JPH11313491A - Ultrasonic motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably supply power to the side of a traveling element by supplying power by a rotary transformer near a rotary shaft from a fixed elastic member with a pressure welding surface to be rotated and the pressure welding surface of a traveling elastic member supported around the rotary shaft, while it is supported in angle variable manner. SOLUTION: An ultrasonic motor is provided with a traveling-side piezoelectric element 41 for giving vibration to a fixed-side elastic member 30 with a rotary- symmetry shape, and a traveling-side elastic member 40 with the rotary-symmetry shape. An output shaft 10 rotating with the elastic member 40 in a single piece, and a rotary transformer 60 for feeding power to the piezoelectric element 41 in a non- contact manner, are provided. The elastic member 30 has a thick part with an annular pressure welding surface 30a on an upper surface, a thin part 30b for supporting the thick part from the inside, and a mounting part for nearly fitting to an inner spacer 14. The traveling-side elastic member 40 has a part with an annular pressure welding surface 40a on a lower surface, a thin part 40b for supporting the thick part from the inside, and a mounting part for transferring torque to the output shaft 10. A piezoelectric element 31 performs expansion and contraction movement for generating vibration, when a driving magnetic field is applied in a thickness direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor that generates a rotational displacement wave on each press-contact surface of a stator and a moving member, and performs a rotational motion in accordance with a driving frequency difference between two rotational displacement waves. The present invention also relates to an ultrasonic motor that performs a rotational motion by generating a rotational displacement wave on a pressure contact surface of a moving element.

[0002]

2. Description of the Related Art In a general traveling wave type ultrasonic motor, a ring-shaped stator and a rotor are pressed against each other, a ring-shaped piezoelectric element is joined to the back surface of the stator, and the traveling wave travels to the pressed-contact surface of the stator. It is configured to convert the elliptical motion of the pressure contact into the rotary motion of the rotor by generating waves (Reference "Ultrasonic motor introduction", co-authored by Hisashi Mishiro and Toshio Sida, published by Sogo Denshi Shuppansha, 1991 Year).

[0003] Compared to an electromagnetic motor, such an ultrasonic motor does not require a magnetic circuit such as a coil winding or an iron core, so that it can be reduced in size and weight, and has the advantage that a high torque can be obtained even at low speed rotation. Yes, it has been put to practical use in the fields of camera lens rotation mechanisms and robot actuators.

A conventional ultrasonic motor employs a method in which a rotor is frictionally driven by a traveling wave on a stator surface, so that a piezoelectric element made of a piezoelectric material having a sharp resonance is used to obtain a traveling wave having a large amplitude. Is driven to resonate. Therefore, when it is desired to variably control the rotational speed of the moving element, it is necessary to change the driving frequency or driving voltage of the traveling wave, but when the driving frequency or driving voltage of the piezoelectric element is changed, the vibration output of the piezoelectric element rapidly decreases And the torque will change. As a result, it is extremely difficult to variably control the rotational speed of the conventional ultrasonic motor, and in reality, it is limited to applications in which the output at a constant rotational speed is on / off controlled like a typical DC motor.

Therefore, a piezoelectric element is provided on each of the stator and the rotor so that the rotation speed of the rotor is continuously variable by the interaction between the traveling wave of the stator and the traveling wave of the rotor. A double drive type ultrasonic motor has been proposed (Japanese Patent No. 2663164).

[0006]

In the latter double-drive type ultrasonic motor, since the piezoelectric element is also provided on the rotor, it is necessary to supply power to the rotating piezoelectric element by some means. The patent specification describes a contact-type power supply mechanism in which a conductive brush is attached to a case cover and a conductive board is attached to a rotor.

In such a contact type power supply mechanism, reliability, life, spark,
The field of practical application is limited in terms of electromagnetic noise.

On the other hand, with respect to the former traveling wave type ultrasonic motor, a power supply system using a combination of a slip ring and a brush or a rotary transformer has been proposed for an ultrasonic motor in which a piezoelectric element is provided on a rotor instead of a stator. (Japanese Patent Laid-Open No. 4-71371). However, although a configuration using a slip ring is specifically described, a specific configuration using a rotary transformer is not described.

An object of the present invention is to provide an ultrasonic motor capable of realizing a stable power supply to the moving element.

