Maintenance method for liquid ejection device

Abstract

To reduce waste of liquid in maintenance processing.SOLUTION: There is provided a maintenance method for a liquid discharge device which comprises a liquid discharge head including a nozzle for discharging liquid, a pressure chamber communicating with the nozzle, and a driving element for giving pressure fluctuation to the liquid in the pressure chamber, and executes printing processing of forming an image on a medium, wherein the printing processing includes discharge processing of driving the driving element, discharging the liquid from the liquid discharge head and causing the liquid to land on the medium, and maintenance processing of driving the driving element and discharging the liquid in the liquid discharge head, the printing processing counts the number of unit periods that is the number of ended unit periods out of a plurality of unit periods obtained by dividing a period required for the printing processing by a first condition, executes the maintenance processing when the number of unit periods reaches a specified number, acquires viscosity information on viscosity of liquid in the liquid discharge head before the number of unit periods reaches the specific number, and decreases the number of unit periods when the viscosity information satisfies a second condition.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a maintenance method for a liquid ejection device. [Background technology]

[0002] In a liquid ejection device that ejects liquid such as ink onto a medium such as printing paper, for example, thickening of the liquid caused by evaporation of water contained in the liquid can be a problem. Patent Document 1 discloses a liquid ejection device that periodically executes a maintenance process that drives a drive element to discharge ink from within the liquid ejection head. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-233904 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional liquid ejection device described above, there are cases where the liquid is ejected excessively during the maintenance process. [Means for solving the problem]

[0005] In order to solve the above problems, one aspect of a maintenance method for a liquid ejection device according to the present invention is a maintenance method for a liquid ejection device that has a liquid ejection head including a nozzle that ejects liquid, a pressure chamber connected to the nozzle, and a drive element that imparts pressure fluctuations to the liquid in the pressure chamber, and that executes a printing process that forms an image indicated by print data on a medium, the printing process including an ejection process that drives the drive element in accordance with the print data to eject liquid from the liquid ejection head and cause it to land on the medium, and a maintenance process that drives the drive element to drain the liquid in the liquid ejection head, and within the printing process, a number of unit periods that is the number of completed unit periods out of a plurality of unit periods obtained by dividing a period required for the printing process by a first condition is counted, and when the number of unit periods reaches a specified number, the maintenance process is executed, and before the number of unit periods reaches the specified number, viscosity information regarding the viscosity of the liquid in the liquid ejection head is obtained, and when the viscosity information satisfies a second condition, the number of unit periods is reduced. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a functional block diagram showing an example of the configuration of an inkjet printer 1 according to a first embodiment. [Diagram 2] 1 is a schematic diagram illustrating an inkjet printer 1. FIG. [Diagram 3] 2 is a schematic partial cross-sectional view of the recording head HD, in which the recording head HD is cut so as to include a discharge portion D. FIG. [Figure 4] 11 is an explanatory diagram for explaining an example of the ink ejection operation in the ejection section D. FIG. [Diagram 5] 11 is an explanatory diagram for explaining an example of the ink ejection operation in the ejection section D. FIG. [Figure 6] 11 is an explanatory diagram for explaining an example of the ink ejection operation in the ejection section D. FIG. [Figure 7] FIG. 2 is a block diagram showing an example of the configuration of a liquid ejection head HU. [Figure 8] FIG. 4 is a timing chart illustrating the operation of the inkjet printer 1 during a recording period Tu. [Figure 9] FIG. 13 is an explanatory diagram for explaining generation of connection state designation signals SLa[m], SLb[m], and SLs[m]. [Figure 10] 4 is an explanatory diagram for explaining generation of determination information Stt in the measurement circuit 9. FIG. [Figure 11] 2A to 2C are explanatory diagrams illustrating a series of operations of the inkjet printer 1. [Figure 12] FIG. 4 is a flowchart showing the operation of the inkjet printer 1 during a printing process. [Figure 13] FIG. 4 is a flowchart showing the operation of the inkjet printer 1 during a printing process. [Figure 14] FIG. 11 is a functional block diagram showing an example of the configuration of an inkjet printer 1a according to a second embodiment. [Figure 15] 3A to 3C are explanatory diagrams illustrating a series of operations of the inkjet printer 1a. [Figure 16] FIG. 4 is a flowchart showing the operation of the inkjet printer 1a during a printing process. [Figure 17] FIG. 4 is a flowchart showing the operation of the inkjet printer 1a during a printing process. [Figure 18] 4A to 4C are explanatory diagrams illustrating a series of operations of the inkjet printer 1b. [Figure 19] FIG. 11 is a flowchart showing the operation of the inkjet printer 1b during a printing process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, the embodiments for carrying out the present invention will be described with reference to the drawings. However, in each drawing, the dimensions and scale of each part are appropriately different from the actual ones. In addition, since the embodiments described below are preferred specific examples of the present invention, various technically preferable limitations are attached, but the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to the effect that the present invention is limited.

[0008] 1. First embodiment In this embodiment, the liquid ejection device will be described by taking as an example an inkjet printer 1 that ejects ink to form an image on recording paper P. The inkjet printer 1 is an example of a "liquid ejection device." Ink is an example of a "liquid." Recording paper P is an example of a "medium."

[0009] 1.1. Overview of Inkjet Printers 1 The configuration of an inkjet printer 1 according to a first embodiment will be described with reference to Figures 1 and 2. Figure 1 is a functional block diagram showing an example of the configuration of an inkjet printer 1 according to a first embodiment. Figure 2 is a schematic diagram illustrating the inkjet printer 1.

[0010] The inkjet printer 1 receives print data Img indicating the image to be formed by the inkjet printer 1, and information indicating the number of copies of the image to be formed by the inkjet printer 1, from a host computer such as a personal computer or digital camera. The inkjet printer 1 executes a printing process to form on recording paper P the image indicated by the print data Img supplied from the host computer.

[0011] 1, the inkjet printer 1 includes a liquid ejection head HU provided with ejection units D that eject ink, a control unit 6 that controls the operation of each unit of the inkjet printer 1, a drive signal generation circuit 2 that generates a drive signal Com for driving the ejection units D, a storage unit 5 that stores the control program for the inkjet printer 1 and other information, a measurement circuit 9 that determines the ejection state of the ejection units D and outputs determination information Stt that indicates the result of the ejection state, and viscosity information μ related to the viscosity of the ink in the ejection units D, a transport mechanism 7 that transports the recording paper P, a movement mechanism 8 that moves the liquid ejection head HU, and a maintenance unit 4 related to a maintenance process that performs maintenance on the ejection units D so that ink is normally ejected from the ejection units D. In the following description, one or more letters x may be used to indicate a specific value of the viscosity information μ, and the viscosity information μx may be used. In addition, the viscosity information μ is an example of a "parameter corresponding to the viscosity of the liquid in the ejection section", an example of a "parameter corresponding to the viscosity of the liquid in the liquid ejection head", and an example of "viscosity information relating to the viscosity of the liquid in the liquid ejection head".

[0012] In this embodiment, the liquid ejection head HU includes a recording head HD having M ejection sections D, a switching circuit 10, and a detection circuit 20. In this embodiment, M is an integer of 2 or more. It should be noted that the M discharge units D are an example of the "plurality of discharge units."

[0013] In the following, in order to distinguish between the M discharge sections D provided in the recording head HD, they may be referred to in order as 1st stage, 2nd stage, ..., Mth stage. Also, the mth stage of discharge sections D may be referred to as discharge section D[m]. In the following description, the variable m is an integer that satisfies 1 to M. Also, when a component, signal, etc. of the inkjet printer 1 corresponds to the stage number m of discharge sections D[m], the subscript [m] indicating that the component, signal, etc. corresponds to the stage number m may be added to the symbol representing the component, signal, etc.

[0014] The switching circuit 10 switches whether or not to supply the drive signal Com output from the drive signal generating circuit 2 to each discharge section D. In addition, the switching circuit 10 switches whether or not to electrically connect each discharge section D and the detection circuit 20.

[0015] The detection circuit 20 generates a residual vibration signal NES[m] indicating the vibration remaining in the discharge section D[m] after the discharge section D[m] is driven, based on the detection signal Vout[m] detected from the discharge section D[m] driven by the drive signal Com, for any m from 1 to M. Hereinafter, this vibration will be referred to as "residual vibration."

[0016] The measurement circuit 9 generates, for any m from 1 to M, determination information Stt[m] indicating the result of the ejection state determination of the ejection section D[m] and viscosity information μ[m] based on the residual vibration signal NES[m]. Note that, hereinafter, the ejection section D that is the subject of the ejection state determination by the measurement circuit 9 may be referred to as the ejection section DH to be determined. Also, a series of processes executed in the inkjet printer 1, including the ejection state determination executed by the measurement circuit 9 and the preparation process for the measurement circuit 9 to execute the ejection state determination, is referred to as the ejection state determination process.

[0017] In this embodiment, it is assumed that the inkjet printer 1 is a serial printer. Specifically, as shown in FIG. 2, the inkjet printer 1 executes a printing process by ejecting ink from the ejection unit D while transporting the recording paper P in the sub-scanning direction and moving the liquid ejection head HU in the main scanning direction. In this embodiment, as shown in FIG. 2, the +X direction and the -X direction opposite to the +X direction are the main scanning direction, and the +Y direction is the sub-scanning direction. Hereinafter, the +X direction and the -X direction are collectively referred to as the "X-axis direction", and the +Y direction and the -Y direction opposite to the +Y direction are collectively referred to as the "Y-axis direction". Furthermore, the direction perpendicular to the X-axis direction and the Y-axis direction and the ink ejection direction is referred to as the -Z direction. The -Z direction and the +Z direction opposite to the -Z direction are collectively referred to as the "Z-axis direction".

[0018] The print head HD and the ejection sections D provided in the print head HD will be described with reference to FIG.

[0019] FIG. 3 is a schematic partial cross-sectional view of the recording head HD, in which the recording head HD is cut so as to include a discharge portion D. 3, the ejection section D includes a piezoelectric element PZ, a cavity 320 filled with ink, a nozzle N communicating with the cavity 320, and a vibration plate 310. In the ejection section D, a drive signal Com is supplied to the piezoelectric element PZ, and the piezoelectric element PZ is driven by the drive signal Com, thereby ejecting ink in the cavity 320 from the nozzle N. The cavity 320 is a space defined by a cavity plate 340, a nozzle plate 330 in which the nozzle N is formed, and the vibration plate 310. The cavity 320 communicates with a reservoir 350 via an ink supply port 360. The reservoir 350 communicates with the liquid container 14 corresponding to the ejection section D via an ink intake port 370. The piezoelectric element PZ is an example of a “driving element.” The cavity 320 is an example of a “pressure chamber.”

[0020] In this embodiment, the piezoelectric element PZ is of a unimorph type as shown in Fig. 3. Note that the piezoelectric element PZ is not limited to the unimorph type, and a bimorph type, a laminated type, or the like may also be used.

[0021] The piezoelectric element PZ has an upper electrode Zu, a lower electrode Zd, and a piezoelectric body Zm provided between the upper electrode Zu and the lower electrode Zd. The piezoelectric element PZ is a passive element that deforms in response to a change in potential of a drive signal Com. When the lower electrode Zd is electrically connected to a power supply line LHd set to a constant potential Vbs and a drive signal Com is supplied to the upper electrode Zu, a voltage is applied between the upper electrode Zu and the lower electrode Zd. The piezoelectric element PZ is displaced in the +Z direction or the -Z direction in response to the applied voltage, and as a result of this displacement, the piezoelectric element PZ vibrates.

[0022] A vibration plate 310 is placed at the opening on the top surface of the cavity plate 340. A lower electrode Zd is bonded to the vibration plate 310. Therefore, when the piezoelectric element PZ is driven to vibrate by the drive signal Com, the vibration plate 310 also vibrates. The volume of the cavity 320 changes due to the vibration of the vibration plate 310, and the ink filled in the cavity 320 is ejected from the nozzle N. When the ink in the cavity 320 decreases due to the ejection of the ink, ink is supplied from the reservoir 350.

[0023] 4 to 6 are explanatory diagrams for explaining an example of the ink ejection operation in the ejection section D. As illustrated in Fig. 5, the control section 6 changes the potential of the drive signal Com supplied to the piezoelectric element PZ included in the ejection section D to generate a distortion that displaces the piezoelectric element PZ in the +Z direction, thereby bending the vibration plate 310 of the ejection section D in the +Z direction. As a result, as illustrated in Fig. 5, the volume of the cavity 320 of the ejection section D is expanded compared to the state illustrated in Fig. 4.

[0024] Next, the control unit 6 changes the potential indicated by the drive signal Com to generate a distortion that displaces the piezoelectric element PZ in the -Z direction, and deflects the vibration plate 310 of the ejection unit D in the -Z direction. As a result, as shown in Fig. 6, the volume of the cavity 320 contracts suddenly, and a part of the ink filling the cavity 320 is ejected as an ink droplet from the nozzle N communicating with the cavity 320. After the piezoelectric element PZ and the vibration plate 310 are driven by the drive signal Com and displaced in the Z-axis direction, residual vibration is generated in the ejection unit D including the vibration plate 310.

[0025] 1 and 2. The transport mechanism 7 transports the recording paper P in the +Y direction. Specifically, the transport mechanism 7 includes a transport roller (not shown) whose rotation axis is parallel to the X-axis direction, and a motor (not shown) that rotates the transport roller under the control of the control unit 6.

[0026] The moving mechanism 8 reciprocates the liquid ejection head HU along the X axis under the control of the control unit 6. As illustrated in Fig. 2, the moving mechanism 8 includes a substantially box-shaped conveying body 82 that houses the liquid ejection head HU, and an endless belt 81 to which the conveying body 82 is fixed.

[0027] The maintenance unit 4 includes a cap 42 for covering the liquid ejection head HU so as to seal the nozzles N of the ejection portion D, a wiper 44 for wiping off foreign matter such as paper dust adhering to the vicinity of the nozzles N of the ejection portion D, a tube pump (not shown) for sucking ink, air bubbles, etc. in the ejection portion D, and a discharged ink receiving portion (not shown) for receiving the ink discharged when discharging the ink in the ejection portion D. The maintenance unit 4 is provided in an area that does not overlap with the recording paper P when viewed in the Z axis direction.

[0028] The storage unit 5 includes volatile memory such as RAM, and non-volatile memory such as ROM, EEPROM, or PROM, and stores various information such as print data Img supplied from the host computer and the control program for the inkjet printer 1. RAM is an abbreviation for Random Access Memory. ROM is an abbreviation for Read Only Memory. EEPROM is an abbreviation for Electrically Erasable Programmable Read-Only Memory. PROM is an abbreviation for Programmable ROM.

