Printing apparatus and ink supply method

Abstract

To prevent a large amount of ink from remaining in a main tank while it cannot be stirred.SOLUTION: A positional relationship between a low level Lml (predetermined position) provided corresponding to a stirring blade 873 (first stirring member) for stirring ink in a main tank 97, and a liquid level of the ink in the main tank 97 is detected (step S102). If the liquid level of the ink in the main tank 97 is detected to be lower than the low level Lml (if YES in step S102), the ink is sent from the main tank 97 to a buffer tank 95 (steps S106-S108).SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] This invention relates to a technique for supplying ink to a discharge head that discharges ink from a nozzle.

Background Art

[0002] Patent Document 1 describes a printing apparatus including an intermediate tank that stores ink supplied to a discharge head and a main tank that stores ink supplied to the intermediate tank. In this printing apparatus, when the ink in the intermediate tank decreases as ink is discharged from the discharge head, ink is supplied from the main tank to the intermediate 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 the printing apparatus as described above, the pigment contained in the ink stored in the main tank may settle. Such pigment sedimentation is particularly prominent, for example, in white ink containing titanium oxide as a pigment. Therefore, it is possible to take measures such as stirring the ink with a stirring member disposed in the main tank. However, as ink is supplied from the main tank to the intermediate tank as the ink in the intermediate tank decreases, the liquid level of the ink in the main tank drops below the position where it can be stirred by the stirring member. As a result, a large amount of ink that cannot be stirred by the stirring member may remain in the main tank.

[0005] This invention has been made in view of the above problems, and an object thereof is to suppress a large amount of ink from remaining unstirred in the main tank.

Means for Solving the Problem

[0006] The printing apparatus according to the present invention includes a discharge head that discharges ink from nozzles, a buffer tank that stores ink supplied to the discharge head, a main tank that stores ink supplied to the buffer tank, a liquid feeding unit that sends ink from the main tank to the buffer tank, a first stirring unit that has a first stirring member disposed in the main tank and stirs the ink stored in the main tank by rotating the first stirring member, a liquid level of the ink in the main tank, a first detection unit that detects a positional relationship between the liquid level of the ink in the main tank and a predetermined position provided corresponding to the first stirring member, and a control unit that controls the liquid feeding unit to execute a first liquid feeding operation of sending ink from the main tank to the buffer tank when the first detection unit detects that the liquid level of the ink in the main tank is lower than the predetermined position.

[0007] The ink supply method according to the present invention includes a step of detecting a positional relationship between a liquid level of ink in a main tank connected to a buffer tank that stores ink supplied to a discharge head that discharges ink from nozzles and a predetermined position provided corresponding to a first stirring member that stirs the ink in the main tank, and a step of sending ink from the main tank to the buffer tank when it is detected that the liquid level of the ink in the main tank is lower than the predetermined position.

[0008] In the present invention (printing apparatus, ink supply method) configured as described above, the positional relationship between the predetermined position provided corresponding to the first stirring member that stirs the ink in the main tank and the liquid level of the ink in the main tank is detected. Then, when it is detected that the liquid level of the ink in the main tank is lower than the predetermined position, ink is sent from the main tank to the buffer tank (first liquid feeding operation). As a result, it is possible to suppress a large amount of ink from remaining in the main tank without being stirred.

[0009] Further, it is provided with a second detection unit that detects the positional relationship between the liquid level of the ink stored in the buffer tank and the normal liquid level range provided for the buffer tank. When the second detection unit detects that the liquid level of the ink in the buffer tank is lower than the lower end of the normal liquid level range and the first detection unit detects that the liquid level of the ink in the main tank is lower than a predetermined position, the control unit may control the liquid feeding unit so as to execute a first liquid feeding operation. In such a configuration, when the liquid level of the ink in the buffer tank decreases below the lower end of the normal liquid level range, the buffer tank can be replenished with ink by the first liquid feeding operation.

[0010] Further, when the second detection unit detects that the liquid level of the ink in the buffer tank is lower than the lower end of the normal liquid level range and the first detection unit detects that the liquid level of the ink in the main tank is at or above a predetermined position, the control unit may control the liquid feeding unit so as to execute a second liquid feeding operation of feeding ink from the main tank to the buffer tank by the liquid feeding unit. In such a configuration, when the liquid level of the ink in the buffer tank decreases below the lower end of the normal liquid level range, the buffer tank can be replenished with ink by the second liquid feeding operation.

[0011] Further, in the second liquid feeding operation, the printing apparatus may be configured to feed ink from the main tank to the buffer tank until the liquid level of the ink in the buffer tank reaches the upper end of the normal liquid level range. In such a configuration, by executing the second liquid feeding operation, the liquid level of the ink in the buffer tank that has decreased below the lower end of the normal liquid level range can be raised to the upper end of the normal liquid level range.

[0012] Further, in the first liquid feeding operation, the printing apparatus may be configured to feed ink from the main tank to the buffer tank until the liquid level of the ink in the buffer tank reaches an upper limit position provided at a position higher than the upper end of the normal liquid level range. In such a configuration, a large amount of ink that has become impossible to be stirred in the main tank can be fed from the main tank to the buffer tank.

[0013] Further, the printing apparatus may be configured to further include a second stirring unit that stirs the ink in the buffer tank. In such a configuration, the ink that has become unable to be stirred in the main tank can be sent to the buffer tank and stirred by the second stirring unit.

[0014] Further, the second stirring unit has a second stirring member disposed in the buffer tank, and stirs the ink stored in the buffer tank by rotating the second stirring member. The printing apparatus may be configured such that the second stirring member is disposed below the normal liquid level range. In such a configuration, the ink in the buffer tank is stirred by the second stirring member disposed below the normal liquid level range. Therefore, the ink that has become unable to be stirred in the main tank can be sent to the buffer tank and surely stirred by the second stirring unit.

