JP2011148169A - Piezoelectric element inspection method, liquid ejection device, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To identify a piezoelectric element in which a non-penetrating crack is formed. <P>SOLUTION: An electric field is applied between both electrodes of a flow path unit 9 and a common electrode 134 so that the flow path unit 9 becomes a high-potential electrode of potential+5V and the common electrode 134 becomes a low-potential electrode of potential 0V (S3), after measuring the resistance value between the both electrodes, the voltage between the both electrodes is released (S4). The measured resistance value is compared with a threshold Rth1 (S5), the measured values equal to or larger than the threshold Rth1 are classified as a group A (S6). An electric field is applied between both electrodes so that the flow path unit 9 becomes the low-potential electrode of potential 0V and the common electrode 134 becomes a high-potential electrode of potential+1V (S7), and the resistance value between the both electrodes is measured while applying the electric field. The measured resistance value is compared with a threshold Rth2 (S8). The measured values equal to or larger than the threshold Rth2 are classified as a group B (S9), and the measured values not larger than the threshold Rth2 are classified as a group C (S10). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a piezoelectric element inspection method, a liquid ejection apparatus, and a method for manufacturing the same.

  As a member that imparts ejection energy to ink, an ink jet head using a piezoelectric element including a piezoelectric material such as lead zirconate titanate (PZT) as an actuator is known. Cracks are unavoidable for piezoelectric elements made of ceramics, and with the recent thinning of piezoelectric elements, cracks are more likely to occur in piezoelectric elements.

  Patent Document 1 describes a method for inspecting whether or not a crack is formed in a piezoelectric actuator (piezoelectric element) of an inkjet head. In the method described in Patent Document 1, after an ink is filled in an ink flow path including a nozzle and a pressure chamber formed in a cavity unit (flow path unit), an electrode closest to the cavity unit in the piezoelectric actuator and conductive The resistance value between the cavity unit having the characteristics is measured. If a crack is formed in the ceramic layer (piezoelectric layer) closest to the cavity unit in the piezoelectric actuator, ink penetrates into the crack and the electrode and the cavity unit are short-circuited, and the resistance value between them is small. It becomes. On the other hand, if no crack is generated, the resistance value between the electrode and the cavity unit is a very large value. Therefore, by measuring this resistance value, it is possible to inspect whether or not a crack reaching the electrode is formed in the ceramic layer closest to the cavity unit. Then, using the inspection result, the inkjet head having the piezoelectric actuator in which the crack reaching the electrode is formed is discarded as a defective product.

JP 2008-195047 A

  In the technique of Patent Document 1, a piezoelectric element including upper and lower piezoelectric layers and an internal electrode sandwiched between these two piezoelectric layers is formed with a piezoelectric element in which a crack reaching only the lower piezoelectric layer and reaching the internal electrode is formed. Therefore, it is impossible to distinguish the piezoelectric element from which a crack penetrating the upper and lower piezoelectric layers is formed. A piezoelectric element in which a crack that reaches only the lower piezoelectric layer and reaches the internal electrode is formed, for example, when an external electrode is arranged on the upper piezoelectric layer and there is no crack that connects the internal electrode and the external electrode. Can be used because there is no short circuit between the electrodes via the ink. Nevertheless, since the technique of Patent Document 1 cannot distinguish between the two, the piezoelectric element in which a crack that penetrates only the lower piezoelectric layer and reaches the internal electrode must be discarded. There's a problem.

  An object of the present invention is to provide a piezoelectric element in which a crack penetrating only a part of the piezoelectric layer in the piezoelectric element is formed, a piezoelectric element in which a crack penetrating all the piezoelectric layers of the piezoelectric element is formed, and a piezoelectric element It is another object of the present invention to provide a method for inspecting a piezoelectric element capable of distinguishing piezoelectric elements that are not formed with cracks penetrating the part of the piezoelectric layer.

  Another object of the present invention is to provide a liquid ejection apparatus that effectively uses two types of liquid ejection heads having different crack states in a piezoelectric element, and a method for manufacturing the same, based on the above-described piezoelectric element inspection method. That is.

  The piezoelectric element inspection method of the present invention is an inspection method for a piezoelectric element having an electrode layer and two piezoelectric layers sandwiching the electrode layer, wherein one of the two piezoelectric layers is a liquid. In the state of contact with the liquid, while applying a first electric field between the electrodes so that the conductor in contact with the liquid outside the piezoelectric element becomes a high potential electrode and the electrode layer becomes a low potential electrode, A first measurement step for measuring a resistance value between the conductor and the electrode layer; and after the application of the first electric field is released, the resistance value measured in the first measurement step is a first value A second measuring step of measuring a resistance value between the conductor and the electrode layer with respect to the piezoelectric element that is less than the threshold value.

  According to the present invention, it is determined whether or not a crack is formed in the piezoelectric element (a crack penetrating at least one of the piezoelectric layers is formed) by performing the resistance value measurement twice. It is possible to know whether the crack is a through crack (a crack penetrating both piezoelectric layers) or a non-penetrating crack (a crack penetrating only one of the piezoelectric layers). Therefore, it is possible to reduce the proportion of piezoelectric elements that are discarded.

  Note that the present invention can also be applied to a purpose of inspecting a piezoelectric element having three or more piezoelectric layers and two or more electrode layers inside (that is, sandwiched between the piezoelectric layers). In that case, the “electrode layer” of the present invention corresponds to an electrode layer that is a low-potential electrode among two or more electrode layers, and the “one piezoelectric layer” of the present invention corresponds to One or a plurality of piezoelectric layers sandwiched between an electrode layer to be a low potential electrode among two or more electrode layers and a piezoelectric layer to be brought into contact with a liquid among the two outermost piezoelectric layers. The “other piezoelectric layer” corresponds to one or a plurality of piezoelectric layers sandwiched between an electrode layer serving as a low-potential electrode and a piezoelectric layer that is not in contact with a liquid among the two outermost piezoelectric layers. Is a layer.

