Image forming device, discharge quantity adjustment method, and program

Abstract

To provide an image forming device, a discharge quantity adjustment method and a program which can suppress quantities of ink that is discharged from a nozzle during a flushing operation, without complicating a structure for performing maintenance.SOLUTION: An image forming device comprises an inkjet head having a nozzle that discharges ink, and a control part that controls a nozzle wiping operation and a flushing operation which is performed to the inkjet head. The control part varies discharge quantities of ink that is discharged from the nozzle during the flushing operation, in accordance with a stand-by time after the nozzle wiping operation is performed until the flushing operation is started.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus, a discharge amount adjustment method, and a program.

Background Art

[0002] Conventionally, an inkjet image forming apparatus is known that forms an image on a recording medium by discharging ink from a plurality of nozzles formed in an inkjet head onto the recording medium conveyed by a conveying device.

[0003] The inkjet head of an inkjet image forming apparatus discharges ink from a plurality of nozzles. At this time, pressure is individually applied to each nozzle. Thereby, discharge control of ink according to the image to be recorded is performed. The ink discharge ports of the nozzles are aligned and opened on the nozzle surface of the inkjet head facing the recording medium during image formation.

[0004] In an inkjet image forming apparatus having such a configuration, when there is adhesion of foreign matter to the nozzle surface, residual of dried and thickened ink, and mixing of bubbles, etc., it becomes difficult to achieve good ink discharge for forming an image. Therefore, in order to maintain a good ink discharge state, a maintenance operation of the inkjet head is performed. In the maintenance operation, generally, a purge operation for discharging the ink in the nozzles from each nozzle, a nozzle wiping operation for removing the ink on the nozzle surface, and a flushing operation for discharging abnormal ink in the nozzles are sequentially performed.

[0005] By the way, in the nozzle wiping operation, usually, the ink is wiped along the arrangement direction of the nozzles. At this time, for example, when the inkjet head is a head capable of discharging a plurality of color inks, abnormalities such as mutual ink moving through the wiping member and ink mixing inside each nozzle may occur.

[0006] Therefore, recently, various techniques for suppressing ink color mixing have been proposed. For example, Patent Document 1 discloses an inkjet image forming apparatus that sequentially performs a flushing operation from nozzles from which ink has been removed by a nozzle wiping operation. In this inkjet image forming apparatus, even if the ink ejected from a certain nozzle penetrates into other nozzles due to the nozzle wiping operation, the ink is ejected from the nozzles in the order in which the ink penetrated. Therefore, it is possible to suppress ink color mixing inside each nozzle.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] By the way, in the conventional flushing operation, a certain amount of ink is ejected from each nozzle formed in the inkjet head so that the abnormal ink that has penetrated into the nozzle is surely removed. Therefore, there is a problem that it is necessary to eject ink unnecessarily.

[0009] Also, in the inkjet image forming apparatus described in Patent Document 1, a flushing operation is performed from the nozzles where the nozzle wiping operation has been performed. Therefore, control for adjusting the timing between the nozzle wiping operation and the flushing operation is required, which increases the device cost. Furthermore, in this case, it is also necessary to control so that the timing of starting the flushing operation is different for each nozzle, which complicates the configuration of the device.

[0010] The present disclosure has been made in view of the problems in the above-described conventional technologies, and an object thereof is to provide an image forming apparatus, a discharge amount adjustment method, and a program capable of suppressing the amount of ink discharged from a nozzle during a flushing operation without complicating the configuration of a maintenance device.

Means for Solving the Problems

[0011] The image forming apparatus according to the present disclosure includes: an inkjet head having nozzles for discharging ink; a control unit that controls a nozzle wiping operation and a flushing operation performed on the inkjet head; and the control unit changes the discharge amount of the ink discharged from the nozzles during the flushing operation according to a standby time from when the nozzle wiping operation is performed until the flushing operation is started.

