Patent Publication Number: US-7896477-B2

Title: Liquid transport apparatus and method for producing liquid transport apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2007-019767, filed on Jan. 30, 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 transport apparatus which transports a liquid, and a method for producing the liquid transport apparatus. 
     2. Description of the Related Art 
     A liquid transport apparatus (piezoelectric pump) has been hitherto known, which transports a liquid by applying the pressure to the liquid by utilizing the deformation of a piezoelectric element brought about when a voltage (electric field) is applied. For example, a piezoelectric pump, which is described in Japanese Patent Application Laid-open No. 6-147104, is provided with two pump chambers which have same shape (circular shape) and which are communicated with each other, a pressure-adjusting chamber which is communicated with the pump chamber disposed on the downstream side and which has the same shape as that of the pump chamber, and piezoelectric elements which are arranged to cover the two pump chambers from upper and lower portions respectively. A voltage is applied to the piezoelectric element corresponding to each of the pump chambers to cause the deformation so that the volume of the pump chamber is changed. Accordingly, the pressure is applied to the liquid contained in the pump chamber, and thus the liquid is transported. Thin films are arranged at upper and lower positions with respect to the pressure-adjusting chamber. The pressure of the liquid fed from the pump chamber is adjusted in the pressure-adjusting chamber by means of the elastic deformation of the thin films. 
     A piezoelectric pump described in Japanese Patent Application Laid-open No. 64-32077 (FIG. 2) is provided with a pump chamber, a liquid supply passage and a liquid discharge passage which are communicated with the pump chamber, and three piezoelectric transducers or oscillators (first, second, and third piezoelectric transducers) which are provided corresponding to the pump chamber, the liquid supply passage, and the liquid discharge passage respectively. The first piezoelectric transducer, which corresponds to the pump chamber, is arranged to cover the pump chamber. The volume of the pump chamber is changed in accordance with the deformation thereof to apply the pressure to the liquid in the pump chamber. On the other hand, the second and third piezoelectric transducers are provided at intermediate portions of the liquid supply passage and the liquid discharge passage respectively. The liquid supply passage and the liquid discharge passage are opened and closed in accordance with their own deformation. In this case, the liquid supply passage and the liquid discharge passage extend from the side wall of the pump chamber in the horizontal direction perpendicular to the side wall. Therefore, the piezoelectric pump described in Japanese Patent Application Laid-open No. 64-32077 has such a three-dimensional structure that the first piezoelectric transducer which is provided to apply the pressure to the liquid in the pump chamber and the second and third piezoelectric transducers which open and close the liquid supply passage and the liquid discharge passage respectively are positioned on mutually different planes. 
     The piezoelectric pump described in Japanese Patent Application Laid-open No. 6-147104 is not provided with any means for closing the flow passage disposed on the upstream side of the pump chamber when the piezoelectric element is deformed to apply the pressure to the liquid in the pump chamber. For this reason, even when the pressure is applied to the liquid in the pump chamber, a part of the pressure wave escapes toward the upstream side. Therefore, the transport efficiency is unsatisfactory. A valve mechanism for opening/closing the flow passage disposed on the upstream side of the pump chamber can be provided distinctly from the piezoelectric pump. However, the number of parts is increased, and the structure is complicated as well, which is disadvantageous in view of the production cost. 
     In the case of the piezoelectric pump described in Japanese Patent Application Laid-open No. 64-32077, the first piezoelectric transducer for applying the pressure to the liquid in the pump chamber and the second and third piezoelectric transducers for opening/closing the liquid supply passage and the liquid discharge passage are not arranged on the same plane. For this reason, the structure of the piezoelectric pump is complicated, and it is difficult to miniaturize the pump. Further, when the pump is produced, it is necessary that the first piezoelectric transducer and the second and third piezoelectric transducers should be arranged in separate steps. The number of steps is increased, and the production cost is increased corresponding thereto. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a liquid transport apparatus which makes it possible to transport the liquid efficiently, which has a simple structure, and which is produced with ease as well. 
     According to a first aspect of the present invention, there is provided a liquid transport apparatus including: a base member having a surface in which a pressure chamber and a liquid flow passage are formed, the liquid flow passage being communicated with the pressure chamber and having a flow passage cross-sectional area smaller than that of the pressure chamber; and a piezoelectric actuator having a pressure-applying portion which applies a pressure to a liquid in the pressure chamber and an opening/closing portion which opens and closes the liquid flow passage, the piezoelectric actuator being formed of a stack including: a vibration plate which is arranged on the surface of the base member and which covers both the pressure chamber and the liquid flow passage; a piezoelectric material layer which is arranged on a surface, of the vibration plate, on a side not facing the base member; a first electrode which is arranged, on one of surfaces of the piezoelectric material layer, at an area thereof corresponding to the pressure chamber; a second electrode which is arranged, on one of the surfaces of the piezoelectric material layer, at an area thereof corresponding to the liquid flow passage; and a third electrode which is arranged on the piezoelectric material layer to face the first electrode and the second electrode, wherein the pressure-applying portion faces the pressure chamber, the opening/closing portion faces the liquid flow passage, and the pressure-applying portion and the opening/closing portion are arranged along the surface of the base member. 
     In the liquid transport apparatus according to the first aspect of the present invention, the pressure-applying portion of the piezoelectric actuator deforms a vibration plate portion which covers the pressure chamber in response to the deformation of the piezoelectric material layer brought about when the difference in electric potential is generated between the first electrode and the third electrode. Accordingly, the volume of the pressure chamber is changed, and the pressure is applied to the liquid therein. Further, the opening/closing portion deforms the vibration plate portion which covers the liquid flow passage so that the liquid flow passage is opened/closed in response to the deformation of the piezoelectric material layer brought about when the difference in electric potential is generated between the second electrode and the third electrode. Therefore, it is possible to efficiently transport the liquid by applying the pressure to the liquid in the pressure chamber at the appropriate timing by the pressure-applying portion while opening and closing the liquid flow passage by the opening/closing portion. No sliding portion is present in the piezoelectric actuator unlike any mechanical pump (for example, a tube pump and a syringe pump) which has been hitherto widely used as a liquid transport pump. Therefore, an advantage is also obtained such that the noise, which is generated during the operation, is small. 
     The piezoelectric actuator further has the stack which includes, for example, the electrodes, the piezoelectric material layer, and the vibration plate extending along one surface of the base member. The portion of the stack, which faces the pressure chamber, is the pressure-applying portion. The portion of the stack, which faces the liquid flow passage, is the opening/closing portion. The pressure-applying portion and the opening/closing portion are arranged on the same plane along one surface of the base member. Therefore, the structure of the piezoelectric actuator is simplified, the piezoelectric actuator is made compact, and thus the liquid transport apparatus can be miniaturized. Further, the pressure-applying portion and the opening/closing portion can be produced simultaneously by stacking a plurality of layers including, for example, the vibration plate and the piezoelectric material layer on one surface of the base member. Therefore, it is also possible to simplify the production steps. 
     It is preferable that the pressure chamber has a large flow passage cross-sectional area (cross-sectional area in the cross section perpendicular to the liquid transport direction) to a certain degree so that the volume change, which is brought about when the pressure is applied to the liquid, is increased to successfully apply the large pressure at once to the liquid therein. On the other hand, it is preferable that the liquid flow passage has a small flow passage cross-sectional area to such an extent that the flow passage resistance is not excessively increased so that the substantially complete closing can be easily realized by the deformation of the piezoelectric material layer corresponding to the opening/closing portion. In consideration of the foregoing viewpoint, in the liquid transport apparatus of the present invention, the flow passage cross-sectional area of the liquid flow passage to be opened and closed by the opening/closing portion is smaller than the flow passage cross-sectional area of the pressure chamber. 
     In the liquid transport apparatus of the present invention, a low rigidity portion, at which rigidity of the stack is locally lowered, may be provided between the pressure-applying portion and the opening/closing portion. When the low rigidity section is provided, it is possible to suppress the mutual interference of the deformation of the piezoelectric material layer and the vibration plate between the pressure-applying portion and the opening/closing portion. 
     In the liquid transport apparatus of the present invention, the low rigidity portion may be a recess formed in the vibration plate at an area thereof facing a boundary between the pressure chamber and the liquid flow passage. When the recess is formed, the thickness of the vibration plate is locally thinned in the area facing the boundary between the pressure chamber and the liquid flow passage. Therefore, the rigidity of the stack is lowered. 
     In the liquid transport apparatus of the present invention, the recess may be formed on the surface, of the vibration plate, on the side not facing the base member. According to this arrangement, when the piezoelectric actuator is produced, a plurality of steps (including, for example, the formation of the recess of the vibration plate and the formation of the piezoelectric material layer), which are applied to the vibration plate, can be executed in the same direction (direction opposite to the base member). Therefore, the piezoelectric actuator is easily produced. Further, it is possible to shorten the steps. Further, the problem, in which any bubble stays in the recess when the liquid is contaminated with the bubble, is not caused unlike the case in which the recess is formed on the surface of the vibration plate on the side of the base member to make contact with the liquid. 
     In the liquid transport apparatus of the present invention, the low rigidity portion may be a recess or a through-hole formed, in the piezoelectric material layer, at an area thereof facing a boundary between the pressure chamber and the liquid flow passage. When the recess or the through-hole is formed for the piezoelectric material layer, the rigidity of the stack is locally lowered in the area facing the boundary between the pressure chamber and the liquid flow passage. 
     In the liquid transport apparatus of the present invention, a flow passage width of the pressure chamber may be greater than a flow passage width of the liquid flow passage. In order to make the flow passage cross-sectional area of the pressure chamber to be greater than the flow passage cross-sectional area of the liquid flow passage, it is appropriate to increase the flow passage width or the flow passage depth. However, the area of the vibration plate, which faces the pressure chamber, is rather widened when the flow passage width is large as in the present invention. Therefore, this arrangement is preferred in view of the fact that the volume change of the pressure chamber can be increased when the pressure is applied. 
     The liquid transport apparatus of the present invention may further include a driver which is connected to the first electrode and the second electrode via independent wirings respectively, and the driver may independently drive the pressure-applying portion and the opening/closing portion by applying a predetermined electric potential to each of the first electrode and the second electrode at a predetermined timing. When the pressure-applying portion and the opening/closing portion are independently driven by the driver at the appropriate timings respectively, the liquid can be transported by efficiently applying the pressure. 