  The inspection method of the present invention may be performed twice, replacing the piezoelectric layer that is in contact with the liquid. That is, in the second inspection, in a state where the other piezoelectric layer of the two piezoelectric layers is in contact with the liquid, a conductor that contacts the liquid outside the piezoelectric element becomes a high potential electrode and the electrode A first measuring step of measuring a resistance value between the conductor and the electrode layer while applying a first electric field between both electrodes so that the layer becomes a low potential electrode; After canceling the application, the resistance value between the conductor and the electrode layer is measured for the piezoelectric element whose resistance value measured in the first measurement step is less than the first threshold value. And a second measuring step. This makes it possible to further identify the piezoelectric element in which a crack penetrating only the other piezoelectric layer is formed. Even in this case, a piezoelectric element having three or more piezoelectric layers and two or more electrode layers therein can be inspected. At this time, another electrode layer may be used as a low potential electrode in the first inspection and the second inspection.

  The liquid discharge apparatus of the present invention is a liquid discharge apparatus including a plurality of liquid discharge heads, and each liquid discharge head is formed with a plurality of individual liquid flow paths each including a discharge port for discharging liquid and a pressure chamber. Further, a flow path unit made of a conductor at least partially exposed to the plurality of individual liquid flow paths, a common electrode layer, two piezoelectric layers sandwiching the common electrode layer, and the common electrode layer are opposed to each other. A plurality of individual electrode layers formed on the surface of one of the two piezoelectric layers, the plurality of individual electrode layers facing the plurality of pressure chambers and the plurality of individual electrodes. And a piezoelectric element attached to the flow path unit such that the electrode layer faces in a direction opposite to the flow path unit. The plurality of liquid ejection heads include a first liquid having the piezoelectric element, the resistance value of which is determined to be greater than or equal to the first threshold value by the piezoelectric element inspection method according to claim 4. Both a discharge head and a second liquid discharge head having the piezoelectric element whose resistance value is determined to be equal to or higher than the second threshold value by the piezoelectric element inspection method according to claim 4 are included. The first liquid discharge head and the second liquid discharge head discharge different types of liquid.

  As a result, the head corresponding to the type of liquid to be ejected can be used effectively, and the yield of the head is improved.

  A method for manufacturing a liquid discharge apparatus according to the present invention is a method for manufacturing a liquid discharge apparatus including a plurality of liquid discharge heads, and a plurality of individual liquid flow paths each including a discharge port for discharging liquid and a pressure chamber are formed. Further, a flow path unit made of a conductor at least partially exposed to the plurality of individual liquid flow paths, a common electrode layer, two piezoelectric layers sandwiching the common electrode layer, and the common electrode layer are opposed to each other. A plurality of individual electrode layers formed on the surface of one of the two piezoelectric layers, the plurality of individual electrode layers facing the plurality of pressure chambers and the plurality of individual electrodes. A head manufacturing process for manufacturing the plurality of liquid ejection heads including a piezoelectric element attached to the flow path unit so that the electrode layer faces in a direction opposite to the flow path unit; and after the head manufacturing process, 2 piezoelectrics When the other piezoelectric layer is in contact with the liquid in the pressure chamber, the conductor in contact with the liquid is a high potential electrode and the common electrode layer is a low potential electrode. A first measurement step of measuring a resistance value between the conductor and the common electrode layer while applying a first electric field to the first electrode, and after releasing the application of the first electric field, A second measuring step of measuring a resistance value between the conductor and the common electrode layer with respect to a piezoelectric element having a resistance value measured in the measuring step being less than a first threshold; The piezoelectric element having a resistance value measured in one measurement step equal to or greater than the first threshold value is one in which a crack penetrating the other piezoelectric layer is not formed, and in the second measurement step The measured resistance is less than the second threshold The piezoelectric element is formed with a crack penetrating the two piezoelectric layers and the common electrode layer, and a resistance value measured in the second measurement step is equal to or greater than the second threshold value. A determination step in which the element is formed with a crack penetrating the other piezoelectric layer and not penetrating the one piezoelectric layer; and the resistance value is the first threshold value in the determination step. A first liquid discharge head having the piezoelectric element determined to be above, and a second liquid discharge head having the piezoelectric element determined to have the resistance value equal to or greater than the second threshold value in the determination step. An assembly step of assembling both the liquid ejection head and a support member that supports the plurality of liquid ejection heads. In the assembly step, the first liquid ejection head is assembled to the support member so that the first liquid can be supplied to the first liquid ejection head, and the second liquid ejection head is attached to the second liquid ejection head. The second liquid discharge head is assembled to the support member so that a second liquid of a type different from the first liquid can be supplied.

  As a result, the head corresponding to the type of liquid to be ejected can be used effectively, and the yield of the head is improved.

  According to the present invention, it is determined whether or not a crack is formed in the piezoelectric element (a crack penetrating at least one of the piezoelectric layers is formed) by performing the resistance value measurement twice. It is possible to know whether the crack is a through crack (a crack penetrating both piezoelectric layers) or a non-penetrating crack (a crack penetrating only one of the piezoelectric layers). Therefore, it is possible to reduce the proportion of piezoelectric elements that are discarded.

1 is a longitudinal sectional view showing an internal configuration of an ink jet printer that is a liquid ejection apparatus according to an embodiment of the present invention. FIG. 2 is a plan view of a head body depicted in FIG. 1 and included in an ink jet printer. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. 2. It is sectional drawing along the IV-IV line shown in FIG. It is an expanded sectional view of an actuator unit, and a top view of an individual electrode. FIG. 2 is a manufacturing process diagram of the ink jet printer depicted in FIG. 1. It is typical sectional drawing which shows the inspection method of the actuator unit which is a piezoelectric element in order. It is typical sectional drawing which shows the inspection method of the actuator unit which is a piezoelectric element in order. It is typical sectional drawing which shows the inspection method of the actuator unit which is a piezoelectric element in order. It is typical sectional drawing which shows the inspection method of the actuator unit which is a piezoelectric element in order.

