Patent Publication Number: US-8529040-B2

Title: Printhead and printing apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a printhead and a printing apparatus including a printhead, and more particularly, to an inkjet printing apparatus in which ink is supplied from a main tank holding a large amount of ink to a printhead through a sub-tank. 
     2. Background Art 
     Recently, inkjet printing apparatuses are widely used as printers of personal computers or copying machines. Since the inkjet printing apparatus is inexpensive and capable of full-color printing, the apparatus&#39; demand is increasing. Also, the technique of inkjet printing is applied in photographic image printing, in which multi-tone image printing is necessary. 
     Such a multi-tone image printer can express a much larger number of tones than the actually mounted number of ink types by using in combination plural types of ink having different densities and superimposing the plural types of ink a couple of times. Recently, inkjet printers are also used in plotters which print photographic images on a large-size sheet, such as A1 (594 mm×841 mm) and A0 (841 mm×1189 mm). 
     However, the above-described plotter and photographic image printer consume a large amount of ink. If an ink tank is mounted on the carriage together with a printhead, the ink tank must be exchanged frequently, and it is inconvenient. 
     Such an inkjet printer consuming a large amount of ink generally uses an ink supply system shown in  FIG. 15 .  FIG. 15  is a schematic diagram of an ink supply system in a conventional inkjet printing apparatus. 
     As shown in  FIG. 15 , a printhead H 301  is mounted on a carriage H 302  which is movable with respect to the apparatus main body. A main tank M 303  is fixed to the apparatus main body. The main tank M 303  is arranged to be exchangeable when the remaining ink in the main tank M 303  is running low. 
     The printhead H 301  is connected with the main tank M 303  by an ink flow passage M 304 , which is consisted of tubes and joints or the like. The carriage H 302  moves reciprocally when printing is executed. The motion of the carriage H 302  is not disturbed because a flexible tube (e.g., silicon tube or polyethylene tube) is used in at least part of the ink flow passage M 304 . 
     The main tank M 303  has an air communication hole M 305 . The inner part of the main tank M 303  is in communication with the atmosphere. When the printhead H 301  discharges ink, ink is refilled from the main tank M 303  to the printhead H 301  through the ink flow passage M 304 . 
     Inside the printhead H 301 , there is a sub-tank H 310  which directly receives ink from the ink flow passage M 304 . Below the sub-tank H 310  is an individual liquid chamber H 309  provided through a filter H 307 . The individual liquid chamber H 309  serves as an ink reserving area for introducing the ink to a printing element substrate H 308 . 
     The pressure inside the printhead H 301  must be maintained in a negative pressure state so that the ink does not leak from the discharge orifice H 306 . The pressure inside the printhead H 301  is determined by the ink level of the main tank M 303 . It is preferable that the ink level of the main tank M 303  be set at the position lower by 20 mm to 100 mm than the position of the discharge orifice H 306  of the printhead H 301 . 
     This method can realize ink supply with an extremely simple configuration. However, since the flexible tube used in the ink flow passage M 304  is made of rubber or resin, the tube has slight gas permeability. 
     Because the inner portion of the tube has negative pressure similarly to the inner portion of the printhead H 301 , air from the atmosphere infiltrates the inner portion of the tube little by little through the tube wall, and bubbles are generated. If the bubbles flow into the sub-tank H 310  in the printhead H 301 , maintaining the negative pressure inside the printhead becomes difficult. Furthermore, ink supply to the individual liquid chamber H 309  becomes insufficient and regular ink droplets cannot be discharged. This causes printing defects. 
     Even if it were possible to prevent air from infiltrating the inner portion of the tube little by little through the tube wall, there is a possibility that air dissolved in the ink may grow into bubbles inside the tube or sub-tank H 310 . Moreover, there is a possibility that bubbles get inside the sub-tank H 310  from the atmosphere. 
     In view of the above situation, an ink supply system shown in  FIG. 16  is proposed as a method for preventing bubbles from getting in the printhead H 301  even if bubbles are produced, and furthermore for removing bubbles in the sub-tank by circulating the bubbles. 
       FIG. 16  is a schematic diagram of another ink supply system in a conventional inkjet printing apparatus.  FIG. 16  shows a printhead H 301 , and a sub-tank H 310  which is provided inside the printhead H 301  for reserving ink to be supplied to a printing element substrate H 308 . 
     The printhead H 301  and the sub-tank  310  are mounted on a carriage H 302  which is movable with respect to the apparatus main body. A main tank M 303  is fixed to the apparatus main body. The main tank M 303  is exchangeable when the remaining ink in the main tank M 303  is running low. The printhead H 301  is connected with the main tank M 303  by two ink flow passages: first and second ink flow passages M 3041  and M 3042 , each consisted of tubes and joints. 
     The first ink flow passage M 3041  transfers the ink contained in the main tank M 303  to the sub-tank H 310 . The second ink flow passage M 3042  transfers back the ink in the sub-tank H 310  to the main tank M 303 . Provided in midstream of the second ink flow passage M 3042  is a pump M 311  that generates ink flow by a piston or by rotating plural rollers. The ink in the sub-tank H 310  is sent to the main tank M 303  by the pump M 311 . 
