JPH01298964A - Vibrator type actuator - Google Patents

Abstract

PURPOSE:To simplify and to reduce in size a structure by forming a piezoelectric vibrator in a columnar state, securing a pair of electrodes to both end faces perpendicular to its longitudinal axis, and bringing a moving element into contact with the side face of the columnar vibrator. CONSTITUTION:An ultrasonic motor for a vibrator type actuator is composed of vibrators 1-2 operating as stators, a rotor 3, a columnar shaft 4 for rotatably supporting it, a spring 5 for pressing the rotor 3 to the vibrators 1-2 under a predetermined pressure, vibrator holding frames 6-7 for holding the vibrators 1-2 through a spongelike rubber plate 8, a housing 20, etc. The rotor 3 is driven by the vibrators 1-2 to rotate around the shaft 4. Thus, when the side face of the vibrator 1 is brought into contact with the rotor 3, the spring 5 presses the rotor 3 to the vibrator 2 with the head 4a of the shaft 4 as a fulcrum. This pressing force can be arbitrarily adjusted by clamping nuts 15, 16. Thus, the efficient actuator can be provided.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an actuator suitable for use in precision mechanical devices such as autofocus cameras, and particularly to a vibrator-type actuator that uses a piezoelectric vibrator as an electromechanical transducer. .

(Prior Art and its Problems) Ultrasonic motors have been put into practical use as vibrator-type actuators that use piezoelectric vibrators as electromechanical conversion means for converting electrical energy into mechanical energy.

There are roughly three types of ultrasonic motors. 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.

However, conventionally known ultrasonic motors have complicated mechanical structures such as piezoelectric vibrators and circuits for driving the piezoelectric vibrators, and are therefore difficult to miniaturize and are expensive.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a vibrator type actuator that has a simple mechanical structure such as a piezoelectric vibrator and a simple circuit for driving the piezoelectric vibrator.

(Means for Solving the Problems) Means provided by the present invention to solve the above-mentioned problems are as follows:
A vibrator-type actuator that uses a piezoelectric vibrator to convert electrical energy into mechanical energy to displace a moving element, wherein the piezoelectric vibrator includes a ceramic piezoelectric body formed in a cylindrical shape, and a longitudinal axis of the piezoelectric body. The piezoelectric vibrator includes a pair of electrodes fixed to both end surfaces perpendicular to the axis, and the moving element is in contact with a cylindrical side surface of the piezoelectric vibrator.

(Function) The vibrator type actuator of the present invention belongs to the complex resonance type of the three types mentioned above, and the piezoelectric vibrator used in this actuator is made of cylindrical ceramic.

It has already been reported that the vibration of a cylindrical vibrator can be considered as a two-dimensional combination of longitudinal vibration and cross-sectional spreading vibration. The length of the cylindrical oscillator is ρ, the density is P, and the Young's modulus is E.
Then, the resonant angular frequency ω of longitudinal vibration in that direction is −πE ωj−ρp (1) If the radius of the cylindrical oscillator is r and Poisson's ratio is δ, the resonant angular frequency ω in the radial direction is, ω , −−7 Samurai Towa+ (2) is given by. However, ζ is the root of the following Bessel function J.

ζJ, (ζ) − (1 − δ) Jl (ζ) −〇 (3)
Generally, the equation giving the resonance angular frequency in the case of an isotropic vibrating body is given by the following equation.

ω' (1-3μ2-2μ3) -ω4 (1-μ2) (ω,'
−t ω, ′ ω 2) + ω2 (ω,
2 ωb 2 +ω, 2 ωe20ωC′ω,′)−ω
2ωb26) e2=O(4) The basic formula for the three-dimensional coupled vibration of the cylinder is obtained as ωa: ωJ1 ωb: ωrl ω・−ω・ (5) in equation (4).

(ω2-"2"Lω, 2) 1+σ 1ω2 (ωJ2+ω, 2)Satω, 2ωr2)=O(
6) In equation (6), the second term becomes ω 4 (1−η 2 ) −ω 2 (ω
O 2 + ω ・ 2 ) 10 ω, ′ω, ′=
O(7), and ω such that the apparent coupling coefficient is η.

It matches the expression of the two-dimensional combination of and ω. When driving a piezoelectric ceramic polarized in the length direction, the vibration ω1=−hi(a1% (a)1−σ obtained from the first term) is not observed.

Figure 4 shows the results of calculating the first resonant frequency fl and the second resonant angular frequency f2 using equation (7) when changing ρ for the same material and using materials with different constants. As can be seen, the experimental value and the theoretical value of the coupled resonant angular frequency of the cylindrical resonator are in relatively good agreement, although they contain some errors.

