Analog drive for ultrasonic probe with tunable phase angle

• US 4,970,656 A
• Filed: 10/20/1989
• Issued: 11/13/1990
• Est. Priority Date: 11/07/1986
• Status: Expired due to Term

• Current Assignee: Alcon Manufacturing Limited (Alcon Incorporated)
• Original Assignee: Alcon Laboratories Incorporated (Alcon Incorporated)
• Inventors: Singh, Ajeet, Escorcio, Tolentino, Zambre, Samuel, Lo, Ying-Ching
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): TRANS, VINCENT N
• Application Number:
  US07/426,465
• Time in Patent Office: 389 Days
• Field of Search: 364/481, 364/482, 364/483, 364/484, 364/492, 323/208, 323/209, 323/210, 323/211, 318/116, 73/589, 73/648, 310/316, 310/317, 310/318, 331/1 R, 331/36 R
• US Class Current: 702/107
• CPC Class Codes: A61B 2017/00017 Electrical control of surgical instruments
• CPC Class Codes: A61B 2017/00084 Temperature
• CPC Class Codes: A61F 9/00745 using mechanical vibrations, e.g. ultrasonic
• CPC Class Codes: B06B 1/0253 taken directly from the generator circuit
• CPC Class Codes: B06B 2201/55 Piezoelectric transducer

Abstract

The system uses a tunable inductor in series with the piezoelectric crystal excitation transducer in the probe which has a flux modulation coil. The bias current through this flux modulation coil is controlled by the system. It is controlled such that the inductance of the tunable inductor cancels out the capacitive reactance of the load impedance presented by the probe when the probe is being driven by a driving signal which matches the mechanical resonance frequency of the probe. The resulting overall load impedance is substantially purely resistive. The system measures the phase angle and monitors the power level. The system uses this information to adjust the bias current flowing through the flux modulation coil to maintain the substantially purely resistive load impedance for changing power levels. This information is also used to adjust the frequency of the driving signal to track changing mechanical resonance conditions for the probe at different power levels. This method of operation insures substantially maximum power transfer efficiency and substantially linear power control over a range of power dissipation levels. There is also disclosed an analog circuit to measure the phase angle for the load driving signal and to adjust the frequency of the driving signal for best performance. This system includes an integrator to eliminate the effect of offset errors caused by operational amplifiers. There is also disclosed a system to determine the mechanical resonance frequency by sweeping the drive frequency and monitoring the drive current for the frequency at which the drive current is a maximum.

Claims

1. A method of driving an ultrasonic probe comprising:

generating a driving signal for said probe and applying said driving signal to said probe;

sensing the phase angle between a current waveform for drive current flowing through said probe resulting from said driving signal and a voltage waveform across said probe caused by said driving signal;

converting the phase angle to a direct current voltage level;

integrating said direct current voltage level to generate a frequency adjust signal;

using said frequency adjust signal to change the driving signal frequency using a voltage controlled oscillator in such a way as to alter said phase angle error toward a selectable value; and

tuning the reactance of a tunable inductor coupled to said probe such that said phase angle is substantially near a predetermined value.

2. The method of claim 1 further comprising the step of reading a user input regarding the desired home value for said phase angle error toward which all phase angles are altered and for causing said frequency of said driving signal to be changed in the proper direction to tend to cause said phase angle error to change in the direction of said home value.

3. The method of claim 2 further comprising the steps of reading a user defined input regarding the desired power level and amplifying said driving signal by an amount proportional to said user defined power level input signal.

4. A method of driving an ultrasonic device having a mechanical resonance frequency comprising:

sensing the phase angle between the drive voltage across said ultrasonic device and the load current through said ultrasonic device and, responding to said phase angle by generating a driving signal having a frequency so as to alter said phase angle toward a predetermined value and applying said driving signal to said ultrasonic device so as to drive it at a frequency substantially near said mechanical resonance frequency; and

sensing the phase angle between the voltage driving said ultrasonic device and the current flowing through said ultrasonic device after the frequency of said driving signal has been adjusted so as to be at or near said mechanical resonance frequency, and electronically altering the inductance of a variable inductor coupled in such a manner that the load current flowing through said ultrasonic device flows through said variable inductor so as to reduce said phase angle to a predetermined value.

5. An apparatus for driving an ultrasonic device having an input part and a mechanical resonance frequency, comprising:

analog means coupled to said ultrasonic device for driving said ultrasonic device with a driving signal having a frequency substantially near said mechanical resonance frequency of said ultrasonic device by varying said frequency of said driving signal until the phase angle between the driving signal voltage across said ultrasonic device and the load current caused by said driving signal to flow through said ultrasonic device has a predetermined value; and

means, including a tunable inductor coupled to said ultrasonic device such that the load current flowing through said ultrasonic device must pass through said tunable inductor, for sensing the phase angle between the driving voltage across said ultrasonic device and the load current flowing through said ultrasonic device when said ultrasonic device is being driven at said mechanical resonance frequency and for electronically and automatically altering the inductance of said tunable inductor so as to make the impedance looking from said input part toward said analog means closer to the complex conjugate of the load impedance presented by said ultrasonic device such that said phase angle is maintained substantially near zero.

