Printing device and method for shutting down a printing device

Abstract

To make it possible to inhibit air intake and ink leakage from a nozzle when power supply from a power source stops.SOLUTION: A pressure difference resolution operation (step S103), in which a pressure generating unit 93 adjusts the pressure in a feed tank 91a to a pressure P3 (third pressure) and a pressure generating unit 94 adjusts the pressure in a collection tank a to the third pressure, is performed before power supply from a power source unit 8 stops. Thereby, the pressure difference is resolved by the time the power supply stops, so that the pressure in a discharge head H can be made relatively uniform.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a technique for dealing with a power outage in a printing device that has an ejection head that ejects ink from nozzles. [Background technology]

[0002] Patent documents 1 and 2 address the issue of ink leaking from nozzles during power outages in continuous inkjet printing devices. In particular, Patent document 1, based on the knowledge that residual pressure in the nozzles during power outages is the cause of ink leakage, provides a return path for draining ink from the nozzles, and prevents ink leakage by draining ink through the return path when power supply is stopped. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-191498 A [Patent Document 2] JP 2006-341555 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, the countermeasure action to prevent ink leakage is executed when the power supply is stopped. Therefore, it cannot be said that it is sufficient to prevent ink leakage caused by the power supply being stopped. Furthermore, problems that occur when the power supply is stopped are not limited to ink leakage from the nozzles, and air may also be sucked into the nozzles.

[0005] This invention has been developed in consideration of the above-mentioned problems, and aims to make it possible to prevent ink leakage and air intake from nozzles when power supply from a power source is stopped in a printing device equipped with an ejection head that ejects ink from nozzles. [Means for solving the problem]

[0006] A printing device according to the present invention is a printing device that prints by ejecting ink onto a printing medium, and includes an ejection head having nozzles that eject ink, a supply tank that stores ink to be supplied to the ejection head, a recovery tank that stores ink recovered from the ejection head, a supply pipe that connects the supply tank and the ejection head through a flow path and sends ink supplied from the supply tank to the ejection head, a recovery pipe that connects the ejection head and the recovery tank through a flow path and sends ink recovered from the ejection head to the recovery tank, a power supply unit that supplies power to each unit of the printing device, a first pressure generation unit that operates with power supplied from the power supply unit to generate pressure on the supply tank, and a recovery tank that operates with power supplied from the power supply unit to generate pressure on the supply tank. The inkjet recording apparatus is equipped with a second pressure generating unit that generates pressure applied to the recovery tank, and a control unit, and the control unit includes a pressure control unit that controls the first pressure generating unit and the second pressure generating unit, and the pressure control unit controls the first pressure generating unit and the second pressure generating unit so that the pressure on the recovery tank is lower than the pressure on the supply tank at least during printing, in which ink is ejected from the ejection head onto a printing medium to print, to transport ink from the supply tank via the ejection head to the recovery tank, and when the supply of power from the power supply unit is stopped, controls the first pressure generating unit and the second pressure generating unit so that a pressure reduction operation is performed to reduce the pressure difference between the pressure on the supply tank and the pressure on the recovery tank before the supply of power is stopped.

[0007] The method for shutting down a printing device according to the present invention involves sending ink from a supply tank to a recovery tank via an ejection head by setting the pressure on a supply tank that supplies ink to an ejection head having nozzles that eject ink to a first pressure by a first pressure generating unit operated by power supplied from a power supply unit, while setting the pressure on a recovery tank that recovers ink that has flowed into the ejection head to a second pressure lower than the first pressure by a second pressure generating unit operated by power supplied from a power supply unit, and the operations of setting the pressure of the supply tank to a third pressure by the first pressure generating unit and setting the pressure of the recovery tank to the third pressure by the second pressure generating unit are performed before the supply of power from the power supply unit is stopped.

[0008] In the present invention (printing device and printing device shutdown method) configured in this manner, a supply tank that stores ink to be supplied to a discharge head having nozzles that discharge ink, and a recovery tank that collects and stores ink that has flowed into the discharge head are provided. The pressure applied to the recovery tank by the second pressure generating unit, which operates with power supplied from the power supply unit, is controlled so that it is lower than the pressure applied to the supply tank by the first pressure generating unit, which operates with power supplied from the power supply unit. In this way, the ink supplied from the supply tank to the discharge head is collected in the recovery tank due to the pressure difference provided between the supply tank and the recovery tank. If the power supply is stopped in a situation where such a pressure difference occurs, the pressure inside the discharge head becomes unstable, which may cause ink to leak from the nozzles or air to be sucked in.

[0009] In response to this, the present invention executes an operation (pressure difference eliminating operation) to eliminate the difference between the pressure applied to the supply tank by the pressure generated by the first pressure generating unit and the pressure applied to the collection tank by the pressure generated by the second pressure generating unit before the power supply from the power supply unit is stopped. This makes it possible to eliminate the pressure difference and make the pressure inside the ejection head relatively uniform before the power supply is stopped. As a result, in a printing device equipped with an ejection head that ejects ink from nozzles, it is possible to prevent ink leakage and air intake from the nozzles when the power supply from the power supply is stopped.

[0010] The printing device may further include a buffer tank for storing ink, a first pipe connecting the buffer tank and the recovery tank, a supply pump provided in the first pipe for sending ink from the buffer tank to the recovery tank, and a supply solenoid valve provided in the first pipe at a position between the supply pump and the recovery tank, and the control unit further includes a valve operation control unit and a pump control unit, and the valve operation control unit controls the supply solenoid valve to open, thereby communicating the ink flow path between the buffer tank and the recovery tank, and the pump control unit drives and controls the supply pump to send ink from the buffer tank to the recovery tank, and when the supply of power from the power supply unit is stopped, the supply solenoid valve is controlled to close after the pressure difference eliminating operation is performed and before the supply of power from the power supply unit is stopped, thereby blocking the flow of ink from the buffer tank to the recovery tank. In this configuration, the supply solenoid valve is closed after the pressure difference eliminating operation is performed. Therefore, the ejection head, in which the pressure has become relatively uniform due to the pressure difference eliminating operation, is blocked from the supply pump side from the supply solenoid valve. Therefore, it is possible to prevent the pressure uniformity in the ejection head from being disturbed by the influence of the pressure on the supply pump side of the supply solenoid valve, and as a result, it is possible to more reliably prevent ink leakage and air intake from the nozzles.

[0011] The pump control unit may be configured in the printing device to control the supply pump so that the supply pump stops before the supply solenoid valve closes. In this configuration, it is possible to prevent problems such as air entering through the joint of the supply solenoid valve due to the operation of the supply pump acting on the closed supply solenoid valve.

