Abstract:
In an ink cartridge, a negative pressure generating mechanism is disposed between an ink storage region and an ink supply port, and has a wall surface having two through-holes for ink flow, and a valve member contacted with and separated from the through-hole by receiving a pressure in an ink supply port side. Ink flowing via the through-hole is supplied via the through-hole to the ink supply port.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of copending application Ser. No. 11/393,633, filed on Mar. 30, 2006, the contents of which are incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field of the Invention 
         [0003]    The present invention particularly relates to a liquid detecting device which is suitable for detecting a residual amount of a liquid (ink) in a liquid ejecting apparatus such as a recording apparatus of an ink jet type, a liquid container including the same device, and a method of manufacturing the liquid detecting device. 
         [0004]    2. Description of the Related Art 
         [0005]    Typical examples of a conventional liquid ejecting apparatus include a recording apparatus of an ink jet type which comprises a recoding head of an ink jet type for recording an image. Examples of other liquid ejecting apparatuses include an apparatus comprising a coloring material ejecting head to be used for manufacturing a color filter of a liquid crystal display, an apparatus comprising an electrode material (conducting paste) ejecting head to be used for forming an electrode of an organic EL display or a surface emitting display (FED), an apparatus comprising a bioorganism ejecting head to be used for manufacturing a biochip, and an apparatus comprising a sample ejecting head to be a precision pipette. 
         [0006]    The recording apparatus of the ink jet type according to the typical example of the liquid ejecting apparatus has such a structure that an ink jet recording head having pressure generating means for pressurizing a pressure generating chamber and a nozzle opening for ejecting a pressurized ink as an ink droplet is mounted on a carriage and the ink in an ink container is consecutively supplied to the recording head through a passage, and printing can be thus carried out continuously. The ink container is constituted as a detachable cartridge which can easily be exchanged by a user when the ink is consumed, for example. 
         [0007]    Conventionally, a method of managing the consumption of the ink by the ink cartridge includes a method of integrating, in software, the number of ejections of the ink droplet by the recording head or an amount of the ink sucked for a maintenance to manage the consumption of the ink by a calculation and a method of attaching an electrode for detecting a liquid level to the ink cartridge, thereby managing a time that the ink is actually consumed in a predetermined amount. 
         [0008]    However, the method of integrating, in software, the number of ejections of the ink droplet or the amount of the ink to manage the consumption of the ink by a calculation has the following drawback. Some heads have a variation in a weight of the ejected ink droplet. The variation in the weight of the ink droplet does not influence picture quality and the ink cartridge is filled with the ink in an amount having a margin in consideration of the case in which an error of the amount of the consumption of the ink which is made by the variation is accumulated. Accordingly, there is a problem in that the ink is left corresponding to a margin depending on an individual. 
         [0009]    On the other hand, the method of managing the time that the ink is consumed by the electrode can detect the actual amount of the ink. Therefore, the residual amount of the ink can be managed with a high reliability. However, the detection of the liquid level of the ink depends on a conductivity of the ink. For this reason, there is a drawback that the type of the ink which can be detected is restricted and a seal structure of the electrode is complicated. Moreover, a noble metal having a high conductivity and a high corrosion resistance is usually used as a material of the electrode. Consequently, a cost for manufacturing the ink cartridge is increased. Furthermore, it is necessary to attach two electrodes. Therefore, a manufacturing process is increased. As a result, the manufacturing cost is increased. 
         [0010]    Therefore, an apparatus developed to solve the problems has been disclosed as a piezoelectric device (referred to as a sensor unit or a liquid detecting device) in JP-A-2001-146024. The sensor unit serves to monitor the residual amount of the ink in the ink cartridge by utilizing the fact that a resonant frequency of a residual oscillation signal caused by a residual oscillation (free oscillation) of an vibration plate after a forced oscillation is varied in the case in which an ink is present or is not present in a cavity opposed to the vibration plate in which a piezoelectric element is laminated. 
         [0011]    In the case in which the sensor unit described in JP-A-2001-146024 is used, it is necessary to cause the ink to freely enter the cavity opposed to the vibration plate. However, it is necessary to prevent the ink from entering a side on which a piezoelectric unit to be an electrical element is disposed. For this reason, different members should be sealed strictly. 
         [0012]    As sealing structure for sealing the sensor unit and the container body, there is known a structure that the sensor unit is bonded directly to the circumferential edge of an opening of the container body or a structure that the sensor unit is bonded directly to the circumferential edge of an opening of a module and then the module is mounted on the container body with an O ring therebetween. However, since the sensor unit is bonded to the circumferential edge of the opening, deviation in size makes it difficult to secure the sealing ability. In addition, when the sensor unit is bonded directly to the circumferential edge of the opening of the container body or the circumferential edge of the opening of the module, it can be easily affected by a wave motion of the ink or bubbles in the ink, thereby causing erroneous detection. 
         [0013]    Furthermore, seal means for sealing the different members in the sensor unit includes means for giving a breaking margin, thereby sealing a clearance by a surface pressure, for example, an O ring. In the seal means such as the O ring, a sealing performance depends on precision in the dimensions of a plurality of components. For this reason, there is a problem in that a mass production is hard to stabilize. Moreover, a component for breaking the O ring is required separately. Consequently, there is also a problem in that a size of a sensor unit (a liquid detecting device) is increased. 
         [0014]    As another seal means, moreover, it can be proposed to seal a clearance between components with an adhesive. In the case in which the adhesive is used, there is a problem in that handling is troublesome and a stabilization of a process in the mass production is hard to implement. In the case in which a plurality of components formed of different materials (for example, ceramics, metals or resins) is combined to fabricate the sensor unit (the liquid detecting device) in order to enhance oscillating characteristics, particularly, it is hard to select the adhesive and it is also demanded that a place for using the adhesive should be limited as greatly as possible. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention has been contrived in consideration of the above-mentioned circumstances. A first object of the invention is to provide a container having a liquid detecting function in which a sealing work at the time of mounting a sensor unit on a container body can be simply and reliably carried out without being affected by accuracy in sizes of components and which has a structure that is little affected by a wave motion of ink or bubbles in the ink. 
         [0016]    A second object of the invention is to provide a liquid detecting device which can reliably seal components formed by different materials without a great influence of precision in the dimensions of the components, and can have a high assembling workability and can stabilize a process in a mass production, and furthermore, can have a high space efficiency and can reduce a size, a liquid container including the liquid detecting device, and a method of manufacturing the liquid detecting device. To accomplish at least one of the objects, an embodiment of the invention has the following configuration: 
         [0017]    (1). A liquid detecting device comprising: a unit base having a recessed portion on an upper face and formed of a resin, a sensor base accommodated in the recessed portion on the upper face of the unit base and formed of a metal, and a sensor chip mounted on an upper face of the sensor base, wherein the sensor chip has a sensor cavity for receiving a liquid to be a detection target and has such a structure that a lower face of the sensor cavity is opened to freely receive the liquid and an upper face is closed with an vibration plate, and a piezoelectric unit is disposed on an upper face of the vibration plate, the sensor base and the unit base have liquid reserving spaces to communicate with the sensor cavity, the sensor chip and the sensor base are fixed and sealed with each other through an adhesive layer provided on the upper face of the sensor base, and the sensor base and the unit base are fixed and sealed with each other through an adhesive film having an inner peripheral portion bonded to the upper face of the sensor base through the adhesive layer and an outer peripheral portion bonded to an upper face wall provided around the recessed portion of the unit base. 
         [0018]    According to the embodiment, by simply incorporating the sensor base mounting the sensor chip into the unit base from above and sticking the adhesive film across upper faces of two components which are arranged, that is, both of the upper faces of the sensor base and the unit base in that state, it is possible to fix and seal the two components formed by different materials (the sensor base formed of a metal and the unit base formed of a resin) at the same time. Accordingly, an assembling workability is very excellent. Moreover, the adhesive film is simply stuck across the two components. Therefore, it is possible to seal the components without a great influence of precision in the dimension of each of the components. In the case in which the adhesive film is to be welded by heating and pressurizing the adhesive film through a mass-produced machine, for example, it is possible to enhance a sealing performance and to carry out a stabilization in the mass production by simply managing a temperature, a pressure and a pressure welding time through the mass-produced machine. Furthermore, the adhesive film to influence the sealing property can easily be attached, and furthermore, a space efficiency is high. Therefore, it is possible to reduce the size of the sensor unit. 
         [0019]    (2). The liquid detecting device according to (1), wherein the sensor base and the unit base have, as the liquid reserving spaces, an entrance-side flow passage and an exit-side flow passage for the sensor cavity respectively, and have such a structure that the liquid is supplied to the sensor cavity through the entrance-side flow passage and is discharged from the sensor cavity through the exit-side flow passage. 
         [0020]    According to the embodiment, moreover, there is employed a structure in which the entrance and exit-side flow passages for the sensor cavity are formed in the sensor base and the unit base respectively and the liquid flows into the sensor cavity through the entrance-side flow passage and is discharged through the exit-side flow passage. Therefore, the liquid persistently flows to the sensor cavity. Consequently, it is possible to prevent an erroneous detection from being caused by the stay of the liquid or air bubbles in the sensor cavity. 
         [0021]    (3). The liquid detecting device according to (1) or (2), wherein the upper face of the sensor base is protruded upward from the recessed portion of the unit base, and the adhesive film is bonded to the upper face of the sensor base in a higher position than a bonding position to the upper face wall provided around the recessed portion of the unit base. 
