JPH0374178A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To improve driving efficiency and to reduce the weight by providing a piezoelectric body for producing ultrasonic vibration upon application of an AC electrical signal and an elastic member to be excited, and composing the piezoelectric body and the elastic member of high polymer material. CONSTITUTION:In an ultrasonic vibrator 11, a first piezoelectric body 22 for exciting bending vibration in an elastic body 21 is applied onto the upper face of a rectangular elastic plate 12 and second piezoelectric bodies 23a, 23b for exciting longitudinal vibration is applied onto the side face approximately perpendicular to the elastic plate 12. The piezoelectric bodies 22, 23 are composed of high polymer material, and the elastic body 21 is composed of approximately same high polymer material as that of the piezoelectric bodies 22, 23.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an ultrasonic motor.

[Prior Art] Conventionally, electromechanical transducers using electrostrictive or magnetostrictive elements have been used to convert electrical vibrations into mechanical vibrations and generate ultrasonic vibrations. The ultrasonic vibrator has a resonant elastic body attached to these electromechanical transducers, and is configured to obtain ultrasonic vibration with a large amplitude. Electrostrictive elements have a larger stored energy than magnetostrictive elements, so
In many cases, PZT-based piezoelectric ceramics that utilize electrostriction are used.

In the ultrasonic vibrator described above, metal materials such as aluminum and brass have been mainly used as the material for the resonant elastic body because of their high mechanical strength, low internal loss, and low cost.

On the other hand, ultrasonic motors are being actively developed by suitably utilizing the above-mentioned ultrasonic transducers.

The operating principle of an ultrasonic motor is that a movable element is brought into contact with a predetermined pressure against an ultrasonic vibrator that generates approximately elliptical vibration, and the movable element is moved by the frictional force between each mass point vibrating approximately elliptically and the movable element. It is something that is driven.

Since such an ultrasonic motor has a simple structure, the ultrasonic vibrator occupies a very large volume, and reducing the size and weight of the ultrasonic vibrator has a great influence on the motor characteristics.

[Problems to be Solved by the Invention] However, since metal is used for the elastic body of the ultrasonic vibrator, which occupies a large volume in the ultrasonic motor, it has been difficult to reduce the weight of the ultrasonic motor.

The present invention was made in order to solve the above-mentioned problems, and its purpose is to obtain a lightweight ultrasonic motor with good drive efficiency.

[Means for Solving the Problems] In order to achieve this object, the ultrasonic motor of the present invention includes a piezoelectric body that generates ultrasonic vibrations when an alternating current electric signal is applied, and a piezoelectric body that is excited by the vibrations of the piezoelectric body. In an ultrasonic motor equipped with an ultrasonic vibrator having an elastic body,
The piezoelectric body and the elastic body are made of a polymer material.

Further, in the above-mentioned ultrasonic motor, the piezoelectric body and the elastic body are directly joined.

[Function] When an AC electric signal is applied to the ultrasonic vibrator made of a polymer material in the ultrasonic motor of the present invention having the above configuration, a large-amplitude approximately elliptical vibration is generated at a predetermined portion of the ultrasonic vibrator. is excited. At this time, impedance matching is achieved by selecting the materials of the piezoelectric body and the elastic body of the ultrasonic vibrator, so that ultrasonic vibrations are excited with high efficiency. When the movable element is brought into contact with the ultrasonic vibrator at a predetermined pressure,
The mover is driven in a predetermined direction.

[Example] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

The ultrasonic transducer used in this example is, for example, Japanese Patent Application No. 1-4
An ultrasonic transducer that excites standing waves in two substantially orthogonal directions as seen in the specification and drawings attached to application No. 6866 is used. An example of the configuration is shown in FIGS. 1 and 2.

The ultrasonic transducer 11 includes an elastic body 21 having a rectangular flat plate shape.
A first piezoelectric body 22 for exciting bending vibration in the elastic body 21 is attached to the upper surface of the elastic body 21 .

In the elastic body 21, second piezoelectric bodies 23a and 23b for exciting longitudinal vibration in the elastic body 21 are attached to the side surfaces substantially orthogonal to the mounting surface.

Fixing bolts 24a and 24b for fixing the elastic body 21 are fixed at the center of the elastic body 21 in the longitudinal direction. The other ends of the fixing bolts 24a and 24b are fixed to bases 25a and 25b.

A positive electrode 26 is provided on the upper surface of the first piezoelectric body 22 . Further, positive electrodes 27a and 27b are provided on the upper surfaces of the second piezoelectric bodies 23a and 23b. The other surfaces of the piezoelectric bodies 22 and 23 are grounded to a base 25.

Furthermore, the elastic body 21 has a predetermined frequency f in its thickness direction.
The shape and dimensions are adjusted so that both free ends bend and vibrate in a secondary mode.

Further, the shape and dimensions are adjusted so that longitudinal vibration occurs in the first-order mode at both free ends in the length direction at the same frequency f.