When an alternating current voltage having the above-mentioned coupled resonance angular frequency is applied to a cylindrical vibrator polarized in the length direction, vibrational displacement occurs on the cylindrical side surface of the vibrator. Figure 5 shows the diameter D (D=2r>
is 1011, and the length g is 10111. A cylindrical piezoelectric vibrator 1 is formed by attaching electrodes 1b and 1c to a cylindrical ceramic piezoelectric body (91C material manufactured by TDK) la having a length g of 10111, and an alternating current having a first resonance frequency fl to this vibrator. When a voltage is applied, the vibrator 1
FIG. 2 is a diagram showing the state of displacement observed on the cylindrical side surface of.

(However, in the figure, the electrode 1b and IC are drawn to have a certain thickness, but in reality, the electrodes are so thin that they can be ignored compared to the length of the piezoelectric body. The same is true in other figures.) 5
Figure 5(a) is a side view of the cylindrical vibrator 1, Figure 5(b) is a perspective view of the vibrator 1, and Figure 5(C) is the vibrator 1 viewed from the direction of arrow A in Figure 5(a). A diagram showing the displacement when looking at
FIG. 5(d) shows the vibrator 1 from the direction of arrow B in FIG. 5(a).
It is a figure which shows the displacement when looking.

In these figures, the direction of the arrow marked on or near the surface of the piezoelectric body 1a indicates the direction of displacement when excited at the frequency f1 in Figure 4, and the length of the arrow indicates the strength of the displacement at that time. (The same applies to FIGS. 6, 7, and 8.) In FIG. 6(a), electrodes 21b and 21c are attached to a cylindrical piezoelectric body 21a with D = 10+m and ρ = 7.31mm. A side view of the cylindrical piezoelectric vibrator 21, (b) is the vibrator 2.
FIG. 1 is a perspective view of FIG. 1, and FIG. Also, Fig. 7(a) shows D
A side view of a cylindrical vibrator 22 formed by attaching electrodes 22b and 22c to a cylindrical piezoelectric body 22a with = 10+m and ρ = 5. Figure (b) is a perspective view of the vibrator 22, and figure (c) 2 is a diagram showing the displacement on the cylindrical side surface of the vibrator 22. FIG. The material of the piezoelectric bodies 21a and 22a in FIGS. 6 and 7 is the same as that of 1a in FIG. 5.

As can be seen from FIG. 5, a strong unidirectional displacement occurs in the vibrator whose diameter and length ρ are equal. Further, in a portion where the displacement in the longitudinal direction is large, the displacement in the circumferential direction is small, and conversely, in a portion where the displacement in the longitudinal direction is small, the displacement in the circumferential direction is large.

In the present invention, 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 displacement in the longitudinal direction is supported by the fixed part. A highly efficient actuator has been realized.

FIG. 8(a) shows a cylindrical vibrator 23 in which a part of the cylindrical side surface is cut off by a plane parallel to the longitudinal axis to form a flat surface.
FIG. 2B is a side view showing the vibrator 23. FIG. Moreover, FIGS. 8(c), 8(d), and 8(e) are diagrams showing the displacement of the vibrator 23 viewed from the directions of arrows A, B, and C in FIG. 8(a).

The vibrator 23 is obtained by cutting out a part of the cylindrical side surface of the vibrator 1 shown in FIG.
This is the same as vibrator 1 in the figure. As is clear from FIG. 8(e), when a part of the cylindrical side surface of the cylindrical vibrator is made into a flat surface, the displacement in the longitudinal direction is small in the flat view. In order to hold the child in the housing, a flat surface may be formed on the cylindrical side surface of the vibrator, and the flat surface may be brought into contact with the housing.

Although FIG. 8 shows a vibrator in which a flat surface is formed at one location, a similar displacement is observed in a vibrator in which flat surfaces are formed at two locations symmetrically about the longitudinal axis.

Note that the polarization direction of the vibrators shown in FIGS. 5 to 8 coincides with the length direction of each vibrator.

(Example) Next, the present invention will be explained in more detail with reference to Examples.

FIG. 1(a) is a sectional view showing a first embodiment of the present invention, and FIG. 1(b) is a plan view thereof. The transducer type actuator in this embodiment is an ultrasonic motor, and the transducers 1, 2, . . . act as stators. Rotor 3゜Cylindrical shaft body 4 that rotatably supports the rotor 3. A spring 5 that presses the rotor 3 against the vibrators 1 and 2 with a predetermined pressure. Vibrator holding frames 6 and 7 that hold the vibrators 1 and 2, respectively, via a sponge-like rubber plate 8. External screws 9 for screwing the housing 20 (corresponding to the aforementioned fixing member) and the vibrator holding frames 6 and 7 to the housing 20
and 10. Nut 15°1 that fixes the shaft body 4 to the housing 20
It consists of 6. The rotor 3 corresponds to the aforementioned moving element, and is driven by the vibrator 1.2 to rotate around the shaft body 4.

