Image forming apparatus and method for controlling the same

In an image forming apparatus, a first duct connects a tank to a syringe. A second duct connects the syringe to a damper. A third duct connects the damper to the tank. A liquid surface sensor senses whether or not a liquid surface of the ink in the tank is located at or below a reference position. In a measurement mode, a controller performs injection of the ink into the damper after closing the first and third ducts. The controller opens the third duct after the damper is deformed. Then, the controller closes the second and third ducts. The controller opens the first duct and recognizes a suction amount of the ink sucked from the start of the suction until an output of the liquid surface sensor changes. The controller determines a variation amount based on the suction amount recognized.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2018-189753 filed on Oct. 5, 2018, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to an image forming apparatus which performs printing by ejecting ink from a nozzle.

There are apparatuses that perform printing with ink. Such printing apparatuses are each provided with a head including a plurality of nozzles. Ink is ejected from the nozzles onto a sheet based on image data. When the ink is consumed, fresh ink is supplied to the head from an ink storage media (a tank). In some of such printing apparatuses, the ink flow path from the tank to the head is configured openable and closable. Regarding this configuration, there has been known the following technology.

Specifically, there is known an inkjet recording apparatus having an ink cartridge attachably and detachably attached in an ink supply path via which ink is supplied, and the ink cartridge has a region formed therein where a flow path is closable. The region of the ink cartridge is pressable, and ink is supplied to a recording head by pressing the region, and with the thereby supplied ink, the recording head performs printing. Then, the recording head is sealed, and a negative pressure is supplied to capping means.

There are cases where a damper is disposed in the middle of an ink flow path from an ink tank to a head. For example, the damper is connected to the head. For example, the damper moderates the variation of pressure applied to the ink inside a nozzle of the head. This helps reduce irregular ink ejection.

On the other hand, ink includes a vaporable component. If a nozzle is left unused (in other words, does not eject ink) for a long time, the ink in the nozzle becomes increasingly viscous (condensed) due to the evaporation of the vaporable component. The increasingly viscous (dried) ink sometimes causes poor ink ejection. Further, dust or fine particles adhered to a nozzle may prevent the nozzle from ejecting ink. To prevent such failures, there are cases where cleaning is performed to forcibly eject ink from nozzles. The cleaning helps prevent occurrence of such failures. Further, there are cases where even if a failure occurs, the failure can be cleared.

To perform forcible ink discharge, ink is sent out of an ink tank. For example, a pump is used to push the ink into a head with a strong force (a high pressure). The high pressure pushes the ink out of the nozzles of the head. Thereby, the highly viscous ink is pushed out of the nozzles. Dust and fine particles are washed away from the nozzles.

In a case where forcible ink discharge is performed, the pressure applied to the ink sometimes caused deformation of the damper. When the damper has a withstanding pressure lower than the pressure applied to the ink, the damper is deformed (expanded). The expanded damper has an increased capacity. As a result of the deformation of the damper, it sometimes happens that the amount of forcibly ejected ink is reduced. If the reduction of the amount is too great, it is impossible to obtain a sufficient effect of cleaning. On the other hand, there are individual differences in the deformation amount (the capacity variation amount) among different dampers. The capacity variation amount differs from damper to damper. To obtain a sufficient effect of cleaning, it is disadvantageously necessary to accurately measure the amount of variation in damper capacity (the amount of variation in damper ink capacity) caused by the deformation. Note that the above-described known technology is not related to damper deformation.

SUMMARY

According to an aspect of the present disclosure, an image forming apparatus includes a head, a tank, a syringe, a damper, a first duct, a second duct, a third duct, a liquid surface sensor, and a controller. The head performs printing by ejecting ink. The tank stores the ink therein. The syringe performs injection or suction of the ink. The damper supplies the ink to the head, and the ink is injected into the damper from the syringe. The first duct is a flow path that connects the tank and the syringe to each other for conveyance of the ink between the tank and the syringe. The second duct is a flow path that connects the syringe and the damper to each other for conveyance of the ink between the syringe and the damper. The third duct is a flow path that connects the damper and the tank to each other for conveyance of the ink between the damper and the tank. The liquid surface sensor senses whether or not a liquid surface of the ink in the tank is located at or below a reference position. The controller receives an output of the liquid surface sensor. In a measurement mode, in which a variation amount indicating an amount of variation in ink capacity of the damper caused by deformation of the damper is measured, the controller performs pressure applying processing, pressure releasing processing, and liquid surface lowering processing. The controller performs the pressure releasing processing after the pressure applying processing. In the pressure applying processing, the controller closes the first duct and the third duct. Then, the controller makes the syringe perform the injection of the ink into the damper to cause deformation of the damper. After the damper is deformed, the controller, in the pressure releasing processing, makes the syringe stop injecting the ink into the damper. The controller opens the third duct. After the pressure releasing processing, the controller performs the liquid surface lowering processing. In the liquid surface lowering processing, the controller closes the second duct and the third duct. The controller, with the first duct open, makes the syringe perform the suction of the ink from the tank. The controller recognizes a suction amount of the ink sucked by the syringe from a start of the suction of the ink until an output of the liquid surface sensor changes. The controller determines the variation amount based on the suction amount recognized.