     In the liquid transport apparatus of the present invention, the predetermined electric potential may include first and second predetermined electric potentials which are mutually different; when the first predetermined electric potential is applied from the driver to the second electrode, the vibration plate may be parallel to the surface of the base member at the opening/closing portion, and when the second predetermined electric potential is applied to the second electrode, the vibration plate may be deformed to project toward the base member at the opening/closing portion; and a recessed valve seat, which is adapted to projection deformation of the vibration plate toward the base member, may be formed in the liquid flow passage of the base member, and when the vibration plate is deformed to project toward the base member to abut against the recessed valve seat, the liquid flow passage may be closed. According to this arrangement, the vibration plate is parallel to one surface of the base member when the first electric potential is applied to the second electrode of the opening/closing portion. Therefore, the gap is formed between the vibration plate and the recessed valve seat, and the liquid flow passage is in the open state. On the other hand, when the second electric potential is applied to the second electrode, and the vibration plate is deformed to project toward the base member, then the vibration plate, which has been deformed to project toward the base member, abuts against the recessed valve seat corresponding to the projection deformation to effect the adhesion or tight contact. Therefore, the liquid flow passage is reliably closed. 
     In the liquid transport apparatus of the present invention, the second electrode may be arranged, on the surface of the piezoelectric layer disposed on a side not facing the base member, at an area thereof facing a central portion in a widthwise direction of the liquid flow passage. According to this arrangement, when the second electric potential is applied to the second electrode facing the central portion of the liquid flow passage in the widthwise direction, the piezoelectric material layer, which is disposed in the area facing the central portion of the liquid flow passage interposed between the second electrode and the third electrode, is shrunk in the in-plane direction. Therefore, the vibration plate is deformed to project toward the base member. 
     In the liquid transport apparatus of the present invention, the predetermined electric potential may include first and second predetermined electric potentials which are mutually different; when the first predetermined electric potential is applied from the driver to the second electrode, the vibration plate may be parallel to the surface of the base member at the opening/closing portion, and when the second predetermined electric potential is applied to the second electrode, the vibration plate may be deformed to project toward a side not facing the base member at the opening/closing portion; and the liquid flow passage of the base member may have a dam-shaped valve seat, which extends entirely over the liquid flow passage in a widthwise direction and which has a top surface positioned in a plane same as that of the surface of the base member, and when the vibration plate is deformed to project toward the side not facing the base member, a gap may be formed between the vibration plate and the top surface of the valve seat to open the liquid flow passage. According to this arrangement, the vibration plate is parallel to one surface of the base member when the first electric potential is applied to the second electrode of the opening/closing portion. Therefore, the vibration plate abuts against the top surface of the dam-shaped valve seat positioned in the same plane as that of one surface of the base member, and the liquid flow passage is reliably closed. On the other hand, when the second electric potential is applied to the second electrode, and the vibration plate is deformed to project toward the side opposite to the base member, then the gap is formed between the vibration plate and the top of the valve seat, and the liquid flow passage is opened. 
     In the liquid transport apparatus of the present invention, the second electrode may include two second-electrode portions arranged, on the surface of the piezoelectric material layer on the side not facing the base member, at areas thereof respectively, the areas facing both ends in a widthwise direction of the liquid flow passage respectively. According to this arrangement, when the second electric potential is applied to the two second electrodes facing the both ends of the liquid flow passage in the widthwise direction respectively, the piezoelectric material layer portions, which are disposed in the areas facing the both ends in the widthwise direction of the liquid flow passage interposed between the two second electrodes and the third electrode, are shrunk in the in-plane direction respectively. Accordingly, the vibration plate portion, which is disposed in the area facing the central portion in the widthwise direction of the liquid flow passage, is deformed to project toward the side opposite to the base member. 
     In the liquid transport apparatus of the present invention, the first electrode and the second electrode may be arranged on one of the surfaces of the piezoelectric material layer, and the third electrode may be arranged on the other of the surfaces of the piezoelectric material layer. According to this arrangement, the third electrode, which corresponds to the first electrode and the second electrode respectively, is arranged on the same surface. Therefore, the third electrode can be arranged commonly for the pressure-applying portion and opening/closing portion. 
     In the liquid transport apparatus of the present invention, in the piezoelectric actuator, the opening/closing portion may include first and second opening/closing portions; the first opening/closing portion may open and close an upstream portion of the liquid flow passage located at an upstream side in a liquid transport direction with respect to the pressure chamber and the second opening/closing portion may open and close a downstream portion of the liquid flow passage located at a downstream side in the liquid transport direction with respect to the pressure chamber. When the two opening/closing portions are provided, the liquid flow passage can be closed on the upstream side and the downstream side of the pressure chamber respectively. Therefore, the pressure can be applied efficiently to the liquid in the pressure chamber. 
     According to a second aspect of the present invention, there is provided a method for producing a liquid transport apparatus, including: forming, on a surface of a base member, a pressure chamber, and a liquid flow passage which is communicated with the pressure chamber and which has a flow passage cross-sectional area smaller than that of the pressure chamber; and producing a piezoelectric actuator arranged on the surface of the base member and including a pressure-applying portion which applies a pressure to a liquid in the pressure chamber, and an opening/closing portion which opens and closes the liquid flow passages, wherein, the production of the piezoelectric actuator includes: forming a piezoelectric material layer on a side of a vibration plate, not facing the base member, the vibration plate being joined to the surface of the base member to cover both the pressure chamber and the liquid flow passage; and arranging, on a surface of the piezoelectric material layer, a first electrode and a second electrode at areas thereof respectively, the surface facing the pressure chamber and the liquid flow passage; and the formation of the piezoelectric material layer includes depositing particles of a piezoelectric material to simultaneously form the piezoelectric material layer, of the pressure-applying portion, facing the pressure chamber and the piezoelectric material layer, of the opening/closing portion, facing the liquid flow passage. 
     In the production method according to the second aspect of the present invention, the particles of the piezoelectric material are deposited on the surface of the vibration plate when the piezoelectric material layer is formed. Accordingly, it is possible to simultaneously form the piezoelectric material layer corresponding to the pressure-applying portion and the opening/closing portion on the vibration plate. Therefore, it is possible to simplify the production steps of the piezoelectric actuator. 
     The method for producing the liquid transport apparatus of the present invention may further include joining the base member and the piezoelectric actuator. 
     In the method for producing the liquid transport apparatus of the present invention, the vibration plate may be conductive. 
     In the method for producing the liquid transport apparatus of the present invention, the production of the piezoelectric actuator may include, before forming the piezoelectric material layer, arranging a third electrode on a surface of the vibration plate, on the side not facing the base member so that the third electrode corresponds to the pressure chamber and the liquid flow passage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic arrangement illustrating an ink-jet printer according to an embodiment of the present invention. 
         FIG. 2  shows a plan view illustrating a pump. 
         FIG. 3  shows a sectional view taken along a line III-III shown in  FIG. 2 . 
         FIG. 4  shows a sectional view taken along a line IV-IV shown in  FIG. 2 . 
         FIG. 5  shows a sectional view taken along a line V-V shown in  FIG. 2 . 
         FIG. 6  shows a plan view illustrating a base member. 
         FIG. 7  shows a plan view illustrating a vibration plate. 
         FIG. 8  shows a sectional view taken along a line VIII-VIII shown in  FIG. 7 . 
         FIG. 9  shows a block diagram schematically illustrating an electric arrangement of the ink-jet printer. 
         FIGS. 10A to 10F  illustrate the operation of the pump, wherein  FIG. 10A  shows a state in which the pump is stopped,  FIG. 10B  shows a state immediately before the pressure is applied to the ink,  FIG. 10C  shows a state in which the ink applied with the pressure is discharged from the pressure chamber,  FIG. 10D  shows a state in which the discharge of the ink is completed,  FIG. 10E  shows a state immediately before the ink is sucked into the pressure chamber, and  FIG. 10F  shows a state in which the ink is sucked into the pressure chamber. 
         FIGS. 11A to 11F  show steps of producing the pump, wherein  FIG. 11A  shows a step of forming the flow passage,  FIG. 11B  shows a step of forming the recess of the vibration plate,  FIG. 11C  shows a step of forming the piezoelectric material layer,  FIG. 11D  shows a step of removing the piezoelectric material from the surface of the recess,  FIG. 11E  shows a step of arranging the electrodes, and  FIG. 11F  shows a step of joining the base member and the piezoelectric actuator. 
         FIG. 12  shows a sectional view illustrating a pump of a first modified embodiment corresponding to  FIG. 3 . 
         FIG. 13  shows a sectional view illustrating a pump of a second modified embodiment corresponding to  FIG. 3 . 
         FIG. 14  shows a plan view illustrating a pump of a third modified embodiment. 
         FIG. 15  shows a sectional view taken along a line XV-XV shown in  FIG. 14 . 
         FIG. 16  shows a plan view illustrating a pump of a fourth modified embodiment. 
         FIG. 17  shows a sectional view taken along a line XVII-XVII shown in  FIG. 16 . 
         FIG. 18  shows a plan view illustrating a pump of a fifth modified embodiment. 
         FIG. 19  shows a sectional view taken along a line XIX-XIX shown in  FIG. 18 . 
         FIG. 20  shows a plan view illustrating a pump of a sixth modified embodiment. 
         FIG. 21  shows a sectional view taken along a line XXI-XXI shown in  FIG. 20 . 
         FIG. 22  shows a sectional view taken along a line XXII-XXII shown in  FIG. 20 . 
         FIG. 23  shows a plan view illustrating a pump of a seventh modified embodiment. 
         FIG. 24  shows a sectional view taken along a line XXIV-XXIV shown in  FIG. 23 . 
         FIG. 25  shows a plan view illustrating a pump of an eighth modified embodiment. 
         FIG. 26  shows a sectional view taken along a line XXVI-XXVI shown in  FIG. 25 . 
         FIG. 27  shows a sectional view taken along a line XXVII-XXVII shown in  FIG. 25 . 
         FIG. 28  shows a sectional view taken along a line XXVIII-XXVIII shown in  FIG. 25 . 
         FIG. 29  shows a sectional view illustrating a pump of a ninth modified embodiment corresponding to  FIG. 3 . 
         FIG. 30  shows a plan view illustrating a pump of a tenth modified embodiment. 
         FIG. 31  shows a sectional view taken along a line XXXI-XXXI shown in  FIG. 30 . 