6. An apparatus to automatically tune the driving frequency of an ultrasonic probe comprising:

means for sensing the phase angle between the current flowing through the ultrasonic probe caused by a driving signal characterized by a driving voltage having said driving frequency and the driving voltage and for generating a first control signal indicative of said phase angle;

analog feedback means coupled to said probe and to said means for sensing, for generating said drive voltage at said driving frequency and for receiving said first control signal and for changing the frequency of the driving voltage until said phase angle changes to a predetermined value, said analog feedback means including integrator means for integrating said first control signal to generate a second control signal, said integrating for eliminating any offset errors or noise from said first control signal, said second control signal being coupled to and used by said analog feedback means for controlling said driving frequency of said driving voltage;

programmable amplifier means coupled between said analog feedback means and said probe and having an input for receiving a gain control signal for amplifying said driving signal by an amount set by said gain control; and

means including a tunable reactance coupled to said ultrasonic probe, for sensing said phase angle and for adjusting said tunable reactance so as to cause said phase angle to be substantially near zero to optimize power transfer to said ultrasonic probe.

7. The apparatus of claim 6 further comprising means coupled to said integrator means for allowing the predetermined value of phase angle to be varied and further comprising means for visibly indicating when phase lock has been achieved.

8. The apparatus of claim 7 wherein the gain level of said programmable amplifier means can be set by a digital word input to said programmable amplifier and wherein said analog feedback means includes a voltage controlled oscillator having a nonlinear relationship defined by a curved function relating a frequency control voltage in the form of said second control signal and the resulting output frequency and wherein the quiescent value of said second control signal is set at an operating point on said curved function where less sensitivity exists between changes in the value of said second control signal and the resulting changes in output frequency.

9. An apparatus as defined in claim 6 wherein said analog feedback means includes a voltage controlled oscillator means for generating said driving signal for said ultrasonic probe having a frequency defined by said second control signal and for providing a second signal which is in phase with the driving voltage of said driving signal, said voltage controlled oscillator having a frequency adjust control input coupled to receive said second control signal from said integrator means and wherein said means for sensing further comprises:

means for receiving a signal in phase with the current flowing through said ultrasonic probe and for converting said signal to a first signal comprised of a train of rectified pulses; and

phase detector means coupled to receive said first and second signals for generating a phase error signal indicative of the phase difference between said first and second signals.

10. The apparatus of claim 9 wherein said phase detector means includes means for generating said phase error signal as a pulse width modulated pulse train.

11. The apparatus of claim 10 further comprising a lower pass filter for filtering said phase error signal and for converting said phase error signal to a D.C. signal having an amplitude proportional to said phase error.

12. The apparatus of claim 11 further comprising means coupled to said integrator means for adjusting a phase angle error operating point such that said phase detector means, said voltage controlled oscillator means and said integrator means combine to operate so as to cause the phase angle to change in the direction of said phase angle operating point.

13. An apparatus for driving an ultrasonic probe having an electrical input impedance comprising:

a zero crossing detector for receiving a current phase sample signal indicative of the current flowing through said ultrasonic probe and for outputting a square wave alternating current waveform first signal;

rectifier means coupled to receive said first signal and to convert said first signal to a direct current phase sample signal comprised of rectangular pulses all of the same polarity relative to some reference voltage;

a frequency divider means for dividing the frequency of a first driving signal to a lower frequency second driving signal for said ultrasonic probe;

a phase detector coupled to receive said direct current phase sample signal and said second driving signal, for generating therefrom a phase angle error signal in the form of a pulse width modulated pulse train where the pulse width is proportional to phase angle error;

means for receiving said pulse width modulated phase angle error signal and for filtering out high frequency components and for converting the pulse width modulated pulse train to an analog phase angle error signal comprising a D.C. voltage proportional to the phase angle error;

means for receiving said analog phase angle error signal and for integrating said phase angle error signal to generate a frequency correction signal having a magnitude and a polarity such that correction of the phase angle error toward a selectable, desired phase angle error is possible and for providing a means for selection of different phase angle error values;

a voltage controlled oscillator means coupled to said frequency divider means for receiving said frequency correction signal and for generating said first driving signal for said ultrasonic probe, said driving signal having a frequency which is a function of said frequency correction signal; and

means including a tunable inductor coupled to said ultrasonic probe for sensing the phase angle associated with said probe'"'"'s input impedance and for tuning said tunable inductor to compensate for the reactive element of said input impedance of said ultrasonic probe so that the power factor is substantially near one.

14. An apparatus as defined in claim 13 further comprising a linear programmable amplifier coupled to receive said second driving signal and for amplifying said second driving signal by a gain amount set through a programming signal to said programmable amplifier.