JP6056522B2 - Inkjet head and inkjet printer equipped with the same - Google Patents

Description

  The present invention relates to an inkjet head including a piezoelectric element that discharges ink from a pressure chamber, and an inkjet printer including the inkjet head.

  2. Description of the Related Art Conventionally, an ink jet printer including an ink jet head having a plurality of channels (pressure chambers) for discharging ink is known. By controlling the ejection of ink while moving the inkjet head relative to a recording medium such as paper or cloth, a two-dimensional image can be output to the recording medium. Ink can be ejected by using an actuator (piezoelectric, electrostatic, thermal deformation, etc.) or by generating bubbles in the ink in the tube by heat. Among them, the piezoelectric actuator has advantages such as high output, modulation, high responsiveness, and choice of ink, and has been frequently used in recent years.

  FIG. 9 is a plan view of a conventional piezoelectric actuator 100 and a cross-sectional view taken along line A-A ′. The piezoelectric actuator 100 is configured by laminating an insulating layer 102, a lower electrode 103, a piezoelectric film 104, and an upper electrode 105 in this order on a substrate 101 having a pressure chamber 101a. The upper wall 101b of the pressure chamber 101a in the substrate 101 constitutes a driven film and is displaced as the piezoelectric film 104 expands and contracts.

  That is, when a voltage is applied from the drive circuit 106 to the lower electrode 103 and the upper electrode 105 and the piezoelectric film 104 expands and contracts, a curvature is generated in the driven film due to a difference in length between the piezoelectric film 104 and the driven film. Displacement in the direction perpendicular to the membrane. Thereby, the ink in the pressure chamber 101a is discharged to the outside. By arranging such piezoelectric actuators 100 in the horizontal direction, an ink jet head is configured.

By the way, perovskite-type metal oxides such as BaTiO ₃ and Pb (Ti / Zr) O ₃ called PZT are widely used for piezoelectric bodies used in piezoelectric actuators. FIG. 10 shows the microscopic crystal structure of PZT.

  In PZT, two types are known: a bulk type in which a powder material is fired, and a thin film type in which a film is formed from a gas phase or a liquid phase. FIG. 11 shows macroscopic crystal structures of bulk type and thin film type PZT. Both the bulk type and the thin film type are polycrystalline bodies in which crystal grains 201 of several micron level gather together, and a grain boundary 201a exists in the gap between adjacent crystal grains 201. At the grain boundary 201a, the crystal structure becomes discontinuous and the composition becomes non-uniform (excessive elements or defects), so that the crystallinity is lowered.

  In addition, the piezoelectric body, which is a metal oxide, is easily reduced due to the effects of peripheral moisture, the catalytic effect of Pt and Au, which are metal materials used as electrodes, and the applied electric field. When the piezoelectric body is reduced, the properties of the metal become stronger and the insulating properties are lowered, so that failure due to pinholes and voltage leakage occurs.

  Further, the crystallinity of the interface between the piezoelectric body and the lower layer (for example, the lower electrode) is lowered similarly to the grain boundary, and when the piezoelectric body is reduced, the adhesiveness with the lower layer is lowered and a failure due to peeling occurs. In particular, when continuously driven in a high-temperature and high-humidity environment, failure due to peeling tends to occur at the periphery of the piezoelectric body or electrode.

  FIG. 12 shows an example of an actuator failure. The upper diagram shows a state in which a pinhole 302a is generated in the piezoelectric body 302 due to the reduction of PZT. When such a pinhole 302 a is generated, a current leak occurs between the lower electrode 301 and the upper electrode 303. Further, the lower diagram shows a state in which the piezoelectric body 302 is peeled from the lower electrode 301 at the periphery by reduction of PZT.

  In order to suppress the reduction of the piezoelectric body, a method of shielding the piezoelectric body from the outside air with a seal or the like has been proposed, but due to initial defects such as pinholes and deterioration of the material over time, moisture gradually enters the piezoelectric body someday. Will damage the piezoelectric body.

  In view of this, there is known a technique for suppressing deterioration or damage of the piezoelectric body or the like by detecting or controlling the humidity in the arrangement space of the piezoelectric body or the piezoelectric element. For example, in Patent Document 1, when the piezoelectric body is driven, the humidity holding means is operated to keep the humidity near the piezoelectric body constant, and when the piezoelectric body is not driven, the humidity holding means is not driven. In this way, by adjusting the humidity only when necessary, deterioration of the piezoelectric body is suppressed and excessive power consumption is suppressed.

