JPH0632569B2 - Ultrasonic motor driving method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a moving body that is installed by generating elastic vibration in a vibrating body using a piezoelectric body such as a piezoelectric ceramic and pressingly contacting the vibrating body. The present invention relates to a driving method of an ultrasonic motor that moves using this elastic vibration as a driving force.

(Structure of Conventional Example and Problems Thereof) Hereinafter, a conventional technique of an ultrasonic motor will be described with reference to the drawings.

FIG. 5 is a cutaway perspective view of a ring type ultrasonic motor. In FIG. 1, reference numeral 1 denotes a ring-shaped elastic substrate having a large number of protrusions formed on one of the ring surfaces, and a ring-shaped piezoelectric ceramic 2 as a driving piezoelectric body is bonded to the other of the ring surfaces by means such as bonding. The ring-shaped vibrating body 3 is formed by coupling. Reference numeral 4 is a friction material made of a wear resistant material, and 5 is an elastic body, which are bonded to each other to form a moving body 6. Although not shown here, the moving body 6 is installed in pressure contact with the vibrating body 3 via a friction material 4, which is not shown here, by a pressing means such as a disc spring.

FIG. 6 is a diagram showing an example of the structure of the drive electrode formed on the piezoelectric ceramic 2, which is a quarter of the elastic traveling wave generated in the vibrating body 3.
Two sets of drive electrode A and drive electrode B are formed that are displaced in position by the wavelength equivalent. Here, the drive electrode A and the drive electrode B are each composed of a group of small electrodes each having a length corresponding to ½ wavelength so that flexural vibration can be efficiently generated. And
The electrodes C and D have lengths corresponding to 3/4 wavelength and 1/4 wavelength, respectively, and are formed to create a positional shift corresponding to 1/4 wavelength between the drive electrodes A and B. Therefore, the drive electrodes required for the operation of the ultrasonic motor are only A and B, and the electrodes C and D do not have to form electrodes.

When two AC voltages having different phases of 90 degrees are applied to the drive electrodes A and B (for example, sin wave and cos wave),
Traveling waves of flexural vibration as shown in FIG. 7 are excited in the vibrating body 3, respectively. Here, FIG. 7 (a) shows the vibration mode of flexural vibration, and FIG. 7 (b) shows the displacement distribution in the radial direction. In the ring-type ultrasonic motor, a progressive wave of flexural vibration in the radial first order and the circumferential third order or higher is excited in the vibrating body 3.
The moving body 6 is frictionally driven by the lateral component of the wave front of the traveling wave to make a rotational movement.

FIG. 8 is a cutaway perspective view of another conventional disk type ultrasonic motor. In the figure, 7 is a ring-shaped elastic substrate having a large number of protrusions 9a formed on one side of the disk, and the piezoelectric ceramics 8 are bonded together by means such as adhesion to form the disk-shaped vibrating body 9. ing. Reference numeral 10 is a friction material made of a wear-resistant material, and 11 is an elastic body, which are bonded to each other to form a moving body 12. The moving body 12 is installed in pressure contact with the vibrating body 9. For the piezoelectric ceramic 8
Two sets of drive electrodes A, which are positionally displaced by 1/4 wavelength
And a drive electrode B are formed.

FIG. 10 is a block diagram of a drive circuit for driving the ultrasonic motor having the above configuration. In FIG. 10, reference numeral 101 is an oscillator circuit having a control terminal T for changing the output oscillation frequency by an applied voltage, and outputs a drive AC signal for the ultrasonic motor. The output signal of the oscillation circuit 101 is divided into two, one of which is phase-shifted by the phase shift circuit 102 by a predetermined phase (for example, 90 degrees), and then the power amplification circuit 103.
Entered in. The other signal is input as it is to the power amplification circuit 104, is power-amplified to a level sufficient to drive each ultrasonic motor, and is then input to the two drive terminals of the vibrating body of each ultrasonic motor. An elastic traveling wave is excited in the vibrating body of the ultrasonic motor, and the moving body starts moving. The fixed resistance element 107 is connected to the drive terminal on one side of the vibrating body of the ultrasonic motor, and the fact that the vibration amplitude of the vibrating body is proportional to the current flowing through the drive terminal is used to vibrate from the voltage across the fixed resistance element 107. The detection circuit 105 detects the vibration amplitude of the vibrating body.