         FIG. 32  shows a sectional view taken along a line XXXII-XXXII shown in  FIG. 30 . 
         FIG. 33  shows a sectional view taken along a line XXXIII-XXXIII shown in  FIG. 30 . 
         FIG. 34  shows a plan view illustrating a pump of an eleventh modified embodiment. 
         FIG. 35  shows a sectional view taken along a line XXXV-XXXV shown in  FIG. 34 . 
         FIG. 36  shows a plan view illustrating a pump of a twelfth modified embodiment. 
         FIG. 37  shows a sectional view taken along a line XXXVII-XXXVII shown in  FIG. 36 . 
         FIG. 38  shows a plan view illustrating a pump of a twelfth modified embodiment. 
         FIG. 39  shows a sectional view taken along a line XXXIX-XXXIX shown in  FIG. 38 . 
         FIG. 40  shows a plan view illustrating a pump of a thirteenth modified embodiment. 
         FIG. 41  shows a sectional view taken along a line XXXXI-XXXXI shown in  FIG. 40 . 
         FIG. 42  shows a sectional view taken along a line XXXXII-XXXXII shown in  FIG. 40 . 
         FIG. 43  shows a sectional view taken along a line XXXXIII-XXXXIII shown in  FIG. 40 . 
         FIG. 44  shows an example in which the present invention is applied to a pump for transporting liquid fuel to a fuel cell. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be explained. This embodiment is an example in which the present invention is applied to a pump for transporting an ink to an ink-jet head of an ink-jet printer. 
     At first, the ink-jet printer  100  of this embodiment will be briefly explained. As shown in  FIG. 1 , the ink-jet printer  100  is provided with, for example, a carriage  1  which is movable in the left-right direction in  FIG. 1 , a serial type ink-jet head  2  which is provided on the carriage  1  and which jets the ink toward the recording paper P, transport rollers  3  which transport the recording paper P in the frontward direction in  FIG. 1 , an ink tank  4  which stores the ink, a pump  5  which supplies the ink in the ink tank  4  to the ink-jet head  2 , and a controller  6  (see  FIG. 9 ) which controls respective parts of the printer  100  including, for example, the ink-jet head  2  and the transport rollers  3 . 
     An ink subtank  7 , which is movable in the scanning direction together with the carriage  1 , is arranged over or above the ink-jet head  2 . Further, the ink subtank  7  is connected to the ink tank  4  via a tube  8  and the pump  5 . The ink, which is stored in the ink tank  4 , is pressurized by the pump  5 , and the ink is transported to the ink subtank  7  via the tube  8 . The ink is once stored in the ink subtank  7 , and then the ink is supplied to the ink-jet head  2 . 
     The ink, which is supplied from the ink subtank  7 , is jetted by the ink-jet head  2  toward the recording paper P from nozzles (not shown) arranged on the lower surface of the ink-jet head  2 , while the ink-jet head  2  is moved in the left-right direction as shown in  FIG. 1  together with the carriage  1 . The transport rollers  3  transport the recording paper P in the frontward direction as shown in  FIG. 1 . The ink-jet printer  100  is constructed such that the transport rollers  3  are controlled to transport the recording paper P in the frontward direction while jetting the ink toward the recording paper P from the nozzles by controlling the ink-jet head  2  by means of the controller  6 , and thus desired images, letters and the like are recorded on the recording paper P. 
     A cap  9  is arranged movably in the vertical direction at the retraction position positioned on one side (left side as shown in  FIG. 1 ) in the widthwise direction of the recording paper from the recording paper transport area in which the recording paper P is transported. The cap  9  is capable of covering the lower surface (ink-jetting surface) of the ink-jet head  2  moved to the retraction position. In this arrangement, when the nozzle clog-up is caused by the contamination with, for example, the bubble or the dust in the ink flow passage in the ink-jet head  2  including the nozzles, the purge operation is executed to forcibly discharge the ink from the nozzles in the state in which the ink-jetting surface of the ink-jet head  2  is covered with the cap  9 . More specifically, the ink is pressurized by the pump  5  to arrive at the pressure higher than the pressure adopted when the ink is ordinarily supplied, and the ink is supplied to the ink-jet head  2 . Accordingly, the ink is jetted from the nozzles at the pressure higher than the pressure adopted during the recording so that the bubble, the dust or the like, with which the ink-jet head  2  is contaminated, is discharged together with the ink. A discharge tube  10  is connected to the cap  9 . The ink, which is jetted into the cap  9  in accordance with the purge operation, is discharged to the outside of the cap  9  via the discharge tube  10 . 
     Next, an explanation will be made with reference to  FIGS. 2 to 5  about the pump  5  (liquid transport apparatus) for transporting the ink in the ink tank  4  to the ink subtank  7 .  FIG. 2  shows a plan view illustrating the pump  5 .  FIG. 3  shows a sectional view taken along a line III-III shown in  FIG. 2 .  FIG. 4  shows a sectional view taken along a line IV-IV shown in  FIG. 2 .  FIG. 5  shows a sectional view taken along a line V-V shown in  FIG. 2 . The explanation will be made, while the direction, which is directed toward the front in the plane of the paper of  FIG. 2 , is defined as the upper direction, and the horizontal direction in  FIG. 2  is defined as the left-right direction. 
     As shown in  FIGS. 2 to 5 , the pump  5  is provided with a base member  20  which has an ink flow passage  22  formed along its upper surface, and a piezoelectric actuator  21  which is arranged on the upper surface of the base member  20 . 
     At first, the base member  20  will be explained.  FIG. 6  shows a plan view illustrating the base member  20 . As shown in  FIGS. 2 and 6 , the base member  20  is a plate-shaped member having a rectangular planner shape. Various materials including, for example, metal materials, synthetic resin materials, and silicon can be used for the base member  20 . However, when the base member  20  is formed of a metal material such as stainless steel, the ink flow passage  22  can be formed with ease by the etching. 
     The ink flow passage  22 , which is formed on the upper surface of the base member  20 , is composed of a pressure chamber  23 , and an ink supply flow passage  24  and an ink discharge flow passage  25  (liquid flow passages) which are communicated with the pressure chamber  23 . The pressure chamber  23  is formed to have a recessed form at a central portion of the upper surface of the base member  20 . The ink supply flow passage  24 , which has a recessed form, is formed in an area disposed on the upper surface of the base member  20  at the left side of the pressure chamber  23 . The ink supply flow passage  24  extends from an ink supply port  26  formed at the left end of the base member  20  to the left end of the pressure chamber  23 . On the other hand, the ink discharge flow passage  25 , which has a recessed form, is formed in an area disposed on the upper surface of the base member  20  at the right side of the pressure chamber  23 . The ink discharge flow passage  25  extends from the right end of the pressure chamber to an ink discharge port  27  formed at the right end of the base member  20 . In other words, the ink supply flow passage  24 , the pressure chamber  23 , and the ink discharge flow passage  25  are arranged to extend on a straight line along the upper surface of the base member  20 . 
     The ink supply port  26  is connected via the tube  8  to the ink tank  4  shown in  FIG. 1 . On the other hand, the ink discharge port  27  is connected via the tube  8  to the ink subtank  7  shown in  FIG. 1 . Therefore, the ink, which inflows from the ink supply port  26  disposed at the left end of the base member  20 , passes through the ink supply flow passage  24 , and the ink is supplied to the pressure chamber  23 . Further, the pressure is applied to the ink which inflowed into the pressure chamber  23  by the piezoelectric actuator  21  which will be described later on. After that, the ink passes through the ink discharge flow passage  25 , the ink is discharged from the ink discharge port  27  disposed at the right end, and the ink is transported to the ink subtank  7 . 
     As shown in  FIG. 2 , the ink supply flow passage  24  and the ink discharge flow passage  25  have flow passage widths (lengths in relation to the horizontal direction (upward-downward direction as shown in  FIG. 2 ) perpendicular to the left-right direction as the ink transport direction) which are narrower than that of the pressure chamber  23 . Further, the ink supply flow passage  24  and the ink discharge flow passage  25  are formed to have such shapes that the flow passage widths are narrowed at the connecting portions with respect to the ink supply port  26  and the ink discharge port  27 . The flow passage shapes of the ink supply flow passage  24  and the ink discharge flow passage  25  are bilaterally symmetrical in relation to the pressure chamber  23 . As a result, the ink flow passage  22  has the largest flow passage width at the pressure chamber  23  disposed at the central portion to provide such a flow passage shape that the flow passage width is narrowed at portions nearer to the ink supply port  26  disposed at the left end and the ink discharge port  27  disposed at the right end as starting from the pressure chamber  23 . 
     In order that a large amount of the ink can be transported at once when the pressure is applied to the ink in the pressure chamber  23  by the piezoelectric actuator  21  as described later on, it is necessary that the flow passage cross-sectional area of the pressure chamber  23  (cross-sectional area in the vertical plane perpendicular to the left-right direction as the ink transport direction) should be increased to secure the volume of the pressure chamber  23  to some extent. On the other hand, as for the ink supply flow passage  24  and the ink discharge flow passage  25 , it is preferable that the flow passage cross-sectional area is small to such an extent that the flow passage resistance is not excessively increased so that the flow passage can be opened and closed by the piezoelectric actuator  21  easily and quickly. 
     Therefore, the flow passage cross-sectional areas of the ink supply flow passage  24  and the ink discharge flow passage  25  are smaller than the flow passage cross-sectional area of the pressure chamber  23 . Specifically, as shown in  FIGS. 2 ,  4 , and  5 , both of the flow passage width and the flow passage depth of each of the ink supply flow passage  24  and the ink discharge flow passage  25  are smaller than the flow passage width and the flow passage depth of the pressure chamber  23  respectively. 
     Further, a valve seat  28 , which closes the ink supply flow passage  24  in cooperation with an opening/closing portion  31  of the piezoelectric actuator  21  as described later on, is provided at an intermediate portion in the left-right direction of the ink supply flow passage  24 . As shown in  FIG. 5 , the upper surface of the valve seat  28  is formed to provide a smooth recess-shaped curved surface which is the deepest at the central portion in the widthwise direction thereof. Similarly, a valve seat  29 , which has the same shape as that of the valve seat  28  of the ink supply flow passage  24 , is also provided at an intermediate portion in the left-right direction of the ink discharge flow passage  25 . 
