EP3318405A1 - Inkjet recording apparatus - Google Patents

Abstract

Provided is an inkjet recording apparatus capable of more efficiently managing defective nozzles. The inkjet recording apparatus includes: a recording unit having a plurality of nozzles that discharge ink; a first storage unit for storing first defective nozzle information for an initially defective nozzle that occurs due to initial failure of the record - ing unit, the initially defective nozzle being a defective nozzle, among the plurality of nozzles, which discharges ink abnormally; and a second storage unit for storing second defective nozzle information for a later-occurring defective nozzle, among defective nozzles, which is not specified as the initially defective nozzle by the first defective nozzle information.

Description

Technological Field
• The present invention relates to an inkjet recording apparatus.
Background Art
• There has been an inkjet recording apparatus that ejects ink from nozzles of a recorder(s) to a recording medium, thereby recording images on the recording medium. In this type of inkjet recording apparatus, nozzles may include nozzles being poor in ejection (defective nozzles) from which no ink is ejected, ink is ejected in a wrong amount, or ink is ejected in a wrong direction (described, for example, in Patent Document 1).
• These defective nozzles lead to decrease in image quality of recorded images. There has been a technique for returning defective nozzles to their normal state by ejecting ink from nozzles to detect defective nozzles, and when detecting defective nozzles, performing maintenance operation, such as pressure purge of pressuring ink to forcibly eject ink from nozzles or wiping of wiping the nozzle surface(s) of recording heads to remove foreign substances and dirt thereon. If there are many defective nozzles that are not brought back to the normal state by the maintenance operation, it is determined that the recorder(s) degrades, and the recorder(s) is replaced.
Related Art Documents Patent Documents
• Patent Document 1: Japanese Patent Application Publication No. 2005-7613
Summary of the Invention Problems to be Solved by the Invention
• However, defective nozzles may include initial defective nozzles due to initial failure of a recorder. Usually, these initial defective nozzles are not brought back to the normal state by the maintenance operation described above. Hence, if, for these initial defective nozzles, maintenance operation or replacement of the recorder is performed as with for nozzles that later become defective, for example, by the nozzles being clogged or by openings of the nozzles being covered with dirt or the like as a result of use of the recorder, efficiency of management of defective nozzles decreases, which is a problem.
• An object of the present invention is providing an inkjet recording apparatus that can manage defective nozzles more efficiently.
Means for Solving the Problems
• In order to achieve the above object, the invention of an inkjet recording apparatus described in claim 1 is an inkjet recording apparatus including:
• a recorder provided with nozzles that eject an ink;
• a first storage in which first defective nozzle information on, among the nozzles, an initial defective nozzle that (i) is a defective nozzle among defective nozzles which do not eject the ink normally and (ii) is due to initial failure of the recorder is stored; and
• a second storage in which second defective nozzle information on, among the defective nozzles, a later-becoming defective nozzle that is not identified as the initial defective nozzle by the first defective nozzle information is stored.
• The invention described in claim 2 is the inkjet recording apparatus according to claim 1, wherein
  the first storage is integrated with the recorder.
• The invention described in claim 3 is the inkjet recording apparatus according to claim 1 or 2, further including:
• a measurement unit that measures a physical quantity reflecting an ink ejection state of each of the nozzles; and
• a detector that detects the defective nozzles from a result of the measurement by the measurement unit, and stores, in the second storage, the second defective nozzle information based on a result of the detection of the defective nozzles.
• The invention described in claim 4 is the inkjet recording apparatus according to claim 3, wherein
  the detector detects the later-becoming defective nozzle by causing the measurement unit to measure the physical quantity reflecting the ink ejection state of, among the nozzles, a nozzle that is not identified as the initial defective nozzle by the first defective nozzle information.
• The invention described in claim 5 is the inkjet recording apparatus according to any one of claims 1 to 4, wherein
  the first defective nozzle information is information on the initial defective nozzle detected by an external inspection apparatus.
• The invention described in claim 6 is the inkjet recording apparatus according to claim 3 or 4, wherein
  the first defective nozzle information is information on the initial defective nozzle detected by an external inspection apparatus and is higher in detection accuracy than the detection by the detector from the result of the measurement by the measurement unit.
• The invention described in claim 7 is the inkjet recording apparatus according to any one of claims 1 to 6, further including:
• a recovery unit that performs a recovery operation to return, among the defective nozzles, a nozzle which is recoverable to a normal state in which the ink is ejected normally to the normal state; and
• a recovery controller that causes the recovery unit to start the recovery operation based on at least one of (i) a number of, among the nozzles, a nozzle and (ii) arrangement of the nozzle in the recorder, the nozzle being identified as the later-becoming defective nozzle by the second defective nozzle information.
• The invention described in claim 8 is the inkjet recording apparatus according to any one of claims 1 to 7, further including:
  a corrector that corrects, based on at least one of the first defective nozzle information and the second defective nozzle information, image data of an image to be recorded on a recording medium.
• The invention described in claim 9 is the inkjet recording apparatus according to claim 8, wherein
  the corrector corrects, based on the first defective nozzle information and the second defective nozzle information, the image data of the image to be recorded on the recording medium, and corrects, of the image data, a part for the initial defective nozzle identified by the first defective nozzle information and a part for the later-becoming defective nozzle identified by the second defective nozzle information based on respective algorithms that are different from each other.
• The invention described in claim 10 is the inkjet recording apparatus according to any one of claims 1 to 9, further including:
• a notification unit; and
• a notification controller that causes the notification unit to perform notification which encourages replacement of the recorder based on at least one of (i) a number of, among the nozzles, a nozzle and (ii) arrangement of the nozzle in the recorder, the nozzle being identified as the later-becoming defective nozzle by the second defective nozzle information.
Advantageous Effects of the Invention
• According to the present invention, there is an effect of being able to manage defective nozzles more efficiently.
Brief Description of the Drawings
• FIG. 1 is a schematic diagram showing configuration of an inkjet recording apparatus that is an embodiment(s) of the present invention.
• FIG. 2 is a block diagram showing main functional components of the inkjet recording apparatus.
• FIG. 3 is a schematic diagram showing configuration of cleaner rollers.
• FIG. 4 is a schematic diagram showing configuration of an inspection unit.
• FIG. 5 is a diagram to explain operation for detection of later-becoming defective nozzles.
• FIG. 6 is a flowchart of control procedure of an image recording process.
• FIG. 7 is a flowchart of control procedure of an image recording process according to a second modification.
Embodiments for Carrying out the Invention
• Hereinafter, one or more embodiments of an inkjet recording apparatus of the present invention are described on the basis of the drawings.
• FIG. 1 is a schematic diagram showing configuration of an inkjet recording apparatus 1 that is an embodiment(s) of the present invention.
• FIG. 2 is a block diagram showing main functional components of the inkjet recording apparatus 1.
• The inkjet recording apparatus 1 includes a conveyor 11, connectors 120, head units 12 (recorders), head unit elevators 13, a maintenance unit 14 (recovery unit), an inspection unit 15 (measurement unit), an operational display 16 (notification unit), an interface 17, a bus 18 and a controller 20.
