JP2003009556A - Ultrasonic motor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotor press-contacting structure that is stable and efficient and does not require a housing space. SOLUTION: An ultrasonic motor device comprises a stator 1 which is composed of a cylindrical piezoelectric element and generates a rotationally driving force to its cylinder end faces, a rotor 2 which is rotationally driven by the rotational driving force of the stator 1 when the rotor 2 is slidingly brought into contact with the cylinder end faces of the stator 1, and a pedestal 7 which is positioned on one side of the rotor 2 opposite to the stator 1 and receives the rotor 2. The motor device also comprises a rotation assisting means which is positioned between the rotor 2 and pedestal 7 and is brought into contact with the rotor 2 to press the rotor 2 against the cylinder end faces of the stator 1. The rotation assisting means is composed of a leaf spring 8 having an annular section 8c which is brought into contact with the pedestal 7 and a plurality of radiated sections 8T which are radially extended from the annular section 8C and brought into contact with the rotor 2. At the front end sections of the radiated sections 8T, semispherical projections 8R which are brought into contact with the rotor 2 are respectively formed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an ultrasonic motor device. More specifically, it relates to a pressure contact structure of a rotor with respect to a stator.

[0002]

2. Description of the Related Art Conventionally, ultrasonic motors have two types, a standing wave type motor and a traveling wave type motor, which are symmetrical excitation modes in which the center of gravity of the oscillator is fixed, and a disc or cylinder which is an oscillator is, for example, 4 There is known an electrostrictive revolution-type motor in which the center of gravity rotates and moves around the center by excitation in an asymmetric mode in which the amplitude is divided and the left and right amplitudes are reversed, and the outer circumference of the circle is eccentric like a hula hoop. Such an ultrasonic motor (hereinafter, also referred to as a piezo motor) applies a high-frequency AC voltage to a piezoelectric element serving as a stator to generate ultrasonic vibrations of about 20 kHz or more, thereby rotationally driving a rotor pressed against the stator. ing. This type of piezo motor has the advantages that it has a simple structure and is suitable for downsizing and weight reduction, and that high torque can be obtained even at low speed rotation and that driving noise is low and quiet. In particular, the latter electrostrictive revolution type motor generates a 3D revolution torque in which, in addition to the diameter and circumferential direction of the cylindrical revolution element, an axial mode is also coupled, as disclosed in Japanese Patent Laid-Open No. 10-272420. It has the feature that it can be used as a child

[0003]

In a piezo motor, a rotor is brought into pressure contact with a sliding surface of a stator which excites ultrasonic vibrations, and a driving torque such as a rotational movement is taken out.
Unless the rotor is brought into pressure contact with the sliding surface of the stator at an appropriate pressure, torque and the number of rotations cannot be obtained, and there is a problem that rotation unevenness occurs. If the friction of the sliding surface of the stator is too large, the same problem tends to occur. Therefore, the sliding surface of the stator has been polished in order to reduce the friction that causes uneven rotation in a necessary range. However,
Polishing the stator requires a lot of man-hours, which results in an increase in manufacturing cost. Further, in order to suppress the above-mentioned uneven rotation, when the rotor is pressed against the stator,
A structure using a ball bearing as a rotor receiving member has also been proposed. However, if the ball bearings are simply used, the bearings collide with each other during the rotational driving of the piezo motor, which becomes a source of noise, which causes inconvenience depending on the application of the piezo motor. Further, using a ball bearing as the receiving member has a disadvantage that the cost is high.

A coil-shaped compression spring has been conventionally used as a means for pressing the rotor against the stator.
However, if a compression spring is used, a space for accommodating the compression spring is required, and thus the size of the ultrasonic motor is increased. Further, when the end of the compression spring is brought into contact with the rotor, a frictional force is generated between the rotor and the compression spring, resulting in a loss of the rotational force of the rotor.

[0005]

SUMMARY OF THE INVENTION In view of the above problems of the prior art, an object of the present invention is to provide a rotor pressure contact structure that is stable and efficient and does not require a storage space.
The following measures have been taken to achieve this purpose. That is,
A stator made of a cylindrical piezoelectric element that generates a rotational driving force on a cylindrical end surface, a rotor that slidably presses against the cylindrical end surface to perform a rotational motion by the rotational driving force, and a rotor between A base positioned on the opposite side of the stator to receive the rotor, and a rotation assisting unit disposed between the rotor and the base to contact the rotor to press the rotor toward the cylindrical end surface of the stator. In the ultrasonic motor device, the rotation assisting means is a leaf spring. Specifically, the leaf spring includes an annular portion that abuts the base and a plurality of radial portions that extend radially from the annular portion and abut the rotor. In this case, a hemispherical projection that contacts the rotor is formed at the tip of each radial portion.

