Abstract:
Provided is a relatively simple structure in which ink can pressure-fill a head. In the structure, a reinforcement plate is attached to a film surface. Therefore, when the head is pressure-filled with the ink, a film of an air damper is not damaged by a pressure at the time when being pressurized. The attachment of the reinforcement plate suppresses bulging of the film, so that the pressure at the time of pressurization is efficiently transmitted to facilitate the ink supply. In addition, the pressurization can easily remove air from an inside of the head, thereby being capable of eliminating discharge failure in the head.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an air damper for generating a negative pressure in a head chip which is applicable to, for example, a printer or a facsimile, and to an ink jet head and an ink jet recording apparatus.  
           [0003]    2. Description of the Related Art  
           [0004]    Up to now, an ink jet recording apparatus has been known in which an ink jet head for discharging ink from plural nozzles is employed to record characters and/or images on a recording medium. In this type of ink jet recording apparatus, an entirety of the desired area is printed by repeating the following operations. That is, a carriage mounted with the ink jet head is moved in a main scanning direction with respect to the recording medium while the ink is discharged from a nozzle of the ink jet head, thereby printing a dot pattern in a predetermined area; and after one main scanning operation ends, the recording medium is moved in a sub-scanning direction by a predetermined amount.  
           [0005]    In a large ink jet recording apparatus, plural ink jet heads corresponding to respective ink colors are mounted to the carriage. This type of large ink jet recording apparatus in which the heads are mounted to the carriage and the carriage moves in the main scanning direction is called a “shuttle type recording apparatus”. The so-called shuttle type recording apparatus is structured such that, in order to perform a large amount of printing for a long period of time, an exchangeable large-capacity ink cartridge is incorporated in the apparatus and connected to the corresponding head through a tube to supply ink. In a method of supplying ink using a tube, when a carriage moves, the ink residing inside the tube moves therein in accordance with the movement of the carriage. When the ink moves, inertia is generated inside the head connected to the tube. Then, a differential pressure due to the inertia inside the head results in breakage of a meniscus that is formed by surface tension of the ink in a nozzle hole provided in a nozzle surface of the head. Thus, the ink cannot be discharged. In view of the above, a part called an “air damper” is generally mounted so as to relax the pressure fluctuation due to the inertia of the ink. In order to relax the pressure fluctuation, one side of the air damper is molded from a rigid body such as plastic to have a recessed portion for storing ink, and a film-shaped sheet is then bonded thereto by thermal welding or the like so as to seal the recessed portion. The film moves due to the pressure fluctuation of the ink in accordance with the movement of the carriage, thereby relaxing the pressure fluctuation of the ink.  
           [0006]    If the large ink jet recording apparatus is employed, it is necessary to increase a length of the tube for supplying the ink from the ink cartridge. The longer tube increases a flow path resistance inside the tube to disturb flow of the ink. Also, if an outside air temperature becomes low, viscosity of the ink increases to harden the ink. Thus, smooth flow of the ink is hindered under only an ordinary suction pressure. There can be employed another method of supplying ink by providing a sub-tank in the vicinity of a head. However, a larger apparatus becomes necessary, which leads to higher costs.  
           [0007]    Up to now, in order to fill the head with the ink, the following method has been employed. That is, a cap formed of rubber is brought in press contact with a nozzle plate of the head to seal an inside portion between the nozzle plate and the cap. Another tube is attached to an exhaust port provided to the cap which communicates with an external portion. Due to suction by a pump via the another tube, a negative pressure is generated inside a space between the cap and the nozzle plate. As a result, the head is filled with the ink via the tube from an ink cartridge. In this type of ink supplying method, the ink is sucked by only suction from the head side. Thus, if the longer tube is used, the head cannot be smoothly filled with the ink due to the generated flow path resistance.  
           [0008]    In view of this, there has been proposed an additional method of filling the head with the ink such that the ink is forced to be pushed out from the ink cartridge side by another pump different from the above pump. However, if being pressurized from the ink cartridge side by using this method, the pressure increases inside the air damper attached to the head which relaxes the inertia of the ink inside the tube, so that the film bonded to the air damper by thermal welding or the like is ruptured due to the internal pressure in some cases.  
         SUMMARY OF THE INVENTION  
         [0009]    In light of the above circumstances, the present invention has an object to provide a relatively simple structure in which ink can pressure-fill a head.  
