Droplet discharge device

Abstract

To provide a droplet discharge device that can suppress droplets from being deviatedly impacted.SOLUTION: A droplet discharge device comprises: a conveying part that conveys a medium to be printed in a conveying direction; a line head having a plurality of nozzles, arranged in the conveying direction and in a crossing direction crossing the conveying direction, which discharge droplets to the medium to be printed; and a control device. The control device makes speed at which an upstream-side nozzle positioned at an upstream-side in the conveying direction of a downstream-side nozzle discharges droplets higher or a timing at which the upstream-side nozzle discharges droplets earlier, than the downstream-side nozzle that is one nozzle of the plurality of nozzles discharges droplets.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to a droplet ejection device that is provided in a printing device such as an inkjet printer. [Background technology]

[0002] In inkjet printers, it is known that vortices are generated by the airflow caused by the ejection of ink droplets from the nozzles, and the ejected ink droplets are affected by the vortexes, causing deviations in their landing positions (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-177418 Summary of the Invention [Problem to be solved by the invention]

[0004] However, while the above-mentioned conventional technology reduces the impact deviation of ink droplets by suppressing vortexes when the ink droplets are ejected from the nozzles, it does not take into account the influence of the transport air currents that are generated when the print medium is transported, and therefore, it has been an issue to reduce the impact deviation of ink droplets by taking into account the influence of the transport air currents.

[0005] Therefore, an object of the present disclosure is to provide a droplet ejection device that can suppress deviation in the landing position of droplets. [Means for solving the problem]

[0006] The droplet ejection device disclosed herein comprises a transport section that transports a print medium in a transport direction, a line head having a plurality of nozzles arranged in the transport direction and an intersecting direction that intersects the transport direction and ejects droplets onto the print medium, and a control device, wherein the control device increases the droplet ejection speed by upstream nozzles, which are nozzles located upstream of the downstream nozzles in the transport direction, compared to downstream nozzles, which are some of the plurality of nozzles, or advances the droplet ejection timing.

[0007] According to the present disclosure, by increasing the droplet ejection speed of the upstream nozzles, which are relatively more susceptible to disturbances such as transport air currents that occur when transporting the printing medium than the downstream nozzles, it is possible to suppress deviation in the landing of droplets. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a droplet ejection device that can suppress deviation in the landing position of droplets. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view showing a droplet ejection device according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the configuration of the ejection head of FIG. [Figure 3] 2 is a block diagram showing an example of components of a printing device in which the droplet ejection device of FIG. 1 is provided. [Figure 4] FIG. 10 is a bottom view showing the configuration of the head bar. [Figure 5] FIG. 2 is a bottom view showing the arrangement of nozzles in the ejection head. [Figure 6] FIG. 10 is a diagram showing the relationship between each head bar and the voltage applied to the actuator corresponding to the nozzle in each head bar. [Figure 7] 5A and 5B are diagrams showing the relationship between each ejection head and the voltage applied to an actuator corresponding to a nozzle in each ejection head. [Figure 8]FIG. 10 is a diagram showing the relationship between each nozzle and the voltage applied to the actuator corresponding to each nozzle. [Figure 9] FIG. 10 is a diagram showing the change in applied voltage in the head bar to be used when there is an unused head bar. [Figure 10] FIG. 5 is an enlarged view of a portion of FIG. [Figure 11] FIG. 10 is a diagram showing voltages applied to actuators corresponding to nozzles in the overlap region and voltages applied to actuators corresponding to nozzles in the non-overlap region. [Figure 12] FIG. 10 is a diagram illustrating a crosswind caused by a transport airflow. [Figure 13] FIG. 4 is a diagram showing the voltages applied to each ejection head of the head bar. [Figure 14] FIG. 10 is a diagram showing the applied voltage to be increased for each nozzle to the actuator. [Figure 15] 10A and 10B are diagrams for explaining the generation of negative pressure and upstream airflow during a high gap. [Figure 16] FIG. 10(a) is a diagram showing that the distance between the platen and the nozzle surface is a high gap, and FIG. 10(b) is a diagram showing that the distance is a low gap. [Figure 17] FIG. 10 is a diagram showing voltages applied to the upstream and downstream ejection heads during printing at a high gap. [Figure 18] 10A is a diagram showing a drive waveform for an actuator corresponding to a downstream nozzle, and FIG. 10B is a diagram showing a drive waveform for an actuator corresponding to an upstream nozzle. DETAILED DESCRIPTION OF THE INVENTION

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

[0011] FIG. 1 is a plan view showing a droplet ejection device 100 according to one embodiment. The droplet ejection device 100 in this embodiment is a line head type. In FIG. 1, directions that are perpendicular to each other are referred to as a first direction Df and a second direction Ds. In this embodiment, the first direction Df corresponds to the transport direction of the print medium W, and the second direction Ds corresponds to the intersecting direction that is perpendicular to the transport direction. Hereinafter, Df will be referred to as the transport direction, and Ds will be referred to as the intersecting direction.

[0012] As shown in FIG. 1, the droplet ejection device 100 includes a line head 70, a pair of transport rollers 60, a platen 61, a plurality of storage tanks 62, and a plurality of tubes 63.

[0013] The line head 70 has a plurality of head bars 71, for example five head bars 71. The head bars 71 are provided corresponding to the ink colors. The head bars 71 are arranged side by side at approximately equal intervals in the transport direction Df. The head bars 71 extend in the cross direction Ds. The head bars 71 are provided with a plurality of ejection heads 10 (FIG. 4), which will be described later.

[0014] The platen 61 supports from below the print medium W. For example, the platen 61 has a predetermined thickness and is made of a rectangular plate material with the transport direction Df as its longitudinal direction.

