Maintenance method for ink jet recording device, ink jet recording device, and program

Abstract

To provide a maintenance method for an ink jet recording device that enables maintenance to be performed at an appropriate timing, an ink jet recording device, and a program.SOLUTION: A maintenance method for an ink jet recording device including an ink jet head having a plurality of nozzles comprises: acquiring a measurement value of a velocity of ink ejected from each nozzle for each of the plurality of nozzles; and determining necessity of executing maintenance for removing foreign matters in the plurality of nozzles of the ink jet head on the basis of an increase ratio vu / vi of a velocity vu of each nozzle relative to a predetermined standard value vi when the acquired velocity of ink of each nozzle is defined as vu, and the standard value of the velocity of ink is defined as vi.SELECTED DRAWING: Figure 20

Description

[Technical Field]

[0001] The present invention relates to a maintenance method for an inkjet recording apparatus, an inkjet recording apparatus, and a program. [Background technology]

[0002] Conventionally, there are inkjet recording devices that record images on a recording medium by ejecting ink onto the recording medium from multiple nozzles provided in an inkjet head. In such inkjet recording devices, if foreign matter adheres near the nozzle openings or inside the nozzles, it can cause abnormalities in the ink ejection direction and flight speed, leading to poor image quality. For this reason, maintenance is performed periodically, such as forcibly ejecting ink from the nozzles and wiping the nozzle surface provided with multiple nozzles, to remove foreign matter and prevent the occurrence of poor image quality. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-212876 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with periodic maintenance, unnecessary maintenance may be performed even when there is no foreign matter adhering that could lead to poor image quality. Such maintenance reduces the operational efficiency of the inkjet recording device and wastes ink for maintenance. Furthermore, periodic maintenance may not be performed immediately even when foreign matter adhering that could lead to poor image quality is detected. In this case, the foreign matter may continue to adhere, making it more difficult to remove. Thus, the above-described conventional techniques have the problem of being unable to perform maintenance at the appropriate time.

[0005] An object of the present invention is to provide a maintenance method for an inkjet recording apparatus, an inkjet recording apparatus, and a program that enable maintenance to be performed at an appropriate timing. [Means for solving the problem]

[0006] In order to achieve the above object, the invention of a maintenance method for an inkjet recording apparatus according to claim 1 comprises: A maintenance method for an inkjet recording apparatus equipped with an inkjet head having a plurality of nozzles, comprising: obtaining, for each of the plurality of nozzles, a measurement of the velocity of ink ejected from each nozzle; When the acquired ink velocity of each nozzle is vu and a predetermined standard value of the ink velocity is vi, the need for maintenance to remove foreign matter from the multiple nozzles of the inkjet head is determined based on the increase rate vu / vi of the velocity vu of each nozzle relative to the standard value vi.

[0007] The invention described in claim 2 is the maintenance method for the inkjet recording apparatus described in claim 1, performing a first maintenance when a ratio of first-type defective nozzles, the increase rate vu / vi of which falls within a predetermined judgment range, among the plurality of nozzles is equal to or greater than a first reference value; If the ratio of the first type defective nozzles is less than the first reference value, the maintenance is not performed.

[0008] The invention described in claim 3 is the maintenance method for the inkjet recording apparatus described in claim 2, when a proportion of second-type defective nozzles, in which the increase rate vu / vi is greater than the upper limit of the judgment range, among the plurality of nozzles is equal to or greater than a second reference value, performing a second maintenance that is more effective at removing the foreign matter than the first maintenance; The first maintenance is performed when the proportion of the second type defective nozzles among the plurality of nozzles is less than the second reference value and the proportion of the first type defective nozzles is equal to or greater than the first reference value.

[0009] The invention described in claim 4 is the maintenance method for the inkjet recording apparatus described in claim 2, The lower limit of the determination range is set to be equal to or less than the maximum value of the increase rate vu / vi of normal nozzles that does not cause poor image quality.

[0010] The invention described in claim 5 is the maintenance method for the inkjet recording apparatus described in claim 2, when a speed reduction rate is defined as a ratio of the ink speed vu after the first maintenance is performed to the ink speed vu before the first maintenance is performed, the speed reduction rate is approximately constant within a range in which the increase rate vu / vi before the first maintenance is performed is equal to or greater than a predetermined value, The upper limit of the determination range is set within a range equal to or less than the predetermined value.

[0011] The invention described in claim 6 is the maintenance method for the inkjet recording apparatus described in claim 1, calculating an average value of the increase rates vu / vi of the plurality of nozzles based on the acquired velocity vu of each of the nozzles; When the average value of the increase rate vu / vi is within a predetermined determination range, the first maintenance is performed; If the average value of the increase rate vu / vi is less than the lower limit of the determination range, the maintenance is not performed.

[0012] The invention described in claim 7 is the maintenance method for the inkjet recording apparatus described in claim 6, When the average value of the increase rate vu / vi is greater than the upper limit of the determination range, the second maintenance, which has a higher effect of removing the foreign matter than the first maintenance, is performed.

[0013] The invention described in claim 8 is the maintenance method for the inkjet recording apparatus described in claim 1, The standard value vi is the average value of the velocity of ink ejected from the plurality of nozzles of the inkjet head in the initial state.

[0014] The invention described in claim 9 is the maintenance method for the inkjet recording apparatus described in claim 1, The measurement value of the velocity vu of each of the plurality of nozzles is calculated based on the formation position in the transport direction of measurement dots formed on the recording medium by ejecting ink from the plurality of nozzles at the same timing onto the recording medium being transported in a transport direction perpendicular to the arrangement direction of the plurality of nozzles.

[0015] The invention described in claim 10 is the maintenance method for the inkjet recording apparatus described in claim 9, calculating the measurement value of the speed vu based on a first formation position in the transport direction of a first measurement dot formed on a recording medium transported at a first transport speed and a second formation position in the transport direction of a second measurement dot formed on a recording medium transported at a second transport speed different from the first transport speed; When the first transport speed is V1, the second transport speed is V2, the distance in the transport direction between a position on the recording medium that faced the nozzle when ink was ejected and the first formation position is D1, the distance in the transport direction between a position on the recording medium that faced the nozzle when ink was ejected and the second formation position is D2, the deviation angle in the transport direction of the ink ejection direction from the direction perpendicular to the recording medium is θ, and the distance from the nozzle to the recording medium is d, two relational expressions are expressed as follows: D1=V1·d / vu-d·tanθ D2=V2·d / vu-d·tanθ The measured value of the velocity vu is calculated based on

[0016] The invention described in claim 11 is the maintenance method for the inkjet recording apparatus described in claim 2, further comprising: The first maintenance includes at least one of a first purge operation that ejects ink from at least the first type defective nozzles among the plurality of nozzles, and a first wiping operation that wipes the nozzle surface 242a on which the plurality of nozzles of the inkjet head are provided with a wiping member by a predetermined cleaning unit.

[0017] The invention described in claim 12 is the maintenance method for the inkjet recording apparatus described in claim 3, the first maintenance includes at least one of a first purge operation in which ink is ejected from at least the first-type defective nozzles among the plurality of nozzles, and a first wiping operation in which a wiping member is used by a predetermined cleaning unit to wipe a nozzle surface 242a on which the plurality of nozzles of the inkjet head are provided, The second maintenance includes at least one of a second purge operation in which ink is ejected from at least the second type defective nozzles among the plurality of nozzles at a pressure stronger than that of the first purge operation, and a second wiping operation in which the nozzle surface 242a is wiped with the wiping member by the cleaning unit or by hand at a pressure stronger than that of the first wiping operation or for a longer period of time than that of the first wiping operation.

[0018] The invention described in claim 13 is the maintenance method for the inkjet recording apparatus described in claim 11 or 12, In the first purge operation, ink is ejected only from nozzles among the plurality of nozzles for which the increase rate vu / vi is equal to or greater than the lower limit of the determination range.

[0019] The invention described in claim 14 is a maintenance method for an inkjet recording apparatus according to claim 1, comprising: obtaining the measured value of the velocity vu for each of the plurality of nozzles measured at a predetermined time; The predetermined timing is either the timing when printing is performed on a predetermined number of recording media using the inkjet head, or the timing when printing work by the inkjet recording device is completed.

[0020] In order to achieve the above object, the invention of the inkjet recording apparatus described in claim 15 is as follows: an inkjet head having a plurality of nozzles; A control unit; Equipped with The control unit obtaining, for each of the plurality of nozzles, a measurement of the velocity of ink ejected from each nozzle; When the acquired ink velocity of each nozzle is vu and a predetermined standard value of the ink velocity is vi, the need for maintenance to remove foreign matter from the multiple nozzles of the inkjet head is determined based on the increase rate vu / vi of the velocity vu of each nozzle relative to the standard value vi.

[0021] In order to achieve the above object, the invention of the program described in claim 16 is as follows: a computer of an inkjet recording apparatus having an inkjet head with a plurality of nozzles is caused to function as a control means; The control means obtaining, for each of the plurality of nozzles, a measurement of the velocity of ink ejected from each nozzle; When the acquired ink velocity of each nozzle is vu and a predetermined standard value of the ink velocity is vi, the need for maintenance to remove foreign matter from the multiple nozzles of the inkjet head is determined based on the increase rate vu / vi of the velocity vu of each nozzle relative to the standard value vi. [Effects of the Invention]

[0022] According to the present invention, maintenance can be performed at an appropriate time. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of an inkjet recording apparatus. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a head unit. [Figure 3] FIG. 10 is a diagram showing a state in which the head unit is moved in the width direction. [Figure 4] FIG. 2 is a diagram illustrating a configuration of a cleaning unit. [Figure 5] FIG. 2 is a block diagram showing the main functional configuration of the inkjet printing apparatus. [Figure 6] FIG. 10 is a diagram showing an example of foreign matter adhering to a nozzle. [Figure 7] FIG. 10 is a graph showing the tendency of the speed increase rate vu / vi and the nozzle's contribution to the occurrence of defects with respect to the change in the amount of adhering foreign matter. [Figure 8] FIG. 10 is a diagram showing the relationship between the velocity increase rate vu / vi of a plurality of nozzles in an inkjet head after a certain period of use and the foreign matter area ratio. [Figure 9] FIG. 9 is a diagram showing changes in the velocity increase rate vu / vi of each nozzle after normal maintenance is performed on the inkjet head of FIG. 8. [Figure 10] FIG. 10 is a diagram showing the change in the speed increase rate vu / vi in ​​FIG. 9 as a speed reduction rate. [Figure 11] FIG. 10 is a graph showing the tendency of changes in the speed increase rate vu / vi and the adhesion force of foreign matter relative to changes in the amount of adhering foreign matter. [Figure 12] 10 is a flowchart showing a control procedure for maintenance preparation processing. [Figure 13] 10 is a flowchart showing a control procedure for ink velocity measurement processing. [Figure 14] FIG. 10 is a diagram illustrating the operation of forming the first measurement dots. [Figure 15] FIG. 10 is a diagram illustrating the operation of forming the first measurement dots. [Figure 16] 10A and 10B are diagrams illustrating the operation of forming second measurement dots. [Figure 17] 10A and 10B are diagrams illustrating the operation of forming second measurement dots. [Figure 18] FIG. 10 is a diagram showing first and second measurement dots formed by an inkjet head in an initial state. [Figure 19] FIG. 10 is a diagram showing a first measurement dot and a second measurement dot formed by an inkjet head after use. [Figure 20] 10 is a flowchart showing a control procedure for maintenance processing. [Figure 21] 10A and 10B are diagrams illustrating the effect of performing maintenance using the method of the modified example in comparison with the reference example. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the scope of the invention is not limited to the illustrated examples.

