JPH09285158A - Drive unit using electromechanical transducing element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving mechanism using an electromechanical transducing element which can adjust a driving speed and a moving distance efficiently without lowering thrust. SOLUTION: In a driving mechanism wherein a driving pulse is supplied to a piezoelectric element 28 to let is extend and contract and then a driven member which is joined to a driving shaft 11 by friction fixed to the piezoelectric element 28 is driven by the extension and contraction of the piezoelectric element 28, the piezoelectric element 28 is divided into a plurality of blocks 28a, 28b, 28c and each of the blocks are made connectable to a driving circuit (a coarse adjustment circuit 23, a fine adjustment circuit 24) through switching devices SW1, SW2, SW3. A driving speed and a moving distance are adjusted by driving only a proper block according to a driving speed in high-speed driving or a moving distance in low-speed driving. In the case of high-speed driving, a control is so made that only part of the blocks may be driven to prevent the appearance of vibration noise of an audio frequency caused by the decline in a resonance frequency of the driving system. In the case of low-speed driving, there is no possibilities that vibration noise appears and so, all the blocks can be selected according to a moving distance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device using an electro-mechanical conversion element, and more particularly to an XY moving stage for precise measurement, a photographing lens of a camera, a projection lens of an over head projector, binoculars. The present invention relates to a driving device using an electro-mechanical conversion element suitable for driving a lens or the like.

[0002]

2. Description of the Related Art When a drive pulse having a waveform consisting of a gentle rising portion and a rapid falling portion following the rising portion is applied to the piezoelectric element, the piezoelectric element gradually expands in the thickness direction at the gentle rising portion of the driving pulse. Displacement occurs, and at the rapidly falling part, contraction occurs rapidly. Therefore, utilizing this characteristic, a drive pulse having the above-described waveform is applied to the piezoelectric element to repeatedly charge and discharge at different speeds, thereby causing the piezoelectric element to vibrate in the thickness direction at different speeds, thereby causing the piezoelectric element to vibrate. 2. Description of the Related Art There is known a driving device that reciprocates a fixed driving member at different speeds and moves a moving member frictionally coupled to the driving member in a predetermined direction (for example, see Japanese Patent Application Laid-Open No. 6-123830).

FIG. 15 is a sectional view showing an example of the construction of a photographing lens driving device of a camera using the above driving device. In the drawing, reference numeral 101 denotes a lens barrel, and a holding frame 102 for the first lens L1 is fixedly attached to the left end thereof, and a right end 101a thereof forms a holding frame for the third lens L3. The second lens L is provided inside the lens barrel 101.
The second holding frame 103 is movably arranged in the optical axis direction. A drive shaft 104 drives the lens holding frame 103 in the optical axis direction. The drive shaft 104 is a first shaft of the lens barrel 101.
Is supported movably in the optical axis direction by a flange portion 101b of the lens holding frame 102 and a flange portion 102b of the lens holding frame 102, and one end thereof is adhesively fixed to one surface of the piezoelectric element 105.

The piezoelectric element 105 is displaced in the thickness direction to displace the drive shaft 104 in the axial direction. One end of the piezoelectric element 105 is adhered and fixed to the drive shaft 104, and the other end is disposed on the lens barrel 10.
It is adhesively fixed to the first second flange portion 101c.

Lens holding frame 1 for holding the second lens L2
Reference numeral 03 includes a slider block 103b which is a moving member extending upward. Slider block 103b
, A drive shaft 104 penetrates in the lateral direction. An opening 103c is formed in an upper portion of the slider block 103b through which the drive shaft 104 passes, and an upper half of the drive shaft 104 is exposed. The drive shaft 10 is provided in the opening 103c.
4 is fitted with a pad 106 which is in contact with the upper half of the pad 4. The pad 106 is provided with a projection 106a on the upper part. The projection 106a of the pad 106 is pushed down by a leaf spring 107, and the pad 106 is brought into contact with the drive shaft 104. A downward biasing force F that is in contact is provided. FIG. 16 is a cross-sectional view showing the structure of the frictional coupling portion between the drive shaft 104, the slider block 103b and the pad 106.