[0015] Further, the first stirring member may be stirring blades that spread by the centrifugal force generated as it rotates, and the printing apparatus may be configured such that the predetermined position is provided corresponding to the position of the stirring blades spread by the centrifugal force. When stirring is performed using such stirring blades, the lower end of the rotating stirring blades rises from the lower end of the stationary stirring blades. Therefore, in the main tank, the ink accumulated at the bottom below the lower end of the rotating stirring blades cannot be stirred. On the other hand, by providing the above-described predetermined position corresponding to the position of the stirring blades spread by the centrifugal force and configuring to execute the first liquid feeding operation, it is possible to suppress a large amount of ink from remaining unstirred at the bottom of the main tank.

[0016] Note that various specific positional relationships between the stirring blades and the predetermined position can be assumed. Therefore, the predetermined position may be provided at the same height as the lower end of the stirring blades spread by the centrifugal force, may be provided at the same height as the upper end of the stirring blades spread by the centrifugal force, or may be provided at a position higher than the stirring blades spread by the centrifugal force.

[0017] Also, when the ink is white ink, the present invention may be applied. By doing so, it becomes possible to suppress the precipitation of the pigment of the white ink by leaving a large amount of white ink in the main tank without being stirred.

Advantages of the Invention

[0018] As described above, according to the present invention, it becomes possible to suppress a large amount of ink from remaining in the main tank without being stirred.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

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Figure 9

Figure 10A

Figure 10B

Figure 11A

Figure 11B

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 feeding roll 11 to a winding 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. 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.

[0021] 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 feeding roll 11 to the winding 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.

[0022] 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 feeding roll 11 to the winding 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.

[0023] The printed medium M carried out from the carry-out port 312 of the printing apparatus 3 passes through the two upper air supply units 61u in the horizontal direction X, and then is folded back by a pair of rollers 62 toward the two middle air supply units 61m. Subsequently, after the printed medium M passes through the two middle air supply units 61m in the horizontal direction X, it is folded back by a pair of air turn bars 63 toward the two lower air supply units 61l. Further, after the printed medium M passes through the two lower air supply units 61l in the horizontal direction X, it is carried out to the outside of the drying apparatus 6.

[0024] The upper air supply unit 61u has two air supply chambers 64 arranged so as to sandwich the printed medium M passing in the horizontal direction X from the vertical direction Z. Each air supply chamber 64 has a plurality of nozzles 65 arranged in the horizontal direction X, and hot air (a gas at 60 degrees or more) is jetted from each nozzle 65 onto the printed medium M. Thus, while the printed medium M passes between the two air supply chambers 64 provided above and below, it is dried by the hot air jetted from the nozzles 65 of these air supply chambers 64. Also, each of the middle air supply unit 61m and the lower air supply unit 61l similarly has two air supply chambers 64 that sandwich the printed medium M from the vertical direction Z, like the upper air supply unit 61u.

[0025] Incidentally, the specific configuration of the upper air supply unit 61u is not limited to this example. For example, instead of the lower air supply chamber 64 among the upper and lower air supply chambers 64 of the upper air supply unit 61u, a plurality of rollers arranged in the horizontal direction X may be provided. In such a configuration, while the back surface M2 of the printed medium M is supported from below by the plurality of rollers, hot air can be jetted from the upper air supply chamber 64 onto the front surface M1 of the printed medium M.

[0026] FIG. 2 is a front view schematically showing a printing apparatus included in the printing system of FIG. 1. In FIG. 2, one side X1 and the other side X2 in the horizontal direction X are appropriately shown. Here, one side X1 is the side facing from the printing apparatus 3 toward the drying apparatus 6, and the other side X2 is the opposite side of the one side X1. The printing apparatus 3 includes a housing 31, a color printing unit 32 disposed in the housing 31, a white printing unit 33 disposed above the color printing unit 32 in the housing 31, and a conveyance unit 4 that conveys a printing medium M by a plurality of rollers disposed in the housing 31.

[0027] The color printing unit 32 has a plurality (six) of head units 321 arranged in the traveling direction of the printing medium M (the direction from the other side X2 toward the one side X1) above the printing medium M conveyed by the conveyance unit 4. The plurality of head units 321 each have nozzles facing the surface M1 of the printing medium M passing therebelow from above, and eject color inks of different colors from the nozzles by an inkjet method. Here, the color ink means an ink other than white, and includes inks such as cyan, magenta, yellow, and black. Thus, the plurality of head units 321 of the color printing unit 32 print a color image on the surface M1 of the printing medium M by ejecting color ink from above onto the surface M1 of the printing medium M passing therebelow.

[0028] Further, the white printing unit 33 has a single head unit 331 disposed above the printing medium M conveyed by the conveyance unit 4. The head unit 331 has a nozzle facing the surface M1 of the printing medium M passing therebelow from above, and ejects white ink from the nozzle by an inkjet method. Thus, 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 therebelow.

[0029] An inlet 311 is open in the side wall on the other side X2 of the housing 31, while an outlet 312 is open in the side wall on the one side X1 of the housing 31. Then, the conveyance unit 4 conveys the printing medium M from the inlet 311 to the outlet 312 while passing through the color printing unit 32 and the white printing unit 33 described above.

[0030] This conveying unit 4 includes a loading unit 41 provided below the color printing unit 32, a lifting conveying unit 42 provided on one side X1 of the color printing unit 32, an upward conveying unit 43 provided above the color printing unit 32, and a downward conveying unit 44 provided on the other side X2 of the color printing unit 32. The loading unit 41 conveys the printing medium M loaded from the loading port 311 to one side X1 by the roller 411. The lifting conveying unit 42 conveys the printing medium M conveyed by the loading unit 41 upward by the roller 421. The upward conveying unit 43 conveys the printing medium M conveyed by the lifting conveying unit 42 to the other side X2 by the roller 431. The downward conveying unit 44 conveys the printing medium M conveyed by the upward conveying unit 43 downward by the roller 441.