     The main tank M 303  has an air communication hole M 305 . The inner part of the main tank M 303  is in communication with the atmosphere. However, since the sub-tank H 310  has an airtight structure, the inner part of the sub-tank H 310  is not in communication with the atmosphere. Therefore, when the pump  311  is driven, the ink in the sub-tank H 310  is sent to the main tank M 303  through the second ink flow passage M 3042 , while the ink in the main tank M 303  is sucked by the sub-tank H 310  through the first ink flow passage M 3041 . In this manner, ink circulation is executed between the sub-tank H 310  and the main tank M 303 . 
     The pressure inside the sub-tank H 310  must be maintained in a negative pressure state so that the ink does not leak from the printhead H 301 . The pressure inside the sub-tank H 310  is determined by the ink level of the main tank M 303 . It is preferable that the ink level of the main tank M 303  be set at the position lower by 20 mm to 100 mm than the position of the printhead H 301  (discharge orifice surface). 
     According to the above-described configuration, bubbles are generated in the first ink flow passage M 3041  similarly to the conventional art shown in  FIG. 15 . However, the bubbles enter the sub-tank H 310 , flow through the second ink flow passage M 3042 , and end up being discharged to the main tank M 303 . Therefore, according to the above-described proposed configuration, the bubbles generated in midstream of the ink flow passage do not enter the sub-tank H 310  in the printhead H 301 . 
     There is another conventional technique, which is disclosed in Japanese Patent Laid-Open No. 8-244250, for removing bubbles by circulating ink between a sub-tank and a main tank. 
     However, in the aforementioned plotters and medical image printers, there is a trend toward increasing types of ink for expressing more complicated tones. 
     For instance, in photographic color plotters, using more than six colors of ink, which include low-density cyan and magenta in addition to regular cyan, magenta, yellow, and black, has been proposed. Also, in medical image printers, at least six densities of black ink are necessary in order to print an image, for example, an X-ray image, where more than 1000 tones are necessary. 
     In a case where six types of ink are used, six ink supply systems must be provided, and twelve (6×2=12) ink flow passages are necessary between the sub-tank and the main tank. 
     As mentioned above, air from outside infiltrates the inner portion of the tube. It has also been confirmed that moisture and solvent in the ink evaporate outside the tube through the tube wall. Therefore, the more the number of ink flow passages between the sub-tank H 310  and the main tank M 303 , the more the moisture and solvent evaporate, and as a result, the ink density changes. In a multi-tone image, particularly in an image having more than 1000 tones, accurate tone expression cannot be realized if the density of each ink changes. 
     Although the configuration for circulation shown in  FIG. 16  can remove bubbles that get mixed inside the sub-tank H 310  by a circulating operation, the circulating operation cannot be performed in the individual liquid chamber H 309  provided below the sub-tank H 310 . To remove bubbles in the individual liquid chamber H 309  which have been generated by printing or the like, a compression mechanism M 306  is operated, and the individual liquid chamber bubbles H 3091  are removed by running ink from the discharge orifice H 306 . This generates waste ink. 
     Furthermore, in the method of removing individual liquid chamber bubbles H 3091  by running ink using the compression mechanism M 306 , there is a possibility that the sub-tank bubbles H 3101  may move to the individual liquid chamber H 309 . When the bubbles pass through the filter H 307 , they become creamy fine bubbles. These fine bubbles tend to remain inside the individual liquid chamber H 309  even if the compression mechanism M 306  is operated. In fact, a large number of bubbles still may remain even after the recovery operation. In view of this, Japanese Patent Laid-Open No. 2000-301737 proposes a configuration for removing bubbles by providing a float valve inside the sub-tank. Moreover, Japanese Patent Laid-Open No. 11-320901 and No. 2006-095868 propose a configuration for removing air inside the sub-tank by providing a communication hole having a check valve in the ink chamber and releasing the check valve by a mechanism outside the printhead. 
     DISCLOSURE OF INVENTION 
     The printhead shown in  FIG. 16  has plural ink chambers, and in particular comprises an individual liquid chamber H 309  below the sub-tank H 310  for supplying ink to the printing element substrate H 308 . A filter H 307  is arranged between the two liquid chambers H 310  and H 309  to filter out impure substances in the ink which has been supplied from outside the printhead. Therefore, it is difficult for the conventional art to reliably remove as many bubbles as possible from each of the liquid chambers, in particular, from inside the individual liquid chamber H 309  which is directly connected to the discharge orifice. 
     The present invention has been made in view of the above problem, and realizes a technique for reducing the amount of waste ink which is generated when bubbles remaining inside a printhead are discharged. 
     Furthermore, the present invention realizes a technique for, when bubbles remaining inside a printhead are to be discharged, reducing bubbles which move from the first ink chamber having an inlet port, which receives ink supply from an ink supply source, to the second ink chamber near the discharge orifice. 
     In order to solve the above problems, the present invention provides a printhead comprising a first ink chamber having an inlet port, to which ink from an ink supply source is supplied, a second ink chamber, to which the ink from the first ink chamber is supplied, a discharge orifice discharging ink from the second ink chamber, a first outlet port discharging fluid from the first ink chamber, a second outlet port discharging fluid from the second ink chamber, and an air-liquid separation unit which restricts liquid ejection and is provided at least either or both place between the first ink chamber and the first outlet port, or/and a place between the second ink chamber and the second outlet port, wherein flow resistance from the inlet port to the first outlet port is smaller than flow resistance from the inlet port to the second outlet port. 
