JPH11191978A - Ultrasonic motor drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a radio noise, by suppressing a high-frequency oscillation being generated when a switching element that is connected to the primary coil of a transformer is turned on. SOLUTION: A voltage generation circuit 38 supplies voltage from a power supply Vcc to a primary side coil 60A of a transformer 60, inputs a switching signal from a duty control circuit 58 to the gate of MOSFETs 50 and 52 at a specific timing and turns off current to the primary side coil 60A of the transformer 60. An AC voltage is induced at a secondary side coil 60B of the transformer 60, is subjected to all wave rectification by diodes 62 and 64, and is smoothed by a transformer 66 and a capacitor 68, and then a DC voltage is supplied to A and B phase amplification circuits 42 and 44. At this time, a resonance circuit is formed by the capacitance of the MOSFET 50, a primary side coil 60A of the transformer 60, and a capacitor 72, and is oscillated at a high frequency, thus generating a radio noise. However, ferrite beads 54 and 56 do not pass 10 MHz or higher frequency component, thus suppressing oscillation and preventing the radio noise 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 the ultrasonic motor is used, for example, in a so-called tilt mechanism or a telescopic mechanism of a steering device of an automobile, a driving circuit of the ultrasonic motor and the ultrasonic motor are used together as shown in FIG. Grounded to the body of the vehicle. For this reason, a loop is formed by the drive circuit, the ultrasonic motor, and the vehicle body, and the current from the drive circuit flows through the ultrasonic motor to the vehicle body and returns to the drive circuit. Generates noise.

In order to reduce the noise generated from the speaker of the radio, as shown in FIG. 4, when the ultrasonic motor is fixed to the vehicle side, the ultrasonic motor is floated to be electrically insulated. There is a technique for reducing radio noise generated from a speaker of a radio by fixing the current from a drive circuit to prevent the current from a drive circuit from flowing to a body of a vehicle through an ultrasonic motor and returning to the drive circuit.

The ultrasonic motor is supplied with a drive voltage from a voltage generating circuit, and the voltage generating circuit has various configurations. As an example, a voltage generating circuit (so-called switching) configured to obtain a DC voltage by full-wave rectifying and smoothing an AC voltage induced in a secondary coil of the transformer by turning on and off a current flowing through a primary coil of the transformer. Power supply) is generally widely known.

FIG. 5 shows an example of the voltage generating circuit having the above configuration. In the voltage generating circuit 130 of FIG. 5, the middle point of the primary coil 120A of the transformer 120 is connected to the power supply line 118.
Is connected to one end of a capacitor 116 and a power supply (not shown) (shown by Vcc in the figure).
The other end of 16 is grounded. Both ends of the primary coil 120A are grounded via MOSFETs 110 and 112.

When the MOSFETs 110 and 112 are turned on and off at a predetermined timing by a switching signal from the duty control circuit 114, an AC voltage is induced in the secondary coil 120B of the transformer 120. This AC voltage is full-wave rectified by diodes 122 and 124, and the coil 1
26, DC voltage is obtained by smoothing with a capacitor 128.

As described above, the duty control circuit 11
4 by the switching signal from the MOSFET 11
By turning on and off 0 and 112, a DC voltage is supplied to drive the ultrasonic motor.

However, since the MOSFET 110 (or 112) generally has a capacitance as shown in FIG. 6A, the MOSFET 110 (or 112) actually has a primary side of the transformer as shown in FIG. It is represented by an equivalent circuit in which the coil 120A, the capacitor 116, and the capacitance of the MOSFET 110 are connected in series, and becomes a so-called LC resonance circuit.

For this reason, the MOSFET 110 (or 1
12), the MO is turned on as shown in FIG.
The drain voltage of the SFET 110 (or 112) is distorted and oscillates at a high frequency. This high-frequency oscillation generates radiation noise from the drive circuit and wire conduction noise from the wire connecting the drive circuit and the ultrasonic motor,
Noise is generated from the radio speakers. In order to reduce the radiation noise and the wire conduction noise generated by the oscillation at the high frequency, there are methods such as shielding the drive circuit or putting a filter in all the wires, but there is a disadvantage that the cost is high.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has as its object to obtain a drive circuit for an ultrasonic motor which has a simple structure and can suppress radio frequency oscillation to reduce radio noise. Is the purpose.

[0013]

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. An AC voltage is induced, and the AC voltage is rectified and smoothed to obtain a DC voltage for driving the ultrasonic motor. It is characterized by having oscillation suppression means for suppressing high-frequency oscillation generated when the element is turned on.

The invention according to claim 2 of the present invention is characterized in that the oscillation suppressing means is a filter element which is connected in series to the switching element and prevents high frequency components from passing therethrough.

According to the first and second aspects of the present invention,
A filter element is connected in series to the switching element. For this reason, it is possible to prevent the high frequency generated when the switching element is turned on from being passed by the filter element, and to suppress the high frequency oscillation and reduce the radio noise.

[0016]

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

FIG. 2 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 an annular shape 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 body 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 other 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.

The microcomputer 32 has one output terminal connected to the oscillation circuit 34 and the other output terminal connected to one input terminal of the switching control circuit 36. 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 oscillates at 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 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 a voltage generator 38, and power is supplied from the voltage generator 38. You. FIG. 1 shows a circuit configuration of the voltage generating circuit 38.

The voltage generating circuit 38 shown in FIG.
0 is connected to one end of a capacitor 72 and a power source (not shown in the drawing, indicated by Vcc) via a power supply line 74 at the middle point of the primary coil 60A of the transformer 60. The end is grounded.

