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Title:
FLUID DISCHARGE DEVICE AND PRINTHEAD
Document Type and Number:
WIPO Patent Application WO/2009/069563
Kind Code:
A1
Abstract:
A fluid discharge device includes a fluid discharge flow passage through which a fluid is discharged upward, a seal portion disposed in the fluid discharge flow passage, a float member which has a specific gravity lower than a specific gravity of a liquid and comes into contact with the seal portion to block the fluid discharge flow passage, and a float chamber in which the float member is movable, wherein an upper end of an inlet port which guides the fluid to flow in the float chamber is arranged above a region along which a sectional area of the float member, which is located at the lowest part in the float chamber, taken along a plane perpendicular to a gravitational direction of the float member is maximum.

Inventors:
SUEOKA MANABU (JP)
KAWASE JUNYA (JP)
YAMAMOTO SHINJI (JP)
ARA YOHJI (JP)
Application Number:
PCT/JP2008/071276
Publication Date:
June 04, 2009
Filing Date:
November 18, 2008
Export Citation:
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Assignee:
CANON KK (JP)
SUEOKA MANABU (JP)
KAWASE JUNYA (JP)
YAMAMOTO SHINJI (JP)
ARA YOHJI (JP)
International Classes:
B41J2/175; F16K24/04
Foreign References:
JPS5649466A1981-05-06
JPS53162929U1978-12-20
JPH07260028A1995-10-13
JP2000309109A2000-11-07
JP2007152884A2007-06-21
JP2006001200A2006-01-05
Attorney, Agent or Firm:
OHTSUKA, Yasunori (KIOICHO PARK BLDG. 3-6, KIOICHO, CHIYODA-K, Tokyo 94, JP)
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Claims:

CLAIMS

1. A fluid discharge device including a fluid discharge flow passage through which a fluid is discharged upward, a seal portion disposed in the fluid discharge flow passage, a float member which has a specific gravity lower than a specific gravity of a liquid and comes into contact with the seal portion to block the fluid discharge flow passage, and a float chamber in which the float member is movable, wherein an upper end of an inlet port which guides the fluid to flow in the float chamber is arranged above a region along which a sectional area of the float member, which is located at the lowest part in the float chamber, taken along a plane perpendicular to a gravitational direction of the float member is maximum.

2. The device according to claim 1, further comprising: a first flow passage which guides the fluid discharged from the fluid discharge device to the inlet port; and a second flow passage which guides the fluid discharged from the fluid discharge device to flow in the float chamber from below the region along which the

sectional area of the float member located at the lowest part in the float chamber is maximum.

3. The device according to claim 2, wherein a resistance of said first flow passage is lower than a resistance of said second flow passage.

4. The device according to claim 2, wherein the inlet port serves as an inlet port of said second flow passage as well.

5. The device according to any one of claims 1 to 4, wherein the fluid is discharged from a liquid flow passage to supply the liquid to a discharge orifice which discharges the liquid to print on a print medium.

6. A printhead comprising: an ink discharge portion to discharge ink; a first ink chamber which communicates with said ink discharge portion; a second ink chamber which reserves ink supplied from an external ink tank, and supplies the reserved ink into said first ink chamber through a filter; an evacuation port formed in said second ink chamber; and a fluid discharge device defined in any one of claims 1 to 5, wherein the fluid discharge flow passage of said fluid discharge device is connected to said evacuation port .

7 . A printhead comprising : an ink discharge portion to discharge ink; a first ink chamber which communicates with said ink discharge portion; a second ink chamber which reserves ink supplied from an external ink tank, and supplies the reserved ink into said first ink chamber through a filter; an evacuation port formed in said first ink chamber; and a fluid discharge device defined in any one of claims 1 to 5, wherein the fluid discharge flow passage of said fluid discharge device is connected to said evacuation port.

8. A fluid discharge device including a fluid discharge flow passage through which a fluid is discharged upward, a seal portion disposed in the fluid discharge flow passage, a float member which has a specific gravity lower than a specific gravity of a liquid and comes into contact with the seal portion to block the fluid discharge flow passage, and a float chamber in which the float member is movable, wherein if a difference between a sectional area of the float member, which is located at the lowest

part in the float chamber, taken along a certain horizontal plane, and a sectional area of the float chamber taken along a horizontal plane identical to the certain horizontal plane is minimum, an upper end of an inlet port which guides the fluid to flow in the float chamber is arranged above the certain horizontal plane.