According to the present invention, the rotation assisting means is used as the pressure contact structure in order to press the rotor against the stator to realize a smooth rotational movement. The rotation assisting means is composed of a leaf spring. Compared to the conventional coil-shaped compression spring, the leaf spring does not require a housing space and can be efficiently incorporated in the ultrasonic motor device. In addition, the rotor can be stably pressed against the stator without impairing the rotational movement. Further, according to the present invention, the stator generates a revolution torque by the electrostrictive revolution resonance of the cylindrical end surface, and the rotor takes out the electrostrictive revolution resonance torque directly as a rotation motion.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic sectional view showing an embodiment of an ultrasonic motor device according to the present invention. As shown in the figure, the present ultrasonic motor device is an electrostrictive revolving rotor type motor composed of a 3D revolving torque generator disclosed in Japanese Unexamined Patent Publication No. 10-272420 as described above, and includes a stator 1 and a rotor 2. It is composed of a base 7 and rotation assisting means. The stator 1 is composed of a piezoelectric element having a cylindrical shape and generates a revolution torque on the end surface of the cylinder. The stator 1 is fixed to a pedestal 6 integrated with a base 7 with an adhesive 6a or the like. The adhesive 6a is for preventing the stator 1 from rotating and moving, and is preferably made of elastic silicone rubber or the like. If strongly fixed to the pedestal 6, the revolution torque of the stator 1 may be impaired. The radial position of the outer peripheral surface of the stator 1 is defined by the positioning portion 6b provided on the pedestal 6. In this state of positioning, the stator 1 is fixed to the pedestal 6 by the adhesive 6a. The rotor 2 slidably contacts the cylindrical end surface of the stator 1 to convert the revolution torque into a rotation motion. In the illustrated example, the rotor 2 is made of an annular metal member or the like, is arranged concentrically with the cylindrical axis of the stator 1, and performs a rotary motion about the cylindrical axis. The base 7 is located on the opposite side of the stator 1 with the rotor 2 in between and receives the rotor 2. The base 7 is attached to the base 6 with screws.

The rotation assisting means is arranged between the rotor 2 and the base 7, and comes into contact with the rotor 2 to press the rotor 2 toward the cylindrical end surface of the stator 1. As a feature of the present invention, this rotation assisting means is composed of a leaf spring 8. As shown, the leaf spring 8 basically comprises an annular portion 8C and a plurality of radial portions 8T. The annular portion 8C is in contact with the base 7. The annular portion 8C is positioned and fixed to a protrusion provided on the base 7. The radial portion 8T has a desired elasticity, extends radially from the annular portion 8C, and abuts on the rotor 2. A hemispherical projection 8R that contacts the rotor 2 is formed at the tip of each radial portion 8T. Unlike the coil-shaped compression spring, the leaf spring 8 has a flat shape as a whole and can be compactly mounted between the base 7 and the rotor 2. Therefore, it contributes to downsizing of the ultrasonic motor device. The leaf spring 8 has a radial portion 8T that contacts the rotor 2, and each radial portion 8T has a hemispherical protrusion 8R at the tip thereof. The rotor 2 has this hemispherical projection 8R
Rotate while rubbing. Since the contact area of the protrusion 8R is small, it is possible to reduce the loss of the rotational force of the rotor 2 due to friction.