         [0022]    According to the embodiment, furthermore, the height of the film bonding face to the unit base is set to be smaller than that of the film bonding face to the sensor base. Therefore, it is possible to press the sensor base with a step by means of the adhesive film and to increase a fixing force of the sensor base to the unit base. Moreover, it is possible to carry out an attachment having no looseness. 
         [0023]    (4). A liquid container comprising: a container body having a delivery passage for feeding a liquid stored in an inner part to an outside; and the liquid detecting device positioned in the vicinity of a terminal of the delivery passage and attached to the container body, wherein the liquid detecting device described above is provided as the liquid detecting device, and the entrance-side flow passage, the sensor cavity and the exit-side flow passage in the liquid detecting device are provided in series in the delivery passage so as to be arranged from an upstream side in this order. 
         [0024]    According to the embodiment, moreover, the liquid detecting device is disposed in the vicinity of the terminal of the delivery passage of the container body, and the entrance-side flow passage, the sensor cavity and the exit-side flow passage in the liquid detecting device are provided in series in the delivery passage so as to be arranged from the upstream side in this order. Therefore, it is possible to accurately detect the residual amount of the liquid in the container body. 
         [0025]    (5). A method of manufacturing a liquid detecting device comprising a unit base having a recessed portion on an upper face and formed of a resin, a sensor base accommodated in the recessed portion on the upper face of the unit base and formed of a metal, and a sensor chip mounted on an upper face of the sensor base, wherein the sensor chip has a sensor cavity for receiving a liquid to be a detection target and has such a structure that the sensor cavity has a lower face opened to freely receive the liquid and an upper face closed with an vibration plate, and a piezoelectric unit is disposed on an upper face of the vibration plate, the sensor chip and the sensor base are fixed and sealed with each other through an adhesive layer provided on the upper face of the sensor base, and the sensor base and the unit base are fixed and sealed with each other through an adhesive film having an inner peripheral portion bonded to the upper face of the sensor base through the adhesive layer and an outer peripheral portion bonded to an upper face wall provided around the recessed portion of the unit base, the method comprising the steps of forming the adhesive layer on the upper face of the sensor base and mounting the sensor chip on the adhesive layer, thereby fixing and sealing the sensor chip and the sensor base integrally through the adhesive layer, and accommodating the sensor base provided integrally with the sensor chip in the recessed portion on the upper face of the unit base and putting the adhesive film from above in that state to bond the inner peripheral portion of the adhesive film to the upper face of the sensor base through the adhesive layer and to bond the outer peripheral portion to the upper face wall provided around the recessed portion of the unit base, thereby fixing and sealing the sensor base and the unit base integrally through the adhesive film. 
         [0026]    According to the embodiment, furthermore, by simply incorporating the sensor base mounting the sensor chip into the unit base from above and sticking the adhesive film across upper faces of the two components which are arranged, that is, both of the upper faces of the sensor base and the unit base in that state, it is possible to fix and seal the two components formed by different materials (the sensor base formed of a metal and the unit base formed of a resin) at the same time. Accordingly, an assembling workability is very excellent. 
         [0027]    (6). A liquid container comprising: a container body having a liquid reservoir therein, a delivery passage for sending out liquid from the reservoir, and a sensor accommodating portion; a sensor unit which is mounted on the sensor accommodating portion and which detects the liquid; buffer chambers which are disposed in the container body, are adjacent to the sensor accommodating portion through a sensor receiving wall, and are disposed in the delivery passage so as to communicate with the upstream side and the downstream side of the delivery passage; a ring-shaped seal member having elasticity and sealing a space between the sensor unit and the sensor receiving wall; and a pressurizing spring for pressurizing the sensor unit against the sensor receiving wall to press the seal member and to give a surface pressure necessary for the sealing to the seal member, the sensor unit, and the sensor receiving wall. 
         [0028]    According to the embodiment, the ring-shaped seal member having elasticity is disposed between the sensor unit and the sensor receiving wall and the space between the sensor unit and the sensor receiving wall is sealed while crushing the seal member by pressurizing the sensor unit against to the sensor receiving wall with the pressurizing spring. Accordingly, when the sensor unit is separately assembled in advance and then the sensor unit is fitted into the container body, the assembly can be performed more simply than the case that the adhesive is used. In addition, since the deviation in size between the components can be absorbed by the use of the elasticity of the seal member, it is possible to satisfactorily perform the sealing work with simple assembly. Further, since a liquid reserving space sealed with the seal member is secured in the front (the opening side) of the sensor cavity, it is little affected by the wave motion of ink or the bubbles in the ink. 
         [0029]    (7). The liquid container according to (6), wherein the sensor unit includes a sensor chip for detecting the liquid, a sensor base for supporting the sensor chip, and a unit base for supporting the sensor base, and wherein the pressurizing spring serves to give a pressurizing force to the unit base through the sensor base or the sensor chip. 
         [0030]    According to the embodiment, the pressurizing force of the pressurizing spring is applied to the unit base through the sensor base or the sensor chip. Accordingly, for example, when the pressurizing force of the pressurizing spring is applied to the sensor chip, the surface pressure of the sealing surfaces between the sensor chip and the sensor base and between the sensor base and the unit base can be together enhanced, thereby enhancing the sealing ability therebetween. For example, when the pressurizing force of the pressurizing spring is applied to the sensor base, the surface pressure of the sealing surface between the sensor base and the unit base can be together enhanced, thereby enhancing the sealing ability therebetween. In the latter, since an unnecessary weight need not be applied to the sensor chip, the detection characteristic is little affected. 
         [0031]    (8). The liquid container according to (7), wherein the sensor chip has a sensor cavity for receiving the liquid as a detection target, in which a lower face of the sensor cavity is opened so as to receive the liquid, an upper face thereof is closed with a vibration plate, and a piezoelectric element is disposed on an upper face of the vibration plate; the sensor base is a metal base body for mounting and fixing the sensor chip thereto, and the unit base is a resin base body for mounting and fixing the sensor base thereto, a lower face of the unit base being opposed to the sensor receiving wall with the seal member when the sensor unit is mounted on the sensor accommodating portion; and a liquid reserving space communicating with the sensor cavity is formed in the sensor base and the unit base and, a flow passage communicating with the liquid reserving space and the buffer chamber is provided at the inside of the ring-shaped seal member in the sensor receiving wall. 
         [0032]    (9). The liquid container according to any one of (6) to (8), wherein the pressurizing spring is interposed between a wall of the sensor accommodating portion opposed to the sensor unit and the sensor unit in a compressed state. 
         [0033]    According to the embodiment, since the pressurizing spring is accommodated in the sensor accommodating portion in a compressed state, the assembly work can be finished only by inserting the pressurizing spring into the sensor accommodating portion together with the sensor unit. 
         [0034]    (10). The liquid container according to any one of (6) to (9), wherein a pressing cover is disposed above the sensor chip, and the pressurizing force of the pressurizing spring is given to the sensor base or the sensor chip through the pressing cover. 
         [0035]    According to the invention, since the pressing cover is disposed above the sensor chip, it is possible to protect the sensor chip. In addition, since the weight of the pressurizing spring is applied to the sensor chip or the sensor base through the pressing cover, the degree of freedom in combination of the pressurizing spring and the sensor chip or the sensor base can be enhanced. 
         [0036]    (11). The liquid container according to any one of (6) to (10), wherein a recessed portion is formed on the upper face of the unit base and the sensor base is accommodated in the recessed portion, the sensor chip and the sensor base are fixed to each other and sealed with an adhesive layer disposed on the upper face of the sensor base, and the sensor base and the unit base are fixed to each other and sealed with an adhesive film of which an inner periphery portion is bonded to the upper face of the sensor base through the adhesive layer therebetween and of which an outer periphery portion is bonded to the upper face wall around the recessed portion of the unit base. 
         [0037]    According to the invention, only by inserting the sensor base mounted with the sensor chip into the unit base from the upside and bonding the adhesive film onto the upper faces of two arranged components, that is, on both upper faces of the sensor base and the unit base, the fixation and sealing between two components made of different materials (the metal sensor base and the resin unit base) can be simultaneously carried out. Accordingly, the workability of assembly is very excellent. Since the adhesive film is bonded to two components, the sealing between the components can be carried out without being affected by the size accuracy of the components. For example, when the adhesive film is heated, pressed, and then fused by the use of a mass production machine, the sealing ability can be improved only by managing the temperature and pressure of the mass production machine, thereby accomplishing the stabilization at the time of mass production. Since the adhesive film having a large influence on the sealing ability can be easy in applicability and excellent in space efficiency, it is possible to accomplish the decrease in size of the sensor unit. 
         [0038]    (12). The liquid container according to (11), wherein the upper face of the sensor base protrudes upwardly from the recessed portion of the unit base and the adhesive film is bonded to the upper face of the sensor base at a position higher than the bonding position on the upper face wall around the recessed portion of the unit base. 
         [0039]    According to the embodiment, since the height of the film bonding face on the unit base is set lower than the height of the film bonding face on the sensor base, the sensor base can be pressed with the adhesive film by a level difference, thereby strengthening the fixing force of the sensor base to the unit base. It causes these components to be assembled without rattled. 
         [0040]    (13). The liquid container according to any one of (6) to (10), wherein the sensor base and the unit base have an entrance-side flow passage and an exit-side flow passage with respect to the sensor cavity, respectively, as the liquid reserving space; and the container body has an upstream buffer chamber communicating with the upstream side of the delivery passage and the entrance-side flow passage and a downstream buffer chamber communicating with the downstream side of the delivery passage and the exit-side flow passage, as the buffer chamber, and wherein the liquid flowing from the upstream side of the delivery passage is supplied to the sensor cavity through the upstream buffer chamber and the entrance-side flow passage and is discharged to the downstream side of the delivery passage through the exit-side flow passage and the downstream buffer chamber from the sensor cavity. 
