JPH01209967A - Controller for ultrasonic motor - Google Patents

Abstract

PURPOSE:To stably start an ultrasonic motor at a low voltage by operating frequency sweeping means at the time of starting the motor, stopping the sweeping after a predetermined speed detection signal is outputted, and operating speed control means. CONSTITUTION:A controller for an ultrasonic motor 6 is composed of a variable oscillator control circuit 1 for controlling the oscillation frequency of a variable oscillator 2 at the time of starting, etc., and a speed control loop is formed of a speed sensor 11, a F/V conversion circuit 12, a compensation filter 13, power amplifier circuits 4-5, and the motor 6. Further, a phase control loop is formed of a voltage detector 7, a current detection circuit 8, a phase comparator 9, a compensation filter 10, a variable oscillator 2, a 90 deg. phase shifter 3, etc. The control circuit 1 outputs a control signal (a) varying to a low voltage from a high voltage as a time goes during a period until the fact that a moving body 25 arrives at a predetermined speed is detected by a speed detector 14 and sweeps from a high frequency to a low frequency at the time of starting the motor. Then, when it arrives at a predetermined speed, the speed control loop is closed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a control device for an ultrasonic motor that generates driving force using a piezoelectric body.

BACKGROUND OF THE INVENTION In recent years, a driving voltage of several 101 Hz is applied to a vibrating body using a piezoelectric material such as piezoelectric ceramic to excite elastic vibration, causing the vibrating body to undergo stretching vibration or thickness vibration, and this vibration is used as a driving force to drive a rotor. By pressing and driving a driven body (such as a moving body), the moving body can be rotated or linearly moved.
Ultrasonic motors are attracting attention.

Hereinafter, the conventional technology of an ultrasonic motor will be explained with reference to the drawings.

FIG. 5 is a perspective view of a toroidal ultrasonic motor, in which a toroidal piezoelectric body 21 is bonded to a toroidal elastic body 20 to create a vibrating body 2.
2. 23 is a wear-resistant material RWI material, 2
4 is an elastic body, which is pasted together to form a moving body 25.
It consists of The moving body 25 is in contact with the vibrating body 22 via the friction material 23. When a voltage is applied to the piezoelectric body 21, bending vibration is excited in the circumferential direction of the vibrating body 22, and this becomes a traveling wave, thereby driving the movable body 25. Note that the vibrating body 22 in the figure has a protrusion 26 for taking out the mechanical output.
is installed.

FIG. 6 shows an example of the electrode structure of the piezoelectric body 21 used in the ultrasonic motor of FIG. In the figure, the structure is such that nine elastic waves are placed in the circumferential direction. In the same figure,
A and B are electrode groups each consisting of a small region corresponding to a half wavelength, C is an electrode group corresponding to a three-quarter wavelength, and D is an electrode group corresponding to a quarter wavelength.

Electrodes C and D create a positional phase difference of 1/4 wavelength (=90°) between electrode groups A and B. Adjacent small electrode parts in electrodes A and B are electrodes used when polarizing the piezoelectric body 21, and the adhesive surface of the piezoelectric body 21 with the elastic body 20 is the opposite side to the surface shown in FIG. The electrodes on that surface are flat electrodes. During use, electrode groups A and B are short-circuited, as indicated by diagonal lines in FIG. 6.

V+=Vn・5in(ωt) for electrodes A and B of the piezoelectric body 21 of the ultrasonic motor configured as above.
(1) V2”Ve・cos(ωt) −
--(2) However, Ve: Instantaneous value of voltage ω: Angular frequency t: If voltages v1 and v2 expressed in time are applied respectively,
For the vibrating body, ξ=ξe・(cos(ωt)◆cos(kX)+5in
(ωt) 11sin(kX))=ξII ・C08(
(1) t-kX) ---(3) However,
ξ: Amplitude value of bending vibration In ξ: Instantaneous value of bending vibration: Wave number (2πlλ) λ: Wavelength

