JPH05211783A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To improve the characteristic of a rod-like ultrasonic motor and, at the same time, to prevent the occurrence of squeaking by making the rotor of the motor to follow the undulation of its contact plane with a vibrator. CONSTITUTION:In a rod-like ultrasonic motor the rotor of which is composed of a main rotor ring 2 and contact spring section 2a which in turn is composed of a contact projecting section 2d, flange section 2c, and base section 2b, the wall thickness of the member constituting the section 2a is increased as going farther from the contact section with a vibrator so as to make the natural frequency of the section 2a in all natural vibration modes twice or more of the driving frequency of the motor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention applies an electric energy to an electro-mechanical energy conversion element provided on a rod-shaped elastic body to vibrate the elastic body as a rod-shaped vibrator to cause circular particles on the surface particles of the vibrator. Or an ultrasonic motor that causes an elliptical motion and frictionally drives a moving body that is pressed against a vibrator,
In particular, the present invention relates to an ultrasonic motor suitable for optical equipment such as cameras and office equipment such as printers.

[0002]

2. Description of the Related Art A rod-shaped ultrasonic motor uses an end face of a rod-shaped vibrator as a drive surface and applies an AC voltage having a predetermined phase difference to a piezoelectric element (PZT) which is sandwiched and fixed between the vibrator structures. By applying a force, a bending or vibration is formed in a plurality of planes including the axis to generate a circular or elliptical motion on the driving surface, and the moving body (rotor) that is in pressure contact with the driving surface is rubbed. Driving is the basic configuration.

Since the size of the circular or elliptical motion generated on the driving surface of the vibrator is about several μm at the most, in order to bring the rotor into contact with the driving surface of the vibrator over the entire circumference, the driving surface of the vibrator is required. Also, the surface accuracy of the contact surface of the rotor that comes into contact with the drive surface must be finished to be equal to or greater than the magnitude of the movement.

However, in reality, in consideration of the machining cost, it is not possible to achieve such high precision, and the contact portion on the rotor side is provided with a spring property so that the contact can be maintained over the entire circumference.

FIG. 2 shows a cross section of a rotor having a spring property (only one half is shown). A rotor main ring 2 is integrally formed with a rotor contact spring portion 2a having a thin plate thickness and a spring property provided from the lower portion thereof, and the lowermost end surface of the rotor contact spring portion 2a is a drive surface (not (Shown in the figure). Note that, in FIG. 2, the dimensions shown in the spring portion 2a of the rotor are shown for the sake of comparison with the embodiment of the present invention while showing that the motor including the rotor is very small.

[0006]

By the way, if the spring characteristics of the rotor are too contradictory, neither the motor rotation speed nor the torque is produced, and if it is too rigid, it is impossible to follow the above-mentioned waviness of the contact plane.
There is no motor output.

Therefore, in general, the spring stiffness is experimentally determined, and as a result, the one having excellent motor characteristics is selected.

However, even if the spring shape is determined by such a method, variations in motor characteristics may occur, or squeal may occur during driving.

An object of the present invention is to solve the above problems.

[0010]

The means for achieving the object of the present invention are as set forth in the claims, and the technical background thereof will be explained by the cause of the occurrence of squeaking shown in FIG. FIG. 3 shows a case where the rotor shown in FIG.
The contact between the rotor and the oscillator is measured by a non-contact optical displacement meter.The thick solid line indicates the vibration waveform on the drive surface of the oscillator, and the thin solid line indicates the rotor contact part vibration waveform. is there.

From the vibration waveform of the rotor contact portion, the rotor contains a large amount of frequency components twice as high as that of the drive, and there is no contact near the apex of the vibrator vibration waveform that maximizes the circumferential speed.

Therefore, the number of rotations of the motor is reduced as compared with the case where the vibrator is in the vicinity of the top of the vibration amplitude. Moreover, the contact is not smooth, which may cause squeaking.

When the frequency of the contact spring of this rotor is examined, as shown in FIG. 4, the natural frequency of the secondary bending mode of the contact spring portion 2a is found to be the oscillator drive frequency (36 to 42 KH).
It was found to exist in the vicinity of twice z).

On the other hand, the displacement distribution of the vibrator is sinusoidal, and the exciting force received by the contact spring 2a pressed by the vibrator has a half-wave rectified wave shape as shown in FIG.

At this time, the exciting force component also includes a large amount of components twice as large as that of the driving force, and if there is natural vibration of the contact spring (particularly secondary bending vibration) at this frequency, the amplitude is expanded and the rotor contact as described above is made. Prevents smooth contact like the vibration waveform of the part.

