JP5614224B2 - Drive device - Google Patents

Description

  The present invention relates to a drive device that drives a piezo actuator.

  For example, Patent Literature 1 and Patent Literature 2 are known as conventional driving devices. The drive device described in Patent Document 1 includes a drive circuit composed of a bridge circuit composed of a first circuit to a fourth circuit composed only of a switch circuit using FETs, and a control circuit that controls driving of the drive circuit. Is done. A power source is connected between the first connection points of the bridge circuit, and a piezoelectric member is connected between the second connection points. The piezoelectric member is alternately reversed in polarity and applied with a power supply voltage. By changing the voltage application period, the expansion operation and the reduction operation are repeated in different periods. The drive device is simplified and miniaturized by removing the current limiting element such as a resistor and configuring the drive circuit only with the switch circuit. In addition, this drive device can greatly simplify the drive circuit by driving a piezo actuator including a piezoelectric member with a rectangular wave.

  In the drive device described in Patent Document 2, a first drive circuit including a first switch and a fourth switch for charging a piezoelectric element by applying a drive voltage from one side thereof, and a drive voltage from the other side to the piezoelectric element. A second drive circuit comprising a second switch and a third switch for charging by applying a voltage, and a discharge circuit comprising a second switch and a fourth switch for discharging the charge charged in the piezoelectric element by each drive circuit. Yes. The first drive circuit and the second drive circuit are driven alternately, and the discharge circuit is driven between the drive period of the first drive circuit and the drive period of the second drive circuit. That is, when the current direction is changed by the first and second drive circuits, the drive device turns on the second switch and the fourth switch, thereby discharging the charge accumulated in the piezoelectric actuator including the piezoelectric element, Current consumption can be reduced.

JP 2000-350482 A JP 2001-21669 A

  However, when the piezo actuator is driven, there is no sound in a steady operation state (because the drive pulse is usually above the audible range), but mechanical noise is generated when the piezo actuator is started and stopped.

  In recent years, movie functions are often installed in mobile phone camera functions and digital still cameras, and mechanical noise generated from piezo actuators due to autofocus and zoom operations during moving image shooting has become a problem. Usually, since the microphone is in the same housing as the piezo actuator, noise is picked up.

  The subject of this invention is providing the drive device which suppresses the mechanical noise which generate | occur | produces at the time of the operation | movement start and stop of a piezoelectric actuator.

In order to solve the above problems, a driving device according to the present invention includes a piezoelectric element, a driving friction member fixed to one end of the piezoelectric element, a fixing member fixed to the other end of the piezoelectric element, and the driving friction member. A piezoelectric actuator having a moving body engaged with a predetermined frictional force so as to be relatively movable in the moving direction of the driving friction member; and a plurality of driving elements connected in series at both ends of the power source. A drive unit that drives the piezo actuator by an on / off operation of the drive element, and a rectangular wave signal that changes the duty with time so that the piezo actuator is changed at a constant moving speed using the characteristics of the piezo actuator. , have a control circuit for applying a該矩square wave signal to said plurality of drive elements, the control circuit may move speed of the duty and the piezoelectric actuator Along the inverse function of the characteristics showing the relationship and generating a square wave signal to vary the duty temporally to vary the piezoelectric actuator at a constant moving speed.

  According to the present invention, the control circuit generates a rectangular wave signal that changes the duty in time so as to change the piezoelectric actuator at a constant moving speed using the characteristics of the piezoelectric actuator, and drives the rectangular wave signal to a plurality of driving directions. Applied to the element to drive the piezo actuator. For this reason, the piezo actuator operates smoothly at the start and stop of the operation, and mechanical noise generated at the start and stop of the operation can be suppressed.

