JP2010233428A - Device for drive of piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a drive circuit failure due to charging of a first active part before the drive circuit performs a drive operation immediately after supply of a power supply voltage from a power supply. <P>SOLUTION: A drive circuit 61 is connected with a first power supply system 70 so as to be applied with a drive potential from a control board 60. An intermediate electrode 44a being the side of one end of a capacitor 81 is connected with a second power supply system 71 branched from the first power supply system 70 so as to be directly applied with the drive potential from the control board 60. A lower electrode 43 being the side of one end of the capacitor 82 is connected to the ground. An upper electrode 45 being the side of the other end of each capacitor 81, 82 is connected to an output terminal of the drive circuit 61 so as to be selectively applied with either one potential of the drive potential and a ground potential. In the second power supply system 71, a resistor 83 is connected in series to the capacitor 81 while a capacitor 84 is connected in parallel to the capacitor 81. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a drive device for a piezoelectric actuator.

  Conventionally, as shown in FIG. 9A, a piezoelectric layer 212 is laminated and disposed on the upper surface of a diaphragm 211 serving as one electrode, and the piezoelectric layer 212 has an electrode 213 formed on the upper surface thereof. An actuator 210 is known. In such a piezoelectric actuator 210, a portion sandwiched between the electrode 213 and the diaphragm 211 of the piezoelectric layer 212 is an active portion R <b> 10 that is deformed by a potential difference between the two, and the ground potential output from the drive circuit 201 to the electrode 213. One of predetermined drive potentials different from the ground potential is applied, and the ground potential is applied to the diaphragm 211. The drive circuit 201 is connected to the power supply 200 and is driven by the power supply voltage supplied from the power supply 200. Then, the piezoelectric actuator 210 drives the object by utilizing the deformation (piezoelectric strain) of the active portion R10 when an electric field is applied due to a potential difference generated between the electrode 213 and the diaphragm 211 (for example, a patent) Reference 1).

  By the way, the active part R10 can be regarded as a capacitor to be charged / discharged since the insulating piezoelectric layer 212 is sandwiched between the electrode 213 and the diaphragm 211. As shown in FIG. 9B, the electrical configuration from the power source 200 to the piezoelectric actuator 210 is such that the power source 200 is connected to the drive circuit 201 and the output terminal of the drive circuit 201 is the active part R10. Can be regarded as an equivalent circuit in which a ground is connected to the other end (diaphragm 211) of the capacitor 202. A capacitor 204 is connected in parallel to the drive circuit 201. The capacitor 204 suppresses a voltage drop so that the power supply voltage supplied from the power supply 200 to the drive circuit 201 is always constant, and prevents a voltage higher than the power supply voltage from being supplied to the drive circuit 201. It is. In such a piezoelectric actuator 210, a high voltage is not applied to the output terminal of the drive circuit 201.

  In addition to the piezoelectric actuator described in Patent Document 1, the first electrode to which the power supply voltage is directly applied from the power source, the second electrode to which the ground potential is applied, and the drive circuit 201 output the piezoelectric actuator. A third electrode to which one of the ground potential and the driving potential is applied, and not only between the second electrode and the third electrode, but also between the first potential and the third potential ( There is what constitutes the first active part).

  For example, in the piezoelectric actuator 32 as described in Japanese Patent Application No. 2008-094150 (see FIG. 6 of this application), two piezoelectric layers 41 and 42 are laminated on the upper surface of the diaphragm 40, On the upper surface of the diaphragm 40, the upper surface of the lower piezoelectric layer 41, and the upper surface of the upper piezoelectric layer 42, a lower electrode 43 (second electrode), an intermediate electrode 44a (first electrode), and an upper electrode 45 ( A third electrode) is formed. A portion of the upper piezoelectric layer 42 sandwiched between the intermediate electrode 44a and the upper electrode 45 is a first active portion R1. On the other hand, the two piezoelectric layers 41 and 42 are sandwiched between the upper electrode 45 and the lower electrode 43, and the outer peripheral part of the first active part R1 in plan view is the second active part R2. In such a piezoelectric actuator 32, the lower electrode 43 is held at the ground potential, while the intermediate electrode 44a is held at a predetermined positive potential (for example, about 20V), the potential of the upper electrode 45 is set to the ground potential. Selectively switch with positive potential. Then, the first active part R1 and the second active part R2 are deformed by switching the potential.

