Patent Publication Number: US-8523321-B2

Title: Liquid droplet jetting apparatus and recording apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2007-126836, filed on May 11, 2007, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid droplet jetting apparatus such as an ink-jet head which jets liquid droplets from a plurality of nozzles, and a recording apparatus which includes the liquid droplet jetting apparatus. 
     2. Description of the Related Art 
     An ink-jet head which jets an ink as liquid droplets has been known as a liquid droplet jetting apparatus. The ink-jet head has a nozzle row which includes a plurality of nozzles and a common liquid chamber to which the ink is supplied from an ink tank. The common liquid chamber extends along the nozzle row and each of the nozzles in the nozzle row is connected to the common liquid chamber via a pressure chamber. In this ink-jet head, the ink is supplied from the ink tank to one end portion, of the common liquid chamber, in a direction in which the nozzle row is arranged, and by applying a pressure fluctuation to the pressure chamber, the ink is jetted from each nozzle as droplets of ink (ink droplets). In the ink-jet head in which, the ink flows through the common liquid chamber from the one end portion to the other end portion, air bubbles which are generated in the ink and grown up are susceptible to be accumulated, and a jetting defect is susceptible to occur in nozzles, in the nozzle row, which are arranged at the other end portion side of the common liquid chamber. Therefore, in a stacked ink-jet recording head described in U.S. Pat. No. 5,748,214A (corresponds to Japanese Patent Application Laid-open No. H8-58086), for example, by arranging so-called dummy nozzles which are not used in an image formation to communicate with a dead end portion of a common ink chamber, and by carrying out a purge operation of nozzles including the dummy nozzles, air bubbles accumulated in the dead end portion of the common ink chamber are discharged. 
     Moreover, in such ink-jet head, when a pressure fluctuation is applied to a pressure chamber to jet the ink from a certain nozzle, a pressure wave is propagated to a common liquid chamber which is connected to this nozzle. The pressure wave propagated in this common liquid chamber causes the pressure fluctuation of a pressure chamber which is connected to the other nozzle, and causes an unnecessary jetting and a variation (unevenness) in a jetting volume, thereby causing a so-called cross-talk which is a printing defect phenomenon. In order to suppress the cross-talk, in a liquid droplet jetting recording head described in Japanese Patent No. 2815958, an inclined wall or a pocket chamber is formed in an end portion inside a common liquid chamber, on a side where an ink jetting port is not formed, and by causing a pressure wave to be reflected at the inclined wall or the pocket chamber, the pressure wave is attenuated. Moreover, in a liquid droplet jetting head described in Japanese Patent Application Laid-open No. 2004-358737, a partition is formed on a wall surface of a common liquid chamber, and by causing the pressure wave to be reflected or to be resisted, a resonance state of the pressure wave is suppressed. 
     Inventors of the present invention, as a result of carrying out various experiments regarding such ink-jet head, found that the pressure wave is concentrated at the other end portion, in the direction of the nozzle row, of the common liquid chamber. Moreover, it was revealed that, when there is a plurality of nozzle rows, and there is a common liquid chamber corresponding to each nozzle row, a pressure wave which is generated by jetting ink droplets from a nozzle in a particular row, is also concentrated in the other end portion, in the direction of the nozzle row, of the common liquid chamber corresponding to the other nozzle row. Therefore, a high pressure fluctuation acts on the dummy nozzles formed in the other end portion in the direction of row, and there has been an occurrence of defect that the ink droplets are jetted from the dummy nozzle due to this pressure fluctuation. Due to such defect, undesired ink droplets are adhered to a recording paper etc. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a liquid droplet jetting apparatus in which it is possible to suppress unnecessary jetting of liquid droplets from a dummy nozzle due to propagation of a pressure wave to a common liquid chamber at the time of jetting the liquid droplets, and a recording apparatus which includes the liquid droplet jetting apparatus. 
     According to a first aspect of the present invention, there is provided a liquid droplet jetting apparatus which jets a droplet of a liquid, including: a common liquid chamber to which the liquid is supplied; a plurality of pressure chambers which communicate with the common liquid chamber and which causes a pressure change in the liquid; a plurality of nozzles which communicate with the pressure chambers respectively, and each of which jets the droplet of the liquid; a pressure attenuation chamber which has a throttled portion having a cross-sectional area smaller than a cross-sectional area of the common liquid chamber, and an attenuation portion having a cross-sectional area greater than the cross-sectional area of the throttled portion, the attenuation portion being connected to the common liquid chamber via the throttled portion; a discharge port which is formed in the pressure attenuation chamber; a discharge channel which is connected to the discharge port and having a throttle in which a channel area of the discharge channel is decreased; and a dummy nozzle which is connected to the discharge port via the discharge channel, and which is open to an atmosphere. 
     In the liquid droplet jetting apparatus of the present invention, even when a pressure wave is propagated to the liquid inside the common liquid chamber due to the pressure change in the liquid inside pressure chamber, it is possible to attenuate the pressure wave in the common liquid chamber by an attenuation portion which is connected to the common liquid chamber via the throttled portion. In this pressure attenuation chamber, the discharge port which is connected to the dummy nozzle via the discharge channel is formed, and a throttle in which the channel area of the discharge channel is reduced is formed in this discharge channel. Accordingly, it is possible to attenuate further the pressure wave which is propagated to the discharge channel. Consequently, even when the pressure wave is propagated to the liquid inside the common liquid chamber due to the pressure change in the liquid inside the pressure chamber, it is possible to attenuate this pressure wave before reaching the dummy nozzle, and to prevent the dummy nozzle from unnecessary jetting of the liquid droplets. 
