Printing apparatus and ink stirring method

Abstract

To enable a stirring member to sufficiently stir ink stored in a tank.SOLUTION: A main tank 97 is retained in an inclination attitude As in which a bottom surface 973s of the main tank 97 gradually lowers as going from one side Du toward the other side Dl in a horizontal direction Dha. The inclination attitude of the main tank 97 enables a center (in other words, a center line C97) of the main tank 97 to approach a stirring blade 873. Further, as shown in side views of a figure 7B and a figure 8, a main stirring unit 87 having a shaft 871 and the stirring blade 873 is retained so as to incline in an inclining direction Ds from the one side Du toward the other side Dl, as the shaft 871 goes from an upper side toward a lower side. Thus, the inclination of the shaft 861 of the main stirring unit 87 enables the stirring blade 873 to approach the center (in other words, the center line C97) of the main tank 97.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] This invention relates to a technique for stirring ink stored in a tank.

Background Art

[0002] Ink used for printing images contains components such as pigments. Therefore, in the tank storing the ink, the components of the ink may settle. Thus, in Patent Document 1, the settlement of the components of the ink is suppressed by stirring the ink with a stirring mechanism provided in the tank.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in order to use the ink stored in the tank for printing, an insertion port for inserting a liquid feed pipe for feeding the ink outside the tank into the tank is required. Further, in order to stir the ink in the tank with a stirring member as described above, an insertion port for inserting the stirring member into the tank is also required. Therefore, it is conceivable to provide insertion ports at both ends of the upper surface of the tank, and use one for inserting the stirring member and the other for inserting the liquid feed pipe. However, when the stirring member is inserted into the tank from the insertion port provided at the end of the upper surface of the tank, the position of the stirring member in the tank is biased toward the end. Therefore, there are cases where the ink on the side opposite to the stirring member in the tank cannot be sufficiently stirred by the stirring member.

[0005] This invention has been made in view of the above problems, and an object thereof is to enable the ink stored in the tank to be sufficiently stirred by a stirring member.

Means for Solving the Problems

[0006] The printing apparatus according to the present invention comprises a tank holding section that holds a tank for storing ink used for printing an image in an inclined position in which the bottom surface of the tank slopes downward from one horizontal side to the other; an agitation unit having a shaft and an agitation member attached to the lower end of the shaft; an agitation unit holding section that holds the agitation unit, in which the agitation member and shaft are inserted into the tank through an insertion hole that opens on the upper surface of the tank on one side from the center of the tank; and a liquid supply pipe inserted into the tank through another insertion port that opens on the upper surface of the tank on the other side from the center of the tank. The agitation unit agitates the ink by rotating the agitation member immersed in the ink in the tank, and the agitation unit holding section holds the agitation unit in an inclined direction from one side to the other as the shaft moves from the top to the bottom.

[0007] The ink stirring method according to the present invention comprises the steps of: stirring the ink in a tank that stores ink used for printing an image by rotating the stirring member of an stirring unit having an stirring member immersed in the ink in the tank and a shaft to which the stirring member is attached at its lower end; and sending the ink from the tank to the outside of the tank by sucking the ink from the tank through a liquid supply pipe inserted into the tank. The tank is held by a tank holding part in an inclined position in which the bottom surface of the tank slopes downward from one side to the other in the horizontal direction. The stirring member of the stirring unit is inserted into the tank through one insertion hole that opens on the upper surface of the tank on one side from the center of the tank. The liquid supply pipe is inserted into the tank through another insertion port that opens on the upper surface of the tank on the other side from the center of the tank. The stirring unit is held by a stirring unit holding part such that the shaft is tilted in an inclined direction from one side to the other as it moves from the top to the bottom.

[0008] In the present invention (printing apparatus and ink stirring method) configured as described above, a stirring member is attached to the lower end of a shaft inserted into the tank through an insertion hole that opens on one side of the tank's center on the top surface of the tank. The ink in the tank is stirred by the rotation of this stirring member. At this time, the tank is held in an inclined position in which the bottom surface of the tank slopes downward from one side to the other in the horizontal direction. By tilting the tank in this way, the center of the tank can be brought closer to the stirring member. Furthermore, the stirring unit having the shaft and the stirring member is held in such a way that the shaft is tilted in an inclined direction from one side to the other as it moves from the top to the bottom. By tilting the shaft of the stirring unit in this way, the stirring member can be brought closer to the center of the tank. As a result, the bias of the stirring member away from the center of the tank is suppressed, and the ink stored in the tank can be sufficiently stirred by the stirring member.

[0009] Incidentally, in this invention, the shafts of both the tank and the stirring unit are tilted to suppress the uneven distribution of the stirring member from the center of the tank. Alternatively, it is conceivable to suppress the uneven distribution of the stirring member by tilting only the tank. However, in this case, the tilt of the tank would be too great, and there would be a risk of ink leaking from the tank. In contrast, by tilting both the tank and the shafts of the stirring unit, it is possible to prevent ink from leaking from the tank while still allowing the ink stored in the tank to be sufficiently stirred by the stirring member.

[0010] Furthermore, the printing apparatus may be configured such that the liquid supply piping has a lower end with a suction port, allowing ink from the tank to be drawn in through the suction port, and the suction port is located on the other side of the tank's center and below the stirring member that rotates to agitate the ink. In such a configuration, ink accumulated at the other end of the tank due to the tank's tilt can be drawn in through the suction port of the liquid supply piping, thereby reducing the amount of ink remaining in the tank that is not used for printing.

[0011] The printing apparatus may also be configured to include: a liquid level detection unit that detects the presence or absence of ink in the tank at a predetermined position above the stirring member; a liquid supply pump attached to the liquid supply piping that drives the ink in the liquid supply piping to draw the ink in the tank into the suction port and deliver the ink from the tank to the outside of the tank; and a control unit, wherein the control unit includes a liquid level detection unit that acquires the detection result of the liquid level detection unit; a stirring unit control unit that controls the stirring unit so that the stirring unit stops rotating the stirring member when the detection result acquired by the liquid level detection unit indicates that there is no ink at the predetermined position; and a liquid supply pump control unit that controls the liquid supply pump so that the liquid supply pump performs an ink delivery operation when the detection result acquired by the liquid level detection unit indicates that there is no ink at the predetermined position. In such a configuration, when the liquid level of ink in the tank falls below the stirring member and the stirring member can no longer stir the ink, the remaining ink can be delivered from the tank to the outside.

[0012] Furthermore, the tank holding unit may be configured such that it includes a horizontally mounted rotating shaft, a holding frame attached to the rotating shaft so as to be rotatable in the rotational direction about the rotating shaft and holding the tank, and a drive unit that drives the holding frame in the rotational direction, and the holding frame is rotatable about the rotating shaft between a horizontal holding position in which the tank is held in a horizontal position where the bottom surface of the tank is horizontal and an inclined holding position in which the tank is held in an inclined position, and the drive unit supports the holding frame in the horizontal holding position by applying a driving force to the holding frame, and when the drive unit releases the driving force, the holding frame that holds the tank rotates from the horizontal holding position to the inclined holding position by gravity.

[0013] The specific configuration of the drive unit can be varied. For example, the drive unit may be an air cylinder that generates driving force by supplying air.

[0014] Furthermore, the printing apparatus may be configured such that the stirring unit holding section includes a pulley provided above the stirring unit, a belt stretched across the pulley and having one end to which the stirring unit is attached, a counterweight attached to the other end of the belt, and a linear guide section that guides the movement of the stirring unit in an inclined direction. With such a configuration, the stirring unit can be easily moved when performing tasks such as inserting the stirring member into the tank, improving the worker's work efficiency.

[0015] Furthermore, the printing apparatus may be configured to include a vortex generation suppression plate, which is integrally attached to the liquid supply piping and suppresses the generation of vortices in the ink caused by stirring by the stirring member. In such a configuration, the generation of vortices caused by stirring by the stirring member can be suppressed, thereby preventing air from mixing with the ink.

[0016] Furthermore, the printing apparatus may be configured such that the stirring member is a stirring blade that expands due to the centrifugal force generated during rotation. In such a configuration, the ink can be stirred while the stirring blade inserted from the inlet expands due to centrifugal force, and the ink can be thoroughly stirred by the large stirring blade.