Description:

DESCRIPTION FLUID DISCHARGE DEVICE AND PRINTHEAD

TECHNICAL FIELD

[0001] The present invention relates to a fluid discharge device and, more specifically, to a fluid discharge device in an ink supply device for supplying ink for use in an inkjet printing apparatus from a main tank to a printhead. The present invention also relates to a printhead having the fluid discharge device.

BACKGROUND ART

[0002] Of printing systems such as a printer, an inkjet printing system which forms, e.g., a text or image on a print medium by discharging ink from a discharge orifice (nozzle) is a low-noise nonimpact printing system that allows a high-density, high-speed printing operation, and is therefore widely adopted nowadays .

[0003] A general inkjet printing apparatus includes an inkjet printhead, a driving unit for driving a carriage which mounts the printhead, a convey unit for conveying a print medium, and a control unit for controlling these constituent components. Such a printing apparatus which prints while moving a carriage is called a serial scan type. On the other hand, a

printing apparatus which prints only by conveying a print medium without moving an inkjet printhead is called a line type. The line type inkjet printing apparatus has an inkjet printhead having a large number of nozzles arrayed across the full width of a print medium in the widthwise direction.

[0004] The inkjet printhead includes an energy generation unit which generates discharge energy supplied to the ink in the nozzle in order to discharge ink droplets from the nozzle. Examples of the energy generation unit are an electromechanical transducer element such as a piezoelectric element, an electrothermal transducer element such as a heating element, and an electromagnetic-to-mechanical transducer element and electromagnetic-to-thermal transducer element which convert an electromagnetic wave such as a radio wave or laser beam into mechanical vibration and heat.

[0005] Of these energy generation systems, the one which uses thermal energy to discharge ink droplets allows high-resolution printing because energy generation units can be arrayed with a high density. Especially an inkjet printhead which uses an electrothermal transducer element as the energy generation unit can be downsized more easily than that which uses an electromechanical transducer element. Moreover, this printhead can advantageously facilitate

high-density packaging and decrease the manufacturing cost by fully utilizing the merits of the IC technology and micropatterning technique that have achieved remarkable progress and a remarkable improvement in reliability in the recent semiconductor manufacturing field.

[0006] In recent years, the inkjet printing apparatus has come to be used even for a plotter which prints a photographic image on a sheet with a size as large as Al or AO.

[0007] To supply ink to the inkjet printhead, there is a so-called head-tank integration scheme which integrates the inkjet printhead and an ink tank for storing ink. As a so-called head-tank separation scheme which separates the inkjet printhead and the ink tank, there is a so-called tube supply scheme which connects the ink tank and the inkjet printhead through a tube. As another head-tank separation scheme, there is a so-called pit-in scheme which moves the inkjet printhead to the position of the ink tank to connect them as needed, and supplies ink from the ink tank to the inkjet printhead.

[0008] As the capacity of the ink tank is increased in order to decrease the replacement frequency of ink tanks, the weight of one ink tank increases. For an inkjet printing apparatus of the serial scan type, this amounts to increasing the weight

on the carriage. In view of this, an inkjet printing apparatus of the serial scan type which requires a large-capacity ink tank to, e.g., output a large-size print image often adopts the tube supply scheme which allows continuous printing over a long time. [0009] In a printer and plotter which use a large amount of ink as described above, the ink tank used is limited to a compact one considering that it is mounted on the carriage, so ink tanks must be disadvantageously, frequently replaced. Still worse, the running costs of these devices are high.

[0010] Under the circumstance, such an inkjet printing apparatus which consumes a large amount of ink generally uses an ink supply system as shown in Fig. 11. [0011] Referring to Fig. 11, a printhead 201 is mounted on a carriage 202 which can move relative to the apparatus main body. A main tank 204 is fixed to the apparatus main body.

