JP2892664B2 - Ultrasonic motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor that generates a traveling vibration wave using a piezoelectric body and drives a rotor.

Conventional technology As an ultrasonic motor drive device, the drive voltage frequency always tracks the frequency determined by the mechanical resonance frequency of the stator, even if the drive conditions change due to changes in the environment such as temperature, preventing a decrease in drive efficiency. In addition, a function of maintaining a stable rotation state is required.

Conventionally, a piezoelectric structure shown in FIG. 2 has been proposed as a sensor unit for detecting a driving condition of an ultrasonic motor.

That is, to detect a voltage generated by the traveling vibration wave, a sensor unit in which the sensor electrode 1 is provided adjacent to the electrodes 3 and 4 for applying a drive voltage to the piezoelectric body 6 is configured.

Further, as described in Japanese Patent Application Laid-Open No. Sho 62-166787, a voltage generated in a sensor section is detected from a detection electrode to shape a waveform, a phase difference with the driving voltage is compared, and a response is made according to the phase difference. A phase difference comparator that generates an output, a variable frequency oscillator that determines an oscillation frequency of a driving voltage based on the output, a phase shifter that generates a two-phase voltage, and a piezoelectric driving circuit. ing.

FIG. 2A shows a sensor unit 1 / 4λ (1 of the traveling vibration wave) for detecting the traveling vibration wave (wavelength λ) almost at the center of the piezoelectric body 6.
/ 4 wavelength) and multiple driving parts 1 / 2λ that generate traveling vibration waves
(Half wavelength of the traveling vibration wave) is provided by polarization processing, and electrodes 3 and 4 for applying a drive voltage to a plurality of drive portions are provided on both sides of the sensor portion. Reference numeral 1 denotes a sensor electrode provided in the sensor unit. Reference numeral 2 denotes a portion that has not been subjected to polarization processing.

FIG. 2 (b) is an explanatory diagram showing a piezoelectric body subjected to a polarization treatment (illustrated by (+,-)) when viewed from the surface opposite to the surface on which the sensor electrode 1 is provided. A sensor section 1 / 4λ is provided substantially at the center, and a plurality of polarized driving sections 1 / 2λ are provided adjacent to both sides thereof.

FIG. 2 (c) shows the sensor electrode 1 and the electrodes 3 and 4 provided on the piezoelectric body, as well as the electrodes provided at opposing positions. The electrode 8 is the electrode 3 and the electrode 5 is the sensor. On the electrode 1, the electrode 7 faces the electrode 4, and the electrodes 5, 7, 8 are connected to the ground line.

Reference numerals 11 to 13 shown in FIG. 2D denote capacitances between the electrodes.

Problems to be Solved by the Invention In the electrode configuration provided on the piezoelectric body as described above, since the sensor electrode 1 provided on the sensor unit is disposed adjacent to the electrodes 3 and 4 for applying the drive voltage, In addition to the voltage generated by vibration, the stray capacitance 9 between electrodes 1 and 3 and between electrodes 1 and 4
Due to the electrical coupling by 10, the driving voltage applied to the electrodes 3 and 4 affected the sensor unit, and it could not be said that a true traveling vibration wave was detected.

Means for Solving the Problems In order to solve the above problems, the present invention generates a traveling vibration wave on the surface of the piezoelectric body by applying a driving voltage to the piezoelectric body, drives the rotor with the traveling vibration wave, 1 / 4λ to which the body drive voltage is not applied (1 of traveling vibration wave
A sensor part for detecting the traveling vibration wave is provided in the (/ 4 wavelength) part, electrodes for applying a drive voltage to the piezoelectric body are provided on both sides of the sensor part, and a sensor electrode is provided in a substantially central part of the sensor part. Two guard electrodes are arranged on both sides of the electrode at a predetermined interval.

