Droplet ejection device, droplet ejection method, and droplet ejection program

Abstract

To provide a droplet discharge device, a droplet discharge method and a droplet discharge program which can suppress deterioration in the image quality.SOLUTION: A droplet discharge device comprises a control device configured to: determine whether a state of discharging droplets from a nozzle in a nozzle array is a first case or a second case where a smaller amount of droplets is discharged despite an attempt made to discharge the same amount of droplets as the first case; when determining to be the first case, execute a first printing process of performing preceding pass printing in interlace printing, then, causing a conveyance unit to convey a printing object medium by a first distance being a prescribed number of pitches, and then, performing succeeding pass printing; or when determining to be the second case, execute a second printing process of performing preceding pass printing in the interlace printing, then, causing the conveyance unit to convey the printing object medium by a second distance longer than the first distance, and then, performing succeeding pass printing.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a droplet ejection device, a droplet ejection method, and a droplet ejection program used in an image recording device such as an inkjet printer. [Background technology]

[0002] Conventionally, inkjet printers equipped with ejection heads that eject ink droplets from nozzles onto a print medium are known. Such ejection heads are provided with, for example, four nozzle arrays. Examples of the four nozzle arrays include a nozzle array having multiple nozzles that eject cyan ink, a nozzle array having multiple nozzles that eject magenta ink, a nozzle array having multiple nozzles that eject black ink, and a nozzle array having multiple nozzles that eject yellow ink. For example, in the inkjet printer disclosed in Patent Document 1, the nozzle arrays that eject cyan, magenta, and black ink each have 180 nozzles, and the nozzle array that ejects yellow ink has 90 nozzles. The resolution of the cyan, magenta, and black raster lines is 180 dpi, and the resolution of the yellow raster lines is 90 dpi. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-296748 Summary of the Invention [Problem to be solved by the invention]

[0004] However, because the resolution of yellow is lower than that of other colors as described above, when color printing is performed by transporting the print medium in the transport direction one nozzle at a time, the nozzles that eject yellow ink must achieve the desired resolution through multiple passes. As a result, raster lines formed by the same nozzles and extending in the carriage movement direction are continuous in the transport direction. However, if there is an abnormality in the yellow nozzles, the raster lines appear as white streaks, degrading image quality.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a droplet ejection device, a droplet ejection method, and a droplet ejection program that can suppress deterioration in image quality. [Means for solving the problem]

[0006] The droplet ejection device of the present invention comprises an ejection head having a nozzle row in which a plurality of nozzles that eject droplets onto a print medium are arranged at a predetermined pitch, a carriage on which the ejection head is mounted and that moves back and forth in a movement direction, a transport unit that transports the print medium in a transport direction that intersects with the movement direction, and a control device, wherein the control device performs pass printing at least twice while moving the carriage in the movement direction to eject droplets from the nozzles, to perform interlaced printing to form a partial image on the print medium with a higher resolution than the pitch, and wherein the state in which droplets are ejected from the nozzles of the nozzle row is a first state. The method determines whether the current case is a first case in which a previous pass printing is performed, or a second case in which a smaller amount of droplets is ejected even when attempting to eject the same amount of droplets as in the first case, and in the first case, after performing the previous pass printing in the interlaced printing, the transport unit transports the printing medium a first distance which is a predetermined number of the pitch, and then executes a first printing process in which the subsequent pass printing is performed, and in the second case, after performing the previous pass printing in the interlaced printing, the transport unit transports the printing medium a second distance which is greater than the first distance, and then executes a second printing process in which the subsequent pass printing is performed.

[0007] According to the present invention, in the second case, in which a smaller amount of droplets are ejected even when attempting to eject the same amount of droplets as in the first case, the print medium is transported in the transport direction by a second distance greater than the first distance between the current pass and the next pass. This prevents two raster lines formed by the same nozzle (i.e., a raster line formed in a preceding pass and a raster line formed in a following pass) from being adjacent in the transport direction. This prevents white streaks in the preceding pass and white streaks in the following pass, which would appear due to ejection defects from the nozzle in question, from being adjacent in the transport direction in the second case. This makes the white streaks less visible, thereby suppressing degradation of image quality. On the other hand, in the first case, in which the nozzles are normal, the print medium is transported in the transport direction by a first distance smaller than the second distance between the preceding pass and the following pass. This allows a relatively large number of nozzles to be used to form a partial image, thereby increasing printing speed. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a droplet ejection device, a droplet ejection method, and a droplet ejection program that are capable of suppressing degradation in image quality. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a plan view showing a schematic configuration of a droplet ejection device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a discharge head of the droplet discharge device of FIG. [Figure 3] 3 is a plan view showing a nozzle row in which a plurality of nozzles in FIG. 2 are arranged at a predetermined pitch. [Figure 4] FIG. 2 is a block diagram showing the configuration of the droplet ejection device of FIG. [Figure 5] FIG. 2 is a plan view showing a detailed configuration of the ejection head of FIG. [Figure 6] 6 is a diagram for explaining a partial image formed by the ejection head of FIG. 5. FIG. [Figure 7]6 is a diagram for explaining pass printing by the ejection head of FIG. 5. FIG. [Figure 8] FIG. 10 is a diagram for explaining a first printing process performed by the control device. [Figure 9] FIG. 10 is a diagram for explaining a second printing process performed by the control device. [Figure 10] FIG. 2 is a block diagram showing a configuration for detecting an abnormality in a nozzle in the ejection head. [Figure 11] 4 is a flowchart showing a control flow by the control device. DETAILED DESCRIPTION OF THE INVENTION

[0010] A droplet ejection device, a droplet ejection method, and a droplet ejection program according to an embodiment of the present invention will be described below with reference to the drawings. The droplet ejection device, the droplet ejection method, and the droplet ejection program described below are merely one embodiment of the present invention. Therefore, the present invention is not limited to the following embodiment, and additions, deletions, and modifications are possible within the scope of the present invention.

