JP2002199749A - Ultrasonic motor drive circuit and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ultrasonic motor drive circuit and method which can effectively prevent noise generated, particularly when an ultrasonic motor stops. SOLUTION: A microcomputer 32 sets a phase control signal, to provide a phase different of 90 deg. between a phase A drive signal outputted from a phase- A amplifying circuit 42 and a phase-B drive signal, outputted from a phase-B amplifying circuit 44 in order to generate the maximum torque, when the ultrasonic motor is driven under normal conditions. When the ultrasonic motor stops its operation, the value of the phase control signal is reduced gradually, thereby a phase difference between the phase-A drive signal and phase-B drive signal is gradually changed from 90 deg. to 0 deg. during the prescribed period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit and a driving method for an ultrasonic motor for driving an ultrasonic motor.

[0002]

2. Description of the Related Art Conventionally, an ultrasonic motor using ultrasonic vibration as a driving force has been known. In a traveling-wave type ultrasonic motor, which is a type of ultrasonic motor, a stator is formed by attaching a piezoelectric body to an annular elastic body, and a rotor attached to a drive shaft is brought into pressure contact with the stator. Have been.

A drive circuit for an ultrasonic motor supplies two-phase drive signals (sine wave and cosine wave) having a predetermined frequency and a phase difference of 90 ° to the piezoelectric body. Ultrasonic vibration (traveling wave) in which antinodes and nodes of vibration move in an annular shape along the elastic body is excited in the elastic body by the mechanical vibration of the piezoelectric body generated by the two-phase drive signals. The traveling wave rotates the rotor and the drive shaft that are in pressure contact with the elastic body.

Such a traveling wave type ultrasonic motor is smaller and lighter than the generated torque as compared with a brushless motor or a motor with a brush, and has a holding torque in a state where power is not supplied to the motor in principle. Is generated, so that there are various advantages such as that power can be saved in a stopped state.

When a traveling wave type ultrasonic motor is used in, for example, a brake system of an automobile, a pressure sensor is disposed on a pressure axis of a brake pad, for example.
If the output value (pressure value) of the pressure sensor is lower than the target pressure value, the ultrasonic motor is rotated in a direction to press the brake pad, and the output value of the pressure sensor is adjusted to the target value. When the pressure value matches, the rotation of the ultrasonic motor is stopped. When the output value of the pressure sensor exceeds the target pressure value, the ultrasonic motor is rotated in a direction to reduce the pressure of the brake pad, and when the output value matches the target pressure value, the rotation of the ultrasonic motor is stopped. Stop.

As described above, when the output value of the pressure sensor matches the target pressure value, the rotation of the ultrasonic motor is stopped, that is, when the supply of the driving voltage to the ultrasonic motor is stopped, the ultrasonic wave is stopped. The motor keeps a constant pressing force according to the principle.

[0007]

However, the ultrasonic motor has an extremely fast response, that is, the supply of the driving current is stopped to stop the rotation of the ultrasonic motor, and then the ultrasonic motor actually stops. However, there is a problem that a sudden change in torque occurs due to a short time until the noise is generated.

FIG. 8A shows a noise signal when the conventional ultrasonic motor is stopped. As shown in FIG. 8A, when the power supply to the ultrasonic motor is stopped while the phase difference between the two-phase drive signals remains 90 °, a large noise is generated.

In order to solve this problem, there is a technique in which the driving voltage supplied to the ultrasonic motor is gradually reduced to gradually reduce the pressing force. However, as shown in FIG. Is not a linear relationship but a non-linear relationship, so even if the drive voltage is gradually reduced, the torque suddenly drops at a certain drive voltage.
There was a problem that noise could not be reduced effectively.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and in particular, to provide a drive circuit and a drive method for an ultrasonic motor which can effectively prevent noise generated when the ultrasonic motor is stopped. Is the purpose.

[0011]

According to a first aspect of the present invention, there is provided a stator for generating a traveling wave by applying a first driving voltage and a second driving voltage of a predetermined frequency; A driving circuit for driving an ultrasonic motor having a rotor that rotates by a wave; a driving voltage output unit that outputs a first driving voltage and a second driving voltage of the predetermined frequency to the stator; Phase difference control means for controlling a phase difference of the second drive voltage with respect to a voltage to gradually change.

