JP3120427B2 - Ultrasonic motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor that generates a traveling wave on a vibrating body using two piezoelectric elements that generate a standing wave whose position and phase are shifted.

[Summary of the Invention] In the present invention, a plurality of projections are provided at a predetermined interval on a predetermined radius of a vibrating body, a moving body is pressed against an upper surface of the projections, and a center angle is π / n (n is an integer of 2). The two piezoelectric elements provided with 2n areas where the directions of expansion and contraction are alternately inverted are substantially π / 2
In an ultrasonic motor that is fixed to the other surface of the vibrating body by shifting by n and applying voltages having phases shifted to these piezoelectric elements, and rotating the moving body by a traveling wave generated in the vibrating body,
The protrusions are formed one at a time in the circumferential center of a section divided into two with respect to the center of each polarization region of the first piezoelectric element, and the second piezoelectric element is π / 2n with respect to the first piezoelectric element. By arranging the piezoelectric elements at a slightly shifted position, the resonance frequencies of the two piezoelectric elements can be easily adjusted, and the sensitivity of the motor is improved.

In addition, the efficiency of the motor is improved and the generation of noise is prevented.

Further, by shifting the two piezoelectric elements slightly from π / 2n, the resonance frequencies of the two piezoelectric elements are matched to further improve the sensitivity of the motor.

[Prior Art] Conventionally, an ultrasonic motor 1 as shown in FIGS.
It has been known.

In FIG. 7, the ultrasonic motor 1 includes a vibrating body 6
And a moving body 9 pressed against one surface of the vibrating body 6 and first and second moving bodies 9 stacked and fixed on the other surface of the vibrating body 6.
And the piezoelectric elements 7, 8.

The vibrating body 6 is made of a disc-shaped metal, and a plurality of comb-shaped projections 6a (24 in this conventional example) are formed at a predetermined interval on a predetermined radius of one surface. The moving body 9 is formed in a disk shape and is pressed against the upper surface of the projection 6a.

The first and second piezoelectric elements 7 and 8 are formed in a circular shape, and are polarized regions 7b and 8b in which the directions of expansion and contraction are reversed, that is, (+) polarized regions 7b and 8b which expand when a voltage is applied and contract (-). 2n polarization regions 7b and 8b are provided alternately in the circumferential direction (n is a vibration mode, which is an integer of 2 or more, and n = 4 in this conventional example).

The second piezoelectric element 8 is fixed to the first piezoelectric element 7 in a state of being rotated by π / 2n so that the position of the wavelength generated when a voltage is applied to each of them is shifted by λ / 4.
Driving electrode patterns 14, 15, 16, 17 are printed on both surfaces of the first and second piezoelectric elements 7, 8, respectively.

As shown in FIG. 8, a projection of the vibrating body 6 indicated by a broken line
6a indicates each extension (+) of the second piezoelectric element 8 indicated by a solid line,
On the shrinking (-) polarization region 8b, three are arranged at regular intervals. The way of arranging the protrusions 6a is as follows. As for the first piezoelectric element 7, the protrusions 6a are halved at both ends on the extending (+) and contracting (-) polarization regions 7b indicated by phantom lines. And two in the center. The second piezoelectric element 8 is provided with a cutout 18 for a common electrode. The drive electrode pattern 15 of the first piezoelectric element 7 exposed from the common electrode notch 18 is used as a common electrode of the first and second piezoelectric elements 7 and 8.

As shown in FIG. 7, a voltage having a phase shifted by π / 2, that is, a cosine wave and a sine wave, are applied to the first and second piezoelectric elements 7 and 8 by a phase shifter (not shown). Apply. Then, standing waves having positions and phases shifted from each other are generated in the first and second piezoelectric elements 7 and 8, and the two types of standing waves are combined, and a traveling wave is generated in the vibrator 6. Then, as shown in FIG. 9, the projection 6a of the vibrating body 6 repeats an elliptical motion, and this projection 6a
The moving body 9 pressed against 6a is rotated by the horizontal component force F of the elliptical motion due to friction.

