Droplet discharge device, droplet discharge method, and droplet discharge program

Abstract

To provide a liquid droplet discharge device, a liquid droplet discharge method and a liquid droplet discharge program capable of making it difficult to cause a discharge failure in a nozzle for discharging ink of a special color.SOLUTION: The droplet discharge device includes a discharge head including a first nozzle for discharging a first liquid to a print medium and a second nozzle for discharging a second liquid different from the first liquid to the print medium, a storage unit, and a control device, wherein the storage unit stores in advance a first lookup table for converting image data into first print data using only the first liquid and a second lookup table for converting image data into second print data using both the first liquid and the second liquid, the controller is configured to execute a process of discharging the liquid droplets onto the medium to be printed based on the first look-up table or the second look-up table in accordance with the dryness degree of the second nozzle.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] Conventionally, there is known a printing device that includes a first nozzle that prints an image on a print medium based on image data using ink of a predetermined base color, and a second nozzle that prints an image on a print medium based on image data using ink of a special color different from the base color (Patent Document 1). Examples of base color inks include cyan ink, yellow ink, magenta ink, and black ink. Furthermore, special color inks are inks of colors different from the base color inks, such as red ink, green ink, or blue ink. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-111540 Summary of the Invention [Problem to be solved by the invention]

[0004] However, spot color inks tend to be used relatively infrequently, and as a result, nozzles that eject spot color inks tend to dry out relatively easily, which poses a problem of ejection failure occurring easily.

[0005] Therefore, an object of the present disclosure is to provide a droplet ejection device, a droplet ejection method, and a droplet ejection program that can reduce the likelihood of ejection defects occurring in nozzles that eject ink of a particular color. [Means for solving the problem]

[0006] The droplet ejection device disclosed herein comprises an ejection head having a first nozzle for ejecting a first liquid onto a printing medium and a second nozzle for ejecting a second liquid different from the first liquid onto the printing medium, a memory unit, and a control device, wherein the memory unit pre-stores a first lookup table for converting image data into first print data using only the first liquid, and a second lookup table which is a lookup table for converting the image data into second print data using both the first liquid and the second liquid, and the control device executes a process of ejecting droplets onto the printing medium based on the first lookup table or the second lookup table depending on the degree of dryness of the second nozzle.

[0007] According to the present disclosure, a second lookup table for converting the second print data is stored in advance in a storage unit. Then, droplets are ejected onto the print medium based on the second lookup table in accordance with the dryness of the second nozzles. In this way, the second liquid is ejected onto the print medium in areas where the second liquid does not actually need to be ejected, superimposed on the first liquid, based on the second lookup table, thereby realizing regular ejection of the second liquid by the second nozzles. This prevents the second nozzles from drying out, thereby making it less likely for ejection defects to occur. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a droplet ejection device, a droplet ejection method, and a droplet ejection program that can make ejection defects less likely to occur in nozzles that eject ink of a particular color. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view showing the configuration of a droplet ejection device according to an embodiment. [Figure 2] FIG. 2 is a diagram showing nozzle rows in each ejection head in FIG. [Figure 3] 2 is a block diagram showing the configuration of a control system of the droplet ejection device of FIG. 1. FIG. [Figure 4] FIG. 10 is a diagram illustrating an example of a first lookup table. [Figure 5] FIG. 5A is a diagram showing an example of a second lookup table including a first spot color ink, and FIG. 5B is a diagram showing an example of a second lookup table including a second spot color ink. [Figure 6] FIG. 10 is a diagram showing an example of a second lookup table in which a certain color difference occurs. [Figure 7] 10 is a flowchart showing an example of a process flow in the droplet ejection device. [Figure 8] 10 is a flowchart showing an example of a process flow in the droplet ejection device. [Figure 9] FIG. 9A is a diagram showing an original image, FIG. 9B is a diagram showing a frequency map, and FIG. 9C is a diagram showing a color difference map. [Figure 10] 10A and 10B are diagrams for explaining the relationship between the allowable amount of color difference and frequency components. 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. Note that, hereinafter, identical or corresponding elements will be designated by the same reference numerals throughout the drawings, and duplicated descriptions will be omitted unless otherwise noted.

[0011] FIG. 1 is a plan view showing the configuration of a droplet ejection device 100 according to one embodiment. FIG. 2 is a diagram showing a nozzle row NL in the ejection head 20 of FIG. 1. FIG. 3 is a block diagram showing the configuration of a control system for the droplet ejection device 100 of FIG. 1. In FIGS. 1 and 2, mutually perpendicular directions are designated as a first direction Df and a second direction Ds. In this embodiment, for example, the first direction Df is the transport direction of the print medium W, and the second direction Ds is the movement direction of a carriage 41, which will be described later. In the following description, Ds will be referred to as the movement direction, and Df will be referred to as the transport direction. However, the above directions are merely examples and are not limiting.

[0012] The droplet ejection device 100 is, for example, a serial head type inkjet printer. The droplet ejection device 100 alternately repeats a pass process in which an inkjet head (hereinafter referred to as a head) 20 is moved in a movement direction Ds to eject ink droplets, and a transport process in which a print medium W is transported in a transport direction Df, based on print data. This causes a predetermined image to be printed on the print medium W. Examples of the print medium W include fabric and sheet-fed film.

[0013] The droplet ejection device 100 includes an ejection head unit HU having a plurality of ejection heads 20, a platen 11, a plurality of tanks 12, a transport device 30, a moving device 40, a receiving section 54, and a housing 101.