[0017] Furthermore, the present invention is particularly useful when the ink is white ink. This allows the white ink stored in the tank to be thoroughly stirred by the stirring member, thereby suppressing the settling of the white ink pigment. [Effects of the Invention]

[0018] As described above, according to the present invention, it is possible to thoroughly agitate the ink stored in the tank using the agitating member. [Brief explanation of the drawing]

[0019] [Figure 1] A schematic front view showing an example of a printing system equipped with the printing device according to the present invention. [Figure 2]Front view schematically showing a printing apparatus included in the printing system of FIG. 1. [Figure 3] View schematically showing the bottom surface of a discharge head included in a head unit. [Figure 4] View schematically showing the configuration of a discharge head and an ink supply mechanism that supplies ink to the discharge head. [Figure 5] View schematically showing a mechanism for supplying ink to a buffer tank. [Figure 6] Block diagram showing the electrical configuration of a printing apparatus. [Figure 7A] View schematically showing a main tank holding portion that holds a main tank. [Figure 7B] View schematically showing a main tank holding portion that holds a main tank. [Figure 8] View schematically showing the positional relationship between a main stirring unit and a front-stage liquid feeding pipe inserted into a main tank held in an inclined posture. [Figure 9] View schematically showing the operation of stirring blades. [Figure 10] View schematically showing an example of the configuration and operation of a stirring unit holding portion.

Mode for Carrying Out the Invention

[0020] 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 in a roll-to-roll manner from a pay-out roll 11 to a take-up roll 12. 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. Further, hereinafter, of both surfaces of the printing medium M, the surface on which an image is printed is appropriately referred to as a front surface M1, and the surface on the opposite side of the front surface M1 is referred to as a back surface M2.

[0021] The printing device 3 prints an image onto the surface M1 of the printing medium M by ejecting water-based ink using an inkjet method onto the surface M1 of the printing medium M, which is transported from the feed roll 11 to the take-up roll 12. The detailed configuration of the printing device 3 will be described later. The printing medium M, on which the image has been printed, is then transported horizontally X from the printing device 3 to the drying device 6.

[0022] The drying apparatus 6 is equipped with a drying oven 60 and dries the printing medium M that has been discharged from the printing apparatus 3 as it is transported from the feed roll 11 to the winding roll 12. Inside the drying oven 60 are two upper air blowing units 61u arranged horizontally in the X direction, two middle air blowing units 61m arranged horizontally in the X direction below these upper air blowing units 61u, and two lower air blowing units 61l arranged horizontally in the X direction below these middle air blowing units 61m.

[0023] The printing medium M discharged from the outlet 312 of the printing device 3 passes through two upper air blowing units 61u in the horizontal direction X, and is then turned back towards two middle air blowing units 61m by a pair of rollers 62. Subsequently, the printing medium M passes through the two middle air blowing units 61m in the horizontal direction X, and is then turned back towards two lower air blowing units 61l by a pair of air turn bars 63. Furthermore, the printing medium M passes through two lower air blowing units 61l in the horizontal direction X, and is then discharged to the outside of the drying device 6.

[0024] The upper air blowing unit 61u has two air blowing chambers 64 positioned to sandwich the printing medium M passing horizontally in the X direction from the vertical Z direction. Each air blowing chamber 64 has a plurality of nozzles 65 arranged horizontally in the X direction, and each nozzle 65 sprays warm air (gas at 60 degrees Celsius or higher) onto the printing medium M. In this way, the printing medium M is dried by the warm air sprayed from the nozzles 65 of the air blowing chambers 64 as it passes between the two air blowing chambers 64 located above and below each other. The middle air blowing unit 61m and the lower air blowing unit 61l also each have two air blowing chambers 64 that sandwich the printing medium M from the vertical Z direction, similar to the upper air blowing unit 61u.

[0025] Incidentally, the specific configuration of the upper air blower unit 61u is not limited to this example. For example, instead of the lower air blower chamber 64 of the upper air blower unit 61u, a plurality of rollers arranged in the horizontal direction X may be provided. In such a 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 air blower chamber 64 onto the front surface M1 of the printing medium M.

[0026] Figure 2 is a schematic front view showing the printing apparatus of the printing system of Figure 1. In Figure 2, one side X1 and the other side X2 in the horizontal direction X are shown as appropriate. Here, one side X1 is the side from the printing apparatus 3 toward the drying apparatus 6, and the other side X2 is the opposite side of one side X1. The printing apparatus 3 comprises a housing 31, a color printing unit 32 located inside the housing 31, a white printing unit 33 located above the color printing unit 32 inside the housing 31, and a transport unit 4 that transports the printing medium M using a plurality of rollers located inside the housing 31.

[0027] The color printing unit 32 has a plurality (6) of 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 (from the other side X2 to the one side X1). Each of the plurality of head units 321 has nozzles that face the surface M1 of the printing medium M passing below them from above, and ejects color inks of different colors from the nozzles using 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 unit 32 eject color inks from above onto the surface M1 of the printing medium M passing below them, thereby printing a color image on the surface M1 of the printing medium M.

[0028] Furthermore, the white printing unit 33 has a single head unit 331 positioned above the printing medium M that is transported by the transport unit 4. The head unit 331 has nozzles that face the surface M1 of the printing medium M passing below it from above, and ejects white ink from the nozzles in an inkjet manner. In this way, the head unit 331 of the white printing unit 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.

[0029] An entrance 311 opens in the side wall X2 of the housing 31, while an exit 312 opens in the side wall X1 of the housing 31. The transport unit 4 then transports the printing medium M from the entrance 311 to the exit 312, passing through the color printing unit 32 and the white printing unit 33.

[0030] This transport unit 4 includes a loading unit 41 located below the color printing unit 32, an upward transport unit 42 located on one side X1 of the color printing unit 32, an upward transport unit 43 located above the color printing unit 32, and a downward transport unit 44 located on the other side X2 of the color printing unit 32. The loading unit 41 transports the printing medium M loaded from the loading entrance 311 to one side X1 using rollers 411, the upward transport unit 42 transports the printing medium M transported by the loading 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.

[0031] 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 the one side X1, and each roller 451 contacts the back surface M2 of the printing medium M from below. In this way, the 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 surface M1 from above.

[0032] Furthermore, the transport unit 4 has rollers 461, 462, and 463 positioned between the color transport unit 45 and the lower transport unit 44 in the direction of travel of the printing medium M. Roller 461 is a drive roller that drives the printing medium M. Rollers 462 and 463 are driven rollers that rotate in accordance with the printing medium M.

[0033] Furthermore, the transport unit 4 has an inversion transport unit 47 that inverts the printing medium M, which has been transported from the color transport unit 45 to one side X1, twice. This inversion transport unit 47 has a plurality of rollers 471 to 477, including a drive roller 471, and these rollers 471 to 477 contact the back surface M2 of the printing medium M while inverting the printing medium M twice. In other words, the inversion transport unit 47 transports the printing medium M transported from the color transport unit 45 downwards by rollers 471 and 472, and then changes the direction of travel of the printing medium M to the other side X2 by roller 472, thereby inverting the front surface M1 and back surface M2 of the printing medium M. Subsequently, the inversion transport unit 47 transports the printing medium M from one side X1 to the other side X2 by a plurality of rollers 473, and then transports the printing medium M upwards by rollers 474 to 476. Furthermore, the reversal transport unit 47 changes the direction of travel of the printing medium M to one side X1 using the roller 476, thereby reversing the front surface M1 and back surface M2 of the printing medium M again, and transports the printing medium M from the other side X2 to the one side X1 using the roller 477.

[0034] Furthermore, the transport unit 4 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, which has been inverted twice by the inversion 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. In this way, the 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 surface M1 from above.

[0035] Furthermore, the transport unit 4 has an unloading unit 49 located above the upper transport unit 43. The unloading unit 49 has a plurality of rollers 491 arranged from the other side X2 to the one side X1 in the horizontal direction X. This unloading unit 49 transports the printing medium M, which has been transported by the white transport unit 48, to the one side X1 using the plurality of rollers 491, thereby unloading it from the unloading outlet 312 of the housing 31 to the drying device 6.

[0036] As described above, the color printing section 32 and the white printing section 33 of the printing device 3 have head units 321 and 331. Next, we will describe the ejection heads H of the head units 321 and 331 and the ink supply mechanism that supplies ink to the ejection heads H. Note that the head units 321 and 331 have a common basic configuration, and the basic configuration of the ink supply mechanism is also common to the head units 321 and 331. Therefore, we will describe the configuration of the head unit 331 that ejects white ink.