The vibrator 1 is a cylindrical ceramic piezoelectric vibrator shown in FIG. 5, and the vibrator 2 is also the same as the vibrator l. The vibrators 1 and 2 are arranged at equal distances from the rotation center of the rotor 3, that is, from the axis of the shaft body 4.

These FA movers 1 and 2 are connected to the rotor 3 at the cylindrical side surface of the part where the displacement in the length direction is greatest when an AC voltage is applied.
The rubber plate 8
Then, the vibrator 1.2 is brought into contact with the rotor 3 such that the direction of displacement of the surface of the vibrator 1.2 in contact with the rotor 3 is as shown in FIG. 1(b).

For example, if the side surface of the vibrator 1 shown by arrow A in FIG. 5 is brought into contact with the rotor 3, the side surface of the vibrator 2 shown by arrow A or C in FIG. , Figure 1 (
As shown in b), align the displacement directions of the vibrators 1 and 2. The spring 5 presses the rotor 3 against the vibrator 2 using the head 4a of the shaft body 4 as a fulcrum. The pressing force (pressing force) by the spring 5 can be arbitrarily adjusted by loosening the nut 15.16, moving the shaft body 4 up or down, and then tightening the nut 15.16 again.

FIG. 9 is a characteristic diagram showing the relationship between input voltage and rotor rotational speed in the embodiment of FIG. 1. In this figure, the rotor 3 is
As is clear from this figure, the characteristics are shown when the vibrator 1.2 is pressed against the vibrator 1.2 with a force of 38 g and 627 g, and an alternating current of H2 is applied to the vibrator 1.2 at 132.4. In the embodiment, the rotor 3 rotates smoothly and at high speed.

FIG. 10 is a characteristic diagram showing the relationship between the input voltage and the stall torque in the embodiment shown in FIG. 1, using the pressing force of the rotor 3 as a parameter. Rotor 3 to vibrator 1.2 1.
3 with Q and the input voltage is set to 35V pp, the stall torque is 300g-■, which is a relatively large value.

In the embodiment shown in FIG. 1, if an alternating current voltage of frequency f is continuously applied to the vibrator 1.2, the rotor 3 rotates continuously.

On the other hand, as shown in FIG. 11, if the AC voltage with the frequency f is applied in a burst manner for a time T1, and the voltage becomes 0 in the next time 1゛2, the rotor 3 will step in each burst. Rotate. That is, the embodiment of FIG. 1 can also be operated as a stepping motor. The angle at which the rotor 3 rotates per burst is proportional to the wave number of the AC voltage within one burst, and therefore the time TI of one burst is is proportional to. It was experimentally confirmed that the wave number per burst and the rotation angle are exactly proportional.

In the embodiment shown in FIG. 1, the rotor 3 is rotatably supported by the shaft 4, but the rotor 3 is fixed to the shaft 4, and the shaft 4 is rotatably supported by the housing 20. The present invention can also be implemented with a structure such as that shown in FIG. The shaft body 4 rotates together with the rotor 3! In the case of R construction, it is preferable that the shaft body 4 is supported by the housing 20 via a bearing.

In addition, in the embodiment shown in FIG. 1, the rotor 3 is pressed against the vibrator 1.2 by a spring 5, but this spring 5 is not essential. If they are in pressure contact with each other, the moving element can be moved by displacement in the longitudinal direction of the vibrator, so instead of the spring 5, a concentric disk-shaped weight may be placed on the rotor 3. However, another spring may be provided below the vibrator 1.2, and the spring may press the vibrators 1 and 2 from bottom to top to bring the rotor 3 and the vibrator 1.2 into pressure contact.

FIGS. 2(a), 2(b), and 2(C) are a plan view, a front view, and a side view, respectively, of a second embodiment of the present invention.

The vibrator type actuator of this embodiment has a movable element 13 sandwiched between vibrators 1 and 2, which are the same as in the embodiment of FIG. In the vibrator type actuator shown in this figure, the mover 13 is
) move up and down in parallel as shown with arrows. In order to press the vibrators 1 and 2 against the movable element 13, an elastic body such as a spring may be used as in the embodiment shown in FIG.

