Printing device and control method for printing device

Abstract

A printing device according to the present invention comprises: an ink head that carries out a pass operation; an acquisition unit that acquires image data created with the number of pass operations in a unit area on a printing medium being a reference number of passes; an input unit that receives input of the number of printing passes, which indicates the number of pass operations when printing an image in the unit area; and a control unit that calculates a drive voltage input into a discharge element of the ink head and causes the ink head to carry out pass operations by the number of printing passes on the basis of the image data. The control unit calculates the drive voltage by correcting a prescribed reference voltage at which the amount of ink discharged by the ink head is a reference amount, using a correction value corresponding to the difference in the number of printing passes with respect to the reference number of passes.

Description

Printing device and method for controlling printing device

[0001] The present disclosure relates to a printing device and a method for controlling a printing device.

[0002] Printing devices such as inkjet printers that print images on print media using a serial printing method include ink heads that eject ink for forming an image toward the print media. In this type of printing device, the ink head prints an image in a unit area on the print medium by performing a pass operation in which the ink head moves in a scanning direction relative to the print medium in accordance with image data and ejects ink. Some printing devices are also configured to be able to switch between a single-pass mode, which enables high-speed printing, and a multi-pass mode, which enables improved print quality. When printing an image in single-pass mode, the ink head performs a single pass operation for each unit area on the print medium. When printing an image in multi-pass mode, the ink head performs multiple passes for each unit area on the print medium.

[0003] Differences in the number of passes of the ink head for each unit area on the printing medium can cause density differences in the image printed in the unit area. A technology for improving such density differences in an image is disclosed in Patent Document 1. The technology disclosed in Patent Document 1 divides image data into multiple divided image data, assigns each divided image data to a pass operation of the ink head, and prints an image in the unit area on the printing medium.

[0004] Japanese Patent Application Laid-Open No. 2009-269261

[0005] A printing device according to a first aspect of the present disclosure includes an ink head including ejection elements capable of performing pass operations to eject ink in accordance with a drive voltage input to the ejection elements while moving in a scanning direction relative to a print medium, an acquisition unit that acquires image data created so that the number of pass operations for each unit area on the print medium is a reference number of passes as data for printing an image in each unit area by the pass operations of the ink head, an input unit that accepts input of a number of printing passes indicating the number of pass operations to be performed when printing the image in each unit area, and a control unit that calculates the drive voltage and causes the ink head to perform the pass operations for the reference number of printing passes based on the image data. The control unit calculates the drive voltage by correcting a predetermined reference voltage at which the amount of ink ejected by the ink head is a reference amount using a correction value corresponding to the difference between the number of printing passes and the reference number of passes.

[0006] A control method for a printing device according to a second aspect of the present disclosure is a control method for a printing device that prints an image in a unit area on a printing medium by pass operations of an ink head that moves in a scanning direction relative to the printing medium and ejects ink in accordance with drive voltages input to ejection elements. This control method for a printing device acquires image data created so that the number of pass operations for the unit area is a reference number of passes, accepts input of a number of printing passes indicating the number of pass operations when printing the image in the unit area, calculates the drive voltage by correcting a predetermined reference voltage at which the amount of ink ejected by the ink head is a reference amount using a correction value corresponding to the difference between the number of printing passes and the reference number of passes, and causes the ink head to perform the pass operations for the number of printing passes based on the image data.

[0007] According to the present disclosure, it is possible to prevent density differences and the like from occurring in an image due to differences in the number of passes of an ink head for a unit area on a print medium.

[0008] FIG. 1 is a schematic cross-sectional view of a printing device according to an embodiment of the present disclosure. FIG. 2 is a diagram illustrating the operation of the printing device when printing an image. FIG. 3 is a diagram illustrating the principle of liquid ejection by a liquid ejection head. FIG. 4 is a block diagram illustrating the electrical configuration of the printing device. FIG. 5 is a diagram illustrating a correction factor table stored in a storage unit. FIG. 6 is a flowchart illustrating a method for controlling the printing device. FIG. 7 is a diagram illustrating measurement results of color difference and density when an image is printed on a first fabric member. FIG. 8 is a diagram illustrating measurement results of color difference and density when an image is printed on a second fabric member.

[0009] In the technology disclosed in Patent Document 1, when printing an image in a unit area on a print medium by pass operation of the ink head, the image data is divided for each pass, which lengthens the preparation time before printing starts and may reduce the printing efficiency of the image. As a result, there is a problem in that it is not possible to efficiently prevent density differences and the like from occurring in the image printed in the unit area due to the different number of passes of the ink head for each unit area on the print medium.

[0010] Therefore, there is a demand for a printing device and a method for controlling a printing device that can suppress density differences in an image caused by different numbers of passes of an ink head for a unit area on a printing medium.

[0011] A printing apparatus and a control method thereof according to an embodiment of the present disclosure will be described below with reference to the drawings.

[0012] [Overall Configuration of Printing Apparatus] Figure 1 is a schematic cross-sectional view of a printing apparatus 1 according to an embodiment of the present disclosure. The printing apparatus 1 is an inkjet printer that prints images by ejecting ink onto a workpiece W, which is a wide, long print medium. The printing apparatus 1 is suitable for digital textile printing, which uses an inkjet method to print images such as letters and patterns on the workpiece W, which is a fabric member made of fabric such as woven fabric or knitted fabric. Of course, the printing apparatus 1 can also be used to print various images on print media such as paper sheets and resin sheets.