According to the present invention, the ultrasonic motor includes a stator made of, for example, a piezoelectric body and an elastic body, and a rotor which is brought into pressure contact with the stator. In such an ultrasonic motor, a traveling wave is generated in the elastic body by applying a first driving voltage and a second driving voltage of a predetermined frequency to the piezoelectric body, and the rotor is rotated by the traveling wave.

In such an ultrasonic motor drive circuit, the drive voltage output means outputs a first drive voltage and a second drive voltage of a predetermined frequency to the stator. Here, by controlling the phase difference of the second drive voltage with respect to the first drive voltage, the drive torque of the ultrasonic motor can be controlled. It may become loud and generate noise.

Therefore, the phase difference control means performs control so that the phase difference between the second drive voltage and the first drive voltage gradually changes. Thus, since the driving torque of the ultrasonic motor also gradually changes, generation of noise can be prevented.

According to a second aspect of the present invention, when the ultrasonic motor starts or stops driving,
The phase difference is controlled so as to gradually change within a predetermined range.

According to the present invention, when the driving is started or stopped, the phase difference is set within a predetermined range, for example, from approximately 0 ° at which the driving torque of the ultrasonic motor becomes minimum to when the driving torque of the ultrasonic motor becomes maximum. It is controlled so as to gradually change in a range of approximately 90 °.

In this case, the phase difference control means controls the phase difference so as to gradually increase from approximately 0 ° to approximately 90 ° at the start of driving of the ultrasonic motor. When the driving of the ultrasonic motor is stopped, the phase difference is controlled so as to gradually decrease from approximately 90 ° to approximately 0 °.

By controlling in this way, it is possible to smoothly drive the drive torque from a minimum state to a maximum state without causing a drastic change in the drive torque at the start of the drive, and to reduce the drive torque at the stop of the drive. Can be smoothly driven from the state where the driving torque is the largest to the state where the driving torque is the smallest without causing a sudden change in the driving torque. Therefore, it is possible to prevent generation of noise at the time of starting or stopping the driving of the ultrasonic motor.

According to a fourth aspect of the present invention, the first frequency of the predetermined frequency
A driving method for driving an ultrasonic motor, comprising: a stator that generates a traveling wave by applying the driving voltage and the second driving voltage; and a rotor that rotates by the traveling wave. The first drive voltage and the second drive voltage are output to the stator, and the phase difference between the first drive voltage and the second drive voltage is controlled so as to gradually change.

According to the present invention, since the control is performed so that the phase difference between the first drive voltage and the second drive voltage gradually changes, the drive torque of the ultrasonic motor also gradually changes.
Noise can be prevented from being generated.

The present invention can be applied to, for example, a vehicle brake device that performs braking by pressing a brake pad against a disk rotor. This can prevent noise from being generated when the vehicle stops, for example.

[0022]

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

FIG. 1 shows a traveling wave type ultrasonic motor 10 according to the present embodiment. The ultrasonic motor 10 includes an annular elastic body 12 made of a copper alloy or the like, and a piezoelectric body 14 is attached to the elastic body 12 to form a stator 28.

The piezoelectric body 14 is made of a piezoelectric material that converts an electric signal into a mechanical signal, and is divided into a ring by a large number of electrodes.
It is arranged and configured. On the other hand, the rotor 18 attached to the drive shaft 16 is formed by bonding an annular slider 22 to a rotor ring 20 made of an aluminum alloy or the like, and the slider 22 is brought into pressure contact with the elastic body 12 by a spring 24. Have been. As the slider 22, for example, engineering plastic or the like is used in order to obtain a stable frictional force and a stable friction coefficient, so that the rotor 18 can be driven with high efficiency.

The elastic element 12 has a piezoelectric element 26 (FIG. 2).
Reference) is affixed. As shown in FIG. 2, one end of the piezoelectric element 26 is grounded, and the other end is connected to the input end of the bandpass filter 40 of the drive circuit 30.

The piezoelectric element 26 detects the vibration of the elastic body 12 and outputs an AC signal (feedback signal) having an amplitude and a cycle corresponding to the vibration. An output terminal of the band-pass filter 40 is connected to one input terminal of the microcomputer 32. The bandpass filter 40 detects a feedback signal output from the piezoelectric element 26 and outputs the detected signal to the microcomputer 32.

