JP2002165469A - Piezo-electric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set, using a simplified structure, a drive frequency of a piezo-electric element to the frequency to allow a driven section to move in the highest speed in a truss-type piezoelectric actuator, in a structure with a truss-type piezoelectric driver formed by coupling an intersecting point of two piezoelectric elements which are crossing in the right angle with a chip member is placed with pressure in contact with the driven section. SOLUTION: A sensor 7 is provided to the driven section 2 in order to detect a rotating speed, an optimum drive frequency setting section 82 is provided within a drive controller 8, a drive voltage of a drive section 3 outputted from a drive signal supplying section 6 is scanned over the prescribed frequency range with the optimum drive frequency setting section 82 at the time of initial setting, the speed characteristic is actually measured by calculating a change of rotating speed of the driven section 2, and the optimum drive frequency to provide the maximum rotating speed is calculated, using this speed characteristic. Moreover, the drive frequency of a drive voltage is set to the optimum drive frequency using a drive frequency setting section 83.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a truss-type piezoelectric drive unit formed by connecting a plurality of displacement members, at least one of which is made of a piezoelectric material, such that their ends are orthogonal to each other, and presses the drive unit to a driven unit. The present invention relates to a truss-type piezoelectric actuator that drives a driven part by causing a part to perform an elliptical or circular motion.

[0002]

2. Description of the Related Art In the field of a method of driving an actuator or an ultrasonic motor using a piezoelectric body, the piezoelectric body vibrates most efficiently when the piezoelectric body is driven at a mechanical resonance frequency of the piezoelectric body or at a frequency near the mechanical resonance frequency. Therefore, conventionally, a technique has been proposed in which, when the frequency of the drive voltage supplied to the piezoelectric body deviates from the optimum frequency at which the drive efficiency becomes highest, the frequency is automatically corrected to the optimum frequency.

For example, Japanese Patent Publication No. 7-2023 discloses that the phase difference θopt between the driving frequency of the piezoelectric body at which the rotational speed of the ultrasonic motor is maximized and the displacement frequency of the piezoelectric body is calculated in advance, and the ultrasonic motor During the driving of the piezoelectric element, the phase difference θ between the driving frequency of the piezoelectric body and the displacement frequency of the piezoelectric body is detected, and the deviation Δθ between the phase difference θ and the optimal phase difference θopt is detected, and based on the deviation Δθ There is disclosed a technique for automatically correcting the driving frequency of the piezoelectric body to a frequency at which the rotational speed of the ultrasonic motor is maximized (that is, a frequency at which Δθ = 0).

[0004]

By the way, a plurality of displacement members, at least one of which is made of a piezoelectric material, are connected to a driven portion which is held so as to be able to move linearly or rotationally so that the respective ends are orthogonal to each other. The truss-type piezoelectric driving section is pressed against the piezoelectric body, and a driving voltage of a predetermined frequency is supplied to the piezoelectric body, so that the coupling section of the displacement member (a section pressed against the driven section; hereinafter, referred to as a pressing section) is subjected to elliptical motion or In a piezoelectric actuator that makes a circular motion and transmits the motion to a driven part to move the driven part in a predetermined direction, the displacement of the pressure contact part (the displacement of the piezoelectric body and the displacement of the other displacement members are vector ) Is transmitted to the driven portion, and in order to efficiently displace (ie, move at the highest speed) the driven portion, the piezoelectric body must have a mechanical resonance frequency. If the piezoelectric element is driven by the side and the phase difference of the displacement between the piezoelectric body and the other displacement member is controlled to a predetermined value (that is, the displacement is controlled so that the press-contact portion moves along a predetermined elliptical or circular orbit). It is known to be good.

In the drive control method for a piezoelectric body described in Japanese Patent Publication No. 7-2023, the phase difference θopt between the drive frequency of the piezoelectric body at which the rotational speed of the ultrasonic motor is maximized and the displacement frequency of the piezoelectric body does not change. Under such a premise, the phase difference θ between the driving frequency of the piezoelectric body and the displacement frequency of the piezoelectric body is tracked to the optimum phase difference θopt.

However, a truss type piezoelectric actuator is
The truss-type piezoelectric drive unit has an elliptical or circular motion of the pressure contact part and transmits a part of its motion trajectory to the driven unit as a driving force. The phase difference between the drive frequency and the displacement frequency of the pressure contact portion of the truss type piezoelectric drive unit is not always constant, and if the displacement trajectory of the pressure contact unit is not appropriate, the moving speed of the driven unit will decrease instead There is.

Therefore, even if the drive control method of the piezoelectric body described in Japanese Patent Publication No. 7-2023 is applied to the truss type piezoelectric actuator, it is difficult to drive and control the driven portion in the most efficient state.

On the other hand, the phase difference between the displacement frequency of the piezoelectric body and the displacement frequency of the other displacement member is detected, and the displacement trajectory of the press-contact portion of the truss-type piezoelectric drive portion is moved based on the phase difference. Although it is desirable to perform fine grain control so that the speed is maximized, this method needs to detect the displacement frequency for each displacement member, calculate the phase difference of displacement between the displacement members, and determine the drive frequency of the piezoelectric body. The configuration for control becomes complicated, which is against the demand for simplification of the circuit and reduction in cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in a piezoelectric actuator comprising a driven portion and a truss-type driving portion pressed against the same, the driven portion is as simple as possible. An object of the present invention is to provide a piezoelectric actuator that can be driven with optimal efficiency.

