JP2009100527A - Piezoelectric actuator driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify a current control circuit in a piezoelectric actuator driving device that controls driving of a piezoelectric actuator by constant-current charging/discharging of the current control circuit. <P>SOLUTION: The driving device 11 is for a piezoelectric actuator including a long driving body having a piezoelectric element 9 and a rotating shaft installed at one end of the driving body. The driving device 11 includes: a first drive circuit 13A that applies voltage to the piezoelectric element 9 to deform the piezoelectric element 9 in one direction; and a second drive circuit 13B that applies voltage to the piezoelectric element 9 to deform the piezoelectric element 9 in another direction different from the one direction. The first and second drive circuits 13A, 13B are alternately actuated to rotate or lock the driving body on the rotating shaft. The current control circuit 21 is provided in series with the first and second drive circuits 13A, 13B. The current control circuit 21 includes a variable resistor Rv and the times of charging and discharging the piezoelectric element 9 are controlled by varying the resistance value of the variable resistor Rv. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In recent years, a piezoelectric actuator using a piezoelectric element which is a kind of electromechanical conversion element has been developed as a small rotation / oscillation type actuator, and its practical use is being promoted. In particular, in a wiper device used for a small CCD camera or the like, a piezoelectric actuator using such a piezoelectric element is being used instead of an electromagnetic motor due to space and design problems.

  In the piezoelectric actuator, the piezoelectric element is configured to be displaced according to the applied voltage. In order to operate the piezoelectric element as an actuator, it is necessary to cause the operation of the piezoelectric element to be slow and slow. As shown, a sawtooth waveform voltage is applied to the piezoelectric element. When the voltage of the sawtooth voltage changes rapidly, the displacement operation of the piezoelectric element is fast, and when the voltage changes slowly, the displacement operation of the piezoelectric element becomes slow. That is, the operation of the piezoelectric element becomes slow due to the difference in the change rate of the applied voltage. And in the piezoelectric actuator which attached the piezoelectric element to the rotating shaft, when the operation | movement of a piezoelectric element becomes slow, a rotating shaft rotates (patent document 1, patent document 2, etc.).

  The sawtooth voltage is supplied to the piezoelectric actuator by a piezoelectric actuator driving device having a circuit configuration as shown in FIG. 12, for example (Patent Document 3). In the drive device 31 of FIG. 12, the piezoelectric element 9 is controlled by the bridge circuit 32 using a switch element. The bridge circuit 32 is provided with transistors Q1 and Q3, N-channel MOS-FETs Q2 and Q4, and a resistor. A current control circuit 41 is provided in series with the bridge circuit 32 on the ground side of the bridge circuit 32. The current control circuit 41 has a configuration in which a constant current circuit 42 and a switching circuit 43 are connected in parallel, and is connected to the bridge circuit 32 at a connection point d. The constant current circuit 42 includes a transistor Q5 and a Zener diode Zd, and the switching circuit 43 includes a transistor Q6. The bases of the transistors Q1 and Q3, the gates of the N-channel MOS-FETs Q2 and Q4, and the bases of the transistors Q5 and Q6 are respectively connected to the control circuit 14, and the transistors Q1 and Q3, the N-channel MOS-FETs Q2 and Q4, the transistors Q5 and Q6 Is controlled by the control circuit 14. The piezoelectric element 9 has one terminal connected to the connection point between the transistor Q1 and the MOS-FET Q2, and the other terminal connected to the connection point between the transistor Q3 and the MOS-FET Q4. Works equivalently.

