Image forming device, method, and storage medium

An image forming device including a deaerator that deaerates liquid, a supply tank for storing liquid, a spray device that sprays liquid, and a controller. The controller executes a control causing supply of deaerated liquid from the deaerator to the supply tank, and from the supply tank to the spray device, and spraying of liquid by the spray device to form an image, and while waiting for image forming or while the supply of liquid from the supply tank to the spray device is stopped, the controller executes a control causing at least some of the liquid stored in the supply tank to be supplied to the deaerator in a direction opposite the supply from the deaerator to the supply tank, and causing the deaerator to deaerate the liquid so supplied.

The entire disclosure of Japanese patent Application No. 2021-085040, filed on May 20, 2021, is incorporated herein by reference in its entirety.

BACKGROUND

Technical Field

The present disclosure relates to techniques of image formation by ejecting liquid ink.

Description of Related Art

Conventionally, an inkjet recording device ejects ink stored in an ink tank via an inkjet head. When the inkjet recording device detects a decrease in an amount of ink stored in the ink tank, a print operation is stopped and ink is refilled from a refill tank to the ink tank. When the ink tank has been refilled with ink, the inkjet recording device resumes the print operation. Therefore, printing cannot be performed during refilling, which may reduce productivity of printing by the inkjet recording device.

According to JP 2015-123726, if a pressure value of an inkjet nozzle is less than a lower limit and height of ink in an ink tank is higher than a defined value, external air is taken into the ink tank to increase the pressure value of the nozzle. On the other hand, if the pressure value of the nozzle is less than the lower limit and the height of the ink in the ink tank is not higher than the defined value, new ink is supplied to increase the pressure value of the nozzle. In this way, the inkjet recording device can refill ink in the ink tank while adjusting pressure of the nozzle without stopping printing operation, thereby preventing printing productivity from being lowered.

SUMMARY

However, according to the inkjet recording device above, when ink is in contact with air for a long time in the ink tank, concentration of gas dissolved in the ink increases. In other words, a degree of degassing of the ink is reduced. When the degree of degassing of the ink is reduced, there is a technical problem that normal pressure is not applied to the ink in the nozzle of the inkjet head, and this may result in image quality deterioration such as image loss due to the ink not being ejected normally.

An object of the present disclosure is to provide an image forming device, a method, and a storage medium capable of suppressing a reduction in a degree of degassing of ink supplied to an ejector, thereby preventing deterioration of image quality.

An image forming device reflecting an aspect of the present disclosure is an image forming device including a deaerator that deaerates liquid, a supply tank for storing liquid, a spray device that sprays liquid, and a controller. The controller executes a control causing supply of deaerated liquid from the deaerator to the supply tank, and from the supply tank to the spray device, and spraying of liquid by the spray device to form an image, wherein while waiting for image forming or while the supply of liquid from the supply tank to the spray device is stopped, the controller executes a control causing at least some of the liquid stored in the supply tank to be supplied to the deaerator in a direction opposite the supply from the deaerator to the supply tank, and causing the deaerator to deaerate the liquid so supplied.

A method reflecting an aspect of the present disclosure is a method used by an image forming device, the image forming device including a deaerator that deaerates liquid, a supply tank for storing liquid, and a spray device that sprays liquid. The method including a first control causing supply of deaerated liquid from the deaerator to the supply tank, and from the supply tank to the spray device, and spraying of liquid by the spray device to form an image, and while waiting for image forming or while the supply of liquid from the supply tank to the spray device is stopped, a second control causing at least some of the liquid stored in the supply tank to be supplied to the deaerator in a direction opposite the supply from the deaerator to the supply tank, and causing the deaerator to deaerate the liquid so supplied.

A storage medium reflecting an aspect of the present disclosure is a non-transitory computer-readable storage medium storing a control program, the program being used by an image forming device including a deaerator that deaerates liquid, a supply tank for storing liquid, and a spray device that sprays liquid. The program causing the image forming device that is a computer to execute: a first control causing supply of deaerated liquid from the deaerator to the supply tank, and from the supply tank to the spray device, and spraying of liquid by the spray device to form an image; and while waiting for image forming or while the supply of liquid from the supply tank to the spray device is stopped, a second control causing at least some of the liquid stored in the supply tank to be supplied to the deaerator in a direction opposite the supply from the deaerator to the supply tank, and causing the deaerator to deaerate the liquid so supplied.

DETAILED DESCRIPTION

Hereinafter, one or more embodiments of the present disclosure will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments.

The following describes an image forming device1as an embodiment according to the present disclosure, with reference to the drawings.

The image forming device1, as illustrated inFIG.1, is provided with a sheet feeder17for accommodating and feeding out sheets, positioned towards a bottom of a housing. A printer16that forms an image by an inkjet method is provided above the sheet feeder17. An operation panel15that displays an operation screen and receives user operations is provided above the printer16. The operation panel15is provided with a display composed of a liquid crystal display panel or the like, and displays content set by a user and various messages. The operation panel15notifies the control circuitry50inside the housing of instructions and the like received due to user operation.

