JP2021154514A - Ink jet printing device - Google Patents

Abstract

To provide an ink jet printing device which can suppress breakage of meniscus during standby while supplying an ink to an ink jet head from an upstream side tank by a water head pressure between the upstream side tank of the ink jet head and a nozzle surface of the ink jet head during ink circulation.SOLUTION: During in circulation, a liquid level 21a in a pressure tank 21 exists at a position higher than a nozzle surface 16a of an ink jet head 11, and an ink is supplied to the ink jet head 11 from the pressure tank 21 by a water head pressure between the pressure tank 21 and the nozzle surface 16a. In a standby state, the liquid level 21a in the pressure tank 21 and a liquid level 25a in a negative pressure tank 25 exist at a position lower than the nozzle surface 16a, and the pressure tank 21 and the negative pressure tank 25 are open to atmosphere.SELECTED DRAWING: Figure 4

Description

The present invention relates to an ink circulation type inkjet printing apparatus.

Ink circulation type inkjet printing that prints by ejecting ink from the inkjet head while circulating ink between the tank arranged on the upstream side of the inkjet head, the inkjet head, and the tank arranged on the downstream side thereof. The device is known.

As such an inkjet printing device, an upstream tank is arranged at a position higher than the inkjet head, and ink is supplied to the inkjet head from the upstream tank by the hydraulic head pressure between the upstream tank and the nozzle surface of the inkjet head. There is something to do (see Patent Document 1). This configuration has an advantage that the pulsation of the nozzle pressure due to the pulsation of the pump can be suppressed as compared with the configuration in which the pressure for ink circulation is generated in the tank on the upstream side by using the pump.

In the above configuration, it is necessary to seal the tank on the upstream side of the inkjet head during standby when ink circulation is not performed. This is to prevent ink from flowing from the tank on the upstream side to the inkjet head and leaking from the nozzle.

Japanese Unexamined Patent Publication No. 2013-10366

However, if the tank on the upstream side of the inkjet head is closed during standby, the pressure inside the tank may fluctuate due to a change in the environmental temperature. Then, due to the pressure fluctuation of this tank, the nozzle pressure of the inkjet head fluctuates, and the meniscus of the ink in the nozzle may be destroyed. If the meniscus is destroyed, ink may leak from the nozzle, or ink may flow from the upstream tank to the downstream tank and the downstream tank may overflow.

The present invention has been made in view of the above. During ink circulation, the head pressure between the tank on the upstream side of the inkjet head and the nozzle surface of the inkjet head causes the ink jet head to be supplied with ink from the tank on the upstream side while standing by. It is an object of the present invention to provide an inkjet printing apparatus capable of suppressing the destruction of meniscus inside.

In order to achieve the above object, the inkjet printing apparatus of the present invention includes an inkjet head having a nozzle surface in which a nozzle for ejecting ink is open, a first tank for storing ink to be supplied to the ink head, and the ink head. A second tank for receiving the unconsumed ink and a circulation path for circulating ink between the first tank, the inkjet head, and the second tank are provided, and when the ink is circulated through the circulation path. In the above, the liquid level of the ink in the first tank is higher than the nozzle surface, and the ink is supplied from the first tank to the inkjet head by the water head pressure between the first tank and the nozzle surface. In the standby state in which ink circulation is not performed, the liquid level of the ink in the first tank and the liquid level of the ink in the second tank are lower than the nozzle surface, and the first tank and the second tank are open to the atmosphere. It is characterized by being done.

According to the inkjet printing apparatus of the present invention, during ink circulation, ink is supplied to the inkjet head from the tank on the upstream side by the water head pressure between the tank on the upstream side of the inkjet head and the nozzle surface of the inkjet head, and the ink is in standby. The destruction of the meniscus can be suppressed.

It is a block diagram which shows the structure of the inkjet printing apparatus which concerns on embodiment. It is a schematic block diagram of the printing part and the pressure generating part of the inkjet printing apparatus shown in FIG. It is a flowchart for demonstrating operation of the inkjet printing apparatus shown in FIG. It is a figure which shows the position of the liquid level of a pressure tank and the position of the liquid level of a negative pressure tank at the time of ink circulation. The water head pressure between the pressure tank and the nozzle surface when shifting from the standby state to the ink circulation state, the water head pressure between the negative pressure tank and the nozzle surface, the pressure generated by the pressure generator in the negative pressure tank, and the nozzle. It is a figure which shows the transition of pressure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or equivalent parts and components are designated by the same or equivalent reference numerals throughout the drawings.

The embodiments shown below exemplify an apparatus or the like for embodying the technical idea of the present invention, and the technical idea of the present invention includes the material, shape, structure, arrangement, etc. of each component. Is not specified as the following. The technical idea of the present invention can be modified in various ways within the scope of claims.

