JP2010184384A - Inkjet printer and ink concentration keeping method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printer and an ink concentration keeping method capable of keeping the concentration of ink constant while maintaining shielding property and other ink characteristics. <P>SOLUTION: The inkjet printer comprises: an inkjet head which ejects ink to a medium; a circulation path which circulates the ink to be supplied to the inkjet head; a supply part which is arranged in the circulation path and stores the ink to be supplied to the inkjet head; and a switching part which selects whether or not to supply the ink to the inkjet head from the circulation path. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inkjet printer and a method for maintaining the concentration of ink used in an inkjet printer.

  In general, an inkjet printer forms a desired image on a medium by ejecting ink supplied from an ink tank to the inkjet head onto the medium from a nozzle of the inkjet head. Ink is supplied from the ink tank to the inkjet head via a tube. The ink is supplied using a pump, and when the image is not formed, the pump is stopped and the ink jet head and the tube are kept filled with ink.

  Ink used in an inkjet printer includes components corresponding to the type of medium on which an image is formed and other conditions. The ink contains a solvent and a pigment or dye. In recent years, media have been diversified, and in addition to media with a white image forming surface such as paper, there is an increasing number of cases where images are formed on non-white or transparent media, and there is an opportunity to use white ink. is increasing.

  In order to improve the shielding property, the white ink preferably contains a pigment having a large particle diameter. As the pigment, for example, titanium oxide is used. The specific gravity of titanium oxide is several times the specific gravity of pigments used in conventional color inks.

  For this reason, if a white ink containing titanium oxide as a pigment is left in the ink tank for a long time, titanium oxide having a large specific gravity tends to precipitate. Even if the ink in such a state is supplied from the ink tank to the inkjet head, the density of the pigment is not uniform, so that the quality of the formed image is lowered and the quality variation is increased. Moreover, there is a possibility that the nozzles of the inkjet head are clogged by the pigment that has precipitated and aggregated.

  On the other hand, in the image recording apparatus described in Patent Document 1, a stirring device is provided in the ink tank, and the ink in the ink tank is stirred before supplying the white ink.

JP 2005-138488 A

  However, in the image recording apparatus of Patent Document 1, although the ink in the ink tank can be stirred, the precipitation of the pigment can occur not only in the ink tank but also in the ink jet head and the tube, so that the image quality is uniform and desired. Is difficult to maintain.

  SUMMARY An advantage of some aspects of the invention is that it provides an ink jet printer and an ink density maintaining method that can maintain a constant ink density while maintaining shielding properties and other ink characteristics.

  In order to solve the above problems, an inkjet printer of the present invention includes an inkjet head that ejects ink onto a medium, a circulation path that circulates ink to be supplied to the inkjet head, and a circulation path that is disposed in the circulation path and supplies the inkjet head. And a switching unit that selects whether or not to supply ink from the circulation path to the ink-jet head.

  The ink jet printer of the present invention preferably includes a stirring device that stirs the ink in the supply unit or the circulation path.

  In the ink jet printer of the present invention, the circulation path preferably includes a pump for circulating the ink.

  In the ink jet printer of the present invention, it is preferable that an adjustment unit for bringing the ink in the ink jet head into a predetermined negative pressure state is provided in the circulation path.

  In the ink jet printer of the present invention, the pump preferably includes a recovery pump that sends ink to the supply unit, and a supply pump that sends ink from the supply unit.

  In the ink jet printer of the present invention, it is preferable that the stirring device is disposed between the supply unit and the ink jet head in the circulation path.

  In the ink jet printer of the present invention, the circulation path is connected to a supply path for supplying ink from the supply section to the ink jet head and a switching section provided in the supply path, and ink is sent from the supply path to the supply section by switching the valve. And a recovery path.

  An ink density maintaining method according to the present invention maintains an ink density of an ink jet printer that includes an ink jet head that discharges ink to a medium and a supply unit that is disposed in a circulation path and stores ink to be supplied to the ink jet head. And a switching step of selecting whether or not to supply ink from the circulation path to the ink jet head.

