JP3105684B2 - 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, and more particularly to an ultrasonic motor driving circuit for optimally driving an ultrasonic motor.

[0002]

2. Description of the Related Art Conventionally, various driving circuits for ultrasonic motors have been proposed. For example, Japanese Unexamined Patent Publication No. Sho 59-204477 discloses an output signal (monitor signal) from a monitor electrode provided in an ultrasonic motor. The voltage value of the monitor signal is monitored by utilizing the fact that the voltage value of ()) becomes maximum at the resonance frequency of the vibrating body of the ultrasonic motor, and based on the voltage value, the resonance frequency or the resonance frequency is calculated. Technical means for driving an ultrasonic motor in a slightly high-frequency region are disclosed.

Japanese Patent Application Laid-Open No. 61-251490 discloses that the phase of the monitor signal is monitored by utilizing the fact that the phase of the monitor signal with respect to the drive voltage greatly changes near the resonance frequency. Technical means for driving an ultrasonic motor at a resonance frequency or a region slightly higher than the resonance frequency based on a phase difference between a signal and the drive voltage is disclosed.

On the other hand, Japanese Patent Application Laid-Open No. 62-92781 discloses an optimum driving frequency of an ultrasonic motor by monitoring a phase difference between a voltage and a current of a driving signal applied to a driving electrode of the ultrasonic motor. Is disclosed.

[0005]

However, Japanese Patent Application Laid-Open Nos. 59-204477 and 61-2514 describe the above.
The technical means disclosed in Japanese Patent Publication No. 90 requires an extra arrangement of a monitor electrode in the ultrasonic motor, which is not preferable because it takes time and effort to manufacture and increases the cost.

On the other hand, the technical means disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 62-92781 does not require a monitor electrode.
The problem relating to the technical means disclosed in JP-A-251490 is solved. However, as shown in FIG. 7, when a load is applied to the ultrasonic motor (in the figure, when the load is applied), the state of the change in the phase difference is significantly changed by the load as compared with the case of no load. For this reason, if the technical means is applied to a camera having a lens with a large load change such that the whole is extended by a photographing lens, the load changes significantly due to a difference in posture during use, and it is difficult to track the optimum drive frequency. There was a problem of becoming.

The present invention has been made in view of the above problems, and provides an ultrasonic motor drive circuit capable of tracking an optimum drive frequency over a wide load range without providing a special monitor electrode. The purpose is to:

[0008]

In order to achieve the above object, an ultrasonic motor drive circuit according to the present invention generates an AC signal based on an induced electromotive force generated when switching an inductive element. The AC signal is transmitted to the ultrasonic motor
By applying to the mechanical energy conversion element to drive the ultrasonic motor, in an ultrasonic motor drive circuit,
A phase difference detection unit that detects a phase difference between a switching signal for switching the inductive element and a signal obtained by shaping the waveform of the AC signal with a predetermined threshold value other than zero, and based on an output of the phase difference detection unit, Frequency control means for controlling the frequency of the AC signal.

[0009]

According to the present invention, in the phase difference detecting means,
A phase difference between a switching signal for switching the inductive element and a signal obtained by shaping the waveform of the AC signal with a predetermined threshold value other than zero is detected, and based on an output of the phase difference detection means, induction is performed by frequency control means. Controlling the frequency of an AC signal based on the induced electromotive force generated when switching the conductive element.

[0010]

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

FIG. 1 is an electric circuit diagram of an ultrasonic motor driving circuit showing a first embodiment of the present invention.

The ultrasonic motor driving circuit according to the first embodiment applies a predetermined two-phase AC signal to a known ultrasonic motor 5 having two electrodes 5A and 5B, monitors the AC signal, and monitors the AC signal. The drive control of the ultrasonic motor 5 is performed.

That is, the driving circuit includes the ultrasonic motor 5
An oscillation circuit 1 for generating and outputting a pulse signal φORG having a frequency approximately four times that of an AC drive signal applied to the oscillating circuit 1;
A pulse conversion circuit 2 that divides and outputs the phase pulse signals φ1 to φ4, and switching transistors Q1 to Q4 that perform switching operations corresponding to the pulse signals φ1 to φ4 output from the pulse conversion circuit 2, respectively. The positive voltage of the DC power supply 10 is supplied to the intermediate tap on the primary side, and the primary side is turned on by the switching operation of the switching transistors Q1 and Q2.
A transformer T1 for outputting an A-phase AC signal VA to the next side;
Similarly, the primary side is turned on by the switching operation of the switching transistors Q3 and Q4, and B
A transformer T2 for outputting a phase AC signal VB, a waveform shaping circuit 4 connected to one end (A phase side) of the output of the transformer T1 and converting the AC signal VA into a predetermined digital signal; And the pulse signal φ2 from the pulse conversion circuit 2
The main part is constituted by comparing the phases of the two signals with each other, that is, the phase comparator 3 for sending the phase difference between the phases of the two signals to the oscillation circuit 1.

The ultrasonic motor 5 is a known traveling wave type ultrasonic motor having a piezoelectric element.
It has two electrodes 5A and 5B. That is, the electrode 5
The two-phase (A-phase and B-phase) AC signals VA and VB whose phases are shifted from each other by about 90 ° are applied to A and 5B, and the two-phase AC signals drive rotation. Is to be done.

The oscillating circuit 1 includes a preset optimum frequency and an output from the phase comparator 3, that is, a digital output signal of the waveform shaping circuit 4 and the pulse signal φ2.
The oscillation frequency to be output is controlled based on the result of the comparison.

FIG. 2 is an electric circuit diagram showing the waveform shaping circuit 4 in the ultrasonic motor driving circuit of the first embodiment. FIG. 3A shows an AC signal which is an input signal of the waveform shaping circuit 4. VA signal waveform, (b) Attenuation waveform due to voltage reduction R1 and R2 in waveform shaping circuit 4, (c) Waveform whose voltage range is limited by clamp diodes D1 and D2 in waveform shaping circuit 4, (d) waveform FIG. 7 is a diagram showing a shaped waveform of an AC signal VA which is an output signal of the shaping circuit 4 and (e) a waveform of the pulse signal φ2 corresponding to each signal of the waveform shaping circuit 4, respectively. In addition, among the waveforms shown in the respective diagrams of FIG. 3, the waveform shown by a dashed line indicates a waveform when a predetermined load is applied to the ultrasonic motor with respect to the waveform state shown by a solid line, and The waveforms shown show waveforms when a further load is applied to the ultrasonic motor.

The waveform shaping circuit 4 includes resistors R1 and R2 for voltage reduction and a clamp diode D as shown in FIG.
, D2 and inverter IV1 with hysteresis
It is composed of The input terminal of the voltage reducing resistor R1 is connected to the output terminal of the transformer T1, whereby the AC signal V generated and output by the transformer T1 is connected.
A is input to the ultrasonic motor 5 and also to the waveform shaping circuit 4.

The AC signal VA (see FIG. 3A) input to the waveform shaping circuit 4 firstly receives a voltage reducing resistor R
1, the voltage is reduced by R2 (see FIG. 3B),
Thereafter, the voltage is rectified by the clamp diodes D1 and D2, and is limited to a predetermined voltage range by the value of the diodes (see FIG. 3C). Further, the digital signal is shaped into a digital signal at a predetermined threshold level of the inverter IV1 (see FIG. 3D), and is input to the phase comparator 3.

When a considerably large load is applied to the ultrasonic motor, the waveform of an AC signal for driving the ultrasonic motor changes as shown in FIG. Assuming that the phase difference between the rise of the switching signal applied to the transformers T1 and T2 and the AC signal applied to the ultrasonic motor is Δφ as shown in FIG. It is conceivable that the difference becomes as small as Δφ ′, which makes it difficult to accurately track the optimum driving frequency.

On the other hand, in the first embodiment, as shown in FIG. 3, the voltage is reduced so that the degree of the change in the waveform of the AC signal VA due to the load change becomes the smallest at the predetermined threshold level of the inverter IV1. Resistance R
The voltage value of the AC signal VA is controlled by setting the values of R1 and R2. Thus, the phase difference Δφ between the waveform of the AC signal VA output from the waveform shaping circuit 4 (see FIG. 3D) and the pulse signal φ2 (see FIG. 3E) is determined by the load of the AC signal VA. It is not affected by the VA waveform change over a fairly wide range.

Next, the operation of the first embodiment will be described.

FIG. 4 shows the phase difference between the AC signal VA in the ultrasonic motor drive circuit of the first embodiment and the pulse signal φ2 which is one output signal from the pulse conversion circuit 2, and the drive of the AC signal VA. FIG. 3 is a diagram illustrating a relationship with a frequency.

As shown in FIG. 4, the A-phase AC signal V
Assuming that the phase difference between A and the pulse signal φ2 is Δφ, if the drive frequency is adjusted by raising and lowering the phase difference Δφ so as to maintain a predetermined value, it is possible to track the optimal drive frequency. In addition,
In the figure, the phase difference Δφ is indicated by a pulse signal φ2−AC signal VA.

More specifically, the oscillation circuit 1 starts oscillating at 44 KHz, which is slightly higher than the expected optimum driving frequency, and gradually monitors the phase difference Δφ based on the output from the phase comparator 3 while gradually monitoring the phase difference Δφ. Then, the driving frequency is lowered. Then, the phase difference Δφ is adjusted so as to be a phase difference corresponding to a preset optimum driving frequency, for example, -145 °. That is, if the phase difference Δφ is larger than −145 °, the drive frequency is increased, and if the phase difference Δφ is smaller, the drive frequency is decreased. In addition, the above-mentioned phase difference−
In the vicinity of 145 °, the phase difference characteristic is such that there is no difference between the loaded state and the unloaded state.

With such an operation, it is possible to track the optimum driving frequency of the ultrasonic motor having no monitor electrode and having a large load variation.

Further, according to the first embodiment, the above-mentioned waveform shaping circuit can be composed of inexpensive components, and if the voltage reducing resistor R1 is increased, power loss of the A-phase AC signal VA hardly occurs. .

Further, as described above, the waveform shaping circuit 4
By setting the threshold level at which the waveform change due to the load is small, and extracting the change in the phase difference caused by the change in the electrical characteristics of the ultrasonic motor, the more the waveform change occurs in the AC signal driving the ultrasonic motor, Even if a large load change occurs, the optimum drive frequency can be more accurately tracked without being affected by the load change.

Next, a second embodiment of the present invention will be described.

FIG. 5 is an electric circuit diagram showing an ultrasonic motor driving circuit according to the second embodiment.

The ultrasonic motor drive circuit according to the second embodiment has substantially the same configuration as that of the first embodiment, except that the memory 6 is added to the oscillation circuit 1.

In general, the characteristics of an ultrasonic motor slightly change due to variations in dimensions or the like in manufacturing. For this reason, each ultrasonic motor has a unique optimum phase difference, that is, an optimum phase difference Δφ between the shaped waveform of the A-phase AC signal VA and the output pulse signal φ2 from the pulse conversion circuit 2 as described above. Will be. The second embodiment focuses on the fact that each ultrasonic motor has a unique optimum phase difference, and stores the optimum phase difference Δφ in the memory 6.
After that, the same frequency control as in the first embodiment is performed.

According to the second embodiment, it is possible to correct variations in the manufacturing of the ultrasonic motors and more accurately track the optimum driving frequency.

In the second embodiment, it is also possible to store a plurality of phase differences Δφ in the memory 6 and select and use the plurality of phase differences Δφ based on a power supply voltage or the like.

In the first and second embodiments, the optimal drive frequency control is performed based on the phase difference between the A-phase AC signal VA and the shaped waveform of the AC signal VA. The phase difference between the AC signal VB and its shaped waveform or the AC signal of both phases and its shaped waveform may be used.

On the other hand, in the first and second embodiments, the oscillating circuit 1 can be constituted by using any oscillating means such as a VCO or a digital frequency division oscillating circuit. By using the above, it is possible to generate the pulse signals φ1 to φ4 described above. further,
The waveform shaping circuit 4 may be configured by using a comparator or the like, and the ultrasonic motor 5 is not limited to the traveling wave type, and the impedance changes depending on the frequency and the like.
Can be used as long as it causes a change.

[0036]

As described above, according to the present invention, the optimum driving frequency can be tracked even with an inexpensive ultrasonic motor having no monitor electrode, and the ultrasonic motor driving circuit is less affected by a large load change. Can be provided.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of an ultrasonic motor drive circuit showing a first embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a configuration of a waveform shaping circuit in the ultrasonic motor drive circuit of the first embodiment.

FIG. 3 is a timing chart showing a relationship among an AC signal VA, a shaped waveform of the AC signal VA, an output pulse signal from a pulse conversion circuit, and the like in the ultrasonic motor driving circuit of the first embodiment.

FIG. 4 shows the waveform of the AC signal VA and the waveform of the pulse signal from the pulse conversion circuit in the ultrasonic motor drive circuit of the first embodiment.
FIG. 4 is a diagram illustrating a relationship between a phase difference Δφ and a driving frequency when a phase difference from an output pulse signal is Δφ.

FIG. 5 is an electric circuit diagram of an ultrasonic motor drive circuit showing a second embodiment of the present invention.

FIG. 6 is a diagram showing an example of an AC signal waveform applied to a conventional ultrasonic motor when a large load is applied to the ultrasonic motor.

FIG. 7 is a diagram showing an example of a relationship between a drive frequency and a current-voltage phase difference of a drive signal between a loaded state and a non-loaded state in a conventional ultrasonic motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oscillation circuit 2 ... Pulse conversion circuit 3 ... Phase comparator 4 ... Waveform shaping circuit 5 ... Ultrasonic motor 10 ... DC power supply

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02N 2/16

Claims (1)

(57) [Claims] An AC signal is generated based on an induced electromotive force generated when an inductive element is switched, and the AC signal is applied to an electro-mechanical energy conversion element of an ultrasonic motor to thereby generate the ultrasonic wave. An ultrasonic motor driving circuit for driving a motor, wherein a phase difference detecting means for detecting a phase difference between a switching signal for switching the inductive element and a signal obtained by shaping the waveform of the AC signal with a predetermined non-zero threshold value. And a frequency control means for controlling the frequency of the AC signal based on the output of the phase difference detection means.