Inkjet recording device and inkjet recording method

Abstract

In this inkjet recording device and inkjet recording method, a first flow direction process, in which a liquid is caused to flow from a first storage part to a second storage part via a head part provided with a nozzle for discharging the liquid, and a second flow direction process, in which the liquid is caused to flow from the second storage part to the first storage part via the head part, are alternately performed.

Description

Inkjet recording apparatus and inkjet recording method

[0001] The present invention relates to an inkjet recording apparatus and an inkjet recording method.

[0002] 2. Description of the Related Art Conventionally, inkjet recording devices are known that print images such as characters and patterns on a target recording medium (workpiece) using an inkjet method (see, for example, Japanese Patent Application Laid-Open No. 2003-121998).

[0003] JP 2023-139439 A

[0004] 2. Description of the Related Art There has been a demand for an inkjet recording apparatus and an inkjet recording method that are equipped with a new system for supplying and recovering liquid to and from an inkjet head unit.

[0005] An inkjet recording apparatus and an inkjet recording method according to one aspect of the present invention alternately perform a first flow direction process in which a liquid is caused to flow from a first storage unit to a second storage unit via a head unit having a nozzle for ejecting the liquid, and a second flow direction process in which the liquid is caused to flow from the second storage unit to the first storage unit via the head unit.

[0006] These and other objects, features and advantages of the present invention will become apparent from the following detailed description and accompanying drawings.

[0007] 1 is a perspective view showing the overall configuration of an inkjet printer according to an embodiment; a schematic cross-sectional view taken along line II-II in FIG. 1; an enlarged perspective view of the carriage shown in FIG. 1; a schematic diagram showing a serial printing method employed in an embodiment; a schematic diagram showing a mechanical configuration, mainly related to the supply and recovery of ink from the ink heads, in the inkjet printer; a block diagram showing an electrical configuration, mainly related to the supply and recovery of ink from the ink heads, in the inkjet printer; a diagram for explaining flow path switching in a five-port solenoid valve as an example of a flow path switching unit; a flowchart showing operations, mainly related to the supply and recovery of ink from the ink heads, in the inkjet printer; a flowchart showing operations related to the supply of ink from the main tank to the second sub-tank in the inkjet printer; a diagram for explaining a modified embodiment; a diagram for explaining a simulation model; a diagram showing an example of pressure fluctuations determined by the simulation; a diagram for explaining the correlation between the simulation model and damping time.

[0008] Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. In addition, components with the same reference numerals in each drawing indicate the same components, and their description will be omitted as appropriate. In this specification, when referring to a general term, a reference numeral without a subscript is used, and when referring to an individual component, a reference numeral with a subscript is used.

[0009] In this embodiment, an inkjet printer equipped with an ink head that ejects ink for forming an image onto a wide, long recording medium is exemplified as a specific example of an inkjet recording apparatus. The inkjet printer of this embodiment is suitable for digital textile printing, which uses an inkjet method to print images such as letters and patterns onto a recording medium (workpiece) made of fabric such as woven or knitted fabric. Of course, the inkjet recording apparatus according to the present disclosure can also be used to print various inkjet images on recording media such as paper sheets and resin sheets.

[0010] [Overall configuration of inkjet printer] Figure 1 is a perspective view showing the overall configuration of an inkjet printer 1 in an embodiment. Figure 2 is a schematic cross-sectional view taken along line II-II in Figure 1. Figure 3 is an enlarged perspective view of the carriage shown in Figure 1. The inkjet printer 1 is a printer that prints images on a wide and long workpiece W (recording medium) using an inkjet method, and includes, as shown in Figures 1 to 3, a device frame 10, a workpiece transport unit 20 incorporated into the device frame 10, and a carriage 3. In this embodiment, the left-right direction is the main scanning direction S when printing on the workpiece W, and the direction from rear to front is the sub-scanning direction F (direction F of transport of the workpiece W).

[0011] The device frame 10 forms a framework for mounting various components of the inkjet printer 1. The work transport unit 20 intermittently feeds the work W so that the work W progresses in a transport direction F through a printing area 12 where printing processing is performed. The carriage 3 is equipped with an ink head 4, a pre-processing head 5, a post-processing head 6, and a sub-tank 7, and moves back and forth in the left and right direction during the inkjet printing processing.

[0012] The device frame 10 includes a central frame 111, a right frame 112, and a left frame 113. The central frame 111 forms a framework for mounting various components of the inkjet printer 1, and has a left-to-right width corresponding to the work transport unit 20. The right frame 112 and left frame 113 are erected to the right and left of the central frame 111, respectively. Between the right frame 112 and the left frame 113 is the printing area 12 where printing processing is performed on the workpiece W.

[0013] The right frame 112 forms the maintenance area 13. The maintenance area 13 is an area where the carriage 3 is retracted when printing processing is not being performed. In the maintenance area 13, the ink heads 4, pre-processing head 5, and post-processing head 6 are subjected to processes such as cleaning and purging of the ejection ports, and are then capped. The left frame 113 forms the turn-around area 14 for the carriage 3. The turn-around area 14 is an area where the carriage 3 temporarily enters after scanning the printing area 12 from right to left during printing processing, before scanning in the opposite direction, from left to right.

[0014] A carriage guide 15 for reciprocating the carriage 3 in the left-right direction is attached to the upper side of the device frame 10. The carriage guide 15 is a flat, plate-shaped member that is long in the left-right direction, and is disposed above the work transport unit 20. A timing belt 16 (moving member) is attached to the carriage guide 15 so as to be able to move in a circular motion in the left-right direction (main scanning direction S). The timing belt 16 is an endless belt that is driven by a drive source (not shown) to move in a circular motion in the left or right direction.

[0015] The carriage guide 15 is equipped with a pair of upper and lower guide rails 17, which are holding members that hold the carriage 3, extending parallel to the left and right. The carriage 3 is engaged with the guide rails 17. The carriage 3 is fixed to a timing belt 16. As the timing belt 16 moves leftward or rightward, the carriage 3 moves leftward or rightward along the carriage guide 15 while being guided by the guide rails 17.

[0016] The workpiece transport unit 20 includes an endless belt 20H, a drive roller 21, and a driven roller 22. The endless belt 20H is stretched between the drive roller 21 and the driven roller 22. When the drive roller 21 rotates, the endless belt 20H rotates in the direction of arrow H1, and the driven roller 22 rotates, transporting the workpiece W so that it passes under the carriage 3.

[0017] The carriage 3 is cantilevered on the guide rail 17 and moves back and forth in a main scanning direction S (left and right in this embodiment) that intersects (orthogonal in this embodiment) with the transport direction F. The carriage 3 includes a carriage frame 30, and an ink head 4, a pre-processing head 5, a post-processing head 6, and a sub-tank 7 that are mounted on the carriage frame 30. The carriage frame 30 includes a head support frame 31 and a back frame 32.

[0018] The head support frame 31 is a horizontal plate that holds these heads 4 to 6. The back frame 32 is a vertical plate that extends upward from the rear edge of the head support frame 31. As described above, the timing belt 16 is fixed to the back frame 32. The guide rail 17 is engaged with the back frame 32. Note that the cantilevered state refers to a state in which the guide rail 17 that holds the carriage 3 is located only on one side, either the upstream or downstream side, of the center of the carriage 3 in the transport direction F, and the side opposite the side where the guide rail 17 is located is not held.

[0019] [Carriage] Figure 3 shows an example in which a carriage 3 is mounted with a plurality of ink heads 4 that eject ink for forming an image onto the workpiece W, a pre-treatment head 5 that ejects a non-color-forming pre-treatment liquid, a post-treatment head 6 that ejects a non-color-forming post-treatment liquid, and a plurality of sub-tanks 7 that supply ink, pre-treatment liquid, and post-treatment liquid to each of these heads 4 to 6.

[0020] Each of the ink heads 4 includes a number of nozzles that eject ink droplets using a method such as a piezoelectric method using a piezoelectric element or a thermal method using a heating element, and ink passages that guide ink to the nozzles. In this embodiment, the ink heads 4 include first through sixth ink heads 4A through 4F, each of which ejects six different colors of ink. For example, the first ink head 4A ejects orange ink (first color). The second ink head 4B ejects green ink (second color). The third ink head 4C ejects yellow ink (third color). The fourth ink head 4D ejects red ink (fourth color). The fifth ink head 4E ejects blue ink (fifth color). The sixth ink head 4F ejects black ink (sixth color). The ink heads 4A through 4F of each color are mounted on the head support frame 31 of the carriage 3 so as to be aligned in the main scanning direction S. Each of the ink heads 4A to 4F for each color has two heads. For example, the first ink head 4A is composed of an upstream head 4A1 located upstream in the transport direction F and a downstream head 4A2 located downstream of the upstream head 4A1 and shifted to the left in the main scanning direction S. The ink heads 4B to 4F for the other colors are similar. Each upstream head of these ink heads 4B to 4F is aligned in the main scanning direction S at the same position as the upstream head 4A1 in the transport direction F, and each downstream head is aligned in the main scanning direction S at the same position as the downstream head 4A2 in the transport direction F.

[0021] The pre-treatment head 5 and post-treatment head 6 are disposed at different positions from the ink heads 4 in the transport direction F. The pre-treatment head 5 is disposed upstream of the ink heads 4 in the transport direction F. FIG. 3 shows an example in which one pre-treatment head 5 is disposed near the right end of the array of ink heads 4. In contrast, the post-treatment head 6 is disposed downstream of the ink heads 4 in the transport direction F. FIG. 3 also shows an example in which two post-treatment heads 6A and 6B are disposed side by side in the main scanning direction S near the right end of the array of ink heads 4. Various arrangement patterns of the ink heads 4, pre-treatment heads 5, and post-treatment heads 6 on the carriage 3 are not limited to the example shown in FIG. 3. Note that a series of heads formed by the ink heads 4 and post-treatment heads 6 along the main scanning direction S is referred to as a head row, or simply as a row. The head row may also include the pre-treatment head 5. A series of heads formed by the ink heads 4, pre-treatment heads 5, and post-treatment heads 6 along the transport direction F is referred to as a head row, or simply as a row.

[0022] The pre-treatment head 5 is configured similarly to the ink head 4, and ejects a pre-treatment liquid for performing a predetermined pre-treatment on the workpiece W. The pre-treatment liquid is ejected from the pre-treatment head 5 onto a position on the workpiece W where ink has not yet been ejected from the ink head 4. The post-treatment head 6 is configured similarly to the ink head 4, and ejects a post-treatment liquid for performing a predetermined post-treatment on the workpiece W to which ink has adhered. The post-treatment liquid is ejected from the post-treatment head 6 onto a position on the workpiece W where ink has been ejected from the ink head 4. The pre-treatment liquid and the post-treatment liquid may be ejected onto substantially the entire surface of the workpiece W, or, like ink, the pre-treatment liquid and the post-treatment liquid may be selectively ejected in accordance with the image to be printed.

[0023] For example, when the pretreatment liquid and the posttreatment liquid are selectively ejected, the pretreatment liquid, the ink, and the posttreatment liquid are ejected in this order onto the portion of the workpiece W where a color is to be printed according to the image. In this case, the ink may be of one color or multiple colors. In the portion where no color is to be printed, i.e., the portion where the ink is not to be ejected, the pretreatment liquid and the posttreatment liquid are basically not ejected either. Note that, in order to adjust the image quality of the printed image and the texture of the workpiece W, the selection of the ejection of the pretreatment liquid and the posttreatment liquid may be partially different from the ejection of the ink. For example, the pretreatment liquid and the posttreatment liquid may be printed in an area slightly larger (e.g., a few pixels) than the area printed with ink.