[0013] The printing device 1 includes a liquid ejection head 2, a transport unit 3 that transports a workpiece W relative to the liquid ejection head 2, and a carriage 10 on which the liquid ejection head 2 is mounted. In this embodiment, the left-right direction is the main scanning direction D1 when printing on the workpiece W, and the direction from rear to front that is perpendicular to the main scanning direction D1 is the sub-scanning direction D2. The transport unit 3 and carriage 10 are incorporated into an apparatus frame that forms the framework of the printing device 1. The transport unit 3 is a mechanism that intermittently feeds (transports) the workpiece W so that the workpiece W advances in the sub-scanning direction D2. The carriage 10 is mounted with the liquid ejection head 2 and moves back and forth in the main scanning direction D1 during printing.

[0014] A carriage guide 1F1 for reciprocating the carriage 10 in the main scanning direction D1 is attached to the upper side of the device frame. The carriage guide 1F1 is a flat, plate-shaped member that is elongated in the main scanning direction D1 and is disposed above the conveying unit 3. A timing belt 1F2 is attached to the carriage guide 1F1 so as to be able to move in a circular motion in the main scanning direction D1. The timing belt 1F2 is an endless belt that is driven to move in a circular motion in the main scanning direction D1. The carriage guide 1F1 is equipped with a pair of upper and lower guide rails 1F3 that extend parallel to the main scanning direction D1 and hold the carriage 10 in a state that allows it to move back and forth in the main scanning direction D1. The carriage 10 is engaged with the guide rails 1F3. The carriage 10 is also fixed to the timing belt 1F2. The carriage 10 moves back and forth in the main scanning direction D1 along the carriage guide 1F1 while being guided by the guide rail 1F3, in accordance with the circular movement of the timing belt 1F2 in the main scanning direction D1.

[0015] The carriage 10 includes a head support frame 11 that supports the liquid ejection head 2, and a back frame 12 that extends upward from the rear end edge of the head support frame 11. The timing belt 1F2 is fixed to the back frame 12. In addition, the guide rail 1F3 is engaged with the back frame 12.

[0016] The conveying unit 3 has an endless belt 31, a drive roller 32, and a driven roller 33. The drive roller 32 and the driven roller 33 stretch the endless belt 31. When the drive roller 32 rotates, the endless belt 31 rotates, and conveys the workpiece W in the sub-scanning direction D2 so that it passes under the carriage 10.

[0017] The liquid ejection head 2 includes an ink head 21 , a pre-treatment head 22 , and a post-treatment head 23 .

[0018] The ink head 21 is capable of ejecting ink onto the workpiece W. The ink ejected by the ink head 21 is not particularly limited, and can be, for example, an ink containing a pigment and a dye. For example, an ink containing a pigment and an aqueous medium can be used. If necessary, the ink may further contain at least one selected from the group consisting of a surfactant, a polyol, and binder resin particles. Examples of pigments include yellow pigments, orange pigments, red pigments, blue pigments, purple pigments, and black pigments. The ink may also contain an anionic pigment.

[0019] The pretreatment head 22 is capable of ejecting a pretreatment liquid onto the workpiece W. The pretreatment liquid ejected by the pretreatment head 22 is a non-coloring treatment liquid that adheres to the workpiece W before the ink, contacts the ink while it is still wet on the workpiece W, and does not develop color even when it adheres to the workpiece W. Any pretreatment liquid can be used. For example, a pretreatment liquid that aggregates the ink pigment to improve color development and fixation. The pretreatment liquid may also suppress the penetration of the ink into the workpiece W, or conversely, promote penetration, print thickly to create a three-dimensional shape, or impart gloss. The pretreatment liquid may contain, for example, a water-soluble cationic polymer, an organic acid salt, and an aqueous medium. Such a pretreatment liquid reacts and aggregates with the pigment contained in the ink to be printed subsequently, improving color development. The cationic polymer contained in the pretreatment liquid and the anionic pigment contained in the ink electrically react and aggregate on the surface of the workpiece W, thereby suppressing the penetration of the binder resin contained in the ink into the workpiece W. This reduces the possibility that the binder resin will penetrate into the gaps between fibers and bind the fibers together when the workpiece W is fabric, thereby improving the texture (feel, etc.) of the fabric to be printed.

[0020] The post-treatment head 23 is capable of ejecting a post-treatment liquid onto the workpiece W. The post-treatment liquid ejected by the post-treatment head 23 adheres to the workpiece W after the ink, comes into contact with the ink while it is not yet dried on the workpiece W, and is a non-color-forming treatment liquid that does not develop color even when it adheres to the workpiece W. Any post-treatment liquid can be used. For example, a post-treatment liquid that improves the texture of the fabric to be printed can be used. The post-treatment liquid may also be used to provide a coating to protect the printed ink, to create a three-dimensional shape by printing thickly, or to impart gloss. It may also be used to perform treatments not directly related to ink printing, such as imparting water repellency to the workpiece W. The post-treatment liquid may contain, for example, emulsified particles containing silicone oil, a surfactant, and an aqueous medium. In other words, the post-treatment liquid is an emulsion in which emulsified particles are dispersed in an aqueous medium, more specifically, an oil-in-water (O / W) emulsion. The silicone oil may also include unmodified silicone oil. Examples of non-modified silicone oils include dimethylpolysiloxane, methylphenylsilicone oil, methylhydrogensilicone oil, etc. Such post-treatment liquids can improve the feel.

[0021] In this embodiment, the pre-treatment head 22 and the post-treatment head 23 may eject the treatment liquid onto substantially the entire surface of the workpiece W, or, similar to the ink head 21, may selectively eject the treatment liquid onto the workpiece W in accordance with the image to be printed. A case will be described in which the pre-treatment head 22 and the post-treatment head 23 selectively eject the treatment liquid onto the workpiece W. The pre-treatment liquid, ink, and post-treatment liquid are applied in this order to the portion of the workpiece W where a color is to be printed in accordance with the image. In this case, the ink may be of one color or multiple colors. The pre-treatment liquid and the post-treatment liquid are generally not applied to the portion of the workpiece W where no color is to be printed, i.e., the portion where no ink is applied. Note that, in order to adjust the image quality of the image to be printed and the texture of the workpiece W, the pre-treatment liquid and the post-treatment liquid may be applied to an area slightly larger than the area where the ink is applied (for example, the area corresponding to several pixels).