[0037] Figure 3 schematically shows the bottom surface of the ejection head of the head unit, and Figure 4 schematically shows the configuration of the ejection head and the ink supply mechanism that supplies ink to the ejection head. In Figure 3, in addition to the horizontal direction X and the vertical direction Z, a horizontal direction Y perpendicular to the horizontal direction X is shown. As shown in Figure 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 horizontal direction Y, and each ejection head H has a rectangle when viewed from below. Note that the arrangement of the multiple ejection heads H is not limited to the example in Figure 3, and the multiple ejection heads H may be arranged in a staggered pattern.

[0038] As shown in Figure 4, the discharge head H has a housing Ha, and at the bottom surface of the housing Ha, multiple nozzles Hn are arranged in a staggered pattern horizontally in the direction Y and open. Inside the housing Ha, there are multiple cavities Hb, each communicating with one of the multiple nozzles Hn, and an ink supply chamber Hc, which communicates with the multiple cavities Hb. Ink supplied from the ink supply chamber Hc is stored in the cavities Hb. In addition, a piezoelectric element D is provided in each cavity Hb, and the piezoelectric element D is displaced in response to a drive signal (electrical signal), causing pressure fluctuations in the ink in the cavity Hb. Due to these pressure fluctuations, the ink is pushed out of the cavity Hb and discharged from the nozzle Hn that communicates with that cavity Hb. Furthermore, at the top of the ejection head H, an ink inlet Hd and an ink outlet He are open, and ink flows from the ink supply mechanism 9a (described later) through the ink inlet Hd into the ink supply chamber Hc, and flows out from the ink supply chamber Hc through the ink outlet He towards the ink recovery mechanism 9b (described later).

[0039] Next, the ink supply, recovery, and circulation mechanism 9, which supplies, recovers, and circulates ink, will be described. The ink supply, recovery, and circulation mechanism 9 comprises an ink supply mechanism 9a that supplies ink to the discharge head H, an ink recovery mechanism 9b that recovers ink from the discharge head H, and an ink return mechanism 9c that returns the recovered ink back to the ink supply mechanism 9a. The ink supply mechanism 9a includes an ink supply unit 91 that supplies ink toward the discharge head H and a pressure generating unit 93 that generates the supply pressure applied to the ink supply unit 91. The ink supply unit 91 includes a supply tank 91a that stores the ink to be supplied to the discharge head H and a supply pipe 91b that delivers the ink supplied from the supply tank 91a to the discharge head H. The ink recovery mechanism 9b includes an ink recovery unit 92 that recovers ink from the discharge head H and a pressure generating unit 94 that generates the pressure applied to the ink recovery unit 92. The ink recovery unit 92 includes a recovery tank 92a for storing the ink recovered from the discharge head H, and a recovery pipe 92b for sending the ink recovered from the discharge head H to the recovery tank 92a.

[0040] The supply tank 91a and the recovery tank 92a are each positioned above the discharge head H. The ink return mechanism 9c includes a return pipe 902 that connects the recovery tank 92a and the supply tank 91a, a circulation pump 90 interposed in the middle of the return pipe 902, and a degassing filter 901 interposed in the middle of the return pipe 902 and positioned 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 91. With this ink supply mechanism 9, the circulation pump 90 can send ink along a first path Ca from the recovery tank 92 to the supply tank 91.

[0041] Furthermore, the ink supply mechanism 9a includes a supply-side pressure generating unit 93 (hereinafter referred to as "pressure generating unit 93" as appropriate) that applies pressure P1 (negative pressure) to the supply tank 91a. This pressure generating unit 93 includes a pressure tank 931, an exhaust pump 932 that exhausts the pressure tank 931 and generates pressure P1 in the pressure tank 931, a flexible tube 933 with one end connected to the pressure tank 931, and a pressure transmission pipe 934 with one end connected to the other end of the tube 933 so as to be able to communicate, with the other end facing the atmosphere inside the supply tank 91a, and which transmits the pressure generated inside the pressure tank 931 to the supply tank 91a. The pressure P1 generated inside the pressure tank 931 by the exhaust pump 932 is then supplied to the supply tank 91a via the tube 933 and the pressure transmission pipe 964.

[0042] In contrast, in the supply tank 91a, gas (air) is accumulated above the ink level. In other words, in the supply tank 91a, ink is stored below the gas-liquid interface, and gas is present 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.

[0043] Furthermore, the ink recovery mechanism 9b includes a recovery-side pressure generating unit 94 (hereinafter appropriately referred to as "pressure generating unit 94") that applies pressure P2 (negative pressure) to the recovery tank 92a. This pressure generating unit 94 includes a pressure tank 941, an exhaust pump 942 that exhausts the pressure tank 941 and generates pressure P2 in the pressure tank 941, a flexible tube 943 with one end connected to the pressure tank 941, and a pressure transmission pipe 944 with one end connected to the other end of the tube 973 so as to be able to communicate, with the other end facing the atmosphere inside the recovery tank 92, and which transmits 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 then supplied to the recovery tank 92a via the tube 943 and the pressure transmission pipe 944.

[0044] In contrast, in the recovery tank 92a, gas (air) accumulates above the ink level. In other words, 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 pressure P2 (negative pressure) to the gas-liquid interface in the recovery tank 92a.

[0045] In the state shown in Figure 4, the pressure P2 applied by the pressure generating unit 94 to the recovery tank 92a is lower than the pressure P1 applied by the pressure generating unit 93 to the supply tank 91a. Due to this difference between pressure P2 and pressure P1, ink flows along the second path Cb from the supply tank 91a through the ink supply chamber Hc of the discharge head H to the recovery tank 92a. 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 goes from the supply tank 91a to the recovery tank 92a via the discharge head H and then back to the supply tank 91a.

[0046] The ink supply, recovery, and 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, and circulation mechanism 9 also includes a pipe 951 connecting the buffer tank 95 and the supply tank 91a, and a pipe 952 connecting the buffer tank 95 and the recovery tank 92a. In other words, the buffer tank 95 is in communication with the supply tank 91a via pipe 951 and with the recovery tank 92a via pipe 952.

[0047] Furthermore, the ink supply, recovery, and circulation mechanism 9 includes a recovery pump 953 attached to piping 951 between the buffer tank 95 and the supply tank 91a, a supply pump 954 attached to piping 952 between the buffer tank 95 and the recovery tank 92a, a solenoid valve 955 attached to piping 951 between the recovery pump 953 and the supply tank 91a, and a solenoid valve 956 attached to piping 952 between the supply pump 954 and the recovery tank 92a. Therefore, with the solenoid valve 955 open, the recovery pump 953 can recover ink from the supply tank 91a to the buffer tank 95 via the solenoid valve 955, and with the solenoid valve 956 open, the supply pump 962 can supply ink from the buffer tank 95 to the recovery tank 92a via the solenoid valve 956.

[0048] In the ink supply, recovery, and circulation mechanism 9 configured in this way, the recovery pump 961 and the supply pump 962 operate, causing ink to flow along a third path Cc from the supply tank 91a through the buffer tank 95 to the recovery tank 92a. The ink that flows into the recovery tank 92a along the third path Cc is returned to the supply tank 91a along the first path Ca by the circulation pump 90. In this way, the ink circulates along a circulation path (third path Cc + first path Ca) that goes from the supply tank 91a to the recovery tank 92a via the buffer tank 95 and then back to the supply tank 91a.

[0049] Furthermore, the ink supply, recovery, and circulation mechanism 9 includes a mechanism for supplying ink to the buffer tank 95. This will be explained using Figure 5. Figure 5 is a schematic diagram showing the mechanism for supplying ink to the buffer tank. As shown in Figure 5, the ink supply, recovery, and circulation mechanism 9 includes a buffer tank 96 that stores the ink supplied to the buffer tank 95, and a main tank 97 that stores the ink supplied to the buffer tank 96. In other words, ink is supplied from the main tank 97 to the buffer tank 96, and then from the buffer tank 96 to the buffer tank 95. The ink stored in the buffer tank 95 is then supplied to the discharge head H and discharged from the nozzle Hn. The buffer tank 96 and the main tank 97 have volumes that can store a larger amount of ink than the buffer tank 95, and the buffer tank 96 has a volume that can store a larger amount of ink than the main tank 97. For example, the buffer tank 95 has a volume of 60 liters, the buffer tank 96 has a volume of 250 liters, and the main tank 97 has a volume of 200 liters. However, the relative sizes of these volumes are not limited to this example. In the following, buffer tank 95 will be referred to as "downstream buffer tank 95" and buffer tank 96 as "upstream buffer tank 96" as appropriate.