FIG. 13 shows the operation of the driving device when driving the piezoelectric actuator in the forward direction and the voltage waveform at that time, and FIG. 14 shows the operation of the driving device when driving the piezoelectric actuator in the reverse direction and the voltage waveform at that time. Show.
When the piezoelectric actuator is driven in the positive direction, the piezoelectric element 9 is charged at a low speed so that a voltage waveform (1) is generated in the piezoelectric element 9 as a capacitor from time t2 to time t3. That is, the transistor Q1 and the MOS-FET Q4 are turned on, the transistor Q2 and the MOS-FET Q3 are turned off, the transistor Q5 is turned on, and the transistor Q6 is turned off. As a result, as shown by a broken line, a circuit such as GND is formed from the power source Vp through the transistor Q1, the piezoelectric element 9, the transistor Q4, and the constant current circuit 42. The piezoelectric element 9 is connected to the constant current circuit 42 through the constant current circuit 42. Be charged. Due to the constant charging current, a slowly changing voltage waveform (1) is generated in the piezoelectric element 9, the shape of the piezoelectric element 9 is slowly displaced, and the rotating shaft (not shown) of the piezoelectric actuator is held by a frictional force. Does not rotate.

  When the charged piezoelectric element 9 is discharged at high speed at time t1 or t4 as shown in the voltage waveform (2), the transistor Q1 and the MOS-FET Q4 are turned off, and the MOS-FET Q2 and the transistor Q3 are turned off. The transistor Q5 is turned off and the transistor Q6 is turned on. As a result, as shown by a one-dot chain line, a circuit from the power source Vp to the ground (GND) is formed via the transistor Q3, the piezoelectric element 9, the MOS-FET Q2, and the switching circuit 43. At this time, the voltage of the power source Vp is directly applied to the piezoelectric element 9 with the opposite polarity to that of the voltage waveform (1), and the piezoelectric element 9 is rapidly discharged and further charged with the opposite polarity. Accordingly, when driving in the forward direction, the transistors Q1, Q4, Q5 and the transistors Q2, Q3, Q6 are alternately turned on and off to apply a voltage having a sawtooth waveform as shown in FIG. When the voltage applied to the piezoelectric element 9 changes suddenly as shown in the voltage waveform (2), the shape of the piezoelectric element 9 is suddenly displaced, and the reaction force causes the rotational axis of the piezoelectric actuator to slip and rotate. .

  On the other hand, when the piezoelectric actuator is driven in the reverse direction, first, the piezoelectric element 9 is charged at high speed so that the voltage waveform (3) shown at time t1 or time t4 is generated in the piezoelectric element 9 as a capacitor. That is, the transistor Q1 and the MOS-FET Q4 are turned on, the MOS-FET Q2 and the transistor Q3 are turned off, the transistor Q5 is turned off, and the transistor Q6 is turned on. As a result, a circuit extending from the power source Vp to the GND via the transistor Q1, the piezoelectric element 9MOS-FET Q4, and the switching circuit 43 is formed as shown by a one-dot chain line in FIG. 14, and the piezoelectric element 9 is rapidly charged by the power source Vp. Is done. When the voltage applied to the piezoelectric element 9 changes suddenly as shown in the voltage waveform (3), the shape of the piezoelectric element 9 is suddenly displaced, and the rotation axis of the piezoelectric actuator rotates.

  When performing low-speed discharge as shown in the voltage waveform (4) from time t2 to time t3 for charging the piezoelectric element 9, the transistor Q1 and the MOS-FET are turned off, the MOS-FET Q2 and the transistor Q3 are turned on, Transistor Q5 is turned on and transistor Q6 is turned off. Thereby, as shown by a broken line in FIG. 14, a circuit extending from the power source Vp to GND via the transistor Q3, the piezoelectric element 9, the MOS-FET Q2, and the constant current circuit 43 is formed. At this time, the piezoelectric element 9 is connected to the power source Vp with a reverse polarity, and the charged electric charge is discharged with a constant current via the constant current circuit 42 and further charged with a reverse polarity. Accordingly, during reverse driving, by repeatedly turning on / off the transistor Q1, the MOS-FET Q4, the transistor Q6 and the MOS-FET Q2, the transistor Q3, and the transistor Q5, the piezoelectric element 9 has a configuration as shown in FIG. A sawtooth voltage is generated. Due to the slowly changing voltage waveform (4), the shape of the piezoelectric element 9 is slowly displaced, and the rotation axis of the piezoelectric actuator does not rotate.