A guard electrode is provided in the vicinity of the sensor electrode provided on the piezoelectric body constituting the ultrasonic motor, and an electrical connection between the sensor electrode and the electrode for applying the drive voltage is shielded by connecting to a ground line. The sensor electrode is
A true traveling vibration wave can be detected.

Embodiment FIG. 1 shows an embodiment of an ultrasonic motor according to the present invention. A sensor 1 / 4λ (1/4 wavelength of the traveling vibration wave) for detecting the traveling vibration wave (wavelength λ) and a plurality of driving portions 1 / 2λ (the traveling vibration Wave 1/2
The electrodes 3 and 4 for applying a drive voltage to a plurality of drive portions are provided on both sides of the sensor portion around the sensor portion. Electrodes 7 and 8 are provided at positions facing electrodes 3 and 4 on the surface. The electrode 5 is also provided on the surface of the sensor portion on which the electrodes 7, 8 are provided, and the electrodes 5, 7, 8 are connected to the ground line.

In the 1 / 4λ sensor section, a sensor electrode 1 is provided at the center, and guard electrodes 23 and 24 are provided at predetermined intervals on both sides thereof.
This guard electrode is connected to an earth line.

Next, an equivalent circuit of the sensor unit will be described. With the above configuration, 14, 15 stray capacitances are generated between the electrodes 1, 3, and 16, 17 stray capacitances are generated between the electrodes 1, 4. Also, 18,19,20,21,2
Reference numeral 2 denotes the interelectrode capacitance of the electrodes 3 and 4, the guard electrodes 23 and 24, and the sensor electrode 1, respectively.

 Hereinafter, the operation of the guard electrodes 23 and 24 of the present invention will be described.

When the guard electrode is configured and connected to the ground line, the stray capacitance from the electrode 1 to the electrode 3 becomes a series circuit of 14 and 15, and the apparent total stray capacitance decreases. Also, by connecting the guard electrode 23 to the earth line, the electrode 1
The electrical coupling between the electrode and the electrode 3 is shielded. The same can be said between the electrode 1 and the electrode 4.

When the sensor electrode 1 is electrically shielded as described above, the influence of the electrodes 3 and 4 to which the drive voltage is applied is shielded.

As described above, according to the present invention, a sensor electrode is provided at a substantially central portion of a 1 / 4λ sensor portion provided on a piezoelectric body constituting an ultrasonic motor, and guard electrodes are provided at predetermined intervals on both sides of the sensor electrode. By providing the electrodes and connecting to the ground line, the electrical coupling between the sensor electrode and the electrode to which the drive voltage is applied is shielded, and the vibration component of the true traveling vibration wave can be detected.

As a result, it was possible to provide an ultrasonic motor that constantly tracks the mechanical resonance frequency and maintains a stable rotation state in response to environmental changes.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an electrode portion of a piezoelectric body of an ultrasonic motor according to one embodiment of the present invention, and an equivalent circuit diagram. FIG. It is an equivalent circuit diagram. 1 ... sensor electrode, 3,4 ... drive voltage application electrode, 23,
24 …… Guard electrode.

Continuation of front page (56) References JP-A-64-12881 (JP, A) JP-A-61-224879 (JP, A) JP-A-62-107686 (JP, A)

Claims (1)

(57) [Claims] 1. A driving voltage is applied to a piezoelectric body to generate a traveling vibration wave on the surface of the piezoelectric body, and a rotor is driven by the traveling vibration wave to a portion where the driving voltage of the piezoelectric body is not applied. In an ultrasonic motor provided with a sensor unit for detecting the traveling vibration wave, the sensor unit is provided in a 1 / 4λ (1/4 wavelength of the traveling vibration wave) portion to which the driving voltage of the piezoelectric body is not applied, Electrodes 3 and 4 for applying a drive voltage to the piezoelectric body are provided on both sides of the sensor unit, and a sensor electrode 1 is provided in the sensor unit at a substantially central portion. Two guards are provided on both sides of the sensor electrode 1 at predetermined intervals. An ultrasonic motor provided with electrodes 23 and 24.