FIG. 1 is a block diagram showing a configuration of an inkjet printing apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a printing unit and a pressure generating unit of the inkjet printing apparatus shown in FIG. In the following description, the vertical direction is the vertical direction, and the vertical direction of the paper surface in FIG. 2 is the vertical direction.

As shown in FIG. 1, the inkjet printing apparatus 1 according to the present embodiment includes four printing units 2, a pressure generating unit 3, a transport unit 4, and a control unit 5.

The printing unit 2 prints an image by ejecting the ink onto the paper conveyed by the conveying unit 4 while circulating the ink. The four printing units 2 eject inks of different colors (for example, black, cyan, magenta, and yellow). The four printing units 2 have the same configuration except that the colors of the ink to be ejected are different.

As shown in FIG. 2, the printing unit 2 includes an inkjet head 11, an ink circulation mechanism 12, and an ink supply unit 13. The configuration of the printing unit 2 shown in FIG. 2 is for one color, and as described above, each of the four printing units 2 has the same configuration.

The inkjet head 11 ejects the ink supplied by the ink circulation mechanism 12. The inkjet head 11 has a plurality of head modules 16.

The head module 16 has an ink chamber (not shown) for storing ink, a plurality of nozzles (not shown) for ejecting ink, and a nozzle surface 16a through which the nozzles are opened. A piezo element (not shown) is arranged in the ink chamber. Ink is ejected from the nozzle by driving the piezo element. The nozzle surface 16a is the lower surface of the head module 16 facing the paper transported by the transport unit 4.

The ink circulation mechanism 12 supplies ink to the inkjet head 11 while circulating the ink. The ink circulation mechanism 12 includes a pressure tank (corresponding to the first tank) 21, a pressure tank liquid level sensor 22, a distributor 23, a collector 24, and a negative pressure tank (corresponding to the second tank) 25. A negative pressure tank liquid level sensor 26, ink circulation pipes 27 to 29, and an ink circulation pump (corresponding to a liquid feeding unit) 30 are provided.

The pressure tank 21 stores the ink to be supplied to the inkjet head 11. The ink in the pressure tank 21 is supplied to the inkjet head 11 via the ink circulation tube 27 and the distributor 23. That is, the pressure tank 21 is arranged on the upstream side of the inkjet head 11 in the ink circulation direction. In the pressure tank 21, an air layer is formed on the liquid surface 21a of the ink. The pressure tank 21 is connected to the pressure common air chamber 51 described later via a pressure communication pipe 52 described later.

In the pressure tank 21, the amount of fluctuation of the liquid level 21a of the pressure tank 21 when the ink is sent from the negative pressure tank 25 to the pressure tank 21 is larger than the amount of fluctuation of the liquid level 25a of the negative pressure tank 25. Is also formed into a large shape. Specifically, in the present embodiment, the pressure tank 21 and the negative pressure tank 25 are formed in a hollow rectangular parallelepiped shape, and the cross-sectional area of the pressure tank 21 along the horizontal plane is the horizontal plane of the negative pressure tank 25. It is smaller than the cross-sectional area along.

The pressure tank liquid level sensor 22 is for detecting whether or not the liquid level 21a of the pressure tank 21 has reached a predetermined reference position during circulation on the pressure side. The pressure tank liquid level sensor 22 outputs a signal indicating "ON" when the liquid level 21a of the pressure tank 21 is at the same position as or higher than the reference position during circulation on the pressure side, and the liquid level 21a is added. A signal indicating "OFF" is output when the position is lower than the reference position during compression side circulation.

The reference position during circulation on the pressurizing side is higher than the nozzle surface 16a of the inkjet head 11. The reference position during circulation on the pressurizing side is set as the height position of the liquid surface 21a capable of generating a predetermined circulation flow rate during ink circulation by the head pressure between the pressurizing tank 21 and the nozzle surface 16a.

The distributor 23 distributes the ink supplied from the pressure tank 21 via the ink circulation pipe 27 to each head module 16 of the inkjet head 11.

The collector 24 collects the ink not consumed by the inkjet head 11 from each head module 16. The ink collected by the collector 24 flows to the negative pressure tank 25 via the ink circulation tube 28.

The negative pressure tank 25 receives and stores the ink that has not been consumed by the inkjet head 11 from the collector 24. That is, the negative pressure tank 25 is arranged on the downstream side of the inkjet head 11 in the ink circulation direction. In the negative pressure tank 25, an air layer is formed on the liquid surface 25a of the ink. The negative pressure tank 25 is connected to the negative pressure common air chamber 58 described later via a negative pressure communication pipe 59 described later.