According to another aspect of the present disclosure, a method for controlling an image forming apparatus includes performing printing by ejecting ink from a head, storing the ink in a tank, performing injection or suction of the ink by using a syringe, supplying the ink from a damper to the head and injecting the ink from the syringe into the damper, a first duct connecting the tank and the syringe to each other, a second duct connecting the syringe and the damper to each other, a third duct connecting the damper and the tank to each other, sensing whether or not a liquid surface of the ink in the tank is located at or below a reference position by using a liquid surface sensor, performing pressure applying processing, pressure releasing processing, and liquid surface lowering processing in a measurement mode, in which a variation amount indicating an amount of variation in ink capacity of the damper caused by deformation of the damper is measured, performing the pressure releasing processing after the pressure applying processing, in the pressure applying processing, closing the first duct and the third duct and then the syringe performing the injection of the ink into the damper to deform the damper, in the pressure releasing processing performed after the damper is deformed, the syringe stopping the injection of the ink into the damper and opening the third duct, performing the liquid surface lowering processing after the pressure releasing processing, in the liquid surface lowering processing, closing the second duct and the third duct, the syringe performing the suction of the ink from the tank, and recognizing a suction amount of the ink sucked by the syringe from a start of the suction until an output of the liquid surface sensor changes, and determining the variation amount based on the suction amount recognized.

Further features and advantages of the present disclosure will become apparent from the description of embodiments given below.

DETAILED DESCRIPTION

The present disclosure accurately measures the amount of variation caused in damper capacity by deformation of the damper occurring when pressure is applied to ink. Hereinafter, with reference toFIG. 1toFIG. 12, an embodiment of the present disclosure will be described. The following description will deal with a printer100as an example of an image forming apparatus. The printer100(an inkjet printing apparatus) performs printing with ink. It should be understood that all the features, in terms of structure, arrangement, and the like, described in connection with the embodiment are merely examples for the sake of description, and are in no way meant to limit the scope of the disclosure.

First, a description will be given of the outline of the printer100according to the embodiment, with reference toFIG. 1. The printer100includes a controller1(control board). The controller1controls each portion of the printer100. The controller1includes a control circuit11and an image processing circuit12. For example, the control circuit11is a CPU. The control circuit performs operations and processing based on a control program and control data stored in a storage media2. The storage media2includes a nonvolatile storage device, such as a ROM, an HDD, and a flash ROM, and a volatile storage device, such as a RAM. The image processing circuit12performs image processing on image data. The image processing circuit12generates image data (image data for ink ejection) to be used in printing. The image data for ink ejection is data for instructing whether or not to eject ink with respect to each nozzle51(pixel).

The printer100includes an operation panel3. The operation panel3includes a display panel31and a touch panel32. The display panel31displays a setting screen and information. The display panel31displays operation images such as of a key, a button, and a tab. The touch panel32detects a touch operation performed with respect to the display panel31. Based on the output of the touch panel32, the controller1recognizes an operated one of the operation images. The control unit1thus recognizes a setting operation performed by a user.

The printer100includes a sheet feeder4a, a sheet conveyor4b, and an image former4c. The sheet feeder4ahas a stack of sheets placed thereon. In a print job, the controller1makes the sheet feeder4aperform sheet feeding. The controller1makes the sheet conveyor4bperform sheet conveyance. The sheet conveyor4bincludes a conveyance motor41and a sheet conveying rotation body. The controller1makes the conveyance motor41rotate. The rotation of the conveyance motor41causes the sheet conveying rotation body to rotate. Thereby, a sheet fed from the sheet feeder4ais conveyed toward a discharge tray (not shown).

The sheet conveyor4bincludes a belt conveyance unit42and an attractor43. The belt conveyance unit42conveys a sheet. The belt conveyance unit42includes a conveyance belt. The conveyance belt is rotatable. A sheet is conveyed on the conveyance belt. Above the belt conveyance unit42, the image former4cis provided. The image former4cis disposed to be above the sheet placed on the conveyance belt. The attractor43is provided in the belt conveyance unit42. By being attracted by the attractor43, the sheet on the conveyance belt does not shift its position. Further, the controller1makes the sheet conveyor4bperform discharging of the sheet after recording (printing) is performed on the sheet.

The image former4cejects ink onto the sheet placed on the conveyance belt, and thereby records (prints) an image on the sheet. As shown inFIG. 1, the printer100includes four line heads5(5Bk,5C,5M,5Y) corresponding to four colors. The line heads are stationary. The positions of the line heads5do not change. The line heads5are arranged to be above the sheet under conveyance. The line head5Bk ejects black ink. The line head5C ejects cyan ink. The line head5M ejects magenta ink. The line head5Y ejects yellow ink.

Ink replenishers6(6Bk,6C,6M,6Y) are provided each to supply ink to a corresponding one of the line heads5. The ink replenisher6Bk supplies the black ink to the line head5for black. The ink replenisher6C supplies the cyan ink to the line head5for cyan. The ink replenisher6M supplies the magenta ink to the line head5for magenta. The ink replenisher6Y supplies the yellow ink to the line head5for yellow.

The printer100includes a communication interface13. The communication interface13includes communication hardware (a connector, a communication circuit) and communication software. The communication interface13communicates with a computer200. The computer200is a personal computer or a server, for example. The controller1receives printing data from the computer200. The printing data includes settings for printing and contents to be printed. For example, the printing data includes data described in a page description language. Based on the received printing data, the controller1(the image processing circuit12) generates image data (raster data) to be used for image formation performed in the image former4c. The image processing circuit12processes the raster data to generate image data for ink ejection.

Next, with reference toFIG. 2, a description will be given of an example of ink ejection control performed in the printer100according to the embodiment. The line head5for each color includes two or more (a plurality of) heads50. The line head5is formed by combining the plurality of heads50. Each head50has a smaller length in a main scanning direction (a direction perpendicular to a sheet conveyance direction) than each line head5. The line head5for each color is formed by arranging the heads50in a staggered manner, for example. The recording heads50each include a plurality of nozzles51. The nozzles51are arranged in a row. The heads50are each fixed such that the nozzles51are arranged in a row in the direction perpendicular to the sheet conveyance direction.