[0025] FIG. 1 is a diagram showing a schematic configuration of an inkjet recording apparatus 1 according to an embodiment of the present invention. The inkjet recording apparatus 1 includes a paper feed unit 10, an image forming unit 20, a paper discharge unit 30, a control unit 40 (see FIG. 5) (control means, computer), and a cleaning unit 60 (see FIG. 4). Under the control of the control unit 40, the inkjet recording apparatus 1 transports a recording medium M stored in the paper feed unit 10 to the image forming unit 20, forms an image on the recording medium M in the image forming unit 20, and transports the recording medium M with the image formed thereon to the paper discharge unit 30. The recording medium M can be any of a variety of media, such as paper such as plain paper or coated paper, as well as fabric or sheet-like resin, on whose surface the ink can be fixed.

[0026] The paper feed unit 10 has a paper feed tray 11 that stores the recording medium M, and a medium supply unit 12 that transports and supplies the recording medium M from the paper feed tray 11 to the image forming unit 20. The medium supply unit 12 has a ring-shaped belt supported on the inside by two rollers, and transports the recording medium M from the paper feed tray 11 to the image forming unit 20 by rotating the rollers with the recording medium M placed on this belt.

[0027] The image forming section 20 includes a conveying section 21, a delivery unit 22, a medium heating section 23, a head unit 24 (ink ejection section), a fixing section 25, an imaging section 26, a delivery section 27, an ionizer 28, a medium sensor 29, and the like.

[0028] The transport unit 21 includes a cylindrical transport drum 211. The transport unit 21 holds the recording medium M placed on a transport surface 21a (mounting surface: see FIG. 3) of the transport drum 211. The transport unit 21 performs a transport operation in which the transport drum 211 holding the recording medium M rotates and moves around a rotation axis (cylindrical axis) extending in the width direction perpendicular to the paper plane in FIG. 1, thereby transporting the recording medium M in the direction of the rotation of the transport drum 211 (hereinafter referred to as the transport direction).

[0029] The transport drum 211 has claws 2111 (see FIG. 3) and an air intake 2112 (see FIG. 3) for holding the recording medium M on the transport surface 21a. The recording medium M is held on the transport surface 21a by having its edges pressed down by the claws 2111 and being drawn to the transport surface 21a by the air intake 2112. The transport unit 21 is connected to a transport drum motor (not shown) for rotating the transport drum 211. The transport drum 211 rotates by an angle proportional to the amount of rotation of the transport drum motor.

[0030] The transfer unit 22 transfers the recording medium M transported by the medium supply unit 12 of the paper feed unit 10 to the transport unit 21. The transfer unit 22 is provided at a position between the medium supply unit 12 of the paper feed unit 10 and the transport unit 21. The transfer unit 22 holds and picks up one end of the recording medium M transported from the medium supply unit 12 with a swing arm unit 221, and transfers it to the transport unit 21 via a transfer drum 222.

[0031] The medium heating unit 23 is provided between the position where the delivery drum 222 is disposed and the position where the head unit 24 is disposed. The medium heating unit 23 heats the recording medium M conveyed by the conveyance unit 21 so that the temperature of the recording medium M falls within a predetermined temperature range. The medium heating unit 23 has, for example, an infrared heater or the like, and energizes the infrared heater based on a control signal supplied from the control unit 40 to cause the infrared heater to generate heat.

[0032] The head unit 24 forms an image by ejecting ink from nozzles N (see FIG. 2) onto the recording medium M at appropriate timing according to the rotation of the transport drum 211 on which the recording medium M is held. The head unit 24 has a nozzle surface 242a (see FIG. 2) that faces the transport surface of the transport drum 211, and openings of the nozzles N are provided on this nozzle surface 242a. The head unit 24 is disposed so that the nozzle surface 242a and the transport surface 21a are separated by a predetermined distance. In this embodiment, four head units 24 corresponding respectively to inks of four colors, yellow (Y), magenta (M), cyan (C), and black (K), are arranged at predetermined intervals from the upstream side in the transport direction of the recording medium M in the order of Y, M, C, and K.

[0033] FIG. 2 is a schematic diagram showing the configuration of the head unit 24. The head unit 24 shows a nozzle surface 242a thereof that faces the transport surface 21a of the transport drum 211. The head unit 24 includes eight inkjet heads 242 attached to a mounting member 244. However, the number of inkjet heads 242 included in the head unit 24 is not limited to eight, and may be seven or fewer, or nine or more. The nozzle surface 242a is the surface of the head unit 24 that faces the transport surface 21a. Each inkjet head 242 includes a plurality of nozzles N and a plurality of image forming elements 2421 (see FIG. 5) that correspond to the plurality of nozzles N. The image forming elements 2421 include a pressure chamber that communicates with the nozzle N and stores ink, a piezoelectric element that is provided on the wall of the pressure chamber and deforms in response to an applied drive signal, and an electrode for applying a voltage to the piezoelectric element. When a drive signal is input to the electrode of the image forming element 2421, the pressure chamber is deformed due to the deformation of the piezoelectric element, and the pressure in the pressure chamber changes, causing ink droplets to be ejected from the nozzle N communicating with the pressure chamber.

[0034] The inkjet head 242 has six nozzle rows L1 to L6, each of which is composed of nozzles N arranged at equal intervals in the width direction. For example, each of the nozzle rows L1 to L6 consists of 300 nozzles N. In this case, one inkjet head 242 has 1,800 nozzles N. The nozzle rows L1 to L3 are arranged so that the arrangement positions of the nozzles N in the width direction are offset from one another. Similarly, the nozzle rows L4 to L6 are arranged so that the arrangement positions of the nozzles N in the width direction are offset from one another. The nozzle rows L1 and L4, the nozzle rows L2 and L5, and the nozzle rows L3 and L6 each have the same arrangement positions of the nozzles N in the width direction. This allows the nozzle rows L1 to L3 and the nozzle rows L4 to L6 to mutually complement each other in ink ejection. The arrangement direction of the nozzle rows may be inclined with respect to the width direction. The number of nozzle rows provided in one inkjet head 242 is not limited to six, and may be five or fewer rows or seven or more rows.

[0035] The eight inkjet heads 242 are arranged so that the nozzle arrays are continuous in the width direction. Specifically, the eight inkjet heads 242 are arranged in a staggered pattern with overlapping regions in which the nozzle arrays N in the width direction partially overlap. The nozzle arrays N included in the head unit 24 in the width direction cover the width of the recording medium M transported by the transport unit 21 where an image is formed. The head unit 24 is used in a state where its position is fixed relative to the rotation axis of the transport drum 211 during image formation. In other words, the head unit 24 has a line head that can eject ink across the image formable width in the width direction of the recording medium M. Therefore, the inkjet recording device 1 forms images in a single pass format.

[0036] The ink used in this embodiment contains a gelling agent in addition to coloring materials such as pigments, and changes phase between a sol state and a gel state depending on the temperature. This ink is in a gel state at room temperature and becomes a sol state when heated to a temperature above its phase transition temperature. The ink used in this embodiment is a UV-curable ink that hardens when exposed to ultraviolet light. The head unit 24 includes an ink heating unit 243 (see FIG. 5) that heats the ink stored in the head unit 24. The ink heating unit 243 operates under the control of the control unit 40 and heats the ink to a temperature at which the ink becomes a sol. The inkjet head 242 ejects the heated, sol-state ink. When this sol-state ink is ejected onto the recording medium M, the ink droplets land on the recording medium M, and then rapidly become a gel state due to natural cooling, solidifying on the recording medium M.

[0037] The head units 24 are provided so as to be able to move individually in the width direction. Fig. 3 is a diagram showing the state in which the head units 24 are moved in the width direction. The head units 24 are driven by a head unit moving section 52 (see Fig. 5) to be able to move in the width direction between a position facing the transport surface 21a of the transport drum 211 and a position facing the cleaning section 60. When performing maintenance on the nozzle surface 242a of the inkjet head 242, the head unit 24 moves to a position facing the cleaning section 60.

