JP5303759B2 - Drive unit for piezoelectric vibrator - Google Patents

Description

The present invention provides a technique for stably generating ultrasonic vibration using a piezoelectric vibrator.

A general Langevin type ultrasonic piezoelectric vibrator has a resonance frequency fr, and has a property of resonance that vibrates most efficiently when a drive signal matching the resonance frequency is given. However, since the resonance range is narrow and changes with temperature or the like, it is always necessary to accurately follow the resonance frequency.
On the other hand, in the piezoelectric vibrator, as shown in the equivalent circuit of FIG. 2, an inductance L corresponding to mass, a capacitor C corresponding to a spring constant, and a resistance R corresponding to a load are connected in series. This LCR series circuit is the vibration of the mechanical system. On the other hand, there is an electrically parasitic capacitance Cd. When resonance occurs, the impedance of L and the impedance of C cancel each other, and the phase of the current flowing through the LCR series circuit matches the phase of the applied voltage.
Therefore, a state close to resonance can be maintained by assembling a PLL circuit so that the phase of the applied current and the current flowing through the piezoelectric vibrator coincide. The error from the resonance point is caused by the current flowing through the parasitic capacitor Cd.
In order to eliminate this error, there is a circuit that cancels out the current flowing through the parasitic capacitor Cd by inserting a correction capacitor in parallel with the piezoelectric vibrator and subtracting the current value as disclosed in Patent Document 1. This has the advantage that no error occurs even if the resonance frequency changes. However, a comparison circuit, a multiplication circuit, and a subtraction circuit are required, and there is a disadvantage that the circuit becomes complicated. Also, the higher the frequency, the more problematic the operation speed of each circuit, and there was a limit.
JP-A-8-117687

The problem is to realize the function of subtracting the current flowing from the correction capacitor connected in parallel with the piezoelectric vibrator from the current flowing from the piezoelectric vibrator with a simple structure and to operate at a higher frequency. .

The present invention has the function of subtracting the current flowing from the correcting capacitor connected in parallel with the piezoelectric vibrator from the current flowing from the piezoelectric vibrator, with the core wire made of a magnetic material having a high magnetic permeability as the center. By rotating in the opposite direction, a magnetic force of a value obtained by subtracting both currents is generated in the magnetic path of the iron core, and by subtracting this magnetic force as an electrical signal by the converter, the subtraction result of both currents can be extracted.

According to the method of claim 1 of the present invention, the influence of the parasitic capacitor Cd can be reliably eliminated with a simple structure. As a result, the resonance frequency can always be accurately followed and high-efficiency vibration can be generated. In addition, since the iron core is simple, the circuit becomes simple and operation at a high frequency is possible.

It is a figure explaining an Example. It is a figure explaining the equivalent circuit of a piezoelectric vibrator. It is a figure explaining the converter of Claim 3. It is a figure explaining the converter of Claim 4.

Embodiments of the present invention will be described below. The embodiments described below are specific examples for carrying out the present invention, and thus various technical limitations are made. However, the present invention is particularly limited in the following description. Unless otherwise specified, the present invention is not limited to these forms.

FIG. 1 shows an embodiment of the present invention. A piezoelectric vibrator 10 and an oscillation source 50 for applying a high frequency driving voltage thereto are provided, and a correcting capacitor 20 is connected in parallel with the piezoelectric vibrator 10 to apply a high frequency driving voltage. By rotating the current flowing through the piezoelectric vibrator 10 and the current flowing through the correction capacitor 20 opposite to each other about the core wire of the core 30 made of a high permeability magnetic material, The magnetic force of the value obtained by subtracting the current of is generated. This magnetic force is taken out as an electrical signal by the converter 40, and the correctly corrected current phase is detected. By comparing the current phase and the voltage phase with a PLL circuit or the like and controlling the frequency of the applied voltage so as to be the same phase, it is possible to accurately follow the resonance frequency.

If the parasitic capacitor capacitance Cd of the piezoelectric vibrator 10 and the capacitance Dd of the correction capacitor 20 are the same, the turns ratio to the iron core 30 may be 1: 1. If Cd: Dd = N: 1, the same effect can be obtained by setting the number of turns to 1: N.
The iron core 30 is made of a material having high magnetic permeability (such as ferrite) and has a rod shape or a ring shape.
As described in claim 3, the converter 40 can be realized by winding a coil around the iron core 30 and connecting resistors to both ends. A current phase obtained by subtracting the current of the parasitic capacitor from the current of the piezoelectric vibrator is obtained as the voltage across the resistor.
As another method, as described in claim 4, there is a method of embedding a Hall element in the magnetic path of the iron core 30 and measuring the current phase from the resistance value of the Hall element.

  The use of ultrasonic waves has spread to cleaning, measurement, processing, and medical care. Realization of highly efficient vibration generation can be expected to improve product output, reduce costs and save energy.

DESCRIPTION OF SYMBOLS 10 Piezoelectric vibrator 20 Correction capacitor 30 Iron core 40 Converter 50 that changes the magnetic force of the magnetic path of the iron core into an electrical signal

Claims (4)

A piezoelectric vibrator 10 and an oscillation source 50 for applying a high frequency driving voltage to the piezoelectric vibrator 10 are provided, and a correction capacitor 20 is connected in parallel with the piezoelectric vibrator 10 so that the current flowing through the piezoelectric vibrator 10 and the correction By rotating the current flowing through the capacitor 20 opposite to the left and right around the core wire of the iron core 30, a magnetic force having a value obtained by subtracting both currents is generated in the magnetic path of the iron core 30, and the converter 40 generates an electric signal. A method of detecting and correcting the corrected current phase. Piezoelectric vibrator 10, oscillation source 50 for applying a high frequency drive voltage to the piezoelectric vibrator 10, correction capacitor 20 connected in parallel with the piezoelectric vibrator 10, current flowing through the piezoelectric vibrator 10 and the correction An iron core 30 in which the current flowing through the capacitor 20 is rotated opposite to each other about the core wire, and a converter 40 that phase-combines the magnetic force flowing in the magnetic path of the iron core 30 into a current signal,
A drive device for a piezoelectric vibrator, comprising: a control circuit for controlling the oscillation source 50 to drive the piezoelectric vibrator 10 at a resonance point. The drive device according to claim 2, wherein the converter (40) includes a coil wound around the iron core (30) and a resistor electrically connected in parallel to both ends of the coil. The drive device according to claim 2, wherein the converter (40) includes a Hall element disposed in a magnetic path of the iron core (30) and a circuit that measures a magnetic field passing through the Hall element.