JPH04138084A - Ultrasonic motor and oscillator thereof - Google Patents

Abstract

PURPOSE:To detect oscillation in different mode by disposing a pair of detecting elements, connected electrically, at positions spaced apart by a predetermined distance. CONSTITUTION:When the interval between detecting elements 51, 52 is set at lambda/2, voltages V51, V52 having approximately same amplitude and phase difference of 180 deg. are produced. When the voltages V51 and V52 are added, a voltage of substantially zero volt is produced. Although the voltages V51, V52 are produced from the detecting elements 51, 52 through different mode vibration, they have unmatched phase and amplitudes in that case. Consequently, a signal representing a different vibration mode can be obtained when the voltages V51, V52 are added.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an ultrasonic motor using traveling waves.

(Prior Art) A conventional ultrasonic morph will be described with reference to FIGS. 11 and 12. A ring-shaped piezoelectric vibrating body 2 is joined to the elastic body l. The piezoelectric vibrator 2 is provided with a first set and a second set of drive vibrators 3.4. The first set of driving vibrators 3 further includes eight vibrating elements 31 to 38.
It is equipped with

The vibration elements 31 to 38 are polarized so that the polarization directions of adjacent vibration elements are opposite to each other. In exactly the same way, the second set of driving vibrators 4 further includes eight vibrating elements 41 to 41.
It is equipped with 48. The vibration elements 41 to 48 are polarized so that the polarization directions of adjacent vibration elements are opposite to each other.

A gap 5.6 having a predetermined distance is formed between the first set of driving vibrators 3 and the second set of driving vibrators 4.

If the desired wavelength of the traveling wave to be generated on the elastic body I is defined as λ, then the vibration elements 31 to 38 degrees 41-48 described above have a wavelength of λ.
/2, and the gap 5 is designed to have a distance equivalent to 3λ/4.

Further, the remaining portion after forming the drive vibrator 3.4 and the gap 5 becomes the gap 6.

When a pair of AC voltages having electrical phases different by 90 degrees are applied to the first set and the second set of driving vibrators 3 and 4, vibration is generated in the elastic body l by the driving vibrators 3 and 4. The generated vibrations interfere with each other in the elastic body 1, and the elastic body l(
This generates a traveling wave.

Ultrasonic motors using traveling waves generated in this way are disclosed in, for example, Japanese Patent Laid-Open No. 59-204477 and Japanese Patent Laid-Open No. 6
It is introduced in the publication No. 3-73887.

Hereinafter, with reference to FIG. 12, the structure of the ultrasonic morph disclosed in Japanese Unexamined Patent Publication No. 63-73887 will be briefly described.

An inner hole of a ring-shaped stator 12 is fitted into the base 11, and the inner circumferential side of the stator is fixed via countersunk screws 13 so that it cannot vibrate. A ring-shaped piezoelectric vibrator 2 is bonded to one surface of the stator 12 so as to transmit vibrations. A large number of protrusions 12a are formed on the surface of the stator 12.

By applying an alternating current voltage to the piezoelectric vibrating body 2, the piezoelectric vibrating body 2 expands and contracts, and traveling wave vibration is generated in the stator 12.

The rotor 16 is constantly pressed against the stator 12 by the pressing force of the disc spring 17. A friction material 16a is bonded to the rotor 16, and the friction material 16a contacts the stator 12. Also, there is a rubber seam) 1 between the disc spring 1) and the rotor 16.
B is caught.

The disc spring 17 is held by a holder portion 20a of the rotating shaft 20. The driving force of the rotor 16 is transmitted to the rotating shaft 20 through the disc spring 17 and the holder portion 20a. The rotating shaft 20 is rotatably supported by a bearing 23 fixed to the base 11 and a bearing 19 fixed to the housing 15.

When an AC voltage is applied to the piezoelectric vibrating body 2 from a drive circuit (not shown), a traveling wave circulating on the stator 12 is generated. The generated traveling wave gives a rotational moment to the rotor 16, causing the rotor 16 to rotate.

(Problem to be solved by the invention) In conventional ultrasonic motors, when the load torque acting on the rotating shaft is too large or when the rotor cannot rotate due to external force (so-called motor lock), the There is a problem in that vibrations at wavelengths other than the desired wavelength (hereinafter referred to as different mode vibrations) occur.