  The electrical configuration from the power source to the piezoelectric actuator in such a configuration includes the output terminal of the drive circuit 201 as shown in FIG. 10 in addition to the electrical configuration from the conventional power source to the piezoelectric actuator as described above. Is connected to one end (upper electrode 45) of the capacitor 205, which is the first active part R1, and can be regarded as an equivalent circuit in which the power source 200 is directly connected to the other end (intermediate electrode 44a).

JP 2005-35018 A

  In general, when a high voltage is applied to an output terminal before a power supply voltage is driven to drive an IC such as a drive circuit, an internal transistor or the like may be destroyed and break down. There is. Here, in the electrical configuration from the power supply 200 to the piezoelectric actuator 32 in the piezoelectric actuator 32 described in Japanese Patent Application No. 2008-094150, the drive circuit 201 is driven immediately after the power supply voltage is supplied from the power supply 200 to the drive circuit 201. Before the charging, the charging of the capacitor 205 which is the first active portion R1 sandwiched between the intermediate electrode 44a and the upper electrode 45 is started, and there is a possibility that a current flows through the capacitor 205 momentarily. Then, the potential of the upper electrode 45 connected to the output terminal of the drive circuit 201 becomes instantaneously high, and as a result, the drive circuit 201 may break down as described above.

  Accordingly, an object of the present invention is to provide a drive device for a piezoelectric actuator that prevents a failure of the drive circuit during charging of the first active part immediately after the power supply voltage is supplied from the power supply to the drive circuit.

  The drive device for a piezoelectric actuator according to the present invention includes a piezoelectric layer and a first electrode, a second electrode, and a third electrode provided on the piezoelectric layer, and the first electrode has a predetermined first potential. A predetermined second potential lower than the first potential is applied to the second electrode, and the potential of the third electrode is switched between the first potential and the second potential; A first active portion composed of a piezoelectric layer sandwiched between one electrode and the third electrode, and acting as a capacitor by a potential difference between the two electrodes; and a piezoelectric sandwiched between the second electrode and the third electrode A drive circuit comprising a layer portion and comprising a second active portion that acts as a capacitor in the same manner as the first active portion, and switches the potential of the third electrode between the first potential and the second potential; A first power supply system for connecting a circuit and a power supply, and the first power supply A second power feeding system that branches from the main and connects the power source and the first electrode without passing through the drive circuit, and applies the first potential to the first electrode, and the second power feeding system. The first resistor is provided in series with the first active portion, and the first capacitor is provided in parallel with the first active portion.

  According to the piezoelectric actuator driving apparatus of the present invention, in the second power feeding system that charges the first active part acting as a capacitor, a resistor is provided in series with the first active part, and a capacitor is provided in parallel. The RC time constant of the second power feeding system is increased to slow the rise of the voltage applied to the first electrode, thereby delaying the charging speed of the first active part. As a result, after the power supply voltage is supplied from the power supply to the drive circuit via the first power supply system, the first active part starts to be slowly charged, and the third electrode (drive circuit) is started before the drive circuit starts driving. No high potential is applied to the output terminal. Therefore, it is possible to prevent a failure of the drive circuit due to charging of the first active part immediately after the power supply voltage is supplied from the power supply and before the drive circuit is driven. The first capacitor suppresses the potential applied from the power source to the first electrode during normal driving of the piezoelectric actuator from being lower than the first potential during charging / discharging of the first active portion, and the first capacitor It also has a role of preventing a potential higher than the first potential from being applied to one electrode.

  In the first power feeding system, it is preferable that a second resistor is provided in series with the drive circuit, and a second capacitor is provided in parallel with the drive circuit. According to this, similarly to the second power supply system, the RC time constant of the first power supply system can be increased by providing a resistor in series with the drive circuit and a capacitor in parallel in the first power supply system. Thus, the supply of power supply voltage from the power supply to the drive circuit can be delayed. Moreover, since the 2nd electric power feeding system connected to the 1st electrode has branched from this 1st electric power feeding system, the influence of the time constant of the 1st electric power feeding system also affects the 2nd electric power feeding system, The rise in the potential of the third electrode caused by charging is further delayed. The second capacitor suppresses the potential applied from the power source to the drive circuit from being lower than the first potential during normal driving of the piezoelectric actuator, and the potential higher than the first potential is applied to the drive circuit. It also has a role to prevent it from being granted.

