Printing control device and method

Abstract

To provide a printing control device and a printing control method which can suppress impact positions of ink droplets discharged from a nozzle positioned at an upper side in a vertical direction from being deviated due to parabolic fall of the droplets, so as to improve a quality of a printed image.SOLUTION: The printing control device comprises a head part 10 in which a plurality of nozzles for discharging liquid droplets are arranged in a vertical direction and a control part 50 that controls discharge energy generated when the nozzles discharge liquid droplets. The control part 50 makes discharge energy of the nozzle positioned at an upper side in the vertical direction larger than discharge energy of the nozzle positioned at a lower side in the vertical direction.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a print control device and method for performing printing by ejecting droplets from a plurality of nozzles arranged in a vertical direction. [Background technology]

[0002] 2. Description of the Related Art Conventionally, inkjet printing devices have been proposed that perform printing by ejecting ink onto a print medium.

[0003] Inkjet printing devices that eject ink from above in a vertical direction onto a printing medium that is positioned so that the printing surface is horizontal, as well as inkjet printing devices that print by ejecting ink from a direction perpendicular to the printing surface onto a printing medium that is positioned so that the printing surface is not horizontal, have been proposed.

[0004] For example, Patent Document 1 proposes a handheld inkjet printing device that prints on a printing medium that is not placed horizontally.

[0005] Furthermore, Patent Documents 2 and 3 propose inkjet printing devices that perform printing by ejecting ink in a horizontal direction onto a printing medium that is transported in a vertical direction. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-150539 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-63564 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-59958 Summary of the Invention [Problem to be solved by the invention]

[0007] When printing on a three-dimensional object having vertically standing sides, such as a cardboard box, it is conceivable to perform printing by arranging a plurality of inkjet heads in the vertical direction.

[0008] When printing is performed with multiple inkjet heads arranged vertically in this way, the pressure on the ink in each nozzle is adjusted so that a meniscus is formed in each nozzle of each inkjet head. However, for example, if the negative pressure is adjusted so that a meniscus is formed without ink leaking from the nozzles of a lower inkjet head, there will be a difference in head pressure between the nozzles of the upper inkjet head and the lower inkjet head, and therefore the retraction pressure will be higher in the nozzles of the upper inkjet head than in the nozzles of the lower inkjet head.

[0009] Therefore, if the upper and lower inkjet heads are subjected to the same ejection control, the upper inkjet head will have a higher retraction pressure and therefore weaker ejection energy, which will cause the ink droplets ejected from the upper inkjet head to fall parabolically due to the influence of gravity, resulting in a downward shift in the landing position on the printing surface of the print medium, resulting in a deterioration in the quality of the printed image.

[0010] Patent Documents 1 to 3 propose various measures to address misalignment caused by the parabolic fall of ink droplets due to the influence of gravity, but do not address the misalignment caused by the difference in retraction pressure between the upper inkjet head and the lower inkjet head as described above.

[0011] Furthermore, the difference in retraction pressure between the upper inkjet head and the lower inkjet head described above also occurs between the upper nozzles and the lower nozzles within a single inkjet head, resulting in the same problem.

[0012] The present invention aims to provide a print control device and method that can suppress deviation in the landing position caused by the parabolic fall of ink droplets ejected from nozzles located vertically above, thereby improving the quality of printed images. [Means for solving the problem]

[0013] The printing control device of the present invention comprises a head unit in which multiple nozzles that eject droplets are arranged vertically, and a control unit that controls the ejection energy when droplets are ejected from the nozzles, and the control unit increases the ejection energy of nozzles located vertically above compared to the ejection energy of nozzles located vertically below. [Effects of the Invention]

[0014] According to the printing control device of the present invention, the ejection energy of nozzles located vertically above is made greater than the ejection energy of nozzles located vertically below, thereby suppressing deviation in the landing position due to parabolic fall of ink droplets ejected from nozzles located vertically above, thereby improving the quality of the printed image. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an external perspective view showing a schematic configuration of a main body of an inkjet printing apparatus using an embodiment of a print control apparatus of the present invention. [Figure 2] FIG. 1 is a diagram showing a schematic configuration of an ink circulation unit and an ink supply unit. [Figure 3] A diagram illustrating the difference in ejection energy between the upper inkjet head and the lower inkjet head. [Figure 4] A block diagram showing the configuration of a control system of the inkjet printing apparatus shown in Figure 1. [Figure 5] FIG. 1 is a diagram showing an example of a normal driving voltage and a driving voltage when the magnitude and waveform of the driving voltage are controlled to increase the ejection energy. [Figure 6] FIG. 10 is a diagram showing an example of the driving voltage when the number of ink drops is increased to increase the ejection energy. [Figure 7] 10A and 10B are diagrams showing an example of document image data before density conversion processing, document image data after density conversion processing, and a density conversion function; [Figure 8] FIG. 10 is a diagram illustrating an example in which the number of ink drops is increased only at the edge of a printed image. [Figure 9] FIG. 10 is a diagram showing a method for controlling ejection energy according to a distance measured by a distance measurement unit. DETAILED DESCRIPTION OF THE INVENTION

