JPH05336763A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To provide an ultrasonic motor which has a high driving efficiency and in which an operation is stabilized by increasing a driving electrode area of a piezoelectric element. CONSTITUTION:A common electrode corresponding to 1/2 of an elastic traveling wave to be excited is mounted at a piezoelectric element 2. A common electrode corresponding to 1/4 of the traveling wave to be excited and a vibration detecting electrode are mounted at the element 2. Thus, since a driving electrode area of the element 2 can be increased, a driving efficiency of an ultrasonic motor can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an ultrasonic motor which uses elastic vibration excited by a piezoelectric body as a driving force.

[0002]

2. Description of the Related Art In recent years, attention has been paid to an ultrasonic motor which excites a vibrating body composed of a piezoelectric body such as a piezoelectric ceramic and uses the vibrating body as a driving force.

A conventional ultrasonic motor will be described below with reference to the drawings. FIG. 11 is a perspective view of a disk type ultrasonic motor, in which the piezoelectric body 2 is bonded to one of the main surfaces of the elastic substrate 1 to form the vibrating body 3. Further, the protrusion 1a is provided on the other main surface of the elastic substrate 1. Reference numeral 4 is an elastic body, and 5 is a wear-resistant friction material, which are bonded to each other to form the moving body 6. The moving body 6 is in pressure contact with the vibrating body 3 via the friction material 5. When an electric field is applied to the piezoelectric body 2, a traveling wave of bending vibration is excited in the circumferential direction of the vibrating body 3, and the moving body 6 is driven by a frictional force.

FIG. 12 shows an example of the electrode structure of the piezoelectric body 2 in the disc type ultrasonic motor.
It is configured to excite bending vibration of waves. In the figure, hatched A ₀ and B ₀ are electrode groups each including a small region corresponding to a half wavelength. C ₀ is an electrode having a quarter wavelength, and D ₀ is an electrode having a length of 3/4 wavelength. Therefore,
The electrode group of A _{0 and} the electrode group of B ₀ have a phase difference of a quarter wavelength (= 90 degrees) with each other. Further, the electrode group A ₀ ,
Adjacent small electrode portions in B ₀ are polarized in the thickness direction opposite to each other. The bonding surface of the piezoelectric body 2 with the elastic substrate 1 is the surface opposite to the surface shown in the figure, and the electrode is a solid electrode. At the time of use, they are short-circuited and used as indicated by the diagonal lines in the figure.

If a voltage V ₁ represented by (Equation 1) and a voltage V ₂ represented by (Equation 2) are applied to the electrode groups A ₀ and B ₀ , respectively,

[0006]

[Equation 1]

[0007]

[Equation 2]

However, V ₀ is the instantaneous value of the voltage, ω is the angular frequency, and t is the time. A traveling wave of bending vibration, which is expressed by (Equation 3) and progresses in the circumferential direction, is excited in the vibrating body 3.

[0009]

[Equation 3]

Where ξ is the amplitude of bending vibration, ξ ₀ is the instantaneous value of amplitude of bending vibration, k is the wave number, λ is the wavelength, and x is the position.

In FIG. 13, a point A on the surface of the vibrating body 3 excites a traveling wave to make an elliptic motion of a long axis 2w and a short axis 2u, and a moving body 6 placed under pressure on the vibrating body 3 is installed. By contacting in the vicinity of the vertex P of the ellipse, the frictional force causes the wave to move in the direction opposite to the traveling direction of the wave at a speed v represented by (Equation 4).

[0012]

[Equation 4]

[0013]

In order to excite the elastic traveling wave in the vibrating body, the drive electrode is installed on the piezoelectric body constituting the vibrating body so that a plurality of standing waves can be excited. However, in the drive electrode configuration as shown in FIG. 12 described in the conventional example,
Since two non-driving electrodes, that is, an electrode C ₀ having a length corresponding to a quarter wavelength of the standing wave and an electrode D _{0 having} a length corresponding to a quarter wavelength, are installed, There is a problem that the output of the motor is small because the electrodes are not used for driving. This problem was a major drawback, especially when the ultrasonic motor became smaller.