  The RC time constant of the second power feeding system is increased to slow the rise of the voltage applied to the first electrode, thereby delaying the charging speed of the first active part. As a result, after the power supply voltage is supplied from the power supply to the drive circuit via the first power supply system, the first active part starts to be slowly charged, and the third electrode (drive circuit) is started before the drive circuit starts driving. No high potential is applied to the output terminal. Therefore, it is possible to prevent a failure of the drive circuit due to charging of the first active part immediately after the power supply voltage is supplied from the power supply and before the drive circuit is driven.

1 is a schematic configuration diagram of a printer according to an embodiment. It is a perspective view of an inkjet head. It is a top view of an inkjet head. (A) is the elements on larger scale of FIG. 3, (b)-(d) is a figure of the surface of the diaphragm of (a) and each piezoelectric layer. It is the VV sectional view taken on the line of Fig.4 (a). It is the VI-VI sectional view taken on the line of Fig.4 (a). It is a figure which shows roughly the connection structure of a piezoelectric actuator and a control board. It is an equivalent circuit diagram from a control board to an upper electrode, an intermediate electrode, and a lower electrode. It is a figure which shows roughly the connection structure from the power supply in the past to two electrodes, (a) is a schematic block diagram, (b) is an equivalent circuit schematic. It is the equivalent circuit schematic from the power supply in the past to an upper electrode, an intermediate electrode, and a lower electrode.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 is a schematic configuration diagram of a printer according to the present embodiment. As shown in FIG. 1, the printer 1 includes a carriage 2, an inkjet head 3, a transport roller 4, a control board 60 (power source: see FIG. 7), and the like.

  The carriage 2 reciprocates in the scanning direction (left and right direction in FIG. 1). The inkjet head 3 is attached to the lower surface of the carriage 2 and ejects ink from nozzles 15 (see FIG. 3) formed on the lower surface. The transport roller 4 transports the recording paper P in the paper feed direction (front side in FIG. 1). In the printer 1, printing is performed on the recording paper P by ejecting ink onto the recording paper P from the nozzles 15 of the inkjet head 3 that reciprocates in the scanning direction together with the carriage 2. Further, the recording paper P for which printing has been completed is discharged in the paper feeding direction by the transport roller 4.

  Next, the inkjet head 3 will be described in detail. FIG. 2 is an exploded perspective view of the inkjet head of FIG. FIG. 3 is a plan view of the inkjet head of FIG. FIG. 4A is a partially enlarged view of FIG. 4B to 4D are views showing the upper surfaces of a diaphragm 40, a lower piezoelectric layer 41, and an upper piezoelectric layer 42, which will be described later, in FIG. 4A, respectively. FIG. 5 is a cross-sectional view taken along line VV in FIG. FIG. 6 is a cross-sectional view taken along line VI-VI in FIG.

  For easy understanding of the drawings, in FIGS. 3 and 4, an ink flow path excluding a pressure chamber 10 and a nozzle 15 of the flow path unit 31 described later is omitted, and in FIG. Illustration of the electrode 43 and the intermediate electrode 44 is omitted. In FIG. 4A, the lower electrode 43 and the intermediate electrode 44, both of which are to be illustrated by dotted lines, are illustrated by two-dot chain lines and one-dot chain lines, respectively. Further, in FIGS. 4B to 4D, a lower electrode 43, an intermediate electrode 44, and an upper electrode 45, which will be described later, are hatched. Further, in FIG. 6, illustration of a portion below the pressure chamber 10 of the flow path unit 31 is omitted.

  As shown in FIGS. 2 to 6, the inkjet head 3 includes a flow path unit 31 and a piezoelectric actuator 32. A COF 50 is connected to the upper surface of the piezoelectric actuator 32 of the inkjet head 3. In the flow path unit 31, a plurality of plates 21 to 27 are stacked on each other, whereby the manifold flow path 11 to which ink is supplied from the ink supply port 9, and the outlet of the manifold flow path 11 through the aperture flow path 12. An ink channel having a plurality of individual ink channels from the pressure chamber 10 to the nozzle 15 through the descender channel 14 is formed. As will be described later, when pressure is applied to the ink in the pressure chamber 10 by the piezoelectric actuator 32, ink is ejected from the nozzle 15 communicating with the pressure chamber 10.

