JP2866534B2 - 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 electric circuit for driving an ultrasonic motor at a low speed.

[0002]

2. Description of the Related Art Generally, a ring-shaped traveling wave type ultrasonic motor has a feature that a low speed and a high torque can be obtained as compared with an electromagnetic motor. Ultrasonic motors have been put to practical use in various fields by taking advantage of their characteristics. For example, in the field of cameras, ultrasonic motors have already been put into practical use as driving sources for driving photographing lenses.

On the other hand, the ring-shaped traveling wave type ultrasonic motor is rotated between a posture in which a mirror housing for holding a mirror main body by a retractable door mirror of an automobile and a retracted posture with respect to a vehicle body. When the mirror housing is used as a drive source of a mechanism for driving the mirror housing, the operation of the mirror housing is too rapid when the motor is directly connected, which causes a problem that the mirror housing is not practical.

As described above, even when an ultrasonic motor capable of rotating at a lower speed than that of an electromagnetic motor is used, the operating speed of a driven object may be too high depending on the application. In such a case, providing the speed reduction mechanism on the output side of the ultrasonic motor causes an increase in the size and cost of the device,
It is not preferable because the characteristics of the ultrasonic motor cannot be utilized. Therefore, instead of using such a mechanical method, the ultrasonic motor is intermittently driven by performing circuit control so as to generate an alternating current having a pause every minute time, and the ultrasonic motor is apparently rotated at a low speed. A driving method has been proposed.

[0005]

The ring-shaped traveling wave type ultrasonic motor comprises a stator having a piezoelectric element adhered to the back surface of an elastic ring, and a rotor pressed against the surface of the stator. A traveling wave is generated on the surface of the stator by applying voltages having a phase difference of 90 ° to opposing electrodes provided separately on the piezoelectric element. When the traveling wave is generated, the rotor is driven to rotate by frictional force. I have. However, since the driving force of the rotor is obtained from the frictional force as described above, the moment of inertia may suddenly act on the rotor during start-up and stop, and the rotor may slip on the stator. Therefore, when the ultrasonic motor is intermittently driven, the rotor repeatedly starts and stops with respect to the stator, so that the rotor continuously slips, which causes a problem that a slip noise is generated.

Accordingly, a technical problem to be solved by the present invention is to provide a circuit for driving an ultrasonic motor at a low speed and capable of reducing slip noise.

[0007]

In order to solve the above-mentioned technical problems, a driving circuit for an ultrasonic motor according to the present invention comprises a first circuit for generating an alternating current having a sine wave curve as a driving current. A drive circuit for an ultrasonic motor having a drive current generation circuit and a second drive current generation circuit for generating an alternating current having a cosine wave curve having a phase different from that of the sine wave current by 90 °, as follows: It is characterized by having been constituted.

That is, while being connected to the first and second drive current generation circuits, a minute drive time and a pause time are alternately set, and the drive current from the first and second drive current generation circuits is set to the drive time. A timer circuit that generates only the clock signal. And while being connected to the first and second drive current generating circuits, the frequency of the drive current is set to a value lower than the resonance frequency of the ultrasonic motor on the start side and the stop side during each intermittent drive, and between the intermediate times. A frequency modulation circuit for modulating the resonance frequency so as to have a value substantially equal to the resonance frequency of the ultrasonic motor is provided. It is preferable that the frequency of the drive current at the time of the intermittent drive between the start side and the stop side is slightly higher than the resonance frequency of the ultrasonic motor.

In the above configuration, the AC current having the sine wave curve and the AC current having the cosine wave curve are generated as the driving current of the ultrasonic motor only for the driving time set by the timer circuit. Emitted from the circuit. The frequency of this drive current is modulated so that the start-side and stop-side frequencies during each intermittent drive are lower than the resonance frequency of the ultrasonic motor, and the intermediate time is approximately equal to the resonance frequency of the ultrasonic motor. .

As described above, since the frequency of the drive current at the time of start and stop at the time of each intermittent drive is set to a value lower than the resonance frequency of the ultrasonic motor, at the time of start and stop, the ultrasonic motor is driven. A strong torque is not suddenly transmitted from the stator to the rotor, and the slip of the rotor that occurs at this time in the conventional drive circuit is suppressed. Therefore, even if the ultrasonic motor is intermittently driven, generation of slip noise can be reduced. Further, at the time between the start and the stop, the frequency of the drive current is substantially equal to the resonance frequency of the ultrasonic motor, so that a sufficiently strong torque is transmitted from the stator to the rotor. In particular, when the frequency of the driving current at the intermediate time is set to a value slightly higher than the resonance frequency of the ultrasonic motor, the rotor is surely rotated at the maximum torque, and a sufficient driving torque as the ultrasonic motor is obtained. We can guarantee.