The ultrasonic motor 10 has a rotation sensor 4
The output terminal of the rotation sensor 46 is connected to the other input terminal of the microcomputer 32. The rotation sensor 46 includes a light emitting element (not shown) and a light receiving element (not shown), and is emitted from the light emitting element and reflected by an annular reflective seal (not shown) attached to the upper surface of the rotor 18. It is arranged so that light is received by the light receiving element. When the rotor 18 rotates, the rotation sensor 46 outputs a pulse signal having a cycle corresponding to the rotation speed of the rotor 18 to the microcomputer 32.

An oscillation circuit 34 is connected to one output terminal of the microcomputer 32, and one input terminal of a switching control circuit (phase shift circuit) 36 is connected to the other output terminal. The output terminal of the oscillation circuit 34 is connected to the other input terminal of the switching control circuit 36. The oscillation circuit 34 outputs (oscillates) a drive pulse having an oscillation frequency according to a signal from the microcomputer 32.

One output terminal of the switching control circuit 36 is connected to one input terminal of the A-phase amplification circuit 42 of the drive signal generation circuit 48, and the other output terminal is connected to the B-phase amplification circuit of the drive signal generation circuit 48. It is connected to one input terminal of the circuit 44. The switching control circuit 36 outputs the drive pulse output from the oscillation circuit 34 to the A-phase amplification circuit 42 and the B-phase amplification circuit 44 while switching according to the phase shift control signal output from the microcomputer 32.

The phase shift control signal indicates a phase shift amount (phase difference) between an A-phase drive signal and a B-phase drive signal to be described later, for example, from 0 ° to 90 °.
°, for example, a signal whose phase shift amount increases as the value of the phase shift control signal increases.

The switching control circuit 36 switches the driving pulse output from the oscillation circuit 34 so that the phase shift amount between the A-phase drive signal and the B-phase drive signal becomes the phase shift amount corresponding to the phase shift control signal. I do.

The other input terminal of the A-phase amplifier circuit 42 and the other input terminal of the B-phase amplifier circuit 44 are connected to the output terminal of the voltage generator 38. The input terminal of the voltage generation circuit 38 is connected to a vehicle battery power supply (for example, 12 V). The voltage generation circuit 38 transforms (for example, 100 V) a DC voltage supplied from a vehicle battery power supply and supplies the DC voltage to an A-phase amplification circuit 42 and a B-phase amplification circuit 44.

FIG. 3 shows a circuit configuration of the voltage generating circuit 38.

The voltage generating circuit 38 shown in FIG.
20 and the primary coil 12 of the transformer 120.
At the midpoint of 0A, a capacitor 116 is connected via a power line 118.
And the other end of the capacitor 116 is grounded.

One end of the primary coil 120A of the transformer 120 is connected to a MOSFET 110 as a switching element.
Connected to the drain of The gate of the MOSFET 110 is connected to one output terminal of the duty control circuit 114, and the source of the MOSFET 110 is grounded.

The other end of the primary coil 120A of the transformer 120 is connected to a MOSFET 112 as a switching element.
Connected to the drain of The gate of the MOSFET 112 is connected to the other output terminal of the duty control circuit 114, and the source of the MOSFET 112 is grounded.

One end of a secondary coil 120B of the transformer 120 is connected to the anode of a diode 122 as a rectifier, and the other end is connected to a diode 1 as a rectifier.
Twenty-four anodes are connected. Also, the transformer 12
The middle point of the secondary coil 120B of 0 is grounded.

The cathodes of the diodes 122 and 124 are connected to one end of a coil 126 as an inductance element. The other end of the coil 126 is connected to one end of a capacitor 128, and the other end of the capacitor 128 is grounded. Further, the other end of the coil 126 is connected to one of the input terminals of the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44, and a DC voltage is supplied to the input terminals from the voltage generation circuit 38.

The A-phase amplifying circuit 42 is connected to the piezoelectric body 14A of the ultrasonic motor 10, and converts a DC voltage supplied from the voltage generating circuit 38 into an AC voltage (for example, 20 V).
0V) and supplies a sine wave signal (sin wave) to the piezoelectric body 14A as an A-phase drive signal.

The B-phase amplification circuit 44 is connected to the piezoelectric body 14B of the ultrasonic motor 10, and converts a DC voltage supplied from the voltage generation circuit 38 into an AC voltage (for example, 200V).
V) Then, a sine wave signal (cos wave) having a different phase by the phase shift amount set by the phase shift control signal from the sine wave signal supplied by the A-phase amplifier circuit 42 is supplied to the piezoelectric body 14B as a B-phase drive signal. I do. The other ends of the piezoelectric bodies 14A and 14B are grounded. The ultrasonic motor 1 is formed by the piezoelectric bodies 14A and 14B.
Thus, a zero piezoelectric body 14 is formed.

