JP2897259B2 - Ultrasonic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a super-torque in which a longitudinal-torsion composite vibrator is used as a stator and a rotor pressed on the stator is rotated through frictional force as a source of rotational torque. It relates to improvement of a sound wave motor.

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

Since an ultrasonic motor using a bending traveling wave propagating along the circumferential direction of a ring or a disk was disclosed by Japanese Patent Application Laid-Open No. 58-148682, the ultrasonic motor has a lower speed than an electromagnetic motor. Due to its characteristic of high torque, research and development have been actively pursued. However, since this ultrasonic motor utilizes bending vibration, there is a disadvantage that it is difficult to obtain a high torque if the diameter is reduced. 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 Patent Application Laid-Open No. 61-52163 has enabled efficient generation of strong elliptical vibration at the interface between the rotor and the stator. However, since the torsional vibration is excited by using the piezoelectric longitudinal vibration, mode conversion is required, so 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 either clockwise or counterclockwise depending on the configuration conditions, and there is a disadvantage that the rotation direction cannot be freely changed.

There has been a demand for the emergence of a motor that can freely change the rotation direction and has a small diameter and high torque. However, as an ultrasonic motor having such a function, the present inventors have disclosed in Japanese Patent Application No.
No. 149726, and the combined longitudinal and torsional oscillator disclosed in the 1988 Autumn Meeting of the Acoustical Society of Japan, No.2-4-10, pp.821-822 (October 1988), are used as the stator. An ultrasonic motor was proposed. FIG. 3 shows the configuration of this ultrasonic motor. In FIG. 3, reference numeral 11 denotes a piezoelectric ceramic element for exciting longitudinal vibration, which is subjected to a polarization treatment in the thickness direction. Reference numeral 12 denotes a piezoelectric ceramic element for exciting torsional vibration, which is polarized in a circumferential direction parallel to the plate surface. These piezoelectric elements 11 and 12 have a head mass 1 made of an Al alloy.
3, firmly tightened by rear mass 14, bolt 15,
The stator 30 is an ultrasonic elliptical vibrator. Also,
20 is a spring that functions to press the rotor 17 against the stator,
19 is a pedestal, 22 is a shaft, 21 is a nut. With this nut 21, the pressure contact force of the spring can be adjusted. Reference numeral 18 denotes a bearing. FIG. 4 shows the operation principle of this ultrasonic motor. The longitudinal vibration acts as a clutch, so to speak, only one-way torsional displacement is transmitted to the rotor.

This ultrasonic motor has been proposed with the aim of simultaneously driving longitudinal and torsional vibrations in resonance, in order to efficiently and effectively excite elliptical vibrations synthesized by longitudinal and torsional vibrations at the interface between the stator and rotor. is there. In order to perform resonance vibration, it is necessary to match the longitudinal and torsional resonance frequencies.
In the ultrasonic motor shown in FIG. 3, the resonance frequency of longitudinal vibration and torsional vibration is barely matched in a weak electric field by setting a shaft of appropriate thickness on the stator and adjusting the pressure contact force between the rotor and the stator. I was able to.

(Invention Problems to be Solved) matching the resonant frequency of the longitudinal vibration and torsional vibration are coincident at a weak electric field, when driving actually the motor at high electric field, the torsional resonance frequency f _T Since the vertical resonance frequency f _L is higher than the vertical resonance frequency f _L , 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 resonance frequency f _{T of} torsional vibration is used.
Is largely determined by the length of the stator portion, and is not significantly affected by the pressing force. However, the resonance frequency f _L of the longitudinal vibration depends on the mass of the rotor and the pressure contact force between the rotor and the stator. The lighter the rotor mass and the larger the pressure contact force, the closer to the torsional resonance frequency. That is, in the ultrasonic motor having the configuration shown in FIG. 3, generally, f _T > f _L. Therefore, in order to achieve f _T = f _L , it is necessary to first reduce the weight of the rotor. For this purpose, the height of the rotor must be reduced. However, it is difficult to generate a large torque. Or,
It is necessary to increase the pressing force extremely, but making the pressing force extremely large inevitably results in excessive stress on the bare bearing, leading to damage to the bearing and shortened life. Is extremely dangerous. Therefore, in the ultrasonic motor shown in the conventional Figure 3, at the time of actual high-power drive, f _T is higher than f _L state, the resulting efficiency is at most about 25% to 40%.

(Means for Solving the Problems) The present invention relates to an ultrasonic wave having a structure in which a vertical-torsion composite vibrator in which a vertical vibration piezoelectric element and a torsional vibration piezoelectric element are sandwiched between two blocks is used as a stator and a rotor is pressed against the stator. An ultrasonic motor, wherein an annular ring made of a material having a product of density and elastic modulus larger than that of the block is arranged on the outer periphery of a block located on the rotor side.