[0024] Openings 31H are provided at the locations where the heads are arranged in the head support frame 31. The ink heads 4A to 4F, pre-processing head 5, and post-processing head 6 are each assembled to the head support frame 31 so as to fit into each opening 31H. Nozzles arranged on the lower end surfaces of the heads 4 to 6 are exposed from each opening 31H.

[0025] The subtanks 7 are supported by the carriage 3 above the heads 4 to 6 via a holding frame (not shown). A subtank 7 is provided corresponding to each of the heads 4 to 6. Each subtank 7 is supplied with ink, pre-treatment liquid, and post-treatment liquid from a cartridge (not shown) or a main tank (not shown) that contains the ink, pre-treatment liquid, and post-treatment liquid. Each subtank 7 supplies the ink, pre-treatment liquid, or post-treatment liquid to each of the heads 4 to 6. Each subtank 7 and the heads 4 to 6 are connected by a conduit (not shown). In this embodiment, the subtank 7 is configured to include a pair of first and second subtanks 71, 72 for each of the heads 4 to 6. The subtank 7 will be described in more detail below in the description of the supply and recovery of ink, pre-treatment liquid, and post-treatment liquid to the heads 4 to 6.

[0026] As described above, the inkjet printer 1 according to this embodiment is an all-in-one printer in which three types of heads, the ink head 4, the pre-treatment head 5, and the post-treatment head 6, are mounted on a single carriage 3. With this printer 1, for example, in the printing process of inkjet printing onto fabric in digital textile printing, the process of ejecting the pre-treatment liquid and the process of ejecting the post-treatment liquid can be carried out in an integrated manner. This makes it possible to simplify the textile printing process and make the textile printing device more compact.

[0027] [Printing Method] The printing method executed by the inkjet printer 1 in this embodiment will be described. The inkjet printer 1 performs printing processing on the workpiece W using a serial printing method. Figure 4 is a schematic diagram showing the serial printing method used in this embodiment. In Figure 4, the carriage 3 is depicted in a simplified manner, with the pre-processing head 5 and post-processing head 6 omitted.

[0028] If the workpiece W has a wide size, it is not possible to print while continuously feeding the workpiece W. The serial printing method is a printing method in which a carriage 3 carrying an ink head 4 of each color moves back and forth in the main scanning direction S, and the workpiece W is intermittently fed in the transport direction F. Here, the ink head 4 has a predetermined printing width Pw in the transport direction F. The printing width Pw is approximately equal to the arrangement range of the ink ejection nozzles of the ink head 4.

[0029] 4, the width of each ink head 4 in the transport direction F is depicted as being approximately equal to the printing width Pw. In reality, the width of each ink head 4 in the transport direction F is greater than the printing width Pw and the arrangement range of the ejection nozzles.

[0030] FIG. 4 shows a state in which the carriage 3 moves in the forward direction SA in the main scanning direction S and has completed printing of a band-shaped image G1 with a printing width Pw. During this scanning in the forward direction SA, the feeding of the workpiece W is stopped. After printing the band-shaped image G1, the workpiece W is sent out in the transport direction F by a pitch corresponding to the printing width Pw. At this time, the carriage 3 waits in the return area 14 on the left end side. After sending out the workpiece W, the carriage 3 returns in the return direction SB as the timing belt 16 reverses. The workpiece W is in a stopped state. Then, as shown in FIG. 4, the carriage 3 moves in the return direction SB and prints a band-shaped image G2 with a printing width Pw upstream of the band-shaped image G1. Similar operations are repeated thereafter.

[0031] The workpiece W after printing by the inkjet printer 1 may be heated and dried by a heater (not shown) or the like provided in the inkjet printer 1. The printed portion of the workpiece W may be transported to a dryer separate from the inkjet printer 1 and dried by the dryer, rather than being wound up on a so-called take-up roller. 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 causes the volatile components contained in the ink and treatment liquid to evaporate and dissipate, facilitating the fixation of the ink and treatment liquid to the workpiece W.

[0032] The distance between heads, the distance between nozzle regions, and the distance between heads and nozzle regions are, for example, the distance along the main scanning direction S, and refer to the distance between the closest points between the heads. Alternatively, the distances may be the distance along the main scanning direction S between the centers of gravity of the areas occupied by the heads when viewed in a plan view.

[0033] Unless otherwise specified, the intervals between adjacent heads in the main scanning direction S (the intervals between the closest parts of each head, or the intervals between the centers of each head) are the same. Similarly, for a head arrangement with multiple rows, the intervals between adjacent heads in the transport direction F (the intervals between the centers of each head) are the same.

[0034] [Ink, Treatment Liquid (Pre-treatment Liquid, Post-treatment Liquid)] The ink ejected from the ink head 4 is not particularly limited, and can be one containing a pigment and a dye. For example, an ink containing a pigment and an aqueous medium can be used. The ink may further contain at least one selected from the group consisting of a surfactant, a polyol, and binder resin particles, as needed. 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. In this case, the cationic polymer contained in the post-treatment liquid and the anionic pigment undergo electrical reaction and aggregation on the surface of the recording medium, thereby preventing the binder resin contained in the ink from penetrating into the recording medium. This prevents the binder resin from penetrating into the gaps between fibers and bonding the fibers together when the recording medium is fabric. This improves the texture (feel, etc.) of the fabric to be printed.

[0035] More specifically, anionic pigments having anionic groups such as carboxyl groups, sulfonic acid groups, phosphate groups, phosphonic acid groups, phenylsulfonic acid groups, and phenylcarboxyl groups are preferred. The aqueous medium contained in the ink is a medium containing water as its main component. The aqueous medium may function as a solvent or as a dispersion medium. Specific examples of aqueous media include water and mixtures of water and polar solvents. Examples of polar solvents contained in aqueous media include methanol, ethanol, isopropyl alcohol, butanol, and methyl ethyl ketone. Furthermore, the ink contains a surfactant, which improves the wettability of the ink to the recording medium.

[0036] The binder resin particles contained in the ink exist in a dispersed state in an aqueous medium. The binder resin particles function as a binder that bonds the subject to be printed with the pigment. Therefore, by including binder resin particles in the ink, it is possible to obtain a printed product with excellent pigment fixation. Examples of resins contained in the binder resin particles include urethane resin, (meth)acrylic resin, styrene-(meth)acrylic resin, styrene-maleic acid copolymer, vinylnaphthalene-(meth)acrylic acid copolymer, and vinylnaphthalene-maleic acid copolymer. Urethane resin is preferred as the resin contained in the binder resin particles.

[0037] The binder resin content may be 1% by weight or more and 20% by weight or less, or 2% by weight or more and 10% by weight or less, based on the total weight of the ink. When the binder resin particle content is 1% by weight or more, a recording medium with excellent pigment fixation can be obtained. On the other hand, when the binder resin particle content is 20% by weight or less, the ink can be stably ejected onto the recording medium.

[0038] Any pretreatment liquid can be used as the pretreatment liquid ejected by the pretreatment head 5. For example, a pretreatment liquid that aggregates the pigment in the ink to improve color development and fixation can be used. The pretreatment liquid may be one that suppresses the penetration of the ink into the recording medium, or conversely, promotes penetration, prints thickly to create a three-dimensional shape, or imparts gloss.

[0039] 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 with and aggregates the pigment contained in the ink to be subsequently printed, improving color development. It can also improve washing fastness and the texture of the fabric. The content of the water-soluble cationic polymer may be 0.1 wt % or more and less than 10 wt % of the total pretreatment liquid. By making the content of the water-soluble cationic polymer less than 10 wt %, sufficient wet rub fastness can be obtained. The aqueous medium contained in the pretreatment liquid can be the same as that of the ink.

[0040] Any post-treatment liquid can be used as the post-treatment liquid ejected from the post-treatment head 6. For example, a post-treatment liquid that improves texture can be used. The post-treatment liquid may be a liquid that coats the printed ink to protect it, prints it thickly to create a three-dimensional shape, or imparts gloss. The post-treatment liquid may also be a liquid that performs a treatment that is not directly related to ink printing, such as imparting water repellency to the recording medium (work).

[0041] The post-treatment liquid may contain, for example, emulsified particles containing silicone oil, a surfactant, and an aqueous medium. That is, 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 contain unmodified silicone oil. Examples of unmodified silicone oil include dimethylpolysiloxane, methylphenylsilicone oil, and methylhydrogensilicone oil. Such a post-treatment liquid can improve the texture.

[0042] The surfactant may include a first surfactant containing an alkyl group having 12 to 14 carbon atoms and a second surfactant containing an alkyl group having 16 to 18 carbon atoms. Polyoxyethylene alkyl ether may be used for both surfactants.

[0043] The aqueous medium contained in the post-treatment liquid may be the same as that contained in the ink. The post-treatment liquid and the pre-treatment liquid are basically different treatment liquids. More specifically, the components contained in the post-treatment liquid and the pre-treatment liquid are different.

[0044] Here, a non-color-forming treatment liquid refers to a treatment liquid that, when printed alone on a recording medium, is not perceived as having a color by the naked eye. Colors here include colors with a saturation of zero, such as black, white, and gray. A non-color-forming treatment liquid is essentially a transparent liquid; however, when viewed in its liquid state, for example, 1 liter of treatment liquid may not be completely transparent, but may appear slightly white. Such colors are so faint that, when printed alone on a recording medium, they are not perceived as having a color by the naked eye. Note that, depending on the type of treatment liquid, when printed alone on a recording medium, changes such as gloss may appear on the recording medium, but such a state is not considered color-forming.

[0045] [Description of Supply and Recovery of Liquid to Heads] The supply and recovery of ink, pre-treatment liquid, and post-treatment liquid to and from the ink head 4, pre-treatment head 5, and post-treatment head 6, respectively, in the inkjet printer 1 of this embodiment will be described.

[0046] The configuration for supplying and recovering ink to and from the ink head 4, the configuration for supplying and recovering pre-treatment liquid to and from the pre-treatment head 5, and the configuration for supplying and recovering post-treatment liquid to and from the post-treatment head 6 are similar, so the configuration and operation for supplying and recovering ink to and from the ink head 4 will be described as a representative, and descriptions of the configuration and operation for supplying and recovering pre-treatment liquid to and from the pre-treatment head 5, and the configuration and operation for supplying and recovering post-treatment liquid to and from the post-treatment head 6 will be omitted. Note that in the description of the configuration and operation for supplying and recovering ink to and from the ink head 4, by replacing the ink head 4 and ink with the pre-treatment head 5 and pre-treatment liquid, respectively, the description of the configuration and operation for supplying and recovering ink to and from the ink head 4 becomes the description of the configuration and operation for supplying and recovering pre-treatment liquid to and from the pre-treatment head 5, and by replacing the ink head 4 and ink with the post-treatment head 6 and post-treatment liquid, respectively, the description of the configuration and operation for supplying and recovering ink to and from the ink head 4 becomes the description of the configuration and operation for supplying and recovering post-treatment liquid to and from the post-treatment head 6.

[0047] Fig. 5 is a schematic diagram showing the mechanical configuration of the inkjet printer, mainly related to the supply and recovery of ink to the ink head. Fig. 6 is a block diagram showing the electrical configuration of the inkjet printer, mainly related to the supply and recovery of ink to the ink head.

[0048] 5 and 6, the inkjet printer 1 includes first and second sub-tanks 71, 72, the ink head 4, and a flow generating unit 80 for supplying and recovering ink to and from the ink head 4. In the example shown in Figures 5 and 6, the inkjet printer 1 also includes a main tank 73, first and second valves 751, 752, first through fourth liquid level detectors 911-914, a temperature measuring unit 92, a control processing unit 93, an input unit 94, a display unit 95, an interface unit (IF unit) 96, first and second heaters 971, 972, and a memory unit 98. Note that a cartridge may be used instead of the main tank 73.

