JP4492756B2 - Piezoelectric actuator - Google Patents

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, an impact type piezoelectric actuator is known in which a driven member is attached to a rod-like driving member by frictional coupling and a piezoelectric element is fixed to one end of the driving member. For example, Japanese Patent Application Laid-Open No. 7-298656 (Patent Document 1) shows an application of an impact-type piezoelectric actuator as an actuator for a photographing lens of a camera. FIG. 20 is a diagram showing a schematic configuration of an impact-type piezoelectric actuator disclosed in the publication.

  In FIG. 20, the impact-type piezoelectric actuator 100 includes a rod-shaped drive member 101, a driven member 102, a laminated piezoelectric element 103, and a drive circuit 104. The driven member 102 is a member to which a driving object such as a photographic lens is fixed, and is engaged with the driving member 101 with a predetermined frictional force. When a force greater than the frictional force is applied, the driven member 102 is axially moved on the driving member 101. It is possible to move along. The laminated piezoelectric element 103 is fixed to one end of the drive member 101 so that the polarization direction coincides with the axial direction of the drive member 101, and the electrode 103a formed at one end is connected to the drive circuit 104, and the other end The electrode 103b formed on the ground is grounded.

  The drive circuit 104 moves the driven member 102 to the front end side (open end side) of the drive member 101 (hereinafter, this moving direction is referred to as a positive direction), and the driven member 102 is the drive member. 101 includes a reverse direction drive circuit 106 that moves to the base end side (piezoelectric element side) of 101 (hereinafter, this movement direction is referred to as a reverse direction) and a control circuit 107 that controls the drive of both drive circuits 105 and 106. ing.

  The piezoelectric actuator 100 configured as described above utilizes a difference in frictional force generated between the driving member 101 and the driven member 102 when the driving member 101 is moved at different speeds along the axial direction. The driven member 102 is moved relative to the driving member 101. That is, the frictional force between the driven member 102 and the driving member 101 decreases when the driving member 101 moves at a high speed and increases when the driving member 101 moves at a low speed. For this reason, when the drive member 101 is moved in the forward direction, the driven member 102 is moved in the forward direction with respect to the drive member 101 (forward drive) by moving at a low speed when moving in the reverse direction, and driven at a high speed. The driven member 102 is moved in the reverse direction with respect to the driving member 101 by moving at a high speed during the forward movement of 101 and at a low speed when moving in the reverse direction (reverse driving).

  Accordingly, the forward direction driving circuit 105 is composed of a low speed charging circuit 105a and a high speed discharging circuit 105b, and the reverse direction driving circuit 106 is composed of a high speed charging circuit 106a and a low speed discharging circuit 106b. The low-speed charging circuit 105a and the high-speed charging circuit 106a apply a power supply voltage Vp in the same direction as the polarization direction to the piezoelectric element 103 (charge the piezoelectric element 103 in the polarization direction), and the piezoelectric element 103 in the polarization direction (driving member 101). This is a circuit that extends in the direction of the axis.

  As shown in FIG. 21, the low-speed charging circuit 105a includes a constant current charging circuit formed by connecting a zener diode ZD in parallel to a fixed bias circuit of a pnp transistor Tr1. In the figure, resistors r1 and r2 are bias resistors of the transistor Tr1, and a Zener diode ZD is connected in parallel to the base bias resistor r2. In other words, the voltage drop of the resistor r1 is stabilized at a predetermined value by holding the base voltage of the transistor Tr1 at a constant value by the Zener diode ZD, and thereby the collector current is suppressed to the predetermined value. As a result, the charging current is limited, the charging speed is suppressed, and the speed when the drive member 101 moves in the forward direction is suppressed.

  Further, as shown in FIG. 22, the low-speed charging circuit 105a may be configured by replacing the parallel circuit of the resistor r2 and the Zener diode ZD in FIG. 21 with an npn transistor Tr2. In the figure, the base and collector of the transistor Tr2 are connected to the emitter and base of the transistor Tr1, respectively, and the emitter of the transistor Tr2 is connected to the power supply Vp. That is, the transistor Tr2 maintains the base voltage of the transistor Tr1 at a constant value, thereby stabilizing the voltage drop of the resistor r1 to a predetermined value, thereby suppressing the collector current to a predetermined value.

  Further, the high-speed discharge circuit 105b and the low-speed discharge circuit 106b give the piezoelectric element 103 a potential in the opposite direction to the polarization direction (grounding the electrode 103a in the figure) and discharge the charged charge to expand the piezoelectric element 103. Is a circuit for reducing

  As shown in FIG. 23, the low-speed discharge circuit 106b includes a constant current discharge circuit in which a Zener diode ZD is connected between the base of the npn transistor Tr3 and the ground. In the figure, a resistor r4 is a resistor that limits the discharge current, and the voltage drop of the resistor r4 is stabilized at a predetermined value by holding the base potential of the transistor Tr3 at a predetermined value by the Zener diode ZD. The emitter current (discharge current) flowing through r4 is suppressed to a predetermined value. As a result, the discharge current is limited, the discharge speed is suppressed, and the speed when the drive member 101 moves in the reverse direction is suppressed.

  The control circuit 107 controls the driving of the forward direction driving circuit 105 and the backward direction driving circuit 106. In the forward direction driving, the control circuit 107 alternately drives the low speed charging circuit 105a and the high speed discharging circuit 105b, while in the reverse direction driving. The high-speed charging circuit 106a and the low-speed discharging circuit 106b are alternately driven.

  When the low-speed charging circuit 105a and the high-speed discharge circuit 105b are alternately driven in the forward direction driving, the piezoelectric element 103 alternately repeats the low-speed extension and the high-speed reduction, thereby causing the driving member 101 to move in the opposite direction to the low-speed movement in the normal direction. Repeat with high-speed movement. On the other hand, when the high speed charging circuit 106a and the low speed discharging circuit 106b are alternately driven in the reverse direction driving, the piezoelectric element 103 alternately repeats the high speed extension and the low speed reduction, thereby causing the driving member 101 to perform the high speed movement in the forward direction. Repeat the slow movement in the opposite direction. Therefore, the driven member 102 moves in the forward direction relative to the driving member 101 in the forward direction driving, and the driven member 102 moves in the opposite direction relative to the driving member 101 in the reverse direction driving. To do.

JP 7-298656 A

  By the way, when an impact-type piezoelectric actuator is applied as a drive source of an optical system in a portable device such as a camera photographing lens or a binocular lens, the drive circuit is as much as possible in consideration of the weight reduction and miniaturization of the portable device. It is desirable to be simple and small. However, in the conventional piezoelectric actuator 100, the charging current or the discharging current is limited by a constant current circuit, so that the number of circuit elements is inevitably increased, and it is difficult to reduce the size of the drive circuit 104.

  In the conventional piezoelectric actuator 100, it is conceivable to change the constants of the circuit elements constituting the constant current circuit in order to adjust the moving speed of the driven member 102. In such a case, a plurality of different constants may be used. Since a circuit element and a switching circuit are required, it is more difficult to reduce the size of the drive circuit 104.

  On the other hand, as means for changing the moving speed of the driven member in the piezoelectric actuator, it has been proposed to use a plurality of piezoelectric elements by switching them or to thin out driving pulses (Japanese Patent Laid-Open No. 9-285156). According to Japanese Patent Laid-Open No. 8-43872), the circuit configuration is complicated when the piezoelectric element is switched and the driving circuit is reduced in size, and the driving speed is uneven when the driving pulse is thinned out. There's a problem.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a piezoelectric actuator that can be miniaturized.