[0029] The control unit 6 includes a CPU. CPU is an abbreviation for Central Processing Unit. However, the control unit 6 may include a programmable logic device such as an FPGA instead of the CPU. FPGA is an abbreviation for Field Programmable Gate Array.

[0030] The control unit 6 has a CPU that operates in accordance with a control program stored in the storage unit 5, causing the inkjet printer 1 to execute a printing process. The printing process includes one or more ejection processes and one or more maintenance processes. The ejection process drives the piezoelectric elements PZ based on the print data Img to eject ink from the liquid ejection head HU and cause it to land on the recording paper P. The inkjet printer 1 repeats the ejection process one or more times to form an image corresponding to the print data Img on the recording paper P. The maintenance process is a process for maintaining the ink ejection state in the ejection unit D in a state where printing is possible with normal quality.

[0031] The control unit 6 generates a print signal SI for controlling the liquid ejection head HU, a waveform designation signal dCom for controlling the drive signal generating circuit 2, a signal for controlling the transport mechanism 7, and a signal for controlling the movement mechanism 8. Here, the waveform designation signal dCom is a digital signal that defines the waveform of the drive signal Com. The drive signal Com is an analog signal for driving the discharge section D. The drive signal generation circuit 2 includes a DA conversion circuit and generates the drive signal Com having a waveform defined by the waveform designation signal dCom. In this embodiment, it is assumed that the drive signal Com includes a drive signal Com-A and a drive signal Com-B. Moreover, the print signal SI is a digital signal for specifying the type of operation of the discharge section D. Specifically, the print signal SI specifies whether or not to supply the drive signal Com to the discharge section D, thereby specifying the type of operation of the discharge section D. Here, specifying the type of operation of the discharge section D means, for example, specifying whether or not to drive the discharge section D, specifying whether or not ink is discharged from the discharge section D when the discharge section D is driven, and specifying the amount of ink discharged from the discharge section D when the discharge section D is driven.

[0032] When the printing process is executed, the control unit 6 first stores the print data Img supplied from the host computer in the storage unit 5. Next, the control unit 6 generates various control signals such as a print signal SI, a waveform designation signal dCom, a signal for controlling the transport mechanism 7, and a signal for controlling the movement mechanism 8 based on various data such as the print data Img stored in the storage unit 5. Then, the control unit 6 controls the liquid ejection head HU so as to drive the ejection unit D while controlling the transport mechanism 7 and the movement mechanism 8 so as to change the relative position of the recording paper P with respect to the liquid ejection head HU based on the various control signals and the various data stored in the storage unit 5. In this way, the control unit 6 adjusts the presence or absence of ink ejection from the ejection unit D, the amount of ink ejection, the timing of ink ejection, and the like, and controls the execution of the printing process to form an image corresponding to the print data Img on the recording paper P.

[0033] The inkjet printer 1 according to this embodiment executes an ejection status determination process that determines whether the ink ejection status from each ejection section D is normal or not, i.e., whether an ejection abnormality has occurred in each ejection section D, based on the determination information Stt output from the measurement circuit 9. Here, the ejection abnormality is a state in which ink cannot be ejected in the manner defined by the drive signal Com even when the ejection unit D is driven by the drive signal Com to eject ink from the ejection unit D. Here, the ink ejection manner defined by the drive signal Com means that the ejection unit D ejects an amount of ink defined by the waveform of the drive signal Com, and the ejection unit D ejects ink at an ejection speed defined by the waveform of the drive signal Com. In other words, the state in which ink cannot be ejected in the ink ejection manner defined by the drive signal Com includes, in addition to a state in which ink cannot be ejected from the ejection unit D, a state in which an amount of ink smaller than the ink ejection amount defined by the drive signal Com is ejected from the ejection unit D, a state in which an amount of ink larger than the ink ejection amount defined by the drive signal Com is ejected from the ejection unit D, or a state in which ink cannot be landed at a desired landing position on the recording paper P because ink is ejected at a speed different from the ink ejection speed defined by the drive signal Com.

[0034] In the ejection state determination process, the inkjet printer 1 executes a series of processes, namely, a first process, a second process, a third process, a fourth process, and a fifth process, which are described below. In the first process, the control unit 6 selects an ejection section DH to be determined from among M ejection sections D provided in the liquid ejection head HU. In the second process, the control unit 6 drives the ejection section DH to be determined, thereby causing residual vibrations in the ejection section DH to be determined. In the third process, the detection circuit 20 generates a residual vibration signal NES based on the detection signal Vout detected from the ejection section DH to be determined. In the fourth process, the measurement circuit 9 performs an ejection state determination for the ejection section DH to be determined based on the residual vibration signal NES, and generates determination information Stt and viscosity information μ indicating the result of the determination. In the fifth process, the control unit 6 stores the determination information Stt and the viscosity information μ in the storage unit 5.

[0035] As described above, the inkjet printer 1 according to this embodiment executes maintenance processing to maintain the ink ejection state of the ejection section D in a state where printing can be performed with normal quality. The inkjet printer 1 of this embodiment executes maintenance processing before and after the printing process, and during the printing process, for keeping the viscosity of the ink in all M ejection sections D within an appropriate range. Furthermore, the inkjet printer 1 of this embodiment determines whether the ink ejection state from the ejection sections D is normal or not before and / or after the printing process, and if the ejection state of any of the ejection sections D is determined to be abnormal, executes maintenance processing according to the state of the ejection section D and restores the ejection section D to a normal state. Specifically, the maintenance process is a process for returning the ink ejection state of the ejection section D to normal by executing one or more of a wiping process, a pumping process, and a flushing process. The wiping process is a process for wiping off foreign matter such as paper powder adhering to the vicinity of the nozzle N of the ejection section D with the wiper 44. The pumping process is a process for sucking ink, air bubbles, etc. in the ejection section D with a tube pump. The flushing process is a process for discharging thickened ink from the ejection section D by driving the ejection section D, and supplying non-thickened ink in the reservoir 350 from the ink supply port 360 into the ejection section D. As described above, the maintenance unit 4 is provided in an area that does not overlap with the recording paper P when viewed in the ejection direction, i.e., the Z-axis direction. Therefore, the flushing process discharges the ink in the liquid ejection head HU to a position that does not overlap with the recording paper P in the ejection direction. The "flushing process" is an example of a "maintenance process for driving the drive element to discharge the liquid inside the liquid ejection head."

[0036] The inkjet printer 1 may be capable of performing multiple types of flushing processes. For example, the inkjet printer 1 may be capable of performing a first flushing process and a second flushing process that has a smaller flushing unit amount than the first flushing process but is capable of ejecting ink even if the ink has thickened to the point where it is difficult to eject it in the first flushing process. In the following, to simplify the explanation, the inkjet printer 1 will be explained as performing one type of flushing process once or multiple times.

[0037] 1.2.Configuration of Liquid Ejection Head HU The configuration of the liquid ejection head HU will be described below with reference to FIG.

[0038] 7 is a block diagram showing an example of the configuration of the liquid ejection head HU. As described above, the liquid ejection head HU includes the recording head HD, the switching circuit 10, and the detection circuit 20. The liquid ejection head HU also includes an internal wiring LHa to which the drive signal Com-A is supplied from the drive signal generation circuit 2, an internal wiring LHb to which the drive signal Com-B is supplied from the drive signal generation circuit 2, and an internal wiring LHs for supplying the detection signal Vout detected from the ejection section D to the detection circuit 20.

[0039] 7, the switching circuit 10 includes M switches SWa[1] to SWa[M], M switches SWb[1] to SWb[M], M switches SWs[1] to SWs[M], and a connection state designation circuit 11 that designates the connection state of each switch. Each switch may be, for example, a transmission gate. Based on at least some of the signals of the print signal SI, latch signal LAT, change signal CH, and period designation signal Tsig supplied from the control unit 6, the connection state designation circuit 11 generates connection state designation signals SLa[1] to SLa[M] that specify the on / off state of switches SWa[1] to SWa[M], connection state designation signals SLb[1] to SLb[M] that specify the on / off state of switches SWb[1] to SWb[M], and connection state designation signals SLs[1] to SLs[M] that specify the on / off state of switches SWs[1] to SWs[M]. For any m from 1 to M, each switch SWa[m] switches between electrical continuity and non-conduction between the internal wiring LHa and the upper electrode Zu[m] of the piezoelectric element PZ[m] provided in the discharge section D[m] in response to the connection state designation signal SLa[m]. For example, the switch SWa[m] is turned on when the connection state designation signal SLa[m] is at a high level, and turned off when the connection state designation signal SLa[m] is at a low level. For any m from 1 to M, the switch SWb[m] switches between electrical continuity and non-conduction between the internal wiring LHb and the upper electrode Zu[m] of the piezoelectric element PZ[m] provided in the discharge section D[m] in response to the connection state designation signal SLb[m]. For example, the switch SWb[m] is turned on when the connection state designation signal SLb[m] is at a high level, and turned off when the connection state designation signal SLb[m] is at a low level. For any m from 1 to M, the switch SWs[m] switches between electrical continuity and non-conduction between the internal wiring LHs and the upper electrode Zu[m] of the piezoelectric element PZ[m] provided in the discharge section D[m] in response to the connection state designation signal SLs[m]. For example, the switch SWs[m] is turned on when the connection state designation signal SLs[m] is at a high level, and turned off when the connection state designation signal SLs[m] is at a low level.

[0040] The detection circuit 20 is supplied with a detection signal Vout[m] output from the piezoelectric element PZ[m] of the discharge section D[m] driven as the discharge section DH to be judged, for any m from 1 to M, via the internal wiring LHs. The detection circuit 20 then generates a residual vibration signal NES based on the detection signal Vout[m].

[0041] 1.3. Operation of Liquid Ejection Head HU Hereinafter, the operation of the liquid ejection head HU will be described with reference to FIGS.

[0042] In this embodiment, the operating period of the inkjet printer 1 includes one or more recording periods Tu. It is assumed that the inkjet printer 1 according to this embodiment performs one of the following during each recording period Tu: driving each ejection section D in the ejection process, and driving the ejection section DH to be judged and detecting residual vibration during preparatory processing for the ejection state judgment process. However, the present invention is not limited to this aspect, and it may be possible to perform both driving each ejection section D in the ejection process, and driving the ejection section DH to be judged and detecting residual vibration during preparatory processing for the ejection state judgment process during each recording period Tu. Generally, the inkjet printer 1 forms an image represented by the print data Img by ejecting ink from each ejection section D one or more times over a number of continuous or intermittent recording periods Tu. The inkjet printer 1 according to this embodiment also executes a preparatory process for an ejection state determination process M times over M continuous or intermittent recording periods Tu, thereby executing an ejection state determination process with each of the M ejection sections D[1] to D[M] as the ejection section DH to be determined.

[0043] FIG. 8 is a timing chart illustrating the operation of the inkjet printer 1 during a recording period Tu. 8, the control unit 6 outputs a latch signal LAT having a pulse PlsL and a change signal CH having a pulse PlsC. As a result, the control unit 6 defines a recording period Tu as a period from the rising edge of the pulse PlsL to the rising edge of the next pulse PlsL. In addition, the control unit 6 divides the recording period Tu into two control periods Tu1 and Tu2 by the pulse PlsC. The print signal SI includes individual designation signals Sd[1] to Sd[M] that designate the driving mode of the discharge sections D[1] to D[M] during each recording period Tu. When at least one of the discharge process and the discharge state determination process is executed during the recording period Tu, the control section 6 supplies the print signal SI including the individual designation signals Sd[1] to Sd[M] to the connection state designation circuit 11 in synchronization with the clock signal CL prior to the start of the recording period Tu, as shown in FIG. 8. In this case, the connection state designation circuit 11 generates connection state designation signals SLa[m], SLb[m], and SLs[m] for any m from 1 to M based on the individual designation signal Sd[m] during the recording period Tu.

[0044] For any m between 1 and M, the individual designation signal Sd[m] according to the present embodiment is a signal that designates one of five drive modes, namely, ejection of an amount of ink corresponding to a large dot, ejection of an amount of ink corresponding to a medium dot, ejection of an amount of ink corresponding to a small dot, non-ejection of ink, and drive as a determination target in the ejection state determination process, for the ejection section D[m] during each recording period Tu. In the following description, the amount corresponding to a large dot may be referred to as a "large amount," and ejection of an amount of ink corresponding to a large dot may be referred to as "formation of a large dot." Similarly, the amount corresponding to a medium dot may be referred to as a "medium amount," and ejection of an amount of ink corresponding to a medium dot may be referred to as "formation of a medium dot." The amount corresponding to a small dot may be referred to as a "small amount," and ejection of an amount of ink corresponding to a small dot may be referred to as "formation of a small dot." Drive as a determination target in the ejection state determination process may be referred to as "drive as the ejection section DH to be determined." In this embodiment, as an example, it is assumed that the individual designation signal Sd[m] is a 3-bit digital signal as illustrated in FIG.

[0045] As shown in FIG. 8, the drive signal generating circuit 2 outputs a drive signal Com-A having a medium dot waveform PX provided in the control period Tu1 and a small dot waveform PY provided in the control period Tu2. In this embodiment, the medium dot waveform PX and the small dot waveform PY are determined so that the potential difference between the highest potential VHX and the lowest potential VLX of the medium dot waveform PX is greater than the potential difference between the highest potential VHY and the lowest potential VLY of the small dot waveform PY. Specifically, for any m from 1 to M, when the discharge section D[m] is driven by the drive signal Com-A having the medium dot waveform PX, the medium dot waveform PX is determined so that a medium amount of ink is discharged from the discharge section D[m]. Also, when the discharge section D[m] is driven by the drive signal Com-A having the small dot waveform PY, the small dot waveform PY is determined so that a small amount of ink is discharged from the discharge section D[m]. Note that the potentials of the medium dot waveform PX and the small dot waveform PY at the start and end are set to the reference potential V0.