  The plurality of pressure chambers 10 have a substantially elliptical planar shape with the scanning direction (left-right direction in FIG. 3) as the longitudinal direction, and are arranged along the paper feed direction (up-down direction in FIG. 3). Two pressure chamber rows 8 are formed, and such pressure chamber rows 8 are arranged in two rows in the scanning direction to form one pressure chamber group 7. Further, five such pressure chamber groups 7 are arranged along the scanning direction. Here, the pressure chambers 10 constituting the two pressure chamber rows 8 included in one pressure chamber group 7 are arranged so as to be shifted from each other in the paper feeding direction. The plurality of nozzles 15 are also arranged in the same manner as the plurality of pressure chambers 10.

  Then, among these five pressure chamber groups 7, black ink is ejected from the nozzles 15 corresponding to the pressure chambers 10 constituting the right two in FIG. 3, and the pressure constituting the left three in FIG. From the nozzles 15 corresponding to the chambers 10, yellow, cyan, and magenta inks are ejected in order from the nozzles arranged on the right side of FIG. The configuration of other portions of the ink flow path is the same as that of the conventional one, and therefore detailed description thereof is omitted here.

  The piezoelectric actuator 32 includes a vibration plate 40, a lower piezoelectric layer 41, an upper piezoelectric layer 42, a lower electrode 43 (second electrode), an intermediate electrode 44 (first electrode), and an upper electrode 45 (third electrode). . The diaphragm 40 is made of a piezoelectric material mainly composed of lead zirconate titanate, which is a mixed crystal of lead titanate and lead zirconate, and is formed on the upper surface of the flow path unit 31 so as to cover the plurality of pressure chambers 10. Has been placed. The thickness of the diaphragm 40 is about 20 μm. The diaphragm 40 does not necessarily need to be made of a piezoelectric material.

  The lower piezoelectric layer 41 and the upper piezoelectric layer 42 are made of the same piezoelectric material as that of the diaphragm 40, and are laminated on each other and disposed on the upper surface of the diaphragm 40. Moreover, the thickness of the lower piezoelectric layer 41 and the upper piezoelectric layer 42 is about 20 μm, respectively.

  The lower electrode 43 is formed on the upper surface of the vibration plate 40, and is disposed between the vibration plate 40 and the lower piezoelectric layer 41, and corresponds to each pressure chamber group 7 and constitutes each pressure chamber group 7. It extends in the paper feed direction along the pressure chamber rows 8 in a row, and faces a plurality of pressure chambers 10 constituting these two pressure chamber rows 8. Although not shown, the portions extending in the paper feeding direction are connected to each other. Further, COM is input to the lower electrode 43 and is always held at the ground potential (second potential).

  The intermediate electrode 44 is formed on the upper surface of the lower piezoelectric layer 41 and is disposed between the lower piezoelectric layer 41 and the upper piezoelectric layer 42. For each pressure chamber group 7, a plurality of facing portions 44a and connecting portions are provided. 44b, 44c. The plurality of facing portions 44 a have a substantially rectangular planar shape whose length in the paper feeding direction is shorter than that of the pressure chamber 10, and is disposed so as to face the central portion of the plurality of pressure chambers 10.

  The connecting portion 44b extends in the paper feeding direction, and among the two pressure chamber rows 8 constituting each pressure chamber group 7, a plurality of pressure chambers 10 constituting the pressure chamber row 8 arranged on the right side in FIG. 4 are connected to each other on the right side in FIG. 4. The connecting portion 44c extends in the paper feeding direction, and among the two pressure chamber rows 8 constituting each pressure chamber group 7, a plurality of pressure chambers 10 constituting the pressure chamber row 8 arranged on the left side in FIG. 4 are connected to each other on the left side in FIG. Further, VDD2 is input to the intermediate electrode 44, and is always held at a predetermined driving potential (for example, about 20 V: the first potential) different from the ground potential.

