JP2007335878A - Piezoelectric device and ink cartridge provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric device that improves vibration characteristics of a vibration part. <P>SOLUTION: A first electrode layer 46, a second electrode layer 49, and an auxiliary electrode layer 48 respectively at each part located in a region corresponding to a cavity 43 form a symmetrical shape, as a whole, that has two symmetric axes O<SB>1</SB>, O<SB>2</SB>passing through the center of a body part 47a of a piezoelectric layer 47 and orthogonal to each other. The two symmetric axes O<SB>1</SB>, O<SB>2</SB>include a first symmetric axis O<SB>1</SB>, which is extended along in an extension direction of an extension part of the piezoelectric layer 47, and a second symmetric axis O<SB>2</SB>that is orthogonal to the first symmetric axis O<SB>1</SB>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric device and an ink cartridge including the piezoelectric device, and more particularly to a piezoelectric device used for liquid detection and an ink cartridge including the piezoelectric device.

  In an ink jet recording apparatus, an ink jet recording head having pressure generating means for pressurizing a pressure generating chamber and a nozzle opening for ejecting the pressurized ink as ink droplets is mounted on a carriage.

  The ink jet recording apparatus is configured to be able to continue printing by continuously supplying ink in an ink tank (ink container) to a recording head via a flow path. The ink tank is configured as a detachable cartridge that can be easily replaced by the user when ink is consumed, for example.

  Conventionally, the ink consumption management method of the ink cartridge includes a method of managing the ink consumption by calculating the number of ink droplets ejected from the recording head and the amount of ink sucked by the maintenance by software, or an ink cartridge. There is a method of managing a point in time when a predetermined amount of ink is actually consumed by attaching an electrode for detecting a liquid level.

  However, the method of managing the ink consumption by calculating the number of ink droplet ejections and the amount of ink by software has the following problems. Some heads have variations in weight of ejected ink droplets. Although the weight variation of the ink droplets does not affect the image quality, the ink cartridge is filled with an amount of ink with a margin in consideration of the accumulation of errors in the ink consumption due to the variation. Therefore, depending on the individual, there is a problem that ink is left by the margin.

  On the other hand, the method of managing the time when ink is consumed by the electrode can detect the actual amount of ink. For this reason, the remaining amount of ink can be managed with high reliability. However, since the detection of the ink level depends on the conductivity of the ink, the types of ink that can be detected may be limited, and the electrode seal structure may be complicated. In addition, as a material for the electrode, a noble metal having high conductivity and high corrosion resistance is usually used, which increases the manufacturing cost of the ink cartridge. Furthermore, since it is necessary to mount two electrodes, the number of manufacturing steps increases, resulting in an increase in manufacturing cost.

  In order to solve the above-mentioned problem, Japanese Patent Application No. 2000-147052 describes a piezoelectric device mounted on a liquid container, which can accurately detect the remaining amount of liquid and does not require a complicated sealing structure.

  According to the technology related to the above-mentioned patent application, the residual generated due to the residual vibration of the vibration part of the piezoelectric device between the case where ink exists in the space facing the vibration part of the piezoelectric device and the case where ink does not exist. The remaining amount of ink in the ink cartridge can be monitored by utilizing the change in the resonance frequency of the vibration signal.

  19 and 20 are diagrams illustrating a conventional piezoelectric device. This piezoelectric device has a base portion 200 formed by laminating a diaphragm 202 on a substrate 201, and a cavity 203 for receiving a medium to be detected is formed in the base portion 200. A lower electrode terminal 204 and an upper electrode terminal 205 are formed at both ends of the base 200. Further, a lower electrode layer 206 connected to the lower electrode terminal 204 is formed in the central portion of the base 200, and a piezoelectric layer 207 is laminated on the lower electrode layer 206, and an upper electrode is formed on the piezoelectric layer 207. A layer 208 is stacked.

  An auxiliary electrode layer 209 is formed on the base 200, and the auxiliary electrode layer 209 electrically connects the upper electrode layer 208 and the upper electrode terminal 205, and a part of the auxiliary electrode layer 209 is connected to the diaphragm 202. The extension part 210 of the piezoelectric layer 207 is supported from below, positioned between the piezoelectric layer 207. In this way, by supporting the extended portion 210 of the piezoelectric layer 207 by the auxiliary electrode layer 209, it is possible to prevent the stepped portion from occurring in the extended portion 210.

  As can be seen from FIG. 20, the auxiliary electrode layer 209 is formed so as to be located outside the region corresponding to the cavity 203. This is because the vibration plate 202, the piezoelectric layer 207, and the like in the region corresponding to the cavity 203 constitute a vibration part of the piezoelectric device, and the auxiliary electrode layer 209 is formed by removing the region of the vibration unit. This is to prevent deterioration of vibration characteristics.

  However, in the above-described conventional piezoelectric device, when the piezoelectric device is driven to vibrate the vibrating portion, cracks are likely to occur in the piezoelectric layer 207 and the upper electrode layer 208 at the position indicated by arrow A in FIG. was there.

  The cause of cracking is considered as follows. That is, as shown in FIG. 20, a gap 211 is formed between the lower electrode layer 206 and the auxiliary electrode layer 209 to ensure the insulation between them. It is formed so as to include a position corresponding to 203a. For this reason, when the vibration part of the piezoelectric device vibrates by driving the piezoelectric device, stress concentration occurs in the piezoelectric layer 207 at a position corresponding to the peripheral edge 203a of the cavity 203, which causes cracks. Conceivable.

  Further, as can be seen from FIG. 19, in the conventional piezoelectric device, the piezoelectric layer 207, the lower electrode layer 206, and the upper electrode layer 208 that constitute the vibrating portion in the region corresponding to the cavity 203 are asymmetric as a whole. Is made. For this reason, there is a problem that the mass balance in the vibration part of the piezoelectric device is deteriorated and the vibration characteristics of the vibration part are deteriorated.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a piezoelectric device that can improve the vibration characteristics of a vibration section.

  In order to solve the above problems, a piezoelectric device according to the present invention is a base having a first surface and a second surface facing each other, and a cavity for receiving a medium to be detected is opened on the first surface side. A first portion including a base portion formed so that the bottom surface portion of the cavity can be vibrated, and a main body portion formed on the second surface side and formed in a region corresponding to the cavity. An electrode layer, a piezoelectric layer laminated on the first electrode layer, a main body formed in a region corresponding to the cavity, and a position corresponding to a peripheral edge of the cavity from the main body A piezoelectric layer having an extending portion; and at least a portion of the piezoelectric layer positioned between the second surface and the extending portion of the piezoelectric layer. Auxiliary electrode for supporting the extension part of the layer And a second electrode layer laminated on the piezoelectric layer and connected to the auxiliary electrode layer, and a portion of the first electrode layer located in a region corresponding to the cavity, the second electrode layer, And the auxiliary electrode layer as a whole has a symmetrical shape defined in the plane of the second surface and having two symmetry axes that pass through the center of the main body of the piezoelectric layer and are orthogonal to each other. The two symmetry axes include a first symmetry axis extending along the extending direction of the extension portion of the piezoelectric layer and a second symmetry axis perpendicular to the first symmetry axis. , To be characterized.

  Preferably, the piezoelectric layer in a portion located in a region corresponding to the cavity has a symmetrical shape having the two symmetry axes.

  The present invention relates to an ink cartridge for use in an ink jet recording apparatus, comprising: an ink container that stores ink; and any one of the piezoelectric devices described above, wherein the cavity of the piezoelectric device is exposed to an ink storage space of the ink container. It is characterized by that.

  A piezoelectric device according to a reference example of the present invention is a base portion having a first surface and a second surface facing each other, and is formed so that a cavity for receiving a medium to be detected opens to the first surface side. A first electrode layer including a base portion formed so that a bottom surface portion of the cavity can vibrate, a main body portion formed in a region corresponding to the cavity formed on the second surface side, and A piezoelectric layer laminated on the first electrode layer, a main body formed in a region corresponding to the cavity, and an extension extending from the main body beyond a position corresponding to a peripheral edge of the cavity; And an auxiliary electrode layer that is formed on the second surface side of the base portion and that is at least partially positioned between the second surface and the extension portion and supports the extension portion. The auxiliary layer is laminated on the piezoelectric layer A second electrode layer connected to the electrode layer, and an insulating gap is formed between the first electrode layer and the auxiliary electrode layer to ensure an insulation state between the electrode layers. The insulating gap is formed by removing a position corresponding to the peripheral edge of the cavity.