         [0041]    According to the embodiment, since the liquid flowing from the upstream side of the delivery passage in the container body is supplied to the sensor cavity through the upstream buffer chamber and the entrance-side flow passages of the unit base and the sensor base and is discharged to the downstream side of the delivery passage through the exit-side flow passages of the sensor base and the unit base and the downstream buffer chamber from the sensor cavity, the liquid always flows in the sensor cavity. Accordingly, it is possible to prevent the erroneous detection due to the staying of the liquid or bubbles in the sensor cavity. 
         [0042]    (14). A liquid container comprising: a container body having a liquid reservoir therein and a delivery passage for sending out liquid from the reservoir; a sensor accommodating portion disposed in the container body in the vicinity of the terminal of the delivery passage; a sensor unit which is disposed in the sensor accommodating portion so as to detect the liquid; buffer chambers which are disposed in the container body, are adjacent to the sensor accommodating portion through a sensor receiving wall, and are disposed in series in the delivery passage so as to communicate with the upstream side and the downstream side of the delivery passage; a ring-shaped seal member having elasticity and sealing a space between the sensor unit and the sensor receiving wall; and a pressurizing spring for pressurizing the sensor unit against the sensor receiving wall to press the seal member and to give a surface pressure necessary for sealing the seal member, the sensor unit, and the sensor receiving wall, wherein the sensor unit includes: a sensor chip having a sensor cavity for receiving the liquid as a detection target, in which a lower face of the sensor cavity is opened so as to receive the liquid, an upper face thereof is closed with a vibration plate, and a piezoelectric element is disposed on the upper face of the vibration plate; a metal sensor base for mounting and fixing the sensor chip thereto; and a resin unit base for mounting and fixing the sensor base thereto, in which a lower face of the unit base is opposed to the sensor receiving wall with the seal member therebetween when the sensor unit is mounted on the sensor accommodating portion, wherein a liquid reserving space communicating with the sensor cavity is formed in the sensor base and the unit base and a flow passage communicating with the liquid reserving space and the buffer chamber is provided at the inside of the ring-shaped seal member in the sensor receiving wall, and wherein the pressurizing spring serves to give the pressurizing force only to the unit base through a force delivering passage bypassing the sensor base and the sensor chip of the sensor unit. 
         [0043]    According to the embodiment, the ring-shaped seal member having elasticity is disposed between the sensor unit and the sensor receiving wall and the space between the sensor unit and the sensor receiving wall is sealed while crushing the seal member by pressurizing the sensor unit against the sensor receiving wall with the pressurizing spring. Accordingly, when the sensor unit is separately assembled in advance and then the sensor unit is fitted into the container body, the assembly work can be performed more simply than the case that the adhesive is used. In addition, since the deviation in size between the components can be absorbed by the use of the elasticity of the seal member, it is possible to satisfactorily perform the sealing work with simple assembly. Further, since a liquid reserving space sealed with the seal member is secured in the front (the opening side) of the sensor cavity, it is little affected by the wave motion of ink or the bubbles in the ink. Furthermore, since the pressurizing force of the pressurizing spring is applied directly to the unit base opposed to the sensor receiving wall, the pressurizing force can be prevented from acting on the sensor base or the sensor chip, thereby enhancing the detection accuracy. 
         [0044]    (15). The liquid container according to (14), wherein the pressurizing spring is interposed between the wall of the sensor accommodating portion opposed to the sensor unit and the sensor unit in a compressed state. 
         [0045]    According to the embodiment, since the pressurizing spring is accommodated in the sensor accommodating portion in a compressed state, the assembly work can be finished only by inserting the pressurizing spring into the sensor accommodating portion together with the sensor unit. 
         [0046]    (16). The liquid container according to (14) or (15), wherein a pressing cover is disposed above the unit base to cover the sensor chip without contacting the sensor chip and the sensor base, and the pressurizing force of the pressurizing spring is given to the unit base through the pressing cover. 
         [0047]    According to the embodiment, since the pressing cover is disposed above the unit base, it is possible to protect the sensor chip and the sensor base. In addition, since the weight of the pressurizing spring is applied to the unit base through the pressing cover, the degree of freedom in combination of the pressurizing spring and the unit base can be enhanced. 
         [0048]    (17). The liquid container according to (14), wherein a cover member for covering the sensor chip and the sensor base is mounted above the unit base without directly contacting the unit base, the cover member is fixed to the container body with a screw, and the pressurizing spring is interposed between the cover member and the unit base in a compressed state. 
         [0049]    According to the embodiment, since the pressing cover is disposed above the unit base, it is possible to protect the sensor chip and the sensor base. In addition, since the cover member is fixed to the container body with screws and the pressurizing spring is disposed between the cover member and the unit base with a compressed posture, it is possible to compactly assemble the pressurizing spring. 
         [0050]    (18) The liquid container according to (17), wherein the pressurizing spring is composed of a leaf spring and the leaf spring is formed integrally with a terminal plate electrically connected to an electrode of the sensor chip. 
         [0051]    According to the embodiment, since the pressurizing spring is composed of a leaf spring and the leaf spring is formed integrally with a terminal plate electrically connected to an electrode of the sensor chip, it is possible to perform a compact assembly work and to reduce the number of components, thereby reducing the number of assembly steps. 
         [0052]    (19) The liquid container according to any one of (14) to (18), wherein a recessed portion is formed on the upper face of the unit base and the sensor base is accommodated in the recessed portion; the sensor chip and the sensor are fixed to each other and sealed with an adhesive layer disposed on the upper face of the sensor base; and the sensor base and the unit base are fixed to each other and sealed with an adhesive film of which an inner periphery portion is bonded to the upper face of the sensor base with the adhesive layer therebetween and of which an outer periphery portion is bonded to the upper face wall around the recessed portion of the unit base. 
         [0053]    According to the embodiment, only by inserting the sensor base mounted with the sensor chip into the unit base from the upside and bonding the adhesive film onto the upper faces of two arranged components, that is, on both upper faces of the sensor base and the unit base, the fixation and sealing between two components made of different materials (the metal sensor base and the resin unit base) can be simultaneously carried out. Accordingly, the workability of assembly is very excellent. Since the adhesive film is bonded to two components, the sealing between the components can be carried out without being affected by the size accuracy of the components. For example, when the adhesive film is heated, pressed, and then fused by the use of a mass production machine, the sealing ability can be improved only by managing the temperature and pressure of the mass production machine, thereby accomplishing the stabilization at the time of mass production. Since the adhesive film having a large influence on the sealing ability can be easy in applicability and excellent in space efficiency, it is possible to accomplish the decrease in size of the sensor unit. 
         [0054]    (20). The liquid container according to (19), wherein the upper face of the sensor base protrudes upwardly from the recessed portion of the unit base and the adhesive film is bonded to the upper face of the sensor base at a position higher than the bonding position on the upper face wall around the recessed portion of the unit base. 
         [0055]    According to the embodiment, since the height of the film bonding face on the unit base is set lower than the height of the film bonding face on the sensor base, the sensor base can be pressed with the adhesive film by a level difference, thereby strengthening the fixing force of the sensor base to the unit base. It causes these components to be assembled without rattled. 
         [0056]    (21). The liquid container according to any one of (14) to (20), wherein the sensor base and the unit base have an entrance-side flow passage and an exit-side flow passage for the sensor cavity, respectively, as the liquid reserving space; and the container body has an upstream buffer chamber communicating with the upstream side of the delivery passage and the entrance-side flow passage and a downstream buffer chamber communicating with the downstream side of the delivery passage and the exit-side flow passage, as the buffer chamber, and wherein the liquid flowing from the upstream side of the delivery passage is supplied to the sensor cavity through the upstream buffer chamber and the entrance-side flow passage and is discharged to the downstream side of the delivery passage through the exit-side flow passage and the downstream buffer chamber from the sensor cavity. 
         [0057]    According to the embodiment, since the liquid flowing from the upstream side of the delivery passage in the container body is supplied to the sensor cavity through the upstream buffer chamber and the entrance-side flow passages of the unit base and the sensor base and is discharged to the downstream side of the delivery passage through the exit-side flow passages of the sensor base and the unit base and the downstream buffer chamber from the sensor cavity, the liquid always flows through the sensor cavity. Accordingly, it is possible to prevent the erroneous detection due to the staying of the liquid or bubbles in the sensor cavity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0058]      FIG. 1  is a perspective view showing a schematic structure of a recording apparatus of an ink jet type (a liquid ejecting apparatus) in which an ink cartridge (a liquid container) according to an embodiment of the invention is used; 
           [0059]      FIG. 2  is an exploded perspective view showing a schematic structure of the ink cartridge according to the embodiment of the invention; 
           [0060]      FIG. 3  is a cross-sectional view illustrating a portion where a sensor unit is fitted to the ink cartridge, as seen from the front side; 
           [0061]      FIG. 4  is an enlarged view illustrating important parts of an ink cartridge according to a first embodiment of the invention; 
           [0062]      FIG. 5  is an enlarged view illustrating important parts of an ink cartridge according to a second embodiment of the invention; 
           [0063]      FIG. 6  is a front view illustrating a portion where a sensor unit is fitted to an ink cartridge according to a third embodiment of the invention; 
           [0064]      FIG. 7  is a cross-sectional view taken along Arrow VII-VII of  FIG. 6 ; 
           [0065]      FIG. 8  is a cross-sectional view taken along Arrow VIII-VIII of  FIG. 7 ; 
           [0066]      FIG. 9  is an enlarged view illustrating important parts of  FIG. 8 ; 
           [0067]      FIG. 10  is a cross-sectional view illustrating important parts of an ink cartridge according to a fourth embodiment of the invention; 
           [0068]      FIG. 11  is a perspective view showing detailed structures of components including a sensor unit (a liquid detecting device) mountable in an ink cartridge according to a fifth embodiment of the invention; 
           [0069]      FIG. 12  is an exploded perspective view showing the sensor unit in  FIG. 11 ; 
           [0070]      FIG. 13  is an exploded perspective view showing the sensor unit in  FIG. 11  as seen at another angle; 
           [0071]      FIG. 14  is a longitudinal sectional view showing a portion to which the sensor unit of the ink cartridge according to the fifth embodiment of the invention is attached; 
           [0072]      FIG. 15  is an enlarged sectional view showing a main part of the sensor unit in  FIG. 14 ; and 
           [0073]      FIG. 16  is a sectional view taken along a XVI-XVI line in  FIG. 15 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0074]    A liquid detecting device according to an embodiment of the invention and an ink cartridge (a liquid container) comprising the liquid detecting device will be described below with reference to the drawings. 