[0010]

In order to achieve the above object, a piezoelectric actuator according to the present invention comprises: a driven part which is held so as to be capable of linear or rotational movement;
A truss-type piezoelectric drive unit formed by connecting a plurality of displacement members each formed of a piezoelectric body such that the respective ends are orthogonal to each other, and press-fit a connection portion of the displacement member of the truss-type piezoelectric drive unit to the driven unit. A piezoelectric actuator comprising a pressing unit and a drive signal supply unit that supplies a drive signal in which a voltage changes at a predetermined frequency to a piezoelectric body of the truss-type piezoelectric drive unit, wherein a displacement speed of the driven unit is detected. A speed detection unit, which supplies the drive voltage to the piezoelectric element while changing the frequency within a predetermined frequency range from the drive signal supply unit, detects the displacement speed of the driven unit by the speed detection unit, A speed characteristic calculating unit that calculates a speed characteristic of the driven unit from the characteristic and the frequency of the driving voltage; and a displacement speed of the driven unit based on the speed characteristic calculated by the speed characteristic calculating unit. And a drive frequency setting unit configured to set the frequency of the drive voltage supplied from the drive signal supply unit to the frequency detected by the frequency detection unit. It is provided with setting means (claim 1).

According to this configuration, the drive voltage is supplied to the piezoelectric element of the drive unit while changing the frequency within a predetermined frequency range from the drive signal supply unit of the drive frequency setting unit, and the driven unit is driven, and the speed detection is performed. The unit detects the displacement speed of the driven unit at each drive frequency (ie, the characteristic of the displacement speed of the driven unit with respect to the drive frequency). Then, the frequency at which the displacement speed of the driven portion becomes the highest speed is detected based on the speed characteristic of the driven portion by the frequency detection portion, and the frequency of the drive voltage supplied from the drive signal supply portion is detected by the drive frequency setting portion. Is set to the frequency detected by the frequency detector.
Thereby, the driven part is driven in the most efficient state.

In the above piezoelectric actuator,
Mode setting means for setting a mode for setting the drive frequency of the drive voltage based on the actually measured speed characteristic is further provided. The drive frequency setting means calculates the speed characteristic when the mode is set by the mode setting means. The frequency of the drive voltage may be set to a drive frequency at which the driven part is displaced at a maximum speed by operating the unit, the frequency detection unit, and the drive frequency setting unit (claim 2).

According to this structure, when the mode is set, the drive frequency setting means actually measures the speed characteristic of the driven part, and sets the optimum drive frequency detected based on the speed characteristic to the drive voltage. Set to frequency.

In the above-mentioned piezoelectric actuator,
The drive frequency setting means operates the speed characteristic calculation section, the frequency detection section, and the drive frequency setting section at the time of initial setting of the drive frequency when the piezoelectric actuator is activated, and sets the frequency of the drive voltage to the received frequency. It is preferable to set a driving frequency at which the driving section is displaced at the maximum speed (claim 3).

According to this structure, the drive frequency setting means actually measures the speed characteristic of the driven portion at the time of initial setting of the drive frequency when the piezoelectric actuator is activated, and detects an optimum value detected based on the speed characteristic. The driving frequency is set to the driving frequency of the driving voltage.

Further, in the above piezoelectric actuator,
The apparatus further comprises speed reduction detecting means for detecting that the speed of the driven part detected by the speed detecting part has decreased to a predetermined threshold value or less, and wherein the driving frequency setting means is provided by the speed reduction detecting means. When the speed of the driven part falls below a predetermined threshold, the speed characteristic calculation part and the frequency detection part are operated to detect the drive frequency of the drive voltage at which the driven part is displaced at the maximum speed. (Claim 4).

According to this configuration, the displacement speed is detected during the driving of the driven portion, and when the displacement speed falls below the predetermined threshold value by the speed reduction detecting means, the driving frequency setting means sets the speed of the driven portion to be lower. Characteristics are actually measured, and an optimum driving frequency is detected based on the speed characteristics.

In this case, when the frequency detecting section detects the frequency of the driving voltage for displacing the driven section at the maximum speed by the frequency detecting section, the driving signal supplying section immediately after the detection. It is preferable that the frequency of the drive voltage supplied to the piezoelectric element is changed to the frequency detected by the frequency detector.

According to this configuration, the displacement speed is detected while the driven portion is being driven, and when the displacement speed falls below a predetermined threshold value by the speed drop detecting means, the driving frequency setting means sets the speed of the driven portion to be lower. The characteristics are measured, and the driving frequency of the driving voltage of the piezoelectric body is changed to the optimum driving frequency detected based on the speed characteristics.

[0020]

FIG. 1 shows the structure of a first embodiment of a piezoelectric actuator according to the present invention.

The piezoelectric actuator 1 comprises a driven part 2, a driving part 3, a pressing part 4, a driving signal switching part 5, a driving signal supplying part 6, a rotation detecting part 7, a driving control part 8, and an operating part 9. ing.

The driven part 2 is made of a disk or a cylinder made of a metal such as iron or aluminum, and is rotatable about a rotation shaft 21. For example, by fixing a member to be driven to the rotating shaft 21 of the driven unit 2, the member can be driven according to the rotation of the driven unit 2. The peripheral surface 22 of the driven part 2 has been subjected to a surface treatment such as a tuffering treatment or an alumite treatment in order to prevent abrasion due to friction with the driving part 3. In the present embodiment, the driven part 2 is a rotating body, but may be a plate-like body capable of linear movement.

The driving section 3 is a driving source for generating a driving force for the driven section 2. The driving unit 3 includes two laminated piezoelectric elements 31,
32 are combined in a truss shape. That is, two stacked piezoelectric elements 31 (hereinafter, referred to as first piezoelectric element 3).
One. ) And a laminated piezoelectric element 32 (hereinafter, referred to as a second piezoelectric element 32) are disposed so as to intersect at a substantially right angle, and a tip that is pressed against the peripheral surface 22 of the driven unit 2 at the tip on the intersecting side. The member 33 (press-contact portion) is joined with an adhesive, and the base ends of the first and second piezoelectric elements 31 and 32 are joined with a ship-shaped base member 34 with an adhesive.