Further, when the admittance frequency characteristics are the same between the drive electrodes of the piezoelectric body, if an alternating voltage having the same amplitude and a phase difference of 90 degrees with respect to time is applied to the drive electrodes, a traveling wave is stably generated in the vibrating body. Can be excited. However, when the lead wire is connected to the common electrode, the resonance frequency or the resonance frequency between the drive electrodes may be affected by the mass of the solder or the mass of the lead wire at the connection portion between the common electrode and the lead wire depending on the connection position. Even if an AC voltage having different resonance resistance and the same amplitude but different phase by 90 degrees with respect to time is applied to the drive electrode, a standing wave component is superimposed on the traveling wave excited in the vibrating body, which causes the operation of the ultrasonic motor to fail. It also had the problem of becoming stable.

On the other hand, in order to detect the vibration excited on the vibrating body, a sensor must be installed on the vibrating body, the moving body, or outside, or a part of the piezoelectric body constituting the vibrating body must be used as the sensor. I won't. However, when the vibration sensor is installed on the vibrating body, the moving body, or the outside, there is a problem that the number of parts constituting the motor and the cost increase.

When a part of the piezoelectric material forming the vibrating body is used as a sensor, the electrode C ₀ or the electrode D ₀ can be used as a vibration sensor when the driving electrode structure shown in FIG. 12 is used. However, there is a problem that the electrode having a length corresponding to one wavelength is not used for driving.

Furthermore, depending on the position where the lead wire is connected to the common electrode and the sensor electrode, the influence of the mass of the connecting portion between the common electrode and the lead wire, the mass of the connecting portion between the sensor electrode and the lead wire, the mass of the lead wire, and the like. Therefore, even if the resonance frequency and the resonance resistance are different between the drive electrodes and an AC voltage having the same amplitude and a temporal phase difference of 90 degrees is applied to the drive electrodes, unnecessary vibration is excited in the vibrating body, or There is also a problem in that a drive control circuit that takes into consideration the difference in resonance frequency and resonance resistance in the above is required.

An object of the present invention is to solve the above problems and to provide an ultrasonic motor which has a large driving electrode area and thus has a high driving efficiency and a stable operation.

[0019]

In order to solve the above problems, the ultrasonic motor of the present invention is provided with an electrode corresponding to a half wavelength of an elastic traveling wave excited in a piezoelectric body, and the electrode is common. In addition to having a structure acting as an electrode, the lead wire connection position of the common electrode has a similar positional relationship to a plurality of standing waves forming an elastic traveling wave to be excited. There is.

Further, a common electrode corresponding to a quarter wavelength of the elastic traveling wave and a vibration detection electrode corresponding to a quarter wavelength are installed on the piezoelectric body, and each electrode is a common electrode and a vibration detection electrode. In addition, the lead wire connection position of the common electrode and the connection position of the vibration detection electrode and the lead wire are respectively different from each other with respect to a plurality of standing waves forming the elastic traveling wave to be excited. It has a structure having a similar positional relationship.

[0021]

Since the driving electrode area of the piezoelectric body can be made large, the driving efficiency of the ultrasonic motor is increased and stable operation can be obtained.

[0022]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 (a) is a plan view of the first surface of the piezoelectric body of the disk type ultrasonic motor, and FIG. 1 (b) is a plan view of the second surface of the piezoelectric body shown in FIG. 1 (a). It is a figure, and the bending vibration of the radial direction primary and the circumferential direction tertiary is excited to the disk-shaped vibrating body.

In FIG. 1B, on the second surface of the piezoelectric body 2, electrodes D and E having a phase difference corresponding to a quarter wavelength of the traveling wave relative to each other and 2 of the traveling wave are provided. An electrode F corresponding to one-half wavelength is configured. In FIG. 1A, on the first surface of the piezoelectric body 2, electrode groups A and B having a phase difference corresponding to a quarter wavelength of the traveling wave relative to each other and a half are provided.
The electrode C corresponding to the wavelength is configured. The electrode group A includes small electrode portions a ₁ and a ₂ corresponding to a half wavelength of the traveling wave and a small electrode portion a ₃ corresponding to a quarter wavelength of the traveling wave. Similarly, the electrode group B includes small electrode portions b ₁ and b ₂ corresponding to a half wavelength of the traveling wave,
It is composed of a small electrode portion b ₃ corresponding to a quarter wavelength. The electrode groups A and B on the first surface and the electrode C are electrodes D and 2 on the second surface, respectively.
It is configured to correspond to E and F. That is, when FIG. 1A is turned over and overlapped with FIG. 1B, the electrode group A faces the electrode D, the electrode group B faces the electrode E, and the electrode C faces the electrode F, respectively.