The image forming device1is connected to an information processing apparatus such as a personal computer (not shown) via a network. The image forming device1receives a print job including a print instruction, a number of repeated prints, image data to be printed, and the like from the information processing apparatus. The image forming device1generates print image data from the image data included in a received print job.

The sheet feeder17includes a sheet cassette90for accommodating sheets, a pickup roller91for feeding out sheets S from the sheet cassette90, and the like. A sheet S fed out from the sheet feeder17is conveyed towards the printer16on a conveyance path92above the sheet feeder17.

The printer16is provided with an endless belt20suspended taut around a driving roller22and a driven roller21. The driving roller22is rotated by a motor51, and rotation of the motor51is controlled by drive circuitry52. According to rotation of the driving roller22, the belt20travels in an X direction. The sheet S is conveyed by the belt20.

A carriage10is provided in a space above the belt20. The carriage10includes inkjet heads241(FIG.3B) for ejecting ink onto the sheet S conveyed on the belt20, according to an inkjet method. An image is formed on the sheet S by ejecting ink from the inkjet heads241based on generated print image data.

The sheet S on which the image is formed is conveyed on the belt20and carried out towards an ejection tray95via a conveyance path94.

FIG.2Ais a cross-section diagram taken along a line A-A inFIG.1of the carriage10of the image forming device1.FIG.2Bis a top view diagram of the carriage10as viewed from a direction B inFIG.1.

As illustrated inFIGS.2A,2B, a guide rail19(guide member) that has a frame shape that is long in a width direction of the belt20is disposed above the belt20and supported by a support member provided in the housing. The carriage10(movement member) on which the inkjet heads241are mounted is attached to the guide rail19so as to allow reciprocating movement. In this way, the guide rail19supports the carriage10so as to allow reciprocating movement. The carriage10reciprocates in a reciprocating direction C along the guide rail19, according to a drive mechanism (not shown).

As the sheet S is conveyed by the belt20to a position directly below the carriage10, the carriage10is moved along the guide rail19from a first end19aof the guide rail19towards a second end19bof the guard rail19, based on the print image data generated from a received print job. While moving, the inkjet heads241eject ink to form an image having a defined width on the sheet S in a main scanning direction. When forming of the image having the defined width is complete, the belt20conveys the sheet S forward by the defined width. Next, the carriage10that has returned to the first end19aof the guide rail19moves along the guide rail19again from the first end19aof the guide rail19towards the second end19bof the guide rail19while the inkjet heads241eject ink.

In this way, by repeating movement of the carriage10along the guide rail19and conveyance of the sheet S by the belt20by the defined width, an image corresponding to the print image data is formed on the sheet S.

As illustrated inFIG.2A,2B, the carriage10is provided with four head units31a,31b,31c,31dlined up in a reciprocating movement direction C of the carriage10.

The head units31a,31b,31c,31deach individually eject one color of ink, collectively ejecting four colors of ink: black (K), yellow (Y), magenta (M), and cyan (C), respectively. One color of ink is supplied to one head unit.

Colors of ink used in the image forming device1are not limited to this example, and other colors such as light yellow (LY), light magenta (LM), and light cyan (LC) can be used. In this case, a head unit corresponding to each color is mounted on the carriage10.

For each color of ink, the image forming device1is provided with a main tank11(FIG.1) for storing ink of the corresponding color, supported by a support member included in the housing. Each main tank11is connected to a corresponding one of the head units via an ink supply pipe. Ink in each main tank11is supplied to the corresponding heat unit via the corresponding ink supply pipe.

For simplicity,FIG.1illustrates only one main tank11. Similarly, for simplicity, one main tank11storing one color of ink is described below, and description of the other main tanks11storing other colors of ink is omitted.

As illustrated inFIG.4, the main tank11is connected to a pump71by an ink supply pipe151, and the pump71is connected to the degassing module14(deaerator) by an ink supply pipe152. Further, the main tank11is connected to a pump72by an ink supply pipe158, and the pump72is connected to a recovery side sub tank13, described later, by an ink supply pipe157.

Under control of printer control circuitry109, described later, drive circuitry61operates the pump71to supply ink stored in the main tank11to the degassing module14(E direction).

Further, under control of the printer control circuitry109, the drive circuitry62operates the pump72to supply ink stored in the recovery side sub tank13to the main tank11(E direction).

FIG.4andFIG.7schematically illustrate connections between the main pump11, the pump71, the degassing module14, the supply side sub tank12, the pump73, the inkjet heads241, the recovery side sub tank13, the pump74, and the pump72, and it should be noted that this does not indicate a vertical arrangement of the main tank11, the degassing module14, the supply side sub tank12, the recovery side sub tank13, and the like. The same applies toFIG.12toFIG.15.

1.5 Details of Head Units31a,31b,31c,31d

The following describes details of the head unit31a, as representative of the head units31a,31b,31c,31d. The head units31b,31c,31dhave the same structure as the head unit31a, and therefore corresponding description is omitted.