FIG. 7 shows that point E on the surface of the vibrating body 22 moves in an ellipse with a major axis of 2v and a minor axis of 2U due to the excitation of the traveling wave, and the movable body 25 placed under pressure on the vibrating body 22 moves in an ellipse. This figure shows how the waves move at a rotational speed of V=ωXU in a direction opposite to the direction of wave propagation due to frictional force due to contact near the apex. Moreover, this speed becomes smaller than the above-mentioned V when there is slippage between the vibrating body 22 and the moving body 25. Arrow F in the same figure indicates the traveling direction of the moving body 25, and arrow G indicates the traveling direction of this traveling wave. Further, the speed V of the moving body 25 described above is proportional to the instantaneous value ξθ of this bending vibration.

By the way, if this ultrasonic motor 6 is shown as an equivalent circuit, the 8th
It is known that the result will be as shown in the figure. In the same figure, Ca
is the electrical capacitance of the vibrating body 22, and CI is the electric capacitance of the vibrating body 22.
, LL corresponds to the mass weight, and R1 corresponds to the braking coefficient and load. This circuit composed of 01, Ll, and R1 is related to mechanical operations such as vibration, and is called a mechanical arm. Out of the current 1 supplied to the electrodes of the piezoelectric body 21, the current i4 flowing through this mechanical arm is It is called arm current. This mechanical arm current has an amount corresponding to the vibration state of the vibrating body 22, that is, the vibration amplitude and vibration phase. When the level of the frequency voltage applied to the ultrasonic motor 6 is kept constant and the frequency is changed, the magnitude of the mechanical arm current i exhibits a characteristic as shown in FIG. 9. In other words, this figure shows that the admittance of the mechanical arm of the ultrasonic motor 6 changes according to the same characteristic curve depending on the frequency of the applied frequency voltage. As described above, the magnitude of this mechanical arm current 11 is proportional to the vibration amplitude of the vibrating body 22, and therefore proportional to the moving speed of the movable body 22.

Now, drive the ultrasonic motor 6 configured as above,
When controlling the moving speed of the moving body 25, this moving speed is detected by some method, for example, by using a well-known FC for the moving body 25.
A speed information detector such as a frequency generator (frequency generator) is attached, and speed control is performed by changing the voltage applied to the ultrasonic motor and changing the value of the mechanical arm current based on the speed information detected by this.

Problems to be Solved by the Invention When starting an ultrasonic motor configured as described above, a frequency voltage of a certain frequency is first applied, but it is very difficult to determine this frequency. This is because the frequency characteristics of the mechanical arm current ip (admittance of the mechanical arm) related to rotation change due to changes in temperature and humidity, load conditions due to contact between the vibrating body 22 and the moving body 25, and external load conditions. , changes as shown in FIG. In other words, in a certain state, if the property was like (g),
Depending on the changes in the environment mentioned above, it may exhibit characteristics like (ri) or (ke).

When the starting frequency is set to f8 shown in Fig. 9, for example, if the characteristic of the mechanical arm current i is as shown in (ri), that is, the admittance of the mechanical arm is very small, no matter how high the voltage ( Even if a voltage (within a range that does not destroy the piezoelectric body 21) is applied, almost no current flows, resulting in a phenomenon in which the ultrasonic motor 6 does not start at all. As a countermeasure for this startup, conventional resonance points (at the peak in the characteristic curve in Figure 9)
In order to prevent the frequency from becoming too low, the startup frequency is experimentally set based on the range of changes in temperature and humidity and fluctuations in load.

However, when setting such a frequency, the level of the applied voltage must be set to a certain degree in order to take into account the characteristic (k), that is, the 7 domitance becomes small at that frequency, and as a result, the power supply becomes large. The problem arises that the polarization state of the piezoelectric body 21 deteriorates.
In addition, if the set frequency becomes a frequency near the resonance point, the admittance will increase, so if a large voltage is applied that takes into consideration the case where the admittance is small as described above, the start-up time will be shortened. There is also the problem that a large mechanical arm current flows through the motor, causing the moving body 25 to move at an abnormally high speed, thereby damaging the equipment in which the ultrasonic motor 6 is incorporated.