When the piezoelectric body 2 is polarized, the second surface is placed on a conductor such as a metal so that the first electrode serves as a common electrode.
The small electrode portions of the electrode groups A and B on the surface and the electrode C are polarized as indicated by the reference numerals shown in FIG. The polarization direction is not limited to this direction, and the electrode C may not be polarized. The piezoelectric body 2 after polarization forms the vibrating body 3 by adhering the first surface to the elastic substrate 1 and electrically connecting the electrode F on the second surface to the elastic substrate 1.

When an electric signal having a phase difference of 90 degrees with respect to time is input to the electrodes D and E of the piezoelectric body 2 having a phase difference of 90 degrees with respect to the position of the piezoelectric body 2, the vibrating body 3 is deflected in the radial direction and in the circumferential direction. Vibration can be excited. Therefore, the electrodes used for driving the vibrating body in the piezoelectric body 2 are the electrodes D and E and the electrode F.
Therefore, only one-half wavelength of the traveling wave is not used for driving.

As described above, according to this embodiment, since the drive electrode area of the piezoelectric body can be made large, it is possible to obtain an ultrasonic motor which has good driving efficiency and stable operation.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows the relationship between the sectional view of the piezoelectric body and the wave excited by the drive electrode of the piezoelectric body.

The piezoelectric body 2 in FIG. 2 shows a cross section of the piezoelectric body 2 in FIG. 1, and the waves α and β are standing waves excited by the drive electrodes D and E, respectively.

FIGS. 3A and 3B show the frequency characteristics of the admittance of the electrodes D and E. FIG. 3A shows the f of the electrode F.
₁ shows the case where the lead wire is connected, and FIG. 3B shows the case where the lead wire is connected at f ₂ .

When the lead wire is connected at f ₁ of the electrode F, the resonance frequency differs between the characteristic Y _D of the electrode _D and the characteristic Y _{E of the} electrode E as shown in FIG. 3 (a). At this time, the piezoelectric body 2
Even if an electric signal having the same amplitude and a phase difference of 90 degrees with respect to time is input to the electrodes D and E, the stable traveling wave cannot be excited in the vibrating body 3. As shown in FIG. 2, the lead wire connection position f ₁ of the electrode F is near the node for the wave α, but near the abdomen for the wave β. This is because the influence of the mass of is different depending on the waves α and β. Therefore, in order to excite a stable traveling wave in the vibrating body 3, a circuit for controlling the electric signals input to the electrodes D and E is required, and the driving circuit becomes complicated.

Next, when the lead wire is connected at f ₂ of the electrode F, as shown in FIG. 3B, the resonance frequency between the characteristic Y _D of the electrode _D and the characteristic Y _{E of the} electrode E is as shown in FIG. Closer than in a). This is because, as shown in FIG. 2, the lead wire connection position f ₂ of the electrode F exists between the abdomen and the node of the vibrations of the waves α and β, and the influence of the mass of the lead wire connection part and the mass of the lead wire. Is substantially the same for the electrodes D and E. At this time, the electrodes D and E of the piezoelectric body 2 have the same amplitude and are 90
A stable traveling wave can be excited by inputting electric signals having different degrees of phase, and the lead wire connection position of the electrode F is f.
_The complicated circuit like the case of ₁ is unnecessary. Even if the lead wire is connected by f ₃ of the electrode F, it is similar to the case of f ₂ .

As described above, by forming the lead wire connection position of the common electrode of the piezoelectric body with the structure of this embodiment, in addition to the effect of the first embodiment, a stable traveling wave can be easily achieved. An ultrasonic motor that can be excited can be realized.

