JP2903425B2 - Ultrasonic motor - Google Patents

Description

The present invention relates to a small motor used for office automation equipment and toys, and more particularly to an ultrasonic motor having a large torque for a small rotor diameter.

[Prior art] Compared to conventional electromagnetic motors, ultrasonic motors have features such as being able to obtain high torque at low rotation, having a stop holding force, and having low electromagnetic noise.
It is used for autofocus of cameras and power motors of automobiles. FIG. 4 is a view schematically showing the structure of a conventional ultrasonic motor. In FIG. 4, a rotor 104 rotatably supported at one end of a combined longitudinal-torsional vibrator 103 including a piezoelectric torsional vibrator 101 and a piezoelectric longitudinal vibrator 102 is press-contacted.

FIG. 5 is a perspective view showing the structure of a conventional piezoelectric torsional vibrator 101. In FIG. 5, a plurality of sector-shaped piezoelectric ceramic plates 105 polarized in the direction of a chord are joined in a disk or ring shape so that the directions of polarization are closed.

6 (a) and 6 (b) are explanatory diagrams of the operation principle of the longitudinal-twist type ultrasonic motor. 6 (a) and 6 (b) show the state of the torsional vibration displacement, the lengthwise extension / contraction displacement of the longitudinal-torsion composite vibrator 103, and the rotation state of the rotor. The direction of each displacement is shown in FIGS. 6 (a) and 6 (b).

[Problems to be Solved by the Invention] In the conventional piezoelectric torsional vibrator 101 shown in FIG. 5, since a plurality of sector-shaped piezoelectric ceramic plates 105 are bonded, the assembling process becomes complicated. Further, there is a drawback that the characteristics vary greatly due to adhesion. Also, in general, a cylindrical vibrator is driven at the resonance frequency of torsional vibration because the resonance frequency of torsional vibration does not match the resonance frequency of longitudinal vibration, and the longitudinal vibration is driven in a non-resonant state. Become. Therefore, there is a disadvantage that the vibration amplitude of the longitudinal vibration becomes small and it is difficult to increase the torque of the ultrasonic motor.

Therefore, a technical problem of the present invention is to provide a small-sized ultrasonic motor having a large torque and a small rotor diameter.

Another technical object of the present invention is to provide an inexpensive ultrasonic motor having a small number of components and a low manufacturing cost.

[Means for Solving the Problems] According to the present invention, an interdigital electrode is formed on an outer peripheral surface of a first piezoelectric ceramic hollow cylinder in a direction at 45 ° to a length direction, and the interdigital electrode is used. A torsional vibrator that polarizes and drives the piezoelectric ceramic hollow cylinder, and interdigital electrodes formed in the outer peripheral surface of the second piezoelectric ceramic hollow cylinder in the circumferential direction and the length direction in parallel with each other. A vertical vibrator for polarizing and driving the piezoelectric ceramic hollow cylinder using the same, and a rotatably supported rotor, wherein one end of each of the torsional vibrator and the vertical vibrator is fixed, and a rotor is provided between the other ends. Thus, an ultrasonic motor characterized in that the ultrasonic motor is configured to be in pressure contact with the nip therebetween.

[Operation] In the present invention, the rotor is press-contacted between the other ends of the torsional vibrator having one end fixed and the longitudinal vibrator so as to sandwich the rotor.

Therefore, when the length of the longitudinal vibrator is increased in synchronization with the displacement of the torsional vibration of the torsional vibrator, the rotor is sandwiched between the two vibrators and rotates in the direction of the torsional displacement.

EXAMPLES Hereinafter, the ultrasonic motor of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing a structural example of a longitudinal-torsional vibrator press contact type ultrasonic motor of the present invention.

In FIG. 1, one end of each of a piezoelectric torsional vibrator 7 and a piezoelectric longitudinal vibrator 9 is fixed to fixed bases 11 and 12, respectively, and the other end of each of the piezoelectric vibrator 7 and the piezoelectric vibrator 9 is fixed. The ends are opposed to each other, and the rotor 13 is rotatably supported between these other ends so as to sandwich the rotor 13 therebetween.

FIG. 2 is a schematic view showing the structure of a piezoelectric torsional vibrator used in the ultrasonic motor of FIG.

In FIG. 2, first and second diagonal cross fingers having first and second diagonal electrodes 5a and 6a on the outer peripheral surface of a piezoelectric ceramic hollow cylinder 8 at 45 ° to the length direction of the hollow cylinder are shown. Electrodes 5 and 6 are formed and connected to common electrodes 5b and 6b, respectively, to form two terminals. First and second oblique interdigital electrodes 5,
When the polarization process is performed using 6, the polarization direction becomes a direction perpendicular to the length direction of the first and second oblique electrodes 5a and 6a. When an AC voltage is applied to the first and second oblique interdigital electrodes 5 and 6 in this state, if the polarity of the voltage is the same as the polarity of the voltage at the time of polarization, an elongation distortion occurs in the direction of the polarization, and the voltage is increased. Is opposite to the polarity of the voltage at the time of polarization, contraction vibration occurs in the polarization direction. When an elongation or contraction strain is generated in the polarization direction, a contraction or elongation distortion is generated in a direction perpendicular to the polarization direction.

As a result, torsional displacement occurs in the piezoelectric ceramic hollow cylinder 8.