[0022] Each of the ink head 21, pre-processing head 22 and post-processing head 23 mounted on the carriage 10 can move relative to the workpiece W in the main scanning direction D1 and the sub-scanning direction D2 as the workpiece W is transported in the sub-scanning direction D2 by the transport unit 3 and the carriage 10 moves back and forth in the main scanning direction D1.

[0023] 2 is a diagram illustrating the operation of printing an image in the printing device 1. The printing device 1 performs printing processing on the workpiece W using a serial printing method. In a serial printing printing device 1, the ink head 21 performs a pass operation in which it ejects ink while moving back and forth in the main scanning direction D1 relative to the workpiece W as the carriage 10 moves. The transport unit 3 then performs a transport operation in which it transports the workpiece W in the sub-scanning direction D2. The printing device 1 prints an image in a unit area WA on the workpiece W by combining the pass operation of the ink head 21 with the transport operation of the transport unit 3. Note that in the pass operation of the ink head 21, the pre-treatment head 22 may eject pre-treatment liquid, and the post-treatment head 23 may eject post-treatment liquid.

[0024] The printing device 1 is configured to be able to switch between a single-pass mode, which enables high-speed printing, and a multi-pass mode, which enables improved print quality. When printing an image in single-pass mode, the ink head 21 performs a single pass operation for a unit area WA on the workpiece W. When printing an image in multi-pass mode, the ink head 21 performs a multiple pass operation for a unit area WA on the workpiece W.

[0025] The workpiece W after printing by the printing device 1 may be heated and dried by a heater (not shown) or the like provided in the printing device 1. Furthermore, the printed portion of the workpiece W may be transported to a dryer separate from the printing device 1 and dried by that dryer, rather than being wound up on a winding roller (not shown). The heating temperature is, for example, 120°C or higher and 180°C or lower. The heating time is, for example, 1 minute or higher and 10 minutes or lower. Heating dries volatile components contained in the ink and treatment liquid, facilitating fixation of the ink to the workpiece W.

[0026] In this embodiment, the ink head 21 includes a plurality of individual heads 211 capable of ejecting ink of a plurality of colors, and these plurality of individual heads 211 are mounted on the carriage 10. The plurality of individual heads 211 are mounted on the carriage 10 so as to be aligned in two rows in the main scanning direction D1. Each color of the individual heads 211 has two heads. Two individual heads 211 that eject ink of the same color are mounted on the carriage 10 so as to be positioned at offset positions relative to each other in the main scanning direction D1 and the sub-scanning direction D2.

[0027] The pre-processing head 22 is mounted on the carriage 10 so as to be positioned upstream of the ink head 21 in the sub-scanning direction D2, which is the transport direction of the workpiece W. Figure 2 shows an example in which one pre-processing head 22 is positioned near one end of the array of multiple individual heads 211 in the ink head 21 in the main scanning direction D1. The post-processing head 23 is mounted on the carriage 10 so as to be positioned downstream of the ink head 21 in the sub-scanning direction D2. Figure 2 shows an example in which one post-processing head 23 is positioned near the other end of the array of multiple individual heads 211 in the ink head 21 in the main scanning direction D1.

[0028] [Principles of Liquid Ejection by Liquid Ejection Heads] The following describes the principles of ink ejection by the ink head 21, the principles of pre-treatment liquid ejection by the pre-treatment head 22, and the principles of post-treatment liquid ejection by the post-treatment head 23. In the following description, the ink head 21, pre-treatment head 22, and post-treatment head 23 will be collectively referred to as the liquid ejection head 2, and the ink, pre-treatment liquid, and post-treatment liquid will be collectively referred to as the liquid.

[0029] 3 is a diagram illustrating the principle of liquid ejection by the liquid ejection head 2. The liquid ejection head 2 has a piezoelectric actuator substrate 2A, a plurality of pressure chambers 2B filled with liquid, and a plurality of nozzles 2C that eject the liquid in the pressure chambers 2B. In the liquid ejection head 2, the piezoelectric actuator substrate 2A is disposed above the plurality of pressure chambers 2B, and the plurality of pressure chambers 2B and the plurality of nozzles 2C are respectively connected to each other. The plurality of pressure chambers 2B and the plurality of nozzles 2C are arranged side by side in the main scanning direction D1 and the sub-scanning direction D2.

[0030] The piezoelectric actuator substrate 2A has a laminated structure in which multiple piezoelectric ceramic layers are stacked, and further has a common electrode 2A1 and individual electrodes 2A2. The individual electrodes 2A2 are electrodes arranged in positions facing each pressure chamber 2B on the upper surface of the piezoelectric actuator substrate 2A. A drive voltage DV is input to the individual electrodes 2A2 in response to the supply of a drive signal. The common electrode 2A1 is an electrode arranged so as to cover each pressure chamber 2B from above. The common electrode 2A1 is grounded and maintained at ground potential.

[0031] The portions of the piezoelectric actuator substrate 2A facing each pressure chamber 2B correspond to individual ejection elements (piezoelectric elements) 2AA corresponding to each pressure chamber 2B and each nozzle 2C. In other words, each ejection element 2AA is built into a laminated structure using multiple piezoelectric ceramic layers on the piezoelectric actuator substrate 2A, and is composed of a piezoelectric ceramic layer located directly above each pressure chamber 2B, a common electrode 2A1, and an individual electrode 2A2. The ejection elements 2AA undergo piezoelectric deformation when a drive voltage DV is input to the individual electrode 2A2 in response to the supply of a drive signal.