As shown inFIG. 2, the recording heads50each include a plurality of nozzles51. For example, the nozzles51are formed by etching or boring a metal sheet. The nozzles51are formed at regular intervals in the main scanning direction. The interval between each two adjacent ones of the nozzles51in the main scanning direction determines a pixel-to-pixel pitch. The openings of these nozzles51face a sheet under conveyance. With respect to each nozzle51, one driving element52is provided. The driving element52is a piezoelectric element (a piezo element). Thus, the heads50are each provided with a plurality of the nozzles51which eject ink and a plurality of the driving elements52which make the nozzles51eject ink.

A plurality of driver circuits53are provided one for each, or one for two or more, of the plurality of heads50.FIG. 3shows a case where a plurality of the driver circuits53are provided one for each head50. Or, one driver circuit53may control two or more of the heads50, instead. The driver circuit53feeds an ejection signal S0to the driving element52of a nozzle51from which ink is to be ejected. The ejection signal S0has a pulse waveform. By the application of the ejection signal S0, the driver circuit53controls the ejection of ink from the nozzle51. The driving element52is deformed when voltage is applied thereto. Pressure caused by the deformation is applied to the nozzle51and to a flow path through which ink is to be supplied to the nozzle51. The thus applied pressure causes the ink to be ejected from the nozzle51. The ink impacts on the sheet under conveyance. Thereby, an image is formed (recorded) on the sheet.

In printing, the controller1(the control circuit11, the image processing circuit12) makes the driver circuit53cause ink to be ejected from the nozzles. Here, the controller1does not make the driver circuit53apply voltage to such a driving element52as corresponds to a pixel at which no ink is to be ejected. The controller1(the image processing circuit12) generates image data for ink ejection for each of the line heads5(that is, for each color). The controller1transmits the generated image data to each of the heads50. The image data for ink ejection is data (binary data) for instructions on whether or not to eject ink with respect to each pixel of each line. The controller1(the image processing circuit12) transmits the image data for ink ejection to each driver circuit53on a line-by-line basis in the main scanning direction.

The driver circuit53, based on the image data for ink ejection, feeds the ejection signal S0(applies voltage) to a driving element52that corresponds to a nozzle51from which ink is to be ejected. Note that, for the sake of convenience, an interior of only the line head5Bk of the plurality of line heads5is illustrated inFIG. 2. The line heads5for the different colors are similar to each other in configuration.

The controller1may feed a clock signal to each of the driver circuits53. Based on the clock signal, an ink-ejection cycle (frequency) is determined. In a print job, the ejection signal S0, which is fed to the driving elements52by the driver circuits53, has a constant frequency (voltage-application frequency). The sheet is conveyed at a sheet conveyance speed such that the sheet moves by a distance corresponding to one dot (one line) in one ink-ejection cycle. The controller1makes the sheet conveyor4bconvey the sheet at a predetermined sheet conveyance speed. Based on the image data, the driver circuit53applies voltage to a driving element52that corresponds to a pixel (a nozzle51) at which ink is to be ejected. This processing is repeated from top to bottom of a page in the sheet conveyance direction (a sub scanning direction), and thereby one page is printed.

Next, a description will be given of an example of the ink replenishers6according to the embodiment, with reference toFIG. 3toFIG. 6. The ink replenishers6are provided one for each of the line heads5.FIG. 3shows the ink replenisher6for one of the line heads5for the four colors. The ink replenishers6in the line heads5for the four colors are similar to each other in configuration. The same description is applicable to all the ink replenishers6. Thus, in the following description, the signs Bk, C, M, and Y, which indicate the four colors, will be omitted.

The ink replenisher6includes an ink container60, a tank7, a syringe8, a damper9, a replenishment pipe6a, a first duct61, a second duct62, a third duct63, a fourth duct64, a liquid surface sensor71, and a pump65.

The ink container60contains ink to be replenished to the line head5. The ink container60for black contains black ink. The ink container60for cyan contains cyan ink. The ink container60for magenta contains magenta ink. The ink container60for yellow contains yellow ink.

The ink container60is connected to the tank7via the replenishment pipe6a. The replenishment pipe6afunctions as an ink flow path from the ink container60to the tank7. Via the replenishment pipe6a, the ink in the ink container60is sent into the tank7. The tank7stores the ink therein. The maximum ink capacity of the tank7is smaller than that of the ink container60.

Inside the tank7, the liquid surface sensor71is provided. The liquid surface sensor71is a sensor for sensing whether or not a position (a height) of the surface of the ink inside the tank7is at or below a reference position H1. The reference position H1indicates the height of the liquid surface to be maintained in the tank7. For example, the reference position H1is at a height that is three-fourths of the entire height of the tank7.

When the liquid surface is located above the reference position H1, the liquid surface sensor71outputs a first-level voltage. When the liquid surface is located at or below the reference position H1, the liquid surface sensor71outputs a second-level voltage. When the first level is High level, the second level is Low level. When the first level is Low level, the second level is High level.

The output of the liquid surface sensor71is fed to the controller1. The controller1is capable of recognizing whether or not the position (the height) of the liquid surface is at or below the reference position H1based on an output level of the liquid surface sensor71. When the liquid surface in the tank7has descended to or below the reference position H1(that is, when the output level of the liquid surface sensor71has become the second level), the controller1makes the pump65operate. The pump65operates to send the ink from the ink container60into the tank7. The controller1makes the pump65continue to operate until the output level of the liquid surface sensor71changes to the first level. When the output level of the liquid surface sensor71has changed to the first level, the controller1makes the pump65stop operating. The height of the liquid surface in the tank7is thus maintained at the reference position H1.