The comparison circuit 106 includes a set value 108 and a vibration detection circuit 105.
The vibration amplitude value of the vibrating body, which is the output of the above, is compared, and this result is input to the control terminal T of the variable oscillation circuit 101.

Now, the drive electrodes A and B have two 90 degrees different phases.
When two AC voltages (for example, sin wave and cos wave) are applied, traveling waves of high-order flexural vibration as shown in FIG. 9 are excited in the vibrating body 9, respectively. Here, FIG. 9A shows the vibration mode of flexural vibration, and FIG. 9B shows the displacement distribution in the radial direction. In the disk type ultrasonic motor, a progressive wave of flexural vibration in the radial second order and the circumferential third order or higher is excited in the vibrating body 9. The moving body 6 is frictionally driven by the lateral component of the wave front of the traveling wave to make a rotary motion, and an output can be taken out via the rotary shaft 13.

FIG. 11 illustrates a contact state between a vibrating body of an ultrasonic motor and a moving body that is in contact with the surface of the vibrating body. An arbitrary point on the surface of the vibrating body makes an elliptical motion due to an elastic traveling wave. This movement is well known in the case of surface waves (for example, see Nobuo Mikoshiba “Sonic Properties”, published by Sanseidosha in 1973), and if one point A on the surface of the elastic body is considered, The locus on the ellipse of the axis 2w and the minor axis 2u is drawn.
Letting the frequency of the elastic traveling wave be the contact point of the moving body at the apex of the elliptical locus of the vibrating body, point A has a velocity of V = 2πu in the negative direction of the x-axis. It is driven at a velocity V in the direction opposite to the traveling of the wave via force. As described above, the ultrasonic motor causes the vibrating body to generate a traveling wave to draw an elliptical locus on the surface of the vibrating body to move the vibrating body, and the frictional force causes the abutting moving body to rotate. The amplitude of this elliptical locus in the major axis w direction is about several μm or less at the maximum, and the amplitude in the minor axis u direction is also about μm or less at the maximum.

(Problem to be Solved by the Invention) The amplitude of the elastic traveling wave used by the ultrasonic motor is about several μm or less at the maximum, and the extremely small vibration amplitude is stably extracted as a driving force through frictional force. It was difficult. The ultrasonic motor has the characteristics of large torque and excellent responsiveness, but it has been difficult to put it into practical use because of its poor stability during low-speed operation. In the past, in order to improve stability, both the contact surfaces of the vibration body and the moving body of the ultrasonic motor were mirror-polished. But,
Since the friction material, which is the contact surface of the moving body, is usually a composite matrix made of plastic, it is difficult to polish the mirror surface, and even if the friction material is made of metal, it is difficult to polish both the vibrating body and the moving body. There is a problem that the manufacturing cost becomes high. Therefore, the operation of the conventional ultrasonic motor aiming at practical use is unstable, and it is difficult to perform accurate control for realizing a specific operation. Also, the driving efficiency is 1
Since it is as low as about 0% or less, heat is generated during driving and there is a problem in reliability.

(Object of the Invention) An object of the present invention is to solve the above-mentioned problems. By efficiently extracting the driving force due to the elastic vibration of the vibrating body, the operation at low speed is stabilized and the driving efficiency is increased, and An object of the present invention is to provide a practical ultrasonic motor driving method capable of reducing the manufacturing cost.

(Structure of the Invention) A method of driving an ultrasonic motor according to the present invention generates an elastic traveling wave in a vibrating body configured by laminating a piezoelectric body on an elastic body, and a moving body installed in contact with the vibrating body. An ultrasonic motor to be moved is driven so that the vibrational displacement of the elastic traveling wave generated in the vibrating body at low speed movement is 1.5 times or more the surface roughness of the contact surface of the vibrating body with the moving body. Is.