         [0075]      FIG. 1  shows a schematic structure of a recording apparatus of an ink jet type (a liquid ejecting apparatus) in which the ink cartridge according to the embodiment is used. In  FIG. 1 , the reference numeral  1  denotes a carriage. The carriage  1  is constituted to be guided by a guide member  4  and reciprocated in an axial direction of a platen  5  through a timing belt  3  to be driven by a carriage motor  2 . 
         [0076]    A recording head  12  of an ink jet type is mounted on a side of the carriage  1  which is opposed to a recording paper  6 , and an ink cartridge  100  for supplying an ink to the recording head  12  is removably attached to an upper part thereof. 
         [0077]    A cap member  13  is disposed in a home position to be a non-printing region of the recording apparatus (a right side in the drawing). The cap member  13  has such a structure as to be pushed against a nozzle forming surface of the recording head  12  and to form a hermetic closed space together with the nozzle forming surface when the recording head  12  mounted on the carriage  1  is moved to the home position. A pump unit  10  for applying a negative pressure to the hermetic closed space formed by the cap member  13  to execute cleaning is disposed below the cap member  13 . 
         [0078]    Moreover, wiping means  11  including an elastic plate such as a rubber is disposed in the vicinity of a printing region side in the cap member  13  so as to be freely moved forward and backward in a horizontal direction with respect to a moving track of the recording head  12 , for example, and has such a structure as to freely sweep away the nozzle forming surface of the recording head  12  if necessary when the carriage  1  is reciprocated toward the cap member  13  side. 
         [0079]      FIG. 2  is a perspective view showing a schematic structure of the ink cartridge  100 . The ink cartridge  100  includes a sensor unit  200  to be the liquid detecting device according to the embodiment. 
         [0080]    The ink cartridge  100  has a cartridge case (a container body)  101  formed of a resin which includes an ink storage portion and a cover  102  formed of a resin which is attached to cover a lower end face of the cartridge case  101 . The cover  102  is provided for protecting various sealing films stuck to the lower end face of the cartridge case  101 . An ink delivery portion  103  is protruded from the lower end face of the cartridge case  101  and a cover film  104  for protecting an ink delivery port (not shown) is stuck to the lower end face of the ink delivery portion  103 . 
         [0081]    Moreover, a sensor accommodating recessed portion  110  for accommodating the sensor unit  200  is provided on a side face having a small width in the cartridge case  101 , and the sensor unit  200  and a spring  300  are accommodated in the sensor accommodating recessed portion  110 . The spring  300  pushes the sensor unit  200  against a sensor receiving wall  120  positioned in an inner bottom part of the sensor accommodating recessed portion  110  to crush a sealing ring  270 , thereby maintaining a sealing property between the sensor unit  200  and the cartridge case  101 . 
         [0082]    The sensor accommodating recessed portion  110  is opened on a side face having a small width in the cartridge case  101 , and the sensor unit  200  and the spring  300  are inserted from the opening on the side face. The opening on the side face of the sensor accommodating recessed portion  110  is closed with a sealing cover  400  having a board  500  from an outside in a state in which the sensor unit  200  and the spring  300  are accommodated therein. 
         [0083]      FIG. 3  is a cross-sectional view illustrating a portion where the sensor unit  200  and the spring  300  are inserted into the sensor accommodating recessed portion  110 , as seen from the front side, and  FIG. 4  is an enlarged view illustrating an example of important parts of an ink cartridge according to a first embodiment of the invention. In  FIG. 3 , some parts including the spring  300  are not shown. The first embodiment of the invention will be described below. 
         [0084]    The sensor receiving wall  120  for receiving the lower end of the sensor unit  200  is provided on the inner bottom portion of the sensor accommodating recessed portion  110  of the cartridge case  101 . The sensor unit  200  is placed on the flat upper face of the sensor receiving wall  120  and is a portion on which the seal ring (ring-shaped seal member)  270  at the lower end of the sensor unit  200  is pressed with an elastic force of the spring  300 . 
         [0085]    A pair of upstream and downstream sensor buffer chambers  122  and  123 , which are horizontally partitioned by a partition wall  127 , are provided below the sensor receiving wall  120 . The sensor receiving wall  120  is provided with a pair of communication holes (flow passages)  132  and  133  to correspond to the sensor buffer chambers  122  and  123 . A delivery passage for delivering the reserved ink, which is not shown, is provided inside the cartridge case  101  and the sensor unit  200  is provided in the vicinity of the terminal (in the vicinity of the ink delivery port) of the delivery passage. 
         [0086]    In this case, the upstream buffer chamber  122  communicates with the upstream side of the delivery passage through an opening  124  (not shown particularly) and the downstream sensor buffer chamber  123  communicates with the downstream side of the delivery passage close to the ink delivery port through a communication hole  125  (not shown particularly). The lower faces of the sensor buffer chambers  122  and  123  are opened, not closed with a rigid wall, and the opening is covered with a seal film  105  made of resin. 
         [0087]    The sensor unit  200  includes a resin unit base  210  of a plate shape having a recessed portion  211  thereon, a metal sensor base  220  of a plate shape received in the recessed portion  211  on the upper face of the unit base  210 , a sensor chip  230  mounted on and fixed to the upper face of the sensor base  220 , an adhesive film  240  for fixing the sensor base  220  to the unit base  210 , a pair of terminal plates  250  disposed on the unit base  210 , a pressing member  260 A of a plate shape for pressurizing the terminal plates  250 , a rubber seal ring  270  disposed on the lower face of the unit base  210 , and a pressing cover  280  disposed on the upper face of the sensor base  220  to cover the sensor chip  230  so as to apply the weight of the spring  300  to the unit base  210 . 
         [0088]    Describing details of the respective elements, as shown in  FIG. 4 , the unit base  210  includes the recessed portion  211  into which the sensor base  220  is inserted at the center of the upper face thereof, as a base body for supporting the sensor base  220 , and an mounting wall  215  having a height greater by a step than that of the upper face wall  214  at the outside of the upper face wall  214  around the recessed portion  211 . The lower face of the recessed portion  211  is provided with an entrance-side flow passage  212  and an exit-side flow passage  213  (liquid reserving space) including circular openings. The lower face of the unit base  210  is provided with a projected portion  217  at outer periphery of which the seal ring  270  is fitted and the entrance-side flow passage  212  and the exit-side flow passage  213  are positioned on the projected portion  217 . The seal ring  270  is formed of a rubber ring packing and has a ring-shaped projected portion  271  having a semi-circular section on the lower face thereof. 
         [0089]    The sensor base  220  is formed of a metal plate such as stainless steel having rigidity greater than that of resin so as to enhance an acoustic characteristic of a sensor. The sensor base  220  includes an entrance-side flow passage  222  and an exit-side flow passage  223  (liquid reserving space) composed of two openings to correspond to the entrance-side flow passage  212  and the exit-side flow passage  213  of the unit base  210 . 
         [0090]    An adhesive layer  242  is formed on the upper face of the sensor base  220 , for example, by attachment of a double-sided adhesive film or application of adhesive. The sensor chip  230  is mounted on and fixed to the adhesive layer  242 . That is, the sensor base  220  serves as a base body for supporting the sensor chip  230 . 
         [0091]    The sensor chip  230  has a sensor cavity  232  for receiving ink (liquid) which is a detection target and has a structure that the lower face of the sensor cavity  232  is opened so as to receive the ink, the upper face is closed with a vibration plate  233 , and a piezoelectric element  234  is disposed on the upper face of the vibration plate  233 . 
         [0092]    Specifically, the sensor chip  230  includes a ceramic chip body  231  having the sensor cavity  232  of a circular opening shape at the center thereof, the vibration plate  233  which is formed on the upper face of the chip body  231  to constitute the bottom wall of the sensor cavity, the piezoelectric element  234  stacked on the vibration plate  233 , and terminals  235  and  236  stacked on the chip body  231 . 
         [0093]    The piezoelectric element  234  includes upper and lower electrode layers  234   a  and  234   b  connected to the terminals  235  and  236 , respectively, and a piezoelectric layer  234   c  formed between the upper and lower electrode layers  234   a  and  234   b . The piezoelectric element serves to detecting the ink end, for example, on the basis of difference in characteristic due to existence or non-existence of the ink in the sensor cavity  232 . The piezoelectric element  234   c  may be made of lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), or a leadless piezoelectric film not containing lead. 