  The plurality of upper electrodes 45 are formed on the upper surface (the surface opposite to the lower piezoelectric layer 41) of the upper piezoelectric layer 42, so as to face almost the entire area of the plurality of pressure chambers 10 corresponding to the plurality of pressure chambers 10. And has a substantially rectangular planar shape whose length in the paper feed direction is longer than the facing portion 44a of the intermediate electrode 44. Further, the upper electrode 45 has a part at the end opposite to the nozzle 15 in the scanning direction extending to a part not facing the pressure chamber 10 in the scanning direction, and this part serves as a connection terminal 45 a connected to the COF 50. Yes. The upper electrode 45 is selectively given either a ground potential or the predetermined drive potential (for example, 20 V) from a drive circuit 61 described later.

  By arranging the lower electrode 43, the intermediate electrode 44, and the upper electrode 45 as described above, the upper electrode 45 and the intermediate electrode 44 are opposed to each other in the portion facing the central portion of the pressure chamber 10 in the upper piezoelectric layer 42. Will be. Then, the region is a first active portion R1 by being polarized upward from the intermediate electrode 44 toward the upper electrode 45.

  Further, in the upper piezoelectric layer 42 and the lower piezoelectric layer 41 that face the pressure chamber 10, the upper electrode 45 and the lower electrode in the outer peripheral part (the part that does not face the intermediate electrode 44) than the part that faces the intermediate electrode 44. 43 will face each other. The region is a second active portion R2 because it is polarized downward from the upper electrode 45 toward the lower electrode 43.

  A portion of the lower piezoelectric layer 41 sandwiched between the intermediate electrode 44 and the lower electrode 43 is polarized downward from the intermediate electrode 44 toward the lower electrode 43.

  Here, the operation of the piezoelectric actuator 32 will be described. First, in the standby state before the piezoelectric actuator 32 performs the operation of discharging ink, as described above, the lower electrode 43 and the intermediate electrode 44 are always connected to the ground potential and the predetermined driving potential (for example, 20 V), respectively. And the potential of the upper electrode 45 is previously held at the ground potential. In this state, the upper electrode 45 has a lower potential than the intermediate electrode 44 and has the same potential as the lower electrode 43.

  As a result, a potential difference is generated between the upper electrode 45 and the intermediate electrode 44, an electric field upward in the same direction as the polarization direction is generated in the first active part R1, and the horizontal direction in which the first active part R1 is orthogonal to this electric field. Shrink to. As a result, so-called unimorph deformation occurs, and the upper piezoelectric layer 42, the lower piezoelectric layer 41, and the portion of the diaphragm 40 facing the pressure chamber 10 are deformed so as to be convex toward the pressure chamber 10 as a whole. In this state, the volume of the pressure chamber 10 is smaller than when the upper piezoelectric layer 42, the lower piezoelectric layer 41, and the diaphragm 40 are not deformed.

  When the piezoelectric actuator 32 is driven to eject ink, the potential of the upper electrode 45 is once switched to the predetermined driving potential and then returned to the ground potential. When the potential of the upper electrode 45 is switched to the predetermined driving potential, the upper electrode 45 becomes the same potential as the intermediate electrode 44 and becomes higher than the lower electrode 43. Thereby, the contraction of the first active part R1 is restored. At the same time, a potential difference is generated between the upper electrode 45 and the lower electrode 43, a downward electric field that is the same as the polarization direction is generated in the second active part R2, and the second active part R2 contracts in the horizontal direction. To do. As a result, the upper piezoelectric layer 42, the lower piezoelectric layer 41, and the vibration plate 40 are deformed so as to be convex on the opposite side to the pressure chamber 10, and the volume of the pressure chamber 10 increases.

  Thereafter, when the potential of the upper electrode 45 is returned to the ground potential, the portions of the upper piezoelectric layer 42, the lower piezoelectric layer 41, and the diaphragm 40 facing the pressure chamber 10 as a whole are changed to the pressure chamber 10 as described above. The pressure chamber 10 is deformed so as to be convex, and the volume of the pressure chamber 10 is reduced. As a result, the pressure of the ink in the pressure chamber 10 increases (pressure is applied to the ink in the pressure chamber 10), and the ink is ejected from the nozzle 15 communicating with the pressure chamber 10.

  Further, when the piezoelectric actuator 32 is driven as described above, when the potential of the upper electrode 45 is switched from the ground potential to a predetermined driving potential, the first active portion R1 expands from the contracted state to the state before the contraction. At the same time, since the second active part R2 contracts, the extension of the first active part R1 is partially absorbed by the contraction of the second active part R2. On the other hand, when the potential of the upper electrode 45 is returned from the predetermined drive potential to the ground potential, the first active portion R1 contracts and the second active portion R2 expands to the state before contraction, so the first active portion R1. Is partially absorbed by the extension of the second active part R2.