Description of Embodiments Embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an enlarged view showing a contact state between a vibrating body and a moving body during operation of the ultrasonic motor. FIG. 1 (a) shows a contact state between the vibrating body and the moving body within a range corresponding to one wavelength when the amplitude of the elastic traveling wave excited on the vibrating body is smaller than the roughness of the contact surface of the vibrating body. In the figure, the surface roughness of the contact surface of the moving body is finished to 8 to 10 μm,
The roughness of the contact surface of the vibrator is finished to about 1 μm. Then, a minute vibration amplitude of about 0.5 μm is generated in the vibrating body. As can be seen from the figure, the moving body is in contact with not only the peaks but also the valleys of the vibration of the elastic traveling wave generated in the vibrating body. In an ultrasonic motor, the driving force acts in the opposite direction on the peaks and troughs of the vibration of the elastic traveling wave, so contacting the peaks and troughs of the elastic traveling wave of the vibrating body at the same time effectively applies the driving force to the moving body. Can not do it. Therefore, the characteristics of the ultrasonic motor were unstable and the efficiency thereof was low when the experiment was conducted under such conditions.

In addition, the contact surface of the moving body is finished with a surface roughness of 8 to 10 μm to about 1 μm, and the contact surface of the vibrating body is finished with a roughness of about 1 μm to generate a minute vibration amplitude of about 0.5 μm on the vibrating body. Even when it was made to be stable, similarly stable characteristics could not be obtained.

FIG. 1 (b) shows a contact state between the vibrating body and the moving body during operation of the ultrasonic motor. In the figure, the surface roughness of the contact surface of the moving body is finished to 8 to 10 μm, and the surface roughness of the contact surface of the vibrating body is finished to about 1 μm. The elastic traveling wave generated in the vibrating body is driven so that the vibration amplitude is about 1.5 to 2 μm. In this state, the moving body and the vibrating body are in contact with each other in the vicinity of the peak of the vibration of the elastic traveling wave generated in the vibrating body, and in the vicinity of the valley of the amplitude in which the direction of the force acting on the moving body is the opposite direction. There are few points. As a result, even if the surface roughness of the contact surface of the moving body is rough, it is possible to realize stable characteristics with high driving efficiency. Even when the surface roughness of the contact surface of the moving body is finished to about 1 μm as in the case of the contact surface roughness of the vibrating body, the vibration amplitude of the vibrating body is 1.5
By driving so as to have a thickness of about 2 μm, of course, similarly stable characteristics could be obtained.

In other words, in an ultrasonic motor that uses elastic traveling waves as the driving force,
It can be seen that the surface roughness of the contact surface of the moving body does not greatly affect the characteristics, and the amplitude of the elastic traveling wave excited in the vibrating body has a great influence on the surface roughness of the vibrating body.

FIG. 2 shows how the traveling speed of the moving body increases when the surface roughness of the moving body and the vibrating body is kept constant and the vibration amplitude generated in the vibrating body is increased. is there. Here, the horizontal axis is the value obtained by dividing the vibrational displacement of the elastic traveling wave excited in the vibrating body by the surface roughness of the vibrating body, and the vertical axis is the traveling speed of the moving body normalized by the maximum speed in the figure. . The surface roughness of the moving body is about 8 to 10 μm, and the surface roughness of the vibrating body is about 1 μm. In the ultrasonic motor, the speed of the moving body is proportional to the magnitude of vibration of the vibrating body according to the theory of operation. Therefore, if the horizontal axis represents the vibrational displacement of the elastic traveling wave and the vertical axis represents the traveling speed of the moving body, the characteristics of the ultrasonic motor theoretically show a straight line. However, in reality, as shown in FIG. 2, when the vibration amplitude generated in the vibrating body is less than 1.5 times the surface roughness of the contact surface of the vibrating body, the transmission loss of the driving force from the vibrating body to the moving body is large, When the traveling speed becomes lower than the theoretical value and the vibration amplitude generated in the vibrating body is 1.5 times or more the surface roughness of the contact surface of the vibrating body, the transmission of the driving force from the vibrating body to the moving body is stable, Moreover, since it is performed efficiently, the running speed approaches the straight line explained in theory.

That is, when the magnitude of the vibration displacement of the elastic traveling wave excited on the vibrating body is 1.5 times or less the surface roughness of the contact surface of the vibrating body,
Since the vibrating body also contacts the peaks and troughs of the vibration amplitude of the stator, the moving body's velocity cannot extract the maximum driving force of the vibrating body, and the average value of the velocity at the contact point with the moving body is used. It is near low speed. When the magnitude of the vibration amplitude of the elastic traveling wave generated in the vibrating body is about 1.5 times the surface roughness of the vibrating body or more, the driving force by the elastic traveling wave of the vibrating body moves efficiently and stably. It is transmitted to the body.