[0012] When the ink is running short, the main tank 204 is replaced with a new one. The printhead 201 and main tank 204 are connected by an ink supply tube 200 including a tube and coupling. Because the carriage 202 reciprocates in printing, at least part of the ink supply tube 200 is formed from a flexible tube (e.g., a silicon tube or polyethylene tube) so as not to interfere with the movement of the carriage 202. The main tank 204 has an atmosphere through hole (not

shown) formed so that its inside communicates with the atmosphere. When ink is discharged from the printhead 201, the printhead 201 is replenished with ink from the main tank 204 through the ink supply tube 200. [0013] Although the use of this method allows ink supply with a very simple structure, the flexible tube used in the ink supply tube 200 has a gas permeability to some extent because it is made of rubber or resin. The inside of the tube is under a negative pressure as in the printhead, so air gradually enters the tube from the atmosphere through the tube wall, resulting in the generation of bubbles. If the bubbles flow in the printhead 201, normal ink droplets can no longer be discharged, resulting in a failure in printing. Even if air can be prevented from gradually entering the tube from the atmosphere through the tube wall, the air dissolved in the ink may grow into bubbles in the tube or sub-tank.

[0014] To avoid this situation, Japanese Patent Laid-Open No. 2000-301737 discloses an ink supply system provided with a mechanism for accumulating the generated bubbles, if any, in the sub-tank mounted on the printhead and discharging the air in the sub-tank so as to prevent air from entering the printhead. [0015] An evacuation mechanism for the sub-tank according to this prior art will be explained with reference to Figs. 12 and 13. Figs. 12 and 13 are

sectional views each showing an inkjet printhead and a tank which reserves ink to be supplied to the inkjet printhead.

[0016] A sub-tank 2 is partitioned into two spaces, i.e., a float chamber 102 and an air buffer chamber 103, The float chamber 102 encapsulates a ball-shaped float member 9. A substance which has a specific gravity lower than that of the ink and hardly reacts with the ink is selected as the material of the float member 9, and polypropylene, for example, is used. As a matter of course, a substance having a specific gravity higher than that of the ink may be used as long as it is processed into a hollow structure with a specific gravity lower than that of the ink when used as a component of the float member 9. The upper portion of a partitioning plate 101 completely insulates the float chamber 102 and the air buffer chamber 103. The lower portion of the partitioning plate 101 has slits 104 formed to continuously align themselves in the longitudinal direction so that the ink and air can freely move between the float chamber 102 and the air buffer chamber 103 while the float member 9 never moves to the air buffer chamber 103. The upper portion of the float chamber 102 has a conical part 105 formed. An evacuation port 108 and a connection part 106 of an evacuation tube 10 are formed at the tip of the conical part 105. A connection part 107 of a supply tube 5 is

formed in the upper portion of the air buffer chamber 103, and a pipe portion 109 extends downward in the sub-tank 2 from the connection part 107. With this structure, the inks in the supply tube 5 and sub-tank 2 are always in contact with each other.

[0017] Fig. 13 shows a state immediately after the end of evacuation in the sub-tank 2. In this state, when printing and non-operation (a standby state and power OFF state) are repeated, bubbles generated in the supply tube 5 gradually enter the sub-tank 2. At this time, a valve (not shown) inserted in the evacuation tube 10 is closed. For this reason, the ink is discharged from a nozzle 6 along with printing and head restoration operations, but the increased amount of air is trapped in the sub-tank 2, so the ink liquid level drops, as shown in Fig. 12.

[0018] In evacuating the air from the sub-tank 2, a head restoration unit 40 lifts to cover the nozzle 6 of a printhead 1, thereby shielding it from the outside air. A pump (not shown) connected to the evacuation tube 10 is then activated to gradually draw the air in the sub-tank 2 by suction so that the pressure in the sub-tank 2 gradually drops. When the pressure drops to a certain degree, ink is supplied from a main tank (not shown) to the sub-tank 2 through the supply tube 5. The air staying in the sub-tank 2 flows out through the evacuation tube 10 upon being replaced by the supplied

_ o _

ink. At this time, the ink level rises uniformly in the state shown in Fig. 12. When the ink level reaches the top slit 104, the air in the float chamber 102 and that in the air buffer chamber 103 are insulated from each other, and therefore only the air in the float chamber 102 is evacuated thereafter. As the air is evacuated so that the ink level rises, the float member 9 naturally moves up accordingly.

