JPH0236773A - Piezoelectric vibrator and vibrator type actuator - Google Patents

Abstract

PURPOSE:To easily and accurately control a vibrating direction by electrically dividing an electrode formed on one end face into two electrodes, and switching the application of a signal to the electrodes. CONSTITUTION:An electrode of one side of a piezoelectric porcelain 1a for forming a vibrator 11 split (into 1bA, 1bB), and the phase of a radial vibration is electrically controlled by selecting the electrode to receive an input signal. An ultrasonic motor is driven with the vibrator 11 as a driven power source to rotate a rotor 13 in contact therewith. The rotor 13 is brought into contact with a section having a larger axial size of a columnar side face of a piezoelectric magnesium 1a, and the output voltage of an AC power source 12 is switched between terminals P, Q by switching a switch 14. Thus, the rotating direction of the rotor 13 in the motor is arbitrarily controlled by switching the switch 14.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a piezoelectric vibrator suitable for use as an electro-mechanical conversion element in a vibrator-type actuator such as an ultrasonic motor, and a piezoelectric vibrator that can be used as a drive source. This invention relates to a vibrator type actuator.

(Prior Art) A vibrator type actuator uses a piezoelectric vibrator as an electromechanical conversion means for converting electrical energy into mechanical energy. Among vibrator-type actuators, ultrasonic motors are being particularly actively developed and have already been put into practical use.

Ultrasonic motors can be divided into three types depending on the vibration form of the piezoelectric vibrator. The first method is called a traveling wave type or mode rotation type, the second method is a standing wave type that uses standing waves, and the third method is called a complex resonance type.

(Problems to be Solved by the Invention) However, all conventionally known ultrasonic motors have complex structures and are expensive.

Furthermore, in the conventional ultrasonic motor, the power supplied to the piezoelectric vibrator must be multiphase in order to control the rotational direction of the motor, and the drive circuit for supplying the power is complicated.

Therefore, an object of the present invention is to provide a piezoelectric vibrator and actuator that can simplify the structure of a vibrator type actuator such as an ultrasonic motor and the drive circuit of the vibrator type actuator, and can easily control the direction of vibration displacement. be.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the piezoelectric vibrator of the present invention includes a columnar piezoelectric ceramic in which @poles are formed on both end faces perpendicular to the polarization axis. The electrode formed on the end face is divided into two electrodes. Further, it includes a columnar piezoelectric ceramic in which electrodes are formed on both end faces perpendicular to the polarization axis, and the electrodes formed on at least one of the end faces are formed only in a part. Furthermore, an actuator is constructed using the vibrational displacement generated on the side surface of the piezoelectric vibrator.

(Function) The present invention has first and second end surfaces perpendicular to the polarization axis,
In the piezoelectric vibrator in which electrodes are formed on the end face,
An electrode formed on at least one end surface is electrically divided into two electrodes.

The direction of the vibration displacement of the vibrator can be controlled by switching the signal application to the divided electrodes. In addition, by forming the electrode on a part of the end face rather than the entire surface, an asymmetrical element is introduced and unidirectional vibration displacement is realized.

Furthermore, by using the vibration displacement that occurs when the piezoelectric vibrator having such a configuration is excited, a simple, highly accurate actuator that can control the vibration direction can be obtained.

(Example) Next, the present invention will be explained in detail.

First, before a detailed explanation of the present invention, the basic principle of the present invention will be explained.

The piezoelectric vibrator of the present invention belongs to a front-tube complex resonance type, and the piezoelectric ceramic has a columnar shape. The coupled resonance (a type of compound resonance) of a piezoelectric vibrator whose piezoelectric ceramic is cylindrical will be described in detail below.

It has already been reported that the vibration of a cylindrical oscillator can be considered as a two-dimensional combination of longitudinal vibration and cross-sectional spreading vibration.0 The length of the cylindrical oscillator is 9, the density is ρ, and Young's modulus is E
Then, the resonant angular frequency ω of longitudinal vibration in that direction is: If the radius of the cylindrical vibrator is r and the Poisson's ratio is σ, then the resonant angular frequency ω in the radial direction is given by: However, ζ is the root of the following Bessel function J.

ζJo(ζ)−(1−δ)Jl(ζ)=O(3) Generally, the resonance angular frequency in an isotropic vibrating body is given by the following equation.

ω'(1-3μ2-2μ') Part 4 (1-μ2) (ω,'+ωb2+ω,2)+ω
2 (ω, 2ωb2+ωb2ω.

+ω. ′ω, 2)−ω12ωb2ω.

=OC! 4) The basic formula for the three-dimensional coupled vibration of a cylinder is obtained as follows in equation (4): ω1=ωJ+ ωb=ω", ω=ωr (5).