[0010]

SUMMARY OF THE INVENTION The present invention provides a fixed elastic member having a rotationally symmetric pressure contact surface, a rotationally symmetric pressure contact surface facing the pressure contact surface of the fixed elastic member, and an angular displacement about a rotationally symmetric axis. A movable elastic member freely supported, a fixed vibration element for generating a rotational displacement wave of frequency Fs on the pressure contact surface of the fixed elastic member, and a rotational vibration wave of frequency Fr on the pressure contact surface of the movable elastic member. An ultrasonic motor in which the movable elastic member is angularly displaced at a rotation speed according to a frequency difference ΔF between the frequency Fs and the frequency Fr, wherein the ultrasonic motor rotates from the pressure contact surfaces of the fixed elastic member and the movable elastic member. An ultrasonic motor including a rotary transformer provided near a symmetric axis and for supplying electric power to a moving vibration element that is angularly displaced together with a moving elastic member.

According to the present invention, by supplying power to the movable vibration element using the rotary transformer, non-contact power supply with little power loss and mechanical loss becomes possible. Also, by providing the rotary transformer near the axis of rotational symmetry from the pressure contact surface of the fixed elastic member and the movable elastic member,
Since a sufficient storage space for the rotary transformer can be secured, the size of the entire motor can be reduced. In addition, since a relatively large rotary transformer can be used, high-output and high-efficiency power supply becomes possible. In particular, when each elastic member is formed in a ring shape, the rotary transformer can be housed inside the ring, so that space can be saved.

Further, the present invention is characterized in that the fixed vibration element and the movable vibration element are rotationally symmetric piezoelectric elements mounted on respective surfaces of the fixed elastic member and the movable elastic member on the opposite side to the press-contact surfaces.

According to the present invention, by using a rotationally symmetric piezoelectric element as the fixed vibration element and the movable vibration element, it is possible to efficiently generate a rotational displacement wave on each press contact surface of the fixed elastic member and the movable elastic member. it can. Note that the rotational displacement wave is a surface wave in which a point on each pressure contact surface moves elliptically in a plane including the traveling direction of the wave and the surface normal direction. When a frequency difference occurs between the opposing points, a speed difference occurs between the fixed elastic member and the movable elastic member, and as a result, the torque is converted into a rotational torque of the movable elastic member.

Further, the present invention is characterized in that the step-up ratio Nr of the rotary transformer is larger than 1.

According to the present invention, when a piezoelectric element is used as the fixed vibration element and the movable vibration element, a relatively high drive voltage is required. It can also function as a transformer. For this reason, conventional traveling wave type ultrasonic motors generally use a fixed transformer for boosting, but in the present invention, a fixed transformer for a moving vibration element can be replaced with a rotary transformer, so that parts can be reduced. become.

Further, the present invention includes a fixed transformer for supplying power to the fixed vibration element, and a ratio Nr / Ns of a step-up ratio Nr of the rotary transformer and a step-up ratio Ns of the fixed transformer.
Satisfy the relationship of 0.5 ≦ Nr / Ns ≦ 2.

According to the present invention, by setting the ratio Nr / Ns of the step-up ratio Nr of the rotary transformer to the step-up ratio Ns of the fixed transformer for the fixed vibration element in the range of 0.5 to 2, the fixed vibration element is set. In addition, the imbalance between the driving voltage and the supplied power to the moving vibration element can be eliminated.

In particular, when the same driving circuit is used for the fixed vibrating element and the moving vibrating element, it is preferable that the boosting ratios Nr and Ns of the two are substantially equal to each other. The operations can be almost matched.

According to the present invention, a first drive electrode and a second drive electrode for two-phase drive and a monitor electrode for detecting a vibration waveform are formed on the surface of the piezoelectric element. It has a first transformer circuit connected to one drive electrode, a second transformer circuit connected to the second drive electrode, and a third transformer circuit connected to the monitor electrode.

According to the present invention, by forming the first drive electrode and the second drive electrode for two-phase drive on the surface of the piezoelectric element, it is possible to generate a rotational displacement wave along the circumferential direction of the piezoelectric element. It becomes possible to provide feedback to the drive circuit of the piezoelectric element by detecting a vibration waveform by providing a monitor electrode. Therefore, by forming three transformer circuits in the rotary transformer, power supply and signal transmission independent of each other become possible.

Further, according to the present invention, a non-magnetic material for suppressing magnetic coupling is provided between a detection system core constituting the third transformer circuit and a drive system core constituting the first transformer circuit and the second transformer circuit. It is characterized by being provided.

According to the present invention, by providing a non-magnetic material for suppressing magnetic coupling between the detection system core and the drive system core, crosstalk from the drive signal line of the piezoelectric element to the detection signal line can be reduced. It can be greatly reduced. Since the detection signal from the monitor electrode is used as a feedback signal to the drive circuit of the piezoelectric element, if noise is mixed in, it becomes a factor that causes instability of the drive circuit. Moreover,
Since this detection signal is obtained by the piezoelectric effect, it has a high impedance output that is easily affected by noise. Therefore, the S / N ratio of the detection signal transmitted to the detection system core can be improved by suppressing the magnetic coupling with the drive system core transmitting the large power.