     In the liquid droplet jetting apparatus of the present invention, the common liquid chamber may extend in a predetermined direction, and the attenuation portion may be connected to an end portion of the common liquid chamber via the throttled portion. By the attenuation portion being connected to the end portion of the common liquid chamber via the throttled portion, it is possible to release the pressure wave concentrated in the end portion of the common liquid chamber to the attenuation portion. Moreover, air bubbles developed inside the common liquid chamber, and accumulated in the end portion of the common liquid chamber flow into the attenuation portion via the throttled portion following the flow of the liquid into the common liquid chamber. On the other hand, since the throttled portion has the cross-sectional area smaller than that of the attenuation portion, it is possible to prevent the air bubbles flowed into the attenuation portion from being flowed to the common liquid chamber against the flow of the liquid inside the common liquid chamber. In other words, it is possible to prevent the air bubbles developed in the common liquid chamber from being accumulated in the common liquid chamber. 
     The liquid droplet jetting apparatus of the present invention may further include a pressure applying mechanism which is formed to cover the pressure chambers. Since the pressure applying mechanism is formed to cover the pressure chambers, it is possible to apply a jetting pressure to the liquid inside the pressure chamber. 
     In the liquid droplet jetting apparatus of the present invention, the dummy nozzle may be formed in the vicinity of the end portion of the common liquid chamber. Since it is possible to secure sufficiently a length of the discharge channel by forming the dummy nozzle in the vicinity of the end portion of the common liquid chamber, it is possible to attenuate the pressure wave which is propagated to the liquid inside the discharge channel. 
     The liquid droplet jetting apparatus of the present invention may further include a plurality of discharge structures each of which includes the discharge port, the discharge channel, and the dummy nozzle. According to the discharge structures, it is possible to disperse the pressure wave which is propagated to the dummy nozzle in each discharge structure, and to decrease the pressure change developed in the dummy nozzle. Therefore, it is possible to suppress further the jetting of the unnecessary liquid droplets from the dummy nozzle due to concentration of the pressure wave in the dummy nozzle. 
     In the liquid droplet jetting apparatus of the present invention, the discharge structures may include a first discharge structure which includes the discharge port formed in the vicinity of the throttled portion, and a second discharge structure which includes the discharge port formed in the attenuation portion at a position away from the throttled portion. In this case, according to a position of the discharge port included in each of the discharge structures, a difference of high and low is developed in the pressure wave which is propagated from the common liquid chamber to the pressure attenuation chamber. Therefore, it is possible to disperse the pressure wave propagated to each dummy nozzle, and to suppress the unnecessary jetting of the liquid droplets from the dummy nozzle. 
     According to a second aspect of the present invention, there is provided a liquid droplet jetting apparatus which jets a droplet of a liquid, including: a liquid supply chamber to which the liquid is supplied; a plurality of pressure chambers which communicate with the liquid supply chamber and which causes a pressure change in the liquid; a plurality of nozzles which communicate with the pressure chambers respectively, and each of which jets the droplet of the liquid; a discharge port group which includes a plurality of discharge ports formed in the liquid supply chamber; a plurality of discharge channels which are connected to the discharge ports of the discharge port group respectively, and which communicate with each other; and a dummy nozzle which is connected to the discharge ports via the discharge channels, and which is open to an atmosphere. 
     In the liquid droplet jetting apparatus of the present invention, since the discharge port group which includes the discharge ports is formed in the liquid supply chamber, and the discharge ports communicate with each other via the discharge channels, and are connected to the dummy nozzle, even when the pressure wave is propagated to the liquid in the liquid supply chamber by the pressure change in the liquid inside the pressure chamber, and even when the pressure wave is propagated to the liquid inside the discharge channels, it is possible to release the pressure wave propagated to the discharge channels toward a discharge port at which the pressure is lower than the other discharge ports. Accordingly, it is possible to suppress the pressure wave propagated to the discharge channel through the discharge port from being concentrated in the dummy nozzle, and to suppress the unnecessary jetting of the liquid droplets from the dummy nozzle. 
     In the liquid droplet jetting apparatus of the present invention, the liquid supply chamber may extend in a predetermined direction, and the discharge ports included in the discharge port group may be formed in the predetermined direction to be isolated from each other. In this case, a difference of high and low is developed in the pressure wave which is propagated in the liquid supply chamber at a position of each discharge port included in the discharge port group, and it is possible to release the pressure wave propagated from one discharge port to the discharge channel, toward a discharge port at which the pressure is lower than the pressure of the other discharge ports. Therefore, it is possible to suppress the pressure wave from being concentrated in the dummy nozzle, and to suppress the unnecessary jetting of the liquid droplets from the dummy nozzle. By forming each discharge port such that a phase of the pressure wave propagated to the discharge channels is shifted, it is possible to suppress more effectively the pressure wave from being concentrated in the dummy nozzle. 
     In the liquid droplet jetting apparatus of the present invention, a total of channel lengths of two discharge channels, among the plurality of discharge channels, communicating with two discharge ports among the plurality of discharge ports in the discharge port group respectively, may be greater than a direct distance between the two discharge ports. By letting the direct distance between the two discharge ports and the total of the channel lengths of two discharge channels communicating with the discharge ports respectively to be different, it is possible to attenuate effectively the pressure wave propagated from each discharge port to the dummy nozzle via the discharge channel, and to release the pressure wave propagated from one discharge port toward a discharge port on a lower pressure side. Accordingly, it is possible to suppress the pressure wave from being concentrated in the dummy nozzle, and to suppress the unnecessary jetting of the liquid droplets from the dummy nozzle. According to this structure, it is possible to shift easily the phase of the two pressure waves, and to suppress the concentration of the pressure wave in the dummy nozzle. 
