JP2009277822A - Piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric actuator that maintains the polarization property of a piezoelectric material element well, and is suitable for a long duration drive. <P>SOLUTION: In the piezoelectric actuator constituted by adhering a pair of piezoelectric material elements 12 to the front and rear of a shim 11 made of a metal thin plate, an alternating voltage is applied to only one side of the pair of the piezoelectric material elements 12 by an alternating current power supply 16, a feed switching means 20 is provided, which switches the piezoelectric material element 12 to which the alternating voltage is applied, for every constant time longer than the cycle of the alternative voltage. If the piezoelectric material element 12 which is made to drive is switched before the vibration displacement of the piezoelectric material element 12 decreases, or before the temperature rise of the piezoelectric material element 12 increases, the deterioration of the polarization property caused by the temperature rise and the deterioration of vibration property of the piezoelectric material element 12 can be prevented, and the piezoelectric material element 12 which is not made to drive acts so as to increase vibration acceleration. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piezoelectric actuator formed by bonding a pair of piezoelectric bodies to the front and back of a shim made of a thin metal plate.

For example, as described in Patent Documents 1 to 3, a piezoelectric actuator used as a drive source (vibration generating element) such as a piezoelectric pump or a piezoelectric vibration gyro has a pair of piezoelectric bodies bonded to the front and back of a shim made of a thin metal plate. It becomes. Piezoelectric materials have polarization characteristics in the front and back directions. When the positive and negative polarities in the same direction as or in the opposite direction to the polarization direction are given between the front and back surfaces, the surface area of one side expands and the surface area of the other side decreases. is there. For this reason, when the positive and negative polarities applied to the front and back sides of the piezoelectric body are alternately reversed, a cycle in which one of the front and back sides extends and the other shrinks is repeated, and the shim vibrates.
JP 60-219971 A Japanese Patent Laid-Open No. 11-89254 JP 2007-221313 A

  Such a piezoelectric actuator has a problem that when the continuous driving time becomes long, the temperature of the piezoelectric body rises due to dielectric loss, and the polarization characteristics of the piezoelectric body partially disappear. When depolarization (depolarization) occurs, the amount of vibration is reduced and the initial vibration characteristics cannot be maintained. For this reason, the conventional piezoelectric actuator has a short continuous drive time and is not suitable for a long time drive.

  It is an object of the present invention to obtain a piezoelectric actuator that can maintain good polarization characteristics of a piezoelectric body and is suitable for long-time driving.

  According to the present invention, if only one side of the shim front and back piezoelectric bodies is driven with an AC voltage and the piezoelectric body to be driven is switched before the vibration displacement is reduced or before the temperature rise of the piezoelectric body is increased, The present invention has been completed by paying attention to the fact that deterioration of the polarization characteristics and vibration characteristics of the body can be prevented, and that the piezoelectric body on the non-driven side acts to increase vibration acceleration.

  That is, according to the present invention, in a piezoelectric actuator in which a pair of piezoelectric bodies are bonded to the front and back of a shim made of a thin metal plate, an AC voltage is applied only to one side of the pair of piezoelectric bodies, The switching power supply means is provided for switching at regular intervals longer than the cycle of the AC voltage.

  As the continuous driving time of the piezoelectric body becomes longer, the temperature rise due to the dielectric loss of the piezoelectric body increases, and the vibration displacement and vibration acceleration tend to decrease due to the depolarization of the piezoelectric body. Therefore, the predetermined time is preferably set in advance based on the time during which the vibration displacement decreases to a predetermined value when the piezoelectric body on one side is continuously driven with an AC voltage. Alternatively, it is preferably set in advance based on the time during which the vibration acceleration decreases to a predetermined value when the piezoelectric body on one side is continuously driven with an AC voltage. Alternatively, it is preferable to set in advance based on the time during which the temperature of the piezoelectric body rises to a predetermined temperature when the piezoelectric body on one side is continuously driven with an alternating voltage. According to this aspect, it is possible to switch the piezoelectric body to be driven by the AC voltage before the vibration displacement is greatly reduced or before the temperature rise of the piezoelectric body is increased.