[0011] Fig. 1 is a plan view showing a schematic configuration of a droplet ejection device 10 according to one embodiment of the present invention. Fig. 2 is a cross-sectional view of an ejection head 20 in the droplet ejection device 10 of Fig. 1, and Fig. 3 is a plan view showing a nozzle row NL in which a plurality of nozzles 21 are arranged at a predetermined pitch Pt. As shown in Fig. 1, the droplet ejection device 10 of this embodiment uses ink as an example of a liquid and ejects ink droplets as an example of a droplet, and includes a storage tank 12, a carriage 16, an ejection head 20, a pair of transport rollers 15, a pair of guide rails 17, and a sub-tank 18. In the droplet ejection device 10, a print medium W is placed on a platen (not shown).

[0012] The carriage 16 is mounted with a discharge head 20. The carriage 16 is supported by a pair of guide rails 17 extending in a movement direction Ds perpendicular to the transport direction Df of the print medium W, which may be, for example, printing paper, and moves back and forth in the movement direction Ds along the guide rails 17. This causes the discharge head 20 to move back and forth in the movement direction Ds. The storage tank 12 and the discharge head 20 are connected by a tube 12a. The movement direction Ds includes a first movement direction Ds1 and a second movement direction Ds2 that is the opposite direction to the first movement direction Ds1.

[0013] The ejection head 20 is an inkjet head that ejects ink droplets. The ejection head 20 has nozzles 21 (described below) that eject ink droplets of each color, for example, yellow (Y), magenta (M), cyan (C), and black (K). As shown in FIG. 3, the ejection head 20 has a nozzle row NL in which a plurality of nozzles 21 that eject each of the ink droplets onto the print medium W are arranged at a predetermined pitch Pt. The nozzle row NL extends along an arrangement direction that is the same direction as the transport direction Df. Details of the ejection head 20 will be described later.

[0014] Ink is stored in the storage tanks 12. The storage tanks 12 are connected to the ejection head 20 via ink flow paths to supply ink to the ejection head 20. A storage tank 12 is provided for each type of ink. For example, four storage tanks 12 are provided, each storing one of the above-mentioned colors of ink. For example, four sub-tanks 18 are mounted on the carriage 16. Each sub-tank 18 is connected to a corresponding storage tank 12 via a tube 12a. Note that while FIG. 1 shows only one tube 12a for simplicity, the number of tubes 12a provided corresponds to the combination of storage tanks 12 and sub-tanks 18.

[0015] The pair of transport rollers 15 are arranged parallel to each other along the movement direction Ds. The transport rollers 15 rotate when a transport motor 31 (FIG. 4) described below is driven, thereby transporting the print medium W on the platen in the transport direction Df. The transport rollers 15 and the transport motor 31 correspond to a transport unit.

[0016] As shown in Figure 2, the ejection head 20 has a plurality of nozzles 21 that eject ink droplets. The ejection head 20 has a laminated body of a flow path forming body and a volume changing unit. A liquid flow path is formed inside the flow path forming body, and a plurality of nozzle holes 21a are opened in the nozzle surface 40a, which is the lower surface of the flow path forming body. The volume changing unit is driven to change the volume of the liquid flow path. At this time, the meniscus vibrates in the nozzle holes 21a, and ink is ejected.

[0017] The flow path forming body of the ejection head 20 is a laminate of multiple plates, and the volume changing section includes a vibration plate 55 and an actuator (piezoelectric element) 60. The actuator 60 applies pressure to the ink stored in the pressure chamber 28, causing ink droplets to be ejected from the nozzle 21 communicating with the pressure chamber 28. An insulating film 56 is connected to the top of the vibration plate 55, and a common electrode 61, which will be described later, is connected to the top of the insulating film 56.

[0018] The multiple plates are stacked including, in order from the bottom, a nozzle plate 46, a spacer plate 47, a first flow path plate 48, a second flow path plate 49, a third flow path plate 50, a fourth flow path plate 51, a fifth flow path plate 52, a sixth flow path plate 53, and a seventh flow path plate 54. The first flow path plate 48, the second flow path plate 49, the third flow path plate 50, the fourth flow path plate 51, and the fifth flow path plate 52 configure the manifold plate 44.

[0019] Each plate has holes and grooves of various sizes formed therein. Inside the flow path forming body where the plates are stacked, the holes and grooves are combined to form a plurality of nozzles 21, a plurality of individual flow paths 64, and a manifold 22 as liquid flow paths.

[0020] The nozzles 21 are formed to penetrate the nozzle plate 46 in the stacking direction. In the nozzle surface 40a of the nozzle plate 46, a plurality of nozzle holes 21a, which are the tips of the nozzles 21, are lined up in an arrangement direction that is the same direction as the transport direction Df to form a nozzle row.

[0021] The manifold 22 supplies ink to the pressure chambers 28 to which an ejection pressure for ink droplets is applied. The manifold 22 extends in the arrangement direction and is connected to one end of each of the individual flow paths 64. In other words, the manifold 22 functions as a common flow path for ink. The manifold 22 is formed by through-holes that penetrate the first flow path plate 48 to the fourth flow path plate 51 in the stacking direction and recesses that are recessed from the lower surface of the fifth flow path plate 52, which are overlapped in the stacking direction.

[0022] The nozzle plate 46 is disposed below a spacer plate 47. The spacer plate 47 is formed of, for example, stainless steel. The spacer plate 47 has a recess 45 formed by, for example, half-etching, recessing the surface on the nozzle plate 46 side in the thickness direction of the spacer plate 47, thereby forming a thin portion constituting the damper portion 47a and a damper space 47b. With this configuration, the damper space 47b is formed as a buffer space between the manifold 22 and the nozzle plate 46.