     In the liquid droplet jetting apparatus of the present invention, the two discharge channels may be joined with each other in a V-shape and then may be connected to the dummy nozzle. In this case, since it is possible to have a sufficient length of two discharge channels, it is possible to attenuate sufficiently the pressure chamber propagated to the dummy nozzle, and to suppress the unnecessary jetting of the liquid droplets from the dummy nozzle. Moreover, it is also possible to overlap the phases of the two pressure waves upon shifting sufficiently, to offset the two pressure waves, and it possible to suppress the concentration of the pressure wave in the dummy nozzle. 
     In the liquid droplet jetting apparatus of the present invention, the discharge channels may be joined with each other at a predetermined position and then may be connected to the dummy nozzle, and a throttle in which a channel area is reduced than those of the discharge channels may be formed between the predetermined position and the dummy nozzle. In this case, it is possible to release the pressure wave propagated to the discharge channels toward a discharge port on a lower pressure side. Furthermore, due to the existence of the throttle between the predetermined position at which the discharge channels are joined, and the dummy nozzle, it is possible to attenuate the pressure wave before reaching the dummy nozzle, and to suppress even more effectively the pressure wave from being concentrated at the dummy nozzle. 
     The liquid droplet jetting apparatus of the present invention may further include a plurality of discharge structures each of which includes the discharge port group, the plurality of discharge channels, and the dummy nozzle. Due to the discharge structures, it is possible to disperse the pressure wave propagated to each dummy nozzle, and to reduce the pressure change developed in the dummy nozzle. Therefore, it is possible to suppress the pressure wave from being concentrated at the dummy nozzle, and to suppress the unnecessary jetting of the liquid droplets from the dummy nozzle. 
     In the liquid droplet jetting apparatus of the present invention, the liquid supply chamber may have a common liquid chamber which extends in a predetermined direction and which is connected to the pressure chambers; and a pressure attenuation chamber which includes a throttled portion having a cross-sectional area smaller than a cross-sectional area of the common liquid chamber, and an attenuation portion having a cross-sectional area greater than the cross-sectional area of the throttled portion, the attenuation portion being connected to an end portion of the common liquid chamber via the throttled portion, and the discharge port group may be formed in the pressure attenuation chamber. In this case, even when the pressure wave is concentrated at the end portion of the common liquid chamber due to the pressure change in the liquid inside the pressure chamber, firstly, it is possible to attenuate the pressure wave in the common liquid chamber, at the attenuation portion which is connected to the common liquid chamber via the throttled portion. Furthermore, since the discharge port group which is connected to the dummy nozzle via the discharge channel is formed in the pressure attenuation chamber, it is possible to suppress the pressure wave attenuated in the attenuation portion from being concentrated in the dummy nozzle upon being propagated through the discharge channels. 
     The liquid droplet jetting apparatus of the present invention may further include a plurality of discharge structures each of which includes the discharge port group, the plurality of discharge channels, and the dummy nozzle; and the discharge structures may have a first discharge structure in which the discharge port group is formed in the vicinity of the throttled portion, and a second discharge structure in which the discharge port group is formed in the attenuation portion at a position away from the throttled portion. In this case, according to a position of the discharge port group included in each discharge structure, a difference of high and low is developed in the pressure wave which is propagated from the common liquid chamber to the pressure attenuation chamber. Therefore, it is possible to disperse the pressure wave propagated to each dummy nozzle, and to suppress the unnecessary jetting of the liquid droplets from the dummy nozzle. 
     In the liquid droplet jetting apparatus of the present invention, the discharge ports of the discharge port group in the first discharge structure may include a discharge port formed in the common liquid chamber and a discharge port formed in the attenuation portion; and the discharge ports of the discharge port group of the second discharge structure may be all formed in the attenuation portion. According to this structure, a difference of high and low is developed in the pressure wave which is propagated in the common liquid chamber and the attenuation portion at a position of each discharge port, and it is possible to release the pressure wave propagated from one discharge port to the discharge channel toward a discharge port on a lower pressure side. Moreover, it is possible to prevent air bubbles from being accumulated at the end portion of the common liquid chamber. 
     In the liquid droplet jetting apparatus of the present invention, the dummy nozzle in each of the first discharge structure and the second discharge structure may be formed in the vicinity of the end portion of the common liquid chamber. Since it is possible to secure sufficiently a length of each discharge channel by forming each dummy nozzle in the vicinity of the end portion of the common liquid chamber, it is possible to attenuate the pressure wave propagated to the liquid inside the discharge channel. 
     The liquid droplet jetting apparatus of the present invention may further include a pressure applying mechanism which is formed to cover the pressure chambers. 
     According to a third aspect of the present invention, there is provided a recording apparatus which performs recording on a recording medium by jetting a droplet of a liquid, including: the liquid droplet jetting apparatus as defined in the second aspect of the present invention; and a transporting mechanism which transports the recording medium in a predetermined direction. 
     According to the recording apparatus of the present invention, it is possible to suppress the unnecessary jetting of the liquid droplets from the dummy nozzle. 
     The recording apparatus of the present invention, may further include a sucking mechanism which covers the nozzles and the dummy nozzle of the liquid droplet jetting apparatus and which sucks the liquid from the nozzles and the dummy nozzle. In this case, by the sucking mechanism, it is possible to suck air bubbles developed in the liquid supply chamber of the liquid droplet jetting apparatus together with the liquid inside the liquid supply chamber. 
