Printing device and ink delivery method therefor

Abstract

To suppress precipitation of a component of ink in a buffer tank for storing ink to be replenished to a discharge head.SOLUTION: When a replenishment solenoid valve Vl1 is closed and a return solenoid valve Vl2 is opened, ink fed by a replenishment pump 951 is prohibited from passing the replenishment solenoid valve Vl1 and the ink is permitted to pass the return solenoid valve Vl2. Therefore, ink is circulated in a circulation path Cc2 (second circulation path) in which ink is fed by a return pipe 961 from a branch point J to a buffer tank 95a after ink is fed to the branch point J by a replenishment pipe 95b from the buffer tank 95a.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a printing technique in which ink is supplied to a discharge head from a buffer tank that stores ink and is discharged from the discharge head. [Background technology]

[0002] The printing device of Patent Document 1 includes a supply tank that stores ink to be supplied to the ejection head, and a recovery tank that stores ink recovered from the ejection head, and supplies ink to the ejection head by sending ink from the supply tank to the recovery tank via the ejection head. Also, when ink is consumed by ejection from the ejection head, ink is sent to the recovery tank from a tank (main tank) that stores replenishment ink. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-044823 Summary of the Invention [Problem to be solved by the invention]

[0004] In printing devices equipped with a tank for storing ink, ink components may settle in the tank. In response to this, Patent Document 1 provides a circulation pump that transfers ink from the recovery tank to the supply tank. Therefore, ink that reaches the recovery tank from the supply tank via the ejection head is returned from the recovery tank to the supply tank by the circulation pump. In this way, ink is circulated between the supply tank and the recovery tank via the ejection head, thereby preventing ink from settling in the supply tank and the recovery tank. Meanwhile, a tank that stores replenishment ink (hereinafter referred to as a "buffer tank") does not have a mechanism for circulating ink. Therefore, ink components stored in the buffer tank may settle.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to make it possible to suppress the settling of ink components in a buffer tank that stores ink to be replenished to a discharge head. [Means for solving the problem]

[0006] a supply pipe that connects the supply tank and the ejection head through a flow path and sends ink from the supply tank to the ejection head; a recovery tank that stores ink recovered from the ejection head; a recovery pipe that connects the recovery tank and the ejection head through a flow path and sends ink from the ejection head to the recovery tank; a first return pipe that connects the recovery tank and the supply tank through a flow path and sends ink from the recovery tank to the supply tank; a circulation pump that is provided on the first return pipe between the recovery tank and the supply tank and sends ink from the recovery tank to the supply tank; a buffer tank that stores ink to be replenished to the recovery tank; a resupply pipe that connects the buffer tank and the recovery tank through a flow path and sends ink from the buffer tank to the recovery tank; a resupply pump that is provided on the resupply pipe between the buffer tank and the recovery tank and sends ink from the buffer tank to the recovery tank; a first solenoid valve that allows ink to be sent to the recovery tank via a supply pipe and, when closed, blocks the supply pump from sending ink from the buffer tank to the recovery tank via the supply pipe; a branch point that is provided in the supply pipe at a position between the first solenoid valve and the supply pump; a second return pipe that connects the buffer tank and a branch point, and sends ink from the branch point of the supply pipe to the buffer tank; a second solenoid valve that is provided in the second return pipe between the branch point and the buffer tank and, when opened, allows ink to be sent from the branch point to the buffer tank via the second return pipe and, when closed, blocks ink from the branch point to the buffer tank via the second return pipe; and a control unit that has a circulation pump control unit that controls the circulation pump, a supply pump control unit that controls the supply pump, a first solenoid valve control unit that controls the first solenoid valve, and a second solenoid valve control unit that controls the second solenoid valve, andFurthermore, ink is circulated in a first circulation path that sends ink from the ejection head to the recovery tank via a recovery pipe, and when the first solenoid valve control unit controls the first solenoid valve so that the first solenoid valve is open, while the second solenoid valve control unit controls the second solenoid valve so that the second solenoid valve is closed, and the resupply pump control unit controls the resupply pump so that the resupply pump sends ink from the buffer tank to the recovery tank, ink is replenished to the recovery tank via a resupply path that sends ink from the buffer tank to the recovery tank via the resupply pipe, while the first solenoid valve control unit controls the first solenoid valve so that the first solenoid valve is closed, while the second solenoid valve control unit controls the second solenoid valve so that the second solenoid valve is open, and the resupply pump control unit controls the resupply pump so that the resupply pump sends ink from the buffer tank to the branch point, ink is circulated in a second circulation path that sends ink from the buffer tank to the branch point via the resupply pipe and then from the branch point to the buffer tank via the second return pipe.

[0007] The ink delivery method for a printing device according to the present invention is an ink delivery method for a printing device including a discharge head having nozzles for ejecting ink, a supply tank for storing ink to be supplied to the discharge head, a supply pipe connecting the supply tank and the discharge head through a flow path and delivering ink from the supply tank to the discharge head, a recovery tank for storing ink recovered from the discharge head, a recovery pipe connecting the recovery tank and the discharge head through a flow path and delivering ink from the discharge head to the recovery tank, a first return pipe connecting the recovery tank and the supply tank through a flow path and delivering ink from the recovery tank to the supply tank, and a circulation pump provided on the first return pipe between the recovery tank and the supply tank and delivering ink from the recovery tank to the supply tank, the circulation pump delivering ink from the recovery tank to the supply tank, a first circulation process in which the circulation pump delivers ink from the recovery tank to the supply tank via the first return pipe, and then the ink is delivered from the recovery tank to the discharge head through the supply pipe, and then the ink is delivered from the discharge head to the recovery tank via the recovery pipe; a refilling step in which ink is sent from the buffer tank to the recovery tank via a refilling pump provided in a refilling pipe that connects a flow path between the buffer tank and the recovery tank and sends ink from the buffer tank to the refilling pipe; and a second circulation step in which ink is sent from the buffer tank to a branch point provided in the refilling pipe between the refilling pump and the recovery tank by the refilling pump, so that after the ink has been sent from the buffer tank to the branch point via the refilling pipe, it is sent from the branch point to the buffer tank via a second return pipe that connects the flow path between the branch point and the buffer tank, a first solenoid valve is provided in the refilling pipe at a position between the branch point and the recovery tank, and the first solenoid valve opens to allow the refilling pump to send ink from the buffer tank to the recovery tank via the refilling pipe and closes to block the send of ink from the buffer tank to the recovery tank via the refilling pipe, and a second solenoid valve is provided in the second return pipe at a position between the branch point and the buffer tank, and the second solenoid valve opens to allow the send of ink from the branch point to the buffer tank via the second return pipe,Closing the valve blocks the transfer of ink from the branch point to the buffer tank via the second return pipe, and in the refilling process, the first solenoid valve opens and the second solenoid valve closes, causing the refill pump to transfer ink from the buffer tank towards the recovery tank, so that the ink is transferred from the buffer tank to the recovery tank via the refill pipe and the first solenoid valve, and in the second circulation process, the first solenoid valve closes and the second solenoid valve opens, causing the refill pump to transfer ink from the buffer tank towards the branch point, so that the ink is transferred from the buffer tank to the branch point via the refill pipe and then from the branch point to the buffer tank via the second return pipe.

[0008] In the present invention configured as described above, ink is circulated through a first circulation path in which ink is sent from the recovery tank via the first return pipe to the supply tank, then sent to the ejection head via the supply pipe, and further sent from the ejection head to the recovery tank via the recovery pipe (first circulation process). This prevents ink components stored in the supply tank and the recovery tank from settling. In addition, a refill pump is attached to the refill pipe connecting the buffer tank and the recovery tank. Therefore, when ink is consumed as ink is ejected from the ejection head, the refill pump can refill ink from the buffer tank via the refill pipe to the recovery tank (refill process).

[0009] In particular, in the present invention, a second return pipe is provided between the supply pump and the recovery tank, connecting a branch point on the supply pipe to the buffer tank. Furthermore, a first solenoid valve is provided on the supply pipe between the branch point and the recovery tank, and a second solenoid valve is provided on the second return pipe between the branch point and the buffer tank. When opened, the first solenoid valve allows the supply pump to send ink from the buffer tank to the recovery tank via the supply pipe, and when closed, it blocks the supply pump from sending ink from the buffer tank to the recovery tank via the supply pipe. When opened, the second solenoid valve allows ink to be sent from the branch point to the buffer tank via the second return pipe, and when closed, it blocks the ink to be sent from the branch point to the buffer tank via the second return pipe. Therefore, when the first solenoid valve is opened and the second solenoid valve is closed, ink sent by the supply pump is allowed to pass through the first solenoid valve, but is prohibited from passing through the second solenoid valve. This allows the supply pump to supply ink from the buffer tank to the recovery tank via the first solenoid valve, as described above. Furthermore, when the first solenoid valve closes and the second solenoid valve opens, ink pumped by the supply pump is prohibited from passing through the first solenoid valve, while the ink is allowed to pass through the second solenoid valve. Therefore, ink is circulated through a second circulation path that is pumped from the buffer tank to a branch point via a supply pipe and then from the branch point to the buffer tank via a second return pipe (second circulation process). As a result, settling of ink components in the buffer tank, which stores ink to be supplied to the ejection head, is suppressed.

[0010] Furthermore, in the present invention, both the supply of ink from the buffer tank to the recovery tank and the circulation of ink in the second circulation path are performed by the supply pump, which has the advantage of reducing the number of pumps required compared to a configuration in which two pumps are provided for each operation.

[0011] The printing device may further include a supply level detection unit provided for the supply tank to detect a supply level, which is the level of ink in the supply tank, and a recovered level detection unit provided for the recovery tank to detect a recovered level, which is the level of ink in the recovery tank, wherein the control unit further includes a supply level acquisition unit that acquires the supply level detected by the supply level detection unit and a recovered level acquisition unit that acquires the recovered level detected by the recovered level detection unit, wherein the first solenoid valve control unit controls the opening and closing of the first solenoid valve based on the supply level detected by the supply level detection unit and the recovered level detected by the recovered level detection unit, and the second solenoid valve control unit controls the opening and closing of the second solenoid valve based on the supply level detected by the supply level detection unit and the recovered level detected by the recovered level detection unit. With this configuration, the recovery tank can be replenished with ink and ink can be circulated in the second circulation path depending on the ink level in the supply tank (supply level) and the ink level in the recovery tank (recovery level).