As described above, in the drive circuit 31, the operation of the transistors Q1 and Q3 of the bridge circuit 32, the N-channel MOS-FETs Q2 and Q4, the transistor Q5 of the current control circuit 42, and the transistor Q6 of the switching circuit 43 are The slow charge shown, the fast discharge shown in the voltage waveform (2), the fast charge shown in the voltage waveform (3), and the slow discharge shown in the voltage waveform (4) are switched appropriately, and the piezoelectric actuator is rotated forward, Reverse rotation drive is controlled.
JP 2003-011786 A JP 2003-200816 A Japanese Patent Laid-Open No. 2005-210769

  However, in the above-described prior art, the current control circuit requires two circuits, a constant current circuit and a switching circuit, and there is a problem that it is desired to simplify the current control circuit. In addition, there is a problem that the temperature of the piezoelectric element changes and it is desired to rotationally drive the piezoelectric actuator at a constant speed.

  The above formula (1) shows the relationship between the voltage gradient S having a sawtooth waveform, the current I flowing through the constant current control circuit, and the capacitance C of the piezoelectric element. Inversely proportional to Here, the electrostatic capacitance C of the piezoelectric element has a property of increasing / decreasing with a temperature change of the piezoelectric element, and as a result, the voltage gradient S changes with the temperature change of the piezoelectric element. In order to rotationally drive the piezoelectric actuator at a constant speed, it is necessary to make the voltage gradient S constant and to make the time of low-speed charge and low-speed discharge constant. However, if the temperature of the piezoelectric element changes, the voltage gradient S should be made constant. I can't. Even if the temperature of the piezoelectric element changes, there is a problem that the piezoelectric actuator is desired to be rotated at a constant speed.

  An object of the present invention is to provide a piezoelectric actuator driving apparatus that controls driving of a piezoelectric actuator by charging and discharging a constant current by a current control circuit, and a piezoelectric actuator that can be rotationally driven at a constant speed even when the temperature of the piezoelectric element changes. It is to provide.

  In order to solve the above problems, there is provided a drive device for a piezoelectric actuator comprising a long drive body including a piezoelectric element and a rotating shaft attached to one end of the drive body, wherein the piezoelectric element is A first drive circuit for applying a voltage to the piezoelectric element to deform in a direction, and a second drive circuit for applying a voltage to the piezoelectric element to deform the piezoelectric element in another direction different from the one direction. A piezoelectric actuator driving device that alternately operates the first and second driving circuits to rotate or swing the driving body around the rotation axis, and is in series with the first and second driving circuits. The current control circuit includes a variable resistor, and controls the charging and discharging time of the piezoelectric element by changing the resistance value of the variable resistor.

  By using a current control circuit using a variable resistor, the circuit configuration can be simplified. Further, the piezoelectric actuator is driven to rotate at a constant speed regardless of the temperature change of the piezoelectric element.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a configuration of a wiper device using a piezoelectric actuator. The wiper device 1 of FIG. 1 is attached to, for example, a CCD camera installed in a side bumper or a front grill of an automobile, and is driven and controlled by a driving device 11 (see FIG. 4) according to the present invention. A rubber wiper blade 3 that swings around a rotation shaft (shaft member) 2 is attached to the wiper device 11. The wiper blade 3 swings on the glass surface 5 of the casing 4 of the CCD camera to remove water droplets and dust on the surface glass surface 5.

  The wiper blade 3 is attached to a driving body 6 of a long piezoelectric actuator 10 using a piezoelectric element 9 which is one of electro-mechanical conversion elements. The driving body 6 has a bimorph piezoelectric element structure, and has a structure in which piezoelectric elements 9 are bonded to both surfaces of a central electrode of a thin metal plate. One end of the driving body 6 is fixed to the rotating shaft 2 and the other end is free. The inside of the rotating shaft 2 is hollow, and lead wires (not shown) for supplying electric power to the piezoelectric elements 9 of the driving body 6 are wired therein. The lead wire is connected to the piezoelectric actuator driving device 11.