  In the ink density maintaining method of the present invention, it is preferable to include a discharge step for discharging the ink in the inkjet head when a predetermined time has elapsed without image formation.

  In the ink density maintaining method of the present invention, it is preferable to include a recovery step of recovering ink in the circulation path to the supply unit when an operation for stopping the power supply of the ink jet printer is performed.

  In the ink density maintaining method of the present invention, it is preferable that in the switching step, the ink jet head is filled with ink in the circulation path when the ink jet printer receives an ink filling instruction from the user.

  According to the present invention, it is possible to provide an ink jet printer and an ink concentration maintaining method capable of maintaining a constant ink concentration while maintaining shielding properties and other ink characteristics.

1 is a diagram illustrating a schematic configuration of an inkjet printer according to a first embodiment. 1 is a block diagram illustrating a configuration of an inkjet printer according to a first embodiment. 3 is a flowchart showing a flow of image formation and ink processing. It is a figure which shows schematic structure of the inkjet printer which concerns on 2nd Embodiment. It is a block diagram which shows the structure of the inkjet printer which concerns on 2nd Embodiment. It is a figure which shows schematic structure of the inkjet printer which concerns on 3rd Embodiment. It is a block diagram which shows the structure of the inkjet printer which concerns on 3rd Embodiment.

  Hereinafter, an ink jet printer and an ink density maintaining method according to an embodiment of the present invention will be described in detail with reference to the drawings.

<First Embodiment>
The ink jet printer according to the first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram illustrating a schematic configuration of an inkjet printer 100 according to the first embodiment. FIG. 2 is a block diagram illustrating a configuration of the inkjet printer 100 according to the first embodiment.

  As shown in FIG. 1, the inkjet printer 100 according to the first embodiment switches between an inkjet head 110, an ink tank 131 as a supply unit, a first tube 141, a second tube 142, and a third tube 160. And a stirring motor 133 and a stirrer 134 as a stirrer.

  The inkjet head 110 forms an image on the medium 124 by ejecting ink from the nozzles onto the medium 124. The medium 124 is conveyed by a recording medium conveyance unit 178 including conveyance rollers 122 and 123. The ink jet head 110 is disposed so that the nozzle surface faces the platen 121, and ink is ejected onto the medium 124 conveyed on the platen 121.

  Here, examples of the medium 124 include paper, cloth, and resin sheet, and the image forming surface can be transparent, black, white, or any other one.

  The ink jet head 110 is moved by the carriage scanning unit 179 along the direction perpendicular to the conveyance direction of the medium 124 above the platen 121, that is, the depth direction in FIG.

  The image data is input from the host computer 173 via the input unit 172, stored in a RAM (Random Access Memory) 174, and read out by the control circuit 171 at the time of image formation. Examples of the input unit 172 include a power switch, a keyboard, a mouse, and an interface circuit with an external device. The control circuit 171 operates the recording medium conveying unit 178 and the carriage scanning unit 179 according to the image data to control the conveyance of the medium 124 and the scanning of the inkjet head 110, respectively, and from a predetermined nozzle of the inkjet head 110 to a predetermined level. Ink is ejected at a timing to form an image on the medium 124.

  The control circuit 171 performs conveyance control of the medium 124, scanning control of the inkjet head 110, and ink ejection pattern control according to a program stored in advance in a ROM (Read Only Memory) 175.

  A home position is provided at one end of the inkjet head 110 in the scanning direction. At the home position, ink can be ejected or sucked while the nozzle surface is airtightly covered with the cap, thereby adjusting the state of ink in the nozzle and cleaning the nozzle surface.

  The cap is moved from the retracted position to a position covering the nozzle surface of the inkjet head 110 by the cap lifting and lowering means 176 when the inkjet head 110 is stationary at the home position. The operation of the cap lifting / lowering means 176 is controlled by the control circuit 171.

  Further, a cap suction means 177 is connected to the cap, and sucks ink in the nozzle surface and the nozzle in a state of being airtightly covered. The cap suction means 177 is, for example, a pump, and the control circuit 171 controls its operation.

