Linear power control for ultrasonic probe with tuned reactance

An apparatus for ultrasonically driving a probe having a mechanical resonant frequency, comprising:

• first means for generating a driving signal for said probe and having an input for receiving a first control signal to control the frequency of said driving signal and for coupling said driving signal to said probe so as to cause load current to flow therein;
• second means coupled to said first means to determine the mechanical resonant frequency of said probe by generating said first control signal so as to incrementally after the frequency of said driving signal throughout a range of frequencies encompassing the mechanical resonance frequency of said probe, and measuring the load current through said probe resulting from said driving signal at each frequency in said range of frequencies and for recording the frequency at which said load current is a maximum and, thereafter, to generate said first control signal so as to tune said first means to generate said driving signal at the frequency which caused said load current to be a maximum;
• a tuning inductor for coupling said drive signal to said probe such that said driving signal passes through said tuning inductor, and having an input for receiving a second control signal which controls the amount of inductance of said tuning inductor;
• means coupled to said tuning inductor for generating said second control signal so as to cause the inductance of said tuning inductor to be at a minimum during the interval when the frequency of said driving signal to being incrementally altered throughout said range of frequencies, and, after said frequency of said driving signal has been set at the frequency which caused said maximum load current, for measuring the phase angle between the voltage of said driving signal and the resultant load current and for generating said second control signal at a level which alters the inductance of said tuning inductor in such a way as to alter said phase angle to be within a predetermined range.

An apparatus for driving an ultrasonic probe with linear power control comprising:

• first means for generating a driving signal for said probe and having an input for receiving a first control signal to control the frequency of said driving signal;
• second means coupled to said first means to occasionally finding the mechanical resonant frequency of said probe under then existing conditions by finding the frequency for said driving signal which causes load current through said probe caused by said driving signal to be maximized and for generating said first control signal to tune said first means so as to generate a driving signal at the mechanical resonant frequency of said probe;
• a tuning inductor including an inductor in series with said probe for coupling said drive signal to said probe and having an input for receiving a second control signal which controls the amount of inductance of said tuning inductor;
• third means coupled to said tuning inductor for minimizing the inductance of said tuning inductor at first predetermined times and for, at second predetermined times, determining the actual phase angle between the driving signal voltage for said probe and the resulting load current and for determining the difference between said actual phase angle and a desired phase angle and for generating said second control signal to tune said tuning inductor to alter said phase angle so as to be within a selected range;
• a foot-operated power control transducer;
• and wherein said first means also has an input for receiving a third control signal which controls the amplitude of the driving signal generated by said first means;
• and
• further comprising means coupled to said first means for determining the desired amount of power to by dissipated in said probe by reading said foot-operated power control transducer and for generating said third control signal so as to control the amplitude of said driving signal linearly in accordance with the setting of said foot-operated power control transducer;
• and further comprising ground fault detection means coupled to said driving signal and to said first means for determining whether said first means and said probe are operating and for generating a control signal which causes said first means to stop generating said driving signal in predetermined circumstances.

An apparatus for driving a phacoemulsification probe containing piezoelectric crystal excitation element comprising:

• a footpedal power control;
• a maximum power control;
• a variable inductor having an inductance value which can be electronically altered;
• first means for generating variable frequency, variable amplitude alternating current driving signal for said crystal and having a first control input for receiving a first control signal which controls the frequency of said driving signal and having a second control input for receiving a second control signal which controls the amplitude of said driving signal;
• second means coupled to said first means for determining the desired power level by reading the position of said footpedal indicating the desired percentage of maximum power and reading the position of said maximum power control to determine the maximum power and calculating the actual power desired using said maximum power and said percentage of maximum power and for generating said second control signal so as to be a linear function of the footpedal position;
• third means coupled to said first means for generating said first control signal so as to sweep said frequency of said driving signal through a range of frequencies and for measuring the load current through said probe at various ones of said frequencies to determine the frequency at which said load current is a maximum and for generating said first control signal such that said driving signal has the frequency which caused the maximum load current to flow;
• means for determining the phase difference between the voltage waveform for the voltage across said probe and current waveforms for the current through said probe resulting from said voltage waveform of the amplified driving signal and for generating an error signal indicating the value of said phase difference;
• means for receiving said error signal and for electronically changing the inductance value of said variable inductor to alter said phase angle to within a range of acceptable values.