JP2002359983A - Ultrasonic motor control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved ultrasonic motor control circuit which controls driving signal frequency, thus stabilizing ultrasonic motor operation. SOLUTION: This ultrasonic motor control circuit includes drives 130/140 which drive an ultrasonic motor 100 corresponding to a drive signal with a predetermined frequency, a detector 160 which detects the driving current flowing through the driving ultrasonic motor 100 and output current data I, and controllers 171-174 which output frequency data F based on the current data I and control the drive signal frequency to stabilize the driving current. These controllers determine a deviation ΔI between the detected current data I and predetermined reference current data I0. Next, they determine a difference ΔF corresponding to ΔI, and further, add the difference Δ F to the frequency data F to update the frequency data F. The renewed frequency data F controls the frequency of driving current, thus stabilizing the driving current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ultrasonic motor control circuit for applying a drive signal to an ultrasonic motor to control the operation thereof. More specifically, the present invention relates to a stabilization technique for controlling a frequency of a drive signal to keep a drive current constant.

[0002]

2. Description of the Related Art A conventional ultrasonic motor control circuit basically comprises a driving section, a detecting section and a control section. The drive unit drives the ultrasonic motor according to a drive signal having a predetermined frequency.
The detection unit detects a drive current flowing through the ultrasonic motor during driving and outputs current value data I. The control unit outputs frequency data F to the drive unit based on the current value data I, and controls the frequency of the drive signal to make the drive current constant. An ultrasonic motor control circuit based on such feedback control is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-147733.

[0003]

FIG. 12 is a graph showing drive frequency / drive current characteristics (F / I characteristics) of an ultrasonic motor. The horizontal axis represents the frequency F of the drive signal applied to the stator composed of the piezoelectric vibrator, and the vertical axis represents the drive current I flowing through the stator. As is clear from the figure,
The driving current I is maximum (Ima) at the resonance frequency fp of the stator.
x). When the frequency F of the drive signal is near fp,
A sufficient drive current I flows through the stator. In response,
Torque is generated in the rotor. Generally, the output torque increases as the current I increases. The frequency F of the drive signal is fp
When the current I decreases, little torque is generated.

Therefore, in order to stably rotate the ultrasonic motor, for example, the operating point D (F) on the graph shown in FIG.
It is preferable to drive the stator at (0, I0). By controlling F, the ultrasonic motor is driven so that I becomes I0.

When I <I0, it is necessary to set the gradient ΔF / ΔI of the F / I characteristic to a relatively large value and perform feedback control, as is apparent from the graph of FIG. On the other hand, when I ≧ I0, ΔF / ΔI needs to be set relatively small for control. However, in the conventional ultrasonic motor control circuit disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 7-143773, ΔF / ΔI is a constant value determined by a circuit constant in both cases of I <I0 and I ≧ I0. For this reason, when I <I0, there is a problem that the correction of F is insufficient and it takes time to stabilize. Conversely, I ≧
In the case of I0, there is a problem that the correction of F becomes excessive and becomes an unstable factor.