Next, the control operation will be described. Lens L2
When it is necessary to move in the direction of arrow a in FIG.
The piezoelectric element 10 is driven with a drive pulse having a waveform including a gentle rising portion and a rapid falling portion that follows.
5

In a gentle rising portion of the driving pulse,
The piezoelectric element 105 gently causes elongation displacement in the thickness direction,
The drive shaft 104 is displaced in the axial direction in the arrow a direction. For this reason, the slider block 103b and the pad 106, which are in pressure contact with the drive shaft 104 by a leaf spring 107 and are frictionally connected thereto.
Also moves in the direction of arrow a, so that the lens holding frame 103 can be moved in the direction of arrow a.

At the rapid falling portion of the drive pulse, the piezoelectric element 105 rapidly contracts in the thickness direction, and the drive shaft 104 is also displaced in the axial direction in the direction opposite to the arrow a. At this time, the slider block 103b, the pad 106, and the lens holding frame 103, which are pressed against the drive shaft 104 by the leaf spring 107, overcome the frictional force between the drive shaft 104 and the drive shaft 104 due to its inertial force and substantially stay at that position. Therefore, the lens holding frame 103 does not move.

The term "substantially" as used herein means that the slider block 103b and the friction coupling surface between the pad 106 and the drive shaft 104 slide in the direction indicated by the arrow a and in the direction opposite thereto while sliding. However, this also includes the movement in the direction of arrow a as a whole due to the difference in driving time.

The lens holding frame 103 can be continuously moved in the direction shown by the arrow a by continuously applying the driving pulse having the above-mentioned waveform to the piezoelectric element 105.

The movement of the lens holding frame 103 in the direction opposite to the arrow a is achieved by applying to the piezoelectric element 105 a drive pulse having a waveform consisting of a rapid rising portion followed by a gentle falling portion. Can be.

[0012]

In the above-described drive device using the piezoelectric element, the sawtooth wave pulse generated by the drive pulse generating circuit is applied to the piezoelectric element, or the constant current charging circuit and the short-circuit discharge circuit are combined. The method of driving by applying a drive pulse composed of constant current charging and rapid discharge or a drive pulse composed of rapid charging and constant current discharge to a piezoelectric element has been adopted.

On the other hand, in this type of drive device, in order to perform precise positioning, the drive speed is generally slowed down. In a drive device using a piezoelectric element, the drive speed can be slowed down by lowering the voltage of the drive pulse to reduce the expansion and contraction displacement of the piezoelectric element, but at the same time, the thrust force (drive force) also decreases, and the drive speed and thrust force also decrease. Has the inconvenience of becoming unstable.

FIG. 1 is a diagram showing the relationship between the voltage of the drive pulse applied to the piezoelectric element and the drive speed. When the voltage of the drive pulse increases, the drive speed increases, and when the voltage of the drive pulse decreases, the drive speed also decreases. Indicates that the drive speed becomes unstable when the voltage of the drive pulse becomes equal to or lower than a predetermined critical value.

FIG. 2 is a diagram showing the relationship between the voltage of the drive pulse applied to the piezoelectric element and the thrust. When the voltage of the drive pulse increases, the thrust also increases, and when the voltage of the drive pulse decreases, the thrust also decreases. , Shows that the thrust becomes unstable when the voltage of the drive pulse becomes equal to or lower than a predetermined critical value.

Further, FIG. 3 is a diagram showing the relationship between the frequency of the drive pulse applied to the piezoelectric element and the drive speed. When the frequency of the drive pulse increases, the drive speed also increases, and when the frequency of the drive pulse decreases, the drive speed also increases. It shows that it will decrease. In this case, the driving speed does not become unstable at a low frequency, but there is a disadvantage that the vibration sound generated at an audible frequency or lower (about 20 kHz or lower) is heard as noise by the human ear.

Further, FIG. 4 is a diagram showing a drive pulse waveform when the drive pulse is thinned out at regular intervals without changing the voltage or frequency of the drive pulse applied to the piezoelectric element, and the voltage and frequency are maintained. Although it is advantageous in that respect, the driving is intermittent because the driving pulses are thinned out. Therefore, there is an inconvenience that a vibrating sound corresponding to the cycle of intermittent driving is generated and is heard as noise by the human ear.

As a countermeasure against this, it is conceivable to reduce the number of stacked unit elements constituting the piezoelectric element without changing the voltage or frequency of the drive pulse applied to the piezoelectric element when the driving speed is slowed. That is, if the unit element constituting the piezoelectric element is divided into a plurality of blocks and a drive pulse having a sufficient amplitude is applied only to a part of the block, the expansion / contraction displacement of the unit element does not change, and the thrust ( The driving force does not change, and the driving speed does not become unstable.