The negative pressure tank liquid level sensor 26 is for detecting whether or not the liquid level 25a of the negative pressure tank 25 has reached a predetermined reference position during circulation on the negative pressure side. The negative pressure tank liquid level sensor 26 outputs a signal indicating “ON” when the liquid level 25a of the negative pressure tank 25 is at the same position as or higher than the reference position during circulation on the negative pressure side, and the liquid level 25a is negative. A signal indicating "OFF" is output when the position is lower than the reference position during compression side circulation.

At the reference position during circulation on the negative pressure side, ink is sent from the negative pressure tank 25 to the pressure tank 21 from the standby state in which the ink jet printing device 1 does not circulate ink, and the liquid level 21a of the pressure tank 21 circulates on the pressure side. It is the height position of the liquid level 25a of the negative pressure tank 25 when the time reference position is reached.

Here, in the standby state of the inkjet printing apparatus 1, as shown in FIG. 2, the liquid level 21a of the pressure tank 21 and the liquid level 25a of the negative pressure tank 25 are located at the same height as each other at a position lower than the nozzle surface 16a. It is in. The standby liquid level position, which is the height position of the liquid levels 21a and 25a in the standby state, is set according to the nozzle pressure of the inkjet head 11 set as the standby nozzle pressure.

The ink circulation pipe 27 connects the pressure tank 21 and the distributor 23. The ink circulation tube 28 connects the collector 24 and the negative pressure tank 25. The ink circulation pipe 29 connects the negative pressure tank 25 and the pressure tank 21. The ink circulation tubes 27 to 29, the distributor 23, and the collector 24 form a circulation path for circulating ink between the pressure tank 21, the inkjet head 11, and the negative pressure tank 25.

The ink circulation pump 30 sends ink from the negative pressure tank 25 to the pressure tank 21 via the ink circulation pipe 29 when shifting from the standby state to the ink circulation state and during ink circulation. Further, when the ink circulation pump 30 supplies ink from the ink supply unit 13 to the ink circulation mechanism 12, the ink circulation pump 30 passes through a part of the connection pipe 37 and the ink circulation pipe 29 described later from the buffer tank 31 to the pressure tank 21 described later. Ink is sent to the liquid.

The ink supply unit 13 supplies ink to the ink circulation mechanism 12. The ink supply unit 13 includes a buffer tank 31, a buffer tank liquid level sensor 32, a buffer tank air release valve 33, a buffer tank air release pipe 34, an air filter 35, an ink supply valve 36, and a connection pipe 37. The ink tank 38, the ink supply pump 39, and the ink supply pipe 40 are provided.

The buffer tank 31 stores the ink supplied to the ink circulation mechanism 12. The buffer tank 31 receives ink from the ink tank 38 and stores the supplied ink. In the buffer tank 31, an air layer is formed on the liquid surface of the ink. The buffer tank 31 is connected to the ink circulation pipe 29 via the connecting pipe 37.

The buffer tank liquid level sensor 32 detects whether or not the liquid level of the ink in the buffer tank 31 has reached a predetermined buffer tank reference position. The buffer tank liquid level sensor 32 outputs a signal indicating "ON" when the liquid level of the buffer tank 31 is at the same level as or higher than the buffer tank reference position, and when the liquid level is lower than the buffer tank reference position. Outputs a signal indicating "off" to.

The buffer tank open-air valve 33 is used to switch the buffer tank 31 between a closed state (a state in which it is shut off from the atmosphere) and an open state (a state in which it is open to the atmosphere). Open and close the flow path of.

The buffer tank open-air pipe 34 forms an air flow path for opening the buffer tank 31 to the atmosphere. One end of the buffer tank open-air pipe 34 is connected to the air layer of the buffer tank 31, and the other end (open end to the atmosphere) is connected to the atmosphere through an air filter 35.

Each of the air filters 35 prevents dust and the like in the air from entering the buffer tank air opening pipe 34. The air filter 35 is installed at the open end of the buffer tank open to the atmosphere pipe 34.

The ink supply valve 36 opens and closes the ink flow path in the connecting pipe 37.

The connecting pipe 37 connects the ink circulation pipe 29 and the buffer tank 31. One end of the connecting pipe 37 is connected to a portion between the negative pressure tank 25 of the ink circulation pipe 29 and the ink circulation pump 30, and the other end is connected to the buffer tank 31.

The ink tank 38 contains ink used for printing by the inkjet 11.

The ink supply pump 39 sends ink from the ink tank 38 to the buffer tank 31 via the ink supply pipe 40.

The ink supply pipe 40 connects the buffer tank 31 and the ink tank 38.

The pressure generating unit 3 generates a pressure (negative pressure) for ink circulation in the negative pressure tank 25 of each printing unit 2. Further, the pressure generating unit 3 generates a pressure (positive pressure) in the pressure tank 21 of each printing unit 2 in order to perform a purge for pushing out ink from the nozzle during maintenance of the inkjet head 11.