It is a block diagram of the drive device which concerns on Example 1 of this invention. It is a figure which shows the characteristic of the duty of the rectangular wave which drives the drive device which concerns on Example 1 of this invention, and the moving speed of a piezoelectric actuator. It is a figure which shows the impact type piezo actuator of the drive device which concerns on Example 1 of this invention. FIG. 6 is a diagram illustrating a drive waveform at the start of operation of the drive device according to the first embodiment and a voltage waveform applied to both ends of the piezo actuator at that time. FIG. 6 is a diagram illustrating a drive waveform when the operation of the drive device according to the first embodiment is stopped and a voltage waveform applied to both ends of the piezoelectric actuator at that time. It is a figure which shows the inverse function curve with respect to the characteristic shown in FIG. It is a figure which shows the speed change curve when changing a duty by the optimal ratio at the time of the operation | movement start of a piezoelectric actuator, and changing a duty by a fixed ratio. FIG. 2 is a configuration block diagram of a control circuit in the drive device according to the first embodiment. It is a figure which shows each setting value when dividing the duty of 0.25-0.5 into 50. It is a figure which shows the speed change at the time of the operation | movement start of the drive device which concerns on Example 1. FIG. FIG. 6 is a diagram illustrating a drive waveform at the start of operation of the drive device according to the first modification of the first embodiment and a voltage waveform applied to both ends of the piezo actuator at that time. It is a figure which shows the drive waveform at the time of the operation | movement start of the drive device which concerns on the modification 2 of Example 1, and the voltage waveform concerning the both ends of the piezoelectric actuator at that time. It is a figure which shows the drive waveform at the time of the operation | movement start of the drive device which concerns on the modification 3 of Example 1, and the voltage waveform concerning the both ends of the piezoelectric actuator at that time. It is a block diagram of the drive device which concerns on Example 2 of this invention.

  Hereinafter, a drive device according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of a driving apparatus according to Embodiment 1 of the present invention. The drive device shown in FIG. 1 includes a piezo actuator 1, a full bridge circuit FB, and a control circuit 10. In FIG. 1, the full bridge circuit FB includes a drive unit composed of MOSFETs Q1 to Q4. A series circuit of a P-type MOSFET Q1 (first switching element) and an N-type MOSFET Q3 (second switching element) is connected between a power supply Vdrv for driving the piezoelectric actuator 1 and the ground. A series circuit of a MOSFET Q2 (third switching element) and an N-type MOSFET Q4 (fourth switching element) is connected.

  A piezo actuator 1 is connected between a connection point P1 between the P-type MOSFET Q1 and the N-type MOSFET Q3 and a connection point P2 between the P-type MOSFET Q2 and the N-type MOSFET Q4. Note that a switching element such as a bipolar transistor or an IGBT (insulated gate transistor) may be used instead of the MOSFET.

  The piezo actuator 1 includes a truss type and an impact type. In the driving apparatus according to the first embodiment, the impact type piezo actuator 1 will be described as an example.

  FIG. 3 is a diagram illustrating an impact type piezo actuator of the driving apparatus according to the first embodiment of the present invention. The piezoelectric actuator shown in FIG. 3 includes a piezoelectric element 2, a driving friction member 3 fixed to one end of the piezoelectric element 2, a fixing member 5 fixed to the other end of the piezoelectric element 2, and driving friction to the driving friction member 3. The movable body 7 is engaged with a predetermined frictional force so as to be relatively movable in the moving direction of the member 3. The movable body 7 can move in the axial direction of the drive friction member 3 when a force greater than a predetermined friction force is applied. A photographing lens or the like (not shown) is fixed to the moving body 7.

  The control circuit 10 generates rectangular wave signals Q1G, Q2G, Q3G, and Q4G for driving the MOSFETs Q1, Q2, Q3, and Q4, and applies these rectangular wave signals to the gates of the MOSFETs Q1, Q2, Q3, and Q4. FIG. 2 is a diagram illustrating characteristics of the duty of the rectangular wave that drives the driving apparatus according to the first embodiment and the moving speed of the piezo actuator. The rectangular wave signals Q1G, Q2G, Q3G, and Q4G use the characteristics of the rectangular wave duty and the moving speed of the piezo actuator 1 shown in FIG. 2, and the piezo actuator 1 is constant when the piezo actuator 1 starts and stops. This is a signal in which the duty is changed every time so as to change at a speed of.

