The resonance frequency drift in the actual working environment of the ultrasonic cleaner
will greatly affect the cleaning efficiency of the ultrasonic cleaner. Therefore, an automatic frequency tracking system of the ultrasonic cleaner is designed. The output frequency of the ultrasonic generator
can track the resonance frequency of the ultrasonic transducer
which changes in the working environment by using the phase control method. .
The magnitude of the phase difference between the voltage at both ends of the transducer and the current flowing through the transducer represents the relationship between the frequency of the excitation signal and the natural frequency of the vibration system. When the transducer is in resonant state, its impedance characteristic is pure resistance characteristic, the phase difference between current and voltage is zero. The phase difference signal between the voltage and current of the transducer is the feedback signal of the resonant frequency of the transducer. According to the feedback signal, the output of the power generator is controlled to realize the automatic frequency tracking. The phase detection circuit is shown in Fig. 4. The collection of load voltage and current signals is realized by Hall sensor, and the signals are sent to the phase detection circuit after current limiting.
If there is a phase difference between current and voltage, when the Q output is high, the current phase is ahead; when the Q output is low, the current phase lags. The phase identification result is sent to the lead pin of the single chip microcomputer, which adjusts the frequency according to the level of the lead. When the low level is read, the current frequency is higher than the resonant frequency, whereas the current frequency is lower than the resonant frequency.