JP2005237144A - Piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric actuator whose power consumption is suppressed by reducing the rush current and to which high voltage can be applied so that it can escape easily from its sticking state. <P>SOLUTION: This piezoelectric actuator has a first drive circuit comprising the first switch circuit 141 and the second switching circuit 142 for applying drive voltage to a piezoelectric element 26 from its one electrode thereby charging it, a second drive circuit comprising the third switching circuit 143 and the fourth switching circuit 144 for applying drive voltage to the piezoelectric element from its other side thereby charging it, a discharge circuit comprising the second switching circuit 142 and the fourth switching circuit 144 for discharging the charge charged in the piezoelectric element by each drive circuit, and an inductive element 146 which constitutes a part of each circuit and is connected in series with the piezoelectric element. This drives the first drive circuit and the second drive circuit alternately, and drives the discharge circuit, capable of changing the drive time during that time and generates inductive potential by the inductive element 146. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a piezoelectric actuator, and more particularly to a piezoelectric actuator suitable for driving an XY moving stage, a camera photographing lens, a projection lens of an overhead projector, a binocular lens, and the like.

  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. 10 is a diagram showing a schematic configuration of a piezoelectric actuator for adjusting the photographing lens position of the camera, and FIG. 11 is a diagram showing displacement of a driving member of the piezoelectric actuator.

  A piezoelectric actuator 100 shown in FIG. 10 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 friction force, and a piezoelectric element. 101 includes a drive circuit 104 that applies 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. 12, the drive circuit disclosed in Patent Document 1 is configured by 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. 13 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. 13, the gate to ground voltage of the FET 73 is E (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 E ( v), only the FET 71 and the FET 72 are in a conducting state, and a voltage of + E (v) is applied to the piezoelectric element 101. On the other hand, in the period B, only the FETs 73 and 74 are in the conductive state, and therefore the voltage of −E (v) is applied to the voltage element 101. As described above, an AC voltage that is twice the power supply voltage E is applied to both ends of the piezoelectric element 101 from the timing chart of FIG.

  Another example of a drive circuit for a piezoelectric actuator is disclosed in Japanese Patent Application Laid-Open No. 2001-21669 (Patent Document 2). This drive circuit has the same circuit configuration shown in FIG. 12 as the drive circuit disclosed in Patent Document 1. FIG. 14 is a timing chart showing an operation sequence of the piezoelectric actuator described in Patent Document 2. The difference from the drive circuit described in Patent Document 1 is that the electric charge charged in the piezoelectric element 101 is once discharged and then reversely charged. The period A and the period B in FIG. 14 are the same operation patterns as the period A and the period B shown in FIG. In period C, the gate-to-ground voltage of FET 71 and FET 73 is E (v), and the gate-to-ground voltage of FET 72 and FET 74 is E (v). It will be short-circuited. Therefore, the electric charge charged in the piezoelectric element 101 in the period A is once discharged in the period C, and in the period B, it is charged in a direction opposite to the charging direction in the period A.

When a voltage is applied to the piezoelectric element as shown in FIGS. 13 and 14, a saw-tooth-shaped displacement as shown in FIG. 11 appears on the drive member according to the duty ratio. Referring to FIG. 11 (a) as an example, in the initial state A of FIG. 11 (a), the drive member 102 and the drive member 102 are driven at a moderate speed from the state of FIG. 10 (a), as shown in FIG. The engaging member 103 frictionally engaged with the member 102 is displaced. Next, in C of FIG. 11A, as shown in FIG. 10C, the displacement of the drive member 102 returns to its original position at a steep speed, so that the friction engagement portion between the engagement member 103 and the drive member 102 is obtained. Slipping occurs, and the engaging member 103 returns slightly. By repeating these operations, the engaging member 103 moves on the driving member 102 in a direction away from the piezoelectric element 101. When the driving member 102 is displaced with a steep extension and a gentle contraction as shown in FIG. 11B, the engaging member 103 moves in a direction approaching the piezoelectric element 102.
JP 2000-350482 A JP 2001-21669 A

  However, since the above drive circuit has the above-described configuration, there is a problem in that a large inrush current flows and power consumption increases when switching the voltage applied to the piezoelectric element 101. That is, in the case of Japanese Patent Laid-Open No. 2000-350482 (Patent Document 1), since the voltage across the piezoelectric element 101 is rapidly switched from + E (V) to −E (V), the inrush power I is I = 2E / r. (R is the total resistance value such as the on-resistance of the FET, the output resistance of the power source, and the line resistance).