The conventional ultrasonic motor control circuit described above operates relatively stably when the deviation ΔI of I with respect to I0 is sufficiently small. However, as shown in the graph of FIG. 12, the ultrasonic motor generates heat when driven, and the F / I characteristics are greatly shifted. Further, it is difficult to detect in advance the temperature inside the stator when starting the ultrasonic motor, and it is difficult to accurately predict how much the F / I characteristic has shifted from the representative characteristic of the ultrasonic motor. It is. Therefore, ΔI increases when the ultrasonic motor is started. Therefore, in the conventional ultrasonic motor control circuit, it takes time from the start to the convergence to the stable operation. In the worst case, the starting frequency is F / I
There is also a possibility that the operation cannot be started out of the operation range of the characteristic.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, the present invention provides an improved ultrasonic motor control circuit for controlling the frequency of a drive signal to stabilize the operation of an ultrasonic motor. The purpose is to provide. The following measures have been taken to achieve this objective. That is, a drive unit that drives the ultrasonic motor according to a drive signal of a predetermined frequency,
A detecting unit that detects a driving current flowing through the ultrasonic motor during driving and outputs current value data I, and outputs frequency data F to the driving unit based on the current value data I to change the frequency of the driving signal. An ultrasonic motor control circuit comprising a control unit that controls the drive current to be constant, wherein the control unit includes:
A deviation ΔI of the detected current value data I with respect to a preset reference current value data I0 is obtained, and then ΔI
And updates the frequency data F by adding the difference ΔF to the frequency data F. The frequency of the driving current is controlled by the updated frequency data F to make the driving current constant. It is characterized by the following. Preferably, the control unit sequentially updates the frequency data F for each ΔT using ΔF obtained for each fixed period ΔT. The control unit converts the deviation ΔI into a difference ΔF using a conversion table stored in advance. In this case, the control unit converts ΔI to ΔF using the conversion table created based on typical driving frequency / driving current characteristics of the ultrasonic motor measured in advance. For example, the conversion table indicates that the driving frequency / driving current characteristic is I = g (F)
Where ΔF = −g ⁻¹ (ΔI + I0) + F
0 (however, F0 = g ⁻¹ (I0)). In some cases, the control unit may add a coefficient α (0 <α ≦ 1) to ΔF obtained from the conversion table.
, And α · ΔF is added to F to update F. Preferably, the driving unit includes a direct digital synthesizer that generates a basic waveform of the driving signal based on the frequency data F.

According to the present invention, the deviation ΔI of the detected current value data I with respect to the reference current value data I0 is obtained, and then the deviation ΔI
Is determined based on a function showing a typical F / I characteristic. The difference ΔF is sequentially added to the frequency data F to update the frequency data F. The frequency of the drive current is controlled by the updated frequency data F to maintain the drive current constant. Since the gradient ΔF / ΔI of the F / I characteristic is determined based on a typical F / I characteristic instead of being obtained by a simple linear approximation as in the related art, the current parameter I based on the more stable and faithful frequency parameter F is obtained. Can be controlled. In other words, the response of the control circuit to the fluctuation of the driving current is improved, and the driving current can be quickly converged to the target current.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic block diagram showing an embodiment of an ultrasonic motor control circuit according to the present invention. This ultrasonic motor control circuit basically includes a drive unit, a detection unit, and a control unit. The drive unit includes a digital frequency synthesis block 110 and drivers 130/140, and drives the ultrasonic motor 100 according to a drive signal of a predetermined frequency. The detector is an analog / digital converter (A /
D) 160, which detects a drive current flowing through the ultrasonic motor 100 during driving and outputs current value data I. The control unit includes a deviation calculation block (I-I0) 171, ΔI / ΔF
It includes a conversion block 172, an adder 173, and a latch 174, outputs frequency data F to the drive unit based on the current value data I, and controls the frequency of the drive signal to keep the drive current constant.

As a characteristic feature, the deviation calculation block 171 on the control unit side includes a deviation ΔI = I of the detected current value data I with respect to a preset reference current value data I0.
-Find I0. ΔI / ΔF conversion block 172 calculates Δ
A difference ΔF corresponding to I is obtained. The adder 173 updates the frequency data F by adding the difference ΔF to the frequency data F. The latch 174 operates according to the control clock, and outputs the frequency data F sequentially updated to the digital frequency synthesis block 110 on the driving unit side. The digital frequency synthesis block 110 sets the frequency of the drive current based on the frequency data F, and applies a drive signal to the ultrasonic motor 110 via the drivers 130/140. By such feedback control, it is possible to converge I to I0 using F as a parameter. Note that the control unit has a fixed period Δ
The frequency data F is sequentially updated for each ΔT using the ΔF obtained for each T.

Preferably, ΔI / ΔF conversion block 17
2 is a deviation Δ using a conversion table stored in advance.
I is converted to a deviation ΔF. At this time, a typical drive frequency / drive current characteristic (F
/ I characteristic is converted into ΔF using a conversion table created on the basis of (/ I characteristic). Specifically, when the conversion table expresses the F / I characteristic by a function of I = g (F),
The following formula ΔF = −g ⁻¹ (ΔI + I0) + F0 (where F0 = g ⁻¹⁾
(I0)). In some cases, the control unit may set the coefficient α to the ΔF obtained from the conversion table.
After multiplying by (0 <α ≦ 1), α · ΔF is added to F to update F. Note that the digital frequency synthesis block 110 included in the drive unit is a direct digital synthesizer (DDS) that generates a basic waveform of a drive signal based on the frequency data F.