[0038] FIG. 4 is a diagram showing the configuration of the cleaning unit 60. The cleaning unit 60 includes a wiping cloth 61 (wiping member), a presser member 62, a feed roller 63, and a take-up roller 64. The cleaning unit 60 uses the wiping cloth 61 to wipe the nozzle surface 242a of the inkjet head 242, thereby removing foreign matter, ink, and the like adhering to the nozzle surface 242a and the inside of the nozzles N and cleaning the nozzle surface 242a. The wiping cloth 61 is a long, replaceable sheet member, and may be made of, for example, a nonwoven fabric. The presser member 62 is a flat plate-like member made of, for example, a porous material that allows air to pass through (such as porous ceramic or liquid-permeable resin). The presser member 62 may be an elastic member. The presser member 62 is movable between a position in contact with the nozzle surface 242a via the wiping cloth 61 and a position spaced apart from the nozzle surface 242a. The pressing member 62 is parallel to the nozzle surface 242a of the head unit 24 and supports the wiping cloth 61 so that it is parallel to the nozzle surface 242a by contacting it with the wiping cloth 61. The wiping cloth 61 is unwound from a winding roller 63, wipes the nozzle surface 242a, and then taken up by a take-up roller 64. The wiping cloth 61 moves up and down together with the pressing member 62 when the pressing member 62 contacts or separates from the nozzle surface 242a. The nozzle surface 242a is wiped by the wiping cloth 61 by moving the head unit 24 in the width direction while the wiping cloth 61 is in contact with the nozzle surface 242a by the pressing member 62. By appropriately setting the pressing force, wiping speed, and number of wipes by the pressing member 62, ink can be wiped off the nozzle surface 242a and foreign matter can be removed. The wiping speed is the relative speed between the wiping cloth 61 and the nozzle surface 242a. The vertical movement of the pressing member 62 and the rotational operations of the unwinding roller 63 and the winding roller 64 are performed under the control of the control unit 40.

[0039] 1, the fixing unit 25 has a light-emitting unit arranged across the width of the conveying unit 21 in the width direction, and irradiates ultraviolet light from the light-emitting unit onto the recording medium M placed on the conveying unit 21 to harden and fix the ink (gel ink) ejected onto the recording medium M. The light-emitting unit of the fixing unit 25 is arranged opposite the conveying surface between the position where the head unit 24 is arranged and the position where the delivery drum 271 of the delivery unit 27 is arranged in the conveying direction.

[0040] The imaging unit 26 is disposed at a position in the conveyance direction between the position where the ink is fixed by the fixing unit 25 and the position where the transfer drum 271 is disposed. The imaging unit 26 has, for example, a line sensor provided across the width of the conveyance drum 211 in the width direction. The imaging unit 26 reads the surface of the recording medium M on the conveyance surface to generate imaging data, and outputs the imaging data to the control unit 40.

[0041] The delivery unit 27 includes a cylindrical delivery drum 271 and a belt loop 272. The delivery drum 271 delivers the recording medium M from the conveyance unit 21 to the belt loop 272. The belt loop 272 has a circular belt supported by two rollers on the inside. The delivery unit 27 transports the recording medium M delivered from the conveyance unit 21 onto the belt loop 272 by the delivery drum 271, using the belt loop 272, and sends it to the paper discharge unit 30.

[0042] The ionizer 28 is disposed in a position between the position of the medium heating unit 23 and the position of the head unit 24 in the transport direction. The ionizer 28 generates a corona discharge by applying a high voltage to an electrode, thereby neutralizing the surface of the recording medium M. Ozone is generated as a result of the corona discharge. The ionizer 28 may be equipped with an exhaust means for sucking in and exhausting this ozone.

[0043] The medium sensor 29 is disposed at a position between the position where the ionizer 28 is disposed and the position where the head unit 24 is disposed in the conveyance direction. The medium sensor 29 detects the leading edge of the recording medium M held and conveyed on the conveyance surface 21a, and outputs the detection result to the control unit 40. The detection method of the medium sensor 29 is not particularly limited. The detection method of the medium sensor 29 may be, for example, an optical method that optically reads the leading edge of the recording medium M, or a contact method that detects physical contact with the leading edge of the recording medium M, or the like.

[0044] The paper discharge unit 30 has a plate-shaped paper discharge tray 31 on which the recording medium M sent out from the image forming unit 20 by the delivery unit 27 is placed.

[0045] 5 is a block diagram showing the main functional configuration of the inkjet recording apparatus 1. The inkjet recording apparatus 1 includes a medium heating section 23, a head control section 241, a head unit 24 having an inkjet head 242 and an ink heating section 243, a fixing section 25, an imaging section 26, an ionizer 28, a medium sensor 29, a control section 40, a transport drive section 51, a head unit moving section 52, an operation display section 53, and a communication section 54. The various sections of the inkjet recording apparatus 1 are connected via a signal transmission path such as a bus. In the following, a description of some of the configuration already described in FIGS. 1 to 4 will be omitted.

[0046] The head control unit 241 outputs various control signals and image data to a head drive unit (not shown) in the inkjet head 242 at a timing corresponding to the control signal input from the control unit 40, thereby causing the head drive unit to supply a drive signal to the image forming element 2421 to deform the piezoelectric element, thereby causing ink droplets to be ejected from the nozzle N.

[0047] The control unit 40 is a hardware processor having a CPU 41 (Central Processing Unit), RAM 42 (Random Access Memory), and a storage unit 43. The CPU 41 reads out a program 431 and setting data stored in the storage unit 43, stores them in the RAM 42, and executes the program 431 to perform various arithmetic processing. In this way, the CPU 41 comprehensively controls the overall operation of the inkjet recording apparatus 1. The RAM 42 provides a working memory space for the CPU 41 and stores temporary data.

[0048] The storage unit 43 stores the program 431 executed by the CPU 41, setting data, etc. For example, a hard disk drive (HDD), flash memory, or read-only memory (ROM) is used as the storage unit 43. The storage unit 43 stores print jobs (image recording commands) input from external devices via the communication unit 54, image data related to the print jobs, image data generated by the imaging unit 26, measurement data of the ink velocity vu (described later), etc.

[0049] The transport drive unit 51 supplies a drive signal to the transport drum motor of the transport drum 211 based on a control signal supplied from the control unit 40, thereby rotating the transport drum 211 at a predetermined speed and timing. In addition, the transport drive unit 51 operates the medium supply unit 12, the delivery unit 22, and the delivery unit 27 based on a control signal supplied from the control unit 40, and causes the recording medium M to be supplied to the transport unit 21 and discharged from the transport unit 21.

[0050] Based on a control signal supplied from the control unit 40, the head unit moving unit 52 outputs a drive signal to a motor or brake of a movement mechanism for moving the head unit 24 in the width direction, thereby moving the head unit 24.

[0051] The operation display unit 53 includes a display device such as a liquid crystal display or an organic EL display, and an input device such as operation keys and a touch panel overlaid on the screen of the display device. The operation display unit 53 displays various information on the display device, and converts user input operations on the input device into operation signals and outputs them to the control unit 40.

[0052] The communication unit 54 is a communication interface that controls communication operations with external devices. The communication unit 54 acquires data related to print jobs from external devices under the control of the control unit 40, and also transmits status information and the like to the external devices.

[0053] (Maintenance method for inkjet recording device) Next, a description will be given of a maintenance method for the nozzle surface 242a of the inkjet head 242 in the inkjet recording apparatus 1, and the operation of the inkjet recording apparatus 1 related to the maintenance method. In this embodiment, the description will be given taking as an example a case where UV-curable ink is used, the ink temperature at the time of ejection is 80°C, and the viscosity of the ink at 80°C is 1 to 10 cps.

[0054] In the inkjet recording device 1, if foreign matter adheres near the opening of the nozzle N or inside the nozzle N, it will cause abnormalities in the ink ejection direction and flight speed. If abnormalities in the ink ejection direction or flight speed occur, poor image quality such as streaks or unevenness will occur in the formed image. Examples of foreign matter include solidified or precipitated ink components, but this is not limited to this and foreign matter can also be mixed in from the outside. Below, a nozzle N in which abnormalities in the ink ejection direction or flight speed have occurred and which may cause poor image quality will be referred to as a "faulty nozzle." Furthermore, nozzles N other than faulty nozzles that do not cause poor image quality will be referred to as "normal nozzles."

[0055] In the inkjet recording apparatus 1, in order to prevent poor image quality caused by faulty nozzles, maintenance of the inkjet head 242 is performed at appropriate times to remove foreign matter and maintain good ink ejection conditions. The inkjet recording apparatus 1 of this embodiment is capable of performing normal maintenance, which is normally performed, and strong maintenance, which is more effective at removing foreign matter than normal maintenance.

[0056] The normal maintenance includes, for example, at least one of a normal purge operation (first purge operation) and a normal wiping operation (first wiping operation). The normal purge operation is an operation that forcibly expels ink from the nozzle N by pressurizing ink from the upstream side of the nozzle N or by suctioning ink from the nozzle surface 242a side. Ink pressurization is performed, for example, by deforming a piezoelectric element in the image forming element 2421. In this case, it is possible to select the nozzle N from which ink is to be ejected in the normal purge operation. Therefore, in the normal purge operation, it is also possible to eject ink only from defective nozzles. Note that ink pressurization may be performed by a method that increases the ink supply pressure to the inkjet head 242. Furthermore, when suctioning ink from the nozzle surface 242a side in the normal purge operation, a suction unit (not shown) that suctions ink while sealing the nozzle surface 242a is provided in the inkjet recording apparatus 1. The suction unit may be provided in the cleaning unit 60. The normal wiping operation is an operation of wiping the nozzle surface 242a with the wiping cloth 61 of the cleaning unit 60. The normal wiping operation may be performed after the normal purging operation.

[0057] The strong maintenance includes, for example, at least one of a strong purge operation (second purge operation) and a strong wiping operation (second wiping operation). The strong purge operation is an operation that forcibly ejects ink from the nozzles N by using a stronger ink pressure or a stronger ink suction force than the normal purge operation. As with the normal ejection operation, the strong ejection operation may also eject ink from only some of the nozzles N, including defective nozzles. The strong wiping operation is, for example, an operation that wipes the nozzle surface 242a with a stronger wiping pressure or for a longer period of time than the normal wiping operation. Wiping for a longer period of time than the normal wiping operation may include wiping at a slower wiping speed than the normal wiping operation. The strong wiping operation may be performed by the cleaning unit 60 or manually. A manual wiping operation may use a cleaning liquid, such as a monomer liquid, used in the ink.

[0058] However, simply performing periodic maintenance can lead to problems such as unnecessary maintenance being performed even when there are few defective nozzles due to foreign matter adhesion, or maintenance not being performed immediately even when there are many defective nozzles. Furthermore, ink ejection defects caused by factors other than foreign matter, such as malfunctions of the image forming element 2421, are difficult to resolve through the above-mentioned maintenance.

