JPH04277A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To obtain a high efficiency and a high torque by driving the title motor so that a longitudinal resonance frequency coincides perfectly with the torsional resonance frequency upon high field driving. CONSTITUTION:The stator of an ultrasonic motor is constituted of a composite longitudinal and torsional oscillator, in which respective members arranged in the sequence of a head mass 12a, a longitudinal oscillation driving piezoelectric element 10, first and second ring members, a torsional oscillation driving piezo-electric element 11 and a rear mass 13 are clamped by a nut 14 and a bolt 15. The first ring member on the side of the longitudinal oscillation driving piezo-electric element 10 is designated so that the product of the density thereof by the speed of sound is higher than 27.28kg/ m<2>.sec and lower than 50.66kg/m<2>.sec while the second ring member on the side of the torsional oscillation driving piezo-electric element 11 is designated so that the product of the density thereof by the speed of sound is higher than 18.71kg/m<2>.sec and lower than 34.75kg/m<2>.sec. The rear mass 13 is designed so that the product of the density thereof and the speed of sound is higher than 18.71kg/m<2>.sec and lower than 34.75kg/m<2>.sec. The node of the longitudinal and torsional oscillation can be positioned at the center of the longitudinal oscillation driving piezo-electric element whereby the resonance frequency of respective members can be designed so as to coincide.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in an ultrasonic motor that uses a longitudinal/torsional composite vibrator as a stator as a source of rotational torque.

(Prior technology) A conventional ultrasonic motor that uses a vertical/torsional compound vibrator as a stator has a stainless steel ring, a piezoelectric element for driving longitudinal vibration,
A support, a piezoelectric element for driving torsional vibration, and a stainless steel rear mass are arranged in this order, and an aluminum alloy head mass is arranged on the side that comes into contact with the stainless steel ring, and a stainless steel head mass is arranged on the side that comes into contact with the rear mass. A vertical and torsional composite vibrator that is tightened with a bolt made of nuts is used as the stator, and the length ratio of the piezoelectric element for driving the vertical and torsional vibrations to the total length of the stator is large.

Further, piezoelectric elements for vertical and torsional vibration are manufactured by laminating thin ring-shaped piezoelectric ceramics in order to lower the driving piezoelectricity.

(Problems to be Solved by the Invention) In longitudinal and torsional vibration, the strain is maximum at each node position, and it is desirable that the piezoelectric element for driving longitudinal and torsional vibrations be arranged at each vibration node position. A piezoelectric element located far from the node position cannot efficiently excite the stator. In addition, the number of laminated ring-shaped piezoelectric ceramics is increased,
A piezoelectric element for vertical and torsional driving in which piezoelectric ceramics are electrically connected in parallel has a small electrical impedance.

Therefore, in the conventional ultrasonic motor described above, the material cost and manufacturing cost of the piezoelectric element account for a large proportion, resulting in an expensive ultrasonic motor. Furthermore, more current flows than necessary, increasing power consumption. The above problems are important issues to be solved in order to reduce the cost and increase the efficiency of ultrasonic motors.

The ultrasonic motor uses a vertical and torsional compound vibrator as a stator.
In order to increase motor efficiency, the resonant frequencies of longitudinal and torsional vibrations are matched, and the nodes of longitudinal vibration and torsional vibration are located in the longitudinal center of the piezoelectric element for longitudinal vibration and the piezoelectric element for torsional vibration, respectively. It is configured as follows. In order to solve the above problems, the length of the piezoelectric element for driving vertical and torsional vibrations arranged in a conventional ultrasonic motor is shortened, and each vibration node is positioned in the center of the piezoelectric ceramic element. , it is impossible to match the resonance frequencies because the phase velocity of longitudinal vibration is 1.6 times larger than the phase velocity of torsion.

(Means for Solving the Problems) The present invention provides a head mass, a piezoelectric element for longitudinal vibration drive, first and second ring members, a piezoelectric element for torsional vibration drive, and a rear mass, which are arranged in the order of a nut. This is an ultrasonic motor whose stator is a longitudinal/torsional compound vibrator that is tightened with bolts, and the first ring member on the side of the piezoelectric element for driving longitudinal vibration has a product of density and sound speed of 27.28 kg/m2・sec.
The above is 50.66 kg/m2・sec or less, and the product of the density of the second ring member on the side of the piezoelectric element for torsional vibration drive and the sound speed is 34.75 at 18.71 kg/m2・SeC or more.
kg/m2・sec or less, and the product of rear mass density and sound speed is 34.75 at 18.71 kg/m2・sec or more.
The ultrasonic motor is characterized in that it is less than kg/m2-sec. The vertical and torsional vibration nodes can be located at the center of the vertical and vibration driving piezoelectric elements, and their respective resonance frequencies can be matched.