     According to the present invention, it is possible to reduce the amount of waste ink which is generated when bubbles remaining inside the printhead are discharged. 
     Furthermore, when bubbles remaining inside the printhead are to be discharged, it is possible to reduce bubbles which move from the first ink chamber having an inlet port, which receives ink supply from an ink supply source, to the second ink chamber near the discharge orifice. 
     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 
       The accompanying drawings, which are incorporated in and constitute part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a diagram showing a configuration of an ink supply system of an inkjet printhead which represents the first embodiment of the present invention. 
         FIGS. 2A to 2C  are detailed views showing a configuration of a float valve mechanism. 
         FIG. 3  is a diagram showing an overall configuration of the ink supply system of an inkjet printing apparatus according to the first embodiment of the present invention. 
         FIG. 4  is a diagram showing the ink flow inside the printhead at the time of air removal according to the first embodiment of the present invention. 
         FIG. 5  is a diagram showing the ink flow inside the printhead at the time of air removal according to the first embodiment of the present invention. 
         FIG. 6  is a diagram showing the ink flow inside the printhead at the time of air removal according to the first embodiment of the present invention. 
         FIG. 7  is a diagram showing an overall configuration of a supply system in an inkjet printing apparatus according to the second embodiment of the present invention. 
         FIG. 8  is a diagram showing a configuration of an ink supply system of an inkjet printhead according to the third embodiment of the present invention. 
         FIGS. 9A to 9C  are detailed views showing a configuration of a float valve mechanism in the inkjet printhead according to the third embodiment of the present invention. 
         FIG. 10  is a diagram showing an overall configuration of a supply system according to the third embodiment of the present invention. 
         FIGS. 11A and 11B  are detailed views showing a configuration of a float valve mechanism according to the fourth embodiment of the present invention. 
         FIG. 12  is a diagram showing a configuration of an ink supply system of an inkjet printhead according to the fifth embodiment of the present invention. 
         FIG. 13  is a diagram showing a configuration of an ink supply system of a full-line inkjet printhead according to the sixth embodiment of the present invention. 
         FIG. 14  is a diagram showing a configuration of an ink supply system of an inkjet printhead according to the seventh embodiment of the present invention. 
         FIG. 15  is a schematic diagram of an ink supply system in a conventional inkjet printing apparatus. and 
         FIG. 16  is a schematic diagram of another ink supply system in a conventional inkjet printing apparatus. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
       FIG. 1  shows a configuration of an ink supply system in an inkjet printhead, to which the present embodiment is applied. 
     As shown in  FIG. 1 , a carriage H 302  holds a printhead H 301  which discharges ink. The printhead H 301  discharges ink from a discharge orifice H 306  and performs printing while the carriage H 302  moves in the main-scanning direction with respect to a print medium which is conveyed in the sub-scanning direction by a conveyance roller or the like. 
     As shown in  FIG. 1 , the printhead H 301  is arranged so that ink from an ink flow passage H 304  directly flows into a sub-tank H 310 , which serves as the first ink chamber in the printhead H 301 , through an inlet port H 305 . Below the sub-tank H 310 , an individual liquid chamber H 309  serving as the second ink chamber is provided for holding ink to be introduced through an ink inlet filter H 3071 , serving as the first filter, to the discharge orifice H 306 . 
     The ink inlet filter H 3071  is arranged at an angle with respect to the gravity direction. Because of this configuration, individual liquid chamber bubbles H 3091 , pooled inside the individual liquid chamber H 309 , can be gathered in one place. On the upper portion of the individual liquid chamber H 309 , an ink outlet filter H 3072  which serves as the second filter is arranged in the place where bubbles are easily gathered because of the inclination. 
     On the upper portion of the sub-tank H 310 , the first air outlet port H 51  (first outlet port) is provided for discharging bubbles. On the upper portion of the individual liquid chamber H 309  which serves as the second ink chamber, the second air outlet port H 52  (second outlet port) is provided for discharging bubbles. The first and second air outlet ports H 51  and H 52  are connected to a waste air-liquid flow passage H 3043  which serves as a discharge passage. The waste air-liquid flow passage H 3043  is connected to a pump M 312  ( FIG. 3 ), which serves as a decompression mechanism. By decompressing the waste air-liquid flow passage H 3043  using the pump and vacuuming fluid from the first and second air outlet ports H 51  and H 52 , bubbles are discharged from the sub-tank H 310  and the individual liquid chamber H 309 . 
     Provided in the first air outlet port H 51  is a sub-tank float valve mechanism consisting of a first float H 91  (first float member) and a seal member H 45  (first float seal member). The sub-tank float valve mechanism constitutes an air-liquid separation mechanism, which allows gas to discharge from the first air outlet port H 51  and restricts liquid from discharging from the first air outlet port H 51 . The first float H 91  is pressed against the seal member H 45  because of the buoyancy of the float in the ink, thereby sealing the first air outlet port H 51 . Provided in the second air outlet port H 52  is an individual liquid chamber float valve mechanism (second float valve mechanism) consisting of a second float H 92  (second float member) and a seal member H 45  (second float seal member). The second float valve mechanism is a second air-liquid separation mechanism. The second float H 92  is pressed against the seal member H 45  because of the buoyancy of the float in the ink, thereby sealing the second air outlet port H 52 . 
