JP3453838B2 - Ultrasonic motor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention utilizes vibrations of different modes such as a longitudinal vibration mode and a bending vibration mode,
The present invention relates to an ultrasonic motor that produces relative motion with a relative motion member, and more particularly to an ultrasonic motor with an improved drive control method.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing a conventional example of a linear ultrasonic motor. In a conventional linear ultrasonic motor, a vibrating transformer 102 is arranged on one end side of a rod-shaped elastic body 101 and a vibrating transformer 103 is arranged on the other end side.
Each of the transformers 102, 103 includes a vibrator 102a, 103
a is joined. An alternating voltage is applied from the oscillator 102b to the vibrator 102a for vibration to vibrate the rod-shaped elastic body 101, and this vibration propagates through the rod-shaped elastic body 101 to become a traveling wave. Due to this traveling wave, the rod-shaped elastic body 10
The moving body 104 that is brought into pressure contact with 1 is driven.

On the other hand, the vibration of the rod-shaped elastic body 101 is transmitted to the vibrator 103a through the vibration damping transformer 103, and the vibrator 103a converts the vibration energy into electric energy. The load 103b connected to the vibrator 103a consumes the electric energy to absorb the vibration. This vibration damping transformer 103 suppresses the reflection of the end surface of the rod-shaped elastic body 101, and the rod-shaped elastic body 1
The generation of standing waves of 01 eigenmodes is prevented.

The linear type ultrasonic motor shown in FIG.
The length of the rod-shaped elastic body 101 is required only for the moving range of 04, and the whole of the rod-shaped elastic body 101 has to be vibrated, so that the device becomes large and the standing wave of the eigenmode is generated. In order to prevent this, there has been a problem that the vibration damping transformer 103 and the like are required.

In order to solve such problems, various self-propelled ultrasonic motors have been proposed.
The "degenerate vertical L1-bending B4 mode flat plate motor" described in "222 Piezoelectric linear motor for moving optical pickup" in "Proceedings of Dynamics Symposium on Electromagnetic Force" is known.

FIG. 6 is a schematic diagram showing a conventional example of a modified degenerate vertical L1-bending B4 mode flat plate motor.
6A is a front view, FIG. 6B is a side view, and FIG. 6C is a plan view. The elastic body 1 includes a rectangular flat plate-shaped base portion 1a,
Protrusions 1b, 1 formed on one surface of the base 1a
and c. The piezoelectric elements 2 and 3 are elastic bodies 1.
Is an element that is attached to the other surface of the base portion 1a to generate a longitudinal vibration L1 mode and a bending vibration B4 mode. The protrusions 1b and 1c of the elastic body 1 are provided at antinodes of the bending vibration B4 mode generated in the base portion 1a, and are brought into pressure contact with a relative motion member (not shown) to perform relative motion.

[0007]

However, as shown in FIG.
The motor is like a longitudinal vibration mode and a bending vibration mode,
Since two modes of vibration are generated, if a conventional ultrasonic motor drive circuit (for example, Japanese Patent Laid-Open No. 63-209482) that generates a progressive vibration wave by superposing the same vibration mode is used, Stable drive control could not be performed. Specifically, when speed control is performed by changing the frequency of the input frequency voltage, depending on how to select the range of the frequency, there is a problem that driving may not be possible when the load fluctuates. there were.

An object of the present invention is to solve the above-mentioned problems and to enable stable drive control even when vibrations of different modes such as a longitudinal vibration mode and a bending vibration mode are utilized. It is to provide an ultrasonic motor.

[0009]

In order to solve the above problems, a first solution means of an ultrasonic motor according to the present invention is a first vibration vibrating in a direction parallel to a moving direction of a relative motion member. In the ultrasonic motor, which uses the mode and a second vibration mode that vibrates in a direction intersecting with a moving direction of the relative motion member, a relative motion is generated between the relative motion member and the relative motion member. Drive control means for controlling in a range higher than both the resonance frequency of the vibration mode and the resonance frequency of the second vibration mode, and the resonance frequency of the first vibration mode to the resonance of the second vibration mode. Higher than the frequency , and the drive control means
Frequency from high frequency to low frequency
It is characterized by changing .

