JPH11191982A - Drive circuit of ultrasonic motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an audible sound from being generated by magnetically shielding a coil so that magnetic induction to each oscillation circuit due to a magnetic noise being generated from the coil that is provided at each voltage- generating circuit can be suppressed. SOLUTION: When ultrasonic motors 10 and 70 are driven simultaneously, coil of a voltage-generating circuit of the ultrasonic motor 10 and that of a voltage-generating circuit of the ultrasonic motor 70 may generate a magnetic noise. However, the magnetic noise is absorbed by permaloy for magnetically shielding the coils, thus preventing the magnetic noise from being magnetically induced to oscillation circuits 34 and 64, hence stabilizing an oscillation frequency and preventing an audible sound from being generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

When used in a so-called tilt mechanism or a telescopic mechanism of an automobile steering system, the ultrasonic motor has an ultrasonic motor, an oscillation circuit, a drive circuit, and the like. The oscillation circuit and the drive circuit are provided on the same substrate.

FIG. 4 shows an example of the ultrasonic motor and the driving circuit of the ultrasonic motor having the above configuration.

As shown in FIG. 4, the ultrasonic motors 10, 70
Are connected to driving circuits 30 and 60, respectively, and the driving circuits 30 and 60 are connected to oscillation circuits 34 and 64 and a microcomputer 32, respectively. Then, a predetermined drive frequency signal is output from the microcomputer 32 to the oscillation circuits 34 and 64, and the drive circuits 30 and 60
When the switching signal is output at a predetermined timing, the ultrasonic motors 10 and 70 are driven. Also,
The microcomputer 32 and the oscillating circuits 34 and 64 are supplied with power from control power supplies (for example, 5 V) 52 and 62, respectively.
(For example, 12 V).

The driving circuit 30 has a configuration as shown in FIG. 3 as an example (the driving circuit 60 has the same configuration). The drive circuit 30 includes a switching control circuit 36, an A-phase amplification circuit 42, a B-phase amplification circuit 44, a voltage generation circuit 38, and a band-pass filter 40. The voltage generating circuit 38 supplies a DC voltage obtained by boosting the DC voltage of 12 V supplied from the constant voltage power supply 50 to the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44.

FIG. 7 shows an example of the voltage generating circuit 38. The voltage generating circuit 38 includes a constant voltage power supply 50 (Vc in the figure).
c) is switched by the duty control circuit 58 of the MOSFETs 54 and 56 as switching elements, thereby inducing a boosted AC voltage to the secondary coil 80B of the transformer 80. Then, the current is rectified by diodes 74 and 76, and
6. The DC voltage smoothed by the capacitor 68 is supplied to the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44.

When the ultrasonic motors 10 and 70 are driven simultaneously, magnetic noise is generated from the coil 66 of the drive circuit 30 and a coil (not shown) of the drive circuit 70 (a coil corresponding to the coil 66 of the drive circuit 30). There is a problem that magnetic induction is generated in the respective oscillating circuits, the oscillating frequency causes frequency modulation, and an audible sound is generated from the ultrasonic motor.

[0010]

In view of the above-mentioned facts, the present invention provides a method of magnetic induction between oscillating circuits due to magnetic noise generated from coils of a voltage generating circuit even when a plurality of ultrasonic motors are driven simultaneously. It is an object of the present invention to provide an ultrasonic motor drive circuit capable of suppressing the occurrence of an audible sound by suppressing noise.

[0011]

According to the first aspect of the present invention, a switching element is connected to a primary coil of a transformer, and the switching element is turned on and off to connect to a secondary coil of the transformer. Inducing an AC voltage, rectifying the AC voltage, and smoothing with a coil and a capacitor to obtain a DC voltage for driving the ultrasonic motor, and a frequency corresponding to the driving frequency of the ultrasonic motor. A drive circuit for an ultrasonic motor having an oscillation circuit for oscillating, wherein when driving a plurality of ultrasonic motors at the same time, the oscillation of each other due to magnetic noise generated from a coil provided in each of the voltage generation circuits. A magnetic shield member for magnetically shielding the coil is provided so as to suppress magnetic induction to a circuit.