[0015] The pair of transport rollers 60 extend in the cross direction Ds. The dimension of the transport roller 60 in the cross direction Ds is larger than the dimension of the print medium W in the cross direction Ds. One of the pair of transport rollers 60 is connected to a transport motor 33 (FIG. 3) described below, and is arranged on one side (e.g., the front) of the platen 61 in the transport direction Df. The other of the pair of transport rollers 60 is arranged on the other side (e.g., the rear) of the platen 61 in the transport direction Df. When the transport motor 33 is driven, the transport roller 60 rotates, thereby transporting the print medium W on the platen 61 in the transport direction Df. In this embodiment, the print medium W is transported from the front to the rear.

[0016] Ink is stored in the storage tanks 62. A storage tank 62 is provided for each type of ink. For example, five storage tanks 62 are provided, each storing black, yellow, cyan, magenta, and white ink. A color image is printed by ejecting ink droplets of the four colors of black, yellow, cyan, and magenta onto the print medium W. A base is formed by ejecting white ink droplets onto the print medium W.

[0017] The tube 63 is provided corresponding to the storage tank 62. The tube 63 connects the storage tank 62 to the plurality of ejection heads 10 provided on the head bar 71.

[0018] Next, the detailed structure of the ejection head 10 will be described. Fig. 2 is a cross-sectional view of the ejection head 10. As the ejection head 10, for example, an inkjet head that ejects ultraviolet-curable ink droplets as the liquid droplets can be used. However, the ejection head 10 is not limited to the above.

[0019] As shown in FIG. 2, the ejection head 10 has a plurality of nozzles 121 that eject ink droplets using ink from a storage tank 62. The ejection head 10 has a laminated body of a flow path forming body and a volume changing unit. An ink flow path is formed inside the flow path forming body, and a plurality of nozzle holes 121a are opened in the nozzle surface NM, which is the lower surface of the flow path forming body. The volume changing unit is driven to change the volume of the ink flow path. At this time, a meniscus vibrates in the nozzle holes 121a, and ink is ejected.

[0020] The flow path forming body of the ejection head 10 is a laminate of a plurality of plates, and the volume changing section includes a vibration plate 155 and an actuator (piezoelectric element) 160. A common electrode 161, which will be described later, is connected to the top of the vibration plate 155.

[0021] The above-mentioned multiple plates are stacked in the following order from the bottom: nozzle plate 146, spacer plate 147, first flow path plate 148, second flow path plate 149, third flow path plate 150, fourth flow path plate 151, fifth flow path plate 152, sixth flow path plate 153, and seventh flow path plate 154.

[0022] 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 121, a plurality of individual flow paths 164, and a manifold 122 as ink flow paths.

[0023] The nozzles 121 are formed to penetrate the nozzle plate 146 in the stacking direction. In the nozzle surface NM of the nozzle plate 146, a plurality of nozzle holes 121a, which are the tips of the nozzles 121, are aligned in the transport direction Df to form a nozzle row.

[0024] The manifold 122 supplies ink to the pressure chambers 128 to which an ejection pressure is applied. The manifold 122 extends in the transport direction Df, and is connected to one end of each of the individual flow paths 164. That is, the manifold 122 functions as a common flow path for the ink. The manifold 122 is formed by through-holes that penetrate the first flow path plate 148 to the fourth flow path plate 151 in the stacking direction and recesses that are recessed from the lower surface of the fifth flow path plate 152, which are overlapped in the stacking direction.

[0025] The nozzle plate 146 is disposed below the spacer plate 147. The spacer plate 147 is formed of, for example, stainless steel. The spacer plate 147 has a recess 145 formed by, for example, half-etching, recessing the surface on the nozzle plate 146 side in the thickness direction of the spacer plate 147, thereby forming a thin portion constituting the damper portion 147a and a damper space 147b. As a result, the damper space 147b is formed as a buffer space between the manifold 122 and the nozzle plate 146.

[0026] A supply port 122a communicates with the manifold 122. The supply port 122a is formed, for example, in a cylindrical shape and is provided at one end in the transfer direction Df. The manifold 122 and the supply port 122a are connected by a flow path (not shown).

[0027] Each individual flow path 164 is connected to the manifold 122. The upstream end of each individual flow path 164 is connected to the manifold 122, and the downstream end is connected to the base end of the nozzle 121. Each individual flow path 164 is composed of a first communication hole 125, a supply throttle path 126 which is an individual throttle path, a second communication hole 127, a pressure chamber 128, and a descender 129, and these components are arranged in this order.

[0028] The first communication hole 125 has a lower end connected to the upper end of the manifold 122, extends upward in the stacking direction from the manifold 122, and penetrates through an upper portion of the fifth flow path plate 152 in the stacking direction.

[0029] The upstream end of supply throttle path 126 is connected to the upper end of first communication hole 125. Supply throttle path 126 is formed by half etching, for example, and is configured as a groove recessed from the lower surface of sixth flow path plate 153. Furthermore, second communication hole 127 has its upstream end connected to the downstream end of supply throttle path 126, extends upward in the stacking direction from supply throttle path 126, and is formed to penetrate sixth flow path plate 153 in the stacking direction.

[0030] The upstream end of the pressure chamber 128 is connected to the downstream end of the second communication hole 127. The pressure chamber 128 is formed to penetrate the seventh flow path plate 154 in the stacking direction.

[0031] The descender 129 is formed by penetrating the spacer plate 147, the first flow path plate 148, the second flow path plate 149, the third flow path plate 150, the fourth flow path plate 151, the fifth flow path plate 152, and the sixth flow path plate 153 in the stacking direction. The descender 129 has an upstream end connected to the downstream end of the pressure chamber 128 and a downstream end connected to the base end of the nozzle 121. The nozzle 121 overlaps the descender 129 in the stacking direction, for example, and is disposed at the center of the descender 129 in the width direction.

[0032] The vibration plate 155 is laminated on the seventh flow path plate 154 and covers the upper openings of the pressure chambers 128 .

[0033] The actuator 160 includes a common electrode 161, a piezoelectric layer 162, and an individual electrode 163, which are arranged in this order. The common electrode 161 covers the entire surface of the vibration plate 155. The piezoelectric layer 162 covers the entire surface of the common electrode 161. The individual electrode 163 is provided for each pressure chamber 128 and is arranged on the piezoelectric layer 162. One individual electrode 163, the common electrode 161, and the portion of the piezoelectric layer 162 sandwiched between the two electrodes constitute one actuator 160.