The same reasoning can be applied to the component of three times the driving frequency or more, but the frequency component of the exciting force is smaller than the component of the two times, and the vibration of the contact spring is greater than the third bending. Since the static rigidity of the mode is considerably higher than that of the secondary bending, it is unlikely that a component three times or more the driving frequency will significantly excite the natural vibration of the contact spring.

From the above, it can be said that the natural frequency of the rotor contact portion should be separated from the frequency twice the drive frequency. However, when the frequency is lower than twice the driving frequency, the vibration force cannot be tracked, and therefore, it is necessary to separate in the higher direction.

[0018]

1 is a sectional view of a rotor showing a first embodiment of an ultrasonic motor according to the present invention. The rotor of this embodiment is
Similar to the conventional rotor shown in FIG. 2, the rotor main ring 2 and the contact spring portion 2a are formed, and the contact spring portion 2a extends from the outer peripheral portion of the rotor main ring 2 downward in the axial direction.
b, and a flange portion 2c which extends inward from the lower end of the base portion 2b and is in a cantilevered support state to have a large spring property.
And a contact protrusion 2b that protrudes axially downward from the inner end of the flange 2c.

Assuming that the thickness of the base portion 2b is t ₁ , the thickness of the flange portion 2c is t ₂ , and the thickness of the contact protrusion portion 2d is t ₃ , then in the present embodiment, the relationship of t ₁ > t ₂ = t ₁ is satisfied. Specifically, t ₁ = 0.5 mm and t ₂ = t ₁ = 0.2 mm.

That is, as the distance from the contact portion with the vibrator is increased, the thickness of the contact spring portion is increased to increase the rigidity.

Incidentally, d ₁ = 5.5 mm, d ₂ = 4.2 m
With m, L ₁ = 1.0 mm and L ₂ = 0.2 mm, the frequency of the natural vibration mode of the secondary bending of the contact spring portion 2a in the conventional rotor shown in FIG. 2 was 80 KHz. In the example, the frequency was increased to 120 KHz, which was 2.5 times or more the driving frequency.

In addition, the natural frequencies of 0, 1, and 3 are conventionally 8
What was at 0 KHz to 105 KHz is 120 to 14
Improved to 0 KHz.

FIG. 6 shows a contact portion vibration waveform when the rotor of this embodiment is used for driving.

As is clear from the comparison with the conventional case shown in FIG. 3, the contact is made even near the top of the vibration of the vibrator, and the motor characteristics are improved in both the motor rotation speed and the torque.

In this embodiment, the tip of the contact protrusion 2d is chamfered to be rounded so that the chamfered part prevents wear of the aluminum rotor during the driving of alumite during motor driving. I have to.

FIG. 7 is a sectional view of a rotor showing a second embodiment of the ultrasonic motor according to the present invention. The rotor of this embodiment has a contact spring portion 2 integrally extended from the rotor main ring 2.
The contact spring part 2 has a truncated cone shape in which a is slanted inward as a whole, and the thickness thereof is reduced toward the tip.
The natural frequency of a is increased.

Incidentally, d ₁ = 5.5 mm, d ₂ = 4.2 m
m, t ₁ = 0.3 mm, t ₃ = 0.2 mm, t ₁ = 0.
The frequency of the natural vibration mode of the contact spring portion 2a was 150 KHz, and the natural frequencies of 0, 1, and 3 orders were all 150 KHz or more. The state of contact was similar to that shown in FIG. 6, and the motor output was also improved.

FIG. 8 is a schematic view showing a third embodiment of the ultrasonic motor according to the present invention.

In this embodiment, the contact spring portion 1a is formed on the driving surface side of the vibrator 1, and the rotor 3 contacts the upper surface of the contact spring portion 1a. On the contact portion of the rotor 3, adhesive,
A coated or coated resin layer 4 for abrasion resistance is provided.

The contact spring portion 1a of the vibrator 1 is formed in the shape of an inverted truncated cone whose thickness becomes thinner toward the driving surface, and the same reason as in the second embodiment shown in FIG. 7 is used.

That is, even in the type in which the contact spring portion is provided on the side of the vibrator 1 as in this embodiment, the vibrator contact spring is shown in FIG.
The contact spring portion 1a receives the excitation force distribution as shown in
The effect of increasing the natural frequency of is the same as that of each of the above-described embodiments.

FIG. 9 shows a fourth ultrasonic motor according to the present invention.
It is sectional drawing of the rotor which shows an Example.