According to the first aspect of the present invention, the coils provided in the voltage generating circuits of the respective ultrasonic motor drive circuits are magnetically shielded by the magnetic shield members. For this reason, it is possible to suppress the magnetic induction generated in the respective oscillation circuits, and it is possible to prevent the generation of an audible sound with a stable oscillation frequency.

The invention according to a second aspect of the present invention is characterized in that the power supplies to the oscillation circuits of the respective ultrasonic motors are independent of each other.

According to the second aspect of the present invention, the power supply to the oscillation circuit of each ultrasonic motor is made independent, so that the oscillation frequency is stabilized. Therefore, the oscillation frequency can be further stabilized by using the technique of magnetically shielding the coil described in claim 1 and the technique of making the power supplied to the oscillation circuit independent.

According to a third aspect of the present invention, the magnetic induction suppressing means is permalloy or ferrite.

According to the third aspect of the present invention, the coil provided in the voltage generating circuit of the ultrasonic motor driving circuit is magnetically shielded with permalloy or ferrite.
Therefore, a drive circuit can be configured with a simple configuration and at low cost.

[0017]

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

FIG. 4 shows an example of a schematic configuration of a plurality of ultrasonic motors and a drive circuit of the ultrasonic motor. One branched output terminal of the constant voltage power supply 50 is further branched and connected to the input terminal of the control power supply 52 and the power supply input terminal of the drive circuit 30, and the other branched output terminal is further branched. Connected to the control power supply 62 and the power supply input terminal of the drive circuit 60. The constant voltage power supply 50 is 12V
Supply a DC voltage.

One branched output terminal of the control power supply 52 is connected to a power input terminal of the microcomputer 32, and the other branched output terminal is connected to a power input terminal of the oscillation circuit 34. The control power supply 52 converts the 12V DC voltage supplied from the constant voltage power supply 50 to a 5V DC voltage.

One drive signal output terminal of the microcomputer 32 is connected to a drive signal input terminal of the oscillation circuit 34, and the other drive signal output terminal is connected to a drive signal input terminal of the oscillation circuit 64. One switching signal output terminal of the microcomputer 32 is connected to the drive circuit 30.
, And the other switching signal output terminal is connected to the switching signal input terminal of the drive circuit 60. Microcomputer 32
Outputs a driving signal to the oscillation circuits 34 and 64 and outputs a switching signal to the driving circuits 30 and 60 at a predetermined timing.

The drive frequency signal output terminal of the oscillation circuit 34
It is connected to the drive frequency signal input terminal of the drive circuit 30. The oscillation circuit 34 is supplied with power from the control power supply 52 and oscillates at a predetermined drive frequency according to a drive signal from the microcomputer 32. The drive circuit 30 is connected to the ultrasonic motor 10 and supplies a predetermined drive voltage to drive the ultrasonic motor 10.

The output terminal of the control power supply 62 is connected to the power input terminal of the oscillation circuit 64. The control power supply 62 converts the 12V DC voltage supplied from the constant voltage power supply 50 into a 5V DC voltage.

The drive frequency signal output terminal of the oscillation circuit 64
It is connected to the drive frequency signal input terminal of the drive circuit 60. The oscillation circuit 64 is supplied with electric power from the control power supply 62 and oscillates at a predetermined driving frequency according to a driving signal from the microcomputer 32. The drive circuit 60 is connected to the ultrasonic motor 70 and supplies a predetermined drive voltage to drive the ultrasonic motor 70.

Although not shown in FIG. 4, in addition to the above, a feedback signal from the ultrasonic motors 10 and 70 described later and a rotation pulse signal are input to the microcomputer 32.

FIG. 2 shows a traveling wave type ultrasonic motor 10. 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. 3).
Reference) is affixed. As shown in FIG. 3, 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 rotation pulse signal input terminal of the microcomputer 32.