[0016] An inkjet printing apparatus using an embodiment of a print control device of the present invention will be described in detail below with reference to the drawings. The inkjet printing apparatus of this embodiment is characterized by ink ejection control, but first, the overall configuration of the inkjet printing apparatus will be described. FIG. 1 is an external perspective view showing the schematic configuration of an inkjet printing apparatus main body 1. In the description of the embodiment below, the up, down, left, right, front, and back directions indicated by arrows in FIG. 1 are defined as the up, down, left, right, front, and back directions of the inkjet printing apparatus main body 1. Furthermore, the up and down directions of the inkjet printing apparatus main body 1 are the vertical direction.

[0017] As shown in FIG. 1, the inkjet printing device main body 1 includes a head unit 10, a transport unit 2, and a distance measurement unit 15.

[0018] The transport unit 2 transports the print medium P in the direction of the arrow shown in Fig. 1. As the print medium P, for example, a three-dimensional object (for example, a box such as a cardboard box) having a printing surface Ps standing upright in a direction perpendicular to the transport surface as shown in Fig. 1 is used.

[0019] The transport unit 2 includes a support table 3 and a transport belt unit 4. The support table 3 is a table that supports the transport belt unit 4.

[0020] The conveyor belt unit 4 includes two platen rollers and a conveyor belt that extend in a direction perpendicular to the conveyance direction of the print medium P. The two platen rollers are arranged parallel to and spaced apart in the conveyance direction of the print medium P. A circular conveyor belt is stretched between the two parallel platen rollers. The platen rollers rotate under the control of the control unit 50, which will be described later, and the conveyor belt moves, thereby conveying the print medium P.

[0021] The head unit 10 performs printing by ejecting ink onto the printing surface Ps of the print medium P transported by the transport unit 2.

[0022] 1, the head unit 10 has four line heads 11, 12, 13, and 14. The four line heads 11 to 14 are provided to extend in the vertical direction and are arranged parallel to the transport direction of the printing medium P. In this embodiment, each of the line heads 11 to 14 corresponds to a head portion of the present invention.

[0023] The four line heads 11 to 14 eject ink of C (cyan), M (magenta), Y (yellow), and K (black), respectively.

[0024] The distance measurement unit 15 measures the distance to the printing surface Ps of the printing medium P transported by the transport unit 2. The distance measurement unit 15 measures the distance using an optical sensor such as a laser displacement sensor. The distance measurement unit 15 is installed at the same position as the head unit 10 in a direction perpendicular to the transport direction, and essentially measures the gap between each of the line heads 11 to 14 and the printing surface Ps of the printing medium P.

[0025] The inkjet printing apparatus of this embodiment also includes an ink circulation unit 20 connected to each of the line heads 11 to 14, and an ink supply unit 40 connected to the ink circulation unit 20.

[0026] 2 is a diagram showing the line head 11, the ink circulation unit 20 connected to the line head 11, and the ink supply unit 40 connected to the ink circulation unit 20. Although only the line head 11 is shown in FIG. 2, the other line heads 12 to 14 have the same configuration, and the ink circulation unit 20 and the ink supply unit 40 are also provided for each of the line heads 12 to 14.

[0027] The line head 11 ejects ink supplied from an ink circulation unit 20. The line head 11 has a plurality of inkjet heads 16.

[0028] The inkjet head 16 has an ink chamber (not shown) that stores ink and a plurality of nozzles (not shown) that eject ink. A piezoelectric element (not shown) is disposed inside the ink chamber. When the piezoelectric element is driven, ink is ejected from the nozzle.

[0029] The line head 11 of this embodiment has six inkjet heads 16. The six inkjet heads 16 are arranged so that their ink ejection surfaces stand upright in the vertical direction (a direction perpendicular to the transport surface of the transport unit 2). The ink ejection surface is a surface on which nozzle ejection openings are arranged. The six inkjet heads 16 are arranged side by side in the vertical direction, and by ejecting ink from the six inkjet heads 16, straight lines extending in the vertical direction are printed.

[0030] The ink circulation unit 20 circulates the ink and supplies it to the line head 11. The ink circulation unit 20 includes a pressurized tank 21, a distributor 22, a collector 23, a negative pressure tank 24, an ink pump 25, an ink temperature adjustment unit 26, an ink temperature sensor 27, and ink circulation pipes 28 to 30.

