Pll Frequency Control For Ultrasonic Generators

2" SIBERIAN RUSSIAN STUDENT WORKSHOP EDM'2001, SECTION II,3-7 JULY, ERLAGOL

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System of Phase-Locked-Loop Frequency Control of Ultirasonic Generators Vladimir N. Khmelev, Roman V. Barsukov, Alexey N. Slivin, Sergey N. Tclnyganok Biysk Technological Institute, Biysk, Altay territov, Russia

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ence occurs, the detuning of frequency of the oscillatory system and the electronic generator takes place. A " f

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he ultrasonic technologies at present are widely used. They are considered to be different technological processes, which run under the influence of ultrasonic fluctuations of high intensity (1-10 W/sm2).The high rate of spreading of these technologies is due to the fact that when ultrasonic energy is entered into the operation zone of significant acceleration almost all known physical, chemical and others processes occurs. The ultrasonic fluctuations of high intensity are formed in the processed technological ambiences with the help of ultrasonic generators (see Fig.l), providing the transformation of the power of industrial electric mains into the energy of ultrasonic fluctuations.

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Fig. 2. Amplitude-frequency characteristic and phase-freiuency per-

formance of ultrasonic oscillatory system

Fig. 1. The scheme of ultrasonic device.

The ultrasonic technological device consists of a generator of electric fluctuations (l), which generates the variable voltage with ultrasonic frequency for the power supply of the mechanical oscillatory system (23. The ultrasonic oscillatory system is represented by the resonance system, incorporating the piezoelectric transducer (3) for transformation of electric fluctuations of ultrasonic frequency into the mechanical fluctuations of the same frequency, and a concentrator (4), intended for enhancement of mechanical fluctuations and co-ordination of impedances of technological ambience and the piezoelectric transducer. I and U are the current and power voltage of piezoelectric transducer oscillatory system. The behaviour of the operating ultrasonic technological device is illustrated in the Fig. 2, where the amplitudefrequency characteristic and phase-frequency performance of the ultrasonic oscillatory system are shown, where x is the amplitude of fluctuations and y is the phase between I and U. Obviously, for obtaining of the maximal amplitude of fluctuations and the maximal effcct of .the ultrasonic influence the system must work under the resonance frequency for this system (point A). Speaking about the variety of technological processes it should be noted that each technological ambience is fully determined by the acoustic load on the electronic generator for that the influence between the ultrasonic oscillatory system and the technological ambiences exists. For this reason, different technological ambience effects on the characteristic oscillatory features of oscillatory system, such as the resonance frequency, the quality factor, and when the change of technological ambi-

On the other hand, the influence of ultrasonic fluctuations on the technological ambience entails the change of their physical and acoustic characteristics and this also results in the changes of the resonance frequency of the oscillatory system. Besides, the functioning ultrasonic oscillatory system is inevitably heating due to the intemal losses that also changes the oscillatory features. In accordance with mentioned above, the different technological ambiences, the changes of the acoustic characteristics under ultrasonic influence, the oscillatory system heating, the instability of frequency of an electronic generator proper are main factors that mostly determine the resonance frequency of the oscillatory system. Thereby to perform an effective function of this ultrasonic device for intensification of different technological processes a generator should have a system for an automatic frequency searching and tuning in terms of changes of the oscillation system resonance frequency. The systems of phase-locked-loop frequency control (PLLFC) with manual resonance frequency searching in the given band of frequencies have been recently used. Such systems require constant checking of the PLLFC work as in consequence of various reasons the generator's "failure" can occur at the resonance point. Moreover, in designing of the complex osYillatory systems it should be taken into account that there are a lot of resonances closely located with each other. Due to this fact, it becomes difficult to tune the necessary resonances and uneven changes in the resonance frequencies occur. The above said causes the development of more intellectual system of searching, tuning, retaining resonance frequency of ultrasonic oscillatory system. In the Fig. 3 the PLLFC system is shown, where microcontroller (MC) is used as a phase comparator RISC. The microcontroller application in the system PLLFC has provided the possibility of establishing of the initiating logic of functioning of the electronic generator depending on the specified conditions and realising of

ISBN: 5-7782-0347-0 0 2001 NSTU

KHMELEV: SYSTEM OF PHASE-LOCKED-LOOP FREQUENCY CONTROL OF ULTRASONIC GENERATORS

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the universal algorithms of ultrasonic device control in consequence of which its reliability and capacity increases. Such system allows to fix all available resonances in operational band of frequencies and to work over the optimum one.

Fig. 3. - PLLFC ultrasonic generators system.

Fig.3 shows that in the combination with the system PLLFC there is VCO (the voltage-controlled oscillator), which works out the band of frequencies f l ...a of the ultrasonic range when the voltage changes at its input within the boundaries Uvco=O....U1. The voltage desired at the input VCO is formed in integrating square-wave pulses by the chain RC, generated by the controller at output D. The change of this voltage is effected via space pulses changes. With. the information on the phase correlation of current and voltages of the oscillatory system of the controller starts the processing of signals, coming to its inputs A and B. On the input A the signalfis flashing at the output VCO which phase is equal to the phase of voltage of the oscillatory system, on the input B the square-wave signalfbaseis given, which phase is a phase of the current flowing through it. Besides measuring of the period of signals on the input A or B it is possible to calculate the current operation frequency. Thus the controller receives entering signals with further processing that enables an effective control of the ultrasonic oscillatory system. The offered system PLLFC was marketable. The algorithms of the system control management were designed and marketed. The studies carried out have shown the high technical features of the given systems under the following conditions: . - when the change of the own resonance frequency of the oscillatory system due to the change of the acoustic features and change of temperature from 0 to 200 degrees is located within 2-3 kHz,the offered system provides stable functioning of the electronic generator at the frequency in correspondence with changing of own frequency of the ultrasonic oscillatory system; - when using the stagger-peaked oscillatory systems, with a majority of stray resonances closed to the main longitudinal resonances, the offered system works efficiently at the frequency of the main resona2ce whereas offer resonances are changing. The offered system was used in the combination of ultrasonic technological devices of different power, intended for the realisation of various technological processes.