(Third Embodiment) A third embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 shows the relationship between the sectional view of the vibrating body and the wave excited by the drive electrode of the piezoelectric body.

The piezoelectric body 2 in FIG. 4 is a cross section of the piezoelectric body 2 in FIG. 1, and the waves α and β are standing waves excited by the drive electrodes D and E, respectively.

When the lead wire is connected at the position f ₁ 'of the vibrating body 3 in FIG. 4, the lead wire connection position f of the electrode F in FIG.
Similar to ₁ , the influence of the mass of the lead wire connection and the mass of the lead wire on the waves α and β is different, and the frequency characteristics of the admittance of the electrodes D and E are different. However, if the lead wire is connected at the position of f ₂ 'of the vibrating body 3, the electrode F of FIG.
Similar to the lead wire connection position f _{2 of FIG. 2} , the influences of the mass of the lead wire connection portion and the mass of the lead wire on the waves α and β become substantially equal, and the frequency characteristics of the admittance of the electrodes D and E become substantially the same. Even if the lead wire is connected at f ₃ ′ of the electrode F, it is the same as in the case of f ₂ ′.

As described above, even if the connecting position of the common line of the piezoelectric body is the structure of this embodiment, the same effect as that of the second embodiment can be obtained.

(Embodiment 4) A fourth embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 shows the second part of the piezoelectric body of the disc type ultrasonic motor.
FIG. 2 is a plan view of a surface and has an electrode configuration similar to that of FIG.

In FIG. 5, a flexible printed circuit board is used to supply electric power to the drive electrodes. When power is supplied by a lead wire, a step of bundling the lead wires after connecting the electrodes and the lead wires is necessary, but
When a flexible printed circuit board is used, the process of line treatment is unnecessary and the manufacturing process can be reduced.

As described above, by using the flexible printed circuit board for supplying electric power to the drive electrodes, an ultrasonic motor having a small number of manufacturing steps can be realized in addition to the effect of the second embodiment.

(Embodiment 5) A fifth embodiment of the present invention will be described below with reference to the drawings.

FIG. 6A is a plan view of the first surface of the piezoelectric body of the disc type ultrasonic motor, and FIG. 6B is a plan view of the second surface of the piezoelectric body shown in FIG. 6A. It is a figure, and the bending vibration of the radial direction primary and the circumferential direction tertiary is excited to the disk-shaped vibrating body. FIG. 7 shows the relationship between the cross-sectional view of the piezoelectric body and the wave excited by the drive electrode of the piezoelectric body, and FIG. 8 shows the frequency characteristic of the admittance of the electrodes K and L.

In FIG. 6B, on the second surface of the piezoelectric body 2, electrodes K and L having a phase difference corresponding to a quarter wavelength of the traveling wave relative to each other and four of the traveling wave are provided. Electrodes M and N corresponding to one-half wavelength are configured. In FIG. 6A, on the first surface of the piezoelectric body 2, electrode groups G and H having a phase difference positionally corresponding to a quarter wavelength of the traveling wave are provided.
Electrodes I and J corresponding to one-half wavelength are formed. The electrode group G includes small electrode portions g ₁ and g ₂ corresponding to a half wavelength of the traveling wave.
And a small electrode portion g ₃ corresponding to a quarter wavelength. Similarly, the electrode group H includes a small electrode portion h corresponding to a half wavelength of the traveling wave.
₁ and h ₂ and a small electrode portion h ₃ corresponding to a quarter wavelength.
The electrode groups G and H on the first surface and the electrodes I and J are configured corresponding to the electrodes K, L, M, and N on the second surface, respectively. That is,
When FIG. 6 (a) is turned over and overlapped with FIG. 6 (b),
The electrode group G faces the electrode K, the electrode group H faces the electrode L, the electrode I faces the electrode M, and the electrode J faces the electrode N.

