JPH0251378A - Ultrasonic motor and driving method thereof - Google Patents

Abstract

PURPOSE:To improve efficiency, and to enhance practicability by utilizing longitudinal resonance and torsional resonance, resonance frequency of which is determined by not only a stator body but also the whole motor including a sub-stator. CONSTITUTION:A torsional-vibration piezoelectric ceramic element 3 and a piezoelectric ceramic element 2 for exciting longitudinal vibrations are held by two columnar metallic blocks 3, 4, and clamped by a bolt 5, thus constituting a stator main section. A sub-stator 6 is installed to the lower sections of the metallic blocks 3, 4 through a sliding material 13 such as a bearing in order to bring longitudinal and torsional resonance frequency close. A rotor 8 is pressure-welded to the end face of said stator by using a bearing 9, a nut 10, a pedestal 11 and a coil spring 12 through an abrasion-resistant material 7, thus constructing an ultrasonic motor. Accordingly, AC voltage is applied independently to both ceramic elements 1, 2, the frequency of the ceramic elements 1, 2 is used as resonance frequency, and the phase difference of 90 deg. is given, thus rotating the rotor 8 with high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultrasonic motor that generates driving force by rotating a rotor using ultrasonic vibrations.

(Prior Art) An ultrasonic motor having a structure in which a vertical-torsion composite piezoelectric vibrator is used as a stator and a rotor is pressed against the end face of the stator to rotate the rotor is disclosed in, for example, Japanese Patent Application Laid-Open No. 12177-1987 by Deku.
It is disclosed in the publication no.

Here, the stator is a stator in which a piezoelectric element for torsional vibration excitation and a piezoelectric element for longitudinal vibration excitation are sandwiched between a cylindrical or cylindrical ultrasonic vibrator. An alternating current voltage is applied to each independently to induce elliptical vibration on the end face of the stator, and this elliptical vibration is used to impart rotational motion to the rotor that is pressed against the end face of the stator.

(Problem to be Solved by the Invention) By the way, since the phase velocity of the torsional vibration wave is approximately 60% of the phase velocity of the longitudinal vibration wave, in the stator having the above configuration, the resonance frequency of the torsional vibration and the resonance of the longitudinal vibration Difficult to match frequencies. Therefore, in the stator having the above configuration, if the torsional vibration is driven resonantly, the longitudinal vibration becomes a non-resonant drive, and conversely, if the longitudinal vibration is driven resonantly, the torsional vibration becomes a non-resonant drive.

As is well known, in comparison with resonant drive, non-resonant drive provides an extremely small amplitude when driven with the same power. As a result, the amplitude of the elliptical vibration induced on the end face of the stator with the above configuration becomes extremely small in either the longitudinal or torsional direction, making it impossible to realize a highly efficient motor. be.

In the stator having the above configuration, it is possible to apply alternating current voltages of different frequencies to the piezoelectric element for torsional vibration excitation and the piezoelectric element for longitudinal vibration excitation to resonantly drive the two types of vibration. In some cases, it is not possible to regularly induce elliptical vibrations on the end face of the stator due to different resonance frequencies, and it is therefore impossible to stably rotate the rotor.

(Means for Solving the Problem) The configuration of an ultrasonic motor according to the present invention is shown in FIG. A torsional vibration piezoelectric ceramic element 1 and a longitudinal vibration excitation piezoelectric ceramic element 2 are mounted on two cylindrical or cylindrical metal blocks 3.
and 4, and tighten firmly using bolts 5 to form the main part of the stator. At this time, when considering only the main part of the stator, the half-wavelength resonance frequency of longitudinal vibration is
This is approximately 1.6 times the half-wavelength resonance frequency of torsional vibration. If the longitudinal and torsional resonance frequencies were to differ significantly, it would be extremely difficult to realize a high-performance ultrasonic motor. For example, a substator 6 made of a cylindrical or cylindrical block made of a highly rigid material such as metal or ceramics is provided via a bearing or a sliding material 13 having a small coefficient of friction. Further, the rotor 8 is attached to the end face of the stator (the end face of the metal block 3) via a wear-resistant material 7, and a bearing 9,
A nut 10, a pedestal 11, and a coil spring 12 are pressed together to form an ultrasonic motor. At this time, the rotor 8, the bearing 9, the wear-resistant material 7, the nut 10, the bolt 5, the substator 6, and the pressure force of the rotor against the stator are adjusted so that the longitudinal resonance frequency of the entire ultrasonic motor matches the half-wavelength resonance frequency of torsional vibration. choose.

In the ultrasonic motor with the above configuration, if an AC voltage is applied independently to the piezoelectric ceramics for torsional vibration excitation and the piezoelectric ceramics for longitudinal vibration excitation, this frequency is set as the resonance frequency, and a phase difference of 90° is applied, the rotor will move at high speed. Rotate with efficiency.

(Function) Although the stator constituting the ultrasonic motor of the present invention has a torsional vibration half-wavelength resonance frequency and a longitudinal vibration half-wavelength resonance frequency different when used alone, a substator is provided via a bearing or a sliding material, and the stator portion By firmly tightening and integrating the substator and substator parts with bolts, the resonant frequency related to torsional vibration hardly changes even if the substator part is installed, but the longitudinal resonant frequency is significantly reduced and the torsional resonant frequency is reduced. Get closer. When the rotor is further pressed against the rotor, similarly, while the torsional resonance frequency hardly changes, the longitudinal resonance frequency becomes a function of the thickness and mass of the rotor and further decreases. At this time, by adjusting the pressure when tightening the rotor and stator, it is possible to match the two resonance frequencies with high precision. Therefore, torsional vibration and longitudinal vibration can be driven resonantly at the same frequency.