In particular, when the wavelength of the different mode vibration is long, unpleasant noise in the audible frequency band may be generated, which is extremely undesirable.

However, since the conventional ultrasonic motor did not have a means for detecting different mode vibrations, it was not possible to prevent the occurrence of different mode vibrations.

The present invention has been made to solve the problems of the conventional device, and its technical problem is to detect the occurrence of different mode vibrations.

[Structure of the invention]

(Means for solving the problem) The technical means taken to achieve the above-mentioned technical problem consists of a first set of vibrators and a second set of vibrators formed at a distance from the first set of vibrators. A vibrating body for an ultrasonic motor including a set of vibrators is provided with a pair of detection elements formed at positions separated by a predetermined distance and electrically connected to each other.

(Function) According to the above-mentioned technical means, when different mode vibration occurs in the vibrating body, a potential difference is generated between the pair of detection elements.

Therefore, by measuring the potential difference between the detection elements, the occurrence of different mode vibrations can be detected.

(Example) First, a preferred first example apparatus to which the present invention is applied will be described. In the following description, the same members as those in the conventional device will be given the same numbers and the description will be omitted.

FIG. 1 is a plan view of a piezoelectric vibrator 2 to which the present invention is applied. A first set of driving vibrators 3 and a second set of driving vibrators 4
A pair of detection elements 51 and 52 are formed in the gap 5 between them. When the wavelength of the desired traveling wave to be generated in the stator 12 is λ, the distance between the detection elements 51 and 52 is λ/2.

Further, the detection elements 51 and 52 are polarized to have the same polarity. Further, the width of the detection elements 51, 52 is designed to be as narrow as possible in order to sharply select and detect different mode vibrations.

When a pair of AC voltages having electrical phases different by 90 degrees are applied to the driving vibrator 3.4, a traveling wave is generated in the stator 12 by the driving vibrator 3.4.

FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, showing how a traveling wave of wavelength λ is generated. When a traveling wave of wavelength λ is generated in the stator 12, the stator 12 is bent as shown in FIG. At this time, a voltage is generated in the detection elements 51 and 52 according to the amount of deflection of the stator 12.

FIG. 3 is a graph of the voltage generated across the sensing elements 51,52. Since the spacing between the detection elements 51 and 52 is λ/2, voltages V51 and VS2 are generated in the detection elements 51 and 52, the phases of which are 180 degrees different from each other and the amplitudes of which are approximately the same. Therefore, when the voltage V51°VS2 is added, a voltage of almost zero volts is output as shown in FIG.

FIG. 5 is a sectional view taken along the line AA in FIG. 1, depicting the occurrence of vibrations other than the wavelength λ (ie, different mode vibrations). Even due to different mode vibrations, the detection elements 51 and 52 have an elastic body
Voltages v51 and VS2 are generated according to the amount of deflection, but the phases and amplitudes of the generated voltages V51°VS2 are uneven. As a result, the voltage V51. When V52 is added, an irregular voltage is output as shown in FIG.

In this way, in the device of this embodiment, the voltage V51. By adding V52, a signal indicating the presence or absence of different mode vibrations can be obtained.

Note that the distance between the detection elements 51 and 52 may be a distance other than λ/2, and generally, the distance d between the detection elements 51 and 52 is an appropriate distance
is expressed by equation (1).

d−n·λ/2 (1) In equation (1), n is an arbitrary natural number. However, if n is an even number, it is necessary to polarize the detection elements 51, 52 in the same direction, and if n is an odd number, it is necessary to polarize the detection elements 51, 52 in opposite directions.

Hereinafter, referring to FIG. 8 and FIG. 9, devices of second and third embodiments to which the present invention is applied will be described.

The devices of the second and third embodiments are examples in which a monitor element 53 for detecting the vibration state of the stator 12 is formed on the piezoelectric vibrating body 2 of the device of the first embodiment. Monitor element 53 is formed in gap 5 or gap 6. In order to detect the average vibration state of the stator 12, the width of the monitor element 53 is designed to be as wide as possible so that it is λ/2 or less.

