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DESCRIPTION JP2000152674

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DESCRIPTION JP2000152674
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
drive device for an ultrasonic transducer. More specifically, the present invention relates to a
drive device of a piezoelectric ultrasonic transducer such as a Langevin type ultrasonic
transducer used for an ultrasonic treatment apparatus for surgical operation, an ultrasonic
welding machine or the like.
[0002]
2. Description of the Related Art In general, a Langevin type ultrasonic transducer is constructed
by sandwiching a laminated body in which piezoelectric elements and electrode plates are
alternately stacked with a metal block and tightening the whole with a bolt. Such an ultrasonic
transducer has a resonant frequency which is physically determined from its structure etc., and
when driven around this resonant frequency, the electrical equivalent circuit of the ultrasonic
transducer has mechanical vibration characteristics. A series resonance circuit consisting of a coil
and a capacitor representing the resistor and a resistor representing a mechanical load is
connected in parallel to a damping capacitor generated by the piezoelectric element and the
electrode plate. Only the current flowing through the series resonant circuit of this equivalent
circuit contributes to the vibration of the ultrasonic transducer. Therefore, by making the current
flowing through the series resonant circuit as large as possible, the ultrasonic transducer is
vibrated most efficiently. In other words, in order to vibrate the ultrasonic transducer most
efficiently, the ultrasonic transducer may be driven at a frequency at which the impedance of the
series resonant circuit of the ultrasonic transducer is minimized, that is, at a resonant frequency.
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However, the coil and capacitor that determine the resonance frequency slightly change
depending on the load conditions applied to the tip of the ultrasonic transducer, environmental
conditions such as temperature, and temporal changes, and the resonant frequency of the
ultrasonic transducer fluctuates.
[0003]
On the other hand, when the ultrasonic transducer resonates, the series resonant circuit of the
equivalent circuit is only a resistor, and the current flowing through the series resonant circuit
and the voltage applied to the ultrasonic transducer are in phase. By adjusting the drive
frequency of the ultrasonic transducer using this fact, the ultrasonic transducer can be driven
following the fluctuation of the resonant frequency.
[0004]
An apparatus disclosed in Japanese Patent Application Laid-Open No. 8-117687 is known as a
drive apparatus for efficiently driving the above Langevin type ultrasonic transducer following
the fluctuation of its resonance frequency. In this ultrasonic transducer driving device, in order to
drive the ultrasonic transducer at the fluctuating resonance frequency, the phase component of
the current flowing in the series resonant circuit of the equivalent circuit of the ultrasonic
transducer is detected by a predetermined method. ing. More specifically, a correction capacitor
is connected in parallel to the ultrasonic transducer, and the current flowing in the correction
capacitor and the current flowing in the ultrasonic transducer are detected. The detected current
flowing through the correction capacitor is amplified by the amplifier at a predetermined
amplification factor. The amplification factor of this amplifier is predetermined so that the
current flowing through the damping capacitor of the ultrasonic transducer is equal to the
amplified current flowing through the correction capacitor. Thus, the amplification factor is
determined, and the current flowing through the correction capacitor amplified by the
amplification factor and the current flowing through the ultrasonic transducer are phase
synthesized to obtain the current flowing through the series resonant circuit of the ultrasonic
transducer. The phase component is calculated. The drive frequency of the ultrasonic transducer
is controlled so as to be in phase with the calculated phase component of the current flowing
through the series resonant circuit and the phase component of the voltage applied to the
ultrasonic transducer. Adjusted with Thus, the ultrasonic transducer is driven following the
fluctuation of its resonance frequency.
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[0005]
SUMMARY OF THE INVENTION In such a driving device for an ultrasonic transducer, an
amplifier is used so that the current flowing through the correction capacitor is equal to the
current flowing through the damping capacitor of the ultrasonic transducer. The amplification
factor of is predetermined. However, when the ultrasonic transducer is driven for a long time or
when the ultrasonic transducer is left in a low temperature atmosphere for a long time, the
temperature change of the ultrasonic transducer itself changes the capacitance of the braking
capacitor Resulting in. As a result, the current flowing to the damping capacitor of the ultrasonic
transducer changes during the driving of the ultrasonic transducer, so even if the current flowing
to the correction capacitor is amplified with a predetermined amplification factor, this amplified
current And the current flowing to the damping capacitor of the ultrasonic transducer are not
equal. Therefore, even if the current flowing in the amplified correction capacitor and the current
flowing in the ultrasonic transducer are phase synthesized, it is possible to properly calculate the
phase component of the current flowing in the series resonant circuit of the ultrasonic
transducer as a result. It was impossible. Since the current flowing through the series resonance
circuit of the ultrasonic transducer thus calculated is not appropriate, PLL control is not properly
performed, and it has been impossible to always drive the ultrasonic transducer at its resonance
frequency.
[0006]
The present invention has been made in view of the above-mentioned problems, and the object of
the present invention is to provide an ultrasonic treatment apparatus for surgical operation in
which an ultrasonic transducer is always driven reliably at its resonance frequency and
diversified. An object of the present invention is to provide a drive device of an ultrasonic
transducer which can easily cope with ultrasonic welding and the like which are diversified.
[0007]
A driving device for an ultrasonic transducer according to the present invention drives an
ultrasonic transducer in a driving device for an ultrasonic transducer for driving an ultrasonic
transducer at its resonance frequency. And a signal oscillation source that superimposes and
outputs a signal of a capacitance measurement frequency for substantially measuring the
capacitance of the ultrasonic transducer, different from the drive frequency, on the signal of the
drive frequency for driving, and ultrasonic vibration First signal detecting means for detecting a
first electric signal generated in the child and second signal detecting means for detecting a
second electric signal generated in a correction element connected in series or in parallel to the
ultrasonic transducer And amplification means for amplifying at least one of the first and second
electrical signals, and a signal obtained by extracting capacitance measurement frequency
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3
components of the first and second electrical signals. Increase to adjust amplification factor
Phase adjustment means, phase signal calculation means for calculating a resonance circuit
phase signal corresponding to a drive frequency component of current flowing in a series
resonance circuit of an ultrasonic transducer, using a signal amplified at an amplification factor
by the amplification means; Frequency control means for controlling a drive frequency of a
superimposed signal oscillation source using a resonant circuit phase signal and a drive
frequency component extracted from an output signal of the superimposed signal oscillation
source or a voltage signal applied to an ultrasonic transducer It is characterized by having.
[0008]
Preferably, the amplifying means amplifies both the first and second electrical signals.
Further preferably, the phase signal calculation means calculates a resonant circuit phase signal
by performing phase synthesis on the signal amplified by the amplification means and either one
of the first and second electric signals.
Alternatively, preferably, the phase signal calculation means calculates a resonant circuit phase
signal by performing phase synthesis of the first electric signal amplified by the amplification
means and the second electric signal amplified by the amplification means.
[0009]
Preferably, the first electrical signal is a voltage signal applied to the ultrasonic transducer, and
the second electrical signal is a voltage signal applied to the correction element. Alternatively,
preferably, the second electrical signal is a current flowing to the correction element, and the
first electrical signal is a current flowing to the ultrasonic transducer. In these cases, the
amplification factor adjustment means may calculate the ratio between the capacitance
measurement frequency component of the first electric signal and the capacitance measurement
frequency component of the second electric signal, and adjust the amplification factor based on
this ratio. desirable. For example, the correction element is a capacitor or a coil.
