Abstract: A closed-loop ultrasonic welding apparatus for sealing or welding thermoplastic material on a continuous basis wherein the material to be welded is fed through a weld station comprising a horn and anvil. The apparatus includes means for providing a first signal commensurate with a desired ultrasonic energy density in the material when welded, a second signal responsive to the feed speed of the material through the weld station, and a third signal commensurate with the power coupled by a power supply via a transducer and the horn to the material at the weld station. Control means receive the first, second and third signals and produce an error signal, which is responsive to the difference between the desired energy density and the actual energy density coupled to the material. After being subjected to further processing the error signal is converted to a control signal for controlling the output from said power supply and/or controlling the engagement force between the horn and material.

Abstract: An ultrasonic power supply for driving piezoelectric transducers in an ultrasonic cleaning apparatus comprises a full-wave rectifier for providing unfiltered direct current to an inverter circuit of the clamped mode resonant converter type, which provides alternating current output at the series resonant frequency condition of the transducers. The inverter circuit switching cycle is controlled responsive to means for causing a set average power level to be maintained, means for causing the resonant frequency to be maintained and including means for causing the resonant frequency to be swept symmetrically by an adjustable sweep frequency. Also, power modulation means are provided for optionally providing to the transducers power bursts of a set amplitude, but at the set average power level. As a result of the unfiltered direct current from the full-wave rectifier, the power supply will operate substantially at unity power factor.