JPH0340771A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To enhance the efficiency of an ultrasonic motor by employing a plurality of materials having different densities as materials used for a head mass part of a stator to optimize it, and bringing vertical resonance into coincidence with torsional resonance. CONSTITUTION:A wear resistant material 24 is adhered to a rotor 19. When a voltage is applied to a vertical piezoelectric element 13 and a torsional piezoelectric element 14, phase difference of voltages is suitably regulated, and vertical resonance frequency is brought into coincidence with torsional resonance frequency at the time of high power excitation, the resonances are combined by vertical and torsional amplitudes in a boundary between a stator 18 and a rotor 19 to cause a strong elliptical vibration. Since head masses 1, 2 made of materials having different densities do not have so high stiffness, they do not contribute to variation in the resonance frequency of the vertical vibration, but act as large inertial mass with respect to the torsional vibration. Accordingly, the resonance frequency of the torsional vibration is remarkably lowered.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to an ultrasonic motor that uses a longitudinal/torsional composite oscillator as a stator and rotates a rotor press-welded onto the stator through frictional force as a source of rotational torque. Concerning improvements to sonic motors.

(Prior Art) An ultrasonic motor is a motor that utilizes rotational torque received through frictional force by a rotor that is pressed against a stator, which is a vibrating body that makes ultrasonic elliptical vibrations.

An ultrasonic motor that uses flexural traveling waves that propagate along the circumferential direction of a ring or a disk opens and closes.58-14868
Since it was disclosed in Publication No. 2, ultrasonic motors have been actively researched and developed because they are characterized by lower speed and higher torque than electromagnetic motors. However, since this ultrasonic motor uses flexural vibration, it has the disadvantage that it is difficult to obtain high torque when the diameter is small. For example, the torque of a traveling wave ultrasonic motor with a diameter of 2 cm is 0.1 to 0.2 kg at most.
It's just f-am.

On the other hand, the standing wave type ultrasonic motor disclosed in Japanese Patent Publication No. 61-52163 makes it possible to efficiently generate strong elliptical vibrations at the interface between the rotor and the stator. However, since this uses piezoelectric longitudinal vibration to excite torsional vibration and requires mode conversion, there are restrictions on the configuration conditions, the shape and size of the vibrator are limited, and the direction of rotation of the generated elliptical vibration is limited. Depending on the configuration conditions, the rotation direction could be either clockwise or counterclockwise, and there was a drawback that the direction of rotation could not be changed freely.

It has been desired to develop a motor that can freely change the direction of rotation and has a small diameter and high torque, and the inventors of the present invention have proposed an ultrasonic motor having such a function in Japanese Patent Application No. 1983-
Specification No. 149726, and 1986 Acoustical Society of Japan Autumn Research Presentation Lecture Paper No. 2-4-10, pp. 82
1,822 (January 1988) and the magazine "Trigger J" published by Nikkan Kogyo Shimbun, pages 50 to 51 of the January 1989 issue discloses an ultrasonic wave using a vertical/torsional compound vibrator as a stator. We have proposed a motor.The configuration of this ultrasonic motor is shown in Figure 3.In the figure, 31 is a piezoelectric ceramic element that excites longitudinal vibration, and is polarized in the thickness direction.32 is a torsion element. A piezoelectric ceramic element that excites vibrations is polarized parallel to the plate surface and in the circumferential direction. 33 is a metal block made of A1 alloy (
Hereinafter, this will be referred to as the head mass), 34 is the rear mass, 35
are support plates, and these and piezoelectric elements 31 and 32 are connected to bolts 36.
, are firmly tightened by nuts 37 to constitute a stator 38 which is an ultrasonic elliptical vibrator. Further, 39 is a spring that serves to press the rotor 40 into contact with the stator 38;
1 is a base, 42 is a shaft, and 43 is a nut. The nut 43 can adjust the pressure force of the spring. Further, 44 is a wear-resistant material, and 45 is a bearing.

This ultrasonic motor was proposed for the purpose of simultaneously resonantly driving longitudinal and torsional vibrations in order to efficiently and strongly excite elliptical vibrations, which are a combination of longitudinal and torsional vibrations, at the interface between the stator and rotor. be. In order to perform resonance drive, it is necessary to match the longitudinal and torsional resonance frequencies.

In the ultrasonic motor shown in Figure 3, by setting a shaft of an appropriate thickness on the stator and adjusting the contact force between the rotor and stator, it is possible to barely match the longitudinal and torsional resonance frequencies in a weak electric field. did it.

(Problems to be Solved by the Invention) This coincidence of the longitudinal and torsional resonance frequencies is a coincidence in a weak electric field, and when actually driving a motor in a strong electric field, the torsion resonance frequency f7. becomes higher than the longitudinal resonance frequency fL, and it is difficult to match the resonance frequencies in a strong electric field, which is an actual driving state. In the ultrasonic motor having the configuration shown in FIG. 3, the torsional resonance frequency fT is almost determined by the length of the stator portion and is not significantly affected by the pressure contact force. However, the longitudinal resonance frequency fL depends on the mass of the rotor and the pressure contact force between the rotor and the stator, and the lighter the mass of the rotor and the larger the pressure contact force, the closer it approaches the torsional resonance frequency. That is, in the ultrasonic motor having the configuration shown in FIG. 3, generally fT>fL.

Therefore, in order to achieve fT: rL, the height of the rotor must be lowered to make it lighter; however, a rotor with such a shape has low rigidity, making it difficult to generate large torque. Next, it is necessary to extremely increase the contact force. Making the pressure contact force extremely large is
Inevitably, excessive stress will be applied to the bearing, leading to damage to the bearing or even shortening the life of the bearing, which is extremely dangerous. Therefore, in the conventional ultrasonic motor shown in FIG. 3, rT becomes higher than fl during actual high-power driving, and the efficiency obtained is about 25% to 40% at most.

An object of the present invention is to perfectly match the longitudinal and torsional resonance frequencies during actual high-power driving in an ultrasonic motor using a longitudinal/torsional compound vibrator as the stator, thereby increasing the efficiency of the motor. .

(Means for Solving the Problems) In the present invention, by optimizing the material used for the stator part, especially the head mass part, by using at least two types of materials with different densities, the longitudinal and torsional resonances are matched. I'm letting you do it. This will be explained in detail below.

FIG. 4 shows the vibration displacement distribution of the conventional ultrasonic motor shown in FIG. 3 when driven by a high electric field. (a) shows a schematic motor configuration diagram, (b) shows vibration displacement distribution in the motor's longitudinal direction (motor axial direction), and (c) shows vibration distribution in the motor's torsional direction (circumferential direction). shows. In Figure 4, the vertical and torsional vibration displacement distributions are different, and the reason for this is that the vertical phase velocity is 1.6 times larger than the torsional phase velocity.
The vertical characteristic mechanical impedance ZOL is Z□L=pC4, A=(n/4)pcL(D02-DI
2) (1) Torsional characteristic mechanical impedance zoT
Similarly, regarding the hollow cylinder, ZoT=pCTJ,=(n/32)pcT(Do'-D
I') (2) where ZOL is the square of the diameter, Z
oT is a function of the fourth power of the diameter; however, in equations (1) and (2), p; density CL; phase velocity CT of longitudinal elastic waves; phase velocity A of torsional elastic waves; hollow cylinder Cross-sectional area Do; Outer diameter DI; Inner diameter JP: Polar second moment of area. A detailed look at the longitudinal and torsional vibration modes in FIG. 4 reveals that the amplitudes are significantly different between the head mass portion and the torsional piezoelectric ceramic element portion. That is, the principle of the present invention is that the characteristic mechanical impedance ZOL,
By changing the zo'r, the vibration mode is changed and the longitudinal and torsional resonance frequencies are matched.

In the present invention, by optimizing the characteristic mechanical impedance of the head mass portion in particular, the longitudinal and torsional resonance frequencies are matched during high power driving.

Concerning the vibration displacement distribution of the herad mass portion of the ultrasonic motor using the conventional vertical/torsional composite vibrator as the stator shown in Fig. 4,
The portion of the head mass close to the vertical piezoelectric ceramic element is located close to the vibration node with respect to longitudinal vibration, and operates as stiffness. Moreover, regarding torsional vibration, it becomes a vibrating abdomen and operates as an inertial mass. In this state, the torsional resonance frequency fT is higher than the longitudinal resonance frequency fI. In order to realize fT == fL, the ultrasonic motor based on the present invention has a head mass of at least two to achieve greater stiffness for longitudinal vibrations and a greater inertial mass for torsional vibrations. It is made up of the above factors. In other words, the tip of the head mass that comes into contact with the rotor is made of a lightweight and highly rigid material such as A1 alloy or Ti alloy, and the side that joins the piezoelectric element, that is, the bottom of the head mass, is made of stainless steel or cemented carbide with high density and elastic modulus. It is made of etc. This head mass is tightly pressed by bolts and nuts, and vibrates as a unit. Therefore, in the ultrasonic motor according to the present invention, by improving the head mass part, it is possible to lower the torsional resonance frequency fT and increase the longitudinal resonance frequency fl, so when driving at high power, fT == f
It is possible to realize L.

(Example) Hereinafter, an example of an ultrasonic motor based on the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of an ultrasonic motor shown in an embodiment of the present invention. In Figure 1, the total length of the ultrasonic motor is 70 mm, head mass 1 is made of A1 alloy, and head mass 2 is made of stainless steel, which is a denser material, and these are joined together by means such as welding, gluing, and driving. It is also integrated with the stainless steel bolt 12 with a collar 25 by welding. The height of the whole head mass is 11 mm, of which the height of Rad mass 2 is 4 mm.
mm.

The height of the head mass 1 is 7 mm, and the outer diameter of both is 20 mm. 13 is a PZT-based piezoelectric ceramic element for longitudinal vibration excitation, 14 is a PZT-based piezoelectric ceramic element for torsional vibration excitation, 15 is a support plate made of stainless steel, and 16 is a rear mass made of brass. The section from the head mass to the rear mass 16 is firmly tightened with bolts 12 and nuts 17, and constitutes a stator 18 which is a vertical/torsional composite vibrator.

19 is a stainless steel rotor with a height of 8 mm, 20 is a bearing, 21 is a pedestal also made of stainless steel, 22 is a spring, and 23 is a nut. supply

The contact force between the rotor and stator can be slightly changed by adjusting the rotation angle of the nut. Also, 2
4 is a wear-resistant material made of engineering plastic, which is bonded to the rotor 19 in this case. When a voltage is applied to the vertical piezoelectric element 13 and the torsional piezoelectric element 14, the phase difference of the voltage is adjusted appropriately, and the longitudinal and torsional resonance frequencies are matched during high power excitation, the interface between the stator and the rotor , the longitudinal and torsional amplitudes can be combined to produce strong elliptical vibrations. head mass 2b
Since it does not have much stiffness for longitudinal vibration, it does not contribute to changing the resonance frequency of longitudinal vibration, but when it comes to torsional vibration, it acts as a large inertial mass, so it significantly reduces the resonance frequency of torsional vibration. There is work.

In the ultrasonic motor having the dimensions and shape shown in FIG.
When high-power excitation was performed with gf constant and the driving voltages of the vertical and torsional piezoelectric ceramic elements both 80 Vrms, the longitudinal resonance frequency was 31.6 kHz and the torsional resonance frequency was 31.1 kHz.

Therefore, we adjusted the frequency by changing the height of head mass 2 and reducing the mass at the bottom, and the result was 31.5kHz.
The longitudinal and torsional resonance frequencies matched. Next, when the drive voltage was left as it was and the phase difference between the vertical and torsional applied voltages was set to 70 degrees, it rotated in the clockwise direction. The measurement results of the rotational speed-torque characteristics at that time are shown in FIG. The operating characteristics of this ultrasonic motor are: no-load rotation speed of 52 Or, p, m, maximum torque of 5.1 kgf"am, and maximum efficiency of 63%.

In addition, it was confirmed that the ultrasonic motor shown in this example can be reversed in the counterclockwise direction by setting the phase difference of the drive voltage to 250 degrees, and its characteristics are almost the same as those shown in Fig. 2. Met.

In addition, in the embodiment of the present invention, two types of materials, AI and stainless steel, are used for the heradomas, but it is also possible to match the resonance by using three other types of materials, such as AI, stainless steel, and W. , the same effect of high motor output can be obtained.

(Effects of the Invention) As detailed above, the ultrasonic motor configured according to the present invention can perfectly match the longitudinal and torsional resonance frequencies during high electric field driving, and can synchronize the stator with low power consumption. Large-amplitude elliptical vibration can be generated at the rotor interface, making it possible to realize a high-efficiency, high-torque ultrasonic motor. Therefore, the technical usefulness of the ultrasonic motor based on the present invention is immeasurably large, and the range of applied and derived technologies cannot be predicted.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an ultrasonic motor that is an embodiment of the present invention, FIG. 2 is a rotation speed and torque characteristic diagram of the ultrasonic motor of the present invention, and FIG. 3 is a sectional view of a conventional ultrasonic motor. FIG. 4 is a diagram for explaining the vibration displacement distribution of a conventional ultrasonic motor. Each symbol in the figure indicates the following content. 12.33... Head mass, 12.36... Bolt, 13.31... Piezoelectric ceramic element for longitudinal vibration, 14
．． 32... Piezoelectric ceramic element for torsional vibration, 15.3
5... Support plate, 16.37... Rear mass, 17.2
3.37.43... Nut, 18.38... Stator, 19.40... Rotor, 20.45... Bearing, 21.41... Pedestal, 22.39... Spring,
24.44...Abrasion resistant material, 25...Tsuba

Claims (1)

[Claims] In an ultrasonic motor that uses a vertical and torsional composite piezoelectric vibrator as a stator to excite ultrasonic vibrations and rotates a rotor that is pressed into contact with the stator, at least two or more types of materials with different densities are bonded to the rotor contact side of the stator. 1. An ultrasonic motor characterized in that a block is provided, a low-density material is arranged on the rotor contact side of the block, and a high-density material is arranged on the bonding side with a piezoelectric vibrator.