  In Patent Document 2, a sealing case that houses a piezoelectric element and a drying unit that dries the inside of the sealing case are connected, and the humidity in the sealing case is measured by a capacitance-type humidity sensor. When the humidity in the stop case tends to increase, the user is notified of the replacement of the drying unit. Accordingly, the drying system is maintained in an appropriate humidity range to suppress the dielectric breakdown of the piezoelectric element, and the piezoelectric element is stably driven for a long time.

  In Patent Document 3, a piezoelectric element is surrounded by a dummy element, and a sealing material is poured into the area surrounded by the dummy element to seal the piezoelectric element, thereby ensuring moisture resistance of the piezoelectric element and preventing dielectric breakdown. I am doing so.

  In Patent Document 4, dry gas is supplied from an air supply hole into a piezoelectric element holding part that protects the piezoelectric element, and gas existing in the piezoelectric element holding part is discharged through an exhaust hole to ventilate the piezoelectric element holding part. Accordingly, the inside of the piezoelectric element holding portion is always maintained at a low humidity, and destruction of the piezoelectric element is prevented for a long period of time.

  In Patent Document 5, a second piezoelectric body for dielectric constant detection is provided separately from the first piezoelectric body for ink ejection, and the dielectric constant sensor detects a change in the dielectric constant of the second piezoelectric body. ing. When a decrease in the dielectric constant of the second piezoelectric body is detected, it can be determined that the hygroscopic property of the hygroscopic agent in the sealed space is lowered and the humidity in the sealed space is increased. Therefore, the dielectric breakdown due to moisture can be prevented by determining the replacement timing of the hygroscopic agent based on the change in the dielectric constant of the second piezoelectric body and prompting the replacement of the hygroscopic agent.

Japanese Patent Laying-Open No. 2011-135001 (see claim 1, paragraphs [0009], [0026], etc.) JP 2009-262421 A (refer to claim 1, paragraphs [0017], [0019], [0143] to [0145], FIG. 9, etc.) JP 2007-237474 A (see claims 1 and 8, paragraphs [0004], [0006], [0023], etc.) Japanese Patent Laying-Open No. 2005-74966 (see claim 1, paragraphs [0008], [0009], etc.) Japanese Unexamined Patent Application Publication No. 2004-25476 (see claims 1, 6, 9, paragraphs [0020], [0025], [0027], [0040], [0075], [0078], etc.)

  By the way, in order to prevent a fatal defect such as ink non-ejection due to a failure of the piezoelectric element, it is necessary to prompt replacement of parts before the failure of the piezoelectric element. It is necessary to predict the occurrence of the failure in advance.

  However, a piezoelectric element failure may occur not only when the ambient humidity is high, but also suddenly due to factors other than humidity, such as the deterioration of film quality over a long period of time, even if the ambient humidity is low. It is generally difficult to predict the occurrence. Even if the lifetime of the piezoelectric element (the number of times it can be repeatedly driven and the driveable time) is determined in advance, the method of deterioration of the piezoelectric element varies depending on the actual usage environment and usage conditions. Does not always meet the prescribed lifetime.

  In this respect, the above-mentioned Patent Documents 1 to 5 only control the humidity around the piezoelectric element using a humidity sensor or the like to suppress deterioration of the piezoelectric element, and predict the occurrence of a failure of the piezoelectric element in advance. In addition, it is not possible to predict the sudden failure of the piezoelectric element including factors other than humidity. Therefore, it is impossible to prevent the occurrence of a fatal defect such as non-ejection of ink by prompting replacement of parts before failure of the piezoelectric element.

  In Patent Document 5, as described above, it is necessary to replace the hygroscopic agent by providing a second piezoelectric body different from the first piezoelectric body for ejecting ink and detecting a change in dielectric constant. However, in order to prevent dielectric breakdown of the second piezoelectric body, the drive voltage is suppressed to 1/10 or less of the maximum voltage. Thus, since the second piezoelectric body is driven at a low voltage and its lifetime seems to be longer than that of the first piezoelectric body (because the first piezoelectric body has a shorter lifetime), the second piezoelectric body When the dielectric constant decreases, there is a high possibility that the first piezoelectric body has already deteriorated. Therefore, the occurrence of a failure in the first piezoelectric body cannot be predicted based on the change in the dielectric constant of the second piezoelectric body.