[0034] The individual electrodes 163 are electrically connected to a head driver IC. This head driver IC receives a control signal from the control device 20 (FIG. 3), generates a drive signal (voltage signal), and applies it to the individual electrodes 163. In contrast, the common electrode 161 is always maintained at ground potential. In this configuration, the active portion of the piezoelectric layer 162 expands and contracts in the planar direction together with the common electrode 161 and the individual electrodes 163 in response to the drive signal. In response, the vibration plate 155 deforms in cooperation with the drive signal, and changes in the direction of increasing or decreasing the volume of the pressure chamber 128. As a result, an ejection pressure is applied to the pressure chamber 128 to eject ink droplets from the nozzle 121.

[0035] In the ejection head 10, ink flows into the manifold 122 via the supply port 122a, then flows from the manifold 122 into the supply throttle passage 126 via the first communication hole 125, and then flows from the supply throttle passage 126 into the pressure chamber 128 via the second communication hole 127. The ink then flows through the descender 129 and into the nozzle 121. When an ejection pressure is applied to the pressure chamber 128 by the actuator 160, ink droplets are ejected from the nozzle hole 121a onto the print medium W.

[0036] FIG. 3 is a block diagram showing an example of components of the printing device 1 in which the droplet ejection device 100 of FIG. 1 is provided.

[0037] 3, the printing device 1 includes operation keys 4, a display unit 5, a controller unit 19, a reading device 26, a motor driver IC 30, a head driver IC 31, an irradiation device driver IC 32, a conveying motor 33, and an ultraviolet irradiation device 40. The conveying motor 33 and the conveying roller 60 correspond to a conveying unit.

[0038] The operation keys 4 accept operation inputs from the user. The display unit 5 is configured, for example, as a touch panel, and displays predetermined information. Part of the display unit 5 also functions as an operation key. The controller unit 19 realizes the printing function based on inputs from the operation keys 4 or external inputs via a communication interface (not shown), and also controls the display of the display unit 5.

[0039] The controller unit 19 has a control device 20 configured by a CPU, storage units (ROM 21, RAM 22, EEPROM 23, HDD 24), and an ASIC 25. The control device 20 is connected to the storage units and controls the driver ICs 30 to 32, the display unit 5, and the reading device 26.

[0040] The control device 20 performs various functions by executing predetermined processing programs stored in the ROM 21. The control device 20 may be implemented as a single processor in the controller unit 19, or may be implemented as multiple processors cooperating with each other. The processing programs are read by the reading device 26 from a computer-readable recording medium KB such as a magneto-optical disk or a USB flash memory, and stored in the ROM 21. The RAM 22 stores image data received from the outside and calculation results of the control device 20. The EEPROM 23 stores various initial setting information input by the user. The HDD 24 stores various information.

[0041] A motor driver IC 30, a head driver IC 31, and an irradiation device driver IC 32 are connected to the ASIC 25. When the control device 20 receives a print job from a user, it outputs a print command to the ASIC 25 based on a processing program. The ASIC 25 drives each of the driver ICs 30 to 32 based on the print command. The control device 20 moves the platen 61 in the transport direction Df by driving the transport motor 33 using the motor driver IC 30.

[0042] The control device 20 converts image data acquired from an external device or the like into ejection data for ejecting ink droplets onto the print medium W. The control device 20 causes the head driver IC 31 to eject ink droplets from the ejection head 10 based on the converted ejection data. The control device 20 also causes the irradiation device driver IC 32 to irradiate ultraviolet light from a light-emitting diode chip provided in the ultraviolet irradiation device 40. The ultraviolet irradiation device 40 is disposed between one head bar 71 and another head bar 71 in the transport direction Df.

[0043] Fig. 4 is a bottom view showing the configuration of the head bar 71. Fig. 5 is a bottom view showing the arrangement of the nozzles 121 in the ejection head 10.

[0044] As shown in FIG. 4, the head bar 71 is provided with ten ejection heads 10 as an example of the multiple ejection heads 10. Of the ten ejection heads 10, five are arranged upstream in the transport direction Df, and the remaining five are arranged downstream in the transport direction Df. The five ejection heads 10 arranged upstream in the transport direction Df are referred to as upstream-side ejection heads HU. The upstream-side ejection heads HU include ejection heads 111, 113, 115, 117, and 119. Meanwhile, the five ejection heads 10 arranged downstream in the transport direction Df are referred to as downstream-side ejection heads HD. The downstream-side ejection heads HD include ejection heads 112, 114, 116, 118, and 120. The upstream-side ejection heads HU are arranged at approximately equal intervals. The downstream-side ejection heads HD are arranged at approximately equal intervals and are shifted a predetermined distance in the intersecting direction Ds from the upstream-side ejection heads HU. That is, the multiple discharge heads 10 in the head bar 71 are arranged in a staggered pattern in the intersecting direction Ds. However, if the multiple discharge heads 10 are arranged in three or more rows in the transport direction Df, it is sufficient that the downstream discharge head HD is one of the multiple discharge heads 10, and the upstream discharge head HU is a discharge head 10 located upstream of the downstream discharge head HD in the transport direction Df.

[0045] 5, the ejection head 10 is provided with a plurality of nozzles 121. The nozzles 121 are regularly arranged in the ejection head 10. Specifically, the nozzles 121 are arranged at approximately equal intervals in both the transport direction Df and the intersecting direction Ds. The nozzles 121 arranged upstream in the transport direction Df are referred to as upstream nozzles NU, and the nozzles 121 arranged downstream in the transport direction Df are referred to as downstream nozzles ND.