           [0010]    In order to solve the above problems, according to a first aspect of the present invention, there is provided an air damper including a reinforcement plate for preventing rupture of a film of the air damper.  
           [0011]    According to a second aspect of the present invention, there is provided an air damper in which the reinforcement plate is formed of a transparent plastic plate.  
           [0012]    According to a third aspect of the present invention, there is provided an air damper in which the reinforcement plate includes on its film side a recessed portion for accepting deformation of the film caused by fluctuation in the ink inside the air damper which is generated when the head moves.  
           [0013]    According to a fourth aspect of the present invention, there is provided an air damper in which the reinforcement plate includes one or plural air holes for, in a case where a liquid surface inside the air damper fluctuates at the time of pressure fluctuation in accordance with the movement of a carriage, introducing air between the reinforcement plate and the film to relax the pressure fluctuation.  
           [0014]    According to a fifth aspect of the present invention, there is provided an air damper in which the reinforcement plate is fixed to the air damper with plural screws.  
           [0015]    According to a sixth aspect of the present invention, in any one of the first to fourth aspects, there is provided an air damper in which the reinforcement plate is fixed to the air damper by ultrasonic welding or the like.  
           [0016]    According to a seventh aspect of the present invention, there is provided an air damper further including recessed portions formed in right and left side surfaces or three surfaces of the right and left side surfaces and another surface of a main body of the air damper, in which: the reinforcement plate includes undercut portions to be fitted to the recessed portions of the air damper; and the reinforcement plate is fixed by inserting the undercut portions into the recessed portions of the air damper. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    In the accompanying drawings:  
         [0018]    [0018]FIG. 1 is a schematic view showing an attachment part of an air damper of the present invention;  
         [0019]    [0019]FIG. 2 is an exploded structural view showing a structure of the air damper of the present invention;  
         [0020]    [0020]FIG. 3 is a perspective view showing an external shape of an ink jet head mounted with the air damper of the present invention;  
         [0021]    [0021]FIG. 4 is an explanatory view showing how ink is pressure-supplied to the air damper of the present invention;  
         [0022]    [0022]FIG. 5 shows one embodiment in a case where a reinforcement plate is attached to the air damper of the present invention; and  
         [0023]    [0023]FIG. 6 shows another embodiment in the case where the reinforcement plate is attached to the air damper of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.  
         [0025]    [0025]FIG. 1 is a schematic view showing a part mounted with an air damper of the present invention, and FIG. 2 is an exploded structural view showing a structure of the air damper of the present invention. Further, FIG. 3 is a perspective view showing an external shape of an ink jet head mounted with the air damper.  
         [0026]    As shown in FIGS.  1  to  3 , a head  1  in accordance with the present invention is composed of: a head chip  10  made of PZT; a nozzle plate  11  which is provided to a front end of the head chip  10  and has a hole for discharging ink; a flow path  12  for supplying the ink to an inside of the head chip  10 ; a base  13  for fixing respective parts; an air damper  14 ; and the like.  
         [0027]    In an ink jet recording apparatus of the present invention, the ink is supplied to the head  1  by the following process. That is, a cap  20  formed of rubber is brought in press contact with the nozzle plate  11  of the head  1  to seal an inside portion between the nozzle plate  11  and the cap  20 . A tube  22  is attached to an exhaust port  21  provided to the cap  20  which communicates with an external portion. Due to suction by a not-shown pump via the tube  22 , a negative pressure is generated inside a space  23  between the cap  20  and the nozzle plate  11 . As a result, the head  1  is filled with the ink via a tube  25  from an ink cartridge  24  along the path shown by the arrows in FIG. 1.  
         [0028]    An ink reservoir portion  16  of the air damper  14  is structured to be sealed by fixing a polyester film  15  or the like to an air damper main body over an entire surface of the ink reservoir portion  16  by thermal welding, ultrasonic welding, adhesion, or the like. As described above, in a case where the head  1  is filled with the ink, if an ink discharging portion of the head  1  is sealed with the cap  20  and the negative pressure is generated on a head  1  side, the ink in the ink cartridge  24  is made to flow into the air damper  14  via the ink tube  25 . If the air damper  14  is filled with the ink, the head  1  is next filled with the ink, the ink is then jetted from the nozzle plate  11 , and air inside the head  1  is pushed out from the exhaust port  21  of the cap  20 . As a result, preparation of printing is complete.  