         [0094]    The sensor chip  230  is integrally fixed to the sensor base  220  with the adhesive layer  242  by placing the lower face of the chip body  231  on the upper center of the sensor base  220 . At the same time, the space between the sensor base  220  and the sensor chip  230  is sealed with the adhesive layer  242 . The entrance-side flow passages  222  and  212  and the exit-side flow passages  223  and  213  (liquid reserving spaces) of the sensor base  220  and the unit base  210  communicate with the sensor cavity  232  of the sensor chip  230 . Accordingly, the ink enters the sensor cavity  232  through the entrance-side flow passages  212  and  222  and is discharged from the sensor cavity  232  through the exit-side flow passages  223  and  213 . 
         [0095]    In this way, the metal sensor base  220  mounted with the sensor chip  230  is received in the recessed portion  211  on the upper face of the unit base  210 . Then, the sensor base  220  and the unit base  210  are integrally fixed to each other by covering them with a resin adhesive film  240  from the upside thereof. 
         [0096]    That is, the adhesive film  240  has an opening  241  at the center thereof and thus exposes the sensor chip  230  to the central opening  241  by covering them with the adhesive film in the state where the sensor base  220  is accommodated in the recessed portion  211  on the upper face of the unit base  210 . By bonding the inner periphery portion of the adhesive film  240  to the upper face of the sensor base  220  through the adhesive layer  242  and bonding the outer periphery portion to the upper face wall  214  around the recessed portion  211  of the unit base  210 , that is, by bonding the adhesive film  240  to the upper faces of two components (the sensor base  220  and the unit base  210 ), the sensor base  220  and the unit base  210  are fixed to each other and sealed. 
         [0097]    In this case, the upper face of the sensor base  220  is projected upwardly from the recessed portion  211  of the unit base  210  and the adhesive film  240  is bonded to the upper face of the sensor base  220  at a position higher than the bonding position of the upper face wall  214  around the recessed portion  211  of the unit base  210 . In this way, by setting the height of the film bonding face on the sensor base  220  to be higher than the height of the film bonding face on the unit base  210 , the sensor base  220  can be pressed with the adhesive film  240  by level difference, thereby strengthening the fixing force of the sensor base  220  to the unit base  210 . It causes these components to be assembled without rattled. 
         [0098]    The respective terminal plates  250  have a spring piece  252  projected from a middle side edge of a base strip and are disposed on the upper face of the mounting wall  215  of the unit base  210 . By placing the pressing member  260  thereon, the terminal plates  250  are interposed between the unit base  210  and the pressing member  260  and in this state, the spring members  252  are in electrical contact with the terminals  235  and  236  on the upper face of the sensor chip  230 . The pressing member  260  has a flat frame shape which is placed on the upper face of the mounting walls  215  of the unit base  210  with the terminal plates  250  therebetween. 
         [0099]    As shown in  FIG. 4 , the pressing cover  280  is disposed above the sensor chip  230  without contacting the sensor chip  230  and the spring members  252  of the terminal plates  250 . The pressing cover  280  serves to protect the sensor chip  230  and to deliver the weight of the spring  300  (indicated by an arrow A 1  in  FIGS. 3 and 4 ) to the upper face of the sensor base  220  to bypass the sensor chip  230 . The bottom of the pressing cover is placed on the portion to which the adhesive film  240  is bonded and the weight A 1  of the spring  300  can be applied to the sensor base  220  from the upside of the adhesive film  240 . When the weight A 1  of the spring  300  is applied to the sensor base  220 , the weight A 1  is delivered to the unit base  210  below and serves as a force for pressing the seal ring  270 . 
         [0100]    In this case, the seal ring  270  is designed to have a diameter as small as possible so as not to unnecessarily enlarge the sealing space and is positioned right under the sensor base  220  or the sensor chip  230 . Therefore, by applying the weight A 1  of the spring  300  to the sensor base  220  having a small area, the pressurizing force of the spring  300  effectively acts on the seal ring  270  right under the sensor base. 
         [0101]    The sensor unit  200  has the above-mentioned configuration and is accommodated in the sensor accommodating recessed portion  110  (sensor accommodating portion) of the cartridge case  100  together with the compressed spring  300 . In this accommodated state, by pressurizing the pressing cover  280  with the spring  300 , the weight A 1  delivered to the unit base  210  through the sensor base  220  presses the seal ring  270  disposed on the lower face of the unit base  210  and brings the seal ring into close contact with the sensor receiving wall  120  in the sensor accommodating recessed portion  110 . Accordingly, the sealing property is secured between the sensor unit  200  and the cartridge case  101 . 
         [0102]    Under the condition that the sealing property is secured by the above-mentioned assembly, the upstream buffer chamber  122  in the cartridge case  101  communicates with the entrance-side flow passages  212  and  222  in the sensor unit  200  through the communication hole  132  of the sensor receiving wall  120  and the downstream buffer chamber  123  in the cartridge case  101  communicates with the exit-side flow passages  213  and  223  in the sensor unit  200  through the communication hole  133  of the sensor receiving wall  120 . The entrance-side flow passages  212  and  222 , the sensor cavity  232 , and the exit-side flow passages  213  and  223  are arranged in series in the delivery passage in the cartridge case  101  in that order from the upstream side. 
         [0103]    Here, the upstream flow passages communicating with the sensor cavity  232  includes the upstream buffer chamber  122  having a large flow-passage section, the communication hole  132 , and the entrance-side flow passages  212  and  222  in the sensor unit  200  having a small flow-passage section (upstream narrow flow passage). The downstream flow passage communicating with the sensor cavity  232  includes the downstream buffer chamber  123  having a large flow-passage section, the communication hole  133 , and the exit-side flow passages  213  and  223  in the sensor unit  200  having a small flow-passage section (downstream narrow flow passage). 
         [0104]    According to the embodiment described above, since the space between the sensor unit  200  and the sensor receiving wall  120  is sealed while pressing the seal ring  270  by interposing the seal ring  270  having elasticity between the sensor unit  200  and the sensor receiving wall  120  and pressurizing the sensor unit  200  against the sensor receiving wall  120  by the use of the spring  300 , an assembly order that the sensor unit  200  is separately assembled in advance and then the sensor unit  200  is fitted into the cartridge case  101  later can be employed. Accordingly, the assembly can be carried out more simply than the case employing an adhesive. 
         [0105]    Since the deviation in size between the sensor unit  200  and the sensor receiving wall  120  can be absorbed with the elasticity of the seal ring  270 , it is possible to carry out the reliable sealing with simple assembly. Since the liquid reserving space (the entrance-side flow passages  212  and  222  and the exit-side flow passages  213  and  223 ) sealed with the seal ring  270  is secured in the front of (at the opening side) the sensor cavity  232 , it is little affected by the wave motion of ink or the bubbles in the ink. 
         [0106]    Since the pressurizing force of the spring  300  is applied to the unit base  210  through the sensor base  220 , the surface pressure of the sealing surface between the sensor base  220  and the unit base  210  can be together enhanced, thereby enhancing the sealing property therebetween. That is, since the weight of the spring  300  is applied to the adhesive film  240  on the upper face of the sensor base  220 , the adhesive film  240  can be more strongly bonded, thereby improving the sealing ability. In this case, since the unnecessary weight is not applied to the sensor chip  230 , the detection characteristic is not affected thereby. 
         [0107]    Since the weight A 1  of the spring  300  is delivered to the sensor base  220  through the pressing cover  280 , it is possible to protect the sensor chip  230  which is an important element and to freely determine combinations of the spring  300  and the sensor base  220 , thereby enabling an easy design. 
         [0108]    Since it is sufficient only if the spring  300  can be received in the sensor accommodating recessed portion  110  in the state that it is compressed, the spring  300  can be easily inserted together with the sensor unit  200 . 
         [0109]    In addition, only by inserting the sensor base  220  mounted with the sensor chip  230  into the unit base  210  from the upside and bonding the adhesive film  240  onto the upper faces of the two arranged components, that is, on both upper faces of the sensor base  220  and the unit base  210 , the fixation and sealing between two components made of different materials (the metal sensor base  220  and the resin unit base  210 ) can be simultaneously carried out. Accordingly, the workability of assembly is very excellent. Since the adhesive film  240  is bonded to two components, the sealing between the components can be carried out without being affected by the size accuracy of the components. For example, when the adhesive film  240  is heated, pressed, and then fused by the use of a mass production machine, the sealing ability can be improved only by managing the temperature and pressure of the mass production machine, thereby accomplishing the stabilization at the time of mass production. Since the adhesive film  240  having a large influence on the sealing ability can be easy in application and excellent in space efficiency, it is possible to accomplish decrease in size of the sensor unit  200 . 
         [0110]    Since the entrance-side flow passages  212  and  222  and the exit-side flow passages  213  and  223  of the sensor cavity  232  are formed in the sensor base  220  and the unit base  210 , respectively, and the ink flows in the sensor cavity  232  through the entrance-side flow passages  212  and  222  and is discharged through the exit-side flow passages  213  and  223 , the ink always passes through the sensor cavity  232 , thereby preventing erroneous detection due to the liquid or bubbles staying in the sensor cavity  232 . 
         [0111]    Since the height of the bonding face of the adhesive film  240  with respect to the unit base  210  is set to be smaller than the height of the bonding face with respect to the sensor base  220 , the sensor base  220  can be pressed with the adhesive film  240  by level difference, thereby strengthening the fixing force of the sensor base  220  to the unit base  210 . They may be provided without level difference. 