In the above configuration, it is preferable that the first and second drive current generating circuits include an amplitude modulation circuit for attenuating the amplitude of the drive current in a low frequency region, that is, the voltage. With this configuration, the driving torque transmitted from the stator to the rotor can be further reduced only on the start side and the stop side during each intermittent drive, so that the generation of noise due to the rotor slip can be more reliably reduced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A drive circuit for an ultrasonic motor according to an embodiment of the present invention shown in FIGS. 1 and 2 will be described below in detail.

FIG. 1 is a block diagram showing the driving circuit.
FIG. 2 is a time chart showing output signals from each circuit shown in FIG. In this drive circuit, as shown in FIG. 1, a battery B is connected to a constant voltage circuit 1 for obtaining a stable voltage and power amplifier circuits 7 and 8. The constant voltage circuit 1 is connected to each of the timer circuit 2, the sweep circuit 3, the pulse oscillation circuit 4, and the 90 ° phase shifter 5,
A stable voltage is applied to each of the circuits 2, 3, 4, and 5.

The timer circuit 2 has a sweep circuit on the output side.
The output side of the sweep circuit 3 is connected to the input side of the pulse oscillation circuit 4. The output side of the pulse oscillation circuit 4 is connected to the first power amplifier circuit 7 and each input side of the 90 ° phase shifter 5, and the output side of the 90 ° phase shifter 5 is connected to the input side of the second power amplifier circuit 8. Is connected to The pulse oscillation circuit 4 and the first power amplification circuit 7 constitute a first drive current generation circuit, and the 90 ° phase shifter 5 and the second power amplification circuit 8 constitute a second drive current generation circuit. ing. The output sides of both drive current generating circuits, that is, the output sides of both power amplifier circuits 7 and 8 are connected to the opposite electrodes of the piezoelectric element of the ultrasonic motor 9. The portion 6 surrounded by a broken line in each of the above circuits is
It can be constituted by a microcomputer, a programmable oscillator incorporating a microcomputer, or the like.

Next, the operation of the ultrasonic motor 9 by this circuit will be described with reference to the time chart shown in FIG. The signals A to E are denoted by reference numerals A to
Corresponds to E. First, the timer circuit 2 sets the driving time t ₁
A pause and time t ₂ Metropolitan repeatedly setting a minute unit time T consisting, for intermittently driving the ultrasonic motor 9 generates a pulse signal C is only the high level drive time t _1, the signal C It is sent to the sweep circuit 3. In the sweep circuit 3, when the pulse signal C is at a high level, the drive time
It increases the voltage in the first half of t ₁ is linearly linearly direct current decrease is output as the signal A in the second half. By this signal A is applied to the pulse oscillation circuit 4, a pulse oscillation circuit 4, both sides of the time t _1, that is the initiator and stop side as the frequency is low, and wider modulated pulse signal B Is output.

This signal B is input to the power amplifier circuit 7,
The power amplification circuit 7 outputs the time t ₁ in response to this pulse.
An alternating current D having a sine wave curve whose frequency becomes lower toward both sides is output, and the voltage is applied to the first electrode of the piezoelectric element of the ultrasonic motor 9. The output pulse B from the pulse oscillation circuit 4 is also input to the 90 ° phase shifter 5. The forward / reverse signal is sent to the 90 ° phase shifter 5, and the obtained output pulse (having a phase different from that of the pulse B by 90 °) is input to the second power amplifier circuit 8. In the power amplification circuit 8, an alternating current E having a cosine wave curve whose phase is different from that of the output signal from the first power amplification circuit 90 by 90 ° is output. 2 electrodes.

The current generated by the power amplifier 7 and 8, the frequency fmin in the end parts of the time t ₁ is the resonance frequency of the ultrasonic motor 9 (hereinafter referred to as f ₀₎ lower than the central portion of the time t ₁ frequency fmax is set to a value slightly higher than the resonance frequency f _0. Therefore, the stator of the ultrasonic motor 9 is
Until the frequency of the drive current reaches the resonance frequency f ₀ not able to turn the rotor at maximum torque, when it reaches the resonance frequency f _0, to rotate the rotor at a maximum torque. After passing the resonance frequency f ₀ , the torque temporarily decreases slightly,
Torque when the frequency of the drive current coincides with the resonance frequency again becomes the maximum value, then the rotation of the rotor is stopped when it becomes downtime t ₂ with reduced torque gradually.

The above operation is performed within the minute time T, and this operation is repeated with the time T as one unit, so that the rotor appears to rotate almost continuously at a low speed. In the conventional method, when the ultrasonic motor is intermittently driven, the frequency of the drive current is almost equal to the resonance frequency of the ultrasonic motor. In addition, slip noise was generated by the resulting slippage, but in this embodiment,
The frequency of the drive current at the time of operation switching is set to a value smaller than the resonance frequency f ₀ , so that strong torque is not suddenly applied to the rotor. Can be reduced. Further, in the configuration of the present embodiment, even if the resonance frequency f ₀ changes due to a manufacturing error occurring in the piezoelectric element or the elastic body constituting the ultrasonic motor, or a change in the environment such as the ambient temperature, etc. If the frequency of the drive current is set in consideration of the range in which the resonance frequency can be covered, those errors can be absorbed.

Further, in the above configuration, as shown by a broken line in FIG. 1, it is preferable to provide a feedback circuit 10 for feeding back an output signal through a low-pass filter or the like in the power amplification stage. By providing this feedback circuit 10, the drive currents D and E can be
Amplitude initiator and stop side of the drive time t ₁ as shown in FIG. 2
It can be converted to drive currents D ′ and E ′ with small (voltage). Therefore, since the torque applied to the stator at the time of starting and stopping can be reduced to suppress the slip of the rotor, the generation of the slip noise at the time of the intermittent driving can be reduced more reliably.

The present invention is not limited to the above embodiment, but includes first and second drive current generating circuits 4, 5, 7, 8 for generating alternating currents having a phase difference of 90 ° from each other. As long as the timer circuit 2 for setting the generation time and the stop time of the drive current and the frequency modulation circuit 3 are provided, each circuit itself can be variously changed using a conventionally known circuit.

For example, in the above embodiment, the sweep circuit 3
Generates a pulse signal B whose frequency and width are modulated by the output signal from the controller, but the pulse width does not necessarily have to be modulated, and in that case, pulse width modulation has been used conventionally. Only the frequency needs to be modulated by the method. In the above embodiment adopts a digital approach using pulsed oscillation circuit 4 to the drive current generation circuit 4, 5, 7, and 8, but performs the frequency modulation in the analog approach, start time t ₁ A drive current having a lower frequency on the side and the stop side may be generated. Further, the modulation of the amplitude of the driving current is performed in addition to the provision of the feedback circuit 10.
A configuration may be employed in which a conventionally known pulse amplitude modulation circuit is connected to the pulse oscillation circuit 4 and its output pulse is input to the power amplification circuits 7 and 8.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a driving circuit of an ultrasonic motor according to one embodiment of the present invention.

FIG. 2 is a time chart showing an output signal of the driving circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Constant voltage circuit 2 Timer circuit 3 Sweep circuit 4 Pulse oscillation circuit 5 90 degree phase shifter 6 Microcomputer 7,8 Power amplifier circuit 9 Ultrasonic motor 10 Feedback circuit

Claims (2)

(57) [Claims] A first drive current generating circuit for generating an alternating current having a sine wave curve as a drive current for an ultrasonic motor (9).
(4, 7) and a second driving current generating circuit (5, 8) that generates an alternating current having a cosine wave curve having a phase difference of 90 ° with respect to the sine wave current, The first and second drive current generation circuits (4, 7, 5, 8) are connected to each other, and the drive time (t ₁ ) and the pause time (t ₂ ) are alternately set, and the first and second drive current generation circuits (4, 7, 5, 8) are set alternately. And a second drive current generating circuit (4, 7,
A timer circuit (2) for generating a drive current only during the drive time (t ₁ ) from (5, 8), and a timer circuit (4, 7, 5, 8) connected to the first and second drive current generation circuits (4, 7, 5, 8). The frequency of the drive current, the start side and the stop side at the time of each intermittent drive becomes a value lower than the resonance frequency of the ultrasonic motor (9), and the intermediate time is the resonance frequency of the ultrasonic motor (9). A drive circuit for an ultrasonic motor, comprising: a frequency modulation circuit (3) for performing modulation so as to have substantially equal values. 2. The first and second drive current generating circuits (7, 8).
2. A drive circuit for an ultrasonic motor according to claim 1, further comprising an amplitude modulation circuit for attenuating an amplitude of said drive current in a low frequency range.