(Function) The present invention is intended to improve the motor efficiency by making the longitudinal and torsional resonance frequencies completely coincide with each other in the actual high-power driving in an ultrasonic motor using a longitudinal-torsional composite vibrator as a stator. It was done. Therefore, in the present invention, the resonance frequency of the longitudinal vibration and the resonance frequency of the torsional vibration are matched by optimizing the material used for the head mass portion, particularly the head mass configuration, of the stator portion. This will be described in detail below.

FIGS. 5 (a) and 5 (b) show the vibration displacement distribution when the conventional ultrasonic motor shown in FIG. 3 is driven by a high electric field. The vibration displacement distributions of longitudinal vibration and torsional vibration are different, because the phase velocity of longitudinal elastic wave is 1.
6 times larger, characteristic of longitudinal vibration Mechanical impedance Z
_0L is Z _0L = ρc _L A = (π / 4) (ρE) ^0.5 (D _O ² −D _I ² ) for the hollow cylinder
(1) characteristic mechanical impedance Z _0T of the torsional _{vibration, Z 0T = ρc T J P} = (π / 32) with respect to same hollow cylinder ^{_{(ρG) 0.5 (D O 4}} -D I 4)
(2) where Z _0L is a quadratic function of the diameter and Z _0T is a quadratic function of the diameter. Here, in equations (1) and (2), ρ; density c _L ; phase velocity of longitudinal elastic wave c _T ; phase velocity of torsional elastic wave A; cross-sectional area of hollow cylinder E; longitudinal elastic modulus G; D _O ; outer diameter D _I ; inner diameter J _P ; second pole moment of area of hollow cylinder. Looking at the vibration modes of the longitudinal vibration and the torsional vibration in FIG. 5 in detail, it can be seen that the amplitude is largely different in the head mass portion. That is, the principles of the present invention in Heddomasu portion, characteristic mechanical impedance Z _0L, by'll change the Z _0T, given a change in the vibration mode is to match the resonant frequency of the longitudinal vibration and torsional vibration.

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

Paying attention to the head mass portion of the vibration displacement distribution of the ultrasonic motor using the conventional longitudinal-torsion composite vibrator as a stator shown in FIGS. 5 (a) and 5 (b), the portion of the head mass close to the vertical piezoelectric ceramic element has a vertical length. With respect to vibration, it is located near the vibration node and operates as stiffness, and with respect to torsional vibration, it acts as a vibration antinode and operates as an inertial mass. In this state, the resonance frequency f _T of the torsional vibration is higher by the resonance frequency f _L of the longitudinal vibration. However, in the ultrasonic motor according to the present invention, the outer periphery of a relatively lightweight head mass such as an Al alloy or a Ti alloy has an inner diameter larger than the outer diameter of the piezoelectric element, and both the density and the elastic modulus are higher than those of the Al alloy and the Ti alloy. By arranging a ring made of a material such as large stainless steel, cemented carbide, etc., the head mass part realizes a greater stiffness against longitudinal vibration and a larger inertial mass for torsional vibration. I have. Therefore, in the ultrasonic motor of the present invention, the above improvement, to reduce the resonance frequency f _T of the torsional vibration, since it is not possible to increase the longitudinal resonance frequency f _L, during high power drive, f _T = f _L can be realized.

(Example) FIG. 1 shows a side sectional view of an example of the present invention. Hereinafter, description will be made with reference to the drawings. The total length of the ultrasonic motor shown in the embodiment is 70 mm, and the diameter of the rear mass 14 is 20 mm. The head mass 13 made of Al alloy has an outer diameter of 20 mm and a height of 11 mm, and the head mass 16 made of stainless steel has an inner diameter of 20 mm and an outer diameter of 24 mm. In this embodiment, the head mass 13 is integrated by driving, but other methods such as welding may be used. Reference numeral 11 denotes a PZT-based piezoelectric ceramic element having an outer diameter of 20 mm and an inner diameter of 10 mm for longitudinal vibration excitation, 12 denotes a PZT-based piezoelectric ceramic element having the same outer diameter of 20 mm and inner diameter of 10 mm, and 14 denotes a rear mass made of stainless steel. The head mass 13 to the rear mass 14 are firmly fastened by stainless steel bolts 15 to constitute the stator 10 which is a vertical-torsion composite vibrator.