  It is practical that the switching power supply means is a switch means for switching between a first power supply path for applying an AC voltage to one piezoelectric body and a second power supply path for applying an AC voltage to the other piezoelectric body. .

  According to the present invention, only one side of the piezoelectric body on the front and back of the shim is driven with an AC voltage, and the driven piezoelectric body is switched before the vibration displacement is greatly reduced or the temperature rise of the piezoelectric body is increased. Without excessively increasing the temperature of the piezoelectric body, the polarization characteristics of the piezoelectric body can be maintained well, and a piezoelectric actuator suitable for long-time driving can be obtained.

FIG. 1 is a sectional view showing a schematic configuration of a piezoelectric actuator according to the present invention. The piezoelectric actuator 10 includes a shim 11 made of a thin metal plate and a pair of piezoelectric bodies 12 bonded to the front and back of the shim 11. Specifically, the shim 11 is made of a thin stainless steel plate having a thickness of about 0.2 mm, and the pair of piezoelectric bodies 12 is made of PZT (Pb (Zr, Ti) O ₃ ) having a thickness of about 0.3 mm. The piezoelectric actuator 10 is used as a drive source (vibration generating element) such as a piezoelectric pump or a piezoelectric vibration gyro.

  The pair of piezoelectric bodies 12 are polarized in the front and back direction (thickness direction). In FIG. 1, when the polarization direction of the pair of piezoelectric bodies 12 is represented by an arrow a or b, polarization processing in the same direction is performed in the thickness direction of the shim 11. Film electrodes 13 are entirely formed on both surfaces of the pair of piezoelectric bodies 12, and the surface on the shim 11 side (bonding surface with the shim 11) is bonded so as to be electrically connected to the shim 11. . The film electrode 13 is formed by printing and baking a conductive paste such as AgPd, for example. The material and forming method of the membrane electrode are well known. The surface side conductor 14A is connected to the exposed surface (film electrode 13) of the piezoelectric body 12A on the shim surface side, and the back surface conductor 14B is connected to the exposed surface (film electrode 13) of the piezoelectric body 12B on the back surface side of the shim. Has been.

  An AC power supply 16 is connected to the shim 11 via a shim-side conductor 15. The AC power supply 16 generates an AC voltage (drive voltage) to be applied to the piezoelectric body 12. A common conductor 17 is connected to the other end of the AC power supply 16.

  The piezoelectric actuator 10 described above includes a changeover switch 20 as a changeover power feeding means between the common conductor 17, the front side conductor 14A, and the back side conductor 14B. The changeover switch 20 is a switch that alternatively connects the front side conductor 14 </ b> A and the back side conductor 14 </ b> B to the common conductor 17. The changeover switch 20 switches the power supply path to the pair of piezoelectric bodies 12 by changing the switch state every predetermined time sufficiently longer than the period of the AC voltage from the AC power supply 16 (vibration period of the piezoelectric actuator 10). The piezoelectric body 12 to be driven with an alternating voltage is switched. FIG. 2 shows the switch state of the changeover switch 20, and FIG. 3 shows the displacement shape of the shim 11. 2 and 3, the membrane electrode 13 is not shown.

  When the changeover switch 20 is in the first state connecting the common conductor 17 and the surface-side conductor 14A (FIG. 2 (a)), the first power supply path indicated by the arrow I1 is formed, and the shim surface-side piezoelectric body is formed. An AC voltage is applied only to 12A. Thereby, the piezoelectric body 12A on the front side of the shim is driven with an AC voltage, and the piezoelectric body 12B on the back side of the shim is not driven. If the polarization direction of the piezoelectric body 12A on the shim surface side is the same as the voltage application direction, the piezoelectric body 12A on the shim surface side contracts and the piezoelectric body 12B on the back surface side of the shim does not expand and contract. Turn over as shown in If the voltage application direction is reverse, the piezoelectric body 12A on the shim surface side extends and the piezoelectric body 12B on the back surface side of the shim does not expand and contract, so that the shim 11 warps downward as shown in FIG. By repeating this, the shim 11 vibrates. During the vibration, the piezoelectric body 12B on the back side of the shim that is not driven acts as a weight of the piezoelectric body 12A on the front side of the shim that is driven, and increases vibration acceleration (see FIG. 5).