• The conveyor 11 includes an annular conveyor belt 113, the inner side of which is supported by two conveyor rollers 111 and 112 that rotate on their rotational axes extending in X direction in FIG. 1. The conveyor 11 conveys a recording medium M in the moving direction of the conveyor belt 113 (conveying direction; Y direction in FIG. 1) by rotating the conveyor rollers 111 and 112 with a not-shown motor and accordingly moving the conveyor belt 113 in the state in which the recording medium M is placed on the conveyance surface of the conveyor belt 113. The recording medium M is drawn from a roller around which the recording medium M is wound and supplied onto the conveyor belt 113, and wound around another roller after images are recorded on the recording medium M. The recording medium M may be flat paper that is cut into sheets of a certain size. In this case, the recording medium M is supplied onto the conveyor belt 113 by a sheer feeder, and ejected from the conveyor belt 113 to a certain sheet receiver by a sheet ejector after images are recorded on the recording medium M.
• As the recording medium M, a variety of media can be used as far as ink ejected onto the surfaces thereof can be fixed. Examples thereof include paper, fabrics and sheet-shaped resins.
• The head units 12 eject, on the basis of image data, ink from nozzles to the recording medium M that is conveyed by the conveyor 11, thereby recording images on the recording medium M. In the inkjet recording apparatus 1 of this embodiment, as shown in FIG. 1, four head units 12 for four color inks of yellow (Y), magenta (M), cyan (C) and black (K) are arranged at predetermined intervals to line up in order of Y, M, C and K from the upstream side in the conveying direction of the recording medium M.
• Each head unit 12 includes: a plurality (seven in this embodiment) of recording heads 122 in each of which recording elements are arranged in a direction crossing the conveying direction (in this embodiment, a direction at right angles to the conveying direction, i.e. X direction) of the recording medium M; and a recording head drive unit 121 that drives the recording heads 122. Further, each head unit 12 is provided with a first storage 124 that is integrated with the head unit 12. The head units 12 perform recording operation(s) in the state of being attached to the connectors 120. The connectors 120 send/receive data to/from the head units 12 from/to the controller 20. Four connectors 120 are provided to correspond to the four head units 12.
• Each recording element included in each recording head 122 includes: a pressure chamber where ink is stored; a piezoelectric element disposed on the wall surface of the pressure chamber; and a nozzle. When the recording head drive unit 121 applies, to the piezoelectric elements, a voltage(s) signal having a drive waveform(s) to operate and transform the piezoelectric elements, the pressure in the pressure chambers changes in response to the voltage signal, and the ink is ejected from the nozzles that communicate with the pressure chambers.
• The array of the recording elements, which are included in each head unit 12, in X direction covers the width in X direction of the image recordable region of the recording medium M, which is conveyed by the conveyor 11. At the time of recording images, the head units 12 are used with their positions fixed with respect to the conveyor 11. That is, the inkjet recording apparatus 1 is an inkjet recording apparatus 1 employing a single-pass system.
• In a head unit(s) 12, some nozzles may be defective nozzles which do not eject ink normally from the time of manufacturing the head unit 12 due to variation in processing in forming nozzles, variation in characteristics of piezoelectric elements, and so forth. Further, some nozzles may later become defective nozzles by the nozzles being clogged or by openings of the nozzles being covered with dirt or the like as a result of use of the head unit(s) 12 in the inkjet recording apparatus 1.
• In this embodiment, as the head units 12, those subjected to detection of defective nozzles (initial defective nozzles) due to initial failure after manufactured are used. Further, in this embodiment, defective nozzles detected later than initial detective nozzles are referred to as later-becoming defective nozzles.
• Initial defective nozzles are detected by an external inspection apparatus (different from the inkjet recording apparatus 1). For example, ink (or liquid droplets for inspection) is ejected from the nozzles of the head units 12, and the inspection apparatus captures the ejected ink from the side of the ink ejection direction and determines the ink ejection state. The inspection apparatus determines that no ink is ejected when no ink is detected in the captured data, determines that the ink ejection direction is abnormal when the ink ejection direction is bent in the captured data, and determines that the ink ejection amount is abnormal when the ink flying speed is not normal in the captured data, and detects nozzles determined as the above as initial defective nozzles. The "the ink ejection direction is bent" means that ink is ejected in a direction angled from its original ejection direction. As the inspection apparatus that detects initial defective nozzles, an apparatus that can detect initial defective nozzles having abnormalities that are difficult to be detected from the below-described measurement results obtained by the inspection unit 15 is used. For example, an apparatus that can detect slight bending of the ink ejection direction, degree of the bending and degree of abnormality of the ink ejection amount is used.
• Each recording head drive unit 121 has: a drive circuit that supplies, to the recording heads 122, a voltage signal(s) having a drive waveform(s) corresponding to image data; and a drive control circuit that supplies the image data to the drive circuit at an appropriate timing. The recording head drive units 121 cause the recording heads 122 to eject inks on the basis of control signals and image data supplied from the CPU 21. More specifically, when the CPU 21 supplies a control signal and image data to a recording head drive unit 121, the drive control circuit of the recording head drive unit 121 causes the drive circuit thereof to output a voltage signal(s) having a drive waveform(s) to the piezoelectric elements of the recording elements of the recording heads 122, thereby causing the recording heads 122 to perform (i) ejection operation of ejecting ink in an ink amount(s) corresponding to a gradation value(s) of the image data from the nozzles of the recording elements or (ii) non-ejection operation of ejecting no ink if (ii-a) the image data correspond to no ejection of ink or (ii-b) it is between image recording operations.
• Each first storage 124 is constituted of a nonvolatile memory, such as a flash memory or an EEPROM (Electrically Erasable Programmable Read Only Memory), and stores therein initial defective nozzle data D1 (first defective nozzle information) on initial defective nozzles described above. In the initial defective nozzle data D1, initial defective nozzles are identified by arrangement numbers of the nozzles in the head unit 12. Further, in the initial defective nozzle data D1, the degree of bending of the ink ejection direction and the degree of abnormality of the ink ejection amount (a variation from a normal amount) of each initial defective nozzle are indicated. Each first storage 124 may be constituted of a ROM (Read Only Memory).
• Each head unit elevator 13 moves, according to the operation of a motor, a not-shown attachment member to which the head unit 12 is attached in a direction perpendicular to the conveyance surface of the conveyor belt 113 (Z direction in FIG. 1), thereby moving up and down the head unit 12 in Z direction. Four head unit elevators 13 are provided to correspond to the four head units 12.
• The maintenance unit 14 performs maintenance operation(s) (recovery operation(s)) to return, among defective nozzles in the head units 12, nozzles that can be brought back to the normal state in which ink is ejected normally to the normal state. This maintenance operation includes: pressure purge of forcibly ejecting ink from the nozzles of the head units 12 to solve clogging of the nozzles; and wiping of wiping the nozzle surfaces, where the nozzles are formed, of the head units 12 to clean the nozzle surfaces.
• The maintenance unit 14 has a not-shown pressure pump(s) that, when pressure purge is performed, pressurizes ink at a predetermined pressurizing position in an ink supply channel that communicates with the pressure chambers of the recording elements.
• The maintenance unit also has cleaner rollers with which the nozzle surfaces are wiped.
• FIG. 3 is a schematic diagram showing configuration of cleaner rollers 141.
• Wiping cloths impregnated with a predetermined medical fluid are wound around the outer circumferential surfaces of the cleaner rollers 141, and the cleaner rollers 141 are arranged such that their rotation axis is parallel to Y direction. The maintenance unit 14 has a not-shown rotation motor(s) and a not-shown conveyance motor(s). The cleaner rollers 141 rotate according to the operation of the rotation motor, and move in Z direction and X direction according to the operation of the conveyance motor. When the above wiping is performed, the cleaner rollers 141 abut the nozzle surfaces of the head units 12 by being moved in Z direction by the operation of the conveyance motor, and wipe the nozzle surfaces of the head units 12 with themselves by, while rotating in this state according to the operation of the rotation motor, moving in X direction according to the operation of the conveyance motor. Four cleaner rollers 141 are provided to correspond to the four head units 12.