[0023] A supply port 22a communicates with the manifold 22. The supply port 22a is formed, for example, in a cylindrical shape and is provided at one end in the arrangement direction.

[0024] The multiple individual flow paths 64 are each connected to the manifold 22. The upstream ends of the individual flow paths 64 are connected to the manifold 22, and the downstream ends are connected to the base ends of the nozzles 21. The individual flow paths 64 are composed of a first communication hole 25, a supply throttle path 26 which is an individual throttle path, a second communication hole 27, a pressure chamber 28, and a descender 29, and these components are arranged in this order, and the pressure chamber 28 is connected to the nozzles 21.

[0025] The first communication hole 25 has a lower end connected to the upper end of the manifold 22, extends upward in the stacking direction from the manifold 22, and penetrates an upper portion of the fifth flow path plate 52 in the stacking direction.

[0026] The upstream end of supply throttle path 26 is connected to the upper end of first communication hole 25. Supply throttle path 26 is formed by half etching, for example, and is configured as a groove recessed from the lower surface of sixth flow path plate 53. Furthermore, second communication hole 27 has its upstream end connected to the downstream end of supply throttle path 26, extends upward in the stacking direction from supply throttle path 26, and is formed to penetrate sixth flow path plate 53 in the stacking direction.

[0027] The upstream end of the pressure chamber 28 is connected to the downstream end of the second communication hole 27. The pressure chamber 28 is formed to penetrate the seventh flow path plate 54 in the stacking direction.

[0028] The descender 29 is formed to penetrate the spacer plate 47, the first flow path plate 48, the second flow path plate 49, the third flow path plate 50, the fourth flow path plate 51, the fifth flow path plate 52, and the sixth flow path plate 53 in the stacking direction, and is disposed on the left side of the manifold 22 in the width direction. The descender 29 has an upstream end connected to the downstream end of the pressure chamber 28, and a downstream end connected to the base end of the nozzle 21. The nozzle 21 overlaps the descender 29 in the stacking direction, for example, and is disposed in the center of the descender 29 in the width direction perpendicular to the stacking direction.

[0029] The vibration plate 55 is laminated on the seventh flow path plate 54 and covers the upper openings of the pressure chambers 28.

[0030] The actuator 60 includes a common electrode 61, a piezoelectric layer 62, and an individual electrode 63, which are arranged in this order. The common electrode 61 covers the entire surface of the vibration plate 55 via an insulating film 56. The piezoelectric layer 62 covers the entire surface of the common electrode 61. The individual electrode 63 is provided for each pressure chamber 28 and is arranged on the piezoelectric layer 62. One individual electrode 63, the common electrode 61, and the portion of the piezoelectric layer 62 sandwiched between the two electrodes constitute one actuator 60.

[0031] The individual electrodes 63 are electrically connected to a driver IC. This driver IC receives a control signal from a control device 71 (described later) to generate a drive signal and apply it to the individual electrodes 63. In contrast, the common electrode 61 is always maintained at ground potential. In this configuration, the active portion of the piezoelectric layer 62 expands and contracts in the planar direction together with the two electrodes 61, 63 in response to the drive signal. In response, the vibration plate 55 deforms in cooperation with the drive signal, and the volume of the pressure chamber 28 changes in a direction that increases or decreases. As a result, an ejection pressure that ejects ink droplets from the nozzle 21 is applied to the pressure chamber 28.

[0032] In the ejection head 20, the supply port 22a is connected to the sub-tank 18 via a pipe. When a pressure pump provided in the pipe is driven, ink passes from the sub-tank 18 through the pipe and flows into the manifold 22 via the supply port 22a. The ink then flows from the manifold 22 into the supply throttle passage 26 via the first communication hole 25, and from the supply throttle passage 26 into the pressure chamber 28 via the second communication hole 27. The ink then flows through the descender 29 and into the nozzle 21. When an ejection pressure is applied to the pressure chamber 28 by the actuator 60, an ink droplet is ejected from the nozzle hole 21a.

[0033] Next, the above-mentioned components and other components of the droplet ejection device 10 of this embodiment will be described with reference to a block diagram.

[0034] 4, the droplet ejection device 10 includes a control device 71 that is composed of a CPU and corresponds to a computer, RAM 72, ROM 73, a head driver IC 74, a sensor 75, a waveform generation circuit 76, a voltage source 80, a detection unit 82, motor driver ICs 30 and 32, a transport motor 31, and a carriage motor 33. The control device 71 corresponds to the interlaced printing instruction means, the discrimination means, the first print processing means, and the second print processing means.

[0035] The control device 71 causes the ejection head 20 to perform pass printing at least twice, in which ink droplets are ejected from the nozzles 21 while moving the carriage 16 in the movement direction Ds. This makes it possible to perform interlaced printing, which forms a partial image with a higher resolution than the above-mentioned pitch Pt on the print medium W. In this embodiment, the ejection head 20 performs pass printing three times, as will be described later.

[0036] The control device 71 also determines whether the state in which ink droplets are ejected from the nozzles 21 of the nozzle row NL is a first case, or a second case in which a smaller amount of droplets are ejected even when attempting to eject the same amount of droplets as in the first case. The first case is when the nozzles 21 are ejecting ink droplets normally, and the second case is when the nozzles 21 are not ejecting ink droplets normally. The method for determining whether the nozzles 21 are normal will be described later.