In this embodiment, the contact spring portion 2a of the rotor is
It is similar to the first embodiment in that it is composed of the base portion 2b, the flange portion 2c, and the contact protrusion portion 2d, but the thickness t ₁ ,
t ₂ and t ₃ have a relationship of t ₁ > t ₃ > t ₂ . Then, the inside of the connecting portion between the flange portion 2c and the contact protrusion portion 2d is chamfered to form the inclined surface 5, thereby reducing the mass of the tip end portion of the contact spring.

As a result, the natural frequency of the contact spring portion is increased.

Note that t ₁ = 0.45 mm, t ₂ = 0.2
mm, t ₃ = 0.3 mm, L ₁ = 1.0 mm, L ₂ =
0.35 mm, L ₂ = 0.2 mm, d ₁ = 5.5 mm,
d ₂ = 4.15 mm.

FIG. 10 is a schematic view of an apparatus using an ultrasonic motor as a drive source according to the present invention.

A ₁ and a ₂ are piezoelectric elements for driving, S is a piezoelectric element for sensor, b ₁ and b ₂ are vibrator structures, and the piezoelectric element a _{1 is} between the vibrator structures b ₁ and b _2. , A ₂ , S and the electrode plate, the vibrator structure b is fixed by the bolt C.
A vibrator in which ₁ and b ₂ are fastened and a piezoelectric element is sandwiched and fixed is formed.

Reference numeral r denotes a rotor, which is brought into pressure contact with the driving surface of the vibrator by a pressure spring e via a spring case d. f is a rotation output member having a gear portion formed on the outer peripheral portion, and a bearing g
And is in frictional contact with the spring case d.
Therefore, it rotates integrally with the rotor r. A fixing member h is fixed to the tip of the bolt C, and is fixed to the mounting member j by a screw with the rubber sheet i interposed.

In the apparatus having the ultrasonic motor as a drive source configured as described above, the gear portion of the rotation output member f is attached to the large gear 54a of the gear 54 integrally including the large gear portion 54a and the small gear portion 54b. It meshes and the output of the ultrasonic motor is taken out.

The small gear portion 54b of the gear 54 is a driven body,
For example, it meshes with a gear portion 55a formed on the outer peripheral portion of the lens barrel 55 of the camera and is rotationally driven by an ultrasonic motor. On the other hand, an encoder slit plate 56 is coaxially attached to the gear 54, and rotation is detected by the photocoupler 57.

[0041]

As described above, according to the present invention, in the rod-shaped ultrasonic motor, the dynamic characteristics of the contact spring portion are important for maintaining a good contact state. One of the conditions is the drive frequency. By setting the total natural frequency of the contact spring to be more than twice, the good contact state is maintained and the motor performance is improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a rotor showing a first embodiment of an ultrasonic motor according to the present invention.

FIG. 2 is a sectional view of a rotor of a conventional ultrasonic motor.

3 is a vibration waveform of a contact portion between a rotor and a vibrator when the rotor of FIG. 2 is used.

FIG. 4 is a diagram showing a secondary bending vibration mode of a contact spring portion of a rotor.

FIG. 5 is a waveform diagram showing an exciting force.

FIG. 6 is a vibration waveform of a contact portion between the rotor and the vibrator of the first embodiment.

FIG. 7 is a sectional view of a rotor showing a second embodiment.

FIG. 8 is a schematic sectional view of an ultrasonic motor showing a third embodiment.

FIG. 9 is a sectional view of a rotor showing a fourth embodiment.

FIG. 10 is a schematic view of an apparatus using an ultrasonic motor as a drive source according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oscillator 1a ... Contact spring part 2 ... Rotor main ring 2a ... Contact spring part 2b ... Base part 2c ... Flange part 2d ... Contact protrusion part 3 ... Rotor 4 ... Wear resistant resin layer

Claims (2)

[Claims] 1. A bending vibration is excited in a plurality of different planes including the axis of the vibrating body by applying an electric signal to an electro-mechanical energy conversion element provided in the rod-shaped vibrating body, and each of them is excited. An ultrasonic motor that causes a rotational movement on the surface of the vibrating body by giving a predetermined phase difference to the vibration, and frictionally drives a moving body press-engaged with the vibrating body. In the body, the vibrating body has a contact spring, and the natural frequencies of all modes of the natural vibration mode of the contact spring are larger than twice the driving frequency. 2. An apparatus including the rod-shaped ultrasonic motor according to claim 1, further comprising an output member that obtains a driving force from a member that is frictionally driven by being pressed by a vibrator.