     Next, the piezoelectric actuator  21  will be explained. As shown in  FIGS. 2 to 5 , the piezoelectric actuator  21  has a pressure-applying portion  30  which applies the pressure to the ink contained in the pressure chamber  23  in order to transport the ink, and opening/closing portions  31 ,  32  which open and close the ink supply flow passage  24  and the ink discharge flow passage  25  respectively. 
     The pressure-applying portion  30  and the opening/closing portion  31  of the piezoelectric actuator  21  are composed of a stack  33  provided by stacking a plurality of layers including a piezoelectric material layer  36 . More specifically, the stack  33  includes a vibration plate  35  which is arranged on the upper surface of the base member  20 , the piezoelectric material layer  36  which is formed on the upper surface of the vibration plate  35  (surface disposed on the side not facing the base member  20 ), a driving electrode  37  (first electrode) which is formed in an area opposed to the pressure chamber  23 , of the upper surface of the piezoelectric material layer  36 , and two flow passage-opening/closing electrodes  38 ,  39  (second electrodes) which are formed in areas opposed to the ink supply flow passage  24  and the ink discharge flow passage  25  respectively. 
     The vibration plate  35  is a metal plate having the same rectangular planner shape as that of the base member  30 . The vibration plate  35  is formed by, for example, an iron-based alloy such as stainless steel, a copper-based alloy, a nickel-based alloy, or a titanium-based alloy. The vibration plate  35  is joined to the upper surface of the base member  20  in a state in which the pressure chamber  23 , the ink supply flow passage  24 , and the ink discharge flow passage  25  are covered therewith from the upper position. The upper surface of the vibration plate  35 , which is conductive, is opposed to the driving electrode  37  and the two flow passage-opening/closing electrodes  38 ,  39  with the piezoelectric material layer  36  intervening therebetween. The upper surface of the vibration plate  35  also serves as a common electrode (third electrode) which generates the electric field in the thickness direction in the piezoelectric material layer  36  with respect to the electrodes  37  to  39 . According to this arrangement, it is unnecessary to form any common electrode on the lower side of the piezoelectric material layer  36  distinctly from the vibration plate  35 . Therefore, the structure of the piezoelectric actuator  21  is simplified corresponding thereto. 
       FIG. 7  shows a plan view illustrating the vibration plate  35 .  FIG. 8  shows a sectional view taken along a line VIII-VIII illustrating the vibration plate  35 . As shown in  FIGS. 2 ,  3 ,  7 , and  8 , recesses  40 ,  41  are formed in areas of the upper surface of the vibration plate  35  (surface disposed on the side not facing the base member  20 ) facing the boundary between the pressure chamber  23  and the ink supply flow passage  24  and the boundary between the pressure chamber  23  and the ink discharge flow passage  25  respectively. Further, recesses  42 ,  43  are also formed in areas of the upper surface of the vibration plate  35  facing the upstream side (left side) from the valve seat  28  of the ink supply flow passage  24  and the downstream side (right side) from the valve seat  29  of the ink discharge flow passage  25  respectively. The four recesses  40  to  43  extend over the entire regions in the widthwise direction of the ink flow passage  22  (pressure chamber  23 , ink supply flow passage  24 , and ink discharge flow passage  25 ). 
     In other words, the thickness of the vibration plate  35  is locally thinned and the rigidity is lowered at the portions at which the four recesses  40  to  43  are formed. The portion of the vibration plate  35  facing the pressure chamber  23 , the portion facing the valve seat  28  of the ink supply flow passage  24 , and the portion facing the valve seat  29  of the ink discharge flow passage  25  are comparted by the recesses  40  to  43  as the rigidity-lowered portions. 
     The piezoelectric material layer  36 , which is composed of the piezoelectric material provided as the solid solution of lead titanate and lead zirconate and containing the main component of lead zirconium titanate (PZT), is formed on the upper surface of the vibration plate  35 . Four through-holes  45  to  48 , which have the same planner shapes as those of the four recesses  40  to  43 , are formed through the piezoelectric material layer  36  so that the four through-holes  45  to  48  face the recesses  40  to  43  respectively. In other words, the piezoelectric material layer  36  is formed on the entire region of the upper surface of the vibration plate  35  except for the areas in which the four recesses  40  to  43  are formed. 
     As shown in  FIG. 2 , the driving electrode  37  has a rectangular planar shape, which is arranged in an area of the upper surface of the piezoelectric material layer  36  facing the central portion of the pressure chamber  23  in relation to the flow passage widthwise direction. On the other hand, the two flow passage-opening/closing electrodes  38 ,  39  have slender rectangular planner shapes having lengths in the left-right direction shorter than that of the driving electrode  37 , which are arranged in areas facing the central portions in the flow passage widthwise direction of the two valve seats  28 ,  29  respectively. Each of the three electrodes  37 ,  38 ,  39  is composed of a conductive material such as gold, copper, silver, palladium, platinum, and titanium. 
     Further, three wirings  50 ,  51 ,  52 , which are independent from each other and which are led from the driving electrode  37  and the two flow passage-opening/closing electrodes  38 ,  39  to areas not facing the ink flow passage  22  (pressure chamber  23 , ink supply flow passage  24 , and ink discharge flow passage  25 ) respectively, are formed on the upper surface of the piezoelectric material layer  36 . The driving electrode  37  and the two flow passage-opening/closing electrodes  38 ,  39  are connected via the three wirings  50  to  52  to a driver IC  60  (driver, see  FIG. 9 ) respectively. Although not especially shown in the drawing, the vibration plate  35 , which also serves as the common electrode, is also connected to the driver IC  60 . The driver IC  60  is constructed as follows. That is, the vibration plate  35  is always maintained at the ground electric potential (first electric potential). Further, the ground electric potential (first electrode) and the predetermined driving electric potential (second electric potential) different from the ground electric potential are selectively applied to the driving electrode  37  and the two flow passage-opening/closing electrodes  38 ,  39  respectively based on the control signal fed from the controller  6  of the ink-jet printer  100 . The driving electrode  37  and the flow passage-opening/closing electrodes  38 ,  39  are arranged on the same plane (upper surface of the piezoelectric material layer  36 ). Therefore, the electrode (third electrode, i.e., the upper surface of the vibration plate  30  in this embodiment), which corresponds to the electrodes  37 ,  38 ,  39 , can be commonly used for the pressure-applying portion  30  and the opening/closing portions  31 ,  32 . 
     When the driving electric potential is applied from the driver IC  60  to the electrode (driving electrode  37  or flow passage-opening/closing electrode  38 ,  39 ) arranged on the upper surface of the piezoelectric material layer  36 , a state is provided such that the electric potential mutually differs between the electrode to which the driving electric potential is applied and the vibration plate  35  which serves as the common electrode disposed on the lower side of the piezoelectric material layer  36  retained at the ground electric potential. Therefore, the electric field is generated in the thickness direction in the piezoelectric material layer  36  interposed between the electrode disposed on the upper side and the vibration plate  35  disposed on the lower side. In this situation, when the direction of polarization of the piezoelectric material layer  36  is the same as the direction of the electric field, then the piezoelectric material layer  36  is elongated in the thickness direction as the direction of polarization, and the piezoelectric material layer  36  is shrunk in the in-plane direction perpendicular to the thickness direction (piezoelectric transverse effect). In this arrangement, the vibration plate  35  is joined to the base member  20  in the area not facing the ink flow passage  22 , and the deformation thereof is restricted. Therefore, when the piezoelectric material layer  36  is shrunk in the in-plane direction, then the portion of the vibration plate  35 , which faces the ink flow passage  22 , is warped, and the portion is deformed to project toward the lower side (toward side of the base member  20 ). 
     In other words, the piezoelectric material layer  36  is not deformed in the area facing the pressure chamber  23  in the state in which the ground electric potential is applied to the driving electrode  37 . Therefore, the vibration plate  35  is parallel to the upper surface of the base member  20  as shown by solid lines in  FIG. 4 . Starting from this state, when the driving electric potential is applied to the driving electrode  37 , then the vibration plate  35  is deformed to project toward the base member  20  (toward the pressure chamber  23 ) as shown by two-dot chain lines in  FIG. 4 , and thus the volume of the pressure chamber  23  is decreased. Accordingly, the pressure is applied to the ink in the pressure chamber  23 . According to the above, the portion of the stack  33  (portion including the driving electrode  37 ), which faces the pressure chamber  23 , constitutes the pressure-applying portion  30  which applies the pressure to the ink in the pressure chamber  23  in order to transport the ink. 
     The piezoelectric material layer  36  is not deformed in the area facing the ink supply flow passage  24  in the state in which the ground electric potential is applied to the flow passage-opening/closing electrode  38 . Therefore, the vibration plate  35  is parallel to the upper surface of the base member  20  as shown by solid lines in  FIG. 5 . In this situation, the gap is formed between the vibration plate  35  and the upper surface of the recessed valve seat  28  provided for the ink supply flow passage  24 . The ink supply flow passage  24  is in the open state. On the other hand, when the driving electric potential is applied to the flow passage-opening/closing electrode  38 , the vibration plate  35  is deformed to project toward the base member  20  (toward the ink supply flow passage  24 ) as shown by two-dot chain lines in  FIG. 5 . In this arrangement, the upper surface of the valve seat  28  provided for the ink supply flow passage  24  is previously formed to have the recessed form corresponding to the projection deformation of the vibration plate  35 . Therefore, the vibration plate  35 , which is deformed to project toward the base member  20 , abuts against the recessed valve seat  28  corresponding to the projection in a state of being substantially adhered or making tight contact therewith. The ink supply flow passage  24  is reliably closed (closed state). For example, when the length in the flow passage widthwise direction of the flow passage-opening/closing electrode  38  is 10 to 15 mm, the amount of deformation of the vibration plate  35  in the direction directed toward the base member  20  may be 0.05 to 0.1 mm. According to the above, the portion of the stack  33  (portion including the flow passage-opening/closing electrode  38 ), which faces the ink supply flow passage  24 , constitutes the opening/closing portion  31  which opens and closes the ink supply flow passage  24 . 
     Similarly, the gap is present between the vibration plate  35  and the valve seat  29  in the state in which the ground electric potential is applied to the flow passage-opening/closing electrode  39 . Therefore, the ink discharge flow passage  25  is in the open state. When the driving electric potential is applied to the flow passage-opening/closing electrode  39 , then the vibration plate  35  is deformed to project, and the vibration plate  35  is allowed to substantially make tight contact with the recessed valve seat  29 . Therefore, the ink discharge flow passage  25  is in the closed state. Therefore, the portion of the stack  33  (portion including the flow passage-opening/closing electrode  39 ), which faces the ink discharge flow passage  25 , constitutes the opening/closing portion  32  which opens and closes the ink discharge flow passage  25 . 
