METHOD FOR IMPROVING THE STARTUP OF AN ULTRASONIC SYSTEM UNDER ZERO LOAD CONDITIONS

摘要

The start up performance of an ultrasonic system under zero load conditions is improved by setting a phase set point in a frequency control loop such that, at start up under zero load conditions, the phase set point intersects a point on a phase-frequency response curve which has a low positive slope. This intersection point on the phase-frequency response curve changes as the load is increased and the system Q is decreased. The controller "seek s" a target 0.degree. impedance phase angle. The frequency of the ultrasonic generator is set to a n off-resonance frequency which is lower than the resonance of any known hand piece/blade combination. In order for the drive voltage to not exceed the physical limit of the system, the drive current is set to a low level. The drive frequency is then smoothly increased in steps unti l the target 0.degree. impedance phase delta is located.