(Whole printer configuration)
As shown in FIG. 1, an inkjet printer 101 according to an embodiment of the present invention including an inkjet head as a liquid discharge head has a rectangular parallelepiped casing 101a. The printer 101 is a line printer. In the housing 101a, there are five inkjet heads 1a, 1b for discharging transparent precoat liquid (P), yellow ink (Y), magenta ink (M), cyan ink (C), and black ink (K), respectively. 1c, 1d, 1e (in the following description, when there is no need to distinguish each other, they may be simply referred to as the head 1) and a transport mechanism 16 are disposed. Above the transport mechanism 16, five inkjet heads 1a to 1e are supported by a frame 3 as a frame-shaped support member. The frame 3 is supported by the housing 101a, and the five heads 1 are arranged along the paper transport direction. A control unit 100 that controls the operation of the five inkjet heads 1 a to 1 e and the transport mechanism 16 is attached to the inner surface of the top plate of the housing 101 a. A paper discharge recess (paper discharge unit) 15 from which the paper P is discharged is provided on the top surface of the top plate. Below the transport mechanism 16, a paper feed unit 101b that can be attached to and detached from the housing 101a is disposed. An ink tank unit 101c that can be attached to and detached from the housing 101a is disposed below the paper supply unit 101b.

  Inside the ink jet printer 101, a paper conveyance path for conveying the paper P is formed along the thick arrow shown in FIG. The paper feed unit 101 b includes a paper feed tray 11 and a paper feed roller 12. The paper feed tray 11 has a box shape opened upward, and stores a plurality of sheets P in a stacked state. The paper feed roller 12 sends out the paper P at the uppermost position of the paper feed tray 11. The fed paper P is guided by the guides 13 a and 13 b of the guide portion and is sent to the transport mechanism 16 by the feed roller pair 14.

  As shown in FIG. 1, the transport mechanism 16 includes a belt roller 6, 7 and an endless transport belt 8 wound between the rollers 6, 7, a nip roller 4 disposed outside the transport belt 8, and It has a peeling plate 5, a rectangular parallelepiped platen 18 and a tension roller 10 disposed inside the conveyor belt 8.

  The belt roller 7 is a driving roller, and is rotated clockwise in FIG. The driving force of the conveyance motor 19 is transmitted through a plurality of gears. At this time, the conveyor belt 8 travels along the thick arrow. The belt roller 6 is a driven roller and rotates clockwise in FIG. 1 as the transport belt 8 travels. The nip roller 4 is disposed so as to face the belt roller 6 and presses the paper P supplied from the preceding guide portion against the outer peripheral surface 8 a of the transport belt 8. Adhesive silicone treatment is applied to the outer peripheral surface 8a, and the paper P is held and conveyed. The peeling plate 5 is disposed so as to face the belt roller 7, and peels the paper P from the outer peripheral surface 8a and guides it to the subsequent guide portion. In the guide portion, the peeled paper P is guided by the guides 29a and 29b and conveyed upward by the two pairs of feed rollers 28. The paper P is discharged from the discharge port 30 at the top of the housing 101a to the paper discharge recess 15.

  The platen 18 is disposed to face the five inkjet heads 1a to 1e and supports the upper loop of the conveyor belt 8 from the inside. Thereby, between the outer peripheral surface 8 a and the ejection surface 2 a of the head 10. A predetermined interval suitable for image formation is formed. The tension roller 10 urges the lower loop of the transport belt 8 downward from the inside, and tension is applied to the transport belt 8.

  Each head 1 has a substantially rectangular parallelepiped shape elongated in the main scanning direction. Each head 1 is a laminate in which a head main body 2, a liquid distribution member (not shown), and a control board (not shown) are laminated from below. The liquid distribution member has a liquid flow path communicating with the head main body 2 and distributes ink supplied from an ink tank 17 described later to the head main body 2. The control board generates a control signal and supplies it to an actuator unit 21 described later. The control board and the actuator unit 21 are electrically connected by a COF (Chip On Film: not shown) which is a flat flexible board. A driver IC is mounted on the COF.

  The five inkjet heads 1a to 1e have the same structure except for the group point related to the crack degree described later.

  The inkjet head 1a is disposed upstream of the remaining four inkjet heads 1b to 1e in the transport direction. At the time of image formation, a precoat liquid (pretreatment liquid) is discharged from the inkjet head 1. The precoat liquid lands on the paper P prior to the ink ejected from the inkjet heads 1b to 1e. The landed precoat liquid suppresses ink bleeding or improves the ink fixing property to the paper P.

  The four inkjet heads 1b to 1e use different colors of ink. More specifically, the inkjet head 1b uses yellow ink, the inkjet head 1c uses magenta ink, the inkjet head d uses cyan ink, and the inkjet head 1e uses black ink. Are discharged respectively.

  The bottom surface of the inkjet head 1 is a discharge surface 2a for discharging ink or precoat liquid (hereinafter, both may be simply referred to as “liquid”). A plurality of discharge ports 108 (see FIG. 4) are formed on the discharge surface 2a. When the conveyed paper P passes just below the five inkjet heads 1a to 1e, the precoat liquid and the inks of the respective colors are sequentially discharged from the discharge port 108 toward the upper surface of the paper P. Thereby, a desired color image is formed on the upper surface of the paper P, that is, the printing surface. At this time, a plurality of pixels along the transport direction constituting the image are formed by ink ejected from one ejection port 108.

  In the ink tank unit 101c, five ink tanks 17a to 17e (which may be simply referred to as the ink tank 17 in the following description when there is no need to distinguish each other) are arranged. The ink tank 17a stores precoat liquid, the ink tank 17b stores yellow ink, the ink tank 17c stores magenta ink, the ink tank 17d stores cyan ink, and the ink tank 17e stores black ink. Each inkjet head 1 is connected to an ink tank 17 that stores any one of the five ink tanks 17a to 17e and stores the same type of liquid as the liquid discharged from the head 1 via a tube (not shown). ing. Ink is supplied from each ink tank 17 to the corresponding inkjet head 1 via this tube.

  In the present embodiment, the inkjet head 1a that ejects the precoat liquid and the inkjet head 1e that ejects the black ink do not have any group A, that is, “non-penetrating crack” and “penetrating crack” in the manufacturing process described later. A head 1 having actuator units 21 classified into groups (simply referred to as “head belonging to group A”) is used. Other heads 1, that is, an inkjet head 1 b that discharges yellow ink, an inkjet head 1 c that discharges magenta ink, and an inkjet head 1 d that discharges cyan ink are group B, that is, “non-through” A head 1 having an actuator unit 21 classified into a group having “cracks” (simply referred to as “head belonging to group B”) is used.