In conventional ultrasonic motors, the resonant frequency of torsional vibration is higher than the resonant frequency of longitudinal vibration, and the resonant frequency of torsional vibration slightly increases and becomes saturated with the pressure contact force between the rotor and stator, and the resonance frequency of longitudinal vibration increases. The frequency increases significantly and approaches the resonant frequency of torsional vibration, and when the pressure contact force is further increased, the respective resonant frequencies match. However, if the pressure contact force is considerably large, the vibration amplitude is suppressed and the ultrasonic motor stops rotating. Therefore, it is necessary to match the resonance frequencies of the longitudinal and torsional vibrations with a moderate contact force.

Next, the reason for limiting the materials of the members will be explained.

In order to match the resonance frequencies of longitudinal and torsional vibrations, there are two methods: decreasing the resonance frequency of torsional vibrations or increasing the resonance frequencies of longitudinal vibrations. In order to increase the resonance frequency of longitudinal vibration, the material of the head mass can be made of a material with a large density-sound velocity product (pc product), such as stainless steel, but this has the disadvantage that the vibration amplitude becomes small. Therefore, it is more appropriate to select the material for the rear mass.

In order to reduce the resonance frequency of torsional vibration, the rear mass may be made of a material with a small pc product. However, for materials whose pC product is less than 18.71 kg/m2・sec, the contact force at which the resonance frequencies of longitudinal vibration and torsional vibration coincide will be significantly lower, and for materials whose pC product is greater than 34.75 kg/m2・sec, longitudinal vibration and When the resonance frequencies of torsional vibrations match, the contact force increases significantly. The material of the ring disposed on the side of the torsional vibration driving piezoelectric element is also the same as that of the rear mass. The pc product of the ring material placed on the side of the piezoelectric element for longitudinal vibration drive is 27.2.
For materials below 8 kg/m2・sec, the pressure welding force at which the resonance frequencies of longitudinal vibration and torsional vibration match becomes significantly lower, and 5
For materials exceeding 0.66 kg/m2·sec, the pressure contact force at which the resonance frequencies of longitudinal vibration and torsional vibration coincide becomes significantly high.

(Example) Hereinafter, an example of an ultrasonic motor based on the present invention will be described with reference to the drawings.

The ultrasonic motor manufactured according to the present invention shown in FIG. 1 has a total length of 45.15 mm. The head mass 12a is made of aluminum alloy and has a diameter of 12 mm and a length of 7 mm. The head mass 12b is made of stainless steel and has a diameter of 13 mm.
, a ring with a length of 3 mm, and a bolt 15 made of stainless steel with a diameter of 4 mm and a length of 25.1 mm, and a head mass 12.
It is integrated into a. The vertical vibration driving piezoelectric element 10 is constructed by bonding two rings each having a thickness of 1 mm and a diameter of 12 mm. The torsional vibration driving piezoelectric element 11 is constructed by bonding two rings each having a thickness of 1 mm and a diameter of 12 mm. Stainless steel (PC
38.97kg/m2・5ee) diameter 12mm,
The intermediate cylinder 16a with a length of 2.9 mm is made of brass (pc area: 26.73 kg/m2・5
ee) diameter 12mm.

An intermediate cylinder 16b with a length of 2.9 mm is arranged, a stainless steel support 17 with a thickness of 0.5 is sandwiched between the intermediate cylinders, and these members are connected to the head mass 3a with a diameter of 12 mm.
, length 11.5mm brass casting (pc area 26.73kg/m
It is sandwiched between rear masses 13 made of 2.5ec) and firmly tightened with nuts 14 made of stainless steel. The rotor 18, which has a diameter of 12 mm and a height of 10 mm, is pressed against the stator with a spring via a bearing so that the rotor 18 rotates around a shaft integrated with the head mass 12a.

An effective value of 50 M was simultaneously applied to the piezoelectric elements for driving longitudinal vibration and torsional vibration of the ultrasonic motor of the present invention so that the phase difference of mechanical vibration was 90 degrees, and frequency characteristics were measured.

When the respective resonance frequencies were plotted when the contact force between the rotor and stator was changed, the results shown in FIG. 2 were obtained. As a result, the ultrasonic motor of the present invention has a pressure contact force of 20 kg.
The resonance frequencies of the longitudinal and torsional vibrations matched at f. The pressure contact force, drive frequency, and phase difference between the voltages applied to the vertical and torsional vibration drive piezoelectric elements of this ultrasonic motor are adjusted so that the rotor rotation speed is maximized, and the rotation speed-torque characteristics and efficiency are measured. The performance shown in FIG. 3 was obtained.

