JPH01305699A - Driving circuit for ultrasonic oscillator - Google Patents

Abstract

PURPOSE:To improve driving efficiency by comparing a signal in response to susceptance at the time of driving an ultrasonic oscillator and another signal in response to the susceptance of the ultrasonic oscillator at the time of mechanical resonance and controlling the driving frequency of the ultrasonic oscillator. CONSTITUTION:The signal in response to the susceptance of an ultrasonic oscillator 1 under a driven state generated with a current detector 3, a voltage detector 4, a phase shifter 5, a multiplier 6, a filter 7, and a divider 8 and a signal omegaCd in response to the susceptance of the ultrasonic oscillator 1 under a mechanical resonance state in which the imaginary number component of a current applied to the ultrasonic oscillator 1 and another current applied to a damping capacity Cd of the ultrasonic oscillator 1 become equal are compared at a differential amplifier 9, and the frequency of a VCO 2 to drive the ultrasonic oscillator 1 is controlled according to the difference. Thus, since the mechanical resonance frequency of the ultrasonic oscillator 1 can be followed and driven even when the mechanical resonance frequency changes due to the fluctuation of a load, a temperature change, etc., the ultrasonic oscillator can be driven efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for an ultrasonic transducer used for industrial or medical purposes.

[Prior Art] A conventional ultrasonic transducer drive circuit uses PLL ( Tracking was performed using a phase-locked loop (phase-locked loop) circuit, or the driving frequency was controlled to maximize the current flowing through the ultrasonic transducer.

Among the drive circuits for the ultrasonic transducers mentioned above, as an example of a circuit that uses a PLL (phase-locked loop) circuit to control the drive frequency so that the phase difference between the voltage and current of the ultrasonic transducer becomes zero, there is a 58-1839
There is a publication No. 68.

JP-A-5E1183968 discloses a method in which a capacitance for voltage reduction is connected in parallel to an electrostrictive vibrator, an inductance for power factor correction and a power source are connected in series to the electrostrictive vibrator, and the inductance is adjusted as seen from the power source side. An ultrasonic oscillator using a PLL circuit is disclosed so that the phase difference between drive voltage and current is zero.

[Problems to be Solved by the Invention] As described above, conventional ultrasonic transducers are driven at the resonant frequency at which the phase difference between voltage and current becomes zero, or at the frequency at which the current flowing through the ultrasonic transducer becomes maximum. Each of these driving frequencies is different from the mechanical resonance frequency where the imaginary component of the current flowing through the ultrasonic transducer is equal to the current flowing through the damping capacity of the ultrasonic transducer, and is a frequency far from the mechanical resonance frequency. There was a drawback in that the efficiency at these drive frequencies was lower than the efficiency of drive at the mechanical resonance frequency.

Therefore, an object of the present invention is to improve the driving efficiency by tracking the mechanical resonance frequency of an ultrasonic transducer.

[Means for Solving the Problems] An ultrasonic transducer drive circuit according to the present invention includes a drive means for driving an ultrasonic transducer at a predetermined frequency, and a susceptance that is detected when the ultrasonic transducer is driven. a first signal generating means that outputs a signal according to the susceptance; and a susceptance of the ultrasonic transducer at the time of mechanical resonance in which the imaginary component of the current flowing through the ultrasonic transducer is equal to the current flowing through the braking capacity of the ultrasonic transducer. A second signal generating means generates a signal according to the ultrasonic vibration, compares the output signal of the first signal generating means and the output signal of the second signal generating means, controls the driving means according to the comparison result, and generates an ultrasonic vibration. means for controlling the drive frequency of the child.

[Operation] According to the present invention, a signal corresponding to the susceptance of the ultrasonic transducer during driving, a mechanical resonance in which the imaginary component of the current flowing through the ultrasonic transducer and the current flowing through the braking capacity of the ultrasonic transducer are equal. It is possible to track the mechanical resonance frequency of the ultrasonic transducer by comparing the signal corresponding to the susceptance of the ultrasonic transducer and controlling the driving frequency of the ultrasonic transducer according to the difference. Become.

[Example] 1)1 of the first embodiment will be explained with reference to FIG.