[0012] The printing device may further include a second pipe connecting the buffer tank and the supply tank, a recovery pump provided in the second pipe for sending ink from the supply tank to the buffer tank, and a recovery solenoid valve provided in the second pipe at a position between the recovery pump and the supply tank, the valve operation control unit controls the recovery solenoid valve to open, thereby communicating the ink flow path between the buffer tank and the supply tank, and the pump control unit drives and controls the recovery pump to send ink from the supply tank to the buffer tank, and when the supply of power from the power supply unit is stopped, the valve operation control unit controls the recovery solenoid valve to close after the supply solenoid valve is closed and before the supply of power from the power supply unit is stopped, thereby blocking the flow of ink from the supply tank to the buffer tank. In this configuration, the recovery solenoid valve is closed after the pressure difference elimination operation is performed. Therefore, the ejection head, the pressure of which has become relatively uniform due to the pressure difference elimination operation, is blocked from the recovery pump side from the recovery solenoid valve. Therefore, it is possible to prevent the pressure on the recovery pump side from being affected, thereby preventing the uniformity of the pressure in the ejection head from being disturbed, and as a result, it is possible to more reliably prevent ink leakage and air intake from the nozzles.

[0013] The pump control unit may be configured to control the recovery pump so that the recovery pump stops before the recovery solenoid valve closes. In this configuration, problems such as air getting in through the joint of the recovery solenoid valve due to the operation of the recovery pump acting on the closed recovery solenoid valve can be suppressed.

[0014] The printing device may be configured such that the control unit further includes a power supply control unit, and the power supply control unit controls the power supply unit so that the power supply supply is stopped after the recovery solenoid valve is closed. This allows the pressure inside the ejection head to be equalized before the power supply by the power supply unit is stopped. This makes it possible to prevent ink leakage and air intake from the nozzles due to the power supply being stopped by the power supply unit. Effect of the Invention

[0015] As described above, according to the present invention, in a printing device equipped with an ejection head that ejects ink from nozzles, it is possible to prevent ink leakage and air intake from nozzles that occurs when power supply from a power source is stopped. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a front view showing a schematic diagram of an example of a printing system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a front view showing a schematic diagram of a printing device included in the printing system shown in FIG. [Diagram 3] FIG. 4 is a diagram illustrating a bottom surface of the ejection head. [Figure 4] FIG. 2 is a diagram illustrating a schematic configuration of a discharge head and an ink supply mechanism that supplies ink to the discharge head. [Diagram 5] FIG. 2 is a block diagram showing an electrical configuration of the printing apparatus. [Figure 6] 11 is a flowchart showing an example of a shutdown process. [Figure 7] FIG. 7 is a diagram showing operations executed in the shutdown process of FIG. 6; [Figure 8] 7 is a diagram showing a state of the ink supply mechanism at the time when the shutdown process in FIG. 6 is completed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] FIG. 1 is a front view schematically showing an example of a printing system including a printing apparatus according to the present invention. In FIG. 1 and the figures shown below, the horizontal direction X and the vertical direction Z are appropriately shown. As shown in FIG. 1, the printing system 1 includes a printing apparatus 3 and a drying apparatus 6 arranged in the horizontal direction X. This printing system 1 conveys a long strip-shaped printing medium M from a pay-off roll 11 to a take-up roll 12 in a roll-to-roll manner. Note that the material of the printing medium M is a film such as OPP (oriented polypropylene) or PET (polyethylene terephthalate). However, the material of the printing medium M is not limited to a film, and may be paper or the like. Such a printing medium M has flexibility. Also, hereinafter, of the two sides of the printing medium M, the surface on which an image is printed is appropriately referred to as the front surface M1, and the surface on the opposite side of the front surface M1 is referred to as the back surface M2.

[0018] The printing apparatus 3 prints an image on the front surface M1 of the printing medium M by discharging aqueous ink in an inkjet manner onto the front surface M1 of the printing medium M conveyed from the pay-off roll 11 to the take-up roll 12. The detailed configuration of such a printing apparatus 3 will be described later. The printing medium M on which the image has been printed in this way is conveyed in the horizontal direction X from the printing apparatus 3 toward the drying apparatus 6.

[0019] The drying apparatus 6 includes a drying furnace 60 and dries the printing medium M unloaded from the printing apparatus 3 as it is conveyed from the pay-off roll 11 to the take-up roll 12. Inside the drying furnace 60, there are provided two upper-stage air supply units 61u arranged in the horizontal direction X, two middle-stage air supply units 61m arranged in the horizontal direction X below these upper-stage air supply units 61u, and two lower-stage air supply units 61l arranged in the horizontal direction X below these middle-stage air supply units 61m.

[0020] The printing medium M discharged from the discharge port 312 of the printing device 3 passes through two upper-stage blowing units 61u in the horizontal direction X, and is then turned back toward the two middle-stage blowing units 61m by a pair of rollers 62. Next, the printing medium M passes through two middle-stage blowing units 61m in the horizontal direction X, and is then turned back toward the two lower-stage blowing units 61l by a pair of air turn bars 63. Furthermore, the printing medium M passes through two lower-stage blowing units 61l in the horizontal direction X, and is then discharged to the outside of the drying device 6.

[0021] The upper blowing unit 61u has two blowing chambers 64 arranged to sandwich the printing medium M passing in the horizontal direction X in the vertical direction Z. Each blowing chamber 64 has a plurality of nozzles 65 arranged in the horizontal direction X, and each nozzle 65 sprays hot air (gas at 60 degrees or higher) 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 blowing chambers 64 while passing between the two blowing chambers 64 arranged above and below. Similarly to the upper blowing unit 61u, each of the middle blowing unit 61m and the lower blowing unit 61l has two blowing chambers 64 that sandwich the printing medium M in the vertical direction Z.

[0022] Incidentally, the specific configuration of the upper blower unit 61u is not limited to this example. For example, instead of the lower blower chamber 64 of the upper and lower blower chambers 64 of the upper blower unit 61u, multiple rollers arranged in the horizontal direction X may be provided. In this configuration, hot air can be sprayed onto the front surface M1 of the printing medium M from the upper blower chamber 64 while the back surface M2 of the printing medium M is supported from below by the multiple rollers.

[0023] Fig. 2 is a front view showing a schematic diagram of a printing device provided in the printing system of Fig. 1. In Fig. 2, one side X1 and the other side X2 of the horizontal direction X are appropriately shown. Here, the 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 to the one side X1. The printing device 3 includes a housing 31, a color printing unit 32 arranged in 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 by a plurality of rollers arranged in the housing 31.