A second solution is an elastic body (11) and electromechanical conversion elements (12, 13) coupled to the elastic body.
It has the door, phase to the elastic body by the electromechanical transducer
Longitudinal vibration mode oscillating in the driving direction of a pair of moving members and its longitudinal
In the ultrasonic motor that generates a bending vibration mode that vibrates in a direction intersecting with the vibration mode and causes relative motion with the relative motion member by the elliptical motion generated by their combined vibration, the longitudinal vibration mode (L1 ) and the bending resonance frequency of the vibration mode (B4) (fL1, fB4) of, Rutotomoni provided a drive control means for controlling at a higher range than the higher resonance frequency (fL1), the longitudinal vibration mode
From the resonance frequency of the bending vibration mode
It is also characterized by making it higher .

A third solving means is the ultrasonic motor according to the first or second solving means, wherein the drive control means changes the frequency from a high frequency to a low frequency at the time of starting. .

A fourth solving means is the ultrasonic motor according to any one of the first to third solving means, wherein the drive control means outputs a detected phase difference signal according to a phase difference between the input voltage and the monitor voltage. The phase difference detector (26) for outputting, the target phase difference setting device (28) for outputting a target phase difference signal corresponding to the target output, and the outputs of the phase difference detector and the target phase difference setting device are compared. And a phase difference controller (27) for controlling the detected phase difference signal so as to approach the target phase difference signal, and the target is set in a range higher than a resonance point having a higher resonance frequency of different vibration modes. The feature is that a phase difference signal is set.

[0013]

According to the present invention, the relative motion is generated between the relative motion member by utilizing the vibrations of the first mode and the second mode different from each other, for example, the longitudinal vibration mode and the bending vibration mode. In this case, among the different vibrations, the control is performed in a range higher than the higher resonance frequency, so that driving is not stopped due to load fluctuations, etc., and stable driving can always be performed. .

[0014]

Embodiments Embodiments will be described in more detail below with reference to the drawings. FIG. 1 is a schematic view showing an embodiment of an ultrasonic motor according to the present invention. The elastic body 11 has a base portion 11a and two protruding portions 11b and 11c, and the material thereof is metal such as stainless steel or aluminum alloy, or plastic. In this embodiment, the elastic body 11 has a thickness t, a length h, and a width b.

The piezoelectric elements 12 to 15 are bonded to the upper surface of the base portion 11a of the elastic body 11. Piezoelectric elements 12, 13
Is an element for generating a longitudinal vibration L1 mode and a bending vibration B4 mode. The piezoelectric elements 12 and 13 have electrodes 12a and 13a printed on their surfaces.
The voltage of the A terminal is applied to the piezoelectric element 12 via 2a, and the voltage of the B terminal is applied to the piezoelectric element 13 via the electrode 13a. In this embodiment, the piezoelectric elements 12 and 13 are
Is polarized in the thickness direction as shown in FIG.
The polarization directions are the same. Further, the voltage of the A terminal and the voltage of the B terminal have the same frequency and are out of phase with each other by π / 2. The polarizations of the two piezoelectric elements 12 and 13 may be opposite to each other.

An electrode 14a is printed on the surface of the piezoelectric element 14, and the electrode 14a is electrically connected to the elastic body 11 by a conductive paint 16. The piezoelectric elements 12 and 13 have the same electric potential as the elastic body 11 on the surface opposite to the surface on which the electrodes 12a and 13a are arranged, and the electric potential passes through the conductive paint 16 and the electrode 14a. Then, it is transmitted to the G terminal. It is preferable that the piezoelectric element 14 is not subjected to polarization treatment in order to reduce the driving force and eliminate the performance difference in the driving direction.

The piezoelectric element 15 has an electrode 15a printed on its surface. The vibration state of the elastic body 11 is converted into an electric signal by the piezoelectric element 15 and transmitted to the P terminal via the electrode 15a. This electric signal contains two different vibration modes, that is, the vibration state of the fourth bending vibration mode and the vibration state of the first longitudinal vibration mode, in a degenerated form. Then, a signal having a magnitude substantially corresponding to the combined vibration amplitude of the elastic body 11 is obtained.

FIG. 2 is a diagram for explaining the operation of the ultrasonic motor according to the present invention. FIG. 2 (A) shows time changes of two-phase high-frequency voltages A and B input to the ultrasonic motor from t1.
It is shown at t9. The horizontal axis of FIG. 2A shows the effective value of the high frequency voltage. FIG. 2B shows how the cross section of the ultrasonic motor is deformed, and shows a temporal change (t1 to t9) of the bending vibration generated in the ultrasonic motor. Figure 2
(C) shows the state of deformation of the cross section of the ultrasonic motor, and changes in longitudinal vibration (t1 to t) generated in the ultrasonic motor.
9) is shown. FIG. 2D shows a temporal change (t1 to t9) of the elliptic motion generated in the protrusions 11b and 11c of the ultrasonic motor.