The first terminal of the ultrasonic transducer 1 is connected to the first terminal of the voltage detector 4 and the first terminal of the current detector 3.
The second terminal of is connected to the first terminal of VCO (voltage controlled oscillator) 2 and the gate. A second terminal of voltage detector 4 is connected to ground. The voltage detector 4 detects the voltage between the first and second terminals, that is, the voltage applied to the ultrasonic transducer 1, and outputs a signal corresponding to the detected voltage to the phase shifter 5. The phase shifter 5 outputs a signal obtained by advancing the phase of the input signal by 90 degrees to the multiplier 6. A second terminal of the VCO is connected to a second terminal of the current detector 3. The current detector 3 detects the current between the first and second terminals, that is, the current flowing through the ultrasonic transducer 1, and outputs a signal corresponding to the detected current to the multiplier 6. A multiplier 6 multiplies the output □ of the phase shifter 5 and the output of the current detector 3 to obtain power, and outputs the obtained power to the filter. Filter 7 outputs an imaginary component of power, and supplies the output imaginary component of power to divider 8 . The divider 8 divides the output of the filter by the voltage amplitude V (fixed voltage) and further divides by the voltage amplitude ■ to obtain a signal proportional to the susceptance. The obtained signal is supplied to the non-inverting input terminal of the differential amplifier 9. The inverting input terminal of the differential amplifier 9 is ωCd (angular frequency ω during mechanical resonance, damping capacity Cd of the ultrasonic vibrator)
is connected to a constant voltage source (not shown) that generates a voltage proportional to . Differential amplifier 9 compares a voltage proportional to susceptance with a voltage proportional to ωCd, and supplies an output to integrator 10 according to the comparison result. An integrator 10 holds the output of the differential amplifier 9 and supplies the held signal to a control terminal of a VCO (voltage controlled oscillator) 2.

Figure @3 is an equivalent circuit of the ultrasonic transducer used in the present invention. To explain it specifically, the equivalent circuit of the ultrasonic transducer is a series resonant circuit of inductance L, capacitance C, and electric resistance R, Braking capacitance C connected in parallel to the series resonant circuit
Consists of d. The entire current of the equivalent circuit of the ultrasonic transducer is I
As, inductance L1 inductive capacitance C% electrical resistance R
The current flowing to the side is Ia, and the current flowing to the braking capacity side is Ib.
shall be. At this time, at the mechanical resonance point of the ultrasonic transducer, the impedance of the series resonant circuit is only the electrical resistance R, and the susceptance of the ultrasonic transducer is ωCd.

FIG. 4 is a diagram showing the frequency characteristics of susceptance and conctance of an ultrasonic transducer. Characteristic a in FIG. 4 shows susceptance, and characteristic A in FIG. 4 shows conductance. fm is the frequency at which the admittance is maximum, and t's is the flow to the ultrasonic transducer? The mechanical resonance frequency at which the lSlS miscarriage number component and the current Ib flowing through the damping capacitance Cd of the ultrasonic transducer are equal, and fr indicates the resonance frequency at which the phase difference between voltage and current of the ultrasonic transducer is zero. The susceptance at the time of mechanical resonance is equal to ωCd (angular frequency ω at the time of mechanical resonance frequency, damping capacity ff1cd of the ultrasonic transducer 1). FIG. 5 shows the frequency characteristics of the admittance of the ultrasonic transducer. The vertical axis shows susceptance, and the horizontal axis shows conductance. The susceptance at the frequency of fr is zero.

Next, the operation of the first embodiment will be explained. According to Figure 1,
It is driven by an alternating current voltage output from the ultrasonic transducer 1 or the VCO 2. The voltage detector 4 detects the voltage applied to the ultrasonic transducer 1, and the current detector 3 detects the current flowing through the ultrasonic transducer 1. 'r5. Pressure detection pressure detector device 5
Supplies detection voltage to The phase shifter 5 supplies the multiplier 6 with an output signal whose phase is 90' ahead of the phase of the input signal. The current detector 3 supplies the detected current to the multiplier 6 by (1).

Multiplier 6 multiplies the output signal of phase shifter 5 and the output signal of current detector 3 to obtain power, and supplies the obtained power to the filter. Filter 7 processes the output of multiplier 6. The output signal of the filter 7 is a signal proportional to the imaginary component of power. The output of the filter is then supplied to a divider 8.