[0059] Therefore, in this embodiment, the control unit 40 determines whether the timing is effective for maintenance, and performs the maintenance if it is. The control unit 40 also selects and performs either the normal maintenance or the strong maintenance described above, whichever is more effective. In particular, the control unit 40 utilizes the fact that there is a positive correlation between the amount of foreign matter adhering to the nozzle N and the speed of ink ejected from the nozzle N, and estimates the occurrence of defective nozzles caused by foreign matter based on the measured value of the ink speed.

[0060] FIG. 6 is a diagram showing an example of foreign matter F adhering to a nozzle N. FIG. 6 is a trace of a photograph of the opening of the nozzle N captured from an imaging direction perpendicular to the opening. FIG. 6 depicts the circular opening of the nozzle N and foreign matter F adhering to the area overlapping the opening when viewed from the imaging direction. Therefore, the foreign matter F may be adhering to the opening of the nozzle N or to the inner wall surface of the nozzle N. In this embodiment, the amount of foreign matter F adhering to the nozzle N (amount of adhering foreign matter) is expressed by the ratio of the area of ​​the foreign matter F to the area of ​​the opening in this figure (foreign matter area ratio). Typically, foreign matter F adheres in an uneven distribution along the circumference of the opening of the nozzle N. Therefore, when foreign matter F adheres, the force applied to the ink during ejection becomes uneven, causing a deviation in the ejection direction of the ink. Furthermore, as the amount of adhering foreign matter increases, the opening area of ​​the nozzle N becomes smaller, resulting in an increase in the pressure applied to the ejected ink. Therefore, the greater the amount of adhering foreign matter, the greater the pressure applied to the ink, and the faster the ink will be ejected. Hereinafter, the speed of ink ejected from nozzle N will be referred to as "speed vu." The standard value of the ink speed will be referred to as "standard value vi." The ratio of speed vu to standard value vi will be referred to as "speed increase rate vu / vi" (increase rate vu / vi). In this embodiment, standard value vi is the average value of the ink speed ejected from each nozzle N of the inkjet head 242 in the initial state. However, the present invention is not limited to this, and standard value vi may be a theoretical value of ink speed, a catalog value, or the like.

[0061] FIG. 7 shows the trend of the speed increase rate vu / vi and the nozzle N's contribution to defect occurrence relative to changes in the amount of foreign matter. The contribution to defect occurrence represents the likelihood of a particular nozzle N causing image quality defects, and may be, for example, the density of streaks produced by that nozzle N. Because the speed vu increases as the amount of foreign matter increases, as shown in FIG. 7, the amount of foreign matter and the speed increase rate vu / vi are positively correlated and have a roughly linear relationship. On the other hand, the amount of foreign matter and the contribution to defect occurrence have a positive correlation but a nonlinear relationship. Specifically, when the amount of foreign matter is below a certain threshold T1, the contribution to defect occurrence hardly increases, but when the amount exceeds the threshold T1, the contribution to defect occurrence increases at a large rate. Here, the speed increase rate vu / vi corresponding to the threshold T1 for the amount of foreign matter is "1.1" for the inkjet head 242 of this embodiment. In other words, a nozzle N with a speed increase rate vu / vi less than 1.1 is a normal nozzle with almost no abnormalities in the ink ejection direction or flight speed. In other words, a nozzle N with a velocity increase rate vu / vi of 1.1 or greater can be said to be a defective nozzle that, although to varying degrees, has some abnormality in the ink ejection direction or flight speed, causing poor image quality.

[0062] FIG. 8 shows the relationship between the velocity increase rate vu / vi of multiple nozzles N in an inkjet head 242 after use and the foreign matter area ratio. FIG. 8 shows the velocity increase rate vu / vi of 1 / 4 of the 300 nozzles N belonging to one nozzle row in an inkjet head 242, i.e., 75 nozzles N selected from every fourth nozzle. Here, an inkjet head 242 that had printed 100,000 recording media M was used. The method for measuring the ink velocity vu will be described later. The foreign matter area ratio was calculated by capturing an image of each nozzle N and using the method shown in FIG. 6 based on the area of ​​the nozzle N and the area of ​​the foreign matter F. In FIG. 8, the velocity increase rate vu / vi of each nozzle N ranges from 1 to 1.7. The solid line in FIG. 8 is an approximation curve (here, a nearly straight line) of the plot of multiple nozzles N. As described above, the velocity increase rate vu / vi and the foreign matter area ratio (amount of attached foreign matter) have a roughly linear relationship.

[0063] Figure 9 is a diagram showing changes in the speed increase rate vu / vi of each nozzle N after regular maintenance has been performed on the inkjet head 242 of Figure 8. The horizontal axis of Figure 9 represents the speed increase rate vu / vi before maintenance, and the vertical axis represents the speed increase rate vu / vi after maintenance. Here, as regular maintenance, a regular wiping operation was performed by the cleaning unit 60 under the following conditions: Wiping speed: 83mm / s Wiping pressure: 15gf / cm 2 Number of wipes: 3

[0064] In Figure 9, the dashed-dotted line represents the case where there is no change in the velocity increase rate vu / vi before and after maintenance. Therefore, the lower the plot is below the dashed-dotted line, the greater the reduction in the velocity increase rate vu / vi, i.e., the greater the reduction in velocity vu, due to normal maintenance. A reduction in the velocity increase rate vu / vi indicates that foreign matter has been removed from nozzle N, i.e., normal maintenance was effective. The solid lines in Figure 9 are approximate curves of the plots for multiple nozzles N. Here, the approximate curve is a connection of three approximate straight lines with different slopes. As can be seen from this approximate curve, for nozzles N whose velocity increase rate vu / vi before maintenance was 1.3 or less, normal maintenance achieved a sufficient reduction in velocity vu. On the other hand, for nozzles N whose velocity increase rate vu / vi before maintenance was greater than 1.3, normal maintenance achieved almost no reduction in velocity vu.

[0065] FIG. 10 is a diagram showing the change in the speed increase rate vu / vi of FIG. 9 as a speed reduction rate. The speed reduction rate represents the ratio of the ink speed vu after normal maintenance to the ink speed vu before normal maintenance. Alternatively, the speed reduction rate may be expressed as the ratio of the ink speed increase rate vu / vi after normal maintenance to the ink speed increase rate vu / vi before normal maintenance. As shown in FIG. 10, the speed reduction rate is approximately constant at R1 when the ink speed increase rate vu / vi before normal maintenance is equal to or less than a first value m1, and is approximately constant at R2 (>R1) when the ink speed increase rate vu / vi is equal to or greater than a second value m2 (predetermined value). On the other hand, the speed reduction rate increases sharply when the ink speed increase rate vu / vi before maintenance is equal to or greater than the first value m1 and equal to or less than a second value m2. Here, the first value m1 is smaller than 1.3, and the second value m2 is greater than 1.3.

[0066] This indicates that, as shown in FIG. 11, the change in the adhesive force of foreign matter F relative to the change in the amount of adhering foreign matter is nonlinear. The "adhesive force of foreign matter" on the right vertical axis in FIG. 11 represents the strength of maintenance required to remove foreign matter F from the nozzle N, e.g., the wiping pressure required to remove foreign matter from the nozzle N during a wiping operation. As shown in FIG. 11, when the amount of adhering foreign matter exceeds a certain threshold T2, the adhesive force of foreign matter F increases rapidly. In areas where the amount of adhering foreign matter exceeds threshold T2, foreign matter F may actually be more firmly attached. In other cases, foreign matter F may be attached further back in the nozzle N, making it more difficult to remove by a wiping operation, resulting in an apparent increase in adhesive force. Therefore, in areas where the amount of adhering foreign matter exceeds threshold T2, maintenance that is more effective at removing foreign matter than normal maintenance is required. The speed increase rate vu / vi corresponding to threshold T2 for the amount of adhering foreign matter is 1.3 for the inkjet head 242 of this embodiment. That is, for nozzles N where the velocity increase rate vu / vi exceeds 1.3, it is clear that normal maintenance cannot effectively remove foreign matter.

[0067] From the descriptions of FIGS. 7 to 11 above, the nozzle N can be classified into the following (i) to (iii) based on the velocity increase rate vu / vi of the nozzle N. Hereinafter, the velocity increase rate vu / vi “1.1” in FIG. 7 and the like is denoted as “vu / vi(min)”. Also, the velocity increase rate vu / vi “1.3” in FIGS. 9 to 11 is denoted as “vu / vi(max)”.

[0068] (i) Nozzle N satisfying vu / vi < vu / vi(min) As described with reference to FIG. 7, this nozzle N is a normal nozzle.

[0069] (ii) Nozzle N satisfying vu / vi(min) ≤ vu / vi ≤ vu / vi(max) This nozzle N is a defective nozzle whose velocity increase rate vu / vi can be effectively reduced by normal maintenance, or in other words, a defective nozzle from which foreign matter can be effectively removed by normal maintenance. Hereinafter, the defective nozzle satisfying this condition is denoted as “type 1 defective nozzle”. Also, the range of the velocity increase rate vu / vi that is not less than vu / vi(min) and not more than vu / vi(max) is denoted as the “judgment range”.

[0070] (iii) Nozzle N satisfying vu / vi(max) < vu / vi This nozzle N is a defective nozzle whose velocity increase rate vu / vi cannot be effectively reduced by normal maintenance, or in other words, a defective nozzle from which foreign matter cannot be effectively removed by normal maintenance. Hereinafter, the defective nozzle satisfying this condition is denoted as “type 2 defective nozzle”.

[0071] Based on these classifications, in this embodiment, the necessity of performing maintenance and the type of maintenance to be performed are determined by the following methods (I) to (III) based on the velocity increase rate vu / vi of each nozzle N.

[0072] (I) Strong maintenance is performed when the proportion RT2 of second-type faulty nozzles, whose velocity increase rate vu / vi is greater than the upper limit (vu / vi(max)) of the judgment range, among the multiple nozzles N of the inkjet head 242, is equal to or greater than a second reference value. This is because, in such a case, even if normal maintenance is performed, many second-type faulty nozzles will remain faulty. In this embodiment, the second reference value is set to 0.05 (5%). However, the second reference value is not limited to this and can be changed as appropriate depending on the application of the inkjet recording apparatus 1, the required image quality, and the like. For example, the second reference value may be set to 0.1 (10%) so that strong maintenance is performed when a larger number of second-type faulty nozzles have occurred. The second reference value may also be changeable by the user. The proportion RT2 of second-type faulty nozzles being equal to or greater than the second reference value can be rephrased as the number of second-type faulty nozzles being equal to or greater than a second reference number. Here, the second reference number is the total number of nozzles in the inkjet head 242 multiplied by the second reference value. Furthermore, strong maintenance is also effective in removing foreign matter from Type 1 defective nozzles.