         [0112]    Since the sensor unit  200  is disposed in the vicinity of the terminal of the delivery passage in the cartridge case  101  and the entrance-side flow passages  212  and  222 , the sensor cavity  232 , and the exit-side flow passages  213  and  223  of the sensor unit  200  are disposed in series in the delivery passage in that order from the upstream side, it is possible to accurately detect the amount of remaining liquid in the ink cartridge  100 . 
         [0113]      FIG. 5  shows configurations of important parts of an ink cartridge according to a second embodiment the invention. In  FIG. 5 , the elements similar to those of the embodiment shown in  FIGS. 1 to 4  are denoted by the same reference numerals and description thereof will be omitted. 
         [0114]    In the first embodiment, the weight A 1  of the spring  300  is applied to the sensor base  220  through the pressing cover  280 , but in the second embodiment, the weight A 2  of the spring  300  is applied to the chip body  231  of the sensor chip  230  through the pressing cover  282 . As a result, the weight A 2  of the spring  300  can be delivered to the unit base  210  through the pressing cover  282 , the chip body  231  of the sensor chip  230 , and the sensor base  220  and can serve as a force pressing the seal ring  270  (that is, a force for securing the sealing ability). 
         [0115]    In this case, the pressing cover  282  is pressed on the chip body  231  at the position not unnecessarily affecting the vibration plate  233  or the piezoelectric element  234 . At this time, the pressing cover should not hinder the contact between the spring members  252  of the terminal plates  250  and the terminals  235  and  236  of spring members  252 . For this reason, by bringing the bottom of the pressing cover  282  into contact with the chip body  231  at the position other than the contact portion between the spring members  252  and the terminals  235  and  236  or by pressurizing the bottom of the pressing cover  282  onto the chip body  231  from the upside of the spring members  252  contacting the terminals  235  and  236 , the spring members  252  can come in close contact with the terminals  235  and  236  with the force of the spring  300  acting on the pressing cover  282 . 
         [0116]    In this way, even when the weight A 2  of the spring  300  is applied to the chip body  231  of the sensor chip  230 , the advantages similar to the above-mentioned embodiment can be obtained. 
         [0117]    Next, an ink cartridge (liquid container) according to a third embodiment will be described with reference to the drawings. 
         [0118]      FIG. 6  is a front view illustrating a portion where the sensor unit  200  and the spring  300  are inserted into the sensor accommodating recessed portion  110 ,  FIG. 7  is a cross-sectional view taken along Arrow VII-VII of  FIG. 6 ,  FIG. 8  is a cross-sectional view taken along Arrow VIII-VIII of  FIG. 7 , and  FIG. 9  is an enlarged view illustrating important parts of  FIG. 8 . In the drawings, the elements similar to the first embodiment described above are denoted by the same reference numerals and description thereof will be omitted. 
         [0119]    In the first and second embodiments the invention, the weight of the spring  300  is applied to the sensor base  220  or the chip body  231  through the pressing covers  280  or  282 , respectively. However, in the third embodiment, the weight of the spring  300  is applied to the unit base  210  through a pressing member  260 B. 
         [0120]    Specifically, the sensor unit  200  includes a resin unit base  210  of a plate shape having a recessed portion  211  on the upper face thereof, a metal sensor base  220  of a plate shape accommodated in the recessed portion  211  on the upper face of the unit base  210 , a sensor chip  230  mounted on and fixed to the upper face of the sensor base  220 , an adhesive film  240  for fixing the sensor base  220  to the unit base  210 , a pair of terminal plates  250  disposed on the unit base  210 , a pressing member  260 B of a plate shape for pressurizing the terminal plates  250  and protecting the sensor chip  230 , and a rubber seal ring  270  disposed on the lower face of the unit base  210 . 
         [0121]    Describing details of the respective elements, as shown in  FIG. 9 , the unit base  210  includes the recessed portion  211  into which the sensor base  220  is inserted at the center of the upper face thereof and an mounting wall  215  having a height greater by a step than that of the upper face wall  214  at the outside of the upper face wall  214  around the recessed portion  211 . The bottom wall of the recessed portion  211  is provided with an entrance-side flow passage  212  and an exit-side flow passage  213  (liquid reserving spaces) including circular openings. The lower face of the unit base  210  is provided with a projected portion  217  at outer periphery of which the seal ring  270  is fitted and the entrance-side flow passage  212  and the exit-side flow passage  213  are positioned on the projected portion  217 . The seal ring  270  is formed of a rubber ring packing and has a ring-shaped projected portion  271  having a semi-circular section on the lower face thereof. 
         [0122]    The respective terminal plates  250  have a spring piece  252  projected from a middle side edge of a base strip and a bent piece  254  formed at the end of the strip, which are disposed on the upper face of the mounting wall  215  of the unit base  210 . By placing the pressing member  260 B thereon, the terminal plates  250  are interposed between the unit base  210  and the pressing member  260 B and in this state, the spring members  252  are in electrical contact with the terminals  235  and  236  on the upper face of the sensor chip  230 . 
         [0123]    The pressing member  260 B has a flat plate shape which is placed on the upper face of the mounting walls  215  of the unit base  210  with the base portions  251  of the terminal plates  250  interposed therebetween and includes a recessed portion  265  which is disposed on the lower face thereof to avoid interference with the spring members  252  of the terminal plates  250  or the sensor chip  230 . The pressing member  260 B is placed on the upper face of the unit base  210  while pressurizing the terminal plates  250  from the upside, thereby protecting the sensor base  220  and the sensor chip  230  accommodated in the recessed portion  211  on the upper face of the unit base  210 . 
         [0124]    The sensor unit  200  has the above-mentioned configuration and is accommodated in the sensor accommodating recessed portion  110  of the cartridge case  100  together with the spring  300  in the state where the spring is compressed. In the accommodated state, by downwardly pressurizing the pressing member  260 B with the spring  300 , the seal ring  270  disposed on the lower face of the sensor unit  200  is pressed onto the sensor receiving wall  120  in the sensor accommodating recessed portion  110 , thereby securing the sealing property between the sensor unit  200  and the cartridge case  101 . In this case, since the pressurizing force of the spring  300  is delivered to the unit base  210  through the pressing member  260 B, the pressurizing force is not applied to the sensor base  220  and the sensor chip  230  at all. That is, the spring  300  gives the pressurizing force only to the unit base  210  through a force delivery path bypassing the sensor base  220  and the sensor chip  230 . 
         [0125]    According to the second embodiment described above, the advantages similar to the first embodiment can be obtained. In addition, since the pressurizing force of the spring  300  passes through the pressing member  260 B but is applied directly to the unit base  210  opposed to the sensor receiving wall  120 , the influence of the pressurizing force cannot be given to the sensor base  220  or the sensor chip  230 , thereby enhancing the detection sensitivity. 
         [0126]    Further, since it is sufficient only if the spring  300  is compressed and accommodated in the sensor accommodating recessed portion  110 , the spring can be easily inserted together with the sensor unit  200 . 
         [0127]    Since the pressing member  260 B is disposed on the unit base  210 , it is possible to protect the sensor chip  230  and the sensor base  210  which are important elements for the vibration characteristic. Since the weight of the spring  300  is applied to the unit base  210  through the pressing member  260 B, it is possible to freely determine the combinations of the spring  300  and the unit base  210 , thereby enabling easy design. 
         [0128]      FIG. 10  shows important parts of an ink cartridge according to a fourth embodiment of the invention. In  FIG. 10 , the elements similar to the embodiments shown in  FIGS. 1 to 9  are denoted by the same reference numerals and description thereof will be omitted. 
         [0129]    In the fourth embodiment, a pressing member  260 C covering the sensor chip  230  and the sensor base  210  is disposed above the unit base  210  so as not to come in contact with the unit base  210  and the pressing member  260 C is fixed to the cartridge case  101  with screws  701 . Leaf springs (pressurizing springs)  259  for pressurizing the unit base  210  to press the seal ring  270  are interposed between the pressing member  260 C and the unit base  210 , in the state where the leaf spring is compressed. 
         [0130]    In this case, the leaf springs  259  are integrally formed in the respective terminal plates  250  and may apply a predetermined pressurizing force only to the unit base  210  in a regular assembling process. The terminal plates  250  are provided with the spring members  252  coming in elastic contact with the terminals  235  and  236  (see  FIG. 10 ) of the sensor chip  230 , but the leaf springs  259  are disposed at the positions where the spring force thereof does not act on the spring members  252  at all. 
         [0131]    As shown in the figure, an end of the respective leaf springs  259  may be inserted at the time of forming the pressing member  260 C and the terminal plates  250  may be integrally formed in the pressing member  260 C. In this case, it is not necessary to particularly support the terminal plates  250 . 
         [0132]    The leaf springs  259  may be manufactured and provided separately from the terminal plates  250  and pressurizing springs other than the leaf springs  259  may be provided as long as the space permits. 
         [0133]    In this way, since the pressing member  260 C is fixed to the cartridge case  101  with the screws  701  and the leaf springs  259  (pressurizing springs) are interposed between the cover member  260 C and the unit base  210  in the state where the leaf springs are compressed, it is possible to perform the compact assembly of the pressurizing springs. Further, since the leaf springs  259  are integrally formed with the terminal plates  250  electrically connected to the terminals  235  and  236  of the sensor chip  230 , it is possible to perform the compact assembly and to reduce the number of components, thereby reducing the number of assembly steps. 