Divider 8 divides the output of filter 7 into voltage amplitude V (fixed voltage)
By dividing by , the imaginary component of the current can be determined, and by further dividing by '1·R pressure amplitude V, the susceptance (imaginary component of admittance) during driving can be determined.

The differential amplifier 9 is proportional to the output of the divider 8 and ωCcl.
Compare the voltage and input the signal corresponding to the difference to the integrator]0.
I'll give you something. Integrator h-0 holds the output of differential amplifier 9. Integrator] 0 supplies the control voltage to VCO2, VC
Controls the oscillation frequency of O2.

For example, if the driving frequency of the ultrasonic transducer is lower than the mechanical resonance frequency, the output (susceptance) of the divider 8 will be ωC
If it is larger than d and larger than the drive frequency of the ultrasonic transducer or the mechanical resonance frequency, the output of the divider 8 is smaller than ωCd, and if it is equal to the drive frequency of the ultrasonic transducer or the mechanical resonance frequency, the output of the divider 8 is The output of is equal to ωCd. Therefore,
Differential amplifier 9 outputs the output (susceptance) of divider 8 and ωC
d is compared, and the output corresponding to the comparison result is integrated by an integrator]0 and fed back to the VCO2, and the output (susceptance) of the divider 8 is increased by 1 from ωCd to increase the oscillation frequency of the VCO2. , if the output (susceptance) of the divider 8 is smaller than ωCd, the mechanical resonance frequency can be tracked by lowering the oscillation frequency of ■C○2, and the drive frequency can always be made equal to the mechanical resonance frequency.

The configuration of the second embodiment will be explained with reference to FIG.

The first terminal of the ultrasonic transducer] is connected to the first terminal of the voltage detector 4 and the first terminal of the current detector 3.

The second terminal is connected to the first terminal of the amplifier]1 and to ground. The second terminal of voltage detector 4 is connected to ground. The voltage detector 4 detects the voltage applied to the ultrasonic transducer between the first and second terminals, and rectifies the signal corresponding to the detected voltage. :'i Supply to 1.2. The rectifier [2] rectifies the input signal and supplies the rectified signal to the smoother [3]. The smoother] 3 smoothes the input signal and supplies the smoothed signal to the variable amplifier 14. Variable amplifier]
4 multiplies the input signal by ωCd to obtain a signal corresponding to the current flowing through the braking capacitor Cd, and supplies the obtained signal to the inverting input terminal of the differential amplifier 9. Amplifier 1] amplifies the output voltage of VCO 2 and applies the amplified voltage to ultrasonic transducer].

The current detector 3 detects the current between the first and second terminals, that is, the current flowing through the ultrasonic transducer, and supplies a signal corresponding to the detected current to the multiplier 6. Phase shifter 5 changes the input signal phase to 9
A signal whose phase is advanced by 0° and whose phase is advanced by 90° is supplied to the multiplier 6. Multiplier 6 provides an output to the filter. The filter 7 obtains a signal corresponding to the imaginary component of the current, and supplies the obtained signal to the non-inverting input terminal of the differential amplifier 9. The differential amplifier 9 supplies a signal corresponding to the difference between the output of the variable amplifier 14 and the output of the filter 7 to the integrator 10. Integrator 10 holds the output of differential amplifier 9 and supplies the held signal to VCO 2. VCO2 supplies output to amplifier 11 and phase shifter 5.

Figure 3 shows an equivalent circuit of the ultrasonic transducer used in the present invention. As explained in the first embodiment, at the mechanical resonance point of the ultrasonic transducer, the impedance of the series resonant circuit is only the electrical resistance R. , the susceptance of the ultrasonic transducer is ωC
d, therefore, the imaginary component 1m of the current {circle around (2)} flowing through the entire ultrasonic vibrator becomes equal to the current Ib flowing through the braking capacitance Cd of the ultrasonic vibrator. Therefore, by comparing the imaginary component Im of the current flowing through the ultrasonic vibrator with the current 1b flowing through the damping capacity '14 Cd of the ultrasonic vibrator, the mechanical resonance frequency can be tracked.