  In the case of Japanese Patent Laid-Open No. 2001-21669 (Patent Document 2), since the electric charge of the piezoelectric element 101 is once discharged and then charged in the reverse direction, the inrush current I becomes I = E / r, which is halved. However, the effect of suppressing inrush current is not sufficient. Furthermore, an actuator that generates a driving force via friction, such as the piezoelectric actuator shown in FIG. 10, causes a phenomenon that the frictional contact portion sticks when left in a high humidity environment for a long period of time. In order to escape from this state, it is necessary to drive the driving member to a greater extent. For this purpose, for example, it is necessary to be able to apply a high voltage.

  Therefore, the technical problem to be solved by the present invention is to provide a piezoelectric actuator capable of applying a high voltage so that inrush current can be reduced, power consumption can be kept low, and the fixed state can be easily escaped. Is to provide.

  In order to solve the above technical problem, the present invention provides a piezoelectric actuator having the following configuration.

According to a first aspect of the present invention, there is provided a piezoelectric element that expands and contracts when a driving voltage is applied, a driving member that is fixed to one end of the piezoelectric element in the extending and contracting direction, and an engagement that is frictionally engaged with the driving member. The drive member is composed of a member, a drive circuit for driving the piezoelectric element, and a drive control means for controlling the operation of the drive circuit, and the piezoelectric element is expanded and contracted so as to have different speeds of expansion and contraction. And a piezoelectric actuator for relatively moving the engaging member,
The drive circuit includes a first drive circuit that charges the piezoelectric element by applying a drive voltage from one side of the electrode, and a second drive that charges the piezoelectric element by applying a drive voltage from the other side of the electrode. A circuit, a discharge circuit that discharges the electric charge charged in the piezoelectric element by each drive circuit, and an inductive element that forms a part of each drive circuit and the discharge circuit and is connected in series with the piezoelectric element. ,
The drive control means alternately drives the first drive circuit and the second drive circuit, and sets the discharge circuit during the drive period of the first drive circuit and the second drive circuit. The drive time can be controlled to be changeable to enable driving, and the capacitive component of the piezoelectric element and the induction of the inductive element at the time of drive switching between the drive circuits and at the time of drive switching from the drive circuit to the discharge circuit. The piezoelectric actuator is characterized in that an electrical vibration induced by a component is applied to the piezoelectric element.

  In the above configuration, the first and second drive circuits apply drive voltages to the piezoelectric elements from opposite directions, and are driven alternately under the control of the drive control means. At this time, when the first drive circuit and the second drive circuit are switched, an electric vibration is generated by the inductive element and the piezoelectric element when the first drive circuit and the second drive circuit are switched. . Therefore, immediately after the switching, since the drive voltage applied by the driving circuit that is driven after the switching, the capacitance component of the piezoelectric element, and the electrical vibration generated by the inductive component of the inductive element are applied to the piezoelectric element, the piezoelectric element A larger voltage will be applied to.

  Further, the drive control means can drive the discharge circuit so that the drive time can be changed during the drive period of the first drive circuit and the second drive circuit. When the discharge circuit is driven later, the electric charge charged in the piezoelectric element by the first drive circuit is discharged by the discharge circuit before the piezoelectric element is charged in the reverse direction by the second drive circuit. In addition, when the discharge circuit is driven after driving the second drive circuit, the charge charged in the reverse direction to the piezoelectric element by the second drive circuit is charged in the reverse direction to the piezoelectric element by the first drive circuit. Before being discharged by the discharge circuit. An inductive potential is generated by the inductive element and the piezoelectric element even during discharge in the discharge circuit. However, the charge charged in the reverse direction does not reach the charge charged in the positive direction by the resistances of the first drive circuit and the second drive circuit, and has a value in a lower range. Therefore, it is sufficient to supply only the insufficient charge from the power source at the moment when the discharge circuit shifts to the first or second drive circuit. Therefore, a part of the charge once charged can be used for charging in the reverse direction and the inrush current can be suppressed, and a positive and negative AC voltage can be applied to the piezoelectric element with low power consumption.