Further, the present invention has a fixed elastic member having a rotationally symmetric pressure contact surface, and a rotationally symmetric pressure contact surface opposed to the pressure contact surface of the fixed elastic member, and is supported so as to be angularly displaceable about a rotationally symmetric axis. An ultrasonic motor comprising a moving elastic member and a moving vibration element for generating a rotational displacement wave on a pressure contact surface of the moving elastic member, wherein the moving elastic member is angularly displaced by the rotational displacement wave. A rotary transformer for supplying drive power to the displaced moving vibration element,
An ultrasonic motor, wherein the boost ratio Nr of the rotary transformer is larger than 1.

According to the present invention, by supplying power to the movable vibration element using the rotary transformer, it is possible to perform non-contact power supply with little power loss and mechanical loss. In addition, it is preferable that the rotary transformer be provided near the axis of rotational symmetry from the pressure contact surfaces of the fixed elastic member and the movable elastic member. With such an arrangement, a sufficient storage space for the rotary transformer can be secured, so that the entire motor can be downsized. In addition, since a relatively large rotary transformer can be used, high-output and high-efficiency power supply becomes possible. In particular, when each elastic member is formed in a ring shape, the rotary transformer can be housed inside the ring, so that space can be saved.

When a piezoelectric element is used as the fixed vibration element and the movable vibration element, a relatively high drive voltage is required. Therefore, by using a rotary transformer having a step-up ratio Nr of more than 1, it can also function as a step-up transformer. Can be done. For this reason, conventional traveling wave type ultrasonic motors generally use a fixed transformer for boosting, but in the present invention, a fixed transformer for a moving vibration element can be replaced with a rotary transformer, so that parts can be reduced. become.

[0026]

FIG. 1A is a sectional view showing the structure of an embodiment of the present invention, and FIG. 1B is a sectional view of FIG.
It is an expanded sectional view of the rotary transformer 60 in the inside. FIG.
FIG. 3 is an exploded perspective view showing an assembling procedure, and FIG. 4 is an enlarged sectional view of the rotary transformer 60 in FIGS.

The ultrasonic motor 1 includes a fixed-side elastic member 30 having a rotationally symmetric shape, a moving-side elastic member 40 having a rotationally symmetric shape, and a fixed-side piezoelectric element 31 for applying vibration to the elastic member 30. A moving-side piezoelectric element 41 that applies vibration to the elastic member 40, an output shaft 10 that rotates integrally with the elastic member 40, a rotary transformer 60 that supplies power to the piezoelectric element 41 in a non-contact manner, and a housing that houses these components. 2
1, 22, and the like.

The housing 21 has a cylindrical box shape having a bottom surface and side surfaces. A through hole is formed in the center of the bottom surface, and a hollow bearing holder 20 having a convex cross section is mounted in the through hole. Steps are formed on the inner surface of the bearing holder 20 from above and below, and bearings 15 and 16 for rotatably supporting the output shaft 10 are mounted and fixed to the steps at predetermined intervals.

The output shaft 10 is inserted so as to substantially fit with the inner rings of the bearings 15 and 16. The bearing 16 is held in contact with the spacer 13 mounted on the stepped surface of the thick shaft portion 10b at the center of the output shaft 10, and the bearing 15 is held by the spacer 12 inserted from the tip of the output shaft 10. The output shaft 10 and the inner rings of the bearings 15 and 16 are integrated by mounting the retaining ring 11 such as an E-ring in the circumferential groove 10a.

An elastic member 30 is mounted on the upper surface of the bearing holder 20, and is substantially fitted with the outer shape of the bearing 16, thereby realizing the center alignment.

The elastic member 30 has a thick portion having a ring-shaped press-contact surface 30a on the upper surface, a thin portion 30b for supporting the thick portion from the inside, and a mounting portion for substantially fitting with the inner spacer 14. , And has a structure that allows vibration in the thickness direction of the thick portion. A ring disk-shaped piezoelectric element 31 is bonded to the lower surface of the thick portion so as to face the pressure contact surface 30a. The pressure contact surface 30a is formed to have a convex cross section so that vibrations generated by the piezoelectric element 31 are efficiently concentrated, and a liner 32 made of a low friction material such as a fluororesin is fixed to an upper surface thereof.