[0012] The discharge amount adjustment method according to the present disclosure includes: performing a nozzle wiping operation on an inkjet head having nozzles for discharging ink; changing the discharge amount of the ink discharged from the nozzles during the flushing operation according to a standby time from when the nozzle wiping operation is performed until the flushing operation is started.

[0013] The program according to the present disclosure causes a computer to execute the above-described discharge amount adjustment method.

Advantages of the Invention

[0014] According to the present disclosure, it is possible to suppress the amount of ink discharged from the nozzles during flushing without complicating the configuration of the apparatus for performing maintenance.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0016] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present disclosure. Also, in each figure, those denoted by the same reference numerals are the same or corresponding ones, which is common throughout the entire specification.

[0017] [Configuration of Inkjet Image Forming Apparatus 1] Hereinafter, the present embodiment will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of the configuration of an inkjet image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, an inkjet image forming apparatus (hereinafter simply referred to as "image forming apparatus") 1 includes a paper feeding unit 10, an image forming unit 20, a paper discharging unit 30, and a control unit 40 (see FIG. 4).

[0018] The image forming apparatus 1 conveys the recording medium P stored in the paper feeding unit 10 to the image forming unit 20 under the control of the control unit 40. Then, the image forming apparatus 1 forms an image on the recording medium P in the image forming unit 20, and conveys the recording medium P on which the image is formed to the paper discharging unit 30. As the recording medium P, various media capable of fixing the landed ink on the surface can be used, such as paper like plain paper and coated paper, as well as cloth or sheet-like resin.

[0019] The paper feeding unit 10 includes a paper feeding tray 11 for storing the recording medium P, and a medium supply unit 12 for conveying and supplying the recording medium P from the paper feeding tray 11 to the image forming unit 20. The medium supply unit 12 includes an annular belt supported by two rollers on the inside, and conveys the recording medium P from the paper feeding tray 11 to the image forming unit 20 by rotating the rollers with the recording medium P placed on the belt.

[0020] The image forming unit 20 includes a conveying unit 21, a delivery unit 22, a heating unit 23, a head unit 24, a fixing unit 25, a delivery unit 28, and the like.

[0021] The conveying unit 21 holds the recording medium P placed on the conveying surface 211a (placement surface) of the cylindrical conveying drum 211. Further, the conveying unit 21 performs a conveying operation of conveying the recording medium P on the conveying drum 211 in the conveying direction (Y direction) by rotating and orbiting around the rotation axis (cylindrical axis) of the conveying drum 211 extending in the X direction (perpendicular to the paper surface in FIG. 1).

[0022] The conveying drum 211 includes a claw portion and an air intake portion (not shown) for holding the recording medium P on its conveying surface 211a. The recording medium P is held on the conveying surface 211a by having its end pressed by the claw portion and being attracted to the conveying surface 211a by the air intake portion. The conveying unit 21 is connected to a conveying drum motor (not shown) for rotating the conveying drum 211. The conveying drum 211 rotates by an angle proportional to the rotation amount of the conveying drum motor.

[0023] The delivery unit 22 delivers the recording medium P conveyed by the medium supply unit 12 of the paper feeding unit 10 to the conveyance unit 21. The delivery unit 22 is disposed at a position between the medium supply unit 12 of the paper feeding unit 10 and the conveyance unit 21. The delivery unit 22 holds one end of the recording medium P conveyed from the medium supply unit 12 with the swing arm unit 221, picks it up, and delivers it to the conveyance unit 21 via the delivery drum 222.

[0024] The heating unit 23 is disposed between the arrangement position of the delivery drum 222 and the arrangement position of the head unit 24. The heating unit 23 heats the recording medium P conveyed by the conveyance unit 21 so that the temperature of the recording medium P falls within a predetermined temperature range. The 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 (see FIG. 4) to cause the infrared heater to generate heat.