  The ink tank 131 as a supply unit accommodates the ink 132 supplied to the inkjet head 110 inside. The ink tank 131 can be made of any material as long as it has durability corresponding to the type of ink to be stored and the external environment. Further, as long as ink can be supplied to the inkjet head 110, a form other than the tank, for example, a pouch can be employed. Further, depending on the capacity and the structure of the ink jet printer 100, it may be composed of a plurality of containers.

  A propeller-like stirrer 134 for stirring the ink 132 is disposed in the ink tank 131. The stirrer 134 is driven to rotate by a stirring motor 133 disposed outside the ink tank 131. The stirring motor 133 is operated by a motor drive circuit 139, and the operation is controlled by a control circuit 171. The stirring device includes a stirring motor 133, a stirring bar 134, and a motor drive circuit 139. The stirrer 134 preferably continues to rotate while the ink jet printer 100 is powered on.

  One end of the first tube 141 is accommodated in the ink tank 131, and the other end is connected to the valve 151. The second tube 142 has one end connected to the valve 151 and the other end connected to the inkjet head 110. The third tube 160 has one end connected to the valve 151 and the other end housed in the ink tank 131. In addition, the 1st tube 141, the 2nd tube 142, and the 3rd tube 160 can use the arbitrary tubes corresponding to the specification of an inkjet printer.

  The first tube 141 and the third tube 160 constitute an ink circulation path through the valve 151, the pump 161, and the ink tank 131. The first tube 141 and the second tube 142 constitute an ink supply path from the ink tank 131 to the inkjet head 110 via the valve 151.

  The third tube 160 includes a pump 161 on the way. The pump 161 is operated by a pump drive circuit 191, and the operation is controlled by the control circuit 171. When the pump 161 is operated, the ink in the third tube 160 is transferred from the valve 151 side to the ink tank 131 side. Thus, the third tube 160, together with the pump 161, constitutes a recovery path for recovering ink from the supply path including the first tube 141, the valve 151, and the second tube 142 to the ink tank 131.

  A valve 151 as a switching unit can select whether or not to supply ink to the inkjet head 110 from the circulation path, and the first tube 141 and the second tube 142 are in communication with each other by operating the valve 151. And the state in which the first tube 141 and the third tube 160 communicate with each other can be selected. The valve 151 is operated by a valve driving circuit 181 and is controlled by the control circuit 171.

  In a state where the first tube 141 and the second tube 142 communicate with each other by the operation of the valve 151, the cap lifting / lowering means 176 is raised to cap the inkjet head 110, and the cap suction means 177 is driven to suck ink from the inkjet head 110. To do. As a result, the ink in the ink tank 131 is filled into the inkjet head 110 via the first tube 141, the valve 151, and the second tube 142.

  On the other hand, when the first tube 141 and the third tube 160 are communicated with each other by operating the valve 151, the ink sent from the ink tank 131 into the first tube 141 is sent from the valve 151 to the third tube 160. Returned to the ink tank 131. The ink that has returned to the ink tank 131 is stirred by the rotating stirrer 134 and supplied to the first tube 141. In this way, the ink circulates in the circulation path constituted by the first tube 141 and the third tube 160 via the valve 151, the pump 161, and the ink tank 131. Ink circulation is performed by operating the pump 161, but a pump (not shown) used when supplying ink to the inkjet head 110 may be used in combination.

  The valve 151 is preferably provided in the vicinity of the inkjet head 110. Further, the valve 151 may be provided in the inkjet head 110 without providing the second tube 142.

  With this configuration, the ink can be circulated through the circulation path except when the ink is ejected from the inkjet head 110, so that the precipitation of the pigment can be prevented and the ink concentration can be kept constant. It becomes. Further, by operating the valve 151, the ink maintained at a desired density can be immediately supplied to the inkjet head 110.

  Further, by controlling the operation of the pump 161, it is possible to easily and reliably collect the ink in the supply path at a desired timing without circulating the circulation path.

The operation of the valve 151 is controlled by the control circuit 171 based on a signal from the input unit 172 or the timer 180.
Examples of the signal from the input unit 172 include a power supply stop signal, an image formation start signal, and a filling instruction signal for the inkjet printer 100.

  When an operation for stopping the power supply of the inkjet printer 100 is performed using the input unit 172, a power supply stop signal is sent to the control circuit 171. The valve 151 further includes a mode for introducing the atmosphere into at least the first tube 141 and the third tube 160, and the control circuit 171 that has received the power stop signal sends a drive signal to the valve drive circuit 181 so that the first The valve 151 is operated so as to introduce air into the tube 141 and the third tube 160. Thereby, the ink in the first tube 141 is collected in the ink tank 131 by its own weight. At the same time, the control circuit 171 operates the pump 161 so as to collect the ink in the third tube 160 in the ink tank 131. Accordingly, it is possible to prevent the ink pigment from precipitating in the first tube 141, the second tube 142, and the third tube 160 and changing the ink density while the power of the inkjet printer 100 is stopped.

  On the other hand, when an image formation start signal or a filling instruction signal is input from the input unit 172, the control circuit 171 sends a drive signal to the valve drive circuit 181 so that the first tube 141 and the second tube 142 are mutually connected. The valve 151 is operated so as to communicate. In this state, when the ink jet head 110 is filled through the first tube 141 and the second tube 142, the ink 132 that is circulated in the circulation path and stirred by the stirrer 134 to have a uniform concentration can be filled. It is easy to return to a state where ink can be ejected, and it is possible to form an image having no variation. The image formation start signal may be image data stored in the RAM in advance, or image data input from the host computer 173.

  Here, it is preferable that the ink is continuously circulated by connecting the first tube 141 and the third tube 160 to each other while the power of the inkjet printer 100 is on and image formation is not being performed. Thereby, precipitation of a pigment can be prevented and ink density can be maintained at a desired constant value. The ink is sufficiently stirred by circulating in the circulation path, but it is more preferable to stir with the stirrer 134 in the ink tank 131 from the viewpoint of maintaining the ink density.

  Here, the flow of processing when the circulation control of ink is performed using the timer 180 will be described with reference to FIG. FIG. 3 is a flowchart showing the flow of image formation and ink processing.

  First, in step S100, the stirrer 134 is rotated before ink supply to stir the ink 132 in the ink tank 131, so that the density of the ink 132 is constant. Subsequently, in step S101, the valve 151 is operated to bring the first tube 141 and the second tube 142 into communication with each other, the cap lifting / lowering means 176 is raised to cap the inkjet head 110, and the cap suction means 177 is driven. Ink is sucked from the inkjet head 110. As a result, the ink in the ink tank 131 is filled into the inkjet head 110 via the first tube 141, the valve 151, and the second tube 142.

  After the ink jet head 110 is filled with ink, in step S102, the valve 151 is operated to bring the first tube 141 and the third tube 160 into communication with each other, and the pump 161 is operated to circulate the ink. After the ink circulation is started in step S102, the elapsed time is measured by the timer 180. In step S103, the control circuit 171 determines whether or not the elapsed time has reached a predetermined time T set in advance. The predetermined time T is preferably set to a time for which the ink does not settle according to the ink characteristics, for example, set to 24 hours.

  If the elapsed time reaches the predetermined time T, that is, if YES in step S103, in step S107, the operation of the pump 161 is once stopped to stop the ink circulation, and the inkjet head 110 is moved to the home position to cap it. The suction means 177 is used to suck ink from the nozzles and discharge it to the outside. In this step, it is preferable to discharge the ink in the inkjet head 110 and the second tube 142. After the ink suction in step S107, the ink circulation is restarted in step S102.

  In this way, when the predetermined time T has elapsed from the start of circulation, in other words, when the time T has elapsed without image formation, the ink is discharged from the inkjet head 110 and the second tube 142, whereby the inkjet Precipitation of pigment in the head 110 and the second tube 142 can be prevented. Furthermore, since ink circulated through the circulation path can be filled, image formation can be performed using ink having a constant density.

  On the other hand, if the elapsed time has not reached the predetermined time T, that is, if NO in step S103, it is determined whether or not to perform image formation in step S104. This determination corresponds to whether or not an image formation start signal or a filling instruction signal is input.