[0049] The first and second sub-tanks 71, 72 are containers that contain ink. Note that ink is an example of a liquid, and the first and second sub-tanks 71, 72 are an example of a first and second container that contain a liquid.

[0050] The ink head 4 is disposed between the first and second sub-tanks 71, 72 and is connected to each of the first and second sub-tanks 71, 72 so that ink can flow therethrough. More specifically, the ink head 4 and the first sub-tank 71 are connected (communicate) with each other by a twelfth tube 742 of a flow path. The ink head 4 and the second sub-tank 72 are connected (communicate) with each other by a fourteenth tube 744 of a flow path. The ink head 4 is connected to each of the first and second storage sections so that the liquid can flow therethrough, and corresponds to an example of a head section that is equipped with a nozzle that ejects the liquid.

[0051] The flow generating unit 80 is a device that alternately performs a first flow direction process, which causes ink to flow from the first subtank 71 to the second subtank 72 via the ink head 4, and a second flow direction process, which causes the ink to flow from the second subtank 72 to the first subtank 71 via the ink head 4. More specifically, the flow generating unit 80 includes differential pressure generating units 81-85 that generate a differential pressure between a first atmospheric pressure applied to a first liquid surface of the ink contained in the first subtank 71 and a second atmospheric pressure applied to a second liquid surface of the ink contained in the second subtank 72, and a control unit 86 (931) that controls the differential pressure. The differential pressure is set so that the amount of ink transferred per unit time from one of the first and second subtanks 71, 72 to the other is greater than the maximum amount of ink ejected per unit time during printing. For example, the differential pressure is set so that the amount of ink transferred is approximately 1.1 times the maximum amount of ink ejected. This makes it possible to prevent the other ink from running out even when printing is performed with the maximum amount of ink ejected.

[0052] More specifically, in the example shown in FIG. 5, the flow generating unit 80 includes a compressor 81 , a vacuum ejector 82 , first and second pressure adjusting units 83 and 84 , and a flow path switching unit 85 .

[0053] The compressor 81 is electrically connected to the control unit 86 (931) and is a device that generates a predetermined positive pressure under the control of the control unit 86 (931). The compressor 81 is connected (communicates) with the first pressure adjustment unit 83 by a 21st pipe 861 of the flow path, and is connected (communicates) with the vacuum ejector 82 by a 23rd pipe 863 of the flow path. Note that the flow generating unit 80 may not include the compressor 81 and may receive pressure from an external pressure source. For example, the flow generating unit 80 may receive a constant-pressure air supply from the outside.

[0054] The vacuum ejector 82 is a device that generates a predetermined negative pressure (negative pressure) using the positive pressure air (compressed air) generated by the compressor 81. The vacuum ejector 82 is connected (communicates) with the second pressure adjustment unit 84 by a 24th pipe 864 of the flow path.

[0055] The first and second pressure adjustment units 83, 84 are each electrically connected to the control unit 86 (931) and are devices that adjust the pressure to a predetermined level in accordance with the control of the control unit 86 (931), and are configured, for example, with a pressure adjustment valve that adjusts the pressure on the primary side to the predetermined pressure on the secondary side by adjusting the opening degree.

[0056] The flow path switching unit 85 is electrically connected to the control unit 86 (931) and is a device that switches the flow path between the primary side and the secondary side under the control of the control unit 86 (931). For example, it is configured with a 5-port solenoid valve 85 having three first to third ports PT1 to PT3 on the primary side and two fourth and fifth ports PT4 and PT5 on the secondary side. The second port PT2 on the primary side is connected (communicated) to the first pressure adjustment unit 83 by a 22nd flow path tube 862. The first and third ports PT1 and PT3 on the primary side are connected (communicated) to the second pressure adjustment unit 84 by a 25th flow path tube 865. The fourth port PT4 on the secondary side is connected (communicated) to the first sub-tank 71 by an 11th flow path tube 741. The fifth port PT5 on the secondary side is connected (communicated) to the second sub-tank 72 by a 13th flow path tube 743.

[0057] In this embodiment, the control unit 86 (931) is functionally configured in the control processing unit 93, as will be described later. The control unit 86 (931) controls the pressure difference generated between the first and second atmospheric pressures. In this embodiment, the control unit 86 (931) also controls the compressor 81, the first and second pressure adjustment units 83 and 84, and the first and second valves 751 and 752 in accordance with the functions of the respective units 81, 83, 84, 751, and 752.

[0058] The main tank 73 is a container that stores ink in order to supply the ink to the second sub-tank 72. The capacity of the main tank 73 is usually larger than the capacity of the second sub-tank 72. The main tank 73 and the second sub-tank 72 are connected (communicated) by a 15th pipe 745 of a flow path. The main tank 73 is connected to the second storage section so that the liquid can flow therethrough, and corresponds to an example of a third storage section that stores the liquid.

[0059] In this configuration, the first and second sub-tanks 71 and 72 are independent in terms of the flow of ink, except that they are connected so that ink can flow through them via the ink head 4 .

[0060] The first valve 751 is disposed between the first sub-tank 71 and the ink head 4. More specifically, the first valve 751 is inserted into the twelfth pipe 742. The first valve 751 is a purge valve that can open and close the ink flow path between the first sub-tank 71 and the ink head 4. The first valve 751 is electrically connected to the control unit 86 (931) and is opened and closed under the control of the control unit 86 (931).

[0061] The second valve 752 is disposed between the second sub-tank 72 and the ink head 4. More specifically, the second valve 752 is inserted into the fourteenth pipe 744. The second valve 752 is a purge valve that can open and close the ink flow path between the first sub-tank 71 and the ink head 4. The second valve 752 is electrically connected to the control unit 86 (931) and is opened and closed under the control of the control unit 86 (931).

[0062] 5 and 6, the inkjet printer 1 is configured to include the first and second valves 751, 752, but it may be configured to include either the first or second valve 751, 752. In other words, the inkjet printer 1 may be configured to include at least one of the first and second valves 751, 752.

[0063] The first liquid level detector 911 is electrically connected to the control processor 93 and is a sensor that, under the control of the control processor 93, detects whether the ink contained in the first subtank 71 has fallen below a first liquid level. The first liquid level detector 911 is, for example, a sensor that detects the presence or absence of ink relative to the sensor and is disposed at a height from the bottom of the first subtank 71 that corresponds to a preset first liquid level. The first liquid level detector 911 is, for example, configured with a capacitance sensor or the like and disposed on the outer circumferential surface of the first subtank 71. The first liquid level is set, for example, so that the first subtank 71 contains at least an amount of ink that enables printing from the start of printing to the start of the next switching period. For example, in the case of a serial printing method, the first liquid level is set at least such that the first subtank 71 contains an amount of ink that enables one-way printing (forward and backward). The first liquid level detector 911 outputs the detection result (first detection result) to the control processor 93 .

[0064] The second liquid level detector 912 is electrically connected to the control processor 93 and is a sensor that, under the control of the control processor 93, detects whether the ink contained in the first subtank 71 exceeds a second liquid level. The second liquid level is set in advance, as appropriate, depending on the specifications, so as to be higher than the first liquid level. The second liquid level is set between the top surface of the first subtank 71 and the first liquid level, and is set, for example, so that the first subtank 71 can store at least an amount of ink that will enable printing from the start of printing to the start of the next switching period. In other words, the second liquid level is set so that the capacity of the first subtank 71 above the second liquid level is greater than the amount of ink that will enable printing from the start of printing to the start of the next switching period. For example, in the case of a serial printing method, the second liquid level is set so that the first subtank 71 can store at least an amount of ink that will enable one-way printing. The second liquid level detection unit 912 is, for example, a sensor that detects the presence or absence of ink in the sensor, and is disposed at a height from the bottom surface that corresponds to the second liquid level height in the first subtank 71. The second liquid level detection unit 912 is configured to include, for example, a capacitance sensor, and is disposed on the outer peripheral surface of the first subtank 71. The second liquid level detection unit 912 outputs its detection result (second detection result) to the control processing unit 93.

[0065] The third liquid level detector 913 is electrically connected to the control processing unit 93 and is a sensor that, under the control of the control processing unit 93, detects whether the ink contained in the second subtank 72 has fallen below a third liquid level. The third liquid level detector 913 is, for example, a sensor that detects the presence or absence of ink relative to the sensor and is disposed at a height from the bottom of the second subtank 72 that corresponds to a preset third liquid level. The third liquid level detector 913 is, for example, configured with a capacitance sensor or the like and disposed on the outer circumferential surface of the second subtank 72. The third liquid level is set so that at least an amount of ink sufficient to enable printing from the start of printing to the start of the next switching period is stored in the second subtank 72. If the first and second subtanks 71 and 72 have the same shape and size, the third liquid level may be lower than the first liquid level, or may be the same as or higher than the first liquid level. This point will be described further below. The third liquid level is set, for example, to a height close to the bottom surface of the second sub-tank 72. The third liquid level detector 913 outputs the detection result (third detection result) to the control processor 93.

[0066] The fourth liquid level detection unit 914 is electrically connected to the control processing unit 93 and is a sensor that, under the control of the control processing unit 93, detects whether the ink contained in the second subtank 72 has exceeded a fourth liquid level. The fourth liquid level is set in advance, for example, according to specifications, so as to be higher than the third liquid level. The fourth liquid level is set, for example, to a height close to the top surface of the second subtank 72. The fourth liquid level detection unit 914 is, for example, a sensor that detects the presence or absence of ink relative to the sensor and is disposed at a height from the bottom surface that corresponds to the fourth liquid level in the second subtank 72. The fourth liquid level detection unit 914 is, for example, configured with a capacitance sensor or the like and is disposed on the outer peripheral surface of the second subtank 72. The fourth liquid level detection unit 914 outputs its detection result (fourth detection result) to the control processing unit 93.

[0067] The interval (first interval) between the first and second liquid level heights is set to be relatively narrow. For example, the first and second liquid level heights are set so that the capacity of the first sub-tank 71 from the first to second liquid level heights allows for approximately 10 round trips of printing using a serial printing method. The amount that allows for 10 round trips of printing may be the amount required for so-called solid printing, which consumes the most liquid. The interval (second interval) between the third and fourth liquid level heights is set to be relatively wide. When the first and second sub-tanks 71, 72 have the same shape and size, the first interval is narrower than the second interval (the second interval is wider than the first interval).

[0068] The temperature measurement unit 92 is electrically connected to the control processing unit 93, and is a sensor that is disposed between the first and second sub-tanks 71, 72 and measures the temperature of the ink under the control of the control processing unit 93. The temperature measurement unit 92 is, for example, disposed on the outer surface of the twelfth tube 742 and is configured with a temperature sensor that indirectly measures the temperature of the ink by measuring the temperature of the twelfth tube 742. The temperature measurement unit 92 outputs the measurement result (ink temperature) to the control processing unit 93. The temperature measurement unit 92 may be disposed on the outer surface of the fourteenth tube 744, or may be disposed in the ink head 4.

[0069] The input unit 94 is electrically connected to the control processing unit 93 and is a device that inputs various commands, such as commands to start printing and commands to start maintenance, and various data required to operate the inkjet printer 1, such as the number of sheets to be printed, to the inkjet printer 1, and is, for example, a plurality of input switches to which predetermined functions are assigned. The display unit 95 is electrically connected to the control processing unit 93 and is a device that displays the commands and data input from the input unit 94 in accordance with the control of the control processing unit 93, and is, for example, a display device such as an LCD (liquid crystal display) or an organic EL display.