     Only one of the sub-tank float valve mechanism or the individual liquid chamber float valve mechanism may be provided. 
     When bubbles are to be discharged, the pump gives negative pressure to the waste air-liquid flow passage H 3043 . Bubbles pooled in the upper portion of the sub-tank H 310  and individual liquid chamber H 309  are vacuumed from the first and second air outlet ports H 51  and H 52 . As the bubbles or gas are discharged, the ink surface in the sub-tank H 310  and individual liquid chamber H 309  rises, and along with the rise, the first and second floats H 91  and H 92 , which have a smaller specific gravity than the ink, also rise. When the ink surface rises to the point close to the first and second air outlet ports H 51  and H 52 , the first and second floats H 91  and H 92  are pressed against the seal member H 45  because of the buoyancy of the floats in the ink. Since the floats block the ports before the ink surface becomes higher than the first and second air outlet ports H 51  and H 52 , it is possible to restrict ink ejection and only the bubbles can be discharged. 
     The present embodiment is arranged in a way that the flow passage resistance from the ink inlet port to the first air outlet port H 51  is smaller than the flow passage resistance from the ink inlet port to the second air outlet port H 52 . Note that the ink inlet port is where ink flows in from the ink flow passage H 304 . 
     Assume that Susmic Filter SH10H produced by Tokyo Rope Manufacturing Co., Ltd. is used as the filter member, and that the area of the ink inlet filter H 3071  is 200 mm 2  while the area of the ink outlet filter H 3072  is 50 mm 2 . The following description is the case where ink having 4 cP viscosity flows at a flow rate of 0.5 ml/second. With the experimental values, about 145.8 mmAq pressure loss is generated in the ink inlet filter H 3071  portion, and about 643.7 mmAq pressure loss is generated in the ink outlet filter H 3072  portion. With the aforementioned conditions of ink viscosity and ink flow rate, the filters alone generate a pressure loss of about 789.5 (145.8+643.7) mmAq. 
     Therefore, by arranging the filters in the above-described manner, bubbles inside the sub-tank H 310  can be removed before bubbles inside the individual liquid chamber are removed. 
     Other configurations may be adopted to make the flow passage resistance from the ink inlet port to the first air outlet port H 51  smaller than the flow passage resistance from the ink inlet port to the second air outlet port H 52 . For instance, the cross-sectional area of the ink flow passage from the sub-tank H 310  to the first air outlet port H 51  (flow passage of the float valve mechanism H 4 A) may be made larger than the cross-sectional area of the ink flow passage from the liquid chamber H 309  to the second air outlet port H 52  (flow passage of the float valve mechanism H 4 B). 
     Alternatively, the length of the ink flow passage from the sub-tank H 310  to the first air outlet port H 51  (flow passage of the float valve mechanism H 4 A) may be made shorter than the length of the ink flow passage from the liquid chamber H 309  to the second air outlet port H 52  (flow passage of the float valve mechanism H 4 B). 
     A detailed configuration of the float valve mechanism according to the present embodiment is shown in  FIG. 2 . As shown in  FIG. 2A , the float valve mechanism H 4  comprises a float housing H 43  and a float upper housing H 44 . In the float housing H 43 , there is a float chamber H 47  where a float H 9  is movably housed. At the fluid outlet of the float chamber H 47 , a seal member H 45  is provided. When the float chamber H 47  is filled with liquid, the lifted float H 9  comes in contact with the float seal member H 45 , thereby blocking the passage from the float chamber H 47  to the waste air-liquid flow passage H 3043  through the air outlet ports H 51  and H 52 . 
     The air moved from each of the liquid chambers to the float valve mechanism H 4  is removed through the waste air-liquid flow passage H 3043 . As shown in  FIGS. 2B and 2C , the sealing portion of the float valve mechanism may be of an O-ring H 451  or a taper seal member H 452 . 
     The overall configuration of the ink supply system of an inkjet printer, to which the present embodiment is applied, is shown in  FIG. 3 . 
     As shown in  FIG. 3 , the printhead H 301  is connected with the main tank M 303 , which serves as an ink supply source, through the ink flow passage H 304 . Between the main tank M 303  and the printhead H 301 , a compression mechanism M 306  may be arranged. Ink from the ink flow passage H 304  enters the sub-tank H 310  in the printhead H 301 , then an impure substance is filtered out by the ink inlet filter H 3071 , and the ink enters the individual liquid chamber H 309 . The ink in the individual liquid chamber H 309  is introduced to a printing element substrate H 308  arranged on the bottom portion of the individual liquid chamber H 309 . The ink outlet filter H 3072  is arranged in the neighborhood of the top portion of the individual liquid chamber H 309 . Above the ink outlet filter H 3072 , the float valve mechanism H 4  is arranged. Bubbles and waste liquid flow to the waste air-liquid flow passage H 3043  through the float valve mechanism H 4 . The waste air-liquid flow passages H 3043  provided respectively above the sub-tank float valve mechanism H 4 A and the individual liquid chamber float valve mechanism H 4 B are integrated inside the printhead, and connected to the main-body&#39;s waste air-liquid flow passage H 3043  outside the printhead as one system. In the printer main body, a waste ink tank M 35  is provided. In the main-body&#39;s waste air-liquid flow passage H 3043  between the printhead H 301  and the waste ink tank M 35 , a waste air-liquid pump M 312  which is necessary for giving negative pressure to the printhead is arranged, and is driven when executing an air removal operation. 