[0025] The head unit 24 discharges ink onto the recording medium P held on the conveyance drum 211 to form an image. Specifically, the head unit 24 discharges ink onto the recording medium P from ink discharge ports formed on the nozzle surface 245 (see FIGS. 2 and 3) facing the conveyance surface 211a of the conveyance drum 211 at an appropriate timing according to the rotation of the conveyance drum 211. The head unit 24 is arranged such that the nozzle surface is separated from the conveyance surface 211a by a predetermined distance.

[0026] In the image forming apparatus 1 according to the present embodiment, four head units 24 corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K) inks are arranged. Specifically, for example, the four head units 24 are arranged at predetermined intervals in the order of Y, M, C, and K colors from the upstream side in the conveyance direction of the recording medium P.

[0027] FIG. 2 is a schematic diagram showing an example of the configuration of the head unit 24. Here, the nozzle surface of the head unit 24 facing the conveyance surface 211a of the conveyance drum 211 is shown.

[0028] The head unit 24 includes four inkjet heads 242 attached to the attachment member 244. Each of the inkjet heads 242 is formed with a plurality of image forming elements (recording elements), each having a pressure chamber for storing ink, a piezoelectric element disposed on the wall surface of the pressure chamber, and a nozzle 243. When a drive signal for deforming the piezoelectric element is input to this image forming element, the pressure chamber deforms due to the deformation of the piezoelectric element, the pressure in the pressure chamber changes, and ink is ejected from the nozzle 243 communicating with the pressure chamber.

[0029] In the inkjet head 242, two nozzle rows composed of nozzles 243 arranged at equal intervals in a direction intersecting the conveyance direction of the recording medium P (in this embodiment, the direction orthogonal to the conveyance direction, that is, the X direction) are formed on the nozzle surface 245. These two nozzle rows are arranged such that the positions of the nozzles 243 are shifted from each other in the X direction by half of the arrangement interval of the nozzles 243 in each nozzle row.

[0030] The four inkjet heads 242 are arranged in a staggered grid pattern such that the arrangement ranges in the X direction of the nozzle rows are continuously connected without gaps. The arrangement range in the X direction of the nozzles 243 included in the head unit 24 covers the width in the X direction of the region where an image is formed on the recording medium P conveyed by the conveyance unit 21. At this time, the position of the head unit 24 is fixed and used with respect to the rotation axis of the conveyance drum 211 during image formation. That is, the head unit 24 has a line head capable of ejecting ink over the image forming width in the X direction with respect to the recording medium P, and the image forming apparatus 1 is a single-pass type image forming apparatus.

[0031] Note that the number of nozzle rows of the inkjet head 242 may not be two, and may be one or three or more. Also, the number of inkjet heads 242 included in the head unit 24 may not be four, and may be three or less or five or more. Further, a water-repellent film having the property of repelling ink may be formed on the nozzle surface 245 of the inkjet head 242.

[0032] Returning to FIG. 1, the fixing unit 25 has a light emitting unit arranged across the width of the conveying unit 21 in the X direction, and irradiates the recording medium P placed on the conveying unit 21 with energy rays such as ultraviolet rays from the light emitting unit to cure and fix the ink ejected onto the recording medium P. The light emitting unit of the fixing unit 25 is arranged to face the conveying surface 211a between the arrangement position of the head unit 24 and the arrangement position of the delivery drum 281 of the delivery unit 28 in the conveying direction.

[0033] The delivery unit 28 has a cylindrical delivery drum 281 that delivers the recording medium P from the conveying unit 21 to the belt loop 282, and a belt loop 282 having an annular belt whose inside is supported by two rollers. The delivery unit 28 conveys the recording medium P delivered from the conveying unit 21 onto the belt loop 282 by the delivery drum 281 and sends it out to the paper discharge unit 30 by the belt loop 282.

[0034] The paper discharge unit 30 has a plate-shaped paper discharge tray 31 on which the recording medium P sent out from the image forming unit 20 by the delivery unit 28 is placed.

[0035] FIG. 3 is a schematic diagram showing an example of the configuration of the ink supply mechanism 55 in the image forming apparatus 1 according to the present embodiment. The ink supply mechanism 55 supplies ink to the inkjet head 242 in the image forming apparatus 1.