  When starting image formation, that is, when YES at step S104, the valve 151 is operated to connect the first tube 141 and the second tube 142, and image formation is started.

  If the image formation is completed, that is, if YES in step S106, in step S102, the valve 151 is operated to circulate ink with the first tube 141 and the third tube 160 in communication.

  On the other hand, if image formation is not started, that is, if NO in step S104, ink circulation and measurement of elapsed time by the timer 180 are continued.

  Thus, when the time during which image formation is not performed is measured using the timer 180 and the ink in the inkjet head 110 and the second tube 142 is discharged when the predetermined time T has elapsed, the inkjet head 110 and the second tube are discharged. It is possible to prevent the ink pigment from precipitating in 142 and changing the ink density.

  The ink from the ink tank 131 to the valve 151 is circulated through the circulation path even when image formation is not being performed, so that precipitation of the pigment in the ink can be prevented and the density can be maintained at a desired constant value. .

  Furthermore, since the valve 151 is provided in the vicinity of the inkjet head 110, the amount of ink filled between the valve 151 and the inkjet head 110 can be reduced. As a result, even if ink is discharged from the inkjet head 110 and the second tube 142 without forming an image for a predetermined time T or longer, it is possible to prevent wasteful consumption of ink because the discharge amount is small.

  Further, since precipitation of the pigment in the inkjet head 110, the first tube 141, the second tube 142, and the third tube 160 can be prevented, a conventional washing operation during precipitation is not required.

<Second Embodiment>
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a diagram illustrating a schematic configuration of an inkjet printer 200 according to the second embodiment. FIG. 5 is a block diagram illustrating a configuration of an inkjet printer 200 according to the second embodiment.

  The inkjet printer 200 according to the second embodiment is different from the inkjet printer 100 according to the first embodiment in that a first pump 252 and a sub tank 235 are provided in the supply path from the ink tank 131 to the inkjet head 110.

  Other configurations are the same as those of the first embodiment, and the same reference numerals are used for the same members.

  In the inkjet printer 200, one end of the first tube 241 is accommodated in the ink tank 131 and the other end is connected to the first pump 252. The first pump 252 is a supply pump that sends out the ink 132 from the ink tank 131 to the inkjet head 110 side. The first pump 252 is operated by the first pump drive circuit 282, and the operation is controlled by the control circuit 171.

  The second tube 242 has one end connected to the first pump 252 and the other end connected to the sub tank 235.

  The sub tank 235 is disposed at a position where the ink in the inkjet head 110 is in a predetermined negative pressure state, and functions as a back pressure tank. The sub tank 235 can be made of any material as long as it has durability corresponding to the type of ink to be stored and the external environment. Moreover, if it functions as a back pressure tank, it can be set as forms other than a tank, for example, the form of a pouch.

  Further, as shown in FIG. 5, the sub tank 235 includes a detection unit 236 that detects the amount of ink inside in a plurality of stages. The detection unit 236 can detect the ink amount in the sub tank 235 in five stages. Specifically, it is detected whether the amount of ink stored in the sub tank 235 is 100%, 75%, 50%, 25%, or 0% with respect to the capacity. As the detector 236, any detector that does not affect the ink composition of the sub tank 235 can be used. For example, a detector that detects the amount of ink optically or electrically can be used. A detection result by the detection unit 236 is output to the control circuit 171.

  The third tube 243 has one end connected to the sub tank 235 and the other end connected to a valve 251 serving as a switching unit. The fourth tube 244 has one end connected to the valve 251 and the other end connected to the inkjet head 110. The fifth tube 260 has one end connected to the valve 251 and the other end accommodated in the ink tank 131.

  In addition, the 1st tube 241, the 2nd tube 242, the 3rd tube 243, the 4th tube 244, and the 5th tube 260 can use the arbitrary tubes corresponding to the specification of an inkjet printer.

  The first tube 241, the first pump 252, the second tube 242, the sub tank 235, the third tube 243, the valve 251, the fifth tube 260, the second pump 261, and the ink tank 131 constitute an ink circulation path. On the other hand, the first tube 241, the first pump 252, the second tube 242, the sub tank 235, the third tube 243, and the fourth tube 244 supply ink from the ink tank 131 to the inkjet head 110 via the valve 251. Configure the route.