[0046] However, the division between the upstream nozzles NU and the downstream nozzles ND is not limited to the example in Figure 5. It is sufficient that the downstream nozzles ND are some of the multiple nozzles 121, and the upstream nozzles NU are nozzles 121 located upstream of the downstream nozzles ND in the transport direction Df. Furthermore, of the multiple nozzles 121, the nozzles 121 located on both sides in the cross direction Ds are referred to as end nozzles NE. The end nozzles NE may include multiple nozzles 121 located at the extreme end in the cross direction Ds and forming a row, or multiple nozzles 121 located at the extreme end in the cross direction Ds and forming one or more rows inside the extreme end in the cross direction Ds. Note that the nozzles 121 arranged between the upstream nozzles NU and the downstream nozzles ND are not shown in Figure 5.

[0047] 6 is a diagram showing the relationship between each head bar 71 and the applied voltage (drive voltage) to the actuator 160 corresponding to the nozzle 121 in each head bar 71. In FIG. 6, the first head bar is the upstream head bar BU, which is the head bar 71 located upstream in the transport direction Df, and the fifth head bar is the downstream head bar BD, which is the head bar 71 located downstream in the transport direction Df. However, it is sufficient that the downstream head bar BD is one head bar 71 out of the multiple head bars 71, and the upstream head bar BU is the head bar 71 located upstream of the downstream head bar BD in the transport direction Df.

[0048] In this embodiment, the control device 20 increases the ink droplet ejection speed of the upstream nozzles NU, which are located upstream of the downstream nozzles ND in the transport direction Df. Specifically, the control device 20 increases the ink droplet ejection speed by increasing the voltage applied to the actuator 160 of the upstream nozzles NU more than the voltage applied to the actuator 160 of the downstream nozzles ND. The amount by which the applied voltage should be increased is set in advance depending on the transport speed of the print medium W, etc. In this embodiment, increasing the applied voltage will be described below for each head bar, each ejection head, and each nozzle.

[0049] When the magnitude of the voltage applied to the actuator 160 is viewed broadly for each head bar 71, it takes the form shown in Figure 6. As shown in Figure 6, when viewed on a head bar basis, the voltage applied to the actuator 160 in each head bar 71 is increased from the downstream side to the upstream side by the control device 20. In other words, the voltage applied to the ejection head 10 of the upstream head bar BU is increased by the control device 20 more than the voltage applied to the ejection head 10 of the downstream head bar BD. This makes the ejection speed of ink droplets by the ejection head 10 of the upstream head bar BU higher than the ejection speed of the ejection head 10 of the downstream head bar BD. This takes into account the fact that the upstream head bar BU is more susceptible to the influence of the transport airflow than the downstream head bar BD.

[0050] Furthermore, when two adjacent head bars 71 are viewed, the voltage applied to the actuator 160 corresponding to the most upstream nozzle 121 in the upstream head bar 71 is made higher by the control device 20 than the voltage applied to the actuator 160 corresponding to the most upstream nozzle 121 in the downstream head bar 71. This is because the most upstream nozzle 121 in the upstream head bar 71 is relatively more susceptible to the influence of the carrier airflow, while the nozzle 121 in the head bar 71 located downstream is less susceptible to the influence of the carrier airflow.

[0051] Furthermore, when two adjacent head bars 71 are considered, the voltage applied to the actuator 160 corresponding to the most upstream nozzle 121 of the downstream head bar 71 is made higher by the control device 20 than the voltage applied to the actuator 160 corresponding to the most downstream nozzle 121 of the upstream head bar 71. This is to take into consideration the possibility of drafts occurring between the head bars 71 due to the transport airflow.

[0052] Note that instead of executing the process of increasing the ink droplet ejection speed as described above, the control device 20 may advance the ink droplet ejection timing by accelerating the input timing of the drive waveform to the actuator 160. Alternatively, the control device 20 may execute both the process of increasing the ink droplet ejection speed and the process of accelerating the ejection timing. The same applies to the aspects described below.

[0053] FIG. 7 is a diagram showing the relationship between each ejection head 10 and the voltage applied to the actuator 160 corresponding to the nozzle 121 in each ejection head 10. In FIG.

[0054] In Fig. 6, the magnitude of the voltage applied to the actuator 160 is broadly expressed in terms of head bar units, but if the magnitude of the applied voltage is viewed in a narrower sense in terms of ejection head units, the result will be the form shown in Fig. 7. As shown in Fig. 7, the voltage applied to the actuator 160 in each ejection head 10 is increased from the downstream side to the upstream side by the control device 20. That is, the voltage applied to the actuator 160 corresponding to the nozzle 121 in the upstream ejection head HU is higher than the voltage applied to the actuator 160 corresponding to the nozzle 121 in the downstream ejection head HD. This takes into account the fact that the nozzle 121 in the upstream ejection head HU is more susceptible to the influence of the transport airflow than the nozzle 121 in the downstream ejection head HD.

[0055] FIG. 8 is a diagram showing the relationship between each nozzle 121 and the voltage applied to the actuator 160 corresponding to each nozzle 121.

[0056] In Fig. 7, the magnitude of the voltage applied to the actuator 160 is shown for each ejection head, but if the magnitude of the applied voltage is viewed more narrowly for each nozzle, the result is the state shown in Fig. 8. As shown in Fig. 8, the voltage applied to the actuator 160 corresponding to each nozzle 121 is increased from the downstream side to the upstream side by the control device 20. In other words, the voltage applied to the actuator 160 corresponding to the upstream nozzle NU is higher than the voltage applied to the actuator 160 corresponding to the downstream nozzle ND. This takes into account the fact that the upstream nozzle NU is more susceptible to the influence of the carrier airflow than the downstream nozzle ND.

[0057] Next, FIG. 9 is a diagram showing the change in the applied voltage to the head bar 71 to be used when there is an unused head bar 71.

[0058] As described above, since the head bars 71 are provided corresponding to ink colors, some head bars 71 may be unused depending on the printing mode. Therefore, the positional relationship between the upstream head bar BU and the downstream head bar BD may change. In this way, if there is an unused head bar 71 among the multiple head bars 71 in printing, the control device 20 determines the upstream head bar BU and the downstream head bar BD from among the multiple head bars 71 to be used. For example, in FIG. 6, if the head bar 71 associated with the first head bar, the head bar 71 associated with the second head bar, and the head bar 71 associated with the third head bar are unused, the control device 20 determines the head bar 71 associated with the fourth head bar as the upstream head bar BU and the head bar 71 associated with the fifth head bar as the downstream head bar BD.