When the piezoelectric body 2 is polarized, the second surface is placed on a conductor such as metal so that the first electrode serves as a common electrode.
The small electrode portions of the electrode groups G and H on the surface and the electrodes I and J are shown in FIG.
It is polarized like the sign shown in. The polarization direction is not limited to this direction, and the electrode I may not be polarized. Moreover, the positional relationship between the electrodes I and J is shown in FIG.
It is needless to say that the same effect can be obtained even if the electrode J is formed at the position of the electrode I in FIG. The piezoelectric body 2 after polarization forms the vibrating body 3 by bonding the first surface to the elastic substrate 1 and electrically connecting the electrode M on the second surface to the elastic substrate 1.

The piezoelectric body 2 in FIG. 7 is a section of the piezoelectric body 2 in FIG. 6, and the waves α ′ and β ′ are standing waves excited by the drive electrodes K and L, respectively.

In FIG. 6B, when an electric signal having a 90 ° phase difference with respect to time is input to the electrodes K and L of the piezoelectric body 2 having a 90 ° phase difference with respect to position, a radial primary order is applied to the vibrating body 3. -It is possible to excite third-order bending vibration in the circumferential direction. Therefore, since the electrodes used for driving the vibrating body in the piezoelectric body 2 are the electrodes K and L, and the electrodes M and N are not used as drive electrodes, only the half wavelength of the traveling wave is equivalent. It will not be used for driving.

Further, the lead wire connection position k in FIG.
l, m, and n are all present between the abdomen and the node of the vibration of the waves α ′ and β ′, and the influence of the mass of the lead wire connecting portion and the mass of the lead wire with respect to the waves α ′ and β ′. Since they are substantially equal to each other, as shown in FIG. 8, the resonance frequency becomes substantially equal between the characteristic Y _K of the electrode _K and the characteristic Y _{L of the} electrode L. At this time,
A stable traveling wave can be excited by inputting to the electrodes K and L of the piezoelectric body 2 an electric signal having the same amplitude and a temporal phase difference of 90 degrees.

As described above, according to the present embodiment, since the drive electrode area of the piezoelectric body can be made large, it is possible to obtain an ultrasonic motor having good driving efficiency and stable operation.

(Embodiment 6) A sixth embodiment of the present invention will be described below with reference to the drawings.

FIG. 9 shows the relationship between the sectional view of the vibrating body and the wave excited by the drive electrode of the piezoelectric body.

The piezoelectric body 2 in FIG. 9 is a cross section of the piezoelectric body 2 in FIG. 6, and the waves α ′ and β ′ are standing waves excited by the drive electrodes K and L, respectively.

When the lead wire is connected at the position m'of the vibrating body 3 in FIG. 9, the lead wire connection position m of the electrode M in FIG.
Similarly, the influences of the mass of the lead wire connecting portion and the mass of the lead wire on the waves α ′ and β ′ become equal, and the frequency characteristics of the admittance of the electrodes K and L become substantially equal.

As described above, even if the connecting position of the common line of the piezoelectric body is the structure of this embodiment, the same effect as that of the fifth embodiment can be obtained.

(Embodiment 7) Hereinafter, a seventh embodiment of the present invention will be described with reference to the drawings.

FIG. 10 is a plan view of the second surface of the piezoelectric body of the disk type ultrasonic motor, which has the same electrode configuration as that of FIG. 6 (b).

In FIG. 10, a flexible printed circuit board is used to supply electric power to the drive electrodes. When power is supplied by the lead wire, it is necessary to perform a process such as bundling the lead wires after connecting the electrode and the lead wire, but when using a flexible printed circuit board, the wire processing process is unnecessary. The manufacturing process can be reduced.

As described above, by using the flexible printed circuit board for supplying electric power to the drive electrodes, an ultrasonic motor having a small number of manufacturing steps can be realized in addition to the effects of the fifth embodiment.

In the above embodiment, the disk type ultrasonic motor using the flexural vibration of the primary disk in the radial direction and the tertiary disk in the circumferential direction has been described, but the present invention is also effective in other vibration modes. Of course, the present invention is also effective for an annular ultrasonic motor using flexural vibration of an annulus.

[0062]

EFFECTS OF THE INVENTION By adopting the drive electrode structure of the piezoelectric body as described above, the drive electrode area of the piezoelectric body can be made large, so that an ultrasonic motor having good drive efficiency and stable operation is provided. can do.

