Control method for liquid ejection device and liquid ejection device

Abstract

To provide a control method for a liquid ejection device and a liquid ejection device that are miniaturized while suppressing thickening of liquid inside nozzles in caps.SOLUTION: There is provided a control method for a liquid ejection device comprising: a liquid ejection head 9 that ejects liquid from a plurality of nozzles N forming a plurality of nozzle groups; and a plurality of caps 20 each covering a divided portion of the plurality of nozzle groups, performs a printing operation in which the liquid is ejected onto a medium, and a capping operation in which the plurality of nozzle groups are covered by the plurality of caps 20. The method includes: a step which, after completion of the printing operation, discharges the liquid in a discharge amount set for each of the plurality of caps 20 from the plurality of nozzle groups into recesses 21 of the plurality of corresponding caps 20; a step in which the nozzles N are covered by the caps 20 in a state where the discharged liquid is stored in the recesses 21; and a step which sets the discharge amount set for each of the plurality of caps 20 to be such an amount that the moisture content of the liquid within each of the caps 20 is equal to or greater than a reference value corresponding to the cap 20.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a liquid ejection apparatus having a liquid ejection head that ejects liquid from nozzles, and to the liquid ejection apparatus. [Background technology]

[0002] 2. Description of the Related Art A liquid ejecting apparatus, typified by an ink jet recording apparatus such as an ink jet printer, is equipped with a liquid ejecting head that can eject liquid such as ink stored in a cartridge or a tank from a nozzle as droplets.

[0003] When a liquid jet head is on standby before and after a printing operation, water evaporates from the liquid in the nozzles, increasing the viscosity of the liquid. This can cause the nozzles to clog with the increased viscosity liquid during the next printing operation, and the ejection characteristics of the droplets, such as the droplet flight speed and droplet weight, can decrease, resulting in a decrease in print quality. For this reason, while covering the nozzle surface of the liquid jet head with a cap while on standby for printing can prevent the liquid in the nozzles from drying out to some extent, this alone is not sufficient.

[0004] For this reason, a liquid ejection device has been provided in which a moisture supply means is provided in a cap that covers the nozzle surface, and moisture is supplied from the moisture supply means into the cap, thereby adjusting the humidity in the space covering the nozzle surface and preventing the ink in the nozzles from drying out (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-334962 Summary of the Invention [Problem to be solved by the invention]

[0006] However, providing a moisture supply means to prevent the liquid in the nozzle from drying out makes it difficult to miniaturize the liquid ejection device, and therefore there is a need for a liquid ejection device that can prevent the viscosity of the liquid in the nozzle from increasing and can be made smaller without providing a moisture supply means. [Means for solving the problem]

[0007] An aspect of the present invention that solves the above-mentioned problem is a control method for a liquid ejection device that includes a liquid ejection head configured to eject liquid from a plurality of nozzles that make up a plurality of nozzle groups, and a plurality of caps configured to divide and cover the plurality of nozzle groups, and that performs a printing operation in which liquid is ejected onto a medium from nozzles that make up the plurality of nozzle groups, selected from the nozzles that make up the plurality of nozzle groups based on an image to be printed on the medium, and a capping operation in which the nozzles of the plurality of nozzle groups are covered with the plurality of caps, wherein after the printing operation is completed, liquid is ejected from the plurality of nozzle groups into recesses of the corresponding plurality of caps in an amount of discharge set for each of the plurality of caps, and with the ejected liquid stored in the recesses, the nozzles are placed facing the recesses and covered with the caps, and the discharge amount set for each of the plurality of caps is set to an amount such that the water content of the liquid in the plurality of caps is equal to or greater than a reference value corresponding to the cap.

[0008] Another aspect of the present invention is a liquid ejection device comprising: a liquid ejection head configured to eject liquid from a plurality of nozzles that constitute a plurality of nozzle groups; a plurality of caps configured to divide and cover the plurality of nozzle groups; and a control unit that executes a printing operation in which liquid is ejected onto the medium from nozzles that constitute the plurality of nozzle groups, selected from the nozzles of the plurality of nozzle groups based on an image to be printed on the medium, and a capping operation in which the nozzles of the plurality of nozzle groups are covered with the plurality of caps, wherein after the printing operation is completed, the control unit ejects liquid from the plurality of nozzle groups into recesses of the corresponding plurality of caps at an amount of discharge set for each of the plurality of caps, and with the discharged liquid stored in the recesses, covers the nozzles with the caps facing the recesses, and sets the discharge amount set for each of the plurality of caps to an amount such that the water content of the liquid in the plurality of caps is equal to or greater than a reference value corresponding to the cap. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing a schematic configuration of a liquid ejecting apparatus according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing a schematic configuration of a maintenance unit according to the first embodiment. [Figure 3] 3 is a cross-sectional view of a main part of a maintenance unit according to the first embodiment. FIG. [Figure 4] FIG. 2 is an exploded perspective view of the head unit according to the first embodiment. [Figure 5] 1 is an exploded perspective view of a liquid jet head according to a first embodiment. [Figure 6] 1 is a plan view of a liquid jet head according to a first embodiment. [Figure 7] 1 is a cross-sectional view of a liquid jet head according to a first embodiment. [Figure 8] 4 is a flowchart illustrating a control method according to the first embodiment. [Figure 9] 1 is a table illustrating the moisture content and discharge amount according to the first embodiment. [Figure 10]10 is a flowchart illustrating a control method according to a modified example of the first embodiment. [Figure 11] 10 is a table illustrating the moisture content and discharge amount according to a modification of the first embodiment. [Figure 12] FIG. 10 is a diagram showing a schematic configuration of a liquid ejecting device according to a second embodiment. [Figure 13] FIG. 10 is a plan view of a liquid jet head according to a second embodiment. [Figure 14] FIG. 10 is a cross-sectional view of a liquid jet head according to a second embodiment. [Figure 15] 10 is a table illustrating the moisture content and discharge amount according to the second embodiment. [Figure 16] 10 is a table illustrating the moisture content and discharge amount according to a modification of the second embodiment. [Figure 17] FIG. 10 is a plan view of a maintenance unit according to another embodiment. [Figure 18] FIG. 10 is a cross-sectional view of a main part of a maintenance unit according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below based on embodiments. However, the following description illustrates one aspect of the present invention and can be modified as desired within the scope of the present invention. In each drawing, the same reference numerals indicate the same components, and their description will be omitted as appropriate. In each drawing, X, Y, and Z represent three spatial axes that are orthogonal to each other. In this specification, the directions along these axes are referred to as the X direction, Y direction, and Z direction. In each drawing, the direction indicated by the arrow is the positive (+) direction, and the direction opposite the arrow is the negative (-) direction. The Z direction indicates the vertical direction, the +Z direction indicates a vertically downward direction, and the -Z direction indicates a vertically upward direction. Furthermore, the directions of the three spatial axes, which are not limited to positive and negative directions, will be described as the X-axis direction, the Y-axis direction, and the Z-axis direction.

[0011] (Embodiment 1) Fig. 1 is a diagram showing a schematic configuration of a liquid ejecting device 1 according to a first embodiment of the present invention. Fig. 2 is a diagram showing a schematic configuration of a head unit 2 and a maintenance unit 8. Fig. 3 is a cross-sectional view of a main part of a liquid ejecting head 9, a cap 20, and a suction mechanism 30. Fig. 4 is an exploded perspective view of the head unit 2 as viewed in the +Z direction.

[0012] 1 and 2, the liquid ejection device 1 is a so-called line printer that includes a liquid ejection head 9 and performs printing by ejecting liquid ink from the liquid ejection head 9 toward the medium S, which is an ejection target medium, in the +Z direction while transporting the medium S in the X-axis direction. Note that the medium S can be made of any material, such as cloth, recording paper, or resin film.

[0013] Such a liquid ejection device 1 includes a head unit 2 equipped with at least one liquid ejection head 9 having a head chip Hc, a liquid storage section 3, a control unit 4 which serves as a control section, a transport mechanism 5 which transports a medium S, a device main body 7, and a maintenance section 8.

[0014] The head unit 2 extends along the Y-axis direction. In this embodiment, the head unit 2 includes one liquid jet head 9 and a support 10 that supports the liquid jet head 9, which will be described in detail later.

[0015] As shown in FIG. 4, the support 10 is configured as a plate-like member formed from a metal material or a resin material, and has mounting holes 10a to which the liquid jet heads 9 are attached. The liquid jet heads 9 are supported by the support 10 with their ends in the +Z direction inserted into the mounting holes 10a. In this embodiment, one liquid jet head 9 is supported by the support 10. Note that the number of liquid jet heads 9 supported by the support 10 is not limited to this, and two or more liquid jet heads 9 may be arranged side by side in the Y-axis direction. Furthermore, the support 10 may be provided with multiple rows in the X-axis direction, each row including two or more liquid jet heads 9 arranged side by side in the Y-axis direction.

