JP4654583B2 - Vibration wave motor - Google Patents

Description

  The present invention relates to a vibration wave motor that generates a traveling vibration wave on a driving surface of a vibrator and drives a moving element that is in pressure contact with the vibrator by the traveling vibration wave.

2. Description of the Related Art Conventionally, as a vibration wave motor, for example, a motor including a vibrator and a mover that is in pressure contact with the vibrator is known. The vibrator includes a piezoelectric body exhibiting a piezoelectric effect and an elastic body joined to the piezoelectric body, and generates a progressive vibration wave on a driving surface of the elastic body by using expansion and contraction of the piezoelectric body. Due to this progressive vibration wave, an elliptical motion is generated on the drive surface of the elastic body, so that the movable element in pressure contact with the wavefront of the elliptical motion is driven.
Since such a vibration wave motor has a characteristic of having a high torque even at a low rotation, when the vibration wave motor is mounted on an appropriate drive device, the gear of the drive device can be omitted. There are advantages such as eliminating gear noise and improving positioning accuracy.

  As described above, the vibrator includes a piezoelectric body and an elastic body, and the piezoelectric body and the elastic body are firmly bonded (bonded) with an adhesive or the like. On the drive surface side opposite to the piezoelectric bonding surface of the elastic body, grooves of equal width are provided at substantially equal intervals. By this groove, the neutral surface of the bending vibration generated inside the elastic body is shifted to the piezoelectric body side, and as a result, the amplitude of the progressive vibration wave generated on the driving surface side of the elastic body is expanded.

  The progressive vibration wave generated in the elastic body is obtained by combining two standing waves of bending vibration generated by the excitation of the piezoelectric body. The performance of the vibration wave motor can be improved by increasing the vibration amplitude of the bending vibration (standing wave). Therefore, in order to obtain bending vibration (standing wave) with large amplitude, for example, the number of grooves of the vibrator is designed to be a multiple of the wave number of the progressive vibration wave, and the vibration of each wave is uniform. There are known ways to make it.

FIG. 5 is a conceptual diagram for explaining the principle of abnormal noise generation in a conventional vibration wave motor.
A corresponds to a groove 12a formed in the elastic body at substantially equal intervals and a protrusion 12b formed between the grooves 12a and including the vibration surface 12c. The number of the groove portions 12a is a multiple of the wave number of the progressive vibration wave.
B is a progressive vibration wave generated in the elastic body, and shows a waveform when the wave head of the progressive vibration wave passes through the protrusion 12b.
C is a progressive vibration wave generated in the elastic body, and shows a waveform when the wave head of the progressive vibration wave passes through the groove 12a.

According to the waveforms B and C, the amplitude when the head of the progressive vibration wave passes through the groove 12a is amplified more than the amplitude when the wave head passes through the groove 12a, and this progressive vibration is generated. Since all the wave heads (here, three) of the wave have switched from the state (waveform B) that has passed through the protrusion 12b at the same time to the state (waveform C) that has passed through the groove 12a, Dynamic movement occurs instantaneously.
As a result, in the vibration wave motor, moments when the vibrator and the moving element do not contact each other occur simultaneously in each wave, for example, when the vibration amplitude increases (that is, when the rotation speed of the vibration wave motor increases). In some cases, abnormal noise was generated.

In order to prevent the occurrence of this abnormal noise, it has been proposed that the number of grooves of the vibrator and the wave number of the progressive vibration wave have a prime relationship (for example, Patent Document 1).
However, in this case, the vibration Q value (a value representing the sharpness of resonance) becomes small, and sufficient vibration amplitude of the standing wave cannot be obtained, which may deteriorate the performance of the vibration wave motor. It was.
Japanese Patent Publication No. 5-30149

  The subject of this invention is providing the vibration wave motor which can prevent generation | occurrence | production of the unusual noise at the time of high rotation, maintaining drive performance.