[0032] When a drive signal is selectively supplied to the individual electrode 2A2, the ejection element 2AA undergoes piezoelectric deformation, and pressure is applied to the liquid in the pressure chamber 2B corresponding to this ejection element 2AA, causing the liquid to be ejected from the nozzle 2C corresponding to the pressure chamber 2B to which pressure has been applied.

[0033] When the individual electrode 2A2 is set to a high potential, the ejection element 2AA undergoes piezoelectric deformation, bending toward the pressure chamber 2B, and enters a standby state awaiting liquid ejection. Each time image data indicating a request for liquid ejection from the nozzle 2C is input, the individual electrode 2A2 is temporarily set to the same ground potential (low potential) as the common electrode 2A1 and then returned to a high potential at a predetermined timing. As a result, a negative pressure is applied to the liquid in the pressure chamber 2B when the individual electrode 2A2 becomes a low potential. This causes the liquid in the pressure chamber 2B to vibrate at its natural vibration period. Specifically, initially, the volume of the pressure chamber 2B begins to increase, and the negative pressure gradually decreases. Next, the volume of the pressure chamber 2B reaches its maximum, and the pressure in the pressure chamber 2B becomes nearly zero. Next, the volume of the pressure chamber 2B begins to decrease, and the pressure in the pressure chamber 2B increases accordingly. Thereafter, when the pressure reaches nearly its maximum, the individual electrode 2A2 is returned to a high potential, and a positive pressure is applied to the liquid in the pressure chamber 2B. As a result, the positive pressure created by the reversal of the initially applied negative pressure and the subsequently applied positive pressure are superimposed, and the liquid in the pressure chamber 2B is subjected to a larger positive pressure. This positive pressure is transmitted to the nozzle 2C connected to the pressure chamber 2B, and the liquid is ejected from the nozzle 2C.

[0034] In other words, when a drive signal including a pulse that sets a high potential as a reference to a low potential for a certain period and then returns to the high potential is supplied to the individual electrode 2A2, the ejection element 2AA deforms accordingly. This changes the pressure in the pressure chamber 2B, causing liquid to be ejected from the nozzle 2C corresponding to that pressure chamber 2B. In principle, if the pulse width of the drive signal is set to AL (Acoustic Length), which is half the natural vibration period of the liquid in the pressure chamber 2B, the liquid ejection speed and ejection amount can be maximized. When adjusting the liquid ejection amount, the pulse width of the drive signal is set to a value outside AL. Note that, while a pulse signal that sets a high potential as a reference to a low potential (ground potential) is exemplified as the drive signal here, the drive signal may be one that changes voltage in other ways as long as it ejects liquid. For example, the drive signal may be a pulse signal that sets a high potential relative to the reference potential.

[0035] In the liquid ejection head 2, the drive voltage DV based on the drive signal can be input to the individual electrodes 2A2 of the ejection elements 2AA in the liquid ejection head 2 in the following two ways. In the first way, a predetermined voltage is supplied to the liquid ejection head 2, and that voltage is input directly to the individual electrodes 2A2 as the drive voltage DV. In the second way, a predetermined voltage is supplied to the liquid ejection head 2, a setting signal is sent to the liquid ejection head 2, and the liquid ejection head 2 inputs the drive voltage DV based on the setting signal to the individual electrodes 2A2 in its internal circuitry.

[0036] In the printing device 1, the ink head 21 performs a pass operation in which it ejects ink in accordance with a drive voltage DV based on a drive signal input to the individual electrodes 2A2 of the ejection elements 2AA, while moving back and forth in the main scanning direction D1 relative to the workpiece W in conjunction with the movement of the carriage 10. During the pass operation of the ink head 21, the pre-treatment head 22 and the post-treatment head 23 eject treatment liquid in accordance with a processing drive voltage based on a drive signal input to the individual electrodes 2A2 of the ejection elements 2AA.

[0037] 4 is a block diagram showing the electrical configuration of the printing device 1. The printing device 1 further includes a control unit 4, an acquisition unit 41, an input unit 42, and a storage unit 43.

[0038] The acquisition unit 41 acquires image data GD for printing an image in a unit area WA on the workpiece W by pass operations of the ink head 21. The image data GD is data created by setting the number of pass operations of the ink head 21 on the unit area WA on the workpiece W to a reference pass number SPN, and is data that indicates the color profile of the image in, for example, TIFF (Tagged Image File Format) format.

[0039] The input unit 42 is composed of a keyboard, mouse, touch panel, etc., and accepts input of various commands by the operator. The input unit 42 accepts input of the number of printing passes PSN, which indicates the number of passes of the ink head 21 when printing an image in a unit area WA on the workpiece W. The input unit 42 also accepts input of a command to select whether or not to perform voltage correction processing, which corrects the drive voltage DV input to the ink head 21, depending on the difference between the number of printing passes PSN and the reference number of passes SPN. The input unit 42 also accepts input of a command to select the type of fabric material for the workpiece W.

[0040] The storage unit 43 stores a correction factor table CRT shown in Fig. 5. The correction factor table CRT is referenced by the control unit 4. The correction factor table CRT will be described in detail later.

[0041] The control unit 4 is composed of a processor capable of information processing. The control unit 4 calculates a drive voltage DV according to the difference between the number of printing passes PSN and the reference number of passes SPN, inputs the calculated drive voltage DV to the individual electrodes 2A2 of the ejection elements 2AA, and causes the ink head 21 to perform pass operations at the number of printing passes PSN based on the image data GD. During pass operations of the ink head 21, the control unit 4 inputs a processing drive voltage to the ejection elements 2AA in the pre-treatment head 22 and post-treatment head 23 to eject the treatment liquid. Furthermore, the control unit 4 causes the transport unit 3 to perform a transport operation to transport the workpiece W in accordance with the pass operations of the ink head 21. By combining the pass operations of the ink head 21 and the transport operation of the transport unit 3 based on the control of the control unit 4, an image corresponding to the image data GD is printed in the unit area WA on the workpiece W.