[Problems to be Solved by the Invention] However, according to the conventional example, there are the following four problems.

In FIG. 8, three projections 6a indicated by broken lines of the vibrating body 6 are located on the respective extending (+) and contracting (-) polarization regions 8b of the second piezoelectric element 8 indicated by solid lines.
8b bears three protrusions 6a as mechanical loads on both sides and an intermediate portion. On the other hand, each of the extending (+) and contracting (-) polarization regions 7b of the first piezoelectric element 7 indicated by the dashed line is two in the middle portion thereof, and is located on both sides 7c side of the polarization region 7b. (The part where the drive electrode pattern 14 is not printed)
That is, the polarization region 7b bears the two mechanically loaded protrusions 6a in the middle part and the half of the protrusions 6a in the boundary part 7c on both sides. Thus, when the 24 projections 6a are arranged as described above, the first
Since the second piezoelectric elements 7 and 8 have different mechanical loads, their resonance frequencies are also significantly different, and the traveling wave may be distorted or the traveling wave may not be produced, and the sensitivity of the motor will be reduced.

In FIG. 9, when the number of the protrusions 6a is large as in the conventional example, the protrusions 6a ₁ located at the peak of the traveling wave completely contact and rotate the moving body 9, but the protrusions 6a ₁ projections 6a ₂ next becomes a impose on the moving body 9 rather not completely contact, easily audible frequency noise is generated.

Further, regarding the first piezoelectric element 7 indicated by a virtual line, a projection 6a located at a node portion of a standing wave, that is, a boundary portion 7c between the extending (+) polarization region 7a and the contracting (-) polarization region 7a.
Does not vibrate substantially and does not convert vibrational energy into rotational energy, so that the efficiency of the motor is low.

For example, each of the first and second piezoelectric elements 7, 8 extends (+).
Protrusion 6a borne by polarized region, contracted (-) polarized region 7b, 8b
, The first piezoelectric element 7 bears the vibrating body 6 on one side and the second piezoelectric element 8 on the other side as a mechanical load, whereas the second piezoelectric element 8 bears the mechanical load on the other side. The piezoelectric element has a vibrating body 6 and a first piezoelectric element 7 on one surface as a mechanical load. In other words, since the manner in which the two members bear the mechanical load is slightly different, it is very difficult to completely match the resonance frequencies of the first and second piezoelectric elements 7, 8.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and the resonance frequencies of the first and second piezoelectric elements 7 and 8 are matched to improve the sensitivity of the motor, prevent noise, and reduce vibration energy. Is effectively converted into rotational energy to improve the efficiency of the motor.

[Means for Solving the Problems] The present invention provides a vibrating body in which a plurality of protrusions are formed at predetermined intervals on a predetermined radius of one surface, a moving body pressed against the upper surface of the protrusion, A first and a second piezoelectric element that are stacked and fixed on the surface, and each of the first and the second piezoelectric elements has 2n pieces (n: n is 2
The above-mentioned polarization regions are alternately provided for each central angle π / n, the first and second piezoelectric elements are arranged shifted from each other, and voltages having phases shifted by π / 2 are applied, respectively. In an ultrasonic motor that rotates a moving body by a traveling wave generated in a vibrating body, one protrusion is formed at each of the circumferential centers of two divided regions with respect to the center of each polarization region of the first piezoelectric element. At the same time, the second piezoelectric element is arranged at a position slightly shifted from π / 2n with respect to the first piezoelectric element, and the resonance frequencies of the first and second piezoelectric elements are matched.
It has that configuration.

[Operation] One protrusion is formed at the center in the circumferential direction of the area divided into two with respect to the center of each polarization region of the first piezoelectric element, and the second piezoelectric element is used as the first piezoelectric element.
By arranging them at positions slightly shifted from each other, the mechanical loads borne by the polarization regions of the first and second piezoelectric elements become the same, and the resonance frequencies of the first and second piezoelectric elements completely match. The distortion of the traveling wave is almost completely eliminated.