[0031] The pressurized tank 21 stores ink to be supplied to the line head 11. The ink in the pressurized tank 21 is supplied to each inkjet head 16 via an ink circulation pipe 28 and a distributor 22. An air layer 31 is formed above the ink liquid surface in the pressurized tank 21. The air layer 31 in the pressurized tank 21 is connected to a pressure application unit 5, which will be described later, via a pressure communication pipe 58, which will be described later. The pressurized tank 21 is disposed at a position lower (below) than the line head 11.

[0032] The distributor 22 distributes the ink supplied from the pressure tank 21 via the ink circulation pipe 28 to each inkjet head 16 of the line head 11 .

[0033] The collector 23 collects ink that has not been consumed by the line head 11 from each inkjet head 16. The ink collected by the collector 23 flows to the negative pressure tank 24 via an ink circulation pipe 29.

[0034] The negative pressure tank 24 receives and stores ink that has not been consumed by the line head 11 from the collector 23 via an ink circulation pipe 29. The negative pressure tank 24 also stores ink that is supplied from ink cartridges 46 of an ink supply unit 40, which will be described later. An air layer 36 is formed above the ink liquid surface inside the negative pressure tank 24. The air layer 36 in the negative pressure tank 24 is connected to the pressure application unit 5 via a negative pressure communication pipe 59, which will be described later. The negative pressure tank 24 is located at the same height as the pressurized tank 21.

[0035] The ink pump 25 sends ink from the negative pressure tank 24 to the pressure tank 21. The ink pump 25 is provided midway along the ink circulation pipe 30.

[0036] The ink temperature adjustment unit 26 adjusts the temperature of the ink in the ink circulation unit 20. The ink temperature adjustment unit 26 is provided midway through the ink circulation pipe 28. The ink temperature adjustment unit 26 includes a heater 41, a heater temperature sensor 42, a heat sink 43, and a cooling fan 44.

[0037] The heater 41 heats the ink in the ink circulation pipe 28. The heater temperature sensor 42 detects the temperature of the heater 41. The heat sink 43 cools the ink in the ink circulation pipe 28 by radiating heat. The cooling fan 44 sends cooling air to the heat sink 43.

[0038] The ink temperature sensor 27 detects the temperature of the ink in the ink circulation unit 20. The ink temperature sensor 27 is provided midway through the ink circulation pipe 28. The ink temperature sensor 27 can be configured by, for example, a power thermistor.

[0039] The ink circulation pipe 28 connects the pressurized tank 21 and the distributor 22. The ink circulation pipe 28 passes through a heat sink 43 and then through a heater 41. Ink flows through the ink circulation pipe 28 from the pressurized tank 21 toward the distributor 22. The ink circulation pipe 29 connects the collector 23 and the negative pressure tank 24. Ink flows through the ink circulation pipe 29 from the collector 23 toward the negative pressure tank 24.

[0040] The ink circulation pipe 30 connects the negative pressure tank 24 and the pressurized tank 21. Ink flows through the ink circulation pipe 30 from the negative pressure tank 24 toward the pressurized tank 21. The ink circulation pipes 28 to 30, the distributor 22, and the collector 23 form a circulation path that circulates ink between the pressurized tank 21, the line head 11, and the negative pressure tank 24.

[0041] The ink supply unit 40 supplies ink from the ink cartridge 46 to the negative pressure tank 24 of the ink circulation unit 20 via the ink supply pipe 48 while the ink supply valve 47 is open.

[0042] The pressure applying unit 5 applies pressure for circulating ink to the air layer 31 of the pressurized tank 21 and the air layer 36 of the negative pressure tank 24. The pressure applying unit 5 can individually isolate or connect the air layer 31 of the pressurized tank 21 and the air layer 36 of the negative pressure tank 24 to the atmosphere.

[0043] The pressure applying unit 5 can apply a positive pressure to the air layer 31 of the pressurized tank 21 via the pressurized communicating pipe 58. The pressure applying unit 5 can also apply a negative pressure to the air layer 36 of the negative pressure tank 24 via the negative pressure communicating pipe 59.

[0044] Then, by adjusting the positive and negative pressures by the pressure applying unit 5, a meniscus is formed at the ejection opening of each nozzle of the inkjet head 16.

[0045] In this embodiment, as described above, six inkjet heads 16 are arranged vertically in each of the line heads 11 to 14. The positive and negative pressures applied by the pressure applying unit 5 are adjusted so that a meniscus is formed in the nozzle of each inkjet head 16.

[0046] However, when the negative pressure is adjusted so that a meniscus is formed without ink leaking from the nozzles of the lower inkjet head 16, there is a difference in head between the nozzles of the upper inkjet head 16 and the nozzles of the lower inkjet head 16, and therefore the retraction pressure of the nozzles of the upper inkjet head 16 is higher than that of the nozzles of the lower inkjet head 16.