     As described above, the pressure-applying portion  30  is constructed by the portion of the stack  33  facing the pressure chamber  23 , while the opening/closing portions  31 ,  32  are constructed by the portions of the stack  33  facing the ink supply flow passage  24  and the ink discharge flow passage  25 . As a result, as shown in  FIG. 3 , the piezoelectric actuator  21  has the structure in which the pressure-applying portion  30  and the two opening/closing portions  31 ,  32  are arranged along the upper surface of the base member  20  (on one plane). 
     The driver IC  60  is connected to the driving electrode  37  and the two flow passage-opening/closing electrodes  38 ,  39  via the independent wirings  50  to  52 . In this arrangement, the driving electric potential is applied at the predetermined timings to the three electrodes  37  to  39  respectively, and thus the pressure-applying portion  30  and the opening/closing portions  31 ,  32  are driven independently from each other. Therefore, it is possible to independently perform the application of the pressure by the pressure-applying portion  30  and the opening and closing of the flow passages  24 ,  25  by the opening/closing portions  31 ,  32 . 
     As described above, the four recesses  40  to  43  are formed on the upper surface of the vibration plate  35  (surface on the side not facing the base member  20 ). The portions of the vibration plate  35 , which face the pressure chamber  23 , the valve seat  28  of the ink supply flow passage  24 , and the valve seat  29  of the ink discharge flow passage  25  respectively, are comparted from each other by the recesses  40  to  43 . Further, the piezoelectric material layer  36  is not formed on the surface of the four recesses  40  to  43 . In other words, the portions, in which the thickness of the stack  33  is locally thinned and the rigidity is lowered, are provided at the both ends of the pressure-applying portion  30  and the opening/closing portions  31 ,  32  in relation to the ink transport direction (left-right direction) respectively. 
     When the rigidities of the vibration plate  35  and the piezoelectric material layer  36  for constructing the stack  33  are locally lowered between the pressure-applying portion  30  and the opening/closing portions  31 ,  32  disposed adjacently to one another as described above, the deformations of the piezoelectric material layer  36  and the vibration plate  35 , which are brought about when the driving electric potential is applied to the electrodes, are hardly transmitted. In other words, the mutual interference of the deformations of the piezoelectric material layer  36  and the vibration plate  35  is suppressed between the pressure-applying portion  30  and the opening/closing portions  31 ,  32 . Therefore, the independent operations of the pressure-applying portion  30  and the opening/closing portions  31 ,  32  are guaranteed. The fact that the rigidity-lowered portions are arranged at the both ends of the pressure-applying portion  30  and the opening/closing portions  31 ,  32  means, in other words, the fact that the rigidities are lowered in the driven areas disposed on the both sides of the area (driving area) in which the piezoelectric material layer  36  is spontaneously deformed while facing the electrode. When the rigidity of the driven area is low as described above, the vibration plate is deformed more largely with ease. Therefore, it is possible to increase the amount of deformation of the vibration plate by using the small driving electric potential. Therefore, it is possible to efficiently drive the pressure-applying portion  30  and the opening/closing portions  31 ,  32 . 
     Next, a brief description will be made with reference to a block diagram shown in  FIG. 9  about the controller  6  which controls the operations of the respective portions of the ink-jet printer  100  (see  FIG. 1 ) including the pump  5  described above. The controller  6  manages the control of the various operations of the printer  100  including, for example, the reciprocating operation of the carriage  1 , the ink-jetting operation of the ink-jet head  2 , the operation for transporting the recording paper P by the transport rollers  3 , and the ink transport operation by the pump  5 . The controller  6  is provided with, for example, CPU (Central Processing Unit) which is the central processing unit or the central processor, ROM (Read Only Memory) which stores, for example, the program and the data for controlling the printer  100 , and RAM (Random Access Memory) which temporarily stores the data to be processed by CPU. 
     The controller  6  controls a carriage-driving motor  61  for reciprocatively driving the carriage  1 , the ink-jet head  2 , and a transport motor  62  for driving the transport rollers  3  based on the data in relation to, for example, the recording image inputted from a data input device  200  such as PC to record, for example, the desired image on the recording paper P. Further, the controller  6  controls the piezoelectric actuator  21  of the pump  5  (specifically the driver IC  60 ) so that the ink, which is stored in the ink tank  4 , is supplied by the pump  5  to the ink-jet head  2 . 
     Next, an explanation will be made with reference to  FIG. 10  about an example of the ink transport operation by the pump  5 . In  FIG. 10 , the symbol “+” indicates the state in which the electrode potential is the driving electric potential, and the symbol “GND” indicates the state in which the electrode potential is the ground electric potential. 
     At first, as shown in  FIG. 10A , when the operation of the pump  5  is stopped, all of the electric potentials of the three electrodes  37  to  39 , i.e., the driving electrode  37  of the pressure-applying portion  30  and the flow passage-opening/closing electrodes  38 ,  39  of the opening/closing portions  31 ,  32  are retained at the ground electric potential by the driver IC  60 . No electric potential difference is generated between the three electrodes  37  to  39  and the vibration plate  35  as the common electrode. Therefore, the shrinkage, which is to be caused by the piezoelectric transverse effect, is not generated in the piezoelectric material layer  36 . The vibration plate  35  is parallel to the upper surface of the base member  20 . In this situation, the gaps are formed between the vibration plate  35  and the valve seats  28 ,  29  in the ink supply flow passage  24  and the ink discharge flow passage  25 . Both of the ink supply flow passage  24  and the ink discharge flow passage  25  are in the open state. 
     Starting from this state, when the electric potential of the flow passage-opening/closing electrode  38  facing the ink supply flow passage  24  is switched to the driving electric potential by the driver IC  60  as shown in  FIG. 10B , the vibration plate  35  is deformed to project toward the base member  20  at the opening/closing portion  31 . In this situation, the vibration plate  35  is allowed to substantially make tight contact with the upper surface of the valve seat  28  formed to have the recessed form, and the gap between the vibration plate  35  and the valve seat  28  is plugged. Therefore, the ink supply flow passage  24  is closed. 
     Further, as shown in  FIG. 10C , when the electric potential of the driving electrode  37  facing the pressure chamber  23  is switched to the driving electric potential, the vibration plate  35  is deformed to project toward the base member  20  at the pressure-applying portion  30 . Accordingly, the volume of the pressure chamber  23  is decreased. Therefore, the pressure is applied to the ink in the pressure chamber  23 , and the ink is discharged from the pressure chamber  23  to the ink discharge flow passage  25 . In this situation, the ink supply flow passage  24 , which is disposed on the upstream side of the pressure chamber  23 , is closed by the opening/closing portion  31 . Therefore, the pressure wave, which is generated in the pressure chamber  23 , is not allowed to escape to the ink supply flow passage  24 . Therefore, it is possible to transport the ink efficiently. 
     Subsequently, as shown in  FIG. 10D , the electric potential of the flow passage-opening/closing electrode  39  of the opening/closing portion  32  facing the ink discharge flow passage  25  is switched to the driving electric potential in conformity with the timing at which the ink discharge from the pressure chamber  23  is completed. Accordingly, the vibration plate  35  is deformed to project toward the base member  20  at the opening/closing portion  32 , and the vibration plate  35  is allowed to substantially make tight contact with the upper surface of the valve seat  29 . Therefore, the ink discharge flow passage  25  is closed. 
     Subsequently, as shown in  FIG. 10E , when the electric potential of the electrode  38  facing the ink supply flow passage  24  is switched to the ground electric potential by the driver IC  60 , the ink supply flow passage  24  is opened again. Further, as shown in  FIG. 10F , when the electric potential of the driving electrode  37  facing the pressure chamber  23  is switched to the ground electric potential, then the vibration plate  35  is returned to have the flat shape at the pressure-applying portion  30 , and the volume of the pressure chamber  23  is increased. In this situation, the ink discharge flow passage  25  is closed by the opening/closing portion  32 . Accordingly, the pressure of the ink in the pressure chamber  23  is suddenly lowered in accordance with the increase in the volume of the pressure chamber  23 , and the ink is allowed to inflow from the ink supply flow passage  24  into the pressure chamber  23 . After that, the ink supply flow passage  24  is closed again by the opening/closing portion  31 . Further, the ink discharge flow passage  25  is opened by the opening/closing portion  32  ( FIG. 10B ), and then the pressure is applied to the ink in the pressure chamber  23  by the pressure-applying portion  30  ( FIG. 10C ). 
     As described above, a series of operations are repeated such that the pressure is applied in the pressure chamber  23  to the ink supplied from the ink supply flow passage  24  into the pressure chamber  23 , and the ink is discharged from the ink discharge flow passage  25 . Thus, the ink contained in the ink tank  4  is transported to the ink subtank  7 . 
     Next, an explanation will be made with reference to  FIG. 11  about a method for producing the pump  5  of this embodiment. At first, as shown in  FIG. 11A , the pressure chamber  23  is formed on the upper surface of the base member  20 , and the ink supply flow passage  24  and the ink discharge flow passage  25 , which are communicated with the pressure chamber  23  and which have the flow passage cross-sectional areas smaller than that of the pressure chamber  23 , are formed on the upper surface of the base member  20  (flow passage-forming step). In this procedure, when the base member  20  is a metal plate, the ink flow passage  22 , which has a relatively complicated shape including the valve seats  28 ,  29 , can be formed with ease by means of the etching. 
     The piezoelectric actuator  21 , which is to be arranged on the upper surface of the base member  20 , is produced concurrently with the flow passage-forming step (actuator-producing step). At first, as shown in  FIG. 11B , the four recesses  40  to  43 , which are provided to locally lower the rigidity of the vibration plate  35 , are formed by means of the etching on the upper surface of the vibration plate  35  formed by the metal material. 