FIG. 2 shows an application example of the ultrasonic motor device according to the present invention, which is used as a power source of a camera lens driving device. FIG. 1 is a schematic vertical sectional view of a camera lens driving device. As shown in the figure, the camera lens driving device is basically composed of an ultrasonic motor including a stator 1 and a rotor 2, and a lens barrel 3. These parts are assembled using the pedestal 6. The stator 1 receives a drive voltage from the outside and excites ultrasonic vibration to generate revolution torque. The rotor 2 converts the revolution torque generated in the stator 1 into a rotation motion. Therefore, the rotor 2 is pressed against the stator 1 by the leaf spring 8. The leaf spring 8 is mounted between the base 7 and the rotor 2. The base 7 is fixed to the bottom of the base 6 with screws. On the other hand, the lens barrel 3 includes the lenses 33 and 34 for the camera.
Is mounted on the pedestal 6 so as to be linearly displaceable in the optical axis Z direction of the lens. Specifically, a stopper 32 is formed on the lens barrel 3 and is engaged with the guide shaft 4 planted on the pedestal 6. Lens barrel 3
Is restricted from rotating by the stopper 32,
It is linearly displaced along the guide shaft 4 in the optical axis Z direction.
A spring 41 for backlashing the lens barrel 3 is attached to the stopper 32 engaged with the guide shaft 4.
Here, the rotor 2 has a ring shape, and a helicoid gear 21 is formed on the inner peripheral surface thereof. A helicoid gear 31 is also formed on the outer peripheral surface of the lens barrel 3. The helicoid gear 21 on the rotor 2 side and the helicoid gear 31 on the lens barrel 3 side are engaged with each other. When the rotor 2 rotates, the lens barrel 3 also tries to rotate due to the engagement of the above-mentioned helicoid gear, but since the rotational displacement is restricted by the stopper 32, the linear displacement along the guide shaft 4 in the optical axis Z direction. Will be done. Such linear displacement of the lens barrel 3 along the optical axis Z direction is used for zooming and focusing of the camera.

FIG. 3 shows a planar shape of the leaf spring 8 incorporated in the ultrasonic motor device shown in FIG. As shown, the leaf spring 8 includes an annular portion 8C and a plurality of radial portions 8C.
It consists of T and. The annular portion 8C is attached to the base 7 shown in FIG. The plurality of radial portions 8T extend radially from the annular portion 8C and have desired elasticity. A hemispherical protrusion 8R that contacts the rotor is formed at the tip of each radial portion 8T.

FIG. 4 is a schematic perspective view showing the entire structure of the ultrasonic motor (piezomotor) shown in FIG. 1 or 2. As shown in the figure, the piezo motor is composed of a cylindrical stator 1 and an annular rotor 2 that is pressed against its rear end. On the outer peripheral surface of the cylindrical stator 1, electrodes 11,
12, ... Are formed. Although not shown, electrodes are also formed on the inner peripheral surface of the cylinder. The electrodes formed on the outer peripheral surface of the cylinder are divided into four, and AC driving voltages A, B, AX, and BX having different phases are applied to the electrodes. The A-phase voltage and the B-phase voltage are 90 degrees out of phase with each other.
Further, the A-phase voltage and the AX-phase voltage are 180 degrees out of phase with each other. In other words, the A phase and the AX phase have opposite polarities. Similarly, the B phase and the BX phase have opposite polarities.

FIG. 5 is a schematic cross-sectional view of the stator shown in FIG. As shown in the figure, an electrode 10 for applying a reference potential is formed on the entire inner peripheral surface of the cylindrical stator 1 made of a piezoelectric element such as ceramics. Four-divided driving electrodes 11 to 14 are formed on the outer peripheral surface of the cylinder. These four-divided electrodes 11 to 14 have four-phase AC voltages A whose phases are mutually shifted by 90 degrees,
B, AX and BX are applied.

The operation of the piezo motor shown in FIGS. 4 and 5 will be described with reference to FIG. In the piezo motor, the ultrasonic vibration that serves as a power source has a constant resonance frequency, so that the current has a substantially constant value. The resonator has a high Q and the rising of the vibration amplitude is considered to be within one cycle, and can be regarded as a non-inertial mechanism. The current changes only within the range affected by the load inertia. Although various configurations of the piezo motor having such characteristics have been developed, the electrostrictive revolution type is particularly effective. The electrostrictive revolution type uses a resonator that can directly excite uniform torque over the entire peripheral surface, instead of changing vibration into torque as in the conventional case. There are two types of conventional ultrasonic transducers, a standing wave type and a traveling wave type, but both can be excited only in a symmetric mode with a fixed center of gravity. On the contrary, when the cylinder is excited in a mode in which the left and right expansions are reversed, the center of gravity vibrates away from the center. When this asymmetrical excitation is performed, a cylindrical resonance mode which cannot be observed by the conventional symmetrical excitation is obtained. Therefore, when the electrode of the stator cylinder is divided into, for example, four parts and excited by rotating electric fields having different phases by 90 degrees, resonance of a mode in which the center of gravity rotates around the center is seen as shown in FIG. At this time, the outer circumference of the circle keeps its original shape,
Since it is eccentric like a hula hoop, the oscillator revolves around the revolution. In the electrostrictive revolution rotor having such a configuration, the direct rotation mode is excited and a strong revolution torque is uniformly generated on the peripheral surface.
At the same time, a strong torque is generated on the end surface of the cylindrical stator in the direction perpendicular to the diameter. This revolution torque is taken out as the rotation motion of the rotor that is directly in pressure contact with the stator.