The syringe8performs injection or suction of the ink. For example, the syringe8sucks (draws up) the ink from the tank7. The syringe8injects (pushes out) the ink into the damper9. The damper9receives the ink from the syringe8. The ink in the damper9is supplied to each of the heads50of the line head5. In other words, the ink in the damper9is supplied into the nozzles51, and ink flow paths provided inside the line head5. Further, the damper9moderates variation of pressure applied to the ink. It is thus possible to reduce variation of the amount of ink ejected when the driving element52is made to operate.

The plurality of ducts are provided for the purpose of conveying (passing) the ink between the tank7, the syringe8, and the damper9. The ducts each function as an ink flow path. The first duct61connects the tank7to the syringe8. The ink directed from the tank7to the syringe8, or from the syringe8to the tank7from the syringe8, passes through the first duct61. The second duct62connects the syringe8to the damper9. The ink directed from the syringe8to the damper9, or from the damper9to the syringe8, passes through the second duct62. The third duct63connects the damper9to the tank7. The ink directed from the damper9to the tank7passes through the third duct63.

Further, one end of the fourth duct64is connected to the syringe8. The fourth duct64is a pipe for releasing air from inside the syringe8. The other end of the fourth duct64is connected to the tank7. The air having been released from the syringe8is blown into the tank7. The air having been blown into the tank7floats up as bubbles. The released air thus eventually mixes with air that is present above the liquid surface.

The printer100(the ink replenisher6) includes a first opening-closing portion91, a second opening-closing portion92, a third opening-closing portion93, and a fourth opening-closing portion94. The first opening-closing portion91performs opening and closing of the first duct61(bringing the ink flow path into a communicating state and a cut-off state). The second opening-closing portion92performs opening and closing of the second duct62(bringing the ink flow path into a communicating state and a cut-off state). The third opening-closing portion93performs opening and closing of the third duct63(bringing the ink flow path into a communicating state and a cut-off state). The fourth opening-closing portion94performs opening and closing of the fourth duct64(bringing the air flow path into a communicating state and a cut-off state).

As shown inFIG. 4, in order to perform operations of bringing the first duct61into the communicating state and the cut-off state, the first opening-closing portion91includes a first opening-closing motor91aand a first opening-closing cam91b. In order to perform operations of bringing the second duct62into the communicating state and the cut-off state, the second opening-closing portion92includes a second opening-closing motor92aand a second opening-closing cam92b. In order to perform operations of bringing the third duct63into the communicating state and the cut-off state, the third opening-closing portion93includes a third opening-closing motor93aand a third opening-closing cam93b. In order to perform operations of bringing the fourth duct64into the communicating state and the cut-off state, the fourth opening-closing portion94includes a fourth opening-closing motor94aand a fourth opening-closing cam94b.

The first duct61, the second duct62, the third duct63, and the fourth duct64are each, for example, a rubber tube, and thus can be bent or warped. They can also be squeezed (pressed from above) to thereby block the flow of substance (ink, air) that exists inside thereof.

As shown inFIG. 5, to open (to let the ink flow through) the first duct61, the controller1rotates (controls) the first opening-closing motor91a. The controller1rotates the first opening-closing cam91bby a rotation angle that does not cause the first opening-closing cam91bto squeeze (press, contact) the first duct61. To close (to block the flow of the ink through) the first duct61, the controller1rotates (controls) the first opening-closing motor91a. The controller1rotates the first opening-closing cam91bby a rotation angle that causes the first opening-closing cam91bto squeeze (press) the first duct61.

To open (to let the ink flow through) the second duct62, the controller1rotates (controls) the second opening-closing motor92a. The controller1rotates the second opening-closing cam92bby a rotation angle that does not cause the second opening-closing cam92bto squeeze (press, contact) the second duct62. To close (to block the flow of the ink through) the second duct62, the controller1rotates (controls) the second opening-closing motor92a. The controller1rotates the second opening-closing cam92bby a rotation angle that causes the second opening-closing cam92bto squeeze (press) the second duct62.

To open (to let the ink flow through) the third duct63, the controller1rotates (controls) the third opening-closing motor93a. The controller1rotates the third opening-closing cam93bby a rotation angle that does not cause the third opening-closing cam93bto squeeze (press, contact) the third duct63. To close (to block the flow of the ink through) the third duct63, the controller1rotates (controls) the third opening-closing motor93a. The controller1rotates the third opening-closing cam93bby a rotation angle that causes the third opening-closing cam93bto squeeze (press) the third duct63.

To open (to let air flow through) the fourth duct64, the controller1rotates (controls) the fourth opening-closing motor94a. The controller1rotates the fourth opening-closing cam94bby a rotation angle that does not cause the fourth opening-closing cam94bto squeeze (press, contact) the fourth duct64. To close (to block the flow of the ink through) the fourth duct64, the controller1rotates (controls) the fourth opening-closing motor93a. The controller1rotates the fourth opening-closing cam94bby a rotation angle that causes the fourth opening-closing cam9bbto squeeze (press) the fourth duct64.

Next, with reference toFIG. 3andFIG. 6, the syringe8will be described. The syringe8includes, for example, an ink cylinder81and a movable member82(a plunger). For example, the ink cylinder81has a circular cylindrical shape. The ink cylinder81has an open top. The ink cylinder81has the first duct61and the second duct62connected to its bottom.