Next, the operation of the ultrasonic motor of this embodiment will be described for each time change (t1 to t9). Time t
2, the high frequency voltage A generates a positive voltage, and the high frequency voltage B similarly generates the same positive voltage, as shown in FIG. As shown in FIG. 2B, the bending motions due to the high frequency voltages A and B cancel each other out, and the mass point Y1
And Z1 have zero amplitude. Further, as shown in FIG. 2C, the longitudinal vibrations due to the high frequency voltages A and B are generated in the extending direction. The mass points Y2 and Z2 show the maximum elongation around the node X, as indicated by the arrow. As a result,
As shown in (D), the above-mentioned both vibrations are combined, and the mass point Y1
The synthesis of the motion of Y and Y2 becomes the motion of the mass point Y, and the synthesis of the motion of the mass points Z1 and Z2 becomes the motion of the mass point Z.

At time t2, as shown in FIG. 2 (A), the high frequency voltage B becomes zero and the high frequency voltage A generates a positive voltage. As shown in FIG. 2 (B), a bending motion is generated by the high frequency voltage A, the mass point Y1 oscillates in the positive direction, and the mass point Z1 oscillates in the negative direction. Further, as shown in FIG. 2 (C), longitudinal vibration due to the high frequency voltage A occurs, and the mass points Y2 and Z2 contract more than at time t1. As a result, as shown in FIG. 2D, the above-mentioned both vibrations are combined, and the mass Y
And Z move clockwise relative to the time t1.

At time t3, as shown in FIG. 2 (A), the high frequency voltage A generates a positive voltage and the high frequency voltage B similarly generates the same negative voltage. As shown in FIG. 2 (B), the bending motions due to the high frequency voltages A and B are combined and amplified, and the mass point Y1 is amplified in the positive direction more than at the time t2, showing the maximum positive amplitude value. Mass point Z1 is time t2
It is amplified in the negative direction more than, and shows the maximum negative amplitude value. Further, as shown in FIG. 2C, the longitudinal vibrations due to the high frequency voltages A and B cancel each other out, and the mass points Y2 and Z2
And return to their original positions. As a result, as shown in FIG. 2D, both of the above vibrations are combined, and the mass points Y and Z move clockwise relative to the time t2.

At time t4, as shown in FIG. 2 (A), the high frequency voltage A becomes zero and the high frequency voltage B generates a negative voltage. As shown in FIG. 2 (B), a bending motion is generated by the high frequency voltage B, and the amplitude of the mass point Y1 is lower than that at the time t3, and the amplitude is lower than that at the mass point Z1 time t3. Further, as shown in FIG. 2C, longitudinal vibration due to the high frequency voltage B is generated, and the mass points Y2 and Z2 contract.
As a result, as shown in FIG. 2 (D), both of the above vibrations are combined, and the mass points Y and Z move clockwise relative to the time t3.

At time t5, as shown in FIG. 2A, the high frequency voltage A produces a negative voltage, and similarly, the high frequency voltage B produces the same negative voltage. As shown in FIG. 2B, the bending motions due to the high frequency voltages A and B cancel each other out, and the masses Y1 and Z1 have zero amplitude. Also, FIG.
As shown in (C), the longitudinal vibration due to the high frequency voltages A and B is generated in the contracting direction. The mass points Y2 and Z2 show the maximum contraction around the node X, as indicated by the arrow. As a result, as shown in FIG. 2 (D), both of the above vibrations are combined, and the mass points Y and Z move clockwise relative to the time t4.

As the time t6 to t9 changes,
Flexural vibrations and longitudinal vibrations are generated in the same manner as the above-described principle, and as a result, as shown in FIG. 2D, the mass points Y and Z move clockwise and make an elliptic motion. Based on the above principle, this ultrasonic motor is configured to generate an elliptic motion at the tips of the protrusions 11a and 11b to extract the driving force.
Therefore, when the tips of the protrusions 11b and 11c are pressed against the relative motion member (not shown), the elastic body 11 self-propels to the relative motion member.

FIG. 3 is a diagram showing the relationship between frequency and vibration amplitude of the ultrasonic motor according to this embodiment, where the horizontal axis represents frequency and the vertical axis represents vibration amplitude. The ultrasonic motor of this embodiment is configured so that the resonance frequency f _L1 of the first longitudinal vibration mode is _{equal to} or higher than the resonance frequency f _{B4 of the} fourth bending vibration mode. The reason is as follows.