[0050] Furthermore, the ink supply, recovery, and circulation mechanism 9 includes a pre-stage liquid delivery unit 81 that delivers ink from the main tank 97 to the pre-stage buffer tank 96. This pre-stage liquid delivery unit 81 has a pre-stage liquid delivery pipe 811 that connects the main tank 97 and the pre-stage buffer tank 96, and the main tank 97 and the pre-stage buffer tank 96 are in communication via the pre-stage liquid delivery pipe 811. The pre-stage liquid delivery unit 81 also has a pre-stage liquid delivery pump 812 attached to the pre-stage liquid delivery pipe 811, which drives the ink in the pre-stage liquid delivery pipe 811 from the main tank 97 to the pre-stage buffer tank 96. In addition, the pre-stage liquid delivery unit 81 has a pre-stage solenoid valve 813 attached to the pre-stage liquid delivery pipe 811 between the pre-stage liquid delivery pump 812 and the main tank 97. This front-stage solenoid valve 813 allows ink to flow between the main tank 97 and the front-stage liquid transfer pump 812 when opened, and blocks ink flow between the main tank 97 and the front-stage liquid transfer pump 812 when closed. In this front-stage liquid transfer unit 81, with the front-stage solenoid valve 813 open, the front-stage liquid transfer pump 812 operates to send ink from the main tank 97 to the front-stage buffer tank 96.

[0051] Furthermore, the ink supply, recovery, and circulation mechanism 9 includes a downstream liquid delivery unit 82 that delivers ink from the upstream buffer tank 96 to the downstream buffer tank 95. This downstream liquid delivery unit 82 has a downstream liquid delivery pipe 821 that connects the upstream buffer tank 96 and the downstream buffer tank 95, and the upstream buffer tank 96 and the downstream buffer tank 95 are in communication via the downstream liquid delivery pipe 821. The downstream liquid delivery unit 82 also has a downstream liquid delivery pump 822 attached to the downstream liquid delivery pipe 821, which drives the ink in the downstream liquid delivery pipe 821 from the upstream buffer tank 96 to the downstream buffer tank 95. Furthermore, the downstream liquid delivery unit 82 has a downstream solenoid valve 823 attached to the downstream liquid delivery pipe 821 between the downstream liquid delivery pump 822 and the upstream buffer tank 96. The downstream solenoid valve 823, when opened, allows ink to flow between the upstream buffer tank 96 and the downstream liquid transfer pump 822, and when closed, blocks ink flow between the upstream buffer tank 96 and the downstream liquid transfer pump 822. The downstream liquid transfer unit 82 also has a downstream solenoid valve 824 attached to the downstream liquid transfer piping 821 between the downstream liquid transfer pump 822 and the downstream buffer tank 95. This downstream solenoid valve 824, when opened, allows ink to flow between the downstream liquid transfer pump 822 and the downstream buffer tank 95, and when closed, blocks ink flow between the downstream liquid transfer pump 822 and the downstream buffer tank 95. In this downstream liquid transfer unit 82, with the downstream solenoid valves 823 and 824 open, the downstream liquid transfer pump 822 operates to send ink from the upstream buffer tank 96 to the downstream buffer tank 95.

[0052] Furthermore, the ink supply, recovery, and circulation mechanism 9 includes an ink return unit 83 that returns ink that has flowed from the upstream buffer tank 96 to the downstream liquid delivery unit 82 back to the upstream buffer tank 96. This ink return unit 83 has an ink return pipe 831 that connects the upstream buffer tank 96 to a branch section 825 provided in the downstream liquid delivery piping 821 between the downstream liquid delivery pump 822 and the downstream solenoid valve 824, and the branch section 825 of the downstream liquid delivery piping 821 and the upstream buffer tank 96 are in communication via the ink return pipe 831. The ink return unit 83 also has an ink return solenoid valve 832 provided in the ink return pipe 831 between the branch section 825 and the upstream buffer tank 96. When the ink return solenoid valve 832 is opened, it allows the flow of ink between the branch section 825 and the upstream buffer tank 96, and when it is closed, it blocks the flow of ink between the branch section 825 and the upstream buffer tank 96. When ink is supplied from the upstream buffer tank 96 to the downstream buffer tank 95, the ink return solenoid valve 832 of the ink return unit 83 is closed, and the flow of ink from the branching section 825 to the upstream buffer tank 96 is blocked.

[0053] On the other hand, during print standby periods when ink ejection from the nozzle Hn of the ejection head H is stopped, the following ink circulation operation is performed by the downstream liquid supply unit 82 and the ink return unit 83 to return the ink that has flowed from the upstream buffer tank 96 to the downstream liquid supply piping 821 back to the upstream buffer tank 96 via the ink return unit 83. Specifically, the downstream solenoid valve 823 opens, the downstream solenoid valve 824 closes, and the ink return solenoid valve 832 opens. Therefore, the flow of ink along the downstream liquid supply piping 821 from the upstream buffer tank 96 to the downstream liquid supply pump 822 is enabled by the downstream solenoid valve 823, the flow of ink from the branch 825 of the downstream liquid supply piping 821 to the downstream buffer tank 95 is blocked by the downstream solenoid valve 824, and the flow of ink along the ink return piping 831 from the branch 825 of the downstream liquid supply piping 821 to the upstream buffer tank 96 is enabled by the ink return solenoid valve 832. In this state, the subsequent liquid transfer pump 822 operates, executing the ink circulation operation described above.

[0054] Furthermore, the ink supply, recovery, and circulation mechanism 9 includes a downstream stirring unit 85 that stirs the ink stored in the downstream buffer tank 95, a upstream stirring unit 86 that stirs the ink stored in the upstream buffer tank 96, and a main stirring unit 87 that stirs the ink stored in the main tank 97. Of the stirring units 85, 86, and 87, the stirring unit 87 is provided only in the ink supply, recovery, and circulation mechanism 9 that supplies white ink, and is not provided in the ink supply mechanism 9 that supplies color ink.

[0055] The downstream stirring unit 85 includes a shaft 851 extending parallel to the vertical Z, a stirring motor 852 that rotates the shaft 851, and a stirring blade 853 attached to the lower end of the shaft 851. The stirring motor 852 is located outside the downstream buffer tank 95. On the other hand, the stirring blade 853 is located inside the downstream buffer tank 95 and is immersed in the ink stored in the downstream buffer tank 95. When the stirring motor 852 rotates the shaft 851, the stirring blade 853 rotates around a rotation axis parallel to the vertical Z. The ink in the downstream buffer tank 95 is stirred by the rotating stirring blade 853.

[0056] The pre-stage stirring unit 86 includes a shaft 861 extending parallel to the vertical Z, a stirring motor 862 that rotates the shaft 861, and a stirring blade 863 attached to the lower end of the shaft 861. The stirring motor 862 is located outside the pre-stage buffer tank 96. On the other hand, the stirring blade 863 is located inside the pre-stage buffer tank 96 and is immersed in the ink stored in the pre-stage buffer tank 96. When the stirring motor 862 rotates the shaft 861, the stirring blade 863 rotates around a rotation axis parallel to the vertical Z. The ink in the pre-stage buffer tank 96 is stirred by the rotating stirring blade 863.

[0057] The main stirring unit 87 includes a shaft 871 extending parallel to the vertical Z, a stirring motor 872 that rotates the shaft 871, and a stirring blade 873 attached to the lower end of the shaft 871. The stirring motor 872 is located outside the main tank 97. The stirring blade 873, on the other hand, is located inside the main tank 97 and is immersed in the ink stored in the main tank 97. When the stirring motor 872 rotates the shaft 871, the stirring blade 873 rotates around a rotation axis parallel to the vertical Z. The ink in the main tank 97 is stirred by the rotating stirring blade 873.

[0058] The stirring blade 873 is a centrifugal-type stirring blade that opens due to centrifugal force. The top surface of the main tank 97 is provided with an insertion port 971 into which the stirring blade 873 can be inserted. In other words, the stirring blade 873 can be placed inside the main tank 97 by inserting it through the insertion port 971 of the main tank 97 in its closed state. Then, when the stirring motor 872 rotates the stirring blade 873, the stirring blade 873 opens due to centrifugal force and stirs the ink.

[0059] By agitating the ink with these agitator blades 853, 863, and 873, the physical properties of the ink stored in the downstream buffer tank 95, the upstream buffer tank 96, and the main tank 97 can be made uniform. In particular, white ink contains a large amount of titanium dioxide as a pigment to ensure a high opacity. As a result, white ink has low viscosity and a high specific gravity of pigment relative to the specific gravity of solvent, making the pigment prone to sedimentation. Such pigment sedimentation can lead to problems such as insufficient opacity or deterioration of the white ink ejection performance from the ejection head H. In contrast, agitating the white ink with the agitator blades 853, 863, and 873 can suppress pigment sedimentation.