[0031] Furthermore, the conveying unit 4 has a color conveying 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 downward conveying unit 44 enters the color conveying unit 45. This color conveying unit 45 has a plurality of rollers 451 arranged from the other side X2 to one side X1, and each roller 451 contacts the back surface M2 of the printing medium M from below. Thus, the surface M1 of the printing medium M supported by the color conveying unit 45 faces upward, and each head unit 321 of the color printing unit 32 discharges color ink while facing this surface M1 from above.

[0032] Also, the conveying unit 4 has rollers 461, 462, and 463 arranged between the color conveying unit 45 and the downward conveying unit 44 in the advancing direction of the printing medium M. The roller 461 is a driving roller that drives the printing medium M. The rollers 462 and 463 are driven rollers that rotate following the printing medium M.

[0033] Furthermore, the conveying unit 4 has a reversing and conveying unit 47 that turns the printing medium M conveyed from the color conveying unit 45 to one side X1 upside down twice vertically. This reversing and conveying unit 47 has a plurality of rollers 471 to 477 including a driving roller 471, and these rollers 471 to 477 contact the back surface M2 of the printing medium M while turning the printing medium M upside down twice vertically. That is, the reversing and conveying unit 47 conveys the printing medium M conveyed from the color conveying 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 conveys it, thereby turning the front surface M1 and the back surface M2 of the printing medium M upside down. Subsequently, the reversing and conveying unit 47 conveys the printing medium M from one side X1 to the other side X2 by a plurality of rollers 473, and then conveys the printing medium M upward by the rollers 474 to 476. Furthermore, the reversing and conveying unit 47 changes the traveling direction of the printing medium M to one side X1 by the roller 476, thereby turning the front surface M1 and the back surface M2 of the printing medium M upside down again, and conveys the printing medium M from the other side X2 to one side X1 by the roller 477.

[0034] In addition, the conveying unit 4 has a white conveying unit 48 that supports the printing medium M facing the white printing unit 33 from below, and the printing medium M turned upside down twice vertically by the reversing and conveying unit 47 enters the white conveying unit 48. This white conveying 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 conveying unit 48 faces upward, and the head unit 331 of the white printing unit 33 discharges white ink while facing this front surface M1 from above.

[0035] In addition, the conveying unit 4 has a discharging unit 49 provided above the upper conveying unit 43. The discharging unit 49 has a plurality of rollers 491 arranged from the other side X2 to one side X1 in the horizontal direction X. This discharging unit 49 conveys the printing medium M conveyed by the white conveying unit 48 to one side X1 by the plurality of rollers 491, and discharges it from the discharge port 312 of the housing 31 to the drying device 6.

[0036] As described above, the color printing unit 32 and the white printing unit 33 of the printing apparatus 3 have head units 321 and 331. Subsequently, the discharge heads H included in the head units 321 and 331 and the ink supply mechanism that supplies ink to the discharge heads H will be described. 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, the configuration related to the head unit 331 that discharges white ink will be described.

[0037] FIG. 3 is a diagram schematically showing the bottom surface of the discharge head included in the head unit, and FIG. 4 is a diagram schematically showing the configuration of the discharge head and the ink supply mechanism that supplies ink to the discharge head. In FIG. 3, in addition to the horizontal direction X and the vertical direction Z, a horizontal direction Y orthogonal to the horizontal direction X is shown. As shown in FIG. 3, in the head unit 331, a plurality of discharge heads H that discharge the same color of ink (white ink) are arranged in a row in the horizontal direction Y, and each discharge head H has a rectangular shape in a bottom view. Note that the arrangement mode of the plurality of discharge heads H is not limited to the example of FIG. 3, and the plurality of discharge heads H may be arranged in a staggered pattern.

[0038] As shown in FIG. 4, the ejection head H has a housing Ha. On the bottom surface of the housing Ha, a plurality of nozzles Hn are arranged in a staggered pattern in the horizontal direction Y and open. Inside the housing Ha, a plurality of cavities Hb respectively communicating with the plurality of nozzles Hn and an ink supply chamber Hc communicating with the plurality of cavities Hb are provided, and the ink supplied from the ink supply chamber Hc is stored in the cavities Hb. Further, a piezoelectric element D is provided in each cavity Hb, and by displacing the piezoelectric element D in response to a drive signal (electrical signal), a pressure fluctuation is imparted to the ink in the cavity Hb. Due to this pressure fluctuation, the ink is pushed out from the cavity Hb, and the ink is ejected from the nozzle Hn communicating with the cavity Hb. Also, on the upper part of the ejection head H, an ink inlet Hd and an ink outlet He are respectively open, and the ink flows into the ink supply chamber Hc from the ink supply mechanism 9a described later through the ink inlet Hd, and flows out from the ink supply chamber Hc through the ink outlet He toward the ink recovery mechanism 9b described later.

[0039] Next, the ink supply, recovery, and circulation mechanism 9 for supplying, recovering, and circulating the ink will be described. The ink supply, recovery, and circulation mechanism 9 includes an ink supply mechanism 9a for supplying ink to the ejection head H, an ink recovery mechanism 9b for recovering ink from the ejection head H, and an ink return mechanism 9c for returning the recovered ink to the ink supply mechanism 9a again. The ink supply mechanism 9a includes an ink supply unit 91 for supplying ink toward the ejection head H and a pressure generation unit 93 for generating a supply pressure to be applied to the ink supply unit 91. The ink supply unit 91 includes a supply tank 91a for storing the ink to be supplied to the ejection head H and a supply pipe 91b for sending the ink supplied from the supply tank 91a to the ejection head H. The ink recovery mechanism 9b includes an ink recovery unit 92 for recovering ink from the ejection head H and a pressure generation unit 94 for generating a pressure to be applied to the ink recovery unit 92. The ink recovery unit 92 includes a recovery tank 92a for storing the ink recovered from the ejection head H and a recovery pipe 92b for sending the ink recovered from the ejection head H to the recovery tank 92a.