  From the above, the deformation of the portion of the lower piezoelectric layer 41 and the upper piezoelectric layer 42 facing the pressure chamber 10 is transmitted to the portion facing the other pressure chamber 10 to communicate with the other pressure chamber 10. In other words, the so-called crosstalk, in which the ink ejection characteristics fluctuate, is suppressed.

  Note that a potential difference is always generated in the portion between the intermediate electrode 44 and the lower electrode 43 of the lower piezoelectric layer 41 during the standby state described above and while the piezoelectric actuator 32 is being driven. An electric field in the same direction as the polarization direction is generated in this portion. Thereby, this portion of the lower piezoelectric layer 41 is always contracted in a direction perpendicular to the electric field direction.

  Next, a connection configuration between the piezoelectric actuator 32 of the inkjet head 3 and the control board 60 of the printer 1 will be described. FIG. 7 is a diagram schematically showing a connection configuration between the piezoelectric actuator and the control board. Two driver ICs 51 a and 51 b for driving the piezoelectric actuator 32 are mounted on the COF 50 connected to the piezoelectric actuator 32. The COF 50 is electrically connected to the control board 60 via a flexible printed circuit board (FPC) 102, a carriage board 104, and a flat cable (FFC) 106. A drive circuit 61 is provided in each of the driver ICs 51a and 51b, and a plurality of output terminals of the drive circuit 61 are connected to a plurality of upper electrodes 45 of the piezoelectric actuator 32, respectively.

  The driver ICs 51a and 51b are connected to the plurality of upper electrodes 45 from the drive circuit 61 via the wiring on the COF 50 based on signals input from the control board 60 via the FPC 102, the carriage board 104, and the FFC 106. One of a predetermined drive potential and a ground potential is selectively applied. Each of the driver ICs 51a and 51b mounted on the COF 50 is configured to apply a potential to half of the upper electrodes 45 associated in advance among all the upper electrodes 45 of the piezoelectric actuator 32. Yes.

  Here, various input signals input from the control board 60 to the driver IC 51 will be briefly described. VDD1 is a voltage input of a control low-voltage power supply (eg, 3.3V) for driving the driver IC 51, VDD2 is a voltage input of a high-voltage power supply (eg, 20V) for driving the piezoelectric actuator 32, and COM is a lower part A ground input CLK for the electrode 43 indicates a data transfer clock from the control board 60 to the driver ICs 51a and 51b. In addition, FIRE 1 to 6 do not eject droplets to one nozzle 15, and six types of driving corresponding to a total of six types of ejection modes of five types of droplet ejection sizes (droplet volumes). Waveform data, SINA_1 to 3 and SINB_1 to 3 are serial input of 3-bit selection data for associating one of six types of injection modes with the injection timing of each nozzle 15 for each of driver ICs 51a and 51b. It is.

  In addition, the wiring to which VDD2 is input is branched on the FPC 102 and VCOM having the same potential as VDD2 is input. This VCOM is directly input to the intermediate electrode 44 without passing through the driver ICs 51a and 51b. Signal. Note that the wiring to which VDD2 is input from the control board 60 to the drive circuits 61 of the driver ICs 51a and 52b is defined as the first power feeding system 70, and the VCOM branches from the wiring to which VDD2 is input (first power feeding system 70). The input wiring is a second power feeding system 71 (see FIG. 8).

  Next, an equivalent circuit from the control board 60 to the upper electrode 45, the intermediate electrode 44a, and the lower electrode 43 will be described. In the present embodiment, wiring and a substrate to which a driving potential and a ground potential are supplied from the control substrate 60 to the upper electrode 45, the intermediate electrode 44a, and the lower electrode 43, specifically, the COF 50, the driver IC 51, and the driving circuit. 61, the FPC 102, the carriage substrate 104, and the FFC 106 correspond to the driving device in the present invention. FIG. 8 is an equivalent circuit diagram from the control board to the upper electrode, the intermediate electrode, and the lower electrode. As shown in FIG. 8, the first active portion R1 that is a drive region of the polarized upper piezoelectric layer 42 sandwiched between the upper electrode 45 and the intermediate electrode 44a can be regarded as a capacitor 81 that performs charging and discharging. Further, the second active portion R2 that is a drive region of the polarized lower piezoelectric layer 41 sandwiched between the upper electrode 45 and the lower electrode 43 can be regarded as a capacitor 82 that performs charging and discharging.