As a material of the tip member 33, tungsten or the like, which can stably obtain a high friction coefficient and is excellent in abrasion resistance, is preferable. As a material of the base member 34, stainless steel or the like which is easy to manufacture and has excellent strength is preferable. Further, as the adhesive, an epoxy resin or the like having excellent adhesive strength and strength is preferable.

The first piezoelectric element 31 is, as shown in FIG.
Plural ceramic thin plates 31a exhibiting piezoelectric characteristics such as PZT
And the electrodes 31b and 31c are alternately laminated, and each ceramic thin plate 31a and the electrodes 31b and 31c are fixed by an adhesive or the like. Further, protective layers 31 d are provided at both ends of the first piezoelectric element 31.

The adjacent ceramic thin plates 31a are stacked so that the polarization directions are opposite to each other. The drive voltage V is supplied from the drive signal supply unit 6 via the drive signal switching unit 5 to every other electrode 31b and electrode 31c. When a predetermined driving voltage V is applied between the electrode 31b and the electrode 31c, the electrode 31b and the electrode 3
1c, an electric field is generated in the direction of polarization in each of the ceramic thin plates 31a.
a is displaced in the polarization direction. Adjacent ceramic plate 31
a, the direction in which the drive voltage V is applied is reversed, but since the polarization directions are opposite to each other, the displacement direction of each ceramic thin plate 31a is the same, and the laminated piezoelectric element 31 is The displacement is performed by the displacement amount obtained by adding the displacement amount of 111a.

The second piezoelectric element 32 is also the second piezoelectric element 3
1 has the same structure as that of FIG. 1, and the drive voltage V output from the drive signal supply unit 6 is switched and supplied via the drive signal switching unit 5. Therefore, the first piezoelectric element 31 expands and contracts with substantially the same drive characteristics.

In a region where the electric field is small and the displacement history is negligible, the electric field generated between each electrode 31b and the electrode 31c and the displacement of the first piezoelectric element 31 can be regarded as a substantially linear relationship. This is shown in FIG. In the figure, the horizontal axis represents the electric field intensity, and the vertical axis represents the distortion rate.

When a drive voltage (for example, a sine-wave or rectangular-wave alternating signal or a dc voltage composed of a pulse train) whose level periodically changes is applied between the electrode 31b and the electrode 31c, the alternating voltage is applied. Accordingly, the respective ceramic thin plates 31a repeatedly expand and contract in the same direction, and the first piezoelectric element 31 repeatedly expands and contracts as a whole.

Here, the principle of rotation of the driven part 2 of the piezoelectric actuator 1 will be described. In the present embodiment, the first
By driving only one of the piezoelectric element 31 and the second piezoelectric element 32, for example, only the first piezoelectric element 31, the first piezoelectric element 3
The first vibration is transmitted to the second piezoelectric element 32 via the base member 34 so that the second piezoelectric element 32 resonates with a predetermined phase difference. When driven in this manner, the chip member 33 provided at the intersection of the first piezoelectric element 31 and the second piezoelectric element 32 is driven to draw an ellipse (including a circle). When the tip member 33 is pressed against, for example, the peripheral surface 22 of the driven part 2 that is rotatable around the rotation axis 21, the elliptical movement (including the circular movement) of the tip member 33 is converted into the rotational movement of the driven part 2. It is possible to do.

Specifically, for example, when the frequency of the sine wave voltage (the driving frequency of the piezoelectric element) applied to the first piezoelectric element 31 or the second piezoelectric element 32 is small and the rotation speed of the tip member 33 is low, The actuator itself follows the displacement of the tip member 33 due to the urging force of the pressure portion 4, and the tip member 33 does not separate from the peripheral surface 22 of the driven portion 2 and contacts the peripheral surface 22 of the driven portion 2. It is driven back and forth in the state where it is set. Therefore, in this case, the driven portion 2 cannot be rotated.

However, when the frequency of the sine wave voltage applied to the first piezoelectric element 31 or the second piezoelectric element 32 is large and the rotational speed of the tip member 33 is high, the actuator itself may be displaced by the urging force of the pressurizing section 4. 4 (b) to 4 (e), the tip member 33 is temporarily separated from the peripheral surface 22 of the driven part 2 as shown in FIGS.

Accordingly, the tip member 33 is moved in a predetermined direction while the tip member 33 is separated from the peripheral surface 22 of the driven portion 2 (see FIGS. 4B and 4C), and the tip member 33 is moved.
Is moved in the direction opposite to the predetermined direction while the contact is in contact with the peripheral surface 22 of the driven part 2 (FIGS. 4D and 4E).
), The driven part 2 can be rotated.

In FIG. 4, (a) and (e) show a state in which the first piezoelectric element 31 and the second piezoelectric element 32 are both extended, and the chip member 33 is in contact with the peripheral surface 22 of the driven part 2.
(B) shows a state in which the first piezoelectric element 31 is contracted, a second piezoelectric element 32 is expanded, and the chip member 33 is separated from the peripheral surface 22 of the driven part 2, and (c) is a state in which the first piezoelectric element 31 and the second piezoelectric element 31 are separated. The element 32 shrinks together, and the chip member 33 is
2D, the first piezoelectric element 31 is extended and the second piezoelectric element 32 is contracted, but the actuator catches up with the movement of the chip member 33 and the chip member 33 is moved away from the peripheral surface 22 of the driven part 2. Shows the state in contact with.