  In order to achieve the above object, a piezoelectric actuator according to one aspect of the present invention includes a piezoelectric body, a driving member that is displaced in the axial direction based on an expansion / contraction operation of the piezoelectric body, and a predetermined frictional force that engages the driving member. A driven member that is movable, first driving means that charges the piezoelectric body by applying a voltage in the same direction as the polarization direction, and a voltage that is opposite to the polarization direction is applied to the piezoelectric body. The driving direction of the driven member is the polarization among the driving time for about one cycle and the driving time for about half cycle with respect to the resonance frequency of the piezoelectric body. If the direction is the same as the direction, the driving time for about one cycle is set in the second driving means, and the driving time for about half a period is set in the first driving means, and the driven When the moving direction of the member is opposite to the polarization direction, Setting change means for setting a driving time for a period to the first driving means and a driving time for about a half cycle to the second driving means, the first driving means and the second driving means, respectively. And a drive control means for alternately driving each other.

  Further, in the above-described piezoelectric actuator, the first driving means discharges the electric charge accumulated in the direction opposite to the polarization direction of the piezoelectric body, and charges the piezoelectric body in the same direction as the polarization direction. A second charge / discharge circuit configured to discharge the electric charge accumulated in the same direction as the polarization direction of the piezoelectric body and charge the piezoelectric body in a direction opposite to the polarization direction; It consists of a circuit.

  According to this configuration, the piezoelectric body is charged in the same direction as the polarization direction after the charge accumulated in the direction opposite to the polarization direction is discharged by the first drive means, and the same as the polarization direction by the second drive means. After the charge accumulated in the direction is discharged, it is charged in the direction opposite to the polarization direction. For this reason, a voltage twice as large as the applied voltage is apparently supplied to the piezoelectric body as a drive voltage. As a result, the expansion / contraction amount of the piezoelectric body per unit voltage is increased, and the drive efficiency of the piezoelectric actuator is improved. .

  In the piezoelectric actuator described above, the first charging / discharging 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 body, and one end connected to the first end. Second switch means connected to the other end of the piezoelectric body and grounded at the other end. The second charge / discharge circuit has one end connected to the power source and the other end connected to the piezoelectric body. It is characterized by comprising third switch means connected to the other end and fourth switch means having one end connected to one end of the piezoelectric body and the other end grounded.

  According to this configuration, the first charging / discharging circuit and the second charging / discharging circuit are each configured by two switch means, and the first charging / discharging circuit and the second charging / discharging circuit are alternately driven. The driven member is moved relative to the driving member. As a result, the piezoelectric actuator is reduced in size as a result of being constituted by circuit elements with few drive circuits.

  In the piezoelectric actuator described above, the first driving unit includes a charging circuit that charges the piezoelectric body in the same direction as the polarization direction, and the second driving unit stores the charge accumulated in the piezoelectric body. It is characterized by comprising a discharge circuit for discharging.

  According to this configuration, the piezoelectric body is charged in the same direction as the polarization direction by the first driving means, and the charge accumulated in the same direction as the polarization direction is discharged by the second driving means. For this reason, as a result of consuming electric power only during charging, electric power consumption is effectively suppressed.

  In the above-described piezoelectric actuator, the charging circuit includes first switch means having one end connected to a power source and the other end connected to one end of the piezoelectric body, and the discharging circuit includes one end Is provided with second switch means connected to one end of the piezoelectric body and grounded at the other end.

  According to this configuration, the charging circuit and the discharging circuit are each configured by one switch means, and the driven member is moved relative to the driving member by alternately driving the charging circuit and the discharging circuit. As a result, the piezoelectric actuator is reduced in size as a result of being constituted by circuit elements with few drive circuits.

  In the above-described piezoelectric actuators, the setting changing unit changes the first driving time and the second driving time so that the driving cycle becomes constant.

  According to this configuration, when the first drive time is changed, the second drive time is also changed so that the drive cycle becomes constant. Thereby, the moving speed of the driven member is adjusted smoothly.

  In the above-described piezoelectric actuators, the setting change unit changes the drive cycle by changing the first drive time or the second drive time.

  According to this configuration, the driving cycle is changed by changing the first driving time or the second driving time. Thereby, the moving speed of the driven member is adjusted smoothly.

  The piezoelectric actuator according to the present invention can be miniaturized.

It is a block diagram showing roughly the composition of the piezoelectric actuator concerning one embodiment of the present invention. It is a perspective view which shows the structural example of the drive part of the piezoelectric actuator shown in FIG. It is sectional drawing which shows the structural example of the driven member of the piezoelectric actuator shown in FIG. It is a figure which shows the structural example of the drive circuit of the piezoelectric actuator shown in FIG. FIG. 5 is a block diagram showing a configuration example of a drive pulse generation circuit in the drive circuit shown in FIG. 4. FIG. 6 is a waveform diagram for explaining the operation of the drive pulse generation circuit shown in FIG. 5. It is a figure which shows the drive pulse in the drive circuit shown in FIG. 5, the ON / OFF state of each switch element, and the waveform of the charging / discharging voltage applied to a piezoelectric member. It is a figure which shows the transient response of the variation | mutation of a piezoelectric member and a to-be-driven member when the drive voltage from which only charging / discharging speed | velocity is substantially the same and only the duty ratio of charging / discharging time differs is applied to a piezoelectric member. It is a figure for demonstrating the movement state of a to-be-driven member when the drive voltage which has substantially the same charging / discharging speed | rate and charging time longer than discharge time to a piezoelectric member is applied. It is a figure which shows the relationship between the charge time with respect to a piezoelectric member, and a drive period. It is a figure which shows the relationship between the charging time with respect to a piezoelectric member, and the moving speed of a to-be-driven member. 3 is a flowchart for explaining the operation of the piezoelectric actuator shown in FIG. 1. 3 is a flowchart for explaining the operation of the piezoelectric actuator shown in FIG. 1. FIG. 5 is a diagram showing a modification of the drive circuit shown in FIG. 4. It is a figure which shows the drive pulse in the drive circuit shown in FIG. 14, the ON / OFF state of each switch element, and the waveform of the charging / discharging voltage applied to a piezoelectric member. FIG. 5 is a diagram showing another configuration example of the drive circuit shown in FIG. 4. It is a figure which shows the ON / OFF state of each switch element in the drive circuit shown in FIG. 16, and the waveform of the charging / discharging voltage applied to a piezoelectric member. FIG. 17 is a diagram showing a modification of the drive circuit shown in FIG. 16. It is a figure which shows the ON / OFF state of each switch element in the drive circuit shown in FIG. 18, and the waveform of the charging / discharging voltage applied to a piezoelectric member. It is a figure which shows schematic structure of the conventional impact type piezoelectric actuator. FIG. 21 is a first circuit example applied to a low-speed charging circuit of the piezoelectric actuator drive circuit shown in FIG. 20. FIG. FIG. 21 is a second circuit example applied to the low-speed charging circuit of the piezoelectric actuator drive circuit shown in FIG. 20. FIG. FIG. 21 is a circuit example applied to a low-speed discharge circuit of the drive circuit of the piezoelectric actuator shown in FIG. 20.

  FIG. 1 is a block diagram schematically showing the configuration of an impact-type piezoelectric actuator according to an embodiment of the present invention. In this figure, the 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 driven member attached to the drive unit 12, and the drive unit 12. A proximal sensor 18 disposed at the proximal end, a distal sensor 20 disposed at the distal end of the drive unit 12, and a control unit 22 for controlling the overall operation are provided.