  The valve 251 can select whether or not to supply ink to the inkjet head 110 from the circulation path. By operating the valve 251, the third tube 243 and the fourth tube 244 communicate with each other, One of the state in which the 3 tube 243 and the fifth tube 260 communicate with each other can be selected. The valve 251 is operated by a valve driving circuit 281 and is controlled by the control circuit 171.

  The fifth tube 260 includes a second pump 261 on the way. The second pump 261 is operated by the second pump drive circuit 291, and the operation is controlled by the control circuit 171. When the second pump 261 is operated, the ink in the fifth tube 260 is transferred from the valve 251 side to the ink tank 131 side. As a result, the fifth tube 260 receives ink from the supply path including the first tube 241, the first pump 252, the second tube 242, the sub tank 235, the third tube 243, the valve 251, and the fourth tube 244 to the ink tank 131. A recovery path for recovering is configured.

  Ink supply to the inkjet head 110 is performed from the sub tank 235 in a state where the valve 251 is operated and the third tube 243 and the fourth tube 244 communicate with each other. When the detection unit 236 detects that the ink amount in the sub tank 235 has become equal to or less than a predetermined amount due to ink supply to the ink jet head 110, the control circuit 171 drives the first pump 252 to ink from the ink tank 131 to the sub tank 235. Supply. The supply of ink from the ink tank 131 to the sub tank 235 may be temporarily stopped when the sub tank 235 is filled with ink, but an amount corresponding to the image to be formed may be continuously supplied.

  Next, ink circulation will be described. First, in a state where the first pump 252 is stopped, the third tube 243 and the fifth tube 260 are communicated with each other by operating the valve 251. In this state, the second pump 261 is driven to collect the ink in the sub tank 235 into the ink tank 131.

  When the detection unit 236 detects that the ink in the sub tank 235 has decreased to a preset amount, the control circuit 171 operates the first pump 252 to supply ink from the ink tank 131 to the sub tank 235. In supplying ink to the sub tank 235, the second pump 261 may be continuously driven. However, from the viewpoint of increasing the amount supplied to the sub tank 235 from the recovered amount, the second pump 261 is stopped. Is preferred.

  When the detection unit 236 detects that the ink amount in the sub tank 235 has reached a predetermined amount, the control circuit 171 stops the first pump 252 and the ink flow between the first tube 241 and the second tube 242. Stop.

The ink supply to the sub tank 235 will be described more specifically. The control of the ink amount in the sub tank 235 is performed by the control circuit 171. The lower limit value and the upper limit value of the ink capacity are stored in the ROM 175 in advance, and the control circuit 171 detects the ink amount of the sub tank 235 by the detection unit 236, and compares the detected ink amount with the stored lower limit value or upper limit value. . Based on the comparison result, the operation of the first pump 252 is controlled, and the supply of ink into the sub tank 235 is controlled. That is, the control circuit 171 instructs the first pump drive circuit 282 to drive the first pump 252 when the detection unit 236 detects that the ink amount falls below a lower limit value stored, for example, 25%. When the first pump 252 is driven, ink is supplied from the ink tank 131 into the sub tank 235. The control circuit 171 controls the first pump drive circuit 282 to drive the first pump 252 until the ink amount detected by the detection unit 236 reaches the stored upper limit value, for example, 100%. The control circuit 171 controls the first pump drive circuit 282 to stop the first pump 252 when the detection unit 236 detects that the ink amount is an upper limit value stored, for example, 100%.
In the printing state, it is necessary for the sub tank 235 to always have ink. For example, the ink amount is controlled to fall within a range of 25% to 100%. More preferably, it is in the range of 75% to 100%. When there is no remaining capacity in the ink tank 131, it is necessary to continue printing with only the ink in the sub tank 235 until ink is added to the ink tank 131 by means (not shown), so the lower limit value of the ink amount in the sub tank 235 is It is preferably set to 75%, specifically 75%.