Further, in order to perform precise positioning with this type of driving device, after high speed driving in which a driving pulse is applied to the piezoelectric element to cause reciprocal displacement to move the driven member to a position near a desired position. There is a method of applying a DC voltage to the piezoelectric element to switch to a low speed drive for generating a desired elongation displacement and moving to a target position.

In such low speed driving, the distance that can be moved is proportional to the number of laminated unit conversion elements forming the piezoelectric element. Therefore, in order to increase the moving distance by low speed driving, the number of laminated unit conversion elements must be increased. Should be increased. However, when the number of laminated unit conversion elements is increased, the resonance frequency of the drive system including the piezoelectric element is lowered. Therefore, there is no particular problem when low speed driving is performed using a piezoelectric element having a large number of unit conversion elements stacked, but this piezoelectric element (piezoelectric element having a large number of unit conversion elements stacked) is commonly used for high speed driving. When it is used, vibrations below the audible frequency (20 kHz or less) are generated, and the vibration sound is heard as noise by the human ear.

[0021]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems and comprises an electro-mechanical conversion element and a drive member fixedly coupled to the electro-mechanical conversion element and displaced together with the electro-mechanical conversion element. The driven member frictionally coupled to the driving member, drive pulse generating means for giving expansion / contraction displacement to the electro-mechanical conversion element, and drive control means are provided, and the electro-mechanical conversion element undergoes expansion / contraction displacement by the drive pulse generating means. To drive the driving member and to move the driven member frictionally coupled to the driving member in a predetermined direction.
In a driving device using a mechanical conversion element, the electric
The mechanical conversion element is composed of a plurality of conversion element aggregates that can be selectively connected to the drive pulse generation means, and the drive control means, when performing high-speed driving, changes the plurality of conversion elements according to a desired drive speed. It is characterized in that a part of the aggregate is controlled to be connected to the drive pulse generating means.

When the low speed driving is performed, the drive control means controls so as to connect a part or all of the plurality of conversion element assemblies to the drive pulse generating means according to a desired moving distance.

Further, the drive control means performs high speed driving, and when only a part of the plurality of conversion element assemblies is connected to the drive pulse generation means in accordance with a desired drive speed,
The conversion element assembly on the side closer to the drive member is controlled so as to be preferentially connected to the drive pulse generation means.

The conversion element assembly constituting the electro-mechanical conversion element is formed by laminating one or more unit conversion elements, and the electro-mechanical conversion element is composed of a plurality of unit conversion elements having different numbers of laminations. It is composed of a conversion element assembly.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The piezoelectric element 28 is constituted by laminating a plurality of blocks constituted by laminating one to a plurality of unit conversion elements, and the first block 28a is composed of one unit conversion element.
The second block 28b is composed of two unit conversion elements, and the third block 28c is composed of four unit conversion elements. The first block 28a goes through the switching element SW1, the second block 28b goes through SW2, and the third block 28c goes through SW3.
, And are respectively connected to drive circuits (coarse movement circuit 23 and fine movement circuit 24). The above-mentioned switching element is a semiconductor switching element controlled by the CPU 21 of the control circuit 20 (see FIG. 5).

The first block 28a to the third block 28
Since c has a different number of conversion elements, the reciprocal displacement when a driving pulse is applied for high-speed driving is different, and as a result, the driving speed is different. Therefore, the optimum block should be selectively driven according to the desired driving speed. Thus, a desired driving speed can be obtained. When the number of laminated unit conversion elements is increased, the resonance frequency of the drive system including the piezoelectric element is lowered, and vibration noise below the audible frequency (below 20 kHz) is generated.
By selecting only a part of the block, the number of laminated layers driven is reduced to prevent the generation of vibration sound at an audible frequency.

In the case of low speed driving, an optimum block can be selectively driven according to a desired moving distance, so that the desired distance can be accurately moved. In this case, no vibrating noise is generated, so that part or all of the block can be used according to the desired moving distance.

[0028]

Embodiments of the present invention will be described below.
FIG. 5 is a block diagram of the drive mechanism 10 and the control circuit 20 when the drive device using the electro-mechanical conversion element of the present invention is applied to a lens device.

The structure of the driving mechanism 10 of the lens device will be briefly described. 28 is a piezoelectric element, one end of which is the frame 1
The drive shaft 1 is bonded and fixed to the piezoelectric element 9 and supported at the other end of the piezoelectric element 28 by a support means (not shown) so as to be axially displaceable.
1 is adhesively fixed.