  Preferably, the insulating gap is entirely located in a region corresponding to the cavity.

  Preferably, the auxiliary electrode layer has a protrusion that protrudes inward from the outside of the region corresponding to the cavity beyond the position corresponding to the periphery of the cavity.

  Preferably, the protrusion of the auxiliary electrode layer has rounded corners.

  Preferably, the protruding portion of the auxiliary electrode layer is formed wider than the extending portion of the piezoelectric layer.

  Preferably, the protruding portion of the auxiliary electrode layer is formed narrower than the extending portion of the piezoelectric layer.

  Preferably, the first electrode layer has an extending portion extending from the inner side of the region corresponding to the cavity to a position corresponding to a peripheral edge of the cavity toward the auxiliary electrode layer, The insulating gap is formed between the extension portion of the first electrode layer and the auxiliary electrode layer, and the entirety thereof is located outside the region corresponding to the cavity.

  Preferably, a portion of the first electrode layer, the second electrode layer, and the auxiliary electrode layer located in a region corresponding to the cavity has at least the center of the main body portion of the piezoelectric layer as a whole. It has a substantially symmetrical shape with one symmetry axis.

  Preferably, the portion of the piezoelectric layer located in a region corresponding to the cavity has a substantially symmetrical shape having the at least one axis of symmetry.

  A piezoelectric device according to a reference example of the present invention is a base portion having a first surface and a second surface facing each other, and is formed so that a cavity for receiving a medium to be detected opens to the first surface side. A first electrode layer including a base portion formed so that a bottom surface portion of the cavity can vibrate, a main body portion formed in a region corresponding to the cavity formed on the second surface side, and A piezoelectric layer laminated on the first electrode layer, a main body formed in a region corresponding to the cavity, and an extension extending from the main body beyond a position corresponding to a peripheral edge of the cavity; And an auxiliary electrode layer that is formed on the second surface side of the base portion and that is at least partially positioned between the second surface and the extension portion and supports the extension portion. The auxiliary layer is laminated on the piezoelectric layer A portion of the first electrode layer, the second electrode layer, and the auxiliary electrode layer that are located in a region corresponding to the cavity, as a whole. It is characterized by having a substantially symmetrical shape with at least one axis of symmetry passing through the center of the body portion of the layer.

  Preferably, the portion of the piezoelectric layer located in a region corresponding to the cavity has a substantially symmetrical shape having the at least one axis of symmetry.

  A piezoelectric device according to a reference example of the present invention is a base portion having a first surface and a second surface facing each other, and is formed so that a cavity for receiving a medium to be detected opens to the first surface side. A first electrode layer including a base portion formed so that a bottom surface portion of the cavity can vibrate, a main body portion formed in a region corresponding to the cavity formed on the second surface side, and A piezoelectric layer laminated on the first electrode layer, a main body formed in a region corresponding to the cavity, and an extension extending from the main body beyond a position corresponding to a peripheral edge of the cavity; And an auxiliary electrode layer that is formed on the second surface side of the base portion and that is at least partially positioned between the second surface and the extension portion and supports the extension portion. The auxiliary layer is laminated on the piezoelectric layer A second electrode layer connected to a polar layer, and the piezoelectric layer in a portion corresponding to the cavity has at least one axis of symmetry passing through a center of the body portion of the piezoelectric layer It is characterized by having a substantially symmetrical shape.

  Preferably, the at least one symmetry axis includes a first symmetry axis extending along an extending direction of the extension portion of the piezoelectric layer, and a second symmetry axis perpendicular to the first symmetry axis. .

  A reference example of the present invention is an ink cartridge used in an ink jet recording apparatus, comprising: an ink container that stores ink; and any one of the piezoelectric devices described above, wherein the cavity of the piezoelectric device stores ink in the ink container. It is exposed to space.

  According to the present invention, the portion of the first electrode layer, the second electrode layer, and the auxiliary electrode layer that are located in the region corresponding to the cavity, as a whole, have at least one axis of symmetry passing through the center of the body portion of the piezoelectric layer. The vibration characteristics of the piezoelectric device can be improved because it is formed so as to have a substantially symmetrical shape.

  According to the present invention, the portion of the piezoelectric layer located in the region corresponding to the cavity is formed to have a substantially symmetrical shape having at least one axis of symmetry passing through the center of the body portion of the piezoelectric layer. The vibration characteristics of the piezoelectric device can be improved.

  According to the reference example of the present invention, since the insulating gap formed between the first electrode layer and the auxiliary electrode layer is formed away from the position corresponding to the peripheral edge of the cavity, the driving of the piezoelectric device is performed. Thus, when the vibration part is vibrated, stress concentration generated in the piezoelectric layer at a position corresponding to the peripheral edge of the cavity can be significantly suppressed. For this reason, generation | occurrence | production of the crack in a piezoelectric layer and an upper electrode layer can be prevented.

Hereinafter, a piezoelectric device according to an embodiment of the present invention and an ink cartridge including the piezoelectric device will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a carriage. The carriage 1 is guided by a guide member 4 through a timing belt 3 driven by a carriage motor 2 and is reciprocated in the axial direction of the platen 5. .

  An ink jet recording head is mounted on the side of the carriage 1 that faces the recording paper 6, and an ink cartridge 7 that supplies ink to the recording head is detachably mounted thereon.

  A cap member 31 is disposed at a home position (right side in the figure) which is a non-printing area of the recording apparatus. When the recording head mounted on the carriage 1 moves to the home position, the cap member 31 performs recording. It is configured to be pressed against the nozzle forming surface of the head to form a sealed space with the nozzle forming surface. A pump unit 10 is disposed below the cap member 31 for applying a negative pressure to the sealed space formed by the cap member 31 to perform cleaning or the like.

  A wiping means 11 having an elastic plate such as rubber is disposed in the vicinity of the print area side of the cap member 31 so as to be able to advance and retreat in the horizontal direction with respect to the movement trajectory of the recording head. When reciprocating to the cap member 31 side, the nozzle forming surface of the recording head can be wiped off as necessary.

  2 and 3 are views showing the piezoelectric device according to the present embodiment. The piezoelectric device 60 includes a base 40 formed by laminating a vibration plate 42 on a substrate 41. The first surface 40a and the second surface 40b are opposed to each other. A circular cavity 43 for receiving the medium to be detected is formed in the base 40 so as to open to the first surface 40a side, and the bottom surface portion 43b of the cavity 43 can be vibrated by the diaphragm 42. Is formed. A lower electrode terminal 44 and an upper electrode terminal 45 are formed at both ends of the base 40 on the second surface 40b side.

  A lower electrode layer (first electrode layer) 46 is formed on the second surface 40 b of the base 40, and the lower electrode layer 46 includes a main body 46 a formed in a region corresponding to the cavity 43, An extending portion 46b extending from the main body portion 46a beyond the position corresponding to the peripheral edge 43a of the cavity 43. The main body 46 a of the lower electrode layer 46 has a circular shape, and its center substantially coincides with the center of the cavity 43. The main body 46 a of the lower electrode layer 46 is configured to have a smaller diameter than the cavity 43.

  A piezoelectric layer 47 is laminated on the lower electrode layer 46. The piezoelectric layer 47 includes a main body portion 47a formed in a region corresponding to the cavity 43, and a peripheral edge 43a of the cavity 43 from the main body portion 47a. And an extending portion 47b extending beyond the position corresponding to the. The main body portion 47 a of the piezoelectric layer 47 has a circular shape, and the center thereof substantially coincides with the center of the cavity 43. The main body portion 47 a of the piezoelectric layer 47 has a smaller diameter than the cavity 43 and a larger diameter than the main body portion 46 a of the lower electrode layer 46.