  The present invention has been made to solve the above-described problems, and its purpose is to predict the occurrence of a failure of a piezoelectric element that ejects ink in consideration of not only humidity but also other failure factors. An ink jet head capable of preventing a fatal defect such as non-ejection of ink by prompting replacement of parts before failure of the ink ejecting piezoelectric element, and an ink jet printer including the ink jet head And to provide.

  An ink jet head according to one aspect of the present invention is an ink jet head for ejecting ink, the ink ejecting piezoelectric element, a monitor piezoelectric element for monitoring a failure of the ink ejecting piezoelectric element, and the ink ejecting A piezoelectric element for driving and a driving unit for repeatedly driving the piezoelectric element for monitoring, and the driving unit is more electrically and mechanically broken during the repeated driving of the piezoelectric element for monitoring than the piezoelectric element for discharging ink. In this configuration, the ink ejection piezoelectric element and the monitor piezoelectric element are driven under a driving condition in which the resistance to the ink is low.

  Due to the drive unit, the monitor piezoelectric element is repeatedly operated under a driving condition such that the resistance to electrical breakdown (for example, current leakage) and mechanical breakdown (for example, film peeling) during repeated driving is lower than the piezoelectric element for ink discharge. Since it is driven, it will fail earlier than the ink ejection piezoelectric element, and from this failure of the monitoring piezoelectric element, it is possible to predict the occurrence of the failure of the ink ejection piezoelectric element. That is, even if a dedicated sensor for monitoring deterioration of the piezoelectric element such as a humidity sensor is not used, it is possible to predict that the failure of the ink ejecting piezoelectric element is near by using the monitoring piezoelectric element instead of the sensor.

  In addition, the actual failure factors of the piezoelectric element for monitoring include not only humidity but also other factors (such as deterioration of film quality over time). In the same head, the piezoelectric element for ink ejection is similar. It can be considered that it is affected by the failure factor. Therefore, the failure of the ink ejection piezoelectric element can be predicted based on the failure of the monitor piezoelectric element, taking into account all the failure factors other than humidity, and ink ejection is much more accurate than when using a humidity sensor. It is possible to predict the failure of the piezoelectric element for use.

  As a result, it is possible to prevent a fatal defect such as non-ejection of ink by urging the user to replace parts (head replacement) before failure of the ink ejection piezoelectric element.

  The drive unit may drive the monitor piezoelectric element with a drive voltage higher than the ink discharge piezoelectric element. The drive unit may drive the monitor piezoelectric element for a longer drive time than the ink ejection piezoelectric element.

  Under any of the above driving conditions, the resistance of the monitoring piezoelectric element against electrical or mechanical breakdown during repeated driving can be made lower than that of the ink discharging piezoelectric element.

  An ink jet printer according to another aspect of the present invention includes the above-described ink jet head, and has a configuration in which a failure of the ink ejection piezoelectric element is notified based on the failure of the monitor piezoelectric element of the ink jet head.

  According to this configuration, it is possible to prevent a fatal defect such as ink non-ejection by prompting the user to replace the head before the failure by notifying the failure of the piezoelectric element for ink ejection.

  The inkjet printer includes a failure detection unit that detects a failure of the monitor piezoelectric element when the ink ejection piezoelectric element and the monitor piezoelectric element of the inkjet head are repeatedly driven, and the failure detection unit includes the monitor piezoelectric element. When a failure of the element is detected, a failure notification unit that notifies the outside may be provided.

  In this case, when the failure detection unit detects a failure of the monitoring piezoelectric element, the failure notification unit notifies the outside, so that the user can perform the head replacement work based on the notification, thereby the ink It is possible to prevent a fatal defect such as non-ejection from occurring.

  According to the above configuration, in consideration of not only humidity but also other failure factors, it is possible to predict the occurrence of failure of the ink ejection piezoelectric element with high accuracy based on the occurrence of failure of the monitoring piezoelectric element. Accordingly, it is possible to prompt parts to be replaced before failure of the ink discharge piezoelectric element, and to prevent a fatal defect such as ink non-discharge.