  The drive circuit 61 is connected to the first power supply system 70 to which VDD2 is input, and a drive potential is applied from the control board 60 (a power supply voltage is supplied). The intermediate electrode 44 a which is one end side of the capacitor 81 is connected to the second power feeding system 71 branched from the first power feeding system 70, and a driving potential is directly applied from the control board 60. The lower electrode 43 which is one end side of the capacitor 82 is connected to the ground. The upper electrode 45 on the other end side of each of the capacitors 81 and 82 is connected to the output terminal of the drive circuit 61.

  With such a circuit configuration, when VDD2 and COM are input from the control board 60, a predetermined drive potential is directly applied to the intermediate electrode 44a and a ground potential is directly applied to the lower electrode 43. Further, when the power supply voltage is input from the control board 60, the drive circuit 61 is driven, and either one of a predetermined drive potential and a ground potential is selectively applied from the drive circuit 61 to the upper electrode 45. Can be granted.

  Here, generally, in the IC such as the drive circuit 61, if a high voltage is applied to the output terminal before the power supply voltage is supplied and the IC is driven, the internal transistors and the like are destroyed, and a failure occurs. There is a risk of it. In the equivalent circuit as shown in FIG. 8, if a resistor 83 and a capacitor 84, which will be described later, are not connected, the drive circuit 61 is driven immediately after the power supply voltage is supplied from the control board 60 to the drive circuit 61. Before the charging, the charging of the capacitor 81 sandwiched between the intermediate electrode 44 and the upper electrode 45 is started, and there is a possibility that a current flows through the capacitor 81 momentarily. Then, the potential of the upper electrode 45 connected to the output terminal of the drive circuit 61 becomes instantaneously high, and as a result, the drive circuit 61 may break down as described above.

  Therefore, in the present embodiment, in the second power feeding system 71, the resistor 83 (first resistor) is connected in series with the capacitor 81, and the capacitor 84 ( (Second capacitor) is connected. In this way, by configuring the RC circuit in the second power feeding system 71, the time constant is increased, the rise of the voltage applied to the intermediate electrode 44a is smoothed, and the charging speed of the capacitor 81 is delayed. Specifically, the resistor 83 and the capacitor 84 are provided on the COF 50 (see FIG. 7).

  As a result, after the power supply voltage is reliably supplied from the control board 60 to the drive circuit 61 via the first power supply system 70, the capacitor 81 starts to be gradually charged. A high potential is not applied to the electrode 45 (the output terminal of the drive circuit 61). As a result, failure of the drive circuit 61 due to charging of the capacitor 81 immediately after the power supply voltage is supplied from the control board 60 and before the drive circuit 61 is driven can be prevented. The capacitor 84 suppresses the potential applied from the control board 60 to the intermediate electrode 44a during normal driving of the piezoelectric actuator 32 from being lower than a predetermined driving potential during charging / discharging of the capacitor 81, and The intermediate electrode 44a also has a role of preventing a potential higher than a predetermined driving potential from being applied.

  Furthermore, in the present embodiment, in the first power feeding system 70, a resistor 85 (second resistor) is connected in series to the drive circuit 61 and a capacitor is connected in parallel to the drive circuit 61. 86 (second capacitor) is connected. Specifically, the resistor 85 and the capacitor 86 are provided on the FFC 106 (see FIG. 7).

  As described above, in the first power feeding system 70, similarly to the second power feeding system 71, the resistor 85 and the capacitor 86 are provided in series with the drive circuit 61, and the RC circuit in the first power feeding system 70 is provided. Thus, the time constant can be increased and the supply of the power supply voltage from the control board 60 to the drive circuit 61 can be delayed. Further, since the second power feeding system 71 connected to the intermediate electrode 44a is branched from the first power feeding system 70, the time constant of the first power feeding system 70 also affects the second power feeding system 71, and the capacitor The rise in the potential of the upper electrode 45 caused by charging 81 is further delayed. The capacitor 86 suppresses the potential applied from the control board 60 to the drive circuit 61 during the normal driving of the piezoelectric actuator 32 from being lower than a predetermined drive voltage, and applies a predetermined drive potential to the drive circuit 61. It also has a role to prevent the above voltage from being applied.