[0047] Therefore, if the upper inkjet head 16 and the lower inkjet head 16 are subjected to the same ejection control, the ejection energy of the upper inkjet head 16 will be weaker due to the higher retraction pressure. As a result, as shown in Figure 3, the ink ejected from the upper inkjet head 16 is more likely to fall parabolically due to the influence of gravity, causing the landing position on the printing surface Ps of the printing medium P to shift downward, resulting in misalignment and a deterioration in the quality of the printed image.

[0048] Therefore, in this embodiment, the control unit 50, which will be described later, increases the ejection energy of the nozzles of the inkjet head 16 located vertically above it compared to the ejection energy of the nozzles of the inkjet head 16 located vertically below it. This makes it possible to suppress deviation in the landing position of ink droplets ejected from the nozzles located vertically above it due to parabolic fall, thereby improving the quality of the printed image. The method of controlling the ejection energy will be described in detail later.

[0049] Furthermore, in the above explanation, the difference in retraction pressure between the upper inkjet head 16 and the lower inkjet head 16 has been described, but a similar difference in retraction pressure occurs between the upper nozzles and the lower nozzles of one inkjet head 16. Therefore, it is preferable to make the ejection energy of the upper nozzles greater than the ejection energy of the lower nozzles, and a method for controlling this ejection energy will be described in detail later.

[0050] 4 is a block diagram showing the configuration of the control system of the inkjet printing apparatus of this embodiment. The control unit 50 includes a CPU (Central Processing Unit) and storage media such as semiconductor memory and a hard disk, and controls the entire inkjet printing apparatus. The control unit 50 executes a control program stored in advance in storage media such as semiconductor memory or a hard disk, and operates electrical circuits to control the operation of each part of the inkjet printing apparatus.

[0051] In particular, as described above, the control unit 50 of this embodiment controls the ejection energy of the upper inkjet head 16 so that it is greater than the ejection energy of the lower inkjet head 16. A method for controlling the magnitude of the ejection energy will now be described in detail.

[0052] Methods for controlling the magnitude of the ejection energy include controlling the waveform of the drive voltage applied to the inkjet head 16, controlling the magnitude of the drive voltage, and controlling the number of ink drops ejected from the nozzles of the inkjet head 16. First, the method for controlling the waveform of the drive voltage applied to the inkjet head 16 will be described.

[0053] Fig. 5A is a diagram showing the waveform of a normal driving voltage applied to the inkjet head 16. The driving voltage for one convex shape shown in Fig. 5A is the driving voltage for ejecting one drop. As shown in Fig. 5A, the driving voltage for one convex shape has a first voltage V1 for pulling in the piezoelectric element, a second voltage V2 for stabilizing the vibration of the piezoelectric element, and a third voltage V3 for ejecting an ink droplet.

[0054] To eject one ink drop, the drive voltage is first pulled in as a first voltage V1, then set to a second voltage V2 to stabilize the vibration, and then set to a third voltage V3 to eject the ink droplet.Then, after stabilizing the vibration again at the second voltage V2, the voltage returns to the first voltage V1 to prepare for the ejection of the next drop.

[0055] Fig. 5B shows an example of a drive voltage waveform shaped to increase the ejection energy compared to the normal drive voltage shown in Fig. 5A. As shown in Fig. 5B, the drive voltage shaped to increase the ejection energy does not transition from the first voltage V1 to the second voltage V2 as in the normal drive voltage waveform shown in Fig. 5A, but instead changes from the first voltage V1 to the third voltage V3. In this way, the ejection energy can be increased by increasing the voltage difference in the drive waveform.

[0056] Next, we will explain how to control the magnitude of the drive voltage applied to the inkjet head 16. Figure 5C is a diagram showing an example of a drive voltage waveform in which the second voltage V2 and the third voltage V3 are set to values ​​higher than the normal drive voltage shown in Figure 5A. Increasing the drive voltage value itself in this way makes it possible to increase the ejection energy.

[0057] Fig. 5D is a diagram showing an example of a driving voltage in which the driving voltage waveform is shaped as shown in Fig. 5B and the magnitude of the driving voltage is increased as shown in Fig. 5C. By controlling both the waveform and magnitude of the driving voltage in this way, the control range of the ejection energy can be further expanded.

[0058] When the ejection energy is increased by controlling the drive voltage as described above, the ejection energy can be controlled by simple control.

[0059] Next, we will explain how to increase the ejection energy by increasing the number of ink drops. The normal drive voltage shown in Figure 5A includes three convex drive voltage waveforms, which results in three drops of ink being ejected. However, to increase the ejection energy, as shown in Figure 6A, for example, a drive voltage waveform for two drops is added, increasing the ejection energy to five drops. In other words, a dot that is normally printed with three drops of ink is printed by increasing the number to five drops.

[0060] 6B shows the drive voltage when the ejection energy is increased by combining the above-mentioned control of the drive voltage waveform, control of the drive voltage magnitude, and an increase in the number of ink drops. Controlling the drive voltage waveform and magnitude alone imposes limitations on the control range of the ejection energy, but by also controlling the number of ink drops, the control range of the ejection energy can be further expanded.