[0037] Furthermore, in the first case, the control device 71 executes a first printing process. The first printing process is a process in which, after performing a preceding pass printing in interlaced printing, the transport roller 15 transports the print medium W a first distance, which is a predetermined number of pitches Pt, and then performs a subsequent pass printing. On the other hand, in the second case, the control device 71 executes a second printing process. The second printing process is a process in which, after performing a preceding pass printing in interlaced printing, the transport roller 15 transports the print medium W a second distance, which is greater than the first distance, and then performs a subsequent pass printing. The first printing process and second printing process will be described in detail later.

[0038] The sensor 75 is a jam sensor that detects the occurrence of a jam (paper jam) of the print medium W. The control device 71 receives the detection result from the sensor 75.

[0039] The waveform generating circuit 76 generates a drive waveform including a drive signal that drives the actuator 60. The drive signals include an ejection drive signal that applies pressure to the ink in the pressure chamber 28 so as to eject ink droplets from the nozzle 21, a non-ejection drive signal that applies pressure to the ink in the pressure chamber 28 so as to vibrate or agitate the meniscus in the nozzle 21 and the ink in the pressure chamber 28, etc., without ejecting ink droplets from the nozzle 21, and a non-vibration signal that does not vibrate the meniscus of the nozzle 21.

[0040] The RAM 72 stores print jobs (image data) and ejection data received from an external personal computer, etc. The ROM 73 stores a droplet ejection program used in the droplet ejection device 10 of this embodiment, a control program for performing various data processing, etc.

[0041] The voltage source 80 applies a high voltage to an electrode 81 (FIG. 10) described below when detecting an abnormality in the nozzle 21. The detection unit 82 detects a voltage change caused by ink droplets that have landed on the electrode 81 when detecting an abnormality in the nozzle 21. The configuration for detecting an abnormality in the nozzle 21 will be described in detail later.

[0042] The head driver IC 74 receives instructions from the control device 71 to cause the ejection head 20 to eject ink droplets. The motor driver IC 30 receives instructions from the control device 71 to control the drive of the transport motor 31. The transport motor 31 operates the transport roller 15 to transport the print medium W in the transport direction Df. Furthermore, the motor driver IC 32 receives instructions from the control device 71 to control the drive of the carriage motor 33. The carriage motor 33 operates the carriage 16 to move the ejection head 20 in the movement direction Ds.

[0043] FIG. 5 is a plan view showing a detailed configuration of the ejection head 20. FIG. 6 is a diagram for explaining a partial image PR formed by the ejection head 20. FIG. 7 is a diagram for explaining pass printing by the ejection head 20 of FIG. 5. Note that "CL" in FIG. 7 indicates a nozzle 21 in any of the nozzle arrays NLm, NLc, and NLy described below. As shown in FIG. 5, the ejection head 20 of this embodiment has, for example, 12 nozzle arrays NL. The 12 nozzle arrays NL include two nozzle arrays NLm that eject magenta ink, two nozzle arrays NLc that eject cyan ink, two nozzle arrays NLy that eject yellow ink, and six nozzle arrays NLk that eject black ink.

[0044] Two nozzle arrays NLm, two nozzle arrays NLc, two nozzle arrays NLy, and six nozzle arrays NLk are arranged in this order from the first movement direction Ds1 to the second movement direction Ds2. The arrangement order of the nozzle arrays NL is not limited to this. The printing resolution achieved by ink ejection from the nozzle array NLk is, for example, 300 dpi, and the printing resolution achieved by ink ejection from each of the nozzle arrays NLm, NLc, and NLy is, for example, 100 dpi. Therefore, when performing color printing at 600 x 300 dpi, for example, one pass printing by the nozzle array NLk is performed, while three passes by each of the nozzle arrays NLm, NLc, and NLy are required. Thus, when forming each partial image that constitutes a full image in color printing, the ejection head 20 has a high-density nozzle array NL2 (nozzle array NLk) that performs one pass printing, and three low-density nozzle arrays NL1 (nozzle arrays NLm, NLc, NLy) that perform three passes printing and have fewer nozzles 21 than the high-density nozzle array NL2.

[0045] The ejection head 20 can perform unidirectional printing or bidirectional printing when forming the partial images. For example, when performing bidirectional printing, the control device 71 causes the ejection head 20 to eject ink droplets while moving the ejection head 20 in both a first movement direction Ds1 and a second movement direction Ds2 using the carriage 16. In this case, as shown in FIG. 6, during the first scan of the carriage 16, the control device 71 causes the ejection head 20 to eject ink droplets while moving the ejection head 20, for example, in the second movement direction Ds2. As a result, a partial image PR1 during the first scan is formed out of the multiple partial images PR that make up the entire image. Note that during the second scan of the carriage 16, the control device 71 causes the ejection head 20 to eject ink droplets while moving the ejection head 20 in the first movement direction Ds1.

[0046] In this embodiment, as described above, when color printing is performed, one pass printing is performed by the nozzle array NLk, and three passes printing is performed by each of the nozzle arrays NLm, NLc, and NLy. In this case, as shown in FIG. 7, during the first scan (first pass) of the carriage 16, the nozzles 21 of the nozzle array NLk eject ink droplets once for each pixel Px. Meanwhile, during the first scan of the carriage 16, the nozzles 21 of any of the nozzle arrays NLm, NLc, and NLy eject ink droplets once for every three pixels Px. Then, during the second scan (second pass) and third scan (third pass) of the carriage 16, the print medium W is transported by one pixel in the transport direction Df. During the second and third scans of the carriage 16, no ink droplets are ejected from the nozzles 21 of the nozzle row NLk, while ink droplets are ejected from the nozzles 21 of one of the nozzle rows NLm, NLc, and NLy (the same nozzles 21 as in the first scan) once for every three pixels Px, as in the first scan.