[0012] The printing device may be configured so that the supply level detection unit detects whether the ink level in the supply tank is in a first supply level range below a first supply threshold, a second supply level range below a second supply threshold higher than the first supply threshold and equal to or greater than the first supply threshold, or a third supply level range below a third supply threshold higher than the second supply threshold and equal to or greater than the second supply threshold, and the recovered level detection unit detects whether the ink level in the recovery tank is in a first recovered level range below the first recovery threshold, a second recovered level range below a second recovery threshold higher than the first recovery threshold and equal to or greater than the first recovery threshold, or a third recovered level range below a third recovery threshold higher than the second recovery threshold and equal to or greater than the second recovery threshold. With this configuration, the recovery tank can be replenished with ink or ink can be circulated in the second circulation path depending on the results of detecting the supply level in the supply tank and the recovered level in the recovery tank in at least three stages.

[0013] Furthermore, the printing device may be configured such that, when the supply liquid level acquired by the supply liquid level acquisition unit is within the second supply liquid level range and the recovery liquid level acquired by the recovery liquid level acquisition unit is within the second recovery liquid level range or the third recovery liquid level range, the first solenoid valve control unit controls the first solenoid valve to close the first solenoid valve, and the second solenoid valve control unit controls the second solenoid valve to open the second solenoid valve, thereby circulating ink in the second circulation path. With this configuration, ink can be circulated in the second circulation path by taking advantage of the timing when the amount of ink in each of the supply tank and the recovery tank is high, thereby suppressing sedimentation of ink in the buffer tank.

[0014] In this case, the printing device may be configured so that when the supply liquid level acquired by the supply liquid level acquisition unit is within the second supply liquid level range and the recovered liquid level acquired by the recovered liquid level acquisition unit is within the third recovered liquid level range, the circulation pump control unit controls the circulation pump to increase the output of the circulation pump to send ink. With this configuration, the amount of ink sent from the recovery tank to the supply tank by the circulation pump is increased, thereby preventing an excess of ink in the recovery tank.

[0015] Furthermore, the printing device may be configured such that, when the supply liquid level acquired by the supply liquid level acquisition unit is within a third supply liquid level range, the first solenoid valve control unit controls the first solenoid valve to close the first solenoid valve, and the second solenoid valve control unit controls the second solenoid valve to open the second solenoid valve, thereby circulating ink in the second circulation path. With this configuration, ink can be circulated in the second circulation path by taking advantage of the timing when the amount of ink in the supply tank is high, thereby suppressing sedimentation of ink in the buffer tank.

[0016] In this case, the printing device may be configured so that if the supply liquid level acquired by the supply liquid level acquisition unit is in the third supply liquid level range and the recovered liquid level acquired by the recovered liquid level acquisition unit is in the first recovered liquid level range or the second recovered liquid level range, the circulation pump control unit controls the circulation pump to reduce the output of the circulation pump to send ink. With this configuration, the amount of ink sent by the circulation pump from the recovery tank to the supply tank can be reduced, preventing an excess of ink in the supply tank.

[0017] Alternatively, the printing device may be configured so that if the supply liquid level acquired by the supply liquid level acquisition unit is within the third supply liquid level range and the recovered liquid level acquired by the recovered liquid level acquisition unit is within the third recovered liquid level range, the circulation pump control unit controls the circulation pump to stop the circulation pump. In this configuration, the circulation pump stops sending ink from the recovery tank to the supply tank, preventing an excess of ink from building up in the supply tank.

[0018] Furthermore, the printing device may be configured such that, when the supply liquid level acquired by the supply liquid level acquisition unit is within a first supply liquid level range and the recovery liquid level acquired by the recovery liquid level acquisition unit is within either the first recovery liquid level range or the second recovery liquid level range, the first solenoid valve control unit controls the first solenoid valve to open the first solenoid valve, and the second solenoid valve control unit controls the second solenoid valve to close the second solenoid valve, thereby sending ink to the buffer tank through the supply path. In this configuration, ink is replenished from the buffer tank to the recovery tank as the amount of ink in the supply tank decreases. The ink replenished in this way to the recovery tank is sent from the recovery tank to the supply tank by the circulation pump. As a result, ink shortages in the supply tank can be resolved.

[0019] In this case, the printing device may be configured so that when the supply liquid level acquired by the supply liquid level acquisition unit is within a first supply liquid level range and the recovered liquid level acquired by the recovered liquid level acquisition unit is within a second recovered liquid level range, the circulation pump control unit controls the circulation pump to increase the output of the circulation pump to send ink. With this configuration, the amount of ink sent from the recovery tank to the supply tank by the circulation pump can be increased, thereby eliminating the shortage of ink in the supply tank.

[0020] Furthermore, the printing device may be configured so that, when the supply liquid level acquired by the supply liquid level acquisition unit is within the second supply liquid level range and the recovered liquid level acquired by the recovered liquid level acquisition unit is within the first recovered liquid level range, the first solenoid valve control unit controls the first solenoid valve to open the first solenoid valve, and the second solenoid valve control unit controls the second solenoid valve to close the second solenoid valve, thereby circulating ink in the first circulation path. With this configuration, when the amount of ink in the recovery tank becomes low, ink is replenished from the buffer tank to the recovery tank, thereby eliminating the shortage of ink in the recovery tank.

[0021] The printing device may also be configured so that, when the supply level acquired by the supply level acquisition unit is within the second supply level range and the recovered liquid level acquired by the recovered liquid level acquisition unit is within the first recovered liquid level range, the circulation pump control unit controls the circulation pump to reduce the output of the circulation pump to pump ink. With this configuration, the amount of ink pumped from the recovery tank to the supply tank by the circulation pump is reduced, preventing the recovery tank from becoming short of ink.

[0022] Furthermore, the printing device may be configured so that, when the supply liquid level acquired by the supply liquid level acquisition unit is within a first supply liquid level range and the recovery liquid level acquired by the recovery liquid level acquisition unit is within a third recovery liquid level range, the first solenoid valve control unit controls the first solenoid valve to close the first solenoid valve, and the second solenoid valve control unit controls the second solenoid valve to open the second solenoid valve. With this configuration, when the amount of ink in the recovery tank is large, ink is not replenished from the buffer tank to the recovery tank, and an excess of ink in the recovery tank can be prevented.

[0023] The printing device may also be configured so that, when the supply level acquired by the supply level acquisition unit is within a first supply level range and the recovered liquid level acquired by the recovered liquid level acquisition unit is within a third recovered liquid level range, the circulation pump control unit controls the circulation pump to increase the output of the circulation pump to deliver ink. With this configuration, the amount of ink delivered by the circulation pump from the recovery tank to the supply tank can be increased, thereby eliminating the shortage of ink in the supply tank.

[0024] Incidentally, when circulating the ink in the second circulation path, it is sufficient that the ink flows to an extent that sedimentation of ink components can be suppressed. Therefore, the printing device may be configured so that the supply pump control unit controls the supply pump so that the output of the supply pump when the ink pumped by the supply pump is circulated along the second circulation path is lower than the output of the supply pump when the ink pumped by the supply pump is replenished from the buffer tank to the recovery tank along the supply path. [Effects of the Invention]

[0025] As described above, according to the present invention, it is possible to prevent ink components from settling in a buffer tank that stores ink to be replenished to a discharge head. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a front view schematically illustrating an example of a printing system including a printing device according to the present invention. [Figure 2] FIG. 2 is a front view schematically showing a printing device included in the printing system of FIG. 1. [Figure 3] FIG. 2 is a diagram schematically illustrating the bottom surface of an ejection head provided in the head unit. [Figure 4] FIG. 2 is a diagram showing a schematic configuration of a discharge head and an ink supply, recovery, supply, and circulation mechanism 9 that supplies, recovers, replenishes, and circulates ink to the discharge head. [Figure 5] FIG. 2 is a diagram showing a schematic configuration of a discharge head and an ink supply, recovery, supply, and circulation mechanism 9 that supplies, recovers, replenishes, and circulates ink to the discharge head. [Figure 6] FIG. 2 is a block diagram showing the electrical configuration of the printing apparatus. [Figure 7] FIG. 4 is a diagram schematically illustrating a detection mode of the ink level. [Figure 8] 10 is a flowchart showing an example of circulation mode control executed by a control unit. [Figure 9] 9 is a diagram showing, in table format, an example of circulation mode data referenced in the circulation mode control of FIG. 8; DETAILED DESCRIPTION OF THE INVENTION

[0027] FIG. 1 is a front view schematically illustrating an example of a printing system equipped with a printing device according to the present invention. In FIG. 1 and the following figures, the horizontal X direction, the horizontal Y direction perpendicular to the X direction, and the vertical Z direction are indicated as appropriate. As shown in FIG. 1, the printing system 1 includes a printing device 3 and a drying device 6 arranged in the X direction. This printing system 1 transports a long strip of printing medium M roll-to-roll from a feed roll 11 to a take-up roll 12. The printing medium M is made of a film such as OPP (oriented polypropylene) or PET (polyethylene terephthalate). However, the material of the printing medium M is not limited to film and may be paper or other materials. The printing medium M is flexible. In the following description, the surface of the printing medium M on which an image is printed will be referred to as the front surface M1, and the surface opposite the front surface M1 will be referred to as the back surface M2.

[0028] The printing device 3 prints an image on the surface M1 of the printing medium M by ejecting aqueous ink by inkjet printing onto the surface M1 of the printing medium M being transported from the supply roll 11 to the take-up roll 12. A detailed configuration of the printing device 3 will be described later. The printing medium M on which the image has been printed in this manner is transported from the printing device 3 to the drying device 6 in the X direction.

[0029] The drying device 6 includes a drying furnace 60, which dries the printing medium M carried out from the printing device 3 as it is transported from the payout roll 11 to the take-up roll 12. The drying furnace 60 includes two upper blower units 61u arranged in the X direction, two middle blower units 61m arranged in the X direction below the upper blower units 61u, and two lower blower units 61l arranged in the X direction below the middle blower units 61m.

[0030] The printing medium M discharged from the discharge port 312 of the printing device 3 passes through the two upper-stage air blowing units 61u in the X direction, and then is turned back toward the two middle-stage air blowing units 61m by a pair of rollers 62. Next, the printing medium M passes through the two middle-stage air blowing units 61m in the X direction, and then is turned back toward the two lower-stage air blowing units 61l by a pair of air turn bars 63. Furthermore, the printing medium M passes through the two lower-stage air blowing units 61l in the X direction, and then is discharged to the outside of the drying device 6.

[0031] The upper air blowing unit 61u has two air blowing chambers 64 arranged to sandwich the printing medium M passing in the X direction in the Z direction. Each air blowing chamber 64 has a plurality of nozzles 65 arranged in the X direction, and hot air (gas at 60 degrees or higher) is sprayed from each nozzle 65 onto the printing medium M. In this way, the printing medium M is dried by the hot air sprayed from the nozzles 65 of these air blowing chambers 64 while passing between the two air blowing chambers 64 arranged above and below. Similarly to the upper air blowing unit 61u, the middle air blowing unit 61m and the lower air blowing unit 61l each have two air blowing chambers 64 that sandwich the printing medium M in the Z direction.

[0032] The specific configuration of the upper blower unit 61u is not limited to this example. For example, the lower blower chamber 64 of the upper and lower blower chambers 64 of the upper blower unit 61u may be replaced with a plurality of rollers arranged in the X direction. In this configuration, the back surface M2 of the printing medium M is supported from below by the plurality of rollers, while hot air can be sprayed from the upper blower chamber 64 onto the front surface M1 of the printing medium M.

[0033] Fig. 2 is a front view showing a schematic representation of a printing device included in the printing system of Fig. 1. In Fig. 2, one side X1 and the other side X2 in the X direction are appropriately shown. Here, one side X1 is the side facing the drying device 9 from the printing device 3, and the other side X2 is the opposite side of one side X1. The printing device 3 includes a housing 31, a color printing unit 32 arranged within the housing 31, a white printing unit 33 arranged above the color printing unit 32 within the housing 31, and a transport unit 4 that transports the printing medium M using multiple rollers arranged within the housing 31.

[0034] The color printing unit 32 has a plurality of (six) head units 321 arranged above the printing medium M transported by the transport unit 4 in the direction of travel of the printing medium M (the direction from the other side X2 to the one side X1). Each of the plurality of head units 321 has nozzles facing from above onto the surface M1 of the printing medium M passing below, and ejects different color inks from the nozzles using an inkjet method. Here, color ink refers to ink other than white, and includes inks such as cyan, magenta, yellow, and black. In this way, the plurality of head units 321 of the color printing unit 32 eject color inks from above onto the surface M1 of the printing medium M passing below, thereby printing a color image on the surface M1 of the printing medium M.

[0035] The white printing section 33 also has a single head unit 331 arranged above the printing medium M transported by the transport section 4. The head unit 331 has nozzles facing from above the surface M1 of the printing medium M passing below it, and ejects white ink from the nozzles using an inkjet method. In this way, the head unit 331 of the white printing section 33 prints a white image on the surface M1 of the printing medium M by ejecting white ink from above onto the surface M1 of the printing medium M passing below it.

[0036] An inlet 311 opens in the side wall on the other side X2 of the housing 31, while an outlet 312 opens in the side wall on the one side X1 of the housing 31. The transport unit 4 transports the printing medium M from the inlet 311 to the outlet 312, passing through the color printing unit 32 and the white printing unit 33.

[0037] The transport unit 4 has an inlet unit 41 provided below the color printing unit 32, an upward transport unit 42 provided on one side X1 of the color printing unit 32, an upward transport unit 43 provided above the color printing unit 32, and a downward transport unit 44 provided on the other side X2 of the color printing unit 32. The inlet unit 41 transports the printing medium M transported from the inlet 311 to the one side X1 using rollers 411, the upward transport unit 42 transports the printing medium M transported by the inlet unit 41 upward using rollers 421, the upward transport unit 43 transports the printing medium M transported by the upward transport unit 42 to the other side X2 using rollers 431, and the downward transport unit 44 transports the printing medium M transported by the upward transport unit 43 downward using rollers 441.

[0038] Furthermore, the transport unit 4 has a color transport unit 45 that supports the printing medium M facing the color printing unit 32 from below, and the printing medium M that has passed through the descending transport unit 44 enters the color transport unit 45. This color transport unit 45 has a plurality of rollers 451 arranged from the other side X2 to one side X1, and each roller 451 contacts the back surface M2 of the printing medium M from below. In this way, the front surface M1 of the printing medium M supported by the color transport unit 45 faces upward, and each head unit 321 of the color printing unit 32 ejects color ink while facing this front surface M1 from above.

[0039] The transport unit 4 also has rollers 461, 462, and 463 arranged between the color transport unit 45 and the downward transport unit 44 in the traveling direction of the printing medium M. The roller 461 is a drive roller that drives the printing medium M. The rollers 462 and 463 are driven rollers that rotate in response to the printing medium M.

[0040] Furthermore, the transport unit 4 has a reverse transport unit 47 that turns upside down twice the printing medium M transported from the color transport unit 45 to one side X1. This reverse transport unit 47 has multiple rollers 471 to 477, including a drive roller 471, and these rollers 471 to 477 turn the printing medium M upside down twice while contacting the back side M2 ​​of the printing medium M. That is, the reverse transport unit 47 transports the printing medium M transported from the color transport unit 45 downward using rollers 471 and 472, and then changes the traveling direction of the printing medium M to the other side X2 using roller 472 and transports it, thereby turning upside down the front side M1 and back side M2 ​​of the printing medium M. Next, the reverse transport unit 47 transports the printing medium M from one side X1 to the other side X2 using multiple rollers 473, and then transports the printing medium M upward using rollers 474 to 476. Furthermore, the reverse conveying section 47 changes the direction of travel of the printing medium M to one side X1 using roller 476, thereby again inverting the front surface M1 and back surface M2 of the printing medium M upside down, and conveys the printing medium M from the other side X2 toward one side X1 using roller 477.

[0041] The transport unit 4 also has a white transport unit 48 that supports the printing medium M facing the white printing unit 33 from below, and the printing medium M that has been turned upside down twice by the reversing transport unit 47 enters the white transport unit 48. This white transport unit 48 has a roller 481 that contacts the back surface M2 of the printing medium M from below. Thus, the front surface M1 of the printing medium M supported by the white transport unit 48 faces upward, and the head unit 331 of the white printing unit 33 ejects white ink while facing this front surface M1 from above.

[0042] The conveying unit 4 also has an output unit 49 located above the upper conveying unit 43. The output unit 49 has a plurality of rollers 491 arranged from the other side X2 to one side X1 in the X direction. The output unit 49 conveys the printing medium M conveyed by the white conveying unit 48 to the one side X1 using the plurality of rollers 491, thereby conveying the printing medium M from the output opening 312 of the housing 31 to the drying device 6.

[0043] As described above, the color printing unit 32 and the white printing unit 33 of the printing device 3 have head units 321 and 331. Next, we will explain the ejection heads H of the head units 321 and 331 and the ink supply, recovery, supply, and circulation mechanism 9 that supplies, recovers, replenishes, and circulates ink to the ejection heads H. The ink supply, recovery, circulation, and supply mechanism 9 includes an ink supply mechanism 9a that supplies ink to the ejection heads H, an ink recovery mechanism 9b that recovers ink from the ejection heads H, an ink return mechanism 9c that returns the recovered ink to the ink supply mechanism 9a, an ink supply mechanism 9d that replenishes ink to the ink recovery mechanism 9b, and an ink return mechanism 9e that returns ink branched from the ink supply mechanism 9d to the ink supply mechanism 9d. The head units 321 and 331 have a common basic configuration, and the basic configuration of the ink supply, recovery, supply, and circulation mechanism 9 is also common to the head units 321 and 331. Therefore, we will explain the configuration of the head unit 331 that ejects white ink.

[0044] Fig. 3 is a diagram schematically showing the bottom surface of an ejection head provided in a head unit, and Fig. 4 is a diagram schematically showing the configuration of an ejection head and an ink supply / recovery / replenishment / circulation mechanism 9 that supplies, recovers, replenishes, and circulates ink to the ejection head. As shown in Fig. 3, in the head unit 331, multiple ejection heads H that eject ink of the same color (white ink) are arranged in a line in the Y direction, and each ejection head H has a rectangular shape when viewed from the bottom. Note that the arrangement of the multiple ejection heads H is not limited to the example in Fig. 3, and the multiple ejection heads H may also be arranged in a staggered pattern.

[0045] As shown in FIG. 4, the ejection head H has a housing Ha, and a plurality of nozzles Hn are open to the bottom surface of the housing Ha, arranged in a staggered pattern in the Y direction. Inside the housing Ha, a plurality of cavities Hb are provided, each communicating with the plurality of nozzles Hn, and an ink supply chamber Hc is provided, communicating with the plurality of cavities Hb. Ink supplied from the ink supply chamber Hc is stored in the cavities Hb. Each cavity Hb is provided with a piezoelectric element E, which is displaced in response to a drive signal (electrical signal), causing a pressure fluctuation in the ink in the cavity Hb. This pressure fluctuation pushes ink out of the cavity Hb, causing the ink to be ejected from the nozzle Hn communicating with the cavity Hb. In addition, an ink inlet Hd and an ink outlet He are opened at the top of the ejection head H, and ink flows from the ink supply mechanism 9a into the ink supply chamber Hc via the ink inlet Hd, and flows out from the ink supply chamber Hc towards the ink recovery mechanism 9b via the ink outlet He.

[0046] The ink supply mechanism 9a includes an ink supply unit 91 that supplies ink toward the ejection head H, and a pressure generating unit 93 that generates a supply pressure to be applied to the ink supply unit 91. The ink supply unit 91 includes a supply tank 91a that stores ink to be supplied to the ejection head H, and a supply pipe 91b that connects the supply tank 91a to the ejection head H and sends the ink supplied from the supply tank 91a to the ejection head H.

[0047] The ink recovery mechanism 9b includes an ink recovery unit 92 that recovers ink from the ejection head H, and a pressure generation unit 94 that generates pressure to be applied to the ink recovery unit 92. The ink recovery unit 92 includes a recovery tank 92a that stores the ink recovered from the ejection head H, and a recovery pipe 92b that connects the recovery tank 92a to the ejection head H and sends the ink recovered from the ejection head H to the recovery tank 92a. The supply tank 91 and the recovery tank 92 are each located above the ejection head H.

[0048] The ink return mechanism 9c includes a return pipe 901 that connects the recovery tank 92a and the supply tank 91a and sends ink from the recovery tank 92a to the supply tank 91a, a circulation pump 902 that is interposed midway along the return pipe 901, a filter 903 that is interposed midway along the return pipe 901 and is arranged between the circulation pump 902 and the supply tank 91, and a degasser 904 that is interposed midway along the return pipe 901 and is arranged between the filter 903 and the supply tank 91a. The circulation pump 902 sends ink from the recovery tank 92a to the supply tank 91a, the filter 903 removes foreign matter from the ink before it flows out of the circulation pump 902 and into the degasser 904, and the degasser 904 degasses the ink before it flows out of the filter 903 and into the supply tank 91a. The ink return mechanism 9c can send ink by a circulation pump 902 along a return path Ca1 that leads from the recovery tank 92a through a return pipe 901 to the supply tank 91a.

[0049] The ink supply mechanism 9a includes a supply-side pressure generating unit 93 (hereinafter referred to as the "pressure generating unit 93") that applies pressure P1 (negative pressure) to the supply tank 91a. The pressure generating unit 93 includes a pressure tank 931, an exhaust pump 932 that exhausts air from the pressure tank 931 to generate pressure P1 in the pressure tank 931, a flexible tube 933 having one end connected to the pressure tank 931, and a pressure transmission pipe 934 that has one end connected to the other end of the tube 933 in a communicable manner and is positioned so that the other end faces the atmosphere in the supply tank 91a and transmits the pressure generated in the pressure tank 931 to the supply tank 91a. The pressure P1 generated in the pressure tank 931 by the exhaust pump 932 is applied to the supply tank 91a via the tube 933 and the pressure transmission pipe 934.

[0050] In contrast, gas (air) accumulates above the ink surface in the supply tank 91a. That is, in the supply tank 91a, ink is stored below the gas-liquid interface, and gas exists above the gas-liquid interface. Therefore, the pressure generating unit 93 applies pressure P1 (negative pressure) to the gas-liquid interface in the supply tank 91a.

[0051] The ink supply mechanism 9a also has a solenoid valve Vg1 provided between the other end of the tube 933 of the pressure generating unit 93 and one end of the pressure transmission pipe 934. This solenoid valve Vg1 connects or disconnects the atmosphere between the pressure tank 931 and the supply tank 91a, thereby applying or blocking the pressure P1 generated in the pressure tank 931 to the supply tank 91a. That is, as shown in FIG. 4, when the solenoid valve Vg1 is open, the atmosphere between the pressure tank 931 and the supply tank 91a is connected, and the pressure P1 is applied to the supply tank 91a from the pressure tank 931 through the tube 933 and the pressure transmission pipe 934. On the other hand, when the solenoid valve Vg1 is closed, the atmosphere between the pressure tank 931 and the supply tank 91a is blocked, and application of the pressure P1 from the pressure tank 931 to the supply tank 91a is stopped. When energized, the solenoid valve Vg1 opens as shown in FIG. 4, connecting the atmosphere between the pressure tank 931 and the supply tank 91a. On the other hand, when not energized, the solenoid valve Vg1 closes to block the atmosphere between the pressure tank 931 and the supply tank 91a.

[0052] Furthermore, in the ink supply mechanism 9a, a check filter 935 is interposed in the pressure transmission pipe 934. This check filter 935 allows the passage of gas from the supply tank 91 to the pressure tank 931, while prohibiting the passage of ink from the supply tank 91a to the pressure tank 931. In this way, the check filter 935 prevents ink from flowing from the supply tank 91a into the tube 933.

[0053] The ink recovery mechanism 9b includes a recovery-side pressure generating unit 94 (hereinafter referred to as the "pressure generating unit 94") that applies pressure P2 (negative pressure) to the recovery tank 92. The pressure generating unit 94 includes a pressure tank 941, an exhaust pump 942 that exhausts air from the pressure tank 941 to generate pressure P2 in the pressure tank 941, a flexible tube 943 having one end connected to the pressure tank 941, and a pressure transmission pipe 944 having one end connected to the other end of the tube 943 in a communicable manner and arranged so that the other end faces the atmosphere in the recovery tank 92a, and transmitting the pressure generated in the pressure tank 941 to the recovery tank 92a. The pressure P2 generated in the pressure tank 941 by the exhaust pump 942 is applied to the recovery tank 92 via the tube 943 and the pressure transmission pipe 944.

[0054] In contrast, gas (air) accumulates above the ink surface in the recovery tank 92a. That is, in the recovery tank 92a, ink is stored below the gas-liquid interface, and gas exists above the gas-liquid interface. Therefore, the pressure generating unit 94 applies pressure P2 (negative pressure) to the gas-liquid interface in the recovery tank 92a.

[0055] The ink recovery mechanism 9b also has a solenoid valve Vg2 provided between the other end of the tube 943 of the pressure applying unit 94 and one end of the pressure transmission pipe 944. This solenoid valve Vg2 connects or disconnects the atmosphere between the pressure tank 941 and the recovery tank 92a, thereby applying or disconnecting the pressure P2 generated in the pressure tank 941 to the recovery tank 92a. That is, as shown in FIG. 4, when the solenoid valve Vg2 is open, the atmosphere between the pressure tank 941 and the recovery tank 92a is connected, and the pressure P2 is applied to the recovery tank 92a from the pressure tank 941 through the tube 943 and the pressure transmission pipe 944. On the other hand, when the solenoid valve Vg2 is closed, the atmosphere between the pressure tank 941 and the recovery tank 92a is disconnected, and the supply of pressure P2 from the pressure tank 941 to the recovery tank 92a is stopped. When energized, the solenoid valve Vg2 opens as shown in FIG. 4, connecting the atmosphere between the pressure tank 941 and the recovery tank 92a. On the other hand, when not energized, the solenoid valve Vg2 closes to block the atmosphere between the pressure tank 941 and the recovery tank 92a.

[0056] Furthermore, in the ink recovery mechanism 9b, a check filter 945 is interposed in the pressure transmission pipe 944. This check filter 945 allows the passage of gas from the recovery tank 92a to the pressure tank 941, while prohibiting the passage of ink from the recovery tank 92a to the pressure tank 941. In this way, the check filter 945 prevents ink from flowing from the recovery tank 92a into the tube 943.

[0057] Furthermore, a communication pipe 900 is provided between the recovery tank 92a and the supply tank 91a, allowing communication between the atmosphere in the recovery tank 92a and the atmosphere in the supply tank 91a. Furthermore, a solenoid valve Vg0 is interposed in this communication pipe 900 to establish / shut off communication between the atmosphere in the recovery tank 92a and the atmosphere in the supply tank 91a. That is, as shown in FIG. 4, when the solenoid valve Vg0 is closed, the atmosphere in the supply tank 91a is shut off from the atmosphere in the recovery tank 92a, and the pressure P1 in the supply tank 91a and the pressure P2 in the recovery tank 92a are independent of each other. On the other hand, when the solenoid valve Vg0 is open, the atmosphere in the supply tank 91a is connected to the atmosphere in the recovery tank 92a, and the pressures in the supply tank 91a and the recovery tank 92a are equal. When energized, the solenoid valve Vg0 closes as shown in FIG. 4, shutting off the atmosphere in the supply tank 91a from the atmosphere in the recovery tank 92a. On the other hand, when not energized, the solenoid valve Vg0 opens to communicate the atmosphere in the supply tank 91a with the atmosphere in the recovery tank 92a.

[0058] In the state shown in FIG. 4, the pressure P2 applied by the pressure generating unit 94 to the recovery tank 92a through the tube 943, the solenoid valve Vg2, and the pressure transmission pipe 944 is lower than the pressure P1 applied by the pressure generating unit 93 to the supply tank 91a through the tube 933 and the solenoid valve Vg1. Due to the difference between the pressures P2 and P1, ink flows from the supply tank 91a through the supply pipe 91b into the ink supply chamber Hc of the ejection head H, and then flows from the ink supply chamber Hc of the ejection head H through the recovery pipe 92b to the recovery tank 92a along a supply-recovery path Cb1. The ink sent to the recovery tank 92a along the supply-recovery path Cb1 is returned to the supply tank 91a by the circulation pump 902 along a return path Ca1. In this way, the ink circulates along a circulation path Cc1 (return path Ca1 + supply-recovery path Cb1) that flows from the supply tank 91a through the ejection head H to the recovery tank 92a and then back to the supply tank 91a.

[0059] As described above, the ink supply, recovery, replenishment, and circulation mechanism 9 includes an ink supply mechanism 9d and an ink return mechanism 9e. Next, the ink supply mechanism 9d and the ink return mechanism 9e will be explained with reference to Figure 5. Here, Figure 5, like Figure 4, is a diagram that schematically shows the configuration of the ejection head and the ink supply, recovery, replenishment, and circulation mechanism 9 that supplies, recovers, replenishes, and circulates ink to the ejection head. However, Figures 4 and 5 differ in the state of the solenoid valves in the ink supply mechanism 9d and the ink return mechanism 9e.

[0060] The ink supply mechanism 9d includes an ink supply unit 95 that supplies ink to the recovery tank 92a of the ink recovery mechanism 9b. The ink supply unit 95 includes a buffer tank 95a that stores the ink to be supplied to the recovery tank 92a. The buffer tank 95a can store a larger amount of ink than the supply tank 91a and the recovery tank 92a.

[0061] The ink supply unit 95 further includes a supply pipe 95b that connects the buffer tank 95a and the recovery tank 92a and sends ink from the buffer tank 95a to the recovery tank 92a, a supply pump 951 that is interposed midway along the supply pipe 95b and is disposed between the buffer tank 95a and the recovery tank 92a, and a supply solenoid valve Vl1 that is interposed midway along the supply pipe 95b and is disposed between the supply pump 951 and the recovery tank 92a. The supply pump 951 sends ink from the buffer tank 95a to the recovery tank 92a along the supply pipe 95b. By opening the supply solenoid valve Vl1 as shown in FIG. 4, the supply pump 951 allows the supply pump 951 to send ink from the buffer tank 95a to the recovery tank 92a via the supply pipe 95b. On the other hand, as shown in FIG. 5, the refill electromagnetic valve Vl1, when closed, blocks the refill pump 951 from sending ink from the buffer tank 95a to the recovery tank 92a via the refill pipe 95b.

[0062] The ink supply unit 95 also has a filter 952 that is interposed midway along the supply pipe 95b and is arranged between the supply pump 951 and the supply solenoid valve Vl1, and a degasser 953 that is interposed midway along the supply pipe 95b and is arranged between the filter 952 and the supply solenoid valve Vl1. The filter 952 removes foreign matter from the ink that flows out from the supply pump 951 and before it flows into the degasser 953, and the degasser 953 degasses the ink that flows out from the filter 952 and before it flows into the supply solenoid valve Vl1.

[0063] The ink return mechanism 9e has an ink return unit 96. The ink return unit 96 includes a return pipe 961 that connects a branch point J, which is provided midway along the supply pipe 95b, to the buffer tank 95a and sends ink from the branch point J to the buffer tank 95a. The branch point J is provided on the supply pipe 95b between the supply pump 951 and the supply solenoid valve Vl1, more specifically, between the degasser 953 and the supply solenoid valve Vl1. The ink return unit 96 also includes a return solenoid valve Vl2 that is interposed midway along the return pipe 961 and is disposed between the branch point J and the buffer tank 95a. When the return solenoid valve Vl2 is open as shown in FIG. 5, it allows ink to be sent from the branch point J to the buffer tank 95a via the return pipe 961. When the return solenoid valve Vl2 is closed as shown in FIG. 4, it blocks ink from being sent from the branch point J to the buffer tank 95a via the return pipe 961.

[0064] In this configuration, as shown in Fig. 4, when the refill solenoid valve Vl1 opens and the return solenoid valve Vl2 closes, and the refill pump 951 sends ink from the buffer tank 95a to the recovery tank 92a via the refill piping 95b, the ink is replenished to the recovery tank 92a along a refill path Cs from the buffer tank 95a to the recovery tank 92a via the refill solenoid valve Vl1. On the other hand, as shown in Fig. 5, when the refill solenoid valve Vl1 closes and the return solenoid valve Vl2 opens, and the refill pump 951 sends ink from the buffer tank 95a to the branch point J, the ink sent by the refill piping 95b along the liquid sending path Ca2 from the buffer tank 95a to the branch point J branches off from the refill piping 95b to the return piping 961 at the branch point J. Furthermore, the ink that branches off to the return piping 961 is sent by the return piping 961 along a return path Cb2 from the branch point J to the buffer tank 95a via the return solenoid valve Vl2, and returns to the buffer tank 95a. That is, after reaching the branch point J of the supply pipe 95b from the buffer tank 95a, the ink is circulated through a circulation path Cc2 (liquid supply path Ca2+return path Cb2) that returns from the branch point J to the buffer tank 95a via the return pipe 961.

[0065] The ink supply / recovery / replenishment / circulation mechanism 9 also has a supply level detection unit 97 that detects the ink level Lf (supply level) stored in the supply tank 91a, and a recovered level detection unit 98 that detects the ink level Lr (recovered level) stored in the recovery tank 92a. As will be described next, the operations of the supply solenoid valve Vl1, return solenoid valve Vl2, and circulation pump 902 are controlled based on the ink level Lf in the supply tank 91a detected by the supply level detection unit 97 and the ink level Lr in the recovery tank 92a detected by the recovered level detection unit 98.

[0066] FIG. 6 is a block diagram showing the electrical configuration of the printing device. As shown in FIG. 6, the printing device 3 includes a control unit 81 and a storage unit 82. The control unit 81 is configured with a CPU (Central Processing Unit) or an FPGA (Field-Programmable Gate Array). The control unit 81 includes a circulation pump control unit 811, a supply pump control unit 812, a supply solenoid valve control unit 813, a return solenoid valve control unit 814, a supply liquid level acquisition unit 815, a recovery liquid level acquisition unit 816, and a circulation mode determination unit 817. If the control unit 81 is a processor such as a CPU, the control unit 81 executes a predetermined program, which causes the control of each of these functional units 811 to 819 to be deployed in the control unit 81. If the control unit 81 is an FPGA, logic circuits that execute the functions of these functional units 811 to 819 are implemented in the FPGA.

[0067] The circulation pump control unit 811 controls the circulation pump 902. That is, the circulation pump 902 starts, increases or decreases its output, or stops based on the control of the circulation pump control unit 811. The supply pump control unit 812 controls the supply pump 951. That is, the supply pump 951 starts, increases or decreases its output, or stops its output, based on the control of the supply pump control unit 812. The supply solenoid valve control unit 813 controls the supply solenoid valve Vl1. That is, the supply solenoid valve Vl1 opens and closes based on the control of the supply solenoid valve control unit 813. The return solenoid valve control unit 814 controls the return solenoid valve Vl2. That is, the return solenoid valve Vl2 opens and closes based on the control of the return solenoid valve control unit 814.

[0068] The supply liquid level acquisition unit 815 acquires the ink level Lf in the supply tank 91a detected by the supply liquid level detection unit 97. Furthermore, the collected liquid level acquisition unit 816 acquires the ink level Lr in the collection tank 92a detected by the collected liquid level detection unit 98. The supply liquid level detection unit 97 and the collected liquid level detection unit 98 detect the ink levels Lf and Lr in four stages, as shown in FIG.

[0069] 7 is a diagram showing a schematic diagram of how the ink level is detected. Because the ink level detection mode is common to both the supply level detection unit 97 and the collected level detection unit 98, the following describes how the ink level Lf in the supply tank 91a is detected by the supply level detection unit 97. The supply level detection unit 97 has three float sensors that detect the presence or absence of ink in the supply tank 91a at different heights LL, LM, and LH. In other words, the supply level detection unit 97 detects the range of the ink level Lf in the supply tank 91a based on the presence or absence of ink at a first height LL, a second height LM higher than the first height LL, and a third height LH higher than the second height LM.

[0070] The specific relationship between the presence or absence of ink at the first height LL, the second height LM, and the third height LH and the range of the ink level Lf is as follows: That is, as shown in the "Low State" column of FIG. 7, when ink is not present at any of the first height LL, the second height LM, and the third height LH, the ink level Lf in the supply tank 91a is in a "Low" range below the first height LL. As shown in the "Mid State" column of FIG. 7, when ink is present at the first height LL but is not present at the second height LM and the third height LH, the ink level Lf in the supply tank 91a is in a "Mid" range above the first height LL but below the second height LM. As shown in the "High State" column of FIG. 7, when ink is present at the first height LL and the second height LM but is not present at the third height LH, the ink level Lf in the supply tank 91a is in a "High" range above the second height LM but below the third height LH. As shown in the "Ovf state" column in Figure 7, when ink is present at all of the first height LL, second height LM, and third height LH, the ink level Lf in the supply tank 91a is in the range Ovf above the third height LH.

[0071] The circulation mode determination unit 817 (Figure 6) controls the circulation mode in which ink is sent by the ink supply, recovery, replenishment, and circulation mechanism 9 based on the ink level Lf in the supply tank 91a obtained by the supply level acquisition unit 815 from the supply level detection unit 97 and the ink level Lr in the recovery tank 92a obtained by the recovery level acquisition unit 816 from the recovery level detection unit 98.

[0072] Fig. 8 is a flowchart showing an example of circulation mode control executed by the control unit, and Fig. 9 is a diagram showing, in table form, an example of circulation mode data referenced in the circulation mode control of Fig. 8. The circulation mode data Dm of Fig. 9 is stored in advance in the circulation mode data storage unit 821 of the storage unit 82, and the circulation mode determination unit 817 reads out the circulation mode data Dm from the circulation mode data storage unit 821 of the storage unit 82 and references it.

[0073] 8, in step S101 of the circulation mode control, the supply liquid level acquisition unit 815 acquires the ink level Lf in the supply tank 91a from the supply liquid level detection unit 97. In addition, in step S102, the collected liquid level acquisition unit 816 acquires the ink level Lr in the collection tank 92a from the collected liquid level detection unit 98. Note that the execution order of steps S101 and S102 is not limited to this example, and they may be reversed or performed simultaneously.

[0074] In step S103, the circulation mode determination unit 817 determines the circulation mode based on the combination of the ink level Lf in the supply tank 91a acquired by the supply level acquisition unit 815 and the ink level Lr in the recovery tank 92a acquired by the recovery level acquisition unit 816, and the circulation mode data Dm. As shown in Fig. 9, the circulation mode data Dm defines the operation of the circulation pump 902, the supply solenoid valve Vl1, and the return solenoid valve Vl2 in circulation modes 1 to 11.

[0075] 9, when the ink level Lf in the supply tank 91a is in the Low range and the ink level Lr in the recovery tank 92a is in the Low range, the circulation mode determination unit 817 determines to execute circulation mode 1. In this circulation mode 1, the circulation pump control unit 811 controls the circulation pump 902 to maintain its output, the resupply solenoid valve control unit 813 controls the resupply solenoid valve Vl1 to open, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to close. In other words, as shown in FIG. 4, ink is replenished from the buffer tank 95a to the recovery tank 92a along a resupply path Cs along which ink flows from the buffer tank 95a to the recovery tank 92a via the resupply solenoid valve Vl1.

[0076] As shown in FIG. 9, when the ink level Lf in the supply tank 91a is in the Low range and the ink level Lr in the recovery tank 92a is in the Mid range, the circulation mode determination unit 817 determines to execute circulation mode 2. In circulation mode 2, the circulation pump control unit 811 controls the circulation pump 902 to increase its output, the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to open, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to close. In other words, as shown in FIG. 4, ink is replenished from the buffer tank 95a to the recovery tank 92a along the above-mentioned supply path Cs. Furthermore, the increase in the output of the circulation pump 902 increases the amount of ink sent from the recovery tank 92a to the supply tank 91a.

[0077] As shown in FIG. 9, when the ink level Lf in the supply tank 91a is in the Low range and the ink level Lr in the recovery tank 92a is in the High range, the circulation mode determination unit 817 determines to execute circulation mode 3. In circulation mode 3, the circulation pump control unit 811 controls the circulation pump 902 to increase its output, the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to close it, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open it. That is, as shown in FIG. 5, ink is circulated along a circulation path Cc2 in which ink is transported from the buffer tank 95a to the branch point J via the supply pipe 95b, branches off to the return pipe 961, and then returns to the buffer tank 95a via the return pipe 961 via the return solenoid valve Vl2. Furthermore, the increased output of the circulation pump 902 increases the amount of ink transported from the recovery tank 92a to the supply tank 91a.

[0078] As shown in FIG. 9, when the ink level Lf in the supply tank 91a is in the Mid range and the ink level Lr in the recovery tank 92a is in the Low range, the circulation mode determination unit 817 determines to execute circulation mode 4. In circulation mode 4, the circulation pump control unit 811 controls the circulation pump 902 to reduce its output, the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to open, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to close. In other words, as shown in FIG. 4, ink is supplied from the buffer tank 95a to the recovery tank 92a along the supply path Cs. Furthermore, the reduction in the output of the circulation pump 902 reduces the amount of ink sent from the recovery tank 92a to the supply tank 91a.

[0079] 9, when the ink level Lf in the supply tank 91a is within the Mid range and the ink level Lr in the recovery tank 92a is within the Mid range, the circulation mode determination unit 817 determines to execute circulation mode 5. In circulation mode 5, the circulation pump control unit 811 controls the circulation pump 902 to maintain its output, the resupply solenoid valve control unit 813 controls the resupply solenoid valve Vl1 to close it, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open it. In other words, as shown in FIG. 5, ink is circulated along a circulation path Cc2 in which ink is transported from the buffer tank 95a to the branch point J via the resupply pipe 95b, branches into the return pipe 961, and then returns to the buffer tank 95a via the return solenoid valve Vl2.

[0080] As shown in FIG. 9, when the ink level Lf in the supply tank 91a is in the Mid range and the ink level Lr in the recovery tank 92a is in the High range, the circulation mode determination unit 817 determines to execute circulation mode 6. In circulation mode 6, the circulation pump control unit 811 controls the circulation pump 902 to increase its output, the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to close it, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open it. In other words, as shown in FIG. 5, ink is circulated along the circulation path Cc2. Furthermore, the increased output of the circulation pump 902 increases the amount of ink sent from the recovery tank 92a to the supply tank 91a.

[0081] As shown in FIG. 9, when the ink level Lf in the supply tank 91a is in the High range and the ink level Lr in the recovery tank 92a is in the Low range, the circulation mode determination unit 817 determines to execute circulation mode 7. In circulation mode 7, the circulation pump control unit 811 controls the circulation pump 902 to reduce its output, the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to close it, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open it. In other words, as shown in FIG. 5, ink is circulated along the circulation path Cc2. Furthermore, the reduction in the output of the circulation pump 902 reduces the amount of ink sent from the recovery tank 92a to the supply tank 91a.

[0082] As shown in FIG. 9, when the ink level Lf in the supply tank 91a is in the High range and the ink level Lr in the recovery tank 92a is in the Mid range, the circulation mode determination unit 817 determines to execute circulation mode 8. In circulation mode 8, the circulation pump control unit 811 controls the circulation pump 902 to reduce its output, the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to close it, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open it. In other words, as shown in FIG. 5, ink is circulated along the circulation path Cc2. Furthermore, the reduction in the output of the circulation pump 902 reduces the amount of ink sent from the recovery tank 92a to the supply tank 91a.

[0083] As shown in FIG. 9, when the ink level Lf in the supply tank 91a is in the High range and the ink level Lr in the recovery tank 92a is in the High range, the circulation mode determination unit 817 determines to execute circulation mode 9. In circulation mode 9, the circulation pump control unit 811 controls the circulation pump 902 to stop, the refill solenoid valve control unit 813 controls the refill solenoid valve Vl1 to close, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open. In other words, as shown in FIG. 5, ink is circulated along the circulation path Cc2. Furthermore, stopping the circulation pump 902 stops the transfer of ink from the recovery tank 92a to the supply tank 91a.

[0084] 9, when the ink level Lf in the supply tank 91a is in the range Ovf, the circulation mode determination unit 817 determines to execute circulation mode 10. In this circulation mode 10, the circulation pump control unit 811 controls the circulation pump 902 to stop it, the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to close it, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open it. In other words, the circulation of ink along the above-mentioned circulation path Cc1 stops, and the circulation of ink along the circulation path Cc2 starts.

[0085] 9, when the ink level Lr in the recovery tank 92a is in the range Ovf, the circulation mode determination unit 817 determines to execute circulation mode 11. In this circulation mode 10, the circulation pump control unit 811 controls the circulation pump 902 to stop it, the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to close it, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open it. In other words, the circulation of ink along the above-mentioned circulation path Cc1 stops, and the circulation of ink along the circulation path Cc2 starts.

[0086] Then, in step S104 of the flowchart in FIG. 8, the circulation mode determined in step S103 as described above is executed.

[0087] In the embodiment described above, ink is circulated through a circulation path Cc1 (first circulation path) in which ink is sent from the recovery tank 92a to the supply tank 91a via the return pipe 901 (first return pipe), then sent to the ejection head H via the supply pipe 91b, and further sent from the ejection head H to the recovery tank 92a via the recovery pipe 92b (first circulation process). This prevents the ink components stored in the supply tank 91a and the recovery tank 92a from settling. In addition, a refill pump 951 is attached to the refill pipe 95b connecting the buffer tank 95a and the recovery tank 92a. Therefore, when ink is consumed due to the ejection of ink from the ejection head H, the refill pump 951 can refill the recovery tank 92a with ink from the buffer tank 95a via the refill pipe 95b (refill process).

[0088] In particular, in this embodiment, a return pipe 961 (second return pipe) is provided between the supply pump 951 and the recovery tank 92a, connecting a branch point J provided in the supply pipe 95b to the buffer tank 95a. Furthermore, a supply solenoid valve Vl1 (first solenoid valve) is provided for the supply pipe 95b between the branch point J and the recovery tank 92a, and a return solenoid valve Vl2 (second solenoid valve) is provided for the return pipe 961 between the branch point J and the buffer tank 95a. When opened, this supply solenoid valve Vl1 allows the supply pump 951 to send ink from the buffer tank 95a to the recovery tank 92a via the supply pipe 95b, and when closed, it blocks the supply pump 951 from sending ink from the buffer tank 95a to the recovery tank 92a via the supply pipe 95b. Furthermore, when the return solenoid valve Vl2 is open, it allows ink to be sent from the branch point J to the buffer tank 95a via the return pipe 961, and when it is closed, it blocks ink from being sent from the branch point J to the buffer tank 95a via the return pipe 961. Therefore, when the resupply solenoid valve Vl1 is open and the return solenoid valve Vl2 is closed, ink sent by the resupply pump 951 is allowed to pass through the resupply solenoid valve Vl1, but this ink is prohibited from passing through the return solenoid valve Vl2. This allows the resupply pump 951 to resupply ink from the buffer tank 95a to the recovery tank 92a via the resupply solenoid valve Vl1, as described above. Furthermore, when the resupply solenoid valve Vl1 is closed and the return solenoid valve Vl2 is opened, ink sent by the resupply pump 951 is prohibited from passing through the resupply solenoid valve Vl1, but this ink is allowed to pass through the return solenoid valve Vl2. Therefore, the ink is circulated through a circulation path Cc2 (second circulation path) in which the ink is transported from the buffer tank 95a to the branch point J by the supply pipe 95b, and then returned from the branch point J to the buffer tank 95a by the pipe 961 (second circulation step). As a result, sedimentation of ink components in the buffer tank 95a that stores the ink to be replenished to the ejection head H is suppressed.

[0089] Furthermore, in this embodiment, both the supply of ink from the buffer tank 95a to the recovery tank 92a and the circulation of ink through the circulation path Cc2 are performed by the supply pump 951. Therefore, compared to a configuration in which two pumps are provided for each operation, there is also the effect of being able to reduce the number of pumps.

[0090] The control unit 81 also includes a supply level detection unit 97 that is provided for the supply tank 91a and detects the ink level Lf (supply level) in the supply tank 91a, and a recovered level detection unit 98 that is provided for the recovery tank 92a and detects the ink level Lr (recovered liquid level) in the recovery tank 92a. Meanwhile, the control unit 81 further includes a supply level acquisition unit 815 that acquires the ink level Lf detected by the supply level detection unit 97, and a recovered level acquisition unit 816 that acquires the ink level Lr detected by the recovered liquid level detection unit 98. The supply solenoid valve control unit 813 (first solenoid valve control unit) controls the opening and closing of the supply solenoid valve Vl1 based on the ink level Lf detected by the supply level detection unit 97 and the ink level Lr detected by the recovered liquid level detection unit 98, and the return solenoid valve control unit 814 (second solenoid valve control unit) controls the opening and closing of the return solenoid valve Vl2 based on the ink level Lf detected by the supply level detection unit 97 and the ink level Lr detected by the recovered liquid level detection unit 98. With this configuration, it is possible to replenish ink to the recovery tank 92a and circulate ink in the circulation path Cc2 according to the ink level Lf in the supply tank 91a and the ink level Lr in the recovery tank 92a.

[0091] In addition, the supply liquid level detection unit 97 detects at least whether the ink level Lf in the supply tank 91a is located in a range Low (first supply liquid level range) where it is less than a first height LL (first supply threshold), a range Mid (second supply liquid level range) where it is less than a second height LM (a higher second supply threshold) than the first height LL and is equal to or greater than the first height LL, or a range High (third supply liquid level range) where it is less than a third height LH (third supply threshold) which is higher than the second height LM and is equal to or greater than the second height LM. Furthermore, the recovered liquid level detection unit 98 detects whether the ink level Lr in the recovery tank 92a is located in a range Low (first recovered liquid level range) below a first height LL (first recovery threshold), a range Mid (second recovered liquid level range) below a second height LM (a higher second recovery threshold) that is lower than the first height LL and equal to or higher than the first height LL, or a range High (third recovered liquid level range) below a third height LH (third recovery threshold) that is higher than the second height LM and equal to or higher than the second height LM. With this configuration, ink can be replenished to the recovery tank 92a and ink can be circulated through the circulation path Cc2 depending on the results of detecting the ink level Lf in the supply tank 91a and the ink level Lr in the recovery tank 92a in at least three stages.