[0014] The ejection heads 20 print an image on the print medium W using predetermined ink droplets based on print data. Examples of the multiple ejection heads 20 included in the ejection head unit HU include a first inkjet head (hereinafter referred to as the first ejection head) 21, a second inkjet head (hereinafter referred to as the second ejection head) 22, and a third inkjet head (hereinafter referred to as the third ejection head) 23. These ejection heads are arranged side by side in the order of the first ejection head 21, the second ejection head 22, and the third ejection head 23 from one side of the transport direction Df. Hereinafter, when referring to the ejection head 20, the ejection head 20 includes the first ejection head 21, the second ejection head 22, and the third ejection head 23. In this embodiment, for example, the first ejection head 21 prints on the print medium W using white ink, the second ejection head 22 prints on the print medium W using special color ink, and the third ejection head 23 prints on the print medium W using color ink. However, the above-mentioned colors of ink ejected by each ejection head 20 are merely examples and can be changed as appropriate.

[0015] The platen 11 has a flat upper surface and defines the distance between the print medium W placed on that upper surface and the nozzle surface of the ejection head 20 provided opposite it. The platen 11 moves back and forth in the transport direction Df. As a result, the print medium W supported by the platen 11 moves back and forth in the transport direction Df.

[0016] Ink is stored in each tank 12. The tanks 12 are connected to the ejection head 20 via a flow path described below to supply ink to the ejection head 20. The tanks 12 are containers for storing ink. The number of tanks 12 is equal to or greater than the number of types of ink. For example, the tanks 12 include four first tanks 12a each storing one of four types of color ink, one or more second tanks 12b storing white ink, and one or more third tanks 12c storing spot color inks. Examples of color inks include cyan ink, magenta ink, yellow ink, and black ink. Examples of spot color inks include orange ink, green ink, and red ink.

[0017] The first tank 12a is connected to the third ejection head 23 via a first flow path 13a. The color ink is supplied from the first tank 12a to the third ejection head 23 via the first flow path 13a. The second tank 12b is connected to the first ejection head 21 via a second flow path 13b. The white ink is supplied from the second tank 12b to the first ejection head 21 via the second flow path 13b. The third tank 12c is connected to the second ejection head 22 via a third flow path 13c. The special color ink is supplied from the third tank 12c to the second ejection head 22 via the third flow path 13c. In this embodiment, the color ink corresponds to the first liquid, and the special color ink corresponds to the second liquid that is different from the first liquid.

[0018] The transport device 30 has a drive unit including, for example, a ball screw or rack and pinion (not shown), and a transport motor 32. The drive unit is connected to the transport motor 32. The rotation of the transport motor 32 moves the platen 11 in the transport direction Df, transporting the print medium W in the transport direction Df.

[0019] The movement device 40 has a carriage 41, two guide rails 42, a movement motor 43, and an endless belt 44. The two guide rails 42 extend in the movement direction Ds above the platen 11 so as to sandwich the carriage 41 between them in the transport direction Df. The carriage 41 holds each ejection head 20. The carriage 41 is supported by the two guide rails 42 so as to be movable in the movement direction Ds. The endless belt 44 extends in the movement direction Ds and is attached to the carriage 41, and is attached to the movement motor 43 via a pulley 45. The movement motor 43 rotates to operate the endless belt 44, and the carriage 41 moves back and forth along the guide rails 42 in the movement direction Ds. As a result, each ejection head 20 moves back and forth in the movement direction Ds by the carriage 41.

[0020] The receiving portion 54 is disposed at one end of the guide rail 42 in the movement direction Ds so as to overlap with a movement region of the carriage 41 along the movement direction Ds. The receiving portion 54 receives ink droplets ejected from the ejection heads 20 during a flushing process performed when the carriage 41 positions each ejection head 20 above the receiving portion 54. More specifically, the receiving portion 54 receives ink droplets of white ink ejected from the nozzles 121 of the first ejection head 21, ink droplets of spot color ink ejected from the nozzles 221 of the second ejection head 22, and ink droplets of color ink ejected from the nozzles 321 of the third ejection head 23. When multiple flushing processes are required, the control device 50 executes a first flushing process in which ink droplets of each color are ejected from the nozzles 121, 221, and 321 onto the receiving portion 54, and a second flushing process in which ink droplets of each color are ejected from the nozzles 121, 221, and 321 onto the receiving portion 54 after the first flushing process. Each ink droplet received by the receiver 54 is drained through a pipe (not shown) connected to the receiver 54 .

[0021] Next, FIG. 2 shows the arrangement of the nozzle rows NL in the first ejection head 21. As shown in FIG. 2, the first ejection head 21 has a plurality of nozzle rows NL, each of which is configured by arranging a plurality of nozzles 121 at predetermined intervals in a predetermined nozzle row direction Dn. That is, each nozzle row NL extends in the nozzle row direction Dn. The nozzle row direction Dn is, for example, parallel to the transport direction Df. The nozzle rows NL are arranged at predetermined intervals in the movement direction Ds. The arrangement of the nozzle rows NL in the second ejection head 22 and the third ejection head 23 can be similar to the arrangement of the nozzle rows NL in the first ejection head 21. Note that in FIG. 2, the nozzles constituting the nozzle row NL in the second ejection head 22 are designated 221, and the nozzles constituting the nozzle row NL in the third ejection head 23 are designated 321. In this embodiment, the nozzle 321 corresponds to the first nozzle for ejecting the first liquid onto the print medium W, and the nozzle 221 corresponds to the second nozzle for ejecting the second liquid onto the print medium W.