[0047] After the partial image PR1 is formed by a total of three scans of the carriage 16 as described above, the control device 71 transports the print medium W a predetermined distance in the transport direction Df. The predetermined distance will be described later. Then, to form the next partial image PR2, the control device 71 causes the carriage 16 to eject ink droplets in the fourth scan (fourth pass) to sixth scan (sixth pass) in the same manner as the ink droplets ejected in the first scan to third scan described above. By repeating the above process, multiple partial images PR are formed, thereby forming the entire image.

[0048] Here, the first printing process and the second printing process by the control device 71 will be described with reference to the drawings. Fig. 8 is a diagram for explaining the first printing process by the control device 71, and Fig. 9 is a diagram for explaining the second printing process by the control device 71.

[0049] As described above, the control device 71 executes the first printing process in the first case. That is, the control device 71 executes the first printing process when ink droplets are normally ejected from the nozzles 21. The first printing process will be described in detail below.

[0050] The nozzles 21 in the nozzle row NLk and each nozzle 21 in the nozzle rows NLm, NLc, and NLy are assigned a common nozzle number that is assigned along the transport direction Df in Figures 8 and 9. These nozzle numbers range from "000" to "209" from one end to the other in the transport direction Df. In other words, there are 210 nozzles 21 in the nozzle row NLk and each nozzle 21 in the nozzle rows NLm, NLc, and NLy arranged along the transport direction Df. Note that the number of nozzles 21 is an example and can be set as desired.

[0051] In Figure 8, the nozzles 21 of the nozzle row NLk and the nozzles 21 of any one of the nozzle rows NLm, NLc, and NLy (hereinafter sometimes collectively referred to as color nozzle rows) that are used to eject ink droplets in the first scan (first pass) are indicated by black circles and are assigned nozzle numbers. That is, in Figure 8, a nozzle number with a black circle means that both the nozzles 21 of the nozzle row NLk and the nozzles 21 of the color nozzle rows are used in the first scan. Also, a nozzle number with a gray circle means that only the nozzles 21 of the nozzle row NLk are used in the first scan.

[0052] As described in Figure 7, in the second scan (second pass) and third scan (third pass), no ink droplets are ejected by the nozzles 21 of the nozzle row NLk. Therefore, in the second and third scans, the nozzle numbers marked with open circles indicate that neither the nozzles 21 of the nozzle row NLk nor the nozzles 21 of the color nozzle row are used. On the other hand, the black circles in the second and third scans indicate that only the nozzles 21 of the color nozzle row are used. From Figure 8, it can be seen that the nozzles 21 of the color nozzle row indicated by black circles move relative to the print medium W by a distance d1 for each scan.

[0053] Based on the above, as shown in Figure 8, in the first printing process, after the first pass of interlaced printing is performed, the transport roller 15 transports the print medium W by one pitch Pt, which is the first distance d1, before the second pass of printing is performed. Also, after the second pass of printing is performed, the transport roller 15 transports the print medium W by one pitch Pt, which is the first distance d1, before the third pass of printing is performed. In this way, a partial image PR1 is formed in the first printing process. Note that the first distance d1 is not limited to the above distance.

[0054] Next, when the control device 71 performs the fourth scan (fourth pass) of the carriage 16 to form the next partial image PR2, it causes the conveyance roller 15 to convey the print medium W a predetermined third distance d3. In FIG. 8, the third distance d3 is set to 208 pitches Pt as an example. Note that the third distance d3 is not limited to the above distance.

[0055] Thereafter, the control device 71 causes the ejection head 20 to perform pass printing for the fourth scan in the same manner as the pass printing for the first scan, to perform pass printing for the fifth scan (fifth pass) in the same manner as the pass printing for the second scan, and to perform pass printing for the sixth scan (sixth pass) in the same manner as the pass printing for the third scan. This forms a partial image PR2 in the first printing process. In the first printing process, the above-described process is repeated every three scans to form a full image.

[0056] On the other hand, the control device 71 executes the second printing process in the second case. That is, the control device 71 executes the second printing process when the ejection of ink droplets from the nozzles 21 is not normal. The second printing process will be described in detail below.

[0057] In FIG. 9, the nozzle numbers marked with black circles (the nozzle numbers marked with black circles for the first scan and the nozzle numbers marked with black circles for the second and third scans), the nozzle numbers marked with gray circles, and the nozzle numbers marked with white circles are the same as those in FIG. 8. Furthermore, the nozzle numbers marked with dotted circles in FIG. 9 are the same as the white circles in FIG. 8 in the sense that neither the nozzles 21 in the nozzle row NLk nor the nozzles 21 in the color nozzle row are used. However, the nozzle numbers marked with dotted circles in FIG. 9 refer to nozzles 21 that are inevitably unused when forming an image with the desired resolution because the transport amount of the print medium W at the end of each pass printing when forming one partial image PR (excluding the transport amount at the end of the final pass (e.g., the third pass) for forming the partial image PR) is greater than in the first printing process. In the second printing process, the nozzles 21 include nozzles 21 used in interlaced printing and nozzles 21 not used in the interlaced printing.

[0058] Based on the above assumptions, as shown in FIG. 9, in the second printing process, after the first pass printing of the interlaced printing scan is performed, the transport roller 15 transports the print medium W a second distance d2 before the second pass printing of the interlaced printing scan is performed. The second distance d2 is a distance equivalent to four pitches Pt. In other words, the second distance d2 in the second printing process is greater than the first distance d1 in the first printing process. Furthermore, after the second pass printing of the interlaced printing scan is performed, the transport roller 15 transports the print medium W a second distance d2, which is four pitches Pt, before the third pass printing of the interlaced printing scan is performed. In this way, a partial image PR1 in the second printing process is formed. Note that the second distance d2 is not limited to the above distance.