     Subsequently, as shown in  FIG. 11C , the piezoelectric material layer  36  is formed on the entire region of the upper surface of the vibration plate  35  on which the four recesses  40  to  43  have been formed (piezoelectric material layer-forming step). In this procedure, in the piezoelectric material layer-forming step, the piezoelectric material layer  36   a  of the pressure-applying portion  30  to face the pressure chamber  23  and the piezoelectric material layers  36   b ,  36   c  of the opening/closing portions  31 ,  32  to face the ink supply flow passage  24  and the ink discharge flow passage  25  respectively can be formed simultaneously by depositing the particles of the piezoelectric material on the upper surface of the vibration plate  35 . For example, the aerosol deposition (AD) method, in which the aerosol prepared by mixing the carrier gas and the particles composed of the piezoelectric material is allowed to collide with the film formation objective (vibration plate  35 ) at a high velocity to deposit the particles thereby, can be adopted as a specified method for forming the piezoelectric material layer  36 . Alternatively, it is also possible to use the sputtering method and the chemical vapor deposition (CVD) method. 
     After that, as shown in  FIG. 11D , the piezoelectric material, which has been deposited on the surfaces of the four recesses  40  to  43 , is removed, for example, by irradiating the laser to form the four through-hole  45  to  48  corresponding to the four recesses  40  to  43  respectively. 
     Alternatively, in the piezoelectric material layer-forming step shown in  FIG. 11C , a mask material, which covers only the four recesses  40  to  43 , may be arranged on the upper surface of the vibration plate  35 , and then the particles of the piezoelectric material may be deposited in the area of the upper surface of the vibration plate  35  not covered with the mask material. In the case of this procedure, the piezoelectric material is not deposited on the surfaces of the recesses  40  to  43  of the vibration plate  35 . Therefore, it is unnecessary to perform the step of removing the piezoelectric material disposed on the recess surface by means of the laser or the like. 
     Subsequently, as shown in  FIG. 11E , the electrodes  37  to  39  are formed at the portions  36   a  to  36   c  of the upper surface of the piezoelectric material layer  36  interposed between the four recesses  40  to  43  respectively (electrode-arranging step). That is, the driving electrode  37  is formed on the upper surface of the piezoelectric material layer  36   a  of the pressure-applying portion  30  to face the pressure chamber  23 . Further, the flow passage-opening/closing electrodes  38 ,  39  are formed on the upper surfaces of the piezoelectric material layers  36   b ,  36   c  of the opening/closing portions  31 ,  32  to face the ink supply flow passage  24  and the ink discharge flow passage  25  respectively. 
     In this procedure, for example, when the screen printing method is used, the driving electrode  37  and the two flow passage-opening/closing electrodes  38 ,  39  can be formed at once on the upper surface of the piezoelectric material layer  36 . Alternatively, the driving electrode  37  and the flow passage-opening/closing electrodes  38 ,  39  may be formed such that a conductive film is formed on the entire surface of the piezoelectric material layer  36 , for example, by means of the vapor deposition method, and then any conductive layer, which is disposed on unnecessary areas, is removed, for example, by the laser. As described above, in this embodiment, the upper surface of the vibration plate  35  also serves as the common electrode (third electrode) facing the three electrodes  37  to  39  disposed on the upper surface of the piezoelectric material layer  36 . Therefore, the step of forming the common electrode on the lower side of the piezoelectric material layer  36  is omitted. According to the steps as described above, the piezoelectric actuator  21  is produced, which has such a structure that the pressure-applying portion  30  and the opening/closing portions  31 ,  32  are arranged along one plane. 
     The recesses  40  to  43  of the vibration plate  35  may be formed on any one of the upper surface and the lower surface. However, in particular, when the recesses  40  to  43  are formed on the upper surface of the vibration plate  35 , all of the plurality of steps (formation of the recesses  40  to  43  of the vibration plate  35  ( FIG. 11B ), formation of the piezoelectric material layer  36  ( FIG. 11C ), removal of the piezoelectric material from the recess surface by means of the laser or the like ( FIG. 11D ), and electrode formation (FIG.  11 E)), which are included in the steps of producing the actuator, can be executed in the same direction (from the upper side). Therefore, it is easy to produce the piezoelectric actuator  21 , and it is possible to shorten the steps. 
     Finally, as shown in  FIG. 11F , the piezoelectric actuator  21  is installed on the upper surface of the base member  20  so that the pressure-applying portion  30  faces the pressure chamber  23 , and the opening/closing portions  31 ,  32  face the ink supply flow passage  24  and the ink discharge flow passage  25 , and the lower surface of the vibration plate  35  and the upper surface of the base member  20  are joined to one another by using, for example, an adhesive. In accordance with the above, the production of the pump  5  is completed. 
     According to the pump  5  of this embodiment as explained above, the following effect is obtained. The pump  5  of this embodiment has the pressure-applying portion  30  which applies the pressure to the ink in the pressure chamber  23 , and the opening/closing portions  31 ,  32  which open and close the ink supply flow passage  24  and the ink discharge flow passage  25  communicated with the pressure chamber  23  respectively. The pressure-applying portion  30  and the opening/closing portions  31 ,  32  are driven independently from each other. Therefore, the pressure is applied to the ink in the pressure chamber  23  at the appropriate timing by means of the pressure-applying portion  30 , while opening and closing the ink supply flow passage  24  and the ink discharge flow passage  25  by means of the opening/closing portions  31 ,  32  respectively. Accordingly, it is possible to efficiently transport the ink. No sliding portion is present in the piezoelectric actuator  21  unlike the mechanical pump (for example, a tube pump and a syringe pump) having been hitherto widely used as the liquid transport pump. Therefore, an advantage is also obtained such that the noise, which is generated during the operation, is small. 
     Further, the piezoelectric actuator  21  has the stack  33  which includes, for example, the vibration plate  35 , the piezoelectric material layer  36 , and the electrodes  37  to  39  allowed to extend along one surface of the base member  20 . The portion of the stack  33 , which faces the pressure chamber  23 , is the pressure-applying portion  30 . The portions of the stack  33 , which face the ink supply flow passage  24  and the ink discharge flow passage  25 , are the opening/closing portions  31 ,  32  respectively. As a result, the pressure-applying portion  30  and the opening/closing portions  31 ,  32  are arranged on the same plane along with one surface of the base member  20 . Therefore, the structure of the piezoelectric actuator  21  is simpler than any three-dimensional structure in which the pressure-applying portion and the opening/closing portion are arranged on distinct planes. It is possible to provide the small size of the pump  5  by making the piezoelectric actuator  21  to be compact. 
     The pressure-applying portion  30  and the opening/closing portions  31 ,  32 , which are positioned on the same plane, can be simultaneously produced by stacking the plurality of layers including the vibration plate  35 , the piezoelectric material layer  36 , and the electrodes  37  to  39  on the upper surface of the base member  20 . In particular, when the method, in which the particles of the piezoelectric material are deposited on the upper surface of the vibration plate  35 , is adopted in the piezoelectric material layer-forming step, the piezoelectric material layers  36  of the pressure-applying portion  30  and the opening/closing portions  31 ,  32  can be simultaneously formed on the vibration plate  35 . Therefore, it is possible to simplify the steps of producing the piezoelectric actuator  21 . 
     Next, an explanation will be made about modified embodiments to which various modifications are applied to the embodiment described above. However, those constructed in the same manner as in the embodiment described above are designated by the same reference numerals, any explanation of which will be appropriately omitted. 
     In the embodiment described above, the recesses  40  to  43  are formed at the both ends of the pressure-applying portion  30  and the opening/closing portions  31 ,  32 . On this condition, the through-holes  45  to  48 , which correspond to the recesses  40  to  43 , are formed through the piezoelectric material layer  36  (see  FIG. 3 ). However, as shown in  FIG. 12 , it is also allowable that no recess is formed on a vibration plate  35 A, and only the four through-holes  45  to  48  are formed through the piezoelectric material layer  36  (first modified embodiment). Alternatively, as shown in  FIG. 13 , it is also allowable that no recess is formed on a vibration plate  35 B, and four recesses  45 B to  48 B are formed on a piezoelectric material layer  36 B in place of the four through-holes  45  to  48  of the first modified embodiment (second modified embodiment). Even when the through-holes and/or the recesses are formed for only the piezoelectric material layer, the rigidity of the stack for constructing the piezoelectric actuator is lowered to some extent. Therefore, an effect is obtained such that the amount of displacement of the vibration plate is increased, and the mutual interference is avoided between the pressure-applying portion and the opening/closing portion. 
     When it is unnecessary to progressively suppress the mutual interference between the pressure-applying portion and the opening/closing portion, for example, when the distance between the pressure-applying portion and the opening/closing portion is sufficiently far, then it is unnecessary to provide any rigidity-lowered portion for the stack for constructing the piezoelectric actuator. In other words, as shown in  FIGS. 14 and 15 , it is also allowable that no recess is formed for a vibration plate  35 C, neither through-hole nor recess is formed for a piezoelectric material layer  36 C as well, and the piezoelectric material layer  36 C is formed continuously while ranging over the pressure chamber  23 , the ink supply flow passage  24 , and the ink discharge flow passage  25  (third modified embodiment). In this arrangement, it is unnecessary to perform the step of forming the recess for the vibration plate and the step of forming the through-hole and/or the recess for the piezoelectric material layer. Therefore, it is possible to simplify the production steps. 
     As shown in  FIGS. 16 and 17 , recesses  40 D to  43 D, which are provided to locally lower the rigidity of a stack  33 D, may be formed on the lower surface of a vibration plate  35 D (fourth modified embodiment). However, in this arrangement, if any bubble is mixed into the ink, the bubble tends to stay in the recesses  40 D to  43 D. Therefore, it is feared that the desired pressure cannot be applied to the ink by means of the pressure-applying portion. On the other hand, when the recesses  40  to  43  are formed on the upper surface of the vibration plate  35  (surface disposed on the side not facing the base member) as in the embodiment described above, the lower surface of the vibration plate  35 , which makes contact with the ink, is the flat surface. Therefore, the bubble hardly stays (see  FIG. 3 ). From this viewpoint, it is preferable that the recesses are formed on the upper surface of the vibration plate. 
     In the embodiment described above, the piezoelectric material layer  36  is formed to the area outside the ink flow passage  22  including, for example, the pressure chamber  23 . Therefore, the deformation of the piezoelectric material layer  36  is restricted, and the amount of displacement of the vibration plate  35  is decreased in the area facing the ink flow passage  22 . Accordingly, as shown in  FIGS. 18 and 19 , it is also allowable that a piezoelectric material layer  36 E is formed in only areas of the upper surface of a vibration plate  35 E facing the pressure chamber  23  and the valve seats  28 ,  29  (fifth modified embodiment). 