On the other hand, similarly to the elastic member 30, the moving-side elastic member 40 has a thick portion having a ring-shaped pressing surface 40a on the lower surface, a thin portion 40b for supporting the thick portion from the inside, and an output shaft 10b. And a mounting portion for transmitting a torque to the thick portion, thereby forming a structure that allows vibration in the thickness direction of the thick portion. A ring disk-shaped piezoelectric element 41 is bonded and fixed to the upper surface of the thick portion so as to face the pressure contact surface 40a. The press contact surface 40a is formed in a convex cross section so that the vibration generated by the piezoelectric element 41 is efficiently concentrated, and a liner 42 made of a low friction material such as a fluororesin is fixed to a lower surface thereof.

It is preferable that the elastic members 30 and 40 are formed of a material having little vibration damping, for example, a metal such as iron or brass.

A ring disc-shaped spring receiving plate 45 is attached to the attachment portion of the elastic member 40. The center alignment is realized by the inside of the spring receiving plate 45 substantially fitting with the step portion 10d of the output shaft 10. A locking plate 43 having two projections 43a is attached to the inside of the upper surface of the spring receiving plate 45. The rotation torque of the elastic member 40 is transmitted to the output shaft 10 by the engagement between the notch 10g formed in the base end 10e of the output shaft 10 and the projection 43a.

A leaf spring 44 is mounted on the base end surface of the output shaft 10, and substantially fits into a projection 10 f formed at the center of the base end of the output shaft 10 and a through hole formed at the center of the leaf spring 44. Center alignment has been achieved.

The leaf spring 44 is formed by a central disk and a plurality of oscillating ends extending radially.
Is pressed uniformly, a pressure contact force between the elastic member 30 and the elastic member 40 is generated.

The rotary transformer 60 is arranged inside a thick portion of the ring-shaped elastic members 30 and 40 and in a ring-shaped space secured between the thin portions of the elastic members 30 and 40 and the mounting portion. Is done.

The rotary transformer 60 is configured such that a ring-shaped fixed core 61 and a ring-shaped movable core 62 face each other with a predetermined gap length. The fixed core 61 is mounted on the ring-shaped spacer 14. Moving core 62
Is substantially fitted to the thick shaft portion 10c formed slightly thicker than the thick shaft portion 10b of the output shaft 10, is mounted on the step surface of the step portion 10d, and rotates integrally with the output shaft 10.

Next, the electric system will be described. FIG. 5 (a)
FIG. 5B is a plan view showing the polarization state and the electrode shape of the piezoelectric element 31, and FIG. 5B is a plan view showing the electrode shape of the piezoelectric element 31 on the surface opposite to FIG. 5A. Note that the piezoelectric element 41 also has the same polarization state and electrode shape as the piezoelectric element 31.

The ring-shaped piezoelectric element 31 expands and contracts in the thickness direction and the circumferential direction by applying a driving electric field in the thickness direction, and generates vibration by changing this expansion and contraction movement at high speed. By changing the phase of the vibration along the circumferential direction, a rotational displacement wave such as a traveling wave or a standing wave is formed. Here, a case where five cycles of displacement waves are generated in one round is illustrated, and as shown in FIG.
Using the wavelength λ of the displacement wave as a unit, two groups A and B composed of four λ / 2 polarization regions whose polarization directions are inverted every λ / 2, and a λ / 4 polarization region interposed between the groups A and B And 3λ / 4 polarization regions. The drive electrode 31a is formed so as to correspond to the group A, the drive electrode 31b is formed to the group B, and the monitor electrode 31c is formed so as to correspond to the λ / 4 polarization region.
The elastic member 30 on which the piezoelectric element 31 is mounted functions as a ring-shaped common electrode facing each of the electrodes A, B, λ / 4, 3λ / 4, and the elastic member 30 is grounded via the housing 21. . The elastic member 40 also functions as a common electrode of the piezoelectric element 41 and is grounded via the housing 21.

When an electric field is applied to the piezoelectric element 31 in the thickness direction (for example, from the front to the back of the paper), the piezoelectric element 31 expands and contracts in the thickness direction and the circumferential direction due to the electrostriction effect. Increases, and the thickness decreases in the negative polarization region indicated by “−”. For example, the driving electrode 3 corresponding to the group A
When a positive voltage is applied to 1a, the deformation direction changes every λ / 2 to form a wave of two wavelengths, and the boundary of the polarization region becomes a node of the wave. When the voltage applied to the drive electrode 31a is changed at a frequency in the ultrasonic range, the wave generated from the group A propagates to the entire piezoelectric element 31. Similarly, when an alternating voltage in the ultrasonic region is applied to the drive electrode 31b, waves of two wavelengths propagate through the entire piezoelectric element 31, and the waves of the group A and the waves of the group B are combined. You. Therefore, a cosine wave is applied to the drive electrode 31a, and the drive electrode 31
By applying a sine wave to b and shifting the phase by 90 degrees from each other, a traveling wave in one direction can be generated.