Returning to FIG. 1, the first and second piezoelectric elements 31, 3
2 has a unique resonance frequency determined by its structure and electrical characteristics. When the frequency of the drive voltage matches the resonance frequency of the first and second piezoelectric elements 31, 32, the impedance of the first and second piezoelectric elements 31, 32 decreases, and the displacement of the first and second piezoelectric elements 31, 32 is reduced. The amount increases. Since the first and second piezoelectric elements 31 and 32 have a small displacement with respect to their outer dimensions, it is desirable to utilize this resonance phenomenon in order to drive at a low voltage.

However, the truss type piezoelectric actuator 1
The truss-type drive unit 3 is assembled by bonding a plurality of displacement members to a press-contact member so that each tip is orthogonal to each other and bonding each base end to a base member. Since the pressure member 4 is pressed against the driven portion 2 by a pressing member 4 such as a spring, even when piezoelectric elements having the same resonance frequency characteristics are used, the driving frequency (the driving voltage supplied to the piezoelectric element The characteristics of the displacement speed of the driven unit 2 with respect to the frequency (hereinafter, referred to as speed characteristics) are different, and the driving frequency at which the driving efficiency is the best (that is, the driving frequency at which the driven unit 2 can be displaced at the maximum speed) is the actuator. Every one is very different. That is, each piezoelectric actuator has a unique speed characteristic, and there is a drive frequency at which the drive efficiency is the best (this drive frequency is referred to as an optimum drive frequency).

The variation in the optimum driving frequency is caused by a combination of factors such as the variation in the resonance frequency of the displacement member alone, the difference in the resonance frequency between the displacement members, the weight of the pressure contact member and the pressure member, and the amount of adhesive applied. The variation range is several tens of kHz.

Therefore, in the present embodiment, as will be described later, a variation range of the optimum driving frequency is checked in advance for each manufacturing lot, and the first piezoelectric element 31 or the second piezoelectric element 31 is changed while changing the driving frequency within the frequency range. By driving the piezoelectric element 32 to actually displace the driven unit 2 and detecting the speed of the driven unit 2 with respect to each drive frequency, the actual speed characteristics of the piezoelectric actuator 1 are obtained, and the optimal driving is performed based on the speed characteristics. The frequency is set to the drive frequency of the drive voltage V output from the drive signal supply unit 6.

That is, the speed characteristics of the piezoelectric actuators of a certain manufacturing lot are different for each piezoelectric actuator as shown in FIG. 5, for example, and the optimal driving frequency f1opt,
Assuming that f2opt, f3opt,... fnopt vary in the range of 78 to 87 [kHz], the optimum driving frequency f of the production lot is determined for each piezoelectric actuator of the production lot.
The drive unit 2 is displaced while changing the drive frequency f in a predetermined step (for example, 0.2 kHz) in a range of 75 to 90 [kHz] in which a margin of 3 kHz is observed on both sides with respect to the variation range of opt. The speed characteristic is calculated by calculating the rotation speed N [rpm] of the driven part 2 at the drive frequency f, and the optimum drive frequency fopt is set based on the speed characteristic.

For example, if the calculated speed characteristic is as shown in FIG. 5, the optimum driving frequency f1opt is set as the driving frequency f of the piezoelectric actuator. Therefore, when the piezoelectric actuator is activated, the driving voltage V having the frequency f1opt is supplied to the first piezoelectric element 31 or the second piezoelectric element 32, and the driven part 2 rotates at a substantially rotational speed N1max [rpm].
Will rotate.

Returning to FIG. 1, the pressing unit 4 presses the tip member 33 of the driving unit 3 against the peripheral surface 22 of the driven unit 2 toward the rotating shaft 21. For example, a pressing unit 4 is provided by a plate spring, a coil spring, an air cylinder, or the like. Become. This pressing force is adjusted to an appropriate value in consideration of the frictional force between the tip member 33 and the peripheral surface of the driven part 2.

The drive signal switching section 5 switches and supplies the drive voltage output from the drive signal supply section 6 to the first piezoelectric element 31 and the second piezoelectric element 32. The drive signal switching unit 5 includes two switches 51 and 52. Switches 51, 5
2 common terminals are one electrode group 31b of the first piezoelectric element 31 and one electrode group 32b of the second piezoelectric element 32, respectively.
(Not shown), one contact of the switches 51 and 52 is connected to the output terminal of the drive signal supply unit 6, and the other contact is grounded. The other electrode groups 31c and 32c of the first and second piezoelectric elements 31 and 32 are grounded.

The switches 51 and 52 are connected so that either one of the common terminals is grounded (that is, when the common terminal of the switch 51 is connected to one contact, the common terminal of the switch 52 is connected to the other contact). Connected, switch 5
When the one common terminal is connected to the other contact, the common terminal of the switch 52 is connected to the one contact) so as to be switched in conjunction with each other, and the switching control is performed by the drive control unit 8.

The drive signal supply section 6 generates a drive voltage (drive signal) for expanding and contracting the first piezoelectric element 31 or the second piezoelectric element 32. The drive signal supply unit 6 includes an oscillator 61 for generating a variable frequency sine wave signal and a power amplifier 62 for amplifying the output of the oscillator 61 to a level at which the first and second piezoelectric elements 31 and 32 can be driven. Since the actually measured speed characteristic of the actuator is an overall characteristic including the driving locus of the tip member 33, when the frequency of the driving voltage V is changed, the tip member 3
Although the driving locus of the tip member 3 also changes, in this embodiment, the driving locus of the chip member 33 does not cause any particular problem as long as the driven portion 2 can be driven at the maximum speed as a whole. The amplitude of the drive voltage V output from the controller is set to a predetermined level, and only the drive frequency is controlled.