  The positions of the five heads 1 a to 1 e in the printer 101 are determined according to the type of liquid ejected from each head 1. The inkjet head 1a that discharges the precoat liquid must be upstream of the other four heads 1b to 1e from the viewpoint of improving the image quality. In addition, since the hue when observed by humans differs according to the order of superimposition of different color inks that have landed on the paper P, the four heads 1b, 1c, 1d, and 1e that eject ink also from that viewpoint. Needs to be determined. In the present embodiment, it is required that the head 1b, the head 1c, the head 1d, and the head 1e are arranged in this order from the upstream along the transport direction. Thus, which of the four colors of ink and precoat liquid is ejected by each head 1 depends on the mounting position of each head 1 with respect to the frame 3.

(Head body)
Next, the head body 2 will be described with reference to FIGS. As shown in FIG. 2, the head body 2 includes a flow path unit 9 and four actuator units 21 fixed to the upper surface 9 a of the flow path unit 9. As shown in FIG. 4, the flow path unit 9 is a conductive laminate composed of nine metal plates 122 to 130. These metal plates 122 to 130 are long in the main scanning direction and have a rectangular planar shape.

  As shown in FIG. 2, ten ink supply ports 105 b are opened on the upper surface 9 a of the flow path unit 9. Each ink supply port 105b is arranged with the actuator unit 21 in between in the main scanning direction. The ink from the liquid distribution member described above flows into each ink supply port 105b. A plurality of pressure chambers 110 are regularly arranged in a matrix as shown in FIG. Each pressure chamber 110 has a substantially rhombic planar shape. As shown in FIGS. 2 to 4, the flow path unit 9 includes a manifold flow path 105 connected to the ink supply port 105 b, a plurality of sub manifold flow paths 105 a branched from the manifold flow path 105, and a sub manifold flow. A plurality of individual ink flow paths 132 from the outlet of the path 105a to the ejection port 108 via the pressure chamber 110 are included. The pressure chamber 110 is connected to the sub-manifold flow path 105a via an aperture 112 as a throttle portion. On the lower surface (discharge surface 2a) of the flow path unit 9, the discharge ports 108 are arranged in a matrix. In FIG. 3, the actuator unit 21 to be drawn with a solid line is drawn with a two-dot chain line, and an aperture 112 to be drawn with a broken line is drawn with a solid line.

  Thus, since the flow path unit 9 is made of metal (conductor), the metal as the conductor is exposed on the inner surfaces of all the individual ink flow paths 132. The ink supplied from the ink supply port 105 b fills the ink flow path of the flow path unit 9 and reaches the discharge port 108. In this state, the metal is in contact with the ink.

  As shown in FIG. 2, the four actuator units 21 have a trapezoidal planar shape, and are arranged in two rows in a staggered manner in the main scanning direction, with the bottom of the trapezoid being outside in the sub-scanning direction. The parallel opposing sides of each row are arranged along the main scanning direction, and the oblique sides of the adjacent actuator units 21 overlap in the sub-scanning direction.

  The actuator unit 21 is made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity, and includes three piezoelectric layers 141 to 143 as shown in FIG. Electrodes are formed on both the upper and lower surfaces of only the uppermost piezoelectric layer 141. The individual electrode 135 far from the pressure chamber 110 has a substantially rhombic planar shape similar to the pressure chamber 110 as shown in FIG. The main part of the individual electrode 135 is disposed so as to face the pressure chamber 110, and one acute angle portion of the rhombus extends outside the pressure chamber 110. A circular land 136 is formed at the tip in the extending direction in a plan view. The land 136 is thicker than the individual electrode 135. On the other hand, the common electrode 134 close to the pressure chamber 110 is sandwiched between two piezoelectric layers 141 and 142, and is formed on almost the entire lower surface of the piezoelectric layer 141 (upper surface of the piezoelectric layer 142). The lower surface of the piezoelectric layer 143 is fixed to the upper surface 9 a of the flow path unit 9 and seals the opening of the pressure chamber 110. A common electrode land (not shown) electrically connected to the common electrode 134 is also formed on the upper surface of the piezoelectric layer 141.

  A COF is connected to each actuator unit 21. The driver IC mounted on the COF generates a drive signal (drive voltage pulse) based on the control signal from the control board, and supplies it to the actuator unit 21. Driving vibration is selectively applied to the individual electrode land 136, and a ground potential of a reference potential is applied to the common electrode land. In the actuator unit 21, the piezoelectric layer 141 is spontaneously displaced by an external electric field, and the piezoelectric layers 142 and 143 are not spontaneously displaced. Furthermore, a portion sandwiched between the individual electrode 135 and the pressure chamber 110 is deformed in a direction orthogonal to the plane independently of other portions, and the volume of the pressure chamber 110 is changed. Between the individual electrode 135 and the pressure chamber 110, each acts as an individual actuator. As described above, the actuator unit 21 includes the same number of piezoelectric actuators as the energy applying members as the pressure chambers 110.

A driving method of the actuator unit 21 for discharging ink droplets from the nozzles will be described. The piezoelectric layer 141 is polarized in the thickness direction. When a drive signal is supplied from the driver IC, an electric field along the thickness direction is generated between the two electrodes 134 and 135 in the piezoelectric layer 141. Electric field application portion (active portion) mainly produce planar direction of the piezoelectric strain (displacement in the vibration mode of d _31). Since the piezoelectric layers 142 and 143 are not spontaneously displaced, there is a difference in strain in the plane direction between the piezoelectric layers 141 (active portions). In the present embodiment, when the electric field application direction is the same as the polarization direction, the actuator portion facing the pressure chamber 110 undergoes unimorph deformation with a strain difference to reduce the volume of the pressure chamber 110. As a result, pressure (discharge energy) is applied to the ink in the pressure chamber 110, and ink droplets are discharged from the discharge ports 108.

(Printer manufacturing method)
Next, a method for manufacturing the printer 101 will be described with further reference to FIGS. First, a plurality of inkjet heads 1 are manufactured (head manufacturing process: S1). The process of manufacturing the inkjet head 1 includes a manufacturing process (S31) of the flow path unit 9, a manufacturing process (S32) of the actuator unit 21, and a fixing process (S33) of the actuator unit 21 to the flow path unit 9. Yes. The manufacturing process (S31) of the flow path unit 9 and the manufacturing process (S32) of the actuator unit 21 are performed independently of each other, and may be performed first or in parallel.