[0073] (II) Normal maintenance is performed when, among the multiple nozzles N of the inkjet head 242, the proportion RT2 of second-type defective nozzles is less than a second reference value and the proportion RT1 of first-type defective nozzles is equal to or greater than a first reference value. In such cases, performing normal maintenance can effectively reduce the number of defective nozzles. In this embodiment, the first reference value is set to 0.1 (10%). However, the second reference value is not limited to this and can be changed as appropriate depending on the application of the inkjet recording apparatus 1, the required image quality, and other factors. For example, the first reference value may be set to 0.05 (5%) so that normal maintenance is performed with fewer first-type defective nozzles. Furthermore, the first reference value may be changeable by the user. The proportion RT1 of first-type defective nozzles being equal to or greater than the first reference value can be rephrased as the number of first-type defective nozzles being equal to or greater than a first reference number. Here, the first reference number is the total number of nozzles in the inkjet head 242 multiplied by the first reference value. (III) If the proportion RT1 of first-type defective nozzles is less than the first reference value and the proportion RT2 of second-type defective nozzles is less than the second reference value, maintenance is not performed. This is because even if maintenance is performed, the absolute number of defective nozzles that will be restored to normal is small, making it unnecessary maintenance.

[0074] If the occurrence of second-type defective nozzles can be ignored, step (I) above may be omitted. In this case, step (III) simply determines that maintenance will not be performed if the proportion RT1 of first-type defective nozzles is less than the first reference value.

[0075] Furthermore, the lower limit of the judgment range, vu / vi(min), only needs to be set to a value equal to or less than the maximum value of the increase rate vu / vi of normal nozzles, and may be set to a value smaller than "1.1" in the examples of Figures 7 to 11.

[0076] Furthermore, vu / vi(max), which is the upper limit of the determination range, may be set within a range equal to or less than the second value m2 in FIG. 10. Preferably, vu / vi(max) is set as large as possible within this range. Alternatively, vu / vi(max) may be set within a range equal to or greater than the first value m1 and equal to or less than the second value m2. Alternatively, vu / vi(max) may be set to the upper limit of the speed increase rate vu / vi within a range in which the speed reduction rate is equal to or less than R1 in FIG. 10 (first value m1 in FIG. 10).

[0077] It is also preferable to change vu / vi(min) and vu / vi(max) as appropriate depending on the model of the inkjet head 242 and the characteristics (particularly viscosity) of the ink used. In other words, if the model of the inkjet head 242 and the characteristics of the ink used are the same, common vu / vi(min) and vu / vi(max) can be used.

[0078] Next, a description will be given of the flow of processing executed by the control unit 40 to perform the maintenance according to the above-described method. To perform the above-described maintenance, the control unit 40 executes the following first and second steps, which can be broadly divided. The first step is to determine appropriate vu / vi(min) and vu / vi(max) according to the model of the inkjet head 242 and the characteristics of the ink used. The second step is to carry out maintenance at an appropriate timing while the inkjet recording apparatus 1 is actually in use. In the first step, the control unit 40 executes a maintenance preparation process shown in Fig. 12. In the second step, the control unit 40 executes a maintenance process shown in Fig. 20. Each process will be described below.

[0079] 12 is a flowchart showing the control procedure for the maintenance preparation process. The maintenance preparation process starts in an initial state, for example, when the inkjet head 242 is attached to the head unit 24 as shipped. When the maintenance preparation process starts, the control unit 40 executes an ink velocity measurement process to identify the standard value vi of the ink velocity (step S101).

[0080] 13 is a flowchart showing the control procedure for the ink velocity measurement process. In the ink velocity measurement process, first measurement dots 71 and second measurement dots 72 (see FIG. 18) are formed on the recording medium M and their positions are measured to calculate the measured value of the ink velocity vu. When the ink velocity measurement process is started, the control unit 40 sends a control signal to the transport drive unit 51 to set the transport speed of the recording medium M by the transport drum 211 to a first transport speed V1 (step S201). While transporting the recording medium M by the transport drum 211, the control unit 40 ejects ink from each nozzle N of the inkjet head 242 at the same timing, thereby forming the first measurement dots 71 on the recording medium M (step S202).

[0081] 14 and 15 are diagrams illustrating the formation operation of the first measurement dots 71. For convenience, in FIGS. 14 and 15, the recording medium M, which is curved along the conveyance surface 21a of the conveyance drum 211, is depicted as being straight during conveyance. In step S202, the control unit 40 ejects ink I from the nozzle N of the inkjet head 242 t0 seconds after the medium sensor 29 detects the leading edge P0 of the recording medium M. FIG. 14 is a diagram illustrating the positional relationship between the inkjet head 242 and the recording medium M at the time of ejection of the ink I. The position of the recording medium M facing the nozzle N when the ink I is ejected is defined as position P1. Furthermore, the distance (interval) between the nozzle N and the medium sensor 29 in the conveyance direction is defined as Y0. Furthermore, the distance from the nozzle N to the recording medium M is defined as d. The distance YA1 between the leading edge P0 and position P1 in the conveyance direction is expressed by the following equation: YA1=t0·V1-Y0

[0082] FIG. 15 shows the positional relationship between the head unit 24 and the recording medium M at the time when the ink I lands on the recording medium M. The position on the recording medium M where the ink I lands in the transport direction is designated as position P2. Position P2 corresponds to the first formation position of the first measurement dot 71 in the transport direction. Also, the deviation angle of the ink ejection direction in the transport direction from the direction perpendicular to the recording medium M is designated as θ. θ is 0 for nozzle N in its initial state, but if the nozzle becomes defective after use, θ can take on a value other than 0. Furthermore, the time t from when the ink I is ejected from nozzle N to when it lands can be expressed as t = d / vu using the ink velocity vu. Therefore, in FIG. 15, the distance from nozzle N to position P1 in the transport direction is d·V1 / vu. Using these, the distance YB1 from the leading edge P0 to position P2 in the transport direction can be expressed by the following equation: YB1=YA1+d·V1 / vu-d·tanθ =V1·(t0+d / vu)-Y0-d·tanθ…(1)

[0083] Returning to FIG. 13, the control unit 40 causes the imaging unit 26 to capture an image of the formed first measurement dot 71, and acquires the captured image data (step S203).

[0084] Next, the control unit 40 sends a control signal to the transport driver 51 to set the transport speed of the recording medium M by the transport drum 211 to a second transport speed V2 that is faster than the first transport speed V1 (step S204). While causing the transport drum 211 to transport the recording medium M, the control unit 40 causes the nozzles N of the inkjet head 242 to eject ink at the same timing, thereby forming second measurement dots 72 on the recording medium M (step S205).

[0085] 16 and 17 are diagrams illustrating the operation of forming the second measurement dots 72. When forming the second measurement dots 72, the control unit 40 also ejects ink I from the nozzles N of the inkjet head 242 t0 seconds after the leading edge P0 of the recording medium M is detected by the medium sensor 29. FIG. 16 is a diagram showing the positional relationship between the inkjet head 242 and the recording medium M at the time of ejection of the ink I. In FIG. 16, position P1 is different from that in FIG. 14. In FIG. 16, the distance YA2 between the leading edge P0 and position P1 in the transport direction is expressed by the following equation. YA2=t0·V2-Y0

[0086] FIG. 17 is a diagram showing the positional relationship between the head unit 24 and the recording medium M at the time when the ink I lands on the recording medium M. In FIG. 17, position P2 is different from that in FIG. 15. Position P2 corresponds to the second formation position in the transport direction of the second measurement dot 72. In FIG. 17, the distance from the nozzle N to position P1 in the transport direction is d·V2 / vu. Therefore, the distance YB2 from the leading edge P0 to position P2 in the transport direction is expressed by the following equation. YB2=YA2+d·V2 / vu-d·tanθ =V2·(t0+d / vu)-Y0-d·tanθ …(2)

[0087] Returning to FIG. 13, the control unit 40 causes the imaging unit 26 to capture an image of the formed second measurement dot 72 and acquires the image data (step S206). The control unit 40 then analyzes the image data acquired in steps S203 and S206 and determines the distance YB1 and the distance YB2 for each nozzle N (step S207). Here, as shown in FIG. 18, the control unit 40 determines the distance YB1 and the distance YB2 based on the length (e.g., the number of pixels) from the leading edge of the imaged recording medium M in the transport direction to the first measurement dot 71 and the second measurement dot 72. FIG. 18 is a schematic diagram showing the first measurement dot 71 and the second measurement dot 72 in the initial state. As shown in FIG. 18, in the initial state, the speed of ink ejected from each nozzle N is approximately the same at the standard value vi, so the distance YB1 and the distance YB2 are approximately uniform.

[0088] The control unit 40 calculates the measured value of the ink velocity vu for each nozzle N (step S208). Here, the control unit 40 substitutes the distances YB1 and YB2 determined in step S207 into the above equations (1) and (2), and calculates the unknowns, the velocity vu and the deviation angle θ, based on the substituted equations (1) and (2). When step S208 is completed, the control unit 40 ends the ink velocity calculation process and returns the process to the maintenance preparation process of FIG. 12.

[0089] It should be noted that the following equations (1a) and (2a) may be used instead of the above equations (1) and (2). D1=V1·d / vu-d·tanθ …(1a) D2=V2·d / vu-d·tanθ …(2a) 15, distance D1 is the distance in the transport direction between position P1 on the recording medium M that faced the nozzle N when the ink was ejected and position P2 where the first measurement dot 71 was formed, and corresponds to YB1-YA1. Also, distance D2 is the distance in the transport direction between position P1 on the recording medium M that faced the nozzle N when the ink was ejected and position P2 where the first measurement dot 71 was formed, and corresponds to YB2-YA2.