[0042] [Printing Device Control Method] In the printing device 1, the acquisition unit 41, input unit 42, and control unit 4 execute the processes of the control method. The control method of the printing device 1 will be described with reference to the flowchart of FIG.

[0043] First, the acquisition unit 41 acquires image data GD created by the ink head 21 performing a pass operation on a unit area WA on the workpiece W at a reference pass number SPN (step S1). The input unit 42 accepts input of the printing pass number PSN (step S2). At this time, the input unit 42 may also accept input of a command selecting whether or not to perform voltage correction processing to correct the drive voltage DV input to the ejection elements 2AA of the ink head 21. The input unit 42 may also accept input of a command selecting the type of fabric material for the workpiece W.

[0044] When a command requesting voltage correction processing is input to the input unit 42, the control unit 4 calculates the drive voltage DV by correcting a predetermined reference voltage SV using a correction value CV corresponding to the difference between the reference pass number SPN and the number of printing passes PSN (step S3). Note that the reference voltage SV is a voltage that causes the ink ejection amount from the ink head 21 to be a reference amount, so that the image density based on the ink adhesion is used as a reference value for the voltage input to the ejection elements 2AA of the ink head 21.

[0045] Specifically, the control unit 4 calculates the correction value CV by multiplying the reference voltage SV by a correction rate CR that is set in advance depending on the difference between the number of printing passes PSN and the reference number of passes SPN, according to the following formula (1): Correction value CV=Reference voltage SV×Correction rate CR (1)

[0046] The control unit 4 then calculates the drive voltage DV by adding the correction value CV to the reference voltage SV according to the following formula (2). The control unit 4 can efficiently calculate the drive voltage DV corrected with respect to the reference voltage SV by using a preset correction factor CR. Drive voltage DV = Reference voltage SV + Correction value CV (2)

[0047] The control unit 4 inputs the calculated drive voltage DV to the ejection elements 2AA of the ink head 21 (step S4) and causes the ink head 21 to perform pass operations based on the image data GD for the number of printing passes PSN (step S5). During the pass operations of the ink head 21, the control unit 4 inputs a processing drive voltage to the ejection elements 2AA of the pre-treatment head 22 and the post-treatment head 23 to eject the treatment liquid. Furthermore, the control unit 4 causes the transport unit 3 to perform a transport operation to transport the workpiece W in accordance with the pass operations of the ink head 21 (step S5). By combining the pass operations of the ink head 21 and the transport operation of the transport unit 3 based on the control of the control unit 4, an image corresponding to the image data GD is printed in the unit area WA on the workpiece W.

[0048] In addition, if a command that does not require voltage correction processing is input to the input unit 42, the control unit 4 omits the processing of step S3, does not correct the reference voltage SV, and inputs the reference voltage SV directly to the ejection element 2AA of the ink head 21 as the drive voltage DV in step S4.

[0049] The control unit 4 determines whether or not the printing process of the image on the workpiece W has been completed. If the printing process of the image on the workpiece W has not been completed, the processes from step S1 to step S5 are repeated.

[0050] As described above, the control unit 4 corrects the reference voltage SV of the ink head 21 using a correction value CV corresponding to the difference between the number of printing passes PSN input to the input unit 42 and the reference number of passes SPN set when the image data GD was created, thereby setting the drive voltage DV to be input to the ejection elements 2AA when the ink head 21 performs a pass operation. In this case, the amount of ink ejected when the ink head 21 performs a pass operation can be adjusted relative to the reference amount depending on the difference between the number of printing passes PSN and the reference number of passes SPN. This makes it possible to prevent differences in image density, etc., caused by differences between the number of printing passes PSN and the reference number of passes SPN.

[0051] Here, the workpiece W, which is a fabric member, includes a first fabric member having an ink penetration level below a standard level and a second fabric member having an ink penetration level higher than the standard level. Figure 7 shows the measurement results of color difference and density when an image is printed on the first fabric member. Figure 8 shows the measurement results of color difference and density when an image is printed on the second fabric member.

[0052] If the workpiece W is a first fabric member with ink penetration below a standard, the ink adhering to the workpiece W tends to remain on the surface of the workpiece W. Therefore, as shown in FIG. 7 , if the drive voltage DV input to the ejection elements 2AA of the ink head 21 is not corrected, the image density increases as the number of passes increases. In other words, if the drive voltage DV input to the ejection elements 2AA of the ink head 21 is not corrected, the color difference (ΔE) and image density differences increase depending on the number of passes. In contrast, if the drive voltage DV input to the ejection elements 2AA of the ink head 21 is corrected depending on the number of passes, the color difference (ΔE) and image density differences caused by the number of passes can be suppressed.

[0053] On the other hand, if the workpiece W is a second fabric member with a higher ink penetration rate than the standard, the ink adhering to the workpiece W is less likely to remain on the surface of the workpiece W and diffuses into the workpiece W. Therefore, as shown in Figure 8, even if the drive voltage DV input to the ejection elements 2AA of the ink head 21 is not corrected, the color difference (ΔE) and the difference in image density depending on the number of passes are small. However, if the drive voltage DV input to the ejection elements 2AA of the ink head 21 is corrected depending on the number of passes, the image density becomes too low as the number of passes increases.

[0054] From the above, it is assumed that when the ink penetration rate in the work W is below the standard, differences in image density tend to occur easily due to the difference between the number of printing passes PSN and the standard number of passes SPN, and on the other hand, when the ink penetration rate in the work W is higher than the standard, differences in image density tend not to occur easily.