[0010]
A second ultrasonic transducer drive apparatus according to the present invention is an
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ultrasonic transducer drive apparatus for driving an ultrasonic transducer at its resonance
frequency, the drive frequency signal for driving the ultrasonic transducer. Different from the
drive frequency, and a superimposing signal oscillation source that superimposes and outputs a
signal of a capacitance measurement frequency for substantially measuring the capacitance of
the ultrasound transducer, and is connected in series to the ultrasound transducer. And second
signal detection means for detecting a second electric signal generated in the correction element,
and any one of two correction elements connected in a bridge shape with respect to the
correction element and the ultrasonic transducer. A third signal detection means for detecting a
third electric signal generated on one side, an amplification means for amplifying at least one of
the second and third electric signals, and an ultrasonic transducer Voltage signal and the second
and third electrical signals The amplification factor adjustment means for adjusting the
amplification factor of the amplification means based on the signal obtained by extracting the
capacitance measurement frequency component of any two signals, and the signal amplified by
the amplification factor by the amplification means Phase signal calculation means for
calculating a resonant circuit phase signal corresponding to a drive frequency component of
current flowing through a series resonant circuit of an ultrasonic transducer, a resonant circuit
phase signal, an output signal of a superimposed signal oscillation source, or an ultrasonic
transducer And a frequency control means for controlling the drive frequency of the
superimposed signal oscillation source using the drive frequency component extracted from the
applied voltage signal.
[0011]
Preferably, the amplifying means amplifies both the second and third electrical signals.
Further preferably, the phase signal calculation means calculates a resonant circuit phase signal
by performing phase synthesis on the signal amplified by the amplification means and either one
of the second and third electric signals. Alternatively, preferably, the phase signal calculation
means calculates a resonant circuit phase signal by performing phase synthesis on the second
electric signal amplified by the amplification means and the third electric signal amplified by the
amplification means.
[0012]
Preferably, the second electrical signal is a voltage signal applied to the correction element, and
the third electrical signal is a voltage signal applied to one of the two correction elements. In
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these cases, the amplification factor adjustment means may calculate the ratio of the capacitance
measurement frequency component of the second electric signal to the capacitance measurement
frequency component of the third electric signal, and adjust the amplification factor based on this
ratio. desirable. For example, the correction element is a capacitor.
[0013]
Preferably, in order to make the drive frequency component of the output signal of the
superimposed signal oscillation source substantially in phase with the drive frequency
component of the voltage signal applied to the ultrasonic transducer, a phase for correcting the
phase of the output signal of the superimposed signal oscillation source Correction means is
provided, and the frequency control means controls the drive frequency of the superimposed
signal oscillation source using the signal obtained by extracting the drive frequency component
of the output signal of the superimposed signal oscillation source and the resonant circuit phase
signal. More preferably, a coil capable of resonating with the combined capacitance of the
ultrasonic transducer and the correction element is connected in series to the ultrasonic
transducer. Then, the frequency control means causes the phase lock loop to have a
predetermined phase difference between the resonant circuit phase signal and the drive
frequency component extracted from the output signal of the superimposed signal oscillation
source or the voltage signal applied to the ultrasonic transducer. It is desirable to perform
control to adjust the drive frequency of the superimposed signal oscillation source.
[0014]
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a circuit diagram showing a drive device of an ultrasonic transducer according to a first
embodiment of the present invention. The driving device of the ultrasonic transducer according
to the first embodiment is a device for driving the ultrasonic transducer 1 as efficiently as
possible. When the ultrasonic transducer 1 is driven near its resonance frequency, the equivalent
circuit of the ultrasonic transducer 1 is, as shown in FIG. 1, a coil (L), a capacitor (C) and a
resistor (R) Are connected in series, and a damping capacitor (Cd) connected in parallel to the
series resonant circuit.
[0015]
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In order to drive the ultrasonic transducer 1 efficiently, the ultrasonic transducer 1 must be
driven at its resonance frequency. Therefore, the frequency of the drive signal for driving the
ultrasonic transducer 1 so as to follow the resonance frequency of the ultrasonic transducer 1
which fluctuates due to the load conditions of the ultrasonic transducer 1 and environmental
conditions such as temperature and the time change. Drive frequency) fo is controlled.
[0016]
On the other hand, when the ultrasonic transducer 1 is driven at the resonance frequency, as
shown in FIG. 2, the series resonant circuit of the ultrasonic transducer 1 becomes only the
resistance (R), and the current iZ and ultrasonic vibration flowing in the series resonant circuit
The voltage signal V1 applied to the element 1 has the same phase. The drive frequency fo of the
ultrasonic transducer 1 is controlled by utilizing this. That is, the drive frequency of the
ultrasonic transducer 1 is performed by performing phase lock loop (PLL) control so that the
current iZ flowing through the series resonant circuit and the voltage signal V1 applied to the
ultrasonic transducer 1 have the same phase. Fo is made to follow the resonance frequency of
the ultrasonic transducer 1.
[0017]
The electrical configuration of the drive device of the ultrasonic transducer according to the first
embodiment will be described in detail. The drive device is provided with a superimposed signal
oscillation source 29 that superposes and outputs signals of two different frequencies as an
oscillation source. The superimposed signal oscillation source 29 is provided with an oscillation
source 31 for outputting a relatively high frequency signal and an oscillation source 28 for
outputting a relatively low frequency signal, and the output signal from the oscillation source 28
is added The output signal from the oscillation source 31 is superimposed by the unit 27. The
oscillation source 31 outputs a signal for driving the ultrasonic transducer 1, and the frequency
of this signal is the drive frequency fo of the ultrasonic transducer 1, for example, 20 to 40 kHz.
The oscillation source 28 substantially outputs a signal for measuring the capacitance of the
ultrasonic transducer 1, that is, the capacitance of the damping capacitor (Cd), and the frequency
of this signal is for capacitance measurement. The capacitance measurement frequency fc is, for
example, 1 kHz.
[0018]
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An output signal in which the signal of the capacitance measurement frequency fc is
superimposed on the signal of the drive frequency fo is output from the superimposed signal
oscillation source 29. The output signal is amplified by the power amplification circuit 32, and
the amplified signal is applied to both ends of the correction capacitor 10 a serially connected to
the ultrasonic transducer 1 and the ultrasonic transducer 1.
[0019]
A first voltage detector 33a is connected to both ends of the ultrasonic transducer 1, and a
second voltage detector 33b is connected to both ends of the correction capacitor 10a. The
voltage signal V1 applied to the ultrasonic transducer 1 and the voltage signal V2 applied to the
correction capacitor 10a are detected by the first and second voltage detectors 33a and 33b,
respectively.
[0020]
The voltage signal V 2 applied to the correction capacitor 10 a is amplified by the amplifier 20 at
an amplification factor A. This amplifier (voltage control amplifier) 20 can adjust the
amplification factor A by voltage control, and the amplification factor A is an amplification factor
adjustment circuit according to the fluctuation of the capacitance of the damping capacitor (Cd)
of the ultrasonic transducer 1 It is adjusted by 22. The voltage signal V2 amplified by the
amplification factor A and the voltage signal V1 applied to the ultrasonic transducer 1 are input
to a phase synthesis computing unit 21 which is a subtractor, and phase synthesis is performed
there. A signal component of the drive frequency fo (hereinafter referred to as a drive frequency
component) is extracted from the phase-combined signal by the high pass filter 26 b. The
extracted drive frequency component, that is, the resonance circuit phase signal Vf2 corresponds
to the drive frequency component of the current iZ flowing in the series resonance circuit of the
equivalent circuit of the ultrasonic transducer 1, for example, with respect to the drive frequency
component of the current iZ. It has a predetermined phase difference (for example, 90 °
advance). The resonant circuit phase signal Vf2 is fed back to the PLL control circuit 30.
[0021]
On the other hand, a drive frequency component is extracted from the voltage signal V1 detected
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by the first voltage detector 33a through the high pass filter 26a. The extracted drive frequency
component, that is, the applied voltage phase signal Vf1 is in phase with the drive frequency
component of the voltage signal V1 applied to the ultrasonic transducer 1, and is fed back to the
PLL control circuit 30. In this PLL control circuit 30, the drive frequency component of the
voltage signal V1 and the drive frequency component of the current iZ flowing in the series
resonance circuit of the ultrasonic transducer 1 have the same phase, that is, the applied voltage
phase signal Vf1 and the resonance circuit PLL control is performed so that the phase signal Vf2
has a predetermined phase difference (for example, 90 °), and the drive frequency fo of the
oscillation source 31 is controlled. By this control, the drive frequency fo of the signal output
from the oscillation source 31 follows the resonance frequency of the ultrasonic transducer 1,
and the ultrasonic transducer 1 is driven at the resonance frequency. The high pass filters 26a
and 26b may be provided so that the signal to be fed back to the PLL control circuit 30 is a
driving frequency component, and these high pass filters 26a and 26b are provided on the input
side of the phase synthesis operator 21 to perform phase synthesis The drive frequency
component may be extracted from the voltage signals V1 and V2 before being input to the
computing unit 21.
[0022]
By the way, the electrostatic capacitance of the damping capacitor (Cd) of the ultrasonic
transducer 1 fluctuates due to the temperature change of the ultrasonic transducer 1 itself due to
long-time driving or the like. The phase of the resonance circuit phase signal Vf2 does not
correspond to the phase of the drive frequency component of the current iZ flowing in the series
resonance circuit of the ultrasonic transducer 1 due to the fluctuation of the capacitance of the
damping capacitor (Cd). Therefore, in the driving device of the ultrasonic transducer according to
the first embodiment, even if the capacitance of the braking capacitor (Cd) changes, the phase of
the driving frequency component of the current iZ flowing in the series resonant circuit of the
ultrasonic transducer 1 With respect to the phase of the resonant circuit phase signal Vf2 having
a predetermined phase difference (for example, 90 ° advance phase), that is, the driving
frequency of the current iZ flowing in the series resonant circuit of the ultrasonic transducer 1
The amplification factor A of the amplifier 20 is adjusted by the amplification factor adjustment
circuit 22 so as to correspond to the component.
[0023]
The amplification factor adjustment circuit 22 receives the voltage signal V1 applied to the
ultrasonic transducer 1 and the voltage signal V2 applied to the correction capacitor 10a via the
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low pass filters 25a and 25b. That is, the signal component of the capacitance measurement
frequency fc of the voltage signals V1 and V2 extracted by the low pass filters 25a and 25b
(hereinafter referred to as capacitance measurement frequency component) is input to the
amplification factor adjustment circuit 22. The amplification factor adjustment circuit 22
includes an A / D conversion circuit 22a, a CPU 22b, and a D / A conversion circuit 22c. The
capacitance measurement frequency components of the voltage signals V1 and V2 input to the
amplification factor adjustment circuit 22 are taken into the A / D conversion circuit 22a and
converted there into a digital signal. Those digital signals are compared with each other in the
CPU 22b, and the value of amplification factor A is calculated based on this comparison. A digital
signal corresponding to the value of the calculated amplification factor A is output from the CPU
22c, converted into an analog signal in the D / A conversion circuit 22c, and the amplification
factor A of the amplifier 20 is adjusted according to this analog signal.
[0024]
By adjusting the amplification factor A as described above, the resonant circuit phase signal Vf2
is made to correspond to the drive frequency component of the current iZ flowing in the series
resonant circuit of the ultrasonic transducer 1, and in the PLL control circuit 30, the resonant
circuit phase signal Vf2 and The drive frequency fo of the oscillation source 31 is controlled such
that the applied voltage phase signal Vf1 has a predetermined phase difference. Thus, the drive
frequency fo is made to follow the resonance frequency of the ultrasonic transducer 1.
[0025]
Here, the drive frequency component of the voltage signal V1 applied to the ultrasonic
transducer 1 and the drive frequency of the current iZ flowing in the series resonant circuit of
the ultrasonic transducer 1 apply the applied voltage phase signal Vf1 and the resonant circuit
phase signal Vf2, respectively. It explains that it corresponds to the component.
[0026]
As shown in FIG. 1, the applied voltage phase signal Vf1 is the drive frequency component itself
of the voltage signal V1 applied to the ultrasonic transducer 1, and the applied voltage phase
signal Vf1 and the drive frequency component of the voltage signal V1 have the same phase. It is
clear that there is one.
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That is, the applied voltage phase signal Vf1 is expressed by equation (1). Vf1 = V1 = V ・ Z / (Z
・ (1 + Cd / Cc) + 1 / (j ・ ωO ・ Cc)) (1) where Cd is the capacitance of the braking capacitor
(Cd) and Cc is It is the capacitance of the correction capacitor 10a. Drive when the combined
impedance of the series resonance circuit of the ultrasonic transducer 1 is Z, the resistance value
of the resistor (R) is R, the inductance of the coil (L) is L, and the capacitance of the capacitor (C)
is C The combined impedance Z at the frequency fo is Z = R + j ・ ωO ・ L + 1 / (j ・ ωO ・ C).
Here, ω O = 2πfo. Further, a driving frequency component of a voltage signal applied to both
ends of the ultrasonic transducer 1 and the correction capacitor 10a is V.
[0027]
The driving frequency component of the voltage signal V2 applied to the correction capacitor
10a is expressed by equation (2). V2 = V. (Z.Cd/Cc+1/ (j..omega.O.Cc)) / (Z. (1 + Cd / Cc) + 1 /
(j..omega.O.Cc)) (2)
[0028]
The resonance circuit phase signal Vf2 is the difference between the drive frequency component
of the voltage signal V1 applied to the ultrasonic transducer 1 and the signal obtained by
amplifying the drive frequency component of the voltage signal V2 applied to the correction
capacitor 10a by the amplification factor A. And is calculated by equation (3). Vf2 = V1-A * V2 =
V * (Z-A * (Z * Cd / Cc + 1 / (j * (omega) O * Cc)) / (Z * (1 + Cd / Cc) + 1 / (j * (omega) O * Cc)) (3)
Here, A is the amplification factor of the amplifier 20, and by setting A = Cc / Cd, the resonant
circuit phase signal Vf2 is expressed by the equation (4). Vf2 = j.V.Z / (Z. (1 + Cd / Cc) + 1 /
(j..omega.O..Cc)) / Z / (. Omega.O.Cd) = j.V1 / Z / (. Omega.O.Cd) = j.iZ Where iZ is a drive
frequency component of the current flowing through the series resonant circuit of the ultrasonic
transducer 1, and iZ = V1 / Z. As apparent from the equation (4), the resonant circuit phase
signal Vf2 is proportional to the drive frequency component of the current iZ flowing in the
series resonant circuit of the ultrasonic transducer 1, and is 90 ° out of phase with the drive
frequency component of the current iZ. It is an advanced signal.
[0029]
As described above, the applied voltage phase signal Vf1 has the same phase as the drive
frequency component of the voltage signal V1 applied to the ultrasonic transducer 1, and the
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phase of the resonant circuit phase signal Vf2 has an appropriate amplification factor A (for
example, When it is set to Cc / Cd), it is advanced by 90 ° from the phase of the drive frequency
component of the current iZ flowing in the series resonant circuit of the ultrasonic transducer 1.
Therefore, in the PLL control in the PLL control circuit 30, the drive frequency component of the
voltage signal V1 applied to the ultrasonic transducer 1 and the drive frequency component of
the current iZ flowing in the series resonant circuit of the ultrasonic transducer 1 are in phase.
For this purpose, the drive frequency fo of the oscillation source 31 may be controlled such that
the phase of the resonant circuit phase signal Vf2 advances by 90 ° with respect to the phase of
the applied voltage phase signal Vf1. Of course, either the applied voltage phase signal Vf1 or the
resonant circuit phase signal Vf2 may be advanced by 90 ° or delayed by 90 °, and control
may be performed such that the signals are in phase.
[0030]
In order to properly control the PLL control circuit 30 described above, it is necessary to make
the resonance circuit phase signal Vf2 correspond to the drive frequency component of the
current iZ flowing in the series resonance circuit of the ultrasonic transducer 1. Therefore, the
amplification factor A of the amplifier 20 must always be set to an appropriate value. For
example, as a result of driving the ultrasonic transducer 1 for a long time, it is assumed that the
damping capacitor (Cd) of the ultrasonic transducer 1 becomes n times the capacitance n · Cd. In
this case, if adjusted to A = Cc / Cd ′ = Cc / (n · Cd), the same relationship as the equations (3) to
(4) holds, and the phase of the resonant circuit phase signal Vf2 is an ultrasonic transducer The
phase is advanced by 90 ° from the phase of the drive frequency component of the current iZ
flowing in the series resonance circuit 1. Therefore, even if the capacitance of the damping
capacitor (Cd) changes significantly, if the amplification factor A is set to an appropriate value,
the resonant circuit phase signal Vf2 is not transmitted to the series resonant circuit of the
ultrasonic transducer 1 of the current iZ. It corresponds to the drive frequency component. As a
result, an appropriate resonant circuit phase signal Vf2 is fed back to the PLL control circuit 30,
and the ultrasonic transducer 1 is driven at its resonant frequency by PLL control.
[0031]
Further, even in the case of driving the ultrasonic transducer 1 in which the capacitances of the
braking capacitors (Cd) are different, when the capacitances of the above-mentioned braking
capacitors (Cd) fluctuate by adjusting the amplification factor A of the amplifier 20 Similarly, the
ultrasonic transducer 1 can be driven at its resonant frequency.
[0032]
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As apparent from the above, in the first embodiment, the amplification factor A of the amplifier
20 is adjusted to make the resonance circuit phase signal Vf2 correspond to the drive frequency
component of the current iZ flowing in the series resonance circuit of the ultrasonic transducer 1
Be done.
Further, the value of the amplification factor A can be calculated from the ratio of the capacitance
Cc of the correction capacitor 10a to the capacitance of the braking capacitor (Cd) of the
ultrasonic transducer 1, and It is changed according to the change in capacitance of Cd).
[0033]
The capacitance Cc of the correction capacitor 10a is substantially constant. On the other hand,
the electrostatic capacitance of the damping capacitor (Cd) of the ultrasonic transducer 1
fluctuates due to the temperature change of the ultrasonic transducer 1 due to the long-time
drive of the ultrasonic transducer 1 or the like. Therefore, in order to calculate the value of the
amplification factor A, it is necessary to measure the capacitance of the varied damping capacitor
(Cd). On the other hand, when the ultrasonic transducer 1 is driven at a frequency different from
the resonant frequency, the impedance Z of the series resonant circuit of the ultrasonic
transducer 1 becomes very large, and the equivalent circuit of the ultrasonic transducer 1 is
shown in FIG. Only the braking capacitor (Cd). The capacitance of the braking capacitor (Cd) can
be measured while driving the ultrasonic transducer 1 by utilizing this. That is, while the
ultrasonic transducer 1 is driven at a frequency different from the resonance frequency, for
example, a relatively low frequency capacitance measurement frequency fc (for example, 1 kHz),
the voltage signal applied to the ultrasonic transducer 1 is detected From the voltage signal, it is
possible to calculate the capacitance of the braking capacitor (Cd).
[0034]
In the first embodiment, in order to measure the capacitance of the damping capacitor (Cd) of the
ultrasonic transducer 1, a signal of the capacitance measurement frequency fc is superimposed
on the signal of the drive frequency fo on the ultrasonic transducer 1. A signal is applied.
Therefore, the voltage signal V1 detected by the voltage detector 33a is obtained by
superimposing the voltage signal when the ultrasonic transducer 1 is driven at the drive
frequency fo and the voltage signal when driven at the capacitance measurement frequency fc.
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The capacitance measurement frequency component is extracted from the voltage signal V1 by
the low pass filter 25a, and the capacitance measurement frequency component is output to the
amplification factor adjustment circuit 22 for calculation of the capacitance of the braking
capacitor (Cd), that is, adjustment of the amplification factor A. It is input.
[0035]
The voltage signal V2 detected by the voltage detector 33b is also a voltage signal of the drive
frequency fo and a voltage signal of the capacitance measurement frequency fc superimposed on
each other. The capacitance measurement frequency component is extracted from the voltage
signal V2 by the low pass filter 25b, and the capacitance measurement frequency component is
input to the amplification factor adjustment circuit 22 for adjustment of the amplification factor
A.
[0036]
In the amplification factor adjustment circuit 22, the ratio of the capacitance measurement
frequency component of the voltage signal V1 to the capacitance measurement frequency
component of the voltage signal V2 is calculated as the value of the amplification factor A. The
capacitance measurement frequency component of the voltage signal V1 is a voltage signal
applied to the damping capacitor (Cd) of the ultrasonic transducer 1, and the capacitance
measurement frequency component of the voltage signal V2 is a voltage signal applied to the
correction capacitor 10a It is. Therefore, in amplification factor adjustment circuit 22, the value
of amplification factor A is A = | V1 | / | V2 | = | V.Cc/ (Cd + Cc) | / |, using capacitance
measurement frequency components of voltage signals V1 and V2. It is calculated by V · Cd / (Cd
+ Cc) | = Cc / Cd. That is, the ratio (Cc / Cd) of the capacitance Cc of the correction capacitor 10a
to the capacitance Cd of the braking capacitor (Cd) is calculated as the value of the amplification
factor A.
[0037]
As described above, while the ultrasonic transducer 1 is driven, the value of the amplification
factor A is calculated by the amplification factor adjustment circuit 22 according to the change of
the braking capacitor (Cd) of the ultrasonic transducer 1 and the calculated value The
amplification factor A of the amplifier 20 is adjusted. Therefore, the resonant circuit phase signal
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Vf2 fed back to the PLL control circuit 30 always corresponds to the drive frequency component
of the current iZ flowing in the series resonant circuit of the ultrasonic transducer 1, and PLL
control is performed correctly. Therefore, the ultrasonic transducer 1 is always driven at its
resonance frequency. When the ultrasonic transducer 1 is driven at the capacitance
measurement frequency fc, the equivalent circuit is only the braking capacitor (Cd) as shown in
FIG. 3, so the current iZ flowing in the series resonant circuit of the ultrasonic transducer 1 There
is no capacitance measurement frequency component, and the current iZ is only the drive
frequency component.
[0038]
According to the ultrasonic transducer driving apparatus of the first embodiment described
above, the superimposed signal in which the signal of the capacitance measurement frequency fc
is superimposed on the signal of the driving frequency fo is applied to the ultrasonic transducer
1. During driving of the ultrasonic transducer 1, the capacitance of the braking capacitor (Cd) of
the ultrasonic transducer 1 is measured, and the amplifier 20 is adjusted by the amplification
factor adjusting circuit 22 according to the capacitance of the braking capacitor (Cd).
Amplification factor A is adjusted. Therefore, even if the temperature change of itself occurs due
to long-time driving of the ultrasonic transducer 1 or the like, and the value of the damping
capacitor (Cd) changes, the adjustment of the amplification factor A causes the appropriate
resonance circuit phase signal Vf2 to be PLL controlled It is fed back to the circuit 30, the PLL
control is properly performed by the PLL control circuit 30, and the ultrasonic transducer 1 is
always driven at its resonance frequency. That is, the ultrasonic transducer 1 is driven efficiently.
Also, when driving ultrasonic transducers having different braking capacitors (Cd), it is possible
to drive at the resonance frequency.
[0039]
Furthermore, since the amplification factor A calculated by the amplification factor adjustment
circuit 22 is the ratio (Cc / Cd) of the electrostatic capacitance Cc of the braking capacitor (Cd)
and the correction capacitor 10a, correction is performed even by temperature change or aging.
Even if the capacitance of the capacitor 10a changes, the change is reflected in the value of the
amplification factor A. Therefore, the amplification factor A is set to an appropriate value, and the
ultrasonic transducer 1 is driven at its resonance frequency.
[0040]
10-04-2019
15
FIG. 4 is a drive device of an ultrasonic transducer according to a second embodiment. The
electrical configuration of the second embodiment differs from the electrical configuration of the
first embodiment in that three correction capacitors 10a, 10b and 10c are used, and the other
points are the same. Hereinafter, only differences from the first embodiment will be described
with respect to differences in the electrical configuration and the accompanying points. In the
second embodiment, the three correction capacitors 10a, 10b, and 10c and the ultrasonic
transducer 1 are connected in a bridge shape. That is, the correction capacitor 10a is connected
in series to the ultrasonic transducer 1, and two correction capacitors 10b and 10c connected in
series to both ends thereof are connected in parallel. The correction capacitor 10b has an
electrostatic capacity m · Cd that is m (arbitrary positive number, for example, 1) times of the
braking capacitor (Cd) of the ultrasonic transducer 1, and the correction capacitor 10c is m of
the correction capacitor 10a. It has doubled capacitance m · Cc. The voltage signals V2 and V3
applied to the correction capacitors 10a and 10c are detected by the voltage detectors 33b and
33c, respectively.
[0041]
The detected voltage signal V2 is amplified at an appropriate amplification factor A, and the
amplified signal and the voltage signal V3 are phase-synthesized by the phase synthesis operator
21. The drive frequency component is extracted through the high-pass filter 26b, and the drive
frequency component is fed back to the PLL control circuit 30 as a resonant circuit phase signal
Vf2.
[0042]
The applied voltage phase signal Vf1 is a signal having the same phase as the drive frequency
component of the voltage signal V1 applied to the ultrasonic transducer 1 as in the first
embodiment, and is expressed by equation (1). The resonant circuit phase signal Vf2 corresponds
to the drive frequency component of the current iZ flowing in the series resonant circuit of the
ultrasonic transducer 1. Here, it will be described that the resonant circuit phase signal Vf2
corresponds to the drive frequency component of the current iZ.
[0043]
10-04-2019
16
The drive frequency component of the voltage signal V2 applied to the correction capacitor 10a
and the drive frequency component of the voltage signal V3 applied to the correction capacitor
10c are expressed by the equations (5) and (6), respectively. V2 = V. (Z.Cd/Cc+1/ (j..omega.O.Cc))
/ (Z. (1 + Cd / Cc) + 1 / (j..omega.O.Cc)) (5) V3 = V.Cd / (Cd + Cc) (6)
[0044]
The resonance circuit phase signal Vf2 is the difference between the drive frequency component
of the voltage signal V3 applied to the correction capacitor 10c and the signal obtained by
amplifying the drive frequency component of the voltage signal V2 applied to the correction
capacitor 10a by the amplification factor A. is there. That is, the resonant circuit phase signal Vf2
is expressed by equation (7). Vf2 = V3-A * V2 = V * Cd / (Cd + Cc) -AV * (Z * Cd / Cc + 1 / (j * ωO
* Cc)) / (Z * (1 + Cd / Cc) + 1 / (j * ωO) Cc)) (7) Here, by setting the amplification factor A to A =
1, the resonance circuit phase signal Vf2 becomes the formula (8). Vf2 = jV / (Z. (1 + Cd / Cc) + 1
/ (j.omega.O.Cc)) / (. Omega.O. (Cd + Cc)) = j.V.Z / (Z. (1 + Cd / Cc) + 1 / ( j · ω O · Cc)) / Z / (ω O ·
(Cd + Cc)) = j · V 1 / Z / (ω O · (Cd + Cc)) = j · iZ / (ω O · (Cd + Cc)) ∽ j · iZ · · · (8) From the
equation (8), the resonant circuit phase signal Vf2 is proportional to the drive frequency
component of the current iZ flowing in the series resonant circuit of the ultrasonic transducer 1,
and leads the phase of the drive frequency component of the current iZ by 90 ° It is a signal.
[0045]
As described above, the applied voltage phase signal Vf1 is a signal having the same phase as the
drive frequency component of the voltage signal V1 applied to the ultrasonic transducer 1, and
the phase of the resonant circuit phase signal Vf2 is the series of the ultrasonic transducer 1. It
corresponds to the phase of the drive frequency component of the current iZ that flows in the
resonant circuit. Therefore, in order to make the voltage signal V1 applied to the ultrasonic
transducer 1 and the drive frequency component of the current iZ flowing in the series resonant
circuit of the ultrasonic transducer 1 have the same phase, as in the first embodiment, The PLL
control circuit 30 may control the drive frequency fo of the oscillation source 31 so that the
phase of the resonant circuit phase signal Vf2 always advances by 90 ° with respect to the
phase of the applied voltage phase signal Vf1. Of course, either one of the applied voltage phase
signal Vf1 or the resonant circuit phase signal Vf2 may be advanced by 90 ° or delayed by 90
°, and the signals may be controlled to be in phase.
10-04-2019
17
[0046]
Also in the second embodiment, if the amplification factor A of the amplifier 20 is set to an
appropriate value, the ultrasonic transducer 1 can be driven at its resonance frequency. In the
equation (8), A = 1 is set. However, when the capacitance of the damping capacitor (Cd) of the
ultrasonic transducer 1 changes, it is necessary to adjust the amplification factor A to an optimal
value. In other words, even if the capacitance of the damping capacitor (Cd) of the ultrasonic
transducer 1 fluctuates, the resonance circuit phase signal Vf2 is a series resonant circuit of the
ultrasonic transducer 1 by adjusting the amplification factor A of the amplifier 20.
Corresponding to the drive frequency component of the current iZ flowing to the For example, as
a result of driving the ultrasonic transducer 1 for a long time, it is assumed that the damping
capacitor (Cd) has n times the capacitance, that is, n · Cd. In this case, if the amplification factor A
is adjusted to A = (n · Cd + Cc) / (n · (Cd + Cc)), the same relationship as the equations (7) to (8)
holds. The detailed calculation formula is complicated and therefore omitted here. Further, in the
second embodiment, even when driving the ultrasonic transducer 1 having different capacitances
of the damping capacitors (Cd), the resonance circuit phase signal Vf2 is always an ultrasonic
wave by adjusting the amplification factor A of the amplifier 20. It corresponds to the drive
frequency component of the current iZ flowing in the series resonance circuit of the vibrator 1.
As a result, an appropriate resonant circuit phase signal Vf2 is fed back to the PLL control circuit
30, and the ultrasonic transducer 1 is driven at its resonant frequency by PLL control.
[0047]
The adjustment of the amplification factor A to obtain an appropriate resonant circuit phase
signal Vf2 is performed by the amplification factor adjustment circuit 22 as in the first
embodiment. That is, the capacity measurement frequency components of voltage signals V2 and
V3 applied to correction capacitors 10a and 10c are input to amplification factor adjustment
circuit 22, and the value of amplification factor A for the capacity measurement frequency
component of voltage signal V2 is input. The ratio of the capacitance measurement frequency
component of the voltage signal V3 is calculated. Therefore, in amplification factor adjustment
circuit 22, the value of amplification factor A is A = | V3 | / | V2 | = | V · Cd / (Cd + Cc) | /, using
the capacitance measurement frequency components of voltage signals V2 and V3. Calculated by
| V · n · Cd / (n · Cd + Cc) | = (n · Cd + Cc) / (n · (Cd + Cc)). However, it is assumed that the
electrostatic capacitance of the braking capacitor (Cd) of the ultrasonic transducer 1 is changed
to n · Cd due to a temperature change or the like. If the amplification factor A is calculated as
described above, even if the capacitances of the correction capacitors 10a, 10b, and 10c
fluctuate due to changes over time or temperature, an appropriate value of the amplification
factor A reflecting the fluctuation can be obtained. .