FIG. 3 is a schematic view showing the structure of the longitudinal vibrator 9 used in the ultrasonic motor of the present invention.

In FIG. 3, first and second cross finger electrodes 3, 4 having first and second peripheral electrodes 3a, 4a are formed on the outer peripheral surface of the piezoelectric ceramic hollow cylinder 10 in a circumferential direction, The first and second peripheral electrodes are a first connection electrode (not shown),
Each is connected to the second connection electrode 4b to form two terminals.

When the polarization process is performed using the first and second cross finger electrodes 3, 4, the polarization direction is changed to the first and second cross finger electrodes 3, 4.
4 is perpendicular to the length direction. When an AC voltage is applied to the interdigital electrode in this state, if the polarity of the voltage is the same as the voltage polarity at the time of polarization, stretching strain occurs in the polarization direction, and the polarity of the voltage is opposite to the polarity of the voltage at the time of polarization. In this case, shrinkage distortion occurs in the polarization direction. As a result, the piezoelectric ceramic hollow cylinder expands and contracts in the length direction.

In FIG. 1, when the length of the vertical vibrator 9 is increased in synchronization with the displacement of the torsional vibration, the rotor 13 is rotated between the two vibrators in the direction of the torsional displacement. In this case, the rotation speed and the torque of the rotor are determined by the magnitude of the vibration amplitude of the torsional vibration and the longitudinal vibration when the driving frequency is constant.

In the ultrasonic motor of the present invention shown in FIG. 1, since the torsional vibration of the torsional vibrator 7 and the torsional vibration of the longitudinal vibrator 9 are independent, each resonance frequency is driven at each resonance frequency. It is possible to increase the vibration amplitude of the torsional vibration and the vibration amplitude of the longitudinal vibration.

The rotation direction of the rotor 13 can be changed by changing one of the phases of the torsional vibration drive voltage and the longitudinal vibration drive voltage by 180 °.

In the above description, as the structure of the piezoelectric vertical vibrator 9, the case where the interdigital electrodes are provided on the outer peripheral surface of the piezoelectric ceramic hollow cylinder in a direction parallel to the circumferential direction has been described. It is also possible to form a piezoelectric vertical vibrator by applying interdigital electrodes in a direction parallel to the length direction of the cylinder, and furthermore, by forming electrodes on almost the entire outer peripheral surface and inner peripheral surface of the piezoelectric ceramic hollow cylinder. A similar effect can be obtained with the piezoelectric longitudinal vibrator thus configured.

[Effects of the Invention] As described above, in the ultrasonic motor of the present invention, the shape of the piezoelectric vibrator for generating the driving force is simple, and it is easy to use the generally used press molding technique. A piezoelectric torsional vibrator and a piezoelectric longitudinal vibrator can be obtained by applying electrode printing, which is also a general technique, to this outer peripheral surface using a piezoelectric ceramic hollow cylinder that can be manufactured. Thus, an ultrasonic motor having less variation in characteristics due to the bonding process and the complicated processing process can be obtained.

Further, in the ultrasonic motor according to the present invention, the resonance frequencies of the piezoelectric torsional vibrator and the piezoelectric longitudinal vibrator can be adjusted independently to be equal to each other, so that the respective vibration amplitudes can be increased. Therefore, an ultrasonic motor having a large torque can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structural example of a longitudinal-torsional vibrator press-contact type ultrasonic motor of the present invention, FIG. 2 is a schematic diagram showing a structure of a piezoelectric torsional vibrator used in the ultrasonic motor of FIG. FIG. 3 is a schematic diagram showing the structure of a longitudinal vibrator 9 used in the ultrasonic motor of the present invention, FIG. 4 is a diagram schematically showing the structure of a conventional ultrasonic motor, and FIG. FIGS. 6A and 6B are diagrams showing a piezoelectric torsional vibrator used in an ultrasonic motor, and FIGS. 6A and 6B are explanatory diagrams of the operation principle of a vertical-torsional ultrasonic motor. In the figure, 3,4... First and second cross finger electrodes, 4b... Second connection electrode, 3a, 4a... First and second peripheral electrodes, 5,6.
.. First and second oblique interdigital electrodes, 5a, 6a... First and second oblique electrodes, 5b, 6b... Common electrode, 7. …… Piezo longitudinal oscillator, 10… Piezoelectric hollow cylinder, 11,12 …… Fixed base, 13 …… Rotor, 101 …… Piezo torsional transducer, 102
…… Piezo longitudinal oscillator, 103 …… Vertical-torsion combined oscillator, 104…
... rotor, 105 ... piezoelectric ceramic plate.

Claims (1)

(57) [Claims] An interdigital electrode is formed on an outer peripheral surface of a first hollow column of a piezoelectric ceramic in a direction at 45 ° to a length direction,
A torsional vibrator that polarizes and drives the piezoelectric ceramic hollow cylinder using the interdigital electrode, and forms an interdigital electrode parallel to the circumferential direction and the length direction on the outer peripheral surface of the second piezoelectric ceramic hollow cylinder. A vertical vibrator that polarizes and drives the piezoelectric ceramic hollow cylinder using the interdigital electrodes,
An ultrasonic motor comprising: a rotatably supported rotor, wherein one end of each of the torsional vibrator and the vertical vibrator is fixed, and the rotor is pressed between the other ends so as to sandwich the rotor.