1 is an enlarged perspective view showing a part of an inkjet printer according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a schematic configuration of the inkjet printer. It is a top view which shows the structure of the principal part of the inkjet head with which the said inkjet printer is provided. FIG. 4 is a cross-sectional view taken along line A-A ′ in FIG. 3. It is a graph which shows the drive voltage (applied voltage) of the piezoelectric element for ink discharge of the said inkjet head, and the piezoelectric element for a monitor. It is a graph which shows the drive time (voltage application time) of the said piezoelectric element for ink discharge and the said piezoelectric element for a monitor. It is sectional drawing which shows the manufacturing process of the said piezoelectric element for ink discharge. It is sectional drawing which shows the other structure of the principal part of the said inkjet head. It is the top view and A-A 'arrow sectional drawing of the conventional piezoelectric actuator. It is explanatory drawing which shows typically the microcrystal structure of PZT. It is explanatory drawing which shows typically the macroscopic crystal structure of each of bulk type and thin film type PZT. It is sectional drawing which shows an example of a failure of an actuator.

  An embodiment of the present invention will be described below with reference to the drawings. In the present embodiment, a monitor piezoelectric element is provided in the inkjet head separately from the ink discharge piezoelectric element, and the monitor piezoelectric element is installed under a drive condition (drive voltage, drive time) that causes failure earlier than the ink discharge piezoelectric element. By driving, it is possible to predict the future failure of the ink discharge piezoelectric element from the occurrence of the failure of the monitor piezoelectric element, and to prompt the head replacement in advance, so that a fatal defect such as ink non-discharge Try to prevent. This will be specifically described below.

[Configuration of inkjet printer and inkjet head]
FIG. 1 is an enlarged perspective view showing a part of an ink jet printer 1 of the present embodiment. The inkjet printer 1 has a carriage 1b that can move in the left-right direction (B direction in the figure) in a housing 1a that is partially open. On the carriage 1b, inkjet heads 10 corresponding to each of a plurality of colors (for example, four colors of yellow, magenta, cyan, and black) are mounted in a line. While conveying a recording medium (not shown) from the back side to the front side (A direction in the figure) of the printer, the carriage 1b is moved left and right to eject ink of each color from the corresponding inkjet head 10, thereby recording the recording medium. A color image can be formed thereon.

  FIG. 2 is a block diagram showing a schematic configuration of the ink jet printer 1. The ink jet printer 1 gives a notice of a failure of the ink discharge piezoelectric element 2 based on the failure of the monitor piezoelectric element 3, and in addition to the ink discharge piezoelectric element 2 and the monitor piezoelectric element 3, a drive unit 4, a failure detection unit 5, a failure time determination unit 6, and a failure notification unit 7. The ink jet piezoelectric element 2, the monitor piezoelectric element 3, and the drive unit 4 constitute an ink jet head 10.

  The ink ejection piezoelectric element 2 is a piezoelectric element that ejects ink from the pressure chamber 11a (see FIG. 4) toward the recording medium. The monitor piezoelectric element 3 is a piezoelectric element for monitoring a failure of the ink ejection piezoelectric element 2. The drive unit 4 is a drive circuit that applies voltage to the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3 to repeatedly (continuously) drive them. In the present embodiment, the drive unit 4 is configured so that the monitor piezoelectric element 3 is less resistant to electrical and mechanical breakdown during repeated driving than the ink discharge piezoelectric element 2 under the driving conditions. The element 2 and the monitoring piezoelectric element 3 are driven, and details thereof will be described later.

  The failure detection unit 5 detects a failure of the monitoring piezoelectric element 3 when the driving unit 4 repeatedly drives the ink ejection piezoelectric element 2 and the monitoring piezoelectric element 3. For example, an LCR meter, a bridge circuit, etc. It is comprised with the well-known dielectric evaluation apparatus. By measuring the internal resistance, dielectric loss (tan δ), capacitance (dielectric constant), resonance frequency, etc. of the piezoelectric layer 14 (see FIG. 4) of the monitoring piezoelectric element 3 with such a dielectric evaluation device, It is possible to detect the presence or absence of a failure such as current leakage or peeling in the piezoelectric layer 14.

  That is, when current leakage increases in the piezoelectric layer 14, the internal resistance of the piezoelectric layer 14 decreases and the dielectric loss increases. Further, when current leakage or peeling increases, the capacitance (dielectric constant) decreases. Further, when the piezoelectric layer 14 is peeled off, the resonance frequency is lowered. Therefore, by detecting the internal resistance, dielectric loss, capacitance, and resonance frequency of the piezoelectric layer 14, it is possible to detect the presence or absence of current leakage or peeling.