FIG.3Ais a schematic diagram of internal structure of the head unit31afrom a side view.FIG.3Bis a schematic view of the head unit31awhen viewed from a sheet S conveyed on the belt20.

The head unit31ais long in a conveyance direction of the sheet S (Y direction).

The head unit31aincludes the inkjet heads241(spray devices). In the example illustrated inFIG.3B,16inkjet heads241are provided in the head unit31a, and each of the16inkjet heads241is one of a set of two inkjet heads for a total of eight ink head modules242. Of the eight ink head modules242, four ink head modules242are arranged in a row in the Y direction and the remaining four ink head modules242are also arranged in a row in the Y direction. Each of the inkjet heads241ejects liquid ink.

The inkjet heads241are provided so that nozzles2411arranged along the Y direction are exposed on a lower surface of the head unit31ato face a sheet S conveyed on the belt20. Each of the nozzles2411is provided with an actuator composed of a piezoelectric element and a diaphragm (not shown), and when a voltage is applied to an electrode included in the piezoelectric element, the actuator is deformed and ink is ejected from the nozzle2411.

In this way, the inkjet heads241eject ink from the nozzles2411to form an image on the sheet S.

1.6 Supply Side Sub Tank12and Recovery Side Sub Tank13

As illustrated inFIG.3A, the head unit31aincludes the supply side sub tank12(supply tank) for storing liquid ink supplied to the inkjet head241and the recovery side sub tank13(recovery tank) for storing liquid ink recovered from the inkjet head241.

As illustrated inFIG.4, the supply side sub tank12is connected to the degassing module14by the ink supply pipe153. Further, the supply side sub tank12is connected to recovery side sub tank13by the ink supply pipe155via the inkjet head241. Further, the supply side sub tank12is connected to the pump73by the ink supply pipe154.

When ink is supplied to the supply side sub tank12, an ink layer made of ink and above the ink layer an air layer made of air are formed inside the supply side sub tank12.

The supply side sub tank12is provided with a sensor41that detects height of a liquid level of the ink stored therein (FIG.3A). The sensor41is, for example, a float sensor. The float sensor is provided inside the supply side sub tank12and detects the height of the liquid level of the ink.

In a case where ink stored in the supply side sub tank12is heated to be within a defined temperature range, the sensor41may be an infrared sensor. The infrared sensor is provided in a space outside the supply side sub tank12so that temperature of a wall surface outside the supply side sub tank12can be measured. The infrared sensor detects the height of the liquid level of think by measuring the temperature of the wall surface of the supply side sub tank12. The ink stored in the supply side sub tank12is heated, and therefore temperature of the ink layer and temperature of the air layer above are different in the supply side sub tank12. The height of the liquid level of the ink can be detected by knowing a position where a temperature difference occurs, based on measurement results by the infrared sensor.

The sensor41outputs a detected liquid level height H0(FIG.6) to the printer control circuitry109.

Further, as illustrated inFIG.4, the recovery side sub tank13is connected to the supply side sub tank12by the ink supply pipe155via the inkjet head241. Further, the recovery side sub tank13is connected to the pump72by the ink supply pipe157, and the pump72is connected to the main tank11by the ink supply pipe158. Further, the recovery side sub tank13is connected to the pump74by the ink supply pipe156.

The recovery side sub tank recovers and stores remaining ink after ink ejection by the inkjet head241.

When ink is supplied to the recovery side sub tank13, an ink layer made of ink and above the ink layer an air layer made of air are formed inside the recovery side sub tank13.

For simplicity, in reference toFIG.4, only one inkjet head241is described, and description of the other inkjet heads241is omitted. In reality, like the inkjet head241illustrated inFIG.4, a plurality of inkjet heads241are connected to the ink supply pipe155.

The image forming device1is provided with a degassing module14for each color (FIG.1), supported at a fixed position by a support member included in the housing. Further, as illustrated inFIG.4, the degassing modules14of each color are connected to the pump71by the ink supply pipe152. Further, the degassing modules14of each color are connected to the supply side sub tank12by the ink supply pipe153. The degassing modules14remove gas from the liquid inks.

For simplicity,FIG.1andFIG.4illustrate only one degassing module14for one color of ink. The degassing modules14corresponding to other ink colors have the same structure, and therefore description here is omitted.

Gas may be dissolved or bubbles may be present in ink. The degassing module14has a function of removing (degassing) dissolved gas and bubbles. The degassing module14includes a hollow fiber filter composed of a gas permeable membrane that allows only gas to pass though from a liquid/gas mix, thereby removing dissolved gas and bubbles from the ink.

The degassing module14removes dissolved gas and the like from ink supplied from the main tank11.

Ink from which dissolved gas and the like has been removed is supplied to the supply side sub tank12by the pump71.

Further, the degassing module14removes dissolved gas and the like from at least some ink supplied from the supply side sub tank12. Ink from which dissolved gas and the like has been removed is supplied to the main tank11by the pump71.