As shown inFIG. 6, the movable member82is inserted inside the ink cylinder81from above the ink cylinder81. The movable member82is reverse T-shaped in vertical section. That is, the movable member82has a shape similar to the shape of a plunger of an injector. A leading end part (a lower side part) of the movable member82is formed as an airtight sealing portion82a. The bottom surface of the airtight sealing portion82a(the movable member82) has substantially the same shape as the inside bottom of the ink cylinder81. The airtight sealing portion82ais a member for achieving airtightness, such as a seal. The airtight sealing portion82adoes not allow the ink inside thereof from leaking over the top thereof.

The fourth duct64is inserted through the movable member82at an inner part (at a center) of the movable member82. The fourth duct64is placed through the movable member82, from the uppermost part through the bottom surface of the movable member82. When the movable member82moves downward, air present under the movable member82inside in the ink cylinder81is released through the fourth duct64. Then, the top surface of the ink inside the ink cylinder81comes into contact with the lower surface of the airtight sealing portion82a. A vertical side surface of the movable member82is provided with a toothed surface83. The toothed surface83has teeth arranged in the vertical direction. Provided to mesh with these teeth is a gear84. A syringe motor85is provided to rotate the gear84. The syringe motor85is rotatable forwardly and reversely. By rotating the syringe motor85, it is possible to vertically move the movable member82.

To inject (push out) the ink from the syringe8into the tank7or the damper9, the controller1rotates the syringe motor85in a direction for causing the movable member82to move downward. To increase the amount of ink in the syringe8(by sucking), the controller1rotates the syringe motor85in a direction for causing the movable member82to move upward. Here, in injecting the ink or sucking the ink, the controller1closes (cuts off) the fourth duct64. Before injecting the ink or sucking the ink, the controller1opens the fourth duct64and makes the movable member82move to release air from inside the ink cylinder81.

Further, the area of the bottom (a horizontal sectional area) of the ink cylinder81is fixed. By multiplying the bottom area with the movement amount (height) of the movable member82, the controller1is able to recognize the amount of ink injected or sucked. For example, the syringe motor85may be a stepping motor. The controller1recognizes a downward movement amount of the movable member82based on the number of rotations (the rotation angle) of the syringe motor85performed from the start till the end of injection. By multiplying the downward movement amount by the bottom area, the controller1recognizes the amount of ink injected.

Likewise, by multiplying the bottom area by the movement amount (height) of the movable member82, the controller1is able to recognize the amount of ink sucked. The controller1recognizes an upward movement amount of the movable member82based on the number of rotations (the rotation angle) of the syringe motor85performed from the start till the end of sucking. By multiplying the upward movement amount by the bottom area, the controller1recognizes the amount of ink sucked.

Next, with reference toFIG. 7, a description will be given of an example of deformation of the damper9according to the embodiment. The printer100is able to perform forcible ink discharge processing. In the forcible ink discharge processing, pressure is applied to the ink. For pressure application, ink is injected into the damper9from the syringe8. Thereby, ink flows out of the nozzles51of the line head5. Through the forcible ink discharge processing, it is possible to discharge highly condensed, highly viscous, residual ink from the nozzles51. Further, the forcible ink discharge processing sometimes helps remove dust adhered on the nozzles51.

Here, the belt conveyance unit42is vertically movable. The printer100includes an elevator mechanism for vertically moving the belt conveyance unit42. To perform the forcible ink discharge processing, the controller1moves the belt conveyance unit42downward. The controller1increases the distance between the line head5(the nozzles51) and the conveyance belt. The controller1puts an ink receiving tray in the created space. The printer100includes a moving mechanism for moving the ink receiving tray. The ink receiving tray receives discharged ink. For example, the ink receiving tray is provided with an ink absorbing sponge. After the forcible ink discharge processing is performed, the controller1retracts the ink receiving tray. The controller1moves the belt conveyance unit42upward. The controller1thereby moves the belt conveyance unit42back to its original position.

The controller1may perform the forcible ink discharge processing when the operation panel3has received an instruction to execute the forcible ink discharge processing. Further, the controller1may perform the forcible ink discharge processing every time the printer100has performed printing on a predetermined number of sheets. Further, the controller1may perform the forcible ink discharge processing at a previously set time.

In performing the forcible ink discharge processing, the controller1applies pressure to the ink to be injected into the line head5. The pressure applied to the ink at this time is greater than that in the normal ink ejection. To apply pressure to the ink, the controller1cuts off (closes) the first duct61(the first opening-closing portion91) and the third duct63(the third opening-closing portion93) (seeFIG. 7). The controller1also cuts off (closes) the fourth duct64(the fourth opening-closing portion94). On the other hand, in order to send the ink into the line head5, the controller1brings the second duct62(the second opening-closing portion92) into the communicating state (open state).

Further, the controller1makes the syringe8perform injection of the ink. The controller1rotates the syringe motor85to move the movable member82downward. Thereby, pressure is applied to the ink so that ink can be pushed out of the nozzles51of the line head5.

The damper9is formed of, for example, a metal sheet. There is a case where pressure applied to the ink in the forcible ink discharge processing causes swelling of the damper9. This deformation increases the inner capacity of the damper9.

For example, assume a case where, in the forcible ink discharge processing, ink of an amount of X mL is injected from the syringe8into the damper9. Here, assume that the damper9is deformed such that the amount of ink held in the damper9increases by Y mL. Then, the amount of ink discharged in the forcible ink discharge processing is (X-Y) mL. In this case, it may be difficult to achieve a sufficient cleaning effect through the forcible ink discharge processing. Further, the amount of ink discharged in the forcible ink discharge processing may be reduced, and it may become difficult to appropriately manage the amount of residual ink.