A slider block 12 has a drive shaft 11 penetrating in the lateral direction. An opening 12a is formed in an upper portion of the slider block 12 through which the drive shaft 11 passes.
The upper half of the drive shaft 11 is exposed. A pad 13 which is in contact with the upper half of the drive shaft 11 is fitted into the opening 12a, and a projection 13a is provided on the upper portion of the pad 13. The projection 13a of the pad 13 is pushed down by a leaf spring 14. The pad 13 is provided with a downward biasing force F which comes into contact with the drive shaft 11. FIG. 6 is a cross-sectional view showing the structure of the friction coupling portion of the drive shaft 11, the slider block 12 and the pad 13.

With the above structure, the slider block 12 including the pad 13 and the drive shaft 11 are pressed against each other by the urging force F of the leaf spring 14 and are frictionally coupled to each other.

A lens holding frame 15 is fixed to the lower side of the slider block 12 so as to hold the lens 16. Reference numeral 17a denotes a magnetoresistive detecting element for detecting the position of the lens 16, which is fixed to the lens holding frame 15. A magnetizing rod 17b in which NS magnetic poles are magnetized at a predetermined interval λ is arranged close to the magnetoresistive detecting element 17a, and a well-known MR sensor 17 is used for the magnetoresistive detecting element 17a and the magnetizing rod 17b. Is configured. When the lens holding frame 15 moves, the current position of the lens can be known from a signal output by the magnetoresistive detecting element 17a of the MR sensor 17 detecting a change in the magnetic pole of the magnetized rod 17b.

The control circuit 20 includes a CPU 21, an MR sensor output signal processing circuit 22 connected to the input port thereof, a coarse movement circuit 23 and a fine movement circuit 24 connected to the output port,
And an impedance adjustment circuit 35 connected in parallel to the piezoelectric element 28. Impedance adjustment circuit 3
5 will be described in detail later.

Further, the piezoelectric element 28 is constituted by laminating a plurality of blocks constituted by laminating one to a plurality of unit conversion elements. In this embodiment, the first block 28a has a unit conversion element number of 1 (2 to the power of 0), the second block 28b has a unit conversion element number of 2 (2 to the power of 1), and the third block 28c has a unit conversion element number of 4 ( 2 squared). The first block 28a goes through the switching element SW1, the second block 28b goes through SW2, and the third block 28c goes through SW.
3 and are connected to a coarse movement circuit 23 and a fine movement circuit 24, respectively. The above-mentioned switching element SW1
˜SW3 are composed of semiconductor switching elements controlled by the CPU 21 of the control circuit 20.

Next, the operation of the control circuit 20 will be described. First, high-speed driving by the coarse movement circuit 23 will be described. In the case of high speed driving, a driving pulse having a predetermined frequency is applied to the piezoelectric element for driving. In this case, if the frequency of the drive pulse is sufficiently lower than the resonance frequency of the drive mechanism including the piezoelectric element (in the experiment, the frequency of the drive pulse is 1/2 or less of the resonance frequency of the drive mechanism), the moving body (here, The speed of the lens) is the product of the amount of expansion of the piezoelectric element and the frequency of the drive pulse.

If the voltage applied to the piezoelectric element is the same, the expansion amount increases as the number of laminated layers forming the piezoelectric element increases, and thus the driving speed increases as the number of laminated layers increases. However, when the number of stacked layers increases, the resonance frequency of the drive mechanism including the piezoelectric element decreases, so that the vibration sound generated at the time of driving not only makes the human ear unpleasant to the audible frequency range, but also increases the resonance frequency. Due to the decrease, the drive speed may be decreased, and the drive may not be possible in the ultrasonic range. In this regard, the number of stacked elements is limited.

In high-speed driving, the switching elements SW1 to SW3 are appropriately selected and operated to connect the first block 28a to the third block 28c to the coarse movement circuit 23 so that the number of stacked layers is suitable for a desired driving speed. By doing so, a desired drive speed can be set. In this case, the higher the resonance frequency of the drive mechanism including the piezoelectric element, the more stable the speed can be obtained.
It is preferable to select the switching element so that the block closer to the side is preferentially driven.