  As shown in FIG. 2, the control circuit 10 gradually changes the duty of the rectangular wave for driving the piezoelectric actuator 1 from approximately 0.5 to an appropriate value (for example, 0.25) at the start of operation, and the duty when the operation is stopped. A rectangular wave signal Q1G, Q2G, Q3G, Q4G that gradually changes from an appropriate value (for example, 0.25) to about 0.5 is generated. With the rectangular wave signals Q1G, Q2G, Q3G, and Q4G, the piezo actuator 1 can be operated smoothly, and mechanical noise generated at the start and stop of the operation can be suppressed.

  FIG. 4 is a diagram illustrating a drive waveform (rectangular wave signals Q1G, Q2G, Q3G, Q4G) at the start of operation of the drive device according to the first embodiment and a voltage waveform (VP21) applied to both ends of the piezoelectric actuator at that time. In FIG. 4, at the time T1, the rectangular wave signals Q1G and Q4G from the control circuit 10 at the start of the operation turn on the MOSFET Q1 and the MOSFET Q4, and the voltage applied to the piezo actuator 1 becomes + Vdrv.

  At time T2, the MOSFET Q2 and the MOSFET Q3 are turned on by the rectangular wave signals Q2G and Q3G from the control circuit 10, and the voltage applied to the piezo actuator 1 becomes −Vdrv. At times T1 and T2, the duty of the rectangular wave signals Q1G to Q4G is 0.5, and the speed in the feeding direction and the speed in the returning direction are the same, so the piezo actuator 1 does not operate.

  Next, after the time T3, the duty of the rectangular wave signals Q1G to Q4G gradually decreases, and the piezo actuator 1 starts to operate accordingly. After time T9, the operation speed of the piezo actuator 1 becomes a maximum duty, and the moving speed becomes the fastest.

  FIG. 5 is a diagram illustrating a drive waveform (rectangular wave signals Q1G, Q2G, Q3G, Q4G) when the operation of the drive device according to the first embodiment is stopped and a voltage waveform (Vp21) applied to both ends of the piezoelectric actuator at that time. In contrast to the rectangular wave signals Q1G to Q4G at the start of the operation shown in FIG. 4, the rectangular wave signals Q1G to Q4G at the time of the operation stop shown in FIG. Let By these operations, the moving body 7 that is a driven member slowly starts or stops operating.

  Here, when the duty is changed along the inverse function of a curve indicating the relationship between the duty shown in FIG. 2 and the moving speed of the piezoelectric actuator 1, mechanical noise can be suppressed.

  FIG. 6 is a diagram illustrating an inverse function curve with respect to the characteristics illustrated in FIG. When the piezo actuator 1 is driven by a rectangular wave signal whose duty is changed every time so that the change of the moving speed of the piezo actuator 1 is increased or decreased constantly along the inverse function curve shown in FIG. 1 starts or stops smoothly. For this reason, the mechanical noise which generate | occur | produces at the time of an operation start and a stop can be suppressed.

  As a simple duty changing method, there is a method of increasing or decreasing the duty at a constant rate. In this case, in order to sufficiently exhibit the effect of suppressing the mechanical noise, it is necessary to take a long time for the change so as to be equivalent to the optimum duty change. FIG. 7 shows a speed change curve CV1 when the duty is changed at an optimum ratio at the start of the operation of the piezoelectric actuator and a speed change curve CV2 when the duty is changed at a constant ratio.

  FIG. 8 is a configuration block diagram of a control circuit in the driving apparatus according to the first embodiment. The control circuit 10 generates a rectangular wave signal as a digital signal, and includes a memory 11, a controller 13, and a pulse generator 15. The memory 11 is a nonvolatile memory, for example, an EEPROM. From the inverse function of the characteristic curve indicating the relationship between the duty of the piezo actuator 1 and the moving speed, the duty is calculated in advance so that the speed changes are equally spaced, and stored in order from the lower address of the memory 11. The rising speed changes depending on the duty interval.

