JPH0251380A - Driving circuit for ultrasonic motor - Google Patents

Abstract

PURPOSE:To stabilize feedback voltage to the temperature change of a stator by connecting electrostatic capacity in parallel with an electrode 1 for feedback. CONSTITUTION:In a driving circuit for an ultrasonic motor, feedback voltage is lowered by a rheostat VR1, rectified and smoothed by a diode D and a capacitor C1 and changed into DC voltage, and input to an operational amplifier OP. A capacitor Ca for stabilization is connected to the feedback voltage input section of a drive power circuit at that time. Accordingly, the variation of capacitance with the modification of cable length with regard to an electrode 1 is small, the variation of feedback voltage can be reduced remarkably, and the circuit is hardly affected, thus easily changing the length of a cable.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides a drive circuit for an ultrasonic motor that frictionally drives a moving body by a traveling wave generated in a stator consisting of an elastic body and an electro-mechanical transducer. In order to optimally control the vibration frequency of the body, the present invention relates to something suitable for stably feeding back a frequency voltage signal detected from vibration of an elastic body to a drive power supply circuit.

[Conventional technology]

In an ultrasonic motor, the stator does not vibrate efficiently unless the frequency of the input excitation frequency voltage is at or near the resonance frequency of the stator, which is composed of an elastic body and an electro-mechanical transducer.

The resonance frequency and vibration amplitude generally fluctuate simultaneously or independently depending on environmental conditions such as changes in temperature and the size of the load. Therefore, fluctuations in the resonance point and vibration amplitude are detected and fed back to the drive circuit. It is necessary to control the excitation frequency to an optimal value.

Therefore, as a method of detecting vibration, the excitation voltage generated by excitation is detected from the part of the electro-mechanical transducer to which the excitation frequency voltage is not applied, and is used by returning it to the drive circuit source (hereinafter referred to as feedback voltage).

This feedback voltage has the same frequency as the excitation frequency of the elastic body, and usually has a value of several tens of kilohertz, and the cable is shielded to prevent leakage of electromagnetic waves.

Therefore, as the cable between the motor body and the drive power supply circuit becomes longer, the line-to-line stray capacitance Cf2 increases, the capacitance component of the input impedance seen from the motor body side becomes smaller, and the feedback voltage becomes inversely proportional to the cable length. This results in significant attenuation.

Therefore, it is troublesome to adjust the circuit portion into which the feedback voltage of the drive power supply circuit is input according to the cable length or to change the circuit constants.

Furthermore, this is a drawback for the user of the general-purpose motor in that the cable length cannot be easily changed.

[Object of the present invention]

The present invention has been made in view of the above-mentioned problems, and it is possible to easily change the cable length without readjusting the drive power circuit, as long as the cable length is within the range of about 10 meters for practical use. An object of the present invention is to provide an ultrasonic motor drive circuit that provides an improved ultrasonic motor drive circuit.

[Explanation of Examples]

The drawings show one embodiment of the invention.

- As shown in Figure 1, the drive circuit for an ultrasonic motor used for boat fishing is such that the feedback voltage is stepped down by a variable resistor VRI, half-wave rectified by a diode D, and smoothed by a capacitor C1 to become a DC voltage, which is then connected to an operational amplifier. Input to OF. Note that the variable resistor VR2 is a motor speed setting polyurethane.

The cable from the vibrator electrode 1, where the feedback voltage is generated, to the variable resistor VR is usually connected over a certain length by a shielded wire.

FIG. 2 shows the circuit configuration of the present invention, in which a stabilizing capacitor C1 is connected to the feedback voltage input section of the drive power supply circuit.

Let Crt be the specific capacitance of the electrode 1, and Cf2 be the stray capacitance of the shielded wire at a practical maximum length of approximately 10 meters.

Here, if the value of the capacitor C1 provided for stabilizing the feedback voltage is at least several times to ten times the value of the stray capacitance Cf2, the combined capacitance as seen from the electrode l is.

Cfft +Cf2 +C@ =Cf1+(2~10)Cfz becomes.

Generally, the capacitance Crt is several hundred PF (picofarad), and the stray capacitance Cf2 is several hundred to 1,000 PF (picofarad).
For example, even if the drive power circuit is adjusted to a cable length of around 1 meter, which is the most commonly used cable length, the cable stray capacitance at that time will decrease to Cf2 /l O, but the combined capacitance Cfft +Cf2 +CB
For example, if we substitute capacitor C1 into stray capacitance cr
When t is taken as 5 times, a Capacity at 10 meters of cable = Cf1 + Cf2 + 5C (2 = Cf + 6Cf2 b Capacity at 1 meter of cable ■ = Cf 1 + 5.1Cf2, and the change of cable length by 10 times (1 meter) Tor→lO
It can be seen that the change in the combined capacity is only about 20% even with respect to the distance (meters).

In this way, the change in capacitance caused by changing the cable length as seen from the electrode 1 is minimal, and the increase or decrease in feedback voltage can be significantly reduced.

The cable length can be easily changed with little effect on the circuit.

The connection position of capacitor C1 has been explained on the drive power supply circuit side, but it goes without saying that the electrical action is exactly the same whether it is near the electrode capacitance Off+ or near the cable stray capacitance Cf2. .

[Effects of the present invention]

As described above, according to the present invention, by connecting a capacitor in parallel to the feedback electrode 1, it is possible to easily change the cable length within a practical range.

Further, since the specific capacitance Crt of the electrode l changes depending on the stator temperature, the present invention compresses the capacitance change and transmits it to the drive power supply circuit, so that the feedback voltage can be adjusted against the stator temperature change. It also has the secondary effect of being stable.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 shows a commonly used ultrasonic motor drive circuit, and FIG. 2 shows an ultrasonic motor drive circuit showing a feedback voltage input section according to the present invention. It is a circuit. 11 ports 1------One electrode C,---One stabilizing capacitor

Claims (1)

[Claims] Excitation generated by excitation from an electrode to which no excitation frequency voltage is applied to the electro-mechanical transducer of an ultrasonic motor that frictionally drives a moving body by a traveling wave generated in a stator consisting of an elastic body and an electro-mechanical transducer. An ultrasonic motor drive circuit characterized in that the circuit is configured such that a capacitance is connected in parallel to the electrode when a voltage is fed back to the drive circuit source.