The rotation sensor 46 includes a magnet (not shown) and a Hall element (not shown), and detects a change in magnetic flux on the surface of the magnet with the Hall element.
Rotates, the microcomputer 18 sends the rotor 18
And outputs a pulse signal having a cycle corresponding to the rotation speed.

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 driving pulse to the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44 while switching the drive pulse according to the oscillation frequency oscillated from the oscillation circuit 34.

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 generation circuit 38. An input terminal of the voltage generation circuit 38 is connected to an output terminal of the constant voltage power supply 50 shown in FIG. 4, and boosts a voltage of 12 V supplied from the constant voltage power supply 50 to a predetermined AC voltage, and further rectifies the voltage. , And supplies the power to the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44 after boosting to a predetermined DC voltage.

The circuit configuration of the voltage generating circuit 38 is as shown in FIG. The voltage generating circuit 38 includes a transformer 120, and the primary coil 1 of the transformer 120
At the midpoint of 20A, the capacitor 11 is connected via the power line 118.
6 and a vehicle battery power supply (represented by Vcc in the figure), 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 rectifying element, and the other end is connected to a diode 1 as a rectifying element.
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 coil 126 has a winding portion covered with a permalloy 127 (see FIG. 8) as a magnetic shield member. Permalloy 127 is an alloy having a high magnetic permeability, and absorbs a magnetic field generated by a current flowing through the coil 126. 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 the A-phase amplification circuit 42,
It is connected to one input terminal of the B-phase amplifier circuit 44, and a DC voltage is supplied from the voltage generating circuit 38 to the input terminal.

The A-phase amplification circuit 42 is connected to the piezoelectric body 14A of the ultrasonic motor 10, and supplies a sine wave signal (sine wave) to the piezoelectric body 14A. The B-phase amplifier circuit 44 is connected to the piezoelectric body 14B of the ultrasonic motor 10,
4B and the sine wave signal supplied by the A-phase
Sine wave signals (cos waves) having different phases are supplied. The other ends of the piezoelectric bodies 14A and 14B are grounded. The piezoelectric members 14A and 14B of the ultrasonic motor 10
Is configured.

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

The structure of the ultrasonic motor 70 and the drive circuit 60 is as follows.
0 has the same configuration as that of FIG.

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.
Output to The oscillation circuit 34 is a microcomputer 3
2. Oscillation starts at the drive frequency specified by 2.

In the voltage generating circuit 38, the primary coil 1 of the transformer 120 is supplied from a constant voltage power supply (represented by Vcc in the figure).
20A is supplied with a voltage and the duty control circuit 114
A switching signal is input to the gates of the MOSFETs 110 and 112 at a predetermined timing from the
The current to the primary coil 120A of 0 is turned on and off.
Then, an AC voltage is induced in the secondary coil 120B of the transformer 120, and the AC voltage is
The DC voltage is supplied to the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44 after being subjected to full-wave rectification at 24 and smoothed by the coil 126 and the capacitor 128. At this time, magnetic noise may be generated in the coil 126. However, since the magnetic noise is generated by the permalloy 127, the influence of the magnetic noise on other circuits is suppressed.

In the switching control circuit 36, the MOSFETs 90 and 9 of the A-phase amplification circuit 42 and the B-phase amplification circuit 44
It outputs switching signals A ₁ , A ₂ , B ₁ , and B ₂ for turning on, off, and ₂ , ₂ , 94, 96, respectively.

As shown in FIG. 6, this switching signal is applied to one of the MOSFETs 90, 92, 94 and 96.
And the other MOSFETs are turned off at a predetermined duty ratio, and the other MOSFETs are turned off.
MOSFETs 90, 9 every 1/4 of the cycle of s
The signal is switched in the order of 4, 92, 96. Thereby, the secondary coil 100B of the transformers 100 and 102,
In 102B, each frequency is the frequency fs at the start of driving,
In addition, an AC drive signal having a phase difference of 90 ° is 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.