To deal with such inconvenience, the printer100has a measurement mode. The measurement mode is a mode for measuring a variation amount21(an increase amount) of the ink capacity of the damper9caused by the deformation. Through this measurement, the controller1determines (recognizes) the variation amount21. Here, the ink might leak from the nozzles51in the measurement mode. In case of such ink leakage, the controller1puts the ink receiving tray below the head line5.

Next, a description will be given of an example of the flow of processing in the measurement mode according to the embodiment, with reference toFIG. 8toFIG. 12. The processing performed in the measurement mode is broadly divided into three kinds of processing, namely, pressure applying processing, pressure releasing processing, and liquid surface lowering processing. After the pressure releasing processing is performed lastly, the liquid surface lowering processing is performed. Measurement is performed with respect to each line head5(ink replenisher6).

First, with reference toFIG. 8toFIG. 10, an example of the pressure applying processing and an example of the pressure releasing processing will be described. “START” inFIG. 8indicates a time point when the measurement is started. That is, it is a time point when the controller1starts measuring the variation amount21. The operation panel3accepts starting of the measurement mode. To have the measurement of the variation amount21started, a user performs a predetermined operation on the operation panel3. In response to the operation panel3accepting the starting of the measurement mode, the controller1starts the processing shown in the flowchart ofFIG. 8.

First, the controller1closes the first duct61, the third duct63, and the fourth duct64(step #11). In other words, the controller1makes the first opening-closing portion91, the third opening-closing portion93, and the fourth opening-closing portion94operate to cut off the first duct61, the third duct63, and the fourth duct64(seeFIG. 9). Further, the controller1opens the second duct62(step #12). In other words, the controller1makes the second opening-closing portion92operate to bring the second duct62into the communicating state (seeFIG. 9).

Next, the controller1makes the syringe8perform injection of the ink of a reference injection amount22(step #13). The controller1makes the movable member82move in the direction (downward direction) in which the ink is to be injected. Since the second duct62is open, the ink is injected into the damper9(see a white arrow inFIG. 9). The controller1makes the syringe motor85rotate to move the movable member82move in the direction in which the ink is to be injected. Each white arrow inFIG. 9indicates the flow of ink caused by the syringe8. A solid arrow inFIG. 9indicates a direction in which the movable member82moves.

The reference injection amount22is determined in advance. For example, through an experiment, there is determined a preferable total amount of ink to be discharged from the nozzles51to achieve a satisfactory cleaning performance. The determined total amount can be used as the reference injection amount22. The storage media2stores the reference injection amount22in a nonvolatile manner (seeFIG. 1).

After the injection (pushing out) of the ink performed by the syringe8, the controller1starts the pressure releasing processing. First, the controller1makes the syringe8stop performing the injection of the ink (step #14). Further, the controller1opens the third duct63(step #15). The controller1makes the third opening-closing portion93operate to bring the flow path of the third duct63into the communicating state (seeFIG. 10). Here, the controller1may close, or may open, the first duct61, the second duct62, and the fourth duct64. InFIG. 10, the ducts are closed. The first, second, and fourth ducts61,62, and64may be opened or closed, as long as the ink of the variation amount21is allowed to flow (return) into the tank7. Through step #14and step #15, the pressure applied to the ink is released. The damper9, having been distorted (deformed), recovers its original shape. As a result, the ink of the variation amount21attributable to the deformation is returned into the tank7(see the white arrow inFIG. 10). As a result, the liquid surface in the tank7rises. The height (position) of the liquid surface is above the reference position H1.

Then, the controller1confirms whether or not the combination of the pressure applying processing and the pressure releasing processing has been performed a predetermined number of execution times (step #16). When the number of times the combination of the pressure applying processing and the pressure releasing processing has been performed is found to have reached the predetermined number of execution times (Yes in step #16), the present flow ends (END). When the number of times the combination of the pressure applying processing and the pressure releasing processing has been performed is found not to have reached the predetermined number of execution times (No in step #16), the flow returns to step #11.

The number of execution times the combination of the pressure applying processing and the pressure releasing processing is to be performed may be one time, or may be a plurality of times. The operation panel3accepts a setting of the number of execution times the combination of the pressure applying processing and the pressure releasing processing is to be performed. The controller1performs the combination of the pressure applying processing and the pressure releasing processing the set number of execution times. In a case where the set number of execution times is one time, the present flow ends when each of the pressure applying processing and the pressure releasing processing has been performed one time. In a case where the set number of times is a plurality of times, the present flow ends when the combination of the pressure applying processing and the pressure releasing processing has been repeated the plurality of times.

Next, with reference toFIG. 11andFIG. 12, an example of the liquid surface lowering processing will be described. “START” inFIG. 11is the time point at which the flowchart ofFIG. 8is finished.

First, the controller1closes the second duct62, the third duct63, and the fourth duct64(step #21). The controller1makes the second opening-closing portion92operate to bring the flow path of the second duct62into the cut-off state. This prevents the ink from being conveyed between the syringe8and the damper9. Further, the controller1makes the third opening-closing portion93operate to cut off the flow path of the third duct63. This prevents the ink from being conveyed between the damper9and the tank7. Further, the controller1makes the fourth opening-closing portion94operate to block the flow of air in the fourth duct64.

Next, the controller1opens the first duct61(step #22). The controller1makes the first opening-closing portion91operate to bring the first duct61into the communicating state. This allows the ink to be conveyed between the tank7and the syringe8.FIG. 12shows the open state and the closed state of the ducts in the liquid surface lowering processing.