[0022] 3, the ejection head 20 has a plurality of drive elements 25. The drive elements 25 are piezoelectric elements, heat generating elements, electrostatic actuators, or the like, and apply pressure to ink droplets to eject the ink droplets from the nozzles.

[0023] The droplet ejection device 100 includes a display device 14, an input device 15, a temperature measurement unit 16, a humidity measurement unit 17, and a control device 50. The control device 50 corresponds to a computer and includes an interface 51, a calculation unit 52, and a memory unit 53. The interface 51 receives various data such as image data from an external device 200 such as a computer, a camera, a communication network, a display, a reading device, or a printer. The image data is raster data representing an image to be printed on a print medium W, and includes information on printing conditions such as the type of print medium W. The control device 50 may be configured as a single device, or may be configured as multiple devices distributed in a central location that work together to operate the droplet ejection device 100.

[0024] The storage unit 53 is a memory accessible from the calculation unit 52 and includes RAM and ROM. The RAM temporarily stores various data, such as image data received from the external device 200 and data converted by the calculation unit 52. The ROM stores printing programs and predetermined data for various data processing operations. The storage unit 53 stores in advance a first lookup table for converting image data into first print data that uses only color inks, and a second lookup table for converting image data into second print data that uses both color inks and spot color inks. The first and second lookup tables will be described in detail later. The droplet ejection program executed by the droplet ejection device 100 of this embodiment may be stored in the storage unit 53 via a reading device from a storage medium, such as a CD-ROM, that can be read by the reading device, or may be downloaded from the Internet or the like and stored in the storage unit 53.

[0025] The calculation unit 52 includes at least one circuit, such as a processor such as a CPU and an integrated circuit such as an ASIC. The calculation unit 52 controls each unit by executing a droplet ejection program, and performs various operations such as printing.

[0026] The display device 14 is, for example, a display, and displays an image related to the image data in accordance with instructions from the control device 50. The input device 15 is, for example, a button, and is operated by a user. The user can use the input device 15 to give instructions to the control device 50 to allow a color difference (described below) that is not zero. The input device 15 may be a touch panel integrated with the display device 14.

[0027] The temperature measurement unit 16 is, for example, a thermometer, and measures the temperature inside the housing 101 of the droplet discharge device 100. The humidity measurement unit 17 is, for example, a hygrometer, and measures the humidity inside the housing 101 of the droplet discharge device 100. Information about the temperature measured by the temperature measurement unit 16 and information about the humidity measured by the humidity measurement unit 17 are sent to the control device 50.

[0028] The control device 50 receives the temperature information transmitted from the temperature measurement unit 16 and also receives the humidity information transmitted from the humidity measurement unit 17 .

[0029] The control device 50 is electrically connected to the transport motor 32 of the transport device 30 via the transport drive circuit 33, and controls the rotational operation of the transport motor 32. This controls the transport of the print medium W by the transport device 30. The control device 50 is also electrically connected to the movement motor 43 of the movement device 40 via a movement drive circuit 46, and controls the drive of the movement motor 43. This controls the movement of the ejection head 20 by the movement device 40. The control device 50 is also electrically connected to the drive element 25 via the ejection head drive circuit 26. The control device 50 outputs a control signal for the drive element 25 to the ejection head drive circuit 26, and the head drive circuit 26 generates a drive signal based on the control signal and outputs it to the drive element 25. The drive element 25 is driven in accordance with the drive signal, causing ink droplets to be ejected from the nozzles.

[0030] In the droplet ejection device 100 having the above configuration, the control device 50 acquires image data and executes a printing operation based on the image data. In this case, the control device 50 ejects ink droplets from the ejection head 20 onto the print medium W while moving the ejection head 20 in the movement direction Ds in the printing pass. The control device 50 then transports the print medium W in the transport direction Df. In this way, the droplet ejection device 100 alternates between printing passes and transport operations. As a result, an image corresponding to the image data is printed on the print medium W.

[0031] Next, the first lookup table and the second lookup table will be described. Fig. 4 is a diagram showing an example of the first lookup table LUT1. Fig. 5A is a diagram showing an example of the second lookup table LUT2 that includes orange ink as the first spot color ink, and Fig. 5B is a diagram showing an example of the second lookup table LUT3 that includes green ink as the second spot color ink. Fig. 6 is a diagram showing an example of the second lookup table LUT4 that produces a certain color difference.

[0032] The control device 50 executes a process of ejecting ink droplets onto the print medium W based on the first lookup table or the second lookup table, depending on the dryness of the nozzle 221 corresponding to the second nozzle. That is, in this embodiment, the control device 50 generates first print data that uses only color ink based on the first lookup table, or generates second print data that uses both color ink and spot color ink based on the second lookup table, depending on the dryness of the nozzle 221.