[0059] 9, the control device 20 increases the applied voltage VC1 to the head bar 71 associated with the fourth head bar when the first, second, and third head bars are used, to set the applied voltage VC2 to the head bar 71 associated with the fourth head bar, which is the upstream head bar BU. The applied voltage VC2 corresponding to the downstream side in the conveying direction Df is substantially the same as the applied voltage VC1 corresponding to the downstream side in the conveying direction Df.

[0060] Next, Fig. 10 is an enlarged view of a portion of Fig. 4. Fig. 11 is a diagram showing the voltage applied to the actuator 160 corresponding to the nozzle 121 in the overlap region and the voltage applied to the actuator 160 corresponding to the nozzle 121 in the non-wrap region.

[0061] As described above, each downstream ejection head HD is positioned at a predetermined distance from each upstream ejection head HU in the intersecting direction Ds, so that the multiple ejection heads 10 are arranged in a staggered pattern in the intersecting direction Ds. As a result, there are regions of the downstream ejection heads HD that do not overlap with the upstream ejection heads HU in the transport direction Df. To explain this point using the example of FIG. 10 , the ejection head 112, which is the downstream ejection head HD, has regions (overlap regions) Rl, Rl that overlap with the ejection heads 111 and 113, which are the upstream ejection heads HU, in the transport direction Df, and a region (non-overlap region) Rn that does not overlap with the ejection heads 111 and 113 in the transport direction Df. Region Rn is the region between one region Rl and the other region Rl in the intersecting direction Ds.

[0062] As described above, the upstream ejection heads HU, 111 and 113, are disposed at equal intervals. This causes draft Fl between the ejection heads 111 and 113 due to the transport airflow. Therefore, the region Rn of the ejection head 112 is more affected by draft Fl than the region Rl. Therefore, as shown in FIG. 11 , the control device 20 increases the ink droplet ejection speed of the nozzles 121 in the region Rn of the downstream ejection heads HD that do not overlap with the upstream ejection head HU in the transport direction Df (non-overlap region) compared to the nozzles 121 in the region Rl of the downstream ejection heads HD that overlap with the upstream ejection head HU in the transport direction Df (overlap region). Note that, like the ejection head 112 among the multiple downstream ejection heads HD, the control device 20 also increases the ink droplet ejection speed of the nozzles 121 in the region Rn of the remaining ejection heads 114, 116, 118, and 120.

[0063] Fig. 12 is a diagram showing a crosswind caused by the transport air current, and Fig. 13 is a diagram showing the voltage applied to each ejection head 10 of the head bar 71.

[0064] 12, an airflow (hereinafter referred to as a crosswind) along the intersecting direction Ds may occur due to the airflow caused by the transport of the print medium W in the transport direction Df. In each head bar 71, of the multiple nozzles 121, the nozzles 121 located on both sides in the intersecting direction Ds are affected by the crosswind to a greater extent than the remaining nozzles 121.

[0065] Therefore, the control device 20 increases the ink droplet ejection speed of the nozzles 121 located on both sides in the intersecting direction Ds among the multiple nozzles 121, compared to the ink droplet ejection speed of the remaining nozzles 121 among the multiple nozzles 121. Specifically, the control device 20 increases the ink droplet ejection speed of the end nozzles NE on one side (i.e., the outer end nozzles NE) described above in FIG. 5 among the multiple nozzles 121 in the ejection head 111 arranged at the end furthest in the intersecting direction Ds, compared to the remaining nozzles 121 in the intersecting direction Ds of the ejection head 111. In this case, as shown in FIG. 13, the applied voltage to a predetermined number of nozzles 121 located inside the end nozzles NE on one side in the intersecting direction Ds is gradually reduced, and the applied voltage to the remaining nozzles 121 in the intersecting direction Ds other than those nozzles 121 is kept constant.

[0066] Similarly, the control device 20 increases the ink droplet ejection speed of the other end nozzles NE (i.e., the outer end nozzles NE) of the multiple nozzles 121 in the ejection head 120 arranged at the farthest end in the intersecting direction Ds, compared to the remaining nozzles 121 in the intersecting direction Ds of the ejection head 120. In this case, as shown in Fig. 13, the applied voltage to a predetermined number of nozzles 121 among the nozzles 121 located more inward in the intersecting direction Ds than the other end nozzles NE is gradually reduced, and the applied voltage to the remaining nozzles 121 in the intersecting direction Ds, excluding these nozzles, is kept constant.

[0067] The applied voltage to ejection head 112 is changed by control device 20 in the same manner as ejection head 111, except that its maximum value is lower than the maximum value of the applied voltage to ejection head 111. Similarly, the applied voltage to ejection head 119 is changed by control device 20 in the same manner as ejection head 120, except that its maximum value is lower than the maximum value of the applied voltage to ejection head 120. Note that for ejection heads 113 to 118 in head bar 71, the applied voltages to the multiple nozzles 121 arranged in the intersecting direction Ds are all kept constant.

[0068] Next, Fig. 14 is a diagram showing the applied voltage to be increased for the actuator 160 for each nozzle 121. In Fig. 14, the applied voltage is determined by the control device 20 taking into consideration the transport air current (hereinafter referred to as vertical wind) flowing in the transport direction Df and the above-mentioned cross wind. This will be explained in detail below. In Fig. 14, in order to identify each nozzle 121, a number as an address is inserted in the circle representing the nozzle 121.

[0069] 14, in each ejection head 10, a first change amount ΔVx by which the voltage applied to the actuator 160 should be increased based on the influence of a crosswind, and a second change amount ΔVy by which the voltage applied to the actuator 160 should be increased based on the influence of a vertical wind, are set in advance for each nozzle 121. Note that the first change amount ΔVx can be set arbitrarily depending on the magnitude of the crosswind caused by factors such as the transport speed of the print medium W, and the second change amount ΔVy can be set arbitrarily depending on the magnitude of the vertical wind caused by factors such as the transport speed of the print medium W.