[0070] The input unit 94 and the display unit 95 may be configured as a touch panel. In this case, the input unit 94 is a position input device, such as a resistive film type or a capacitive type, that detects an operation position and inputs the information. In this touch panel, the position input device is provided on the display surface of the display unit 95, and one or more input content options are displayed on the display unit 95. When the user touches the display position showing the input content they want to input, the position is detected by the position input device, and the content displayed at the detected position is input to the inkjet printer 1 as the user's operation input content. With such a touch panel, the user can easily intuitively understand input operations, providing an inkjet printer 1 that is easy for the user to use.

[0071] The IF unit 96 is electrically connected to the control processing unit 93 and is a circuit that inputs and outputs data to and from, for example, an external device under the control of the control processing unit 93, and is, for example, an interface circuit for RS-232C, which is a serial communication method, an interface circuit using the Bluetooth (registered trademark) standard, an interface circuit using the USB standard, etc. The IF unit 96 may also be, for example, a communication interface circuit that transmits and receives communication signals to and from an external device, such as a data communication card or a communication interface circuit conforming to the IEEE 802.11 standard, etc.

[0072] Data (image data) of the image to be printed on the workpiece W is stored in a storage medium such as a USB (Universal Serial Bus) memory or an SD card (registered trademark), and is input from the storage medium to the inkjet printer 1 via the IF unit 96. Alternatively, for example, the image data is recorded on a storage medium such as a CD-R (Compact Disc Recordable) or a DVD-R (Digital Versatile Disc Recordable), and is input from the storage medium to the inkjet printer 1 via a drive device for the storage medium and the IF unit 96. Alternatively, for example, the image data is input to the inkjet printer 1 from a management server that manages the image data, via a network and the IF unit 96.

[0073] The first heating unit 971 is electrically connected to the control processing unit 93 and is a device that heats the ink contained in the first sub-tank 71 in accordance with the control of the control processing unit 93. The first heating unit 971 is configured to include, for example, a heater disposed in the first sub-tank 71.

[0074] The second heating unit 972 is electrically connected to the control processing unit 93, and is a device that heats the ink contained in the second sub-tank 72 in accordance with the control of the control processing unit 93. The second heating unit 972 is configured to include, for example, a heater disposed in the second sub-tank 72.

[0075] The storage unit 98 is electrically connected to the control processing unit 93 and is a circuit that stores various predetermined programs and various predetermined data under the control of the control processing unit 93. The various predetermined programs include, for example, a control processing program, which includes, for example, a control program, a supply control program, and a heating control program. The control programs are programs that control each part of the inkjet printer 1 according to its function. The supply control program is a program that supplies ink contained in the main tank 73 to the second sub-tank 72 when the third liquid level detection unit 913 detects that the ink has fallen below a third liquid level. The supply control program is further a program that stops the supply of ink contained in the second sub-tank 72 when the fourth liquid level detection unit 914 detects that the ink has exceeded a fourth liquid level. The supply control program is also a program that issues an alarm to the outside when the fourth liquid level detection unit 914 detects that the ink has exceeded the fourth liquid level. The heating control program is a program that controls the first and second heating units 971, 972 so as to heat the ink contained in the first and second sub-tanks 71, 72, respectively, based on the ink temperatures measured by the temperature measurement unit 92. The various types of predetermined data include data necessary for executing these programs.

[0076] The storage unit 98 includes, for example, a ROM (Read Only Memory), which is a nonvolatile storage element, or an EEPROM (Electrically Erasable Programmable Read Only Memory), which is a rewritable nonvolatile storage element. The storage unit 98 also includes a RAM (Random Access Memory), which serves as a working memory for the control processing unit 93 and stores data generated during execution of the predetermined program. The storage unit 98 may also include a hard disk drive or solid state drive (SSD) with a relatively large storage capacity.

[0077] The control processing unit 93 is a circuit that controls each unit of the inkjet printer 1 according to the function of that unit, and prints an image on the workpiece W. The control processing unit 93 is configured, for example, to include a CPU (Central Processing Unit) and its peripheral circuits. When the control processing program is executed in the control processing unit 93, a control unit 931 (86), a supply control unit 932, and a heating control unit 933 are functionally configured.

[0078] The control unit 931 (86) controls each part of the inkjet printer 1 according to the function of each part, and is responsible for overall control of the inkjet printer 1. With regard to the supply and recovery of ink to the ink head 4, the control unit 931 (86) controls the differential pressure by controlling the five-port solenoid valve 85, which is an example of a flow path switching unit, as described above, and also controls the compressor 81, first and second pressure adjustment units 83, 84, and first and second valves 751, 752 according to the functions of each of the parts 81 to 84, 751, 752.

[0079] More specifically, the control unit 931 (86) operates the compressor 81 to generate a predetermined positive pressure. When the positive pressure is generated, a predetermined negative pressure is generated in the vacuum ejector 82 by the positively pressurized air (compressed air) generated by the compressor 81. The control unit 931 (86) controls the first pressure adjustment unit 83 so that the predetermined positive pressure becomes a predetermined air pressure (first adjusted air pressure), and controls the second pressure adjustment unit 83 so that the predetermined negative pressure becomes a predetermined air pressure (second adjusted air pressure) lower than the first adjusted air pressure. The difference between the first adjusted air pressure and the second adjusted air pressure is the differential pressure, and the control unit 931 (86) controls the differential pressure generated between the first air pressure applied to a first liquid surface of the ink contained in the first sub-tank 71 and the second air pressure applied to a second liquid surface of the ink contained in the second sub-tank 72.

[0080] The flow generating unit 80 performs a first flow direction process by controlling the pressure difference using the control unit 931 (86) so that the first atmospheric pressure is greater than the second atmospheric pressure, and performs a second flow direction process by controlling the pressure difference using the control unit 931 (86) so that the second atmospheric pressure is greater than the first atmospheric pressure, and switches between these first and second flow direction processes while printing is paused (temporarily stopped). For example, if the inkjet printer 1 uses a serial printing method, switching between these first and second flow direction processes is performed during a switching period when printing is temporarily stopped to switch between the forward pass and the return pass.

[0081] 7A and 7B are diagrams illustrating switching of flow paths in a five-port solenoid valve as an example of a flow path switching unit. Fig. 7A shows a state of a first flow path in which the second port PT2 and the fourth port PT4 are communicable with each other and the third port PT3 and the fifth port PT5 are communicable with each other. Fig. 7B shows a state of a second flow path in which the first port PT1 and the fourth port PT4 are communicable with each other and the second port PT2 and the fifth port PT5 are communicable with each other.

[0082] 7A , during a printing pause, the control unit 931 (86) controls the position of the spool SP of the five-port solenoid valve 85 so as to enable communication between the second port PT2 and the fourth port PT4 and between the third port PT3 and the fifth port PT5. As a result, the first adjusted pressure is applied as a first atmospheric pressure to the first liquid level of ink in the first subtank 71, and the second adjusted pressure is applied as a second atmospheric pressure to the second liquid level of ink in the second subtank 72. As a result, the first atmospheric pressure (= first adjusted pressure) becomes greater than the second atmospheric pressure (= second adjusted pressure), causing ink to flow from the first subtank 71 to the second subtank 72 via the ink head 4, thereby performing the first flow direction process. 7B , during a printing pause, the control unit 931 (86) controls the position of the spool SP of the five-port solenoid valve 85 so as to enable communication between the first port PT1 and the fourth port PT4 and between the second port PT2 and the fifth port PT5. As a result, the second adjusted pressure is applied as a first adjusted pressure to the first liquid level of ink in the first subtank 71, and the first adjusted pressure is applied as a second adjusted pressure to the second liquid level of ink in the second subtank 72. As a result, the second adjusted pressure (= first adjusted pressure) becomes greater than the first adjusted pressure (= second adjusted pressure), and ink flows from the second subtank 72 to the first subtank 71 via the ink head 4, thereby performing the second flow direction process.

[0083] Such a five-port solenoid valve 85 corresponds to an example of a flow path switching unit that switches between a combination of connecting the first storage unit to the supply source of the first atmospheric pressure and connecting the second storage unit to the supply source of the second atmospheric pressure, and a combination of connecting the first storage unit to the supply source of the second atmospheric pressure and connecting the second storage unit to the supply source of the first atmospheric pressure.

[0084] The control unit 931 (86) controls the differential pressure, which is the difference between the first adjusted pressure and the second adjusted pressure, so as to maintain a meniscus formed by ink in the nozzles that eject ink in the ink head 4. More specifically, in this embodiment, the first and second adjusted pressures are set appropriately in advance so that the differential pressure is slightly positive or negative in order to maintain the meniscus, and the control unit 931 (86) controls the first pressure adjustment unit 83 to set the pressure to the first adjusted pressure and the second pressure adjustment unit 84 to set the pressure to the second adjusted pressure. Note that, although the first adjusted pressure is a positive pressure and the second adjusted pressure is a negative pressure in the above description, the differential pressure may be generated with both the first and second adjusted pressures being positive pressures, in which case the vacuum ejector 82 can be omitted.

[0085] Switching between the first and second flow direction processes in this manner typically causes fluctuations (transient response) in the differential pressure. For this reason, the inkjet printer 1, under the control of the control processing unit 93, resumes printing after a predetermined time (first time) has passed during which the fluctuations in the differential pressure subside. That is, the control processing unit 93 pauses (temporarily stops) printing when switching from the second flow direction process to the first flow direction process, and resumes printing after the differential pressure has reached a steady state. The control processing unit 93 pauses (temporarily stops) printing when switching from the first flow direction process to the second flow direction process, and resumes printing after the differential pressure has reached a steady state. The first time is set appropriately in advance, for example, based on multiple samples. Setting the first time in this manner enables stable printing and maintains a predetermined print quality.

[0086] The maximum amplitude and duration of the fluctuation in the differential pressure (transient response time, the time from the start of the flow direction process until the fluctuation disappears) depend on, for example, the flow path resistance of the twelfth tube 742, the flow path resistance of the fourteenth tube 744, the inertance of the ink in the first subtank 71, the inertance of the ink in the second subtank 72, the compliance of the ink in the first subtank 71, and the compliance of the ink in the second subtank 72, and the maximum amplitude and duration can be adjusted by adjusting one or more of these. Alternatively, for example, the maximum amplitude and duration depend on the differential pressure, the flow rate of ink flowing from the first subtank 71 to the second subtank 72 in the first flow direction process, and the flow rate of ink flowing from the second subtank 72 to the first subtank 71 in the second flow direction process, and the maximum amplitude and duration can be adjusted by adjusting one or more of these. Alternatively, for example, the maximum amplitude and the duration depend on the switching speed of the flow path in the five-port solenoid valve 85 (the movement speed of the spool SP), and the maximum amplitude and the duration can be adjusted by adjusting this. Therefore, in order to suppress fluctuations in the differential pressure, the flow generating unit 80 may gradually change the magnitude of the differential pressure, thereby gradually changing the pressure from the first adjusted pressure to the second adjusted pressure at the first atmospheric pressure, and from the second adjusted pressure to the first adjusted pressure at the second atmospheric pressure, and also gradually changing from the first adjusted pressure to the second adjusted pressure at the second atmospheric pressure, and from the second adjusted pressure to the first adjusted pressure at the first atmospheric pressure.

[0087] In addition, the flow path resistance of the ink head 4, the inertance of the ink at the meniscus, and the compliance of the ink at the meniscus may be designed so that the meniscus can be maintained against fluctuations in the differential pressure, and the ink head 4 may be formed according to the design.

[0088] Furthermore, when the liquid transfer is reversed, the transfer can be switched quickly. When the transfer is switched by switching the pressure, the pressure, which is the driving source, basically switches abruptly, and the amount of fluctuation is larger than at the start or end of transfer (the pressure change at the start of transfer is 0 to +P (P is the pressure value) for supply and 0 to -P for recovery, whereas the pressure change when the transfer is reversed is -P to +P for supply and +P to -P for recovery, resulting in a pressure fluctuation that is twice as large). It is desirable to be able to maintain the meniscus even in the face of such pressure fluctuations.