Further, since each of the protrusions is formed at the center in the circumferential direction of a section divided into two with respect to the center of each polarization region of the first piezoelectric element, the central symmetry of both the first and second piezoelectric elements is formed. Is maintained. In addition, since the mechanical loads of the first and second piezoelectric elements are the same and the number of protrusions is minimized, when a certain protrusion is at the maximum position of the amplitude of the traveling wave and the moving body is rotated, The protrusion at the intermediate position of the amplitude next to it does not fog on the moving body.

[Embodiment] Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

3 and 4, a bracket fitting hole 2a is formed in the base 2 of the ultrasonic motor 1, and the bracket 3 is fitted in the bracket fitting hole 2a. The rotating shaft 4 is rotatably inserted into the shaft insertion hole 3a of the bracket 3,
A bearing 5 is provided between the rotating shaft 4 and the bracket 3. The outer periphery of the bracket 3 is fitted with a vibrating body 6 and bracket fitting holes 6b, 7a, 8a of first and second piezoelectric elements 7, 8 fixed to the lower surface of the vibrating body 6.
The vibrating body 6 is made of a disc-shaped metal, and a plurality of comb-shaped protrusions 6a are formed in a radial direction on a predetermined radius of one surface (the upper surface in the figure). An outer peripheral portion 9a of a moving body 9 formed in a disk shape is in contact with the upper surface of the projection 6a, and the rotary shaft 4 is fitted in a shaft fitting hole 9c in a central portion 9b. A friction material 10 is provided on the lower surface of the outer peripheral portion 9a of the moving body 9. A spring seat receiving recess 9d is formed at an intermediate portion between the central portion 9b and the outer peripheral portion 9a of the moving body 9. A spring seat 11 is housed in the spring seat housing recess 9d, and a spring holder 12 fitted to the rotary shaft 4 is in contact with the upper surface of the spring seat 11. The upper surface of the spring retainer 12 is an E-ring 13 fixed to the rotating shaft 4.
The upward movement of the movable body 9 is restricted, and the movable body 9 is pressed against the upper surface of the projection 6a of the vibrating body 6 by the spring seat 11 at a predetermined pressure.

As shown in FIGS. 1 and 2, on the other surface (the lower surface in FIG. 1) of the vibrating body 6, two first and second piezoelectric elements 7, 8 are provided.
The sheets are stacked and bonded to each other with an adhesive. The first and second piezoelectric elements 7 and 8 have bracket fitting holes 7a and 8a at the center.
(+) Polarization regions 7b, 8b which are formed in a circular shape and have the direction of deflection inverted, that is, extend when a voltage is applied.
(N) (n = an integer of 2 or more in the vibration mode, n = 4 in this embodiment) are provided so that the (−) polarization regions 7b and 8b that shrink are arranged alternately at a predetermined angle in the circumferential direction. These first
A driving electrode pattern 1 for energizing the first and second piezoelectric elements 7, 8 on one surface of the second piezoelectric elements 7, 8 on the vibrating body 6 side;
Reference numerals 4 and 16 are printed in a fan shape corresponding to the polarization regions 7b and 8b. Further, on the other surfaces of the first and second piezoelectric elements 7, 8, electrode patterns 15, 17 for energizing these piezoelectric elements 7, 8 are printed over substantially the entire surface.

As shown in FIG. 1, in the drawing of the vibrating body 6, a projection 6a shown by a broken line is surrounded by a dashed line, and the extension (+) or the extension (+) of the first piezoelectric element 7 shown by an oblique line in the dashed line. A region surrounded by a two-dot chain line in which the contracted (−) polarized region 7b and the extended (+) or contracted (−) polarized region 8b of the second piezoelectric element 8 indicated by a solid line are overlapped with each other, One each is provided at the center in the direction. That is, since the second piezoelectric element 8 is shifted by half of the central angle π / n of each polarization region 7b of the first piezoelectric element 7, that is, π / 2n, the first piezoelectric element 7 extends (+) or Two projections 6a are provided in the shrinking (−) polarization region 7b,
In addition, the projections 6a are respectively arranged at the center in the circumferential direction of the area divided into two in the circumferential direction. The number and the arrangement of the protrusions 6a are such that two protrusions 6a are simultaneously provided in the extension (+) or contraction (-) polarization regions 8b of the second piezoelectric element 8, and the protrusions 6a Similarly to the first piezoelectric element 7, is located at the center in the circumferential direction of a section obtained by dividing each polarization region 8b into two in the circumferential direction.