[0019] ' At first, the float member 9 moves up without targeting any position in the horizontal direction in the float chamber 102. However, when the float member 9 reaches the conical part 105, it moves up to come close to the virtual tip of the conical part 105 thereafter. Finally, the float member 9 stops at the position at which its entire circumference comes into contact with the conical part 105 as shown in Fig. 7 to block the evacuation port 108, and the evacuation operation ends.

DISCLOSURE OF INVENTION

[0020] In recent years, there is a demand for further improvement in performance of the inkjet printing apparatus.

[0021] For example, it is demanded to decrease the nozzle pitch in order to output an image with a higher resolution, and increase the number of inks used to widen the color representation range. It is also

demanded to increase the number of nozzles in order to further increase the printing speed, and increase the moving speed of the carriage.

[0022] Increasing the number of inks used requires a larger number of printheads and a system for supplying inks in a number corresponding to that of printheads accordingly, resulting in increases in the size and weight of the apparatus.

[0023] As the size and weight of the printhead increase, a load imposed on the carriage upon its movement increases, which is disadvantageous to highspeed printing as well.

[0024] To solve this problem, the inkjet printing apparatus is required to have a smaller size and lighter weight while incorporating the function for higher performance as described above. The ink supply structure is also required to be further downsized. [0025] Unfortunately, the downsizing of the printing apparatus with the above-described structure poses the following problem.

[0026] If bubbles flow in the float chamber, they push up the float member. Alternatively, if not only bubbles but also a small amount of liquid flows in the float chamber, the gap between the float member and the float chamber is sealed by the bubbles and the small amount of liquid. [0027] In this state, suction by the suction

mechanism from the side of the evacuation tube causes a difference in pressure between the upstream and downstream sides of the float chamber so that the float member moves to come into contact with the seal member, thereby closing the evacuation tube. This makes it impossible to sufficiently discharge the gas in the ink tank.

[0028] The present invention has been made in consideration of the above-described problem, and has as its object to attain a fluid discharge technique which can satisfactorily discharge any unnecessary bubbles and gas even when a printing apparatus is downsized.

[0029] In order to achieve the above-described object, according to the present invention, there is provided a fluid discharge device including a fluid discharge flow passage through which a fluid is discharged upward, a seal portion disposed in the fluid discharge flow passage, a float member which has a specific gravity lower than a specific gravity of a liquid and comes into contact with the seal portion to block the fluid discharge flow passage, and a float chamber in which the float member is movable, wherein an upper end of an inlet port which guides the fluid to flow in the float chamber is arranged above a region along which a sectional area of the float member, which is located at the lowest part in the float chamber,

taken along a plane perpendicular to a gravitational direction of the float member is maximum. [0030] Also, according to the present invention, there is provided a printhead comprising an ink discharge portion to discharge ink; a first ink chamber which communicates with the ink discharge portion, a second ink chamber which reserves ink supplied from an external ink tank, and supplies the reserved ink into the first ink chamber through a filter, an evacuation port formed in the second ink chamber, and a fluid discharge device defined above, wherein the fluid discharge flow passage of the fluid discharge device is connected to the evacuation port. [0031] There is also provided a printhead comprising an ink discharge portion to discharge ink; a first ink chamber which communicates with the ink discharge portion; a second ink chamber which reserves ink supplied from an external ink tank, and supplies the reserved ink into the first ink chamber through a filter; an evacuation port formed in the first ink chamber; and a fluid discharge device defined above, wherein the fluid discharge flow passage of the fluid discharge device is connected to the evacuation port. [0032] There is provided a fluid discharge device including a fluid discharge flow passage through which a fluid is discharged upward, a seal portion disposed in the fluid discharge flow passage, a float member

which has a specific gravity lower than a specific gravity of a liquid and comes into contact with the seal portion to block the fluid discharge flow passage, and a float chamber in which the float member is movable, wherein if a difference between a sectional area of the float member, which is located at the lowest part in the float chamber, taken along a certain horizontal plane, and a sectional area of the float chamber taken along a horizontal plane identical to the certain horizontal plane is minimum, an upper end of an inlet port which guides the fluid to flow in the float chamber is arranged above the certain horizontal plane. [0033] According to the present invention, it is possible to satisfactorily discharge any unnecessary bubbles and gas even when a printing apparatus is downsized.