[0046] For any m between 1 and M, when the individual designation signal Sd[m] designates the formation of a large dot for the discharge section D[m], the connection state designation circuit 11 sets the connection state designation signal SLa[m] to a high level during the control periods Tu1 and Tu2, and sets the connection state designation signals SLb[m] and SLs[m] to a low level during the recording period Tu. In this case, the discharge section D[m] is driven by the drive signal Com-A of the medium dot waveform PX during the control period Tu1 to discharge a medium amount of ink, and is driven by the drive signal Com-A of the small dot waveform PY during the control period Tu2 to discharge a small amount of ink. As a result, the discharge section D[m] discharges a total of a large amount of ink during the recording period Tu, and a large dot is formed on the recording paper P. Furthermore, when the individual designation signal Sd[m] designates the ejection section D[m] to form a medium dot, the connection state designation circuit 11 sets the connection state designation signal SLa[m] to a high level during the control period Tu1 and to a low level during the control period Tu2, and sets the connection state designation signals SLb[m] and SLs[m] to a low level during the recording period Tu. In this case, the ejection section D[m] ejects a medium amount of ink during the recording period Tu, and a medium dot is formed on the recording paper P. Furthermore, for any m from 1 to M, when the individual designation signal Sd[m] designates the ejection section D[m] to form a small dot, the connection state designation circuit 11 sets the connection state designation signal SLa[m] to a low level during the control period Tu1 and to a high level during the control period Tu2, and sets the connection state designation signals SLb[m] and SLs[m] to a low level during the recording period Tu. In this case, the ejection section D[m] ejects a small amount of ink during the recording period Tu, and a small dot is formed on the recording paper P. Furthermore, for any m from 1 to M, when the individual designation signal Sd[m] designates the discharge section D[m] not to discharge ink, the connection state designation circuit 11 sets the connection state designation signals SLa[m], SLb[m], and SLs[m] to a low level during the recording period Tu. In this case, the discharge section D[m] does not discharge ink and does not form dots on the recording paper P during the recording period Tu.

[0047] As shown in FIG. 8, the driving signal generating circuit 2 outputs a driving signal Com-B having a test waveform PS provided in the recording period Tu. In this embodiment, the test waveform PS is determined so that the potential difference between the highest potential VHS and the lowest potential VLS of the test waveform PS is smaller than the potential difference between the highest potential VHY and the lowest potential VLY of the small dot waveform PY. Specifically, for any m from 1 to M, when the driving signal Com-B having the test waveform PS is supplied to the discharge section D[m], the test waveform PS is determined so that the discharge section D[m] is driven to such an extent that ink is not discharged from the discharge section D[m]. Note that the potential of the test waveform PS at the start and end is set to the reference potential V0. The control unit 6 also outputs a period designation signal Tsig having a pulse PlsT1 and a pulse PlsT2, which divides the recording period Tu into a control period TSS1 from the start of the pulse PlsL to the start of the pulse PlsT1, a control period TSS2 from the start of the pulse PlsT1 to the start of the pulse PlsT2, and a control period TSS3 from the start of the pulse PlsT2 to the start of the next pulse PlsL.

[0048] Then, for any m from 1 to M, when the individual designation signal Sd[m] designates the ejection section D[m] as the ejection section DH to be judged, the connection state designation circuit 11 sets the connection state designation signal SLa[m] to a low level during the recording period Tu, sets the connection state designation signal SLb[m] to a high level during the control periods TSS1 and TSS3 and to a low level during the control period TSS2, and sets the connection state designation signal SLs[m] to a low level during the control periods TSS1 and TSS3 and to a high level during the control period TSS2. In this case, the ejection section DH to be judged is driven by the driving signal Com-B of the test waveform PS during the control period TSS1. Specifically, the piezoelectric element PZ of the ejection section DH to be judged is displaced by the driving signal Com-B of the test waveform PS during the control period TSS1. As a result, vibration occurs in the ejection section DH to be judged, and this vibration remains in the control period TSS2. Then, during the control period TSS2, the upper electrode Zu of the piezoelectric element PZ of the ejection section DH to be judged changes its potential according to the residual vibration occurring in the ejection section DH to be judged. In other words, during the control period TSS2, the upper electrode Zu of the piezoelectric element PZ of the ejection section DH to be judged shows a potential according to the electromotive force of the piezoelectric element PZ caused by the residual vibration occurring in the ejection section DH to be judged. Then, the potential of the upper electrode Zu can be detected as a detection signal Vout during the control period TSS2.

[0049] Fig. 9 is an explanatory diagram for explaining the generation of connection state designation signals SLa[m], SLb[m], and SLs[m] for any m from 1 to M. The connection state designation circuit 11 decodes the individual designation signal Sd[m] according to Fig. 9, and generates the connection state designation signals SLa[m], SLb[m], and SLs[m]. As shown in Figure 9, the individual designation signal Sd[m] in this embodiment indicates any one of the following values: a value (1,1,0) that specifies the formation of a large dot, a value (1,0,0) that specifies the formation of a medium dot, a value (0,1,0) that specifies the formation of a small dot, a value (0,0,0) that specifies no ink ejection, or a value (1,1,1) that specifies driving of the ejection section DH to be judged. The connection state designation circuit 11 sets the connection state designation signal SLa[m] to a high level during control periods Tu1 and Tu2 when the individual designation signal Sd[m] indicates (1,1,0), sets the connection state designation signal SLa[m] to a high level during control period Tu1 when the individual designation signal Sd[m] indicates (1,0,0), sets the connection state designation signal SLa[m] to a high level during control period Tu2 when the individual designation signal Sd[m] indicates (0,1,0), sets the connection state designation signal SLa[m] to a high level during control period TSS1 and TSS3 when the individual designation signal Sd[m] indicates (1,1,1), and sets the connection state designation signal SLb[m] to a high level during control periods TSS1 and TSS3, and sets the connection state designation signal SLs[m] to a high level during control period TSS2, and sets each signal to a low level if the above does not apply.

[0050] As described above, the detection circuit 20 generates the residual vibration signal NES based on the detection signal Vout. The residual vibration signal NES is a signal obtained by amplifying the amplitude of the detection signal Vout and removing noise components from the detection signal Vout, thereby shaping the detection signal Vout into a waveform suitable for processing in the measurement circuit 9. The residual vibration signal NES is an analog signal. The detection circuit 20 may be configured to include, for example, a negative feedback amplifier for amplifying the detection signal Vout, a low-pass filter for attenuating high frequency components of the detection signal Vout, and a voltage follower for converting impedance and outputting a low impedance residual vibration signal NES.

[0051] 1.4.Measuring circuit 9 Next, the measurement circuit 9 will be described.

[0052] Generally, the residual vibration occurring in the ejection section D has a natural vibration frequency determined by the shape of the nozzle N, the weight of the ink filled in the cavity 320, the viscosity of the ink filled in the cavity 320, and the like. In addition, in general, when an ejection abnormality occurs in the ejection part D due to air bubbles being mixed in the cavity 320 of the ejection part D, the frequency of the residual vibration is higher than when air bubbles are not mixed in the cavity 320. In general, when an ejection abnormality occurs in the ejection part D due to foreign matter such as paper powder adhering to the vicinity of the nozzle N of the ejection part D, the frequency of the residual vibration is lower than when no foreign matter is adhering. In general, when the viscosity of the ink filled in the cavity 320 of the ejection part D is high, the frequency of the residual vibration is lower than when the viscosity is low. In general, when an ejection abnormality occurs in the ejection part D due to the viscosity of the ink filled in the cavity 320 of the ejection part D being increased, the frequency of the residual vibration is lower than when foreign matter such as paper powder is adhering to the vicinity of the nozzle N of the ejection part D. In general, when an ejection abnormality occurs in the ejection section D because the cavity 320 of the ejection section D is not filled with ink, or when an ejection abnormality occurs in the ejection section D because the piezoelectric element PZ has broken down and cannot be displaced, the amplitude of the residual vibration becomes smaller.

[0053] As described above, the residual vibration signal NES shows a waveform corresponding to the residual vibration occurring in the ejection section DH to be judged. Specifically, the residual vibration signal NES shows a frequency corresponding to the frequency of the residual vibration occurring in the ejection section DH to be judged, shows an amplitude corresponding to the amplitude of the residual vibration occurring in the ejection section DH to be judged, and shows a damping rate corresponding to the damping rate of the residual vibration occurring in the ejection section DH to be judged. The damping rate indicates the degree to which the amplitude of the vibration decreases in a unit period. Based on the residual vibration signal NES, the measurement circuit 9 can detect the judgment information Stt used for ejection state judgment to judge the ejection state of the ink in the ejection section DH to be judged. Also, based on the residual vibration signal NES, the measurement circuit 9 can detect the viscosity information μ of the ink in the ejection section DH to be judged.

[0054] The viscosity information μ is a parameter indicating the characteristics of the residual vibration indicated by the residual vibration signal NES. The parameter indicating the characteristics of the residual vibration is, for example, the amplitude, period, or attenuation rate of the residual vibration. The measurement circuit 9 specifies the parameter indicating the characteristics of the residual vibration based on the residual vibration signal NES of the ejection section DH to be judged. The measurement circuit 9 outputs the parameter indicating the characteristics of the residual vibration as the viscosity information μ to the control section 6. In this way, the viscosity information μ in the first embodiment is a parameter corresponding to the viscosity of the ink and is information based on the residual vibration. The parameter corresponding to the viscosity of the ink is a parameter that changes according to the viscosity of the ink, and therefore the viscosity of the ink can be estimated. For example, the parameter corresponding to the viscosity of the ink is a parameter that correlates with the viscosity of the ink. As an example, when the ink becomes more viscous, the amplitude of the residual vibration becomes smaller, the frequency of the residual vibration becomes lower, and the attenuation rate of the residual vibration becomes larger, as described above.

[0055] The measurement circuit 9 measures the time length NTc of one period of the residual vibration signal NES, and generates period information Info-T indicative of the measurement result. The measurement circuit 9 also generates amplitude information Info-S indicating whether the residual vibration signal NES has a predetermined amplitude. Specifically, the measurement circuit 9 determines whether the potential of the residual vibration signal NES is equal to or higher than a threshold potential Vth-O that is higher than the potential Vth-C of the amplitude center level of the residual vibration signal NES and is equal to or lower than a threshold potential Vth-U that is lower than the potential Vth-C during the period in which the time length NTc of one cycle of the residual vibration signal NES is measured. If the result of the determination is positive, the measurement circuit 9 sets the amplitude information Info-S to a value indicating that the residual vibration signal NES has a predetermined amplitude, for example, "1", and if the result of the determination is negative, the measurement circuit 9 sets the amplitude information Info-S to a value indicating that the residual vibration signal NES does not have a predetermined amplitude, for example, "0". Then, the measurement circuit 9 generates the determination information Stt indicating the determination result of the ink ejection state in the ejection section DH to be determined, based on the period information Info-T and the amplitude information Info-S.

[0056] FIG. 10 is an explanatory diagram for explaining the generation of determination information Stt in the measurement circuit 9. As shown in FIG. 10, the measurement circuit 9 determines the discharge state in the discharge unit D-H to be determined by comparing the time length NTc indicated by the period information Info-T with some or all of the threshold values Tth1, Tth2, and Tth3, and generates determination information Stt indicating the result of the determination. Here, the threshold value Tth1 is a value for indicating the boundary between the time length of one cycle of residual vibration when the discharge state of the discharge unit D-H to be determined is normal and the time length of one cycle of residual vibration when bubbles are mixed into the cavity 320. Further, the threshold value Tth2 is a value for indicating the boundary between the time length of one cycle of residual vibration when the discharge state of the discharge unit D-H to be determined is normal and the time length of one cycle of residual vibration when foreign matter adheres near the nozzle N. Further, the threshold value Tth3 is a value for indicating the boundary between the time length of one cycle of residual vibration when foreign matter adheres near the nozzle N of the discharge unit D-H to be determined and the time length of one cycle of residual vibration when the ink in the cavity 320 thickens. Note that the threshold values Tth1 to Tth3 satisfy “Tth1 < Tth2 < Tth3”.

[0057] As shown in FIG. 10, in the present embodiment, when the value of the amplitude information Info-S is “1” and the time length NTc indicated by the period information Info-T satisfies “Tth1 ≦ NTc ≦ Tth2”, it is regarded that the ink discharge state in the discharge unit D-H to be determined is normal. And in this case, the measurement circuit 9 sets the value “1” indicating that the discharge state of the discharge unit D-H to be determined is normal in the determination information Stt. Further, when the value of the amplitude information Info-S is “1” and the time length NTc indicated by the period information Info-T satisfies “NTc < Tth1”, it is regarded that a discharge abnormality due to bubbles has occurred in the discharge unit D-H to be determined. And in this case, the measurement circuit 9 sets the value “2” indicating that a discharge abnormality due to bubbles has occurred in the discharge unit D-H to be determined in the determination information Stt. Also, when the value of the amplitude information Info-S is "1" and the time length NTc indicated by the period information Info-T satisfies "Tth2 < NTc ≤ Tth3", it is regarded that a discharge abnormality due to foreign matter adhesion has occurred in the determination target discharge unit D-H. And in this case, the measurement circuit 9 sets the value "3", which indicates that a discharge abnormality due to foreign matter adhesion has occurred in the determination target discharge unit D-H, in the determination information Stt. Also, when the value of the amplitude information Info-S is "1" and the time length NTc indicated by the period information Info-T satisfies "Tth3 < NTc", it is regarded that a discharge abnormality due to thickening has occurred in the determination target discharge unit D-H. And in this case, the measurement circuit 9 sets the value "4", which indicates that a discharge abnormality due to thickening has occurred in the determination target discharge unit D-H, in the determination information Stt. Also, even when the value of the amplitude information Info-S is "0", it is regarded that a discharge abnormality has occurred in the determination target discharge unit D-H. And in this case, the measurement circuit 9 sets the value "5", which indicates that a discharge abnormality has occurred in the determination target discharge unit D-H, in the determination information Stt. Then, the control unit 6 associates the determination information Stt generated by the measurement circuit 9 with the stage number m of the determination target discharge unit D-H corresponding to the determination information Stt, and stores it in the storage unit 5. Thereby, the control unit 6 manages the determination information Stt[1] to Stt[M] corresponding to the discharge units D[1] to D[M].

[0058] As described above, when a discharge abnormality occurs in the discharge unit D because the ink filled in the cavity 320 of the discharge unit D has thickened, the frequency of the residual vibration becomes lower compared to the case where foreign matter such as paper powder adheres near the nozzle N of the discharge unit D. Furthermore, as the thickening progresses, the degree of attenuation of the amplitude of the residual vibration with the passage of time becomes larger. The inkjet printer 1 executes maintenance processing for normally restoring the ink discharge state of the discharge unit D by executing one or more of the wiping processing, pumping processing, and flushing processing described above according to the determination information Stt[1] to Stt[M] corresponding to the discharge units D[1] to D[M].

[0059] 1.5. Timing of flushing process Next, the execution timing of the flushing process will be described with reference to FIG.