[0092] Furthermore, when the ink level Lf acquired by the supply level acquisition unit 815 is in the Mid range and the ink level Lr acquired by the recovery level acquisition unit 816 is in the Mid or High range (circulation modes 5 and 6), the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to close it, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open it, thereby circulating ink in the circulation path Cc2. With this configuration, ink is circulated in the circulation path Cc2 when the amount of ink in each of the supply tank 91a and the recovery tank 92a is high, making it possible to suppress sedimentation of ink in the buffer tank 95a.

[0093] At this time, when the ink level Lf acquired by the supply level acquisition unit 815 is in the Mid range and the ink level Lr acquired by the recovered level acquisition unit 816 is in the High range (circulation mode 6), the circulation pump control unit 811 controls the circulation pump 902 to increase the output with which the circulation pump 902 pumps ink. With this configuration, the amount of ink pumped from the recovery tank 92a to the supply tank 91a by the circulation pump 902 is increased, thereby preventing the recovery tank 92a from becoming excessively ink.

[0094] Furthermore, when the ink level Lf acquired by the supply level acquisition unit 815 is in the High range (circulation modes 7, 8, and 9), the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to close it, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open it, thereby circulating ink through the circulation path Cc2. With this configuration, ink is circulated through the circulation path Cc2 when the amount of ink in the supply tank 91a is high, making it possible to prevent ink from settling in the buffer tank 95a.

[0095] At this time, if the ink level Lf acquired by the supply level acquisition unit 815 is in the High range and the ink level Lr acquired by the recovered level detection unit 98 is in the Low or Mid range (circulation modes 7 and 8), the circulation pump control unit 811 controls the circulation pump 902 to reduce the output of the circulation pump 902 to pump ink. With this configuration, the amount of ink pumped from the recovery tank 92a to the supply tank 91a by the circulation pump 902 is reduced, preventing excess ink in the supply tank 91a.

[0096] Alternatively, when the ink level Lf acquired by the supply level acquisition unit 815 is in the High range and the ink level Lr acquired by the recovered level acquisition unit 816 is in the High range (circulation mode 9), the circulation pump control unit 811 controls the circulation pump 902 to stop the circulation pump 902. In this configuration, the circulation pump 902 stops sending ink from the recovery tank 92a to the supply tank 91a, thereby preventing an excess of ink from building up in the supply tank 91a.

[0097] Furthermore, when the ink level Lf acquired by the supply level acquisition unit 815 is in the Low range and the ink level Lr acquired by the recovered ink level acquisition unit 816 is in the Low or Mid range (circulation modes 1 and 2), the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to open, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to close, and ink is sent to the buffer tank 95a via the supply path Cs. In this configuration, ink is replenished from the buffer tank 95a to the supply tank 91a as the amount of ink in the supply tank 91a decreases. The ink replenished in this way to the recovery tank 92a is sent from the recovery tank 92a to the supply tank 91a by the circulation pump 902. As a result, the ink shortage in the supply tank 91a can be resolved.

[0098] At this time, if the ink level Lf acquired by the supply level acquisition unit 815 is in the range Low and the ink level Lr acquired by the recovered level acquisition unit 816 is in the range Mid (circulation mode 2), the circulation pump control unit 811 controls the circulation pump 902 to increase the output of the circulation pump 902 to pump ink. With this configuration, the amount of ink pumped from the recovery tank 92a to the supply tank 91a by the circulation pump 902 can be increased, thereby eliminating the shortage of ink in the supply tank 91a.

[0099] Furthermore, when the ink level Lf acquired by the supply level acquisition unit 815 is in the Mid range and the ink level Lr acquired by the recovered level acquisition unit 816 is in the Low range (circulation mode 4), the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to open, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to close, thereby circulating ink in the circulation path Cc1. With this configuration, when the amount of ink in the recovery tank 92a becomes low, ink is replenished from the buffer tank 95a to the recovery tank 92a, thereby eliminating the shortage of ink in the recovery tank 92a.

[0100] Furthermore, when the ink level Lf acquired by the supply level acquisition unit 815 is in the Mid range and the ink level Lr acquired by the recovered level acquisition unit 816 is in the Low range (circulation mode 4), the circulation pump control unit 811 controls the circulation pump 902 to reduce the output of the circulation pump 902 to pump ink. In this configuration, the amount of ink pumped from the recovery tank 92a to the supply tank 91a by the circulation pump 902 is reduced, preventing the amount of ink in the recovery tank 92a from becoming too low.

[0101] Furthermore, when the ink level Lf acquired by the supply level acquisition unit 815 is in the Low range and the ink level Lr acquired by the recovered level acquisition unit 816 is in the High range (circulation mode 3), the supply solenoid valve control unit 813 controls the supply solenoid valve Vl1 to close it, and the return solenoid valve control unit 814 controls the return solenoid valve Vl2 to open it. With this configuration, ink is circulated through the circulation path Cc2 when the amount of ink in the recovery tank 92a is high, making it possible to prevent ink from settling in the buffer tank 95a.

[0102] Furthermore, when the ink level Lf acquired by the supply level acquisition unit 815 is in the Low range and the ink level Lr acquired by the recovered level acquisition unit 816 is in the High range (circulation mode 3), the circulation pump control unit 811 controls the circulation pump 902 to increase the output of the circulation pump 902 to pump ink. In this configuration, the amount of ink pumped from the recovery tank 92a to the supply tank 91a by the circulation pump 902 is increased, thereby eliminating the shortage of ink in the supply tank 91a.

[0103] In the embodiment described above, the printing device 3 corresponds to an example of the "printing device" of the present invention, the control unit 81 corresponds to an example of the "control unit" of the present invention, the circulation pump control unit 811 corresponds to an example of the "circulation pump control unit" of the present invention, the supply pump control unit 812 corresponds to an example of the "supply pump control unit" of the present invention, the supply solenoid valve control unit 813 corresponds to an example of the "first solenoid valve control unit" of the present invention, the return solenoid valve control unit 814 corresponds to an example of the "second solenoid valve control unit" of the present invention, the supply liquid level acquisition unit 815 corresponds to an example of the "supply liquid level acquisition unit" of the present invention, the recovered liquid level acquisition unit 816 corresponds to an example of the "recovered liquid level acquisition unit" of the present invention, the return pipe 901 corresponds to an example of the "first return pipe" of the present invention, the circulation pump 902 corresponds to an example of the "circulation pump" of the present invention, the supply tank 91a corresponds to an example of the "supply tank" of the present invention, the supply pipe 91b corresponds to an example of the "supply pipe" of the present invention, and the recovery tank 92a corresponds to an example of the "recovered liquid level acquisition unit" of the present invention. the supply liquid level detection unit 97 corresponds to an example of the "supply liquid level detection unit" of the present invention; the recovered liquid level detection unit 98 corresponds to an example of the "recovery liquid level detection unit" of the present invention; the circulation path Cc1 corresponds to an example of the "first circulation path" of the present invention; the supply path Cs corresponds to an example of the "supply path" of the present invention; the circulation path Cc2 corresponds to an example of the "second circulation path" of the present invention; the discharge head H corresponds to an example of the "discharge head" of the present invention; the supply solenoid valve Vl1 corresponds to an example of the "first solenoid valve" of the present invention; and the return solenoid valve Vl2 corresponds to an example of the "second solenoid valve" of the present invention.

[0104] The present invention is not limited to the above-described embodiment, and various modifications other than those described above are possible without departing from the spirit of the present invention. For example, the threshold values ​​used by the supply liquid level detection unit 97 to detect the ink level Lf in the supply tank 91a are not limited to the above-described examples of the first height LL, second height LM, and third height LH, and may be higher or lower than these.

[0105] Furthermore, the variations in circulation modes that can be implemented in the ink supply, recovery, replenishment, and circulation mechanism 9 are not limited to the example shown in FIG.

[0106] Furthermore, when circulating ink in circulation path Cc2 (second circulation path), it is sufficient that the ink flows to an extent that sedimentation of ink components can be suppressed. Therefore, the supply pump control unit 812 may control the supply pump 951 so that the output of the supply pump 951 when ink sent by the supply pump 951 is circulated along circulation path Cc2 (for example, circulation modes 5 to 9) is lower than the output of the supply pump 951 when ink sent by the supply pump 951 is circulated along circulation path Cc2 (for example, circulation modes 1, 2, and 4). [Industrial Applicability]

[0107] The present invention is applicable to all printing techniques in which ink supplied to a discharge head from a buffer tank that stores ink is discharged from the discharge head. [Explanation of symbols]

[0108] 3...Printing device 81...Control unit 811...Circulation pump control unit 812...supply pump control unit 813... Replenishment solenoid valve control unit (first solenoid valve control unit) 814...Return solenoid valve control section (second solenoid valve control section) 815…Supply liquid level acquisition unit 816...Recovered liquid level acquisition unit 901...Return pipe (first return pipe) 902...Circulation pump 91a...Supply tank 91b...Supply piping 92a...Recovery tank 92b...Recovery piping 95a...Buffer tank 95b...supply piping 951...supply pump 961...Return pipe (second return pipe) 97…Supply liquid level detection part 98...Recovered liquid level detection unit Cc1...Circulation path (first circulation path) Cc2...Circulation route (second circulation route) Cs…Supply route H...Discharge head Vl1... Replenishment solenoid valve (first solenoid valve) Vl2...Return solenoid valve (second solenoid valve)