When the ultrasonic motor 70 is driven, it is driven in the same manner as the ultrasonic motor 10, and a detailed description is omitted.

Here, when the ultrasonic motor 10 and the ultrasonic motor 70 are driven simultaneously, the coil 126 of the voltage generating circuit 38 of the ultrasonic motor 10 and the ultrasonic motor 7
A coil (not shown) of the voltage generator circuit (not shown) of 0 (corresponding to the coil 126 of the voltage generator circuit 38) may generate magnetic noise (see FIG. 9A).
Magnetic noise is absorbed by a permalloy 127 that magnetically shields the coil 126 and a permalloy not shown that magnetically shields a coil not shown (see FIG. 9B). For this reason, magnetic noise is generated by the oscillation circuits 34 and 6 of each other.
4 can be prevented from being magnetically induced, and the oscillation frequency is stabilized, so that no audible sound is generated.

Since the power supplied to the oscillation circuits 34 and 64 is supplied independently from the control power supplies 52 and 62, the fluctuation of the oscillation frequency due to noise to the control power supply is reduced, and the oscillation frequency is stabilized. I do.

In this embodiment, permalloy has been described as an example of the magnetic shield member, but ferrite may be used instead of permalloy. Ferrite is a magnetic material of metal oxide, sintered as ceramic, and has the property of absorbing magnetic noise, so that the same effect as permalloy can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a voltage generation circuit in an ultrasonic motor drive circuit according to the present invention.

FIG. 2 is a partially sectional perspective view showing a schematic configuration of an ultrasonic motor.

FIG. 3 is a block diagram illustrating a schematic configuration of an ultrasonic motor and an ultrasonic motor drive circuit.

FIG. 4 is a block diagram illustrating a schematic configuration of a plurality of ultrasonic motors and an ultrasonic motor drive circuit.

FIG. 5 is a circuit diagram illustrating an example of a drive signal generation circuit.

FIG. 6 is a diagram illustrating a switching signal output from a switching control circuit and a drive signal induced by a transformer.

FIG. 7 is a circuit diagram showing a voltage generation circuit in a conventional ultrasonic motor drive circuit.

FIG. 8 is a perspective view showing a coil which is magnetically shielded with permalloy.

9A is an explanatory diagram for explaining magnetic noise when the coil is not magnetically shielded, and FIG. 9B is an explanatory diagram for explaining magnetic noise when the coil is magnetically shielded.

[Explanation of symbols]

 10, 70 Ultrasonic motor 30, 60 Drive circuit 32 Microcomputer 34, 64 Oscillation circuit 38 Voltage generation circuit 50 Constant voltage power supply 52, 62 Control power supply 110, 112 Switching element 114 Duty control circuit 120 Transformer 122, 124 Diode 126 Coil 127 Permalloy (magnetic shield member) 128 Capacitor

Claims (3)

[Claims] 1. A switching element is connected to a primary coil of a transformer, and an AC voltage is induced in a secondary coil of the transformer by turning on and off the switching element.
A voltage generating circuit that rectifies the AC voltage and obtains a DC voltage for driving the ultrasonic motor by smoothing with a coil and a capacitor; and an oscillation circuit that oscillates at a frequency corresponding to a driving frequency of the ultrasonic motor. A driving circuit of the ultrasonic motor, wherein when driving a plurality of ultrasonic motors at the same time, magnetic induction to each of the oscillation circuits by magnetic noise generated from a coil provided in each of the voltage generating circuits. A driving circuit for an ultrasonic motor, comprising: a magnetic shield member for magnetically shielding the coil so as to suppress the coil. 2. The drive circuit for an ultrasonic motor according to claim 1, wherein the power supplied to the oscillation circuit of each ultrasonic motor is independent. 3. The drive circuit according to claim 1, wherein the magnetic shield member is made of permalloy or ferrite.