In view of these points, the present invention can always start stably even if the characteristics of the mechanical arm of the ultrasonic motor change, and can suppress the voltage applied to the piezoelectric body lower than in the past. An object of the present invention is to provide a control device for an ultrasonic motor that does not unnecessarily widen the dynamic range of a control loop by reducing fluctuations in admittance of the ultrasonic motor.

Means for Solving the Problems The present invention drives a piezoelectric body with a frequency voltage to excite an elastic wave to a vibrating body constructed from the piezoelectric body and an elastic body, so that the piezoelectric body is placed in contact with the vibrating body. an ultrasonic motor for moving a moving object that has been moved; a speed information detection means for detecting information regarding the moving speed of the moving object; a predetermined speed detection means that detects that the ultrasonic motor has reached a predetermined speed and outputs a predetermined speed detection signal; and when the ultrasonic motor is started, the frequency of the frequency voltage is swept from a higher side to a lower side, and the sweeping operation is stopped by the predetermined speed detection signal. a frequency sweep means for detecting a vibration state of the vibrating body; a speed control means for controlling the moving speed of the moving body based on the output information of the speed information detector after the frequency sweep operation is stopped; and a vibration state for detecting a vibration state of the vibrating body. a detection means, detecting the phase of the frequency voltage and the output of the buzzing state detection means from the start of the sweep operation, and the phase detected at the time when the predetermined speed detection signal is output after the frequency sweep; and a phase control means for controlling the phase relationship between the frequency voltage and the output of the vibration state detection means to be the reference value by using the value of the vibration state detection means as a phase reference value.

According to the above-described configuration, the present invention operates the frequency sweep means when starting the ultrasonic motor, and after the speed detection means outputs a predetermined speed detection signal, the frequency sweep means stops sweeping, and the speed control means operates. At the same time, a phase control means is operated to control the frequency of the applied voltage so that the phase relationship between the applied voltage and the current becomes the phase value detected during frequency sweeping.

Embodiment FIG. 1 shows a block diagram of an ultrasonic motor control device in an embodiment of the present invention. In Figure 1, l
2 is a variable oscillator control circuit that controls the oscillation frequency of the variable oscillator 2 that is waiting for startup, 2 is a variable oscillator whose output frequency is determined by the manually input voltage value, and 3 is a 90% output from the output of variable oscillator 2
A 90° phase shift circuit 4.5 generates two signals with different phases, and amplifies each signal with different phases of 90° to a voltage level sufficient to drive the ultrasonic motor 6, and generates a piezoelectric A power amplifier circuit whose amplification degree is controlled by the DC voltage value applied to each electrode of the piezoelectric body 21, and 7 detects the voltage applied to the electrode of the piezoelectric body 21 and outputs it at a logic level. Voltage detection circuit, 8
9 is a current detection circuit that detects the mechanical arm current i and outputs it at a logic level; 9 is a current detection circuit that determines the phase relationship between the applied voltage and current from the outputs of the voltage detection circuits 7 and 8; and the difference between that value and the phase reference value. 10 is a compensation filter for stabilizing the phase control loop; 11 is a magnetized plastic magnet attached around the moving body 25 that is proportional to the moving speed. A speed sensor 12 is a speed information detection means such as a well-known frequency generator that detects changes in magnetic flux using a magnetoresistive element.
13 is a compensation filter for stabilizing the speed control loop; 14 monitors the output of the F-V conversion circuit 12; 15 is a phase reference setting circuit that sets the phase reference value of the phase comparison circuit 9; 16 is a speed detection circuit that detects whether the moving speed of the moving body 25 has reached a predetermined value; 16 is a phase reference setting circuit that sets the phase reference value of the phase comparison circuit 9; Detection circuit 1
A switch (S
W), 17 is a switch whose contact selection is controlled by the output of the speed detection circuit 11 so that the signal applied to the control input of the power amplifier circuit 4.5 becomes the output of the compensation filter 9 or a constant voltage V r I (S
W), 18 is the start/stop of the ultrasonic motor 6! This is a control terminal for

In this block diagram, speed sensor II, F-V conversion circuit! 2. Compensation filter 13, power P! Width circuit 4.5
A speed control loop is formed by the ultrasonic motor 6, voltage detection circuit 7, current detection circuit 8, phase comparison circuit 9, compensation filter lO1 variable oscillator 2.90"1l) IB@vIi
3. A phase control loop is formed by the x power row @rqvIi4.5 Oyohi and tf sonic motor 6.