[0040] Each of the supply tank 91a and the recovery tank 92a is disposed above the discharge head H. The ink return mechanism 9c includes a return pipe 932 that fluidly connects the recovery tank 92a and the supply tank 91a, a circulation pump 90 interposed at a position in the middle of the return pipe 932, and a degassing filter 901 interposed at a position 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 91. Such an ink supply mechanism 9 can send ink along a first path Ca from the recovery tank 92 to the supply tank 91 by the circulation pump 90.

[0041] Furthermore, the ink supply mechanism 9a includes a supply-side pressure generation unit 93 (hereinafter, appropriately referred to as the "pressure generation unit 93") that applies a pressure P1 (negative pressure) to the supply tank 91a. The pressure generation unit 93 includes a pressure tank 931, an exhaust pump 932 that evacuates the pressure tank 931 to generate the 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 having one end communicably connected to the other end of the tube 933 and disposed so that the other end faces the atmosphere in the supply tank 91a to transmit the pressure generated in the pressure tank 931 to the supply tank 91a. Then, the pressure P1 generated in the pressure tank 931 by the exhaust pump 932 is applied to the supply tank 91a via the tube 933 and the pressure transmission pipe 964.

[0042] On the other hand, in the supply tank 91a, gas (air) accumulates above the liquid level of the ink. 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 generation unit 93 applies the 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 generation unit 94 (hereinafter, appropriately referred to as the "pressure generation unit 94") that applies a pressure P2 (negative pressure) to the recovery tank 92b. 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 the tube 973 and the other end arranged to face the atmosphere in the recovery tank 92 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.

[0044] On the other hand, in the recovery tank 92a, gas (air) is accumulated above the ink liquid level. 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.

[0045] In the state shown in FIG. 4, the pressure P2 applied by the pressure generation unit 94 to the recovery tank 92a is lower than the pressure P1 applied by the pressure generation unit 93 to the supply tank 91a. Due to the difference between this pressure P2 and the 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. Further, 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, ink circulates in a circulation path (the second path Cb + the first path Ca) that returns to the supply tank 91a after reaching the recovery tank 92a from the supply tank 91a via the discharge head H.

[0046] The ink supply, recovery, and circulation mechanism 9 includes a buffer tank 95, and the buffer tank 95 can store a larger amount of ink than the supply tank 91a and the recovery tank 92a. Also, the ink supply, recovery, and circulation mechanism 9 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. That is, 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.

[0047] Furthermore, the ink supply, recovery, and 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 can recover ink from the supply tank 91a to the buffer tank 95, and the supply pump 962 can supply ink from the buffer tank 95 to the recovery tank 92a.

[0048] In the ink supply, recovery, and circulation mechanism 9 configured as described above, by operating the recovery pump 961 and the supply pump 962, ink flows along a third path Cc from the supply tank 91a through the buffer tank 95 to the recovery tank 92a. Also, the ink that has flowed 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, ink circulates in a circulation path (the third path Cc + the first path Ca) that returns to the supply tank 91a after reaching the recovery tank 92a through the buffer tank 95 from 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 described with reference to FIG. 5. FIG. 5 is a diagram schematically showing the mechanism for supplying ink to the buffer tank. As shown in FIG. 5, the ink supply, recovery, and circulation mechanism 9 includes a main tank 97 for storing ink. The main tank 97 has a volume capable of storing a larger amount of ink than the buffer tank 95, and the volume of the main tank 97 is, for example, twice or more the volume of the buffer tank 95.

[0050] Also, the ink supply, recovery, and circulation mechanism 9 includes a liquid feeding unit 98 for feeding ink from the main tank 97 to the buffer tank 95. This liquid feeding unit 98 has a pipe 981 connecting the main tank 97 and the buffer tank 95, and the main tank 97 and the buffer tank 95 communicate with each other via the pipe 981. Further, the liquid feeding unit 98 has a liquid feeding pump 982 attached to the pipe 981 and a solenoid valve 983 attached to the pipe 981 between the liquid feeding pump 982 and the buffer tank 95. This solenoid valve 983 enables the flow of ink between the liquid feeding pump 982 and the buffer tank 95 when opened, and blocks the flow of ink between the liquid feeding pump 982 and the buffer tank 95 when closed. In such a liquid feeding unit 98, with the solenoid valve 983 open, the liquid feeding pump 982 feeds ink from the main tank 97 to the buffer tank 95.

[0051] Also, the ink supply, recovery, and circulation mechanism 9 includes a stirring unit 85 for stirring the ink stored in the buffer tank 95 and a stirring unit 87 for stirring the ink stored in the main tank 97. Among the stirring units 85 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.

[0052] The stirring unit 85 includes a shaft 851 extending parallel to the vertical direction Z, a stirring motor 852 for rotating the shaft 851, and a stirring blade 853 attached to the lower end of the shaft 851. The stirring motor 852 is disposed outside the buffer tank 95. On the other hand, the stirring blade 853 is disposed inside the buffer tank 95 and is immersed in the ink stored in the buffer tank 95. When the stirring motor 852 rotates the shaft 851, the stirring blade 853 rotates about a rotation axis parallel to the vertical direction Z. The ink is stirred by the rotating stirring blade 853 in this way.

[0053] The stirring unit 87 includes a shaft 871 extending parallel to the vertical direction Z, a stirring motor 872 for rotating the shaft 871, and a stirring blade 873 attached to the lower end of the shaft 871. The stirring motor 872 is disposed outside the main tank 97. On the other hand, the stirring blade 873 is disposed 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 about a rotation axis parallel to the vertical direction Z. The ink is stirred by the rotating stirring blade 873 in this way.