Generally, the resonant frequency of longitudinal vibration propagating in an elastic body depends on the length of the elastic body. Further, the resonance frequency of bending vibration in the thickness direction of the elastic body depends on the length and thickness. Therefore, it is easy to design the elastic body 21 as described above.

In the ultrasonic vibrator having the above configuration, substantially elliptical vibration is excited in the elastic body 21 by combining longitudinal vibration and bending vibration. This elliptical shape can be arbitrarily controlled by adjusting the amplitude or phase of the applied voltage.

In the ultrasonic transducer 11 configured as described above, the piezoelectric bodies 22 and 23 are made of a polymeric material, such as polyvinylidene fluoride (hereinafter abbreviated as PvDF).

PVDF is a polarized polymer that is poled under a strong electric field to impart stable polarization to the film. Because the molecular chain contains atoms with a dipole moment, it has a large piezoelectricity and polarization in an electric field. It shows electrical property.

On the other hand, the elastic body 21 of the ultrasonic transducer 11 is made of a polymeric material having mechanical properties similar to or substantially the same as those of the piezoelectric bodies 22 and 23, and the two are directly bonded. As a result, PZ
Compared to a conventional ultrasonic vibrator using a T-based inorganic piezoelectric material and a metal elastic body, a much lighter ultrasonic vibrator can be obtained without significantly changing vibration characteristics such as vibration amplitude.

Polymer piezoelectric materials such as PVDF have other advantages unique to polymers, such as impact resistance, flexibility, and low acoustic impedance, as well as less performance deterioration due to driving electric fields and less deterioration over time. It has various characteristics not found in inorganic piezoelectric materials.

The configuration of a linear ultrasonic motor that suitably utilizes the ultrasonic transducer 11 described above will be explained based on FIG. 3.

In the same figure, each member given the same reference numeral as in FIGS. 1 and 2 means the same as each component described in detail above.

The linear ultrasonic motor 31 has a drive section 32 formed at the end that provides the maximum amplitude of the ultrasonic vibrator 11, and is crimped to a rail 34 by a support member 33.

The crimping mechanism for applying the crimping force includes a first guide 36 disposed between the rail 34 and the support member 33 and supported by a roller bearing 35, a coil spring 37, a spring guide 38, and three spring pressers. It is composed of This is done by rotating a spring retainer 39 along a screw groove attached to the spring guide 38 and changing the length of the coil spring 37 to adjust the pressing force.

On the other hand, the linear ultrasonic motor 3 is attached to the support member 33.
A second guide 40 is fixed with bolts 41 to prevent sideways displacement of the drive unit 1 . The second guide 40 is configured to hold the rail 34 with roller bearings 42.

Further, the linear ultrasonic motor 31 is formed with a first support member 43 for preventing yawing and a second support member 44 for preventing rolling.

When an AC electric signal is applied to the linear ultrasonic motor 31 configured as described above, approximately elliptical vibration is generated in the drive unit 32, and it receives a driving force due to the frictional force with the rail 34, and as shown by the arrow in the figure. Move in direction B.

Although the above embodiments have been explained using a standing wave type linear ultrasonic motor as an example, the invention is not limited to this, and can be used in various motors such as traveling wave type ultrasonic motors and rotary type ultrasonic motors. A similar effect can be obtained.

Further, although an example in which the elastic body and piezoelectric body of the ultrasonic transducer are rectangular flat plates has been described, they can take various shapes such as a disk shape, a cylindrical shape, an annular shape, a rectangular shape, and a rod shape.

In addition, various modifications can be made without departing from the spirit of the present invention.

[Effects of the Invention] As is clear from the detailed description above, according to the present invention, it is possible to obtain a lightweight ultrasonic transducer capable of highly efficient excitation, and the ultrasonic transducer can be suitably used. As a result, it is possible to obtain a lightweight ultrasonic motor with good drive efficiency.

[Brief explanation of drawings]

1 to 3 show embodiments embodying the present invention. FIG. 1 is a top view of the ultrasonic vibrator used in the ultrasonic motor of this embodiment, and FIG. 2 is a side view thereof. , Figure 3 (a
) is a side view of the present linear ultrasonic motor, and FIG. 3(b) is a sectional view taken along line AA in FIG. 3(a). In the figure, 11 is an ultrasonic transducer, 21 is an elastic body, and 22 is a first
A piezoelectric body, 23 is a second piezoelectric body, and 31 is a linear ultrasonic motor.

Claims (1)

[Claims] 1. An ultrasonic transducer comprising a piezoelectric body that generates ultrasonic vibrations when an alternating current electric signal is applied, and an elastic body that is excited by the vibrations of the piezoelectric body. An ultrasonic motor, characterized in that the piezoelectric body and the elastic body are made of a polymer material. 2. The ultrasonic motor according to claim 1, wherein the piezoelectric body and the elastic body are directly joined.