[0060] Figure 11 is an explanatory diagram illustrating a series of operations of the inkjet printer 1. When the inkjet printer 1 is turned on in response to a user's operation, it waits for the supply of print data Img. When print data Img is supplied during period Ta1 shown in Figure 11 while waiting for print processing, period Ta1 ends and the inkjet printer 1 performs maintenance processing before the print processing. During period Ta2 during which maintenance processing before the print processing is performed, the inkjet printer 1 releases the seal on the nozzles N by the caps 42 and performs a flushing process.

[0061] When the maintenance process before the printing process is completed, in other words, when the period Ta2 shown in FIG. 11 is completed, the inkjet printer 1 executes a printing process during the period Ta3 to form an image indicated by the print data Img supplied from the host computer on the recording paper P.

[0062] During the printing process, the inkjet printer 1 executes a flushing process at a timing that corresponds to the viscosity of the ink, in order to prevent poor ejection caused by thickening of the ink between multiple ejection processes and deterioration of image quality caused by thickening of the ink. In other words, in this embodiment, the period between multiple maintenance processes that are executed during the printing process is changed according to the viscosity of the ink in the ejection sections D[1]-[M]. Specifically, in the first embodiment, the inkjet printer 1 counts the number of completed unit periods Tb among the multiple unit periods Tb obtained by dividing the period Ta3 required for the printing process according to the division conditions. In the following, in order to distinguish each of the multiple unit periods Tb, a number or an alphabet may be written after "Tb", such as unit period Tb1, unit period Tb2, unit period Tb3, etc. The lengths of the multiple unit periods Tb may be the same or different, but it is preferable that they are as close to the same as possible. Furthermore, the number of counted unit periods Tb is referred to as the "count number Cn". The value of the count number Cn can also be said to be a value that estimates the viscosity state of the ink in the ejection section D. The count number Cn is an integer equal to or greater than 0. Then, when the count number Cn reaches a preset specified number Spn, in other words, when it is estimated that the ink in the ejection section D has thickened to a degree that requires a flushing process, the inkjet printer 1 performs a flushing process on the ejection section D. The division condition for dividing the period Ta3 required for the print process is an example of a “first condition.” The count number Cn is an example of a “number of unit periods.”

[0063] The division condition for dividing the period Ta3 required for the printing process may be, for example, one of the following three modes. The division condition in the first mode is that one unit period Tb is determined to have ended when an image has been formed on a predetermined number of sheets of recording paper P. The division condition in the second mode is that one unit period Tb is determined to have ended when the liquid ejection head HU has moved from one end to the other end in the X-axis direction and then returned to the other end a predetermined number of times. The division condition in the third mode is that one unit period Tb is determined to have ended when a predetermined period has ended. The predetermined period is, for example, an integer multiple of the recording period Tu, which is one cycle of the drive signal Com illustrated in FIG. 8.

[0064] As described above, the count number Cn can be said to be a value that estimates the viscosity state of the ink in the ejection section D. Generally, over time, the ink solvent in the ejection section D[m] evaporates, causing the ink in the ejection section D[m] to thicken. Therefore, the number of completed unit periods Tb corresponds to the progress of viscosity increase of the ink in the ejection section D[m]. Therefore, the inkjet printer 1 assumes a case in which ink is not ejected even once from the nozzle N of the ejection section D[m] during the unit period Tb, and increases the count number Cn each time the unit period Tb ends. On the other hand, when ink is ejected from the nozzle N[m], the viscosity of the ink in the ejection portion D[m] decreases because the thickened ink in the ejection portion D[m] is discharged and the ink in the reservoir 350 is supplied to the ejection portion D[m] from the ink supply port 360. Therefore, when the inkjet printer 1 determines that the count number reduction condition, which indicates that the viscosity of the ink in the ejection portion D has been reduced to a predetermined viscosity state by the ejection process, is met, it reduces the count number Cn. In this embodiment, the inkjet printer 1 measures the viscosity information μ[1]-[M] of the discharge sections D[1]-[M] at a predetermined timing within the period Ta3 required for the printing process, and when it is determined that all of the viscosity information μ[1]-[M] are equal to or less than a predetermined threshold μth and the count number reduction condition is satisfied, the inkjet printer 1 reduces the count number Cn. That is, the count number reduction condition in this embodiment is that the viscosity information μ[1]-[M] is equal to or less than a predetermined threshold μth. The threshold μth and the value by which the count number Cn is reduced when the count number reduction condition is satisfied are determined in advance by the manufacturer or user of the inkjet printer 1. The threshold μth and the value by which the count number Cn is reduced when the count number reduction condition is satisfied may be any value. However, the value by which the count number Cn is reduced when the count number reduction condition is satisfied is set to a value corresponding to the threshold μth. For example, in the first embodiment, the viscosity at which the ink is not thickened, that is, the viscosity at which the flushing process is unnecessary corresponding to the viscosity state immediately after the flushing process, is set to the threshold μth, and the value by which the count number is reduced is determined to be equal to or greater than the specified number Spn. Here, since the count number Cn is an integer equal to or greater than 0, if the count number Cn becomes less than 0 as a result of decrementing the count number Cn, the inkjet printer 1 sets the count number Cn to 0. In the first embodiment, if all of the viscosity information μ[1] through μ[M] are equal to or less than the threshold μth, a value equal to or greater than the specified number Spn is decremented from the count number Cn. As a result, if all of the viscosity information μ[1] through μ[M] are equal to or less than the threshold μth, the ink in the ejection sections D[1] through D[M] has not increased in viscosity, and so the count number Cn becomes "0", just like immediately after the flushing process. The count number decrease condition is an example of a "second condition." Moreover, when the flushing process is executed for the discharge section D[1] to the discharge section D[M], the count number Cn is reset, that is, set to 0.

[0065] Next, the counting of the count number Cn will be described in more detail. The inkjet printer 1 increases the count number Cn every time the unit period Tb ends, and measures the viscosity information μ[1]-[M] of the discharge sections D[1]-[M] before determining that the count number Cn has reached the specified number Spn, and decreases the count number Cn if the measured viscosity information μ[1]-[M] is equal to or less than the threshold value μth. The timing for measuring the viscosity information μ[1]-[M] may be any time before determining that the count number Cn has reached the specified number Spn, and the number of times the viscosity information μ[1]-[M] is measured may be any number of times. For example, the inkjet printer 1 may measure the viscosity information μ[1]-[M] when the count number Cn reaches a value obtained by subtracting a predetermined number from the specified number Spn. In the first embodiment, the inkjet printer 1 measures the viscosity information μ[1]-[M] when the count number Cn is incremented by one, in other words, every time one unit period Tb ends.

[0066] If it is determined that the count number Cn has reached the specified number Spn, the inkjet printer 1 executes a flushing process on the ejection sections D[1]-[M]. The specified number Spn is a value determined in advance by the manufacturer or user of the inkjet printer 1. For example, the manufacturer of the inkjet printer 1 may determine the specified number Spn as a value obtained by dividing the period of time it takes from a state in which the ink has not yet thickened to a state in which the ink has thickened without any ink being ejected and is about to cause an ejection defect by the length of one unit period Tb. In other words, if no ink is ejected from the ejection section D[m] until just before the final ejection process within the last unit period Tb of the number of unit periods Tb corresponding to the specified number Spn, and ink is ejected from the ejection section D in the final ejection process, no ejection defect will occur. However, if the ejection process is continued without performing the maintenance process for consecutive unit periods Tb that are greater than the specified number Spn, if no ink is ejected from the ejection section D[m] during the unit periods Tb equal to the specified number Spn, and ink is ejected from the ejection section D[m] during the ejection process of the next unit period Tb, ejection defects may occur. In other words, the specified number Spn corresponds to a period during which stable ejection of ink from the ejection section D can be guaranteed, regardless of the ink ejection status of the ejection section D. The determined prescribed number Spn is stored in the storage unit 5.

[0067] FIG. 11 illustrates a printing process in which the prescribed number Spn is 3. FIG. 11 also illustrates the viscosity information μ[1] and count number Cn in the discharge section D[1] at the end of each of the unit periods Tb1, Tb2, Tb3, Tb4, Tb5, Tb6, and Tb7. Furthermore, it is assumed that all of the viscosity information μ5[1] to μ5[M] measured at the end of the unit period Tb5 are equal to or less than the threshold μth, and the count number reduction condition is satisfied. Furthermore, it is assumed that all of the viscosity information μ1[1], μ2[1], μ3[1], μ4[1], μ6[1], and μ7[1] measured at the end of each of the unit periods Tb1, Tb2, Tb3, Tb4, Tb6, and Tb7 are greater than the threshold μth, and the count number reduction condition is not satisfied. The threshold value μth is determined to a value corresponding to the viscosity state immediately after the flushing process, and the value by which the count number is decreased when the count number decrease condition is satisfied is determined to be 3, which is the same as the specified number Spn.

[0068] The inkjet printer 1 increases the count number Cn by 1 at the end of each of the unit periods Tb1, Tb2, and Tb3. However, since at least the viscosity information μ[1] is a value that exceeds the threshold μth, the count number decrease condition is not met and the inkjet printer 1 does not decrease the count number Cn. At the end of the unit period Tb3, the count number Cn reaches the specified number Spn of 3, so the inkjet printer 1 executes a flushing process on the discharge sections D[1] to D[M]. When the flushing process is executed, the inkjet printer 1 resets the count number Cn. Next, at the end of each of the unit periods Tb4 and Tb5, the inkjet printer 1 increases the count number Cn by 1 but does not decrease it. At the end of the unit period Tb5, all of the viscosity information μ5[1] to μ5[M] is equal to or less than the threshold μth and the count number decrease condition is met, so the inkjet printer 1 increases the count number Cn by 1 and decreases it by 3, resulting in the count number Cn being 0. Next, at the end of each unit period Tb6, unit period Tb7, and unit period Tb8, the inkjet printer 1 increments the count number Cn by 1 but does not decrement it. At the end of unit period Tb8, the count number Cn reaches the specified number Spn of 3, so the inkjet printer 1 executes a flushing process on the ejection sections D[1]-[M].

[0069] When the printing process has ended, when the period Ta3 has ended in the example of Fig. 11, or during the period Ta4 in the example of Fig. 11, the maintenance process after the printing process is executed. In the maintenance process after the printing process has ended, the inkjet printer 1 executes a flushing process.

[0070] 1.6. Operations during printing The operation of the inkjet printer 1 during the printing process will be described in more detail using Figures 12 and 13. Figures 12 and 13 are flow charts showing the operation of the inkjet printer 1 during the printing process. In step S1, the control unit 6 receives print data Img from the host computer. Next, in step S2, the control unit 6 sets the count number Cn to 0. Furthermore, in the next step S3, the control unit 6 sets the count for measuring one unit period Tb to 0. Note that, as the division condition for dividing the period Ta3 involved in the printing process in this flowchart, the division condition of the first aspect is adopted, in which it is determined that one unit period Tb has ended when images are formed on Pr sheets of recording paper P. Therefore, in step S3, the control unit 6 sets the number of prints Pc, which is the number of prints on recording paper P, to 0. Note that, if the division condition for dividing the period Ta3 involved in the printing process is the second aspect, in step S3, the control unit 6 can set the number of passes Pc', which is the number of printings performed on the recording paper P in one movement of the liquid ejection head HU in the X-axis direction, to 0. Also, if the division condition for dividing the period Ta3 involved in the printing process is the third aspect, in step S3, the control unit 6 can set the count Pc'' for measuring a predetermined period to 0. Next, in step S4, the control unit 6 judges whether or not the formation of the image on the recording paper P is completed. For example, when all dots constituting the image indicated by the print data Img have been formed on the recording paper P, or when the user instructs the control unit 6 to stop the execution of the printing process, the control unit 6 judges the result of the judgment in step S4 to be positive, and ends the printing process.

[0071] If the determination result in step S4 is negative, that is, if the image formation has not yet ended, in step S6, the control unit 6 determines whether one unit period Tb has ended. In this flowchart, since the division condition for dividing the period Ta3 involved in the printing process is the first mode, it is determined whether Pr sheets of recording paper P, the number of printed sheets Pc of which corresponds to one unit period Tb, have been printed. In this embodiment, Pr is set to "1". In other words, one unit period Tb corresponds to a period for forming an image on one sheet of recording paper P. Note that, if the division condition for dividing the period Ta3 involved in the printing process is the second mode, the control unit 6 can determine in step S6 whether printing on the recording paper P associated with one movement of the liquid ejection head HU in the X-axis direction has been performed Pr' times corresponding to one unit period Tb. Also, if the division condition for dividing the period Ta3 involved in the printing process is the third mode, in step S6, the control unit 6 can determine whether the count number for measuring a predetermined period has reached the count number Pr'' corresponding to one unit period Tb.

[0072] If the result of the determination in step S6 is negative, that is, if one unit period Tb has not ended, in step S8, the control unit 6 executes printing on the recording paper P based on the print data Img. In this flowchart, since the division condition for dividing the period Ta3 involved in the printing process is the first mode, if the number of printed sheets Pc of the recording paper P does not reach the number of printed sheets Pr corresponding to one unit period Tb and the result of the determination in step S6 is negative, in step S8, the control unit 6 executes printing for one sheet of the recording paper P based on the print data Img. Note that, if the division condition for dividing the period Ta3 involved in the printing process is the second mode, if the number of movements of the liquid ejection head HU in the X-axis direction does not reach the number of movements Pr' corresponding to one unit period Tb and the result of the determination in step S6 is negative, in step S8, the control unit 6 can execute printing on the recording paper P by moving the liquid ejection head HU in the X-axis direction based on the print data Img. Furthermore, in the case where the division condition for dividing the period Ta3 required for the printing process is the third mode, if the count number for measuring the predetermined period does not reach the count number Pr'' corresponding to one unit period Tb and the judgment result in step S6 is judged to be negative, in step S8, the control unit 6 can execute printing on the recording paper P by a predetermined number of ejection processes based on the print data Img. Note that, although not shown in FIG. 12, in step S8, the liquid ejection head HU receives a print signal SI generated by the control unit 6 based on the print data Img for each recording period Tu, and each of the ejection units D[1] to D[M] of the liquid ejection head HU executes an operation of ejecting or not ejecting ink based on the received print signal SI as the ejection process. Next, in step S10, the control unit 6 executes a process for measuring one unit period Tb in response to the execution of printing on the recording paper P in step S8. In this flowchart, since the division condition for dividing the period Ta3 involved in the printing process is the first mode, the control unit 6 adds 1 to the number of printed sheets Pc of the recording paper P. If the division condition for dividing the period Ta3 involved in the printing process is the second mode, a number corresponding to the number of passes Pc', which is the number of printings performed on the recording paper P in one movement of the liquid ejection head HU in the X-axis direction, executed in step S8, can be added. If the division condition for dividing the period Ta3 involved in the printing process is the third mode, a count number corresponding to the printing executed in step S8 can be added to the count number Pc'' for measuring a predetermined period. After the process of step S10 ends, the inkjet printer 1 returns the process to step S4.