[0059] Next, when the control device 71 performs the fourth scan (fourth pass) of the carriage 16 to form the next partial image PR2, it causes the transport roller 15 to transport the print medium W a predetermined fourth distance d4. In FIG. 9, the fourth distance d4 is set to 196 pitches Pt as an example. In other words, the fourth distance d4 in the second printing process is shorter than the third distance d3 in the first printing process. Note that the fourth distance d4 is not limited to the above distance.

[0060] Thereafter, the control device 71 causes the ejection head 20 to perform pass printing for the fourth scan in the same manner as the pass printing for the first scan, to perform pass printing for the fifth scan (fifth pass) in the same manner as the pass printing for the second scan, and to perform pass printing for the sixth scan (sixth pass) in the same manner as the pass printing for the third scan. This forms a partial image PR2 in the second printing process. In the second printing process, the above-described process is repeated every three scans to form a full image.

[0061] Comparing Fig. 8, which shows the first printing process performed in the first case, with Fig. 9, which shows the second printing process performed in the second case, it can be seen that the number of nozzles 21 not used in interlaced printing (nozzles with nozzle numbers circled in dotted lines) is smaller in the first case than in the second case. In other words, the number of nozzles 21 used in interlaced printing is relatively greater in the first case.

[0062] Here, even in the second case, if the control device 71 determines from the image data (image data of the partial image PR) that the nozzles 21 in the second case will not eject ink droplets, the control device 71 executes the first printing process in interlaced printing. The nozzles 21 include the nozzles 21 in the first case (i.e., normal nozzles 21) and the nozzles 21 in the second case (i.e., abnormal nozzles 21). Specifically, in FIG. 9, for example, if the nozzle 21 assigned nozzle number 200 is the nozzle 21 in the second case, the control device 71 executes the first printing process if it is determined from the image data that the nozzle 21 with nozzle number 200 will not eject ink droplets. That is, the control device 71 makes the transport amount of the print medium W relatively small at the end of pass printing when forming one partial image PR, and makes the transport amount of the print medium W relatively large after forming one partial image PR.

[0063] Furthermore, even in the second case, if the ink droplets ejected from the nozzles 21 in the second case are a first color as a predetermined color, the control device 71 executes the first printing process in interlaced printing. In this embodiment, the first color is yellow, which does not change significantly in color difference with respect to the white stripe. Therefore, in the ejection head 20, the nozzle row NLy corresponds to the nozzle row that ejects ink droplets of the first color, and any one of the nozzle rows NLm, NLc, and NLk corresponds to the nozzle row that ejects ink droplets of the second color. Specifically, in FIG. 9, for example, if the nozzle 21 assigned nozzle number 200 is the nozzle 21 in the second case and the ink droplets ejected from that nozzle 21 are yellow ink droplets, the control device 71 executes the first printing process.

[0064] Furthermore, the control device 71 executes the second printing process in interlaced printing when the sensor 75 detects a jam in the print medium W. In this case, the print medium W is likely to come into contact with the nozzle surface 40a of the ejection head 20 due to a jam in the print medium W, which makes it more likely that the nozzles 21 will not eject. For this reason, the control device 71 executes the second printing process when a jam is detected. In other words, the control device 71 increases the transport amount of the print medium W at the end of each pass printing when forming one partial image PR, and decreases the transport amount of the print medium W after forming one partial image PR.

[0065] Next, a description will be given of a configuration for detecting abnormalities in the nozzles 21 of the ejection head 20. FIG.

[0066] As shown in FIG. 10 , an electrode 81 is provided below the ejection head 20. The electrode 81 is a conductive substrate, such as a metal plate. When ink droplets are ejected from the ejection head 20, a voltage source 80 applies a high voltage to the electrode 81. In this state, when a charged ink droplet ejected from the ejection head 20 lands on the electrode 81, the voltage at the electrode 81 changes. A detection unit 82 detects the changed voltage. In this case, the amount of charge possessed by the ink droplet is proportional to the volume of the ink droplet, so the degree of change in the voltage is based on the volume of the ink droplet. Thus, by detecting the change in voltage using the detection unit 82, the control device 71 can determine that the second case has occurred, in which a smaller amount of ink droplets are ejected even when the nozzle 21 attempts to eject the same amount of ink droplets as in the first case. Note that the configuration for detecting an abnormality in the nozzle 21 of the ejection head 20 is not limited to the above configuration, and various known configurations can be used.

[0067] Fig. 11 is a flowchart showing the control flow by the control device 71. As shown in Fig. 11, the control device 71 determines whether the printing to be performed is the first printing after the sensor 75 detects a jam in the print medium W (step S1). If the printing to be performed is the first printing after the jam is detected (YES in step S1), the control device 71 executes the second printing process as described above (step S6).

[0068] On the other hand, if the printing to be performed is not the first printing since the jam was detected (NO in step S1), the control device 71 determines whether the nozzles 21 are normal (step S2). If the nozzles 21 are normal (YES in step S2), the control device 71 executes the first printing process (step S3). On the other hand, if there is an abnormal nozzle 21 (NO in step S2), the control device 71 determines whether color information for the ink droplets ejected by the abnormal nozzle 21 exists in the image data (step S4).

[0069] If the image data does not contain color information for ink droplets ejected by the abnormal nozzle 21 (NO in step S4), the control device 71 executes the first printing process (step S3). On the other hand, if the image data contains color information for ink droplets ejected by the abnormal nozzle 21 (YES in step S4), the control device 71 determines whether the color information is yellow (step S5).

[0070] If the color information is yellow (YES in step S5), the control device 71 executes the first printing process (step S3). On the other hand, if the color information is not yellow (NO in step S5), the control device 71 executes the second printing process (step S6).