The pressure generation unit 3 includes a pressurization common air chamber 51, a pressurization communication pipe 52, a pressurization air pump 53, a pressurization pressure generation pipe 54, a pressurization pressure adjusting valve 55, and a pressurizing pressure adjusting pipe 56. , Pressurized pressure sensor 57, negative pressure common air chamber 58, negative pressure communication pipe 59, negative pressure air pump 60, atmospheric communication pipe 61, air filter 62, negative pressure adjusting valve 63, and negative pressure. A pressure adjusting pipe 64 and a negative pressure pressure sensor 65 are provided.

The pressurized common air chamber 51 is an air chamber for equalizing the pressure of the pressure tank 21 of each printing unit 2. The pressurized common air chamber 51 is connected to the pressure tank 21 of each printing unit 2 via a pressure communicating pipe 52 corresponding to each printing unit 2. As a result, the pressure tanks 21 of the printing units 2 are communicated with each other via the pressure common air chamber 51 and the pressure communication pipe 52.

The pressurized communication pipe 52 communicates the pressurized common air chamber 51 with the air layer of the pressurized tank 21. One pressure communication pipe 52 is provided for each printing unit 2. One end of the pressurized communication pipe 52 is connected to the pressurized common air chamber 51, and the other end is connected to the air layer of the pressurized tank 21.

The pressurized air pump 53 sends air to the pressurized common air chamber 51 in order to generate a positive pressure in the pressurized tank 21 for purging at the time of maintenance.

The pressurized pressure generation pipe 54 forms an air flow path for sending air to the pressurized common air chamber 51 by the pressurized air pump 53. One end of the pressurized pressure generating pipe 54 is connected to the pressurized common air chamber 51, and the other end is connected to a portion of the atmospheric communication pipe 61 between the negative pressure air pump 60 and the air filter 62.

The pressurizing pressure adjusting valve 55 adjusts the pressure of the pressurizing common air chamber 51 and the pressurizing tank 21, and makes the pressurizing common air chamber 51 and the pressurizing tank 21 between the closed state and the open state to the atmosphere. In order to switch, the air flow path in the pressurizing pressure adjusting pipe 56 is opened and closed.

The pressurizing pressure adjusting pipe 56 switches the pressurizing common air chamber 51 and the pressurizing tank 21 for pressure adjustment of the pressurizing common air chamber 51 and the pressurizing tank 21 and between a closed state and an open state to the atmosphere. Form a flow path for air. One end of the pressurized pressure adjusting pipe 56 is connected to the pressurized common air chamber 51, and the other end is connected to a portion of the atmospheric communication pipe 61 between the negative pressure air pump 60 and the air filter 62.

The pressurizing pressure sensor 57 detects the pressure in the pressurizing common air chamber 51 and in the pressurizing tank 21.

The negative pressure common air chamber 58 is an air chamber for equalizing the pressure of the negative pressure tank 25 of each printing unit 2. The negative pressure common air chamber 58 is connected to the negative pressure tank 25 of each printing unit 2 via a negative pressure communication pipe 59 corresponding to each printing unit 2. As a result, the negative pressure tanks 25 of each printing unit 2 are communicated with each other via the negative pressure common air chamber 58 and the negative pressure communication pipe 59.

The negative pressure communication pipe 59 communicates the negative pressure common air chamber 58 with the air layer of the negative pressure tank 25. One negative pressure communication pipe 59 is provided for each printing unit 2. One end of the negative pressure communication pipe 59 is connected to the negative pressure common air chamber 58, and the other end is connected to the air layer of the negative pressure tank 25.

The negative pressure air pump 60 sucks air from the negative pressure common air chamber 58 in order to generate a negative pressure for ink circulation in the negative pressure tank 25. The negative pressure air pump 60 is arranged in the middle of the atmospheric communication pipe 61.

The air communication pipe 61 forms an air flow path for sucking air from the negative pressure common air chamber 58 by the negative pressure air pump 60. One end of the air communication pipe 61 is connected to the negative pressure common air chamber 58, and the other end (open end to the atmosphere) communicates with the atmosphere through the air filter 62. A pressure pressure generating pipe 54, a pressure pressure adjusting pipe 56, and a negative pressure pressure adjusting pipe 64 are connected to the air communication pipe 61. As a result, the pressurized pressure generating pipe 54, the pressurized pressure adjusting pipe 56, and the negative pressure pressure adjusting pipe 64 are communicated with the atmosphere.

The air filter 62 prevents dust and the like in the air from entering the air communication pipe 61. The air filter 62 is installed at the open end of the atmospheric communication pipe 61.