Next, low speed driving by the fine movement circuit 24 will be described. The low-speed drive is a drive in which a direct current voltage is applied to the piezoelectric element to generate an extension displacement in the piezoelectric element and the piezoelectric element is moved by a minute distance. Since the amount of expansion of the piezoelectric element is determined by the applied DC voltage, if the relationship between the applied DC voltage and the amount of expansion of the unit piezoelectric element is determined beforehand by measurement, etc., if the applied DC voltage is constant, the unit The moving distance can be represented by the product of the expansion amount of the piezoelectric element and the number of stacked layers, and the moving distance can be accurately determined in advance.

The larger the number of laminated piezoelectric elements to be driven, the longer the moving distance. However, if the number of laminated piezoelectric elements is increased, the accuracy of the moving distance decreases due to the variation in the amount of expansion of each laminated piezoelectric element. Further, in setting the moving distance, the DC voltage applied to the piezoelectric element is not changed in order to obtain a stable thrust, and the desired moving distance is set as a whole by increasing or decreasing the number of piezoelectric elements applied.

Therefore, in low-speed driving, the switching element S is adjusted so that the number of stacked layers is suitable for a desired moving distance.
A desired movement distance can be set by selectively operating W1 to the switching element SW3 to connect the first block 28a to the third block 28c to the fine movement circuit 24. Further, in order to obtain a stable thrust, it is advantageous that the block used is close to the drive shaft 11 side.
It is preferable that the switching element is selected so that the block close to the drive shaft 11 side is preferentially used according to the desired moving distance.

FIG. 7 is a diagram showing an example of the drive speed by the coarse movement circuit and the movement distance by the fine movement circuit. FIG. 7A illustrates the speed obtained by selecting the switching elements SW1 to SW3 when a driving pulse of 20 kHz and 30 V is supplied from the coarse movement circuit 23. The switching elements SW1 to SW3 are shown in FIG. ON
30 mm / sec, switching element SW
10 when 1 and SW2 are ON and SW3 is OFF
mm / sec, switching element SW1 ON, SW2
It is shown that a speed of 3 mm / sec can be obtained when SW3 and SW3 are turned off.

FIG. 7B shows the fine movement circuit 24 from 0 to 15
The moving distance and the moving accuracy obtained by selecting the switching elements SW1 to SW3 when a DC voltage of 0 V is supplied are illustrated. When the switching elements SW1 to SW3 are turned on, the moving range is 0 to 0.
Switching element SW1 with accuracy of 100 nm at 10 μm
When SW2 is turned on and SW3 is turned off, the moving range is 0 to 3 μm, the accuracy is 30 nm, and the switching element S
When W1 is turned on and SW2 and SW3 are turned off, the moving range is 0 to 1 μm and the accuracy is 10 nm.

FIG. 8 shows a modification in which the number of piezoelectric elements in the first embodiment is increased and this is divided into four blocks. In this way, by increasing the block division number of the piezoelectric element to form the first block 28a, the second block 28b, the third block 28c, and the fourth block 28d, and by appropriately selecting these blocks by the switching elements SW1 to SW4, The driving speed in the case of high-speed driving and the moving distance in the case of low-speed driving can be set more finely.

FIG. 9 is a diagram showing the relationship between the selection of blocks and the driving speed in the case of high-speed driving when the above-mentioned piezoelectric element is divided into four blocks. Line (a) is first
When the block 28a (the number of unit conversion elements is the power of 2 = 1) is selected, the line (b) selects the first block 28a and the second block 28b (the number of the unit conversion elements is the power of 2 = 2). In this case, the line (c) indicates the first block 28a, the second block 28b, and the third block 28c (where the number of unit conversion elements is 2).
Squared = 4) is selected, showing that the driving speed increases as the frequency of the driving pulse applied to the piezoelectric element increases.

The line (d) indicates the first block 28a to the fourth block 28d (the number of unit conversion elements is the power of 2 = 8).
Shows the case where blocks of all piezoelectric elements up to are selected. In this case, since the resonance frequency of the drive mechanism including the piezoelectric element decreases, the moving speed of the moving body is zero at the frequency in the ultrasonic region of 20 kHz or higher. It has become.
Under these conditions, it is better not to selectively drive the fourth block 28d of the piezoelectric element in the case of high speed driving. 4th
If the block 28d is not selectively driven, it can be driven in the ultrasonic region.