  The controller 13 sequentially reads from the lower address of the memory 11 when the operation of the piezo actuator 1 is started, and outputs duty information set according to the read lower address to the pulse generator 15. The pulse generator 15 generates a pulse signal having a duty corresponding to the duty information from the controller 13, and outputs the pulse signal as rectangular wave signals Q1G to Q4G to the gates of the MOSFETs Q1 to Q4.

  When the highest address of the memory 11 is reached, the duty is maintained and generation of the pulse signal is continued.

  When the operation is stopped, the controller 13 can obtain a desired operation by sequentially reading from the upper address to the lower address of the memory 11 and generating a duty, contrary to when the operation is started. Further, when operating in the reverse direction, the duty may be reversed by a similar operation.

  In the case of controlling with a digital signal, the settable duty is discrete. However, since the amount of movement of one pulse of the piezo actuator 1 is very small, there is no problem with the closest settable duty. As a specific example, consider the case where the master clock, which is often used in piezo actuator drivers, is 10 MHz and the drive frequency is 50 kHz. Since the master clock is 10 MHz, the waveform control has a resolution of 100 ns.

  Therefore, the settable duty when the drive frequency is 50 kHz is 201 patterns of 0.005 steps. FIG. 9 is a diagram showing each set value when the duty of 0.25 to 0.5 is divided into 50. FIG. In FIG. 9, the first column from the left indicates the time divided by 50. The second column shows the duty at which the speed change is equally spaced from the inverse function of the characteristic curve of the duty and the moving speed. The third column shows a settable duty value closest to the duty value in the second column. The fourth column shows memory values. In the example shown in FIG. 9, when the settable duty in the third column is converted into a memory address, 0.5 is 0, 0.45 is 10, (omitted), and 0.25 is 50.

  The fifth column shows the memory address. The value in the fourth column is written in the memory 11 in advance according to the memory address in the fifth column. The controller 13 reads memory values in order from the lower address of the memory 11 at the start of operation. Since the memory value is 0 when the memory address is 0, the controller 13 generates a pulse generator so as to generate a rectangular wave signal having an H level output of 100 pulses of the master clock and an L level output of 100 pulses of the master clock. An instruction is output to 15.

  Next, when the memory address is 1 and the memory value is 10, the controller 13 generates a rectangular wave signal having an H level output of 90 pulses of master clock and an L level output of 110 pulses of master clock. An instruction is output to the pulse generator 15.

  Thereafter, similar processing is repeated, and when the highest memory address is reached, the duty is maintained and generation of pulses is continued. When the operation is stopped, a desired rectangular wave signal can be generated by sequentially reading from the upper address to the lower address of the memory 11. FIG. 10 shows a speed change at the start of the operation of the driving apparatus according to the first embodiment. In this example, the duty is divided by 50. However, if the number of divisions is increased, the rising speed of the piezo actuator 1 is decreased, and if the number of divisions is decreased, the rising speed of the piezo actuator 1 is increased. The generation of noise changes depending on the load, the size of the housing, etc., so an appropriate rising speed is set.

  Next, digital control for increasing / decreasing the duty at a constant rate by the control circuit 10 will be described. In this case, the memory 11 shown in FIG. 8 is not necessary. At the start of the operation, the controller 13 sequentially subtracts the duty from 0.5, generates a pulse signal having a duty corresponding to the subtracted duty information, and uses the pulse signal as the rectangular wave signals Q1G to Q4G to each MOSFET Q1 to Q4. Output to the gate. When the desired duty is reached, the duty is maintained and pulse signal generation continues.