FIG. 6 is a graph showing how a traveling wave is generated. FIG. 6A is a linear development view of the piezoelectric element 31, and FIG. 6G shows voltage waveforms of the drive electrodes 31a and 31b. FIGS. 6B to 6F show waveforms of the traveling wave at times t0 to t4 in FIG. 6G. At time t0, only group A generates a surface wave of amplitude 1 and propagates through the entire ring. At time t1, group A,
B generates a surface wave having an amplitude of 1 / √2 with a phase difference of 90 degrees, and the composite wave moves to the left by λ / 8 compared to time t0. At time t2, only group B generates a surface wave of amplitude 1 and moves to the left by λ / 8 compared to time t1. Hereinafter, similarly, at time t3 and t4, it also moves to the left by λ / 8, and it can be seen that a traveling wave that moves to the left with time is generated.

Further, a sine wave is applied to the drive electrode 31a and a cosine wave is applied to the drive electrode 31b, and the phase is shifted by 90 degrees in the opposite direction.
If it is shifted by a degree, a traveling wave in the opposite direction to that described above can be generated. In this way, by driving the spatial phase difference between the groups A and B in association with the temporal phase difference of the drive waveform, a traveling wave traveling in a desired direction can be generated. Thus, the expansion and contraction change of the piezoelectric element 31
Since the piezoelectric element 31 is attached to and integrated with the elastic member 30, the wave has a predetermined amplitude. Then, two waves having different phases are combined to form a traveling wave, and the traveling wave propagates through the elastic member 30 and becomes a traveling wave on the press-contact surface 30a. Similarly, a traveling wave generated by a change in expansion and contraction of the piezoelectric element 41 propagates through the elastic member 40 and becomes a traveling wave on the press contact surface 40a.

The monitor electrode 31c is formed by the piezoelectric effect.
The vibration waveform of the traveling wave generated in the piezoelectric element 31 is detected as an electric signal. Lines PA, PB, and PC are connected to the drive electrodes 31a and 31b and the monitor electrode 31c, respectively, and are drawn out through drawer holes formed in the housing 21, as shown in FIG.

Similarly, for the piezoelectric element 41, the drive electrode 41a, 41b and the monitor electrode 41c have the line Q
A, QB, and QC are connected respectively, and a rotary transformer 60 is interposed in the middle.

FIG. 1 shows a rotary transformer 6 for two-phase driving.
An example using 0 is shown, and the rotary transformer 60 has three transformer circuits corresponding to the lines QA, QB, and QC. As shown in FIG. 1B, five ring-shaped projections are formed concentrically on the fixed-side core 61 and the movable-side core 62, of which three outer-side projections are formed by lines QA and QB.
, And the two inner protrusions function as detection-side cores 61c and 62c which form the transformer circuit of the line QC. Each of the ring-shaped protrusions is grooved at a predetermined angle to form a plurality of partial protrusions, and a coil is mounted so as to wind each of the partial protrusions. Supply and signal transmission are performed without contact.

A non-magnetic material such as plastic is inserted between the drive-side cores 61a and 62a and the detection-side cores 61c and 62c, and separators 61b and 62b for suppressing magnetic coupling between the two cores. May be formed. Further, such separators 61b and 62b are
It may be inserted not only between 1a, 62a and the detection-side cores 61c, 62c, but also between lines QA, QB, and QC. By providing such nonmagnetic separators 61b and 62b, magnetic coupling between the transformer circuits can be suppressed. The separators 61b and 62b may be formed by filling with an adhesive.

FIGS. 2 to 4 show an example in which a rotary transformer 60 for three-phase driving is used.
0 has four transformer circuits corresponding to the lines SA, SB, SC, and SD. As shown in FIG.
Six ring-shaped protrusions are formed concentrically on the first and moving side cores 62, of which four protrusions on the outer peripheral side function as drive side cores 61 a and 62 a constituting a transformer circuit of lines SA, SB and SC, The two inner protrusions constitute the detection circuits 61c and 62 constituting the transformer circuit of the line SD.
Functions as c. Each of the ring-shaped protrusions is grooved at a predetermined angle to form a plurality of partial protrusions, and a coil is mounted so as to wind each of the partial protrusions. Supply and signal transmission are performed without contact.

A non-magnetic material such as plastic is inserted between the drive-side cores 61a and 62a and the detection-side cores 61c and 62c, and separators 61b and 62b for suppressing magnetic coupling between the two cores. May be formed.