The operation of the second embodiment will be explained. According to FIG. 2, the ultrasonic transducer 1 is driven by an alternating current voltage output from the VCO 2 and amplified by an amplifier 11. Voltage detector 4 detects the voltage applied to ultrasonic transducer 1 . The current detector 3 detects the current flowing through the ultrasonic transducer 1. Voltage detector 4 provides an output to rectifier 12 . Rectifier 12 provides an output to smoother 13. smoother] 3 is variable amplifier 1
4. The variable amplifier 14 supplies an output to the inverting input terminal of the differential amplifier 9. That is, the ultrasonic transducer 1
The voltage applied to the variable amplifier 14 is rectified and smoothed.
The damping capacity ff at the mechanical resonance frequency is amplified by ωCd.
i Obtain a voltage proportional to the current 1b flowing through Cd.

On the other hand, the phase shifter 5 advances the phase of the reference voltage of the VCO 2 by 90°. A multiplier 6 multiplies the output of the phase shifter 5 and the output of the current detector 3 to obtain a voltage proportional to the current flowing through the ultrasonic transducer. The output of multiplier 6 is supplied to filter 7. Filter 7 supplies an output to the non-inverting input terminal of differential amplifier 9.

The output signal of the filter 7 is a signal proportional to the imaginary component of the current flowing through the ultrasonic transducer.

Therefore, as shown in FIG. 4, if the driving frequency of the ultrasonic vibrator is lower than the mechanical resonance frequency, the susceptance becomes large, and as a result, the imaginary component Im of the current flowing through the ultrasonic vibrator 1 becomes thicker than Ib.

If the driving frequency is higher than the mechanical resonance frequency, the susceptance becomes smaller, and as a result, the imaginary component 1m of the current flowing through the ultrasonic transducer 1 becomes smaller than Ib.

Using this characteristic, by comparing Ib and Im with a differential amplifier, integrating the difference, and feeding it back to VCO2, I
If +++ is larger than Ib, increase the driving frequency and
If Irrl is smaller than Ib, the driving frequency is lowered, and the part where Irrl is equal to Ib can be tracked and driven at the mechanical resonance frequency at all times. Further, the ultrasonic transducer drive circuit according to the second embodiment does not require a divider and is therefore cheaper than the ultrasonic transducer drive circuit according to the first embodiment.

[Effects of the Invention] Even if the mechanical resonance frequency of the ultrasonic transducer changes due to load fluctuations, temperature changes, etc., the ultrasonic transducer can be driven efficiently by always tracking the mechanical resonance frequency. Furthermore, since the efficiency is high, damage to the ultrasonic transducer, heat generation, etc. can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a drive circuit for an ultrasonic transducer according to an embodiment of the present invention, FIG. 2 is a diagram showing a drive circuit for an ultrasound transducer according to another embodiment of the present invention, and FIG. FIG. 4 is a diagram showing an equivalent circuit of the ultrasonic transducer of the invention, FIG. 4 is a diagram showing the frequency characteristics of the ultrasonic transducer of the invention, and FIG. 5 is a diagram showing the admittance characteristics of the ultrasonic transducer of the invention. . DESCRIPTION OF SYMBOLS 1... Ultrasonic vibrator, 2... VCO13... Current detector, 4... Voltage detector, 5... Phase shifter, 6...
- Multiplier, 7... Filter, 8... Divider, 9... Differential amplifier, 10... Integrator, 11... Amplifier, 12...
... Rectifier, 13... Smoother, 14... Variable amplifier. Applicant's agent Patent attorney Jun Tsuboi (';'-L') EIL'T, bLah (SLLJ
) 'l 'l'JlyL,, b'-, Lots Punishment Fire Shishi Rat City Masu Body Ju Kidney Mu City

Claims (1)

[Claims] a driving means for driving the ultrasonic vibrator at a predetermined frequency; a first signal generating means for detecting the susceptance of the ultrasonic vibrator when it is driven and outputting a signal according to the detected susceptance; and the ultrasonic vibration. a second signal generating means for generating a signal corresponding to the susceptance of the ultrasonic vibrator at the time of mechanical resonance in which the imaginary component of the current flowing through the ultrasonic vibrator is equal to the current flowing through the braking capacity of the ultrasonic vibrator; The ultrasonic transducer comprises means for comparing the output signal of the first signal generating means and the output signal of the second signal generating means, controlling the driving means according to the comparison result, and controlling the driving frequency of the ultrasonic transducer. Ultrasonic transducer drive circuit.