Method and apparatus for operating a generator supplying a high-frequency power to an ultrasonic transducer

The method of operating a a generator supplying electrical high frequency power to an electroacoustic transducer operable at a predetermined ultrasonic frequency at which said transducer and a horn coupled thereto art rendered resonant for transmitting ultrasonic energy to a workpiece which is in forced contact with said horn, and wherein the phase angle between the current and the voltage of said power is sensed and digitally processed for controlling the frequency and power supplied by said generator to said transducer, said method comprising the steps of:

• with said horn free of contact with a workpiece, controlling said generator to produce a swept frequency power to said transducer for determining the frequency range between the series resonant frequency and the parallel resonant frequency of said transducer and said horn coupled thereto by sensing the maximum and the minimum current values of the electrical current supplied to said transducer;
• controlling said generator to supply initially to said transducer power having a predetermined start frequency which is above that of said parallel resonant frequency under the conditions when said horn is free of contact with a workpiece and above the parallel resonant frequency under the conditions when said horn is in forced contact with a workpiece;
• and
• in response to the subsequent detection of contact between said horn and a work piece, controlling said generator to lower in discrete steps the frequency of the power supplied to said transducer from said start frequency to the then prevailing parallel resonant frequency as sensed by a substantially zero phase angle, the quantity of discrete steps and at the speed of step changing being responsive to said frequency range.