An arc-shaped common electrode notch 18 is provided at a part of the outer peripheral edge of the second piezoelectric element 8 shown in FIG. The notch 18 for the common electrode is the first
When a voltage is applied to both the second piezoelectric element 8 via the first piezoelectric element 7 and the driving electrode pattern 16 by energizing the driving electrode pattern 15 of the piezoelectric element 7 as a common electrode, It is also.

Harnesses 20, 21 and 22 are provided on the vibrating body 6, the driving electrode pattern 15 exposed from the common electrode notch 18 and the driving electrode pattern 17 of the second piezoelectric element 8 on the side opposite to the vibrating body 6, respectively. Are electrically connected. Vibrator 6
The reason why the harness 20 is electrically connected is that the vibrating body 6 is made of metal and is electrically connected to the driving electrode pattern 14 on the vibrating body 6 side of the first piezoelectric element 7. As shown in FIG. 2, a power supply is connected to these harnesses 20, 21, and 22, and a cos wave is applied to the first piezoelectric element, and a sin wave, that is, a voltage shifted in phase is applied to the second piezoelectric element 8. Is applied.

Next, the operation of the above embodiment will be described with reference to FIGS.

Generally, the basic formula of a traveling wave is represented by Z (θ, t) = asin (nθ + ωt) (n = vibration mode). By transforming this equation, Becomes That is, the cos wave represented by the equation and the s represented by the equation
A traveling wave can be obtained by combining two standing waves of the in wave. This sin wave is Only the position is shifted with respect to the cosine wave.

Therefore, as shown in the principle diagram of FIG. 2, the first and second piezoelectric elements 7 and 8 are shifted from each other by π / 2n (λ / 4), and the first piezoelectric element 7 Since a voltage of a sine wave (the phase is shifted by π / 2 with respect to the cos wave) is applied to the second piezoelectric element 8, the following equation is applied to the first piezoelectric element 7: a sin nθ θcos ωt Standing wave is generated, and the second piezoelectric element Standing wave is generated.

The first and second piezoelectric elements 7 and 8 are provided on the lower surface of the vibrating body 6.
Since the sheets are stacked and fixed, the standing wave represented by the above equation and the equation is synthesized in the vibrating body 6, and a traveling wave of the equation is generated. Then, as shown in FIG. 5, the upper surface of the projection 6a of the vibrating body 6 repeats an elliptical motion, and a horizontal component force F is applied to the moving body 9 pressed by a predetermined pressure on the projection 6a. Act and rotate. Then, the rotating shaft 4 to which the moving body 9 is connected via the spring 11 rotates.

At this time, as shown in FIG.
Is surrounded by an alternate long and two short dashes line of the extension (+) or contraction (−) polarization regions 7b and 8b of both the first piezoelectric element 7 and the second piezoelectric element 8, and is surrounded by a dotted line. One is provided at the center of the direction. That is, in the figure, the first dashed line
(+) Or contracted (-) polarized region 7b of the piezoelectric element 7
Bears two projections 6a as mechanical loads,
6a is arranged at the center of the area where the polarization region 7b is bisected in the circumferential direction. Similarly, the extension (+) or contraction (-) polarization region 8b of the second piezoelectric element 8 shown by a solid line also bears two projections 6a as a mechanical load, and each of the projections 6a surrounds the polarization region 8b. It is provided at the center in the circumferential direction of the area bisected in the direction. As described above, since the protrusions 6a are provided so that the mechanical loads of the first and second piezoelectric elements 7 and 8 and the manner of the load are substantially the same, the resonance frequencies thereof are also substantially the same, and the traveling wave Is substantially eliminated, and the sensitivity of the motor is improved. The number of the protrusions 6a is the same as that of the polarization regions 7b, 8b of the first and second piezoelectric elements 7, 8.
The mechanical load is the number or the 4n minimum to become substantially the same (16 in this example), the when the projections 6a ₁ in as shown in FIG. 5 is in the maximum amplitude of the traveling wave Protrusion 6
projections 6a ₂ in the middle amplitude next to a ₁ is no longer possible to rub the moving body 9 can prevent noise of the motor.