  Next, modified embodiments in which various modifications are made to the embodiment will be described. However, components having the same configuration as in the above embodiment are given the same reference numerals and description thereof is omitted as appropriate.

  In the present embodiment, the resistor 83 is provided on the COF 50. However, the resistor 83 may be provided at any position as long as it is on the second power feeding system 71, that is, on the wiring to which VCOM is input. Further, although the capacitor 84 is provided on the COF 50, the capacitor 84 may be provided at any position as long as it is between the second power feeding system 71, that is, the wiring to which VCOM is input and the wiring to which COM is input. Further, the resistor 85 is provided on the FFC 106. However, the resistor 85 may be provided at any position such as the carriage substrate 104 or the FPC 102 as long as it is on the first power feeding system 70, that is, the wiring to which VDD2 is input. The capacitor 86 is provided on the FFC 106. However, any capacitor such as the carriage substrate 104 or the FPC 102 may be used as long as it is between the first power feeding system 70, that is, between the wiring to which VCOM is input and the wiring to which COM is input. It may be provided at a position.

  Further, the resistors 83 and 85 may be resistance components depending on the length and width of the wiring instead of the resistance elements. For example, when it is desired to increase the resistance value of the resistor, the length of the wiring is increased or the width is decreased. This eliminates the need for a space for arranging the resistance element, and can save space.

  Further, in the present embodiment, in the first power feeding system 70, the resistor 85 is connected in series to the drive circuit 61, and the capacitor 86 is connected in parallel to the drive circuit 61. However, when the piezoelectric actuator 32 is normally driven, the potential applied from the control board 60 to the intermediate electrode 44a is prevented from being lower than a predetermined drive potential during charging / discharging of the capacitor 81, and the intermediate electrode 44a If only the role of preventing a potential higher than a predetermined drive potential from being applied is provided, only the capacitor 86 may be provided without providing the resistor 85.

  In the present embodiment, the active portion is configured by sandwiching the piezoelectric layer between the two electrodes in the thickness direction. However, the two electrodes are arranged apart from each other in the plane direction of the piezoelectric layer. May be the active part. At this time, the active portion is polarized in the direction in which the electrodes face each other (the surface direction of the piezoelectric layer).

  As described above, in the embodiment described above and the modifications thereof, the present invention is applied to a piezoelectric actuator driving device for an inkjet head that ejects ink onto a recording sheet and records an image or the like. The present invention is not limited to such piezoelectric actuators for ink jet heads, and can be applied to piezoelectric actuator driving devices used for various purposes.

DESCRIPTION OF SYMBOLS 1 Printer 3 Inkjet head 32 Piezoelectric actuator 40 Diaphragm 41, 42 Piezoelectric layer 45 Upper electrode 44 Intermediate electrode 43 Lower electrode 60 Control board 61 Drive circuit 70 1st electric power feeding system 71 2nd electric power feeding system 81, 82, 84, 86 Capacitor 83 , 85 resistor R1 first active part R2 second active part

Claims (2)

A piezoelectric layer, and a first electrode, a second electrode, and a third electrode provided on the piezoelectric layer;
A predetermined first potential is applied to the first electrode, a predetermined second potential lower than the first potential is applied to the second electrode, and the potential of the third electrode is the first potential and the first potential Switched between the second potential,
A piezoelectric layer portion sandwiched between the first electrode and the third electrode, and sandwiched between the second electrode and the third electrode, and a first active portion that acts as a capacitor due to a potential difference between the electrodes. A piezoelectric layer portion, and a second active portion that acts as a capacitor in the same manner as the first active portion,
A drive circuit for switching the potential of the third electrode between the first potential and the second potential;
A first power supply system for connecting the drive circuit and a power source;
Branching from the first power supply system, connecting the power source and the first electrode without going through the drive circuit, and having a second power supply system for applying the first potential to the first electrode,
In the second feeding system, a first resistor is provided in series with the first active part, and a first capacitor is provided in parallel with the first active part. A drive device for a piezoelectric actuator. In the first power feeding system, a second resistor is provided in series with the drive circuit, and a second capacitor is provided in parallel with the drive circuit. Actuator drive.

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