Abstract:
An ink jet head has a substrate, partition walls disposed on a main surface of the substrate and spaced apart at a preselected interval to form channels for receiving ink. An ink chamber plate is connected to the substrate to define with the partition walls an ink chamber for supplying ink to the channels. A passage forming member is connected to the ink chamber plate and has an ink supply passage disposed in communication with the ink chamber for supplying ink contained in an ink storage device to the ink chamber and at least one ink discharge passage for discharging ink from the ink chamber. The ink discharge passage is independent from the ink supply passage so that ink is supplied directly to the ink chamber through the ink supply passage without passing through at least a portion of the ink discharge passage.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink jet head and an ink jet recording apparatus that prints by discharging ink droplets through nozzle apertures, and to a method for removing unwanted substances including dust particles and bubbles from the ink jet head. 
     2. Description of the Related Art 
     There is known a conventional ink jet recording apparatus that records characters and images on a recording medium by using an ink jet head having a plurality of nozzles for discharging ink. In this ink jet recording apparatus, the nozzles of the ink jet head are formed in a head holder in such a position as to face the recording medium. The head holder is mounted on a carriage and performs scanning in a direction perpendicular to a transport direction of the recording medium. 
       FIG. 7  is an exploded schematic diagram showing an example of such an ink jet head. As shown in  FIG. 7 , a plurality of grooves  102  are formed in parallel in a piezo-ceramic plate  101 , and the grooves  102  are separated by side walls  103 . One end portion of each groove  102  in the longitudinal direction extends up to one end face of the piezo-ceramic plate  101 , whereas the other end portion of each groove  102  does not extend up to the other end face of the piezo-ceramic plate  101  and gradually decreases in depth. Electrodes  105  for applying drive voltages are formed in the opening-side surfaces of both side walls  103  of each groove  102  so as to extend in the longitudinal direction thereof. 
     An ink chamber forming substrate  107 , which forms an ink chamber  106  communicating with the end portion of each groove  102  where the depth is decreased, is joined to the piezo-ceramic plate  101  on the side where the grooves  102  are opened. Further, a passage forming member  109 , which seals one side of the ink chamber  106  and has an ink supply passage  108  for supplying ink to the ink chamber  106 , is fixed to the ink chamber forming substrate  107 . 
     A nozzle plate  110  is joined to the end face of the joined body of the piezo-ceramic plate  101  and the ink chamber forming substrate  107  on the side where the grooves  102  are opened. Nozzle apertures  111  are formed in the nozzle plate  110  in such positions as to face the respective grooves  102  of the nozzle plate  110 . 
     In the recording head that is constructed in the above-mentioned manner, when the ink is supplied to the grooves  102  via the ink supply passage  10  and predetermined driving electric fields are applied to both side walls  103  of a predetermined groove  102  through the electrodes  105 , the side walls  103  are deformed to change the capacity of the predetermined groove  102  so that the ink can be discharged from the groove  102  through the nozzle aperture  111 . 
     The above-described ink jet head is disadvantageous because the ink cannot be satisfactorily discharged due to dust, bubbles, etc. in the ink. To address this problem, a filter  112  is usually provided at the end of the ink supply passage  108  by the side of the ink chamber  106  so as to prevent dust and bubbles in the ink from entering the ink chamber  106 . 
     Although the use of the filter  112  can prevent the entry of dust and bubbles of a certain size, it is difficult to completely prevent the entry of dust and bubbles. Although the use of a finely meshed filter would prevent the entry of dust to a larger degree, such a filter disturbs the flow of ink. It is therefore impossible to use a finely meshed filter. 
     Dust which passes through the filter  112  is removed by a so-called cleaning operation in which the ink contained in the grooves  102  and the ink chamber  106  is absorbed through the nozzle apertures  111 . This cleaning operation, however, cannot completely remove the dust. The head from which the dust has not been removed must be disposed of. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an ink jet head and an ink jet recording apparatus that are capable of removing dust therein reliably and relatively easily, and a method for removing dust from the head. 
     To accomplish the above object, according to the first mode of the present invention, there is provided an ink jet head, which comprises a plurality of chambers being in communication with nozzle apertures and an ink chamber for supplying ink to the chambers, and which changes the capacity of the chambers to discharge ink contained in the chambers through the nozzle apertures, the ink jet head comprising a passage forming member having an ink supply passage constituting a part of a passage connecting an ink storage means storing ink therein to the ink chamber, the passage forming member having at least one communicating passage capable of discharging the ink from the ink chamber. 
     According to the second mode of the present invention, with the above arrangement in the first mode, the communicating passage is formed in each of regions in proximity to both ends of the ink chamber in the longitudinal direction. 
     According to the third mode of the present invention, with the above arrangement in the first mode, the communicating passage has a check valve permitting only a flow from the ink chamber to outside. 