  When the operation of the piezo actuator 1 is stopped, the duty signal is sequentially added starting from the duty 0.25 contrary to the time when the operation is started, and a pulse signal having a duty corresponding to the added duty information is generated, and the pulse signal is converted into the rectangular wave signals Q1G to Q4G. Is output to the gates of the MOSFETs Q1 to Q4. Further, when the piezo actuator 1 is operated in the reverse direction, the duty may be reversed by a similar operation.

(Modification 1)
As a first modification of the first embodiment, as shown in FIG. 2, the control circuit 10 changes the duty of the rectangular wave for driving the piezo actuator 1 from approximately 0 to an appropriate value at the start of operation, or from approximately 1 to an appropriate value. When stopping, a rectangular wave signal that gradually changes from an appropriate value to approximately 0 or from an appropriate value to approximately 1 may be generated, and the rectangular wave signal may be output to the gates of the MOSFETs Q1 to Q4. In the case of the first modification, the same effect as that of the first embodiment can be obtained. FIG. 11 shows a drive waveform at the start of operation of the drive device according to the first modification of the first embodiment and a voltage waveform applied to both ends of the piezo actuator at that time. FIG. 11 shows a state in which the piezo actuator 1 is changed from approximately 0 to an appropriate value at the start of operation.

(Modification 2)
As a second modification of the first embodiment, when the control circuit 10 changes the direction of the current flowing through the piezo actuator 1 by alternately turning on and off the MOSFETs Q1 and Q4 and the MOSFETs Q2 and Q3 of the full bridge circuit shown in FIG. It is also possible to generate a rectangular wave signal provided with a timing to turn on the low-side MOSFETs Q3 and Q4 at the same time, and output the rectangular wave signal to the gates of the MOSFETs Q1 to Q4.

  FIG. 12 shows a drive waveform (rectangular wave signal) at the start of operation of the drive device according to the second modification of the first embodiment and a voltage waveform applied to both ends of the piezo actuator 1 at that time. In FIG. 12, MOSFETs Q3 and Q4 are turned on at times T15 to T16 including time T15, and the voltage applied to the piezoelectric actuator 1 becomes 0V.

  According to the driving device of the second modification of the first embodiment, the effect of the driving device of the first embodiment can be obtained, and further, the electric charge accumulated in the piezo actuator 1 can be discharged, and the current consumption can be reduced. Can do.

(Modification 3)
As a third modification of the first embodiment, when the control circuit 10 changes the direction of the current flowing through the piezo actuator 1 by alternately turning on and off the MOSFETs Q1 and Q4 and the MOSFETs Q2 and Q3 of the full bridge circuit shown in FIG. It is also possible to generate a rectangular wave signal having a timing for simultaneously turning off the MOSFETs Q1 to Q4 and output the rectangular wave signal to the gates of the MOSFETs Q1 to Q4.

  FIG. 13 shows a drive waveform at the start of operation of the drive device according to the third modification of the first embodiment and a voltage waveform applied to both ends of the piezo actuator at that time. In FIG. 13, at time T17 to T19 including time T18, the MOSFETs Q1 to Q4 are turned off, and the piezo actuator 1 enters a high impedance state. According to the driving device of the third modification of the first embodiment, the effect of the driving device of the first embodiment can be obtained.

  FIG. 14 is a configuration diagram of a driving apparatus according to Embodiment 2 of the present invention. The drive device shown in FIG. 14 includes a piezo actuator 1, a half bridge circuit HB, and a control circuit 10a. In FIG. 14, the half-bridge circuit HB is composed of a drive unit composed of MOSFETs Q1 and Q2. A series circuit of a P-type MOSFET Q1 and an N-type MOSFET Q2 is connected between the power supply Vdrv and the ground. A piezo actuator 1 is connected between the drain and source of the N-type MOSFET Q2. The power supply Vdrv requires a voltage about twice that of the power supply Vdrv in order to obtain the same speed as that of the first embodiment shown in FIG.

  Note that a switching element such as a bipolar transistor or IGBT (insulated gate transistor) may be used instead of the MOSFET.