In the characteristic example of FIG. 2, the surface roughness of the moving body is 8 to 10 μm.
It was confirmed that the same result was obtained by changing the surface roughness of the moving body. Further, in the characteristic example of FIG. 2, the surface roughness of the vibrating body is about 1 μm, but the same thing was confirmed by the experiment even if the surface roughness of the vibrating body was changed. This means that the characteristics of the ultrasonic motor have little relation to the surface roughness of the contact surface of the moving body, and the vibration amplitude generated in the vibrating body is 1.5 times or more the surface roughness of the contact surface of the moving body. By driving the ultrasonic motor as described above, it is possible to improve the driving efficiency of the ultrasonic motor and to stabilize its characteristics, which is extremely important for practical use.

FIG. 3A shows a block diagram of one embodiment of a drive circuit for realizing the drive method of the present invention. In the figure, 2
Reference numeral 0 denotes an oscillator circuit having a control terminal T whose output oscillation frequency can be changed by an applied voltage, and outputs a drive AC signal for the ultrasonic motor. The output signal of the oscillator circuit 20 is divided into two, and one of them is divided into a predetermined phase (for example, 90
Phase) and then input to the power amplifier circuit 22.
The other signal is input as it is to the power amplification circuit 23, is power-amplified to a level sufficient to drive each ultrasonic motor, and is then input to two drive terminals of the vibrating body of each ultrasonic motor. An elastic traveling wave is excited in the vibrating body of the ultrasonic motor, and the moving body starts moving. A fixed resistance element 2 is provided on one drive terminal of the vibrator of the ultrasonic motor.
5 is connected and the vibration detection circuit 24 detects the vibration amplitude of the vibrating body from the voltage across the fixed resistance element 25 by utilizing the fact that the vibration amplitude of the vibrating body is proportional to the current flowing through the drive terminal. The comparison circuit 26 compares a preset value 27 based on the vibration amplitude corresponding to 1.5 times the surface roughness of the vibrating body with the vibration amplitude value of the vibrating body which is the output of the vibration detection circuit 24. The result is input to the control terminal T of the variable oscillator circuit 20.

FIG. 4 is a characteristic diagram for explaining the operation of the drive circuit for the ultrasonic motor shown in FIG. In the figure, the horizontal axis represents the drive frequency of the vibrating body of the ultrasonic motor, and the vertical axis represents the vibration amplitude of the vibrating body. The surface roughness of the vibration body of the ultrasonic motor is measured in advance, and a value larger than the vibration amplitude value corresponding to 1.5 times that value is set as the set value 27. And the third
When the amplitude value of the elastic traveling wave of the vibrating body becomes smaller than the set value in the drive circuit of FIG. 7A, the comparison circuit 26 detects this and drives the ultrasonic motor drive frequency through the control terminal T. Shift. By this control, the vibration amplitude of the vibrating body of the ultrasonic motor is always kept larger than 1.5 times the surface roughness of the vibrating body, and it is possible to provide an ultrasonic motor that realizes stable operation and improved efficiency. In FIG. 4, the driving frequency of the ultrasonic motor is higher than the resonance frequency and the vibration amplitude of the vibrating body is 1.5 times the surface roughness of the vibrating body in order to obtain stable operation and high efficiency. Is set to a frequency that also increases.

When the amplitude value of the vibrating body deviates from the set value, the oscillation circuit 2
Instead of controlling the frequency of 0, the amplitude of the vibrating body can be controlled even if the voltage applied to the vibrating body is changed by controlling the power amplifying circuits 22 and 23 as shown in FIG. 3 (b). it can.

V ₁ ~V ₅ to definitive Figure 4 is a circuit FIG. 3 (b), the change in vibration amplitude of the vibrating body in the case of changing the voltage applied to the vibrator by controlling the power amplifier circuit 22 and 23 It is shown. As described above, the vibration amplitude of the vibrating body can be maintained at 1.5 times or more of the surface roughness of the vibrating body regardless of whether the voltage or the frequency is controlled.