The negative pressure adjusting valve 63 adjusts the pressure of the negative pressure common air chamber 58 and the negative pressure tank 25, and the negative pressure common air chamber 58 and the negative pressure tank 25 are between the closed state and the open state to the atmosphere. In order to switch, the air flow path in the negative pressure adjusting pipe 64 is opened and closed.

The negative pressure adjusting pipe 64 switches the negative pressure common air chamber 58 and the negative pressure tank 25 for pressure adjustment of the negative pressure common air chamber 58 and the negative pressure tank 25, and switches the negative pressure common air chamber 58 and the negative pressure tank 25 between the closed state and the open state to the atmosphere. Form a flow path for air. One end of the negative pressure adjusting pipe 64 is connected to the negative pressure common air chamber 58, and the other end is connected to a portion of the atmospheric communication pipe 61 between the negative pressure air pump 60 and the air filter 62.

The negative pressure pressure sensor 65 detects the pressure in the negative pressure common air chamber 58 and the negative pressure tank 25.

The transport unit 4 takes out the paper from the paper feed tray (not shown) and transports the paper along the transport path. The transport unit 4 includes a roller for transporting the paper, a motor for driving the roller (neither of them is shown), and the like.

The control unit 5 controls the operation of each unit of the inkjet printing device 1. The control unit 5 includes a CPU, RAM, ROM, a hard disk, and the like.

Next, the operation of the inkjet printing apparatus 1 will be described.

FIG. 3 is a flowchart for explaining the operation of the inkjet printing apparatus 1. The processing of the flowchart of FIG. 3 is started when a print job is input to the inkjet printing apparatus 1.

Here, in the inkjet printing apparatus 1 in the standby state before the printing job is input, the pressurizing pressure adjusting valve 55 and the negative pressure adjusting valve 63 are opened, and the pressurizing tank 21 and the negative pressure tank 25 are in the atmosphere. It is in an open state. Then, as described above, the liquid level 21a of the pressure tank 21 and the liquid level 25a of the negative pressure tank 25 are at the standby liquid level positions. Since the liquid level position during standby is lower than the nozzle surface 16a, ink flows from the pressure tank 21 and the negative pressure tank 25 to the inkjet head 11 even when the pressure tank 21 and the negative pressure tank 25 are open to the atmosphere. Is prevented.

Further, in the inkjet printing apparatus 1 in the standby state, the buffer tank air release valve 33 and the ink supply valve 36 are closed.

When the print job is input, in step S1 of FIG. 3, the control unit 5 starts driving the ink circulation pump 30. As a result, the ink starts to be sent from the negative pressure tank 25 to the pressure tank 21 via the ink circulation pipe 29.

Next, in step S2, the control unit 5 determines whether or not the pressure tank liquid level sensor 22 is turned on. When it is determined that the pressure tank liquid level sensor 22 is not turned on (step S2: NO), the control unit 5 repeats step S2.

When it is determined that the pressure tank liquid level sensor 22 is turned on (step S2: YES), in step S3, the control unit 5 stops the ink circulation pump 30.

As a result, as shown in FIG. 4, the liquid level 21a of the pressurizing tank 21 is at the reference position during circulation on the pressurizing side, and the liquid level 25a of the negative pressure tank 25 is at the reference position during circulation on the negative pressure side. The processes of steps S1 to S3 are performed on each printing unit 2.

Returning to FIG. 3, in step S4, the control unit 5 controls the pressure generation unit 3 so as to generate a pressure (negative pressure) for ink circulation in the negative pressure tank 25 of each printing unit 2. Specifically, the control unit 5 closes the negative pressure adjusting valve 63 and starts driving the negative pressure air pump 60. As a result, the negative pressure tank 25 of each printing unit 2 begins to be depressurized. Then, the control unit 5 lowers the pressure of the negative pressure tank 25 until it reaches a preset pressure for ink circulation.

When the set pressure is generated in the negative pressure tank 25 as a result, the transition from the standby state of the inkjet printing apparatus 1 to the ink circulation state is completed.

After that, the control unit 5 controls the negative pressure air pump 60 and the negative pressure pressure adjusting valve 63 so as to maintain the set pressure of the negative pressure tank 25. Further, in the ink circulation state, the control unit 5 opens the buffer tank atmospheric release valve 33.

In the ink circulation state, ink is supplied from the pressure tank 21 to the inkjet head 11 by the water head pressure between the pressure tank 21 and the nozzle surface 16a. Further, the ink is recovered from the inkjet head 11 to the negative pressure tank 25 due to the negative pressure of the negative pressure tank 25 and the water head pressure between the negative pressure tank 25 and the nozzle surface 16a.

Further, in the ink circulation state, when the pressure tank liquid level sensor 22 is off and the negative pressure tank liquid level sensor 26 is on by the liquid level maintenance control described later, the ink circulation pump 30 is applied from the negative pressure tank 25. The ink is sent to the pressure tank 21. In this way, ink circulation is performed between the pressure tank 21, the inkjet head 11, and the negative pressure tank 25 via the circulation path (ink circulation tubes 27 to 29, the distributor 23, and the collector 24).