[0016] The liquid jet head 9 includes a plurality of head tips Hc that jet the liquid supplied from the liquid storage section 3 as droplets in the +Z direction (see FIG. 5).

[0017] The liquid storage unit 3 individually stores multiple types of liquid with different colors and components to be ejected from the head chip Hc. Examples of the liquid storage unit 3 include a cartridge that is detachable from the liquid ejecting device 1, a bag-shaped ink pack made of flexible film, and an ink tank that can be refilled with ink. The liquid storage unit 3 may be separated into a main tank and a sub-tank. The sub-tank may be connected to the head chip Hc, and the liquid consumed by ejecting droplets from the head chip Hc may be replenished from the main tank to the sub-tank.

[0018] The control unit 4 comprehensively controls each element of the liquid ejection device 1, i.e., the head chip Hc, the transport mechanism 5, the maintenance unit 8, etc. The control unit 4 includes, for example, a control device such as a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array), and a storage device such as a semiconductor memory. The control unit 4 also includes a power supply device that supplies power supplied from an external power source such as a commercial power source to each element of the liquid ejection device 1. The control unit 4 is electrically connected to the liquid ejection head 9 via external wiring (not shown). The control unit 4 comprehensively controls each element of the liquid ejection device 1 by the control device executing a program stored in the storage device.

[0019] The transport mechanism 5 transports the medium S in the X-axis direction, and includes, for example, a transport roller 5a that is rotated by a transport motor that is driven under the control of the control unit 4.

[0020] The head chip Hc performs an ejection operation in which the liquid supplied from the liquid storage section 3 is ejected as droplets from each of the multiple nozzles N (see FIG. 5) in the +Z direction under the control of the control unit 4. This ejection operation by the head chip Hc is performed in parallel with the transport of the medium S by the transport mechanism 5, thereby applying the liquid to the medium S, i.e., performing so-called printing. In other words, the control unit 4 performs a printing operation by ejecting droplets onto the medium S from a nozzle N selected from the multiple nozzles N of the liquid ejection head 9 based on the image to be printed on the medium S.

[0021] The liquid ejecting device 1 also has a maintenance unit 8 that performs maintenance on the head chips Hc. As shown in Figures 2 and 3, the maintenance unit 8 includes caps 20 corresponding to each head chip HC, a suction mechanism 30, and a waste liquid storage unit 40.

[0022] Each cap 20 is provided so as to be movable in the Z-axis direction between a spaced position shown in FIG. 2 and a capping position shown in FIG.

[0023] Each cap 20 is sized to come into contact with each head chip Hc and cover all of the multiple nozzles N of each head chip Hc. Specifically, cap 20 includes cap body 22 in which recess 21 having a concave shape with an opening on the surface facing the -Z direction is formed, seal portion 23 provided in an annular shape around the circumferential direction at the opening edge of recess 21 of cap body 22, and absorbing portion 24 provided within recess 21.

[0024] The seal portion 23 is made of an elastic material such as rubber, elastomer, etc. When the seal portion 23 comes into contact with the head chip Hc, the recess 21 of the cap 20 is closed to form a closed space.

[0025] The absorbing portion 24 absorbs and holds the liquid discharged from the nozzle N, and is made of, for example, a porous material.

[0026] The suction mechanism 30 includes a discharge path 31 connecting the cap 20 and the waste liquid storage unit 40, and a discharge pump 32 provided midway along the discharge path 31. One end of the discharge path 31 is connected to the recess 21 of the cap 20, and the other end is connected to the waste liquid storage unit 40. The discharge path 31 is configured, for example, by a tube or the like that deforms as the cap 20 moves in the Z-axis direction. The liquid discharged from the nozzle N of the head chip Hc and held in the absorption unit 24 in the recess 21 of the cap 20 remains in this state unless the suction mechanism 30 is operated. Furthermore, by operating the suction mechanism 30, the liquid held in the absorption unit 24 in the recess 21 of the cap 20 is sucked and sent to the waste liquid storage unit 40. Note that a valve for opening and closing the discharge path 31 may be provided midway along the discharge path 31, and the liquid may be held in the recess 21 of the cap 20 by closing the discharge path 31 with the valve.

[0027] The maintenance unit 8 also includes a lifting mechanism (not shown) for raising and lowering the cap 20 in the Z-axis direction. The lifting mechanism raises and lowers the cap 20 between a spaced position where the cap 20 is spaced from the head chip Hc and a capping position where the cap 20 is in contact with the head chip Hc.

[0028] In addition to the cap 20, the maintenance unit 8 may include a wiping unit that wipes the ejection surface of the liquid ejection head 9, etc.

[0029] Fig. 5 is an exploded perspective view of the liquid jet head 9 as seen in the -Z direction. Fig. 6 is a plan view of the liquid jet head 9 as seen in the -Z direction. Fig. 7 is a cross-sectional view taken along line AA' in Fig. 6.

[0030] The directions of the liquid jet head 9 will be described based on the directions when the liquid jet head 9 is mounted on the liquid jet apparatus 1, that is, the X-axis direction, the Y-axis direction, and the Z-axis direction.

[0031] As shown in the figure, the liquid jet head 9 includes a plurality of head chips Hc, a holder 50, a flow path member 60, and a cover head 70.

[0032] A plurality of head chips Hc and a cover head 70 are fixed to the surface of the holder 50 facing the +Z direction, and a flow path member 60 is fixed to the surface of the holder 50 facing the -Z direction.

[0033] The head chip Hc has a plurality of nozzles N opening on a surface facing the +Z direction. In this embodiment, two nozzle arrays L, each consisting of a plurality of nozzles N arranged in a line along the Y axis direction, are provided spaced apart in the X axis direction. In this embodiment, the two nozzle arrays L are referred to as nozzle array La and nozzle array Lb in order in the +X direction. Hereinafter, when there is no need to distinguish between nozzle arrays La and Lb, they will be referred to as nozzle array L. These nozzle arrays La and Lb are arranged in the Y axis direction with a shift of half the pitch of the nozzles N, or so-called half a pitch. In other words, all the nozzles N in the nozzle arrays La and Lb are arranged in a staggered pattern along the Y axis direction. Of course, the nozzles N in the nozzle arrays La and Lb may be arranged at the same position in the Y axis direction.

[0034] Inside the head chip Hc (not shown), there are provided flow paths communicating with each nozzle N and drive elements that generate pressure changes in the liquid in the flow paths. Examples of drive elements that can be used include a piezoelectric actuator having a piezoelectric material with electromechanical conversion function, which changes the volume of the flow path by deforming it, thereby generating a pressure change in the liquid in the flow path and ejecting droplets from the nozzle N. Other drive elements that can be used include a heater element disposed in the flow path, which generates heat to generate bubbles that eject droplets from the nozzle N, and a so-called electrostatic actuator, which generates electrostatic force between a diaphragm and an electrode, which deforms the diaphragm by the electrostatic force and ejects droplets from the nozzle N.

[0035] The holder 50 has storage portions 51 that can store the head chips Hc. The storage portions 51 have a concave shape that opens on a surface of the holder facing the +Z direction, and are independently provided for each liquid jet head 9. In this embodiment, the holder 50 is provided with four storage portions 51, and a total of four head chips Hc are stored therein. Of course, the storage portions 51 may be provided continuously across a group made up of a plurality of head chips Hc.

[0036] Here, four head chips Hc are provided on the holder 50 along the Y-axis direction. The four head chips Hc are arranged in a staggered pattern along the Y-axis direction. Here, arranging the multiple head chips Hc in a staggered pattern along the Y-axis direction means that the head chips Hc arranged in parallel in the Y-axis direction are arranged with an alternating offset in the X-axis direction. In other words, two rows of head chips Hc aligned along the Y-axis are arranged side by side along the X-axis, and the two rows of head chips Hc are arranged with an offset of half a pitch in the Y-axis direction. By arranging the multiple head chips Hc in a staggered pattern along the Y-axis in this way, the nozzle rows L of two head chips Hc are partially overlapped in the Y-axis direction, thereby forming a row of nozzles N that is continuous across the Y-axis direction of the liquid ejection head 9.

