JP2504197B2 - 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. The present invention relates to improvement of a sonic motor.

(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 bending traveling wave propagating along the circumferential direction of the ring or the disk is disclosed by JP-A-58-148682, the ultrasonic motor has a lower speed than the electromagnetic motor. Since it has a characteristic of high torque, research and development have been actively conducted. However, since this ultrasonic motor utilizes bending vibration, there is a drawback in 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 Patent Laid-Open 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 one of clockwise and counterclockwise rotation, and there is a drawback that the direction of rotation cannot be freely changed.

It has been desired to develop a motor whose rotation direction can be freely changed and which has a small diameter and high torque. However, as an ultrasonic motor having such a function, the present inventors have proposed Japanese Patent Application No. 63-1.
The stator is the longitudinal / torsional composite oscillator disclosed in 49726, and the 1988 Autumn Meeting of the Acoustical Society of Japan No.2-4-10, pp.821-822 (October 1988), etc. An ultrasonic motor was proposed. The structure of this ultrasonic motor is shown in FIG. 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 is a piezoelectric ceramic element that excites torsional vibration, and is polarized in a circumferential direction parallel to the plate surface. These piezoelectric elements 11 and 12 are head masses 13 made of Al alloy,
The rear mass 14 and the bolts 15 are firmly tightened to form a stator 30 which is an ultrasonic elliptical oscillator. Further, 20 is a spring that acts to press the rotor 17 against the stator, 19 is a pedestal, 22 is a shaft, and 21 is a nut. This nut 21
With this, the pressure contact force of the spring can be adjusted. Also, 18
Is a bearing. FIG. 4 shows the operation principle of this ultrasonic motor. The longitudinal vibration acts as a clutch, so to speak, and only torsional displacement in one direction is transmitted to the rotor.

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 with an appropriate thickness on the stator and adjusting the pressure contact force between the rotor and the stator, the resonance frequencies of longitudinal vibration and torsional vibration are barely matched under a weak electric field. I was able to do it.

(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 the} torsional vibration is
Is almost determined by the length of the stator portion and is not so affected by the pressure contact 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, and as the mass of the rotor is lighter and the pressure contact force increases, the resonance frequency approaches the torsion resonance frequency. That is, in the ultrasonic motor having the configuration shown in FIG. 3, generally f _T > f _L. Therefore, in order to realize f _T = f _L , it is necessary to lighten the rotor first, and in order to do so, it is unavoidable to reduce the height of the rotor. However, it becomes difficult to generate a large torque. Alternatively,
It is necessary to make the pressure contact force extremely large, but making the pressure contact force extremely large inevitably causes excessive stress to the bearing, leading to damage to the bearing and shortening the life of the bearing, It is extremely dangerous. Therefore, in the ultrasonic motor shown in the conventional Figure 3, at the time of actual high-power drive, a state f _T is higher than f _L,
The efficiency obtained is at most 25% to 40%.

(Means for Solving the Problem) The present invention provides an ultrasonic wave configuration in which a longitudinal-torsion composite oscillator 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. In the motor, between the block located on the rotor side and the piezoelectric element,
The ultrasonic motor is characterized in that a disk made of a material having an outer diameter larger than that of the piezoelectric element and having a product of density and elastic modulus larger than that of the material of the metal block is arranged.

(Operation) In the ultrasonic motor using the longitudinal-torsion composite oscillator as a stator, the longitudinal and torsional resonance frequencies are made to completely match at the time of actual high-power driving to improve the efficiency of the motor. It was made. For this reason, in the present invention, the resonance frequencies of the longitudinal vibration and the torsional vibration are matched by optimizing the material used for the head mass part of the stator part and the head mass structure. The details will be described below.

The vibration displacement distribution of the conventional ultrasonic motor shown in FIG. 3 when driven by a high electric field is shown in FIGS. The vibration displacement distributions of longitudinal vibration and torsional vibration are different, because the phase velocity of the longitudinal elastic wave is 1.
About 6 times larger, longitudinal vibration characteristic mechanical impedance Z
_{0L is, Z 0L = ρc L A =} (II / 4) with respect to the hollow cylinder ^{_{(ρE) 0.5 (D O 2}} -D I 2) (1) characteristic mechanical impedance Z _0T of the torsional vibration, like Z regard hollow cylinder _0T = Ρ c _T J _P = (II / 32) (ρ _G ) ^0.5 (D _O ⁴ −D _I ⁴ )
(2) given by, Z _0L is due to that is the quadratic function, quartic function of Z _0T diameter diameter. Here, in the 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 E of hollow cylinder E; longitudinal elastic modulus G; shear elastic modulus D _O ; outer diameter D _I ; inner diameter J _P ; second polar moment of area of the hollow cylinder. When the vibration modes of the longitudinal vibration and the torsional vibration shown in FIG. 5 are examined in detail, it is found that the amplitudes are greatly 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.

According to the present invention, the characteristic mechanical impedance of the head mass portion is optimized to match the longitudinal and torsional resonance frequencies during high power driving.