[0073] If the determination result in step S6 is positive, that is, if one unit period Tb has ended, the control unit 6 increments the count number Cn by 1 in step S16. Next, in step S18, the inkjet printer 1 measures the viscosity information μ[1] to [M] of the discharge sections D[1] to [M] and stores it in the storage unit 5. More specifically, the control unit 6 selects the discharge section D[m] from among the discharge sections D[1] to [M] as the discharge section DH to be determined, obtains the viscosity information μ[m] from the measurement circuit 9, and stores the viscosity information μ[m] in the storage unit 5. This process is performed for each of the discharge sections D[1] to D[M].

[0074] After the process of step S18 is completed, the control unit 6 determines in step S22 whether the viscosity information μ[1] to [M] satisfies the count number decrease condition. If the viscosity information μ[1] to [M] satisfies the count number decrease condition and the determination result of step S22 is positive, the process proceeds to step S24, where the control unit 6 decreases the count number Cn, and the process proceeds to step S32. In this embodiment, in step S24, the control unit 6 decreases the count number Cn by 3, which is the same number as the specified number Spn, and sets the count number Cn to "0". In the example of FIG. 11, at the end of the unit period Tb5, the control unit 6 determines that all of the viscosity information μ5[1] to μ5[M] are equal to or less than the threshold value μth and the determination result of step S22 is positive. On the other hand, at the end of each of the unit periods Tb1, Tb2, Tb3, Tb4, Tb6, and Tb7, the control unit 6 determines that the judgment result of step S22 is negative because at least the viscosity information μ[1] of the discharge unit D[1] is greater than the threshold μth. If any of the viscosity information μ[1] to μ[M] exceeds the threshold μth in step S22 and the judgment result is negative, the control unit 6 advances the process to step S32.

[0075] In step S32, the control unit 6 determines whether the count number Cn has reached the specified number Spn. If the count number Cn has reached the specified number Spn and the determination result in step S32 is positive, the inkjet printer 1 executes a flushing process on the ejection sections D[1]-[M] in step S40. After completing step S40, the control unit 6 returns the process to step S2 and resets the count number Cn.

[0076] On the other hand, if the count number Cn does not reach the specified number Spn in step S32 and the determination result is negative, the inkjet printer 1 proceeds to step S34. In the process of step S34, the control unit 6 determines whether or not there is a value equal to or greater than the flushing necessary threshold in the viscosity information μ[1]-[M]. The flushing necessary threshold is a viscosity at which a flushing process is necessary, specifically, a viscosity at which ink ejection defects may occur during the next unit period Tb. The flushing necessary threshold is determined in advance by the manufacturer or user of the inkjet printer 1. For example, the manufacturer of the inkjet printer 1 determines the viscosity at which ink ejection defects may occur depending on the ink ejection status of the ejection section D during the next unit period Tb as the flushing necessary threshold. In other words, if the viscosity information μ is equal to or less than the flushing necessary threshold, stable ejection of ink from the ejection section D is guaranteed at least during the next unit period Tb, regardless of the ink ejection status of the ejection section D. The flushing necessary threshold value is an example of "viscosity at which maintenance processing is necessary."

[0077] If the viscosity information μ[1]-[M] contains a value equal to or greater than the flushing necessary threshold and the determination result in step S34 is positive, the inkjet printer 1 executes a flushing process on the discharge sections D[1]-[M] in step S40. After completing step S40, the control section 6 returns the process to step S2 and resets the count number Cn. On the other hand, if the viscosity information μ[1]-[M] does not contain a value equal to or greater than the flushing necessary threshold and the determination result in step S34 is negative, the inkjet printer 1 returns the process to step S3 and resets the count number Cn to measure one unit period Tb while keeping it counted.

[0078] 1.7. Summary of the First Embodiment As described above, the inkjet printer 1 includes a liquid ejection head HU including a nozzle N that ejects ink, a cavity 320 that communicates with the nozzle N, and a piezoelectric element PZ that applies pressure fluctuations to the ink in the cavity 320, and executes a printing process that forms an image indicated by print data Img on recording paper P. The printing process includes an ejection process that drives the piezoelectric element PZ in accordance with the print data Img to eject ink from the liquid ejection head HU and land it on the recording paper P, and a flushing process that drives the piezoelectric element PZ to discharge the ink in the liquid ejection head HU. In the printing process, the inkjet printer 1 executes a maintenance method that adds the number of completed unit periods Tb out of a plurality of unit periods Tb obtained by dividing a period required for the printing process according to a division condition to a count number Cn, executes a maintenance process for the ejection unit D when the count number Cn reaches a specified number Spn, acquires viscosity information μ related to the viscosity of the ink in the liquid ejection head HU before the count number Cn reaches the specified number Spn, and decreases the count number Cn when the viscosity information μ satisfies a count number decrease condition. The ink discharged by the flushing process is ink that does not form dots that constitute an image, and excessive discharge results in a waste of ink. For example, in a mode in which the flushing process is performed periodically at regular intervals, even if an image is printed on the recording paper P at a high duty, in which the ratio of the discharge process in which ink is discharged from the discharge section D is high among the multiple discharge processes included in the unit period Tb, and the thickening of the ink in the liquid discharge head HU is eliminated, the flushing process is forcibly performed at regular timing, resulting in a waste of ink. Moreover, unnecessary flushing processes not only waste ink, but also lead to a decrease in the number of printed sheets per unit period, i.e., a decrease in throughput. On the other hand, in this embodiment, the count number Cn, which can be said to be an estimate of the thickened state of the ejection section D, is incremented according to the completed unit period Tb, while being decremented when a count number decrement condition is met, to adjust the timing of executing the flushing process. Therefore, compared to a mode in which the flushing process is periodically executed at regular intervals, the inkjet printer 1 in this embodiment can reduce the number of times the flushing process is executed while maintaining a state in which no ink ejection defects occur, that is, good print quality. By reducing the number of times the flushing process is executed, ink waste can be reduced and throughput can be improved.

[0079] Moreover, the viscosity information μ is a parameter corresponding to the viscosity of the ink in each of the M discharge sections D. For any m from 1 to M, the measurement circuit 9 measures the viscosity information μ[1]-[M] corresponding to each of the discharge sections D[1]-[M] each time one of the unit periods Tb included in the plurality of unit periods Tb ends. When the measured viscosity information μ[1]-[M] satisfies a count number reduction condition, the control section 6 reduces the count number Cn. When the viscosity information μ[1]-[M] satisfies the count number reduction condition, it indicates that the thickening of the ink in the ejection sections D[1]-[M] has been resolved. Therefore, by decreasing the count number Cn when the viscosity information μ[1]-[M] satisfies the count number reduction condition, the count number Cn can accurately indicate the thickened state of the ink in the ejection sections D[1]-[M]. By having the count number Cn accurately indicate the thickened state of the ink, it is possible to prevent the flushing process from being executed even if the thickening of the ink in the ejection section D has not progressed to a level that requires the flushing process. In addition, since the discharge sections D[1] to D[M] are arranged in one plane of the liquid discharge head HU, the degree of viscosity may differ between the discharge sections D located at the ends of the array group and the discharge sections D located in the center of the array group. In addition, the degree of viscosity may differ in a plurality of discharge sections D due to manufacturing variations in the flow paths. In particular, in the discharge process, discharge is performed from the discharge sections D[1] to D[M] according to the print data Img, so the discharge status of the nozzles N in each discharge section D is different, and the flow state of the ink in each discharge section D is different. In addition, the influence of the wind generated by the relative movement between the liquid discharge head HU and the recording paper P in the printing process and the influence of the environmental condition around the liquid discharge head HU differ depending on the position of the discharge section D, so the degree of viscosity of the discharge sections D[1] to D[M] after the printing process is executed varies. In the first embodiment, it is determined whether the viscosity information μ[1] to [M] measured in each of the M ejection sections D satisfies the count number reduction condition, so that the thickening of the ink in each of the multiple ejection sections D can be appropriately eliminated.

[0080] The liquid ejection head HU has M ejection parts D, each having a nozzle N, a cavity 320, and a piezoelectric element PZ. When the viscosity information μ of all of the M ejection parts D is equal to or lower than the viscosity at which maintenance processing is not required, the control unit 6 resets the count number Cn, i.e., sets it to 0. The inkjet printer 1 manages the timing of the flushing process using a common count number Cn for the M ejection sections D, and resets the viscosity information μ of all of the M ejection sections D when it is equal to or lower than a viscosity at which the flushing process is unnecessary, which corresponds to the viscosity state immediately after the flushing process. This allows the inkjet printer 1 to reduce the number of times the flushing process is performed while maintaining a state in which no ink ejection problems occur, through simple processing.

[0081] Furthermore, if the viscosity information μ of each of the M discharge sections D is equal to or greater than the flushing necessary threshold, the inkjet printer 1 executes the flushing process for the discharge section D. The inkjet printer 1 can prevent ink ejection defects from occurring by executing a flushing process when even one of the M ejection sections D has viscosity information μ that is equal to or greater than the flushing necessary threshold. However, the flushing process is not limited to be performed on all M ejection sections D. For example, if there is viscosity information μ that is equal to or greater than the flushing necessary threshold, the inkjet printer 1 may perform the flushing process on only the ejection sections D that correspond to the viscosity information μ that is equal to or greater than the flushing necessary threshold. In this case, however, the count number Cn is not reset.

[0082] 2. Second embodiment In the first embodiment, the viscosity information μ relating to the viscosity of the ink was a parameter indicating the characteristics of the residual vibration indicated by the residual vibration signal NES, but the viscosity information μ is not limited to this. The viscosity information μ in the second embodiment differs from the first embodiment in that it is the ejection amount, which is the amount of ink ejected from the ejection section D[m] within one unit period Tb. In addition, the count number reduction condition in the first embodiment is that the viscosity information μ is equal to or less than the threshold μth, but the count number reduction condition is not limited to this. The count number reduction condition in the second embodiment is different from the first embodiment in that the discharge amount of the discharge section D in one unit period Tb is equal to or more than a threshold. Furthermore, while in the first embodiment the count number Cn was counted as a common count number Cn for the discharge sections D[1] to [M], in the second embodiment the count number Cn is counted as count numbers Cn[1] to [M] for each discharge section D[1] to [M], which differs from the first embodiment. The second embodiment will be described below.

[0083] Figure 14 is a functional block diagram showing an example of the configuration of an inkjet printer 1a according to the second embodiment. The inkjet printer 1a differs from the inkjet printer 1 in that it has a control unit 6a instead of the control unit 6, a liquid ejection head HUa instead of the liquid ejection head HU, and does not have a measurement circuit 9. Note that while Figure 14 shows a configuration in which the inkjet printer 1a does not have the measurement circuit 9 and detection circuit 20, it can also be configured to have a measurement circuit 9 and detection circuit 20 in order to detect ejection abnormalities in the ejection section D.

[0084] 2.1. Execution Timing of Flushing Process in the Second Embodiment Next, the execution timing of the flushing process in the second embodiment will be described with reference to FIG.

[0085] 15 is an explanatory diagram illustrating a series of operations of the inkjet printer 1a. In the second embodiment, the print processing wait in period Ta1, the maintenance processing before the print processing in period Ta2, the maintenance processing after the print processing in period Ta4, and the print processing wait in period Ta5 are the same as in the first embodiment, so descriptions thereof will be omitted.

[0086] During the printing process in period Ta3, the inkjet printer 1a also performs a flushing process each time a period that varies depending on the ink viscosity ends, in order to prevent ejection problems due to thickening of the ink and deterioration of image quality due to thickening of the ink, in the second embodiment as well. The inkjet printer 1a in the second embodiment counts the number of completed unit periods Tb out of a plurality of unit periods Tb obtained by dividing the period Ta3 involved in the printing process according to the division condition, for each ejection section D, in other words, manages count numbers Cn[1]-[M] corresponding to each of the ejection sections D[1]-[M].

[0087] For any m between 1 and M, when any of the count numbers Cn[1] to [M] reaches the specified number Spn, the inkjet printer 1a executes a flushing process on the discharge sections D[1] to [M]. The inkjet printer 1a increments each of the count numbers Cn[1] to [M] each time a unit period Tb ends. The viscosity information μ in the second embodiment is the ejection amount, which is the amount of ink ejected from the ejection section D[m] in one unit period Tb, as described above. Specifically, the control section 6a specifies the total amount of ink ejected from the ejection sections D[1]-[M] in one unit period Tb as the period ejection amount Am[1]-[M], respectively. For example, the total amount of ink ejected from the ejection section D[m] in one unit period Tb is specified as the period ejection amount Am[m]. Furthermore, when the period ejection amount Am[m], which is the viscosity information μ[m] of the ejection section D[m] in one unit period Tb, satisfies the count number reduction condition, the control section 6a reduces the count number Cn[m] corresponding to the ejection section D[m]. In the following description, the ejection amount, which is the total amount of ink ejected from the ejection section D[m] in one unit period Tb, is referred to as the "period ejection amount Am[m]". The period ejection amount Am[m] is, for example, the weight of ink ejected from the ejection section D[m] within one unit period Tb. The periodic discharge amount Am[m] is an example of "information on the discharge state for each period of the discharge section."

