JP3533322B2 - Ultrasonic motor drive circuit - Google Patents

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 piezoelectric body is attached to a ring-shaped elastic body to form a stator, and a rotor attached to the drive shaft makes pressure contact with this stator. Has been done.

A drive circuit of an ultrasonic motor supplies two-phase drive signals (sin wave and cos wave) having a predetermined frequency and a phase difference of 90 ° to the piezoelectric body. Due to the mechanical vibration of the piezoelectric body generated by the two-phase drive signals, ultrasonic vibration (traveling wave) in which the antinodes and nodes of the vibration move annularly along the elastic body is excited in the elastic body. The traveling wave rotates the rotor and the drive shaft that are pressed into contact with the elastic body.

When the ultrasonic motor is used, for example, in a so-called tilt mechanism of a steering device of an automobile, a telescopic mechanism, or the like, it operates by being supplied with power from a battery power source (for example, 12V) for the vehicle.

An example of a drive circuit for the ultrasonic motor is shown in FIG.
Shown in. As shown in FIG. 8, the drive circuit 130 includes a microcomputer 132, an oscillation circuit 134, a switching control circuit 136, a bandpass filter 140, a drive signal generation circuit 148 including an A phase amplification circuit 142 and a B phase amplification circuit 144. It

The microcomputer 132 outputs a drive frequency signal to the oscillator circuit 134, and the oscillator circuit 134 oscillates at the drive frequency designated by the microcomputer 132. The switching control circuit 136 outputs a switching signal to the A-phase amplifier circuit 142 and the B-phase amplifier circuit 144 at a predetermined timing. The A-phase amplifier circuit 142 and the B-phase amplifier circuit 144 convert a DC voltage (for example, 12V) supplied from a vehicle battery power source into an AC voltage corresponding to a predetermined driving frequency, and a piezoelectric body 141A of the ultrasonic motor 50.
Supply to 141B.

A-phase amplifier circuit 142, B-phase amplifier circuit 144
Are each provided with a transformer (not shown) (as an example, the winding ratio of the primary side coil to the secondary side coil is 1:18). A DC voltage of 12V is supplied from the battery power source. Then, a MOSFE as a switching element (not shown)
By turning on / off T in accordance with the switching signal input from the switching control circuit 36, the secondary coils of the respective transformers have a phase difference of 90 ° from each other and a boosted AC voltage (for example, 210 V). Is induced. This AC voltage is the piezoelectric body 1 of the ultrasonic motor 50.
The ultrasonic motor 50 is driven by being supplied to 41A and 141B, respectively.

FIG. 7 shows a circuit diagram of a drive circuit of an ultrasonic motor, which is schematically shown for explaining the boosting.

As shown in FIG. 7, the drive signal generating circuit 14 supplies the DC voltage of 12V supplied from the vehicle battery power source.
8 transformers A (the transformers (not shown) provided in the A-phase amplifier circuit 142 and the B-phase amplifier circuit 144, respectively, are schematically shown as transformer A)
The double-boosted AC voltage of 210 V is supplied to the ultrasonic motor 50.

As described above, in the case of boosting to a high voltage of about 210 V by one-step boosting by the transformer A, the voltage supplied to the ultrasonic motor 50 is controlled by switching control such as a so-called switching power supply. I can't.

Generally, the ratio of the input voltage to the output voltage of the transformer is equal to the winding ratio of the windings of the primary side coil and the secondary side coil of the transformer, so that when the voltage supplied to the primary side coil fluctuates. Under the influence, the voltage induced in the secondary coil also changes.

[0012] Further, the battery power source for a vehicle may have an unstable power source voltage due to the effect of turning the engine on or off. In such a case, as described above, the transformer A is used.
Since the voltage supplied to the primary coil of the ultrasonic motor 50 varies, the voltage induced in the secondary coil also varies.
The voltage supplied to it fluctuates.

Therefore, for example, if the voltage supplied to the ultrasonic motor 50 becomes too high, the ultrasonic motor 50 will be broken, and conversely, if the voltage supplied to the ultrasonic motor 50 becomes too low, the ultrasonic motor 50 will be damaged. There is a problem that will not rotate.

[0014]

SUMMARY OF THE INVENTION In consideration of the above facts, the present invention can stably supply a driving voltage to be supplied to an ultrasonic motor even if the power supply voltage supplied from a predetermined power supply fluctuates. The purpose is to obtain a drive circuit for an ultrasonic motor that can be used.

