JPH072022B2 - Ultrasonic motor driving method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of an ultrasonic motor device that uses an elastic traveling wave as a driving force.

2. Description of the Related Art Recently, an ultrasonic motor that uses a piezoelectric body such as a piezoelectric ceramic to excite an elastic traveling wave in a driving body to move a moving body installed on the driving body has been announced. It is a topic because of its characteristics. (For example, Nikkei Mechanical 'February 28, 1983 issue P44-48) Hereinafter, a conventional ultrasonic motor device will be described with reference to the drawings.

FIG. 1 is a sectional view of an annular ultrasonic motor. In the figure, a ring-shaped piezoelectric ceramic 2 is bonded to one of the main surfaces of a ring-shaped elastic body 1 to form a piezoelectric driving body 3.
Reference numeral 4 denotes a slider made of a wear resistant material, 5 denotes an elastic body, which are bonded to each other to form a moving body 6. The moving body 6 is in contact with the driving body 3 via the slider 4. When an electric field is applied to the piezoelectric ceramic 2, a traveling wave of bending vibration is excited in the driving body 3 and the moving body 6 rotates.

FIG. 2 shows the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor of FIG. In the figure, the electrodes are configured so that the bending vibration in the circumferential direction has 9 wavelengths.

Each of A and B is an electrode group including eight small regions corresponding to one-half wavelength, C is three-quarter wavelength, and D is an electrode corresponding to one-quarter wavelength. Adjacent small electrode portions in the electrode groups A and B are polarized in the thickness direction in directions opposite to each other.

The surface opposite to the surface shown in FIG. 1 is a solid electrode and is bonded to the elastic body 1. Therefore, if the elastic body 1 is a conductor, the terminal can be taken out from the elastic body 1 as one of the electrodes.

In use, the electrode groups A and B are short-circuited as shown by the hatched lines in FIG. 2, and a voltage is applied between the electrodes and the solid electrodes.

According to the above description, the electrode groups A and B each have a positional phase shift corresponding to a quarter wavelength.

The operation of the ultrasonic motor configured as described above will be described below. When a voltage V represented by V = V _o sin (ωt) (1) V _o : instantaneous value of voltage V ω: angular frequency t: time is applied to the electrode group A of the piezoelectric ceramic 2, the driving body 3 is circular. Bending vibration in the circumferential direction.

FIG. 3 is a perspective view modeling the driving body 3 of the ultrasonic motor shown in FIG. 1. The upper part of FIG. 3 shows a state before a voltage is applied to the piezoelectric ceramic 2, and the lower part of the figure shows a voltage applied to the piezoelectric ceramic 2. The state when a voltage is applied is shown.

In FIG. 4, the contact state between the moving body 6 and the driving body 3 is enlarged and drawn. The electrode group A of the piezoelectric ceramic 2 has V = V _o sin (ωt) (2) and the other electrode group B has V = V _o cos (ωt) (3), which are temporally mutually phase π /. If two different voltages are applied, the two bending vibrations are superimposed and a traveling wave of bending vibrations is generated in the circumferential direction of the driving body 3.

Because, in general, a traveling wave has an amplitude of ξ, ξ = ξ _o cos (ωt−kx) (4) ξ _o : instantaneous value of amplitude ξ k: wave number (2π / λ), λ: wavelength x: It can be expressed as a position (taken in the circumferential direction).

Equation (4) is ξ = ξ _o [cos ωt cos kx ＋ sin ωt sin kx] ……
It can be rewritten as (5). Equation (5) shows that traveling waves are waves cos ωt and sin ωt whose phases are shifted by π / 2 in time, and π / 2 in position.
It is shown that it can be obtained by the sum of the products of cos kx and sin kx which are out of phase with each other.

From the above description, the piezoceramics 2 are positioned π relative to each other
It has electrode groups A and B which are out of phase with each other by / 2, and a progressive wave of bending vibration can be generated in the driving body 3 by applying a voltage with a phase difference of π / 2 to each of them.

FIG. 4 shows that the point A of the driving body 3 has a long axis 2w,
It shows a state in which an elliptic motion of the minor axis 2u is made, and the moving body 6 placed on the driving body 3 contacts at the apex of the ellipse, so that v = ω · u in the direction opposite to the traveling direction of the wave. It shows the movement at the speed of (6).

That is, the moving body 6 is pressed against the driving body 3 with an arbitrary static pressure and comes into contact with the surface of the driving body 3, and the frictional force between the moving body 6 and the driving body 3 causes the moving body 6 to move at a speed u in the direction opposite to the traveling direction of the wave. Driven. When the work done to the outside cannot be ignored with respect to this frictional force, slippage occurs between the moving body 6 and the driving body 3, and the speed becomes smaller than v.