The ultrasonic motor generally controls the speed by changing the input frequency. At this time, if the drive is performed at a frequency lower than the resonance frequency, a phenomenon may occur in which the drive cannot be started or the drive is stopped at the time of overload. Therefore, it is necessary to operate above the resonance frequency. However, in the motor of the principle that is driven by utilizing the degeneracy of two kinds of vibration modes, that is, the longitudinal vibration mode and the bending vibration mode, like the ultrasonic motor of this embodiment, the longitudinal vibration that mainly contributes to the speed is increased. It is considered desirable to control the speed by changing the frequency for each mode. At that time, the bending vibration mode has its resonance frequency f _B4.
When it is driven at a lower frequency, the bending vibration may stop. Therefore, in this embodiment, the resonance frequency f _L1 of the first longitudinal vibration mode is set to be _{equal to} or higher than the resonance frequency f _B4 of the fourth bending vibration mode. As a result, even if the input frequency is set to any range higher than the resonance frequency f _L1 of the first longitudinal vibration mode, it does not become lower than the resonance frequency f _{B4 of the} fourth bending vibration mode, so that it can be started. It will not occur or the phenomenon that the drive will stop when overloaded will not occur, and the drive will be stable.

Here, in order to make the resonance frequency f _L1 of the first longitudinal vibration mode higher than the resonance frequency f _B4 of the fourth bending vibration mode, the thickness t of the elastic body 11 (the fourth bending) The vibration direction of the vibration mode) may be thinned. Elastic body 11
Is h, the longitudinal elastic modulus is E, and the density is ρ, the resonance frequency f _{L1 of the} first-order longitudinal vibration mode and the resonance frequency f _{B4 of the} fourth-order bending vibration mode are approximately f _B4 = (14 .137 / 2πL ² ) ・ (E / ρ) ^1/2・
It is expressed as (t / 12 ^1/2 ) f _L1 = (1 / 2L) · (E / ρ) ^1/2 . By making the thickness t of the elastic body 11 thin, the resonance frequency f _L1 of the first longitudinal vibration mode can be made higher than the resonance frequency f _B4 of the fourth bending vibration mode. To be precise, it is desirable to determine the resonance frequency in consideration of the influence of the piezoelectric material such as PZT and the protrusions 11b and 11c.

FIG. 4 is a block diagram showing the drive circuit of the ultrasonic motor according to this embodiment. Initial value generation means 21
When the power is turned on and the ultrasonic motor 10 is instructed to start, the oscillator 22 instructs the oscillator 22 to have an initial frequency. This initial frequency is sufficiently larger frequency than the resonance frequency f _L1 of the primary longitudinal vibration mode, by a change in environmental temperature, even if the resonance frequency f _L1 of the primary longitudinal vibration mode is changed, it It does not exceed the value.

The oscillator 22 oscillates the initial frequency instructed by the initial value generating means 21, its output is branched, and one output is amplified by the first amplifier 23, and then the B layer voltage. As the electrode 13 of the piezoelectric element 13
Input to a. The other branched output is connected to the phase shifter 24. The phase shifter 24 shifts the phase of the B layer voltage by π / 2 to obtain the A layer voltage, and then the second amplifier 25. Through the electrode 12 of the piezoelectric element 12
Input to a.

The phase difference circuit 26 is a circuit to which the B layer voltage from the first amplifier 23 and the output of the P terminal connected to the piezoelectric element 15 are input, and which calculates the phase difference between the two voltages.
The output is input to the comparator 27. The comparator 27 is
The reference phase difference set by the reference phase difference output circuit 28 is compared with the output of the phase difference circuit 26, and a signal corresponding to the difference between the two phase differences is output to the oscillator 22. The oscillator 22 changes the oscillation frequency in the direction in which the signal corresponding to the phase difference becomes zero. As a result, the vibration amplitude of the ultrasonic motor is maintained at a predetermined magnitude.

In the reference phase difference output circuit 28, the reference phase difference is within the control range (≧ f
Since it is set to a value corresponding to _L1 ), the oscillation frequency is always equal to or higher than the resonance frequency f _{L1 of the} first longitudinal vibration mode and is higher than the resonance frequency f _{B4 of the} fourth bending vibration mode. It won't get too low, so you can't start,
The phenomenon that the drive stops when overloaded does not occur and the drive becomes stable.

