JP2555572B2 - Ultrasonic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an ultrasonic motor in which a rotor is rotationally driven by a progressive vibration wave formed by a stator.

B. Prior Art In this type of ultrasonic motor, an electrostrictive element is attached to the back surface of an annular stator, and a frequency voltage is applied to this electrostrictive element to form a progressive vibration wave in the stator. The rotor is vibrated by a progressive vibration wave by bringing the rotor into pressure contact with the stator.

By the way, various pressurizing means for this kind of ultrasonic motor have been conventionally proposed. For example, Japanese Patent Laid-Open No. 59-185179 discloses a permanent magnet for applying a pressing force. Further, Japanese Patent Laid-Open No. 185180/1984 discloses a device for obtaining a pressing force by an electromagnet.

C. Problems to be Solved by the Invention However, in the above ultrasonic motor, the magnetic force acts on the sliding surface of the stator and the rotor, and it is necessary to obtain sufficient magnetic force on the sliding surface. Alternatively, the magnetic material is provided at a position close to the sliding surface of the rotor. For this reason, the resonance system on the rotor side is affected by the permanent magnet or the like, and the number of design restrictions increases, which makes optimum design difficult. Also, disposing the permanent magnet in such a place is difficult in terms of design.

Further, in the former case, since the stator and the rotor are constantly in pressure contact with each other due to the magnetic force, a large driving force is required when rotating the rotor from the outside. Furthermore, the latter type has a problem in terms of power consumption because it always requires an electromagnetic force when driving the rotor.

An object of the present invention is to provide an ultrasonic motor that solves the above-mentioned problems by efficiently using the magnetic force and electromagnetic force of a permanent magnet.

D. Means for Solving the Problems The present invention will be described with reference to FIG. 1 showing an embodiment of the present invention.
A rotor 6 that is rotationally driven by a progressive vibration wave, a permanent magnet 4 that polarizes in the rotation axis direction of the rotor 6 and pressurizes and contacts the stator 1 and the rotor 6 with magnetic force, and a magnetic field generated by the permanent magnet 4. Electrode means 4 and 5 for generating a magnetic field for canceling the
Is arranged so that the magnetic force acts on the stator 1 and the rotor 6 at a place other than the sliding surface of the stator 1 and the rotor 6, the above-mentioned object is achieved.

E. Action When the rotor 6 is rotationally driven by the progressive vibration wave generated in the stator 1, the rotor 6 and the stator 1 are brought into pressure contact with each other by the magnetic force of the permanent magnet 4. When the rotor 6 is rotationally driven from the outside, a magnetic field is generated by the electromagnetic means 4; 5 to cancel the magnetic force of the permanent magnet 4. As a result, the pressure applied between the rotor 6 and the stator 1 is released, and the rotor 6 can be rotationally driven with a small force. Also,
The magnetic forces of the permanent magnet 4 and the electromagnetic means 4 and 5 act on portions other than the sliding surfaces of the stator 1 and the rotor 6.

F. Embodiment One embodiment of the present invention will be described with reference to FIG.

An electrostrictive element 2 is provided on the back surface of a stator 1 on a disk, which is a magnetic material, and projections 3 for amplifying vibration are provided on the front surface at predetermined intervals. At the center of the stator 1, a cylindrical permanent magnet 4 whose polarity is differentiated in the longitudinal direction is press-fitted and erected, and a coil 5 is wound around the permanent magnet 4 to form an electromagnet (electromagnetic means). Is configured.
The leads 5a and 5b of the coil 5 are routed to the outside of the protrusion from the gap 3a of the protrusion 3. Reference numeral 6 is a rotor made of a magnetic material on a hollow cylinder. The other end of the permanent magnet 4 is fitted into a hole 6a bored in the central portion, and the open end surface 6c of the peripheral wall 6b of the rotor 6 has the projection 3
Placed on top.

The rotor 6 is rotatable about the axis of the permanent magnet 4 while the open end surface 6c slides on the protrusion 3.

The operation of the ultrasonic motor configured as above will be described.

The coil 5 is not energized, and the rotor 6 and the stator 1 are brought into pressure contact with each other by the magnetic force of the permanent magnet 4. When a frequency voltage is applied to the electrostrictive element 2 from a drive circuit (not shown) to form a progressive vibration wave in the stator, the progressive vibration wave causes the rotor 6 to rotate around the axis of the permanent magnet 4.

On the other hand, when the coil 5 is energized to generate a magnetic field opposite to the magnetic field generated by the permanent magnet 4, the two cancel each other out, and the pressing force between the rotor 6 and the stator 1 is canceled. Therefore, the rotor 6 can be rotated from the outside with a small force.

In this embodiment, the permanent magnet 4 is used as the rotary shaft of the ultrasonic motor, and the coil 5 is wound so as to also constitute the electromagnetic means, so that the configuration is extremely simplified and contributes to downsizing of the ultrasonic motor. To do.

The ultrasonic motor described above can be used, for example, as a motor for driving the photographic lens optical system of an automatic focusing camera, and during automatic focusing, the magnetic force of the permanent magnet causes the stator and rotor to come into pressure contact with each other, and the manual focusing When adjusting, the coil is energized to remove the applied pressure, which allows the range ring to be operated with a small force. Also,
In the present embodiment, the magnetic force of the permanent magnet 4 and the coil 5 attracts the stator 6 downward in FIG. 1 to bring it into pressure contact with the stator 1. Therefore, since it is not necessary to dispose a permanent magnet or the like in the vicinity of the sliding surface of the rotor 6 and the stator 1, that is, in the vicinity of the open end surface 6C, it is easy to control the resonance system of the rotor 6 and the permanent magnet or the like is incorporated. Design difficulties can be avoided.

G. Effect of the Invention According to the present invention, since the pressing force between the rotor and the stator is obtained by the permanent magnet and the magnetic force is canceled by the electromagnetic force, it is driven with small power consumption and small. An ultrasonic motor that can operate a rotor with force can be provided. In addition, because the magnetic force acts on the parts other than the sliding surface of the stator and rotor, it is not necessary to place permanent magnets in the vicinity of the sliding parts of the stator and rotor. A sonic motor can be provided.

[Brief description of drawings]

 FIG. 1 is an exploded perspective view showing an embodiment of the present invention. 1: Stator, 2: Electrostrictive element 3: Protrusion, 4: Permanent magnet 5: Coil, 6: Rotor

Claims (1)

(57) [Claims] 1. A stator in which a progressive vibration wave is formed, a rotor rotatably driven by the progressive vibration wave, a polarity is differentiated in a rotation axis direction of the rotor, and the stator and the rotor are magnetized by a magnetic force. A permanent magnet that is brought into pressure contact, and electromagnetic means that generates a magnetic field that cancels the magnetic field of the permanent magnet, wherein the magnetic field is generated in a place other than the sliding surface of the stator and the rotor, and controls the magnetic field. The ultrasonic motor, wherein the permanent magnet and the electromagnetic means are arranged so that the pressing contact force is controlled by doing so.