FIG. 2 is a diagram for explaining the method of detecting the mechanical arm current i, in which at least one of two frequency voltages with different phases is applied to the piezoelectric body 21 via the transformer 19 (in the figure). is the output of the power amplifier circuit 4), and the voltage detection circuit 7 that detects the applied voltage includes a transformer 19 as shown in the figure.
The voltage on the secondary side of is input. In addition, the current detection circuit 8 is connected to a resistor R1 connected to the secondary side of the transformer 19 as shown in the figure.
It consists of an amplifier circuit that amplifies the voltage applied to I, capacitors C1 and R[l, and a waveform shaping circuit that shapes the output to a logic level. Here, if the capacitor C0' is equal to C9 in the equivalent circuit of Fig. 8 and the turns ratio of Citrans 19 is set to 1=1, the current iRs flowing through the resistor Ri+ is i R11: (1/(24[!'Ce'・S+I ))
' i m, but the corner frequency of the first term on the right side of this equation is several MH2, and compared to that, the driving frequency is several tens of kilometres.
Since H2, the above equation can be approximated as iR=I+@. Therefore, the voltage applied to the resistor RII is proportional to the mechanical arm current 1m, and by detecting this voltage as shown in the figure, the mechanical arm current 1I11 can be detected.

FIG. 3 is an operating waveform diagram when the control device for the ultrasonic motor 6 shown in FIG. 1. Command to stop with the control signal, (a) is the output of the variable oscillator control circuit l, and (ii) is the variable oscillator control signal.
(■) is the output of the F-V conversion circuit 12, which is a speed proportional signal proportional to the moving speed of the moving object 25, and (■) is the output of the speed detection circuit 14, which is a speed detection signal that becomes pFlp level when the moving object 25 reaches a predetermined speed. It is.

FIG. 4 is a diagram showing the frequency characteristics of the magnitude of the mechanical arm current 15 and the corresponding frequency characteristics of the phase difference θ with respect to the applied voltage when the applied voltage level is constant.

The operation of the ultrasonic motor control device of this embodiment configured as described above will be described below.

In order to start the ultrasonic motor 6, the control terminal 1
When the motor start/stop signal (7) inputted manually at step 8 goes from the '14 level to the '■' level, the variable oscillator control circuit l detects the speed of the moving object 25 by the speed detection circuit 14, which will be described later, as shown in FIG. A variable oscillator control signal (a) that changes from a high voltage to a low voltage with time is output until it is detected that the motor has reached a predetermined speed (FIG. 3, t). At this time, since 5WI6 is connected to the n side, this output is inputted to the variable oscillator 2. The variable oscillator 2 outputs a frequency voltage that sweeps from a high frequency (fn) to a low frequency (ft) in response to this signal. Here, the frequencies fn and fc are set within a range that sufficiently covers changes in the characteristics of the mechanical arm due to changes in the environment, etc., as described above.

The output of the variable oscillator 2 is applied to the ultrasonic motor 6 (piezoelectric body 21) through the 90° phase shift circuit 3 and the power amplification circuit 4.5. When this frequency voltage is applied, the moving body 25 starts rotating. At this time, a constant voltage Vrl is applied to each control input so that the amplification degree of the power amplifier circuit 4.5 is approximately at the center of the variable range (SW 17 is connected to the l side). Therefore, a constant level of frequency voltage is applied to the ultrasonic motor 6.

Under this constant voltage, when the oscillation frequency of the variable oscillator 2 is changed to lower by the variable oscillator control circuit 1,
If the characteristics of the mechanical arm shown in Figure 9 are as shown in (ke), (ri)
The admittance of the mechanical arm increases as the mechanical arm current 1. also increases, so the speed of the moving body 25 becomes faster. The speed of the moving body 25 is extracted by the speed sensor 11 and the F-V conversion circuit 12 as a DC voltage proportional to the speed (speed proportional signal in FIG. 3).