[0090] 12 is completed, the control unit 40 calculates the standard value vi of the ink velocity (step S102). Here, the control unit 40 calculates the average value of the velocities vu of each nozzle N calculated in step S101, and sets this as the standard value vi.

[0091] Next, the control unit 40 executes a predetermined head deterioration process to deteriorate the inkjet head 242 (step S103). The contents of the head deterioration process are not particularly limited as long as the number of defective nozzles increases in accordance with deterioration. In this embodiment, the deterioration process involves printing a predetermined test image on 100,000 sheets of recording medium M in an environment with an ozone concentration of 0.5 ppm. The test image was an image with a uniform density and a print rate of 3%. This head deterioration process results in defective nozzles due to the adhesion of foreign matter.

[0092] The control unit 40 executes the ink velocity measurement process of FIG. 13 again using the inkjet head 242 that has undergone the head deterioration process (step S104). The first measurement dots 71 and second measurement dots 72 formed in step S104 vary in position for each nozzle N, as shown in FIG. 19. Furthermore, the nozzle N with a greater amount of foreign matter has a faster velocity vu, so the distance YB1 and the distance YB2 are shorter than those in FIG. 18. The control unit 40 calculates the velocity increase rate vu / vi for each nozzle N (step S105).

[0093] The control unit 40 acquires imaging data of each nozzle N of the inkjet head 242 and measures the amount of foreign matter adhering to each nozzle N (foreign matter area ratio) based on this imaging data (step S106). For example, microscope image data at a magnification of 2000x is used as the imaging data. Next, the image of each nozzle N is converted into a binary image so that the portion inside the nozzle N excluding the foreign matter F is represented by black pixels, and the remaining portion including the foreign matter F is represented by white pixels. The circumscribing circle of the boundary between the white pixels and the black pixels is then calculated. The area between the boundary line and the circumscribing circle is then taken as the foreign matter area, and the foreign matter area ratio is calculated using the circumscribing circle as the nozzle area.

[0094] The control unit 40 calculates the correlation between the speed increase rate vu / vi and the amount of adhering foreign matter, as shown in Fig. 8, and determines the speed increase rate vu / vi at which the amount of adhering foreign matter is equal to or less than the threshold value T1 shown in Fig. 7 as vu / vi(min), i.e., the lower limit of the determination range (step S107). The threshold value T1 is specified in advance based on the model of the inkjet head 242 and the characteristics of the ink used, and is stored in the storage unit 43, for example.

[0095] The control unit 40 performs normal maintenance on the same inkjet head 242 (step S108). For example, the control unit 40 causes the head unit moving unit 52 to move the head unit 24 provided with the inkjet head 242 to a position facing the cleaning unit 60, and causes the cleaning unit 60 to perform a normal wiping operation. Thereafter, the control unit 40 performs the ink velocity measurement process of Fig. 13 using the inkjet head 242 for which normal maintenance has been completed (step S109).

[0096] As shown in Fig. 10, the control unit 40 calculates a speed reduction rate of the speed increase rate vu / vi after maintenance relative to the speed increase rate vu / vi before maintenance (step S110). Then, the control unit 40 determines vu / vi(max), i.e., the lower limit of the determination range, within a range excluding the range in which the speed reduction rate is constant around 1 (a range equal to or less than the second value m2 in Fig. 10) (step S111). For example, the control unit 40 determines vu / vi(max) within a range equal to or greater than the first value m1 and equal to or less than the second value m2 in Fig. 10. When step S111 is completed, the control unit 40 ends the maintenance preparation process.

[0097] Next, the maintenance process executed in the second step will be described. Fig. 20 is a flowchart showing the control procedure of the maintenance process. This maintenance process is executed, for example, when the inkjet recording apparatus 1 is started up.

[0098] When the maintenance process is started, the control unit 40 executes a printing operation of printing an image on the recording medium M according to the input print job (step S301). The control unit 40 determines whether it is the measurement timing of the ink velocity vu (step S302). The measurement timing of the ink velocity vu is predetermined. The measurement timing may be, for example, either the timing every time printing is performed on a predetermined number of recording media M using the inkjet head 242 or the timing when the printing operation by the inkjet recording apparatus 1 is completed. If it is determined that it is not the measurement timing ( "NO" in step S302), the control unit 40 returns the process to step S301. If it is determined that it is the measurement timing ( "YES" in step S302), the control unit 40 executes the ink velocity measurement process of FIG. 13 (step S303).

[0099] For each nozzle N, the control unit 40 calculates the velocity increase rate vu / vi (step S304). Then, the control unit 40 calculates the ratio RT1 of the first type of defective nozzles for which the velocity increase rate vu / vi satisfies vu / vi(min) ≦ vu / vi ≦ vu / vi(max) (step S305). Further, the control unit 40 calculates the ratio RT2 of the second type of defective nozzles for which the velocity increase rate vu / vi satisfies vu / vi(max) < vu (step S306).

[0100] The control unit 40 determines whether the ratio RT2 is equal to or greater than the second reference value (step S307). If it determines that the ratio RT2 is equal to or greater than the second reference value (step S307: YES), the control unit 40 executes strong maintenance (step S308). For example, the control unit 40 sends a control signal to the cleaning unit 60 specifying the wiping speed, wiping pressure, and number of wiping operations as conditions for strong maintenance, causing the cleaning unit 60 to perform a strong wiping operation. Alternatively, the control unit 40 may send a control signal to the head control unit 241 to eject ink from only the second-type defective nozzles at the ejection pressure for strong maintenance, causing the head control unit 241 to perform a strong purge operation for the second-type defective nozzles. Alternatively, the control unit 40 may perform a strong purge operation for the first-type defective nozzles and the second-type defective nozzles. Alternatively, the control unit 40 may perform a strong purge operation for all nozzles N. Alternatively, the control unit 40 may cause the operation display unit 53 to display a notification message urging the user to perform heavy maintenance manually, so that heavy maintenance is performed manually.

[0101] On the other hand, if the control unit 40 determines that the ratio RT2 is less than the second reference value ("NO" in step S307), the control unit 40 determines whether the ratio RT1 is equal to or greater than the first reference value (step S309). If the control unit 40 determines that the ratio RT1 is equal to or greater than the first reference value ("YES" in step S309), the control unit 40 executes standard maintenance (step S310). For example, the control unit 40 sends a control signal to the cleaning unit 60 specifying the wiping speed, wiping pressure, and number of wipes as predetermined standard maintenance conditions, causing the cleaning unit 60 to perform a standard wiping operation. Alternatively, the control unit 40 may send a control signal to the head control unit 241 to eject ink from only the first-type defective nozzles at the ejection pressure for normal maintenance, causing the head control unit 241 to perform a normal purge operation on the first-type defective nozzles. Alternatively, the control unit 40 may perform a normal purge operation on only the first-type defective nozzles and the second-type defective nozzles. Alternatively, the control unit 40 may cause all the nozzles N to undergo the normal purge operation.

[0102] If the control unit 40 determines that the ratio RT1 is less than the first reference value ("NO" in step S309), the control unit 40 shifts the process to step S311 without performing maintenance. The control unit 40 also shifts the process to step S311 when the maintenance in step S308 or S310 is completed. In step S311, the control unit 40 determines whether the printing operation by the inkjet recording apparatus 1 has been completed. If the control unit 40 determines that the printing operation has not been completed ("NO" in step S311), the control unit 40 returns the process to step S301. If the control unit 40 determines that the printing operation has been completed ("YES" in step S311), the control unit 40 terminates the maintenance process.

[0103] (Variation) Next, a modified example of the above embodiment will be described. This modified example differs from the above embodiment in the method of determining whether maintenance is necessary and the type of maintenance to be performed (strong maintenance or normal maintenance), but is otherwise similar to the above embodiment. The differences from the above embodiment will be described below.

[0104] In this modified example, instead of using the rate RT1 of type 1 defective nozzles or the rate RT2 of type 2 defective nozzles, the average value of the speed increase rates vu / vi of all nozzles N (hereinafter referred to as the "average speed increase rate vuav / vi"). More specifically, if the average speed increase rate vuav / vi is within a predetermined judgment range, normal maintenance is performed, and if the average speed increase rate vuav / vi is below the lower limit of the judgment range, maintenance is not performed. Furthermore, if the average speed increase rate vuav / vi is greater than the predetermined judgment range, strong maintenance is performed.

[0105] The lower limit of the determination range in this modified example can be vu / vi(min) (for example, "1.1"), as in the above embodiment. The upper limit of the determination range in this modified example is a value smaller than vu / vi(max) in the above embodiment. This takes into consideration that the average velocity increase rate vuav / vi is pushed down by the large number of normal nozzles included in the total nozzles N. For example, the upper limit of the determination range in this modified example may be the intermediate value (1.2) between vu / vi(min) (1.1) and vu / vi(max) (1.3) in the above embodiment.

[0106] Figure 21 is a diagram showing the effect of performing maintenance using the method of the modified example, in comparison with a reference example. Examples 1 to 4 in Figure 21 are cases in which maintenance was performed according to the method of this modified example on an inkjet head 242 that had undergone head deterioration processing. Comparative Examples 1 and 2 are cases in which maintenance was performed using a method that does not follow the method of this modified example on an inkjet head 242 that had undergone the same head deterioration processing. The experiment in Figure 21 was conducted under the following conditions. Ink viscosity: 5 cps at 80°C Head deterioration treatment: Printing up to 100,000 test images with a print rate of 3% in an environment with an ozone concentration of 1 ppm. Inkjet heads 242 with different numbers of prints were used in the experiments of each example and reference example. Lower limit of the average velocity increase rate vuav / vi (vu / vi(min))...1.1 Upper limit of the range for determining the average velocity increase rate vuav / vi (vu / vi(max))...1.2 Strong wiping operation: The wiping pressure is twice as high as in normal wiping operation, and the number of wipes is twice as long.

[0107] The experimental method was as follows. The speed vu of the inkjet head 242 after the head deterioration treatment was measured, and the average speed increase rate vuav / vi was calculated. Maintenance was then performed using the maintenance method shown in Figure 21. The defective nozzle ratio Rb before maintenance and the defective nozzle ratio Ra after maintenance were calculated, and the change (Ra / Rb) was calculated. If Ra / Rb was 0.5 or less, i.e., if the number of defective nozzles was reduced by half, the effect of the maintenance was deemed "OK." If Ra / Rb was greater than 0.5, i.e., if the number of defective nozzles was not reduced by half, the effect of the maintenance was deemed "NG."