[0034] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings .

BRIEF DESCRIPTION OF DRAWINGS

[0035] Fig. 1 is a view showing the schematic structure of an ink supply system of a fluid discharge device according to the first embodiment of the present invention; [0036] Fig. 2 is a view showing the detailed

structure of the fluid discharge device according to the first embodiment;

[0037] Fig. 3 is a view showing the detailed structure of the fluid discharge device according to the first embodiment;

[0038] Fig. 4 is a view showing the detailed structure of a fluid discharge device according to the second embodiment;

[0039] Fig. 5 is a view showing the detailed structure of a fluid discharge device according to the third embodiment;

[0040] Figs. 6A and 6B are views showing the detailed structure of a fluid discharge device according to the fourth embodiment;

[0041] Figs. IA and 7B are views showing the structure of an inkjet printhead to which a fluid discharge device according to the fifth embodiment is applied;

[0042] Figs. 8A to 8D are views for explaining the fluid discharge function of the fluid discharge device according to the third embodiment;

[0043] Fig. 9 is a view showing the sixth embodiment in which the fluid discharge device according to one of the above-described embodiments is applied to an inkjet printhead;

[0044] Fig. 10 is a view showing the seventh embodiment in which the fluid discharge device

according to one of the above-described embodiments is applied to an inkjet printhead;

[0045] Fig. 11 is a view showing the schematic structure of an ink supply system of a conventional inkjet printing apparatus;

[0046] Fig. 12 is a sectional view showing a conventional ink chamber evacuation mechanism; and

[0047] Fig. 13 is a sectional view showing the conventional ink chamber evacuation mechanism.

BEST MODE FOR CARRYING OUT THE INVENTION [0048] Embodiments of the present invention will be described below with reference to the accompanying drawings .

[0049] Fig. 1 is a view showing the schematic structure of an ink supply system of an inkjet printing apparatus according to the first embodiment, to which a fluid discharge device according to the present invention is applied.

[0050] Referring to Fig. 1, a printhead 1 includes a printing element chip 51 serving as an ink discharge unit in which a plurality of printing elements and a plurality of orifices 52 for discharging ink are arrayed. The printhead 1 also includes a first ink chamber 50 commonly connected to the plurality of orifices 52. The printhead 1 also includes a sub-tank (second ink chamber) 53 for receiving and reserving ink

supplied from an external main tank 56 through a first filter, and supplying the ink into the first ink chamber 50.

[0051] A buffer tank 54 for temporarily reserving the ink is inserted between the inkjet printhead 1 and the main tank 56. A fluid discharge device 57 for discharging a gas taken into the buffer tank 54 or a supply tube 55 which constitutes a liquid flow passage is mounted on the buffer tank 54.

[0052] Ink is introduced from the main tank 56 to the printhead 1 by a suction operation using a cap 59 set to seal the orifices 52, and a pump 61 serving as a suction unit connected to the cap 59. [0053] The buffer tank 54 mounts the fluid discharge device 57 so as to prevent a gas mixed in the supply tube 55 and that taken into the buffer tank 54 upon replacing the main tank 56 from entering the printhead 1. The fluid discharge device 57 is connected to the pump 61 by an evacuation tube 58. [0054] The ink supply to the printhead 1 and the evacuation of the buffer tank 54 are switched by a switching valve 60 inserted between the cap 59 and the pump 61.

[0055] Figs. 2 and 3 are views showing details of the fluid discharge device 57 shown in Fig. 1. [0056] Referring to Fig. 2, the fluid discharge device 57 includes a fluid discharge flow passage 62

for discharging the gas from the buffer tank 54, and a float chamber 64 inserted in the fluid discharge flow passage 62. The upper portion of the float chamber 64 is connected to the evacuation tube 58. A seal portion 65 is formed in an evacuation port 58a which communicates with the evacuation tube 58. [0057] The float chamber 64 movably accommodates a float member 63 having a specific gravity lower than the liquid supplied to the printhead 1. When the float member 63 comes into contact with the seal portion 65, the evacuation port 58a which communicates with the evacuation tube 58 is blocked.