Next, the controller1makes the syringe8start performing the suction of the ink (step #23). The controller1makes the movable member82move in the direction (upward direction) in which the ink is to be sucked. The controller1makes the syringe motor85rotate to make the movable member82move in the direction in which the ink is to be sucked. The white arrow inFIG. 12indicates the flow of ink caused by the syringe8. The solid arrow inFIG. 12indicates a direction in which the movable member82moves.

Simultaneously with the suction of the ink, the controller1starts measuring a suction amount of ink (step #24). For example, the controller1counts the number of rotations of the syringe motor85. The suction amount of ink per rotation of the syringe motor85is fixed. The controller1measures the suction amount of ink based on the number of rotations or the rotation angle of the syringe motor85counted or measured from the start of the suction of the ink.

The controller1continues to confirm whether or not the output level of the liquid surface sensor71has become the second level (step #25, No in step #25→step #25). In other words, the controller1confirms whether or not the syringe8has sucked the ink of an amount sufficient to lower the position of the liquid surface in the tank7to or below the reference position H1. The controller1makes the syringe8continue to perform the suction of the ink until the liquid surface in the tank7falls to or below the reference position H1. Note that, in the measurement mode, even when the output level of the liquid surface sensor71becomes the second level, the controller1does not immediately start replenishing the ink into the tank7(that is, does not make the pump65operate).

When the output level of he liquid surface sensor71has become the second level (Yes in step #25), the controller1makes the syringe8stop the suction of the ink (step #26). That is, the controller1makes the syringe motor85stop rotating.

The controller1recognizes the amount of ink sucked by the syringe8from the start of the suction of the ink until the output level of the liquid surface sensor71changes to the second level (step #27). Thereby, the controller1recognizes the amount of ink having been sent into the tank7through the pressure applying processing and the pressure releasing processing after the start of the measurement mode. For example, when the suction amount of ink per rotation of the syringe motor85is A mL, and the number of rotations of the syringe motor85from the start of the suction of the ink until the output level of the liquid surface sensor71changes to the second level is 7.5 times, the controller1recognizes that the suction amount is 7.5 A mL.

Based on the recognized suction amount, the controller1obtains the variation amount21(increase amount) of the capacity of the damper9caused by deformation (step #28). The controller1makes the storage media2store the thus obtained variation amount21in a nonvolatile manner (step #29, seeFIG. 1). Then, the present flow is finished (END).

In the case where the number of execution times the combination of the pressure applying processing and the pressure releasing processing is to be performed is one time, the controller1recognizes, as the variation amount21, the suction amount having been recognized in the liquid surface lowering processing.

In the case where the combination of the pressure applying processing and the pressure releasing processing has been repeated a plurality of times (when the number of execution times is a plurality of times), the controller1recognizes, as the variation amount21, a value obtained by dividing the suction amount having been recognized in the liquid surface lowering processing by the number of times the combination has been repeated (the set number of execution times). For example, when the combination is repeated five times, the controller1divides the recognized suction amount by five.

Next, with reference toFIG. 1, a description will be given of an example of correction performed in the printer100by using the recognized variation amount21.

(1) Forcible Ink Discharge Processing

In the forcible ink discharge processing, the syringe8injects ink into the damper9. With pressure applied thereto, the damper9becomes deformed (swollen), as a result of which the capacity (the ink capacity) of the damper9increases. Due to the deformation of the damper9, the amount of ink discharged from the nozzles51becomes smaller than the reference injection amount22. To deal with this, the controller1, based on the variation amount21, increases the amount of ink to be injected by the syringe8in the forcible ink discharge processing.

In the forcible ink discharge processing, the controller1closes the first duct61and the third duct63. The controller1makes the first opening-closing portion91cut off the flow path of the first duct61. Further, the controller1makes the third opening-closing portion93cut off the flow path of the third duct63. Here, the controller1may make the syringe8inject, toward the damper9, the ink of an amount equal to the sum of the reference injection amount22and the variation amount21. Thereby, even when the damper9is deformed, the total amount of ink discharged from the nozzles51is equal to the reference injection amount22.

(2) Management of Ink Consumption

The storage media2stores a cumulative consumption amount23in a nonvolatile manner (seeFIG. 1). The cumulative consumption amount23is, for example, data for managing the amount of ink consumed from when a new ink container60is installed until a current time point. For example, when a value obtained by subtracting the cumulative consumption amount23from the full ink capacity of the ink container60is found to be equal to or smaller than a predetermined value, the controller1makes the display panel31display a notification that only a small amount of ink remains in the ink container60. Thus, it is possible to notify the user that the ink container60will need to be replaced before long.

In the forcible ink discharge processing, ink is consumed. To the cumulative consumption amount23, the amount of ink consumed in the forcible ink discharge processing needs to be added. When the forcible ink discharge processing has been performed, the controller1makes the storage media2update the cumulative consumption amount23. When ink of an amount (an addition amount) equal to the sum of the reference injection amount22and the variation amount21has been injected into the damper9, the controller1makes the storage media2store the sum of the cumulative consumption amount23before update and the reference injection amount22as a new cumulative consumption amount23.

When the controller1has made the syringe8perform the injection of the ink of only the reference injection amount22, the controller1makes the storage media2store the sum of the cumulative consumption amount23before update and a subtraction value as a new cumulative consumption amount23. The subtraction value is a value obtained by subtracting the variation amount21from the reference injection amount22.