     According to the fourth mode of the present invention, with the above arrangement in the first mode, the communicating passage is sealed by securing a cap member to the passage forming member through an O-ring. 
     According to the fifth mode of the present invention, with the above arrangement in the first mode, a filter is provided between the ink supply passage and the ink chamber, and ink is supplied from the ink storage means to the ink chamber through the filter. 
     According to the sixth mode of the present invention, the present invention also provides an ink jet recording apparatus having the ink jet head with the above arrangement in the mode, the ink jet recording apparatus comprising absorbing means connected to the communicating passage, the absorbing means absorbing ink in the ink chamber through the communicating passage. 
     According to the seventh mode of the present invention, there is provided a head dust removing method for removing dust in a passage of an ink jet head which comprises a plurality of chambers connected to nozzle apertures, an ink chamber for supplying ink to the chambers, and a plurality of communicating passages capable of discharging the ink from the ink chamber, the method comprising: a stirring step of absorbing the ink in the ink chamber through the communicating passages with different timings and stirring the ink in the ink chamber; and a discharging step of absorbing ink including dust in the ink chamber and discharging the same to outside. 
     According to the eighth mode of the present invention, with the above arrangement in the seventh mode, the communicating passages are formed in respective regions corresponding to both ends of the ink chamber in the longitudinal direction, and the stirring step comprises absorbing the ink in the ink chamber through the communicating passages alternately. 
     According to the present invention, the ink contained in the ink chamber is absorbed and discharged through the communicating passages formed in the passage forming member. This makes it possible to remove the dust from the ink reliably and relatively easily. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is an assembly perspective view showing an ink jet head according to an embodiment of the present invention; 
         FIG. 2  is a sectional view showing a principal part of an ink jet head according to an embodiment of the present invention; 
       FIG.  3 A and  FIG. 3B  are exploded perspective views showing a head chip according to an embodiment of the present invention; 
         FIG. 4  is a schematic sectional view showing a principal part of a head chip according to an embodiment of the present invention; 
         FIG. 5  is a perspective view showing a passage forming member according to an embodiment of the present invention; 
       FIG.  6 A through  FIG. 6C  are schematic diagrams showing the procedure for removing dust according to an embodiment of the present invention; and 
         FIG. 7  is an exploded perspective view showing the outline of an ink jet head according to the prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with reference to the drawings showing an embodiment thereof. 
       FIG. 1  is an assembly perspective view showing an ink jet head according to an embodiment of the present invention,  FIG. 2  is a sectional view showing a principal part of the ink jet head, and  FIGS. 3A and 3B  are perspective view showing a head chip of the ink jet head. 
     As shown in  FIGS. 1 and 2 , the ink jet head  10  of this embodiment is comprised of the head chip  11 , a passage forming member  12  disposed at one side of the head chip  11 , and a wiring substrate  14  on which a drive circuit for driving the head chip  11  and the like are fabricated. These members are fixed to a base member  15 . 
     First, the structure of the head chip  11  will be described. As shown in  FIGS. 3A and 3B , a plurality of channels or grooves  17  are formed in parallel in a piezo-ceramic plate  16  of the head chip  11 , and the grooves  17  are separated by side walls  18 . On end portion of each groove  17  extends up to one end face of the piezo-ceramic plate  16 , whereas the other end portion of each groove  17  does not extend up to the other end face of the piezo-ceramic plate  16  and gradually decreases in depth. The grooves  17  are formed in the piezo-ceramic plate  16  by a disc-shaped dice cutter or the like. The shallow portions of the grooves  17  ar unnecessary, but they are inevitably formed due to the shape of the dice cutter. 
     Electrodes  19  for applying electric fields to drive the side walls  18  are formed on the side walls  18 , which are formed at both sides of the respective grooves  17  in the direction of the width thereof, in the longitudinal direction on the side where the grooves  17  are open. 
     An ink chamber plate  21 , which forms an ink chamber  20  communicating with each groove  17 , is joined to the opening side of the grooves  17  in the piezo-ceramic plate  16  on which the grooves  17 , the electrodes  19  and the like are formed as stated above. The ink chamber  20  and the respective grooves  17  communicate with each other in proximity to the other end portions of the respective grooves  17  where the depth is decreased. 
     Although the ink chamber plate  21  may be formed of a ceramic plate, a metallic plate, or the like, it is preferably formed of a ceramic plate whose coefficient of thermal expansion is approximate to that of the piezo-ceramic plate  16  in terms of deformation and the like after the joint with the piezo-ceramic plate  16 . 
     A nozzle plate  22  is joined to the end face of the joined body of the piezo-ceramic plate  16  and the ink chamber plate  21  on the end face where the grooves  17  are open. Nozzle apertures  23  are formed in the nozzle plate  22  in such a position as to face the respective grooves  17 . 