     The ink flow in the printhead at the time of executing an air removal operation is shown in  FIGS. 4 to 6 . In the initial state as shown in  FIG. 4 , the bubbles H 3101  and H 3091  exist in the sub-tank H 310  and the individual liquid chamber H 309 . First, the waste air-liquid pump M 312  is driven. As mentioned above, the flow passage resistance from the ink flow passage H 304  to the sub-tank float valve mechanism H 4 A is smaller than the flow passage resistance from the ink flow passage H 304  to the individual liquid chamber float valve mechanism H 4 B. Therefore, when the waste air-liquid pump M 312  is driven, an air removal operation of the sub-tank H 310  which has the smaller flow passage resistance is first executed, and air in the sub-tank H 310  is removed as shown in  FIG. 5 . After the air removal in the sub-tank H 310  is completed, the float H 91  of the sub-tank float valve mechanism H 4 A comes in contact with the seal member H 45 , thereby sealing the air outlet port. 
     With this state, the waste air-liquid pump M 312  is kept driven. The air removal operation is executed to remove air in the individual liquid chamber H 309  through the individual liquid chamber float valve mechanism H 4 B. Ultimately, air can be removed from both the sub-tank H 310  and the individual liquid chamber H 309  as shown in  FIG. 6 . 
     According to the configuration of the present embodiment, since bubbles in the individual liquid chamber H 309  can be removed after bubbles in the sub-tank H 310  are removed, bubbles in the sub-tank H 310  no longer get inside the individual liquid chamber H 309 . In other words, it is possible to prevent such situation where the bubbles passing through the ink inlet filter H 3071  turn into fine bubbles in the individual liquid chamber H 309  and become difficult to remove. Furthermore, a relief valve M 33  which serves as an atmospheric air communication mechanism is arranged between the waste air-liquid pump M 312  and the printhead H 301  so that the sub-tank float valve mechanism H 4 A and the individual liquid chamber float valve mechanism H 4 B can be released to the atmospheric air. Compared to the conventional recovery method which has produced a large amount of waste ink, according to the above-described configuration, it is possible to reduce the amount of waste ink and remove as many bubbles as possible from the sub-tank H 310  and the individual liquid chamber H 309 . 
     Second Embodiment 
     Shown in  FIG. 7  is an overall configuration of a supply system according to the second embodiment in an inkjet printing apparatus, to which the present invention is applied. As shown in  FIG. 7 , the printhead H 301  is connected with the main tank M 303  through the ink flow passage H 304 . Between the main tank M 303  and the printhead H 301 , a compression mechanism M 306  may be arranged. 
     Ink from the ink flow passage H 304  enters the sub-tank H 310  in the printhead H 301 , then an impure substance is filtered out by the ink inlet filter H 3071 , and the ink enters the individual liquid chamber H 309 . The ink in the individual liquid chamber H 309  is introduced to a printing element substrate H 308  arranged on the bottom portion of the individual liquid chamber H 309 . The ink outlet filter H 3072  is arranged in the neighborhood of the top portion of the individual liquid chamber H 309 . Above the sub-tank H 310 , a sub-tank float valve mechanism H 4 A is arranged. 
     Above the ink outlet filter H 3072 , an individual liquid chamber float valve mechanism H 4 B is arranged. Bubbles and waste liquid flow to the waste air-liquid flow passage H 3043  through the float valve mechanism H 4 . 
     In the present embodiment, the waste air-liquid flow passage H 3043  is arranged inside the printhead H 301 , and is introduced to the surface, where the discharge orifice H 306  is provided, then to the opening which is provided on the bottom surface of the printhead H 301 . In the apparatus main body, a cap M 32  is provided at the position facing the ink discharge surface. Further provided are the main body&#39;s waste air-liquid flow passage H 3043  for discharging bubbles and waste liquid from the cap M 32 , and the waste ink tank M 35 . Provided in midstream of the main body&#39;s waste air-liquid flow passage H 3043  is a waste air-liquid pump M 312  that can give negative pressure to the printhead H 301  through the cap M 32 . 
     When an air discharge operation using the float valve mechanism H 4  is executed, the cap M 32  is firmly attached to the opening. By driving the waste air-liquid pump M 312 , air can be removed from the float valve mechanism H 4 . Compared to the conventional recovery method which has produced a large amount of waste ink, according to the above-described configuration having the float valve mechanism H 4 , it is possible to reduce the amount of waste ink. Also, by virtue of the configuration for removing air from the float valve mechanism using the suction cap M 32 , the apparatus main body can be downsized. 