[0070] The control device 20 executes a process for increasing the applied voltage to the actuator 160 by the larger of the first change amount ΔVx and the second change amount ΔVy for each actuator 160. The control device 20 also executes a process for changing the timing of ink droplet ejection by the nozzle 121 corresponding to the actuator 160 in accordance with the difference between the first change amount ΔVx and the second change amount ΔVy for each actuator 160.

[0071] Using the example of FIG. 14, for example, for the actuator 160 corresponding to the nozzle 121 at address 1, both the first change ΔVx and the second change ΔVy are +1.0 V. Therefore, the control device 20 increases the applied voltage by 1.0 V to the actuator 160 corresponding to the nozzle 121 at address 1. In contrast, for the actuator 160 corresponding to the nozzle 121 at address 6, the first change ΔVx is +1.0 V, but the second change ΔVy is +0.7 V. Therefore, the control device 20 increases the applied voltage by 1.0 V to the actuator 160 corresponding to the nozzle 121 at address 6. However, this increased applied voltage of 1.0 V is 0.3 V higher than the second change ΔVy (i.e., +0.7 V), resulting in a voltage value that overly considers the effects of vertical wind. As a result, the impact position of the ink droplets is shifted in the transport direction Df. Therefore, the control device 20 executes a process to change the timing of ejection of ink droplets from the nozzle 121 in accordance with the difference between the first change amount ΔVx and the second change amount ΔVy. In this case, if the difference between the first change amount ΔVx and the second change amount ΔVy is relatively small, an ejection timing that is slightly delayed from the initial ejection timing is adopted, and if the difference is relatively large, an ejection timing that is significantly delayed from the initial ejection timing is adopted.

[0072] Next, Fig. 15 is a diagram for explaining the generation of negative pressure and upstream airflow when the gap is high. Fig. 16(a) is a diagram showing that the distance between the platen 61 and the nozzle surface NM is a high gap, and Fig. 16(b) is a diagram showing that the distance is a low gap. Fig. 17 is a diagram showing the applied voltages to the upstream ejection head HU and the downstream ejection head HD when printing when the gap is high.

[0073] As shown in FIG. 16(a), the distance h between the platen 6 and the nozzle surface NM is the longest when it is the high gap GH. Also, as shown in FIG. 16(b), the distance h between the platen 6 and the nozzle surface NM is the shortest when it is the low gap GL. The high gap GH is, for example, 18 mm. The low gap GL is, for example, 2 mm. The print mode when the distance h is the high gap GH is the high gap print mode, and the print mode when the distance h is the low gap GL is the low gap print mode. The print job includes information specifying the high gap print mode, in which printing is performed at the high gap GH, and the low gap print mode, in which printing is performed at the low gap GL.

[0074] When the high gap printing mode is executed, as shown in FIG. 15 , the transport airflow passes through a region below the ejection head 10, generating negative pressure in the region between the region below and the ejection head 10. This generates an upstream airflow moving from the downstream side to the upstream side in the transport direction Df of the ejection head 10. Therefore, when the printing mode is the high gap printing mode, the control device 20 increases the ink droplet ejection speed of the nozzles 121 located downstream in the transport direction Df compared to the nozzles 121 located upstream in the transport direction Df. Specifically, as shown in FIG. 17 , the control device 20 applies the same voltage to the actuators 160 corresponding to the nozzles 121 in the upstream ejection head HU as in FIG. 7 above. On the other hand, unlike in FIG. 7 above, the control device 20 applies a higher voltage to the actuators 160 corresponding to the nozzles 121 located downstream in the transport direction Df for the downstream ejection head HD than to the nozzles 121 located upstream in the transport direction Df. As a result, the speed at which ink droplets are ejected by the nozzles 121 located downstream in the transport direction Df is increased compared to the speed at which ink droplets are ejected by the nozzles 121 located upstream in the transport direction Df.

[0075] Here, as described above, when forming a base on the print medium W using white ink droplets, the control device 20 does not execute the process of increasing the ejection speed or the process of accelerating the ejection timing. Even when forming a base on the print medium W, misalignment of ruled lines may occur at the downstream end of the base in the transport direction Df. Therefore, when forming the base, the control device 20 increases the ejection speed of ink droplets from the nozzles 121 located upstream of the nozzles 121 located downstream in the transport direction Df, for the downstream portion of the print medium W in the transport direction Df. The downstream portion of the print medium W in the transport direction Df is, for example, the portion where the last dot is to be formed in the transport direction Df.

[0076] Next, FIG. 18(a) is a diagram showing a drive waveform Wd1 for the actuator 160 corresponding to the downstream nozzle ND, and (b) is a diagram showing a drive waveform Wd2 for the actuator 160 corresponding to the upstream nozzle NU.

[0077] As shown in Figure 18(a), the drive waveform Wd1 has a pulse width Pd1 and its drive voltage is Vd. On the other hand, as shown in Figure 18(b), the drive waveform Wd2 has a pulse width Pd2 that is larger than the pulse width Pd1 and its drive voltage is the same as the drive voltage Vd of the drive waveform Wd1. The control device 20 controls the actuator 160 of the upstream nozzle NU based on the drive waveform Wd2, which has a faster ejection speed than the drive waveform Wd1 for the actuator 160 of the downstream nozzle ND. In this way, the control device 20 controls the actuator 160 of the upstream nozzle NU using the drive waveform Wd2 with a larger pulse width without increasing the drive voltage.

[0078] As described above, the droplet ejection device 100 can suppress misalignment of the ink droplets by increasing the ejection speed of the ink droplets from the upstream nozzles NU, which are relatively more susceptible to disturbances such as transport air currents that occur when transporting the printing medium W than the downstream nozzles ND.

[0079] Furthermore, in this embodiment, the control device 20 increases the drive voltage applied to the actuator 160 of the upstream nozzle NU more than the drive voltage applied to the actuator 160 of the downstream nozzle ND, thereby increasing the ink droplet ejection speed. In this case, the ink droplet ejection speed can be easily increased.