The circuit configurations of the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44 are as shown in FIG. The A-phase amplifier circuit 42 includes a transformer 100, and the transformer 10
One end of the branch of the power supply line 84 is connected to the middle point of the primary coil 100A of 0, and the other end of the power supply line 84 is connected to the output end of the voltage generation circuit 38 described above. .

One end of the primary coil 100 A of the transformer 100 is connected to the drain of the MOSFET 90 as a switching element, and the other end is connected to the drain of the MOSFET 92. The sources of the MOSFETs 90 and 92 are grounded. Both ends of the secondary coil 100B of the transformer 100 are connected to the piezoelectric body 14A.

The B-phase amplifier circuit 44 has a transformer 102, and the other end of the power supply line 84 is connected to the middle point of the primary coil 102A of the transformer 102.

One end of the primary coil 102 A of the transformer 102 is connected to the drain of a MOSFET 94 as a switching element, and the other end is connected to the drain of a MOSFET 96. The sources of the MOSFETs 94 and 96 are grounded. Both ends of the secondary coil 102B of the transformer 102 are connected to the piezoelectric body 14B.

The gates of the MOSFETs 90, 92, 94, and 96 are respectively connected to the switching control circuit 36. Each of the MOSFETs 90, 92, 94, and 96 includes switching signals A ₁ , A ₂ , It is turned on and off according to B ₁ and B ₂ .

Next, the operation of the embodiment of the present invention will be described in detail with reference to the drawings.

When driving the ultrasonic motor 10, the microcomputer 32 outputs a drive frequency signal to the oscillation circuit 34.
And a phase shift control signal is output to the switching control circuit 36.

The phase shift amount (phase difference) between the A-phase drive signal and the B-phase drive signal by the phase shift control signal is initially set to 90 °, for example, as shown in FIG.

The oscillation circuit 34 starts oscillating at the drive frequency fs specified by the microcomputer 32.

In the voltage generation circuit 38, a voltage is supplied from the vehicle battery power supply to the primary coil 120 A of the transformer 120, and a switching signal is input from the duty control circuit 114 to the gates of the MOSFETs 110 and 112 at a predetermined timing. The current to the primary coil 120A of the transformer 120 is turned on and off. Then, an AC voltage is induced in the secondary coil 120B of the transformer 120. The AC voltage is full-wave rectified by the diodes 122 and 124, smoothed by the coil 126 and the capacitor 128, and the DC voltage is converted to the A-phase amplifier circuits 42 and B. It is supplied to the phase amplification circuit 44.

In the switching control circuit 36, the A-phase amplification circuit 42 and the A-phase amplification circuit 42 are controlled so that the phase shift between the A-phase drive signal and the B-phase drive signal becomes 90 ° in accordance with the phase shift control signal output from the microcomputer 32. M of the B-phase amplifier circuit 44
The switching signals A ₁ , A ₂ , B ₁ , and B ₂ for turning on and off the OSFETs 90, 92, 94, and 96 are generated and output to the A-phase amplification circuit 42 and the B-phase amplification circuit 44, respectively.

The relationship between the phase difference between the A-phase drive signal and the B-phase drive signal and the drive torque of the ultrasonic motor 10 is as shown in FIG. 7, and when the phase difference is 0 °, the drive torque is the highest. The driving torque is largest when the phase difference is small and the phase difference is 90 °, and the driving torque also changes substantially linearly as the phase difference changes from 0 ° to 90 °.

Therefore, by setting the phase difference to 90 °, the ultrasonic motor 10 can be driven with the maximum torque.

The switching signals A ₁ and A ₂ are MOS
This is a signal that turns on or off one of the FETs 90 and 92 at a predetermined duty ratio and turns off the other MOSFETs, and switches the MOSFETs to be turned on and off in the order of the MOSFETs 90 and 92 at a predetermined timing. Similarly, the switching signals B ₁ and B ₂ are
MOSFETs for turning on / off one of the MOSFETs 94 and 96 at a predetermined duty ratio and turning off the other MOSFETs,
It is a signal that switches in the order of the MOSFETs 94 and 96 at a predetermined timing.

The switching signals A ₁ and A ₂ are turned on and off every １ ／ of the cycle of the drive frequency fs. Similarly, the switching signals B ₁ and B ₂ are also switched on and off of the cycle of the drive frequency fs. On / off is switched every four cycles.