[0060] Furthermore, the downstream buffer tank 95 is provided with a downstream liquid level sensor S95 for detecting the liquid level of the ink stored in the downstream buffer tank 95, the upstream buffer tank 96 is provided with an upstream liquid level sensor S96 for detecting the liquid level of the ink stored in the upstream buffer tank 96, and the main tank 97 is provided with a main liquid level sensor S97 for detecting the liquid level of the ink stored in the main tank 97.

[0061] Figure 6 is a block diagram showing the electrical configuration of a printing device. As shown in Figure 6, the printing device 3 includes a control unit 5 that comprehensively controls the entire device. This control unit 5 is a processor, for example, composed of a CPU (Central Processing Unit). The printing device 3 also includes a UI (User Interface) 301 having input devices such as a keyboard and mouse, and output devices such as a display, and the control unit 5 has a UI control unit 501 that controls the UI 39. The UI control unit 501 performs control in response to the operator's input operations on the input devices of the UI 39, while also controlling the UI 39 so that the output devices of the UI 39 display information to the operator. Note that the input devices and output devices of the UI 39 may be integrated using, for example, a touch panel display.

[0062] The control unit 5 includes a stirring motor control unit 502 that controls the stirring motor 872 of the main stirring unit 87. By controlling the stirring motor 872 so that it rotates, the stirring blades 873 rotate, and the ink in the main tank 97 is stirred. The control unit 5 also includes a main sensor output acquisition unit 503 that acquires the detection result of the main liquid level sensor S97.

[0063] The control unit 5 has a pre-stage solenoid valve control unit 504 that controls the opening and closing of the pre-stage solenoid valve 813 of the pre-stage liquid delivery unit 81, and the pre-stage solenoid valve 813 opens and closes according to the control of the pre-stage solenoid valve control unit 504. The control unit 5 also has a pre-stage pump control unit 505 that controls the pre-stage liquid delivery pump 812 of the pre-stage liquid delivery unit 81, and the pre-stage liquid delivery pump 812 starts or stops the ink delivery according to the control of the pre-stage pump control unit 505.

[0064] The control unit 5 includes a stirring motor control unit 506 that controls the stirring motor 862 of the upstream stirring unit 86. By controlling the stirring motor 862 so that it rotates, the stirring blades 863 rotate, and the ink in the upstream buffer tank 96 is stirred. The control unit 5 also includes an upstream sensor output acquisition unit 507 that acquires the detection result of the upstream liquid level sensor S96.

[0065] The control unit 5 includes a downstream solenoid valve control unit 508 that controls the opening and closing of the downstream solenoid valve 823 of the downstream liquid supply unit 82, and the downstream solenoid valve 823 opens and closes according to the control of the downstream solenoid valve control unit 508. The control unit 5 also includes a downstream pump control unit 509 that controls the downstream liquid supply pump 822 of the downstream liquid supply unit 82, and the downstream liquid supply pump 822 starts or stops supplying ink according to the control of the downstream pump control unit 509.

[0066] The control unit 5 includes a downstream solenoid valve control unit 510 that controls the opening and closing of the downstream solenoid valve 824 of the downstream liquid supply unit 82, and the downstream solenoid valve 824 opens and closes according to the control of the downstream solenoid valve control unit 510. The control unit 5 also includes a return solenoid valve control unit 511 that controls the opening and closing of the ink return solenoid valve 832 of the ink return unit 83, and the ink return solenoid valve 832 opens and closes according to the control of the return solenoid valve control unit 511.

[0067] Furthermore, the control unit 5 includes a stirring motor control unit 512 that controls the stirring motor 852 of the downstream stirring unit 85. The stirring motor control unit 512 controls the stirring motor 852 so that it rotates, causing the stirring blades 853 to rotate and the ink in the downstream buffer tank 95 to be stirred. The control unit 5 also includes a downstream sensor output acquisition unit 513 that acquires the detection result of the downstream liquid level sensor S95.

[0068] The control unit 5 includes a recovery pump control unit 514 that controls the recovery pump 953, and the recovery pump 953 starts or stops supplying ink according to the control of the recovery pump control unit 514. The control unit 5 also includes a supply pump control unit 515 that controls the supply pump 954, and the supply pump 954 starts or stops supplying ink according to the control of the supply pump control unit 515.

[0069] Furthermore, the control unit 5 has a solenoid valve control unit 516 that controls the opening and closing of the solenoid valve 955, and the solenoid valve 955 opens and closes according to the control of the solenoid valve control unit 516. In addition, the control unit 5 has a solenoid valve control unit 517 that controls the opening and closing of the solenoid valve 956, and the solenoid valve 956 opens and closes according to the control of the solenoid valve control unit 517.

[0070] Furthermore, as will be explained below, the printing apparatus 3 includes a tank holding section 71 that holds the main tank 97, and this tank holding section 71 has an air cylinder 741 to support the main tank 97. In contrast, the control unit 5 has an air supply control unit 518 that controls an air supply section 70 that supplies air to the air cylinder 741.

[0071] Figures 7A and 7B schematically show the main tank holding section that holds the main tank. In Figures 7A and 7B, the inside of the main tank 97 is shown transparently. The vertical direction Z, the horizontal direction Dha, and the horizontal direction Dhb are shown, as well as Du and Dl on one side of the horizontal direction Dha. Here, the horizontal direction Dha and the horizontal direction Dhb are orthogonal to each other, and Du and Dl on one side of the horizontal direction Dha face opposite directions to each other.

[0072] As shown in Figures 7A and 7B, the main tank 97 has a shape that is rotationally symmetric with respect to the center line C97, and has a bottom plate portion 973 that is circular in plan view with the center line C97 as the center, and a side wall portion 974 that is erected on the upper side from the periphery of the bottom plate portion 973. The main tank 97 also has an upper plate portion 975 attached to the upper end of the side wall portion 974. The upper plate portion 975 is circular in plan view with the center line C97 as the center, and has an insertion opening 971 and an insertion opening 972. In other words, two insertion openings 971 and 972 open on the upper surface 975s of the upper plate portion 975. The insertion opening 971 is located on one side Du from the center line C97, or in other words, it is located at the end of one side Du of the upper plate portion 975. The insertion port 972 is located on the other side Dl from the center line C97, in other words, it is located at the other side Dl end of the upper plate portion 975. In the main tank 97, a storage chamber 976 is formed by the bottom plate portion 973, the side wall portion 974, and the upper plate portion 975, and ink is stored in this storage chamber 976.

[0073] In contrast, the tank holding section 71 includes a base member 711, a holding frame 72 for holding the main tank 97, and a rotating support section 73 that rotatably supports the holding frame 72 with respect to the base member 711. The rotating support section 73 includes a rotating shaft 731 attached to the holding frame 72 and a pivot member 732 attached to the base member 711. The rotating shaft 731 is provided parallel to the horizontal direction Dhb, and the pivot member 732 pivotally supports the rotating shaft 731 so that it can rotate around a rotation center parallel to the horizontal direction Dhb. Therefore, the holding frame 72 is rotatable with respect to the base member 711 in the rotation direction Dr about the rotating shaft 731. The holding frame 72 includes a bottom frame 721 that supports the main tank 97 from below, and a side frame 722 that is erected from the other end Dl of the bottom frame 721 and supports the main tank 97 from the other end Dl.

[0074] Furthermore, the tank holding section 71 includes a column member 712 erected from the other end Dl of the base member 711, and an air cylinder 741 attached to the column member 712. The air cylinder 741 is located on the other end Dl of the holding frame 72 and has a rod 742 that extends to the one side Du as air is supplied. More specifically, the printing apparatus 3 is equipped with an air supply section 70 (Figure 6) that supplies air to the rod 742. When the air supply section 70 supplies air to the air cylinder 741, the rod 742 of the air supply section 70 extends to the one side Du due to the air pressure. This rod 742 is positioned to contact the holding frame 72 and drives the holding frame 72 to the one side Du by extending to the one side Du. As a result, the holding frame 72 rotates in the rotational direction Dt around the rotation axis 731. In other words, the rod 742 of the air cylinder 741 can drive the holding frame 72 in the rotational direction Dt with a driving force corresponding to the air supplied to the air cylinder 741 from the air supply unit 70.

[0075] As described above, the supply of air to the air cylinder 741 by the air supply unit 70 is controlled by the air supply control unit 518. The air supply unit 70 can be configured, for example, by a solenoid valve that adjusts the supply of air to the air cylinder 741. Therefore, air is supplied to the air cylinder 741 when the air supply control unit 518 controls the air supply unit 70 so that the solenoid valve constituting the air supply unit 70 opens. Conversely, the supply of air to the air cylinder 741 is stopped when the air supply control unit 518 controls the air supply unit 70 so that the solenoid valve constituting the air supply unit 70 closes.

[0076] In the tank holding section 71 configured in this way, the holding frame 72 rotates in the rotational direction Dt or Dr between the horizontal holding position Ph and the inclined holding position Ps. That is, when air is supplied to the air cylinder 741, the rod 742 presses the holding frame 72 toward one side Du due to the driving force generated in response to the air supply. As a result, the holding frame 72 is supported in the horizontal holding position Ph (Figure 7A). Also, the holding frame 72 located in the horizontal holding position Ph holds the main tank 97 in a horizontal position Ah where the bottom surface 973s of the main tank 97 is horizontal. On the other hand, when the supply of air to the air cylinder 741 is stopped, the driving force that supports the holding frame 72 in the horizontal holding position Ph by the rod 742 is released. As a result, the holding frame 72 rotates in the rotational direction Dr from the horizontal holding position Ph to the inclined holding position Ps due to gravity (Figure 7B). At this time, the rod 742 is pushed by the holding frame 72 and retracts toward the other side Dl. Furthermore, the holding frame 72 located in the inclined holding position Ps holds the main tank 97 in an inclined position As, where the bottom surface 973s of the main tank 97 is inclined from one side Du to the other side Dl in the horizontal direction Dha.

[0077] Figure 8 schematically shows the positional relationship between the main stirring unit and the upstream liquid supply piping inserted into the main tank, which is held in an inclined position. As described above, the bottom surface 973s of the main tank 97, which is held in an inclined position As, is inclined downward from one side Du to the other side Dl in the horizontal direction Dha, and is tilted at an angle θh (an acute angle greater than zero, for example, 5 degrees) with respect to a straight line Lh parallel to the horizontal direction Dha.

[0078] The pipe insertion section 811e, located at the end of the upstream liquid supply piping 811, is inserted into the storage chamber 976 of the main tank 97 from the insertion port 972, parallel to the centerline C97 of the main tank 97. A suction port 811v opens at the lower end of this pipe insertion section 811e. This suction port 811v opens to the ink stored in the storage chamber 976 of the main tank 97. Therefore, when the upstream liquid supply pump 812 performs liquid supply with the upstream solenoid valve 813 open, the ink drawn in from the suction port 811v is supplied to the outside of the main tank 97 by the pipe insertion section 811e. Furthermore, a baffle plate 819 is attached to the pipe insertion section 811e. This baffle plate 819 protrudes laterally from the outer circumference of the pipe insertion section 811e and functions as a vortex breaker to suppress the generation of vortices in the ink due to the agitation of the ink by the stirring blades 873.

[0079] As shown in Figure 8, the shaft 871 of the main stirring unit 87 has a long, small-diameter section 871d and a shorter, larger-diameter section 871u attached to the upper end of the small-diameter section 871d, with stirring blades 873 attached to the lower end of the small-diameter section 871d. The shaft 871 is inserted into the storage chamber 976 of the main tank 97 from the inlet 971, and the stirring blades 873 attached to the lower end of the shaft 871 are located inside the storage chamber 976 of the main tank 97.

[0080] In particular, the shaft 871 is inserted parallel to the inclination direction Ds. Here, the inclination direction Ds is the direction from one side Du to the other side Dl as the shaft 871 moves from the top to the bottom. As a result, the shaft 871 is inclined by an angle θs (an acute angle greater than zero, for example, 5 degrees) with respect to a straight line Lz parallel to the vertical direction Z. Incidentally, the centerline C97 of the main tank 97 is inclined according to the inclination of the bottom surface 973s of the main tank 97. In other words, the straight line Lc parallel to the centerline C97 of the main tank 97 is inclined by an angle θh with respect to a straight line Lz parallel to the vertical direction Z. In this case, the direction in which the centerline C97 of the main tank 97 is inclined with respect to the straight line Lz parallel to the vertical direction Z is opposite to the direction in which the shaft 871 is inclined, and the angle at which the shaft 871 is inclined with respect to the centerline C97 of the main tank 97 is the sum of the angles θs and θh. Incidentally, in this example, the angle θs at which shaft 871 is tilted is equal to the angle θh at which the bottom surface 973s of main tank 97 is tilted. However, these angles θs and θh do not need to be equal to each other. Therefore, angle θs can be greater than or less than angle θh.

[0081] Figure 9 is a schematic diagram illustrating the operation of the agitator blade. As shown in Figure 9, the agitator blade 873 has multiple rotating blades 873a that rotate around a pivot axis 871a located at the lower end of the shaft 871. As shown in the "Stationary State" column of Figure 9, when the agitator blade 873 is stationary, the rotating blades 873a hang down from the pivot axis 871a due to gravity, and the agitator blade 873 closes. In this closed state, the agitator blade 873 is inserted into the storage chamber 976 of the main tank 97 through the insertion port 971. On the other hand, as shown in the "Rotating State" column of Figure 8, when the agitator blade 873 is rotating, the rotating blades 873a are subjected to centrifugal force and rotate upward around the pivot axis 871a, causing the agitator blade 873 to open. In this way, the ink stored in the main tank 97 is agitated by the rotating agitator blade 873. Incidentally, the suction port 811v (Figure 8) of the preceding liquid supply piping 811 opens below the position of the rotating stirring blade 873 (ink stirring position) which rotates to agitate the ink.

[0082] As shown in Figure 8, the main liquid level sensor S97 detects the presence or absence of ink in the main tank 97 at level Lv97, which is above the stirring blade 873. When the detection result of the main liquid level sensor S97 acquired by the main sensor output acquisition unit 503 (Figure 6) indicates that there is no ink at level Lv97 in the main stirring unit 87, the preceding solenoid valve control unit 504 controls the preceding solenoid valve 813 to open, and the preceding pump control unit 505 controls the preceding liquid supply pump 812 to execute ink supply. As a result, the ink in the main tank 97 is drawn in through the suction port 811v and sent to the preceding buffer tank 96 via the preceding liquid supply piping 811. Consequently, the ink level in the main tank 97 drops below the position of the stirring blade 873 (ink stirring position). Furthermore, if the detection result of the main liquid level sensor S97 acquired by the main sensor output acquisition unit 503 indicates that there is no ink at level Lv97 in the main stirring unit 87, the stirring motor control unit 502 controls the stirring motor 872 so that the stirring motor 872 of the stirring unit 87 stops rotating the stirring blades 873.

[0083] Furthermore, the printing apparatus 3 includes a stirring unit holding section 75 (Figure 10) that holds the shaft 871 of the main stirring unit 87 in the inclined direction Ds. Figure 10 is a schematic diagram showing an example of the configuration and operation of the stirring unit holding section. As shown in Figure 10, the main stirring unit 87 has a coupler 874 that connects the stirring motor 872 to the large-diameter portion 871u of the shaft 871, and a motor holder 875 that holds the stirring motor 872. As the motor holder 875 moves, the stirring motor 872, coupler 874, shaft 871, and stirring blade 873 move together (i.e., the main stirring unit 87 moves).

[0084] In contrast, the stirring unit holder 75 has a main body 751 and a linear guide 76 attached to the main body 751. A mounting plane 752 parallel to the inclination direction Ds is provided on the side of the main body 751, and the linear guide 76 is attached to this mounting plane 752. The linear guide 76 has a guide rail 761 and a plurality of sliders 762 that engage with the guide rail 761 and move along the guide rail 761. The guide rail 761 is attached to the mounting plane 752 of the main body 751 and is arranged parallel to the inclination direction Ds. The sliders 762 are attached to the side of the motor holder 875 of the main stirring unit 87. Therefore, the main stirring unit 87 can move in the inclination direction Ds according to the guidance of the linear guide 76. Incidentally, various arrangements of the linear guide 76 are conceivable, for example, a pair of linear guides 76 may be arranged in parallel.