[0089] In the above description, printing is resumed after a predetermined time (first time) has elapsed during which the fluctuations in the differential pressure subside, but printing may also be resumed after a predetermined time has elapsed during which the fluctuations in the liquid caused by the switching subside. The predetermined time during which the fluctuations in the liquid subside is, for example, the time until a parameter such as pressure, flow rate, or flow velocity becomes a predetermined percentage or less of its initial value, or the time until the parameter attenuates to a predetermined value or less. For example, the predetermined time during which the fluctuations in the liquid subside is the time until the pressure becomes 1 / 10 or less, or even 1 / 100 or less, of the initial value of the fluctuations, or even less, and becomes the level of fluctuations caused by disturbances or the ejection itself, which occur even in a steady state.

[0090] As described above, the inkjet printer 1 performs printing on the workpiece W using a serial printing method, and therefore switching between the first and second flow direction processes may be performed while the carriage 3 is located in the return area 14 or while the carriage 3 is located in the maintenance area 13. In other words, the flow generating unit 80 switches between the first and second flow direction processes during at least one of a first switching period in which the movement direction of the ink head 4 is switched from the forward path to the backward path when the ink head 4 is reciprocated along a first direction (main scanning direction) S that intersects with a second direction (transport direction) F in which the workpiece W moves, and a second switching period in which the movement direction of the ink head 4 is switched from the forward path to the backward path. The start of the first switching period can be determined, for example, by the end of printing the forward path of the image data, and the start of the second switching period can be determined by the end of printing the backward path of the image data. Alternatively, a photointerrupter may be provided in the turn-around area 14 and used to detect the carriage 3 entering the turn-around area 14, thereby determining the start of the first switching period, and a photointerrupter may be provided in the maintenance area 13 and used to detect the carriage 3 entering the maintenance area 13, thereby determining the start of the second switching period. The time lengths of the first and second switching periods are known in advance based on the specifications of the inkjet printer 1.

[0091] In this embodiment, switching between the first and second flow direction processes is possible both while the carriage 3 is located in the turning area 14 (first switching period) and while the carriage 3 is located in the maintenance area 13 (second switching period). This reduces the amount of ink below the first liquid level height and the amount of ink above the second liquid level height, which is advantageous in terms of head difference. Note that switching between the first and second flow direction processes may be possible only during the longer of the first and second switching periods. This increases the possibility of implementing the first and second flow direction processes without changing the length of the previous switching period.

[0092] As described above, the inkjet printer 1 has multiple heads 4 to 6 arranged side by side in the main scanning direction on the carriage 3. Therefore, when the multiple heads 4 to 6 are moved back and forth along the main scanning direction S, the first time period may be the time from when the rearmost head 4 to 6 in the moving direction of the multiple heads 4 to 6 stops printing until when the head 4 to 6 starts printing again when the direction of the reciprocating movement is switched. By setting the first time period in this way, switching between the first and second flow direction processes can be performed reliably.

[0093] Then, when the first liquid level detection unit 911 detects that the ink has fallen below the first liquid level height while the first flow direction process is being performed, the flow generation unit 80 switches from the first flow direction process to the second flow direction process during the next switching period for switching between the first and second flow direction processes, and when the second liquid level detection unit 912 detects that the ink has exceeded the second liquid level height while the second flow direction process is being performed, the flow generation unit 80 switches from the second flow direction process to the first flow direction process during the next switching period. More specifically, when the flow generation unit 80 switches from the second flow direction process to the first flow direction process, the flow generation unit 80 stores a predetermined flag (flow direction flag) in the memory unit 98 while the first flow direction process is being performed. When the flow generation unit 80 switches from the first flow direction process to the second flow direction process, the flow generation unit 80 stores the flow direction flag in the memory unit 98 while the second flow direction process is being performed. The flow direction flag is information indicating the flow direction process currently being performed. For example, when the first flow direction process is being performed, it is represented by "1" and when the second flow direction process is being performed, it is represented by "2." When the first liquid level detection unit 911 detects that the ink has fallen below the first liquid level height, the flow generation unit 80 stores a predetermined flag (switching flag) in the memory unit 98 as an instruction to switch the flow direction process. The switching flag is information indicating an instruction to switch the flow direction process in the next switching period. For example, an instruction to switch the flow direction process is represented by "1," and an instruction not to switch the flow direction process is represented by "0." When the second liquid level detection unit 912 detects that the ink has exceeded the second liquid level height, the flow generation unit 80 stores the switching flag in the memory unit 98 as an instruction to switch the flow direction process (=1). During forward printing, when the first switching period begins, the flow generation unit 80 references the flow direction flag and the switching flag stored in the memory unit 98 to determine whether the flow direction process is currently being performed and whether there is an instruction to switch the flow direction process. If this determination determines that the first flow direction process is currently being performed and there is an instruction to switch the flow direction process (flow direction flag = 1, switching flag = 1), the flow generation unit 80 switches from the first flow direction process to the second flow direction process, stores the flow direction flag in the memory unit 98 as indicating that the second flow direction process is currently being performed (= 2), and stores the switching flag in the memory unit 98 as an instruction not to switch the flow direction process (= 0).If the result of the above determination indicates that the second flow direction process is being performed and an instruction to switch the flow direction process is instructed (flow direction flag = 2, switch flag = 1), the flow generation unit 80 switches from the second flow direction process to the first flow direction process, stores the flow direction flag in the memory unit 98 as "first flow direction process in progress" (= 1), and stores the switch flag in the memory unit 98 as "not to switch the flow direction process" (= 0). If the result of the above determination indicates an instruction not to switch the flow direction process (flow direction flag = 1 or 2, switch flag = 0), the flow generation unit 80 continues the currently performed flow direction process. On the other hand, during the return pass printing, when the second switching period begins, the flow generation unit 80 references the flow direction flag and switch flag stored in the memory unit 98 to determine whether the currently performed flow direction process and an instruction to switch the flow direction process are instructed. The flow generation unit 80 operates in the same manner as described above depending on the result of this determination.

[0094] The inkjet printer 1 starts printing after the first time or more has elapsed since the control processing unit 93 switched between the first and second flow direction processes. During printing while the first flow direction process is being performed, ink is supplied from the first subtank 71 to the ink head 4 and the ink is recovered from the ink head 4 to the second subtank 72. During printing while the second flow direction process is being performed, ink is supplied from the second subtank 72 to the ink head 4 and the ink is recovered from the ink head 4 to the first subtank 71. By supplying and recovering ink in this manner, it is possible to prevent ink from accumulating near the ejection openings (nozzles). The differential pressure (first differential pressure) when switching between the first and second flow direction processes and the differential pressure (second differential pressure) between the first and second atmospheric pressures during printing may be equal to or different from each other. In either case, the first and second differential pressures are controlled (set) so as to maintain a meniscus formed in the nozzle.

[0095] The first flow path resistance from the nozzles of the ink head 4 that eject droplets to the first sub-tank 71 and the second flow path resistance from the ejection ports to the second sub-tank 72 may be different. However, as described above, because ink flows alternately in both directions through the ink head 4, the first flow path resistance and the second flow path resistance may be equal. This allows the print quality of the first flow direction process and the print quality of the second flow direction process to be approximately equal. The ink head 4 includes, for example, a member that forms a first common flow path connected to (communicating with) the twelfth tube 742, multiple individual flow paths connected to (communicating with) the first common flow path, and a second common flow path connected to (communicating with) the multiple individual flow paths. The second common flow path is connected to (communicating with) the fourteenth tube 744. Each of the multiple individual flow paths has a nozzle formed therein, and a pressure element, such as a piezoelectric element, that pressurizes the ink flowing through the individual flow path. When the pressure element is activated, the ink is pressurized, causing it to be ejected from the nozzle. In this configuration, the ink head 4 includes multiple nozzles. In this example, the first flow path resistance is the flow path resistance of the individual flow paths from the nozzles (the individual flow paths from the nozzles to the first common flow path), the first common flow path, and the twelfth tube 742. The second flow path resistance is the flow path resistance of the individual flow paths from the nozzles (the individual flow paths from the nozzles to the second common flow path), the second common flow path, and the fourteenth tube 744. In the first flow direction process, ink flows from the first subtank 71 to the second subtank 72 via the twelfth tube 742, the first common flow path, each of the multiple individual flow paths, the second common flow path, and the fourteenth tube 744. In the second flow direction process, ink flows from the second subtank 72 to the first subtank 71 via the fourteenth tube 744, the second common flow path, each of the multiple individual flow paths, the first common flow path, and the twelfth tube 742.

[0096] The supply control unit 932 supplies the ink contained in the main tank 73 to the second sub-tank 72 when the third liquid level detection unit 913 detects that the ink has fallen below the third liquid level. For example, a pump (not shown) is inserted into the fifteenth pipe 745, and ink is supplied from the main tank 73 to the second sub-tank 72 by operating the pump. This ink supply is stopped, for example, when the third liquid level detection unit 913 detects that the ink has exceeded the third liquid level. Alternatively, the ink supply may be continued for only a predetermined time (second time) that is appropriately set in advance.

[0097] By controlling in this manner, ink is alternately transferred so that the liquid level in the first subtank 71 fluctuates between the first liquid level height and the second liquid level height. This alternate transfer of ink causes the liquid level in the second subtank 72 to fluctuate between the third liquid level height and a height somewhere between the third liquid level height and the fourth liquid level height. Even if there is no decrease in ink due to printing, the liquid level in the second subtank 72 will not reach the fourth liquid level height.

[0098] When the fourth liquid level detection unit 914 detects that the ink level exceeds the fourth liquid level while the ink is being supplied from the main tank 73 to the second subtank 72, the supply control unit 932 stops the supply. This prevents ink from being supplied beyond the capacity of the second subtank 72 due to a malfunction, failure, or other problem. The liquid level in the second subtank 72 reaching the fourth liquid level is caused by some kind of malfunction. For example, this could occur if one of the liquid level detection units makes an erroneous detection, or if excessive ink is supplied from the main tank 73 to the second subtank 72. The supply control unit 932 also issues an alarm to the outside when the fourth liquid level detection unit 914 detects that the ink level exceeds the fourth liquid level. In this embodiment, the supply control unit 932 displays an error message on the display unit 95 as the warning. This allows the malfunction to be reported to the outside. The inkjet printer 1 may also be equipped with a buzzer or speaker, for example, to issue the alarm by sound.

[0099] The heating control unit 933 controls the first and second heating units 971 and 972 to heat the ink contained in the first and second sub-tanks 71 and 72, respectively, based on the ink temperature measured by the temperature measurement unit 92. More specifically, the heating control unit 933 compares the ink temperature measured by the temperature measurement unit 92 with a predetermined threshold (first temperature threshold) and, if the comparison results in the ink temperature being below the first temperature threshold, operates the first and second heating units 971 and 972, for example, for a predetermined time (third time) that is appropriately set in advance. Alternatively, for example, while the first and second heating units 971 and 972 are operating, the heating control unit 933 stops the operation of the first and second heating units 971 and 972 if the ink temperature measured by the temperature measurement unit 92 exceeds a predetermined threshold (second temperature threshold). The second temperature threshold is set to a value greater than the first temperature threshold. The first and second heating sections 971, 972 heat the ink contained in the first and second sub-tanks 71, 72, respectively, so that the temperature of the ink in the ink head 4 can be made uniform and the temperature distribution range can be reduced.

[0100] The control processing unit 93 and the storage unit 98 can be configured by a computer such as a one-chip computer or a one-board computer.

