(b) is merely an example, and the replaced droplet data can be set by the user as appropriate. For example, you could set it to replace only the droplet data from the previous timing, or you could set it to replace only the droplet data from the next timing.

[0051] Then, after the droplet data replacement unit 54 performs the droplet data replacement process (step S60), the history management unit 51 performs the processes from step S70 onwards as described above.

[0052] As explained above, if it is necessary to change the ejection parameters during image printing, there may be ejection failure timings in which ink droplets cannot be ejected from the nozzles for a temporary period. In this case, the head controller 5 of this embodiment replaces the droplet data at the timing immediately before, immediately after, or both of the ejection failure timings with complementary droplet data indicating larger droplets. Therefore, ejection failures that occur during the printing of the image can be compensated for during the printing of the image by increasing the size of the droplets ejected at the timings before and after the ejection failure.

[0053] The embodiments described above are illustrative in all respects and not restrictive. Not all of the configurations shown in the embodiments are essential, and configurations can be modified or omitted as needed.

[0054] In the above embodiment, the head controller 5 has a droplet data replacement table 56, and the droplet data replacement unit 54 performs droplet data replacement processing (step S60) by referring to the droplet data replacement table 56, but it is not limited to this. For example, the head controller 5 does not have to have a droplet data replacement table 56. In this case, the droplet data replacement unit 54 may store a plurality of conditional expressions in advance, and calculate supplementary droplet data based on the droplet data at the discharge failure timing and the discharge timings before and after it, and the conditional expressions.

[0055] In the above embodiment, the head controller 5 had five history management areas 57A to 57E, but it may have six or more history management areas.

[0056] In the above embodiment, the number and arrangement of the heads 1 included in each printing section can be changed as appropriate. Furthermore, the number and arrangement of the nozzles N included in each head 1 can also be changed as appropriate.

[0057] Furthermore, in the above embodiment, white, yellow, orange, magenta, violet, cyan, and black inks were ejected from the printing units 10A to 10H, but the invention is not limited to these, and inks of any appropriate color may be ejected.

[0058] In the above embodiment, the transport device 20 was not subject to control by the controller 6, but this is not limited to that. The controller 6 may control the transport of the medium M by the transport device 20.

[0059] In the above embodiment, roll paper was used as the medium M, but any medium of an appropriate material can be used as needed. For example, the medium M may be a roll of resin film or cloth.

[0060] Controller 6 does not necessarily have to be located inside the CS cabinet; it may be a PC or other device located outside the CS cabinet. [Explanation of Symbols]

[0061] 1 head 2 Flow channel members 3 Actuator Member 4 Driver ICs 5 Head Controller 6 Controllers 10A~10H Printing section 20 Conveying device 20A feed roller 20B Recovery Roller 51 History Management Department 52 Parameter change instruction receiving unit 53 Discharge failure timing identification unit 54 Droplet data replacement section 55 Image data storage unit 56 Droplet Data Replacement Table 57A~57E History Management Area 100 Printing Systems

Claims

1. A printing method performed by a head controller that is electrically connected to a droplet ejection head that ejects droplets from a nozzle onto a conveyed medium, Multiple droplet data from multiple consecutive dispensing timings are stored in memory. Regarding the aforementioned nozzle, From the aforementioned multiple dispensing timings, identify the dispensing failure timing at which droplets can no longer be dispensed due to a change in the dispensing parameters, The memory stores, and the droplet data from the ejection timing immediately preceding the ejection failure timing, the droplet data from the ejection timing immediately following the ejection failure timing, or both, are replaced with complementary droplet data. The process includes discharging the droplets from the nozzle into the medium based on the supplemental droplet data stored in the memory at the discharging timing immediately preceding the discharging failure timing, the discharging timing immediately following the discharging failure timing, or both. A printing method wherein the size of the droplets indicated by the supplemental droplet data is larger than the size of the droplets indicated by the droplet data before replacement with the supplemental droplet data.

2. The printing method according to claim 1, wherein the ejection failure timing is determined based on the transport speed of the medium and the plurality of ejection timings.

3. The printing method according to claim 2, wherein, among the plurality of droplet data stored in the memory, both the droplet data at the ejection timing immediately preceding the ejection failure timing and the droplet data at the ejection timing immediately following the ejection failure timing are replaced with the complementary droplet data.

4. The printing method according to claim 2, wherein, of the plurality of droplet data stored in the memory, only the droplet data at the ejection timing immediately preceding the ejection failure timing is replaced with the supplemental droplet data.

5. The printing method according to claim 2, wherein, of the plurality of droplet data stored in the memory, only the droplet data at the ejection timing one after the ejection failure timing is replaced with the supplemental droplet data.

6. The head controller is equipped with a droplet data replacement table that associates droplet data at the dispensing timing immediately preceding the dispensing failure timing with droplet data at the dispensing failure timing, droplet data at the dispensing timing immediately following the dispensing failure timing, and the replacement droplet data. The printing method according to claim 1, further comprising reading the complementary droplet data from the droplet data replacement table based on droplet data at the ejection timing immediately preceding the ejection failure timing, droplet data at the ejection failure timing, and droplet data at the ejection timing immediately following the ejection failure timing, which are stored in and read from the memory.

7. The printing method according to claim 1, further comprising calculating the complementary droplet data based on droplet data at the ejection timing immediately preceding the ejection failure timing, droplet data at the ejection failure timing, and droplet data at the ejection timing immediately following the ejection failure timing.

8. A printing system, A droplet dispensing head having a nozzle and dispensing droplets from the nozzle, The system includes a head controller that controls the aforementioned droplet dispensing head, The head controller has multiple history management areas in which droplet data indicating the size of the droplet to be discharged is stored for each of a series of discharge timings for the nozzle. The aforementioned head controller is From the aforementioned series of consecutive dispensing timings, a dispensing failure timing is identified where droplets can no longer be dispensed due to a change in the dispensing parameters. Of the multiple droplet data stored in each of the aforementioned multiple history management areas, the droplet data at the dispensing timing immediately preceding the dispensing failure timing, the droplet data at the dispensing timing immediately following the dispensing failure timing, or both, are replaced with complementary droplet data. At the discharge timing immediately preceding the discharge failure timing, the discharge timing immediately following the discharge failure timing, or both, the droplet is discharged from the nozzle based on the supplementary droplet data stored in the plurality of history management areas. A printing system in which the droplet size indicated by the supplemental droplet data is larger than the droplet size indicated by the droplet data before replacement with the supplemental droplet data.

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