     In the recording apparatus of the present invention, the liquid supply chamber of the liquid droplet jetting apparatus may extend in the predetermined direction, and the discharge ports included in the discharge port group may be formed in the predetermined direction to be isolated from each other. Furthermore, the liquid supply chamber may have a common liquid chamber which extends in the predetermined direction and which is connected to the pressure chambers; and a pressure attenuation chamber including a throttled portion of which a cross-sectional area is smaller than a cross-sectional area of the common liquid chamber and an attenuation portion of which a cross-sectional area is greater than the cross-sectional area of the throttled portion, the attenuation portion being connected to an end portion of the common liquid chamber via the throttled portion; and the discharge port group may be formed in the pressure attenuation chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of an ink-jet printer having an ink-jet head according to an embodiment of the present invention; 
         FIG. 2  is a plan view of the ink-jet head shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along a line III-III in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view taken along a line IV-IV in  FIG. 2 ; 
         FIG. 5  is a perspective view showing an outline of a space inside the ink-jet head shown in  FIG. 1 ; and 
         FIG. 6  is a cross-sectional view taken along a line VI-VI in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The accompanying diagrams are diagrams in which a liquid droplet jetting apparatus of the present invention is substantiated in an ink-jet head  10 .  FIG. 1  is a schematic perspective view of an ink-jet printer  1  which includes the ink-jet head  10 . The ink-jet printer  1  has a guide rod  3  which is installed in a casing  2 , and a carriage  4  which is slidably supported by the guide rod  3 . The ink-jet head  10  is provided at a lower portion of the carriage  4 , and ink droplets are jetted from the ink-jet head  10  toward a recording paper  6  which is transported by a paper feeding roller  5  (transporting mechanism) below the ink-jet head  10 . The carriage  4  is joined to a timing belt  8  which is put around a pair of pulleys  7 , and the timing belt  8  is arranged parallel to an axial direction of the guide rod  3 . A motor  9  which rotates in a normal and reverse direction is provided to one of the pulleys  7 , and by this pulley  7  being driven in the normal and reverse direction of rotation, the timing belt  8  reciprocates. By the reciprocation movement of the timing belt  8 , the carriage  4  joined to the timing belt  8  and the ink-jet head  10  installed on the carriage  4  move along the guide rod  3 . In the following description, a “scanning direction” is a direction in which the carriage  4  moves, and an “extending direction” is a direction in which a common liquid chamber  40 , which will be described later, extends (direction of a row of pressure chambers  42 ), and is a direction orthogonal to the scanning direction. 
       FIG. 2  is a plan view of the ink-jet head  10  shown in  FIG. 1 .  FIG. 3  is a cross-sectional view taken along a line III-III in  FIG. 2 .  FIG. 4  is a cross-sectional view taken along a line IV-IV in  FIG. 2 .  FIG. 5  is a perspective view showing an outline of a space inside the ink-jet head  10  shown in  FIG. 1 . As shown in  FIG. 3  and  FIG. 4 , the ink-jet head  10  includes a channel unit  11  in which a plurality of plates are stacked, and an actuator  12  (pressure applying mechanism) which overlaps with and is adhered to a part of an upper surface of the channel unit  11 . A plurality of nozzles  44  is formed in a lower surface of the channel unit  11 , and ink droplets (liquid droplets) are jetted downward from the nozzles  44 . Moreover, at a location on the upper surface of the channel unit  11  which is not covered with the actuator  12 , filters  16  which remove dust mixed in the ink are arranged to cover an ink inlet ports  49 . 
     As shown in  FIG. 3  and  FIG. 4 , the channel unit  11  is formed by stacking in order from a top, a pressure chamber plate  20 , a first communication passage plate  21 , a second communication passage plate  22 , a third communication passage plate  23 , a fourth communication passage plate  24 , a first manifold plate  25 , a second manifold plate  26 , a damper plate  27 , a cover plate  28 , and a nozzle plate  29 , and adhering these plates. The nozzle plate  29  is a resin sheet of a material such as polyimide, and each of the plates  20  to  28  other than the nozzle plate  29  is a metallic plate of a material such as 42% nickel alloy steel (42 alloy). Each plate has a thickness of about 50 μm to 150 μm. Openings or recesses which form channels are formed in each of the plates  20  to  29  by a method such as an electrolytic etching, a laser machining, and a plasma-jet machining. 
     As it is shown in  FIGS. 2 to 4 , the pressure chamber plate  20  has a plurality of pressure chamber holes  20   a  arranged in a plurality of rows (two rows in the embodiment) along a long side of the pressure chamber plate  20 . Each of the pressure chamber hole  20   a  has an elliptical shape with a long axis of the ellipse in the scanning direction in a plan view. Each pressure chamber hole  20   a  has an upper side and a lower side thereof closed by the actuator  12  and the first communication passage plate  21  respectively, thereby forming the pressure chamber  42 . In other words, the actuator  12  is formed to cover the pressure chamber holes  20   a . The nozzle plate  29  has a plurality of nozzle holes  29   a  each having a tapered shape with a diameter narrowed gradually in a downward direction, and each corresponding to one of the pressure chamber holes  20   a.    
     Manifold holes  25   a  and  26   a  are formed in the first manifold plate  25  and the second manifold plate  26  under one of the rows of the pressure chamber holes  20   a  respectively, each extending in a direction of the row. Both the manifold holes  25   a  and  26   a  have an outline shape almost coinciding mutually, and the manifold holes  25   a  and  26   a  communicate with each other. Each of the manifold holes  25   a  and  26   a  has both ends extending to be longer than the row of the pressure chamber holes  20   a . The manifold holes  25   a  and  26   a  have protrusions  25   c  and  26   c  respectively at one end portions thereof (end portions at an upper side in  FIG. 2 ) not corresponding vertically to the pressure chamber holes  20   a . Each of the protrusions  25   c  and  26   c  narrows a distance in a direction orthogonal to the extending direction. 
