JP2615953B2 - Ultrasonic motor and its driving method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor and a method of driving the same, and more particularly, to ultrasonically oscillate a piezoelectric vibrator serving as a stator to apply a frictional force to a rotor pressed against the stator. The present invention relates to an ultrasonic motor rotated by a motor and a driving method thereof.

[Conventional technology]

Conventionally, as such an ultrasonic motor, there has been known an ultrasonic motor having a configuration in which a rotor is pressed against an end face of a stator having a vertical one-twist composite piezoelectric vibrator and the rotor is rotated by frictional force. For example, such a motor is as described in JP-A-61-12177.

FIG. 4 is a sectional view of an ultrasonic motor showing an example of such a conventional motor.

As shown in FIG. 4, in this conventional ultrasonic motor, a piezoelectric element 41 for torsional vibration excitation and a piezoelectric element 42 for longitudinal vibration excitation are sandwiched between cylindrical or cylindrical ultrasonic vibrators 43 and 44 and tightened with bolts. And a rotor 45 pressed against the end face of the stator by applying independent AC voltages to the piezoelectric element 41 for torsional vibration excitation and the piezoelectric element 42 for longitudinal vibration excitation, respectively. The elliptical motion is induced in the rotor 45, and the elliptical motion is used to give a rotary motion to the rotor 45.

[Problems to be solved by the invention]

By the way, since the sound speed of the torsional vibration wave is about 60% of the longitudinal vibration wave, it is difficult to make the resonance frequency of the torsional vibration coincide with the resonance frequency of the longitudinal vibration in the stator having the above-described configuration. Accordingly, in the stator having the above-described configuration, if the torsional vibration is driven by resonance, the longitudinal vibration becomes non-resonant drive, and if the longitudinal vibration is driven by resonance, the torsional vibration becomes non-resonant drive.

As is well known, the amplitude obtained in non-resonant driving when driving with the same power is extremely small compared to resonant driving. As a result, the amplitude of the elliptical motion induced on the end face of the stator having the above-described configuration is reduced in either the longitudinal direction or the torsional direction. .

Further, in the stator having the above-described configuration, it is also possible to drive two kinds of vibrations in resonance by applying AC voltages having different frequencies to the piezoelectric element for torsional vibration excitation and the piezoelectric element for longitudinal vibration excitation. However, in this case, since the resonance frequencies are different, there is a disadvantage that the elliptical motion cannot be induced regularly on the end face of the stator, and the rotor cannot be rotated stably.

An object of the present invention is to provide an ultrasonic motor capable of rotating the stator and the rotor with high efficiency and stably, and a driving method thereof.

[Means for solving the problem]

The ultrasonic motor of the present invention is an ultrasonic motor that excites ultrasonic vibration using a vertical one-twist composite piezoelectric vibrator as a stator and rotates a rotor pressed against the stator.
The pressure contact surface of the rotor is a convex surface, and the rotor is bored so that the convex surface forms a spring means in the pressure contact direction.

Also, the ultrasonic motor driving method according to the present invention is the ultrasonic motor driving method for driving an ultrasonic motor, wherein the pressure contact force between the rotor and the stator is adjusted to make contact between the convex surface of the rotor and the stator surface. By changing the area,
The rotor and the stator are driven such that the resonance frequency of the longitudinal vibration of the entire rotor and the stator match the resonance frequency of the torsional vibration.

[Action]

The stator constituting the ultrasonic motor according to the present invention has a torsional vibration half-wave resonance frequency and a longitudinal vibration half-wave resonance frequency different from each other. However, when the rotor is pressed against the stator, the torsional vibration does not restrict the vibration because the pressure-contact boundary between the stator and the rotor is a sliding surface, and the torsional vibration resonance frequency hardly changes. Is a vibration in the direction in which the vibration acts, so that a longitudinal vibration resonance frequency is generated due to the entire configuration including the stator and the rotor. The rotor of the present invention has a pressing surface having a convex surface, and the convex surface is boring so as to have spring properties in the pressing direction.
Accordingly, when the rotor is tightened and pressed against the stator by means such as a screw, the contact area between the rotor convex surface and the stator surface increases due to an increase in the pressing force. This change in the contact area results in a change in the coupling force between the stator and the rotor, and a change in the resonance frequency of the longitudinal vibration. Therefore, by adjusting the tightening force of the rotor and the stator, the longitudinal vibration can be matched with the resonance frequency of the torsional vibration, and the resonance drive can be performed at the same frequency.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of an ultrasonic motor showing one embodiment of the present invention.

As shown in FIG. 1, this embodiment includes a stator 10 and a boring rotor 17 having a convex surface 21 that comes into contact with the stator 10. The stator 10 is constructed by sandwiching a piezoelectric ceramic element 11 for torsional vibration excitation and a piezoelectric ceramic element 12 for longitudinal vibration excitation between two metal blocks 13 and 14, and firmly tightening them with bolts 15 and nuts 16. This torsional vibration excitation piezoelectric ceramic element 11 is formed by laminating circumferentially polarized ceramic plates having an outer diameter of 20 mm, an inner diameter of 8 mm, and a thickness of 0.5 mm, and the upper and lower surfaces of each ceramic plate are metallized, and They are stacked so that the polarities are opposite to each other with the metal sheet sandwiched therebetween. Such thin metal plates are electrically connected in parallel outside. Also, a piezoelectric ceramic element for longitudinal vibration excitation
Reference numeral 12 denotes a laminated ceramic plate having an outer diameter of 20 mm, an inner diameter of 8 mm, and a thickness of 0.5 mm which is polarized in the thickness direction, and has a configuration similar to that of the torsional vibration excitation 11 described above.