[0061] As shown in FIG. 6B, the control unit 50 may perform a combination of the above-mentioned control of the waveform of the driving voltage, control of the magnitude of the driving voltage, and increase in the number of ink drops, or may perform at least one of the three ejection energy control methods.

[0062] Furthermore, when controlling the waveform of the drive voltage as described above, the drive voltage is increased from the first voltage V1 to the third voltage V3, which may cause a large amount of deformation of the piezoelectric element and result in a large amount of ink mist being generated when ink is ejected. The generation of ink mist may result in contamination inside the device and on the printing medium P.

[0063] Therefore, when the user sets and inputs a mode to suppress ink mist, the waveform of the driving voltage is not controlled, but when priority is given to suppressing deviation of landing position over ink mist, that is, when the mode to suppress ink mist is not set and input, the waveform of the driving voltage is controlled, and the control unit 50 may switch between whether to control the waveform of the driving voltage depending on whether the user sets and inputs a mode to suppress ink mist. In this way, by switching between whether to control the waveform of the driving voltage and whether to prioritize suppression of ink mist or suppression of deviation of landing position.

[0064] Furthermore, when the control unit 50 increases the ejection energy by controlling both the magnitude and waveform of the driving voltage, if the user sets and inputs a mode that suppresses ink mist, the control unit 50 may control only the magnitude of the driving voltage without controlling the waveform of the driving voltage, and if the user does not set and input a mode that suppresses ink mist, the control unit 50 may control both the magnitude and waveform of the driving voltage.

[0065] The above is an explanation of the method for controlling the magnitude of the ejection energy.

[0066] The control unit 50 controls the ejection energy of the upper inkjet heads 16 so that it is greater than the ejection energy of the lower inkjet heads 16, and the number of inkjet heads 16 for which the ejection energy is to be increased is set appropriately.

[0067] Specifically, for example, when six inkjet heads 16 are arranged in the vertical direction as in this embodiment, a normal drive voltage is applied to the lower three inkjet heads 16, and a drive voltage that increases the ejection energy as described above is applied to the upper three inkjet heads 16. The number of lower inkjet heads 16 to which a normal drive voltage is applied and the number of upper inkjet heads 16 to which a drive voltage that increases the ejection energy are applied are not limited to the above example and may be set as appropriate.

[0068] Furthermore, the change in ejection energy is not limited to the two stages described above, but if the method allows for changing the ejection energy in three or more stages, such as by controlling the magnitude of the driving voltage or by increasing the number of ink drops, the ejection energy may be changed in three or more stages.

[0069] Specifically, for example, when six inkjet heads 16 are arranged in the vertical direction as in this embodiment, a normal drive voltage may be applied to the two inkjet heads 16 that are second from the bottom, a drive voltage that results in one level higher ejection energy may be applied to the two inkjet heads 16 that are third and fourth from the bottom, and a drive voltage that results in one level higher ejection energy than the third and fourth inkjet heads 16 may be applied to the first and second inkjet heads from the top.

[0070] Furthermore, while the waveform and magnitude of the drive voltage are controlled for each inkjet head 16, the number of ink drops can be controlled for each nozzle of the inkjet head 16. Therefore, the ejection energy can be increased by increasing the number of ink drops from the upper nozzles of one inkjet head 16 compared to the lower nozzles. In this case, as with control for each inkjet head, the number of nozzles for which the number of ink drops is increased can be set appropriately, and the nozzles in one inkjet head 16 can be divided into three or more sections, and the number of ink drops can be changed in three or more stages.

[0071] When the ejection energy of the inkjet head 16 is increased as in the above embodiment, not only when the number of ink drops is increased but also when the magnitude and waveform of the driving voltage are controlled, the ink droplets become larger than when a normal driving voltage is used, resulting in a higher density printed image. Therefore, in this embodiment, the original document image data is diluted for the printed image printed by the inkjet head 16 with increased ejection energy, so that the density of the final printed image becomes the same as when a normal driving voltage is used.

[0072] Specifically, the control unit 50 includes a document receiving unit 51 and a density conversion unit 52 as shown in FIG.

[0073] The document receiving unit 51 receives document image data to be printed. The document image data may be, for example, RGB image data generated and output by a computer or RGB image data photoelectrically read by a scanner.

[0074] The density conversion unit 52 performs density conversion processing on the document image data received by the document receiving unit 51. Specifically, the density conversion unit 52 identifies the range of the document image data that is to be printed by the upper inkjet head 16 with the increased ejection energy, and performs density conversion processing on the identified document image data to reduce the density.

[0075] Fig. 7A is a diagram showing an example of document image data before density conversion processing. It is assumed here that the document image data shown in Fig. 7A is printed by the upper inkjet head 16 with increased ejection energy.