     The manifold holes  25   a  and  26   a  have an upper side and a lower side closed by the fourth communication passage plate  24  and the cover plate  27  respectively, thereby forming the common liquid chamber  40  and a pressure attenuation chamber  51 . The common liquid chamber  40  communicates, at an end portion corresponding to the other end portions of the manifold holes  25   a  and  26   a  (end portions at a lower side in  FIG. 2 ), with the ink inlet port  49  which is formed vertically through the first communication passage plate  21 , second communication passage plate  22 , and the third communication passage plate  23 . 
     The pressure attenuation chamber  51  has a portion narrowed by the protrusions  25   c  and  26   c  as a throttled portion  52  and a portion on an opposite side of the common liquid chamber  40  with respect to the throttled portion  52  as an attenuation portion  53 . The throttled portion  52  is formed to have a channel cross-sectional area in a direction orthogonal to the extending direction to be smaller than a channel cross-sectional area of the common liquid chamber  40 , and moreover, the attenuation portion  53  is formed to have a channel cross-sectional area to be larger than the channel cross-sectional area of the throttled portion  52 . A liquid supply chamber is formed by the attenuation portion  53 , the throttled portion  52 , and the common liquid chamber  40 . The attenuation portion  53  communicates with the common liquid chamber  40  via the throttled portion  52 . In other words, in the embodiment, the throttled portion  52  is formed at an end portion  40   a  (one end portion) of the common liquid chamber  40  on an opposite side of the ink inflow port  49 , and the attenuation portion  53  communicates with the common liquid chamber  40  via the throttled portion  52 . Consequently, an air bubble which is developed in the common liquid chamber  40  follows a flow of ink heading from the ink inflow port  49  to the end portion  40   a , and flows into the attenuation portion  53  via the throttled portion  52 . Since the cross-sectional area of the throttled portion  52  is smaller than the cross-sectional area of the attenuation portion  53 , it is possible to prevent the air bubble which has flowed into the attenuation portion  53  from flowing back to the common liquid chamber  40 . In other words, it is possible to prevent assuredly the air bubble which is developed in the common liquid chamber  40  from being accumulated in the common liquid chamber  40 . 
     Each pressure chamber  42  in one row of the pressure chambers  42  communicates with the common liquid chamber  40  positioned at a lower side thereof via a communication passage  41 . The communication passage  41  is formed by a connecting hole  21   a  of the first communication passage plate  21 , a second connecting hole  22   a  of the second communication passage plate  22 , an elongate hole  23   a  of the third communication passage plate  23 , and a communicating hole  24   a  of the fourth communication passage plate  24 . The elongate hole  23   a  is formed to be long and slender in a direction of a flat surface of the third communication passage plate  23 , and one end in a longitudinal direction thereof communicates with one end of the pressure chamber  42  via the connecting hole  21   a  and the second connecting hole  22   a , and the other end communicates with an upper surface of the common liquid chamber via the communicating hole  24   a . In the communication passage  41 , a communication passage throttled portion  41   a  is formed by the elongate hole  23   a . The communication passage  41  has a channel cross-sectional area much smaller and a channel resistance much higher than those of an outflow channel  43  which will be described later. 
     The other end of the pressure chamber  42  communicates with one of the nozzle holes  29   a  via the outflow channel  43 . The outflow channel  43  is formed by through holes  21   b ,  22   b ,  23   b ,  24   b ,  25   b ,  26   b ,  27   b , and  28   a  which communicate with each other and are formed through the first communication passage plate  21 , the second communication passage plate  22 , the third communication passage plate  23 , and the fourth communication passage plate  24 , the first manifold plate  25 , the second manifold plate  26 , the damper plate  27 , and the cover plate  28 , respectively. The nozzle  44  is formed by the nozzle hole  29   a  in the nozzle plate  29 . 
     The damper plate  27  has a damper wall  27   a  which is made thin by forming a recess from a side opposite to the manifold hole  26   a.    
     The ink-jet head  10  has a dummy nozzle  60  which does not perform jetting for image formation. The dummy nozzle  60  communicates with the pressure attenuation chamber  51  which will be described later, and is formed for discharging air bubbles accumulated in the end portion  40   a  of the common liquid chamber  40  on a side opposite to the ink inflow port  49 . 
     In the embodiment, two discharge structures  70  each of which includes the dummy nozzle  60  have been provided.  FIG. 6  is a cross-sectional view taken along a line VI-VI in  FIG. 2 . The description will be made while referring also to  FIG. 2 ,  FIG. 3 , and  FIG. 5 . The two discharge structures  70  are different from each other in a shape and a connecting position of a channel in a plan view, but have same basic structure. A formation of only one discharge structure  70  will be described below, and regarding the other discharge structure, only the shape and the connecting position of the channel in a plan view will be described. 
     The nozzle plate  29  has dummy nozzle holes  29   b  each of which forms one of the dummy nozzles  60 . A diameter of each of the dummy nozzle holes  29   b  becomes smaller in a downward direction. 
     The pressure chamber plate  20 , further has a dummy pressure chamber holes  20   c . Each of the dummy pressure chamber holes  20   c  has an elliptical shape with a long axis of the ellipse in the scanning direction. A length of the dummy pressure chamber hole  20   c  is shorter than a length of the pressure chamber hole  20   a . The dummy pressure chamber hole  20   c  has an upper and a lower side closed by the actuator  12  and the first communication passage plate  21 , thereby forming a dummy pressure chamber  62 . The dummy pressure chambers  62  are arranged to be lined up with the pressure chambers  42  in a direction of the row of the pressure chambers  42 , on an opposite side of the ink inflow port  49 , and are arranged such that one ends of the dummy pressure chambers  62  overlap with the dummy nozzles  60  in a plan view respectively. 