As described above, the ultrasonic motor according to the present invention (which drives large torsional resonance and longitudinal resonance at the same frequency) can realize a highly efficient motor.

(Example) Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the present invention, and the principle and structure are as described above. The piezoelectric ceramic element 1 for torsional vibration excitation consists of 8 piezoelectric ceramic plates polarized in the circumferential direction, each having an outer diameter of 20 mm, an inner diameter of 8 mm, and a thickness of 0.5 mm.
It is constructed by laminating layers. The front and back surfaces of each ceramic plate are metallized, and the ceramic plates are laminated with a thin metal plate sandwiched between them so that the polarities are opposite to each other. The metal sheets are electrically connected in parallel externally. On the other hand, the piezoelectric ceramic element 2 for longitudinal vibration excitation is made of one piezoelectric ceramic plate (outer diameter 20 mm, inner diameter 8 mm, thickness 0.5 mm) polarized in the thickness direction.
The piezoelectric ceramic element 1 is made by laminating two layers, and the structure is similar to the piezoelectric ceramic element 1 for torsional vibration excitation described above. Metal blocks 3, 4. The substator 6 and the pedestal 9 were all made of styrene steel. Further, the parts of the bolts 5 and nuts 14 and 10 to which large static or dynamic stresses are applied are made of high-tensile steel, and the rotor part 8 is made of lightweight and highly rigid alumina ceramics. The rotor 8 is pressed against the metal block 3 of the stator using a bearing 9, a pedestal 11, a coil spring 12, a bolt 5, and a nut 10. 16.17.18 is
In order to enable the piezoelectric elements 1 and 2 to be driven independently, the inserted insulating plate is made of alumina ceramics and has a thickness of 0.4 mm. 7 is a wear-resistant material made of organic material. Reference numeral 15 denotes a disc spring, which is provided to minimize changes in bias stress applied to the piezoelectric elements 1 and 2 due to temperature changes.

The length of the stator body from metal block 3 to metal block 4 was 36 mm, and when the stator body was bolted, the torsional resonance frequency was 26.7 kHz and the longitudinal resonance frequency was 38.3 kHz. Furthermore, bearing 1
The substator 6 is added via the bolt 5 and the nut 14 so that a compressive bias stress of 120 kg/cm2 is applied to the piezoelectric elements 1 and 2 together with the disc spring 15. As a result, the change in the torsional resonance frequency is 200 Hz. However, the resonance frequency of longitudinal vibration was 28 kHz. Next, the rotor 8 with a thickness of 3 mm is pressed against the stator via the wear-resistant material 7 using a coil spring 12, etc., and the longitudinal resonance frequency and torsional resonance frequency are completely adjusted by varying the pressure contact force between the stator and the rotor. I tried to match it. As a result, it was found that the longitudinal resonance frequency increased as the pressure contact force was increased, and it was possible to match the two resonance frequencies at 26.2 kHz with a pressure contact force of 45 kgf.

Furthermore, the driving force of the motor was measured with the same electric power while varying the thickness of the rotor, but as the thickness of the rotor became thicker, the torque and rotation speed decreased. That is, in the ultrasonic motor having this configuration, it can be said that the thinner the rotor is, the more efficient the motor can be obtained, as long as the rigidity of the rotor can be maintained. This is because the thinner the rotor, the closer the interface between the stator and rotor is to the free end of longitudinal vibration, ensuring a larger amplitude.

FIG. 2 is a diagram showing the characteristics of the motor of this example. A sine wave having a frequency of 26.2 kHz and a voltage of 100 V and having a phase difference of 90° was applied to the piezoelectric ceramic element for exciting torsional vibration and longitudinal vibration. As a result, the no-load rotation speed was 28O
rpm, maximum torque4. We were able to achieve unprecedented high performance of Okgf-cm.

(Effects of the Invention) As described above, the present invention utilizes longitudinal resonance and torsional resonance, which determine the resonance frequency not only in the stator body but also in the entire motor including the substator, and only the resonance frequency of the longitudinal vibration is determined by the rotor. Since the configuration changes depending on the pressure contact force between the stator and the stator, it is possible to easily match the two resonance frequencies. Therefore, a highly efficient and highly practical ultrasonic motor can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a motor of the present invention. Figure 2 shows
FIG. 3 is a diagram showing characteristics of an example motor according to the present invention. In the figure, 1 is a piezoelectric ceramic element for torsional vibration excitation, 2 is a piezoelectric ceramic element for longitudinal vibration excitation, 3 and 4 are metal blocks, 5 is a bolt 6 is a substator, 7 is a wear-resistant material, 8 is a rotor, 9 and 13 are Bearing, 10.14 is nut, 1
1 is a pedestal, 12 is a coil spring, 15 is a disc spring, 16.1
7.18 is an insulating plate.

Claims (2)

[Claims] 1. In an ultrasonic motor configured by using a vertical-torsional composite piezoelectric vibrator as a stator and press-fitting a rotor to the stator, one end surface of the vertical-torsional composite vibrator constituting the stator body,
An ultrasonic motor characterized in that a substator is provided via a predetermined sliding part. 2. In the method for driving an ultrasonic motor according to claim 1, by providing a sub-stator, two resonance frequencies, torsional and longitudinal, are brought close to each other, and further, the rotor is pressed against the stator, and the pressure contact force is adjusted, so that the two resonance frequencies are reduced. An ultrasonic motor driving method characterized by matching frequencies.