[0076] Fig. 7B shows original image data that has undergone density conversion processing using the density conversion function shown in Fig. 7C, and Fig. 7D shows original image data that has undergone density conversion processing using the density conversion function shown in Fig. 7E.

[0077] The original image data of this embodiment is data with 256 gradations from 0 to 255, with 0 being the highest density data and 255 being white data. In the density conversion functions shown in FIGS. 7C and 7E, the horizontal axis represents input data and the vertical axis represents output data after density conversion processing. The density conversion function shown in FIG. 7C outputs 87 as output data when the input data is 0 (highest density), while the density conversion function shown in FIG. 7E outputs 159 as output data when the input data is 0 (highest density). Since larger numerical values ​​of the output data are closer to white, the density conversion function shown in FIG. 7E is a density conversion function that lightens the density more than the density conversion function shown in FIG. 7C. The density conversion processing is performed on each of the R, G, and B original image data.

[0078] The density conversion function shown in Figure 7C and the density conversion function shown in Figure 7E are used by changing them depending on the magnitude of the ejection energy. Also, when the ejection energy is changed in three stages, the density conversion function shown in Figure 7E is used for the original image data printed by the inkjet head 16 with the highest ejection energy, and the density conversion function shown in Figure 7C is used for the original image data printed by the inkjet head 16 with the next highest ejection energy.

[0079] Regarding the density conversion function according to the magnitude of the ejection energy, for example, the density value of the printed image when printed with a predetermined ejection energy is confirmed in advance by an experiment or the like using document image data that has been subjected to density conversion processing using a predetermined density conversion function, and a correspondence relationship between the density conversion function and the ejection energy that brings the density value of the printed image into an appropriate density range (for example, the density of the document image data before the density conversion processing) can be determined and set in advance. Then, when the ejection energy is changed as in this embodiment, the density conversion function according to the magnitude of the ejection energy can be determined based on the above-mentioned correspondence relationship that has been set in advance.

[0080] As described above, by performing density conversion processing on the document image data corresponding to the print image printed by the inkjet head 16 with increased ejection energy, the density of the final print image can be made the same as that in the case of a normal driving voltage.

[0081] The control unit 50 then performs color conversion processing on the RGB format document image data that has been subjected to density conversion processing in the density conversion unit 52, thereby generating CMYK format image data.

[0082] Next, the control unit 50 performs halftone processing on the image data for each of the C, M, Y, and K colors, converting the data into at least three values ​​to generate multi-value data. The multi-value data in this embodiment defines the number of ink drops ejected from one nozzle of the inkjet head to form one dot of the printed image, and is hereinafter referred to as ink drop data. Examples of halftone processing include halftone processing using a dither method and halftone processing using an error diffusion method.

[0083] The control unit 50 then generates drive voltages for controlling each inkjet head 16 of the C, M, Y, and K line heads 11-14 based on the C, M, Y, and K ink drop data, and performs processes such as controlling the magnitude of the drive voltage according to the ejection energy, controlling the waveform of the drive voltage, and increasing the number of ink drops, as described above. The control unit 50 outputs the generated drive voltages to the line heads 11-14 to drive each inkjet head 16 and perform printing.

[0084] The deviation in landing position due to the parabolic fall of ink droplets is noticeable when it occurs at the edge of a printed image, but if it occurs inside the edge of a printed image, it is less noticeable than at the edge.

[0085] Therefore, for example, when increasing the number of ink drops to increase the ejection energy, the control unit 50 may increase only the ejection energy of the nozzle when printing the edge portion of the print image, and may control the normal drive voltage when printing areas other than the edge portion of the print image.

[0086] FIG. 8 is a diagram illustrating an example of increasing the number of ink drops only in the edge portions of a print image. FIG. 8A shows original image data, and FIG. 8B is a diagram schematically illustrating ink drop data generated from the original image data shown in FIG. 8A. One circle in FIG. 8B represents three-drop data. FIG. 8C is a diagram schematically illustrating ink drop data when the number of ink drops is increased only in the edge portions of a print image. The darker circle in FIG. 8C represents five-drop data, where the number of ink drops is increased by two. As shown in FIG. 8C, only the ink drop data corresponding to the edge portions of the print image is set to five-drop data, and the ejection energy is increased.

[0087] In this way, by increasing only the ink drop data corresponding to the edge portions of the print image and increasing the ejection energy, it is possible to suppress deviation in the landing position and prevent an increase in the density of the interior of the print image. Note that, when increasing only the ink drop data corresponding to the edge portions of the print image as described above, the density conversion process that reduces the density of the document image data described above is not performed.

[0088] In addition, in this embodiment, the ejection energy is changed between the upper inkjet head 16 and the lower inkjet head 16, but the ejection energy may also be changed according to the distance measured by the distance measurement unit 15.