In order to solve the above-mentioned problem, the invention of claim 1 is divided into two phases, and two mutually shifted vibrations generated from the two phases are generated by a drive signal input to each of the two phases. A vibrator having a piezoelectric body to be excited, an elastic body that is joined to the piezoelectric body and generates two progressive vibration waves on a driving surface by combining two vibrations out of phase; and a driving surface of the elastic body And a movable body driven by the progressive vibration wave, wherein the elastic body has a plurality of grooves on its drive surface side, and the progressive vibration The vibration wave motor is characterized in that the wave number is 9, and the greatest common divisor between the number of the groove portions and the wave number of the progressive vibration wave is 3 .
According to a second aspect of the present invention, there is provided a piezoelectric body that is divided into two phases and that is driven by two driving signals that are input to each of the two phases and that are deviated from each other and generated from the two phases. A vibrator having an elastic body that is joined to the piezoelectric body and generates a traveling vibration wave on a driving surface by combining two vibrations that are out of phase, and in pressure contact with the driving surface of the elastic body; And a movable body driven by a traveling vibration wave, wherein the elastic body has a plurality of grooves on the drive surface side, and the wave number of the traveling vibration wave is 8. The vibration wave motor is characterized in that the greatest common divisor of the number of the groove portions and the wave number of the progressive vibration wave is four .
According to a third aspect of the present invention, there is provided a piezoelectric body that is divided into two phases, and two vibrations generated from the two phases are excited by driving signals input to the two phases, A vibrator having an elastic body that is bonded to a piezoelectric body and generates two progressive vibration waves on a driving surface by combining two vibrations that are out of phase with each other, and is in pressure contact with the driving surface of the elastic body, and A movable body driven by a natural vibration wave, wherein the elastic body has a plurality of grooves on its drive surface side, and the wave number of the progressive vibration wave is 10, The vibration wave motor is characterized in that the greatest common divisor between the number of grooves and the wave number of the progressive vibration wave is five .

A fourth aspect of the present invention, in the vibration wave motor according to any one of claims 1 to 3, wherein the vibration generated from the two phases to the piezoelectric body, the phase is shifted 1/4 wavelength from each other, This is a characteristic vibration wave motor.
A fifth aspect of the present invention, in the vibration wave motor according to claim 4, between the two phases, that the there is a quarter-wave length intervals of a vibration, a vibration wave motor according to claim.
A sixth aspect of the present invention is the vibration wave motor according to any one of the first to fifth aspects, wherein the piezoelectric body is alternately polarized at every half wavelength of the vibration. This is a vibration wave motor.
A seventh aspect of the present invention is the vibration wave motor according to any one of the first to sixth aspects, wherein the wave head in the groove portion and the groove portion among the plurality of wave heads of the progressive vibration wave are provided. It is a vibration wave motor characterized by the fact that there is no wave head at the same time.

The vibration wave motor of the present invention includes (1) an elastic body which is bonded to a piezoelectric body excited by a drive signal, generates a progressive vibration wave on the drive surface by excitation, and has a plurality of grooves formed on the drive surface side. A vibrator having a pressure contact with the driving surface of the elastic body and driven by a progressive vibration wave. The greatest common divisor between the number of grooves and the wave number of the progressive vibration wave is Since it is an integer smaller than the wave number of the vibration wave and larger than 1, the number of groove portions is not a multiple of the wave number of the progressive vibration wave, and the number of groove portions and the wave number of the progressive vibration wave are relatively prime ( It is not the relationship that two integers have no common divisor other than 1.
For this reason, all of the wave heads of the progressive vibration waves generated on the drive surface of the elastic body do not simultaneously pass through the groove part, and at least one of the wave heads of the progressive vibration wave passes through the groove part. Therefore, it is possible to prevent the generation of abnormal noise during high rotation while maintaining drive performance.

(2) When the wave number of the progressive vibration wave is 8, the greatest common divisor is either 4 or 2. Similarly, when the wave number is 9, the greatest common divisor is 3, and the wave number Is 10, the greatest common divisor is set to either 5 or 2, so that the maximum driving rotational speed at which no abnormal noise is generated can be increased.

  The purpose of the present invention is to prevent the generation of abnormal noise during high rotation while maintaining the driving performance, and to the number of the plurality of grooves formed on the driving surface side of the elastic body and the driving surface side of the elastic body. This is realized by making the greatest common divisor with the wave number of the progressive vibration wave to be generated smaller than the wave number of the progressive vibration wave.