     According to the present embodiment, the area of the nozzle plate  22  is larger than that of the end face of the joined body of the piezo-ceramic plate  16  and the ink chamber plate  21  on the side where the grooves  17  are open. The nozzle plate  22  is constructed by forming nozzle apertures  23  in polyimide film or the like by using, e.g. an excimer laser apparatus. Although not illustrated, a water-repellent film is formed at one side of the nozzle plate  22 , which faces a printed matter, in order to prevent the adhesion of ink and the like. 
     According to this embodiment, a nozzle support plate  24  is disposed around the end portion of the joined body of the piezo-ceramic plate  16  and the ink chamber plate  21  on the side where the grooves  17  are open. The nozzle support plate  24  is used to stably hold the nozzle plate  22 . The nozzle support plate  24  is joined to outer side of the end face of the joined body of the nozzle plate  22 , and is fixed to the base member  15 . 
     The passage forming member  12  is joined to one side of the ink chamber plate  21  constituting the head chip  11  by an adhesive agent or the like as shown in FIG.  4 . One side of the ink chamber  20  is sealed by the passage forming member  12 . The passage forming member  12  is fixed in such a manner as to be tightly joined to the ink chamber  20 . For example, an O-ring may be provided between the ink chamber plate  21  and the passage forming member  12 , and the passage forming member  12  may be fastened by a screw member or the like. The passage forming member  12  now will be described. As shown in  FIGS. 4 and 5 , in the substantially central area of the passage forming member  12  in the longitudinal direction, there is provided an ink supply passage  26  that constitutes a part of an ink passage, which connects an ink storage means (not illustrated) for storing ink in an ink tank or the like to the ink chamber  20 . In their respective regions in proximity to both ends of the passage forming member  12  in the longitudinal direction thereof, there are provided ink discharge passages or communicating passages  27  and  28  that connect the ink chamber  20  to the outside so as to discharge the ink from the ink chamber  20  to the outside. Each of the communicating passages  27  and  28  is independent from the ink supply passage  20  so that ink supplied into the ink chamber  20  through the ink supply passage  26  does not pass through at least a portion of each of the communicating passages  27  and  28  (e.g., a portion of each of the communicating passages  27 ,  28  extending from an exterior surface of the passage forming member  12 ). 
     The ink supply passage  26  is provided with an air tank  29  that adjusts the negative pressure of the ink supplied to each head chip so that the negative pressure of the ink supplied to the ink chamber  20  from the ink storage means can be constant. A filter  30  is provided at the end of the ink supply passage  26  by the side of the ink chamber  20 . The ink is supplied into the ink chamber  20  after the dust is removed by the filter  30  to a certain degree. 
     On the other hand, according to this embodiment, a check valve  31  is provided in each of the communication passages  27  and  28  formed in the regions corresponding to both ends of the ink chamber  20  in the longitudinal direction. The check valve  31  permits only a flow from the ink chamber  20  to the outside so that the ink in the ink chamber  20  can be discharged to the outside through the communication passage  27  and  28  without being exposed to the air. Although described later in further detail, the unwanted substances included in the ink in the ink chamber  20  and the grooves  17  is removed by absorbing the ink in the ink chamber  20  and the grooves  17  through at least one of the communication passages  27  and  28  when the ink jet head is manufactured, maintained, or the like. It should be noted that in this description the word “unwanted substances” includes, for example, dust particles and bubbles. 
     When the ink is absorbed, it is necessary to continuously supply the ink into the ink chamber  20  and the grooves  17  so as to prevent the air from being absorbed into the ink chamber  20  and the grooves  17  through the nozzle apertures  23 , etc. According to the present embodiment, when the ink is absorbed, a container for storing ink therein is disposed in the ink jet head  10  by the side of the nozzle plate  22 , and the nozzle plate  22  is immersed in the ink so that the ink can flow into the grooves  17  through the nozzle apertures  23  by absorption through the communicating passages  27  and  28 . It is to be understood, however, that the method for supplying the ink into the ink chamber  20  and the grooves  17  is not restricted to the above-described one. For example, the ink may be supplied from an ink storage means through the ink supply passage  26  with the nozzle apertures  23  being sealed. 
     Although there are no particular limitations regarding the procedure for removing the dust by absorbing the ink, it is preferable to carry out a stirring step for absorbing the ink through the communicating passages  27  and  28  with different timings and stirring the ink contained in the ink chamber  20  and the grooves  17 . An example of the procedure for removing the dust will now be described.  FIGS. 6A through 6C  are diagrams explaining the procedure for removing the dust. The structure of the passage forming member  12  shown in  FIGS. 6A through 6C  is slightly different from the actual structure. 