[0024] The color printing section 32 has a plurality of (six) head units 321 arranged in the traveling direction of the printing medium M (direction from the other side X2 to the one side X1) above the printing medium M transported by the transport section 4. The plurality of head units 321 have nozzles facing from above the surface M1 of the printing medium M passing below each of them, and eject color inks of different colors from the nozzles by an inkjet method. Here, color ink means 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 section 32 eject color inks from above onto the surface M1 of the printing medium M passing below each of them, thereby printing a color image on the surface M1 of the printing medium M.

[0025] Furthermore, the white printing section 33 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 by 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.

[0026] An inlet 311 opens in a side wall on the other side X2 of the housing 31, while an outlet 312 opens in a side wall on the one side X1 of the housing 31. The transport unit 4 transports the print medium M from the inlet 311 to the outlet 312, passing through the color printing unit 32 and the white printing unit 33.

[0027] The transport section 4 has an entrance section 41 provided below the color printing section 32, an upward transport section 42 provided on one side X1 of the color printing section 32, an upward transport section 43 provided above the color printing section 32, and a downward transport section 44 provided on the other side X2 of the color printing section 32. The entrance section 41 transports the printing medium M carried in from the entrance 311 to the one side X1 by rollers 411, the upward transport section 42 transports the printing medium M transported by the entrance section 41 to the upward side by rollers 421, the upward transport section 43 transports the printing medium M transported by the upward transport section 42 to the other side X2 by rollers 431, and the downward transport section 44 transports the printing medium M transported by the upward transport section 43 to the downward side by rollers 441.

[0028] 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 the downward 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 the 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.

[0029] 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 following the rotation of the printing medium M.

[0030] Furthermore, the transport unit 4 has a reversing transport unit 47 that turns upside down the printing medium M transported from the color transport unit 45 to the one side X1 twice. The reversing transport unit 47 has a plurality of rollers 471 to 477 including a drive roller 471, and turns upside down the printing medium M twice while these rollers 471 to 477 contact the back side M2 ​​of the printing medium M. That is, the reversing transport unit 47 transports the printing medium M transported from the color transport unit 45 downward by the rollers 471 and 472, and further changes the traveling direction of the printing medium M to the other side X2 by the roller 472 and transports it, thereby turning upside down the front surface M1 and the back surface M2 of the printing medium M. Next, the reversing transport unit 47 transports the printing medium M from the one side X1 to the other side X2 by the plurality of rollers 473, and then transports the printing medium M upward by the rollers 474 to 476. Furthermore, the inversion and transport section 47 changes the direction of travel of the printing medium M to one side X1 using rollers 476, thereby again inverting the front surface M1 and back surface M2 of the printing medium M, and transports the printing medium M from the other side X2 to the one side X1 using rollers 477.

[0031] The transport unit 4 also has a white transport unit 48 that supports the printing medium M facing the white printed 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 printed unit 33 ejects white ink while facing this front surface M1 from above.

[0032] The conveying unit 4 also has an unloading unit 49 provided above the upper conveying unit 43. The unloading unit 49 has a plurality of rollers 491 arranged from the other side X2 to one side X1 in the horizontal direction X. The unloading unit 49 conveys the print medium M conveyed by the white conveying unit 48 to the one side X1 by the plurality of rollers 491, thereby unloading the print medium M from the unloading opening 312 of the housing 31 to the drying device 9.

[0033] As described above, the color printing section 32 and the white printing section 33 of the printing device 3 have the head units 321 and 331. Next, the ejection heads H of the head units 321 and 331 and the ink supply, recovery and circulation mechanism 9 that supplies, recovers and circulates ink to the ejection heads H will be described. The ink supply, recovery and circulation mechanism 9 includes an ink supply mechanism 9a that supplies ink to the ejection heads 321 and 331, an ink recovery mechanism 9b that recovers ink from the ejection heads 321 and 331, and an ink return mechanism 9c that returns the recovered ink to the ink supply mechanism 9a. The head units 321 and 331 have a common basic configuration, and the basic configuration of the ink supply, recovery and circulation mechanism 9 is also common to the head units 321 and 331. Therefore, the configuration of the head unit 331 that ejects white ink will be described.

[0034] 3 is a diagram showing a schematic bottom surface of an ejection head included in a head unit, and FIG. 4 is a diagram showing a schematic configuration of an ejection head, an ink supply mechanism a that supplies ink to the ejection head, an ink recovery mechanism 9b that recovers ink from the ejection head, and an ink return mechanism 9c that returns the recovered ink to the ink supply mechanism 9a. In FIG. 3, in addition to a horizontal direction X and a vertical direction Z, a horizontal direction Y perpendicular to the horizontal direction X is shown. As shown in FIG. 3, in the head unit 331, a plurality of ejection heads H that eject ink of the same color (white ink) are arranged in a line in the horizontal direction Y, and each ejection head H has a rectangular shape when viewed from the bottom. Note that the arrangement of the plurality of ejection heads H is not limited to the example of FIG. 3, and the plurality of ejection heads H may be arranged in a staggered pattern.

[0035] As shown in FIG. 4, the ejection head H has a housing Ha, and a plurality of nozzles Hn are opened on the bottom surface of the housing Ha in a staggered arrangement in the horizontal direction Y. Inside the housing Ha, a plurality of cavities Hb each communicating with the plurality of nozzles Hn and an ink supply chamber Hc communicating with the plurality of cavities Hb are provided, and ink supplied from the ink supply chamber Hc is stored in the cavities Hb. Each cavity Hb is provided with a piezoelectric element D, and the piezoelectric element D is displaced in response to a drive signal (electrical signal), thereby applying a pressure fluctuation to the ink in the cavity Hb. This pressure fluctuation pushes the ink out of the cavity Hb, and the ink is 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.

[0036] The ink supply mechanism 9a includes an ink supply unit 91 that supplies ink to 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 sends the ink supplied from the supply tank 91a to the ejection head H. The ink recovery mechanism 9b includes an ink recovery unit 92 that recovers ink from the ejection head H, and a pressure generating unit 94 that generates a pressure to be applied to the ink recovery unit 92. The ink recovery unit 92 includes a recovery tank 92a that stores ink recovered from the ejection head H, and a recovery pipe 92b that 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 disposed above the ejection head H. The ink return mechanism 9c includes a return pipe 932 that connects the recovery tank 92a and the supply tank 91a, a circulation pump 90 that is interposed in the middle of the return pipe 932, and a degassing filter 901 that is interposed in the middle of the return pipe 932 and disposed between the circulation pump 90 and the supply tank 91. The circulation pump 90 sends ink from the recovery tank 92a to the supply tank 91a, and the degassing filter 901 removes gas from the ink before it flows out of the circulation pump 90 and into the supply tank 91a. The ink return mechanism 9c can send ink along a first path Ca from the recovery tank 92a to the supply tank 91a by the circulation pump 90.

