JP2658233B2 - Ultrasonic motor and its driving method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ultrasonic motor that generates a driving force by rotating a rotor by ultrasonic vibration.

2. Description of the Related Art An ultrasonic motor for rotating a rotor by pressing a rotor against an end face of the stator by using a vertical-torsion composite piezoelectric vibrator as a stator is disclosed in, for example, JP-A-61-12177 by Kumada. I have.

Here, a torsion-vibration excitation piezoelectric element and a longitudinal-vibration excitation piezoelectric element are sandwiched between cylindrical or cylindrical ultrasonic vibrators, and integrated by tightening with bolts to form a stator. An independent AC voltage is applied to each of the vibration-exciting piezoelectric elements to induce an elliptical vibration on the end face of the stator, and the elliptical vibration is used to give a rotary motion to the rotor pressed against the end face of the stator.

(Problems to be Solved by the Invention) Since the phase velocity of the torsional vibration wave is about 60% of the phase velocity of the longitudinal vibration wave, the resonance frequency of the torsional vibration and the longitudinal vibration It is difficult to match the resonance frequencies. Therefore, in the stator having the above-described configuration, if the torsional vibration is driven by resonance, the longitudinal vibration becomes non-resonant, and if the longitudinal vibration is driven by resonance, the torsional vibration is driven by resonance.

As is well known, non-resonant driving, when driven at the same voltage, is extremely smaller in amplitude than resonant driving. As a result, the amplitude of the elliptical vibration induced on the end face of the stator having the above-described configuration becomes extremely small in either the vertical direction or the horizontal direction, so that a highly efficient motor cannot be realized. In particular, when the torsional vibration is driven by resonance and the longitudinal vibration is driven by non-resonance, the amplitude of the longitudinal vibration is so small that the rotor cannot move away from the stator surface even for a moment, so the sliding between the rotor and the stator is constant. Friction occurs. This sliding friction causes heat and abrasion, thereby deteriorating the stability of the motor and causing a problem that the motor cannot be operated for a long time.

In the stator having the above configuration, it is possible to apply AC voltages having different frequencies to the piezoelectric element for torsional vibration excitation and the piezoelectric element for longitudinal vibration excitation to drive two kinds of vibrations resonantly. Since the resonance frequencies of the torsional vibration and the longitudinal vibration are significantly different due to the difference in the phase velocities of the two, the elliptical vibration cannot be induced regularly on the end face of the stator. Therefore, also in this case, it is impossible to rotate the rotor stably.

(Means for Solving the Problem) FIG. 1 shows a configuration example of an ultrasonic motor according to the present invention. The main part of the torsional vibrator is formed by sandwiching a ring-shaped piezoelectric ceramic element for torsional vibration excitation 11 between a cylindrical block 12 and a block 13 having a hole through which bolts are formed in the bottom surface. A bolt-fastened Langevin-type vertical drive element 14 is disposed inside the cylindrical block 12 and the ring-shaped torsional vibration excitation piezoelectric ceramic element 11, and fixed and integrated. A composite vibrating body 15, in which the torsional vibrating body main part whose bottom is almost closed and the Langevin-type vertical drive element 14 are integrated,
That is, the stator of the ultrasonic motor is formed, and with such a configuration, it is possible to make the longitudinal resonance frequency and the torsional resonance frequency extremely close as described later. Furthermore, the rotor 16, the bearing 17, and the wear-resistant material
Using 18, bolt 19, nut 20, and coil spring 26, pressure contact is made to form an ultrasonic motor. At this time, the longitudinal resonance frequency of the ultrasonic motor including the rotor is smaller than the torsional resonance frequency.
There is a strong dependence on the pressure contact force between the rotor and the stator. When the pressure contact force is increased, the longitudinal resonance frequency increases. Therefore,
By appropriately selecting the pressing force, the resonance frequency of the longitudinal vibration can be completely matched with the resonance frequency of the torsional vibration.