[0071] As described above, according to this embodiment, in the second case, in which a smaller amount of ink droplets are ejected even when attempting to eject the same amount of ink droplets as in the first case, the print medium W is transported in the transport direction Df between the current pass and the next pass by a second distance d2 greater than the first distance d1. This prevents two raster lines formed by the same nozzle 21 (i.e., a raster line formed in a preceding pass and a raster line formed in a following pass) from being adjacent to each other in the transport direction Df. This prevents a white streak in the preceding pass and a white streak in the following pass, which would otherwise appear due to an ejection defect of the nozzle 21, from being adjacent to each other in the transport direction Df in the second case. This makes the white streak less visible, thereby suppressing degradation of image quality. On the other hand, in the first case, in which the nozzle 21 is normal, the print medium W is transported in the transport direction Df by a first distance d1 smaller than the second distance d2 between the preceding pass and the following pass. This allows a relatively large number of nozzles 21 to be used to form the partial image PR, thereby increasing the printing speed.

[0072] Furthermore, in this embodiment, in the first printing process, the transport roller 15 transports the print medium W a third distance d3, and in the second printing process, the transport roller 15 transports the print medium W a fourth distance d4, which is smaller than the third distance d3. As a result, in the first printing process when there is no abnormality in the nozzle 21, the number of passes can be reduced, thereby increasing the printing speed. On the other hand, in the second printing process when there is an abnormality in the nozzle 21, the number of passes increases, which can slow the printing speed depending on the image data, but the increased number of passes can suppress deterioration in image quality.

[0073] Furthermore, in this embodiment, the number of nozzles 21 that are not used in interlaced printing is smaller in the first case than in the second case. In other words, the number of nozzles 21 that are used in interlaced printing is relatively greater in the first case. As a result, the number of pass printing passes is relatively small in the first printing process executed in the first case, and therefore the printing speed is faster.

[0074] Furthermore, in this embodiment, even in the second case, if the control device 71 determines from the image data of the partial image PR that ink droplets will not be ejected from the nozzles 21 in the second case, the control device 71 executes the first printing process in interlaced printing. In this case, there is no need to intentionally reduce the number of nozzles 21 used, and so the printing speed can be increased by using more nozzles 21.

[0075] Furthermore, in this embodiment, even in the second case, if the ink droplets ejected from the nozzles 21 in the second case are yellow, the control device 71 executes the first printing process in interlaced printing. In this case, the color difference between the yellow color and the white stripes is not significantly different, so even if yellow stripes occur, they are not very noticeable. Therefore, by executing the first printing process, the printing speed can be increased.

[0076] Furthermore, in this embodiment, the ejection head 20 has a high-density nozzle row NL2 (nozzle row NLk) that performs one pass printing, and three low-density nozzle row NL1 (nozzle rows NLm, NLc, NLy) that perform three pass printing and have fewer nozzles 21 than the high-density nozzle row NL2. The ejection head 20 configured in this way can suppress deterioration in image quality when forming each partial image PR that makes up the entire image in color printing.

[0077] Furthermore, in this embodiment, the control device 71 executes the second printing process in interlaced printing when the sensor 75 detects a jam in the print medium W. In this case, as described above, the nozzles 21 are prone to ejection failure. For this reason, the control device 71 executes the second printing process when a jam is detected. This makes it possible to prevent a decrease in image quality.

[0078] (Variation) The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, the following modifications are possible.

[0079] In the above embodiment, an ejection head 20 having a high-density nozzle row NL2 and three low-density nozzle rows NL1 was described, but from the perspective of making white streaks less noticeable and suppressing deterioration in image quality, an ejection head having a single-density nozzle row can also be adopted.

[0080] Furthermore, in the above embodiment, the number of abnormal nozzles that serves as the criterion when executing the second printing process may be at least one.

[0081] Furthermore, in the above embodiment, a jam of the print medium W is detected by the sensor 75, but the jam detection method is not limited to this. For example, the transport time between the timing when the leading end of the print medium W arrives and the timing when the trailing end passes may be measured. In this case, if the transport time is less than a predetermined time, the control device 71 determines that the print medium W is being transported smoothly through the transport path and that a jam has not occurred. On the other hand, if the transport time reaches the predetermined time, the control device 71 determines that the print medium W is not being transported and that a jam has occurred.

[0082] Furthermore, in the above embodiment, an abnormality in the nozzle 21 is determined by detecting a change in voltage at the electrode 81 using the detection unit 82, but the method for determining an abnormality in the nozzle 21 is not limited to this. For example, the following method may be adopted. A pressure wave is applied to the ink droplet by driving the actuator 60. This pressure wave remains in the ink droplet inside the pressure chamber 28 as residual vibration even after the ink droplet is ejected from the nozzle 21. Therefore, the residual vibration deforms the stationary actuator 60, causing a current to be generated from the actuator 60. Because the current generated by the residual vibration depends on the volume of the ink droplet, an abnormality in the nozzle 21 may be determined by detecting the current generated from the actuator 60.

[0083] Furthermore, the following method can be given as another example of a method for determining whether a nozzle 21 is malfunctioning. The actuator 60 receives heat from the ink droplets via the diaphragm 55. The capacitance of the actuator 60 changes depending on the heat of the ink droplets. In other words, the capacitance of the actuator 60 depends on the temperature of the ink droplets. Furthermore, since the temperature of the ink droplets depends on the volume of the ink droplets, a malfunction of the nozzle 21 may be determined by detecting the capacitance of the actuator 60.