[0058] As shown in Fig. 3, the fluid discharge flow passage 62 has a first flow passage 67 which guides the fluid into the float chamber 64. The fluid flowing through the first flow passage 67 flows in the float chamber 64 from its inlet port 67a. An upper end 74 of the inlet port 67a is arranged above a region 75 along which the sectional area of the float member 63, which is located at the lowest part in the float chamber 64, taken along a plane perpendicular to the gravitational direction of the float member 63 is maximum. For this reason, the fluid flowing through the first flow passage 67 flows in the float chamber 64 from above the region along which the horizontal sectional area of the float member 63 is maximum. In other words, the fluid flowing through the first flow

passage 67 flows in the float chamber 64 from above a region along which the horizontal sectional area of the gap between the float member 63 and the wall surface of the float chamber 64 is minimum. In other words again, if the difference between the sectional area of the float member 63, which is located at the lowest part in the float chamber 64, taken along a certain horizontal plane, and that of the float chamber 64 taken along a horizontal plane identical to the certain horizontal plane is minimum, the upper end of the inlet port 67a is arranged above the certain horizontal plane. [0059] Note that when the float member 63 is located at the lowest part in the float chamber 64, the float member 63 is in contact with a bottom surface 64a of the float chamber 64 by the gravity of the float member 63, as shown in Fig. 3.

[0060] In this way, even when bubbles 66 flow in the float chamber 64, most of them pass through the upper portion of the float member 63. For this reason, the float member 63 never moves due to the presence of any bubbles, and therefore never shuts off the evacuation tube 58 before gas evacuation is completed. [0061] By applying a negative pressure to the evacuation tube 58 by the pump 61, ink supplied from the main tank 56 fills the buffer tank 54 so that the ink liquid level in the buffer tank 54 rises. The bubbles 66 which have been accumulated above the ink

liquid level in the buffer tank 54 flow in the float chamber 64 before the ink flows in it. The bubbles 66 are discharged from the evacuation tube 58 without floating the float member 63.

[0062] As the ink liquid level further rises, the ink flows in the float chamber 64. When the float member 63 floats by the ink having flown in the float chamber 64 and comes into contact with the seal portion

65, it shuts off the evacuation port 58a, and the evacuation operation ends.

[0063] Note that the seal portion 65 may be integrated with the float chamber 64 or may be another member.

[0064] In this way, it is possible to surely evacuate the gas in the buffer tank 54 without wastefully discharging ink.

[0065] Fig. 4 is a view showing the structure of a fluid discharge device according to the second embodiment .

[0066] In a fluid discharge device 57 according to the second embodiment, a fluid discharge flow passage

62 branches into a first flow passage 67 and second flow passage 68, which are connected to a float chamber

64.

[0067] The first flow passage 67 guides the fluid from the fluid discharge flow passage 62 to flow in the float chamber 64 from above a region along which the

horizontal sectional area of a float member 63 located at the lowest part in the float chamber 64 is maximum. [0068] The second flow passage 68 guides the fluid from the fluid discharge flow passage 62 to flow in the float chamber 64 from below the region along which the horizontal sectional area of the float member 63 located at the lowest part in the float chamber 64 is maximum.

[0069] Fig. 5 is a view showing the structure of a fluid discharge device according to the third embodiment .

[0070] Fig. 5 shows a structure in which the resistance of the first flow passage 67 shown in Fig. 4 is lower than that of the second flow passage 68 shown in Fig. 4. More specifically, the "sectional area/length" of a first flow passage 67 is larger/longer than that of a second flow passage 68. [0071] Figs. 6A and 6B are views showing the structure of a fluid discharge device according to the fourth embodiment .

[0072] Figs. 6A and 6B show a structure in which the first flow passage 67 and second flow passage 68 shown in Fig. 4 are combined into one flow passage 69. Fig. 6A is a sectional view taken along a line D - D in Fig. 6B.