• The inspection unit 15 performs predetermined measurement operation(s) to inspect the ink ejection state of each nozzle.
• FIG. 4 is a schematic diagram showing configuration of the inspection unit 15.
• The inspection unit 15 includes a light emitter 151, a light receiver 152, a moving unit 153, a moving belt 154, rollers 155a and 155b, a motor 156 and a linear encoder 157. The inspection unit 15 emits light with the light emitter 151 to the ink flying course from the nozzles, and measures the light amount of the light with the light receiver 152. The ink ejection state of each nozzle is inspected by determining whether the measured light amount is decreased by ink at a proper position for the nozzle. The inspection unit 15 performs measurement operation, as shown in FIG. 4 as an example, on the head unit 12 moved to the more positive side in Z direction by the head unit elevator 13 than the position where the head unit 12 performs recording operation. Alternatively, the measurement operation may be performed on the head unit 12 moved to the position of the inspection unit 15.
• The light emitter 151 outputs light (here, visible light) in the optical axis L direction. The light receiver 152 detects the light output from the light emitter 151. The light output from the light emitter 151 has directionality. If no light-blocking matter, namely, ink, is present between the light emitter 151 and the light receiver 152, the light receiver 152 detects most of the output light. Meanwhile, the light receiver 152 is determined in such a way as to be narrow within the range in which the dimming amount when the ink to be detected enters the light receiving area is equal to or more than a detectable rate with respect to the total incident light amount, and be wide within the range in which the position of the ink is not outside the light receiving area even when displacement due to mounting accuracy of the inspection unit 15 or rotation accuracy of the motor 156 occurs.
• The moving unit 153 is a plate-like member, and the light emitter 151 and the light receiver 152 are fixed onto the surface of the plate-like member. One end of the moving unit 153 is fixed to the moving belt 154.
• The moving belt 154 is annular, and rotationally driven by the rollers 155a and 155b that are disposed on the inner circumferential surface. By being rotationally driven, the moving belt 154 moves the moving unit 153 in X direction.
• The motor 156 rotates the roller 155a. The rotation speed of the motor 156 can be appropriately changed on the basis of a control signal from the controller 20.
• The linear encoder 157 outputs signals that indicate movements of the moving unit 153. The linear encoder 157 is not particularly limited to but includes, for example, one employing a system of reading the scale with an optical sensor.
• The operational display 16 includes: a display, such as a liquid crystal display or an organic EL display; and an inputter, such as operation keys or a touch panel disposed on the screen of the display. The operational display 16 displays a variety of pieces of information on the display, and converts input operations of a user(s) on the inputter into operation signals and outputs the operation signals to the controller 20.
• The interface 17 sends/receives data to/from an external apparatus 2, and is constituted of, for example, one or a combination of a variety of serial interfaces and a variety of parallel interfaces.
• The bus 18 is a channel to send/receive signals to/from the controller 20 from/to the other components.
• The controller 20 includes a CPU 21 (Central Processing Unit) (detector, recovery controller, corrector, notification controller), a RAM 22 (Random Access Memory), a ROM 23 and a second storage 24.
• The CPU 21 reads programs for various types of control and setting data stored in the ROM 23, stores the read ones in the RAM 22, and executes the programs and thereby performs various types of arithmetic processing. Thus, the CPU 21 controls the entire operation of the inkjet recording apparatus 1. For example, the CPU 21 causes the head units 12 to eject inks from the nozzles to the recording medium M on the basis of image data stored in the second storage 24 while causing the conveyor 11 to convey the recording medium M, thereby recording images on the recording medium M.
• The RAM 22 provides a memory space for work for the CPU 21 and temporarily stores data therein. The RAM 22 stores therein a maintenance-done flag(s) that is used to determine whether maintenance operation has been performed. The maintenance-done flag is binary data indicated in a single bit. The RAM 22 may contain a nonvolatile memory.
• The ROM 23 stores therein the programs for various types of control that are executed by the CPU 21, the setting data and so forth. The programs include, for example, a defective nozzle detection program to cause the inspection unit 15 to operate to detect defective nozzles, a maintenance program to cause the maintenance unit 14 to perform maintenance operation, and an image recording program to correct image data and record images using the corrected image data on the recording medium M. The setting data includes: data on a first reference number that indicates the number of later-becoming defective nozzles and serves as a reference to start maintenance operation; and data on a second reference number that indicates the number of consecutive defective nozzles. Instead of the ROM 23, a rewritable nonvolatile memory, such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory, may be used.
• The second storage 24 stores therein later-becoming defective nozzle data D2 (second defective nozzle information) on later-becoming defective nozzles in the head units 12 detected by the operation of the inspection unit 15. In the later-becoming defective nozzle data D2, later-becoming defective nozzles are identified by arrangement numbers of the nozzles in their head units 12. The later-becoming defective nozzle data D2 are data generated by the below-described operation for detection of later-becoming defective nozzles. In the later-becoming defective nozzle data D2, later-becoming defective nozzles due to no ejection of ink and abnormality of the ink ejection direction are identified. The second storage 24 also stores therein image recording commands and image data input from the external apparatus 2 via the interface 17 and image data corrected by the CPU 21. As the second storage 24, for example, an HDD (Hard Disk Drive) is used, or a DRAM (Dynamic Random Access Memory) or the like may be used together.
• The external apparatus 2 is, for example, a personal computer, and supplies the image recording commands, the image data and so forth to the controller 20 via the interface 17.
• Next, various types of operation for management of defective nozzles in the inkjet recording apparatus 1 are described. Management of defective nozzles includes: detection of later-becoming defective nozzles; setting for supplementing no ejection of ink from defective nozzles by correcting image data; maintenance operation on the head units 12; and replacement of the head unit(s) 12.
• First, operation for detection of later-becoming defective nozzles performed in the inkjet recording apparatus 1 is described.
• In the inkjet recording apparatus 1, detection of later-becoming defective nozzles in each head unit 12 is performed when a predetermined condition is satisfied. The predetermined condition can be, for example, that recording operation by each head unit 12 has been performed a predetermined number of times or more since the last operation for detection of later-becoming defective nozzles. Alternatively, the predetermined condition may be that a predetermined ink amount or more has been consumed since the last operation for defection of later-becoming defective nozzles. Still alternatively, detection of later-becoming defective nozzles may be started by a user's instruction.
• FIG. 5 is a diagram to explain operation for detection of later-becoming defective nozzles.
• This diagram schematically shows positions of nozzles 123 of recording heads 122 in a plan view of the recording heads 122 of a head unit 12 and the moving unit 153 of the inspection unit 15 viewed from the side facing the conveyance surface of the conveyor belt 113.
• When detection of later-becoming defective nozzles starts, a head unit 12 is moved to the more positive side in Z direction by the head unit elevator 13 than the position where the head unit 12 performs recording operation, and the inspection unit 15 is disposed between the head unit 12 and the conveyor belt 113. Alternatively, the head unit 12 may be moved to the position above the inspection unit 15.