  In step S31, first, a plurality of metal plates constituting the flow path unit 9 are prepared, and grooves and through holes are formed in each metal plate by etching or the like. And a thermosetting adhesive is apply | coated to each metal plate, it laminates | stacks, aligning mutually, and the flow path unit 9 is completed through a heating and pressurization process.

  In step S32, first, three green sheets to be trapezoidal piezoelectric layers 141 to 143 formed in advance in consideration of the shrinkage amount due to firing are prepared. Then, Ag-Pd-based conductive paste is screen-printed with a pattern of a plurality of individual electrodes 135 on the green sheet to be the piezoelectric layer 141 and a pattern of the common electrode 134 on the green sheet to be the piezoelectric layer 142. . Then, while aligning using a jig, the green sheet to be the piezoelectric layer 42 is overlaid on the green sheet to be the piezoelectric layer 143 that has not been printed, with the surface on which the common electrode 134 is printed facing upward. A green sheet to be the piezoelectric layer 141 is overlaid thereon with the surface on which the individual electrode 135 and the surface electrode 145 are printed facing up. Next, this green sheet laminate is degreased in the same manner as a known ceramic and fired at a predetermined temperature. Thus, the three green sheets become the piezoelectric layers 141 to 143, and the conductive paste becomes the individual electrode 135 and the common electrode 134. Further, conductive lands 136 are printed on the individual electrodes 135 using a patterned mask.

  In step S33, the four actuator units 21 manufactured in step S32 are fixed on the upper surface of the flow path unit 9 manufactured in step S31 so that the individual electrode 135 faces in the opposite direction to the flow path unit 9. To do. At this time, the epoxy unit thermosetting adhesive is interposed between the flow path unit 9 and the actuator unit 21 to perform heating and pressurization, whereby both are fixed and shown in FIG. As described above, alignment is performed so that most of the individual electrodes 135 overlap the pressure chamber 110 in plan view. Thereby, the head body 2 is completed. Further, a COF is bonded to the upper surface of each actuator unit 21 using a conductive adhesive so that each land 136 is electrically connected to a terminal on the COF, and then a liquid distribution member is mounted on the upper surface of the flow path unit 9. Fix tightly. Furthermore, the inkjet head 1 is completed by attaching other members such as a control board. In step S1, at least the head main body 2 may be manufactured, and other members such as a liquid distribution member and a control substrate may be attached to the head main body 2 in a later step.

  Here, the crack formed in the actuator unit 21 is demonstrated. Cracks may be formed in the actuator unit 21 when firing in step S32, when fixing to the flow path unit 9 in step S33, and when bonding COF. Cracks formed in the actuator unit include cracks penetrating at least the piezoelectric layers 141, 142, 143 and the common electrode 134 (referred to as “penetrating cracks” in this embodiment) depending on the length and location thereof, and the piezoelectric layer 142, 143, and reaches the common electrode 134 but does not penetrate the piezoelectric layer 141 (referred to as “non-penetrating crack” in the present embodiment), and at least the piezoelectric layer 141 penetrates the common electrode. It is classified into cracks that reach 134 but do not penetrate through the piezoelectric layers 142 and 143 (referred to as “upper cracks” in the present embodiment), and other relatively short cracks.

  When the through crack is formed in the actuator unit 21 among the above four types of cracks, the individual electrode 135 and the common electrode 134 are short-circuited through the liquid that has penetrated into the through crack from the pressure chamber 110 by capillary action. Therefore, there is a high possibility that the actuator unit 21 does not operate normally. Further, when the non-penetrating crack is formed in the actuator unit 21, the actuator unit 21 may not operate normally when the crack grows for some reason in the future. Perform the action.

  Therefore, in the present embodiment, through the steps described below, the actuator unit 21 (group C) in which a through crack is formed, the actuator unit 21 (group B) in which a non-through crack is formed, and other actuators The printer 101 is manufactured using the head 1 belonging to the group A and the head 1 belonging to the group B by distinguishing from the unit 21 (group A). Furthermore, considering that the actuator unit 21 of group B is more likely to cause a future failure than the actuator unit 21 of group A, the head 1 belonging to group B is used less frequently than the head 1 belonging to group A. It is used for discharging liquid, and for discharging liquid that has a lower degree of attack on the piezoelectric layer or a corrosive action on the common electrode 134 than the head 1 belonging to group A.

  The actuator unit 21 in which the upper crack is formed operates normally at the same time as the actuator unit 21 in which the non-penetrating crack is formed, but is normal when the crack grows for some reason in the future. There is a possibility that it will not work. Therefore, the actuator unit 21 in which the upper crack is formed is preferably classified into the same group as the actuator unit 21 in which the non-penetrating crack is formed. However, in order to identify the actuator unit 21 in which the upper crack is formed, the inspection process described below needs to be additionally performed once more as described later. Therefore, in the present embodiment, in order to avoid the complexity of manufacturing the printer, the actuator unit 21 in which the upper crack is formed is replaced with a relatively short crack other than the three types of cracks, a through crack, a non-through crack, and an upper crack. Are treated as belonging to the same group A as the actuator unit 21 formed. Also in this case, the head 1 belonging to the group A and the head 1 belonging to the group B are distinguished from each other in the printer 101, so that the heads 1 of both the groups A and B are not distinguished from each other. It is possible to reduce the failure frequency of the head 1.

  Returning to FIG. 6, after step S <b> 1, an appropriate liquid is introduced into the head body 2 by pressurization with a pump (S <b> 2). Thereby, all the individual ink flow paths 132 in the head main body 2 are filled with the liquid. As the liquid introduced into the head main body 2, a liquid obtained by removing the pigment component from the ink can be used.

  FIG. 7A schematically shows the head 1 having the actuator unit 21 that will be determined to belong to the group B in which the non-penetrating crack 151 is formed at the end of step S2. FIG. 7B schematically shows the head 1 having the actuator unit 21 that will be determined to belong to the group C in which the through crack 152 is formed at the end of step S2. FIG. 7C schematically shows the head 1 having the actuator unit 21 that will be determined to belong to the group A at the end of step S2. In FIGS. 7A and 7B, the non-penetrating crack 151 and the penetrating crack 152 are drawn with a width larger than the actual width.