[0073] Referring to Figs. 6A and 6B, a fluid discharge flow passage 62 guides the fluid into a float

chamber 64 from the lower side of a bottom surface 64a of the float chamber 64 along the gravitational direction.

[0074] In both the structures shown in Figs. 4 and 6A and 6B, the upper end of an inlet port 67a of the float chamber 64 is arranged above a region along which the sectional area of a float member 63 is maximum. For this reason, the fluid from the fluid discharge flow passage 62 flows in the float chamber 64 from above the region along which the sectional" area of the float member 63 located at the lowest part in the float chamber 64 is maximum. Hence, the float member 63 never floats due to the presence of any bubbles, and the fluid discharge apparatus can maximally exhibit a function of surely discharging any gas without wastefully discharging ink.

[0075] Figs. 7A and 7B are views showing the structure of a fluid discharge device according to the fifth embodiment.

[0076] Figs. 7A and 7B show a structure in which two flow passages identical to the flow passage 69 shown in Figs. 6A and 6B are connected into the float chamber 64. Fig. 7A is a sectional view taken along a line E - E in Fig. 7B. In this way, it is possible to form two or more flow passages as long as there is a margin of space. [0077] Referring to Figs. 7A and 7B, a fluid

discharge flow passage 62 guides the fluid into a float chamber 64 from the lower side of a bottom surface 64a of the float chamber 64 along the gravitational direction.

[0078] Figs. 8A to 8D are views for explaining the fluid discharge function of the fluid discharge device according to one of the above-described embodiments. Note that the fluid discharge device according to the third embodiment shown in Fig. 5 will be exemplified herein.

[0079] Fig. 8A shows the initial state before fluid discharge. There is no liquid in the liquid discharge device, and a float member 63 is located at the lowest part of the float chamber 64. [0080] Fig. 8B shows a state in which suction in the direction indicated by an arrow is started by applying a negative pressure to an evacuation tube 58 by a pump 61. The ink liquid level in a buffer tank 54 rises so that a gas or bubbles 66 in the buffer tank 54 are discharged through a first flow passage 67 and second flow passage 68. At this time, most of the gas or bubbles 66 are discharged through the first flow passage 67. The bubbles 66 are discharged from the evacuation tube 58 without floating the float member 63. [0081] As the suction further continues, the ink liquid level rises as shown in Fig. 8C so that the ink flows in the float chamber 64. Along with the rise in

the ink liquid level, the float member 63 moves up. [0082] As the suction further continues, the float member 63 comes into contact with a seal portion 65 as shown in Fig. 8D to block the evacuation tube 58, and the fluid discharge ends.

[0083] In this way, the bubbles 66 are prevented from pushing up the float member 63 by guiding the fluid to flow in the float chamber 64 from above a region along which the horizontal sectional area of the float member 63 located at the lowest part of the float chamber 64 is maximum. This makes it possible to efficiently discharge the gas and bubbles in the tank. [0084] Fig. 9 is a view showing the sixth embodiment in which the fluid discharge device according to one of the above-described embodiments is applied to an inkjet printhead.

[0085] Referring to Fig. 9, reference numeral 51 denotes a printing element chip in which a plurality of printing elements (not shown) and a plurality of orifices 52 for discharging ink are arrayed; and 70, a first ink chamber commonly connected to the plurality of orifices 52.

[0086] A second ink chamber 71 for reserving ink supplied from an external main tank 56 through a supply tube 55 is set above the first ink chamber 70. The ink reserved in the second ink chamber 71 is supplied into the first ink chamber 70 through a filter 72.

[0087] The second ink chamber 71 has an evacuation port 73 formed, and a fluid discharge device 57 is set above the second ink chamber 71.

[0088] In the fluid discharge device 57, a fluid discharge flow passage 62 branches into a first flow passage 67 and second flow passage 68, which are connected to a float chamber 64.

[0089] The upper end of an inlet port 67a of the float chamber 64 is arranged above a region along which the sectional area of a float member 63 is maximum.