  On the other hand, when the changeover switch 20 is in the second state in which the common conductor 17 and the back side conductor 14B are connected (FIG. 2B), a second power supply path indicated by an arrow I2 is formed, and the shim back side An AC voltage is applied only to the piezoelectric body 12B. As a result, the piezoelectric body 12B on the back side of the shim is driven with an alternating voltage, and the piezoelectric body 12A on the front side of the shim is not driven. If the direction of voltage application is the same as the polarization direction of the piezoelectric body 12B on the back side of the shim, the piezoelectric body 12A on the front side of the shim does not expand and contract, and the piezoelectric body 12B on the back side of the shim contracts. Warps downward as shown in (b). If the voltage application direction is reverse, the piezoelectric body 12A on the front side of the shim does not expand and contract, and the piezoelectric body 12B on the back side of the shim extends, so that the shim 11 warps upward as shown in FIG. By repeating this, the shim 11 vibrates. During this vibration, the non-driven shim surface side piezoelectric body 12A acts as a weight of the shim back surface side piezoelectric body 12B and increases vibration acceleration (see FIG. 5).

  The switch state of the changeover switch 20 may be configured to be automatically switched by a timer, or may be configured to be switched by an external control means.

  As described above, the changeover timing of the changeover switch 20 is every fixed time sufficiently longer than the cycle of the AC voltage applied to the piezoelectric body 12. The period of the AC voltage is about 1 Hz or more (1 sec) to several hundred Hz, and sufficiently longer than the period of the AC voltage means not a unit of seconds or minutes but a unit of time.

4 shows a piezoelectric actuator 10 of FIG. 1 in which one side of a pair of piezoelectric bodies 12 is driven with an alternating voltage (± 90 V, 20 Hz), and vibration acceleration [m / s ² ] and vibration displacement [μm] with respect to drive time [hour]. It is a graph which shows the change of]. As is apparent from FIG. 4, there is no significant deterioration in both vibration acceleration and vibration displacement for several hours after the start of driving, and both vibration acceleration and vibration displacement deteriorate rapidly as the driving time becomes longer than about 3 hours. ing.

  Referring to the characteristics of FIG. 4, the predetermined time for switching the switch state is based on the time during which the vibration displacement decreases to a predetermined value D when one side of the pair of piezoelectric bodies 12 is continuously driven with an AC voltage. Is set. The predetermined value D is preferably about 70 to 90% of the vibration displacement at the start of driving. In the piezoelectric actuator 10 of this embodiment, since the deterioration of vibration acceleration and vibration displacement is small from the start of driving to 2 hours, the switch state is switched in 2 hours.

FIG. 5 is a graph showing a result of measuring the vibration acceleration [m / s ² ] of the resin block 32 generated by the vibration of the piezoelectric actuator 10 while changing the AC voltage [Vp−p] applied to the piezoelectric body 12. The case where only one side of the pair of piezoelectric bodies 12 is driven is compared with the case where both sides are driven. This measurement is performed in a state where the piezoelectric actuator 10 is fixed with a screw 33 to a resin block 32 supported by a soft sponge 31 as shown in FIG. The acceleration pickup 34 is installed on the opposite side of the resin block 32 from the piezoelectric actuator 10 side, and measures vibration acceleration generated in the resin block 32 during driving of the piezoelectric actuator 10. Based on the measured vibration acceleration, the excitation force generated by the piezoelectric actuator 10 is known. A rectangular wave AC voltage having a frequency of 50 Hz was used as the AC voltage applied to the piezoelectric body 12.

  As is apparent from FIG. 5, the vibration acceleration is greater when only one piezoelectric body 12 is driven than when both piezoelectric bodies 12 are driven. It is considered that when only one piezoelectric body 12 is driven, it acts as a weight of the piezoelectric body 12 driven by the non-driven piezoelectric body 12 and increases vibration acceleration. As the AC voltage applied to the piezoelectric body 12 increases, the vibration acceleration increases, and the vibration acceleration difference between driving only one side of the pair of piezoelectric bodies 12 and driving the piezoelectric bodies 12 on both sides also increases. .