  For the head 1 having the non-penetrating crack 151, as shown in FIG. 7A, the liquid in the pressure chamber 110 tries to penetrate into the non-penetrating crack 151 by capillary action. Since the cap is covered with 141, the liquid hardly penetrates into the non-penetrating crack 151 only by the capillary force. With respect to the head 1 having the through crack 152, as shown in FIG. 7B, the liquid in the pressure chamber 110 penetrates into the through crack 152 due to a capillary phenomenon. However, the liquid penetrates only to the extent that the water level does not reach the common electrode 134. For the head 1 in which neither the non-penetrating crack 151 nor the penetrating crack 152 is formed, since the crack facing the pressure chamber 110 is not formed as shown in FIG. 7C, the liquid in the pressure chamber 110 is not formed. Does not enter the actuator unit 21.

  Next, an electric field is applied between the two electrodes so that the flow path unit 9 becomes a high potential electrode having a potential of + 5V and the common electrode 134 becomes a low potential electrode having a potential of 0V (S3). Then, with respect to the head 1 having the non-penetrating crack 151, as shown in FIG. 8A, the liquid in the pressure chamber 110 rises in the non-penetrating crack 151 due to electroosmosis accompanying the electrolysis of the liquid component. Then, the water level reaches the common electrode 134. As a result, the flow path unit 9 and the common electrode 134 are short-circuited, and the resistance value between them becomes very small. Here, the magnitude of the voltage of +5 V is larger than the minimum voltage at which the liquid in the pressure chamber 110 rises in the non-penetrating crack 151 and the water level reaches the common electrode 134, and is generated by electrolysis. This is determined from the viewpoint that the voltage is lower than the voltage that causes delamination of the piezoelectric layers 142 and 143 by hydrogen. Note that whether or not delamination occurs depends not only on the voltage value but also on the voltage application time. Therefore, when a voltage higher than 5 V is applied, it is effective to shorten the application time. On the other hand, with respect to the head 1 having the through crack 152, as shown in FIG. 8B, the liquid in the pressure chamber 110 rises in the through crack 152 due to electroosmosis, and the water level reaches the common electrode 134. Even after reaching, it continues to rise and finally reaches the individual electrode 135. As a result, the flow path unit 9 and the common electrode 134 are short-circuited, and the resistance value between them becomes very small.

  Further, in step S3, the resistance value between the two electrodes is measured while the above electric field is applied (first measurement step). As a result, a very small resistance value is obtained for the head 1 having the non-penetrating crack 151 and the penetrating crack 152, but a large resistance value is obtained for the other heads 1. At this time, if at least one non-penetrating crack 151 or penetrating crack 152 is formed in four actuator units 21 in one head 1, the resistance value between both electrodes becomes a very small value.

  Thereafter, the voltage between both electrodes is released (S4). As a result, with respect to the head 1 having the non-penetrating crack 151, as shown in FIG. 9A, the water level of the liquid that has reached the common electrode 134 decreases due to the influence of air pressure, and the liquid is separated from the common electrode 134. Will not touch. On the other hand, unlike the case of the non-penetrating crack 151, the head 1 having the penetrating crack 152 is not affected by the air pressure unlike the case of the non-penetrating crack 151, so that the liquid level does not decrease. If the resistance value between both electrodes is measured at this stage, the head 1 having non-penetrating cracks shows a large resistance value, but the head 1 having penetrating cracks remains small.

  In step S5, the measured resistance value obtained in step S3 is compared with the threshold value Rth1. This comparison may be performed by a human or a computer based on the measured resistance value obtained in step S3. Then, the actuator unit 21 (FIG. 7C) whose measured value is equal to or greater than the threshold value Rth1 is classified into group A in step S6 (part of the determination step). Note that steps S5 and S6 may be performed after step S3 and before step S4.

  Next, with respect to the actuator unit 21 that has not been grouped yet and whose resistance measurement value is less than the threshold value Rth1 by the comparison in step S5, the flow path unit 9 is a low potential electrode having a potential of 0V. Then, an electric field is applied between both electrodes so that the common electrode 134 becomes a high potential electrode of potential +1 V (S7). Here, the electric field is applied by causing electroosmosis in the direction opposite to that in step S3, so that when the non-penetrating crack 151 is formed, the liquid level does not decrease sufficiently and the liquid is applied to the common electrode 134. This is to prevent the situation of being in contact. This improves the discrimination between crack penetration and non-penetration. That is, with respect to the head 1 having the non-penetrating crack 151, the liquid does not come into contact with the common electrode 134 reliably as shown in FIG. On the other hand, for the head 1 having the through crack 152, the liquid level may decrease due to the electroosmosis in the direction opposite to that in the step S3, but the voltage is smaller than that in the step S3, so that the voltage exceeds the common electrode 134. Therefore, the liquid level does not decrease. Therefore, as shown in FIG. 10B, the liquid level is still above the common electrode 134.

  Further, in step S7, the resistance value between the two electrodes is measured while applying the electric field (second measurement step). As a result, a very small resistance value is obtained for the head 1 having the through-crack 152, but a large resistance value is obtained for the head 1 having the non-penetrating crack 151. Thereafter, the voltage between both electrodes is released. This voltage release may be performed in a later process.

  In step S8, the measured resistance value obtained in step S7 is compared with a threshold value Rth2. This comparison may be performed by a human or a computer based on the measured resistance value obtained in step S7. Then, the actuator unit 21 (FIG. 7A) whose measured value is greater than or equal to the threshold value Rth2 is classified into group B (part of the determination step) in step S9, and the actuator whose measured value is less than the threshold value Rth2. The unit 21 (FIG. 7B) is classified into a group C in step S10 (part of the determination step). The head 1 having the actuator unit 21 classified in the group C is discarded in step S11.