In the second embodiment device shown in FIG.
is located approximately in the middle of the drive vibrator 3.4. Therefore, the voltage generated in the monitor element 53 when the rotor 16 rotates in the normal direction and the voltage generated in the monitor element 53 when the rotor 16 rotates in the reverse direction have substantially the same characteristics.

In the third embodiment shown in FIG. 9, the monitor element 53
Since the monitor element 53 is located in the gap 6, the width of the monitor element 53 can be designed more freely and wider than in the second embodiment.

The monitor element 53 detects the amplitude of the traveling wave generated in the stator 12 and generates a voltage approximately proportional to the magnitude of the amplitude. Therefore, by adjusting the frequency of the AC voltage applied to the drive vibrator 3.4 so that the voltage generated at the monitor element 53 is approximately constant, the stator can be Even if the resonance frequency of 12 changes, a stable traveling wave is always generated with high efficiency.

FIG. 10 is a block diagram depicting a drive circuit 100 capable of driving the devices of the second and third embodiments shown in FIGS. 8 and 9.

A piezoelectric vibrator 2 and a switch SW are connected to the drive circuit 100. Detection element 51 formed on piezoelectric vibrator 2
．． 52 are connected to each other by conductive wires. Therefore, the voltage generated at the detection element 51.52 is the sum of the voltages generated at the pixel element 51.52 (more precisely, the average value).

Switch SW is used to determine the rotation direction of rotor 16. The state of the switch SW is input to the phase shift circuit PH3 and the oscillation circuit OSC through the input circuit IF.

When the contact CW is grounded by the switch SW, the phase shift circuit PH3 delays the phase of the AC signal supplied to the drive circuit DRV2 by 90 degrees with respect to the AC signal supplied to the drive circuit DRVI, thereby rotating the rotor 16 clockwise. . When the contact CCW is grounded by the switch SW, the phase shift circuit PH
3 delays the phase of the AC signal supplied to the drive circuit DRVI by 90 degrees with respect to the AC signal supplied to the drive circuit 0Rv2, and rotates the rotor 16 counterclockwise. switch SW
When contact 5TOP is grounded by
stops the rotor 16. Switch SW is contact 5TO
Immediately after switching from contact point P to contact point CW or contact point CCW, oscillation circuit O8C performs processing for starting rotor 16. Since the phase shift circuit PH3 and the oscillation circuit O3C having these functions have already been introduced in many documents and are well known, detailed explanations thereof will be omitted.

The oscillation port 803C outputs an alternating current signal of a predetermined frequency.The alternating current signal output from the zero oscillation circuit OSC is supplied to the phase shift circuit PH3. The phase shift circuit PH3 divides the frequency of the AC signal and outputs a pair of signals whose phases differ by 90 degrees from each other. Phase shift circuit P
The AC signal output by H3 is sent to drive circuits DRVI and DRV2.
After being amplified by , the signal is supplied to the driving vibrator 3.4. At this time, the piezoelectric vibrator 2 generates a traveling wave in the stator 12.

The traveling wave generated in the stator 12 causes the monitor element 5 to
3, a voltage is generated according to the amplitude of the traveling wave. The voltage generated in the monitor element 53 is fed back to the oscillation circuit O3C through the smoothing circuit SCI. The oscillation circuit O8C is
When the voltage of the monitor element 53 is low (that is, when the amplitude of the traveling wave is small), the oscillation frequency is brought closer to the resonant frequency of the stator 12, and the amplitude of the traveling wave is increased (on the contrary, the oscillation circuit O8C When the voltage of the monitor element 53 is high (i.e.
When the amplitude of the traveling wave is large), the oscillation frequency is moved away from the resonant frequency of the stator 12 to reduce the amplitude of the traveling wave. In this way, the amplitude of the traveling wave on the stator 12 is maintained within an optimal range, and the rotor 16 is efficiently driven.

When the load torque acting on the rotating shaft 20 is too large,
When a motor lock occurs, different mode vibrations may occur on the stake 12. When different mode vibration occurs on the stator 12, a voltage is generated in the detection elements 51 and 52. Detection element 51.5! The voltage generated is input to the comparison port i1cMP through the smoothing circuit SC2. A base tjA voltage generation circuit REF is connected to the comparison circuit CMP.