In the ultrasonic motor having the above structure, an AC voltage is applied independently to the piezoelectric ceramic element for torsional vibration excitation and the piezoelectric ceramic element for longitudinal vibration excitation, so that the frequency of the AC voltage matches the resonance frequency, and a phase difference of 90 °. , The rotor rotates with high efficiency.

(Operation) The ultrasonic motor according to the present invention can make the resonance frequency of the longitudinal vibration and the resonance frequency of the torsional vibration relatively close to each other by itself, and can excite the strong elliptical vibration at the end face of the stator in contact with the rotor. it can.

The reason why the longitudinal resonance frequency and the torsional resonance frequency approach each other in the present stator will be described below. Both longitudinal and torsional vibrations belong to the vibration of a distributed constant system with a degree of freedom of one. For a rod made of a single structural material with a uniform cross section, it is well known that the phase velocity (elastic wave velocity) differs greatly, as is well known. It is known to exhibit almost similar behavior. However, when the vibrating body is made of a plurality of structural materials and the cross-sectional areas of the respective parts are different, as is well known, the resonance frequencies of the longitudinal and torsional vibrations are both functions of the length of the member and the characteristic mechanical impedance. . Assuming that the density of the member is ρ, the velocity of the longitudinal elastic wave is c ₁ , and the cross-sectional area is S, the characteristic mechanical impedance Z ₁ regarding longitudinal vibration is ρc ₁ s. S is proportional to the square of the diameter.

Meanwhile, the characteristic mechanical impedance Z _t about torsional vibrations represented by rho] c _t J _p, where c _t is the velocity of the torsional acoustic wave, J _p is the cross-sectional polar moment of inertia. J _p is proportional to the fourth power of the diameter. Therefore, while Z ₁ is proportional to the square of the diameter, Zt
Is proportional to the fourth power of the diameter.

In the ultrasonic motor of this configuration, the bolt-fastened Langevin type vertical drive element 14 has a considerably smaller diameter than the main part of the cylindrical torsional vibrator, so that the vertical drive element 14 has a very large resonance frequency of the torsional vibrator. Has no effect. That is, due to the configuration in which the vertical drive element 14 is provided inside the cylindrical torsional vibrator, the torsional resonance frequency does not decrease so much as compared with the vertical resonance frequency. The torsional vibration in the stator performs an operation close to a half-wave mode resonance in which both ends correspond to antinodes of the vibration.

On the other hand, for the reasons described above, the bolt-fastened Langevin type vertical drive element 14 has a great influence on the vertical resonance frequency in the stator. In the case of the stator having this configuration, the cylindrical metal block 13 that contacts the vertical drive element 14 can be used as a vibration node of the vertical vibration. That is, in this case, the resonance mode of the longitudinal vibration looks like being folded at the metal block 13, and the end face of the stator abutting on the rotor becomes the antinode of the longitudinal vibration. Therefore, since the stator of this configuration performs an operation close to the quarter wavelength mode with respect to the longitudinal vibration, the resonance frequency of the longitudinal vibration can be considerably reduced for the actual length of the stator. Furthermore, the bottom portion 13 of the stator is slightly vibrated due to a difference in cross-sectional area from the vertical drive element, and this portion functions as a flexural compliance, which effectively acts to lower the frequency of the vertical vibration mode.

For the reasons described above, it is possible to make the longitudinal resonance frequency considerably close to the torsional resonance frequency in the stator portion of the ultrasonic motor according to the present invention.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention, and the principle and configuration are as described above. The ring-shaped piezoelectric ceramic element 11 for torsional vibration excitation is formed by laminating circumferentially polarized ceramic plates having an outer diameter of 30 mm, an inner diameter of 20 mm, and a thickness of 0.5 mm. The upper and lower surfaces of each ceramic plate are metallized, with 0.
Adjacent ceramic plates are stacked so that the polarities are opposite to each other with a 1 mm thick metal plate interposed therebetween.
The metal sheets are electrically connected in parallel outside. The bolted Langevin type vertical drive element 14 has a configuration in which a laminated piezoelectric ceramic element 21 is firmly fastened with a hollow bolt 23 and nuts 24 and 25 via a metal block 22.

The rotor 16 has a thickness of 0.
Placed through 1mm wear resistant material. Further, a bearing is arranged at the center of the rotor so that the shafts are aligned. The pressure contact force between the rotor and the stator is applied using the bolt 19, the nut 20, the coil spring 26, and the pedestal 27. still,
The multilayer piezoelectric ceramic element 21 is manufactured using a multilayer ceramic process technology, and Pt is used as an internal electrode,
The layer interval is 100 μm, the outer diameter is 18 mm, and the inner diameter is 8 mm. In the present embodiment, stainless steel is used for each of the metal blocks 12, 13, 22 and the pedestal 27, and bolts 19, 23, nuts 24,
25 and high tensile steel were used. The dimensions of the ultrasonic motor are about 40 mm in total length.

The longitudinal resonance frequency of the stator portion, which is the longitudinal-torsion composite vibrator, excluding the rotor portion, was 31 kHz, and the torsional resonance frequency was only 4 kHz lower, 27 kHz. As a result of various experiments, it was found that when the rotor was pressed against the stator, the torsional resonance frequency did not change much, but the longitudinal resonance frequency decreased depending on the mass and the pressing force of the rotor. In this embodiment,
Since the longitudinal and torsional resonance frequencies are not so far apart, a lightweight and rigid Al alloy was used as the rotor material. By reducing the mass of the rotor in this way, the feature that the response speed of the ultrasonic motor is fast can be increased. When the tightening pressure was set to 48 kgf, in the ultrasonic motor of this embodiment, both the torsional and longitudinal resonance frequencies coincided at 28 kHz. Furthermore, as a result of applying resonance driving by applying a 100V sine wave to the torsional piezoelectric ceramic element and a 20V sine wave to the vertical piezoelectric ceramic element so that their phases are different from each other by 90 °,
A no-load rotation speed of 250 rpm and a maximum torque of 6.9 kgf · cm were easily achieved.

(Effect of the Invention) As described above, in the ultrasonic motor according to the present invention, the stator itself, which is a longitudinal-torsion composite vibrator, has longitudinal and torsional resonance frequencies close to each other, and the longitudinal and torsional resonance frequencies. Can be completely matched by the tightening pressure of the rotor and the stator, and resonance drive is possible. Therefore, a highly efficient and highly practical ultrasonic motor can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an ultrasonic motor according to the present invention. In the figure, 11 is a ring-shaped piezoelectric ceramic element for torsional vibration excitation, 12 is a cylindrical metal block, 13 is a cylindrical metal block, 14 is a bolted Langevin type vertical drive element, 15 is a stator, 16 is a rotor, and 17 is a bearing. , 18 is a wear-resistant material, 19 is a bolt, 20 is a nut, 21 is a piezoelectric ceramic element for longitudinal vibration excitation, 22 is a metal block, 23 is a hollow bolt, 2
4, 25 are nuts, 26 is a coil spring, and 27 is a pedestal.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Sadayuki Takahashi 5-33-1, Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Inventor Tadasuho 5-3-1, Shiba, Minato-ku, Tokyo NEC Inside the corporation

Claims (2)

(57) [Claims] 1. A torsional vibrating body portion comprising a torsional vibration exciting ring-shaped piezoelectric ceramic element sandwiched between a cylindrical block and another block, and a center axis aligned with the torsional vibrating body portion inside the ring. A vertical-torsion composite vibrator with a bolt-fastened Langevin type vertical drive element is used as a stator,
An ultrasonic motor, wherein a rotor is pressed against the stator. 2. The method for driving an ultrasonic motor according to claim 1, wherein the pressing force between the stator and the rotor is adjusted.
A method of driving an ultrasonic motor, wherein two resonance frequencies of vertical and torsion are matched to perform resonance driving.