     Also in the fifth modified embodiment, wirings  50 E to  52 E, which are independent from each other, are led from the three electrodes  37  to  39  formed on the upper surface of the piezoelectric material layer  36 E. However, the wirings  50 E to  52 E cannot be led to the area outside the ink flow passage  22  (conduction is caused with the upper surface of the vibration plate  35 E retained at the ground electric potential, because the piezoelectric material layer  36 E is absent in the area outside the ink flow passage  22 ). Therefore, the fifth modified embodiment include contacts which are provided at the ends of the three wirings  50 E to  52 E on the side opposite to the electrodes and which make connection between the electrodes  37  to  39  and the driver IC  60 , for example, via FPC (flexible printed circuit board). The contacts are positioned in areas facing the ink flow passage  22  (pressure chamber  23  and valve seats  28 ,  29 ). 
     When the wiring is led from the electrode formed on the upper surface of the piezoelectric material layer, any unnecessary electrostatic capacity (parasitic capacitance) is generated in the piezoelectric material layer between the wiring and the vibration plate when the driving electric potential is applied to the electrode. Accordingly, as shown in  FIGS. 20 to 22 , an insulating layer  70 , which is composed of an insulative material having a dielectric constant lower than that of the piezoelectric material layer  36 , may be formed between the upper surface of the piezoelectric material layer  36  and the wirings  50  to  52  (sixth modified embodiment). The insulating layer  70  can be formed of, for example, a ceramics material such as alumina and zirconia or a rein material such as polyimide. 
     It is not necessarily indispensable that the electrode, which is disposed on the upper surface of the piezoelectric material layer, is arranged in the area facing the central portion in the widthwise direction of the ink flow passage  22  of the pressure chamber  23  or the like. For example, as shown in  FIGS. 23 and 24 , electrodes  37 G to  39 G may be arranged in areas corresponding to one side in the flow passage widthwise direction of the upper surface of a piezoelectric material layer  36 G (seventh modified embodiment). In this arrangement, when the driving electric potential is applied to the electrodes  37 G to  39 G, the vibration plate  35  is deformed to project toward the base member  20  on one side in the widthwise direction of the flow passage arranged with the electrodes  37 G to  39 G. 
     The piezoelectric actuator may be constructed as follows. That is, the vibration plate is deformed to project toward the side not facing the base member, when the driving electric potential is applied to the driving electrode or the flow passage-opening/closing electrode. When the vibration plate is deformed as described above, the ink supply flow passage and/or the ink discharge flow passage is opened. 
     For example, in the case of a pump of an eighth modified embodiment shown in  FIGS. 25 to 28 , three types of electrodes  37 H to  39 H, which are included in a pressure-applying portion  30 H and opening/closing portions  31 H,  32 H respectively, are provided on the upper surface of the piezoelectric material layer  36 . Further, each of the electrodes  37 H to  39 H is divided into two electrodes which are arranged at the both ends in the widthwise direction of the flow passage. That is, the driving electrode  37 H is divided into the two electrodes  37   a ,  37   b  which are arranged in areas corresponding to the both ends of the pressure chamber  23  in the widthwise direction of the flow passage respectively. The flow passage-opening/closing electrode  38 H is divided into the two electrodes  38   a ,  38   b  which are arranged in areas corresponding to the both ends in the widthwise direction of the flow passage of the valve seat  28 H of the ink supply flow passage  24  respectively. Further, the flow passage-opening/closing electrode  39 H is divided into the two electrodes  39   a ,  39   b  which are arranged in areas corresponding to the both ends in the widthwise direction of the flow passage of the valve seat  29 H of the ink discharge flow passage  25  respectively. The electrodes divided into two (electrode  37   a  and electrode  37   b , electrode  38   a  and electrode  38   b , electrode  39   a  and electrode  39   b ) mutually make conduction by means of wirings  37   c  to  39   c  which are thinner than the divided electrodes. In other words, the same electric potential is simultaneously applied to the electrodes divided into two. 
     On the other hand, dam-shaped valve seats  28 H,  29 H, which extend over the entire regions in the widthwise direction of the flow passages  24 ,  25 , are formed for the ink supply flow passage  24  and the ink discharge flow passage  25  respectively. As shown in  FIG. 26 , the top surfaces (upper surfaces) of the two valve seats  28 H,  29 H are positioned on the same plane as that of the upper surface of the base member  20 . 
     When the driving electric potential is applied to the divided three types of the electrodes  37 H to  39 H, the piezoelectric material layer  36  is shrunk in the in-plane direction in the areas corresponding to the both ends in the widthwise direction of the flow passage in which the divided electrodes are arranged. Accordingly, the vibration plate  35  is deformed to project toward the upper side (side not facing the base member  20 ) in the area corresponding to the central portion in the widthwise direction of the flow passage in accordance with the shrinkage of the piezoelectric material layer  36  at the both ends in the widthwise direction. 
     Therefore, as shown by two-dot chain lines in  FIG. 27 , when the vibration plate  35  is deformed to project in the upward direction when the driving electric potential is applied to the driving electrode  37 H at the pressure-applying portion  30 H, then the volume of the pressure chamber  23  is increased. Therefore, the ink is allowed to inflow into the pressure chamber  23 . After that, when the ground electric potential is applied to the driving electrode  37 H, then the vibration plate  35  is returned to have the flat shape as shown by solid lines in  FIG. 27 , and the volume of the pressure chamber  23  is decreased. Accordingly, the pressure is applied to the ink in the pressure chamber  23 . 
     On the other hand, when the ground electric potential (first electric potential) is applied to the flow passage-opening/closing electrode  38 H at the opening/closing portion  31 H corresponding to the ink supply flow passage  24 , then the vibration plate  35  is in the flat state as shown by solid lines in  FIG. 28 , and the lower surface thereof abuts against the top surface of the dam-shaped valve seat  28 H in a tight contact manner. Therefore, the ink supply flow passage  24  is closed. Starting from this state, when the driving electric potential (second electric potential) is applied to the flow passage-opening/closing electrode  38 H, and the vibration plate  35  is deformed to project upwardly as shown by two-dot chain lines in  FIG. 28 , then the lower surface of the vibration plate  35  is separated from the top surface of the valve seat  28 H. Accordingly, the gap is formed between the vibration plate  35  and the valve seat  28 H. Therefore, the ink supply flow passage  24  is opened. 
     Similarly, when the ground electric potential is applied to the flow passage-opening/closing electrode  39 H at the opening/closing portion  32 H corresponding to the ink discharge flow passage  25 , the ink discharge flow passage  25  is closed. On the other hand, when the driving electric potential is applied to the flow passage-opening/closing electrode  39 H, then the gap is formed between the vibration plate  35  and the top surface of the valve seat  29 H, and the ink discharge flow passage  25  is opened. 
     According to the arrangement of the eighth modified embodiment, it is enough that the top surfaces of the valve seats  28 H,  29 H have the flat shapes, and it is unnecessary to process the top surfaces. Therefore, the valve seats can be easily formed as compared with the valve seats  28 ,  29  of the embodiment described above (see  FIGS. 3 and 6 ) in which the valve seats are formed to have the recessed forms corresponding to the projection deformation of the vibration plate. 
     As described above, the seventh modified embodiment has been referred to as the example of the piezoelectric actuator in which the vibration plate is deformed to project toward the side not facing the base member when the driving electric potential is applied to the driving electrode and/or the flow passage-opening/closing electrode. However, the vibration plate  35  can be deformed to project upwardly even in the case of the electrode structure of the piezoelectric actuator  21  of the embodiment described above (see  FIGS. 2 to 5 ). However, the driving electric potential, which is applied from the driver IC  60  to the driving electrode  37  and the flow passage-opening/closing electrodes  38 ,  39 , is a negative electric potential lower than the ground electric potential. When the negative electric potential is applied as the driving electric potential as described above, the direction of the electric field, which acts on the piezoelectric material layer  36  interposed between the upper and lower electrodes, is the direction opposite to that of the case in which the driving electric potential is positive, the direction being opposite to the direction of polarization. Accordingly, the piezoelectric material layer  36  is elongated in the in-plane direction. As a result, the vibration plate  35  is deformed to project toward the upper side (toward the side not facing the base member  20 ) conversely to the embodiment described above. 
     In the embodiment described above, the vibration plate  35  is formed by the metal material having the conductivity. The upper surface of the vibration plate  35  also serves as the common electrode (third electrode) corresponding to the driving electrode  37  and the flow passage-opening/closing electrodes  38 ,  39 . However, as shown in  FIG. 29 , a common electrode  72 , which is retained at the ground electric potential distinctly from the vibration plate  35 , may be provided on the lower surface of the piezoelectric material layer  36  (ninth modified embodiment). However, when the vibration plate  35  is formed by the conductive material, an insulating layer  80 , which electrically insulates the common electrode  72  and the vibration plate  35 , is provided between the common electrode  72  and the upper surface of the vibration plate  35 . The insulating layer  80  can be formed of a ceramics material such as alumina and zirconia or a resin material such as polyimide. When the vibration plate  35  is formed by silicon, it is also appropriate that a silicon oxide film is formed as the insulating layer  80  on the upper surface of the vibration plate  35 . On the other hand, when the vibration plate  35  is formed by an insulative material, it is unnecessary to provide the insulating layer  80 . 
     As shown in  FIGS. 30 to 33 , the following arrangement is also available. That is, a driving electrode  37 J (first electrode) and flow passage-opening/closing electrodes  38 J,  39 J (second electrodes) are arranged on the lower surface of a piezoelectric material layer  36 J. Electrodes  82  to  84  (third electrodes), which face the driving electrode  37 J and the flow passage-opening/closing electrodes  38 J,  39 J, are arranged on the upper surface of the piezoelectric material layer  36 J respectively (tenth modified embodiment). Also in the tenth modified embodiment, when the vibration plate  35  is formed by a conductive material, it is necessary that an insulating layer  85 , which electrically insulates the driving electrode  37 J and the flow passage-opening/closing electrodes  38 J,  39 J and the upper surface of the vibration plate  35 , is provided between the driving electrode  37 J and the flow passage-opening/closing electrodes  38 J,  39 J and the upper surface of the vibration plate  35 . However, the electrodes  82  to  84  can be retained at the ground electric potential by merely allowing the ends of the electrodes  82  to  84  to make conduction with the upper surface of the vibration plate  35  retained at the ground electric potential. On the other hand, when the vibration plate  35  is formed by an insulative material, it is unnecessary to provide the insulating layer  85 . However, it is necessary to distinctly provide wirings which connect the electrodes  82  to  84  to the driver IC  60  to retain them at the ground electric potential. 