Speed detection circuit 1 consisting of a well-known voltage comparator etc.
4 monitors the speed of the moving body 25 using this voltage, and when a certain predetermined speed, that is, a speed proportional signal (two) reaches a predetermined level (
When Vr2) is reached, the output is changed to "1.Vr2)" as shown in FIG.
level to ``2'' and outputs it as a speed detection signal (1) to 5W16.5W17, the phase reference setting circuit 15, and the variable oscillator control circuit l.

In this embodiment, this predetermined speed is made to substantially match the set speed (moving speed during steady state).

The variable oscillator control circuit 1 receives the “■ Lebel speed detection signal (
When I) is input manually, the variable oscillator control signal (A) stops changing from a high voltage to a low voltage and maintains that state, as shown in FIG. Also, when the speed detection signal (1) is output, 5W17 is connected to the m side, the speed control loop is closed, and the amplification degree of the power amplifier circuit 4.5 is changed based on the information from the speed sensor. Let ultrasonic motor 6
It operates to keep the speed of the moving body 25 constant by changing the voltage applied to the mechanical arm and controlling the mechanical arm current 10.

By the way, even after the ultrasonic motor 6 is operated, the admittance of the mechanical arm will naturally change due to environmental changes such as temperature and humidity, fluctuations in load, etc. For example, due to losses such as friction between the moving body 25 and the vibrating body 22, the ultrasonic When the temperature of the motor 6 body increases, the frequency characteristics of the mechanical arm TL flows l, l shift from () to the tracing frequency as shown in <h> in Fig. 4(a).In such a case, the speed control loop After operation 5.l If the frequency of the frequency voltage applied to the ultrasonic motor 6 is constant, the following gap will occur. This will be explained using Fig. 4. In order to start the ultrasonic motor 6. When the frequency is swept from high to low, the mechanical arm current 11 increases in the direction of arrow H, and the characteristic curve of the mechanical arm current i at this time is (o)), and the speed of the moving body 25 increases accordingly. As mentioned above, when the specified speed is reached, the speed detection signal is output, the frequency sweep stops, and the speed control loop operates.The frequency at this time is f+ (the magnitude of the mechanical arm current of 1 m Saha i
1).

After the speed control loop operates, if the frequency of the applied voltage is always 1, the ultrasonic motor 6
If the temperature of increases and the characteristics of the mechanical arm change like (force), then the admittance of the mechanical arm at frequency f1 becomes smaller, and therefore the mechanical arm current 11 to achieve a predetermined speed increases.
In order to supply this, it is necessary to increase the voltage level applied to the ultrasonic motor 6. Therefore, if the frequency of the applied voltage is kept constant, there still remains the problem that the dynamic range of the speed control loop must be made considerably large to take into account this change in the mechanical arm.

In order to solve this problem, the present invention performs the following operation simultaneously with the start-up of the speed control loop described above.

From the start of the ultrasonic motor 6, the applied voltage is detected by the voltage detection circuit 7, the mechanical arm current i is detected by the above-mentioned current detection circuit 8, and the outputs of both are sent to the phase comparison circuit 9 and the phase reference setting circuit 15. Man-powered. The phase reference setting circuit 15 is a circuit that outputs the phase reference value of the phase control loop and outputs the speed detection signal (
1), a signal corresponding to the phase difference between the signals obtained momentarily from the voltage detection circuit 7 and the current detection circuit 8 is outputted. When the speed of the moving body 25 reaches a predetermined value and a speed detection signal (1) is output, the phase reference setting circuit 15
fixes the output to a signal with a value corresponding to the phase difference between the output signal of the voltage detection circuit 7 and the output signal of the current detection circuit 8 at that time (that is, the phase difference between the applied voltage and the mechanical arm current at that time),
This value is manually input to the phase comparator circuit 9 as a reference value during phase control loop operation.