The oscillator 61 is, for example, a voltage-controlled oscillator (Vo
ltage Control Oscillator) and Numerically Controlled Oscillator (Numeri
The oscillation frequency of the oscillator 61 is controlled by the drive control unit 8.

The rotation detecting section 7 detects that the driven section 2 makes one rotation, and is constituted by, for example, a position detecting sensor. This position detection sensor 7 is provided on the peripheral surface 22 of the driven portion 2.
Is provided at a predetermined position (a position where the driving section 3 is not pressed against the pressure) and a position facing the peripheral surface 22 of the driven section 2 and on a movement locus of the index plate 71. And a transmission type photointerrupter 72.

When the index plate 71 rotates by the rotation of the driven part 2 and passes through the photo interrupter 72, the passage of the index plate 71 is detected by the photo interrupter 72. This detection signal is input to the drive control unit 8, and the rotational speed N (rpm) of the driven unit 2 is calculated based on the detection signal in a speed calculation unit 82b described later.

The drive control section 8 controls the frequency f of the drive voltage output from the drive signal supply section 6 to an optimum drive frequency fopt at which the rotation speed N of the driven section 2 is maximized.
It controls the direction of rotation of the driven part 2.

The drive control unit 8 includes, for example, an MPU (Micro Pr
Ocessing Unit). Driving direction switching unit 81 in driving control unit 8, optimal driving frequency setting unit 8
2. The drive frequency setting unit 83 and the mode setting unit 84 show functional blocks for executing the control function of the drive control unit 8 described above.

The drive direction switching section 81 controls switching of the switches 51 and 52 of the drive signal switching section 5. For example, when information on the rotation direction of the driven unit 2 is input from the operation unit 9, the drive direction switching unit 81 connects the switches 51 and 52 to predetermined contacts based on the information. For example, FIG.
When the driven part 2 is rotated clockwise in the above, the contacts of the switches 51 and 52 of the drive signal switching part 5 are connected in the relationship shown in FIG.

The optimum drive frequency setting section 82 calculates the speed characteristic of the piezoelectric actuator 1 by actually driving the driven section 2 while changing the drive frequency within the predetermined frequency range as described above. To the optimal drive frequency f
opt is set.

The process of setting the optimum drive frequency fopt is often performed when the assembly is completed in the manufacturing process of the piezoelectric actuator 1 or when the piezoelectric actuator 1 is sold after maintenance. I do it. For this reason, if the drive frequency f of the first and second piezoelectric elements 31 and 32 is set to the optimum drive frequency fopt based on the speed characteristics actually measured at the time of product manufacture, the optimum drive frequency fopt is reset by maintenance. Unless otherwise, the first and second piezoelectric elements 31, 32
Is the optimal driving frequency fopt set previously.
Is held.

The optimum driving frequency setting section 82 includes a frequency scanning section 82a, a speed calculating section 82b, a speed characteristic storing section 82c, and an optimum driving frequency calculating section 82d. Frequency scanning unit 8
2a outputs scanning information of the driving frequency f to the oscillator 61 in order to obtain the speed characteristics. The frequency scanning unit 82a sequentially outputs frequency information within a preset scanning range (in the above example, 75 to 90 [kHz]) at a preset pitch (for example, 0.2 [kHz] described above). This frequency information is also output to the speed characteristic storage unit 82c.

The speed calculating section 82b calculates the rotational speed N of the driven section 2. The speed calculation unit 82b calculates the rotation speed N of the driven unit 2 by counting the detection signal of the index plate 71 output from the position detection sensor 7 within a unit time. The information on the rotation speed N is stored in the speed characteristic storage unit 82c.
Is output to

The speed characteristic storage section 82c stores data of the actually measured speed characteristics of the piezoelectric actuator 1. The speed characteristic storage unit 82c stores the data of the rotation speed N (i) (i = 1, 2,... N) input from the speed calculation unit 82b into the driving frequency f (i) input from the frequency scanning unit 82a.
(I = 1, 2,..., N) is stored in association with the data of the speed characteristic.

The optimum drive frequency calculating section 82d calculates a drive frequency f at which the rotational speed N of the driven portion 2 reaches the maximum rotational speed Nmax by using the speed characteristic data stored in the speed characteristic storage section 82c. The frequency f to the optimal driving frequency f
opt. Specifically, the optimum driving frequency calculation unit 82d
Calculates the maximum rotation speed Nmax by sorting the data of the rotation speed N, and sets the driving frequency f corresponding to the maximum rotation speed Nmax as the optimum driving frequency fopt.

FIG. 6 is a flowchart showing a processing procedure of the optimum driving frequency setting section 82. When the operation unit 9 sets a mode for actually measuring the speed characteristics and setting an optimum driving frequency (hereinafter, this mode is referred to as a driving frequency optimization mode), the optimum driving frequency setting unit 82 sets a flowchart shown in FIG. To set the optimum driving frequency.

First, the drive frequency f (1) of the first sampling is set to the lower limit value of the preset frequency scan range based on the variation range of the optimum drive frequency in the frequency scanning section 82a (# 1). For example, in the above example, f (1) = 7
Set to 5kHz. The drive frequency f (1) is output to the drive signal supply unit 6 and the speed characteristic storage unit 82c, and the drive voltage V having the frequency f (1) is supplied from the drive signal supply unit 6 via the drive signal switching unit 5 to the drive unit. 3 is output.