[0108] Reference Example 1 is an experiment in which normal wiping operation was performed when the average speed increase rate vuav / vi was 1.07, that is, below the lower limit of the judgment range. In this experiment, the number of defective nozzles was originally low at 4%, so the number of defective nozzles was not effectively reduced and the maintenance effect was NG. Example 1 is an experiment in which a normal wiping operation was performed when the average speed increase rate vuav / vi was 1.12, that is, within the judgment range. In this experiment, the number of defective nozzles was reduced by half, and the maintenance effect was deemed acceptable. Example 2 is an experiment in which a normal wiping operation was performed when the average speed increase rate vuav / vi was 1.20, that is, within the judgment range. In this experiment, the number of defective nozzles was reduced by half, and the maintenance effect was found to be OK. Reference Example 2 is an experiment in which normal wiping operation was performed when the average speed increase rate vuav / vi was 1.27, i.e., greater than the upper limit of the judgment range. In this experiment, the number of defective nozzles was not reduced by half, and the maintenance effect was found to be NG. In Examples 3 and 4, the strong wiping operation and the strong purging operation were performed when the average velocity increase rate vuav / vi was 1.27, i.e., greater than the upper limit of the judgment range. In both of these experiments, the number of defective nozzles was reduced by half, and the maintenance effect was deemed acceptable.

[0109] (effect) As described above, in the maintenance method for the inkjet recording apparatus 1 according to this embodiment, a measurement value of the velocity of ink ejected from each of the multiple nozzles N is acquired. Furthermore, the necessity of performing maintenance to remove foreign matter F from the multiple nozzles N of the inkjet head 242 is determined based on the velocity increase rate vu / vi of the velocity vu of each nozzle N relative to the standard value vi. Because the ink velocity vu and velocity increase rate vu / vi are positively correlated with the amount of foreign matter F adhering to the nozzle N, the above method allows maintenance to be performed to remove foreign matter F at an appropriate timing when the amount of foreign matter F adhering to the nozzle N has increased in a predetermined manner. This prevents unnecessary maintenance from being performed when there is no foreign matter adhering that could lead to poor image quality. It also prevents ineffective maintenance from being performed on defective nozzles that are not caused by foreign matter F. This prevents unnecessary reductions in the operating efficiency of the inkjet recording apparatus 1 and unnecessary consumption of ink for maintenance. Furthermore, because maintenance can be performed at the appropriate timing, it prevents problems such as the foreign matter F being left adhering for a long period of time, which causes the foreign matter to adhere and progress, making it difficult to remove. These features can extend the product life of the inkjet head 242. In other words, the state of the inkjet head 242 can be appropriately monitored, and maintenance can be performed at the appropriate time when necessary.

[0110] Furthermore, in the above maintenance method, normal maintenance is performed when, among the multiple nozzles N, the proportion RT1 of first-type defective nozzles whose speed increase rate vu / vi falls within a predetermined judgment range is equal to or greater than a first reference value. Furthermore, maintenance is not performed when the proportion RT1 of first-type defective nozzles is less than the first reference value. This allows normal maintenance to be performed at an appropriate time when the proportion RT1 of first-type defective nozzles from which foreign matter F can be effectively removed by normal maintenance has increased to or above the predetermined proportion RT1. Furthermore, unnecessary maintenance is prevented from being performed when the proportion RT1 of first-type defective nozzles has not yet reached the predetermined proportion RT1.

[0111] Furthermore, in the above maintenance method, when the proportion RT2 of second-type defective nozzles among the multiple nozzles N, whose speed increase rate vu / vi is greater than the upper limit of the judgment range, is equal to or greater than a second reference value, strong maintenance, which is more effective at removing foreign matter F than normal maintenance, is performed. Furthermore, when the proportion RT2 of second-type defective nozzles among the multiple nozzles N is less than the second reference value and the proportion RT1 of first-type defective nozzles is equal to or greater than the first reference value, normal maintenance is performed. This allows strong maintenance that can remove foreign matter F from second-type defective nozzles when the proportion RT2 or greater of second-type defective nozzles, from which foreign matter F cannot be effectively removed by normal maintenance, is increased. Furthermore, it is possible to avoid unnecessarily strong maintenance when the proportion RT2 of second-type defective nozzles has not yet been reached. Therefore, appropriate maintenance can be selected and performed according to the condition and number of defective nozzles.

[0112] Furthermore, the lower limit of the judgment range is set to be equal to or less than the maximum value of the speed increase rate vu / vi for normal nozzles that does not cause poor image quality. This means that even if the speed increase rate vu / vi increases within a range that does not cause poor image quality, the nozzle will not be judged to be faulty, making it possible to more appropriately prevent unnecessary maintenance from being performed.

[0113] Furthermore, the ratio of the ink velocity vu after normal maintenance to the ink velocity vu before normal maintenance is performed is defined as the velocity reduction rate. In this case, the velocity reduction rate is approximately constant around 1 in the range in which the velocity increase rate vu / vi before normal maintenance is performed is equal to or greater than the second value m2. Furthermore, the upper limit of the determination range is set within the range equal to or less than the second value m2. This makes it possible to set the upper limit of the determination range so that normal maintenance is effective. Furthermore, it is possible to appropriately classify first-type faulty nozzles and second-type faulty nozzles.

[0114] In a modified example, an average speed increase rate vuav / vi, which is the average value of the speed increase rates vu / vi of multiple nozzles N, is calculated based on the acquired speed vu of each nozzle N. If the average speed increase rate vuav / vi is within a predetermined judgment range, normal maintenance is performed, and if the average speed increase rate vuav / vi is below the lower limit of the judgment range, maintenance is not performed. This method also makes it possible to perform maintenance at an appropriate time. Furthermore, the average speed increase rate vuav / vi, which is an index for determining whether maintenance is required and the type of maintenance, can be calculated by the simple process of averaging the speed increase rates vu / vi for all nozzles N.

[0115] In addition, in a modified example, strong maintenance is performed when the average speed increase rate vuav / vi is greater than the upper limit of the judgment range. This makes it possible to select and perform appropriate maintenance depending on the state and number of defective nozzles.

[0116] The standard value vi is the average value of the speed of ink ejected from the multiple nozzles N of the inkjet head 242 in the initial state. This makes it possible to set an appropriate standard value vi based on the actual speed of ink from normal nozzles.

[0117] Furthermore, in the above maintenance method, a measured value of the velocity vu of each of the multiple nozzles N is calculated based on the formation position of the measurement dots in the transport direction. The measurement dots are formed on the recording medium M by ejecting ink from the multiple nozzles N at the same timing onto the recording medium M, which is transported in a transport direction perpendicular to the arrangement direction of the multiple nozzles N. This makes it possible to measure the ink velocity vu in a simple manner without providing any additional equipment to the inkjet recording apparatus 1.

[0118] Furthermore, in the above maintenance method, a measurement value of the velocity vu is calculated based on a first formation position (position P2 in FIG. 15) in the transport direction of a first measurement dot 71 formed on a recording medium M transported at a first transport speed V1 and a second formation position (position P2 in FIG. 17) in the transport direction of a second measurement dot 72 formed on a recording medium M transported at a second transport speed V2. Furthermore, when the distance in the transport direction between position P1 on the recording medium M that faced the nozzle N when the ink was ejected and the first formation position (position P2 in FIG. 15) is D1, the distance in the transport direction between position P1 on the recording medium M that faced the nozzle N when the ink was ejected and the second formation position (position P2 in FIG. 17) is D2, the deviation angle of the ink ejection direction in the transport direction from the direction perpendicular to the recording medium M is θ, and the distance from the nozzle N to the recording medium M is d, the measurement value of the velocity vu is calculated based on the following two relational expressions: D1=V1·d / vu-d·tanθ D2=V2·d / vu-d·tanθ This makes it possible to calculate the measured value of the ink velocity vu using a simple method for measuring the formation positions of the first measurement dot 71 and the second measurement dot 72 on the recording medium M.

[0119] Furthermore, the normal maintenance includes at least one of a normal purging operation and a normal wiping operation, which makes it possible to effectively remove foreign matter F from the first type defective nozzles.

[0120] Furthermore, the strong maintenance includes at least one of a strong purge operation and a strong wiping operation, which allows foreign matter F to be effectively removed from second-class defective nozzles. Furthermore, by changing the settings of the normal maintenance for the strong maintenance, it is possible to perform both the normal maintenance and the strong maintenance using a common cleaning unit 60.

[0121] Furthermore, in the normal purge operation, ink may be ejected only from nozzles N of the plurality of nozzles N whose velocity increase rate vu / vi is equal to or greater than the lower limit of the determination range, thereby reducing the amount of ink consumed in the purge operation.

[0122] Furthermore, in the above maintenance method, a measurement value of the velocity vu for each of the multiple nozzles N is obtained at a predetermined timing. The predetermined timing is either the timing after printing on a predetermined number of recording media M using the inkjet head 242, or the timing when printing work by the inkjet recording apparatus 1 is completed. This makes it possible to measure the ink velocity vu at an appropriate timing, neither too much nor too little.

[0123] The inkjet recording apparatus 1 according to this embodiment also includes an inkjet head 242 having a plurality of nozzles N, and a control unit 40. The control unit 40 acquires a measurement value of the velocity of ink ejected from each of the plurality of nozzles N. The control unit 40 also determines whether or not maintenance is required to remove foreign matter F from the plurality of nozzles N of the inkjet head 242, based on the velocity increase rate vu / vi of the velocity vu of each nozzle N relative to a standard value vi. This allows maintenance to be performed to remove foreign matter F at an appropriate timing when the amount of adhesion of foreign matter F has increased in a predetermined manner.

[0124] Furthermore, the program 431 according to this embodiment causes the control unit 40 of the inkjet recording apparatus 1, which is equipped with an inkjet head 242 having a plurality of nozzles N, to function as control means. The control means acquires a measurement value of the velocity of ink ejected from each of the plurality of nozzles N. The control means also determines whether or not maintenance to remove foreign matter F from the plurality of nozzles N of the inkjet head 242 is required, based on the velocity increase rate vu / vi of the velocity vu of each nozzle N relative to a standard value vi. This allows maintenance to be performed to remove foreign matter F at an appropriate timing when the amount of adhesion of foreign matter F has increased in a predetermined manner.