Circulation of ink from the main tank11to the main tank11via the degassing module14, the supply side sub tank12, the inkjet head241, and the recovery side sub tank13is described below with reference toFIG.4.

Under control of the printer control circuitry109, the drive circuitry61operates the pump71to supply ink stored in the main tank11to the degassing module14(E direction).

The degassing module14removes dissolved gas and the like from the ink.

Under control of the printer control circuitry109, the drive circuitry61operates the pump71to supply ink from which the degassing module14has removed dissolved gas and the like to the supply side sub tank12(E direction).

Under control of the printer control circuitry109, the drive circuitry63operates the pump73to make air pressure of the air layer in the supply side sub tank12positive, and under control of the printer control circuitry109, the drive circuitry64operates the pump74to make air pressure of the air layer in the recovery side sub tank13negative.

As a result of setting air pressure of the air layer in the supply side sub tank12positive and the air pressure of the air layer in the recovery side sub tank13negative, the ink stored in the supply side sub tank12is supplied to the nozzles of the inkjet head241via the ink supply pipe155(E direction).

Under control of the printer control circuitry109, some ink supplied to the nozzles of the inkjet head241is ejected from the nozzles by using piezoelectric elements that convert voltage into force. In this way, under control of the printer control circuitry109, an image is formed on the sheet S.

Remaining ink not ejected by the inkjet head241is supplied to the recovery side sub tank13via the ink supply pipe155(E direction).

Under control of the printer control circuitry109, the drive circuitry62operates the pump72to supply ink stored in the recovery side sub tank13to the main tank11(E direction).

In this way, under control of the printer control circuitry109, ink is supplied from the main tank11to the degassing module14. Subsequently, under control of the printer control circuitry109, degassed ink is supplied from the degassing module14to the supply side sub tank12. Subsequently, under control of the printer control circuitry109, ink is supplied from the supply side sub tank12to the inkjet head241. Subsequently, under control of the printer control circuitry109, recovered ink is supplied from the inkjet head241to the recovery side sub tank13. Subsequently, under control of the printer control circuitry109, ink supplied to the recovery side sub tank13is supplied to the main tank11. Next, under control of the printer control circuitry109, ink is returned from the main tank11to the supply side sub tank12via the degassing module14. Such circulating supply of ink can be referred to as liquid circulation (or circulation operation).

Liquid circulation is executed from a time when power of the image forming device1is turned on until a time when the power is turned off, except when an error occurs in the image forming device1.

Liquid circulation has an effect of preventing nozzles from drying out and an effect of preventing ink from settling when the ink is a dense pigment.

Here, the printer control circuitry109executes a control to stop liquid circulation (circulation operation) when an error occurs in image forming processing or when power of the image forming device1is turned off.

As described above, when subsequent image forming is performed, or when ink is next supplied from the supply side sub tank12to the inkjet head241, the printer control circuitry109executes a control to supply ink from the main tank11to the supply side sub tank12, and supply ink supplied to the supply side sub tank12to the recovery side sub tank13via the inkjet head241. Further, the printer control circuitry109executes a control so that image forming is performed after the liquid level of the supply side sub tank12and the liquid level of the recovery side sub tank13reach a defined height.

As illustrated inFIG.5, the control circuitry50includes a central processing unit (CPU)101, read-only memory (ROM)102, random access memory (RAM)103, image memory104, image processing circuitry105, network communication circuitry106, input/output circuitry108, the printer control circuitry109(control means), storage circuitry110, and the like.

The CPU101, the ROM102, and the RAM103constitute a main controller101a.

The RAM103temporarily stores various control variables and image forming conditions set by the operation panel15, and also provides a work area for program execution by the CPU101.

The ROM102stores a control program and the like for executing various jobs such as an image forming operation.

The CPU101operates according to a control program stored in the ROM102.

The CPU101, operating according to the control program, causes the main controller101ato uniformly control the image memory104, the image processing circuitry105, the network communication circuitry106, the input/output circuitry108, the printer control circuitry109, the storage circuitry110, and the like.

As described above, the control circuitry50is a computer system including a microprocessor and memory. The memory stores a computer program (control program) and the microprocessor operates according to the computer program. Here, the computer program is configured by combining instruction codes indicating commands to the computer in order to achieve a defined function.

The network communication circuitry106receives a print job from an information processing device such as a personal computer via a network such as a local area network (LAN).

When a print job is received by the network communication circuitry106, the main controller101acontrols the printer control circuitry109to execute image forming processing based on the received print job.

The image memory104temporarily stores image data from a print job or the like.

The image processing circuitry105, for example, executes various data processing on image data of each color component included in a print job, and converts image data into print image data of reproduction colors Y, M, C, K.

The input/output circuitry108relays transmission and reception of information between the operation panel15and the main controller101a.

The storage circuitry110includes an area for storing data.

The printer control circuitry109is described below.