Here, the phase reference setting circuit 15 is configured to count the time gap between the rising or falling edges of the output signals of the voltage detection circuit 7 and the current detection circuit 8 using clock pulses, and use that value as an output signal.

By the way, since 5W16 is connected to the 0 side by the speed detection signal (1), the phase control loop will operate from this point on, and from this point on, the phase comparator circuit 9 will be connected to the phase standard setting circuit 15 described above using a well-known technique. A phase reference value that should result in a phase relationship between the applied voltage and the mechanical arm current i when the output speed of the moving body 25 reaches a predetermined value, and the applied voltage obtained from the voltage detection circuit 7 and the current detection circuit 8. The phase difference (θ1) of the mechanical arm current i is compared, a phase error signal proportional to the difference is output, and the variable oscillator 2 is operated through the compensation filter 10 to change its oscillation frequency, so that θ is always the same as the above-mentioned phase. Operates to be equal to the reference value. The characteristic of the mechanical arm at the time of startup is the curve 0) in Fig. 4(a) as before, and the corresponding frequency characteristic of θ is the curve (9) (
Assume that the situation is as shown in FIG. 4(b)). When the speed of the moving body 25 reaches a predetermined value and the speed detection signal (I) is output, if the frequency is fl, the phase difference between the mechanical arm current i and the applied voltage at that time is θ1, and a signal corresponding to that value is generated. is output from the phase reference setting circuit 15, and this value becomes the reference value of the phase control loop. Even if the characteristics of the mechanical arm change as shown in Figure 4 (h) due to temperature rise, and the corresponding phase difference characteristics change as shown in (b), the phase control loop will always maintain the phase difference θ as described above. The variable oscillator 2 is controlled so that the frequency becomes f2 in this case. That is, as described above, the phase control works to keep the admittance of the mechanical arm at the operating point substantially constant. Therefore, if the mechanical arm current required to obtain a predetermined speed is, for example, 11, there is no need to greatly change the level of the applied voltage even if the characteristics of the mechanical arm change (Figure 4).
. From this, there is no need to increase the dynamic range of the speed control loop, including changes in the characteristics of the mechanical arm.

As described above, according to this embodiment, at startup, instead of fixing the frequency as in the conventional case, the frequency is swept from high to low to change (increase) the admittance of the mechanical arm. Since the mechanical arm current l required to obtain the set speed is obtained, there is no need to apply a high voltage that takes into account changes in characteristics, and even if the characteristics of the mechanical arm change, it is necessary to apply a high voltage at startup. It is sufficient that the frequency voltage level is always lower than the conventional starting voltage and is approximately at a level that is the center of operation during speed control. Therefore, the deterioration of the polarization of the piezoelectric body 21 is also reduced compared to the prior art. In addition, since the frequency sweep is always performed from the side with the smallest admittance as described above, the mechanical arm current 17 flows instantaneously during startup, unlike in the conventional case, and the speed of the moving body 25 becomes abnormally high, causing a slight ta on the equipment. I have nothing to give.

Furthermore, in this embodiment, at startup, the amplification degree of the power amplifier circuit 4.5 is set to be approximately at the center of the variable range, and furthermore, at the time of speed control switching (at the time when the speed detection signal (I) is output).
Since the phase is controlled so that the phase difference between the mechanical arm current i of Sufficient dynamic range can be maintained against control end load fluctuations.

In the embodiment described above, a method was adopted in which the mechanical arm current was controlled by changing the voltage level applied to the ultrasonic motor 6 using a power tank f@ circuit whose amplification degree changed depending on the control signal. A similar effect can be obtained without any problems by applying a so-called P WM L/voltage whose pulse width is varied depending on a signal to vary the average value of the mechanical arm current. In this case, the PWM duty is approximately 5o until the startup speed detection signal is output.
:50, the dynamic range can be sufficiently wide during speed control, as in the case described above.

Furthermore, in the above embodiment, a method was adopted in which the moving speed of the moving body was detected by a speed sensor such as an FC and controlled by the output signal, but the speed was detected by the magnitude of the mechanical arm current and its level was kept constant There is no equivalent problem even if a method is adopted in which the speed is controlled so that the speed becomes constant as a result.