It matches the expression of the two-dimensional combination of and ω. When driving a piezoelectric ceramic polarized in the length direction, the vibration obtained from the first term is not observed.

From equation (7), the first and second resonance frequencies are −ω2 (ω
12+ω, 2) 10ωj2ωr2)=O(6) In equation (6), the second term is, however, using the relational expression ω4 (1~η2)−ω2 (ωJ2+ω 2)10ω
2ω, 2=O(7) is given.

P>>1, that is, ω in the limit of r>>A.

is equal to equation (2), and ω2 becomes ω1 such that the apparent coupling coefficient is η, which corresponds to the thickness vibration of a thin disk.

Also, pkuku1, that is, r<<j! In the limit where ω
1 corresponds to equation (1), and ω1 becomes, which corresponds to the radial expansion vibration of an infinitely long cylinder.

Figure 8 shows the results when the diameter and length are changed using the same material.
and the first one using materials (71B and 910) with different constants.
2 at the resonant frequency f1 and the second resonant frequency (9), (10
) The correspondence between calculated values calculated using the formula and actually measured values is shown. Although the error is somewhat large, this is because the above calculation formula is applied to pure elastic vibration or to a vibrator with a small electromechanical coupling coefficient, whereas the electric vibration of the vibrator used in this experiment is It is thought that the error occurred because the mechanical coupling coefficient was as large as 70% or more, and in addition to the elastic vibration, the piezoelectric term could no longer be ignored.

Figure 9 shows the free admittance and phase frequency 'tIl# characteristics of a cylindrical vibrator (FM-71B material).The first resonance and the second resonance correspond to the lowest zero frequency. do. Regarding the vibration mode, the first resonance corresponds to vibration in which the axial and radial vibrations are in antiphase to each other (coupled vibration in antiphase mode), and the second resonance corresponds to the vibration in the axial and radial directions. are in phase with each other (coupled vibration of in-phase modes), and in the case of anti-phase mode, two orthogonal
Since two vibrations are excited with a phase difference of π/2, an elliptical motion is formed on the side surface of the vibrator. Although elliptical motion is also formed in the in-phase mode vibration, the elliptical displacement is expected to be small because the vibration intensity is weaker than the first resonance vibration.

Below, the above-mentioned vibration B will be mathematically studied.

As shown in Figure 10, the coordinates are defined as the diameter of the cylinder a, the length ρ, the radial direction r, and the axial direction 2.0 The displacement in two directions at any mass point within the cylinder is us, Let the displacement in the r direction be U, and JiUs = UIIo-cos ωt
(14) Ur = Uro-c
o s (ωt−φ) (15). Here, U,,,U,. are the respective displacement amplitudes, and ω and φ represent the angular frequency and phase of the ultrasonic vibration.

Also, IJto=A-s inkt ・z
(16) A: axial displacement at z=±1/2, r=o, B: radial displacement at z=o, r=a/2, K,,k,: wavelength constant, Jl: first-order When it vibrates in the anti-phase mode, which is the Be5sel function, it is φ-π/2, so the locus of the mass point is expressed as , and it can be seen that it draws an elliptical motion. Here, φ is set to π/2, but any φ
The locus of the mass point becomes an ellipse.

Now, the degree of coupling between the two vibration components of a cylindrical vibrator is determined by their size ratio and material constant, and vibration displacement also has a correlation with these.

In order to clarify the relationship between the dimension ratio and material constants and displacement distribution, we observed the mechanical displacement distribution on each side using vibrators with different dimension ratios and material constants, and examined the differences. The experimental method was to use a bearing (diameter 1
9+m wide, 5 mm wide) is crimped to the side of the vibrator, and its rotation direction corresponds to the direction of displacement, and the number of rotations of the bearing corresponds to the strength of displacement.

Figure 11 shows the material constants of the vibrator used this time.

The numbers shown here are 10 mA in length, 10 m in diameter,
In this case, all four types of polarization are applied in the axial direction. In addition, all the following explanations are made regarding the vibration mode of the first resonance.

FIG. 12 shows the observed displacement distribution characteristics on the surface of the cylindrical vibrator, where the direction of the arrow represents the direction of rotation of the bearing, and the length represents the strength of rotation. Because non-axisymmetric vibrations are not piezoelectrically excited due to the symmetry of the electrode shape, the axial displacement shows a symmetrical distribution with the 2=0 plane as the boundary. Furthermore, exactly the same displacement distribution was observed for the four types of vibrators. FIG. 13 is a mode diagram of an elliptic displacement format showing the concept of elliptic displacement formation.