Comparison port IIICMP outputs a drive stop signal to phase shift circuit PH3 when the voltage supplied from smoothing circuit SC2 exceeds the voltage supplied from reference voltage generation circuit REF.

When the phase shift circuit PH3 is supplied with the drive stop signal from the comparator circuit CMP, it does not output an AC signal to the drive circuits DRVI and DRv2. 2 is stopped, and generation of unpleasant noise is prevented.

As described above, in the vibrating body 2 to which the present invention is applied,
Vibrations other than traveling waves having a pre-designed desired wavelength λ, that is, different mode vibrations, can be detected in real time by the detection elements 51 and 52.

Detection element 51,5! can be formed by polarizing the ring-shaped piezoelectric vibrating body 2, so it is very inexpensive and suitable for producing large lids.

Furthermore, in the ultrasonic motor using the drive circuit shown in FIG. 10, the drive circuit lOO is stopped immediately after the generation of different mode vibrations, so that harsh noise can be completely prevented.

Note that in the above-described embodiment device, only an example in which the detection elements 51 and 52 were formed in the gap 5 was shown, but the detection elements 51 and 5
2 may be formed in the gap 6, and the detection elements 51 and 52 are
It is sufficient if it is formed in a part of the piezoelectric vibrating body 2 or a part of the stator 12.

〔Effect of the invention〕

According to the present invention, when different mode vibration occurs in the vibrating body, a potential difference is generated between the pair of detection elements.

Therefore, by measuring the potential difference between the detection elements, the occurrence of different mode vibrations can be detected in real time.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a first embodiment of the apparatus to which the present invention is applied. Figure 2 is A of Figure 1, which depicts how the predetermined wavelength λ is generated.
-A sectional view. FIG. 3 is a graph of the voltage applied to each detection element when a predetermined wavelength λ is generated. FIG. 4 is a graph of voltages supplied from a pair of detection elements when a predetermined wavelength λ is generated. FIG. 5 is a cross-sectional view taken along the line AA in FIG. 1, showing how different mode vibrations occur. FIG. 6 is a graph of voltages generated in individual detection elements when different mode vibrations occur. FIG. 7 is a graph of voltages supplied from a pair of detection elements when different mode vibrations occur. FIG. 8 is a plan view of a second embodiment of the device to which the present invention is applied. FIG. 9 is a plan view of a device according to a third embodiment of the present invention. FIG. 10 is a block diagram depicting a drive circuit capable of driving the devices of the second and third embodiments. FIG. 11 is a plan view depicting a conventional vibrating body. FIG. 12 is a longitudinal sectional view depicting the structure of a conventional ultrasonic motor. DESCRIPTION OF SYMBOLS 1... Elastic body, 2... Piezoelectric vibrating body, 3.4... Drive vibrator, 5, 6... Gap, 12... Stator,
16...Rotor, 51.52...Detection element, 53.
...Monitor element, SC2...Smoothing circuit (drive stop means), REF...Reference voltage generation circuit (drive stop means)
, CMP...comparison circuit (drive stop means).

Claims (3)

[Claims] (1) A vibrator for an ultrasonic motor comprising a first set of vibrators, and a second set of vibrators formed at a position apart from the first set of vibrators, formed at a predetermined distance apart. A vibrator for an ultrasonic motor, comprising a pair of detection elements electrically connected to each other. (2) a vibrating body having a first set of vibrators and a second set of vibrators formed at a position apart from the first set of vibrators; a stator to which the vibrating body is fixed; In an ultrasonic motor comprising: a rotor that is pressed into contact with a stator; and a drive circuit that drives the vibrating body, the vibrating body further includes a pair of electrically connected What is claimed is: 1. An ultrasonic motor comprising: a detection element; wherein the drive circuit further includes drive stop means for stopping driving of the vibrating body when a voltage is generated in the detection element. (3) The vibrator for an ultrasonic motor according to claim 1, wherein the predetermined distance is n·λ/2, where λ is a desired wavelength of the traveling wave and n is a natural number.