As has been described above, the image forming apparatus (the printer100) according to the embodiment includes the head50, the tank7, the syringe8, the damper9, the first duct61, the second duct62, the third duct63, the liquid surface sensor71, and the controller1. The head50performs printing by ejecting ink. The tank7stores the ink therein. The syringe8performs injection or suction of the ink. The damper9supplies the ink to the head50, and the ink is injected into the damper9from the syringe8. The first duct61is a flow path that connects the tank7and the syringe8to each other for conveyance of the ink between the tank7and the syringe8. The second duct62is a flow path that connects the syringe8and the damper9to each other for conveyance of the ink between the syringe8and the damper9. The third duct63is a flow path that connects the damper9and the tank7to each other for conveyance of the ink between the damper9and the tank7. The liquid surface sensor71senses whether or not the liquid surface of ink in the tank7is located at or below the reference position H1. The controller1receives an output of the liquid surface sensor71. In the measurement mode, in which the variation amount21indicating an amount of variation in ink capacity of the damper9caused by deformation of the damper9is measured, the controller1performs the pressure applying processing, the pressure releasing processing, and the liquid surface lowering processing. The controller1performs the pressure releasing processing after the pressure applying processing. In the pressure applying processing, the controller1closes the first duct61and the third duct63. Then, the controller1makes the syringe8inject ink into the damper9to deform the damper9. After the damper9is deformed, in the pressure releasing processing, the controller1makes the syringe8stop injecting ink into the damper9. The controller1opens the third duct63. After the pressure releasing processing, the controller1performs the liquid surface lowering processing. In the liquid surface lowering processing, the controller1closes the second duct62and the third duct63. The controller1, with the first duct61open, makes the syringe8such the ink from the tank7. The controller1recognizes the suction amount of ink sucked by the syringe8from the start of the suction of the ink until the output of the liquid surface sensor71changes. Based on the recognized suction amount, the controller1determines the variation amount21.

The pressure applying processing makes it possible to intentionally apply pressure to the ink to cause deformation of the damper9. The pressure releasing processing makes it possible to return, into the tank7, the ink of the variation amount21which indicates an amount of variation in ink capacity of the damper9(that is, the ink of an amount equal to the variation amount21indicating an amount of variation in ink capacity of the damper9caused by deformation of the damper9). It is possible to measure the variation amount21based on the amount of ink sucked by the syringe8until the height of the liquid surface in the tank7which has been caused to rise by the ink returned into the tank7lowers to the reference position H1. It is possible to obtain a correct variation amount21.

In the measurement mode, the controller1may perform each of the pressure applying processing and the pressure releasing processing one time. In this case, the controller1recognizes, as the variation amount21, the suction amount recognized in the liquid surface lowering processing. By performing each of the pressure applying processing, the pressure releasing processing, and the liquid surface lowering processing just one time, the variation amount21can be obtained (measured). Thus, it is possible to quickly measure the variation amount21in a minimum time.

Further, in the measurement mode, the controller1may repeat the combination of the pressure applying processing and the pressure releasing processing a plurality of times. In this case, the controller1starts the liquid surface lowering processing when the pressure releasing processing performed lastly is finished. The controller1recognizes, as the variation amount21, a value obtained by dividing the suction amount recognized in the liquid surface lowering processing by the number of times the combination has been performed. That is, the average value of the measurements performed the plurality of times can be obtained as the variation amount21. It is possible to obtain the variation amount21as the average value of amounts of ink returned into the tank7in the pressure applying processing and the pressure releasing processing performed the plurality of times. By calculating the average value, it is possible to obtain an accurate value as the variation amount21.

The image forming apparatus (the printer100) includes the first opening-closing portion91which performs switching between the open state and the closed state of the first duct61, the second opening-closing portion92which performs switching between the open state and the closed state of the second duct62, and the third opening-closing portion93which performs switching between the opens state and the closed state of the third duct63. Thus, it is possible to control opening and closing (communicating state and cut-off state) of each of the first duct61, the second duct62, and the third duct63.

The reference injection amount22of ink to be injected from the syringe8into the damper9in the forcible ink discharge processing, in which ink is forcibly discharged from the head50, is determined in advance. When performing the forcible ink discharge processing, the controller1closes the first duct61and the third duct63. When injecting ink into the damper9, the controller1may make the syringe8inject an amount equal to the sum of the reference injection amount22and the variation amount21. In the forcible ink discharge processing, even if the damper9is deformed, it is possible to have ink of a fixed amount forcibly discharged from the damper9. Even with individual differences between the dampers9in terms of deformation, it is possible to have ink of a fixed amount (the reference injection amount22) forcibly discharged from the dampers9.

The image forming apparatus includes the storage media2in which the cumulative consumption amount23is stored. When the forcible ink discharge processing is performed, the controller1closes the first duct61and the third duct63. When the syringe8has injected, into the damper9, ink of an amount equal to the sum of the reference injection amount22and the variation amount2, the controller1makes the storage media2update the cumulative consumption amount23by adding the reference injection amount22to it. When the syringe8has injected, into the damper9, ink of an amount equal to the reference injection amount22, the controller1makes the storage media2update the cumulative consumption amount23by adding thereto a value obtained by subtracting the variation amount21from the reference injection amount22. Thus, it is possible to accurately manage the amount of ink having been consumed in the image forming apparatus. Such accurate management of the cumulative consumption amount23makes it possible to make known an accurate remaining amount of ink. Moreover, it is possible to make an accurate notification that the amount of remaining ink has decreased.

It should be understood that the embodiments of the present disclosure described above are in no way meant to limit its scope; the present disclosure can be implemented with any modifications made without departing from its spirit.