     The first communication passage plate  21  and the second communication passage plate  22  further have channel chamber holes  21   c  and  22   c  each extending in a longitudinal direction of the plates (extending direction) in a plan view. Each of the channel chamber holes  21   c  and  22   c  branches at an intermediate portion thereof in a short side direction of the plate (scanning direction), thereby forming a T-shape. Both the channel chamber holes  21   c  and  22   c  have outline shapes that almost coincide mutually, and communicate with each other. The T-shaped channel chamber holes  21   c  and  22   c  have an upper side and a lower side closed by the pressure chamber plate  20  and the third communication passage plate  23  respectively, thereby forming a channel chamber  63  having the T-shape. 
     Moreover, one end in a longitudinal direction of the T-shaped channel chamber  63  communicates with the pressure attenuation chamber  51  via communicating holes  23   e  and  24   c  made through the third communication passage plate  23  and the fourth communication passage plate  24 , and the other end in the longitudinal direction of the T-shaped channel chamber  63  communicates with the pressure attenuation chamber  51  via communicating holes  23   f  and  24   d  made through the same third communication passage plate  23  and the fourth communication passage plate  24 . More elaborately, an open end of the communicating hole  24   c  opening toward the pressure attenuation chamber  51  forms a discharge port  67 , and opens at a position in the vicinity of the throttled portion  52 , in the pressure attenuation chamber  51 , on a side of the common liquid chamber  40 . An open end of the communicating hole  24   d  opening toward the pressure attenuation chamber  51  forms a discharge port  68 , and opens at a position in the vicinity of the throttled portion  52 , in the pressure attenuation chamber  51 , on a side of the attenuation portion  53 . 
     The T-shaped channel chamber  63  has a portion branched in the scanning direction from a position inclined on one side from a center between the discharge ports  67  and  68  of the channel chamber  63 . A front end of the branched portion communicates with the dummy nozzle  60  which is formed in the vicinity of the common liquid chamber  40  on a side of the throttled portion  52 , via a throttle  64 , a connecting channel  65  for the dummy nozzle and an outflow channel  66  for the dummy nozzle. 
     The throttle  64  is formed by an upper side and a lower side of an elongate hole  23   c , which extends in the extending direction and has been drilled through the third communication passage plate  23 , being closed by the second communication passage plate  22  and the fourth communication passage plate  24 . The connecting channel  65  for the dummy nozzle is formed by an upper side and a lower side of an elongate hole  22   d , having been drilled through the second communication passage plate  22 , being closed by the first communication passage plate  21  and the third communication passage plate  23 . The front end of the branched portion of the T-shaped channel chamber  63  overlaps with one end of the throttle  64 , and the other end of the throttle  64  communicates with one end of the connecting channel  65  for the dummy nozzle, thereby communicating mutually. A channel cross-sectional area of the throttle  64  is smaller than a channel cross-sectional area of the connecting channel  65  for the dummy nozzle, and the outflow channel  66  for the dummy nozzle, and a channel resistance of the throttle  64  is high. 
     The other end of the connecting channel  65  for the dummy nozzle communicates with the dummy nozzle  60  via the outflow channel  66  for the dummy nozzle. The outflow channel  66  for the dummy nozzle is formed by through holes  23   d ,  24   e ,  25   d ,  26   d ,  27   d , and  28   b  which communicate with each other and are formed through the fourth communication passage plate  24 , the first manifold plate  25 , the second manifold plate  26 , the damper plate  27 , and the cover plate  28 , respectively. 
     Moreover, discharge channel  69  which connects the pair of discharge ports  67  and  68  (discharge port group) and the dummy nozzle  60  is formed by the communicating holes  23   e ,  23   f ,  24   c ,  24   d , the channel chamber  63 , the throttle  64 , the connecting channel  65  for the dummy nozzle, and the outflow channel  66  for the dummy nozzle. The discharge structure  70  (first discharge structure) is formed by the pair of discharge ports  67  and  68 , the discharge channel  69 , and the dummy nozzle  60 . 
     The other discharge structure  70  (second discharge structure) will be described below. The channel chamber  63  is formed to be V-shaped in a plan view, and an apex  63   a  of the V shape communicates with the dummy nozzle  60  formed in the vicinity of the common liquid chamber  40  on a side of the throttled portion  52 , via the throttle  64 , the connecting channel  65  for the dummy nozzle, and the outflow channel  66  for the dummy nozzle. Moreover, both end portions of the V-shape communicate with the pair of discharge ports  67  and  68  respectively, via the communicating holes  23   e ,  23   f ,  24   c , and  24   d . The discharge ports  67  and  68  are arranged to be isolated from each other in the extending direction, and communicate with the attenuation portion  53  at positions of the attenuation portion  53  away from the throttled portion  52 , in the extending direction, farther than the discharge structure  70  described above. Preferably, one discharge port  68  is arranged adjacent to the front end portion of the attenuation portion  53  in the extending direction (innermost end when viewed from the common liquid chamber  40 ). Various holes, chambers, and channels etc. forming the other discharge structure  70  are formed in the same plates as in the discharge structure  70  described above. In the following description, for describing the two discharge structures  70  distinctly, a reference numeral “A” is assigned to one discharge structure  70  and a reference numeral “B” is assigned to the other discharge structure  70 . 
     As the actuator  12 , various types of actuators such as a piezoelectric drive actuator, an electrostatic drive actuator, and a heat generating actuator are applicable. In the embodiment, the piezoelectric drive actuator is used. As shown in  FIG. 3 ,  FIG. 4 , and  FIG. 6 , in the actuator  12 , a multiple number of piezoelectric sheets  30 ,  31 ,  32 , and  33  (hereinafter sheets  30  to  33 ) made of a ceramics material of lead zirconium titanate (PZT), each having a thickness of about 30 μm, and a top sheet  34  which has an insulating property are stacked. On an upper surface of each of the odd numbered sheets  30  and  32  when counted upward from the lowermost piezoelectric sheet  30  from among the piezoelectric sheets  30  to  33 , a common electrode  35  which is arranged continuously corresponding to the plurality of pressure chambers  42  is formed by printing. On an upper surface of each of the even numbered sheets  31  and  33  when counted upward from the lowermost piezoelectric sheet  30 , a plurality of individual electrodes  36  each of which is arranged corresponding to one of the pressure chambers  42  is formed. 