17 is a stainless steel rotor with a height of 8 mm, 18 is a bearing, 19 is a stainless steel pedestal, 22 is a stainless steel shaft, 20 is a spring, 21 is a nut, a shaft 22, a spring 2
0, the nut 21 supplies a force for pressing the rotor 17 against the stator 10. The pressure contact force between the rotor and the stator can be delicately changed by adjusting the rotation angle of the nut.
An AC voltage is applied to the piezoelectric element 11 for longitudinal vibration excitation and the piezoelectric element 12 for torsional vibration excitation to adjust the phase difference of the voltage appropriately, and the resonance frequency of longitudinal vibration and torsional vibration coincide with each other during high power excitation. In this case, a strong elliptical vibration in which the amplitudes of the longitudinal vibration and the torsional vibration are combined can be caused at the interface between the stator 10 and the rotor 17. Head mass 16
Does not have much stiffness for longitudinal vibration, so it hardly contributes to the change of resonance frequency of longitudinal vibration.However, for torsional vibration, it acts as a large inertial mass, so the resonance frequency of torsional vibration is significantly reduced. There is a function to make it. In the ultrasonic motor having the dimensions and shape shown in FIG. 1 of the embodiment, a high-power excitation was performed with the pressure contact force between the rotor and the stator fixed at 50 kgf, and the driving voltage of the vertical and torsional piezoelectric ceramic elements set at 80 V _rms. The resonance frequency of longitudinal vibration was 31.6 kHz and the resonance frequency of torsional vibration was 31.1 kHz. Then, the frequency was adjusted by shaving the outer periphery of the head mass 16 to reduce the mass, and the resonance frequency of the longitudinal vibration and the torsional vibration matched at 31.5 kHz. Next, while keeping the drive voltage, the piezoelectric element 11
When the phase difference of the voltage applied to 12 was driven at 70 degrees, it turned clockwise. FIG. 2 shows the measurement results of the rotational speed-torque characteristics at that time. The characteristics of this ultrasonic motor are: 520 rpm at no load, maximum torque 5.1 kgfcm, maximum efficiency 6
3%.

The ultrasonic motor shown in the present example was confirmed to reverse in the counterclockwise direction by setting the phase difference of the drive voltage to 250 degrees, and its characteristics were almost the same as those shown in FIG. there were.

In the above embodiment, the head mass 16 is made of stainless steel,
The head mass 13 is made of an Al alloy, and the ratio of the square root of the product of the density and the elastic modulus of the head mass 16 and the head mass 13 is k = (ρ _b E
_b ) ^0.5 / (ρ _a E _a ) ^0.5 is 2.8. Even if the material of the head mass 16 is changed to k = 2.4 copper and k = 1.7 titanium,
Under the condition of 50 kgf, the resonance frequency of the longitudinal vibration and the resonance frequency of the torsional vibration could be matched with the outer diameter of the head mass 16 being 24 mm or less, and the characteristics of the ultrasonic motor at that time were almost the same as those in FIG. However, when using tin with k = 1.4,
Even when the outer diameter of the head mass 16 was 24 mm, f _L <f _T and the resonance frequencies could not be matched. In this case, if the outer diameter of the head mass 16 is further increased, it is clear that the resonance frequency will match. However, it is desirable that the outer diameter of the head mass 16 be smaller to reduce the overall diameter of the ultrasonic motor. In order to make the resonance frequencies of the longitudinal vibration and the torsional vibration coincide with each other when the ratio between the head mass 16 and the head mass 13 is 1.2 or less, the ratio of the product of the density and the elastic modulus needs to be 1.5 or more.

(Effects of the Invention) As described above in detail, the ultrasonic motor having the configuration according to the present invention can completely match the resonance frequency of the longitudinal vibration and the torsional vibration during the high electric field driving, and consumes little power. A large-amplitude elliptical vibration can be generated at the interface between the stator and the rotor, and a high-efficiency, high-torque ultrasonic motor can be realized. Therefore, the technical usefulness of the ultrasonic motor based on the present invention is immensely large, and the range of applied technologies and derivative technologies is unpredictable.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an embodiment of the ultrasonic motor of the present invention,
FIG. 2 is a characteristic diagram of the ultrasonic motor of the present invention, FIG. 3 is a sectional side view of the conventional ultrasonic motor, FIG. 4 is an operation principle diagram of the ultrasonic motor, and FIGS. 5 (a) and 5 (b). FIG. 3 is a displacement distribution diagram of a conventional ultrasonic motor. In the figure, 10, 30 ... stator, 11 ... piezoelectric ceramic element for longitudinal vibration drive, 12 ... piezoelectric ceramic element for torsional vibration drive, 13 ... head mass, 14 ... rear mass, 15 ...
Bolt, 16 ... annular head mass, 17 ... rotor, 18
…… Bearing, 19 …… Pedestal, 20 …… Coil spring, 21…
... nuts, 22 ... shafts.

Continuation of the front page (72) Inventor Tadaho Uchikawa 5-33-1, Shiba, Minato-ku, Tokyo NEC Corporation (56) References JP-A-3-40772 (JP, A) JP-A-3-40771 ( JP, A) JP-A-55-145575 (JP, A) Patent 2504197 (JP, B2) Patent 2814583 (JP, B2) Patent 2596129 (JP, B2) Patent 2638943 (JP, B2) (58) Int.Cl. ⁶ , DB name) H02N 2/00

Claims (1)

(57) [Claims] 1. An ultrasonic motor having a structure in which a longitudinal-torsion composite vibrator in which a longitudinal vibration piezoelectric element and a torsional vibration piezoelectric element are sandwiched between two blocks is used as a stator and a rotor is pressed against the stator. An ultrasonic motor, wherein an annular ring made of a material whose product of density and elastic modulus is larger than that of the block is arranged on the outer periphery of the block.