Focusing on the head mass portion of the vibration displacement distribution of the ultrasonic motor using the conventional longitudinal-torsion composite oscillator shown in FIGS. 5 (a) and 5 (b) as a stator, the longitudinal portion of the head mass is close to the longitudinal piezoelectric ceramic element. Regarding vibration, it operates as a stiffness in the position close to the vibration node, and regarding torsional vibration, it functions as a vibration antinode and operates as an inertial mass. In this state, the resonance frequency f _T of torsional vibration is higher than the resonance frequency f _L of longitudinal vibration. However, in the ultrasonic motor according to the present invention, between the relatively lightweight head mass such as Al alloy or Ti alloy and the piezoelectric element, the outer diameter is larger than the outer diameter of the piezoelectric element, and the density is higher than that of the Al alloy or Ti alloy. By arranging a disk made of a material such as stainless steel or cemented carbide, which has a large elastic modulus, the head mass section realizes greater stiffness against longitudinal vibration and a larger inertial mass with respect to torsional vibration. Has been realized. Therefore, in the ultrasonic motor of the present invention, by the above improvement,
Since the resonance frequency f _T of the torsional vibration can be lowered and the resonance frequency f _L of the longitudinal vibration can be increased, f _T = f _L can be realized during high power driving.

(Embodiment) A side sectional view of an embodiment of the present invention is shown in FIG. Hereinafter, description will be given with reference to the drawings. The ultrasonic motor shown in the embodiment has a total length of 70 mm and the rear mass 14 has a diameter of 20 mm. The head mass 13 made of Al alloy has an outer diameter of 20 mm and a height of 6 mm, and the stainless steel head mass 16 has an inner diameter of 9 mm, an outer diameter of 24 mm and a height of 5 mm. Reference numeral 11 is a PZT-based piezoelectric ceramic element having an outer diameter of 20 mm and inner diameter of 10 mm for longitudinal vibration excitation, 12 is also a PZT-based piezoelectric ceramic element of 20 mm outer diameter and an inner diameter of 10 mm for torsional vibration excitation, and 14 is a stainless steel rear mass. The head mass 13 to the rear mass 14 are firmly tightened by stainless steel bolts 15 to form a stator 10 which is a vertical-torsion composite oscillator.
Although the bolt 15 is fastened to the head mass 13 in the present embodiment, the head mass 13 and the head mass 16 may be integrated by means such as welding and the bolt 15 may be fastened to the head mass 16 with the same effect as in the present embodiment. It is clear that

17 is a stainless steel rotor with a height of 8 mm, 18 is a bearing, 19 stainless steel pedestal, 22 is a stainless steel shaft, 20 is a spring, 21 is a nut, shaft 22, spring 20,
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. The head mass 16 increases the resonance frequency by increasing the stiffness with respect to the longitudinal vibration, and acts as a large inertial mass with respect to the torsional vibration, and thus has a function of remarkably decreasing the resonance frequency. 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 kept constant at 50 kgf, and the driving voltages of the longitudinal and torsional piezoelectric ceramic elements are both set.
Resonance frequency of longitudinal vibration is 32.2kHz, resonance frequency of torsional vibration is 31.1kHz when high-power excitation is performed at 80V _rms.
Met. Therefore, when the frequency was adjusted by cutting the outer periphery of the head mass 16 to reduce the mass, the resonance frequencies of the longitudinal vibration and the torsional vibration were matched at 32.1 kHz. Next, when the driving voltage was maintained and the phase difference between the voltages applied to the piezoelectric elements 11 and 12 was driven at 70 degrees, the piezoelectric elements rotated clockwise. FIG. 2 shows the results of measurement of the rotational speed-torque characteristics at that time. The characteristics of this ultrasonic motor are 560r.
pm, maximum torque 5.3kgf · cm, maximum efficiency 65%.

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 drive voltage to 250 degrees, and its characteristics are almost the same as those shown in FIG. there were.

In the above embodiment, the head mass 16 is made of stainless steel,
An Al alloy is used for the head mass 13, 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 copper with k = 2.4 and titanium with k = 1.7, the pressure contact force
Under the condition of 50 kgf, the resonance frequency of the longitudinal vibration and the torsional vibration can be matched with the outer diameter of the head mass 16 of 24 mm or less, and the characteristics of the ultrasonic motor at that time were almost the same as those in FIG. However, with tin of 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, it is obvious that if the outer diameter of the head mass 16 is further increased, the resonance frequencies match each other. However, it is desirable that the outer diameter of the head mass 16 is small in order 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 of 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 immeasurable, and there are some applications and derived technologies that cannot be predicted.

[Brief description of drawings]

FIG. 1 is a side sectional view of an embodiment of an ultrasonic motor of the invention, FIG.
FIG. 3 is a characteristic diagram of the ultrasonic motor of the present invention, FIG. 3 is a side sectional view of a conventional ultrasonic motor, FIG. 4 is an operation principle diagram of the ultrasonic motor, and FIGS. 5 (a) and 5 (b) are conventional. FIG. 3 is a displacement distribution map of the ultrasonic ultrasonic motor. In the figure, 10, 30 ... Stator, 11 ... Longitudinal vibration driving piezoelectric ceramic element, 12 ... Torsional vibration driving piezoelectric ceramic element, 13 ... Head mass, 14 ... Rear mass, 15 ... Bolt, 16 ...
Disc-shaped head mass, 17 ... Rotor, 18 ... Bearing, 19
… Pedestal, 20… Coil spring, 21… Nut, 22… Shaft.

Claims (1)

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