  The ink circulation is performed as described above. Here, if the ink recovery capabilities of the first pump 252 and the second pump 261 are the same, the ink circulation can be continued with both being driven. In this case, the ink circulation is started by collecting the ink in the sub tank 235 first.

In the circulating state, the smaller the amount of ink in the sub-tank 235, the lower the possibility that it will stay in the sub-tank 235 and precipitate, which is preferable. Specifically, when the amount of ink in the sub tank 235 is controlled to be small, for example, in the range of 25% to 50% of the capacity, the effect of suppressing the precipitation of ink in the sub tank 235 can be enhanced. However, the ink amount in the sub tank 235 is not set to 0 in order to maintain a state where printing can be performed immediately.
The ink that has returned to the ink tank 131 is agitated by the rotating agitator 134 and supplied to the first tube 241. In this way, ink circulates in the circulation path via the valve 251 and the ink tank 131.

  If the amount of ink in the sub tank 235 is controlled within the range of 25% and 0% of the capacity, the effect of suppressing the precipitation of ink in the sub tank 235 can be enhanced.

  Other configurations, operations, and effects are the same as those in the first embodiment.

<Third Embodiment>
Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 6 is a diagram illustrating a schematic configuration of an inkjet printer 300 according to the third embodiment. FIG. 7 is a block diagram illustrating a configuration of an inkjet printer 300 according to the third embodiment.

  In the inkjet printer 300 according to the third embodiment, the second valve 353 is provided in the fifth tube 360 corresponding to the fifth tube 260 of the second embodiment, and the main tank 330 and the second valve 353 are provided in the second valve 353. The point from which the pump 361 is connected differs from 2nd Embodiment. Other configurations are the same as those of the second embodiment, and the same reference numerals are used for the same members.

  In addition, the first tube 341, the second tube 342, the third tube 343, the fourth tube 344, the first valve 351, the first pump 352, the second pump 361, the first valve drive circuit 381, the third embodiment, The first pump drive circuit 382, the second pump drive circuit 391, the sub tank 335, and the detection unit 336 are the first tube 241, the second tube 242, the third tube 243, the fourth tube 244, the valve 251, and the second embodiment of the second embodiment. Since it corresponds to the 1 pump 252, the second pump 261, the valve drive circuit 281, the first pump drive circuit 282, the second pump drive circuit 291, the sub tank 235, and the detection unit 236, detailed description is omitted.

  The fifth tube 360 has one end connected to the first valve 351 and the other end connected to the second valve 353. A main tank 330 as a supply unit and a second pump 361 are connected to the second valve. One end of a sixth tube 362 is connected to the second pump 361, and the other end of the sixth tube 362 is accommodated in the ink tank 131.

  First tube 341, first pump 352, second tube 342, sub tank 335, third tube 343, first valve 351, fifth tube 360, second valve 353, second pump 361, sixth tube 362, and ink The tank 131 constitutes an ink circulation path. Meanwhile, the second pump 361, the sixth tube 362, the first tube 341, the first pump 352, the second tube 342, the sub tank 335, the third tube 343, and the fourth tube 344 are the ink tank 131 and the first valve 351, respectively. Thus, an ink supply path from the main tank 330 to the inkjet head 110 is configured.

  The first valve 351 is operated by the first valve driving circuit 381, and this operation is controlled by the control circuit 171. The first valve 351 can select whether or not to supply ink from the circulation path to the inkjet head 110.

  The second valve 353 is operated by the second valve driving circuit 383, and this operation is controlled by the control circuit 171. By operating the second valve 353, one of a state in which the main tank 330 and the second pump 361 are connected and a state in which the fifth tube 360 and the second pump 361 are connected is selected.

  The ink tank 131 is preferably disposed between the inkjet head 110 and the main tank 330 and between the pump 352 and the main tank 330. The main tank 330 can be replaced.

  When supplying ink from the main tank 330 to the inkjet head 110, the second valve 353 and the first valve 351 are operated, and the second valve 353, the second pump 361, the sixth tube 362, the ink tank 131, the first A supply path is formed so as to communicate with the inkjet head 110 from the main tank 330 via the tube 341, the first pump 352, the second tube 342, the sub tank 335, the third tube 343, the first valve 351, and the fourth tube 344. To do.