[0085] Furthermore, the stirring unit holding section 75 includes a pulley 77 positioned above the main stirring unit 87 and a support member 753 that rotatably supports the pulley 77 relative to the main body section 751. In addition, the stirring unit holding section 75 includes a chain belt 78 stretched across the pulley 77 and a counterweight 79 having the same weight as the main stirring unit 87. One end 781 of the chain belt 78 is attached to the motor holder 875 of the main stirring unit 87, and the other end 782 of the chain belt 78 is attached to the counterweight 79. Therefore, when the main stirring unit 87 rises along the inclination direction Ds, the counterweight 79 descends, and when the main stirring unit 87 descends along the inclination direction Ds, the counterweight 79 rises. Thus, as shown in Figure 10, the main stirring unit 87 moves along the inclination direction Ds between a stirring position Pr and a retracted position Pe above the stirring position Pr. This raising and lowering of the main stirring unit 87 is performed by an operator. Incidentally, when the main stirring unit 87 is in the stirring position Pr, the stirring blades 873 are positioned below level Lv97, as shown in Figure 8. Also, when the main stirring unit 87 is in the retracted position Pe, the stirring blades 873 move upward from the insertion port 971.

[0086] In the printing apparatus 3 described above, a stirring blade 873 (stirring member) is attached to the lower end of a shaft 871 inserted into the main tank 97 from an insertion opening 971 (one insertion hole) that opens on one side Du from the center (center line C97) of the main tank 97 on the upper surface 975s of the main tank 97. The ink in the main tank 97 is stirred by the rotation of this stirring blade 873. At this time, as shown in the side view in Figures 7B and 8, the main tank 97 is held in an inclined position As in which the bottom surface 973s of the main tank 97 is lowered as it moves from one side Du to the other side Dl in the horizontal direction Dha. By tilting the main tank 97 in this way, the center of the main tank 97 (in other words, the center line C97) can be brought closer to the stirring blade 873. Furthermore, as shown in the side views of Figures 7B and 8, the main stirring unit 87, which has a shaft 871 and stirring blades 873, is held such that the shaft 871 tilts in a direction Ds from one side Du to the other side Dl as it moves from the top to the bottom. By tilting the shaft 861 of the main stirring unit 87 in this way, the stirring blades 873 can be brought closer to the center of the main tank 97 (in other words, the center line C97). As a result, the deviation of the stirring blades 873 from the center of the main tank 97 is suppressed, and the ink stored in the main tank 97 can be sufficiently stirred by the stirring blades 873.

[0087] Incidentally, in this embodiment, the shafts 871 of both the main tank 97 and the main stirring unit 87 are tilted in order to suppress the uneven distribution of the stirring blades 873 from the center of the main tank 97. Alternatively, it is conceivable to suppress the uneven distribution of the stirring blades 873 by tilting only the main tank 97. However, in this case, the tilt of the main tank 97 would be greater, and there would be a risk of ink leaking from the main tank 97. In contrast, by tilting both the main tank 97 and the shafts 871 of the main stirring unit 87, it is possible to prevent ink from leaking from the main tank 97 while still allowing the ink stored in the main tank 97 to be sufficiently stirred by the stirring blades 873.

[0088] Furthermore, the pipe insertion section 811e of the preceding liquid supply pipe 811 (liquid supply pipe) has a lower end from which a suction port 811v opens, allowing ink in the main tank 97 to be drawn in through the suction port 811v. This suction port 811v is located Dl on the other side of the center (center line C97) of the main tank 97, and is positioned below the stirring blade 873 that rotates to agitate the ink. With this configuration, ink accumulated at the other end of the main tank 97 due to the tilt of the main tank 97 can be drawn in by the pipe insertion section 811e of the preceding liquid supply pipe 811, thereby suppressing the amount of ink remaining in the main tank 97 that is not used for printing.

[0089] The printing apparatus 3 also includes a main liquid level sensor S97 (liquid level detection unit) that detects the presence or absence of ink in the main tank 97, and a pre-stage liquid supply pump 812 (liquid supply pump) attached to the pre-stage liquid supply piping 811. The main liquid level sensor S97 detects the presence or absence of ink in the main tank 97 at a level Lv97 (a predetermined position) above the stirring blade 873. The pre-stage liquid supply pump 812 drives the ink in the pre-stage liquid supply piping 811 to draw the ink from the main tank 97 into the suction port 811v and perform an ink supply operation to supply ink from the main tank 97 to the outside of the main tank 97. In contrast, the control unit 5 includes a main sensor output acquisition unit 503 (detected liquid level acquisition unit), a stirring motor control unit 502 (stirring unit control unit), and a pre-stage pump control unit 505 (liquid supply pump control unit). The main sensor output acquisition unit 503 acquires the detection result of the main liquid level sensor S97. When the detection result acquired by the main sensor output acquisition unit 503 indicates that there is no ink at level Lv97, the stirring motor control unit 502 controls the stirring motor 872 of the main stirring unit 87 to stop the rotation of the stirring blade 873. Furthermore, when the detection result acquired by the main liquid level sensor S97 indicates that there is no ink at level Lv97, the upstream liquid transfer pump 812 controls the upstream liquid transfer pump 812 to perform an ink transfer operation. In this configuration, when the liquid level of ink in the main tank 97 falls below the level of the stirring blade 873 and the stirring blade 873 can no longer agitate the ink, the remaining ink can be transferred from the main tank 97 to the outside.

[0090] Furthermore, the tank holding section 71 includes a rotating shaft 731 provided parallel to the horizontal direction Dhb, a holding frame 72 attached to the rotating shaft 731 so as to be rotatable in the rotational direction Dt or Dr around the rotating shaft 731 and holding the main tank 97, and an air cylinder 741 (drive unit) that drives the holding frame 72 in the rotational direction Dt. The holding frame 72 is rotatable around the rotating shaft 731 in the rotational direction Dt or Dr between a horizontal holding position Ph, which holds the main tank 97 in a horizontal position Ah where the bottom surface 973s of the main tank 97 is horizontal, and an inclined holding position Ps, which holds the main tank 97 in an inclined position As. The air cylinder 741 supports the holding frame 72 in the horizontal holding position Ph by applying a driving force to the holding frame 72, and when the air cylinder 741 releases the driving force, the holding frame 72 that holds the main tank 97 rotates from the horizontal holding position Ph to the inclined holding position Ps by gravity. In this configuration, the holding frame 72 that holds the main tank 97 is positioned in the tilted holding position Ps by gravity. Therefore, the air cylinder 741 does not need to generate driving force to position the holding frame 72 in the tilted holding position Ps. Consequently, the main tank 97 can be held in the tilted position As without consuming energy.

[0091] Furthermore, the stirring unit holding section 75 includes a pulley 77 provided above the main stirring unit 87, a chain belt 78 (belt) stretched across the pulley 77 and having one end 781 to which the main stirring unit 87 is attached, a counterweight 79 attached to the other end 782 of the chain belt 78, and a linear guide 76 (linear guide section) that guides the movement of the main stirring unit 87 in the inclined direction Ds. With this configuration, the main stirring unit 87 can be easily moved when performing tasks such as inserting the stirring blades 873 into the main tank 97, improving the work efficiency of the operator.

[0092] Furthermore, a baffle plate 819 (vortex generation suppression plate) is provided, which is integrally attached to the upstream liquid supply piping 811 to suppress the generation of vortices in the ink caused by stirring by the stirring blades 873. With this configuration, the generation of vortices caused by stirring by the stirring blades 873 can be suppressed, thereby preventing air from mixing with the ink.

[0093] Furthermore, the stirring blade 873 is a centrifugal-type stirring blade that expands due to the centrifugal force generated as it rotates. In this configuration, the ink can be stirred while the stirring blade 873 inserted from the insertion port 971 expands due to centrifugal force, and the ink can be thoroughly stirred by the large stirring blade 873.

[0094] Incidentally, the configurations shown in Figures 7A to 9 do not need to be applied to all the main tanks 97 of all colors in the printing apparatus 3. However, it is preferable to apply this configuration to the main tank 97 that stores white ink. This allows the white ink stored in the main tank 97 to be sufficiently stirred by the stirring blades 873, thereby suppressing the settling of the white ink pigment.