[0101] In the supply and recovery of the pre-treatment liquid to the pre-treatment head 5, the pre-treatment liquid corresponds to another example of the liquid, and the pre-treatment head 5 corresponds to another example of the head unit. In the supply and recovery of the post-treatment liquid to the post-treatment head 6, the post-treatment liquid corresponds to another example of the liquid, and the post-treatment head 6 corresponds to another example of the head unit.

[0102] Next, the operation will be described. Fig. 8 is a flowchart showing the operation of the inkjet printer, mainly related to the supply and recovery of ink to the ink head. Fig. 9 is a flowchart showing the operation of the inkjet printer, related to the supply of ink from the main tank to the second sub-tank.

[0103] When the inkjet printer 1 is powered on, it initializes the necessary components and begins operation. With regard to the supply and recovery of ink to the ink heads, the control processing unit 93 functionally configures a control unit 931 (86), a supply control unit 932, and a heating control unit 933 by executing a control processing program. Upon starting operation, the inkjet printer 1 executes one of the first and second flow direction processes, for example, the first flow direction process, using the control unit 931 (86) of the control processing unit 93. In this example, the inkjet printer 1 stores a flow direction flag of "1" in the memory unit 98 and a switching flag of "0" in the memory unit 98. With regard to the supply and recovery of ink to the ink heads, the inkjet printer 1 then repeatedly executes the following processes S11 through S23 at predetermined intervals.

[0104] In FIG. 8, the ink jet printer 1 acquires the detection results from the first to third liquid level detection units 911 to 913, respectively, and acquires the measured temperature from the temperature measurement unit 92, using the control unit 931 (86) (S11).

[0105] Next, the inkjet printer 1, using the control unit 931 (86), references the detection result (first detection result) of the first liquid level detection unit 911 and determines whether the ink level has fallen below the first liquid level (S12). If the result of this determination shows that the first detection result indicates that the ink level has fallen below the first liquid level (Yes), the control unit 931 (86) then executes process S14. If the result of the determination shows that the first detection result does not indicate that the ink level has fallen below the first liquid level (No), the control unit 931 (86) then executes process S13.

[0106] In process S13, the inkjet printer 1 uses the control unit 931 (86) to refer to the detection result (second detection result) of the second liquid level detection unit 912 and determine whether the ink has exceeded the second liquid level height. If the second detection result indicates that the ink has exceeded the second liquid level height (Yes), the control unit 931 (86) then executes process S14. If the second detection result does not indicate that the ink has exceeded the second liquid level height (No), the control unit 931 (86) then executes process S15.

[0107] In step S14, the ink jet printer 1 stores the switching flag "1" in the storage unit 98 by the control unit 931 (86), and then executes step S15.

[0108] In process S15, the inkjet printer 1 uses the control unit 931 (86) to refer to the detection result (third detection result) of the third liquid level detection unit 913 and determine whether the ink level has fallen below the third liquid level. If the result of this determination shows that the third detection result indicates that the ink level has fallen below the third liquid level (Yes), the control unit 931 (86) then instructs the supply control unit 932 to supply ink from the main tank 73 to the second sub-tank 72 (S16), and then executes process S17. The operation of supplying ink from the main tank 73 to the second sub-tank 72 will be described later. If the result of the determination shows that the third detection result does not indicate that the ink level has fallen below the third liquid level (No), the control unit 931 (86) then executes process S17.

[0109] In process S17, the inkjet printer 1 determines whether the measured temperature has fallen below the first temperature threshold using the heating control unit 933 of the control processing unit 93. If the result of this determination is that the measured temperature is below the first temperature threshold (Yes), the heating control unit 933 then starts heating the first and second heating units 971, 972, and causes the control unit 931 (86) to execute process S19 (S18). If the result of the determination is that the measured temperature is not below the first temperature threshold (No), the control unit 931 (86) then executes process S19.

[0110] When the heating control unit 933 starts the heating, it operates each of the first and second heating units 971, 972 for, for example, a predetermined time (third time) that is appropriately set in advance. Therefore, in this case, the heating control unit 933 ends (stops) the operation of each of the first and second heating units 971, 972 when the third time has elapsed since the start of operation.

[0111] In step S19, the inkjet printer 1 uses the control unit 931 (86) to determine whether the first switching period has begun. If the result of this determination is that the first switching period has begun (Yes), the control unit 931 (86) then executes step S21. If the result of the determination is that the first switching period has not begun (Yes), the control unit 931 (86) then executes step S20.

[0112] In step S20, the inkjet printer 1 uses the control unit 931 (86) to determine whether the second switching period has begun. If the result of this determination is that the second switching period has begun (Yes), the control unit 931 (86) then executes step S21. If the result of this determination is that the second switching period has not begun (Yes), the control unit 931 (86) ends the processing for the current timing.

[0113] In step S21, the inkjet printer 1 uses the control unit 931 (86) to refer to the switching flag to determine whether or not to switch between the first and second flow direction processes. If the result of this determination is an instruction not to switch (No), the control unit 931 (86) ends the processing at this timing. If the result of this determination is an instruction to switch (Yes), the control unit 931 (86) then executes step S22.

[0114] In step S22, the inkjet printer 1 performs the switching using the control unit 931 (86). More specifically, the control unit 931 (86) determines the flow direction process currently being performed by referencing the flow direction flag, and switches the flow direction process according to the result of the determination.

[0115] Next, the ink jet printer 1 processes the flow direction flag and the switching flag (S23) using the control unit 931 (86), and ends the processing at this timing.

[0116] In the above description, when the process S14 is executed, the execution of the processes S12, S13, and S14 may be skipped in the repetition of the processes S11 to S23 until the processes S21, S22, and S23 are executed.

[0117] The operation of supplying ink from the main tank 73 to the second sub-tank 72 will be described.

[0118] When the ink supply instruction is received, in FIG. 9, the ink jet printer 1 starts supplying ink from the main tank 73 to the second sub-tank 72 by the supply control unit 932 of the control processing unit 93 (S31).

[0119] Next, the ink jet printer 1 causes the supply control unit 932 to acquire the detection result from the fourth liquid level detection unit 914 (S32).

[0120] Next, the inkjet printer 1 uses the supply control unit 932 to refer to the detection result (fourth detection result) of the fourth liquid level detection unit 914 and determine whether the ink has exceeded the fourth liquid level height (S33). If the result of this determination shows that the fourth detection result indicates that the ink has exceeded the fourth liquid level height (Yes), the supply control unit 932 then executes process S36. If the result of the determination shows that the fourth detection result does not indicate that the ink has exceeded the fourth liquid level height (No), the supply control unit 932 then executes process S34.

[0121] In this process S34, the supply control unit 932 determines whether or not the ink supply has ended. If the result of this determination is that the ink supply has ended (Yes), the supply control unit 932 then ends the ink supply (S35) and ends this process. If the result of this determination is that the ink supply has not ended (No), the supply control unit 932 returns the process to process S32. Therefore, the supply control unit 932 continues the ink supply until it determines that the ink supply has ended.

[0122] In step S36, the ink jet printer 1 causes the supply control unit 932 to stop the supply of ink.

[0123] Next, the inkjet printer 1 issues an alarm to the outside via the supply control unit 932 (S37), and ends this process. The inkjet printer 1 stops due to the error.

[0124] In the inkjet printer 1 that operates in this manner, when the third liquid level detection unit 913 detects that the ink has fallen below the third liquid level height, ink is supplied from the third main tank 73 to the second subtank 72, and when the third liquid level detection unit 913 detects that the ink has risen above the third liquid level height, if the operation is stopped, in the second flow direction process, ink flows from the second subtank 72 to the first subtank 71, the liquid level in the second subtank 72 drops, and the liquid level in the first subtank 71 rises. During this time, the difference between the average liquid level in the first subtank 71 and the average liquid level in the second subtank 72 gradually decreases, and the head difference between the first and second subtanks 71, 72 also gradually decreases. The liquid level in the second subtank 72 then further drops, and when it falls below the third liquid level, ink is supplied from the main tank 73. Since the second flow direction process is in progress, the liquid level in the second subtank 72 is maintained at approximately the third liquid level, while the liquid level in the first subtank 71 rises. As a result, the difference between the average liquid level in the first subtank 71 and the average liquid level in the second subtank 72 gradually increases, and the head difference between the first and second subtanks 71, 72 also gradually increases. When the liquid level in the first subtank 71 exceeds the second liquid level, the first flow direction process is performed, and the liquid level in the first subtank 71 drops and the liquid level in the second subtank 71 rises. As a result, the difference between the average liquid level in the first subtank 71 and the average liquid level in the second subtank 72 gradually decreases, and the head difference between the first and second subtanks 71, 72 also gradually decreases. This process is usually repeated. As a result, while ink is being supplied from the main tank 73 to the second sub-tank 72, the difference in liquid level between the first sub-tank 71 and the second sub-tank 72 becomes the largest, and the head difference between the first and second sub-tanks 71, 72 also becomes the largest.In order to improve ink ejection from the ink head 4, it is preferable that the head difference between the first and second sub-tanks 71, 72 is small, and therefore the third liquid level height at which the third liquid level detection unit 913 is arranged should be higher than the first liquid level height at which the first liquid level detection unit 911 is arranged.For example, when the volume from the first liquid level height to the second liquid level height in the first sub-tank 71 is V, the volume from the first liquid level height to the third liquid level height in the second sub-tank 72 may be V / 2 or less, or may be V / 4 or less.

[0125] The volume from the first liquid level height to the third liquid level height may be considered to be the volume of ink accumulated in the second sub-tank 72 up to the third liquid level height minus the volume of ink accumulated in the second sub-tank 72 up to the first liquid level height. Considering this, if the first liquid level height is higher than the third liquid level height, the volume from the first liquid level height to the third liquid level height will be a negative value. Including such a case, the volume from the first liquid level height to the third liquid level height may be -V / 4 or greater, or may be 0 (zero) or greater. In other words, the first liquid level height may be equal to or less than the third liquid level height.

[0126] This reduces the difference in liquid level between the first and second sub-tanks 71, 72. The difference in liquid level is the difference in pressure applied to the suction and discharge holes of the ink head 4, and since this difference affects the ejection characteristics, it is acceptable for it to be small. The third liquid level may be lower than the second liquid level, but considering various printing situations and estimating the occurrence of multiple factors that increase the pressure difference, it is better to make the third liquid level equal to the first liquid level. To reduce the average pressure difference, the third liquid level should be TL / 20 to TL / 5 above the first liquid level, where TL is the length from the first liquid level to the second liquid level, or the third liquid level should be above the first liquid level and have a volume V / 20 to V / 5 between them. Furthermore, when the horizontal cross-sectional areas of the first sub-tank 71 and the second sub-tank 72 are the same, if the amount of ink transferred per unit time when no printing is performed is L2 and the maximum amount of ink ejected per unit time during printing is L1 (<L2), it is preferable that the third liquid level height is higher than the first liquid level height and its height from the first liquid level height is T×(L2-L1) / (2×L1) or less.

[0127] Furthermore, when purging is performed during the maintenance, the control unit 931 (86) of the control processing unit 93 controls one of the first and second valves 751, 752 to open and the other to close, thereby generating the differential pressure. As a result, purging is performed from the one valve controlled to be open. Then, the control unit 931 (86) controls the other valve to be open and the one valve to be closed, thereby generating the differential pressure. As a result, purging is performed from the other valve controlled to be open. For example, with the first valve 751 open and the second valve 752 closed, a first purge is performed in which ink from the first sub-tank 71 is sent to the ink head 4 and ejected from the nozzles. With the second valve 752 open and the first valve 751 closed, a second purge is performed in which ink from the second sub-tank 72 is sent to the ink head 4 and ejected from the nozzles. By purging the ink head 4 in both directions, any obstructions such as air bubbles on the first sub-tank 71 side relative to the ejection ports (nozzles) of the ink head 4 can be eliminated, and any obstructions on the second sub-tank 72 side relative to the ejection ports can be eliminated. The inkjet printer 1 may be configured to include either the first or second valve 751, 752.

