JP2005237145A - Drive circuit for piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive circuit for a piezoelectric element, which can enlarge the amplitude of the piezoelectric element and can raise the travel speed of an engaging member in case that it is used for an actuator. <P>SOLUTION: The piezoelectric element 26 is equipped with a first drive circuit comprising a first switching circuit 141 and a second switching circuit 142 for applying drive voltage HV from its positive direction to the polarizing direction of itself, and a second drive circuit comprising the third switching circuit 143 and the fourth switching circuit 144 for applying a drive voltage V from its negative direction to the polarizing direction of the element to the piezoelectric element 26. The absolute value of the drive voltage HV, supplied to the first drive circuit, is made larger than the absolute value of the drive voltage V supplied to the second drive circuit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention drives a piezoelectric element particularly used for driving an XY moving stage, a camera photographing lens, a projection lens of an overhead projector, a binocular lens, a head feeding of a fixed magnetic disk device, and the like. This relates to a driving circuit.

  2. Description of the Related Art Conventionally, there has been an impact type piezoelectric actuator configured such that an engaging member to which a photographic lens or the like is attached is frictionally engaged with a rod-like driving member with a predetermined frictional force, and a piezoelectric element is fixed to one end of the driving member. Are known. For example, FIG. 12 is a diagram showing a schematic configuration of a piezoelectric actuator for adjusting the photographing lens position of the camera, and FIG. 13 is a diagram showing an example of displacement of a driving member of the piezoelectric actuator.

  12 includes a piezoelectric element 101, a rod-like drive member 102 driven by the piezoelectric element 101, an engagement member 103 frictionally engaged with the drive member 102 with a predetermined frictional force, and the piezoelectric element 101. And a drive circuit 104 for applying a drive voltage.

  The piezoelectric element 101 expands and contracts according to the drive voltage applied by the drive circuit 104, and one end in the expansion / contraction direction is fixed to one end in the axial direction of the drive member 102. The engaging member 103 has a photographing lens L, which is a driving object, fixed to a predetermined location, and is movable along the axial direction on the driving member 102.

  A drive circuit used for this piezoelectric actuator is disclosed in, for example, Japanese Patent Laid-Open No. 2000-350482 (Patent Document 1). As shown in FIG. 14, the drive circuit disclosed in Patent Document 1 includes an H-type bridge circuit, and includes drive P-channel FETs (field effect transistors) 71 and 73, drive N-channel FETs 72 and 74. It has. Each FET has its control terminal connected to the control circuit 104a, and switches the conduction state and the interruption state of each FET 71 to 74 in response to a control signal from the control circuit 104a.

FIG. 15 is a timing chart showing the operation sequence of the piezoelectric actuator of FIG. 12, and shows the voltage applied to the gate-to-ground battery and the piezoelectric element 101 of each FET. The P-channel FETs (71, 73) are turned on when the gate voltage is 0 (v), and are turned off when the gate voltage is E (v). The N-channel FETs (72, 74) are cut off when the gate voltage is 0 (v), and are turned on when the gate voltage is E (v). For example, in the period A in FIG. 15, the gate to ground voltage of the FET 73 is V, the gate to ground voltage of the FET 71 is 0 (v), the gate to ground voltage of the FET 74 is 0 (v), and the gate to ground voltage of the FET 72 is V. Only the FET 72 becomes conductive, and a voltage of + V is applied to the piezoelectric element 101. On the other hand, in the period B, only the FETs 73 and 74 are in a conductive state, and thus a voltage of −V is applied to the voltage element 101. As described above, from the timing chart of FIG. 15, an AC voltage twice the power supply voltage V is applied to both ends of the piezoelectric element 101.
JP 2000-350482 A

  However, the conventional piezoelectric actuator has a problem that the displacement of the driving member 102 is small and the moving speed of the engaging member 103 cannot be increased. Here, the moving speed of the engaging member 102 is substantially proportional to the driving frequency and deformation amount of the piezoelectric element. Further, since the amount of deformation of the piezoelectric element can be increased by increasing the driving voltage, increasing the moving speed of the engaging member can be realized by increasing the driving frequency or driving voltage. That's right.