When the drive voltage V is supplied, the pressure contact portion 33 of the drive section 3 makes an elliptical or circular motion, and the driven section 2 is rotated in a predetermined direction (# 3). The rotation of the driven unit 2 around the rotation axis 21 is detected by the rotation detection unit 7, and the detection signal is input to the drive control unit 82, and the speed calculation unit 82b
Then, the rotation speed N (1) of the driven unit 2 is calculated (# 5).
The calculation result is input to the speed characteristic storage unit 82c, input from the frequency scanning unit 82a, and stored in association with the driving frequency f (1) (# 7).

Subsequently, it is determined whether or not the driving frequency f (1) matches the upper limit value of the frequency scanning range (90 kHz in the above example) (# 9). Since the current drive frequency f (1) is the lower limit value (NO in # 9), the process proceeds to step # 11, where the drive frequency f (2) for the second sampling is set and returns to step # 5. The drive frequency f (2) is set to a value of 75.2 kHz obtained by adding a predetermined frequency pitch Δf (for example, 0.2 kHz) to the previous drive frequency f (1).

Returning to step # 5, the rotation speed N (2) of the driven part 2 with respect to the drive frequency f (2) of the second sampling is calculated in the same manner as in the case of the above-mentioned first sampling, and the speed characteristic is stored. (# 5, # 5)
7). Then, it is determined again whether or not the driving frequency f (2) matches the upper limit value of the frequency scanning range (90 kHz in the above example) (# 9). Since the driving frequency f (2) also does not exceed the upper limit of the frequency scanning range (NO in # 9),
Proceeding to step # 11, the drive frequency f (3) (= f (2) + Δf = 75.4 kHz) for the third sampling is set,
In steps # 5 and # 7, the rotation speed N (3) of the driven unit 2 with respect to the drive frequency f (3) is calculated, and the speed characteristic storage unit 82
c (# 5, # 7).

Hereinafter, while increasing the drive frequency f by Δf in the same manner, each drive frequency f (i) (n = 4,...)
The rotation speed N (i) of the driven unit 2 with respect to n) is calculated, and the calculation result is stored in the speed characteristic storage unit 82c (# 5).
To # 11 loop). When the drive frequency f (n) (= f (n-1) + Δf) of the n-th sampling matches the upper limit value of the frequency scanning range (YES in # 9), the calculation of the speed characteristics is completed, and step # 13 is performed. The driving frequency f corresponding to the maximum rotation speed Nmax is calculated from the speed characteristics,
Further, the driving frequency f is set as the optimum driving frequency fopt (# 15).

In this embodiment, the pitch of the sampling frequency is fixed to Δf, and the speed characteristic is calculated from the beginning with high resolution. However, after measuring the low-resolution speed characteristic, the frequency scanning range is changed. It is also possible to narrow down and actually measure a high-resolution speed characteristic. That is, initially, Δf is set to a large value such as 1 kHz to calculate a rough speed characteristic of the sampling frequency, and it is found from the speed characteristics that the maximum rotation speed Nmax exists near 80 kHz, for example. The scanning range is changed to, for example, 80 ± 1 kHz, and the frequency pitch Δf is set to, for example, 0.2 kHz.
The speed characteristic may be calculated with a small sampling frequency by reducing the value to z.

Alternatively, the drive frequency f at which the maximum rotation speed Nmax is obtained may be calculated by calculating the speed characteristics at a medium high resolution and performing an interpolation operation. This method has an advantage that the time for actually measuring the speed characteristics can be shortened.

In this embodiment, the optimum drive frequency fopt is calculated using the speed characteristics after the speed characteristics are actually measured. However, the rotation speed N (i) with respect to the drive frequency f (i) is calculated. The maximum rotation speed Nmax may be calculated by performing a sorting process every time. According to this method, the drive frequency fmax corresponding to the maximum rotation speed Nmax can be detected before the actual measurement of the speed characteristics is completed, so that the setting process of the optimal drive frequency fopt can be speeded up.

Returning to FIG. 1, the drive frequency setting section 83 sets the drive frequency f of the drive section 3 in the normal drive mode. In the normal drive mode, the drive frequency setting unit 83 replaces the optimum drive frequency fopt calculated by the optimum frequency calculation unit 82d with information on the drive frequency f (VCO 61
To the drive signal supply unit 6. In the drive signal supply unit 6, a sine-wave drive voltage having a frequency fopt is generated by the oscillator 61 based on the control voltage information, and the drive voltage is amplified to a predetermined level by the power amplifier 62 and output to the drive unit 3.

The mode setting section 84 switches between a normal drive mode and a drive frequency optimization mode based on operation information input from the operation section 9. The mode setting information is input to the optimum driving frequency setting unit 82 and the driving frequency setting unit 83. As shown in FIG. 7, when the setting information of the drive frequency optimization mode is input (NO in # 21), the optimum drive frequency setting unit 82 performs the actual measurement processing of the speed characteristics and the calculation processing of the optimum drive frequency fopt (FIG. 7). # 25).
On the other hand, when the setting information of the normal driving mode is input (YES in # 21), the driving frequency setting unit 83 sends the information of the optimum driving frequency fopt set by the optimum driving frequency setting unit 82 to the driving signal supply unit 6. Then, the driving section 3 is driven by the driving signal of the optimum driving frequency fopt (# 23).

As described above, the piezoelectric actuator 1 measures the actual speed characteristics, and based on the speed characteristics, the first piezoelectric element 31 or the second piezoelectric element 3 having the highest driving efficiency.
Since the driving frequency f of 2 is set, the driving efficiency of the actuator can be controlled to the highest state with a simple structure.

FIG. 8 is a diagram showing the configuration of a second embodiment of the piezoelectric actuator according to the present invention.