The printer control circuitry109(controller) is also, like the control circuitry50, constituted by a CPU, ROM, RAM, and the like (not shown).

The RAM temporarily stores various control variables and provides a work area for program execution by the CPU. The ROM and the RAM store control programs and the like for executing various jobs such as an image forming operation. The CPU operates according to a control program stored in the ROM or RAM.

The printer control circuitry109fulfils its function by operating the CPU according to a control program stored in the ROM or RAM.

The printer control circuitry109controls the drive circuitry52to cause the belt20to travel.

Further, the printer control circuitry109(movement controller) controls the drive mechanism described above to cause reciprocating movement of the carriage10along the guide rail19in a reciprocating movement direction C.

Further, the printer control circuitry109controls the drive circuitry61,62,63,64to operate the pumps71,72,73,74, respectively, controlling ink supply from the main tank11to the main tank11, via the degassing module14, the supply side sub tank12, the inkjet head241, and the recovery side sub tank13(E direction inFIG.4).

Further, the printer control circuitry109executes a control such that while waiting for image formation (that is, waiting for reception of a print job or waiting for printing), or when supply of liquid from the supply side sub tank12to the inkjet head241is stopped, ink stored in the supply side sub tank12is returned again to the main tank11from the supply side sub tank12via the degassing module14by controlling the drive circuitry61to operate the pump71(F direction inFIG.7).

In this way, the pump71operates so that ink flows both in the E direction (FIG.4) and the opposite direction, the F direction (FIG.7).

Further, the printer control circuitry109receives the height H0(FIG.6) of the liquid level of the ink in the supply side sub tank12from the sensor41provided in the supply side sub tank12. The printer control circuitry109compares the height H0to a defined height H1(FIG.6), and if the height H0is lower than the defined height H1, controls the drive circuitry61to operate the pump71to control the supply of ink from the main tank11to the supply side sub tank12.

The printer control circuitry109executes a control such that an image is formed after the height H0reaches the defined height H1.

Further, when an error occurs in image forming processing or when power of the image forming device1is turned off, the printer control circuitry109executes a control with respect to the drive circuitry61, the drive circuitry62, the drive circuitry63, and the drive circuitry64such that liquid circulation is stopped.

1.11 Flow of Ink to Prevent Image Deterioration

Flow of ink for the purposes of suppressing a decrease in degassing of ink and preventing deterioration of image quality is described below, with reference toFIG.7.

For example, when a defined time T1has elapsed since printing was last stopped, the drive circuitry61operates the pump71under the control of the printer control circuitry109prior to execution of a next print, to supply at least some ink stored in the supply side sub tank12to the degassing module14(F direction inFIG.7), which is the direction opposite a supply direction from the degassing module14to the supply side sub tank12(E direction inFIG.4).

Here, the defined time T1may be 1 day, for example. When one day has passed since printing was last stopped, it may be considered that ink stored in the supply side sub tank12has been in contact with air in the supply side sub tank12for a long time, and therefore the degree to which the ink is degassed decreases.

Further, the defined time T1changes depending on an operating environment of the image forming device1.

Under control of the printer control circuitry109, the degassing module14removes air and the like dissolved in the ink supplied from the supply side sub tank12.

Further, under control of the printer control circuitry109, ink from which dissolved air and the like has been removed is supplied from the degassing module14to the main tank11(F direction) and stored in the main tank11.

Subsequently, when printing is executed, then as indicated inFIG.4, under control of the printer control circuitry109, the ink stored in the main tank11from which dissolved air and the like has been removed is supplied to the inkjet head241via the supply side sub tank12(E direction).

In this way, when the defined time T1has elapsed since printing was stopped, then under control of the printer control circuitry109, at least some of the ink of the supply side sub tank12is supplied to the degassing module14in a direction opposite a supply direction from the degassing module14to the supply side sub tank12. The degassing module14removes dissolved air and the like from the ink, and the ink from which dissolved air and the like has been removed is supplied to and stored in the main tank11.

Further, while waiting for image forming, for example while waiting for a print job or while supply of liquid from the supply side sub tank12to the inkjet head241is stopped, under control of the printer control circuitry109, at least some ink stored in the supply side sub tank12may be supplied to the degassing module14for degassing, in the direction opposite the supply direction from the degassing module14to the supply side sub tank12. Under control of the printer control circuitry109, the ink from which dissolved air and the like has been removed is further supplied to and stored in the main tank11.

Here, stopping of supply of liquid from the supply side sub tank12to the inkjet head241is stopping of the circulation operation described above.

Subsequently, when ink is used in printing, dissolved air and the like has been removed from the ink, and therefore a decrease in a degree of degassing can be suppressed, and deterioration of image quality can be prevented.

1.12 Operations of Image Forming Device1

Operations of the image forming device1are described below.

(1) Overall Operation of Image Forming Device1

Overall operation of the image forming device1is described with reference to a flowchart illustrated inFIG.8andFIG.9.