         [0134]    Next, an ink cartridge according to a fifth embodiment will be described bellow.  FIG. 11  is an exploded perspective view showing each of structures of a sensor unit  1200 , a spring  1300 , a sealing cover  1400  and a board  1500 , which can be accommodated in the ink cartridge. Moreover,  FIG. 12  is an exploded perspective view showing the sensor unit  1200 ,  FIG. 13  is an exploded perspective view showing the sensor unit  1200  seen at another angle, and  FIG. 14  is a longitudinal sectional view showing the sensor unit accommodating portion of the ink cartridge  1100 . Moreover,  FIG. 15  is a sectional view showing a main part of the sensor unit  1200  and  FIG. 16  is a sectional view taken along a XVI-XVI line in  FIG. 15 . 
         [0135]    As shown in  FIG. 14 , the sensor receiving wall  1120  for receiving a lower end of the sensor unit  1200  is provided in the inner bottom part of the sensor accommodating recessed portion  1110  of the cartridge case  1101 . The sensor receiving wall  1120  has an upper face mounting the sensor unit  1200  thereon and is a portion with which the seal ring  1270  provided on a lower end of the sensor unit  1200  comes in pressure contact by an elastic force of the spring  1300 . 
         [0136]    A pair of sensor buffer chambers  1122  and  1123  on upstream and downstream sides which are divided from each other with a partition wall  1127  interposed therebetween are provided on a lower side of the sensor receiving wall  1120 , and the sensor receiving wall  1120  is provided with a pair of communication holes  1132  and  1133  corresponding to the sensor buffer chambers  1122  and  1123 . A delivery passage for feeding the stored ink to an outside is provided in the cartridge case  1101 , which is not shown. The sensor unit  1200  is positioned in the vicinity of the terminal of the delivery passage (the vicinity of the ink delivery port). In this case, the sensor buffer chamber  1122  on the upstream side is caused to communicate with a delivery passage on the upstream side through a communication hole  1124  and the sensor buffer chamber  1123  on the downstream side is caused to communicate with the delivery passage on the downstream side which is close to the ink delivery port through a communication hole  1125 . Moreover, lower faces of the sensor buffer chambers  1122  and  1123  are not sealed with a rigid wall but opened and the openings are covered with a sealing film  1105  formed of a resin. 
         [0137]    As shown in  FIGS. 12 and 13 , the sensor unit  1200  is constituted by a plate-shaped unit base  1210  having a recessed portion  1211  on an upper face and formed of a resin, a plate-shaped sensor base  1220  accommodated in the recessed portion  1211  provided on the upper face of the unit base  1210  and formed of a metal, a sensor chip  1230  mounted and fixed onto the upper face of the sensor base  1220  and formed of ceramic, for example, an adhesive film  1240  for fixing the sensor base  1220  to the unit base  1210 , a pair of terminal plates  1250  disposed on an upper side of the unit base  1210 , a plate-shaped pressing cover  1260  for pressing the terminal plate  1250  and protecting the sensor chip  1230 , and the seal ring  1270  provided on a lower face of the unit base  1210  and formed of a rubber. 
         [0138]    Each of the components will be described in detail. As shown in  FIG. 13 , the unit base  1210  is formed by a material such as polyethylene and has the recessed portion  1211  for fitting the sensor base  1220  which is provided on a center of an upper face, and has an attachment wall  1215  set to be higher than an upper face wall  1214  by one step on an outside of the upper face wall  1214  around the recessed portion  1211 . A pair of attachment walls  1215  are provided to be opposed to each other with the recessed portion  1211  interposed therebetween, and four support pins  1216  are positioned on the attachment walls  1215  and are erected on four corners of the upper face of the unit base  1210 . Moreover, an entrance-side flow passage  1212  and an exit-side flow passage  1213  (liquid reserving spaces) constituted by circular through holes are provided on a bottom wall of the recessed portion  1211 . Furthermore, an elliptical projected portion  1217  for fitting the seal ring  1270  is provided on a lower face of the unit base  1210  as shown in  FIG. 12 , and the entrance-side flow passage  1212  and the exit-side flow passage  1213  are positioned on the projected portion  1217 . The seal ring  1270  is constituted by a ring packing formed of a rubber and has a lower face provided with an annular projected portion  1271  taking a semicircular section. 
         [0139]    The sensor base  1220  is constituted by a metal plate such as stainless which has a higher rigidity than a resin in order to enhance acoustic characteristics of the sensor. The sensor base  1220  takes the shape of a rectangular plate having four chamfered corners and includes an entrance-side flow passage  1222  and an exit-side flow passage  1223  (liquid reserving spaces) formed by two through holes corresponding to the entrance-side flow passage  1212  and the exit-side flow passage  1213  in the unit base  1210 . 
         [0140]    An adhesive layer  1242  is formed on the upper face of the sensor base  1220  by sticking a double-sided adhesive film or applying an adhesive, for example, and the sensor chip  1230  is mounted and fixed onto the adhesive layer  1242 . It is preferable that the adhesive layer  1242  should have a high adhesiveness of the sensor base  1220  and the sensor chip  1230 . For example, it is preferable to use an olefin type film. 
         [0141]    The sensor chip  1230  has a sensor cavity  1232  for receiving an ink (a liquid) to be a detection target, and has such a structure that the sensor cavity  1232  has a lower face opened too freely receive the ink and an upper face closed with an vibration plate  1233 , and a piezoelectric unit  1234  is provided on an upper face of the vibration plate  1233 . 
         [0142]    More specifically, the sensor chip  1230  is constituted by a chip body  1231  having, on a center, the sensor cavity  1232  constituted by a circular opening and formed of ceramic, the vibration plate  1233  laminated on an upper face of the chip body  1231  and constituting a lower face wall of the sensor cavity  1232 , the piezoelectric unit  1234  laminated on the vibration plate  1233 , and terminals  1235  and  1236  laminated on the chip body  1231  as shown in  FIGS. 14 and 15 . 
         [0143]    The piezoelectric unit  1234  is constituted by upper and lower electrode layers connected to the terminals  1235  and  1236  and a piezoelectric layer laminated between the upper and lower electrode layers, which is not specifically shown, and fulfills the function of deciding an ink end based on a difference in an electrical characteristic depending on the existence or non-existence of the ink in the sensor cavity  1232 , for example. For a material of the piezoelectric layer, it is possible to use lead zirconate titanate (PZT), lanthanum lead zirconate titanate (PLZT) or a lead-free piezoelectric film which does not utilize lead. 
         [0144]    In the sensor chip  1230 , a lower face of the chip body  1231  is mounted on a central part of the upper face of the sensor base  1220  and is thus fixed integrally with the sensor base  1220  through the adhesive layer  1242 , and the sensor base  1220  and the sensor chip  1230  are sealed with the adhesive layer  1242  at the same time. The entrance-side flow passages  1222  and  1212  and the exit-side flow passages  1223  and  1213  (the liquid reserving spaces) in the sensor base  1220  and the unit base  1210  communicate with the sensor cavity  1232  of the sensor chip  1230 . By this structure, the ink enters the sensor cavity  1232  through the entrance-side flow passages  1212  and  1222  and is discharged from the sensor cavity  1232  through the exit-side flow passages  1223  and  1213 . 
         [0145]    Thus, the sensor base  1220  formed of a metal on which the sensor chip  1230  is mounted is accommodated in the recessed portion  1211  on the upper face of the unit base  1210 . The adhesive film  1240  formed of a resin is put from thereabove so that the sensor base  1220  and the unit base  1210  are bonded integrally with each other. 
         [0146]    More specifically, the adhesive film  1240  has an opening  1241  on a center and is put from above in a state in which the sensor base  1220  is accommodated in the recessed portion  1211  on the upper face of the unit base  1210  so that the sensor chip  1230  is exposed from the opening  1241  on the center. Moreover, the adhesive film  1240  has an inner peripheral portion bonded to the upper face of the sensor base  1220  through the adhesive layer  1242  and an outer peripheral portion bonded to the upper face wall  1214  provided around the recessed portion  1211  of the unit base  1210 , that is, the adhesive film  1240  is stuck across the upper faces of the two components (the sensor base  1220  and the unit base  1210 ) so that the sensor base  1220  and the unit base  1210  are fixed to each other and are sealed at the same time. 
         [0147]    It is preferable that the adhesive film  1240  should be formed by a material having a high adhesiveness to both the adhesive layer  1242  on the sensor base  1220  and the unit base  1210 . Preferable examples of the adhesive film  1240  include a film in which an ester type and an olefin type are laminated and the olefin type is set to be a bonding side. 
         [0148]    In this case, the upper face of the sensor base  1220  is protruded upward from the recessed portion  1211  of the unit base  1210 . Consequently, the adhesive film  1240  is bonded to the upper face of the sensor base  1220  in a higher position than a bonding position to the upper face wall  1214  provided around the recessed portion  1211  of the unit base  1210 . Thus, the height of a film bonding face to the sensor base  1220  is set to be greater than that of a film bonding face to the unit base  1210 . Consequently, the sensor base  1220  can be pressed by means of the adhesive film  1240  with a step so that a fixing force of the sensor base  1220  to the unit base  1210  can be increased. Moreover, it is possible to carry out an attachment having no looseness. 
         [0149]    Moreover, each of the terminal plates  1250  has a band-shaped board portion  1251 , a spring piece  1252  protruded from a side edge of the board portion  1251 , an attachment hole  1253  formed on both sides of the board portion  1251 , and a bent piece  1254  formed on both ends of the board portion  1251 , and is disposed on an upper face of the attachment wall  1215  of the unit base  1210  in a state in which the support pins  1216  are inserted through the attachment holes  1253  to carry out positioning, respectively. The pressing cover  1260  is mounted from thereabove so that the terminal plate  1250  is interposed between the unit base  1210  and the pressing cover  1260 , and the spring pieces  1252  are conducted in contact with the terminals  1235  and  1236  provided on the upper face of the sensor chip  230  in that state. 