FIG. 3 is a conceptual diagram showing a third embodiment of the present invention. The vibrator type actuator of this embodiment is an ultrasonic motor.In the vibrator 11 used in the embodiment shown in the figure, the electrodes fixed to one end surface of the columnar piezoelectric body 1a are electrically separated from each other. consisting of electrodes 1bA and 1b,
The vibrator 11 has the same structure as the vibrator 1 shown in FIG. 5, except that one of the electrodes of the -pair is divided into two. In the embodiment shown in FIG.
8 is provided to switch the output voltage of the AC power supply 12 to the terminal P or Q. The direction of displacement in the vibrator 11 is opposite between when applying an AC voltage from the terminal P to the electrode 1b^ and when applying an AC voltage from the terminal Q to the electrode lbe. The rotor 14 is pressed against the cylindrical side surface of the vibrator 11, and rotates in the direction of displacement of the vibrator 11 at the contact surface with the vibrator 11. Therefore, the rotation direction of the rotor 14 can be arbitrarily selected by switching the switch 18.

(Effects of the Invention) As explained above in detail, according to the present invention, the mechanical structure of the piezoelectric vibrator etc. is simple, and the AC voltage applied to the piezoelectric vibrator can be applied to a single phase, so that the piezoelectric vibrator can be driven. A vibrator type actuator with a simple circuit can be provided. In addition, by dividing only one of the pair of electrodes of the cylindrical piezoelectric vibrator into two, and arbitrarily switching and applying the alternating current voltage to either one of the two divided electrodes,
The vibrator type actuator of the present invention, in which the moving direction of the movable element can be arbitrarily selected, has a simple structure, has excellent reliability, and can be easily manufactured at low cost. Another advantage of the actuator of the present invention is that it can be operated at high speed and high torque with low power.

[Brief explanation of the drawing]

FIG. 1(a) is a sectional view showing a first embodiment of the present invention, FIG. 1(b) is a plan view of the first embodiment, and FIG. 2(a)
, (b) and (C) are a plan view, front view, and side view showing the second embodiment of the present invention, FIG. 3 is a conceptual diagram showing the third embodiment of the present invention, and FIG. 4 is a cylinder. 5 to 8 are diagrams showing examples of cylindrical oscillators and displacement situations on the cylindrical side surfaces of these cylindrical oscillators. A characteristic diagram showing the relationship between input voltage and rotor rotational speed in the embodiment, FIG. 10 is a characteristic diagram showing the relationship between input voltage and stall torque in the embodiment shown in FIG. 1, and FIG. 11 is an example of burst AC voltage. FIG. 1, 2, 11.21.22.23... Cylindrical piezoelectric vibrator, 3.14. ...Rotor, 4...Shaft body, 5.
...Spring, 6.7... Vibrator holding frame, 8...
Sponge-like rubber plate, 9.10... male screw, 12...
AC power supply, 13... mover, 15, 16... nut, 18... switch.

Claims (7)

[Claims] 1. In a vibrator type actuator that uses a piezoelectric vibrator to convert electrical energy into mechanical energy and displace a moving element, the piezoelectric vibrator comprises:
It consists of a ceramic piezoelectric body formed into a cylindrical shape and a pair of electrodes fixed to both end faces perpendicular to the longitudinal axis of the piezoelectric body. A vibrator type actuator characterized by: 2. Claim 1, further comprising means for pressing the cylindrical side surface of the piezoelectric vibrator and the moving element into pressure contact with each other.
The vibrator type actuator described. 3. A claim characterized in that the mover has a disk shape, a shaft is coaxially fixed to the disk-shaped mover, and the shaft is rotatably supported by a fixed member by a bearing. The vibrator type actuator according to item 1 or 2. 4. One of the pair of electrodes is composed of an electrode A and an electrode B that are electrically separated from each other, and a switch is provided to switch and supply the electrical energy to either the electrode A or the electrode B. The vibrator type actuator according to claim 1, 2 or 3, characterized in that: 5. The vibrator type actuator according to claim 1, characterized in that a plurality of said piezoelectric vibrators are provided. 6. A part of the cylindrical side surface of the piezoelectric vibrator is cut off by a plane parallel to the longitudinal axis to form a flat surface, and when the flat surface contacts the fixing member, the piezoelectric vibrator is fixed. A vibrator-type actuator, characterized in that the piezoelectric vibrator is supported by a member, and the piezoelectric vibrator is in contact with the movable element at a position of about 90 degrees in a circumferential direction with respect to the longitudinal axis. 7. 7. The vibrator type actuator according to claim 6, wherein the flat surface is provided at two locations symmetrical with respect to the longitudinal axis.