[0036] As shown in FIG. 3, the ink supply mechanism 55 includes a sub-tank 60, an atmosphere release valve 64, an inkjet head side flow path 70, a circulation flow path 72, a solenoid valve 74, and the like. The sub-tank 60 corresponds to the "ink tank" of the present disclosure.

[0037] A main tank (not shown) is disposed outside the head unit 24. The main tank stores ink of a color (yellow (Y), magenta (M), cyan (C), or black (K)) corresponding to the head unit 24. The ink stored in the main tank is pumped out by a supply pump that operates based on a control signal supplied from the control unit 40, and is supplied to the sub-tank 60 via the main-tank side flow path. Note that a pump having a backflow prevention function is used as the supply pump.

[0038] The sub-tank 60 is connected to a flow path (main-tank side flow path and inkjet head side flow path 70) between the main tank and the inkjet head 242. The sub-tank 60 stores the ink L pumped out and supplied from the main tank. In the present embodiment, a metal container having a capacity of about 40 liters is used as the sub-tank 60. The sub-tank 60 is controlled by the control unit 40 so that the internal back pressure value becomes a predetermined value.

[0039] The atmosphere release valve 64 receives the control of the control unit 40, adjusts the amount of air in the atmosphere sucked into the sub-tank 60 via the atmosphere release pipe 62, and raises the pressure in the sub-tank 60 toward the atmospheric pressure.

[0040] When an image is formed on the recording medium P, the ink L stored in the sub-tank 60 is supplied to the inkjet head 242 via the inkjet head side flow path 70. Then, the control unit 40 supplies the ink L stored in the sub-tank 60 to the inlet of the inkjet head 242 by increasing the back pressure of the ink L in the sub-tank 60. Then, the inkjet head 242 discharges the ink supplied from the sub-tank 60 toward the recording medium P.

[0041] The ink that has not been discharged by the inkjet head 242 is returned from the outlet of the inkjet head 242 to the sub-tank 60 via the circulation flow path 72.

[0042] The electromagnetic valve 74 adjusts the flow rate of the ink flowing through the circulation channel 72 under the control of the control unit 40.

[0043] Figure 4 is a block diagram showing the main functional configuration of the image forming apparatus 1. The image forming apparatus 1 includes a heating unit 23, a head driving unit 241 and an inkjet head 242, a fixing unit 25, a control unit 40, a conveyance driving unit 51, an operation display unit 52, an input / output interface 53, and an ink removing unit 80.

[0044] The head driving unit 241 supplies a driving signal that deforms the piezoelectric element in accordance with the image data at an appropriate timing to the image forming element of the inkjet head 242. Thereby, the head driving unit 241 discharges an amount of ink corresponding to the pixel value of the image data from the nozzles 243 of the inkjet head 242.

[0045] The control unit 40 includes a CPU 41 (Central Processing Unit), a RAM 42 (Random Access Memory), a ROM 43 (Read Only Memory), and a storage unit 44.

[0046] The CPU 41 reads out various control programs and setting data stored in the ROM 43, stores them in the RAM 42, and executes the programs to perform various arithmetic processes. Further, the CPU 41 comprehensively controls the overall operation of the image forming apparatus 1.

[0047] The RAM 42 provides a working memory space for the CPU 41 and stores temporary data. The RAM 42 may include a non-volatile memory.

[0048] The ROM 43 stores various control programs and setting data to be executed by the CPU 41. Note that an electrically erasable programmable read only memory (EEPROM) or a rewritable non-volatile memory such as a flash memory may be used instead of the ROM 43.

[0049] The storage unit 44 stores a print job (image formation command) input from the external device 2 via the input / output interface 53, image data related to the print job, and the like. Among these, the print job includes, in addition to information specifying the image data related to the image to be formed, information related to the type of the recording medium P on which the image is to be formed (for example, the size and thickness of the recording medium P). As the storage unit 44, for example, an HDD (Hard Disk Drive) is used, and a DRAM (Dynamic Random Access Memory) or the like may be used in combination.