• Then, as shown in FIG. 5, on the basis of a signal(s) about a measurement(s) from the linear encoder 157, the moving unit 153 is moved to the position to face a recording head 122. That is, the moving unit 153 is moved to the position where the optical axis L of the light that is output from the light emitter 151 and detected by the light receiver 152 crosses the ink flying course from the top nozzle 123. The top nozzle 123 is a nozzle 123 located at the end on the positive side in X direction (the left end in FIG. 5) of the recording head 122, the recording head 122 being located on the most positive side in X direction. Next, while ink is ejected for a predetermined time from each of the nozzles 123 of the recording head 122 in order, the light emitter 151 and the light receiver 152 moved to the position for each of the nozzles 123 are operated to inspect the ink ejection state on the basis of the measurement results of the light amount obtained by the light receiver 152. That is, if decrease in the light amount by the ink is not detected at the position for a nozzle 123, no ejection of ink is detected, whereas if the position where decrease in the light amount is detected is different from the position for the nozzle 123, bending of the ink ejection direction is detected. The nozzle 123 from which ink is ejected changes from one nozzle 123 to another nozzle 123 in order in the negative X direction in FIG. 5 to the last nozzle 123 (at the right end in FIG. 5) of the recording head located on the most negative side in X direction. The speed of this change is set to be constant, and the moving unit 153 is moved at a constant speed corresponding to the constant speed of the change.
• No ink is ejected from the nozzles 123 identified as initial defective nozzles by the initial defective nozzle data D1 stored in the first storage 124. Hence, inspection of the ink ejection state is not performed on such nozzles 123.
• In detection of later-becoming defective nozzles, the above operation is performed on each of the four head units 12.
• Thus, by the operations of the light emitter 151 and the light receiver 152, the light amount reflecting the ink ejection state of, among the nozzles 123 of each head unit 12, a nozzle(s) 123 not identified as an initial defective nozzle in the initial defective nozzle data D1 is measured, and the ink ejection state of the nozzle 123 is inspected with the measurement result. As a result of the inspection, if no ejection of ink or bending of the ink ejection direction is detected, such a nozzle is identified as a later-becoming defective nozzle. When a later-becoming defective nozzle(s) is identified, later-becoming defective nozzle data D2, which indicates later-becoming defective nozzles, is generated on the basis of the arrangement number of the identified nozzle 123 in the head unit 12 and stored in the second storage 24.
• If later-becoming defective nozzle data D2 is already stored in the second storage 24, new later-becoming defective nozzle data D2 is generated and stored in the second storage 24. By storing later-becoming defective nozzle data D2 generated at different timings, the history (record) of the generation state of later-becoming defective nozzles can be referred to. If the history of the generation state of later-becoming defective nozzles is unnecessary, the existing later-becoming defective nozzle data D2 may be overwritten with the new later-becoming defective nozzle data D2.
• Because it is difficult to detect the ink flying speed from the measurement result of the light amount obtained by the inspection unit 15, later-becoming defective nozzles due to abnormality of the ink ejection amount are not detected. Hence, in the later-becoming defective nozzle data D2, later-becoming defective nozzles having abnormality of the ink ejection amount are not identified, and accordingly data indicating the degree of abnormality from a normal value of the ink ejection amount is not contained. Further, because the degree of bending of ink cannot be detected with a high accuracy from the measurement result of the light amount obtained by the inspection unit 15, in the later-becoming defective nozzle data D2, data indicating the degree of bending of the ink ejection direction is not contained.
• Thus, the later-becoming defective nozzle data D2 do not contain information on the degree of poor ejection, whereas the initial defective nozzle data D1 contain the information on the degree of poor ejection. Further, the number of types of poor ejection (defect modes) identified as defective nozzles by the initial defective nozzle data D1 is more than that identified by the later-becoming defective nozzle data D2. Hence, the initial defective nozzle data D1 are higher in detection accuracy of defective nozzles and larger in information amount than the later-becoming defective nozzle data D2.
• Next, correction of image data based on the initial defective nozzle data D1 and the later-becoming defective nozzle data D2 is described.
• In the inkjet recording apparatus 1, when defective nozzles are identified by at least one of the initial defective nozzle data D1 and the later-becoming defective nozzle data D2, image data is corrected to prevent disturbance in recorded images due to defective nozzles, and then images are recorded. For example, if a nozzle 123a shown in FIG. 5 is identified as a defective nozzle, image data is corrected such that no ink is ejected from the nozzle 123a, and also corrected such that the ink ejection amounts of adjacent nozzles (e.g. nozzles 123b in FIG. 5) to the defective nozzle or neighboring nozzles ( e.g. nozzles 123b and 123c in FIG. 5) to the defective nozzle are increased to supplement no ejection of ink from the defective nozzle. Then, on the basis of the corrected image data, ink is ejected from the head unit 12 to the recording medium M, so that an image with decrease in image quality due to defective nozzles suppressed is recorded.
• If a head unit 12 is replaced, and an image is to be recorded by an unused head unit 12, this head unit 12 has no later-becoming defective nozzles. Hence, the later-becoming defective nozzle data D2 for the head unit 12 is reset. Initial defective nozzles in the unused head unit 12 can be identified by the initial defective nozzle data D1 stored in the first storage 124 of this head unit 12. Hence, image data to be supplied to this head unit 12 is corrected on the basis of the initial defective nozzle data D1. Thus, when a head unit 12 is replaced by an unused one, image data can be corrected without performing operation for detection of defective nozzles thereon, and an image is recorded on the basis of the corrected image data.
• Next, maintenance operation based on the initial defective nozzle data D1 and the later-becoming defective nozzle data D2 is described.
• In the inkjet recording apparatus 1, when at least one of (i) the number of later-becoming defective nozzles in a head unit 12 and (ii) arrangement of the later-becoming defective nozzle(s) in the head unit 12, which are indicated by the later-becoming defective nozzle data D2, satisfies a predetermined condition(s), the maintenance unit 14 starts maintenance operation, which includes pressure purge and wiping.
• The predetermined condition about the number of later-becoming defective nozzles can be that the number of later-becoming defective nozzles indicated by the later-becoming defective nozzle data D2 exceeds a predetermined first reference number. This first reference number is set within the range of the number of defective nozzles in which decrease in image quality can be suppressed to the extent that, by supplementing no ejection of ink from defective nozzles with nozzles around the defective nozzles, poor image quality due to defective nozzles in recorded images is hardly recognized, preferably a larger value within the range in order to lower the frequency of maintenance operation.
• The predetermined condition about arrangement of later-becoming defective nozzle(s) can be that the number of consecutive defective nozzles exceeds a predetermined second reference number, and these defective nozzles include a later-becoming defective nozzle(s). This second reference number is set within the range of the number of consecutive defective nozzles in which decrease in image quality can be suppressed to the extent that, by supplementing no ejection of ink from the defective nozzles adjacent to each other with nozzles around the defective nozzles, poor image quality due to defective nozzles in recorded images is hardly recognized.
• Pressure purge, which is one of maintenance operation, is performed by pressurizing ink with the pressure pump of the maintenance unit 14 at a predetermined pressurizing position on the ink supply channel that communicates with the pressure chambers of the recording elements. This ink pressurization forcibly ejects ink from the nozzles 123 of the recording elements to solve clogging of the nozzles 123. Pressure purge is performed in the state in which a predetermined ink receiver is located under the nozzle surface of the head unit 12.
• When wiping, which is another one of maintenance operation, is performed, the head unit 12 is moved to a predetermined cleaning position where the cleaner roller 141 is disposed, and the cleaner roller 141 is moved to abut the nozzle surface of the head unit 12. From this state, the cleaner roller 141 moves in X direction while abutting the nozzle surface and rotating according to the operations of the conveyance motor and the rotation motor of the maintenance unit 14. Consequently, the entire nozzle surface is wiped with the wiping cloth that is wound around the outer circumferential surface of the cleaner roller 141, and the ink and foreign substances adhering to the nozzle surface and the openings of the nozzles 123 are removed accordingly.
• Because maintenance operation of this embodiment is to solve later-occurring clogging of nozzles and blocking of the openings of the nozzles with dirt or the like, defective nozzles having a possibility of being brought back to the normal state by the maintenance operation are usually later-becoming defective nozzles. It is very rare that initial defective nozzles are brought back to the normal state by the maintenance operation.