On the other hand, a rotor disposed opposite to the stator 10 having the above-described configuration.
In 17, a bearing 18 is inserted and fitted into a bolt 15,
The metal block 13 of the stator 10 is tightened and pressed by the pressing nut 19 and the spacer 20. This rotor
In 17, a pressure contact surface 21 facing the stator 10 is a tapered convex surface, and the inside of the rotor 17 is bored so that the pressure contact surface 21 has a spring property. Therefore, when the rotor 17 is fastened to the stator 10 by the pressing nut 19, the rotor 17 receives the tightening force and the pressing surface 21 is deformed.

FIG. 2 is a sectional view of such a rotor constituting the ultrasonic motor in FIG.

As shown in FIG. 2, when the rotor 17 receives a tightening force indicated by arrows A and B by the pressing nut, the pressing surface 21 is deformed as shown by a broken line.

At this time, since the press contact surface 21 is convex, the contact area increases so as to conform to the surface of the stator 10 as the tightening force increases. As a result, a resonance frequency of the longitudinal vibration of the entire motor is generated by joining the stator 10 and the rotor 17, so that the resonance frequency of the longitudinal vibration can be matched with the resonance frequency of the torsional vibration by adjusting the tightening force. As a result,
Since vertical and torsional vibrations can be driven at the same resonance frequency,
The rotor 17 can rotate with high efficiency.

In addition, since the rotor 17 of the present embodiment has a spring property by itself, it is easy to adjust the tightening force and the resonance frequency of the longitudinal vibration. Further, by boring the rotor 17, rotors having various spring properties can be obtained, so that the resonance frequency of the synthetic vibration can be adjusted by changing the shape and size.

FIG. 3 is a sectional view of a rotor constituting an ultrasonic motor for explaining another embodiment of the present invention.

As shown in FIG. 3, the pressure contact surface 23 of the rotor 22 in this embodiment forms a spherical convex surface, and
Is boring. Even in the case of such a rotor 22, the two resonance frequencies can be matched in the same manner as in the above-described embodiment by changing the tightening force between the rotor 22 and the stator that comes into contact with the press contact surface 23.

〔The invention's effect〕

As described above, the ultrasonic motor and the driving method of the present invention utilize longitudinal vibration in which the resonance frequency is determined by the overall configuration of the motor and torsional vibration resonance which is determined substantially by the stator. By adopting a configuration in which only the resonance frequency is changed by the tightening force of the rotor and the stator,
Since the two resonance frequencies can be easily matched, there is an effect that a highly efficient ultrasonic motor can be realized.

In addition, the present invention has an effect that a small and stable ultrasonic motor and a method of driving the ultrasonic motor can be realized since the coil spring is unnecessary by giving the rotor itself a spring property.

[Brief description of the drawings]

1 is a sectional view of an ultrasonic motor showing one embodiment of the present invention, FIG. 2 is a sectional view of a rotor constituting the ultrasonic motor in FIG. 1, and FIG. 3 is another embodiment of the present invention. FIG. 4 is a cross-sectional view of a rotor constituting an ultrasonic motor for explaining the present invention, and FIG. 4 is a cross-sectional view of an ultrasonic motor showing an example of the related art. 10: stator, 11: piezoelectric ceramic element for torsional vibration excitation, 12: piezoelectric ceramic element for longitudinal vibration excitation, 13, 14
…… Metal block, 15… Bolt, 16 …… Nut, 17,2
2 ... Rotor, 18 ... Bearing, 19 ... Pressing nut, 20 ... Spacer, 21,22 ... Press contact surface.

Continuation of the front page (72) Inventor Takeshi Inoue 5-33-1, Shiba, Minato-ku, Tokyo NEC Corporation (72) Inventor Sadayuki Takahashi 5-33-1, Shiba, Minato-ku, Tokyo NEC Corporation

Claims (2)

(57) [Claims] 1. An ultrasonic motor that excites ultrasonic vibrations by using a longitudinally-twisted composite piezoelectric vibrator as a stator and rotates a rotor pressed against the stator, wherein the pressing surface of the rotor has a convex surface and the convex surface thereof An ultrasonic motor, wherein the rotor is bored such that the surface of the rotor forms a spring means in the pressing direction. 2. A method of driving an ultrasonic motor for driving an ultrasonic motor according to claim 1, wherein a contact area between a convex surface of said rotor and a stator surface is changed by adjusting a pressure contact force between said rotor and said stator. The driving method of the ultrasonic motor, wherein the driving is performed by making the resonance frequency of the longitudinal vibration of the entire rotor and the stator coincide with the resonance frequency of the torsional vibration.