FIG. 10 is a diagram showing an example of the driving speed by the coarse movement circuit and the movement distance by the fine movement circuit in the example in which the piezoelectric element shown in FIG. 8 is divided into four blocks, and FIG. The speed obtained by selecting the switching elements SW1 to SW4 when the drive pulse of 20 kHz and 30 V is supplied from the driving circuit 23 is shown as an example. The switching elements SW1 to SW4 are turned on.
0 mm / sec, switching element SW1
~ 30 mm when SW3 is ON and SW4 is OFF
/ Sec, switching elements SW1 and SW2 are turned on,
10 mm / se when SW3 and SW4 are OFF
c, it is shown that a speed of 3 mm / sec can be obtained when the switching element SW1 is turned on and SW2 to SW4 are turned off.

FIG. 10B shows the fine movement circuit 24 with 0 to 1
The moving distance and the moving accuracy obtained by selecting the switching elements SW1 to SW4 when a DC voltage of 50 V is supplied are illustrated. When the switching elements SW1 to SW4 are turned on, the moving range is 0.
Accuracy of 300 nm at -30 μm, switching element SW
When 1 to SW3 is ON and SW4 is OFF, the moving range is 0 to 10 μm and the accuracy is 100 nm, SW1 and SW
When 2 is turned on and SW3 and SW4 are turned off, the movement range is 0 to 3 μm and the accuracy is 30 nm. When switching element SW1 is turned on and SW2 to SW4 is turned off, the movement range is 0 to 1 μm and the accuracy is 10 nm. It indicates that there is.

Therefore, in high speed driving, the switching element SW4 is turned off and the switching element SW1 is turned on.
~ SW3 sets a desired drive speed, and in low speed drive, switching elements SW1 ~ S are set according to a desired moving distance.
It may be set appropriately by W4. In this case, by selecting the fourth block 28d by the switching element SW4, it is possible to set a longer moving distance than in the case of the example shown in FIG.

Coarse movement circuit 2 in the control circuit shown in FIG.
An example of the 3 and the fine movement circuit 24 is shown in FIG. Coarse circuit 2
Since 3 and the fine movement circuit 24 have the same circuit configuration, only the coarse movement circuit 23 will be described. The coarse movement circuit 23 is a semiconductor switching element SWa or SW controlled by the known constant current circuits 31 and 32 and the CPU 21 (see FIG. 5) of the control circuit.
It is composed of b, SWc, and SWd.

For high speed driving, a driving pulse for slowly charging and rapidly discharging or a driving pulse for rapidly charging and slowly discharging is supplied to the piezoelectric element. That is,
When supplying a drive pulse for gently charging and rapidly discharging the piezoelectric element 28, SWa and SWd are maintained in the OFF state by a signal output from the CPU 21. When SWc is turned on in this state, a current from the power source V flows through the piezoelectric element 28 at a constant current through the SWc and constant current circuit 31, and is gradually charged. Next, when SWb is turned on,
The electric charge charged in the piezoelectric element 28 is rapidly discharged through SWb. SWc and SWb are alternately turned ON / O at a predetermined cycle.
By performing FF control, it is possible to supply a drive pulse having a predetermined cycle to the piezoelectric element.

When a drive pulse for rapidly charging and slowly discharging the piezoelectric element 28 is supplied, SWc and SWb are maintained in the OFF state by a signal output from the CPU 21. When SWa is turned on in this state, the piezoelectric element 28
Current from the power supply V flows through SWa and is rapidly charged. Next, when SWd is turned on, the electric charge charged in the piezoelectric element 28 flows through SWd and the constant current circuit 32 at a constant current, and is gently discharged. By alternately controlling ON / OFF of SWa and SWd at a predetermined cycle, it is possible to supply a drive pulse of a predetermined cycle to the piezoelectric element.

For low speed driving, direct current is supplied to the piezoelectric element so that the piezoelectric element is slowly charged (or slowly discharged). That is, in order to generate a predetermined expansion corresponding to the movement distance, the switching element SWc of the fine movement circuit 24 (having the same circuit configuration as the coarse movement circuit 23) is turned on, and the direct current supplied from the power source V is applied to the piezoelectric element 28. Charge gently to generate a predetermined elongation. In this case, the switching element SWb is turned on to discharge the charge. Also, to generate a predetermined shrinkage corresponding to the movement distance,
After the switching element SWa is turned on to charge the battery once rapidly, the switching element SWd is turned on to slowly discharge the battery to generate a predetermined contraction.

The drive circuit for driving the piezoelectric element is usually constructed so as to match the impedance of the piezoelectric element, which is the load of the circuit, by matching the impedance so that there is no loss.