[0054] Note that the stirring blade 873 is a centrifugal type stirring blade that opens by centrifugal force. In contrast, an insertion port 971 into which the stirring blade 873 can be inserted is provided on the upper surface of the main tank 97. That is, the stirring blade 873 in the closed state can be inserted into the main tank 97 through the insertion port 971 of the main tank 97, so that the stirring blade 873 can be disposed inside the main tank 97. When the stirring motor 872 rotates the stirring blade 873, the stirring blade 873 opens by centrifugal force and stirs the ink.

[0055] By stirring the ink with such stirring vanes 853 and 873, the physical properties of the ink stored in the buffer tank 95 and the main tank 97 can be made uniform. In particular, white ink contains a large amount of titanium oxide as a pigment for the purpose of ensuring a high hiding power. Therefore, the white ink has a low ink viscosity and a large pigment specific gravity with respect to the solvent specific gravity, so the pigment is likely to settle. When such pigment sedimentation occurs, problems such as insufficient hiding power or deterioration of the discharge performance of the white ink from the discharge head H may occur. On the other hand, by stirring the white ink with the stirring vanes 853 and 873, sedimentation of the pigment can be suppressed.

[0056] The printing apparatus 3 including the above-described ink supply mechanism 9 controls the liquid feeding from the main tank 97 to the buffer tank 95 based on the result of detecting the liquid levels of the ink stored in the buffer tank 95 and the main tank 97 by the liquid level sensors. Subsequently, the configuration and operation for controlling the liquid feeding from the main tank 97 to the buffer tank 95 will be described.

[0057] FIG. 6 is a block diagram showing an electrical configuration of the printing apparatus for executing the liquid feeding control, FIG. 7 is a diagram schematically showing a detection position of the liquid level sensor provided for the buffer tank for executing the liquid feeding control, and FIG. 8 is a diagram schematically showing a detection position of the liquid level sensor provided for the main tank for executing the liquid feeding control.

[0058] As shown in FIG. 6, the printing apparatus 3 includes a control unit 300 that comprehensively controls the entire apparatus. This control unit 300 is a processor composed of, for example, a CPU (Central Processing Unit) or the like. Further, the printing apparatus 3 includes a UI (User Interface) 301 having input devices such as a keyboard and a mouse and output devices such as a display. The control unit 300 executes control in response to an input operation of an operator on the input device of the UI 301, and shows information to the operator using the output device of the UI 301. Note that, for example, the input device and the output device of the UI 301 may be integrally configured by a touch panel display or the like. Furthermore, the control unit 300 controls the above-described liquid feed pump 982, solenoid valve 983, agitation motor 852, and agitation motor 872. The control unit 300 receives detection signals of a plurality of liquid level sensors Sb1, Sbh, Sbt that detect the liquid level of the ink stored in the buffer tank 95 described later, and a detection signal of a liquid level sensor Sml that detects the liquid level of the ink stored in the main tank 97, and based on the received results, controls the liquid feed pump 982 and the solenoid valve 983 to adjust the liquid feed of the ink from the main tank 97 to the buffer tank 95.

[0059] As shown in FIG. 6, the printing apparatus 3 includes a plurality of liquid level sensors Sbl, Sbh, Sbt that detect the ink stored in the buffer tank 95. On the other hand, as shown in FIG. 7, for the buffer tank 95, a low level Lbl, a high level Lbh higher than the low level Lbl, and a limit level Lbt higher than the high level Lbh are provided. The liquid level sensor Sbl detects the presence or absence of ink at the low level Lbl, the liquid level sensor Sbh detects the presence or absence of ink at the high level Lbh, and the liquid level sensor Sbt detects the presence or absence of ink at the limit level Lbt. As such liquid level sensors Sbl, Sbh, Sbt, various level sensors such as a capacitance sensor or a float sensor can be used, and the liquid level sensors Sbl, Sbh, Sbt can be arranged inside or outside the buffer tank 95 according to the type of sensor used.

[0060] In such a configuration, when the liquid level sensor Sbl outputs an off signal without detecting ink, the liquid level of the ink in the buffer tank 95 is below the low level Lbl. When the liquid level sensor Sbl detects ink and outputs an on signal while the liquid level sensor Sbh outputs an off signal without detecting ink, the liquid level of the ink in the buffer tank 95 is equal to or higher than the low level Lbl and lower than the high level Lbh. When the liquid level sensor Sbh detects ink and outputs an on signal while the liquid level sensor Sbt outputs an off signal without detecting ink, the liquid level of the ink in the buffer tank 95 is equal to or higher than the high level Lbh and lower than the limit level Lbt. When the liquid level sensor Sbt detects ink and outputs an on signal, the liquid level of the ink in the buffer tank 95 is equal to or higher than the limit level Lbt.

[0061] Based on the detection results of the liquid level sensor Sbl and the liquid level sensor Sbh, the control unit 300 controls the liquid feeding by the liquid feeding pump 982 to adjust the liquid level of the ink in the buffer tank 95 within the normal liquid level range R from the low level Lbl to the high level Lbh. On the other hand, the stirring blade 853 is arranged below the normal liquid level range R (in other words, below the low level Lbl). Therefore, the stirring blade 853 is located below the liquid level adjusted to the normal liquid level range R and is immersed in the ink in the buffer tank 95.

[0062] As shown in FIG. 6, the printing apparatus 3 includes a liquid level sensor Sml that detects the ink stored in the main tank 97. On the other hand, as shown in FIG. 8, a low level Lml is provided for the main tank 97, and the liquid level sensor Sml detects the presence or absence of ink at the low level Lml. As such a liquid level sensor Sml, various level sensors such as a capacitance sensor or a float sensor can be used, and depending on the type of sensor used, the liquid level sensor Sml can be arranged inside or outside the main tank 97. Note that the liquid level sensor Sml for the main tank 97 is provided only in the ink supply / recovery / circulation mechanism 9 that supplies white ink, and is not provided in the ink supply / recovery / circulation mechanism 9 that supplies color ink.

[0063] As shown in FIG. 8, the low level Lml is provided corresponding to the height of the stirring blade 873 disposed in the main tank 97. This stirring blade 873 has a plurality of rotating blades 873a that rotate about a rotating shaft 871a provided at the lower end of the shaft 871. As shown in the "stationary state" column of FIG. 8, when the stirring blade 873 is stationary, the rotating blade 873a hangs down from the rotating shaft 871a by gravity, and the stirring blade 873 closes. On the other hand, as shown in the "rotating state" column of FIG. 8, when the stirring blade 873 rotates, the rotating blade 873a rotates upward about the rotating shaft 871a under the action of centrifugal force, and the stirring blade 873 opens. And the low level Lml is provided at the same height as the lower end of the stirring blade 873 that opens by rotating.

[0064] In such a configuration, when the liquid level sensor Sml outputs an off signal without detecting the ink, the ink liquid level in the main tank 97 is lower than the low level Lml. On the other hand, when the liquid level sensor Sml detects the ink and outputs an on signal, the ink liquid level in the main tank 97 is equal to or higher than the low level Lml.

[0065] FIG. 9 is a flowchart showing an example of ink feeding control executed in the printing apparatus, and FIGS. 10A and 10B are diagrams schematically showing the operations executed in the ink feeding control of FIG. 9. The ink feeding control of FIG. 9 controls the feeding of white ink from the main tank 97 to the buffer tank 95, and is executed by the control unit 300. Note that the ink feeding control of FIG. 9 is not applied to the feeding of color ink. Also, at the start of the ink feeding control of FIG. 9, the stirring blade 853 rotates to stir the ink in the buffer tank 95, and the stirring blade 873 rotates to stir the ink in the main tank 97. Also, the solenoid valve 983 is open and the liquid feeding pump 982 is stopped.

[0066] In step S101, based on the output of the liquid level sensor Sbl provided in the buffer tank 95, it is confirmed whether the liquid level of the ink in the buffer tank 95 is lower than the low level Lbl. As shown in the column of "S101" in FIG. 10A, when the liquid level of the ink in the buffer tank 95 is lower than the low level Lbl (when "YES" in step S101), the process proceeds to step S102.

[0067] In step S102, based on the output of the liquid level sensor Sml provided in the main tank 97, it is confirmed whether the liquid level of the ink in the main tank 97 is lower than the low level Lml. As shown in the column of "S102" in FIG. 10A, when the liquid level of the ink in the main tank 97 is equal to or higher than the low level Lml (when "NO" in step S102), the liquid feeding operations in steps S103 to S105 are executed, and as shown in the columns of "S103" and "S105" in FIG. 10A, the liquid level of the ink in the buffer tank 95 rises.

[0068] In step S103, the liquid feed pump 982 starts feeding the ink from the main tank 97 to the buffer tank 95. As a result, while the liquid level of the ink in the main tank 97 decreases, the liquid level of the ink in the buffer tank 95 rises. Then, when it is confirmed based on the output of the liquid level sensor Sbh that the liquid level of the ink in the buffer tank 95 has exceeded the low level Lbl and reached the high level Lbh (when "YES" in step S104), the liquid feeding by the liquid feed pump 982 is stopped (step S105). Then, the process returns to step S101.

[0069] On the other hand, as shown in the column of "S102" in FIG. 10B, when the liquid level of the ink in the main tank 97 is lower than the low level Lml (when "YES" in step S102), the liquid feeding operations in steps S106 to S108 are executed, and as shown in the columns of "S106" and "S107" in FIG. 10B, the liquid level of the ink in the buffer tank 95 rises.

[0070] In step S106, the liquid feed pump 982 starts to feed ink from the main tank 97 to the buffer tank 95. As a result, the liquid level of the ink in the main tank 97 decreases, while the liquid level of the ink in the buffer tank 95 increases. Then, when it is confirmed based on the output of the liquid level sensor Sbt that the liquid level of the ink in the buffer tank 95 has reached the limit level Lbt exceeding the low level Lbl and the high level Lbh (”YES” in step S107), the liquid feed by the liquid feed pump 982 is stopped (step S108).

[0071] The liquid feed operation in steps S106 to S108 feeds a larger amount of ink from the main tank 97 to the buffer tank 95 than the liquid feed operation in steps S103 to S105. By executing the liquid feed operation in steps S106 to S108, leaving only a small amount of ink within a predetermined range from the bottom in the main tank 97 (for example, ink about 1 to 5% of the volume of the main tank 97), the other ink is sent from the main tank 97 to the buffer tank 95. As a result, the remaining amount of ink in the main tank 97 becomes substantially zero. Therefore, the control unit 300 notifies the operator of a remaining amount warning indicating that the ink in the main tank 97 has run out, using the UI301 (step S109).

[0072] In the above embodiment, the positional relationship between the low level Lml (predetermined position) provided corresponding to the stirring blade 873 (first stirring member) that stirs the ink in the main tank 97 and the liquid level of the ink in the main tank 97 is detected (step S102). Then, when it is detected that the liquid level of the ink in the main tank 97 is lower than the low level Lml (”YES” in step S102), ink is sent from the main tank 97 to the buffer tank 95 (steps S106 to S108). Thereby, it is possible to suppress a large amount of ink from remaining in the main tank 97 without being stirred.

[0073] In addition, a liquid level sensor Sbl, Sbh (second detection unit) is provided to detect the positional relationship between the liquid level of the ink stored in the buffer tank 95 and the normal liquid level range R provided for the buffer tank 95. When the liquid level sensor Sbl detects that the liquid level of the ink in the buffer tank 95 is lower than the lower end (low level Lbl) of the normal liquid level range R (YES in step S101), and the liquid level sensor Sml (first detection unit) detects that the liquid level of the ink in the main tank 97 is lower than the low level Lml (YES in step S102), the control unit 300 executes the liquid feeding operation (first liquid feeding operation) in steps S106 to S108. In such a configuration, when the liquid level of the ink in the buffer tank 95 decreases below the lower end (low level Lbl) of the normal liquid level range R, the buffer tank 95 can be replenished with ink by the liquid feeding operation in steps S106 to S108.

[0074] In addition, when the liquid level sensor Sbl detects that the liquid level of the ink in the buffer tank 95 is lower than the lower end (low level Lbl) of the normal liquid level range R (YES in step S101), and the liquid level sensor Sml detects that the liquid level of the ink in the main tank 97 is equal to or higher than the low level Lml (NO in step S103), the control unit 300 executes the liquid feeding operation (second liquid feeding operation) in steps S103 to S105. In such a configuration, when the liquid level of the ink in the buffer tank 95 decreases below the lower end (low level Lbl) of the normal liquid level range R, the buffer tank 95 can be replenished with ink by the liquid feeding operation in steps S103 to S105.

[0075] In addition, in the liquid feeding operation in steps S103 to S105, ink is sent from the main tank 97 to the buffer tank 95 until the liquid level of the ink in the buffer tank 95 reaches the upper end (high level Lbh) of the normal liquid level range R. In such a configuration, by executing the liquid feeding operation in steps S103 to S105, the liquid level of the ink in the buffer tank 95 that has decreased below the lower end (low level Lbl) of the normal liquid level range R can be raised to the upper end (high level Lbh) of the normal liquid level range R.

[0076] Also, in the ink feeding operation of steps S106 to S108, ink is sent from the main tank 97 to the buffer tank 95 until the liquid level of the ink in the buffer tank 95 reaches the limit level Lbt (upper limit position) provided at a position higher than the upper end (high level Lbh) of the normal liquid level range R. With such a configuration, a large amount of ink that has become unable to be stirred in the main tank 97 can be sent from the main tank 97 to the buffer tank 95.

[0077] In addition, a stirring unit 85 (second stirring section) for stirring the ink in the buffer tank 95 is provided. With such a configuration, ink that has become unable to be stirred in the main tank 97 can be sent to the buffer tank 95 and stirred by the stirring unit 85.

[0078] Further, the stirring unit 85 (second stirring section) has stirring blades 853 (second stirring members) disposed in the buffer tank 95, and stirs the ink stored in the buffer tank 95 by rotating the stirring blades 853. Moreover, the stirring blades 853 are disposed below the normal liquid level range R. With such a configuration, the ink in the buffer tank 95 is stirred by the stirring blades 853 disposed below the normal liquid level range R. Therefore, ink that has become unable to be stirred in the main tank 97 can be sent to the buffer tank 95 and surely stirred by the stirring blades 853.

[0079] Further, the stirring blade 873 (first stirring member) is a centrifugal - type stirring blade that spreads due to the centrifugal force generated during rotation, and the low level Lml of the main tank 97 is provided corresponding to the position (height) of the stirring blade 873 spread by the centrifugal force. When stirring is performed using such a stirring blade 873, the lower end of the rotating stirring blade 873 rises from the lower end of the stationary stirring blade 873 (FIG. 8). Therefore, in the main tank 97, the ink accumulated at the bottom below the lower end of the rotating stirring blade 873 cannot be stirred. On the other hand, by providing the low level Lml corresponding to the position of the stirring blade 873 spread by the centrifugal force and configuring to execute the liquid - feeding operations in steps S106 to S108, it is possible to suppress a large amount of ink from remaining unstirred at the bottom of the main tank 97.

[0080] Also, the above - described liquid - feeding control is applied to the ink supply mechanism 9 that supplies white ink, which is preferable. Thereby, it becomes possible to suppress the pigment of the white ink from settling due to a large amount of white ink remaining unstirred in the main tank 97.

[0081] In the embodiment described above, the printing apparatus 3 corresponds to an example of the "printing apparatus" of the present invention, the control unit 300 corresponds to an example of the "control unit" of the present invention, the stirring unit 85 corresponds to an example of the "second stirring unit" of the present invention, the stirring blade 853 corresponds to an example of the "second stirring member" of the present invention, the stirring unit 87 corresponds to an example of the "first stirring unit" of the present invention, the stirring blade 873 corresponds to an example of the "first stirring member" and the "stirring blade" of the present invention, the buffer tank 95 corresponds to an example of the "buffer tank" of the present invention, the main tank 97 corresponds to an example of the "main tank" of the present invention, the liquid feeding pump 982 corresponds to an example of the "liquid feeding unit" of the present invention, the discharge head H corresponds to an example of the "discharge head" of the present invention, the nozzle Hn corresponds to an example of the "nozzle" of the present invention, the limit level Lbt corresponds to an example of the "upper limit position" of the present invention, the low level Lml corresponds to an example of the "predetermined position" of the present invention, the normal liquid level range R corresponds to an example of the "normal liquid level range" of the present invention, the liquid level sensors Sbl and Sbh correspond to an example of the "second detection unit" of the present invention, the liquid level sensor Sml corresponds to an example of the "first detection unit" of the present invention, steps S103 to S105 correspond to an example of the "second liquid feeding operation" of the present invention, and steps S106 to S108 correspond to an example of the "first liquid feeding operation" of the present invention.

[0082] Note that the present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit thereof. For example, the height of the low level Lml provided corresponding to the stirring blade 873 may be appropriately changed. FIGS. 11A and 11B are diagrams schematically showing a modification example of the low level provided corresponding to the stirring blade.

[0083] In the example of FIG. 11A, the low level Lml is provided at the same height as the upper end of the stirring blade 873 spread by centrifugal force, and the liquid level sensor Sml for detecting the ink in the main tank 97 detects the presence or absence of ink at this low level Lml.