[0033] The control device 50 determines the dryness level of the nozzle 221 based on any one of the following criteria: temperature measured by the temperature measuring unit 16, humidity measured by the humidity measuring unit 17, the type of spot color ink, a combination of the temperature and the humidity, a combination of the temperature and the type of spot color ink, a combination of the humidity and the type of spot color ink, and a combination of the temperature, the humidity, and the type of spot color ink. In this case, when determining the dryness level of the nozzle 221 based on temperature alone, humidity alone, or temperature and humidity, the first lookup table or the second lookup table to use may be determined by comparison with a predetermined threshold value. Furthermore, when determining the dryness level of the nozzle 221 based on criteria including the color of the spot color ink, a weight may be set in advance depending on the color of the spot color ink. In this case, the first lookup table or the second lookup table to use may be determined based on the weight, or, if the criteria include temperature or humidity, based on a comparison between the weight and the threshold value.

[0034] 4, the first lookup table LUT1 is a color conversion table that is used when converting the RGB values ​​of a certain color in image data into CMYK values ​​(process color values) of print data. In this way, the first lookup table LUT1 converts RGB values ​​into CMYK values, but not into component values ​​of spot color inks.

[0035] In contrast, as shown in Fig. 5A, the second lookup table LUT2 is a color conversion table that is used when converting the RGB values ​​of a certain color in the image data into both CMYK values ​​in the print data and the component values ​​of orange ink as the first spot color ink. Similarly, as shown in Fig. 5B, the second lookup table LUT3 is a color conversion table that is used when converting the RGB values ​​of a certain color in the image data into both CMYK values ​​in the print data and the component values ​​of green ink as the second spot color ink. In this way, the second lookup tables LUT2 and LUT3 convert RGB values ​​into both CMYK values ​​and the component values ​​of a specific spot color ink, and are different from the first lookup table LUT1, which converts RGB values ​​into only CMYK values.

[0036] The second lookup table LUT2 in Fig. 5A and the second lookup table LUT3 in Fig. 5B show examples in which the color difference between the target color (i.e., input color) and the output color after conversion into both CMYK values ​​and component values ​​of specified spot color inks is zero. However, there are cases in which a color difference between the target color and the output color occurs due to factors such as the type of ink and the type of ejection head 20.

[0037] On the other hand, there are cases where the color difference between the target color and the output color after conversion into both CMYK values ​​and the component values ​​of the specified spot color ink is not zero. As shown in FIG. 6, when converting RGB values ​​into both CMYK values ​​and the component values ​​of the specified spot color ink, the second lookup table LUT4 is such that the color difference (ΔE) between the target color and the output color after conversion into both CMYK values ​​and the component values ​​of the specified spot color ink is not zero. Therefore, when color conversion is performed based on the second lookup table LUT4, a certain color difference occurs. Note that the second lookup table LUT4 stores values ​​related to the color difference calculated in advance by color measurement using a colorimeter.

[0038] Even when a color difference occurs between the target color and the output color after conversion into both CMYK values ​​and the component values ​​of the specified spot color inks, as described above, the user can use the input device 15 to instruct the control device 50 to allow the color difference to be non-zero. That is, the user can instruct the control device 50 to allow the color difference to be non-zero between the first color, which is the color output based on the image data of the first print data (print data using only color inks), and the second color, which is the color output based on the second print data (print data using both color inks and spot color inks). In this case, when the user issues the instruction using the input device 15, the control device 50 executes a reception process to accept the instruction. In this way, if the user has issued an instruction to allow the color difference to be non-zero, the control device 50 references the second lookup table LUT4. On the other hand, if the user has not issued an instruction to allow the color difference to be non-zero, i.e., if the user does not want to print with a color difference, the control device 50 references the first lookup table LUT1 for converting to first print data that does not use spot color inks.

[0039] Next, when referring to the second lookup table LUT4, the control device 50 executes a process to acquire the color difference between the first color, which is the color output based on the first print data, and the second color, which is the color output based on the second print data. In the example of FIG. 6, for example, a color difference of 5 is acquired for color 3. Note that acquiring the color difference by the control device 50 means reading out a value related to the color difference from the second lookup table LUT4. In this case, in the example of FIG. 6, the control device 50 reads out, for example, a color difference of 5 for color 3.

[0040] Next, the control device 50 executes a process to determine whether the acquired color difference is equal to or less than a predetermined threshold. In this case, the control device 50 determines that the acquired color difference is equal to or less than the threshold. Therefore, the control device 50 generates second print data by converting the image data based on the second lookup table LUT4. Then, based on the second print data, the control device 50 ejects ink droplets of color ink from the nozzle 321 onto the print medium W, and also ejects ink droplets of spot color ink from the nozzle 221 onto the print medium W. Note that the threshold may be set to, for example, 5, which is a value that can be perceived as a general visual characteristic, or may be set to a desired value by the user.

[0041] On the other hand, if the color difference is not equal to or less than the threshold, for example, if the color difference exceeds 5, the control device 50 generates first print data by converting the image data based on the first lookup table LUT1. Then, the control device 50 ejects ink droplets of color ink from the nozzles 321 onto the print medium W based on the first print data. In other words, the control device 50 refers to the first lookup table LUT1 and ejects ink droplets of color ink from the nozzles 321 onto the print medium W based on the first lookup table LUT1.

[0042] Unlike the above-described case in which the user has given an instruction to allow the color difference to be non-zero, if such an instruction has not been given, the control device 50 executes the following process. Specifically, the control device 50 determines whether an area containing high-frequency components is present in an image based on image data, the area being equal to or greater than a predetermined area. In this case, the control device 50 performs frequency conversion processing on the image data to obtain a frequency map in which the intensities of two-dimensional spatial frequency components (specifically, high-frequency components, mid-frequency components, low-frequency components, etc.) are extracted. The control device 50 then determines whether an area containing high-frequency components is present in the frequency map, the area being equal to or greater than a predetermined area. Note that instead of a frequency map, a spectrum indicating the intensities of two-dimensional spatial frequency components may be obtained. Examples of the frequency conversion processing include well-known processes such as fast Fourier transform (FFT) and edge detection.