[Brief description of drawings]

FIG. 1A is a plan view of a first surface of a piezoelectric body of a disc type ultrasonic motor according to an embodiment of the present invention, and FIG. 1B is a plan view of a second surface of the piezoelectric body.

FIG. 2 is a relationship diagram between a piezoelectric body and a standing wave of an ultrasonic motor according to a second embodiment of the present invention.

FIG. 3A is a frequency characteristic diagram of admittance of a piezoelectric body not implementing the second embodiment, and FIG. 3B is a frequency characteristic diagram of admittance of a piezoelectric body in the second embodiment.

FIG. 4 is a relationship diagram between a piezoelectric body and a standing wave of an ultrasonic motor according to a third embodiment of the present invention.

FIG. 5 is a plan view of a second surface of a piezoelectric body of a disk type ultrasonic motor according to a fourth embodiment of the present invention.

FIG. 6A is a plan view of a first surface of a piezoelectric body of a disk type ultrasonic motor according to a fifth embodiment of the present invention. FIG. 6B is a plan view of a second surface of the same piezoelectric body.

FIG. 7 is a relationship diagram between a piezoelectric body and a standing wave of an ultrasonic motor according to a fifth embodiment.

FIG. 8A is a frequency characteristic diagram of admittance of a piezoelectric body not implementing the fifth embodiment, and FIG. 8B is a frequency characteristic diagram of admittance of a piezoelectric body in the fifth embodiment.

FIG. 9 is a relationship diagram between a piezoelectric body and a standing wave of an ultrasonic motor according to a sixth embodiment of the present invention.

FIG. 10 is a plan view of a second surface of a piezoelectric body of a disk type ultrasonic motor according to a seventh embodiment of the present invention.

FIG. 11 is a cutaway perspective view of a disc type ultrasonic motor.

FIG. 12 is a plan view showing an electrode structure of a piezoelectric body of a disc type ultrasonic motor.

FIG. 13: Principle of operation of ultrasonic motor

[Explanation of symbols]

 1 Elastic Substrate 1a Projection 2 Piezoelectric 3 Vibrating 4 Elastic 5 Friction 6 Moving 7 Flexible Printed Circuit Board

Claims (6)

[Claims] 1. A movement installed in contact with the vibrating body by driving the piezoelectric body with an AC voltage to excite an elastic traveling wave in the vibrating body composed of the piezoelectric body and the elastic body. In a ring-type or disk-type ultrasonic motor for moving a body, a common electrode corresponding to a half wavelength of the elastic traveling wave is installed together with a drive electrode on the piezoelectric body forming the vibrating body. And ultrasonic motor. 2. The ultrasonic motor according to claim 1, wherein the common electrode provided on the piezoelectric body has a structure that acts as a common electrode of the piezoelectric body. 3. The lead wire connection position of the common electrode installed on the piezoelectric body has the same positional relationship with respect to a plurality of standing waves forming the elastic traveling wave to be excited. The ultrasonic motor according to 1. 4. A movement installed in contact with the vibrating body by driving the piezoelectric body with an AC voltage to excite an elastic traveling wave in the vibrating body composed of the piezoelectric body and the elastic body. In a ring-type or disk-type ultrasonic motor for moving a body, a common electrode corresponding to a quarter wavelength of the elastic traveling wave is provided on the piezoelectric body forming the vibrating body together with a drive electrode, and the elastic traveling wave. The ultrasonic motor is characterized in that a vibration detection electrode corresponding to a quarter wavelength is installed. 5. A structure in which a common electrode installed on the piezoelectric body acts as a common electrode of the piezoelectric body, and a vibration detection electrode installed on the piezoelectric body detects vibration excited on the piezoelectric body. The ultrasonic motor according to claim 4, wherein the ultrasonic motor has a structure. 6. The lead wire connection positions of the common electrode and the vibration detection electrode installed on the piezoelectric body have the same positional relationship with each other with respect to a plurality of standing waves forming an elastic traveling wave to be excited. The ultrasonic motor according to claim 4, wherein: