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A method for flating the phase characteristic of a differential detection signal in one higher and lower regions thereof relative to its resonance frequency by controlling a differential characteristic. A searching, over a range, which is wider than the width of the flat region, is accomplished prio

A method for flating the phase characteristic of a differential detection signal in one higher and lower regions thereof relative to its resonance frequency by controlling a differential characteristic. A searching, over a range, which is wider than the width of the flat region, is accomplished prior to phase characteristic being effected thereby discriminating a fundamental resonance frequency. After this discrimination of the fundamental resonance frequency, automatic tracking is effected under stable corrected phase characteristics for the fundamental resonant frequency whereby high electro-mechanical conversion efficiency can be maintained.

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1. In a driving frequency controlling method for an ultrasonic transducer driving apparatus of the type wherein by differential detection equal damping current components are offset from and cancel each other while the difference between voltages proportional to dynamic current components produces a

1. In a driving frequency controlling method for an ultrasonic transducer driving apparatus of the type wherein by differential detection equal damping current components are offset from and cancel each other while the difference between voltages proportional to dynamic current components produces a vibration velocity signal which is used as a frequency controlling signal for effecting the locking feature of PLL tracking, the improvement wherein one of higher and lower ranges of a phase characteristic of a transducer resonant frequency is made flat by controlling the proportionality characteristic of the voltages whereafter the frequency of a voltage controlled oscillator is swept through one of said flat ranges toward a resonant frequency to determine the fundamental resonant frequency. 2. In a driving frequency controlling method for an ultrasonic transducer driving apparatus of the type wherein by differential detection equal damping current components are offset from and cancel each other and while the difference between voltage proportional to dynamic current components produces a vibration velocity signal which is used as a frequency controlling signal for effecting the locking function PLL tracking, the improvement wherein one of higher and lower ranges of a phase characteristic of a differential detection signal relative to a resonant frequency is made flat by controlling the differential characteristic whereafter the frequency of a voltage controlled oscillator is swept from the flat region toward a resonant frequency to discriminate a fundamental resonant frequency, and then the flat frequency widths of the higher and lower ranges of the phase characteristic when the differential characteristic of a differential detecting circuit is balanced so as to be detected in order to correct the differential characteristics thereof in accordance with values obtained by said detection thereby causing the frequency widths of the flat ranges to be symmetrical with each other. 3. In a driving frequency controlling method for an ultrasonic transducer driving apparatus of the type wherein by differential detection equal damping current components are offset from and cancel each other and while the difference between voltages proportional to dynamic current produces a vibration velocity signal which is used as a frequency controlling signal for effecting the locking function of a PLL tracking, the improvement wherein one of higher and lower ranges of a phase characteristic of a differential detection signal relative to a resonant frequency is made flat by controlling the differential characteristic whereafter the frequency of a voltage controlled oscillator is swept from the flat region toward a resonant frequency to discriminate a fundamental resonant frequency, and a measuring operation of the frequency of said voltage controlled oscillator upon initiation of sweeping and after each lapse of a fixed period of time during PLL tracking as well as an operation for self-compensation of a frequency drift of said voltage controlled oscillator by an oscillation frequency controlling DA converter are effected. 4. A driving frequency control method for an ultrasonic transducer driving apparatus of the type wherein, by differential detection damping equal current components are offset from and cancel each other and while the difference between voltage proportional to dynamic current components produce a vibration velocity signal which is used as a frequency controlling signal effecting the locking function PLL tracking comprising the steps of: making flat one of higher and lower ranges of a phase characteristic of a differential detection signal relative to a resonant frequency by controlling the differential characteristics; and sweeping the frequency of a voltage controlled oscillator from the flat region toward a resonance frequency thereby discriminating a fundamental resonance frequency. 5. A driving frequency control method for an ultrasonic transducer driving apparatus of the type wherein, by differential detection damping equal current components are offset from and cancel each other and while the difference between voltage proportional to dynamic current components produce a vibration velocity signal which is used as a frequency controlling signal effecting the locking function of a PLL tracking, comprising the steps of: making flat one of higher and lower ranges of a phase characteristic of a differential detection signal relative to a resonant frequency by controlling the differential characteristics; sweeping the frequency of a voltage controlled oscillator from the flat region toward a resonant frequency thereby discriminating a fundamental resonance frequency; detecting the flat frequency width of the higher and lower ranges of the phase characteristic when the phase characteristics of a differential detecting circuit is perfectly balanced; and correcting the differential characteristics when the phase characteristics of a differential detection circuit is perfectly balanced; and correcting the differential characteristics in accordance with values obtained by said detecting step thereby making the frequency widths of the flat ranges symmetrical to each other. 6. A driving frequency control method for an ultrasonic transducer driving apparatus of the type wherein, by differential detection damping equal current components are offset from and cancel each other and while the difference between voltage proportional to dynamic current components produce a vibration velocity signal which is used as a frequency controlling signal effecting the locking function of a PLL tracking, comprising the steps of: making flat one of higher and lower ranges of a phase characteristic of a differential detection signal relative to a resonant frequency by controlling the differential characteristics; sweeping the frequency of a voltage controlled oscillator from the flat region toward a resonant frequency thereby discriminating a fundamental resonance frequency; measuring the frequency of said voltage controlled oscillator upon initiation of sweeping and after each lapse of a predetermined fixed period of time during PLL tracking; and self-compensating any frequency drift of said voltage controlled oscillator by an oscillation frequency controlling DA converter.