[0050] In addition, the storage unit 44 stores various types of information necessary when the control unit 40 controls each unit. For example, in the present embodiment, the storage unit 44 stores in advance ink amount information used when performing a maintenance operation described later. Details of the ink amount information will be described later.

[0051] The conveyance drive unit 51 supplies a drive signal to the conveyance drum motor of the conveyance drum 211 based on a control signal supplied from the control unit 40 to rotate the conveyance drum 211 at a predetermined speed and timing.

[0052] In addition, the conveyance drive unit 51 supplies a drive signal to the motors for operating the medium supply unit 12, the delivery unit 22, and the delivery unit 28 based on a control signal supplied from the control unit 40. Thereby, the conveyance drive unit 51 causes the supply of the recording medium P to the conveyance unit 21 and the discharge from the conveyance unit 21.

[0053] The operation display unit 52 includes a display device such as a liquid crystal display or an organic EL display, and an input device such as an operation key or a touch panel arranged to overlap the screen of the display device. The operation display unit 52 causes the display device to display various types of information, and converts a user's input operation on the input device into an operation signal and outputs it to the control unit 40.

[0054] The input / output interface 53 mediates the transmission and reception of data between the external device 2 and the control unit 40. The input / output interface 53 is constituted by, for example, any one of various serial interfaces, various parallel interfaces, or a combination thereof.

[0055] The external device 2 is, for example, a personal computer, and supplies print jobs, image data, etc. to the control unit 40 via the input / output interface 53.

[0056] The ink removal unit 80 executes a wiping operation of bringing the wiping member 82 into contact with and moving it along the nozzle surface 245 of the inkjet head 242 under the control of the control unit 40.

[0057] [Maintenance Operations of the Image Forming Apparatus 1] Next, the maintenance operations of the image forming apparatus 1 having the above configuration will be described. In the image forming apparatus 1, if foreign matter adheres to the nozzle surface 245 on which the nozzles 243 for discharging ink are formed, dried and thickened ink remains, or air bubbles are mixed in, good ink discharge for performing image formation cannot be achieved. Therefore, in the image forming apparatus 1, maintenance operations are performed to maintain a good ink discharge state. In the present embodiment, as maintenance operations, for example, a purge operation, a nozzle wiping operation, and a flushing operation are sequentially performed.

[0058] The purge operation is an operation of discharging the ink in the nozzles 243 by pressurization from the upstream side of the nozzles 243 or suction from the nozzle surface 245 side. By the purge operation, foreign matter, dried and thickened ink, and mixed air bubbles, etc. are removed together with the discharged ink.

[0059] The nozzle wiping operation is performed after the purge operation. The nozzle wiping operation is an operation of removing the ink remaining on the nozzle surface 245 by bringing the wiping member 82 into contact with the nozzle surface 245 and moving it in the left - right direction in FIG. 3. In the nozzle wiping operation, a wiping member 82 such as an absorbent sponge member, a cloth member such as a cloth or non - woven fabric, or a rubber blade (blade member) for scraping off ink is used.

[0060] The flushing operation is performed after the nozzle wiping operation. The flushing operation is an operation of discharging the abnormal ink that has entered the nozzle 243. For example, the ink removed by the nozzle wiping operation may enter the nozzle 243, or ink may remain at the ink discharge port of the nozzle 243, resulting in abnormal ink in the nozzle 243. In such a case, the flushing operation is performed to discharge the abnormal ink in the nozzle 243.

[0061] The abnormal ink is ink different from the normal ink discharged from the nozzle 243. For example, it is a mixed - color ink generated when ink of a color different from the color of the ink discharged from a certain nozzle 243 enters the nozzle 243. Also, for example, the abnormal ink is the ink remaining after the ink discharged from a certain nozzle 243 dries and thickens.