The first flow passage 67 guides the fluid from the fluid discharge flow passage 62 to flow in the float chamber 64 from above the region along which the horizontal sectional area of the float member 63 located at the lowest part in the float chamber 64 is maximum.

[0090] The second flow passage 68 guides the fluid from the fluid discharge flow passage 62 to flow in the float chamber 64 from below the region along which the horizontal sectional area of the float member 63 located at the lowest part in the float chamber 64 is maximum.

[0091] An evacuation tube 58 on the evacuation side of the fluid discharge device 57 is connected to a suction mechanism (not shown) such as a pump. When the pressure of the evacuation tube 58 is reduced by the pump, any bubbles can be discharged while preventing

the bubbles from pushing up the float member 63, as in the above-described embodiments. As the bubbles are discharged so that the ink liquid level rises, the float member 63 comes into contact with a seal portion 65 to block the evacuation tube 58, and the fluid discharge ends.

[0092] In this way, applying the fluid discharge device according to one of the above-described embodiments to an ink jet printhead effectively prevents a failure in ink discharge due to the presence of any bubbles. That is, it is possible to remove any bubbles while minimizing wasteful ink discharge, thus providing a compact, high-reliability inkjet printing apparatus.

[0093] Fig. 10 is a view showing the seventh embodiment in which the fluid discharge device according to one of the above-described embodiments is applied to an inkjet printhead.

[0094] The structure shown in Fig. 10 is different from that shown in Fig. 9 in that a flow passage which can discharge the fluid even from a first ink chamber 70 located downstream of a filter 72 is formed, and a fluid discharge device is inserted in this flow passage. That is, a first fluid discharge device 571 is mounted in the first ink chamber 70, and a second fluid discharge device 572 is mounted in a second ink chamber 71. Each of the fluid discharge devices 571 and 572

includes a float chamber 64, float member 63, seal portion 65, first flow passage 67, and second flow passage 68, as in the structure shown in Fig. 9. [0095] Ink supply and gas discharge processes will be explained with reference to Fig. 10. [0096] An ink. supply tube 77 is connected to an ink tank (not shown) by, e.g., a tube. [0097] In the gas discharge operation, first, a cap 59 is moved to come into tight contact with the periphery of orifices 52, thereby sealing the orifices 52. Subsequently, a switching valve 60 communicates a pump 61 and fluid discharge flow passage 78. [0098] Next, the pump 61 is activated to reduce the pressure of the fluid discharge flow passage 78. The discharge of the fluid in the second ink chamber 71 is started first according to a relationship of the resistances of flow passages. Along with the gas discharge, ink is supplied from the ink supply tube 77. The fluid in the second ink chamber 71 is discharged through the second fluid discharge device 572. In the second fluid discharge device 572, when any bubbles are discharged first and the float chamber 64 is filled with the ink as in the embodiment shown in Fig. 9, the float member 63 and seal portion 65 block the flow passages toward the fluid discharge flow passage 78. [0099] Lastly, the gas in the first ink chamber 70 is discharged in the same way as described above,

thereby efficiently discharging any unnecessary gas in a printhead 1. The end of the gas discharge process is determined by time setting or inserting a pressure detector (not shown) into the fluid discharge flow passage 78 and detecting that it has reached a prescribed pressure.

[0100] In this way, mounting fluid discharge devices 571 and 572 according to one of the above- described embodiments in both the first ink chamber 70 and second ink chamber 71 of the inkjet printhead 1 effectively prevents a failure in ink discharge due to the presence of any bubbles. That is, it is possible to satisfactorily remove any bubbles and therefore to minimize wasteful ink discharge, thus attaining a compact inkjet printing apparatus with higher reliability.

[0101] Note that a substance which has a specific gravity lower than that of the ink and hardly reacts with the ink is selected as the material of the float member 63, and polypropylene, for example, is used. However, a substance having a specific gravity higher than that of the ink may be used as long as it is processed into a hollow structure with a specific gravity lower than that of the ink when used as a component of the float member 63. [0102] While the present invention has been described with reference to exemplary embodiments, it

is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. [0103] This application claims the benefit of Japanese Patent Application No. 2007-304502, filed November 26, 2007, which is hereby incorporated by reference herein in its entirety.