[0037] In this embodiment, the four head chips Hc are referred to in order in the +Y direction as the first head chip Hc1, the second head chip Hc2, the third head chip Hc3, and the fourth head chip Hc4. Hereinafter, when there is no need to distinguish between the first head chip Hc1 to the fourth head chip Hc4, they will be collectively referred to as head chips Hc. In this embodiment, the same type of liquid is ejected from the four nozzle arrays La of the first head chip Hc1 to the fourth head chip Hc4. In addition, the same type of liquid is ejected from the four nozzle arrays Lb of the first head chip Hc1 to the fourth head chip Hc4. In this embodiment, the liquid ejected from the four nozzle arrays La is a different type of liquid from the liquid ejected from the four nozzle arrays Lb. In this embodiment, the liquid ejected from the nozzle array La is referred to as liquid A, and the liquid ejected from the nozzle array Lb is referred to as liquid B. Liquids A and B contain water. Liquids A and B may contain materials such as colorants. Furthermore, liquids A and B may contain humectants such as polyhydric alcohols, such as glycerin and diethylene glycol. Liquid A and liquid B may have different amounts of water, for example. Of course, liquid A and liquid B may be the same type of liquid. Incidentally, as described above, since each cap 20 covers nozzle rows La and Lb of head chip Hc, the type of liquid ejected from nozzle rows L corresponding to each of the multiple caps 20 is the same.

[0038] Further, the holder 50 is provided with a first flow path 52 that communicates with the flow path of the head chip Hc accommodated in the accommodation portion 51.

[0039] The cover head 70 is fixed to the surface of the holder 50 facing the +Z direction. The cover head 70 defines the space of the accommodation portion 51 that accommodates the head chips Hc. The cover head 70 is also fixed to the surface of the head chips Hc facing the +Z direction. The cover head 70 is large enough to cover four head chips Hc. The cover head 70 is also provided with an exposure opening 71 that exposes the nozzle row L of the head chip Hc in the +Z direction, independently for each head chip Hc. The surface of the cover head 70 facing the +Z direction forms part of the ejection surface of the liquid ejection head 9. In other words, the ejection surface of the liquid ejection head 9 includes the surface where the nozzles N of the head chip Hc open and the surface of the cover head 70 facing the +Z direction.

[0040] The flow path member 60 is fixed to a surface of the holder 50 facing the -Z direction. A second flow path 61 that communicates with the first flow path 52 of the holder 50 is provided inside the flow path member 60. The liquid supplied from the liquid storage section 3 is supplied to the head chip Hc via the second flow path 61 of the flow path member 60 and the first flow path 52 of the holder 50. A second flow path 61 is provided independently for each nozzle row L. In this embodiment, as described above, the same type of liquid is ejected from the four nozzle rows La of the first head chip Hc1 to the fourth head chip Hc4, and the same type of liquid is ejected from the four nozzle rows Lb. For this reason, the second flow path 61 may be branched into four paths midway and communicate with the four nozzle rows La or the four nozzle rows Lb of each of the first head chips Hc1 to Hc4. Further, a filter (not shown) that captures dust or air bubbles contained in the liquid passing through the second flow path 61, a pressure adjustment mechanism (not shown) that adjusts the pressure of the liquid supplied from upstream and supplies it downstream, or the like may be provided midway along the second flow path 61. Furthermore, the second flow path 61 may be directly connected to the flow path of the head chip Hc without providing the first flow path 52 in the holder 50.

[0041] As described above, the cap 20 is provided independently for each head chip Hc. That is, one cap 20 covers the nozzle rows La and Lb of one head chip Hc with the same recess 21 and seals them in the same closed space. In other words, the nozzles N constituting the total of eight nozzle rows L of the four head chips Hc of the liquid ejection head 9 are an example of "plurality of nozzle groups," and the multiple caps 20 cover the multiple nozzle groups by dividing them into groups for each head chip Hc. The caps 20 are also arranged in the Y-axis direction, which is the arrangement direction of the head chips Hc.

[0042] After a printing operation is performed, the control unit 4 ejects droplets of liquid to recover the viscosity, commonly known as flushing, which discharges the thickened liquid in the nozzle N into the recess 21 of the cap 20 before the next printing operation is performed.

[0043] Furthermore, after flushing, the control unit 4 performs a capping operation to cover the nozzles N of each head chip Hc with a cap 20 in order to prevent water from evaporating from the liquid inside the nozzles N. Note that in this embodiment, the capping operation is performed after flushing, but this is not particularly limited, and flushing to restore viscosity of the liquid inside the nozzles N may not be performed.

[0044] In addition, after flushing and before performing the capping operation, the control unit 4 injects droplets from the liquid ejection head 9 into the recess 21 of the cap 20, and adjusts the humidity of the closed space formed when the nozzle N is covered with the cap 20, i.e., the moisture content of the liquid discharged into the cap 20.

[0045] A specific control method for such a liquid ejection device 1 will be described with reference to Figures 8 and 9. Figure 8 is a flowchart illustrating the control method for the liquid ejection device 1 of this embodiment. Figure 9 is a table Ta1 showing the water content of the liquid in the nozzle N, the ejection amount required to restore viscosity of the liquid in the nozzle N, the water adjustment amount, and the total ejection amount, all of which are performed by the control method of Figure 8.

[0046] In step S1, the control unit 4 estimates and obtains the water content M1 of the liquid in each nozzle N of the nozzle arrays La, Lb. The water content M1 of the nozzle arrays La, Lb is the average value, mode, or median of the water content of all the nozzles N that make up each of the nozzle arrays La, Lb.

[0047] Here, the liquid in the nozzles N that ejected many droplets in the previous printing operation has a high moisture content M1 because new liquid is constantly being supplied from the upstream side. In contrast, the liquid in the nozzles N that ejected few or no droplets in the previous printing operation has a low moisture content M1 because the moisture evaporates during the printing operation. Therefore, the moisture content M1 in the nozzles N constituting each nozzle row L can be estimated from the ejection history of each nozzle N in the previous printing operation. For example, if 10 pages were printed in the previous printing operation, the moisture content M1 of each nozzle N can be estimated from the ejection history of at least the last 1 to 2 pages. This is because the ejection of droplets in the last 1 to 2 pages significantly affects the moisture content M1 of the liquid in the nozzles N after printing is completed. Of course, the moisture content M1 of the liquid in the nozzles N can also be estimated from the ejection history of each nozzle N for all 10 pages. Furthermore, for example, when a piezoelectric actuator formed of a piezoelectric element is used as the driving element, the water content of the liquid in the nozzle N can be calculated by detecting a signal indicating fluctuations in the excess voltage (electromotive voltage) generated in the piezoelectric actuator due to the piezoelectric element vibrating due to pressure vibrations remaining in the liquid in the flow path after the piezoelectric actuator is driven, and then calculating the viscosity of the liquid inferred from the state of vibration (residual vibration) of the piezoelectric element, for example, the period and amplitude of the residual vibration. In other words, if the viscosity of the liquid changes, the period, amplitude, and vibration damping state of the residual vibration of the electromotive voltage detected by the piezoelectric actuator will also change, so by determining in advance through experiments or the like the relationship between the period, amplitude, and vibration damping state of the residual vibration and the water content M1 of the liquid, the water content M1 of the liquid can be inferred from the residual vibration.

[0048] It should be noted that the water content M1 of the liquid inside the nozzle N may be estimated by other methods. When the viscosity changes due to a change in the water content of the liquid, the flight speed of the droplets ejected from the nozzle N changes. In other words, as the viscosity increases, the flight speed decreases. For this reason, the water content M1 of the liquid can be estimated by capturing and detecting the flight speed of the droplets ejected from the nozzle N with a camera or the like. Alternatively, the water content M1 of the liquid may be estimated by causing the liquid to land on the medium S and estimating the flight speed from the landing position.

[0049] In this embodiment, the water content M1 of each of the liquids in the nozzle arrays La and Lb of the first head chip Hc1 to the fourth head chip Hc4 estimated by the control unit 4 from the ejection history is as shown in Table Ta1.

[0050] Next, in step S2, the control unit 4 calculates the ejection amount required to restore the viscosity of the liquid in each nozzle N. Specifically, the control unit 4 calculates the ejection amount required to restore the viscosity of the liquid in the nozzle N from the water content of the nozzle N estimated in step S1 and a two-dimensional table or formula previously determined through experiments or the like. In this embodiment, the ejection amount required to restore the viscosity is calculated as the number of droplet shots.