  In step S12, the two heads 1 belonging to the group A and the three heads 1 belonging to the group B are assembled to the frame 3 (an assembling step). At this time, the frame 3 may be supported in the printer 101 or may not be supported in the printer 101 yet. In the assembling process, the two heads 1 belonging to the group A are positioned on the frame 3 such as the head 1a for discharging the precoat liquid and the head 1e for discharging the black ink, that is, the mounting positions of the five heads 1 respectively. Among them, they are fixed to the leftmost and rightmost in FIG. Further, the three heads 1 belonging to the group B are positioned on the frame 3 to be the heads 1b, 1c, and 1d that discharge yellow ink, magenta ink, and cyan ink, that is, the mounting positions of the five heads 1, respectively. In FIG. 1, the second, third, and fourth positions from the left are fixed.

  When step S12 is to fix the five heads 1 to the frame 3 that is not yet supported in the printer 101, the frame 3 is assembled at a predetermined position in the printer 101 after step S12. The printer 101 is completed through the above steps.

  According to the inspection method of the actuator unit 21 according to the present embodiment described above, the actuator unit 21 is group A (without the non-penetrating crack 151 and the through crack 152) by performing relatively simple two resistance value measurements. It is possible to know whether it is group B (with non-penetrating crack 151) or group C (with through crack 152). Therefore, since the actuator unit 21 of the group B that has been discarded in the past can be used without being discarded, the proportion of the actuator units 21 that are discarded can be reduced. At this time, the actuator unit 21 can be easily classified by comparing the resistance value obtained by the measurement with the two threshold values Rth1 and Rth2.

  Further, in step S7, by applying an electric field opposite to that in step S3, the identification accuracy for the form of cracks is increased. For example, although the non-penetrating crack 151 is formed, it is possible to prevent erroneous detection in which the liquid level does not decrease and the resistance value is detected small while the liquid is in contact with the common electrode 134. Furthermore, since the electric field applied in step S7 is smaller than the electric field applied in step S3, it is possible to prevent the liquid level from being excessively lowered when the through crack 152 is formed. Therefore, it is possible to prevent erroneous detection in which a large resistance value is detected even though the through crack 152 is formed.

  Further, in the ink jet printer 101 according to the present embodiment, since the two types of heads 1 belonging to the group A and the group B are selectively used according to the type of liquid to be ejected, the number of discarded heads 1 is reduced and the heads The yield of 1 can be improved. In particular, in the present embodiment, since the head 1 belonging to the group A is used as the head 1a that discharges the precoat liquid having a higher corrosive action than the ink on the common electrode 134, the failure rate can be reduced. Furthermore, since the head 1 belonging to the group A is used as the head 1e that ejects black ink that is used more frequently than color (yellow, magenta, cyan) ink, the failure rate can be reduced.

  Note that the inspection described in the above embodiment can be performed on the manufactured printer 101. In this case, when a head 1 of group C is newly found, the individual electrode 135 is applied to the head 1 while applying an electric field so that the individual electrode 135 becomes a low potential electrode and the flow path unit 9 becomes a high potential electrode. The resistance value between 135 and the flow path unit 9 is measured. If the through crack 152 is formed in a region overlapping the individual electrode 135 of the actuator unit 21 in plan view, the resistance value obtained by measurement is smaller than the threshold value. On the contrary, if the resistance value obtained by the measurement is larger than the threshold value, it is estimated that the through crack 152 is not formed in the region overlapping the individual electrode 135 in plan view. By performing such an operation for all the individual electrodes 135 of the head 1, it is possible to specify in which region of the actuator unit 21 the through crack 152 is formed. Therefore, until the replacement operation of the head 1 is performed, it is possible to perform printing while avoiding the failure of the head by performing an emergency treatment in which a drive signal is not applied to the individual electrode 135.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various design changes can be made to the above-described embodiments as long as they are described in the claims. It is possible to apply. For example, in the embodiment described above, the actuator unit 21 is inspected by bringing a liquid into contact with the piezoelectric layer 143. In order to identify the actuator unit 21 in which the upper crack is formed, the piezoelectric layer 141 is made into a liquid. The above-described inspection may be performed once again by contact. At this time, the probe is brought into contact with the liquid disposed on the upper surface of the piezoelectric layer 141 as a conductor (high potential electrode), and a voltage of 5 V is applied between the probe and the common electrode 134. If the resistance value measured in this state is smaller (than the threshold value), it is determined that the actuator unit 21 has an upper crack. This inspection is preferably performed before the connection of the COF. As a result, the actuator unit 21 is divided into four groups (the group C described above is further divided into one having an upper crack and one having no upper crack, through crack, and non-through crack). It becomes possible to do. As a result, it is possible to treat a head having an upper crack equivalent to the head 1 belonging to the group B, and it is possible to use the head 1 more efficiently.

  In the second measurement step of step S7, it is not necessary to apply an electric field.

  In the embodiment described above, Step S2 to Step S11 are performed on the head 1 on which the individual electrode 135 is formed. However, even if the individual electrode 135 is formed on the actuator unit 21 after performing Step S2 to Step S11. Good. Steps S2 to S11 are performed after the COF is connected to the actuator unit 21 in the head manufacturing step (S1), but before the COF is connected, the connection between the flow path unit 9 and the actuator unit 21 is performed. You may go before. Thereby, there is no waste of discarding the head 1 in a state where components other than the flow path unit 9 and the actuator unit 21 are attached. Note that cracks may occur when the COF is connected, but since the land 136 where the connection point is separated from the pressure chamber 110 is a connection point, the crack is hardly exposed in the pressure chamber 110.

  The heads 1 belonging to the group A may be used only for ejecting the precoat liquid, and the heads 1 that eject ink may all be the heads 1 belonging to the group B. Further, the head 1 belonging to the group B may be used for discharging yellow ink, and other inks may be discharged using the head 1 belonging to the group A.

  When the liquid ejection apparatus according to the present invention is used for an application other than a printer, the heads 1 belonging to the two groups A and B eject different types of liquid. Preferably, the heads 1 belonging to the two groups A and B are fixed to the liquid ejection device so that the heads belonging to the group B eject liquid that is used less frequently than the heads belonging to the group A.

  The method for inspecting a piezoelectric element of the present invention can also be used for inspecting a piezoelectric element that is not related to a liquid ejection apparatus including an ink jet printer.

  The piezoelectric element inspection method of the present invention can also be applied to a piezoelectric element having two or more electrodes therein.