  FIG. 2 is a perspective view illustrating a configuration example of the drive unit 12. In this figure, the drive unit 12 includes a support member 24, a piezoelectric member 26, a drive member 28, and a driven member 30. The support member 24 holds the piezoelectric member 26 and the drive member 28, and is formed by scoring through the interior leaving the axially opposite ends 241 and 242 and the substantially central partition wall 243. The housing space 244 and the second housing space 245 are provided. In the first accommodation space 244, the piezoelectric member 26 is accommodated such that the stacking direction thereof coincides with the axial direction of the support member 24. The second accommodation space 245 accommodates the driving member 28 and a part of the driven member 30.

  The piezoelectric member 26 is composed of a laminated piezoelectric body in which a plurality of plate-like piezoelectric elements having a required thickness are bonded by sandwiching thin film electrodes (not shown) between the piezoelectric elements. . The plurality of piezoelectric elements are stacked so that the polarization directions of adjacent piezoelectric elements are opposite to each other. The piezoelectric elements are laminated in this way because each electrode is expanded and contracted in the same direction because a drive voltage is applied in parallel so that the positive and negative polarities are reversed between adjacent electrodes. This is because a large amount of expansion and contraction can be obtained as a whole of the piezoelectric member.

  In the piezoelectric member 26, one end face in the longitudinal direction that is the stacking direction is fixed to the end face on the opposite side of the partition wall 243 of the first accommodation space 244. A round hole is formed in one end 242 of the support member 24 (the tip of the support member 24) and the partition wall 243 at the center position, and the rod-like drive member has a round cross section through both the round holes. 28 is accommodated in the second accommodating space 245 so as to be movable along the axial direction. The cross section of the drive member 28 is not limited to a round shape, and may be an arbitrary shape such as an elliptical shape or a rectangular shape.

  An end portion of the driving member 28 protruding into the first housing space 244 is fixed to the other end surface of the piezoelectric member 26, and an end portion of the driving member 28 protruding outside the second housing space 245 is fixed by a leaf spring 32. The piezoelectric member 26 is biased by pressure. The urging of the drive member 28 by the leaf spring 32 is to stabilize the axial displacement of the drive member 28 based on the expansion / contraction operation of the piezoelectric member 26.

  FIG. 3 is a cross-sectional view illustrating a configuration example of the driven member 30. In this figure, the driven member 30 includes a base portion 301 having ear portions 302 on both sides, and a squeezing member 303 fitted between both ear portions 302. A round hole 304 having a diameter slightly larger than that of the drive member 28 is formed at the base portion of both ear portions 302 of the base portion 301. The driven member 30 penetrates the driving member 28 through the round hole 304 in a loosely fitted state, and squeezes the driving member 28 with the base 301 and the squeezing member 303 along the axial direction of the driving member 28. It is mounted movably. A protrusion 303a protruding from the upper surface of both ears 302 is formed on the upper portion of the squeezing member 303, and a leaf spring 305 is fixed to the upper surface of both ears 302 so as to be pressed against the protrusion 303a. Thus, the swallowing member 303 is biased toward the drive member 28 with a required spring pressure.

  The spring pressure by the leaf spring 305 is the friction during the forward movement that occurs between the drive member 28 and the base 301 and the squeezing member 303 in the axial reciprocation of the drive member 28 based on the expansion and contraction of the piezoelectric member 26. This is to make a difference between the force and the frictional force at the time of backward movement so that the driven member 30 can move along the axial direction of the driving member 28. That is, when the driving member 28 moves (extends or shrinks) at a high speed due to the spring pressure of the leaf spring 305, the driving member 28 and the driven member 30 are moved to such an extent that the driven member 30 can move relative to the driving member 28. When a low frictional force is generated between the driving member 30 and the driving member 28 moves (extends or contracts) at a low speed, the driving member 28 and the driven member are driven so that the driven member 30 can move together with the driving member 28. A high frictional force is generated between the member 30 and the member 30.

  In the present embodiment, the leaf spring 305 is used as the urging means for pressing the squeezing member 303 against the driving member 28. However, the urging force is not limited to this as long as urging force is generated. Other elastic members such as a coil spring and rubber can also be used. The driven member 30 is attached with a lens L which is a driving object.

  FIG. 4 is a diagram illustrating a configuration example of the drive circuit 14. In this figure, the drive circuit 14 includes a first switch circuit 141 composed of a switch element Q1 which is a MOS FET between a connection point a to which a drive voltage + Vp is supplied from the drive power supply PS and a connection point b to be grounded. And a series circuit of a second switch circuit 142 consisting of a switch element Q2 which is a MOS type FET, and a third switch circuit 143 consisting of a switch element Q3 which is a MOS type FET and a switch element Q4 which is a MOS type FET. The fourth switch circuit 144 is connected in series, and a drive pulse generation circuit 145 is connected as a control signal supply means for supplying a drive control signal to each of the switch circuits 141 to 144.

  The switch element Q1 constituting the first switch circuit 141 and the switch element Q2 constituting the second switch circuit 142 are P-channel FETs, and constitute the switch element Q3 and the fourth switch circuit 144 constituting the third switch circuit 143. The switch element Q4 is an N-channel FET.

  The piezoelectric member 26 is connected between the connection point c of the first switch circuit 141 and the third switch circuit 143 and the connection point d of the second switch circuit 142 and the fourth switch circuit 144 (the connection point c is a piezoelectric member). 26 is connected to the + side electrode 261 with reference to the polarization direction indicated by the arrow P of FIG. 26, and the connection point d is connected to the − side electrode 262 of the piezoelectric member 26). The drive pulse generation circuit 145 is directly connected to the gates of the FETs of the 2-switch circuit 142 and the fourth switch circuit 144, and the drive pulse generation circuit 145 is connected to the gates of the FETs of the first switch circuit 141 and the third switch circuit 143. Are connected via an inverting circuit 147.

  In this drive circuit 14, the polarity of the drive voltage connected between the connection points a and b and the polarization direction of the piezoelectric member 26 connected between the connection points c and d can be arbitrarily set. For example, FIG. As shown in FIG. 4, when the connection point a is the positive electrode of the drive voltage, the piezoelectric member 26 is polarized in the direction of the arrow P, and the + polarization side is connected to the connection point c (the -polarization side is connected to the connection point d). Then, the first switch circuit 141 and the fourth switch circuit 144 apply the drive voltage + Vp to the piezoelectric member 26 in the same direction as the polarization direction (direction in which the polarization is increased) and charge the piezoelectric member 26 until the inter-terminal voltage Vs becomes + Vp. 1 drive circuit (first drive means), and the second switch circuit 142 and the third switch circuit 143 apply a drive voltage + Vp to the piezoelectric member 26 in the direction opposite to the polarization direction to thereby apply the first drive circuit. Charged by Discharges, and, so that the inter-terminal voltage Vs corresponds to a second driving circuit (second driving means) for charging until -Vp. When the piezoelectric member 26 is charged to −Vp by the second drive circuit, the first drive circuit discharges the charged charge and then charges to + Vp.

  When the piezoelectric member 26 is connected in the direction opposite to that shown in FIG. 4, the second switch circuit 142 and the third switch circuit 143 serve as a first drive circuit that charges the piezoelectric member 26 in the same direction as the polarization direction. The circuit 141 and the fourth switch circuit 144 serve as a second drive circuit that charges the piezoelectric member 26 in the direction opposite to the polarization direction.