  The failure time determination unit 6 determines (predicts) the failure time of the ink ejection piezoelectric element 2 based on the detection result of the failure detection unit 5, and includes a control unit such as a CPU (Central Processing Unit). , And a storage unit. For example, when the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3 are repeatedly driven by a prior test, the drive time from the failure of the monitor piezoelectric element 3 to the failure of the ink ejection piezoelectric element 2 is calculated. If measurement is performed and the drive time is stored in the storage unit as an initial value, when the monitor piezoelectric element 3 fails during actual use (image drawing), the monitor piezoelectric element 3 fails. The date and time obtained by adding the time stored in the storage unit to the date and time of occurrence can be predicted as the time when the failure of the piezoelectric element 2 for ink ejection occurs.

  The drive time of the ink ejection piezoelectric element 2 at the time of image drawing differs for each channel (corresponding to the pressure chamber 11a) according to the image to be drawn. Therefore, the drive time is stored in the storage unit for each channel. The failure time of the ink ejection piezoelectric element 2 is predicted for each channel from the failure time of the monitoring piezoelectric element 3, and the failure time in the channel with the earliest failure time is determined as the failure time of the ink ejection piezoelectric element 2 itself (head May be predicted.

  The failure notifying unit 7 notifies the outside of the failure of the monitoring piezoelectric element 3 based on a control signal from the failure timing determining unit 6 when the failure detecting unit 5 detects a failure of the monitoring piezoelectric element 3. There are, for example, an LED, a (liquid crystal) display unit, a ringing unit, and the like. That is, when the failure detection unit 5 detects a failure, the failure notification unit 7 turns on the LED, displays the fact that the failure has occurred on the display unit, or emits a buzzer or sound to the outside. The failure of the monitoring piezoelectric element 3 can be notified. By notifying such a failure, the user can recognize that the failure of the piezoelectric element 2 for ejecting ink is almost occurring, and can prompt the user to replace the inkjet head 10. Therefore, it is possible to prevent a fatal defect such as non-ejection of ink from the ink ejection piezoelectric element 2 from occurring due to such component replacement. Note that the failure notification unit 7 notifies (for example, displays) the failure time of the ink ejection piezoelectric element 2 predicted by the failure time determination unit 6 at the same time that the failure of the monitoring piezoelectric element 3 is notified. Good.

[Configuration of piezoelectric element]
Next, details of the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3 will be described. 3 is a plan view showing the configuration of the main part of the inkjet head 10, and FIG. 4 is a cross-sectional view taken along the line AA 'in FIG. In the plan view of FIG. 3, the monitor piezoelectric element 3 is hatched for the purpose of clearly distinguishing from the ink ejection piezoelectric element 2.

  The ink ejection piezoelectric element 2 is configured by laminating a thermal oxide film 12, a lower electrode 13, a piezoelectric layer 14, and an upper electrode 15 in this order on a substrate 11 having a pressure chamber 11a. The upper wall 11b of the pressure chamber 11a in the substrate 11 constitutes a driven film and is displaced as the piezoelectric layer 14 expands and contracts. The lower electrode 13 and the upper electrode 15 are connected to the drive unit 4 described above. In the substrate 11, a plurality of pressure chambers 11a are formed in a staggered manner and arranged in two rows.

  The monitor piezoelectric element 3 also has the same layer structure as the ink ejection piezoelectric element 2, and a thermal oxide film 12, a lower electrode 13, a piezoelectric layer 14 and an upper electrode 15 are arranged in this order on a substrate 11 having a pressure chamber 11a. It is configured by stacking. Also in the monitoring piezoelectric element 3, the upper wall 11 b of the pressure chamber 11 a in the substrate 11 forms a driven film and is displaced as the piezoelectric layer 14 expands and contracts. The lower electrode 13 and the upper electrode 15 are connected not only to the drive unit 4 described above but also to the failure detection unit 5. The pressure chambers 11a of the monitoring piezoelectric element 3 are located on both sides in the arrangement direction of the pressure chambers 11a of the ink ejection piezoelectric element 2.

  The substrate 11, the thermal oxide film 12, and the lower electrode 13 are common to the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3, and the piezoelectric layer 14 and the upper electrode 15 are formed in a staggered pattern on the substrate 11. It is formed corresponding to each pressure chamber 11a. That is, the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3 are configured by laminating the lower electrode 13, the piezoelectric layer 14, and the upper electrode 15 on the same substrate 11. Accordingly, it is possible to simultaneously manufacture the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3 in the same manufacturing process only by changing the patterning of the piezoelectric layer 14 and the upper electrode 15, thereby reducing the manufacturing cost. Details of the manufacturing method will be described later.