  An auxiliary electrode layer 48 is formed on the second surface 40b side of the base 40, and this auxiliary electrode layer 48 is preferably made of the same material and the same thickness as the lower electrode layer 46. A part of the auxiliary electrode layer 48 is located between the second surface 40b and the extending portion 47b of the piezoelectric layer 47, and supports the extending portion 47b of the piezoelectric layer 47 from below. In this way, by supporting the extended portion 47 b of the piezoelectric layer 47 by a part of the auxiliary electrode layer 48, it is possible to prevent a step from being generated in the piezoelectric layer 47.

  An upper electrode layer (second electrode layer) 49 is laminated on the piezoelectric layer 47. The upper electrode layer 49 includes a main body 49a formed on the main body 47a of the piezoelectric layer 47, and the main body 49a. An extending portion 49b extending beyond a position corresponding to the peripheral edge 43a of the cavity 43. The extending portion 49 b of the upper electrode layer 49 is connected to the auxiliary electrode layer 48, and the upper electrode layer 49 and the upper electrode terminal 45 are electrically connected via the auxiliary electrode layer 48. By connecting the upper electrode layer 49 to the upper electrode terminal 45 through the auxiliary electrode layer 48 in this way, a step caused by the total thickness of the piezoelectric layer 47 and the lower electrode layer 46 is reduced. It can be absorbed by both the layer 48. For this reason, it is possible to prevent the mechanical strength from being lowered due to a large step in the upper electrode layer 49.

  The main body 49 a of the upper electrode layer 49 has a circular shape, and the center thereof substantially coincides with the center of the cavity 43. The main body 49 a of the upper electrode layer 49 is formed to have a smaller diameter than the main body 47 a and the cavity 43 of the piezoelectric layer 47 and a larger diameter than the main body 46 a of the lower electrode layer 46.

  As described above, the main body portion 47 a of the piezoelectric layer 47 is sandwiched between the main body portion 49 a of the upper electrode layer 49 and the main body portion 46 a of the lower electrode layer 46. Thereby, the piezoelectric layer 47 can be effectively deformed and driven.

  As described above, the cavity 43 has the largest area among the main body 49a of the upper electrode layer 49, the main body 47a of the piezoelectric layer 47, the main body 46a of the lower electrode layer 46, and the cavity 43. Due to such a structure, the vibration region of the diaphragm 42 that actually vibrates is determined by the cavity 43.

  In addition, since the areas of the main body portion 49 a of the upper electrode layer 49, the main body portion 47 a of the piezoelectric layer 47, and the main body portion 46 a of the lower electrode layer 46 are smaller than the area of the cavity 43, the vibration plate 42 is more likely to vibrate. ing.

  Furthermore, the main body 46 a of the lower electrode layer 46 is smaller than the main body 46 a of the lower electrode layer 46 and the main body 49 a of the upper electrode layer 49 that are electrically connected to the piezoelectric layer 47. Accordingly, the main body portion 46 a of the lower electrode layer 46 determines a portion of the piezoelectric layer 47 that generates the piezoelectric effect.

  The centers of the main body portion 47 a of the piezoelectric layer 47, the main body portion 49 a of the upper electrode layer 49, and the main body portion 46 a of the lower electrode layer 46 substantially coincide with the center of the cavity 43. In addition, the center of the circular cavity 43 that determines the vibrating portion of the diaphragm 42 is positioned substantially at the center of the entire piezoelectric device 60. Accordingly, the center of the vibration part of the piezoelectric device 60 substantially coincides with the center of the piezoelectric device 60.

  Further, since the main body portion 47a of the piezoelectric layer 47, the main body portion 49a of the upper electrode layer 49, the main body portion 46a of the lower electrode layer 46, and the vibration portion of the diaphragm 42 have a circular shape, the vibration portion of the piezoelectric device 60 is The shape is symmetrical with respect to the center of the piezoelectric device 60. Thus, since the vibration part of the piezoelectric device 60 has a symmetrical shape with respect to the center of the piezoelectric device 60, unnecessary vibrations that may arise from the asymmetry of the structure are not excited. For this reason, the detection accuracy of the resonance frequency is improved.

  Further, since the vibration part of the piezoelectric device 60 has an isotropic shape, the piezoelectric device 60 is hardly affected by variations in fixation when the piezoelectric device 60 is bonded, and can be evenly bonded to the ink container. That is, the mountability of the piezoelectric device 60 to the ink container is good.

  Furthermore, since the compliance of the diaphragm 42 is large, vibration attenuation is reduced, and the accuracy of detection of the resonance frequency can be improved.

  The members included in the piezoelectric device 60 are preferably integrally formed by firing each other. By integrally forming the piezoelectric device 60, the piezoelectric device 60 can be easily handled.

  Furthermore, the vibration characteristics can be improved by increasing the strength of the substrate 41. That is, by increasing the strength of the substrate 41, only the vibration part of the piezoelectric device 60 vibrates, and parts other than the vibration part of the piezoelectric device 60 do not vibrate. In order to increase the vibration of the vibration part, in addition to increasing the strength of the substrate 41, the piezoelectric layer 47, the upper electrode layer 49, and the lower electrode layer 46 of the piezoelectric device 60 are made thin and small, and It is effective to make the plate 41 thinner.

  As a material of the piezoelectric layer 47, it is preferable to use lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), or a lead-less piezoelectric film that does not use lead. As a material of the substrate 41, it is preferable to use zirconia or alumina. The diaphragm 42 is preferably made of the same material as the substrate 41. For the upper electrode layer 49, the lower electrode layer 46, the upper electrode terminal 45, and the lower electrode terminal 44, a conductive material, for example, a metal such as gold, silver, copper, platinum, aluminum, or nickel can be used.

  As shown in FIG. 3, an insulating gap 50 is formed between the lower electrode layer 46 and the auxiliary electrode layer 48. The insulating gap 50 is formed by removing the position corresponding to the peripheral edge 43 a of the cavity 43, and more specifically, the insulating gap 50 is located in a region corresponding to the cavity 43 as a whole. It is formed like this.

  Thus, by positioning the entire insulating gap 50 in the region corresponding to the cavity 43, the position corresponding to the peripheral edge 43 a of the cavity 43 when the vibrating portion is vibrated by driving the piezoelectric device 60. The stress concentration generated in the piezoelectric layer 47 can be greatly suppressed. For this reason, the generation of cracks in the piezoelectric layer 47 and the upper electrode layer 49 can be prevented.

  Further, the auxiliary electrode layer 48 has a protrusion 48 a that protrudes from the outside to the inside of the region corresponding to the cavity 43 beyond the position corresponding to the peripheral edge 43 a of the cavity 43, and the protrusion 48 a The corners are rounded.

  In this way, by rounding the corners of the protrusions 48 a of the auxiliary electrode layer 48, it is possible to prevent cracks in the piezoelectric layer 47 at the edge portion of the auxiliary electrode layer 48. Further, in consideration of the case where a displacement occurs during the formation of the auxiliary electrode layer 48, if a corner exists in the protrusion 48a of the auxiliary electrode layer 48, the corner of the protrusion 48a corresponds to the cavity 43 due to the displacement during formation. Move inside or outside the area. For this reason, there is a possibility that the vibration characteristics of each piezoelectric device 60 may vary. On the other hand, by rounding the corners of the protrusions 48a of the auxiliary electrode layer 48 as in the present embodiment, it is possible to greatly suppress variations in vibration characteristics due to misalignment when the auxiliary electrode layer 48 is formed. it can.

  FIG. 4 shows a piezoelectric device 60 and its equivalent circuit used in this embodiment. The piezoelectric device 60 detects a change in acoustic impedance by detecting a resonance frequency due to residual vibration, and detects a consumption state of the liquid in the ink cartridge.

  4A and 4B show an equivalent circuit of the piezoelectric device 60. FIG. 4C and 4D show the periphery including the piezoelectric device 60 and its equivalent circuit when the ink is filled in the ink cartridge, respectively, and FIG. 4E and FIG. F) shows the periphery including the piezoelectric device 60 and its equivalent circuit when there is no ink in the ink cartridge.

  The piezoelectric device 60 shown in FIGS. 2 to 4 is mounted at a predetermined position of the ink container of the ink cartridge 7 so that the cavity 43 comes into contact with the liquid (ink) accommodated in the ink container. That is, at least a part of the vibrating portion of the piezoelectric device 60 is exposed in the ink container housing space. When the liquid is sufficiently stored in the ink container, the inside of the cavity 43 and the outside thereof are filled with the liquid.