When power of the image forming device1is turned on (step S101), the printer control circuitry109receives the height H0of the liquid level of the ink in the supply side sub tank12from the sensor41. The printer control circuitry109compares the height H0received with the defined height H1and determines whether or not the height H0reaches the defined height H1(step S102).

If it is determined that the height H0has not reached the defined height H1(“NO” in step S102), the printer control circuitry109controls the drive circuitry61such that ink is supplied from the main tank11to the supply side sub tank12(step S103). Next, the printer control circuitry109causes a return to step S102and repeat processing.

If it is determined that the height H0has reached the defined height H1(“YES” in step S102), the printer control circuitry109instructs the drive circuitry61, the drive circuitry62, the drive circuitry63, and the drive circuitry64to execute liquid circulation, and liquid circulation is repeatedly executed (step S120).

Next, the printer control circuitry109determines whether or not the defined time T1has elapsed since printing was last stopped (step S105). Note that the printer control circuitry109may determine whether or not the defined time T1has elapsed since liquid circulation was last stopped. When it is determined that the defined time T1has elapsed (“YES” in step S105), the printer control circuitry109controls the drive circuitry61, the drive circuitry62, the drive circuitry63, and the drive circuitry64such that ink is supplied from the supply side sub tank12to the main tank11via the degassing module14(F direction inFIG.7), and from the recovery side sub tank13to the main tank11(E direction inFIG.7).

If it is determined that the defined time T1has not yet elapsed (“NO” in step S105), this processing by the printer control circuitry109does not occur.

The network communication circuitry106receives a print job or the operation panel15receives a user input operation (step S107).

If a print job is received (“YES” in step S108), the printer control circuitry109receives the height H0of ink in the supply side sub tank12from the sensor41. The printer control circuitry109compares the height H0received with the defined height H1and determines whether or not the height H0reaches the defined height H1(step S109).

If it is determined that the height H0has not reached the defined height H1(“NO” in step S102), the printer control circuitry109controls the drive circuitry61such that ink is supplied from the main tank11to the supply side sub tank12(step S114). Next, the printer control circuitry109causes a return to step S109and repeat processing.

If it is determined that the height H0has reached the defined height H1(“YES” in step S109), the printer control circuitry109causes execution of printing according to the print job (step S111). Next, the printer control circuitry109determines a print state (step S112). If it is determined that printing is completed normally (“normal completion” in step S112), the printer control circuitry109causes a return to step S105and repeat processing.

If it is determined that an error has occurred during printing (“error occurred” in step S112), the printer control circuitry109controls the drive circuitry61, the drive circuitry62, the drive circuitry63, and the drive circuitry64such that liquid circulation is stopped (step S113), and waits until the error that occurred is resolved.

If a power off operation is received (“YES” in step S115) instead of a print job (“NO” in step S108), the image forming device1powers off (step S116). When powering off, liquid circulation is of course stopped.

If a print job is not received (“NO” in step S108) and a power off operation is not received (“NO” in step S115), the image forming device1executes other processing corresponding to an input operation (step S117), the printer control circuitry109causes a return to step S105, and repeat processing.

This completes a series of processing.

(2) Liquid Circulation Operation

The liquid circulation operation is described below, with reference to the flowchart ofFIG.10.

The operation described here is the details of step S120inFIG.8.

The printer control circuitry109executes a control causing operation of the pump73by the drive circuitry63such that air pressure in the air layer in the supply side sub tank12becomes positive (step S131).

The printer control circuitry109executes a control causing operation of the pump74by the drive circuitry64such that air pressure in the air layer in the recovery side sub tank13becomes negative (step S132).

Step S131and step S132may be performed simultaneously.

Next, the printer control circuitry109executes a control causing operation of the pump72by the drive circuitry62such that ink in the recovery side sub tank13is supplied to the main tank11(step S133).

According to operations of step S131and operations of S132, ink stored in the supply side sub tank12is supplied to the recovery side sub tank13via the inkjet head241. Further, according to operation of step S133, ink stored in the recovery side sub tank13is recovered to the main tank11.

The printer control circuitry109executes a control such that steps S131to S133are repeatedly executed.

In this way, liquid circulation is implemented.

(3) Stopping Liquid Circulation

Stopping of liquid circulation is described below, with reference to the flowchart ofFIG.11.

The operation described here is the details of step S113inFIG.9.

The printer control circuitry109executes a control causing operation of the pump73by the drive circuitry63and operation of the pump74by the drive circuitry64, such that air pressure of the air layer in the supply side sub tank12and air pressure of the air layer in the recovery side sub tank13are equalized (step S141).

When air pressure of the air layer in the supply side sub tank12and air pressure of the air layer in the recovery side sub tank13are equalized, supply of ink stored in the supply side sub tank12to the recovery tank13via the inkjet head241is stopped.