  The rotating shaft 2 is rotatably attached to the housing 4 by a bearing portion 7. A tension spring 8 is provided between the rotary shaft 2 and the housing 4, and the rotary shaft 2 is biased by the bearing portion 7 by the spring force of the tension spring 8, and the rotary shaft 2 is rotated by the bearing portion 7. Resistance force (friction force) is applied.

  The drive body 6 performs a swinging motion around the rotation shaft 2. FIG. 2 is an explanatory diagram illustrating a waveform of a voltage applied to the piezoelectric element of the driving body, and FIG. 3 is an explanatory diagram illustrating a behavior of the driving body when the voltage of FIG. 2 is applied. Here, when the voltage at the connection point c is a plus (+) voltage with respect to the voltage at the connection point b shown in FIG. 4, the driving body 6 is displaced to the right (one direction) in FIG. When the voltage at the connection point c is a negative (−) voltage with respect to the voltage at the connection point b, the voltage is displaced to the left (in the other direction) in the figure.

When the voltage at the connection point c changes as shown in FIG. 2 with respect to the voltage at the connection point b, first, at time t1, the voltage (1) is ± 0 [V], and the driver 6 is in the initial position P _0. It is in a stopped state. Next, when the applied voltage changes from the time t1 to the time t2, a plus (+) voltage is applied to the piezoelectric element 9, and therefore, examples of (1) and (1 → 2) in FIG. 3 are shown. Thus, the driving body 6 is displaced to the right. Thereafter, when the applied voltage changes from the plus (+) voltage to the minus (−) voltage as shown in the voltage (2) to the voltage (3) in FIG. 2 in a short time from the time t2, the driving body 6 also responds accordingly. As shown in the example (2 → 3) in FIG.

Compared with the case where the applied voltage changes from the voltage (1) to the voltage (2) from the time t1 to the time t2, the applied voltage is changed from the voltage (2) to the voltage (3 in FIG. ), The voltage change is rapid, and there is a difference between the deformation speed of the driving body 6 from time t1 to time t2 and the deformation speed of the driving body 6 in a short time from time t2. . That is, the driving body 6 bends slowly from the time t1 to the time t2, and suddenly bends in the reverse direction after a short time from the time t2. When the driving body 6 bends, its center of gravity G is moved in the direction of displacement. At this time, an inertial force F that is a force that inhibits the movement of the center of gravity G acts on the moving body 6. Then, from the difference between the deformation speed of the drive member 6, towards the inertial force F ₂₃ is greater in a short time from the time t2 than the inertial force F ₁₂ from the time t1 until the time t2.

A rotational resistance force (friction force) Fr applied to the rotary shaft 2 acts on the inertial force F. That is, the inertial force F and the rotational resistance force Fr are opposed to each other as the driving body 6 is deformed. In the piezoelectric actuator 10, when the applied voltage until the time t1 to the time t2 is changed from the voltage (1) to a voltage (2), the rotation resistance force Fr is larger than the inertial force _{F 12,} a slight time t2 in time, when the applied voltage is changed from the voltage (2) to a voltage (3), the rotation resistance force Fr is set to be smaller than the inertial force _{F 23 (F 12 <Fr <} F 23). Therefore, at the time t2 from time t1, the inertia force F ₁₂ becomes a shape which is canceled by the rotation resistance force Fr, the drive member 6 is only slowly displaced angle corresponding to the voltage value, the center of gravity G also moves slowly Correspondingly The rotating shaft 2 does not rotate. In contrast, in the short time from the time t2, the inertia force F ₂₃ is not canceled by the rotation resistance force Fr. Therefore, the inertial force F ₂₃ trying to leave the center of gravity G of the drive member 6 is moved to the right to play becomes larger than the rotation resistance force FR, the rotation shaft 2 is rotated counterclockwise.