It can be seen that this corresponds well to the observation results in Figure 12.

Figure 14 shows the measured relationship between the voltage applied to the vibrator and the rotational speed of the bearing crimped to the side surface of the vibrator.9 rotations indicates that the electromechanical coupling coefficient kss and the piezoelectric constant dss have large values. It can be seen that the vibrators made of materials 71B and 91C are strong, while the vibrators made of materials 71A and 71D, which have smaller values, have weaker rotation, but this is due to the difference in the degree of elastic coupling between longitudinal vibration and radial vibration. This is thought to be due to

Next, in order to examine the relationship with the size ratio (p = length / diameter), the strongest rotational motion was observed when p = 1.
Using the 1B material, the displacement distribution when the dimension ratio p was varied from 0.73 to 0.5 was observed by the method described above. As a result, the displacement distribution is symmetrical with respect to the 2=0 plane, as in the case where p is 1, but as shown in Figure 14, the number of rotations for the same human force is weaker than in the case where p=1. I know it will happen.

From the above results, in order to efficiently form elliptical displacement, the electromechanical coupling coefficient ksx and the piezoelectric constant dos
It is sufficient to select a vibrator with a large dimension ratio of 1.

In a cylindrical piezoelectric vibrator, the cylindrical side surface with a large displacement in the longitudinal direction (axial direction) is brought into contact with the mover, and the cylindrical side surface with a small longitudinal displacement is supported by the fixed part, resulting in an efficient actuator. can be realized.

However, since the piezoelectric vibrator shown in each figure above cannot control the direction of vibration displacement, an actuator that uses this vibrator as a driving force source cannot move the vibrator in any direction. When considering the application as such, it is preferable for the elliptic motion displacement to be unidirectional on the same side.

Therefore, in the piezoelectric vibrator of the present invention, by adopting a structure in which at least one of the electrodes formed on the end face of the columnar piezoelectric ceramic is divided into two parts, the direction of vibration displacement can be easily controlled arbitrarily. I'm trying to make it possible. By providing two divided electrodes in this manner, the direction of vibration displacement in the piezoelectric ceramic can be arbitrarily changed by simply switching and applying alternating current power to electrodes A and B.

Further, in the present invention, by removing a part of the electrode on one side and introducing an asymmetric element, non-axisymmetric radial vibration is excited, and unidirectional vibration displacement is realized on the same side surface.

Fig. 1 is a perspective view of an embodiment of a vibrator in which one electrode is divided into two, and Figs. 2 (a), (b), and (c) are a left side view and a front view of the embodiment in Fig. 1, respectively. Figure and right side view are shown.

In the vibration displacement direction control by dividing one side electrode into two in the present invention, as described above, the direction of the elliptical displacement is determined by the phase relationship between the longitudinal vibration and the radial vibration. That is, the present invention focuses on the fact that if the phase of vibration can be controlled, the direction of elliptical displacement on the side surface of the vibrator can also be controlled.

In the present invention, the electrode on one side of the piezoelectric ceramic 1a constituting the vibrator 11 is divided into two (lbA, lbe), and an input signal is applied! By selecting @, the phase of radial vibration can be electrically controlled. In Figure 1, 1c indicates the electrode on the other side.

FIG. 3 is a vibration mode diagram of coupled vibration of longitudinal vibration and non-axisymmetric vibration. As shown in the figure, when a signal is applied to the electrode 1bA, radial vibration is excited as shown by the dotted line, and when a signal is applied to the electrode 1bs, radial vibration is excited as shown by the solid line.

Since the radial vibration can be phase-shifted by π by switching the electrode to which the signal is applied, the direction of the elliptical displacement can be changed, and the elliptical displacement can be reversed on the same side.

FIG. 4 shows an embodiment in which the present invention is used as an actuator.

The actuator in FIG. 4 is an ultrasonic motor, which uses the piezoelectric vibrator of the embodiment in FIG. 1 as a driving force source, and this piezoelectric vibrator 1
12 is an AC power source, and 14 is a switch having terminals P and Q. The rotor 13 is brought into contact with a portion of the cylindrical side surface of the piezoelectric ceramic 1a that experiences a large vibrational displacement in the axial direction (however, in FIG. 4, the means for bringing the rotor 13 into pressure contact with the piezoelectric ceramic 1a is omitted; (A spring or the like is used as the pressure welding means.) By switching the switch 14, the output voltage of the AC power supply 12 is switched to the terminal P or Q.

As mentioned above, the rotor 1 in the ultrasonic motor shown in FIG.
The rotational direction of 3 can be arbitrarily controlled by switching the switch 14.