  In addition, each pressure chamber 11a of the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3 is connected to an ink flow path communicating with the common ink chamber, so that ink ejection is possible. In the piezoelectric element 2 for ink ejection and the piezoelectric element 3 for monitoring, when a voltage is applied from the driving unit 4 to the lower electrode 13 and the upper electrode 15 and the piezoelectric layer 14 expands and contracts, the difference in length between the piezoelectric layer 14 and the driven film Thus, a curvature is generated in the driven film, and the driven film is displaced in a direction perpendicular to the film. Thereby, the ink in the pressure chamber 11a is discharged outside.

  A member (sponge or shutter) that absorbs or blocks the ejected ink is disposed on the ink ejection side of the monitor piezoelectric element 3 so that the ink does not adhere to the recording medium. That is, the role of ejecting ink onto the recording medium to form an image is exclusively given to the ink ejecting piezoelectric element 2, and the monitoring piezoelectric element 3 does not have the role of performing image formation.

In each of the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3, the substrate 11 is configured by a semiconductor substrate made of a single crystal Si (silicon) or a SOI (Silicon on Insulator) substrate having a thickness of about 300 to 500 μm, for example. Has been. The thermal oxide film 12 is made of, for example, SiO ₂ (silicon oxide) having a thickness of about 0.1 μm, and is formed for the purpose of protecting and insulating the substrate 11.

  The lower electrode 13 is formed by laminating a Ti (titanium) layer and a Pt (platinum) layer. The Ti layer is formed in order to improve the adhesion between the thermal oxide film 12 and the Pt layer. The thickness of the Ti layer is, for example, about 0.02 μm, and the thickness of the Pt layer is, for example, about 0.1 μm.

The piezoelectric layer 14 is composed of a thin film of PZT (lead zirconate titanate) which is a solid solution of PTO (PbTiO ₃ ; lead titanate) and PZO (PbZrO ₃ ; lead zirconate). The film thickness of the piezoelectric layer 14 is, for example, 3 to 5 μm.

  The upper electrode 15 is configured by laminating a Ti layer and a Pt layer. The Ti layer is formed in order to improve the adhesion between the piezoelectric layer 14 and the Pt layer. The thickness of the Ti layer is about 0.02 μm, for example, and the thickness of the Pt layer is about 0.1 to 0.2 μm, for example.

  In the present embodiment, as described above, the driving unit 4 has a driving condition in which the monitoring piezoelectric element 3 is less resistant to electrical and mechanical breakdown during repeated driving than the ink discharging piezoelectric element 2. Thus, the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3 are driven. Specifically, the drive unit 4 drives the monitor piezoelectric element 3 with a drive voltage higher than that of the ink discharge piezoelectric element 2 as shown in FIG. 5, or the ink discharge piezoelectric element 2 as shown in FIG. The monitor piezoelectric element 3 is driven for a longer drive time.

  In the inkjet printer 1, since the ink is ejected according to the density of the image, the piezoelectric layer 14 corresponding to each channel of the ink ejecting piezoelectric element 2 is not always driven. Therefore, the driving time of the monitoring piezoelectric element 3 can be made longer than that of the ink discharging piezoelectric element 2 by always driving the monitoring piezoelectric element 3 when the printer is turned on. Further, by driving the monitoring piezoelectric element 3 between the pages to be drawn, while stopping the driving of the ink discharging piezoelectric element 2, the monitoring piezoelectric element 3 is driven more than the ink discharging piezoelectric element 2. Driving time can be lengthened.

  When the voltage application time to the piezoelectric layer 14 is constant, the higher the drive voltage, the greater the electric field strength, so that the reduction reaction is likely to proceed and the deterioration of the piezoelectric layer 14 is accelerated. Further, when the applied voltage to the piezoelectric layer 14 is constant, the reduction reaction in the piezoelectric layer 14 progresses as the driving time is longer, so that the deterioration of the piezoelectric layer 14 is accelerated. In any case, current leakage and peeling easily occur due to deterioration of the piezoelectric layer 14. Accordingly, by driving the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3 under the driving conditions of FIGS. 5 and 6, the monitor piezoelectric element 3 is more electrically driven during repeated driving than the ink ejection piezoelectric element 2. Less resistance to mechanical and mechanical failure.