  However, with regard to increasing the drive frequency, there is an upper limit on the drive frequency because of the mechanical resonance characteristics of the elastic body composed of the piezoelectric element 101 and the drive member 102, and the drive frequency cannot be increased too much. On the other hand, for increasing the voltage, for example, in the drive circuit of FIG. 14, the power supply voltage V is applied to both electrodes of the piezoelectric element 101 in the positive direction and the negative direction. When applied, there is a problem that the polarization is released and the actuator does not function.

  FIG. 16 is a diagram showing the electric field induced strain characteristics of the piezoelectric element 101. When the piezoelectric element 101 is used as an actuator, a high electric field up to the strain A point is applied to give a hysteresis characteristic as shown. (Hereinafter, this is referred to as polarization.) As shown by L1 in the figure after polarization, an alternating electric field (± V) having a strain characteristic in which a strain history remains even when no electric field is applied, and is smaller than the polarization electric field Em. By applying, a distortion having a substantially linear correlation between the applied electric field and the distortion, such as point a to point b in FIG. 16, is generated, and a displacement corresponding to the applied voltage is obtained. On the other hand, when the negatively applied electric field −V exceeds the coercive electric field −Ex, the illustrated hysteresis characteristic changes and the polarization is released. In order to prevent this depolarization, there is a limit to the negative voltage in the polarization direction to be applied, and it is necessary to set the drive voltage so that the applied voltage does not exceed the negative coercive field. For this reason, the width of the drive voltage applied to the drive circuit is limited by the magnitude of the negative drive voltage with respect to the polarization direction, and the distortion of the obtained piezoelectric element is limited to the range indicated by L in FIG. .

  Therefore, the technical problem to be solved by the present invention is to provide a driving circuit for a piezoelectric element that can increase the vibration width of the piezoelectric element and increase the moving speed of the engaging member when used in an actuator. Is to provide.

  In order to solve the above technical problem, the present invention provides a drive circuit for a piezoelectric element having the following configuration.

According to a first aspect of the present invention, there is provided a drive circuit for driving a piezoelectric element that expands and contracts when a drive voltage is applied,
A first driving circuit for applying a driving voltage to the piezoelectric element from a positive direction in the polarization direction of the piezoelectric element; and a second driving circuit for applying a driving voltage to the piezoelectric element from a negative direction in the polarization direction of the piezoelectric element. The first drive circuit and the second drive so that the absolute value of the drive voltage supplied to the drive circuit and the first drive circuit is larger than the absolute value of the drive voltage supplied to the second drive circuit. There is provided a drive circuit for a piezoelectric element, comprising voltage supply means for supplying a drive voltage to the circuit.

  In the above configuration, the polarization direction is a direction in which a polarization electric field is applied so as to have a strain characteristic in which a strain history remains even when no electric field is applied before the piezoelectric element is used. Of the two drive circuits that apply the drive voltage to the piezoelectric element, the drive voltage in the polarization direction is applied by the first drive circuit, and the drive voltage is applied from the negative direction in the polarization direction by the second drive circuit. The voltage supply means supplies the drive voltage to both drive circuits so that the drive voltage applied by the first drive circuit is greater than the drive voltage applied by the second drive circuit. Therefore, when a drive voltage in the polarization direction is applied by the first drive circuit, the piezoelectric element is greatly deformed, and the deformation amount of the piezoelectric element as a whole increases.

According to a second aspect of the present invention, the first drive circuit includes first switch means having one end connected to the first electrode of the power supply means and the other end connected to one end of the piezoelectric element. A second switch means having one end connected to the other end of the piezoelectric element and the other end connected to the second electrode of the power supply means;
The second drive circuit includes third switch means having one end connected to the first electrode of the power supply means and the other end connected to the other end of the piezoelectric element, and one end connected to the piezoelectric element. A piezoelectric element drive circuit according to a first aspect is provided, comprising: a fourth switch means connected to one end and the other end connected to a second electrode of the power supply means.

According to a third aspect of the present invention, the first drive circuit includes fifth switch means having one end connected to the first electrode of the power supply means and the other end connected to one end of the piezoelectric element. Including
The second drive circuit includes sixth switch means having one end connected to the second electrode of the power supply means and the other end connected to one end of the piezoelectric element;
The first aspect is characterized in that the other end of the piezoelectric element is connected to a third electrode having a potential between the potential of the first electrode and the potential of the second electrode of the power supply means. A driving circuit for the piezoelectric element is provided.