Here, the water head pressure between the pressure tank 21 and the nozzle surface 16a, the water head pressure between the negative pressure tank 25 and the nozzle surface 16a, and the pressure generation unit from the start of driving the ink circulation pump 30 in step S1. FIG. 5 shows the transition of the generated pressure of the negative pressure tank 25 and the nozzle pressure according to No. 3. The head pressure between the pressure tank 21 and the nozzle surface 16a and the head pressure between the negative pressure tank 25 and the nozzle surface 16a are based on the nozzle surface 16a.

In FIG. 5, the time t1 is the timing at which the ink circulation pump 30 in step S3 of FIG. 3 is stopped. Further, the time t2 is the timing when the set pressure is generated in the negative pressure tank 25 by the pressure generating unit 3.

As shown in FIG. 5, until the ink circulation pump 30 is stopped at time t1, the head pressure between the pressure tank 21 and the nozzle surface 16a of the negative pressure tank 25 is the liquid level 21a of the pressure tank 21. It changes according to the rise and the fall of the liquid level 25a of the negative pressure tank 25. Since the amount of increase in the liquid level 21a of the pressure tank 21 is larger than the amount of decrease in the liquid level 25a of the negative pressure tank 25, the nozzle pressure of the inkjet head 11 slightly increases from the nozzle pressure during standby.

After that, the nozzle pressure changes according to the depressurization of the negative pressure tank 25 by the pressure generating unit 3, and the nozzle pressure at the time of printing is generated. The nozzle pressure at the time of printing is set as an appropriate nozzle pressure when printing is performed by ejecting ink from the inkjet head 11.

Returning to FIG. 3, when the set pressure is generated in the negative pressure tank 25 in step S4 and the transition from the standby state of the inkjet printing apparatus 1 to the ink circulation state is completed, in step S5, the control unit 5 executes the print job. To start. Specifically, based on the print job, the control unit 5 ejects ink from the inkjet head 11 onto the paper conveyed by the transfer unit 4 to print an image.

During the execution of this print job, the control unit 5 performs liquid level maintenance control. The liquid level maintenance control is a control for circulating ink while maintaining the positions of the liquid levels of the pressure tank 21, the negative pressure tank 25, and the buffer tank 31. In the liquid level maintenance control, the control unit 5 sets the ink circulation pump 30, the ink supply valve 36, and the ink supply pump 39 according to the positions of the liquid levels of the pressure tank 21, the negative pressure tank 25, and the buffer tank 31. Control.

Specifically, when both the pressure tank liquid level sensor 22 and the negative pressure tank liquid level sensor 26 are on, the control unit 5 turns off the ink circulation pump 30 and closes the ink supply valve 36. Similarly, when the pressure tank liquid level sensor 22 is on and the negative pressure tank liquid level sensor 26 is off, the control unit 5 turns off the ink circulation pump 30 and closes the ink supply valve 36.

When the pressure tank liquid level sensor 22 is off and the negative pressure tank liquid level sensor 26 is on, the control unit 5 turns on the ink circulation pump 30 and closes the ink supply valve 36. As a result, the ink is sent from the negative pressure tank 25 to the pressure tank 21.

When both the pressure tank liquid level sensor 22 and the negative pressure tank liquid level sensor 26 are off, the control unit 5 turns on the ink circulation pump 30 and opens the ink supply valve 36. As a result, the ink is sent from the buffer tank 31 to the pressure tank 21.

Further, when the buffer tank liquid level sensor 32 is off, the control unit 5 turns on the ink supply pump 39. As a result, the ink is sent from the ink tank 38 to the buffer tank 31. When the buffer tank liquid level sensor 32 is on, the control unit 5 turns off the ink supply pump 39.

During the execution of the print job, ink is supplied from the pressure tank 21 to the inkjet head 11, and the ink not consumed by the inkjet head 11 is collected in the negative pressure tank 25. When the pressure tank liquid level sensor 22 is off and the negative pressure tank liquid level sensor 26 is on, the ink circulation pump 30 sends ink from the negative pressure tank 25 to the pressure tank 21 by the above-mentioned liquid level maintenance control. Liquid. Printing is performed while the ink is circulated in this way.

When both the pressure tank liquid level sensor 22 and the negative pressure tank liquid level sensor 26 are turned off, the ink circulation pump 30 sends ink from the buffer tank 31 to the pressure tank 21 by the above-mentioned liquid level maintenance control. Liquid. As a result, ink is supplied to the ink circulation mechanism 12.