  As a result, during repeated driving, the monitoring piezoelectric element 3 fails earlier than the ink ejection piezoelectric element 2, and the failure of the ink ejection piezoelectric element 2 is caused by the failure of the monitoring piezoelectric element 3. It becomes possible to predict. At this time, in this embodiment, a dedicated sensor for monitoring deterioration of the piezoelectric element such as a humidity sensor is not provided separately, and the monitor is a piezoelectric element of the same type (similar layer configuration) as the ink discharging piezoelectric element 2. By using the piezoelectric element 3 for ink instead of the sensor, it can be predicted that the failure of the piezoelectric element 2 for ink ejection is near.

  In addition, the actual failure of the monitoring piezoelectric element 3 includes not only the surrounding humidity but also other factors such as deterioration of the film quality over time, and the ink ejection piezoelectric element provided in the same head. Similarly, the element 2 is considered to be affected by factors such as humidity and deterioration of film thickness over time. Accordingly, it is possible to predict the failure of the ink ejection piezoelectric element 2 from the failure of the monitor piezoelectric element 3 including failure factors other than humidity, which is much higher than when the above humidity sensor is used. It is possible to predict the occurrence of a failure in the ink discharge piezoelectric element 2 with high accuracy.

  As a result, it is possible to prompt the user to replace the inkjet head 10 before failure of the ink discharge piezoelectric element 2 and to prevent a fatal defect such as ink non-discharge.

  In particular, in this embodiment, when the failure detection unit 5 detects a failure of the monitoring piezoelectric element 3, the failure notification unit 7 notifies the outside, so that the user can replace the inkjet head 10 based on the notification. This makes it possible to reliably prevent the occurrence of fatal defects such as ink ejection failure.

[Piezoelectric element manufacturing method]
Next, a method for manufacturing the piezoelectric element of this embodiment will be described. FIG. 7 is a cross-sectional view showing a manufacturing process of the ink ejection piezoelectric element 2. The manufacturing method of the monitoring piezoelectric element 3 is the same as that of the ink discharging piezoelectric element 2, and therefore the description thereof is omitted here.

  First, the substrate 11 is prepared. As the substrate 11, crystalline silicon (Si), which is often used in MEMS (Micro Electro Mechanical Systems), can be used. Here, two Si substrates 11c and 11d are joined via an oxide film 11e. An SOI (Silicon on Insulator) structure is used.

The substrate 11 is put into a heating furnace and held at about 1500 ° C. for a predetermined time, and thermal oxide films 12a and 12b made of SiO ₂ are formed on the surfaces of the Si substrates 11c and 11d, respectively. Next, each layer of titanium and platinum is sequentially formed on one thermal oxide film 12a by a sputtering method, and the lower electrode 13 is formed.

  Subsequently, the substrate 11 is reheated to about 600 ° C., and a lead zirconate titanate (PZT) layer 14a to be a displacement film is formed by sputtering. Then, the photosensitive resin 21 is applied to the substrate 11 by a spin coating method, and unnecessary portions of the photosensitive resin 21 are removed by exposure and etching through a mask, and the shape of the piezoelectric layer 14 to be formed is transferred. Thereafter, using the photosensitive resin 21 as a mask, the shape of the layer 14 a is processed using a reactive ion etching method to form the piezoelectric layer 14.

  Next, a titanium layer and a platinum layer are sequentially formed by sputtering on the lower electrode 13 so as to cover the piezoelectric layer 14 to form a layer 15a. Subsequently, the photosensitive resin 22 is applied onto the layer 15a by a spin coating method, and unnecessary portions of the photosensitive resin 22 are removed by exposure and etching through a mask, and the shape of the upper electrode 15 to be formed is transferred. To do. Thereafter, using the photosensitive resin 22 as a mask, the shape of the layer 15a is processed using a reactive ion etching method to form the upper electrode 15.

  Next, a photosensitive resin 23 is applied to the back surface of the substrate 11 by a spin coat method, and exposure and etching are performed through a mask, thereby removing unnecessary portions of the photosensitive resin 23 and forming the pressure chamber 11a to be formed. Transfer the shape of. Then, using the photosensitive resin 23 as a mask, the substrate 11 is removed using a reactive ion etching method to form the pressure chamber 11a. Thereby, the piezoelectric element 2 for ink discharge is completed. Thereafter, the thermal oxide film 12b is removed, and the substrate 11 and the intermediate glass, and the intermediate glass and the nozzle plate are anodically bonded, whereby the inkjet head 10 is completed. Note that holes are formed in the intermediate glass and the nozzle plate for discharging the ink in the pressure chamber 11a to the outside.