[0043] If the frequency map includes an area containing high frequency components that is equal to or larger than a predetermined area, the control device 50 refers to the second lookup table LUT4. On the other hand, if the frequency map includes no area containing high frequency components that is equal to or larger than a predetermined area, the control device 50 refers to the first lookup table LUT1.

[0044] 7 is a flowchart showing an example of the flow of processing in the droplet ejection device 100. The flow of processing performed by the control device 50 will now be described with reference to the flowchart shown in FIG.

[0045] As shown in FIG. 7, first, the control device 50 performs a frequency conversion process on the image data to obtain a frequency map in which the intensities of two-dimensional spatial frequency components (specifically, high-frequency components, mid-frequency components, and low-frequency components) are extracted (step S1).

[0046] Next, the control device 50 executes a flushing process before starting printing (step S2). In this case, the control device 50 moves each ejection head 20 to a position above the corresponding receiving portion 54 using the carriage 41, and in this state, ejects ink droplets from the nozzles 121, 221, and 321 toward the receiving portion 54.

[0047] Thereafter, the control device 50 starts printing in the first pass by ejecting ink droplets of color ink from the third ejection head 23 (step S3). In this case, the control device 50 refers to the first lookup table LUT1 to convert the image data (more specifically, the data of the part of the image data that corresponds to the first pass) into first print data, and ejects ink droplets from the third ejection head 23 based on the first print data.

[0048] Next, the control device 50 acquires the temperature measured by the temperature measurement unit 16 and determines whether the temperature is equal to or higher than a predetermined temperature (step S4). If the temperature is equal to or higher than the predetermined temperature (Yes in step S4), it can be assumed that the nozzle 221 is highly dry, and therefore the control device 50 turns on a flag for a flushing process to be performed in a subsequent process (step S5).

[0049] On the other hand, if the temperature is not equal to or higher than the predetermined temperature (No in step S4), the control device 50 then acquires the humidity measured by the humidity measuring unit 17 and determines whether the humidity is equal to or higher than the predetermined humidity (step S6). If the humidity is not equal to or higher than the predetermined humidity (No in step S6), it can be assumed that the nozzles 221 are very dry, and the control device 50 turns on a flag for a flushing process to be performed in a subsequent process (step S5). On the other hand, if the humidity is equal to or higher than the predetermined humidity (Yes in step S6), the control device 50 continues printing for the first pass and determines whether printing for the first pass is complete (step S10).

[0050] Next, the control device 50 determines whether an instruction has been received from the user to allow a color difference between a first color, which is a color output based on the first print data (print data using only color inks), and a second color, which is a color output based on the second print data (print data using both color inks and spot color inks), to be non-zero (step S7). If the instruction has been received (Yes in step S7), the control device 50 continues printing for the first pass and determines whether printing for the first pass has been completed (step S8).

[0051] On the other hand, if the instruction has not been received (No in step S7), the control device 50 determines whether or not a region containing high-frequency components of a predetermined area or more exists in the portion of the image based on the image data corresponding to the next printing pass (e.g., second pass) (step S9). If the region of a predetermined area or more exists (Yes in step S9), the control device 50 executes the process of step S8. On the other hand, if the region of a predetermined area or more does not exist (No in step S9), the control device 50 executes the process of step S10.

[0052] Thereafter, when printing for the first pass is completed (Yes in step S8), the control device 50 refers to the second lookup table LUT4 to generate second print data by converting the part of the image data corresponding to the next printing pass (e.g., the second pass) (step S11).

[0053] Next, the control device 50 determines whether the color difference in the second lookup table LUT4 is equal to or less than a threshold value (step S12). If the color difference is equal to or less than the threshold value (Yes in step S12), the control device 50 executes the process of step S13 described below. On the other hand, if the color difference is not equal to or less than the threshold value (No in step S12) and if printing for the first pass is completed (Yes in step S10), the control device 50 refers to the first lookup table LUT1 to generate first print data by converting the data of the portion of the image data corresponding to the next printing pass (e.g., the second pass) (step S14). Then, the control device 50 executes the process of step S13 described below.

[0054] In the process of step S13, the control device 50 determines whether or not there is a next printing pass. If there is no next printing pass (No in step S13), the control device 50 ends the printing process.

[0055] On the other hand, if there is a next printing pass (Yes in step S13), the control device 50 causes the platen 11 to transport the print medium W in the transport direction Df by one pass (step S15).The control device 50 then generates print data corresponding to the next printing pass based on the lookup table referenced in the above process, either the first lookup table LUT1 or the second lookup table LUT4, and executes printing based on the print data (step S16).

[0056] Next, the control device 50 determines whether or not the flag for the flushing process is on in the process of step S5 (step S17). If the flag for the flushing process is on (Yes in step S17), the control device 50 executes the flushing process (step S18). After the process of step S18, and if the flag for the flushing process is not on (No in step S17), the control device 50 returns to the process of step S4 and repeats the subsequent processes.

[0057] Next, a description will be given of another example of the flow of processing in the droplet ejection device 100. Figure 8 is a flowchart showing another example of the flow of processing in the droplet ejection device 100.