According to a second aspect of the present invention, there is provided a piezoelectric element that expands and contracts when a driving voltage is applied, a driving member that is fixed to one end of the piezoelectric element in the extending and contracting direction, and an engagement that is frictionally engaged with the driving member. The drive member is composed of a member, a drive circuit for driving the piezoelectric element, and a drive control means for controlling the operation of the drive circuit, and the piezoelectric element is expanded and contracted so as to have different speeds of expansion and contraction. And a piezoelectric actuator for relatively moving the engaging member,
The drive circuit includes a first drive circuit that charges the piezoelectric element by applying a drive voltage from one side of the electrode, and a second drive that charges the piezoelectric element by applying a drive voltage from the other side of the electrode. A circuit, a discharge circuit for discharging the electric charge charged in the piezoelectric element by each drive circuit, and a first induction that forms part of the first drive circuit and the discharge circuit and is connected in series with the piezoelectric element And a second inductive element constituting a part of the second drive circuit and the discharge circuit and connected in series with the piezoelectric element,
The drive control means alternately drives the first drive circuit and the second drive circuit, and sets the discharge circuit during the drive period of the first drive circuit and the second drive circuit. The drive time is controlled to be changeable to enable driving, and the capacitance component of the piezoelectric element and the inductive element of each of the inductive elements at the time of driving switching between the driving circuits and at the time of switching driving from the driving circuit to the discharging circuit. The piezoelectric actuator is characterized in that an electrical vibration induced by an inductive component is applied to the piezoelectric element.

  In the above configuration, even if the inductive element is divided into two places and the inductance is halved, for example, the total capacitance value is the same as that in the first embodiment, so that power consumption is reduced. The effect can be the same, while the vibration frequency due to the capacitive components of the first and second induction elements and the piezoelectric element is increased, and the generated acceleration of the drive member can be increased. Therefore, when the drive member and the engaging member are fixed as described later, it is possible to easily escape from the fixed state.

According to a third aspect of the present invention, the first drive circuit includes a first switch means having one end connected to a power source and the other end connected to one end of the piezoelectric element, and one end connected to the other end of the piezoelectric element. A second switch means connected to one end and grounded at the other end;
The second drive circuit includes a third switch means having one end connected to the power source and the other end connected to the other end of the piezoelectric element, and one end connected to one end of the piezoelectric element and the other end connected to the other end of the piezoelectric element. Comprising a grounded fourth switch means;
The discharge circuit is composed of the second switch means and the fourth switch means,
The control terminals of the first switch means to the fourth switch means are connected to the drive control means,
The drive control means sets the first and second switch means in a conductive state and the third and fourth switch means in a disconnected state when driving the first drive circuit, and the second drive circuit. When driving the first and second switch means, the third and fourth switch means are turned on, and when driving the discharge circuit, the second and fourth switch means are turned on. The piezoelectric actuator according to the first aspect or the second aspect is characterized in that the first and third switch means are in a disconnected state while being in a state.

  According to a fourth aspect of the present invention, in the piezoelectric actuator according to the fourth aspect of the present invention, when the drive control unit starts from the stop state to the drive state, the drive time of the discharge circuit in the first predetermined number of drive times continues thereafter The driving time of the discharge circuit is shorter.

  In the piezoelectric actuator according to the fifth aspect of the present invention, when the engagement member becomes inoperable, the drive control unit makes the drive time of the discharge circuit shorter than the normal drive time. Features.

In the piezoelectric actuator according to the sixth aspect of the present invention, when the capacitance of the piezoelectric element is C and the inductance of the inductive element is L, the driving time of the discharge circuit in the normal driving time is π (L · C ) Characteristic of ^1/2 .

According to the piezoelectric actuator according to the present invention, it is possible to change the driving mode of the piezoelectric actuator by making it possible to control the driving time of the discharge circuit provided between the driving of the first and second driving circuits. . By shortening the driving time, the driving voltage applied to the piezoelectric element can be increased by the action of the inductive element. For example, when the piezoelectric actuator is an impact drive type in which the drive member and the engagement member are moved relative to each other by generating a steep expansion / contraction displacement with different speeds of expansion and contraction in the piezoelectric element, the length of the piezoelectric actuator It is possible to easily escape from the sticking phenomenon that occurs when left for a period of time. On the other hand, power consumption can be suppressed by lengthening the driving time. When the capacitance of the piezoelectric element is C and the inductance of the inductive element is L, the driving time of the discharge circuit is π (L · C ) Power consumption can be minimized by setting it to ^1/2 .

  Hereinafter, a piezoelectric actuator according to each embodiment 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 applying a driving voltage to the electrodes allows the piezoelectric elements to be piezoelectric. The element is deformed. One end face in the longitudinal direction, which is the expansion / contraction direction (stacking direction), is fixed to the end face on the one end portion 241 side of the first accommodation space 244. The other end portion 242 and the partition wall 243 of these support members 24 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 and is pivoted to the second accommodation space 245. It is accommodated so as to be movable along the direction.