[0089] As described above, the distance measurement unit 15 measures the gap between each of the line heads 11-14 and the printing surface Ps of the printing medium P. The wider the gap between each of the line heads 11-14 and the printing surface Ps of the printing medium P, the longer the distance that ink droplets ejected from the inkjet head 16 travel to land on the printing surface Ps, and the greater the distance they fall parabolically, resulting in greater deviation in the landing position. In particular, if the printing medium P is a cardboard box, the gap is set wide because the cardboard box would be severely damaged if it were to collide with each of the line heads 11-14, so the deviation in the landing position becomes larger and more noticeable.

[0090] Therefore, the ejection energy of the inkjet head 16 is changed according to the distance measured by the distance measurement unit 15. In the present embodiment, as described above, the ejection energy between the upper inkjet head 16 and the lower inkjet head 16 of each of the line heads 11 to 14 is changed. In addition to this change in ejection energy, control of the ejection energy according to the distance measured by the distance measurement unit 15, which will be described below, is further performed.

[0091] FIG. 9 is a diagram showing a method of controlling the ejection energy according to the distance measured by the distance measurement unit 15. The control unit 50 controls the magnitude of the drive voltage and the number of ink droplets according to the distance measured by the distance measurement unit 15, and performs a density reduction process according to the control. Further, D0 to D3 shown in FIG. 9 are preset threshold values, and the relationship is D0 < D1 < D2 < D3.

[0092] As shown in FIG. 9, when the distance (gap amount) Dg measured by the distance measurement unit 15 is D0 or less, for example, the control unit 50 does not perform control of the ejection energy according to the distance because the influence of the distance between the printing medium P and each of the line heads 11 to 14 on the landing position of the ink droplets is small.

[0093] Further, when the gap amount Dg is such that D0 < Dg ≤ D1, the control unit 50 increases the drive voltage compared to the case where Dg = D0. Further, as the density conversion process according to the gap amount, the control unit 50 performs a density conversion process of small reduction. Note that small reduction, medium reduction, and large reduction mean the degree of reducing the density in the density conversion process. Small reduction has the smallest degree of reducing the density, large reduction has the largest degree of reducing the density, and medium reduction is between small reduction and large reduction.

[0094] Further, when the gap amount Dg is such that D1 < Dg ≤ D2, the control unit 50 increases the drive voltage in the same manner as when D0 < Dg ≤ D1, and increases the number of ink droplets by one drop. Further, as the density conversion process according to the gap amount, the control unit 50 performs a density reduction process of medium reduction.

[0095] Further, when the gap amount Dg satisfies D2 < Dg ≦ D3, the control unit 50 increases the drive voltage in the same manner as when D0 < Dg ≦ D1, and increases the number of ink drops by two drops. Further, as the density conversion process according to the gap amount, the control unit 50 performs a density reduction process of a large reduction.

[0096] By controlling the ejection energy according to the distance measured by the distance measurement unit 15 as described above, it is possible to suppress the landing position deviation due to the gap between each of the line heads 11 to 14 and the printing surface Ps of the printing medium P.

[0097] Note that the control of the ejection energy according to the gap amount described above may not be performed by the user's selection. That is, the control unit 50 may receive a setting input by the user as to whether to perform the control of the ejection energy according to the gap amount, and switch the presence or absence of the control of the ejection energy according to the gap amount according to the received content.

[0098] Further, the density reduction process according to the gap amount described above may not be performed by the user's selection. That is, the control unit 50 may receive a setting input by the user as to whether to perform the density reduction process according to the gap amount, and switch the presence or absence of the density reduction process according to the gap amount according to the received content.

[0099] Note that the present invention is not limited to the above-described embodiment, and the components can be modified and embodied without departing from the gist thereof at the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of components disclosed in the above-described embodiment. For example, all the components shown in the embodiment may be appropriately combined. Needless to say, various modifications and applications are possible within the scope not departing from the gist of the invention.

[0100] Regarding the present invention, the following supplementary notes are further disclosed. (Supplementary Note)

[0101] In the print control device of the present invention, the control unit can increase the ejection energy by increasing the number of droplets ejected from the nozzles.

[0102] In the print control device of the present invention, the control unit can increase the ejection energy by controlling the drive voltage supplied to the head unit.

[0103] In the printing control device of the present invention, the control unit accepts setting input as to whether or not to suppress ink mist when increasing ejection energy by controlling the waveform of the driving voltage supplied to the head unit, and if the setting input is to suppress ink mist, the waveform of the driving voltage is not controlled, and if the setting input is not to suppress ink mist, the waveform of the driving voltage is controlled.

[0104] The printing control device of the present invention can be equipped with a manuscript acceptance unit that accepts manuscript image data to be printed, and a density conversion unit that performs density conversion processing on the manuscript image data accepted by the manuscript acceptance unit in accordance with control of ejection energy.

[0105] In the print control device of the present invention, the control unit can increase the ejection energy only when ejecting droplets onto the edge portion of the print image.