Claims

1. an ejection head having nozzles for ejecting ink; a supply tank that stores the ink to be supplied to the ejection head; a supply pipe that connects the supply tank and the ejection head to send the ink from the supply tank to the ejection head; a recovery tank that stores the ink recovered from the ejection head; a collection pipe that connects the collection tank and the ejection head to a flow path and sends the ink from the ejection head to the collection tank; a first return pipe that connects the recovery tank and the supply tank and sends the ink from the recovery tank to the supply tank; a circulation pump provided on the first return pipe between the recovery tank and the supply tank, the circulation pump sending the ink from the recovery tank to the supply tank; a buffer tank that stores the ink to be replenished to the recovery tank; a supply pipe that connects the buffer tank and the recovery tank and sends the ink from the buffer tank to the recovery tank; a refill pump provided on the refill pipe between the buffer tank and the recovery tank, the refill pump sending the ink from the buffer tank to the recovery tank; a first solenoid valve that is provided in the refill pipe between the refill pump and the recovery tank, that allows the refill pump to send the ink from the buffer tank to the recovery tank via the refill pipe when it is open, and that blocks the refill pump from sending the ink from the buffer tank to the recovery tank via the refill pipe when it is closed; a second return pipe that connects a branch point provided on the supply pipe between the first solenoid valve and the supply pump to the buffer tank, and that sends the ink from the branch point of the supply pipe to the buffer tank; a second solenoid valve that is provided in the second return pipe between the branch point and the buffer tank, that allows the ink to be sent from the branch point to the buffer tank via the second return pipe when opened, and that blocks the ink from being sent from the branch point to the buffer tank via the second return pipe when closed; a control unit including a circulation pump control unit for controlling the circulation pump, a supply pump control unit for controlling the supply pump, a first solenoid valve control unit for controlling the first solenoid valve, and a second solenoid valve control unit for controlling the second solenoid valve; Equipped with When the circulation pump control unit controls the circulation pump so that the circulation pump sends the ink from the recovery tank to the supply tank, the ink is sent from the recovery tank to the supply tank via the first return pipe, and then sent to the ejection head via the supply pipe, and the ink is circulated in a first circulation path that sends the ink from the ejection head to the recovery tank via the recovery pipe, When the first solenoid valve control unit controls the first solenoid valve so as to open, the second solenoid valve control unit controls the second solenoid valve so as to close, and the refill pump control unit controls the refill pump so as to send the ink from the buffer tank to the recovery tank, the ink is replenished to the recovery tank through a refill path in which the ink is sent from the buffer tank to the recovery tank via the refill piping through the first solenoid valve, When the first solenoid valve control unit controls the first solenoid valve so that the first solenoid valve is closed, the second solenoid valve control unit controls the second solenoid valve so that the second solenoid valve is opened, and the supply pump control unit controls the supply pump so that the supply pump sends the ink from the buffer tank toward the branch point, the ink is circulated in a second circulation path in which the ink is sent from the buffer tank to the branch point by the supply piping and then sent from the branch point to the buffer tank by the second return piping.

2. a supply liquid level detection unit provided for the supply tank, the supply liquid level being the liquid level of the ink in the supply tank; a recovered liquid level detection unit provided for the recovery tank and configured to detect a recovered liquid level, which is the liquid level of the ink in the recovery tank; Furthermore, the control unit further includes a supply liquid level acquisition unit that acquires the supply liquid level detected by the supply liquid level detection unit, and a recovered liquid level acquisition unit that acquires the recovered liquid level detected by the recovered liquid level detection unit, the first solenoid valve control unit controls opening and closing of the first solenoid valve based on the supply liquid level detected by the supply liquid level detection unit and the recovered liquid level detected by the recovered liquid level detection unit; The printing device according to claim 1, wherein the second solenoid valve control unit controls the opening and closing of the second solenoid valve based on the supply liquid level detected by the supply liquid level detection unit and the recovered liquid level detected by the recovered liquid level detection unit.

3. the supply level detection unit detects whether the ink level in the supply tank is located in a first supply level range below a first supply threshold, a second supply level range below a second supply threshold higher than the first supply threshold and equal to or greater than the first supply threshold, or a third supply level range below a third supply threshold higher than the second supply threshold and equal to or greater than the second supply threshold; 3. The printing device according to claim 2, wherein the recovered liquid level detection unit detects whether the ink level in the recovery tank is located in a first recovered liquid level range in which it is less than a first recovery threshold, a second recovered liquid level range in which it is less than a second recovery threshold that is higher than the first recovery threshold and is equal to or greater than the first recovery threshold, or a third recovered liquid level range in which it is less than a third recovery threshold that is higher than the second recovery threshold and is equal to or greater than the second recovery threshold.

4. 4. A printing device as described in claim 3, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is within the second supply liquid level range and the recovered liquid level acquired by the recovered liquid level acquisition unit is within the second recovered liquid level range or the third recovered liquid level range, the first solenoid valve control unit controls the first solenoid valve so that the first solenoid valve is closed, and the second solenoid valve control unit controls the second solenoid valve so that the second solenoid valve is open, thereby circulating the ink in the second circulation path.

5. A printing device as described in claim 4, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is within the second supply liquid level range and the recovery liquid level acquired by the recovery liquid level acquisition unit is within the third recovery liquid level range, the circulation pump control unit controls the circulation pump so that the output of the circulation pump to deliver the ink increases.

6. 6. A printing device according to claim 3, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is within the third supply liquid level range, the first solenoid valve control unit controls the first solenoid valve so that the first solenoid valve is closed, and the second solenoid valve control unit controls the second solenoid valve so that the second solenoid valve is opened, thereby circulating the ink in the second circulation path.

7. A printing device as described in claim 6, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is in the third supply liquid level range and the recovery liquid level acquired by the recovery liquid level acquisition unit is in the first recovery liquid level range or the second recovery liquid level range, the circulation pump control unit controls the circulation pump so that the output of the circulation pump to deliver the ink is reduced.

8. A printing device as described in claim 6 or 7, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is within the third supply liquid level range and the recovery liquid level acquired by the recovery liquid level acquisition unit is within the third recovery liquid level range, the circulation pump control unit controls the circulation pump so that the circulation pump stops.

9. 9. A printing device according to claim 3, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is within the first supply liquid level range and the recovered liquid level acquired by the recovered liquid level acquisition unit is within the first recovered liquid level range or the second recovered liquid level range, the first solenoid valve control unit controls the first solenoid valve so that the first solenoid valve opens, and the second solenoid valve control unit controls the second solenoid valve so that the second solenoid valve closes, and the ink is sent to the buffer tank via the supply path.

10. A printing device as described in claim 9, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is within the first supply liquid level range and the recovery liquid level acquired by the recovery liquid level acquisition unit is within the second recovery liquid level range, the circulation pump control unit controls the circulation pump so that the output of the circulation pump to deliver the ink increases.

11. A printing device described in any one of claims 3 to 10, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is within the second supply liquid level range and the recovered liquid level acquired by the recovered liquid level acquisition unit is within the first recovered liquid level range, the first solenoid valve control unit controls the first solenoid valve so that the first solenoid valve opens, and the second solenoid valve control unit controls the second solenoid valve so that the second solenoid valve closes, thereby circulating the ink in the first circulation path.

12. A printing device as described in claim 11, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is within the second supply liquid level range and the recovery liquid level acquired by the recovery liquid level acquisition unit is within the first recovery liquid level range, the circulation pump control unit controls the circulation pump so that the output of the circulation pump to deliver the ink is reduced.

13. A printing device described in any one of claims 3 to 12, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is within the first supply liquid level range and the recovery liquid level acquired by the recovery liquid level acquisition unit is within the third recovery liquid level range, the first solenoid valve control unit controls the first solenoid valve so that the first solenoid valve is closed, and the second solenoid valve control unit controls the second solenoid valve so that the second solenoid valve is open.

14. A printing device as described in claim 13, wherein when the supply liquid level acquired by the supply liquid level acquisition unit is within the first supply liquid level range and the recovery liquid level acquired by the recovery liquid level acquisition unit is within the third recovery liquid level range, the circulation pump control unit controls the circulation pump so that the output of the circulation pump to deliver the ink increases.

15. 15. A printing device according to claim 1, wherein the supply pump control unit controls the supply pump so that the output of the supply pump when the ink delivered by the supply pump is circulated along the second circulation path is lower than the output of the supply pump when the ink delivered by the supply pump is replenished from the buffer tank to the recovery tank along the supply path.

16. a supply pipe that connects the supply tank and the ejection head through a flow path and sends the ink from the supply tank to the ejection head; a recovery tank that stores the ink recovered from the ejection head; a recovery pipe that connects the recovery tank and the ejection head through a flow path and sends the ink from the ejection head to the recovery tank; a first return pipe that connects the recovery tank and the supply tank through a flow path and sends the ink from the recovery tank to the supply tank; and a circulation pump that is provided on the first return pipe between the recovery tank and the supply tank and sends the ink from the recovery tank to the supply tank, a first circulation step in which the circulation pump sends the ink from the recovery tank to the supply tank, so that the ink is sent from the recovery tank to the supply tank via the first return pipe, and then sent from the supply tank to the ejection head via the supply pipe, and further sent from the ejection head to the recovery tank via the recovery pipe; a replenishing step of connecting a buffer tank that stores the ink to be replenished to the recovery tank to a flow path of the recovery tank, and sending the ink from the buffer tank to the recovery tank through the replenishing pipe by a replenishing pump provided on a replenishing pipe that sends the ink from the buffer tank to the recovery tank; a second circulation step in which the ink is sent from the buffer tank to a branch point provided on the supply pipe between the supply pump and the recovery tank by the supply pump, so that the ink is sent from the buffer tank to the branch point by the supply pipe, and then sent from the branch point to the buffer tank by a second return pipe connecting the branch point and the buffer tank; Equipped with a first electromagnetic valve is provided in the supply pipe at a position between the branch point and the recovery tank; the first solenoid valve, when opened, allows the supply pump to send the ink from the buffer tank to the recovery tank via the supply pipe, and when closed, blocks the supply pump from sending the ink from the buffer tank to the recovery tank via the supply pipe; a second electromagnetic valve is provided for the second return pipe at a position between the branch point and the buffer tank, the second solenoid valve, when opened, allows the ink to be sent from the branch point to the buffer tank via the second return pipe, and when closed, blocks the ink from being sent from the branch point to the buffer tank via the second return pipe; In the replenishing step, the first electromagnetic valve is opened and the second electromagnetic valve is closed, and the replenishing pump sends the ink from the buffer tank to the recovery tank, whereby the ink is sent from the buffer tank to the recovery tank through the replenishing pipe and the first electromagnetic valve; In the second circulation process, the first solenoid valve closes and the second solenoid valve opens, and the supply pump sends the ink from the buffer tank toward the branch point, so that the ink is sent from the buffer tank to the branch point via the supply piping, and then sent from the branch point to the buffer tank via the second return piping.

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