  When the bridge circuit 146 is configured by the drive circuit 14 and the piezoelectric member 26 as described above, a voltage of −Vp to + Vp is applied to the piezoelectric member 26, so that the drive voltage of the piezoelectric member 26 is equivalently 2 Vp. As a result, there is an advantage that a piezoelectric actuator having a large displacement can be obtained even when the drive power supply is at a low voltage.

  FIG. 5 is a block diagram illustrating a configuration example of the drive pulse generation circuit 145. In this figure, a drive pulse generation circuit 145 counts up an oscillation element 150 such as a crystal oscillator that outputs a clock pulse of 125 ns and a pulse signal output from the oscillation element 150 and outputs a count value thereof. 151, a first memory 152 for setting the drive pulse period, a second memory 153 for setting the charging time for the piezoelectric member 26, and predetermined values (in the first memory 152 and the second memory 153). And a pulse width control unit 154 for controlling the ON / OFF timing of the drive pulse by setting (time). The counter 151 resets its count value to zero when a reset signal is input from a first comparator 155 described later.

The drive pulse generation circuit 145 further compares the set value (T _M ) of the first memory 152 with the count value (T _C ) output from the counter 151, and the count value (T _C ) is set to the set value. When (T _M ) is reached (T _C ≧ T _M ), the first comparator 155 outputs a reset signal to the counter 151, the set value (T _N ) of the second memory 153, and the count output from the counter 151 When the count value (T _C ) is smaller than the set value (T _N ) (T _C <T _N ), the high signal “H” is output while the count value (T _C ) is compared. _C ) reaches the set value (T _N ) (T _C ≧ T _N ) and outputs a low signal “L”, and operates based on the output control signal from the control unit 22 And the second comparator 156 when the drive pulse is output. And the output produced al as the driving pulse, when the drive pulse output is stopped and an output control circuit 157 for fixing the driving pulses to a high state.

As shown in FIG. 6, when the count value (T _C ) of the counter 151 reaches the set value (T _N ) of the second memory 153, the drive pulse generation circuit 145 configured in this way When the output high signal is switched to the low signal and the count value (T _C ) of the counter 151 reaches the set value (T _M ) of the first memory 152 after a lapse of time, the output signal is output from the output control circuit 156. The low signal is switched to a high signal. At this time, a reset signal is simultaneously output from the first comparator 155 to the counter 151, whereby the count value (T _C ) of the counter 151 is reset to zero. By repeatedly executing the above operation in this way, drive pulses are continuously output from the drive pulse generation circuit 145 at a predetermined cycle. Here, the first memory 152 for setting the drive pulse period, the second memory 153 for setting the charging time for the piezoelectric member 26, and the pulse width control unit 154 include the first drive circuit and the second drive. The setting change means 159 for setting the cycle of the driving time of the circuit or setting the charging time so that the driving cycle becomes constant is configured.

  Note that the first drive circuit including the first switch circuit 141 and the fourth switch circuit 144 is driven during the high signal output period t1 shown in FIG. 6, and the second switch during the low signal output period t2 shown in FIG. The second drive circuit composed of the circuit 142 and the third switch circuit 143 is driven. Here, the set value of the first memory 152 is kept constant, and the on period (drive time) t1 of the first drive circuit is set in a state where the drive period is made constant by changing the set value of the second memory 153. The ON period (driving time) t2 of the second driving circuit can be adjusted (the duty ratio is adjusted). Further, by changing the set value of the first memory 152, the driving cycle including the on period t1 of the first driving circuit and the on period t2 of the second driving circuit can be adjusted.

  Returning to FIG. 1, the member sensor 16 is disposed within a movable range of the driven member 30, and includes a sensor such as an MRE (Magneto Resistive Effect) element or PSD (Position Sensitive Device). The proximal sensor 18 and the distal sensor 20 are configured by sensors such as a photo interrupter.

  The control unit 22 includes a CPU (Central Processing Unit) that performs arithmetic processing, a ROM (Read-Only Memory) that stores processing programs and data, and a RAM (Random Access Memory) that temporarily stores data. Based on a signal input from the member sensor 16 or the like, a pulse signal having a predetermined duty ratio is output from the drive pulse generation circuit 145, and the first drive circuit and the second drive circuit are alternately driven by the drive pulse. . That is, the control unit 22 alternately drives the first drive circuit composed of the first switch circuit 141 and the fourth switch circuit 144 and the second drive circuit composed of the second switch circuit 142 and the third switch circuit 143. The drive control means is configured. The controller 22 is connected to a movement instruction switch 34 for instructing movement of the driven member 30 and a timer 36 for detecting the moving speed of the driven member 30.

  The piezoelectric actuator 10 configured as described above is not provided with a constant current circuit composed of a plurality of circuit elements such as a transistor, a Zener diode, and a resistor for limiting current in the charge / discharge circuit as in the prior art. The circuit 14 can be as simple as possible. Thereby, the drive circuit 14 can be simplified and miniaturized, and the piezoelectric actuator 10 can be miniaturized. In addition, since the constant current circuit is not provided in the charge / discharge circuit as in the prior art, the charging speed when the drive voltage in the same direction as the polarization direction is applied to the piezoelectric member 26 and the polarization direction with respect to the piezoelectric member 26. The discharge rate when a drive voltage in the opposite direction is applied is substantially the same (that is, the charge / discharge rate for the piezoelectric member 26 is substantially the same).

  7 shows the drive pulse output from the drive pulse generation circuit 145 of the drive circuit 14 shown in FIG. 4, the ON / OFF states of the switch elements Q1 to Q4, and the waveform of the drive voltage applied to the piezoelectric member 26. FIG. As shown in this figure, when the piezoelectric actuator 10 is driven, the drive pulse output from the drive pulse generation circuit 145 is input as it is to the switch elements Q2 and Q4 as drive control signals, while the drive pulse generation circuit 145 is provided. The drive pulse output from is input to the switch elements Q1 and Q3 as a drive control signal in a state where the drive pulse is inverted through the inversion circuit 147. As a result, the switch elements Q1, Q4 and the switch elements Q2, Q3 are alternately turned on, and the drive voltage Vp is applied to the piezoelectric member 26 during the on period.

  When the driven member 30 is moved to the distal end side of the support member 24 (hereinafter, driving in this direction is referred to as “forward driving”), the ON period t1 of the first driving circuit and the second driving circuit. A ratio D to the ON period t2 (D = t1 / (t1 + t2), hereinafter referred to as duty ratio D) is set to a relatively small value of 0.5 or less. When the driven member 30 is moved to the base end side of the support member 24 (hereinafter, driving in this direction is referred to as “reverse driving”), the ON period t1 of the first driving circuit and the second driving are performed. The duty ratio D with respect to the on-period t2 of the circuit is set to a relatively large value of 0.5 or more. That is, in the present invention, the drive direction (forward drive or reverse drive) of the piezoelectric actuator 10 is controlled by making the charge / discharge speeds with respect to the piezoelectric member 26 substantially the same and by varying the charge / discharge time duty ratio D. ing. Since the switch elements Q1 and Q2 are P-channel FETs, they are turned on when the drive control signal is at a low level, and since the switch elements Q3 and Q4 are N-channel FETs, they are turned on when the drive control signal is at a high level. Turn on.

