JP2723121B2 - Ultrasonic motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor. 2. Description of the Related Art First, an ultrasonic motor will be described with reference to FIG. FIG. 1a shows an example of an ultrasonic motor,
In the figure, reference numeral 1 denotes a ring-shaped piezoelectric body such as PZT, and a ring-shaped common electrode 2 made of silver or the like is used as a ring-shaped piezoelectric body 1
Is coated (coated) on one entire surface. The other surface of the ring-shaped piezoelectric body 1 is coated with a segment electrode group 3 made of silver or the like. The segment electrode group 3 includes 16 segment electrodes 3a-3p. The segment electrode 3a has a length of ／ λ in the circumferential direction (λ is a bending vibration wavelength in the present specification), and the segment electrode 3b
Has a length of １ ／ λ in the circumferential direction and is shifted by 180 ° from the segment electrode 3a. Segment electrode 3c-
3i each have a length of λ / 2 in the circumferential direction and are on one side between the segment electrodes 3a and 3b. On the other hand, the segment electrodes 3j to 3p each have a length of λ / 2 in the circumferential direction, and are on the other side between the electrodes 3a and 3b. A ring-shaped piezoelectric body 1 in which segment electrodes 3c to 3i and 3j to 3p of length λ / 2 face each other
Are polarized such that the polarization direction is different from that of the adjacent region. For example, in the ring-shaped piezoelectric body 1, the regions where the segment electrodes 3c are in contact and the regions where the segment electrodes 3d are in contact have opposite polarization directions. [Table 1] Indicates that the polarization directions are opposite. The segment electrodes 3c to 3i having a length of λ / 2 are driving AC application electrodes, which are connected to each other by a conductive paste 4a, to which an input AC voltage is applied from an input terminal R. The segment electrodes 3j to 3p are also driving AC application electrodes,
Similarly, they are connected by the paste 4b, and an input AC voltage is applied from the input terminal L. The segment electrode 3 a having a length of ／ λ is connected to the ring-shaped common electrode 2 on the back surface of the ring-shaped piezoelectric body 1 by a conductive paste 4 c provided on the outer peripheral end of the ring-shaped piezoelectric body 1. A ground potential is applied to the segment electrode 3a from the ground terminal G. That is, the segment electrode 3a merely functions as a lead electrode of the ring-shaped common electrode 2. Further, the segment electrode 3b is merely formed in the manufacturing process of the segment electrode group 3, and has no function. The ring-shaped piezoelectric body 1 has an elastic ring 6 made of brass or the like fixed to the ring electrode 2 side with an adhesive 5. The rotor 7 is in contact with the elastic ring 6 at a certain contact pressure. Vibration is caused by the ring-shaped piezoelectric body 1 and the elastic ring 6.
The moving element 20 is constituted. Next, the operation of the ultrasonic motor having the above configuration will be described. Between input terminals R-G and input terminal L-
When an AC voltage having a predetermined frequency that is 90 ° out of phase with that between the G electrodes is applied, bending vibration of wavelength λ occurs in the ring-shaped piezoelectric body 1 and the elastic ring 6, and the rotor 7 is rotated. In order to increase the efficiency of this motor, it is necessary to keep the AC frequency at an optimum value. [0005] However, the optimum value varies depending on fluctuations in external conditions such as the contact pressure between the rotor 7 and the ring 6 of the elastic body and the temperature of the motor. Therefore, if the frequency of the AC voltage is always kept constant, a highly efficient ultrasonic motor cannot be obtained. In order to solve the above problems, it is conceivable to provide a detecting means for detecting the vibration state of the traveling vibration wave, and to always keep the frequency of the input power supply at an optimum value according to the external condition. However, if the elastic body is provided with the detecting means, the vibration may be adversely affected. Accordingly, an object of the present invention is to provide an ultrasonic motor capable of minimizing an adverse effect on vibration caused by a detection unit. As a result of the inventor's intensive research for the above-mentioned object, the present inventors have found that a mechanical-electrical conversion element having a length that is an integral multiple of a predetermined spatial phase difference can be used to advance a vibrator. The present invention has been found to be arranged on the path of the oscillating wave and to be configured to convert the vibration of the traveling oscillating wave into an electric signal by the electromechanical transducer to minimize the adverse effect on the vibration. Reached. That is, in the present invention, the first electromechanical transducer (the segment electrodes 3c to 3i of the ring-shaped piezoelectric body 1)
And a second electromechanical transducer (a portion corresponding to the segment electrodes 3j to 3p of the ring-shaped piezoelectric body 1).
And a vibrator (20) arranged with a predetermined spatial phase difference (λ / 4, λ is the wavelength of a traveling vibration wave), and a first drive signal is supplied to the first electromechanical transducer. (AC voltage) is applied to the second electromechanical transducer and the second electromechanical transducer has a predetermined temporal phase difference from the first drive signal.
A drive signal (AC voltage shifted by 90 ° phase) is applied, and a progressive vibration wave is generated in the vibrator, and an ultrasonic wave causing relative motion between the vibrator and a relative motion member (rotor 7) A motor provided with a electromechanical transducer (part corresponding to the segment electrode 3b or 30b of the ring-shaped piezoelectric body 1) for converting the vibration of the traveling vibration wave into an electric signal;
This electromechanical transducer is formed to have a length that is an integral multiple of the predetermined spatial phase difference on the vibrator, and is disposed on the vibrator and on the traveling path of the traveling vibration wave. An ultrasonic motor is provided. It should be noted that the spatial phase difference refers to the electrode 3
b length (λ / 4) or electrode 30b length (3λ /
4). In the above construction, the electro-mechanical transducer having a length equal to an integral multiple of the predetermined spatial phase difference is arranged on the path of the traveling vibration wave of the vibrator, and the electro-mechanical transducer causes the progressive vibration. Since the vibration of the wave is converted into an electric signal, the adverse effect on the vibration can be minimized. FIG. 2 shows a preferred embodiment of the present invention. In the embodiment of FIG. 2, a terminal S is provided in a portion corresponding to the segment electrode 3b in FIG. 1, and a region of the ring-shaped piezoelectric body 1 facing the segment electrode 3b is also polarized in the second embodiment. 2 only in FIG.
Unlike the one of FIG. 2, the other structure of the embodiment of FIG. 2 is the same as that of FIG. In FIG. 2, the segment electrode 3b
Is an electrode to which no input AC voltage is applied, and when the motor is driven and a bending vibration occurs in the ring-shaped piezoelectric body 1, an AC corresponding to the bending vibration appears on the segment electrode 3b. This phenomenon is due to the property that the piezoelectric material generates vibration when an AC is applied, and generates an AC when the vibration is applied. FIG. 3 shows a rotation control circuit of the ultrasonic motor shown in FIG. The rotation control circuit includes a controllable oscillator 8, a 90 ° phase shifter 9, amplifiers 10a and 10b, inductances 11a and 11b, an ultrasonic motor 12, a band-pass filter 13, and an oscillation controller 14 shown in FIG. I have. A sine wave of a certain frequency is output from the oscillator 8 and input to the amplifier 10a and the 90 ° phase shifter 9. The output of the 90 ° phase shifter 9 is input to the amplifier 10b. The amplifiers 10a and 10b connect the AC voltages having phases shifted by 90 ° from each other to terminals R and R via matching inductances 11a and 11b.
L is applied to the ultrasonic motor 12. The rotation state of the ultrasonic motor is output from a terminal S connected to the segment electrode 3b with the magnitude of an AC voltage, and is input to the band-pass filter 13. As described later with reference to FIG. 5, unnecessary signals are removed by the band-pass filter 13, and only signals useful for controlling rotation are input to the oscillation controller 14 and fed back to the controllable oscillator 8. . Note that the oscillating means is the oscillator 8 in FIG.
1 shows a phase shifter 9 and amplifiers 10a and 10b. FIG. 4 shows that the number of revolutions of the ultrasonic motor at the input frequency f to the ultrasonic motor in FIG. 2 is N, and the voltage output to the terminal S of the vibration detecting segment electrode 3b of the ultrasonic motor at that time is N. FIG. 4 is a characteristic curve diagram showing a relationship when a detected voltage (for example, an effective value) is set to V. In the figure, characteristics and properties of the detected voltage V ₁ of the motor rotational speed N ₁ to the input frequency under certain external conditions is as shown in the figure, it is both maximum at the optimum input frequency f _1. When the external condition changes, the motor speed characteristics and the detected voltage characteristics with respect to the input frequency become N ₂ and V ₂ , and at this time, N ₂ and V ₂ become the maximum with respect to the optimum input frequency f ₂ .
Thus, under certain external conditions, it has been experimentally found that the frequency at which the peak of the motor rotation speed and the frequency at which the peak of the detection voltage are substantially coincide with each other. Now, despite changing environmental conditions, still the input frequency, for example by holding f _1, the motor rotation speed N also becomes possible to greatly reduced detection voltage V. Therefore, in the present invention, as shown in the circuit diagram of FIG. 3, the oscillation controller 14 controls the oscillator 8 in accordance with the output voltage from the terminal S of the segment electrode 3b of the ultrasonic motor (that is, the detection voltage). The oscillation frequency, that is, the input frequency to the ultrasonic motor, is always controlled to the optimum value (for example, f ₁₂ ) of the external condition at that time. The above-mentioned optimum value of the external condition indicates a point where the voltage signal has a peak. The oscillation controller 14 is a device for controlling the oscillation frequency so that the voltage signal from the terminal S becomes a peak.
A hill-climbing circuit known in, for example, Japanese Patent No. 51164 is used. The oscillation controller 14 includes a detecting unit 15 as shown in FIG.
, A difference hold circuit 16 and an oscillation control unit 17.
The hill-climbing circuit is indicated by 18 in the figure, and is a circuit including the band-pass filter 13, the detecting unit 15, and the difference hold circuit 16. The voltage signal from which the unnecessary frequency band has been removed through the band-pass filter 13 is continuously detected by the detection unit 15, and the detected voltage signal is output to the difference hold circuit 16. Difference hold circuit 1
In step 6, the voltage signal is sampled and held at regular time intervals, and a comparison operation is performed to determine whether the voltage signal is increasing or decreasing with respect to time. The obtained information is output to the oscillation control unit 17, and the oscillation control unit 17 controls the oscillator 8 so that the voltage direction always increases. In this way, the optimum frequency is always output from the oscillator 8 even if the resonance frequency between the ring-shaped piezoelectric body and the elastic body in the ultrasonic motor changes under the influence of disturbance. Is kept optimal. On the other hand, the segment electrode 3b of the ultrasonic motor
The detection voltage V from the terminal S connected to the motor takes the maximum value at the input frequency to the motor which gives the maximum value of the motor rotation speed N as described above, and also has the frequency f which is far away therefrom as shown in FIG. _There may be a small peak at ₃ . Therefore, in the control circuit of FIG. 3, the band-pass filter 13 is provided between the motor-side output terminal S and the oscillation control circuit 14, and a frequency band that gives the maximum value of the motor rotation speed N, for example, the frequency f _{1 of} FIG. ~f through near _2, it is to be cut other frequency bands such as including the frequency f ₃ of the above. In the embodiment shown in FIG. 2, the segment electrodes 3b for detecting vibration are distributed from the innermost circumference to the outermost circumference of the ring-shaped piezoelectric body 1. The present invention is not limited to this, and may be any position as long as vibration of the piezoelectric body can be detected. For example, as shown in FIG. 6, the electrode 3b may be coated only on the outer peripheral portion of the ring-shaped piezoelectric body. The electrode for vibration detection does not need to use the segment electrode 3b. For example, the electrode 3a in FIG. 6 is divided in the radial direction to form two electrodes 30a and 30b insulated from each other as shown in FIG. The inner peripheral electrode 30a is connected to the ring-shaped common electrode 2 by the conductive paste 4c, and is connected to the ground terminal G to be used as an extraction electrode of the ring-shaped electrode. The terminal S is connected to the outer peripheral electrode 30b. Connected to form a vibration detection electrode. Similarly, the segment electrodes 3c to
Any of 3p can be divided to form a drive AC application electrode and a vibration detection electrode. The advantages of the case where the vibration detecting electrode is provided on the outer peripheral side of the ring-shaped piezoelectric body as shown in FIGS. 6 and 7 will be described below. If the elastic body has a ring shape as shown in FIG. 2, for example, the resonance frequency differs between the inside and the outside of the ring. Also, the surface wave driving the ultrasonic motor, specifically the rotor, is concentrated outside the ring. Therefore,
It is desirable that the monitor voltage is obtained by detecting the vibration of the outer periphery of the ring of the piezoelectric body. Therefore, by coating the segment electrode for vibration detection only on the outer peripheral portion of the ring-shaped piezoelectric body, the vibration on the outer peripheral portion of the ring-shaped piezoelectric body can be detected. In the above-described embodiment, a segment electrode for vibration detection is provided in a part of the segment electrode group 3, and the electrode for vibration detection and the ring-shaped electrode 2 opposed to the electrode 1 with the piezoelectric body 1 interposed therebetween. Although the vibration detection signal was extracted, the present invention is not limited to this. For example, a small portion of the ring-shaped electrode 2 is insulated from the rest, and this small portion is used as a vibration detection electrode,
On the other hand, a portion of the segment electrode group 3 opposed to the vibration detection electrode with the piezoelectric body 1 interposed therebetween is insulated from the others, and this portion is used as a counter electrode of the vibration detection electrode. A vibration detection signal can also be extracted. Of course, when this counter electrode corresponds to the segment electrode 3a or 3b to which no AC voltage is applied, this electrode 3
a or 3b can be used as a counter electrode as it is. In the above-described example, the vibration detecting electrode and the opposing electrode which are opposed to each other with the piezoelectric body interposed therebetween are used as the pair of electrodes for detecting the vibration. Alternatively, it can be provided on the segment electrode group 3 side. Specifically, for example, a pair of adjacent electrodes insulated from the other may be provided on one of the surfaces of the piezoelectric body so as to be located in the same polarization region of the piezoelectric body. As described above, according to the present invention, the electromechanical transducer having a length that is an integral multiple of the predetermined spatial phase difference is arranged on the traveling path of the traveling vibration wave of the vibrator. Since the vibration of the progressive vibration wave is converted into an electric signal by the electromechanical transducer, the adverse effect on the vibration caused by the electromechanical transducer can be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an ultrasonic motor, (a) is a plan view thereof, and (b) is a front view thereof. FIG. 2 is a plan view of an ultrasonic motor according to one embodiment of the present invention. FIG. 3 is a diagram showing a rotation control circuit of the ultrasonic motor in FIG. 2; FIG. 4 is a characteristic curve diagram showing a relationship between an input frequency to an ultrasonic motor under different external conditions and a motor rotation speed and a detection voltage from the terminal in FIG. 2; FIG. 5 is a diagram showing a case where a plurality of peaks appear in a characteristic curve showing a relationship between a motor rotation speed and a detection voltage with respect to an input frequency. FIG. 6 is a plan view showing another embodiment of the ultrasonic motor according to the present invention. FIG. 7 is a plan view showing still another embodiment of the ultrasonic motor according to the present invention. FIG. 8 is a diagram showing a configuration of an oscillation controller 14 of FIG. 3; [Description of Signs] 1 Electromechanical transducer 6 Ring of elastic body 7 Relative motion members 3c to 3i First electromechanical transducer 3j to 3p Second electromechanical transducer 3b Electromechanical transducer S Terminal 8 Oscillator 14 Oscillation Controller 15 Detection unit 17 Oscillation control unit 18 Climbing circuit 20 Oscillator

Claims (1)

(57) [Claims] First electromechanical transducer and second electromechanical transducer
DOO comprises a vibrator which is disposed at a predetermined spatial phase difference, the first driving signal to said second electromechanical transducer with the first drive signal is applied to said first electro-mechanical conversion element
No. a predetermined second drive signal having a time phase difference is applied, traveling vibration wave is generated in the vibrator, said vibrator
An ultrasonic motor that causes relative motion between the member and a relative motion member , wherein the electromechanical device converts the vibration of the traveling vibration wave into an electric signal.
Comprising a conversion element, said electro-mechanical transducer, said formed to a length of an integral multiple of the predetermined spatial phase difference of the oscillator, the traveling vibration wave propagation path on a on the transducer An ultrasonic motor, wherein the ultrasonic motor is disposed. 2. The predetermined spatial phase difference is λ / 4 or 3λ /
4, the ultrasonic motor according to claim 1, characterized in that the (lambda is the wavelength of the traveling vibration wave).