[0062] (Ink discharge by the flushing operation) Here, when performing the flushing operation, in order to surely remove the abnormal ink in each nozzle 243, generally, a certain amount of ink is discharged from each nozzle 243. However, in this case, since a certain amount of ink is discharged regardless of the state of the ink in the nozzle 243, ink may be discharged more than necessary.

[0063] On the other hand, the inventor has found that in each nozzle 243 (or each inkjet head 242), the amount of ink required to surely remove abnormal ink by the flushing operation varies according to the elapsed time from when the nozzle wiping operation is performed until the flushing operation is started.

[0064] FIG. 5 is a graph for explaining the total amount of ink ejected during the flushing operation. In FIG. 5, the horizontal axis indicates the waiting time, which is the elapsed time from when the nozzle wiping operation is performed until the flushing operation is started. The vertical axis indicates the total amount of ink ejected from a plurality of nozzles 243 formed in one inkjet head 242.

[0065] Also, in this graph, the total amount of ink required during the flushing operation is shown when the back pressure of the ink L in the sub-tank 60 (hereinafter appropriately referred to as "sub-tank back pressure") and the presence or absence of a water-repellent film formed on the nozzle surface 245 of the inkjet head 242 are changed.

[0066] The solid-line graph shows the total amount of ink with respect to the waiting time when the sub-tank back pressure is -1.2 kPa and no water-repellent film is formed on the nozzle surface 245 of the inkjet head 242. The dashed-line graph shows the total amount of ink with respect to the waiting time when the sub-tank back pressure is -1.2 kPa and a water-repellent film is formed on the nozzle surface 245 of the inkjet head 242. The dash-dotted-line graph shows the total amount of ink with respect to the waiting time when the sub-tank back pressure is -0.5 kPa and no water-repellent film is formed on the nozzle surface 245 of the inkjet head 242. The double-dashed-line graph shows the total amount of ink with respect to the waiting time when the sub-tank back pressure is -0.5 kPa and a water-repellent film is formed on the nozzle surface 245 of the inkjet head 242.

[0067] As shown in FIG. 5, regardless of the presence or absence of the sub-tank back pressure and the water-repellent film, during the flushing operation, the total amount of ink required to remove abnormal ink changes according to the standby time. More specifically, during the flushing operation, the total amount of ink required to remove abnormal ink increases as the standby time becomes longer. This is presumably because during the standby time, the state of the ink at the ink ejection openings formed on the nozzle surface 245 deteriorates over time.

[0068] Therefore, in the present embodiment, during the maintenance operation, control is performed to change the amount of ink ejected from each nozzle 243 according to the standby time after the nozzle wiping operation is performed at each nozzle 243 or each inkjet head 242. At this time, the control unit 40 stores in advance in the storage unit 44, as ink amount information, the relationship between the standby time shown in FIG. 5 and the total amount of ink required during the flushing operation.

[0069] [Discharge Amount Adjustment Process] FIG. 6 is a flowchart showing an example of the flow of the discharge amount adjustment process according to the present embodiment. In this example, different single-color inks are ejected from each of a plurality of head units 24, and the case where the discharge amount adjustment process is performed in the image forming apparatus 1 capable of ejecting a plurality of colors of ink will be described. Specifically, in this example, it is assumed that the image forming apparatus 1 includes four head units 24 each capable of ejecting one color of ink of Y, M, C, or K. And it is assumed that the same color ink is ejected from the nozzles 243 of the plurality of inkjet heads 242 arranged in one head unit 24.

[0070] First, in step S1, after causing the purge operation in the maintenance operation to be executed, the control unit 40 controls the ink removal unit 80 to execute a nozzle wiping operation in which the wiping member 82 is brought into contact with the nozzle surface 245 and moved.