When the buffer tank liquid level sensor 32 is turned off, the ink supply pump 39 sends ink from the ink tank 38 to the buffer tank 31 by the liquid level maintenance control described above. As a result, the buffer tank 31 is replenished with ink.

Next, in step S6, the control unit 5 determines whether or not the print job has been completed. When it is determined that the print job has not been completed (step S6: NO), the control unit 5 repeats step S6.

When it is determined that the print job is completed (step S6: YES), in step S7, the control unit 5 opens the negative pressure tank 25 to the atmosphere. Specifically, the control unit 5 ends the control for maintaining the set pressure of the negative pressure tank 25 by the pressure generating unit 3, and opens the negative pressure pressure adjusting valve 63. Further, the control unit 5 closes the buffer tank air release valve 33.

Since the pressure tank 21 is open to the atmosphere during ink circulation, the pressure tank 21 and the negative pressure tank 25 are opened to the atmosphere by opening the negative pressure tank 25 to the atmosphere. As a result, the pressure tank 21 passes through the inkjet head 11 until the liquid level 21a of the pressure tank 21 drops to the standby liquid level position and the liquid level 25a of the negative pressure tank 25 rises to the standby liquid level position. The ink moves to the negative pressure tank 25. As a result, the inkjet printing apparatus 1 is put into a standby state, and a series of operations is completed.

As described above, in the inkjet printing apparatus 1, the liquid level 21a of the pressure tank 21 is at the pressure side circulation reference position, which is higher than the nozzle surface 16a, during ink circulation, and the pressure tank 21 and the nozzle surface are present. Ink is supplied from the pressure tank 21 to the inkjet head 11 by the water head pressure between 16a. In the standby state, the liquid level 21a of the pressure tank 21 and the liquid level 25a of the negative pressure tank 25 are at the standby liquid level positions lower than the nozzle surface 16a, and the pressure tank 21 and the negative pressure tank 25 are in the atmosphere. It is open.

Here, if the liquid levels 21a and 25a are lower than the nozzle surface 16a in the standby state, the pressure tank 21 and the negative pressure tank 25 are inkjetd from the pressure tank 21 and the negative pressure tank 25 without sealing the pressure tank 21 and the negative pressure tank 25. It is prevented that the ink flows to the head 11 and leaks from the nozzle. Therefore, the pressure tank 21 and the negative pressure tank 25 can be opened to the atmosphere in the standby state.

In the inkjet printing apparatus 1, as described above, since the pressure tank 21 and the negative pressure tank 25 are open to the atmosphere in the standby state, even if the environmental temperature changes, the pressure tank 21 and the negative pressure tank 25 Pressure fluctuations can be avoided. Therefore, since the fluctuation of the nozzle pressure of the inkjet head 11 is suppressed, the destruction of the meniscus of the ink in the nozzle can be suppressed.

Therefore, according to the inkjet printing apparatus 1, the ink is supplied from the pressure tank 21 to the inkjet head 11 by the water head pressure between the pressure tank 21 and the nozzle surface 16a during ink circulation, and the meniscus is destroyed during standby. It can be suppressed.

Further, in the inkjet printing apparatus 1, in the pressure tank 21, the amount of fluctuation of the liquid level 21a of the pressure tank 21 when the ink is sent from the negative pressure tank 25 to the pressure tank 21 is the negative pressure tank 25. It is formed in a shape that is larger than the fluctuation amount of the liquid level 25a.

As a result, the amount of ink required to send ink from the negative pressure tank 25 to the pressure tank 21 and change the liquid level 21a from the standby liquid level position to the pressure side circulation reference position can be suppressed. Therefore, the amount of ink in the ink circulation mechanism 12 can be suppressed. Further, since the pressure tank 21 can be formed into a shape thinner than the negative pressure tank 25, the device can be miniaturized.

Further, in the inkjet printing apparatus 1, when the control unit 5 shifts from the standby state to the ink circulation state, the ink circulation pump 30 presses negative pressure until the liquid level 21a of the pressurizing tank 21 reaches the reference position at the time of circulation on the pressurizing side. After the ink is sent from the tank 25 to the pressure tank 21, the pressure generating unit 3 generates a negative pressure for ink circulation in the negative pressure tank 25.

As a result, the ink is sent from the negative pressure tank 25, which causes the pressure fluctuation of the pressure tank 21 and the negative pressure tank 25, to the pressure tank 21, and the negative pressure tank 25, which causes the pressure fluctuation of the negative pressure tank 25, Negative pressure generation is performed separately in time. Therefore, the expansion of nozzle pressure fluctuation can be suppressed. As a result, it is possible to suppress the destruction of the meniscus of the ink in the nozzle.