  After the sawtooth applied voltage suddenly changes in a short time from time t2 in FIG. 2, the voltage gradually changes to the plus (+) side from time t2 to time t3, and the driving body 6 Is displaced to the right as (3 → 4) in FIG. In this case, since the voltage change rate is small, the drive body 6 bends slowly, and the influence of the inertial force F of the drive body 6 is small, and the drive body 6 is displaced rightward by a displacement amount corresponding to the voltage. The shaft 2 does not rotate. In a short time from time t3 in FIG. 2, the voltage suddenly changes again from the voltage value (4) to the voltage value (5). Also at this time, as in a short time from time t2, a large inertia force F is generated due to the magnitude of the deformation speed of the driving body 6, whereby the rotating shaft 2 rotates counterclockwise.

  When a sawtooth voltage is applied to the driving body 6, the driving body 6 gradually moves to the right as shown in FIG. 3 by the action of the inertial force F based on the speed difference when the driving body 6 is deformed. Rotate around. In FIG. 3, the line segment Q indicates the center of the drive body 6 after one reciprocal vibration. As shown in the examples (2 → 3) and (4 → 5) in FIG. The line segment Q also moves to the right from the line segment Q1 to the line segment Q2. 3 indicates the position (initial position) of the driving body 6 in the case of the example (1) in FIG.

  By repeating the operation of the driving body 6 that slowly bends and returns suddenly, the driving body 6 self-runs toward the displacement side when it is slowly bent. Then, when the voltage change slowly changes to the left as opposed to FIG. 2, and suddenly changes to the right, the driving body 6 rotates to the left (clockwise) in FIG. It will be. Therefore, the driver 6 can appropriately reciprocate by switching the voltage change pattern.

  FIG. 4 is an explanatory diagram showing the configuration of the piezoelectric actuator driving apparatus according to the embodiment of the present invention. The sawtooth voltage shown in FIG. 2 is supplied to the bridge circuit 12 by the driving device 11 shown in FIG. The driving device 11 includes first to fourth switching circuits 13 to 16 constituting a bridge circuit 12 and a current control circuit 21. The first and third switching circuits 13 and 15 are composed of pnp transistors Q1 and Q3 and resistors. The second and fourth switching circuits 14 and 16 are composed of N-channel MOS-FETs Q2 and Q4 and resistors. The bases of the pnp transistors Q1 and Q3 and the gates of the N-channel MOS-FETs Q2 and Q4 are connected to the control circuit 17. The connection point a of the bridge circuit 12 is connected to the power source Vp, and the piezoelectric element 9 of the driver 6 is connected between the connection points b and c.

  The bridge circuit 12 including the first to fourth switching circuits 13 to 16 is a basic circuit that applies a forward or reverse voltage to the piezoelectric element 9. Here, when the state without the current control circuit 21 is considered, the polarity of the voltage applied to the piezoelectric element 9 is switched by turning on / off the transistor Q1, the MOS-FET Q4 and the transistor Q2, and the MOS-FET Q3, and the driver 6 Driven in the forward or reverse direction. That is, by turning on the transistor Q1 and the MOS-FET Q4 and turning off the transistor Q2 and the MOS-FET Q3, the first power source Vp is connected to the GND via the transistor Q1, the transistor Q2 piezoelectric element 9, and the MOS-FET Q4. One driving circuit 13A is formed, and the driving body 6 is deformed in the first direction. When the transistors Q1 and Q4 are turned off and the transistors Q2 and Q3 are turned on, the second drive circuit 13B extending from the power source Vp to the GND via the transistor Q2 and the piezoelectric elements 9 and Q3 is formed. Deforms in the direction opposite to the direction of.