[0071] In step S2, the control unit 40 obtains the waiting time, which is the elapsed time since the nozzle wiping operation was executed, for each nozzle 243. Here, the control unit 40 measures the waiting time based on, for example, the moving speed of the wiping member 82 that operates during the nozzle wiping operation and the length of the inkjet head 242 in the width direction (the left-right direction in FIG. 3). Also, not limited to this, for example, a counter may be provided in the control unit 40, and the control unit 40 may measure the elapsed time since the nozzle wiping operation was executed to obtain the waiting time for each nozzle 243.

[0072] Next, in step S3, the control unit 40 reads out the ink amount information from the storage unit 44. In step S4, the control unit 40 determines the amount of ink necessary to remove abnormal ink for each nozzle 243 based on the waiting time for each nozzle 243 and the read ink amount information. That is, the control unit 40 determines the amount of ink to be ejected from each nozzle 243 based on the waiting time and the ink amount information.

[0073] In step S5, the control unit 40 controls the driving of the image forming element so that each nozzle 243 ejects the determined amount of ink, and starts the flushing operation. At this time, the control unit 40 adjusts the amount of ink ejected from each nozzle 243, for example, according to the number of ejections or the size of the ink droplets of the ejected ink.

[0074] Also, the control unit 40 may adjust the amount of ink ejected from each nozzle 243 by, for example, changing the driving frequency of the driving signal input to the image forming element. Specifically, for example, when the control unit 40 increases the amount of ink ejected from each nozzle 243, it increases the driving frequency.

[0075] In this way, in the ejection amount adjustment process, the amount of ink ejected from the nozzle 243 is changed according to the waiting time since the nozzle wiping operation was started. Therefore, during the flushing operation, it is possible to eject an appropriate amount of ink suitable for reliably removing abnormal ink.

[0076] Here, the total amount of ink necessary for removing abnormal ink during the flushing operation may be set according to the diffusion rate of the ink ejected from each nozzle 243. Specifically, the total amount of ink necessary during the flushing operation is set to increase as the diffusion rate of the ink increases.

[0077] The diffusion rate of the ink varies depending on, for example, the viscosity of the ink. Therefore, during the flushing operation, the total amount of ink necessary for removing abnormal ink may be set according to the viscosity of the ink ejected from each nozzle 243.

[0078] Also, the diffusion rate of the ink varies depending on, for example, the back pressure of the ink in the sub-tank 60. And from the graph of FIG. 5, the total amount of ink necessary during the flushing operation differs depending on the value of the sub-tank back pressure. That is, during the flushing operation, the total amount of ink necessary for removing abnormal ink may be set according to the back pressure of the ink in the sub-tank 60. In particular, in this case, it is preferable that the total amount of ink necessary for the flushing operation is set to increase as the back pressure of the ink in the sub-tank 60 increases in the negative direction.

[0079] Also, during the flushing operation, the total amount of ink necessary for removing abnormal ink may be set according to the presence or absence of a water-repellent film on the nozzle surface 245 of the inkjet head 242. For example, from the graph of FIG. 5, it can be seen that the total amount of ink necessary for removing abnormal ink during the flushing operation differs depending on the presence or absence of a water-repellent film on the nozzle surface 245. In particular, when no water-repellent film is formed on the nozzle surface 245, the total amount of ink necessary during the flushing operation is larger than when a water-repellent film is formed.

[0080] Furthermore, from this, when a water-repellent film is formed on the nozzle surface 245, when the water-repellent film is deteriorated, the total amount of ink necessary during the flushing operation changes according to the degree of deterioration of the water-repellent film.

[0081] Therefore, during the flushing operation, the total amount of ink necessary for removing abnormal ink may be set according to the presence or absence of the water-repellent film or the degree of deterioration of the water-repellent film.

[0082] As described above, the image forming apparatus 1 according to the present embodiment changes the discharge amount of the ink discharged from the nozzle 243 according to the waiting time, which is the time from when the nozzle wiping operation is performed until the flushing operation is started. Thereby, during the flushing operation, an appropriate amount of ink is discharged from the nozzle 243 when removing abnormal ink. Therefore, it is possible to prevent the discharge of an unnecessary amount of ink and suppress the discharge amount of ink during the maintenance operation.