  On the other hand, when the ink is circulated, the second valve 353 and the first valve 351 are operated, and the first tube 341, the first pump 352, the second tube 342, the sub tank 335, the third tube 343, A circulation path is formed so that the first valve 351, the fifth tube 360, the second valve 353, the second pump 361, and the sixth tube 362 communicate with each other.

  Other configurations, operations, and effects are the same as those in the second embodiment.

  Although the present invention has been described with reference to the above embodiment, the present invention is not limited to the above embodiment, and can be improved or changed within the scope of the purpose of the improvement or the idea of the present invention.

  As described above, the ink jet printer and the ink density maintaining method according to the present invention are useful when using an ink whose ink density is likely to change when left for a long time.

DESCRIPTION OF SYMBOLS 100 Inkjet printer 110 Inkjet head 121 Platen 122, 123 Conveyance roller 124 Medium 131 Ink tank 132 Ink 133 Stirrer motor 134 Stirrer 139 Motor drive circuit 141 First tube 142 Second tube 151 Valve 160 Third tube 161 Pump 171 Control circuit 172 Input means 173 Host computer 174 RAM
175 ROM
176 Cap raising / lowering means 177 Cap suction means 178 Recording medium conveying means 179 Carriage scanning means 180 Timer 181 Valve drive circuit 191 Pump drive circuit 200 Inkjet printer 235 Sub tank 236 Detector 241 First tube 242 Second tube 243 Third tube 244 Fourth Tube 251 Valve 252 1st pump 260 5th tube 261 2nd pump 281 Valve drive circuit 282 1st pump drive circuit 291 2nd pump drive circuit 300 Inkjet printer 330 Main tank 335 Sub tank 336 Detector 341 1st tube 342 2nd tube 343 3rd tube 344 4th tube 351 1st valve 352 1st pump 353 2nd valve 360 5th tube 361 2nd Pump 362 Sixth tube 381 First valve drive circuit 382 First pump drive circuit 383 Second valve drive circuit 391 Second pump drive circuit

Claims (11)

An inkjet head that ejects ink onto a medium;
A circulation path for circulating ink to be supplied to the inkjet head;
A supply unit that is disposed in the circulation path and stores ink to be supplied to the inkjet head;
A switching unit for selecting whether to supply ink from the circulation path to the inkjet head;
An ink jet printer comprising:   The inkjet printer according to claim 1, further comprising a stirring device that stirs the ink in the supply unit or the circulation path.   The inkjet printer according to claim 1, wherein the circulation path includes a pump that circulates ink.   The inkjet printer according to claim 1, wherein the circulation path is provided with an adjusting unit that brings the ink in the inkjet head into a predetermined negative pressure state.   The ink jet printer according to claim 3, wherein the pump includes a recovery pump that sends ink to the supply unit, and a supply pump that sends ink from the supply unit.   The ink jet printer according to claim 1, wherein the stirring device is disposed between the supply unit and the ink jet head in the circulation path.   The circulation path is connected to a supply path for supplying ink from the supply section to the inkjet head and the switching section provided in the supply path, and ink is sent from the supply path to the supply section by switching valves. The inkjet printer according to claim 1, further comprising a collection path. An inkjet head that ejects ink onto a medium;
A supply unit that is disposed in the circulation path and stores ink to be supplied to the inkjet head;
A method of maintaining the ink density of an inkjet printer comprising:
A circulation step for circulating ink in the circulation path;
A switching step for selecting whether to supply ink from the circulation path to the inkjet head;
An ink density maintaining method comprising:   The ink density maintaining method according to claim 8, further comprising a discharging step of discharging ink in the inkjet head when a predetermined time has passed without image formation.   The ink density maintaining method according to claim 8, further comprising a recovery step of recovering ink in the circulation path to the supply unit when an operation to stop the power supply of the inkjet printer is performed.   The ink density maintaining method according to claim 10, wherein, in the switching step, the ink jet head is filled with ink in the circulation path when the ink jet printer receives an ink filling instruction from a user.

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