  Further, the present invention is applicable not only to a line printer head as in the above-described embodiment, but also to a serial printer head. Further, the present invention can be applied to a head that discharges liquid other than ink.

1a, 1b, 1c, 1d, 1e Inkjet head (liquid ejection head)
2 Head body 3 Frame (support member)
DESCRIPTION OF SYMBOLS 8 Conveyance belt 9 Flow path unit 16 Conveyance mechanism 17a-17e Ink tank 21 Actuator unit 100 Control part 101 Inkjet printer 101b Paper feed unit 101c Ink tank unit 108 Discharge port 110 Pressure chamber 134 Common electrode 135 Individual electrode 141-143 Piezoelectric layer

Claims (8)

An inspection method of a piezoelectric element having an electrode layer and two piezoelectric layers sandwiching the electrode layer,
In a state where one of the two piezoelectric layers is in contact with a liquid, a conductor that contacts the liquid outside the piezoelectric element becomes a high potential electrode, and the electrode layer becomes a low potential electrode. A first measurement step of measuring a resistance value between the conductor and the electrode layer while applying a first electric field between the electrodes;
After the application of the first electric field is canceled, the piezoelectric element whose resistance value measured in the first measurement step is less than the first threshold value is between the conductor and the electrode layer. And a second measuring step for measuring the resistance value of the piezoelectric element.   In the second measuring step, while applying a second electric field between the electrodes so that the conductor becomes a low potential electrode and the electrode layer becomes a high potential electrode, the conductor and the electrode layer The method for inspecting a piezoelectric element according to claim 1, wherein a resistance value between the two is measured.   The method for inspecting a piezoelectric element according to claim 2, wherein the second electric field is smaller than the first electric field. The piezoelectric element whose resistance value measured in the first measurement step is not less than the first threshold value is one in which a crack penetrating the one piezoelectric layer is not formed,
The piezoelectric element whose resistance value measured in the second measurement step is less than a second threshold value is one in which a crack penetrating the two piezoelectric layers and the electrode layer is formed.
The piezoelectric element whose resistance value measured in the second measuring step is equal to or greater than the second threshold is formed with a crack that penetrates the one piezoelectric layer and does not penetrate the other piezoelectric layer. The method for inspecting a piezoelectric element according to any one of claims 1 to 3, further comprising a determination step of determining that there is one. A liquid discharge apparatus including a plurality of liquid discharge heads,
Each liquid discharge head
A plurality of individual liquid flow paths each including a discharge port for discharging liquid and a pressure chamber are formed, and a flow path unit made of a conductor at least partially exposed to the plurality of individual liquid flow paths;
A plurality of individual electrodes formed on the surface of one of the two piezoelectric layers so as to face the common electrode layer; and a common electrode layer, two piezoelectric layers sandwiching the common electrode layer A piezoelectric layer attached to the flow path unit so that the plurality of individual electrode layers face the plurality of pressure chambers and the plurality of individual electrode layers face away from the flow path unit. Elements and
In the plurality of liquid ejection heads,
A first liquid ejection head having the piezoelectric element, the resistance value of which is determined to be equal to or greater than the first threshold value by the piezoelectric element inspection method according to claim 4;
And a second liquid discharge head having the piezoelectric element, the resistance value of which is determined to be equal to or greater than the second threshold value by the piezoelectric element inspection method according to claim 4,
The liquid discharge apparatus, wherein the first liquid discharge head and the second liquid discharge head discharge different types of liquid. The first liquid discharge head discharges the pretreatment liquid;
The liquid ejecting apparatus according to claim 5, wherein the second liquid ejecting head ejects ink. The first liquid discharge head discharges black ink;
The liquid discharge apparatus according to claim 5, wherein the second liquid discharge head discharges color ink. A method of manufacturing a liquid discharge apparatus including a plurality of liquid discharge heads,
A plurality of individual liquid flow paths each including a discharge port and a pressure chamber for discharging liquid, a flow path unit made of a conductor at least partially exposed to the plurality of individual liquid flow paths, a common electrode layer, Two piezoelectric layers sandwiching the common electrode layer, and a plurality of individual electrode layers formed on the surface of one of the two piezoelectric layers so as to face the common electrode layer A piezoelectric element attached to the flow path unit such that the plurality of individual electrode layers face the plurality of pressure chambers and the plurality of individual electrode layers face in a direction opposite to the flow path unit. A head manufacturing process for manufacturing the plurality of liquid discharge heads;
After the head manufacturing process, when the other piezoelectric layer of the two piezoelectric layers is in contact with the liquid in the pressure chamber, the conductor in contact with the liquid becomes a high potential electrode and the common electrode layer A first measurement step of measuring a resistance value between the conductor and the common electrode layer while applying a first electric field between the electrodes so that the electrode becomes a low potential electrode;
After the application of the first electric field is canceled, the electric conductor and the common electrode layer are applied to the piezoelectric element whose resistance value measured in the first measurement step is less than a first threshold value. A second measuring step for measuring a resistance value between the two,
The piezoelectric element whose resistance value measured in the first measurement step is equal to or greater than the first threshold value has no crack penetrating the other piezoelectric layer, and the second measurement The piezoelectric element whose resistance value measured in the process is less than the second threshold value is one in which a crack penetrating the two piezoelectric layers and the common electrode layer is formed. In the second measurement process, Determination step of determining that a piezoelectric element having a measured resistance value equal to or greater than the second threshold is formed with a crack that penetrates the other piezoelectric layer and does not penetrate the one piezoelectric layer. When,
A first liquid ejection head having the piezoelectric element, in which the resistance value is determined to be greater than or equal to the first threshold value in the determination step; and the resistance value in the determination step is the second threshold value. An assembly step of assembling both the second liquid ejection head having the piezoelectric element determined to be the above and a support member that supports the plurality of liquid ejection heads,
In the assembly step, the first liquid discharge head is assembled to the support member so that the first liquid can be supplied to the first liquid discharge head, and the first liquid discharge head is attached to the second liquid discharge head. A method of manufacturing a liquid ejection apparatus, wherein the second liquid ejection head is assembled to the support member so as to be able to supply a second liquid of a type different from that of the liquid.

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