     Next, an operation of the ink-jet head will be described below. Ink which is infused through the ink infusion hole  49  is filled from the common liquid chamber  40  up to the nozzle  44 . Moreover, the ink is filled from the pressure attenuation chamber  51  up to the dummy nozzle  60 . The ink forms a meniscus inside the nozzle  44  and the dummy nozzle  60 , which is an interface with an atmosphere. This meniscus, when the ink is not being jetted, is maintained to be in a concave surface form by a back pressure (a pressure which pulls in a direction opposite to a direction of jetting) which acts on the ink as it has hitherto been known, and the ink does not overflow. 
     As shown in  FIG. 3 , when a voltage is selectively applied to the individual electrode  36  of the actuator  12 , and an electric potential difference is developed between the individual electrode  36  and the common electrode  35 , an electric field acts on an active portion positioned between the common electrode  35  and the individual electrode  36  of the piezoelectric sheets  30  to  33 , and there is a deformation due to a distortion in a direction of stacking. Due to the deformation of the active portion, when a pressure (pressure change) is caused in the ink inside the pressure chamber  42 , the ink passes through the outflow channel  43  and is jetted as an ink droplet from the nozzle  44 . When the ink is jetted, a pressure wave is generated due to the pressure change in the ink inside the pressure chamber  42 . This pressure wave has not only a forward-moving component which moves toward the nozzle  44  for jetting the ink droplets from the nozzle  44  but also a backward moving component which moves toward the common liquid chamber  40 . The backward-moving component of the pressure wave is intercepted to some extent by a communication passage throttled portion  41   b , but a part of the backward-moving component is propagated to the common liquid chamber  40 . The backward-moving component of the pressure wave which is propagated to the common liquid chamber  40  is absorbed to some extent by an elastic deformation of the damper wall  27   a  which is thin. 
     Furthermore, the channel cross-sectional area of the throttled portion  52  being smaller than the channel cross-sectional area of the common liquid chamber  40 , a part of the backward-moving component of the pressure wave is reflected at a boundary between the throttled portion  52  and the common liquid chamber  40 , and returns toward the common liquid chamber  40 , and the remaining part of the backward-moving component passes through the throttled portion  52  and is propagated up to the attenuation portion  53 . 
     Moreover, the channel cross-sectional area of the attenuation portion  53  being greater than the channel cross-sectional area of the throttled portion  52 , a part of the pressure wave which is propagated to the attenuation portion  53  and returns to the throttled portion  52  after being reflected inside the attenuation portion  53 , returns to the attenuation portion  53  after being reflected at the boundary between the attenuation portion  53  and the throttled portion  52 , and the remaining part of the pressure wave passes through the throttled portion  52  and is propagated to the common liquid chamber  40 . Accordingly, it is possible to attenuate the pressure wave efficiently in the common liquid chamber  40 , and a so-called cross-talk, in which the backward-moving component of the pressure wave generated in the pressure chamber  42  is propagated to the other pressure chamber  42  via the common liquid chamber  40 , is suppressed effectively. 
     When the backward-moving component of the pressure wave passes through the throttled portion  52 , a part of the backward-moving component passes through one discharge port  67 A, and is propagated to the channel chamber  63 A. Moreover, a part of the backward-moving component passes through the other discharge port  68 A and is propagated to the channel chamber  63 A. A part of the pressure wave which is propagated from both ends of the channel chamber  63 A makes an attempt to be propagated to the throttle  64 A, but due to the high channel resistance thereof, the part of the pressure wave is escaped toward the discharge port on a lower pressure side, out of the discharge ports  67 A and  68 A. When a length of each of the discharge channels extending from both discharge ports  67 A and  68 A up to a merging point inside the channel chamber  63 A is set such that there occurs a phase difference in the pressure wave, it is possible to offset the pressure wave which is propagated from both sides, to some extent. 
     As a result of this, it is possible to reduce the pressure wave which is propagated to the throttle  64 A. Since it is possible to attenuate the pressure wave further in the throttle  64 A, a high-pressure wave does not reach the dummy nozzle  70 , and it is possible to prevent unnecessary jetting of ink droplets due to the concentration of the pressure wave. Such action and effect are shown similarly in the discharge structure  70 B, and it is possible to prevent unnecessary jetting of ink droplets from the dummy nozzle  60 B due to the concentration of the pressure wave. 
     Moreover, in each discharge structure  70 , since both the discharge ports  67  and  68  are arranged to be isolated in a direction of extension of the common liquid chamber  40 , a difference of high and low is developed in the pressure wave which is propagated to the pressure attenuation chamber  51  at a position of each of the discharge ports  67  and  68 . Accordingly, it is possible to release the pressure wave propagated from one discharge port  67  (or  68 ) to the discharge channel, to one of the discharge ports  67  and  68  at which the pressure is lower than the other discharge port. 