  As described above, the charge / discharge speed for the piezoelectric member 26 is made substantially the same, and the drive direction of the piezoelectric actuator 10 is controlled only by the duty ratio D of the charge / discharge time. This is based on the experimental result that the driven member 30 moves relative to the driving member 28 under a certain condition by providing a relatively large difference between the charging direction in the direction and the reverse direction.

  FIG. 8 is a diagram showing a transient response of the displacement of the piezoelectric member when a drive voltage is applied in which the charge / discharge speed with respect to the piezoelectric member 26 is substantially the same and only the duty ratio D of the charge / discharge time with respect to the piezoelectric member 26 is different. Based on this figure, the reason why the driven member 30 moves in the forward direction and the reverse direction with respect to the drive member 28 by changing the duty ratio D of the charge / discharge time will be described.

  The waveform shown in the lower part of FIG. 8 indicates that the charging time when the driving voltage in the same direction as the polarization direction is applied to the piezoelectric member 26 is longer than the discharging time when the driving voltage in the direction opposite to the polarization direction is applied. One cycle of the drive voltage having a long predetermined duty ratio is shown, and the waveform shown in the upper stage is a diagram showing a transient expansion and contraction operation of the piezoelectric member 26 and the drive member 28 when the drive voltage is applied. For convenience of explanation, the transient waveform of the expansion / contraction operation of the piezoelectric member 26 and the drive member 28 shown in FIG. 8 is represented by the waveform of the fundamental wave of the resonance frequency.

  Now, when the piezoelectric member 26 is charged by applying the driving voltage + Vp in the same direction as the polarization direction, the piezoelectric member 26 expands, and the piezoelectric member 26 is accumulated by applying the driving voltage -Vp in the direction opposite to the polarization direction. When the electric charge is discharged and charged in the opposite direction, the piezoelectric member 26 shrinks. However, since the piezoelectric member 26 and the driving member 28 have elasticity, for example, when the extension operation is transiently viewed, the piezoelectric member 26 is determined by the piezoelectric member 26 itself, the driving member 28, the driven member 30, and the like. It extends to a predetermined length while vibrating at a resonance frequency of. That is, as shown in FIG. 8, for example, when the drive voltage + Vp is applied to the piezoelectric member 26 at the point a, the piezoelectric member 26 expands greatly at a high speed, then starts to shrink at the point b, and then expands in a vibrational manner. Then, the amount of expansion near the point c is settled by repeating the above and the reduction (see the waveform indicated by the phantom line from the point c in FIG. 8). The situation of such a transient displacement operation is the same for the reduction operation. When −Vp is applied after + Vp is applied, it is greatly reduced at a high speed and then starts to expand with a certain amount of displacement, and then vibrates. Then, reduction and expansion are repeated to settle down to a predetermined reduction amount (see the waveform indicated by the phantom line from point d in FIG. 8).

  That is, when a drive voltage having a waveform as shown in FIG. 8 is repeatedly applied to the piezoelectric member 26, the voltage + Vp is applied to the piezoelectric member 26 at the point a from the state of being charged at −Vp, and charging is performed. When this occurs, the piezoelectric member 26 expands to the point b at a high speed, but thereafter contracts to the point c at a speed slower than the expansion speed (in FIG. 8, the inclination between bc is gentler than the inclination between a and b). become). This is because if the expansion and contraction are performed in substantially the same time, the reduction amount is smaller than the expansion amount due to the viscosity of the piezoelectric member 26, the drive member 28, and the like.

  Next, at the timing of point c at which the reduction operation is almost completed (this timing corresponds to the timing of about one cycle of the resonance frequency of the piezoelectric member 26 when charged in the same direction as the polarization direction). When −Vp is applied and discharged, and when charged with −Vp, the piezoelectric member 26 further reduces from the displacement position to point d. At this time, since the expansion amount of the piezoelectric member 26 is close to the reduction amount when the discharge is regularly performed, the reduction speed is lower than the expansion speed between a and b. That is, the inclination between cd becomes gentler than the inclination between a and b.

  Then, the timing at which the reduction operation is almost completed (this timing corresponds to a timing corresponding to about 1/2 cycle of the resonance frequency of the piezoelectric member 26 when charged in the direction opposite to the polarization direction). When the voltage + Vp is applied to the member 26 and charging is performed, the piezoelectric member 26 again performs an extension operation at a high speed. Hereinafter, the expansion and contraction of the above-described piezoelectric member 26 according to the waveform of the drive voltage as shown in FIG. The operation is repeated.

  In the expansion / contraction operation of the piezoelectric member 26 described above, the expansion operation is performed at a high speed and the contraction operation is performed at a lower speed. Therefore, when the driving member 28 repeats reciprocation by the expansion / contraction operation of the piezoelectric member, the high-speed forward movement is performed. At times, the frictional force between the driving member 28 and the driven member 30 is low, and the frictional force between the driving member 28 and the driven member 30 is high at the time of reverse movement at a low speed. It moves together with the drive member 28 only during the movement. Therefore, as shown in FIG. 9, the driven member 30 repeatedly stops and moves in accordance with the reciprocating movement of the driving member 28, and performs reverse driving as a whole.

  FIG. 9 shows an example in which a drive voltage having a predetermined duty ratio D having a charging time longer than the discharging time is applied to the piezoelectric member 26. The predetermined duty ratio D having a charging time shorter than the discharging time is applied to the piezoelectric member 26. When the drive voltage having the above is applied, the above charge / discharge speed relationship is reversed, and the piezoelectric member 26 contracts at a high speed when charged with -Vp and expands at a low speed when charged with + Vp. The driven member 30 repeats moving and stopping according to the reciprocating motion of the driving member 28, and performs the forward driving as a whole.

  Therefore, in FIG. 4, when a drive pulse having a predetermined value with a duty ratio D greater than 0.5 is output from the drive pulse generation circuit 145, the piezoelectric member 26 alternately repeats high speed expansion and low speed reduction. Therefore, the driven member 30 moves to the base end side of the support member 24 (reverse direction driving). Further, when a drive control signal having a predetermined value with a duty ratio D smaller than 0.5 is output from the drive pulse generation circuit 145, the piezoelectric member 26 alternately repeats the low speed extension and the high speed reduction, so The drive member 30 moves to the front end side of the support member 24 (forward direction drive).

  In order to stably move the driven member 30 in the desired direction, as described above, the charging time (see the time a to c in FIG. 8) of the piezoelectric member 26 when charging in the same direction as the polarization direction is performed. In the period of about one cycle of the resonance frequency, the discharge time (see time cd in FIG. 8) is about ½ cycle of the resonance frequency of the piezoelectric member 26 when charged in the direction opposite to the polarization direction. However, due to factors such as the mounting structure of the piezoelectric member 26 to the support member 24 and the driving member 28, the displacement waveforms of the piezoelectric member 26 and the driving member 28 are actually as shown in FIG. It becomes a distorted waveform in which other frequency components are superimposed. Therefore, the drive voltage for the appropriate piezoelectric member 26 is adjusted and set for each piezoelectric actuator.

  Even if the duty ratio D of the charge / discharge time of the drive pulse is not accurately related to the resonance frequency of the piezoelectric member 26, the driven member 30 is moved in the forward direction or the reverse direction according to the duty ratio D. It is possible.

  Further, depending on the mounting structure and conditions between the piezoelectric member 26, the driving member 28, and the driven member 30, it is possible to drive in the direction opposite to that shown in FIG. That is, the driven member 30 is moved in the reverse direction by setting the duty ratio D of the drive pulse to a value smaller than 0.5, and the driven member 30 is set by setting the duty ratio D to a value larger than 0.5. Can be moved in the positive direction.