FIG. 7 is a block diagram showing an example of the drive control circuit of the ultrasonic motor. Here, an example of a circuit in which the stator is the main drive and the rotor is the slave drive is shown. The elastic members 30 and 40 of the ultrasonic motor 1 are electrically grounded via the output shaft 10 and the housing 21 while being pressed against each other. Piezoelectric element 3 attached to fixed elastic member 30
Lines PA, PB, and PC are connected to one drive electrode 31a, 31b and monitor electrode 31c, respectively. In the middle of the lines PA and PB, step-up transformers 70 and 71 for generating a high voltage required for piezoelectric driving are interposed. The step-up transformers 70 and 71 are fixed to a circuit board or the like.

Lines QA, QB and QC are respectively connected to the drive electrodes 41a and 41b and the monitor electrode 41c of the piezoelectric element 41 attached to the movable elastic member 40, and a rotary transformer 60 is interposed in the middle. here,
When the step-up ratio Nr of the rotary transformer 60 is set to 1 or less, a step-up transformer for generating a high voltage for piezoelectric driving is separately required, but the step-up ratio Nr of the rotary transformer 60 is required.
Is set to be greater than 1 so that the step-up transformer 7
Since the same function as 0 and 71 can be provided, the step-up transformer on the moving side can be omitted.

In order to make the amplitudes of the traveling waves in the elastic members 30 and 40 equal, it is preferable that the electric characteristics and the mechanical characteristics of the fixed side and the moving side are almost the same. Nr and step-up transformer 70, 7
The ratio Nr / Ns to the step-up ratio Ns of 1 is 0.5 ≦ Nr / Ns
If it is within the range of ≦ 2, the imbalance can be eliminated, and in particular, Ns
≒ Nr is more preferred.

The frequency control oscillator 82 on the stator side outputs an ultrasonic drive signal (for example, a sine wave or a pulse wave) of the frequency Fs, and after being amplified by the amplifier 86, is output to the line PA. And applied to the drive electrode 31b of the piezoelectric element 31. Further, the ultrasonic drive signal of the frequency control oscillator 82 is also input to an amplifier 88 via a phase shifter 84 for shifting the phase by 90 degrees, and after being amplified by the amplifier 88, the line P
B is converted to a high voltage by the step-up transformer 71 and applied to the drive electrode 31 a of the piezoelectric element 31.

The detection signal generated on the monitor electrode 31c of the piezoelectric element 31 is input to the waveform shaping limiter circuit 90 via the line PC, and further input to the frequency control oscillator 82 as a feedback signal. The frequency controlled oscillator 82 is a PLL composed of a VCO (voltage controlled oscillator), a phase comparator, and an LPF (low-pass filter).
(Phase Locked Loop) circuit and operates in a self-driving state.

On the rotor side, the frequency control circuit 83 outputs an ultrasonic drive signal (for example, a sine wave or a pulse wave) of the frequency Fr based on the ultrasonic drive signal of the frequency Fs output from the frequency control oscillator 82, and the amplifier 87 After being amplified by, it is output to the line QA, converted to a high voltage by the rotary transformer 60, and applied to the drive electrode 41 a of the piezoelectric element 41. Further, the ultrasonic drive signal from the frequency control circuit 83 is also input to the amplifier 89 via the phase shifter 85 for shifting the phase by 90 degrees, and is output to the line QB after being amplified by the amplifier 89. The voltage is converted to a high voltage by the rotary transformer 60 and the drive electrode 41 of the piezoelectric element 41 is
b.

The detection signal generated on the monitor electrode 41c of the piezoelectric element 41 is not used when the rotor is driven in a subordinate manner. When detecting the angular deviation between the rotor and the stator, the phase difference between the signals is detected using the feedback signals on the rotor side and the stator side.

When a command is input from an external host device 80 such as a computer, the frequency control circuit 83 analyzes the command, receives the frequency Fs from the frequency control oscillator 82, and controls the frequency Fr. .

For example, when the command from the external host device 80 is a rotation speed command, a frequency difference ΔF is added to the signal from the oscillator 82 to maintain the frequency difference ΔF corresponding to the rotation speed, and the frequency Fr is changed. Control. Then, as described above, the piezoelectric elements 31, 41 have the frequencies Fs, Fs
r, and these vibrations are generated by the elastic members 30, 40.
To generate rotational displacement waves WA and WB having displacement components along the circumferential direction at the press contact surfaces 30a and 40a, respectively. Since the rotational displacement waves WA and WB of the press contact surfaces 30a and 40a are shifted by the frequency difference ΔF, the movable elastic member 40 relatively rotates with respect to the fixed elastic member 30. The torque is extracted from the output shaft 10 shown in FIG. Since the rotation speed of the elastic member 40 changes in proportion to the frequency difference ΔF, it is possible to control the rotation speed of the ultrasonic motor 1 with high accuracy by the frequency control circuit 83 controlling the frequency difference ΔF with high accuracy. it can.