The initial value generating means 11 to the oscillator 12
When the initial frequency is instructed to start up, immediately after that, the initial frequency is gradually changed to a lower frequency.

The present invention is not limited to the embodiments described above, and various modifications and changes are possible, which are also included in the present invention. For example, as the electromechanical conversion element, the piezoelectric element has been described as an example, but an electrostrictive element may be used. Further, as the different vibration modes, the vibration of the L1-B4 mode has been described as an example, but other modes such as L1-B2, L1-B6, L2-B4 may be used. Further, the different vibration modes have been described by using the example of the longitudinal vibration and the bending vibration, but the same can be applied to the case of the two vibration modes of the longitudinal vibration and the torsional vibration. Furthermore, when using three or more types of vibration modes, control may be performed in a range higher than the highest resonance frequency. Although the self-propelled example has been described, the elastic body side may be fixed and the long relative movement member may be moved.

[0034]

As described in detail above, according to the present invention, when vibrations of different modes are utilized to cause relative motion with the relative motion member, the higher vibration of the different vibrations is used. Since the control is performed in a range higher than the resonance frequency of No. 1, there is an effect that driving is not stopped due to a change in load, and stable driving can always be performed.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of an ultrasonic motor according to the present invention.

FIG. 2 is a diagram illustrating a driving operation of the ultrasonic motor according to the present embodiment.

FIG. 3 is a diagram showing a relationship between frequency and vibration amplitude of the ultrasonic motor according to the present embodiment.

FIG. 4 is a block diagram showing a drive circuit of the ultrasonic motor according to the present embodiment.

FIG. 5 is a diagram showing a conventional example of a linear ultrasonic motor.

FIG. 6 is a schematic diagram showing an example of a modified degenerate vertical L1-bending B4 mode flat plate motor.

[Explanation of symbols]

11 elastic body 12, 13, 14, 15 Piezoelectric element 21 initial value generation means 22 oscillator 23 First amplifier 24 Phase shifter 25 Second amplifier 26 Phase difference circuit 27 comparator 28 Reference phase difference output circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-344764 (JP, A) JP-A-5-161369 (JP, A) JP-A-63-56178 (JP, A) JP-A-5- 91766 (JP, A) JP 5-344765 (JP, A) JP 3-22870 (JP, A) JP 3-164076 (JP, A) JP 5-3688 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02N 2/00

Claims (4)

(57) [Claims] 1. A first vibration mode that vibrates in a direction parallel to the moving direction of the relative motion member, and a second vibration mode that vibrates in a direction intersecting the moving direction of the relative motion member. In the ultrasonic motor that utilizes the relative motion member to generate a relative motion, a drive for controlling in a range higher than both the resonance frequency of the first vibration mode and the resonance frequency of the second vibration mode. The resonance frequency of the first vibration mode is set higher than the resonance frequency of the second vibration mode while the control means is provided, and the drive control means sets the high frequency at the time of startup.
The ultrasonic motor is characterized by changing the frequency from low to low . 2. A longitudinal vibration mode having an elastic body and an electromechanical conversion element coupled to the elastic body, wherein the electromechanical conversion element causes the elastic body to vibrate in a driving direction of a relative motion member and a longitudinal vibration mode thereof. A bending vibration mode that vibrates in a direction intersecting with the vibration mode is generated, and the elliptical motion generated by their combined vibration causes
In an ultrasonic motor that causes relative motion between the relative motion member and the elastic body, a drive for controlling in a range higher than the higher resonance frequency of the resonance frequencies of the longitudinal vibration mode and the bending vibration mode. An ultrasonic motor characterized in that a resonance frequency of the longitudinal vibration mode is set higher than a resonance frequency of the bending vibration mode while providing control means. The ultrasonic motor according to claim 3] 請 Motomeko 2, the drive control unit, ultrasonic motor toward lower frequencies from a frequency higher at startup, and changing the frequency. 4. The ultrasonic motor according to claim 1, wherein the drive control unit outputs a detected phase difference signal according to a phase difference between an input voltage and a monitor voltage. A phase difference detector, a target phase difference setting device that outputs a target phase difference signal corresponding to the target output, and comparing the outputs of the phase difference detector and the target phase difference setting device, the detected phase difference signal is And a phase difference controller for controlling so as to approach the target phase difference signal, wherein the target phase difference setter is a target phase difference signal in a range higher than a resonance point of a resonance frequency of a different vibration mode. The ultrasonic motor is characterized by setting.