Further, in the above embodiment, the vibration state of the vibrating body 22 was detected by the mechanical arm current, but as described in Japanese Patent Application Laid-Open No. 62-85684, a monitor electrode is provided on the vibrating body 22, thereby detecting the vibration state of the vibrating body 22. The object of the present invention can also be achieved by detecting the vibration state and using the output instead of the arm current.

As described in detail, according to the present invention, even if the characteristics of the ultrasonic motor change due to changes in temperature, humidity, or load, the ultrasonic motor can be stably started at a low voltage without applying more voltage than necessary. Moreover, even during speed control, it is possible to provide an ultrasonic motor control device that can be controlled almost centering on the operation even if the characteristics of the mechanical arm change, and its practical effects are great.

[Brief Description of the Drawings] Fig. 1 is a block diagram of an ultrasonic motor control device according to an embodiment of the present invention, Fig. 2 is a block diagram of a current detection circuit in the same embodiment, and Fig. 3 is a block diagram of the same embodiment. Figure 4 (a) and (b) are characteristic diagrams showing the relationship between the frequency characteristics of the mechanical arm current and the phase difference between the applied voltage, and Figure 5 is a cutaway perspective view of the annular ultrasonic motor. Figure 6 is a plan view showing the shape and electrode structure of the piezoelectric body used in the ultrasonic motor of Figure 5, Figure 7 is an explanatory diagram of the operating principle of the ultrasonic motor, and Figure 8 is a diagram of the ultrasonic motor. The equivalent circuit, FIG. 9, is a frequency characteristic diagram of mechanical arm current. ! ...Variable oscillator control circuit, 2...Variable oscillator, 3
...90° phase shift circuit, 4.5... Power amplifier circuit, 6
...Ultrasonic motor, 7...Voltage detection circuit, 8...
Current detection circuit, 9... Phase comparison circuit, lO.13...
・Compensation filter, 11...Speed sensor, 12...
F-V conversion circuit, 14... Speed detection circuit, 15...
Phase reference setting circuit. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 p Figure 8 Figure 9

Claims (3)

[Claims] (1) A piezoelectric body is driven with a frequency voltage to excite elastic waves in a vibrating body composed of the piezoelectric body and an elastic body, thereby moving a moving body placed in contact with the vibrating body. an ultrasonic motor, a speed information detecting means for detecting information regarding the moving speed of the moving object, and detecting that the moving speed of the moving object has reached a predetermined value based on output information of the speed information detecting means. a predetermined speed detection means for outputting a speed detection signal; a frequency sweep means for sweeping the frequency of the frequency voltage from a higher side to a lower side when starting the ultrasonic motor and stopping the sweeping operation in response to the predetermined speed detection signal; After the frequency sweep operation is stopped, a speed control means for controlling the moving speed of the moving body based on the output information of the speed information detector, a vibration state detection means for detecting the vibration state of the vibrating body, and the sweep operation. The phase of the frequency voltage and the output of the vibration state detection means is detected from the start of the period, and after the frequency sweep, the phase value detected at the time when the predetermined speed detection signal is output is used as the phase reference value. A control device for an ultrasonic motor, comprising: a phase control means for controlling the phase relationship between the frequency voltage and the output of the vibration state detection means to the reference value. (2) A voltage control amplification means for amplifying the frequency voltage applied to the ultrasonic motor by changing the degree of amplification according to a control signal in the speed control loop of the speed control means, and a predetermined speed detection means when the ultrasonic motor is started. 2. The ultrasonic motor control device according to claim 1, wherein a constant value is given as the control signal until a predetermined speed detection signal is output. (3) A pulse width modulation power amplification means for applying a voltage whose pulse width is changed according to a control signal to the ultrasonic motor is included in the speed control loop of the speed control means, and when the ultrasonic motor is started, a predetermined speed detection means is provided. 2. The ultrasonic motor control device according to claim 1, wherein the duty of the pulse width is set to a constant value until a predetermined speed detection signal is output.