  On the other hand, when the liquid in the ink container is consumed and the liquid level drops below the mounting position of the piezoelectric device, the liquid does not exist in the cavity 43, or the liquid remains only in the cavity 43 and outside of it. It will be in the state where gas exists.

  The piezoelectric device 60 detects a difference in acoustic impedance caused by this change in state. As a result, the piezoelectric device 60 can detect whether the ink container is in a state where the liquid is sufficiently stored or whether a certain amount of liquid is consumed.

Next, the principle of liquid level detection using a piezoelectric device will be described.
The piezoelectric device 60 can detect the change in the acoustic impedance of the liquid using the change in the resonance frequency. The resonance frequency can be detected by measuring a counter electromotive force generated by residual vibration remaining in the vibration part after the vibration part of the piezoelectric device vibrates. That is, the piezoelectric layer 47 of the piezoelectric device 60 generates a counter electromotive force due to residual vibration remaining in the vibration portion of the piezoelectric device 60. The magnitude of the counter electromotive force varies depending on the amplitude of the vibration part of the piezoelectric device 60. Therefore, detection is easier as the amplitude of the vibration part of the piezoelectric device 60 is larger.

  Further, the period in which the magnitude of the counter electromotive force changes depends on the frequency of the residual vibration in the vibration part of the piezoelectric device 60. That is, the frequency of the vibration part of the piezoelectric device 60 corresponds to the frequency of the counter electromotive force. Here, the resonance frequency refers to a frequency in a resonance state between the vibrating portion of the piezoelectric device 60 and the medium in contact with the vibrating portion.

  The vibration region of the piezoelectric device 60 is a portion corresponding to the cavity 43 in the vibration plate 42. When the liquid is sufficiently stored in the ink container, the cavity 43 is filled with the liquid, and the vibration region is in contact with the liquid in the ink container. On the other hand, when there is not enough liquid in the ink container, the vibration region is in contact with the liquid remaining in the cavity 43 in the ink container, or is not in contact with the liquid but in contact with gas or vacuum.

  Here, the operation and principle of detecting the state of the liquid in the ink container from the resonance frequency between the medium obtained by measuring the counter electromotive force and the vibration part of the piezoelectric device 60 will be described with reference to FIGS. To do.

  In the piezoelectric device 60, a voltage is applied to the upper electrode layer 49 and the lower electrode layer 46 through the upper electrode terminal 45 and the lower electrode terminal 44, respectively. Then, an electric field is generated in a portion of the piezoelectric layer 47 sandwiched between the upper electrode layer 49 and the lower electrode layer 46. The piezoelectric layer 47 is deformed by this electric field. When the piezoelectric layer 47 is deformed, the vibration region of the vibration plate 42 is flexibly vibrated. For a while after the piezoelectric layer 47 is deformed, the flexural vibration remains in the vibrating portion of the piezoelectric device 60.

  The residual vibration is free vibration between the vibration part of the piezoelectric device 60 and the medium. Therefore, by setting the voltage applied to the piezoelectric layer 47 to a pulse waveform or a rectangular wave, it is possible to easily obtain the resonance state between the vibrating portion and the medium after the voltage is applied. The residual vibration is vibration of the vibration part of the piezoelectric device 60 and is accompanied by deformation of the piezoelectric layer 47. For this reason, the piezoelectric layer 47 generates a counter electromotive force. This counter electromotive force is detected through the upper electrode layer 49, the lower electrode layer 46, the upper electrode terminal 45 and the lower electrode terminal 44. The resonance frequency can be specified by the detected back electromotive force. Based on this resonance frequency, the presence or absence of liquid in the ink container can be detected.

In general, the resonant frequency fs is
fs = 1 / (2 * π * (M * Cact) _1/2 ) (Formula 1)
It is represented by Here, M is the sum of the inertance Mact and the additional inertance M ′ of the vibration part. Cact is the compliance of the vibration part.

  FIGS. 4A and 4B are equivalent circuits of the vibrating portion of the piezoelectric device 60 and the cavity 43 when no ink remains in the cavity 43. FIG.

Mact is obtained by dividing the product of the thickness of the vibration part and the density of the vibration part by the area of the vibration part. Specifically, as shown in FIG.
Mact = Mpzt + Melectrode1 + Melectrode2 + Mvib (Formula 2)
It is expressed.

  Here, Mpzt is obtained by dividing the product of the thickness of the piezoelectric layer 47 and the density of the piezoelectric layer 47 in the vibrating portion by the area of the piezoelectric layer 47. Melectrode1 is obtained by dividing the product of the thickness of the upper electrode layer 49 and the density of the upper electrode layer 49 in the vibration part by the area of the upper electrode layer 49. Melectrode2 is obtained by dividing the product of the thickness of the lower electrode layer 46 and the density of the lower electrode layer 46 in the vibration part by the area of the lower electrode layer 46. Mvib is obtained by dividing the product of the thickness of the vibration plate 42 and the density of the vibration plate 42 in the vibration portion by the area of the vibration region of the vibration plate 42.

  However, the respective areas of the vibration regions of the piezoelectric layer 47, the upper electrode layer 49, the lower electrode layer 46, and the vibration plate 42 are as follows so that Mact can be calculated from the thickness, density, and area of the entire vibration part: Although having the magnitude relationship as described above, it is preferable that the difference in mutual area is small.

  In the present embodiment, in the piezoelectric layer 47, the upper electrode layer 49, and the lower electrode layer 46, portions other than the circular main body portions 47a, 49a, and 46a that are the main portions thereof can be ignored with respect to the main portions. It is preferable that it is very small. Therefore, in the piezoelectric device 60, Mact is the sum of the inertances of the vibration regions of the upper electrode layer 49, the lower electrode layer 46, the piezoelectric layer 47, and the vibration plate 42. The compliance Cact is a compliance of a portion formed by the vibration region of the upper electrode layer 49, the lower electrode layer 46, the piezoelectric layer 47 and the vibration plate 42.

4A, 4 </ b> B, 4 </ b> D, and 4 </ b> F show an equivalent circuit of the vibration unit of the piezoelectric device 60 and the cavity 43. In these equivalent circuits, Cact is the vibration of the piezoelectric device 60. Indicates compliance of the department. Cpzt, Celectrode1, Celectrode2, and Cvib indicate the compliance of the piezoelectric layer 47, the upper electrode layer 49, the lower electrode layer 46, and the vibration plate 42 in the vibration part, respectively. Cact is expressed by Equation 3 below.
1 / Cact = (1 / Cpzt) + (1 / Celectrode1) + (1 / Celectrode2)
+ (1 / Cvib) (Formula 3)
From Formula 2 and Formula 3, FIG. 4 (A) can also be expressed as FIG. 4 (B).

  The compliance Cact represents the volume of the medium that can be received by deformation when pressure is applied to the unit area. That is, the compliance Cact represents the ease of deformation.

FIG. 4C is a cross-sectional view of the piezoelectric device 60 in a case where the liquid is sufficiently stored in the ink container and the periphery of the vibration region of the piezoelectric device 60 is filled with the liquid. M′max in FIG. 4C is an additional inertance (additional mass (influence on the vibration of the vibration region) when the ink container is sufficiently filled with the liquid and the periphery of the vibration region of the piezoelectric device 60 is filled with the liquid. Mass)) divided by the square of the area). M'max is
M′max = (π * ρ / (2 * k ₃ )) * (2 * (2 * k * a) ₃ / (3 * π)) / (π * a ₂ ) ₂ (Formula 4)
(A is the radius of the vibration part, ρ is the density of the medium, and k is the wave number.)
It is represented by

  Equation 4 is established when the vibration region of the piezoelectric device 60 is a circle having a radius a. The additional inertance M ′ is an amount indicating that the mass of the vibration part is apparently increased by the medium in the vicinity of the vibration part. As can be seen from Equation 4, M′max varies greatly depending on the radius a of the vibrating part and the density ρ of the medium.