     In the procedure for removing the dust according to this embodiment, the stirring step for stirring the dust in the ink is carried out first. Specifically, as shown in  FIG. 6A , the ink contained in the ink chamber  20  and the grooves  17  is absorbed through one communicating passage  27 . This absorbs the dust in the vicinity of the communicating passage  27  as well as the ink, and generates a flow in the ink to stir the dust included in the grooves  17  at the center. The dust included in the ink is schematically indicated by the dots in the figures. 
     According to this embodiment, the check valve  31  provided in each of the communicating passages  27  and  28  prevents the air from coming into the ink chamber  20  through one communicating passage  28  when the ink is absorbed through the other communicating passage  27 . Therefore, the ink is supplied into the grooves  17  and the ink chamber  20  through the nozzle apertures  23  such that the grooves  17  and the ink chamber  20  are constantly filled with the ink. 
     As shown in  FIG. 6B , the ink in the ink chamber  20  and the grooves  17  is then absorbed through the communicating passage  28 . This generates a flow in the ink in a direction reverse to the flow generated by absorption through the communicating passage  27 , so that the dust in the grooves  17  can be further stirred. 
     Although the ink is absorbed to such an extent as to remove the dust in the vicinity of the communicating passages  27  and  28  in the stirring step according to this embodiment, the dust should not necessarily be absorbed in the stirring step insofar as the flow can be generated in the ink to stir the dust in the grooves  17 . Therefore, the ink may be absorbed a plurality of times through the respective communicating passages  27  and  28  alternately with a relatively weak absorbing power. 
     After the dust included in the ink is stirred in the stirring step as stated above, a dust absorption step is carried out. Specifically, the ink in the ink chamber  20  and the grooves  17  is absorbed through both communicating passages  27  and  28  in  FIG. 6C , and this absorbs the ink and the stirred dust to reliably remove the dust from the ink chamber  20  and the grooves  17 . It is needless to say that the ink may be absorbed only through one communicating passage with the other communicating passage being sealed. 
     As stated above, according to this embodiment, the passage forming member  12  is provided with the communicating passages  27  and  28  that connect the ink chamber  20  to the outside. When, for example, the head is manufactured, the ink contained in the ink chamber  20  and the grooves  17  is absorbed through the communicating passages  27  and  28  so as to remove the dust from the ink. It is therefore possible to remove the dust reliably and relatively easily even if the dust cannot be removed by absorption through the nozzle apertures  23 . Moreover, bubbles can be removed from the ink at the same time. It is therefore possible to uniformalize the characteristics of the ink discharged through the respective nozzle apertures  23  and to maintain the satisfactory ink discharge characteristics. 
     According to this embodiment, the check valve  31  is provided in each of the communicating passages  27  and  28  so as to prevent the air from coming into the ink chamber  20  through the communicating passages  27  and  28 . Alternatively, the communicating passages  27  and  28  may be sealed by securing a cap member thereto through an O-ring or the like without providing the check valve  31 . 
     Although the passage forming member  12  is provided with two communicating passages  27  and  28  according to this embodiment, the number of communicating passages is not restricted to two. For example, the passage forming member  12  may be provided with three or more communicating passages, or only one communicating passage. 
     It should be noted that the wiring substrate  14 , on which a drive circuit and the like are fabricated, is fixed on the base member  15  to which the above-described ink jet head  10  is fixed, and the wiring substrate  14  and a wiring  19  of the head chip  11  are connected with each other via a flexible cable  32  or the like and mounted on a carriage of the ink jet recording apparatus. 
     Although the ink contained in the ink chamber  20  and the grooves  17  is absorbed through the communicating passages  27  and  28  when, for example, the ink jet head is manufactured according to the present embodiment, the method for absorbing the ink is not restricted to this. For example, the ink jet recording apparatus may be provided with the above-described ink jet head  10  and an absorbing means such as a vacuum pump that is connected to the communicating passages  27  and  28  of each ink jet head  10  so that the ink contained in the ink chamber  20  and the grooves  17  can be absorbed with predetermined timings. 
     Although such an absorbing means may be additionally provided in the ink jet recording apparatus, it is possible to use the absorbing means that is used for the so-called cleaning operation in which the ink is absorbed through the nozzle apertures. 
     As stated above, the ink jet recording apparatus is provided with the ink jet head having the communicating passages and the absorbing means so that the ink contained in the ink chamber and the grooves can be absorbed with predetermined timings through the communicating passages. It is therefore possible to reliably remove the dust included in the ink contained in the ink chamber and the grooves, thus maintaining the excellent printing quality and improving the durability. 
     As set forth hereinabove, according to the present invention, the passage forming member constituting the ink jet head is provided with the communicating passages that connect the ink chamber to the outside. It is therefore possible to reliably remove the dust included in the ink by absorbing the ink in the ink chamber and the grooves through the communicating passages.