[0051] Furthermore, in step S2, the control unit 4 calculates the moisture content M2 of the liquid in the cap 20 when droplets are ejected into the recess 21 of the cap 20 with the calculated number of shots required for viscosity recovery. That is, the control unit 4 calculates the moisture content M2 of the liquid discharged into the recess 21 of the cap 20 when the liquid with the moisture content M1 in the nozzle N calculated in step S1 is discharged into the recess 21 of the cap 20 with the number of shots calculated in step S2. Here, the cap 20 covering the first head chip Hc1 is referred to as cap 201, the cap 20 covering the second head chip Hc2 as cap 202, the cap 20 covering the third head chip Hc3 as cap 203, and the cap 20 covering the fourth head chip Hc4 as cap 204. For example, liquid A and liquid B are discharged into cap 201 covering the first head chip Hc1 from nozzle array La and nozzle array Lb, respectively, and therefore, the water content M2 of the liquid discharged into cap 20 is calculated using a two-dimensional table or formula from the number of shots in nozzle arrays La and Lb of the first head chip Hc1 and the water content M1 of the liquid in nozzle N. In this embodiment, as shown in Table Ta1, the water content M2 of the liquid in cap 201 covering the first head chip Hc1 is 53.8%, the water content M2 of the liquid in cap 202 covering the second head chip Hc2 is 70.0%, the water content M2 of the liquid in cap 203 covering the third head chip Hc3 is 61.4%, and the water content M2 of the liquid in cap 204 covering the fourth head chip Hc4 is 58.3%.

[0052] Next, in step S3, the control unit 4 calculates the amount of droplets to be ejected to bring the water content of the liquid in each cap 20 to the reference value Mb. In this embodiment, the amount of droplets to be ejected to bring the water content of the liquid in each cap to the reference value is referred to as the "water adjustment amount." Specifically, the control unit 4 calculates the water adjustment amount, which is the amount of droplets to be ejected to bring the water content of the liquid in each cap 20 to the reference value Mb, based on the water content M2 calculated in step S2. In other words, if the water content M2 of the liquid discharged into the cap 20 to recover from the increased viscosity in the nozzle N is significantly lower than the water content of the liquid in the nozzle N, the liquid discharged into the cap 20 will remove water from the liquid in the nozzle N when the capping operation is performed as is, causing the water content of the liquid in the nozzle N to decrease and increase in viscosity. Conversely, if the water content of the liquid in the cap 20 is greater than or approximately equal to the water content of the liquid in the nozzle N, the liquid discharged into the cap 20 is less likely to remove water from the liquid in the nozzle N, and the liquid in the nozzle N is less likely to thicken. In this embodiment, the water content of liquid A in the liquid storage section 3 is 80%, and the water content of liquid B in the liquid storage section 3 is 60%. For example, when liquid is ejected into the caps 201 to 204 corresponding to the first to fourth head chips Hc1 to Hc4 to restore viscosity, the water content of the liquid in cap 201 is 53.8%, the water content of the liquid in cap 202 is 70.0%, the water content of the liquid in cap 203 is 61.4%, and the water content of the liquid in cap 204 is 58.3%. After restoration of viscosity, the water content of the liquid in the nozzles N of nozzle row La is approximately 80%, and the water content of the liquid in the nozzles N of nozzle row Lb is approximately 60%. If the nozzles N are covered with the caps 20 after only this viscosity recovery has been performed, the lower the water content of the liquid in the caps 20, the more water is taken from the liquid in the nozzles N, causing the water content of the liquid in the nozzles N to decrease and become more viscous. As a result, the viscosity of the liquid in the nozzles N differs for each head chip Hc during the capping operation, and in the subsequent printing operation, the droplet ejection characteristics, i.e., the droplet flight speed and droplet weight, differ depending on the head chip Hc, resulting in reduced print quality.Therefore, by matching the moisture content of the liquid in each cap 20, the viscosity of the liquid in the nozzles N for each head chip Hc during the capping operation can be roughly equalized, thereby suppressing degradation of print quality in the subsequent printing operation. Therefore, a moisture adjustment amount is calculated, which is the amount of droplets ejected so that the moisture content of the liquid in the cap 20 reaches a reference value Mb—65% or more in this embodiment. In this embodiment, because the liquid A ejected from nozzle row La has a higher moisture content than the liquid B ejected from nozzle row Lb, the liquid A with the higher moisture content is ejected into the cap 20. By adjusting the moisture content using liquid A with a higher moisture content in this way, the amount of liquid discharged into the cap 20 can be reduced, thereby reducing costs. The moisture content of the liquid referred to here refers to the moisture content in the liquid storage section 3.

[0053] That is, in the first head chip Hc1, liquid A is ejected from nozzle row La, and liquid B is ejected from nozzle row Lb. One cap 201 covers the nozzle rows La and Lb of the first head chip Hc1 in the same space. The water content of liquid A in the liquid storage section 3 is 80%, and the water content of liquid B in the liquid storage section 3 is 60%. Therefore, in the cap 201 corresponding to the first head chip Hc1, the water adjustment amount set for nozzle row La is greater than the water adjustment amount set for nozzle row Lb. That is, in this embodiment, nozzle row La of the first head chip Hc1 is an example of a "third nozzle group," and nozzle row Lb of the first head chip Hc1 is an example of a "fourth nozzle group."

[0054] In this embodiment, the ejection amount required to adjust the water content of the liquid in the cap 20 is calculated as the number of droplet shots.

[0055] Furthermore, the reference value Mb of the water content of the liquid inside the cap 20 can be set to any numerical value. For example, it may be the average value of the water content of the liquid supplied to the nozzles N covered by the same cap 20. In this embodiment, the nozzle row La to which liquid A with a water content of 80% is supplied and the nozzle row Lb to which liquid B with a water content of 60% are supplied are covered by the same cap 20, so the reference value Mb may be set to 70%, which is the average value of liquid A and liquid B.

[0056] Furthermore, the reference value Mb of the water content of the liquid in the cap 20 may be set to 50% or more and 90% or less of the highest water content of the liquid supplied to the nozzle rows La, Lb corresponding to each cap 20. In this embodiment, for example, the nozzle row La to which liquid A with a water content of 80% is supplied and the nozzle row Lb to which liquid B with a water content of 60% are supplied are covered by the same cap 20, so the reference value Mb may be set to 50% or more and 90% or less of the highest water content of 80% of liquid A, in other words, the reference value Mb may be set to 40% or more and 72% or less.

[0057] In step S2, the second head chip Hc2 causes the moisture content of the liquid in the cap 20 to reach 70%, which is greater than the reference value Mb of 65% in this embodiment, due to the ejection for viscosity recovery. Because it is difficult to reduce the moisture content of the liquid in the cap 20, the moisture adjustment amount is set to 0 (zero) for caps 20 with a moisture content M2 equal to or greater than the reference value Mb. In other words, adjustment using the moisture adjustment amount is not required for caps 20 with a moisture content M2 equal to or greater than the reference value Mb.

[0058] However, when the type of liquid ejected from the nozzle rows L corresponding to each of the multiple caps 20 is the same, as in this embodiment, it is preferable to make the difference in water content of the liquid ejected into each cap 20 before the capping operation 10%. This makes it possible to prevent variations in the degree of viscosity increase of the liquid inside the nozzles N when the capping operation is performed, and to prevent a decrease in print quality.

[0059] Next, in step S4, the control unit 4 causes the liquid ejection head 9 to eject droplets into the recesses 21 of each cap 20 at a total ejection amount that is the sum of the thickening recovery amount, which is the number of droplet shots for thickening recovery calculated in step S2, and the moisture adjustment amount, which is the number of droplet shots for moisture adjustment calculated in step S3. As a result, the moisture content of the liquid ejected into each cap 20 becomes equal to or greater than the reference value Mb, and there is no cap that does not satisfy the reference value Mb.

[0060] Next, in step S5, the control unit 4 performs a capping operation in which each cap 20 covers each of the nozzle groups of the liquid ejection head 9. When the capping operation is performed in this manner, the water content of the liquid discharged into the caps 20 is equal to or greater than 65%, which is the reference value Mb. Therefore, when the capping operation is performed, the water content of the liquid in the nozzles N in each cap 20 is prevented from being significantly lost to the liquid in the cap 20, thereby preventing evaporation of the water from the liquid in the nozzles N. This prevents the liquid in the nozzles N from significantly thickening during the next printing operation, and prevents the ejection of thickened liquid from reducing the droplet ejection characteristics, i.e., the droplet flight speed and droplet weight, and thus reducing print quality. Furthermore, in this embodiment, by discharging the liquid from the nozzles N into each cap 20, the water content of the liquid in each cap 20 can be made equal to or greater than the reference value Mb. This eliminates the need for a special water supply unit to supply water to each cap 20, reducing the number of parts and making the liquid ejection device 1 more compact. Furthermore, in this embodiment, the moisture content of the liquid in each cap 20 can be made equal to or greater than the reference value Mb, thereby preventing variations in the degree of viscosity increase of the liquid in the nozzle N when the capping operation is performed, and preventing a decrease in print quality.

[0061] That is, as shown in Table Ta1, in the nozzle rows La and Lb corresponding to the cap 201 covering the first head chip Hc1 and the nozzle rows La and Lb corresponding to the cap 202 covering the second head chip Hc2, the amount of liquid ejected from the nozzles N during the printing operation, at least immediately before the end of the printing operation, is greater in the second head chip Hc2 than in the first head chip Hc1. Therefore, the moisture content M1 in the nozzles N of the first head chip Hc1 is smaller than the moisture content M1 in the nozzles N of the second head chip Hc2. Therefore, the viscosity recovery amount set for the first head chip Hc1 is greater than the viscosity recovery amount set for the nozzle row L of the second head chip Hc2. Furthermore, the moisture adjustment amount set for the nozzle row L of the first head chip Hc1 is greater than the moisture adjustment amount set for the nozzle row L of the second head chip Hc2. Note that in this embodiment, the cap 201 corresponding to the first head chip Hc1 is an example of a "first cap," and the cap 202 corresponding to the second head chip Hc2 is an example of a "second cap." Furthermore, the nozzle rows La and Lb of the first head chip Hc1 are an example of a "first nozzle group," and the nozzle rows La and Lb of the second head chip Hc2 are an example of a "second nozzle group."

[0062] In the above-described embodiment, the water content M2 of the liquid in the cap 202 corresponding to the second head chip Hc2 was higher than the reference value Mb of 65% due to the discharge of the liquid for viscosity recovery. In this modification, the control unit 4 compares the calculated water content M2 of the liquid in the cap 20 resulting from the discharge of the liquid for viscosity recovery with the preset reference value Mb, and sets the higher value as the new reference value. This modification of the first embodiment is shown in FIGS. 10 and 11. FIG. 10 is a flowchart showing a modification of the control method for the liquid ejection device 1 of the first embodiment. FIG. 11 is a table Ta2 showing the water content of the liquid in the nozzle N, the ejection amount, water adjustment amount, and total ejection amount required for the viscosity recovery of the liquid in the nozzle N, performed by the control method of FIG. 10. Note that a duplicated description of the same control method as the flowchart shown in FIG. 8 will be omitted.

[0063] 10, after steps S1 and S2 are performed, in step S10, it is determined whether the moisture content M2 of the liquid in all of the caps 20 calculated in step S2 is equal to or less than a reference value Mb. If the moisture content M2 of the liquid in all of the caps 20 is equal to or less than the reference value Mb (M2≦Mb) in step S10 (step S10: Yes), steps S3 to S5 are performed using the existing reference value Mb. If the moisture content M2 of the liquid in all of the caps 20 is not equal to or less than the reference value Mb in step S10, that is, if there is at least one case where M2>Mb (step S10: No), in step S11, the highest moisture content M2 of the calculated moisture contents M2 of the liquid in the caps 20 is set as a new reference value Mb′, and steps S3 to S5 are performed using the new reference value Mb′. In this embodiment, as shown in FIG. 11 , the calculated water content M2 of the liquid in the cap 202 corresponding to the second head chip Hc2 is 70%, which is higher than the reference value Mb of 65%, and this 70% is the highest water content M2. Therefore, the water content M2 of the liquid in the cap 202 corresponding to the second head chip Hc2 becomes the new reference value Mb′. In step S3, the control unit 4 calculates the water adjustment amount required to set the water content of the liquid in each cap 20 to the reference value Mb′. Then, in step S4, the liquid is actually discharged into the cap 20, and the capping operation is performed in step S5. At this time, the water content of the liquid discharged into all caps 20 can be made uniform at 70%. This reduces the variation in the water content of the liquid in the nozzles N between the head chips Hc currently being capped with multiple caps 20. Therefore, when the next printing operation is performed, large variations in the viscosity of the liquid in the nozzles N between the head chips Hc can be suppressed, improving print quality. Furthermore, in this embodiment, by discharging liquid from the nozzle N into each cap 20, the moisture content of the liquid in each cap 20 can be made equal to or greater than the reference value Mb, eliminating the need for a special moisture supply means for supplying moisture into each cap 20, thereby reducing the number of parts and making the liquid injection device 1 smaller.

[0064] In this embodiment, the X-axis direction is an example of a "direction of relative movement between the medium and the liquid jet head," and the Y-axis direction is an example of a "first direction."

[0065] (Embodiment 2) 12 is a diagram showing a schematic configuration of a liquid ejecting device 1 according to a second embodiment of the present invention. Note that the same members as those in the above-described embodiment are given the same reference numerals, and redundant explanations will be omitted.

[0066] 12, the liquid ejecting device 1 of this embodiment is a so-called serial printer that includes a liquid ejecting head 9 and performs printing by ejecting droplets from the liquid ejecting head 9 toward the medium S in the +Z direction while transporting the medium S in the X-axis direction and moving the liquid ejecting head 9 back and forth in the Y-axis direction. The liquid ejecting device 1 of this embodiment differs from the line printer of embodiment 1 in that it includes a movement mechanism that moves the liquid ejecting head 9 in the Y-axis direction.

[0067] The liquid ejection device 1 of this embodiment comprises a liquid ejection head 9 having a head chip Hc, a liquid storage section 3, a control unit 4, a transport mechanism 5 for transporting a medium S, a device main body 7, a maintenance section 8, and a movement mechanism 11.

[0068] The movement mechanism 11 is a mechanism for reciprocating the liquid ejection head 9 in the Y-axis direction, and includes a holder 11a that holds the liquid ejection head 9, and a conveyor belt 11b that is an endless belt that is stretched along the Y-axis direction. The control unit 4 controls the driving of a conveyor motor (not shown) to rotate the conveyor belt 11b, and moves the liquid ejection head 9 back and forth in the Y-axis direction together with the holder 11a fixed to the conveyor belt 11b.

[0069] The liquid storage section 3, control unit 4, transport mechanism 5, and maintenance section 8 are the same as those in the above-described embodiment, and therefore redundant explanations will be omitted.

[0070] Fig. 13 is a plan view of the liquid jet head 9 according to embodiment 2 as seen in the -Z direction. Fig. 14 is a cross-sectional view taken along line BB' in Fig. 13.

[0071] As shown in the figure, the liquid jet head 9 includes a plurality of head chips Hc, a holder 50, a flow path member 60, and a cover head 70.

[0072] Holder 50 has a storage section 51 that stores multiple head chips Hc, four in this embodiment. Within this storage section 51, the four head chips Hc are arranged side by side in the Y-axis direction so that their positions in the X-axis direction are the same. In this embodiment, the four head chips Hc are referred to in order in the +Y direction as the first head chip Hc1, the second head chip Hc2, the third head chip Hc3, and the fourth head chip Hc4. When there is no need to distinguish between the first head chip Hc1 to the fourth head chip Hc4, they are referred to as head chips Hc. Each head chip Hc has two nozzle rows L in which nozzles N are arranged side by side in the X-axis direction. The two nozzle rows L are arranged side by side in the Y-axis direction. In this embodiment, the two nozzle rows L are referred to in order in the +Y direction as nozzle row La and nozzle row Lb. Different types of liquids are ejected from the nozzle row La of the first head chip Hc1, the nozzle row Lb of the first head chip Hc1, the nozzle row La of the second head chip Hc2, and the nozzle row Lb of the second head chip Hc2. In this embodiment, liquid A is ejected from the nozzle row La of the first head chip Hc1, liquid B is ejected from the nozzle row Lb, liquid C is ejected from the nozzle row La of the second head chip Hc2, and liquid D is ejected from the nozzle row Lb. Liquids A to D have different water contents. Furthermore, the same type of liquid C as the nozzle row La of the second head chip Hc2 is ejected from the nozzle row Lb of the third head chip Hc3, and the same type of liquid D as the nozzle row Lb of the second head chip Hc2 is ejected from the nozzle row La of the third head chip Hc3. In other words, of the eight nozzle rows L aligned in the Y-axis direction, liquid A, liquid B, liquid C, and liquid D are ejected in the +Y direction from the nozzle row L at the end in the -Y direction, and liquid A, liquid B, liquid C, and liquid D are ejected in the -Y direction from the nozzle row L at the end in the +Y direction. This makes it possible to ensure that the order in which liquids A to D are ejected and land on the medium S when the liquid ejection head 9 moves in the +Y direction is the same as the order in which liquids A to D are ejected and land on the medium S when the liquid ejection head 9 moves in the -Y direction, thereby preventing a decrease in print quality due to differences in the order in which they land. Note that in this embodiment, for example, the water content of liquid A, liquid B, liquid C, and liquid D when stored in the liquid storage unit 3 is 80%, 70%, 78%, and 72%, respectively.

[0073] Moreover, the holder 50, the flow path member 60, and the cover head 70 are the same as those in the first embodiment, and therefore redundant explanations will be omitted.

[0074] The liquid ejecting device 1 also has a maintenance unit 8. The maintenance unit 8 is arranged in a non-printing region that is an end of the holder 11a in the movement direction. The maintenance unit 8 is equipped with a cap 20. The cap 20 covers the nozzles N for each head chip Hc. In other words, in this embodiment, a total of four caps 20 are provided, the same number as the head chips Hc. The type of liquid ejected from the nozzle rows L corresponding to the cap 201 covering the first head chip Hc1 and the cap 204 covering the fourth head chip Hc4 is the same. The type of liquid ejected from the nozzle rows L corresponding to the cap 202 covering the second head chip Hc2 and the cap 203 covering the third head chip Hc3 is the same. The type of liquid ejected from the nozzle rows L corresponding to the cap 201 covering the first head chip Hc1 and the cap 202 covering the second head chip Hc2 is not the same. The types of liquid ejected from the nozzle rows corresponding to the cap 203 covering the third head chip Hc3 and the cap 204 covering the fourth head chip Hc4 are not the same. Note that the other basic configuration of the maintenance unit 8 is the same as in the first embodiment described above, so redundant explanations will be omitted.

[0075] The liquid ejection head 9 ejects the liquid supplied from the liquid storage unit 3 in the form of droplets toward the +Z direction onto the medium S under the control of the control unit 4. Then, when the medium S is transported in the X-axis direction by the transport mechanism 5 and the liquid ejection head 9 is transported along the Y-axis direction by the movement mechanism 11, the liquid ejection head 9 ejects droplets onto the medium S, thereby forming a desired image on the medium S.

[0076] A control method for such a liquid ejecting device 1 will be described based on the flowchart of Fig. 8 shown in the above-mentioned first embodiment and table Ta3 of Fig. 15. Fig. 15 is table Ta3 showing the water content of the liquid in the nozzle N, the ejection amount required to recover the viscosity of the liquid in the nozzle N, the water adjustment amount, and the total ejection amount, which are performed by the control method of Fig. 8.

[0077] In step S1, the control unit 4 estimates and acquires the water content M1 of the liquid in the nozzles N of each nozzle row L of each head chip Hc, as shown in table Ta3 in FIG.

[0078] Next, in step S2, the control unit 4 calculates the amount of injection required to restore the viscosity of the liquid in each nozzle N. Specifically, the control unit 4 calculates the amount of injection required to restore the viscosity of the liquid in the nozzle N from the water content M1 of the nozzle N estimated in step S1 and a two-dimensional table or formula previously determined by an experiment or the like.

[0079] Furthermore, in step S2, the control unit 4 calculates the moisture content M2 of the liquid in the cap 201 when droplets are ejected into the recess 21 of the cap 20 with the calculated number of shots required for viscosity recovery. That is, the control unit 4 calculates the moisture content M2 of the liquid discharged into the recess 21 of the cap 20 when the liquid with the moisture content M1 in the nozzle N calculated in step S1 is discharged into the recess 21 of the cap 20 with the number of shots calculated in step S2. For example, since liquid A and liquid B are discharged from the nozzle array La and nozzle array Lb, respectively, into the cap 20 covering the first head chip Hc1, the control unit 4 calculates the moisture content M2 of the liquid discharged into the cap 20 using a two-dimensional equation from the number of shots at the nozzle arrays La and Lb of the first head chip Hc1 and the moisture content M1 of the liquid in the nozzle N. In this embodiment, as shown in Table Ta3, the water content M2 of the liquid in cap 201 covering the first head chip Hc1 is 60%, the water content M2 of the liquid in cap 202 covering the second head chip Hc2 is 65%, the water content M2 of the liquid in cap 203 covering the third head chip Hc3 is 69%, and the water content M2 of the liquid in cap 204 covering the fourth head chip Hc4 is 63%.

[0080] Next, in step S3, the control unit 4 calculates a "moisture adjustment amount," which is the amount of droplets to be ejected to bring the moisture content of the liquid in each cap 20 to the reference value Mb. Specifically, the control unit 4 calculates the moisture adjustment amount, which is the amount of droplets to be ejected to bring the moisture content of the liquid in each cap 20 to the reference value Mb, for the moisture content M2 calculated in step S2.

[0081] In this embodiment, for example, the reference value Mb is set to 80% of the water content of the highest liquid among the liquids discharged from the nozzle rows L corresponding to each cap 20. For example, since liquid A, which has a water content of 80%, and liquid B, which has a water content of 70%, are discharged onto the cap 201 covering the first head chip Hc1, the reference value Mb is set to 80% of the water content of the higher liquid A (80%), that is, 64%. The reference value Mb of the cap 204 covering the fourth head chip Hc4, from which the same liquids A and B are discharged, is also 64%, the same as that of the cap 201 covering the first head chip Hc1. Similarly, since liquid C, which has a water content of 78%, and liquid D, which has a water content of 72%, are discharged onto the cap 202 corresponding to the second head chip Hc2, the reference value Mb is set to 62.4%, which is 80% of the water content of the higher liquid C (78%). Similarly, the reference value Mb of the cap 203 corresponding to the third head chip Hc3 is also 62.4%.

[0082] In this embodiment, of the liquids A and B discharged from the first head chip Hc1 and the fourth head chip Hc4, liquid A has a higher water content than liquid B, and therefore liquid A, which has the higher water content, is sprayed into the cap 20. In this embodiment, the water adjustment amount is adjusted so that the cap 201 covering the first head chip Hc1 and the cap 204 covering the fourth head chip Hc4 each have the same reference value Mb (64%).

[0083] Similarly, in the cases of the second head chip Hc2 and the third head chip Hc3, it is sufficient to discharge the liquid C with a high moisture content. Note that the moisture content M2 (65%) of the liquid in the cap 202 covering the second head chip Hc2 is equal to or greater than the reference value Mb (62.4%), so the moisture adjustment amount is 0 (zero). Similarly, the moisture content M2 (69%) of the liquid in the cap 203 covering the third head chip Hc3 is equal to or greater than the reference value Mb (62.4), so the moisture adjustment amount is 0 (zero). In other words, adjustment using the moisture adjustment amount is not necessary for caps 20 whose moisture content M2 is equal to or greater than the reference value Mb.

[0084] Thereafter, as in the first embodiment described above, in step S4, the control unit 4 causes the liquid ejection head 9 to eject droplets into the recesses 21 of each cap 20 at a total ejection amount that is the sum of the viscosity recovery amount, which is the number of droplet shots for viscosity recovery calculated in step S2, and the moisture adjustment amount, which is the number of droplet shots for moisture adjustment calculated in step S3. As a result, the moisture contents of the liquid ejected into the cap 201 corresponding to the first head chip Hc1 and the cap 204 corresponding to the fourth head chip Hc4 are made to be the same reference value. Furthermore, the moisture contents of the liquid in the plurality of caps 20 can be made equal to or greater than the reference value Mb of each cap 20.

[0085] Next, in step S5, the control unit 4 performs a capping operation in which each cap 20 covers each of the nozzle groups of the liquid ejection head 9. When the capping operation is performed in this manner, the water content of the liquid ejected into each of the caps 20 is equal to or greater than the reference value Mb for each cap 20. Therefore, when the capping operation is performed, the water content of the liquid in the nozzles N in each cap 20 is prevented from being significantly lost to the liquid in the cap 20, thereby preventing excessive evaporation of water from the liquid in the nozzles N. This prevents the liquid in the nozzles N from significantly thickening during the next printing operation, and prevents the ejection of thickened liquid from reducing the droplet ejection characteristics, i.e., the droplet flight speed and droplet weight, and thus reducing print quality. In particular, the water content of the liquid ejected into the cap 201 corresponding to the first head chip Hc1 and the cap 204 corresponding to the fourth head chip Hc4, from which a common liquid is ejected, can be made equal. Therefore, the moisture content of the liquid in the nozzles N of the first head chip Hc1 and the fourth head chip Hc4, which eject a common liquid, can be made uniform, thereby further improving print quality. Furthermore, in this embodiment, for all caps, the reference value Mb of the cap 20 is set to 80% of the highest moisture content of the liquid filled in the nozzle row L covered by that cap 20. This reduces the variation in the degree of evaporation of moisture from the liquid in the nozzles N between the caps 20. This reduces the large variation in viscosity of the liquid in the nozzles N between the head chips Hc when performing the next printing operation, thereby improving print quality. Furthermore, in this embodiment, by discharging liquid from the nozzles N into each cap 20, the moisture content of the liquid in each cap 20 can be made equal to or greater than the reference value Mb. This eliminates the need for a special moisture supplying device for supplying moisture into each cap 20, reducing the number of parts and making the liquid ejection device 1 more compact.

[0086] In this embodiment, the liquid jet head 9 has four head chips Hc, but the number is not limited to this, and the liquid jet head 9 may have one head chip Hc or two or more head chips Hc.