  As described above, in the present embodiment, the first power supply path and the second power supply path are switched via the changeover switch 20 every predetermined time sufficiently longer than the cycle of the AC voltage, and are driven by the AC voltage. Body 12 changes. If the pair of piezoelectric bodies 12 on the front and back of the shim are driven one side in this way, the temperature rise due to the dielectric loss of the piezoelectric body 12 can be suppressed as compared to the case where the pair of piezoelectric bodies 12 are driven on both sides. Polarization deterioration of the piezoelectric body 12 can be avoided. Thereby, the polarization characteristics of the piezoelectric body 12 can be maintained satisfactorily, and the piezoelectric actuator 10 suitable for long-time driving can be obtained.

  Although the switching timing of the changeover switch 20 is set using vibration displacement as a parameter in this embodiment, vibration acceleration or the temperature of the driven piezoelectric body 12 can be used as a parameter instead of vibration displacement. . When using vibration acceleration, it is preferable to set in advance based on the time during which vibration acceleration decreases to a predetermined value A when one side of the pair of piezoelectric bodies 12 is continuously driven with an AC voltage. The predetermined value A is about 70 to 90% of the vibration acceleration at the start of driving. When the temperature of the driven piezoelectric body 12 is used, the temperature is set in advance based on the time during which the temperature of the piezoelectric body rises to a predetermined temperature T1 when the piezoelectric body on one side is continuously driven with an AC voltage. Is preferred. The predetermined temperature T1 is set to a temperature that is lower than the temperature T2 at which the depolarization of the piezoelectric body 12 occurs and does not significantly deteriorate the vibration displacement (T1 <T2).

  The piezoelectric actuator according to the present invention can be used in various applications other than a driving source such as a piezoelectric pump and a piezoelectric vibration gyro.

It is sectional drawing which shows schematic structure of the piezoelectric actuator by this invention. (A) (b) It is a schematic diagram which shows the switch state of a changeover switch. (A) (b) It is a schematic cross section which shows the displacement shape of a shim. It is a graph which shows the relationship between the continuous drive time of a piezoelectric material, vibration acceleration, and vibration displacement. It is a graph which shows the relationship between the alternating voltage applied to a piezoelectric material, and vibration acceleration. It is (a) top view explaining the measurement state of FIG. 5, (b) B arrow directional view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piezoelectric actuator 11 Shim 12 Piezoelectric body 12A Shim surface side piezoelectric body 12B Shim back surface side piezoelectric body 13 Film electrode 14A Front surface side conductor 14B Back surface side conductor 15 Shim side conductor 16 External power supply 17 Common conductor 20 Changeover switch 31 Sponge 32 Resin block 33 Screw 34 Accelerometer

Claims (5)

In a piezoelectric actuator formed by bonding a pair of piezoelectric bodies to the front and back of a shim made of a thin metal plate,
A piezoelectric device comprising switching power feeding means for applying an alternating voltage only to one side of the pair of piezoelectric bodies and switching the piezoelectric body to which the alternating voltage is applied at a predetermined time longer than the period of the alternating voltage. Actuator. 2. The piezoelectric actuator according to claim 1, wherein the predetermined time is set in advance based on a time during which the vibration displacement decreases to a predetermined value when the piezoelectric body on one side is continuously driven with an AC voltage. 2. The piezoelectric actuator according to claim 1, wherein the predetermined time is set in advance based on a time during which the vibration acceleration decreases to a predetermined value when the piezoelectric body on one side is continuously driven with an AC voltage. 2. The piezoelectric actuator according to claim 1, wherein the predetermined time is set in advance based on a time during which the temperature of the piezoelectric body rises to a predetermined temperature when the piezoelectric body on one side is continuously driven with an AC voltage. Actuator. 5. The piezoelectric actuator according to claim 1, wherein the switching power supply unit applies a first power supply path for applying an AC voltage to one piezoelectric body and an AC voltage to the other piezoelectric body. 6. A piezoelectric actuator which is switch means for switching between the second power supply path.

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