[0084] Furthermore, in the above embodiment, a mode in which one ejection dot 20 is mounted on the carriage 16 has been described, but this is not limiting. Two or more ejection dots 20 may be mounted on the carriage 16, and when an ejection head that ejects ultraviolet-curable ink is used, a light source unit may also be mounted on the carriage 16. [Explanation of symbols]

[0085] 10 Droplet discharge device 15 Conveyor roller 16 Carriage 20 Discharge head 21 nozzles 28 Pressure Chamber 31 Transport motor 71 Control device 75 sensors Df Conveying direction Ds moving direction d1 First distance d2 2nd distance d3 Third distance d4 Fourth distance NL1 Low density nozzle row NL2 high density nozzle array NL,NLm,NLc,NLy,NLk nozzle rows PR, PR1, PR2 partial images W Printing medium

Claims

1. an ejection head having a nozzle row in which a plurality of nozzles that eject droplets onto a print medium are arranged at a predetermined pitch; a carriage on which the ejection head is mounted and which moves back and forth in a movement direction; a transport unit that transports the print medium in a transport direction that intersects with the movement direction; a control device; The control device performing interlaced printing by performing pass printing at least twice, in which droplets are ejected from the nozzles while moving the carriage in the movement direction, to form a partial image on the print medium with a resolution higher than the pitch; determining whether the state in which droplets are ejected from the nozzles of the nozzle row is a first case or a second case in which a smaller amount of droplets are ejected even when attempting to eject the same amount of droplets as in the first case; In the first case, in the interlaced printing, after a preceding pass printing is performed, the conveying unit conveys the print medium by a first distance, which is a predetermined number of the pitch, and then a first printing process is executed to perform a subsequent pass printing; In the second case, in the interlaced printing, after performing the preceding pass printing, the droplet ejection device causes the transport unit to transport the printing medium a second distance greater than the first distance, and then executes a second printing process to perform the subsequent pass printing.

2. The control device In the first case, when forming a next partial image after forming the partial image, the conveying unit conveys the print medium by a predetermined third distance; The droplet ejection device according to claim 1, wherein in the second case, when forming the next partial image after forming the partial image, the transport unit transports the printing medium a fourth distance that is smaller than the third distance.

3. the nozzles include nozzles used in the interlaced printing and nozzles not used in the interlaced printing; The droplet ejection device according to claim 2 , wherein the number of the nozzles not used in the interlaced printing is smaller in the first case than in the second case.

4. The nozzles include a nozzle in the first case and a nozzle in the second case, A droplet ejection device as described in any one of claims 1 to 3, wherein the control device executes the first printing process in the interlaced printing when it determines from the image data of the partial image that the droplets will not be ejected from the nozzles in the second case, even in the second case.

5. the nozzles include a nozzle in the first case and a nozzle in the second case, the ejection head has a plurality of the nozzle rows, and the plurality of nozzle rows include a nozzle row in which a plurality of nozzles that eject droplets of a first color are arranged, and a nozzle row in which a plurality of nozzles that eject droplets of a second color different from the first color are arranged, The droplet ejection device according to any one of claims 1 to 4, wherein the control device executes the first printing process in the interlaced printing even in the second case when the droplets ejected from the nozzles in the second case are the first color.

6. 6. The droplet ejection device according to claim 1, wherein the ejection head has a high-density nozzle row that performs the pass printing once when forming the partial image, and a low-density nozzle row that performs the pass printing at least twice and has a smaller number of nozzles than the high-density nozzle row.

7. a sensor for detecting a jam of the print medium; The droplet ejection device according to claim 1 , wherein the control device executes the second printing process in the interlaced printing when the jam is detected by the sensor.

8. A droplet ejection device comprising: an ejection head having a nozzle row in which a plurality of nozzles that eject droplets onto a print medium are arranged at a predetermined pitch; a carriage on which the ejection head is mounted and that moves back and forth in a movement direction; and a transport unit that transports the print medium in a transport direction that intersects with the movement direction, performing interlaced printing by performing pass printing at least twice, in which droplets are ejected from the nozzles while moving the carriage in the movement direction, to form a partial image on the print medium with a resolution higher than the pitch; determining whether the state in which droplets are ejected from the nozzles of the nozzle row is a first case or a second case in which a smaller amount of droplets are ejected even when attempting to eject the same amount of droplets as in the first case; In the first case, in the interlaced printing, after a preceding pass printing is performed, the conveying unit conveys the print medium by a first distance, which is a predetermined number of the pitch, and then a first printing process is executed to perform a subsequent pass printing; In the second case, in the interlaced printing, after the preceding pass printing is performed, the transport unit transports the printing medium a second distance greater than the first distance, and then a second printing process is performed to perform the subsequent pass printing.

9. A droplet ejection program to be executed by a computer in a droplet ejection device including: an ejection head having a nozzle row in which a plurality of nozzles that eject droplets onto a print medium are arranged at a predetermined pitch; a carriage on which the ejection head is mounted and that moves back and forth in a movement direction; and a transport unit that transports the print medium in a transport direction that intersects with the movement direction, The computer an interlaced printing instruction means for performing pass printing at least twice, in which droplets are ejected from the nozzles while moving the carriage in the movement direction, to form a partial image on the print medium with a resolution higher than the pitch; a determining means for determining whether the state in which droplets are ejected from the nozzles of the nozzle row is a first case or a second case in which a smaller amount of droplets are ejected even when attempting to eject the same amount of droplets as in the first case; In the first case, a first print processing means for, in the interlaced printing, performing a preceding pass printing, then transporting the print medium by the transport unit by a first distance that is a predetermined number of the pitch, and then performing a subsequent pass printing; and In the second case, the droplet ejection program functions as a second printing processing means that, in the interlaced printing, after performing the preceding pass printing, causes the transport unit to transport the printing medium a second distance greater than the first distance, and then performs the subsequent pass printing.

Images