As described above, according to at least one embodiment, while waiting for image forming or while supply of liquid from the supply side sub tank12to the inkjet head241is stopped, at least some ink stored in the supply side sub tank12is supplied to the degassing module14where air and the like dissolved in the ink is removed, and the ink from which dissolved air and the like has been removed is supplied to and stored in the main tank11. Subsequently, when ink is used in printing, dissolved air and the like has been removed from the ink, and therefore a decrease in a degree of degassing of ink supplied to the inkjet head241can be suppressed, and deterioration of image quality can be prevented.

(a) Errors as mentioned above may include occurrence of detection of a sheet jam, a sheet feed failure, an image forming defect, or the like. Further, stopping of liquid circulation of ink may be executed upon detection of a sheet jam, a sheet feed failure, an image forming defect, or the like.

A defect in image forming may be detected as follows. A sensor may be provided for image capture of an image formed on a sheet S conveyed on the belt20, an image of a defined pattern formed on the sheet S, and a comparison made between the defined pattern image and the image obtained by the sensor can be used to detect a defect in image forming.

(b) As described above, the supply side sub tank12is provided with the sensor41that detects height of a liquid level of ink stored inside, but the recovery side sub tank13may also, like the supply side sub tank12, be provided with a sensor that detects height of a liquid level of ink stored inside.

Further, in steps S102and S109inFIG.8, the printer control circuitry109receives the height H0of the liquid level of ink in the supply side sub tank12, compares the height H0to the defined height H1, and determines whether the height H0has reached the defined height H1, but may also determine whether or not the height of the liquid level in the recovery side sub tank13has reached a defined height based on detection by the sensor provided to the recovery side sub tank13.

Further, the printer control circuitry109may determine whether or not liquid level heights for both the supply side sub tank12and the recovery side sub tank12have reached a defined level. The printer control circuitry109may execute a control such that ink is supplied from the main tank11to the supply side sub tank12and the recovery side sub tank13until liquid levels for both the supply side sub tank12and the recovery side sub tank12have reached a defined height.

Further, in step S109ofFIG.8, the printer control circuitry109may execute a control to start printing execution when the liquid levels in both the supply side sub tank12and the recovery side sub tank13reach a defined height.

(c) Step S117inFIG.8can be said to be entering a state of waiting for reception of a print job. Further, step S113inFIG.9is stopping liquid circulation (circulation operation).

Thus, when waiting for printing or stopping liquid circulation, the printer control circuitry109may execute a control such the ink is supplied from the supply side sub tank12to the main tank11via the degassing module14and from the recovery side sub tank13to the main tank11.

Further, while waiting for printing, after a defined time has elapsed, the printer control circuitry109may execute a control such the ink is supplied from the supply side sub tank12to the main tank11via the degassing module14and from the recovery side sub tank13to the main tank11.

Here, the define time is determined depending on ink temperature.

Further, while liquid circulation is stopped, after a defined time has elapsed, the printer control circuitry109may execute a control such the ink is supplied from the supply side sub tank12to the main tank11via the degassing module14and from the recovery side sub tank13to the main tank11.

In this case, the printer control circuitry109may execute a control such that the supply side sub tank12and the recovery side sub tank13are emptied of ink.

(d) The printer control circuitry109may execute a control causing at least some liquid stored in the supply side sub tank12to be supplied to the degassing module14and causing the degassing module14to deaerate the liquid while waiting for image forming, before image forming.

Further, the printer control circuitry109may execute a control causing at least some liquid stored in the supply side sub tank12to be supplied to the degassing module14and causing the degassing module14to deaerate the liquid while waiting for image forming, when starting image forming.

Further, the printer control circuitry109may execute a control causing at least some liquid stored in the supply side sub tank12to be supplied to the degassing module14and causing the degassing module14to deaerate the liquid while waiting for image forming, after a defined time has elapsed since image forming was last executed.

Further, the printer control circuitry109may execute a control causing at least some liquid stored in the supply side sub tank12to be supplied to the degassing module14and causing the degassing module14to deaerate the liquid while the circulation operation is stopped, before a next circulation operation.

Further, the printer control circuitry109may execute a control causing at least some liquid stored in the supply side sub tank12to be supplied to the degassing module14and causing the degassing module14to deaerate the liquid while the circulation operation is stopped, when starting a next circulation operation.

Further, the printer control circuitry109may execute a control causing at least some liquid stored in the supply side sub tank12to be supplied to the degassing module14and causing the degassing module14to deaerate the liquid while the circulation operation is stopped, after a defined time has elapsed since the circulation operation was last stopped.

2 Other Modifications

Aspects of the present disclosure have been described with reference to the above embodiments, but are not limited to the embodiments described above.

According to Modification 1 of an embodiment, a head unit31xillustrated inFIG.12is provided instead of the head unit31a. The head unit31xmay also replace the head units31b,31c,31d.

The head unit31xincludes a pump75and drive circuitry65in addition to the structure of the head unit31a. The recovery side sub tank13and the pump75are connected by an ink supply pipe161, and the supply side sub tank12and the pump75are connected by an ink supply pipe162.

Under control of the printer control circuitry109, the drive circuitry causes the pump75to operate to supply ink stored in the recovery side sub tank13to the supply side sub tank12(G direction).