One end of a primary coil 60A of the transformer 60 is connected to one end of a ferrite bead 54 as a filter element, and the other end is connected to one end of a ferrite bead 56. The ferrite beads 54, 56
Is used that does not pass high frequency, for example, a frequency component of 10 MHz or more. Ferrite beads 5
4 has a MOSFET 50 as a switching element.
Connected to the drain of The gate of the MOSFET 50 is connected to one output terminal of the duty control circuit 58, and the source of the MOSFET 50 is grounded.

The other end of the ferrite bead 56 is connected to the drain of the MOSFET 52 as a switching element. The gate of the MOSFET 52 is connected to the other output terminal of the duty control circuit 58,
The source of T52 is grounded.

One end of the secondary coil 60B of the transformer 60 is connected to the anode of a diode 62 as a rectifying element, and the other end is connected to the anode of a diode 64 as a rectifying element. The middle point of the secondary coil 60B of the transformer 60 is grounded.

The cathodes of the diodes 62 and 64 are connected to one end of a coil 66 as an inductance element. The other end of the coil 66 is connected to one end of a capacitor 68, and the other end of the capacitor 68 is grounded. Further, the other end of the coil 66 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.

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 configuration of the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44 is 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 amplifying 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, and 96 are connected to the switching control circuit 36, respectively, and the MOSFETs 90, 92, 94, and 96 each have 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, a driving frequency signal is supplied from the microcomputer 32 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, a voltage is supplied from the power supply Vcc to the primary side coil 60A of the transformer 60, and the voltage is supplied from the duty control circuit 58 to the MOS transistor at a predetermined timing.
A switching signal is input to the gates of the FETs 50 and 52, and the current to the primary coil 60A of the transformer 60 is turned on and off. The secondary coil 6 of the transformer 60
0B is induced in the AC voltage, the AC voltage is full-wave rectified by diodes 62 and 64, and a transformer 66 and a capacitor 6
The DC voltage is smoothed at 8 and supplied to the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44.

At this time, as described above, the MOSFET
50 capacitance, primary coil 6 of transformer 60
0A, a resonant circuit is formed by the capacitor 72, and a high frequency (1
Oscillation occurs at about 0 MHz) and radio noise is generated. However, in the present embodiment, the ferrite beads 54 (or 56) do not pass a frequency component of 10 MHz or more, so that oscillation is suppressed and radio noise is generated. There is no.

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. 10, this switching signal turns on or off one of the MOSFETs 90, 92, 94, and 96 at a predetermined duty ratio, and turns off and on the other MOSFETs. The MOSFETs 90, 9 are turned on every 1/4 of the cycle of the frequency fs of the drive signal at the start of driving.
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 driving 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 driving 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.

As described above, the primary side coil 60A of the transformer 60 of the voltage generating circuit 38 and the MOSFETs 50 and 52
By providing ferrite beads 54 and 56 between
Oscillation at a high frequency generated when the OSFETs 50 and 52 are turned on can be suppressed, and radio noise can be reduced.

Further, by using the present invention together with the above-mentioned technique of mounting the ultrasonic motor and fixing the ultrasonic motor in a floating state, and fixing the ultrasonic motor in an electrically insulated state to reduce radio noise, Radio noise can be reduced comprehensively.

In the present embodiment, the present invention is applied to the voltage generating circuit 38. However, the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44 also use the MOS as a switching element as described above.
The present invention may be applied to the A-phase amplifying circuit 42 and the B-phase amplifying circuit 44 because the configuration includes the FET and the transformer.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a voltage generation circuit in a drive circuit of an ultrasonic motor 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 a drive circuit of the ultrasonic motor.

FIG. 4 is an explanatory diagram for explaining a loop current generated in an ultrasonic motor and a drive circuit of the ultrasonic motor.

FIG. 5 is a circuit diagram showing a voltage generation circuit in a conventional ultrasonic motor drive circuit.

FIG. 6A is a circuit diagram for explaining a part of a conventional actual voltage generating circuit. (B) is an equivalent circuit diagram of the circuit shown in (a).

FIG. 7A is a circuit diagram illustrating a part of an actual voltage generating circuit according to the present invention. (B) is (a)
3 is an equivalent circuit diagram of the circuit shown in FIG.

FIG. 8A is a waveform diagram of a drain voltage of a conventional MOSFET. (B) is a waveform diagram of the drain voltage of the MOSFET according to the present invention.

FIG. 9 is a circuit diagram illustrating an example of a drive signal generation circuit.

FIG. 10 is a diagram illustrating a switching signal output from a switching control circuit and a drive signal induced by a transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ultrasonic motor 30 Drive circuit 32 Microcomputer 34 Oscillation circuit 36 Switching control circuit 38 Voltage generation circuit 42 A-phase amplifier circuit 44 B-phase amplifier circuit 50, 52 MOSFET (switching element) 54, 56 Ferrite bead (oscillation suppression means) 58 Duty control circuit 60 Transformer 62, 64 Diode 66 Coil 68 Capacitor

Claims (2)

[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 drive circuit for an ultrasonic motor that is electrically insulated and fixed to a fixed member, rectifies and smoothes the AC voltage to obtain a DC voltage for driving the ultrasonic motor, generated when the switching element is turned on. A driving circuit for an ultrasonic motor, comprising: an oscillation suppressing means for suppressing oscillation at a high frequency. 2. The drive circuit for an ultrasonic motor according to claim 1, wherein said oscillation suppressing means is a filter element connected in series to said switching element to prevent a high-frequency component from passing therethrough.