  FIG. 10 shows a driving cycle tp composed of a charging time t1 (driving time t1 of the first driving circuit shown in FIG. 6) and a discharging time t2 (driving time t2 of the second driving circuit shown in FIG. 6) for the piezoelectric member 26. Of the driven member 30 with respect to the driving member 28 when the charging time t1 is changed by 125 ns in the range of 9.5 μs to (tP−1.5 μs). The speed (moving speed toward the base end side) is measured and expressed as a contour map.

  As is apparent from this contour map, the moving speed of the driven member 30 toward the base end side is the fastest in the vicinity of the driving cycle of 14.5 μs and the charging time of 10.25 μs, and centered on that point within the predetermined range. It decreases as the driving cycle tP or the charging time t1 changes. The moving speed changes most smoothly when the driving cycle tP is set to 14.5 μs and the charging time is increased from 10.25 μs. The contour map of FIG. 10 is for the case where the driven member 30 is moved to the base end side of the driving member 28, but the case where the driven member 30 is moved in the reverse direction (the tip end side of the driving member 28) is almost the same. Similar measurement results could be obtained. However, the moving speed of the driven member 30 toward the tip end side is the fastest in the vicinity of a driving cycle of 14.5 μs and a charging time of 3.25 μs, and within a predetermined range, the driving cycle tp (= t1 + t2) It decreases as the charging time t1 changes. The moving speed changes most smoothly when the driving cycle tp is set to 14.5 μs and the charging time is decreased from 3.25 μs.

  Further, as shown in FIG. 11, when the driving cycle tp is set to 14.5 μs, the moving speed of the driven member 30 reaches the peak when the charging time t1 is around 10.25 μs. As time t1 becomes longer, it decreases gently. Therefore, in the present embodiment, the speed of the driven member 30 is controlled by setting the driving cycle tp to 14.5 μs and changing the charging time t1 within the range of 11 μs to 12 μs. Further, when the driven member 30 is moved to the tip end side of the driving member 28, the driving cycle tp is set to 14.5 μs, and the charging time t1 is changed within the range of 2.5 μs to 3.5 μs. The speed of the driven member 30 is controlled. Note that these numerical values are based on the experimental results in the present embodiment, and needless to say, are appropriately changed according to the configuration of the piezoelectric actuator 10.

  12 and 13 are flowcharts for explaining the operation of the control unit 22 that controls the speed of the driven member 30. First, when a power switch (not shown) of the piezoelectric actuator 10 is turned on, it is determined whether or not the movement instruction switch 34 is turned on after the initial state is set (step # 1). If this determination is affirmed, it is determined whether or not the tip sensor 20 is turned on (step # 3), and if this determination is affirmed, the first memory 152 that sets the period of the drive pulse (drive period) is set to “ 116 ”(116 × 0.125 μs = 14.5 μs) is set (step # 5). If the determination in step # 1 is negative, the process waits until the movement instruction switch 34 is turned on.

  Next, “92” (92 × 0.125 μs = 11.5 μs) is set in the second memory 153 for setting the charging time (step # 7), and then driving pulse output is started from the driving pulse generation circuit 145. (Step # 9). Then, the timer 36 is started and time is counted in accordance with the movement of the driven member 30 (step # 11), and it is subsequently determined whether or not the proximal sensor 18 is turned on (step # 13). ). If the determination in step # 13 is negative, it is determined whether or not, for example, 10 ms has elapsed (step # 15), and if the determination is affirmative, whether or not the movement distance to the proximal end has exceeded 24 μm, for example. Is discriminated (step # 17).

  If the determination in step # 13 is affirmative, output of the drive pulse is stopped (step # 19), and the process returns to step # 1 and the subsequent operations are repeated. If the determination is negative in step # 15, the process returns to step # 13 and the subsequent operations are repeated. The determination of time in step # 15 is performed based on the output value from the timer 36, and the determination of the movement distance in step # 17 is performed based on the output value from the member sensor 16. That is, until a certain time (for example, 10 ms) elapses, the driven member 30 is moved under the conditions of a driving cycle of 14.5 μs and a charging time of 11.5 μs, and the time until the certain time (for example, 10 ms) elapses. When the end position is reached, further movement becomes impossible, and output of the drive pulse is stopped.

  If the determination in step # 17 is negative, it is determined whether or not the moving distance to the base end side is less than 22 μm, for example (step # 21). If this determination is negative, the process returns to step # 11 and the subsequent steps The operation is executed repeatedly. That is, as long as the movement distance of the driven member 30 is within a predetermined range (for example, 22 μm to 24 μm) even after a certain time (for example, 10 ms) has elapsed, the driving cycle is 14.5 μs and the charging time is 11.5 μs. The driven member 30 is moved.

  If the determination in step # 17 is affirmative, “1” is added to the second memory 153 (increase by 0.125 μs) (step # 23), and then the set value of the second memory 153 exceeds “96”. It is determined whether or not (step # 25). If the determination in step # 25 is affirmative, output of the drive pulse is stopped (step # 27), and then an abnormality warning is displayed on a display device (not shown) (step # 29), and the operation ends. That is, when the moving distance of the driven member 30 exceeds a predetermined value (for example, 24 μm), the charging time is sequentially increased from 11.5 μs, the moving speed is gradually reduced, and even if the charging time reaches 12 μs, the proximal sensor If the position does not reach the 18th position, it is determined that an abnormality has occurred, and the drive pulse output is stopped, and a warning is issued at the same time.

  If the determination in step # 21 is affirmative, “1” is subtracted from the second memory 153 (decrease by 0.125 μs) (step # 31), and then the set value of the second memory 153 is “88”. Is determined (step # 33). If the determination is affirmative in step # 33, the process proceeds to step # 27. If the determination is negative in step # 33, the process returns to step # 11 and the subsequent operations are repeated. That is, when the moving distance of the driven member 30 does not reach a predetermined value (for example, 22 μm) even after a certain time (for example, 10 ms) has elapsed, the charging time is sequentially decreased from 11.5 μs to increase the moving speed. If the acceleration is sequentially performed and the position of the base sensor 18 is not reached even when the charging time reaches 11 μs, it is determined that there is an abnormality, the drive pulse output is stopped, and a warning is issued at the same time.

  On the other hand, if the determination in step # 3 is negative, it is determined whether or not the proximal sensor 18 is turned on (step # 35). If this determination is affirmative, “116” (116 ×) is stored in the first memory 152. 0.125 μs = 14.5 μs) is set (step # 37). If the determination is negative in step # 35, the process returns to step # 3 again and the subsequent operations are repeated.

  Next, “24” (24 × 0.125 μs = 3.0 μs) is set in the second memory 153 (step # 39), and then drive pulse output is started from the drive pulse generation circuit 145 (step # 41). ). That is, until the above-described step # 33, the driven member 30 moves from the distal end side to the proximal end side of the driving member 28, whereas after step # 37, the driven member 30 moves the driving member 28. This is an operation of moving from the proximal end side toward the distal end side.

  Next, the timer 36 is started and time is counted in accordance with the movement of the driven member 30 (step # 43), and it is subsequently determined whether or not the tip sensor 20 is turned on (step # 45). . If the determination is negative in step # 45, it is determined whether or not, for example, 10 ms has elapsed (step # 47), and if the determination is affirmative, whether or not the moving distance to the tip side has exceeded 24 μm, for example. A determination is made (step # 49).