Wave number k is
k = 2 * π * fact / c (Formula 5)
(Fact is the resonance frequency of the vibration part. C is the speed of sound propagating through the medium.)
It is represented by

  FIG. 4D shows the vibration portion of the piezoelectric device 60 and the cavity 43 in the case of FIG. 4C in which the ink container is sufficiently filled with liquid and the liquid is filled around the vibration region of the piezoelectric device 60. An equivalent circuit is shown.

  FIG. 4E shows the piezoelectric device 60 when the liquid in the ink container is consumed and there is no liquid around the vibration region of the piezoelectric device 60, but the liquid remains in the cavity 43 of the piezoelectric device 60. A cross-sectional view is shown.

Expression 4 is an expression representing the maximum inertance M′max determined from the density ρ of the ink when the ink container is filled with the liquid. On the other hand, the additional inertance M ′ when the liquid in the ink container is consumed and the liquid around the vibration region of the piezoelectric device 60 is replaced with gas or vacuum while the liquid remains in the cavity 43 is generally In addition,
M ′ = ρ * t / S (Formula 6)
(For more details, see Equation 8 below.) Here, t is the thickness of the medium involved in vibration. S is the area of the vibration region of the piezoelectric device 60. When the vibration region is a circle having a radius a, S = π * a ² .

  Therefore, the additional inertance M ′ is based on Equation 4 when the liquid is sufficiently contained in the ink container and the liquid is filled around the vibration region of the piezoelectric device 60. On the other hand, when the liquid is consumed and the liquid around the vibration region of the piezoelectric device 60 is replaced with gas or vacuum while the liquid remains in the cavity 43, Equation 6 is satisfied.

  Here, as shown in FIG. 4E, when the liquid in the ink container is consumed and there is no liquid around the vibration region of the piezoelectric device 60, the liquid remains in the cavity 43 of the piezoelectric device 60. The additional inertance M ′ is referred to as M′cav for the sake of convenience, and is distinguished from the additional inertance M′max when the liquid is filled around the vibration region of the piezoelectric device 60.

  4F shows that the liquid in the ink container is consumed and there is no liquid around the vibration region of the piezoelectric device 60, but the liquid remains in the cavity 43 of the piezoelectric device 60. The equivalent circuit of the vibration part and cavity 43 of the piezoelectric device 60 in the case is shown.

  Here, the parameters related to the state of the medium are the density ρ of the medium and the thickness t of the medium in Equation 6. When the liquid is sufficiently stored in the ink container, the liquid comes into contact with the vibrating portion of the piezoelectric device 60. On the other hand, when the liquid is not sufficiently stored in the ink container, the liquid remains in the cavity 43 or a gas or a vacuum contacts the vibrating portion of the piezoelectric device 60. The additional inertance M′var in the process of transition from M′max in FIG. 4C to M′cav in FIG. 4E is consumed in the vicinity of the piezoelectric device 60, and the liquid is contained in the ink container. As a result, the density ρ of the medium and the thickness t of the medium change. Thereby, the resonance frequency fs also changes. Therefore, the amount of liquid in the ink container can be detected by specifying the resonance frequency fs.

Here, when t = d as shown in FIG. 4 (E), when M′cav is expressed using Equation 6, the cavity depth d is substituted into t in Equation 6,
M′cav = ρ * d / S (Formula 7)
It becomes.

  Further, if the medium is a different type of liquid, the density ρ varies depending on the composition, and therefore the additional inertance M ′ and the resonance frequency fs are different. Therefore, the type of liquid can be detected by specifying the resonance frequency fs.

  FIG. 5A is a graph showing the relationship between the amount of ink in the ink tank and the resonance frequency fs of the ink and the vibration part. Here, ink will be described as an example of liquid. The vertical axis represents the resonance frequency fs, and the horizontal axis represents the ink amount. When the ink composition is constant, the resonance frequency fs increases as the remaining ink amount decreases.

  When ink is sufficiently contained in the ink container and the ink is filled around the vibration region of the piezoelectric device 60, the maximum added inertance M'max is a value expressed by Equation 4. On the other hand, when the ink is consumed and the ink remains in the cavity 43, but the ink is not filled around the vibration region of the piezoelectric device 60, the additional inertance M′var is calculated based on the thickness t of the medium. 6 is calculated. Since t in Equation 6 is the thickness of the medium involved in the vibration, by reducing the depth d of the cavity 43 of the piezoelectric device 60 where the ink remains, that is, by sufficiently reducing the thickness of the substrate 41, It is also possible to detect a process in which ink is gradually consumed (see FIG. 4C). Here, tink is the thickness of ink involved in vibration, and tink-max is the tink at M'max.

  For example, the piezoelectric device 60 is disposed substantially horizontally with respect to the ink level on the bottom surface of the ink cartridge. In this case, when the ink is consumed and the liquid level of the ink falls below the height of tink-max from the piezoelectric device 60, M′var gradually changes according to Equation 6, and the resonance frequency fs gradually changes according to Equation 1. . Therefore, as long as the ink level is within the range t, the piezoelectric device 60 can gradually detect the ink consumption state.

  Alternatively, the piezoelectric device 60 may be disposed on the side wall of the ink cartridge substantially perpendicular to the ink level. In this case, when the ink is consumed and the liquid level of the ink reaches the vibration region of the piezoelectric device 60, the additional inertance M 'decreases as the water level decreases. As a result, the resonance frequency fs gradually increases according to Equation 1. Accordingly, as long as the ink level is within the range of the diameter 2a of the cavity 43 (see FIG. 4C), the piezoelectric device 60 can gradually detect the ink consumption state.

  A curve X in FIG. 5A is obtained when the cavity 43 of the piezoelectric device 60 disposed on the bottom surface is sufficiently shallow, or when the vibration region of the piezoelectric device 60 disposed on the side wall is sufficiently large or long. This represents the relationship between the amount of ink stored in the ink tank and the resonance frequency fs of the ink and the vibration part. It can be understood that the amount of ink in the ink tank decreases and the resonance frequency fs of the ink and the vibration part gradually changes.

  More specifically, the case where the process in which ink is gradually consumed can be detected refers to the presence of both liquid and gas having different densities around the vibration region of the piezoelectric device 60 and vibration. Is the case. As the ink is gradually consumed, the medium involved in vibration around the vibration region of the piezoelectric device 60 decreases in liquid while increasing in gas.

For example, when the piezoelectric device 60 is disposed horizontally with respect to the ink surface and when tink is smaller than tink-max, the medium involved in the vibration of the piezoelectric device 60 includes both ink and gas. Therefore, when the area S of the vibration region of the piezoelectric device 60 is used and the state of M′max or less in Equation 4 is expressed by the additional mass of ink and gas
M ′ = M′air + M′ink = ρair * tair / S + ρink * tink / S (Formula 8)
It becomes. Here, M′air is an inertance of air, and M′ink is an inertance of ink. ρair is the density of air, and ρink is the density of ink. tair is the thickness of air involved in vibration, and tink is the thickness of ink involved in vibration.

  Among the media involved in vibration around the vibration region of the piezoelectric device 60, as the liquid decreases and the gas increases, tair increases when the piezoelectric device 60 is arranged substantially horizontally with respect to the ink surface. Then, tink decreases. Thereby, M′var gradually decreases and the resonance frequency gradually increases. Therefore, it is possible to detect the amount of ink remaining in the ink tank or the amount of ink consumed. The reason why only the liquid density is calculated in Expression 7 is that it is assumed that the air density is negligibly small relative to the liquid density.

In the case where the piezoelectric device 60 is disposed substantially perpendicular to the ink surface, among the vibration regions of the piezoelectric device 60, the region where the medium involved in the vibration of the piezoelectric device 60 is only ink and the vibration of the piezoelectric device 60. It is considered that the medium involved in the above is an equivalent circuit (not shown) in parallel with a region containing only gas. If the medium related to the vibration of the piezoelectric device 60 is Sink, the area of the ink-only region is Sink, and the area of the medium only related to the vibration of the piezoelectric device 60 is Sair is Sair.
1 / M ′ = 1 / M′air + 1 / M′ink = Sair / (ρair * tair) + Sink / (ρink * tink)
(Formula 9)
It becomes.