In addition, the polarization regions 7b, 8b of the first and second piezoelectric elements 7, 8
Since the protrusions 6a, which are mechanical loads, are disposed symmetrically with respect to the center of the piezoelectric element, it is possible to eliminate the disturbance of the standing waves of the first and second piezoelectric elements and further reduce the distortion of the traveling wave. it can.

Further, the protrusion 6a vibrates without being provided at the boundary portions 7c, 8c (nodes of the standing wave) of the respective polarization regions in which one of the first and second piezoelectric elements 7, 8 does not vibrate. Each polarization region 7b, 8
The vibration energy is efficiently converted to rotational energy because the vibration energy is arranged at b.

Next, a second embodiment of the present invention will be described with reference to FIG.

In this embodiment, the structure is substantially the same as that described above, and the description of the same components is omitted. However, in this embodiment, the protrusion 6a of the vibrating body 6 is formed by the extension (+) of the first piezoelectric element 7b. ), Shrinking (-) polarization region 7b is provided at the center in the circumferential direction of each of the hatched areas bisected in the circumferential direction. Then, the second piezoelectric element 8 is connected to the first piezoelectric element 7.
Slightly less than π / 2n for The first and second piezoelectric elements 7 and 8 are almost completely matched in resonance frequency. This is because, when the protrusions 6a are evenly arranged as mechanical loads with respect to the first and second piezoelectric elements 7 and 8 as in the first embodiment, strictly speaking, the first piezoelectric element vibrates on one surface thereof. The body 6 is provided as a mechanical load, and the second piezoelectric element 8 is provided as a mechanical load on the other surface. On the other hand, since the second piezoelectric element 8 bears both the vibrating body 6 and the first piezoelectric element 7 as a mechanical load only on one surface, resonance of the first and second piezoelectric elements 7 and 8 is prevented. The frequencies will be slightly different. Therefore, as described above, the position of the projection 6a with respect to each polarization region 8b of the second piezoelectric element 8 is slightly shifted by slightly shifting the second piezoelectric element 8 with respect to the first piezoelectric element 7 by more than π / 2n. By slightly changing the mechanical load, the mechanical loads of the first and second piezoelectric elements 7 and 8 can be completely matched, and the resonance frequency can be completely equalized. As a result, the distortion of the traveling wave can be almost completely eliminated, and the efficiency of the motor can be further improved.

Further, in the first embodiment, the protrusion 6a is connected to the first
The protrusions 6a are arranged one by one at the circumferential center of the overlapping area 19 of the extending (+) or contracting (-) polarized regions 7b, 8b of both the second piezoelectric elements 7, 8.
Need not necessarily be provided at the center position in the circumferential direction, as long as it is provided at a position corresponding to each of the overlapping areas 19. Also, the number of the protrusions 6a is not limited to the configuration provided one by one in the overlapping area 19, and the extending (+) region and the contracting (-) polarized region of both the first and second piezoelectric elements 7, 8 are provided. If the position corresponding to the overlapping area 19 of 7b, 8b is a plurality, for example, a configuration provided two by two,
The resonance frequencies of the first and second piezoelectric elements 7 and 8 can be matched. In addition, the driving electrode patterns 14 and 16 on the vibrating body 6 side of the first and second piezoelectric elements 7 and 8 are not provided, and these driving electrodes are formed by the vibrating body 6 and the driving electrode pattern 15 made of metal. It may be a configuration that also serves.