Problems to be Solved by the Invention As described above, in the conventional ultrasonic motor, slippage occurs between the driving body and the moving body when an attempt is made to work outside, and the speed v determined by the speed (6) equation of the moving body is larger than the speed v. Also becomes smaller.

Further, even if the voltage value of the electric signal applied to the two electrode groups is kept constant as in the conventional case, if the temperature or the mechanical load applied to the driver changes, the piezoelectric ceramic electrode groups A and B
Of the piezoelectric ceramics change their respective electric impedances, and the currents flowing into the piezoelectric ceramic electrode groups A and B also change.

The minor axis 2u of the elliptic motion of the mass point on the elastic body surface of the driver is u∝ξ _o ∝I (7), which is proportional to the maximum amplitude ξ _o current I of bending vibration of the elastic body. Therefore, the speed of the moving body changes from the equation (7).

That is, even if the voltage value, the application time, and the phase of the electric signal applied to the two electrodes of the piezoelectric driver are kept constant, if the load of the ultrasonic motor changes or the temperature changes, the speed of the ultrasonic motor changes. Will change.

Then, in order to control the speed of the ultrasonic motor, if the voltage values of the two electric signals applied to the piezoelectric body are simultaneously changed in the same manner as in the conventional case, the impedance seen from the two drive terminals changes differently. At times, there is a problem in that the controllability is deteriorated or the control range is narrowed, and the ultrasonic motor is affected by load fluctuations.

Further, as a method of changing the voltage values of two electric signals in the same manner, there is a method of changing the gain of a power amplifier for generating a driving electric signal of a piezoelectric driver or a method of changing a power supply voltage. There is also a problem that the driving circuit becomes complicated and the cost becomes high.

The present invention corrects the speed fluctuation of the ultrasonic motor, which is the problem of the conventional example described above, regardless of the change of the ambient temperature or the change of the load, and accurately or simply corrects the ultrasonic motor at a constant speed. An object of the present invention is to provide a driving method of an ultrasonic motor that can be driven.

Means for Solving the Problems In order to solve the above-mentioned problems, the first invention of the present application is a piezoelectric device having two electrode groups that are out of phase with each other in position relative to an elastic body. An ultrasonic wave having a piezoelectric driving body configured by bonding bodies, driving electric signal applying means for applying a driving electric signal to an electrode group of the piezoelectric body, and a movable body installed on the elastic body of the driving body. In the motor, there is provided an ultrasonic motor driving method for moving the movable body by exciting a traveling wave of bending vibration in the driving body by the driving electric signal applied to the electrode group by the driving electric signal applying means, and moving the movable body, By the drive electric signal applying means, the phase difference is shifted by π / 2 in the drive electrode group and the signal application time of only one drive electric signal in one cycle is controlled. Two driving electrical signals are applied An ultrasonic motor driving method comprising Rukoto.

Further, a second invention of the present application is a piezoelectric drive body configured by laminating a piezoelectric body having two electrode groups that are mutually phase-shifted by a quarter wavelength relative to an elastic body, and an electrode of the piezoelectric body. Drive electric signal applying means for applying a drive electric signal to the group,
In an ultrasonic motor having a movable body installed on an elastic body of the driving body, a traveling electric wave of bending vibration is excited in the driving body by the driving electric signal applied to the electrode group by the driving electric signal applying means. In the ultrasonic motor driving method of moving the movable body, the phase difference of the drive electric signals applied to the two drive electrode groups can be varied with reference to π / 2 by the drive electric signal applying means. It is an ultrasonic motor driving method characterized by controlling.

Action According to the above means, the amplitude value of the traveling wave of the bending vibration can be changed and the speed of the moving body can be controlled as described below.

Two electrode groups A and B formed on the piezoelectric ceramic forming the driving body are equal in amplitude and have a temporal phase of π / 2.
If an electric signal deviated by a certain amount is applied, the traveling wave of bending vibration is excited in proportion to the value of the current flowing through the piezoelectric ceramic from equation (7), and the lateral elliptic motion proportional to the maximum amplitude value ξ _o of the traveling wave is excited. The component 2u is generated, and the moving body moves at the velocity v shown by the equation (6).

Therefore, the velocity of the moving body changes if the instantaneous value ξ _o of the amplitude of bending vibration excited in the driving body is changed.

Therefore, of the driving electric signals applied to the two electrode groups formed on the piezoelectric ceramic, one of the driving electric signals
According to the first invention of the present application in which the application time in the cycle is changed, the voltage value of the drive electric signal can be effectively changed, and thus the instantaneous value ξ _o of the bending vibration amplitude is changed to change the speed of the moving body. Can be controlled.

Hereinafter, this operation will be described in detail.

What is drawn on the signal waveform shown in FIG. 5 is a waveform when a voltage is applied during one cycle, and the lower part has a shorter application time than the upper waveform. The drive frequency component of the lower waveform becomes smaller than the same component of the upper waveform, which means that the voltage value is effectively changed.

Now, set the impedance of the piezoelectric ceramic electrode group to Z _A and Z _B.
And the voltages applied to them are V _A and V _B , then ξ = K ・ (V _A / Z _A ) ・ cos kx + K ・ (V _B / Z _B ) ・ sin ωt ・ sin _{kx = Kξ A cos ωt cos kx} + Kξ B sin ωt sin kx = Kξ 0 cos (ωt-kx) ...... (8) K: proportional constant _{Kξ A = K A V A /} Z A, Kξ B = K B V B / Z _B ξ _o = ξ _A = ξ _B.

Is. From the equations (6) and (7), the velocity v of the moving body is v∝ω · ξ _o (9).

Now, if the applied voltage V _B of one of the electrode groups is effectively reduced by ΔV by shortening the energization time in one cycle by Δt, from equation (8), ξ = Kξ _o cos ωt · cos kx + K (Ξ _o −Δξ 0) si
nωt · sin kx = K (ξ _o −Δξ _o ) cos (ωt−kx) + KΔξ _o
cos ωt · cos kx (10) Δξ _o is the amplitude decreased by ΔV and becomes ΔΔ _o = KΔV / Z _B , and the speed of the moving body is reduced by the amount proportional to ω · Δξ _o from the equation (9). The second term of the equation (10) is a standing wave standing in the driving body and does not contribute to the velocity of the moving body.

However, if the standing wave component becomes too large, the operation of the ultrasonic motor becomes unstable, so when the precise control is required, the impedance ZA,
The energizing time in one cycle is controlled according to each change of ZB, and the applied voltage is effectively changed to drive.

Next, in the second invention of the present application in which the phase difference between the two electric signals applied to the two electrode groups A and B is variably controlled with reference to π / 2, the instantaneous vibration amplitude of the bending vibration is as follows. Value ξ
_It is possible to change _o, and thus control the speed of the moving body.

Now, the phase of the electric signal applied to the electrode group B is set to the reference π / 2.
By shifting by −φ, ξ = ξ _o cos ωt · cos kx + ξ _o sin (ωt−φ) ·
sin kx = ξ _o [cos φ · cos (ωt−kx) + cos ωt {cos kx−cos (kx−φ)}] (12) In equation (12), the instantaneous value of the amplitude of the traveling wave is ξ _o cosφ
Means that the velocity v of the moving body is cosφ times (Oc
os φ1).

As described above, according to the first and second aspects of the present invention, it is possible to realize the ultrasonic motor driving method with high control accuracy or simple control.

Example Hereinafter, an example of the present invention will be described with reference to the drawings.

Example 1 The first invention of the present application will be described based on an example thereof.

In this embodiment, one of the two electric signals applied to the two electrode groups when the electric impedance of the piezoelectric ceramic changes due to a change in external load or a change in temperature and the speed of the moving body changes, The speed of the moving body is controlled by changing the voltage application time during the cycle.

FIG. 6 is a block diagram of a control circuit embodying the driving method of this embodiment. The ultrasonic motor used in the figure and in the following shows only the piezoelectric ceramic constituting the driving body so that the electric role can be clearly understood. Further, the back surface of the piezoelectric ceramic is adhered to an elastic body such as metal so that the entire surface is at ground potential.

FIG. 7 is a timing chart for explaining the function of the block diagram of FIG.

In FIG. 6, the traveling wave of bending vibration excited by the signals applied to the electrode groups A and B is detected by the electrode C through the piezoelectric effect, and the power is passed through the bandpass filter 8 that passes only the driving frequency component. It returns to the amplifier 7. This loop causes the driver to self-oscillate near its resonance frequency.

This oscillating signal passes through the 90 ° phase shifter 9 and signal a in FIG.
Becomes The signal a passes through the absolute value circuit 11 to become the signal b, and when a voltage level at the control terminal (-terminal) of the comparison circuit 12 is applied so that the standing wave component of the output waveform of the electrode C becomes small. The output of the comparison circuit 12 becomes the signal c, and if the switch circuit 13 is controlled by the signal c, the signal d is obtained.

That is, the signal applied to the electrode group B becomes the signal d, which is applied to the electrode group B of the piezoelectric body by shortening the energization time (voltage application time) by 2t ₁ per cycle as shown in FIG. The drive frequency component of the electric signal that is effective for driving the moving body is reduced.

With this configuration, the gain of the power amplifier 10 may be constant, and the speed of the moving body of the ultrasonic motor can be controlled with a simple circuit configuration.

(Embodiment 2) The second invention of the present application will be explained based on FIG. 8 showing an embodiment thereof.

Although the embodiment shown in FIG. 6 shows the case of the self-excited oscillation method, the same holds true for the separately excited oscillation method.

FIG. 8 shows a case of the separately excited oscillation system, which has an oscillation circuit 14. The oscillator circuit 14 is adjusted to oscillate at the resonance frequency of the driver. Reference numeral 15 denotes a variable phase shifter, which varies the phase of the signal applied to the electrode group B by applying a voltage to the control terminal of the variable phase shifter 15 with π / 2 as a reference.

Thereby, the speed of the moving body can be easily controlled.
It goes without saying that the output of the electrode C is also controlled in this embodiment so that the speed of the moving body becomes stable.

EFFECTS OF THE INVENTION As described above, in the drive electrode group, the phase difference is deviated by π / 2 and only one drive electric signal is controlled for the signal application time in one cycle. By applying a drive electric signal or variably controlling the phase difference between the drive electric signals applied to the two drive electrode groups with reference to π / 2, the speed control accuracy is high or the structure of the speed control means is simple. The method of driving the ultrasonic motor device can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view of a conventional ultrasonic motor. FIG. 2 is a plan view showing the shape and electrode structure of a piezoelectric ceramic used in the conventional motor. FIG. 3 is a driving body of the ultrasonic motor. Fig. 4 is a model diagram showing a vibration state. Fig. 4 is an explanatory diagram of the operating principle of the ultrasonic motor. Fig. 5 is a waveform diagram showing an example of controlling the application time of an electric signal applied to the electrode group. 1 is a block diagram of a control system in an embodiment of the invention of FIG. 1. FIG. 7 is a signal waveform diagram in a main block of the control system of the embodiment. FIG. 8 is a diagram of a control system in an embodiment of the second invention of the present application. It is a block diagram. 7, 10 ... Power amplifier, 8 ... Bandpass filter, 9
...... 90 ° phase shifter, 11 …… Absolute value circuit, 12 …… Comparison circuit,
13 …… Switch circuit, 14 …… Oscillation circuit, 15 …… Variable phase shifter.

Front page continuation (72) Inventor Akira Tokushima 1006 Kadoma, Domonshin-shi Matsushita Electric Industrial Co., Ltd. (72) Inventor Hiroshi Ouchi 1006 Kadoma, Domonshin-shi Matsushita Electric Industrial Co., Ltd. (56) References JP 60-176470 (JP, A) JP 59-216482 (JP, A)

Claims (2)

[Claims] 1. A piezoelectric driving body configured by laminating a piezoelectric body having two electrode groups that are mutually phase-shifted from each other by a quarter wavelength relative to an elastic body, and driving electric power to the electrode group of the piezoelectric body. In an ultrasonic motor having drive electric signal applying means for applying a signal and a movable body installed on the elastic body of the drive body, the drive electric signal applied to the electrode group by the drive electric signal applying means An ultrasonic motor driving method for moving the movable body by exciting a traveling wave of bending vibration in the driving body, wherein the driving electric signal applying unit causes the driving electrode group to have a phase difference of π / 2. A method for driving an ultrasonic motor, wherein two individually controlled drive electrical signals are applied, in which only one drive electrical signal is controlled and a signal application time in one cycle is controlled. 2. A piezoelectric driving body configured by laminating a piezoelectric body having two electrode groups that are mutually phase-shifted from each other by a quarter wavelength relative to an elastic body, and driving electric power to the electrode group of the piezoelectric body. In an ultrasonic motor having drive electric signal applying means for applying a signal and a movable body installed on the elastic body of the drive body, the drive electric signal applied to the electrode group by the drive electric signal applying means An ultrasonic motor driving method in which a traveling wave of bending vibration is excited in the driving body to move the movable body, wherein the driving electric signal applying unit applies a driving electric signal to the two driving electrode groups. An ultrasonic motor driving method characterized in that the phase difference is variably controlled with reference to π / 2.