     Third Embodiment 
     The third embodiment, to which the present invention is applied, is shown in  FIG. 8 . As shown in  FIG. 8 , the carriage H 302  holds the printhead H 301  which discharges ink. A print operation on a print medium, which is not shown in the drawing, is executed by scanning the carriage in the main-scanning direction and discharging ink to the print medium while the print medium is conveyed in the sub-scanning direction by a print medium conveyance roller or the like which is not shown in the drawing. 
     As shown in  FIG. 8 , the printhead H 301  is arranged so that ink from the ink flow passage H 304  directly flows into the sub-tank H 310 . Below the sub-tank H 310 , the individual liquid chamber H 309  is provided for holding ink to be introduced through the ink inlet filter H 3071  to the discharge orifice H 306 . The ink inlet filter H 3071  is arranged at an angle with respect to the gravity direction. Because of this configuration, individual liquid chamber bubbles H 3091 , pooled inside the individual liquid chamber H 309 , can be gathered in one place. On the upper portion of the individual liquid chamber H 309 , the ink outlet filter H 3072  is arranged in the place where bubbles are easily gathered because of the inclination. 
     In the printhead H 301  having the above-described configuration, a sub-tank float valve mechanism H 4 A and an individual liquid chamber float valve mechanism H 4 B are arranged respectively above the sub-tank H 310  and the ink outlet filter H 3072 . 
     The sub-tank float valve mechanism H 4 A comprises a first float chamber H 47 A, where the first float H 91  is movably housed, between the sub-tank H 310  and the first air outlet port H 51 . The individual liquid chamber float valve mechanism H 4 B comprises a second float chamber H 47 B, where the second float H 92  is movably housed, between the individual liquid chamber H 309  and the second air outlet port H 52 . 
     A detailed configuration of each float valve mechanism H 4  according to the present embodiment is shown in  FIG. 9A . As shown in  FIG. 9A , the float valve mechanism H 4  comprises a float housing H 43  and a float upper housing H 44 . In the float upper housing H 44 , an opening/closing valve H 41  which has a downward projection is provided for atmospheric air communication control. The opening/closing valve provided in the upper portion of the first float chamber H 47 A is a first opening/closing valve. The opening/closing valve provided in the upper portion of the second float chamber H 47 B is a second opening/closing valve. Between the opening/closing valve H 41  and a seal keeping member H 46 , a spring member H 48  is arranged. On top of the opening/closing valve H 41 , a depressing mechanism H 40  is arranged. The float valve mechanism H 4  is sealed by flexible film H 42 . 
     In the downstream of the opening/closing valve H 41 , the waste air-liquid flow passage H 3043  is provided. Air moved from the sub-tank H 310  or individual liquid chamber H 309  to the float valve mechanism H 4  is removed through the waste air-liquid flow passage H 3043 . Above the depressing mechanism H 40 , a depressing member M 2 , such as a cam, is arranged outside the printhead, and driven by a driving source which is not shown in the drawing. 
     Next described is an operation when the depressing member M 2  is driven to drive the float valve mechanism H 4 . When the depressing member M 2  is not driven, the float upper housing H 44  is attached firmly to the opening/closing valve seal portion H 411  by the spring member H 48  so that the negative pressure in the printhead H 301  is maintained. 
     When a bubble removal operation is to be executed, as shown in  FIG. 9B  the depressing member M 2  is driven to push the depressing mechanism H 40  downward, thereby opening the opening/closing valve H 41 . Moreover, the depressing mechanism H 40  can be pushed down further as shown in  FIG. 9C . By this operation, a depressing rod at the bottom end of the depressing mechanism H 40  can detach the float H 9 , which has been attached to the seal member H 45 , apart from the seal member H 45 . Releasing the opening/closing valve H 41  is realized at the same time as detaching the float H 9  from the seal member H 45 . The depressing mechanism H 40  constitutes the detaching mechanism which detaches the float H 9  from the seal member H 45 . The mechanism acting on the first float is the first detaching mechanism, while the mechanism acting on the second float is the second detaching mechanism. 
     Shown in  FIG. 10  is an overall configuration of a supply system of an inkjet printing apparatus, to which the present embodiment is applied. As shown in  FIG. 10 , the printhead H 301  is connected with the main tank M 303  through the ink flow passage H 304 . Between the main tank M 303  and the printhead H 301 , a compression mechanism M 306  may be arranged. Ink from the ink flow passage H 304  enters the sub-tank H 310  in the printhead H 301 , then an impure substance is filtered out by the ink inlet filter H 3071 , and the ink enters the individual liquid chamber H 309 . The ink in the individual liquid chamber H 309  is introduced to the printing element substrate H 308  arranged on the bottom portion of the individual liquid chamber H 309 . 
     The ink outlet filter H 3072  is arranged in the neighborhood of the top portion of the individual liquid chamber H 309 . Above the ink outlet filter H 3072 , an individual liquid chamber float valve mechanism H 4 B is arranged. Above the sub-tank H 310 , a sub-tank float valve mechanism H 4 A is arranged. Bubbles and waste liquid flow to the waste air-liquid flow passage H 3043  through the float valve mechanism H 4 . The waste air-liquid flow passages H 3043  provided respectively above the sub-tank float valve mechanism H 4 A and the individual liquid chamber float valve mechanism H 4 B are integrated inside the printhead, and connected to the main-body&#39;s waste air-liquid flow passage H 3043  outside the printhead as one system. 