[0088] The control unit 6a specifies the period discharge amount Am[m] for each discharge unit D[m], for example, based on the individual designation signal Sd[m] of each of the multiple discharge processes included in one unit period Tb. The period discharge amount Am[m] can be specified in the following two ways. In the first and second ways, the storage unit 5 stores a discharge amount corresponding to one large dot, a discharge amount corresponding to one medium dot, and a discharge amount corresponding to one small dot. In the first way, the control unit 6a initializes the period discharge amount Am[m] to 0 for each discharge unit D[m] when one unit period Tb starts, and sequentially adds discharge amounts corresponding to the individual designation signal Sd[m] of each of the multiple discharge processes to the period discharge amount Am[m] until one unit period Tb ends. Specifically, when the individual designation signal Sd[m] is a value that designates the formation of a large dot, the control unit 6a adds the discharge amount corresponding to one large dot stored in the storage unit 5 to the period discharge amount Am[m]. Furthermore, when the individual designation signal Sd[m] is a value that specifies the formation of a medium dot, the control unit 6a adds the ejection amount equivalent to one medium dot stored in the memory unit 5 to the period ejection amount Am[m]. Furthermore, when the individual designation signal Sd[m] is a value that specifies the formation of a small dot, the control unit 6a adds the ejection amount equivalent to one small dot stored in the memory unit 5 to the period ejection amount Am[m]. In the second mode, the control unit 6a counts the number of times each discharge unit D[m] discharges in a plurality of discharge processes included in one unit period Tb, and specifies the value obtained by multiplying the counted number of times discharged by the discharge amount discharged in one time as the period discharge amount Am[m]. However, since the amounts of ink discharged in large dots, medium dots, and small dots are different, for example, the control unit 6a counts the number of times each large dot, medium dot, and small dot discharged in a plurality of discharge processes executed in one unit period Tb for each discharge unit D[m]. When one unit period Tb ends, the control unit 6a specifies the total value of the number of times a large dot is discharged multiplied by the discharge amount corresponding to a large dot, the number of times a medium dot is discharged multiplied by the discharge amount corresponding to a medium dot, and the number of times a small dot is discharged multiplied by the discharge amount corresponding to a small dot as the period discharge amount Am[m]. In the following description, the specific aspect of the periodic discharge amount Am [m] will be described as a first aspect from the viewpoint of ease of explanation.

[0089] The count number reduction condition in the second embodiment is that the periodic discharge amount Am[m] is equal to or greater than a predetermined amount Ath. In the explanation of the second embodiment, when the term "count number reduction condition" is simply stated, it means the count number reduction condition in the second embodiment. The predetermined amount Ath and the value by which the count number Cn[m] is reduced when the count number reduction condition is satisfied are determined in advance by the manufacturer or user of the inkjet printer 1a. The value by which the count number Cn[m] is reduced when the predetermined amount Ath and the count number reduction condition are satisfied may be any value. However, the value by which the count number Cn[m] is reduced when the count number reduction condition is satisfied is set to a value corresponding to the predetermined amount Ath. For example, the manufacturer of the inkjet printer 1 determines as a predetermined amount Ath the ejection amount from the ejection section D that can reduce the viscosity of the ink from the viscosity at which ink ejection defects occur to a viscosity at which ink ejection defects do not occur, and can guarantee stable ejection from the ejection section D during a period equivalent to one unit period Tb regardless of the ink ejection status of the ejection section D in that period, and determines the value by which the count number Cn[m] is reduced when the count number reduction condition is satisfied to be 1.

[0090] Furthermore, when the period discharge amount Am[m] is equal to or greater than the predetermined amount Ath, the control unit 6a decreases the count number Cn[m] by a value corresponding to the period discharge amount Am[m]. Specifically, when the period discharge amount Am[m] is a first amount, the control unit 6a decreases the count number Cn[m] by the first value. Also, when the period discharge amount Am[m] is a second amount, the control unit 6a decreases the count number Cn[m] by the second value. The first amount and the second amount are equal to or greater than the predetermined amount Ath. The first amount is greater than the second amount, and the first value is greater than the second value. That is, when the period discharge amount Am[m] increases, the control unit 6a increases the decrease in the count number Cn[m] accordingly.

[0091] 15 illustrates a printing process in which the specified number Spn for the discharge section D[1] is 3. In addition, FIG. 15 illustrates the period discharge amount Am[1] and the count number Cn[1] corresponding to the discharge amount from the discharge section [1] in each unit period Tb, which are unit period Tb1, unit period Tb2, unit period Tb3, unit period Tb4, unit period Tb5, unit period Tb6, and unit period Tb7. In addition, it is assumed that the period discharge amount Am5[1] for the unit period Tb5 is equal to or greater than the predetermined amount Ath, and satisfies the count number reduction condition. Furthermore, it is assumed that the discharge amounts Am1[1], Am2[1], Am3[1], Am4[1], Am6[1], and Am7[1] during the unit periods Tb1, Tb2, Tb3, Tb4, Tb6, and Tb7 are all less than the predetermined amount Ath, and the count number reduction condition is not satisfied. Furthermore, it is assumed that none of the count numbers Cn[1] to [M] after the end of the unit period Tb6 has reached the specified number Spn.

[0092] At the end of each of the unit periods Tb1, Tb2, and Tb3, the inkjet printer 1a increases the count number Cn[1] by 1 without decreasing it. At the end of the unit period Tb3, at least the count number Cn[1] among the count numbers Cn[1] to [M] reaches the specified number Spn of 3, so the inkjet printer 1a executes a flushing process for the discharge sections D[1] to [M]. Here, it is also possible to configure the inkjet printer 1a to execute a flushing process only for the corresponding discharge section D[m] when the count number Cn[m] for each discharge section D[m] reaches the specified number Spn. However, in that case, the timing of the flushing process for the discharge sections D[1] to [M] is shifted, so the frequency of interrupting the printing process to execute a flushing process for any of the discharge sections D[m] within the period Ta3 required for the printing process increases, and the throughput decreases. Therefore, it is preferable to perform flushing processing for all of the ejection sections D[1]-[M] when any of the count numbers Cn[1]-[M] reaches the specified number Spn. When the flushing processing is performed, the count numbers Cn[1]-[M] are reset. Next, the inkjet printer 1a increases the count number Cn[1] by 1 at the end of each of the unit periods Tb4 and Tb5 without decreasing the count number Cn[1]. At the end of the unit period Tb5, the period discharge amount Am5[1] satisfies the count number decrease condition, so the inkjet printer 1a increases the count number Cn[1] by 1 while decreasing the count number Cn[1] by 1. Next, the inkjet printer 1a increases the count number Cn[1] by 1 at the end of each of the unit periods Tb6 and Tb7 without decreasing the count number Cn[1]. As described above, in this example, none of the count numbers Cn[1]-[M] after the unit period Tb5 ends has reached the specified number Spn. Furthermore, at the end of the unit period Tb7, the inkjet printer 1a increases the count number Cn[1] by 1 without decreasing it.As a result, at the end of the unit period Tb7, at least the count number Cn[1] has reached the specified number Spn, which is 3, so the inkjet printer 1a executes the flushing process on the ejection sections D[1] to [M].

[0093] 2.2. Operation during printing process in the second embodiment The operation of the inkjet printer 1a during the printing process will be described in more detail with reference to Figures 16 and 17. Figures 16 and 17 are flow charts showing the operation of the inkjet printer 1a during the printing process. In step S101, the control unit 6a receives print data Img from the host computer. Next, in step S102, the control unit 6a sets each of the count numbers Cn[1] to [M] to 0. Furthermore, in the next step S103, the control unit 6a sets the count for measuring one unit period Tb to 0. Note that in this flowchart, as in the first embodiment, the first aspect is adopted as the division condition for dividing the period Ta3 involved in the printing process, and therefore in step S103, the control unit 6a sets the number of prints Pc, which is the number of printed sheets of recording paper P, to 0. Note that in the case where the second or third aspect is adopted as the division condition for dividing the period Ta3 involved in the printing process, the explanation is the same as in the first embodiment, and therefore will be omitted in this embodiment. Next, in step S104, the control unit 6a initializes the periodic discharge amounts Am[1] to Am[M], that is, sets them to 0. Then, in step S106, the control unit 6a determines whether or not the formation of an image on the recording paper P has been completed.

[0094] If the determination result in step S106 is negative, that is, if the image formation has not yet ended, in step S108, the control unit 6a determines whether one unit period Tb has ended. For example, it determines whether Pr sheets of recording paper P, the number of prints Pc of which corresponds to one unit period Tb, have been printed. In this embodiment, Pr is set to "1".

[0095] If the number of printed sheets Pc of the recording paper P has not reached the number of printed sheets Pr corresponding to one unit period Tb and the judgment result of step S108 is negative, that is, if one unit period Tb has not ended, the control unit 6a performs printing of one sheet of recording paper P based on the print data Img in step S110, and specifies the period discharge amount Am[1]-[M] corresponding to the total amount of ink discharged from each nozzle N of the discharge unit D[1]-[M] when printing the one sheet of recording paper P. For example, the discharge amount according to each individual designation signal Sd[m] of the multiple discharge processes generated based on the print data Img corresponding to one sheet of recording paper P is added to the period discharge amount Am[m]. As a result, the period discharge amount Am[1]-[M] corresponding to each of the discharge units D[1]-[M] is specified.

[0096] Next, in step S112, the control unit 6a executes a process for measuring one unit period Tb in response to the execution of printing on the recording paper P in step S110. In this flowchart, the division condition for dividing the period Ta3 required for the printing process is the first mode, so the control unit 6a adds 1 to the number of printed sheets Pc of the recording paper P. Although not shown in FIG. 16, in step S110, the liquid ejection head HUa receives a print signal SI generated by the control unit 6b based on the print data Img for each recording period Tu, and each of the ejection units D[1] to D[M] of the liquid ejection head HUa executes an operation of ejecting or not ejecting ink based on the received print signal SI as the ejection process. After the process of step S112 ends, the inkjet printer 1a returns the process to step S106.

[0097] If the number of printed sheets Pc of the recording paper P has reached the number of printed sheets Pr corresponding to the unit period Tb and the judgment result of step S108 is positive, i.e., if one unit period Tb has ended, the control unit 6a assigns 1 to the variable m in step S132, and in step S134, adds 1 to the count number Cn[m] for the ejection section D[m].

[0098] Next, in step S136, the control unit 6a judges whether the period discharge amount Am[m] corresponding to the viscosity information μ[m] of the discharge unit D[m] satisfies the count number reduction condition. Specifically, the control unit 6a judges whether the period discharge amount Am[m] is equal to or greater than a predetermined amount Ath. If the period discharge amount Am[m] is equal to or greater than the predetermined amount Ath and the judgment result in step S136 is positive, that is, if the count number reduction condition is satisfied, the control unit 6a decreases the count number Cn[m] according to the period discharge amount Am[m] in step S138 and proceeds to step S139. On the other hand, if the period discharge amount Am[m] is less than the predetermined amount Ath and the judgment result in step S136 is negative, that is, if the count number reduction condition is not satisfied, the control unit 6a proceeds to step S139 without executing the process in step S138.

[0099] In step S139, the control unit 6a judges whether or not the variable m coincides with M, which is the number of discharge units D. If the judgment result in step S139 is negative, that is, if the variable m has not reached M, the control unit 6a adds 1 to the variable m in step S150 and returns the process to step S134. On the other hand, if the judgment result in step S139 is positive, that is, if the variable m has reached M, the control unit 6a advances the process to step S140.

[0100] In step S140, the control unit 6a judges whether any of the count numbers Cn[1] to [M] has reached the specified number Spn. If the judgment result in step S140 is negative, that is, if any of the count numbers Cn[1] to [M] has not reached the specified number Spn, the control unit 6a returns the process to step S103.

[0101] On the other hand, if the determination result in step S140 is positive, that is, if any of the count numbers Cn[1] to [M] reaches the specified number Spn, the control unit 6a executes a flushing process on the discharge sections D[1] to [M] in step S142. After completing the process of step S142, the control unit 6a returns the process to step S102.

[0102] In this way, the periodic emission amount Am[1] to [M] is reset each time one unit period Tb ends. In other words, the periodic emission amount Am[m] can be said to be information regarding the emission state of the emission section D[m] for each unit period Tb.

[0103] If the determination result in step S106 is positive, the inkjet printer 1 ends the series of processes shown in FIGS.

[0104] 2.3. Summary of the second embodiment As described above, the inkjet printer 1a decreases the count number Cn[m] when the periodic discharge amount Am[m] of the discharge section D[m] satisfies the count number decrease condition for any m from 1 to M. Furthermore, when any of the count numbers Cn[1] to [M] reaches the specified number Spn, the inkjet printer 1a executes a flushing process. When ink is ejected from the nozzle N[m], the thickened ink is discharged and the viscosity of the ink in the ejection section D[m] decreases. Therefore, when the period ejection amount Am[m] satisfies the count number reduction condition, the count number Cn[m] is reduced, so that the count number Cn[m] can accurately indicate the thickened state of the ink in the ejection section D[m].

[0105] In addition, the count reduction condition in this embodiment is that, for any m from 1 to M, the period ejection amount Am[m], i.e., the amount of ink ejected from the ejection section D[m] in one unit period Tb, is greater than or equal to a predetermined amount Ath. By appropriately setting the predetermined amount Ath, the count number Cn[m] can accurately indicate the viscosity state of the ink in the ejection section D[m].

[0106] In addition, for any m from 1 to M, when the period discharge amount Am[m] is equal to or greater than the predetermined amount Ath, the control unit 6a decreases the count number Cn[m] for the discharge unit D[m] by a value according to the period discharge amount Am[m]. When the ink in the discharge section D[m] has thickened, the degree to which the ink viscosity is reduced increases as the amount of ink discharged from the discharge section D[m] within the unit period Tb increases. Therefore, by decreasing the count number Cn[m] by a value corresponding to the periodic discharge amount Am[m], the count number Cn[m] can accurately indicate the ink viscosity state.

[0107] 3. Third embodiment In the first embodiment, the control unit 6 adds 1 to the count number Cn every time the unit period Tb ends, and executes the flushing process when the count number Cn reaches the specified number Spn, but this is not limited to this. In the third embodiment, the control unit 6 measures the viscosity information μ[1]-[M] every time the unit period Tb ends, as in the first embodiment, but differs from the first embodiment in that it does not count the count number Cn, and executes the flushing process when any of the viscosity information μ[1]-[M] is equal to or greater than a predetermined threshold value μbth. The third embodiment will be described below.

[0108] The configuration of the inkjet printer 1 according to the third embodiment is the same as that of the inkjet printer 1 according to the first embodiment, and so a description thereof will be omitted. For ease of description, the inkjet printer 1 according to the third embodiment will be referred to as inkjet printer 1b, and the control unit 6 according to the third embodiment will be referred to as control unit 6b.

[0109] 3.1. Execution Timing of Flushing Process in Third Embodiment 18 is an explanatory diagram illustrating a series of operations of the inkjet printer 1b. In the third embodiment, the print processing wait in period Ta1, the maintenance processing before the print processing in period Ta2, the maintenance processing after the print processing in period Ta4, and the print processing wait in period Ta5 are the same as in the first embodiment, so descriptions thereof will be omitted.