Further, the switching signals A ₁ and B ₁ are:
On / off switching is performed so that the phase difference is set by the phase shift control signal, and the switching signals A ₂ , B
₂ is switched on and off so as to have a phase difference set by the phase shift control signal.

[0057] MOSFET During normal driving, the phase difference such that the maximum torque is generated is set to 90 °, the switching signal _{A 1, A 2, B 1} , B 2 , as shown in FIG. 5, which are turned on and off Is equal to 1 of the period of the driving frequency fs.
MOSFETs 90, 94, 92, 96 for every / 4 cycle
In this order.

Thus, two of the transformers 100 and 102
Each of the secondary coils 100B and 102B has an AC A having a frequency fs at the start of driving and a phase difference of 90 °.
A phase drive signal and a B-phase drive signal are induced.

When this drive signal is supplied to the piezoelectric bodies 14A and 14B, a traveling wave is excited in the elastic body 12 of the ultrasonic motor 10, and the drive shaft 16 and the rotor 18 are rotated. Further, the vibration of the elastic body 12 is converted into an electric signal by the piezoelectric element 26, and as a feedback signal through the band pass filter 40 through the microcomputer 3.
2 is input. Further, a rotation pulse signal corresponding to the rotation speed of the rotor 18 is input to the microcomputer 32 from a rotation sensor 46 attached to the ultrasonic motor 10.

In the microcomputer 32, while monitoring the feedback signal and the rotation pulse signal, the frequency of the drive signal gradually approaches and matches the optimum drive frequency of the ultrasonic motor 10, and further follows the optimum drive frequency. MOSFETs 90, 92, 9 to be turned on and off
The frequency of the drive signal is controlled by changing the switching timing between 4, 96.

The ultrasonic motor 10 is driven in this manner. When the stop of the ultrasonic motor 10 is instructed at time t1 shown in FIG.
Gradually decreases the value of the phase shift control signal (reduces the phase difference) over time T (t2-t1) until time t2 shown in FIG. Thereby, as shown in FIG. 6, the phase difference between the A-phase drive signal and the B-phase drive signal gradually changes from 90 ° to 0 °.

Accordingly, the A-phase drive signal and B
Since the phase difference between the phase driving signal and the driving torque is substantially linear, the phase difference between the A-phase driving signal and the B-phase driving signal gradually changes from 90 ° to 0 °. The drive torque of the sound wave motor also gradually decreases as shown in FIG. Therefore, it is possible to prevent noise from being generated when the ultrasonic motor stops.

If the time T during which the phase difference between the A-phase drive signal and the B-phase drive signal gradually changes from 90 ° to 0 ° is too short, the noise reduction effect is small, and if it is too long, the ultrasonic motor stops. Since the time until the time becomes longer, the time is determined based on a balance between a required noise reduction effect and an allowable stop time. For example, it is preferably set to about 4 to 6 msec, and more preferably about 6 msec.

For example, when T = 4 msec, the waveform of the noise signal generated when the ultrasonic motor stops is as shown in FIG. 8B. When T = 6 msec, the ultrasonic motor FIG. 8C shows the waveform of the noise signal of the noise generated when the operation is stopped.

As shown in FIG. 8B, the phase difference between the A-phase drive signal and the B-phase drive signal is about 4 ms from 90 ° to 0 °.
8 (A) by gradually changing over ec.
As compared with the conventional case shown in FIG.

As shown in FIG. 8 (C), the phase difference between the A-phase drive signal and the B-phase drive signal is gradually changed from 90 ° to 0 ° over about 6 msec.
Noise is further reduced as compared with the conventional case shown in FIG.

As described above, by gradually changing the phase difference between the A-phase drive signal and the B-phase drive signal from 90 ° to 0 ° over a predetermined time, the drive torque can be changed abruptly. But gradually decreases. Therefore, generation of noise when the ultrasonic motor is stopped can be suppressed.

In the present embodiment, the phase difference between the A-phase drive signal and the B-phase drive signal is set to 90 when the ultrasonic motor is stopped.
The case where the predetermined time is required to gradually change from 0 ° to 0 ° has been described.
The phase difference between the phase drive signal and the B phase drive signal is from 0 ° to 90 °
Up to a predetermined time may be required to change gradually.