[0083] Further, in the image forming apparatus 1 according to the present embodiment, since the amount of ink necessary for the flushing operation is changed according to the waiting time, it is possible to suppress the amount of ink used during the maintenance operation without complicating the configuration for performing the maintenance operation.

[0084] Although the embodiments have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications and applications are possible without departing from the gist of the present disclosure. For example, in the present embodiment, the image forming apparatus 1 has been described as a single-pass type image forming apparatus, but the present disclosure is not limited thereto, and for example, a scanning type image forming apparatus may be used.

[0085] Also, in the present embodiment, the amount of ink to be discharged is determined for each nozzle 243, but the present disclosure is not limited thereto. For example, the amount of ink to be discharged may be determined for each inkjet head 242. In this case, the control unit 40 controls the driving of the image forming element so that the same amount of ink is discharged from each of the plurality of nozzles 243 formed in the inkjet head 242 for each inkjet head 242. Further, for example, the inkjet head 242 may be divided into predetermined regions, and the amount of ink to be discharged may be determined for each divided region.

[0086] Furthermore, in the present embodiment, the discharge amount adjustment process has been described as being performed in the image forming apparatus 1 having a plurality of head units 24 that discharge single-color ink, but this is not limited to this example. For example, the discharge amount adjustment process may be performed in the image forming apparatus 1 having a head unit 24 that discharges a plurality of colors of ink such as two colors.

Explanation of Signs

[0087] 1 Inkjet image forming apparatus 10 Paper feeding unit 20 Image forming unit 24 Head unit 30 Paper discharging unit 40 Control unit 41 CPU 42 RAM 43 ROM 44 Storage unit 55 Ink supply mechanism 60 Sub-tank 80 Ink removal unit 82 Wiping member 241 Head drive unit 242 Inkjet head 243 Nozzle 244 Mounting member 245 Nozzle surface

Claims

1. An inkjet head having nozzles for ejecting ink, A control unit that controls a nozzle wiping operation and a flushing operation performed on the inkjet head Comprising, The control unit, According to the waiting time from when the nozzle wiping operation is performed until the flushing operation is started, the ejection amount of the ink ejected from the nozzle during the flushing operation is changed An image forming apparatus.

2. The control unit, The longer the waiting time, the greater the ejection amount of the ink The image forming apparatus according to claim 1.

3. The control unit, Set the ejection amount of the ink according to the diffusion rate of the ink The image forming apparatus according to claim 1.

4. The control unit, Set the ejection amount of the ink so that the ejection amount increases as the diffusion rate of the ink increases The image forming apparatus according to claim 3.

5. The factor affecting the diffusion rate of the ink is the viscosity of the ink, The control unit, Set the ejection amount of the ink so that the ejection amount increases as the viscosity of the ink decreases The image forming apparatus according to claim 3.

6. The factor affecting the diffusion rate of the ink is the back pressure of the ink in the ink tank, The control unit, Set the ejection amount of the ink so that the ejection amount increases as the back pressure of the ink in the ink tank increases The image forming apparatus according to claim 3.

7. The control unit, Set the ejection amount of the ink according to the presence or absence of a water-repellent film formed on the nozzle surface where the nozzles of the inkjet head are formed The image forming apparatus according to claim 1.

8. The inkjet head ejects single-color ink, Comprising a plurality of the inkjet heads The image forming apparatus according to claim 1.

9. The inkjet head has nozzles for ejecting inks of a plurality of colors The image forming apparatus according to claim 1.

10. Perform a nozzle wiping operation on an inkjet head having nozzles for ejecting ink, According to the waiting time from when the nozzle wiping operation is performed until the flushing operation is started, change the ejection amount of the ink ejected from the nozzle during the flushing operation An ejection amount adjustment method.

11. A program that causes a computer to execute the ejection amount adjustment method according to claim 10.

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