  Equation 9 is applied when ink is not held in the cavity 43 of the piezoelectric device 60. The additional inertance when ink is held in the cavity 43 of the piezoelectric device 60 can be calculated by the sum of M ′ according to Equation 9 and M′cav according to Equation 7.

  Since the vibration of the piezoelectric device 60 changes from the depth of tink-max to the depth d where ink remains, the piezoelectric device 60 is disposed on the bottom surface so that the ink remaining depth is slightly smaller than tink-max. If this is the case, it is not possible to detect a process in which the ink gradually decreases. In this case, a change in the ink amount is detected from a vibration change of the piezoelectric device due to a slight change in the ink amount from tink-max to the remaining depth d. Further, when the cavity 43 is arranged on the side surface and the diameter of the cavity 43 is small, the vibration change of the piezoelectric device 60 while passing through the cavity 43 is very small. Whether it is above or below 43 is detected.

  For example, the curve Y in FIG. 5A shows the relationship between the amount of ink in the ink tank and the resonance frequency fs of the ink and the vibration part in the case of a small circular vibration region. A state is shown in which the resonance frequency fs of the ink and the vibration part changes drastically between the difference Q of the ink amount before and after the liquid level of the ink in the ink tank passes through the mounting position of the piezoelectric device 60. From this, it is possible to binaryly detect whether or not a predetermined amount of ink remains in the ink tank.

  Since the method of detecting the presence or absence of liquid using the piezoelectric device 60 detects the presence or absence of ink by the diaphragm 42 coming into direct contact with the liquid, the detection accuracy is higher than the method of calculating the ink consumption by software. high. Furthermore, the method of detecting the presence or absence of ink by conductivity using an electrode can be influenced by the position of the electrode attached to the ink container and the type of ink, but the method of detecting the presence or absence of liquid using the piezoelectric device 60 is It is difficult to be influenced by the attachment position of the piezoelectric device 60 to the ink container and the type of ink.

  Furthermore, since both oscillation and detection of the presence / absence of liquid can be performed using a single piezoelectric device 60, the method is compared with a method in which oscillation and detection of presence / absence of liquid are performed using different sensors. Thus, the number of sensors attached to the ink container can be reduced. Therefore, an ink container having a liquid amount detection function can be manufactured at low cost. In addition, it is preferable that the sound generated during the operation of the piezoelectric device 60 is made quiet by setting the vibration frequency of the piezoelectric layer 47 in a non-audible region.

  FIG. 5B shows an example of the relationship between the ink density and the resonance frequency fs of the ink and the vibration part. Here, ink is described as an example of a liquid, and “ink full” and “ink empty” (or “no ink”) mean two relative states, so-called ink full state and ink end state. It doesn't mean. As shown in FIG. 5B, when the ink density is high, the additional inertance increases, and therefore the resonance frequency fs decreases. That is, the resonance frequency fs varies depending on the type of ink. Therefore, by measuring the resonance frequency fs, it is possible to confirm whether or not inks having different densities are mixed when refilling the ink. That is, it is possible to identify ink tanks containing different types of ink.

  Subsequently, when the size and shape of the cavity 43 are set so that the liquid remains in the cavity 43 of the piezoelectric device 60 even when the liquid in the ink container is empty, the state of the liquid can be accurately detected. The conditions will be described in detail. If the piezoelectric device 60 can detect the liquid state when the cavity 43 is filled with the liquid, the piezoelectric device 60 can detect the liquid state even when the cavity 43 is not filled with the liquid.

  The resonance frequency fs is a function of the inertance M. The inertance M is the sum of the inertance Mact and the additional inertance M ′ of the vibration part. Here, the additional inertance M ′ is related to the liquid state. The additional inertance M ′ is an amount indicating that the mass of the vibration part is apparently increased by the medium in the vicinity of the vibration part. That is, it means an increase in the mass of the vibration part due to apparent absorption of the medium by the vibration of the vibration part (inertance related to vibration increases).

  Therefore, when M ′ cav is larger than M ′ max in Equation 4, all the medium that apparently absorbs is the liquid remaining in the cavity 43. Therefore, it is the same as the state where the ink container is filled with the liquid. In this case, since the medium related to vibration does not become smaller than M'max, a change cannot be detected even if ink is consumed.

  On the other hand, when M ′ cav is smaller than M ′ max in Equation 4, the apparently absorbing medium is the liquid remaining in the cavity 43 and the gas or vacuum in the ink container. At this time, unlike the state in which the ink container is filled with liquid, M ′ changes, so the resonance frequency fs changes. Therefore, the piezoelectric device 60 can detect the state of the liquid in the ink container.

  That is, when the liquid in the ink container is empty and the liquid remains in the cavity 43 of the piezoelectric device 60, the condition that the piezoelectric device 60 can accurately detect the liquid state is that M'cav is M'max. Is smaller than that. It should be noted that the condition M′max> M′cav that allows the piezoelectric device 60 to accurately detect the liquid state is not related to the shape of the cavity 43.

Here, M′cav is the mass inertance of the liquid having a volume approximately equal to the volume of the cavity 43. Therefore, from the inequality M′max> M′cav, the condition that the piezoelectric device 60 can accurately detect the liquid state can be expressed as the capacity condition of the cavity 43. For example, if the radius of the circular cavity 43 is a and the depth of the cavity 43 is d,
M′max> ρ * d / πa ₂ (Formula 10)
It is. When formula 10 is expanded, a / d> 3 * π / 8 (formula 11)
This condition is required. Therefore, if the piezoelectric device 60 has the cavity 43 that has the radius a of the opening 161 and the depth d of the cavity 43 satisfying Expression 11, the liquid in the ink container is empty and the cavity 43 has Even when the liquid remains, the state of the liquid can be detected without malfunction.

In addition, Formula 10 and Formula 11 are materialized only when the shape of the cavity 43 is circular. When the shape of the cavity 43 is not circular, the corresponding M′max formula is used, and πa ₂ in the formula 10 is replaced with the area, and the relationship between the dimensions such as the width and length of the cavity 43 and the depth is calculated. Can be derived.

  Since the additional inertance M ′ also affects the acoustic impedance characteristic, it can be said that the method of measuring the counter electromotive force generated in the piezoelectric device 60 due to residual vibration detects at least a change in acoustic impedance.

  6A and 6B show a residual vibration waveform of the piezoelectric device 60 and a method for measuring the residual vibration after a drive signal is supplied to the piezoelectric device 60 to vibrate the vibration part. The upper and lower levels of the ink level at the mounting position level of the piezoelectric device 60 in the ink cartridge can be detected by a change in the frequency or amplitude of the residual vibration after the piezoelectric device 60 oscillates. 6A and 6B, the vertical axis represents the voltage of the counter electromotive force generated by the residual vibration of the piezoelectric device 60, and the horizontal axis represents time. The residual vibration of the piezoelectric device 60 generates a voltage analog signal waveform as shown in FIGS. 6 (A) and 6 (B). Next, the analog signal is converted (binarized) into a digital numerical value corresponding to the frequency of the signal. In the example shown in FIGS. 6A and 6B, the time when four pulses from the fourth pulse to the eighth pulse of the analog signal are generated is measured.

  More specifically, after the piezoelectric device 60 oscillates, the number of times a predetermined reference voltage set in advance is crossed from the low voltage side to the high voltage side is counted. Then, a digital signal is generated with High between 4 counts and 8 counts, and the time from 4 counts to 8 counts is measured by a predetermined clock pulse.

  FIG. 6A shows a waveform when the ink level is higher than the mounting position level of the piezoelectric device 60. On the other hand, FIG. 6B shows a waveform when there is no ink at the mounting position level of the piezoelectric device 60. Comparing FIG. 6A and FIG. 6B, it can be seen that FIG. 6A has a longer time from 4 to 8 counts than FIG. 6B. In other words, the required time from 4 counts to 8 counts varies depending on the presence or absence of ink. The consumption state of ink can be detected using the difference in the required time.