A current control circuit 21 is connected in series between the connection point d of the bridge circuit 12 and the ground point GND. The current control circuit 21 includes an npn transistor Q5, a digital variable resistor Rv, a resistor _R0 , a Zener diode Zd, and a power supply Vc. The resistor _R0 is connected to the power supply Vc having a voltage of 12V. The collector of the npn transistor Q5 is connected to the connection point d of the bridge circuit 12, and the base is connected to the resistor _R0 at the connection point e. One end of the digital variable resistor Rv is connected to the emitter of the npn-type transistor Q5 at the connection point f, and the other end is connected to the ground point GND at the connection point g. The cathode of the Zener diode Zd is connected to the resistor _R0 and the base of the npn transistor Q5 at the connection point e, and the anode is connected to the ground point GND at the connection point g. The digital variable resistor Rv is connected to the control circuit 14, and the resistance value is controlled by a signal from the control circuit 14.

Next, the operation of the current control circuit 21 will be described. Rvd the resistance value of the digital variable resistor Rv, Vz a Zener voltage of the Zener diode Zd, the base of the npn-type transistors Q5 - to-emitter voltage and _{V BE,} the current I flowing through the digital variable resistor Rv is as follows Can be shown.

As shown in the above equation, the current I is inversely proportional to the resistance value Rvd of the digital variable resistor Rv. Here, the current I ′ flowing through the piezoelectric element 9 and the current I flowing through the digital resistor Rv are set to be substantially the same (I′≈I). Therefore, the current I ′ flowing through the piezoelectric element 9 can be controlled by controlling the resistance value Rvd of the digital variable resistor Rv with the control circuit 14. In the present embodiment, the Zener voltage Vz is set to 3.9 V, and the base-emitter voltage V _BE is set to 0.6 V.

The operation of the driving device 11 according to the present embodiment will be described with reference to FIGS. 5 and 6 show the operation of the driving device when the piezoelectric actuator is driven in the positive direction. FIG. 5 shows the operation during low-speed charging, and FIG. 6 shows the operation during high-speed discharge. Figure 7 shows a time-series signal voltage V ₉ is applied to the resistance value and the piezoelectric element of the digital resistor Rv at low speed charge time and high-rate discharge.

First, when performing slow charge at time T1 during forward driving, the resistance value R _VD of the digital variable resistor Rv is set to the high resistance value Hi, and the transistors Q1 and Q4 are turned on. The transistors Q2 and Q3 are turned off. As a result, as indicated by a broken line in FIG. 5, a circuit is formed from the power source Vp to the ground point GND, which is a common potential, via the transistor Q1, the piezoelectric element 9, the transistor Q4, and the current control circuit 21. Since the resistance value R _VD is set to the high resistance value Hi, the current I becomes a small current from the equation (2), and the piezoelectric element 9 is charged at a low speed with a constant current flowing through the current control circuit 21. .

At time T2, in the case of performing high-speed discharge, shown in the waveform (2), the resistance value R _VD of the digital variable resistor Rv is set to a low resistance value Lo, the transistors Q1, Q OFF, the transistors Q2, Q3 Turn it on. As a result, a circuit from the power source Vp to Q3, the piezoelectric element 9, the transistor Q2, and the current control circuit 21 is formed to the ground point GND as indicated by a broken line in FIG. At this time, the power source Vp is applied to the piezoelectric element 9 with a polarity opposite to that of the waveform (1). Further, since the digital variable resistor R _VD is set to the low resistance value Lo, the current I becomes a high current from the equation (2), and the piezoelectric element 9 is rapidly discharged. Therefore, when driving in the positive direction, at time T1, the transistors Q1 and Q4 are turned on, the transistors Q2 and Q3 are turned off, the digital variable resistor is at a high resistance value Hi, and at time T2, the transistors Q1 and Q4 are turned off, and the transistors Q2, Q2, By repeatedly turning on Q3 and setting the digital variable resistor Rv to the low resistance value Lo, a voltage having a sawtooth waveform as shown in FIG.