[0087] A modified example of the second embodiment will now be described with reference to Table Ta4 in Fig. 16. Fig. 16 is Table Ta4 showing the water content of the liquid in the nozzles N, the ejection amount required to restore viscosity of the liquid in the nozzles N, the water adjustment amount, and the total ejection amount, all of which are performed using the control method in Fig. 8. In this modified example, the water adjustment amount is adjusted so that the ratio between the water content of the liquid discharged into each cap 20 and the water content of the liquid supplied to the nozzle rows L corresponding to each cap 20 is equal for all of the caps 20.

[0088] Specifically, in step S3 described above, the control unit 4 calculates the moisture adjustment amount, which is the amount of droplets to be ejected to bring the moisture content of the liquid in each cap 20 to the reference value Mb, based on the moisture content M2 calculated in step S2.

[0089] In this modified example, the ratio R of the water content M2 calculated in step S2 to the liquid with the highest water content among the liquids discharged from the nozzle row L corresponding to the cap 20 is calculated. For example, liquid A with a water content of 80% and liquid B with a water content of 70% are discharged into the cap 201 corresponding to the first head chip Hc1, so the liquid with the highest water content is liquid A with a water content of 80%. For the first head chip Hc1, liquid A has the highest water content of 80%, while the water content M2 of the liquid in the cap 20 calculated in step S2 is 60%, so the ratio R1 is 75%. Similarly, for the cap 202 corresponding to the second head chip Hc2, the ratio R2 is 83%, for the cap 203 corresponding to the third head chip Hc3, the ratio R3 is 88%, and for the cap 204 corresponding to the fourth head chip Hc4, the ratio R4 is 79%. The water content of the liquid in the caps 20 corresponding to each of the first head chip Hc1, the second head chip Hc2, and the fourth head chip Hc4 is adjusted so that it matches the highest ratio of ratios R1 to R4, which in this embodiment is 88% which is the ratio R3 of the cap 203 corresponding to the third head chip Hc3. That is, in step S3, the water adjustment amount is calculated so that the ratio R is 88% in all caps 20 using the liquid discharged from each head chip Hc into the cap 20. For example, since the liquid A, which has the highest water content among the liquids discharged from the nozzle row L corresponding to the cap 201 of the first head chip Hc1, has 80%, in order to set the ratio R1 in the cap 201 to 88%, liquid A should be discharged in step S3 so that the water content of the liquid in the cap 201 is 70%. Similarly, in the cap 202 corresponding to the second head chip Hc2, the liquid with the highest water content is liquid C at 78%, so in order to set ratio R2 to 88%, liquid C should be discharged in step S3 so that the water content of the liquid in cap 202 becomes 69%. Similarly, in the cap 204 corresponding to the fourth head chip Hc4, the liquid with the highest water content is liquid A at 80%, so in order to set ratio R4 to 88%, liquid C should be discharged in step S3 so that the water content of the liquid in cap 204 becomes 70%. Note that calculation of the water adjustment amount is not required for the third head chip Hc3.

[0090] In this way, by adjusting the moisture content so that the ratio between the moisture content of the liquid discharged into each cap 20 and the highest moisture content of the liquid supplied to the nozzle rows L covered by each cap 20 is equal for all caps 20, it is possible to equalize the rate at which moisture is removed from the liquid in the nozzles N in each cap 20 when a capping operation is performed. Therefore, it is possible to reduce the difference in the degree of viscosity of the liquid in the nozzles N among multiple nozzle rows L, and improve print quality.

[0091] (Other embodiments) Although the embodiments of the present invention have been described above, the basic configuration of the present invention is not limited to those described above.

[0092] Modified examples of the cap 20 are shown in Figures 17 and 18. Figure 17 is a plan view of the cap 20 according to another embodiment, viewed in the +Z direction. Figure 18 is a cross-sectional view taken along line CC' in Figure 17. Note that the same members as those in the above-described embodiment are given the same reference numerals, and redundant explanations will be omitted.

[0093] As shown in Figures 17 and 18, in the maintenance unit 8, the recesses 21 of the two caps 20 are provided with a communication passage 25 that communicates with each other, and a valve 26 provided midway along the communication passage 25. One end of the communication passage 25 communicates with the recess 21 of one cap 20, and the other end communicates with the recess 21 of the other cap 20. The valve 26 opens and closes the communication passage 25. The communication passage 25 is formed, for example, by a tube or the like that deforms in accordance with movement of the cap 20 in the Z-axis direction. The opening area of ​​the communication passage 25 is, for example, 20 µm 2 More than 100μm 2The following is an explanation. When each of these two caps 20 covers the nozzle row L of each head chip Hc, the space defined by the recess 21 of one cap 20 and the head chip Hc communicates with the space defined by the recess 21 of the other cap 20 and the head chip Hc via the communicating passage 25. This allows the humidity levels in these two spaces to be equalized. That is, even if the moisture content of the liquid discharged between the two caps 20 differs slightly when the capping operation is performed after moisture adjustment according to each of the above-described embodiments, the humidity of the space can be adjusted via the communicating passage 25 to equalize the different moisture contents. Furthermore, the presence of the communicating passage 25 allows the moisture content of the liquid discharged into the spaces defined by the two recesses 21 to be equalized without the moisture adjustment described above. When suction cleaning is performed by the maintenance unit 8 to suck liquid from the nozzles N, suction cleaning can be performed for each head chip Hc by closing the communicating passage 25 with the valve 26.

[0094] Furthermore, the present invention is broadly applicable to liquid ejection devices in general that include a liquid ejection head. Examples of liquid ejection heads include various inkjet recording heads used in image recording devices such as printers, and colorant ejection heads used in manufacturing color filters for liquid crystal displays and the like. Examples of liquid ejection heads include electrode material ejection heads used in forming electrodes for organic EL displays, FEDs (field emission displays), and the like, and bioorganic material ejection heads used in biochip manufacturing, and the present invention can also be applied to liquid ejection devices that include these liquid ejection heads.

[0095] (Addendum) From the above-described exemplary embodiments, the following configurations can be understood, for example.

[0096] A control method for a liquid ejection device according to aspect 1, which is a preferred aspect, is a control method for a liquid ejection device that includes a liquid ejection head configured to eject liquid from a plurality of nozzles that constitute a plurality of nozzle groups, and a plurality of caps configured to divide and cover the plurality of nozzle groups, and that performs a printing operation in which liquid is ejected onto a medium from nozzles that constitute the plurality of nozzle groups and are selected based on an image to be printed on the medium from the nozzles that constitute the plurality of nozzle groups, and a capping operation in which the nozzles of the plurality of nozzle groups are covered with the plurality of caps.After the printing operation is completed, liquid is ejected from the plurality of nozzle groups into the recesses of the corresponding plurality of caps at an amount of discharge set for each of the plurality of caps, and with the discharged liquid stored in the recesses, the nozzles are placed facing the recesses and covered with the caps, and the discharge amount set for each of the plurality of caps is set to an amount such that the water content of the liquid in the plurality of caps is equal to or greater than a reference value corresponding to the cap.

[0097] According to this, by discharging the liquid from the nozzle into the cap and adjusting the water content of the liquid in the cap to a reference value or higher, it is possible to prevent the liquid discharged into the cap from removing water from the liquid in the nozzle when the capping operation is performed, and to prevent the liquid in the nozzle from thickening. Furthermore, by discharging the liquid from the nozzle into the cap and adjusting the water content of the liquid in the cap to a reference value or higher, a special water supply means is not required, reducing the number of parts and making the device more compact.

[0098] In Aspect 2, which is a specific example of Aspect 1, the ratio of the reference value corresponding to each cap to the water content of the liquid supplied to the nozzle row corresponding to each cap is equal among the multiple caps. By making the ratio of the reference value to the water content equal among the multiple caps, it is possible to suppress variations in the degree of thickening of the liquid in the nozzles covered by the multiple caps.

[0099] In Aspect 3, which is a specific example of Aspect 1, the reference value corresponding to each cap is the average value of the water content of the liquid supplied to the nozzle row corresponding to the cap. This makes it possible to suppress thickening of the liquid in the nozzles when the capping operation is performed.

[0100] In Aspect 4, which is a specific example of Aspect 1, the reference value corresponding to each cap is a value between 50% and 90% of the highest water content of the liquid supplied to the nozzle row corresponding to that cap, thereby making it possible to suppress thickening of the liquid in the nozzles when the capping operation is performed.

[0101] In aspect 5, which is a specific example of aspect 1, the caps are arranged along a first direction intersecting the direction of relative movement between the medium and the liquid ejection head, the type of liquid ejected from the nozzle arrays corresponding to each of the caps is the same, and the difference in water content of the liquid ejected to each cap is within 10%. This reduces the difference in water content of the liquid among the caps, thereby suppressing variation in the degree of viscosity increase of the liquid in the nozzles covered by each cap.