In summary, the digital frequency synthesis block 110 generates a basic drive waveform having a frequency corresponding to the given frequency data F. Driver 130/14
0 generates a drive signal for the ultrasonic motor 100 based on the basic drive waveform. When this drive signal is applied to the ultrasonic motor 100, the stator resonates and a drive current flows. A / D1
60 detects this and performs A / D conversion to obtain current value data I. As described above, the deviation calculation block 171 calculates the deviation ΔI from the reference current value data I0. The ΔI / ΔF conversion block 172 obtains ΔF from ΔI using the above-described conversion table. By applying a predetermined control clock to the latch 174, F is updated by ΔF. That is, Fn + 1 = Fn + ΔF.

The operation principle of the ultrasonic motor control circuit shown in FIG. 1 will be described with reference to FIG. The F / I characteristic of the ultrasonic motor to be controlled is exactly the representative characteristic I = g
In the case represented by (F), when this ultrasonic motor is driven at the drive frequency F0, the drive current I = I0, and the drive current becomes equal to the target reference current. F for some reason
/ I characteristic shifts from I = g (F) to I ′ = g ′
When the state changes to (F), at the drive frequency F0, the drive current becomes I = I1, which deviates from the reference current I0. In order to make the drive current I the reference current I0, it is necessary to set F = F2 = F0 + ΔF as is clear from the graph of FIG.
In general, g and g 'can be regarded as a parallel shift, so that the following equation (1) holds. ΔF = F2−F0 = F0−F1 (1) Here, since I1 = I0 + ΔI = g (F1), the following equation (2) holds. F1 = g ⁻¹ (I0 + ΔI) (2) From the above equations (1) and (2), the following equation (3) is obtained. ΔF = −g ⁻¹ (ΔI + I0) + F0 (3) Accordingly, ΔF is calculated from ΔI based on the equation (3), and F
By adding to 0, the drive current I can be controlled toward the reference current I0.

By increasing the control clock applied to the latch,
Shortening the update cycle of F may cause excessive correction of F due to the response delay of the stator. In order to avoid this, a stable operation is possible by multiplying ΔF obtained by Expression (3) by a coefficient α to suppress the correction amount. This is represented by the following equation (4). ΔF ′ = α · ΔF = α · (−g ⁻¹ (ΔI + I0) + F0) (4) where 0 ≧ α ≧ 1.

FIG. 3 is a schematic block diagram showing another embodiment of the ultrasonic motor control circuit according to the present invention. To facilitate understanding, parts corresponding to those of the previous embodiment shown in FIG. 1 are denoted by corresponding reference numerals. In the present embodiment, a CPU 170 is used as a control unit. The present ultrasonic motor control circuit applies a drive signal to the ultrasonic motor 100 to control its operation.
Oscillator 120, pre-driver 130, power driver 1
40, a current monitor 150, an analog / digital converter (A / D converter) 160, and a CPU 170. The DDS 110 operates according to the clock signal fc, and outputs a basic waveform fd0 having a frequency that changes according to control data F given by a numerical value. The basic configuration of the DDS is disclosed in, for example, JP-A-2000-151284. The oscillator 120 has the DD
The clock signal fc is supplied to S110. The pre-driver 130 outputs the basic waveform fd0 output from the DDS 110.
To generate a multi-phase drive signal fd. The power driver 140 supplies a drive current id to the ultrasonic motor 100 according to the drive signal fd output from the pre-driver 130, and drives the ultrasonic motor 100. The current monitor 150 sequentially detects the drive current id flowing through the ultrasonic motor 100, and outputs the result as a detection voltage Vid. A / D converter 160 outputs Vid representing the amount of the detected drive current,
It is converted into digital current value data I. CPU 170
Calculates the control data F based on the digital current value data I output from the A / D converter 160,
Input to DS110.

The CPU 170 performs feedback control based on a predetermined program, and outputs frequency control data F to the DDS 110 according to the current value data I.
The CPU 170 adjusts the control data F by such feedback control so that the drive current flowing through the ultrasonic motor 100 becomes a constant current value I0. By making the drive current id flowing through the ultrasonic motor 100 constant, the output torque and the number of revolutions of the ultrasonic motor 100 become constant, so that the ultrasonic motor 100 can be stabilized in a steady operation.

Referring to FIG. 4, CPU 17 shown in FIG.
The control program executed by 0 will be specifically described. After starting the control, first, in step S1, F = F0 and an initial value F0 is set in the DDS. Proceeding to step S2, a drive waveform is created with the initial value F0 and applied to the motor to start. In step S3, a timer is started and a predetermined period ΔT is measured. After confirming the completion of the time measurement of ΔT in step S4, the process proceeds to step S5 to acquire current value data I from the driver side of the ultrasonic motor. In step S6, a deviation ΔI = I−I0 from the reference current value I0 is determined.

In step S7, it is determined whether or not ΔI ≧ 0. If the result of the determination is YES, the process proceeds to step S8 to perform table conversion and obtain ΔF from ΔI. In step S9, F is updated by ΔF and given to the DDS. On the other hand, if the determination in step S7 is NO, step S7
Then, an absolute value of ΔI is obtained. Then step S
In step 11, ΔF is obtained from ΔI by table conversion. Thereafter, the process proceeds to step S12, where ΔF is subtracted from the current F to obtain F
Is updated and given to the DDS. Thereafter, the process proceeds to step S13 to check whether the stop signal has been turned ON. The control loop described above is continued until the stop signal is turned on. If the stop signal is turned on, the process proceeds to step S14 to stop the motor.

FIG. 5 is a schematic perspective view showing a specific configuration example of the ultrasonic motor (piezo motor) 100 shown in FIG. As shown in the figure, a piezo motor 100 is an electrostrictive revolving motor composed of a 3D revolving torque resonator disclosed in Japanese Patent Application Laid-Open No. 10-272420, and is pressed against a cylindrical stator 1 at a rear end thereof. Annular rotor 2
It is composed of On the outer peripheral surface of the cylindrical stator 1,
Electrodes 11, 12, 13, and 14 are formed. Although not shown, electrodes are also formed on the inner peripheral surface of the cylinder. The electrode formed on the outer peripheral surface of the cylinder is divided into four parts, and AC driving currents A, B, AX, and BX having different phases are supplied. The phases of the A-phase current and the B-phase current are different from each other by 90 degrees. The phase of the A-phase current and the phase of the AX-phase current are different by 180 degrees. In other words, the A phase and the AX phase have opposite polarities. Similarly, the B phase and the BX phase have opposite polarities.

FIG. 6 is a schematic cross-sectional view of the stator shown in FIG. As shown in the figure, an electrode 10 for applying a reference potential is formed on the entire inner peripheral surface of a cylindrical stator 1 made of a piezoelectric element such as ceramic. Drive electrodes 11 to 14 divided into four are formed on the outer peripheral surface of the cylinder. These four divided electrodes 11 to 14 are supplied with four-phase AC drive currents A, B, AX, and BX whose phases are shifted by 90 degrees from each other.

The operation of the piezo motor shown in FIGS. 5 and 6 will be described with reference to FIG. The present invention is shown in FIGS.
It is needless to say that the present invention is not limited to the piezo motor (ultrasonic motor) shown in FIG. In the case of a piezo motor, since the ultrasonic vibration serving as a power source has a constant resonance frequency, the current has a substantially constant value. The resonator has a high Q and the rise of the vibration amplitude is considered to be within one cycle, and can be regarded as a non-inertial mechanism. The current changes only within the range affected by the load inertia. Various configurations of the piezo motor having such characteristics have been developed, and the electrostrictive revolution type is particularly promising. The electrostrictive revolution type uses a resonator that can directly excite a uniform revolution torque over the entire peripheral surface, instead of converting vibration into torque as in the related art. There are two types of conventional ultrasonic transducers, a standing wave type and a traveling wave type, but both can excite only in a symmetric mode with a fixed center of gravity. On the contrary,
When the cylinder is excited in a mode in which the expansion and contraction of the left and right are reversed, the center of gravity vibrates away from the center. With this asymmetric excitation,
A cylindrical resonance mode that could not be observed with the conventional symmetric excitation is obtained. Therefore, when the electrode of the stator cylinder is divided into, for example, four and excited by rotating electric fields having phases different by 90 degrees,
As shown in FIG. 7, resonance in a mode in which the center of gravity rotates around the center is observed. At this time, the outer periphery of the cylinder keeps its original shape and is eccentric like a hula hoop, so that the vibrator orbits. In the electrostrictive revolving rotor type motor having such a configuration, the direct rotation mode is excited and can be used as a 3D revolving torque generator in which the axial mode is coupled in addition to the diameter and circumferential direction of the cylindrical revolving element. This revolution torque is directly taken out as the rotation of the rotor.

FIG. 8 is a schematic block diagram showing a specific configuration example of the DDS 110 shown in FIG. DDS1
Reference numeral 10 includes an adder and a latch. The adder is C
16-bit control data F given as a numerical value from PU
Are sequentially added, and the result is sent to the latch. The latch operates according to the clock signal fc, and feeds back the latched addition result to the adder side. The latch sets the MSB to f when overflow (carry) occurs due to addition by the adder.
Output as d0. Thus, the DDS110 is a CPU
The frequency f represented by the following equation according to the frequency setting data F given by
Generate a basic waveform of d0. fd0 = F × fc / 2 ^N (N: number of data bits)

The ordinary DDS converts the latched output data into waveform data such as a sine wave using a lookup table LUT, and then performs digital / analog conversion to obtain an output waveform. However, the ultrasonic motor can be basically driven by a rectangular wave drive signal. Therefore, the DD of this example
In S, a square wave output may be used, so that the most significant bit MSB of the latched data can be used as an output waveform as it is. Therefore, the LUT and the digital / analog converter are omitted from the present DDS.

FIG. 9 shows the pre-driver 130 shown in FIG.
FIG. 7 is a waveform diagram showing a multi-phase drive signal fd output from the control circuit. As described above, based on the basic waveform fd0 output from the DDS, the pre-driver performs multi-phase drive signals fd (A), fd (B), fd (AX),
Generate fd (BX). The frequency of each drive signal fd is equal to the basic waveform fd0 or a frequency obtained by dividing the frequency. In the illustrated example, each drive signal fd has a waveform obtained by dividing the basic waveform fd0 by half. As shown, A
The B phase is shifted by 90 degrees, the AX phase is shifted by 180 degrees, and the BX phase is shifted by 270 degrees with respect to the phases. Like this 90
A rotating electric field is formed by applying an AC drive signal having a phase that differs by degrees to the stator, and the stator directly excites the rotation mode in response to this. As described above, the pre-driver generates four types of drive waveforms having different phases by 90 degrees. The frequency fd of the driving waveform is 1 of the fundamental frequency fd0.
/ 2. These waveforms can be easily created from the basic waveform fd0 by a logic IC such as a counter and an inverter.

FIG. 10 shows a power driver 140 and a current monitor 1 included in the ultrasonic motor control circuit shown in FIG.
FIG. 4 is a circuit diagram showing a specific example of the configuration of the circuit 50; As shown, the power driver connected to the ultrasonic motor 100 includes a pair of H-bridges 140A and 140B. Here, a pair of drive signals fd (A) and fd (A
X) is an ultrasonic motor 100 via an H-bridge 140A.
Are applied to a pair of electrodes facing each other. Similarly, another pair of drive signals fd (B) and fd (BX) are applied to another pair of stator electrodes facing each other via another H bridge 140B. H bridge 140A, 140B
Are power amplifiers for supplying sufficient output currents A, B, AX and BX to the stator electrodes in response to respective input signals. As described above, the power driver is constituted by a pair of H bridges. As an element constituting the bridge, MO must be switched at high speed.
An SFET is used.

On the other hand, the current monitor 150
P, a smoothing capacitor C, and a plurality of resistors R1 to R3. The current monitor 150 basically has a low-pass filter configuration, and outputs a voltage value Vid according to the drive current flowing through the H bridges 140A and 140B via the resistor R1. The detection of the drive current is performed by smoothing the voltage generated in the resistor R1 having a low resistance value (for example, 1Ω) with the capacitor C and amplifying the voltage with the amplifier OP. As described above, this output voltage Vid is sent to the A / D converter side.

Finally, FIG. 11 shows an application example of the ultrasonic motor (piezo motor) shown in FIGS.
1 shows a camera lens driving device using a piezo motor as a power source. It is needless to say that the application example of the piezo motor according to the present invention is not limited to the camera lens driving device. This camera lens driving device basically includes a piezo motor including a stator 1 and a rotor 2, a lens barrel 3, and a transmission member connecting these. The stator 1 is made of a piezoelectric element and receives an AC voltage to excite ultrasonic vibration and generate a revolving torque. The rotor 2 is pressed against the stator 1 and rotates by its revolution torque. The lens barrel 3 mounts a camera lens (not shown) and is incorporated so as to be linearly displaceable in the optical axis Z direction of the lens. The stator 1, the rotor 2, and the lens barrel 3 are incorporated in a barrel frame 6. The rear end of the lens barrel 6 in the optical axis Z direction is shielded by a base 7. A transmission member that connects the rotor 2 of the piezo motor and the lens barrel 3 converts the rotation of the rotor 2 into a linear displacement of the lens barrel 3 and transmits it.

The stator 1 is composed of a cylindrical piezoelectric element having a cylindrical axis parallel to the optical axis Z. On the other hand, the lens barrel 3 is disposed inside the cylindrical stator 1, and can move forward and backward from the front end of the barrel frame 6 along the optical axis Z. By arranging the lens barrel 3 inside the cylindrical stator 1 in this manner, the size of the camera lens driving device can be reduced.

In this embodiment, the rotor 2 and the lens barrel 3
Includes a helicoid tube 4 integrated with the lens barrel 3. However, the lens barrel 3 and the helicoid barrel 4 need not necessarily be formed integrally, and the lens barrel 3 may be built into the helicoid barrel 4 later in some cases. The helicoid cylinder 4 is basically cylindrical so as to house the lens barrel 3 inside, and a screw 41 is cut on the outer peripheral surface thereof. At the front end of the helicoid tube 4, a stopper 42 is attached to prevent rotation of the helicoid tube 4 itself, and is engaged with the lens barrel frame 6. As a result, the helicoid cylinder 4 performs a linear motion along the optical axis Z direction. The transmission member further includes a helicoid gear 5 formed integrally with the rotor 2 and screwed to the helicoid cylinder 4. In the present embodiment, the rotor 2 made of an annular metal and the helicoid gear 5 made of a resin such as polycarbonate are integrally formed by, for example, outsert. The helicoid gear 5 also rotates with the rotation of the rotor 2. The helicoid gear 5 is provided with a screw 51 on its inner peripheral surface. The screw 41 formed on the outer peripheral surface of the helicoid cylinder 4 and the screw 51 formed on the inner peripheral surface of the helicoid gear 5 mesh with each other. When the helicoid gear 5 rotates with the rotation of the rotor 2, the helicoid cylinder 4
Is linearly displaced along the optical axis Z. The rotor 2 is attached to the rear end of the cylindrical stator 1. A rotation assisting means 8 is arranged between the base 7 and the rotor 2, and the rotor 2 is slidably pressed against the rear end of the stator 1 to thereby rotate the stator 1.
Is taken out as the rotation of the rotor 2. The rotation assisting means 8 includes a contact plate 82 provided with a convex curved projection 82 </ b> R that comes into contact with the rotor 2, and a spring member 83 that presses the contact plate 82 toward the rotor 2.

[0030]

As described above, according to the present invention, the ultrasonic motor control circuit obtains the deviation ΔI of the detected current value data I from the preset reference current value data I0, and then calculates ΔI The difference ΔF corresponding to
/ I characteristic, and further adds and updates the difference ΔF to the frequency data F to control the frequency of the drive current based on the updated frequency data F. As a result, the responsiveness of the ultrasonic motor control circuit to the fluctuation of the driving current is improved, and even if the driving current deviates from the reference current due to a change in the temperature of the stator or other factors, it is possible to quickly return. Further, even when the drive current set at the time of startup deviates from the reference current, it is possible to quickly converge on the reference current. As a result, a stable and high-speed ultrasonic motor can be started.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an ultrasonic motor control circuit according to the present invention.

FIG. 2 is a waveform chart for explaining the operation of the ultrasonic motor control circuit shown in FIG. 1;

FIG. 3 is a block diagram showing another embodiment of the ultrasonic motor control circuit according to the present invention.

FIG. 4 is a flowchart for explaining the operation of the ultrasonic motor control circuit shown in FIG. 3;

FIG. 5 is a schematic perspective view of an ultrasonic motor.

FIG. 6 is a cross-sectional view of the ultrasonic motor.

FIG. 7 is an operation explanatory view of the ultrasonic motor.

8 is a block diagram showing a specific configuration example of a DDS included in the ultrasonic motor control circuit shown in FIG.

FIG. 9 is a waveform chart for explaining the operation of a pre-driver included in the ultrasonic motor control circuit shown in FIG. 3;

10 is a circuit diagram showing a specific configuration example of a power driver and a current monitor included in the ultrasonic motor control circuit shown in FIG.

11 is a sectional view showing an application example of the ultrasonic motor control circuit shown in FIG. 1 or FIG.

FIG. 12 is a graph showing operating characteristics of the ultrasonic motor.

[Explanation of symbols]

100: ultrasonic motor, 110: digital frequency synthesis block, 130/140: driver, 16
0: A / D converter, 170: CPU, 17
1: difference operation block, 172: ΔI / ΔF conversion block, 173: adder, 174: latch

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Miyazaki 2-18-10 Shimura, Itabashi-ku, Tokyo Inside Nidec Copal Corporation (72) Inventor Kiyoshi Toma 2- 18-10 Shimura, Itabashi-ku, Tokyo Nidec Copal Corporation F-term (reference) 5H680 AA00 AA09 BB01 BB11 BB12 BB15 CC02 DD01 DD15 DD23 DD67 DD88 EE21 FF22 FF25 FF30 FF33

Claims (7)

[Claims] A driving unit that drives an ultrasonic motor according to a driving signal of a predetermined frequency; a detecting unit that detects a driving current flowing through the ultrasonic motor during driving and outputs current value data I; An ultrasonic motor control circuit comprising: a control unit that outputs frequency data F to the drive unit based on the current value data I and controls the frequency of the drive signal to make the drive current constant. A deviation ΔI of the detected current value data I with respect to a preset reference current value data I0, a difference ΔF corresponding to ΔI is obtained, and a difference ΔF is added to the frequency data F to obtain the frequency An ultrasonic motor control circuit, wherein data F is updated, and the frequency of the drive current is controlled by the updated frequency data F to keep the drive current constant. 2. The ultrasonic motor control circuit according to claim 1, wherein the control unit sequentially updates the frequency data F every ΔT using ΔF obtained every predetermined period ΔT. 3. The ultrasonic motor control circuit according to claim 1, wherein the control unit converts the deviation ΔI into a difference ΔF using a conversion table stored in advance. 4. The control unit converts ΔI to ΔF using the conversion table created based on typical driving frequency / driving current characteristics of an ultrasonic motor measured in advance. Item 7. An ultrasonic motor control circuit according to item 3. 5. The conversion table, when the drive frequency / drive current characteristic is represented by I = g (F), the following equation: ΔF = −g ⁻¹ (ΔI + I0) + F0 (where F0 = g ⁻¹⁾
The ultrasonic motor control circuit according to claim 4, wherein the ultrasonic motor control circuit is created based on (I0)). 6. The control unit multiplies ΔF obtained from the conversion table by a coefficient α (0 <α ≦ 1),
The ultrasonic motor control circuit according to claim 5, wherein .DELTA.F is added to F to update F. 7. The ultrasonic motor control circuit according to claim 1, wherein the drive unit includes a direct digital synthesizer that generates a basic waveform of the drive signal based on the frequency data F. .