10-04-2019
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[0048]
Also in the second embodiment described above, as in the first embodiment, an ultrasonic wave
is generated by applying a superimposed signal in which a signal of the capacitance
measurement frequency fc is superimposed on a signal of the drive frequency fo to the ultrasonic
transducer 1. During driving of the vibrator 1, the amplification factor A of the amplifier 20 is
adjusted by the amplification factor adjustment circuit 22 in accordance with the capacitance of
the braking capacitor (Cd). Therefore, by adjusting the amplification factor A, an appropriate
resonant circuit phase signal Vf2 is fed back to the PLL control circuit 30, PLL control is properly
performed by the PLL control circuit 30, and the ultrasonic transducer 1 is always driven
efficiently at its resonant frequency. Ru.
[0049]
FIG. 5 shows a circuit diagram of a driving device of an ultrasonic transducer according to the
third embodiment. The third embodiment is different from the first embodiment in that the
correction capacitor 10 a is connected in parallel to the ultrasonic transducer 1, except that the
correction capacitor 10 a is additionally changed. It is similar to the first embodiment. Only the
differences will be described below.
[0050]
In the third embodiment, the correction capacitor 10a is connected in parallel to the ultrasonic
transducer 1, and the voltage detector 33a is provided in parallel to the ultrasonic transducer 1,
and ultrasonic vibration is generated by the voltage detector 33a. The voltage signal V1 applied
to the element 1 is detected, and the drive frequency component of the voltage signal V1 is
extracted by the high pass filter 26a and is fed back to the PLL control circuit 30. Further, a
current detector 34a is connected in series to the ultrasonic transducer 1, and a current detector
34b is connected in series to the correction capacitor 10a. The current detectors 34a and 34b
detect the current i1 flowing to the ultrasonic transducer 1 and the current i2 flowing to the
correction capacitor 10a, respectively, and convert the currents i1 and i2 into voltage signals
with a predetermined conversion coefficient. Be done. Then, the voltage signal corresponding to
the current i2 is amplified by the amplification factor A, and the amplified signal and the voltage
signal corresponding to the current i1 are phase-synthesized by the phase synthesis computing
10-04-2019
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unit 21 which is a subtractor, and the phase synthesis is performed The drive signal is extracted
by the high pass filter 26b. The extracted drive frequency component is fed back to the PLL
control circuit 30 as a resonant circuit phase signal Vf2.
[0051]
Further, voltage signals corresponding to each of the currents i1 and i2 have capacitance
measurement frequency components extracted by the low pass filters 25a and 25b, and these
capacitance measurement frequency components are input to the amplification factor adjustment
circuit 22, where the amplification factor A is appropriately selected. A value is calculated, and
the amplification factor A of the amplifier 20 is adjusted to the calculated value.
[0052]
Also in the third embodiment, the applied voltage phase signal Vf1 fed back to the PLL control
circuit 30 has the same phase as the drive frequency component of the voltage signal V1 applied
to the ultrasonic transducer 1 as in the first embodiment. Signal.
In the third embodiment, the resonant circuit phase signal Vf2 fed back to the PLL control circuit
30 corresponds to the drive frequency component of the current iZ flowing in the series resonant
circuit of the ultrasonic transducer 1, for example, the drive of the current iZ It is a signal in
phase with frequency components. Hereinafter, it will be described that the applied voltage phase
signal Vf1 and the resonant circuit phase signal Vf2 are signals having the same phase as the
drive frequency components of the voltage signal V1 and the current iZ, respectively.
[0053]
The applied voltage phase signal Vf1 is the drive frequency component of the voltage signal V1
applied to the ultrasonic transducer 1 itself. Therefore, the applied voltage phase signal Vf1 is
expressed by equation (9). Vf1=V1 ・・・(9)
[0054]
The resonance circuit phase signal Vf2 is a drive frequency component extracted by the high
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20
pass filter 26b from the output signal of the phase synthesis computing unit 21, and amplifies
the drive frequency component of the voltage signal corresponding to the current i2 flowing to
the correction capacitor 10a. This signal is a signal obtained by subtracting the signal amplified
by the ratio A from the drive frequency component of the voltage signal corresponding to the
current i 1 flowing to the ultrasonic transducer 1. Here, it is assumed that the currents i1 and i2
are respectively detected by the current detectors 34a and 34b, and then converted into voltage
signals by the conversion coefficient k. In this case, the output signals from the current detectors
34a and 34b are k · i1 and k · i2, respectively. Therefore, the resonant circuit phase signal Vf2 is
expressed by equation (10). Vf 2 = k i 1 −A · k i 2 = k · (iZ + iCd) −A · k iCc = k · iZ + k · (iCd−A ·
iCc) (10) where iCd and iCc are respectively damping capacitors (Cd) is a drive frequency
component of the current flowing through the correction capacitor 10a. Here, when the
amplification factor A is determined as A = iCd / iCc = Cd / Cc so that the relationship of iCd = A ·
iCc is established, a resonant circuit phase signal Vf2 is expressed by equation (11). Vf2 = kiz iZ
(11) As apparent from the equation (11), the resonant circuit phase signal Vf2 is in proportion to
the drive frequency component of the current iZ flowing in the series resonant circuit of the
ultrasonic transducer 1 And is in phase with the drive frequency component of the current iZ.
[0055]
Also in the third embodiment, as in the first embodiment, by setting the amplification factor A of
the amplifier 20 to an appropriate value, the current iZ flowing through the resonant circuit
phase signal Vf2 in the series resonant circuit of the ultrasonic transducer 1 It is possible to
correspond to the drive frequency component of
[0056]
For example, as a result of driving the ultrasonic transducer 1 for a long time and raising its own
temperature, it is assumed that the damping capacitor (Cd) has n-fold capacitance Cd '= n.Cd.
In this case, if the amplification factor A is adjusted to A = Cd ′ / Cc = n · Cd / Cc, the same
relationship as the equations (10) to (11) is established. Therefore, by adjusting the amplification
factor A, the resonance circuit phase signal Vf2 can be made to correspond to the drive
frequency component of the current iZ flowing in the series resonance circuit of the ultrasonic
transducer 1. That is, even if the damping capacitor (Cd) of the ultrasonic transducer 1 fluctuates,
the appropriate resonance circuit phase signal Vf2 is fed back to the PLL control circuit 30 by
adjusting the amplification factor A as in the first embodiment. Then, if the drive frequency fo of
the oscillation source 31 is adjusted such that the resonant circuit phase signal Vf2 and the
applied voltage phase signal Vf1 have the same phase, the ultrasonic transducer 1 is driven at
10-04-2019
21
the resonant frequency. Also, when driving the ultrasonic transducer 1 with different
capacitances of the braking capacitors (Cd), if the amplification factor A of the amplifier 20 is
adjusted, the ultrasonic transducer 1 can be controlled similarly by the PLL control circuit 30.
Can be driven at its resonant frequency.