[0080] Furthermore, in this embodiment, the control device 20 increases the ink droplet ejection speed of the upstream ejection head HU compared to the downstream ejection head HD, thereby suppressing deviation in the landing position of ink droplets in each of the multiple ejection heads 10 arranged in a staggered pattern.

[0081] Furthermore, in this embodiment, the control device 20 increases the ink droplet ejection speed of the nozzles 121 in the region Rn of the downstream ejection head HD that do not overlap with the upstream ejection head HU in the transport direction Df, compared to the nozzles 121 in the region Rl of the downstream ejection head HD that overlap with the upstream ejection head HU in the transport direction Df. In this regard, the region Rn is more susceptible to disturbances such as transport air currents. According to the above configuration, increasing the ink droplet ejection speed of the nozzles 121 in the region Rn can suppress impact deviation of the ink droplets.

[0082] Furthermore, in this embodiment, the control device 20 increases the ejection speed of ink droplets from the ejection heads 10 of the upstream head bar BU to be higher than the ejection speed of the ejection heads 10 of the downstream head bar BD. This makes it possible to suppress deviation in the landing position of ink droplets from the ejection heads 10 of the multiple head bars 71 arranged side by side in the transport direction Df.

[0083] Furthermore, in this embodiment, if there are any unused head bars 71 among the multiple head bars 71 in printing, the control device 20 determines the upstream head bar BU and the downstream head bar BD to be used from among the multiple head bars 71. In this case, it is possible to exclude head bars 71 that do not need to be designed to suppress ink droplet landing deviation.

[0084] 5 (i.e., outer end nozzle NE) of the plurality of nozzles 121 in the ejection head 111 arranged at the outermost end in the intersecting direction Ds, is set to be higher than the remaining nozzles 121 in the intersecting direction Ds of the ejection head 111. Similarly, the control device 20 sets to be higher than the remaining nozzles 121 in the intersecting direction Ds of the ejection head 120, the other end nozzle NE (i.e., outer end nozzle NE) of the plurality of nozzles 121 in the ejection head 120 arranged at the outermost end in the intersecting direction Ds, is set to be higher than the remaining nozzles 121 in the intersecting direction Ds of the ejection head 120. In this case, by increasing the ejection speed of ink droplets from the nozzle 121 that is relatively susceptible to the influence of crosswinds, it is possible to suppress deviation in the landing position of ink droplets.

[0085] Furthermore, in this embodiment, the control device 20 executes a process for increasing the applied voltage to each actuator 160 by the larger of the first change amount ΔVx and the second change amount ΔVy. The control device 20 also executes a process for each actuator 160 for changing the timing of ink droplet ejection by the nozzle 121 corresponding to the actuator 160 in accordance with the difference between the first change amount ΔVx and the second change amount ΔVy. In this case, ejection control that takes both vertical and horizontal winds into consideration can be achieved. This further improves the accuracy of suppressing ink droplet impact deviation.

[0086] Furthermore, in this embodiment, when the printing mode is the high gap printing mode, the control device 20 increases the ink droplet ejection speed of the nozzles 121 located downstream in the transport direction Df compared to the nozzles 121 located upstream in the transport direction Df among the multiple nozzles 121. In this case, by increasing the ink droplet ejection speed of the downstream nozzles 121, which are more susceptible to the influence of the airflow caused by the negative pressure described above than the upstream nozzles 121 in the transport direction Df, it is possible to suppress deviations in the landing of ink droplets during high gap printing.

[0087] Furthermore, in this embodiment, the control device 20 does not execute the process of increasing the ejection speed or the process of accelerating the ejection timing when forming a base using white ink droplets on the print medium W. In this case, it is possible to omit the ejection control when forming a base, which does not pose any particular problems even if the ink droplets are misaligned.

[0088] Furthermore, in this embodiment, when forming the base, the control device 20 increases the ink droplet ejection speed from the nozzles 121 located upstream of the nozzles 121 located downstream in the transport direction Df, among the multiple nozzles 121, for the portion of the print medium W that is downstream in the transport direction Df. In this case, when forming the base, it is possible to suppress landing deviation at the end of the print medium W that is downstream in the transport direction Df. This makes it possible to suppress ruled line deviation at the end of the base on the print medium W that is downstream in the transport direction Df.

[0089] Furthermore, in this embodiment, the control device 20 controls the actuator 160 of the upstream nozzle NU based on the drive waveform Wd2, which has a faster ejection speed than the drive waveform Wd1 for the actuator 160 of the downstream nozzle ND. In this case, if the drive voltage for the actuator 160, which has high voltage sensitivity, is increased, the size of the ejected ink droplets may not be uniform, which could result in printing unevenness in the thickness of, for example, ruled lines. According to the above configuration, the actuator 160 of the upstream nozzle NU is controlled based on the drive waveform Wd2 without increasing the drive voltage, which makes it easier to uniform the thickness of ruled lines and reduces printing unevenness.

[0090] 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.

[0091] In the above embodiment, in order to increase the ink droplet ejection speed, the temperature of the ink to be ejected by the upstream nozzles NU may be made higher than the temperature of the ink to be ejected by the downstream nozzles ND.

[0092] Furthermore, in the above embodiment, when forming the base, the control device 20 increases the ink droplet ejection speed of the nozzles 121 located upstream of the nozzles 121 located downstream in the transport direction Df among the multiple nozzles 121 for the portion of the print medium W that is downstream in the transport direction Df. However, this is not limiting, and the landing position of the ink droplets for the portion of the print medium W that is downstream in the transport direction Df may be controlled by changing the ejection timing.

[0093] Furthermore, although a plurality of head bars 71 are provided in the above embodiment, the number of head bars 71 may be one. Alternatively, the head bar 71 may not be provided at all. Furthermore, although a plurality of ejection heads 10 are provided, the number of ejection heads 10 may be one.