[0106] The print control device of the present invention can be provided with a distance measurement unit that measures the distance between the head unit and the printing medium, and the control unit can control the ejection energy according to the distance measured by the distance measurement unit. The printing control method of the present invention is a printing control method that performs printing by ejecting droplets from each nozzle of a head unit in which multiple nozzles that eject droplets are arranged vertically, and ejects droplets by increasing the ejection energy of nozzles located vertically above compared to the ejection energy of nozzles located vertically below. [Explanation of symbols]

[0107] 1 Inkjet printing device 2 Transport unit 3 Support stand 4 Conveyor belt section 5 Pressure application section 10 Head Unit 11~14 Line Head 15 Distance measurement unit 16 Inkjet head 20 Ink circulation section 21 Pressurized Tank 22 Distributor 23 Collector 24 Negative pressure tank 25 Ink pump 26 Ink temperature adjustment unit 27 Ink temperature sensor 28~30 Ink circulation pipe 31 Air Layer 36 Air Layer 40 Ink supply unit 41 Heater 42 Heater temperature sensor 43 Heat sink 44 Cooling fan 46 Ink Cartridges 47 Ink supply valve 48 Ink supply pipe 50 control section 51 Manuscript Reception Department 52 Density conversion section 58 Pressurized connecting pipe 59 Negative pressure communicating pipe P Print media Ps printing side V1 First voltage V2 Second voltage V3 Third voltage

Claims

1. A manuscript receiving unit that receives manuscript image data to be printed; a head unit in which a plurality of nozzles are arranged in a vertical direction to eject droplets according to the document image data; a control unit that controls ejection energy when droplets are ejected from each of the nozzles, the control unit increases the ejection energy of a nozzle positioned vertically above the nozzle positioned vertically below the nozzle, and a print control device including a density conversion unit that performs density conversion processing to reduce the density of document image data corresponding to a printing area of ​​the nozzles positioned vertically above the print control device;

2. The print control device according to claim 1 , wherein the control unit increases the ejection energy by increasing the number of droplets ejected from the nozzles.

3. 3. The print control device according to claim 1, wherein the control unit increases the ejection energy by controlling a drive voltage supplied to the head unit.

4. A head unit in which a plurality of nozzles for ejecting droplets are arranged in a vertical direction; a control unit that controls ejection energy when droplets are ejected from each of the nozzles, the control unit increases the ejection energy of a nozzle positioned vertically above the nozzle positioned vertically below the nozzle, and A printing control device that accepts setting input for whether or not to suppress ink mist when the ejection energy is increased by controlling the waveform of the driving voltage supplied to the head unit, and if the setting input for suppressing ink mist is made, does not control the waveform of the driving voltage, and if the setting input for suppressing ink mist is not made, controls the waveform of the driving voltage.

5. A head unit in which a plurality of nozzles for ejecting droplets are arranged in a vertical direction; a control unit that controls ejection energy when droplets are ejected from each of the nozzles, A printing control device in which, when the control unit increases the ejection energy of a nozzle located vertically above it compared to the ejection energy of a nozzle located vertically below it, the control unit increases the ejection energy only when ejecting droplets into the printing area of ​​the nozzle located vertically above it, at the edge of the printed image.

6. a distance measuring unit that measures the distance between the head unit and the print medium; The print control device according to claim 1 , wherein the control unit controls the ejection energy in accordance with the distance measured by the distance measurement unit.

7. A printing control method for receiving original image data to be printed, and printing by ejecting droplets from each nozzle of a head unit having a plurality of nozzles arranged vertically, the nozzles ejecting droplets corresponding to the original image data, comprising: The ejection energy of a nozzle positioned vertically above is made larger than the ejection energy of a nozzle positioned vertically below, A print control method for performing density conversion processing to reduce density on document image data corresponding to a printing area of ​​the nozzles positioned vertically above.

8. A printing control method for printing by ejecting droplets from each nozzle of a head unit in which multiple nozzles for ejecting droplets are arranged in a vertical direction, comprising: The ejection energy of a nozzle positioned vertically above is made larger than the ejection energy of a nozzle positioned vertically below, A printing control method that, when increasing the ejection energy by controlling the waveform of the drive voltage supplied to the head section, accepts a setting input as to whether or not to suppress ink mist, and if the setting input is to suppress ink mist, does not control the waveform of the drive voltage, and if the setting input is not to suppress ink mist, controls the waveform of the drive voltage.

9. A printing control method for printing by ejecting droplets from each nozzle of a head unit in which multiple nozzles for ejecting droplets are arranged in a vertical direction, comprising: A printing control method in which, when the ejection energy of a nozzle located vertically above is made greater than the ejection energy of a nozzle located vertically below, the ejection energy is increased only when droplets are ejected into the printing area of ​​the nozzle located vertically above at the edge of a printed image.

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