  If the determination in step # 45 is affirmative, output of the drive pulse is stopped (step # 51), and the process returns to step # 1 and the subsequent operations are repeated. If the determination is negative in step # 47, the process returns to step # 45 and the subsequent operations are repeated. The time determination in step # 47 is performed based on the output value from the timer 36, and the movement distance determination in step # 49 is performed based on the output value from the member sensor 16. In other words, the driven member 30 is moved under the conditions of a driving period of 14.5 μs and a charging time of 3.0 μs until a certain time (for example, 10 ms) elapses, and the tip is reached until a certain time (for example, 10 ms) elapses. When the position is reached, no further movement is possible, and output of the drive pulse is stopped.

  If the determination is negative in step # 49, it is determined whether or not the moving distance to the tip side is less than 22 μm, for example (step # 53). If this determination is negative, the process returns to step # 43 and the subsequent operations Is repeatedly executed. That is, as long as the movement distance of the driven member 30 is within a predetermined range (for example, 22 μm to 24 μm) even after a predetermined time (for example, 10 ms) has passed, the driving cycle is 14.5 μs and the charging time is 3.0 μs. The driven member 30 is moved.

  If the determination in step # 49 is affirmative, “1” is subtracted from the second memory 153 (decrease by 0.125 μs) (step # 55), and then the set value of the second memory 153 is less than “20”. Is discriminated (step # 57). If the determination in step # 57 is affirmative, the output of the drive pulse is stopped (step # 59), and then an abnormality warning is displayed on a display device (not shown) (step # 61), and the operation ends. That is, when the moving distance of the driven member 30 exceeds a predetermined value (for example, 24 μm), the charging time is sequentially reduced from 3.0 μs, the moving speed is sequentially reduced, and even if the charging time reaches 2.5 μs, the tip is reached. When the sensor 20 position is not reached, it is determined that there is an abnormality, the drive pulse output is stopped, and a warning is issued at the same time.

  If the determination in step # 53 is affirmative, “1” is added to the second memory 153 (increase by 0.125 μs) (step # 63), and then the set value of the second memory 153 is “28”. Is determined (step # 65). If the determination is affirmative in step # 65, the process proceeds to step # 59. If the determination is negative in step # 65, the process returns to step # 43 and the subsequent operations are repeatedly executed. That is, when the moving distance of the driven member 30 does not reach a predetermined value (for example, 22 μm) even after a certain time (for example, 10 ms) has elapsed, the charging time is sequentially increased from 3.0 μs and the moving speed is increased. If the position is not accelerated even if the charging time reaches 3.5 μs and the position of the tip sensor 20 is not reached, it is determined that an abnormality has occurred and the drive pulse output is stopped and a warning is issued at the same time.

  FIG. 14 is a diagram illustrating a modification of the drive circuit 14. 14 differs from that shown in FIG. 4 in that a resistor R is connected between the connection point b in the bridge circuit 146 and the ground. Since the resistor R is connected between the connection point b and the ground, the waveform until the piezoelectric member 26 is charged to + Vp and −Vp becomes gentle as shown in FIG. The basic operation is the same as that shown in FIG.

  Although not shown, instead of the modification shown in FIG. 14, a resistor R is connected in series to one or both of the switch element Q1 and the switch element Q4 constituting the first drive circuit, and the second It is also possible to adopt a circuit configuration in which a resistor R is connected in series to one or both of the switch element Q2 and the switch element Q3 constituting the drive circuit. Even in this case, the waveform until the piezoelectric member 26 is charged to + Vp and −Vp becomes gentle as in the case shown in FIG. 15, but the basic operation is the same as that shown in FIG. .

  Further, a resistor R is connected in series to one or both of the switch element Q1 and the switch element Q4 constituting the first drive circuit, or the switch element Q2 and the switch element Q3 constituting the second drive circuit. It is also possible to adopt a circuit configuration in which a resistor R is connected in series to either or both of the above. In this case, in the case where the resistor R is connected in series to one or both of the switch element Q1 and the switch element Q4, the waveform until the piezoelectric member 26 is charged to + Vp becomes gentle, and the switch element Q2 and In the case where the resistor R is connected in series to either one or both of the switch elements Q3, the waveform until the piezoelectric member 26 is charged to -Vp becomes gradual. It is the same as that shown in FIG.

  FIG. 16 is a diagram illustrating another configuration example of the drive circuit 14. In the drive circuit 14 ′ shown in FIG. 16, the first drive circuit shown in FIG. 4 is composed of two switch circuits (first switch circuit 141 and fourth switch circuit 144) constituting a charge / discharge circuit, The second drive circuit is composed of the other two switch circuits (second switch circuit 142 and third switch circuit 143) constituting the charge / discharge circuit, whereas the first drive circuit is replaced with the charge circuit. It is different in that it is composed of one switch circuit (first switch circuit 141 ') that constitutes, and the second drive circuit is composed of one switch circuit (second switch circuit 142') that constitutes a discharge circuit. is doing. The first and second switch circuits 141 ′ and 142 ′ are driven by a drive pulse supplied from a drive pulse generation circuit 145 having the same configuration as that shown in FIG. A drive voltage Vp is applied from the power supply PS.

  That is, the first switch circuit 141 ′ constituting the charging circuit applies the drive voltage Vp to the + -side electrode 261 with reference to the polarization direction indicated by the arrow P of the piezoelectric member 26, and causes the piezoelectric member 26 to have the same polarization direction. It is charged in the direction, and is composed of a switch element Q5 made of a P-channel MOS type FET connected between the drive power source PS and the electrode 261. In addition, the second switch circuit 142 ′ constituting the discharge circuit grounds the electrode 261 of the piezoelectric member 26 (that is, gives a potential in the opposite direction to the voltage between the terminals of the piezoelectric member 26) to the piezoelectric member 26. It discharges the accumulated electric charge and is composed of a switch element Q6 made of an N-channel MOS type FET connected between the electrode 261 and the ground.

  FIG. 17 is a diagram showing the ON / OFF state of each switch element of the drive circuit 14 ′ shown in FIG. 16 and the waveform of the charging voltage applied to the piezoelectric member. As shown in this figure, when the drive pulse is supplied from the drive pulse generation circuit 145 and the switch element Q5 is turned on, the switch element Q6 is turned off, and the piezoelectric member 26 is charged with the voltage Vp in the same direction as the polarization direction. When the switch element Q6 is turned on, the switch element Q5 is turned off, and the charge of the piezoelectric member 26 is discharged.

  Even when the drive circuit 14 shown in FIG. 4 is configured as the drive circuit 14 ′, when the duty ratio D between the charging time t1 and the discharging time t2 is smaller than 0.5, the driving is performed in the positive direction, and the duty ratio D is When it is larger than 0.5, the driving is in the reverse direction, and it is confirmed that the operation is the same as that shown in FIG.

  FIG. 18 is a diagram showing a modification of the drive circuit 14 ′ shown in FIG. 18 differs from that shown in FIG. 16 in that resistors R are connected between the switch element Q5 and the drive power source PS and between the switch element Q6 and the ground. . Since the resistor R is connected as described above, the waveform until the piezoelectric member 26 is charged to Vp and the waveform until the charged charge is discharged to zero level are gentle as shown in FIG. The basic operation is the same as that shown in FIG.