In the above-described embodiment, the pressure tank 21 and the negative pressure tank 25 have a hollow rectangular parallelepiped shape, but the shape is not limited to this. The amount of fluctuation of the liquid level 21a of the pressure tank 21 when the pressure tank 21 sends ink from the negative pressure tank 25 to the pressure tank 21 is larger than the amount of fluctuation of the liquid level 25a of the negative pressure tank 25. It suffices as long as it is formed in a large shape.

The present invention is not limited to the above-described embodiment as it is, and at the implementation stage, the components can be modified and embodied within a range that does not deviate from the gist thereof. In addition, various inventions can be formed by an appropriate combination of the plurality of components disclosed in the above-described embodiment. For example, some components may be removed from all the components shown in the embodiments.

[Additional Notes]
The present application discloses the following inventions.

(Appendix 1)
An inkjet head having a nozzle surface with an open nozzle for ejecting ink,
A first tank for storing ink supplied to the inkjet head and
A second tank that receives ink that has not been consumed by the inkjet head,
A circulation path for ink circulation between the first tank, the inkjet head, and the second tank is provided.
When the ink is circulated through the circulation path, the liquid level of the ink in the first tank is higher than the nozzle surface, and the water head pressure between the first tank and the nozzle surface causes the ink from the first tank. Ink is supplied to the inkjet head,
In the standby state in which ink circulation is not performed, the liquid level of the ink in the first tank and the liquid level of the ink in the second tank are lower than the nozzle surface, and the first tank and the second tank are open to the atmosphere. An inkjet printing device characterized by being used.

(Appendix 2)
In the first tank, the amount of fluctuation of the liquid level of the first tank when the ink is sent from the second tank to the first tank is larger than the amount of fluctuation of the liquid level of the second tank. The inkjet printing apparatus according to Appendix 1, wherein the ink jet printing apparatus is formed in such a shape.

(Appendix 3)
A liquid feeding unit that feeds ink from the second tank to the first tank, and
A pressure generating unit that generates negative pressure in the second tank,
When shifting from the standby state to the ink circulation state, the liquid feeding unit moves the ink from the second tank until the liquid level of the ink in the first tank reaches a predetermined height position higher than the nozzle surface. The description according to Appendix 1 or 2, further comprising a control unit for generating a negative pressure for ink circulation in the second tank after the ink is sent to the first tank by the pressure generating unit. Ink printing equipment.

1 Inkjet printing device 2 Printing unit 3 Pressure generating unit 4 Conveying unit 5 Control unit 11 Inkjet head 12 Ink circulation mechanism 13 Ink supply unit 16 Head module 16a Nozzle surface 21 Pressurized tank 22 Pressurized tank Liquid level sensor 23 Distributor 24 Assembly Instrument 25 Negative pressure tank 26 Negative pressure tank Liquid level sensor 27-29 Ink circulation pipe 30 Ink circulation pump 51 Pressurized common air chamber 52 Pressurized communication pipe 53 Pressurized air pump 54 Pressurized pressure generation pipe 55 Pressurized pressure adjusting valve 56 Pressurized pressure adjusting pipe 57 Pressurized pressure sensor 58 Negative pressure common air chamber 59 Negative pressure communication pipe 60 Negative pressure air pump 62 Air filter 63 Negative pressure pressure adjusting valve 64 Negative pressure pressure adjusting pipe 65 Negative pressure pressure sensor

Claims (3)

An inkjet head having a nozzle surface with an open nozzle for ejecting ink,
A first tank for storing ink supplied to the inkjet head and
A second tank that receives ink that has not been consumed by the inkjet head,
A circulation path for ink circulation between the first tank, the inkjet head, and the second tank is provided.
When the ink is circulated through the circulation path, the liquid level of the ink in the first tank is higher than the nozzle surface, and the water head pressure between the first tank and the nozzle surface causes the ink from the first tank. Ink is supplied to the inkjet head,
In the standby state in which ink circulation is not performed, the liquid level of the ink in the first tank and the liquid level of the ink in the second tank are lower than the nozzle surface, and the first tank and the second tank are open to the atmosphere. An inkjet printing device characterized by being used. In the first tank, the amount of fluctuation of the liquid level of the first tank when the ink is sent from the second tank to the first tank is larger than the amount of fluctuation of the liquid level of the second tank. The inkjet printing apparatus according to claim 1, wherein the ink jet printing apparatus is formed in such a shape. A liquid feeding unit that feeds ink from the second tank to the first tank, and
A pressure generating unit that generates negative pressure in the second tank,
When shifting from the standby state to the ink circulation state, the liquid feeding unit moves the ink from the second tank until the liquid level of the ink in the first tank reaches a predetermined height position higher than the nozzle surface. The invention according to claim 1 or 2, further comprising a control unit that causes the pressure generating unit to generate a negative pressure for ink circulation in the second tank after the ink is sent to the first tank. Ink printing equipment.

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