Development of a hand-held multicell inverter-based ultrasonic plastic welder

Abstract

This thesis presents the design and development of a multicell inverter for ultrasonic plastic welding applications and other ultrasonic applications. An overview of the main multilevel topologies is given, but this research focuses on the multicelll inverter, because of its capacitor voltage balancing properties. Loading effects of various plastic materials to an ultrasonic plastic welding tool are provided in this thesis. A simple method to create an approximate electrical equivalent circuit of the ultrasonic welding tool, using an impedance analyser, loaded with different plastics is discussed and illustrated. Experimental results of the four-level multicell inverter driving a resistive load and an ultrasonic transducer tool are presented in this thesis. These results provide proof that the multicell inverter topology is capable of driving a non-linear load. The inverter was tested with the ultrasonic load as an ultrasonic plastic welder and an ultrasonic drill. The welding joints on the plastic samples are also evaluated in order to evaluate whether or not this solution is suitable for plastic welding. The ultrasonic drilling results are also shown in this thesis. It is further illustrated that the ultrasonic tool and power supply combination may be used in other ultrasonic applications.