[0057]
The amplification factor adjustment circuit 22 receives the capacitance measurement frequency
component of the voltage signal corresponding to the currents i1 and i2 flowing through the
ultrasonic transducer 1 and the correction capacitor 10a. The capacitance measurement
frequency component of the voltage signal corresponding to the current i1 is a signal when the
equivalent circuit of the ultrasonic transducer 1 is only the braking capacitor (Cd) as shown in
FIG. It corresponds to the capacitance. Therefore, in the CPU 22b of the amplification factor
adjustment circuit 22, using the capacitance measurement frequency component of the voltage
signal corresponding to the currents i1 and i2 as the value of the amplification factor A, A = | k ·
i1 | / | k · i2 | = | j · k · ωc · Cd · V1 | / | j · k · ωc · Cc · V1 | = Cd / Cc is calculated. The
amplification factor A of the amplifier 20 is set to the calculated value. However, it is (omega) c =
2 (pi) fc.
[0058]
Also in the above third embodiment, as in the first embodiment, while the ultrasonic transducer 1
is being driven, in accordance with the capacitance change of the damping capacitor (Cd) of the
ultrasonic transducer 1, that is, The amplification factor A is calculated by the amplification
factor adjustment circuit 22 based on the capacitance measurement frequency components of
the currents i1 and i2 flowing through the ultrasonic transducer 1 and the correction capacitor
10a, and the amplification factor A of the amplifier 20 is adjusted. By adjusting the amplification
factor A, an appropriate resonant circuit phase signal Vf2 is fed back to the PLL control circuit
30, correct PLL control is performed, and the ultrasonic transducer 1 is always driven efficiently
at the resonant frequency. In addition, when driving the ultrasonic transducer 1 having different
capacitances of the damping capacitor (Cd), correct PLL control is performed by adjusting the
amplification factor A, and the ultrasonic transducer 1 is driven at its resonance frequency. can
do.
[0059]
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22
The drive device of the ultrasonic transducer according to the fourth embodiment will be
described with reference to FIG. The fourth embodiment is different from the third embodiment
in that a correction coil 11 is provided in parallel to the ultrasonic transducer 1 in place of the
correction capacitor 10a of the third embodiment. The third embodiment is the same as the third
embodiment except that the second embodiment is changed along with this point. Only the
differences will be described below.
[0060]
The correction coil 11 is connected in parallel to the ultrasonic transducer 1, and the inductance
of the coil 11 is Ld. The current i2 flowing through the correction coil 11 is detected by a current
detector 34b connected in series to the coil 11, and the current i2 is converted into a voltage
signal with a predetermined conversion coefficient. The voltage signal corresponding to the
current i2 is amplified by the amplifier 20, and the amplified signal and the voltage signal
corresponding to the current i1 are phase synthesized by the phase synthesis computing unit 21
which is an adder, and the phases are synthesized. The drive frequency component of the signal
is fed back to the PLL control circuit 30 as a resonant circuit phase signal Vf2. In addition, lowpass filters 25a and 25b respectively extract voltage measurement frequency components
corresponding to the currents i1 and i2 flowing through the ultrasonic transducer 1 and the
correction coil 11, and these capacity measurement frequency components are amplified by the
amplification factor adjustment circuit 22. The value of amplification factor A is calculated there.
[0061]
In the fourth embodiment, the resonant circuit phase signal Vf2 is expressed by equation (12).
Vf2 = k.i1 + A.k.i2 = k. (IZ + iCd) + A.k.iLd = k.iZ + k. (ICd + A.iLd) (12) where k is a conversion
coefficient in the current detectors 34a and 34b. And iLd is a drive frequency component of the
current flowing through the correction coil 11. Here, when the amplification factor A is set so
that the relational expression of iCd + A · iLd = 0 holds, the resonant circuit phase signal Vf2 is
expressed by the equation (11).
[0062]
The correction coil 11 has an inductance Ld that resonates in parallel with the damping capacitor
10-04-2019
23
(Cd) of the ultrasonic transducer 1 at the resonance frequency of the ultrasonic transducer 1, and
Ld = 1 / ((ω r) 2 · C d) It is. However, assuming that the resonance frequency is fr, ωr = 2πfr.
Therefore, the amplification factor A for which the relational expression of iCd + A · iLd = 0 holds
is A = 1, and this value is j · ωr · Cd · V1 + A · V1 / (j · ωr · Ld) = 0, Ld = 1 / It is obtained by
substituting ((ω r) 2 · C d).
[0063]
As described above, also in the fourth embodiment, as in the third embodiment, even if the
capacitance of the damping capacitor (Cd) of the ultrasonic transducer 1 changes, the
amplification factor A of the amplifier 20 is appropriately set. By setting the value to a proper
value, the resonant circuit phase signal Vf2 becomes a signal in the same phase as the drive
frequency component of the current iZ flowing in the series resonant circuit of the ultrasonic
transducer 1.
[0064]
For example, it is assumed that the electrostatic capacitance of the braking capacitor (Cd)
becomes n times the electrostatic capacitance n · Cd.
In this case, if the amplification factor A is adjusted to A = n, the same relationship as the
equations (12) and (11) is established. Therefore, by adjusting the amplification factor A, the
resonant circuit phase signal Vf2 is made to correspond to the drive frequency component of the
current iZ flowing in the series resonant circuit of the ultrasonic transducer 1, and the resonant
circuit phase signal Vf2 and the applied voltage phase signal Vf1 If the drive frequency fo of the
oscillation source 31 is adjusted by the control of the PLL control circuit 30 so as to be in the
same phase, the ultrasonic transducer 1 is driven at the resonance frequency.
[0065]
Also in the fourth embodiment, as in the third embodiment, amplification is performed from the
capacitance measurement frequency component of the voltage signal corresponding to the
currents i1 and i2 flowing through the ultrasonic transducer 1 and the correction coil 11 in the
amplification factor adjustment circuit 22. The rate A is calculated. The capacitance measurement
frequency component of the voltage signal corresponding to the current i1 input to the
amplification factor adjustment circuit 22 is a signal when the equivalent circuit of the ultrasonic
10-04-2019
24
transducer 1 is only the braking capacitor (Cd) as shown in FIG. And corresponds to the
capacitance of the braking capacitor (Cd). Therefore, in the CPU 22b of the amplification factor
adjustment circuit 22, using the capacitance measurement frequency component of the voltage
signal corresponding to the currents i1 and i2 as the value of the amplification factor A, A = (.
Omega.r /.omega.c)@2. I2 | = ([omega] r / [omega] c) 2 || jk * [omega] c * n * Cd * V1 | / | k * V1
/ (j * [omega] c * Ld) | = n * ([omega] r) 2 * Cd * Ld = n is calculated (here (ω r) 2 · C d · L d = 1 is
used). The amplification factor A of the amplifier 20 is determined by the amplification factor
adjustment circuit 22 to this calculated value. However, the inductance Ld of the correction coil
11 is set so that the braking capacitor (Cd) and the correction coil 11 resonate in parallel, and ωr
in the above equation is the angular frequency at the time of the parallel resonance, It is a value.
Also, ω c is an angular frequency at the capacitance measurement frequency fc, which is a
known value.
[0066]
Also in the fourth embodiment described above, as in the third embodiment, the amplification
factor A of the amplifier 20 is equal to that of the braking capacitor (Cd) of the ultrasonic
transducer 1 while the ultrasonic transducer 1 is driven. The resonance circuit phase signal Vf2
can be made to correspond to the drive frequency component of the current iZ flowing in the
series resonance circuit of the ultrasonic vibrator 1 by adjusting according to the capacitance
change, and the correct PLL control is performed. It is possible to always drive the acoustic
transducer 1 efficiently at its resonance frequency. In addition, when driving the ultrasonic
transducers 1 having different braking capacitors (Cd), it is possible to drive the ultrasonic
transducers 1 at the resonance frequency.