However, as described above, when the number of conversion elements forming the piezoelectric element is changed according to the driving speed and the moving distance, the impedance of the piezoelectric element changes. For this reason, impedance mismatching occurs with the drive circuit (coarse movement circuit 23 or fine movement circuit 24), loss occurs, and the waveform of the drive pulse collapses. FIG. 12 is a diagram showing the ON / OFF state of the switching element of the coarse movement circuit, the waveform of the drive pulse applied to the piezoelectric element, and the collapse of the waveform. In FIG. 12A, SWc and SWb are turned ON / OFF. OFF
FIG. 12B shows the case where SWa and SWd are controlled to generate a drive pulse composed of gentle charge and rapid discharge.
The figure shows the case of a drive pulse consisting of rapid charging and gentle discharging by controlling ON / OFF.

Mismatching of the impedance between the impedance of the piezoelectric element and the drive circuit (coarse movement circuit 23 or fine movement circuit 24) which occurs when the number of conversion elements constituting such a piezoelectric element is changed. To avoid
The problem can be solved by preparing a plurality of drive circuits having impedances according to the number of driven elements and switching the drive circuits according to the number of driven elements. However, this method results in an increase in cost because a plurality of drive circuits must be prepared. Therefore, in the present invention, the impedance adjusting circuit 35 is provided in parallel with the piezoelectric element so that the impedance does not change even if the number of elements forming the piezoelectric element is changed.

FIG. 13 shows a portion of the piezoelectric element 28 and the impedance adjustment circuit 35 in the control circuit 20 shown in FIG. The impedance adjustment circuit 35 drives a capacitor C5 having a capacitance corresponding to the capacitance component of the second block 28b and a capacitor C4 having a capacitance corresponding to the capacitance component of the third block 28c of the piezoelectric element by switching elements SW5 and SW4, respectively. It is configured to be connectable to. This is because the impedance of the piezoelectric element mainly has a capacitance component and supplements the capacitance component of the piezoelectric element separated from the drive circuit.

When only the first block 28a of the piezoelectric element is driven, the switching elements SW4 and SW5 are turned on and the capacitors C4 and C5 are connected in parallel to the driving circuit, and the second block separated from the driving circuit.
The capacity components of the block 28b and the third block 28c are supplemented. When the first block 28a and the second block 28b of the piezoelectric element are driven, the switching element SW4 is turned on and the capacitor C4 is connected in parallel to the drive circuit.
The capacitance component of the third block 28c separated from the drive circuit is supplemented.

FIG. 14 shows a modified example of the impedance adjustment circuit 35 for compensating for the capacitance component shown in FIG. 13, which is designed to compensate not only for the capacitance component but also for the inductance component.
The dance adjustment circuit 36. Coils L4 and L5 are respectively inserted in series in capacitors C4 and C5 of the impedance adjustment circuit 35 shown in FIG. 13 so that the inductance component is also compensated.

The impedance adjustment circuit described above is
It can also be used to adjust the waveform distortion that occurs when the output of the drive circuit (coarse movement circuit 23 or fine movement circuit 24) is amplified by an amplifier.

In each of the embodiments described above, the piezoelectric element is formed by stacking a plurality of blocks formed by stacking a plurality of unit conversion elements. These blocks are formed by stacking the unit conversion elements. Numbers are 1, 2, 4, ---, etc. and n of 2
An example is shown in which the number is increased by the power (n is a positive integer). However, the number of stacked unit conversion elements forming the block is not limited to this, and may be an exponentially increasing number of stacked layers such as 3 to the n-th power and 10 to the n-th power.

[0061]

As described above in detail, according to the present invention, in the driving device using the electro-mechanical conversion element, the electro-mechanical conversion element is composed of a plurality of blocks,
The optimum block is selectively driven according to the desired drive speed in high-speed drive or the desired travel distance in low-speed drive, so the thrust (driving force) decreases and the drive speed becomes unstable. It is possible to efficiently adjust the driving speed or the moving distance without causing any trouble.

Further, in the case of high speed driving, only a part of the plurality of blocks of the electro-mechanical conversion element is controlled to be driven, so that the generation of the vibration sound of the audible frequency due to the lowering of the resonance frequency of the drive system is prevented. Further, in the case of low speed driving, there is no possibility of generating a vibration sound of an audible frequency, and therefore one or all blocks can be selected according to a desired moving distance, so that a long moving distance can be efficiently achieved. It can be moved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a driving pulse voltage applied to a piezoelectric element and a driving speed.