FIG. 7 is a waveform diagram of A-phase, B-phase, AX-phase, and BX-phase voltages applied to each of the four-divided stator electrodes. As shown in the figure, the B phase is shifted by 90 degrees, the AX phase is shifted by 180 degrees, and the BX phase is shifted by 270 degrees with respect to the A phase. In this way, a rotating electric field is formed by applying alternating voltage with different phases by 90 degrees to the stator,
In response to this, the stator directly excites the revolution mode.

Finally, FIG. 8 shows a drive circuit for the piezo motor. As shown, a pair of drive signals A and AX
Is applied to a pair of electrodes of the stator 1 facing each other via the H bridge A. Similarly, another pair of signals B, B
X is also applied to the other pair of stator electrodes facing each other via the H bridge B. Each H-bridge is a driver circuit for supplying a sufficient output current to the stator electrode in response to an input signal.

[0016]

As described above, according to the present invention, in the ultrasonic motor device, the rotation assisting means is composed of a leaf spring provided with a hemispherical projection that contacts the rotor. By using a leaf spring to press the rotor to the stator,
The storage space can be reduced, which leads to downsizing of the ultrasonic motor device. Also, by providing a hemispherical protrusion at the location where it contacts the rotor, the friction between the rotor and the leaf spring is reduced,
It is possible to prevent the loss of the rotational force of the rotor.

[Brief description of drawings]

FIG. 1 is a schematic partial cross-sectional view showing an embodiment of an ultrasonic motor device according to the present invention.

FIG. 2 is a schematic partial cross-sectional view showing an embodiment of a camera lens driving device using the ultrasonic motor device according to the present invention as a driving source.

FIG. 3 is a plan view showing the shape of a leaf spring incorporated in the device shown in FIG.

FIG. 4 is a schematic perspective view showing an appearance of an ultrasonic motor device according to the present invention.

FIG. 5 is a cross-sectional view of the ultrasonic motor device according to the present invention.

FIG. 6 is a schematic diagram for explaining the operation of the ultrasonic motor device according to the present invention and the generation of revolution torque.

FIG. 7 is a waveform diagram for explaining the operation of the ultrasonic motor device according to the present invention.

FIG. 8 is a drive circuit diagram of the ultrasonic motor device according to the present invention.

[Explanation of symbols]

1 ... Stator, 2 ... Rotor, 7 ... Base, 8
... Leaf spring, 8C ... Annular portion, 8T ... Radial portion, 8R ... Protrusion

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyoji Hosono             2-18-10 Shimura, Itabashi-ku, Tokyo Nidec             Sankopal Co., Ltd. (72) Inventor Kiyoshi Toma             2-18-10 Shimura, Itabashi-ku, Tokyo Nidec             Sankopal Co., Ltd. F-term (reference) 2H044 BE04 BE05 BE06 BE07 BE09                       BE20 DB04 DB07                 5H680 AA06 AA19 BB01 BB16 BC01                       DD01 DD15 DD23 DD53 DD59                       DD66 DD73 DD88 DD92 FF04                       FF08 FF26 FF33 FF35 GG19                       GG42

Claims (4)

[Claims] 1. A stator comprising a cylindrical piezoelectric element for generating a rotational driving force on an end surface of a cylinder, a rotor slidably pressed against the end surface of the cylindrical member to perform a rotational motion by the rotational driving force, A base that is located on the opposite side of the stator with the rotor in between and receives the rotor, and is disposed between the rotor and the base to contact the rotor and press the rotor toward the cylindrical end surface of the stator. In the ultrasonic motor device including the rotation assisting means, the rotation assisting means includes a leaf spring. 2. The leaf spring comprises an annular portion that abuts on the base, and a plurality of radial portions that extend radially from the annular portion and abut the rotor. Ultrasonic motor device. 3. The ultrasonic motor device according to claim 2, wherein a hemispherical protrusion that contacts the rotor is formed at the tip of each radial portion. 4. The stator according to claim 1, wherein the cylindrical end surface generates an orbital torque by electrostrictive orbital resonance, and the rotor directly takes out the electrostrictive orbital resonant torque as a rotational motion. Ultrasonic wave device.