That is, the value of the phase shift control signal is gradually increased (the phase difference is increased) over the time T from the start of driving of the ultrasonic motor. As a result, as shown in FIG. 10, the phase difference between the A-phase drive signal and the B-phase drive signal changes from 0 ° to 90 °.
° gradually changes. Thus, the driving torque gradually increases without abrupt change. Therefore, it is possible to suppress generation of noise at the start of driving of the ultrasonic motor.

When the ultrasonic motor is applied to a brake system of a vehicle, the output value (pressurized value) of a pressurizing sensor disposed on a pressurizing shaft of a brake pad and a target pressurized value are determined. , The phase difference between the A-phase drive signal and the B-phase drive signal may be controlled. Thereby, the drive of the ultrasonic motor can be further smoothed, and the noise can be further reduced.

In this embodiment, the voltage generation circuit 3
8 is a vehicle battery power supply, the DC voltage output from the voltage generation circuit 38 is 100 V, and the AC voltage output from the A-phase amplification circuit 42 and the B-phase amplification circuit 44 is 200 V.
Although described as V, the invention is not limited to this.

[Brief description of the drawings]

FIG. 1 is a partially sectional perspective view showing a schematic configuration of an ultrasonic motor.

FIG. 2 is a block diagram illustrating a schematic configuration of an ultrasonic motor and a drive circuit of the ultrasonic motor.

FIG. 3 is a circuit diagram showing a configuration of a voltage generation circuit in a drive circuit of the ultrasonic motor.

FIG. 4 is a circuit diagram showing a configuration of a drive signal generation circuit in the drive circuit of the ultrasonic motor.

FIG. 5 is a diagram showing a relationship between a switching signal output from a switching control circuit and a signal induced by a transformer of a drive signal generation circuit.

FIG. 6 is a diagram for explaining a change in a phase shift control signal when the ultrasonic motor is stopped.

FIG. 7 is a diagram showing a relationship between a phase difference between an A-phase drive signal and a B-phase drive signal and drive torque.

8A is a waveform diagram showing a waveform of a noise signal when the conventional ultrasonic motor stops, and FIG. 8B is a waveform diagram showing a waveform of a noise signal when the ultrasonic motor according to the present embodiment stops. (C) is a waveform diagram showing a waveform of a noise signal when the ultrasonic motor according to the present embodiment is stopped.

FIG. 9 is a diagram showing a relationship between a driving voltage and a driving torque of an ultrasonic motor.

FIG. 10 is a diagram for explaining a change in a phase shift control signal at the start of driving of an ultrasonic motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ultrasonic motor 30 Drive circuit 32 Microcomputer (phase difference control means) 34 Oscillation circuit 36 Switching control circuit (phase difference control means) 38 Voltage generation circuit 40 Bandpass filter 42 A-phase amplification circuit (drive voltage output means) 44 B Phase amplifier circuit (drive voltage output means)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H680 AA06 AA09 AA18 BB03 BB16 CC07 DD01 DD02 DD23 DD53 DD66 DD73 DD85 EE23 EE24 FF23 FF25 FF27 FF30 FF33 FF36 FF38 GG23 GG25

Claims (4)

[Claims] 1. A drive of an ultrasonic motor comprising: a stator that generates a traveling wave by applying a first driving voltage and a second driving voltage of a predetermined frequency; and a rotor that rotates by the traveling wave. In the circuit, a drive voltage output unit that outputs a first drive voltage and a second drive voltage of the predetermined frequency to the stator; and a phase difference between the second drive voltage and the first drive voltage gradually changes. A driving circuit for an ultrasonic motor, comprising: 2. The method according to claim 1, wherein the phase difference control means controls the phase difference so as to gradually change within a predetermined range when the ultrasonic motor is started or stopped. 2. A drive circuit for the ultrasonic motor according to claim 1. 3. The phase difference control means, wherein when the ultrasonic motor starts driving, the phase difference is substantially 0 ° to approximately 90 °.
3. The ultrasonic motor according to claim 2, wherein the phase difference is gradually reduced from approximately 90 ° to approximately 0 ° when the driving of the ultrasonic motor is stopped. The drive circuit of the sound wave motor. 4. An ultrasonic motor comprising: a stator that generates a traveling wave by applying a first driving voltage and a second driving voltage of a predetermined frequency; and a rotor that rotates by the traveling wave. A first driving voltage and a second driving voltage of the predetermined frequency are output to the stator, and a phase difference of the second driving voltage with respect to the first driving voltage gradually changes. A method for driving an ultrasonic motor, characterized in that: