JPH0787711B2 - Ultrasonic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention uses a longitudinal / torsion composite oscillator as a stator to rotate a rotor pressed against the stator through frictional force as a source of rotational torque. Related to sound wave motors.

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

Since the ultrasonic motor utilizing the flexural signal wave propagating along the circumferential direction of the ring or the disk is disclosed by JP-A-58-148682, the ultrasonic motor is operated at a lower speed than the electromagnetic motor. Since it has the characteristic of high torque, research and development have been actively conducted. However, since this ultrasonic motor uses flexural vibration, it has a drawback that it is difficult to obtain high torque when the diameter is small. For example, the torque of a traveling wave type ultrasonic motor having a diameter of 2 cm is at most 0.1 to 0.2 kgf · cm.

On the other hand, the standing wave type ultrasonic motor disclosed in Japanese Unexamined Patent Publication No. 61-52163 enables efficient generation of strong elliptical vibration at the interface between the rotor and the stator. However, this also excites torsional vibration using piezoelectric longitudinal vibration and requires mode conversion, so there are restrictions on the configuration conditions, the shape and size of the vibrator are limited, and the direction of rotation of the elliptic vibration generated is limited. Depending on the constitutional conditions, there is a drawback that the direction of rotation cannot be changed freely, either clockwise or counterclockwise.

The advent of a motor having a small diameter and high torque, which can freely change the rotation direction, has been desired. However, the present inventors have proposed an ultrasonic motor having such a function in Japanese Patent Application No. 63-14.
No. 9726, and 1988, Acoustical Society of Japan Autumn Research Presentation Lecture No. 2-4-10, pp.821-822 (October 1988)
And an ultrasonic motor using a longitudinal-torsion composite oscillator as a stator, which is disclosed on pages 50 to 51 of the magazine "Trigger" published by Nikkan Kogyo Shimbun, January 1989. The structure of this ultrasonic motor is shown in FIG. In the figure, reference numeral 31 denotes a piezoelectric ceramic element for exciting longitudinal vibration, which is polarized in the plate thickness direction. Reference numeral 32 denotes a piezoelectric ceramic element that excites torsional vibration, and is polarized in the circumferential direction parallel to the plate surface. 33 is a metal block made of an Al alloy (hereinafter referred to as a head mass), 34 is a rear mass, 35 is a support plate, and these piezoelectric elements 31, 32 are bolts 36, nuts.
The stator 38, which is an ultrasonic elliptical oscillator, is firmly tightened by the 37 and the head mass 33. Further, 39 is a spring that serves to press the rotor 40 against the stator 38, 41
Is a pedestal, 42 is a shaft, and 43 is a nut. With the nut 43, the pressure contact force of the spring can be adjusted. Further, 44 is a wear resistant material and 45 is a bearing.

This ultrasonic motor was proposed for the purpose of resonantly driving longitudinal and torsional vibrations at the same time in order to efficiently and strongly excite elliptical vibrations synthesized by longitudinal and torsional vibrations at the interface between the stator and rotor. is there. In order to perform the resonance drive, it is necessary to match the resonance frequencies of the vertical and the torsion.
In the ultrasonic motor shown in FIG. 3, by setting a shaft of an appropriate thickness on the stator and adjusting the pressure contact force between the rotor and the stator, it is possible to barely match the longitudinal and torsional resonance frequencies under a weak electric field. did it.

(Problems to be Solved by the Invention) However, if the shaft is thickened, the volume of the piezoelectric ceramic element which is a drive element is reduced unless the outer diameter of the motor is thickened, and the motor output is reduced.

In addition, the matching of the resonance frequencies of the vertical and torsion is the matching when the electric field is weak, and when actually driving the motor in the strong electric field,
Since the torsional resonance frequency f _T becomes higher than the longitudinal resonance frequency f _L , it is difficult to match the resonance frequencies in a strong electric field that is the actual driving state. In the ultrasonic motor having the configuration shown in FIG. 3, the resonance frequency f _{T of the} torsion is almost determined by the length of the stator portion and is not so affected by the pressure contact force. However, the longitudinal resonance frequency f
_L depends on the mass of the rotor and the pressure contact force between the rotor and the stator, and as the mass of the rotor is lighter and the previous pressure contact force is larger, it approaches the resonance frequency of torsion. That is, in the ultrasonic motor having the configuration shown in FIG. 3, generally f _T > f _L. Therefore, f _T = f _L
In order to realize the above, the height of the rotor is reduced to make it lighter, and the rotor having such a shape has low rigidity, and it is difficult to generate a large torque. Next, it is necessary to extremely increase the pressure contact force. Making the pressure contact force extremely large inevitably causes excessive stress to the bearing, which damages the bearing and shortens the life of the bearing, which is extremely dangerous. Therefore, in the conventional ultrasonic motor shown in FIG. 3, f _T becomes higher than f _L when actually driving in a strong electric field, and the obtained efficiency is at most 25% to 40%.

An object of the present invention is to increase the efficiency of a motor in an ultrasonic motor that uses a longitudinal / torsional composite oscillator as a stator by matching the resonance frequencies of the longitudinal and torsion in both strong electric field driving and weak electric field driving. is there.

(Means for Solving the Problems) In the present invention, by optimizing the material used for the head mass using at least two types of materials having different densities and materials having different cross-sectional areas, the longitudinal and torsional The resonance frequencies are matched. That is, the material of the head mass on the rotor contact side has a lower density than that of the piezoelectric vibrator side, and at least the rotor contact side has a smaller cross-sectional area toward the rotor.

FIG. 4 shows the vibration displacement distributions of the conventional ultrasonic motor shown in FIG. 3 and the ultrasonic motor of the present invention during high electric field driving. The practice is the present invention, and the broken line is the conventional example. The above figure shows a schematic motor configuration diagram. The motor of the present invention shows an example in which two kinds of materials having different densities and cross-sectional areas are used for the head mass. The middle figure shows the vibration displacement distribution in the vertical direction of the motor (motor axis direction), and the lower figure shows the vibration distribution in the motor torsion direction (circumferential direction). In FIG. 4, in the conventional example, the vibration displacement distributions of the longitudinal and the torsion are different. This is because the longitudinal phase velocity is about 1.6 times as large as the torsional phase velocity, and the longitudinal characteristic mechanical impedance Z _0L and the torsional characteristic mechanical impedance Z _0T are Z _0L = ρc _L A = (π ^{_{/ 4) ρc L (D 2}} O -D 2 I) (1) Z 0T = ρc T J p = (π / 32) ρc T (D 4 O -D 4 I) is given by (2), Z _0L Is the square of the diameter, and Z _0T is a function of the fourth power of the diameter. However, in equations (1) and (2), ρ; density c _L ; longitudinal elastic wave c _T ; phase velocity of torsional elastic wave A; cross-sectional area of hollow cylinder D _O ; outer diameter D _I ; inner diameter Jp; cross-section pole It is the second moment. When the longitudinal and torsional vibration modes of the conventional example in FIG. 4 are viewed in detail, the amplitude of the head mass 33 near the rotor 40 is large in the longitudinal vibration mode, but in the torsional vibration mode, the amplitude of the head mass 33 near the piezoelectric ceramic element is large. It turns out that is large.

Regarding the vibration displacement distribution of the head mass portion of the ultrasonic motor using the conventional longitudinal / torsion decoding oscillator shown in FIG.
Regarding the longitudinal vibration, the portion of the head mass that is close to the vertical piezoelectric ceramic element is located near the vibrating node and operates as stiffness. Regarding torsional vibration, it serves as a vibration antinode and operates as an inertial mass. In this state, the torsional resonance frequency f _T is higher than the longitudinal resonance frequency f _L.

Principle In characteristic mechanical impedance Z _0L in Heddomasu part of the present invention, by'll change the Z _0T, given a change in the vibration mode is to match the resonant frequency of the longitudinal and torsional. In the ultrasonic motor according to the present invention, in order to realize f _T = f _L , a larger stiffness is realized with respect to longitudinal vibration, and with regard to gripping vibration, at least two head masses are used in order to realize a larger inertial mass. It consists of one or more elements. That is, the tip of the head mass that comes into contact with the rotor part is made of a lightweight and highly rigid material such as a Ti alloy, and the joint side with the piezoelectric element, that is, the bottom of the head mass is made of stainless steel, cemented carbide, or the like with a large density and elastic modulus. is made of. Furthermore, the tip end portion of the head mass has a shape in which the cross-sectional area decreases along the tip end, and the bottom portion of the head mass has a larger cross-sectional area than the tip end portion of the head mass. This head mass is firmly pressed by bolts and nuts and vibrates as a unit. Therefore, in the ultrasonic motor according to the present invention, the resonance frequency f _T of the torsion can be lowered and the resonance frequency f _{L of the} longitudinal direction can be increased by improving the head mass portion. It is possible to realize f _T = f _L during driving. In this way, even in the vibration mode, the amplitude of both vibration modes can be maximized at the rotor interface as shown by the solid line in FIG. 4, and the efficiency can be improved.

(Operation) (Example) An example of an ultrasonic motor according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an ultrasonic motor according to an embodiment of the present invention. In FIG. 1, the total length of the ultrasonic motor is 70 mm, the head mass 11 is an Al alloy, and the head mass is
12 is stainless steel of higher density material than that,
These are joined and integrated by means such as welding, adhesion, and driving, and are further integrated with the flange 13 by being welded to stainless steel 14. The total height of the head mass is 11 mm, of which the height of the head mass 12 is 4 mm and the outer diameter is 24 mm.
The height of the head mass 11 is 7 mm, the outer diameter is 20 mm at the base, and the tip portion is 16 mm in a tapered shape. 15 is PZT for longitudinal vibration excitation
16 is a PZT piezoelectric ceramic element for torsional vibration excitation, 17 is a support plate made of stainless steel, and 18 is a rear mass made of brass. Head mass 11 to rear mass 18
Until it is firmly tightened with bolt 14 and nut 19,
A stator 20 which is a longitudinal / torsion composite oscillator is configured.

21 is a stainless steel rotor with a height of 8 mm, 22 is a bearing, 23 is a pedestal and is also made of stainless steel, 24 is a spring, 25 is a nut, and the spring 24 and the nut 25 are used to press the rotor 21 against the stator 20. Supply. The pressure contact force between the rotor and the stator can be delicately changed by adjusting the rotation angle of the nut. Further, 26 is an abrasion resistant material made of engineering plastic, and in this case, it is adhered to the rotor 21. When a voltage is applied to the longitudinal piezoelectric element 15 and the torsional piezoelectric element 16 to appropriately adjust the phase difference between the voltages, and when the resonant frequencies of the longitudinal and torsion are matched during strong electric field excitation, the stator and rotor are At the interface, a strong elliptical vibration can be generated that is composed of longitudinal and torsional amplitudes. The head masses 11 and 12 do not contribute so much to the change in the resonance frequency of the longitudinal vibration because they do not have much stiffness with respect to the longitudinal vibration, but regarding the torsional vibration, they act as a large inertial mass, so that the resonance frequency of the torsional vibration is increased. It has the function of remarkably lowering. In the ultrasonic motor having the dimensions and shape shown in FIG. 1 of the embodiment, the pressure contact force between the rotor and the stator is fixed at 50 kgf, the driving voltage of the longitudinal and torsional piezoelectric ceramic elements are both 80 V _rms , and the strong electric field When excited, the longitudinal resonance frequency was 31.6 kHz and the torsional resonance frequency was 31.1 kHz. Therefore, the protrusion 50 of the head mass
When the frequency was adjusted by slightly scraping to reduce the mass of the protrusion, the longitudinal and torsional resonance frequencies were matched at 31.5 kHz. Next, when the drive voltage was left as it was and the phase difference between the longitudinal and torsional applied voltages was driven by 70 degrees, it rotated clockwise. The measurement result of the rotation speed-torque characteristic at that time is
Shown in the figure. The characteristics of this ultrasonic motor are the number of revolutions at no load.
The maximum torque is 520r.pm, the maximum torque is 5.1kgf · cm, and the maximum efficiency is 63%.

In addition, it was confirmed that the ultrasonic motor shown in the present embodiment was inverted in the counterclockwise direction by setting the phase difference of the driving voltage to 250 degrees, and its characteristics are almost the same as those shown in FIG. It was the same.

In the embodiment of the present invention, the head mass having a high density is provided with the protrusion having a constant diameter, but the protrusion 50 may be tapered. In addition, although two types of materials, Al and stainless steel, are used for the head mass, resonance can be matched by using other three types of materials such as Al, stainless steel, and tungsten, and the same effect of high motor output can be obtained. Is obtained.

(Effects of the Invention) As described in detail above, the ultrasonic motor having the configuration according to the present invention can completely match the longitudinal and torsional resonance frequencies during the strong electric field driving or the weak electric field driving, and the A large amplitude elliptical vibration can be generated at the interface between the stator and the rotor with power consumption, and an ultrasonic motor with high efficiency and high torque can be realized. Therefore, the technical usefulness of the ultrasonic motor according to the present invention is immeasurable,
The extent of applied technology and derivative technology is unpredictable.

[Brief description of drawings]

1 is a sectional view of an ultrasonic motor according to an embodiment of the present invention, FIG. 2 is a rotational speed-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 the ultrasonic motors of the related art and the present invention. Each symbol in the figure indicates the following contents. 11,12,13 …… Head mass, 13 …… Temperature, 14,36 …… Bolt, 15,31 …… Piezoelectric ceramic element for longitudinal vibration, 16,32 ……
Piezoelectric ceramic element for torsional vibration, 17,35 …… Support plate, 18,
37 …… rear mass, 19,25,37,43 …… nut, 20,38 …… stator, 21,40 …… rotor, 22,45 …… bearing, 23,4
1 ... Pedestal, 24,39 ... Spring, 26,44 ... Abrasion resistant material, 50 ...
…protrusion.

Claims (1)

[Claims] 1. An ultrasonic motor comprising: a stator having a longitudinal and torsion composite piezoelectric vibrator sandwiched between a head mass and a rear mass; and a rotor pressed against the head mass of the stator, wherein the head mass is a rotor compared to the piezoelectric vibrator side. An ultrasonic motor characterized in that the material on the contact side has a low density, and at least the rotor contact side has a smaller cross-sectional area toward the rotor.