[0102] In Aspect 6, which is a specific example of Aspect 1, the discharge amount set for each of the plurality of caps is set to an amount based on a viscosity recovery amount set based on the amount of liquid ejected by the nozzle group corresponding to that cap during the printing operation, and a moisture adjustment amount set based on the moisture content of the liquid discharged at that viscosity recovery amount and a reference value corresponding to each cap. This makes it possible to suppress thickening of the liquid in the nozzles during the capping operation while recovering from thickening of the liquid in the nozzles caused by printing.

[0103] In Aspect 7, which is a specific example of Aspect 1, the plurality of nozzle groups includes a first nozzle group and a second nozzle group, the plurality of caps include a first cap corresponding to the first nozzle group and a second cap corresponding to the second nozzle group, and when the amount of liquid ejected from the nozzles of the second nozzle group is greater than that of the first nozzle group during at least a period immediately before the end of the printing operation, the viscosity recovery amount set for the first nozzle group is greater than the viscosity recovery amount set for the second nozzle group, and the moisture adjustment amount set for the first nozzle group is greater than the moisture adjustment amount set for the second nozzle group. This makes it possible to recover from viscosity increase in the liquid in the nozzles caused by printing while suppressing viscosity increase in the liquid in the nozzles during the capping operation.

[0104] In Aspect 8, which is a specific example of Aspect 1, the plurality of nozzle groups include a third nozzle group and a fourth nozzle group, the plurality of caps include third caps corresponding to the third nozzle group and the fourth nozzle group, the water content of the liquid in a liquid storage section that supplies liquid to the third nozzle group is higher than the water content of the liquid in a liquid storage section that supplies liquid to the fourth nozzle group, and the water adjustment amount set for the third nozzle group is higher than the water adjustment amount set for the fourth nozzle group. In this way, by performing water adjustment using a large amount of liquid with a high water content, water adjustment can be performed with a small discharge amount.

[0105] In Aspect 9, which is a specific example of Aspect 1, the two caps communicate with each other via a communication passage. With this, even if a difference occurs in the water content of the liquid discharged into the two caps, the difference can be reduced by communicating the two caps with each other via the communication passage.

[0106] A liquid ejection device according to a preferred aspect 10 comprises a liquid ejection head configured to eject liquid from a plurality of nozzles constituting a plurality of nozzle groups; a plurality of caps configured to divide and cover the plurality of nozzle groups; and a control unit that performs a printing operation in which liquid is ejected onto a medium from nozzles selected from the nozzles constituting the plurality of nozzle groups based on an image to be printed on the medium, and a capping operation in which the nozzles of the plurality of nozzle groups are covered with the plurality of caps, and after the printing operation is completed, the control unit ejects liquid from the plurality of nozzle groups into the recesses of the corresponding plurality of caps at an amount of discharge set for each of the plurality of caps, and with the discharged liquid stored in the recesses, covers the nozzles with the caps facing the recesses, and sets the discharge amount set for each of the plurality of caps to an amount such that the water content of the liquid in the plurality of caps is equal to or greater than a reference value corresponding to the cap.

[0107] According to this, by discharging the liquid from the nozzle into the cap and adjusting the water content of the liquid in the cap to a reference value or higher, it is possible to prevent the liquid discharged into the cap from removing water from the liquid in the nozzle when the capping operation is performed, and to prevent the liquid in the nozzle from thickening. Furthermore, by discharging the liquid from the nozzle into the cap and adjusting the water content of the liquid in the cap to a reference value or higher, a special water supply means is not required, reducing the number of parts and making the device more compact. [Explanation of symbols]

[0108] Hc...head chip, Hc1 to Hc4...first head chip to fourth head chip, L, La, Lb...nozzle array, M1 to M2...moisture content, Mb...reference value, N...nozzle, R, R1 to R4...ratio, S...medium, 1...liquid ejection device, 2...head unit, 3...liquid storage section, 4...control unit, 5...transport mechanism, 5a...transport roller, 7...device main body, 8...maintenance section, 9...liquid ejection head, 10...support, 11...movement mechanism, 20, 201 to 204...caps, 21...recess, 22...cap main body, 23...seal section, 24...absorption section, 25...communicating passage, 26...valve, 30...suction mechanism, 31...discharge path, 32...discharge pump, 40...waste liquid storage section, 50...holder, 51...storage section, 52...first flow path, 60...flow path member, 61...second flow path, 70...cover head, 71...exposure opening.

Claims

1. a liquid ejection head configured to eject liquid from a plurality of nozzles that constitute a plurality of nozzle groups; a plurality of caps configured to cover the plurality of nozzle groups in a divided manner; Equipped with a control method for a liquid ejecting device that executes a printing operation of ejecting liquid onto a medium from nozzles selected from among the nozzles constituting the plurality of nozzle groups based on an image to be printed on the medium, and a capping operation of covering the nozzles of the plurality of nozzle groups with the plurality of caps, After the printing operation is completed, liquid is discharged from the plurality of nozzle groups into the corresponding recesses of the plurality of caps at a discharge amount set for each of the plurality of caps; With the discharged liquid stored in the recess, the nozzle is placed facing the recess and covered with the cap; the discharge amount set for each of the plurality of caps is set to an amount at which the water content of the liquid in the plurality of caps is equal to or greater than a reference value corresponding to the cap; A method for controlling a liquid ejection device.

2. a ratio of the reference value corresponding to each cap to the water content of the liquid supplied to the nozzle row corresponding to each cap is equal among the plurality of caps; The method for controlling a liquid ejection apparatus according to claim 1 .

3. the reference value corresponding to each cap is an average value of the water content of the liquid supplied to the nozzle row corresponding to each cap; The method for controlling a liquid ejection apparatus according to claim 1 .

4. the reference value corresponding to each cap is a value between 50% and 90% of the highest water content of the liquid supplied to the nozzle row corresponding to each cap, The method for controlling a liquid ejection apparatus according to claim 1 .

5. the plurality of caps are arranged along a first direction intersecting a direction of relative movement between the medium and the liquid ejection head, the type of liquid ejected from the nozzle arrays corresponding to the plurality of caps is the same; The difference in moisture content of the liquid discharged into each cap is within 10%. The method for controlling a liquid ejection apparatus according to claim 1 .

6. the discharge amount set for each of the plurality of caps is set to an amount based on a viscosity recovery amount that is set based on the amount of liquid ejected by the nozzle group corresponding to the cap during the printing operation, and a moisture adjustment amount that is set based on the moisture content of the liquid discharged at the viscosity recovery amount and a reference value corresponding to each cap. The method for controlling a liquid ejection apparatus according to claim 1 .

7. the plurality of nozzle groups include a first nozzle group and a second nozzle group, the plurality of caps include a first cap corresponding to the first nozzle group and a second cap corresponding to the second nozzle group, when the amount of liquid ejected from the nozzles of the second nozzle group is greater than that of the first nozzle group at least during the period immediately before the end of the printing operation, the thickening recovery amount set for the first nozzle group is greater than the thickening recovery amount set for the second nozzle group, and the moisture adjustment amount set for the first nozzle group is greater than the moisture adjustment amount set for the second nozzle group; The method for controlling a liquid ejection apparatus according to claim 1 .

8. the plurality of nozzle groups include a third nozzle group and a fourth nozzle group, the plurality of caps include third caps corresponding to the third nozzle group and the fourth nozzle group, a water content of the liquid in a liquid storage portion that supplies liquid to the third nozzle group is higher than a water content of the liquid in a liquid storage portion that supplies liquid to the fourth nozzle group; a moisture adjustment amount set for the third nozzle group is greater than a moisture adjustment amount set for the fourth nozzle group; The method for controlling a liquid ejection apparatus according to claim 1 .

9. The two caps communicate with each other via a communication passage. The method for controlling a liquid ejection apparatus according to claim 1 .

10. a liquid ejection head configured to eject liquid from a plurality of nozzles that constitute a plurality of nozzle groups; a plurality of caps configured to cover the plurality of nozzle groups in a divided manner; a control unit that executes a printing operation in which liquid is ejected onto the medium from nozzles selected from among the nozzles that constitute the plurality of nozzle groups based on an image to be printed on the medium, and a capping operation in which the nozzles of the plurality of nozzle groups are covered with the plurality of caps, the control unit, after the printing operation is completed, discharges liquid from the plurality of nozzle groups into the corresponding recesses of the plurality of caps at a discharge amount set for each of the plurality of caps; With the discharged liquid stored in the recess, the nozzle is placed facing the recess and covered with the cap; the discharge amount set for each of the plurality of caps is set to an amount at which the water content of the liquid in the plurality of caps is equal to or greater than a reference value corresponding to the cap; A liquid ejection device characterized by:

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