[0037] Furthermore, the ink supply mechanism 9a includes a supply-side pressure generating unit 93 (hereinafter, appropriately 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 so as to be communicative and is disposed 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 91 via the tube 933 and the pressure transmission pipe 934.

[0038] 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.

[0039] The ink supply mechanism 9a also has a solenoid valve V1 provided between the other end of the tube 933 of the pressure generating unit 93 and one end of the pressure transmission pipe 934. The solenoid valve V1 connects / blocks the atmosphere between the pressure tank 931 and the supply tank 91a, thereby applying / 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 V1 is open, the atmosphere between the pressure tank 931 and the supply tank 91a is connected, and the pressure P1 is applied from the pressure tank 931 to the supply tank 91a through the tube 933 and the pressure transmission pipe 934. On the other hand, when the solenoid valve V1 is closed, the atmosphere between the pressure tank 931 and the supply tank 91a is blocked, and the application of the pressure P1 from the pressure tank 931 to the supply tank 91a is stopped.

[0040] Further, in the ink supply mechanism 9a, a check filter F1 is interposed in the pressure transmission pipe 934. This check filter F1 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. Thus, the inflow of ink from the supply tank 91a into the tube 933 is prevented by the check filter F1.

[0041] Furthermore, the ink recovery mechanism 9b includes a recovery-side pressure generation unit 94 (hereinafter, appropriately referred to as the "pressure generation unit 94") that applies a pressure P2 (negative pressure) to the recovery tank 92. This pressure generation unit 94 includes a pressure tank 941, an exhaust pump 942 that exhausts the pressure tank 941 to generate the 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 communicably connected to the other end of this tube 943 and the other end arranged to face the atmosphere in the recovery tank 92a, and transmitting the pressure generated in the pressure tank 941 to the recovery tank 92a. Then, 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.

[0042] On the other hand, in the recovery tank 92a, gas (air) is accumulated above the liquid level of the ink. 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 generation unit 94 applies the pressure P2 (negative pressure) to the gas-liquid interface in the recovery tank 92a.

[0043] The ink recovery mechanism 9b also has a solenoid valve V2 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 V2 connects / blocks the atmosphere between the pressure tank 941 and the recovery tank 92a, thereby applying / blocking 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 V2 is open, the atmosphere between the pressure tank 941 and the recovery tank 92a is connected, and the pressure P2 is applied from the pressure tank 941 to the recovery tank 92a through the tube 943 and the pressure transmission pipe 944. On the other hand, when the solenoid valve V2 is closed, the atmosphere between the pressure tank 941 and the recovery tank 92a is blocked, and the supply of the pressure P2 from the pressure tank 941 to the recovery tank 92a is stopped.

[0044] Furthermore, in the ink recovery mechanism 9b, a check filter F2 is interposed in the pressure transmission pipe 944. This check filter F2 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 F2 prevents ink from flowing from the recovery tank 92a into the tube 943.

[0045] Furthermore, a communication pipe 963 is provided between the recovery tank 92a and the supply tank 91a, which is connected so that the atmosphere of the recovery tank 92a and the atmosphere of the supply tank 91a can communicate with each other. Furthermore, a solenoid valve V0 is interposed in this communication pipe 963 for connecting / blocking the atmosphere of the recovery tank 92a and the atmosphere of the supply tank 91a. That is, as shown in FIG. 4, when the solenoid valve V0 is closed, the atmosphere of the supply tank 91a and the atmosphere of the recovery tank 92a are blocked, 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 V0 is open, the atmosphere of the supply tank 91a and the atmosphere of the recovery tank 92a are connected with each other, and the pressures inside the supply tank 91a and the recovery tank 92a are equal to each other.

[0046] 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 V2, 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 V1. Due to the difference between the pressures P2 and P1, ink flows along the second path Cb from the supply tank 91a to the recovery tank 92a through the ink supply chamber Hc of the ejection head H. In addition, the ink that has flowed into the recovery tank 92a along the second path Cb is returned to the supply tank 91a by the circulation pump 90 along the first path Ca. In this way, the ink circulates along a circulation path (second path Cb+first path Ca) that travels from the supply tank 91a to the ejection head H, reaches the recovery tank 92a, and then returns to the supply tank 91a.

[0047] The ink supply / recovery / circulation mechanism 9 includes a buffer tank 95, which can store a larger amount of ink than the supply tank 91a and the recovery tank 92a. The ink supply / recovery / circulation mechanism 9 also includes a pipe 951 that connects the buffer tank 95 to the supply tank 91a, and a pipe 952 that connects the buffer tank 95 to the recovery tank 92a. In other words, the buffer tank 95 communicates with the supply tank 91a via the pipe 951, and communicates with the recovery tank 92a via the pipe 952.

[0048] Furthermore, the ink supply / recovery / circulation mechanism 9 includes a recovery pump 961 attached to the pipe 951 between the buffer tank 95 and the supply tank 91a, and a supply pump 962 attached to the pipe 952 between the buffer tank 95 and the recovery tank 92a. Therefore, the recovery pump 961 recovers ink from the supply tank 91a to the buffer tank 95, and the supply pump 962 supplies ink from the buffer tank 95 to the recovery tank 92a.

[0049] The ink supply / recovery / circulation mechanism 9 also includes a solenoid valve V3 attached to a pipe 951 between the recovery pump 961 and the supply tank 91a, and a solenoid valve V4 attached to a pipe 952 between the supply pump 962 and the recovery tank 92a. Therefore, the buffer tank 95 and the supply tank 91a can be communicated with each other by opening the solenoid valve V3, while the buffer tank 95 and the supply tank 91a can be cut off from each other by closing the solenoid valve V3. The buffer tank 95 and the recovery tank 92a can be communicated with each other by opening the solenoid valve V4, while the buffer tank 95 and the recovery tank 92a can be cut off from each other by closing the solenoid valve V4.

[0050] In the ink supply / recovery / circulation mechanism 9 configured as described above, by operating the recovery pump 961 and the supply pump 962 with the solenoid valves V3 and V4 open, ink flows along the third path Cc that leads from the supply tank 91a to the recovery tank 92a via the buffer tank 95. Furthermore, the ink that flows into the recovery tank 92a along the third path Cc is returned to the supply tank 91a by the circulation pump 90 along the first path Ca. In this way, the ink circulates along a circulation path (third path Cc+first path Ca) that leads from the supply tank 91a to the recovery tank 92a via the buffer tank 95, and then returns to the supply tank 91a.