• Next, display of head unit retracement information that encourages replacement of a head unit(s) 12 is described.
• In the inkjet recording apparatus 1, after the above maintenance operation but before the next image recording, detection of later-becoming defective nozzles based on the inspection result obtained by the inspection unit 15 is performed. The later-becoming defective nozzles detected as a result of this are later-becoming defective nozzles that are not brought back to the normal state by the maintenance operation (hereinafter referred to as "unrecoverable later-becoming defective nozzles"). In the inkjet recording apparatus 1, when at least one of (i) the number of unrecoverable later-becoming defective nozzles in a head unit 12 and (ii) arrangement of the unrecoverable later-becoming defective nozzle(s) in the head unit 12 satisfies a predetermined condition(s) that is the same as the above condition(s) to start maintenance operation, the operational display 16 displays head unit replacement information indicating that it is time to replace the head unit 12 so as to encourage the user to replace the head unit 12.
• Whether to replace a head unit 12 may be determined on the basis of a condition about the number of unrecoverable later-becoming defective nozzles to which the number of initial defective nozzles is added and/or a condition about arrangement of unrecoverable later-becoming defective nozzle(s) to which arrangement of initial defective nozzle(s) is added.
• Next, control procedure of an image recording process performed in the inkjet recording apparatus 1 is described.
• FIG. 6 is a flowchart of the control procedure of the image recording process.
• This image recording process is stated when image data of an image to be recorded on the recording medium M and an image recording command to record the image are supplied from the external apparatus 2 via the interface 17 and stored in the second storage 24.
• When the image recording process is started, the CPU 21 determines whether an unexecuted image recording command(s) is stored in the second storage 24 (Step S1). When determining that no unexecuted image recording command is stored in the second storage 24 (Step S1; NO), the CPU 21 ends the image recording process.
• When determining that an unexecuted image recording command(s) is stored in the second storage 24 (Step S1; YES), the CPU 21 determines whether the condition to start detection of later-becoming defective nozzles is satisfied (Step S2). If image recording operation has been performed by the head units 12 a predetermined number of times or more since the last detection of later-becoming defective nozzles (Step S3), the CPU 21 determines that the condition to start detection of later-becoming defective nozzles is satisfied.
• When determining that the condition to start detection of later-becoming defective nozzles is satisfied (Step S2; YES), the CPU 21 detects later-becoming defective nozzles (Step S3). That is, the CPU 21 (i) causes the motors of the head unit elevators 13 to operate so that the head unit elevators 13 move the head units 12 in the positive Z direction, and also (ii) moves the inspection unit 15 to between the head units 12 and the conveyor belt 113. Then, the CPU 21 refers to the initial defective nozzle data D1 and supplies control signals to the recording head drive units 121 so that the recording head drive units 121 output voltage signals of drive waveforms to the recording heads 122, thereby ejecting inks from the nozzles 123 excluding initial defective nozzles of the head units 12. Further, the CPU 21 causes the light emitter 151 and the light receiver 152 of the inspection unit 15 to operate in such a way as to be in sync with timings of ejection of the inks while causing the motor 156 of the inspection unit 15 to operate to move the moving unit 153 in time with ejection of the inks, and obtains detection signals of the light output from the light receiver 152. The CPU 21 detects later-becoming defective nozzles on the basis of the obtained detection signals, and generates later-becoming defective nozzle data D2 and stores the same in the second storage 24.
• The CPU 21 determines, for each head unit 12, whether the number of the detected later-becoming defective nozzle(s) in the head unit 12 or arrangement thereof in the head unit 12 satisfies a predetermined condition (Step S4). If the number of later-becoming defective nozzles indicated by the later-becoming defective nozzle data D2 is larger than the first reference number stored in the ROM 23, the CPU 21 determines that the condition about the number of later-becoming defective nozzles is satisfied. Further, if the number of consecutive defective nozzles indicated by the initial defective nozzle data D1 and the later-becoming defective nozzle data D2 exceeds the second reference number stored in the ROM 23, and these defective nozzles include a later-becoming defective nozzle(s), the CPU 21 determines that the condition about arrangement of later-becoming defective nozzle(s) is satisfied.
• When determining that both the number and arrangement of later-becoming defective nozzles do not satisfy their respective predetermined conditions (Step S4; NO), or when determining in Step S2 that the condition to start detection of later-becoming defective nozzles is not satisfied (Step S2; NO), the CPU 21 determines whether any one or more of the head units 12 has a defective nozzle(s) (Step S5). That is, the CPU 21 determines whether a detective nozzle(s) is identified by at least one of the initial defective nozzle data D1 and the later-becoming defective nozzle data D2 for each head unit 12.
• When determining that one or more of the head units 12 has a defective nozzle(s) (Step S5; YES), the CPU 21 corrects image data on the basis of the initial defective nozzle data D1 and the later-becoming defective nozzle data D2 (Step S6). That is, the CPU 21 refers to the initial defective nozzle data D1 and the later-becoming defective nozzle data D2 and corrects image data relating to the image recording command such that no ink is ejected from the defective nozzle(s) and this no ejection of ink from the defective nozzle(s) is supplemented, and stores the corrected image data in the second storage 24.
• The CPU 21 records an image on the basis of the image data corrected in Step S6 (Step S7). That is, the CPU 21 supplies a control signal to the motor that drives the conveyor rollers 111 and 112 of the conveyor 11 so as to move the conveyor belt 113 and convey the recording medium M accordingly. Then, the CPU 21 supplies the corrected image data and control signals to the recording head drive units 121 so as to cause the recording head drive units 121 to output voltage signals of drive waveforms to the recording heads 122 at appropriate timings according to the movement of the conveyor belt 113, thereby causing the head units 12 to eject inks from the nozzles onto the recording medium M, which is conveyed by the conveyor 11, and record an image on the recording medium M accordingly.
• When determining in Step S5 that none of the head units 12 has a defective nozzle (Step S5; NO), the CPU 21 causes the head units 12 to record an image on the basis of image data relating to the image recording command without correcting the image data.
• When finishing Step S7, the CPU 21 moves to Step S1.
• When determining in Step S4 that the number or arrangement of the detected later-becoming defective nozzle(s) satisfies a predetermined condition (Step S4; YES), the CPU 21 determines whether a maintenance-done flag is set to OFF (Step S8).
• When determining that the maintenance-done flag is set to OFF (Step S8; YES), the CPU 21 causes the maintenance unit 14 to perform maintenance operation (Step S9). That is, the CPU 21 positions a predetermined ink receiver under the nozzle surface(s) of the head unit(s) 12, and causes the maintenance unit 14 to operate the pressure pump to pressurize the inks, thereby performing pressure purge of forcibly ejecting the inks from the nozzles 123 of the head units 12. When pressure purge finishes, the CPU 21 moves the head units 12 to their predetermined cleaning positions, and causes the rotation motor and the conveyance motor of the maintenance unit 14 to operate to perform wiping with the cleaner rollers 141.
• When finishing Step S9, the CPU 21 sets the maintenance-done flag to ON (Step S10). When finishing Step S10, the CPU 21 moves to Step S3.
• When determining in Step S8 that the maintenance-done flag is set to ON (Step S8; NO), the CPU 21 causes the operational display 16 to display the head unit replacement information (Step S11). Thus, determining in Step S8 that the maintenance-done flag is set to ON means that although maintenance operation is performed in Step S9, in Step S3, in one or more of the head units 12, (i) unrecoverable later-becoming defective nozzles, the number of which is more than the first reference number, are detected, or (ii) there are consecutive defective nozzles, the number of which is more than the second reference number, and the defective nozzles include a later-becoming defective nozzle(s). Then, in order to encourage the user to replace such a head unit(s) 12, the operational display 16 displays the head unit replacement information.