  It is also possible to connect the resistor R between the switch element Q5 and the drive power source PS or between the switch element Q6 and the ground. In this case, in the case where the resistor R is connected between the switch element Q5 and the drive power source PS, the waveform until the piezoelectric member 26 is charged to Vp becomes gradual, and the switch element Q6 is grounded between the switch element Q6 and the ground. In the case where the resistor R is connected, the waveform until the piezoelectric member 26 is discharged becomes gentle, but in any case, the basic operation is the same as that shown in FIG.

  The piezoelectric actuator 10 according to the present embodiment, as described above, applies a voltage in the same direction as the polarization direction to the piezoelectric member to charge and discharge, and applies a voltage in the direction opposite to the polarization direction to the piezoelectric member. A second driving circuit that is charged and discharged at a rate substantially the same as the charging / discharging speed of the first driving circuit, and the driving time of the driving member, the first driving time by the first driving means and the second driving time. The setting change means for changing the setting of at least one of the second drive times by the drive means and the drive control means for alternately driving the first drive means and the second drive means are provided. Since such a constant current circuit becomes unnecessary, the size can be reduced, and the drive circuit is driven by continuous drive pulses, so that the moving speed of the drive member can be adjusted smoothly. In addition, since the piezoelectric actuator 10 can be reduced in size, the cost reduction of the piezoelectric actuator 10 can be promoted.

  The piezoelectric actuator is not limited to the one in the above embodiment, and various modifications can be made. For example, the drive unit 12 may have a configuration other than that shown in FIGS. 2 and 3, and a junction FET, a bipolar transistor, a GTO can be used as a switch element constituting the drive circuits 14 and 14 ′. An electronic switch element other than a MOS type FET such as (Gate Turn-off Thyristor) can also be used. In addition, in the above embodiment, the moving speed of the driven member 30 is adjusted by changing the charging time so that the driving cycle is constant. However, the driving speed is changed by changing the charging time or the discharging time. You may make it carry out by changing a period.

  As described above, according to one aspect, the first driving unit that charges and discharges the piezoelectric body by applying a voltage in the same direction as the polarization direction, and the voltage that is opposite to the polarization direction is applied to the piezoelectric body. A second driving unit that charges and discharges the piezoelectric body at a rate substantially the same as a charging / discharging rate by the first driving unit; a driving time of the driving member, the first driving time by the first driving unit; Since there is provided a setting change means for changing the setting of at least one of the second drive times by the two drive means and a drive control means for alternately driving the first drive means and the second drive means, it is compact. It is possible to realize a piezoelectric actuator that can be adjusted and the moving speed of the driven member can be adjusted smoothly.

  According to another aspect, the first driving means discharges the charge accumulated in the direction opposite to the polarization direction of the piezoelectric body, and charges the piezoelectric body in the same direction as the polarization direction. The second drive means comprises a second charge / discharge circuit that discharges charges accumulated in the same direction as the polarization direction of the piezoelectric body and charges the piezoelectric body in a direction opposite to the polarization direction. Therefore, a voltage twice as large as the applied voltage is apparently supplied to the piezoelectric body as a driving voltage, and the expansion / contraction amount of the piezoelectric body per unit voltage is increased, thereby improving the driving efficiency of the piezoelectric actuator.

  According to another aspect, the first charging / discharging circuit includes a first switch unit in which one end is connected to a power source and the other end is connected to one end of the piezoelectric body, and one end is piezoelectric. A second switch means connected to the other end of the body and having the other end grounded. The second charge / discharge circuit has one end connected to the power source and the other end connected to the other end of the piezoelectric body. Since the third switch means and the fourth switch means having one end connected to one end of the piezoelectric body and the other end grounded, the drive circuit is configured with few circuit elements. Therefore, miniaturization of the piezoelectric actuator is promoted.

  According to another aspect, the first driving means includes a charging circuit that charges the piezoelectric body in the same direction as the polarization direction, and the second driving means discharges the charge accumulated in the piezoelectric body. Therefore, power is consumed only during charging, and power consumption can be effectively suppressed.

  According to another aspect, the charging circuit includes first switch means having one end connected to the power source and the other end connected to one end of the piezoelectric body, and the discharging circuit includes one end. Since the second switch means is connected to one end of the piezoelectric body and the other end is grounded, it is composed of circuit elements with a small number of drive circuits, and miniaturization of the piezoelectric actuator is promoted.

  According to another aspect, the setting changing unit changes the first driving time and the second driving time so that the driving cycle becomes constant, and thus the moving speed of the driven member is smooth. Can be adjusted.

  According to another aspect, the setting change means changes the drive cycle by changing the first drive time or the second drive time, so that the moving speed of the driven member can be made smooth. Can be adjusted.

DESCRIPTION OF SYMBOLS 10 Piezoelectric actuator 12 Drive part 14 Drive circuit 16 Member sensor 18 Base end sensor 20 Tip sensor 22 Control part (drive control means)
24 support member 26 piezoelectric member (piezoelectric body)
28 Drive member 30 Driven member 159 Setting change means 141 First switch circuit (first drive means)
142 Second switch circuit (second driving means)
143 Third switch circuit (second driving means)
144 Fourth switch circuit (first driving means)
Q1, Q5 switch element (first switch means)
Q2 switch element (third switch means)
Q3 switch element (fourth switch means)
Q4, Q6 switch element (second switch means)
PS drive power supply

Claims (6)

A piezoelectric body;
A drive member that is displaced in the axial direction based on the expansion and contraction of the piezoelectric body;
A driven member engaged with the driving member with a predetermined frictional force and movable;
First driving means for charging the piezoelectric body by applying a voltage in the same direction as the polarization direction;
Second driving means for charging the piezoelectric body by applying a voltage in a direction opposite to the polarization direction;
When the moving direction of the driven member is the same direction as the polarization direction among the driving time for about one cycle and the driving time for about a half cycle with respect to the resonance frequency of the piezoelectric body, The driving time for about one cycle is set for the second driving means, the driving time for about half a period is set for the first driving means, and the moving direction of the driven member is opposite to the polarization direction. If the direction is a direction, setting change means for setting the driving time for about one cycle in the first driving means, and setting the driving time for about half a cycle in the second driving means,
A piezoelectric actuator comprising: drive control means for alternately driving the first drive means and the second drive means. The first driving means comprises a first charging / discharging circuit that discharges charges accumulated in a direction opposite to the polarization direction of the piezoelectric body and charges the piezoelectric body in the same direction as the polarization direction,
The second driving means includes a second charging / discharging circuit that discharges charges accumulated in the same direction as the polarization direction of the piezoelectric body and charges the piezoelectric body in a direction opposite to the polarization direction. The piezoelectric actuator according to claim 1. The first charging / discharging 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 body, and one end connected to the other end of the piezoelectric body. Second switch means having the other end grounded,
The second charging / discharging 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 body, and one end connected to one end of the piezoelectric body. The piezoelectric actuator according to claim 2, further comprising a fourth switch means having the other end grounded. The first driving means comprises a charging circuit that charges the piezoelectric body in the same direction as the polarization direction,
The piezoelectric actuator according to claim 1, wherein the second driving unit includes a discharge circuit that discharges electric charges accumulated in the piezoelectric body. The charging circuit includes first switch means having one end connected to a power source and the other end connected to one end of the piezoelectric body,
The piezoelectric actuator according to claim 4, wherein the discharge circuit includes second switch means having one end connected to one end of the piezoelectric body and the other end grounded. The piezoelectric actuator according to any one of claims 1 to 5, wherein the setting change unit changes the first drive time and the second drive time so that a drive cycle becomes constant. .

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