[0094] In the above embodiment, a color image is printed by ejecting ink droplets of four colors, black, yellow, cyan, and magenta, onto the print medium W, and a base is formed by ejecting white ink droplets onto the print medium W, but this is not limiting. A configuration for ejecting other inks, such as clear ink, onto the print medium W in addition to the inks mentioned above may be added to the droplet ejection device 100.

[0095] In the above embodiment, the print medium W may be pre-cut printing paper, roll paper or fabric that is cut in a post-printing process, or the like.

[0096] Furthermore, in the above embodiment, each downstream-side ejection head HD is disposed at a predetermined distance from each upstream-side ejection head HU in the intersecting direction Ds, thereby disposing the multiple ejection heads 10 in a staggered pattern in the intersecting direction Ds. However, this is not limiting, and for example, the position of ejection head 112 in the intersecting direction Ds may be the same as the position of ejection head 111 in the intersecting direction Ds. The positional relationship between ejection head 114 and ejection head 113, the positional relationship between ejection head 116 and ejection head 115, the positional relationship between ejection head 118 and ejection head 117, and the positional relationship between ejection head 120 and ejection head 119 may also be the same as the positional relationship between ejection head 112 and ejection head 111. [Explanation of symbols]

[0097] 1 Printing device 10 Discharge head 20 Control device 33 Transport motor 60 Conveyor roller 61 Platen 70 Line Head 71 Head Bar 100 Droplet discharge device 121 nozzle 128 Pressure Chamber 160 Actuator BD Downstream Head Bar BU Upstream head bar Df Conveying direction Ds cross direction HD downstream discharge head HU upstream discharge head ND downstream nozzle NM nozzle surface NU Upstream nozzle Rl wrap area Rn non-wrapping region W Printing medium Wd2 drive waveform ΔVx First change ΔVy Second change

Claims

1. a conveying unit that conveys the print medium in a conveying direction; a line head having a plurality of nozzles arranged in the transport direction and an intersecting direction intersecting the transport direction, the nozzles ejecting droplets onto the print medium; a control device; The control device increases the droplet ejection speed by the upstream nozzles, which are nozzles located upstream of the downstream nozzles in the transport direction, compared to the downstream nozzles, which are some of the multiple nozzles, or advances the droplet ejection timing.

2. the line head includes a pressure chamber provided for each of the nozzles and an actuator that applies a discharge pressure to the pressure chamber; The droplet ejection device according to claim 1 , wherein the control device increases the drive voltage applied to the actuator of the upstream nozzle more than the drive voltage applied to the actuator of the downstream nozzle to increase the ejection speed of the droplets.

3. The line head has a plurality of ejection heads, each having a plurality of nozzles, arranged in a staggered pattern along the intersecting direction, The droplet ejection device according to claim 1, wherein the control device increases the droplet ejection speed of the upstream ejection head, which is one of the plurality of ejection heads, and is located upstream in the transport direction compared to the downstream ejection head, or advances the ejection timing of the droplets.

4. The droplet ejection device according to claim 3, wherein the control device increases the droplet ejection speed by the nozzles in a region of the downstream ejection head that does not overlap with the upstream ejection head in the transport direction, or advances the droplet ejection timing, compared to the nozzles in a region of the downstream ejection head that overlaps with the upstream ejection head in the transport direction.

5. the line head includes a head bar arranged in parallel in the transport direction, the head bar including a plurality of ejection heads, each of the plurality of nozzles arranged along at least the intersecting direction; The droplet ejection device according to claim 1, wherein the control device increases the droplet ejection speed of the ejection head of the upstream head bar, which is a head bar located upstream in the transport direction, compared to the ejection head of the downstream head bar, which is one of the multiple head bars, or advances the ejection timing of the droplets.

6. The droplet ejection device according to claim 5 , wherein the control device determines the upstream head bar and the downstream head bar to be used among the plurality of head bars when there are unused head bars among the plurality of head bars.

7. The droplet ejection device according to claim 1 , wherein the control device increases the ejection speed of the droplets from the nozzles located on both sides of the plurality of nozzles in the intersecting direction to be higher than the ejection speed of the droplets from the remaining nozzles of the plurality of nozzles.

8. the line head includes a pressure chamber provided for each of the nozzles and an actuator that applies a discharge pressure to the pressure chamber; The control device a process of increasing the drive voltage for each of the actuators by a larger amount of change between a first amount by which the drive voltage for the actuator should be increased, which is set in advance based on the transport airflow flowing in the cross direction, and a second amount by which the drive voltage for the actuator should be increased, which is set in advance based on the transport airflow flowing in the transport direction; The droplet ejection device according to claim 2 , further comprising: a process for changing, for each of the actuators, the timing at which the droplets are ejected by the nozzles corresponding to the actuators in accordance with the difference between the first change amount and the second change amount.

9. a platen for supporting the print medium; the line head has a nozzle surface, 2. The droplet ejection device according to claim 1, wherein when the printing mode is a high gap printing mode out of a low gap printing mode in which the distance between the nozzle face and the platen is a low gap and a high gap printing mode in which the distance is a high gap greater than the low gap, the control device increases the droplet ejection speed by nozzles located downstream in the transport direction among the plurality of nozzles, or advances the droplet ejection timing, compared to nozzles located upstream in the transport direction.

10. The droplet ejection device according to claim 1 , wherein the control device does not execute the process of increasing the ejection speed and the process of accelerating the ejection timing when a base is formed on the print medium.

11. The droplet ejection device according to claim 1, wherein when forming a base on the printing medium, the control device increases the droplet ejection speed or advances the droplet ejection timing by nozzles located upstream in the transport direction compared to nozzles located downstream in the transport direction among the plurality of nozzles for the downstream portion of the printing medium in the transport direction.

12. the line head includes a pressure chamber provided for each of the nozzles and an actuator that applies a discharge pressure to the pressure chamber; The droplet ejection device according to claim 1 , wherein the control device controls the actuator of the upstream nozzle based on a drive waveform whose ejection speed is faster than a drive waveform for the actuator of the downstream nozzle.

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