         [0150]    The pressing cover  1260  has a plate portion  1261  to be mounted on the upper face of the attachment wall  1215  of the unit base  1210  with the board portion  1251  of the terminal plate  1250  interposed therebetween, four attachment holes  1262  provided on four corners of the plate portion  1261  and fitted in the support pins  1216  of the unit base  1210 , an erected wall  1263  provided on an upper face of a center of the plate portion  1261 , a spring receiving seat  1264  provided on the erected wall  1263 , and a recessed portion  1265  provided on a lower face of the plate portion  1261  and forming a relief of the spring piece  1252  of the terminal plate  1250 , and is mounted on the upper face of the unit base  1210  while pressing the terminal plate  1250  from above and thus protects the sensor plate  1220  and the sensor chip  1230  which are accommodated in the recessed portion  1211  formed on the upper face of the unit base  1210 . 
         [0151]    In order to assemble the sensor unit  1200  by the above components, first of all, the adhesive layer  1242  is formed on the whole upper face of the sensor base  1220  and the sensor chip  1230  is mounted on the adhesive layer  1242 . Consequently, the sensor chip  1230  and the sensor base  1220  are fixed and sealed integrally with each other through the adhesive layer  1242 . 
         [0152]    Subsequently, the sensor base  1220  provided integrally with the sensor chip  1230  is accommodated in the recessed portion  1211  formed on the upper face of the unit base  1210  and the adhesive film  1240  is put from above in that state. Consequently, the adhesive film  1240  has the inner peripheral portion bonded to the upper face of the sensor base  1220  through the adhesive layer  1242  and the outer peripheral portion bonded to the upper face wall  1214  provided around the recessed portion  1211  of the unit base  1210 . Consequently, the sensor base  1220  and the unit base  1210  can be fixed and sealed integrally with each other through the adhesive film  1240 . 
         [0153]    Next, the terminal plate  1250  is provided on the unit base  1210  while the attachment hole  1253  is fitted around the support pin  1216  of the unit base  1210 , and the pressing cover  1260  is disposed thereabove. Moreover, the seal ring  1270  is fitted around the projected portion  1217  formed on the lower face of the unit base  1210  in an optional stage. Thus, the sensor unit  1200  can be assembled. 
         [0154]    The sensor unit  1200  is constituted as described above and is accommodated in the sensor accommodating recessed portion  1110  of the cartridge case  1100  together with the spring  1300 . When the spring  1300  presses the pressing cover  1260  downward in the accommodating state as shown in  FIG. 14 , the seal ring  1270  provided on the lower face of the sensor unit  1200  comes in pressure contact with the sensor receiving wall  1120  in the sensor accommodating recessed portion  1110  while crushing. Consequently, a sealing property between the sensor unit  1200  and the cartridge case  1101  is maintained. 
         [0155]    By carrying out the assembly, the buffer chamber  1122  on the upstream side in the cartridge case  1101  is caused to communicate with the entrance-side flow passages  1212  and  1222  in the sensor unit  1200  through the communication hole  1132  of the sensor receiving wall  1120  and the buffer chamber  1123  on the downstream side in the cartridge case  1101  is caused to communicate with the exit-side flow passages  1213  and  1223  in the sensor unit  1200  through the communication hole  1133  of the sensor receiving wall  1120  under the condition that the sealing property is maintained. The entrance-side flow passages  1212  and  1222 , the sensor cavity  1232  and the exit-side flow passages  1213  and  1223  are provided in series on the delivery passage in the cartridge case  1101  so as to be arranged from the upstream side in this order. 
         [0156]    The passage on the upstream side connected to the sensor cavity  1232  is constituted by the buffer chamber  1122  on the upstream side having a large passage section, the communication hole  1132 , and the entrance-side flow passages  1212  and  1222  (narrow and small passages on the upstream side) in the sensor unit  1200  having a small passage section. Moreover, the passage on the downstream side connected to the sensor cavity  1232  is constituted by the buffer chamber  1123  on the downstream side having a large passage section, the communicating port  1133 , and the exit-side flow passages  1213  and  1223  (narrow and small passages on the downstream side) in the sensor unit  1200  having a small passage section. 
         [0157]    As shown in  FIG. 11 , moreover, the sealing cover  1400  for closing the opening on the side face of the sensor accommodating recessed portion  1110  has such a structure that a recessed portion  1402  for fitting the board  1500  is provided on an external surface of a plate-shaped body  1401 , and an opening  1403  from which the bent piece  1254  of each terminal plate  1250  is exposed and pins  1406  and  1407  for positioning the board  1500  are provided on a bottom wall of the recessed portion  1402 , and an engagement click  1405  to be engaged with a predetermined portion in the sensor accommodating recessed portion  1110  is protruded from an internal surface of the body  1401 , and is attached to the cartridge case  1101  in a state in which the sensor unit  1200  and the spring  1300  are accommodated in the sensor accommodating recessed portion  1110 . In this state, the board  1500  is attached to the recessed portion  1402  of the sealing cover  1400 . Consequently, a predetermined contact  1501  of the board  1500  and the terminal plate  1250  are conducted in contact with each other. The board  1500  is provided with a notch  1506  and a hole  1507  to be engaged with the pins  1406  and  1407  for positioning. 
         [0158]    According to the embodiment described above, by simply incorporating the sensor base  1220  mounting the sensor chip  1230  into the unit base  1210  from above and sticking the adhesive film  1240  across upper faces of two components which are arranged, that is, both of the upper faces of the sensor base  1220  and the unit base  1210  in that state, it is possible to fix and seal the two components formed by different materials (the sensor base  1220  formed of a metal and the unit base  1210  formed of a resin) at the same time. Accordingly, an assembling workability is very excellent. Moreover, the adhesive film  1240  is simply stuck across the two components. Therefore, it is possible to seal the components without a great influence of precision in the dimension of each of the components. In the case in which the adhesive film  1240  is to be welded by heating and pressurizing through a mass-produced machine, for example, it is possible to enhance a sealing performance by simply managing a temperature and a pressure through the mass-produced machine. Therefore, it is possible to carry out a stabilization in the mass production. Furthermore, the adhesive film  1240  to influence the sealing property can easily be attached, and furthermore, a space efficiency is high. Therefore, it is possible to reduce the size of the sensor unit  1200 . 
         [0159]    Moreover, there is employed a structure in which the entrance-side flow passages  1212  and  1222  and the exit-side flow passages  1213  and  1223  for the sensor cavity  1232  are formed in the sensor base  1220  and the unit base  1210  respectively and the ink flows into the sensor cavity  1232  through the entrance-side flow passages  1212  and  1222  and is discharged through the exit-side flow passages  1213  and  1223 . Therefore, the ink persistently flows to the sensor cavity  1232 . Consequently, it is possible to prevent an erroneous detection from being caused by the stay of the liquid or air bubbles in the sensor cavity  1232 . 
         [0160]    Furthermore, the height of the bonding face of the adhesive film  1240  to the unit base  1210  is set to be smaller than that of the bonding face to the sensor base  1220 . Therefore, it is possible to press the sensor base  1220  with a step by means of the adhesive film  1240  and to increase a fixing force of the sensor base  1220  to the unit base  1210 . Moreover, it is possible to carry out an attachment having no looseness. 
         [0161]    In addition, the sensor unit  1200  is disposed in the vicinity of the terminal of the delivery passage in the cartridge case  1101 , and the entrance-side flow passages  1212  and  1222 , the sensor cavity  1232  and the exit-side flow passages  1213  and  1223  in the sensor unit  1200  are provided in series in the delivery passage so as to be arranged from the upstream side in this order. Therefore, it is possible to accurately detect the residual amount of the liquid in the ink cartridge  1100 . 
         [0162]    Next, a principle for detecting ink will be described by using, as an example, the sensor unit  200  according to the first embodiment of the invention. 
         [0163]    When the ink in the ink cartridge  101  is consumed, the reserved ink is sent to the printing head  12  of the inkjet printer from the ink delivery portion  103  through the sensor cavity  232  of the sensor unit  200 . 
         [0164]    At this time, when the ink sufficiently remains in the ink cartridge  100 , the sensor cavity  232  is filled with the ink. On the other hand, when the amount of ink remaining in the ink cartridge  100  is reduced, the sensor cavity  232  is not filled with the ink. 
         [0165]    Therefore, the sensor unit  200  detects difference in acoustic impedance due to the variation in such a state. Accordingly, it is possible to detect whether the ink sufficiently remains or whether a part of the ink is consumed and the amount of remaining ink is reduced. 
         [0166]    Specifically, when a voltage is applied to the piezoelectric element  234 , the vibration plate  233  is deformed with the deformation of the piezoelectric element  234 . When the application of the voltage is released after compulsorily deforming the piezoelectric element  234 , flexural vibration remains in the vibration plate  233  for a moment. The residual vibration is free vibration of the vibration plate  233  and the medium in the cavity  232 . Therefore, by allowing the voltage applied to the piezoelectric element  234  to have a pulse waveform or a rectangular waveform, it is possible to easily obtain resonance between the vibration plate  233  and the medium after the application of the voltage. 
         [0167]    The residual vibration is vibration of the vibration plate  233  and accompanies the deformation of the piezoelectric element  234 . For this reason, the piezoelectric element  234  generates the back electromotive force with the residual vibration. The back electromotive force is detected externally through the terminal plates  250 . 
         [0168]    Since the resonance frequency can be specified by the detected back electromotive force, it is possible to detect the existence of ink in the ink cartridge  100  on the basis of the resonance frequency.