[0095] In the embodiments described above, the printing device 3 corresponds to an example of the "printing device" of the present invention, the control unit 5 corresponds to an example of the "control unit" of the present invention, the stirring motor control unit 502 corresponds to an example of the "stirring unit control unit" of the present invention, the main sensor output acquisition unit 503 corresponds to an example of the "detection liquid level acquisition unit" of the present invention, the pre-stage pump control unit 505 corresponds to an example of the "liquid supply pump control unit" of the present invention, the tank holding unit 71 corresponds to an example of the "tank holding unit" of the present invention, the holding frame 72 corresponds to an example of the "holding frame" of the present invention, and the rotating shaft 731 corresponds to an example of the "rotating shaft" of the present invention. For example, the air cylinder 741 corresponds to an example of the "drive unit" and "air cylinder" of the present invention, the stirring unit holding unit 75 corresponds to an example of the "stirring unit holding unit" of the present invention, the pulley 77 corresponds to an example of the "pulley" of the present invention, the chain belt 78 corresponds to an example of the "belt" of the present invention, the counterweight 79 corresponds to an example of the "counterweight" of the present invention, the linear guide 76 corresponds to an example of the "linear guide unit" of the present invention, the pre-stage liquid supply piping 811 corresponds to an example of the "liquid supply piping" of the present invention, and the suction port 811v corresponds to an example of the "suction port" of the present invention. The preceding liquid transfer pump 812 corresponds to an example of the "liquid transfer pump" of the present invention, the baffle plate 819 corresponds to an example of the "vortex generation suppression plate" of the present invention, the shaft 871 corresponds to an example of the "shaft" of the present invention, the main stirring unit 87 corresponds to an example of the "stirring unit" of the present invention, the stirring blade 873 corresponds to an example of the "stirring member" of the present invention, the main tank 97 corresponds to an example of the "tank" of the present invention, the inlet 971 corresponds to an example of the "one insertion hole" of the present invention, the inlet 972 corresponds to an example of the "other insertion hole" of the present invention, and the bottom surface 973s corresponds to an example of the "bottom surface" of the present invention. The horizontal posture Ah corresponds to an example of the "horizontal posture" of the present invention, the inclined posture As corresponds to an example of the "inclined posture" of the present invention, the horizontal holding position Ph corresponds to an example of the "horizontal holding position" of the present invention, the inclined holding position Ps corresponds to an example of the "inclined holding position" of the present invention, the horizontal direction Dha corresponds to an example of the "horizontal direction" of the present invention, one side Du corresponds to an example of the "one side" of the present invention, the other side Dl corresponds to an example of the "other side" of the present invention, the main liquid level sensor S97 corresponds to an example of the "liquid level detection unit" of the present invention, and the level Lv97 corresponds to an example of the "determined position" of the present invention.

[0096] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. For example, the specific configuration of the pre-stage liquid delivery unit 81 can be changed as appropriate, and the pre-stage solenoid valve 813 does not need to be provided.

[0097] Furthermore, it is not essential that the stirring blade 873 be a centrifugal type stirring blade; the stirring blade 873 may be a stirring blade fixed to the shaft 871.

[0098] Furthermore, it is not essential to integrate the baffle plate 819 with the preceding liquid supply piping 811.

[0099] Furthermore, the configuration of the tank holding portion 71 may be changed as appropriate, and it is not essential that the tank holding portion 71 is rotatable in the rotational direction Dr. In other words, the tank holding portion 71 may be fixedly provided in the inclined holding position Ps.

[0100] Furthermore, the configuration of the stirring unit holding section 75 may be changed as appropriate, and the stirring unit holding section 75 does not need to have a function to guide the movement of the main stirring unit 87 in the inclined direction Ds. [Industrial applicability]

[0101] The present invention is applicable to all techniques for agitating ink stored in a tank. [Explanation of Symbols]

[0102] 3...Printing device 5…Control Unit 502... Stirring motor control unit (stirring unit control unit) 503...Main sensor output acquisition unit (detected liquid level acquisition unit) 505...Pre-stage pump control unit (liquid delivery pump control unit) 71... Tank holding section 72... Retaining frame 731... Rotation axis 741... Air cylinder (drive unit) 75...Stirring unit holding section 76…Linear guide (linear motion guide unit) 77...Pulley 78... Chain belt (belt) 79... Counterweight 811...Pre-stage liquid supply piping (liquid supply piping) 811v…Suction port 812...Pre-stage liquid transfer pump (liquid transfer pump) 819... Baffle plate (vortex generation suppression plate) 87…Main stirring unit (stirring unit) 871... Shaft 873…Agitation blade (agitation component) 97... Main Tank (Tank) 971... Insertion opening (first insertion hole) 972... Insertion port (other insertion ports) 973s…bottom Ah...Horizontal posture As…tilted posture Ph…Horizontal holding position Ps…Tilt holding position Dha…horizontal direction Du... one side Dl...the other side S97...Main liquid level sensor (liquid level detection unit) Lv97... Level (designated location)

Claims

1. A tank holding unit that holds a tank for storing ink used for printing images in an inclined position in which the bottom surface of the tank slopes downward from one horizontal side to the other, A stirring unit having a shaft and a stirring member attached to the lower end of the shaft, The upper surface of the tank includes a stirring unit holding section that holds the stirring unit, in which the stirring member and the shaft are inserted into the interior of the tank through an insertion hole that opens on one side from the center of the tank, A liquid supply pipe is inserted into the tank from another inlet that opens on the upper surface of the tank on the other side from the center of the tank, Equipped with, The stirring unit stirs the ink by rotating the stirring member that is immersed in the ink in the tank. The stirring unit holding portion holds the stirring unit such that the shaft is tilted in an inclined direction from one side to the other as it moves from the top to the bottom. Printing device.

2. The liquid supply piping has a lower end with a suction port, and the ink in the tank can be drawn out through the suction port. The suction port is located on the other side of the center of the tank and below the stirring member that rotates to agitate the ink. The printing apparatus according to claim 1.

3. A liquid level detection unit that detects the presence or absence of ink in the tank at a predetermined position above the stirring member, A liquid supply pump is attached to the liquid supply piping and performs an ink supply operation in which it drives the ink in the liquid supply piping to draw the ink in the tank into the suction port and supply the ink from the tank to the outside of the tank, Control unit and Furthermore, The control unit, A liquid level detection unit that acquires the detection result of the liquid level detection unit, When the detection result obtained by the liquid level detection unit indicates that there is no ink at the predetermined position, the stirring unit control unit controls the stirring unit so that the stirring member stops rotating, When the detection result obtained by the detection liquid level acquisition unit indicates that there is no ink at the predetermined position, the liquid pump control unit controls the liquid pump so that the liquid pump performs the ink supply operation, Having, The printing apparatus according to claim 2.

4. The tank holding section is A horizontally positioned rotating shaft, A holding frame is attached to the rotating shaft so as to be rotatable in the rotational direction about the rotating shaft and holds the tank, A drive unit that drives the holding frame in the rotational direction, It has, The holding frame is rotatable around the rotation axis between a horizontal holding position in which the tank is held in a horizontal position where the bottom surface of the tank is horizontal, and an inclined holding position in which the tank is held in an inclined position. The drive unit supports the holding frame in the horizontal holding position by applying a driving force to the holding frame. When the drive unit releases the driving force, the holding frame that holds the tank rotates from the horizontal holding position to the inclined holding position due to gravity. The printing apparatus according to claim 1.

5. The drive unit is an air cylinder that generates the driving force by supplying air. The printing apparatus according to claim 4.

6. The stirring unit holding section is A pulley provided above the aforementioned stirring unit, A belt stretched over the pulley and having one end to which the stirring unit is attached, A counterweight attached to the other end of the aforementioned belt, A linear guide unit that guides the movement of the stirring unit in the aforementioned inclined direction, Having, The printing apparatus according to claim 1.

7. The printing apparatus according to claim 1, further comprising a vortex generation suppression plate integrally attached to the liquid supply piping to suppress the generation of ink vortices caused by stirring by the stirring member.

8. The stirring member is a stirring blade that expands due to the centrifugal force generated as it rotates. The printing apparatus according to claim 1.

9. The aforementioned ink is white ink. The printing apparatus according to claim 1.

10. A process of stirring the ink in a tank that stores ink used for printing images by rotating the stirring member of a stirring unit having a stirring member immersed in the ink in the tank and a shaft to which the stirring member is attached at its lower end, The process involves transferring the ink from the tank to the outside of the tank by sucking the ink from the tank through a liquid supply pipe inserted into the tank, Equipped with, The tank is held by the tank holder in an inclined position such that the bottom surface of the tank slopes downward from one side to the other in the horizontal direction. The stirring member of the stirring unit is inserted into the tank through an insertion hole that opens on one side of the center of the tank on the upper surface of the tank. The liquid supply piping is inserted into the tank from another inlet that opens on the upper surface of the tank, on the other side from the center of the tank. The stirring unit is held by the stirring unit holder such that the shaft is tilted in an inclined direction from one side to the other as it moves from the top to the bottom. Method of stirring ink.

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