  The control circuit 10a generates rectangular wave signals Q1G and Q2G for driving the MOSFETs Q1 and Q2 and applies them to the gates of the MOSFETs Q1 and Q2 to alternately turn on and off the MOSFETs Q1 and MOSFETQ2.

  The rectangular wave signals Q1G and Q2G use the characteristics of the rectangular wave duty and the moving speed of the piezo actuator 1 shown in FIG. 2, and the piezo actuator 1 changes at a constant speed when the piezo actuator 1 starts and stops. Thus, the signal is obtained by changing the duty every time.

  According to the driving device of the second embodiment configured as described above, the driving device operates in the same manner as the driving device of the first embodiment, and the same effect can be obtained.

  In addition, this invention is not limited to the drive device which concerns on the Example mentioned above. In the driving devices of Examples 1 and 2, the characteristic indicating the relationship between the duty and the moving speed of the piezo actuator 1 is a curve as shown in FIG. 2, but the present invention is a piezo actuator 1 as shown in FIG. Without being limited to these characteristics, the characteristics of the piezo actuator 1 may be other characteristics. Also in this case, the control circuit 10 generates a rectangular signal for changing the duty with time so as to change the piezoelectric actuator 1 at a constant moving speed along the inverse function of the characteristic curve of the piezoelectric actuator 1. What is necessary is just to apply to the gate of each MOSFET.

  The present invention is applicable to a photographing apparatus such as a mobile phone camera or a digital still camera.

DESCRIPTION OF SYMBOLS 1 Piezo actuator 2 Piezoelectric element 3 Driving friction member 5 Fixed member 7 Moving body 10, 10a Control circuit 11 Memory 13 Controller 15 Pulse generators Q1-Q4 MOSFET

Claims (3)

A piezoelectric element, a driving friction member fixed to one end of the piezoelectric element, a fixing member fixed to the other end of the piezoelectric element, and a predetermined movement movably relative to the driving friction member in the moving direction of the driving friction member A piezoelectric actuator having a moving body engaged with the frictional force of
A drive unit that has a plurality of drive elements connected in series at both ends of a power supply and drives the piezo actuator by an on / off operation of the plurality of drive elements;
A control circuit that generates a rectangular wave signal that changes the duty with time so as to change the piezoelectric actuator at a constant moving speed using the characteristics of the piezoelectric actuator, and applies the rectangular wave signal to the plurality of driving elements. When,
I have a,
The control circuit generates a rectangular wave signal that changes the duty with time so as to change the piezo actuator at a constant movement speed along an inverse function of a characteristic indicating a relationship between the duty and the movement speed of the piezo actuator. A drive device characterized by generating . The drive unit includes a first series circuit connected in series with a high-side first switching element and a low-side second switching element at both ends of the power supply, and a high-side third switching element and a low-side at both ends of the power supply. A fourth switching element and a second series circuit connected in series,
The piezoelectric actuator is connected between a connection point between the first switching element and the second switching element and a connection point between the third switching element and the fourth switching element.
When the control circuit changes the direction of the current flowing through the piezoelectric actuator by alternately turning on and off the first switching element, the fourth switching element, the second switching element, and the third switching element, 2. The driving device according to claim 1, wherein a rectangular wave signal having a timing for simultaneously turning on the second switching element and the fourth switching element is generated . The drive unit includes a first series circuit connected in series with a high-side first switching element and a low-side second switching element at both ends of the power supply, and a high-side third switching element and a low-side at both ends of the power supply. A fourth switching element and a second series circuit connected in series,
The piezoelectric actuator is connected between a connection point between the first switching element and the second switching element and a connection point between the third switching element and the fourth switching element.
When the control circuit changes the direction of the current flowing through the piezoelectric actuator by alternately turning on and off the first switching element, the fourth switching element, the second switching element, and the third switching element, 2. The driving device according to claim 1, wherein a rectangular wave signal is provided that has a timing for simultaneously turning off the first switching element to the fourth switching element .

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