[Other configurations]
FIG. 8 is a cross-sectional view showing another configuration of the main part of the inkjet head 10. The ink ejection piezoelectric element 2 and the monitor piezoelectric element 3 may be configured by laminating a thermal oxide film 12, a lower electrode 13, a piezoelectric layer 14, and an upper electrode 15 on different substrates 11 and 11, respectively. Thus, even if the ink ejection piezoelectric element 2 and the monitor piezoelectric element 3 are separate, the occurrence of the failure of the ink ejection piezoelectric element 2 is predicted based on the failure of the monitor piezoelectric element 3. Is possible. Further, the degree of freedom of arrangement of the monitor piezoelectric element 3 increases, and the degree of freedom of design of the inkjet head 10 also increases.

In the present embodiment, PZT is used as the material constituting the piezoelectric layer 14, but a piezoelectric material other than PZT may be used. For example, PZT with various impurities such as Nb, La, Mn added, PMN-PT (solid solution of (PbMg _1/3 Nb _2/3 ) O ₃ and PbTiO ₃ ), etc. with high piezoelectric properties, BaTiO Lead-free materials such as ₃ can be used as the piezoelectric material.

  In the present embodiment, the case where the pressure chamber 11a of the monitoring piezoelectric element 3 is connected to the ink flow path has been described, but it may not be connected to the ink flow path. In this case, as compared with the case where ink is present in the pressure chamber 11a, the load at the time of displacement of the driven film is reduced, so that the displacement of the driven film is increased when the piezoelectric layer 14 is expanded and contracted. Accordingly, the failure of the monitoring piezoelectric element 3 is more likely to occur, and the occurrence of the failure of the ink ejection piezoelectric element 2 can be predicted under more severe failure conditions.

  In the present embodiment, the case where the piezoelectric layer 14 is configured by a piezoelectric thin film has been described. However, the driving method of the present embodiment can be applied even when the piezoelectric layer 14 is configured by a bulk.

  The ink jet head of the present invention can be used in an ink jet printer.

DESCRIPTION OF SYMBOLS 1 Inkjet printer 2 Piezoelectric element for ink discharge 3 Piezoelectric element for monitor 4 Drive part (drive circuit)
5 Failure detection unit 7 Failure notification unit 10 Inkjet head 11a Pressure chamber

Claims (4)

A piezoelectric element for ink ejection;
A monitoring piezoelectric element for monitoring a failure of the ink ejection piezoelectric element;
A drive unit that repeatedly drives the piezoelectric element for ink ejection and the piezoelectric element for monitoring,
The monitoring voltage element is the same kind of piezoelectric element as the ink ejection piezoelectric element,
The ink ejection piezoelectric element and the monitor voltage element are each configured by laminating an oxide film, a lower electrode, a piezoelectric layer, and an upper electrode in this order on a substrate having a pressure chamber,
The monitor piezoelectric element substrate, oxide film, lower electrode, piezoelectric layer, and upper electrode are separated from the ink ejection piezoelectric element substrate, oxide film, lower electrode, piezoelectric layer, and upper electrode, respectively.
The drive unit is configured so that the monitor piezoelectric element has a lower resistance to electrical or mechanical breakdown during repeated driving than the ink discharge piezoelectric element under the driving conditions. An inkjet head that drives a piezoelectric element for monitoring;
The drive unit drives the monitor piezoelectric element for a longer drive time than the ink ejection piezoelectric element by constantly driving the monitor piezoelectric element when the power is turned on,
When the ink ejection piezoelectric element and the monitor piezoelectric element are repeatedly driven, a failure is detected using any one or more of internal resistance, induction loss, capacitance, and resonance frequency of the monitor piezoelectric element. Equipped with a failure detector,
An ink jet printer comprising: a failure notification unit that notifies the outside when the failure detection unit detects a failure of the monitoring piezoelectric element.   The inkjet printer according to claim 1, wherein the driving unit drives the monitoring piezoelectric element with a driving voltage higher than the ink discharging piezoelectric element. The ink jet printer according to claim 1 or 2, characterized in that it comprises a failure time determining section for determining the timing of the piezoelectric element fails for ejecting ink based on the failure of the piezoelectric element for the monitor. The inkjet printer according to claim 3 , wherein the failure time determination unit includes a control unit and a storage unit.

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