8 and 9 show the operation of the driving device when the piezoelectric actuator is driven in the reverse direction. FIG. 8 shows the operation at high speed charging, and FIG. 9 shows the operation at low speed discharging. Figure 10 shows a time series signal of the voltage V ₉ is applied during high-speed charge time and slow discharge resistor value and the piezoelectric element of the digital resistor Rv.

When performing fast charging at time T3 during reverse driving, the resistance value R _VD of the digital variable resistor Rv is set to the low resistance value Lo, the transistors Q1 and Q4 are turned on, and the transistor Q2 is turned on. , Q3 is turned off. As a result, as indicated by a broken line in FIG. 8, a circuit is formed from the power source Vp to the ground point GND through the transistor Q1, the piezoelectric element 9, the transistor Q4, and the current control circuit 21. Since the resistance value R _VD is set to the low resistance value Lo, the current I becomes a high current from the equation (2), and the piezoelectric element 9 is charged at high speed by the drive circuit 11.

In time T4, when performing low-rate discharge as shown in waveform (4), the resistance value R _VD of the digital variable resistor Rv is set to a high resistance value Hi, turns off the transistor Q1, Q4, the transistors Q2, Q3 Turn it on. Thereby, as indicated by a broken line in FIG. 6, a circuit from the power source Vp to the ground point GND is formed via the transistor Q3, the piezoelectric element 9, the transistor Q2, and the current control circuit 21. At this time, the power source Vp is directly applied to the piezoelectric element 9 with the opposite polarity to that of the waveform (1). Further, since the resistance value R _VD is set to the high resistance value Hi, the current I becomes the low current Lo from the equation (2), and the piezoelectric element 9 is discharged at a low speed. Therefore, at the time of reverse driving, the transistors Q1 and Q4 are turned on at time T3, the transistors Q2 and Q3 are turned off, the digital variable resistor Rvd is at a low resistance value Lo, the transistors Q1 and Q4 are turned off at time T4, the transistors Q2, By repeatedly turning on Q3 and setting the digital variable resistor Rvd to Hi, a voltage having a sawtooth waveform as shown in FIG. 10 is applied to the piezoelectric element 9.

In this way, in the drive circuit 11, the first to fourth switching circuits 13 to 16 and the current control circuit 21 are used to perform the slow charge of the waveform (1), the fast discharge of the waveform (2), the fast charge of the waveform (3), The piezoelectric element 9 can be charged and discharged with a constant current by sequentially switching the low-speed discharge of the waveform (4). Here, the current control circuit 21 includes an npn transistor Q5, a Zener diode Zd, and a digital variable resistor Rv, and has a simple configuration with a small number of components.
The current control circuit 21 may be connected between a bridge circuit and a power source. In this case, a pnp transistor is used as the transistor Q5, and the digital variable resistor Rv is an emitter of the pnp transistor. The zener diode Zd is connected to the base of the pnp transistor and the power source as the common potential.

  Further, since the digital variable resistor Rv can freely change the resistance value Rvd, as shown in the equation (1), the digital variable resistor Rv can freely cope with the change in the capacitance C due to the temperature change of the piezoelectric element 9. it can. For example, a temperature sensor may be provided in the piezoelectric element 9 to monitor the temperature, and the resistance value Rvd may be varied so that the voltage gradient during low-speed discharge and low-speed charging is constant in response to the temperature change of the piezoelectric element 9. Is possible.

It is sectional drawing which shows the structure of the wiper apparatus which uses a piezoelectric actuator. It is explanatory drawing which shows the waveform of the voltage applied to the piezoelectric element of a drive body. It is explanatory drawing which shows the behavior of the drive body when the voltage of FIG. 2 is applied. It is explanatory drawing which shows the structure of a piezoelectric actuator drive device. It is explanatory drawing which shows operation | movement of the drive device at the time of low speed charge. It is explanatory drawing which shows operation | movement of the drive device at the time of high-speed discharge. The time series signal of the electric current which flows through the drive device in the case of driving a piezoelectric actuator to a positive direction, and the voltage applied to a piezoelectric element is shown. It is explanatory drawing which shows operation | movement of the drive device at the time of high-speed charge. It is explanatory drawing which shows operation | movement of the drive device at the time of low speed discharge. The time series signal of the electric current which flows through a drive device in the case of driving a piezoelectric actuator to a reverse direction, and the voltage applied to a piezoelectric element is shown. It is explanatory drawing which shows the waveform of the voltage applied to a piezoelectric element. It is explanatory drawing which shows the circuit structure of the conventional piezoelectric actuator drive device. FIG. 13 is an explanatory diagram showing the operation of the drive device of FIG. 12, wherein (a) shows the operation of the drive device when the piezoelectric actuator is driven in the positive direction, and (b) shows the voltage waveform applied to the piezoelectric element at that time. Is shown. FIG. 13 is an explanatory diagram showing the operation of the driving device of FIG. 12, wherein (a) shows the operation of the driving device when driving the piezoelectric actuator in the reverse direction, and (b) shows the voltage waveform applied to the piezoelectric element at that time. Is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wiper apparatus 2 Rotating shaft 3 Wiper blade 4 Housing | casing 5 Glass surface 6 Driver 9 Piezoelectric element 10 Piezoelectric actuator 11 Drive apparatus 12 Bridge circuit 13 1st switching circuit 14 2nd switching circuit 15 3rd switching circuit 16 4th switching circuit 17 control circuit 21 current control circuit 31 drive device 32 bridge circuit 41 current control circuit 42 constant current circuit 43 switching circuit Q1, Q3 transistor (switching element)
Q2, Q4 MOS-FET (switching element)
Q5 Transistor (switching element)
R0 resistor Zd Zener diode Rv (digital) variable resistor

Claims (4)

A drive device for a piezoelectric actuator comprising a long drive body including a piezoelectric element and a rotating shaft attached to one end of the drive body,
A first drive circuit for applying a voltage to the piezoelectric element to deform the piezoelectric element in one direction;
A second drive circuit for applying a voltage to the piezoelectric element to deform the piezoelectric element in another direction different from the one direction;
A piezoelectric actuator driving device that alternately operates the first and second driving circuits to rotate or swing the driving body around the rotation axis;
A current control circuit is provided in series with the first and second drive circuits;
The current control circuit includes a variable resistor, and controls a charging and discharging time of the piezoelectric element by changing a resistance value of the variable resistor. The piezoelectric actuator driving device according to claim 1, wherein the piezoelectric actuator driving device connects first to fourth switching circuits including switching elements in series,
A first power source is connected to a connection point between the first switching circuit and the third switching circuit, or a connection point between the second switching circuit and the fourth switching circuit;
A bridge circuit in which the piezoelectric element is connected between a connection point of the first switching circuit and the second switching circuit and between the third switching circuit and the fourth switching circuit;
The first drive circuit includes the power source and the first and fourth switching circuits,
The piezoelectric actuator driving apparatus, wherein the second driving circuit includes the power source and the second and third switching circuits. The piezoelectric actuator driving device according to claim 1 or 2, wherein the current control circuit includes a transistor, a resistor, a Zener diode, and a power source.
One terminal of the resistor is connected to the power source;
A collector of the transistor is connected to a connection point of the first and second drive circuits, and a base is connected to the other terminal of the resistor;
One end of the variable resistor is connected to the emitter of the transistor, and the other end is connected to GND.
A piezoelectric actuator driving device, characterized in that the Zener diode has a cathode connected to the other end of the resistor and the base of the transistor, and an anode connected to the first power supply GND. 3. The piezoelectric actuator driving device according to claim 1, wherein the driving device includes a control circuit, and controls a resistance value of the variable resistor by a signal from the control circuit. A piezoelectric actuator driving device.

Images