[0051] Furthermore, the ink supply / recovery / circulation mechanism 9 includes a liquid level sensor 971 provided in the supply tank 91a and a liquid level sensor 972 provided in the recovery tank 92a. The liquid level sensor 971 detects the liquid level of the ink stored in the supply tank 91a, and the liquid level sensor 972 detects the liquid level of the ink stored in the recovery tank 92a. The liquid level sensors 971, 972 can be configured with various level switches, such as float type, electrode type, or capacitance type. Furthermore, the ink supply / recovery / circulation mechanism 9 includes a pressure sensor S1 that detects the pressure in the supply tank 91a, and a pressure sensor S2 that detects the pressure in the recovery tank 92a.

[0052] FIG. 5 is a block diagram showing an electrical configuration of the printing device. As shown in FIG. 5, the printing device 3 includes a control unit 300 that controls the entire device. The control unit 300 is a processor that includes, for example, a CPU (Central Processing Unit) or the like. The control unit 300 also includes, as its functional units, a pressure control unit 300a, a valve operation control unit 300b, a pump control unit 300c, a power supply control unit 300d, and a power stop determination unit 300e. The pressure control unit 300a controls the operation of an exhaust pump 932 that constitutes the pressure generating unit 93, and controls the pressure generated in the pressure tank 931. The pressure control unit 300a also controls the operation of an exhaust pump 942 that constitutes the pressure generating unit 94, and controls the pressure generated in the pressure tank 941. The valve operation control unit 300b controls the opening and closing of each of the solenoid valves V0, V3, and V4, and controls the flow / cutoff of the ink in each pipe in which these solenoid valves are provided. The valve operation control unit 300b cuts off the opening and closing of the solenoid valves V1 and V2, and controls the application / cut-off of pressure from the pressure generating unit 93 to the supply tank 91a, and the application / cut-off of pressure from the pressure generating unit 94 to the recovery tank 92a. The pump control unit 300c controls the driving of the circulation pump 90, the recovery pump 961, and the supply pump 962, and controls the ink delivery operation. The power supply control unit 300d controls the timing at which the power supply from the power supply unit 8 is completely stopped. The power stop determination unit 300e determines whether an instruction to stop the power supply from the main power supply 81 described later has been issued, or whether a power outage has occurred and the power supply from the main power supply has been stopped, and also determines whether the power supply from the main power supply 81 has been switched to the power supply from the auxiliary power supply 83 described later, and further whether the power supply from the auxiliary power supply is stopped.

[0053] Furthermore, the printing device 3 includes a power supply unit 8 that supplies power to the control unit 300. The power supply unit 8 includes a main power supply 81 and a relay 82 provided between the main power supply 81 and the control unit 300, and the power generated by the main power supply 81 is supplied to the control unit 300 via the relay 82. Furthermore, power is supplied from the main power supply 81 to each unit of the printing device. Note that the relay 82 is not essential, and power may be directly supplied from the main power supply 81 to the control unit 300 without providing the relay 82. Furthermore, the power supply unit 8 includes an auxiliary power supply 83 connected to the main power supply 81. The auxiliary power supply 83 is, for example, an uninterruptible power supply device, and stores the power supplied from the main power supply 81. Then, when the power supply from the main power supply 81 is lost due to a power outage or the like, the auxiliary power supply 83 executes the power supply to the control unit 300. As a result, the supply of power to the control unit 300 is continued before and after the loss of the power supply from the main power supply 81, and power is also supplied to each unit of the printing device 3.

[0054] The printing device 3 also includes a UI (User Interface) 301 that accepts input operations from an operator. For example, the operator can execute an input operation on the UI 301 to instruct the main power source 81 to be turned off, and when the input operation is executed, the control unit 300 turns off the main power source 81 in conjunction with the execution of a shutdown process described below.

[0055] The control unit 300 supplies power from the power supply unit 8 to the solenoid valves V0, V1, and V2. The solenoid valve V0 closes during power supply to disconnect the supply tank 91a from the recovery tank 92a, and opens when the power supply is stopped to connect the supply tank 91a to the recovery tank 92a. The solenoid valve V1 opens during power supply to connect the atmosphere between the supply tank 91a and the pressure tank 931a, and closes when the power supply is stopped to disconnect the atmosphere between the supply tank 91a and the pressure tank 931. The solenoid valve V2 opens during power supply to connect the atmosphere between the recovery tank 92a and the pressure tank 941, and closes when the power supply is stopped to disconnect the atmosphere between the recovery tank 92a and the pressure tank 941.

[0056] Furthermore, the control unit 300 supplies power from the power supply unit 8 to the liquid level sensors 971, 972, the circulation pump 90, the pressure sensors S1, S2, the exhaust pump 932, the exhaust pump 942, the recovery pump 961, the solenoid valve V3, the supply pump 962 and the solenoid valve V4, and executes the following control through the pressure control unit 300a, the valve operation control unit 300b and the pump control unit 300c.

[0057] That is, the control unit 300 operates the circulation pump 90 based on the detection results of the liquid level sensor 971 and the liquid level sensor 972, thereby keeping the difference in liquid level between the supply tank 91a and the recovery tank 92a below a predetermined value. Specifically, when the liquid level in the recovery tank 92a indicated by the liquid level sensor 972 becomes higher than the liquid level in the supply tank 91a indicated by the liquid level sensor 971 by a predetermined value or more, the pump control unit 300c of the control unit 300 sends ink from the recovery tank 92 to the supply tank 91a by the circulation pump 90. That is, the circulation pump 90 does not send liquid while the difference in liquid level between the recovery tank 92a and the supply tank 91a is less than the predetermined value, and starts sending liquid when the difference in liquid level between the recovery tank 92a and the supply tank 91a becomes the predetermined value or more.

[0058] The pressure control unit 300a of the control unit 300 controls exhaust by the exhaust pump 932 based on the result of detecting the pressure in the supply tank 91a by the pressure sensor S1, thereby supplying pressure P1 into the supply tank 91a. Furthermore, the pressure control unit 300a of the control unit 300 controls exhaust by the exhaust pump 942 based on the result of detecting the pressure in the recovery tank 92a by the pressure sensor S2, thereby supplying pressure P2 into the recovery tank 92a.

[0059] Furthermore, the valve operation control section 300b and the pump control section 300c of the control section 300 operate the recovery pump 961 while opening the solenoid valve V3, thereby sending ink from the supply tank 91a to the buffer tank 95. Furthermore, the valve operation control section 300b and the pump control section 300c of the control section 300 operate the supply pump 962 while opening the solenoid valve V4, thereby sending ink from the buffer tank 95 to the recovery tank 92a.

