JP3140237B2 - 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.

Also, 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 based on the resonance frequency or a region slightly higher than the resonance frequency 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. 6, when a load is applied to the ultrasonic motor (in the figure, when a load is applied), the state of the change in the phase difference is significantly changed by the load as compared with 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, a first ultrasonic motor driving circuit according to the present invention comprises a coil motor.
Switching the current flowing through the
Generates an AC signal based on the induced electromotive force
And converting the AC signal into the electric-mechanical energy of the ultrasonic motor.
Driving the ultrasonic motor by applying to the conversion element, the ultrasonic motor driving circuit, the switching
Phase difference detecting means for detecting a phase difference between a switching signal applied to an element and the AC signal, and the ultrasonic motor
Storage means for storing a unique optimum phase difference;
Comprising a frequency control means for controlling the frequency of the AC signal based on the output of the output and the storage means of the difference detecting means, the
It is characterized by having done.

Further , in order to achieve the above object, the present invention
The second ultrasonic motor drive circuit according to
In the wave motor drive circuit, the storage means includes a power supply voltage
Stored multiple optimum phase differences specific to ultrasonic motors according to the
It is characterized by being.

[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.

As shown in FIG. 2, the waveform shaping circuit 4 comprises a current reducing resistor R1, clamp diodes D1, D2
And an inverter IV1 having hysteresis and a normal inverter IV2. The input terminal of the current reducing resistor R1 is connected to the output terminal of the transformer T1, whereby the AC signal VA generated and output by the transformer T1 is input to the ultrasonic motor 5 and the waveform It is also input to the shaping circuit 4.
Then, the AC signal VA input to the waveform shaping circuit 4
Is rectified by the clamp diodes D1 and D2,
Further, the signal is shaped into a digital signal by the two inverters IV1 and IV2 and input to the phase comparator 3.

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

According to the measurements of the present applicant, as shown in FIG. 4, the shaped waveform of the A-phase AC signal VA and the pulse conversion circuit 2
Assuming that the phase difference from the output pulse signal φ2 is Δφ, the phase difference Δφ and the driving frequency (corresponding to the frequency of the A-phase AC signal VA) have a relationship as shown in FIG. As shown in FIG. 3, if the drive frequency is adjusted by raising or lowering the drive frequency so as to keep the phase difference Δφ at, for example, 3 °, it becomes possible to track the optimum drive frequency.

More specifically, the oscillation circuit 1 starts oscillating at 44 KHz, which is slightly higher than the optimum driving frequency expected, and gradually lowers the driving frequency while monitoring the phase difference Δφ to reduce the phase difference Δφ. Adjust to 3 ゜. That is, when the phase difference Δφ is larger than 3 °, the oscillation frequency is changed so that the drive frequency is increased, and when the phase difference Δφ is decreased, the drive frequency is decreased.

With such an operation, it is possible to track the optimum drive 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 constituted by inexpensive components, and if the current reducing resistor R1 is increased, power loss of the A-phase AC signal VA hardly occurs. . Further, since both the A-phase AC signal VA and the pulse signal φ2 are digital signals, the above-described signal processing can be realized very easily.

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 of the second embodiment has substantially the same structure as that of the first embodiment, and differs only in that a 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 manufacturing variations 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 oscillating circuit 1 can be constructed 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. On the other hand, the waveform shaping circuit 4 may be configured using a comparator or the like. Further, the ultrasonic motor 5 has a phase difference Δ
Any type that changes φ can be used.

[0028]

As described above, according to the present invention, an ultrasonic motor drive circuit which can track the optimum drive frequency even with an inexpensive ultrasonic motor having no monitor electrode, and is less affected by load fluctuations. 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 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. 4 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 drive circuit of the first embodiment.

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 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 Continuation of the front page (56) References JP-A-3-112379 (JP, A) JP-A-3-112378 (JP, A) JP-A-3-145976 (JP, A) JP-A-3-112379 273876 (JP, A) JP-A-4-183283 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02N 2/16

Claims (2)

(57) [Claims] An electric current flowing through a coil is supplied to a switching element.
Based on induced electromotive force generated when switching more
To generate an AC signal, and the AC signal is
-Driving an ultrasonic motor by applying to a mechanical energy conversion element, in an ultrasonic motor drive circuit, a phase difference detection means for detecting a phase difference between a switching signal applied to the switching element and the AC signal, Storage storing the optimum phase difference specific to the ultrasonic motor.
Means , based on the output of the phase difference detection means and the output of the storage means.
And a frequency control means for controlling the frequency of the AC signal. 2. The storage device according to claim 1, wherein said storage means includes an ultrasonic wave corresponding to a power supply voltage.
The feature is that multiple optimal phase differences unique to the motor are stored.
The ultrasonic motor drive circuit according to claim 1, wherein