[0055] Therefore, the control unit 4 calculates the drive voltage DV by correcting the reference voltage SV using a correction value CV based on the correction factor CR, taking into account the ink penetration level corresponding to the type of workpiece W input to the input unit 42. That is, when the workpiece W is a first fabric member having an ink penetration level below the standard level for the type of workpiece W input to the input unit 42, the control unit 4 calculates the drive voltage DV by correcting the reference voltage SV using the correction value CV. On the other hand, when the workpiece W is a second fabric member having an ink penetration level higher than the standard level, the control unit 4 does not correct the reference voltage SV, but instead uses the reference voltage SV as the drive voltage DV. In this case, the control unit 4 can calculate the drive voltage DV according to the ink penetration level for each type of workpiece W. This allows the ink ejection volume when the ink head 21 performs a pass operation to be adjusted relative to the standard volume in accordance with the difference between the number of printing passes PSN and the standard number of passes SPN, taking into account the ink penetration level for each type of workpiece W. This allows for consideration of the ink penetration level for each type of workpiece W, making it possible to prevent differences in image density, etc., from occurring due to differences in the number of printing passes PSN relative to the reference number of passes SPN.

[0056] In the above description, the control unit 4 does not correct the reference voltage SV and sets it as the drive voltage DV when the workpiece W is a second cloth member having a higher ink penetration rate than the reference value. However, the present invention is not limited to this. The control unit 4 may calculate the drive voltage DV by correcting the reference voltage SV using a correction value CV having a smaller absolute value for a second cloth member having a higher ink penetration rate than the first cloth member.

[0057] Furthermore, when the pretreatment liquid ejected from the pretreatment head 22 adheres to the workpiece W, the ink penetration rate in the workpiece W changes. Therefore, the correction rate CR may be set taking into consideration not only the type of workpiece W but also pretreatment-related factors that affect the ink penetration rate, such as the amount of pretreatment liquid ejected by the pretreatment head 22 and the type of pretreatment liquid. In this case, the control unit 4 can calculate the drive voltage DV by correcting the reference voltage SV using a correction value CV based on the correction rate CR according to the type of workpiece W and the pretreatment-influencing factors. This allows the ink ejection rate when the ink head 21 performs a pass operation to be adjusted relative to the reference amount in accordance with the difference between the number of printing passes PSN and the reference pass number SPN, taking into consideration the ink penetration rate for each type of workpiece W and each pretreatment-influencing factor.

[0058] Furthermore, the control unit 4 may calculate the drive voltage DV using the correction factor CR registered in a correction factor table CRT stored in the storage unit 43. By using the correction factor CR registered in the correction factor table CRT, the control unit 4 can efficiently calculate the drive voltage DV corrected with respect to the reference voltage SV.

[0059] 5, the correction rate table CRT is a table in which a correction rate CR is associated with each of a plurality of pass number combinations PC of a reference pass number SPN and a printing pass number PSN. In the example of Fig. 5, "1," "2," and "4" are set as the pass numbers for each of the reference pass number SPN and the printing pass number PSN.

[0060] In the correction rate table CRT, combination groups indicating sets of multiple pass number combinations PC having the same reference pass number SPN but different printing pass numbers PSN include a first combination group PCG1 in which the reference pass number SPN is a first value of "1," a second combination group PCG2 in which the reference pass number SPN is a second value of "2" that is larger than the first value, and a third combination group PCG3 in which the reference pass number SPN is a third value of "4" that is larger than the second value. In the first combination group PCG1, the second combination group PCG2, and the third combination group PCG3, a correction rate CR is associated with each of the multiple pass number combinations PC having different printing pass numbers PSN of "1," "2," and "4," respectively.

[0061] The correction rate CR associated with each of the multiple pass number combinations PC in the correction rate table CRT is a value calculated in advance based on the measurement results of the image density according to the change in the pass number when an image is printed on the first fabric member without correcting the drive voltage DV, as shown in Figure 7.

[0062] For example, in the correction rate table CRT, the correction rate CR of "-10.0%" associated with the pass number combination PC in which the reference pass number SPN is "1" and the printing pass number PSN is "2" is calculated as follows: That is, the measurement results for the density of an image printed on the first fabric member showed that the density when the pass number was "2" (2 passes) was 10.0% higher than the density when the pass number was "1" (1 pass). To prevent the image density from increasing due to such an increase in the pass number, the correction rate CR is set to "-10.0%" with the goal of reducing the amount of ink ejected by the ink head 21 by 10.0%. In this way, the correction rate CR registered in the correction rate table CRT can be calculated based on the measurement results of the image density corresponding to changes in the pass number.

[0063] In the correction rate table CRT, the correction rate CR associated with a pass number combination PC in which the reference pass number SPN and the printing pass number PSN are the same is set to zero (0.0%). In the example shown in Fig. 5, the correction rate CR set to zero is associated with the pass number combination PC in which the reference pass number SPN and the printing pass number PSN are both "1", the pass number combination PC in which the reference pass number SPN and the printing pass number PSN are both "2", and the pass number combination PC in which the reference pass number SPN and the printing pass number PSN are both "4".

[0064] When the reference pass number SPN set when the image data GD was created and the printing pass number PSN input to the input unit 42 are the same, the control unit 4 uses the correction rate CR set to zero in the correction rate table CRT to calculate a drive voltage DV equivalent to the reference voltage SV according to the above equations (1) and (2).The control unit 4 then inputs the drive voltage DV equivalent to the reference voltage SV to the ejection elements 2AA of the ink head 21 when causing the ink head 21 to perform a pass operation.This allows the ink ejection volume when the ink head 21 performs a pass operation to be adjusted to the reference volume when the reference pass number SPN and the printing pass number PSN are the same.

[0065] In the correction rate table CRT, the correction rate CR associated with a pass number combination PC in which the printing pass number PSN is greater than the reference pass number SPN is set to a negative value. In the example shown in FIG. 5 , a correction rate CR set to "-10.0%" is associated with a pass number combination PC in which the reference pass number SPN is "1" and the printing pass number PSN is "2." A correction rate CR set to "-15.0%" is associated with a pass number combination PC in which the reference pass number SPN is "1" and the printing pass number PSN is "4." A correction rate CR set to "-5.0%" is associated with a pass number combination PC in which the reference pass number SPN is "2" and the printing pass number PSN is "4." In this case, the correction rate CR does not have to be the same for each pass of the printing pass number PSN, and the correction rate CR may be different for each pass. For example, the correction rate CR set for a pass number combination PC in which the reference pass number SPN is "1" and the printing pass number PSN is "4" does not have to be the same "-15.0%" over the "4" passes indicated by the printing pass number PSN, and may be changed over the "4" passes.

[0066] When the number of printing passes PSN input to the input unit 42 is larger than the reference number of passes SPN set when the image data GD was created, the control unit 4 uses the correction rate CR set to a negative value in the correction rate table CRT to calculate a drive voltage DV lower than the reference voltage SV according to the above equations (1) and (2). The control unit 4 then inputs a drive voltage DV lower than the reference voltage SV to the ejection elements 2AA of the ink head 21 when causing the ink head 21 to perform a pass operation. This allows the ink ejection volume when the ink head 21 performs a pass operation to be adjusted to a volume lower than the reference volume if the image density tends to be high due to the number of printing passes PSN being larger than the reference number of passes SPN.

[0067] In the correction rate table CRT, the correction rate CR associated with a pass number combination PC in which the printing pass number PSN is smaller than the reference pass number SPN is set to a positive value. In the example shown in FIG. 5 , a correction rate CR set to "+5.0%" is associated with a pass number combination PC in which the reference pass number SPN is "2" and the printing pass number PSN is "1." A correction rate CR set to "+8.0%" is associated with a pass number combination PC in which the reference pass number SPN is "4" and the printing pass number PSN is "1." A correction rate CR set to "+4.0%" is associated with a pass number combination PC in which the reference pass number SPN is "4" and the printing pass number PSN is "2." In this case, the correction rate CR does not have to be the same for each pass of the printing pass number PSN, and the correction rate CR may be different for each pass. For example, the correction rate CR set for a pass number combination PC in which the reference pass number SPN is "4" and the printing pass number PSN is "2" does not have to be the same "+4.0%" over the "2" passes indicated by the printing pass number PSN, and may be changed over the "2" passes.

[0068] When the number of printing passes PSN input to the input unit 42 is smaller than the reference number of passes SPN set when the image data GD was created, the control unit 4 uses the correction rate CR set to a positive value in the correction rate table CRT to calculate a drive voltage DV higher than the reference voltage SV according to the above equations (1) and (2). The control unit 4 then inputs a drive voltage DV higher than the reference voltage SV to the ejection elements 2AA of the ink head 21 when causing the ink head 21 to perform a pass operation. This allows the ink ejection volume when the ink head 21 performs a pass operation to be adjusted to a volume higher than the reference volume if the image density tends to be low because the number of printing passes PSN is smaller than the reference number of passes SPN.

[0069] When the first combination group PCG1 and the second combination group PCG2 are compared in the correction rate table CRT, the difference between the correction rate CR associated with the pass number combination PC with the smallest number of printing passes PSN and the correction rate CR associated with the pass number combination PC with the largest number of printing passes PSN is greater for the first combination group PCG1 than for the second combination group PCG2. Specifically, in the first combination group PCG1, the correction rate CR associated with the pass number combination PC with the smallest number of printing passes PSN of "1" is "0.0%," and the correction rate CR associated with the pass number combination PC with the largest number of printing passes PSN of "4" is "-15.0%". Therefore, the difference in the first combination group PCG1 is "15.0". On the other hand, in the second combination group PCG2, the correction rate CR associated with the pass count combination PC in which the number of printing passes PSN is the smallest, "1," is "+5.0%, while the correction rate CR associated with the pass count combination PC in which the number of printing passes PSN is the largest, "4," is "-5.0%." Therefore, the difference in the second combination group PCG2 is "10.0." As a result, while the difference in the first combination group PCG1 is "15.0," the difference in the second combination group PCG2 is "10.0," and therefore the difference is greater in the first combination group PCG1 than in the second combination group PCG2.

[0070] Furthermore, when the second combination group PCG2 and the third combination group PCG3 are compared in the correction rate table CRT, the difference between the correction rate CR associated with the pass number combination PC with the smallest number of printing passes PSN and the correction rate CR associated with the pass number combination PC with the largest number of printing passes PSN is larger for the second combination group PCG2 than for the third combination group PCG3. Specifically, in the second combination group PCG2, the correction rate CR associated with the pass number combination PC with the smallest number of printing passes PSN of "1" is "+5.0%," while the correction rate CR associated with the pass number combination PC with the largest number of printing passes PSN of "4" is "-5.0%." Therefore, the difference in the second combination group PCG2 is "10.0." On the other hand, in the third combination group PCG3, the correction rate CR associated with the pass count combination PC in which the number of printing passes PSN is the smallest, "1," is "+8.0%, while the correction rate CR associated with the pass count combination PC in which the number of printing passes PSN is the largest, "4," is "0.0%." Therefore, the difference in the third combination group PCG3 is "8.0." As a result, while the difference in the second combination group PCG2 is "10.0," the difference in the third combination group PCG3 is "8.0," so the difference in the second combination group PCG2 is greater than the third combination group PCG3.