[0058] As shown in FIG. 8, first, the control device 50 performs a frequency conversion process on the image data to obtain a frequency map in which the intensities of two-dimensional spatial frequency components (specifically, high-frequency components, medium-frequency components, and low-frequency components) are extracted (step S21).

[0059] Next, the control device 50 executes a flushing process before starting printing (step S22). In this case, the control device 50 moves each ejection head 20 to a position above the corresponding receiving portion 54 using the carriage 41, and in this state, ejects ink droplets from the nozzles 121, 221, and 321 toward the receiving portion 54.

[0060] Thereafter, the control device 50 starts printing in the first pass by ejecting ink droplets of color ink from the third ejection head 23 (step S23). In this case, the control device 50 refers to the first lookup table LUT1 to convert the image data (more specifically, the data of the part of the image data that corresponds to the first pass) into first print data, and ejects ink droplets from the third ejection head 23 based on the first print data.

[0061] Next, the control device 50 determines whether a predetermined time has elapsed since the flushing process was last performed (step S24). If the predetermined time has elapsed since the flushing process was last performed (Yes in step S24), it can be assumed that the nozzle 221 is highly dry, and the control device 50 turns on a flag for a flushing process to be performed in a subsequent process (step S25). In other words, the control device 50 determines the dryness of the nozzle 221 based on the time elapsed since the flushing process was last performed.

[0062] On the other hand, if a predetermined time has not elapsed since the last flushing process was executed (No in step S24), the control device 50 then determines whether a predetermined time has elapsed since the last ink droplet was ejected from the nozzle 221 (step S26). If a predetermined time has elapsed since the last ink droplet was ejected from the nozzle 221 (Yes in step S26), it can be assumed that the nozzle 221 is highly dry, and the control device 50 turns on a flag for a flushing process to be executed in a subsequent process (step S25). On the other hand, if a predetermined time has not elapsed since the last ink droplet was ejected from the nozzle 221 (No in step S26), the control device 50 continues printing for the first pass and determines whether printing for the first pass is complete (step S30).

[0063] Next, the control device 50 determines whether an instruction has been received from the user to allow a color difference between a first color, which is a color output based on the first print data (print data using only color inks), and a second color, which is a color output based on the second print data (print data using both color inks and spot color inks), to be non-zero (step S27). If the instruction has been received (Yes in step S27), the control device 50 continues printing for the first pass and determines whether printing for the first pass has been completed (step S28).

[0064] On the other hand, if the instruction has not been received (No in step S27), the control device 50 determines whether or not a region containing high-frequency components of a predetermined area or more exists in the portion of the image based on the image data corresponding to the next printing pass (e.g., second pass) (step S29). If the region of a predetermined area or more exists (Yes in step S29), the control device 50 executes the process of step S28. On the other hand, if the region of a predetermined area or more does not exist (No in step S29), the control device 50 executes the process of step S30.

[0065] Thereafter, when printing for the first pass is completed (Yes in step S28), the control device 50 refers to the second lookup table LUT4 to generate second print data by converting the part of the image data corresponding to the next printing pass (second pass, etc.) (step S31).

[0066] Next, the control device 50 determines whether the color difference in the second lookup table LUT4 is equal to or less than a threshold value (step S32). If the color difference is equal to or less than the threshold value (Yes in step S32), the control device 50 executes the process of step S33 described below. On the other hand, if the color difference is not equal to or less than the threshold value (No in step S32) and if printing for the first pass is completed (Yes in step S30), the control device 50 refers to the first lookup table LUT1 to generate first print data by converting the data of the portion of the image data corresponding to the next printing pass (e.g., the second pass) (step S34). Then, the control device 50 executes the process of step S33 described below.

[0067] In the process of step S33, the control device 50 determines whether or not there is a next printing pass. If there is no next printing pass (No in step S33), the control device 50 ends the printing process.

[0068] On the other hand, if there is a next printing pass (Yes in step S33), the control device 50 causes the platen 11 to transport the print medium W in the transport direction Df by one pass (step S35).The control device 50 then generates print data corresponding to the next printing pass based on the lookup table referenced in the above process, either the first lookup table LUT1 or the second lookup table LUT4, and executes printing based on the print data (step S36).

[0069] Next, the control device 50 determines whether or not the flag for the flushing process is on in the process of step S25 (step S37). If the flag for the flushing process is on (Yes in step S37), the control device 50 executes the flushing process (step S38). After the process of step S38, and if the flag for the flushing process is not on (No in step S37), the control device 50 returns to the process of step S24 and repeats the subsequent processes.

[0070] As described above, in the droplet ejection device 100 of this embodiment, the second lookup tables LUT2, LUT3, and LUT4 for converting image data into second print data using both color inks and spot color inks are stored in advance in the storage unit 53. Then, ink droplets of color inks are ejected from the nozzle 321 onto the print medium W based on the second lookup tables LUT2, LUT3, and LUT4 depending on the dryness level of the nozzle 221, and ink droplets of spot color ink are ejected from the nozzle 221 onto the print medium W. In this way, by ejecting the spot color ink onto the color inks in a layer based on the second lookup tables LUT2, LUT3, and LUT4 onto areas of the print medium W where the spot color ink does not actually need to be ejected, the nozzle 221 is able to periodically eject the spot color ink. This prevents the nozzle 221 from drying out, thereby making it less likely that ejection defects will occur.

[0071] Furthermore, in this embodiment, the dryness level of the nozzle 221 is determined based on any one of the following criteria: the temperature measured by the temperature measuring unit 16, the humidity measured by the humidity measuring unit 17, the type of spot color ink, a combination of the temperature and the humidity, a combination of the temperature and the type of spot color ink, a combination of the humidity and the type of spot color ink, and a combination of the temperature, the humidity, and the type of spot color ink. By using such criteria, the dryness level of the nozzle 221 can be determined appropriately.

[0072] Furthermore, in this embodiment, if the user has given an instruction to allow the color difference to be non-zero, the control device 50 refers to the second lookup tables LUT2, LUT3, and LUT4. In this way, based on the user's wishes, a printing process can be executed in which ink droplets of color ink are ejected from nozzle 321 onto the print medium W, and ink droplets of spot color ink are ejected from nozzle 221 onto the print medium W. This prevents the nozzle 221 from drying out.

[0073] Furthermore, in this embodiment, the control device 50 determines whether or not there is an area in the frequency map that includes high-frequency components that is equal to or larger than a predetermined area. If there is an area in the frequency map that includes high-frequency components that is equal to or larger than a predetermined area, the control device 50 references the second lookup table LUT4. If there is an area in the frequency map that includes high-frequency components that is equal to or larger than a predetermined area, color reproducibility will not be significantly reduced even if spot color ink is ejected into that area together with color ink. In such a case, a printing process is executed in which ink droplets of color ink are ejected from nozzle 321 onto the print medium W, and ink droplets of spot color ink are ejected from nozzle 221 onto the print medium W, thereby preventing drying at nozzle 221.

[0074] Furthermore, in this embodiment, if the color difference is not equal to or less than the threshold, the control device 50 generates first print data by converting the image data based on the first lookup table LUT1. Then, the control device 50 ejects ink droplets of color ink from the nozzle 321 onto the print medium W based on the first print data. In this case, even if the user has given an instruction to allow the color difference to be non-zero, if the color difference is not equal to or less than the threshold, a printing process is executed in which ink droplets of color ink are ejected from the nozzle 321 without ejecting ink droplets of spot color ink from the nozzle 221. This makes it possible to perform printing while placing importance on color reproducibility on the print medium W.

[0075] Furthermore, in this embodiment, the degree of dryness of the nozzle 221 is determined based on the time elapsed since the most recent flushing process or the time elapsed since the most recent ejection by the nozzle 221. This allows the degree of dryness of the nozzle 221 to be determined appropriately.

[0076] The present disclosure is not limited to the above-described embodiment, and modifications can be made without departing from the spirit of the present disclosure. For example, the following modifications are possible.

[0077] Fig. 9A is a diagram showing an original image, Fig. 9B is a diagram showing a frequency map, Fig. 9C is a diagram showing a color difference map, and Fig. 10 is a diagram for explaining the relationship between the allowable amount of color difference and frequency components.

[0078] The frequency map of FIG. 9B is obtained by the control device 50 performing a frequency conversion process on the image (original image) corresponding to the image data of FIG. 9A. In the frequency map of FIG. 9B, regions corresponding to high frequency components are indicated by "high," regions corresponding to mid-frequency components are indicated by "medium," and regions corresponding to low frequency components are indicated by "low." The color difference map of FIG. 9C indicates the color differences to be reproduced corresponding to each region of the frequency map of FIG. 9B. In the color difference map of FIG. 9C, regions with large color differences are indicated by "large," regions with small color differences are indicated by "small," and regions with intermediate color differences are indicated by "medium." FIG. 10 also shows the relationship between the allowable amount of color difference specified by the user and frequency components, and this relationship can be obtained using a predetermined table or calculation.

[0079] In this example, the control device 50 is configured to allow the user to specify the allowable color difference. Based on the solid line in FIG. 10 showing the relationship between the allowable color difference and frequency components, the control device 50 acquires the frequency components corresponding to the allowable color difference specified by the user. For example, if the user does not allow a large color difference (i.e., if the user allows a minimum amount of color difference), the control device 50 ejects a spot color ink with a small color difference in the second lookup table LUT4 to the high-frequency component area in the frequency map of FIG. 9B. On the other hand, if the user allows a large color difference, the control device 50 ejects a spot color ink with a large color difference in the second lookup table LUT4 to the low-frequency component area in the frequency map of FIG. 9B. The color difference threshold and frequency threshold can be adjusted as appropriate based on the allowable color difference specified by the user. The slope of the solid line in FIG. 10 showing the relationship between the allowable color difference and frequency components can be changed as appropriate, as shown by the dashed line.

[0080] In the above embodiment, the threshold value for color difference may be adjusted based on whether the object to be printed on the print medium W is, for example, a document or a photograph. For example, if the object to be printed on the print medium W is a document, the importance of color reproducibility is relatively low, so the threshold value may be increased.

[0081] In the above embodiment, the first discharge head 21, the second discharge head 22, and the third discharge head 23 are arranged in this order from one side of the transport direction Df, but this is not limitative. The arrangement order of the first discharge head 21, the second discharge head 22, and the third discharge head 23 in the transport direction Df can be changed as appropriate.

[0082] In the above embodiment, the nozzle 221 that ejects the special color ink is used as an example of the dryness level of the second nozzle, but this is not limiting. The ejection process may be performed by referring to each lookup table depending on the dryness level of the nozzle 121 that ejects the white ink, the nozzle 321 that ejects the color ink, or the nozzle that ejects the clear ink.

[0083] Furthermore, in the above embodiment, ink droplets of a special color ink may be ejected adjacent to ink droplets of a color with a relatively high erosion rate (for example, black or yellow). In this case, the special color ink is less noticeable because it is more likely to be eroded by ink droplets of black ink or the like.

[0084] Although the droplet ejection device 100 includes the thermometer unit 16 in the above embodiment, temperature may be measured using a different method. For example, the first ejection head 21, the second ejection head 22, and the third ejection head 23 eject ink droplets when a voltage associated with an ejection waveform is applied. After the ink droplets are ejected, the ink temperatures in the first ejection head 21, the second ejection head 22, and the third ejection head 23 may be estimated based on the shape of the pressure wave remaining in the first ejection head 21, the second ejection head 22, and the third ejection head 23, i.e., the shape of the residual pressure wave. Alternatively, the first ejection head 21, the second ejection head 22, and the third ejection head 23 may each include a piezoelectric element. Since the piezoelectric element can be regarded as a capacitor, its capacitance changes depending on the ink temperature. Therefore, the ink temperatures in the first ejection head 21, the second ejection head 22, and the third ejection head 23 may be estimated based on the electrostatic capacitance of the piezoelectric element. [Explanation of symbols]

[0085] 16 Temperature measurement section 17 Humidity measurement section 20 Discharge head 21 First ejection head 22 Second ejection head 23 Third ejection head 50 Control device 53 Memory section 54 Receiving part 100 Droplet discharge device 121,221,321 nozzles LUT1 First lookup table LUT2, LUT3, LUT4 Second lookup table W Printing medium

Claims

1. an ejection head having a first nozzle for ejecting a first liquid onto a print medium and a second nozzle for ejecting a second liquid different from the first liquid onto the print medium; A memory unit; a control device; the storage unit pre-stores a first lookup table for converting image data into first print data that uses only the first liquid, and a second lookup table that is a lookup table for converting the image data into second print data that uses both the first liquid and the second liquid; The control device a droplet ejection device that executes a process of ejecting droplets onto the print medium based on the first lookup table or the second lookup table in accordance with the degree of dryness of the second nozzles;

2. The device further includes a temperature measuring unit that measures temperature and a humidity measuring unit that measures humidity, The droplet ejection device of claim 1, wherein the control device determines the degree of dryness of the second nozzle based on any one of the temperature measured by the temperature measuring unit, the humidity measured by the humidity measuring unit, the type of the second liquid, a combination of the temperature and the humidity, a combination of the temperature and the type of the second liquid, a combination of the humidity and the type of the second liquid, and a combination of the temperature, the humidity, and the type of the second liquid.

3. The control device executes a receiving process for receiving, from a user, an instruction to allow a color difference between a first color, which is a color of the image data output based on the first print data, and a second color, which is a color of the image data output based on the second print data, to be non-zero; The droplet ejection device according to claim 1 , wherein the second lookup table is referenced when a user has given an instruction to allow the color difference to be non-zero.

4. The control device If the user has not given an instruction to allow the color difference to be non-zero, a process is executed to determine whether or not an area containing high frequency components is present in an image based on the image data, the area being equal to or larger than a predetermined area; The droplet ejection device according to claim 3 , wherein the second lookup table is referenced when the number of the areas in the image is equal to or greater than a predetermined value.

5. The control device A process of acquiring a color difference between a first color that is a color output based on the first print data and a second color that is a color output based on the second print data; a process of determining whether the color difference is equal to or less than a threshold value; 2. The droplet ejection device according to claim 1, further comprising: if the color difference is not equal to or less than a threshold value, referring to the first lookup table and ejecting droplets from the first nozzle onto the printing medium based on the first lookup table.

6. a receiving portion for receiving droplets ejected from the second nozzle, The control device a first flushing process in which droplets are ejected from the second nozzles onto the receiving portion; a second flushing process in which droplets are ejected from the second nozzles onto the receiving portion after the first flushing process; The droplet ejection device according to claim 1 , further comprising: a process of determining the degree of dryness of the second nozzle based on the elapsed time since the second flushing process.

7. The droplet ejection device according to claim 1 , wherein the control device determines the degree of dryness of the second nozzle based on the time elapsed since the last ejection by the second nozzle.

8. A droplet ejection method using a droplet ejection device including: an ejection head having first nozzles for ejecting a first liquid onto a print medium and second nozzles for ejecting a second liquid different from the first liquid onto the print medium; and a storage unit that stores in advance a first lookup table for converting image data into first print data using only the first liquid, and a second lookup table that is a lookup table for converting the image data into second print data using both the first liquid and the second liquid, A droplet ejection method, comprising ejecting droplets onto the print medium based on the first lookup table or the second lookup table in accordance with the degree of dryness of the second nozzles.

9. A droplet ejection program to be executed by a computer in a droplet ejection device including: an ejection head having first nozzles for ejecting a first liquid onto a print medium and second nozzles for ejecting a second liquid different from the first liquid onto the print medium; and a storage unit that stores in advance a first lookup table for converting image data into first print data using only the first liquid, and a second lookup table that is a lookup table for converting the image data into second print data using both the first liquid and the second liquid, a droplet ejection program that causes the computer to function as an ejection instruction unit that ejects droplets onto the print medium based on the first lookup table or the second lookup table in accordance with the degree of dryness of the second nozzles;

Images