  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 switching element Q1 that is a MOS FET between a connection point a to which a drive voltage + E is supplied from a drive power supply and a connection point b to be grounded. A series circuit of a switch circuit 141 and a fourth switch circuit 144 composed of a switch element Q4 which is a MOS FET is connected, and a third switch circuit 143 composed of a switch element Q3 which is a MOS FET and a switch which is a MOS FET. The series circuit of the 2nd switch circuit 142 which consists of element Q2 is connected, and the control circuit 145 as a control signal supply means which supplies drive control signal Sc1, Sc2, Sc3, Sc4 to each switch circuit 141-144 is connected, and is comprised. Has been.

  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 147 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 bridge circuit, an inductive element 146 is provided in series with the piezoelectric element 26 between the connection point c and the connection point d.

  In the drive circuit 14 configured as described above, the first switch circuit 141 and the second switch circuit 142 are charged until the drive voltage + E is applied to the piezoelectric element 26 from one side until the inter-terminal voltage Vs becomes + E. The fourth switch circuit 144 and the third switch circuit 143 apply the drive voltage + E to the piezoelectric element 26 from the other side (that is, from the reverse direction) to apply the inter-terminal voltage Vs. Constitutes a second drive circuit for charging until becomes -E.

  When the bridge circuit 147 is configured by the drive circuit 14 and the piezoelectric element 26 as described above, a voltage of −E to + E is applied between both electrodes of the piezoelectric element 26, so that the drive voltage amplitude of the piezoelectric element 26 is 2E. As a result, it is possible to obtain the piezoelectric actuator 10 having a large displacement even when the drive power supply is at a low voltage.

  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. That is, the control unit 22 and the control circuit 145 include the first drive circuit including the first switch circuit 141, the second switch circuit 142, and the inductive element 146, the fourth switch circuit 144, the third switch circuit 143, and the inductive element. While alternately driving the second drive circuit composed of the elements 146, a drive control means for driving a discharge circuit composed of a second switch circuit 142, a fourth switch circuit 144 and an inductive element 146, which will be described later, is configured. The inductive element 146 constitutes a part of all the circuits of the first drive circuit, the second drive circuit, and the discharge circuit.

  Next, the operation principle of the drive circuit 14 will be described. 4A and 4B are diagrams showing a pulse waveform of the drive voltage of the drive circuit 14, wherein FIG. 4A shows that the duty ratio D (D = N / M) is set to 0.3, and FIG. The duty ratio D (D = N / M) is set to be 0.7. As will be described later, when the drive voltage composed of the rectangular wave shown in FIG. 4A 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. 4B 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. 5 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. 6 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 the expansion and contraction of the piezoelectric element. FIG. FIG. 4B shows a case where the drive voltage shown in FIG. 4B is applied. As described above, when a drive voltage having a duty ratio of 0.3 shown in FIG. 4A 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 steep falling portion. When the drive voltage having a duty ratio of 0.7 shown in FIG. 4B is applied to the piezoelectric element 26, the sawtooth shape has 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. 6 (a), and the slider 30 extends gently, 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. 6A, and the piezoelectric element 26 rapidly shrinks, the slider 30 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 drive voltage shown in FIG. 6A 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. 6B, the drive voltage shown in FIG. 6B is repeatedly applied to the piezoelectric element 26. As a result, the slider 30 moves intermittently in the return direction.

  7 and 8 are diagrams for explaining the operation of the drive circuit 14 applied to the piezoelectric actuator 10 according to the present embodiment. Each of the diagrams is output from the control circuit 145 that controls the drive circuit 14 shown in FIG. The drive pulses applied to the switch 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. 7 is a timing chart showing a normal operation sequence of the piezoelectric actuator according to the embodiment of the present invention. The period during which both the switch elements Q1, Q2 are turned on (the switch elements Q3, Q4 are both off) is the period A, and the period during which both the switch elements Q2, Q4 formed after the period A are turned on (at this time) , Switching elements Q1 and Q3 are both off) during period C, and switching elements Q3 and Q4 formed after this period C are both on (switching elements Q1 and Q2 are both off) during period B, A period D is a period in which both the switch elements Q2 and Q4 formed after the period B are turned on (at this time, both the switch elements Q1 and Q3 are off).

  As shown in FIG. 7, in the period A, high level drive control signals Sc2 and Sc3 are input from the control circuit 145 to the switch elements Q2 and Q3, and low level drive control signals Sc1 and Sc4 are input to the switch elements Q1 and Q4. Entered. In the period B, low-level drive control signals Sc3 and Sc4 are input to the switch elements Q3 and Q4, and high-level drive control signals Sc1 and Sc4 are input to the switch elements Q1 and Q4. 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 (period A), the piezoelectric element 26 is charged to + E, and when the switch elements Q4 and Q3 are on (period B), the piezoelectric element 26 is charged to -E. The

  The control circuit 145 includes a charging period (period A) for the piezoelectric element 26 that is the driving period of the switching elements Q1 and Q2 and a charging period (period B) for the piezoelectric element 26 that is the driving period of the switching elements Q4 and Q3. The control signal can be transmitted so that a discharge period (period C, period D) for discharging the electric charge charged in the piezoelectric element 26 by driving the switch elements Q2 and Q4 is formed. When the switch elements Q2 and Q4 are turned on at the same time, the circuit configuration is such that both electrodes of the piezoelectric element 26 are short-circuited, and a discharge circuit that discharges the electric charge charged in the piezoelectric element 26 is configured.

  Specifically, after both of the switch elements Q1 and Q2 are turned on and the drive voltage Vp is applied to the piezoelectric element 26 to be charged (period A), both of the switch elements Q3 and Q4 are turned on (period B) A period (period C) in which both the switch elements Q2 and Q4 are turned on is formed before. At this time, the charge of + E charged in the piezoelectric element 26 is discharged via the switch elements Q2 and Q4.

  Further, after both the switch elements Q4 and Q3 are turned on and the piezoelectric element 26 is charged by applying the drive voltage E from the opposite direction (period B), both the switch elements Q1 and Q2 are turned on (period). A) Before the switch elements Q2 and Q4 are both turned on, a period (period D) is formed. At this time, the charge −E charged in the piezoelectric element 26 is discharged through the switch elements Q2 and Q4.

  In the period C and the period D, electrical vibration is generated by the inductive component of the inductive element 146 and the capacitive component of the piezoelectric element 26, and the voltage across the piezoelectric element 26 is reversed. When the capacitance of the piezoelectric element 26 is C, the inductance of the inductive element 146 is L, and the resistances of the switch elements Q2 and Q4 are ignored, the behavior of the both-ends voltage Ec of the piezoelectric element in the period C and the period D is expressed by the following equation: Can do.

That is, immediately after the period A, Ec = E at time t = 0 becomes Ec = −E at time t = π (LC) ^1/2 , for example, the charge charged in the positive direction is reversed. The charge is charged in the negative direction. Actually, Ec does not reach -E due to the on-resistances of the respective switch elements Q2 and Q4, but becomes a value in the range of 0 to -Ec, and only the insufficient charge is supplied from the power supply voltage at the moment of shifting to the period B. The Therefore, since a part of the charged electric charge is used for charging in the reverse direction, it is possible to apply positive and negative AC voltages to the piezoelectric element 26 with low power consumption. Note that the time of the period C and the period D is preferably π (LC) ^1/2 or a value ^{close to it} , from the above formula (1).

It is necessary to select an appropriate value for the inductance L of the inductive element 146. If the L value is too large, the waveform of the voltage applied to the piezoelectric element 26 becomes gradual, the power supply voltage E is not reached during the period A, and the predetermined performance of the piezoelectric actuator cannot be obtained. On the other hand, if the L value is too small, the effect of reducing the power consumption due to the charge inversion described above is reduced. For example, when the piezoelectric element 26 has a driving capacity of 100 nF, a driving frequency of 100 kHz, and (period A + C (D)) :( period B + C (D)) = 1: 2, the period A + C is about 3.3 μsec. If the period C is half of the period A, the voltage across the piezoelectric element 2 sufficiently reaches the power supply voltage E during the period A, so the period C is 1.1 μsec. From the conditional expression of t = π (LC) ^1/2 , the L value is about 1.2 μH.

  As described above, a discharge period is formed by driving the switch elements Q2 and Q4 between the drive period of the switch elements Q1 and Q2 and the drive period of the switch elements Q3 and Q4, so that the piezoelectric element 26 is charged to + E. Since it is only necessary to supply the charge required for charging both when charging and when charging to -E, unnecessary power consumption can be reduced.

  On the other hand, when the discharge period by driving the switch elements Q2 and Q4 is not formed, for example, a sticking avoidance operation sequence in which the slider of the piezoelectric actuator is released from the sticking state can be used. FIG. 8 is a timing chart showing another operation sequence of the piezoelectric actuator according to the first embodiment of the present invention.

In the timing chart shown in FIG. 8, the period C and the period D (both ends short-circuit time) do not exist as compared with the timing chart described in FIG. Therefore, the voltage applied to the piezoelectric element 26 at the time of switching from the period A to the period B or from the period B to the period A becomes oscillating as illustrated. At this time, since the voltage applied to the piezoelectric element 26 exceeds the power supply voltage E, the behavior of the piezoelectric element 26 becomes larger than that during normal driving, and the slider 30 can easily escape from the fixed state. This operation sequence can be suitably used when the power source E is supplied to the drive circuit to drive for the first time, or when the moving body does not move due to fixation. Switching between the normal operation and the main operation is performed by the control circuit 22. In the operation of FIG. 8, the case where the period C and the period D are zero and has no such period has been described. However, the time of the periods C and D is larger than zero and smaller than π (LC) ^1/2. Even in this case, the voltage applied to the piezoelectric element can be increased, and the effect of avoiding sticking is recognized. As the time of the periods C and D approaches zero, the vibration amplitude of the voltage applied to the piezoelectric element increases, so that the sticking avoidance effect increases. On the other hand, power consumption increases.

  FIG. 9 is a diagram illustrating another configuration example of the drive circuit. In this figure, a drive circuit 14 'is a first switch circuit comprising a switch element Q1 which is a MOS FET between a connection point a to which a drive voltage + E is supplied from a drive power supply and a connection point b to be grounded. A series circuit of a fourth switch circuit 144a including a switch element Q4 that is a 141a and a MOS FET is connected, and a third switch circuit 143a including a switch element Q3 that is a MOS FET and a switch element Q2 that is a MOS FET. The series circuit of the 2nd switch circuit 142a which consists of is connected and comprised.

  A control circuit 145a as a control signal supply means for supplying drive control signals Sc1, Sc2, Sc3, Sc4 is connected to each switch circuit 141a to 144a. 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. In addition, the second inductive element 146b is connected between the fourth switch circuit 144a and the connection point b, and the first inductive element 146a is connected between the second switch circuit 142a and the connection point b. Has been.

  The switch element Q1 constituting the first switch circuit 141a and the switch element Q3 constituting the third switch circuit 143a are P-channel FETs, and constitute the switch element Q2 and the fourth switch circuit 144a constituting the second switch circuit 142a. The switch element Q4 is an N-channel FET. The bridge circuit 147a is configured by connecting the piezoelectric element 26 between the connection point c of the first switch circuit 141a and the second switch circuit 142a and the connection point d of the third switch circuit 143a and the fourth switch circuit 144a. Has been.

  In the drive circuit 14 ′ configured as described above, when the slider 30 is moved, the first switch circuit 141 a and the second switch circuit 142 a apply the drive voltage + E to the piezoelectric element 26 from one side. The first drive circuit (first drive means) is charged until the inter-terminal voltage Vs becomes + E. The third switch circuit 143a and the fourth switch circuit 144a are connected to the piezoelectric element 26 from the other side ( That is, a second driving circuit (second driving means) is configured to apply the driving voltage + E and charge the terminal until the voltage Vs between the terminals becomes −E (from the reverse direction).

  When the bridge circuit 147a is configured by the drive circuit 14 ′ and the piezoelectric element 26 in this way, a voltage of −E to + E is applied to the piezoelectric element 26 as in the case of the drive circuit 14, so As a result of the drive voltage being equivalently 2E, the piezoelectric actuator 10 having a large displacement can be obtained even when the drive power supply is at a low voltage.

  The control unit 22 (see FIG. 1) of the piezoelectric actuator has the same configuration as the control unit described above, and outputs a drive pulse with a predetermined duty ratio from the control circuit 145 based on a signal input from the member sensor 16 or the like. The first driving circuit and the second driving circuit are alternately driven by this driving pulse. That is, the control unit 22 includes a first drive circuit including the first switch circuit 141, the second switch circuit 142, and the first inductive element 146a, the fourth switch circuit 144a, the third switch circuit 143a, and the second switch circuit. While alternately driving the second drive circuit composed of the inductive element 146b, a second switch circuit 142a, a fourth switch circuit 144a and a discharge circuit composed of the first and second inductive elements 146a and 146b, which will be described later, are provided. A drive control means for driving is configured. That is, the first and second inductive elements 146a and 146b are included in the first drive circuit and the discharge circuit, the second drive circuit and the discharge circuit, respectively, and function as described later.

  The drive circuit 14 'operates according to the operation sequence shown in FIGS. Similar to the drive circuit described above, in period A, high level drive control signals Sc2 and Sc3 are input from the control circuit 145 to the switch elements Q2 and Q3, and low level drive control signals Sc1 and Sc4 are input to the switch elements Q1 and Q4. Is input. In the period B, low-level drive control signals Sc3 and Sc4 are input to the switch elements Q3 and Q4, and high-level drive control signals Sc1 and Sc4 are input to the switch elements Q1 and Q4. By repeatedly outputting the drive control signal as described above from the control circuit 145a, 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 (period A), the piezoelectric element 26 is charged to + E, and when the switch elements Q4 and Q3 are on (period B), the piezoelectric element 26 is charged to -E. The

  The control circuit 145 includes a charging period (period A) for the piezoelectric element 26 that is the driving period of the switching elements Q1 and Q2 and a charging period (period B) for the piezoelectric element 26 that is the driving period of the switching elements Q4 and Q3. The control signal is transmitted so that a discharge period (period C, period D) for discharging the electric charge charged in the piezoelectric element 26 by driving the switch elements Q2 and Q4 is formed. Therefore, the switch elements Q2 and Q4 constitute a discharge circuit that discharges the electric charge charged in the piezoelectric element 26 when they are driven simultaneously.

  That is, after both the switch elements Q1 and Q2 are turned on and the drive voltage E is applied to the piezoelectric element 26 and charging is performed (period A), before both the switch elements Q3 and Q4 are turned on (period B). A period (period C) during which both switch elements Q2 and Q4 are turned on is formed. At this time, the charge of + E charged in the piezoelectric element 26 is discharged via the switch elements Q2 and Q4.

  Further, after both the switch elements Q4 and Q3 are turned on and the piezoelectric element 26 is charged by applying the drive voltage E from the opposite direction (period B), both the switch elements Q1 and Q2 are turned on (period). A) Before the switch elements Q2 and Q4 are both turned on, a period (period D) is formed. At this time, the charge −E charged in the piezoelectric element 26 is discharged through the switch elements Q2 and Q4.

  In period C, vibration is caused by the inductive components of the two inductive elements 146a and 146b and the capacitive component of the piezoelectric element 26, and in period D, vibration is caused by the inductive components of the two inductive elements 146a and 146b and the capacitive component of the piezoelectric element 26. Thus, the voltage across the piezoelectric element 26 is reversed. At this time, only in the case of charge inversion in the period C and the period D, since both the first and second inductive elements 146a and 146b are passed, the period C and the period D can be lengthened. The effect of reducing power consumption due to inversion is greater than in the first embodiment.

  Conversely, if the inductance values of the first and second inductive elements 146a and 146b are set to half the inductance value of the inductive element 146 shown in the drive circuit described above, the power consumption reduction effect is obtained. 3 is the same as the drive circuit shown in FIG. 3, because the vibration frequency due to the capacitive component of the first inductive element 146a or the second inductive element 146b and the piezoelectric element 26 increases, and the generated acceleration of the drive shaft 28 increases. , Sticking out easily.

  In FIG. 9, inductive elements 146a and 146b are connected in series to the source of the N-channel FET, but may be connected to the drain side. Further, the inductive elements 146a and 146b may be connected to either the source side or the drain side of the P-channel FET, and the same effect is obtained even in these cases.

  As described above, according to the piezoelectric actuator according to the above-described embodiment, when the electric charge charged in the piezoelectric element when the first and second drive circuits are driven is discharged by the discharge circuit, the charged electric charge is The battery is reversed and charged in the reverse direction, so that the power consumption can be reduced. Further, the inductive element provided in common for each of these circuits can solve the problem that a large inrush current flows through the circuit and power consumption increases.

  Furthermore, by controlling the time for which the discharge circuit is driven, the driving driving force of the slider can be increased, and for example, escape from the fixed state can be facilitated.

  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 slider, which is the engaging member, moves in the piezoelectric actuator, and the piezoelectric element is configured to be fixed. It may be configured to be movable.

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 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 a rectangular wave, and the moving speed 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 in Fig.4 (a) applied FIG. 4B shows a case where the drive voltage shown in FIG. 4B is applied. 2 is a timing chart showing an ordinary operation sequence of the piezoelectric actuator of FIG. 1. 6 is a timing chart showing another operation sequence of the piezoelectric actuator of FIG. 1. 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 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. It is a timing chart showing the operation | movement sequence of the piezoelectric actuator of FIG. 13 is a timing chart showing another operation sequence of the piezoelectric actuator of FIG.