In the embodiment of FIG. 3, the detection of the vibration amplitude 1.5 times the surface roughness of the vibrating body is detected by the value of the current flowing through the drive terminal of the vibrating body. Even if the detection is performed using the arm current value, the voltage generated by the sensor electrode configured in the piezoelectric element that is proportional to the vibration amplitude, and the output of the encoder installed on the moving body to calculate the vibration amplitude Control can be realized.

As described above, in the ultrasonic motor, by always keeping the vibration amplitude of the vibrating body larger than 1.5 times the surface roughness of the vibrating body, it is possible to realize stable operation and improvement of drive efficiency even at low speed operation. That can be done. The speed of the moving body of the ultrasonic motor is proportional to the vibration amplitude of the elastic traveling wave excited in the vibrating body from the theory of operation, and the surface roughness of the vibrating body is smaller than 1 / 1.5 of the vibration amplitude of the elastic traveling wave. It is necessary to. For example, a ring type ultrasonic motor having a diameter of 50 mm operates at a speed of about 600 rpm, or a disk type ultrasonic motor having a diameter of 40 mm operates at a high speed of about 1200 rpm, but the surface roughness of the vibrator may be large. In order to realize the following stable operation at low speed, it is necessary to further reduce the surface roughness of the vibrating body. That is,
This means that the required surface roughness of the vibrating body is determined by the speed at which the ultrasonic motor performs stable operation.

In the ultrasonic motor driving method described above, the elastic traveling wave is generated in the vibrating body configured by bonding the piezoelectric body to the elastic body, and the moving body placed in contact with the elastic body is moved. It is obvious that the same applies to other ultrasonic motors of the type.

(Effects of the Invention) As described above, according to the ultrasonic motor driving method of the present invention, the vibration amplitude generated in the vibrating body at the time of low-speed operation is the movement of the vibrating body regardless of the contact surface accuracy of the moving body. By driving so that the surface roughness of the contact surface with the body is 1.5 times or more, the driving force of the vibrating body is efficiently and stably transmitted to the moving body, and the driving efficiency of the ultrasonic motor is improved. At the same time, the operation becomes stable. Moreover, since it is not necessary to raise the contact surface accuracy of the moving body more than necessary, the manufacturing cost can be reduced, which is an excellent effect.

[Brief description of drawings]

FIG. 1 is an enlarged view showing a contact state between a vibrating body of an ultrasonic motor and a moving body, and FIG. 2 is a characteristic diagram of a vibration amplitude generated in the vibrating body and a traveling speed of the moving body, and FIG. ) And (b) are block diagrams of an embodiment of a drive circuit for realizing the drive method of the present invention, FIG. 4 is a characteristic diagram for explaining the operation of the drive circuit of the ultrasonic motor of FIG. 3, and FIG. A cutaway perspective view of a conventional ring type ultrasonic motor, FIG. 6 is a structural diagram of a drive electrode formed on a piezoelectric ceramic, and FIG. 7A is a vibration mode diagram of bending vibration of a ring type ultrasonic motor. 7 (b) is a radial displacement distribution diagram of the ring type ultrasonic motor, FIG. 8 is a cutaway perspective view of a conventional disc type ultrasonic motor, and FIG. 9 (a) is a disc type ultrasonic motor. Vibration mode diagram of flexural vibration, Fig. 9 (b) shows radial displacement of disk type ultrasonic motor FIG. 10 is a distribution diagram, FIG. 10 is a diagram showing a drive circuit of a conventional ultrasonic motor, and FIG. 11 is a diagram showing a contact state between a vibrating body of the ultrasonic motor and a moving body that is in contact with the surface thereof. 20 ... Oscillation circuit, 21 ... Phase shift circuit, 22, 23 ...
Power amplification circuit, 24 ... Vibration detection circuit, 25 ... Fixed resistance element, 26 ... Comparison circuit, 27 ... Set value.

Claims (1)

[Claims] 1. An ultrasonic motor for generating an elastic traveling wave in a vibrating body formed by laminating a piezoelectric body on an elastic body, and moving a moving body that is placed in contact with the vibrating body.
The driving is performed so that the vibrational displacement of the elastic traveling wave generated in the vibrating body during low speed movement is 1.5 times or more the surface roughness of the contact surface of the vibrating body with the moving body. Driving method of ultrasonic motor.