In the first embodiment, the optimum drive frequency fopt is set by actually measuring the speed characteristics by mode setting. However, in the second embodiment, when the rotation speed N of the drive unit 2 falls below a predetermined threshold value. In this case, the optimum drive frequency fopt is reset by actually measuring the speed characteristics, and the frequency of the drive voltage is corrected.

Therefore, FIG. 8 shows the operation unit 9 shown in FIG.
And the mode setting unit 84 is changed to a speed reduction determining unit 85. The speed reduction determining unit 85 compares the rotation speed N of the driven unit 2 calculated by the speed calculation unit 82b with a predetermined threshold Nr, and determines the rotation speed N
Is decreased to the threshold value Nr or less, the determination result is output to the optimal driving frequency setting unit 82 and the driving frequency setting unit 83. The optimum drive frequency setting unit 82 receives the determination result and performs the above-described calculation process of the speed characteristics and the process of setting the optimum drive frequency fopt. Further, the drive frequency setting unit 83 changes the drive frequency f output to the drive signal supply unit 6 to the optimal drive frequency fopt reset by the optimal drive frequency setting unit 82.
Change to

FIG. 9 is a flowchart showing the control processing of the driving frequency of the piezoelectric actuator according to the second embodiment.

As shown in the figure, when the rotation speed N of the driven part 2 is higher than a predetermined threshold value Nr (N in # 31)
O), when the drive frequency f is not corrected and the rotation speed N falls below the predetermined threshold value Nr (YES in # 31), the optimum drive frequency setting unit 82 measures the speed characteristics and performs the optimum drive based on the speed characteristics. The frequency fopt is calculated (#
33) The drive frequency setting unit 83 corrects the frequency of the drive voltage output from the drive signal supply unit 6 to the newly set optimum drive frequency fopt (# 35).

That is, assuming that the frequency of the drive voltage output from the drive signal supply unit 6 is initially set to the optimum drive frequency f1opt based on the speed characteristic of FIG. 5, the speed characteristic changes to that of FIG. Then, when the rotation speed N of the driven unit 2 decreases to N1 equal to or less than the predetermined threshold value Nr, the speed characteristic by the optimum driving frequency setting unit 82 is actually measured,
The optimum driving frequency f2opt is set based on the speed characteristics. Then, the frequency of the drive voltage output from the drive signal supply unit 6 by the drive frequency setting unit 83 is f1opt
To f2opt.

As a result, the speed characteristic of the actuator changes due to environmental changes such as load fluctuations, ambient temperature, etc., aging, and the like. When the rotation speed N of the driven part 2 drops below a predetermined threshold value Nr, the drive frequency f becomes lower. Since the driving speed is automatically corrected to the optimum driving frequency fopt at which the driving efficiency becomes the best in the current speed characteristics, the actuator can be driven with the driving efficiency being the best possible.

In the second embodiment, the drive frequency f is changed when the drive efficiency drops below a predetermined threshold value by directly detecting the decrease in the rotation speed N of the driven part 2. When a change in environmental conditions such as temperature and humidity affecting the change in the temperature is detected and it is estimated that the environmental conditions have changed to such an extent that the drive efficiency drops below a predetermined threshold, the drive frequency f is changed. Alternatively, the driving frequency f may be changed when either one of the two conditions changes to a state in which the driving efficiency is reduced to a predetermined threshold value or less.

In the second embodiment, when the rotation speed N of the driven part 2 falls below the predetermined threshold value Nr, the speed characteristic is immediately measured and the driving frequency f is corrected to the newly obtained optimum driving frequency fopt. However, during the current driving, the actual measurement of the speed characteristics and the correction processing of the driving frequency are not performed, and the speed characteristics are actually measured only when the power is turned on and the initial setting of the driving frequency f is performed. The optimal driving frequency fopt calculated based on the characteristic may be set as the driving frequency f.

In the description of the above embodiment, the two displacement elements 31 and 32 for driving the tip member 33 are arranged so as to be orthogonal to each other. However, the present invention is not limited to this. For example, the angle may be any angle such as 45 ° or 135 °. Furthermore, the number of displacement elements is 2
The present invention is not limited to this, and three or more driving units may be used to drive three or four degrees of freedom.
Further, as the driving source of the displacement element, not only the piezoelectric element but also another electric or mechanical displacement element such as a magnetostrictive element may be used. In addition, at least one of the plurality of displacement elements may be configured as a electromechanical conversion element such as a piezoelectric element, and the other displacement elements may be configured with elastic members.

In the above embodiment, two first and second
The so-called one-side drive type piezoelectric actuator that switches and drives one of the piezoelectric elements 31 and 32 has been described, but the present invention relates to the first and second piezoelectric elements 31 and 32.
Can be applied to a double-sided drive type piezoelectric actuator that simultaneously drives both. In this case, the speed characteristics when only the first piezoelectric element 31 is driven and the speed characteristics when only the second piezoelectric element 32 is driven are obtained, and the optimum driving frequency fopt is calculated from each speed characteristic. The optimum driving frequency f may be set using both optimum driving frequencies fopt.

The two-sided drive type piezoelectric actuator is more driven than the one-sided drive type piezoelectric actuator.
There is an advantage that the rotation speed of the can be increased.

[0081]

As described above, according to the present invention,
In a truss type piezoelectric actuator, a drive voltage is supplied to a piezoelectric element while changing the frequency within a predetermined frequency range from a drive signal supply unit, and a displacement speed of a driven portion is detected. Since the speed characteristic of the driven part is calculated and the frequency of the drive voltage supplied to the piezoelectric body is set to the frequency at which the displacement speed of the driven part becomes the maximum speed based on the speed characteristic, a simple structure is adopted. Accordingly, the driving of the piezoelectric actuator can be controlled with the highest possible efficiency.