[0060] In such a printing device 3, during a standby period in which a printing operation of ejecting ink from the nozzles Hn of the ejection head H to print an image on the printing medium M is not performed, the control unit 300 controls each control object via the pressure control unit 300a, the valve operation control unit 300b, and the pump control unit 300c, and circulates the ink through a circulation path consisting of the first path Ca and the second path Cb, and a circulation path consisting of the first path Ca and the third path Cc. If the power supply is lost while the ink is circulating in this manner, unpredictable ink flow and pressure may occur inside the ejection head H, causing problems such as ink leakage from the nozzles Hn and air getting mixed in.

[0061] Therefore, when the power supply is lost, the control unit 300 executes the shutdown process shown in Fig. 6 and Fig. 7 by controlling the pressure control unit 300a, the valve operation control unit 300b, and the pump control unit 300c. Fig. 6 is a flow chart showing an example of the shutdown process, and Fig. 7 is a diagram showing the operation executed in the shutdown process of Fig. 6. As shown in the "initial state" of Fig. 7, at the time of starting the shutdown process of Fig. 6, pressure P1 is applied to the supply tank 91a and pressure P2 is applied to the recovery tank 92a. The supply pump 962 is in an ON state capable of delivering liquid, and the solenoid valve V4 is open. The recovery pump 961 is in an ON state capable of delivering liquid, and the solenoid valve V3 is open. Furthermore, the main power supply 81 of the power supply unit 8 is executing the supply of power.

[0062] 7, the circulation pump 90 is in an ON state where liquid can be delivered. However, since the difference in liquid level between the supply tank 91a and the recovery tank 92a falls within a predetermined range through the execution of steps S103 to S107 described below, the circulation pump 90 hardly delivers liquid.

[0063] In step S101, the power stop determination unit 300e of the control unit 300 determines whether an input operation to instruct turning off the main power supply 81 has been performed on the UI 301. If an instruction to turn off the main power supply has been received (if "YES" in step S101), the process proceeds to step S103. If an instruction to turn off the main power supply has not been received (if "NO" in step S101), the process proceeds to step S102. In step S102, the power stop determination unit 300e of the control unit 300 determines whether the power supply from the main power supply 81 has been lost due to, for example, a power outage and the power supply from the auxiliary power supply 83 has started. If the power supply from the main power supply 81 has been lost (if "YES" in step S102), the process proceeds to step S103. If the power supply from the main power supply 81 is being performed (if "NO" in step S102), the process returns to step S101.

[0064] When the power stop determination unit 300e of the control unit 300 determines that an instruction to turn off the power has been issued (if "YES" in step S101), the pressure control unit 300a, valve operation control unit 300b, and pump control unit 300c of the control unit 300 execute steps S103 to S109 using the power supplied by the main power source 81. On the other hand, when the power stop determination unit 300e determines that the power supply from the main power source 81 has been lost (if "YES" in step S102), the pressure control unit 300a, valve operation control unit 300b, and pump control unit 300c of the control unit 300 execute steps S103 to S109 using the power supplied by the auxiliary power source 83.

[0065] In step S103, the pressure control section 300a of the control section 300 controls exhaust by the exhaust pump 932 based on the result of detecting the pressure in the supply tank 91a by the pressure sensor S1, thereby supplying pressure P3 (negative pressure) into the supply tank 91a. Furthermore, the pressure control section 300a of the control section 300 controls exhaust by the exhaust pump 942 based on the result of detecting the pressure in the recovery tank 92a by the pressure sensor S2, thereby supplying pressure P3 into the recovery tank 92a. In other words, the pressures of both the supply tank 91a and the recovery tank 92a are adjusted to the same pressure P3. This pressure P3 is a negative pressure that prevents ink leakage from the nozzle Hn by supporting the ink against the head pressure from the gas-liquid interface of the supply tank 91a and the recovery tank 92a to the nozzle Hn. This almost completely eliminates the pressure difference between the supply tank 91a and the recovery tank 92a.

[0066] When the adjustment to pressure P3 is thus completed, in step S104, the pump control section 300c of the control section 300 stops the supply pump 962 (turns off the supply pump 962). This prevents the supply pump 962 from sending any more liquid. Then, in step S105, the valve operation control section 300b of the control section 300 controls the solenoid valve V4 to close. This blocks the flow of ink between the recovery tank 92a and the supply pump 962 and the buffer tank 95, which are located on the opposite side of the solenoid valve V4 from the recovery tank 92a.

[0067] Furthermore, in step S106, the pump control section 300c of the control section 300 stops the recovery pump 961 (turns off the recovery pump 961). This prevents the recovery pump 961 from pumping liquid thereafter. Next, in step S107, the valve operation control section 300b of the control section 300 controls the solenoid valve V3 to close. This blocks the flow of ink between the supply tank 91a and the recovery pump 961 and the buffer tank 95, which are located on the opposite side of the solenoid valve V3 from the supply tank 91a. Note that the time from when the solenoid valve V4 is closed to when the solenoid valve V3 is closed should be, for example, within 5 seconds.

[0068] In this way, the supply tank 91a and the recovery tank 92a, which are adjusted to the same pressure P3, are isolated from the effects of the recovery pump 961, the supply pump 962, and the buffer tank 95, and the power supply control unit 300d of the control unit 300 waits for a predetermined time (e.g., 20 seconds or more) to pass. Then, when the predetermined time has passed, the power supply control unit 300d of the control unit 300 stops the power supply from the power supply unit 8 (main power supply 81 or auxiliary power supply 83) (i.e., turns off the power supply unit 8). In this way, the shutdown process is completed.

[0069] Fig. 8 is a diagram showing the state of the ink supply, recovery, and circulation mechanism 9 at the time when the shutdown process of Fig. 6 is completed. As shown in the figure, when the power supply unit 8 is turned off, the power supply to the solenoid valves V0, V1, and V2 is lost. As a result, the solenoid valve V0 opens to connect the supply tank 91a and the recovery tank 92a, the solenoid valve V1 closes to cut off the atmosphere between the supply tank 91a and the pressure tank 931, and the solenoid valve V2 closes to cut off the atmosphere between the recovery tank 92a and the pressure tank 941. In this way, after the shutdown process of Fig. 6 is executed, the pressure in the supply tank 91a and the pressure in the recovery tank 92a become the same pressure P3.