[0015]

According to a first aspect of the present invention, a DC voltage supplied from a predetermined power source is converted into an AC voltage corresponding to a predetermined driving frequency, and the AC voltage is converted into the AC voltage.
In a drive circuit of an ultrasonic motor that obtains a driving force by being supplied as a drive voltage signal to a piezoelectric body, a voltage conversion unit that transforms the DC voltage at least twice or more to obtain the AC voltage, and the drive voltage. Depending on the signal level of the signal
The duty ratio of the switching signal.
The duty control circuit and the first DC voltage transformation
Current to the voltage conversion means
Turn on and off based on the
Induces a boosted AC voltage to the voltage conversion means.
It is characterized by having a MOSFET and an AC / DC converter provided after the first transformation and before the final transformation to convert an AC voltage into a DC voltage.

According to the invention described in claim 1, a DC voltage supplied from a predetermined power source is converted into small <br/> Kutomo twice or more transformers has been AC voltage by the voltage converting means. Only
Also during two or more voltage transformations in the voltage conversion means
After the first transformation, before the final transformation, the AC voltage
There Ru is converted into a DC voltage by AC / DC converter.
The AC voltage generated by the final transformation is the drive voltage signal.
Is supplied to the piezoelectric body, which drives the ultrasonic motor.
To be done. Also, in the voltage conversion means, DC power from the power source
When the pressure is first transformed (ie
In this case, the voltage conversion means for turning the MOSFET on and off
Current is applied to the
The generated voltage becomes an AC voltage. Now turn on the MOSFET
The duty ratio of the switching signal for turning off and on is
Signal level of drive voltage signal in the duty control circuit
Can be changed according to. Therefore, the voltage conversion means
Converted AC voltage, or further voltage conversion means thereafter
AC voltage converted by the AC / DC converter
DC voltage generated by the conversion from the
Stable even if the supplied voltage fluctuates. in this way
The stable DC voltage is transformed by the voltage conversion means in the final transformation.
The AC voltage generated by the
The drive voltage (drive voltage signal) can be supplied to the ultrasonic motor, and the ultrasonic motor can be smoothly driven.

According to a second aspect of the present invention, the voltage conversion means is a transformer in which the output voltage changes according to the winding ratio of the primary side coil and the secondary side coil, and the voltage is gradually boosted. It is characterized by going.

According to the second aspect of the present invention, by using the transformer as the voltage converting means, it is possible to arbitrarily combine a plurality of transformers having different winding ratios to boost the voltage.

According to a third aspect of the present invention, the voltage converting means is a transformer in which the output voltage changes according to the winding ratio of the primary side coil and the secondary side coil, and the final stage transformer. It is characterized in that the transformation ratio in 1 is set to 1: 1.

According to the third aspect of the invention, by setting the transformation ratio in the final stage transformer to 1: 1 it is possible to suppress the loss during the final stage transformation and to stabilize the ultrasonic motor. Can be supplied with a drive voltage.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below 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 for converting 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 adhering 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. Has been done. An engineering plastic or the like is used as the slider 22 in order to obtain a stable frictional force and coefficient of friction, and the rotor 18 can be driven with high efficiency.

The elastic body 12 has a piezoelectric element 26 (see FIG. 3).
(See) is attached. As shown in FIG. 3, the piezoelectric element 26 has one end grounded and the other end 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. The output end of the bandpass filter 40 is connected to one input end of the microcomputer 32. The bandpass filter 40 detects the feedback signal output from the piezoelectric element 26 and outputs it to the microcomputer 32.

The ultrasonic motor 10 has a rotation sensor 4
6 is attached, and the output end of the rotation sensor 46 is connected to the other input end of the microcomputer 32.

The rotation sensor 46 is composed of a magnet (not shown), a hall element (not shown), etc., and detects changes in the magnetic flux on the surface of the magnet by means of the hall element.
Is rotated, the rotor 18 is transferred to the microcomputer 32.
It outputs a pulse signal with a cycle corresponding to the rotation speed of the.

One input end of the oscillation circuit 34 is connected to one output end of the microcomputer 32, and one input end of the switching control circuit 36 is connected to the other output end. 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 the drive frequency signal from the microcomputer 32.

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

The power input terminal of the A-phase amplifier circuit 42 and the power input terminal of the B-phase amplifier circuit 44 are connected to the power output terminal of the voltage generating circuit 38. A vehicle battery power source (12 V as an example) is connected to a power source input terminal of the voltage generation circuit 38, and a DC voltage supplied from the vehicle battery power source is transformed to transform the A-phase amplifier circuit 42 and the B-phase amplifier circuit. 44.

One output terminal of the A-phase amplifier circuit 42 is connected to one signal input terminal of the voltage generating circuit 38, and the other output terminal of the B-phase amplifier circuit 44 is branched to the other signal input terminal. One output end is connected. These signal input terminals are connected to the piezoelectric bodies 14A and 14B of the ultrasonic motor 10.
The drive voltage signals supplied to the respective terminals are input.

The circuit configuration of the voltage generating circuit 38 is shown in FIG. The voltage generating circuit 38 shown in FIG.
(As an example, the winding ratio of the primary side coil to the secondary side coil is 1: 6), the duty control circuit 114, the MOSFETs 110 and 112 as the switching elements, and the AC /
It is composed of the DC converter 121 and the like.

The middle point of the primary coil 120A of the transformer 120 is connected to one end of a capacitor 116 and a vehicle battery power source (indicated by Vcc in the figure) via a power line 118, and the other end of the capacitor 116 is connected. It is grounded.

One end of the primary coil 120A of the transformer 120 is connected to the drain of the MOSFET 110. The gate of the MOSFET 110 is connected to one output end of the duty control circuit 114, and
The source of T110 is grounded.

The other end of the primary coil 120A of the transformer 120 is connected to the drain of the MOSFET 112. The gate of the MOSFET 112 is connected to the other output end of the duty control circuit 114, and the MOSFET
The source of T112 is grounded.

Although not shown in FIG. 4, one input end of the duty control circuit 114 is connected to one output end branched from the A-phase amplifier circuit 42, and the other input end is connected to B. One output end branched from the phase amplifier circuit 44 is connected.

One end of the 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 the 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 other end of the coil 126 is connected to one end of a capacitor (for example, an electrolytic capacitor) 128, and the other end of the capacitor 128 is grounded. Furthermore, coil 1
The other end of 26 is branched and connected to the power input terminals of the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44, respectively. A DC voltage (about 70 V) obtained by boosting the voltage supplied from the vehicle battery power supply by about 6 times by the voltage generation circuit 38 is supplied to each power supply input terminal.

The other branched output end of the A-phase amplifier circuit 42 is connected to the piezoelectric body 14A of the ultrasonic motor 10 and converts the DC voltage supplied from the voltage generating circuit 38 into an AC voltage to generate a sine wave. A signal (sin wave) is supplied to the piezoelectric body 14A.

The other branched output end of the B-phase amplifier circuit 44 is connected to the piezoelectric body 14B of the ultrasonic motor 10 and converts the DC voltage supplied from the voltage generating circuit 38 into an AC voltage to generate A A sine wave signal (cos wave) having a 90 ° phase difference from the sine wave signal supplied by the phase amplifier circuit 42 is supplied to the piezoelectric body 14B. The other ends of the piezoelectric bodies 14A and 14B are grounded. The piezoelectric bodies 14A and 14B form the piezoelectric body 14 of the ultrasonic motor 10.

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 (as an example, the winding ratio of the primary side coil to the secondary side coil is 1: 3), and the middle point of the primary side coil 100A of the transformer 100 is: The power supply line 84 is connected to the power supply output terminal of the voltage generation circuit 38.

One end of the primary coil 100A of the transformer 100 is connected to the drain of a MOSFET 90 serving as a switching element, and the other end is connected to the drain of a 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 (as an example, the winding ratio of the primary side coil to the secondary side coil is 1:
3) is provided, and the primary coil 10 of the transformer 102 is provided.
At the midpoint of 2A, the voltage generating circuit 38 is connected via the power supply line 84.
It is connected to the power output terminal of.

One end of the primary coil 102A of the transformer 102 is connected to the drain of a MOSFET 94 serving 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 signal output terminals of the switching control circuit 36, respectively. MOSFET 90, 92, 94, 96
Are turned on / off in accordance with the switching signals A ₁ , A ₂ , B ₁ and B ₂ input from the switching control circuit 36. This switching signal causes the transformer 1
The DC voltage of about 70 V supplied from the voltage generating circuit 38 to the secondary coils 100B and 102B of 00 and 102 is about 3
An AC voltage (about 210 V) that is doubled is induced.

FIG. 1 shows a circuit diagram of a drive circuit of an ultrasonic motor, which is schematically shown to explain the boosting.

As shown in FIG. 1, a 12V DC voltage is supplied from the vehicle battery power source, and the MOSFET is generated by the switching signal output from the duty control circuit 114.
110 and 112 (the MOSFET 112 is not shown) are turned on and off, and a transformer B (corresponding to the transformer 120 in FIG. 4) boosts the voltage by about 6 times to obtain an AC voltage (about 70 V). This AC voltage is converted into a DC voltage (about 70V) by the AC / DC converter 121. That is, the diodes 122 and 124 (the diode 124 is not shown)
Is rectified by and is smoothed by the coil 126 and the capacitor 128 to obtain a DC voltage. Then, this DC voltage is applied to the transformer C.
An AC voltage (210 V) boosted by about 3 times (corresponding to the transformers 100 and 102 in FIG. 5) is supplied to the ultrasonic motor 10.

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

When the ultrasonic motor 10 is driven, a driving frequency signal is sent from the microcomputer 32 to the oscillation circuit 34.
Is output to. The oscillation circuit 34 starts oscillation at the drive frequency designated by the microcomputer 32.

In the voltage generating circuit 38, a voltage is supplied from the vehicle battery power source to the primary coil 120A of the transformer 120, and further the piezoelectric body 14A of the ultrasonic motor 10 is supplied.
The drive voltage signals supplied to 14B are input to the duty control circuit 114 of the voltage generation circuit 38, respectively. Then, the duty ratio of the switching signal input from the duty control circuit 114 to the gates of the MOSFETs 110 and 112 changes according to the signal level of the drive voltage signal. This switching signal causes the transformer 1
The current to the primary coil 120A of 20 is turned on and off,
An AC voltage (about 70V) boosted by about 6 times is induced in the secondary coil 120B of the transformer 120. The AC voltage is full-wave rectified by the diodes 122 and 124, further smoothed by the coil 126 and the capacitor 128, and the boosted DC voltage (about 70 V) is supplied to the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44.

The duty ratio of the switching signal output from the duty control circuit 114 depends on the signal level of the drive voltage signal supplied to the piezoelectric bodies 14A and 14B of the ultrasonic motor 10 and is point D shown in FIG. Change so that the voltage of is stable. Therefore, the voltage at point D is almost constant (about 70
V).

In the switching control circuit 36, the MOSFETs 90 and 9 of the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44 are included.
Switching signals A ₁ , A ₂ , B ₁ and B ₂ for turning on / off ₂ , 94 and 96 are output.

This switching signal is supplied to one of the MOSFETs 90, 92, 94 and 96 as shown in FIG.
One of the MOSFETs is turned on and off at a predetermined duty ratio, the other MOSFETs are turned off, and the MOSFETs to be turned on and off are set to the frequency f of the drive signal at the start of driving.
MOSFETs 90, 9 are provided for each quarter of the cycle of s.
It is a signal for switching in the order of 4, 92, and 96. As a result, the secondary side coils 100B of the transformers 100 and 102,
102B has the frequency fs at the start of driving.
In addition, an AC voltage (about 210 V) having a phase difference of 90 ° and boosted about three times is induced.

At this time, even if the power supply voltage supplied from the vehicle battery power supply to the voltage generating circuit 38 fluctuates due to the effect of turning the engine on or off, as described above,
Since the DC voltage output from the voltage generation circuit 38 is approximately constant at 70V, the drive voltage supplied to the ultrasonic motor 10 is also approximately constant at 210V.

By supplying this AC voltage 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.

The vibration of the elastic body 12 is caused by the piezoelectric element 26.
Is converted into an electric signal by the and is input to the microcomputer 32 as a feedback signal via the bandpass filter 40. Furthermore, a rotation pulse signal corresponding to the rotation speed of the rotor 18 is output from the rotation sensor 46 attached to the ultrasonic motor 10 to the microcomputer 32.
Entered in.

In the microcomputer 32, while monitoring the feedback signal and the rotation pulse signal, the frequency of the drive signal gradually approaches the optimum drive frequency of the ultrasonic motor 10 and coincides with the optimum drive frequency, and further follows the optimum drive frequency. , The timing of turning on / off the MOSFETs 90, 92, 94, 96 is controlled to control the frequency of the drive signal.

As described above, the voltage supplied from the vehicle battery power source is boosted by the transformer B by about 6 times.
The DC voltage converted by the AC / DC converter 121 is output from the duty control circuit 114.
The duty ratio of the switching signal
Drive voltage signal supplied to the piezoelectric bodies 14A and 14B
Change so that the voltage stabilizes according to the signal level of
This makes it possible to stabilize the engine regardless of the effect of turning it on and off. Therefore, the drive voltage supplied to the ultrasonic motor 10 can be stably supplied.

When the winding ratio of the primary side coil and the secondary side coil of the final stage transformer is set to 1: 1, the driving voltage supplied to the ultrasonic motor 10 is further stabilized.

In this embodiment, the transformer B and C are used to boost the voltage in two stages, the transformer B boosts the voltage approximately 6 times, the transformer C boosts the voltage approximately 3 times, and the total voltage is boosted approximately 18 times. Alternatively, the winding ratios of the transformers B and C can be freely selected, and the target drive voltage may be obtained by boosting the voltage by the transformer B and reducing the voltage by the transformer C. Further, the boosting is not limited to the two-stage boosting, and a transformer may be further provided to boost the boosting to the three-stage and the four-stage.

[Brief description of drawings]

FIG. 1 is a part of a drive circuit for an ultrasonic motor according to the present invention,
FIG. 3 is a circuit diagram schematically showing an ultrasonic motor and a vehicle battery power supply.

FIG. 2 is a partial cross-sectional perspective view showing a schematic configuration of an ultrasonic motor.

FIG. 3 is a block diagram showing a schematic configuration of a drive circuit for an ultrasonic motor and an ultrasonic motor according to the present invention.

FIG. 4 is a circuit diagram showing a voltage generation circuit in a drive circuit for an ultrasonic motor.

FIG. 5 is a circuit diagram showing a drive signal generation circuit in the drive circuit of the ultrasonic motor.

FIG. 6 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 generating circuit.

FIG. 7: Part of a conventional ultrasonic motor drive circuit,
FIG. 3 is a circuit diagram schematically showing an ultrasonic motor and a vehicle battery power supply.

FIG. 8 is a block diagram showing a schematic configuration of a conventional ultrasonic motor drive circuit and an ultrasonic motor.

[Explanation of symbols]

10 Ultrasonic motor 30 drive circuit 32 microcomputer 34 Oscillation circuit 36 Switching control circuit 38 Voltage generation circuit 40 bandpass filter 42 A-phase amplifier circuit 44 B-phase amplifier circuit 100, 102, 120 transformer (voltage conversion means) 121 AC / DC converter

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-115784 (JP, A) JP-A-4-127875 (JP, A) Actually opened 55-74286 (JP, U) Actually opened 55- 102392 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02N 2/00 H02M 3/00

Claims (3)

(57) [Claims] 1. A DC voltage supplied from a predetermined power source,
In the drive circuit of the ultrasonic motor, the drive voltage is converted into an AC voltage according to a predetermined drive frequency, and the AC voltage is supplied to the piezoelectric body as a drive voltage signal to obtain a drive force. Voltage conversion means for converting the voltage at least twice to obtain the AC voltage , and switching according to the signal level of the drive voltage signal.
Duty control circuit that changes the duty ratio of a signal
And to the voltage conversion means that transforms the DC voltage for the first time.
The current is turned on and off based on the switching signal,
To the voltage conversion means for converting the DC voltage for the first time
A drive circuit for an ultrasonic motor, comprising: a MOSFET that induces a boosted AC voltage ; and an AC / DC converter that converts the AC voltage, which is provided after the first and last transformation, into a DC voltage. 2. The voltage converting means includes a primary coil and a secondary coil.
2. The ultrasonic motor drive circuit according to claim 1, wherein the transformer is an transformer whose output voltage changes according to the winding ratio of the secondary coil, and which gradually increases the voltage. 3. The voltage converting means comprises a primary coil and a secondary coil.
2. The drive circuit for an ultrasonic motor according to claim 1, wherein the transformer has an output voltage that changes in accordance with the winding ratio of the secondary coil, and the transformer in the final stage has a transformation ratio of 1: 1.