     In the embodiment and the modified embodiments thereof described above, both of the driving electrode (first electrode) and the flow passage-opening/closing electrode (second electrode) are arranged on one surface of the piezoelectric material layer, and the common electrode (third electrode) is arranged on the other surface of the piezoelectric material layer. However, the driving electrode and the flow passage-opening/closing electrodes may be arranged on different surfaces of the piezoelectric material layer respectively. For example, as shown in  FIGS. 36 and 37 , the driving electrode  37  may be arranged on the surface of the piezoelectric material layer  36 C not facing the vibration plate  35 C, and the flow passage-opening/closing electrodes  38 ,  39  may be arranged on the surface of the piezoelectric material layer  36 C facing the vibration plate  35 C. Alternatively, as shown in  FIGS. 38 and 39 , the driving electrode  37  may be arranged on the surface of the piezoelectric material layer  36 C facing the vibration plate  35 C, and the flow passage-opening/closing electrodes  38 ,  39  may be arranged on the surface of the piezoelectric material layer  36 C not facing the vibration plate  35 C. In these arrangements, the electrodes (third electrodes)  37 ′,  38 ′,  39 ′, which face the driving electrode  37  and the flow passage-opening/closing electrodes  38 ,  39  respectively, are also arranged on the mutually different surfaces. 
     The shapes of the pressure chamber, the ink supply flow passage, and the ink discharge flow passage are not limited to the shapes of the embodiments described above. 
     For example, as shown in  FIGS. 34 and 35 , a pressure chamber  23 K may have a planar shape of a circular shape (eleventh modified embodiment). When the pressure chamber  23 K is circular, and a circular driving electrode  37 K is arranged in an area corresponding to the central portion thereof, then the amount of displacement of the central portion of the vibration plate  35 , i.e., the amount of volume change of the pressure chamber  23 K is increased as compared with the case in which the pressure chamber is rectangular. Therefore, the pressure can be efficiently applied to the ink. 
     The ink supply flow passage and the ink discharge flow passage, which are positioned on the left and right sides respectively, may be formed to have asymmetrical shapes in relation to the pressure chamber. It is not especially indispensable that the ink supply flow passage, the pressure chamber, and the ink discharge flow passage are arranged on the straight line as shown in  FIG. 2  as well. The ink supply flow passage and the ink discharge flow passage may be arranged in a form of being folded at the pressure chamber as viewed in a plan view. 
     In the embodiment and the modified embodiments described above, the vibration plate is either deformed to project toward the base member, or the vibration plate is deformed to project toward the side not facing the base member. However, the electrode may be arranged so that the deformation is effected to project in both of the direction in which the vibration plate is allowed to make approach to the base member and the direction in which the vibration plate is allowed to make separation from the base member. In this arrangement, for example, the valve seat of the base member may be formed so that the ink supply flow passage and/or the ink discharge flow passage is closed by deforming the vibration plate to project in the direction to make approach to the base member. 
     For example, as shown in  FIGS. 40 and 41 , three types of electrodes  37 H to  39 H, which are included in a pressure-applying portion  30 H and opening/closing portions  31 H,  32 H, are provided on the upper surface of the piezoelectric material layer  36 . Further, three electrodes are arranged as each of the electrodes  37 H to  39 H at a central portion and both ends in the widthwise direction of the flow passage. That is, as for the driving electrode  37 H, three electrodes  37   a ,  37   b ,  37   d  are arranged at the central portion and the both ends of the pressure chamber  23  in the widthwise direction of the flow passage respectively. As for the flow passage-opening/closing electrode  38 H, three electrodes  38   a ,  38   b ,  38   d  are arranged at the central portion and the both ends of the valve seat  28  of the ink supply flow passage  24  in the widthwise direction of the flow passage respectively. Further, as for the flow passage-opening/closing electrode  39 H, three electrodes  39   a ,  39   b ,  39   d  are arranged at the central portion and the both ends of the valve seat  29  of the ink discharge flow passage  25  in the widthwise direction of the flow passage respectively. On the other hand, electrodes  37   a ′,  37   b ′,  37   d ′,  38   a ′,  38   b ′,  38   d ′,  39   a ′,  39   b ′,  39   d ′, which correspond to the respective electrodes, are arranged on the lower surface of the piezoelectric material layer  36 . The electrodes disposed at the both ends in the widthwise direction of the flow passage are allowed to make conduction with each other by means of unillustrated wirings for each of the electrodes  37 H to  39 H. The same electric potential can be simultaneously applied to the electrodes which are in conduction. For example, as for the electrode  37 H, the electrode  37   a  and the electrode  37   b  are allowed to make conduction, and the electrode  37   a ′ and the electrode  37   b ′ are allowed to make conduction. As for the electrode  38 H, the electrode  38   a  and the electrode  38   b  are allowed to make conduction, and the electrode  38   a ′ and the electrode  38   b ′ are allowed to make conduction in the same manner as described above. Further, as for the electrode  39 H, the electrode  39   a  and the electrode  39   b  are allowed to make conduction, and the electrode  39   a ′ and the electrode  39   b ′ are allowed to make conduction in the same manner as described above. 
     In this state, in order that the area, which corresponds to the pressure-applying portion  30 H of the vibration plate  35 , is deformed to project in the direction to make separation from the base member as shown by two-dot chain lines in  FIG. 42 , it is appropriate that the predetermined electric potential is applied to the electrode  37   a  and the electrode  37   b , and the other electrodes  37   d ,  37   a ′,  37   b ′,  37   d ′ are allowed to have the ground electric potential. In this situation, the electrode  37   a  and the electrode  37   a ′, and the electrode  37   b  and the electrode  37   b ′ have the mutually different electric potentials at the both ends of the pressure chamber  23  in the flow passage widthwise direction respectively. On the other hand, the electrode  37   d  and the electrode  37   d ′ have the same electric potential at the central portion of the pressure chamber  23  in the flow passage widthwise direction. Therefore, the piezoelectric effect is generated at the both ends of the pressure chamber  23  in the flow passage widthwise direction, and the vibration plate  35  is deformed to project in the direction to make separation from the base member. 
     On the other hand, in order that the area, which corresponds to the pressure-applying portion  30 H of the vibration plate  35 , is deformed to project in the direction to make approach to the base member as shown by dotted lines in  FIG. 42 , it is appropriate that the predetermined electric potential is applied to the electrodes  37   a ,  37   b ,  37   d  and the electrodes  37   a ′,  37   b ′, and the electrode  37   d ′ is allowed to have the ground electric potential. In this situation, the electrode  37   a  and the electrode  37   a ′, and the electrode  37   b  and the electrode  37   b ′ have the same electric potential at the both ends of the pressure chamber  23  in the flow passage widthwise direction respectively. On the other hand, the electrode  37   d  and the electrode  37   d ′ have the different electric potentials at the central portion of the pressure chamber  23  in the flow passage widthwise direction. Therefore, the piezoelectric effect is generated at the central portion of the pressure chamber  23  in the flow passage widthwise direction, and the vibration plate  35  is deformed to project in the direction to make approach to the base member. 
     The areas of the vibration plate  35  corresponding to the opening/closing portions  31 H,  32 H can be deformed in both of the direction to make separation from the base member (see two-dot chain lines in  FIG. 43 ) and the direction to make approach to the base member (see dotted lines in  FIG. 43 ) by applying the electric potentials to the respective electrodes in the same manner as the case of the area corresponding to the pressure-applying portion  30 H described above. 
     According to this arrangement, the vibration plate can be deformed to project in both of the direction to make separation from the base member and the direction to make approach to the base member by merely switching the electric potential to be applied to each of the electrodes. Therefore, even when the same driving voltage is adopted, it is possible to secure the large amount of displacement of the vibration plate as compared with the arrangement in which the vibration plate is deformed in only any one of the direction to make separation from the base member and the direction to make approach to the base member. 
     In the embodiments described above, both of the flow passage width and the flow passage depth of the pressure chamber are greater than those of the ink supply flow passage and the ink discharge flow passage in order that the flow passage cross-sectional area of the pressure chamber is greater than the flow passage cross-sectional areas of the ink supply flow passage and the ink discharge flow passage. However, only one of the flow passage width and the flow passage depth of the pressure chamber may be greater than those of the ink supply flow passage and the ink discharge flow passage. When the flow passage width is increased, the area of the vibration plate facing the pressure chamber has a widened areal size. Therefore, this arrangement is preferred in that the volume change of the pressure chamber can be increased upon the deformation of the vibration plate. 
     In the embodiments described above, the piezoelectric actuator is provided with the two opening/closing portions for opening and closing the ink supply flow passage and the ink discharge flow passage respectively. However, any one of the two opening/closing portions may be omitted. Even in this arrangement, when the pressure of the ink in the pressure chamber is fluctuated, then one of the ink supply flow passage and the ink discharge flow passage is closed by the opening/closing portion, and thus the escape of the pressure wave from the pressure chamber can be avoided to some extent. Therefore, the pressure can be efficiently applied to the ink in the pressure chamber. A check valve, which is operated when the pressure on the downstream side is higher than the pressure on the upstream side to avoid any counter flow, may be provided in the flow passage from which the opening/closing portion is omitted. 
     Further, the base member may be formed with the pressure chamber and three of more flow passages communicated with the pressure chamber. The piezoelectric actuator may be provided with three or more opening/closing portions for opening/closing the three or more communicated flow passages respectively. 
     The present invention has been explained above as exemplified by the case as the embodiment in which the present invention is applied to the ink supply pump of the ink-jet printer. However, the form, to which the present invention is applicable, is not limited thereto. For example, as shown in  FIG. 44 , the present invention is applicable to a pump  95  which is provided between a fuel cartridge  90  for storing the liquid fuel such as methanol and a fuel cell  91  which consumes the liquid fuel to generate the electric power and which transports the liquid fuel to the fuel cell. Other than the above, the present invention is also applicable to a liquid transport apparatus for transporting a liquid such as a reagent solution and/or a biochemical solution in a micro total analysis system (μTAS), and a liquid transport apparatus for transporting a liquid such as a solvent and/or a chemical solution in a micro chemical system.