     In the printer main body, a waste ink tank M 35  is provided. In the main-body&#39;s waste air-liquid flow passage H 3043  between the printhead H 301  and the waste ink tank M 35 , a waste air-liquid pump M 312  which is necessary for giving negative pressure to the printhead H 301  is arranged, and is driven when executing an air removal operation. 
     When the air removal operation is completed, the depressing members M 2 , which are provided respectively above the sub-tank float valve mechanism H 4 A and the individual liquid chamber float valve mechanism H 4 B, are driven. Driving the depressing members M 2  pushes the float H 9  which may have been attached to the seal member H 45 , and executes an attachment prevention operation to prevent the float H 9  from being attached to the seal member H 45 . Furthermore, a relief valve M 33  which serves as an atmospheric air communication mechanism is arranged between the waste air-liquid pump M 312  and the printhead H 301  so that the printhead H 301  can be released to the atmospheric air. 
     In the conventional recovery method, a large amount of waste ink is generated. However, according to the above-described configuration which comprises the float valve mechanisms H 4 A and H 4 B using the depressing mechanism M 2 , it is possible to reduce the amount of waste ink. Furthermore, by virtue of eliminating malfunction caused by the float H 9  being attached to the seal member H 45 , and providing the opening/closing valve H 41  inside the float valve mechanism H 4 , it is possible to downsize the apparatus. 
     Fourth Embodiment 
     The fourth embodiment of the float valve mechanism, to which the present invention is applied, is shown in  FIGS. 11A and 11B . 
     As shown in  FIG. 11A , each float valve comprises a float housing H 43  and a float upper housing H 44 . Between the depressing mechanism H 40  and the seal keeping member H 46 , a spring member H 48  is arranged. The float valve mechanism H 4  is sealed by flexible film H 42 . In the downstream of the float H 9 , the waste air-liquid flow passage H 3043  is provided so that air moved from the sub-tank H 310  or individual liquid chamber H 309  to the float valve mechanism H 4  is removed through the waste air-liquid flow passage H 3043 . Above the depressing mechanism H 40 , a depressing member M 2 , such as a cam, is arranged outside the printhead, and driven by a driving source which is not shown in the drawing. 
     As shown in  FIG. 11B , the depressing member M 2  is driven to push the depressing mechanism H 40  downward. By this operation, the float H 9  which has been attached to the seal member H 45  can be detached, and as a result, a highly reliable float valve system can be realized. 
     Fifth Embodiment 
       FIG. 12  shows an overall configuration of a supply system according to the fifth embodiment in an inkjet printing apparatus, to which the present invention is applied. As shown in  FIG. 12 , the carriage H 302  holds the printhead H 301  which discharges ink. A print operation on a print medium, which is not shown in the drawing, is executed by scanning the carriage in the main-scanning direction and discharging ink to the print medium while the print medium is conveyed in the sub-scanning direction by a print medium conveyance roller or the like which is not shown in the drawing. As shown in  FIG. 12 , the printhead H 301  is arranged so that ink from the ink flow passage H 304  directly flows into the sub-tank H 310 . Below the sub-tank H 310 , the individual liquid chamber H 309  is provided for holding ink to be introduced through the ink inlet filter H 3071  to the discharge orifice H 306 . The ink inlet filter H 3071  is arranged at an angle with respect to the gravity direction. Because of this configuration, individual liquid chamber bubbles H 3091 , pooled inside the individual liquid chamber H 309 , can be gathered in one place. 
     On the upper portion of the individual liquid chamber H 309 , the ink inlet filter H 3071  is arranged in the place where bubbles are easily gathered because of the inclination. In the printhead H 301  having the above-described configuration, a sub-tank float valve mechanism H 4 A is arranged above the sub-tank H 310 . However, no float valve mechanism is provided above the ink outlet filter H 3072  of the individual liquid chamber H 309 . Instead, a flow resistance increasing mechanism H 49  is provided. The flow resistance increasing mechanism H 49  is consisted of a narrow flow passage and a plurality of filters in the flow passage. In this embodiment, when the waste air-liquid pump M 312  is driven, air inside the sub-tank H 310  is first removed by the sub-tank float valve mechanism H 4 A, thereafter the air inside the individual liquid chamber H 309  is removed together with ink. By virtue of having the aforementioned flow resistance increasing mechanism H 49 , the air inside the individual liquid chamber H 309  can be removed with little amount of waste ink without requiring a special mechanism. 
     Sixth Embodiment 
       FIG. 13  shows an overall configuration of a supply system of an inkjet printing apparatus, to which the present invention is applied. 
     As shown in  FIG. 13 , a plurality of printing element substrates H 308  are arranged serially or in a staggered manner on a supporting substrate H 32  in the printhead H 3011  according to the present embodiment. The printhead is a full-line inkjet printhead where ink discharge orifices are arranged throughout the entire width of a print paper. 