[0067]
A driving device for an ultrasonic transducer according to a fifth embodiment will be described
with reference to FIG. The fifth embodiment differs from the first embodiment in that a phase
correction circuit 35 is provided, a voltage detector 33 d is connected to both ends of the
superimposed signal oscillation source 29, and the superimposed signal detected by the voltage
detector 33 d The output signal V4 of the oscillation source 29 is the point where the drive
frequency component is extracted through the high pass filter 26c and is fed back to the PLL
control circuit 30 as the applied voltage phase signal Vf1. Only the differences will be described
below. In the phase correction circuit 35, the output of the superimposed signal oscillation
source 29 is determined by appropriately determining the phase correction amount so that the
applied voltage phase signal Vf1 corresponds to the drive frequency component of the voltage
10-04-2019
25
signal V1 applied to the ultrasonic transducer 1. The drive frequency component of the signal V4
is phase corrected. Thereby, an applied voltage phase signal Vf1 corresponding to the drive
frequency component of the voltage signal V1 applied to the ultrasonic transducer 1 is fed back
to the PLL control circuit 30. Although the phase of the capacitance measurement frequency
component of the output signal V4 of the superimposed signal oscillation source 29 is also
changed by the phase correction circuit 35, the phase of the capacitance measurement frequency
component of the voltage signal V1 and the voltage signal V2 is also changed. The phase change
of the capacity measurement frequency component of V4 does not adversely affect the
calculation of the amplification factor A by the amplification factor adjustment circuit 22.
[0068]
Usually, a large voltage signal of several tens to several hundreds of volts is applied to the
ultrasonic transducer 1. In order to feed this voltage signal back to the PLL control circuit 30, it
is necessary to reduce the magnitude of the voltage signal. The voltage value of the voltage signal
applied to the ultrasonic transducer 1 changes depending on the driving state of the ultrasonic
transducer 1, and the magnitude of the signal fed back to the PLL control circuit 30 according to
the change of the voltage value. Needs to be adjusted. According to the ultrasonic transducer
drive device of the fifth embodiment shown in FIG. 7, the output signal V4 of the superimposed
signal oscillation source 29 has a constant magnitude (voltage value regardless of the drive state
of the ultrasonic transducer 1). , And it is not necessary to adjust the magnitude of the signal fed
back to the PLL control circuit 30 as described above, and the proper applied voltage phase
signal Vf1 is fed back to the PLL control circuit 30, and correct PLL control is performed.
Thereby, the ultrasonic transducer 1 is efficiently driven at the resonance frequency.
[0069]
The phase correction circuit 35 and the voltage detector 33 d applied to the fifth embodiment
are similarly applicable to the second to fourth embodiments as described in each of the
embodiments. The output signal V4 of the superimposed signal oscillation source 29 is fed back
to the PLL control circuit 30, and proper PLL control is performed without adjusting the
magnitude of the signal to be fed back. Further, as shown in FIG. 8, a phase correction circuit 35
is provided between the oscillation source 31 and the adder 27, and the output signal V4 of the
oscillation source 31 is directly detected and fed back to the PLL control circuit 30 as an applied
voltage phase signal Vf1. It may be configured to
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26
[0070]
The sixth embodiment will be described with reference to FIG. The sixth embodiment is different
from the first embodiment in that a coil 36 is connected in series to the ultrasonic transducer 1.
The coil 36 has an inductance Ls that is in series resonance with the combined capacitance of the
ultrasonic transducer 1 and the correction capacitor 10 a at the resonance frequency of the
ultrasonic transducer 1. That is, assuming that the combined capacitance of the ultrasonic
transducer 1 and the correction capacitor 10 a is Cs, the combined capacitance Cs is Cs = Cd · Cc
/ (Cd + Cc), so the inductance Ls of the coil 36 is Ls = (Cd + Cc It becomes / (((omega) r) * Cd *
Cc). By connecting such a coil 36, the driving frequency component of the voltage signal V 1
applied to the ultrasonic transducer 1 is proportional to the mechanical load (R) acting on the
ultrasonic transducer 1. In other words, the connection of the coil 36 realizes a mechanical load
tracking mechanism.
[0071]
In this case, even if the drive frequency component of the output voltage Vs of the power
amplification circuit 32 is constant, the drive frequency component of the voltage signal V1
applied to the ultrasonic transducer 1 acts mechanically on the ultrasonic transducer 1 It is
proportional to the load (R). This can be explained from the fact that the drive frequency
component of the voltage signal V1 applied to the ultrasonic transducer 1 is shown by the
equation (13). V1 = Vs ・ (R / (1 + jωωr ・ Cd ・ R)) / (j ・ ωr ・ Ls + 1 / (j ・ ωr ・ Cc) + R /
(1 + j ・ ωr ・ Cd ・ R)) = Vs ・ R / ( j · ωr · Ls + 1 / (j · ωr · Cc) + R · ((Cd + Cc) / Cc-(ωr) 2 · Ls ·
Cd) =-j · ωr · Cd · Vs · R (13) where Vs Is a drive frequency component of the output voltage of
the power amplification circuit 32, and Ls is the inductance of the coil 36. Here, the ultrasonic
transducer 1 is driven at its resonance frequency, and it is used that the synthetic impedance Z of
the series resonant circuit of the ultrasonic transducer 1 is Z = R. In the equation (13), the
angular velocity ωr is substantially constant because it is determined by the resonance
frequency of the ultrasonic transducer 1, and the capacitance of the damping capacitor (Cd) has
temperature dependency but does not fluctuate extremely. Since the drive frequency component
of the output voltage Vs of the circuit 32 is constant, it can be seen that the drive frequency
component of the voltage signal V1 applied to the ultrasonic transducer 1 is approximately
proportional to the mechanical load (R). In general, since the voltage amplification factor of the
power amplification circuit 32 is constant, the drive frequency component of the output voltage
Vs is constant unless the input voltage to the power amplification circuit 32 is changed.
[0072]
10-04-2019
27
In the sixth embodiment described above, the coil 36 is connected in series to the ultrasonic
transducer 1. Thereby, even if the drive frequency component of the output voltage Vs of the
power amplification circuit 32 is constant, the mechanical frequency (R) on which the drive
frequency component of the voltage signal V1 applied to the ultrasonic transducer 1 acts on the
ultrasonic transducer 1 It becomes proportional and a mechanical load following mechanism is
constituted. Further, in comparison with the method of detecting the current flowing through the
ultrasonic transducer 1 that fluctuates according to the mechanical load (R) and increasing or
decreasing the voltage signal applied to the ultrasonic transducer 1, in the sixth embodiment The
circuit configuration can be greatly simplified. The coil 36 applied to the sixth embodiment is
similarly applicable to the second, third and fifth embodiments.
[0073]
The seventh embodiment shown in FIGS. 10 and 11 is effective when it is desired to drive the
ultrasonic transducer 1 in a floating manner, and in the ultrasonic transducer driving device
shown in FIG. 10, the insulating transformers 37a and 37b, 37 c is provided, and an insulation
transformer 37 a is provided in the ultrasonic transducer drive device shown in FIG. 11. The
configuration in which the ultrasonic transducer 1 is driven in a floating manner by the
insulating transformers 37a, 37b, and 37c is similarly applicable to the second to sixth
embodiments.
[0074]
In the equations (1) to (13) described above, V, V1, V2, V3, Vs, i1, i2, iZ, iCd, iCc, iLd are voltage
signals V, V1, V2, V3, Vs, respectively. Drive frequency components of the current i1, i2, iZ, iCd,
iCc, and iLd. Further, Z is a combined impedance of the series resonance circuit of the ultrasonic
transducer 1 at the drive frequency fo.
[0075]
According to the present invention, the ultrasonic transducer can be always driven with its
resonance frequency at all times, and the ultrasonic treatment apparatus for surgical operation,
which is diversified, and ultrasonic welding, etc., can easily be diversified. A compatible ultrasonic
transducer driving device is provided.
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