Further, by controlling the frequency difference ΔF to zero by matching the frequencies Fs and Fr, the ultrasonic motor 1 is stationary, and the pressure contact force between the elastic members 30 and 40 functions as a motor holding torque. Therefore, the brake mechanism can be omitted.

When the command from the external host device 80 is a rotation angle command, a predetermined rotation speed corresponding to the frequency difference ΔF is held for a time corresponding to the rotation angle command, and thereafter, the frequencies Fs and Fr are made to match. Stop by Therefore, rotation angle control like a stepping motor is also possible.

As described above, the frequency control circuit 83 can freely control the rotation speed, rotation angle, rotation direction, and the like of the ultrasonic motor 1 by arbitrarily controlling the frequency Fr in response to the signal from the oscillator 82.

FIG. 8 is a block diagram showing another example of the drive control circuit of the ultrasonic motor. Here, an example of a circuit in which the rotor is the main drive and the stator is the slave drive is shown.

The frequency control oscillator 82 outputs an ultrasonic drive signal (for example, a sine wave or a pulse wave) having a frequency Fr,
After being amplified by the amplifier 87, it is output to the line QA, converted to a high voltage by the rotary transformer 60, and applied to the drive electrode 41a of the piezoelectric element 41. Further, the ultrasonic drive signal of the frequency control oscillator 82 is also input to an amplifier 89 via a phase shifter 85 for shifting the phase by 90 degrees, is amplified by the amplifier 89, and is output to a line QB. It is converted to a high voltage by the transformer 60,
The voltage is applied to the drive electrode 41b of the piezoelectric element 41.

The detection signal generated on the monitor electrode 41c of the piezoelectric element 41 is input to a waveform shaping limiter circuit 90 via a line QC, and furthermore, a frequency control oscillator 82
As a feedback signal. The frequency controlled oscillator 82 includes a PLL (Phas) including a VCO (Voltage Controlled Oscillator), a phase comparator, and an LPF (Low Pass Filter).
e Locked Loop) circuit and operates in a self-driven state.

On the stator side, the frequency control circuit 83 outputs an ultrasonic drive signal (for example, a sine wave or a pulse wave) of the frequency Fs based on the ultrasonic drive signal of the frequency Fr output from the frequency control oscillator 82, and the amplifier 86 After being amplified by, the voltage is output to the line PA, converted to a high voltage by the step-up transformer 70, and applied to the drive electrode 31b of the piezoelectric element 31. Further, the ultrasonic drive signal from the frequency control circuit 83 is also input to the amplifier 88 via the phase shifter 84 for shifting the phase by 90 degrees, and is output to the line PB after being amplified by the amplifier 88. The voltage is converted into a high voltage by the step-up transformer 71 and applied to the drive electrode 31 a of the piezoelectric element 31.

The detection signal generated at the monitor electrode 31c of the piezoelectric element 31 is not used when the stator is driven. When detecting the angular deviation between the rotor and the stator, the phase difference between the signals is detected using the feedback signals on the rotor side and the stator side.

When a command is input from an external host device 80 such as a computer, the frequency control circuit 83 analyzes the command, receives the frequency Fr from the frequency control oscillator 82, and controls the frequency Fs. . Thus, the rotation speed, the rotation angle, the rotation direction, and the like of the ultrasonic motor 1 can be freely controlled according to the command from the external host device 80.

In the above configuration, the elastic member 3 on the stator side
The piezoelectric element 3 is provided on both the
Although the description has been given of the double drive type ultrasonic motor in which the piezoelectric elements 31 and 41 are arranged, the configuration using the rotary transformer 60 also serving as a step-up is such that the piezoelectric element 41 on the stator side is omitted and the piezoelectric element 31 is provided on the elastic member 40 on the rotor side. It is also applicable to a single drive type ultrasonic motor in which is disposed.

[0069]

As described above in detail, according to the present invention, by supplying electric power to the moving vibration element using the rotary transformer, space-saving and high-efficiency non-contact power supply becomes possible. A high output ultrasonic motor can be realized.

Further, by using a rotationally symmetric piezoelectric element as the fixed vibration element and the movable vibration element, it is possible to efficiently generate a rotational displacement wave on each press contact surface of the fixed elastic member and the movable elastic member.

In addition, by using a rotary transformer having a step-up ratio Nr greater than 1, a rotary transformer can be used instead of a fixed transformer for a moving vibration element, so that parts can be reduced.

The ratio Nr / Nr of the step-up ratio Nr of the rotary transformer and the step-up ratio Ns of the fixed transformer for the fixed vibrating element is calculated.
By setting Ns in the range of 0.5 to 2, it is possible to eliminate imbalance in the drive voltage and supply power to the fixed vibration element and the movable vibration element.