[0125] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in the above embodiment, one example of a method for determining whether or not maintenance is necessary and the type of maintenance based on the ink velocity vu is shown, but the present invention is not limited to this. Any method can be used as long as it determines upper and lower limit values ​​for an evaluation value corresponding to the ink velocity vu, and performs normal maintenance when the evaluation value calculated using an actual inkjet head exceeds the lower limit value, and performs strong maintenance when the evaluation value exceeds the upper limit value.

[0126] Furthermore, in the above embodiment, the recording medium M on which the first measurement dots 71 and the second measurement dots 72 are formed is photographed by the imaging unit 26, and the control unit 40 analyzes the photographed data to calculate the measured value of the velocity vu, but this method is not limited to this. For example, the analysis of the photographed data may be performed by a device external to the inkjet recording apparatus 1. Furthermore, the measured value of the velocity vu may be calculated manually using the recording medium M on which the first measurement dots 71 and the second measurement dots 72 are formed.

[0127] Furthermore, the contents of the normal maintenance as the first maintenance and the strong maintenance as the second maintenance are not limited to those exemplified in the above embodiment. The normal maintenance and the strong maintenance can be any method as long as they are effective in removing foreign matter from the nozzle N and the foreign matter removal effect of the strong maintenance is greater than that of the normal maintenance.

[0128] Furthermore, the method for measuring the velocity vu is not limited to the method using the formation positions of the first measurement dot 71 and the second measurement dot 72. For example, if the deviation angle θ of the ejection direction can be ignored, the measurement value of the velocity vu may be calculated using only the first measurement dot 71 according to equation (1) where θ = 0. Furthermore, the velocity vu may be measured directly by an optical method such as taking multiple strobe images of the ink from the time it is ejected from the nozzle N until it hits the ink.

[0129] In the above embodiment, the recording medium M is transported by the transport drum 211, but this is not intended to be limiting. For example, the recording medium M may be transported by a transport belt that is supported by two or more rollers and moves in accordance with the rotation of the rollers.

[0130] Furthermore, in the above embodiment, the inkjet recording apparatus 1 of a single pass type has been described as an example, but the present invention may also be applied to an inkjet recording apparatus that records an image while scanning the recording head.

[0131] In the above embodiment, the inkjet recording apparatus 1 is described as an example in which ink that is in a gel state at room temperature and turns into a sol state when heated is heated to a sol state and then ejected, but the present invention is not limited to this, and ink that is in a sol state or liquid state at room temperature may also be used. Ink that does not have the property of being cured by energy rays such as ultraviolet rays may also be used.

[0132] In the above embodiment, the inkjet recording device 1 is a piezoelectric type that uses a piezoelectric element, but the present invention is not limited to this. For example, a thermal type inkjet recording device that generates bubbles in ink by heating and ejects the ink may be used.

[0133] Although several embodiments of the present invention have been described, the scope of the present invention is not limited to the above-described embodiments, but includes the scope of the invention described in the claims and its equivalents. [Explanation of symbols]

[0134] 1. Inkjet recording device 10 Paper feed section 20 Image forming unit 21 Conveyor 211 Transport drum 24 Head Unit 242 Inkjet head 242a Nozzle surface 26 Imaging unit 29 Media Sensor 40 Control unit (control means, computer) 60 Cleaning Section 71 First measuring dot 72 Second measuring dot F Foreign object M Recording medium N nozzle

Claims

1. A maintenance method for an inkjet recording apparatus equipped with an inkjet head having a plurality of nozzles, comprising: obtaining, for each of the plurality of nozzles, a measurement of the velocity of ink ejected from each nozzle; A maintenance method for an inkjet recording device, which determines whether or not maintenance is required to remove foreign matter from the multiple nozzles of the inkjet head, based on an increase rate vu / vi of the ink velocity vu of each nozzle relative to the standard value vi, where vu is the ink velocity of each nozzle obtained and vi is a predetermined standard value of the ink velocity.

2. performing a first maintenance when a ratio of first-type defective nozzles, the ratio of which is within a predetermined judgment range among the plurality of nozzles, is equal to or greater than a first reference value; If the ratio of the first type defective nozzles is less than the first reference value, the maintenance is not performed. A maintenance method for the inkjet recording apparatus according to claim 1.

3. when a proportion of second-type defective nozzles, in which the increase rate vu / vi is greater than the upper limit of the determination range, among the plurality of nozzles is equal to or greater than a second reference value, performing a second maintenance operation that is more effective at removing foreign matter than the first maintenance operation; performing the first maintenance when the proportion of the second type defective nozzles among the plurality of nozzles is less than the second reference value and the proportion of the first type defective nozzles is equal to or greater than the first reference value; The maintenance method for the inkjet recording apparatus according to claim 2 .

4. the lower limit of the determination range is set to be equal to or less than the maximum value of the increase rate vu / vi of normal nozzles that does not cause poor image quality; The maintenance method for the inkjet recording apparatus according to claim 2 .

5. when a ratio of the ink velocity vu after the first maintenance is performed to the ink velocity vu before the first maintenance is performed is defined as a velocity reduction rate, the velocity reduction rate is approximately constant within a range in which the increase rate vu / vi before the first maintenance is performed is equal to or greater than a predetermined value, The upper limit of the determination range is set within a range equal to or less than the predetermined value. The maintenance method for the inkjet recording apparatus according to claim 2 .

6. calculating an average value of the increase rates vu / vi of the plurality of nozzles based on the acquired velocity vu of each nozzle; When the average value of the increase rate vu / vi is within a predetermined determination range, the first maintenance is performed; When the average value of the increase rate vu / vi is less than the lower limit value of the determination range, the maintenance is not performed. A maintenance method for the inkjet recording apparatus according to claim 1.

7. When the average value of the increase rate vu / vi is greater than the upper limit value of the determination range, a second maintenance is performed, which has a higher effect of removing the foreign matter than the first maintenance. The maintenance method for the inkjet recording apparatus according to claim 6.

8. the standard value vi is an average value of the velocity of ink ejected from the plurality of nozzles of the inkjet head in an initial state; A maintenance method for the inkjet recording apparatus according to claim 1.

9. calculating the measured value of the velocity vu of each of the plurality of nozzles based on the formation positions in the transport direction of measurement dots formed on the recording medium by ejecting ink from the plurality of nozzles at the same timing with respect to the recording medium being transported in a transport direction perpendicular to the arrangement direction of the plurality of nozzles; A maintenance method for the inkjet recording apparatus according to claim 1.

10. calculating the measurement value of the speed vu based on a first formation position in the transport direction of a first measurement dot formed on a recording medium transported at a first transport speed and a second formation position in the transport direction of a second measurement dot formed on a recording medium transported at a second transport speed different from the first transport speed; The first conveying speed is V 1 , the second conveying speed is V 2 The distance in the transport direction between the position on the recording medium that faced the nozzle when the ink was ejected and the first formation position is D 1 The distance in the transport direction between the position on the recording medium that faced the nozzle when the ink was ejected and the second formation position is D 2 When the deviation angle of the ink ejection direction from the direction perpendicular to the recording medium to the transport direction is θ and the distance from the nozzle to the recording medium is d, two relational expressions are satisfied: D 1 =V 1 ・d / vu-d・tanθ D 2 =V 2 ・d / vu-d・tanθ calculating the measured value of the velocity vu based on The maintenance method for the inkjet recording apparatus according to claim 9.

11. the first maintenance includes at least one of a first purge operation in which ink is ejected from at least the first-type defective nozzles among the plurality of nozzles, and a first wiping operation in which a wiping member is used by a predetermined cleaning unit to wipe a nozzle surface 242 a on which the plurality of nozzles of the inkjet head are provided; The maintenance method for the inkjet recording apparatus according to claim 2 .

12. the first maintenance includes at least one of a first purge operation that ejects ink from at least the first-type defective nozzles among the plurality of nozzles, and a first wiping operation that wipes a nozzle surface 242 a on which the plurality of nozzles of the inkjet head are provided with a wiping member by a predetermined cleaning unit; The second maintenance includes at least one of a second purge operation in which ink is ejected from at least the second-type defective nozzles among the plurality of nozzles at a pressure stronger than that of the first purge operation, and a second wiping operation in which the nozzle surface 242a is wiped by the cleaning unit or by hand with the wiping member at a pressure stronger than that of the first wiping operation or for a longer period of time than that of the first wiping operation. The maintenance method for the inkjet recording apparatus according to claim 3.

13. In the first purge operation, ink is ejected only from nozzles among the plurality of nozzles whose increase rate vu / vi is equal to or greater than a lower limit value of the determination range.

13. A maintenance method for an inkjet recording apparatus according to claim 11 or 12.

14. obtaining the measured value of the velocity vu for each of the plurality of nozzles measured at a predetermined timing; the predetermined timing is either a timing when printing is performed on a predetermined number of recording media using the inkjet head, or a timing when printing work by the inkjet recording device is completed. A maintenance method for the inkjet recording apparatus according to claim 1.

15. an inkjet head having a plurality of nozzles; A control unit; Equipped with The control unit obtaining, for each of the plurality of nozzles, a measurement of the velocity of ink ejected from each nozzle; an inkjet recording apparatus that determines whether or not maintenance is required to remove foreign matter from the multiple nozzles of the inkjet head, based on an increase rate vu / vi of the ink velocity vu of each nozzle relative to the standard value vi, where vu is the ink velocity of the acquired nozzles and vi is a predetermined standard value of the ink velocity.

16. a computer of an inkjet recording apparatus having an inkjet head with a plurality of nozzles is caused to function as a control means; The control means obtaining, for each of the plurality of nozzles, a measurement of the velocity of ink ejected from each nozzle; A program that determines whether or not maintenance is required to remove foreign matter from the multiple nozzles of the inkjet head, based on the increase rate vu / vi of the ink velocity vu of each nozzle relative to the standard value vi, where vu is the ink velocity of each nozzle obtained and vi is a predetermined standard value of the ink velocity.

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