In the ultrasonic motor shown in FIG. 4, the drive circuit is made up of only a single-phase AC power supply 12 and a switch 14, and the piezoelectric vibrator 11 itself is composed of a cylindrical piezoelectric ceramic 1a, electrodes 1bA, 1b@, and an IC.
It has an extremely simple configuration.

Next, an example in which part of the electrode is removed will be explained.

Figure 5 schematically shows the observation results of the displacement distribution characteristics on the vibrator surface with a part of the electrode removed.As is clear from Figure 0, the part with large displacement in the axial direction is In areas where the displacement in the direction is small and the displacement is large in the circumferential direction, the displacement in the axial direction is small, showing an asymmetrical displacement distribution with respect to the central axis. The displacement in the axial direction is unidirectional on the same side surface, and since there is a side surface portion where the displacement is small in the axial direction, it can be confirmed that support is easy.

FIG. 6 shows the free admittance and phase frequency characteristics of the vibrator in this example, and it can be seen that resonance cracking occurs at the first resonance point due to the removal of the electrode.

Further, FIG. 7 shows a mode diagram of elliptic motion displacement formation, and it can be seen that it corresponds well to the observation results.

As described above, by removing a portion of the electrode, the symmetry of the electrode is lost, and surfaces with large and small amplitude displacements can be identified.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to provide a piezoelectric vibrator that can extremely simplify the structure of a vibrator type actuator such as an ultrasonic motor and the drive rotation of the vibrator type actuator. . Furthermore, the direction of vibration displacement of the vibrator can be easily controlled.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an embodiment of the present invention, Fig. 2(a)
, (b) and (c) are respectively a left side view, a front view, and a right side view of the embodiment in FIG. 1, and FIG. Fig. 4 is a conceptual diagram of an ultrasonic motor using the embodiment shown in Fig. 1 as a driving force source, Fig. 5 is a displacement distribution characteristic diagram on the surface of a vibrator in another embodiment of the present invention, and Fig. 6 is a diagram showing the embodiment shown in Fig. 5. The frequency characteristic diagram of free admittance and phase in the example, Figure 7 is
The mode diagrams of the elliptic motion displacement configuration in the illustrated embodiment and FIGS. 8 to 14 are diagrams for explaining the basic principle of the present invention,
Fig. 8 is a diagram showing calculated values and actual measured values of the coupled resonance frequency of a cylindrical resonator, Fig. 9 is a diagram showing the frequency characteristics of free admittance and phase, and Fig. 10 is a diagram showing the coordinate system of the cylinder.
Figure 11 is a diagram showing the number of oscillators and material chambers used in the experiment, Figure 12 is a displacement distribution characteristic diagram on the surface of a cylindrical oscillator, Figure 13 is a mode diagram of elliptic motion displacement formation, and Figure 14 is FIG. 3 is a diagram showing the relationship between applied voltage and bearing rotation speed. la--piezoelectric ceramic, lbA, lbs, 1c...electrode, 11...vibrator, 12...AC power supply, 13...
・Rotor, 14...Switch.

Claims (7)

[Claims] (1) A piezoelectric device comprising a columnar piezoelectric ceramic having electrodes formed on both end faces perpendicular to the polarization axis, and characterized in that the electrode formed on at least one end face is divided into two electrodes. vibrator. (2) A columnar piezoelectric ceramic is provided in which an electrode divided into two is formed on at least one of both end surfaces perpendicular to the polarization axis, and an alternating current signal having a frequency equal to the resonant frequency of the piezoelectric ceramic is applied. A vibrator-type actuator characterized by using vibrational displacement that sometimes occurs on the side. (3) A piezoelectric device comprising a columnar piezoelectric ceramic in which electrodes are formed on both end faces perpendicular to the polarization axis, and the electrode formed on at least one of the end faces is formed only on a part of the piezoelectric ceramic. vibrator. (4) A columnar piezoelectric ceramic in which an electrode is formed on at least a part of one of both end surfaces perpendicular to the polarization axis, and when an alternating current signal of a frequency equal to the resonance frequency of the piezoelectric ceramic is applied, the side surface A vibrator-type actuator characterized in that it uses vibrational displacement caused by. (5) The piezoelectric vibrator according to claim 1 or 3, wherein the piezoelectric ceramic has a cylindrical shape, and the polarization axis is parallel to the axis of the piezoelectric ceramic. (6) The two divided electrodes formed on the one end surface have semicircular shapes of the same size, and the electrodes are formed on the entire surface of the other end surface. The piezoelectric vibrator according to claim 1. (7) The piezoelectric vibrator according to claim 1 or 3, wherein the piezoelectric ceramic has a large electromechanical coupling coefficient and a large piezoelectric constant, and has substantially equal length and diameter.