Further, by forming three transformer circuits for the first drive electrode, the second drive electrode, and the monitor electrode of the piezoelectric element in the rotary transformer, power supply and signal transmission independent of each other become possible.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view illustrating a configuration of an embodiment of the present invention, and FIG. 1B is an enlarged cross-sectional view of a rotary transformer 60 in FIG. 1A.

FIG. 2 is an exploded perspective view showing an assembling procedure.

FIG. 3 is an exploded perspective view showing an assembling procedure.

FIG. 4 is an enlarged sectional view of the rotary transformer 60 in FIGS. 2 and 3;

5A is a plan view showing a polarization state of the piezoelectric element 31, and FIG. 5B is a plan view showing an electrode shape of the piezoelectric element 31. FIG.

6A and 6B are graphs showing how a traveling wave is generated. FIG. 6A is a linear development view of the piezoelectric element 31, FIG. 6G is a voltage waveform of drive electrodes 31a and 31b, and FIG. ~ FIG.
(F) shows the waveform of the traveling wave at times t0 to t4 in FIG. 6 (g).

FIG. 7 is a block diagram illustrating an example of a drive control circuit of the ultrasonic motor.

FIG. 8 is a block diagram showing another example of the drive control circuit of the ultrasonic motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultrasonic motor 10 Output shaft 15, 16 Bearing 21, 22 Housing 30, 40 Elastic member 30a, 40a Pressure contact surface 31, 41 Piezoelectric element 31a, 31b, 41a, 41b Drive electrode 31c, 41c Monitor electrode 32, 42 Liner 44 Plate Spring 60 Rotary transformer 61 Fixed side core 62 Moving side core 70, 71 Step-up transformer 82 Frequency controlled oscillator 83 Frequency control circuit 84, 85 Phase shifter 86-89 Amplifier

Claims (7)

[Claims] 1. A fixed elastic member having a rotationally symmetric pressure contact surface, and a movable elastic member having a rotationally symmetric pressure contact surface facing the pressure contact surface of the fixed elastic member and supported so as to be angularly displaceable about a rotationally symmetric axis. A fixed vibration element for generating a rotational displacement wave of frequency Fs on the pressure contact surface of the fixed elastic member, and a moving vibration element for generating a rotational displacement wave of frequency Fr on the pressure contact surface of the movable elastic member, An ultrasonic motor in which a movable elastic member is angularly displaced at a rotational speed corresponding to a frequency difference ΔF between a frequency Fs and a frequency Fr, wherein the ultrasonic motor is provided near a rotationally symmetric axis from a pressure contact surface of the fixed elastic member and the movable elastic member, and moves. An ultrasonic motor comprising a rotary transformer for supplying electric power to a moving vibration element that angularly displaces together with an elastic member. 2. The fixed vibration element and the movable vibration element are rotationally symmetric piezoelectric elements mounted on respective surfaces of the fixed elastic member and the movable elastic member opposite to the pressing surfaces. Ultrasonic motor. 3. The ultrasonic motor according to claim 2, wherein the step-up ratio Nr of the rotary transformer is larger than 1. 4. A fixed transformer for supplying electric power to a fixed vibration element, wherein a ratio Nr / Ns between a boost ratio Nr of the rotary transformer and a boost ratio Ns of the fixed transformer is 0.5 ≦.
The ultrasonic motor according to claim 3, wherein a relationship of Nr / Ns≤2 is satisfied. 5. A first phase for two-phase driving is provided on a surface of a piezoelectric element.
A drive electrode, a second drive electrode, and a monitor electrode for detecting a vibration waveform are formed, and the rotary transformer has a first transformer circuit connected to the first drive electrode and a second transformer electrode connected to the second drive electrode. The ultrasonic motor according to claim 2, further comprising a two transformer circuit and a third transformer circuit connected to the monitor electrode. 6. A non-magnetic material for suppressing magnetic coupling is provided between a detection system core forming a third transformer circuit and a drive system core forming a first transformer circuit and a second transformer circuit. The ultrasonic motor according to claim 5, wherein: 7. A movable elastic member having a rotationally symmetric pressure contact surface and a rotationally symmetric pressure contact surface opposed to the rotational contact surface of the stationary elastic member, and supported to be angularly displaceable about the rotational symmetry axis. An ultrasonic motor having a moving vibration element for generating a rotational displacement wave on the pressure contact surface of the movable elastic member, wherein the movable elastic member is angularly displaced by the rotational displacement wave; An ultrasonic motor comprising a rotary transformer for supplying drive power to a vibrating element, wherein the boost ratio Nr of the rotary transformer is greater than 1.