When the displacement speed of the driven part falls below a predetermined threshold, the speed characteristic of the driven part is calculated, and the frequency of the drive voltage supplied to the piezoelectric body is immediately changed based on the speed characteristic. Since the frequency at which the displacement speed of the driving unit is changed to the maximum speed is changed, the driving efficiency of the piezoelectric actuator can be maintained in the best state with a simple structure.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a piezoelectric actuator according to the present invention.

FIG. 2 is a diagram showing a structure of a laminated piezoelectric element used for a piezoelectric actuator according to the present invention.

FIG. 3 is a diagram showing a relationship between an electric field generated between electrodes of a multilayer piezoelectric element and a strain rate of a piezoelectric member between the electrodes.

FIG. 4 is a diagram showing the principle of rotation of the piezoelectric actuator.

FIG. 5 is a diagram showing variations in speed characteristics of a piezoelectric actuator.

FIG. 6 is a flowchart illustrating a processing procedure of an optimum driving frequency.

FIG. 7 is a flowchart illustrating a drive frequency optimization process according to the first embodiment.

FIG. 8 is a diagram showing a configuration of a second embodiment of the piezoelectric actuator according to the present invention.

FIG. 9 is a flowchart illustrating a drive frequency optimization process according to the second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Actuator 2 Driven part 21 Rotary shaft 22 Peripheral surface 3 Drive part (truss type piezoelectric drive part) 31, 32 Stacked piezoelectric element 33 Chip member (pressure contact part) 34 Base member 4 Pressurization part 5 Drive signal switching part 6 Drive Signal supply unit 61 Oscillator 62 Power amplifier 7 Rotation detection unit (component of speed detection unit) 8 Drive control unit (drive frequency setting unit) 81 Drive direction switching unit 82 Optimal drive frequency setting unit 82a Frequency scanning unit (speed characteristic calculation unit) 82b Speed calculation unit (component of speed detection unit and speed characteristic calculation unit) 82c Speed characteristic storage unit (component of speed characteristic calculation unit) 82d Optimal drive frequency calculation unit (frequency detection unit) 83 Drive frequency setting Unit 84 Mode setting unit (mode setting unit) 85 Speed drop judgment unit (speed drop detection unit) 9 Operation unit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshinori Maruyama 2-3-13 Azuchicho, Chuo-ku, Osaka City Inside Osaka International Building Minolta Co., Ltd. No.13 Osaka International Building Minolta Co., Ltd. F-term (reference) 5H680 AA04 AA06 AA08 BB01 BB15 BB16 CC02 DD01 DD23 DD27 DD37 DD53 DD55 DD67 DD73 DD74 DD88 DD95 EE22 EE23 EE24 FF08 FF17 FF25 FF26 FF30 FF33 GG20

Claims (5)

[Claims] 1. A truss-type piezoelectric drive unit comprising a driven unit held so as to be capable of a linear motion or a rotary motion, and a plurality of displacement members at least one of which is made of a piezoelectric material such that the tips are orthogonal to each other. And a pressurizing section for pressing the coupling portion of the displacement member of the truss-type piezoelectric drive section against the driven section, and a drive signal whose voltage changes at a predetermined frequency to the piezoelectric body of the truss-type piezoelectric drive section. A driving signal supply unit for detecting a displacement speed of the driven portion; and a piezoelectric device for changing the driving voltage from the drive signal supply unit while changing the frequency within a predetermined frequency range. A speed characteristic calculating unit that detects the displacement speed of the driven unit by supplying the element to the speed detecting unit and calculates the speed characteristic of the driven unit from the speed characteristics and the frequency of the driving voltage; A frequency detecting unit that detects a frequency of the driving voltage at which the displacement speed of the driven unit becomes a maximum speed based on the speed characteristic calculated by the speed characteristic calculating unit; and the driving supplied from the driving signal supplying unit. A piezoelectric actuator, comprising: a driving frequency setting unit including a driving frequency setting unit that sets a frequency of a voltage to the frequency detected by the frequency detection unit. 2. The piezoelectric actuator according to claim 1, further comprising mode setting means for setting a mode for setting a driving frequency of the driving voltage based on an actually measured speed characteristic, wherein the driving frequency setting means sets the mode setting. When the mode is set by the means, the speed characteristic calculation unit, the frequency detection unit, and the drive frequency setting unit are operated to set the frequency of the drive voltage to a drive frequency at which the driven unit is displaced at a maximum speed. A piezoelectric actuator. 3. The piezoelectric actuator according to claim 1, wherein the drive frequency setting means is configured to set the drive frequency calculating section, the frequency detecting section, and the drive frequency at an initial setting of the drive frequency when the piezoelectric actuator is activated. A piezoelectric actuator, wherein a frequency of the drive voltage is set to a drive frequency at which the driven part is displaced at a maximum speed by operating a setting unit. 4. The piezoelectric actuator according to claim 1, further comprising a speed drop detecting means for detecting that the speed of the driven portion detected by the speed detecting portion has dropped below a predetermined threshold value. The drive frequency setting means operates the speed characteristic calculation section and the frequency detection section when the speed of the driven section falls below a predetermined threshold value by the speed drop detection section, so that the driven section has a maximum speed. A driving frequency of the driving voltage that is displaced by the driving frequency. 5. The piezoelectric actuator according to claim 4, wherein the drive frequency setting section detects the frequency of the drive voltage that causes the driven section to be displaced at a maximum speed by the frequency detection section, immediately after the detection. A frequency of a drive voltage supplied from the drive signal supply unit to the piezoelectric element to a frequency detected by the frequency detection unit.