[0071] In the correction rate table CRT, for each of the first combination group PCG1, the second combination group PCG2, and the third combination group PCG3, the greater the difference between the number of printing passes PSN and the reference number of passes SPN, the greater the absolute value of the correction rate CR. For example, in the first combination group PCG1, the reference number of passes SPN is "1," and the greater the difference between the number of printing passes PSN (1, 2, 4), the greater the absolute values ​​of the correction rates CR (0.0%, -10.0%, -15.0%).

[0072] The control unit 4 uses a correction factor CR with a larger absolute value the greater the difference between the number of printing passes PSN and the reference number of passes SPN, thereby calculating a drive voltage DV with a larger difference from the reference voltage SV according to the above equations (1) and (2).The control unit 4 then inputs a drive voltage DV corresponding to the difference between the number of printing passes PSN and the reference number of passes SPN to the ejection elements 2AA of the ink head 21 when causing the ink head 21 to perform a pass operation.This makes it possible to prevent image density differences from increasing due to a larger difference between the number of printing passes PSN and the reference number of passes SPN.

[0073] [Modified Embodiments] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to these, and may take on modified embodiments such as those described below.

[0074] In the above embodiment, the control unit 4 calculates the drive voltage DV to be input to the ejection elements 2AA of the ink head 21 by correcting the reference voltage SV using a correction value CV based on a preset correction rate CR in accordance with the difference between the printing pass number PSN and the reference pass number SPN. Here, the ink head 21 includes multiple individual heads 211 capable of ejecting multiple colors of ink. The multiple individual heads 211 are mounted on the carriage 10 so as to be aligned in two rows in the main scanning direction D1. When calculating the drive voltage DV for each of the multiple individual heads 211, the control unit 4 may use the same correction rate CR for each individual head 211, or may use different correction rates CR depending on the ink type and the position in the main scanning direction D1 or the sub-scanning direction D2.

[0075] In addition, the control unit 4 may input a processing drive voltage corrected according to the difference between the number of printing passes PSN and the reference number of passes SPN to the ejection elements 2AA of the pre-processing head 22 and the post-processing head 23, just like the ink head 21.

[0076] Furthermore, when the number of printing passes PSN input to the input unit 42 differs from the reference number of passes SPN, the control unit 4 may output notification information to notify this fact.

[0077] REFERENCE SIGNS LIST 1 Printing device 2 Liquid ejection head 21 Ink head 2AA Ejection element 4 Control unit 41 Acquisition unit 42 Input unit 43 Storage unit

Claims

1. A printing device comprising: an ink head including ejection elements, capable of performing pass operations to eject ink in accordance with a drive voltage input to the ejection elements while moving in a scanning direction relative to a printing medium; an acquisition unit that acquires image data created so that the number of pass operations for the unit area is a reference number of passes as data for printing an image in a unit area on the printing medium by the pass operations of the ink head; an input unit that accepts input of the number of printing passes indicating the number of pass operations when printing an image in the unit area; and a control unit that calculates the drive voltage and causes the ink head to perform the pass operation for the reference number of printing passes based on the image data, wherein the control unit calculates the drive voltage by correcting a predetermined reference voltage at which the amount of ink ejected by the ink head is a reference amount using a correction value corresponding to the difference between the number of printing passes and the reference number of passes.

2. The printing device described in claim 1, wherein the control unit calculates the correction value by multiplying the reference voltage by a predetermined correction factor according to the difference between the number of printing passes and the reference number of passes, and calculates the drive voltage by adding the calculated correction value to the reference voltage.

3. A printing device as described in claim 2, further comprising a memory unit that stores a correction rate table in which the correction rate is associated with each of a plurality of combinations of the reference number of passes and the number of printing passes, and the control unit calculates the drive voltage using the correction rate registered in the correction rate table.

4. A printing device as described in claim 3, wherein in the correction rate table, the correction rate associated with the pass number combination in which the reference pass number and the printing pass number are the same is set to zero, the correction rate associated with the pass number combination in which the printing pass number is larger than the reference pass number is set to a negative value, and the correction rate associated with the pass number combination in which the printing pass number is smaller than the reference pass number is set to a positive value.

5. A printing device as described in claim 4, wherein in the correction rate table, in a group of combinations showing a set of multiple pass number combinations in which the reference pass number is the same but the number of printing passes is different, the greater the difference between the number of printing passes and the reference pass number, the greater the absolute value of the correction rate.

6. A printing device as described in claim 5, wherein in the correction rate table, for each combination group having a different standard number of passes, when a first combination group in which the standard number of passes is a first value is compared with a second combination group in which the standard number of passes is a second value greater than the first value, the difference between the correction rate associated with the pass number combination with the smallest number of printing passes and the correction rate associated with the pass number combination with the largest number of printing passes is greater for the first combination group than for the second combination group.

7. A printing device according to any one of claims 1 to 6, wherein the printing medium is a cloth member made of cloth material.

8. The printing device according to claim 7, wherein the control unit calculates the drive voltage according to the degree of ink penetration into the fabric member.

9. A control method for a printing device that prints an image in a unit area on a printing medium by pass operations of an ink head that moves in a scanning direction relative to the printing medium and ejects ink in accordance with a drive voltage input to an ejection element, comprising: acquiring image data created so that the number of pass operations for the unit area is a reference number of passes; accepting input of the number of printing passes indicating the number of pass operations when printing an image in the unit area; calculating the drive voltage by correcting a predetermined reference voltage at which the amount of ink ejected by the ink head is a reference amount using a correction value corresponding to the difference between the number of printing passes and the reference number of passes; and causing the ink head to perform the pass operations for the number of printing passes based on the image data.

Images