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, 141a First switch circuit 142, 142a Second switch circuit 143, 143a Third switch circuit 144, 144a Fourth switch circuit 146, 146a, 146b Inductive element Q1-Q4 Switch element

Claims (6)

A piezoelectric element that expands and contracts when a driving voltage is applied thereto, a driving member fixed to one end of the piezoelectric element in the extending and contracting direction, an engaging member frictionally engaged with the driving member, and driving the piezoelectric element And a drive control means for controlling the operation of the drive circuit. The piezoelectric element is expanded and contracted so as to have different speeds of expansion and contraction, whereby the drive member and the engagement member are relatively moved. In the moving piezoelectric actuator,
The drive circuit includes a first drive circuit that charges the piezoelectric element by applying a drive voltage from one side of the electrode, and a second drive that charges the piezoelectric element by applying a drive voltage from the other side of the electrode. A circuit, a discharge circuit that discharges the electric charge charged in the piezoelectric element by each drive circuit, and an inductive element that forms a part of each drive circuit and the discharge circuit and is connected in series with the piezoelectric element. ,
The drive control means alternately drives the first drive circuit and the second drive circuit, and sets the discharge circuit during the drive period of the first drive circuit and the second drive circuit. The drive time can be controlled to be changeable to enable driving, and the capacitive component of the piezoelectric element and the induction of the inductive element at the time of drive switching between the drive circuits and at the time of drive switching from the drive circuit to the discharge circuit. A piezoelectric actuator characterized by applying an electrical vibration induced by a component to the piezoelectric element. A piezoelectric element that expands and contracts when a driving voltage is applied thereto, a driving member fixed to one end of the piezoelectric element in the extending and contracting direction, an engaging member frictionally engaged with the driving member, and driving the piezoelectric element And a drive control means for controlling the operation of the drive circuit. The piezoelectric element is expanded and contracted so as to have different speeds of expansion and contraction, whereby the drive member and the engagement member are relatively moved. In the moving piezoelectric actuator,
The drive circuit includes a first drive circuit that charges the piezoelectric element by applying a drive voltage from one side of the electrode, and a second drive that charges the piezoelectric element by applying a drive voltage from the other side of the electrode. A circuit, a discharge circuit for discharging the electric charge charged in the piezoelectric element by each drive circuit, and a first induction that forms part of the first drive circuit and the discharge circuit and is connected in series with the piezoelectric element And a second inductive element constituting a part of the second drive circuit and the discharge circuit and connected in series with the piezoelectric element,
The drive control means alternately drives the first drive circuit and the second drive circuit, and sets the discharge circuit during the drive period of the first drive circuit and the second drive circuit. The drive time is controlled to be changeable to enable driving, and the capacitance component of the piezoelectric element and the inductive element of each of the inductive elements at the time of driving switching between the driving circuits and at the time of driving switching from the driving circuits to the discharging circuit A piezoelectric actuator characterized in that an electrical vibration induced by an inductive component is applied to the piezoelectric element. The first drive circuit includes a first switch means having one end connected to a power source 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 the other end grounded. Second switch means,
The second drive circuit includes a third switch means having one end connected to the power source and the other end connected to the other end of the piezoelectric element, and one end connected to one end of the piezoelectric element and the other end connected to the other end of the piezoelectric element. Grounded fourth switch means,
The discharge circuit includes the second switch means and the fourth switch means,
The control terminals of the first switch means to the fourth switch means are connected to the drive control means,
The drive control means sets the first and second switch means in a conductive state and the third and fourth switch means in a disconnected state when driving the first drive circuit, and the second drive circuit. When driving the first and second switch means, the third and fourth switch means are turned on, and when driving the discharge circuit, the second and fourth switch means are turned on. 3. The piezoelectric actuator according to claim 1, wherein the first and third switch means are in a disconnected state at the same time.   When the piezoelectric actuator is started from the stop state to the drive state, the drive control means shortens the drive time of the discharge circuit at the first predetermined number of times of driving to be shorter than the drive time of the discharge circuit at the subsequent normal time. The piezoelectric actuator according to any one of claims 1 to 3, wherein the piezoelectric actuator is characterized in that   5. The drive control unit according to claim 1, wherein when the engagement member becomes inoperable, the drive time of the discharge circuit is made shorter than the drive time of a normal time. The piezoelectric actuator described in 1. When the drive control means has C as the capacitance of the piezoelectric element and L as the inductance of the inductive element, the drive time of the discharge circuit in the normal time is π (L · C) ^1/2 . The piezoelectric actuator according to claim 4 or 5, characterized in that:

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