The conventional ultrasonic motor shown in Figure 4 has a total length of 37.3 m.
It is m. The head mass 12a is made of aluminum alloy and has a diameter of 12 mm and a length of 7 mm. The head mass 12b is made of stainless steel and has a diameter of 13 mm and a length of 3 mm.
The bolt 15 is made of stainless steel and has a diameter of 4 mm and a length of 18.
3 mm, and is integrated into the head mass 12a.

The vertical vibration driving piezoelectric element 10 has a thickness of 1 mm and a diameter of 12 mm.
It is made up of four rings glued together. The piezoelectric element 11 for torsional vibration drive consists of four rings each having a thickness of 1 mm and a diameter of 12 mm.
It is made up of two pieces glued together. A stainless steel support 17 with a thickness of 0.5 is sandwiched between the piezoelectric element 10 for longitudinal vibration drive and the piezoelectric element 11 for torsional vibration drive, and these members are connected to the head mass 12.
a and a stainless steel rear mass 13 with a diameter of 12 mm and a length of 1 mm, and is firmly tightened with a nut 14. The stator with the above configuration has a diameter of 12 mm and a height of 10 mm.
The rotor 18 is pressed against the stator by a spring via a bearing so that the rotor 18 rotates around a shaft integrated with the head mass 12a.

An effective value of 50 (V) was simultaneously applied to piezoelectric elements for driving longitudinal vibration and torsional vibration of a conventional ultrasonic motor so that the phase difference of mechanical vibration was 90 degrees, and frequency characteristics were measured. When the respective resonance frequencies were plotted when the pressure contact force between the rotor and the stator was changed, the results shown in FIG. 5 were obtained. As a result, the conventional ultrasonic motor has a pressure force of 23 kg.
The resonance frequencies of the longitudinal and torsional vibrations matched at f. When the pressure contact force, drive frequency, and phase difference of the voltages applied to the vertical and torsional vibration drive piezoelectric elements of this ultrasonic motor are adjusted so that the rotor rotational speed is maximized, and the rotational speed-torque characteristics and efficiency are measured, As shown in FIG. 6, performance was significantly inferior to that of the present invention.

Also, with the configuration of the present invention, the pc product is 18.71 kg1m2・s
When a metal material below ec was used for the intermediate cylinder 16b and the rear mass, the resonance frequency of longitudinal vibration became higher than the resonance frequency of torsional vibration under low pressure contact force conditions. When the intermediate cylinder 16b and the rear mass were made of a metal material with a pc product exceeding 34.75 kg/m2·sec, the resonance frequencies of longitudinal and torsional vibrations matched only under conditions of higher contact force than in a conventional ultrasonic motor. Furthermore, p
When a metal material with a C product of less than 27.28 kg/m2·sec was used as the intermediate cylinder 16a, the resonance frequency of longitudinal vibration became higher than the resonance frequency of torsional vibration under low contact force conditions. PC product is 50.66kg/m
When a metal material with a vibration resistance exceeding 2.sec was used as the intermediate cylinder 16b, the resonance frequencies of the longitudinal and torsional vibrations matched only under conditions of a higher pressure contact force than in the conventional ultrasonic motor.

(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 Description of the Drawings] Fig. 1 is a cross-sectional view of the ultrasonic motor of the present invention, Fig. 2 is a resonant frequency-pressing force characteristic diagram of the ultrasonic motor of the present invention used in an example, and Fig. 3 is a diagram of an embodiment of the ultrasonic motor. A motor characteristic diagram of the ultrasonic motor of the present invention used in the example, FIG. 4 is a sectional view of a conventional ultrasonic motor, and FIG. 5 is a resonance frequency-pressing force characteristic diagram of the conventional ultrasonic motor used in the example. , FIG. 6 shows a motor characteristic diagram of the conventional ultrasonic motor used in the example. In the figure, 10... piezoelectric element for longitudinal vibration drive, 11-
0. Piezoelectric element for torsional vibration drive, 12a...Aluminum alloy helad mass, 12b...Stainless steel head mass ring, 1300. Brass rear mass, 14...
・Nando, 15... Bolt, 16a, 16b...
Brass intermediate cylinder, 17... Support, 18...
The rotor is shown.

Claims (1)

[Claims] Head mass, vertical vibration drive piezoelectric element, first and second
An ultrasonic motor whose stator is a vertical/torsional composite vibrator in which each member is arranged in the order of a ring member, a piezoelectric element for driving torsional vibration, and a rear mass, and is tightened with nuts and bolts. The first ring member on the element side is 50.66 kg when the product of density and sound speed is 27.28 kg/m^2・sec or more.
/m^2・sec or less, and the product of the density of the second ring member on the side of the piezoelectric element for torsional vibration drive and the speed of sound is 18.71k.
g/m^2・sec or more: 34.75kg/m^2・s
ec or less, and the product of rear mass density and sound speed is 34.75 kg at 18.71 kg/m^2・sec or more.
/m^2・sec or less.