[0110] During the period Ta3, the inkjet printer 1b also performs a flushing process each time a variable period corresponding to the ink viscosity ends, in order to prevent ejection defects due to increased ink viscosity and deterioration of image quality due to increased ink viscosity, in the third embodiment. In the third embodiment, the inkjet printer 1b measures the viscosity information μ[1]-[M] for each ejection section D[1]-[M] for each unit period Tb obtained by dividing the period Ta3 required for the printing process according to the division condition, and performs a flushing process if any of the viscosity information μ[1]-[M] is equal to or greater than a predetermined threshold value μbth. The predetermined threshold value μbth is determined in advance by the manufacturer or user of the inkjet printer 1b. For example, the manufacturer of the inkjet printer 1 determines the viscosity at which ejection defects may occur in the ejection section D before the next unit period Tb has elapsed as the predetermined threshold value μbth.

[0111] 18, the viscosity information μ[1] at the end of each of the unit periods Tb1, Tb2, Tb3, Tb4, Tb5, Tb6, and Tb7 is illustrated. Furthermore, it is assumed that the viscosity information μ3[1] and μ7[1] measured at the end of each of the unit periods Tb3 and Tb7 are equal to or greater than a predetermined threshold μbth. Furthermore, it is assumed that the viscosity information μ1[1]-[M], μ2[1]-[M], μ4[1]-[M], μ5[1]-[M], and μ6[1]-[M] measured at the end of each of the unit periods Tb1, Tb2, Tb4, Tb5, and Tb6 are all less than the predetermined threshold μbth.

[0112] The inkjet printer 1a measures the viscosity information μ[1]-[M] of the discharge sections D[1]-[M] at the end of each of the unit periods Tb1, Tb2, and Tb3. At least the viscosity information μ3[1] measured at the end of the unit period Tb3 is equal to or greater than the predetermined threshold μbth, so the inkjet printer 1b executes a flushing process on the discharge sections D[1]-[M]. After executing the flushing process, the inkjet printer 1a measures the viscosity information μ[1]-[M] of the discharge sections D[1]-[M] at the end of each of the unit periods Tb4, Tb5, Tb6, and Tb7. The viscosity information μ[1]-[M] measured at the end of each of the unit periods Tb4, Tb5, and Tb6 is less than the predetermined threshold μbth, so the inkjet printer 1b does not execute a flushing process on the discharge sections D[1]-[M]. Because at least the viscosity information μ7[1] measured at the end of the unit period Tb7 is equal to or greater than the predetermined threshold value μbth, the inkjet printer 1b executes the flushing process on the ejection sections D[1]-[M].

[0113] 3.2. Operation during printing process in the third embodiment The operation of the inkjet printer 1b during the printing process will be described in more detail with reference to Figure 19. Figure 19 is a flow chart showing the operation of the inkjet printer 1b during the printing process. In step S162, the control unit 6b receives the print data Img from the host computer. Next, in step S163, the control unit 6b sets the count to 0 to measure one unit period Tb. In this flowchart, as in the first embodiment, the first aspect is adopted as the division condition for dividing the period Ta3 involved in the printing process, so in step S163, the control unit 6b sets the number of printed sheets Pc, which is the count number of printed sheets of recording paper P, to 0. In addition, in the case where the second or third aspect is adopted as the division condition for dividing the period Ta3 involved in the printing process, the explanation is the same as in the first embodiment, so it is omitted in this embodiment. Next, in step S164, the control section 6b determines whether or not the formation of an image on the recording paper P has been completed.

[0114] If the determination result in step S164 is negative, i.e., if image formation has not yet ended, in step S166, the control unit 6 determines whether one unit period Tb has ended. For example, it determines whether Pr sheets of recording paper P, the number of prints Pc of which corresponds to one unit period Tb, have been printed. In this embodiment, it is assumed that Pr is set to "1".

[0115] If the number of printed sheets Pc of the recording paper P has not reached the number of printed sheets Pr corresponding to one unit period Tb and the judgment result of step S166 is negative, that is, if one unit period Tb has not ended, in step S168, the control unit 6b executes printing of one sheet of the recording paper P based on the print data Img. Next, in step S170, the control unit 6b executes a process for measuring one unit period Tb in response to the execution of printing on the recording paper P in step S168. In this flowchart, since the division condition for dividing the period Ta3 related to the printing process is the first mode, the control unit 6b adds 1 to the number of printed sheets Pc of the recording paper P. Although not shown in FIG. 19, the liquid ejection head HU receives a print signal SI generated by the control unit 6b based on the print data Img for each recording period Tu, and each of the ejection units D[1] to D[M] of the liquid ejection head HU executes an operation of ejecting or not ejecting ink based on the received print signal SI as an ejection process. After completing step S170, the inkjet printer 1b returns to step S164.

[0116] If the number of prints Pc of the recording paper P has reached the number of prints Pr corresponding to the unit period Tb and the judgment result of step S166 is positive, i.e., if one unit period Tb has ended, the control unit 6b measures the viscosity information μ[1]~[M] of the ejection sections D[1]~[M] in step S174 and stores the measured viscosity information μ[1]~[M] in the memory unit 5.

[0117] After completing step S174, the control unit 6b determines in step S178 whether any of the viscosity information μ[1]-[M] is equal to or greater than the predetermined threshold μbth. If any of the viscosity information μ[1]-[M] is equal to or greater than the predetermined threshold μbth and the determination result in step S178 is positive, the inkjet printer 1b executes a flushing process on the discharge sections D[1]-[M] in step S180, and returns the process to step S163.

[0118] On the other hand, if none of the viscosity information μ[1]-[M] is equal to or greater than the predetermined threshold μbth and the determination result in step S178 is negative, the inkjet printer 1b returns the process to step S163.

[0119] If the determination result in step S164 is positive, the inkjet printer 1b ends the series of processes shown in FIG.

[0120] 3.3. Summary of the third embodiment As described above, the inkjet printer 1b measures the viscosity information μ each time the unit period Tb ends, and executes the flushing process if the viscosity information μ is equal to or greater than a predetermined threshold value μbth. According to the third embodiment, the flushing process is performed each time a variable period corresponding to the viscosity state of the ink ends, so that the number of times the flushing process is performed can be reduced while maintaining a state in which no ink ejection problems occur, compared to a configuration in which the flushing process is performed periodically.

[0121] 4. Variations The above-mentioned embodiments can be modified in various ways. Specific modified embodiments are exemplified below. Two or more embodiments selected from the following examples can be combined as long as they are not mutually contradictory.

[0122] 4.1. First modified example In the first and third embodiments, the viscosity information μ relating to the viscosity of the ink is a parameter indicating the characteristics of the residual vibration indicated by the residual vibration signal NES, but is not limited to this. For example, the viscosity information μ may be any one of the number of ink ejections, the ink ejection amount, the ink flight speed, or the amount of deviation of the landing position of the test pattern.

[0123] When the viscosity information μ is the flight speed of the ink, the inkjet printer 1 measures the flight speeds [1]-[M] of the droplets discharged from the nozzles N[1]-[M] of the discharge sections D[1]-[M] after the unit period ends, and acquires the measured flight speeds [1]-[M] as viscosity information μ[1]-[M] related to the viscosity of the ink in the discharge sections D[1]-[M]. When the ink in the discharge section D thickens, the flight speed of the droplets discharged from the nozzles N decreases. Therefore, it can be said that the flight speed represents the viscosity of the ink in the discharge section D. In order to measure the flight speed of the droplets, the inkjet printer 1 has a measurement mechanism used to measure the flight speed, for example, at a position in the -Z direction from the liquid discharge head HU. This measurement mechanism has, for example, a light emitting section that emits some kind of light such as infrared light or ultraviolet light, and a light receiving section that receives the above-mentioned light when there is no obstacle. First, the measurement mechanism obtains the time when the droplet blocks the light beam emitted from the light-emitting unit and the light-receiving unit does not receive the light beam. Next, the inkjet printer 1 determines the period from the time when the piezoelectric element PZ is displaced so that ink is ejected from the ejection unit D to the time when the light-receiving unit does not receive the light beam as the flight period. The flight distance from the position of the nozzle N to the position where the droplet blocks the light beam emitted from the light-emitting unit is a predetermined distance. Then, the inkjet printer 1 calculates the flight speed by dividing the flight distance by the flight period.

[0124] When the viscosity information μ is the amount of deviation of the landing position of the test pattern, the inkjet printer 1 causes droplets discharged from the discharge units D[1]-[M] to land on the recording paper P while moving the liquid discharge head HU and the recording paper P relative to each other at a predetermined speed, measures the amount of deviation [1]-[M] of the landing position of the droplets on the recording paper P, and acquires the measured amount of deviation [1]-[M] as viscosity information μ[1]-[M] related to the viscosity of the ink in the discharge units D[1]-[M]. When the viscosity of the ink in the discharge units D increases, the flying speed of the droplets discharged from the nozzles N decreases. Since the liquid discharge head HU and the recording paper P move relative to each other at a predetermined speed, when the flying speed of the droplets discharged from the nozzles N decreases, it takes longer for the droplets to land on the recording paper P and the relative movement distance between the liquid discharge head HU and the recording paper P during that time increases, so the landing position of the droplets on the recording paper P is shifted from the position where the droplets should land. Therefore, it can be said that the amount of deviation represents the viscosity of the ink in the ejection section D. To measure the amount of deviation, the inkjet printer 1 has an imaging section that images the recording paper P. First, the inkjet printer 1 eliminates the increase in viscosity of the ink in any one of the M ejection sections D arranged in a direction intersecting the relative movement direction of the liquid ejection head HU and the recording paper P, and sets the ink in the any one of the M ejection sections D as a reference ejection section DS. Next, while moving the liquid ejection head HU and the recording paper P relatively, the inkjet printer 1 simultaneously ejects droplets from the reference ejection section DS and a measurement target ejection section DM for which the viscosity of the ink is to be measured, among the M ejection sections D, and causes the droplets to land on the recording paper P. The imaging section images the recording paper P including the droplets ejected from the reference ejection section DS and landed on the recording paper P, and the droplets ejected from the measurement target ejection section DM and landed on the recording paper P. The inkjet printer 1 acquires imaging information indicating the imaging result captured by the imaging section. Based on the imaging information, the inkjet printer 1 identifies a first position of a droplet ejected from the reference ejection section DS and landing on the recording paper P, and a second position of a droplet ejected from the measurement target ejection section DM and landing on the recording paper P, and identifies the distance between the first position and the second position in the direction of relative movement between the liquid ejection head HU and the recording paper P as the amount of deviation.

[0125] 4.2. Second variant In the second embodiment, for any m from 1 to M, the period discharge amount Am[m] was described as an example of "information on the discharge state of the discharge unit for each period", but the "information on the discharge state of the discharge unit for each period" is not limited to the period discharge amount Am[m]. The information on the discharge state of the discharge unit D[m] for each unit period Tb may be, for example, the number of times the discharge unit D[m] discharges ink in one unit period Tb. In the second modified example, the count number reduction condition, which is the second condition, is that the number of times the discharge unit D[m] discharges ink in one unit period Tb is a predetermined number or more. In addition, the control unit 6 may count the discharge of an amount of ink equivalent to one small dot as a number of discharges, the discharge of an amount of ink equivalent to one medium dot as a1 number of discharges, and the discharge of an amount of ink equivalent to one large dot as a2 number of discharges. a1 is greater than a, and a2 is greater than a1. For example, a is 1, a1 is 2, and a2 is 3.

[0126] 4.3.Third Modification In the second embodiment, the first modification, and the second modification, in other words in a configuration in which the residual vibration signal NES is not used as the viscosity information μ, a heating element that heats the ink in the cavity 320 may be used instead of the piezoelectric element PZ. In the third modification, the heating element is an example of a "driving element".

[0127] 4.4. Fourth Modification In the first embodiment and the first modified example based on the first embodiment, the threshold value μth is determined to be a viscosity that does not require flushing processing corresponding to the viscosity state immediately after the flushing processing, and when the count number reduction condition is satisfied, a value equal to or greater than the specified number Spn is reduced from the count number Cn, and the count number Cn is set to "0", but this is not limited thereto. For example, the threshold value μth can be determined to be another threshold value μth that is a value between the ink viscosity immediately after the flushing processing and the ink viscosity that requires flushing processing. In this case, the value by which the count number Cn is reduced when the count number reduction condition is satisfied is determined to be a value corresponding to the other threshold value μth. When the count number reduction condition is satisfied in which all of the measured viscosity information μ[1] to [M] are equal to or less than the other threshold value μth, the count number Cn may be reduced by a value corresponding to the other threshold value μth. For example, the highest viscosity value in the viscosity range in which there is no risk of ejection defects occurring in the ejection section D within one or more remaining unit periods Tb can be determined as the other threshold value μth, and if all of the viscosity information μ[1] to viscosity information μ[M] are below the other threshold value μth and the count number reduction condition is satisfied, the value of the count number Cn can be reduced to the value of the specified number Spn-1. According to the fourth modified example, by decreasing the count number Cn by a value according to the viscosity information μ, the count number Cn can accurately indicate the thickened state of the ink.

[0128] 4.5. Fifth Modification In the first embodiment, the first modified example based on the first embodiment, and the fourth modified example, the viscosity information μ[1]-[M] is measured every time one unit period Tb ends, but this is not limited thereto. For example, the control unit 6 may change the frequency of measuring the viscosity information μ[1]-[M] according to the count number Cn. For example, when the count number Cn is equal to or less than a first threshold, the control unit 6 may measure the viscosity information μ[1]-[M] every time n1 unit periods Tb ends, and when the count number Cn is greater than the first threshold, the control unit 6 may measure the viscosity information μ[1]-[M] every time n2 unit periods Tb ends. n1 is greater than n2. The first threshold is a value smaller than the specified number Spn. The first threshold is determined by the manufacturer or user of the inkjet printer 1. For example, when n1 is 2 and n2 is 1, the control unit 6 measures the viscosity information μ[1]~[M] every time two unit periods Tb end if the count number Cn is less than or equal to the first threshold, and measures the viscosity information μ[1]~[M] every time one unit period Tb ends if the count number Cn is greater than the first threshold, as in the first embodiment. According to the fifth modification, when the count number Cn is equal to or less than the first threshold value, the control unit 6 can measure the viscosity information μ[1]-[M] less frequently than in a mode in which the viscosity information μ[1]-[M] is measured every time less than n1 unit periods Tb are completed, thereby improving throughput. Furthermore, when the count number Cn is greater than the first threshold value, the control unit 6 can more easily detect a state in which the viscosity of the ink is increased and ejection defects may occur by measuring the viscosity information μ[m] more frequently than in a mode in which the viscosity information μ[1]-[M] is measured every time n1 unit periods Tb are completed, making it easier to detect such a state. This makes it easier to ensure good print quality without lengthening the period Ta3 required for the print process.