  The reason for counting from the fourth count of the analog waveform is to start measurement after the vibration of the piezoelectric device 60 is stabilized. The count from the fourth count is merely an example, and the count may be counted from an arbitrary count. Here, signals from the 4th count to the 8th count are detected, and the time from the 4th count to the 8th count is measured by a predetermined clock pulse. Based on this time, the resonance frequency can be determined. The clock pulse does not need to be measured until the eighth count, and may be counted up to an arbitrary count. In FIG. 6, the time from the 4th count to the 8th count is measured, but the time within different count intervals may be detected according to the circuit configuration for detecting the frequency.

  For example, when the ink quality is stable and the fluctuation of the peak amplitude is small, the resonance frequency may be obtained by detecting the time from the 4th count to the 6th count in order to increase the detection speed. . When the ink quality is unstable and the fluctuation of the pulse amplitude is large, the time from the 4th count to the 12th count may be detected in order to accurately detect the residual vibration.

  FIG. 7 is a perspective view showing a configuration in which the piezoelectric device 60 is integrally formed as the mounting module body 100. The module body 100 is attached to a predetermined portion of the ink container of the ink cartridge. The module body 100 is configured to detect the consumption state of the liquid in the ink container by detecting at least a change in acoustic impedance of the medium in the ink container.

  The module body 100 of the present embodiment has an ink container mounting portion 101 for mounting the piezoelectric device 60 to the ink container. The ink container mounting portion 101 includes a base 102 having a substantially rectangular plane, and a cylindrical portion 116 on the base 102 that houses the piezoelectric device 60 that oscillates in response to a drive signal. Further, the module body 100 is configured such that the piezoelectric device 60 of the module body 100 cannot be contacted from the outside when mounted on the ink cartridge. Thereby, the piezoelectric device 60 can be protected from external contact. The leading edge of the cylindrical portion 116 is rounded so that it can be easily fitted into a hole formed in the ink cartridge.

  FIG. 8 is an exploded view of the module body 100 shown in FIG. The module body 100 includes an ink container mounting portion 101 made of resin, and a piezoelectric device mounting portion 105 (see FIG. 7) having a plate 110 and a recess 113. Furthermore, the module body 100 includes lead wires 104a and 104b, a piezoelectric device 60, and a film. Preferably, the plate 110 is made of a material that hardly rusts, such as stainless steel or a stainless alloy.

  The cylindrical portion 116 and the base 102 included in the ink container mounting portion 101 are formed with an opening 114 at the center so that the lead wires 104a and 104b can be accommodated, and the piezoelectric device 60, the film 108, and the plate 110 are provided. A recess 113 is formed around the opening 114 so as to be accommodated.

  The piezoelectric device 60 is joined to the plate 110 via the film 108, and the plate 110 and the piezoelectric device 60 are fixed to the recess 113 (ink container mounting portion 101). Accordingly, the lead wires 104 a and 104 b, the piezoelectric device 60, the film 108, and the plate 110 are attached integrally to the ink container attaching portion 101.

  The lead wires 104a and 104b are coupled to the upper electrode terminal 45 and the lower electrode terminal 44 of the piezoelectric device 60, respectively, to transmit a drive signal to the piezoelectric layer 47, while recording a signal having a resonance frequency detected by the piezoelectric device 60. Communicate to etc.

  The piezoelectric device 60 oscillates temporarily based on the drive signal transmitted from the lead wires 104a and 104b. Further, the piezoelectric device 60 undergoes residual vibration after oscillation, and generates back electromotive force by the vibration. At this time, the resonance frequency corresponding to the liquid consumption state in the ink container can be detected by detecting the vibration period of the back electromotive force waveform.

  The film 108 bonds the piezoelectric device 60 and the plate 110 to make the piezoelectric device 60 liquid-tight. The film 108 is preferably formed of polyolefin or the like and bonded by heat fusion. By bonding and fixing the piezoelectric device 60 and the plate 110 in a planar shape with the film 108, there is no variation depending on the location of bonding, and portions other than the vibrating portion do not vibrate. Therefore, even if the piezoelectric device 60 is bonded to the plate 110, the vibration characteristics of the piezoelectric device 60 do not change.

  The plate 110 has a circular shape, and the opening 114 of the base 102 is formed in a cylindrical shape. The piezoelectric device 60 and the film 108 are formed in a rectangular shape. The lead wires 104 a and 104 b, the piezoelectric device 60, the film 108, and the plate 110 may be detachable from the base 102. The base 102, the lead wires 104 a and 104 b, the piezoelectric device 60, the film 108 and the plate 110 are arranged symmetrically with respect to the central axis of the module body 100. The centers of the base 102, the piezoelectric device 60, the film 108, and the plate 110 are disposed on the substantially central axis of the module body 100.

  The area of the opening 114 of the base 102 is formed larger than the area of the vibration region of the piezoelectric device 60. A through hole 112 is formed at a position facing the vibrating portion of the piezoelectric device 60 at the center of the plate 110. As shown in FIGS. 2 to 4, a cavity 43 is formed in the piezoelectric device 60, and the through hole 112 and the cavity 43 together form an ink reservoir. The thickness of the plate 110 is preferably smaller than the diameter of the through hole 112 in order to reduce the influence of residual ink. For example, it is preferable that the depth of the through hole 112 is not more than one third of the diameter. The through-hole 112 has a substantially perfect circular shape that is symmetric with respect to the central axis of the module body 100. Further, the area of the through hole 112 is larger than the opening area of the cavity 43 of the piezoelectric device 60. The peripheral edge of the cross section of the through hole 112 may be tapered or stepped.

  The module body 100 is mounted on the side, top, or bottom of the ink container so that the through hole 112 faces the inside of the ink container. When the ink is consumed and the ink around the piezoelectric device 60 is used up, a change in the ink level can be detected based on a large change in the resonance frequency of the piezoelectric device 60.

  FIG. 9 is a cross-sectional view of the vicinity of the bottom of the ink container 20 when the module body 100 shown in FIG. 7 is attached to the ink container 20 of the ink cartridge 7. The module body 100 is mounted in a through hole formed in the side wall of the ink container 20. An O-ring 90 is provided on the joint surface between the side wall of the ink container 20 and the module body 100, and the module body 100 and the ink container 20 are kept liquid-tight. Since the O-ring 90 can be sealed as described above, the module body 100 preferably includes a cylindrical portion as described with reference to FIG.

  When the tip of the module body 100 is exposed to the ink storage space 20 a of the ink container 20, the ink in the ink container 20 comes into contact with the piezoelectric device 60 through the through hole 112 of the plate 110. Since the resonance frequency of the residual vibration of the piezoelectric device 60 differs depending on whether the vibration part of the piezoelectric device 60 is liquid or gas, the ink consumption state can be detected using the module body 100.

  Next, as a modification of the embodiment shown in FIGS. 2 and 3, the protrusion 48 a of the auxiliary electrode layer 48 is formed to be narrower than the extension 47 b of the piezoelectric layer 47 as shown in FIG. 10. You may do it.

  In this way, the area of the auxiliary electrode layer 48 that overlaps the region corresponding to the cavity 43 is reduced, so that the vibration characteristics of the piezoelectric device 60 can be improved. Further, since the necessary amount of the material for forming the auxiliary electrode layer 48 can be reduced, the manufacturing cost can also be reduced.

  As another modified example, as shown in FIG. 11, the protruding portion 48 a of the auxiliary electrode layer 48 can be formed wider than the extending portion 47 b of the piezoelectric layer 47. Thereby, the peripheral part of the cavity 43 can be reinforced.

Furthermore, as another modified example, as shown in FIGS. 12 to 14, the lower electrode layer 46, the upper electrode layer 49, and the auxiliary electrode layer 48 are entirely arranged at the center of the main body portion 47a of the piezoelectric layer 47. It can be formed in a substantially symmetric shape having symmetric axes O ₁ and O ₂ passing therethrough. Thus, the vibration characteristics of the piezoelectric device 60 can be improved by arranging the plurality of members constituting the piezoelectric device 60 in a symmetrical shape as a whole. In particular, the vibration characteristics of the piezoelectric device 60 are improved by making the lower electrode layer 46, the upper electrode layer 49, and the auxiliary electrode layer 48 located in a region corresponding to the cavity 43 symmetrical as a whole.

  Next, a piezoelectric device according to another embodiment of the present invention will be described with reference to FIG. In the following description, parts different from the embodiment shown in FIGS. 2 and 3 will be described.