[0128] As described above, according to this embodiment, it is possible to provide an inkjet printer 1 equipped with a new system for supplying and recovering liquids such as ink, pre-treatment liquid, and post-treatment liquid to and from head portions such as the ink head 4, pre-treatment head 5, and post-treatment head 6, in which the first and second flow direction treatments are alternately performed, and an inkjet recording method implemented therein.

[0129] 5 , in the inkjet printer 1 and inkjet recording method, the first and second sub-tanks 71, 72 are independent in terms of the flow of ink, except that they are connected so that ink can flow through them via the ink head 4. For this reason, the inkjet printer 1 and inkjet recording method do not require a circulation path and pump that return the recovered ink to the supply side, which are required when ink is supplied and recovered by flowing it in one direction to the ink head 4 during printing. For this reason, in this embodiment, there is no need to consider pump failure or coarse powder generated by the pump, and the risks associated with this can be reduced.

[0130] By alternately transferring ink between the first and second sub-tanks 71, 72, it is possible to prevent ink from accumulating near the ejection ports (nozzles). Furthermore, ink flows in the first and second sub-tanks 71, 72 as ink flows out and as ink flows in. This causes the ink in the first and second sub-tanks 71, 72 to be agitated. Even if there are uneven areas in the ink, this agitation can make them uniform. Furthermore, by providing an agitator such as a propeller in the first and second sub-tanks 71, 72 and performing an action such as rotation, the ink can be made more uniform.

[0131] When the inkjet printer 1 alternately transfers ink while waiting to print, the same ink is repeatedly transferred alternately because the ink stored in the first and second sub-tanks 71, 72 and the ink head 4 is not ejected and new ink is not supplied. Even when the inkjet printer 1 is printing, a similar situation can occur if the amount of printing is small. For example, this may occur when only a specific color is printed and other colors are printed in small amounts or not printed at all.

[0132] Here, the volume of the first sub-tank 71 is V1, the volume of the second sub-tank 72 is V2, the volume of the flow path in the ink head 4 is V4, the volume of the twelfth pipe 742 is V12, and the volume of the fourteenth pipe 744 is V14. If the volume of the inter-tank flow path, which is the flow path from the first sub-tank 71 to the second sub-tank 72, is V3, then V3 = V4 + V12 + V14.

[0133] When V1 ≧ V3 and V2 ≧ V3, ink can be alternately transferred without stagnation in the inter-tank flow path. For example, ink equal to or greater than V3 can be stored in the first subtank 71 (storage is possible because V2 ≧ V3), the second subtank 72 is empty, and the inter-tank flow path is filled with ink, i.e., V3 of ink is present (a state in which all of these are present is referred to as the first state). Then, ink transfer from the first subtank 71 to the second subtank 72 begins. When the first subtank 71 runs out of ink, the second state is reached in which V3 or more of ink has accumulated in the second subtank 72 (storage is possible because V2 ≧ V3). At this time, all of the ink present in the inter-tank flow path in the first state has been transferred to the second subtank 72, and is mixed in the second subtank 72 with some of the ink that accumulated in the first subtank 71 in the first state. In other words, it is possible to prevent some of the ink present in the inter-tank flow path in the first state from remaining in the inter-tank flow path when the second state is reached. If there is ink present in the inter-tank flow path in both the first state and the second state, even if the first state and the second state are alternately repeated, the ink is unlikely to mix with other inks because it does not enter either the first sub-tank 71 or the second sub-tank 72. If alternate transfer is repeated in a state where there is almost no ink ejection, the ink will have different properties from the other inks, such as an increased viscosity, and this could cause ejection problems when printing is resumed.

[0134] As described above, when V1≧V3 and V2≧V3, ink can be alternately transferred without stagnation in the inter-tank flow paths. More specifically, when the volume from the first liquid level height to the second liquid level height in the first sub-tank 71 is V, if V≧V3, the amount V of ink alternately transferred is greater than the volume V3 of the inter-tank flow paths, preventing some ink from remaining in the inter-tank flow paths over the transfer period. Furthermore, when V2≧V, ink of volume V can be transferred from the first sub-tank 71 to the second sub-tank 72.

[0135] Similarly, when multiple ink heads 4 are connected to the first sub-tank 71 and the second sub-tank 72, the volume of the flow path including all the ink heads 4 between the first sub-tank 71 and the second sub-tank 72 can be set to V3.

[0136] The volume of each flow path varies depending on the size of the inkjet printer 1, but in the case of a single ink head 4, the following volumes may be used: The volume V1 of the first subtank 71 and the volume V2 of the second subtank 72 may be, for example, 20 mL or more and 200 mL or less. The volume V4 of the flow path of the ink head 4 may be, for example, 1 mL or more and 10 mL or less. The volume V12 of the twelfth tube 742 and the volume V14 of the fourteenth tube 744 may be, for example, 0.5 mL or more and 5 mL or less. In other words, V3 may be 2 mL or more and 20 mL or less. V may be, for example, V1 / 4 or more and V1 / 2 or less. Even when n ink heads 4 are connected to the first sub-tank 71 and the second sub-tank 72, the total volume of the n 12th tubes 742, the total volume of the n 14th tubes 744, and the total volume of the n flow paths between the first sub-tank 71 and the second sub-tank 72 are each roughly n times larger than when one ink head 4 is connected.

[0137] In the above-described embodiment, the inkjet printer 1 may alternate between the first and second flow direction processes even while waiting to print. "Waiting to print" refers to, for example, the period from when the inkjet printer 1 is turned on and ink is supplied to the first and second subtanks 71 and 72 and the ink head 4, etc., while waiting to start printing; or the period from when the inkjet printer 1 is turned on and waiting for a few minutes to a few hours, or even a day, after finishing printing, while waiting to start the next printing. For example, the flow direction process that was being performed before the printing pause is continued during the printing pause, and then the flow direction process is alternately changed. This can prevent ink from accumulating in the heads, such as the ink head 4, pre-treatment head 5, and post-treatment head 6, particularly near the ejection openings (nozzles).

[0138] In the above-described embodiment, a filter may be disposed between the main tank 73 and the second sub-tank 72. Also, a filter may be disposed between the first sub-tank 71 and the second sub-tank.

[0139] In the above embodiment, the first and second switching periods are each set to a length of time equal to or greater than the first time, but they may be set appropriately regardless of whether or not there is a switch between the first and second flow direction processes. This allows the reversal time of the carriage 3 to be unified, making it possible to predict the printing time for the workpiece W.

[0140] 10 is a diagram illustrating a modified embodiment. In the above-described embodiment, the first sub-tank 71 having a bottom area larger than the cross-sectional area of ​​the twelfth tube 742 is used as an example of the first storage section, and the second sub-tank 71 having a bottom area larger than the cross-sectional area of ​​the fourteenth tube 744 is used as an example of the second storage section. However, as shown in FIG. 10 , a first tube 761 having a cross-sectional area substantially equal to the cross-sectional area of ​​the twelfth tube 742 may be used as another example of the first storage section, and a second tube 762 having a cross-sectional area substantially equal to the cross-sectional area of ​​the fourteenth tube 744 may be used as another example of the second storage section. In this case, the twelfth tube 742 and the first tube 761 may be integrated, and the fourteenth tube 744 and the second tube 762 may be integrated.

[0141] Furthermore, in the above embodiment, when ink is being supplied from the main tank 73 to the second sub-tank 72, the supply of ink is stopped if the ink level exceeds the fourth liquid level, but a second flow direction process may be performed in which ink flows from the second sub-tank 72 to the first sub-tank 71. In this case, if the ink level exceeds the second liquid level and also exceeds the fourth liquid level, the supply of ink is stopped, an alarm is issued externally, and the inkjet printer 1 is shut down due to an error.

[0142] Next, a simulation (numerical experiment) performed for a predetermined time period during which the pressure fluctuation caused by switching between the first and second flow direction processes subsides will be described.

[0143] FIG. 11 is a diagram for explaining the simulation model. FIG. 12 is a diagram showing an example of pressure fluctuations obtained by the simulation. The horizontal axis of FIG. 12 represents elapsed time [sec], and the vertical axis represents pressure [kPa]. FIG. 13 is a diagram for explaining the correlation between the simulation model and the decay time. The horizontal axis of FIG. 13 represents the simulation model: a×ln(R)+b×ln(C)+c×ln(M), where R, C, M, and T are defined as described below, and the coefficients of each term are a, b, and c, and the vertical axis represents ln(T). Note that ln(x) is the natural logarithm of x.

[0144] In this simulation, as shown in Figure 11, the ink head 4 was modeled to include a nozzle, a first supply and discharge hole, a second supply and discharge hole, a third flow path connecting the first supply and discharge hole and the nozzle, a fourth flow path connecting the second supply and discharge hole and the nozzle, a first damper provided in the third flow path, and a second damper provided in the fourth flow path.A transfer function was obtained from the first connecting flow path (twelfth tube 742) connecting the first sub-tank 71 and the first supply and discharge hole to the second connecting flow path (fourteenth tube 744) connecting the second sub-tank 72 and the second supply and discharge hole via the ink head 4, and the pressure fluctuations in the first and second sub-tanks 71, 72 were calculated.

[0145] Here, the average flow path resistance of the third flow path and the fourth flow path (abbreviated as "average flow path resistance" in the explanation of this simulation) is R [Ns / m ５ ], and the average compliance of the first damper and the second damper (abbreviated as "average compliance" in the explanation of this simulation) is C [m ５ / N], and the average inertance of the first connecting flow path and the second connecting flow path (abbreviated as "average inertance" in the explanation of this simulation) is M [kg / m ４ ], and the average flow path resistance of the first connecting flow path and the second connecting flow path is set to 1.1E8 [Ns / m ５ ], the simulation conditions and the decay time T obtained under those simulation conditions are as shown in Table 1 below. In this simulation, the elements of mean flow path resistance R, mean compliance C, and mean inertance M, which have a significant effect on pressure fluctuations, were taken into consideration. Elements other than mean flow path resistance R, mean compliance C, and mean inertance M, which have only a small effect on pressure fluctuations, were ignored in the simulation. In this simulation, the pressure fluctuations that occurred after switching from a state (first state) in which a pressure of +10 kPa was applied to the first subtank 71 and a pressure of −10 kPa was applied to the second subtank 72, to a state (second state) in which a pressure of −10 kPa was applied to the first subtank 71 and a pressure of +10 kPa was applied to the second subtank 72, were obtained. The decay time T was defined as the time until the envelope of the pressure fluctuations became 0.1 kPa or less, specifically, 1 / 200 of the initial value or less. The pressure of 0.1 kPa is within the range of pressure fluctuations that allows ink to be ejected.

[0146]

[0147] As an example, R = 9.8E9 [Ns / m ５ ], C=9.3E-12[m ５ / N], pressure fluctuations for M=1.9E7 are shown in FIG.

[0148] In the simulations under condition numbers "1", "2", "3" and "4", the average compliance C and the average inertance M are fixed to respective predetermined values ​​(respective first predetermined values), and the average flow path resistance R is set to 2.5E9 [Ns / m ５ ] to 2.0E10 [Ns / m ５ As can be seen from Table 1, the average flow path resistance R and the decay time T show a positive correlation.

[0149] In the simulations under condition numbers "1", "5", "6" and "7", the average flow resistance R and the average compliance C are fixed to respective predetermined values ​​(respective second predetermined values), and the average inertance M is set to 1.0E7 [kg / m ４ ] to 4.0E7 [kg / m ４ As can be seen from Table 1, the average inertance M and the decay time T show a positive correlation.

[0150] In the simulations under condition numbers "1", "8", "9" and "10", the average flow resistance R and the average inertance M are fixed to respective predetermined values ​​(respective third predetermined values), and the average compliance C is set to 5.0E-12 [m ５ / N] to 1.0E-10 [m ５ / N]. As can be seen from Table 1, the average compliance C and the decay time T show a positive correlation.

[0151] Therefore, when the relationship between the average flow path resistance R, average compliance C, and average inertance M and the damping time T was examined using a model of the linear sum of a × ln(R) + b × ln(C) + c × ln(M) and ln(T), a positive correlation was found between them, as shown in Figure 13. In this simulation, the relational equation obtained was ln(T) = 0.76 × ln(R) + 0.51 × ln(C) + 0.25 × ln(M) - 9.1.

[0152] From these results, the decay time of an inkjet printer 1 having a mean flow path resistance R, mean compliance C, and mean inertance M can be estimated as t [seconds], calculated from ln(t) = 0.76 × ln(R) + 0.51 × ln(C) + 0.25 × ln(M) - 9.1. Simulations using values ​​other than those in Table 1 also showed similar trends for mean flow path resistance R in the range of 1E9 to 1E11, mean compliance C in the range of 1E-12 to 1E-10, and mean inertance M in the range of 1E7 to 1E8. The decay time t calculated from this relational expression satisfies t≦3 [seconds]. With such an inkjet printer 1, the predetermined time required for differential pressure fluctuations to subside is approximately 3 seconds or less, enabling good printing when printing is resumed after switching the flow direction process during a printing pause. More specifically, an inkjet printer 1 can be created that limits the printing pause that occurs when the carriage 3 is turned back to approximately 3 seconds. A shorter printing pause, such as when the carriage 3 is folded back, increases production efficiency and also makes the print boundary less noticeable during reciprocating printing. To achieve this, t≦1 second may be satisfied, or t≦0.5 seconds may be satisfied. Note that the decay time t related to the first time is the time estimated from the parameters to fall below the required level, and 3 seconds is within a practical range.

[0153] This application is based on Japanese Patent Application No. 2024-54520 filed on March 28, 2024, the contents of which are incorporated herein by reference.

[0154] In order to express the present invention, the present invention has been properly and sufficiently described above through the embodiments with reference to the drawings, but it should be recognized that those skilled in the art can easily change and / or improve the above-mentioned embodiments. Therefore, unless the changes or improvements made by those skilled in the art are at a level that causes departure from the scope of the claims described in the claims, such changes or improvements are interpreted as being included in the scope of the claims.

[0155] According to the present invention, it is possible to provide an inkjet recording apparatus and an inkjet recording method for supplying and recovering liquid to a head unit of an inkjet system.

Claims

1. An inkjet recording device comprising: first and second storage units for storing a liquid; one or more head units connected to the first and second storage units so that the liquid can flow therethrough and equipped with nozzles for ejecting the liquid; and a flow generating unit that alternately performs a first flow direction process for causing the liquid to flow from the first storage unit to the second storage unit via the head unit, and a second flow direction process for causing the liquid to flow from the second storage unit to the first storage unit via the head unit.

2. The inkjet recording device according to claim 1, wherein, when the volume of the first storage section is V1, the volume of the second storage section is V2, and the volume of the flow path from the first storage section to the second storage section via the head section is V3, the relationships V1 ≧ V3 and V2 ≧ V3 are satisfied.

3. The inkjet recording device according to claim 1, wherein the switching between the first and second flow direction processes during printing is performed by pausing printing, and printing is resumed after a predetermined time has passed during which fluctuations in the liquid caused by the switching have subsided.

4. An inkjet recording device as described in claim 3, comprising: a transport unit that transports a workpiece in a transport direction; and a carriage that has the head unit and moves back and forth in a main scanning direction that intersects with the transport direction, wherein when the direction of the reciprocating movement of the carriage is switched, the time from when the head unit pauses printing to when it resumes printing is equal to or longer than the specified time.

5. An inkjet recording device as described in any one of claims 1 to 4, wherein the flow generating unit comprises: a differential pressure generating unit that generates a differential pressure between a first atmospheric pressure applied to a first liquid surface of the liquid contained in the first storage unit and a second atmospheric pressure applied to a second liquid surface of the liquid contained in the second storage unit; and a control unit that controls the differential pressure.

6. The inkjet recording device according to claim 5, wherein the flow generating unit performs a first flow direction process by controlling the differential pressure using the control unit so that the first atmospheric pressure is greater than the second atmospheric pressure, and performs a second flow direction process by controlling the differential pressure using the control unit so that the second atmospheric pressure is greater than the first atmospheric pressure, and switches between the first and second flow direction processes while printing is paused, and the inkjet recording device starts printing after a predetermined time has passed since the fluctuations in the differential pressure ceased.

7. An inkjet recording device as described in claim 6, comprising: a transport unit that transports a workpiece in a transport direction; and a carriage that has the head unit and moves back and forth in a main scanning direction that intersects with the transport direction, wherein when the direction of the reciprocating movement of the carriage is switched, the time from when the head unit pauses printing to when it resumes printing is equal to or longer than the specified time.

8. An inkjet recording device according to claim 7, wherein the carriage is provided with a plurality of head units, and when the direction of the reciprocating movement of the carriage is switched, the time from when the head unit located at the rearmost end of the plurality of head units provided on the carriage in the movement direction pauses printing to when it starts printing is equal to or longer than the predetermined time.

9. The inkjet recording apparatus according to claim 5, wherein the control unit controls the differential pressure so as to maintain a meniscus formed by the liquid in the nozzle.

10. An inkjet recording device as described in any one of claims 1 to 9, comprising: a transport unit that transports a workpiece in a transport direction; and a carriage that has the head unit and moves back and forth in a main scanning direction that intersects with the transport direction, wherein the flow generating unit switches between the first and second flow direction processes during at least one of a first switching period in which the reciprocating movement switches from the outbound path to the return path, and a second switching period in which the return path switches to the outbound path.

11. An inkjet recording apparatus according to any one of claims 1 to 10, wherein a first flow path resistance from the nozzle to the first storage section is equal to a second flow path resistance from the nozzle to the second storage section.

12. The head portion includes the nozzle, a first supply / discharge hole, a second supply / discharge hole, a third flow path connecting the first supply / discharge hole and the nozzle, a fourth flow path connecting the second supply / discharge hole and the nozzle, a first damper provided in the third flow path, and a second damper provided in the fourth flow path, and further includes a first connecting flow path connecting the first storage portion and the first supply / discharge hole, and a second connecting flow path connecting the second storage portion and the second supply / discharge hole, and an average flow path resistance of the third flow path and the fourth flow path is R [Ns / m ５ ], the average compliance of the first damper and the second damper is C [m ５ / N], the average inertance of the first connecting flow path and the second connecting flow path is M [kg / m ４ 12. The inkjet recording apparatus according to claim 1, wherein, when ln(t)=0.76×ln(R)+0.51×ln(C)+0.25×ln(M)−9.1, the following relationship is satisfied: t≦3.

13. An inkjet recording device as described in any one of claims 1 to 12, further comprising a first liquid level detection unit that detects whether the liquid contained in the first storage unit has fallen below a first liquid level height, and a second liquid level detection unit that detects whether the liquid contained in the first storage unit has exceeded a second liquid level height that is higher than the first liquid level height, wherein the flow generation unit, when the first liquid level detection unit detects that the liquid has fallen below the first liquid level height while performing the first flow direction process, switches from the first flow direction process to perform the second flow direction process in the next switching period for switching between the first and second flow direction processes, and switches from the second flow direction process to perform the first flow direction process in the next switching period for switching between the first and second flow direction processes when the second liquid level detection unit detects that the liquid has exceeded the second liquid level height while performing the second flow direction process.

14. An inkjet recording device according to claim 13, wherein, when the volume of the first storage section from the first liquid level height to the second liquid level height is V, the volume of the second storage section is V2, and the volume of the flow path from the first storage section to the second storage section via the head section is V3, the relationship V2 ≧ V ≧ V3 is satisfied.

15. An inkjet recording device as described in claim 13, further comprising: a third storage section connected to the second storage section so that the liquid can flow therethrough and which stores the liquid; a third liquid level detection section which detects whether the liquid stored in the second storage section has fallen below a third liquid level; and a supply control section which supplies the liquid stored in the third storage section to the second storage section when the third liquid level detection section detects that the liquid has fallen below the third liquid level.

16. An inkjet recording device according to claim 13, wherein, when the volume of the first storage section from the first liquid level height to the second liquid level height is V, the volume of the second storage section from the first liquid level height to the third liquid level height is V / 2 or less.

17. An inkjet recording device as described in claim 13, further comprising a fourth liquid level detection unit that detects whether the liquid contained in the second storage unit has exceeded a fourth liquid level height that is higher than the third liquid level height, and the supply control unit stops the supply when the fourth liquid level detection unit detects that the liquid has exceeded the fourth liquid level height while the liquid is being supplied from the third storage unit to the second storage unit.

18. An inkjet recording device as described in claim 13, further comprising a fourth liquid level detection unit that detects whether the liquid contained in the second container has exceeded a fourth liquid level that is higher than the third liquid level, and the supply control unit issues an alarm to the outside when the fourth liquid level detection unit detects that the liquid has exceeded the fourth liquid level.

19. An inkjet recording device as described in any one of claims 1 to 18, further comprising at least one of a first purge valve arranged between the first storage unit and the head unit and capable of opening and closing a first flow path of the liquid between the first storage unit and the head unit, and a second purge valve arranged between the second storage unit and the head unit and capable of opening and closing a second flow path of the liquid between the second storage unit and the head unit.

20. The inkjet recording apparatus of claim 18, wherein the flow generating unit comprises: a differential pressure generating unit that generates a differential pressure between a first atmospheric pressure applied to a first liquid surface of the liquid contained in the first container and a second atmospheric pressure applied to a second liquid surface of the liquid contained in the second container; and a control unit that controls the differential pressure, and further comprises a flow path switching unit that switches between a combination that connects the first container to a supply source of the first atmospheric pressure and connects the second container to a supply source of the second atmospheric pressure, and a combination that connects the first container to the supply source of the second atmospheric pressure and connects the second container to the supply source of the first atmospheric pressure.

21. An inkjet recording device as described in claim 18, which is equipped with both the first valve and the second valve, and which, when purging, performs a first purge in which, with the first valve open and the second valve closed, the liquid in the first container is sent to the head section and released from the nozzles, and a second purge in which, with the second valve open and the first valve closed, the liquid in the second container is sent to the head section and released from the nozzles.

22. An inkjet recording device as described in any one of claims 1 to 21, further comprising: a temperature measuring unit disposed between the first and second storage units, for measuring the temperature of the liquid; a first heating unit for heating the liquid stored in the first storage unit; a second heating unit for heating the liquid stored in the second storage unit; and a heating control unit for controlling each of the first and second heating units to heat each of the liquids stored in the first and second storage units, respectively, based on the temperature of the liquid measured by the temperature measuring unit.

23. An inkjet recording device according to any one of claims 1 to 22, wherein the first and second storage sections are independent with respect to the flow of the liquid, except that the first and second storage sections are connected so that the liquid can flow through the head section.

24. An inkjet recording method for an inkjet recording device comprising first and second storage sections for storing a liquid, and a head section connected to each of the first and second storage sections so that the liquid can flow therethrough and equipped with nozzles for ejecting the liquid, the inkjet recording method alternately performing a first flow direction process for causing the liquid to flow from the first storage section to the second storage section via the head section, and a second flow direction process for causing the liquid to flow from the second storage section to the first storage section via the head section.

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