JP3114954B2 - Ultrasonic motor drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving apparatus for a traveling wave type ultrasonic motor having a driving element and an oscillating electrode on a piezoelectric element of a stator.

[0002]

2. Description of the Related Art The driving frequency for driving a traveling wave type ultrasonic motor is the same as or close to the resonance frequency (natural frequency) of the stator of the ultrasonic motor, and the frequency and generation frequency are the most efficient. The torque will be the highest. However, if the drive frequency ■ _m of the motor matches the resonance frequency ■ _{0 of the} stator in FIG. 5, resonance occurs, and vibration increases, so-called surging occurs, generating vibration noise, or the piezoelectric element There is a problem that it is damaged. Therefore, by driving the stator with a drive frequency voltage having a frequency closest to the resonance point and higher than the resonance point within a range where vibration noise is not generated, it is possible to achieve both a high rotation speed and a high torque and a suppression of vibration due to resonance. ing. However, when the temperature of the stator rises due to an increase in the temperature of the motor, the resonance frequency of the stator changes, and the resonance frequency of the stator becomes too close to or close to the drive frequency, so that the vibration may increase. Further, when the driving frequency deviates from the optimum frequency range, the efficiency is deteriorated. Therefore, stable rotation cannot be obtained unless the drive frequency is controlled according to the temperature change of the stator.

Conventionally, in order to solve the above-mentioned problem and to ensure a reliable start, Japanese Patent Laid-Open Publication No. Hei 3-150076 discloses that the output voltage of a monitoring piezoelectric element electrode for detecting the amplitude of vibration of a stator becomes constant. As described above, the drive frequency is controlled by resetting the oscillation frequency of the oscillation circuit to the initial oscillation frequency by the feedback circuit. However,
According to the above method, the output voltage of the monitoring piezoelectric element does not reach a certain reference voltage when the ultrasonic motor is at a high temperature or under a high load, so that the ultrasonic motor cannot be driven. Japanese Patent Laying-Open No. 4-75474 discloses a solution to the above problem. According to the solution, the driving frequency is controlled based on a comparison result between the detected vibration amount and a predetermined reference voltage value, and when the driving frequency reaches a predetermined value, a reference voltage for comparing with the output voltage of the monitoring piezoelectric element. By decreasing the value, the output voltage of the monitoring piezoelectric element is prevented from reaching the reference voltage, and the stator of the ultrasonic motor is prevented from being unable to be driven.

[0004]

However, the driving frequency is controlled on the basis of the result of comparison between the detected vibration amount and a predetermined reference voltage value disclosed in Japanese Patent Laid-Open No. 4-75474. According to the method of lowering the reference voltage when a predetermined value is reached, a microcomputer serving as predetermined frequency setting means, frequency monitoring means and reference changing means is required as shown in FIG. Therefore, there are problems that the structure is complicated and the cost is high. The present invention has been made in order to solve the above-described problems, and it is possible to stably drive the stator even when the temperature of the stator rises at a high temperature, and to provide a simple and inexpensive ultrasonic motor. It is an object to provide a driving device.

[0005]

According to the present invention, as a specific means for achieving the above object, as shown in FIG. 1, a piezoelectric element 3 is fixed to one surface of an elastic body 15, and Driving electrodes 3-1 and 3-2 and an oscillating electrode 3-3 in the element
And an oscillation electrode 3 of the stator 2
Oscillating means 7 for generating a reference frequency voltage by oscillation using a reactance component of -3, and a driving frequency voltage having a predetermined phase difference and a driving frequency is generated by the reference frequency voltage of the oscillating means. Driving frequency voltage generating means 4-1 to 4-2, 5-1 to 5-4, 6, 8, 9 for applying to the driving electrodes 3-1 and 3-2 of the stator 2;
Ultrasonic motor drive device 1 comprising:
Is provided.

[0006]

According to the ultrasonic motor driving apparatus 1 having the above-described configuration, the oscillation means 7 generates the reference frequency voltage which is the reference of the driving frequency voltage from the reactance (capacitance and inductance) of the piezoelectric element 3. Let me. Therefore, even if the temperature of the stator 2 changes and the piezoelectric element 3 is affected and the resonance frequency of the stator 2 changes, the reference frequency voltage is generated using the reactance of the piezoelectric element 3 having the same temperature coefficient. Therefore, since the temperature change rate of the resonance frequency and the temperature change rate of the reference frequency can be made equal,
Even when the temperature of the stator elastic body changes, a reference frequency voltage is generated based on the temperature change, so that an optimal drive frequency voltage according to the temperature change is obtained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the ultrasonic motor driving device 1 according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a configuration diagram showing a driving device 1 of an ultrasonic motor. Driving electrodes 3-1 and 3-2 for applying driving frequency voltages having different phases to the stator 2 composed of the elastic body 15 and the piezoelectric element 3, and an oscillating electrode 3- for oscillating an oscillation frequency for determining the driving frequency.
3 is provided. The driving electrodes 3-1 and 3-2 are connected to secondary sides of transformers 4-1 and 4-2, respectively. The collectors of the switching transistors 5-1 to 5-4 are connected to both ends of the primary sides of the transformers 4-1 and 4-2, respectively, and a voltage of 12 V is applied to the intermediate tap. The switching transistors 5-1 to 5
The base side of -4 is connected to the output terminal of the ring counter 6, and the emitter side is connected to ground. The input side of the ring counter 6 is connected to an oscillator 7, and the oscillator 7
Is connected to the oscillation electrode 3-3. As shown in FIG. 3, the oscillator 7 includes a capacitance component of a Colpitts oscillator using an oscillation electrode 3-3. As shown in FIG. 2, the stator 2 has a ring shape, and a ring-shaped piezoelectric element (not shown) is fixed thereto, and the driving electrode 3-1 is formed.
And 3-2 and an oscillation electrode 3-3. FIG.
FIG. 3 is a cross-sectional view of the ultrasonic motor. The stator 2 is configured by fixing an elastic body 15 to a casing 16 and fixing the piezoelectric element 3 to the elastic body 15. The rotor 17 is inserted into a rotor shaft 18 rotatably supported by a casing 16.