In the above-described embodiment, the circular moving plate, the diaphragm, and the first and second piezoelectric elements are used. Further, a structure in which the diaphragm and the first and second piezoelectric elements are fitted to the inside of the short cylindrical moving plate sequentially with the central axis being common may be used.

[Effects of the Invention] As is clear from the above description, a vibrating body in which a plurality of protrusions are formed at regular intervals on a predetermined radius of one surface, a moving body pressed against the upper surface of the protrusion, A first piezoelectric element and a second piezoelectric element that are stacked and fixed on the other surface,
The first and second piezoelectric elements are provided with 2n (n: n is an integer of 2 or more) polarization regions alternately arranged at every center angle π / n, the direction of expansion and contraction being reversed. In an ultrasonic motor in which the second piezoelectric elements are arranged to be shifted from each other, voltages having phases shifted by π / 2 are applied, and the moving body is rotated by a traveling wave generated in the vibrating body, the protrusion is formed by the first A single piezoelectric element is formed at the center in the circumferential direction with respect to the center of each polarization region of the piezoelectric element, and the second piezoelectric element is slightly shifted from π / 2n with respect to the first piezoelectric element. In this case, the resonance frequencies of the two piezoelectric elements are completely matched with each other to eliminate the distortion of the traveling wave, thereby improving the sensitivity of the motor.

Further, since each of the protrusions is formed one at the center in the circumferential direction of a region divided into two with respect to the center of each polarization region of the first piezoelectric element, the distortion of the traveling wave is further eliminated, and the efficiency of the motor is improved. Is also reduced, so that there is also an effect of preventing the generation of noise due to the projection moving on the moving body.

[Brief description of the drawings]

FIGS. 1 to 5 show a first embodiment of the present invention. FIG. 1 is a layout explanatory view showing the layout of a projection of a vibrating body of an ultrasonic motor and first and second piezoelectric elements. FIG. 2 is a diagram illustrating the principle,
FIG. 3 is an exploded perspective view, FIG. 4 is a sectional view, FIG. 5 is a view for explaining the principle, and FIG. 6 shows a second embodiment.
7 to 9 show a conventional example. FIG. 7 is a view for explaining the principle, and FIG. 8 is a diagram showing the projections of the vibrating body and the first and second piezoelectric elements. Explanatory drawing of arrangement with piezoelectric elements,
FIG. 9 is a diagram illustrating the principle. 1 ... Ultrasonic motor, 6 ... Vibrator, 6a ... Protrusion, 7 ...
... First piezoelectric element, 7b... Expanding (+), contracting (−) polarization region, 8... Second piezoelectric element, 8b.
Shrinking (-) polarization region, 19 ... A region where both regions of the first and second piezoelectric elements overlap.

Claims (1)

(57) [Claims] 1. A vibrating body in which a plurality of protrusions are formed at predetermined intervals on a predetermined radius of one surface; a moving body pressed against an upper surface of the protrusion; and two moving bodies pressed and fixed on the other surface of the vibrating body. The first and second piezoelectric elements each have 2n (n: n is an integer of 2 or more) polarization regions whose reversing directions are reversed. The first and second piezoelectric elements are alternately provided for every π / n, and are arranged so as to be shifted from each other, and are applied with voltages whose phases are shifted by π / 2, respectively, and are moved by traveling waves generated in the vibrating body. An ultrasonic motor for rotating a body, wherein the protrusion is formed with respect to the center of each polarization region of the first piezoelectric element.
One piece is formed at the center of each of the divided sections in the circumferential direction, and the second piezoelectric element is set to π with respect to the first piezoelectric element.
An ultrasonic motor, wherein the ultrasonic motor is disposed at a position slightly shifted from / 2n, and the resonance frequencies of the first and second piezoelectric elements are matched.