     Moreover, in the discharge structure  70 A, a total of channel length of a discharge channel from one discharge port  67  up to a joining point of the channel chamber  63 A through the communicating holes  23   e  and  24   c , and channel length of a discharge channel from the other discharge port  68  up to the joining point of the channel chamber  63 A through the communicating holes  23   f  and  24   d , is formed to be greater than a direct distance between the both discharge ports  67  and  68 . By forming the channel chamber  63 B to be V-shaped as in the discharge structure  70 B, it is possible to increase further the difference in the distance described above. Accordingly, it is possible to attenuate effectively the pressure wave which is propagated from each of the discharge ports  67  and  68  up to the dummy nozzle  60  via the discharge channel  69 , and to release the pressure wave which is propagated from one discharge port  67  (or  68 ) to the discharge port at a low pressure. As a result of this, it is possible to suppress the pressure wave from being concentrated at the dummy nozzle  60 , and to suppress the unnecessary jetting of liquid droplets from the dummy nozzle  60 . Moreover, it is easily possible to shift the phase of the two pressure waves, and to suppress the concentration of the pressure waves at the dummy nozzle  60 . 
     Furthermore, even by forming the two discharge structures  70 A and  70 B, it is possible to disperse the pressure wave which acts on each of the dummy nozzles  60 A and  60 B. Particularly, when the two discharge structures  70  are arranged to be separated by a distance in the extending direction which is the direction in which the pressure wave is propagated, these two discharge structures  70  attenuate the pressure wave independently without affecting mutually, and it is possible to reduce the pressure change which acts on each of the dummy nozzles  60 A and  60 B. 
     In the embodiment, a case in which two discharge structures  70  are provided has been described. However, the number of the discharge structures is not restricted to two, and there may be one discharge structure  70 , or three or more discharge structures  70  may be provided. Or, the discharge ports  67  and  68  in the discharge structure  70  are not restricted to two, and there may be three or more discharge ports. Furthermore, the shape of the channel chamber  63  is not restricted to the shape described above, and it may be a U-shape, provided that it communicates with at least two discharge ports and dummy nozzles  60 . In such cases, the pressure attenuation chamber  51  is not necessarily required to be provided at the end portion side of the common liquid chamber  40 . 
     Moreover, in a structure, in which the pressure wave inside the common liquid chamber  40  is attenuated by the pressure attenuation chamber  51  and the pressure wave which is propagated to the dummy nozzle  60  is attenuated by the throttle  64  of the discharge channel  69 , the discharge structure  70  may include only one discharge port  67  (or  68 ). In order to remove an air bubble accumulated in the common liquid chamber  40  and the pressure attenuation chamber  51 , the air bubble may be sucked together with the ink from the nozzles  44  and the dummy nozzles  60 . For example, it is possible to apply a negative pressure to all the nozzles  44  and the dummy nozzles  60  upon covering the plurality of nozzles  44  and the dummy nozzles  60  by a cap  80  which is connected to a suction pump P (sucking mechanism) as shown in  FIG. 1 , thereby sucking the air bubble from the nozzles  44  and the dummy nozzles  60 . Conversely, the air bubble may be pushed together with the ink from the nozzles  44  and the dummy nozzles  60  by applying a positive pressure to an ink supply source connected to the ink inflow port  49 . In these cases, the channel resistance from the common liquid chamber  40  up to the dummy nozzles  60  (two dummy nozzles) being set to be lower than the channel resistance from the common liquid chamber  40  up to the nozzles  44 , a flow of ink from the ink inflow port  49  toward the common liquid chamber  50  and the pressure attenuation chamber  51  is generated, and it is possible to discharge the air bubble together with the ink from the dummy nozzle  60  through the discharge ports  67  and  68 . 
     In a case of one dummy nozzle  60 , it is preferable to set the channel resistance to be greater than a diameter of the nozzle  44  by increasing a diameter of the dummy nozzle  60 . 
     Moreover, by forming the dummy pressure chamber  62  above the dummy nozzle  60 , it is possible to uniform a stiffness of the pressure chamber  42  formed near the dummy pressure chamber  62  and a stiffness of the other pressure chambers  42 , and to uniform the ink droplets jetted from each nozzle  44 . 
     It is also possible to connect the connecting channel  65  for the dummy nozzle to one end of the dummy pressure chamber  62 , and to connect the other end of the dummy pressure chamber  62  to the outflow channel  66  for the dummy nozzle. Moreover, it is also possible to arrange the common electrode  35  and the individual electrode  36  in the actuator  12  corresponding to the upper side of the dummy pressure chamber  62 . By the structure described above, although the dummy nozzle  60  is not used for the image formation, at the time of a flushing operation, it is possible to jet an air bubble together with the ink droplets from the dummy nozzle  60  by driving the actuator  12 . 
     In the embodiment described above, the dummy nozzle  60  is formed in the vicinity of the one end portion  40   a  of the common liquid chamber  40 . However, a position of forming the dummy nozzle  60  is not restricted to this position, provided that, it is a position which makes it possible to secure the channel length of the discharge channel  69 , and to attenuate sufficiently the pressure wave which is propagated to the dummy nozzle  60 . Moreover, the cap  80  need not cover all the plurality of nozzles  44  and the dummy nozzles  60 , and may be formed to cover only the dummy nozzles  60 , for example. It is possible to remove an air bubble developed in the common liquid chamber  40  and the pressure attenuation chamber  51  even by sucking the ink only from the dummy nozzles  60  by applying the negative pressure only to the dummy nozzles  60 . 
     The embodiment described above is an embodiment in which the present invention is applied to an ink-jet head used in an ink-jet printer. However, the present invention is also applicable to any other apparatus, provided that the apparatus has a dummy nozzle which discharges an air bubble developed in a liquid chamber, and it is necessary to prevent the dummy nozzle from jetting undesired liquid droplets caused by propagation of a pressure wave at the time of jetting liquid droplets. In this case, a liquid to be jetted is not restricted to ink and may be a liquid such as a reagent, a biomedical solution, a wiring material solution, an electronic material solution, and a colored liquid. Moreover, the recording medium is not restricted to a recording paper, and may be medium such as a cloth and a resin sheet, and the similar effect is achieved.