  As shown in FIG. 15, in the piezoelectric device 70 according to the present embodiment, the lower electrode layer 46 is located at a position corresponding to the peripheral edge 43 a of the cavity 43 from the circular main body portion 46 a located in the region corresponding to the cavity 43. And an extending portion 46 c extending toward the auxiliary electrode layer 48. On the other hand, the auxiliary electrode layer 48 is entirely formed outside the region corresponding to the cavity 43. The insulating gap 50 is formed between the extended portion 46 c of the lower electrode layer 46 and the auxiliary electrode layer 48, and the entire insulating gap 50 is located outside the region corresponding to the cavity 43. Yes.

  Thus, by positioning the whole insulating gap 50 outside the region corresponding to the cavity 43, when the vibrating portion is vibrated by driving the piezoelectric device 70, the position is corresponding to the peripheral edge 43 a of the cavity 43. Stress concentration generated in the piezoelectric layer 47 can be significantly suppressed. For this reason, the generation of cracks in the piezoelectric layer 47 and the upper electrode layer 49 can be prevented.

As a modification of the embodiment shown in FIG. 15, as shown in FIG. 16, the lower electrode layer 46, the upper electrode layer 49, and the auxiliary electrode layer 48 as a whole are arranged at the center of the main body portion 47 a of the piezoelectric layer 47. Can be formed in a substantially symmetric shape having symmetry axes O ₁ and O ₂ passing through. Thus, the vibration characteristics of the piezoelectric device 70 can be improved by arranging the plurality of members constituting the piezoelectric device 70 in a symmetrical shape as a whole. In particular, the vibration characteristics of the piezoelectric device 70 are improved by making the lower electrode layer 46, the upper electrode layer 49, and the auxiliary electrode layer 48 located in a region corresponding to the cavity 43 symmetrical as a whole.

  In particular, in the present modification, the insulating gap 50 is positioned outside the region corresponding to the cavity 43, so that the portions of the lower electrode layer 46, the upper electrode layer 49, and the portion positioned in the region corresponding to the cavity 43, As a result, the symmetry of the auxiliary electrode layer 48 as a whole increases, and as a result, vibration characteristics can be further improved.

Next, as another embodiment of the present invention, in each of the above-described embodiments and modifications, the shape of the piezoelectric layer 47 in the region corresponding to the cavity 43 is changed to the shape of the main body portion 47 a of the piezoelectric layer 47. The shape may be substantially symmetrical with at least one axis of symmetry passing through the center. More preferably, the shape of the portion of the piezoelectric layer 47 located in the region corresponding to the cavity 43 is divided into a first symmetry axis O ₁ extending along the extending direction of the extending portion 47 b of the piezoelectric layer 47, and the first symmetry axis. A substantially symmetrical shape having a _second axis of symmetry O ₂ orthogonal to O ₁ is formed.

  17 shows an example in which the shape of the piezoelectric layer 47 is changed in the above example shown in FIG. 14, and FIG. 18 shows an example in which the shape of the piezoelectric layer 47 is changed in the above example shown in FIG. Yes.

In the example shown in FIGS. 17 and 18, the piezoelectric layer 47, the lower electrode layer 46, the upper electrode layer 49, and the auxiliary electrode layer 48 as a whole have an axis of symmetry O passing through the center of the main body portion 47 a of the piezoelectric layer 47. ₁ and O ₂ are formed in a substantially symmetrical shape. Thus, the vibration characteristics of the piezoelectric device 60 can be improved by arranging the plurality of members constituting the piezoelectric device 60 in a symmetrical shape as a whole. In particular, the vibration characteristics of the piezoelectric device 60 are improved by making the piezoelectric layer 47, the lower electrode layer 46, the upper electrode layer 49, and the auxiliary electrode layer 48 located in a region corresponding to the cavity 43 symmetrical as a whole. To do.

  In particular, since the piezoelectric layer 47 has a relatively large mass compared to the lower electrode layer 46, the upper electrode layer 49, and the auxiliary electrode layer 48, vibration characteristics are greatly improved by making the piezoelectric layer 47 symmetrical. Can be improved.

1 is a perspective view illustrating a schematic configuration of an ink jet recording apparatus in which an ink cartridge according to an embodiment of the present invention is used. It is a figure which shows the piezoelectric device in one Embodiment of this invention. It is sectional drawing which expanded and showed a part of piezoelectric device shown in FIG. It is a figure which shows the periphery of the piezoelectric device shown in FIG.2 and FIG.3, and its equivalent circuit. It is a figure which shows the relationship between the resonant frequency of the ink detected by the piezoelectric apparatus shown in FIG.2 and FIG.3, and the density of ink. It is a figure which shows the back electromotive force waveform of the piezoelectric apparatus shown in FIG.2 and FIG.3. It is a perspective view which shows the module body incorporating the piezoelectric device shown in FIG.2 and FIG.3. It is an exploded view which shows the structure of the module body shown in FIG. It is a figure which shows the example of the cross section which mounted | wore the ink container of the ink cartridge with the module body shown in FIG. It is the figure which showed the piezoelectric device by the modification of embodiment shown in FIG.2 and FIG.3. It is the figure which showed the piezoelectric device by the other modification of embodiment shown in FIG.2 and FIG.3. It is the figure which showed the piezoelectric device by the other modification of embodiment shown in FIG.2 and FIG.3. It is the figure which showed the piezoelectric device by the other modification of embodiment shown in FIG.2 and FIG.3. It is the figure which showed the piezoelectric device by the other modification of embodiment shown in FIG.2 and FIG.3. It is the figure which showed the piezoelectric device by other embodiment of this invention. FIG. 16 is a view showing a piezoelectric device according to a modification of the embodiment shown in FIG. 15. It is the figure which showed the suitable example of the piezoelectric device by other embodiment of this invention. It is the figure which showed the other suitable example of the piezoelectric device by other embodiment of this invention. It is the figure which showed the conventional piezoelectric device. It is sectional drawing which expanded and showed a part of conventional piezoelectric device shown in FIG.

Explanation of symbols

7 Ink cartridge 20 Ink container 46 Lower electrode layer 46a Lower electrode layer body portion 46b Lower electrode layer extension portion 47 Piezoelectric layer 47a Piezoelectric layer body portion 47b Piezoelectric layer extension portion 48 Auxiliary electrode layer 48a Auxiliary electrode layer Projection 49 Upper electrode layer 49a Upper electrode layer main body 49b Upper electrode layer extension 60, 70 Piezoelectric device

Claims (3)

A base portion having a first surface and a second surface facing each other, and a cavity for receiving a medium to be detected is formed so as to open to the first surface side, and the bottom surface portion of the cavity can vibrate A base formed in the
A first electrode layer formed on the second surface side and including a main body formed in a region corresponding to the cavity;
A piezoelectric layer laminated on the first electrode layer, the main body formed in a region corresponding to the cavity, and an extension extending from the main body beyond a position corresponding to the periphery of the cavity And a piezoelectric layer having
An auxiliary electrode layer that is formed on the second surface side of the base portion, and at least a part of the auxiliary electrode layer is located between the second surface and the extension portion of the piezoelectric layer and supports the extension portion of the piezoelectric layer. When,
A second electrode layer laminated on the piezoelectric layer and connected to the auxiliary electrode layer,
The portion of the first electrode layer, the second electrode layer, and the auxiliary electrode layer located in a region corresponding to the cavity has a symmetry axis defined in the plane of the second surface as a whole, and The piezoelectric layer has a symmetrical shape having two symmetry axes that pass through the center of the main body portion and are orthogonal to each other, and the two symmetry axes extend along the extending direction of the extending portion of the piezoelectric layer. And a second symmetry axis perpendicular to the first symmetry axis. A piezoelectric device comprising:   2. The piezoelectric device according to claim 1, wherein a portion of the piezoelectric layer located in a region corresponding to the cavity has a symmetrical shape having the two symmetry axes. In an ink cartridge used in an ink jet recording apparatus,
An ink container for containing ink;
A piezoelectric device according to claim 1 or 2,
An ink cartridge, wherein the cavity of the piezoelectric device is disposed so as to be in contact with ink in an ink cartridge.

Images