[0070] In the embodiment described above, a supply tank 91a and a recovery tank 92a are provided, each of which communicates with an ejection head H having a nozzle Hn for ejecting ink. Then, a pressure generating unit 93 (first pressure generating unit) operated by power supplied from a power supply unit 8 adjusts the pressure applied to the supply tank 91a to a pressure P1 (first pressure), and a pressure generating unit 94 (second pressure generating unit) operated by power supplied from the power supply unit 8 adjusts the pressure applied to the recovery tank 92a to a pressure P2 (second pressure) lower than the pressure P1. In this way, the ink supplied from the supply tank 91a to the ejection head H is recovered in the recovery tank 92 by the pressure difference provided between the supply tank 91a and the recovery tank 92a. If the power supply from the power supply unit 8 is stopped in a situation where such a pressure difference occurs, the pressure inside the ejection head H becomes unstable, and ink leakage from the nozzle Hn or air suction may occur.

[0071] In contrast, in this embodiment, the pressure generating unit 93 adjusts the pressure in the supply tank 91a to pressure P3 (third pressure), and the pressure generating unit 94 adjusts the pressure in the recovery tank 92a to pressure P3, a pressure difference eliminating operation (step S103) is executed before the power supply from the power supply unit 8 is stopped. This makes it possible to eliminate the pressure difference and make the pressure inside the ejection head H relatively uniform before the power supply is stopped. As a result, in a printing device 3 equipped with an ejection head H that ejects ink from the nozzles Hn, it is possible to prevent ink leakage and air intake from the nozzles Hn due to the stop of the power supply from the power supply unit 8.

[0072] Also provided are a buffer tank 95 for storing ink, a supply pump 962 for sending ink from the buffer tank 95 to the recovery tank 92a, and a solenoid valve V4 (supply solenoid valve) provided between the supply pump 962 and the recovery tank 92a. Thus, when the solenoid valve V4 is opened, the supply pump 962 communicates with the recovery tank 92a, and the ink stored in the buffer tank 95 is sent to the recovery tank 92a by the supply pump 962 via the solenoid valve V4, and when the solenoid valve V4 is closed, the flow of ink between the supply pump 962 and the recovery tank 92a is blocked. Then, the valve operation control unit 300b of the control unit 300 controls the solenoid valve V4 to close after the pressure difference eliminating operation in step S103 is performed and before step S109 in which the supply of power by the power supply unit 8 is stopped (step S105). In this configuration, the solenoid valve V4 is closed after the pressure difference eliminating operation in step S103 is performed, and thus the ejection head H, in which the pressure has become relatively uniform due to the pressure difference eliminating operation, is blocked from the supply pump 962 side of the solenoid valve V4. This makes it possible to prevent the pressure on the supply pump 962 side of the solenoid valve V4 from affecting the uniformity of the pressure in the ejection head H. As a result, it is possible to more reliably prevent ink leakage and air intake from the nozzles Hn.

[0073] Further, the pump control unit 300c of the control unit 300 stops the supply pump 962 before the solenoid valve V4 closes (step S104). With such a configuration, since the operation of the supply pump 962 acts on the closed solenoid valve V4, it is possible to suppress the occurrence of problems such as air mixing from the joint of the solenoid valve V4.

[0074] Also, a recovery pump 961 for sending ink from the supply tank 91a to the buffer tank 95 and a solenoid valve V3 (recovery solenoid valve) provided between the recovery pump 961 and the supply tank 91a are provided. Therefore, when the solenoid valve V3 opens, the recovery pump 961 communicates with the supply tank 91a, and the ink stored in the supply tank 91 is sent to the buffer tank 95 by the recovery pump 961 via the solenoid valve V3. When the solenoid valve V3 closes, the recovery pump 961 and the supply tank 91a are cut off. Then, the valve operation control unit 300b of the control unit 300 controls the solenoid valve V3 to close after closing the solenoid valve V4 in step S105 and before step 109 where the power supply by the power supply unit 8 stops. With such a configuration, since the solenoid valve V3 is closed after the execution of the pressure difference elimination operation in step S103, the discharge head H with relatively uniform pressure due to the pressure difference elimination operation and the side of the recovery pump 961 from the solenoid valve V3 are cut off. Therefore, it is possible to suppress the disturbance of the pressure uniformity of the discharge head H due to the influence of the pressure on the side of the recovery pump 961 from the solenoid valve V3. As a result, it is possible to more reliably suppress the occurrence of ink leakage and air suction from the nozzle Hn.

[0075] Also, the pump control unit 300c of the control unit 300 stops the recovery pump 961 before closing the solenoid valve V3 (step S106). With such a configuration, since the operation of the recovery pump 961 acts on the closed solenoid valve V3, it is possible to suppress the occurrence of problems such as air mixing from the joint of the solenoid valve V3.

[0076] Furthermore, the power supply control unit 300d of the control unit 300 closes the solenoid valve V3 and then stops the power supply from the power supply unit 8 (step S109). This makes the pressure inside the ejection head H uniform, and then stops the power supply from the power supply unit 8. This makes it possible to prevent ink leakage and air intake from the nozzles Hn due to the stop of the power supply from the power supply unit 8.

[0077] In the embodiment described above, the printing device 3 corresponds to an example of the “printing device” of the present invention, the control unit 300 corresponds to an example of the “control unit” of the present invention, the pressure control unit 300a corresponds to an example of the “pressure control unit” of the present invention, the valve operation control unit 300b corresponds to an example of the “valve operation control unit” of the present invention, the pump control unit 300c corresponds to an example of the “pump control unit” of the present invention, the power supply control unit 300e corresponds to an example of the “power supply control unit” of the present invention, the power supply unit 8 corresponds to an example of the “power supply unit” of the present invention, the supply tank 91a corresponds to an example of the “supply tank” of the present invention, the recovery tank 92a corresponds to an example of the “recovery tank” of the present invention, the pressure generation unit 93 corresponds to an example of the “first pressure generation unit” of the present invention, and the pressure generation unit 94 corresponds to an example of the “second pressure generation unit” of the present invention. the recovery pump 961 corresponds to an example of a "recovery pump" of the present invention, the supply pump 962 corresponds to an example of a "supply pump" of the present invention, the discharge head H corresponds to an example of an "discharge head" of the present invention, the nozzle Hn corresponds to an example of a "nozzle" of the present invention, pressure P1 corresponds to an example of a "first pressure" of the present invention, pressure P2 corresponds to an example of a "second pressure" of the present invention, pressure P3 corresponds to an example of a "third pressure" of the present invention, solenoid valve V3 corresponds to an example of a "recovery solenoid valve" of the present invention, solenoid valve V4 corresponds to an example of a "supply solenoid valve" of the present invention, and step S103 corresponds to an example of a "pressure difference elimination operation" of the present invention.