FIG. 2 is a diagram showing a relationship between a drive pulse voltage applied to a piezoelectric element and thrust.

FIG. 3 is a diagram showing the relationship between the frequency of a drive pulse applied to a piezoelectric element and the drive speed.

FIG. 4 is a diagram showing a drive pulse waveform when a drive pulse applied to a piezoelectric element is thinned out.

FIG. 5 is a block diagram of a drive mechanism and a control circuit when the drive device using the electro-mechanical conversion element of the present invention is applied to a lens device.

FIG. 6 is a cross-sectional view of a friction coupling portion between a drive shaft, a slider block, and a pad.

FIG. 7 is a diagram showing an example of a driving speed by a coarse movement circuit and a movement distance by a fine movement circuit.

FIG. 8 is a diagram illustrating a modified example in which a piezoelectric element is divided into four blocks.

FIG. 9 is a diagram illustrating the relationship between block selection and drive speed in the case of high-speed drive in a modification in which a piezoelectric element is divided into four blocks.

FIG. 10 is a diagram showing an example of a driving speed by a coarse movement circuit and a movement distance by a fine movement circuit in a modified example in which a piezoelectric element is divided into four blocks.

FIG. 11 is a block diagram showing an example of a coarse movement circuit and a fine movement circuit in the control circuit.

FIG. 12: ON / OFF of the switching element of the coarse movement circuit
6A and 6B are diagrams for explaining the state of FIG. 6B, the waveform of the drive pulse applied to the piezoelectric element, and the waveform collapse.

FIG. 13 is a diagram illustrating a block division of a piezoelectric element and an impedance adjustment circuit.

FIG. 14 is a diagram illustrating another example of the impedance adjustment circuit.

FIG. 15 is a cross-sectional view illustrating an example of a lens driving mechanism of a camera by a driving mechanism using a conventional piezoelectric element.

16 is a cross-sectional view of a friction coupling portion of a drive shaft, a slider block, and a pad of the drive mechanism shown in FIG.

FIG. 17 is a diagram showing an example of a waveform of a drive pulse applied to a piezoelectric element.

[Explanation of symbols]

 10 Drive mechanism 11 Drive shaft 12 Slider block 13 Pad 14 Leaf spring 15 Piezoelectric element 17 MR sensor 20 Control circuit 21 CPU 22 Signal processing circuit 23 Coarse movement circuit 24 Fine movement circuit 28 Piezoelectric element 28a Piezoelectric element first block 28b Piezoelectric element Second block 28c Third block of piezoelectric element 35 Impedance adjusting circuit

Claims (5)

[Claims] 1. An electro-mechanical conversion element, a drive member fixedly coupled to the electro-mechanical conversion element and displaced together with the electro-mechanical conversion element, a driven member frictionally coupled to the drive member, and the electro-mechanical conversion element. A drive pulse generating means for giving expansion / contraction displacement to the mechanical conversion element, and a drive control means are provided, and the expansion / contraction displacement of the electro-mechanical conversion element is caused by the drive pulse generation means to drive the driving member, In a driving device using an electro-mechanical conversion element for moving a driven member frictionally coupled in a predetermined direction, the electro-mechanical conversion element is a plurality of conversion element aggregates selectively connectable to the drive pulse generating means. In the case of performing high-speed driving, the drive control means is configured to drive only a part of a plurality of conversion element aggregates according to a desired drive speed by the drive pulse generation means. A drive device using an electro-mechanical conversion element, characterized in that the drive device is controlled so as to be connected to. 2. The drive control means controls to connect a part or all of the plurality of conversion element assemblies to the drive pulse generation means according to a desired moving distance when low speed driving is performed. A drive device using the electro-mechanical conversion element according to claim 1. 3. The drive control means is configured to be close to the drive member when connecting only a part of the plurality of conversion element assemblies to the drive pulse generation means in accordance with a desired drive speed in order to perform high speed drive. The drive device using the electro-mechanical conversion element according to claim 1, wherein the conversion element assembly on the side is controlled so as to be preferentially connected to the drive pulse generating means. 4. The electro-mechanical conversion element according to claim 1, wherein the conversion element assembly forming the electro-mechanical conversion element is formed by laminating one or more unit conversion elements. Drive device using. 5. The electro-mechanical conversion element according to claim 1, wherein the electro-mechanical conversion element is composed of a plurality of conversion element assemblies in which the number of unit conversion elements laminated is different. Drive.