  According to the fourth aspect of the present invention, the absolute value of the drive voltage applied by the second drive circuit is obtained by setting the displacement direction thickness of the piezoelectric element to the coercive electric field determined by the electrolytically induced strain characteristic of the piezoelectric element. Provided is a piezoelectric element drive circuit according to any one of the first to third aspects, wherein the absolute value of the drive voltage applied by the first drive circuit is smaller than the multiplied value and greater than the coercive electric field. To do. According to the above configuration, even when a driving voltage having a negative polarization direction is applied, the polarization of the piezoelectric element is not released and the piezoelectric element is not destroyed. Further, since the polarization direction drive voltage is larger than the coercive electric field, the deformation amount of the piezoelectric element can be greatly increased.

  According to a fifth aspect of the present invention, the piezoelectric element includes the driving member fixed to one end in the expansion / contraction direction of the piezoelectric element, and the engaging member frictionally engaged with the driving member. The first to fourth aspects are piezoelectric elements used in a piezoelectric actuator that moves the drive member and the engagement member relative to each other by expanding and contracting the members so that the expansion and contraction have different speeds. A drive circuit for the piezoelectric element is provided.

  According to the drive circuit for a piezoelectric element of the present invention, the design of the piezoelectric element can be easily changed in various ways as required. For example, since the high drive voltage is applied only in the positive direction with respect to the polarization direction, the deformation amount of the piezoelectric element can be increased. In general, if the drive voltage in the negative direction is reduced in the polarization direction, a high voltage is applied in the negative direction in the polarization direction for some reason. Even in this case, the amount of deformation is not reduced by increasing the drive voltage applied in the positive direction accordingly.

  Further, the driving circuit includes an H-type bridge circuit including a first driving circuit including a first switching unit and a second switching unit, and a second driving circuit including a third switching unit and a fourth switching unit. By forming a half bridge circuit composed of a first drive circuit including the fifth switch means and a second drive circuit including the sixth switch means, the voltage applied to the piezoelectric element is Since only a high drive voltage and a low drive voltage from the second drive circuit are applied, the piezoelectric element can be used for an actuator or the like even if the relationship between the drive voltage and the deformation amount is not directly proportional. .

  Also, by preventing the driving voltage in the negative direction from exceeding the coercive electric field and making the driving voltage in the positive direction exceed the coercive electric field, the polarization of the piezoelectric element is released and the piezoelectric element is prevented from being destroyed. On the other hand, the deformation amount of the piezoelectric element can be increased. Therefore, when this piezoelectric element is used for a piezoelectric actuator, for example, the moving speed of the engaging member can be increased.

  Hereinafter, a piezoelectric actuator according to an embodiment using a drive circuit for a piezoelectric element of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing a basic configuration of an impact type piezoelectric actuator according to an embodiment of the present invention. In FIG. 1, a piezoelectric actuator 10 includes a drive unit 12, a drive circuit 14 that drives the drive unit 12, a member sensor 16 that detects the position of a slider that is an engagement member attached to the drive unit 12, and a drive The proximal end sensor 18 disposed at the proximal end of the unit 12, the distal end sensor 20 disposed at the distal end of the drive unit 12, and a control unit 22 that controls the entire operation.

  FIG. 2 is a perspective view illustrating a configuration example of the drive unit 12. In this figure, the drive unit 12 has an element-fixed structure, and includes a support member 24, a piezoelectric element 26, a rod-like drive shaft 28 and a slider 30.

  The support member 24 holds the piezoelectric element 26 and the drive shaft 28, and is formed by scoring the inside leaving the axial end portions 241 and 242 and the substantially central partition wall 243. Storage space 244 and second storage space 245. In the first accommodation space 244, the piezoelectric element 26 is accommodated so that the expansion / contraction direction, which is the polarization direction, coincides with the axial direction of the support member 24. In addition, the drive shaft 28 and a part of the slider 30 are accommodated in the second accommodation space 245.

  The piezoelectric element 26 is configured by, for example, laminating a plurality of piezoelectric substrates having a required thickness via electrodes (not shown) between the piezoelectric substrates, and a longitudinal direction that is an expansion / contraction direction (lamination direction). One end face of the first housing space 244 is fixed to one end face 241 side end face. The other end 242 of the support member 24 and the partition wall 243 are provided with through holes at the center positions, and the rod-shaped drive shaft 28 having a round cross section passes through these through holes in the second housing space 245 in the axial direction. It is housed so that it can move along.