[0129] 4.6. Sixth Modification In the first embodiment, the first modified example based on the first embodiment, the fourth modified example, and the fifth modified example, the timing of the flushing process is determined by the common count number Cn for the discharge sections D[1] to [M], but this is not limited to this. For example, the count number Cn[m] may be managed individually for each discharge section D[1] to [M], the value of the completed unit period Tb may be added to the count number Cn[m], and when the viscosity information μ[m] is equal to or less than the threshold value μth, the count number Cn[m] may be subtracted. In this case, when any of the count numbers Cn[m] reaches the specified number Spn, the flushing process may be executed in all of the discharge sections D[1] to [M]. 4.7. Seventh Variation In the second embodiment, the second modification, the third modification based on the second embodiment or the second modification, and the sixth modification, the control unit 6 manages the count numbers Cn[1]-[M] for each discharge section D[1]-[M], and when the count number Cn[m] of any of the count numbers Cn[1]-[M] reaches the specified number Spn, the control unit 6 executes the flushing process for all of the discharge sections D[1]-[M], but is not limited thereto. For example, the flushing process can be executed only for the discharge section D[m] corresponding to the count number Cn[m] that reaches the specified number Spn. In this manner, the number of times the flushing process is executed by the liquid discharge head HU increases, but it is possible to discharge the appropriate amount of ink for each of the multiple discharge sections D according to the variation in the degree of viscosity increase of the discharge sections D[1]-D[M].

[0130] 4.8. Eighth Variation Of the above aspects, in the aspect using residual vibration like the first embodiment, the test waveform PS was determined so that the discharge unit D[m] was driven to such an extent that ink was not discharged, but the test waveform PS may be determined so that the discharge unit D[m] is driven to such an extent that ink is discharged. However, when the test waveform PS is determined so that the discharge unit D[m] is driven to such an extent that ink is discharged, the inkjet printer 1 executes the discharge state determination process at a position where the liquid discharge head HU does not overlap the recording paper P when viewed in the Z axis direction.

[0131] 4.9. Ninth Variation In each of the above-mentioned aspects, a serial type inkjet printer 1 in which the transport body 82 housing the liquid ejection head HU is moved back and forth in the X-axis direction has been exemplified, but the present invention is not limited to such aspects. The inkjet printer may be a line type inkjet printer in which multiple nozzles N are distributed across the entire width of the recording paper P. The division condition in the ninth modified example is any one of the first and third aspects described in the first embodiment.

[0132] 4.10. Tenth Variation The inkjet printers exemplified in the above-mentioned embodiments can be used in various devices such as facsimile machines and copy machines, in addition to devices dedicated to printing. However, the use of the liquid ejection device of the present invention is not limited to printing. For example, a liquid ejection device that ejects a solution of a coloring material is used as a manufacturing device for forming a color filter of a liquid crystal display device. Furthermore, a liquid ejection device that ejects a solution of a conductive material is used as a manufacturing device for forming wiring and electrodes of a wiring board.

[0133] 5. Notes From the above-described exemplary embodiments, the following configurations can be understood, for example.

[0134] A maintenance method for a liquid ejection device according to a first embodiment, which is a preferred aspect, is a maintenance method for a liquid ejection device having a liquid ejection head including a nozzle that ejects liquid, a pressure chamber communicating with the nozzle, and a drive element that applies pressure fluctuations to the liquid in the pressure chamber, and which executes a printing process to form an image indicated by print data on a medium, the printing process including an ejection process that drives the drive element in accordance with the print data to eject liquid from the liquid ejection head and cause it to land on the medium, and a maintenance process that drives the drive element to drain the liquid in the liquid ejection head, the method including: counting, within the printing process, a number of unit periods which is the number of completed unit periods out of a plurality of unit periods obtained by dividing a period required for the printing process by a first condition; executing the maintenance process when the number of unit periods reaches a specified number; obtaining viscosity information regarding the viscosity of the liquid in the liquid ejection head before the number of unit periods reaches the specified number; and reducing the number of unit periods when the viscosity information satisfies a second condition. In the first aspect, the timing of performing the maintenance process is adjusted according to the number of unit periods, which can be said to be an estimated value of the viscosity state of the ink in the liquid ejection head. Therefore, compared to an aspect in which the maintenance process is performed periodically, the liquid ejection device in the first aspect can reduce the number of times that the maintenance process is performed while maintaining a state in which no liquid ejection defects occur, i.e., good print quality. By reducing the number of times that the maintenance process is performed, it is possible to reduce waste of liquid and improve throughput.

[0135] In a second aspect, which is a specific example of the first aspect, the viscosity information is a parameter corresponding to the viscosity of the liquid in the liquid ejection head, and each time one of the plurality of unit periods ends, the parameter corresponding to the viscosity of the liquid in the liquid ejection head is measured, and if the measured parameter satisfies the second condition, the number of unit periods is reduced. When the viscosity information satisfies the second condition, it indicates that the thickening of the liquid in the liquid ejection head is being resolved. Therefore, by decreasing the number of unit periods when the second condition is satisfied, the number of unit periods can accurately indicate the thickened state of the liquid in the liquid ejection head. According to the second aspect, since the number of unit periods accurately indicates the thickened state of the liquid, it is possible to prevent the maintenance process from being performed even when the thickening of the liquid is not progressing.

[0136] In a third aspect, which is a specific example of the second aspect, the liquid ejection head has a plurality of ejection sections, each of which has the nozzle, the pressure chamber, and the driving element, the viscosity information is a parameter corresponding to the viscosity of the liquid in each of the plurality of ejection sections, the parameter corresponding to the viscosity of the liquid in each of the plurality of ejection sections is measured, and if the parameters of all of the plurality of ejection sections are below a viscosity at which the maintenance processing is unnecessary, the number of unit periods is set to 0. According to the third aspect, by setting the number of unit periods for all of the plurality of ejection sections to 0, it is possible to reduce the number of times that the maintenance process is performed while maintaining a state in which no liquid ejection defects occur.

[0137] In a fourth aspect, which is a specific example of the second or third aspect, the liquid ejection head has a plurality of ejection sections, each of which has the nozzle, the pressure chamber, and the driving element, and if any of the parameters of each of the plurality of ejection sections has a viscosity that is equal to or higher than the viscosity that requires the maintenance treatment, the maintenance treatment is performed. According to the fourth aspect, by carrying out the maintenance process when there is a parameter that is equal to or higher than the viscosity that requires the maintenance process, it is possible to prevent the occurrence of liquid ejection defects.

[0138] In the fifth aspect, which is a specific example of the first aspect, the liquid ejection head has a plurality of ejection sections, each of which has the nozzle, the pressure chamber, and the driving element, the viscosity information is information regarding the ejection state of the ejection section for each unit period, the number of unit periods is counted for each of the plurality of ejection sections, the viscosity information is obtained for each of the plurality of ejection sections, and in counting the number of unit periods corresponding to each of the plurality of ejection sections, if the corresponding viscosity information satisfies the second condition, the corresponding number of unit periods is reduced, and if at least one of the numbers of unit periods corresponding to the plurality of ejection sections reaches the specified number, the maintenance process is performed on the plurality of ejection sections. When liquid is ejected from the nozzle, the thickened liquid is discharged and the viscosity of the liquid in the ejection section decreases. Therefore, according to the fifth aspect, when the information on the ejection state of the ejection section satisfies the second condition, the number of unit periods is decreased, so that the number of unit periods can accurately indicate the thickened state of the liquid in the ejection section.

[0139] In a sixth aspect, which is a specific example of the fifth aspect, the information regarding the ejection state of the ejection section for each unit period is the total amount of liquid ejected from the ejection section within the unit period, and the second condition is that the total amount of liquid ejected from the ejection section within the unit period is greater than or equal to a predetermined amount. By appropriately setting the predetermined amount, according to the sixth aspect, the number of unit periods can accurately indicate the thickened state of the liquid in the ejection portion.

[0140] In a seventh aspect, which is a specific example of the sixth aspect, in counting the number of unit periods corresponding to each of the multiple ejection sections, if the total amount of liquid ejected from the corresponding ejection section within the unit period is a first amount that is greater than or equal to the predetermined amount, the corresponding number of unit periods is reduced by a first value, and if the total amount of liquid ejected from the corresponding ejection section within the unit period is a second amount that is greater than or equal to the predetermined amount, the corresponding number of unit periods is reduced by a second value, the first amount being greater than the second amount and the first value being greater than the second value. In a state where the viscosity of the liquid has progressed, the degree to which the viscosity of the liquid is resolved increases as the discharge amount of the discharge unit increases. Therefore, according to the seventh aspect, by reducing the number of unit periods by a value corresponding to the amount of liquid discharged from one discharge unit, the number of unit periods can accurately indicate the viscosity of the liquid. [Explanation of symbols]

[0141] 1, 1a, 1a, 1b... inkjet printer, 2... drive signal generating circuit, 4... maintenance unit, 5... memory unit, 6, 6a, 6b... control unit, 7... transport mechanism, 8... movement mechanism, 9... measurement circuit, 10... switching circuit, 11... connection state designation circuit, 14... liquid container, 20... detection circuit, 42... cap, 44... wiper, 81... endless belt, 82... transport body, 310... vibration plate, 320... cavity, 330... nozzle plate, 340... cavity plate port, 350... reservoir, 360... ink supply port, 370... ink intake port, Am... periodic discharge amount, Ath... predetermined amount, CH... change signal, CL... clock signal, Cn... count number, Com... drive signal, D... discharge unit, HD... recording head, HU, HUa... liquid discharge head, Img... print data, LAT... latch signal, LHa, LHb... internal wiring, LHd... power supply line, LHs... internal wiring, N... nozzle, NES... residual vibration signal, NTc... time length, P... recording Recording paper, PS...Test waveform, PX...Medium dot waveform, PY...Small dot waveform, PZ...Piezoelectric element, PlsC, PlsL, PlsT1, PlsT2...Pulse, SI...Print signal, SLa, SLb, SLs...Connection status designation signal, SWa, SWb, SWs...Switch, Sd...Individual designation signal, Spn...Regulated number, Stt...Judgment information, TSS1, TSS2, TSS3...Control period, Ta1, Ta2, Ta3, Ta4, Ta5...Period, Tb, Tb1, Tb2, Tb3, Tb4,Tb5,Tb6,Tb7...Unit period, Tsig...Period specification signal, Tth1,Tth2,Tth3...Threshold value, Tu...Unit period, Tu1,Tu2...Control period, V0...Reference potential, VBs...Constant potential, VHS, VHX, VHY ...highest potential, VLS, VLX, VLY...lowest potential, Vout...detection signal, Zd...lower electrode, Zm...piezoelectric material, Zu...upper electrode, dCom...waveform specification signal, μ, μ1, μ3, μ5, μ7…viscosity information, μbth, μth…threshold.

Claims

1. A nozzle for discharging liquid, a pressure chamber communicating with the nozzle, and a pressure chamber for applying pressure to the liquid in the pressure chamber. and a driving element for applying a change in the amount of the ink droplets to the ink droplets. Maintenance method for liquid ejection device which executes printing process for forming an image indicated by print data on a medium It is a law, The printing process drives the driving element in accordance with the print data to print the liquid ejection head. A discharge process for discharging liquid from the liquid ejection head and landing the liquid on the medium; and a discharge process for driving the driving element to discharge the liquid. A maintenance process for discharging the liquid from the liquid ejection head, In the printing process, a period required for the printing process is divided into a plurality of units according to a first condition. Count the number of unit periods, which is the number of unit periods that have ended among the first period, When the number of unit periods reaches a specified number, the maintenance process is executed; Before the number of the unit periods reaches the specified number, one of the unit periods of the plurality of unit periods ends. Each time, a parameter corresponding to the viscosity of the liquid in each of the plurality of ejection parts is -Measure the If the measured parameter satisfies a second condition, decreasing the number of unit periods; The parameters of all of the plurality of ejection parts are set to a viscosity that does not require the maintenance process. If the number of unit periods is equal to or smaller than the predetermined number, the number of unit periods is set to 0. Maintenance methods.

2. The liquid ejection head includes a plurality of nozzles, a plurality of pressure chambers, and a plurality of driving elements. A number of discharge portions are provided. Among the parameters of each of the plurality of ejection parts, the maintenance process If any parameter is greater than or equal to the required viscosity, the maintenance process is performed. The maintenance method according to claim 1 .

3. A nozzle for discharging liquid, a pressure chamber communicating with the nozzle, and a pressure chamber for applying pressure to the liquid in the pressure chamber. and a driving element for applying a change in the amount of the ink droplets to the ink droplets. Maintenance method for liquid ejection device which executes printing process for forming an image indicated by print data on a medium It is a law, The printing process drives the driving element in accordance with the print data to print the liquid ejection head. A discharge process for discharging liquid from the liquid ejection head and landing the liquid on the medium; and a discharge process for driving the driving element to discharge the liquid. A maintenance process for discharging the liquid from the liquid ejection head, In the printing process, a period required for the printing process is divided into a plurality of units according to a first condition. The number of unit periods, which is the number of unit periods that have ended among the unit periods, is counted for each of the plurality of ejection sections. death, At least one of the unit periods corresponding to the plurality of discharge units reaches a specified number. If so, the maintenance process is performed on the plurality of ejection units; Before the number of the unit periods reaches the specified number, Obtain information about the discharge status of In counting the number of unit periods corresponding to each of the plurality of ejection sections, If the information about satisfies a second condition, the corresponding number of unit periods is decreased. Maintenance methods.

4. The information on the discharge state of the discharge unit for each unit period is is the total amount of liquid dispensed from the nozzle, The second condition is that the total amount of liquid discharged from the discharge portion within the unit period is equal to or greater than a predetermined amount. It is to be on top, The maintenance method according to claim 3.

5. In counting the number of unit periods corresponding to each of the plurality of ejection sections, The total amount of liquid discharged from the corresponding discharge portion within the unit period is equal to or greater than the predetermined amount. if the first amount is a first amount, then decreasing the corresponding number of unit periods by a first value; The total amount of liquid discharged from the corresponding discharge portion within the unit period is equal to or greater than the predetermined amount. if the second amount is a second amount, then decreasing the corresponding number of unit periods by a second value; the first amount is greater than the second amount, and the first amount is greater than the second amount; The maintenance method according to claim 4.

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