Dimensionamento e controllo di un generatore ad ultrasuoni per dispositivi piezoelettrici

This thesis deals with the project of the control of amplifier for ultrasonic welding devices. Despite of other ways of welding (hotplate welding, friction stir welding, plasma welding, electric welding) ultrasonic welding is clean, reliable, consistent and affordable process. It needs no pre-weld or post-weld operations, it uses no consumables of any nature, it is user and environment friendly and it is rapid, repeatable process. Invariably, ultrasonic assembly weld times are less than one second, far less than moulding times. Moreover the consumption of energy is perhaps the lowest by any other process. The power delivered to welder has to treated very carefully and the project of ultrasonic generator is strictly connected with the mechanical configuration of welder. Ultrasonic generator must stress only the resonance frequency of piezoelectric transducer that is the first electromechanical component that converts electrical energy to mechanical one. Ultrasonic transducer has to be connected to generator in order to receive the maximum power generated. A number of different matching circuits that allow the maximum efficency coupling are studied. One of this, ”L” matching circuit, is the best solution for ultrasonic welders. This thesis collects a number of measures taken of ultrasonic welder machine available at DTG (Department of Management and Engineering) of University of Padova. This measures are useful to understand how the generator work and the general control scheme for ultrasonic welders. Usually we have to keep systems far from resonance point: this control must to maintain the mechanics system in resonance to maximize the electromechanical power conversion from piezoelectric transducer to welding point. This can be possible with PLL control and maximum seeking control algorithms. Assuming that the transducer can be modeled with BVD electrical scheme, a Simulink scheme of ultrasonic generator and PLL control is developed and compared with measures of prototype in use. The foundamental result is the possibility to use ”L” matching to maximize power delivered to the piezoelectric transducer at resonance frequency. PLL control is investigated and Extremum seeking control theory is introduced to optimize results