The operation of the above embodiment will be described. When a power supply voltage is applied to the oscillator 7, a reference frequency voltage is generated and sent to the ring counter 6 as a clock signal. The ring counter 6 generates a driving frequency voltage having a phase difference by sequentially transmitting signals from the switching transistors 5-1 to 5-4 for each amplitude of the reference frequency voltage. Therefore, the reference frequency voltage is 1 / n of the drive frequency voltage.
(N is the number of output terminals of the ring counter 6; in this embodiment, n =
It is necessary to set the capacitance, inductance and resistance of the oscillator 7 so that the frequency becomes 4). Switching transistor 5 receiving a signal from ring counter 6
1 to 5-4 are respectively turned on, and pass current to the connected transformers 4-1 and 4-2. And the transformer 4-1
And 4-2, a driving frequency voltage having a predetermined phase difference and a driving frequency is generated on the secondary side. The driving frequency voltage is applied to the driving electrodes 3-1 and 3-2, and a bending vibration wave is generated in the elastic body 15 by the piezoelectric element 3, whereby the rotor 17 is driven.

Next, during driving of the ultrasonic motor, the stator 2
Next, the operation when there is a temperature change will be described. Since the reference frequency voltage is oscillated by the oscillator 7 using a part of the capacitance component of the piezoelectric element 3, the temperature change rate of the resonance frequency of the stator 2 and the temperature change rate of the reference frequency can be made equal. Even if the temperature changes, a driving frequency voltage generated by the ring counter 6, the switching transistors 5-1 to 5-4, and the transformers 4-1 to 4-2 is generated from the reference frequency voltage of the oscillator 7 to obtain the temperature. The drive frequency can be changed according to the change, and the ultrasonic motor can be driven stably with respect to temperature change without requiring a conventional microcomputer.

As another embodiment, as shown in FIG. 6, a power amplifier 9 directly amplifies a reference frequency voltage of an oscillator 7 by a power amplifier 9 and a power amplifier 9 generates a phase difference through a phase shifter 8. By amplifying,
It is also possible to generate a driving frequency voltage. The oscillating means is not limited to the oscillator 7 using the Colpitts oscillation principle, and other oscillators can be used. further,
It is also possible to use a reactance component including the inductance of the piezoelectric element 3. According to the embodiment described above, since the drive frequency voltage is generated from the reference frequency voltage, it is possible to omit the procedure of changing the monitor voltage comparison reference value while monitoring the drive frequency and the temperature as in the conventional example, No control by a conventional microcomputer is required.

[0011]

The ultrasonic motor driving apparatus according to the present invention has the above-described structure, and uses a part of the reactance component of the piezoelectric element even when the temperature of the stator rises at a high temperature or the like with a simple and inexpensive structure. Since the reference frequency voltage is oscillated by the oscillating means 7 and the reference frequency voltage is used to generate the drive frequency voltage, an excellent effect that the ultrasonic motor can be driven stably is provided. is there.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a driving device of an ultrasonic motor according to the present invention.

FIG. 2 is a front view showing a stator.

FIG. 3 is a circuit diagram showing an oscillator.

FIG. 4 is a sectional view showing an embodiment of the ultrasonic motor.

FIG. 5 is an explanatory diagram showing a relationship between a generated frequency and an amplitude of a stator.

FIG. 6 is a configuration diagram showing another embodiment of the driving device of the ultrasonic motor.

FIG. 7 is a configuration diagram showing a conventional example.

[Explanation of symbols]

1. Ultrasonic motor drive 2. Stator
3. Piezoelectric element, 3-1 to 3-2 ... Driving electrode, 3
-3 ... Oscillation electrode, 4-1 to 4-2 ... transformer,
5-1 to 5-4 ... switching transistors,
6 ... Ring counter, 7 .... Oscillator, 8 ... phase shifter, 9 .... Power amplifier, 15 ... elastic body.

Claims (1)

(57) [Claims] 1. A driving device for driving a traveling wave type ultrasonic motor.
A location, fixing a piezoelectric element to one surface of the elastic body, a stator provided with a drive electrode and oscillation electrodes to the piezoelectric element, depending on the oscillation utilizing reactance of the oscillator electrode <br / An oscillating means for generating a reference frequency voltage, a driving frequency voltage having a predetermined phase difference and a driving frequency is generated by the reference frequency voltage of the oscillating means, and the driving frequency voltage is applied to a driving electrode of the stator. A driving device for an ultrasonic motor, comprising: driving frequency voltage generation means.