  An end portion of the drive shaft 28 protruding into the first accommodation space 244 is fixed to the other end surface of the piezoelectric element 26, and an end portion of the drive shaft 28 protruding outside the second accommodation space 245 is predetermined by the leaf spring 32. Is biased toward the piezoelectric element 26 by the spring pressure. The biasing to the drive shaft 28 by the leaf spring 32 is to stabilize the axial displacement of the drive shaft 28 based on the expansion / contraction operation of the piezoelectric element 26.

  The slider 30 includes a base portion 302 having mounting portions 301 on both sides in the axial direction of the drive shaft 28, and a sandwiching member 303 mounted between the mounting portions 301. The base portion 302 is loosely fitted to the drive shaft 28. At the same time, when the sandwiching member 303 is pressed by the leaf spring 304, the slider 30 is coupled to the drive shaft 28 with a predetermined frictional force, and the slider 30 is more than the frictional force. It is possible to move along the axial direction of the drive shaft 28 when a large drive force is applied. The slider 30 is attached with a lens L (see FIG. 1) which is a driving object.

  The member sensor 16 is disposed within a movable range of the slider 30 and is configured by a sensor such as an MR (Magneto Resistive Effect) element or a PSD (Position Sensitive Device) element. The proximal sensor 18 and the distal sensor 20 are configured by sensors such as a photo interrupter. As a result, the position of the slider 30 is detected by the member sensor 16 so that the movement of the slider 30 to a predetermined position can be controlled, while the position of the slider 30 is detected by the proximal sensor 18 and the distal sensor 20. Thus, the slider 30 is prohibited from moving further.

  FIG. 3 is a diagram illustrating a configuration example of the drive circuit 14. As shown in FIG. 3, the drive circuit 14 includes a first switch circuit 141 including a switch element Q1 that is a MOS FET between a connection point a1 to which the drive voltage HV is supplied and a connection point b to be grounded. And a series circuit of a fourth switch circuit 144 composed of a switch element Q4 which is a MOS type FET is connected, and a MOS type is connected between a connection point a2 to which a drive voltage V is supplied and a connection point b to be grounded. A series circuit of a third switch circuit 143 formed of a switch element Q3 that is an FET and a second switch circuit 142 formed of a switch element Q2 that is a MOS type FET is connected, and drive control signals Sc1, Sc2, and the like are connected to the switch circuits 141 to 144, respectively. A control circuit 145 is connected as a control signal supply means for supplying Sc3 and Sc4.

  The switch element Q1 constituting the first switch circuit 141 and the switch element Q3 constituting the third switch circuit 143 are P-channel FETs, and constitute the switch element Q2 and the fourth switch circuit 144 constituting the second switch circuit 142. The switch element Q4 is an N-channel FET. The switch elements Q1 and Q3 that are P-channel FETs are turned on when the drive control signal is at a low level, and the switch elements Q2 and Q4 that are N-channel FETs are turned on when the drive control signal is at a high level. The bridge circuit 146 is configured by connecting the piezoelectric element 26 between the connection point c of the first switch circuit 141 and the fourth switch circuit 144 and the connection point d of the third switch circuit 143 and the second switch circuit 142. Has been.

  In the drive circuit 14 configured as described above, the first switch circuit 141 and the second switch circuit 142 apply the drive voltage HV to the piezoelectric element 26 from the positive direction in the polarization direction, and the inter-terminal voltage Vs becomes + HV. The fourth switch circuit 144 and the third switch circuit 143 are driven from the other side with respect to the piezoelectric element 26 (that is, from the negative direction with respect to the polarization direction). A second drive circuit is configured to apply a drive voltage V lower than the voltage HV and charge the voltage until the inter-terminal voltage Vs becomes −V.

  FIG. 4 is a diagram illustrating a configuration example of a voltage supply circuit that supplies drive voltages having different voltages to the drive circuit of FIG. FIG. 4 shows an example using a DC battery in which a plurality of batteries are connected in series for voltage supply. The battery 50 is configured by connecting a plurality of batteries in series, and a terminal y is provided between the positive terminal x and the negative terminal z. The voltage HV between xy is configured to be higher than the voltage V between yz. The positive terminal x is connected to point a1 of the drive circuit 14, the negative terminal z is connected to point b of the drive circuit 14, and the intermediate terminal y is connected to point a2 of the drive circuit 14. When the bridge circuit 146 is configured by the drive circuit 14 and the piezoelectric element 26 as described above, a voltage of −V to + HV is applied to the piezoelectric element 26.

  The piezoelectric actuator control unit 22 (see FIG. 1) includes a CPU that performs arithmetic processing, a ROM that stores processing programs and data, a RAM that temporarily stores data, and the like, and signals that are input from the member sensor 16 and the like. The control circuit 145 outputs a drive pulse having a predetermined duty ratio based on the above, and the first drive circuit and the second drive circuit are alternately driven by this drive pulse.

  Next, the operation principle of the drive circuit 14 will be described. FIG. 5 is a diagram showing a pulse waveform of the drive voltage of the drive circuit 14, where (a) is set so that the duty ratio D (D = B / A) is 0.3, and (b) is The duty ratio D (D = B / A) is set to be 0.7. As will be described later, when a drive voltage composed of a rectangular wave shown in FIG. 5A is applied to the piezoelectric element 26, the slider 30 moves along the drive shaft 28 in the feeding direction (direction away from the piezoelectric element 26). When a drive voltage composed of a rectangular wave shown in FIG. 5B is applied to the piezoelectric element 26, the slider 30 moves along the drive shaft 28 in the return direction.

  In addition, as a result of confirming the relationship between the duty ratio of the drive voltage composed of a rectangular wave and the moving direction of the slider 30, the relationship shown in FIG. 6 is obtained. That is, when the duty ratio D is in the range of 0.05 to 0.45 (0.05 <D <0.45), the slider 30 moves in the feeding direction, and the duty ratio D is 0.55 to 0.00. When it is within the range of 95 (0.55 <D <0.95), the slider 30 moves in the return direction. Therefore, the duty ratio D can be appropriately set within a range of 0.05 <D <0.45 or 0.55 <D <0.95 as necessary.

  FIG. 7 is a diagram showing the correspondence between the pulse waveform of the drive voltage applied from the drive circuit applied to the piezoelectric element and the displacement due to expansion and contraction of the piezoelectric element. FIG. 7 (a) shows the correspondence between the drive voltage shown in FIG. FIG. 5B shows a case where the drive voltage shown in FIG. 5B is applied. As described above, when a drive voltage having a duty ratio of 0.3 shown in FIG. 5A is applied to the piezoelectric element 26, the sawtooth having a rising portion where the displacement waveform of the piezoelectric element 26 is slow and a sharp falling portion. When the drive voltage having a duty ratio of 0.7 shown in FIG. 5B is applied to the piezoelectric element 26, the sawtooth shape having a sharp rising portion and a slow falling portion of the displacement waveform of the piezoelectric element 26. It becomes.

  When the displacement of the piezoelectric element 26 has a gradual rising portion as shown in FIG. 7A and is gently extended, the slider 30 moves in the feeding direction together with the drive shaft 28. On the other hand, when the displacement of the piezoelectric element 26 has a steep falling portion as shown in FIG. 7A and the piezoelectric element 26 is rapidly reduced, the slider 30 is moved even if the drive shaft 28 moves in the return direction. Overcomes the frictional force with the drive shaft 28, stays at substantially the same position and does not move. For this reason, when the driving voltage shown in FIG. 7A is repeatedly applied to the piezoelectric element 26, the slider 30 moves intermittently in the feeding direction.

  Conversely, when the displacement of the piezoelectric element 26 has a steep rise and a gentle fall as shown in FIG. 7B, the drive voltage shown in FIG. 7B is repeatedly applied to the piezoelectric element 26. As a result, the slider 30 moves intermittently in the return direction.

  FIG. 8 is a diagram for explaining the operation of the drive circuit 14 applied to the piezoelectric actuator 10 according to the present invention. Each switch is output from the control circuit 145 for controlling the drive circuit 14 shown in FIGS. The drive pulse applied to the elements Q1 to Q4 and the waveform of the drive voltage applied to the piezoelectric element 26 are shown. As described above, the drive voltage applied to the piezoelectric element 26 is a rectangular wave, and the duty ratio D is set to 0.3 for the waveform in the feeding direction, and the duty ratio D is set for the waveform in the return direction. Set to 0.7.

  Next, the drive operation of the drive circuit 14 applied to the piezoelectric actuator 10 of the present invention will be described. FIG. 8 is a timing chart showing an operation sequence of the piezoelectric actuator according to the embodiment of the present invention. A period during which both switch elements Q1, Q2 are turned on (at this time, both switch elements Q3, Q4 are off) and a period during which both switch elements Q2, Q4 formed after this period are turned on (at this time, The switch elements Q1 and Q3 are both off).

  As shown in FIG. 8, during the period when both of the switch elements Q1 and Q2 are turned on, the high-level drive control signals Sc2 and Sc3 are input from the control circuit 145 to the switch elements Q2 and Q3, and the low-level drive control signal Sc1. , Sc4 are input to the switch elements Q1, Q4. Further, during the period when both the switch elements Q2 and Q4 are turned on, the low level drive control signals Sc3 and Sc4 are input to the switch elements Q3 and Q4, and the high level drive control signals Sc1 and Sc4 are input to the switch elements Q1 and Q4. Entered. By repeatedly outputting the drive control signal as described above from the control circuit 145, the switch elements Q1 and Q2 and the switch elements Q4 and Q3 are alternately turned on and off in a predetermined cycle. That is, when the switch elements Q1 and Q2 are on, the piezoelectric element 26 is charged to + HV, and when the switch elements Q4 and Q3 are on (period B), the piezoelectric element 26 is charged to -V.

  Since a larger driving voltage is applied in the polarization direction of the piezoelectric element 26 in this way, the deformation amount of the piezoelectric element 26 increases, and as a result, the vibration width of the driving shaft 28 increases. By increasing the vibration width of the drive shaft 28, the amount of movement of the slider is increased by a single vibration, and the moving speed of the slider can be increased.

  FIG. 9 is a diagram showing electric field induced strain characteristics of the piezoelectric element for explaining the operating principle of the drive circuit for the piezoelectric element according to the present embodiment. As described above, when a piezoelectric element is used as an actuator, a high electric field is applied to the strain A point for polarization to provide hysteresis characteristics. In this state, when a driving voltage is applied between −V and HV, the distortion of the piezoelectric element correlates with the applied electric field, so that distortion M occurs in the range from point a to point c in FIG. When the driving voltage is applied in the range from -V to + V, the distortion L is larger than the distortion L generated in the range from the point a to the point b. At this time, even if the driving voltage HV in the polarization direction is larger than the coercive electric field Ex on the polarization side, the piezoelectric element is not destroyed due to depolarization. On the other hand, the displacement amount of the piezoelectric element can be increased by increasing the driving voltage in the negative direction with respect to the polarization direction. On the other hand, if the drive voltage is excessively increased, the reliability for depolarization is lowered. That is, the drive voltage in the negative direction with respect to the polarization direction must not exceed a value obtained by multiplying the coercive electric field -Ex of the piezoelectric element by the displacement direction thickness of the piezoelectric material so as not to release the polarization of the piezoelectric element. There is. The drive voltage HV is preferably in the range of about 2-3 times in absolute value with respect to the drive voltage V.

  FIG. 10 is a diagram illustrating another configuration example of the drive circuit. In this figure, the drive circuit 14 'includes a switch element Q5 which is a MOS FET between a connection point a1 to which a drive voltage + HV is supplied from a drive power supply and a connection point b connected to the polarization direction side electrode of the piezoelectric element. The fifth switch circuit 147 and the piezoelectric element are connected in series, and between the connection point a2 to which the drive voltage −V is supplied from the drive power supply and the connection point b connected to the polarization direction side electrode of the piezoelectric element. A sixth switch circuit 148 made up of a switch element Q6, which is a MOS type FET, is connected.

  A control circuit 145a serving as a control signal supply means for supplying drive control signals Sc5 and Sc6 to the switch circuits 147 and 148 is connected. The control circuit 145a controls each switch circuit under the control of the control unit 22 as in the case of the driving circuit 14. The switch element Q5 constituting the fifth switch circuit 147 is a P-channel FET, and the switch element Q6 constituting the sixth switch circuit 148 is an N-channel FET.

  In the drive circuit 14 ′ configured as described above, the fifth switch circuit 147 charges the piezoelectric element 26 by applying the drive voltage HV from the positive direction to the polarization direction until the inter-terminal voltage Vs becomes + HV. The sixth switch circuit 148 forms a first drive circuit, and applies a drive voltage V lower than the drive voltage HV to the piezoelectric element 26 from the other side (that is, from a negative direction with respect to the polarization direction). Thus, a second drive circuit that charges until the inter-terminal voltage Vs becomes −V is configured. The piezoelectric element has a polarization direction side terminal connected to point b and the other end grounded.

  FIG. 11 is a diagram illustrating a configuration example of a voltage supply circuit that supplies drive voltages having different voltages to the drive circuit of FIG. FIG. 11 shows an example using a DC battery in which a plurality of batteries are connected in series for voltage supply. The battery 50 is configured by connecting a plurality of batteries in series, and a terminal y is provided between the positive terminal x and the negative terminal z. The voltage HV between xy is configured to be higher than the voltage V between yz. The positive terminal x is connected to point a1 of the drive circuit 14, and the negative terminal z is connected to point b of the drive circuit 14. The intermediate terminal y is connected to the other end of the piezoelectric element and grounded.

  The piezoelectric actuator control unit 22 (see FIG. 1) includes a CPU that performs arithmetic processing, a ROM that stores processing programs and data, a RAM that temporarily stores data, and the like, and signals that are input from the member sensor 16 and the like. The control circuit 145a outputs a drive pulse with a predetermined duty ratio based on the above, and the first drive circuit and the second drive circuit are alternately driven by this drive pulse. When the drive circuit 14 is configured in this way, a voltage of −V to + HV is applied to the piezoelectric element 26, and a high drive voltage is applied in the polarization direction, whereby the amount of displacement of the piezoelectric element can be increased. The moving speed of the slider can be increased.

  As described above, according to the piezoelectric actuator according to the above-described embodiment, the magnitudes of the drive voltages applied to the first and second drive circuits are varied, and the range is large only for the polarization direction of the piezoelectric element, By increasing the width of the drive voltage applied to the piezoelectric element, the amount of displacement of the piezoelectric element can be increased. Further, a driving voltage exceeding the coercive electric field in the negative direction is applied to the piezoelectric element, so that the piezoelectric element is not depolarized and the piezoelectric element is not destroyed. Therefore, the moving speed of the slider that is the engaging member can be increased.

  For example, when the actuator according to the above embodiment is applied to a head feed mechanism of a 3.5-inch fixed magnetic disk device, 12 V and 5 V are supplied to these disk devices, so that HV is 12 V, V By setting 5 to 5V, the head feed speed can be increased.

  In addition, when the drive voltage applied in the negative direction is -5V, the piezoelectric element is designed so that the limit value (coercive electric field) of the drive voltage is about -10V. In this case, as the negative voltage to be applied is closer to the limit value, the voltage across the piezoelectric element 1 increases, and an improvement in speed can be expected, but on the other hand, there is a balanced relationship that the reliability for depolarization decreases. In the above-described embodiment, while the voltage applied in the negative direction with respect to the polarization direction is kept small, the moving speed can be increased by increasing the drive voltage only in the positive direction. The possibility of destruction of the piezoelectric element can be reduced.

  In addition, this invention is not limited to the said embodiment, It can implement in another various aspect. For example, in the above-described embodiment, the case where the piezoelectric element is used for the piezoelectric actuator has been described. However, the piezoelectric element can be used for other devices.

  Further, when the piezoelectric element is used for the piezoelectric actuator, in the above-described embodiment, the slider as the engaging member moves and the piezoelectric element is configured to be fixed. The member may be fixed and the piezoelectric element may be configured to be movable together with the support member.