     At the position opposite to each of the printing element substrates H 308  on the supporting substrate H 32 , the aforementioned individual liquid chamber H 309  which supplies ink to the printing element substrate H 308  is provided. Above the supporting substrate H 32 , a chip tank H 33  is arranged in a way that a sub-tank H 310  is formed between the chip tank H 33  and the supporting substrate H 32 . In the chip tank H 33 , there is an ink flow passage H 304  which is connected to the external main tank M 303 . The ink inlet filter H 3071  is arranged between the sub-tank H 310  and each of the plurality of individual liquid chambers H 309  to filter out an impure substance, which gets in from outside the printhead, from the ink which is to be supplied to the printing element substrates H 308 . 
     Furthermore, the ink outlet filter H 3072  is provided on the upper portion of each of the individual liquid chambers H 309 . Air or ink discharged from the ink outlet filter H 3072  is integrated respectively in an individual liquid chamber waste air-liquid flow passage H 34 , and moved to the ink tank M 35  outside the printhead by the individual liquid chamber float valve mechanism H 4 B. 
     The ink outlet filter H 3072  may be arranged in each of the individual liquid chambers H 309  as mentioned above, or one ink outlet filter H 3072  may be provided somewhere between the individual liquid chamber float valve mechanism H 4 B and the individual liquid chamber waste air-liquid flow passage H 34  where discharged air or ink is integrated. Note that the ink outlet filter H 3072  is not necessarily required. 
     The full-line printhead H 3011  having the above-described configuration is constructed in a way that the flow passage resistance from the ink flow passage H 304  to the first air outlet port H 51  is smaller than the flow passage resistance from the ink flow passage H 304  to the second air outlet port H 52 . By virtue of this configuration, bubbles in the individual liquid chamber H 309  can be removed by the float valve mechanism H 4  after bubbles in the sub-tank H 310  are removed. Because the float valve mechanism H 4  is used, bubbles can be removed with a reduced amount of waste liquid, and bubbles in the sub-tank H 310  no longer get inside the individual liquid chamber H 309 . Therefore, it is possible to reliably remove as many bubbles as possible from the individual liquid chamber H 309 . 
     Seventh Embodiment 
     The seventh embodiment to which the present invention is applied is shown in  FIG. 14 . As shown in  FIG. 14 , the printhead H 301  is arranged so that ink from the ink flow passage H 304  directly flows into the sub-tank H 310 . 
     Below the sub-tank H 310 , the individual liquid chamber H 309  is provided for holding ink to be introduced through the ink inlet filter H 3071  to the discharge orifice H 306 . Further, the ink inlet filter H 3071  is arranged at an angle with respect to the gravity direction so that the individual liquid chamber bubbles H 3091 , pooled inside the individual liquid chamber H 309 , can be gathered in one place. 
     On the upper portion of the individual liquid chamber H 309 , an ink outlet filter H 3072  is arranged in the place where bubbles are easily gathered because of the inclination. In the printhead H 301  having the above-described configuration, the first and second air-liquid separation film H 61  and H 62  are arranged respectively above the sub-tank H 310  and the ink outlet filter H 3072 . By giving negative pressure to the waste air-liquid flow passage H 3043  using the waste air-liquid pump M 312 , bubbles accumulated in the lower side of the first and second air-liquid separation film H 61  and H 62  can be removed. 
     Furthermore, the flow passage from the first air-liquid separation film H 61  to the waste air-liquid flow passage H 3043  and the flow passage from the second air-liquid separation film H 62  to the waste air-liquid flow passage H 3043  join together along the way. The first air outlet port H 51  is provided at the flow passage exit of the sub-tank H 310 , while the second air outlet port H 52  is provided at the flow passage exit of the ink outlet filter. 
     The printhead according to the present embodiment is also constructed in a way that the flow resistance from the ink flow passage H 304  to the first air outlet port H 51  is smaller than the flow resistance from the ink flow passage H 304  to the second air outlet port H 52 . By virtue of this configuration, bubbles in the individual liquid chamber H 309  can be removed after bubbles in the sub-tank H 310  are removed. In other words, because the air-liquid separation film H 61  and H 62  are used, bubbles can be removed with a reduced amount of waste liquid, and bubbles in the sub-tank H 310  no longer get inside the individual liquid chamber H 309 . Therefore, it is possible to reliably remove as many bubbles as possible from the individual liquid chamber H 309 . 
     Each of the above-described embodiments is arranged in a way that the flow passage resistance from the ink flow passage H 304  to the first air outlet port H 51  is smaller than the flow passage resistance from the ink flow passage H 304  to the second air outlet port H 52 . By virtue of this configuration, when bubbles are to be removed from the float valve mechanism, bubbles in the sub-tank H 310  are first removed and the float valve of the sub-tank float valve mechanism H 4 A is sealed, thereafter bubbles in the individual liquid camber H 309  are removed. As a result, bubble removal can be realized with a reduced amount of waste ink compared to the conventional configuration. Furthermore, because bubbles in the sub-tank H 310  no longer get inside the individual liquid chamber H 309  through the ink inlet filter H 3071 , more bubbles can be removed from the individual liquid chamber H 309 . 
     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. 
     This application claims the benefit of Japanese Patent Application No. 2007-302977, filed Nov. 22, 2007, which is hereby incorporated by reference herein in its entirety.