         [0029]    In the case where the ink has a high viscosity or the viscosity of the ink increases at a low temperature, a sufficient amount of ink cannot be supplied by an ordinary suction process. Such insufficient ink supply causes ink shortage and residual air inside the head  1 , so that the ink cannot be normally discharged from the head  1 . In this case, not only the suction process but also the following process may be employed. That is, as shown in FIG. 4, the cartridge  24  is directly pressurized in a direction shown by the arrow A to push out the ink. Alternatively, the tube  25  is pressed by a pump  26  to push out the ink from the tube  25 . Thus, the air damper  14  is rapidly filled with the ink, thereby making it possible to fill the head  1  with the ink.  
         [0030]    In this case, if the ink reservoir portion  16  with only the film  15  is pressure-filled with the ink, the film  15  bulges toward the external portion. If the film  15  bulges to such an extent that a tension of the film  15  reaches or exceeds its maximum tension and an adhesive force at an adhesive boundary between the air damper  14  main body and the film  15 , the film  15  can be ruptured. Also, if the film  15  bulges at the time of pressurization, a pressure for pushing out the ink decreases and there is a case where efficient pressure-filling cannot be performed.  
         [0031]    In order to suppress deficiency due to the bulging of the film  15  and transmit the pressure efficiently, as shown in FIG. 2, the air damper  14  of the present invention employs a structure in which a reinforcement plate  17  is fixed onto a not-shown film surface so as to prevent the film  15  from bulging. The reinforcement plate  17  can be formed of plastic or a metal plate. At the time of pressurization, a pressure of 1 to 2 atm is applied to the air damper  14 , so that the reinforcement plate  17  has rigidity enough to withstand the pressure at the time of pressure-filling of the ink. It is necessary that the reinforcement plate  17  formed of plastic has a thickness of 2 mm or more and the reinforcement plate  17  formed of a sheet metal has a thickness of 1 mm or more. For firm fixation, it is further necessary to use screws  18  and nuts  19  to fix the reinforcement plate  17  robustly. For this purpose, fixation holes  31  for fixing the reinforcement plate  17  are formed in the reinforcement plate  17  and the air damper  14 . Also, one or plural small holes  30  may be formed in the reinforcement plate  17  such that, in the case where a liquid surface inside the air damper  14  fluctuates at the time of pressure fluctuation in accordance with the movement of a carriage to thereby inhibit a movement of the film  15 , air is introduced between the reinforcement plate  17  and the film  15 , thereby making it possible to relax the pressure fluctuation. If respective structural parts disassembled as shown in FIG. 2 are reassembled, the head  1  according to this embodiment as shown in FIG. 3 is complete.  
         [0032]    In this embodiment, the screws  18  and the nuts  19  are connected via the through holes  31  of the air damper  14  and the reinforcement plate  17  to fix the reinforcement plate  17 . However, it is also possible to fix the reinforcement plate  17  by using the air damper  14  main body insert-molded with nuts or using self-tapping screws. Alternatively, in another method, as shown in FIG. 5, U-shaped undercut portions  27  are formed in side surfaces of the reinforcement plate  17  while recessed portions  28  to be fitted to the undercut portions  27  are formed in the air damper  14 . Therefore, the undercut portions  27  may be inserted into the recessed portions  28  to fix the reinforcement plate  17 . Similarly in this method, the fixation may require use of screws in some cases.  
         [0033]    Further, as another method of attaching the reinforcement plate  17 , as shown in FIG. 6, the reinforcement plate  17  may be fixed by ultrasonic welding or the like. In this case, the movement of the film  15  of the air damper  14  is regulated by the reinforcement plate  17 . Thus, a recessed portion  29  may be formed in the surface of the reinforcement plate  17  which opposes to the film  15  so that the film  15  can easily fluctuate. Note that, in this case, if the recessed portion  29  has a depth that is too large, the film  15  adheres to the recessed portion  29  of the reinforcement plate  17  or deforms due to the pressure at the time of pressurization. Thus, the depth of the recessed portion  29  is suitably set within the range of 0.3 to 1 mm.  
         [0034]    As has been described above, according to the present invention, the head can be filled with the ink by pressurization and suction simultaneously. Also, in the case where the ink has a high viscosity or the viscosity of the ink increases at a low temperature, the head can be easily filled with the ink.  
         [0035]    Hereinabove, the description has been made of the embodiments of the present invention. However, the present invention is not limited to the aforementioned structures and any modifications and variations may be made thereto without departing from the gist of the present invention as disclosed herein and claimed as appended herewith.