As a result, a part of liquid circulation is realized. As with embodiments described above, liquid circulation has an effect of preventing nozzles from drying out and an effect of preventing ink from settling when the ink is a dense pigment.

Further, similarly to the head unit31a, in the head unit31x, while waiting for image forming or when supply of liquid from the supply side sub tank12to the inkjet head241is stopped, as illustrated inFIG.13, ink stored in the supply side sub tank12is supplied to the degassing module14. The degassing module14removes dissolved air and the like from the ink. Ink from which dissolved air or the like has been removed is supplied to the main tank11and stored. Subsequently, when the ink is used for printing, dissolved air or the like has been removed from the ink, and therefore a decrease in degree of degassing can be suppressed, and deterioration of image quality can be prevented.

According to Modification 2 of an embodiment, a head unit31yillustrated inFIG.14is provided instead of the head unit31a. The head unit31ymay also replace the head units31b,31c,31d.

In the head unit31y, in addition to the structure of the head unit31a, an ink supply pipe171is connected to the supply side sub tank12.

Further, in the image forming device1, a pump76and drive circuitry66are provided and supported by a support member included in the housing, the supply side sub tank12and the pump76are connected by the ink supply pipe171, and the main tank11and the pump76are connected by an ink supply pipe172.

The printer control circuitry109controls the drive circuitry66to cause the pump76to operate such that at least some ink stored in the supply side sub tank12is supplied to the main tank11via the ink supply pipes171,172(supply path, H direction).

Here, when a defined time has elapsed since image forming was last executed, or when a defined time has elapsed since supply of liquid from the supply side sub tank12to the inkjet head241was stopped, the printer control circuitry109controls the drive circuitry66to cause the pump76to operate such that at least some ink stored in the supply side sub tank12is supplied to the main tank11via the ink supply pipes171,172(supply path, H direction).

As a result, a part of liquid circulation is realized. As with embodiments described above, liquid circulation has an effect of preventing nozzles from drying out and an effect of preventing ink from settling when the ink is a dense pigment.

Further, according to the head unit31y, while waiting for image forming or while liquid supply from the supply side sub tank12to the inkjet head241is stopped, the printer control circuitry109executes a control such that ink stored in the supply side sub tank12is supplied to the degassing module14. The degassing module14removes dissolved air and the like from the ink. Ink from which dissolved air or the like has been removed is supplied to the main tank11and stored. Subsequently, when the ink is used for printing, dissolved air or the like has been removed from the ink, and therefore a decrease in degree of degassing can be suppressed, and deterioration of image quality can be prevented.

Further, according to the head unit31y, while waiting for image forming, or while supply of liquid from the supply side sub tank12to the inkjet head241is stopped, the printer control circuitry109may control the drive circuitry66to cause the pump76to operate such that at least some ink stored in the supply side sub tank12is supplied to the main tank11via the ink supply pipes171,172(supply path, H direction).

According to Modification 3 of an embodiment, a head unit31zillustrated inFIG.15is provided instead of the head unit31a. The head unit31zmay also replace the head units31b,31c,31d.

The head unit31zincludes the pump75and the drive circuitry65in addition to the structure of the head unit31a. The recovery side sub tank13and the pump75are connected by the ink supply pipe161, and the supply side sub tank12and the pump75are connected by the ink supply pipe162.

Under control of the printer control circuitry109, the drive circuitry causes the pump75to operate to supply ink stored in the recovery side sub tank13to the supply side sub tank12(G direction).

As a result, a part of liquid circulation is realized.

Further, in the head unit31z, in addition to the structure of the head unit31a, the ink supply pipe171is connected to the supply side sub tank12.

Further, in the image forming device1, the pump76and the drive circuitry66are provided and supported by a support member included in the housing, the supply side sub tank12and the pump76are connected by the ink supply pipe171, and the main tank11and the pump76are connected by the ink supply pipe172.

Under control of the printer control circuitry109, the drive circuitry66operates the pump76to supply ink stored in the recovery side sub tank12to the main tank11(H direction).

As a result, a part of liquid circulation is realized.

As with embodiments described above, liquid circulation has an effect of preventing nozzles from drying out and an effect of preventing ink from settling when the ink is a dense pigment.

Further, according to the head unit31z, while waiting for image forming or while liquid supply from the supply side sub tank12to the inkjet head241is stopped, ink stored in the supply side sub tank12is supplied to the degassing module14. The degassing module14removes dissolved air and the like from the ink. Ink from which dissolved air or the like has been removed is supplied to the main tank11and stored. Subsequently, when the ink is used for printing, dissolved air or the like has been removed from the ink, and therefore a decrease in degree of degassing can be suppressed, and deterioration of image quality can be prevented.

(4) The image forming device1may further include an image reader that scans a document to generate image data.

(5) The embodiments and modifications described above may be combined with each other.

Although one or more embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for the purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by the terms of the appended claims.