It is the schematic which shows the basic composition of the impact type piezoelectric actuator which concerns on embodiment of this invention. It is a perspective view which shows the structural example of the drive part of the piezoelectric actuator of FIG. It is a figure which shows the structural example of the drive circuit of the piezoelectric actuator of FIG. It is a figure which shows the structural example of the voltage supply circuit which supplies the drive voltage from which a voltage differs to the drive circuit of FIG. It is a figure which shows the pulse waveform of the drive voltage of the drive circuit of the piezoelectric actuator of FIG. It is a graph which shows the relationship between the duty ratio of the drive voltage which consists of rectangular waves, and the moving direction of a slider. It is a figure which shows the correspondence of the pulse waveform of the drive voltage from the drive circuit applied to a piezoelectric element, and the displacement by expansion / contraction of a piezoelectric element, (a) is the drive voltage shown to Fig.5 (a) was applied. FIG. 5B shows a case where the drive voltage shown in FIG. 5B is applied. 2 is a timing chart showing an operation sequence of the piezoelectric actuator of FIG. 1. It is a figure which shows the electric field induced distortion characteristic of the piezoelectric element for demonstrating the operation principle of the drive circuit of the piezoelectric element concerning this embodiment. It is a figure which shows another structural example of the drive circuit of the piezoelectric actuator of FIG. It is a figure which shows the structural example of the voltage supply circuit which supplies the drive voltage from which a voltage differs to the drive circuit of FIG. It is a figure which shows schematic structure of the piezoelectric actuator using the piezoelectric element for adjusting the taking lens position of a camera. It is a figure which shows the displacement of the drive member of the piezoelectric actuator of FIG. It is a figure which shows the drive circuit of the piezoelectric actuator of FIG. 13 is a timing chart showing another operation sequence of the piezoelectric actuator of FIG. It is a figure which shows the electric field induced distortion characteristic of a piezoelectric element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piezoelectric actuator 12 Drive part 14, 14 'Drive circuit 22 Control part 24 Support member 26 Piezoelectric element 28 Drive shaft (drive member)
30 Slider (engagement member)
141 1st switch circuit 142 2nd switch circuit 143 3rd switch circuit 144 4th switch circuit 147 5th switch circuit 148 6th switch circuit Q1-Q6 switch element

Claims (5)

A drive circuit for driving a piezoelectric element that expands and contracts when a drive voltage is applied,
A first drive circuit for applying a drive voltage to the piezoelectric element from a positive direction in the polarization direction of the piezoelectric element; and a second drive circuit for applying a drive voltage to the piezoelectric element from a negative direction in the polarization direction of the piezoelectric element. The first drive circuit and the second drive so that the absolute value of the drive voltage supplied to the drive circuit and the first drive circuit is larger than the absolute value of the drive voltage supplied to the second drive circuit. A drive circuit for a piezoelectric element, comprising voltage supply means for supplying a drive voltage to the circuit. The first drive circuit includes first switch means having one end connected to the first electrode of the power supply means and the other end connected to one end of the piezoelectric element, and one end connected to the other end of the piezoelectric element. And a second switch means connected to the second electrode of the power supply means at the other end,
The second drive circuit includes third switch means having one end connected to the first electrode of the power supply means and the other end connected to the other end of the piezoelectric element, and one end connected to the piezoelectric element. The piezoelectric element drive circuit according to claim 1, further comprising fourth switch means connected to one end and having the other end connected to the second electrode of the power supply means. The first drive circuit includes fifth switch means having one end connected to the first electrode of the power supply means and the other end connected to one end of the piezoelectric element;
The second drive circuit includes sixth switch means having one end connected to the second electrode of the power supply means and the other end connected to one end of the piezoelectric element;
The other end of the piezoelectric element is connected to a third electrode having a potential between the potential of the first electrode and the potential of the second electrode of the power supply means. A drive circuit for the piezoelectric element according to 1.   The absolute value of the drive voltage applied by the second drive circuit is smaller than a value obtained by multiplying the coercive electric field determined by the electrolytically induced strain characteristic of the piezoelectric element by the displacement direction thickness of the piezoelectric element, 4. The piezoelectric element drive circuit according to claim 1, wherein an absolute value of a drive voltage applied by the drive circuit is larger than the coercive electric field. 5. The piezoelectric element includes a drive member fixed to one end in the expansion / contraction direction of the piezoelectric element and an engagement member frictionally engaged with the drive member, and the drive member has different speeds of expansion and contraction. The piezoelectric element according to any one of claims 1 to 4, wherein the piezoelectric element is used in a piezoelectric actuator that relatively moves the drive member and the engagement member by extending and contracting. Driving circuit.

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