[0084] In the example of FIG. 11B, a low level Lml is provided at a position higher than the stirring blade 873 spread by centrifugal force, and the liquid level sensor Sml that detects the ink in the main tank 97 detects the presence or absence of ink at this low level Lml. In the example of FIG. 11B, for example, when the liquid level of the ink in the main tank 97 is in a state where it is above the stirring blade 873 spread by centrifugal force and below the low level Lm, and the liquid feeding operation of steps S106 to S108 is executed, the liquid level of the ink in the main tank 97 drops below the stirring blade 873 spread by centrifugal force. Thus, a large amount of ink is sent from the main tank 97 to the buffer tank 95.

[0085] Also, the amount of ink remaining in the main tank 97 after the completion of the liquid feeding operation in steps S106 to S108 can be appropriately changed, and is not limited to the above 1 to 5%, and may be more than 5%. Alternatively, without leaving any ink in the main tank 97, all the ink in the main tank 97 may be sent to the buffer tank 95.

[0086] Also, along with the execution of the ink liquid feeding control in FIG. 9, the rotation of the stirring blade 853 or the stirring blade 873 may be controlled. For example, in step S102, when it is determined that the liquid level of the ink in the main tank 97 is less than the low level Lml (in the case of "YES"), the rotation of the stirring blade 873 may be stopped.

[0087] Also, in the above, the details of the control for feeding the color ink from the main tank 97 to the buffer tank 95 have not been particularly described. However, the feeding of the color ink can be executed by a flowchart that sequentially executes steps S101, S103, S104, and S105 in FIG. 9, for example. Such feeding of the color ink can be appropriately executed by the control that has been conventionally performed.

Industrial Applicability

[0088] The present invention is applicable to the entire technology of supplying ink to a discharge head that discharges ink from a nozzle.

Explanation of Reference Numerals

[0089] 3… Printing device 300… Control unit 85… Stirring unit (second stirring section) 853… Stirring blade (second stirring member) 87… Stirring unit (first stirring section) 873… Stirring blade (first stirring member) 95… Buffer tank 97… Main tank 982… Liquid feed pump (liquid feed section) H… Discharge head Hn… Nozzle Lbt… Limit level (upper limit position) Lml… Low level (predetermined position) R… Normal liquid level range Sbl… Liquid level sensor (second detection section) Sbh… Liquid level sensor (second detection section) Sml… Liquid level sensor (first detection section) S103~S105… Liquid feed operation (second liquid feed operation) S106~S108… Liquid feed operation (first liquid feed operation)

Claims

1. A discharge head that discharges ink from a nozzle, A buffer tank that stores the ink supplied to the discharge head, A main tank that stores the ink supplied to the buffer tank, A liquid feeding unit that sends ink from the main tank to the buffer tank, A first stirring unit having a first stirring member disposed in the main tank, and stirring the ink stored in the main tank by rotating the first stirring member, A first detection unit that detects the positional relationship between the liquid level of the ink in the main tank and a predetermined position provided corresponding to the first stirring member, When the first detection unit detects that the liquid level of the ink in the main tank is lower than the predetermined position, a control unit that controls the liquid feeding unit to execute a first liquid feeding operation of sending ink from the main tank to the buffer tank A printing apparatus comprising the same.

2. A second detection unit that detects the positional relationship between the liquid level of the ink stored in the buffer tank and a normal liquid level range provided for the buffer tank, The control unit, when the second detection unit detects that the liquid level of the ink in the buffer tank is lower than the lower end of the normal liquid level range and the first detection unit detects that the liquid level of the ink in the main tank is lower than the predetermined position, controls the liquid feeding unit to execute the first liquid feeding operation. The printing apparatus according to claim 1.

3. The control unit, when the second detection unit detects that the liquid level of the ink in the buffer tank is lower than the lower end of the normal liquid level range and the first detection unit detects that the liquid level of the ink in the main tank is at or above the predetermined position, controls the liquid feeding unit to execute a second liquid feeding operation of sending ink from the main tank to the buffer tank. The printing apparatus according to claim 2.

4. In the second liquid feeding operation, the printing apparatus according to claim 3, wherein ink is fed from the main tank to the buffer tank until the liquid level of the ink in the buffer tank reaches the upper end of the normal liquid level range.

5. In the first liquid feeding operation, the printing apparatus according to any one of claims 2 to 4, wherein ink is fed from the main tank to the buffer tank until the liquid level of the ink in the buffer tank reaches an upper limit position provided at a position higher than the upper end of the normal liquid level range.

6. The printing apparatus according to any one of claims 2 to 5, further comprising a second stirring unit that stirs the ink in the buffer tank.

7. The second stirring unit has a second stirring member disposed in the buffer tank, and stirs the ink stored in the buffer tank by rotating the second stirring member. The printing apparatus according to claim 6, wherein the second stirring member is disposed below the normal liquid level range.

8. The first stirring member is a stirring blade that spreads by centrifugal force generated by rotation. The printing apparatus according to any one of claims 1 to 7, wherein the predetermined position is provided corresponding to the position of the stirring blade spread by centrifugal force.

9. The printing apparatus according to claim 8, wherein the predetermined position is provided at the same height as the lower end of the stirring blade spread by centrifugal force.

10. The printing apparatus according to claim 8, wherein the predetermined position is provided at the same height as the upper end of the stirring blade spread by centrifugal force.

11. The printing apparatus according to claim 8, wherein the predetermined position is provided at a position higher than the stirring blade spread by centrifugal force.

12. The printing apparatus according to any one of claims 1 to 11, wherein the ink is white ink.

13. A step of detecting a positional relationship between a liquid level of ink in a main tank connected to a buffer tank that stores ink supplied to a discharge head that discharges ink from a nozzle and a predetermined position provided corresponding to a first stirring member that stirs the ink in the main tank; When it is detected that the liquid level of the ink in the main tank is lower than the predetermined position, a step of sending ink from the main tank to the buffer tank; An ink supply method comprising the above.

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