[0078] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. Therefore, the configuration and operation of the ink supply mechanism 9 can be appropriately modified, and it is not essential to provide the solenoid valves V0, V1, and V2, for example.

[0079] Furthermore, the specific configuration of the auxiliary power supply 83 is not limited to an uninterruptible power supply, but may be, for example, a supercapacitor.

[0080] Moreover, the pressure P2 is not limited to a negative pressure, but may be, for example, a positive pressure.

[0081] In addition, steps S104 to S108 are not essential and may be omitted as appropriate. In other words, by performing the pressure difference eliminating operation in step S103, it is possible to achieve the effect of suppressing ink leakage and air intake from the nozzles Hn. [Industrial Applicability]

[0082] The present invention can be applied to all techniques for printing by ejecting ink from nozzles of an ejection head. [Explanation of symbols]

[0083] 3...Printing device 300...Control unit 300a...pressure control section 300b... Valve operation control section 300c…Pump control section 300e…Power supply control unit 8...Power supply section 91a…Supply tank 92a…Recovery tank 91b…Supply piping 92b…Recovery pipe 93...pressure generating unit (first pressure generating unit) 94...pressure generating unit (second pressure generating unit) 95…Buffer tank 961…Recovery pump 962…Supply pump H…Discharge head Hn…Nozzle P1…Pressure (first pressure) P2…Pressure (second pressure) P3…Pressure (third pressure) V3: Solenoid valve (recovery solenoid valve) V4…Solenoid valve (supply solenoid valve) S103...Step (pressure difference elimination operation)

Claims

1. A printing device that prints by ejecting ink onto a print medium, an ejection head having a nozzle for ejecting the ink; a supply tank that stores ink to be supplied to the ejection head; a recovery tank that stores ink recovered from the ejection head; a supply pipe that connects the supply tank and the ejection head through a flow path and delivers ink supplied from the supply tank to the ejection head; a recovery pipe that connects the ejection head and the recovery tank through a flow path and delivers ink recovered from the ejection head to the recovery tank; a power supply unit that supplies power to each unit of the printing device; a first pressure generating unit that generates pressure applied to the supply tank by operating using power supplied from the power supply unit; a second pressure generating unit that generates pressure applied to the collection tank by operating using power supplied from the power supply unit; A buffer tank for storing ink; a first pipe that connects the buffer tank and the recovery tank; a supply pump provided in the first pipe for sending ink from the buffer tank to the recovery tank; a supply solenoid valve provided on the first pipe at a position between the supply pump and the recovery tank; A control unit; Equipped with The control unit is A pressure control unit that controls the first pressure generating unit and the second pressure generating unit; A valve operation control unit; A pump control unit; Including, The pressure control unit is at least during printing, in which ink is ejected from the ejection head onto a print medium, the first pressure generating unit and the second pressure generating unit are controlled so that the pressure applied to the recovery tank is lower than the pressure applied to the supply tank, and ink is sent from the supply tank to the recovery tank via the ejection head; when the supply of power from the power supply unit is stopped, the first pressure generating unit and the second pressure generating unit are controlled so as to perform a pressure difference eliminating operation for eliminating a pressure difference between a pressure applied to the supply tank and a pressure applied to the recovery tank before the supply of power is stopped; The valve operation control unit is By controlling the supply solenoid valve to open, an ink flow path between the buffer tank and the recovery tank is opened, and further the pump control unit drives and controls the supply pump to send ink from the buffer tank to the recovery tank; When the supply of power from the power supply unit is stopped, A printing device that, after performing the pressure difference elimination operation and before the power supply from the power supply unit is stopped, controls the supply solenoid valve to close, thereby cutting off the flow of ink from the buffer tank to the recovery tank.

2. The printing apparatus according to claim 1 , wherein the pump control unit controls the supply pump so that the supply pump stops before the supply electromagnetic valve closes.

3. a second pipe that connects the buffer tank and the supply tank; a recovery pump provided in the second pipe for transferring ink from the supply tank to the buffer tank; a recovery solenoid valve provided on the second pipe at a position between the recovery pump and the supply tank; Further equipped with The valve operation control unit is By controlling the recovery solenoid valve to open, an ink flow path between the buffer tank and the supply tank is opened, and further the pump control unit drives and controls the recovery pump to send ink from the supply tank to the buffer tank; 3. The printing device according to claim 1, wherein when the supply of power from the power supply unit is stopped, the valve operation control unit controls the recovery solenoid valve to close after the supply solenoid valve is closed and before the supply of power from the power supply unit is stopped, thereby cutting off the flow of ink from the supply tank to the buffer tank.

4. The printing apparatus according to claim 3 , wherein the pump control unit controls the recovery pump so that the recovery pump stops before the recovery solenoid valve closes.

5. The control unit is Further comprising a power supply controller; The power supply control unit is 5. The printing apparatus according to claim 3, wherein the power supply unit is controlled so that the supply of the electric power by the power supply unit is stopped after the recovery solenoid valve is closed.

6. A method for shutting down a printing device, comprising: setting pressure on a supply tank that stores ink to be supplied to an ejection head having nozzles that eject ink to a first pressure by a first pressure generating unit that operates by power supplied from a power source unit; and setting pressure on a recovery tank that recovers ink that has flowed into the ejection head to a second pressure lower than the first pressure by a second pressure generating unit that operates by power supplied from the power source unit, thereby sending ink from the supply tank to the recovery tank via the ejection head, a pressure control unit of a control unit having a pressure control unit that controls the first pressure generating unit and the second pressure generating unit performs a pressure difference eliminating operation to eliminate a pressure difference between the pressure applied to the supply tank and the pressure applied to the recovery tank by setting the pressure of the supply tank to a third pressure by the first pressure generating unit and setting the pressure of the recovery tank to the third pressure by the second pressure generating unit before the supply of power from the power supply unit is stopped; The printing device includes: A buffer tank for storing ink; a first pipe that connects the buffer tank and the recovery tank; a supply pump provided in the first pipe for sending ink from the buffer tank to the recovery tank; a supply solenoid valve provided on the first pipe at a position between the supply pump and the recovery tank; Equipped with The control unit is A valve operation control unit; A pump control unit; Further comprising: The valve operation control unit is By controlling the supply solenoid valve to open, an ink flow path between the buffer tank and the recovery tank is opened, and further the pump control unit drives and controls the supply pump to send ink from the buffer tank to the recovery tank; When the supply of power from the power supply unit is stopped, A method for shutting down a printing device, which includes controlling the supply solenoid valve to close after the pressure difference elimination operation is performed and before the power supply from the power supply unit is stopped, thereby cutting off the flow of ink from the buffer tank to the recovery tank.

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