• When finishing Step S11, the CPU 21 ends the image recording process.
• As described above, the inkjet recording apparatus 1 according to this embodiment includes: the head unit(s) 12 provided with the nozzles 123 that eject an ink; the first storage 124 in which the initial defective nozzle data D1 on, among the nozzles 123, an initial defective nozzle that (i) is a defective nozzle among defective nozzles which do not eject the ink normally and (ii) is due to initial failure of the head unit 12 is stored; and the second storage 24 in which the later-becoming defective nozzle data D2 on, among the defective nozzles, a later-becoming defective nozzle that is not identified as the initial defective nozzle by the initial defective nozzle data D1 is stored. This configuration can easily identify initial defective nozzles and later-becoming defective nozzles that each head unit 12 has by the initial defective nozzle data D1 and the later-becoming defective nozzle data D2, respectively, and accordingly enables more efficient management of defective nozzles based on the information on the initial defective nozzles and/or the later-becoming defective nozzles, or targeted at the later-becoming defective nozzles.
• Further, the first storage 124 is integrated with the head unit 12. This can, when a head unit 12 is replaced by an unused head unit 12, identify detective nozzles (i.e. initial defective nozzles) that this head unit 12 has without performing detection of defective nozzles on this head unit 12.
• Further, the inkjet recording apparatus 1 further includes the inspection unit 15 that measures a physical quantity reflecting the ink ejection state of each of the nozzles 123, and the CPU 21 (detector) detects the defective nozzles from a result of the measurement by the inspection unit 15, and stores, in the second storage 24, the later-becoming defective nozzle data D2 based on a result of the detection of the defective nozzles. This configuration can detect and identify later-becoming defective nozzles in the inkjet recording apparatus 1.
• Further, the CPU 21 detects the later-becoming defective nozzle by causing the inspection unit 15 to measure the physical quantity reflecting the ink ejection state of, among the nozzles 123, a nozzle 123 that is not identified as the initial defective nozzle by the initial defective nozzle data D1. This configuration can reduce the ink amount that is consumed to detect defective nozzles.
• Further, the initial defective nozzle data D1 is information on the initial defective nozzle detected by an external inspection apparatus. This configuration enables more efficient management of defective nozzles with reference to the initial defective nozzle data D1 that are based on the highly accurate detection results of defective nozzles obtained by an inspection apparatus different from the inkjet recording apparatus 1.
• Further, the initial defective nozzle data D1 is information on the initial defective nozzle detected by an external inspection apparatus and is higher in detection accuracy than the detection by the CPU 21 as the detector from the result of the measurement by the inspection unit 25. This can identify initial defective nozzles due to abnormality of the ejection direction, which is difficult for the inkjet recording apparatus 1 to detect, and enables more appropriate management of defective nozzles.
• Further, the inkjet recording apparatus 1 further includes the maintenance unit 14 that performs maintenance operation to return, among the defective nozzles, a nozzle 123 which is recoverable to the normal state in which the ink is ejected normally to the normal state, and the CPU 21 (recovery controller) causes the maintenance unit 15 to start the maintenance operation based on at least one of (i) the number of, among the nozzles 123, nozzle(s) 123 and (ii) arrangement of the nozzle(s) 123 in the head unit 12, the nozzle(s) 123 being identified as the later-becoming defective nozzle by the later-becoming defective nozzle data D2. This can start maintenance operation at the appropriate timing based on at least one of the number and arrangement of recoverable later-becoming defective nozzles, which have a possibility of being brought back to the normal state by the maintenance operation, and accordingly enables more efficient management of defective nozzles.
• Further, the CPU 21 (corrector) corrects, based on at least one of the initial defective nozzle data D1 and the later-becoming defective nozzle data D2, image data of an image to be recorded on a recording medium M. This can suppress decrease in image quality due to defective nozzles in images to be recorded. Further, immediately after replacement of a head unit(s) 12, image data can be corrected on the basis of the initial defective nozzle information stored in the first storage(s) 124 without performing detection of defective nozzles on a head unit(s) 12 that has replaced the head unit(s) 12. Further, even if there are defective nozzles of the defect modes (e.g. bending of the ejection direction, abnormality of the ejection amount, etc.), which are difficult for the inkjet recording apparatus 1 to detect, if these defective nozzles of the defect modes are identified and the initial defective nozzle data D1 are generated by an inspection apparatus different from the inkjet recording apparatus 1, image data can be corrected on the basis of the initial defective nozzle data D1, and accordingly, of the image data, parts for initial defective nozzles can be corrected more appropriately. Thus, decrease in image quality due to defective nozzles in images to be recorded can be suppressed more effectively.
• Further, the inkjet recording apparatus 1 further includes the operational display 16, and the CPU 21 (notification controller) causes the operational display 16 to perform notification which encourages replacement of the head unit 12 based on at least one of (i) the number of, among the nozzles 123, nozzle(s) 123 and (ii) arrangement of the nozzle(s) 123 in the head unit 12, the nozzle(s) 123 being identified as the later-becoming defective nozzle by the later-becoming defective nozzle data D2. This can encourage replacement of a head unit(s) 12 at the appropriate timing based on at least one of the number and arrangement of later-becoming defective nozzles.
(First Modification)
• Next, a first modification of the above embodiment is described. The first modification is different from the above embodiment in algorithm for correction of image data in Step S6 of the image recording process shown in FIG. 6. Other than that, the first modification is the same as the above embodiment.
• In the first modification, of image data, parts for initial defective nozzles indicated by the initial defective nozzle data D1 and parts for later-becoming defective nozzles indicated by the later-becoming defective nozzle data D2 are corrected on the basis of their respective algorithms different from each other.
• That is, among initial defective nozzles, for abnormal-ejection-amount initial defective nozzles that are identified by the initial defective nozzle data D1 as being poor in ejection due to abnormality of the ink ejection amount, instead of the correction not to eject ink from the nozzles, correction to increase or decrease the ink ejection amounts of the nozzles according to the deficiency or surplus of the ejection amounts thereof is performed. For initial defective nozzles due to no ejection of ink and bending of the ink ejection direction, as with the above embodiment, the correction not to eject ink from the initial defective nozzles and increase the ink ejection amounts of their neighboring nozzles 123 so as to supplement this no ejection of ink is performed on image data. Thus, for initial defective nozzles, correction is performed on the basis of the algorithm that changes the correction method according to the type of poor ejection (defect mode) of each nozzle 123.
• On the other hand, for later-becoming defective nozzles, on the basis of the same algorithm as that of the embodiment, the correction not to eject ink from all the later-becoming defective nozzles and increase the ink ejection amounts of their neighboring nozzles so as to supplement this no ejection of ink is performed.
• It is possible that correction for abnormal-ejection-amount initial defective nozzles is performed on image data in advance, and, after detection of later-becoming defective nozzles, correction for the other initial defective nozzles and the detected later-becoming defective nozzles is additionally performed thereon.
• As described above, in the inkjet recording apparatus 1 according to the first modification, the CPU 21 corrects, based on the initial defective nozzle data D1 and the later-becoming defective nozzle data D2, the image data of the image to be recorded on the recording medium M, and corrects, of the image data, a part for the initial defective nozzle identified by the initial defective nozzle data D1 and a part for the later-becoming defective nozzle identified by the later-becoming defective nozzle data D2 based on respective algorithms that are different from each other. This can appropriately correct image data according to the difference in information amount about poor ejection between the initial defective nozzle data D1 and the later-becoming defective nozzle data D2, and accordingly can suppress decrease in image quality due to defective nozzles in images to be recorded more efficiently.
(Second Modification)
• Next, a second modification of the above embodiment is described. The second modification is different from the above embodiment in the point that detection of later-becoming defective nozzles is performed immediately after maintenance operation only. Other than that, the second modification is the same as the above embodiment.
• FIG. 7 is a flowchart of control procedure of an image recording process according to the second modification. The image recording process shown in FIG. 7 is modified from the image recording process of the above embodiment shown in FIG. 6 as follows: Step S2 is changed to Step S2a, Step S9 is performed before Step S3, and Step S8 and Step S10 are eliminated. Hereinafter, the point different from the image recording process shown in FIG. 6 is mainly described.
• When finishing Step S1, the CPU 21 determines whether the condition to start maintenance operation is satisfied (Step S2a). If a predetermined ink amount or more has been consumed by each head unit 12 recording images since the last maintenance operation (Step S9), the CPU 21 determines that the condition to start maintenance operation is satisfied. When determining that the condition to start maintenance operation is not satisfied (Step S2a; NO), the CPU 21 moves to Step S5.
• When determining that the condition to start maintenance operation is satisfied (Step S2a; YES), the CPU 21 causes the maintenance unit 14 to perform maintenance operation (Step S9). When finishing Step S9, the CPU 21 detects later-becoming defective nozzles (Step S3). When determining in Step S4, which is performed after Step S3, that the number or arrangement of the later-becoming defective nozzle(s) satisfies a predetermined condition (Step S4; YES), the CPU 21 causes the operational display 16 to display the head unit replacement information (Step S11).
• According to the image recording process of the second modification, detection of later-becoming defective nozzles is performed immediately after maintenance operation only. This can reduce the execution frequency of detection of later-becoming defective nozzles.
• The present invention is not limited to the above embodiment and modifications and hence can be modified in a variety of aspects.
• For example, in the above embodiment and modifications, it is described as an example that the first storage 124 is provided for each head unit 12, which is a recorder, and the initial defective nozzle data D1 on initial defective nozzles that the recording heads 122 of the head unit 12 have is stored in the first storage 124. Alternatively, a first storage may be provided for each recording head 122, and initial defective nozzle data on initial defective nozzles that the recording head 122 has may be stored in the first storage. In this case, a recorder is constituted of recording heads 122 integrated with first storages. This configuration can, when one or more of the recording heads 122 of a head unit 12 is replaced, identify initial defective nozzles that a recording head(s) 122 which has replaced the recording head(s) 122 has without performing detection of defective nozzles on the recording head(s) 122.
• Further, in the above embodiment and modifications, it is described as an example that the later-becoming defective nozzle data D2 are stored in the second storage 24. However, in the second storage 24, the initial defective nozzle data D1 may also be stored. For example, when the head units 12 are connected to the connectors 120, the CPU 21 may read the initial defective nozzle data D1 from the first storages 124 and write the same in the second storage 24. Alternatively, the initial defective nozzle data D1 may be directly written in the second storage 24 on the basis of the detection result of initial defective nozzles of each head unit 12 obtained by an inspection apparatus different from the inkjet recording apparatus 1. If the initial defective nozzle data D1 and the later-becoming defective nozzle data D2 are stored in the second storage 24 without being distinguished from each other, later-becoming defective nozzles can be identified by excluding initial defective nozzles identified by the initial defective nozzle data D1 stored in the first storage 124 from defective nozzles identified by the initial defective nozzle data D1 and the later-becoming defective nozzle data D2 stored in the second storage 24. Hence, in Step S4 of the image recording processes shown in FIG. 6 and FIG. 7, the determination can be made on the basis of thus-identified later-becoming defective nozzles.
• This configuration can, in Step S6 of the image recording processes shown in FIG. 6 and FIG. 7, correct image data without accessing the first storages 124. In this case, the second storage 24 is the first storages and the second storage.
• If the initial defective nozzle data D1 and the later-becoming defective nozzle data D2 are stored in the second storage 24, the head units 12 or the recording heads 122 may be provided with no first storages in which the initial defective nozzle data D1 are stored.
• Further, in the above embodiment and modifications, it is described as an example that the inspection unit 15 measures the light amount as the physical quantity reflecting the ink ejection state of each nozzle 123 to identify later-becoming defective nozzles from the measurement results. However, this is not a limit. For example, detection of later-becoming defective nozzles may be performed by: recording a predetermined inspection image on the recording medium M; and analyzing captured data obtained by capturing this inspection image with an image reader, such as a line sensor or an area sensor. The predetermined inspection image can be, for example, a line pattern formed of lines recorded with inks ejected from the nozzles 123 that the head units 12 have. If, in the captured data obtained by capturing this line pattern, there is a line(s) that is broken or not recorded at a proper position for a nozzle 123, the nozzle 123 corresponding to the line can be identified as a defective nozzle. In this case, the light amount of light reflected by each line in the inspection image corresponds to the physical quantity reflecting the ink ejection state, and the image reader that measures this light amount is the measurement unit.
• Further, in the above embodiment and modifications, it is described as an example that maintenance operation is performed on the whole of each head unit 12. Alternatively, maintenance operation may be performed on some or one of nozzles 123 that each head unit 12 has. For example, flashing of ejecting ink only from nozzles 123 identified as later-becoming defective nozzles by the later-becoming defective nozzle data D2 (or the later-becoming defective nozzle data D2 and the initial defective nozzle data D1) may be performed. This enables more efficient maintenance operation.
• Further, in the above embodiment and modifications, it is described as an example that, in detection of later-becoming defective nozzles with the inspection unit 15, no ink is ejected from initial defective nozzles. Alternatively, ink may be ejected from all the nozzles 123 including initial defective nozzles to detect defective nozzles; and identifying later-becoming defective nozzles by excluding initial defective nozzles indicated by the initial defective nozzle data D1 from the detection result.
• Further, in the above embodiment and modifications, it is described as an example that detection of initial defective nozzles is performed with an inspection apparatus different from the inkjet recording apparatus 1. Alternatively, detection of initial defective nozzles may be performed with the inspection unit 15 after the head units 12 are connected to the connectors 120 of the inkjet recording apparatus 1.
• Further, in the above embodiment and modifications, it is described as an example that the user is notified that it is time to replace the head unit(s) 12 by displaying on the operational display 16. Alternatively, the user may be notified that it is time to replace a head unit(s) 12 by lightening up a lamp, generating a predetermined alarm sound, or sending an email to a preset address, each of the lamp, the alarm sound and the email indicating that it is time to replace a head unit(s) 12.
• Further, in the above embodiment and modifications, it is described as an example that the recording medium M is conveyed by the conveyor 11 having the conveyor belt 113. However, this is not a limit. For example, the conveyor 11 may hold and convey the recording medium M on the outer circumferential surface of a conveyor drum that rotates.
• Further, in the above embodiment and modifications, it is described as an example that the inkjet recording apparatus 1 employs the single-pass system. However, the present invention may be applied to an inkjet recording apparatus that records images while scanning recording heads.
• Although some embodiments of the present invention are described, the scope of the present invention is not limited to the above embodiments but includes the scope of claims and the scope of their equivalents.
Industrial Applicability
• The present invention is applicable to an inkjet recording apparatus.
Description of Reference Numerals

1

Inkjet Recording Apparatus

2

External Apparatus

11

Conveyor

111, 112

Conveyor Roller

113

Conveyor Belt

12

Head Unit

120

Connector

121

Recording Head Drive Unit

122

Recording Head

123

Nozzle

124

First Storage

13

Head Unit Elevator

14

Maintenance Unit

141

Cleaner Roller

15

Inspection Unit

151

Light Emitter

152

Light Receiver

153

Moving Unit

154

Moving Belt

155a, 255b

Roller

156

Motor

157

Linear Encoder

16

Operational Display

17

Interface

18

Bus

20

Controller

21

CPU

22

RAM

23

ROM

24

Second Storage

D1

Initial Defective Nozzle Data

D2

Later-becoming Defective Nozzle Data

L

Optical Axis

M

Recording Medium

Claims (10)

1. An inkjet recording apparatus comprising:

   a recorder provided with nozzles that eject an ink;

   a first storage in which first defective nozzle information on, among the nozzles, an initial defective nozzle that (i) is a defective nozzle among defective nozzles which do not eject the ink normally and (ii) is due to initial failure of the recorder is stored; and

   a second storage in which second defective nozzle information on, among the defective nozzles, a later-becoming defective nozzle that is not identified as the initial defective nozzle by the first defective nozzle information is stored.
2. The inkjet recording apparatus according to claim 1, wherein the first storage is integrated with the recorder.
3. The inkjet recording apparatus according to claim 1 or 2, further comprising:

   a measurement unit that measures a physical quantity reflecting an ink ejection state of each of the nozzles; and

   a detector that detects the defective nozzles from a result of the measurement by the measurement unit, and stores, in the second storage, the second defective nozzle information based on a result of the detection of the defective nozzles.
4. The inkjet recording apparatus according to claim 3, wherein the detector detects the later-becoming defective nozzle by causing the measurement unit to measure the physical quantity reflecting the ink ejection state of, among the nozzles, a nozzle that is not identified as the initial defective nozzle by the first defective nozzle information.
5. The inkjet recording apparatus according to any one of claims 1 to 4, wherein the first defective nozzle information is information on the initial defective nozzle detected by an external inspection apparatus.
6. The inkjet recording apparatus according to claim 3 or 4, wherein the first defective nozzle information is information on the initial defective nozzle detected by an external inspection apparatus and is higher in detection accuracy than the detection by the detector from the result of the measurement by the measurement unit.
7. The inkjet recording apparatus according to any one of claims 1 to 6, further comprising:

   a recovery unit that performs a recovery operation to return, among the defective nozzles, a nozzle which is recoverable to a normal state in which the ink is ejected normally to the normal state; and

   a recovery controller that causes the recovery unit to start the recovery operation based on at least one of (i) a number of, among the nozzles, a nozzle and (ii) arrangement of the nozzle in the recorder, the nozzle being identified as the later-becoming defective nozzle by the second defective nozzle information.
8. The inkjet recording apparatus according to any one of claims 1 to 7, further comprising:

   a corrector that corrects, based on at least one of the first defective nozzle information and the second defective nozzle information, image data of an image to be recorded on a recording medium.
9. The inkjet recording apparatus according to claim 8, wherein the corrector corrects, based on the first defective nozzle information and the second defective nozzle information, the image data of the image to be recorded on the recording medium, and corrects, of the image data, a part for the initial defective nozzle identified by the first defective nozzle information and a part for the later-becoming defective nozzle identified by the second defective nozzle information based on respective algorithms that are different from each other.
10. The inkjet recording apparatus according to any one of claims 1 to 9, further comprising:

    a notification unit; and

    a notification controller that causes the notification unit to perform notification which encourages replacement of the recorder based on at least one of (i) a number of, among the nozzles, a nozzle and (ii) arrangement of the nozzle in the recorder, the nozzle being identified as the later-becoming defective nozzle by the second defective nozzle information.

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