Hereinafter, the present invention will be described in more detail with reference to the drawings and the like. In the following embodiments, an ultrasonic motor using an ultrasonic vibration region will be described as an example of the vibration wave motor.
FIG. 1 is a schematic view showing an ultrasonic motor according to the present invention.
FIG. 2 is an external view of the transducer and the moving element of the ultrasonic motor according to the present embodiment.
The ultrasonic motor 10 includes, for example, a vibrator 11 and a moving element 17, and the vibrator 11 side is fixed, and the moving element (relative motion member) 17 side is rotationally driven. A buffer member 14, a pressure plate 15, a pressure member 16, a support member 19A, and the like are disposed on the lower side, and a vibration absorbing member 18, a rotation member 19B, and the like are disposed on the upper side of the mover 17. Has been placed.

  The vibrator 11 is joined to an elastic body 12 and an electromechanical conversion element (hereinafter referred to as a piezoelectric body) 13 such as a piezoelectric element or an electrostrictive element that is joined to the elastic body 12 and converts electric energy described later into mechanical energy. And. In this vibrator 11, a traveling vibration wave (hereinafter referred to as a traveling wave) is generated. In this embodiment, as an example, a description is given of nine traveling waves.

The elastic body 12 is made of a metal material having a high resonance sharpness, and has a ring shape. The elastic body 12 has a groove 12a cut on a surface opposite to a surface to which the piezoelectric body 13 is bonded (that is, a surface facing the moving element 17), and a protruding portion (a portion without the groove 12a) 12b. The front end surface of this becomes the drive surface 12 c and is brought into pressure contact with the moving element 17. Note that the number of the grooves 12a and the number of the protrusions 12b are the same.
The reason why the groove 12a is formed in the elastic body 12 is to make the traveling wave neutral surface as close as possible to the piezoelectric body 13 side, thereby amplifying the amplitude of the traveling wave on the drive surface 12c.

  The piezoelectric body 13 is divided into two phases (A phase and B phase) along the circumferential direction, and in each phase, the elements in which polarization is alternated every 1/2 wavelength are arranged, A quarter wavelength interval is provided between the A phase and the B phase.

As described above, the buffer member 14, the pressure plate 15, the pressure member 16, the support member 19 </ b> A, and the like are disposed below the piezoelectric body 13. The buffer member 14 is disposed below the piezoelectric body 13 and is a member for preventing the vibration of the vibrator 11 from being transmitted to the pressure plate 15 and the pressure member 16. For example, a nonwoven fabric or felt is used. ing.
The pressure plate 15 is a plate for receiving pressure from the pressure member 16. The pressure member 16 is a member that is disposed below the pressure plate 15 and generates a pressurizing force. In this embodiment, the pressure member 16 is a disc spring. However, the present invention is not limited to this, and a coil spring, a wave spring, or the like may be used. The support member 19A is a member that supports the ultrasonic motor 10 on the fixed side.

  The mover 17 is made of a light metal such as aluminum, and the surface of the sliding surface 17a is subjected to surface treatment for improving wear resistance. As described above, the vibration absorbing member 18 such as rubber is disposed on the upper side of the moving element 17 in order to absorb the vibration in the pressurizing direction of the moving element 17. Above the vibration absorbing member 18, a rotating member 19B such as a bearing is disposed.

FIG. 3 is a block diagram showing a drive control apparatus for the ultrasonic motor 10 according to the present embodiment.
The drive control device 20 includes, for example, an oscillation unit 21, a control unit 22, a phase shift unit 23, amplification units 24 and 25, a detection unit 26, and the like.
The oscillating unit 21 generates a drive signal having a desired frequency according to a command from the control unit 22. The phase shifter 23 divides the drive signal generated by the oscillator 21 into two drive signals having a 90 ° phase difference. The amplifiers 24 and 25 boost the two drive signals divided by the phase shifter 23 to desired voltages, respectively. Drive signals from the amplifying units 24 and 25 are transmitted to the ultrasonic motor 10, and a traveling wave is generated in the vibrator 11 by the application of the drive signal, and the moving element 17 is driven.
The detection unit 26 includes an optical linear encoder and the like, detects the position and speed of a driven body (not shown) driven by driving the moving element 17, and outputs a detection signal to the control unit 22.

  The control unit 22 controls the drive of the ultrasonic motor 10 based on a drive command from the CPU. For example, the control unit 22 receives a detection signal from the detection unit 26 and based on the value, position information and speed information. The frequency of the oscillator 21 is controlled so that the driven body is positioned at the target position.

Next, the operation of the drive control device 20 will be described.
First, the target position is transmitted to the control unit 22. The oscillating unit 21 generates a drive signal. The drive signal is divided into two drive signals having a phase difference of 90 ° by the phase shift unit 23 and amplified to a desired voltage by the amplifiers 24 and 25. The drive signals amplified by the amplifying units 24 and 25 are applied to the piezoelectric body 13 of the ultrasonic motor 10, and the piezoelectric body 13 is excited. By this excitation, the ninth-order bending vibration is generated in the elastic body 12 joined to the piezoelectric body 13.

  The piezoelectric body 13 is divided into an A phase and a B phase, and drive signals are applied to the A phase and the B phase, respectively. The 9th-order bending vibration generated from the A-phase and the 9th-order bending vibration generated from the B-phase are such that the positional phase is shifted by ¼ wavelength, and the A-phase drive signal and the B-phase drive Since the signal is 90 ° out of phase, the two bending vibrations are combined into nine traveling waves.

An elliptical motion is generated at the wave head of the traveling wave. Here, since the moving element 17 is in pressure contact with the drive surface 12c, it is frictionally driven by this elliptical motion. The moving element 17 obtains a driving force in the direction opposite to the traveling direction of the traveling wave from the elastic body 12, and this driving force is, for example, a protrusion in which the wave head of the traveling wave is formed on the elastic body 12. Obtained when passing through the section 12b.
The detection unit 26 is disposed on a driven body that is driven by driving the moving element 17, and an electric pulse signal generated from the detection unit 26 is transmitted to the control unit 22. The control unit 22 can obtain the current position and the current speed based on this signal, and controls the drive frequency of the oscillation unit 21 based on the position information, the speed information, and the target position information.

FIG. 4 is a diagram comparing the performance of the ultrasonic motor 10 according to the present embodiment based on the number of grooves 12a and the wave number of traveling waves.
On the drive surface 12c side of the elastic body 12 of the present embodiment, 48 equal-width groove portions 12a are formed at equal intervals along the circumferential direction, and 48 protrusion portions 12b are also formed (hereinafter, the number of grooves is 48). It will be explained by the number of grooves). Here, the number of grooves 48 is a relationship in which the greatest common divisor is 3 (that is, smaller than the wave number 9) with respect to the wave number 9 of the traveling wave. It is not a multiple of wave number 9, and the groove number 48 and the wave number 9 of the traveling wave are not relatively prime (no two integers have a common divisor other than 1) ("NO. 2" described later). Corresponding).

Further, the present inventor made a prototype with a different number of grooves in the vibrator 11 in which the wave number 9 of the traveling wave is generated, and the performance of the ultrasonic motor using each prototype and the abnormal noise at the time of high rotation investigated.
In order to show the performance of the ultrasonic motor, the maximum efficiency (%) when the rated frequency is input (≈the frequency at which the maximum drive speed NH is obtained), the minimum drive speed NL (rpm) and the maximum drive speed There is a ratio (NH / NL ratio) to NH (rpm).
The maximum drive speed NH is the maximum drive speed at which no abnormal noise is generated, and it is preferable that the value be large. Further, as for the NH / NL ratio, a large value indicates that the controllability is good. For example, the stop time is short when incorporating an application, and the stop accuracy is improved.

In “NO. 1”, as shown in the figure, the number of grooves is 54 (a multiple of the wave number 9 of the traveling wave), and the performance of the ultrasonic motor using the samples “1-1, 1-2, 1-3”. Compared.
In “NO. 2”, as described above, the number of grooves 48 (the greatest common divisor with the wave number 9 of the traveling wave is 3, which is not a multiple of the wave number 9 of the traveling wave, and the wave number 9 of the traveling wave is Are not prime relations), and the performance of the ultrasonic motor was compared using samples “2-1, 2-2, 2-3”.
In “NO.3”, the number of grooves is 47 (which is relatively prime with the wave number 9 of the traveling wave), and the performance of the ultrasonic motor using the samples “3-1, 3-2, 3-3”. Compared.
In “NO.4”, the number of grooves was 45 (multiple of wave number 9 of traveling wave), and the performance of the ultrasonic motor was compared using samples “4-1, 4-2, 4-3”.

Hereinafter, while comparing the above “NO. 1 to 4”, the performance of the ultrasonic motor will be described based on the number of grooves and the number of traveling waves.
“NO.1, 4” has a higher maximum efficiency than “NO.2,3”, but has a lower maximum drive speed at which no abnormal noise occurs.
“NO.3” has a higher maximum drive speed at which no abnormal noise is generated, but has a lower maximum efficiency than “NO.1 and 4”.
In contrast, “NO. 2” has substantially the same maximum efficiency as “NO. 1, 4”, and the maximum drive speed at which no abnormal noise occurs is higher than “NO. 1, 3, 4”. large.

“NO. 1, 4” in which the number of grooves is a multiple of the wave number will be described.
The reason why the maximum efficiency of “NO. 1, 4” is large is that the number of grooves is a multiple of the wave number, so that the vibration of each standing wave of bending vibration is uniform, and as a result A high Q value can be obtained and a large vibration amplitude can be obtained.
On the other hand, when the vibration amplitude becomes large (that is, when the rotational speed becomes high), abnormal noise is likely to be generated when the wave head of the progressive vibration wave passes through the groove 12a. In order to switch from a state in which the amplitude differs when passing through the protrusion 12b and each wave passes through the groove 12a (protrusion 12b) at the same time to a state of passing through the protrusion 12b (groove 12a), the mover This is because a vertical movement occurs in FIG. Thereby, it is assumed that the moment when the vibrator 11 and the moving body 17 do not come into contact with each other and abnormal noise is generated.

“NO. 3” in which the number of grooves and the wave number are relatively prime will be described.
The reason why the maximum drive rotational speed at which no abnormal noise of “NO. 3” occurs is larger than that of “NO. 1, 4” is because the number of grooves and the wave number are a prime relationship. This is because the crest of the wave is switched from a state where it has passed through the groove 12a (protrusion 12b) to a state where it has passed through the protrusion 12b (groove 12a). .
On the other hand, in “NO. 3”, since the number of grooves and the wave number are relatively prime, the vibration of each wave when the standing wave is generated is not uniform, and the Q value becomes small. Since the amplitude cannot be obtained, the maximum efficiency is reduced.

Next, as described above, the greatest common divisor of the number of grooves and the wave number is smaller than the wave number. More specifically, the number of grooves is not a multiple of the wave number, and the number of grooves and the wave number are not prime. “NO.2” will be described.
“NO.2” is a relationship in which the greatest common divisor between the number of grooves and the wave number is 3, and in this case, when a standing wave of bending vibration is generated, vibration of three of the nine waves Becomes uniform (the same vibration is divided into three groups). For this reason, in “NO. 2”, a certain Q value is ensured and the vibration amplitude does not decrease, and as a result, the maximum efficiency substantially the same as “NO. 1, 4” can be obtained.
Further, in “NO. 2”, the wave head of each wave of the progressive vibration wave changes from a state where it passes through the groove 12a (protrusion 12b) every three groups to a state where it passes through the protrusion 12b (groove 12a). Since the switching is performed, the vertical movement of the moving element 17 is smaller than that of “NO. 1, 4”, and as a result, the maximum driving rotational speed at which no abnormal noise occurs is increased.

  Therefore, according to this embodiment, as in “NO. 2”, the relationship between the number of grooves and the wave number is set so that the greatest common divisor between the number of grooves and the wave number is smaller than the wave number. The vibration amplitude of the standing wave is ensured, and the momentary vertical movement of the moving element 17 at the time of high rotation can be suppressed. As a result, the maximum efficiency when the rated frequency is input is increased and the generation of abnormal noise is achieved. It is possible to increase the maximum number of rotations that are not performed, and to increase the NH / NL ratio. For example, the ultrasonic motor 10 having a short stop time and good stop accuracy can be obtained.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the equivalent scope of the present invention.
In the ultrasonic motor 10 described above, the case where 48 grooves 12a are formed on the driving surface side of the elastic body 12 with 9 traveling waves has been described. However, the present invention is not limited thereto, and the wave number of the traveling wave is 8, Even in the case of 10, the same effect can be obtained by considering the relationship between the number of grooves and the number of traveling waves.
(1) If the wave number of the traveling wave is 8, and the number of grooves is 44 (that is, the number of grooves is not a multiple of the wave number and is not a prime relationship), in this case, the number of grooves Since the greatest common divisor between the wave number and the wave number is 4, which is smaller than the wave number, for example, it is possible to obtain an ultrasonic motor that has good performance such as efficiency and does not generate abnormal noise even at high rotation.
(2) If the wave number of the traveling wave is 10, and the number of grooves is 55 (that is, the number of grooves is not a multiple of the wave number and is not a prime relationship), in this case, the number of grooves Since the greatest common divisor of 5 and the wave number is 5 and smaller than the wave number, for example, it is possible to obtain an ultrasonic motor that has good performance such as efficiency and does not generate abnormal noise even at high rotation.

It is the schematic which shows the ultrasonic motor by this invention. It is an external view of the vibrator | oscillator and moving element of the ultrasonic motor of a present Example. It is a block diagram which shows the drive control apparatus of the ultrasonic motor 10 by a present Example. It is the figure which compared the performance of the ultrasonic motor 10 by a present Example based on the number of the groove parts 12a, and the wave number of a traveling wave. It is a conceptual diagram for demonstrating the generation principle of the unusual noise in the conventional vibration wave motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Ultrasonic motor 11 Vibrator 12 Elastic body 12a Groove part 12b Protrusion part 12c Drive surface 13 Piezoelectric body 14 Buffer member 15 Pressure plate 16 Pressure member 17 Movable element 18 Vibration absorption member 19A Support member 19B Rotating member 20 Drive control device 21 Oscillation Unit 22 Control unit 23 Phase shift unit 24, 25 Amplification unit 26 Detection unit

Claims (7)

The piezoelectric material is divided into two phases, and is joined to the piezoelectric material, and the piezoelectric material is excited by two mutually shifted vibrations generated from the two phases by a driving signal input to each of the two phases. A vibrator having an elastic body that combines two vibrations out of phase to generate a progressive vibration wave on a drive surface;
A mover that is in pressure contact with the drive surface of the elastic body and is driven by the progressive vibration wave;
A vibration wave motor comprising:
The elastic body has a plurality of grooves on its drive surface side,
The wave number of the progressive vibration wave is 9, and the greatest common divisor between the number of the groove portions and the wave number of the progressive vibration wave is 3 .
Vibration wave motor characterized by The piezoelectric body is divided into two phases, and is joined to the piezoelectric body by driving vibrations that are shifted from each other and generated from the two phases according to the driving symbols inputted to the two phases, A vibrator having an elastic body that combines two vibrations out of phase to generate a progressive vibration wave on a driving surface;
A mover that is in pressure contact with the drive surface of the elastic body and is driven by the progressive vibration wave;
A vibration wave motor comprising:
The elastic body has a plurality of grooves on its drive surface side,
The wave number of the progressive vibration wave is 8, and the greatest common divisor between the number of the groove portions and the wave number of the progressive vibration wave is 4.
Vibration wave motor characterized by The piezoelectric material is divided into two phases, and is joined to the piezoelectric material, and the piezoelectric material is excited by two mutually shifted vibrations generated from the two phases by a driving signal input to each of the two phases. A vibrator having an elastic body that combines two vibrations out of phase to generate a progressive vibration wave on a drive surface;
A mover that is in pressure contact with the drive surface of the elastic body and is driven by the progressive vibration wave;
A vibration wave motor comprising:
The elastic body has a plurality of grooves on its drive surface side,
The wave number of the progressive vibration wave is 10, and the greatest common divisor between the number of the groove portions and the wave number of the progressive vibration wave is 5.
Vibration wave motor characterized by In the vibration wave motor according to any one of claims 1 to 3 ,
Wherein the vibration generated from the two phases to the piezoelectric body, the phase is shifted 1/4 wavelength from each other,
Vibration wave motor characterized by The vibration wave motor according to claim 4 ,
There is an interval of ¼ wavelength of the vibration between the two phases,
Vibration wave motor characterized by In the vibration wave motor according to any one of claims 1 to 5 ,
The piezoelectric body has alternating polarization for every half wavelength of the vibration,
Vibration wave motor characterized by The vibration wave motor according to any one of claims 1 to 6 ,
Among the plurality of wave heads of the progressive vibration wave, a wave head in the groove and a wave head not in the groove are present simultaneously.
Vibration wave motor characterized by

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